The condensed-phase heats of formation of BF,,Me,SO, BF,,MeCO,Et, and BF,,C,H,N from gaseous reactants are -42-3 & 0.2, -32-9 f 0-2, and 46 & 2 kcal. mole-l, respectively. This indicates that, with respect to BF,, the donor strengths of the ligands decrease in the series C,H,N > Me,SO > MeC0,Et. Displacement reactions are consistent with this order.The complex BCl,,Ph,SO afforded P-C1*C6H4*SC6H, when heated.RECENTLY, we examined the reactions of dimethyl sulphoxide and ethyl acetate with some halides of Group I11 and IV elements. In general, the first step is the formation of molecular addition compounds. These have variable stability and some [e.g., BCl,,Ph,SO (see below) or BCl,,MeCO,Et readily deconpose irreversibly. The boron trifluoride complexes, on the other hand, dissociate when heated. The sulphoxide-boron trichloride system is quite complicated. With dimethyl sulphoxide, we previously showed that the M. I;.