Synthesis and Reactivity of Ruthenium and Platinum Complexes with Non-dative Heteroatomic Ligands: Studies of Carbon-hydrogen Bond Activation

Abstract

Several ruthenium complexes with non-dative heteroatomic ligands were prepared and fully characterized, including TpRu(PMe3)2X (X = OH, OPh, OMe, SH; Tp = hydridotris(pyrazolyl)borate). At elevated temperatures (90 °C — 130 °C), complexes of the type TpRu(PMe3)2X (X = OH, OPh, Me, Ph or NHPh) undergo regioselective H⁄D exchange with deuterated arenes. In addition, for X = OH or NHPh, H⁄D exchange occurs at hydroxo and anilido ligands, respectively. For X = OH, OPh, Me, Ph or NHPh, isotopic exchange occurs at the Tp 4-positions with only minimal deuterium incorporation at the Tp 3- or 5-positions. TpRu(PMe3)2Cl, TpRu(PMe3)2OTf (OTf = trifluoromethanesulfonate) and TpRu(PMe3)2SH do not initiate H⁄D exchange in C6D6 after extended periods of time at elevated temperatures. Mechanistic studies indicate that the likely pathway for the H⁄D exchange involves ligand dissociation (PMe3 or NCMe), Ru-mediated activation of an aromatic C-D bond, and deuteration of basic heteroatomic ligand (hydroxo or anilido) or Tp positions via intermolecular D+ transfer.

The Ru(II) complexes TpRu(PMe3)2OR (R = H or Ph) react with excess phenylacetylene at elevated temperatures to produce the phenylacetylide complex TpRu(PMe3)2(CCPh). Kinetic studies indicate that the reaction of TpRu(PMe3)2OH and phenylacetylene likely proceeds through a pathway that involves TpRu(PMe3)2OTf as a catalyst. The reaction of TpRu(PMe3)2OH with 1,4-cyclohexadiene at elevated temperature forms benzene and TpRu(PMe3)2H, while TpRu(PMe3)2OPh does not react with 1,4-cyclohexadiene even after 20 days at 85 C. The paramagnetic Ru(III) complex [TpRu(PMe3)2OH][OTf] is formed upon single-electron oxidation of TpRu(PMe3)2OH with AgOTf. Reactivity studies suggest that [TpRu(PMe3)2OH][OTf] initiates reactions, including hydrogen atom abstraction, with C-H bonds that have bond dissociation energy ≤ 82 kcal⁄mol. Experimentally, the O-H bond strength of the Ru(II) cation [TpRu(PMe3)2(OH2)[OTf] is estimated to be between 82 and 85 kcal⁄mol, while computational studies yield a BDE of 84 kcal⁄mol, which are in reasonable agreement with the observed reactivity of [TpRu(PMe3)2OH]+.

The preparation of the monomeric octahedral platinum(IV) complex (NCN')PtMe2NHPh (NCN' = 2,6-bis[(3,5-dimethylpyrazol-1-yl)methyl]bromobenzene) was achieved through metathesis of platinum triflate complex with alkali metal amido complex. This complex has been isolated and characterized by 1H NMR spectroscopy.