Li, Ti(III), and Ti(IV) trisamidotriazacyclononane complexes. Syntheses, reactivity, and structures

The preparations of 1,4,7-(NHPhSiMe2)(3)-1,4,7-triazacyclononane (H3N3-tacn) and its lithium and sodium derivatives are described. The X-ray structure of the THF adduct of the lithium derivative, Li3N3-tacn(THF)(2), shows that one of the macrocycle pendant arms is bent to allow the coordination of the its lithium ion to two tacn amines, In solution, a fluxional process makes all the pending arms magnetically equivalent. The reactions of Li3N3-tacn or Na3N3-tacn with either TiCl4 and TiCl3(THF)(3) led to the formation of [Ti(N-3-tacn)], 5. The oxidation of 5 with various oxidizing reagents gave cationic complexes [Ti(N-3-tacn)]X, 6 (X = I, Cl, SCN, PF6, BPh4), that exist as a pair of enantiomers, Lambda(lambdalambdalambda)/Delta(deltadeltadelta), which interconvert in solution. The molecular structures of 5 and 6 (X = 1, BPh4) show the coordination of the six nitrogen donor set to the titanium. Due to the short length of the tacn pendant arms, the hexacentate bonding mode of the ligand is mainly achieved through the sharpening of the N-Si-N angles. The reaction of [Ti(N-3-tacn)]I, 6a, with W(CO)(6) led to the synthesis of [Ti(N-3-tacn)][W(CO)(5)I], 7.