Titanium phosphinimide complexes for ethylene polymerization catalysis: Synthetic, computational and polymerization testing investigations.

The influences of the steric and electronic properties of phosphinimide ligands on the ethylene polymerization activity of cyclopentadienyl titanium phosphinimide complexes have been investigated. These efforts resulted in a new family of very high activity ethylene polymerization catalysts and have defined the principles required for future improvements in related catalyst systems. A reliable polymerization testing method that allows control of variables which affect polymerization activity has been established. For example, a series of experiments employing the Cp*TiMe2[NP(N(Et)(Ph)) 3]/B(C6F5)3 catalyst system resulted in polymerization activities ranging from 0 to 5500 g mmol-1 hr-1 atm-1, thus illustrating the sensitivity of the catalyst activity to the polymerization conditions. Density functional theory methods were used to investigate the effects of the electronic properties of the phosphinimide ligand on the first two insertions of ethylene using the model catalyst system CpTiMe2[NPR 3]/BCl3 (R = Me, NH2, H, Cl, F). The results of this study predict that electron donating groups should increase the polymerization activity, primarily by assisting displacement of the counterion prior to coordination of ethylene. Cyclopentadienyl titanium complexes containing a phosphinimide ligand with a pendant pyridyl substituent, Cp\u27TiCl2[NP(R) 2(2-CH2Py)] (Cp\u27 = Cp, Cp*, R = i-Pr, t-Bu), and the donor-acceptor complexes, CpTiCl 2[NP(R)2(2-CH2Py)·B(C6F 5)3 (R = i-Pr, t-Bu), demonstrated very low to moderate polymerization activities upon activation by MAO. Polymerization testing of Cp*TiMe2[NP(t-Bu)2(2-CH 2Py)] using B(C6F5)3 as the co-catalyst resulted in an improved catalyst system. Employing electron-donating amino (-NR1R2) substituents on the phosphinimide ligand led to the new family of very high activity ethylene polymerization catalysts of general formula Cp\u27 TiMe2[NP(NR1R2)3]. Polymerization testing revealed a qualitative relationship between the steric bulk of the phosphinimide ligand and the polymerization activity. Under the appropriate conditions, using B(C6F5)3 as a co-catalyst, polymerization activities for these pre-catalysts ranged from 2000 to 10000 g mmol-1 hr-1 atm -1. Cp*TiMe2[NP(N(n-Pr)2) 3] demonstrated a polymerization activity of 10000 g mmol-1 hr-1 atm-1 upon activation by B(C6F5)3, nearly twice as high as the very successful pre-catalysts CpTiMe2[NP(t-Bu) 3] and Cp*TiMe2[NP(t-Bu)3] under the same conditions, and thus represents a significant advance in the development of new successful Group 4 phosphinimide ethylene polymerization catalysts.Dept. of Chemistry and Biochemistry. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2004 .B433. Source: Dissertation Abstracts International, Volume: 66-07, Section: B, page: 3703. Thesis (Ph.D.)--University of Windsor (Canada), 2004

Photoreversible multiple additions of hydrogen to a highly unsaturated platinum-rhenium cluster complex

The compound Pt3Re2(CO)6(PBut3)3, 1, was obtained from the reaction of Re2(CO)10 with Pt(PBut3)2 in octane solvent at reflux. Compound 1 consists of a trigonal bipyramidal cluster of five metal atoms with three platinum atoms in the trigonal plane and the two rhenium atoms in the apical positions. The metal cluster is formally unsaturated by 10 electrons. Compound 1 sequentially adds 3 equiv of hydrogen at room temperature/1 atm to form the series of compounds Pt3Re2(CO)6(PBut3)3(mu-H)2, 2, Pt3Re2(CO)6(PBut3)3(mu-H)4, 3, and Pt3Re2(CO)6(PBut3)3(mu-H)6, 4. A small but significant kinetic isotope effect was observed, kH/kD = 1.3. The rate of addition of hydrogen is unaffected by the presence of a 20-fold excess of free PBut3 in solutions of 1. Compounds 2-4 each consist of a trigonal bipyramidal cluster of three platinum and two rhenium atoms similar to that of 1. The hydrido ligands in 2-4 bridge the platinum-rhenium bonds and are arranged to give structures having overall C2v symmetry for 2 and 3 and approximate D3h symmetry for 4. Some of the hydrido ligands were expelled from 4 in the form of hydrogen upon exposure of solutions to UV-vis irradiation to yield compound 3 and then 2 in reasonable yields, but the elimination of all hydrido ligands to yield 1 was achieved only under the most forcing UV irradiation and then only with a major loss of the complex due to decomposition. The electronic structures of 1-4 were investigated by DFT calculations. Additional DFT calculations have suggested some mechanisms for the activation of hydrogen at multicenter metal sites without ligand eliminations prior to the hydrogen additions

