Electron Transfers in Organometallic Chemistry and Catalysis: integrated computational/experimental studies

Electron transfer processes are ubiquitous and appealing when involving a transition metal. These events are fast and hard to monitor experimentally, but the modern computational methods highlight the milestones in possible reaction pathways also correlating stereochemistry, electronic structure and energy costs. With DFT calculations, different Ru complexes have been investigated, able to activate organic azides, phosphine oxides and diiodine, respectively. The processes are relevant in the fields of catalysis, tautomerization and the dynamic evolution of halogen-bonded systems. Initially, comparable Ru-porphyrin complexes will be discussed for their roles in amination and aziridination catalysis involving azides. After the N2 departure, a "NR" group (uncharged or in the imido form) remains linked to the metal. The theoretical analysis indicated that the nitrene ligand, as a diradical, can activate a C H linkage of some organic substrate, leading to different nitrogen products, in catalytic fashion. In particular, two interconnected cycles were foreshadowed, both involving the so called "rebound mechanism". In anyone, the N-H and N-C bonds would form in a sequence. The theoretically envisaged reaction mechanisms were also corroborated by ad-hoc experiments. Another case study highlights the Ru role in the H3PO-->H2POH tautomerization, in which H transfer is not of the acid-base type but implies electron transfer through the metal, while in its absence H3PO is unreactive. Finally, the reaction between [Ru(CNtBu)4Cl2] and I2 was investigated, due to the thermodynamically disfavored substitution of the Cl- with the I- ligands to give the 1D solid state product {[Ru(CNtBu)4Cl2]*I2}n. The theoretical-experimental study indicates its stepwise formation through in-situ formed mixed trihalide. Eventually, I-Cl separates from the I-coordinated ClI2- ligand. The process is endergonic, hence facilitated by higher temperatures.