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The Ag-Sn based system in the nano-size regime is one of the strongest candidates for lead-free solders. Besides, the investigation of several other applications of Ag-Sn nanostructures, especially in catalysis, remains scarce which makes it an interesting system to synthesize and explore its chemistry. In this report, nearly monodisperse ε-Ag

A series of iridium and rhodium complexes M(COD)((PNP)-P-Ph-P-H)]Cl {M = Ir (1), Rh (2)}, MH2Cl((PNP)-P-Ph-P-H)] {M = Ir (3), Rh (4)} and IrH3((PNP)-P-Ph-P-H)] (6) supported by pincer ligand HeN(CH2CH2PPh2)(2) {(PNP)-P-Ph-P-H} have been synthesized and characterized. All complexes were isolated in good yields. The iridium trihydride complex IrH3((PNP)-P-Ph-P-H)] (6) was found to be an active catalyst for the hydrogenation of CO2 in 1 M aqueous KOH solution. It also acts as a catalyst for the base-free hydrogenation of carbonyl and imine substrates in MeOH. Under similar hydrogenation conditions, 2-cyclohexen-1-one undergoes solvent assisted tandem Michael addition-reduction mediated by bifunctional Lewis-acid-catalyst IrH3((PNP)-P-Ph-P-H)] in ROH (R = Me, Et) at room temperature. The complexes 1, 3, 4, and 6 were characterized by X-ray crystallography. Extensive hydrogen bonding interactions N-H center dot center dot center dot H-Ir (2.15 angstrom), N-H center dot center dot center dot center dot Cl (2.370 angstrom) were noted in the crystal structures of these complexes. (C) 2018 Elsevier B.V. All rights reserved.

Herein, we report a simple solid state synthetic route to prepare carbon-Fe based magnetic nanoparticles with different compositions and morphologies through annealing of amorphous Fe nanoparticles under appropriate conditions. Tri-n-octylphosphine (TOP) capped amorphous Fe nanoparticles with a mean diameter of 3.2 nm were synthesized using solvated metal atom dispersion (SMAD) method. Annealing of as-prepared Fe nanoparticles at 300 °C produced carbon encapsulated crystalline bcc-Fe nanoparticles, whereas at higher temperatures i.e., 400 °C and 500 °C, spherical Fe 3 C/C core-shell nanoparticles were obtained. Annealing of as-prepared Fe nanoparticles in the presence of tri-n-octylphosphine oxide (TOPO) ligand under optimized conditions yielded rod shaped Fe 3 C/C core-shell morphology. The size, composition and particle morphology of these magnetic nanoparticles could be controlled by changing the reaction time, temperature and the concentration of the TOPO ligand. Magnetic measurements show that rod shaped Fe 3 C nanoparticles exhibit enhanced coercivity (Hc) values compared with spherical Fe 3 C nanoparticles, which is due to shape anisotropy. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Ruthenium hydride complexes bearing an N-heterocyclic carbene ligand RuHCl(CO)(IMes)(PPh3)(L/L')] (L = py, 2; 4Mepy, 3; L' = MeCN, 4; Me3CCN, 5) have been synthesized in high-yields via reaction of RuHCl(CO)(IMes)(PPh3)] (1) with pyridyl ligands L (L = py and 4Mepy) or nitrile ligands L' (L' = MeCN and Me3CCN). The ligands L/L' are labile in all the ruthenium hydride complexes; they can be easily replaced by Lewis bases. The X-ray structures of complexes 2 and 3 show intramolecular pi-pi interactions between the aromatic ring of PPh3, IMes, and pyridyl ligands. The protonation reaction of 2-5 gives the corresponding dihydrogen complexes of the type RuCl(eta(2)-H-2)(CO)(IMes)(PPh3)(L/L')]OTf] complexes (L = py, 6; 4Mepy, 7; L' = MeCN, 8; Me3CCN, 9). In all the dihydrogen complexes, H-H bond distances of eta(2)-H-2 ligand is temperature-dependent 0.98 angstrom to 0.93 angstrom in the temperature range of 183-233 K. Attempts to synthesize analogous ruthenium hydride complexes bearing phosphine ligands resulted in a mixture of cis and trans- RuHCl(CO)(PPh3)(2)(L)] L = py, 10/11 (trans(HCl)/cis(HCl)); 4Mepy, 12/13 (trans(HCl)/cis(HCl))] complexes. A comparative study has been done to get an insight into the temperature-dependent H-H bond distances in complexes 6-8 by synthesizing analogous ruthenium dihydrogen complexes, RuCl(eta(2)-H-2)(CO)(PPh3)(2) (L)](OTf) (L = py, 15; 4Mepy, 17). All the complexes have been characterized using NMR spectroscopy. The X-ray crystal structures of complexes 2, 3, and 12 have also been determined.

Identifying crystal structure sensitivity of a catalyst for a particular reaction is an important issue in heterogeneous catalysis. In this context, the activity of different phases of ruthenium catalysts for benzene hydrogenation has not yet been investigated. The synthesis of hcp and fcc phases of ruthenium nanosponges by chemical reduction method has been described. Reduction of ruthenium chloride using ammonia borane (AB) and tert-butylamine borane (TBAB) as reducing agents gave ruthenium nanosponge in its hcp phase. On the other hand, reduction using sodium borohydride (SB) afforded ruthenium nanosponge in its fcc phase. The as prepared hcp ruthenium nanosponge was found to be catalytically more active compared to the as prepared fcc ruthenium nanosponge for hydrogenation of benzene. The hcp ruthenium nanosponge was found to be thermally stable and recyclable over several cycles. This self-supported hcp ruthenium nanosponge shows excellent catalytic activity towards hydrogenation of various substituted benzenes. Moreover, the ruthenium nanosponge catalyst was found to bring about selective hydrogenation of aromatic cores of phenols and aryl ethers to the respective alicyclic products without hydrogenolysis of the C-O bond.

