Zur Kenntnis der carbonylmethylenierenden Molybdän-Aluminium- und Wolfram-Aluminium-μ-methylen-Komplexe

MoCl5, MoOCl3(THF)(2), MoO2Cl2, (MeO)(2)MoCl3, (MeO)(4)MoCl, WOCl3(THF)(2), and WOCl4 form carbonyl-methylenating complexes and 1-2 equiv. of CH4 by reacting with 2 equiv. of Me(3)Al. These thermolabile complexes are prepared in solution and differ in their properties (e.g. ability to transfer mostly more than 1 CH2 unit per Mo or W atom in carbonyl-olefinating processes; high sensitivity to water, no hydroxy ketone affinity) from the carbonyl-olefinating 1, 3-dimetallacyclobutanes (M = Mo, W) and are believed to be mono- and bicyclic analogs (e. g. hypothic structures 3, 6 - 8) of the Tebbe reagent (1), containing Mo - mu CH2, - Al or W - mu CH2, - Al groups, respectively. Analogous complexes seem to be produced by treating MoOCl3(THF)(2) with 2 Me(2)Zn or (MeO)(2)MoCl3 and (MeO)(4)MoCl with 2 MeMgBr in each case. Unlike the dimeric and, due to a Mo-Mo bond, diamagnetic Mo-V derivatives (MeO)(2)MoCl3 and (MeO)(4)MoCl (according to H-1-NMR structure 9 or 10 and 11 or 12, respectively) the complexes obtained by the reactions (MeO)(2)MoCl3 + 2 Me(3)Al and (MeO)(4)MoCl + 2 Me(3)Al are paramagnetic, indicating the expected absence of a Mo-Mo bond. The H-1-NMR spectrum of the reaction mixture obtained by treating the Mo-VI derivative MoO2Cl2 with 2 Me(3)Al in THF shows various signals for mu-CH2 groups, whereas signals of t-CH2 ligands are missing (t = terminal). In analogy to 1 the carbonyl-olefinating activity of the Mo-Al and W-Al reagents is activated by the addition of 2 equiv. of HMPA. Treatment of PhCOCH(2)NEt(2) (19) with {MoO2Cl2 + 2 Me(3)Al} leads to carbonyl olefination with formation of 20 and also to alpha-methylation with formation of PhCOCH(Me)-NEt(2) (21), pointing to the intermediate formation of a t-CH2-Mo ligand. {MoO2Cl2 + 2 Me(3)Al + 2 HMPA} has found to be the best reagent for the carbonyl olefination of aldehydes, whereas {WOCl3(THF)(2) + 2 Me(3)Al+ 2 HMPA} was optimal for ketones. In 1:1 reactions both reagents normally give better yields than the Tebbe reagent. By applying {WOCl3(THF)(2) + 2 Me(3)Al} and {MoO2Cl2 + 2 Me(3)Al} on ketones 16 - 18 an interesting neighbour group effect of electron donor atoms in the delta position to the keto group was observed.