Organometallics 1995, 14, 1221-1231
1221
Syntheses and Reactivities of Indole and Indolyl Complexes of (Cymene)ruthenium(II) Sylvia Chen, V. Carperos, B. Noll, R. Jeffrey Swope, and M. Rakowski DuBois"
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 Received August 8, 1994@ The reaction of [(p-cymene)Ru(OTf")2Ix with a series of indoles has led to the synthesis of new Ru(I1) indole complexes of the formula [(cymene)Ru(ind)l(OTf)z,where ind = indole (3a),l-methylindole (3b),2,3-dimethylindole (3c),and 2-methylindole (3d). Complex 3b has been characterized by an X-ray diffraction study. The complex crystallized in space group P21/n with a = 16.180(3) A, b = 9.028(2) A, c = 18.827(4) A, /? = 109.54(2)", V = 2591.7(9) A3, and 2 = 4. The structural study confirmed that the dication has a sandwich structure with parallel $-cymene and $-1-methylindole ligands. Complexes 3a,c , and d can be deprotonated a t the indole nitrogen t o form monocations [(cymene)Ru(indolyl)lOTf, 4a for indolyl, 4c for 2,3-dimethylindolyl, and 4d for 2-methylindolyl. The aqueous pK, values for the indole ligands in 3a,c , and d have been determined from titration data to be 7.71,8.15, and 8.02, respectively. A tetraphenylborate salt of an indolyl derivative, [(cymeneb Ru(2,3-dimethylindolyl)lBPh4,was obtained as a single crystal. The complex crystallized in space group C2/c with a = 40.050(14) A, b = 11.049(4)A, c = 16.778(6)A, /? = 109.70(3)", and 2 = 8. A preliminary X-ray diffraction study confirmed a sandwich structure with the indolyl ligand coordinated through the carbocyclic ring in an $-bonding mode. Complex 4c reacted with PdCl2PPh3(CH&N) to form a heteronuclear complex, [(cymene)Ru(2,3dimethylindolyl)PdCl~PPh~l0Tf (5), in which the indolyl ligand undergoes fhoordination to ruthenium and rl-N-coordination to Pd. The reaction of 4c with [CUOTfl2+csH6 led to the formation of a trinuclear product { [(cymene)Ru(2,3-dimethylindolyl)l2Cu)(OTfl3(61,in which the copper ion is proposed to coordinate to two indolyl nitrogens. Reactions of 3,4,and 6 with nucleophiles have been compared. Although the reactions of 3 and 4 gave complex mixtures of products, the reaction of 6 with LiAl(O-t-Bu)sH at -78 "C resulted in the clean formation of a single isomer, formulated as { [(cymene)Ru(2,3-dimethylindolyl-H)lzCu)( (7a). The latter is proposed to result from hydride addition to C4 in each indolyl ligand of
6. Introduction We have recently synthesized and characterized the reaction chemistry of the sandwich complexes containing the tetramethylpyrrolyl ligand [(cymene)Ru(NC4Me4)10Tf(1)and the neutral pentamethylpyrrole ligand [(cymene)Ru(MeNC4Me4)1(OTf)a(2).l We found that both complexes reacted with nucleophiles such as hydride or methoxide ion. Nucleophilic addition to 1 occurred at the cymene ligand to give y5-cyclohexadienyl derivatives, while nucleophilic addition to 2 occurred at the a-carbon atom of the pentamethylpyrrole ligand. Further protonation at the nitrogen heterocycle in the latter product led t o dissociation of a reduced cyclic iminium ion. In this paper, we report the synthesis and characterization of related sandwich complexes of (cymene)Ru(11) containing the indole and indolyl ligands. We wished t o compare the effect of metal n-coordination on the reactivities of the pyrrole and indole rings. Previous reports of n-bound indole complexes2-6include(indole)Cr(C0)3,2Cp'Ru(X-ind~le),~~~ and [(Cola Mn (indole)]+ derivatives. These complexes were proposed to involve y6-coordination of the heterocycle and were found to promote regioselective nucleophilic substitution or ad~~
Abstract published in Advance ACS Abstracts, February 15, 1995. (1)Kvietok, F.;Allured, V.; Carperos, V.; Rakowski DuBois, M. Organometallzcs 1994,13, 60. @
dition reactions or metalation reactions at the indole six-membered ring. These reactions are of considerable interest because of their potential application in the synthesis of natural products based on the indole structure. Relatively few syntheses of metal complexes involving n-coordination of the anionic indolyl ligand have been r e p ~ r t e d . ~Deprotonation ~,~ of an @indole derivative of Ir(II1) was proposed to result in a ring shift isomerbut reactivity ization to an v5-indolyl complex, eq 1,6c (2) (a) Semmelhack, M. F.; Wulff, W.; Garcia, J . L. J. Organomet. Chem. 1982,240,C5. (b) Kozikowski, A. P.; Isobe, K. J . Chem. SOC., Chem. Commun. 1978, 1076. (c) Beswick, P. J.; Greenwood, C. S.; Mowlem, T. J.; Nechvatal, G.; Widdowson, D. A. Tetrahedron 1988, 44,7325. (d) Masters, N. F.; Mathews, N.; Nechvatal, G.; Widdowson, D. A. Tetrahedron 1989,45,5955. (3) (a) Moriarty, R. M.; Ku, Y. Y.; Gill, U. S. Organometallics 1988, 7,660.(b) Moriarty, R. M.; Gill, U. S.; Ku, Y. Y. J. Organomet. Chem. 1988,350,157. (c) Gill, U. S.; Moriarty, R. M.; Ku, Y. Y.; Butler, I. R. J. Organomet. Chem. 1991,417,313. (4)Lomenzo, S. A,; Nolan, S. P.; Trudell, M. L. Organometallics 1994,13, 676. (5)Ryan, W. J.;Peterson, P. E.; Cao, Y.; Williard, P. G.; Sweigart, D. A,; Baer, C. D.; Thompson, C. F.; Chung, Y. K.; Chung, T. M. Inorg. Chim. Acta 1993,211,1. (6)(a) Fish, R. H.; Barolt, E.; Kim, H. S. Organometallics 1991,10, 1965.(b) Fairhurst, G.; White, C. J . Chem. SOC.,Dalton Trans. 1979, 1531. (c) White, C.; Thompson, S. J.; Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1977,1654. (7) (a) Pauson, P. L., Qazi, A. R.; Rockett, B. W. J. Organomet. Chem. 1967,7,325. (b) Ji, L. N.; Kerschner, D. L.; Derek, M. E.; Basolo, F. J . Organomet. Chem. 1986,296, 83. (c) Jeffreys, J . A. D.; Metters, C. J. Chem. SOC.,Dalton Trans. 1977,1624.