A series of coordinatively unsaturated, 16-electron, cationic ruthenium complexes bearing PNP pincer ligands of the type [RuH(L)(PNRP)]+ (L = PPh3, R = PhCH2 (3), Ph (4); L = CO, R = PhCH2 (5); PNRP = RN(CH2CH2PPh2)2) has been prepared and characterized. These complexes exhibit agostic interaction in the sixth coordination site. The binding of various X–H (X = H, Si, B, and C) bonds in small molecules such as H2, silanes, tetracoordinate boranes, and CH4 to the ruthenium center via displacement of the relatively weak agostic interaction in these complexes has been studied. Structures of [RuH(L)(PNRP)]+ (L = PPh3, R = PhCH2 (3), Ph (4); L = CO, R = PhCH2 (5); PNRP = RN(CH2CH2PPh2)2) complexes and the sigma-borane complex trans-[RuH(CO)(η1-H-BH2·NMe3)(PNRP)]+ (R = PhCH2 (15)) have been established by X-ray crystallography. The relative binding strengths of the X–H bonds to ruthenium center in these complexes has been studied using computational methods.

A series of new homobimetallic hydride complexes of ruthenium bearing N-heterocyclic carbene ligand of the type [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (4,4’-bpy = 4,4’-bipyridine) (2), [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyen)] (4,4’-dpyen = 1,2-bis(4-pyridyl)ethylene) (4), and [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyan)] (4,4’-dpyan = 1,2-bis(4-pyridyl)ethane) (5) has been synthesized and characterized starting from [RuHCl(IMes)(PPh3)(CO)] (1). The pyridyl-based ligands, (4,4’-bpy), (4,4’-dpyen), and (4,4’-dpyan) in these complexes act as the bridging ligands between the two ruthenium fragments. The bridging ligand in these bimetallic complexes is very labile. Reaction of these complexes with PMe3 led to extensive substitution of not only the bridging ligand but also the PPh3 ligands. Reaction of complexes 2, 4, and 5 with HOTf at low temperatures result in the formation of the corresponding dihydrogen complexes, [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-bpy)][OTf]2 (9), [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyen)][OTf]2 (10), and [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyan)][OTf]2 (11), respectively. These are the first examples of homobimetallic ruthenium dihydrogen complexes bearing NHC ligands. The intact nature of the H–H bond in these derivatives was established by variable temperature 1H (400 MHz) spin-lattice relaxation time (T1, ms) measurements and from the H, D coupling constants of the corresponding HD isotopomers. The H–H distances (dHH) in these complexes fall in the range 0.95–0.98 A. Hydrogen evolution takes place upon warming the dihydrogen complexes generated at low temperatures, indicating the labile nature of the H2 ligand in these complexes. The X-ray crystal structure of [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] complex (2) has been determined.

Three dimensional porous structures offer high specific surface areas and large pore volumes, which enhance substrate diffusion within the porous structures and provide a large number of surface active sites. Such types of structures find applications in catalysis. Herein, we report a simple synthetic strategy for the preparation of iridium nanosponges by the capping agent dissolution method. An Ir@BNHx nanocomposite was prepared starting from different iridium precursors by a solid state reduction method using ammonia borane wherein iridium(0) nanoparticles are embedded in a BNHx polymer. Capping agent (here, the BNHx polymer) dissolution using water under ambient conditions resulted in the formation of a mesoporous iridium nanosponge. This iridium nanosponge exhibits a surface area of 33.5 m2 g-1. The iridium nanosponge was found to be catalytically active for hydrogenation of a variety of olefinic substrates including linear and cyclic alkenes and α,β-unsaturated esters under relatively mild conditions and exhibits high turnover frequencies. It was also found to exhibit much better catalytic activity as compared to other iridium based heterogeneous catalysts for olefin hydrogenation reactions. Additionally, catalyst recovery was achieved via simple filtration from the hydrogenation reaction mixture. The catalytically active surface area of iridium nanosponge was estimated using H2-temperature programmed desorption (TPD) experiments. Moreover, the catalyst was found to be thermally quite robust. The catalyst was recyclable over seven cycles of styrene hydrogenation and was found to be capable of hydrogenating 99% of styrene to ethyl benzene after seven cycles.

Ruthenium pincer complex RuHCl(PPh3)(PNP)] (PNP = Me-N(CH2CH2PPh2)(2)) (1) was synthesized by reaction of RuHCl(PPh3)(3) with Me-N(CH2CH2PPh2)(2) and characterized. Abstraction of chloride ligand in complex 1 using NaBA(4)(f) in the presence of small molecules such as N-2, H-2, O-2, and CO resulted in the formation of trans-RuH(L)(PPh3)(PNP)]BAr4f {L = N-2 (2), H-2 (4), O-2 (5), CO (6)} complexes. Complexes 2, 4, 5, and 6 have been characterized by various techniques. The reaction of RuHCl(PPh3)(PNP)] complex with NaBH4 gave a borohydrido complex RuH(eta(1)-BH4)(PPh3)(PNP)] (7) which upon reaction with NEt3 generates a mixture of cis and trans dihydrides RuH2(PPh3)(PNP)] (8). The reaction of dihydride complexes with CO2 leads to the formation of formate complex RuH(eta(1)-HCO2)(PPh3)(PNP)] (9). In addition, dihydrogen complexes Ru(eta(2)-H-2)(L)(PPh3)(PNP)](n+) (L = Cl (10), CO (11)) having different trans donor ligands were synthesized by protonation of trans-RuH(L)(PPh3)(PNP)](n+) {n = 0, L = CI; n = 1, L = CO} complexes with HOTf at low temperature. Complexes I and 6 have been characterized by X-ray crystallography. (C) 2016 Elsevier B.V. All rights reserved.

