The upper rim of 1,3,5-triaza-7-phosphaadamantane (PTA) has been modified for the first time. Lithiation of PTA, with n-butyllithium, resulted in deprotonation of an R-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-PPh2) was synthesized, in racemic form, by the reaction of PTA-Li with ClPPh2. PTAPPh(2) has been fully characterized in solution by multinuclear NMR spectroscopy and mass spectrometry and in the solid state by X-ray crystallography. The P-31 NMR spectrum contains a pair of doublets at -19.8 and -100.1 ppm (d, (2)J(PP) = 65 Hz). Unlike PTA, the new bidentate phosphine, PTA-PPh2, is insoluble in aqueous solutions. Two group 6 metal carbonyl complexes, [M(CO)(4)(PTA-PPh2)] (M = W and Mo), were synthesized by the addition of PTA-PPh2 to cis-[M(CO)(4)(pip)(2)] and characterized by NMR spectroscopy, IR spectroscopy, and X-ray crystallography. Also reported are the solid-state structures of cis-[W(CO)(4)PTA(2)], cis-[W(CO)(4)(PTA)(PPh3)], and [W(CO)(4)DPPM] (DPPM = diphenylphosphinomethane). PTA-PPh2 appears to be sterically similar to and slightly more electron-donating than DPPM.