Synthesis and structure of pyrrolidinobromodiboranes(4)

The reaction of tetrapyrrolidinodiborane(4) (1) with BBr3 in a 1:1 molar ratio yields a mixture of 1,2-dibromo-1,2-dipyrrolidinodiborane(4) (2) and bromotripyrrolidino- diborane(4) (3), while a 1:2 molar ratio leads in Et2O to compound 2 as the main product along with a small amount of [(C4H8N)(2)B2Br3(OEt)] (4). The new compounds have been characterized by NMR and MS data, as well as by X-ray structure analyses of 2 and 4, of which the former exhibits an interesting polymorphism phenomenon.