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Anionic Phosphinimine-Chelate Complexes of Rhodium and Iridium:  Steric and Electronic Influences on Oxidative Addition of CH2Cl2

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journal contribution
posted on 02.02.2004, 00:00 by Katie T. K. Chan, Liam P. Spencer, Jason D. Masuda, Jenny S. J. McCahill, Pingrong Wei, Douglas W. Stephan
The phosphinimines Ph3PNR (R = Ph 1, 2,6-Me2C6H3 2, 3,5-Me2C6H3 3, 2,6-i-Pr2C6H3 4) were prepared and used to generate the species of the form [Li(o-C6H4PPh2NR)]2·Et2O (R = Ph 5, 2,6-Me2C6H3 6, 3,5-Me2C6H3 7, 2,6-i-Pr2C6H3 8). Subsequent reactions with [Rh(μ-Cl)(COD)]2 gave the complexes Rh(COD)(o-C6H4PPh2NR) (R = Ph 9, 2,6-Me2C6H3 10, 3,5-Me2C6H3 11, 2,6-i-Pr2C6H3 12). Similarly, the Ir analogue of 9 (13) was prepared using [Ir(μ-Cl)(COD)]2. The reaction of 9 with (CH2PPh2)2 afforded Rh(PPh2CH2CH2PPh2)(o-C6H4PPh2NPh) (14). Compound 9 was also shown to react with CH2Cl2 to give two products, one of which was confirmed to be [Rh(o-C6H4PPh2NPh)(CH2-o-C6H4PPh2NPh)(μ-Cl)2Rh(COD)] (15). Similar treatment of 10 and 12 with CH2Cl2 showed no reaction, while reaction of 11 with CH2Cl2 gave a mixture of unidentified products. The related imidazole-phosphinimine ligands (N2C3H3)PPh2NR (R = Ph 18, 2,6-Me2C6H3 19) were also prepared. These ligands react with NaH to give the corresponding Na-imidazolate-phosphinimines, 20 and 21, and subsequent reaction with [Rh(μ-Cl)(COD)]2 gave the complexes Rh(COD)((N2C3H2)PPh2NR) (R = Ph 22, 2,6-Me2C6H3 23). The compounds 22 and 23 do not react with CH2Cl2. The effects of steric and electronic modifications to the ligands on oxidative addition of C−Cl bonds are discussed. DFT calculations were performed on the model fragments [Rh((C6H4)PH2NH)] and [Rh((N2C3H2)PH2NH)], and the calculated atomic charges provide some insight into the reactivity of these compounds.