Bifunctional Effect of a Triple-Bond Heterobimetallic Zr/Co System for Hydrogen Activation

The heterobimetallic systems recently emerged as effective catalysts for hydrogen storage and related chemical transformations. Different from previous Lewis base-transition metal, Lewis acid-transition metal, and frustrated Lewis pair bifunctional catalysis, the function of the heterobimetallic centers in catalysis is still ambiguous. This theoretical study focuses on the Zr/Co complex, aiming to elucidate the important role of the Zr≡Co triple bond in catalytic H2 activation and hydrogenation. Our results suggest that the Lewis acidic Zr center is stabilized by the Zr≡Co triple bond. For hydrogen activation, the Zr/Co complex prefers the fac-addition mechanism, in which the cobalt center mainly activates the hydrogen cleavage with the assistance of the Lewis acidic Zr center. The Lewis acidic Zr site is activated by breaking the Zr≡Co triple bond, promoting the formation of the bridging hydride bond. The bridging hydride is stabilized by the zirconium d orbital to form a 3c–2e bond, resulting in a less nucleophilic bridging hydride. The hydride reactivity and the conjugated effect are two main factors affecting the subsequent hydrogenation. However, the E/Z selectivity is derived from the steric hindrance of the iPr group. Furthermore, based on the understanding of the bifunctional mode of the heterobimetallic multiple bond, catalysts were designed for divergent E/Z selectivity. These results highlight the importance of the bifunctional function of the heterobimetallic multiple bond, which should be valuable for the rational design of heterobimetallic catalysts.