Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

Abstract

ABSTRACT:The first crystallographically characterized tetrahedral cobalt salen (salen = N,N'-ethylenesalicylimine) complex was synthesized by using a 1,1'-ferrocene derivative, salfen (salfen = 1,1′-di(2,4-di-tert-butyl-6-salicylimine)ferrocene). The complex undergoes two oxidation events at low potentials, which were assigned as iron and ligand centered by comparison to the corresponding zinc complex. The cobalt complex was found to catalyze the hydroalkoxylation of styrenes, similarly to related square planar cobalt salen complexes, likely due to its fluxional behavior in alcoholic solvents. Furthermore, the one electron oxidized species was found to be inactive toward hydroalkoxylation. Thus, the hydroalkoxylation reactivity could be turned on/off in situ by redox chemistry.

Switchable Ring‐Opening Polymerization by a Ferrocene Supported Aluminum Complex

“…Linear sweep voltammetry was also employed to confirm that the cathodic and anodic currents were similar (Figures S24–25). In CH 2 Cl 2 , 1 exhibited another redox event at 1.2 V (Figure S26); a similar event was observed for (salfen)Co and (thiolfan*)Zr(NEt 2 ) 2 , when it was attributed to the phenoxide part of the ligand. Next, the in situ redox reactions with Ac FcBAr F ( Ac Fc=acetylferrocene, BAr F =tetrakis(3,5‐bis(trifluoromethyl)phenyl)borate) and Ac FcTFSI (TFSI=bis(trifluoromethane)sulfonamide) as oxidants and CoCp 2 as a reductant in C 6 D 6 were monitored by 1 H NMR spectroscopy using an internal standard (Figures S4–5).…”

“…The solid state molecular structure shows a pentacoordinate aluminum center with an eclipsed Cp configuration. The metal‐Fe distance was measured as 3.87 Å, which is shorter than in (thiolfan*)Al(O t Bu) at 4.61 Å, (salfen)In(O t Bu) at 3.98 Å, (salfen)Zr(O i Pr) 2 at 4.05 Å, but comparable to that of (salfen)Co at 3.72 Å . The Al‐heteroatom distances are similar to those in other tetradentate ONNO‐type salen (salen= N,N′ ‐bis(salicylidene)ethylenediamine) supported aluminum complexes…”

Investigation of redox switchable titanium and zirconium catalysts for the ring opening polymerization of cyclic esters and epoxides

“…13 Many approaches [14][15][16] have been used to regulate the nature of polymerization reactions, such as allosteric, 17 chemical, [18][19][20] electrochemical, 21 photochemical, [22][23][24][25] and mechanochemical control. 26 Our group is focused on the use of chemical control via redox active systems [27][28][29][30][31][32][33][34][35] that switch between two stable oxidation states with different catalytic efficiencies. [36][37][38][39][40][41][42][43] Since one pre-catalyst is able to have two different active species, the cost of synthesizing two completely different metal complexes is eliminated.…”

Ferrocene-bis(phosphinimine) Nickel(II) and Palladium(II) Alkyl Complexes: Influence of the Fe–M (M = Ni and Pd) Interaction on Redox Activity and Olefin Coordination

“…17 Recently, there have been efforts by our group and others to expand the application of redox-controlled systems beyond ROP. 10 Such examples include ferrocene-based ligands capable of modulating monomer selectivity in palladium systems for olefin polymerization [25][26][27] and Buchwald-Hartwig cross-cou-pling reactions, 28 utilization of cobalt complexes for olefin hydroalkoxylation, 29 and of gold mesoionic carbenes for heterocycles synthesis. 30 However, in all cases of redox-controlled catalysis, the ferrocene unit is distant from the primary metal center and no direct interaction exists between iron in ferrocene and the metal involved in a substrate transformation.…”