Secured Nanosynthesis-Deposition Aerosol Process for Composite Thin Films Incorporating Highly Dispersed Nanoparticles.

Application of nanocomposites in daily life requires not only small nanoparticles (NPs) well dispersed in a matrix, but also a manufacturing process that is mindful of the operator and the environment. Avoiding any exposure to NPs is one such way, and direct liquid reaction-injection (DLRI) aims to fulfill this need. DLRI is based on the controlled in situ synthesis of NPs from the decomposition of suitable organometallic precursors in conditions that are compatible with a pulsed injection mode of an aerosol into a downstream process. Coupled with low-pressure plasma, DLRI produces nanocomposite with homogeneously well-dispersed small nanoparticles that in the particular case of ZnO-DLC nanocomposite exhibit unique properties. DLRI favorably compares with the direct liquid injection of ex situ formed NPs. The exothermic hydrolysis reaction of the organometallic precursor at the droplet-gas interface leads to the injection of small and highly dispersed NPs and, consequently, the deposition of fine and controlled distribution in the nanocomposite. The scope of DLRI nanosynthesis has been extended to several metal oxides such as zinc, tin, tungsten, and copper to generalize the concept. Hence, DLRI is an attractive method to synthesize, inject, and deposit nanoparticles and meets the prevention and atom economy requirements of green chemistry.

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial.

Shaping ability of hybrid nanomaterials is a key point for their further use in devices. It is therefore crucial to control it. To this end, it is necessary that the macroscopic properties of the material remain constant over time. Here, we evidence by multinuclear Magic-Angle Spinning Nuclear Magnetic Resonance spectroscopic study including 17 O isotope exchange that for a ZnO-alkylamine hybrid material, the partial carbonation of amine into ammonium carbamate molecules is behind the conversion from highly viscous liquid to a powdery solid when exposed to air. This carbonation induces modification and reorganization of the organic shell around the nanocrystals and affects significantly the macroscopic properties of the material such as it physical state, its solubility and colloidal stability. This study, straightforwardly extendable, highlights that the nature of the functional chemical group allowing connecting the stabilizing agent (SA) to the surface of the nanoparticles is of tremendous importance especially if the SA is reactive with molecules present in the environment.

Nanocrystal-ligand interactions deciphered: the influence of HSAB and pK a in the case of luminescent ZnO.

Despite all the efforts made by the scientific community to rationalize the interaction of organic molecules with nanocrystals (Ncs), we are still at the level of the empirical recipe when the material behavior in solution is concerned. In an effort to address this issue, the analysis of the luminescence measurements of ZnO Ncs in the presence of various organic substrates using a Langmuir adsorption model was carried out to determine for the first time the affinity constants and the number of binding sites as well as to rank the interaction strengths of these substrates with regard to ZnO Ncs. The results were confirmed by NMR spectroscopic studies, which, besides, provided a deep understanding of the substrate-ZnO Nc interactions. Analysis of the results using pK a and HSAB theory demonstrates that the interaction of a given substrate can be determined by its pK a versus the pK a of the organic molecules present at the surface of pristine Ncs and that the hard or soft character of the substrates can govern the emission intensity of the ZnO Ncs.

Highly Active Iminopyridyl Iron-Based Catalysts for the Polymerization of Isoprene.

