Lewis acidic yttrium(III) and titanium(IV) derivatives of anionic, metal-tethered carbenes apparently act as bifunctional catalysts for the polymerisation of D,L-lactide, using a combination of Lewis acid and base functionalities to initiate ring opening of the cyclic monomer; the alcohol- and amino-functionalised carbenes from which they derive provide models for the first insertion step, and also display metal-free polymerisation catalysis to generate polylactic acid.

a bidentate amine-imidazolium bromide affords a new amine-functionalized carbene, and by a protonolysis reaction, the first f-element complex with a covalently bound, potentially hemilabile, N-heterocyclic carbene.Since the early use of di-N-phenyl, -methyl, and -adamantyl functionalized imidazolium salts and electronrich alkenes as precursors for metal-carbene complexes and stable nucleophilic carbenes, [1] it is now apparent that a wide range of N-functional groups are tolerated in nucleophilic

Lithium(I) and uranium(VI) amido-tethered Bu(t)-substituted N-heterocyclic carbene (NHC) complexes exhibit very distorted metal-carbene bonds; the corresponding magnesium(II) and mesityl-substituted NHC uranium(VI) complexes are undistorted; the distortion does not affect the ligand binding strength, suggesting a dominance of electrostatic character in closed-shell electropositive metal-carbene bonds.

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A series of titanium(IV) adducts of an amido-tethered N-heterocyclic carbene (NHC) of the form Ti(L)(OiPr) n (Br)3 - n (n = 1−3, L = tBuNHCH2CH2[C{NtBu(CHCH)N}]) have been synthesized and characterized. Structural characterization of the n = 2 complex shows marked bending of the two ligands cis (and perpendicular) to the plane of the NHC group in the direction of the carbene, suggestive of a pseudo-back-bonding interaction between adjacent ligands and the carbene p orbital, consistent with a bonding model recently proposed for d0 metal-NHC complexes. However, inspection of a space-filling model and the calculation of bond order using DFT methods suggest that the bending is due to repulsions between lone pairs on the adjacent π-donor ligands in the complexes and not any specific interaction between the NHC and cis π-donor ligands.