Organoactinides promote the Tishchenko reaction: the myth of inactive actinide-alkoxo complexes.

Neutral and cationic organoactinide complexes have been extensively studied in the past decade as catalysts for several organic transformations.1,2 Polymerization of alkenes,3,4 oligomerization,5,6 intermolecular hydroamination,7-9 and hydrosilylation of terminal alkynes,10 and 1,1-insertion of isonitriles into terminal alkynes11 comprise some of these processes. However, because of the high oxophilicity of the actinide complexes, all the substrates containing oxygen atoms were excluded because of the expected low activity of these complexes owing to the predictable oxygen-actinide interaction. Lin et al. have demonstrated this guideline in actinide chemistry, based on the extremely low activity of actinide complexes containing alkoxy ligands in the catalytic hydrogenation of olefins.12 In our attempts to discover new catalytic reactions for actinidebased complexes, Barnea et al. reported their surprising activity toward the polymerization of cyclic monoand diesters.13 This discovery arouses the conceptual question about the activity of actinide-alkoxo complexes. To expand the scope of the actinides in catalysis, we have pursued the Tishchenko reaction (dimerization of aldehydes to give the corresponding esters (eq 1)).14,15 Herein we report the catalytic Tishchenko reaction between two similar (eq 1) or different (eq 2) aldehydes to give the symmetric (3 and 4) or asymmetric (5 and 6) esters, correspondingly. To show the generality of the process, and to be able to propose a suitable mechanistic pathway, we have studied two organoactinide complexes Cp*2ThMe2 (1) (Cp* ) C5Me5) and Th(NEtMe)4 (2),7,17,18 in addition to kinetic and thermodynamic studies using complex 1.