Ruthenium nanoparticles inside porous [Zn4O(bdc)3] by hydrogenolysis of adsorbed [Ru(cod)(cot)]: a solid-state reference system for surfactant-stabilized ruthenium colloids

The gas-phase loading of [Zn4O(bdc)3] (MOF-5; bdc = 1,4-benzenedicarboxylate) with the volatile compound [Ru(cod)(cot)] (cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) was followed by solid-state (13)C magic angle spinning (MAS) NMR spectroscopy. Subsequent hydrogenolysis of the adsorbed complex inside the porous structure of MOF-5 at 3 bar and 150 degrees C was performed, yielding ruthenium nanoparticles in a typical size range of 1.5-1.7 nm, embedded in the intact MOF-5 matrix, as confirmed by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (PXRD), and X-ray absorption spectroscopy (XAS). The adsorption of CO molecules on the obtained Ru@MOF-5 nanocomposite was followed by IR spectroscopy. Solid-state (2)H NMR measurements indicated that MOF-5 was a stabilizing support with only weak interactions with the embedded particles, as deduced from the surprisingly high mobility of the surface Ru-D species in comparison to surfactant-stabilized colloidal Ru nanoparticles of similar sizes. Surprisingly, hydrogenolysis of the [Ru(cod)(cot)]3.5@MOF-5 inclusion compound at the milder condition of 25 degrees C does not lead to the quantitative formation of Ru nanoparticles. Instead, formation of a ruthenium-cyclooctadiene complex with the arene moiety of the bdc linkers of the framework takes place, as revealed by (13)C MAS NMR, PXRD, and TEM.     

Ruthenium catalyzed selective synthesis of enol carbamates by fixation of carbon dioxide

Secondary amines react with carbon dioxide and terminal alkynes in the presence of a catalytic amount of 4-1,5-cyclooctadiene) (6-1,3,5-cyclooctatriene)ruthenium [Ru(COD)(COT)] and tertiary phosphine in toluene to give enol carbamates in good yields with high regio- and stereoselectivity. Cyclic enol carbamates, 5-methylene-2-oxazolidinones are obtained from N-substituted propargylamines and carbon dioxide in high yields.     

Hydrogen elimination from a hydroxycyclopentadienyl ruthenium(II) hydride: study of hydrogen activation in a ligand-metal bifunctional hydrogenation catalyst

At high temperatures in toluene, [2,5-Ph(2)-3,4-Tol(2)(eta(5)-C(4)COH)]Ru(CO)(2)H (3) undergoes hydrogen elimination in the presence of PPh(3) to produce the ruthenium phosphine complex [2,5-Ph(2)-3,4-Tol(2)-(eta(4)-C(4)CO)]Ru(PPh(3))(CO)(2) (6). In the absence of alcohols, the lack of RuH/OD exchange, a rate law first order in Ru and zero order in phosphine, and kinetic deuterium isotope effects all point to a mechanism involving irreversible formation of a transient dihydrogen ruthenium complex B, loss of H(2) to give unsaturated ruthenium complex A, and trapping by PPh(3) to give 6. DFT calculations showed that a mechanism involving direct transfer of a hydrogen from the CpOH group to form B had too high a barrier to be considered. DFT calculations also indicated that an alcohol or the CpOH group of 3 could provide a low energy pathway for formation of B. PGSE NMR measurements established that 3 is a hydrogen-bonded dimer in toluene, and the first-order kinetics indicate that two molecules of 3 are also involved in the transition state for hydrogen transfer to form B, which is the rate-limiting step. In the presence of ethanol, hydrogen loss from 3 is accelerated and RuD/OH exchange occurs 250 times faster than in its absence. Calculations indicate that the transition state for dihydrogen complex formation involves an ethanol bridge between the acidic CpOH and hydridic RuH of 3; the alcohol facilitates proton transfer and accelerates the reversible formation of dihydrogen complex B. In the presence of EtOH, the rate-limiting step shifts to the loss of hydrogen from B.     

