Synthesis and reactions of the heterobimetallic complex [ClPd(µ-Ph2PCH2PPh2)2PtCl]

Abstract

New methods of preparing [ClPd(µ-dppm)₂PdCl](1b)(dppm = Ph₂PCH₂PPh₂) are described, such as reduction of [PdCl₂(dppm-PP′)] with zinc dust, formic acid, or hydrazine. Treatment of [Pd₂Cl₂(η³-allyl)₂] with an excess of dppm gives pure (1b) readily, albeit in only 45% yield. [(η³-C₃H₅)ClPd(µ-dppm)PdCl(η³-C₃H₅)] is also described. The best route to (1b) is to treat [Pd(PPh₃)₄] and dppm with [PdCl₂(NCPh)₂], giving yields of 80–90%. Similar treatment of [Pt(PPh₃)₄] and dppm with [PtCl₂(NCBu^t)₂] gives [ClPt(µ-dppm)₂PtCl](la), often contaminated, however, with ca. 10% of [PtCl₂(dppm-PP′)]. Treatment of dppm and [Pd(PPh₃)₄] with [PtCl₂(NCBu^t)₂] gives the previously unknown heterobimetallic complex [ClPt(µ-dppm)₂PdCl](1c) in excellent yield (83–92%) and purity. The corresponding dibromide, di-iodide, and dithiocyanate were prepared from (1c) by metathesis. Complex (1c) readily reacts with some small molecules, SO₂, CO, MeO₂CCCCO₂Me or CS₂, to give ‘A-frames’[ClPt(µ-SO₂)(µ-dppm)₂PdCl], [ClPt(µ-CO)(µ-dppm)₂PdCl], [ClPt(µ-MeO₂CCCCO₂Me)(µ-dppm)₂PdCl], and [ClPt(µ-CS₂)(µ-dppm)₂PdCl] respectively. The addition of SO₂, CO, or CS₂ is reversible and SO₂ promotes or catalyses the displacement of CO. Hydrogen-1, ³¹P-{¹H}, and ¹⁹⁵Pt n.m.r. data are given and discussed as are some i.r. data.