Mechanism of the conversion of intermediate 16-electron tungstenocene alkyls into alkene hydrides and fluxionality within [W(.eta.-C5H5)2(CH2 = CHCH3)H]PF6

Agostic interactions in transition metal compounds

“…The classical view of this process is that insertion occurs to form an unsaturated species followed by C-C bond rotation and return of a different ␤-hydrogen to metal as shown in Scheme 6 Upper. There is growing evidence (74)(75)(76)(77)(78)(79) C ␣ -C ␤ bond as shown in Scheme 6 Lower. The unsaturated metal center never relinquishes contact with electron density in ␤-CH bonds.…”

The Dynamics of the β-Agostic Isopropyl Complex (ArNC(R)−C(R)NAr)Pd(CH(CH2-μ-H)(CH3))+BAr4‘-(Ar = 2,6-C6H3(i-Pr)2): Evidence for In-Place Rotation versus Dissociation of the Agostic Methyl Group

“…The insertion of an olefin into a transition-metal hydride bond is a common step in a number of organometallic reactions, and thus, there have been several studies aimed at understanding this fundamental transformation. − The exchange of a metal hydride with hydrogens in an olefinic ligand has been detected by both H/D exchange reactions and dynamic NMR experiments. Examining the simplest case, an ethylene hydride complex, 1 , the exchange can be envisioned to occur through a classical mechanism involving a coordinatively unsaturated metal ethyl complex, 2 , (eq 1) or via a β-agostic intermediate, 3 , which undergoes facile “in-place” methyl rotation where the CH 3 group remains bound to the metal in the transition state for exchange (eq 2).…”

Synthesis and characterisation of cationic bis(cyclopentadienyl)tungsten(IV) complexes †

“…19, 20 The olefin complex [W(η-C 5 H 5 ) 2 H(η 2 -CH 2 CHC 6 H 5 )][PF 6 ] 4 was prepared as described for related complexes 27,28 by treating the neutral dichloride [W(η-C 5 H 5 ) 2 Cl 2 ] with an excess of the Grignard reagent 29 [MgBr(CHCH 3 C 6 H 5 )]. Compound 4 was isolated as a mixture of endo and exo isomers in the ratio 4 : 3, a typical ratio found for olefin hydride complexes of tungstenocene, 28 Scheme 1. We presume that the observed isomer ratio is an equilibrium position attained by a base catalysed proton-Table 2 Selected bond lengths (Å) and angles (Њ) for the complexes 2, 3 and exo-4 ation/deprotonation process of the hydride ligand during work-up.…”

“…We presume that the observed isomer ratio is an equilibrium position attained by a base catalysed proton-Table 2 Selected bond lengths (Å) and angles (Њ) for the complexes 2, 3 and exo-4 ation/deprotonation process of the hydride ligand during work-up. 28 The analytical and spectroscopic data for 4 are given in Table 1. The resonances for the endo and exo forms in the 1 H NMR spectrum of the isomeric mixture were assigned using integrals, and an observed coupling between the methylene protons of the lesser isomer (J(HH) = 1.2 Hz) by a through-space interaction.…”

“…system, in which insertion of the propene ligand into the tungsten-hydride bond has been studied using Spin Population Transfer experiments. 28 The insertion product 5 contains an alkyl with an electron withdrawing group which has the effect of stabilising the alkyl towards β-hydride elimination. Qualitative analysis of a series of d 6 -acetone 1 H NMR spectra of 5 taken over a period of ] is consistent with the photochemical mechanism proposed earlier.…”