Hydrido-oxo complexes of rhenium(V): synthesis, structure, spectroscopic properties, and reactions with acids and bases

Abstract

The reaction of [ReH 4(η 2-H 2)(Cyttp)]X (X=SbF 6 ( 1(SbF 6)), OTf ( 1OTf)); Cyttp=PhP(CH 2CH 2CH 2PCy 2) 2, OTf=O 3SCF 3) with neat acetone at reflux temperature affords the dihydrido-oxo complex [ReH 2(O)(Cyttp)]X (X=SbF 6 ( 2(SbF 6)), OTf ( 2(OTf))). The isotopomers [ReH 2( 18O)(Cyttp)]SbF 6 ( 2- 18O(SbF 6)), [ReD 2(O)(Cyttp)]SbF 6 ( 2- d 2(SbF 6)), and [ReD 2( 18O)(Cyttp)]SbF 6 ( 2- d 2, 18O(SbF 6)) were prepared, respectively, by treatment of 2(SbF 6) with H 2 18O, D 2 under photolysis, and D 2 followed by H 2 18O. The structure of 2 (as 2(SbF 6)·3/4MeOH) was determined by single-crystal X-ray diffraction analysis and shown to contain a meridionally-coordinated Cyttp and an oxo ligand approximately cis to each of the three phosphorus donor atoms (Re–O=1.732(7) Å). The hydrido ligands were not located; however, their presence in the positions essentially cis and trans to the oxide in a severely distorted coordination octahedron of the metal is suggested by the elucidated molecular structure. The 1H NMR signals at δ −1.04 (tt) and −12.62 (dtd) and the IR ν(ReH) absorptions at 2030 and 1716 cm −1 provide strong evidence for this assignment. The IR ν(Re 16O) band of 2(SbF 6) at 923 cm −1 surprisingly shifts to 897 cm −1 in 2- d 2(SbF 6). Similarly, the ν(Re 18O) of 2- 18O(SbF 6) at 887 cm −1 moves to 854 cm −1 in 2- d 2, 18O(SbF 6). Changes are also observed for one of the δ(ReH) absorptions of 2(SbF 6) at 817 cm −1, which appears at 810 cm −1 in 2- 18O(SbF 6). A simple analysis of the ν(ReO) and δ(ReH or ReD) vibrational frequencies suggests that a resonance interaction occurs between the ν(ReO) and one of the δ(ReH) modes. Complex 2(OTf) reacts at low temperature with KOH–pyridine to form [Re(O) 2(py)(Cyttp)]OTf, and with Li[BEt 3H] in excess to give ReH 5(Cyttp). Treatment of 2(OTf) with aqueous HCl in benzene yields a green solid which is formulated as [ReH 2(OH)Cl(Cyttp)]OTf from spectroscopic evidence.