Linearly ordered Pt2Rh and Pt2Ir heterotrinuclear complexes bridged by tridentate phosphine ligands

Reactions of the diplatinum complex supported by two tridentate phosphine ligands, syn[Pt-2(mu -dpmp)(2)L-2] (PF6)(2) (1), with [MCl(cod)](2) (M = Rh, Ir) afforded the linearly ordered Pt-Pt-M clusters [Pt-2{MClL}(mu -dpmp)(2)L](PF6)(2) (6a, M = Rh; 6b, M = Ir) and the asymmetrical A-frame clusters [Pt-2{M(mu -Cl)L}(mu -dpmp)(2)L](PF6)(2) (7a, M = Rh; 7b, M = Ir), where dpmp = bis(diphenylphosphinomethyl)phenyphosphine and L = 2,6-xylyl isocyanide (XylNC). Complexes 6 involve a linear Pt2M trinuclear core supported by two dpmp ligands. The three metals are joined by two metal-metal bonds, where the Pt-Pt and Pt-M bonds can be viewed, respectively, as a d(9)-d(9) covalent and a d(9)<--d(8) dative interactions. Complexes 7 consists of an asymmetrical Pt-2(-Cl)M A-frame structure. Reaction of 6a with 1 equiv of L (= XylNC) yielded [Pt-2{RhClL2}(mu -dpmp)(2)L](PF6)(2) (8a), and that with excess L led to [Pt-2{RhL3}(mu -dpmp)(2)L] (PF6)(3) (9a). The additional isocyanide molecules are attached exclusively to the Rh center. Complex 6a by treatment with CO was readily converted into an CO adduct, [Pt-2(RhClL(mu -CO)}(mu -dpmp)(2)L] (PF6)(2) (10a), which easily regenerated 6a with dinitrogen passed through its solution. The structure of 10a was determined by X-ray analysis to show that a carbon monoxide molecule was added to the Pt-Rh bond (2.762(2) Angstrom), resulting in an asymmetrical CO bridging structure. The similar reaction of 7a with CO yielded another kind of CO adduct, [Pt-2{Rh(mu -Cl)(mu -CO)L}(mu -dpmp)(2)L](PF6)(2) (11a), which did not regenerate the starting complex 7a. Reaction of 6a with an electron-deficient alkyne, HC=CCO2Me, led to the alkyne-inserted compound [Pt(mu -HC=CCO2Me)Pt{RhClL}{mu -dpmp)(2)L](PF6)(2) (12a), in which the alkyne is site-selectively inserted into the Pt-Pt bond. The present results suggested that the Rh center has an electrophilic property and the Pt-2 unit has a nucleophilic one in the linear Pt2Rh structure.