Orbital Symmetry Control of Electronic Coupling in a Symmetrical, All-Carbon-Bridged 鈥淢ixed Valence鈥?Compound: Synthesis, Spectroscopy, and Electronic Structure of [{Mo(dppe)(畏-C7H7
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- 作者：Emma C. Fitzgerald ; Neil J. Brown ; Ruth Edge ; Madeleine Helliwell ; Hannah N. Roberts ; Floriana Tuna ; Andrew Beeby ; David Collison ; Paul J. Low ; Mark W. Whiteley
- 刊名：Organometallics
- 出版年：2012
- 出版时间：January 9, 2012
- 年：2012
- 卷：31
- 期：1
- 页码：157-169
- 全文大小：500K
- 年卷期：v.31,no.1(January 9, 2012)
- ISSN：1520-6041
文摘
The cycloheptatrienyl molybdenum alkynyl complex [Mo(C鈮H)(dppe)(畏-C7H7)], 1 (dppe = Ph2PCH2CH2PPh2), undergoes oxidative dimerization on reaction with [FeCp2]PF6 in thf at 鈭?8 掳C to give the bis(vinylidene) [{Mo(dppe)(畏-C7H7)}2(渭-C鈺怌H-CH鈺怌)][PF6]2, [2][PF6]2. Deprotonation of [2][PF6]2 with KOBut yields butadiyndiyl-bridged [{Mo(dppe)(畏-C7H7)}2(渭-C鈮-C鈮)], 3, which undergoes in situ aerial oxidation to give [{Mo(dppe)(畏-C7H7)}2(渭-C4)][PF6], [3]PF6, as the major product. The cyclic voltammogram of [3]PF6 exhibits a series of four redox processes indicative of sequential formation of [{Mo(dppe)(畏-C7H7)}2(渭-C4)]n+ (n = 0, 1, 2, 3, 4) with the comproportionation constant, KC, for [3]PF6 of 1.9 脳 107. Spectroscopic investigations on [3]PF6 by IR, Raman, NIR, and EPR spectroscopy reveal properties characteristic of a d5/d6 mixed valence complex with a localized electronic structure and an estimated intramolecular electron transfer rate in the range 108鈥?010 s鈥?. The experimental NIR spectrum of [3]PF6 is consistent with the predicted spectral characteristics of a three-state model for bridge-mediated, electron transfer in a weakly coupled, symmetrical mixed valence system. The dication [3][PF6]2 was isolated by chemical oxidation and structurally characterized; magnetic susceptibility measurements on [3][PF6]2 in the temperature range 2鈥?00 K reveal strong antiferromagnetic coupling with the exchange coupling constant Jab (defined according to the Hamiltonian 膜spin = 鈥?i>Jab路Ŝa路Ŝb) determined as 鈭?06 (卤3) cm鈥?.