The preparation of the complexes TpMo(NO)(DMAP)(η-PhCF) (5) and TpMo(NO)(DMAP)(η-benzene) (3) is described. The CF group is found to stabilize the metal-arene bond strength in 5 by roughly 3 kcal/mol compared to that in 3, allowing the large-scale synthesis and isolation of the trifluorotoluene analogue (5, 37 g, 70%). When a benzene solution of 5 is allowed to stand, clean conversion to the benzene analogue 3 occurs, and this complex may be precipitated from solution upon the addition of pentane and isolated. The trifluorotoluene complex is shown to be a synthetic precursor to functionalized cyclohexadienes: In solution, it selectively protonates at the ortho position, and the resulting η-arenium species undergoes reactions with nucleophiles at the adjacent meta carbon. Thus, reactions of 5, triflic acid, and either N-methylpyrrole or 1-methoxy-2-methyl-1-(trimethylsilyloxy)-1-propene result in 5-substituted-1,3-cyclohexadienes after removal of the metal.

The dearomatization of naphthalene and anthracene is explored by their η 2 coordination to {TpMo-(NO)(MeIm)} and {TpMo(NO)(DMAP)} (where Tp = hydridotris(pyrazolyl)borate, MeIm = 1-methylimidazole, and DMAP = 4-(dimethylamino)pyridine). The DMAP and MeIm complexes have nearly identical redox properties and abilities to bind these polycyclic aromatic hydrocarbons (PAHs), but unlike MeIm, the DMAP ligand can be protonated at N while remaining bound to the metal. This action enhances the πacidic properties of DMAP, resulting in greater stability of the molybdenum toward oxidation by acid. Utilizing this feature of the DMAP ligand, several new 1,2-dihydronaphthalenes and 1,2-dihydroanthracenes were prepared. Furthermore, it was found that acetals and Michael acceptors could function as electrophiles for the PAHs using the DMAP system, resulting in several new mono-and 1,4-dialkylated products.

The preparation and properties of the complex (R Mo ,R)-MoTp(NO)(DMAP)(η 2 -α-pinene) are described (∼10 g scale; DMAP = 4-(dimethylamino)pyridine; Tp = hydridotris(pyrazolyl)borate). This complex undergoes exchange of the pinene with a wide range of other π ligands including acetone, ethyl acetate, N,N-dimethylformamide, acetonitrile, and naphthalene. Treatment of the α-pinene complex with iodine results in the complex (S)-MoTp(NO)(DMAP)(I), which is recovered in enantioenriched form (er = 99:1; yield >90%; scale 4.6 g). Reduction of this molybdenum(I) precursor results in enantioenriched molybdenum(0) complexes, including (R)-MoTp-(NO)(DMAP)(η 2 -trifluorotoluene). Sequential treatment of this arene complex with acid, a masked enolate, and iodine regenerates MoTp(NO)(DMAP)(I) along with an alkylated 1-(trifluoromethyl)cyclohexa-1,3-diene with an er value as high as 99:1. This process demonstrates the efficient transfer of asymmetry from α-pinene to the diene product. Accompanying studies with (1R)-myrtenal reveal a redox-catalyzed pinene/myrtenal ligand exchange occurring through Mo(I) intermediates.

Polycyclic aromatic hydrocarbons (PAHs; e.g., naphthalene and anthracene) form stable η2-bound complexes with the dearomatizing fragment {TpMo­(NO)­(MeIm)} (where Tp = hydridotris­(pyrazolyl)­borate; MeIm = 1-methylimidazole). These complexes undergo protonation at the α carbon followed by regioselective nucleophilic addition at the adjacent β carbon. The nucleophile (a pyrrole or an enolate) adds stereoselectively, anti to the face of metal coordination. The resulting 1,2-dihydroarene ligand may be isolated via metal oxidation by iodine to provide the free 1,2-dihydroarene in moderate yield (∼60%), as well as TpMo­(NO)­(MeIm)­(I), the precursor of the original PAH complex (∼80–90%). Thus, a formal catalytic cycle for the dearomatization of naphthalene and anthracene has been demonstrated.

The large-scale synthesis of the scorpionate ligand Ttz (hydrotris(1,2,4-triazol-1-yl)borate) is reported as well as syntheses of Group VI complexes K[M(L)(CO)3] and M(L)(NO)(CO)2 (L = Ttz or Tp (hydrotris(pyrazol-1-yl)borate), M = Mo or W). The redox characteristics of the metal in these Ttz complexes are shown to be reversibly modulated by interactions between the exo-4-N lone pairs of the triazolyl rings and Brønsted or Lewis acids. The basicity of the scorpionate ligand in [M(Ttz)(CO)3]- is quantified (pKaH2O values range from 1.1 to 4.6) and found to be dependent on both the oxidation state and identity of the metal. In the presence of Brønsted acids, the observed redox behavior for the one-electron oxidation of the Group VI metal center is consistent with a proton-coupled electron transfer (PCET). Indeed, for both Mo and W derivatives, a one-electron oxidation decreases the pKa by ∼3.5 units.

