title: Bridgehead isomer effects in bis(phosphido)-bridged diiron hexacarbonyl proton reduction electrocatalysts.
abstract: The influence of the substitution, orientation and structure of the phosphido bridges in [Fe2(CO)6(μ-PR2)2] electrocatalysts of proton reduction has been studied. The isomers e,a-[Fe2(CO)6{μ-P(Ar)H}2] (1a(Ar): Ar = Ph, 2'-methoxy-1,1'-binaphthyl (bn')), e,e-[Fe2(CO)6{μ-P(Ar)H}2] (1b(Ar): Ar = Ph, bn') were isolated from reactions of iron pentacarbonyl and the corresponding primary phosphine, syntheses that also afforded the phosphinidene-capped tri-iron clusters, [Fe3(CO)9(μ-CO)(μ3-Pbn')] (2) and [Fe3(CO)9(μ3-PAr)2] (3(Ar), Ar = Ph, bn'). A ferrocenyl (Fc)-substituted dimer [Fe2(CO)6{μ:μ'-1,2-(P(CH2Fc)CH2)2C6H4}] (4), in which the two phosphido bridges are linked by an o-xylyl group, was also prepared. The molecular structures of complexes 1a(Ph), 1b(Ph), 1b(bn'), 2 and 4 were established by X-ray crystallography. All complexes have been examined as electrocatalysts for proton reduction using p-toluene sulfonic acid in tetrahydrofuran. Cyclic voltammograms of the dimers with acid exhibit two catalysis waves for proton reduction. The first wave, which appears at the potential of the primary reduction, reaches maximum current (turnover) at moderate acid concentrations and is rapidly overtaken by the second wave, which appears at more negative potential. Both of these reductive waves show an initial first order dependence on acid. The electrochemistry and electrocatalyses of the [Fe2(CO)6(μ-PR2)2] dimers show subtle variations with the nature of the bridging phosphido group(s), including the orientation of bridgehead hydrogen atoms.
authors.affiliation: Chemical Physics, Department of Chemistry, Lund University, Box 120, SE-221 00 Lund, Sweden. Ebbe.Nordlander@chemphys.lu.se.
authors.forename: Ahibur
authors.initials: A
authors.lastname: Rahaman
authors.affiliation: School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia. s.colbran@unsw.edu.au.
authors.forename: Carolina
authors.initials: C
authors.lastname: Gimbert-Suriñach
authors.affiliation: School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
authors.forename: Arne
authors.initials: A
authors.lastname: Ficks
authors.affiliation: School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia. s.colbran@unsw.edu.au.
authors.forename: Graham E
authors.identifier: http://orcid.org/0000-0002-0716-2286
authors.initials: GE
authors.lastname: Ball
authors.affiliation: School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia. s.colbran@unsw.edu.au.
authors.forename: Mohan
authors.initials: M
authors.lastname: Bhadbhade
authors.affiliation: Department of Chemistry, University of Jyväskylä, Box 111, FI-40014, Jyväskylä, Finland.
authors.forename: Matti
authors.identifier: http://orcid.org/0000-0002-6744-7208
authors.initials: M
authors.lastname: Haukka
authors.affiliation: School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
authors.forename: Lee
authors.initials: L
authors.lastname: Higham
authors.affiliation: Chemical Physics, Department of Chemistry, Lund University, Box 120, SE-221 00 Lund, Sweden. Ebbe.Nordlander@chemphys.lu.se.
authors.forename: Ebbe
authors.identifier: http://orcid.org/0000-0001-9575-4929
authors.initials: E
authors.lastname: Nordlander
authors.affiliation: School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia. s.colbran@unsw.edu.au.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Colbran