Study on the preparation and the self‐assembly of poly(propyleneimine)–poly(styrene) nanoparticles

Using 2‐chloropropionamide derivative of poly(propyleneimine) dendrimer DAB‐dendr‐(NH₂)₃₂ (DAB‐32‐Cl) as the macroinitiator, atom transfer radical polymerization of styrene was successfully carried out in DMF medium. The monodisperse poly(propyleneimine)–polystyrene (dendrimer–PSt) particles with diameters smaller than 100 nm could be prepared. The morphology, size, and size distribution of the dendrimer–PSt particles were characterized by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The effects of reaction temperature, the ratio of St/macroinitiator, and reaction time on the size, and size distribution of the dendrimer–PSt nanoparticles were investigated. In a selective solvent (DMF/H₂O), polymers can self‐assemble into different aggregate configurations such as regular microsphere and wire‐like thread. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2658–2666, 2008     

Monodispersed PEG‐b‐PSt nanoparticles prepared by atom transfer radical emulsion polymerization under microwave irradiation

Atom transfer radical emulsion polymerization of styrene using PEG‐Cl as macroinitiator under microwave irradiation was successfully conducted and monodispersed nanoparticles were prepared. The PEG‐Cl macroinitiator was synthesized, and confirmed by FTIR spectrum. The structure of the PEG‐b‐PSt diblock copolymer was characterized by ¹H‐NMR and the number of styrene unit in the diblock copolymer was calculated. The morphology, size, and size distribution of the nanoparticles were characterized by transmission electron microscope (TEM) and photon correlation spectroscopy (PCS). The effects of the ratio of macroinitiator and monomer, the ratio of catalyst and macroinitiator on the size and size distribution of nanoparticles were investigated. It was found that the diameters of PEG‐b‐PSt nanoparticles prepared under microwave irradiation were smaller (<50 nm) and more monodispersed than those prepared with conventional heating. Moreover, with the increasing of the ratio of St/PEG‐Cl, the hydrodynamic diameters (D_h) of the nanoparticles increased and the poly index decreased, both D_h and poly index of the nanoparticles prepared under microwave irradiation were smaller then those prepared with conventional heating; as the concentration of catalyst increased, the D_h of the nanoparticles decreased and the poly index of the nanoparticles increased. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 481–488, 2008     

Quaternary ammonium ion dendrimers from methylation of poly(propylene imine)s

The poly(propylene imine) dendrimers DAB‐dendr‐(NH₂)₈, DAB‐dendr‐(NH₂)₃₂, and DAB‐dendr‐(NH₂)₆₄ were fully converted with iodomethane to quaternary ammonium ions at both chain ends and branch points and, with less iodomethane, were partially converted to quaternary ammonium ions mainly at end groups. Amidation of the primary amine ends followed by treatment with iodomethane gave the first dendrimers with quaternary ammonium ions only at branch points. After an exchange of iodide counterions for chloride, all of the quaternary ammonium ion dendrimers slightly increased the rate of decarboxylation of 6‐nitrobenzisoxazole‐3‐carboxylate ion in an aqueous solution. Similar quaternary ammonium ion dendrimers with more hydrophobic interiors or more hydrophobic chains on the ends were much more active catalysts for the decarboxylation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 821–832, 2001     

Polyelectrolyte behavior and interpolyelectrolyte matching of AstramolTM poly(propylene imine) dendrimers

Polyelectrolyte behavior of Astramol^TM poly(propylene imine) dendrimers of five generations, G1‐G5, namely DAB‐dendr‐(NH₂)_x (where x is equal to 4, 8, 16, 32 or 64) was studied by means of potentiometric titration in salt‐free water solutions and also in the presence of a shielding low molecular electrolyte (NaCI). In addition to x outer primary amine groups the dendrimer molecule contains x‐2 inner tertiary amine groups. The repeating unit, the core molecule and the fifth generation dendrimer structure are shown in the following Scheme.     

