CLEAVAGE AND REASSEMBLY OF TRINUCLEAR PALLADIUM CLUSTERS IN REACTIONSWITH AN ISOCYANIDE LIGAND

Reaction of the trinuclear cluster cation [Pd3(mu3-CO)(mu-dppM)3]2+ [d ppm = bis(diphenylphosphino)-methane] with excess xylyl isocyanide, 2, 6-Me2C6H3N = C, led to cleavage giving the binuclear palladium(I) comp lex cation [Pd2(CNC6H3Me2-2,6)2(mu-dppm)2]2+, and unidentified palladi um(0) species. The 2,6-Me2CH3NC ligands in [Pd2(CNC6H3Me2-2,6)2(mu-dpp m)2]2+ undergo rapid exchange with excess 2,6-Me2C6H3N = C and, at low temperature, an adduct is formed and identified spectroscopically as Pd2(CNC6H3Me2-2,6)2(mu-CNC6H3Me2-2,6)(mu-dppM)2]2+ . A dppm ligand of [Pd2(CNC6H3Me2-2,6)2(mu-dppm)2]2+ is deprotonated and oxidized in the presence of an excess of dppm and oxygen to give CNC6H3Me2-2,6)2{mu-Ph 2PCHPPh2(=O)-C,P}(mu-dppm)]+, which has been characterized by a struct ure determination {crystal data for the [PF6]-.Me2CO salt: triclinic, space group P1BAR, a = 14.523(2), b = 22.448(4), c = 12.203(3) angstro m, alpha = 95.52(2), beta = 110.98(2), gamma = 108.21(l)-degrees, Z = 2, R = 0.0563, R' = 0.0574}. Complex [Pd2(CNC6H3Me2-2,6)2(mu-dppm)2]2 can react with the palladium(o) species, which is formed in the initi al cluster cleavage reaction, by formal addition of Pd(CNC6H3Me2-2,6)2 to give the trinuclear A-frame cluster complex C6H3Me2-2,6)2{mu-Pd(CN C6H3Me2-2,6)2)(mu-dppm)2]2+, thus completing the fragmentation and rea ssembly of trinuclear clusters. This complex has been characterized by a structure determination {crystal data for the 2[PF6]-.0.5Me2CO salt : orthorhombic, space group P2(1)2(1)2(1), a = 21.810(3), b = 21.879(4 ), c = 18.274(5) angstrom, z = 4, R = 0.0566, R' = 0.06321; in solutio n, it slowly loses Pd(CNC6H3Me2-2,6)2 to reform [Pd2(CNC6H3Me2-2,6)2(m u-dppm)2]2+.