No description available.

A series of complexes of the type [(L-L)Pd(alkene)], where (L-L) is a diphosphine ligand and the alkene is dibenzylideneacetone (dba), benzoquinone or tetracyanoethene have been synthesised. These complexes have been evaluated as pre-catalysts in the methoxycarbonylation of ethene (80 C, 10 bar CO/ethene, MeOH, 20 MeSO(_3)H). Where (L-L) is the diphosphine l,2-bis(di-tert-butylphosphinomethyl)benzene and the alkene is dba, rates in excess of 40,000 moles methyl propionate/mole Pd/hr are obtained at 99.6% selectivity. The catalytic activity and selectivity is found to critically depend on the nature of the diphosphine ligand, with l,2-bis(diphenylphosphinomethyl)benzene complexes giving rise to high molecular weight, perfectly alternating CO/ethene co-polymer. Several of the pre-catalyst complexes have been characterised by single crystal X-ray diffraction, and factors common to both methyl propionate selective catalysts and co-polymer selective catalysts have been identified. The phosphine ligands chosen in this study all readily form complexes with Pd(_2)(dba)(_3). The complexes have the formula [(P-P)Pd(dba)] where the bidentate phosphine binds as a chelate ligand to a single palladium atom. The environment around the palladium is essentially trigonal planar, with only small dihedral angles between P(-2)Pd and PdC(_2) planes observed. Detailed studies of the reaction of the complexes [(L-L)Pd(alkene)] with methanesul- phonic acid have been undertaken. The reaction product is shown to depend on the nature of the diphosphine ligand and the alkene. The catalytic activity is discussed with reference to the ability of the reaction products to enter the catalytic cycle. The coordination chemistry of several diphosphines when mixed with Pd(II) salts has been studied. Several complexes have been characterised by X-ray crystallography and the features related to the observed catalytic activity. The reaction chemistry has also been explored and related to the observed catalysis. A mechanism which takes account of all the results reported in this thesis is presented.

Degree: Master of Science Department: Science / Metal-ligand models and complex stability constants of newly synthesised chelating ligands, N,N’-bis(2-hydroxycyclopentyl)-ethylenediamine (Cyp2EN) and N,N’-bis(2-hydroxycyclohexyl)-ethylenediamine (Cy2EN), with metal ions Cd2+, Cu2+, Ni2+, Pb2+ and Zn2+ were established in this work. Stability constants were determined by Glass Electrode Potentiometry (GEP) and polarography as electrochemical techniques. A new concept, termed Virtual Potentiometry (VP), was also used for the evaluation of stability constants. In this concept, polarographic or polarographic + potentiometric data were evaluated using potentiometric computer software (ESTA). This concept assisted in obtaining a final model for Cd–Cyp2EN and Pb–Cyp2EN systems. It could refine M(HL) complex inaccessible via polarographic study of Pb–Cyp2EN system and refined the hydroxo–complex ML2(OH) that in turn was inaccessible using GEP for Cd– Cyp2EN system. For all metals studied, the complexes ML formed with the ligand Cy2EN were found more stable than the complexes ML formed with the ligand Cyp2EN. The complex M(HL) was obtained for all systems studied, but it seemed to be a minor species. The complex ML2 was obtained in different systems studied with the ligand Cy2EN while this complex was only found in Cd–Cyp2EN system. In several systems potentiometric (ESTA) and voltammetric (3D–CFC) software could not distinguish which hydroxo–complexes were present as these species were formed in the pH range where the ligand was fully deprotonated. Selectivity trends for Cyp2EN and Cy2EN were compared and related to DHEEN as a function of metal ion radius. It was observed that the large metal ions were favoured by the addition of cyclopentyl bridges in DHEEN while the small metal ions were favoured when cyclohexyl bridges were added.

