Processes in green chemistry have become increasingly important in organic synthesis as we seek to step away from rare and expensive metals, harsh reaction conditions, and hazardous waste generation. The motivation of this work is developing new methods using mild, sustainable photocatalysts by leveraging recent advances in accessing and functionalizing carbon-centered radicals. Chapter 1 details progress with Vitamin B12 (VB12) photocatalysis, emphasizing its applications in cooperative catalysis. Progress toward green synthetic methods using VB12 is discussed as well as the typical reactivity of VB12 both as a nucleophile and radical generator via C-Co bond homolysis. Chapter 2 describes three VB12 photocatalytic systems. Initially, we explore mild terminal olefin formation via halogen elimination. This reactivity was extrapolated to a novel 2,3-elimination reaction by incorporating a Co(II) salen cocatalyst. Following this, we explored epoxide reactivity under varying VB12- photocatalyzed conditions. Utilizing a thiol HAT donor, we allow Markovnikov alcohol formation following mild epoxide ring-opening. Minor change allows epoxide deoxygenation, forming terminal olefins. All mentioned reactions proceed under relatively mild conditions, furnishing high-value products and tolerate a wide range of functional groups otherwise incompatible with established reactions utilizing harsher conditions, demonstrating opportunities for VB12-photocatalysis and cooperative catalysis. Chapter 3 discusses the properties and reactivity of tetrabutylammonium decatungstate (TBADT), a photoactive polyoxometalate capable of generating carbon-centered radicals under mild conditions. Here we explore the process of TBADT excitation, its use in C-H activation and green chemistry processes, and recent examples of TBADT photocatalyzed systems. The increasing application in co-operative photocatalytic systems is also discussed. Chapter 4 discloses our recent addition to TBADT co-operative photocatalysis in hydrofunctionalization of terminal olefins using inert solvent molecules. Leveraging a low TBADT loading of 1 mol % and a cheap thiol co-catalyst, we see excellent selectivity in our product formation and a notable tolerance of otherwise reactive sites under TBADT photocatalysis. Overall, our newly developed methods expand the toolkit of synthetic chemists, allowing for easy access to highly desirable radical intermediates under mild reaction conditions. By exploring and expanding the known reactivity of cobalt- and tungsten-based catalysts, we provide synthetic chemists cheap and sustainable alternatives in functionalization of important compounds.