Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Chemistry

Major

Inorganic Chemistry

First Advisor

Aaron D. Sadow

Abstract

A series of rhodium and iridium organometallic complexes supported by 1-cyclopentadienyl-1,1-bis(4,4-dimethyl-2-oxazolinyl)ethane (MeC(OxMe2)2(C5H4); BoMCp) and 1-fluorenyl-1,1-bis(4,4-dimethyl-2-oxazolinyl)ethane (MeC(OxMe2)2(C13H8); BoMFlu) are described. Metalation of BoMCp readily occurred through salt metathesis from a thallium intermediate or protonolysis with appropriate metal precursors. In contrast, metalation of the more basic BoMFlu ligand required in situ generation of a potassium carbanion with potassium benzyl and salt metathesis with appropriate metal precursors. The piano-stool complexes of BoMCpM (M = Rh or Ir) were unreactive to substitution chemistry and forcing condition required for C–H activation reactions resulted in decomposition of catalysts prior to successful reactions. However, the two-electron oxidation of BoMCpRh(C2H4)2 with Br2 results in BoMCpRhBr2, a new RhIII species. BoMFluM (M = Rh or Ir) complexes readily underwent substitution chemistry. In addition, BoMFluRhL2 (L2 = C8H12 or C16H12) displayed unique electrochemistry of two reversible 1-electron oxidations. The RhII species could be generated in solution with life time greater than 24 hours for L2 = C16H12.

A series of lanthanide organometallic complexes, Ln{C(SiHMe2)3}3 (Ln = La, Ce, Pr, Nd) were activated by the abstraction of Si–H with 1 and 2 equivalents B(C6F5)3 to generate Ln{C(SiHMe2)3}2HB(C6F5)3 and Ln{C(SiHMe2)3{HB(C6F5)3}2 respectively. The addition of AlR3 (R = Me or iBu) to Ln{C(SiHMe2)3}3 resulted in the complexation of the weaker lewis acid rather than Si–H abstraction. The hydridoborate alkyl complexes, with AliBu3 co-catalysts, are active in butadiene polymerization. Neodymium and cerium were shown to be the most active and all lanthanides showed a ~50:50 selectivity for cis-1,4:trans-1,4 insertions, with exception of lanthanum which showed a slightly higher selectivity for trans-1,4. Further studies with precatalysts Nd{C(SiHMe2)3}3 indicate a polymerization with living character with respect to reaction time but also showed a dependence of molecular weight on Nd:AliBu3 ratio supporting the proposed chain transfer mechanism. Polymerization in saturated hydrocarbon solvent (heptane) improved cis-1,4 selectivity to nearly 90% with Nd{C(SiHMe2)3}3 pre-catalyst.

Nd{C(SiHMe2)3{HB(C6F5)3}2 with 10 equivalents AliBu3 was >95% selective in the polymerization of isoprene to cis-1,4 polyisoprene with good activity in toluene. In contrast, Nd{C(SiHMe2)3}2HB(C6F5)3 was less active in the polymerization of isoprene and displayed a lower selectivity yielding ~40% trans-1,4 polyisoprene. The activation of Nd{C(SiHMe2)3}3 in toluene with different protocols containing the organochloride Ph3CCl were also successful for cis-1,4 selective polymerizations of isoprene. In addition, activation protocols with Ph3CCl improved the cis-1,4 selectivity of polybutadiene to 90% and above. Attempts to utilize Ph3CCl based activations in heptane resulted in highly reactive polymerization ultimately isolating gelled polybutadiene.

Functionalizing agents for the functionalization of polydienes were synthesized from modified literature procedures. The modifications allowed for higher yields for compounds such as (EtO)3Si-CC-Si(OEt)3. The application of (EtO)3Si-CC-Si(OEt)3 as a quenching agent for neodymium-based diene polymerizations resulted in the incorporation of silyl functionalized polydiene and improved physical properties of the resulting rubber composites. 2-Me2XSi-1,3-C4H5 (X = OiPr, OtBu, and NiPr2) monomers were also synthesized and studied for the functionalization of polydienes. No functional group incorporation during neodymium-based polymerizations was observed for X = OiPr or OtBu. However, when X = NiPr2 SiMe groups were observed to be incorporated into polydienes indicating successful functionalization.

Copyright Owner

Bradley M Schmidt

Language

en

File Format

application/pdf

File Size

198 pages

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