Dynamic Behaviour of the [(Triphos)Rh(η 1 :η 2 ‐P 4 RR′)] n + Complexes [Triphos = MeC(CH 2 PPh 2 ) 3 ; R = H, Alkyl, Aryl; R′ = Lone Pair, H, Me; n = 0, 1]: NMR and Computational Studies

Solution multinuclear and multidimensional NMR analyses of the [(triphos)Rh(η 1 :η 2 ‐P 4 RR′)] n + complex cations [triphos = MeC(CH 2 PPh 2 ) 3 ; R = H, Me, Ph; R′ = lone pair, H, Me; n = 0, 1] confirm the same primary structure determined by X‐rays in the solid state. In addition, 2D 1 H NOESY and 31 P{ 1 H} exchange NMR spectroscopy show that these complexes are nonrigid on the NMR time‐scale over the 253–318 K temperature range. A dynamic process that involves the terminal phosphane groups of the triphos ligand is displayed by each compound. The NMR spectroscopic data indicate a slow scrambling motion in which the P 4 R unit tumbles with respect to the (triphos)Rh moiety. DFT calculations outline a possible turnstile mechanism involving the threefold and twofold rotors into which the complex is subdivided. The process goes through a transition state in which the axial and equatorial dispositions of the PRR′ and P=P donating groups of the P 4 RR′ ligand are inverted with respect to the ground state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)