Methyl trans influence

The magnitude of J(Pt—P) for some phosphine-substituted SiPt complexes depends on the covalency of the Pt—P bond (136). Such a bond is relatively ionic in a system where it lies trans to a ligand of high trans influence and J(Pt—P) is then small. The coupling in cis complexes decreased in the order Cl > C > Si and since a comparable situation has been observed for methyl-Pt compounds it is suggested that the effect is one of a- rather than tr-interaction. 

In view of the coordination pattern in protein-bound methylcobalamin (see below), the thermodynamic studies on the effect of the coordination of the dimethylbenzimidazole base to the a-side of the cobalt center on the homolytic and heterolytic (Co/3-C)-bond dissociation energy in (4) (thermodynamic effect of the trans hgand or trans influence ) were extended to corresponding investigations with CojS-methyl-imidazolylcobamides, such as (9), where imidazole replaces the dimethylbenzimidazole these studies showed this change of the nature of the axial base to have httle effect on the two relevant bond-dissociation energies of the corresponding methylcobamide. ... 

The most stable isomer of the complexes (PnN)PtXY is the one in which the ligand with the smaller trans influence is trans to the PR3 ligand [7]. Thus, the thermodynamically preferred isomers of the methyl-substituted complexes (PnN)Pt(X)CH3 are... 

In both complexes, llb,d, the Pd-I bond trans to the phosphorus atom (Pdl—12 in 11b and Pdl-Il in lid) is longer (0.08 and 0.09 A) than the Pd-I bond trans to the nitrogen atom, which might be attributed to the larger trans influence of the phosphorus compared to nitrogen (imine and pyridine) [45]. In the solid state one of the o-aryl substituents in complex llb,d (methyl in the case of 11b and isopropyl in the case of lid) is oriented above/below the coordination plane. A connection between shielding of the metal center along the z-axis and chain transfer reactions was found for several diimine complexes [22 c, 33 b, 41, 42 c]. 

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