Preparation, structure, and chemistry of (O-acyl imidato)- and (O-alkyl imidato)carbene pentacarbonyl complexes of chromium

Article abstract of DOI:10.1021/om00111a016

The first examples of the insertion of organonitriles (R²CN; R² = Me, Ph, n-Pr, i-Pr, t-Bu, CH₂Ph, p-MeOC₆H₄, 2-furyl) into the metal-carbon bond of heteroatom-stabilized Fischer carbene complexes ((CO)₅CrC(OMe)R¹; R¹ = Ph, Me) to give imidatocarbene complexes are described. The structures of the imino complexes 14 and 12 from the reaction of the phenyl complex 2 with benzonitrile and tert-butyl cyanide were determined by X-ray diffraction and found to have C-N-C angles of 153° and 174°, respectively, indicating that the nitrogen plays a significant role in stabilizing the carbene carbon of the imino carbene complex. The kinetic methylation of the imino complex 13 from the reaction of the phenyl complex 2 and benzyl cyanide gave a 14:1 mixture of separable diastereomers 38a and 38b which is a consequence of an axis of chirality about the C-N-C 2-azaallenyl linkage. The stereochemistry of the major diastereomer 38a was determined by X-ray diffraction analysis which reveals that the dihedral angle about the C-N-C linkage is nearly perpendicular at 94.1°. The first example of the reversible insertion of a nitrile into a transition-metal carbene complex was found in the investigation of the reaction of the tert-butyl imino complex 12 with 1-pentyne. The first examples of (O-acyl imidato)carbene complexes are described which are prepared by the double acylation of aminocarbene complexes. The two methods described for this double acylation are the acylation of anions stoichiometrically generated from amino complexes and the acylation in the presence of triethylamine and 4-(dimethylamino)pyridine. The solid-state structure of the O-acyl imidate complex 32 was found to be quite similar to that of the O-alkyl imidate complexes. Crystal data for 32: space group P2₁/n, Z = 4, a = 13.268 (5) A?, b = 11.573 (4) A?, c = 15.951 (7) A?, β = 109.20 (2)°, R = 0.059, and R_w = 0.056 for the 3032 reflections with F_o > 2.33σ(F_o). Finally, an optimized procedure was found for the selective mono-alkylation of the phenylaminocarbene complex 21.