Carbon-13 and oxygen-17 NMR spectra of some arenechromium(0) tricarbonyls and their monothiocarbonyl derivatives

JOURNAL

OF

MAGNETIC

RESONANCE

33, 149-157

(1979)

Carbon-13 and Oxygen-17 NMR Spectra of Some Arenechromium(0) Tricarbonyls and Their Monothiocarbonyl Derivatives* DANIELCOZAK,IIANS.BUTLER,ANDJAMES

P. HICKEY

Department of Chemistry, McGill University, Montreal, Quebec, Canada H3A 2K6 AND

LEEJ.TODD

Department of Chemistry, Indiana University, Bloomington, Indiana 47401 Received

March

10, 1978

The 13C and “0 NMR spectra of a series of arenechromium(0) complexes, (n6CeHe-,R,) Cr(CO),(CX) (R= H, Cl, Me, OMe, NH*, NMes, COaMe; X= 0, S; n = O-3). have been measured at 30°C in CHzClz solution. Linear regression analyses relating the observed i3C and “0 chemical shifts of the CO and CS ligands with the approximate primary CX stretching force constants, k cx, indicate a definite correlation only for S(13CO) vs koo. The much poorer correlations for S(i3CS) and 6(C”O) suggest that these chemical shifts are not influenced by the same factors as 6(‘3CO). In contrast to 13C and “0 NMR studies on other substituted metal carbonyls, replacement of a CO group by CS in (n6-CeH6-nR,)Cr(CO)3 produces an upfield shift in 6(i3CO) and a downfield shift in 6(C”O). This difference is attributed to the greater net electronwithdrawing capacity of CS compared to CO in the Cr(CO),(CS) moiety. The 13C and I’0 carbonyl shielding values exhibit opposite trends on going from 0 to S in CX and on changing the electronegativity of R in the C6HswnRn ring [with the exception of the aniline (R = NHs) derivatives].

INTRODUCTION

There has been considerable interest lately in the comparative properties of isoelectronic transition metal thiocarbonyls and carbonyls, since it is evident that CS is a better cr donor and 7~acceptor ligand than CO (1). However, while there have been extensive 13C NMR studies reported for metal carbonyls [for recent views, see Ref. (Z)], there are relatively few 6(r3CS) data for metal thiocarbonyls in the literature: M(CO),(CS) (M = Cr, W) (3), (q’-C5H#l’(CO)2(CS) (M’ = Mn, Re) (4, and [(q5-C5H5)Fe(CO)(CS)L]+ (5). We now report the results of a detailed examination of the 13C NMR spectra of some arenechromium(0) thiocarbonyl complexes, (q6-C6H6-,R,)CR(CO)2(CS) (R = H, Cl, Me, OMe, NH*, NMe2, C02Me; n = O-3), and the corresponding tricarbonyl complexes. The I70 NMR chemical shifts of the carbonyl ligands for most of these complexes have also been * Taken in part from the Ph.D. Thesis of D.C., McGill University, 1977; presented Canadian Chemical Conference, London, Ontario, June 1976. t Present address: Anorganisch-chemisches Institut der Technichen Universitat West Germany. 149

in part

at the 59th

Miinchen,

Munich,

0022-2364/79/010149-09$02.00/0 Copyright @ 1979 by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain

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measured, and these data are of particular interest as they are among the first I70 NMR spectra ever reported for metal carbonyl complexes (6). EXPERIMENTAL

