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.