A series of iminopyridyl-based ligands, 6-[(Ar)N=C(R)]-2-C6H5N [(Ar = 2,6-Me2-C6H3, R = Me (L1); Ar = 2,6-iPr2-C6H3, R = Me (L2); Ar = 2,6-Me2-C6H3, R = H (L3); Ar = 2,6-iPr2-C6H3, R = H (L4); Ar = 3,5-(CF3)2-C6H3, R = Me (L5); Ar = C6F5, R = Me (L6)], and their corresponding iron (II) complexes were developed to investigate their application in the controlled coordinative polymerization of isoprene. The modulation of steric and electronic properties within this family of ligands/pre-catalysts has shown to influence the stereo-selectivity and activity of the polymerization of isoprene after activation. Upon activation with various co-catalysts such as AliBu3/[Ph3C][B(C6F5)4], AlEt3/[Ph3C][B(C6F5)4] or MAO, the resulting catalysts produced polyisoprenes with an excellent conversion (>99% of 500-5000 equiv.) within less than 1 h (TOF > 500 h-1) and having a variety of stereo-/regio-regularities. The presence of electron-donating and withdrawing groups drastically impacted the activity and the stereoselectivity of the catalysts during the course of the polymerization of isoprene. When activated with AliBu3/[Ph3C][B(C6F5)4], the complexes {6-[(2,6-Me2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C1) and {6-[(2,6-iPr2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C2) exhibited moderate trans-1,4 selectivity (>67%) while the iron-based systems bearing related aldiminopyridyl ligands {6-[(2,6-Me2-C6H3)N=C(H)]-2-C6H5N}FeCl2 (C3) and {6-[(2,6-iPr2-C6H3)N=C(H)]-2-C6H5N}FeCl2 (C4) were found to afford significant cis-1,4 selectivity at low temperature (>86% at -40 °C). On the other hand, the ternary {6-[(3,5-(CF3)2-C6H3)N=C(Me)]-2-C6H5N}FeCl2 (C5) or {6-[(C6F5)N=C(Me)]-2-C6H5N}FeCl2 (C6)/AliBu3/[Ph3C][B(C6F5)4] catalytic combinations showed exceptional activity for the polymerization of isoprene (TOF > 1,000,000 h-1), albeit providing less stereoselectivity.

Multinuclear solid-state NMR study: a powerful tool for understanding the structure of ZnO hybrid nanoparticles.

Characterization of hybrid materials is crucial for gaining an in-depth understanding of nano-objects. Here, it is evidenced that the use of multinuclear 1H, 2H, 13C, 15N, 67Zn and 17O MAS NMR spectroscopy is a very powerful approach to acquire both structural and dynamic information on hybrid ZnO nanomaterials prepared from an organometallic approach. Not only is the coordination mode of the organic part onto the inorganic surface evidenced but also important information about the dynamics of the organic capping molecules and some particularities of the nanocrystal structure itself are obtained.

Evidence for Core Oxygen Dynamics and Exchange in Metal Oxide Nanocrystals from In Situ 17O MAS NMR.

Long-term stability of the properties of nanocrystals (NCs) is of paramount importance for any applicative development. However, these are jeopardized by chemical and structural alterations of the NCs induced by the environment and the working conditions. Among the species that alter the NCs properties, water molecules are of tremendous importance. We used 17O solid-state NMR spectroscopy to follow this process and the dynamics of O atoms in metal oxide NCs. Using ZnO as reference material, different chemical environments for the O atoms are characterized and a dynamic exchange process between the NCs and the O atoms from water is evidenced. The exchange does not involve only surface atoms but also ones located deeper inside the ZnO core of the NCs. Finally, a postsynthesis process based on watering/drying cycles is proposed that may greatly improve the long-term stability of metal oxide NCs.

Copper-Carbene Intermediates in the Copper-Catalyzed Functionalization of O-H Bonds.

Copper-carbene [Tp(x)Cu=C(Ph)(CO2Et)] and copper-diazo adducts [Tp(x)Cu{η(1)-N2C(Ph)(CO2Et)}] have been detected and characterized in the context of the catalytic functionalization of O-H bonds through carbene insertion by using N2=C(Ph)(CO2Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N-bound diazo adduct is a dormant species and is not en route to the formation of the copper-carbene intermediate.

Ligand adducts of bis(acetylacetonato)iron(II): a 1H NMR study.