The arenechromium(0) tricarbonyls were either purchased from Strem Chemical Company or were prepared by standard literature procedures (7). The monothiocarbonyl derivatives were synthesized following the method reported for (n6C6HSR)Cr(C0)2(CS) (R= H, C02Me) (8-10). The only differences were in the solvent mixtures used as eluents in the final chromatographic purification: Arene = C6HSR [R= H (A/B, 3/l); R = Cl, Me, COzMe (B/C, l/3); R = NMez (B/C, l/4)]; Arene = CSH4R2 [RZ = o-Me2 (B/C, l/4); RZ = m-(Me)COzMe (A/B, 4/l)] where A is petroleum ether (30-6O”C), B is diethyl ether, and C is hexane. The monothiocarbonyl complexes are slightly darker (orange-red) than the corresponding tricarbonyls and precede them down the column. Satisfactory elemental analyses and molecular weights (mass spectra) were obtained for all new compounds prepared (10). The approximate CO and CS stretching force constant, kc. and kc-, were calculated from the observed v(C0) and v(CS) bands (10) using established procedures (II). The 13C NMR spectra were recorded at 30°C on a Bruker WH90 spectrometer operating in the pulsed Fourier transform mode at 22.63 MHz. The instrument is equipped with a pulse unit which delivers a 90” pulse in 20 gsec and a Nicolet BNC-12. data system with 16K, 20 bits core memory. The 13C chemical shifts were measured using saturated CHQ;? solutions of the complexes in lo-mm NMR tubes containing 10% (V/V) Me&i as the internal standard peak and are reported positive downfield relative to Me4Si [G(TMS) = 0.01. A D20 stabilization lock was contained in a 5-mm coaxial tube. To aid in the relaxation of the carbon nuclei, tris(acetylacetonato)chromium(III) (ca. 0.1-0.2 M) was added to each NMR sample (12, 13). A pulse interval of 2.5 set was used to optimize the Ti relaxation recovery of the chalcocarbonyl ligands. All the spectra were proton decoupled (0 to 9-ppm region) with modulated wideband rf (5 W). Digital resolution was 0.07 ppm (1.6 Hz in a 9090~Hz spectral window), and the observed chemical shifts are considered accurate to f 0.1 ppm. The “0 NMR spectra were obtained with a Varian XL-loo-15 spectrometer operating in the pulsed Fourier transform mode at 13.57 MHz. The instrument is equipped with a Transform Technology, Inc. pulse unit which delivers a 90” pulse in 20 wsec and a 36K Nicolet computer system with disk. The “0 chemical shifts were measured at 30°C using saturated CH2C12 solutions relative to an external “Oenriched Hz0 sample as standard, with downfield values positive. A spectral width of 10,000 Hz was used with the pulse set at t0(H2”0) = 0.0 Hz. Pulsing was performed at the upfield end of the spectral window (owing to machine limitations), causing a complete reflection of the spectrum which was corrected for by means of a “spectrum reverse” computer manipulation. Because of the quadrupolar properties of 170, a pulse width of 25 psec followed by a pulse interval of 0.11 set was used for each scan in order to obtain an average optimal peak width at half-height of 25 Hz (1.8 ppm) after an average of 131-K scans. All the spectra were obtained using natural

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abundance samples; digital resolution was 0.09 ppm (1.2 Hz), and the chemical shifts reported here are considered accurate to *0.15 ppm (2.0 Hz). RESULTS

AND

DISCUSSION

The observed 13C NMR chemical shifts for the arene ligands and the 13C and I70 chemical shifts for the chalcocarbonyl ligands in the arenechromium(0) complexes TABLE OBSERVED'?

Arene C6H6

CeHsCl C6HsC02Me c6HsMe C6HsNMe2 c6H50Me C&sNHz 1,2,6-C6HsNHs(Me)s

NMR CHEMICAL (~I~-ARENE)C~(CO)~ Complex

(1) (11) (1) (11) (1) (11) (1) (11) (1) (11) 0) (11) (1) (I)*

o-CeH4C12 o-CeH4Me2

(1) (1) (11)

P-Cd&M‘% 1,3,5-C6HsMes

(1) (1)

o-c6&NH2(Me) m-&H,COaMe(Me)

I

SHIFTS OFTHE ARENE RING (I) AND (q'-ARENE)Cr(CO),(CS)

K(1)

SC(2,6)

SC(3,5)

SC(4)

93.7 99.3 113.4 116.1 90.3 96.2 110.4 115.3 136.0 138.7 143.7 146.3 128.6

93.7 99.3 92.2 97.2 95.3 99.9 95.4 100.4 75.3 79.5 78.9 84.1 78.3 97.5

93.7 99.3 94.4 99.2 90.9 96.3 93.7 99.2 97.9 103.1 95.8 101.4 97.4 92.7

93.7 99.3 89.4 94.9 95.9 100.1 90.6 96.0 83.7 88.0 86.1 91.4 84.2 85.8

6C(1,2)

6C(3,6)

6C(4,5)

109.7 108.7 113.5

93.0 96.0 100.6

91.0 92.7 97.8

6C(1,4), SC(1,3,5),

107.4 111.5

SC(l)

