Transition metal-carbon single bonds aryls

Photochemical cleavage of metal-carbon bonds constitutes a brief part of a recent review on the photochemistry of metal carbonyls. Reviews of metal-alkyl and -aryl complexes have also appeared, one of which is concerned solely with metals in Groups IV— VII. The other deals with the formation, stability, and decomposition pathways of transition metal-carbon a-bonds, subjects of much interest in recent years. Consequently the recent isolation of the first stable methylene complex [Ta(Me)(CHa)(jj-C6H6)2] and its unequivocal characterization by a single-crystal JlT-ray diffraction study is of great interest in view of the probability that related derivatives are involved in the recently reported (see Vol, 4, p. 293) examples of a-hydride elimination in metal alkyls. 

Carbon-heteroatom reductive elimination from dinuclear transition metal complexes, as was proposed by us [96,109] as the product-forming step in Pd-catalyzed C-H acetoxylation and chlorination reactions, is rare. The two formulations of the high-valent, dinuclear Pd intermediate in arylation proposed by Sanford (60 and 61) highlight that reductive elimination from dinuclear Pd structures could, in principle, proceed with either redox chemistry at both metals (bimetallic reductive elimination reductive elimination from 60) or with redox chemistry at a single metal (monometallic redox chemistry reductive elimination from 61). While structures 60 and 61 do not differ in composition, they do differ in their respective potentials for metal-metal redox cooperation to be involved in C-C bond-forming reductive elimination. 

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