Structural studies of organoboron compounds XXIII:' preparation and crystal and molecular structures of 2,2-diphenyl-l,3-dioxa-4a-

azonia-2-borata-1,2,3,4-tetrahydronaphthalene and 4,4-diphenyl-3- oxa-l-aza-4a-azonia-4-borata-l,2,3,4-tetrahydronaphthalene

Institut fiir Pharmazeutische Chemie, der Technischen Vniversitat Braunschweig, 3300 Braunschweig, Beethovenstrasse 55, Bundesrepublik Deutschland

AND

STEVEN J. RETTIG AND JAMES TROTTER Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T IY6

Received August 7, 1985

W. KLIEGEL, H.-W. MOTZKUS, D. NANNINGA, STEVEN J. RETTIG, and JAMES TROTTER. Can. J. Chem. 64, 507 (1986). Details of the synthesis, physical properties, and the crystal molecular structures of 2,2-diphenyl-l,3-dioxa-4a-azonia-2-

borata-1,2,3,4-tetrahydronaphthalene, 5, and 4,4-diphenyl-3-oxa-l-aza-4a-azonia-4-borata-l,2,3,4-tetrahydronaphthalene, 9, are reported. Crystals of 5 are monoclinic, a = 9.972(1), b = 11.848(1), c = 13.561(2) A, P = 106.231(5)", Z = 4, space group P21/c and those of 9 are orthorhombic, a = 20.676(1), b = 15.4199(9), c = 9.7533(4) A, Z = 8, space group Pbca. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to R values of 0.036 and 0.045 for 1060 and 1700 reflections with I 2 3u(4 respectively. Compound 5 has the expected cyclic B,N-betaine structure, resulting from N-aklylation of 2(1H)-pyridone with formaldehyde followed by reaction with (Ph2B)20. The aza analog, however, does not have the analogous structure. The alkylation of 2-aminopyridine with formaldehyde in the presence of (Ph2B)20 yields 9, derived from alkylation of the amine rather than the pyridine ring nitrogen atom.

W. KLIEGEL, H.-W. MOTZKUS, D. NANNINGA, STEVEN J.RETTIG et JAMES TROTTER. Can. J. Chem. 64, 507 (1986). On rapporte les details relatifs a la synthkse, aux proprittts physiques et aux structures cristallines et moltculaires du

diphtnyl-2,2 dioxa-1,3 azonia-4a borata-2 tttrahydro-1,2,3,4 naphtalkne (5) et du diphtnyl-4,4 oxa-3 aza-1 azonia4a borata-4 tttrahydro- 1,2,3,4 naphtalkne (9). Les cristaux du compost 5 sont monocliniques, avec a = 9,972(1), b = 1 1,848(1), c = 13,561(2) A, P = 106,23 1(5)", Z = 4 et groupe d'espace P21 / c alors que ceux du compost 9 sont orthorhombiques avec a = 20,676(1), b = 15,4199(9), c = 9,7533(4) A, Z = 8 et groupe d'espace Pbca. On artsolu les deux structures par des mtthodes directes et on les a affintes par la mkthode des moindres carrts (matrice entikre) jusqu'i des valeurs R de 0,036 et 0,045 respectivement pour 1060 et 1700 kflexions avec I 2 3 4 4 . Les compost 5 posskde la structure attendue d'une B,N-Etalne cyclique qui provient d'une N-alcoylation de la 1 H-pyridone-2 avec le formaldehyde suivie d'une rtaction avec le (Ph2B)20. Toutefois, I'analogue azott ne posskde pas une structure analogue. L'alcoylation de I'amino-2 pyridine par le formaldehyde en presence de (Ph2B)20 conduit au compost 9, qui provient d'une alcoylation de l'amine plut6t que de I'atome d'azote du noyau pyridinique.

[Traduit par le journal]

Introduction The tautomeric system 2(1H)-pyridone ++ 2-hydroxy-

pyridine 1 has been the subject of several experimental and theoretical studies (1-6). The alkylation of this bifunctional nucleophile still appears to be somewhat puzzling in spite of a number of detailed studies. For example, some thorough work is found in the literature (7-10) which demonstrates the possibility of both N- and 0-alkylation to a variable extent depending on the alkylation reagent and the conditions of the reaction. The alkylation of 2(1 H)-pyridones with formaldehyde has been shown to result in N-alkylation products (1 1,12). We have prepared 1-hydroxymethyl-2-pyridone 2 according to the literature (11) and allowed this compound to react with oxybis(dipheny1borane) to yield the diphenylboron chelate 5 . The cyclic B,N-betaine 5 is a ring-enlarged analog (by formal methylene insertion) of the diphenylboron chelate 4 which has recently been synthesized (13) and characterized by X-ray

