SYNTHESIS AND CHARACTERIZATION OF A SERIES OF DIPHOSPHINE LIGATED PT-AU CLUSTER COMPOUNDS

A series of diphosphine {Ph2P(CH2)(n)PPh2, n=2-4, abbreviated P-n-P} l igated platinum-gold cluster compounds has been synthesized in high yi eld by ligand exchange reactions with PPh3 ligated, hydride Pt-Au clus ters. The exchange reaction between [(H)(PPh3)Pt(AuPPh3)(7)](2+) and t he P-2-P and P-3-P ligands gives the clusters [(PPh3)PtAug(P-n-P)(4)]( 2+) (1,2), and with P-4-P the cluster [(P-4-P)PtAu6(P-4-P)(3)](2+) (3) is formed. The higher nuclearity cluster [PtAu10(P-3-P)(5)](2+) (8) w as prepared by reaction of [(H)Pt(AuPPh3)(9)](2+) with P-3-P. All of t hese clusters have the 18-electron configuration and thus are unreacti ve with small electron donor molecules such as CO, Hg and H-2. Cluster s 2, 3 and 8 react with the Lewis acids MX (MX = CuCl and AgNO3) givin g tri-metallic compounds of higher nuclearity. The products of the MX addition to 1 and 2 are the four new clusters [(PPh3)Pt(MCl)Au-g(P-n-P )(4)](2+) where n = 2 and 3 and M = Cu and Ag (4-7). The reaction of M X with 8 gives only the double addition products [Pt(MCl)(2)Au-10(P-3- P)(5)](2+) (9, 10). The molecular structures of clusters 2, 3, 5, 7 an d 8 were determined by single crystal X-ray diffraction (Mo K alpha, l ambda = 0.71037 Angstrom, 173 K; crystal data for 2: P1, a = 17.1484(4 ), b = 20.8146(5), c =23.1098(5), alpha=71.284(1) Angstrom, beta = 70. 717(1), gamma= 71.632(1)degrees, V= 7169.6(3) Angstrom(3), Z=2, R = 0. 10; 3: P1, a = 14.833(1), b = 15.905(2), c = 27.068(3) Angstrom, alpha = 81.175(7), beta = 77.088( 12), gamma = 67.742(6)degrees, V=5743.7(1 0) Angstrom(3), Z=2, R=0.051; 5: P2(l)/c, a=24.353(3), b=26.326(3), c= 20.554(2) Angstrom, beta=108.082(6)degrees, V=12526(2) Angstrom(3), Z= 4, R=0.067; 7: P1, a = 17.4401(3), b = 18.4505(2), c= 23.1111(3) Angst rom, alpha=97.615(1), beta = 104.731(1), gamma = 104.275(1)degrees, V = 6817.3(2) Angstrom(3), Z=2, R = 0.087; 8: P1, a=16.048(3), b=16.015( 3), c=30.790(5) Angstrom, alpha=83.408(12), beta=89.677(12), gamma=65. 135(13)degrees, V=7124(2) Angstrom(3), Z=2, R=0.096). All have Pt-cent ered, icosahedral fragment geometries for their PtMAug metal frames wi th the diphosphine ligands bridging adjacent Au atoms and also chelate d to Pt in 3. The diphosphine ligated clusters are less labile and les s fluxional than their PPh, analogs due to constraints on the number o f skeletal rearrang ement pathways imposed by the bridging diphosphine ligands. (C) 1997 Elsevier Science S.A.