Fluxionality and Phosphane Arm‐off Reactions of Octahedral Rhodium(III) Complexes with the Tripodal Polyphosphane MeC(CH 2 PPh 2 ) 3

Treatment of [RhCl 3 (triphos)] or [Rh(MeCN) 3 (triphos)](CF 3 SO 3 ) 3 [triphos= MeC(CH 2 PPh 2 ) 3 ] with Na(S 2 C‐NEt 2 ) affords the complexes [RhCl(S 2 CNEt 2 )(triphos)]Cl ( 1 ) and [Rh(S 2 CNEt 2 )(MeCN)(triphos)](CF 3 SO 3 ) 2 ( 2 ). Whereas 1 is stereochemically rigid in solution at 25°C, 2 and the analogous complex [Rh(S 2 CNBz 2 )(MeCN)(triphos)](CF 3 SO 3 ) 2 ( 3 ) exhibit a rapid exchange of their phosphorus environments. In contrast, the 31 P‐NMR spectra of both 2 and 3 at –30°C consist of well‐resolved A 2 MX spin systems. k 2 P ‐coordinated complexes of the type [Rh(S 2 CNR 2 ) 2 (triphos‐ k 2 P )] + (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(S 2 CNEt 2 ) 2 (triphosO‐ k 2 P )]Cl ( 6 ) [triphosO = O=P(Ph) 2 CH 2 C(Me)(CH 2 PPh 2 ) 2 ]. The analogous compound [Rh(mpy) 2 (triphosO‐ k 2 P )]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 k 3 P ' k 3 P dissociation equilibrium.