pubs.acs.org/OrganometallicsPublished on Web 03/17/2010r 2010 American Chemical Society

Organometallics 2010, 29, 1797–1805 1797

DOI: 10.1021/om100037t

Addition of Alkynes to Zwitterionic μ-Vinyliminium Diiron Complexes:

New Selenophene (Thiophene) and Vinyl Chalcogenide Functionalized

Bridging Ligands

Luigi Busetto,† Fabio Marchetti,‡,§ Filippo Renili,‡ Stefano Zacchini,† andValerio Zanotti*,†

†Dipartimento di Chimica Fisica e Inorganica, Universit�a di Bologna, Viale Risorgimento 4, 40136 Bologna,Italy, and ‡Dipartimento di Chimica e Chimica Industriale, Universit�a di Pisa, Via Risorgimento 35, I-56126

Pisa, Italy. §Fabio Marchetti, born in 1974 in Bologna, Italy.

Received January 15, 2010

Zwitterionic vinyliminium complexes [Fe2{μ-η1:η3-Cγ(R

0)dCβ(E)CRdN(Me)(R)}(μ-CO)(CO)-(Cp)2][SO3CF3] (R = R0 = Me, E = Se, 1a; R = Xyl, R0 = Tol, E = Se, 1b; R = Xyl, R0 = Tol,E = S, 2a; R = Xyl, R0 = Tol, E = S, 2b; Tol = 4-MeC6H4, Xyl = 2,6-Me2C6H3) undergo alkyneaddition by different reaction modes. Complexes 1a and 2a undergo 1,3 dipolar cycloaddition withalkynes [HCtCCO2Me and C2(CO2Me)2], affording new 1-(2-amino)-seleno(thio)phene-alkylidenediiron complexes [Fe2{μ-κ

1(N):η1(C):η1(C):-Cγ(R0)CβEC(CO2Me)dC(R00)CRN(Me)(R)}(μ-CO)-

(CO)(Cp)2] (R = R0 = Me, E = Se, R00 = CO2Me, 3a; R = R0 = Me, E = Se, R00 = H, 3b; R =Me,R0 =Tol, E=S,R00 =CO2Me, 4). The hemilabile character of the bridging ligand in 3a is investi-gated by reaction with CNBut, which replaces NMe2 coordination, affording [Fe2{μ-Cγ(Me)CβSeC-(CO2Me)dC(CO2Me)CRN(Me)2}(μ-CO)(CO)(CNBut)(Cp)2] (5). Complexes 2a and 2b react with twoequivalentsofHCtCCO2Me, leading to the formation of [Fe2{μ-κ

1(O):η1(C):η3(C)-Cδ(CtCCO2Me)-Cγ(R

0)Cβ(SCHdCHCO2Me)CR(O)N(Me)(Xyl)}(μ-CO)(Cp)2] (R0 = Tol, 6a; R0 = Me, 6b). Finally,

complexes 1b, 2a, and 2b react with different alkynes, in the presence of NH4PF6, affording the vinylsulfide and vinyl selenide vinyliminium complexes [Fe2{μ-η

1:η3-Cγ(R0)dCβ(ECR

00dCHCO2Me)-CRdN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][PF6] (R

0 = Tol, E = S, R00 = H, 7a; R0 = Me, E = S, R00 =H,7b; R0 =Tol, E=S,R00=CO2Me, 7c; R0 =Me,E=S,R00 =CO2Me, 7d; R0 =Tol, E=Se,R00 =H, 8a; R0 = Tol, E = Se, R00 = CO2Me, 8b). The molecular structures of 3a, 5, and 6b have beenelucidated by X-ray diffraction.

Introduction

Zwitterionic organometallic complexes are potentialsources of unique reactivity due to the properties associatedwith the presence of integral opposite charges, linkedthrough a path of covalent bonds and located in separatedregions of the complex.1 For instance, zwitterionic com-plexes combine the advantage of a charged metal centerwith the solubility of neutral complexes, which can signifi-cantly enhance their catalytic activity.2 Further potentialapplications can be envisaged in the field of optically activecompounds and in the development of new approaches tometal-catalyzed 1,3-cycloaddition reactions.We have recently described the synthesis of zwitterionic

vinyliminium diiron complexes.3 Some of these species,

reported in Scheme 1, are the compounds investigated inthis work.The peculiar character of these complexes consists in the

fact that both charges are formally located on the bridgingligand: the negative charge on the S/Se atom and the positivecharge on theN atomof the iminiummoiety. This is unusual,in that zwitterionic complexes generally display a positive ornegative charge located on the metal center. As a conse-quence, complexes 1 and 2 exhibit some of the propertiestypical of zwitterionic ligands,4 featuring sites able to bind ametal cation, both as mono and as chelating ligand.5 So far,our investigations have concerned metalation, alkylation,and oxidative dimerization of the zwitterionic complexes,6

but other possible reactions are to be expected in considera-tion of the dipolar character of the bridging ligand. Inparticular, cycloaddition with appropriate dipolarophiles

*Towhomcorrespondence shouldbeaddressed.E-mail: valerio.zanotti@unibo.it.(1) Chauvin, R. Eur. J. Inorg. Chem. 2000, 577.(2) (a) Cipot, J.; McDonald, R.; Stradiotto, M. Chem. Commun.

2005, 4932. (b) Lundgren, R. J.; Rankin, M. A.; McDonald, R.; Schatte,G.; Stradiotto, M. Angew. Chem., Int. Ed. 2007, 46, 4732. (c) Cipot, J.;McDonald, R.; Ferguson, M. J.; Schatte, G.; Stradiotto, M.Organometallics2007, 26, 594.(3) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V. Organo-

metallics 2006, 25, 4808.

(4) (a) Forgan, R. S.; Davidson, J. E.; Galbraith, S. G.; Henderson,D. K.; Parsons, S.; Tasker, P. A.; White, F. J. Chem. Commun. 2008,4049. (b) Tasker, P. A.; Tong, C. C.; Westra, A. N.Coord. Chem. Rev. 2007,251, 1868.

(5) Busetto, L.; Marchetti, F.; Mazzoni, R.; Salmi, M.; Zacchini, S.;Zanotti, V. Eur. J. Inorg. Chem. 2009, 1268.

(6) Busetto, L.; Dionisio, M.; Marchetti, F.; Mazzoni, R.; Salmi, M.;Zacchini, S.; Zanotti, V. J. Organomet. Chem. 2008, 693, 2383.

1798 Organometallics, Vol. 29, No. 7, 2010 Busetto et al.

(e.g., alkynes) are likely to occur and are the subject of thepresent report.The aim was to explore new potential routes to hetero-

cycles and other addition products, by reaction of alkyneswith bridging ligands in diiron complexes.

Results and Discussion

1,3 Dipolar Cycloaddition with Alkynes. The Se- andS-functionalized vinyliminium complexes 1 and 2 react withactivated alkynes [HCtCCO2Me, C2(CO2Me)2] to give thenovel 1-(2-amino)-selenophene-alkylidene complexes 3a,band 1-(2-amino)-thiophene-alkylidene 4, respectively, inabout 80% yields (Scheme 2).

In Scheme 2, the three carbon atoms of the bridging chainare denoted by greek letters (R, β, and γ) to better identifythem as components of the heterocycle products 3 and 4.

Complexes 3a, 3b, and 4 have been characterized byspectroscopy and elemental analysis. Moreover, the mole-cular structure of 3a 3CH2Cl2 has been determined by X-raydiffraction: the ORTEP molecular diagram is shown inFigure 1 together with most relevant bond lengths andangles.