Thesis advisor: Kian L. Tan / Chapter 1. Directing groups are a powerful means of controlling the selectivity in reactions. The field of hydroformylation has used directing group strategies to control regio- and diastereoselectivity with much success. However, directing groups are inherently inefficient as they must be installed and removed from the molecule of interest, and generate a stoichiometric byproduct in the process. Strategies to solve this problem have included the use of exchange reactions that allow for transient binding of substrate to a molecule that can direct the course of the reaction. This allows the use of catalytic quantities of the directing functionality to effect the desired transformation, and obviates the need for installation and removal of the directing functionality in separate steps. Chapter 2. Our lab has developed a phosphorous based ligand that incorporates an N,O-acetal moiety that allows for reversible binding of both alcohol substrates and a metal catalyst. These ligands rapidly exchange with alcohols in the presence of catalytic amounts of p-TsOH. The racemic ligand was found to undergo epimerization on exchange with a chiral alcohol in an effort to isolate enantioenriched material. However, a strategy using a thermodynamic gearing effect of adjacent stereocenters was found to be successful in producing a chiral ligand. Chapter 3. Using catalytic quantities of our scaffolding ligand we are able to effect branch- and diastereoselective hydroformylation of homoallylic alcohols. We offer a model based on A1,3 strain for the origin of the diastereoselectivity, and tested substrates to lend support to the model. We also investigated the use of chiral scaffolding ligands in the enantioselective hydroformylation of homoallylic alcohols, and preliminary results show modest enantioselectivity. Chapter 4. We have expanded the substrate scope of our scaffolding ligand strategy to include the hydroformylation of allylic alcohols. We are able to produce β-hydroxy carbonyl compounds in good yields and with excellent selectivities, which offers an alternative to the formaldehyde aldol reaction. We show that our strategy is successful in the hydroformylation of trisubstituted olefins, which are a difficult class of hydroformylation substrates, where we are able to produce single diastereomers in good yields under mild conditions. We investigated the enantioselective hydroformylation of allylic alcohols and found that while racemization may be a problem with these substrates, in-situ hemi-acetal protection may offer a solution to the problem. / Thesis (PhD) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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The design and application of late transition metal complexes as olefin polymerization catalysts have made tremendous progress in recent years. The advantage of using late transition metal complexes is that they can tolerate a variety of functional groups. We have developed a series of P-N and P-N-P ligands. By using excess n-BuLi to deprotonate H[2b], H[2c] and H[4], we obtained Li[2b](THF)2, Li[2c](THF)2 and Li[4](THF)2 successfully. Li[2b](THF)2 was confirmed by X-ray single crystal diffraction. Using Li[2b](THF)2 as starting material, reacted with 1 eqiv. benzyl chloride and 1 eqiv. Ni(COD)2 in ether solution result in the clean formation of [2b]Ni(CH2Ph).

