Showing papers by "Maurice Brookhart published in 2003"
TL;DR: The kinetic data obtained from these experiments are used to present an overall picture of the ethylene polymerization mechanism for (alpha-diimine)Ni catalysts, including effects of reaction temperature and ethylene pressure on catalyst activity, polyethylene branching, and polymer architecture.
Abstract: The synthesis of a series of (α-diimine)NiR2 (R = Et, nPr) complexes via Grignard alkylation of the corresponding (α-diimine)NiBr2 precursors is presented. Protonation of these species by the oxonium acid [H(OEt2)2]+[BAr‘4]- at low temperatures yields cationic Ni(II) β-agostic alkyl complexes which model relevant intermediates present in nickel-catalyzed olefin polymerization reactions. The highly dynamic nature of these agostic alkyl cations is quantitatively addressed using NMR line broadening techniques. Trapping of these complexes with ethylene provides cationic Ni alkyl ethylene species, which are used to determine rates of ethylene insertion into primary and secondary carbon centers. The Ni agostic alkyl cations are also trapped by CH3CN and Me2S to yield Ni(R)(L)+ (L = CH3CN, Me2S) complexes, and the dynamic behavior of these species in the presence of varied [L] is discussed. The kinetic data obtained from these experiments are used to present an overall picture of the ethylene polymerization mech...
263 citations
TL;DR: In this article, living polymerization of ethylene with palladium(II) diimine complexes coupled with use of a functionalized initiator and/or cleavage of the palladium−polymer bond with various reagents provides a protocol for synthesis of mono-and di-end functionalized, branched, amorphous polyethylenes.
Abstract: Living polymerizations of ethylene with palladium(II) diimine complexes coupled with use of a functionalized initiator and/or cleavage of the palladium−polymer bond with various reagents provides a protocol for synthesis of mono- and di-end-functionalized, branched, amorphous polyethylenes. The functional initiator used is the chelate complex (Ar = 2,6-(iPr)2C6H3) (3). The alkyl chain is cleaved by insertion of alkyl acrylates or methyl vinyl ketone, followed by cleavage with Et3SiH to generate alkyl ester or methyl ketone end groups, respectively. Insertion of 5-hexen-1-ol, followed by chain running and β-elimination, results in formation of aldehyde end groups. Conditions for living polymerization of propylene, 1-hexene, and 1-octadecene have also been established. Rates of first monomer insertion and subsequent chain growth are shown to be a sensitive function of the palladium complex used for initiation and the nature and concentration of auxiliary nitrile ligands. Block copolymers of ethylene and 1-o...
215 citations
TL;DR: In this article, a method for the synthesis of bulky 2-anilinotropones has been developed, utilizing palladium-catalyzed cross-coupling techniques, which produces ethylene polymerization catalysts of the general formula [[(R-6-R]C6H3]NC7H5O]Ni(Ph)(PPh3)].
132 citations
TL;DR: In this paper, a general synthetic route for the preparation of 2-anilinoperinaphthenones is reported, and the key features of these nickel complexes are a hindered N-aryl ring, a five-membered-ring nickel chelate and an anionic N-donor moiety.
131 citations
TL;DR: A general mechanism is presented on the basis of an X-ray crystal structure determination of an intermediate isolated from the reaction involving 4-methoxybenzonitrile and kinetic studies performed on the C-C bond cleavage of para-substituted aryl cyanides.
Abstract: Cationic Rh(III) complex [Cp*(PMe3)Rh(SiPh3)(CH2Cl2)]BAr4‘ (1) activates the carbon−carbon bond of aryl and alkyl cyanides (R−CN, where R = Ph, (4-(CF3)C6H4), (4-(OMe)C6H4), Me, iPr, tBu) to produce complexes of the general formula [Cp*(PMe3)Rh(R)(CNSiPh3)]BAr4‘. With the exception of the tBuCN case, every reaction proceeds at room temperature (t1/2 < 1 h for aryl cyanides, t1/2 < 14 h for alkyl cyanides). A general mechanism is presented on the basis of (1) an X-ray crystal structure determination of an intermediate isolated from the reaction involving 4-methoxybenzonitrile and (2) kinetic studies performed on the C−C bond cleavage of para-substituted aryl cyanides. Initial formation of an η1-nitrile species is observed, followed by conversion to an η2-iminoacyl intermediate, which was observed to undergo migration of R (aryl or alkyl) to rhodium to form the product [Cp*(PMe3)Rh(R)(CNSiPh3)]BAr4‘.
115 citations
TL;DR: In this article, a series of Ni(II and Pd(II) catalysts have been synthesized from the P,O chelating ligands phenacyl(aryl)2phosphine.
84 citations
31 Jul 2003
58 citations
TL;DR: In this article, tetramethyl(2-methylthioethyl)cyclopentadienylcobalt diiodide (4) was shown to polymerize ethylene to linear polyethylene with Mn's in the range of 5000−68
29 citations
TL;DR: The Pd methyl−ethylene complex (P,O)PdMe(η2-C2H4)+BAr‘4- ((P, O) = phenacyldi-tert-butylphosphine; Ar‘ = 3,5-(CF3)2C6H3) has been isolated and structurally characterized by X-ray crystallography as discussed by the authors.
15 citations
TL;DR: A simple catalytic procedure based on rhodium C-H bond activation for the synthesis of diheteroatom alkenes of the type R(3)SiOCH=CHG (G = -OR, -NRR').
Abstract: While 1,2-diheteroatom-substituted alkenes represent useful synthetic building blocks, there are no simple, general procedures available for preparation of such compounds. We describe here a simple catalytic procedure based on rhodium C−H bond activation for the synthesis of diheteroatom alkenes of the type R3SiOCHCHG (G = −OR, −NRR‘).
15 citations
Patent•
05 Mar 2003TL;DR: In this paper, the nickel complexes of the anions of certain 2-aminotropones are used as olefin polymerization catalysts, and the methods of making these 2aminotropone catalysts are described.
Abstract: Selected nickel complexes of the anions of certain 2-aminotropones are olefin polymerization catalysts. Novel 2-aminotropones and their nickel complexes are also disclosed together with methods of making these 2-aminotropones.
TL;DR: In this paper, a simple catalytic procedure based on rhodium C−H bond activation for the synthesis of diheteroatom alkenes of the type R3SiOCHCHG (G = −OR, −NRR) was described.
Abstract: While 1,2-diheteroatom-substituted alkenes represent useful synthetic building blocks, there are no simple, general procedures available for preparation of such compounds. We describe here a simple catalytic procedure based on rhodium C−H bond activation for the synthesis of diheteroatom alkenes of the type R3SiOCHCHG (G = −OR, −NRR‘).