Triphenylphosphine-Functionalized Core-Cross-Linked Micelles and Nanogels with a Polycationic Outer Shell: Synthesis and Application in Rhodium-Catalyzed Biphasic Hydrogenations.

Unimolecular amphiphilic nanoreactors with a poly(4-vinyl-N-methylpyridinium iodide) (P4VPMe+ I- ) polycationic outer shell and two different architectures (core-cross-linked micelles, CCM, and nanogels, NG), with narrow size distributions around 130-150 nm in diameter, were synthesized by RAFT polymerization from an R0 -4VPMe+ I- 140 -b-S50 -SC(S)SPr macroRAFT agent by either chain extension with a long (300 monomer units) hydrophobic polystyrene-based block followed by cross-linking with diethylene glycol dimethacrylate (DEGDMA) for the CCM particles, or by simultaneous chain extension and cross-linking for the NG particles. A core-anchored triphenylphosphine (TPP) ligand functionality was introduced by using 4-diphenylphosphinostyrene (DPPS) as a comonomer (5-20 % mol mol-1 ) in the chain extension (for CCM) or chain extension/cross-linking (for NG) step. The products were directly obtained as stable colloidal dispersions in water (latexes). After loading with [RhCl(COD)]2 to yield [RhCl(COD)(TPP@CCM)] or [RhCl(COD)(TPP@NG)], respectively, the polymers were used as polymeric nanoreactors in Rh-catalyzed aqueous biphasic hydrogenation of the model substrates styrene and 1-octene, either neat (for styrene) or in an organic solvent (toluene or 1-nonanol). All hydrogenations were rapid (TOF up to 300 h-1 ) at 25 °C and 20 bar of H2 pressure, the biphasic mixture rapidly decanted at the end of the reaction (<2 min), the Rh loss was negligible (<0.1 ppm in the recovered organic phase), and the catalyst phase could be recycled 10 times without significant loss of catalytic activity.

Recent Representative Advances on the Synthesis and Reactivity of N-Heterocyclic-Carbene-Supported Zinc Complexes.

The present account reviews the most recent noteworthy developments on the synthesis, structure and catalytic applications of Zn-NHC species, a class of complexes that have attracted attention over the past five to ten years due to their enhanced robustness and hydrolytic stability versus classical Zn organometallics. In particular, thanks to NHC stabilization, access to unprecedented Zn species were recently achieved, including two-coordinate Zn(II) organocations and thermally stable molecularly well-defined Zn hydride species, opening the way to effective Zn-mediated hydro-silylation/-boration catalysis of various unsaturated substrates under mild conditions. The potential of NHC-Zn species for the stabilization of unprecedented Zn species and use in various catalytic applications is only emerging and the vast array of readily available NHC structures should promote future developments of the field.

Fluoroalkyl Radical Generation by Homolytic Bond Dissociation in Pentacarbonylmanganese Derivatives.

Thermal decarbonylation of the acyl compounds [Mn(CO)5 (CORF )] (RF =CF3 , CHF2 , CH2 CF3 , CF2 CH3 ) yielded the corresponding alkyl derivatives [Mn(CO)5 (RF )], some of which have not been previously reported. The compounds were fully characterized by analytical and spectroscopic methods and by several single-crystal X-ray diffraction studies. The solution-phase IR characterization in the CO stretching region, with the assistance of DFT calculations, has allowed the assignment of several weak bands to vibrations of the [Mn(12 CO)4 (eq-13 CO)(RF )] and [Mn(12 CO)4 (ax-13 CO)(RF )] isotopomers and a ranking of the RF donor power in the order CF3

Reductive Termination of Cyanoisopropyl Radicals by Copper(I) Complexes and Proton Donors: Organometallic Intermediates or Coupled Proton-Electron Transfer?

Cyanoisopropyl radicals, generated thermally by the decomposition of azobis(isobutyronitrile) (AIBN), participate in reductive radical termination (RRT) under the combined effect of copper(I) complexes and proton donors (water, methanol, triethylammonium salts) in acetonitrile or benzene. The investigated copper complexes were formed in situ from [CuI(MeCN)4]+BF4- in CD3CN or CuIBr in C6D6 using tris[2-(dimethylamino)ethyl]amine (Me6TREN), tris(2-pyridylmethyl)amine (TPMA), and 2,2'-bipyridine (BIPY) ligands. Upon keeping all other conditions constants, the impact of RRT is much greater for the Me6TREN and TPMA systems than for the BIPY system. RRT scales with the proton donor acidity (Et3NH+ ≫ H2O > CH3OH), it is reduced by deuteration (H2O > D2O and CH3OH > CD3OD), and it is more efficient in C6D6 than in CD3CN. The collective evidence gathered in this study excludes the intervention of an outer-sphere proton-coupled electron transfer (OS-PCET), while an inner-sphere PCET (IS-PCET) cannot be excluded for coordinating proton donors (water and methanol). On the other hand, the strong impact of RRT for the noncoordinating Et3NH+ in CD3CN results from the formation of an intermediate CuI-radical adduct, suggested by DFT calculations to involve binding via the N atom to yield keteniminato [L/Cu-N═C═CMe2]+ derivatives with only partial spin delocalization onto the Cu atom.

