RHENIUM POLYHYDRIDE COMPLEXES THAT CONTAIN THE TRIPODAL PHOSPHINE CH3C(CH2PPH2)3 (TRIPHOS)

The compound ReCl3(triphos) (triphos = CH3C(CH2PPh2)3) reacts with NaBH4 in ethanol to afford the pentahydrido complex ReH5(triphos), which when treated with HBF4.Et2O in RCN (R = Me, Et) converts to [ReH(NCR)3(triphos)](BF4)2. The direct reaction of ReH5(triphos) with EPh3 (E = P, As, Sb), dppe (Ph2PCH2CH2PPh2), and arphos (Ph2PCH2CH2AsPh2) produces the trihydrides ReH3(triphos)(EPh3), ReH3(triphos)(eta-1-dppe), and ReH3(triphos)(eta-1-arphos), respectively, the latter complex existing as a mixture of linkage isomers ReH3(triphos)(arphos-P) and ReH3(triphos)(arphos-As). A more convenient and higher yield preparation of the compounds ReH3(triphos)L involves the direct reaction of ReCl3(triphos) with NaBH4 and EPh3, dppe, or arphos. The trihydrides can be protonated by HBF4.Et2O to produce [ReH4(triphos)L]BF4, which are in turn readily deprotonated by NEt3. In the absence of ligand L, solutions of ReH5(triphos) evolve H-2 and the dark red dinuclear complex Re2H4(triphos)2 is formed cleanly. It is very easily oxidized (E1/2(ox) = -0.55 V vs Ag/AgCl in 0.1 M TBAH-CH2Cl2) to the green monocation [Re2H4(triphos)2]+. Single-crystal X-ray structure determinations have been carried out on the compounds fac-ReCl3(triphos) (1) and [Re2H4(triphos)2]ReO4.5C6H6 (2). Crystal data for 1 at 20-degrees-C: orthorhombic space group Pna2(1), a = 17.332 (5) angstrom, b = 12.032 (3) angstrom, c = 17.542 (4) angstrom, V = 3658 (3) angstrom3, and Z = 4. The structure was refined to R = 0.039 (R(w) = 0.047) for 1812 data with I > 3-sigma(I). Crystal data for 2 at -61-degrees-C: monoclinic space group P2(1)/n, a = 16.765 (2) angstrom, b = 23.065 (3) angstrom, c = 25.109 (4) angstrom, beta = 98.38 (1)-degrees, V = 9605 (4) angstrom3, and Z = 4. The structure was refined to R = 0.028 (R(w) = 0.035) for 9496 data with I > 3.0-sigma(I). The structure of the cation can be represented as [(triphos)HRe(mu-H)3Re(triphos)]+. Although the terminally bound hydride ligand was not located in this structure determination, its position can be inferred from the angular distortions that are present about one of the Re atoms. The Re-Re distance of 2.5389 (4) angstrom is typical of a mixed polyhydride-phosphine complex of dirhenium in which there are three or four bridging hydride ligands present.