Chemistry of lanthanide metals in their zerovalent state at the nanoscale remains unexplored due to the high chemical reactivity and difficulty in synthesizing nanoparticles by conventional reduction methods. In the present study, europium(0) nanoparticles, the most reactive of all the rare earth metals have been synthesized by solvated metal atom dispersion (SMAD) method using hexadecyl amine as the capping agent. The as-prepared europium nanoparticles show surface Plasmon resonance (SPR) band in the visible region of the electromagnetic spectrum. This lead to the investigation of its surface enhanced Raman scattering (SERS) using visible light excitation source. The SERS activity of europium nanoparticles has been followed using 4-aminothiophenol and biologically important molecules such as hemoglobin and Cyt-c as the analytes. This is the first example of lanthanide metal nanoparticles as SERS substrate which can possibly be extended to other rare-earth metals. Since hemoglobin absorbs in the visible region, the use of visible light excitation source leads to surface enhanced resonance Raman spectroscopy (SERRS). The interaction of biomolecules with Eu(0) has been followed using FT-IR and UV-visible spectroscopy techniques. The results indicate that there is no major irreversible change in the structure of biomolecules upon interaction with europium nanoparticles.

We report a general strategy for the synthesis of metal nanosponges (M = Ag, Au, Pt, Pd, and Cu) using a capping agent dissolution method where addition of water to the M@BNHx nanocomposite affords the metal nanosponges. The B-H bond of the BNHx polymer gets hydrolysed upon addition of water and produces hydrogen gas bubbles which act as dynamic templates leading to the formation of nanosponges. The rate of B-H bond hydrolysis has a direct impact on the final nanostructure of the materials. The metal nanosponges were characterized using powder XRD, electron microscopy, XPS, and BET surface area analyzer techniques. The porous structure of these nanosponges offers a large number of accessible surface sites for catalytic reactions. The catalytic activity of these metal nanosponges has been demonstrated for the reduction of 4-nitrophenol where palladium exhibits the highest catalytic activity (k = 0.314 min-1). The catalytic activity of palladium nanosponge was verified for the tandem dehydrogenation of ammonia borane and the hydrogenation of nitroarenes to arylamines in methanol at room temperature. The reduction of various substituted nitroarenes was proven to be functional group tolerant except for a few halogenated nitroarenes (X = Br and I) and >99% conversion was noted within 30-60 min with high turnover frequencies (TOF) at low catalyst loading (0.1 mol%). The catalyst could be easily separated out from the reaction mixture via centrifugation and was recyclable over several cycles, retaining its porous structure.

The five-coordinated 16-electron complex [Ru(Me)(dppe)2][OTf] (3) undergoes methane elimination at room temperature to afford the ortho-metalated species [(dppe){(C6H5)(C6H4)PCH2CH2P(C6H5)2}Ru][OTf] (7). Methane elimination, monitored using NMR spectroscopy, revealed no intermediate throughout the reaction. The NOE between Ru–Me protons and ortho phenyl protons and an agostic interaction trans to the methyl group were found in complex 3 by NMR spectroscopy, which form the basis for three plausible pathways for methane elimination and ortho metalation: pathway I (through spatial interaction), pathway II (through oxidative addition and reductive elimination), and pathway III (through agostic interaction). Methane elimination from complex 3 via pathway I was discounted, since it involves interactions through space and not through bonds. Moreover, the calculated energy barrier for the pathway I transition state was quite high (71.3 kcal/mol), which also indicates that this pathway is very unlikely. Furthermor...

A new ruthenium pincer complex [RuHCl(CO)(PNP)] (PNP = PhCH2N(CH2CH2PPh2)2) (1) was synthesized and characterized. The reactivity of complex 1 with electrophilic reagents XOTf (X = H, CH3, and Me3Si; OTf = CF3SO3) was studied by variable temperature NMR spectroscopy with an aim to observe and characterize sigma complexes of type [Ru(η2-HX)Cl(CO)(PNP)][OTf] (X = H (2), CH3 (3), Me3Si (4)). Reaction of complex 1 with HOTf resulted in the formation of the dihydrogen complex, [Ru(η2-H2)Cl(CO)(PNP)[OTf] (2). On the other hand, the reaction between complex 1 and MeOTf and Me3SiOTf resulted in the direct elimination of MeCl and Me3SiCl via a SN2 type of reaction without the intermediacy of the respective sigma complexes 3 and 4. This contrasting reactivity behaviour has been rationalized taking into consideration the approach of the relatively bulky electrophiles CH3+ and Me3Si+ onto the hydride moiety of the ruthenium fragment, which is sterically hindered.

Two new Ru(II)-complexes [RuH(Tpms)(PPh3)2] 1 (Tpms = (C3H3N2)3CSO3, tris-(pyrazolyl)methane sulfonate) and [Ru(OTf)(Tpms)(PPh3)2] 2 (OTf = CF3SO3) have been synthesized and characterized wherein Ru–H and Ru–OTf are the key reactive centers. Reaction of 1 with HOTf results in the [Ru(η2-H2)(Tpms)(PPh3)2][OTf] complex 3, whereas reaction of 1 with Me3SiOTf affords the dihydrogen complex 3 and complex 1 through an unobserved σ–silane intermediate. In addition, an attempt to characterize the sigma methane complex via reaction of complex 1 with CH3OTf yields complex 2 and free methane. On the other hand, reaction of [Ru(OTf)(Tpms)(PPh3)2] 2 with H2 and PhMe2SiH at low temperature resulted in σ–H2, 3 and a probable σ–silane complexes, respectively. However, no σ–methane complex was observed for the reaction of complex 2 with methane even at low temperature.

