Catalysis and Mechanism of H2 Release from Amine-Boranes by Diiron Complexes
详细信息 查看全文
- 作者：Allen M. Lunsford ; Jan H. Blank ; Salvador Moncho ; Steven C. Haas ; Sohail Muhammad ; Edward N. Brothers ; Marcetta Y. Darensbourg ; Ashfaq A. Bengali
- 刊名：Inorganic Chemistry
- 出版年：2016
- 出版时间：January 19, 2016
- 年：2016
- 卷：55
- 期：2
- 页码：964-973
- 全文大小：648K
- ISSN：1520-510X
文摘
Studies focused on the dehydrogenation of amine-borane by diiron complexes that serve as well-characterized rudimentary models of the diiron subsite in [FeFe]-hydrogenase are reported. Complexes of formulation (μ-SCH2XCH2S)[Fe(CO)3]2, with X = CH2, CMe2, CEt2, NMe, NtBu, and NPh, 1-CO through 6-CO, respectively, were determined to be photocatalysts for release of H2 gas from a solution of H3B ← NHMe2 (B:As), dissolved in THF. The thermal displacement of the tertiary amine-borane, H3B ← NEt3 (B:At) from photochemically generated (μ-SCH2XCH2S)[Fe(CO)3][Fe(CO)2(μ-H)(BH2–NEt3)], 1-B:At through 6-B:At, by P(OEt)3 was monitored by time-resolved FTIR spectroscopy. Rates and activation barriers for this substitution reaction were consistent with a dissociative mechanism for the alkylated bridgehead species 2-CO through 6-CO, and associative or interchange for 1-CO. DFT calculations supported an intermediate [I] for the dissociative process featuring a coordinatively unsaturated diiron complex stabilized by an agostic interaction between the metal center and the C–H bond of an alkyl group on the central bridgehead atom of the SRS linker. The rate of H2 production from the initially formed 1-B:As through 6-B:As complexes was inversely correlated with the lifetime of the analogous 1-B:At through 6-B:At adducts. Possible mechanisms are presented which feature involvement of the pendent nitrogen base as well as a separate mechanism for the all carbon bridgeheads.