I structure analysis (14). Since no unambiguous assignment of the structure of the

; chelate 5 could be made by chemical or spectroscopic means, an X-ray crystallographic study of 5 represented the best method for ruling out the alternate structure 6, a possible result of

or Part XXII, see ref. 30.

hypothetical 0-alkylation of 1 to 3. A very similar analytical problem arose with the aza-analogous diphenylboron chelate which was obtained by the reaction of 2-aminopyridine (7), formaldehyde, and oxybis(dipheny1borane) in a single step (without first forming the intermediate formaldehyde adduct). Since 2-aminopyridine also possesses two nucleophilic centers, both alternative structures, 8 and 9, must be considered for the chelated alkylation product. Simple ir and nmr data were not sufficient for a definitive structural assignment, therefore an X-ray crystallographic analysis was undertaken.

Experimental 2,2-diphenyl-l,3-dioxa-4a-azonia-2-borata-l,2,3,4-tetr~hydro-

naphthalene, 5 1-Hydroxymethyl-2-pyridone (0.50 g, 4 mmol), prepared according

to the literature (1 l), and oxybis(dipheny1borane) (0.70 g, 2 mmol) were dissolved in 20 mL ethanol. After reacting the solution under reflux conditions for 2-3 min and cooling down, colorless crystals were obtained. Intense cooling yielded 1.1 1 g (96%) of 5 mp 169-171°C (from benzene - petroleum ether); ir (KBr): 1650 cm-' (C=N/C=O); 'H nrnr (CDC13-TMS) 6 (ppm): 5.50 (s, N-CH2-0), 6.30-6.73 (m, 14 H of Ph2B and pyridone). Anal. calcd. for C18H16BN02: C 74.80, H 5.58, N 4.85; found: C 74.94, H 5.83, N 4.85. The substance gives a blue color reaction (15) with diphenylcarbazone in methanolic solution. Crystals suitable for X-ray

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CAN. J. CHEM. VOL. 64. 1986

CH20 - 11 and (or) 11

analysis were obtained by recrystallization from benzene-cyclo- hexane.

4,4-Diphenyl-3-oxa-1 -aza-4a-azonia-4- borata-1,2,3,4-tetra- hydronaphthalene, 9

2-Arninopyridine (0.47 g, 5 mmol), formaldehyde (5 mmol, 40% aqueous solution), and oxybis(diphenylborane) (0.87 g, 2.5 mmol) were dissolved in 10 rnL ethanol at room temperature. Intense cooling produced 1.08 g (75%) of colorless crystals, m 164-168°C (from ethanol); ir (KBr): 3260 (N-H), 1640 cm-' (C=N); 'H nmr (d6-DSMO - TMS) 8 (ppm): 4.72 (s, N-CH2-0), 6.52, 6.78, and 7.59 (3 m, 3 H of pyridine), 7.18 (s, 10H of Ph2B), 8.46 (m, N-H). Anal. calcd. for C18H17BN20: C 75.03, H 5.95, N 9.72; found: C 75.15, H 5.99, N 9.72. The substance gives a blue color reaction (15) with diphenylcarbazone in methanolic solution. Crystals suitable for X-ray analysis were obtained by recrystallization from ethanol.

X-ray crystallographic analyses 2,2-diphenyl-1,3-dioxa-4a-azonia-2-borata- ,2,3,4-tetrahydro-

naphthalene, 5 A crystal bounded by the 12 faces (followed by their distances in mm

from a common origin): k (1 -1 O), 0.12, +(1 OO), 0.08, k (1 1 O), 0.14, ?(O 1 l), 0.19 f-(0 -1 l ) , 0.19, +(1 02),0.18 was mountedina general orientation. Unit-cell parameters were refined by least-squares on the 2 sin 0/A values for 25 reflections (20 = 25-40") measured on a diffractometer with Mo-Ku radiation (A(Ku,) = 0.70930, A(Ku2) = 0.71359 A). Crystal data at 22°C are:

ClgH16BN02 fw = 289.14 Monoclinic, a = 9.972(1), b = 11.848(1), c = 13.561(2) A, P = 106.231(5)", V = 1538.2(3)A3, Z = 4, p, = 1 . 2 4 9 ~ ~ m - ~ , F(000) = 608, ~ ( M o - K a ) = 0.75 cm-'. Absent reflections: h01,l odd, and OM>, k odd, uniquely indicate the space group P2, /c (C:,,, NO. 14).

