Phosphorano-Stabilized Carbene Complexes with Short Thorium(IV)– and Uranium(IV)–Carbon Bonds

While no alkylidene
complexes of the f elements are known, the
use of phosphorano-stabilized carbene complexes to produce short actinide–carbon
bonds has been previously demonstrated. Complexes of the form, (C5Me5)2­An­(X)­(CHPPh3), with short thorium­(IV)– and uranium­(IV)–carbon­(carbene)
bonds have been synthesized from the reaction of (C5Me5)2­An­(X)­(CH3) (An =
Th, U; X = Cl, Br, or I) with the ylide, CH2​PPh3. The resulting uranium complexes feature the shortest uranium­(IV)–carbon
bonds reported to date. The molecular and electronic structure of
the thorium phosphorano-stabilized carbene complexes is detailed using
X-ray crystallography, 13C NMR spectroscopy, and density
functional theory calculations, and compared to thorium methandiide
complexes.