molecular and solution structure of 5,6-benzo-1,3,2-dioxaphosphinin-4-one derivatives

1070-3632/02/7208-1195$27.00C2002 MAIK [Nauka/Interperiodica]

Russian Journal of General Chemistry,Vol. 72, No. 8,2002, pp. 119531201. Translated from Zhurnal ObshcheiKhimii, Vol. 72, No. 8,2002,pp. 127631282.Original Russian Text CopyrightC 2002 by Ishmaeva, Vereshchagina, Yarkova, Burnaeva,Litvinov, Krivolapov, Gubaidullin, Mironov, Fattakhova.

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Molecular and Solution Structureof 5,6-Benzo-1,3,2-dioxaphosphinin-4-one Derivatives

E. A. Ishmaeva, Ya. A. Vereshchagina, E. G. Yarkova, L. M. Burnaeva, I. A. Litvinov,D. B. Krivolapov, A. T. Gubaidullin, V. F. Mironov, and G. R. Fattakhova

Kazan State University, Kazan, Tatarstan, Russia

Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center,Russian Academy of Sciences, Kazan, Tatarstan, Russia

Kazan State Technological University, Kazan, Tatarstan, Russia

Received October 23, 2000

Abstract-2-X-5,6-benzo-1,3,2-dioxaphosphinin-4-ones (X = N=C=O, Cl, NEt2), regardless of theiraggregative state, prefer one and the same conformation (flattened sofa); the exocyclic substituent occupieseither an axial (N=C=O, NEt2) or an equatorial (Cl) position.

The conformational structure of organophosphoruscompounds, phosphorus-containing heterocyclesinclusive, is presently well-documented [132]. Themain aspects of the problem concerning the structureof acyclic organophosphorus compounds in solutionshave been covered in great detail in the reviews [3, 4],and the structure of low-coordination phosphoruscompounds have been discussed in [5]. At the sametime, there have been little work on the steric andelectronic structure of six-membered phosphorus (PIV)heterocycles fused with a planar fragment, such asphenyl and/or carbonyl group [6310].

Recently Nedaet al. [11] reviewed the synthesis,reactivity, structure, and biologic activity of benzo-diaza-, benzoxa-, and benzodioxaphosphininones, butgave X-ray diffraction data for only a few representa-tives of the two former classes of phosphinines ortheir metal complexes. The information on the struc-ture of 5,6-benzo-1,3,2-dioxaphosphinin-4-ones([salicyl phosphites]) is limited by the photoelectronspectra reported in [12]. The interest in salicyl phos-phites is mostly associated with the fact that theycontain several reaction centers and may exhibitpeculiar reactivity. As derivatives of salicylic acids,salicyl phosphites are potentially biologically activecompounds. These compounds hold promise as mildphosphorylating and acylating agents for biochemicalapplications. Salicyl phosphites contain both a nucleo-philic (PIII ) and electrophilic centers (endo- and exo-cyclic carbonyl groups), which imparts to themdiverse reactivity, i.e. ability to facile reactions withelectrophiles and nucleophiles [13].

In the present work we studied the structure of

salicyl phosphitesI3III by X-ray diffraction, IR spec-troscopy, and dipole moment measurements.

5;O

=QC3O

P3X

:oO

4 35

6

4

12

8

910

7

X = N=C=O (I ), Cl (II ), NEt2 (III ).

The spatial arrangement of 2-isocyanato-substitutedsalicyl phosphiteI is shown in Fig. 1. Tables 1 and 2list atomic coordinates, as well as selected bondlengths and bond and torsion angles in moleculeI .The O1P2O3C4C5C6 six-membered ring has asofaconformation, and the O3C4C5C6O1 fragment is planarwithin 0.010(3) A. The phosphorus atom deviatesfrom this plane by 0.5904(6)A and the O4, by0.012(2)A to the opposite side. The isocyanato groupat the phosphorus atom is axial. The flattening of theheteroring (Fig. 1) is apparently explained by conjuga-tion of the carbonyl group at C4 with the p system ofthe condensed benzene ring. The phosphorus atomwith its lone electron pair has a distorted tetrahedralcoordination typical of PIII compounds. The endo-cyclic bond angle of the phosphorus atom [99.4(1)o]is slightly larger than exocyclic angles [95.7(1) and98.0(1)o]. Endocyclic P3O bond lengths are slightlydifferent [1.629(2) and 1.649(2)A] but both fall in therange of values typical of PIII compounds (1.61431.642 A) [14]. The exocyclic P3N bond length[1.711(2)A], too, is a normal value. The isocyanatogroup is linear. The bond angle at the nitrogen atomis increased to 136.2(2)o.

RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 8 2002

1196 ISHMAEVA et al.

O12

C11

N2

P2O1

C6

O4

C5

C7

C8

C9C10

Fig. 1. Conformation of 2-isocyanato-5,6-benzo-1,3,2-dioxaphosphinin-4-one (I ) in crystal.

It will be emphasized that, according to data in[9, 10], PIV phosphorinanes containing a carbonylgroup have achair conformation in crystal. However,the same heterocycle condensed with a planar fragmentis not only strongly flattened, but also assumes adistorted sofa form [15, 16].

Examining the crystal packing of compoundI , onenotes lack of any appreciable intermolecular interac-tions in the crystal cell. Therewith, no appreciableintermolecular interactions, except for usual van der

Table 1. Atomic coordinates in salicyl phosphiteI , equi-valent isotropic thermal parameters of non-hydrogen atoms

3 3B = 4/3 S S (aiaj)B(i, j) (A2), and isotropic thermal

i = 1 j = 1

parameters of hydrogen atomsViso (A2)ÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄAtom³ x ³ y ³ z ³B or VisoÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄ

P2 ³ 0.79639(8)³ 0.01302(4)³ 0.8409 ³ 1.39(1)O1 ³ 0.5993(2) ³ 0.0461(1)³ 0.8544(3)³ 1.59(3)O3 ³ 0.8105(3) ³ 30.0012(1)³ 0.5941(4)³ 1.67(4)O4 ³ 0.8120(3) ³ 0.0529(1)³ 0.2863(4)³ 2.38(4)O12 ³ 1.0616(3) ³ 0.1885(1)³ 1.0627(4)³ 2.63(4)N2 ³ 0.8978(3) ³ 0.1059(1)³ 0.8424(4)³ 1.62(4)C4 ³ 0.7484(4) ³ 0.0527(2)³ 0.4519(5)³ 1.44(4)C5 ³ 0.6038(3) ³ 0.1041(2)³ 0.5169(5)³ 1.30(4)C6 ³ 0.5332(4) ³ 0.0991(1)³ 0.7111(4)³ 1.35(4)C7 ³ 0.3937(4) ³ 0.1464(2)³ 0.7667(5)³ 1.71(5)C8 ³ 0.3206(3) ³ 0.1985(2)³ 0.6252(6)³ 1.89(5)C9 ³ 0.3875(4) ³ 0.2042(2)³ 0.4319(5)³ 2.04(5)C10 ³ 0.5267(4) ³ 0.1575(2)³ 0.3765(4)³ 1.55(5)C11 ³ 0.9790(4) ³ 0.1449(2)³ 0.9617(4)³ 1.66(5)H9 ³ 0.337(5) ³ 0.239(3)³ 0.353(6) ³ 3.7(9)H10 ³ 0.570(5) ³ 0.166(2)³ 0.263(7) ³ 2.7(8)H8 ³ 0.227(5) ³ 0.236(3)³ 0.656(5) ³ 4(1)H7 ³ 0.362(4) ³ 0.140(2)³ 0.885(4) ³ 0.6(5)ÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄ

Table 2. Selected bond lengths (d, A) and bond (w, deg) and torsion (j, deg) angles in salicyl phosphiteIÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÒÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÒÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄ

Bond ³ d º Bond ³ d º Bond ³ dÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄ

P23O1 ³ 1.629(2) º O43C4 ³ 1.200(4) º C53C10 ³ 1.408(4)P23O3 ³ 1.649(2) º O123C11 ³ 1.169(4) º C63C7 ³ 1.383(4)P23N2 ³ 1.711(2) º N23C11 ³ 1.195(4) º C73C8 ³ 1.387(4)O13C6 ³ 1.383(3) º C43C5 ³ 1.468(4) º C83C9 ³ 1.382(5)O33C4 ³ 1.375(4) º C53C6 ³ 1.397(4) º C93C10 ³ 1.375(4)

ÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄBond angle ³ w º Bond angle ³ w º Bond angle ³ w

ÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄO1P2O3 ³ 99.4(1) º O3C4O4 ³ 118.5(3) º O1C6C5 ³ 121.2(2)O1P2N2 ³ 98.0(1) º O3C4C5 ³ 115.9(2) º O1C6C7 ³ 117.5(3)O3P2N2 ³ 95.7(1) º O4C4C5 ³ 125.5(3) º C5C6C7 ³ 121.3(3)P2O1C6 ³ 121.4(2) º C4C5C6 ³ 122.4(2) º C6C7C8 ³ 119.2(3)P2O3C4 ³ 124.1(2) º C4C5C10 ³ 119.3(3) º C5C10C9 ³ 120.4(3)P2N2C11 ³ 136.2(2) º C6C5C10 ³ 118.2(2) º O12C11N2 ³ 173.2(3)

ÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄTorsion angle ³ j º Torsion angle ³ j º Torsion angle ³ j

ÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄO3P2O1C6 ³ 339.7(2) º P2O1C6C5 ³ 23.1(3) º O3C4C5C10 ³ 3176.4(2)N2P2O1C6 ³ 57.5(2) º P2O1C6C7 ³ 3157.5(2) º O4C4C5C6 ³ 178.3(3)O1P2O3C4 ³ 43.0(2) º P2O3C4O4 ³ 154.94 º O4C4C5C10 ³ 1.7(4)N2P2O3C4 ³ 356.2(2) º P2O3C4C5 ³ 326.8(3) º C4C5C6O1 ³ 1.4(4)O1P2N2C11 ³ 105.6(3) º P2N2C11O12 ³ 173(2) º C4C5C6C7 ³ 3178.0(3)O3P2N2C11 ³ 3154.1(3) º O3C4C5C6 ³ 0.2(4) º C10C5C6O1 ³ 178.0(2)

ÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÐÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÐÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄ


MOLECULAR AND SOLUTION STRUCTURE 1197

Waals contacts, are observed. The heteroring planesof all the molecules are parallel to the 0z axis (Fig. 2),implying certain anisotropy in crystal properties.

To find out whether phosphitesI3III are conforma-tionally homogeneous or inhomogeneous, wemeasured their IR spectra in the solid phase and insolvents of different polarity (methylene chloride andacetonitrile). The C=O vibration frequencies of salicylphosphiteI only slightly vary with aggregative state,n, cm31: 1736 v.s (mineral oil), 1760 v.s (CH2Cl2), and1756 (MeCN) (Dn 20324 cm31) and almost insensitiveto solvent (Dn 4 cm31).

The characteristic vibration frequencies of theO3C(O) group [n, cm31: first band: 1204 s (mineraloil), 1224 v.s (CH2Cl2 and MeCN); second band: 1232(mineral oil) and 1210 (CH2Cl2 and MeCN)], too,vary with aggregative state and do not vary withsolvent. The characteristic vibration frequencies of thePh3O group [n, cm31: 1292 s (solid phase), 1298 s(CH2Cl2), and 1288 v.s (MeCN)] scarcely vary. Thesame pattern is characteristic of the P3O bonds;therewith, these two P3O bonds are nonequivalent(the molecule has no symmetry axis), and this showsup in the spectra: Apparently, one of the P3O bondsappears at,n, cm31, 890 s (solid phase), 900 v.s(CH2Cl2), and 896 s (MeCN), and the other, at 872 s(solid phase), 888 s (CH2Cl2), and 880 s (MeCN). Thecharacteristic vibration frequencies of the N=C=Ogroup (2256 cm31, v.s) do not vary both with aggrega-tive state and with solvent.

The C=O stretching vibration frequencies of salicylphosphite II (n, cm31: 1776 v.s (mineral oil) and1768 v.s (CH2Cl2 and MeCN)] vary only slightly withaggregative state. The same is true of the characteris-tic O3C(O) vibration frequencies [n, cm31: 1220(mineral oil) and 1224 (CH2Cl2 and MeCN) and Ph3Ogroups [n, cm31: 1272 v.s (mineral oil) and 1288 v.s(CH2Cl2 and MeCN)]. The characteristic O3P vibra-tion frequencies scarcely vary [n, cm31: first band:904 s (mineral oil), 904 v.s (CH2Cl2); second band:880 m (mineral oil and MeCN) and 888 s (CH2Cl2)].The P3Cl vibration frequency (480 cm31) scarcelychange both with aggregative state and with solvent.