0276-733319512314-1221$09.00/0 0 1995 American Chemical Society
1222 Organometallics, Vol. 14, No. 3, 1995
?P*
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ir
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Chen et al.
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studies of such derivatives have not been carried out. q5-Coordination of indolyl t o a cationic metal ion has the potential for activating the pyrrolic ring to reduction or ring-opening reactions. Such processes would provide important potential models for proposed steps in the commercial hydrodenitrogenation reactions catalyzed by heterogeneous metal catalysts.8 The Ru complexes reported here permit us to further explore the coordination modes and reactivities of the neutral and anionic ligand forms of this ring system.
Results and Discussion Syntheses and Characterization of Indole Derivatives. The reaction of [(cymene)Ru(OTf)&with a neutral indole ligand in diethyl ether at room temperature resulted in the formation of the dications [(cymene)Ru(ind)](OTf)z,where ind = indole (3a),1-methylindole (3b),2,3-dimethylindole (3c),and 2-methylindole (3d), eq 2. Deprotonation of 3c followed by alkylation with [(Cymene)Ru(OTD2lX+
,R*
N
R' 3a: R = R' = R' = H 3b: R = Me, R' = R' = H JC: R = H, R' = R" = M e 3d: R = R " = H,R' = Me
methyl triflate gave the dication with the 1,2,3-trimethylindole ligand, 3e. The products were characterized by lH and 13C NMR and FAB mass spectroscopic data. Single crystals of [(cymene)Ru(l-methylindole)](0Tf)z(3b)were isolated from a THF/ether solution, and an X-ray diffraction study of this product is discussed below. The lH NMR data for the new complexes are listed in Table 1. Two-dimensional COSY (lH-lH) NMR data were used to assign the resonances of the aromatic protons. Chemical shifts for the protons of the cymene ligand lie generally between 6 and 7 ppm; shifts for H3, H5, and H6 of the indole ligand are also in this range, while two lower field resonances (7.3-7.9 ppm) are assigned to H4 and H7. The resonance assigned to H2 in the indole ligands in 3a,b (-8.2 ppm) is shifted downfield by 1.0-1.6 ppm relative to that of the free ligand^.^ (8) Ho, T. C. Catal. Rev.-Sci. Eng. 1988,30,117. (9) (a) Chadwick, D. J. In Comprehensive Heterocyclic Chemistry;
Bird, C. W., Cheeseman, G. W. H., Eds.; Pergamon Press: Oxford, U.K., 1984; Vol. 4, p 155, and references within. (b) The structure of free indole is subject to disorder problems, but comparisons of structural data of 3b with those of 3-substituted indoles were made.sa (c) Rosenberg, E.; Williamson, K. L.; Roberts, J. D. Org. Magn. Res. 1976, 8, 117.
