Organic Magnetic Resonance, 1975, Vol. 7 , pp. 76 to 77.

NMR Spectral Analysis of 1,3,2=Dithiaphosphorinanes and 1,3=Dithianes

J. Martin and J. B. Robert* Laboratoire de Chimie Organique Physique, D ipartement de Recherche Fondamentale, Centre d'Etudes Nucliaires de Grenoble, B.P. 85, Centre de Tr i , F. 38041, Grenoble Cidex, France

(Received 21 August 1974; accepted (revised) 4 November 1974)

Abstract-The full set of NMR spectral parameters (lH, 13C, 31P) are reported for 2-phenyl-l,3,2-dithiaphosphorinane and 2-phenyl- 1,3-dithiane. The stereochemical dependence of the coupling constants is discussed.

THERE exists in the literature only a few papers concerned with the NMR spectral analysis of 1,3,2-dithiaphos- ph0rinanes.l From a stereochemical and NMR view- point, it is useful to know the full set of NMR parameters (J, S) of the unsubstituted parent molecule of a family of compounds. We wish to report here the complete NMR spectral analysis of 2-phenyl-I ,3,2-dithiaphos- phorinane (1) (lH, 13C, 31P) and of 2-phenyl-1,3- dithiane (2).

Compounds 1 and 2 have been prepared according to standard procedures by reacting I ,3-propanedithiol and dichlorophenylphosphine or benzaldehyde, respec- tively.1*2 The ring protons of compounds 1 and 2 exhibit an AA'BB'CDX (X phosphorus) and AA'BB'CDpattern, respectively. Complete analysis of the proton spectrum of compound 1 was accomplished by 31P spin decoupling. This provided a simpler spectrum from which good approximate values for the chemical shifts and coupling constants could be extracted and refined using the iterative NMR program LAOCOON 3. The best parameters from the total analysis are presented in Table 1. The proton identification (a = axial, e = equatorial) is easily made on the basis of the existence of a large 3J(HH) coupling between axial protons.

The molecular structure of the dithiane (2) in the solid state, as determined by X-ray diffraction, shows a somewhat flattened chair conformation with the phenyl group in the equatorial p o ~ i t i o n . ~ The IH NMR data reported in Table 1 indicate that 1 adopts similar con- formations in the solid state and in solution.

The close similarity of the 2J(HH) and 3J(HH) values as measured in compounds 1 and 2 (Table 1) shows that the S-CH2-CH,-CH,-S fragment adopts a closely related conformation in both compounds. The R value, as defined to characterise the ring distortion from the perfect chair conf~rmat ion ,~ shows that the puckering for the S-C-4-C-5-C-6-S fragment is larger for the dithiaphosphorinane (1) (R, = 3.85) than for the dithiane (2) (R2 = 3.21).

The examination of the P C values (Table 2) reveals a very pronounced high field shift for carbon atoms 4 and 6 in going from 2 to 1. This shift could be due to the y effect,5 assuming an axial orientation of the phenyl group as already suggested for various 173,2-dithiaphos- ph0rinanes.l

The 3J(PH) and 4J(PH) NMR couplings have the same sign. This result has been obtained by comparing the plots of the recorded and calculated spectra for the different sets of possible signs.

It is interesting and somewhat surprising to note that in compound 1 the3J(PH,) coupling value is larger than the 3J(PH,,), which is the opposite of that previously re- ported for the 1,3,2-dioxaphosphorinane~~ and for the 1,3,2-dia~aphosphorinanes.~ As the 3J(PSCH) values are known in only a few rigid molecules,* this result is difficult to explain. However, we would like to present some preliminary comments on this point.

A Karplus-like relationship has been proposed to account for the angular dependence of the 3J(POCH) c o ~ p l i n g . ~ The 3J(POCH) =f($) plot exhibits two maxima for 180" and O", respectively and a minimum for a $ value close to 90". An angular dependence of this type is entirely consistent with the gross features of the 3J(POCH) coupling and also accounts for the values

TABLE 1. J((HH) A N D J(PH) NMR COUPI.iNG CONSTANTS FOR 2-PHENYL-I ,3,2-D1THIAPHOSPHORINANE (1) AND 2-PHENYL-i,3- DITHIANE (2)"

13.9 2.1 12.3 2.5 5.4 -14.7 0.8 5 2 . 6 $0.2 1 3 . 1 27 .9

a The coupling constants are given in Hz. * Author to whom correspondence should be addressed, Hevden & Son Limited.

Printed in Northern Ireland. 76

NMR Special Analysis of 1,3,2-Dithiaphosphorinanes and 1,3-Dithianes 17

TABLE 2. 'H, "c, 31P CHEMICAL SHIFTS AND J(,'Pl3C) NMR COUPLING CONSTANTS FOR 2-PHENYL-1,3,2-DITHIAPHOSPHORINANE (1) AND 2- PHENYL-I,3-DITHIANE (2)&

SH4,,ea bH4,,6, bHba 6H5, 61aC4,6 b13C6 "(PC,) 3J(PC5) b3'P

2.51 1.99 1.91 1.28 25-1 27.8 12.3 0.5

- - 2.91 2.76 1.98 1.82 32.1 75.1

--40.0

-

a The 'H and 13C chemical shifts are given in ppm from TMS as internal reference and the ,'P chemical shift is given in ppm from external H,P04. The spectra have been recorded in C,D, for 1 and in CDCI, for 2.

3 observed in P(OCH,),

and P(OC2H5), (7.8 Hz, J = f(60)).1° From the ,J(PSCH) values obtained for P(SCH,),

( J = 9.8 Hz) and P(SC,H,), (J = 9 Hz), and assuming similar conformations for P(SCH,), and P(OCH,), on the one hand and P(SC,H,), and P(OC,H,), on the other, a Karplus-like dependence of ,J(PSCH) should provide f(60) = 9 Hz, f(180) = 11.4 Hz. These two values,which are significantly different from the3J(PSCH) values measured in the dithiaphosphorinane (l), suggest that either ,J(PSCH) does not follow a simple Karplus- like dependence, or that 1 exhibits a conformation significantly different from a chair conformation.

The large 4J(PSCCH,) value (7.9 Hz) is also quite re- markable by comparison with the 4J(POCCH) reported for dioxaphosphorinanes.ll The near zero 4J(PSCCH) values measured for P(SC,H,), are indicative of a large stereochemical dependence of this NMR coupling.

Acknowledgernents-We wish to acknowledge assistance from R. Nardin in recording the NMR spectra.

t We assume here the usual eclipsed conformation, whereas the IR data of P(OCH,), suggest that the overall symmetry of the molecule might be less than C,, [R. A. Nyqvist, Spectrochim. Acta 22, 1315 (1966)l.

1.

2.

3. 4. 5.

6.

7.

8.

9.

10.

11.

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