ISOCYANIDE AND DIISOCYANIDE COMPLEXES OF A TRIPALLADIUM CLUSTER

New cluster complexes derived from the reactions of [Pd3(mu3-CO)(mu-dppm)3]2+, 2a, with XyN-=C (Xy = 2,6-C6H3Me2) and 1,4-C=NC6Me4N=C are reported. Reaction of XyNC with 2a gives[Pd3(mu3-eta-CNXy)(mu-dppm)3]2+, 6, which contains the very unusual mu3-eta1-bonding mode of the isocyanide and which has been characterized crystallographically [monoclinic, P2(1)/n, a = 13.624(i) angstrom, b = 42.373(3) angstrom, c = 14.025(1) angstrom, beta = 98.78(5)degrees, Z = 4, R = 0.0597, R(w) = 0.0641]. This 42-electron cluster reversibly adds XyNC to form the 44-electron cluster [Pd3(mu3-CNXy)2(mu-dppm)3]2+. Reaction of 2a or 6 with 1/2 equiv of the diisocyanide ligand 1,4-C6Me4(NC)2 gave the complex cation [{Pd3(mu-dppm)3]}2(CNC6Me4NC)][PF6]4, 8, with displacement of CO or XyNC respectively. Reaction of 2a, as either the [PF6]- or CF3CO2- salt, with 1 equiv of 1,4-C6Me5(NC)2 gave the corresponding complex {[Pd3(CNC6Me4NC)(mu-dppm)3]X2}n, 9. In 8, the diisocyanide bridges between Pd3 cluster units, using the same mu3-eta1-bonding mode as in 6, but in 9 partial dissociation leads to some monodentate diisocyanide units. The palladium clusters with isocyanides tend to adopt the 42-electron configuration with triply bridging isocyanides and are different from the platinum analogs, for which the 44-electron configuration with terminal isocyanides is strongly preferred, and the nickel complexes, for which a 48-electron configuration with triply bridging isocyanide is preferred.