In the 13C spectra of the dications, the expected number of resonances were observed for the aromatic carbons. For some of the derivatives, lH-13C HETCOR data were used t o distinguish the quaternary and methine carbons and to assign the resonances of the latter. These data are summarized in Table 2. For example, in the spectra of 3a, c, and e, resonances for the methine carbons of the cymene and carbocyclic indole rings were found in the region between 78 and 93 ppm. These are shifted significantly upfield from those of the free cymene and indole ligands. Shifts of the indole carbocyclic ring in this range are similar to those observed for the CpRu indole systems3aand are consistent with an @-coordination of indole. The resonances of the pyrrole carbons in the coordinated ligand of 3a (C2,145 ppm; C3,104 ppm) are shiRed downfield relative to those of the free ligand (C2, 123 ppm; C3, 102 ppmhgC X-ray Diffraction Study of [(Cymene)Ru(lmethylindole)l(OTf)z(3b). Single crystals of 3b were grown by diffusion of diethyl ether into a THF solution of the compound. The complex crystallized in space group P21/n with four molecules per unit cell. A perspective drawing is shown in Figure 1,and selected bond distances are given in Table 3. The data confirm a sandwich structure with two parallel y6-areneligands. The angle between the ruthenium ion and the center of each ring is 178.9'. The distance between Ru and the center of the cymene ring (1.706 A) is somewhat longer than the average distance in other cymene complexes (1.678 &,lo but it is significantly shorter than the Ruindole distance of 1.761A. A similar trend was observed ene)Ru(NC4Me4)1+,where RU-Cym(centroid) = in 1.698 and Ru-TMP(centroid) = 1.812 A.1 Within the accuracy of the data, the bond lengths of the indole ligand are not significantly different from those reported for a y6-indole-manganese complex5or for a free indole molecule.9a,b Syntheses and Characterization of [(Cymene). Ru(indolyl)l+Derivatives. When the dicationic complexes containing an NH group, 3a,c,d, were eluted through a neutral alumina column with EtOH, an immediate color change from yellow to red or orange was observed. The resulting products were isolated as oily noncrystalline materials and identified as the N-deprotonated derivatives [(cymene)Ru(indolyl)]OTf, 4a,c,d, eq 3. The deprotonations could also be achieved
[(p-si?n
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with other bases in solution. For example, 4c could be isolated from the reaction of 3c with NaOH in aqueous solution, and the addition of triflic acid to the monocation regenerated its conjugate acid, 3c. Only one previous example has been reported in which both the indole and indolyl derivatives of a complex have been (10)McCormick, G. B.; Cox, D. D.; Gleason, W. B. Organometallics 1993,12, 610,and references within.
Organometallics, Vol.14,No. 3, 1995 1223
Indole and Indolyl Complexes of (Cymene)Ru(II) Table 1.
NMR Data for Indole and Indolvl Complexes (Triflate Salts)" indole
complex
cymene
[(cym)Ru(indo1e)l2+(3a)
[(cym)Ru( l-methylindole)12+ (3b)
6.82d [6.79 6.78 [6.65
[(~ym)Ru(2-methylindole)]~+ (3d)
[(cym)Ru(1,2,3-trimethylindo1e)l2+(3e)
6.43
6.54 L6.49 6.43 [6.34
[(cym)Ru(indolyl)]+ (4a)
[(cym)Ru(2,3-dimethylindolyl)]+ (4c)
carbocyclic ring 7.47 (d, J = 5 , H4)C 6.39 (t, J = 5 H5) 6.43 (t, J = 6 , H6) 7.62 (d, J = 6, H7)' 7.52 (d, J = 6, H4) 6.45 (m, H5.6) 7.63 (d, J = 6, H7)
[ (cym)Ru(2-methylindolyl)]+(4d)
