A Synthetic and Mechanistic Study of Oxycarbene-like Coupling Reaction Patterns of Actinide η2-Acyl Complexes with Carbon Monoxide and Isocyanides

Article abstract of DOI:10.1021/ja00261a010

This contribution reports the synthesis and characterization of the ylide complexes <*> (Cp' = η⁵-C5Me5; R = Me, Ph) formed by the carbonylation of Cp'2Th(Cl)(η²-COCH2-t-Bu) (1) in the presence of phosphines.Isotopic tracer studies with 13CO indicate that the labeled carbon atom is incorporated regiospecifically at the ylide α-carbon atom position.The carbonylation of 1 to yield the enedionediolate <*> (2) or the ylide complexes was found to obey a second-order rate law where rate = kP_CO<1>; k = 1.50(5) x 1E-5 min^-1 torr^-1 for both carbonylations at 30.8 deg C.The rate of formation of the ylide complexes was also found to be independent of solvent, phosphine concentration, and type of phosphine used.The carbonylation of 1 is therefore inferred to involve a rate-determining coupling of CO with the acyl to yield an intermediate ketene-like complex.The reaction of acyl 1 or Cp'2Th(Cl)(η²-COCH2Ph) with a variety of isocyanides (RNC; R = t-Bu, C6H11, 2,6-Me2C6H3) results in the formation of ketenimine complexes of the type Cp'2Th(Cl) and Cp'2Th(Cl).Addition of a second equivalent of isocyanide yields simple adducts of the type Cp'2Th(CNR)(Cl) and Cp'2Th(CNR)(Cl).These new complexes have been fully characterized by standard techniques and the ketenimine Cp'2Th(Cl) by single-crystal X-ray diffraction.Under the appropriate conditions, the N-aryl complexes suffer secondary reactions in which the η²-acyl ultimately undergoes coupling with 2 equiv of isocyanide to yield acetylindolate and acetylindoleninate derivatives.The η²-acyl was also found to undergo coupling with 1 equiv of diphenylketene to yield the complex <*>.These coupling products have been fully characterized by conventional analytical and structural methodology.The mechanistic and reactivity results of this study are discussed in terms of the anchored Fischer carbene-like character of actinide η²-acyls and the mechanism by which the carbonylation of 1 yields the enedionediolate 2.