Low‐Temperature Kinetic NMR Studies on the Insertion of a Single Olefin Molecule into a ZrC Bond: Assessing the Counterion–Solvent Interplay

Abstract

Sticky counterions: Low‐temperature kinetic NMR studies were performed to determine ΔH≠ and ΔS≠ values for the insertion of a single 2‐methyl‐1‐heptene molecule into a ZrC bond of [Cp2Zr(η2‐CH2NMePh)][X] (1a: X−=MeB(C6F5)3−, 1b: B(C6F5)4−) in [D8]toluene and a 1:1 mixture of [D8]toluene and [D5]chlorobenzene. Both activation parameters critically depend on the interplay of the counterion and the solvent.

An NMR study on the reaction of substituted dimethyl zirconocenes with dimethylanilinium borate

“…In line with previous findings [20,21], we observed a quantitative coordination of the amine at the metal center and subsequent CeH activation of the NMe group leading to the formation of stable zirconaaziridinium ion pairs (Scheme 1) that were characterized in terms of interionic structure [18,19], intramolecular dynamics [22] and reactivity with olefins [23].…”

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

“…Despite the complication of overlapping 1 HNMR resonanceso f1,A l iBu 3 ,a nd 4,c areful analysisby 1 HROESY NMR (see Supporting Information) reveals dipolar interactions of H18a with H7 and H8, ando fH 21 with H15 andH 16, suggesting that, similart o3, 4 anti is prevalent in solution.Analogous to 2 and 3 anti ,NMR parameters (Table 1) indicate selective a-agostic interactions involving both bridging units of 4.E quilibrium constants( K eq )f or the reversible formation of 4 are estimated by integration of 1 HNMR resonances relative to an externals tandard in the temperature range of 233-273K.V an't Hoff analysis( see Supporting Information) yields the corresponding thermodynamic parameters, DH 0 = À13.3 kJ mol À1 and DS 0 = À40.6 Jmol À1 K À1 . [20] Albeit these values are in general agreement with the associative nature of the reaction, the small value of the standarde ntropy, usuallyi n the range of À100 to À180 Jmol À1 K À1 for ab imolecular associative process, [21] suggestst hat aw eak ligand (likely C 6 D 5 Cl solvent) is coordinated to Hf in complex 1 and released upon formation of 4.…”

Nucleophilicity of Alkyl Zirconocene and Titanocene Precatalysts, and Kinetics of Activation by Carbenium Ions and by B(C6F5)3

“…The kinetic method described above for the determination of the rates of methyl and benzyl anion abstractions by benzhydrylium ions has also been employedt om easure the rate constantso ft he analogous reactions with tritylium ions 3, which have often been used as co-initiators in polymerization reactions and in FLP catalysis (Table 3). [2][3][4] Whereas the negative counterions are known to have as ignificant effect on the rates of insertion of zirconocenium ions in olefinicd ouble bonds and on the propagation rate constants, [15] the trityl salts 3b-B(C 6 F 5 ) 4 À and 3b-BF 4 À have now been found to abstract benzyl anionsf rom zirconocene 1b at equal rates (Table 3). Although the zirconocene 1a reacted with benzhydrylium ions with similar rates in dichloromethane and acetonitrile (cf.…”