Rational Design of a Carbon-Boron Frustrated Lewis Pair for Metal-free Dinitrogen Activation

Abstract

Molecular nitrogen (N 2 ) is abundant in the atmosphere and, found in many biomolecules, an essential element of life. The Haber–Bosch process, developed over 100 years ago, requires relatively harsh conditions to activate N 2 on the iron surface and generate ammonia for use as fertilizer or to produce other chemicals, leading to consumption of more than 2 % of the world's annual energy supply. Thus, developing “green” approaches for N 2 activation under mild conditions is particularly important and urgent. Here we demonstrate that a metal-free N 2 activation could be favorable both thermodynamically and kinetically (with an activation energy as low as 9.1 kcal mol −1 ) by using a carbon-boron formal frustrated Lewis pair, which is supported by high-level coupled cluster calculations. Mechanistic studies reveal that aromaticity plays a crucial role in stabilizing both the transition state and the product. Our findings highlight the importance of a combination of an N-heterocyclic carbene with a methyleneborane unit in metal-free N 2 activation, providing conceptual guidance for experimental realization.