Reaction of 2,2′-bipyridine (bpy) with dinuclear complexes [RuCl(dfppe)(μ-Cl)3Ru(dmso-S)3] (dfppe = 1,2-bis(dipentafluorophenyl phosphino)ethane (C6F5)2PCH2CH2P(C6F5)2; dmso = dimethyl sulfoxide) (1) or [RuCl(dfppe)(μ-Cl)3RuCl(dfppe)] (2) affords the mononuclear species trans-[RuCl2(bpy)(dfppe)] (3). Using this precursor complex (3), a series of new cationic Ru(II) electrophilic complexes [RuCl(L)(bpy)(dfppe)][Z] (L = P(OMe)3 (5), PMe3 (6), CH3CN (7), CO (8), H2O (9); Z = OTf (5, 6, 7, 8), BArF4 (9) have been synthesized via abstraction of chloride by AgOTf or NaBArF4 in the presence of L. Complexes 5 and 6 were converted into the corresponding isomeric hydride derivatives [RuH(PMe3)(bpy)(dfppe)][OTf] (10a, 10b) and [RuH(P(OMe)3)(bpy)(dfppe)][OTf] (11a, 11b) respectively, when treated with NaBH4. Protonation of the cationic monohydride complex (11a) with HOTf at low temperatures resulted in H2 evolution accompanied by the formation of either solvent or triflate bound six coordinated species [Ru(S)(P(OMe)3)(bpy)(dfppe)][OTf]n [(S = solvent (n = 2), triflate (n = 1)] (13a/13b); these species have not been isolated and could not be established with certainty. They (13a/13b) were not isolated, instead the six-coordinated isomeric aqua complexes cis-[Ru(bpy)(dfppe)(OH2)(P(OMe)3)][OTf]2 (14a/14b) were isolated. Reaction of the aqua complexes (14a/14b) with 1 atm of H2 at room temperature in acetone-d6 solvent resulted in heterolytic cleavage of the H–H bond. Results of the studies on H2 lability and heterolytic activation using these complexes are discussed. The complexes 3, 5, 11a, and 14a have been structurally characterized.

A new solid state synthetic route has been developed toward metal and bimetallic alloy nanoparticles from metal salts employing amine-boranes as the reducing agent. During the reduction, amine-borane plays a dual role: acts as a reducing agent and reduces the metal salts to their elemental form and simultaneously generates a stabilizing agent in situ which controls the growth of the particles and stabilizes them in the nanosize regime. Employing different amine-boranes with differing reducing ability (ammonia borane (AB), dimethylamine borane (DMAB), and triethylamine borane (TMAB)) was found to have a profound effect on the particle size and the size distribution. Usage of AB as the reducing agent provided the smallest possible size with best size distribution. Employment of TMAB also afforded similar results; however, when DMAB was used as the reducing agent it resulted in larger sized nanoparticles that are polydisperse too. In the AB mediated reduction, BNH(x) polymer generated in situ acts as a capping agent whereas, the complexing amine of the other amine-boranes (DMAB and TMAB) play the same role. Employing the solid state route described herein, monometallic Au, Ag, Cu, Pd, and Ir and bimetallic CuAg and CuAu alloy nanoparticles of

Electrochemical oxidation of sodium borohydride (NaBH4) and ammonia borane (NH3BH3) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH4 as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm−2 at a load current density of 83 mA cm−2 is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm−2 at 105 mA cm−2 is obtained in the case of AB-based fuel cell at 353 K.

Activation of the B-H sigma-bond of amine-boranes on the chromium(0) center of arene chromium tricarbonyl complexes (eta(6)-arene) Cr(CO)(3) (arene = fluorobenzene, 1a; benzene, 1b and mesitylene, 1c) has been studied. Photolysis of 1b in presence of ammonia-borane (H3N center dot BH3, AB) and tert-butylamine-borane ((BuH2N)-Bu-t center dot BH3, TBAB) resulted in H-2 evolution and precipitation of a BNHx polymer. On the other hand, photolysis in the presence of trimethylamine-borane (Me3N center dot BH3, TMAB) resulted in the formation of a sigma-borane complex (2) along with Cr(CO)(5)(eta(1)-HBH2 center dot NMe3) (3). The sigma-borane complexes (eta(6)-arene) Cr-( CO)(2)(eta(1)-HBH2 center dot NMe3) (arene = fluorobenzene, 2a; benzene, 2b and mesitylene, 2c) were characterized in solution by H-1, B-11, and C-13 NMR spectroscopy. Electron withdrawing substituents on the arene ring provide the more stable sigma-borane moiety in this series of complexes. (C) 2011 Elsevier B.V. All rights reserved.

The 16-electron, coordinatively unsaturated, dicationic ruthenium complex Ru(P(OH)(2)(OMe))(dppe)(2)]OTf](2) (1a) brings about the heterolysis of the C-H bond in phenylacetylene to afford the phenylacetylide complex trans-Ru(C CPh)(P(OH)(2)(OMe))(dppe)(2)]OTf] (2). The phenylacetylide complex undergoes hydrogenation to give a ruthenium hydride complex trans-Ru(H)(P(OH)(2)(OMe))(dppe)(2)]OTf] (3) and phenylacetylene via the addition of H-2 across the Ru-C bond. The 16-electron complex also reacts with HSiCl3 quite vigorously to yield a chloride complex trans-Ru(Cl)(P(OH)(2)(OMe))(dppe)(2)]OTf] (4). On the other hand, the other coordinatively unsaturated ruthenium complex Ru(P(OH)(3))(dppe)(2)]OTf](2) (1b) reacts with a base N-benzylideneaniline to afford a phosphonate complex Ru(P(O)(OH)(2))(dppe)(2)]OTf] (5) via the abstraction of one of the protons of the P(OH)(3) ligand by the base. The phenylacetylide, chloride, and the phosphonate complexes have been structurally characterized. The phosphonate complex reacts with H-2 to afford the corresponding dihydrogen complex trans-Ru(eta(2)-H-2)(P(O)(OH)(2))(dppe)(2)]OTf] (5-H2). The intact nature of the H-H bond in this species was established using variable temperature H-1 spin-lattice relaxation time measurements and the observation of a significant J(H,D) coupling in the HD isotopomer trans-Ru(eta(2)-HD)(P(O)(OH)(2))(dppe)(2)]OTf] (5-HD). (C) 2010 Elsevier B. V. All rights reserved.

