From aggregates to clusters. Facile formation of hetero-metal-metal bonds through reductive desulfurization by CO in a decapacitative transformation of a {Pt2MS2} Tbp frame to a {Pt2MS} tetrahedral core (M = Ag, Cu, and Ru)

Abstract

[Pt2(PPh3)4(μ-S2] (1) reacts with AgCl(PPH3) and CuCl under a mild pressure of CO (60 psi) to give [Pt2(CO)(PPh3)3(μ3-S)MCl] [M = Ag (4) and Cu (6)] via the intermediates [Pt2(PPh3))4(μ3-S)2Ag(PPh3)]Cl (2a), [Pt2(PPh3)5(μ3-S)2CuCl] (5), respectively. These transformations demonstrate an precedented concomitant process which involve heterometalation, carbonylation, reductive desulfurization, and metal-metal bond formation. The Ru-Pt aggregate of [Pt2(PPh3)4(μ3-S)2(RuCl(PPh3)2]Cl (7), prepared from 1 and RuCl2(PPh3)3, similarly converts to a [Pt2(CO2(PPh3)2(PPh3)2(μ3-S)RuCl(CO)(PPh3)]Cl (8) cluster under a CO atmosphere. Such transformation establishes a synthetic relationship between the {Pt2MS2} trigonal bipyramidal aggregates and {Pt2MS} tetrahedral clusters and provides a general entry to triangular heterometallic sulfide clusters of platinum. All complexes are characterized by IR, 31P{1H}, and 13C NMR spectroscopy and conductivity measurements. The structures of 4, 6, and the PF6 - derivative of 2a (viz. 2b) have also determined by single-crystal X-ray diffraction analyses. The structure of 2b shows a sulfide-bicapped Ag-Pt mixed-metal triangle without significant Pt···Pt [3.351(2) and 3.375(2) Å] or Ag···Pt [av 3.064(1) and 3.101(1) Å] interactions. Complex 2b crystallizes in two polymorphic modifications with different degrees of disposition of the Ag moieties with respect to the {Pt2S2} core. As a result, the Ag-S bonds [2.479(1) vs 2.585(1) Å and 2.502(2) vs 2.607(2) Å] are significantly different between the polymorphs in which the Ag···Pt distances are near-equivalent[3.061(1) Å] in one form but significantly different [2.9621(1) vs 3.240(1) Å] in the other. Complex 4 shows a triangular {AgPt2} cluster mono-capped by sulfide. Removal of a capping sulfur atom from 2a effectively reduces both Pt(II) centers and favors Pt-Pt bond formation [Pt-Pt 2.658(2) Å] and heterometallic Ag-Pt interactions [av Ag-Pt 2.965(1) Å in 4. Both the Pt-S and Ag-S bonds also strengthen significantly from 2b to 4. Cluster 6 is isostructural to 4 with similar homo-[Pt-Pt 2.657(1) Å] and heterometal [av Cu-Pt 2.832(1) Å interactions. Both 4 and 6 thus constitute a {MPt2S} distorted tetrahedral cluster frame. A facile and general aggregates-to clusters conversion through the elimination of COS gas is thus established.