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

Article abstract of DOI:10.1039/b008154j

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-l,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 nitrileimine 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-l,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]Cl₂. All isolated metal complexes were characterized by elemental analyses, FAB mass spectrometry, IR, ¹H, ¹³C-{¹H} and ¹⁹⁵Pt NMR spectroscopies and cis-[PtCl₄{Z-NH=C(Et)N=CPh₂}₂] also by X-ray single-crystal diffraction.