C_(sp3)–H Oxidative Addition at Tantalocene Hydrides

Abstract

Although late transition metals are well-known to activate alkane C–H bonds through oxidative addition, this mechanistic step is atypical for early transition metals. Instead, prior examples of intermolecular C(sp3)–H activation at early transition metals tend to proceed through σ-bond metathesis or 1,2-addition mechanisms. Recent theoretical work suggested that tantalocenes may be capable of activating aliphatic C–H bonds by oxidative addition. Herein, we demonstrate that monoalkyl-substituted tantalocenes R Cp2TaH3 undergo H/D exchange on the alkyl substituent “R” in the presence of C6D6, indicating that intramolecular C(sp3)–H activation takes place. Moreover, Cp2TaH3 was found to catalyze H/D exchange between H2 and octane-d 18 and methylcyclohexane-d 14, an indication of the involvement of an intermolecular C(sp3)–H activation step. Density functional theory calculations support C(sp3)–H oxidative addition at transient Ta­(III), a mechanistic step that has not been previously seen for intermolecular activation of alkanes at tantalum.

Electron-rich pyridines with para-N-heterocyclic imine substituents: ligand properties and coordination to CO2, SO2, BCl3 and PdII complexes

“…47 Based on the molecular electrostatic potential (MESP) [48][49][50] topology analysis, Krishnapriya and Suresh recently indicated that NHI substituents are very effective at increasing the electron-density at the pyridine-N atom which leads to strong donor interactions with metal centers. 51 Here we report the synthesis of two electron-rich pyridines bearing different NHI groups at the para position (Fig. 2) and investigate their potential to act as strong donor ligands in coordination chemistry.…”