Functional Short-Bite Ligands: Synthesis, Coordination Chemistry, and Applications of N-Functionalized Bis(diaryl/dialkylphosphino)amine-type Ligands.

The aim of this review is to highlight how the diversity generated by N-substitution in the well-known short-bite ligand bis(diphenylphosphino)amine (DPPA) allows a fine-tuning of the ligand properties and offers a considerable scope for tailoring the properties and applications of their corresponding metal complexes. The various N-substituents include nitrogen-, oxygen-, phosphorus-, sulfur-, halogen-, and silicon-based functionalities and directly N-bound metals. Multiple DPPA-type ligands linked through an organic spacer and N-functionalized DRPA-type ligands, in which the PPh2 substituents are replaced by PR2 (R = alkyl, benzyl) groups, are also discussed. Owing to the considerable diversity of N-functionalized DPPA-type ligands available, the applications of their mono- and polynuclear metal complexes are very diverse and range from homogeneous catalysis with well-defined or in situ generated (pre)catalysts to heterogeneous catalysis and materials science. In particular, sustained interest for DPPA-type ligands has been motivated, at least in part, by their ability to promote selective ethylene tri- or tetramerization in combination with chromium. Ligands and metal complexes where the N-substituent is a pure hydrocarbon group (as opposed to N-functionalization) are outside the scope of this review. However, when possible, a comparison between the catalytic performances of N-functionalized systems with those of their N-substituted analogs will be provided.

Accessing Two-Coordinate ZnII Organocations by NHC Coordination: Synthesis, Structure, and Use as π-Lewis Acids in Alkene, Alkyne, and CO2 Hydrosilylation.

Discrete two-coordinate ZnII organocations of the type (NHC)Zn-R+ are reported, thanks to NHC stabilization. In preliminary reactivity studies, such entities, which are direct cationic analogues of long-known ZnR2 species, act as effective and tunable π-Lewis acid catalysts in alkene, alkyne, and CO2 hydrosilylation.

N-Heterocyclic Carbene Based Tri-organyl-Zn-Alkyl Cations: Synthesis, Structures, and Use in CO2 Functionalization.

Tri-organyl and tricoordinate N-heterocyclic carbene (NHC) Zn-NHC alkyl cations [(nNHC)2 Zn-Me]+ (nNHC=C2-bonded-IMes/-IDipp; 3+ and 4+ ; IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene, IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were first synthesized and structurally characterized by ionization of the corresponding neutral precursors [(nNHC)ZnMe2 ] with [Ph3 C][B(C6 F5 )4 ] in the presence of one equivalent of free NHC. Whereas cation [(nIMes)2 Zn-Me]+ (3+ ) is stable, its sterically congested analogue [(nIDipp)2 Zn-Me]+ (4+ ) readily undergoes an nNHC-to-aNHC isomerization in the presence of THF or IDipp to afford the more thermodynamically stable [(aIDipp)(nIDipp)Zn-Me]+ (aIDipp=C4-bonded IDipp, 5+ ), reflecting the adaptable-to-sterics coordination chemistry of these cations for improved stability. Cations 3+ -5+ are the first Zn cations of the type Zn(C)(C')(C'')+ (C, C', C''=σ-donor carbyl ligand). Kinetic studies combined with DFT calculations agree with an nNHC-to-aNHC process proceeding through the initial deprotonation of 4+ (at a Zn-bonded C4-IDipp moiety) by IDipp. Unlike 3+ and 4+ , the rearranged cation 5+ reacts with CO2 through insertion into the Zn-Me bond yielding the corresponding Zn(κ2 -OAc)+ cation 6+ . Both cations 5+ and 6+ were successfully used in CO2 hydrosilylation catalysis for silylformate formation.

