Synthesis and Coordination Chemistry of a Novel Bidentate Phosphine:  6-(Diphenylphosphino)-1,3,5-triaza-7-phosphaadamantane (PTA-PPh₂)

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 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-PPh₂) was synthesized, in racemic form, by the reaction of PTA-Li with ClPPh₂. PTA-PPh₂ has been fully characterized in solution by multinuclear NMR spectroscopy and mass spectrometry and in the solid state by X-ray crystallography. The ³¹P NMR spectrum contains a pair of doublets at −19.8 and −100.1 ppm (d, ²J_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)₄PTA₂], cis-[W(CO)₄(PTA)(PPh₃)], and [W(CO)₄DPPM] (DPPM = diphenylphosphinomethane). PTA-PPh₂ appears to be sterically similar to and slightly more electron-donating than DPPM.