123264-24-4Relevant academic research and scientific papers
Cationic zirconium and hafnium isobutyl complexes as models for intermediates in metallocene-catalyzed propylene polymerizations. Detection of an α-agostic interaction in (C5Me5)2Hf(CH2CHMe 2)(PMe3)+
Guo, Zhaoyu,Swenson, Dale C.,Jordan, Richard F.
, p. 1424 - 1432 (2008/10/08)
A series of cationic Zr and Hf isobutyl complexes has been prepared to model the Cp2M{CH2CH(R)(R′)}+ and Cp2M{CH2CH(R)(R′)}(α-olefin)+ intermediates in metallocene-catalyzed α-olefin polymerizations (R′ = growing poly(α-olefin) chain). The cationic hydride [Cp′2Zr(H)(THF)][BPh4] (5, Cp′ = C5H4Me) reversibly inserts isobutylene at 23°C to afford [Cp′2Zr(CH2CHMe2)(THF)][BPh4] (6), in which the isobutyl group adopts a normal structure. The reaction of 6 with PMe3 yields [Cp′2Zr(CH2CHMe2)(PMe 3)][BPh4] (7) which adopts a β-agostic structure and undergoes β-H elimination above -13°C. The reaction of the hafnacyclobutane Cp*2Hf(CH2CHMeCH2-) (10) with [HNBu3][BPh4] in the presence of PMe3 yields [Cp*2Hf(CH2CHMe2)(PMe 3)][BPh4] (12). NMR data, including isotope perturbation of resonance results for deuterium labeled analogues, establish that the isobutyl group of 12 is distorted by an α-agostic interaction. The reaction of 12 with THF, and the reaction of 10 with [HNBu3][BPh4] in THF yield [Cp*2Hf(CH2CHMe2)(THF)][BPh4] (14). Solution NMR data, solid state IR data, and X-ray crystallographic results establish that the isobutyl group of 14 is distorted (Hf-C-C angle 137.5(8)°) but that Hf?Hα agostic interactions are absent. Crystal data for 14: space group P21/c, a = 10.747(3) A?, b = 21.417(3) A?, c = 21.783(8) A?, β = 101.83(4)°, V = 5365(6) A?3, Z = 4, R = 0.053, Rw = 0.086. 14 undergoes predominant β-Me elimination at 58°C. The structures of Cp′2Hf(nBu)(L)+ (17, L = THF, normal butyl group; 19, L = PMe3, β-agostic butyl group) are analogous to those of the corresponding Cp′2Zr(nBu)(L)+ complexes. The structures and reactivity of 6, 7, 12, and 14 are rationalized in terms of the steric and electronic properties of the C5R5- and L ligands.
Synthesis and chemistry of cationic alkyl, alkenyl, and allyl complexes derived from the soluble, cationic hydride (C5H4Me)2Zr(H)(THF)+
Jordan, Richard F.,LaPointe, Robert E.,Bradley, Prudence K.,Baenziger, Norman
, p. 2892 - 2903 (2008/10/08)
Reaction of Cp′2Zr(CH2Ph)2 (Cp′ = C5H4Me) with [Cp′2Fe] [BPh4] in THF produces the cationic benzyl complex [Cp′2Zr(CH2Ph)(THF)] [BPh4] (4) which contains a normal η1-benzyl ligand. Hydrogenolysis of 4 in THF solution (1 atm of H2, 23°C) produces the soluble cationic hydride complex [Cp′2Zr(H)-(THF)][BPh4] (5). Hydride 5 reacts with olefins H2C=CH2R to yield cationic alkyl complexes [Cp′2Zr-(CH2CH2R)(THF)][BPh4] (8a, R = H; 8b, R = Me; 8c, R = Et), with 2-butyne to give the cationic 2-butenyl complex [Cp′2Zr(CE)-C(Me)=C(H)(Me)}(THF)][BPh4] (9), and with allene to give the allyl complex [Cp′2Zr(η3-C3H 6)(THF)][BPh4] (13). Solutions of 4, 5, or 13 in CH2Cl2 catalyze the polymerization of ethylene to polyethylene. Solutions of 5 and of 8a,c in THF catalyze the oligomerization of ethylene to butene, hexene, and octene. Alkyl complexes 8a-c also insert 2-butyne to give cationic alkenyl complexes [Cp′2Zr{(Z)-C(Me)=C(Me)(R)}(THF)][BPh4] (10a, R = Et; 10b, R = nPr; 10c, R = nBu). No evidence for multiple 2-butyne insertion or for competing β-H elimination reactions is observed. The structure of the cationic alkenyl complex [Cp′2Zr{(Z)-C(Me)=C(Me)(nPr)}(THF)] [BPh4] (10b) has been determined by X-ray diffraction. Complex 10b crystallizes in space group P21/n with a = 12.084 (4) A?, b = 20.469 (9) A?, c = 16.436 (2) A?, β= 100.26 (2)°, V = 4000 (2) A?3, and Z = 4. The alkenyl ligand lies in the plane between the two Cp′ ligands in the exo conformation, and the THF ligand is rotated 50° from the optimum conformation for Zr-O π bonding.
