DFT study on chemical N2 fixation by using a cubane-type RuIr3S4 cluster: energy profile for binding and reduction of N2 to ammonia via Ru-N-NHx (x = 1-3) intermediates with unique structures.

The N-N bond activation of the dinitrogen ligand in the cubane-type mixed-metal sulfido cluster, [(Cp*Ir) 3{Ru(tmeda)(N 2)}(mu 3-S) 4] (tmeda = Me 2NCH 2CH 2NMe 2), is investigated by using DFT calculations at the B3LYP level of theory. The elongated N-N bond distance, red-shifted N-N stretching, and negatively charged N 2 ligand indicate that the dinitrogen is reductively activated by complexation. The degree of the N-N bond activation is classified into the "moderately activated" category, [ Studt, F. ; Tuczek, F. J. Comput. Chem. 2006, 27, 1278 ] as in the Mo-triamidoamine complex that can catalyze N 2 reduction [ Yandulov, D. V. ; Schrock, R. R. Science 2003, 301, 76 ]. Availability of the RuIr 3S 4 cluster as a catalyst for N 2 reduction is discussed by optimizing possible intermediates in a catalytic cycle analogous to that proposed by Yandulov and Schrock. A calculated energy profile of the catalytic cycle demonstrates that the RuIr 3S 4 cluster can transform dinitrogen into ammonia in the presence of lutidinium cation and Cp* 2Co as proton and electron sources, respectively. The RuIr 3S 4 clusters with an NNH x ( x = 1-3) ligand, which are intermediates in the catalytic cycle, have a significantly bent Ru-N-N linkage, although precedent NNH x complexes generally adopt a linear M-N-N array. The unique structures of the nitrogenous ligands in these intermediates are interpreted in terms of the bonding interaction between the hydrogen atom bonded to the N 2 ligand and the adjacent iridium atom in the cuboidal RuIr 3S 4 framework.

Syntheses and structures of mono-, di- and tetranuclear rhodium or iridium complexes of thiacalix[4]arene derivatives.

The reactions of [Cp*MCl2]2(Cp*=eta5-C5Me5, M = Rh, Ir) with thiacalix[4]arene (TC4A(OH)4) and tetramercaptothiacalix[4]arene (TC4A(SH)4) gave the mononuclear complexes [(Cp*M){eta3-TC4A(OH)2(O)2}] and the dinuclear complexes [(Cp*M)2{eta3eta3-TC4A(S)4}] respectively, while the analogous reactions with dimercaptothiacalix[4]arene (TC4A(OH)2(SH)2) produced the tetranuclear complexes [(Cp*M)2(Cp*MCl2)2-{eta3eta3eta1eta1-TC4A(O)2(S)2}].

Ti-Mo heterobimetallic thiacalix[4]arene complex containing an unusual alpha-agostic micro2-eta5:eta2-cyclopentadienyl ligand.

A stepwise reaction of p-tert-butylthiacalix[4]arene (TC4A-(OH)(4)) with [CpTiCl3]-NEt(3) and cis-[Mo(N(2))(2)(PMe(2)Ph)(4)] afforded a new Ti-Mo heterobimetallic complex [TC4A-(O)(4)Ti(micro2-C(5)H(5))MoH(PMe(2)Ph)(2)] which shows an unusual alpha-agostic micro2-eta5:eta2-coordination of a cyclopentadienyl ligand.

Mono(sulfido)-bridged mixed-valence nitrosyl complex: protonation and oxidative addition of iodine across the Ir(II)-Ir(0) bond.

Treatment of [Cp*IrH(SH)(PMe3)] (Cp* = eta5-C5Me5) with [IrCl2(NO)(PPh3)2] in the presence of triethylamine yielded the sulfido-bridged Ir(II)Ir0 complex [Cp*Ir(PMe3)(mu-S)Ir(NO)(PPh3)], which further reacted with I2 and triflic acid to give the diiodo complex [Cp*Ir(PMe3)(mu-I)(mu-S)IrI(NO)(PPh3)] and the hydrido complex [Cp*Ir(PMe3)(mu-H)(mu-S)Ir(NO)(PPh3)][OSO2CF3], respectively.

Synthesis of Heterobimetallic Fe-M (M = Ni, Pd, Pt) Complexes Containing the 1,1'-Ferrocenedithiolato Ligand and Their Conversion to Trinuclear Complexes.

