Organomolybdän‐ und Organowolfram‐;Reagenzien, III. Chemoselektive, nichtbasische Carbonylmethylenierungs‐;Reagenzien aus MoOCl 3 (THF) 2 und MoOCl 4 : Bildung, Thermolabilität, Struktur

Organomolybdenum and Organotungsten Reagents, III. — Selective, Nonbasic Carbonylmethylenation Reagents from MoOCl 3 (THF) 2 and MoOCl 4 : Formation, Thermolability, Structure From the family of more than 20 carbonylolefinating μ‐methylene molybdenum and tungsten complexes [1,2] the reagent “3”, obtained in solution by treatment of MoOCl 3 (THF) 2 with two equivalents of methyllithium, is probably the most favorable one for chemoselective carbonylolefination reactions. As judged by the 13 C‐ and 1 H‐NMR spectra the reagent is not a single species, but a mixture of either isomeric 1,3‐dioxo‐1,3‐dimolybda(V)cyclobutane complexes 3 , differing in the position of the ligands Cl, O, and THF at the molybdenum atoms, or of oligomers of 3 . — Treatment of MoOCl 4 with two equivalents of methyllithium gave a carbonylolefinating reagent “4” which, according to NMR data, consists of isomeric or oligomeric 1,3‐dioxo‐1,3‐dimolybda(VI)cyclobutane complexes 4 . Both reagents are labile at room temperature, but differ from the classical carbonylolefinating reagents by an acidic rather than a basic character, resistance to hydroxy groups, and high selectivity.