Ruthenium complexes with a terminal hydrazido ligand. Synthesis, spectroscopy, and X-ray crystal structure

Bis(1,1-diphenylhydrazido(1-))ruthenium(IV) porphyrins, [Ru(IV)(Por)(NHNPh2)2] (Por = TPP, TTP, 4-Cl-TPP, 4-MeO-TPP), were prepared in approximately 60% yields through the reaction of dioxoruthenium(VI) porphyrins, [Ru(VI)(Por)O2], with 1,1-diphenylhydrazine in ethanol. This new type of ruthenium complex has been characterized by 1H NMR, IR, UV-vis, and FABMS with elemental analysis. The crystal structure of [Ru(IV)(TTP)(NHNPh2)2], which reveals an eta1-coordination mode for both hydrazido axial ligands, has been determined. The average Ru-NHNPh2 distance and Ru-N-N angle were found to be 1.911(3) A and 141.1(3) degrees, respectively. The porphyrin ring exhibits a ruffling distortion that is unprecedentedly large for ruthenium complexes with simple porphyrinato ligands (such as TTP). This is probably due to the steric effect of the axial hydrazido(1-) ligands.     

Mechanistic study of hydrogen transfer to imines from a hydroxycyclopentadienyl ruthenium hydride. Experimental support for a mechanism involving coordination of imine to ruthenium prior to hydrogen transfer

Reaction of [2,3,4,5-Ph(4)(eta(5)-C(4)COH)Ru(CO)(2)H] (2) with different imines afforded ruthenium amine complexes at low temperatures. At higher temperatures in the presence of 2, the complexes decomposed to give [Ru(2)(CO)(4)(mu-H)(C(4)Ph(4)COHOCC(4)Ph(4))] (1) and free amine. Electron-rich imines gave ruthenium amine complexes with 2 at a lower temperature than did electron-deficient imines. The negligible deuterium isotope effect (k(RuHOH)/k(RuDOD) = 1.05) observed in the reaction of 2 with N-phenyl[1-(4-methoxyphenyl)ethylidene]amine (12) shows that neither hydride (RuH) nor proton (OH) is transferred to the imine in the rate-determining step. In the dehydrogenation of N-phenyl-1-phenylethylamine (4) to the corresponding imine 8 by [2,3,4,5-Ph(4)(eta(4)-C(4)CO)Ru(CO)(2)] (A), the kinetic isotope effects observed support a stepwise hydrogen transfer where the isotope effect for C-H cleavage (k(CHNH)/k(CDNH) = 3.24) is equal to the combined (C-H, N-H) isotope effect (k(CHNH)/k(CDND) = 3.26). Hydrogenation of N-methyl(1-phenylethylidene)amine (14) by 2 in the presence of the external amine trap N-methyl-1-(4-methoxyphenyl)ethylamine (16) afforded 90-100% of complex [2,3,4,5-Ph(4)(eta(4)-C(4)CO)]Ru(CO)(2)NH(CH(3))(CHPhCH(3)) (15), which is the complex between ruthenium and the amine newly generated from the imine. At -80 degrees C the reaction of hydride 2 with 4-BnNH-C(6)H(9)=NPh (18), with an internal amine trap, only afforded [2,3,4,5-Ph(4)(eta(4)-C(4)CO)](CO)(2)RuNH(Ph)(C(6)H(10)-4-NHBn) (19), where the ruthenium binds to the amine originating from the imine, showing that neither complex A nor the diamine is formed. Above -8 degrees C complex 19 rearranged to the thermodynamically more stable [Ph(4)(eta(4)-C(4)CO)](CO)(2)RuNH(Bn)(C(6)H(10)-4-NHPh) (20). These results are consistent with an inner sphere mechanism in which the substrate coordinates to ruthenium prior to hydrogen transfer and are difficult to explain with the outer sphere pathway previously proposed.     

Stoichiometric and catalytic reactivity of the N-heterocyclic carbene ruthenium hydride complexes [Ru(NHC)(L)(CO)HCl] and [Ru(NHC)(L)(CO)H(eta2-BH4)] (L=NHC, PPh3)

