Platinum(iv)-mediated hydrolysis of nitriles giving metal-bound iminols

Abstract

The platinum(IV) complexes cis/trans-[PtCl₄(MeCN)₂] and trans-[PtCl₄(EtCN)₂] react smoothly and under mild conditions with water, contained in non-dried commercial acetone, to afford trans-[PtCl₄{N(H)C(OH)Me}₂]·Me₂CO (1) or trans-[PtCl₄{N(H)C(OH)Et}₂] (2); no hydroxide is required, in contrast to relevant platinum(II) systems, to furnish the metal-bound carboxamides which are stable in the iminol form. In non-dried acetone, reaction between trans-[PtCl₄(EtCN)₂] and MeC(O)NH₂ gives a mixture of 1 (derived from substitution) and 2 (derived from the hydrolysis), while in non-dried dichloromethane an isomorphic mixture of cis-[PtCl₄{N(H)C(OH)Me}₂] and cis-[PtCl₄{N(H)C(OH)Et}₂], i.e.cis-[PtCl₄{Z-N(H)C(OH)Me}₂]_0.66·cis-[PtCl₄{Z-N(H)C(OH)Et}₂]_0.33 (3) is obtained. Complexes 1–3 were characterised by elemental analyses (C, H, N), FAB⁺-MS, IR, ¹H- and ¹³C{¹H}-NMR spectroscopy. Complexes 2 and 3 were also characterised by ¹⁹⁵Pt-NMR spectroscopy. Crystal structures of 2 and 3 provide the first examples of structurally characterised platinum(IV) complexes with amides in their iminol form. The equilibrium structures for the geometrical and linkage isomers of the platinum(II) complexes [Pt^IICl₂{N(H)C(OH)Me}₂] and [Pt^IICl₂{OC(NH₂)Me}₂] and the platinum(IV) compounds [Pt^IVCl₄{N(H)C(OH)Me}₂] and [Pt^IVCl₄{OC(NH₂)Me}₂] were calculated at the B3PW91 level of theory and the study shows that the most stable isomers for both platinum(II) and platinum(IV) complexes are the trans-(iminol)Pt forms, in accord with the experimental results.