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Papers by Peter Maitlis

Research paper thumbnail of The migratory insertion of carbon monoxide in pentamethylcyclopentadienyliridium (III) complexes. Structural effects on reactivity and mechanism for rhodium and iridium systems

Inorganica Chimica Acta, 1995

The reactions of complex (CsMe5)Ir(C1)(CO)(Me) (la) with cyclohexylisocyanide and phosphines (L=C... more The reactions of complex (CsMe5)Ir(C1)(CO)(Me) (la) with cyclohexylisocyanide and phosphines (L=CyNC, PHPh2, PMePh2, PMe2Ph) give the products of alkyl migratory insertion (CsMes)Ir(C1)(COMe)(L), in toluene or tetrahydrofuran at 323 K or higher temperature. The phenyl analogue (C5Me5) Ir (C1) (CO) (Ph) or the iodide complexes (C~Mes) Ir (I) (CO) (R) ( R = Me, Ph ) are not reactive under the same conditions. The reaction of (C5Me~) Ir (C1) (CO) (Me) with PMePh2 and PMe2Ph in acetonitrile yields the chloride substitution product [ (CsMes)Ir(CO) (L) (Me) ] +CI-. Kinetic measurements for the reactions of (C~Mes)Ir(C1) (CO) (Me) in toluene are first order in the iridium complex and exhibit a saturation dependence on the incoming donors L. Analysis of the data suggests a two-step process involving (i) rapid formation of a molecular complex [ (C5Mes)Ir(C1) (CO) (Me), (L) ], in which the structure of la is unperturbed within the limits of spectroscopic analysis, and (ii) rate determining methyl migration. The reaction parameters are K for the pre-equilibrium step (K= 1.5 (CyNC), 7.3 (PHPh2), 7.1 (PMePh2) dm 3 mol-1 at 323 K) and k2 for the slow carbon-carbon bond formation (k2(10 s) =6.9 (CyNC), 1.2 (PHPh2), 1.0 (PMePh2) s-1 at 323 K). The activation parameters for the methyl migration step in the reaction with PMePh2, obtained between 308 and 338 K, are AH ~ = 106_+ 16 kJ mol-~ and AS* = -14 + 5 J K-1 mol-1. The reaction of la with PMePh2 proceeds at similar rates in tetrahydrofuran (K = 3.7 dm 3 mol-1, k2 ( 1 05 ) = 1.2 s-1,323 K). The crystal structure of (CsMe 5) lr (C1) (COMe) (PMe2Ph) has been determined by X-ray diffraction. C2oH29CIOPIr: Mr = 544.1, monoclinic, P21/n, a = 8.084(2), b = 9.030(2), c = 28.715(3) /~, fl = 91.41 (3)°, Z = 4, D c = 1.71 g cm-3 V = 2095.5/~3 room temperature, Mo K a, A = 0.71069,/z = 65.55 cm-~, F(000) = 1044, R = 0.037 for 2453 independent observed reflections. The complex shows a deformed tetrahedral coordination assuming the r/5-CsMe5 molecular fragment as a single coordination site. The iridium-chlorine bond is staggered with respect to two adjacent C(ring)-methyl bonds, while the Ir-P and the k-COMe bonds are eclipsed with respect to C (ring)-methyl bonds. * Dedicated to Professor Fred Basolo on his 75th birthday. * Corresponding authors. 0020-1693/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSD10020-1693 (95)04573-R We have recently reported a direct rate comparison between rhodium and iridium (M) for the oxidative addition of methyl iodide to [M(CO)212]-and to [(CsMes)M-(CO) 2 ], and for the methyl migratory insertion in [ (C5Me 5)-M(CI) (CO)Me] [3]. The migration of methyl onto CO in corresponding systems is 105-106 times faster for Rh(III) than for Ir(III).

Research paper thumbnail of The migratory insertion of carbon monoxide in pentamethylcyclopentadienyliridium (III) complexes. Structural effects on reactivity and mechanism for rhodium and iridium systems

Inorganica Chimica Acta, 1995

The reactions of complex (CsMe5)Ir(C1)(CO)(Me) (la) with cyclohexylisocyanide and phosphines (L=C... more The reactions of complex (CsMe5)Ir(C1)(CO)(Me) (la) with cyclohexylisocyanide and phosphines (L=CyNC, PHPh2, PMePh2, PMe2Ph) give the products of alkyl migratory insertion (CsMes)Ir(C1)(COMe)(L), in toluene or tetrahydrofuran at 323 K or higher temperature. The phenyl analogue (C5Me5) Ir (C1) (CO) (Ph) or the iodide complexes (C~Mes) Ir (I) (CO) (R) ( R = Me, Ph ) are not reactive under the same conditions. The reaction of (C5Me~) Ir (C1) (CO) (Me) with PMePh2 and PMe2Ph in acetonitrile yields the chloride substitution product [ (CsMes)Ir(CO) (L) (Me) ] +CI-. Kinetic measurements for the reactions of (C~Mes)Ir(C1) (CO) (Me) in toluene are first order in the iridium complex and exhibit a saturation dependence on the incoming donors L. Analysis of the data suggests a two-step process involving (i) rapid formation of a molecular complex [ (C5Mes)Ir(C1) (CO) (Me), (L) ], in which the structure of la is unperturbed within the limits of spectroscopic analysis, and (ii) rate determining methyl migration. The reaction parameters are K for the pre-equilibrium step (K= 1.5 (CyNC), 7.3 (PHPh2), 7.1 (PMePh2) dm 3 mol-1 at 323 K) and k2 for the slow carbon-carbon bond formation (k2(10 s) =6.9 (CyNC), 1.2 (PHPh2), 1.0 (PMePh2) s-1 at 323 K). The activation parameters for the methyl migration step in the reaction with PMePh2, obtained between 308 and 338 K, are AH ~ = 106_+ 16 kJ mol-~ and AS* = -14 + 5 J K-1 mol-1. The reaction of la with PMePh2 proceeds at similar rates in tetrahydrofuran (K = 3.7 dm 3 mol-1, k2 ( 1 05 ) = 1.2 s-1,323 K). The crystal structure of (CsMe 5) lr (C1) (COMe) (PMe2Ph) has been determined by X-ray diffraction. C2oH29CIOPIr: Mr = 544.1, monoclinic, P21/n, a = 8.084(2), b = 9.030(2), c = 28.715(3) /~, fl = 91.41 (3)°, Z = 4, D c = 1.71 g cm-3 V = 2095.5/~3 room temperature, Mo K a, A = 0.71069,/z = 65.55 cm-~, F(000) = 1044, R = 0.037 for 2453 independent observed reflections. The complex shows a deformed tetrahedral coordination assuming the r/5-CsMe5 molecular fragment as a single coordination site. The iridium-chlorine bond is staggered with respect to two adjacent C(ring)-methyl bonds, while the Ir-P and the k-COMe bonds are eclipsed with respect to C (ring)-methyl bonds. * Dedicated to Professor Fred Basolo on his 75th birthday. * Corresponding authors. 0020-1693/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSD10020-1693 (95)04573-R We have recently reported a direct rate comparison between rhodium and iridium (M) for the oxidative addition of methyl iodide to [M(CO)212]-and to [(CsMes)M-(CO) 2 ], and for the methyl migratory insertion in [ (C5Me 5)-M(CI) (CO)Me] [3]. The migration of methyl onto CO in corresponding systems is 105-106 times faster for Rh(III) than for Ir(III).