The structure of 3a is composed of a bridging 1-(2-amino)-selenophene-alkylidene ligand coordinated to a cis-Fe2(μ-CO)-(CO)(Cp)2 core. Coordination of the former occurs via abridging alkylidene moiety and a terminal amino function-ality. Both the bridging carbonyl [Fe(1)-C(11) 1.958(4) A;Fe(2)-C(11) 1.861(4) A] and bridging alkylidene ligands[Fe(1)-C(13) 2.043(4) A; Fe(2)-C(13) 1.978(3) A] show acertain degree of asymmetry, with the shorter contacts to theelectron richer amino-coordinated Fe(2) center. The highlyfunctionalized selenophene group is almost perfectly planar[mean deviation from the C(14) C(15) C(16) C(17) Se(1) least-squares plane 0.0220 A], in agreement with sp2 hybridization

of the C atoms. Within the five-membered ring, the C(14)-C(15) [1.369(5) A] and C(16)-C(17) [1.361(5) A] interactionsdisplay a strong double-bond character, whereas C(15)-C(16) [1.419(5) A] displays considerably minor π-character.The C(14)-Se(1) [1.888(3) A] and C(17)-Se(1) [1.868(4) A]interactions are as expected for single C(sp2)-Se bonds.Coordination of N(1) to Fe(2) results in the formation of asecond five-memberedmetallacycle condensed via theC(14)-C(15) edge to the selenophene ring, and also this second ring isalmost planar [mean deviation from the Fe(2) C(13) C(14)C(15) N(1) least-squares plane 0.0592 A]. Condensation ofthese two nearly coplanar five-membered rings [mean devia-tion from the common least-squares plane 0.0835 A] probablyforces a sizable elongation of the C(13)-C(14) contact[1.444(5) A] compared to a normalC(sp3)-C(sp2) single bond[1.51 A]. Finally, coordination of N(1) to the iron centercauses C(15)-N(1) [1.460(4) A] to be longer than aC(sp2)-Nsingle bond [1.38 A], whereas N(1)-C(19) and N(1)-C(20)[1.493(5) A] are longer than theC(sp3)-Nsinglebond [1.47 A].7

The NMR data of 3a,b and 4 evidence the presence, insolution, of one single isomeric form for each compound.This is noticeable in the case of 3b, in that the cycloadditionof the primary and asymmetric alkyne HCtCCO2Mecould, in theory, produce two regioisomers, as a conse-quence of two possible modes of inclusion within the five-membered cycle. Conversely, the [3þ2] cycloaddition isregioselective and the CH termination of the primaryalkyne is exclusively bound to the Se atom, as shown bythe structure observed in the solid state. In compounds 3a,b,the NMe groups are not equivalent and give rise to distinctresonances in both the 1H and 13NMR spectra. In the 13CNMR spectra of 3a,b and 4, the resonances due to CR, Cβ,and Cγ are in the range typical for vinylalkylidene carbons:the bridging alkylidene carbon (Cγ) exhibits a low-fieldresonance at about 180.7 ppm, and the CR and Cβ reso-nances are at about 160 ppm.

Scheme 1. Zwitterionic VinyliminiumComplexes Investigated in

This Work

Scheme 2

Figure 1. ORTEP drawing of 3a (all H atoms are omitted forclarity). Thermal ellipsoids are at the 30% probability level.Only the main image of the disordered Cp ligand bondedto Fe(2) is represented. Relevant bonding parameters (A):Fe(1)-C(11) 1.958(4), Fe(2)-C(11) 1.861(4), Fe(1)-C(13)2.043(4), 1.978(3), C(13)-C(14) 1.444(5), C(14)-C(15) 1.369(5),C(15)-C(16) 1.419(5), C(16)-C(17) 1.361(5), C(17)-Se(1)1.868(4), C(14)-Se(1) 1.888(3), C(15)-N(1) 1.460(4), N(1)-C(20) 1.493(5), N(1)-C(19) 1.493(5).

(7) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 1987, 12, S1–S19.

Article Organometallics, Vol. 29, No. 7, 2010 1799

Formation of the selenophene/thiophene rings in 3a,b and4 is clearly the result of a [3þ2] cycloaddition that involvesthe bridging zwitterionic ligand, in the form of a Cþ-C-X-

1,3-dipole (X = S or Se), and the alkyne. Thus, the reactionhas to be included in the field of 1,3 dipolar cycloadditionreactions, which constitute one of the most powerful proto-cols in organic synthesis.8 Analogies can be envisages withthe 1,3 dipolar cycloaddition of azomethine ylides, in that thepositive charge in the dipolar unit is placed on an iminiumgroup,9 and with Huisgen dipolar cycloaddition of azidesand alkynes.10 The latter is often referred as the “clickreaction” and is the most representative of the syntheticconcepts developed by Sharpless.11 The dipole cycloadditionshown in Scheme 2 is far from achieving the status of a clickreaction, in that the structure of the dinuclear complex is toocomplex tomeet the requirement of readily available startingmaterials; neither the efficiency, selectivity, nor reliabilityseems adequate. Much closer similarities can be found withthe cycloadditions involving thiocarbamoyl benzimidazo-lium (or imidazolinium) salts, which can act as 1,3 dipolarC-C-S species.12

One of the most relevant aspects of the reaction shown inScheme 2 is the formation of selenophenes and thiophenes bya [3þ2] cycloaddition, which is an uncommon syntheticapproach. To the best of our knowledge, examples arelimited to the cycloadditions of the thiocarbamoyl azoliumsalt above-mentioned and the reactions of thiocarbonylylides with electron-poor olefinic dipolarophiles.13

A further interesting and unique feature is that the dipolarcycloaddition involves a bridging vinyliminium ligand,which is consequently converted into a bridging alkylidene,connected to a selenophene (thiophene) ring. The latter isfurther coordinated to one Fe center through a pendantN(Me)R function. Therefore, the observed cycloaddition isthe result of a combination of two major features: the dipolar(zwitterionic) character of the ligand and also the versatility ofthe bridging coordination, which can easily undergo adjust-ment in response to modifications of the bridging frame.

The 1,3 dipolar cycloaddition of alkynes with zwitterionicligands is also to be comparedwith other previously reportedcyclizations involving alkynes and bridging C3 ligands, inrelated diiron complexes. This is the reaction of μ-vinylalk-ylidene complexes [Fe2{μ-η

1:η3-CRCHdCH(NMe2)}(μ-CO)-(CO)(Cp)2] with alkynes, which leads to the formation offunctionalized ferrocenyl products, as shown in Scheme 3.14

In these ferrocene complexes, the polysubstituted cyclopen-tadienyl ligand results from a [3þ2] cycloaddition of the vinyl-alkylidene ligand with alkynes. In this case the cycloaddition

doesnothaveadipolar character and showscloseanalogieswithtypical cycloadditions of R,β-unsaturated alkylidene ligandswith alkynes.15 A further relevant difference is that the reactionshown in Scheme 3 leads to the fragmentation of the dinuclearcomplexes, whereas the 1,3 dipolar cycloaddition does not, andthe resulting five-membered heterocycle remains coordinated asa bridging ligand.

Besides the unprecedented nature of the bridging frame in3a,b and 4, the coordination mode is also uncommon in thatligands containing selenophene or thiophene rings are gen-erally coordinated through the heteroatom and/or theπ-bond.16 Conversely, in compounds 3a,b and 4 the hetero-cycles are connected to the metal centers exclusively throughthe alkylidene and the N(Me)R group, which are substitu-ents of the five-membered ring. Moreover, the bridgingframe might exhibit hemilabile character,17 since the brid-ging alkylidene moiety appears firmly coordinated, whereas,in theory, the coordination through the pendant aminogroup should be easier to displace. In order to investigatethis point, we examined the reactivity of 3a with isocyanides(CNBut) and phosphines (PMe3), both good candidates todisplace the N(Me)R group from metal coordination. How-ever, neither PPh3 nor CNBut reacts with 3a in THF solutionat room temperature. Therefore, N-coordination is not verylabile; only treatment of 3a in THF at reflux temperature, inthe presence of CNBut, produces the expected displacement,affording 5, in high yield (Scheme 4).

