Synthesis, Characterization, and Reactivity of the Half-Sandwich Ruthenium (II) Hydride Complexes of 1,3,5-Triaza-7-Phosphaadamantane
AuthorLanorio, Jocelyn Pineda
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A new water-soluble bis-PTA ruthenium (II) hydride complex, IndRu(PTA)2H, is obtained by conversion of the mixed-phosphine ruthenium complex IndRu(PTA)(PPh3)Cl into IndRu(PTA)(PPh3)H followed by addition of 1,3,5-triaza-7-phosphaadamantane (PTA). IndRu(PTA)2H is air sensitive and reacts with chlorinated solvents yielding IndRu(PTA)2Cl. The synthesis, isolation, reactivity, and crystal structure of IndRu(PTA)2H and IndRu(PTA)2Cl are described. H/D exchange reactions of IndRu(PTA)2H with D2O was performed and compared with DpRu(PTA)2H and the previously studied CpRu(PTA)2H. The rate of H/D exchange of the hydride complexes was found to be in the order of DpRu(PTA)2H > CpRu(PTA)2H > IndRu(PTA)2H. Insertion of CS2 into the Ru-H bond of Cp'Ru(PTA)(PR3)H (Cp' = Cp, Tp, Dp, Ind, Cp*; PR3 = PTA, PPh3) was successfully accomplished to make a series of air-stable Cp'Ru(PTA)(PR3)(SC(S)H) complexes. All compounds were structurally characterized both in solution (multinuclear (1H, 13C, 31P) NMR spectroscopic studies, and ESI-MS) and in the solid state (IR, and single-crystal X-ray crystallography). The rate of CS2 insertion observed for Cp'Ru(PTA)(PPh3)H is in the order of Cp* > Tp > Dp > Cp> Ind, a result of interplay of electronic and steric factors of the Cp' capping ligand. Insertion of the isoelectronic CO2 into the Ru-H bonds was investigated and found to be unfavorable. The CO2-inserted products Cp'Ru(PTA)2(OC(O)H) (Cp' = Cp, Dp) were unstable and non-isolable, easily reverting back to the corresponding hydrides upon warming or by purging with N2. Insertion of bulkier molecules such as phenyl isothiocyanate and phenyl isocyanate into the Ru-H bonds of Cp'Ru(PTA)(PR3)H are also described. Cp'Ru(PTA)2CH3 where Cp' = Cp, Dp, Ind was synthesized by the reaction of CH3Li with Cp'Ru(PTA)2Cl in THF. The methylation products were characterized using 1H, 13C and 31P NMR spectroscopy. The properties of these novel Cp'Ru(PTA)2CH3 complexes are described. The efficiency of the chloride version of the catalysts has been explored for the atom transfer radical addition (ATRA) of CCl3CO2Et to styrene in the presence of AIBN as a radical source. A series of kinetics plots for the addition of CCl3CO2Et to styrene catalyzed by Cp'Ru(PPh3)(PR3)Cl (where Cp' = Cp, Cp*; PR3 = PTA, PMe3) obtained using 1H NMR spectroscopy were used to investigate the effects of [AIBN], [PPh3], Cp* and PR3 ligands.