Highly Reduced Carbene Complexes: Formation of an Alkoxymalonate by Coupling of Carbon Dioxide with the Nucleophilic Carbene in (Cr(CO4)=C(OMe)PH)2-.

摘要

Reduction of a mixture of cis and trans (Cr(C0)4(PBu3)(C(OMe)Ph)) with 2.0 equiv. of potassium naphthalenide leads to formation of a highly reduced complex with carbonyl absorptions at 1859(s) and 1737(s)/cm, consistent with formation of the dianionic carbene complex (Cr(CO)4(C(OMe)Ph))(2-)(1(2-)). A crystalline salt of 1(2-) can be obtained by 18-crown-6 complexation of the K+ counterion of samples prepared by reduction of trans(Cr(CO)4(PCy3)-(C(OMe)Ph)). The proposed formulation is supported by an unprecedented bis-carboxylation of the carbene ligand in 12- to give the unusual methoxy-malonate (K2(Ph(MeO)C(CO2))2) (K25, 82%), characterized by H+/CH2N2 esterification to give Ph(MeO)C(CO2Me)2 in 85% yield. The malonate K25 can be prepared directly from readily available (Cr(CO)5(C(OMe)Ph)) (2) in a single pot in 53% overall yield. Keywords: Fischer carbene complexes, Organic chemistry, Chemical reactions. (kt)