upfield region 2.58 (spt, cym-CHMe2) 1.93 (s, cym-Me) 1.20 (d, cym-i-Pr) 1.19 (d, cym-i-Pr) 3.85 (s, NMe) 2.60 (spt, cym-CHMez) 1.92 (s, cym-Me) 1.19 (d, cym-i-Pr) 1.16 (d, cym-i-Pr) 2.70 (spt, i-F'r-CH) 2.51 ( s , NCCH,) 2.30 ( s , NC=CCH3 ) 1.88 (s, cym-Me) 1.19 (d, i-Pr) 1.17 (d, i-Pr) 2.58 (spt, i-Pr-CH) 2.54 ( s , NCCH3) 1.96 (s, cym-Me) 1.20 (d, i-Pr) 3.72 (s,NMe) 2.63 (spt i-Pr-CH) 2.43 ( s , NCCH,) 2.25 ( s , NC=CCH3) 1.87 (s, cym-Me) 1.20, 1.17 (2d, cym-i-Pr) 2.41 (sept, CHMe2) 1.80 (s, cym-Me) 1.16, 1.15 (2d, cym-i-Pr)
8.19 (d,J = 3, H2) 6.71 (d, J = 3, H3)
7.76 (d, J = 6, H4) 6.21 (t, J = 6, H5) 6.64 (t, J = 6, H6) 7.88 (d, J = 6, H7)
11.8 (br s, NH)
7.34 (m, H4) 6.31 (2t, J = 6, H5, 6) 7.49 (m, H7)
11.0 (br s, NH) 6.42 (s, H3)
7.34 (m, H4) 6.34 (m, H5,6) 7.48 (m, H7)
7.30 (d, J = 5 , H4) 6.05 (m, H5, H6) 7.40 (d, J = 5, H7) 6.31d 16.17
pyrrole ring 8.26 (d, J = 3, H2) 6.72 (d, J = 3, H3) 10.84 (br s, NH)
8.60 (d, J = 1, H2) 6.33 (d, J = 1, H3)
7.01 (d, J = 6, H4) 5.84 (t, J = 6, H5) 6.09 (t, J = 6, H6) 7.23 (d, J = 6, H7) 7.15 (d, J = 6, H4) 6.04 (t, J = 6, H5) 5.98 (t, J = 6, H6) 7.32 (d, J = 6, H7) 6.84 (d, J = 6, H4) 5.96 (t, J = 6, H5) 5.83 (t, J = 6, H6) 7.40 (d, J = 6, H7)
[ (cym)Ru(2,3-dimethylindolyl)PdC12PPh3]+(5)
6.58'
{ [(cym)R~(2,3-dimethylindolyl)]2Cu}~+(6)
6.45
7.27 (d, J = 6 , H4) 6.27 (m, H4,5) 7.44 (d, J = 6, H7)
{ [(cym)Ru(2,3-dimethylindolyl-H)]~Cu}+(7a)
6.01
{ [(cym)Ru(2,3-dimethylindolyl-H)]2Cu}+(7b)
6.00
3.54 (dd, J = 14, J = 5 , H4 endo) 3.01 (d, J = 14, H4 exo) 3.75 (t, J = 6, H5) 4.62 (t, J = 6, H6) 6.54 (d, J = 5 , H7) 6.35 (d, H4) 4.55 (t, H5) 3.66 (t, H6) 3.42 (dm, J = 15, H7 endo) 3.23 (d, J = 15, H7 exo)
6.12 (s, H3)
2.52 (sept, CHMe2) 2.45 (s, NCMe) 2.22 (s, NC=CMe) 1.77 (s, cym-Me) 1.21 (d, cym-i-Pr) 1.18 (d, cym-i-Pr) 2.54 (s,NCMe) 2.47 (sept, CHMe2) 1.86 (s, cym-Me) 1.21, 1.20 (2d, cym-i-Pr) 2.56 (sept, CHMe2) 2.48 (s,NCMe) 1.99 (s,NC=CMe) 1.58 (s, cym-Me) 1.14, 1.08 (2d, cym-i-Pr) 2.59 (sept, CHMe2) 2.45 (s, NCMe) 2.22 (s,NC=CMe) 1.86 (s, cym-Me) 1.19, 1.17 (2d, cym-i-Pr) 2.27 (spt, CHMe2) 2.04 (s, NCMe) 1.89 (s, NCCMe) 1.79 (s, cym-Me) 1.14, 1.11 (2d, cym-i-Pr) 2.3 (spt, CHMe2) 2.12 (s, NCMe) 1.86 (s,NCCMe) 1.75 (s, cym-Me) 1.1 (d, cym-i-Pr)
Chemical shifts are reported in ppm. Assignments were made on the basis of COSY spectra recorded in CD3CN, unless otherwise specified. J values are reported in hertz. The numbering scheme for the indole positions is shown in eq 2. The cymene resonances are doublets with J % 6 Hz. Mutually coupled doublets are indicated. Resonances of H4 and H7 are not distinguished by COSY data. We have tentatively assigned the lower field resonance to H7 by analogy to assigments made for other indole c o m p l e x e ~ .We ~ ~should ~ ~ ~ note, ~ however, that the lower field resonance in free indole is assigned to H4.9a3C Spectrum recorded in CDC13. e Spectrum recorded in DMSO-&. Phenyl resonances of the triphenylphosphine ligand were also observed as a multiplet at 7.26-7.53 ppm.
isolated. While [Cp*Ir(indole)12'and [Cp*Ir(indolyl)l+ have been characterized,6csimilar attempts t o deprotonate the analogous Co and Rh indole derivatives led to decomposition.6b,c We have considered the possibility that the deprotonation of 3 promotes a ring shift isomerization of the indolyl ligand to produce y5-coordinationof the hetero-
cycle in 4. mBonding through the five-membered heterocycle might be favored because of the high electron density in this anionic ring. A similar shift has been proposed, but not verified by structural data, for the indole and indolyl complexes of iridium; see eq 1.6c However, spectroscopic data do not support the suggested ring shift isomerization for the ruthenium com-
1224 Organometallics, Vol. 14, No. 3, 1995
Chen et al.
