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 Pt(CN)42- and Pt(CNR)42+ (R = CH3 or C2H5).

The mixed ligand complexes tetra-n-butylammonium tricyanomethylisocyanideplatinate(II) (1), cis-dicyanobismethylisocyanideplatinum(II) (2) and cis-dicyanobisethylisocyanideplatinum(II) (3) have been synthesized and characterized by 195Pt NMR, 1H NMR and single crystal X-ray diffraction. Replacement of cyano ligands with isocyanide ligands leads to progressive changes in the NMR spectra as well as in the Pt–CNR bond lengths.Figure optionsDownload as PowerPoint slide