K(2)

K(3)

(I)* (IS

130.3 89.7

96.2 94.9

99.5 107.6

(II)’

96.7

99.4

113.0

n In parts per million (downfield positive) from * Assignments were made by comparison with compound. ’ See Ref. (20) for discussion of the assignment 90.3; 6C(2), 97.0; SC(3), 107.6; K(4), 97.6; complex (II): SC(l), 96.1; K(2), 101.0; 6C(3),

SC[(2,6), 6(3(2,4,6), K(4)

(3,5)],95.2 92.4 6C(5)

SC(6)

85.1 95.8

92.0 92.0

79.2 92.6

100.1

97.4

97.6

CARBON ATOMS (II)" '"

IN

Other

S(Me), 6(Me), s(Me), S(Me), S(Me), S(Me), S(Me), 6(Me),

53.1; 53.0; 20.9 20.4 40.0 40.2 56.0 56.6

S(Me),

17.5

S(Me), 6(Me),

18.9 18.5

6(Me), 6(Me),

20.3 20.8

S(COJ, S(CO,),

165.9 165.1

S(Me), 17.7 S(Me),20.9; S(COsMe), 53.3; 6(CO*), 166.5 6(Me),20.3; 6(COsMe), 53.1; 6(C02), 165.1

Me4Si (CHaCls solution). the data given in Ref. (15) for the corresponding

ethyl

method used. Calculated values for complex (I): 6C(l), 6C(5), 90.9; 6C(6), 92.2 ppm. Calculated values for 112.3; Z(4), 101.2: SC(S), 96.2; K(6), 96.6 ppm.

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studied are given in Tables 1 and 2, respectively. The r3C NMR spectra of several of the monosubstituted benzene complexes were reported earlier (14), but in the absence of Cr(acac)3. For this reason and for the sake of internal consistency, we have included our data for these complexes in the tables. TABLE 2 OBSERVED CX (X=O,S) 13C AND I70 NMR CHEMICAL SHE-&' AND CALCULATED APPROXIMATE CX STRETCHING FORCE CONSTANTS FOR (v~-ARENE)C~(CO), (I) AND (n6-ARENE)Cr(CO)s(CS) (II) k

Arene o -C6H.&ls C6HsC02MeC m-CsH&OsMe(Me) G,HsCl’

C&kc C6HsMec &H,OMe’ o-C,H,+Mes

o-C6H4NHs(Me) 1,2,6-C6H3NHz(Me)s [r)6-mC6H4C0sMe(Me)jCr(C0) (CS) (PPh3)

Complex

0) (1) (II) (1) 00 (1) (II) 0) (11) (1) (II) (1) (11) (1) (II) (1) (1) 0) 0) 01) 0) (1)

6(13CO)

6(C170)

230.0 231.4 229.5 232.1 229.9 232.1 230.0 233.4 231.5 233.1 231.7 233.7 231.8 234.2 232.2 234.3 234.5 235.1 235.4 233.4 235.6 235.8

377.5 374.1 376.1

346.9

376.4

347.2

231.6

6(13CS)

347.2 370.7 374.1 370.0 372.0

346.3 347.0 346.1

310.1 374.8 370.1 368.2 369.4 312.1

347.6

(mdynCH-l)b 15.41 15.20 15.51 15.12 15.38 15.12 15.37 14.98 15.27 14.87 15.22 14.88 15.13 14.83 15.15 14.81

k.s (mdyn A-‘)b

1.71 1.71 1.13 7.64 7.62 7.51 7.63

345.9

14.17 14.65 14.96 14.68 14.60

7.52

352.4

13.85

7.18

370.5 371.6

a In parts per million (downfield positive) from MedSi (i3C measurements) and Hsi’O (I70 measurements), respectively, in CH2C1s solution. ’ Calculated from the observed v(CX) bands in CSs solution (10). ’ 6(13CO) values have been reported previously for these tricarbonyl complexes, but in the absence of Cr(acac)s (14). In general, our values are within kO.4 ppm of those published.

