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)phen ylphosphine (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 recrystalliza tion 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 me tal 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 t wo terminal phosphine units are uncoordinated. At reflux in CH3CN or b y treatment with [Cu(CH3CN)(4)](PF6), complexes ga and 2a lose one iso cyanide 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)(Xyl NC)](PF6)(2) (4, Pt-Pt; = 2.7150(7) Angstrom), respectively. Reactions of the syn-dimer (1) with [M-3(XylNC)(6)] readily afforded the linear ly ordered trinuclear clusters, linear-[Pt2M(mu-dpmp)(2)(XylNC)(2)](PF 6)(2) (M = Pt (5), Pd(6)), The additional zerovalent metal atom is inc orporated into the terminal position of the trinuclear aggregation, re sulting in a d(9)-d(10)-d(9) configuration via one electron transfer f rom 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) A ngstrom (5), Pt-Pt/Pd = 2.690(1) Angstrom) and are symmetrically bridg ed by two dpmp ligands, to form a linearly ordered trinuclear structur e (Pt-Pt-M = 178.66(8)degrees (5), 180.0 degrees (6)). The similar rea ctions 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)](PF 6)(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, r esulting 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 i nto the middle position of the trinuclear core, through the insertion of d(10) ML2 fragment into the Pt-Pt sigma-bond, which is interestingl y contrasted with the terminal position observed in the reactions of t he syn-dimer.