THE BICLUSTER OXIDATIVE ADDITION AS A ROUTE TO BICAPPED HEXAPLATINUM CLUSTERS

The reaction of either the 84-electron cluster [Pt-6(mu-CO)(6)(mu-dppm )(3)] (1) or the 82-electron cluster [Pt-6(CO)(6)(mu-dppm)(3)(])(2+) ( 2), dppm=Ph2PCH2PPh2, with SnX3- or Hg2X2 gave the corresponding bicap ped trigonal prismatic 86-electron clusters [Pt-6(mu(3)-SnX3)(2)(mu-CO )(6)(mu-dppm)(3)] (3:X=F (3a), Cl (3b), Br (3c)) or [Pt-6(mu(3)-HgX)(2 )(mu-CO)(6)(mu-dppm)(3)] (4:X = Cl (4a),Br (4b), I (4c)), respectively . The new clusters 3 and 4 have been characterized spectroscopically a nd 4c has also been characterized by X-ray diffraction. Crystals of 4c . CH2Cl2 . 2Et(2)O are monoclinic, space group P2(1)/c, a=20.092(9), b=18.718(7), c=26.258(7) Angstrom, beta=108.09(3)degrees, V=9387(6) An gstrom(3), Z=4. The molecular core in 4c is a Pt-6 trigonal prism with each triangular Pt-3 face capped by an HgI fragment. The intertriangl e Pt-Pt bond distances (2.910(1)-2.948(1) Angstrom) are longer than th e intratriangle Pt-Pt distances (2.634(1)-2.687(1) Angstrom) and this is consistent with EHMO calculations. The reaction of 1 with Hg2X2 to give 4 is termed a bicluster oxidative addition; according to predicti ons from EHMO calculations it should lead to stronger intertriangle Pt -Pt bonding in 3 and 4 than in the precursor cluster 1, bur this is no t supported by structural data observed in 3c and 4c. (C) 1997 Elsevie r Science S.A.