Coupling of platinated triguanides with platinum-activated nitriles as a novel strategy for generation of dimetallic systems

Abstract

One of two Pt^IV-activated propanenitriles in trans-[PtCl₄(EtCN)₂] is involved in platinum(IV)-mediated nitrile–imine coupling with the platinum(II)-based metallacycles [PtCl₂{NHC(NR₂)N(Ph)C(NH)N(Ph)C(NR₂)NH}] [R₂ = Me₂ (1a), C₅H₁₀ (1b)] yielding diplatinum products, whose structures depend on molar ratios between the reactants. At a 1 : 1 ratio, the mixed-valence platinum(II)/platinum(IV) species [PtCl₄{NHC(NR₂)N(Ph)C{[(N(Et)CNH)PtCl₂(EtCN)]}N(Ph)C(NR₂)NH}] [R₂ = Me₂ (2a), (CH₂)₅ (2b)] were generated, whereas at a 1 : 2 ratio the dinuclear platinum(II)/platinum(II) complexes [PtCl₂{NHC(NR₂)N(Ph)C{[(N(Et)CNH)PtCl₂(EtCN)]}N(Ph)C(NR₂)NH}] [R₂ = Me₂ (3a), (CH₂)₅ (3b)] were obtained. In contrast to the nitrile–imine coupling observed for the platinum(IV) dinitrile complex, the reaction between the platinum(II) congener trans-[PtCl₂(EtCN)₂] and any one of 1a,b gives exclusively the substituted dimetallic platinum(II)/platinum(II) products [PtCl₂{NHC(NR₂)N(Ph)C{[(NH)PtCl₂(EtCN)]}N(Ph)C(NR₂)NH}] [R₂ = Me₂ (6a), (CH₂)₅ (6b)] featuring platinum-containing guanidine 1 as one of the ligands. Complexes 2a,b, 3a,b, and 6a,b were characterized by elemental analyses (C, H, N), HRESI-MS, IR, ¹H NMR spectroscopy, and DTA/TG. The molecular and crystal structure of 2a·2CDCl₃ was additionally studied by single-crystal X-ray diffraction. Complexes 2a,b undergo further redox transformation in solutions, and single crystals of [PtCl₂{NHC(NMe₂)N(Ph)C{[(N(Et)CNH)PtCl₂(MeCN)]}N(Ph)C(NMe₂)NH}]·2CH₂Cl₂ (3′a·2CH₂Cl₂) were obtained from 2a in a CH₂Cl₂–MeCN–C₂H₄Cl₂ mixture and studied by X-ray crystallography. The driving forces for the generation of diplatinum products 2 and 3 were elucidated based on a quantum-chemical study.