Mendeleev Communications Electronic Version, Issue 4, 2001 (pp. 125.164) The first metal complex with a vic-dihydroxyamine and its oxidised derivative Sergei V. Fokin, Galina V. Romanenko and Victor I. Ovcharenko* International Tomography Centre, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 33 1399; e-mail: ovchar@tomo.nsc.ru 10.1070/MC2001v011n04ABEH001460 The NiII complex with a vic-dihydroxyamine has been synthesised, characterised by X-ray analysis and oxidised to unusual bischelate containing fully dehydrogenated hydroxyamine groups. 2,3-Dihydroxyamino-2,3-dimethylbutane 1 is widely used for syntheses of nitronylnitroxides.1,2 However, vic-dihydroxyamines were never investigated as ligands. Here, we report on the synthesis and structure of the first NiII complex with vic-dihydroxyamine, which may be oxidised to a bischelate with fully dehydrogenated hydroxyamine groups.We found that the interaction between aqueous NiCl2 and 1 forms a finely dispersed yellow precipitate of 2 (Scheme 1), which is sparingly soluble in water and organic solvents.¢Ó The same product crystallised from the reaction mixture on the addition of a base (Na2CO3 or NaOH).Compound 2 is stable in the solid state but gradually decomposes in solution during two to three days. The single-crystal study¢Ô showed that the structure of the coordination site in 2 is a nearly regular square formed by Ni2+ and the N atoms of two bidentately coordinated molecules of 1, one of which is deprotonated (Figure 1).¡× The chloride ion is not involved in coordination.The cation has two nonequivalent intramolecular H-bonds between the coordinated ligands, because of which 2 is related to classical metal dioximates. However, the Ni.N bond in 2 is much longer (1.92 A) than that in metal dioximates (~1.87 A), and 2 is much less stable in solution, where it is readily decomposed by dilute acids.An interesting property of 2 is its ability to be oxidised to unusual complex 3, where the ligand is the product of complete dehydrogenation of hydroxyamine groups. Dehydrogenation occurs readily in the oxidative system 2.PbO2.C6H6.H2O.NaOH, whereupon 3 may be isolated from the benzene extract. Compound 3 is stable as a solid but much less stable in solutions ¢Ó [Ni(H3L)H4L]Cl 2.A mixture of powdered Ni(H2O)6Cl2 (0.45 g) and 1¡�H2SO4¡�H2O6 (1 g) was dissolved in 15 ml of water, the solution was filtered, and 10 ml of aqueous Na2CO3 (0.5 g) was added to the solution. The reaction mixture was allowed to stand at room temperature. Yellow crystals suitable for X-ray diffraction analysis formed in a day. They were filtered off, washed with cold water and ethanol and dried in air.Yield 58%. Tdecomp. = 186 ¡ÆC. Found (%): C, 37.1; H, 7.7; N, 14.3; Ni, 14.9; Cl, 8.5. Calc. for NiC12H31N4O4Cl (%): C, 37.0; H, 8.0; N, 14.4; Ni, 15.0; Cl, 9.1. NiL2 3. Benzene (50 ml) was added to 2 (0.4 g), and solid NaOH (0.3 g) and water (5 ml) were added in sequence with vigorous stirring. After 3 min, PbO2 (3 g) was added to the mixture. The colour of the benzene layer deepened to black green.The reaction mixture was additionally stirred for 1 h, the organic layer was separated and dried with CaCl2. Then, the mixture was filtered, and the filtrate was evaporated to dryness on a rotary evaporator. Yield 43%. When stored in normal conditions, the solid compound is stable. A toluene solution of 3 saturated at room temperature was allowed to