Mono- and binuclear complexes of rhodium involving a new series of hemilabile o-phosphinoaniline ligands

Dalton Trans. 2009 Jun 7;(21):4213-26. doi: 10.1039/b822170g. Epub 2009 Apr 6.

Abstract

Monophosphines of the type Ph(x)PAr(3-x) (x = 0, 1 or 2, Ar = o-N-methylanilinyl) and the diphosphine, Ar(2)PCH(2)PAr(2) (mapm) have been synthesized for use as chelating and/or bridging P,N-ligands within mono- and binuclear rhodium(i) complexes, respectively. The previously prepared phosphines, Ph(x)PAr'(3-x) (x = 0, 1 or 2, Ar' = o-N,N-dimethylanilinyl) and Ar'(2)PCH(2)PAr'(2) (dmapm), have also been used to prepare analogous mono- and binuclear complexes. Variable temperature (1)H NMR spectroscopy of the mononuclear complexes, [RhCl(CO)(L)] (L = PhPAr(2), PhPAr'(2), PAr(3) and PAr'(3)), and line-shape analyses of the resultant spectra indicate the substantially increased lability of the N,N-dimethylanilinyl donors relative to the related monomethylanilinyl groups. X-Ray structural analyses of the mononuclear complexes suggest that the enhanced Type II hemilability in the dimethylanilinyl complexes compared to their monomethyl analogues results from increased steric interactions involving the coordinated dimethylanilinyl substituents. In the case of the binuclear, dmapm-bridged compound [Rh(2)Cl(2)(CO)(2)(micro-dmapm)], there are additional transannular repulsions between the chloro ligand on one metal and the coordinated dimethylanilinyl group on the other, which result in a Rh-Rh separation of over 4.1 A. For the analogous mapm-bridged species, the transannular interactions between the chloro ligands and the amine hydrogens are in fact attractive, resulting in a much closer Rh-Rh separation (3.450 A). The chloride substituents of [Rh(2)Cl(2)(CO)(2)(micro-mapm)] can be replaced to generate the complexes, [Rh(2)(X)(2)(CO)(2)(micro-mapm)] (X = I, CF(3)SO(3), CH(3)CO(2)), the last of which also exhibits pronounced transannular hydrogen-bonding interactions in the solid state.