Micellar catalysis: Polymer bound palladium catalyst for carbon-carbon coupling reactions in water.

Metallosurfactants, defined here as hydrophobic metal-containing groups embedded in hydrophilic units when dispersed in water, emanate in the formation of metallomicelles. This approach continues to attract great interest for its ability to serve as micellar catalysts for various metal-mediated chemical transformations in water. Indeed, relevant to green chemistry, micellar catalysis plays a preeminent function as a replacement for organic solvents in a variety of chemical reactions. There are several methods for the interaction of metal complexes (catalysts or catalyst precursors) and surfactants for producing micellar aggregates. A very effective manner for achieving this involves the direct bonding of the metal center to the amphiphilic polymeric materials. Herein, we describe the synthesis of a metallosurfactant containing a palladium complex covalently incorporated into a CO2-based triblock polycarbonate derived using a dicarboxylic acid chain-transfer agent. This amphiphilic polycarbonate was shown to self-assemble in water to provide uniform and spherical micelles, where the catalytic metal center is located in the hydrophobic portion of the micelle. The resulting metallosurfactant was demonstrated to effectively catalyze carbon-carbon coupling reactions at very low catalyst loadings.

Structural Metamorphoses of d-Xylose Oxetane- and Carbonyl Sulfide-Based Polymers In Situ during Ring-Opening Copolymerizations.

Polymers constructed from copolymerizations of carbohydrates with C1 feedstocks are promising targets that provide transformation of sustainably sourced building blocks into next-generation, environmentally degradable plastic materials. In this work, the initial intention was to expand beyond polycarbonates prepared by the copolymerization of oxetanes derived from d-xylose with CO2 and incorporate sulfur atoms through the establishment of monothiocarbonates that would provide the ability to modulate the backbone compositions and result in unique effects upon the chemical, physical, and mechanical properties. Therefore, the syntheses of poly(1,2-O-isopropylidene-α-d-xylofuranose monothiocarbonate)s were investigated by ring-opening copolymerizations of 3,5-anhydro-1,2-O-isopropylidene-α-d-xylofuranose with carbonyl sulfide (COS) facilitated by (salen)CrCl/cocatalyst systems. Unexpectedly, when copolymerization temperatures exceeded 40 °C, oxygen/sulfur exchange reactions occurred, causing in situ dynamic backbone restructuring through a series of inter-related and complex mechanistic pathways that transformed monothiocarbonate monomeric repeating units into carbonate and thioether dimeric repeating units. These backbone structural compositional transformations were investigated through a combination of Fourier transform infrared and nuclear magnetic resonance spectroscopic techniques and were demonstrated to be easily tuned via temperature and catalyst/cocatalyst stoichiometries. Furthermore, the regiochemistries of these d-xylose-based sulfur-containing polymers revealed that monothiocarbonate monomeric repeating units had a head-to-tail connectivity, while the carbonate and thioether dimeric repeating units had dual head-to-head and tail-to-tail connectivities. These sulfur-containing polymers exhibited enhanced thermal stabilities compared to their oxygen-containing polycarbonate analogues and revealed variations in the effects upon glass transition temperatures, demonstrating the effect of sulfur incorporation in the polymer backbone. These findings contribute to the advancement of sustainable polymer production by using feedstocks of natural origin coupled with COS.

Enabling New Approaches: Recent Advances in Processing Aliphatic Polycarbonate-Based Materials.

Aliphatic polycarbonates (aPCs) have become increasingly popular as functional materials due to their biocompatibility and capacity for on-demand degradation. Advances in polymerization techniques and the introduction of new functional monomers have expanded the library of aPCs available, offering a diverse range of chemical compositions and structures. To accommodate the emerging requirements of new applications in biomedical and energy-related fields, various manufacturing techniques have been adopted for processing aPC-based materials. However, a summary of these techniques has yet to be conducted. The aim of this paper is to enrich the toolbox available to researchers, enabling them to select the most suitable technique for their materials. In this paper, a concise review of the recent progress in processing techniques, including controlled self-assembly, electrospinning, additive manufacturing, and other techniques, is presented. We also highlight the specific challenges and opportunities for the sustainable growth of this research area and the successful integration of aPCs in industrial applications.