Intensities were measured with graphite-monochromated Mo-Ka radiation on an Enraf-Nonius CAD4-F diffractometer. An 0-20 scan at 1.06-10.06" min-' over a range of (1.00 + 0.35 tan 0) degrees in o (extended by 25% on both sides for background measurement) was employed. Data were measured to 20 = 52". The intensities of three check reflections, measured every 3600 s throughout the data collec- tion, remained constant to within 4%. Of the 3018 independent reflections measured and processed,2 1060(35.1%) had intensities greater than o r e ual to 341) above background where u2(1) = S + 2B + (O.M(S - B)Q with S = scan count and B = normalized background count. The majority of observed data had 20 < 35". Higher angle data were collected to maximize the number of observations. A 2u cutoff would only increase the number of observed reflections by 32.

The structure was solved by direct methods. The positions of the non-hydrogen atoms being determined from an E-map. In the final stages of refinement the non-hydrogen atoms were refined with anisotropic thermal parameters and the hydrogen atoms were included as fixed contributors in idealized positions (C(sp3)-H = 0.98, C(sp2)-H = 0.97 A), recalculated after each cycle of refinement. The scattering factors of ref. 16 were used for non-hydrogen atoms and those of ref. 17 for hydrogen atoms. The weighting scheme w = 1 /u2(F), where u2(F) is derived from the previously defined u2(1), gave uniform average values of w(I Fol - I ~ ~ 1 ) ' over ranges of both I FoI and sin 0/A and was employed in the final stages of full-matrix refinement of variables. Reflections with 1 < 3u(I) were not included in the refinement. Convergence was reached at R = 0.036 and R,,, = 0.040 for 1060 reflections with I ? 3u(f). The function minimized was Zw(lFOl - IF,^)^, R = CllFol - l ~ ~ l l / ~ l ~ ~ l and R,, = (Zw(lFoI - I F ~ I ) ~ / Z W I F ~ I ~ ) ~ ~ ~ .

On the final cycle of refinement the mean and maximum parameter shifts corresponded to 0.007 and 0.04u, respectively. The mean error in an observation of unit weight was 1.690. The final difference map was essentially featureless, residual densities ranging from -0.15 to

he computer programs used include locally written programs for data processing and locally modified versions of the following: MULTAN 80, multisolution program by P. Main, S. J . Fiske, S . E. Hull, L. Lessinger, G. Germain, J . P. Declercq, andM. M. Woolfson; ORFLS, full-matrix least-squares, and ORFFE, function and errors, by W. R. Busing, K. 0 . Martin, and H. A. Levy; FORDAP, Patterson and Fourier syntheses, by A. Zalkin; ORTEP 11, illustrations, by C. J. Johnson.

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KLIEGEL ET AL. 509

TABLE 1. Final ositional (fractional) and isotropic thermal parameters f0.14 e A-3. The final positional and thermal parameters appear in 2 . . (U x lo3 A ) with estimated standard deviations in parentheses Tables 1 and 6 respectively.3 Calculated hydrogen atom parameters appear inTable 5 .3 Measured and calculated structure factors have been

Atom x Y z u,,/u,,, placed in the Depository of Unpublished ~ a t a . ~

4,4-diphenyl-3-oxa-1 -aza-4a-azonia-4-borata-1,2,3,4-tetra- hydronaphthalene, 9

Experimental details are as above except where noted. The 12 bounding planes of the crystal used for data collection were: {l 1 11, 0.17, ?(O 1 O), 0.31, ?(1 OO), 0.31 mm (from a common origin). Reflections employed in the refinement of the unit-cell parameters had 20 = 30-41". Crystal data:

C I ~ H I ~ B N ~ O fw = 288.16 Orthorhombic, a = 20.676(1), b = 15.4199(9), c = 9.7533(4)A, V = 3110.1(3) A3, Z = 8, p, = 1.231 MgmP3, F(000) = 1216, ~ ( M o - K a ) = 0.7 1 cm- I. Absent reflections: Okl, k odd, h01, 1 odd, and hk0, h odd, uniquely indicate the space group Pbca (D::, NO. 61).

An 0-20 scan at 1 .01- 10.06' min-' over a range of (0.62 + 0.35 tan 0)" in o was employed. Of 45 17 independent reflections measured (to 20 = 60°), 1700 had intensities greater than 3u(I) above background. The intensities of the check reflections remained constant to within 3%.

