Mitsushiro Nomura

Formation and reaction of three-membered cobaltathiaziridine ring in (η5-cyclopentadienyl)(substituted imido-κN-thio-κS-ethene-2-thiolato-κS)cobalt(III). Ring opening and closure and transfer of imido group

Abstract Three-membered cobaltathiaziridine rings are formed in the reactions of [CpCo{S 2 C 2 (COOMe) 2 }] either with some azides (RN 3 : p -toluenesulfonyl azide (TsN 3 ), methanesulfonyl azide (MsN 3 ), and ethyl azidoformate (EtOOCN 3 )) or with N -(phenyliodonio)- p -toluenesulfonamidate (PhI=NTs) to afford imido-bridged complexes, [CpCo{S 2 C 2 (COOMe) 2 }(NR)]. The ring undergoes unique ring opening and reforming reactions. Hydrogen chloride brings about the cleavage of the CoN bond to give S -iminodithiolatocobalt(III) complexes [Cp(Cl)Co{S(NR)C(COOMe)C(COOMe)S)}], which very easily regenerates the cobaltathiaziridine ring on treatment with bases, such as pyridine and even with the very weak base, water. The reaction with triphenylphosphine at room temperature results in the ring opening to give an ylide. The heating of a benzene solution of the ylide at 80°C (under reflux) gives a product in which a sulfonylimido moiety migrates to a carbon atom of the cyclopentadienyl ring. The reduction halfwave potential values of the imido-bridged complexes depend on the substituent of bridging moiety. The CV of sulfonylimido-bridged complex shows one-electron two-step reduction processes. We found that the reductant of the original complex is regenerated not by the first reduction, but by the second reduction according to CV and OTTLE measurements.

Experimental and theoretical evaluation of magnetic coupling in organometallic radicals: the eloquent case of face-to-face Cp⋯Cp interactions

The solid state magnetic properties of an extensive series of neutral radical (S = ½) complexes associating cyclopentadienyl (Cp) and dithiolene ligands and formulated as [CpNi(dithiolene)]˙, are successfully rationalized through a combination of structural analysis of the crystal structures and broken symmetry DFT calculations. The highly delocalized spin density of these complexes allows for strong antiferromagnetic interactions between radical species, which involve not only short intermolecular S⋯S contacts but also S⋯Cp and Cp⋯Cp contacts, demonstrating that the cyclopentadienyl moiety can effectively act as a non-innocent ligand in metal complexes where it bears a sizeable fraction of the spin density, for example, up to 20% in these [CpNi(dithiolene)]˙ neutral radical complexes.

(CpNi(diselenolene)) Neutral Radical Complexes: Electron Paramagnetic Resonance and Density Functional Theory Investigations

77Se-enriched CpNi(bds) (bds = 1,2-benzenediselenolate), has been synthesized and its g tensor and 77Se hyperfine tensors have been obtained from its frozen solution electron paramagnetic resonance (EPR) spectrum. These parameters are consistent with those calculated by density functional theory (DFT); it is shown that 10% of the spin is localized on each selenium and that the direction associated to the maximum 77Se couplings is aligned along the gmin direction, perpendicular to the Ni(bds) plane. EPR measurements and DFT calculations are also carried out on the 77Se enriched complex CpNi(dsit) as well on the two dithiolene analogues CpNi(bdt) and CpNi(dmit). The optimized structures of the isolated CpNi(bds) and CpNi(bdt) complexes have been used to generate the idealized dimers (bds)NiCp...CpNi(bds) and (bdt)NiCp...CpNi(bdt) characterized by Cp...Cp overlap. The exchange parameters J calculated at the DFT level for these systems are in reasonable accord with the experimental values. The influence of the geometry of the dimer on its magnetic properties is assessed by calculating the variation of J as a function of the relative orientation of the two Ni(diselenolene) or Ni(dithiolene) planes.

