Damien Guironnet

Insertion Polymerization of Acrylate

Multiple insertions of acrylate in copolymerization with ethylene, and an insertion homo-oligomerization of methyl acrylate were observed for the first time. Key to these findings, and to mechanistic insights reported, are labile-substituted complexes as catalyst precursors.

Mechanistic insights on acrylate insertion polymerization.

Complexes [{(PwedgeO)PdMe}(n)] (1(n); PwedgeO = kappa(2)-P,O-Ar(2)PC(6)H(4)SO(2)O with Ar = 2-MeOC(6)H(4)) are a single-component precursor of the (PwedgeO)PdMe fragment devoid of additional coordinating ligands, which also promotes the catalytic oligomerization of acrylates. Exposure of 1(n) to methyl acrylate afforded the two diastereomeric chelate complexes [(PwedgeO)Pd{kappa(2)-C,O-CH(C(O)OMe)CH(2)CH(C(O)OMe)CH(2)CH(3)}] (3-meso and 3-rac) resulting from two consecutive 2,1-insertions of methyl acrylate into the Pd-Me bond with the same or opposite stereochemistry, respectively, in a 3:2 ratio as demonstrated by comprehensive NMR spectroscopic studies and single crystal X-ray diffraction. These six-membered chelate complexes are direct key models for intermediates of acrylate insertion polymerization, and also ethylene-acrylate copolymerization to high acrylate content copolymers. Studies of the binding of various substrates (pyridine, dmso, ethylene and methyl acrylate) to 3-meso and 3-rac show that hindered displacement of the chelating carbonyl moiety by pi-coordination of incoming monomer significantly retards, but does not prohibit, polymerization. For 3-meso,3-rac + C(2)H(4) right arrow over left arrow 3-meso-C(2)H(4,) 3-rac-C(2)H(4) an equilibrium constant K(353 K) approximately 2 x 10(-3) L mol(-1) was estimated. Reaction of 3-meso, 3-rac with methyl acrylate afforded higher insertion products [(PwedgeO)Pd(C(4)H(6)O(2))(n)Me] (n = 3, 4) as observed by electrospray ionization mass spectrometry (ESI-MS). Theoretical studies by DFT methods of consecutive acrylate insertion provide relative energies of intermediates and transition states, which are consistent with the aforementioned experimental observations, and give detailed insights to the pathways of multiple consecutive acrylate insertions. Acrylate insertion into 3-meso,3-rac is associated with an overall energy barrier of ca. 100 kJ mol(-1).

Reactivity of Methacrylates in Insertion Polymerization

Polymerization of ethylene by complexes [{(P^O)PdMe(L)}] (P^O = κ(2)-(P,O)-2-(2-MeOC(6)H(4))(2)PC(6)H(4)SO(3))) affords homopolyethylene free of any methyl methacrylate (MMA)-derived units, even in the presence of substantial concentrations of MMA. In stoichiometric studies, reactive {(P^O)Pd(Me)L} fragments generated by halide abstraction from [({(P^O)Pd(Me)Cl}μ-Na)(2)] insert MMA in a 1,2- as well as 2,1-mode. The 1,2-insertion product forms a stable five-membered chelate by coordination of the carbonyl group. Thermodynamic parameters for MMA insertion are ΔH(++) = 69.0(3.1) kJ mol(-1) and ΔS(++) = -103(10) J mol(-1) K(-1) (total average for 1,2- and 2,1-insertion), in comparison to ΔH(++) = 48.5(3.0) kJ mol(-1) and ΔS(++) = -138(7) J mol(-1) K(-1) for methyl acrylate (MA) insertion. These data agree with an observed at least 10(2)-fold preference for MA incorporation vs MMA incorporation (not detected) under polymerization conditions. Copolymerization of ethylene with a bifunctional acrylate-methacrylate monomer yields linear polyethylenes with intact methacrylate substituents. Post-polymerization modification of the latter was exemplified by free-radical thiol addition and by cross-metathesis.

Control of molecular weight in Ni(II)-catalyzed polymerization via the reaction medium

The reaction medium controls polymerization with highly active (kappa(2)-P,O)-phosphinesulfonato nickel methyl complexes to afford polyethylenes ranging from low molecular weight (M(n)) branched material to high molecular weight (M(n)) strictly linear polymer.

Synthesis and characterization of carbazolide-based iridium PNP pincer complexes. Mechanistic and computational investigation of alkene hydrogenation: Evidence for an Ir(III)/Ir(V)/Ir(III) catalytic cycle