Complex 5 has been characterized by spectroscopy andX-ray diffraction. The ORTEP molecular diagram is shownin Figure 2, together with most relevant bond lengths andangles. The molecular structure of 5 confirms the displace-ment of N(1) and the coordination of CNBut to Fe(2), withthe Fe2(μ-CO)(CO)(Cp)2 core that retains the cis-conforma-tion. Interestingly, the μ-CO ligand maintains the sameasymmetry present in 3a [Fe(1)-C(11) 1.935(7) A andFe(2)-C(11) 1.847(7) A in 5; Fe(1)-C(11) 1.958(4) A andFe(2)-C(11) 1.861(4) A in 3a], showing the longer contact tothe terminally CO-coordinated Fe(1) center, whereas itssense is reversed concerning the bridging alkylidene ligand[Fe(1)-C(13) 2.002(6) A and Fe(2)-C(13) 2.029(7) A in 5;Fe(1)-C(13) 2.043(4) A and Fe(2)-C(13) 1.978(3) A in 3a].The selenophene ring is almost perfectly planar [mean devia-tion from the C(14) C(15) C(16) C(17) Se(1) least-squaresplane 0.0189 A], as in the parent 3a, and the bondingparameters within the five-membered ring are very similar

Scheme 3

(8) (a) Huisgen, R. 1,3-Dipolar Cycloaddition Chemistry; Padwa, A.,Ed.; Wiley: New York, 1984; Vol. 1 . (b) Harwood, L. M.; Vickers, R. J.Synthetic Applications of 1,3-Dipolar Cycloaddition Chemistry TowardHeterocycles and Natural Products; Padwa, A., Pearson, W. H., Eds.;Wiley: New York, 2002.(9) Gothelf, K. V.; Jørgensen, K. A. Chem. Rev. 1998, 98, 863.(10) (a) Huisgen, R. Pure Appl. Chem. 1989, 61, 613. (b) Huisgen, R.;

Szeimies, G.; Moebius, L. Chem. Ber. 1967, 100, 2494. (c) Bastide, J.;Hamelin, J.; Texier, F.; Vo Quang, Y. Q. Bull. Soc. Chim. Fr. 1973, 2555.(11) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int.

Ed. 2001, 40, 2004.(12) (a) Liu,M.-F.;Wang, B.; Cheng, Y.Chem. Commun. 2006, 1215.

(b) Cheng, Y.; Liu, M.-F.; Fang, D.-C.; Lei, X.-M.Chem.;Eur. J. 2007, 13,4282. (c) Li, J.-Q.; Liao, R.-Z.; Ding, W.-J.; Cheng, Y. J. Org. Chem. 2007,72, 6266. (d) Ma, Y. G.; Cheng., Y. Chem. Commun. 2007, 5087.(13) Komatsu,M.; Choi, J.;Mihara,M.; Oderaotoshi, Y.;Minakata,

S. Heterocycles 2002, 57, 1989.(14) Busetto, L.; Marchetti, F.; Mazzoni, R.; Salmi, M.; Zacchini, S.;

Zanotti, V. Organometallics 2009, 28, 3465.

(15) D€otz, K. H.; Stendel, J., Jr. Chem. Rev. 2009, 109, 3227.(16) (a) Angelici, R. J. Coord. Chem. Rev. 1990, 105, 61. (b) Chen, J.;

Angelici, R. J. Coord. Chem. Rev. 2000, 206-207, 63. (c) Waldbach, T. A.;van Eldik, R.; van Rooyen, P. H.; Lotz, S. Organometallics 1997, 16, 4056.(d) Paneque, M.; Poveda, M. L.; Salazar, V.; Taboada, S.; Carmona, E.;Gutierrez-Puebla, E.; Monge, A.; Ruiz, C. Organometallics 1999, 18, 139.

(17) (a) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658.(b) Braunstein, P.; Naud, F.Angew. Chem., Int. Ed. 2001, 40, 680. (c) Bader,A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27. (d) Braunstein, P.J. Organomet. Chem. 2004, 689, 3953. (e) Angell, S. E.; Rogers, C. W.;Zhang, Y.; Wolf, M. O.; Jones, W. E. Coord. Chem. Rev. 2006, 250, 1829.

1800 Organometallics, Vol. 29, No. 7, 2010 Busetto et al.

to those of the parent compound, with alternated single[C(15)-C(16) 1.430(9) A; C(17)-Se(1) 1.852(6) A; C(14)-Se(1) 1.865(6) A] and double bonds [C(14)-C(15) 1.388(9)A; C(16)-C(17) 1.353(9) A]. The opening of the second five-membered metallacycle present in 3a as a consequence ofdisplacement of N(1) from Fe(2) in 5 results in some strain,and, thus, C(13)-C(14) [1.505(9) A] is rather elongated in 5

compared to the parent 3a [1.444(5) A] and as expected for aC(sp3)-C(sp2) single bond [1.51 A]. Finally, as consequenceof the loss of N-coordination C(15)-N(1) [1.416(8) A],N(1)-C(19) [1.469(10) A], and N(1)-C(20) [1.451(9) A]are shortened compared to 3a [1.460(4), 1.493(5), and1.493(5) A, respectively], approaching the expected valuesfor C(sp2)-N [1.38 A] and C(sp3)-N [1.47 A] single bonds.7

The NMR spectroscopic data are consistent with the struc-ture shown in Figure 2, and it is reasonable to assume that 5adopts, in solution, the same conformation shown in the solid,with the selenophene substituent far from the sterically de-manding CNBut ligand. The most relevant feature is theequivalence of the NMe2 protons, which give rise to a singlesignal at 2.80ppm. Indeed, free rotationaround theCR-NMe2bond, together with inversion at the N atom, provides anexchangemechanism thatmakes themethyl groups equivalenton the NMR time scale. This was not the case of the parentcomplex 3a, in which the nitrogen coordination to Fe did notallow rotation around the CR-NMe2 interaction.Addition of Two Alkyne Units at the Bridging Ligand, with

CO Bond Cleavage. The cyclization reaction shown inScheme 2 is not general, and the S(Se)-functionalized vinyl-iminiumdiiron complexes can combinewith alkynes throughdifferent reaction routes. In fact, complexes [Fe2{μ-η

1:η3-Cγ-(R0)dCβ(S)CRdN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3][R0 = Tol, 2a; R0 = Me, 2b] react with an excess of HCtCCO2Me, in CH2Cl2 solution at room temperature, to formthe vinyl sulfide functionalized bridging allylidene complexes6a and 6b, respectively, obtained in about in 80-90% yields(Scheme 5).

Complexes 6a,b have been characterized by spectroscopyand elemental analysis. Moreover, the X-ray molecularstructure of 6b has been determined (Figure 3).

