Reactions of lactams with titanocene- and zirconocene-alkyne complexes as elemental steps in catalytic anionic ring-opening polymerization of lactams

Depending on the nature of the metal and the ring size, lactams react with titanocene and zircocene complexes of bis(trimethylsilyl)acetylene Cp(2)Ti(Me(3)SiC(2)SiMe(3)) and Cp(2)Zr(L)(Me(3)SiC(2)SiMe(3)) (L = Py, THF) to yield different products. In the reaction of Cp(2)Zr(Py)(Me(3)SiC(2)SiMe(3)) with N-methyl-epsilon-caprolactam a simple ligand exchange reaction occurs and the complex Cp(2)Zr(Me(3)SiC(2)SiMe(3))[O = C-N(Me)-(CH2)(5)] (1) was isolated. With beta-propiolactam the alkenyl-amido complex Cp(2)Zr[-C(SiMe(3)) = C(H)(SiMe(3))][-N-CO-CH2-CH2] (2) was obtained, which indicates that an agostic metal-hydrogen interaction has taken place. The reaction of Cp(2)Ti(Me(3)-SiC(2)SiMe(3)) with epsilon-caprolactam gives after elimination of the alkyne and molecular hydrogen the first early transition metal complex with a deprotonated coordinated epsilon-caprolactam in a eta(2)-amidate bonding fashion Cp(2)Ti-O-C-N-(CH2)(5) (3). The obtained complexes were characterized by NMR spectra (1, 2) and crystal structure analysis (1-3) and discussed as elemental steps in anionic ring-opening polymerization of lactams catalyzed by metallocene-alkyne complexes.