2-(Dimethylamino)pyridine (2-DMAP) and 2-(dimethylamino)pyrimidine derivatives form η2-bound complexes with the dearomatization agent {TpW(NO)(PMe3)} that are each capable of undergoing a double protonation. In the case of 2-DMAP, the resulting π-allyl species reacts with the α-carbon of thiophene or 2-methylfuran, thereby coupling the heterocyclic rings. In the case of the thiophene-derived product, subsequent oxidative decomplexation using ceric ammonium nitrate affords a novel organic amidine derivative. Examples of tungsten-promoted acetylation and fluorination of the aminopyridine ring are also described.

Ruthenium(II) complexes with the general formula TpRu(L)(NCMe)Ph (Tp = hydrido(trispyrazolyl)borate, L = CO, PMe3, P(OCH2)3CEt, P(pyr)3, P(OCH2)2(O)CCH3) have previously been shown to catalyze arene alkylation via Ru-mediated arene C–H activation including the conversion of benzene and ethylene to ethylbenzene. Previous studies have suggested that the catalytic performance of these TpRu(II) catalysts increases with reduced electron-density at the Ru center. Herein, three new structurally related Ru(II) complexes are synthesized, characterized, and studied for possible catalytic benzene ethylation. TpRu(NO)Ph2 exhibited low stability due to the facile elimination of biphenyl. The Ru(II) complex (TpBr3)Ru(NCMe)(P(OCH2)3CEt)Ph (TpBr3 = hydridotris(3,4,5-tribromopyrazol-1-yl)borate) showed no catalytic activity for the conversion of benzene and ethylene to ethylbenzene, likely due to the steric bulk introduced by the bromine substituents. (Ttz)Ru(NCMe)(P(OCH2)3CEt)Ph (Ttz = hydridotris(1,2,4-triazol-1-yl)borate) catalyzed approximately 150 turnover numbers (TONs) of ethylbenzene at 120 °C in the presence of Lewis acid additives. Here, we compare the activity and features of catalysis using (Ttz)Ru(NCMe)(P(OCH2)3CEt)Ph to previously reported catalysis based on TpRu(L)(NCMe)Ph catalyst precursors.

ii I am fortunate to have so many people to thank. I truly would not be here, having written all of the pages before you if it weren't for the huge amounts of love and support that I have received from so many along the way. Most of the people listed in this section know that I have a difficult time expressing my feelings. I will attempt to overcome that difficulty here and hopefully give a small amount of something back to all those who have contributed so much to me. I know that I will not do justice to the feelings that I have, but will try my best to express them here. With that in mind, know that as you read on that this was the most difficult, and time consuming part of my thesis to write. It is because I have been fortunate enough to come into contact with a great many wonderful people that any of the subsequent chapters exist; so to say that these acknowledgements are the foundation of my thesis would be an understatement.So here we go. I will start with those who have supported me from the start, my parents. My parents have always encouraged, nurtured, loved and supported me in any venture that I have undertaken. As teachers, they have shown me the importance of education in so many ways. As their way of life, in their professional lives, and also at home. They always stressed the importance of reading, but also looked to establish education in other less traditional ways. These have included travel, and along the way sparked my love of both history and the outdoors, which have continued to be passions of mine to this day. Through my parents I also learned a great deal about the world around me that was not covered in the classroom curriculum. Learning how to build and fix things from my Dad has been a skill that has helped me countless times throughout life, although it also came with the unfortunate side effect of having to constantly fix the rotovap. My Dad also instilled in me the time and money sinks of boating and woodworking, both of which have given me countless hours of joy, and a means of finding peace at stressful times in my life as an adult. In the classroom my parents taught me to iii appreciate all subjects, which I did (except for English class, I hate grammar as anyone at Dean's writing workshop could tell you). This eventually led me to chemistry, which astonished my parents. I went off to college and pursued chemistry, becoming more interested as classes progressed, although I still could not shake my humanities leaning, and ended up with degrees in both chemistry and history.My parents continued to give me support when I set off for Charlottesville. They helped in my apartment search and moving the large amount of stuff that I had accumulated. They then made several house hunting trips, and we drove circles around Charlottesville and the surrounding counties. When I finally bought my first home in the spring of my first year, they both used nearly all of their vacation time to come down and help me with the seemingly endless remodels. I never could have finished it without them. All ...