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Abstract

Titanium complexes bearing a pyridine-diamide ligand [2,6-(RNCH2)2NC5H3]2' (R = 2,6-diisopropylphenyl (BDPP); R = 2,6-dimethylphenyl (BDMP)) have been synthesized. The dichloride complexes [2,6-(RNCH2)2NC5H3]TiCl2 are prepared in high yield from {2,6- [(Me3Si)RNCH2J2NC5H3} and TiCl4 via the elimination of 2 equiv of ClSiMe3. Monoalkyl and bis(alkyl) complexes are prepared from [2,6-(RNCH2)2NC5H3]TiCl2 and various Grignard reagents. Reduction of the dichloride precursors (BDPP)TiCl2 and (BDMP)TiCl2 with excess 1% Na/Hg amalgam in the presence of >2 equiv of internal (PhC=CPh, EtC=CEt, PrC^CPr) or terminal (HC=CSiMe3, PhC^CH) alkynes yields metallacyclopentadiene derivatives in good yield No cyclotrimerization of alkyne is observed. Ligand activation is observed in certain cases for complexes bearing the BDMP ligand. In a similar way, the reaction of {2,6-[(Me3Si)RNCH2]2NC5H3} with TaCl5 yields the complex, w^r-(BDPP)TaCl„ and two equiv of ClSiMe3. The reduction of the trichloride complex with excess Na/Hg in the presence of alkynes yields the pseudo 5-coordinate Ta(III) derivatives, (BDPP)Ta(rr-RC=CR')Cl (R = R' = Pr, Et, Ph; R = Ph, R' = H). The 4-octyne compound reacts with LiC^CR to give the acetylide octyne derivatives (BDPP)Ta(r|2-PrC=CPr)(C=CR) (R = Ph, Bu, SiMe3, o-Me3SiC6H4). The phenylacetylide complex reacts with phenylacetylene to give the metallacyclic derivative (BDPP)Ta[(r|2-PhC=C)PrC=CPrHC=CPh]. Similarly, (BDPP)Ta(r|2-PrC=CPr)(C=CBu) and (BDPP)Ta(Ti2-PrCsCPr)(C=CSiMe3) react with HC^CBu and HC=CSiMe3 to give the expected metallacycles. (BDPP)Ta(ri2-PrC^CPr)(C