Crystallographic Characterisation of Organolithium and Organomagnesium Intermediates in Reactions of Aldehydes and Ketones

We report reactions of LiNacNac and NacNacMg(TMP) with common organic substrates (TMP=2,2,6,6-tetramethylpiperidide). Using bulky beta-diketiminate compound NacNac (Me, Dipp), we have trapped metalated intermediates amenable to X-ray crystallographic study. LiNacNac and acetone produced the NacNac-free hexameric diacetone alkoxide [{LiO(MeC(= O)CH2C(Me)(2)}(6)]; whereas pinacolone gave the simple monomeric donor-acceptor complex [Li{(MeCN-2,6-(Pr2C6H3)-Pr-i)(2)CH}{O=C(Me)Bu-t}]. Benzaldehyde produced dimeric [Li{(MeCN-2,6-(Pr2C6H3)-Pr-i)(2)CC(= O)Ph}{O=C(Ph)OCH2Ph}](2), where one benzaldehyde molecule has inserted in to the gamma-carbon position of the NacNac ligand, with a molecule of benzyl benzoate derived from a Tishchenko reaction of the aldehyde acting as a terminal donor to lithium. Tetranuclear, mixed dimer [{LiO(MeCN-2,6-(Pr2C6H3)-Pr-i)(2)CH-CH(Ph)}(2){LiO(PhC(= O)}(2)] containing the same modified NacNac ligand was the fortuitous product from repeating the reaction of LiNacNac and benzaldehyde in a solution presumably contaminated with benzoic acid. Combining NacNacMg(TMP) with pinacolone affords monomeric heteroleptic [Mg{(MeCN-2,6-(Pr2C6H3)-Pr-i)(2)CH} {OC(Bu-t)(Me)CH2C(= O)Bu-t}] with an aldolate constituting the second anion. Completing the set is dimeric [Mg {(MeCN-2,6-(Pr2C6H3)-Pr-i)(2)CH}{O(C=CH2)Ph}(2)], where the enolate derived from acetophenone bridges the magnesium centres.