Synthesis and reactivity of rhodium and iridium alkene, alkyl and silyl complexes supported by a phenyl-substituted PNP pincer ligand

摘要

New rhodium and iridium complexes supported by the phenyl-substituted PNP pincer ligand PNP~(Ph)H (HN(2-PPh_2-4-Me-C_6H _3)_2) (1) were synthesized. The reaction of 2 equiv. of 1 with [(COD)IrCl]_2 afforded the coordination complex [(PNP ~(Ph)H)Ir(COD)]Cl (2) featuring hydrogen bonding between the N-H group and the chloride anion, as characterized by NMR spectroscopy and X-ray crystallography. Reaction of 1 with [(COE)_2IrCl]_2 or [(COE)_2RhCl]_2 in benzene provided a mixture of complexes including (PNP~(Ph)H)MHCl_2 (M = Ir (4), M = Rh (7)) and (PNP)M(COE) (M = Ir (5), M = Rh (8)). Alkene complexes of the type (PNP ~(Ph))M(L) (M = Ir, L = COD (3) and COE (5); M = Rh, L = COE (8) and L = ethylene (9)) were synthesized by reaction of (PNP~(Ph))Li with the appropriate alkene chloride complexes. Reactions of silanes with 5, 8 or 9 produced silyl hydride complexes (PNP~(Ph))MH(SiR_3) (M = Ir, R = Ph (16) and R = Et (17); M = Rh, R = Ph (18), Et (19) and Ph_2Cl (20)) via Si-H oxidative addition. The J_(SiH) coupling constants for rhodium complexes 18, 19 and 20 were determined to be ca. 35 Hz, while iridium complexes 16 and 17 exhibited coupling constants less than 10 Hz. X-Ray crystal structures of 16 and 18 reveal isostructural complexes featuring a trigonal bipyramidal geometry about iridium with a mer binding of the PNP~(Ph) ligand. A hydride ligand, located from the Fourier map for 18, has a short contact of 1.83(3) ? with the silicon atom. Oxidative addition of iodomethane to 5 and 8 afforded (PNP~(Ph))M(Me)(I)(THF) (M = Rh (14), M = Ir (12)), respectively. Arene C-H activation upon thermolysis of 12 in benzene produced (PNP~(Ph))M(Ph)(I)(THF). Iridium silyl iodide complexes (PNP~(Ph))IrI(SiR_3) (SiR_3 = SiPh_3 (21), SiH_2Mes (22) and SiH_2Xyl (23)) resulted from addition of organosilanes to 12, via elimination of CH_4.