Click-type PtII-mediated hydroxyguanidine–nitrile coupling provides useful catalysts for hydrosilylation cross-linking

Abstract

The nitrile complexes trans-[PtCl2(RCN)2] (R = Et NC1, tBu NC2, Ph NC3, p-BrC6H4 NC4) and cis-[PtCl2(RCN)2] (R = Et NC5, tBu NC6, Ph NC7) react with 1 equiv of the hydroxyguanidine OC4H8NC(=NOH)NH2 (HG) furnishing the mono-addition products cis- and trans-[PtCl2(RCN){NH=C(R)ON=C(NH2)NC4H8O}] (1–4 and 9–11; 7 examples; 54–74%). Treatment any one of NC1–NC7 with HG in a 1:2 molar ratio about generation of the bis-addition products cis- and trans-[PtCl2{NH=C(R)ON=C(NH2)NC4H8O}2] (5–8 and 12–14; 7 examples; 69–89%). The PtII-mediated coupling between nitrile ligands and HG proceeds substantially faster than the relevant reactions involving amid- and ketoximes and gives redox stable products under normal conditions. All new complexes 1–14 and previously unreported NC4 were characterized by elemental analyses (C, H, and N), IR, high resolution ESI-MS, 1H and 13C{1H} NMR spectroscopies. Complexes 1, 6•4CH2Cl2, 7•4CH2Cl2, 8•2CH2Cl2, and NC4 were studied by X-ray crystallography. Platinum(II) species 1–3, 10–11, and especially 9, efficiently catalyze hydrosilylation cross-linking of vinyl terminated poly(dimethylsiloxane) and trimethylsilyl terminated poly(dimethylsiloxane-co-ethylhydrosiloxane) giving high quality thermally stable silicon resins with no structural defects. The usage of these platinum species as the catalysts do not require any inhibitors and, moreover, the complexes and their mixtures with vinyl- and trimethylsilyl terminated polysiloxanes are shelf-stable in air.