Search

The first examples of vinylidene complexes of the cycloheptatrienyl tungsten system [W(CCHR)(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 HCCR; a one-pot synthesis of 1from [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 synto the cycloheptatrienyl ring. Variable temperature 1H NMR investigations on [W(CCH2)(dppe)(η-C7H7)][PF6], 3, estimate the energy barrier to rotation about the WCαbond as 62.5 ± 2 kJ mol−1; approximately 10 kJ mol−1greater than for the molybdenum analogue. Deprotonation of 4and 5with KOButyields the alkynyls [W(CCR)(dppe)(η-C7H7)] (R = Ph, 6; C6H4-4-Me, 7) which undergo a reversible one-electron oxidation at a glassy carbon electrode in CH2Cl2with E½values 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 dz2character and this dominates the structural and spectroscopic properties of the system. [ABSTRACT FROM AUTHOR]

In situ31P NMR spectroscopic studies of the reaction of the primary diphosphine 1,2-(PH2)2-C6H4with the mixed-metal base system nBuLi/Sb(NMe2)3, combined with X-ray structural investigations, strongly support a mechanism involving a series of deprotonation steps followed by antimony-mediated reductive C–P bond cleavage. The central intermediate in this reaction is the tetraphosphide dianion [C6H4P2]22−([4]) from which the final products, the 1,2,3-triphospholide anion [C6H4P3]−(3) and [PhPHLi] (8·Li), are evolved. An EPR spectrocopic study suggests that homolytic C–P bond cleavage is likely to be involved in this final step. [ABSTRACT FROM AUTHOR]

The 2c–2e−P–P bonded dimers [(CH)2(NR)2P]2dissociate in solution to give the persistent new 7π radicals [(CH)2(NR)2P], which are isoelectronic with the well known S/N thiazolyl radicals. [ABSTRACT FROM AUTHOR]