In this case the reaction with alkynes does not produce the1,3 dipolar cycloaddition described above. Conversely, twoalkyne units are incorporated in the bridging frame: one isbound to the S atom; the second is incorporated in thebridging hydrocarbyl chain as alkynyl group. Interestingly,also a CO is incorporated in the bridging frame; thus theoverall result consists of a remarkable growth of the bridgingligand, due to a one-pot formation of several C-C andC-heteroatombonds.The inclusionofCOandof one alkyne,in the form of an alkynyl substituent, very closely resemblesthe previously reported acetylide addition to diiron vinylimi-nium complexes, which is shown in Scheme 6.18

Scheme 4

Figure 2. ORTEP drawing of 5 (all H atoms are omitted forclarity). Thermal ellipsoids are at the 30% probability level.Only the main image of the disordered But group is represented.Relevant bonding parameters (A): Fe(1)-C(11) 1.935(7), Fe-(2)-C(11) 1.847(7), Fe(1)-C(13) 2.002(6), 2.029(7), C(13)-C-(14) 1.505(9), C(14)-C(15) 1.388(9), C(15)-C(16) 1.430(9),C(16)-C(17) 1.353(9), C(17)-Se(1) 1.852(6), C(14)-Se(1)1.865(6), C(15)-N(1) 1.416(8), N(1)-C(20) 1.451(9), N(1)-C-(19) 1.469(10).

Scheme 5

Figure 3. ORTEP drawing of 6b (all H atoms are omitted forclarity). Thermal ellipsoids are at the 30% probability level.Only one of the two independent molecules present within theunit cell is represented. Relevant bonding parameters (A): Fe-(1)-C(12) 1.943(7) and 1.944(7); Fe(2)-C(12) 2.002(6) and1.993(7); Fe(2)-C(13) 2.024(6) and 2.039(6); Fe(2)-C(14)2.136(6) and 2.133(6); C(12)-C(13) 1.403(9) and 1.397(9); C-(13)-C(14) 1.459(8) and 1.452(8); C(21)-C(22) 1.360(9) and1.317(9) (for the two independent molecules, respectively).

(18) (a) Busetto, L.; Marchetti, F.; Zacchini, S.; Zanotti, V. Eur.J. Inorg. Chem. 2006, 285. (b) Busetto, L.; Marchetti, F.; Zacchini, S.;Zanotti, V. Eur. J. Inorg. Chem. 2007, 1799.

Article Organometallics, Vol. 29, No. 7, 2010 1801

Labeling experiments demonstrated that the reactionshown in Scheme 6 was initiated by acetylide attack at aCO ligand, which was consequently cleaved. Both fragments(C and O), as well as the alkynyl group, were included inthe bridging frame (shown as Cδ and O bound to CR, inScheme 6). A very similar process presumably occurs also inthe formation of 6a and 6b, but the architecture of theresulting bridging frame is made more intricate by theaddition of an other alkyne unit. Indeed, the complexity ofthe bridging frame is well evidenced in the X-ray structure of6b (Figure 3), which is quite similar to that of II, previouslyreported.18a Thus, the molecule is composed of a Fe2(μ-CO)-(Cp)2 core with a bridging amido-vinylsulfido- functionalizedallylidene μ-κ1(O):η1(C):η3(C)-{C(CtCCO2Me)C(Me)-C(SCHdCHCO2Me)C(O)N(Me)(Xyl)}. As for most of thebridging vinylalkylidene (allylidene) dinuclear complexes,19

the highly delocalized nature of the π-interaction within thebridging frame is better illustrated by considering severalrepresentation forms (e.g.,A,B, andC, Scheme 7). These areextreme representations, and a full description of the bond-ing necessarily involves taking into consideration differentcontributions of each. Thus, the bridging ligand is σ-coordi-nated to Fe(1) [Fe(1)-C(12) 1.943(7) and 1.944(7) A for thetwo independent molecules present within the unit cell;compare 1.923(4) A in II] and η3-coordinated to Fe(2)[Fe(2)-C(12) 2.002(6) and 1.993(7) A; Fe(2)-C(13) 2.024(6)and 2.039(6) A; Fe(2)-C(14) 2.136(6) and 2.133(6) A; com-pare 2.004(4), 2.030(4), and 2.157(4) A in II] in an allyl-likefashion (see structure A). However, the Fe(2)-C(14) interac-tion is significantly longer than Fe(2)-C(12) and Fe(2)-C-(13), which is consistent with the formulation B, where theC(12)-C(13)-C(14) sequence is viewed as a vinyl-substitutedμ-alkylidene. Moreover, since C(12)-C(13) [1.403(9) and1.397(9) A; compare 1.417(5) A in II] is shorter than C(13)-C(14) [1.459(8) and 1.452(8) A; compare 1.455(6) A in II], adescription of the ligand as η1:η2-vinyl connected to analkynyl and an amido functionality also appears appropriate(structure C). Concerning the vinyl sulfide group, it adopts aZ-configuration with C(21)-C(22) [1.360(9) and 1.317(9) Afor the two independent molecules, respectively] in the usualrange for a double bond.

The spectroscopic data of 6a,b are in agreement with thestructure shown in the solid state (Figure 3) and are alsoconsistent with the data reported for the related complex II

(Scheme 6). The NMR data indicate that also in solutioncomplexes 6a and 6b exist in a single isomeric form. Thispoint is remarkable in consideration of the complex structureof the bridging frame, containing several insaturations,and of the number of bonds that have been generated in asingle step. Thus, the observed assembly and transformationexhibit a considerable regio- and stereoselectivity. For exam-ple, S-C bond formation, between the bridging zwitterionic

ligand and the alkyne, occurs selectively at the primary carbonof the alkyne (anti-Markovnikov addition), and the resultingvinyl sulfide group exhibits aZ-configuration, as indicated bythe coupling constant of the hydrogen atoms in theSCHdCHCO2Me group. Likewise, the arrangement of thebridging allylidene fragment formed by the incorporation ofthe CγCtCR unit takes place in a single conformation. 13CNMR resonances due to CR and Cδ evidence the strongsimilarity to the corresponding carbons in the bridging chainof II (e.g., for 6a at 175.1 and 155.3 ppm, respectively, vs 179.7and 155.5 of II).18

Despite the complexity of the transformation occurring inthe double alkyne addition, it is possible to formulate ahypothesis concerning the formation of 6a,b, based upon theacetylide addition reaction previously reported (Scheme 6).Indeed, it is reasonable to assume a multistep reactionsequence that includes acetylide attack at CO, similarly tothat established in the case of the conversion of I to II.Accordingly, the following sequence can be proposed(Scheme 8), in which the initial step is the nucleophilic attackof the thiolate group to the alkyne.

This is also consistentwith the observation that alkyneswithelectron-withdrawing groups (e.g., COOMe) are required. Theresulting intermediate should give proton abstraction fromanother alkyne molecule, instead of undergoing cyclization.This sequence should lead to the formation of a cationicintermediate E (Scheme 8), with an acetylide as counteranion.The latter might consequently undergo an intramolecularrearrangement similar to that described in Scheme 6, affording6a,b as final products.Addition of Alkynes in the Presence of NH4PF6: Synthesis

of Vinyl Chalcogenide Vinyliminium Complexes. Protonremoval fromalkyne reagent is a crucial step in themechanismformulated in Scheme 8: it is required to form to a vinyl sulfidegroup, avoiding the formation of the thiophene (selenophene)ring, and it is also necessary to generate a nucleophilicacetylide, which sustains the subsequent addition and rear-rangement. Any modification of the reaction conditions ableto interfere with this step is expected to produce consequencesin the reaction outcome, thus providing more clues on thereaction mechanism. On the basis of these considerations, weinvestigated the reaction with alkynes in the presence of aproton source, such as NH4PF6, that is more acidic and abetter proton supply than primary alkynes. The result, shownin Scheme 9, is the following: complexes 2a,b react with anexcess of alkyne (HC2CO2Me), in the presence of NH4PF6 inCH2Cl2 solution, to give the vinyl sulfide species 7a and 7b,respectively, instead of 6a and 6b.

