Selenium imides: 77Se NMR investigations of the SeCl2-tBuNH2 reaction and X-ray structures of Se3(NtBu)3, tBuNSe(mu-NtBu)2SO2, and tBuNSe(mu-NtBu)2SeO.

Abstract

The reaction of SeCl2 with tert-butylamine in various molar ratios in THF at -78 degrees C has been investigated by 77Se NMR spectroscopy. In addition to the known Se-N heterocycles Se6(NtBu)2 (1) and Se9(NtBu)6 (2), the acyclic imidoselenium(II) dichlorides ClSe[N(tBu)Se]nCl (4, n = 1; 5, n = 2) and two new cyclic selenium imides [Se3(NtBu)2]n (3, n = 1 or 2) and Se3(NtBu)3 (6) have been isolated and identified. An X-ray analysis shows that 6 is a six-membered ring in a chair conformation with magnitude of d(Se-N) = 1.833 A. Crystal data: 6, trigonal, P3c1, a = 9.8660(3) A, c = 20.8427(7) A, V = 1757.0(1) A3, Z = 6. The 1H, 13C, and 77Se NMR data for 1-6 are reported, and some reassignments of earlier literature data for 1-3 (n = 1) are made. The decomposition of tBuN=Se=NtBu at 20 degrees C in toluene was monitored by 77Se NMR. The major products are 6 and 3. The Se(IV)-N systems tBuNSe(mu-NtBu)2E (7, E = SO2; 8, E = SeO) were prepared by the reaction of a mixture of SeCl4 and excess tBuNH2 with SO2Cl2 or SeOCl2, respectively. Compound 8 is also generated by the cycloaddition reaction of tBuNSeNtBu with tBuNSeO. Both 7 and 8 consist of slightly puckered four-membered rings. The mean terminal and bridging Se-N distances in 7 are 1.665(2) and 1.948(2) A, respectively. The corresponding values for 8 are 1.687(4) and 1.900(4) A, and d(Se=O) = 1.628(4) A. Crystal data: 7, monoclinic, P2(1)/c, a = 18.669(4) A, b = 12.329(2) A, c = 16.463(3) A, beta = 115.56(3) degrees, V = 3418.4(11) A3, Z = 4; 8, triclinic, P1, a = 6.372(1) A, b = 9.926(2) A, c = 14.034(3) A, alpha = 99.320(3) A, beta = 95.764(3) A, gamma = 103.876(3) A, V = 841.3(3) A3, Z = 2.