Brandon A. Rodriguez

Bimetallic effects for enhanced polar comonomer enchainment selectivity in catalytic ethylene polymerization.

The synthesis and characterization of the bimetallic 2,7-di-[(2,6-diisopropylphenyl)imino]-1,8-naphthalenediolato group 10 metal polymerization catalysts {[Ni(CH(3))](2)[1,8-(O)(2)C(10)H(4)-2,7-[CH=N(2,6-(i)Pr(2)C(6)H(3))](PMe(3))(2)} and {[Ni(1-naphthyl)](2)[1,8-(O)(2)C(10)H(4)-2,7-[CH=N(2,6-(i)Pr(2)C(6)H(3))](PPh(3))(2)} [FI(2)-Ni(2)(PR(3))(2)] are presented, along with the synthesis and characterization of the mononuclear analogues {Ni(CH(3))[3-(t)Bu-2-(O)C(6)H(3)CH=N(2,6-(i)Pr(2)C(6)H(3))](PMe)(3)} and {Ni(1-naphthyl)[3-(t)Bu-2-(O)C(6)H(3)CH=N(2,6-(i)Pr(2)C(6)H(3))](PPh)(3)} [FI-Ni (PR(3))]. Monometallic Ni catalysts were also prepared by functionalizing one ligation center of the bimetallic ligand with a trimethylsilyl group (TMS), yielding {Ni(CH(3))[1,8-(O)(TMSO)C(10)H(4)-2,7-[CH=N(2,6-(i)Pr(2)C(6)H(3))](PMe(3))} [TMS-FI(2)-Ni(PMe(3))]. The FI(2)-Ni(2) catalysts exhibit significant increases in ethylene homopolymerization activity versus the monometallic analogues, as well as increased branching and methyl branch selectivity, even in the absence of a Ni(cod)(2) cocatalyst. Increasing ethylene concentrations significantly suppress branching and alter branch morphology. FI(2)-Ni(2)-mediated copolymerizations with ethylene + polar-functionalized norbornenes exhibit a 4-fold increase in comonomer incorporation versus FI-Ni, yielding copolymers with up to 10% norbornene copolymer incorporation. FI(2)-Ni(2)-catalyzed copolymerizations with ethylene + methylacrylate or methyl methacrylate incorporate up to 11% acrylate comonomer, while the corresponding mononuclear FI-Ni catalysts incorporate negligible amounts. Furthermore, the FI(2)-Ni(2)-mediated polymerizations exhibit appreciable polar solvent tolerance, turning over in the presence of ethyl ether, acetone, and even water. The mechanism by which the present cooperative effects take place is investigated, as is the nature of the copolymer microstructures produced.

Retraction of “Bimetallic Effects for Enhanced Polar Comonomer Enchainment Selectivity in Catalytic Ethylene Polymerization”

The authors have been unable to reproduce the synthesis and spectroscopic characterization of the ethylene/acrylate copolymer described in this article. Accordingly, the authors are retracting this publication due to concerns over the validity of the aforementioned data. The authors regret any confusion that may have been created by publication of this work. In contrast, the results reported in related publications regarding the synthesis of a binuclear catalyst and its ethylene homopolymerization properties, and on ligand steric and fluoroalkyl substituent effects on enchainment cooperativity and stability in bimetallic nickel(II) polymerization catalysts, have been reproduced.

Tetra­aqua­bis{μ2-2,7-bis­[(2,6-diisopropyl­phen­yl)imino­meth­yl]naphthalene-1,8-diolato}di-μ3-hydroxido-di-μ2-hydroxido-bis­(trimethyl­phosphine oxide)tetra­nickel(II)–trimethyl­phosphine oxide–diethyl ether–water (1/2/2/2)

The title complex, [Ni4(C36H40N2O2)2(OH)4(C3H9OP)2(H2O)4]·2C4H10O·2C3H9OP·2H2O, is centrosymmetric with a central core that can be described as a defect double cubane. The four metal ions in the cluster are held together by four bridging hydroxide groups. Each NiII atom adopts a distorted octahedral geometry.