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The optimisation of I-alkene polymerisation processes by highly active metallocene systems such as racSBIZrMe2 activated by [Ph3C][CN{B(C6Fs)3h] (I) or by [Ph3C][B(C~s)4] (II) was perfonned. Subsequently. a systematic quantitative study of ligand effects on polymerisation activity, molecular weight and polymer microstructure was carried out. Non-bridged and bridged C2y-symmetry zirconocene dimethyls and dichlorides alkylated (or alkyl exchanged) by AlBu'3 (TIBA) and activated by 1 are much less active than Crsymmetric zirconocenes. Propene polymerisations catalysed by those systems afford low molecular weight atactic polypropene. TIBA rapidly alkylates dichloride zirconocenes affording pre-catalysts which, once activated, give a catalytic profile comparable with that obtained with dimethyl zirconocenes. Activities of Crsymmetry raczirconocenes / AlBui3 / I or [Ph3C][H2N{B(C6Fs)3h] (III) in propene polymerisation decrease according to the order SBMbiZrCh (17) > SBIZrCh (16) > EBIZrCh (13) > MBBIZrCh (18) > EBIDMZrCh (19) > EBTHIZrCb (20) > SBSCZrCh (14) > SBBCZrCh (15). These values are not distorted by side effects such as mass transport limitation, so represent real activities, which are the highest reported to date for most of these catalysts under the experimental conditions fixed. The molecular weight of polypropene obtained in propene polymerisation reactions at 1 bar monomer pressure and 20°C ranges from high to low molecular weight (336000 to 4600 g/mol), decreasing according to the precatalyst, in the following order: SBMbiZrCh (17) > SBIZrCh (16) > MBBIZrCh (18) > EBIZrCh (13) > EBTHIZrCh (20) > SBsczrCh (14) > EBIDMZrCh (19) > SBBCZrCh (15). Experiments carried out at 1 bar of monomer pressure and 60°C afford polymers of medium to low molecular weight and the same trend. The order of isotacticity and regiospecificity of the polypropene obtained is: SBMbiZrCh (17) > SBSCZrCh (14) > SBBCZrCh (15) > MBBIZrCh (18) >EBIZrCh (13) > EBDMIZrCh (19) The trityl salt 1 generates more active catalysts than III for the polymerisations perfonned at 20°C, but the situation is reversed at 60 0c. The molecular weight of the polymers obtained by systems activated by III is slightly higher than those obtained using I under both experimental regimes (20 and 60°C / 1 bar). Reactions of L2ZrMe2 (where 4, L= CsMes; 6, L= CSMe4H) with III in presence of AIMe3, fonn [(~)Zr(JlMe) 2AIMe2][H2N{B(C6Fs)3h] (23, L= CsMes; 24, L= CSMe4H) whereas with I, ~ZrMe(Il-Me)B-(C6F5h and L2ZrMe(Il-NC)B-(C6FS)3 were obtained. The protolysis reaction ofY[N(SiMe3)2h with (2-C~sN=CH)(6-Bu)C6H30H (HL3 ) led to a variety of products. Y[N(SiMe3)2h(L3) (29), alongside Y[N(SiMe3)2](L3)2 (30) and Y(L3h (31) were synthesised. M(CH2SiMe3)2(THF)(Ll) (25, M = Sc; 26, M = Y; and L 1 = 2,3,6-Me3C6H3N=CH(6-Bu')C~30H) are highly effective catalysts for the ring-opening polymerisation of E-caprolactone. 26 and 30 also initiate polymerisation of cyc10hexene oxide (CHO).

No description available.

Electrospray ionization mass spectrometry (ESI-MS) is well-established in the detection of large fragile organic molecules such as polymers, peptides and proteins. The study of catalysis by transition metal complexes is complicated by difficulties including ligand lability, complex neutrality and air- and moisture-sensitivity. This work is focused on establishing methods to solve these problems and to apply them to well-understood systems in order to establish credibility before applying them to new systems. Attempts to synthesize a 2,2’-bipyridine (bipy)-type ligand designed to have proton sponge-like properties after binding to a metal are presented. The synthesis of 3,3’-N,N’-bis(dimethylamino)-2,2’-bipyridine was stymied by the formation of two strong intramolecular hydrogen bonds, which are clearly evident in the X-ray crystal structure of the isolated dimethylated 3,3’-bis(methylamino)-2,2’-bipyridine. A simple, one step synthesis of a charge-tagged phosphine from commercially available precursors was developed. Monoalkylation of bisphosphines is a highly convenient approach to such ligands, avoiding the multi-step routes demanded for phosphine/ammonium ligands. 4-diphenylphosphino-1-benzyldiphenylphosphonium-butane tetrafluoroborate was used for the investigation of hydrogenation of olefins by RhCl(PPh3)3 (Wilkinson’s catalyst) by ESI-MS. The results obtained by ESI-MS and ESI-MS/MS on the speciation of the reaction as well as the potential reactivity of select species are in agreement with results obtained by traditional techniques. This work serves as a proof of principle that the methodology employed in our lab is suited to these investigations. The same ligand was used to examine the poorly understood dehydrocoupling of di(n-hexyl)silane by the same catalyst. Continuous monitoring of the reaction over 48 minutes added the time dimension to the data, and insight into the dynamics of the reaction was obtained. Key intermediates were observed, along with decomposition products and circumstantial evidence supporting the formation of a silylene intermediate was also obtained. Lastly, some collaborative work is presented in which some of the techniques and methods developed in our laboratory were applied to problems of interest to other scientists. The formation of a heteronuclear ruthenium-gold cluster is monitored by ESI-MS and further analyzed by ESI-MS/MS. The characteristics that affect the surface activity of an ion are discussed and solutions of a dication with two different anions are examined. Biologically active ruthenium trimers were studied by EDESI-MS/MS, and their fragmentation behaviour shown to be analogous to their properties as CO-releasing molecules. / Graduate