The strucure was solved by direct methods, the non-hydrogen atoms being positioned from an E-map. After refinement of the non-hydrogen atoms with anisotropic thermal parameters to R = 0.082, the hydrogen atoms were positioned from a difference map and were subsequently refined with isotropic thermal parameters. Convergence was reached at R = 0.045 and R, = 0.046 for 1700 reflections with I ? 3u(I). The mean and maximum parameter shifts on the final cycle of refinement were 0.02 and 0 . 1 5 ~ and the mean error in an observation of unit weight was 1.813. The final difference map showed maximum fluctuations of -0.24 and +0.15 e A-3.

Analysis of thermal motion The thermal motion in the two molecules (Fig. 1) has been analysed

in terms of the rigid-body modes of translation, libration, and screw-motion (TLS model) (18). The rms errors in the Uij (derived from the least-squares analyses) are 0.0021 and 0.0015 A2, respective- ly for 5 and 9. Analyses of the entire molecules indicated independent motion of the phenyl groups. Subunits consisting of PhB groups and the ten atoms of the fused-ring systems were separately analysed for both structures (rms A Uii = 0.0025-0.0034 A2 and 0.0024-0.0026 A2 for 5 and 9 respectively). The appropriate bond distances have been corrected for libration (18,19), using shape parameters q2 of 0.08 for all atoms involved. Corrected bond lengths appear in Table 2 along with the uncorrected values; corrected bond angles do not differ by more than l u from the uncorrected values given in Table 3. Intra-annular torsion angles defining the conformations of chelate rings are listed in Table 4. Bond lengths and angles involving hydrogen and a complete listing of torsion angles (Tables 7-9) are included in the supplementary material.

Results and discussion Compound 5 has the expected structure derived from the

ligand 2, the N-alkylation product of 2(1H)-pyridone with formaldehyde. The molecule 5 is related to the cyclic B,N- betaine 4, which may be regarded as a diphenylboron chelate of an "0-adduct" of pyridone while 5 may be thought of as the corresponding chelate of an "OCH2-adduct" of pyridone. Surprisingly, the aza analog does not have the analogous structure 8 which would be less sterically hindered about the Ph2B moiety than in the observed structure 9, in which an

3 ~ h e structure factor table, Table 6 (anisotropic thermal parameters) and other material mentioned in the text may be purchased from the Depository of Unpublished Data, CISTI, National Research Council of Canada, Ottawa, Ont., Canada KIA 0S2.

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A A

FIG. 1. Stereoscopic views of the 2,2-diphenyl-1,3-dioxa-4a-azonia-2-borata-l,2,3,4-tetrahydr0naphthalene (top) and 4,4-diphenyl-3- oxa-l-aza-4a-azonia-4-borata-1,2,3,4-tetrahydronaphthalene (bottom) molecules; 50% probability thermal ellipsoids are shown for the non- hydrogen atoms. Hydrogen atoms have been assigned artificially small thermal parameters for the sake of clarity.

intramolecular N-B interaction involving the pyridine ring nitrogen occurs. The structure 9 is consistent, however, with that postulated by Gragg et al. (20) on the basis of mass spectral

I data of the addition products of (2-pyridy1amino)diphenyl- borane and various carbonyl compounds. Similar addition products with the basic ring structure of 9 were also formulated by Dorokhov et al. (21) on the basis of spectroscopic data and by analogy with the chemical behavior of comparable amidine adducts (22).

The pyridone C-0 distance4 of 1.308(3) A in 5, similar to the corresponding value of 1.3 16(3) A observed for a compound of the type 4 (14), is indicative of considerable single bond character. The intracyclic C(1)-N bond of the pyridine ring in 5 is short at 1.348(4) A, indicating double bond character. The corresponding C-0 and C-N distances in 2-pyridones (both

4Libration-corrected bond lengths are employed throughout the discussion and are compared with similarly derived parameters.

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KLIEGEL ET AL.

TABLE 2. Bond lengths (A) with estimated standard deviations in parentheses

Bond Uncorr. Corr. Bond Uncorr. Corr.

experimental and calculated) have been summarized in ref. 14 A similar, but more pronounced, situation is noted in the case of andrange 1.221-1.264 and 1.373-1.410 A, respectively. The 9 where the short and long bonds differ by an average of observed geometry of 5 is thus consistent with a greater 0.046(5) A. This type of bond length alternation was not contribution of structure 5a to the overall mesomeric structure observed for closely related molecules of the type 4 (14). 5a t, 5b.

