RESUMO
[reaction: see text]. An efficient solid-phase synthesis of polymer-supported N-arylmaleimides has been developed. Various N-arylmaleimidobenzoic acids (MBA) were elaborated onto Rink and SASRIN resins by reaction of the aniline precursors with maleic anhydride followed by facile cyclative dehydration of the resulting maleimic acids. Applications of these acid-cleavable MBA resins in the solid-phase synthesis of highly decorated pyrrolidines and as thiol scavengers are presented.
RESUMO
Our interest in higher nuclearity sulfido-bridged Fe-S clusters, because of their occurrence in several proteins including nitrogenase, prompted us to investigate the solution chemistry of the functionalized cluster [Fe(4)S(4)(SH)(4)](2)(-) (1). (n-Pr(4)N)(2)[1] crystallizes in space group P2(1)/n of the monoclinic system with a = 26.201(1) Å, b = 11.4999(5) Å, c = 28.090(1) Å, and beta = 110.735(1) degrees. The X-ray structure reveals the conventional cubane-type geometry with an [Fe(4)S(4)](2+) core symmetry more closely approaching T(d)() than the tetragonally distorted D(2)(d)() symmetry reported for the (PPh(4))(2)[1] (Müller, A.; Schladerbeck, N. H.; Bögge, H. J. Chem. Soc., Chem. Commun. 1987, 35). In solution, 1 exists in dynamic equilibrium with self-condensation products formed through elimination of H(2)S and formation of sulfido-bridged cluster oligomers, one of which (4) is prevalent. The self-condensation equilibrium is shifted toward cluster 1. When acetonitrile solutions of 1 were treated with thiols more acidic than H(2)S, it was possible to detect hydrosulfido terminal ligand substitution products of 1 as well as those of the major self-condensation product 4. Detailed analysis of the products in acetonitrile solutions of 1, as well as those generated in solutions of 1 treated with acidic thiol, by electrospray mass spectrometry, and both (19)F and (1)H NMR spectroscopy indicates the presence of a sulfido-bridged acyclic trimer of [Fe(4)S(4)](2+) clusters, i.e. {[Fe(4)S(4)(SH)(3)](2)[Fe(4)S(4)(SH)(2)](&mgr;-S)(2)}(6)(-) (4), a hitherto unprecedented Fe-S structural pattern, as the principal Fe-S cluster self-condensation product.
RESUMO
Attempts to prepare tris(ligand) metal complexes of technetium in intermediate oxidation states with potentially bidentate oxazoline- and thiazoline-containing ligands were unsuccessful; when pertechnetate was reduced in the presence of excess ligand, TcO(2).xH(2)O was produced. Instead, by reaction with preformed M.O cores, a series of oxotechnetium(V) and oxorhenium(V) complexes of the formula MOXL(2) (M = Re, X = Br; M = Tc, X = Cl) and HL = 2-(2'-hydroxyphenyl)-2-oxazoline (Hoz), 2-(2'-hydroxy-3'-methylphenyl)-2-oxazoline (Hmoz), 2-(2'-hydroxyphenyl)-2-thiazoline (Hthoz), and 2-(2'-hydroxyphenyl)-2-benzoxazoline (Hhbo) have been prepared. These compounds have been characterized by a variety of techniques including single-crystal X-ray diffraction. Crystals of Hthoz (C(9)H(9)NOS) are monoclinic, with space group P2(1)/n, a = 7.5342(6) Å, b = 12.2187(6) Å, c = 9.3942(8) Å, beta = 94.233(7) degrees, and Z = 4; those of TcOCl(thoz)(2) (C(18)H(16)ClN(2)O(3)S(2)Tc) are monoclinic, with space group P2(1)/n, a = 16.506(1) Å, b = 7.664(1) Å, c = 16.3216(6) Å, beta = 111.154(4) degrees, and Z = 4; those of ReOBr(oz)(2) (C(18)H(16)BrN(2)O(5)Re) are orthorhombic, with space group Pbca, a = 12.864(2) Å, b = 25.369(2) Å, c = 11.025(2) Å, and Z = 8. The structures were solved by direct (Hthoz) or Patterson (metal complexes) methods and were refined by full-matrix least-squares procedures to R = 0.033, 0.032, and 0.028 for 1600, 3152, and 2651 reflections with I >/= 3sigma(I), respectively. In the two complexes, the geometry around the metals is distorted octahedral with the halide ligands in each bound cis, and one phenolate oxygen from one ligand in each bound trans to the metal-oxo linkage. In ReOBr(oz)(2), the two oxazoline nitrogens are coordinated trans to one another; in TcOCl(thoz)(2), the two thiazoline nitrogens are found cis to one another.