表 有機金属化合物に使用される一般的な配位子 (Collman, J. P.; Hegedus, L. S., “Principles and Applications of Organotransition Metal Chemistry”, 2nd Ed., Univ. Sci. Book, 1987)

Ligand name Formal charge

Number of electrons donated

H (terminal or bridging hydride) -1 2 X (terminal F, Cl, Br, I, or pseudohalide such as a cyanide) -1 2 µ-Xa (bridging halide)

MX

M

-1 4

OR, SR(terminal alkoxide or thiolate) -1 2 µ-OR, µ-SR (bridging alkoxide or thiolate)

M

RO

M

-1 4

ΝR2, PR2 (terminal amide or phosphide) -1 2 µ- NR2, µ- PR2 (bridging amide or phophide)

M

R2

NM M

R2

PM

-1 4

ER3, EX3 (E = Si, GE, Sn) -1 2 CH3 or other alkyl -1 2 µ- CH3 or other alkyl(bridging alkyl)b

M

H3

CM

-1 2b

η1-aryl, alkenyl (vinyl), alkynyl (terminal and bound through only one carbon)

HM

M

-1 2

η2-alkenyl (vinyl) (terminal but bound through two carbons)

M

-1 4

µ-η2-alkenyl (bridging and bound to one metal through both carbons)

M M

-1 4

η3-allyl (bound through three carbons)

M

-1 4

η4-cyclobutadiene or acyclic diene (bound through four carbons)

M

0 4

η5-cyclopentadienyl or cyclic or acyclic dienyl (bound through five carbons)

M

-1 6

η6-arene (bound through six carbons)

M

0 6

η7-cycloheptatrienyl (bound through seven carbons)

M

-1 8c

η1-acyl (bound through carbon only)

M C R

O

-1 2

η2-acyl (bound through carbon and oxygen)

M C R

O

-1 4

η2-ketone (bound through carbon and oxygen)

MC

R

OM

0 2

η2-alkene (bound through both carbons)

M

0 2

η3-cyclopropenyl

M

-1c 4c

η2-alkyne (bound through both carbons)

M

0 2d

µ-η2-alkyne (bridging and bound to both metals through two carbons)

C C

M M

0 4

CYR (terminal carbene, where Y is a substituent capable of π interaction with the carbene carbon)e

M=CCl2 M=CPh2 M=C(OMe)R

0 2

CR2 (terminal alkylidene or carbene, where no substituent is capable of π interaction with the carbene carbon)e

H

C

R

M

-2 4

µ-CYR or µ-CR2 (bridging alkylidene or carbene)

C

M

RR

M

-2 4

CR, CX (terminal alkylidene or carbene)

M CCH3 M CNR2

-3 6

µ-CR (bridging alkylidene)

C

MM

R

M

-3 6

CO (terminal or bridging carbonyl) 0 2 µ-η2-CO

MC

O

M

0 4

CNR (isocyanide, isonitrile) 0 2

N2 (terminal dinitrogen) 0 2

NO (terminal or bridging nitrosyls)f M-N=O (linear)

+1f 2

NO (terminal or bridging nitrosyls) M-N=O (terminal type --- linear)

M MN

O

(bridging type --- like bridging CO)

0 3

NO (terminal nitorosyls) M-N=O(bent)

-1 2

N2R (diazenides)f

M-N=NR

+1f 2

NR (terminal imide) 0 2

M=NR PR3, PX3, AsR3, SbR3, and amines, imines, and nitriles 0 2 ER2 (E = O, S, Se, Te) 0 2 N (nitride) -3 6 O (terminal or bridging oxide) -2 4 O2 (terminal or bridging peroxide)

M

O O

-2 4

O2 (superoxide)

M

O O

-1 2

a A µ in front of a Ligand indicates that it bridges two or more metals. b This assumes that the C-H bonds interact with neither metal. Bridging alkyls which have a C-H bond interacting with a metal will be discussed in Chapter 3; they are formed 4-electron donors.

c The formal Ligand charges and numbers of electrons donated given for η7-cycloheptatrienyl and η3-cyclopropenyl are consistent with those assigned which is given below. However, the older literature frequently considered a η7-cycloheptatrienyl ligand to be a formal cation because of the aromaticity of the latter when uncoordinated. The older assignment gave the misleading impression that η7-cycloheptatrienyl ligands were more susceptible to nucleophilic attack than other coordinated polyenes; in fact, as we shall see in Chapter 7, η7-cycloheptatrienyl ligands are the least susceptible to nucleophilic attack of all common coordinated polyenes.

d As we shall see later in this chapter and in Chapter 3, alkynes sometimes also serve as π donors and thus are sometimes called four-electron donors.

e These two types of carbine ligands, which are treated differently in the literature, are the “electrophilic” and “nucleophilic” carbenes that will be discussed in Chapter 3.

f Both of these ligands, as will be discussed in Chapter 3, sometimes accepted substantial amounts of additional electron density, and change from a linear to a bent geometry. If nitrosyls and diazenides are known to be bent, they are given formal charges of -1; they remain two-electron donors.