Colloids of palladium nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. The as-prepared Pd colloid consists of particles with an average diameter of 2.8 +/- 0.1 nm. Digestive ripening of the as-prepared Pd colloid, a process involving refluxing the as-prepared colloid at or near the boiling point of the solvent in the presence of a passivating agent, dodecanethiol resulted in a previously reported Pd-thiolate cluster, Pd(SC12H25)(2)](6) but did not render the expected narrowing down of the particle size distribution. Solventless thermolysis of the Pd-thiolate complex resulted in various Pd systems such as Pd(0), PdS, and Pd@PdO core-shell nanoparticles thus demonstrating its versatility. These I'd nanostructures have been characterized using high-resolution electron microscopy and powder X-ray diffraction methods. (C) 2010 Elsevier Inc. All rights reserved.

Colloid of palladium nanoparticles has been prepared by the Solvated Metal Atom Dispersion (SMAD) method. Reaction of Pd(0) nanopowder obtained upon precipitation from the colloid, with ammonia borane (H3N center dot BH3, AB) in aqueous solutions at room temperature results in the generation of active hydrogen atoms. The active hydrogen atoms either combine with one another resulting in H-2 evolution or diffuse into the Pd lattice to afford PdHx. Diffusion of hydrogen atoms leads to an expansion of the Pd lattice. The diffused hydrogen atoms are distributed uniformly over the entire particle. These features were established using powder XRD and electron microscopy studies. The H-1 NMR spectral studies of PdHx before and after desorption of H-2 revealed that the hydrogen atoms trapped inside Pd lattice are hydridic in nature. Desorption of hydrogen from PdHx did not result in complete reversibility suggesting that some hydrogen atoms are strongly trapped inside the Pd lattice. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Co-Co(2)B and Ni-Ni(3)B nanocomposites were synthesized by the reduction of Co(2+) and Ni(2+) ions using ammonia-borane in methanol. The Co-Ni-B nanocomposite was synthesized by the co-reduction of Co(2+) and Ni(2+) ions. The catalytic activities of these metal nanocomposites were studied for the dehydrogenation of ammonia-borane in methanol. Three moles of H(2) were liberated in 2.5 min and 4.2 min in case of Co-Co(2)B and Ni-Ni(3)B nanocomposites, respectively (catalyst/AB = 0.2). The Co-Ni-B nanocomposite showed greater activity compared to individual metal-metal boride nanocomposites: 3 moles of H(2) were liberated in 1.5 min (catalyst/AB = 0.2). The catalysts were highly recyclable and the activities remained almost unchanged even after several cycles.

Ammonia-borane (AB) hydrolysis for the generation of hydrogen has been studied using first row transition metal ions, such as $Co^{2+}$, $Ni^{2+}$, and $Cu^{2+}$. In the cases of cobalt- and nickel-assisted AB hydrolysis, amorphous powders are formed that are highly catalytically active for hydrogen generation. Annealing of these amorphous powders followed by powder X-ray diffraction measurements revealed the presence of Co(O) and $Co_2B$ and Ni(O) and $Ni_3B$, respectively. On the other hand, copper-assisted AB hydrolysis was catalyzed by in situ generated $H^+$ and Cu(0) nanoparticles. The reduction ability of AB for the realization of coinage metal nanoparticles from the respective metal salts has also been studied. These reduction reactions were found to be facile, affording colloids of pure metal nanoparticles. Nanoparticles prepared in this manner were characterized by UV-visible spectroscopy and high-resolution electron microscopy.

In this work, we compare different precursor approaches for the mild decomposition to copper–aluminum and –gallium powder materials in nonaqueous solution. Referring to previous work on the preparation of Cu–Al alloy materials from [(AlCp*)4] and [CpCu(PMe3)], the amine-stabilized metal trihydrides [(Me3N)AlH3] and [(quinuclidine)GaH3] were used as alternative sources for Al and Ga. In a comparative study, [(Me3N)AlH3] and [(AlCp*)4] were treated with the Cu precursors [CpCu(PMe3)] and [{Cu(mesityl)}5] in mesitylene solution in various molar ratios at 150 °C and 3 bar H2 to give metallic precipitates of the composition Cu1–xAlx (x = 0.67, 0.50, 0.31). Whereas the combination [(AlCp*)4] with [{Cu(mesityl)}5] did not yield an intermetallic phase, all other Cu/Al precursor combinations led to alloyed Cu–Al materials. For x = 0.67, the θ-CuAl2 phase formed, as shown by X-ray powder diffraction (XRD) and solid-state magic-angle-spinning (MAS)NMR spectroscopic studies. Similarly, the reaction of [{Cu(mesityl)}5] with [(quinuclidine)GaH3] immediately led to the precipitation of a gray powder, without the addition of hydrogen. The powder was identified by means of XRD as θ-CuGa2. At x = 0.50 and below, the reactions were less phase selective depending on the precursor combination. [CpCu(PMe3)] combined with both Al precursors afforded a mixture of several Cu–Al phases, whereas [{Cu(mesityl)}5] was treated with [(Me3N)AlH3] to yield a material whose X-ray signature was assigned to the monoclinic Cu0.51Al0.49 phase. The γ-Cu9Al4 phase could not be obtained from [CpCu(PMe3)]; instead, solid solutions of α-Cu were obtained. The treatment of [{Cu(mesityl)}5] with [(Me3N)AlH3] in the Cu/Al molar ratio of 9:4 (x = 0.31) gave a gray powder, which could be identified by XRD as γ-Cu9Al4.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A simple and high yielding method was developed for the synthesis of novel α-aminophosphonates from imines, obtained from 2-chloroquinoline-3-carbaldehyde, by using triethylphosphite in the presence of chlorotrimethylsilane (TMSCl). This method developed for the synthesis of α -aminophosphonates gave excellent yields.

