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 sp 3 -C 1 -alkylidene-bridged Cp/amido ligand systems [C 5 H 4 −CHR−NPh] 2 - ( 6a, R = CH 3; 6b, R = p -tolyl; each with Li + cations). Transmetalation of 6a from lithium to zirconium was achieved by treatment with ZrCl 4 (THF) 2 ( 7a ) to yield the metallacyclic sp 3 -C 1 -linked spiro constrained geometry complex (η 5 -C 5 H 4 −CHMe−NPh-κ N ) 2 Zr ( 2a ). Treatment of 6a with Cl 2 Ti(NMe 2 ) 2 ( 7c ) gave the alkylidene-bridged Cp/amido titanium complex (η 5 -C 5 H 4 −CHMe−NPh-κ N )Zr(NMe 2 ) 2 ( 2b ). Analogous treatment of Cl 2 Zr(NEt 2 ) 2 (THF) 2 ( 7b ) with 6a or 6b furnished the related (CpCN)Zr complexes (C 5 H 4 −CHR−NPh)Zr(NEt 2 ) 2 ( 2c, R = CH 3; 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 (C 5 H 4 ) CHCMe 3 ( 13a ) to yield Li[C 5 H 4 −CH(CMe 3 )(NH- p -tolyl)] ( 14a ), which was subsequently NH-deprotonated by treatment with LDA to yield the dianionic reagent [C 5 H 4 −CH(CMe 3 )(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 Li 2 [C 5 H 4 −CH(NCMe 3 )CMe 3 ] ( 6d ). Lithium tert -butylamide added to 1,2,3,4-tetramethylpentafulvene ( 13b ) to yield Li[C 5 Me 4 −CH 2 −NH(CMe 3 )] ( 14c ), which was subsequently NH-deprotonated by treatment with tert -butyllithium to yield Li 2 [C 5 Me 4 −CH 2 N(CMe 3 )] ( 6e ). Transmetalation of 6c by treatment with Cl 2 Ti(NMe 2 ) 2 ( 7c ) or Cl 2 Zr(NEt 2 ) 2 (THF) 2 ( 7b ) cleanly gave the respective CpCN group 4 metal complexes [C 5 H 4 −CH(CMe 3 )(N−p-tolyl)]M(NR 2 ) 2 ( 2e, M = Ti; 2f, M = Zr). Similarly, the sp 3 -C 1 -bridged “constrained geometry” system [C 5 H 4 −CH(CMe 3 )(NCMe 3 )]Zr(NEt 2 ) 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 [C 5 Me 4 −CH 2 −N(CMe 3 )]Zr(NEt 2 ) 2 ( 2h, 65% isolated). Activation of the (CpCN)M(NR 2 ) 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).