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Solid State Structure of N,N-DibenzylhydroxylamineNorbert W. Mitzel+, Jürgen Riede,Klaus Angermaier, Hubert Schmidbaur*Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstraße 4, D-85747 Garching, GermanyZ. Naturforsch. 50b, 699-701 (1995); received October 31, 1994Solid State Structure,N,N-Dibenzylhydroxylamine

The solid-state structure of N,N-dibenzyl- hydroxylamine (1) has been determined by single crystal X-ray diffraction. The compound crys­tallizes in the monoclinic space group P 2 \ln with four formula units in the unit cell. N,N-dibenzyl- hydroxylamine dimerizes to give N20 2H2 six- membered rings as a result of the formation of two hydrogen bonds O -H —N in the solid state.

The preparative chemistry of hydroxylamine and its organic derivatives as discovered by Lossen in 1865 [1] is well established [2], In particular, the use of hydroxylamine in polymer chemistry (poly­amide via the caprolactam process [3]) has stimu­lated research in this area. Theoretical contri­butions have mainly dealt with the conformation of the N -O skeleton in hydroxylamine and its de­rivatives [4], but the structural chemistry of simple hydroxylamines has only been sparingly devel­oped. The crystal structure of unsubstituted hy­droxylamine, H2NOH, was elucidated in an early work of Meyers and Lipscomb [5] in 1955, but the hydrogen positions could not be located at this time. Rankin and Riddel have determined the gas-phase structures of O-methylhydroxylamine, N-methylhydroxylamine, N,0-dimethylhydroxyl- amine and N,N,0-trimethylhydroxylamine [6] by electron diffraction. The molecular geometries ob­tained in this way are those of free molecules which are undistorted by intermolecular or pack­ing forces. In the condensed states, however, inter­molecular interactions are very important for an understanding of any structural details. With NH

+ Current address: Department of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH 9 3JJ, U.K.

* Reprint requests to Prof. Dr. H. Schmidbaur.

or OH functions present in the molecules, the for­mation of hydrogen bridges is likely to contribute significantly to the molecular and crystal structure.

Recently, we have demonstrated that silylated hydroxylamines have unusual molecular geo­metries [7], Unlike most other silicon nitrogen compounds [8], the silylhydroxylamines feature a pyramidal configuration at the nitrogen atom. Turning now to simple organic derivatives of hy­droxylamine, we report here the solid state struc­ture of N,N-dibenzylhydroxylamine (1).

OH 1

According to a well established literature pro­cedure [2], compound i was prepared by the benzylation of hydroxylamine hydrochloride and identified by its analytical and spectroscopic data. Crystals were grown from diethylether solutions. In the monoclinic crystals, space group P 2 xln with Z = 4 formula units in the unit cell, molecules of compound 1 are present as dimers (Fig. 1). Hydro­gen bonding between the OH proton of one mol­ecule and the nitrogen atom of another leads to the formation of quasi-rectangular N20 2H 2 six- membered rings.

Hydrogen bonding is often observed for OH- functionalized hydroxylamines: N,N'-dihydroxy - N,N'-dimethylmethanediamine [9] forms dimers with eight-membered CN30 2H 2 rings; N-methane- sulfonyl-N-phenylhydroxylamine [10] forms OH —O bridges; l-(3-(N-r-butylhydroxyamino)-

Fig. 1. Structure of the dimer of 1.

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Bz—.

Bz

u\

H/

H

/O\

\//

— O

.Bz

Bz

Bz

Scheme 1. A: Hydrogen bonding as found in 1. B: Pro­posed alternative aggregation type for 1 (not observed experimentally).

4-chlorophenyl)-l,3-butadiyne [11] occurs in N O H - NOH chains.

The formation of N20 2H 2 rings is known for many oximes, but only for a few hydroxylamines such as l,8-dihydroxy-l,8-diazacyclotetradecane (2) [12] and N-hydroxy-3-nitro-4-azahexacyclodo- decane (3) [13]. The surprising feature of this type of aggregation (Scheme 1 A) is the short distance between the centres of electron density ato the positively polarized hydrogen atoms [2.16(6) A] of the dimer, despite of repulsive Coulomb forces. An alternative aggregation not realized in the crystals of 1 is proposed in Scheme 1B. Within this nine-membered N30 3H3 ring, Coulomb repulsion between the positively charged hydrogen atoms would be reduced as compared with the aggre­gation type A, and the O - H -N units could adopt their ideal unstrained linear geometry.

The O -N ' distance in 1 is 2.875(3) Ä which is in the same range as for 2 (2.875 A) and 3 [2.84(1) A].

The nitrogen atom of 1 has a pyramidal con­figuration, with the sum of angles at the N atom at only o 321.5°. The N -O bond length is1.456(2) A, only marginally shorter than that found for 2 (1.469 A) [12], with the same type of hydrogen bonding, and also in good agreement

Table I. Selected geometric parameters for 1.

Bond lengths [A] Bond angles [°]

N -O 1.456(2) O -N - C l 105.5(1)N -C l 1.480(2) 0 - N - C 2 105.2(1)N -C 2 1.472(2) C 1 -N -C 2 110.8(1)C l - C l l 1.499(3) N -C 1-C 11 111.5(1)C2-C21 1.502(3)O - H l 0.88(3) H 1 - O - N 98(2)H l - N 2.02(3) O - H l - N ' 164(3)H 1 -H 1' 2.16(6) O - N - H l ' 97.3(8)O - N ' 2.875(3)sum of angles at N: 321.5°

with the data of crystalline H2NOH (1.476(3) A)[5]. For comparison, the N -O distances inO-methylhydroxylamine, N-methylhydroxylamine. N,0-dimethylhydroxylamine and N,N,0-trimethyl- hydroxylamine, as determined by gas-phase elec­tron diffraction [6], are 1.463(3), 1.477(2), 1.496(9). and 1.513(9) A, respectively.