The reaction of [NiCl(2)(PMe(2)Ph)(2)] with fc(SH)(2) (fcS(2) = 1,1'-ferrocenedithiolato) afforded the Ni-Fe heterobimetallic complex containing an Fe-->Ni dative bond [Ni(S(2)fc)(PMe(2)Ph)] (1) with concurrent liberation of one of the PMe(2)Ph ligands. In contrast, similar treatment of [MCl(2)(dppe)] (M = Ni, Pd, Pt; dppe = Ph(2)PCH(2)CH(2)PPh(2)) gave a series of group 10 metal-ferrocenedithiolato complexes [M(S(2)fc)(dppe)] (2) which do not contain such a dative bond. Furthermore, oxidation of complexes 2 with 1 equiv of [(eta(5)-C(5)H(5))(2)Fe][PF(6)] resulted in the formation of 1,1'-ferrocenedithiolato-bridged complexes [{M(dppe)}(2)(&mgr;-S(2)fc)][PF(6)](2) (3) along with poly(1,1'-ferrocenylene disulfide). Complexes 2 were also converted into the Fe-Ru-M heterotrimetallic complexes [(p-cymene)RuCl(&mgr;-S(2)fc)M(dppe)][PF(6)] (4; p-cymene = 4-isopropyltoluene) by the reaction of 2 with [(p-cymene)RuCl(2)](2) and NH(4)PF(6) in acetonitrile. The detailed structures of 1, [Ni(S(2)fc)(dppe)] (2a), [Pd(S(2)fc)(dppe)] (2b), [{Ni(dppe)}(2)(&mgr;-S(2)fc)][PF(6)](2) (3a), and [(p-cymene)RuCl(&mgr;-S(2)fc)Ni(dppe)][PF(6)] (4a) have been determined by X-ray crystallography.

Preparation of Cationic Dinuclear Hydrido Complexes of Ruthenium, Rhodium, and Iridium with Bridging Thiolato Ligands and Their Reactions with Nitrosobenzene.

A series of cationic dinuclear hydrido complexes with bridging thiolato ligands [CpMH(&mgr;-SPr(i))(2)MCp][OTf] (4, M = Ru; 6a, M = Rh; 7a, M = Ir; Cp = eta(5)-C(5)Me(5), OTf = OSO(2)CF(3)) were synthesized by treatment of the corresponding chloro complexes [CpRuCl(&mgr;-SPr(i))(2)Ru(OH(2))Cp][OTf] (1) or [CpM(&mgr;-Cl)(&mgr;-SPr(i))(2)MCp][OTf] (2, M = Rh; 3, M = Ir) with HSiEt(3). The dirhodium and diiridium complexes 6 and 7 have been shown to possess a bridging hydrido ligand by crystallographic analysis, while the diruthenium complex 4 is proposed to have a terminal hydrido ligand that undergoes facile migration between the two ruthenium centers in solution. Complexes 4, 6a, and 7a reacted with nitrosobenzene to give the paramagnetic dinuclear nitrosobenzene complexes [CpM(&mgr;-PhNO)(&mgr;-SPr(i))(2)MCp](+) (M = Ru, Rh, Ir) along with azoxybenzene. The molecular structures of the three nitrosobenzene complexes have been determined by X-ray diffraction study to reveal that in each case nitrosobenzene acts as a &mgr;-eta(1):eta(1)-N,O ligand. Judging from the molecular structures and the ESR spectra, the unpaired electron is considered to be located mainly on the nitrosobenzene ligand, at least in the diruthenium and dirhodium complexes. On the other hand, complex 2 reacted with nitrosobenzene to give the incomplete cubane-type trinuclear cluster [(CpRh)(3)(&mgr;-Cl)(2)(&mgr;(3)-S)(&mgr;-SPr(i))](+), whose molecular structure has also been determined crystallographically.

Metal-Metal Bonding in Pentanuclear Bow-Tie Metal Sulfido Clusters. Synthetic and Structural Studies on the Cationic Pentanuclear Clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](n)()(+) (M = Fe, Co, Ni; n = 1, 2).

