Synthesis and Structural Aspects of Phosphane – Boranes Derived from Tris(diphenylphosphino)methane, HC(PPh 2 ) 3

The structure of tris(diphenylphosphino)methane, HC(PPh 2 ) 3 ( 1 ), has been determined by X‐ray diffraction. The molecules have approximate C 3 symmetry with the lone pairs at the three phosphorus atoms in an “ all‐trans ” orientation. Variable‐temperature NMR experiments (+ 35 to − 90°C in CH 2 Cl 2 ) show free intramolecular motion in solution. The partially or fully borylated adducts HC(PPh 2 ) 2 [PPh 2 (BH 3 )] ( 2 ), HC(PPh 2 )[PPh 2 ;‐(BH 3 )] 2 ( 3 ), and HC[PPh 2 (BH 3 )] 3 ( 4 ) have been prepared from 1 and THF · BH 3 or Me 2 S · BH 3 . For 2 and 3 the internal rotation about the phosphorus‐methine carbon bonds is also essentially unhindered, but has been shown to be restricted in 4 ( E a =31.2 kJ/mol). The chemical shifts of the methine protons in these compounds can be calculated on the basis of a BH 3 substituent constant.