Formation of both 1:1 and 2:1 complexes of Et(,2)Mg with 15-crown-5 in diethyl ether was observed. In THF or pyridine, no measurable amounts of crown ether complexes formed. The rate of metalation of fluorene by Et(,2)Mg was significantly increased by 15-crown-5. The rate expression for the 15-crown-5 influenced metalation was determined to be the following: rate = k{fluorene}{15-crown-5}{Et(,2)Mg}('3). ET(,2)Mg normally reacts by a 1,2-addition with pyridine. However, in the presence of 15-crown-5, the 1,4-addition predominated. The rate of reaction was also increased 20-fold when 15-crown-5 was present. The influences on the reactions of Et(,2)Mg were postulated to be due to species such as (Mg('2+)(.)15-crown-5)(Et(,3)Mg('-))(,2) or (Mg('2+)(.)15-crown-5)(Et(,6)Mg(,2)('2-)). The reactive complex was postulated to react by a nucleophilic mechanism or an electron transfer mechanism. Efforts to observe evidence for the electron transfer mechanism were unsuccessful.
