Tungsten and Molybdenum Alkyl or Aryl Complexes That Contain the [(C6F5NCH2CH2)3N]3- Ligand
1998-02-18T00:00:00Z (GMT) by
[N3NF]W(OC6F5) and [N3NF]W(O-3,5-Me2C6H3) ([N3NF]3- = [(C6F5NCH2CH2)3N]3-) can be prepared readily from [N3NF]WCl in good yields. An X-ray study of the latter revealed an approximately trigonal structure with the phenoxide in the trigonal pocket. Alkylation of [N3NF]WCl with LiCH2R (R = Me, n-Pr, SiMe3, CMe3) reagents in toluene at room temperature led to the evolution of molecular hydrogen and formation of the corresponding tungsten(VI) alkylidyne complexes, [N3NF]W⋮CR (R = Me, n-Pr, SiMe3, CMe3). The intermediate [N3NF]W(CH2SiMe3) decomposed in a first-order manner to give [N3NF]W⋮CSiMe3 (ΔH⧧ = 20.3 ± 0.2 kcal/mol, ΔS⧧ = −7 ± 1 eu). An X-ray study of [N3NF]W⋮CSiMe3 showed it to have the expected, relatively undistorted, structure in which the W−C triple bond distance is 1.768(6) Å. Although attempts to prepare [N3NF]WCH3 were not successful, [N3NF]W⋮CH could be prepared by reacting [N3NF]WCl with cyclopropyllithium in toluene. [N3NF]MoCl reacts with LiCH2SiMe3 or LiCH2CMe3 in toluene to yield [N3NF]Mo(CH2CMe3) or [N3NF]Mo(CH2SiMe3), respectively. Thermolysis of [N3NF]Mo(CH2CMe3) produced [N3NF]Mo⋮CCMe3 in a first-order reaction at 121 °C (k = 7.9(5) × 10-5 s-1). Several labeling experiments are consistent with the proposal that β-elimination competes with α-elimination and loss of molecular hydrogen in the [N3NF]3- system. [N3NF]WI reacts with aryllithium reagents (Ar = Ph, 3,5-Me2C6H3) to yield [N3NF]WPh and [N3NF]W(3,5-Me2C6H3). The aryl complexes react with hydrogen (3 atm) in toluene at 40 °C to yield diamagnetic [N3N]WH3 and are cleanly oxidized by pyridine N-oxide. An X-ray study of [N3NF]W(O)(3,5-Me2C6H3) revealed it to have a pseudo-octahedral structure. [N3NF]W(3,5-Me2C6H3) reacts with trimethylsilyl azide to give [N3NF]W(NSiMe3)(3,5-Me2C6H3).
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