An NMR study of mixed, tartrate-containing TiIV complexes

The reactions of amines and amino alcohols with diisopropyl or diethyl R,R- or S,S-tartrate and Ti(O i Pr) 4 were examined by 1 H and 13 C NMR to obtain and characterize nonfluxional complexes with the tartrate units in novel binding modes. The mildly acidic 8-hydroxyquinoline and N-phenyl-N-benzoylhydroxylamine selectively formed the products of a double O i Pr substitution, Ti 2 (tartrate) 2 (ligand) 2 (O i Pr) 2 , and the products of double tartrate substitution, Ti(ligand) 2 (O i Pr) 2 , while 2,4-pentanedione formed only the latter Basic amino alkanols formed diastereomerically pure Ti 2 (tartrate) 2 (aminoalkoxide)(O i Pr) 3 species. N,N-Dimethyl-2-aminoethanol (Hdmae) also and uniquely formed monomeric Ti(tartrate) 2 (Hdmae) 2 species that could be described as doubly zwitterionic. Secondary or tertiary amines formed triply C 2 -symmetric Ti 3 (tartrate) 4 (amine) 2 (O i Pr) 4 assemblies. Some minor components were believed to be μ-O i Pr species. All mixed complexes except Ti(tartrate) 2 (Hdmae) 2 contained chelating and bridging tartrate units, without coordination by ester carbonyls. A nonchelating, nonbridging tartrate unit was also present in the amino alcohol cases. Primary amines, aromatic amines, and hydrazines all failed to provide identifiable complexes. As well, N,N-dibenzylhydroxylamine failed to generate in solution the complex that had previously been characterized by X-ray crystallography. Amidst the rich chemistry of Ti IV -tartrate systems, the evident selectivities in product formation were ascribed to macro-ring closures that are specifically directed by the electronic nature of the addend. Transient O i Pr-bridged intermediates were also implicated.