REACTIONS OF ALKYLLITHIUM AND GRIGNARD-REAGENTS WITH ENTADIENYL)DICARBONYL(2-METHYLBUTADIENE)MOLYBDENUM - OBSERVATIONS OF SOLVENT EFFECTS ON REGIOSELECTIVITY

The regioselectivity that is observed during reactions of the title co mplex with hydride and carbon nucleophiles was found to be solvent-dep endent. In diethyl ether solution, alkyllithiums and Grignard reagents add preferentially to C-1, while in THF and other solvents C-4 additi on dominates. Inclusion of complexing agents (TMEDA or HMPA) in the re actions in ether leads to a reversal of selectivity. All hydride nucle ophiles add selectively at C-1, irrespective of solvent. Decomplexatio n of the C-1 adducts, with concomitant addition of a second nucleophil e, allows the completely stereoselective construction of trisubstitute d carbon-carbon double bonds. The first example of osmylation of an al kene substituent in the presence of a pi-allyl-Mo-(CO)2Cp group is des cribed.