365215-02-7Relevant articles and documents
First direct structural comparison of complexes of the same metal fragment to ketenes in both C,C- and C,O-bonding modes
Grotjahn,Collins,Wolpert,Bikzhanova,Lo,Combs,Hubbard
, p. 8260 - 8270 (2007/10/03)
Using a series of Ir(I) and Rh(I) ketene complexes, conclusions about the structure and bonding of complexes of the fundamentally important ketene ligand class are reached. In a unique comparison of X-ray structures of the same metal fragment to ketenes in both the η2-(C,C) and the η2-(C,O) binding mode, the Ir-C1 bond distances in complexes of trans-Cl(Ir)[P(i-Pr)3]2 to phenylketene [4, η2-(C, C)] and diphenylketene [2a, η2-(C,O)] are 2.371(3) and 2.285 A, respectively. This would be consistent with greater trans influence of a ketene ligand bound to a metal through its C=C bond than one connected by its C=O bond. Backbonding of Ir(I) and Rh(I) to diphenylketene was assessed using trans-Cl(M)[P(i-Pr)3]2η2-(C,O)-diphenylketene] (2a and 2d). Most bond lengths and angles are identical, but slightly greater back-bonding by Ir(I) is suggested by the somewhat greater deformation of the ketene C=C=O system [C-C-O angles are 136.6(4) and 138.9(4) in the Ir and Rh cases 2a and 2d, respectively]. Syntheses of new labeled ketenes Ph2C= 13C=O and Ph2C=C=18O and their RH(I) complexes are reported, along with the generation of an Ir(I) complex of PhCH=13C=O. The effects of isotopic substitution on infrared absorption data for ketene complexes are presented for the first time. Preliminary normal coordinate mode analysis allowed definitive assignment of absorptions ascribed to the C-O stretching frequencies of coordinated ketenes, which are near the absorptions for aromatic ring systems commonly found as substituents on ketenes. For free diphenylketene and four of its complexes and a phenylketene complex characterized by X-ray diffraction, the magnitude of the 13C-13C coupling between the two ketene carbons is correlated to carbon-carbon bond distance.
