o-Bisguanidinobenzene, a Powerful Hydrogen Acceptor:  Crystal Structures of Organic Complexes with Benzoic Acid, Phenol, and Benzyl Alcohol

An o-phenylenediamine-bisguanidine derivative, o-phenylenebis(N,N'-dimethyl-N,N'-ethylene)guanidine (BG), was designed as a powerful hydrogen acceptor. The complexation of BG with a variety of hydrogen donor aromatics carrying OH groups such as benzoic acid (BA), phenol (PH), and benzyl alcohol (BAL) led to the successful isolation of the expected 1 + 1 crystalline complexes, regardless of the acidity of the hydrogen donors. In the case of BA, additional 1 + 2 and 1 + 4 BG−BA crystalline complexes were formed under rigorous conditions of stoichiometry-controlled complexation. These crystals were fully characterized by X-ray crystallographic analysis, indicating that nonbonded interactions in addition to N−H hydrogen bonding play an important role during the crystallization process. Mutual interconversion among the BG−BA crystalline complexes was achieved by the addition of either component to the original complex. Thus, BG was found to act as a powerful hydrogen acceptor in hydrogen bond-based complexation with hydrogen donor aromatics.