First observation of metal-mediated nitrile-imine coupling giving ligated 1,3-diaza-1,3-dienes

Coupling between benzophenone imine and coordinated organonitriles in the platinum(IV) complexes [PtCl4(RCN)(2)] (R=Me or Et) proceeded rapidly under mild conditions to afford the 1,3-diaza-1,3-diene compounds [PtCl4{NH=C(R)N=CPh2}(2)] in good yield and this reaction is the first observation of metal-assisted nucleophilic addition of an imine to a ligated nitrile. [PtCl4{NH=C(R)N=CPh2}(2)] were reduced to the corresponding platinum(II) complexes [PtCl2{NH=C(R)N=CPh2}(2)] by the carbonyl-stabilized phosphorus ylide Ph3P=CHCO2Me. The [PtCl2{NH=C(Me)N=CPh2}(2)] complex was also detected in a mixture formed in the reaction between the platinum(II) nitrile complex [PtCl2(MeCN)(2)] and Ph2C=NH, but the selectivity of the platinum(II)-mediated nitrile-imine coupling was enhanced by employing for the reaction with benzophenone imine the phenyl cyanide complex [PtCl2(PhCN)(2)] to give [PtCl2(NH=CPh2){NH=C(Ph)N=CPh2}]. Liberation of 1,3-diaza-1,3-dienes was exemplified by the reaction of [PtCl2{NH=C(Et)N=CPh2}(2)] with two equivalents of 1,2-bis(diphenylphosphino)ethane in CHCl3 to give, along with free NH=C(Et)N=CPh2 retained in solution, the solid complex [Pt(dppe)(2)]Cl-2. All isolated metal complexes were characterized by elemental analyses, FAB mass spectrometry, IR, H-1, C-13-{H-1} and Pt-195 NMR spectroscopies and cis-[PtCl4{Z-NH=C(Et)N=CPh2}(2)] also by X-ray single-crystal diffraction.