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This thesis examines the interaction of hydrides of the group 13 metals aluminium and gallium with transition metal centres. Furthermore, a gallium-based system is developed which activates a wide range of E-H bonds, with the product of H2 activation found to act as a catalyst for the reduction of CO2 to a methanol derivative. Chapter 3 details the synthesis of a number of alane and gallane adducts of expanded-ring N-heterocyclic carbene (NHC) ligands, which are more strongly σ-donating and sterically shielding analogues of classical NHCs. These NHC adducts are found to be apposite for the formation of σ-alane and σ-gallane complexes at group 6 metal carbonyl fragments, which has allowed the characterisation of the first κ2 σ-gallane complexes. The attempted formation of a terminally coordinated κ3 σ-alane complex leads instead to the isolation of a novel dinuclear cluster featuring both μ:κ1,κ1 and μ:κ2,κ2 coordination to Mo(CO)3 units. The work presented in Chapter 4 probes the interaction of the β-diketiminate stabilised gallane Dipp2NacNacGaH2 with transition metal carbonyls. Far from simply mimicking the chemistry of the alane congener Dipp2NacNacAlH2, which forms simple κ1 and κ2 σ-alane complexes, the gallane shows a marked propensity towards dehydrogenation and formation of direct M-Ga(I) bonds. This represents a rare mode of reactivity among group 13 hydrides, being unprecedented beyond boron chemistry, and provides a new route to M-Ga bond formation. Experimental and computational investigations of the mechanism suggest that initial Ga-H oxidative addition is facile, and is generally followed by rate-limiting loss of H2. The reaction of Dipp2NacNacAlH2 with Co2(CO)2 is shown to yield an unusual alane complex which displays an unprecedented degree of Al-H activation in a σ-alane complex. Chapter 5 represents an extension of the work described in Chapter 5, investigating the interaction of Dipp2NacNacMH2 (M = Al, Ga) with cationic group 9 transition metal fragments supported by ancillary phosphine ligands. While attempts to isolate unsupported, cationic σ-alane complexes prove unsuccessful, Dipp2NacNacGaH2 readily binds to cationic rhodium and iridium centres, forming the first cationic σ-gallane complexes as well as cationic gallylene complexes resulting from complete Ga-H oxidative addition. The extent of Ga-H bond activation is shown to be markedly dependent on the nature of the phosphine co-ligands. In particular, a series of rhodium complexes is reported which represents snapshots of the oxidative addition process, from a Rh(I) σ-gallane complex to a Rh(III) gallylene dihydride, with two further complexes which are on the cusp of these two oxidation states. Described in Chapter 6 are the synthesis and reactivity studies of an ambiphilic system, Dipp2NacNac′Ga(tBu), featuring a three-coordinate gallium centre supported by a deprotonated NacNac ligand. The combination of this electrophilic gallium centre with the highly nucleophilic exocyclic alkene functionality facilitates the cooperative activation of protic, hydridic and apolar E-H bonds. Accordingly, molecules including H2, NH3, H2S and SiH4 may be cleaved under mild conditions. Moreover, the hydride product of H2 activation is shown to be a competent catalyst in conjunction with HBpin for the reduction of CO2 to the methanol derivative MeOBpin.

Traditional methods to perform cyclopropane synthesis typically utilize nucleophiles orcarbenoid intermediates reacting with olefins to form two C–C bonds in a single reaction. In order to find new ways to synthesize these functional groups, it is necessary to find orthogonal techniques that offer new ways to access similar products and stereochemical outcomes as these methods. One way to accomplish this is by using alcohols, one of the most prevalent functional groups in chemistry, as a starting material. Alcohols will readily generate electrophiles, such as sulfonates and halides, that can be activated by transition metals. Methods utilizing this reactivity will be reported in this dissertation to perform cross-electrophile coupling reactions that generate cyclopropanes. In Chapter 1, a nickel-catalyzed cross-electrophile coupling to synthesize alkylcyclopropanes from 1,3-dimesylates is reported. This reaction is tolerant of a range of pendent aryl substituents to provide mono- and di-substituted cyclopropanes. The mechanism of the reaction was investigated to show a stereoablative oxidative addition at the secondary electrophilic center. Notably, the reaction proceeds through a 1,3-diiodide that is formed in-situ using the Grignard reagent. This reaction took advantage of the secondary radical intermediate to render the method diastereoselective towards trans-disubstituted cyclopropanes. Finally, an enantioenriched 1,3-dimesylate substrate provided an enantiopure disubstituted cyclopropane without requiring directing groups, a technique traditionally used in asymmetric cyclopropane synthesis. The mechanism of this reaction was further defined in Chapter 3, leading to new insights in the iodide source, stereochemistry, and radical intermediates in the reaction. After stereospecific 1,3-diiodide formation by the agency of the Grignard reagent, the nickel catalyst engages the secondary mesylate in a halogen atom transfer to form a long-lived alkyl radical. Radical rebound of the nickel catalyst allows for a stereospecific SN2-type reaction onto the primary alkyl iodide leading to double inversion at the primary center. A reaction to synthesize fluorinated cyclopropanes from benzylic ethers and gemdifluoromethyl groups is reported in Chapter 2. Utilizing recent methods in photocatalytic olefin difluoromethylation, the substrates were accessed in two synthetic steps. This reaction is proposed to undergo a stereospecific oxidative addition of the benzylic ether and subsequent SN2-type reaction onto the alkyl fluoride to synthesize the cyclopropane products. In order to expand the substrate scope of the cross-electrophile coupling of 1,3-dimesylates, new conditions were developed (Chapter 4). 1,3-Dimesylates are readily transformed into 1,3- dihalides using halide salts in organic solvents. Reacting these 1,3-dihalides, formed in-situ, with zinc dust provides a scalable synthesis of cyclopropane products in high yields low-cost reagents. End stage modification of statin medicinal agents was performed to show the wide functional group tolerance of these conditions. Finally, a method to synthesize vinyl fluoride-substituted cyclopropanes from secondary mesylates and allylic gem-difluorides is reported in Chapter 5. This reaction is tolerant of a range of functional groups by using zinc metal as a reductant for the nickel catalyst. Mechanistic investigations of this reaction support an oxidative addition by the nickel catalyst to the allylic gem-difluoride before an SN2-type reaction on the mesylate to form the products. Computational studies show two mechanistic pathways that are hypothesized to occur with similar rates, both starting with coordination of the nickel catalyst to the electron-deficient alkene.

Computational chemistry has gained interest as a characterization tool to predict photoluminescence, reactivity and structural properties of organic and transition metal complexes. With the rise of methods including relativity, these studies have been expanded to the accurate modeling of luminescence spectra of complexes with considerable spin-orbit splitting due to heavy metal centers as well as the reaction pathways for these complexes to produce natural products such as hydrogen gas. These advances have led to the synthesis and utility of more effective catalysis as well as the development of more effective organic light emitting diodes (OLEDs) through the incorporation of organometallic complexes as emitters instead of typical organic emitters. In terms of significant scientific advancement presented in this work is in relation to the discovery of significant spin-orbit splitting in a gold(I) alkylphosphine complex, where the splitting results in the states that emit in different colors of the visible region of the electromagnetic spectrum. This work also reveals the discovery both computationally and experimentally, of a genuine polar-covalent bond between two-closed shell metals. This work highlights a complex with an incredibly short gold(I) – copper(I) intermetallic distance leading to a vibrational frequency and dissociation energy that is on par with those of other systems with single-bonded metal centers. Lastly, this work outlines a strategy for the production of hydrogen gas through the use of trinuclear cyclic coinage metal complexes as catalysis to split hydrohalic acids.