Investigation in transition metal dihydrogen and dihydride chemistry

The tungsten carbonyls W(CO)₆, (PMe₃)W(CO) ₅, and (PMe₃)₂W(CO)₄ were each photolyzed at low temperature in toluene and reacted with hydrogen gas. In all cases the result was the formation of new tungsten (II) dihydrides. These results were not the expected dihydrogen complexes predicted from a variety of computational studies. The complexes rapidly decomposed in the absence of hydrogen atmospheres, and were not isolated but they were definitively characterized as dihydrogen complexes by NMR techniques. This work demonstrates the importance of steric effects upon the structure of transition metal hydrides.; The complex [Cp*Ru(dppm)(H₂)]+ was studied and NMR experiments found this complex to have novel temperature and isotopic dependence of the dihydrogen ligand bond length r_HH . This confirmed recent computational predictions made for a model complex. The observed behavior of the dihydrogen ligand is unprecedented for any isolable compound. A series of related complexes were prepared and studied and the ground state H-H bond length was found to be the crucial factor determining isotopic and temperature dependence of r_HH in these complexes.; The complex Cp*Ru(dmpm)Cl was observed to have an extremely labile chloride ligand allowing for its ready displacement and reactivity with a variety of molecules. The new dihydrogen complex [Cp*Ru(dmpm)(HD)]+ and the new nitrogen dimer [(Cp*Ru(dmpm)₂N₂]++ were isolated from these studies. Several new compounds were investigated by NMR spectroscopy, including a new highly reactive 16-electron complex [Cp*Ru(dmpm)] +, and a new silane complex [Cp*Ru(dmpm)(H-SiEt₃)] +. Preliminary evidence for possible alkane C-H bond activation was also observed in the course of this study. The direct reaction of Cp*Ru(dmpm)Cl with H₂ gas was also observed in MeOH. The H NMR spectra of [Cp*Ru(dmpm)H] + demonstrated evidence for novel hydrogen bonding in solution.