The synthesis of colloids of copper and zinc nanoparticles by solvated metal atom dispersion (SMAD) is described. The as-prepared colloids with a large size distribution of the particles are transformed into colloidal nanoparticles of a narrow size distribution by the digestive ripening process which involves refluxing the colloid at or near the boiling point of the solvent in the presence of a passivating ligand. The copper nanoparticles of 2.1 ± 0.3 nm and zinc nanoparticles of 3.9 ± 0.3 nm diameters have thus been obtained. Digestive ripening of the as-prepared copper and zinc colloids together in the presence of a passivating agent gave Cu@ZnO core−shell nanoparticles, with an average diameter of 3.0 ± 0.7 nm. Particles synthesized in this manner were characterized by UV−visible spectroscopy, high-resolution electron microscopy, energy-filtered electron microscopy, and powder X-ray diffraction methods which confirm the core−shell structure.

A series of new dicationic dihydrogen complexes of the type trans-$[Ru(\eta^2-H_2)(L)(dppm)_2][X]_2 (L=CH_3CN, CH_2=CHCN, C_6H_5CN, C_6H-5NC, CO; X 5 BF_4, OTf; dppm = Ph_2PCH_2PPh_2)$ have been prepared by protonating the precursor hydrides using either $HBF_4 . Et_2O or HOTf$. The variable temperature spinlattice relaxation times $(T_1, ms)$ and the H, D coupling constants of the $\eta^2-HD$ isotopomers indicate the intact nature of the H-H bond in these derivatives. The H-H distances of the dihydrogen complexes bearing trans-nitrile ligands are not significantly affected by the sterics and the electronics of the nitrile. On the other hand, the H-H distances of the dihydrogen complexes bearing either isonitrile or CO ligand are comparable to those possessing chelating diphosphine ligands of greater bite angle. Also, the thermal stabilities of these complexes are significantly less than those bearing diphosphines of greater bite angle. The trans- $[Ru(H)(CH_3CN)(dppm)_2][BF_4]$ complex has been characterized by X-ray crystallography.

New dicationic dihydrogen complexes of the type trans- $[M(\eta ^2-H_2)(PF_3)(diphosphane)_2]^2+ [M = Ru, diphosphane = dppm (Ph_2PCH_2PPh_2); M = Fe, Ru, diphosphane = dppe (Ph_2PCH_2CH_2PPh_2)]$ have been prepared from the precursor hydrides trans- $[M(H)(PF_3)(diphosphane)_2]^+ $ upon reaction with HOTf. In the case of dppm, in addition to the trans-dihydrogen complex ci \varsigma-$[Ru(\eta^2-H_2)(PF_3)(dppm)_2]^2+ $was also obtained in the protonation reaction. The intact nature of the H-H bond in these derivatives has been established using the spin-lattice relaxation time measurements (short$ T_1$ values) and the large $J_H_,_D$ coupling constant of the H-D isotopomers. The H-H bond lengths and the stabilities of the dihydrogen complexes are discussed in terms of the \pi acidity of the $PF_3$ ligand and compared with other systems possessing trans CO and CNH ligands. The trans-$[Ru(\eta^2-H_2)(PF_3)(dppe)_2]^2+ $ complex was found to be remarkably stable with respect to the loss of bound H$_2$ for a period of about 16 h. The H-D isotopomer of this complex exhibits small temperature variations in the J$_H_,_D$ coupling constant. The X-ray crystal structure of trans-$[Ru(H)(PF_3)(dppm)_2][BF_4]$ has been determined

Transestrification of methyl/ethyl ketoesters with primary, secondary, allylic, cyclic and benzylic alcohols has been carried out in moderate to good yields under solvent-free condition using borate zirconia solid acid catalyst. The process has simpler work up procedure and the catalyst has been successfully recovered and recycled. The catalyst has been characterized by different techniques like X-ray diffraction, X-ray photoelectron spectroscopy, differential thermal analysis, temperature-programmed desorption of ammonia, scanning electron microscopy and surface area measurements. Transesterification using borate zirconia catalyst under solvent-free condition is an economical and environment friendly process.

Here we present digestive ripening facilitated interatomic diffusion for the phase controlled synthesis of homogeneous intermetallic nanocrystals of Au-Sn system. Au and Sn metal nanoparticles synthesized by a solvated metal atom dispersion (SMAD) method are employed as precursors for the fabrication of AuSn and Au5Sn which are Au-rich Au-Sn intermetallic nanocrystals. By optimizing the stoichiometry of Au and Sn in the reaction mixture, and by employing growth directing agents, the formation of phase pure intermetallic AuSn and Au5Sn nanocrystals could be realized. The as-prepared Au and Sn colloidal nanoparticles and the resulting intermetallic nanocrystals are thoroughly characterized by powder X-ray diffraction, transmission electron microscopy (TEM and STEM-EDS), and optical spectroscopy. The results obtained here demonstrate the potential of solution chemistry which allows synthesizing phase pure Au-Sn intermetallics with tailored morphology.