Zwitterionic Cobalt Complexes with Bis(diphenylphosphino)(N-thioether)amine Assembling Ligands: Structural, EPR, Magnetic, and Computational Studies.

The coordination of two heterofunctional P,P,S ligands of the N-functionalized DPPA-type bearing an alkylthioether or arylthioether N-substituent, (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), respectively, toward cobalt dichloride was investigated to examine the influence of the linker between the PNP nitrogen and the S atoms. The complexes [CoCl2(1)]2 (3) and [CoCl2(2)]2 (4) have been isolated, and 3 was shown by X-ray diffraction to be a unique dinuclear, zwitterion containing one CoCl moiety bis-chelated by two ligands 1 and one CoCl3 fragment coordinated by the S atom of a thioether function. The FT-IR, UV-vis, and EPR spectroscopic features of 3 were analyzed as the superposition of those of constitutive fragments identified by a retrosynthetic-type analysis. A similar approach provided insight into the nature of 4 for which no X-ray diffraction data could be obtained. A comparison between the spectroscopic features of 4 and of its constitutive fragments, [CoCl(2)2]PF6 (7) and [H2']2[CoCl4] (8) (2' = NH2(p-C6H4)SMe), and between those of 4 and 3 suggested that 4 could either have a zwitterionic structure, similar to that of 3, or contain a tetrahedral dicationic bis-chelated Co center associated with a CoCl4 dianion. Magnetic and EPR studies and theoretical calculations were performed. Doublet spin states were found for the pentacoordinated complexes [CoCl(1)2]PF6 (5) and 7 and anisotropic quadruplet spin states for the tetrahedral complexes [CoCl3(H1')] (6) (1' = NH2(CH2)3SMe) and 8. A very similar behavior was observed for 3 and 4, consisting in the juxtaposition of noninteracting doublet and quadruplet spin states. Antiferromagnetic interactions explain the formation of dimers for 6 and of layers for 8. The EPR signatures of 3 and 4 correspond to the superposition of low-spin nuclei in 5 and 7 and high-spin nuclei in 6 and 8, respectively. From DFT calculations, the solid-state structure of 4 appears best described as zwitterionic, with a low-spin state for the Co1 atom.

Unsymmetrical Chelation of N-Thioether-Functionalized Bis(diphenylphosphino)amine-Type Ligands and Substituent Effects on the Nuclearity of Iron(II) Complexes: Structures, Magnetism, and Bonding.

Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), the Fe(II) complexes [FeCl2(1)]n (3), [FeCl2(2)]2 (4), [Fe(OAc)(1)2]PF6 (5), and [Fe(OAc)(2)2]PF6 (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,P-pseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the −SMe group. In both compounds, one Fe­P bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl2(SR2){R21PN(R2)P'R23}] (R = H, Me; R1, R2, and R3 = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe­P bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe­P bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra- and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.

Janus microspheres for visual assessment of molecular interconnects.

A rigid S-functionalized metalloligand is used to pair Janus Au-coated silica microspheres and the resulting assemblies are assessed with optical microscopy. New Pd complexes provide stable molecular interconnects, and the metal centre controls the structure of the linker and provides the desired rigidity, by virtue of its well-established coordination chemistry.

A mononuclear cobalt(III) carboxylate complex with a fully O-based coordination sphere: CoIII-O bond homolysis and controlled radical polymerisation from [Co(acac)2(O2CPh)].

The addition of benzoyl peroxide to [CoII(acac)2] in a 1 : 2 ratio selectively produces [CoIII(acac)2(O2CPh)], a diamagnetic (NMR) mononuclear CoIII complex with an octahedral (X-ray diffraction) coordination geometry. It is the first reported mononuclear CoIII derivative with a chelated monocarboxylate ligand and an entirely O-based coordination sphere. The compound degrades in solution quite slowly by homolytic CoIII-O2CPh bond cleavage upon warming above 40 °C to produce benzoate radicals and can serve as a unimolecular thermal initiator for the well-controlled radical polymerisation of vinyl acetate. Addition of ligands (L = py, NEt3) induces benzoate chelate ring opening and formation of both cis and trans isomers of [CoIII(acac)2(O2CPh)(L)] for L = py under kinetic control, then converting quantitatively to the cis isomer, whereas the reaction is less selective and equilibrated for L = NEt3. The py addition strengthens the CoIII-O2CPh bond and lowers the initiator efficiency in radical polymerisation, whereas the NEt3 addition results in benzoate radical quenching by a redox process. In addition to clarifying the mechanism of the radical polymerisation redox initiation by peroxides and rationalizing the quite low efficiency factor for the previously reported [CoII(acac)2]/peroxide-initiated organometallic-mediated radical polymerisation (OMRP) of vinyl acetate, this investigation provides relevant information on the CoIII-O homolytic bond cleavage process.