Thus, all characteristic vibration frequencies ofsalicyl phosphiteI slightly vary, except for those ofthe isocyanato group. This may imply both certainspecific features of vibrations of the correspondingbonds and groups in the molecule and certain con-formational lability of the ring. However, the fact thatthe characteristic vibration frequencies of the N=C=Ogroup remain almost invariable, while not ruling outconformational transitions in solution, still suggestsexistence of a single, preferable conformer, since it is

a

c0 b

Fig. 2. Crystal packing of compoundI as viewed alongthe 0z axis.

well known that the absorption frequencies of exo-cyclic substituents in 1,3,2-dioxaphosphorinanesstrongly depend on whether the substituent is axial orequatorial [2]. The conformational equilibriumsofa7647 chair would produce more radical changesin the vibration spectra, especially in regard to vibra-tions of exocyclic substituents. Since this is not thecase, we presumably deal here with slightly changeddihedral angles in thesofa conformer which, never-theless, still remains preferable.

The conclusion on the low conformational labilityof the phosphorus-containing heteroring even strongerrelates to dioxaphosphinineII .

The existing conformers were identified by themethod of dipole moments. Table 3 lists the experi-mental and calculated dipole moments of salicylphosphitesI3III . As seen, the compounds are ratherpolar and close in polarity to 1,3,2-dioxaphosphori-nanes with the same exocyclic substituents. Thus, thedipole moments of 2-isocyanato- and 2-chloro-1,3,2-dioxaphosphorinanes are 3.55 [17] and 3.47 D [18].The dipole moments were calculated by the generaland fractional vector-additive schemes, followingrecommendations of Arbuzovet al. [19], in view ofthe revealed high electronic lability of 1,3-dihetero-atomic derivatives of PIII phosphorinane derivatives,caused by stereodirected migration of electron densityin the phosphorus-containing moiety, dependent onthe nature of the exocyclic substituent on phosphorus.Orbital analysis allowed the referees [19] to assignthis effect to n3s* hyperconjugation.



H

H

H

H

C4

O4

O3

O1

NC

O

(a)

43o48̀(a)

35o37̀

136o12̀

79o25̀

79o25̀49o42̀

N C O (e)

y

z

xP

(b)H

H

H

H

C4

O4

O3

O1

R (a)

79o25̀

79o25̀49o42̀

R (e)

P

z

y

x

Fig. 3. Orientation of molecules (a)I and (b) II, III in the coordinate system.

The orientation of moleculesI3III in the coordi-nate system is shown in Figs. 3a and 3b. For com-pound I , the geometric parameters determined byX-ray diffraction were used. The following bond andgroup moments were also used, D: general additivescheme: m(O6P) 0.51 {calculated frommexp ofMe(CH2O)3P [18]}, m(P6Cl) 0.58 {calculated frommexp of PCl3 [18]}, m(C¤O) 1.94 {calculated frommexp of PhCOMe [20]}, m(H6Csp2) 0.7 [21],m(P6N) 0.31 {calculated frommexp of (Me2N)3P[18]}, m(N6P) 0.25 {calculated frommexp ofMe[CH23N(Me)]3P [22]}, m(N=C=O) 2.26 (calculatedfrom mexp of MeNCO [23]), m(Et6N) 0.81 {calcu-lated from mexp of Et3N [23]}, and m(Csp26O) 0.4{combined determination frommexp of (PhO)3P and(1,3,5-t-Bu3C6H2O)3P [24]}; and fractional additivescheme:m(P6O) 0.65 andm(P6N) 0.37 {com-bined determination frommexp of 2-diethylamino-1,3,2-dioxaphosphorinane and its spiro analog (Et2N)2 .

[P(O2C2H4]2C [18]}, m(P6Cl) 0.92 andm(O6P)0.72 {combined determination frommexp of 2-chloro-1,3,2-dioxaphosphorinane and its spiro analogCl2[PO2(C2H4)2]C [18]}.

