Site-selective incorporation of zerovalent platinum and palladium fragments into diplatinum centers supported by a triphosphine ligand

Reaction of [Pt-2(RNC)(6)](PF6)(2) (R = 2,6-xylyl (Xyl) (a) and 2,4,6-mesityl (Mes) (b)) with 2 equiv of bis((diphernylphosphino)methyl)phenylphosphine (dpmp) afforded a mixture of isomeric diplatinum complexes, syn-[Pt-2(mu-dpmp)(2)(RNC)(2)](PF6)(2) (1) and anti-[Pt-2(mu-dpmp)(2)(RNC)(2)](PF6)(2) (2), which were purified by cycles of recrystallization and were characterized by X-ray crystallography. Complexes 1 and 2 consist of a diplatinum core (Pt-Pt = 2.7094(8) Angstrom (1a) and 2.683(2) Angstrom (2a)) asymmetrically bridged by two dpmp ligands. The central phosphorus atoms of the dpmp ligands coordinate to the same metal center in the syn-dimer (1) and to different, metal centers in the anti-dimer (2). Complexes 1 and 2 were fluxional in solution through symmetrical structures of syn-1' and anti-2', respectively, in which two terminal phosphine units are uncoordinated. At reflux in CH3CN or by treatment with [Cu(CH3CN)(4)](PF6), complexes ga and 2a lose one isocyanide molecule to be transformed into syn-[Pt-2(mu-dpmp)(2)(XylNC)](PF6)(2) (3, Pt-Pt = 2.6834(8) Angstrom) and anti-[Pt-2(mu-dpmp)(2)(XylNC)](PF6)(2) (4, Pt-Pt; = 2.7150(7) Angstrom), respectively. Reactions of the syn-dimer (1) with [M-3(XylNC)(6)] readily afforded the linearly ordered trinuclear clusters, linear-[Pt2M(mu-dpmp)(2)(XylNC)(2)](PF6)(2) (M = Pt (5), Pd(6)), The additional zerovalent metal atom is incorporated into the terminal position of the trinuclear aggregation, resulting in a d(9)-d(10)-d(9) configuration via one electron transfer from the additional metal to the diplatinum core. The three metal atoms are joined by two metal-metal sigma-bonds (average Pt-Pt = 2.724(2) Angstrom (5), Pt-Pt/Pd = 2.690(1) Angstrom) and are symmetrically bridged by two dpmp ligands, to form a linearly ordered trinuclear structure (Pt-Pt-M = 178.66(8)degrees (5), 180.0 degrees (6)). The similar reactions of the anti-dimer (2) with [M-3(RNC)(6)] led to a formation of the A-frame trinuclear clusters, A-frame-[Pt2M(mu-dpmp)(2)(RNC)(2)](PF6)(2) (7, M = Pt, R = Xyl; 8, M = Pd, R = Mes). The three metal atoms are joined by two metal-metal bonds (Pt-M = 2.6039(7) Angstrom (7), 2.599(3) Angstrom (8)) and asymmetrically bridged by two dpmp ligands, resulting in a so-called trimetallic A-frame structure (Pt-M-Pt = 76.76(3)degrees (7), 78.5(1)degrees (8)). The additional metal is trapped into the middle position of the trinuclear core, through the insertion of d(10) ML2 fragment into the Pt-Pt sigma-bond, which is interestingly contrasted with the terminal position observed in the reactions of the syn-dimer.