Synthesis, Structural Features, and Formation of Organometallic Derivates of C₁-Bridged Cp/Amido Titanium and Zirconium “CpCN-Constrained Geometry” Systems

A series of C₁-bridged Cp/amido group 4 metal complexes [(“CpCN”)MX₂] was prepared. The starting compound 6-tert-butylfulvene (7) was reacted with LiNHR (R = o-anisyl (a), p-anisyl (b), phenyl (c), or tert-butyl (d)) to yield the Li(C₅H₄-CH(tBu)-NHR) compounds (8). Subsequent deprotonation with n-butyllithium, followed by transmetalation with Cl₂Ti(NMe₂)₂, yielded the (“CpCN”)Ti(NR₂)₂ complexes 10 (a−d). A second synthetic series started from 6-(dimethylamino)fulvene (11). The reaction with the LiNHR reagents led to addition followed by HNMe₂ elimination to yield the respective imino-substituted cyclopentadienides Li(C₅H₄-CHNR) (13). Addition of methyllithium to 13 gave the (Li⁺)₂(C₅H₄-CHMe-NR)^2-, (“CpCN”)^2-, ligands (14). Transmetalation with Cl₂Ti(NMe₂)₂ subsequently yielded the corresponding μ-CHMe-bridged Cp/amido group 4 complexes 15 (a−c). Treatment with Me₂SiCl₂ cleanly converted the (“CpCN”)M(NR₂)₂ complexes to the respective (“CpCN”)MCl₂ systems [3a−d, 4a−c (Ti), 5a (Zr)]. These were transformed to the (“CpCN”)M(CH₃)₂ complexes [μ-CHCMe₃:  17a−d (Ti), 19a (Zr), μ-CHMe:  18a−c (Ti)] and the (s-cis-supine-η⁴-butadiene)(“CpCN”)Ti systems 21a−d and 22b,c. With respect to X-ray structure analyses the (CpCN)MX₂ systems must be regarded as more “constrained” than their (“CpSiN”)MX₂ analogues. The (“CpCN”)MCl₂ and (“CpCN”)M(CH₃)₂ complexes were used as catalysts for ethene homopolymerization and ethene/1-octene copolymerization. All systems gave active catalysts, but these were quite different in their catalytic performance when compared with the usually applied (“CpSiN”)TiX₂-derived catalysts. The (“CpCN”)M catalyst activities and selectivities were very dependent on the specific activator components employed.