We report here a thorough (1)H NMR study of Fe(acac)(2) solutions in a wide variety of noncoordinating and coordinating solvents, as well as the interaction of this complex with Et(3)N, pyridine, PMe(2)Ph, and R(2)PCH(2)CH(2)PR(2) [R = Ph (dppe), Et (depe)] in C(6)D(6). The study reveals that Fe(acac)(2) is readily transformed into Fe(acac)(3) in solution under aerobic conditions and that the commercial compound is usually contaminated by significant amounts of Fe(acac)(3). The (1)H NMR resonances of Fe(acac)(2) are rather solvent-dependent and quite different than those reported in the literature. The compound is unstable in CDCl(3) and stable in CD(2)Cl(2), C(6)D(6), CD(3)CN, acetone-d(6), DMSO-d(6), THF-d(8), and CD(3)OD. The addition of the above-mentioned ligands (L) reveals only one paramagnetically shifted band for each type of acac and L proton, the position of which varies with the L/Fe ratio, consistent with rapid ligand exchange equilibria on the NMR time scale. A fit of the NMR data at a high L/Fe ratio allows the calculation of the expected resonances for all protons in the Fe(acac)(2)L(2) molecules. The system with the bidentate depe ligand shows evidence for a slow ligand exchange at low depe/Fe ratios, proposed to involve a species with the cis-chelated mononuclear Fe(acac)(2)(depe) structure, whereas the fast exchange at a higher ratio is proposed to involved a trans-Fe(acac)(2)(κ(1)-depe)(2) complex. Complex Fe(acac)(2)(dppe) cannot be investigated in solution because of low solubility in a noncoordinating solvent and because of the poor dppe competition for binding in coordinating solvents. The compound was crystallized, and its X-ray structure reveals a 1-dimensional polymeric structure with dppe-bridged Fe centers having the trans-octahedral Fe(acac)(2)(κ(1)-dppe)(2) coordination environment.

Tris(1,1,1,5,5,5-hexa-fluoro-2,4-pentane-dionato-κO,O')molybdenum(III).

In the title compound, [Mo(C(5)HF(6)O(2))(3)], the unit cell is built up by three independent Mo(III) atoms located on two different threefold axes. The three independent mol-ecules are roughly identical and each Mo(III) atom is surrounded by three chelating hexa-fluoro-acetonate ligands in a three-bladed propeller-like arrangement, as observed in related compounds with acetyl-acetonate-type ligands. The structure of the title compound is very similar to the trigonal form of the Cr(III) analogue. However, the latter crystallizes in a higher-symmetry space group, Pc1. Both crystals are twinned by merohedry with the same twin law (0/010/00) in reciprocal space, but the symmetry of the Laue group in which it operates is different, to m for the title complex, and m to 6/mmm for the Cr(III) complex.

Bis(imino)quaterpyridine-bearing multimetallic late transition metal complexes as ethylene oligomerisation catalysts.

The bis(imino)quaterpyridine, 6,6'''-{(2,4,6-i-Pr(3)C(6)H(2))N=CMe}(2)-2,2':6',2'':6'',2'''-C(20)H(12)N(4) (L(tripp)), can be prepared in good yield by the condensation reaction of 6,6'''-bis(acetyl)quaterpyridine with 2,4,6-triisopropylaniline; the 2,6-diisopropylphenyl derivative 6,6'''-{(2,6-i-Pr(2)C(6)H(3))N=CMe}(2)-2,2':6',2'':6'',2'''-C(20)H(12)N(4) (L(dipp)) is also reported. Reactions of L(tripp) with 2.5 equivalents of MX(2) (MX(2) = CoCl(2), CoBr(2), (DME)(2)NiCl(2) and FeCl(2)) in n-butanol at 100 degrees C overnight results in self-assembly to form the paramagnetic salts [(L(tripp))M(2)X(3)](2)[MX(4)] [M = Co, X = Cl (1a); M = Co, X = Br (1b); M = Ni, X = Cl (2); M = Fe X = Cl (3)] in moderate yield. The molecular structures of the acetonitrile/water adducts 1a(NCMe)(2), 1b(NCMe)(OH(2)) and 2(NCMe)(4) reveal that L(tripp) acts as a bis(tridentate) ligand that can support a range of structural motifs for the cationic units including [(L(tripp))CoCl(mu-Cl)CoCl(NCMe)](+), [(L(tripp))CoBr(2)CoBr(OH(2))(NCMe)](+), [(L(tripp))CoBr(mu-Br)CoBr)](+) and [(L(tripp))NiCl(NCMe)(mu-Cl)NiCl(NCMe)](+). On activation with MAO (methylaluminoxane), 1-3 show modest activities for ethylene oligomerisation (1a/MAO approximately 1b/MAO > 2/MAO) or are inactive (3/MAO). Notably, the two cobalt systems (1a/MAO, 1b/MAO) afford highly linear alpha-olefins while the nickel system (2/MAO) yields methyl-branched waxes composed of mostly internal unsaturation along with lower levels of alpha-olefins. In addition to 1a(NCMe)(2), 1b(NCMe)(2)(OH(2)) and 2(NCMe)(3), a single crystal X-ray determination has been performed on the structurally related salt [(L(tripp))Ni(2)Br(3)(OH(2))(2)][Br] (4).