Scheme 6 Scheme 7

(19) Busetto, L.; Maitlis, P. M.; Zanotti, V. Coord. Chem. Rev. 2010,254, 470.

1802 Organometallics, Vol. 29, No. 7, 2010 Busetto et al.

Complexes 7a and 7b have been purified by chromato-graphy on alumina and characterized by IR and NMRspectroscopy and elemental analysis. The IR spectra (inCH2Cl2 solution) show two ν-CO absorptions attributed toterminal and bridging carbonyls (at ca. 1990 and 1830 cm-1,respectively). Further adsorptions are due to the CO2Megroup (at ca. 1700 cm-1) andCR-Nbond (at ca. 1615 cm-1).The NMR spectra evidence the presence of a single productin a single isomeric form, indicating that the alkyne additionand subsequent protonation take place with the same regio-and steroselectivity observed in the formation of 6a and 6b.More in detail, the 1HNMR resonances due to vinyl protons(e.g., for 7b, at 7.37 and 6.25 ppm) display a couplingconstant of about 9.5 Hz. These values indicate that thevinyl sulfide group is originated from nucleophilic attack atthe primary carbon of the alkyne and that the resultingalkene displays a Z-configuration.

Comparison of the reactions shown in Schemes 5 and 9clearly evidences that the presence of a readily availableproton source (NH4PF6) modifies the reaction outcome:alkyne addition at the zwitterionic ligand and protonationto form a vinyl sulfide takes place without requiring protonabstraction from a second alkynemolecule. In the absence ofan acetylide counteranion, further additions and rearrange-ments are blocked. Therefore, this result fits well in the aboveproposed mechanism, and complexes 7a and 7b are theequivalent of the intermediate E (Scheme 8). The presenceof the non-nucleophilic PF6

- anion in place of the acetylideanion makes the products more stable and prevents furtherrearrangements.

The overall result shown in Scheme 9 consists in thehydrothiolation of alkynes, which selectively affords anti-Markovnikov products (7a and 7b), in the Z isomeric form.Indeed, sulfur-hydrogen bond addition to alkynes is awell-recognized synthetic method in C-S bond formation,

resulting in vinyl sulfides.20 Several procedures have beendeveloped based on free radical21 or nucleophilic additionmechanisms,22 but these methods generally lack completeregio- and stereoselectivity. Conversely, the field of metal-catalyzed hydrothiolation,23 which promises higher selecti-vity, is rapidly expanding,24 also due to the increasing interesttoward vinyl sulfides, as valuable synthetic intermediates.

In the mechanism suggested above, alkyne hydrothiola-tion is initiated by a nucleophilic attack of the thiolate,followed by protonation.An alternative sequence, consistingin protonation of the S atom as initial step, is unlikely, in thatprotonation of the S atom in the zwitterionic complexes oftype 2 is not achieved by using NH4PF6, but requires strongacids, such as HSO3CF3.

6

Another point to be remarked is that hydrothiolation iscompetitive with cyclization: in other words, the initialnucleophilic S addition to the alkyne can be followed byprotonation (e.g., to form complexes of the type 7) or byintramolecular attack at the iminium carbon with conse-quent cyclization (e.g., to form thiophene complexes of thetype 4). Protonation seems more favorable, if there is areadily available proton source. This point is evidenced byobserving that in the presence of NH4PF6 the reaction of 2with (CO2Me)CtC(CO2Me), which normally forms the 1,3cycloaddition product 4 (Scheme 2), affords the vinyl sulfidecomplex 7c, as shown in Scheme 9.Furthermore, the reactionhas amore general character, in that other zwitterionc diironcomplexes, containing S or Se, react with different alkynes(both primary and internal alkynes) in the presence ofNH4PF6, yielding vinyl sulfide and vinyl selenide products(Scheme 10). Thus, it is appropriate to describe the reactionas a hydrochalcogenation of alkynes,25 which involves thebridging zwitterionic frame. In the case of primary alkynesthe addition is regioselective anti-Markovnikov.

Complexes 7c,d and 8a,b have been characterized byspectroscopy and elemental analysis. Their spectroscopicfeatures resemble those discussed above for 7a,b. Chemicalshifts and coupling constants of the vinyl protons in 8a

indicate that the configuration of the vinyl unit is the sameas that described for 6a,b and 7a,b (Z-configuration). In 7c,

Scheme 8 Scheme 9

(20) Peach, M. E. In The Chemistry of the Thiol Group; Patai, S., Ed.;Wiley: London, 1974; Vol. 2.(21) (a) Ichinose, Y.; Wakamatsu, K.; Nozaki, K.; Birbaum, J.-L.;

Oshima, K.; Utimoto, K. Chem. Lett. 1987, 1647. (b) Benati, L.; Capella,L.; Montevecchi, P. C.; Spagnolo, P. J. Chem. Soc., Perkin Trans. 1995,1035. (c) Griesbaum, K. Angew. Chem., Int. Ed. Engl. 1970, 9, 273.(22) (a) Truce, W. E.; Simms, J. A. J. Am. Chem. Soc. 1956, 78, 2756.

(b) Carson, J. F.; Boggs, L. E. J.Org. Chem. 1966, 31, 2862. (c) Truce,W. E.;Tichenor, G. J.W. J.Org. Chem. 1972, 37, 2391. (d) Katritzky, A. R.; Ramer,W. H.; Ossana, A. J. Org. Chem. 1985, 50, 847. (e) Kondoh, A.; Takami, K.;Yorimitsu, H.; Oshima, K. J. Org. Chem. 2005, 70, 6468.

(23) Kondo, T.; Mitsudo, T. Chem. Rev. 2000, 100, 3205.(24) For recent examples see: (a) Field, L.D.;Messerle, B.A.; Vuong,

K.Q.; Turner, P. J. Chem. Soc., DaltonTrans. 2009, 3599. (b)Weiss, C. J.;Wobser, S. D.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 2062. (c) Yang, J.;Sabarre, A.; Fraser, L. R.; Patrick, B. O.; Love, J. A. J. Org. Chem. 2009, 74,182. (d)Wang, Z.-L.; Tang, R.-Y.; Luo, P.-S.; Deng, C.-L.; Zhong, P.; Li, J.-H.Tetrahedron 2008, 64, 10670. (e)Malyshev, D. A.; Scott, N.M.;Marion, N.;Stevens, E. D.; Ananikov, V. P.; Beletskaya, I. P.; Nolan, S. P. Organo-metallics 2006, 25, 4462.

(25) Beletskaya, I. P.; Ananikov, V. P. Eur. J. Org. Chem. 2007, 3441.

Article Organometallics, Vol. 29, No. 7, 2010 1803

two isomers in comparable ratio are observed in solution.These are presumably attributable toE andZ isomers, due tolack of selectivity in the addition of the disubstituted alkyne.Conversely, the NMR spectra of complexes 7d and 8b

contain a single set of resonances, indicating that the forma-tion of the S(Se)-vinyl unit is stereoselective.However,NMRexperiments did not clarify which configuration, E or Z, isadopted in such cases.

Conclusions

The reactions of zwitterionic vinyliminium diiron com-plexes with alkynes provide multifaceted results, whichaccount for the variety of activation modes offered by di-nuclear coordination. Three different transformations havebeen evidenced: (a) 1,3 dipolar cycloaddition of alkynes withtheCþ-C-X- 1,3 dipole (X=Sor Se) in the briding ligand,which yields thiophene or selenophene species; (b) hydro-thiolation (hydroselenation) of alkynes obtained by chalco-genide nucleophilic addition in the presence of NH4PF6;(c) addition of two alkyne units, one undergoing hydrothio-lation and the second incorporated in the bridging frame asalkynyl unit.Interestingly, the different possibilities can be controlled

by choosing the appropriate reaction conditions. This pointis well evidenced by the reactions of 2a shown in Scheme 11,since the products depend on the nature of the alkyne(primary and internal alkynes), and by the presence orabsence of an external proton source.A further remarkable aspect is that each transformation is

selective, and in most of the cases one single product in asingle isomeric form is observed.Our findings add a further piece of evidence on the

potential of bridging C3 ligands in diiron complexes inproviding new synthetic approaches to uncommon species.

