REACTIONS OF COMPLEX LIGANDS .45. (ACYLAMINO)CARBENE COMPLEXES - SYNTHESIS, STRUCTURE, AND REACTIVITY

Fischer type aminocarbene complexes of chromium, molybdenum and tungsten undergo N-acylation under DMAP catalysis followed by decarbonylation affording tetracarbonyl ((acylamino)carbene) chelates. These complexes are characterized by a short metal-carbene and a long metal-oxygen bond in the chelate ring. A remarkable chemoselectivity is observed upon reaction with alkynes which is governed by the metal and the N-substitution pattern and which may be rationalized in terms of a stereoselective alkyne insertion into the metal-carbene bond. (CO)4Cr = C(p-Tol)NRCOC(CH3)3 prefers E insertion leading either to carbene annelation (indene, naphthalene derivatives) or to double alkyne insertion products (phenol ester). The molybdenum analogues add the alkyne to give presumed Z-alkenylcarbene intermediates, reasonable precursors for the isolated pyrrol and pyrrolone cycloaddition products.