Tricarbonylchromium complexes of centro-polyindans. Part 2. Synthesis and structure of tricarbonylchromium mono-and bis-complexes of 4b, 5, 9b, 10-tetrahydroindeno [2, 1-a] indene

J. CHEM. SOC. PERKIN TRANS. 2

1992

1111

Tricarbonylchromium Complexes of centro-Polyindans. Part 2.t Synthesis and Structure of Tricarbonylchromium Mono- and Bis-complexes of 4b,5,9b,lOTetrahydroindeno[2,1 -a]indene Albert0 Ceccon,8 Alessandro Gambaro,a Francesco Manoli," Alfonso Venzo," Paolo Ganis,c Dietmar Kuckd and Giovanni VaIlee a Dipartimento di Chimica Fisica, Via Loredan 2, 35131 Padova, Italy CNR, Centro Studi Stati Molecolari Radicalici Eccitati, Via Loredan 2, 35 731 Pado va, Italy Dipartimento di Chimica, Universita di Napoli, Via Mezzocannone 4, 80134 Napoli, Italy Fakultat fur Chemie, Universitat Bielefeld, Universitatsstrasse 25, 4800 Bielefeld 1, Germany CNR, Centro di Studio sui Biopolimeri, Via Marzolo, 3, 35131 Padova, Italy The reaction of 4b,5,9b,l O-tetrahydro[2,1 -a]indene, DIN, with Cr(CO), in Bu,O-THF (9: 1) affords t w o mono-complexes with the inorganic unit bonded to the convex or to the concave side of the ligand, respectively. Prolonged reaction times cause the formation of two bis-complexes, bearing the t w o Cr(CO), units bonded both to the convex side of DIN in one case, and to the convex and to the concave side in the other. Steric factors seem important in the kinetic control of the stereochemistry of both the first and the second complexation reaction. Combined X-ray and NMR spectroscopic analyses indicate that coordination with two Cr(CO), groups at the convex side of DIN changes the structure of the ligand into a less bent and less favourable structure. Until quite recently arene coordination reactions with tricarbonylchromium were known only for mono-, di- and polycyclic fused planar ligands.' The complexation of bent di- or poly-arenes have received some attention in recent papers since the coordination with the inorganic group on either the convex or concave face of the arene is expected to occur with different rates giving rise to stereoisomers which in turn have different physical and chemical properties. We have reported, for example, that for 10-methyltribenzotriquinacene,MTBT, a bent triarene of C3" symmetry and rigid g e ~ m e t r y , ~ complexation of the convex side of a free benzene ring is favoured for steric reasons and that the stereoisomer with the tricarbonylchromium coordinated to the concave face (syn) is less stable than that complexed at the convex face (anti).The two isomers manifest different reactivity towards further complexation, and some specific 'H and I3C NMR spectroscopic characteristics have been correlated with different conformations adopted by the inorganic unit when bonded to the convex or concave side of the ligand.4 The linearly fused di-indan 4b,5,9b,lO-tetrahydroindeno[2,1alir~dene,~ DIN, represents a different type of bent hydrocarbon and exhibits a C2 symmetry axis.*

C(1'). In fact a clockwise or an anticlockwiserotation must take place primarily in order to avoid the eclipsed conformation about this bond, thus affording two energetically non equivalent conformers, viz. A and B.

A

B

Moreover, the di-indan ligand contains methylene hydrogen atoms both of syn and anti type. Their presence will play an essential role in the insertion process of Cr(CO), in either of the conformers. The NMR spectroscopic and X-ray analyses could clarify in terms of geometrical considerations the relevant chemical results and physicochemical properties of the complexes described in this work.

Results

4

6'

. I

DIN

Unlike MTBT, the DIN molecule displays a certain degree of flexibility mainly due to possible limited torsions (ca. 20-30") about the bond joining the two methine carbon atoms C(l) and

* In our laboratories, the title di-indan has been conveniently synthesized in 80% yield from the corresponding 5,lO-diketone(see ref. 5 4 by reduction with H,/Pd/C (10%)in ethanol (Parr hydrogenation apparatus; 5 bar, 25 "C, 1 d). t For Part 1, see ref. 4.