Experimental Section

General Data. All reactions were routinely carried out undera nitrogen atmosphere, using standard Schlenk techniques.Solvents were distilled immediately before use under nitrogenfrom appropriate drying agents. Chromatography separationswere carried out on columns of SiO2. Glassware was oven-driedbefore use. Infrared spectra were recorded at 298K on a Perkin-Elmer Spectrum 2000 FT-IR spectrophotometer, and elementalanalyses were performed on a ThermoQuest Flash 1112 SeriesEA instrument. All NMR measurements were performed on aVarianMercury Plus 400 instrument. The chemical shifts for 1H

and 13C were referenced to internal TMS. The spectra were fullyassigned via DEPT experiments and 1H,13C correlation mea-sured through gs-HSQC and gs-HMBC experiments.26 Unlessotherwise stated, NMR spectra were recorded at 298 K. NMRsignals due to a second isomeric form (where it has been possibleto detect and/or resolve them) are italicized. NOE measure-ments were recorded using the DPFGSE-NOE sequence.27 Allthe reagents were commercial products (Aldrich Co.) of thehighest purity available and used as received. Complexes 1a,band 2a,b were prepared by published methods.3

Synthesis of [Fe2{μ-K1(N):η1(C):η1(C)-Cγ(R0)CβEC(R

0 0)dC-(CO2Me)CrN(Me)(R)}(μ-CO)(CO)(Cp)2] (R=R0 =Me, E=

Se, R0 0 =CO2Me, 3a; R=R0 =Me, E=Se, R0 0 =H, 3b; R=

Xyl, R0 = Tol, E = S, R0 0 = CO2Me, 4). A solution of 1a(120 mg, 0.254 mmol), in CH2Cl2 (15 mL), was treated withC2(CO2Me)2 (0.10 mL, 0.81 mmol). The resulting mixture wasstirred for 20 min. Removal of the solvent and chromatographyof the residue on an alumina column, with CH2Cl2 as eluent,gave a brown band of 3a (133 mg, 85%). Crystals suitable forX-ray analysis were obtained by a CH2Cl2 solution layered withpentane, at-20 �C.Anal. Calcd for C24H25Fe2NO6Se: C, 46.94;H, 4.10;N, 2.28. Found: C, 47.02;H, 4.18;N, 2.36. IR (CH2Cl2):ν(CO) 1932 (vs), 1749 (s), 1735 (s), 1697 (m) cm-1. 1H NMR(CDCl3): δ 4.51, 4.38 (s, 10 H, Cp); 3.80, 3.70 (s, 6 H, CO2Me);3.64 (s, 3 H, CγMe); 2.46, 2.01 (s, 6 H, NMe). 13C NMR(CDCl3): δ 289.1 (μ-CO); 215.1 (CO); 187.7 (Cγ); 168.0, 164.3,163.2, 160.2 (CR, Cβ, and CO2Me); 137.9, 134.1 (CCO2Me);87.8, 83.8 (Cp); 59.6, 52.7 (CO2Me); 51.9 (NMe); 47.4 (CγMe).

Compounds 3b and 4 were obtained by the same proceduredescribed for 3a, by reacting 1a and 2a with HCtCCO2Me andC2(CO2Me)2, respectively.

3b (yield: 75%). Anal. Calcd for C22H23Fe2NO4Se: C, 47.52;H, 4.17;N, 2.52. Found: C, 47.55;H, 4.06;N, 2.49. IR (CH2Cl2):ν(CO) 1925 (vs), 1750 (s), 1734 (s) cm-1. 1H NMR (CDCl3): δ

Scheme 10 Scheme 11a

aAncillary Cp and CO ligands are omitted for clarity.

(26) Wilker, W.; Leibfritz, D.; Kerssebaum, R.; Beimel, W. Magn.Reson. Chem. 1993, 31, 287.

(27) Stott, K.; Stonehouse, J.; Keeler, J.; Hwang, T. L.; Shaka, A. J.J. Am. Chem. Soc. 1995, 117, 4199.

1804 Organometallics, Vol. 29, No. 7, 2010 Busetto et al.

8.58 (s, 1 H, CH); 4.50, 4.37 (s, 10 H, Cp); 3.87 (s, 3 H, CO2Me);3.57 (s, 3 H, CγMe); 2.55, 2.22 (s, 6 H, NMe). 13C NMR(CDCl3): δ 291.3 (μ-CO); 215.9 (CO); 187.0 (Cγ); 167.2, 164.4,163.4 (CR, Cβ, and CO2Me); 138.0, 133.5 (CCO2Me); 87.6, 83.8(Cp); 57.2 (CO2Me); 51.7, 51.1 (NMe); 48.6 (CγMe).

4 (yield: 80%). Anal. Calcd for C37H35Fe2NO6S: C, 60.59; H,4.81; N, 1.91. Found: C, 60.66; H, 4.75; N, 1.94. IR (CH2Cl2):ν(CO) 1933 (vs), 1756 (s), 1738 (s), 1695 (m) cm-1. 1H NMR(CDCl3): δ 8.02-6.60 (7 H, Me2C6H3 and MeC6H4); 4.84, 3.96(s, 10 H, Cp); 4.01, 3.78 (s, 6 H, CO2Me); 2.70, (s, 3 H, NMe);2.31, 2.24 (s, 6 H,Me2C6H3); 1.98 (s, 3 H,MeC6H4).

13C NMR(CDCl3): δ 276.6 (μ-CO); 218.7 (CO); 180.7 (Cγ); 168.9,162.2 (CO2Me); 168.7 (Cβ); 156.2 (CR); 147.4 (Cipso-Xyl); 141.3(Cipso-Tol); 135.8-128.4 (Carom and C-CO2Me); 89.3, 84.6 (Cp);53.5, 51.7 (CO2Me); 42.4 (NMe); 21.3 (MeC6H4); 18.1, 17.7(Me2C6H3).Synthesis of [Fe2{μ-Cγ(Me)CβSeC(CO2Me)dC(CO2Me)-

CrN(Me)2}(μ-CO)(CO)(CNBut)(Cp)2] (5). A solution of 3a

(80 mg, 0.130 mmol), in THF (8 mL), was treated with CNBut

(0.150 mmol). The mixture was heated at reflux temperature for15min; then it was allowed to cool to room temperature. Solventremoval and chromatography of the residue on an Al2O3

column with CH2Cl2 as eluent gave 5. Yield: 77 mg, 85%.Crystals suitable for X-ray analysis were obtained by a CH2Cl2solution layered with pentane, at -20 �C. Anal. Calcd forC29H34Fe2N2O6Se: C, 49.96; H, 4.92; N, 4.02. Found: C,50.02; H, 4.86; N, 3.95. IR (CH2Cl2): ν(CtN) 2122 (vs),ν(CO) 1942 (m), 1931 (s), 1762 (vs), 1750 (vs), 1732 (s), 1698(m) cm-1. 1H NMR (CDCl3): δ 4.73, 4.59 (s, 10 H, Cp); 3.89,3.76 (s, 6 H, CO2Me); 3.15 (s, 3 H, CγMe); 2.80 (s, 6 H, NMe);0.96 (s, 9 H, But). 13C NMR (CDCl3): δ 280.1 (μ-CO); 213.2(CO); 195.4 (Cγ); 168.7, 162.7 (CO2Me); 159.4 (Cβ); 142.3 (CR);139.3, 124.5 (C-CO2Me); 122.0 (CN); 88.8, 87.6 (Cp); 60.0(CC3H9); 56.5 (CγMe); 52.4, 51.9 (CO2Me); 44.3 (NMe); 29.9(CC3H9).Synthesis of [Fe2{μ-K1(O):η1(C):η3(C)-Cδ(CtCCO2Me)-

