Cyclometallation Reactions in Neopentyl and Trimethylsilyl methyl Systems of Rhodium(III) and Iridium(III). Formation and X-Ray Crystal Structures of the Four-membered Metallacycles [Rh(CH2CMe2CH2)(eta-5-C5Me5)(PPh3)] and [Ir(CH2SiMe2CH2)(eta-5-C5Me5) (PPh3)]

full title:Cyclometallation reactions in neopentyl and trimethylsilylmethyl systems of rhodium(III) and iridium(III). Formation and X-ray crystal structures of the four-membered metallacycles [Rh(CH2CMe2CH2)(η5-C 5Me5)(PPh3)] and [Ir(CH2SiMe2CH2)(η5-C 5Me5)(PPh3)] The interaction of [RhCl2(η5-C5Me5) (PPh3)] with Mg(CH2CMe3)Cl in pentane gives the rhodacyclo butane [Rh(CH2)(η5-C5Me5)(PPh 3)] (2). The analogous reaction of [MCl2(η5-C5Me5)(PPh 3)] (M = Rh or Ir) with Mg(CH2SiMe3)Cl allows the isolation of the dialkyl derivatives [M(CH2SiMe3)2(η5-C 5Me5)(PPh3)]. Thermolysis of [Ir(CH2SiMe3)2(η5-C 5Me5)(PPh3)] in cyclohexane leads to the iridasilacyclobutane derivative [Ir(CH2SiMe3CH2) (η5-C5Me5) (PPh3)] (6). The mechanism of formation of the metallacyclobutane derivatives is discussed. The X-ray crystal structures of (2) and (6) have been determined. The two metallacycle compounds give isostructural crystals belonging to the P21/n space group with four molecules in the unit cell of dimensions for (2): a = 17.199(6), b = 10.987(4), c = 16.064(5) Å,β = 109.54(2)°; (6): a = 17.098(7), b = 11.294(5), c = 15.977(7) Å,β = 108.17(2)°. Their crystal structures, refined to R = 0.0441 and 0.0389 for (2) and (6) respectively, are built up of deformed 'three-legged piano stools', one leg being the M-P bond [Rh-P = 2.230(2), Ir-P = 2.236(2) Å], the other two being the M-C a bonds [Rh-C = 2.1 00(5) (av.), Ir-C = 2.1 59(7) Å (av.)] of the metallacyclobutane ring with C-Rh-C = 66.8(2) and C-Ir-C = 77.3(4)°. These rings are puckered: angle between M-C ⋯ C and E-C ⋯ C = 16.5(4) and 18.9(6)° for (2) (E = C) and (6) (E = Si), respectively.