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-C5Me5)(PPh3)] and [Ir(CH2SiMe2CH2)(η5-C5Me5)(PPh3)]

Abstract

The interaction of [RhCl₂(η⁵-C₅Me₅)(PPh₃)] with Mg(CH₂CMe₃)Cl in pentane gives the rhodacyclo butane [[graphic omitted]H₂)(η⁵-C₅Me₅)(PPh₃)](2). The analogous reaction of [MCl₂(η⁵-C₅Me₅)(PPh₃)](M = Rh or Ir) with Mg(CH₂SiMe₃)Cl allows the isolation of the dialkyl derivatives [M(CH₂SiMe₃)₂(η⁵-C₅Me₅)(PPh₃)]. Thermolysis of [Ir(CH₂SiMe₃)₂(η⁵-C₅Me₅)(PPh₃)] in cyclohexane leads to the iridasilacyclobutane derivative [[graphic omitted]H₂)(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.