Thermolysis of [Ru(AsPh3)3(CO)H2] with the N-aryl heterocyclic carbenes (NHCs) IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) or the adduct SIPr.(C6F5)H (SIPr=1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene), followed by addition of CH2Cl2, affords the coordinatively unsaturated ruthenium hydride chloride complexes [Ru(NHC)2(CO)HCl] (NHC=IMes , IPr , SIPr ). These react with CO at room temperature to yield the corresponding 18-electron dicarbonyl complexes . Reduction of and [Ru(IMes)(PPh3)(CO)HCl] () with NaBH4 yields the isolable borohydride complexes [Ru(NHC)(L)(CO)H(eta2-BH4)] (, L=NHC, PPh3). Both the bis-IMes complex and the IMes-PPh3 species react with CO at low temperature to give the eta1-borohydride species [Ru(IMes)(L)(CO)2H(eta1-BH4)] (L=IMes , PPh3), which can be spectroscopically characterised. Upon warming to room temperature, further reaction with CO takes place to afford initially [Ru(IMes)(L)(CO)2H2] (L=IMes, L=PPh3) and, ultimately, [Ru(IMes)(L)(CO)3] (L=IMes , L=PPh3). Both and lose BH3 on addition of PMe2Ph to give [Ru(IMes)(L)(L')(CO)H2](L=L'=PMe2Ph; L=PPh3, L'=PMe2Ph). Compounds and have been tested as catalysts for the hydrogenation of aromatic ketones in the presence of (i)PrOH and H2. For the reduction of acetophenone, catalytic activity varies with the NHC present, decreasing in the order IPr>IMes>SIMes.     

Ruthenium(II)-catalyzed isomer-selective cyclization of 1,6-dienes leading to exo-methylenecyclopentanes: unprecedented cycloisomerization mechanism involving ruthenacyclopentane(hydrido) intermediate.

In the presence of a catalytic amount of ruthenium(II) complexes, [RuCl(2)(cod)](n)(), RuCl(2)(cod)(MeCN)(2), [RuCl(2)(nbd)](n)(), [RuCl(2)(CO)(3)](2), and Cp*Ru(cod)Cl, 1,6-dienes were effectively converted into the corresponding exo-methylenecyclopentanes in good to excellent yields with good isomer purity in i-PrOH at 90 degrees C. The alcoholic solvent was essential for the present catalytic cyclization, and the efficiency increased in the following order: t-BuOH < EtOH < or = i-PrOH. In contrast, a Ru(0) complex, (C(6)Me(6))Ru(cod), catalyzed the cycloisomerization only in 1,2-dichloroethane. The unusual isomer-selectivity occurred when a 1,7-octadiene was subjected to cyclization to give a similar exo-methylenecyclopentane isomer as the major product. The identical isomer selectivity was observed for the cyclization of unsymmetrical 1,6-dienes having one terminal- and one internal-alkene termini. On the basis of the results from the studies using the known ruthenium hydrides and deuterium-labeling substrates, the novel mechanism via the Ru(II) <--> Ru(IV) system involving a ruthenacyclopentane(hydrido) intermediate was proposed, which better explains the particular regiochemistry of the present cyclization than other previous mechanisms.     

Ruthenium dihydrogen complexes with wide bite angle diphosphines

The wide bite angle diphosphines homoxantphos (10,11-dihydro-4,5,-bis(diphenylphosphino)dibenzo[b,f]oxepine), sixantphos (4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin), and thixantphos (2,8-dimethyl-4,6-bis(diphenylphosphino)phenoxathiin) were used to prepare cis[MH(2)(diphosphine)(2)] complexes (1a-f) by reaction of [Ru(cod)(cot)] (cod = cyclo-octa-1,5-diene, cot = cyclo-octa-1,3,5-triene) with 2 equiv of the diphosphine under dihydrogen pressure. The electronic properties of the thixantphos ligand were varied. Complexes 1a-f can be protonated with HBF(4) or CF(3)COOH to yield hydrido(dihydrogen) complexes cis[MH(H(2))(diphosphine)(2)](+) (2a-f), which were characterized by VT (variable temperature) NMR and T(1) measurements. These complexes show fast hydrogen atom exchange between the eta(2)-H(2) and the terminal hydride at all temperatures studied. They are thermally unstable toward dihydrogen loss yielding the cationic monohydride complexes cis[MH(diphosphine)(2)](+) (3a-f). Coordination of the eta(2)-H(2) is dominated by sigma --> d donation, and hence, the H-H distance is hardly influenced by the electronic properties of the ligands.     