Electronic and steric ligand effects in the radical polymerization of vinyl acetate mediated by beta-ketoiminate complexes of cobalt(II).

Complexes Co[OC(Ph)CHC(Me)NAr](2) [Ar=Ph, 1; o,o'-C(6)H(3)Me(2) (Xyl), 2; p-C(6)H(4)CF(3), 3] are tested in the polymerization of vinyl acetate (VAc) initiated by V-70 (0.8 equiv) at 30 degrees C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected M(n) values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2>1>3. Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V-70/1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(beta-diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.

Radical polymerization of vinyl acetate with bis(tetramethylheptadionato)cobalt(II): coexistence of three different mechanisms.

The complex [Co(II)(tmhd)(2)] (4; tmhd = 2,2,6,6-tetramethylhepta-3,5-dionato) has been investigated as a mediator for controlled radical polymerization of vinyl acetate (VAc) and compared with the analogue [Co(II)(acac)(2)] (1; acac = acetylacetonato). A relatively well controlled process occurs, after an induction time, with 2,2'-azobis(4-methoxyl-2,4-dimethylvaleronitrile) (V-70) as radical initiator at 30 degrees C. However, whereas the polymerization essentially stops after about six initiator half-lives in the presence of 1, it continues with a first-order rate law in the presence of 4. The successful simulation of the kinetic data shows that 4 operates simultaneously by associative (degenerative transfer, DT) and dissociative (organometallic radical polymerization, OMRP) mechanisms. The occurrence of OMRP was confirmed by an independent polymerization experiment starting from an isolated and purified [Co(tmhd)(2)](PVAc) macroinitiator. The polymer molecular weight evolves linearly with conversion in accordance with the expected values for one chain per Co atom when DT is the predominant mechanism and also during the pure OMRP process; however, observation of stagnating molecular weights at long reaction times with concomitant breakdown of the first-order rate law for monomer consumption indicates a competitive chain-transfer process catalyzed by an increasing amount of Co(II). In the presence of external donors L (water, pyridine, triethylamine) the DT pathway is blocked and the OMRP pathway is accelerated, and polymerization with complex 4 is then about five times slower than with complex 1. The reversal of relative effective OMRP rate constants k(eff) (4>1 in the absence of external donors, 4<1 in their presence) is rationalized through competitive steric effects on Co(III)-C and Co(II)-L bond strengths. These propositions are supported by (1)H NMR studies and by DFT calculations.

Pd(I) phosphine carbonyl and hydride complexes implicated in the palladium-catalyzed oxo process.

