Multinuclear nuclear magnetic resonance and X-ray crystallographic investigation of some mixed ligand alkylisocyanide platinum(II) complexes

Single crystal X-ray diffraction structure determination of tetra-n-butylammonium tricyanomethylisocyanideplatinate(II) (1) show that the complex does not feature stacking of the anions or significant Pt-Pt orbital interactions. The cis-dicyanobismethylisocyanideplatinum(II) (2) and cis-dicyanobisethylisocyanideplatinum(II) (3) complexes do crystallize with the platinum atoms collinear with one another but with a Pt-Pt separation distance on the order of 3.5 Å, which is too great for significant orbital overlap. In each of the complexes studied, the Pt-CNR bond lengths of the isocyanides are shorter than the Pt-CN bond lengths of the cyanide ligands. Additionally, each of these complexes have Pt-CNR bond distances marginally shorter than in the parent complex, Pt(CNR)₄]BF₄]₂ (5). The shortened Pt-CNR distances in the mixed complexes are consistent with the isocyanide ligand being a stronger π-acid than the cyanide ligand, resulting in a preferred cis configuration of the mixed ligand complexes. In solution, the NMR spectra of these complexes are unusual because they display ¹⁹⁵Pt-¹⁴N and ¹H-¹⁴N coupling with high resolution. The NMR parameters of these complexes are compared with those of and (R = CH₃ or C₂H₅).