STERIC CROWDING IN A RHENIUM POLYHYDRIDE INDUCED BY A CHELATING DISILYL LIGAND - SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF REH5(DISIL)(PPH(3))(2) (DISIL=1,2-BIS(DIMETHYLSILYL)BENZENE AND 1,2-BIS(DIMETHYLSILYL)ETHANE)

1,2-Bis(dimethylsilyl)benzene (dmsbH(2), 2a) and 1,2-bis(dimethylsilyl )ethane (dmseH(2), 2b) react with ReH7(PPh(3))(2) (1) to give the firs t chelating bis(silyl) polyhydride complexes, ReH5(disil)(PPh(3))(2) ( 3a,b). These have been characterized by spectroscopic techniques and, in one case, by single-crystal X-ray diffraction. The structure is not the expected tricapped trigonal prism found for all the other 9-coord inate rhenium polyhydrides. Instead, a dodecahedral structure typical of 8-coordination is adopted. We propose that the compound is ReH3(H-2 )(disil)-(PPh(3))(2) and contains a stretched eta(2)-H-2 ligand (where stretched H-2 complexes have d(H...H) = 1.1-1.6 Angstrom). Crystals o f ReH5(dmsb)(PPh(3))(2) (3a) belong to the space group P2(1)/n (No. 14 ) with lattice parameters a = 11.063 (7) Angstrom, b = 21.016(7) Angst rom, c = 18.490(7) Angstrom, beta = 106.84(4)degrees, V = 4114(6) Angs trom(3), Z = 4, and rho(calc) = 1.463 g/cm(3). The complexes catalytic ally dehydrogenate alkanes in the presence of tert-butylethylene.