Binding H2, N2, H-, and BH3 to transition-metal sulfur sites: synthesis and properties of [RuL(PR3)(N2Me2S2)] Complexes (L=eta2-H2, H-, BH3; R=Cy, iPr).

The reactions of [Ru(N(2))(PR(3))('N(2)Me(2)S(2)')] ['N(2)Me(2)S(2)'=1,2-ethanediamine-N,N'-dimethyl-N,N'-bis(2-benzenethiolate)(2-)] [1 a (R=iPr), 1 b (R=Cy)] and [micro-N(2)[Ru(N(2))(PiPr(3))('N(2)Me(2)S(2)')](2)] (1 c) with H(2), NaBH(4), and NBu(4)BH(4), intended to reduce the N(2) ligands, led to substitution of N(2) and formation of the new complexes [Ru(H(2))(PR(3))('N(2)Me(2)S(2)')] [2 a (R=iPr), 2 b (R=Cy)], [Ru(BH(3))(PR(3))('N(2)Me(2)S(2)')] [3 a (R=iPr), 3 b (R=Cy)], and [Ru(H)(PR(3))('N(2)Me(2)S(2)')](-) [4 a (R=iPr), 4 b (R=Cy)]. The BH(3) and hydride complexes 3 a, 3 b, 4 a, and 4 b were obtained subsequently by rational synthesis from 1 a or 1 b and BH(3).THF or LiBEt(3)H. The primary step in all reactions probably is the dissociation of N(2) from the N(2) complexes to give coordinatively unsaturated [Ru(PR(3))('N(2)Me(2)S(2)')] fragments that add H(2), BH(4) (-), BH(3), or H(-). All complexes were completely characterized by elemental analysis and common spectroscopic methods. The molecular structures of [Ru(H(2))(PR(3))('N(2)Me(2)S(2)')] [2 a (R=iPr), 2 b (R=Cy)], [Ru(BH(3))(PiPr(3))('N(2)Me(2)S(2)')] (3 a), [Li(THF)(2)][Ru(H)(PiPr(3))('N(2)Me(2)S(2)')] ([Li(THF)(2)]-4 a), and NBu(4)[Ru(H)(PCy(3))('N(2)Me(2)S(2)')] (NBu(4)-4 b) were determined by X-ray crystal structure analysis. Measurements of the NMR relaxation time T(1) corroborated the eta(2) bonding mode of the H(2) ligands in 2 a (T(1)=35 ms) and 2 b (T(1)=21 ms). The H,D coupling constants of the analogous HD complexes HD-2 a ((1)J(H,D)=26.0 Hz) and HD-2 b ((1)J(H,D)=25.9 Hz) enabled calculation of the H--D distances, which agreed with the values found by X-ray crystal structure analysis (2 a: 92 pm (X-ray) versus 98 pm (calculated), 2 b: 99 versus 98 pm). The BH(3) entities in 3 a and 3 b bind to one thiolate donor of the [Ru(PR(3))('N(2)Me(2)S(2)')] fragment and through a B-H-Ru bond to the Ru center. The hydride complex anions 4 a and 4 b are extremely Brønsted basic and are instantaneously protonated to give the eta(2)-H(2) complexes 2 a and 2 b.

Synthesis, reactivity, and structure of strictly homologous 18 and 19 valence electron iron nitrosyl complexes.

The 18 and 19 valence electron (VE) nitrosyl complexes [Fe(NO)('pyS4')]BF4 ([1]BF4) and [Fe(NO)('pyS4')] (2) have been synthesized from [Fe('pyS4')]x ('pyS4'(2-) = 2,6-bis(2-mercaptophenylthiomethyl)pyridine(2-)) and either NOBF4 or NO gas. Complex [1]BF4 was also obtained from [Fe(CO)('pyS4')] and NOBF4. The cation [1]+ is reversibly reduced to give 2. Oxidation of 2 by [Cp2Fe]PF6 afforded [Fe(NO)('pyS4')]PF6 ([1]PF6). The molecular structures of [1]PF6 and 2 were determined by X-ray crystallography. They demonstrate that addition of one electron to [1]+ causes a significant elongation of the Fe-donor atom bonds and a bending of the FeNO angle. Density functional calculations show that the unpaired electron in 2 occupies an orbital, which is antibonding with respect to all Fe-ligand interactions. As expected from qualitative Molecular Orbital (MO) theory, it has a large contribution from a pi* type NO orbital. The nu(NO) frequency decreases from 1893 cm(-1) in [1]BF4 to 1648 cm(-1) in 2 (in KBr). The antibonding character of the unpaired electron explains the ready reaction of 2 with excess NO to give [Fe(NO)2('pyS4')] (3), the facile NO/CO exchange of 2 to afford [Fe(CO)('pyS4')], and the easy oxidation of 2 to [1]+.