Acetate ion addition to and exchange in (1,5-cyclooctadiene)rhodium(I) acetate: relevance for the coagulation of carboxylic acid-functionalized shells of core-crosslinked micelle latexes.

The solution behavior of complex [Rh(COD)(µ-OAc)]2 in the absence and presence of PPN+OAc- in dichloromethane has been investigated in detail by multinuclear NMR spectroscopy. Without additional acetate ions, the compound shows dynamic behavior at room temperature, consistent with an inversion of its C2v structure. Addition of PPN+OAc- reveals an equilibrated generation of [Rh(COD)(OAc)2]-. Rapid exchange is observed at room temperature between the neutral dimer and the anionic mononuclear complex, as well as between the anionic complex and free acetate. Lowering the temperature to 213 K freezes the exchange between the two Rh complexes, but fast exchange between the anionic Rh complex and free acetate maintains coalesced Me (1H and 13C) and COO (13C) NMR resonances. DFT calculations support the experimental data and lean in favour of a dissociative mechanism for the acetate exchange in [Rh(COD)(OAc)2]-. The acetate ligands in complex [Rh(COD)(µ-OAc)]2 are also exchanged in a biphasic (water/organic) system with the methacrylic acid (MAA) functions of hydrosoluble [MMA0.5-co-PEOMA0.5]30 copolymer chains (PEOMA = poly(ethylene oxide) methyl ether methacrylate), resulting in transfer of the Rh complex to the aqueous phase. Exchange with the MAA functions in the same polymer equally takes place for the chloride ligands of [Rh(COD)(µ-Cl)]2. The latter phenomenon rationalizes the coagulation of a core-crosslinked micelle (CCM) latex, where MMA functions are present on the hydrophilic CCM shell, when a dichloromethane solution of [Rh(COD)(µ-Cl)]2 is added.

Phosphine-Functionalized Core-Crosslinked Micelles and Nanogels with an Anionic Poly(styrenesulfonate) Shell: Synthesis, Rhodium(I) Coordination and Aqueous Biphasic Hydrogenation Catalysis.

Stable latexes containing unimolecular amphiphilic core-shell star-block polymers with a triphenylphosphine(TPP)-functionalized hydrophobic core and an outer hydrophilic shell based on anionic styrenesulfonate monomers have been synthesized in a convergent three-step strategy by reversible addition-fragmentation chain-transfer (RAFT) polymerization, loaded with [RhCl(COD)]2 and applied to the aqueous biphasic hydrogenation of styrene. When the outer shell contains sodium styrenesulfonate homopolymer blocks, treatment with a toluene solution of [RhCl(COD)]2 led to undesired polymer coagulation. Investigation of the interactions of [RhCl(COD)]2 and [RhCl(COD)(PPh3)] with smaller structural models of the polymer shell functions, namely sodium p-toluenesulfonate, sodium styrenesulfonate, and a poly(sodium styrenesulfonate) homopolymer in a biphasic toluene/water medium points to the presence of equilibrated Rh-sulfonate interactions as the cause of coagulation by inter-particle cross-linking. Modification of the hydrophilic shell to a statistical copolymer of sodium styrenesulfonate and poly(ethylene oxide) methyl ether methacrylate (PEOMA) in a 20:80 ratio allowed particle loading with the generation of core-anchored [RhCl(COD)TPP] complexes. These Rh-loaded latexes efficiently catalyze the aqueous biphasic hydrogenation of neat styrene as a benchmark reaction. The catalytic phase could be recovered and recycled, although the performances in terms of catalyst leaching and activity evolution during recycles are inferior to those of equivalent nanoreactors based on neutral or polycationic outer shells.

Rhodium nanoparticles inside well-defined unimolecular amphiphilic polymeric nanoreactors: synthesis and biphasic hydrogenation catalysis.