Table 2. 13CNMR Data for Indole and Indolyl Complexes (Triflate Saltspb quatemary C
aromatic methine C
upfield region
[(cym)Ru(indole)12+(3a)
comp1ex
172.7 (OTf) 124.0 119.8 113.7 109.0
31.6 (CHMe2) 22.3, 22.1 (CHMe2) 17.2 (PhMe)
[(cym)Ru(2,3-dimethylindole)12+(3c)
154.1 (OTf) 117.7 117.3 112.2 108.8 108.7 104.6
[(cym)Ru( 1,2,3-trimethylindole)I2+ (3e)
156.4 (OTf) 124.1 119.8 114.6 109.8 109.7 103.5 173.1 (OTV 123.1 114.1 109.6 104.1
145.3 (C2) 104.2 (C3) 93.4 (cym) 92.8 (cym) 90.7 (cym) 90.5 (cym) 89.1 (C5 or 6) 88.7 (C5 or 6) 88.1 (C4) 81.3 (C7) 92.1 91.9 89.4 87.3 87.0 (cym) 86.9 (cym) 84.9 (C4) 79.8 (C7) 92.6 92.4 90.1 89.8 87.6 (2) 85.7 78.9 164.0 (C2) 101.0 (C3) 90.8 (cym) 90.1 (cym) 87.6 (2, cym) 86.3 (C7) 84.7 (c5 or c6) 84.4 (C4) 83.8 (c5 Or c6) 89.8 (cym) 89.3 (cym) 86.6 (cym) 86.5 (cym) 83.4 (C4 or C7) 83.3 (Cd or CI) 82.7 (C5) 82.5 (C6) 98.4 (C3) 90.2 (cym) 89.2 (cym) 86.8 (cym) 86.5 (cym) 84.0 (C7) 83.1 (C6) 82.9 (C5) 82.8 (C4) 134.5 (d, J = 10, PPh3) 133.9 (d, J = 10, PPh3) 131.2 (s, p-C of PPh3) 128.3 ( d , J = 11, PPh3) 91.7 89.2 87.8 87.2 84.9 83.0 82.6 80.6 91.0 (2) 85.2 84.8 88.1 (2) 84.1 (C4) 83.3 (C7)
[(cym)Ru(indolyl)]+ (4a)
a
[(cym)Ru(2,3-dimethylindolyl)]+ (4c)
171.5 (OTQC 122.4 113.6 111.3 106.5 104.2 (2)
[(cym)Ru(2-methylindolyl)]+(4d)
176.8 (OTW 123.2 113.3 112.4 103.9 (2)
[(cym)Ru(2,3-dimethylindolyl)PdCl2PPh~]+(5)
162.2 (0TQd 127.7 119.0 113.6 107.9 106.2 105.6
{ I(cym)Ru(2,3-dimethylindolyl)2Cu}3+ ( 6 )
168.5 (OTf) 124.2e 122.2 119.9 115.3 108.1 107.8 106.6
31.2 (CHMe2) 21.9, 21.8 (CHMe2) 16.8 (PhMe) 12.5 (NCMe) 7.5 (NC = CMe)
32.2 NMe 32.0 CHMe2 22.5 CHMe2 17.8 Me 12.2 Me 8.7 Me 30.9 CHMe2 22.8 CHMe2 18.7 PhMe
31.1 (CHMe2) 22.9, 22.7 (CHMe2) 17.3 (NCMe) 16.8 (PhMe) 8.8 (NC = CMe)
30.5 (CHMe2) 22.4, 22.3 (CHMe) 19.0 (NCMe) 16.2 (PhMe)
30.4 (CHMe2) 22.1 22.0 17.2 15.6 8.4
31.6 (CHMe2) 22.5, 22.3 (CHMez) 17.1 (NCMe) 16.8 (PhMe) 8.5 (NC = CMe)
Assignments are based on two-dimensional heteronuclear correlation (HETCOR) spectra. In CD3CN unless otherwise specified. In CDCl3. In DMSO-
&,. e Only six quatemary ring carbons are expected for this compound. The impurity peak has not been identified.
plexes, but rather suggest that derivatives of 4 retain V6-coordinationof the indole ligand. In the lH NMR
spectra of 4a, c, and d, the resonances of the indole ligand are shiRed upfield (0.2-0.7 ppm) relative to those
Indole and Indolyl Complexes of (Cymene)Ru(II)
Organometallics, Vol. 14, No. 3, 1995 1225 more acute than in the structure of the dication 3b. The distances between Ru and the center of each ring were determined to be Ru-c ene(cent,oid)= 1.705A and RUindOlyl(cen~oid) = 1.760 These are similar to the values observed for the structure of 3b. The acidity of pyrrole rings has been found to increase dramatically upon n-coordination to a metal ion.lJ3 A similar qualitative effect can be predicted for indole coordination, but no pKa data for n-coordinated indole ligands have been reported. pH titrations of 3c and d were carried out with NaOH in aqueous solutions, and 4a was titrated with HC1. Each titration gave a curve with a single inflection point. The PKa values of the coordinated indole ligands, determined at the halfequivalence point of each curve, were found to be 7.71 f 0.06 for 3a, 8.02 k 0.04 for 3d, and 8.15 k 0.05 for 3c. The pKa values increase, as expected, as the methyl substitution on the indole ring increases. The results demonstrate that the @-coordination of indole significantly increases the acidity of the ligand, as the aqueous pKa value for free indole was reported to be 16.97.14 Reactions of Indole and Indolyl Complexes With Nucleophiles. As noted above, previous metal indole complexes have been used to carry out nucleophilic substitution and addition reactions on the activated indole ligand. Addition reactions at the C4 and C7 carbon atoms of the unsubstituted ligand were f a ~ o r e d . ~ - ~ A survey of the reactivity of [(cymene)Ru(l-methylindole)l(OTf)z(3b) with nucleophiles was carried out in order t o compare the electrophilic activation by the cymene-Ru(I1) fragment. The reaction of 3b with LiCH(COzEt)2in THF at -78 "C led to the formation of two major product isomers in a -2:l ratio. The NMR spectrum of this mixture was too complex to make structural assignments for the products. However, some assigmments for cymene and indole protons have been made on the basis of COSY data (see Experimental Section). In particular, the triplet patterns of H5 and/ or H6 of the indole ring could be distinguished in the region 4.8-4.4 ppm, and these upfield shifts relative to those of 3b suggest that nucleophilic addition to the carbocyclic ring may have occurred. Reactions of 3b with other nucleophiles, including LiAl(O-t-Bu)sH, LiBEt3H, MeLi, or NaOMe, led to a mixture of products or to decomposition. Attempts at purification by column chromatography were unsuccessful, and no identification of products was possible on the basis of the very complicated NMR spectra. The reactions of the monocationic complex [(cymene)Ru(2,3-dimethylindolyl)lOTf(4c)with nucleophiles were also surveyed in order to compare the reactivity to that characterized previously for [(cymene)Ru(NC4Me4)1OTf. In the latter system, hydride and alkoxide nucleophiles
