First Direct Structural Comparison of Complexes of the Same Metal Fragment to Ketenes in Both C,C- and C,O-Bonding Modes

Abstract

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 eta(2)-(C,C) and the eta(2)-(C,O) binding mode, the Ir-Cl bond distances in complexes of trans-Cl(Ir)[P(i-Pr)(3)](2) to phenylketene [4, eta(2)-(C,C)] and diphenylketene [2a, eta(2)-(C,O)] are 2.371(3) and 2.285(2) 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. Back-bonding of Ir(I) and Rh(I) to diphenylketene was assessed using trans-Cl(M)[P(i-Pr)(3)](2)[eta(2)-(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 Ph(2)C=(13)C=O and Ph(2)C=C=(18)O and their Ir(I) and Rh(I) complexes are reported, along with the generation of an Ir(I) complex of PhCH=(13)C=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 (13)C-(13)C coupling between the two ketene carbons is correlated to carbon-carbon bond distance.

Structural Distortions of Coordinated Ketene Molecule Induced by the Pseudo Jahn-Teller Effect

“…In the complex VCp 2 -H 2 C 2 O the η 2 -(C-O) binding mode takes place, the ketene molecule undergoes the in-plane distortion ( ( C-C-O= 137.10º) with the signifi cant elongation of the C-O bond (1.29Å versus 1.17Å in free molecule). The same C-O bond elongation and C-C-O moiety bending in η 2 -(C-O) coordinated ketenes is also observed in other early transition metal complexes [1,3,7]. The η 2 -(C-C) binding mode is preferred in the complex (II).…”

“…In this case the off-diagonal matrix element F Q (1,2) can be simply expressed (Eq. (5)) by means of the off-diagonal orbital…”

“…To date, a number of complexes with ketenes were synthesized and structurally determined by X-ray diffraction [1][2][3][4][5][6][7]. It is generally accepted that early transition metal complexes favor the η 2 -(C-O) bonding mode [3,6], the η 2 -(C-C) mode is preferred by late transition metal complexes [2,7].…”

“…It is generally accepted that early transition metal complexes favor the η 2 -(C-O) bonding mode [3,6], the η 2 -(C-C) mode is preferred by late transition metal complexes [2,7]. Moreover, in the fi rst case the ketene molecule undergoes the in-plane distortion, while the η 2 -(C-C) coordination mode leads to the out-of-plane distortion of ketene [1,7,8]. Some theoretical investigations of ketene binding to Ni, Pt [7], and Pd [8] were reported.…”

An investigation into the photochemistry of, and the electrochemically induced CO-loss from, [(CO)5MC(OMe)Me](M = Cr or W) using low-temperature matrix isolation, picosecond infrared spectroscopy, cyclic voltammetry, and time-dependent density functional theory

“…10,11 In trans-Ir(P(i-Pr) 3 ) 2 Cl (diphenylketene) however, the ketene ligand coordinates to the Ir atom as a (η 2 -C,O) ligand. 12 The CvCvO angle is 136.6(4)°a nd the ν CCvO absorption occurs at 1636 cm −1 i.e. to the low energy side of the bridging carbonyl region.…”