The molecular structure of an individual mol­ecule of 1 shows trans conformation, i. e. the lone pairs at N and O are located at a maximum dis­tance. Only this trans conformation allows for the observed type of hydrogen bonding. As the con­formation and the type of hydrogen bonding are dependent upon each other, it is not clear whether the trans conformation also corresponds to the po­tential energy minimum for the isolated molecule. Molecular orbital calculations generally predict two minima for the rotation about the N -O bond in hydroxylamines, and favour the trans confor­mation by about 3 kJ/mol in energy [4c, d]. How­ever, in some cases IR studies of H2NOH and its methyl derivatives give contadictary results as far as the conformation is concerned [14].

ExperimentalCompound 1 was prepared by the reaction of

benzyl chloride with hydroxylamine hydrochloride in the presence of potassium carbonate [2]. It was recrystallized from diethylether.

Crystal data for 1: C 14H 15NO; Mr = 213.28; monoclinic; space group P 2 Jn\ a = 9.292(1); b = 10.397(1); c = 12.309(1) Ä; ß = 94.68(1)°; V = 1185.1(2) Ä 3; Z = 4; Dc = 1.20 gem “3, F(000) = 456; /i(M o -K a) = 0.8 cm-1; 2704 reflections meas­ured, 2244 unique, and 1802 observed [F0 > 4cr(F0)]. No absorption correction was applied. Structure solution was by Direct Methods, with all missing atoms located by successive Fourier syntheses.

Refinement of 205 parameters converged at R = 0.0517 and R w = 0.0547; w = [a2(F0) + 0.005 F02]“ '. Maximum and minimum residual electron densi­ties in the difference Fourier map were 0.202 and -0.391 e A -3, respectively. [T = 22 °C; Enraf- Nonius CAD 4 diffractometer; A(M o-Ka) = 0.71069 Ä]*.

Further information on the X-ray structure determi­nation can be obtained from Fachinformationszen- trum Karlsruhe, Gesellschaft für wissenschaftlich- technische Information mbH, D-76344 Eggenstein- Leopoldshafen, on quoting the depository number CSD 58677, the names of the authors, and the jour­nal citation.

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Acknowledgement

This work has been supported by the Deutsche Forschungsgemeinschaft and the Commission of

[1] W. Lossen, Z. Chem. 1865, 551.[2] B. Zeeh, H. Metzger, Hydroxylamine, in: Methoden

der organischen Chemie (Houben-Weyl), Bd. X /l, Thieme-Verlag, Stuttgart (1971).

[3] G. Zinner, Chemiker-Ztg. 114, 197 (1990).[4] a) A. Rastelli, M. Cocchi, J. Chem. Soc. Faraday

Trans. 87, 249 (1991);b) W. A. Latahn, L. A. Curtis, W. J. Hehre, J. B. Lisle, J. A. Pople, Progr. Phys. Org. Chem. 11, 175 (1974);c) W. J. Orville-Thomas, The Structure of Small Molecules, Elsevier, Amsterdam (1966);d) D. M. Gange, E. A. Kellel, J. Chem. Soc. Chem. Commun. 1992, 824.

[5] E. A. Meyers, W. N. Lipscomb, Acta Crystallogr. 8, 583 (1955).

[6] a) F. G. Riddell, E. S. Turner, D. W. H. Rankin, M. R. Todd, J. Chem. Soc. Chem. Commun. 1979,72;b) D. W. H. Rankin, M. Todd, F. G. Riddell, E. S. Turner, J. Mol. Struct. 71, 171 (1981);c) L. Pauling, L. O. Brockway, J. Am. Chem. Soc. 57, 2684 (1935).

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the European Union (NWM). We are grateful to Dr. S. Parsons (Univ. of Edinburgh) for a search of the Cambridge Database.

[7J a) N. W. Mitzel, K. Angermaier, H. Schmidbaur, Organometallics 13, 1762 (1994);b) N. W. Mitzel, H. Schmidbaur, Z. Anorg. Allg. Chem. 620, 1087 (1994);c) N. W. Mitzel, M. Hofmann, E. W aterstradt, P. v. R. Schleyer, H. Schmidbaur, J. Chem. Soc. Dalton Trans. 1994, 2503.

[8] E. Lukevics, O. Pudova, R. Strukokovich, Molecular Structure of Organosilicon Compounds, Ellis Hor- wood, Chichester (1989).

[9] W. Kliegel, S. J. Rettig, J. Trotter, Can. J. Chem. 67, 1959 (1989).

[10] C. Rizzoli, P. Sgarabotto, G. Ugozzoli, L. Cardinelli, L. Greci, G. Tosi, Acta Cryst. C 47, 1515 (1991).

[11] K. Inoue, N. Koga, H. Iwamura, J. Am. Chem. Soc.113, 9803 (1991).

[12] C. J. Brown, J. Chem. Soc. C 1966, 1108.[13 W. H. Watson, A. P. Marchand, P. R. Dave, Acta

Cryst. C 43, 1569 (1987).[14] a) P. A. Giguere, I. D. Lin, Can. J. Chem. 30, 984

(1952);b) M. Davies, N. A. Spiers, J. Chem. Soc. 1959, 3971.