D I P O L E M O M E N T S A N D C O N F O R M A T I O N S OF

BEN Z Y L D I P H E N Y L P H O S P H I N E O X I D E S

p

E. A. I s h m a e v a , E. N. T s v e t k o v , E . N. S t r e l k o v a , a n d I . [ . P a t s a n o v s k i i

UDC 541.67: 541.63:547.1 '118

A quite detailed study has been made of the internal rotation around the C s p 3 - P bond in the ser ies of te t racoordinated phosphorus compounds [1-6]. By employing the methods of vibrat ional spect roscopy, dipole moments (DM), and the Kerr effect it has been shown that, as a rule, a conformat ional equil ibrium of the forms with a gauche and trans a r rangement of the P = Y and Csp 2-X bonds is rea l ized for compounds of type R2P(Y)CH2X. Depending on the type of substituents on the P (R)atom and the a - c a r b o n atom (~;) ei ther the gauche or the t rans forms predominate in the equilibrium. Compounds with X = Alk [1] and Hal [2-6] (R = Alk, Ph, Hal, CH2Hal ) were studied previously.

We studied the p-substi tuted benzyldiphenylphosphine oxides p-XC6H4CH2P(O)Ph 2 (X = H(I), Me (II), NO 2 (II[), CN (IV)), for which we determined the experimental DM, respec t ive ly equal to 4.24, 4.40, 6.67 and 6.90 D. The calculated DM for the conformations with a gauche and t rans or ientat ion of the C s p 3 - C s p 2 bonds and the phosphoryl groups are respect ively equal to 4.25, 3.93; 4.12, 4.12; 6.83, 0.20; 6.92, 0.28 D.

As can be seen, the experimental DM of (I), (IIf), and (IV) correspond to those calculated for the confor - mations with a gauche a r rangement of the Csp3-Csp 2 and P ----O bonds. The calculated DM of the gauche and t rans forms of (II) a re the same, since m(p-MeC6H 4 ~Csp3) and m(H--Csp2) have the same value.

A preference of the gauche form in solution (~ 90~) is also observed for Ph2P(O)CH2CI [2], which in the crysta l l ine state has exclusively the gauche conformation [7]. This fact is explained by the s ter ic hindrance that is created by the bulky phenyl groups in the t rans form. With decrease in the size of the R substituents on the P atom in the R2P(O)CH2C1 ser ies of compounds the conformat ional equil ibrium is shifted toward the t rans form [2] (90~ when R = Me), which is, more favorable from the standpoint of the e lec t ros ta t ic interaction of the P -----O and C - C 1 dipoles.

In compounds (I)-(W) the determining role is probably played by s ter ic f ac to r s , which a re responsible for the preference of the gauche conformation, the same as in the case of Ph2P(O)CH2C1 [2].

The following DM of the bonds and groups (D) were used in the calculat ions: m(P = O ) = 2.95 [8], m ( P h - P ) = 1.09 [9], m(Csp3-P) = 0.55 [10], m(H-Csp3) = 0.28. The group DM (D): m(Csp3~ Ph) = 0.07, m(p-MeC6H4-Csp3 ) = 0.28, m(Csp 3 -" C6H4NO2-p) = 4.02, and m(Csp 3 -- C6H4CN-p) = 4.12 were calculated f rom the experimental DM [11] of toluene (0.34), p-xylene (0), p-nitrotoluene (4.30), and benzonitr i le {4.05) r e s p e c - tively. The valence angles of the P atom were taken equal t o : ~ C s p 2 - P - C s p 2 = / C s p 2 - P - C s p 3 = 106 ~ [7], and those of carbon were taken to be tetrahe,dral.

The synthesis of the studied compounds is described in [12].

TABLE 1. Experimental Dipole Moments of Benzyldiphenylphosphine Oxides, Coefficients of Calculation Equations, and Melting Points

Compound a ~ :"or. cM, ~. D mp , "c

(I) (II) (III) (~V)

8,292 8,543

t6,736 t8,836

0,526 0,580 0,t38 0,029

37t,747 399,597 920,i95 982,580

424 4,40 6,67 6,90

t98--t99 t98-199 2i3-213,5 22t-222

Ul 'yanov-Lenin Kazan State University. Institute of Physiological ly Active Compounds, Academy of Sci- ences of the USSR, Chernogolovka. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1179-1180, May, 1982. Original ar t ic le submitted September 7, 1981.

1052 0568-5230/82/3105- 1052 $07.50 �9 1982 Plenum Publishing Corpora t ion

The e x p e r i m e n t a l DM of (I)-(IV) (in dioxane at 25 ~ and the coeff icients of the calculat ion equations a re given in Table 1,.

C O N C L U S I O N S

The p-subs t i tu ted benzyldiphenylphosphine oxides in solution have a conformat ion with a gauche o r i e n t a - tion of the Csp3-Cspz and P = O bonds.

LITERATURE CITED

1. O . A . Raevski i , N. G. Mumzhieva , T. A. Zyablikova, A. N. Vereshchagin , E. I. Gr i tsaev, and M. M. Gilyazov, Izv. Akad. Nauk SSSR, Ser. Khim., 197____~8, 614.

2. O . A . Raevsk i i , F. G. KhalitDv, A. N. Vereshchagin , and I. M. Vetluzskikh, [zv. Akad. Nauk SSSR, Set . Khim., 1972, 2446.

3. L . S . Khaikin, L. V. Vilkov, A. Y. Vas i l ' ev , N. N. Mel 'nikov, T. Y. Tulyakova, and M. G. Anoshkin, Dokl, Akad. Nauk SSSR, 203, 1090 (1972).

4. O . A . Raevski i , A. N. Vereshchagin , g. G. Khalitov, and Yu. A. Donskaya, Izv. Akad. Nauk SSSR, Set . Khim., 1972.., 710.

5. O . A . Raevsk i i , A. N. Vereshehag in , F. G. Khalitov, and E. N. Tsvetkov, Izv. Akad. Nauk SSSR, Ser. Khim., 19_1 ~ . ~ 995.

6. O . A . Raevski i , A. N. Vereshchag in , Yu. A. Donskaya, Y. G. ghal i tov, and E. N. Tsvetkov, Izv. Akad. Nauk SSSR, Ser . Khim. , 1974, 787.

7. G. Bernard ine l l i and R. Gerdi l , Crys t . Struct. Commun. , 8_, 921 (1979). 8. B . A . Arbuzov and R. P. Arsh inova , Dokl. Akad. Nauk SSSR, 226, 1361 (1976). 9. E . A . I s h m a e v a , M. G. Zirnin, R. M. Galeeva, and A. N. Pudovik, Izv. Akad. Nauk SSSR, Set . Khim., 197__~1,

538. 10. t~. A. I s h m a e v a , M. A. Pudovik, S. A. T e r e n t ' e v a , and A. N. Pudovik, Dokl. Akad. Nauk SSSR, 1966, 630

(1971). 11. O . A . Osipov, V. [. Minkin, and A. D. Garnovski i , Handbook on Dipole Moments [in Russian] , Vysshaya

Shkola, Moscow (1971). 12. S . P . Mesya t s , E. N. Tsve tk0v , ~ . S. Pe t rov , N. N. Shchelganova, T. M. Shcherbina, A. I. Shatenshtein,

and M. L Kabaehnik, Izv. Akad. Nauk SSSR, Set . Khim., 1974, 2497.

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