Benzene hydrogenation utilizing organometallic early transition metal precursors

Abstract

Arene hydrogenation is an important catalytic reaction for the production of intermediates used in the synthesis of nylon, purification of gasoline fuels, and development of liquid organic hydrogen carriers. Herein is described the general utilization of organometallic complexes of early transition metals as pre-catalysts for the hydrogenation of benzene to cyclohexane. The metal precursors investigated for group 4 were [M(CH₂tBu)₄] (M = Ti, Zr, and Hf) and [V(CH₂SiMe₃)₃(THF)] and [M₂(μ₂-CSiMe₃)₂(CH₂SiMe₃)₄] (M = Nb and Ta) were chosen for group 5. These pre-catalysts were tested under semi-batch conditions at 120 °C and 400 psi of H₂, with the highest initial activity from group 4 being [Hf(CH₂tBu)₄] (TOF = 1155 mol C₆H₆ mol M⁻¹ h⁻¹) and for group 5 [Nb₂(μ₂-CSiMe₃)₂(CH₂SiMe₃)₄] (TOF = 1055 mol C₆H₆ mol M⁻¹ h⁻¹). These activities surpass 5 wt% Pd/C (TOF = 393 mol C₆H₆ mol M⁻¹ h⁻¹) and RANEY® nickel (TOF = 72 mol C₆H₆ mol M⁻¹ h⁻¹) tested under similar conditions. These catalytic performances offer new avenues in developing base metal catalysts for hydrocarbon conversion.