Investigation of some acidic ruthenium dihydrogen and hydride complexes

grantor: University of TorontoThe reaction of Cp*Ru(dfepe)Cl (1) in dry CH2Cl 2 at -78°C with H2 (g) and AgOTf produced a mixture of Cp*Ru(dfepe)H (2) and [Cp*Ru(dfepe)(H)2] + as shown by 1H NMR spectroscopy. The addition of excess HOW to the mixture of monohydride and dihydride under H2 (g) gave only the dihydride. X-ray diffraction studies of the dfepe complexes 1 and 2 revealed close contacts between the fluorine atoms of the dfepe ligand and the hydrogen atoms on the methyl groups of the Cp* ligand. Cyclic voltammetry studies, were carried out on 1 and 2 and the redox potentials were found to be quite positive. The EL value of 1/2 dfepe was found to be 0.89 V (NIHE), similar to CO. From the X-ray diffraction study, the complex Cp*Ru(tmbp)H (6) has a distorted three-legged piano stool structure and the tmbp ligand is relatively planar. The 'E'L value of 1/2 tmbp was found to be 0.52 V (NHE), similar to dppm. The hydrido cyano ruthenium (II) complexes 'trans'-[RuH(CN)(L) 2] (L = dppe or depe) were protonated with one equivalent of acid to produce 'trans'-[RuH(CNH)(dppe)2](OTf) (12 ) and 'trans'-[Ru([eta]2-H2)(CN)(depe) 2](BF4) (21). The addition of a second equivalent of acid to complex 12 produced the dihydrogen Complex ' trans'-RU([eta]2-H2)(CN)(dPPe)2](TfO···HOTf) (15). The highly acidic dicationic dihydrogen complex, ' trans'-[Ru([eta]2-H2)CNH(dppe)2](TfO···HOTf) 2 (13), was observed when two equivalents of acid was added to complex 15. Complex 13 was deprotonated by El 2O, reforming complex 15. Complex 15 was unstable and readily lost H2 under Ar forming 'trans'-[Ru(OTf)(CNH)(dppe) 2](OTf) (14). When complex 14 was placed under H2 gas, complex 15 reformed. This is a rare example of the formation of an acidic dihydrogen complex from H2 gas. Both dihydrogen complexes 13 and 15 have H-H distances of 0.88 Å which were determined from 1'J'(HD) values (32.4 Hz and 32.0 Hz, respectively). Another example of the formation of an acidic dihydrogen complex from H2 gas is the formation of the termally unstable complex ' trans'-[Ru([eta]2-H2)(CN)(dppe)2](OTf) (18) from 'trans'-[Ru(OTf)(CN)(dppe)2] (17). The dihydrogen complex rearranges to the thermodynamically stable complex 12 at room temperature. The Inelastic Neutron Scattering (INS) study of 'trans'-[Ru([eta] 2-H2)H(dppe)2][BPh4] revealed weak [pi]-backbonding from the Ru centre to the dihydrogen ligand. The room temperature solution 2H NMR spectrum revealed that 'trans'-[Ru([eta] 2-D2)Cl(dppe)2]PF6 (22) readily undergoes H/D exchange with the dppe ligands. From the variable temperature solid state 2H NMR spectra of 22, the coherent tunneling frequency of the deuterons of the dideuterium ligand was observed to be 60.8 kHz. (Abstract shortened by UMI.)Ph.D