Hydride-Bridged NiRh Complexes with Tunable N3S2 Dithiolato Ligands and Their Utilization as Catalysts for Hydrogenation of Aldehydes and CO2 in Aqueous Media

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• 作者：Bunsho Kure ; Ayami Taniguchi ; Takayuki Nakajima ; Tomoaki Tanase
• 刊名：Organometallics
• 出版年：2012
• 出版时间：July 9, 2012
• 年：2012
• 卷：31
• 期：13
• 页码：4791-4800
• 全文大小：432K
• 年卷期：v.31,no.13(July 9, 2012)
• ISSN：1520-6041

文摘

New N₃S₂ dithiolato ligands, 1,4-bis(2-mercaptoethyl)-7-R-1,4,7-triazacyclononane (RTACN-S₂H₂; R = Ts, ⁱPr) were synthesized and reacted with Ni^II ion to give mononuclear complexes [Ni(RTACN-S₂)] (R = Ts (1a), ⁱPr (1b)). Complexes 1a and 1b were further transformed by treatment with Rh^III species into a series of Ni^IIRh^III heterodimetallic compounds, [Ni(RTACN-S₂)RhCp*X]X鈥?(R = Ts, X = Cl, X鈥?= Cl, OTf ([2a]X鈥?; R = Ts, X = X鈥?= NO₃ ([3a]NO₃); R = ⁱPr, X = Cl, X鈥?= Cl, NO₃, PF₆ ([2b]X鈥?). Complexes [3a]NO₃ and [2b]NO₃ were readily reacted with H₂ (0.1 MPa) in water at room temperature to afford hydride-bridged Ni^IIRh^III dinuclear complexes, [(RTACN-S₂)Ni(渭-H)RhCp*]NO₃ (R = Ts ([4a]NO₃), ⁱPr ([4b]NO₃)), which were successfully characterized by X-ray crystallography. Upon the heterolytic activation of H₂, the Ni鈥揜h interatomic distances were dramatically decreased from 3.2130(6)鈥?.262(2) 脜 ([2a]OTf, [2b]NO₃, [3a]NO₃) to 2.6921(6)鈥?.7228(4) 脜 ([4a]NO₃, [4b]NO₃), resulting in semibridging Ni(渭-H)Rh cores. In addition, the stability of the hydride of [4a]⁺ and [4b]⁺ were interestingly tuned by varying the R group of the TACN ligand through trans influence at the Ni^II center (Ni鈥揘R = 2.188(3) 脜 ([4a]⁺), 2.056(2) 脜 ([4b]⁺). In fact, [4a]⁺ was quite stable and capable of reducing benzaldehyde in water, although [4b]⁺ quickly decomposed under similar conditions. Catalytic hydrogenation of aldehydes and CO₂ in water has been established by using [3a]NO₃ and [2a]Cl as precursors of an active species, [4a]⁺, and found to be interestingly contrasted to the inactive precursor [2b]NO₃ with R = ⁱPr. These results indicated that the properties and reactivity of the Ni(渭-H)Rh complexes can be controlled by changing the substituents of the N₃S₂ supporting ligands.