As seen from Table 3, the experimental dipolemoment of salicyl phosphiteI corresponds to thepolarity of the sofa conformation both with an axialand with an equatorial isocyanato group. This con-clusion is independent on the model [bicyclic phos-phorous triamide or acyclic phosphorous triamide] forthe general vector-additive scheme. These findingsallow no conclusions as to the orientation of the exo-cyclic substituent. The same was earlier observed [25]with 1,3,2-dioxaphosphorinan-5-ones. The high dipolemoment of the heteroring explains the fact that thecalculated dipole moments of conformers are contri-buted mostly by the polar carbonyl groups and, there-fore, are close to each other. On the other hand, it is

Table 3. Experimental and calculated dipole moments of salicyl phosphitesI3IIIÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Comp.

³Conformation

³ mcalc, Da ³ mcalc, Db ³ mexp, D, solvent³ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄ

no.

³of exocyclic

³ ³ ³³

substituent³

models: bicyclic³ models: bicyclic ³ models: 1,3,2- ³

CCl4

³C6H6³ ³

structures³ structures ³ dioxaphosphorinanes³ ³

³ ³ ³ and P(NMe2)3 ³ and their spiro analogs³ ³ÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄ

I ³ (P3NCO)a ³ 4.20 ³ 4.22 ³ 2.98 ³ 3 ³ 4.23³ (P3NCO)e ³ 4.13 ³ 4.30 ³ 3.11 ³ 3 ³ 3

II ³ (P3Cl)a ³ 3.04 ³ 3 ³ 3.00 ³ 3.80 ³ 4.02³ (P3Cl)e ³ 3.67 ³ 3 ³ 4.08 ³ ³

III ³ (P3NEt2)a ³ 3.86 ³ 3.51 ³ 3.00 ³ 3.88 ³ 4.17³ (P3NEt2)e ³ 2.68 ³ 2.95 ³ 2.42 ³ ³

ÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄa General vector-additive scheme.b Fractional vector-additive scheme.



known (1H NMR spectroscopy and dielcometry [17])that in thechair conformer of 2-isocyanato-4-methyl-1,3,2-dioxaphosphorinane the N=C=O group is axial.It will be remembered that, according to spectral data,salicyl phosphiteI prefers one conformer. Most likely,the same conformer is preferred in solution, i.e.sofawith an axial isocyanato group. The fractional additivescheme with parameters calculated from the polaritiesof models containing no planar groups does not work(the resulting dipole moments are much underesti-mated). It should also be noted that the exocyclicsubstituent on PIII in dioxaphosphorinanes is mostfrequently axial, but our studies on salicyl phosphitesII and III have cast some doubt on the appropria-teness of such analogies.

It will be remembered that the IR spectra of salicylphosphite II provide an even stronger evidence infavor of its conformational homogeneity. The experi-mental dipole moment of salicyl phosphiteII is closeto that calculated for thesofa form with an equatorialchlorine atom (Table 3). This conclusion is indepen-dent of whether the dipole moment is calculated bythe general or fractional additive scheme. The dipolemoments calculated for thesofa form with an axialchlorine atom (both by the general and fractionaladditive scheme) prove much (by 1 D) underestimated(Table 3). On the other hand, apparently, the planarphenyl and carbonyl groups in the heteroring radicallychange the electron density distribution in the mole-cule and thus can make the exocyclic substituent toreorient. Note that it is halo derivatives (in particular,of 1,3,2-dioxaphosphorinanes), in which the strongestelectron density redistribution have been revealed [19].It, however, should be borne in mind that the X-raydiffraction data for 2-fluoro-5,6-benzo-1,3,2-diaza-phosphinin-4-one [11], too, point to axial orientationof the fluorine atom. In this connection, it is notunreasonable to suggest that in solution, too, an axialconformer may exist, involving strong intramolecularinteractions (apart from those characteristic of aceto-phenone) which give rise to such a strong exaltationof the experimental and calculated dipole moments.In any case, the structure of compoundII is to berefined by X-ray diffraction analysis. We expect thatfurther information will be gained from intendedquantum-chemical calculations.