Rhodium nanoparticles (Rh NPs) embedded in different amphiphilic core-crosslinked micelle (CCM) latexes (RhNP@CCM) have been synthesized by [RhCl(COD)(TPP@CCM)] reduction with H2 (TPP@CCM = core-anchored triphenylphosphine). The reduction rate depends on temperature, on the presence of base (NEt3) and on the P/Rh ratio. For CCMs with outer shells made of neutral P(MAA-co-PEOMA) copolymer chains (RhNP@CCM-N), the core-generated Rh NPs tend to migrate toward the hydrophilic shell and to agglomerate depending on the P/Rh ratio and core TPP density, whereas the MAA protonation state has a negligible effect. Conversely, CCMs with outer shells made of polycationic P(4VPMe+I-) chains (RhNP@CCM-C) maintain core-confined and well dispersed Rh NPs. All RhNP@CCMs were used as catalytic nanoreactors under aqueous biphasic conditions for acetophenone, styrene and 1-octene hydrogenation. Styrene was efficiently hydrogenated by all systems with high selectivity for vinyl reduction. For acetophenone, competition between benzene ring and carbonyl reduction was observed as well as a limited access to the catalytic sites when using CCM-C. Neat 1-octene was also converted, but the activity increased when the substrate was diluted in 1-nonanol, which is a better core-swelling solvent. Whereas the molecular RhI center was more active than the Rh0 NPs in 1-octene hydrogenation, the opposite trend was observed for styrene hydrogenation. Although Rh NP migration and agglomeration occurred for RhNP@CCM-N, even at high P/Rh, the NPs remained core-confined for RhNP@CCM-C, but only when toluene rather than diethyl ether was used for product extraction before recycling.

Fluoroalkyl Pentacarbonylmanganese(I) Complexes as Initiators for the Radical (co)Polymerization of Fluoromonomers.

The use of [Mn(RF)(CO)5] (RF = CF3, CHF2, CH2CF3, COCF2CH3) to initiate the radical polymerization of vinylidene fluoride (F2C=CH2, VDF) and the radical alternating copolymerization of vinyl acetate (CH2=CHOOCCH3, VAc) with tert-butyl 2-(trifluoromethyl)acrylate (MAF-TBE) by generating primary RF• radicals is presented. Three different initiating methods with [Mn(CF3)(CO)5] (thermal at ca. 100 °C, visible light and UV irradiations) are described and compared. Fair (60%) to satisfactory (74%) polyvinylidene fluoride (PVDF) yields were obtained from the visible light and UV activations, respectively. Molar masses of PVDF reaching 53,000 g·mol-1 were produced from the visible light initiation after 4 h. However, the use of [Mn(CHF2)(CO)5] and [Mn(CH2CF3)(CO)5] as radical initiators produced PVDF in a very low yield (0 to 7%) by both thermal and photochemical initiations, while [Mn(COCF2CH3)(CO)5] led to the formation of PVDF in a moderate yield (7% to 23%). Nevertheless, complexes [Mn(CH2CF3)(CO)5] and [Mn(COCHF2)(CO)5] efficiently initiated the alternating VAc/MAF-TBE copolymerization. All synthesized polymers were characterized by 1H and 19F NMR spectroscopy, which proves the formation of the expected PVDF or poly(VAc-alt-MAF-TBE) and showing the chaining defects and the end-groups in the case of PVDF. The kinetics of VDF homopolymerization showed a linear ln[M]0/[M] versus time relationship, but a decrease of molar masses vs. VDF conversion was noted in all cases, which shows the absence of control. These PVDFs were rather thermally stable in air (up to 410 °C), especially for those having the highest molar masses. The melting points ranged from 164 to 175 °C while the degree of crystallinity varied from 44% to 53%.

Crystal structure of penta-carbon-yl(2,2-di-fluoro-propane-thio-ato-κS)manganese(I).

The title compound, [Mn{SC(O)CF2CH3}(CO)5], has been isolated as a by-product during the reaction of K[Mn(CO)5] with CH3CF2COCl. It is built up from a di-fluoro-methyl-propane-thio-ate bonded to an Mn(CO)5 moiety through the S atom. The Mn atom has an almost perfect octa-hedral coordination sphere. It is one of the rare examples of compounds containing the (CO)5MnS-C fragment. In the crystal, the methyl group occupies a pocket surrounded by the O atoms of three carbonyl groups of the Mn(CO)5 moiety; however, the H⋯O distances are rather long. These inter-actions lead to the formation of layers lying parallel to (101), which enclose R 4 4(15) and R 4 4(16) ring motifs. The CF2 group is disordered over two sets of sites with occupancies of 0.849 (3) and 0.151 (3).

Mono- and polynuclear Ag(i) complexes of N-functionalized bis(diphenylphosphino)amine DPPA-type ligands: synthesis, solid-state structures and reactivity.

