Synthesis, structure, and reactivity of titanacyclopentadiene complexes bearing ancillary pyridine diamide ligands

Titanium complexes bearing the pyridine diamide ligands [2,6-(RNCH(2))(2)NC5H3](2-) (R = 2,6-diisopropylphenyl (BDPP); R = 2,6-dimethylphenyl (BDMP)) have been synthesized, Reduction of the dichloride precursors (BDPP)TiCl2 (1a) and (BDMP)TiCl2 (1b) with excess 1% Na/Hg amalgam in the presence of > 2 equiv of internal (PhC=CPh, EtC=CEt, PrC=CPr) or terminal (HC=CSiMe(3), PhC=CH) alkynes yields metallacyclopentadiene derivatives in good yield. The alpha,beta'-substituted titanacycle (BDPP)Ti[C4H2(SiMe(3))(2)] (5a) was characterized by X-ray crystallography and is best described as a distorted square pyramid with the metallacycle carbon C(4) occupying the apical position. The alpha,alpha'-substituted titanacycle (BDMP)Ti[C4H2(SiMe(3))(2)] (5b) reacts with excess 3-hexyne and 4-octyne to give the asymmetric metallacycles (BDMP)Ti[C(4)Et(2)H(SiMe(3))] (7b) and (BDMP)Ti[C4Pr2H(SiMe(3))] (8b), respectively. No cyclotrimerization of alkyne is observed. Ligand activation is observed in certain cases for complexes bearing the BDMP ligand.