Fluxionality and Phosphane Arm-off Reactions of Octahedral Ruthenium(II) Complexes with the Tripodal Polyphosphane MeC(CH2PPh2)3

Abstract

Treatment of [RhCl3(triphos)] or [Rh(MeCN)3(triphos)](CF3SO3)3 [triphos= MeC(CH2PPh2)3] with Na(S2C-NEt2) affords the complexes [RhCl(S2CNEt2)(triphos)]Cl (1) and [Rh(S2CNEt2)(MeCN)(triphos)](CF3SO3)2 (2). Whereas 1 is stereochemically rigid in solution at 25°C, 2 and the analogous complex [Rh(S2CNBz2)(MeCN)(triphos)](CF3SO3)2 (3) exhibit a rapid exchange of their phosphorus environments. In contrast, the 31P-NMR spectra of both 2 and 3 at –30°C consist of well-resolved A2MX spin systems. k2P-coordinated complexes of the type [Rh(S2CNR2)2(triphos-k2P)]+ (R = Et 4, R = Me 5) with ABX spin systems may be obtained by treatment of the starting compounds with two equivalents of the respective dialkyl dithiocarbamate. The dangling phosphane arm can be readily oxidised to a phosphane oxide as in [Rh(S2CNEt2)2(triphosO-k2P)]Cl (6) [triphosO = O=P(Ph)2CH2C(Me)(CH2PPh2)2]. The analogous compound [Rh(mpy)2(triphosO-k2P)]Cl (7) (Hmpy = 2-mercaptopyridine) was isolated as the OC-6-13 isomer with trans-positioned sulphur atoms, a siting which is in accordance with a reaction mechanism involving a phosphane arm-off k3P' k3P dissociation equilibrium.