Synthesis and characterization of osmium(II) trispyrazolylborate complexes

Treatment of H2OsBr6 with excess 1,5-cyclooctadiene (cod) in boiling tert-butyl alcohol affords the polymer [OsBr2(cod)]x (1), which reacts with acetonitrile to form the mononuclear adduct OsBr2(cod)(CH3CN)2 (2). Polymer 1 reacts with potassium trispyrazolylborate (KTp) in ethanol to afford the hydride TpOs(cod)H (3) and the bromide complex TpOs(cod)Br (4). Bromide complex 4 reacts with sodium methoxide in methanol to afford TpOs(cod)OMe (5), which has been structurally characterized. Treatment of hydride 3 with methyl trifluoromethanesulfonate (MeOTf) in diethyl ether results in loss of methane and formation of the triflate complex TpOs(cod)OTf (6), which reacts with MgMe2 to give the methyl complex TpOs(cod)Me (7). The addition of bis(dimethylphosphino)methane (dmpm) to the known compound TpOs(PPh3)2Cl yields a mixture of the substitution products TpOs(eta1-dmpm)(PPh3)Cl (8) and TpOs(eta2-dmpm)Cl (9); the latter reacts with methyllithium to generate the methyl compound TpOs(dmpm)Me (10). NMR and IR data for these new compounds are reported. Crystal data for 5.MeOH at -80 degrees C are as follows: monoclinic, P2(1)/n, a = 10.728(1) A, b = 14.004(2) A, c = 13.906(2) A, beta = 102.42(6) degrees , V = 2040.3(5) A3, Z = 4, R(F) = 0.0247 for I > or = 2sigma(I), and R(wF2) = 0.0539 for all data.     

In situ formed catalytically active ruthenium nanocatalyst in room temperature dehydrogenation/dehydrocoupling of ammonia-borane from Ru(cod)(cot) precatalyst

The development of simply prepared and effective catalytic materials for dehydrocoupling/dehydrogenation of ammonia-borane (AB; NH(3)BH(3)) under mild conditions remains a challenge in the field of hydrogen economy and material science. Reported herein is the discovery of in situ generated ruthenium nanocatalyst as a new catalytic system for this important reaction. They are formed in situ during the dehydrogenation of AB in THF at 25 °C in the absence of any stabilizing agent starting with homogeneous Ru(cod)(cot) precatalyst (cod = 1,5-η(2)-cyclooctadiene; cot = 1,3,5-η(3)-cyclooctatriene). The preliminary characterization of the reaction solutions and the products was done by using ICP-OES, ATR-IR, TEM, XPS, ZC-TEM, GC, EA, and (11)B, (15)N, and (1)H NMR, which reveal that ruthenium nanocatalyst is generated in situ during the dehydrogenation of AB from homogeneous Ru(cod)(cot) precatalyst and B-N polymers formed at the initial stage of the catalytic reaction take part in the stabilization of this ruthenium nanocatalyst. Moreover, following the recently updated approach (Bayram, E.; et al. J. Am. Chem. Soc.2011, 133, 18889) by performing Hg(0), CS(2) poisoning experiments, nanofiltration, time-dependent TEM analyses, and kinetic investigation of active catalyst formation to distinguish single metal or in the present case subnanometer Ru(n) cluster-based catalysis from polymetallic Ru(0)(n) nanoparticle catalysis reveals that in situ formed Ru(n) clusters (not Ru(0)(n) nanoparticles) are kinetically dominant catalytically active species in our catalytic system. The resulting ruthenium catalyst provides 120 total turnovers over 5 h with an initial turnover frequency (TOF) value of 35 h(-1) at room temperature with the generation of more than 1.0 equiv H(2) at the complete conversion of AB to polyaminoborane (PAB; [NH(2)BH(2)](n)) and polyborazylene (PB; [NHBH](n)) units.     

General synthesis of (salen)ruthenium(III) complexes via N...N coupling of (salen)ruthenium(VI) nitrides