The assignments given in Table 1 for the 13C NMR resonances of the arene ring carbon atoms of the tricarbonyl and monothiocarbonyl complexes are based chiefly on those reported earlier for the free arenes (15) and the related (n6C6H5R)Cr(C0)3 complexes (14). In line with the work of others on (v6C6H5R)Cr(C0)3 (14) and (q6-p-C6H4RF)Cr(CO)3 (16), there are excellent linear correlations (F > 0.97) between the corrected chemical shifts of the C(4) atoms of the

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arene rings and the Swain-Lupton ring substituent parameters. Also, these correlations are greater than 98% resonance-effect dependent, and it appears that in all the systems studied to date the electronic properties of the arene 7~framework are not affected appreciably by complexation to a Cr(CO),(CX) (X = 0, S) moiety. The 6(13CO) values for the carbonyl carbons in the tricarbonyl and monothiocarbony1 complexes given in Table 2 fall in the ranges 230.0 to 235.8 and 229.5 to 233.4 ppm, respectively. The carbonyl carbons in the thiocarbonyls are shielded relative to those in the corresponding tricarbonyls. The linear relationship (T = 0.99) between S(13CO) for all the complexes studied and the associated kc0 values are shown in Fig. 1. From this plot, it is clear that there is a high-field shift for the carbonyl carbons in the monothiocarbonyls with increasing kc0 relative to the parent tricarbonyl complexes. This shift is opposite to that always found for transition metal carbonyls upon substitution of CO by other two-electron donors such as amines and tertiary phosphines and phosphites, which are considered to be better u donors and poorer IT acceptors than CO (2). We attribute this difference to the greater net electron-withdrawing ((T donor + IT acceptor) capacity of CS compared to CO in the Cr(CO),(CS) moiety. This suggestion is supported by the fact that electron-withdrawingsubstituents on the arene ring (e.g., R = Cl, C02Me) lead to similar increases in both S(13CO) and kc0 for the (n6-C6H6-,R,)Cr(CO),(CX) complexes as compared to the unsubstituted (T6-C6H6)Cr(CO),(CX) derivatives,

SPCO) (PPM)

234

230

FIG. 1. Plot of 6(‘3CO) vs kco for (w6-Arene)Cr(CO), (0) and (q6-Arene)Cr(CO)z(CS) (0),where the numbers indicate the arene ligand bonded to the Cr atom: (1) 1,2,6-C6H3NH2(Me)z; (2) C6H5NMe2; (3) oGH4NH2(Me); (4) GHsNH,; (5) 1,3,5-CeH,Me$ (6) p-C6H4Me2; (7) o-C6H4Me2; (8) C6HSMe; (9) C6H50Me; (10) C,H,; (11) C,H,CI; (12) m-C,H4COzMe(Me); (13) C6HSC02Me; (14) o-CgH&l2.

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FIG. 2. Plot of S(C”0) vs kc0 for (v6-Arene)Cr(CO), the numbers indicate the arene ligand bonded to the Cr atom Fig. 1.

(e) and (v6-Arene)Cr(CO),(CS) and the numbering scheme

(o), where is the same as for

The “0 NMR resonances for the carbonyl oxygens in the tricarbonyls and monothiocarbonyls appear in the regions 368.2 to 377.5 and 372.0 to 376.4 ppm, respectively. The carbonyl oxygens of the thiocarbonyls are deshielded relative to the parent tricarbonyls. The linear relationship between 6(c”O) and kc0 (Fig. 2) is poorer (P = 0.84) than in the case of S(13CO). However, it is apparent that there is a low-field shift for the carbonyl oxygens in the monothiocarbonyl compounds with increasing kc0 relative to those in the parent tricarbonyls. There is also a downfield shift in S(C170) with a change from electron-donating to electron-withdrawing substituents on the arene rings. The low-field shift observed when CO is replaced by CS is opposite to that found when CO is replaced by other Lewis bases such as amines, olefins, isocyanides, and tertiary phosphines (6). There is no direct correlations between 6(C”O) and 6(13CO), but it is clear that the trends observed for the carbonyl 170 chemical shifts are opposite to those for the carbonyl 13C shieldings (Fig. 3). Any deshielding influence on the carbonyl carbons in the complexes studied appears to shield the carbonyl oxygen atoms. In fact, this will probably prove to be a general rule for all transition metal carbonyl derivatives (6). In view of the lOO-ppm range found earlier for S(Cl’O) (6), compared to the 30-ppm range for S(13CO) (Z), we had expected to observe a larger range than 10 ppm for S(C”0) for the arenechromium(0) complexes. Apparently, the greater distance of the oxygen atoms from the metal centre diminishes the effects associated with changes in electron density at the metal centre. Moreover, molecular models show that the oxygen atoms are much better geometrically situated for greater