Reactions of [CpMCl(&mgr;(2)-SH)(2)MCpCl] (1, M = Ir; 2, M = Rh; Cp = eta(5)-C(5)Me(5)) with excess FeCl(2).4H(2)O in THF gave the paramagnetic trinuclear clusters [(CpM)(2)(&mgr;(3)-S)(2)FeCl(2)] (3, M = Ir; 4, M = Rh), which were further converted into the dicationic 78e(-) pentanuclear bow-tie cluster [(CpIr)(2)(&mgr;(3)-S)(2)Fe(&mgr;(3)-S)(2)(IrCp)(2)](2+) (5) by treatment with NaBPh(4). When complex 1 was allowed to react with CoCl(2) and NiCl(2).6H(2)O or Ni(cod)(2) (cod = cyclooctadiene), the related pentanuclear 79e(-) and 80e(-) bow-tie clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](2+) (6, M = Co; 7, M = Ni) were obtained directly, respectively. Cyclic voltammograms of 5[BPh(4)](2), 6[BPh(4)](2), and 7[BPh(4)](2) showed two reversible reduction waves at -0.25 to -0.43 V and -1.04 to -1.34 V. In both redox couples, the redox potential was in the order Fe < Co < Ni. One-electron reduction of clusters 5[BPh(4)](2), 6[BPh(4)](2), and 7[BPh(4)](2) with Co(eta(5)-C(5)H(5))(2) gave the corresponding monocationic pentanuclear 79-81e(-) bow-tie clusters [(CpIr)(2)(&mgr;(3)-S)(2)M(&mgr;(3)-S)(2)(IrCp)(2)](+) (8, M = Fe; 9, M = Co; 10, M = Ni). The molecular structures of 3, 4, 5[BPh(4)](2).CH(2)Cl(2), 6[CoCl(3)(NCMe)](2), 7[NiCl(4)].CH(2)Cl(2), 8[BPh(4)], 9[BPh(4)], and 10[BPh(4)] were unambiguously determined by X-ray diffraction study. The structures of the pentanuclear bow-tie cluster cores remarkably changed stepwise as the core electrons increased from 78 to 81. Two of the M-Ir (M = Fe, Co) bonds in the 79e(-) clusters 6 and 8 show significant elongation in comparison with the Fe-Ir bonds in the 78e(-) cluster 5. Two different types of the bow-tie structures were observed for the 80e(-) clusters 7 and 9. Cluster 7 has a Z-shaped metal core with only two Ni-Ir bonds, while in cluster 9, the six metal-metal bonds in the bow-tie structure are retained with slight elongation of the Co-Ir bonds in comparison with the corresponding dication 6. The 81e(-) cluster 10 has two normal Ni-Ir bonds and one long Ni-Ir bonding interaction with the fourth nonbonding Ni-Ir contact. This structural variation is interpreted in terms of the total electron counts and molecular orbital calculations of the clusters.

Heterometallic cubane-type clusters [M'Mo3S4] (M' = Au, Ag and Cu): synthesis, structures and electrochemical properties.

The heterometallic cubane-type clusters [(Cp*Mo)(3)(mu(3)-S)(4)Au(PR(3))][PF(6)][X] (Cp* = eta(5)-C(5)Me(5); 2a: R = Ph, X = BF(4); 2b: R = Cy, X = PF(6); 2c: R = (t)Bu, X = PF(6)), [(Cp*Mo)(3)(mu(3)-S)(4)Ag(PPh(3))][PF(6)][OTf] (3, OTf = OSO(2)CF(3)) and [(Cp*Mo)(3)(mu(3)-S)(4)CuI][PF(6)] (4) have been prepared by the reaction of [(Cp*Mo)(3)(mu(2)-S)(3)(mu(3)-S)][PF(6)] (1) with complexes [(R(3)P)Au][X], [(Ph(3)P)Ag][OTf] and CuI, respectively. These clusters have been spectroscopically and crystallographically characterized. In addition, the electrochemical properties of clusters 2a, 2b, 2c and 4 are also discussed.

Synthesis and reactivity of a bis(disulfide)-bridged RuMo3S4 double-cubane cluster: a new family of nona- or decanuclear mixed-metal sulfide clusters with two RuMo3S4 units.

A bis(disulfide)-bridged RuMo3S4 double-cubane cluster [{(Cp*Mo)3(mu3-S)4Ru}(mu2-eta2:eta1-S2)]2[PF6]2 (2, Cp* = eta5-C5Me5) is readily available from cluster [(Cp*Mo)3(mu3-S)4RuH2(PPh3)][PF6] (1) and S8. The reactions of cluster 2 with [M(PPh3)4] (M = Pd, Pt) give rise to the formation of a new family of nona- or decanuclear mixed-metal sulfide clusters, [{(Cp*Mo)3(mu3-S)4Ru}2(mu3-S)2{Pd(S)(PPh3)}][PF6]2 (3), [{(Cp*Mo)3(mu3-S)4Ru}2(mu3-S)2{(Pd(PPh3))2(mu2-S)}][PF6]2 (4), and [{(Cp*Mo)3(mu3-S)4Ru}2(mu3-S)2{Pt(PPh3)2}][PF6]2 (5), with two RuMo3S4 cubane units, the structures of which have been determined by X-ray diffraction studies.

