Nucleophilic attack on carbon monoxide in carbonyl phosphine complexes of rhodium(I) and ruthenium(II): A novel route to complexes of rhodium(-I)

Article abstract of DOI:10.1021/om00110a012

Reaction of [Rh(CO)₂(triphos)]PF₆ (triphos = MeC(CH₂PPh₂)₃) with sodium borohydride in CD₂Cl₂ results in the formation of the hydride RhH(CO)(triphos) and the formyl complex Rh(HCO)(CO)(triphos). In contrast, treatment of [Rh(CO)₂(triphos)]PF₆ with excess methyllithium in THF results in the formation of the rhodium(-I) complex Li[Rh(CO)(triphos)]. The mechanism of this unusual reaction appears to involve (i) nucleophilic attack of MeLi on a carbonyl carbon of [Rh(CO)₂(triphos)]PF₆ to yield the acetyl complex Rh(MeCO)(CO)(triphos), (ii) attack by a second mole of MeLi on the acetyl group to produce the complex Li[Rh(Me₂CO)(triphos)], and (iii) elimination of acetone to form product. In the presence of excess MeLi, the acetone reacts further to form tert-butoxide, which is also detected in the reaction mixture. The rhodium(-I) complex Li[Rh(CO)(triphos)] reacts with proton sources to yield the hydride RhH(CO)(triphos), with alkyl and acyl halides to form the alkyl complexes RhR(CO)(triphos) (R = Me, Et, Ph, MeCO), with trimethyltin chloride to form Rh(SnMe₃)(CO)(triphos), and with CO to form Li[Rh(CO)₂(η²-triphos)], with a pendant phosphine. The complex [Ru(CO)₃(triphos)][AlCl₄]₂ can be synthesized by treating [RuCl-(CO)₂(triphos)]Cl with AlCl₃ under an atmosphere of CO. The dicationic complex [Ru(CO)₃(triphos)]²⁺ is very susceptible to nucleophilic attack at CO and reacts with ethanol, water, and NaBH₃CN to form the alkoxycarbonyl complex [Ru(CO₂Et)(CO)₂(triphos)]⁺, the hydride complex [RuH(CO)2(triphos)]⁺ (presumably via [Ru(CO₂H)(CO)₂(triphos)]⁺), and the formyl complex [Ru(HCO)(CO)₂(triphos)]⁺, respectively.