Chirality-Guided Isomerization of Mn2S2 Diamond Core Complexes: A Mechanistic Study.

Occasioned by the discovery of a ligand transfer from M(N2S2) to MnI in Mn(CO)5Br, the resulting H2N2S2 ligand-tethered dimanganese complex, (µ4-N,N'-ethylenebis(mercaptoacetamide))[Mn2(CO)6], was found to have myriad analogues of the type (µ-S-E)2[Mn2(CO)6], making up an under-studied class containing Mn2S2 rhombs. The attempt to synthesize a nontethered version resulted in a solid-state structure in an anti-conformation. However, a direct comparison of the Fourier-transform infrared spectra of the tethered versus nontethered complexes in combination with theoretical frequency calculation suggested the coexistence of syn- and anti-isomers and their interconversion in solution. Analysis of the syn- versus anti-version of the dimanganese components led to the understanding that whereas the anti-form exists as centrosymmetric RS isomers, the syn-form is restricted by C2 symmetry to be either RR or SS. Molecular scrambling experiments indicated monomeric, pentacoordinate, 16-e- (S-O)Mn(CO)3 intermediates with lifetimes sufficiently long to sample R and S monomers. Density functional theory analysis of the mechanistic pathway and a kinetic study corroborated that the proposed isomerization involves the cleavage and reformation of the dimeric structures.

Kinetic and Computational Analysis of CO Substitution in a Dinuclear Osmium Carbonyl Complex: Intersection between Dissociative and Dissociative-Interchange Mechanisms.

The mechanism for the CO substitution reaction involving the diosmium carbonyl sawhorse complex Os2(µ-O2CH)2(CO)6, which contains an Os-Os single bond, two axial CO ligands, and four equatorial CO ligands, was investigated experimentally and theoretically. Kinetic measurements show 13CO axial substitution proceeding by a dissociative reaction that is first-order in the complex and zero-order in 13CO but with an unexpectedly negative entropy of activation. The corresponding electronic structure calculations yield an enthalpy of activation for axial CO dissociation that is much larger than that determined by the kinetic experiments, but in agreement with the complex's stability with respect to CO loss. Additional calculations yield a dissociative interchange transition state whose free energy, enthalpy, and entropy of activation are in good agreement with those obtained from the kinetic measurements for the apparently dissociative substitution. These results point to an exchange reaction mechanism that is surprisingly close to the poorly understood transition from a dissociative mechanism with a CO-loss intermediate to a dissociative interchange mechanism with a transition state involving both the entering and the leaving COs. The key to explain these findings is provided by the vibrational analysis, which shows very low energy wagging motions for the axial COs. Thus, the incoming CO only displaces the outgoing CO when the complex has an outgoing CO near the wag's turning point. This dissociative interchange mechanism predicted by the calculation explains the unexpected combination of kinetics and stability characteristics. Kinetics reveals that the reaction is first-order in the Os dimer with a negative Eyring entropy, while a stability study shows that the Os dimer's decomposition rate is several orders of magnitude slower than CO exchange.

Amphiphilic Polycarbonate Micellar Rhenium Catalysts for Efficient Photocatalytic CO2 Reduction in Aqueous Media.

A triblock amphiphilic polymer derived from the copolymerization of CO2 and epoxides containing a bipyridine rhenium complex in its backbone is shown to effectively catalyze the visible-light-driven reduction of CO2 to CO. This polymer provides uniformly spherical micelles in aqueous solution, where the metal catalyst is sequestered in the hydrophobic portion of the nanostructured micelle. CO2 to CO reduction occurs in an efficient visible-light-driven process in aqueous media with turnover numbers up to 110 (>99 % selectivity) in the absence of a photosensitizer, which is a 37-fold enhancement over the corresponding molecular rhenium catalyst in organic solvent. Notably, the amphiphilic polycarbonate micelle rhenium catalyst suppresses H2 generation, presumably by preventing deactivation of the active catalytic center by water.