Unsaturated platinum-rhenium cluster complexes. Synthesis, structures and reactivity

Two new compounds PtRe3(CO)12(PBut3)(micro-H)3, 9, and PtRe2(CO)9(PBut3)(micro-H)2, 10, were obtained from the reaction of Pt(PBut3)2 with Re3(CO)12(micro-H3), 8, at room temperature. Compound 9 contains a butterfly cluster of four metals formed by the insertion of the platinum atom from a Pt(PBut3) group into one of the hydride-bridged metal-metal bonds of 8. The three hydrido ligands are bridging ligands across each of three new Pt-Re bonds. Compound 10 contains a triangular PtRe2 cluster with two hydrido ligands; one bridges a Pt-Re bond, and the other bridges the Re-Re bond. The new compound Pt2Re2(CO)7(PBut3)2(micro-H)2, 11, was obtained from the reaction of 8 with Pt(PBut3)2 in hexane at reflux. Compound 11 was also obtained from 10 by reaction with an additional quantity of Pt(PBut3)2. Compound 11 contains a tetrahedral cluster of four metal atoms with two dynamically active hydrido ligands. A CO ligand on one of the two platinum atoms also exchanges between the two platinum atoms rapidly on the NMR time scale. Compound 11 is electronically unsaturated and was found to add hydrogen at room temperature to form the tetrahydrido cluster complex, Pt2Re2(CO)7(PBut3)2(micro-H)4, 12. Compound 12 has a structure similar to 11 but contains one triply bridging hydrido ligand, two edge bridging hydrido ligands, and one terminal hydrido ligand on one of the two platinum atoms. A kinetic isotope effect D/H of 1.5(1) was determined for the addition of H2 to 11. Hydrogen can be eliminated from 12 by heating to 97 degrees C or by the application of UV-vis irradiation at room temperature. Compound 12 adds CO at room temperature to yield the complex Pt2Re2(CO)8(PBut3)2(micro-H)4, 13, which contains a planar cluster of four metal atoms with a Pt-Pt bond and four edge bridging hydrido ligands. Compounds 11 and 12 react with Pt(PBut3)2 to yield the known five metal cluster complexes Pt3Re2(CO)6(PBut3)3(micro-H)2, 14, and Pt3Re2(CO)6(PBut3)3(micro-H)4, 15, respectively. Density functional calculations confirm the hydride positions in the lowest energy structural isomers of 11 and 12 and suggest a mechanism for H2 addition to 11 that occurs on the Pt atom with the lower coordination number

Superloading of Tin Ligands into Rhodium and Iridium Carbonyl Cluster Complexes

The reactions of Rh4(CO)12 and Ir4(CO)12 with Ph3SnH have yielded the new Rh−Sn and Ir−Sn cluster complexes M3(CO)6(μ-SnPh2)3(SnPh3)3, 1 (M = Rh) and 2 (M = Ir). Both compounds contain triangular M3 clusters with three bridging SnPh2 and three terminal SnPh3 ligands. The M−M bonds are unusually long. Molecular orbital calculations indicate that this is due to the importance of M−Sn bonding and weak direct M−M interactions. Reaction of 1 with Ph3SnH at reflux in 1,2-dichlorobenzene solvent yielded the complex Rh3(CO)3(SnPh3)3(μ-SnPh2)3(μ3-SnPh)2, 3, which contains eight tin ligands:  three terminal SnPh3, three edge-bridging SnPh2, and two triply bridging SnPh ligands

The Osmium–Silicon Triple Bond: Synthesis, Characterization, and Reactivity of an Osmium Silylyne Complex

The first silylyne complex of a metal beyond group 6, [Cp*­(^<i>i</i>Pr₃P)­(H)­OsSi­(Trip)]­[HB­(C₆F₅)₃], was prepared by a new synthetic route involving hydride abstraction from silicon. NMR and DFT computations support the presence of a silylyne ligand, and NBO and ETS-NOCV analysis revealed the nature of this Os–Si interaction as a triple bond consisting of a covalent σ bond and two strong π back-donations. The discovery of this complex allowed observations of the first cycloadditions involving a silylyne complex, and terminal alkynes are shown to react <i>via</i> C–H bond additions across the OsSi bond