Pnictogen bonding at the service of gold catalysis: the case of a phosphinostiborane gold complex

The search for alternative gold catalyst activators has led us to consider the design of platforms in which a phosphine gold chloride moiety could be activated via formation of a pnictogen bond with a neighboring antimony unit. Here, we describe that such a system can be accessed from 4-(diphenylphosphino)-5-(diphenylstibino)-2,7-di-tert-butyl-9,9-dimethylxanthene, by oxidation of the stibine with 3,5-di-tert-butyl-o-benzoquinone and by coordination of an AuCl unit to the phosphine. This strategy affords a complex in which a Lewis acidic or pnictogen-bond donor catecholatostiborane unit flanks the adjacent gold chloride moiety. This design impacts the catalytic reactivity of the gold center, as reflected by the ability of this complex to catalyze propargyl amide cyclization reactions. Comparisons with a phosphinostiborane ferrocene analog and computations point to the formation of an intramolecular Au-Cl -> Sb(v) interaction as responsible for the observed catalytic activity. Intramolecular pnictogen bonding between a stiborane and a gold-bound chloride ligand is proposed to activate carbophilic catalysis at the late transition metal.

Automated summary

The design of a gold catalyst activation system through the formation of a pnictogen bond with a neighboring antimony unit is described. The resulting complex shows efficient catalytic reactivity, possibly through an intramolecular Au-Cl -> Sb(v) interaction for carbophilic catalysis.