Carbene complexes trans influence

Palladium isocyanide complexes react with amines and alcohols to give palladium Carbene Complexes (equation 15) in a reaction that is a nucleophihc attack on the isonitrile carbon. These complexes easily lose a halide if it is trans to the carbene hgand, since the carbene carbon has a high trans influence. The structures of these compounds have the carbene carbon and its two heteroatom groups in one plane, which is perpendicular to the coordination plane of the Pd. 

Further evidence that hybridization change is the dominant factor in trans-influence was afforded by the C NMR parameters of methylplatinum carbene complexes. See Tables XXIV, XXV, and XXVII. 

The magnitudes of Jpt-c (carbene) were not found to follow the exact trans-influence order previously established (37, 39) for other organoplatinum (2+) complexes. However, it was agreed that changes in hybridization of the Pt-C (carbene) bond are monitored by Jpt-c- For phosphorus-carbene couplings it was noted that Jp-pt-c (trans) > Jp-pt-c (cis). Data for these 1,3-di-organoimidazolidin-2-ylidene complexes are given in Table XXXVIII. 

The increased donor properties of non-classical carbenes relative to their classical analogues were demonstrated both theoretically and experimentally. Complexes 14 and 15 were analysed by X-ray photoelectron spectroscopy. Both the palladium 3d and 3p electron binding energies in the abnormal complex 15 were lower by 0.5 eV than in the normal complex 14, which reflected the stronger donor capabilities of the abnormal carbene ligand. Furthermore, X-ray diffraction and infrared spectroscopic studies were used to demonstrate the larger trans influence of abnormal carbenes when compared to their normal analogues. ... 

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