Metallodithiolates as Ligands to Dinitrosyl Iron Complexes: Toward the Understanding of Structures, Equilibria, and Spin Coupling

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• 作者：Tiffany A. Pinder ; Steven K. Montalvo ; Chung-Hung Hsieh ; Allen M. Lunsford ; Ryan D. Bethel ; Brad S. Pierce ; Marcetta Y. Darensbourg
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：September 2, 2014
• 年：2014
• 卷：53
• 期：17
• 页码：9095-9105
• 全文大小：548K
• ISSN：1520-510X

文摘

Metallodithiolate ligands are used to design heterobimetallic complexes by adduct formation through S-based reactivity. Such adducts of dinitrosyl iron were synthesized with two metalloligands, namely, Ni(bme-daco) and V鈮(bme-daco) (bme-daco = bismercaptoethane diazacyclooctane), and, for comparison, an N-heterocyclic carbene, namely, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (Imes), by cleavage of the (渭-I)₂[Fe(NO)₂]₂ dimer of electronic configuration {Fe(NO)₂}⁹ (Enemark鈥揊eltham notation). With Fe(NO)₂I as Lewis acid acceptor, 1:1 adducts resulted for both the IMes路Fe(NO)₂I, complex 2, and V鈮(bme-daco)路Fe(NO)₂I, complex 4. The NiN₂S₂ demonstrated binding capability at both thiolates, with two Fe(NO)₂I addenda positioned transoid across the NiN₂S₂ square plane, Ni(bme-daco)路2(Fe(NO)₂I), complex 3. Enhanced binding ability was realized for the dianionic vanadyl dithiolate complex, [Et₄N]₂[V鈮(ema)], (ema = N,N鈥?ethylenebis(2-mercaptoacetamide)), which, unlike the neutral (V鈮)N₂S₂, demonstrated reactivity with the labile tungsten carbonyl complex, cis-W(CO)₄(pip)₂, (pip = piperidine), yielding [Et₄N]₂[V鈮(ema)W(CO)₄], complex 1, whose 谓(CO) IR values indicated the dianionic vanadyl metalloligand to be of similar donor ability to the neutral NiN₂S₂ ligands. The solid-state molecular structures of 1鈥? were determined by X-ray diffraction analyses. Electron paramagnetic resonance (EPR) measurements characterize the {Fe(NO)₂}⁹ complexes in solution, illustrating superhyperfine coupling via the ¹²⁷I to the unpaired electron on iron for complex 2. The EPR characterizations of 3 [Ni(bme-daco)路2(Fe(NO)₂I)] and 4 [V鈮(bme-daco)路Fe(NO)₂I] indicate these complexes are EPR silent, likely due to strong coupling between paramagnetic centers. Within samples of complex 4, individual paramagnetic centers with localized superhyperfine coupling from the ⁵¹V and ¹²⁷I are observed in a 3:1 ratio, respectively. However, spin quantitation reveals that these species represent a minor fraction (<10%) of the total complex and thus likely represent disassociated paramagnetic sites. Computational studies corroborated the EPR assignments as well as the experimentally observed stability/instability of the heterobimetallic DNIC complexes.