Stereochemically non-rigid transition metal complexes of 2,6-bis(phenyliminomethyl)pyridine and derivatives. Crystal structure of fac- ReBr(CO)(3)(PMTFA) (PMTFA=2,6-pyridylene-bis-(methylene-2-trifluoromethylaniline)

Creber, M. L., Orrell, K. G., Osborne, A. G., Sik, V., Bingham, A. L. and Hursthouse, M. B. (2001) Stereochemically non-rigid transition metal complexes of 2,6-bis(phenyliminomethyl)pyridine and derivatives. Crystal structure of fac- ReBr(CO)(3)(PMTFA) (PMTFA=2,6-pyridylene-bis-(methylene-2-trifluoromethylaniline). Journal of Organometallic Chemistry, 631 (1-2), 125-134. (doi:10.1016/S0022-328X(01)01050-6).

Abstract

The Schiff bases 2,6-bis(phenyliminomethyl)pyridine and its derivatives (L) form bidentate chelate complexes with transition metals Re-I, Pt-IV and Pd-II of general formulation fac-[ReBr(Co)(3)L], fac-[PtXMe3L] (X = Cl, Br or I), and cis-[Pd(p-CF3C6F4)(2)L]. In solution these complexes are stereochemically non-rigid, undergoing 1,4-metallotropic shifts and restricted rotations of the substituted aromatic rings attached to the metal-coordinated imino nitrogen. Rates and activation energies of these internal motions were measured by one-dimensional NMR bandshape analysis and two-dimensional EXSY NMR experiments over a range of solution temperatures. Free energy values, DeltaG(double dagger) (298.15 K), for the fluxional shifts were in the range 76-97 kJ mol(-1) with the Pd-II complexes having the lowest energies. An X-ray crystal structure of fac-[ReBr(CO)(3)PMTFA] (PMTFA = 2,6-pyridylene-bis(methylene-2-trifluoroaniline)) showed the pendant imine function to be in an E-conformation with its nitrogen trans to the pyridyl nitrogen.

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