Creber, M. L., Orrell, K. G., Osborne, A. G., Sik, V., Hursthouse, M. B. and Malik, K. M. A.
Dynamic NMR investigations of fluxionality of 2-(dimethoxymethyl)pyridine and 2,6-bis(dimethoxymethyl)pyridine in rhenium(I) and platinum(IV) complexes
Journal of the Chemical Society Dalton Transactions, (22), . (doi:10.1039/b005821l).
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The ligands 2-(dimethoxymethyl)pyridine (L-1) and 2,6-bis(dimethoxymethyl)pyridine (L-2) formed bidentate chelate complexes with the isoelectronic transition metal moieties (ReX)-X-I(CO)(3) and (PtXMe3)-X-IV (X=halide). The complexes [ReX(CO)(3)L-1] (X=Cl or Br), [PtXMe3L1] (X=Br or I) and [ReBr(CO)(3)L-2] in organic solvents were shown by NMR to undergo fluxional processes which interconvert co-ordinated and pendant OMe groups. Rates and activation energies of these fluxions were measured by NMR methods (1-dimensional bandshape analysis or 2-dimensional exchange spectroscopy). Magnitudes of DeltaG double dagger (;) (298.15 K) for the fluxions were in the range 59-85 kJ mol(-1) with the order being Re-I-L-1> Re-I-L-2> Pt-IV-L-1. A carbon-carbon bond rotation mechanism is proposed for the fluxions in the L-1 complexes and concerted C-C bond rotation/metallotropic shift processes for the L-2 complexes. Crystal structures of [ReCl(CO)(3)L-1] and [PtIMe3L1] revealed distorted octahedral metal centres with N-M-O 'bite' angles of 73-75 degrees and a trans relationship of the axial halide and pendant OMe group.
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