3D Printed CO2 -Based Triblock Copolymers and Post-Printing Modification.

We report the facile synthesis and 3D printing of a series of triblock copolymers consisting of soft and hard blocks and demonstrate that alkene pendant groups of the hard block can be covalently modified. The polymers are prepared using a salenCo(III)TFA/PPNTFA binary catalyst system and 1,2-propanediol as a chain transfer agent, providing an efficient one-pot, two-step strategy to tailor polymer thermal and mechanical properties. Thixotropic inks suitable for direct ink write printing were formulated by dissolving the block copolymers in organic solvent and dispersing NaCl particles. After printing, porous structures were produced by removing solvent and NaCl with water to give printed structures with surfaces that could be modified via UV-initiated thiol-ene click reactions. Alternatively, a tetra-thiol could be incorporated into the ink and used for cross-linking to give objects with high solvent resistance and selective degradability.

TEMPO Containing Radical Polymonothiocarbonate Polymers with Regio- and Stereo-Regularities: Synthesis, Characterization, and Electrical Conductivity Studies.

We report the synthesis of a (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl) (TEMPO) appended polymonothiocarbonates through the ring-opening copolymerization of (4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (GTEMPO) in the presence of carbonyl sulfide under ambient conditions. We have prepared the atactic and isotactic versions of this polymer, using enantiopure R or S forms of the GTEMPO monomer in the latter instances. Cyclic voltammetry studies revealed both oxidation and reduction events that were characteristic of TEMPO radicals. Electrical conductivity of these polymers was measured as solid-state films after annealing the samples above their glass transition temperatures. At room temperature the isotactic polymer shows much greater conductivity (ca. 10-4  S cm-1 ) than the atactic (ca. 10-7  S cm-1 ), attributed to the well-defined stereochemistry and regulated charge transport pathway of isotactic polymer chains in contrast to the irregular structure of the atactic counterpart.

Randomly Distributed Sulfur Atoms in the Main Chains of CO2 -Based Polycarbonates: Enhanced Optical Properties.

Polymeric materials possessing both high refractive indices and high Abbe numbers are much in demand for the development of advanced optical devices. However, the synthesis of such functional materials is a challenge because of the trade-off between these two properties. Herein, a synthetic strategy is presented for enhancing the optical properties of CO2 -based polycarbonates by modifying the polymer's topological structure. Terpolymers with thiocarbonate and carbonate units randomly distributed in the polymers' main chain were synthesized via the terpolymerization of cyclohexene oxide with a mixture of CO2 and COS in the presence of metal catalysts, most notably a dinuclear aluminum complex. DFT calculations were employed to explain why different structural sequence were obtained with distinct bimetallic catalysts. Varying the CO2 pressure made it possible to obtain terpolymers with tunable carbonate linkages in the polymer chain. More importantly, optical property studies revealed that terpolymers with comparable thiocarbonate and carbonate units exhibited a refractive index of 1.501 with an enhanced Abbe number as high as 48.6, much higher than the corresponding polycarbonates or polythiocarbonates. Additionally, all terpolymers containing varying thiocarbonate content displayed good thermal properties with Tg >109 °C and Td >260 °C, suggesting little loss in the thermal stability compared to the polycarbonate. Hence, modification of the topological structure of the polycarbonate is an efficient method of obtaining polymeric materials with enhanced optical properties without compromising thermal performance.

Synthetic Metallodithiolato Ligands as Pendant Bases in [FeIFeI], [FeI[Fe(NO)]II], and [(µ-H)FeIIFeII] Complexes.

