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

Abstract

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 (carried out at 60 °C) and the copolymerization of ethene with 1-octene (at 90 °C).

(N-Arylaminomethyl)pyridine-N-oxides: Synthesis and characterization of potential ligand systems and the formation of their N,O-chelate aluminum complexes

“…50% yield that clearly was not the corresponding amine but rather a coupled product between two pyridine cores of the starting material (see Scheme 5). This became evident from the observation of two imino 13 C NMR signals at d 167.4 and d 165.6. The 1 H NMR spectrum (see Fig.…”

“…alkyllithium nucleophiles [13], followed by hydrolysis. We have, therefore, treated the ketimino compound 11a with methyl lithium.…”

Metallocenes

“…Some interesting polymer compositions can be generated by postpolymerization reactivity of metallocene-generated polymers. Vinylterminated polyethylene macromers have been incorporated onto a polypropylene backbone by metallocene polymerization (67). Polar groups are generally avoided in olefin polymerizations due to poisoning effects, but protecting schemes can enable their incorporation, allowing conversion to polar graft copolymers of polyethylene (223) or polypropylene (224).…”

Catalysis and Organometallic Chemistry of Monometallic Species

“…58 The chemistry of hybrid -Cp ligands in constrained geometry complexes have also been investigated. Examples include titanium and zirconium() Cp-phosphido, 59 Cp-imido, 60 and chiral-at-metal titanium and zirconium() Cp-amido complexes. 61,62…”