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Michel R Gagné

Publications and source records attributed to Michel R Gagné.

11 recordsLinked to original sources
PubMed2006

Modular catalysts for diene cycloisomerization: rapid and enantioselective variants for bicyclopropane synthesis.

Deconstructing the tridentate (triphos)Pt(II) first-generation catalysts into mixed diphosphine/monophosphine combinations (P(2)P) has led to new, more active catalysts for the cycloisomerization of 1,6-, and 1,7-dienes into bicyclo-[3.1.0] and -[4.1.0] products. When the diphosphine was the small bite angle dppm, reaction rates were approximately 20-fold faster than with triphos, although reaction rates and diastereoselectivities were also sensitive to the monophosphine (PMe(3) being optimal for rate, PPh(3) being optimal for selectivity). When the diphosphine was xyl-BINAP or SEGPHOS, the catalysts were enantioselective, and enantio-ratios up to 98:2 were observed. Both sets of catalysts showed enhanced functional group tolerance in comparison to the original (triphos)Pt(2+) catalyst. X-ray structures for both precatalysts are also reported.

Alkenes↗
PubMed2006

The discovery of an enantioselective receptor for (-)-adenosine from a racemic dynamic combinatorial library.

The use of laser polarimetry detection coupled with HPLC is demonstrated to enable the discovery of enantioselective receptors from racemic dynamic combinatorial libraries. Templating with an enantiopure analyte, such as (-)-adenosine, leads to amplification of one enantiomer of the cyclic dimer. A result confirmed with a pseudo-racemic library wherein one of the enantiomers was d-labeled for mass spec analysis. The resulting dimer is thus an enantioselective receptor for (-)-adenosine.

Adenosine↗
PubMed2005

Cycloisomerization of dienes with carbophilic lewis acids: mimicking terpene biosynthesis with Pt(II) catalysts.

[reaction: see text]. Dicationic Pt(II) complexes containing triphosphine pincer ligands are excellent catalysts for the cycloisomerization of 1,6- and 1,7-dienes into bicyclopropane carbocycles. In analogy to the biosynthetic route to these monoterpene-like compounds, carbocation intermediates are proposed and supported by trapping experiments. Reactivation of the trapped intermediates indicates that cation generation by C-C bond formation is both rapid and reversible.

Alkadienes↗
PubMed2005

Synthesis and ligand exchange reactions of P2Pd(II) and P2Pt(II) salicylaldimates.

Reaction of (dppe)MCl(2)(dppe = 1,2-bis(diphenylphosphino)ethane) with 2-(N-phenyliminomethyl)phenol leads to air-stable (dppe)M(N,O) chelates (M = Pd, 1a; M = Pt, 1b). The N-4-methylphenyl derivative of 1a has been characterized by X-ray analysis. The N,O ligands are kinetically labile and exchange occurs in solution in the presence of other salicylaldimines. In the presence of anilines, a metal-mediated imine exchange process occurs. Hammett analysis reveals that the platinum complexes are sensitive to the electronics at N but not at O. Electron donating groups on the N-aryl ring stabilize the metal complex.

Chelating Agents↗
PubMed2004

Platinum(II)-catalyzed 1,6-diene cycloisomerizations: turnover in the absence of beta-hydride elimination.

Electrophilic pincer-ligated Pt(II)-dications are efficient catalysts for the cycloisomerization of 1,6-dienes, initiated by alkene activation. The tridentate ligands inhibit beta-hydride elimination and thus enable cationic mechanisms that turnover by Pt(II) extrusion. PPP ligands lead to cyclopropane products, while PNP ligands provide cyclohexene products; mechanistic issues are also discussed.

Catalysis↗
PubMed2004

Exploiting the synergy between coordination chemistry and molecular imprinting in the quest for new catalysts.

The synthesis of transition metal active sites by the molecular imprinting of polymerizable metal complexes into highly cross-linked organic polymers is described. The emphasis of this Account is on the synergy between the long-term goals associated with new catalyst development and the more short-term goal of addressing fundamental questions in coordination chemistry, particularly emphasizing stereochemistry and structure. An argument is presented that the latter is necessary for ultimately achieving the more difficult but more important goal of designer catalysts that achieve reaction selectivities and reactivities not obtainable with traditional homo- or heterogeneous catalysts.

Binding Sites↗
PubMed2003

Fluorophobic effect promotes partitioning of organics into macroporous organic polymers: a method for achieving high local concentrations.

The efficiency for partitioning small organic compounds from fluorinated solvents of varying quality into highly cross-linked, macroporous, and insoluble organic polymers is described. The solvating qualities of the poly(acrylates) together with the solvating quality of the solvent are key to describing the partitioning thermodynamics. Partitioning measurements for 9-anthracene methanol 1 are reported as a function of fluorous content in perfluoromethylcyclohexane (PFMC):hexanes mixtures, comonomer structure and loading, and temperature. The best comonomer for the sorption of 1 is methacrylamide. Concentration enhancements of up to approximately 200-fold are obtainable, and are proposed to account for previously observed rate accelerations in catalyst-containing porous polymers. Partition efficiency (PE) measurements, described as the ratio of polymer to original solution concentrations, are presented for a variety of organic compounds. The PE is sensitive to analyte structure and ranges from 1 to 170 (180 being the maximum under the conditions employed), with linear alkanes at the low end of the spectrum and polar functional groups at the opposite.

Journal Article↗