Water‐Soluble and Air‐Stable <i>P</i>,<i>N</i>‐Pyridyl Ligands Derived from 1,3,5‐Triaza‐7‐Phosphaadamantane

1,3,5‐Triaza‐7‐phosphaadamantane (PTA) derivatives PTA–CH(2‐py)OH ( 1 ), PTA–CH(3‐py)OH ( 2 ), and PTA–CH(4‐py)OH ( 3 ) are prepared by reacting lithiated PTA (PTA–Li) with the corresponding pyridinecarboxaldehydes. The air‐stable phosphines 1 – 3 are highly water‐soluble, with S 25° = 426 ( 1 ), 159 ( 2 ), and 578 ( 3 ) g L −1 (0.6–2.2 M). The crystal packing structures of the PTA–pyridyl compounds and their P ‐oxides show the presence of several different solid‐state intermolecular hydrogen bonding patterns. Water‐soluble and air‐stable ruthenium(II)–arene complexes of 1 and 2 are synthesized and characterized. 1 coordinates to ruthenium in a κ 2 ‐ P , N binding mode, while 2 and 3 bind in a κ 1 ‐ P mode. The 3‐ and 4‐pyridyl ligands 2 and 3 appear capable of bridging to additional metal centers, complicating their syntheses. The ruthenium–arene complexes of ligands 1 and 2 are found to have significant water solubility and activity toward aqueous‐phase nitrile hydration.