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Download fileDiiron Carbonyl Complexes Bearing an N,C,S-Pincer Ligand: Reactivity toward Phosphines, Heterolytic Fe–Fe Cleavage, and Electrocatalytic Proton Reduction
journal contribution
posted on 2014-08-25, 00:00 authored by Masakazu Hirotsu, Kiyokazu Santo, Chiaki Tsuboi, Isamu KinoshitaThe
thiolate-bridged diiron carbonyl complex [{Fe(μ-PyBPT-κ3N,C,S)(CO)2}Fe(CO)3] (1) consists of two units, Fe(PyBPT)(CO)2 and Fe(CO)3, where the N,C,S-pincer ligand PyBPT is a
doubly deprotonated form of 3′-(2″-pyridyl)-1,1′-biphenyl-2-thiol.
The two Fe complex units are connected through a thiolate S atom,
π coordination, and an Fe–Fe bond. Diiron complex 1 reacted with 1 equiv of dimethylphenylphosphine to form
the CO substitution product [{Fe(μ-PyBPT-κ3N,C,S)(CO)2}Fe(CO)2(PMe2Ph)] (3) via the phosphine adduct [{Fe(μ-PyBPT-κ3N,C,S)(CO)2}Fe(CO)3(PMe2Ph)] (2), which has a polarized Fe–Fe
bond. A further reaction of 3 with PMe2Ph
produced the N,C,S-pincer iron(II) complex trans-[Fe(PyBPT-κ3N,C,S)(CO)(PMe2Ph)2] (4) and the iron(0) complex trans-[Fe(CO)3(PMe2Ph)2]. 1,2-Bis(diphenylphosphino)benzene
(dppbz) abstracted the Fe(CO)3 unit from 1 to give the dimeric diiron(II,II) complex [{Fe(μ-PyBPT-κ3N,C,S)(CO)2}2] (7) and the iron(0) complex [Fe(CO)3(dppbz)]. The
asymmetric bridging ligand PyBPT and coordination of the phosphines
induce polarization of the Fe–Fe bond, which leads to the formation
of the iron(II) and iron(0) complexes via heterolytic Fe–Fe
cleavage. Electrochemical properties of 3 and 4 were investigated by cyclic voltammetry. Complex 3 showed
two one-electron-reduction processes, the potentials of which are
ca. 0.4 V more negative than those of 1. Electrocatalytic
proton reduction by 3 was investigated, and the efficiency
was comparable to that of 1.