Reaction of [Ru (VI)(N)(L (1))(MeOH)] (+) (L (1) = N, N'-bis(salicylidene)- o-cyclohexylenediamine dianion) with excess pyridine in CH 3CN produces [Ru (III)(L (1))(py) 2] (+) and N 2. The proposed mechanism involves initial equilibrium formation of [Ru (VI)(N)(L (1))(py)] (+), which undergoes rapid N...N coupling to produce [(py)(L (1))Ru (III) N N-Ru (III)(L (1))(py)] (2+); this is followed by pyridine substituion to give the final product. This ligand-induced N...N coupling of Ru (VI)N is utilized in the preparation of a series of new ruthenium(III) salen complexes, [Ru (III)(L)(X) 2] (+/-) (L = salen ligand; X = H 2O, 1-MeIm, py, Me 2SO, PhNH 2, ( t )BuNH 2, Cl (-) or CN (-)). The structures of [Ru (III)(L (1))(NH 2Ph) 2](PF 6) ( 6), K[Ru (III)(L (1))(CN) 2] ( 9), [Ru (III)(L (2))(NCCH 3) 2][Au (I)(CN) 2] ( 11) (L (2) = N, N'-bis(salicylidene)- o-phenylenediamine dianion) and [N ( n )Bu 4][Ru (III)(L (3))Cl 2] ( 12) (L (3) = N, N'-bis(salicylidene)ethylenediamine dianion) have been determined by X-ray crystallography.     

Ruthenium complex-catalyzed allylic alkylation of carbonucleophiles with allylic carbonates

Allylic carbonates except for allyl methyl carbonate reacted with carbonucleophiles such as ethyl acetoacetate in the presence of a catalytic amount of Ru(cod)(cot) [cod = cycloocta-1,5-diene, COT = cycloocta-1,3,5-triene] in N-methylpiperidine at 80°C to give the corresponding monoallylated carbonucleophiles in high yields with high regioselectivity. The regioselectivity was quite different from that in the palladium-catalyzed reactions. The allylation of carbonucleophiles using allyl methyl carbonate selectively gave the diallylated carbonucleophiles in high yields.     

Ruthenium(III) triazacyclononane dithiocarbamate,pyridinecarboxylate, or aminocarboxylate complexes as scavengers of nitric oxide

The preparation of a series of [Ru(III)(tacn)(eta(2)-dtc)(eta(1)-dtc)][PF(6)] (tacn = 1,4,7-triazacyclononane; dtc = dimethyldithiocarbamate, diethyldithiocarbamate, pyrrolidinedithiocarbamate, l-prolinedithiocarbamate, l-prolinemethyl ester dithiocarbamate, l-N-methylisoleucinedithiocarbamate) complexes, 5-11, is described. Complex 5 reacts with NO to form the ruthenium nitrosyl complex 12. A series of [Ru(III)(tacn)(pyc)Cl][PF(6)] (pyc = 2-pyridinecarboxylic acid, 2,4- and 2,6-pyridinecarboxylic acid) complexes, 14-16, were prepared along with [Ru(III)(tacn)(mida)][PF(6)] (mida = N-methyliminodiacetic acid), 13, and [Ru(III)(Hnota)Cl], 17, (Hnota = 1-acetic acid-4,7-bismethylcarboxylate-1,4,7-triazacyclononane). Complexes 5-17 were evaluated for use as NO scavengers in an in vitro assay using RAW264 murine macrophage cells. [Ru(III)(tacn)(eta(2)-dtc)(eta(1)-dtc)][PF(6)] complexes 5-11 are very efficient NO scavengers in this assay.     

Ruthenium(II) polypyridyl complexes: potential precursors, metalloligands, and topo II inhibitors

Neutral and cationic mononuclear complexes containing both group 15 and polypyridyl ligands [Ru(kappa3-tptz)(PPh3)Cl2] [1; tptz=2,4,6-tris(2-pyridyl)-1,3,5-triazine], [Ru(kappa3-tptz)(kappa2-dppm)Cl]BF4 [2; dppm=bis(diphenylphosphino)methane], [Ru(kappa3-tptz)(PPh3)(pa)]Cl (3; pa=phenylalanine), [Ru(kappa3-tptz)(PPh3)(dtc)]Cl (4; dtc=diethyldithiocarbamate), [Ru(kappa3-tptz)(PPh3)(SCN)2] (5) and [Ru(kappa3-tptz)(PPh3)(N3)2] (6) have been synthesized. Complex 1 has been used as a metalloligand in the synthesis of homo- and heterodinuclear complexes [Cl2(PPh3)Ru(micro-tptz)Ru(eta6-C6H6)Cl]BF4 (7), [Cl2(PPh3)Ru(mu-tptz)Ru(eta6-C10H14)Cl]PF6 (8), and [Cl2(PPh3)Ru(micro-tptz)Rh(eta5-C5Me5)Cl]BF4 (9). Complexes 7-9 present examples of homo- and heterodinuclear complexes in which a typical organometallic moiety [(eta6-C6H6)RuCl]+, [(eta6-C10H14)RuCl]+, or [(eta5-C5Me5)RhCl]+ is bonded to a ruthenium(II) polypyridine moiety. The complexes have been fully characterized by elemental analyses, fast-atom-bombardment mass spectroscopy, NMR (1H and 31P), and electronic spectral studies. Molecular structures of 1-3, 8, and 9 have been determined by single-crystal X-ray diffraction analyses. Complex 1 functions as a good precursor in the synthesis of other ruthenium(II) complexes and as a metalloligand. All of the complexes under study exhibit inhibitory effects on the Topoisomerase II-DNA activity of filarial parasite Setaria cervi and beta-hematin/hemozoin formation in the presence of Plasmodium yoelii lysate.     

