Synthesis and reactivity of σ-alkynyl/P-bonded phosphinoalkyne platinum complexes toward cis-[M(C6F5)2(thf)2] (M = Pt, Pd)

The reactivity of cis-bis(alkynyl)bis((diphenylphosphino)alkyne)platinum(II) complexes cis-[Pt(C=CR)(2)L-2] (R = Ph, Bu-t; L = PPh2C=CPh (L-1), PPh2C=CBut (L-2); 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-(mu-eta(1):eta(2)-C=CR)(2)}M(C6F5)(2)] (5-12) with exclusive formation of doubly alkynyl-bridged systems. The molecular structure of [{((BuC)-C-t=CPh2P)(2)Pt(mu-eta(1):eta(2)-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)(2)L-2] (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(mu-kappa(P):eta(2)-PPh2C=CPh)(2)(mu-eta(1):eta(2)-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 Pt-3 (16B) derivatives which display terminal phosphinoalkyne ligands and, hence, contain the alkynyl groups acting as mu(3)-eta(2) (sigma-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).