Phosphino[tris(trimethylsilyl)methyl]Boranes and 2,4‐Bis[tris(trimethylsilyl)methyl]‐1,3,2,4‐diphosphadiboretanes [1]

The reaction of tris(trimethylsilyl)methylboron dihalides (Me 3 Si) 3 CBX 2 (X = Cl, F) with the lithium phosphides LiPH t Bu and LiPHmes leads to the phosphinoboranes (Me 3 Si) 3 CBX‐(PHR), (Me 3 Si) 3 CB(PHR) 2 or the 1,3,2,4‐diphosphadiboretanes [(Me 3 Si) 3 CB(PR)] 2 , depending on the ratio of the reagents, the reaction temperature and concentration. High dilution and low temperatures are required for the synthesis of (Me 3 Si) 3 CB(Hal)PHR ( 1–3 ) in order to prevent the formation of (Me 3 Si) 3 CB(PHR) 2 ( 4 and 5 ). The latter compounds are best prepared in a two step phosphination from (Me 3 Si) 3 CBHal 2 and LiPHR. At higher temperatures the four‐membered 1,3,2,4‐diphosphadiboretanes [(Me 3 Si) 3 CB(PR)] 2 6 and 7 are the most stable compounds. On the other hand, compounds of type (Me 3 Si) 3 CB(Hal)PR 2 , 8 and 9 , are thermally more stable than the monophosphinoboranes 1 – 3 . Phosphinoboranes of type (Me 3 Si) 3 CB(PR 2 ) 2 (R = t Bu, mes) could not be prepared. NMR and mass spectral data are in accord with the monomeric nature of compounds 1 to 9 .