Novel Products from Pentachlorocyclopropane: A Synthetic and Structural Investigation

Abstract

Primary and secondary amines react with pentachlorocyclopropane to form a variety of novel products. Amidines, allyl and cyclopropenyl cations are easily reached by these reactions. The 1,1,3,3-tetra-aminoallyl cations of this series can be reversibly protonated at C(2) to give diamidinium ions. Action of KOH on the diamidinium species CH2[C(NHBut)2]2 2+ produces the diamidine CH2[C(NBut)(NHBut)]2 which hydrolyses to the formamidine CH(NBut)(NHBut). Bis- and tris-amino substituted Cyclopropenylium ions are formed by the action of secondary amines on pentachlorocyclopropane. The cations of this study are stabilised by electron back-donation from nitrogen atoms of substituent groups- The subject of back-bonding was probed in several ways. crystallographically determined structures of representative salts afforded bond length data from which deductions about back-bonding were made. The measurement of barriers to bond rotation is another way that this effect was investigated. Using the technique of variable temperatue NMR, VT-NMR, spectroscopy, energies of activation about unsaturated bonds of allyl, amidinium and cyclopropenylium cations were found. UV-spectra provided additional information concerning bonding in these species. Tautomerism of N,N’-disubstituted amidines was investigated by VT-NMR spectroscopy. Individual tautomers were identified in NMR spectra (13C,1H). Tris-alkylaminocyclopropenylium ions were oxidised to form intensely coloured radical dications. The first Raman spectrum of a cyclopropenyl radical dication was determined. Using the technique of pulse radiolysis we were able to reduce the cyclopropenylium cation, [C3(Net2)3]+, to the molecular radical. Further, pulse experiments enabled standard reduction potentials of representative [C3(NR2)3]2+ and allyl radical dications to be measured and compared. In general, tertiary amines reacted with pentachlorocyclopropane to generate product mixtures. Reaction of para-dimethylaminopyridine, DMAP, on pentachlorocyclopropane was a case in exception. The novel allylide product is the same as that formed via an alternative route. The direct reaction of ammonia on pentachlorocyclopropane product several products including the formamidine NC-N=CH-NH2. A polyamide was prepared from the hydrolysis of a diamidinium ion. The mechanism of formation and the characterisation of this glossy, thermoplastic material is discussed.