Crystal Engineering of Polymeric Structures with Dative Boron Nitrogen Bonds: Design Criteria and Limitations

A database analysis of known adducts between pyridyl donor ligands and Lewis acidic boronate esters revealed a preference for a particular conformation at the boron centers. On the basis of this analysis, we designed two tritopic pyridyl ligands, which were expected to form polymeric structures upon combination with ditopic bis(benzenedioxaborole) Lewis acids. Instead of two-dimensional networks, we observed the formation of chains of macrocycles for different ester/N-donor combinations. This kind of structural motif is unprecedented for polymeric B-N adducts. The predictability of the chemistry was compromised by the low strength of the dative B-N bond, which resulted in incomplete adduct formation and/or cocrystallization of starting materials.