Catalysis vs. oxophilicity: Breaking the myth of inactive actinide-oxo complexes

Abstract

For many decades, compounds containing oxygen atoms were excluded from the actinide-catalysis field because of the high oxophilic nature of these complexes. Pursuing the conceptual question about the potential activity of actinide-oxo bonds we were surprised to find that the coupling of aromatic aldehydes catalyzed by Cp*2ThMe2 and Th(NEtMe)4 via thoriumalkoxide intermediates take place in high yields to produce the corresponding esters. Here we present our breakthrough results including comprehensive mechanistic, deuterium labeling, kinetic and thermodynamic studies. In addition, the tetrachloride salt of uranium reacts with one equivalent of Li2[(C5Me4)2SiMe2] in DME to form the complex [η5-(C5Me4)2SiMe2]UCl2·2LiCl·2DME (13), which reacts with equimolar amounts of water in DME yielding the coordinative unsaturated bridged mono oxide and mono chloride uranium lithium salt complex {[η5- (C5Me4)2SiMe2]UCl}2(μ-O)(μ-Cl)•Li(DME)3•DME (14). The alkylation of complexes 14 with BuLi gives the mono bridged dibutyl complex {[η5-(C5Me4)2SiMe2]UBu}2(μ-O) (16). Complex 16 is an active catalyst for the disproportionation metathesis of TMSC≡CH and the cross-metathesis of TMSC≡CH or TMSC≡CTMS with various terminal alkynes. PhSiH3 reacts with complex 16 producing Ph2SiH2 and SiH4 (caution) indicating the cleavage of the trimethylsilyl group from the phenyl moiety and the formation of uranium-silyl intermediate.