Preparation of chalcogenolato-bridged dinuclear Tp*Rh-Cp*Ru complexes (Tp*= hydrotris(3,5-dimethylpyrazol-1-yl)borate, Cp*=eta(5)-pentamethylcyclopentadienyl) and binding of dioxygen to their Ru sites.

Reactions of [Tp*Rh(coe)(MeCN)](1; Tp*= hydrotris(3,5-dimethylpyrazol-1-yl); coe = cyclooctene) with one equiv of diphenyl dichalcogenides PhEEPh (E = Se, Te) afforded the mononuclear Rh(III) complexes [Tp*Rh(EPh)(2)(MeCN)](2b: E = Se; 2c: E = Te), as reported previously for the formation of [Tp*Rh(SPh)(2)(MeCN)](2a) from the reaction of 1 and PhSSPh. Complexes 2a-2c were treated with the Ru(II) complex [(Cp*Ru)(4)(mu(3)-Cl)(4)](Cp*=eta(5)-C(5)Me(5)) in THF at room temperature, yielding the chalcogenolato-bridged dinuclear complexes [Tp*RhCl(mu-EPh)(2)RuCp*(MeCN)](3). Complex 3a (E = S) in solution was converted slowly into a mixture of 3a and the sterically less encumbered dinuclear complex [Tp*RhCl(SPh)(mu-eta(1)-S-eta(6)-Ph)RuCp*](4a) at room temperature. In 4a, one SPh group binds only to the Rh center as a terminal ligand, while the other SPh group bridges the Rh and Ru atoms by coordinating to the former at the S atom and to the latter with the Ph group in a pi fashion. The Se analogue 3b also underwent a similar transformation under more forcing conditions, e.g. in benzene at reflux, whereas formation of the mu-eta(1)-Te-eta(6)-Ph complex was not observed for the Te analogue 3c even under these forcing conditions. When complexes 3 was dissolved in THF exposed to air, the MeCN ligand bound to Ru was substituted by dioxygen to give the peroxo complexes [Tp*RhCl(mu-EPh)(2)RuCp*(eta(2)-O(2))](5a: E = S; 5b: E = Se; 5c: E = Te). X-Ray analyses have been undertaken to determine the detailed structures for 2c, 3a, 3b, 4a, 5a, 5b, and 5c.

Cleavage of hydrazine N-N bonds by RuMo3S4 cubane-type clusters.

The mixed-metal cubane-type clusters [(Cp*Mo)3(mu3-S)4RuH2(PR3)][PF(6)] [Cp* = eta5-C5Me5; R = Ph (2), Cy (5)] were effective for the N-N bond cleavage of hydrazine and phenylhydrazine via a disproportionation reaction. The ammonia cluster [(C*Mo)3(mu3-S)4Ru(NH3)(PPh3)][PF6] (3) and/or the unprecedented double-cubane-type cluster with bridging nitrogenous ligands [{(Cp*Mo)3(mu3-S)4Ru}2(mu2-NH2)(mu2-NHNH2)][PF6]2 (4) were isolated from the reaction mixtures, and their structures were determined by X-ray diffraction studies.

Ruthenium-catalyzed propargylic substitution reactions of propargylic alcohols with oxygen-, nitrogen-, and phosphorus-centered nucleophiles.

The scope and limitations of the ruthenium-catalyzed propargylic substitution reaction of propargylic alcohols with heteroatom-centered nucleophiles are presented. Oxygen-, nitrogen-, and phosphorus-centered nucleophiles such as alcohols, amines, amides, and phosphine oxide are available for this catalytic reaction. Only the thiolate-bridged diruthenium complexes can work as catalysts for this reaction. Results of some stoichiometric and catalytic reactions indicate that the catalytic propargylic substitution reaction proceeds via an allenylidene complex formed in situ, whereby the attack of nucleophiles to the allenylidene C(gamma) atom is a key step. Investigation of the relative rate constants for the reaction of propargylic alcohols with several para-substituted anilines reveals that the attack of anilines on the allenylidene C(gamma) atom is not involved in the rate-determining step and rather the acidity of conjugated anilines of an alkynyl complex, which is formed after the attack of aniline on the C(gamma) atom, is considered to be the most important factor to determine the rate of this catalytic reaction. The key point to promote this catalytic reaction by using the thiolate-bridged diruthenium complexes is considered to be the ease of the ligand exchange step between a vinylidene ligand on the diruthenium complexes and another propargylic alcohol in the catalytic cycle. The reason why only the thiolate-bridged diruthenium complexes promote the ligand exchange step more easily with respect to other monoruthenium complexes in this catalytic reaction should be that one Ru moiety, which is not involved in the allenylidene formation, works as an electron pool or a mobile ligand to another Ru site. The catalytic procedure presented here provides a versatile, direct, and one-step method for propargylic substitution of propargylic alcohols in contrast to the so far well-known stoichiometric and stepwise Nicholas reaction.

