Cooperative Bond Activation and Catalytic CO 2 Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene.

Metal-ligand cooperativity has emerged as an important strategy to tune the reactivity of transition-metal complexes for the catalysis and activation of small molecules. Studies of main-group compounds, however, are scarce. Here, we report the synthesis, structural characterization, and reactivity of a geometrically constrained (silylene)-stabilized borylene. The one-pot reaction of [(SiNSi)Li(OEt)] (SiNSi = 4,5-(silylene)-2,7,9,9-tetramethyl-9-acridin-10-ide) with 1 equiv of [BBr(SMe)] in toluene at room temperature followed by reduction with 2 equiv of potassium graphite (KC) leads to borylene [(SiNSi)B] (), isolated as blue crystals in 45% yield. X-ray crystallography shows that borylene () has a tricoordinate boron center with a distorted T-shaped geometry. Computational studies reveal that the HOMO of represents the lone pair orbital on the boron center and is delocalized over the Si-B-Si unit, while the geometric perturbation significantly increases its energy. Borylene () shows single electron transfer reactivity toward tris(pentafluorophenyl)borane (B(CF)), forming a frustrated radical pair [(SiNSi)B][B(CF)], which can be trapped by its reaction with PhSSPh, affording an ion pair [(SiNSi)BSPh][PhSB(CF)] (). Remarkably, the cooperation between borylene and silylene allows the facile cleavage of the N-H bond of aniline, the P-P bond in white phosphorus, and the C═O bond in ketones and carbon dioxide, thus representing a new type of main-group element-ligand cooperativity for the activation of small molecules. In addition, is a strikingly effective catalyst for carbon dioxide reduction. Computational studies reveal that the cooperation between borylene and silylene plays a key role in the catalytic chemical bond activation process.