TETRAAZA MACROCYCLIC DERIVATIVES OF ARSENIC - HCYCLENAS, HCYCLENAS.GAME3, AND HCYCLAMAS

Treatment of cyclen, a 12-atom tetraaza macrocycle, with tris(dimethylamino)arsine leads to HcyclenAs, the structure of which is best described as a distorted pseudo trigonal bipyramid (tbp) with two nitrogens and a lone pair of electrons at the equatorial positions and two nitrogens at the axial sites. One of the axial nitrogens is protonated and leads to a longer ("transannular") As...N distance [of 2.400 (7) angstrom]. A 1:1 complex, HcyclenAs.GaMe3, is formed when HcyclenAs is treated with trimethylgallium where the site of complexation is the nonprotonated axial nitrogen The geometry of the HcyclenAs moiety m the complex is essentially unchanged from the free ligand. Treatment of the larger 14-atom tetraaza macrocycle cyclam with tris(dimethylamino)arsine leads to the corresponding HcyclamAs species which has a structure similar to that of HcyclenAs except for a longer transannular interaction [2.722 (8) angstrom]. Thus, both macrocycles stabilize similar geometries about arsenic, and the three macrocyclic compounds can be envisioned as zwitterionic arsoranide (R4As-) species. Although cyclen also stabilizes a tbp geometry around phosphorus in cyclenPH, the latter contains a P-H rather than an N-H bond. The lack of an As-H bond is most likely due to the lower thermodynamic stability of this linkage. The X-ray data for HcyclenAs are as follows: C8H17N4As, a = 21.532 (5) angstrom, b = 11.796 (2) angstrom, c = 17.396 (4) angstrom, beta = 105.08 (2)-degrees, monoclinic, C2/c, Z = 16. The X-ray data for HcyclenAs.GaMe3 are as follows: C11H25N4GaAs, alpha = 7.620 (2) angstrom, b = 13.073 (5) angstrom, c = 15.784 (5) angstrom, beta = 90.00, orthorhombic, P2(1)2(1)2(1), Z = 4. The X-ray data for HcyclamAs are as follows: C10H21N4As, a = 15.866 (5) angstrom, b = 8.460 (3) angstrom, c = 9.333 (4) angstrom, beta = 100.98 (3)-degrees, monoclinic, P2(1)/c, Z = 4.