Insertion of Terminal and Internal Acetylenes into the Zr−μ-Methylene Bond of the Dinuclear Cationic Zirconium Complex [{Zr(η⁵-C₅H₅)}₂(μ-CH₂)(μ-Cl)(μ-η⁵-C₅H₄-η⁵-C₅H₄)][BMe(C₆F₅)₃]. Synthetic Aspects, NMR Spectroscopic Study, and Dynamic Behavior in Solution

Abstract

The dinuclear cationic zirconium species [{Zr(η 5 -C 5 H 5 )} 2 (µ-CH 2 )(µ-Cl)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )]-[BMe(C 6 F 5 ) 3 ] (1) reacts in dichloromethane at -78 °C with terminal alkynes, via insertion into the Zr-µ-methylene bond, to give various dinuclear cationic derivatives. Reaction of 1 with Me 3 SiCtCH gives the hydrido complex [{Zr(η 5 -C[BMe(C 6 F 5 ) 3 ] (4). Compounds 3 and 4 show dynamic behavior in solution involving an interchange between two enantiomeric structures through a suprafacial migration of the "-RCdCH 2 " moiety. When compound 1 was treated with a molar equivalent of internal alkynes RCtCR (R ) Et, n Pr), formation of [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C(Et)dC(Et)}(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] (5) and [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C( n Pr)dC( n Pr)}(µ-η 5 -C 5 H 4η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] (6) was observed, which were isomerized to the [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C(Et)CHdCHMe}(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )] [BMe(C 6 F 5 ) 3 ] (7) and [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C( n Pr)CHdCHEt}(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] (8) derivatives at room temperature, through a β-R hydrogen migration. The new complexes reported were characterized by elemental analysis and IR and NMR spectroscopy.

Mono- and Dinuclear Cyclopentadienylsiloxo Titanium Complexes: Synthesis, Reactivity, and Catalytic Polymerization Applications

“…The behavior described here for compound 1c parallels that observed for the related dinuclear titanium compound [(TiBz 2 ) 2 (μ-{η 5 -C 5 H 4 SiMe 2 O} 2 )], for which the benzyl-bridged intermediate was unstable in aromatic solvents, decomposing to give unidentified paramagnetic species . The substitution of the benzyl by a halide bridge occurring in halogenated solvents is clearly favored by the π-donating ability of this substituent, which increases the electron density, reducing their positive charge. − Cationic dinuclear group 4 complexes with halide bridges have also been formed by rearrangement of mononuclear cationic derivatives in halogenated solvents. ,, …”

Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts

“…Intermediate A evolves via β-H elimination from the 1,3-μ 2 -propylene group to the more stable structure B ( rac isomer, Δ E = −16.1 kcal/mol) with a μ 2 -H bridge, methyl displacement toward to the Ti2 center, and a new allylic fragment at Ti1 . A similar Ti 2 complex, reminiscent of intermediate B , was observed experimentally by Cuenca et al . DFT yields similar results for meso- 5 ; however, intermediates A and B are far less stable than rac- 5 (Δ E = −1.7 kcal/mol and −2.5 kcal/mol for A and B , respectively).…”

A Trimetallic Fulvalene‐Bridged Dizirconocene–Gallium Complex

“…[25] It should be noted that the 1 H NMR spectrum of 1 displays two singlets for the Cp ligands and eight well-resolved multiplets (see the Experimental Section) for the fulvalene ligand (resulting in two ABCD spin systems). [19,26] We did not observe a Ga À H IR stretch in the expected region (1800-2100 cm À ). [27][28][29][30] In an effort to better elucidate the nature of the hydride, we performed density functional theory (DFT) computations on 1 a, in which the meta terphenyl ligand of 1 has been replaced with a 2,6-dimethylphenyl ligand.…”

“…[11] The Ga ( . [19] Other 1 H NMR signals for bridging zirconium hydrides range from d = À5.32 to 0.95 ppm, [20][21][22][23] whereas terminal zirconium hydride 1 H NMR signals may range from d = 3.03 to 7.25 ppm. [20][21][22][23][24] The computed 1 H NMR spectrum of a model of 1, [(C 10 H 8 )(CpZr) 2 (m-H)(m-Cl)(mGaR)] (1 a; R = 2,6-Me 2 C 6 H 3 ), at the GIAO-PW91PW91/ LANL2DZ/-/PW91/LANL2DZ level showed that the computed hydride d value of À5.00 ppm is comparable to the experimental value observed for 1.…”