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Steric and Electronic Parameters Characterizing Bulky and Electron-Rich Dialkylbiarylphosphines

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journal contribution
posted on 28.03.2011, 00:00 by Olivier Diebolt, George C. Fortman, Hervé Clavier, Alexandra M. Z. Slawin, Eduardo C. Escudero-Adán, Jordi Benet-Buchholz, Steven P. Nolan
The steric and electronic properties of several sterically demanding tertiary phosphines (dicyclohexylphosphino)biphenyl (2a), 2-dicyclohexylphosphino-2′-methylbiphenyl (2b), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (2c), 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl (2d), 2-diphenylphosphino-2′-(N,N-dimethylamino)biphenyl (2e), 2-di-tert-butylphosphino-2′-(N,N-dimethylamino)biphenyl (2f), and di(cyclohexyl)phenylphosphine (2g) have been studied by synthesizing and characterizing iridium complexes of types [IrCl(cod)(L)] (L = 2ad) and cis-[IrCl(CO)2(L)] (L = 2ad and 2g). The infrared stretching frequencies of the carbonyl complexes permit an estimation of the ligand donor properties (basicity) and suggest that the donor properties of ligands 2ad reside between that of 2g and PCy3. The crystal structures of several [IrCl(cod)(L)] (L = 2ad) and cis-[IrCl(CO)2(L)] (L = 2ad and 2g) complexes are reported and used to quantify the ligand steric parameter.