Roan Fraser

Fischer aminocarbene conformers containing a 2-thienyl or 2-furyl ring: a crystallographic, NMR, and DFT study

Fischer aminocarbene complexes [(CO)5M=C(NHR)Y] (M=Cr or W; R=H, Cy or C2H4NH2; Y=2-thienyl or 2-furyl) containing an amino group exist as two isomers in solution, the E and Z isomers. The two isomers arise from restricted rotation about the N–Ccarbene bond, that exhibits double bond character due to π-donation from nitrogen to the carbene carbon. Each isomer exists as two conformers in fast equilibrium with each other. The conformers arise from the rotation of the aryl ring around the Ccarbene–Caryl single bond with a DFT calculated rotation barrier of 0.1–0.5 eV. The main isomer, isolated in the solid state, generally exhibits a syn orientation of the aryl ring relative to the amino substituent and a Z configuration of the amino substituent relative to the metal. Graphical abstract

[N,N′-Bis(2,4,6-trimethyl­phen­yl)ethane-1,2-diimine-κ2N,N′]tetra­carbonyl­chromium(0)

The octahedral coordination of the Cr0 atom in the title compound, [Cr(C20H24N2)(CO)4], displays some distortion. This is manifested by an exocyclic torsion angle C(mesitylene)—N—Cr—C(carbonyl) that deviates by more than 20° from planarity. Another structural feature is the significant distortion from linearity of the Cr—C—O angles of the two carbonyl groups that interact with both ortho-methyl groups of the two mesitylene rings. The remaining two carbonyl groups overlap with the centres of the mesitylene rings themselves and are linear within <3°.