Thermolysis of (MeCp)2 Nb(η2-CO2)R complexes: Decarbonylation vs. insertion

Article abstract of DOI:10.1016/0022-328X(95)05667-E

A series of carbon dioxide complexes of the type Cp′₂ Nb(η²-CO₂)R (Cp′ = MeC₅H₄; R = -CH₂SiMe₃, 1a; -CH₂CMe₃, 1b; -CH₂Ph, 1c; -CH₃, 1d) was prepared and the thermolyses of 1a-1c investigated. When heated at 60°C in THF, complexes 1a and 1b are converted to the corresponding oxo derivatives (MeC₅H₄)₂ Nb(=O)R (2a, 2b) and CO. The structure of 2a was established by X-ray diffraction and consists of a pseudotetrahedral Cp₂MXY arrangement. That the oxo group of 2 is derived from coordinated CO₂ was confirmed by ¹³C labeling. Thermolysis of benzyl derivative 1c exhibits concentration dependent behavior, converting to the corresponding oxoalkyl derivative 2c in dilute solutions but forming a mixture of 2c and the carbonyl complex (MeC₅H₄)₂ Nb(CO)CH₂Ph (4) in more concentrated solutions. With extended reaction times 2c and 4 decompose producing PhCH₃, PhCH₂ CH₂Ph, PhCH₂OH, and PhCHO, the products of apparent M-C homolysis and oxidation.