Photoinitiated intramolecular hydrogen transfer from rhenium polyhydrides to C8 cyclopolyolefins

Article abstract of DOI:10.1021/om00122a014

The phototransient ReH₅P₂ (P = PMe₂Ph), formed by photolysis of ReH₅P₃, reacts with cyclooctatetraene to give first (η⁴-C₈H₁₀)ReH₃P₂ as a stereochemically rigid complex of cyclooctatriene. This undergoes a thermal reaction at 25°C to give (η⁵-C₈H₁₁)ReH₂P₂, shown to be a 1-5-η⁵-cyclooctadienyl complex by NMR spectroscopy and X-ray diffraction. This complex has a piano stool form with a diag-ReH₂P₂ unit forming the base. The two hydride ligands lie in a mirror plane of the open pentadienyl ligand, and these hydrides are thus inequivalent; the spectral data show that this complex is stereochemically rigid. Analogous η⁴-diene complexes are made from 1,5-cyclooctadiene and ReH₅P₃ (photochemically) and from ReH₇P₂ (thermally). Deuterium labeling experiments (employing ReD₅P₃ and C₈H₈) reveal that the transfer of three hydrides from metal to ring in the production of (η⁵-C₈H₁₁)ReH₂P₂ is regiospecific (i.e., no scrambling) and is wholly endo, consistent with an intramolecular mechanism. Crystallographic data (at -160°C): orthorhombic, Pbca with Z = 8 and a = 12.391 (4) A?, b = 17.882 (6) A?, and c = 20.441 (8) A?.