Organomolybdän‐ Und Organowolfram‐;Reagenzien, III. Chemoselektive, Nichtbasische Carbonylmethylenierungs‐;Reagenzien Aus MoOCl3(THF)2 Und MoOCl4: Bildung, Thermolabilität, Struktur

Organomolybdenum and Organotungsten Reagents, III. — Selective, Nonbasic Carbonylmethylenation Reagents from MoOCl3(THF)2 and MoOCl4: Formation, Thermolability, StructureFrom the family of more than 20 carbonylolefinating μ‐methylene molybdenum and tungsten complexes[1,2] the reagent “3”, obtained in solution by treatment of MoOCl3(THF)2 with two equivalents of methyllithium, is probably the most favorable one for chemoselective carbonylolefination reactions. As judged by the 13C‐ and 1H‐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 MoOCl4 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.