ASYMMETRICAL A-FRAME TRIPLATINUM CLUSTERS BRIDGED BY SMALL ORGANIC-MOLECULES AND BIS((DIPHENYLPHOSPHINO)METHYL)PHENYLPHOSPHINE

Reactions of the linear triplatinum complex [Pt-3(mu-dpmp)(2)(XylNC)(2 )](2+) (3) with small organic molecules led to formation of asymmetric al A-frame triplatinum complexes with an additional bridge across one of the metal-metal bonds, where dpmp is bis((diphenylphosphino)methyl) phenylphosphine. Reaction of complex 3 with electron deficient alkynes (R(1)C=CR(2): R(1) = R(2) = CO(2)Me; R(1) = H, R(2) = CO(2)Me; R(1) = R(2) = CO(2)Et) afforded a new series of triplatinum clusters formula ted as Pt-3(mu-dpmp)(2)(mu-R(1)CCR(2))(XylNC)(2)](PF6)(2) (5a, R(1) = R(2) = CO(2)Me; 5b, R(1) = H, R(2) = CO(2)Me; 5c, R(1) = R(2) = CO(2)E t) in good yields. The complex cation of 5b was characterized by X-ray crystallography to have an asymmetrical A-frame structure comprising three Pt atoms bridged by two dpmp ligands, in which an acetylene mole cule was inserted into one of the Pt-Pt bonds (triclinic, <P(1)over ba r>, a = 19.507-(3) Angstrom, b = 20.327(4) Angstrom, c = 14.499(4) Ang strom, alpha = 107.69(2)degrees, beta = 102.08(2)degrees, gamma = 71.3 0(1)degrees, V = 5148 Angstrom(3), Z = 2, R = 0.070, and R(w) = 0.084) . The Pt-Pt bond length is 2.718(1) Angstrom and the Pt ... Pt nonbond ed distance is 3.582(1) Angstrom. Treatment of 3 with an excess of HBF 4 . Et(2)O gave the asymmetrical cluster [Pt-3(mu-dpmp)(2)(mu-H)-(XylN C)(2)](BF4)(3) . CH2Cl2 (6 . CH2Cl2), in 61% yield, and a similar reac tion with p-NO2C6H4NC led to the formation of [Pt-3(mu-dpmp)(2)(mu-R(3 )NC)(XylNC)(2)](PF6)(2) . CH2Cl2 (7 . CH2Cl2) in 94% yield (R(3) = p-N O2C6H4). Complexes 6 and 7 are assumed to have a single atom-bridged, asymmetrical A-frame structures. Reaction of the complex syn-[Pt-2(mu- dpmp)(2)(XylNC)(2)](2+) (1) With [MCl(2)(cod)] (M = Pt, Pd) gave the d imer-monomer combined trinuclear cluster [Pt(2)MCl(2)(mu-dpmp)(2)(XylN C)(2)](PF6)(2) (8a, M = Pt, 89%; 8b, M = Pd, 55 %). The structure of 8 a was determined by X-ray crystallography to be comprised of a metal-m etal-bonded diplatinum core and a monomeric platinum center bridged by two dpmp ligands with a face-to-face arrangement (triclinic, <P(1)ove r bar>, a = 18.082(7) Angstrom, b = 19.765(6) Angstrom, c = 15.662(4) Angstrom, alpha = 98.51(2)degrees, beta = 94.24(3)degrees, gamma = 109 .82(2)degrees, V = 5161 Angstrom(3), Z = 2, R = 0.069, and R(w) = 0.08 0). The Pt-Pt bond length is 2.681(2) Angstrom and the Pt ... Pt nonbo nded distance is 3.219(2) Angstrom. The heteronuclear complex 8b was t ransformed to an A-frame trinuclear cluster, [Pt2PdCl(mu-Cl)(mu-dpmp)( 2)(XylNC)]-(PF6)(2) (9), which was characterized by X-ray crystallogra phy (monoclinic, C2/c, a = 33.750(9) Angstrom, b = 28.284(9) Angstrom, c = 23.845(8) Angstrom, beta = 118.19(4)degrees, V = 20066 Angstrom(3 ), Z = 8, R = 0.082, and R(w) = 0.077). The diplatinum unit (Pt-Pt = 2 .606(2) Angstrom) is connected to the mononuclear Pd center by a chlor ide bridge (Pt ... Pd = 3.103(3) Angstrom, Pt-Cl-Pd = 79.6(3)degrees).