Branched poly(styrene‐b‐tert‐butyl acrylate) and poly(styrene‐b‐acrylic acid) by ATRP from a dendritic poly(propylene imine)(NH2)64 core

With the aim of creating highly branched amphiphilic block copolymers, the primary amine end groups of the poly(propylene imine) dendrimers DAB‐dendr‐(NH₂)₈ and DAB‐dendr‐(NH₂)₆₄ were converted to 2‐bromoisobutyramide groups. Poly (styrene‐b‐tert‐butyl methacrylate) (PS‐b‐PtBMA) was synthesized by ATRP from the eight end group initiator, and poly(styrene‐b‐tert‐butyl acrylate) (PS‐b‐PtBA) was synthesized from the 64 end group initiator. The tert‐butyl groups were removed to produce poly(styrene‐b‐methacrylic acid) (PS‐b‐PMAA) and poly(styrene‐b‐acrylic acid) (PS‐b‐PAA). Comparison of size exclusion chromatography (SEC) absolute molecular weight analyses of the polystyrenes with calculated molecular weights showed that the eight end group initiator produced a polystyrene with about eight branches, and that the 64 end group initiator produced polystyrene with many fewer than 64 branches. The PS‐b‐PtBA materials also have many fewer than 64 branches. The PS‐b‐PAA samples dissolved molecularly in DMF but formed aggregates in water even at pH 10. AFM images of the PS‐b‐PtBAs spin coated from THF and DMF onto mica showed aggregates. AFM images of the PS‐b‐PAAs spin coated from various mixtures of DMF and water at pH 10 showed flat disks and worm‐like images similar to those observed with linear PS‐b‐PAAs. Use of a PS‐b‐PAA and a PS‐b‐PMAA as templates for emulsion polymerization of styrene produced latexes 100–200 nm in diameter. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4623–4634, 2007     

Polystyrene latices containing dodecanamide‐modified poly(propyleneimine) dendrimers

Polymerization of styrene in aqueous dispersions of the dodecanamide derivative of poly(propyleneimine) dendrimer DAB‐dendr‐(NH₂)₆₄ and sodium dodecyl sulfate (SDS) produced stable latices. With initial SDS concentrations of 10 mM or less, molar ratios of SDS to dendrimer end groups ranging from 2.3:1 to 9.5:1, and less than 10 wt % of SDS relative to styrene, the polystyrene latices had diameters of 30–60 nm and coefficients of variation of diameters of less than 10% when measured by transmission electron microscopy. Higher concentrations of SDS gave more polydisperse latices. The polystyrene latices formed with SDS and the dodecanamide‐modified dendrimer were almost the same size and polydispersity as those formed with SDS and the parent primary amine dendrimer DAB‐dendr‐(NH₂)₆₄. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 597–605, 2003     

Preparation,characterization and catalytic application of PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐terminated poly(propylene imine) dendrimer

PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐stabilized poly(propylene imine) dendrimer (G3‐M(Pd_x Pt_10−x ) DSNs) have been prepared via synthesis of a 15‐membered triolefinic macrocycle‐modified third‐generation poly(propylene imine) dendrimer (G3‐M) and then synchronous ligand exchange with Pd(PPh₃)₄/Pt(PPh₃)₄ complexes. The structure and catalytic activity of the DSNs were characterized using Fourier transform infrared, ¹H NMR, transmission electron microscopy, energy‐dispersive X‐ray and X‐ray photoelectron analyses. As a novel catalyst system, it can be concluded that the composition of the bimetallic nanoparticles has an influence on the catalytic activity of the hydrogenation reaction of acrylonitrile–butadiene rubber, which can be related to synergistic effect. Furthermore, the selectivity and recyclability of G3‐M(Pd_x Pt_10−x ) DSN catalyst are also discussed.     

Evaluation of synthesis conditions for plastic scintillation foils used to measure alpha- and beta-emitting radionuclides

Plastic scintillation foils of polystyrene and polycarbonate with a thickness between 45 and 200 μm, have been produced using the solvent evaporation method. PSfoils presented a reproducible thickness (10–20%). PSfoils were characterized by the measurement of ³⁶Cl or ²⁴¹Am. For ³⁶Cl spectrum is located at medium energies since not all energy is deposited in the scintillator and not all betas interact with the foils. For ²⁴¹Am the efficiency values are very high and spectrum is a sharp peak located at high energies. ²²²Rn absorption (L_D and K) and desorption capacities of the PSfoils have been also evaluated.

