Supramolecular Allosteric Cofacial Porphyrin Complexes

Supramolecular Allosteric Cofacial Porphyrin ComplexesChristopher G. Oliveri, Nathan C. Gianneschi, SonBinh T. Nguyen,*,Chad A. Mirkin,*, Charlotte L. Stern, Zdzislaw Wawrzak,and Maren PinkJ. Am. Chem. Soc. 2007, 128, 16286 - 16296 Speaker

Allosteric RecognitionChad A. Mirkin et. al. Angew. Chem. Int. Ed. 2006, 45, 941 944The allosteric-effector-mediated shape change of a macrocycle.

Introduction-Porphyrin 93

Supramolecular Coordination ChemistryHolliday, B. J. et. al. Angew. Chem. Int. Ed. 2001, 40, 2022-2043.Hydrogen bondingp-p interactionMetal to ligand bindingvan der Waals forces

The Directional-Bonding ApproachHolliday, B. J. et. al. Angew. Chem. Int. Ed. 2001, 40, 2022-2043.

The Symmetry-Interaction Approach The symmetry-interaction synthetic strategy has granted researchers access to a variety of elegant shapes andarchitectures (for example, helicates, tetrahedra, and adamantoidstructures) through the predictable coordination chemistry of multibranched chelating ligands with transition and main group metal centers.Holliday, B. J. et. al. Angew. Chem. Int. Ed. 2001, 40, 2022-2043.

The Weak-Link Approach A critical feature of this approach is that themetals used in the assembly process are available forfurther reactions without destroying the supramolecularstructure. This approach targets condensed structures that contain strategically placed strong(metal-phosphine) and weak (metal-X) bonds.Mirkin, C. A. Acc. Chem. Res. 2005,38,825-837.

Catalytic Acyl Transfer by a Cyclic Porphyrin TrimerSanders, J. K. M. et. al. J. Am. Chem. Soc. 1994,116, 3141-3142.

Design of Allosteric Porphyrin-Based SupramoleculesPPh2 = diphenylphosphineMES = 1,3,5-trimethylbenzene

( i ) 1-bromo-2-chloroethane, K2CO3, Acetone, Reflux( ii) 1,3-propanedithiol, Y(OTf)3 (5 mol %), CH3CN(iii) KPPh2, THF(iv) S8, THF( v) NaNO2,AcCl/H2O, CH2Cl2, 0 C rtSynthesis of Ether-Based Ligand 7 and Macrocycles 8a and 8b

( vi ) 5-mesityldipyrromethane, BF3OEt2, DDQ, NEt3, CHCl3, 4 Molecular Sieves(vii ) Zn(OAc)22H2O, 4:1 CHCl3/MeOH, Reflux(viii) Cp2ZrHCl, THF, 60 C

(ix) [Rh(CO)2(Cl)]2, CH2Cl2/THF( x) [Cu(CH3CN)4]PF6, CH2Cl2/THF

X-ray crystal structure of 8aDABCO as viewed (A) from the side and (B) from the topGrayCPinkRh, RedO, YellowCl, GreenP, BlueN, Light BlueZnZn-Zn distance of 7.09 Rh-Rh distance of 24.85 P-Rh-P distance of 4.64

X-ray crystal structure of 8cDABCO as viewed (A) from the side and (B) from the topZn-Zn distance6.99 Cu-Cu distance22.6 GrayCBrownCu, RedO, YellowCl, GreenP, BlueN, Light BlueZn

( i ) ClCH2CH2PPh2, Cs2CO3, CH3CN, Reflux( ii) S8, THF(iii) n-BuLi, DMF, THF, -78 C 5-mesityldipyrromethane, BF3OEt2, DDQ, NEt3,CHCl3, 4 Molecular SievesSynthesis of Thioether-Based Ligand 13 and Macrocycles 14a-b, 15a-b

( v ) Zn(OAc)22H2O, 4:1 CHCl3/MeOH, Reflux( vi ) Cp2ZrHCl, THF, 60 C( vii) for 14a: [Rh(NBD)Cl]2, AgBF4, CH2Cl2/THF(viii) for 14b: [Cu(CH3CN)4]PF6, CH2Cl2/THF

(ix) for 15a: PPNCl/CO (1 atm)( x) for 15b: C5D5N.

NMR Data of 14a and 14bChad A. Mirkin et. al. Inorg. Chem. 2000, 39, 3432-3433Comp. 2

31P{1H} NMR (CD2Cl2)64 ppm (d,JRh-P=161 Hz)Comp. 14a

31P{1H} NMR (CD2Cl2)64.5 ppm (d,JRh-P=162 Hz)

X-ray crystal structure of 15aDABCO as viewed (A) from the side and (B) from the topGrayCPinkRh, RedO, OrangeS,YellowCl, GreenP, BlueN, Light BlueZnZn-Zn distance7.02 Rh-Rh distance22.59 P-Rh-P distance4.60 Dihedral angles17.8

X-ray crystal structure of 15cDABCO as viewed (A) from the side and (B) from the topGrayCBrownCu, RedO, YellowCl, GreenP, BlueN, Light BlueZnZn-Zn distance7.05 Cu-Cu distance22.38

Acyl transfer reactions catalyzed by a closed macrocycle vs. the corresponding open macrocycle.

Formation of 4-(acetoxymethyl)pyridine (4-AMP) plotted as concentration vs. time for 14a and 15a.

Formation of 4-(acetoxymethyl)pyridine (4-AMP) plotted as concentration vs. time for [Zn(TPP) + 16a] and [Zn(TPP) + 16b]

Catalytic efficiency of 4-PC15a14a = 2115amonomer = 141

14a is probably dynamic when in solution and the observed catalytic activity may originate from the conformational flexibility around the S atoms.

Catalytic efficiency of 3-PCDrop slightly with respect to 4-PC

=> the cavities of 14a and 15a are still flexible enough to accommodate the change in transition state distance for acyl transfer from acetylimidazole upon binding.

Catalytic efficiency of 2-PCDrop significantly with respect to 3-PC and 4-PCSimilar to those observed for the monomer

=> Unfavorable transition state (in comparison to those for 3-PC and 4-PC) for productive acyl transfer.

ConclusionThey have developed a coordination chemistrybased synthetic approach for the quantitative preparation of flexible cofacial porphyrin assemblies in which the porphyrins act as functional sites within an allosteric framework that istunable via modulation of peripheral structure control domains.

This capability enables the cofacial porphyrin structuresto act as allosteric catalysts capable of discriminatingdifferent substrate combinations and selectively transformingthem into the desired products.

Table 1. X-ray Crystallographic Data for 8aDABCO and 15aDABCO

Table 1. X-ray Crystallographic Data for 8cDABCO and 15cDABCO.

Homework1. paper15a14bAns

2. Weak-link approach (WLA)transition metalAnsTransition metalRh()Pd()1macrocycletransition metald8Rh()d10Cu()d6

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Supramolecular Allosteric Cofacial Porphyrin Complexes