The development of ligands with specific stereo- and electrochemical requirements that are necessary for catalyst design challenges synthetic chemists in academia and industry. The crucial aza-dithiolate linker in the active site of [FeFe]-H2ase has inspired the development of synthetic analogues that utilize ligands which serve as conventional σ donors with pendant base features for H+ binding and delivery. Several MN2S2 complexes (M = Ni2+, [Fe(NO)]2+, [Co(NO)]2+, etc.) utilize these cis-dithiolates to bind low valent metals and also demonstrate the useful property of hemilability, i.e., alternate between bi- and monodentate ligation. Herein, synthetic efforts have led to the isolation and characterization of three heterotrimetallics that employ metallodithiolato ligand binding to di-iron scaffolds in three redox levels, (µ-pdt)[Fe(CO)3]2, (µ-pdt)[Fe(CO)3][(Fe(NO))II(IMe)(CO)]+, and (µ-pdt)(µ-H)[FeII(CO)2(PMe3)]2+ to generate (µ-pdt)[(FeI(CO)3][FeI(CO)2·NiN2S2] (1), (µ-pdt)[FeI(CO)3][(Fe(NO))II(IMe)(CO)]+ (2), and (µ-pdt)(µ-H)[FeII(CO)2(PMe3)][FeII(CO)(PMe3)·NiN2S2]+ (3) complexes (pdt = 1,3-propanedithiolate, IMe = 1,3-dimethylimidazole-2-ylidene, NiN2S2 = [N,N'-bis(2-mercaptidoethyl)-1,4-diazacycloheptane] nickel(II)). These complexes display efficient metallodithiolato binding to the di-iron scaffold with one thiolate-S, which allows the free unbound thiolate to potentially serve as a built-in pendant base to direct proton binding, promoting a possible Fe-H-···+H-S coupling mechanism for the electrocatalytic hydrogen evolution reaction (HER) in the presence of acids. Ligand substitution studies on 1 indicate an associative/dissociative type reaction mechanism for the replacement of the NiN2S2 ligand, providing insight into the Fe-S bond strength.

Metal-Templated, Tight Loop Conformation of a Cys-X-Cys Biomimetic Assembles a Dimanganese Complex.

With the goal of generating anionic analogues to MN2 S2 ⋅Mn(CO)3 Br we introduced metallodithiolate ligands, MN2 S22- prepared from the Cys-X-Cys biomimetic, ema4- ligand (ema=N,N'-ethylenebis(mercaptoacetamide); M=NiII , [VIV ≡O]2+ and FeIII ) to Mn(CO)5 Br. An unexpected, remarkably stable dimanganese product, (H2 N2 (CH2 C=O(µ-S))2 )[Mn(CO)3 ]2 resulted from loss of M originally residing in the N2 S24- pocket, replaced by protonation at the amido nitrogens, generating H2 ema2- . Accordingly, the ema ligand has switched its coordination mode from an N2 S24- cavity holding a single metal, to a binucleating H2 ema2- with bridging sulfurs and carboxamide oxygens within Mn-µ-S-CH2 -C-O, 5-membered rings. In situ metal-templating by zinc ions gives quantitative yields of the Mn2 product. By computational studies we compared the conformations of "linear" ema4- to ema4- frozen in the "tight-loop" around single metals, and to the "looser" fold possible for H2 ema2- that is the optimal arrangement for binucleation. XRD molecular structures show extensive H-bonding at the amido-nitrogen protons in the solid state.

Facile Synthesis of Well-Defined Branched Sulfur-Containing Copolymers: One-Pot Copolymerization of Carbonyl Sulfide and Epoxide.