The tricarbonylchromium complexes 1-4 of DIN (Scheme 1) were prepared by boiling the hydrocarbon and Cr(CO), in a 90:10 v/v mixture of butyl ether-tetrahydrofuran (THF). Separation of the complexes was accomplished by medium pressure column chromatography on silica under argon, as described in the Experimental section. By working with an excess of complexing agent and prolonged reaction times, we obtained 60% conversion of DIN into four different complexes (1-4) which were obtained in the yields indicated in Table 1 (run 1). They were isolated as bright, yellow, crystalline air-stable solids. On the basis of the NMR and mass spectra, and on X-ray measurements (see below), they have been identified as anti-Cr(CO),-DIN, 1, syn-Cr(CO),DIN, 2, anti,syn-[Cr(CO),],-DIN, 3,and anti,anti-[Cr(CO),],DIN, 4. In order to drive the reaction towards monocomplexation, an excess of DIN over Cr(CO), and shorter reaction times were used in run 2. In these experiments (conversion ca. 24%) the relative yields of the isomers 1 and 2

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J. CHEM. SOC. PERKIN TRANS. 2

Table 2

1992

' H NMR parameters" for DIN and complexes 1-4 Chemical shifts (Si)

2

1

3

4

Scheme1 Orientation oftheCr(CO), unitsin mono-and bis-complexed DINs

H(i)

DIN

1

2

3

4

1 1' 2a 2'a 2b 2'b 4 5 6 7 4'

4.004 4.004 3.45 1 3.45 I 3.187 3.187 7.121 7.073 7.127 7.318 7.121 7.073 7.127 7.3 18

4.030 4.127 3.490 3.428 3.127 3.033 7.192 7.168 7.201 7.329 5.782 5.492 5.51 1 5.989

4.03 1 3.986 3.336 3.483 3.226 3.07 1 7.214 7.143 7.150 7.293 5.340 5.643 5.247 5.929

4.136 4.018 3.417 3.537 3.190 3.130 5.906 5.553 5.554 6.086 5.456 5.769 5.362 6.02 1

3.954 3.954 3.301 3.020 3.301 3.020 5.753 5.563 5.577 5.936 5.753 5.563 5.577 5.936

5'

6' 7'

Table 1 Complexation products of free and Cr(CO),-complexed DIN Relative yields (%)

Runa

Substrate/ Cr(CO),: mol substrate

1 2 3 4

DIN DIN I 2

Conversion

3: 1 1:l 2: 1 2: 1

t/h

(%I

24 6

60 24 221 17

15

15

1

2

53 29 63 29

3

4

13 5 6 2 c c 100

Solvent, butyl ether-THF, 90: 10 v/v; T 140 "C. Conversions and yields were calculated from NMR spectra of the crude reaction mixture. The substrate was detected by NMR spectroscopy to the extent of the difference to 100%. A 3j4 ratio of ca. 2 was roughly estimated.

a

I

I

I, DIN 4.2 Ic

I

-"L

4 7

5 6 (PPm)

3.4

3.0

Fig. 2 High field portion of the 'H NMR spectra of DIN and the complexes 1 4 . For the experimental conditions, see Fig. 1

DIN 6

3.8

6 (PPm)

2

1 4

3

Fig. 1 'H NMR spectra of the free and Cr(CO),-complexed DINs. Solvent, [2H,Jacetone; T 289 K; vo 400.13 MHz; 6 in ppm from internal Me,%

were only slightly changed, and the formation of the biscomplexes 3 and 4 was reduced to a half. Reaction of 2 with Cr(CO), for 15 h (run 4) gave a 17% yield of the 3 as the only reaction product; on the other hand, complex 1 was found to be very poorly reactive under the same conditions (ca. 1% conversion), and an approximately 2: 1 mixture of 3 and 4 was obtained (run 3).

N M R Spectroscopic Measurements.-The 'H (see Fig. 1) and 13C NMR spectra of 1-4 have been used for identification. The proton assignments given in Table 2 were performed by selective decoupling and ('H)-'H NOE measurements. The spectra of the aliphatic moiety of the molecules are shown in Fig. 2, and selected 3 & H coupling constant values are listed in Table 3. The 13C NMR resonances were attributed to the corresponding nuclei by selective proton decoupling experiments and partially relaxed spectra, and they are reported in values. Table 4 together with the corresponding lJC-H The ligand. The 'H spectrum of DIN exhibits an ABCD pattern due to the aromatic protons in the range 6 7.4-7.0; the multiplet centred at S 4.004 is attributed to the methine H(l) and H(1') protons, and the signals due to the methylene protons appear at S 3.451 and 3.187. The lower field resonance exhibits a 7.95 Hz coupling constant with the adjacent methine proton, this coupling being reduced to 1.79 Hz for the high field signal. O n the basis of geometrical considerations on the aliphatic part of the molecule, we assign the lower field resonance to the

