Tridentate phosphine/amine-based

A well-known piece of phosphorus chemistry is the functionalization of a P-H bond by direct reaction with a twofold excess of formaldehyde in acidic conditions, which leads to the formation of an air- and moisture-stable phosphonium salt [60, 61]. Subsequent treatment of a phosphonium salt with a base was followed by the addition of a nucleophile, typically an amine (including ammonia, primary, or secondary amines) [62]. In this way, achiral mono- [63], di-[60,64], and tridentate [65] ligands have been synthesized by combining two modules, namely the phosphine unit and the amine group. 

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