Topological polymers possess many advantages over linear polymers. However, when it comes to the poly(monothiocarbonate)s, no topological polymers have been reported. Described herein is a facile and efficient approach for synthesizing well-defined branched poly(monothiocarbonate)s in a "grafting through" manner by copolymerizing carbonyl sulfide (COS) with epichlorohydrin (ECH), where the side-chain forms in situ. The lengths of the side-chains are tunable based on reaction temperatures. More importantly, enhancement in thermal properties of the branched copolymer was observed, as the Tg  value increased by 22 °C, compared to the linear analogues. When chiral ECH was utilized, semicrystalline branched poly(monothiocarbonate)s were accessible with a Tm  value of 112 °C, which is 40 °C higher than that of the corresponding linear poly(monothiocarbonate)s. The strategy presented herein for synthesizing branched polymers provides efficient and concise access to topological polymers.

Cyanide Docking and Linkage Isomerism in Models for the Artificial [FeFe]-Hydrogenase Maturation Process.

Linkage isomerization of the cyanide on the [2Fe] subsite of the [FeFe]-H2ase active site was reported to occur during the docking of various synthetic diiron complexes onto a carrier protein, apo-HydF, as the initial step for the artificial maturation of the [FeFe]-H2ase enzyme (Berggren et al., Nature, 2013, 499, 66-70). An investigation of our triiron organometallic models (FeFe-CN/NC-Fe') revealed that, once a Fe-CN-Fe connection is formed, high barriers prevent such cyanide linkage isomerization ( Chem. Sci., 2016, 7, 3710-3719). To explore effects of variable oxidation states of the receiver unit, we introduce copper(I/II) fragments, precedented in Holm's models of cytochrome c oxidase to induce cyanide isomerization (Cu-CN/NC-Fe), to the diiron synthetic analogues of [FeFe]-H2ase. For comparison, a zinc variant of the cytochrome c oxidase model is also examined. According to the oxidation state of copper, a cyanide flip was induced during the formation of both Zn-NC-Cu and FeFe-CN-Cu complexes. Density functional theory calculations are used to predict the mechanisms for such linkage isomerization and account for optimal conditions including oxidation states of metals, spin states, and solvation. These results on synthetic paradigms imply a role for oxidation state control of cyanide isomerization during hydrogenase active site assembly.

Directed Self-Assembly of Polystyrene-b-poly(propylene carbonate) on Chemical Patterns via Thermal Annealing for Next Generation Lithography.

Directed self-assembly (DSA) of block copolymers (BCPs) combines advantages of conventional photolithography and polymeric materials and shows competence in semiconductors and data storage applications. Driven by the more integrated, much smaller and higher performance of the electronics, however, the industry standard polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) in DSA strategy cannot meet the rapid development of lithography technology because its intrinsic limited Flory-Huggins interaction parameter (χ). Despite hundreds of block copolymers have been developed, these BCPs systems are usually subject to a trade-off between high χ and thermal treatment, resulting in incompatibility with the current nanomanufacturing fab processes. Here we discover that polystyrene-b-poly(propylene carbonate) (PS-b-PPC) is well qualified to fill key positions on DSA strategy for the next-generation lithography. The estimated χ-value for PS-b-PPC is 0.079, that is, two times greater than PS-b-PMMA (χ = 0.029 at 150 °C), while processing the ability to form perpendicular sub-10 nm morphologies (cylinder and lamellae) via the industry preferred thermal-treatment. DSA of lamellae forming PS-b-PPC on chemoepitaxial density multiplication demonstrates successful sub-10 nm long-range order features on large-area patterning for nanofabrication. Pattern transfer to the silicon substrate through industrial sequential infiltration synthesis is also implemented successfully. Compared with the previously reported methods to orientation control BCPs with high χ-value (including solvent annealing, neutral top-coats, and chemical modification), the easy preparation, high χ value, and etch selectivity while enduring thermal treatment demonstrates PS-b-PPC as a rare and valuable candidate for advancing the field of nanolithography.

Poly(monothiocarbonate)s from the Alternating and Regioselective Copolymerization of Carbonyl Sulfide with Epoxides.