Reduction of compound "Pd(bcope)(OTf)2" [bcope = (c-C8H14-1,5)PCH2CH2P(c-C8H14-1,5); OTf = O3SCF3] with H2/CO yields a mixture of Pd(I) compounds [Pd2(bcope)2(CO)2](OTf)2 (1) and [Pd2(bcope)2(mu-CO)(mu-H)](OTf) (2), whereas reduction with H2 or Ph3SiH in the absence of CO leads to [Pd3(bcope)3(mu3-H)2](OTf)2 (3). Exposure of 3 to CO leads to 1 and 2. The structures of 1 and 3 have been determined by X-ray diffraction. Complex [Pd2(bcope)2(CO)2](2+) displays a metal-metal bonded structure with a square planar environment for the Pd atoms and terminally bonded CO ligands and is fluxional in solution. DFT calculations aid the interpretation of this fluxional behavior as resulting from an intramolecular exchange of the two inequivalent P atom positions via a symmetric bis-CO-bridged intermediate. A cyclic voltammetric investigation reveals a very complex redox behavior for the "Pd(bcope)(OTf)2"/CO system and suggests possible pathways leading to the formation of the various observed products, as well as their relationship with the active species of the PdL2(2+)/CO/H2-catalyzed oxo processes (L2 = diphosphine ligands).

Mechanistic insights into the cobalt-mediated radical polymerization (CMRP) of vinyl acetate with cobalt(III) adducts as initiators.

Over the past few years, cobalt-mediated radical polymerization (CMRP) has proved efficient in controlling the radical polymerization of very reactive monomers, such as vinyl acetate (VAc). However, the reason for this success and the intimate mechanism remained basically speculative. Herein, two mechanisms are shown to coexist: the reversible termination of the growing poly(vinyl acetate) chains by the Co(acac)2 complex (acac: acetylacetonato), and a degenerative chain-transfer process. The importance of one contribution over the other strongly depends on the polymerization conditions, including complexation of cobalt by ligands, such as water and pyridine. This significant progress in the CMRP mechanism relies on the isolation and characterization of the very first cobalt adducts formed in the polymerization medium and their use as CMRP initiators. The structure proposed for these adducts was supported by DFT calculations. Beyond the control of the VAc polymerization, which is the best ever achieved by CMRP, extension to other monomers and substantial progress in macromolecular engineering are now realistic forecasts.

Sterically variable dizinc complexes bearing bis(iminopyridyl)phenolate ligands: synthesis, structures and reactivity studies.

A series of chiral dizinc complexes of the type [(2,6-{ArN=C(Me)C5H3N}2C6H3O)Zn2(micro-Cl)Cl2] [Ar=2,6-i-Pr2C6H3 (), 2,6-Me2C6H3 (), 2,4,6-Me3-C6H2 (), 2,4-Me2C6H3 ()] can be conveniently prepared in good yield by the template reaction of 2,6-{O=C(Me)C5H3N}2C6H3OH with an excess of the corresponding aniline and two equivalents of zinc dichloride in n-BuOH at elevated temperature. Alternatively, the pro-ligands, 2,6-{(ArN=C(Me)C5H3N}2C6H3OH [Ar=2,6-i-Pr2C6H3 (L1-H), 2,6-Me2C6H3 (L2-H), 2,4,6-Me3C6H2 (L3-H), 2,4-Me2C6H3 (L4-H)], can be isolated and then treated with two equivalents of zinc dichloride to afford . Interaction of with two equivalents of NaOAc in the presence of TlBF4 gives the diacetate-bridged salt [(L1)Zn2(micro-OAc)2](BF4) () while with Nadbm (dbm=dibenzoylmethanato) the bis(dbm)-chelated salt [(L1)Zn2(dbm)2](BF4) () is obtained. Hydrolysis occurs on reaction of with TlOEt to furnish [(L1)Zn2(micro-OH)Cl2] () as the only isolable product. Conversely, reaction of with Tlhp (hp=2-pyridonate) affords the neutral bis(pyridonate)-bridged trimetallic complex [(L1)Zn3(micro-hp)2Cl3] () as the major product along with as the minor one. Complex and mixtures of / act as modest activators for the ring-opening polymerisation of epsilon-caprolactone. Single crystal X-ray diffraction studies have been performed on , , , , and reveal Zn...Zn separations in the range: 3.069(4)-4.649(6) A.

Spacially confined M2 centers (M = Fe, Co, Ni, Zn) on a sterically bulky binucleating support: synthesis, structures and ethylene oligomerization studies.