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C6H6-“R, FIG. 3. Plots of S(13CO) and S(C”0) vs arene ligand for (q6-Arene)Cr(C0)3 (*) and (q6Arene)Cr(CO)z(CS) (O), where the numbers indicate the arene Iigand bonded to the Cr atom and the numbering scheme is the same as for Fig. 1.

through-space interactions with the arene ring substituents than are the carbonyl carbon atoms, and such interactions may be the reason for the poorer correlations associated with S(C”0) than with 8(13CO). Indeed, a closer examination of the *‘O chemical shifts in Table 2 reveals that the aniline derivatives are anomalous with respect to all the other arenes (see also the dashed line through points 1,3, and 4 in Fig. 2). The “0 chemical shift trend for these three tricarbonyl complexes parallels that for the corresponding 13C shifts. Increasing methyl substitution on the arene ring or the amine nitrogen atom causes both the 13C and the I70 shielding values to shift downfield. The analogous strictly methylarene derivatives exhibit the usual opposing trends in their 13C and “0 chemical shifts. The NMR data for the aniline complexes together with molecular models strongly suggest that the lone pair of electrons on the nitrogen atom can interact through-space directly with the orbitals of the carbonyl groups. Similarly, a molecular model of (q6-C6HsNMe2)Cr(CO)3 shows that a direct interaction of the methyl groups with the oxygen atoms of the carbonyl groups is possible. Thus, we feel that the postulate of a direct through-space interaction in these aniline derivatives is quite reasonable and that this interaction is responsible for the marked deviation of the I70 chemical shifts compared to those for all the other complexes investigated. The factors affecting the variations in the “0 chemical shifts of carbonyl groups obviously merit further attention, as does the fact that no I70 resonances are observed for the oxygen atoms in the arene ring substituents, e.g., -C02Me.

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The 13C NMR resonances of the CS groups in the arenechromium(0) complexes appear in the range 345.9 to 347.2 ppm (Table 2), i.e., about 120 ppm downfield from S(13CO). Very poor linear correlations (f - 0.67) are obtained when S(13CS) is plotted against kco or kcs. For example, a comparison of (n6-C6H&l)Cr(CO)2(CS) with (n6-C6H6)Cr(C0)2(CS) shows an increase in both kco and kos, but 6(i3CO) decreases whiIe S(13CS) increases. These results contrast with those reported recently for the cationic iron(I1) thiocarbonyl complexes, [(q’-C5H5)Fe(CO) (CS)L]+ [L= co, PPh3, P(C.&F)3, P(C6Hld31 (51, f or which it was noted that S(13CS) paralleled 6(i3CO) with changes in L. During the course of our work, we also prepared [q6-m-C6H4Me(Me)]Cr(CO)(CS)(RI’h3) and measured its 13C NMR spectrum (10). A comparison of the data with those for the parent monothiocarbonyl complex (Table 2) reveals that there is a large downfield shift of both 6(13CO) and S(13CS) observed together with a sharp increase in both kc0 and kcs, in agreement with the iron(I1) work. Clearly, although S(13CS) is sensitive to the overall changes in electron density at the metal center, it is not apparently affected by the same factors which affect S(13CO). This means that S(13CS) may not be such a good measure of the electron density at the metal center as is S(i3CO). It should be mentioned, however, that one possible reason for the ambiguous behavior of S(13CS) with variations in kcs is that these force constants may not be as accurate as the kc0 values owing to the much greater mixing between the C-S and Cr-C(S) vibrations than the C-O and Cr-C(0) vibrations (17). The transition metal carbene and thiocarbene moieties, M-C(ER)R’ (E = 0, S; R, R’= alkyl or aryl), can be considered to be somewhat analogous to the M-CX (X= 0, S) moieties. The 13C NMR chemical shifts of the carbene carbon atoms in some closely related carbene and thiocarbene complexes have been investigated: (1) W(CO)5[C(EMe)Me] (18); (2) W(CO)5[C(OMe)C6H4Y] and W(CO)5[C(SC6H4Y)Me] (Y = OH, OMe, Me, etc.) (19). In the former case, replacement of 0 by S has virtually no effect on the carbene carbon atom chemical shift. For the latter case, a plot of S[i3C(carbene)] for the carbene and thiocarbene complexes gives a scattered array of points, and the authors concluded that while both series of tungsten carbene complexes reflect overall changes in electron density induced by variations in Y, either the change from 0 to S causes a difference in the sensitivity of the carbene carbon atom to these variations or some other unknown parameters tend to obscure a direct correlation between the 13C shieldings. It is clear, therefore, that further work will be necessary before the effects of replacing 0 by S in metal carbonyls and other complexes containing M-C(O) linkages are fully understood. CONCLUSIONS