     

Multiarm star nanocarriers containing a poly(ethylene imine) core and polylactide arms

Star polymers (SPs) containing a hyperbranched poly(ethylene imine) (PEI; number‐average molecular weight = 10,000) core and polylactide arms were synthesized via the ring‐opening polymerization of lactide. PEI was used as a multifunctional macroinitiator for the ring‐opening polymerization of lactide. Different lactide monomer/amino‐functional group (LA/NH_n; n = 1 or 2) ratios were used for preparing SPs with different molecular weights. SPs were able to encapsulate small guest molecules such as Rose Bengal; they also transported small, hydrophilic molecules from water to the organic phase. The transport capacity of all the nanocarriers depended on the LA/NH_n ratio used for synthesizing the SPs. Nanocarriers with a higher LA/NH_n ratio had higher transport capacities. The size of all the nanocarriers depended on the type of solvent. In chloroform, these nanoparticles had several sizes that were related to the self‐assembly of these nanocarriers, but in acetone, they were monodisperse, and their size was smaller than that in chloroform. Also, the transport of polar dyes from water to the chloroform phase was possible. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5740–5749, 2006     

Synthesis and characterization of macroinitiator‐amino terminated PEG and poly(γ‐benzyl‐L‐glutamate)‐PEO‐poly(γ‐benzyl‐L‐glutamate) triblock copolymer

Macroinitiator‐amino terminated poly(ethylene glycol) (PEG) (NH₂‐PEO‐NH₂) was prepared by converting both terminal hydroxyl groups of PEG to more reactive primary amino groups. The synthetic route involved reactions of chloridize, phthalimide and finally hydrazinolysis. Furthermore, poly(γ‐benzyl‐L ‐glutamate)‐poly(ethylene oxide)‐poly(γ‐benzyl‐L ‐glutamate) (PBLG‐PEO‐PBLG) triblock copolymer was synthesized by polymerization of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (Bz‐L‐GluNCA) using NH₂‐PEO‐NH₂ as macroinitiator. The resultant NH₂‐PEO‐NH₂ and triblock copolymer were characterized by FT‐IR, ¹H‐NMR and gel permeation chromatography (GPC) techniques. The results demonstrated that the degree of amination of the NH₂‐PEO‐NH₂ could be up to 1.95. The molecular weight of the PBLG‐PEO‐PBLG triblock copolymer could be adjusted easily by controlling the molar ratio of Bz‐L ‐Glu NCA to the macroinitiator NH₂‐PEO‐NH₂. Copyright © 2004 John Wiley & Sons, Ltd.     

Electronic structure of metastable isomers of Ru nitroso complexes

Geometrical structures of nitroso complexes trans- [Ru(NO)(NH₃)₄(Cl)]²⁺, trans-[Ru(NO)(NH₃)₄(H2O)]³⁺, [Ru(NO)(Cyclam)(Cl)]²⁺(Cyclam is 1,4,8,11-tetraazocyclodecane), and [Ru(NO)(Bipy)₂(Cl)]²⁺ (Bipy is 2,2-bipyridine) are optimized using the density functional method. The potential energy surface of all four complexes was found to contain local minima corresponding to a stable state with the ¹-coordination of NO through the N atom and to two metastable isomers with the ¹-O and ²-NO coordination. For [Ru(NO)Cl₅)]^2-, trans-[Ru(NO)(NH₃)₄(Cl)]²⁺, and trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺, the lowest electronically excited triplet states are calculated, as well as the reduced complexes with one additional electron. It is shown that the electron excitation and reduction are accompanied by bending of the RuNO group with a substantial elongation of the Ru-O and N-O bonds, which makes this group unstable. These processes do not cause any significant changes in the metal or in the nitroso ligand oxidation states because of the electron density delocalization in the RuNO group.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 1, 2005, pp. 32–42.Original Russian Text Copyright © 2005 by Sizova, Lubimova.     

Blends of fatty‐acid‐modified dendrimers with polyolefins

Blends were made by solution and melt‐mixing fatty‐acid‐modified dendrimers with various polyolefins. Small‐angle neutron scattering (SANS) was used to determine the miscibility of the blends. Poly(propylene imine) (PPI) dendrimers G1, G3, and G5 [DAB‐dendr‐(NH₂)_y] with y = 4, 16, and 64, were reacted with stearic acid or stearic acid‐d₃₅ forming amide bonds. The modified dendrimers were then blended with high‐density polyethylene (HDPE), high‐density polyethylene‐d₄ (HDPE‐d₄), low‐density polyethylene (LDPE), amorphous polypropylene (PP), or an ethylene–butylene copolymer (E‐co‐B). Limiting power law behavior shows that all of the blends are immiscible. It is likely that the dendrimers form a second phase, being finely dispersed, but thermodynamically immiscible. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 95–100, 2000     

