4 research outputs found
Metal Catalyzed Group 14 And 15 Bond Forming Reactions: Heterodehydrocoupling And Hydrophosphination
Investigation of catalytic main-group bond forming reactions is the basis of this dissertation. Coupling of group 14 and 15 elements by several different methods has been achieved. The influence of Si–N heterodehydrocoupling on the promotion of α-silylene elimination was realized. Efficient Si–N heterodehydrocoupling by a simple, earth abundant lanthanide catalyst was demonstrated. Significant advances in hydrophosphination by commercially available catalysts was achieved by photo-activation of a precious metal catalyst.
Exploration of (N3N)ZrNMe2 (N3N = N(CH2CH2NSiMe3)33–) as a catalyst for the cross-dehydrocoupling or heterodehydrocoupling of silanes and amines suggested silylene reactivity. Further studies of the catalysis and stoichiometric modeling reactions hint at α-silylene elimination as the pivotal mechanistic step, which expands the 3p elements known to engage in this catalysis and provides a new strategy for the catalytic generation of low-valent fragments. In addition, silane dehydrocoupling by group 1 and 2 metal bis(trimethylsilyl)amide complexes was investigated. Catalytic silane redistribution was observed, which was previously unknown for d0 metal catalysts.
La[N(SiMe3)2]3THF2 is an effective pre-catalyst for the heterodehydrocoupling of silanes and amines. Coupling of primary and secondary amines with aryl silanes was achieved with a loading of 0.8 mol % of La[N(SiMe3)2]3THF2. With primary amines, generation of tertiary and sometimes quaternary silamines was facile, often requiring only a few hours to reach completion, including new silamines Ph3Si(nPrNH) and Ph3Si(iPrNH). Secondary amines were also available for heterodehydrocoupling, though they generally required longer reaction times and, in some instances, higher reaction temperatures. By utilizing a diamine, dehydropolymerization was achieved. The resulting polymer was studied by MS and TGA. This work expands upon the utility of f-block complexes in heterodehydrocoupling catalysis.
Stoichiometric and catalytic P–E bond forming reactions were explored with ruthenium complexes. Hydrophosphination of primary phosphines and activated alkenes was achieved with 0.1 mol % bis(cyclopentadienylruthenium dicarbonyl) dimer, [CpRu(CO)2]2. Photo-activation of [CpRu(CO)2]2 was achieved with a commercially available UV-A 9W lamp. Preliminary results indicate that secondary phosphines as well as internal alkynes may be viable substrates with this catalyst. Attempts to synthesize ruthenium phosphinidene complexes for stoichiometric P–E formation have been met with synthetic challenges. Ongoing efforts to synthesize a ruthenium phosphinidene are discussed.
The work in this dissertation has expanded the utility of metal-catalyzed main-group bond forming reactions. A potential avenue for catalytic generation low-valent silicon fragments has been discovered. Rapid Si–N heterodehydrocoupling by an easily obtained catalyst has been demonstrated. Hydrophosphination with primary phosphines has been achieved with a commercially available photocatalyst catalyst, requiring only low intensity UV light
A Commercially Available Ruthenium Compound for Catalytic Hydrophosphination
Hydrophosphination with a commercially available ruthenium compound, bis(cyclopentadienylruthenium dicarbonyl) dimer ([CpRu(CO)2]2), was explored. Styrene derivatives or Michael acceptors react readily with either primary or secondary phosphines in the presence of 0.1 mol% of [CpRu(CO)2]2 under photolysis with an inexpensive and commercially available UV-A 9W lamp. In comparison to related photoactivated hydrophosphination reactions with [CpFe(CO)2]2 as a catalyst, these ruthenium-catalyzed reactions proceed at greater relative rates with lower catalyst loadings. <br /
Si–N Heterodehydrocoupling with a Lanthanide Compound
[LaÂ{NÂ(SiMe<sub>3</sub>)<sub>2</sub>}<sub>3</sub>THF<sub>2</sub>] (<b>1</b>) is an effective precatalyst
for the heterodehydrocoupling
of silanes and amines. Coupling of primary and secondary amines with
aryl silanes was achieved with a loading of 0.8 mol % of [LaÂ{NÂ(SiMe<sub>3</sub>)<sub>2</sub>}<sub>3</sub>THF<sub>2</sub>]. With primary amines,
generation of tertiary and sometimes quaternary silamines was facile,
often requiring only a few hours to reach completion, including new
silamines Ph<sub>3</sub>SiÂ(<sup><i>n</i></sup>PrNH) and
Ph<sub>3</sub>SiÂ(<sup><i>i</i></sup>PrNH). Secondary amines
were also available for heterodehydrocoupling, though they generally
required longer reaction times and, in some instances, higher reaction
temperatures. This work expands upon the utility of <i>f</i>-block complexes in heterodehydrocoupling catalysis
Analysis of Polymeryl Chain Transfer Between Group 10 Metals and Main Group Alkyls during Ethylene Polymerization
The
ability of various group 10 α-diimine and salicylaldimine
polymerization catalysts to undergo chain transfer with main group
metal alkyls during ethylene polymerization has been investigated
in depth. The catalyst systems with the most efficient chain transfer
were found to be cationic (α-diimine)Ni catalysts paired with
dialkyl zinc chain-transfer reagents, in which all growing polymeryl
chains were transferred to Zn on the basis of <sup>13</sup>C NMR analysis.
In these systems, chain transfer was found to be dependent on the
sterics of both the catalyst and the chain-transfer reagent (CTR).
When less sterically encumbered catalysts or CTRs were utilized, the
relative rate of bimetallic chain transfer to chain propagation was
increased; however, in cases where chain termination via β-H
elimination was extremely rapid, chain transfer to Zn was kinetically
not viable. Importantly, chain transfer from (α-diimine)Ni catalysts
to Zn alkyls is also very sensitive to the strength of the Zn–C
bond: ZnMe<sub>2</sub> (186 kJ/mol) is a significantly poorer chain-transfer
reagent than ZnEt<sub>2</sub> (157 kJ/mol), despite being less sterically
encumbered. Finally, the nature of the catalyst counteranion (MAO
or BÂ(ArF)<sub>4</sub><sup>–</sup> ArF = 3,5-(CF<sub>3</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) does not have a significant
impact on the rate of chain transfer to ZnR<sub>2</sub> relative to
propagation, indicating that the same factors that determine propagation
rates also determine bimetallic chain-transfer rates