96

Reference Data

I3C NMR Structural Analysis of a Series of Tricarbonyl(diene)iron Complexes

J. RODRIGUEZ, P. BRUN, J. P. ZAHRA and B. WAEGELL (to whom correspon- dence should be addressed) Laboratoire de Stereochimie Associe au CNRS, U.A. (109), Facultk des Sciences de St. Jkrome, Universitl dAix-Marseille 111, 13397 Marseille Cedex 13, France

The 13C N M R spectra of two series of sub- stituted tricarbonyl(cyc1ohexadiene)iron complexes and of substituted tri- carbonyl(vinylcyc1ohexene)iron complexes were recorded; 1 - and 2-substituted com- plexes can be distinguished by chemical shift comparison with parent compound.

KEY WORDS 13C N M R Substituted tricarbonyl(diene) iron complexes

it was shown that the chemical shifts of the diene carbon atoms are strongly influenced by the chemical nature of the sub- stituents and also by the acyclic or cyclic nature of the d i e ~ ~ e . ~ . ' Omission of such fea- tures had previously led to erroneous assign- ments.'=

EXPERIMENTAL

The I3C NMR spectra were recorded using a Varian XL-200 spectrometer operating at 50.3 MHz. Spectra were measured for CDCI, solutions of 0.2 M concentration, with TMS as internal reference in a 10 mm tube, via Fourier transform techniques. The pulse con- ditions were 60" pulses, 1 s repetition rates and 32K transform for a 14 kHz sweep width. As the various carbon types are easily distinguished by the APT procedure, it is possible to make unambiguous assignments for sp, carbons. The few ambiguities which remained for methylenic carbons could be solved by simple heteronuclear carbon- hydrogen decoupling. Chemical shifts are given with an accuracy of f0.5 ppm.

Fe(CO), complexation and isomerization of easily accessible functionalized 4- vinylcyclohexene derivatives.

The C-2 and C-1 chemical shifts in 1-7 and 813 allow an easy distinction between the 2- and 1-substituted series when compared with the corresponding carbon in reference com- pound 14. The introduction of a CH,R sub- stituent either in the 2- or 1-position results in a deshielding of the corresponding sp, carbon signal (15-23 ppm), whereas the chemical shifts of the unsubstituted sp, carbons remain almost unaffected. The deshielding effect decreases with the electron- withdrawing character of the R group, and a more eficient iron back-donation might be the origin of this effect6

The polar effect of the R group is more important in the exocyclic series (compounds IS20, Table 3), for which the most reason- able reference is the acyclic diene complex 21. There is a marked difference between the chemical shifts of C-1 and C-4 and an increasing shielding of the C-1 signal on going from 16 to 20.

INTRODUCTION

A complete analysis of the 13C NMR spectra of substituted tricarbonyl(diene)iron com- plexes was required in the course of mecha- nistic and synthetic studies reported elsewhere.' Although the I3C NMR spectral analysis of such complexes has already been

RESULTS AND DISCUSSION

We report the chemical shifts of 2- and 1-substituted tricarbonyl(cyc1ohexadiene)iron complexes (1-7 and 813, respectively, Tables 1 and 2) and of functionalized tricarbonyl(vinylcyc1ohexene)iron complexes (1520, Table 3) which were obtained by

References

1. (a) J. Rodriguez, P. Brun and B. Waegell, Tetrahedron Lett. 27, 835 (1986); (b) J. Rodriguez, P. Brun and B. Waegell, J . Organomet. Chem. 333, C25 (1 987).

2. J. W. Faller, Adv. Organomet. Chem. 16, 211 (1977).

Table 1. * 'C chemical shifts (ppm) of 2-substituted tricarbonyl(cyc1ohexadiene)iron complexes'

Compound C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 C-10 C-11 C-12 CO

1 H 65.3 102.8 85.7 58.7 21 2.1

2 CH, 64.3 108.6 83.9 58.9 23.9 24.8 29.0 14.2 21 2.3

3 CH,CH, 64.7 107.1 85.0 59.0 23.8 24.7 38.9 24.6 13.8 21 2.9

8

8 9

8 9 10 4 CH,CH,OCH, 64.6 106.5 84.9 59.1 23.8 24.7 33.3 31.2 71.8 58.6 21 2.1

5 E H , S ~ G 65.0 105.8 85.0 59.1 23.6 24.7 38.9 37.7 140.8 126.3 128.7 128.5 212.2 F

8 9 10 6 CH,COCH, 64.5 105.0 85.1 59.4 23.8 24.7 35.2 31.7 172.8 51.7 21 1.9

7 EHJN 64.7 102.3 85.6 59.9 23.6 24.5 32.7 19.5 118.7 21 1.5

a Compounds 2-7 are classified according to the progressive shielding effect observed on C-2.

97

Reference Data

3. A. J. Pearson, Aust. J. Chem. 29, 1679

4. S. Zobl-Ruh and W. von Philipsborn,

5. K. Bachman and W. von Philipsborn, 6. J. Rodriguez, P. Brun and 8. Waegell, J. (1 976) ; 30,407 (1 977).

Helv. Chim. Acfa 63, 773 (1980).

Org. Magn. Reson. 8,648 (1 976). Organomet. Chem. in press.

~

Table 2. "C chemical shifts (ppm) of 1-substituted tricarbonyl(cyc1ohexadiene)ion complexesP

4 'WR

Fe (CO$ 5

Compound C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 C-10 C-11 '2-12 CO

8 EH, 85.8 87.8 81.5 61.1 24.7 26.2 33.2 14.3 21 1.2

21 2.7

21 2.7

8 9

8 9 10

9 CH,CH, 84.3 88.0 81.1 60.9 24.8 26.7 42.8 23.2 14.3

10 CH,CH,OCH, 77.1 88.0 81.6 61.0 26.7 29.9 32.4 37.0 72.5 58.5 8 11 CH,Ph 82.7 87.9 87.7 61.1 24.9 28.8 42.8 31.4 130.1 21 2.1

21 2.4 8 9 10

12 CH,COCH, 81.0 88.1 82.0 61.4 24.7 26.4 34.1 35.3 172.8 51.6

13 EHJN 77.0 88.0 82.7 61.8 24.8 26.1 35.8 17.2 119.4

14 Q 62.5 85.4 85.4 62.5 23.9 23.9

21 1.8

21 2.2

Fe(c013 a Compounds S13 are classified with the same order of substituent polarity as in Table 1.

Table 3. I3C chemical shifts (ppm) of 1-substituted tricarbonyl(vinylcyc1ohexene)iron complexesP

co Compound C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 C-10 C-11 C-12

21 2.7 21 3.1

15 H 36.1 78.3 106.1 62.0 26.7 22.7 22.6 29.5 16 OCH, 57.8 98.7 98.7 71.2 26.3 22.6 22.6 29.3 60.3

17 a,2 57.1 77.4 102.1 60.7 26.4 22.7 22.6 29.9 140.3 128.3 126.3 126.1 212.4 w

18 EH, 53.1 83.3 101.9 60.3 26.4 22.9 22.7 29.7 19.0

19 EOOFH, 42.6 80.2 105.4 62.7 26.4 22.3 22.2 29.2 173.3 51.5

20 EN 21.1 77.9 106.7 63.5 26.3 22.0 22.0 28.8 122.1

21 3.3

21 0.4

197.5

21 2.2

67.0 84.7 85.5 60.0 32.7 40.1 30.5 12.6

Fe(CO13

21 2.8

a Compounds 1&20 are classified according to the substituent shielding effect on C-1.