Ruthenium complexes of substituted hydrazine: new solution- and solid-state binding modes

The methylhydrazine complex [Ru(NH(2)NHMe)(PyP)(2)]Cl(BPh(4)) (PyP=1-[2-(diphenylphosphino)ethyl]pyrazole) was synthesised by addition of methylhydrazine to the bimetallic complex [Ru(mu-Cl)(PyP)(2)](2)(BPh(4))(2). The methylhydrazine ligand of the ruthenium complex has two different binding modes: side-on (eta(2)-) when the complex is in the solid state and end-on (eta(1)-) when the complex is in solution. The solid-state structure of [Ru(PyP)(2)(NH(2)NHMe)]Cl(BPh(4)) was determined by X-ray crystallography. 2D NMR spectroscopic experiments with (15)N at natural abundance confirmed that in solution the methylhydrazine is bound to the metal centre by only the -NH(2) group and the ruthenium complex retains an octahedral conformation. Hydrazine complexes [RuCl(PyP)(2)(eta(1)-NH(2)NRR')]OSO(2)CF(3) (in which R=H, R'=Ph, R=R'=Me and NRR'=NC(5)H(10)) were formed in situ by the addition of phenylhydrazine, 1,1-dimethylhydrazine and N-aminopiperidine, respectively, to a solution of the bimetallic complex [Ru(mu-Cl)(PyP)(2)](2)(OSO(2)CF(3))(2) in dichloromethane. These substituted hydrazine complexes of ruthenium were shown to exist in an equilibrium mixture with the bimetallic starting material.     

trans-[Ru(II)(dpp)Cl2]: a convenient reagent for the preparation of heteroleptic Ru(dpp) complexes, where dpp is 2,9-di(pyrid-2'-yl)-1,10-phenanthroline

The reaction of 2,9-di(pyrid-2'-yl)-1,10-phenanthroline (dpp) with [RuCl(3)·3H(2)O] or [Ru(DMSO)(4)Cl(2)] provides the reagent trans-[Ru(II)(dpp)Cl(2)] in yields of 98 and 89%, respectively. This reagent reacts with monodentate ligands L to replace the two axial chlorides, affording reasonable yields of a ruthenium(II) complex with dpp bound tetradentate in the equatorial plane. The photophysical and electrochemical properties of the tetradentate complexes are strongly influenced by the axial ligands with electron-donating character to stabilize the ruthenium(III) state, shifting the metal-to-ligand charge-transfer absorption to lower energy and decreasing the oxidation potential. When the precursor trans-[Ru(II)(dpp)Cl(2)] reacts with a bidentate (2,2'-bipyridine), tridentate (2,2';6,2'-terpyridine), or tetradentate (itself) ligand, a peripheral pyridine on dpp is displaced such that dpp binds as a tridentate. This situation is illustrated by an X-ray analysis of [Ru(dpp)(bpy)Cl](PF(6)).     