Imido-transfer reactions to carbonyl moiety induced by the reactions of imido-bridged cobaltadithiolene complexes with trivalent phosphorus halides

Abstract The reactions of the imido-bridged cobaltadithiolene complexes [CpCo{S2C2(COOMe)2}(NR)] (R=Ts, Ms) with PCl3 led to the imido-transfer reactions to the carbonyl moiety, and these reactions gave the novel imine complexes [CpCo{S2C2(COOMe)(CNROMe)}]. In the case of PI3, another imido-transfer reaction to carbonyl moiety occurred and the novel amide complexes [CpCo{S2C2(COOMe)(CONHR)}] were formed. PBr3 showed an intermediate reactivity value in between that of PCl3 and that of PI3. Both novel imido-transfer reactions were caused by intermolecular reactions, these reaction processes were determined by crossover experiments.

Reactions of cobaltadithiolene complexes with aryl azides: Formations of metal chelate rings containing nitrogen atoms by substitution reactions via nitrene

Abstract In the reactions of cobaltadithiolene complexes [CpCo(S 2 C 2 Z 2 )] (Z=CN, COOMe, Ph, Me) with aryl azides, two types of substitution reactions occurred. One is the replacements of the sulfur of cobaltadithiolene by arylimido groups and the other is the replacements of the SCZCZ moiety of cobaltadithiolene. The product of latter reaction was also formed by the reactions of the metal cluster complex [Cp 4 Co 4 S 6 ] with aryl azides. The azides with electron-donating substituents gave these products in higher yields than those with electron-withdrawing substituents. In these reactions, arylnitrenes as intermediates were predictable. The reactions of [CpCo(dmit)] (dmit=C 3 S 5 ) with phenyl azide and tosyl azide led to the replacements of the terminal sulfur (CS) of the dmit ligand by imido groups to give novel imine complexes [CpCo(S 2 C 2 S 2 CNR)] (R=Ph, Ts).

Synthesis and Electrochemistry of Organometallic Cobaltadithiaazulenes

Reaction of tropolone or hinokitiol with phosphorus pentasulfide (P(2)S(5)) directly gives the sulfurized precursor [PS(2)(SST)](2) or [PS(2)(SSH)](2) (SST = dithiotropolonato or SSH = dithiohinokitiolato). The resulting [PS(2)(SST)](2) or [PS(2)(SSH)](2) is further reacted with [CpCoI(2)(CO)] (Cp = η(5)-cyclopentadienyl) to form the organometallic [CpCo(I)(SST)] (1) or [CpCo(I)(SSH)] (2), respectively. 1 and 2 have a cobaltadithiaazulene ring containing one cobalt and two sulfur atoms in the five-membered ring of azulene. Although X-ray structure analysis of 1 reveals the iodide-coordinated structure, 1 becomes the iodide-free complex [CpCo(SST)](+) (4(+)) in solution. Electrochemical studies of 4(+) by CV and spectroelectrochemical measurements (ESR, UV-vis-NIR) in solution are carried out. 4(+) is stepwise reduced by 2e(-) to form the stable neutral radical (4(•)) and unstable anion (4(-)). It is proposed that the anion 4(-) undergoes dimerization to afford the dimer (6(2-)) by anion radical coupling at the 5 or 7 position in the seven-membered ring of the cobaltadithiaazulene, since the similar anion radical coupling of a reduced azulene has been reported. Electrochemical reoxidation of 6(2-) slowly undergoes monomerization, giving the original monomer 4(•). DFT calculation of 4(+) explains that there is a delocalized lowest unoccupied molecular orbital (LUMO) in the whole molecule, and that of radical 4(•) has a delocalized singly occupied molecular orbital (SOMO). In these CpCo-SST (or SSH) complexes, there could be metal/ligand electron transfer since the SST (or SSH) ligand is potentially redox active. The spin density distribution of 4(-) obtained by the DFT method supports the mechanism of the anion radical coupling at the 5 or 7 position in the seven-membered ring.

An organometallic dithiolene complex exhibiting electrochemically initiated hydrogen generation

We clarify the electrochemical behavior of an organometallic cobalt dithiolene complex (1-NH) with a secondary sulfonyl amide (–NHSO(2)–) substituted Cp ligand involving proton dynamics. The reductions of 1-NH and its deprotonated derivative (1-N(−)) are centered on the CpCoS(2) moiety. The 2e(−) reduction of 1-NH quantitatively gives 1-N(−) with hydrogen generation.