[Pt2(PPh3)4(μ-S)2] as a metalloligand toward main-group Lewis acids: Theoretical study of intermetallic complexes with T1(I), Pb(II), In(III) and Ga(III)

Abstract

This paper describes theoretical studies on adducts of Pt2(PPh3)4(μ-S)2 with Tl(I), Pb(II), In(III) and Ga(III). Using one of the Pb compounds as an example, the fundamental principle of competition for interactions (M-ligand vs. M-S; M-S vs. Pt-S) is illustrated; in particular, any ligand bound trans to an M-S bond will cause the latter to be weakened more than the other M-S bond. The polarizable phosphine ligands also play a role in moderating changes in the Pt-S interactions. The general weakening of the M-S bonds upon ligand coordination, which is also demonstrated by binding energies of Pt2(PPh3)4(μ-S)2 to various heterometal fragments, could explain why Ga, Pb and Tl do not accept additional ligands. In (PPh3)4Pt2(μ2-S) 2InCl3, the In atom is square pyramidally coordinated. Calculations indicate strong pπ-pπ and dπ-pπ bonding between In and the Cl atom at the apex of the square pyramid, thus accounting for the unusually short In-Cl bond length. With regard to the trend of increasing Pt-S-S-Pt dihedral angle with increasing heterometal size, it is found that in the parent compound (without the heterometal M), the dihedral angle determines the character of the sulfur lone pairs; it is inferred that the "optimal" orientation of the lone pairs for interactions with the heterometal depends on the size of the latter. This result has implications for all binuclear Pt(II) or Pd(II) compounds with bridging sulfur ligand(s). © 1997 Elsevier Science B.V. All rights reserved.