Dynamic NMR investigations of fluxionality of 2-(dimethoxymethyl)pyridine and 2,6-bis(dimethoxymethyl)pyridine in rhenium(I) and platinum(IV) complexes

Creber, M. L., Orrell, K. G., Osborne, A. G., Sik, V., Hursthouse, M. B. and Malik, K. M. A. (2000) 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), 4218-4226. (doi:10.1039/b005821l).

Abstract

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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