Synthesis and Reactivity of σ-Alkynyl/<i>P</i>-Bonded Phosphinoalkyne Platinum Complexes toward <i>cis</i>-[M(C₆F₅)₂(thf)₂] (M = Pt, Pd)

Abstract

The reactivity of cis-bis(alkynyl)bis((diphenylphosphino)alkyne)platinum(II) complexes cis-[Pt(C⋮CR)2L2] (R = Ph, But; L = PPh2C⋮CPh (L1), PPh2C⋮CBut (L2); 1−4), formed by displacement of the COD ligand from [Pt(C⋮CR)2(COD)], toward cis-[M(C6F5)2(thf)2] (M = Pt, Pd, thf = tetrahydrofuran; in both a 1:1 and 1:2 molar ratio) has been investigated. Treatment of 1−4 with 1 equiv of cis-[M(C6F5)2(thf)2] affords dinuclear derivatives [{L2Pt(μ-η1:η2-C⋮CR)2}M(C6F5)2] (5−12) with exclusive formation of doubly alkynyl-bridged systems. The molecular structure of [{(ButC⋮CPh2P)2Pt(μ-η1:η2-C⋮CPh)2}Pd(C6F5)2], 10, is presented. In contrast, it was found that the course of the reactions with 2 equiv of cis-[M(C6F5)2(thf)2] strongly depend on the alkynyl substituents and metal centers. Thus, treatment of tert-butylalkynyl derivatives cis-[Pt(C⋮CBut)2L2] (2, 4) with 2 equiv of cis-[M(C6F5)2(thf)2] (M = Pt, Pd) only gives the expected trinuclear complexes 15A and 18A, in the case of the reactions with cis-[Pt(C6F5)2(thf)2]. The molecular structure of the complex [{Pt(μ-κ(P):η2-PPh2C⋮CPh)2(μ-η1:η2-C⋮CBut)2}{Pt(C6F5)2}2], 15A, reveals that both the complexed cis-Pt(C6F5)2 moieties are symmetrically linked to the precursor “cis-[Pt(C⋮CBut)2(PPh2C⋮CPh)2]”, with the platinum atoms connected by two unusual mixed alkynyl/phosphinoalkyne bridging systems. On the other hand, similar reactions of phenylethynyl derivatives (1, 3) with 2 equiv of cis-[Pd(C6F5)2(thf)2] and 3 (L = PPh2C⋮CBut) with cis-[Pt(C6F5)2(thf)2] lead, instead, to the unexpected trinuclear PtPd2 (14B, 17B) and Pt3 (16B) derivatives which display terminal phosphinoalkyne ligands and, hence, contain the alkynyl groups acting as μ3-η2 (σ-Pt edge Pd or Pt) bridging ligands. However, a mixture of both types of isomers 13A and 13B (50:32) is observed in the reaction system cis-[Pt(C⋮CPh)2(PPh2C⋮CPh)2] (1)/cis-[Pt(C6F5)2(thf)2]. The following order of bonding capability is deduced from this study: alkynyl > P-bonded phosphinoalkyne and XC⋮CPh fragments > XC⋮CBut (X = Pt, P).