Carbonyl sulfide (COS) is an air pollutant that causes acid rain, ozonosphere damage, and carbon dioxide (CO2) generation. It is a heterocumulene and structural analogue of CO2. Relevant to organic synthesis, it is a source of C═O or C═S groups and thus an ideal one-carbon (C1) building block for synthesizing sulfur-containing polymers through the similar route of CO2 copolymerization. In contrast, traditional synthesis of sulfur-containing polymers often involves the condensation of thiols with phosgene and ring-opening polymerization of cyclic thiocarbonates that are generally derived from thiols and phosgene; thus, COS/epoxide copolymerization is a "greener" route to supplement or supplant current processes for the production of sulfur-containing polymers. This Accounts highlights our efforts on the discovery of the selective formation of poly(monothiocarbonate)s from COS with epoxides via heterogeneous zinc-cobalt double metal cyanide complex (Zn-Co(III) DMCC) and homogeneous (salen)CrX complexes. The catalytic activity and selectivity of Zn-Co(III) DMCC for COS/epoxide copolymerization are similar to those for CO2/epoxide copolymerization. (salen)CrX complexes accompanied by onium salts exhibited high activity and selectivity for COS/epoxide copolymerization under mild conditions, affording copolymers with >99% monothiocarbonate units and high tail-to-head content up to 99%. By way of contrast, these catalysts often show moderate or low activity for CO2/epoxide copolymerization. Of note, a specialty of COS/epoxide copolymerization is the occurrence of an oxygen-sulfur exchange reaction (O/S ER), which may produce carbonate and dithiocarbonate units. O/S ER, which are induced by the metal-OH bond regenerated by chain transfer reactions, can be kinetically inhibited by changing the reaction conditions. We provide a thorough mechanistic understanding of the electronic/steric effect of the catalysts on the regioselectivity of COS copolymerization. The regioselectivity of the copolymerization originates from the solely nucleophilic attack of the sulfur anion to methylene of the epoxide, and thus, the chiral configuration of the monosubstituted epoxides is retained. COS-based copolymers are highly transparent sulfur-containing polymers with excellent optical properties, such as high refractive index and Abbe number. Thanks to their good solubility and many available epoxides, COS/epoxide copolymers can potentially be a new applicable optical material. Very recently, crystalline COS-based polymers with or without chiral carbons have been synthesized, which may further expand the scope of application of these new materials.

Perfectly Alternating and Regioselective Copolymerization of Carbonyl Sulfide and Epoxides by Metal-Free Lewis Pairs.

The preparation of perfectly alternating and regioslective copolymers derived from the copolymerization of carbonyl sulfide (COS) and epoxides by metal-free Lewis pair catalysts composed of a Lewis base (amidine, guanidine, or quaternary onium salts) and a Lewis acid (triethyl borane) is described. Colorless and highly transparent copolymers of poly(monothiocarbonate) were successfully obtained with over 99 % tail-to-head content and high molecular weight (up to 92.5 kg mol-1 ). In most instances, oxygen-sulfur exchange reactions (O/S ERs), which would generate random thiocarbonate and carbonate units, were effectively suppressed. The turnover frequencies (TOF) of these Lewis pair catalyzed processes were as high as 119 h-1 at ambient temperature.

Environmentally Benign CO2-Based Copolymers: Degradable Polycarbonates Derived from Dihydroxybutyric Acid and Their Platinum-Polymer Conjugates.

