Bio-inspired, side-on attachment of a ruthenium photosensitizer to an iron hydrogenase active site model

Abstract

The first ruthenium-diiron complex [(mu-pdt)Fe2(CO)5{PPh2(C6H4CCbpy)}Ru(bpy)2]2+ 1 (pdt = propyldithiolate, bpy = 2,2'-bipyridine) is described in which the photoactive ruthenium trisbipyridyl unit is linked to a model of the iron hydrogenase active site by a ligand directly attached to one of the iron centers. Electrochemical and photophysical studies show that the light-induced MLCT excited state of the title complex is localized towards the potential diiron acceptor unit. However, the relatively mild potential required for the reduction of the acetylenic bipyridine together with the easily oxidized diiron portion leads to a reductive quenching of the excited state, instead. This process results in a transiently oxidized diiron unit which may explain the surprisingly high light sensitivity of complex 1.

Electrochemical Synthesis of Mono‐ and Disubstituted Diiron Dithiolate Complexes as Models for the Active Site of Iron‐Only Hydrogenases

“…Such an apical orientation for the incoming ligand was previously reported in [Fe 2 (S 2 C 3 H 6 )(CO) 5 CCSi(CH 3 ) 3 }, [47] whereas the basal position was occupied when L = P(NC 4 H 8 ) 3 , [48] PTA (1,3,5-triaza-7-phosphaadamantane), [31] η 1 -Ph 2 P-CH 2 -PPh 2 , [23] and H 2 NPr. [49] Each iron atom in 2 displays the usual pentacoordinate squarepyramidal structure, where both metal centers are displaced from the basal plane toward the apical position by 0.37 Å for Fe(1) and by 0.41 Å for Fe(2).…”

“…Ligand coordination in an apical/apical fashion was previously reported in complexes of type [Fe 2 (S 2 C 3 H 6 )(CO) 4 L 2 ], where L = tBuNC, [39] PMe 2 Ph, [40] and PPh 2 (C 6 H 4 Br). [47] In analo- gous disubstituted complexes, basal/basal trans isomers have also been observed in the solid state when L = PMe 3 [50] and L = PTA, [31] while L = CN - [14] and L = NHC [32] led to basal/apical isomers. These results show that the ligand size is not the determining factor that affects the structure of [Fe 2 (S 2 C 3 H 6 )(CO) 4 L 2 ] complexes in the solid state.…”

A Ferrocene–Peptide Conjugate as a Hydrogenase Model System

“…[17][18][19][20][21] To this end, diiron model compounds or even ruthenium complexes (for which no natural precedent exists) with a variety of unnatural ligands such as phosphanes and carbenes have been employed. [18,19,22,23] Other examples have reported attachment of the active-site cluster models to electrochemical sensors such as porphyrins, [24] a ruthenium-based photosentizer [25][26][27] or even models of the natural [Fe 4 S 4 ] cubane unit. [28] In the bimetallic [NiFe] H 2 ase, the Ni atom is coordinated to four sulfur atoms from cysteine amino acids, two of which bridge the Fe atom.…”

Synthesis, DNA-binding and photocleavage studies of ruthenium(II) complexes [Ru(btz)3]2+ and [Ru(btz)(dppz)2]2+

“…The photoactive drug photofrin is in use for the photodynamic treatment of lung and oesophageal cancers [2][3][4][5] . Ruthenium(Ⅱ) complexes with polypyridine ligands, due to their rich photophysical repertoire and light-activated reactions with DNA, have also begun to be investigated as PDT agents in vitro or in vivo [6][7][8] .…”