Fixation of Metallo Nitrile Ylides and Metallo Nitrile Imines as Ligands in Transition Metal Complexes [1]

1,3‐Dipoles of the type metallo nitrile ylide and metallo nitrile imine were prepared by mono‐α‐deprotonation of CH‐acidic {[W(CO)₅CHCH₂PPh₃]PF₆, M(CO)₅CNCH₂CO₂R (M = Cr, W; R = Me, Et), [Pt(Cl)(CNCH₂CO₂Et)(PPh₃)₂]BF₄} and NH‐acidic isocyanide complexes (Cr(CO)₅CNNH₂) and were stabilized by coordination to a second transition metal complex fragment {Cr(CO)₅, [M(CO)₅]⁺ (M = Mn, Re), [FeCp(CO)₂]⁺, [Pt(Cl)(PR₃)₂]⁺ (R = Et, Ph)}. All dinuclear products 1 – 7 , 10 , and 11 are neutral species except [(Ph₃P)₂(Cl)Pt{μ₂‐CNCH(CO₂Et)}Pt(Cl)(PPh₃)₂]BF₄ ( 8 ). Complex (OC)₅W{μ₂‐CNCH(CO₂Et)}Pt(Cl)(PEt₃)₂ ( 5b ) was characterized by X‐ray diffraction. Twofold deprotonation/platination to give (OC)₅Cr{μ₃‐CNC(Ph)}[Pt(Cl)(PPh₃)₂]₂ ( 9 ) was achieved in the case of Cr(CO)₅CNCH₂Ph.     

Mirror‐Image Organometallic Osmium Arene Iminopyridine Halido Complexes Exhibit Similar Potent Anticancer Activity

Four chiral Os^II arene anticancer complexes have been isolated by fractional crystallization. The two iodido complexes, (S_Os,S_C)‐[Os(η⁶‐p‐cym)(ImpyMe)I]PF₆ (complex 2 , (S)‐ImpyMe: N‐(2‐pyridylmethylene)‐(S)‐1‐phenylethylamine) and (R_Os,R_C)‐[Os(η⁶‐p‐cym)(ImpyMe)I]PF₆ (complex 4 , (R)‐ImpyMe: N‐(2‐pyridylmethylene)‐(R)‐1‐phenylethylamine), showed higher anticancer activity (lower IC₅₀ values) towards A2780 human ovarian cancer cells than cisplatin and were more active than the two chlorido derivatives, (S_Os,S_C)‐[Os(η⁶‐p‐cym)(ImpyMe)Cl]PF₆, 1 , and (R_Os,R_C)‐[Os(η⁶‐p‐cym)(ImpyMe)Cl]PF₆, 3 . The two iodido complexes were evaluated in the National Cancer Institute 60‐cell‐line screen, by using the COMPARE algorithm. This showed that the two potent iodido complexes, 2 (NSC: D‐758116/1) and 4 (NSC: D‐758118/1), share surprisingly similar cancer cell selectivity patterns with the anti‐microtubule drug, vinblastine sulfate. However, no direct effect on tubulin polymerization was found for 2 and 4 , an observation that appears to indicate a novel mechanism of action. In addition, complexes 2 and 4 demonstrated potential as transfer‐hydrogenation catalysts for imine reduction.     

A Bis(phenoxy‐imine)Zr Complex for Ultrahigh‐Molecular‐Weight Amorphous Ethylene/Propylene Copolymer

A new bis(phenoxy‐imine)Zr complex has been developed. This complex in conjunction with ⁱBu₃Al/Ph₃CB(C₆F₅)₄ at 70°C produces ultrahigh‐molecular‐weight amorphous ethylene/propylene copolymer with a weight‐average molecular weight of 10 200 000 g/mol versus polystyrene standards, which represents the highest molecular weight known for linear, synthetic copolymers to date.     