fr
C151
Figure 1. Perspective drawing for [(cymene)Ru(l-methylindole)](OTf)z(3b).Thermal ellipsoids are shown at the 50%probability level. of the dications 3a, c, and d. These shifts are consistent with the increased shielding expected for the monocation and are similar to those reported for [CpRu($ind~le-Cl)I+.~" Perhaps more diagnostic data are provided by the 13C NMR spectra of 4a, c, and d. In each case, resonances for the methine carbons of the indolyl six-membered ring (82-90 ppm) occur significantly upfield from those of the free ligand and are characteristic of y6-coordination in these Ru complexes. The spectral data can be compared to that reported for [(cymene)Ru(naphthalene)12+. The13Cresonances for the coordinated ring of naphthalene are shifted upfield to 94 ppm while the resonances for the uncoordinated ring of the ligand occur from 100 to 140 ppm.ll A comparison of the reported 13C data for the proposed [Cp*Ir(~5-indolyl)l+ shows that the resonances for the carbocyclic indole ring are also found in the region from 80 to 90 ppm, upfield from those of the free ligand, and a $-indole formulation may be more appropriate for this system as well. 13C NMR data for other proposed q5-indolylcomplexes have not been r e p ~ r t e d ,but ~ ~ a, ~structural study has confirmed the q5 coordination of the ligand in (2methylind0lyl)Mn(CO)3.~~ In order to confirm the structural assignment suggested by the spectroscopic data, we attempted to obtain single crystals of a derivative of 4. The triflate salts of 4 were not successfully crystallized, but the metathesis reaction of 4c with NaBPh4 resulted in the formation of an orange microcrystalline product, identified as [(cymene)Ru(2,3-dimethylindolyl)lBPh4. Single crystals of this product were obtained by diffusion of EtOH into a CH2C12 solution of the compound. However, the crystalline sample diffracted poorly and complete refinement of the structure has been hampered by a disorder problem.12 Nevertheless, the preliminary structural data confirm that the cation is a sandwich structure with both $-cymene and @-indolyl ligands. A perspective drawing of the major orientation of the molecule is shown in Figure 2, and tables of the preliminary data are given in the supplementary material. The @-indolyl ligand is slightly tilted with respect to the cymene ring, and the angle between the center of each ring and the ruthenium ion is 173.4", somewhat (11)Suravajala, S.; Polam, J. R.; Porter, L. C. Organometallics 1994,13,37.
(12)A crystal was selected and mounted on a Siemens P4RA diffractometer. Crystal data: a = 40.050(14) A, b = 11.049(4) A, c = 16.778(6)A, p = 109.70(3)". Space group C2/c (No. 1 5 ) , Z = 8. Final R = 0.114 for 146 parameters and 1854 data, F e 4dF). The structure was solved via direct methods. Solution and refinement used the SHELXTL PLUS suite of pro ams. The largest residual electron density peaks, 2.19 and 2.12 e/$, could not be satisfactorily resolved but are consistent with a disorder that exchanges the cymene ligand with the indolyl. Examination of thermal parameters also supports such a conclusion. Analysis of the crystal structure indicates these ligands are similarly sized and sufficient space appears to exist to accommodate such disorder. The ratio between the two forms is -65: 35. Full details are provided in the supplementary material. Further studies are under way to better resolve this structure. (13) Kuhn, N.; Schulten, M.; Zauder, E.; Augart, N.; Boese, R. Chem. Ber. 1989,122,1891. (14) Yagil, G. Tetrahedron 1967,23,2855.
1226 Organometallics, Vol. 14,No. 3, 1995
Chen et al.
Table 3. Selected Bond Distances (A) for [(Cymene)Ru(l-methylindole)l(OTf)~ (3b) RU (1)-C (4) RU (l)-C (6)
1.400 (17) 1.443 (15) 1.420 (20) 1.415 (13) 2.218 (11) 2.172 (15) 2.350 (13) 2.200 (10)
2.327 (11) 2.207 (16) 2.246 (13) 2.220 (11) 2.240 (11) 2.213 (11) 1.406 (16) 1.438 (23)
RU (1)-C (8) RU (1)-C (11) RU (1)-C (13) RU (1)-C (15) N ( l ) - C (2) N ( l ) - C (10)
C5
9
w c10 Figure 2. Perspective drawing for [(cymene)Ru(X,S-dimethylindolyl)]BPh4.Thermal ellipsoids are shown at the 50% probability level.