J. CHEM. SOC. PERKIN TRANS. 2

1992

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Table 3 Selected 3J(H,,Hj) values for DIN and complexes 1 4 ' Hi,Hj nuclei Compound

H(l),H(2a)

H(l),H(2b)

H(l'),H(2'a)

H(l'),H(2'b)

H(l),H(l')

DIN 1 2 3

7.95(0.03) 9.23(0.01) 8.43i0.06) 8.67(0.02) 9.3l(0.02)

1.79i0.03) 3.93(0.01) 1.29(0.06) 1.53i0.02) 8.OS(O.O 1)

7.95(0.03) 8.85(0.01) 8.85(0.09) 9.39(0.02) 9.31(0.02)

1.79(0.03) 3.90(0.01) 1.97(0.06) 1.63(0.02) 8.08(0.01)

7.46(0.04) 8.00(0.01) 8.31(0.06) 8.1 l(0.02) 8.25(0.02)

4

H(2a),H(2b) - 16.20(0.02) - 16.63(0.01) - 16.44(0.06) - 16.76(0.02) - 16.32(0.01)

H(2'a),H(2'b)

- 16.20(0.02) - 16.45(0.01) - 16.54(0.06) - 16.97(0.02) - 16.32(0.01) ~

~~~

" Values given in Hz (standard errors in parentheses). For experimental conditions, see Table 2. A full list of the Ji,j coupling constant values is deposited as supplementary material.

Table 4 13C NMR chemical shifts," 6 (ppm), and *J,,/Hz (in parentheses) for DIN and complexes 1-4 C(i)

1

2 3 4

5 6 7 8

CEO 1' 2' 3' 4' 5'

6' 7' 8' C'=O

DIN

1

2

3

4

49.50 (130) 39.48 (130) 143.34

39.48 (130) 39.98 (132) 146.36

47.89 48.08 (137) (140) 39.37 38.85 (1 3Q135) (134) 142.28 120.13

50.0 1 (142) 39.15 (129;139) 117.76

(-1

i-)

i-1

(-)

(-->

125.13 (158) 127.35 ( 160) 127.60 ( 159) 124.30 (157) 147.46

125.55 (159) 128.11 (160) 127.91 ( 160) 125.33 (1 5 8 ) 142.57

126.33 (158) 127.88 (1 59) 127.38 (159) 124.81 (1 56) 146.62

93.51 (175) 94.63 ( 174) 93.87 (175) 92.75 (173) 116.01

92.16 (175) 94.21 (176) 94.26 (175) 92.24 (176) 115.09

(-1

(-1

(-1

(-1

(-1

(-1

-

49.50 (130) 39.48 (130) 143.34

49.88 (138) 39.70 (133) 120.14

48.04 (137) 38.60 (130;132) 118.46

234.70 235.16 50.01 47.89 (142) ( 140) 39.15 38.47 ( 135; 132) (129;139) 117.76 117.58

(-1

(-1

(-1

(-)

92.63 (176) 94.38 (175) 94.00 (175) 92.65 ( 176) 116.48

86.84 (174) 97.35 (173) 89.73 (175) 93.97 (1 72) 117.13

87.20 (1 73) 98.03 (174) 90.20 (176) 94.3 1 (173) 116.28

(-1

(-1

(-1

(-1

125.13 (158) 127.35 ( 160) 127.60 (159) 124.30 (157) 147.46 -

-

235.05

-

234.09

234.16

92.16 (175) 94.2 1 (175) 94.26 (175) 92.24 (175) 115.09

(-1

234.70

" T 298 K, solvent ['HJacetone,

internal standard Me& For carbon labelling, see Scheme 1. The uncertainties are 10.01 ppm.

methylene hydrogens located in the convex side of the molecule, i.e. to the anti-H(2a) and the higher field one to the syn-H(2b) protons. The assignments were confirmed by NOE measurements, which also allow us to attribute the lowest field resonance system occurring at 6 7.318 to H(7), i.e. to the protons at the ortho position with respect to the methine position. This is a common feature for the 'H NMR spectra of all the DIN derivatives reported here. Mono-complexes 1 and 2. By complexation of one benzene ring with Cr(CO), to the convex or to the concave side of DIN the molecular symmetry of the ligand is removed. The effect of the complexation on the chemical shifts is sufficient to make all the resonances of both the aromatic and the aliphatic moieties of the mono-complexes clearly distinguishable (see Fig. 1). In particular, the 'H NMR spectra of 1 and 2 consist of an ABCD system between 6 7.4 and 7.1 attributed to the protons of the

uncomplexed ring on the basis of the chemical shift values. Another ABCD pattern belonging to the protons of the complexed ring is found between 6 6.0 and 5.4 for 1 and between 6 6.0 and 5.2 for 2. The signals due to the aliphatic nuclei appear as two distinct sets, as expected, and the assignments were accomplished by NOE measurements. The number of signals in the proton decoupled NMR spectra is consistent with the absence of molecular symmetry in the two complexes. The most important difference between the two spectra is the value of the difference of the chemical shift, A613c, found for the two quaternary carbon atoms belonging to the complexed ring, uiz. 