Synthesis and Coordination Chemistry of a Novel Bidentate Phosphine:  6-(Diphenylphosphino)-1,3,5-triaza-7-phosphaadamantane (PTA-PPh<sub>2</sub>)

The upper rim of 1,3,5-triaza-7-phosphaadamantane (PTA) has been modified for the first time. Lithiation of PTA, with <i>n</i>-butyllithium, resulted in deprotonation of an α-phosphorus methylene and the formation of 1,3,5-triaza-7-phosphaadamantane-6-yllithium (PTA-Li). The chiral chelating phosphine 6-(diphenylphosphino)-1,3,5-triaza-7-phosphaadamantane (PTA-PPh<sub>2</sub>) was synthesized, in racemic form, by the reaction of PTA-Li with ClPPh<sub>2</sub>. PTA-PPh<sub>2</sub> has been fully characterized in solution by multinuclear NMR spectroscopy and mass spectrometry and in the solid state by X-ray crystallography. The <sup>31</sup>P NMR spectrum contains a pair of doublets at −19.8 and −100.1 ppm (d, <sup>2</sup><i>J</i><sub>PP</sub> = 65 Hz). Unlike PTA, the new bidentate phosphine, PTA-PPh<sub>2</sub>, is insoluble in aqueous solutions. Two group 6 metal carbonyl complexes, [M(CO)<sub>4</sub>(PTA-PPh<sub>2</sub>)] (M = W and Mo), were synthesized by the addition of PTA-PPh<sub>2</sub> to <i>cis</i>-[M(CO)<sub>4</sub>(pip)<sub>2</sub>] and characterized by NMR spectroscopy, IR spectroscopy, and X-ray crystallography. Also reported are the solid-state structures of <i>cis</i>-[W(CO)<sub>4</sub>PTA<sub>2</sub>], <i>cis</i>-[W(CO)<sub>4</sub>(PTA)(PPh<sub>3</sub>)], and [W(CO)<sub>4</sub>DPPM] (DPPM = diphenylphosphinomethane). PTA-PPh<sub>2</sub> appears to be sterically similar to and slightly more electron-donating than DPPM.