Metal-ligand cooperativity employs both ligand and metal active sites to perform multi-component small molecule activation. Over the past few decades, researchers have shown that main-group, p-block elements can perform reactions akin to oxidative addition, reductive elimination, and σ-bond metathesis without the use of transition metals. For example, geometrically constrained, tri-substituted organophosphorus species have been reported to oxidatively add amines and alcohols; cleaving the N-H or O-H bonds via the P(III)/P(V) redox couple. This chemistry is similar to what is observed in traditional organometallic chemistry in that phosphorus is ambiphilic, behaving as both an electron donor and acceptor to break chemical bonds. It is of note that metal-ligand cooperativity that implements transition metals and group 15 elements like phosphorus is not new in concept; however, these ligand scaffolds typically make use of phosphorus in a spectator capacity. My current work focuses on attempts to utilize phosphorus as more than a spectator ligand by taking advantage of ambiphilic character of non-trigonal organophosphorus species. These ligands, paired with first row transition metals, can perform more complex bond making/breaking reactions than either species can perform alone. Towards this goal I have synthesized several different ligand scaffolds with geometrically distorted σ3 phosphorus centers. These ligands contain either di- or trianionic cores bound to phosphorus with either ureate or pyridyl donors to coordinate transition metal ions. To date, I have preliminary evidence of coordination of both Fe(II) and Co(II) as evidenced by paramagnetically-shifted 1H-NMR data. Current investigations are centered around the determination of the identity of these complexes and studying their reactivity. Reactions that will be explored involve initial activation of the N-H or O-H bonds of polar amines or alcohols and subsequent transfer of these functional groups to unsaturated substrates such as olefins. It is proposed that this chemistry will take place by the cooperative reactions of both the non-trigonal phosphorus ligand and the transition metal center.

Synthesis and characterization of transition metal complexes coordinated to non-trigonal, ambiphilic phosphorus ligands

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ACS Fall 2022

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