3.76 ppm for 1 and 1.33 ppm for 2, together with the more pronounced spread of the resonances of the tertiary carbon nuclei of the complexed ring, uiz. 1.75 ppm for 1 and 10.51 ppm for 2. In addition, the C=O resonance of 1 (6 235.06) appears at a significant lower field than that of 2 (6 234.09). This has been already found for the Cr(CO), complexes of MTBT.4 Bis-complexes 3 and 4. The 'H NMR spectrum of the firsteluted bis-complexed DIN, 3, indicates the absence of molecular symmetry. In fact, two different ABCD systems were found in the range 6 6.1-5.3, together with two sets of resonances due to the aliphatic moiety. In addition, all the 16 carbon nuclei resonances of the organic moiety are found in the ' 3C spectrum, and two different signals for the C=O carbons are also observed at 6 235.16 and 234.16. The results clearly indicate that the two Cr(CO), units are coordinated one to the convex and the other to the concave side of the ligand, as confirmed by the X-ray structure (see below). The proton and carbon NMR spectra of 4, on the contrary, show the presence of two equivalent Cr(CO),coordinated benzene rings, as indicated by the single ABCD pattern for the aromatic protons occurring between 6 6.0 and 5.5, together with only one methine resonance pattern centred at 6 3.954 and only one set of resonances due to the methylene protons at 6 3.301 and 3.020 for the anti and syn hydrogen atoms. In addition to the equivalence of the aromatic, methine and methylene carbon atoms, only one signal for the C r O carbon atoms is found in the 13C spectrum at 6 234.70. X-Ray Measurements.-Suitable crystals for diffractometric analysis were obtained by slow evaporation under an inert atmosphere of concentrated solutions of 3 and 4 in a 1 : 1 : 1 mixtureofacetone,methanol andmethylenedichloride.No single crystals could be obtained from solutions of 2 in the above mentioned and other similar solvent mixtures. Even though good crystals were obtained for 1, the structure could not be resolved owing to an exceedingly high crystallographic disorder. The results of the X-ray analysis for the two bis-complexes are shown in Figs. 3 and 4. In complex 3 one of the two Cr(CO), units is bonded to the convex side of the organic ligand and the other to the concave one. The two metal groups in 4 are both bonded in equivalent positions to the concave side of DIN in the anti,anti positions. Crystal data and details of the intensity data collected for complexes 3 and 4 are reported in Table 5.

J. CHEM. SOC. PERKIN TRANS. 2

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1992

preference of ca. 2 can be estimated from the product ratios 1:2 in both the runs 1 and 2. This result parallels the trend reported for the MTBT ligand, and the difference in reactivity between the convex and the concave side is likely to be ascribed to steric reasons. Runs 1 and 2 show also that the formation of the bis-complex 3 is favoured with respect to that of the complex 4, and the result is confirmed by the results of runs 3 and 4. In fact, by reacting 1 with Cr(CO),, the bis-complexes were hardly detectable in contrast with the higher reactivity of complex 2 which produces only the species 3. Therefore, the reactivity towards the second metallation depends on the syn or anti coordination of the adjacent benzene ring.

Fig. 3 Projection of the molecule of 3 as viewed along the C(1)-C(1') bond

Fig. 4 Projection of the molecule of 4 as viewed along the C(1)-C(1') bond

Table 5 Summary of crystal data and intensity collection for complexes 3 and 4 Compound

3

4

Formula M

CzzH,4CrzO, 478.34 16.374(9) 11.OO2(6) 11.109(6) 101.0(2) 1964.5 4 1.62

CzzHl4CrzO6 478.34 18.677(9) 7.087(5) 15.088(8) 91.1(1) 1996.7

%la 0.2 x 0.3 x 0.2

C2/C 0.3 x 0.15 x 0.15

a/A blA CIA

PI"

VIA3

z

D,/g cmP3 Space group Crystal dimensions/mm T/K Radiation p/cm-' Take-off angle/" Scan speed/" min-' 28 range/" Unique data [Fi > 2cr(Fg)] R (on Fo)