(S)-3,4-Dihydroxybutyric acid ((S)-3,4-DHBA), an endogenous straight chain fatty acid, is a normal human urinary metabolite and can be obtained as a valuable chiral biomass for synthesizing statin-class drugs. Hence, its epoxide derivatives should serve as promising monomers for producing biocompatible polymers via alternating copolymerization with carbon dioxide. In this report, we demonstrate the production of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) from racemic-tert-butyl 3,4-epoxybutanoate (rac-(t)Bu 3,4-EB) and CO2 using bifunctional cobalt(III) salen catalysts. The copolymer exhibited greater than 99% carbonate linkages, 100% head-to-tail regioselectivity, and a glass-transition temperature (Tg) of 37 °C. By way of comparison, the similarly derived polycarbonate from the sterically less congested monomer, methyl 3,4-epoxybutanoate, displayed 91.8% head-to-tail content and a lower Tg of 18 °C. The tert-butyl protecting group of the pendant carboxylate group was removed using trifluoroacetic acid to afford poly(3,4-dihydroxybutyric acid carbonate). Depolymerization of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) in the presence of strong base results in a stepwise unzipping of the polymer chain to yield the corresponding cyclic carbonate. Furthermore, the full degradation of the acetyl-capped poly(potassium 3,4-dihydroxybutyrate carbonate) resulted in formation of the biomasses, ß-hydroxy-γ-butyrolacetone and 3,4-dihydroxybutyrate, in water (pH = 8) at 37 °C. In addition, water-soluble platinum-polymer conjugates were synthesized with platinum loading of 21.3-29.5%, suggesting poly(3,4-dihydroxybutyric acid carbonate) and related derivatives may serve as platinum drug delivery carriers.

Construction of Versatile and Functional Nanostructures Derived from CO2 -based Polycarbonates.

The construction of amphiphilic polycarbonates through epoxides/CO2 coupling is a challenging aim to provide more diverse CO2 -based functional materials. In this report, we demonstrate the facile preparation of diverse and functional nanoparticles derived from a CO2 -based triblock polycarbonate system. By the judicious use of water as chain-transfer reagent in the propylene oxide/CO2 polymerization, poly(propylene carbonate (PPC) diols are successfully produced and serve as macroinitiators in the subsequent allyl glycidyl ether/CO2 coupling reaction. The resulting ABA triblock polycarbonate can be further functionalized with various thiols by radical mediated thiol-ene click chemistry, followed by self-assembly in deionized water to construct a versatile and functional nanostructure system. This class of amphiphilic polycarbonates could embody a powerful platform for biomedical applications.

Thermal and photochemical reactivity of manganese tricarbonyl and tetracarbonyl complexes with a bulky diazabutadiene ligand.

The manganese tricarbonyl complex fac-Mn(Br)(CO)3((i)Pr2Ph-DAB) (1) [(i)Pr2Ph-DAB = (N,N'-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene)] was synthesized from the reaction of Mn(CO)5Br with the sterically encumbered DAB ligand. Compound 1 exhibits rapid CO release under low power visible light irradiation (560 nm) suggesting its possible use as a photoCORM. The reaction of compound 1 with TlPF6 in the dark afforded the manganese(I) tetracarbonyl complex, [Mn(CO)4((i)Pr2Ph-DAB)][PF6] (2). While 2 is comparatively more stable than 1 in light, it demonstrates high thermal reactivity such that dissolution in CH3CN or THF at room temperature results in rapid CO loss and formation of the respective solvate complexes. This unusual reactivity is due to the large steric profile of the DAB ligand which results in a weak Mn-CO binding interaction.

Bond Trading: Intramolecular Metal and Ligand Exchange within a NO/Ni/Co Complex.

With the goal of generating hetero-redox levels on metals as well as on nitric oxide (NO), metallodithiolate (N2 S2 )CoIII (NO- ), N2 S2 = N,N- dibenzyl-3,7-diazanonane-1,9-dithiolate, is introduced as ligand to a well-characterized labile [Ni0 (NO)+ ] synthon. The reaction between [Ni0 (NO+ )] and [CoIII (NO- )] has led to a remarkable electronic and ligand redistribution to form a heterobimetallic dinitrosyl cobalt [(N2 S2 )NiII ∙Co(NO)2 ]+ complex with formal two electron oxidation state switches concomitant with the nickel extraction or transfer as NiII into the N2 S2 ligand binding site. To date, this is the first reported heterobimetallic cobalt dinitrosyl complex.