Cγ(R0)Cβ(SCHdCHCO2Me)-Cr(O)N(Me)(Xyl)}(μ-CO)(Cp)2]

(R0 =Tol, 6a;R0 =Me,6b).Compound 2a (100mg, 0.169mmol),inCH2Cl2 (15mL),was treatedwithHCtC(CO2Me) (0.4mmol).The solution was stirred for 20 min; then it was filtered throughalumina. A brown band was collected by using CH2Cl2 as eluent,affording 6a, upon solvent removal. Yield: 99 mg, 77%. Anal.Calcd for C39H37Fe2NO6S: C, 61.68; H, 4.91; N, 1.84. Found: C,61.76; H, 5.00; N, 1.79. IR (CH2Cl2): ν(CtC) 2162 (m), ν(CO)1773 (s), 1698 (vs), ν(CdC) 1564 (w), ν(CRdO) 1512 (w) cm-1. 1HNMR (CDCl3): δ 7.90-6.90 (7 H,Me2C6H3 andMeC6H4); 7.38,5.58 (d, 2 H, 3JHH = 10 Hz, CH); 4.65, 4.33 (s, 10 H, Cp); 3.82,3.67 (s, 6 H, CO2Me); 2.39 (s, 3 H, NMe); 2.32 (s, 3 H,MeC6H4);2.01, 1.41 (s, 6H,Me2C6H3).

13CNMR (CDCl3): δ 286.6 (μ-CO);175.1 (CR); 166.3, 153.0 (CO2Me); 155.3 (Cδ) 147.5 (Cβ); 141.7-126.8 (Carom); 115.7, 89.3 (CtC); 111.0, 102.1 (CH); 106.7 (Cγ);86.4, 85.2 (Cp); 52.3 50.9 (CO2Me); 40.0 (NMe); 19.4 (C6H4Me);18.9, 17.5 (Me2C6H3).

Compound 6bwas obtained by the same procedure describedfor 6a, by reacting 2bwith HC2(CO2Me). Crystals of 6b suitablefor X-ray analysis were obtained by a CH2Cl2 solution layeredwith pentane, at -20 �C.

6b (yield: 92%). Anal. Calcd for C33H33Fe2NO6S: C, 58.00;H, 4.87;N, 2.05. Found: C, 58.05;H, 4.79; N, 2.00. IR (CH2Cl2):ν(CtC) 2169 (m), ν(CO) 1772 (s), 1697 (vs), ν(CRdO) 1521 (w)cm-1. 1H NMR (CDCl3): δ 7.34, 5.55 (d, 2 H, 3JHH = 9.51 Hz,CH); 7.27-6.80 (3 H, Me2C6H3); 4.60, 4.24 (s, 10 H, Cp); 3.91,3.61 (s, 6 H, CO2Me); 3.00 (s, 3 H, CγMe); 2.40 (s, 3 H, NMe);2.00, 1.48 (s, 6 H, Me2C6H3).

13C NMR (CDCl3): δ 287.8(μ-CO); 175.3 (CR); 166.2, 154.2 (CO2Me); 156.4 (Cδ); 147.1(Cβ); 142.1 (Cipso-Xyl); 134.8-127.2 (Carom); 115.8, 91.5 (CtC);110.2, 101.8 (CH); 104.5 (Cγ); 85.4, 84.5 (Cp); 52.4, 50.9(CO2Me); 39.9 (NMe); 23.0 (CγMe); 19.1, 17.2 (Me2C6H3).Synthesis of [Fe2{μ-η

1:η3

-Cγ(R0)dCβ(ECR

00dCHCO2Me)-CrdN(Me)(Xyl)}(μ-CO)(CO)(Cp)2][PF6] (R

0 = Tol, E = S,

R0 0 =H,7a;R0 =Me,E=S,R00 =H,7b;R0 =Tol,E=S,R0 0 =CO2Me, 7c; R0 =Me, E= S, R0 0 =CO2Me, 6e; R0 =Tol, E=Se, R0 0 = H, 8a; R0 = Tol, E = Se, R0 0 = CO2Me, 8b). To asolution of complex 2a (100mg, 0.169mmol), inCH2Cl2 (25mL),were added NH4PF6 (400 mg, 2.454 mmol) and HCtC(CO2Me)(0.035 mL, 0.393 mmol) in the order given. The mixture wasstirred for 2 h; then it was filtered on a Celite pad. Removal of thesolvent gave a residue that was washed with diethyl ether (2 �20 mL). Crystallization from a CH2Cl2 solution layered withdiethyl ether, at-20 �C, gave 7a as a brownmicrocrystalline solid.Yield: 111 mg, 80%. Anal. Calcd for C35H34F6Fe2NO4PS: C,51.18; H, 4.17; N, 1.71. Found: C, 51.26; H, 4.19; N, 1.79. IR(CH2Cl2): ν(CO) 1990 (vs), 1832 (s), 1702 (s) cm-1. 1H NMR(CDCl3): δ 7.65-7.26 (7 H, Me2C6H3 and MeC6H4); 7.36, 5.93(d, 2H, 3JHH=9.88Hz, SCHdCH); 5.17, 5.16 (s, 10H,Cp); 3.69(s, 3H,CO2Me); 3.51 (s, 3H,NMe); 2.55, 2.03 (s, 6H,Me2C6H3);2.43 (s, 3 H,MeC6H4).

13CNMR (CDCl3): δ 248.8 (μ-CO); 227.4(CR); 211.5 (CO); 210.2 (Cγ); 166.2 (CO2Me); 149.2 (Cipso-Tol);148.0, 114.4 (SCHdCH); 140.4 (Cipso-Xyl); 136.6-126.6 (Carom);93.3, 88.6 (Cp); 63.7 (Cβ); 51.4 (NMe); 51.3 (CO2Me); 21.0(MeC6H4) 18.0, 17.6 (Me2C6H3).

Complexes 7b-d and 8a,b were prepared by the same proce-dure described for 7a, by reacting the appropriate alkyne with2a,b and 1b, respectively.

7b (yield: 82%). Anal. Calcd for C29H30F6Fe2NO4PS: C,46.74; H, 4.06; N, 1.88. Found: C, 46.77; H, 4.00; N, 1.79. IR(CH2Cl2): ν(CO) 1988 (vs), 1825 (s), 1701 (w) cm-1. 1H NMR(CDCl3): δ 7.45-7.10 (3 H, Me2C6H3); 7.37, 6.25 (d, 2 H,3JHH = 9.51 Hz, SCHdCH); 5.63, 4.93 (s, 10 H, Cp); 4.17 (s,3 H, CγMe); 3.83 (s, 3 H, CO2Me); 3.40 (s, 3 H, NMe); 2.51, 2.01(s, 6 H, Me2C6H3).

13C NMR (CDCl3): δ 250.4 (μ-CO); 226.5(CR); 213.0 (CO); 210.5 (Cγ); 166.7 (CO2Me); 147.4, 117.0(SCHdCH); 140.5 (Cipso-Xyl); 134.1-129.0 (Carom); 92.4, 89.1(Cp); 66.6 (Cβ); 51.8 (NMe); 50.2 (CO2Me); 39.8 (CγMe); 17.9,17.8 (Me2C6H3).

