Neutral square-planar olefin/alkyl platinum(ii) complexes containing a N,N′-imino-amide ligand. Experimental and theoretical evidence of relevant π-back-donation in the platinum-olefin bond

A new class of platinum(II) compounds of the formula [PtMe(olefin)(N,N'- imino-amide chelate)] is described (olefin = ethylene, propylene, styrene, allyl alcohol, methyl vinyl ketone, methyl acrylate; N,N'-imino-amide chelate = N,N'-(1,2-dimethyl-1,2-ethanediylidene)bis-(2,6-diisopropylaniline)). The neutral complexes exhibit square-planar coordination with a cis arrangement of the olefin and the alkyl group. The compounds have been characterized through one- and two-dimensional NMR spectroscopy, which has disclosed that only one isomer is present in solution. This isomer exhibits the alkene and the N(amido) atom in trans positions, while the alkene substituent is oriented toward the Pt-Me vector. The nature and the arrangement of the ligands seem suitable to favor a π-back-donation contribution to the Pt-olefin bond to an extent unprecedented for square-planar compounds, as discussed on the basis of NMR parameters and theoretical calculations.