Terminal and Bridging Parent Amido 1,5‐Cyclooctadiene Complexes of Rhodium and Iridium

The ready availability of rare parent amido d⁸ complexes of the type [{M(μ‐NH₂)(cod)}₂] (M=Rh ( 1 ), Ir ( 2 ); cod=1,5‐cyclooctadiene) through the direct use of gaseous ammonia has allowed the study of their reactivity. Both complexes 1 and 2 exchanged the di‐olefines by carbon monoxide to give the dinuclear tetracarbonyl derivatives [{M(μ‐NH₂)(CO)₂}₂] (M=Rh or Ir). The diiridium(I) complex 2 reacted with chloroalkanes such as CH₂Cl₂ or CHCl₃, giving the diiridium(II) products [(Cl)(cod)Ir(μ‐NH₂)₂Ir(cod)(R)] (R=CH₂Cl or CHCl₂) as a result of a two‐center oxidative addition and concomitant metal–metal bond formation. However, reaction with ClCH₂CH₂Cl afforded the symmetrical adduct [{Ir(μ‐NH₂)(Cl)(cod)}₂] upon release of ethylene. We found that the rhodium complex 1 exchanged the di‐olefines stepwise upon addition of selected phosphanes (PPh₃, PMePh₂, PMe₂Ph) without splitting of the amido bridges, allowing the detection of mixed COD/phosphane dinuclear complexes [(cod)Rh(μ‐NH₂)₂Rh(PR₃)₂], and finally the isolation of the respective tetraphosphanes [{Rh(μ‐NH₂)(PR₃)₂}₂]. On the other hand, the iridium complex 2 reacted with PMe₂Ph by splitting the amido bridges and leading to the very rare terminal amido complex [Ir(cod)(NH₂)(PMePh₂)₂]. This compound was found to be very reactive towards traces of water, giving the more stable terminal hydroxo complex [Ir(cod)(OH)(PMePh₂)₂]. The heterocyclic carbene IPr (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) also split the amido bridges in complexes 1 and 2 , allowing in the case of iridium to characterize in situ the terminal amido complex [Ir(cod)(IPr)(NH₂)]. However, when rhodium was involved, the known hydroxo complex [Rh(cod)(IPr)(OH)] was isolated as final product. On the other hand, we tested complexes 1 and 2 as catalysts in the transfer hydrogenation of acetophenone with iPrOH without the use of any base or in the presence of Cs₂CO₃, finding that the iridium complex 2 is more active than the rhodium analogue 1 .     

Water Soluble Gold(I)‐diacetyl‐1,3,5‐triaza‐7‐phosphaadamantane‐arylazoimidazole Complexes: Synthesis and Spectroscopic Study

Reaction of [Au(DAPTA)(Cl)] with RaaiR’ in CH2Cl2 medium following ligand addition leads to [Au(DAPTA)(RaaiR’)](Cl) [DAPTA＝diacetyl-1,3,5-triaza-7-phosphaadamantane, RaaiR’＝p-R-C6H4-N＝N- C3H2-NN-1-R’, (1—3), abbreviated as N,N’-chelator, where N(imidazole) and N(azo) represent N and N’, respectively; R＝H (a), Me (b), Cl (c) and R’＝Me (1), CH2CH3 (2), CH2Ph (3)]. The 1H NMR spectral measurements in D2O suggest methylene, CH2, in RaaiEt gives a complex AB type multiplet while in RaaiCH2Ph it shows AB type quartets. 13C NMR spectrum in D2O suggest the molecular skeleton. The 1H-1H COSY spectrum in D2O as well as contour peaks in the 1H-13C HMQC spectrum in D2O assign the solution structure.     

3‐Rhoda‐1,2‐diazacyclopentanes: A Series of Novel Metallacycle Complexes Derived From CN Functionalization of Ethylene

Rh‐containing metallacycles, [(TPA)Rh^III(κ²‐(C,N)‐CH₂CH₂(NR)₂‐]Cl; TPA=N,N,N,N‐tris(2‐pyridylmethyl)amine have been accessed through treatment of the Rh^I ethylene complex, [(TPA)Rh(η²‐CH₂CH₂)]Cl ([ 1 ]Cl) with substituted diazenes. We show this methodology to be tolerant of electron‐deficient azo compounds including azo diesters (RCO₂N?NCO₂R; R=Et [ 3 ]Cl, R=iPr [ 4 ]Cl, R=tBu [ 5 ]Cl, and R=Bn [ 6 ]Cl) and a cyclic azo diamide: 4‐phenyl‐1,2,4‐triazole‐3,5‐dione (PTAD), [ 7 ]Cl. The latter complex features two ortho‐fused ring systems and constitutes the first 3‐rhoda‐1,2‐diazabicyclo[3.3.0]octane. Preliminary evidence suggests that these complexes result from N–N coordination followed by insertion of ethylene into a [Rh]?N bond. In terms of reactivity, [ 3 ]Cl and [ 4 ]Cl successfully undergo ring‐opening using p‐toluenesulfonic acid, affording the Rh chlorides, [(TPA)Rh^III(Cl)(κ¹‐(C)‐CH₂CH₂(NCO₂R)(NHCO₂R)]OTs; [ 13 ]OTs and [ 14 ]OTs. Deprotection of [ 5 ]Cl using trifluoroacetic acid was also found to give an ethyl substituted, end‐on coordinated diazene [(TPA)Rh^III(κ²‐(C,N)‐CH₂CH₂(NH)₂‐]⁺ [ 16 ]Cl, a hitherto unreported motif. Treatment of [ 16 ]Cl with acetyl chloride resulted in the bisacetylated adduct [(TPA)Rh^III(κ²‐(C,N)‐CH₂CH₂(NAc)₂‐]⁺, [ 17 ]Cl. Treatment of [ 1 ]Cl with AcN?NAc did not give the Rh?N insertion product, but instead the N,O‐chelated complex [(TPA)Rh^I ( κ²‐(O,N)‐CH₃(CO)(NH)(N?C(CH₃)(OCH?CH₂))]Cl [ 23 ]Cl, presumably through insertion of ethylene into a [Rh]?O bond.     