Formation of ammonia in the reactions of a tungsten dinitrogen with ruthenium dihydrogen complexes under mild reaction conditions

Treatment of cis-[W(N2)2(PMe2Ph)4] (5) with an equilibrium mixture of trans-[RuCl(eta 2-H2)(dppp)2]X (3) with pKa = 4.4 and [RuCl(dppp)2]X (4) [X = PF6, BF4, or OTf; dppp = 1,3-bis(diphenylphosphino)propane] containing 10 equiv of the Ru atom based on tungsten in benzene-dichloroethane at 55 degrees C for 24 h under 1 atm of H2 gave NH3 in 45-55% total yields based on tungsten, together with the formation of trans-[RuHCl(dppp)2] (6). Free NH3 in 9-16% yields was observed in the reaction mixture, and further NH3 in 36-45% yields was released after base distillation. Detailed studies on the reaction of 5 with numerous Ru(eta 2-H2) complexes showed that the yield of NH3 produced critically depended upon the pKa value of the employed Ru(eta 2-H2) complexes. When 5 was treated with 10 equiv of trans-[RuCl(eta 2-H2)(dppe)2]X (8) with pKa = 6.0 [X = PF6, BF4, or OTf; dppe = 1,2-bis(diphenylphosphino)ethane] under 1 atm of H2, NH3 was formed in higher yields (up to 79% total yield) compared with the reaction with an equilibrium mixture of 3 and 4. If the pKa value of a Ru(eta 2-H2) complex was increased up to about 10, the yield of NH3 was remarkably decreased. In these reactions, heterolytic cleavage of H2 seems to occur at the Ru center via nucleophilic attack of the coordinated N2 on the coordinated H2 where a proton (H+) is used for the protonation of the coordinated N2 and a hydride (H-) remains at the Ru atom. Treatment of 5, trans-[W(N2)2(PMePh2)4] (14), or trans-[M(N2)2(dppe)2] [M = Mo (1), W (2)] with Ru(eta 2-H2) complexes at room temperature led to isolation of intermediate hydrazido(2-) complexes such as trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf (19), trans-[W(OTf)(NNH2)(PMePh2)4]OTf (20), and trans-[WX(NNH2)(dppe)2]+ [X = OTf (15), F (16)]. The molecular structure of 19 was determined by X-ray analysis. Further ruthenium-assisted protonation of hydrazido(2-) intermediates such as 19 with H2 at 55 degrees C was considered to result in the formation of NH3, concurrent with the generation of W(VI) species. All of the electrons required for the reduction of N2 are provided by the zerovalent tungsten.     

Interplay of cubic building blocks in (et6-arene)ruthenium-containing tungsten and molybdenum oxides

A series of molybdenum and tungsten organometallic oxides containing [Ru(arene)]2+ units (arene =p-cymene, C6Me6) was obtained by condensation of [[Ru(arene)Cl2]2] with oxomolybdates and oxotungstates in aqueous or nonaqueous solvents. The crystal structures of [[Ru(eta6-C6Me6]]4W4O16], [[Ru(eta6-p-MeC6H4iPr]]4W2O10], [[[Ru-(eta6-p-MeC6H4iPr)]2(mu-OH)3]2][[Ru(eta6-p-MeC6H4iPr)]2W8O28(OH)2[Ru(eta6-p-MeC6H4iPr)(H2O)]2], and [[Ru(eta6-C6Me6)]2M5O18[Ru(eta6-C6Me6)(H2O)]] (M = Mo, W) have been determined. While the windmill-type clusters [[Ru(eta6-arene)]4(MO3)4(mu3-O)4] (M = Mo, W; arene =p-MeC6H4iPr, C6Me6), the face-sharing double cubane-type cluster [[Ru(eta6-p-MeC6H4iPr)]4(WO2)2(mu3-O)4(mu4-O)2], and the dimeric cluster [[Ru(eta6-p-MeC6H4iPr)(WO3)3(mu3-O)3(mu3-OH)Ru(eta6-pMeC6H4iPr)(H2O)]2(mu-WO2)2]2- are based on cubane-like units, [(Ru(eta6-C6Me6)]2M5O18[Ru(eta6-C6Me6)(H2O)]] (M = Mo, W) are more properly described as lacunary Lindqvist-type polyoxoanions supporting three ruthenium centers. Precubane clusters [[Ru(eta6-arene)](MO3)2(mu-O)3(mu3-O)]6- are possible intermediates in the formation of these clusters. The cluster structures are retained in solution, except for [[Ru(eta6-p-MeC6H4iPr)]4Mo4O16], which isomerizes to the triple-cubane form.     

Synthesis, characterization, and reactivity of ruthenium diene/diamine complexes including catalytic hydrogenation of ketones

Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an excess of N,N,N',N'-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd, 1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II) precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N',N'-tetraethylethylene diamine (teeda) resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N-H functionalities in the coordinated diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod, amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective.