title: Synthesis, spectroscopy and electronic structure of the vinylidene and alkynyl complexes [W(C=CHR)(dppe)(η-C₇H₇)](+) and [W(C≡CR)(dppe)(η-C₇H₇](n+) (n = 0 or 1).
abstract: The first examples of vinylidene complexes of the cycloheptatrienyl tungsten system [W(C=CHR)(dppe)(η-C₇H₇)](+) (dppe = Ph₂PCH₂CH₂PPh₂; R = H, 3; Ph, 4; C₆H₄-4-Me, 5) have been synthesised by reaction of [WBr(dppe)(η-C₇H₇)], 1, with terminal alkynes HC≡CR; a one-pot synthesis of 1 from [WBr(CO)₂(η-C₇H₇)] facilitates its use as a precursor. The X-ray structure of 4[PF₆] reveals that the vinylidene ligand substituents lie in the pseudo mirror plane of the W(dppe)(η-C₇H₇) auxiliary (vertical orientation) with the phenyl group located syn to the cycloheptatrienyl ring. Variable temperature ¹H NMR investigations on [W(C=CH₂)(dppe)(η-C₇H₇)][PF₆], 3, estimate the energy barrier to rotation about the W=C(α) bond as 62.5 ± 2 kJ mol⁻¹; approximately 10 kJ mol⁻¹ greater than for the molybdenum analogue. Deprotonation of 4 and 5 with KOBu(t) yields the alkynyls [W(C≡CR)(dppe)(η-C₇H₇)] (R = Ph, 6; C₆H₄-4-Me, 7) which undergo a reversible one-electron oxidation at a glassy carbon electrode in CH₂Cl₂ with E(½) values approximately 0.12 V negative of Mo analogues. The 17-electron radicals [6](+) and [7](+) have been investigated by spectroelectrochemical IR, UV-visible and EPR methods. The electronic structures of representative vinylidene (3) and alkynyl (6) complexes have been investigated at the B3LYP/Def2-SVP level. In both cases, electronic structure is characterised by a frontier orbital with significant metal d(z²)character and this dominates the structural and spectroscopic properties of the system.
authors.affiliation: School of Chemistry, University of Manchester, Manchester, UKM13 9PL.
authors.forename: Hannah N
authors.initials: HN
authors.lastname: Lancashire
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Brown
authors.forename: Laura
authors.initials: L
authors.lastname: Carthy
authors.forename: David
authors.initials: D
authors.lastname: Collison
authors.forename: Emma C
authors.initials: EC
authors.lastname: Fitzgerald
authors.forename: Ruth
authors.initials: R
authors.lastname: Edge
authors.forename: Madeleine
authors.initials: M
authors.lastname: Helliwell
authors.forename: Mark
authors.initials: M
authors.lastname: Holden
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Low
authors.forename: Joseph J W
authors.initials: JJ
authors.lastname: McDouall
authors.forename: Mark W
authors.initials: MW
authors.lastname: Whiteley