Preparation of mononuclear and dinuclear Rh hydrotris(pyrazolyl)borato complexes containing arenethiolato ligands and conversion of the mononuclear complexes into dinuclear Rh-Rh and Rh-Ir complexes with bridging arenethiolato ligands.

Reactions of [Tp*Rh(coe)(MeCN)](; Tp*= HB(3,5-dimethylpyrazol-1-yl)(3); coe = cyclooctene) with one equiv. of the organic disulfides, PhSSPh, TolSSTol (Tol = 4-MeC(6)H(4)), PySSPy (Py = 2-pyridyl), and tetraethylthiuram disulfide in THF at room temperature afforded the mononuclear Rh(III) complexes [Tp*Rh(SPh)(2)(MeCN)](3a), [Tp*Rh(STol)(2)(MeCN)](3b), [Tp*Rh(eta(2)-SPy)(eta(1)-SPy)](6), and [Tp*Rh(eta(2)-S(2)CNEt(2))(eta(1)-S(2)CNEt(2))](7), respectively, via the oxidative addition of the organic disulfides to the Rh(I) center in 1. For the Tp analogue [TpRh(coe)(MeCN)](2, Tp = HB(pyrazol-1-yl)(3)), the reaction with TolSSTol proceeded similarly to give the bis(thiolato) complex [TpRh(STol)(2)(MeCN)](4) as a major product but the dinuclear complex [[TpRh(STol)](2)(micro-STol)(2)](5) was also obtained in low yield. Complex 3 was treated further with the Rh(III) or Ir(III) complexes [(Cp*MCl)(2)(micro-Cl)(2)](Cp*=eta(5)-C(5)Me(5)) in THF at room temperature, yielding the thiolato-bridged dinuclear complexes [Tp*RhCl(micro-SPh)(2)MCp*Cl](8a: M = Rh, 8b: M = Ir). Dirhodium complex [TpRhCl(micro-STol)(2)RhCp*Cl](9) was obtained similarly from 4 and [(Cp*RhCl)(2)(micro-Cl)(2)]. Anion metathesis of 8a proceeds only at the Rh atom with the Cp* ligand to yield [Tp*RhCl(micro-SPh)(2)RhCp*(MeCN)][PF(6)](10), when treated with excess KPF(6) in CH(2)Cl(2)-MeCN. The X-ray analyses have been undertaken to determine the detailed structures of 3b, 4, 5, 6, 7, 8a, 9, and 10.

Ruthenium-catalyzed cycloaddition of propargylic alcohols with phenol derivatives via allenylidene intermediates: catalytic use of the allenylidene ligand as the C(3) unit.

Novel ruthenium-catalyzed cycloaddition of propargylic alcohols with 2-naphthols and phenols bearing electron-donating groups via allenylidene intermediates has been developed to give the corresponding 1H-naphtho[2,1-b]pyrans and 4H-1-benzopyrans, respectively, in moderate to excellent yields with complete regioselectivity.

Ruthenium-catalyzed propargylic substitution reaction of propargylic alcohols with thiols: a general synthetic route to propargylic sulfides.

A novel cationic methanethiolate-bridged diruthenium complex [Cp*RuCl(mu2-SMe)2RuCp*(OH2)]OTf (1e) has been disclosed to promote the catalytic propargylic substitution reaction of propargylic alcohols bearing not only terminal alkyne group but also internal alkyne group with thiols. It is noteworthy that neutral thiolate-bridged diruthenium complexes (1a-1c), which were known to promote the propargylic substitution reactions of propargylic alcohols bearing a terminal alkyne group with various heteroatom- and carbon-centered nucleophiles, did not work at all. The catalytic reaction described here provides a general and environmentally friendly preparative method for propargylic sulfides, which are quite useful intermediates in organic synthesis, directly from the corresponding propargylic alcohols and thiols.

Ruthenium-catalyzed carbon-carbon bond formation between propargylic alcohols and alkenes via the allenylidene-ene reaction.

A novel ruthenium-catalyzed carbon-carbon bond formation between propargylic alcohols and alkenes via the allenylidene-ene reaction has been found to afford the corresponding 2,4-disubstituted-1-hexen-5-ynes in moderate yields. The finding described here discloses a new reactivity of allenylidene complexes. As a synthetic application, intramolecular cyclization of propargylic alcohols bearing an alkene moiety has been developed to give the corresponding syn-substituted chromanes in high yields with an excellent diastereoselectivity.