Synthesis and Dynamic Features of (Chloro)zirconocene Cations Stabilised by Pendant (Diarylphosphanyl)alkyl and (Dimethylamino)alkyl Substituents at Their Cyclopentadienyl Ring Systems

Abstract

Treatment of the substituted (diarylphosphanyl)methyl group‐4 metallocene complexes [(C5H4−CR1R2−PAr2)2ZrCl2] (2: R1/R2 = CH3/CH3, H/CH3, H/aryl) with Li[B(C6F5)4] in dichloromethane solution results in chloride ligand abstraction (with LiCl precipitation) to yield the complexes [(C5H4−CR1R2−PAr2)2Zr−Cl+] (5), with both phosphanyl groups internally coordinated to the metal centre. Three possible diastereoisomers are observed in the case of 5c (R1 = H; R2 = CH3), while bulkier R2 substituents give higher selectivities. The thermally induced (reversible) cleavage of the Zr−phosphane linkage results in dynamic NMR behaviour. Gibbs activation energies of ΔG≠(298 K) = 14.8 ± 0.5 and 14.5 ± 0.5 kcal/mol were obtained for these intramolecular equilibration processes in the complexes trans‐5d (R1 = H; R2 = Ph) and trans‐5e (R1 = H; R2 = ferrocenyl), respectively. Treatment of the substituted (dimethylamino)methyl metallocene complexes [(C5H4−CR1R2−NMe2)2ZrCl2] (6a, 6b) with Li[B(C6F5)4] proceeds analogously to yield the cation systems [{C5H4−C(CH3)2−NMe2}2ZrCl+] (12a) and [{C5H4−CH(CH3)−NMe2}2ZrCl+] (12b, three possible diastereoisomers). Both complexes have their pairs of amino groups coordinated to the metal centre. The complexes exhibit dynamic NMR spectra. Selective equilibration of the diastereotopic N(CH3)A(CH3)B resonances of complex 12a is observed [ΔG≠(233 K) = 11.5 ± 0.2 kcal/mol], whereas the adjacent C(CH3)A(CH3)B methyl groups remain diastereotopic. The dynamic equilibration of the latter was observed at a markedly higher temperature [ΔG≠(333 K) = 17.3 ± 0.2 kcal/mol]. Treatment of [{C5H4−C(CH3)2−NMe2}CpZrCl2] (10) with Li[B(C6F5)4] resulted in the formation of complex [{C5H4−C(CH3)2−NMe2}CpZr−Cl+] (11), which shows the internal −N(CH3)A(CH)B equilibration proceeding with a markedly higher activation barrier [ΔG≠(333 K) = 17.6 ± 0.2 kcal/mol] than in 12a, and a stereochemical memory effect indicative of solvent coordination to the metal centre of the resulting highly electrophilic chlorozirconocene cation intermediate. Complex 11 was characterised by an X‐ray crystal structure analysis, which shows the internal Zr←amine coordination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Cationic Group 4 Metallocene–(o‐Phosphanylaryl)oxido Complexes: Synthetic Routes to Transition‐Metal Frustrated Lewis Pairs

“…The comparatively inert HCPh 3 or MeCPh 3 byproducts are not known to coordinate to the cationic metal and are easily removed. [38,39] For this chemistry, the reagent must also be obtained in impeccable purity, which was only possible by multiple precipitations from compatible solvents (fluorobenzene). The resulting ion pairs [Cp 2 ZrR][RB(C 6 F 5 ) 3 ] are often in equilibrium with the zwitterionic complexes, [Cp 2 ZrR(μ-R)B-(C 6 F 5 ) 3 ], in which the alkyl (or hydride) ligand is only partially dissociated.…”

Allyldimethylsilylcyclopentadienyl Hafnium Complexes: Formation and Trapping of Hafnocenium Cations

“…Formation and Dynamic Behavior of Cationic Species. Reaction of the dibenzyl hafnocene complex 5 with B(C 6 F 5 ) 3 was carried out in CD 2 Cl 2 using a Teflonvalved NMR tube and monitored by 1 H, 13 C, and 19 F NMR spectroscopy at variable temperature.…”

“…Group 4 metallocenes are well-known precursors for single-site alkene polymerization catalysts. − The active metal alkyl cation is formed by reaction of these precursors with different alkylating agents and strong Lewis acid activators − (MAO, B(C 6 F 5 ) 3 , [CPh 3 ][B(C 6 F 5 ) 4 ]). Alkene coordination to the metal alkyl cation followed by alkyl migration to the coordinated alkene is the generally accepted mechanism of propagation.…”

1-Methylimidazolin-2-yl functionalized cyclopentadienyl complexes of titanium and zirconium. Crystal structure of {[η5:η1-κN-C5H4CPh2CH2-(1-Me–C3H4N2)]ZrCl2}2(μ-Cl)2

“…The Group 4 transition metal complexes with cyclopentadienyl ligands bearing a nitrogen-containing n-donor moiety in the side chain have been extensively studied (see reviews [1][2][3]) and still attract considerable attention [4][5][6][7][8][9][10][11][12][13][14]. In the most complexes of this type, the nitrogen atom is bound to aliphatic substituents and is either in an sp 3 -hybridized state (N ?…”