Influence of Hydrogen Bonding in Competition with Lattice Interactions on Carbonyl Coordination at Phosphorus. Implications for Phosphoryl Transfer Activated States<sup>1</sup>

A series of phosphorus compounds containing carboxyl groups that serve as mimics for amino acid residues was synthesized. The series was composed of the phosphonium salts <b>1A</b>, <b>1B</b>, and <b>2</b>, the anionic phosphines <b>3A</b> and <b>3B</b>, and the anionic phosphine oxide <b>4</b>. X-ray structural analysis revealed that P−O coordination occurred in the presence of extensive hydrogen bonding and led to pseudo or regular trigonal bipyramidal geometries. <sup>31</sup>P chemical shifts indicated retention of the basic coordination geometries in solution. The two forms observed for <b>1</b> and <b>3</b> revealed the influence of hydrogen bonding on the P−O donor interactions while <b>2</b> and <b>4</b> showed the influence of molecular packing effects in competition with hydrogen bonding interactions. The results suggest that phosphoryl transfer enzyme mechanisms should benefit by taking into account P−O donor interactions by residues at active sites that can be manipulated by hydrogen bonding and molecular packing effects in enhancing nucleophilic attack at phosphorus centers.