ISSN:
0009-2940
Keywords:
Carbonyl olefination
;
Molbydenum aluminium complexes, organo
;
Tungsten aluminium complexes, organo
;
Tebbe reagent
;
Aluminium, molybdenum and tungsten complexes
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Organomolybdenum and Organotungsten Reagents, VI[1]. On the Carbonyl-Methylenating Molybdenum-Aluminium and Tungsten-Aluminium μ-Methylene ComplexesMoCl5, MoOCl3(THF)2, MoO2Cl2, (MeO)2MoCl3, (MeO)4MoCl, WOCl3(THF)2, and WOCl4 form carbonyl-methylenating complexes and 1-2 equiv. of CH4 by reacting with 2 equiv. of Me3Al. 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-μCH2 Al or W -μCH2 Al groups, respectively. Analogous complexes seem to be produced by treating MoOCl3(THF)2 with 2 Me2Zn or (MeO)2MoCl3 and (MeO)4MoCl with 2 MeMgBr in each case. Unlike the dimeric and, due to a Mo—Mo bond, diamagnetic Mo derivatives (Me—O)2MoCl3 and (MeO)4MoCl (according to 1H—NMR structure 9 or 10 and 11 or 12, respectively) the complexes obtained by the reactions (MeO)2MoCl3 + 2 Me3Al and (MeO)4MoCl + 2 Me3Al are paramagnetic, indicating the expected absence of a Mo—Mo bond. The 1H—NMR spectrum of the reaction mixture obtained by treating the MoVI derivative MoO2Cl2 with 2 Me3Al in THF shows various signals for μ—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 PhCOCH2NEt2 (19) with {MoO2Cl2 + 2 Me3Al} leads to carbonyl olefination with formation of 20 and also to α-methylation with formation of PhCOCH(Me)-NEt2 (21), pointing to the intermediate formation of a t-CH2—Mo ligand. {MoO2Cl2 + 2 Me3Al + 2 HMPA} has found to be the best reagent for the carbonyl olefination of aldehydes, whereas {WOCl3(THF)2 + 2 Me3Al + 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 Me3Al} and {MoO2Cl2 + 2 Me3Al} on ketones 16-18 an interesting neighbour group effect of electron donor atoms in the δ position to the keto group was observed.
Additional Material:
5 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19941270121
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