The C(2)-N(2) bond in 9 between the 2-amino group and the pyridine ring is relatively short at 1.335(3) A. The correspond- ing distances5 in 2-aminopyridine (23) and 3-aminopyridine (24) (which does not have an amidine grouping) are 1.355(2) and 1.390(4) A, respectively. The endocyclic C-N bond within the amidine grouping of 9 , 1.354(3) A, does not differ significantly from the corresponding distance of 1.359(2) A in 2-aminopyridine. The related N(1)-C(2) distance in 3- aminopyridine is slightly shorter at 1.345(4) A. The structural data for 9 are consistent with a more important contribution of the canonical form 9 b to the overall structure 9a t, 9b. It is noteworthy that the main contributing canonical forms 5a and 9b of the overall mesomeric structures of 5 and 9 both represent 1,4-betaines with the greatest spatial separation of the formal positive and negative charges on nitrogen and boron, respectively.

The pyridine ring in 5 exhibits a distinct and significant alternation of double and single bond character, the averaGe difference between the short and long bonds being 0.035(6) A.

'Corrected for libration from data in refs. 23 and 24 (rms AU,, = 0.0012 and 0.0014 for the entire molecules).

'The 0-B distances in 5 are significantly different; the longer of the two (1.578(4) A) involves the pyridone oxygen atom and is similar to the nearly equal 0-B distances in compounds of the type 4 (1.557(3)-1.580(3) A) and in other diphenylboron chelates with o oxide^ (25-27) or carbonyl (28, 29) oxy en coordinated to boron. The O(2)-C(6) distance of 1.369(4) 1 in 5 is significantly shoGer than the corresponding 0-C(l) distance of 1.411(3) A in 9 , indicating some double bond character in the former. Other bond lengths and angles in both structures (Tables 2 and 3) are normal.

6 ~ . Kliegel, S. J. Rettig, and J. Trotter. 1.552(4) A for 4,4- dimethyl-2,2-diphenyl-l,3-dioxa-4-azonia-2-boratacyclohexane. In preparation.

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CAN. J . CHEM. VOL. 64. 1986

TABLE 3. Bond angles (deg) with estimated standard deviations in parentheses

Bonds Angle(deg) Bonds Angle(deg)

The chelate rings in 5 and 9 have slightly irregular O(2)- and 0-envelope conformations (torsion angles in Table 4). The aromatic rings in 5 are all slightly but significantly nonplanar. (x2 = 10.1-21.5, maximum deviation from the mean plane 0.009(4) A). In 9 the C(7)-phenyl ring is planar within experimental error while the C(13)-phenyl and pyridine rings are significantly nonplanar (x2 = 67.0 and 209.0, maximum deviations from the mean planes 0.0 15(3) and 0.0 19(2) A). The pyridine ring in 9 is found to possess a flattened C(2),C(5)-boat

conformation (see Table 4) with the B and N(2) atqms displaced from the mean plane by 0.170(2) and 0.078(2) A in opposite directions, presumably a steric effect. The N(2) a t c p displays near planar geometry, being displaced 0.061(2) A from the plane of its substituents, this plane being rotated 2.5(5)" with respect to the mean plane of the pyridine ring.

The crystal structure of 5 consists of discrete molecules separated by normal van der Waals distances and that of 9 consists of infinite chains of molecules linked b.1 weak N(2)-H(N2)...0(1/2 - x , l - y,z - 112) hydrogen bonds [H...O = 2.32(3), N...O = 3.127(3) A, N-H...O = 161(2)"]. Both molecules show intramolecular interactions of possible significance [C(12)-H(12).-.0(2) in 5, C(8)-H(8)-..0, and C(14)-H(14)...N(l) in 9 with H.-.(O/N) distances of 2.46, 2.53(2), and 2.54(2) A; C...(O/N) distances of 2.844(4), 2.873(3), and 2.976(3) A; and C-H..-(O/N) angles of 103, 100(1), 102(1)" respectively], the C-H...N interaction in 9 involving the aromatic T-system of the pyridine ring.

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KLIEGEL ET AL. 513

TABLE 4. Intra-annular torsion angles (deg) standard deviations in parentheses

Atoms Value(deg)

Acknowledgments We thank the Natural Sciences and Engineering Research

Council of Canada and the Fonds der Chemischen Industrie, Frankfurt a m Main, for financial support and the University of British Columbia Computing Centre for assistance.

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