Comparison of the experimental and calculated (bythe general scheme) dipole moments of 2-diethyl-amino-substituted salicyl phosphiteIII (Table 3) givesunambiguous evidence showing that it prefers thesofaconformation with an axial diethylamino group. Thesame orientation of the bis(2-chloroethyl)amino groupwas found by X-ray diffraction analysis in a crystal-line diazaphosphorinanone containing the planar

Table 4. Coefficients of equations and orientationalpolarization of salicyl phosphitesI3IIIÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄComp.³

Solvent³

b³

g³

Po, cm3 ³ mexp,no. ³ ³ ³ ³ ³ D

ÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄI ³ C6H6 ³ 9.874³ 0.596 ³ 365.039 ³ 4.23II ³ CCl4 ³14.764³ 0.980 ³ 294.286 ³ 3.80

³ C6H6 ³ 9.145³ 0.331 ³ 334.448 ³ 4.02III ³ CCl4 ³12.365³ 0.186 ³ 307.751 ³ 3.88

³ C6H6 ³ 8.228³ 0.190 ³ 360.811 ³ 4.17ÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄ

phenyl fragment [26]. Worth mentioning are also datafor 4-methyl-1,3,2-dioxaphosphorinanes with axialPhNH [27] and C4H4N groups [28]. At the same time,1,3,2-dioxaphosphorinanes with an equtorial nitrogen-containing substituent are known [29]. Apparently,the problem is rather intricate and calls for furtherinvestigations.

Thus, our present knowledge of the solution struc-ture of 1,3,2-dioxaphosphorinanones containing planarfragments allows no certain prognosis of fine featuresof the conformational behavior of exocyclic substi-tuents. Note that the presence in the phosphorus-containing heterorings of compoundsI and III ofplanar fragments makes inapplicable the fractionaladditive scheme for estimating their dipole moments.Therefore, while using in calculations models withthe same exocyclic substituents is very important, noless important are ring substituents. In intricate cases,preference should be given to the general scheme withreliable dipole moments obtained from experimentaldata for symmetrical molecules and/or sterically rigidbicyclic structures. As follows from the dipolemoments, there is no strong electron density redistribu-tion (i.e. over that observed in acetophenone whichwas chosen as model in calculating the carbonyl bondmoment) in the compounds studied.

EXPERIMENTAL

The IR spectra of salicyl phosphitesI3II were ob-tained on a Specord M-80 spectrometer (in the solidphase and in 0.130.001 M methylene chloride andacetonitrile solutions). The dipole moments of freshlyprepared compounds were measured according to [30]in carbon tetrachloride and benzene at 25oC underargon.

Solvents were prepared before use by known pro-cedures [31]. Coefficients of equations and orientati-onal polarizations are listed in Table 4.

Crystals of compoundI , C8H4O4N1P1, mp 54oC,



rhombic, space groupPna21. Unit cell parameters at3150oC: a 7.789(4), b 16.358(6), c 6.603(2) A; V841.3(6) A3, Z 4, dcalc 1.65 g/cm3. The unit cellparameters and the intensities of 1034 reflections, 897of which had I > 3s, were measured on an Enraf3

Nonius CAD-4 automatic four-circle diffractometer at3150oC (lMoK

aradiation, graphite monochromator,

w/2q scanning,q < 26.9o). No intensity decay of threestandard reflections was observed during data collec-tion. Absorption was not included (mMo 3.01 cm31).The structure was solved by the direct method by theSIR program [32] and refined first isotropically andthen anisotropically. Hydrogen atoms were locatedfrom difference maps and refined isotropically in thefinal refinement step. The structure was refined toR0.037 andRW 0.050 on 874 unique reflections withF 2

> 3s. All calculations were performed using theMolEN program package [33] on Alpha Station 200.Molecular drawings were obtained using thePLATON program [34].

CompoundsI3III were synthesized according to[35].

ACKNOWLEDGMENTS

E.A. Ishmaeva, Ya.A. Vereshchagina, V.F. Miro-nov, L.M. Burnaeva, and G.R. Fattakhova are gratefulto the Universitety Rossii3fundamental’nye issledo-vaniya Program (project no. 015.05.01.17) and theProgram for Support of Leading Scientific Schools(project no. 00-15-97424) and I.A. Litvinov, D.B. Kri-volapov, and A.G. Gubaidullin, to the RussianFoundation for Basic Research (project no. 98-03-33266) for financial support.

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molecular and solution structure of 5,6-benzo-1,3,2-dioxaphosphinin-4-one derivatives

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