Reactivity of the Bifunctional Ambiphilic Molecule 8-(dimesitylboryl)quinoline: Hydrolysis and Coordination to CuI, AgI and PdII

Abstract

The ambiphilic molecule 8-(dimesitylboryl)quinoline (1) was synthesized by treatment of 8-bromoquinoline or 8-iodoquinoline with n-BuLi followed by dimesitylboronfluoride. Hydrolysis of 1 is unusually rapid compared to bulky triorganoboranes with the sequential loss of mesitylene and formation of mesityl(quinolin-8-yl)borinic acid (2) and 8-quinoline boronic acid dimer (3). Cooperativity within the bifunctional ambiphilic site leads to water activation and protodeboronation of the B–C(Mes) bonds. Blocking of the ambiphilic site of 1 by methylation of the quinoline nitrogen atom leads to an air-stable N-methyl-quinolinium salt. Coordination complexes were formed by reaction of 1 with CuCl, Ag(OTf), and PdCl₂(PhCN)₂ with coordination of the quinolinyl nitrogen to the metal ion. The Cu^I and Ag^I centers are stabilized by η³-BC_ipsoC_ortho π-interaction. The isolated Pd^II complex is a product of cyclometalation, resulting from elimination of HCl upon deprotonation of the ortho-methyl group of nearby mesityl. The bonding in 7 could be understood as a 16-electron Pd complex that features an anionic η³-C_ipso-C_ortho-C_benzyl allylic ligand fragment plus a Pd→B bond, or an η⁴-BC_ipso-C_ortho-C_benzyl boratabutadiene anion fragment.