Ground-State and Excited-State Structures of Tungsten鈥揃enzylidyne Complexes
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- 作者：Benjamin M. Lovaasen ; Jenny V. Lockard ; Brian W. Cohen ; Shujiang Yang ; Xiaoyi Zhang ; Cheslan K. Simpson ; Lin X. Chen ; Michael D. Hopkins
- 刊名：Inorganic Chemistry
- 出版年：2012
- 出版时间：May 21, 2012
- 年：2012
- 卷：51
- 期：10
- 页码：5660-5670
- 全文大小：492K
- 年卷期：v.51,no.10(May 21, 2012)
- ISSN：1520-510X
文摘
The molecular structure of the tungsten鈥揵enzylidyne complex trans-W(鈮Ph)(dppe)2Cl (1; dppe = 1,2-bis(diphenylphosphino)ethane) in the singlet (dxy)2 ground state and luminescent triplet (dxy)1(蟺*(WCPh))1 excited state (1*) has been studied using X-ray transient absorption spectroscopy, X-ray crystallography, and density functional theory (DFT) calculations. Molecular-orbital considerations suggest that the W鈥揅 and W鈥揚 bond lengths should increase in the excited state because of the reduction of the formal W鈥揅 bond order and decrease in W鈫扨 蟺-backbonding, respectively, between 1 and 1*. This latter conclusion is supported by comparisons among the W鈥揚 bond lengths obtained from the X-ray crystal structures of 1, (dxy)1-configured 1+, and (dxy)2 [W(CPh)(dppe)2(NCMe)]+ (2+). X-ray transient absorption spectroscopic measurements of the excited-state structure of 1* reveal that the W鈥揅 bond length is the same (within experimental error) as that determined by X-ray crystallography for the ground state 1, while the average W鈥揚/W鈥揅l distance increases by 0.04 脜 in the excited state. The small excited-state elongation of the W鈥揅 bond relative to the M鈥揈 distortions found for M(鈮)Ln (E = O, N) compounds with analogous (dxy)1(蟺*(ME))1 excited states is due to the 蟺 conjugation within the WCPh unit, which lessens the local W鈥揅 蟺-antibonding character of the 蟺*(WCPh) lowest unoccupied molecular orbital (LUMO). These conclusions are supported by DFT calculations on 1 and 1*. The similar core bond distances of 1, 1+, and 1* indicates that the inner-sphere reorganization energy associated with ground- and excited-state electron-transfer reactions is small.