DIRHENIUM COMPLEXES OF THE TRIPODAL PHOSPHINE CH3C(CH2PPH2)3 (TRIPHOS) - THE ISOLATION AND CHARACTERIZATION OF THE CONFACIAL BIOCTAHEDRAL SPECIES [(TRIPHOS) RE(MU-X)3RE(TRIPHOS)](N+) (N = 1 OR 0)

The reactions of Re2(O2CCH3)2X4L2 (X = Cl or Br; L = py or H2O) with the tripodal phosphine CH3C(CH2PPh2)3 (triphos) in refluxing ethanol provide a route to the confacial bioctahedral dirhenium(II) complexes [Re2(mu-X)3(triphos)2]Y, where Y = Cl, Br or BPh4. The structural identity of the dirhenium cation has been established by X-ray crystallography on a crystal of composition [ReCl3(triphos)2]Cl. Crystal data at +20-degrees-C: triclinic space group P1BAR (No. 2), a=12.868(2), b=13.174(1), c=25.432(3) angstrom, alpha=94.761(8), beta=96.76(1), gamma=114.235(8)-degrees, V=3862(2) angstrom3, Z=2. The structure was refined by full-matrix least-squares to R=0.040 (R(w)=0.058) for 7523 data with I>3sigma(I). The confacial bioctahedral dirhenium(II) cation has a surprisingly long Re-Re distance (3.199(1) angstrom), which implies the absence of an Re-Re bond. The paramagnetism of these complexes accords with this result; all show well-defined contact-shifted H-1 NMR spectra and are ESR silent. The cations display four metal centered redox processes (two one-electron oxidations, two one-electron reductions); the first reduction can be accessed by cobaltocene to form the neutral complexes Re2(mu-X)3(triphos)2 in which there is an Re-2(3+) core present.