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A facile surface amide-coupling method was examined to attach dye and catalyst molecules to silatrane-decorated NiO electrodes. Using this method, electrodes with a push–pull dye were assembled and characterized by photoelectrochemistry and transient absorption spectroscopy. The dye-sensitized electrodes exhibited hole injection into NiO and good photoelectrochemical stability in water, highlighting the stability of the silatrane anchoring group and the amide linkage. The amide-coupling protocol was further applied to electrodes that contain a molecular proton reduction catalyst for use in photocathode architectures. Evidence for catalyst reduction was observed during photoelectrochemical measurements and via femtosecond-transient absorption spectroscopy demonstrating the possibility for application in photocathodes.

The chemistry of Fe2(μ-SH)2(CO)4(PPh3)2(2HH) is described with attention to S–S coupling reactions. Produced by the reduction of Fe2(μ-S2)(CO)4(PPh3)2(2), 2HHis an analogue of Fe2(μ-SH)2(CO)6(1HH), which exhibits well-behaved S-centered redox. Both 2HHand the related 2MeHexist as isomers that differ with respect to the stereochemistry of the μ-SR ligands (R = H, Me). Compounds 2HH, 2MeH, and 2protonate to give rare examples of Fe-SH and Fe-S2hydrides. Salts of [H2]+, [H2HH]+, and [H2MeH]+were characterized crystallographically. Complex 2HHreduces O2, H2O2, (PhCO2)2, and Ph2N2, giving 2. Related reactions involving 1HHgave uncharacterizable polymers. The differing behaviors of 2HHand 1HHreflect stabilization of the ferrous intermediates by the PPh3ligands. When independently generated by the reaction of 2HHwith 2,2,6,6-tetramethyl-1-piperidinyloxy, 2*quantitatively converts to 2or, in the presence of C2H4, is trapped as the ethanedithiolate Fe2(μ-S2C2H4)(CO)4(PPh3)2. Evidence is presented that the Hieber–Gruber synthesis of 1involves polysulfido intermediates [Fe2(μ-Sn)2(CO)6]2–(n> 1). Two relevant experiments are as follows: (i) protonation of [Fe4(μ-S)2(μ-S2)CO)12]2–gives 1and 1HH, and (ii) oxidation of 1HHby sulfur gives 1.

Described are the syntheses of several Ni(μ-SR)2Fe complexes, including hydride derivatives, in a search for improved models for the active site of [NiFe]-hydrogenases. The nickel(II) precursors include (i) nickel with tripodal ligands: Ni(PS3)−and Ni(NS3)−(PS33–= tris(phenyl-2-thiolato)phosphine, NS33–= tris(benzyl-2-thiolato)amine), (ii) traditional diphosphine-dithiolates, including chiral diphosphine R,R-DIPAMP, (iii) cationic Ni(phosphine-imine/amine) complexes, and (iv) organonickel precursors Ni(o-tolyl)Cl(tmeda) and Ni(C6F5)2. The following new nickel precursor complexes were characterized: PPh4[Ni(NS3)] and the dimeric imino/amino-phosphine complexes [NiCl2(PCH═NAn)]2and [NiCl2(PCH2NHAn)]2(P = Ph2PC6H4-2-). The iron(II) reagents include [CpFe(CO)2(thf)]BF4, [Cp*Fe(CO)(MeCN)2]BF4, FeI2(CO)4, FeCl2(diphos)(CO)2, and Fe(pdt)(CO)2(diphos) (diphos = chelating diphosphines). Reactions of the nickel and iron complexes gave the following new Ni–Fe compounds: Cp*Fe(CO)Ni(NS3), [Cp(CO)Fe(μ-pdt)Ni(dppbz)]BF4, [(R,R-DIPAMP)Ni(μ-pdt)(H)Fe(CO)3]BArF4, [(PCH═NAn)Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH2NHAn)Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH═NAn)Ni(μ-pdt)(H)Fe(dppbz)(CO)]BF4, [(dppv)(CO)Fe(μ-pdt)]2Ni, {H[(dppv)(CO)Fe(μ-pdt)]2Ni]}BF4, and (C6F5)2Ni(μ-pdt)Fe(CO)2(dppv) (DIPAMP = (CH2P(C6H4-2-OMe)2)2; BArF4–= [B(C6H3-3,5-(CF3)2]4–)) Within the context of Ni-(SR)2-Fe complexes, these new complexes feature new microenvironments for the nickel center: tetrahedral Ni, chirality, imine, and amine coligands, and Ni–C bonds. In the case of {H[(dppv)(CO)Fe(μ-pdt)]2Ni}+, four low-energy isomers are separated by ≤3 kcal/mol, one of which features a biomimetic HNi(SR)4site, as supported by density functional theory calculations.

The synthesis and redox properties are presented for the electron-rich bis(monothiolate)s Fe2(SR)2(CO)2(dppv)2for R = Me ([1]0), Ph ([2]0), CH2Ph ([3]0). Whereas related derivatives adopt C2-symmetric Fe2(CO)2P4cores, [1]0–[3]0have Cssymmetry resulting from the unsymmetrical steric properties of the axial vs equatorial R groups. Complexes [1]0–[3]0undergo 1e–oxidation upon treatment with ferrocenium salts to give the mixed valence cations [Fe2(SR)2(CO)2(dppv)2]+. As established crystallographically, [3]+adopts a rotated structure, characteristic of related mixed valence diiron complexes. Unlike [1]+and [2]+and many other [Fe2(SR)2L6]+derivatives, [3]+undergoes C–S bond homolysis, affording the diferrous sulfido-thiolate [Fe2(SCH2Ph)(S)(CO)2(dppv)2]+([4]+). According to X-ray crystallography, the first coordination spheres of [3]+and [4]+are similar, but the Fe–sulfido bonds are short in [4]+. The conversion of [3]+to [4]+follows first-order kinetics, with k= 2.3 × 10–6s–1(30 °C). When the conversion is conducted in THF, the organic products are toluene and dibenzyl. In the presence of TEMPO, the conversion of [3]+to [4]+is accelerated about 10×, the main organic product being TEMPO-CH2Ph. DFT calculations predict that the homolysis of a C–S bond is exergonic for [Fe2(SCH2Ph)2(CO)2(PR3)4]+but endergonic for the neutral complex as well as less substituted cations. The unsaturated character of [4]+is indicated by its double carbonylation to give [Fe2(SCH2Ph)(S)(CO)4(dppv)2]+([5]+), which adopts a bioctahedral structure.