Constrained geometry catalysts (CGC) are known to be active in the polymerization and copolymerization of alkenes with a distinct control over polymer tacticity. The tethering of one η5-cyclopentadienyl moiety and one pendant donor gives these compounds an accessible metal center as well as ability to maintain their structure throughout the catalytic process. Complexes of this type typically feature one pendant amido donor. Replacement of the pendant amido donor with a nitrogen heterocycle such as an indolyl- or pyrrolyl-group should result in electrophilic metal centers due to reduced N → M π donation, a consequence of electron delocalization of the nitrogen lone pair in the aromatic system. This dissertation reports the development of a new series of constrained geometry ligands that feature indolyl- and pyrrolyl- donor moieties.
In chapter 2, the synthesis and characterization of a series of acetal precursors and their corresponding di(3-methylindolyl)ethane and dipyrrolylethane constrained geometry ligands is reported. Within this report are two new acetal precursors, fluorenyl acetaldehyde diethylacetal, and indenyl acetaldehyde diethylacetal. Also described are the new constrained geometry ligands fluorenyl di(3-methylindolyl)ethane (H3FDI), fluorenyl dipyrrolylethane (H3FDP), indenyl di(3-methylindolyl)ethane (H3IDI), and indenyl dipyrrolylethane (H3IDP). These compounds have been characterized by 1H and 13C NMR spectroscopy as well as mass spectrometry and elemental analysis. The molecular structure of H3FDI·THF has been confirmed by X-ray crystallography. This new set of ligands serves as a framework for constrained geometry complexes of group 4 and 5 transition metals.
Chapter 3 reports the synthesis and characterization of group 4 and 5 constrained geometry complexes of fluorenyl di(3-methylindolyl)ethane (H3FDI) and indenyl di(3-methylindolyl)ethane (H3IDI). Within this report are the first examples of 3-methylindolyl-based CGC’s of group 4 and 5 metals, specifically in the complexes (HFDI)Zr(NEt2)2(THF), (HFDI)Ti(NEt2)2, (IDI)Zr(NEt2), which were prepared using amine elimination methods, and (IDI)Nb(NtBu)(py), (IDI)Nb(NPh), (FDI)Zr(CH3), and (FDI)Ti(CH3), which were prepared via salt metathesis. These complexes have been characterized by 1H and 13C NMR spectroscopy. X-ray crystallography confirmed the bidentate nature of the HFDI ligand in (HFDI)Zr(NEt2)2(THF) as well as the η5-coordination of the indene moiety in (IDI)Zr(NEt2). The structures of analogous complexes (HFDI)Ti(NEt2)2 and (IDI)Nb(NtBu)(py) were determined by 1H and 13C NMR spectroscopy. Another η5-coordinated complex, (FDI)Zr(CH3) was characterized by NMR spectroscopy. This complex exhibits a methyl resonance indicative of transition metal-methyl complexes. These constrained geometry complexes serve as a representative sample for the preparation of various CGC’s with this ligand framework.
Chapter 3 also reports the initial preparation of titanium metal-imido complexes that feature di(3-methylindolyl)methane ligands with one neutral pendant donor. Three complexes, (tBuN)Ti{(2-py)di(3-methylindolyl)methane}, (tBuN)Ti{(N-methylimidazolyl)di(3-methylindolyl)methane}, and (tBuN)Ti{(2-MeOC6H4)di(3-methylindolyl)methane} were characterized by 1H and 13C NMR spectroscopy. X-ray crystallographic analysis of (tBuN)Ti{(2-py)di(3-methylindolyl)methane}, while incomplete, confirmed the connectivity of this complex.
In chapter 4, the in situ generation of copper(I)-pyridine derivative complexes and their olefin binding properties are reported. The new complexes [(Me-nic)3Cu(NCCH3)]PF6 (Me-nic = methylnicotinate), [(3-MeOpy)3Cu(NCCH3)]PF6, and [(3-HOpy)3Cu(NCCH3)]PF6 have been generated in situ and characterized by 1H and 13C NMR spectroscopy. These complexes were examined for their affinity to bind ethylene, propylene, 1-hexene, and cis- and trans-3-hexene. Variable-temperature NMR spectra of these alkene complexes revealed a dynamic system with fast exchange between free and coordinated alkene at temperatures as low as -80 °C. Using an extrapolation method, room temperature binding constants were determined for these alkene complexes. These copper(I) compounds exhibit binding constants for ethylene and propylene that are significantly lower than those of complexes featuring multidentate amine-based donor ligands. Furthermore, these complexes do not appear to bind 1-hexene, cis-3-hexene, or trans-3-hexene.
Appendix 1 reports the synthesis and characterization of metallophosphinate complexes of aluminum and gallium. These complexes are believed to consist of a M2P2O4 (M = Al, Ga) ring structure, which was confirmed by X-ray crystallographic analysis of [Ph2AlO2PPh2]2. Specifically, the complexes [Ph2AlO2PPh2]2, [Ph2GaO2PPh2]2, [Ph2AlO2P(OPh)2]2, and [Ph2GaO2P(OPh)2]2 have been synthesized. Also reported in this appendix are reactions of triphenylaluminum and triphenylgallium with phosphonic acids. Products isolated in reactions with phosphonic acids were difficult to characterize due to their insoluble nature and amorphous morphology.