A series of new dicationic dihydrogen complexes of ruthenium of the type $trans-[(dppe)_2Ru(\eta^2-H_2)(RCN)][BF_4]_2$ $[dppe = Ph_2PCH_2CH_2PPh_2; R = CH_3, CH_3CH_2, CH_3CH_2CH_2, CH_2=CH, p-CH_3-C_6H_4-CH_2, C_6H_5, and (CH_3)_2N]$ have been prepared by the protonation reaction of the precursor hydrides, trans- $[(dppe)_2Ru(H)(RCN)][BF_4]$ using $HBF_4·OEt_2$. The variable temperature spin-lattice relaxation times $(T_1, ms)$ and the H, D coupling constants of the $\eta^2$ -HD isotopomers indicate the intact nature of the H-H bond in these complexes. It was found that the spectroscopic and chemical properties of these derivatives are not very sensitive to the change in the trans nitrile ligand. The $pK_a$ values of the dihydrogen complexes have been determined using the equilibrium: trans- $[(dppe)_2Ru(H)(RCN)][BF_4] + HBF_4\cdot OEt_2 \rightleftharpoons trans- [(dppe)_2Ru(\eta^2-H_2)(RCN)][BF_4]_2 + Et_2O$ by $^1H\hspace{2mm}NMR$ spectroscopy.

Metal nanoparticles (NPs) of Cu (air-stable), Ag, and Au have been prepared using an atom-economy green approach. Simple mechanical stirring of solid mixtures (no solvent) of a metal salt and ammonia borane at 60 degrees C resulted in the formation of metal NPs. In this reaction, ammonia borane is transformed into a BNH(x) polymer, which protects the NPs formed and halts their growth. This results in the formation of the BNH(x) polymer protected monodisperse NPs. Thus, ammonia borane used in these reactions plays a dual role (reducing agent and precursor for the stabilizing agent).

A series of new dicationic dihydrogen complexes of ruthenium of the type trans-[(dppe)2Ru(η2-H2)(L‘)][BF4]2 (dppe = Ph2PCH2CH2PPh2; L‘ = PF(OMe)2, PF(OEt)2, PF(OiPr)2) have been prepared by protona...

The highly electrophilic, 16-electron, coordinatively unsaturated [Ru(P(OMe)(OH)2)(dppe)2][OTf]2 complex brings about the heterolytic activation of H2(g) and spontaneously generates HOTf. In addition, trans-[Ru(H)(P(OMe)(OH)2)(dppe)2]+ and an unprecedented example of a phosphorous acid complex, [Ru(P(OH)3)(dppe)2]2+, are formed. The [Ru(P(OMe)(OH)2)(dppe)2][OTf]2 complex also cleaves the Si−H bond in EtMe2SiH in a heterolytic fashion, resulting in the trans-[Ru(H)(P(OMe)(OH)2)(dppe)2]+ derivative.

Using thermal and photochemical methods a series of new chromium complexes has been prepared: ( ν 6 - p -C 6 H 4 F 2 )Cr(CO) 3 ; ( ν 6 -C 6 H 5 CF 3 )Cr(CO) 3 ; [ m -C 6 H 4 (CF 3 ) 2 ]Cr(CO) 3 ; ( ν 6 -C 6 H 5 F)Cr(CO) 2 H(SiCl 3 ); ( ν 6 -C 6 H 5 F)Cr(CO) 2 (SiCl 3 ) 2 ; ( p -C 6 H 4 F 2 )Cr(CO) 2 -H(SiCl 3 ); (C 6 H 5 CF 3 )Cr(CO) 2 H(SiCl 3 ( p -C 6 H 4 F 2 )Cr(CO) 2 (SiCl 3 ) 2 ; C 6 H 5 CF 3 )Cr(CO) 2 (SiCl 3 ) 2 ; [ m -C 6 H 4 (CF 3 ) 2 ]Cr(CO) 2 -H(SiCl 3 ); [ m -C 6 H 4 (CF 3 ) 2 ]Cr(CO) 2 (SiCl 3 ) 2 . Two compounds were structurally characterized by X-ray diffraction. These data combined with IR and 1 H NMR have allowed assessment of some of the electronic and steric effects. The Cr-arene bond is considerably longer in the Cr(II) derivatives than in the Cr(0) species. Also the Cr center, as might be expected, is less electron rich in the Cr(II) dicarbonyl disilyl derivatives. The ν 6 - p -C 6 H 4 F 2 ligands are slightly folded so that the CF carbons are moved further away from the Cr center. Comparison of structural and electronic effects is made with a series of similar chromium compounds reported in the literature. These new (arene)Cr(II) derivatives possess more labile ν 6 -arene ligands, which promise a rich chemistry at the chromium center.

In an attempt to obtain chromium-arene derivatives possessing high arene lability, (C6 H5F)Cr(CO)2 (SiCl3)2, (C6H4F2)Cr(CO)2(SiCl3)2, (C6H5F)Cr(CO)3, and (C6H4F2)Cr(CO)3 have been investigated. Kinetics of arene exchange have been studied showing that the Cr(II) derivatives exhibit ten-fold higher rates than the Cr(O) derivatives. Both electronic and steric effects appear to be important, although electronic effects dominate. Arene displacement by phosphine and phosphite ligands has also been studied. Although arene displacement took place, unexpected rearrangement and disproportionation reactions occurred yielding seven-coordinate (CO)4Cr(PR3)(SiCl3)2 species.

