Donor-Acceptor Complexes between Organoamines and Phosphorus Tribromide

Z. Naturforsch. 56 b, 1163-1171 (2001); received July 17, 2001 Hypervalence, Phosphines, Lewis Acid-Base Adducts Lewis acid-base adducts between NMe3, tmeda (A^A^Af'-tetramethylethylenediamine), and 1.4-dimethylpiperazine as donors and PBr3 as acceptor have been prepared and structurally characterized. NMe3 and tmeda form 1:1 adducts (Me3 N)PBr3 (1) and (tmeda)PBr3 (2), re­ spectively, while 1,4-dimethylpiperazine adds 2 molecules of PBr3 leading to [(1,4-dimethylpiperazine)(PBr3):] (3). Adduct 2 is found in two modifications 2a and 2b with different crystal and molecular structures. (Crystal data of 1: monoclinic P2\/n, a = 5.983(3), b = 10.821(2), c = 13.877(5) Ä, ß = 99.70(2)°, Z = 4. 2a: monoclinic P2i/c, a = 7.891(1), b = 12.826(1), c = 12.218(2) A ,ß = 102.162(6)°, Z = 4. 2b: monoclinic P2]/n, a = 11.687(2), b = 8.375(1), c = 12.668(1) A, ß = 102.74(1)°, Z = 4. 3: monoclinic P2Jc, a = 6.383(3), b = 16.36(3), c = 8.407(3) A , ß = 101.49(2)°, Z= 2). The molecular structures of 1 and 2 indicate a partially ionic character with a strongly bonded amine and one (1 ) or two (2 ) weakly bonded bromine atoms. In 2 the donor tmeda is bonded through both nitrogen atoms to one phosphorus atom. In 3 the 1.4-dimethylpiperazine ring is in chair conformation, the methyl and PBr3 substituents being in equatorial and axial positions, respectively. Due to axial-axial repulsion the N-P donor-acceptor bonds are long while the P-Br bonds are rather uniform in length.