stand overnight at .30 ¡ÆC to give single crystals suitable for X-ray diffraction analysis.Tdecomp. = 126.128 ¡ÆC. 1H NMR (C6D6) d: 0.81 (s, Me). The electronic absorption spectrum [EtOH, lmax/nm (e)]: 364 (18840), 560 (1920), 927 (6860). Found (%): C, 41.9; H, 7.2; N, 16.1. Calc. for NiC12H24N4O4 (%): C, 41.5; H, 7.0; N, 16.1. MS, m/z: 346.11474 (M+, calc. 346.11509). ¢Ô Cambridge Structural Database does not contain any information concerning metal complexes with vic-dihydroxyamines. NHOH NHOH + Ni(H2O)6Cl2 Na2CO3 H2O N N H H O O Ni N N H H O O H H H Cl PbO2 C6H6.H2O NaOH N N O O Ni N N O O 1 2 3 Scheme 1 ¡× Crystal data for 2: C12H31ClN4NiO4, M = 389.57, at 293 K crystals are orthorhombic, space group Pbca, a = 13.380(3), b = 12.825(3), c = 21.077(4) A, V = 3616.8(13) A3, Z = 8, dcalc = 1.431 g cm.3, m(MoK¥á) = = 1.242 mm.1, 2394 reflections were collected (2394 unique) on a Bruker AXS P4, (MoK¥á, graphite monochromator, q/2q scan, 1.93 < q < 24.91¡Æ, empirical absorption correction).The structure was solved by the program SIR97 and refined by the full-matrix least-square technique in an anisotropic approximation for all non-hydrogen atoms.Positions of all hydrogen atoms were located in a difference Fourier map and then refined in isotropic approximation. The final R indexes are R1 = 0.0767, wR2 = = 0.1084, for 2394 unique Ihkl > 2s(I), GOOF = 0.970. All calculations were carried out using SHELX97 program. Crystal data for 3: C12H24N4NiO4, M = 347.06, at 293 K crystals are monoclinic, space group P21/n, a = 6.7692(9), b = 9.853(2), c = = 11.583(2) A, b = 98.45(1)¡Æ, V = 764.2(2) A3, Z = 2, dcalc = 1.508 g cm.3, m(MoK¥á) = 1.291 mm.1, 1228 reflections were measured on a Bruker AXS P4 four-circle automated diffractometer (MoK¥á, graphite monochromator, q/2q scan, 3.68 < q < 24.96¡Æ).The structure was solved by the program SIR97 and refined by the full-matrix least-square technique in an anisotropic approximation for all non-hydrogen atoms.Positions of all hydrogen atoms were located in a difference Fourier map and then refined in an isotropic approximation. The final R indexes are R1 = 0.0316 and wR2 = 0.0480 for 1133 unique Ihkl > 2s(I), GOOF = 0.765. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/87. H(4) H(8) H(3) C(11) H(5) H(7) C(12) C(1) H(14) H(6) C(22) H(13) H(12) C(2) H(10) H(11) H(9) C(21) N(2) O(2) H(16) O(3) H(18) N(3) N(1) H(2) O(1) H(1) Ni H(15) H(25) H(19) C(3) H(20) H(22) H(24) C(32) H(23) C(31) H(21) H(27) C(4) C(42) H(29) H(28) H(30) C(41) N(4) H(26) H(31) Cl O(4) H(32) Figure 1 Molecular structure of 2.Selected bond lengths (A): Ni.N(1) 1.897(3), Ni.N(3) 1.920(6), Ni.N(2) 1.931(6), Ni.N(4) 1.935(6), O(1).N(1) 1.449(8), N(2).O(2) 1.395(8), O(3).N(3) 1.457(8), N(4).O(4) 1.396(8), N.C 1.506(9).1.520(9), O(1)¡�¡�¡�O(4) 2.504(8), O(2)¡�¡�¡�O(3) 2.510(8); selected bond angles (¡Æ): N(1).Ni.N(2) 84.0(3), N(3).Ni.N(4) 84.7(3).Mendeleev Communications Electronic Version, Issue 4, 2001 (pp. 125.164) (e.g., in benzene, toluene, chloroform and ethanol). When stored for a few days, deep green solutions of 3 are gradually decolourised, and 3,3,4,4-tetramethyl-1,2-diazetine-1,2-dioxide precipitates. Noteworthy, the oxidation of free 1 by Pb4+ compounds leads to acetoxime.3 Formally, 3 may be regarded as a complex with the previously unknown nitrosohydroxyamine radical anion .O.