Date of Award
Doctor of Philosophy (PhD)
Cyclopentadienyl first row transition-metal compounds have been well studied since the 1950's, with the nearly ubiquitous CpFe(CO)2Me (FpMe) (Cp = η5-C5H5) being one of the first organometallics to be fully characterized. Despite the decades of study that have been poured into this complex, reactions between FpMe and primary phosphines have not been reported. Catalytic reactions with primary phosphines are generally understudied, including dehydrocoupling and P-C bond forming reactions such as hydrophosphination. A novel mechanism of dehydrocoupling and P-C bond formation that has received even more limited attention is α-elimination. This dissertation describes efforts in proving that FpMe is a competent catalyst for α-phosphinidene elimination through detailed trapping, labelling, and mechanistic studies. Additionally, the potential of α-elimination for the catalytic synthesis of phospholes from commercially available starting materials is shown, which is currently unknown.
In the course of α-elimination studies, it was found that [CpFe(CO)2]2 (Fp2) is a visible-light activated photocatalyst for a variety of main-group bond forming reactions, including amine borane dehydrocoupling, siloxane formation, silylcyanation, and the double hydrophosphination of terminal alkynes with secondary phosphines. By utilizing commercially available and inexpensive LED bulbs Fp2 was an active catalyst for these reactions, which avoided the use of expensive, hazardous, and energy inefficient mercury arclamps.
During studies to determine whether other cyclopentadienyl first row transition-metal compounds could catalyze α-elimination, it was found that CpCo(CO)I2 and Cp*Co(CO)I2 (Cp* = η5-C5Me5) are active catalysts for ammonia borane dehydrocoupling and transfer hydrogenation. These compounds are rare examples of cobalt compounds able to catalytically dehydrocouple amine boranes as well as catalyze a rare example of transfer hydrogenation that utilizes ammonia borane as a hydrogen source.
I will also describe my year of research at Los Alamos National Laboratory (LANL) working under Dr. Jaqueline Kiplinger. Two primary projects are described herein: the first of which is the use of phenylsilane as a safe, versatile method for the synthesis of the bis(cyclopentadienyl) actinide hydrides [Cp*2An(H)(µ-H)]2 from the bis-alkyl complexes Cp*2AnMe2. It is shown that these hydrides are excellent precursors for the synthesis of a variety of actinide metallocenes. Additionally, in the case of uranium, by adjusting the equivalents of phenylsilane added, the oxidation state and nuclearity of the hydrides synthesized can be altered. Second, efforts in synthesizing a variety of novel actinacycles including actinacyclopentadienes, actinacyclocumulenes, a novel uranacyclopropene, and actinacyclopentadienecyclobutabenzenes that display alternating aromatic and antiaromatic character.
Number of Pages
Pagano, Justin Kane, "Cyclopentadienyl Compounds of the First Row Transition Metals and Early Actinides: Novel Main-Group Bond Forming Catalysis and New Metallacycles" (2017). Graduate College Dissertations and Theses. 700.