80974-26-1Relevant academic research and scientific papers
Monomeric pentacoordinated TaBr3(PPhMe2)2. Synthesis, crystal structure, and aliphatic C-H activation in solution
Hovnanian,Hubert-Pfalzgraf,Le Borgne
, p. 4647 - 4651 (2008/10/08)
Reduction of TaBr5 by magnesium turnings activated by diethyl ether in CH2Cl2 in the presence of phenyldimethylphosphine offers the paramagnetic compound TaBr3(PhPMe2)2, which is the first monomeric Ta(III) adduct to be structurally characterized. It crystallizes in the monoclinic system (P21/c) with unit cell dimensions a = 8.46 (1) ?, b = 20.80 (2) ?, c = 8.836 (8) ?, β = 98.77 (5)°, and Z = 4. TaBr3(PhPMe2)2 consists of square-pyramidal molecules, with one bromine in two possible apical positions. The phosphorus ligands occupy cis positions in a flat square-pyramidal polyhedron (basal angle ? 173°). The apical tantalumbromine bond (2.382 (2) ? average) is significantly shorter than the basal one (2.524 (2) ? average). The solution behavior of this unsaturated d2 compound is puzzling. Dynamic equilibrium between diamagnetic species and paramagnetic TaBr3(PhPMe2)2 stabilized by aromatic agostic C-H interactions is observed in CH2Cl2 solutions. Spontaneous intra- and intermolecular oxidative C-H additions involving the methyl groups occur in acetonitrile with formation of Ta(V) species having η2-CHPMePh or bridging η2-CH2PMePh moieties.
