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Flexible ambiphilic ligand scaffolds have garnered attention in catalysis due to their ability to adopt multiple binding orientations. Recently, several platinum group metal complexes featuring the flexible, ambiphilic b-phosphinoethylborane ligand were reported in the literature; however, the impact of primary coordination sphere ligands and solvent on the properties of the Lewis acidic borane moiety remain underexplored. Rhodium and iridium complexes ligated by 9-borabicyclo[3.3.1]nonanyl-based b- diphenylphosphinoethylborane were studied using a combination of crystallography and 11B NMR spectroscopy. The studies revealed that both the primary coordination sphere and solvent had an impact on the formation of Lewis acid–base adducts. Specifically, inner-sphere Lewis pair formation was dependent on the nature of the X-type ligand bound to the metal center. Similar dependencies were identified with solvents in which Lewis acid interaction was found to correlate with solvent donor number. 

A unique class of β-boron-functionalized non-steroidal anti-inflammatory compound (pinB-NSAID) was previously synthesized via copper-catalyzed 1,2-difunctionalization of the respective vinyl arene with CO2 and B2pin2 reagents. Here, pinacolylboron-functionalized ibuprofen (pinB-ibuprofen) was used as a model substrate to develop the conditions for pinacol deprotection and subsequent boron functionalization. Initial pinacol-boronic ester deprotection was achieved by transesterification with diethanolamine (DEA) from the boralactonate organic salt. The resulting DEA boronate adopts a spirocyclic boralactonate structure rather than a diazaborocane–DABO boronate structure. The subsequent acid-mediated hydrolysis of DEA and transesterification/transamination provided a diverse scope of new boron-containing ibuprofen derivatives. 

In this comment, insights gained from density functional the- ory into the mechanism by which the Cu(I)-catalyzed boracar- boxylation of vinyl arenes occurs with specific focus on the CO2 insertion step are presented. Preliminary calculations indicated a potential non-covalent interaction between boron and CO2 in the carboxylation transition state, implicating cooperative CO2 activation. A study of boron Lewis acidity was conducted through substitution of sp2 mono-boron substituents. An inverse correlation between boron valence deficiency (BVD) and the enthalpic barrier of CO2 insertion into the β- borylbenzyl-Cu(I) bond was revealed, supporting Lewis acid/ base cooperativity between boron and the proximal oxygen of CO2 at the carboxylation insertion transition state. These find- ings suggest that future methodology development should consider strategic incorporation of similar Lewis acidic func- tionality to facilitate carboxylation of challenging substrates.