Methane Activation by 5 d Transition Metals: Energetics, Mechanisms, and Periodic Trends.

Although it has been known for almost three decades that several 5d transition-metal cations will activate methane at room temperature, a more detailed examination of these reactions across the periodic table has only recently been completed. In this Minireview, we compare and contrast studies of the kinetic energy dependence of these reactions as studied using guided-ion-beam tandem mass spectrometry. Thermochemistry for the various products observed (MH+ , MH2+ , MC+ , MCH+ , MCH2+ , and MCH3+ ) are collected and periodic trends evaluated and discussed. The mechanisms for the reactions as elucidated by synergistic quantum chemical calculations are also reviewed. Recent spectroscopic evidence for the structures of the MCH2+ dehydrogenation products are discussed as well.