Richard A. Kemp

Synthesis, characterization, and structural study of sterically hindered magnesium alkoxide and siloxide compounds

Abstract A series of sterically hindered Mg(OR) 2 , [OR=OC(CH 3 )(C 6 H 5 ) 2 (DPE), and OSi(C 6 H 5 ) 3 (TPS)] were synthesized from the reaction of Mg(Bu) 2 with 2 HOR in a variety of solvents. The resultant products were crystallographically characterized as Mg 3 (μ 3 -DPE)(μ-DPE) 3 (DPE) 2 ( 1 ), Mg[(μ-TPS) 2 Mg(TPS)] 2 ( 2 ), [Mg(μ-DPE)(DPE)(solv)] 2 (solv=THF, 3 ; py, 4 ), and [Mg(TPS) 2 (solv)] 2 (solv=THF, 5 ; py, 6 ). For 1 , the three metal centers are in a triangular arrangement and are bound by a single μ 3 -DPE, three μ-DPE, and two terminal DPE ligands. Two of the three Mg cations are tetrahedrally (Td) coordinated while the remaining metal center adopts a trigonal pyramidal geometry. In contrast, 2 displays a more linear arrangement of the Mg centers supported by four μ-TPS and two terminal TPS ligands. Two of the Mg cations adopt trigonal planar arrangements while the remaining central Mg exhibits a distorted Td geometry. For the dinuclear complexes ( 3 – 6 ), each metal possesses a Td geometry satisfied by two μ-OR, one terminal OR, and one coordinated solvent. 1 H NMR characterization indicates that 1 is likely fluxional in solution while 2 – 5 remain intact in solution and 6 is disrupted by pyridine to yielding a monomer.

Calixarenes as a new class of external electron donors in Ziegler-Natta polypropylene catalysts

Abstract In this work we have shown that calixarenes form a new type of external donor ligand which can function effectively as a selectivity control agent to increase the yield of isotactic polypropylene in late-generation Ziegler–Natta catalysts. The procatalyst prepared utilized dibutylphthalate as the internal donor to function with the calixarene. We have synthesized and characterized a wide variety of new substituted calixarenes containing hydroxy- and methoxy-end groups. All of these calixarenes were evaluated in the bulk polymerization of propylene and found to increase significantly the amount of i-PP formed relative to reactor runs performed without the calixarene.

Solvent Influences on the Molecular Aggregation of Magnesium Aryloxides

Magnesium aryloxides were prepared in a variety of solvents through the reaction of dibutyl magnesium with sterically varied aryl alcohols: 2,6-dimethylphenol (H-DMP), 2,6-diisopropylphenol (H-DIP), and 2,4,6-trichlorophenol (H-TCP). Upon using a sufficiently strong Lewis-basic solvent, the monomeric species Mg(DMP){sub 2}(py){sub 3} (1, py = pyridine), Mg(DIP){sub 2}(THF){sub 3}, (2a, THF = tetrahydrofuran) Mg(TCP){sub 2}(THF){sub 3} (3) were isolated. Each of these complexes possesses a five-coordinate magnesium that adopts a trigonal bipyramidal geometry. In the absence of a Lewis base, the reaction with H-DIP yields a soluble trinuclear complex, [Mg(DIP){sub 2}]{sub 3} (2b). The Mg metal centers in 2b adopt a linear arrangement with a four-coordinate central metal while the outer metal centers are reduced to just three-coordinate. Solution spectroscopic methods suggest that while 2b remains intact, the monomeric species (1, 2a, and 3) are involved in equilibria, which facilitate intermolecular ligand transfer.

Synthesis and structural characterization of Group 14 complexes containing two {9-[2-(dimethylamino)ethyl]fluorenyl-} ligands and a unique coupling product

Abstract Reaction of two equivalents of {9-[2-(dimethylamino)ethyl]fluorenyl}lithium (FlNLi) with either Me2GeCl2 or Me2SnCl2 leads cleanly to the new compounds (FlN)2MMe2, where M=Ge, Sn. These new complexes are the first compounds that contain multiple FlN ligands which have been characterized by X-ray diffraction. Attempts to prepare the analogous Pb compound using Et2PbCl2 were not successful, yielding instead a product where the two FlN ligands have coupled. Structural characterization of the coupled product is presented. Neither of the main-group complexes showed significant activity for the polymerization of propylene using either MAO or BARF salts as activators.

GUAIACOL-SUBSTITUTED SILANES AS SELECTIVITY CONTROL AGENTS FOR ZIEGLER-NATTA POLYPROPYLENE CATALYSTS

Several series of silanes containing at least one guaiacol moiety were conveniently prepared by direct treatment of dichlorosilanes with o-methoxyphenol (guaiacol) in the presence of triethylamine. Af ter isolation and characterization, the compounds were evaluated as external donors (or selectivity control agents, SCAs) , for heterogeneous fourth-generation Ziegler-Natta catalysts in liquid propylene (LIPP) polymerizat ions. The isotactic polypropylene polymers formed using these SCAs covered a wide range of xylene solubles from 5 % to 16%. The most effective guaiacol-containing SCAs were those containing both sterically bulky groups on the central silicon atom as well as an attached methoxy group.