RU (1)-C (14) RU (1)-C (16) N ( l ) - C (9) c (2)-C (3) c (4)-c (5) C (51-42 (6) C (7)-C (8)
2.242 (11) 2.189 (13) 1.328 (18) 1.394 (24) 1.381 (19) 1.396 (17) 1.389 (22)
data (Tables 1and 2) were consistent with the formation of a single product in which the Ru z-coordination of the carbocyclic ring of the indolyl ligand is mantained, and the nitrogen atom of the ligand serves as a donor to the palladium ion. The 31P NMR spectrum of 5, which showed a singlet at 27.6 ppm, supported the f 0 r m a tion of only one isomer, but the stereochemistry at palladium in 5 (or in the starting Pd reagent) has not been determined. Previous examples of the interaction of palladium(I1) with the nitrogen atom in rearranged indole ligands and in indolyls have been reported.16 The reaction of 4 c with [CuOTflsGH6 also proceeded to form a new yellow heteronuclear complex which was formulated as {[(cymene)Ru(~6-indolyl)l~-~1-Cu}(OTf)~ (6), eq 5. Evidence for the trinuclear formulation was
a 2
I
Ru
+ +
reacted cleanly with the cymene ligand at room temperature to form cyclohexadienyl derivatives.l In contrast, the reactions of the indolyl complex with hydride or alkoxide reagents under similar conditions led to a complicated mixture of products which were not identified. Syntheses of Heteronuclear Indolyl Complexes. As discussed above, the indolyl ligand in the (cymene)Ru(I1) derivatives can be protonated or alkylated at the anionic nitrogen site. We attempted t o extend this reactivity in reactions with electrophilic transition metal derivatives. Related examples of bi- and trinuclear 6 pyrrolyl complexes that make use of +N, q5-bonding modes of the pyrrolyl ligand have been synthesized.15 observed in the FAB mass spectrum. An envelope at The reaction of 4c with PdC12(PPh3)(CH&N)proceeded mle 1270, which corresponded to the parent ion of 6, in dichloromethane to give a single product, which was showed good agreement with calculated intensity ratios identified as [(cymene)Ru(~6-indolyl)-~1-PdC12(PPh~)1for two rutheniums and one copper ion in the proposed OTf (51, eq 4. The FAB mass spectrum of the product formulation. Fragments that corresponded t o loss of
a
(4)
OTf and to loss of one (cymene)Ru(indolyl)unit were also observed. No evidence was observed for the formation of a 1:l Ru-Cu complex. For example, complete conversion to 6 was achieved regardless of whether lI2 or 1equiv of copper ion was used in the synthesis. The lH NMR spectrum of 6 at room temperature gave no indication of ligand dissociation at the copper ion. A sharp spectrum was observed that was similar to that of the starting ruthenium complex 4c. The chemical shifts for the ring hydrogens in the dimethylindolyl ligand of 6 were shifted downfield by -0.2 ppm relative
showed an envelope that corresponded to the parent ion of the proposed cation at mle 818. lH and 13C NMR
(15)(a) Pyshnograeva, N. I.; Batsanov, A. S.; Struchkov, Y. T.; Ginsberg, A. G.; Setkina, V. N. J. Organomet. Chem. 1985,297, 69. (b) Pyshnograeva, N. I.; Setkina, V. N.; Andrianov, V. G.; Struchkov, Y. T.; Kursanov, D. N. J. Organomet. Chem. 1978, 157, 431. ( c ) Losilkina, V. I.; Pyshnograeva, N. I.; Baranetskaya, N. K.; Setkina, V. N. Izu. Akad. Nauk SSSR, Ser. Khim. 1985,2780. (d) Kuhn, N. Bull. SOC.Chem. Belg. 1990, 99, 707. (16) (a) Yamauchi, 0.; Takani, M.; Toyoda, K.; Masuda, H. Inorg. Chem. 1990,29, 1856. (b) Robson, R. Inorg. C h i n . Acta 1982,57, 71.
+
I
Ru
+
a
+
I
PdCI,(CH&N1PPh,
Ru I
CI,( PPh,) Pd 5
Indole and Indolyl Complexes of (Cymene)Ru(II) to those in 4c. lH and 13C NMR data for 6 are included in Tables 1 and 2. Reaction of the Heteronuclear Complex 6 with Nucleophiles. We were interested in determining whether simultaneous @,+coordination of the indolyl ligand in the heteronuclear complexes would lead to altered or enhanced selectivity in the reactions of the coordinated ligand with nucleophiles. In reactions of 6 with a hydride reagent, we found no evidence that coordination to the Cu+ ion activated the nitrogen ring toward nucleophilic addition. However, we did find that the selectivity of the attack on the carbocyclic ring was significantly improved. The reaction of 6 with excess (5-6 equiv) LiAl(O-t-Bu)sHin THF at -78 "C resulted in much cleaner product formation than was observed for the mononuclear Ru-indole or indolyl complexes. A single isomer of a new complex was isolated by solvent evaporation and extraction with CH2C12 at 0 "C. The product was formulated on the basis of 'H NMR, COSY, and mass spectral data as { [(cymene)Ru(2,3-dimethylindolyl-H)lzCu}OTf(7a),a symmetrical isomer which resulted from hydride addition to an equivalent atom in each indolyl ligand of 6, eq 6.