Two new bulky aryl-bridged pyridyl-imine compartmental (pro)ligands, 2,6-{(2,6-i-Pr(2)C6H3)N=C(Me)C5H3N}2C6H3Y (Y = H L1, OH L2-H), have been prepared in moderate to good overall yields via a Stille-type cross-coupling approach. The molecular structure of L2-H reveals a transoid configuration within the pyridyl-imine units with a hydrogen-bonding interaction maintaining the phenol coplanar with one of the adjacent pyridine rings. The interaction of 2 equiv of MX2 with L1 in n-BuOH at 110 degrees C gives the binuclear complexes, [(L1)M2X4] (M = Fe, X = Cl (1a); M = Co, X = Cl (1b); M = Ni, X = Br (1c); M = Zn, X = Cl (1d)), in which the metal centers adopt distorted tetrahedral geometries and occupy the two pyridyl-imine cavities in L1. In contrast, deprotonation of L2-H occurs upon reaction with 2 equiv of MX2 to afford the phenolate-bridged species [(L2)M2(mu-X)X2] (M = Fe, X = Cl (2a); M = Co, X = Cl (2b); M = Ni, X = Br (2c); M = Zn, X = Cl (2d)). 1H NMR studies of diamagnetic 1d and 2d reveal that the limited rotation of the N-aryl groups in 1d is further impeded in 2d by steric interactions imparted by the two closely located N-aryl groups. Partial displacement of the bridging bromide in 2c results upon its treatment with acetonitrile to afford [(L2)Ni2Br3(NCMe)] [2c(MeCN)]; no such reaction occurs for 2a, 2b, or 2d. Upon activation with excess methylalumoxane (MAO), 1b, 1c, 2b, and 2c show some activity for alkene oligomerization forming low molecular-weight materials with methyl-branched products predominating for the nickel systems. Single-crystal X-ray diffraction studies have been performed on L2-H, 1c, 2b, 2c, 2c(NCMe), and 2d.

Mono- vs. bi-metallic assembly on a bulky bis(imino)terpyridine framework: a combined experimental and theoretical study.

The bis(imino)terpyridine ligands, 6,6''-{(2,6-i-Pr2C6H3)N=CR}2-2,2':6',2''-C15H9N3 (R = H L1, Me L2), have been prepared in high yield from the condensation reaction of the corresponding carbonyl compound with two equivalents of 2,6-diisopropylaniline. The molecular structure of L2 reveals a transoid relationship between the imino and pyridyl nitrogen groups throughout the ligand framework. Treatment of aldimine-containing L1 with one equivalent or an excess of MX2 in n-BuOH at 110 degrees C gives the mononuclear five-coordinate complexes, [(L1)MX2] (M = Fe, X = Cl 1a; M = Ni, X = Br 1b; M = Zn, X = Cl 1c), in which the metal centre occupies the terpyridine cavity and the imino groups pendant. Conversely, reaction of ketimine-containing L2 with excess MX2 in n-BuOH at 110 degrees C affords the binuclear complexes, [(L2)M2X4] (M = Fe, X = Cl 3a; M = Ni, X = Br 3b; M = Zn, X = Cl 3c), in which one metal centre occupies a bidentate pyridylimine cavity while the other a tridentate bipyridylimine cavity. 1H NMR studies on diamagnetic 3c suggests a fluxional process is operational at ambient temperature in which the central pyridine ring undergoes an exchange between metal coordination. Under less forcing conditions (room temperature in dichloromethane), the monometallic counterpart of 1b [(L2)NiBr2] (2b) has been isolated which can be converted to 3b by addition of one equivalent of (DME)NiBr2 (DME = 1,2-dimethoxyethane) in n-BuOH at 110 degrees C. Quantum mechanical calculations (DFT) have been performed on [(L1)ZnCl2] and [(L2)ZnCl2] for different monometallic conformations and show that 1a is the energetically preferred structure for L1 while there is evidence for dynamic behaviour in L2-containing species leading to bimetallic formation. Single-crystal X-ray diffraction studies have been performed on 1a, 1b, 1c, 2b, 3a, 3b(H2O) and 3c.