Regioselective HON-addition of bifunctional hydrazone oximes to Pt(iv)-bound nitriles

Abstract

Treatment of trans-[PtCl₄(RCN)₂] (R = Me, Et) with the hydrazone oximes MeC(NOH)C(R′)NNH₂ (R′ = Me, Ph) at 45 °C in CH₂Cl₂ led to the formation of trans-[PtCl₄{NHC(R)ONC(Me)C(R′)NNH₂}₂] (R/R′ = Me/Ph 1, Et/Me 2, Et/Ph 3) due to the regioselective OH-addition of the bifunctional MeC(NOH)C(R′)NNH₂ to the nitrile group. The reaction of 3 and Ph₃PCHCO₂Me allows the formation of the Pt(II) complex trans-[PtCl₂{NHC(Et)ONC(Me)C(Ph)NNH₂}₂] (4). In 4, the imine ligand was liberated by substitution with 2 equivalents of bis(1,2-diphenylphosphino)ethane (dppe) in CDCl₃ to give, along with the free ligand, the solid [Pt(dppe)₂]Cl₂. The free iminoacyl hydrazone, having a restricted life-time, decomposes at 20–25 °C in about 20 h to the parent organonitrile and the hydrazone oxime. The Schiff condensation of the free NH₂ groups of 4 with aromatic aldehydes, i.e. 2-OH-5-NO₂-benzaldehyde and 4-NO₂-benzaldehyde, brings about the formation of the platinum(II) complexes trans-[PtCl₂{NHC(Et)ONC(Me)C(Ph)NNCH(C₆H₃-2-OH-5-NO₂}₂] (5) and trans-[PtCl₂{NHC(Et)ONC(Me)C(Ph)NNCH(C₆H₄-4-NO₂}₂] (6), respectively, containing functionalized remote peripherical groups. Metallization of 5, which can be considered as a novel type of metallaligand, was achieved by its reaction with M(OAc)₂·nH₂O (M = Cu, n = 2; M = Co, n = 4) in a 1 ∶ 1 molar ratio furnishing solid heteronuclear compounds with composition [Pt] ∶ [M] = 1 ∶ 1. The complexes were characterized by C, H, N elemental analyses, FAB⁺ mass-spectrometry, IR, ¹H, ¹³C{¹H} and ¹⁹⁵Pt NMR spectroscopies; X-ray structures were determined for 3, 4 and 5.