Contrasting reactivity of B-Cl and B-H bonds at [Ni(IMes)₂] to form unsupported Ni-boryls

[Ni(IMes)(2)] reacts with chloroboranes via oxidative addition to form rare unsupported Ni-boryls. In contrast, the oxidative addition of hydridoboranes is not observed and products from competing reaction pathways are identified. Computational studies relate these differences to the mechanism of oxidative addition: B-Cl activation proceeds via nucleophilic displacement of Cl-, while B-H activation would entail high energy concerted bond cleavage.