Synthesis and Crystal Structures of N,N′-Disubstituted Piperazines

Abstract

The structure of 1,4-diphenylpiperazine (1) was determined; it crystallized in the orthorhombic space group Pbca, a = 8.6980(7), b = 8.4287(7), c = 17.6359(15), V = 1292.94(19), Z = 4. Three novel N,N′-disubstituted piperazines were synthesized via reductive amination of piperazine or N-diphenylmethylpiperazine. The products were characterized by NMR and X-ray crystallography. 1,4-Diphenethylpiperazine (2) crystallized in the monoclinic space group C2/c, a = 17.9064(13), b = 6.2517(5), c = 14.9869(11), β = 90.613(4), V = 1677.6(2), Z = 4. 1-Benzhydryl-4-benzylpiperazine (3) crystallized in the monoclinic space group Pn, a = 5.9450(2), b = 19.0722(4), c = 8.6084(2), β = 96.4600(10), V = 98.1790(10), Z = 2. 1-Benzhydryl-4-(pyridin-2-ylmethyl)piperazine (4) crystallized in the monoclinic space group P2/c, a = 13.5637(2), b = 5.82170(10), c = 24.0645(4), β = 90.613(4), V = 1888.16(5), Z = 4. Comparison of the structures showed significant sp2 character for the piperazine nitrogen atoms in 1. Each structure showed multiple intermolecular non-bonding interactions. The structures of 1,4-diphenylpiperazine, diphenethylpiperazine, 1-benzhydryl-4-benzylpiperazine, and 1-benzhydryl-4-(pyridin-2-ylmethyl)piperazine are reported.