7c (yield: 74%). Anal. Calcd for C37H36F6Fe2NO6PS: C,50.33; H, 4.13; N, 1.59. Found: C, 50.42; H, 4.03; N, 1.63. IR(CH2Cl2): ν(CO) 1998 (vs), 1834 (s), 1728 (s) cm-1. 1H NMR(CDCl3): δ 7.56-7.02 (7 H, Me2C6H3 and MeC6H4); 6.44, 5.95(s, 1 H, SCdCH); 5.02, 4.99, 4.97, 4.88 (s, 10 H, Cp); 3.78, 3.75,3.74, 3.73 (s, 6 H, CO2Me); 3.70, 3.57 (s, 3 H, NMe); 2.56, 2.04,2.02 (s, 6 H, Me2C6H3); 2.44, 2.42 (s, 3 H, MeC6H4). Isomerratio 1:1. 13CNMR (CDCl3): δ 249.9, 249.2 (μ-CO); 227.7, 226.8(CR); 210.0, 209.8 (CO); 208.9, 208.6 (Cγ); 163.3, 163.2 (CO2Me);149.6, 149.2 (Cipso-Tol); 140.4 (Cipso-Xyl); 137.6-124.0 (Carom);120.3 (SCdCH); 93.1, 93.0, 88.8 (Cp); 64.6, 62.3 (Cβ); 53.7, 53.4(NMe); 52.3, 52.1, 51.1, 50.5 (CO2Me); 21.2-17.7 (MeC6H4 andMe2C6H3).

7d (yield: 81%). Anal. Calcd for C31H32F6Fe2NO6PS: C,46.35; H, 4.02; N, 1.74. Found: C, 46.39; H, 3.98; N, 1.80. IR(CH2Cl2): ν(CO) 1997 (vs), 1822 (s), 1737 (s), 1719 (s) cm-1. 1HNMR(CDCl3): δ 7.26-6.87 (4H,Me2C6H3 and SCdCH); 5.22,4.67 (s, 10 H, Cp); 3.97 (s, 3 H, CγMe); 3.75, 3.70 (s, 6 H,CO2Me); 3.43 (s, 3 H, NMe); 2.54, 2.06 (s, 6 H, Me2C6H3).

13CNMR (CDCl3): δ 252.0 (μ-CO); 226.5 (CR); 211.0 (CO); 209.8(Cγ); 169.4, 165.5 (CO2Me); 141.7 (Cipso-Xyl); 134.0-128.6(Me2C6H3); 113.0 (CH); 91.3, 87.6 (Cp); 69.4 (Cβ); 52.1(NMe); 51.9, 49.9 (CO2Me); 38.2 (CγMe); 18.1, 17.5 (Me2C6H3).

8a (yield: 88%). Anal. Calcd for C35H34F6Fe2NO4PSe: C,48.42; H, 3.95; N, 1.61. Found: C, 48.46; H, 4.00; N, 1.55. IR(CH2Cl2): ν(CO) 1998 (vs), 1823 (s), 1712 (w) cm-1. 1H NMR(CDCl3): δ 7.35-6.62 (9 H, Me2C6H3, MeC6H4, andSeCHdCH); 4.71, 4.37 (s, 10 H, Cp); 3.75 (s, 3 H, CO2Me);2.96 (s, 3 H, NMe); 2.40 (s, 3 H, MeC6H4); 2.11, 1.91 (s, 6 H,Me2C6H3).

13C NMR (CDCl3): δ 252.3 (μ-CO); 229.3 (CR);209.1 (CO); 207.7 (Cγ); 166.7 (CO2Me); 147.4-121.7 (Carom andSeCHdCH); 91.7, 87.0 (Cp); 68.5 (Cβ); 53.1 (CO2Me); 51.8(NMe); 21.0 (MeC6H4); 17.7, 17.0 (Me2C6H3).

8b (yield: 79%). Anal. Calcd for C37H36F6Fe2NO6PSe: C,47.98; H, 3.92; N, 1.51. Found: C, 48.03; H, 3.96; N, 1.46. IR

Article Organometallics, Vol. 29, No. 7, 2010 1805

(CH2Cl2): ν(CO) 1997 (vs), 1820 (s), 1737 (s), 1719 (s) cm-1. 1HNMR (CDCl3): δ 7.63-6.85 (3 H, Me2C6H3); 5.46 (s, 1 H,SeCdCH); 4.59, 4.54 (s, 10H,Cp); 3.75 (s, 6H,CO2Me); 3.55 (s,3 H, NMe); 2.43, 2.20 (s, 6H,Me2C6H3); 2.39 (s, 3 H, C6H4Me).13C NMR (CDCl3): δ 253.4 (μ-CO); 229.6 (CR); 208.1 (CO);206.4 (Cγ); 165.4 165.2 (CO2Me); 147.8-122.3 (Carom andSeC(CO2Me)dCH); 91.8, 88.0 (Cp); 69.1 (Cβ); 53.1 (NMe);52.2, 51.9 (CO2Me); 21.1-17.7 (MeC6H4 and Me2C6H3).X-ray Crystallography. The diffraction experiments were

carried out on a Bruker APEX II diffractometer equipped withaCCDdetector usingMoKR radiation.Datawere corrected forLorentz polarization and absorption effects (empirical absorp-tion correction SADABS).28 Structures were solved by directmethods and refined by full-matrix least-squares based on alldata using F2.29 All hydrogen atoms were fixed at calculatedpositions and refined by a riding model. All non-hydrogenatoms were refined with anisotropic displacement parameters,unless otherwise stated.

3a 3CH2Cl2. Similar U restraints were applied to the C atoms(s.u. 0.01). The Cp ligand bonded to Fe(2) is disordered over twopositions. Disordered atomic positions were split and refinedisotropically usingoneoccupancyparameter perdisorderedgroup.

5. SimilarU restraints were applied to the C, O, and N atoms(s.u. 0.01). The But group in the isonitrile ligand is disordered

over two positions. Disordered atomic positions were split andrefined isotropically using one occupancy parameter per dis-ordered group.

6b. Two independent molecules are present within the unitcell, showing the same connectivity, only minor differences inthe bonding parameters, and opposite absolute structure. Thecrystals display combined pseudomerohedral (monoclinic withβ approximately 90�, which emulates orthorhombic) and race-mic twinning. The appropriate twinningmatrix was used duringrefinement (TWIN 1 0 0 0 -1 0 0 0 -1 -4), and the four twincomponents refined resulting in the following refined twincomponent factors: 0.20920, 0.40583, and 0.26416 (the fourthcomponent is the complement at one). SimilarU restraints wereapplied to the C and O atoms (s.u. 0.005), and rigid bondrestraints (s.u. 0.005) were applied to all atoms.

Acknowledgment. WethanktheMinisterodell’Universit�ae della Ricerca (M.I.U.R.) (project: “New strategies for thecontrol of reactions: interactions of molecular fragments withmetallic sites inunconventional species”) and theUniversityofBologna for financial support.

Supporting Information Available: Crystallographic data forcompounds 3a, 5, and 6b in CIF format. Tables with selectedbond lengths and bond angles for 3a, 5, and 6b. Crystal dataand experimental details for 3a 3CH2Cl2, 5, and 6b. Thismaterial is available free of charge via the Internet at http://pubs.acs.org.

(28) Sheldrick, G. M. SADABS, Program for empirical absorptioncorrection; University of G€ottingen: Germany, 1996.(29) Sheldrick, G. M. SHELX97, Program for crystal structure

determination; University of G€ottingen: Germany, 1997.