A highly electrophilic ruthenium center in the RuCl(dppe)(2)]OTf] complex brings about the activation of the B H bond in ammonia borane (H3N center dot BH3, AB) and dimethylamine borane (Me2HN center dot BH3, DMAB). At room temperature, the reaction between RuCl(dppe)(2)]OTf] and AB or DMAB results in trans-RuH(eta(2)-H-2)(dppe)(2)]OTf] trans-RuCl(eta(2)-H-2)(dppe)(2)]OTf], and trans-RuH(Cl)(dppe)(2)], as noted in the NMR spectra. Mixing the ruthenium complex and AB or DMAB at low temperature (198/193 K) followed by NMR spectral measurements as the reaction mixture was warmed up to room temperature allowed the observation of various species formed enroute to the final products that were obtained at room temperature. On the basis of the variable-temperature multinuclear NMR spectroscopic studies of these two reactions, the mechanistic insights for B-H bond activation were obtained. In both cases, the reaction proceeds via an eta(1)-B-H moiety bound to the metal center. The detailed mechanistic pathways of these two reactions as studied by NMR spectroscopy are described.

Nanoclusters of 25 nm sized Mg-THF have been prepared by the solvated metal atom dispersion method. Room-temperature digestive ripening of these nanoclusters in the presence of hexadecylamine (HDA) resulted in highly monodisperse colloidal Mg-HDA nanoparticles of 2.8 +/- 0.2 nm. An insight into the room-temperature digestive ripening process was obtained by studying the disintegration of clusters for various Mg:HDA ratios. The Mg colloids are quite stable with respect to precipitation of particles under Ar atmosphere. Using this procedure, pure Mg(0) nanopowders were obtained in gram scale quantities. The Mg powder precipitated from the colloid was fully hydrided at 33 bar and 118 degrees C. Initial desorption of H(2) from samples of MgH(2) was achieved at a remarkably low temperature, 115 degrees C compared to350 degrees C in bulk Mg, demonstrating the importance of the size on the desorption temperatures.

Composing nanocomposites: Co-digestive ripening of as-prepared Mg and Cu colloids prepared by the solvated metal atom dispersion method results in a highly monodisperse colloid of Mg/Cu nanocomposite with an average particle size of 3.0 +/- 0.5 nm. Annealing of these samples at 300 degrees C gives the Cu/MgO nanocomposite.

Copper nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. Oxidation of the SMAD prepared copper colloids resulted in Cu@Cu2O core shell structures (7.7 ± 1.8 nm) or Cu2O nanoparticles depending on the reaction conditions. The nano Cu, Cu@Cu2O core shell, and Cu2O particles were found to be catalytically active for the generation of hydrogen from ammonia–borane either viahydrolysis or methanolysis reaction.

The reaction of eta(5)-Cp*TiCl3 and (LiNHBu)-Bu-t in hexanes yields a novel [eta(5)-Cp*Ti(=(NBu)-Bu-t)((NHBu)-Bu-t)(2)]Li . (NH2Bu)-Bu-t complex with a terminal tert-butylimido moiety. The synthesis and X-ray structural characterization are described. (C) 1999 Elsevier Science S.A. All rights reserved.

Five new monocationic dihydrogen complexes of ruthenium of the type trans-$[RuCl(\eta^2-H_2)(PP)_2][BF_4]$ (PP = bis-1,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, 1a, benzyl, 2a, m-methylbenzyl, 3a, p-methylbenzyl, 4a, p-isopropylbenzyl, 5a) have been prepared by protonating the precursor hydride complexes trans-$[RuCl(H)(PP)_2]$ using $HBF_4·OEt_2$. The dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H-H bond in these derivatives has been established from the short spin-lattice relaxation times $(T_1, ms)$ and cobservation of substantial H, D couplings in the HD isotopomers. The H-H bond distances $(d_{HH}, \AA)$increase systematically from 0.97 to 1.03 \AA as the electron-donor ability of the substituent on the diphosphine ligand increases from the p-fluorobenzyl to the p-isopropylbenzyl moiety. The $d_{HH}$ in trans-$[Ru(\eta^2-H_2)(Cl)((C_6H_5-CH_2)_2PCH_2CH_2P(CH_2C_6H_5)_2)_2][BF_4]$, 2a,was found to be 1.08(5) \AA by X-ray crystallography. In addition, two new 16-electron dicationic dihydrogen complexes of the type $[Ru(\eta^2-H_2)(PP)_2]$ $[OTf]_2$ $(PP = (ArCH_2)_2PCH_2CH_2P(CH_2Ar)_2$, $Ar = m-CH_3C_6H_4-,6a, p-CH_3C_6H_4-, 7a)$ have also been prepared and characterized. These derivatives were found to possess elongated dihydrogen ligands.

A 16-electron dicationic dihydrogen complex $[Ru(\eta^2-H^{...}H)(PP)_2]-[OTf]_2\hspace{2mm}[4; PP )= (C_6H_5CH_2)_2PCH_2CH_2P(CH_2C_6H_5)_2]$ has been prepared and characterized by protonating the precursor hydride complex $[Ru(H)(PP)_2)][OTf]$ (2) using HOTf. The hydride and dihydrogen complexes are stabilized via agostic interaction of the ortho C-H fragment of the phenyl ring on the benzyl group. The intact nature of the H-H bond in this derivative was established from the short spin-lattice relaxation time and the observation of a substantial J(H,D) of 22.0 Hz for the HD isotopomer. The H-H bond distance calculated from J(H,D) is 1.05 \AA, which falls under the category of elongated dihydrogen ligands.

New dinuclear cyclopentadienylrhenium derivatives with four bridging sulfur ligands have been synthesized and characterized. The disulfide ligands in [Cp‘Re(μ-S2)]2Cl2 have been found to react with dihydrogen, acetylene, and ethene under mild conditions.