New carbazolide-based iridium pincer complexes ((carb)PNP)Ir(C2H4), 3a, and ((carb)PNP)Ir(H)2, 3b, have been prepared and characterized. The dihydride, 3b, reacts with ethylene to yield the cis-dihydride ethylene complex cis-((carb)PNP)Ir(C2H4)(H)2. Under ethylene this complex reacts slowly at 70 °C to yield ethane and the ethylene complex, 3a. Kinetic analysis establishes that the reaction rate is dependent on ethylene concentration and labeling studies show reversible migratory insertion to form an ethyl hydride complex prior to formation of 3a. Exposure of cis-((carb)PNP)Ir(C2H4)(H)2 to hydrogen results in very rapid formation of ethane and dihydride, 3b. DFT analysis suggests that ethane elimination from the ethyl hydride complex is assisted by ethylene through formation of ((carb)PNP)Ir(H)(Et)(C2H4) and by H2 through formation of ((carb)PNP)Ir(H)(Et)(H2). Elimination of ethane from Ir(III) complex ((carb)PNP)Ir(H)(Et)(H2) is calculated to proceed through an Ir(V) complex ((carb)PNP)Ir(H)3(Et) which reductively eliminates ethane with a very low barrier to return to the Ir(III) dihydride, 3b. Under catalytic hydrogenation conditions (C2H4/H2), cis-((carb)PNP)Ir(C2H4)(H)2 is the catalyst resting state, and the catalysis proceeds via an Ir(III)/Ir(V)/Ir(III) cycle. This is in sharp contrast to isoelectronic (PCP)Ir systems in which hydrogenation proceeds through an Ir(III)/Ir(I)/Ir(III) cycle. The basis for this remarkable difference is discussed.

Ethylene polymerization in supercritical carbon dioxide with binuclear nickel(II) catalysts

A series of new, highly fluorinated neutral (kappa(2)-N,O) chelated Ni(II) binuclear complexes based on salicylaldimines bridged in p-position of the N-aryl group were prepared. The complexes are single-component catalyst precursors for ethylene polymerization in supercritical carbon dioxide and toluene. Solubility of the catalyst precursors in supercritical carbon dioxide is effected by a large number of up to 18 trifluoromethyl groups per molecule. Semicrystalline polyethylene with a low degree of branching is formed (ca. 10 branches/1000 carbon atoms). Polymer microstructures are independent of the nature of the bridging moiety, while stability of the catalysts appears to differ.

Preparation and characterization of conjugated polymers made by postpolymerization reactions of alternating polyketones.

Conjugated polymers possessing a poly(2,5-dimethylene-2,5-dihydrofuran) backbone were prepared through postpolymerization reaction of styrenic polyketones with bromine in one-pot reactions. The modification is proposed to proceed via condensation of two repeating units to form a fully characterized polymer with a poly(2,5-dimethylenetetrahydrofuran) backbone. Subsequent bromination and elimination of HBr yield a polymer with a fully conjugated carbon backbone. The new conjugated polymers were characterized by NMR, IR, and UV-vis spectroscopies and by CV. These polymers have strong absorption in the visible region, with the absorption peaks shifted to the NIR region upon doping with acids. The ease of the synthesis of the starting polyketone and of the modifications allows large-scale preparation of those conjugated polymers.

Kinetic Study of Living Ring-Opening Metathesis Polymerization with Third-Generation Grubbs Catalysts

The rate of living ring-opening metathesis polymerization (ROMP) of N-hexyl-exo-norbornene-5,6-dicarboximide initiated by Grubbs third-generation catalyst precursors [(H2IMes)(py)2(Cl)2Ru═CHPh] and [(H2IMes)(3-Br-py)2(Cl)2Ru═CHPh] is measured to be independent of catalyst concentration. This result led to the development of a rate law describing living ROMP initiated by a Grubbs third-generation catalyst that includes an inverse first-order dependency in pyridine. Additionally, it is demonstrated that one of the two pyridines coordinated to the solid catalyst is fully dissociated in solution. The monopyridine adduct formation is confirmed in solution by 1H DOSY (diffusion-ordered NMR spectroscopy), and a Vant Hoff analysis of the equilibrium between mono- and dipyridine adducts (extrapolated Keq,0 ∼ 0.5 at 25 °C). Finally, the difference in polymerization rates between two catalyst precursors is demonstrated to correspond to the difference in coordination strength between the two pyridines, suggesting that the catalytic species involved in the polymerizations rate-determining step is not coordinated to pyridine.

Encapsulation of catalyst in block copolymer micelles for the polymerization of ethylene in aqueous medium

The catalytic emulsion polymerization of ethylene has been a long-lasting technical challenge as current techniques still suffer some limitations. Here we report an alternative strategy for the production of semi-crystalline polyethylene latex. Our methodology consists of encapsulating a catalyst precursor within micelles composed of an amphiphilic block copolymer. These micelles act as nanoreactors for the polymerization of ethylene in water. Phosphinosulfonate palladium complexes were used to demonstrate the success of our approach as they were found to be active for hours when encapsulated in micelles. Despite this long stability, the activity of the catalysts in micelles remains significantly lower than in organic solvent, suggesting some catalyst inhibition. The inhibition strength of the different chemicals present in the micelle were determined and compared. The combination of the small volume of the micelles, and the coordination of PEG appear to be the culprits for the low activity observed in micelles.Olefin and emulsion polymerizations are incompatible due to the water sensitivity of olefin polymerization catalysts and thus direct synthesis of semi-crystalline polyolefin latexes is difficult. Here, the authors encapsulate a catalyst precursor in micelles which act as nanoreactors for ethylene polymerization in water.

Catalytic synthesis of functionalized (polar and non-polar) polyolefin block copolymers

Herein, we report a methodology for the synthesis of polyolefin containing block-copolymers using a catalytic postpolymerization modification strategy.