The reactivity of the N-functionalized DPPA-type ligands (Ph2P)2N(p-Z)C6H4 [Z = H (1a), SMe (1b), OMe (1c)] with AgBF4 was investigated and revealed an unexpected influence of the para substituent Z of the N-aryl ligand. In acetone, the mononuclear bis-chelated [Ag{(1a-1c)-P,P}2]BF4 (2a·BF4-2c·BF4) and dinuclear bridged [Ag2{µ2-(1a-1c)-P,P}2](BF4)2 [3a·(BF4)2-3c·(BF4)2] complexes were obtained with a 1 : 2 and 1 : 1 AgBF4/ligand molar ratio, respectively. While the molecular structures of 2a·BF4 and 2b·BF4 determined in the solid-state by X-ray diffraction revealed their mononuclear nature and the absence of cation/anion interaction, complexes 3b·(BF4)2 and 3c·(BF4)2 form 2D coordination polymers through intermolecular Ag-S or Ag-O interactions, respectively, involving the N-function of the respective DPPA-type ligand, and display direct interactions between one BF4 anion and both Ag(i) cations. Surprisingly, the equimolar reaction between ligands 1a-1c and AgBF4 in CH2Cl2 led to different proportions of the dinuclear complexes 3a·(BF4)2-3c·(BF4)2 and clusters [Ag3(µ3-Cl)2{µ2-(1b-1c)-P,P}3]BF4 (4b·BF4-4c·BF4), depending on the nature of the para substituent Z of the N-aryl ligand. The trinuclear complexes resulted from C-Cl bond activation of the chlorinated solvent and were characterized by NMR spectroscopy and X-ray diffraction, and could be selectively produced by addition of 2/3 equiv. of [NMe4]Cl to the corresponding dinuclear complexes or by a one-pot procedure involving the correct amount of each reagent. A series of experiments and kinetic NMR investigations were performed to gain further insight into the formation of the trinuclear Ag3Cl2 core clusters.

Catalyzed Chain Transfer in Vinyl Acetate Polymerization Mediated by 9-Oxyphenalenone Cobalt(II) Complexes.

The vinyl acetate (VAc) radical polymerization initiated by V-70 at 30 °C in the presence of [CoII(OPN)2] (OPN = deprotonated 9-oxyphenalenone), 1, leads to PVAc of lower molecular weight (MW) than expected for organometallic-mediated radical polymerization (OMRP), whether reversible termination or degenerate transfer conditions are used. This represents the first clear evidence of catalyzed chain transfer (CCT) in VAc polymerization. The bis-pyridine adduct [CoII(OPN)2(py)2], 2, shows a marginally lower polymerization rate and an increased CCT activity relative to 1, whereas the activity decreases with marginal effect on the polymerization rate upon addition of excess py. However, raising the temperature to 80 °C (with AIBN as initiator) led to a low MW polymer even in the presence of a large py excess. The CCT was confirmed by 1H NMR characterization of the chain ends and by a MALDI-TOF MS analysis of the recovered polymer. The collective trends are consistent with greater CCT activity for the 5-coordinate complex [CoII(OPN)2(py)] relative to 1 and 2. The presence of py association/dissociation equilibria relating these three complexes was confirmed by a 1H NMR investigation.

Mononuclear salen-gallium complexes for iso-selective ring-opening polymerization (ROP) of rac-lactide.

A series of mononuclear salen-supported gallium amido/alkoxide derivatives were prepared and structurally characterized and subsequently used as initiators in rac-lactide ring-opening polymerisation (ROP). The reaction of variously substituted salen ligands (1a-1f) with 0.5 equiv. of Ga2(NMe2)6 allowed the isolation of the corresponding (salen)Ga-NMe2 chelates (2b-2d, 2f) via an amine elimination route, as poorly soluble compounds in common solvents. The (salen)Ga-OBn derivatives (3a-3e) may be readily accessed by an amine-elimination/alcoholysis sequence and the molecular structures of 3a, 3d and 3e were confirmed through X-ray crystallography diffraction analysis. The present (salen)Ga-X species may effectively mediate the iso-selective ROP of rac-LA in a controlled manner (Pm up to 0.77 using a 1/1 2f/BnOH mixture as ROP initiator), with a ROP activity greatly dependent upon steric hindrance and geometrical constraints imposed by the variously substituted salen ligands. Based on the present study, salen ligands with limited steric hindrance and a certain degree of flexibility appear best suited for iso-selective ROP by (salen)Ga chelates. The salen-gallium complex 3a is also effective for the controlled ROP of ε-caprolactone (CL) and the production of PCL-b-PLA copolymers.