The 13C and 170 NMR data described above indicate that the electronic properties of the arene ring substituents in the (776-C6H6-,R,)Cr(C0)2(CX) (X= 0, S) complexes are transmitted to the carbonyl ligands. The carbonyl carbon i3C shielding values shift upfield both on changing 0 to S in the CX ligand and with increasing electronegativity of the ring substituents R, while the corresponding carbonyl oxygen 170 shieldings move to lower fields in both cases (with the exception of the aniline

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derivatives) but are less influenced by these changes. Also, although there is no correlation for S(‘3CS) with either k co or kcs, CS is clearly a better net electronwithdrawing ((T donor + T acceptor) ligand than CO, as we concluded earlier on the basis of a less exhaustive r3C NMR study of the manganese(I) complexes, (n’C5H4R)Mn(C0)2(CS) (R = H, Me) (4). ACKNOWLEDGMENTS We thank Professor A. S. Perlin and Dr. N. Cyr (McGill University) for their assistance in using the r3C NMR spectrometer. This research was generously supported by the National Research Council of Candada and the Quebec Department of Education. One of us (D.C.) thanks the same granting agencies and McGill University (McConnell Foundation) for the award of graduate scholarships. REFERENCES 1. I. S. BUTLER, Accounts Chem. Res. 10, 359 (1977), and references therein. 2. (a) M. H. CHISHOLM AND S. GODLESKI, in “Progress in Inorganic Chemistry” (S. J. LIPPARD, ed.) Vol. 20, Wiley-Interscience, New York, 1976; (b) L. J. TODD AND J. R. WILKINSON, J. Organometal. Chem. 77, 1 (1974). 3. B. D. DOMBEK AND R. J. ANGELICI, Inorg. Chem. 15, 1089 (1976). 4. D. COZAK AND I. S. BUTLER, Spectrosc. Let?. 9,673 (1976). 5. L. BUSE?TO AND A. PALAZZI, Inorg. Chim. Acta 19,233 (1976). 6. J. P. HICKEY, Ph.D. Thesis, Indiana University, Bloomington, 1977. 7. M. D. RAUSCH, G. A. MOSER, E. J. ZAIKO, AND A. L. LIPMAN, JR., J. Organometal. Chem. 23, 185 (1970). 8. I. S. BUTLER, N. J. COVILLE, AND D. COZAK, J. Organometal. Chem. 133,59 (1977). 9. G. SIMONNEAUX, A. MEYER, AND G. JAOUEN, J. Chem. Sot., Chem. Commun. 69 (1975). 10. D. COZAK, Ph.D. Thesis, McGill University, Montreal, Quebec, Canada, 1977. 11. P. S. BRATERMAN, “Metal Carbonyl Spectra,” Academic Press, New York, 1975. 12. 0. A. GANSOW, A. R. BURKE, AND G. N. LAMAR, J. Chem. Sot., Chem. Commun. 456 (1972). 13. G. C. LEVY AND R. A. KOMOROSKI, .I. Am. Chem. Sot. %, 678 (1974). 14. G. M. BODNER AND L. J. TODD, Inorg. Chem. 13,360,1335 (1974). 15. L. F. JOHNSON AND W. C. JANKOWSKI, “C-13 NMR Spectra,” Wiley, New York, 1972. 16. J. L. FLETCHER AND M. J. MCGLINCHEY, Can. J. Chem. 53,1525 (1975). 17. I. S. BUTLER, A. GARCIA-RODRIGUEZ, K. R. PLOWMAN, AND C. F. SHAW III, Inorg. Chem. 15, 2602

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(1976).