Heteroleptic and Homoleptic Iron(III) Complexes with a Tris(N‐Heterocyclic Carbene) Borate Ligand: Synthesis, Characterization, and Catalytic Application

Abstract

Heteroleptic and homoleptic iron(III) complexes supported by a tris(N-heterocyclic carbene) borate ligand have been prepared and crystallographically characterized. The strong electrondonating character of the tris(carbene) donor was revealed by UV-vis absorption spectroscopy and electrochemical measurements combined with quantum chemical calculations. The catalytic activity of each complex was evaluated in cyclohexane oxidation reaction using meta-chloroperoxybenzoic acid (= mCPBA) as an oxidant, and both complexes show high catalytic activity and selectivity with TON = ~350 and A/(K + L) = 8-10. Mechanistic studies suggested that radical-chain processes are involved in the reaction due to mCPBA acting as a one-electron oxidant, concomitant with the pathway of metal-based reactive species. Moreover, it was found that the homoleptic and heteroleptic complexes differed significantly in the involvement of metal-based active species, with the homoleptic complex exhibiting more metal-based reactions.

Oxygenase mimicking immobilised iron complex catalysts for alkane hydroxylation with H2O2

“…26 There are many reports on reduced alcohol selectivity in alkane oxidation using metal complexes as catalysts and peroxides as oxidants in a homogeneous liquid phase reaction in the presence of O 2 . 27 In our system, therefore, the retention of the high alcohol selectivity even in the presence of O 2 indicates that the major source of the oxygen atom in the products is H 2 O 2 and autoxidation through the cyclohexyl radical diffused from the hydrophobic active site to the liquid phase would be a minor reaction pathway. The efficiency of H 2 O 2 utilization, however, is quite low due to the non-productive decomposition of H 2 O 2 proceeding.…”

Efficient Inhibition of Deep Conversion of Partial Oxidation Products in C-H Bonds’ Functionalization Utilizing O2 via Relay Catalysis of Dual Metalloporphyrins on Surface of Hybrid Silica Possessing Capacity for Product Exclusion

“…As for part IV of the reaction mechanism in C-H bonds' oxidation utilizing O2 through the catalysis of Si@Porp. Co&Cu, it was the classic Russell rearrangement mechanism (blue arrow) [72][73][74], in which corresponding alcohol, ketone, and O2 were produced in a molar ratio of 1:1:1 from two ROO•, and the free-radical chain propagation was terminated in this process, too. As a brief summary of above mechanism study, the four parts in Scheme 4 connected with each other closely and existed simultaneously in C-H bonds' oxidation utilizing O2 through the catalysis of Si@Porp.…”

“…As for part IV of the reaction mechanism in C-H bonds' oxidation utilizing O 2 through the catalysis of Si@Porp. Co&Cu, it was the classic Russell rearrangement mechanism (blue arrow) [72][73][74], in which corresponding alcohol, ketone, and O 2 were produced in a molar ratio of 1:1:1 from two ROO•, and the free-radical chain propagation was terminated in this process, too.…”