Bent metal carbene geometries in amido N-heterocyclic carbene complexes

Abstract

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.

Functionalised Saturated‐Backbone Carbene Ligands: Yttrium and Uranyl Alkoxy–Carbene Complexes and Bicyclic Carbene–Alcohol Adducts

“…A C H T U N G T R E N N U N G (2.633(7) ), [40] and [UO 2 Cl 2 {CA C H T U N G T R E N N U N G (NMesCH) 2 } 2 ] (2.626 (7) ). [42] The U À OC distances of 2.…”

“…[ 40] The asymmetric OUO stretch, ñ asymm A C H T U N G T R E N N U N G (OUO), is observed in the FTIR spectrum at ñ = 851 cm…”

Synthesis and Small Molecule Reactivity of Uranium(IV) Alkoxide Complexes with both Bound and Pendant N‐heterocyclic Carbene Ligands

“…[2][3][4][5] We have shown how the incorporation of an anionic functional group into an NHC-based ligand stabilises electropositive metal cations, and have made NHC complexes of potassium(i) (A) and uranium(vi) (B) cations using uninegative alkoxide-NHC-L (where L = OCMe 2 CH 2 [1-C(NCHCHNiPr)]) and amido-NHC ligands. [6,7] The U À C(carbene) bond in complex B is most simplistically viewed as a two-electron dative bond. Two trivalent and one tetravalent adduct of the simplest NHC, C-(NMeCMe) 2 , have been reported recently, in which the NHC is used as a two-electron donor ligand to control the compounds nuclearity.…”

Sterically induced differences in N-heterocyclic carbene transition metal complexes

“…It can be expected that this rigidity will have an influence on the optimal tether length between the carbene and a pendant chelating functional group with respect to the size of the metal centre. An excellent example for this was presented by Arnold et al [27] in a series of amido tethered chelating carbene complexes of lithium, magnesium and uranium with the ligand (see Fig. 17).…”

“…Could the unsymmetrical coordination of a tethered and chelating NHC ligand [26] not be explained by an insufficient tether length rather than undirected "ionic" bonding [27,28] and could the equatorial coordination of NHC ligands in a trigonal bipyramidal coordination geometry [24,[29][30][31] not be caused by the steric demand of the wingtip groups rather than any irregularities of the NHC's electronic structure (see Fig. 2)?…”