Electrocatalytic proton reduction catalysed by the low-valent tetrairon-oxo cluster [Fe₄(CO)₁₀(κ²-dppn)(μ₄-O)]^2- [dppn = 1,1′-bis(diphenylphosphino)naphthalene]

TY - JOUR

T1 - Electrocatalytic proton reduction catalysed by the low-valent tetrairon-oxo cluster [Fe4(CO)10(κ2-dppn)(μ4-O)]2- [dppn = 1,1′-bis(diphenylphosphino)naphthalene]

AU - Ghosh, Shishir

AU - Holt, Katherine B.

AU - Kabir, Shariff E.

AU - Richmond, Michael G.

AU - Hogarth, Graeme

N1 - Publisher Copyright: © The Royal Society of Chemistry 2015.

PY - 2015

Y1 - 2015

N2 - The 62-electron oxo-capped tetrairon butterfly cluster, Fe4(CO)10(κ2-dppn)(μ4-O) (1) {dppn = 1,8-bis(diphenylphosphino)naphthalene}, undergoes reversible one-electron oxidation and reduction events to generate the 61- and 63-electron radicals [Fe4(CO)10(κ2-dppn)(μ4-O)]+ (1+) and [Fe4(CO)10(κ2-dppn)(μ4-O)]- (1-) respectively. Addition of a second electron affords the 64-electron cluster [Fe4(CO)10(κ2-dppn)(μ4-O)]2- (12-) which has more limited stability but is stable within the time frame of the electrochemical experiment. While 1 and 1- are inactive as proton reduction catalysts, dianionic 12- is active for the formation of hydrogen from both CHCl2CO2H and CF3CO2H. This occurs via two separate mechanistic cycles branching at the mono-protonated species [Fe4(CO)10(κ2-dppn)(μ4-O)H]- (1H-) resulting from the rapid protonation of 12-. This intermediate then undergoes competing protonation and reduction events leading to EECC and ECEC catalytic cycles respectively with 1- being pivotal to both. In order to understand the nature of [Fe4(CO)10(κ2-dppn)(μ4-O)]2- (12-) and its protonated products density functional theory (DFT) calculations have been employed. Theoretical calculations reveal that the cluster core remains intact in 12-, but the two consecutive one-electron reductions lead to an expansion of one of the trigonal-pyramids of this trigonal-bipyramidal cluster. The two-electron reduced cluster 12- protonates at dppn-bound iron, accompanied by a wingtip-hinge iron-iron bond scission, and then reacts with a second proton to evolve hydrogen.

AB - The 62-electron oxo-capped tetrairon butterfly cluster, Fe4(CO)10(κ2-dppn)(μ4-O) (1) {dppn = 1,8-bis(diphenylphosphino)naphthalene}, undergoes reversible one-electron oxidation and reduction events to generate the 61- and 63-electron radicals [Fe4(CO)10(κ2-dppn)(μ4-O)]+ (1+) and [Fe4(CO)10(κ2-dppn)(μ4-O)]- (1-) respectively. Addition of a second electron affords the 64-electron cluster [Fe4(CO)10(κ2-dppn)(μ4-O)]2- (12-) which has more limited stability but is stable within the time frame of the electrochemical experiment. While 1 and 1- are inactive as proton reduction catalysts, dianionic 12- is active for the formation of hydrogen from both CHCl2CO2H and CF3CO2H. This occurs via two separate mechanistic cycles branching at the mono-protonated species [Fe4(CO)10(κ2-dppn)(μ4-O)H]- (1H-) resulting from the rapid protonation of 12-. This intermediate then undergoes competing protonation and reduction events leading to EECC and ECEC catalytic cycles respectively with 1- being pivotal to both. In order to understand the nature of [Fe4(CO)10(κ2-dppn)(μ4-O)]2- (12-) and its protonated products density functional theory (DFT) calculations have been employed. Theoretical calculations reveal that the cluster core remains intact in 12-, but the two consecutive one-electron reductions lead to an expansion of one of the trigonal-pyramids of this trigonal-bipyramidal cluster. The two-electron reduced cluster 12- protonates at dppn-bound iron, accompanied by a wingtip-hinge iron-iron bond scission, and then reacts with a second proton to evolve hydrogen.

UR - http://www.scopus.com/inward/record.url?scp=84924308392&partnerID=8YFLogxK

U2 - 10.1039/c4dt03323j

DO - 10.1039/c4dt03323j

M3 - Article

AN - SCOPUS:84924308392

SN - 1477-9226

VL - 44

SP - 5160

EP - 5169

JO - Dalton Transactions

JF - Dalton Transactions

IS - 11

ER -