4

1.59

298 298 graphite-monochromated MO-KZ( A = 0.7107 A) 12.78 12.57 3.0 3.0 2.0 in the 8 mode 3.0 I28 145 4625 2162 0.065 0.052

Discussion The results summarized in Table 1 indicate that the complexation with one Cr(C0)3 group at the convex side of the ligand is favoured as compared to syn complexation, and an antilsyn

X-Ray Data.-The di-indan ligand of the complexes described here is a bent hydrocarbon with C2 symmetry, and contains two stereoisomeric centres on C(l) and C(1') having the same configuration. As a first approximation this molecule can be considered quite rigid except for a limited torsional freedom about the C(1)-C(1') bond of the two indan moieties; a rotation is required, however, in order to avoid an 'eclipsed' conformation about this bond and the unfavoured planar conformation of the two five membered rings. Though not structurally determined two possible conformations are predictable. As discussed above, an anticlockwise rotation about this bond (ca. 20-30") affords the conformer A, while a clockwise rotation (ca. - 20 to 30") gives the conformer B (the sense of rotation obviously depends on the enantiomer chosen). Due to the enantiomorphic character of the ligand, these conformers are geometrically and energetically non equivalent. The relevant features expected for A are: (a) the five membered rings are puckered towards the concave side of the molecule thus increasing the bent shape of the whole ligand; (b) the orientation of the methine hydrogen atoms H(l) and H(1') with respect to the adjacent methylene hydrogen atoms H(2a) and H(2b) and H(2'a) and H(2'b) are defined by torsion = +20-30" and u2 = angles o 1 = H(l)-C(l)-C(2)-H(2a) H(1)- C(l)-C(2)-H(2b) = -90 to 100" [the same holds for d I =H(l')-C(l')-C(2')-H(2'a) and d2= H(1')-C(1')C(2')-H(2'b), respectively]; (c) the two methylene syn-hydrogen atoms H(2b) and H(2'b) move further away from each other and from the central normal to the adjacent benzene ring; ( d ) the methylene anti-hydrogen atoms H(2a) and H(2'a) and the methine hydrogen atoms H(l) and H(1') get closer to each other. One can easily realize that insertion of a syn-Cr(CO), group is only possible under condition (c), and among the possible conformations of the Cr(CO), tripod the more favoured is the ex0 one., All these features have been found in the structure of the syn-anti bis-[Cr(CO),], di-indan complex 3 (see Fig. 3 and Table 6). The syn-Cr(CO), tripod is rotated ca. 10" about the chromium-arene bond from an idealized 'staggered' conformation giving rise to distances from the C(13)-O(5) and C(12)-0(4) bond middle points to H(2b) and H(2'b) of ca. 2.65 and 3.00 A, respectively. This recurring feature is present in almost all these and similar complexes and it does not seem to be imposed by steric requirements; on the contrary, it is probably due to a stabilizing interaction between H(2b) and the nearby carbonyl group, as already discussed in a previous paper.4 The chromium atom lies almost exactly on the central normal to its complexed benzene ring. The NMR spectra (vide infra) are in agreement with feature (b).Feature ( d ) ,imposed by the syn complexation, is completely unfavourable for either a staggered endo or e m conformation of an anti-Cr(CO), tripod complexed on the other benzene ring. As a consequence, the only allowed conformation of this group must be the 'eclipsed' one, as actually found in the structure where again one CEO

J. CHEM. SOC. PERKIN TRANS. 2

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Table 6 Some relevant geometrical parameters for the complex 3 Bond lengths and intramolecular interatomic distances/A Cr( 2)-C( 3’) 2.239(7) Cr( 1)-C(3) 2.224(6) 2.209(9) 2.16 l(6) Cr( 1)-C(4) Cr(2)-C(4’) 2.179(9) Cr(2)-C( 5’) Cr( 1)-C(5) 2.158(6) 2.179(8) 2.2 18(6) Cr(2)-C( 6’) Cr( 1)-C(6) 2.209(8) 2.279(7) Cr(2)