[Ru(HNO)('py(bu)S4')], the first HNO complex resulting from hydride addition to a NO complex ('pybuS4'2-=2,6-Bis(2-mercapto-3,5-di-tert-butylphenylthio)dime thylpyridine(2-1)).

Treatment of the nitrosyl complex [Ru(NO)('pybuS4')]Br (1a) with NaBH4 in CH3OH yielded [Ru(HNO)('pybuS4')](2), which could be completely characterized. The X-ray structure determination of 2 confirmed the N coordination of the HNO ligand. Density functional theory calculations enabled us to assign the nu(NO) IR band of 2, which appears in KBr at 1358cm(-1) and in THF at 1378 cm(-1). The unprecedented hydride addition to nitrosyl complexes yielding HNO complexes fills a white spot on the map of chemical reactions, represents the as yet unknown counterpart to the well-established formyl complex formation from CO complexes and hydrides, and distinctly differs from the formation reaction of [Os(HNO)(CO)Cl2(PPh3)2], the only other HNO complex characterized structurally. The HNO complex 2 is oxidized stepwise by [Cp2Fe]PF6 in the presence of NEt3 and directly by Bronsted acids to give [Ru(NO)('pybuS4')]+ in 2e- oxidations. H+/D+ exchange indicates acidity of the HNO proton.

Dinuclear diazene iron and ruthenium complexes as models for studying nitrogenase activity.

The strength of hydrogen bonds has been investigated in various dinuclear diazene FeII, FeIII, and RuII complexes by use of the recently developed shared-electron number approach. Hydrogen bonding in these compounds plays an essential role in view of designing a model system for nitrogenase activity. The general conclusions for iron-sulfur complexes are: hydrogen bonds can stabilize diazene by at least 20% of the total coordination energy; the strength of the hydrogen bonds can be directly controlled through the hydrogen-sulfur bond length; reducing FeIII centers to FeII can double the hydrogen bond energy.

[Ni]

How do [NiFe] hydrogenases activate H(2)? Hydrogenases are key enzymes in the biological hydrogen and energy metabolism; the mechanism of H(2) activation, however, is unclarified. In particular, the oxidation states of the metals involved are discussed controversially. The title complex demonstrates that a distorted diamagnetic Ni(II) center and thiolate donors are sufficient (see picture) to catalyze the key reaction of hydrogenases, the H(2) heterolysis.

Activation and desoxygenation of CO, CO2, and SO2 with sulfur-rich azide and amide.

The azide and amide complexes (NBu4)[Ni(N3)('S3')] (2) and (NBu4)[Ni[N(SiMe3)2]('S3')] (4) were found to react with CO, CO2, and SO2 under very mild conditions at temperatures down to -50 degrees C. Depending on the N oxidation state of the nitrogen ligands, addition or partial to complete desoxygenation of the oxides takes place. The reaction between 2 and CO gives (NBU4)[Ni(NCO)('S3')] (3). The reactions between 4 and CO, CO2, and SO2 afford selectively the cyano, isocyanato, and sulfinylimido complexes (NBu4)[Ni(X)('S3')] with X = CN- (5), NCO- (3), and NSO- (6). The silyl groups act as oxygen acceptors. Mechanisms are suggested which have in common the formation of reactive five-coordinate (NBu4)[Ni(L)(L')('S3')] intermediates. In these reactions, highly activated L and L' react with each other. The complexes were characterized by standard methods, and (NBu4)[Ni(CN)('S3')] (5) was also analyzed by X-ray crystallography.