¡�N.CMe2.CMe2.N=O (Scheme 1).Since 3 is diamagnetic, probably, because of very strong antiferromagnetic exchange interactions between the unpaired electrons of nitroxyl groups, the presence of a radical fragment may be detected using an approach developed for the metal complexes with ¥á-hydroxyaminooximes. 4 This approach consist in the elimination of a ligand from the coordination sphere. Indeed, the addition of an equimolar amount of dimethylglyoxime to a solution of 3 leads to a short-lived quintiplet with g = 2.006 and aN = 0.70 mT, which is typical of the EPR spectra of nitronylnitroxides. This indicates strong spin density delocalization in the .N.¡�NNi2+N=O fragment occurring via the metal ion and actually leading to the equivalence of N.O groups in 3.The e¡� of N.O groups is also indicated by the results of X-ray diffraction analysis of 3. In the molecule of 3, the square environment of the metal, which is responsible for the low-spin configuration of NiII, is formed by four N atoms (Figure 2).The Ni.N bond lengths are similar [1.827(3) and 1.839(3) A], also indicating strong delocalization and uniform electron density distribution in the {O.N.Ni.N.O} fragment. In contrast to 2, dimethylglyoximate complexes and metal bischelates with ¥á-hydroxyaminooximes,5 the molecular structure of 3 contains no intramolecular hydrogen bonds. Nevertheless, the coordination node is planar with much shorter Ni.N distances in 3, as compared to 2 or classical NiII dioximates.It is reasonable to assume that this is a consequence of strong delocalization and electron density conjugation in .O.¡�NNi2+.N=O fragments. In summary, the interaction of vic-dihydroxyamine 1 with NiII gives rise to bischelate 2, which contains two nonequivalent intramolecular H-bonds between the coordinated ligands.Compound 2 may be oxidised to unusual bischelate 3 whose structure contains the fragments of 1 with fully dehydrogenated hydroxyamine groups. Note that, the square-planar environment of the central atom was retained in dehydrogenated product 3, even though a molecule of 3 has no intramolecular H-bonds in contrast to 2.This work was supported in part by the U.S. Civilian and Development Foundation (grant no. REC-008) and the Russian Foundation for Basic Research (grant nos. 00-03-32987 and 00-03-04006). References 1 J. H. Osiecki and E. F. Ullman, J. Am. Chem. Soc., 1968, 90, 1078. 2 E. F. Ullman, J. H. Osiecki, D. G. B. Boocock and R. Darcy, J. Am.Chem. Soc., 1972, 94, 7049. 3 G. V. Shustov, N. B. Tavakalyan, L. L. Shustova, A. P. Pleshkova and R. G. Kostyanovskii, Izv. Akad. Nauk SSSR, Ser. Khim., 1982, 364 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1982, 31, 330). 4 V. N. Kirichenko, S. V. Larionov, I. A. Mikhailov, E. G. Boguslavskii and L. B. Volodarskii, Zh. Neorg. Khim., 1984, 29, 2835 (Russ. J. Inorg. Chem., 1984, 29, 1624). 5 E. O. Schlemper and R. K.Murmann, Inorg. Chem., 1983, 22, 1077. 6 V. I. Ovcharenko, S. V. Fokin, G. V. Romanenko, I. V. Korobkov and P. Rey, Izv. Akad. Nauk, Ser. Khim., 1999, 1539 (Russ. Chem. Bull., 1999, 48, 1519). O(2) N(2) Ni C(21) N(1) O(1) H(21B) H(21C) H(21A) C(2) C(1) H(12C) H(12A) H(12B) C(12) C(11) H(11A) H(11B) H(11C) C(22) H(22A) H(22B) H(22C) Figure 2 Molecular structure of 3. Selected bond lengths (A): Ni.N(1) 1.827(3), Ni.N(2) 1.839(3), N(1).O(1) 1.230(3), N(2).O(2) 1.218(3), N(1). C(1) 1.543(4), N(2).C(2) 1.531(4), O(1)¡�¡�¡�O(2') 2.574(3); selected bond angles (¡Æ): N(1).Ni.N(2) 83.9(1). Received: 12th April 2001; Co