Structure and reactivity of bridging dimanganese and -rhenium ethane-1,2-dionyl compounds

Article abstract of DOI:10.1021/om00121a010

The synthesis, spectroscopic properties, and reactivity of binuclear manganese and rhenium compounds in which the metals are linked by an ethane-1,2-dionyl bridge are described. The compounds M(CO)₅C-(=O)C(=O)M(CO)₅ (M = Mn, Re) are prepared by treatment of the respective pentacarbonyl anions with oxalyl chloride. These complexes have been characterized by ¹³C NMR, IR, UV/visible, and mass spectrometries and, in the case of M = Re, by an X-ray diffraction study. Re(CO)₅C(=O)C(=O)Re(CO)₅ crystallizes in space group P2₁/c and has unit cell dimensions a = 5.627 (4) ?, b = 12.392 (6) ?, c = 10.192 (6) ?, and β = 95.69 (8)° with Z = 2. Molecules of the complex lie such that the midpoint of the central C-C bond coincides with a crystallographic inversion center. The central Re-CO-CO-Re unit is planar, with the Re(CO)₅ substituents mutually trans and staggered relative to the ethane-1,2-dionyl plane. The dionyl C-Re bonds are of length appropriate to Re-C_sp2 single bonds, 2.228 (12) ?, and the central C-C bond is also single, length 1.558 (21) ?. Attempts to convert the ethane-1,2-dionyl moiety, which can be regarded as two carbon-carbon coupled CO molecules, into C₂ oxygenates have not met with much success, either in catalytic or in stoichiometric reactions. Decomposition of the M₂(CO)₁₂ species to M₂(CO)₁₀ + 2CO (M = Mn, Re) is the preferred reaction in all cases. Aspects of the reactivity of M(CO)₅C(=O)C-(=O)M(CO)₅ (M = Mn, Re) toward hydride donor reagents, hydrogen, and neopentyllithium are reported.