Activation and discovery of earth-abundant metal catalysts using sodium tert-butoxide

First-row, earth-abundant metals offer an inexpensive and sustainable alternative to precious-metal catalysts. As such, iron and cobalt catalysts have garnered interest as replacements for alkene and alkyne hydrofunctionalization reactions. However, these have required the use of air- and moisture-sensitive catalysts and reagents, limiting both adoption by the non-expert as well as applicability, particularly in industrial settings. Here, we report a simple method for the use of earth-abundant metal catalysts by general activation with sodium tert-butoxide. Using only robust air- and moisture-stable reagents and pre-catalysts, both known and, significantly, novel catalytic activities have been successfully achieved, covering hydrosilylation, hydroboration, hydrovinylation, hydrogenation and [2π+2π] alkene cycloaddition. This activation method allows for the easy use of earth-abundant metals, including iron, cobalt, nickel and manganese, and represents a generic platform for the discovery and application of non-precious metal catalysis

Electrochemical and Computational Study of Tungsten(0) Ferrocene Complexes: Observation of the Mono-Oxidized Tungsten(0) Ferrocenium Species and Intramolecular Electronic Interactions

The series [(CO)5W=C(XR)Fc], 1 (XR = OEt) and 3 (XR = NHBu) as well as [(CO)5W=C(XR)-Fc'-(XR)C=W(CO)5], 2 (XR = OEt) and 4 (XR = NHBu) of mono- and biscarbene tungsten(0) complexes with Fc = FeII(C5H5)(C5H4) for monosubstituted derivatives and Fc¢ = FeII(C5H4)2 for disubstituted derivatives were synthesized and characterized spectroscopically. The oxidized ferrocenium complex [1+]•PF6 was also synthesized and characterized. Electrochemical and computational studies were mutually consistent in confirming the sequence of redox events for the carbene derivatives 1 - 4 as first a carbene double bond reduction to a radical anion, -W-C•, at peak cathodic potentials smaller than -2 V, then a ferrocenyl group oxidation in the range 0.206 < Eo' < 0.540 V and finally an electrochemically irreversible three-electron W(0) oxidation at Epa > 0.540 V vs. FcH/FcH+ in CH2Cl2 / [(nBu4)N][PF6]. This contrasts the sequence of oxidation events in ferrocenylcarbene complexes of chromium where Cr(0) is first oxidised in a one electron transfer process, then the ferrocenyl group, and finally formation of a Cr(II) species. The unpaired electron of the reductively formed radical anion is mainly located on the carbene carbon atom. Electronic interactions between two carbene double bonds (for biscarbenes 2 and 4) as well as between two W centers (for 4) were evident. Differences in redox potentials between the “a” and “b” components of the threeelectron W oxidation of 4 in CH2Cl2 or CH3CN / [(nBu4)N][PF6] are DEo' = Epa W(0) oxd 1b – Epa W(0) oxd 1a = ca. 51 and 337 mV respectively. Tungsten oxidation was restricted to a W0/II couple in CH2Cl2 / [(nBu4)N][B(C6F5)4]. From the computational results, the short-lived W(II) species were observed to be stabilized by agostic CH···W interactions.National Research Foundation, South Africa, (DIB, Grant number 76226; JCS, Grant number 81829), and by the Spanish MICINN and CAM (IF, Grants CTQ2010-20714-CO2-01/BQU, Consolider-Ingenio 2010, CSD2007-00006, S2009/PPQ-1634).http://pubs.acs.org/journal/orgnd7hb201