Acid‐Labile Amphiphilic PEO‐b‐PPO‐b‐PEO Copolymers: Degradable Poloxamer Analogs

Poly ((ethylene oxide)‐b‐(propylene oxide)‐b‐(ethylene oxide)) triblock copolymers commonly known as poloxamers or Pluronics constitute an important class of nonionic, biocompatible surfactants. Here, a method is reported to incorporate two acid‐labile acetal moieties in the backbone of poloxamers to generate acid‐cleavable nonionic surfactants. Poly(propylene oxide) is functionalized by means of an acetate‐protected vinyl ether to introduce acetal units. Three cleavable PEO‐PPO‐PEO triblock copolymers (M_n,total = 6600, 8000, 9150 g·mol⁻¹; M_n,PEO = 2200, 3600, 4750 g·mol⁻¹) have been synthesized using anionic ring‐opening polymerization. The amphiphilic copolymers exhibit narrow molecular weight distributions (Ð = 1.06–1.08). Surface tension measurements reveal surface‐active behavior in aqueous solution comparable to established noncleavable poloxamers. Complete hydrolysis of the labile junctions after acidic treatment is verified by size exclusion chromatography. The block copolymers have been employed as surfactants in a miniemulsion polymerization to generate polystyrene (PS) nanoparticles with mean diameters of ≈200 nm and narrow size distribution, as determined by dynamic light scattering and scanning electron microscopy. Acid‐triggered precipitation facilitates removal of surfactant fragments from the nanoparticles, which simplifies purification and enables nanoparticle precipitation “on demand.”

     

CNN Pincer Ruthenium Catalysts for Hydrogenation and Transfer Hydrogenation of Ketones: Experimental and Computational Studies

Reaction of [RuCl(CNN)(dppb)] ( 1‐Cl ) (HCNN=2‐aminomethyl‐6‐(4‐methylphenyl)pyridine; dppb=Ph₂P(CH₂)₄PPh₂) with NaOCH₂CF₃ leads to the amine‐alkoxide [Ru(CNN)(OCH₂CF₃)(dppb)] ( 1‐OCH₂CF₃ ), whose neutron diffraction study reveals a short RuO ??? HN bond length. Treatment of 1‐Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)] ? (EtOH)_n ( 1‐OEt?n EtOH ), which equilibrates with the hydride [RuH(CNN)(dppb)] ( 1‐H ) and acetaldehyde. Compound 1‐OEt?n EtOH reacts reversibly with H₂ leading to 1‐H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1‐OEt?n EtOH and 1‐H reveal hydrogen bond interactions and exchange processes. The chloride 1‐Cl catalyzes the hydrogenation (5 atm of H₂) of ketones to alcohols (turnover frequency (TOF) up to 6.5×10⁴ h^?1, 40 °C). DFT calculations were performed on the reaction of [RuH(CNN′)(dmpb)] ( 2‐H ) (HCNN′=2‐aminomethyl‐6‐(phenyl)pyridine; dmpb=Me₂P(CH₂)₄PMe₂) with acetone and with one molecule of 2‐propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru‐hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH₂ is mediated by the alcohol and leads to the key “amide” intermediate. Regeneration of the hydride complex may occur by reaction with 2‐propanol or with H₂; both pathways have low barriers and are alcohol assisted.