Formation of sp3-C1-Bridged Cp/Amido Titanium and Zirconium “CpCN” Constrained-Geometry Ziegler−Natta Catalyst Systems

Addition of methyllithium or p-tolyllithium to the C-6 carbon atom of the lithium (N-phenylformimidoyl)cyclopentadienide reagent 5 resulted in the formation of the dianionic sp3-C1-alkylidene-bridged Cp/amido ligand systems [C5H4−CHR−NPh]2- (6a, R = CH3; 6b, R = p-tolyl; each with Li+ cations). Transmetalation of 6a from lithium to zirconium was achieved by treatment with ZrCl4(THF)2 (7a) to yield the metallacyclic sp3-C1-linked spiro constrained geometry complex (η5-C5H4−CHMe−NPh-κN)2Zr (2a). Treatment of 6a with Cl2Ti(NMe2)2 (7c) gave the alkylidene-bridged Cp/amido titanium complex (η5-C5H4−CHMe−NPh-κN)Zr(NMe2)2 (2b). Analogous treatment of Cl2Zr(NEt2)2(THF)2 (7b) with 6a or 6b furnished the related (CpCN)Zr complexes (C5H4−CHR−NPh)Zr(NEt2)2 (2c, R = CH3; 2d, R = p-tolyl) each in ≥70% yield. The complexes 2a and 2b were both characterized by X-ray crystal structure analyses. The observation that both exhibit Cp(centroid)−M−N angles that are by ca. 10° smaller than those of their respective dimethylsilanediyl-bridged analogues renders the CpCN group metal complexes as more constrained than their conventional (Cp*SiN)M analogues. Lithium 4-methylanilide adds to the C-6 carbon atom of the non-CH-acidic pentafulvene (C5H4)CHCMe3 (13a) to yield Li[C5H4−CH(CMe3)(NH-p-tolyl)] (14a), which was subsequently NH-deprotonated by treatment with LDA to yield the dianionic reagent [C5H4−CH(CMe3)(N-p-tolyl)]2- (6c, as the dilithium compound). Analogous addition of lithium tert-butylamide to 13a, followed by NH-deprotonation by treatment with tert-butyllithium, yielded Li2[C5H4−CH(NCMe3)CMe3] (6d). Lithium tert-butylamide added to 1,2,3,4-tetramethylpentafulvene (13b) to yield Li[C5Me4−CH2−NH(CMe3)] (14c), which was subsequently NH-deprotonated by treatment with tert-butyllithium to yield Li2[C5Me4−CH2N(CMe3)] (6e). Transmetalation of 6c by treatment with Cl2Ti(NMe2)2 (7c) or Cl2Zr(NEt2)2(THF)2 (7b) cleanly gave the respective CpCN group 4 metal complexes [C5H4−CH(CMe3)(N−p-tolyl)]M(NR2)2 (2e, M = Ti; 2f, M = Zr). Similarly, the sp3-C1-bridged “constrained geometry” system [C5H4−CH(CMe3)(NCMe3)]Zr(NEt2)2 (2g) was obtained in good yield (70%) from the reaction of 6d with 7b, and treatment of 6e with 7b furnished the (Cp*CN)Zr complex [C5Me4−CH2−N(CMe3)]Zr(NEt2)2 (2h, 65% isolated). Activation of the (CpCN)M(NR2)2 systems by treatment with a large excess of methylalumoxane in toluene solution gave homogeneous Ziegler−Natta catalysts for the polymerization of ethylene (ca