r - i
+3
+
+ I Ru
signal in the spectrum was the doublet for the external hydride substituents (Hex,,)on the indolyl ligands at 3.00 ppm ( J = 14 Hz). The large J value arose from geminal coupling with the endo hydrogen substituent. The upfield chemical shift and large geminal coupling constant for the exo hydrogens are similar to those seen in the 'H NMR spectra of other hydride addition p r ~ d u c t s . ' , ~ , ~ A doublet of doublets at 3.54 ppm was assigned to the endo hydrogen at the 4 position of the indolyl ring. The multiplicity was the result of both geminal coupling to the exo hydride substituent ( J = 14 Hz) and vicinal coupling to the adjacent hydrogen, H5 ( J = 5.4 Hz). The dihedral angle between the C-H bonds of He,, and H5 was estimated to be close to go", and the vicinal coupling between these two hydrogens was therefore not observed. Regioselectivity in the formation of 7 was found to be dependent upon temperature. When the product workup was carried out at 20 "C instead of 0 "C, the lH NMR spectrum of the product displayed resonances for an approximate 1 . 5 1 mixture of isomers. In addition to the resonances identified for 7a, a second set for the minor isomer were observed and assigned to the product of hydride addition to C7 in each indolyl ligand, 7b. A resonance at 3.13 ppm with J = 15 Hz was assigned to the exo hydrogen of 7b. Distinct resonances for the other indolyl hydrogens were also observed and have been tentatively assigned on the basis of the COSY NMR data, Table 1. Statistically, the isomer resulting from hydride addition to C4 of one indolyl ligand and C7 of the other is also expected to form. However, the lH NMR spectrum does not show separate resonances for the "mixed isomer.
Summary and Conclusions
2 Al(O-t-Bu)3H d
,cu Me
Organometallics, Vol. 14,No. 3, 1995 1227
Me
2
7P
The mass spectrum of the product gave an envelope consistent with the parent cation of the proposed formulation. The COSY spectrum of 7a gave coupling patterns which indicated that this product was the result of hydride addition t o either C4 or C7 in each indolyl ligand. Although the NMR data do not distinguish the two possibilities, we propose that C4 is the preferred site of addition in 7a. The presence of the Cu(I) moiety on the nitrogen atom is expected t o cause steric hindrance to nucleophilic addition t o C7 with the bulky hydride reagent. The reactions of (CO)sCr(indole) and [(C0)3Mn(indole)l+ complexes with nucleophiles were reported t o show a similar selectivity for addition to C4 over C7 in most cases, especially when a bulky group (e.g., SiPh&Bu), CH2Ph) was present on the indole n i t r ~ g e n . ~The ~ , ~hydride additions are also presumed to be exo to the Ru ions on the basis of the established stereochemistries of other nucleophilic additions to arene ruthenium The lH NMR spectrum of 7a is shown in Figure 3, and the COSY spectrum of the expanded region from 3 to 7 ppm is shown in Figure 4. The most diagnostic
Both indole and indolyl derivatives of (cymene)Ru(11)have been synthesized and characterized. The $coordination of the carbocyclic ring of the bicyclic ligand has been confirmed by X-ray diffraction studies for both the indole and indolyl complexes. The aqueous pK, values of the coordinated indole, 2-methyl- and 2,3dimethylindole ligands were determined to be 7.71,8.02, and 8.15, respectively. Coordination of a second metal ion to [(cymene)Ru(2,3-dimethylindolyl)lOTf occurred at the anionic nitrogen of the pyrrolyl ring and the heteronuclear $-ql complexes [(cymene)Ru(2,3-dimethylindolyl)PdC12PPh310Tf (5) and { [(cymene)Ru(2,3dimethylindolyl)l~Cu}(OTf73 (6)have been isolated. The coordination of the Cu(1) ion in the indolyl complex led to a pattern of nucleophilic addition for 6 similar to that observed for [(cymene)Ru(l-methylindole12+(3b). However, the selectivity of the reaction with 6 was significantly enhanced, and only a single regioisomer of the hydride addition product was formed at -78 "C. In these studies of the (cymene)Ru(II) derivatives, no evidence for q5-coordinationof the indolyl ligand or for activation of the hyeterocyclic ring toward nucleophilic attack has been observed. Further studies of how metal ion coordination might affect the reactivity of the indole and indolyl ligands are in progress. (17) The coupling constant is proportional to cos24, where 4 is the dihedral angle between C-H bonds: Silverstein, R. M.; Bassler, G. C.; Morrill, T.C . Spectrometric Identification of Organic Compounds, 5th ed.; Wiley: New York, 1991; p 196.
Chen et al.
1228 Organometallics, Vol. 14, No. 3, 1995
1
6
7
' I " '
I
' "
4
,
,
a
3
--
"
'
pan
1
Figure 3. 300 MHz lH NMR spectrum of 7a in CD3CN. See Table 1for assignments.
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
Fl (PPm)
Figure 4. COSY spectrum for 7a in the region from 3.0 to 7.0 ppm.
Experimental Section Materials. [(p-Cymene)RuClzlzand [(p-cymene)Ru(OTfhk were synthesized by literature procedures.l8Jg PdClZ(CH&N)2 was obtained from Strem, and [Cu(OTf)lz(CsH~) was obtained from Johnson Matthey. Indoles and other reagents were obtained from Aldnch and used as received. Dichloromethane and acetonitrile were distilled from CaH2. Tetrahydrofuran and diethyl ether were distilled from sodiumhenzophenone. Reactions were carried out under nitrogen using standard Schlenk techniques. Column chromatography was carried out with Fischer Scientific neutral alumina absorption (80-200 mesh). Elemental analyses were performed by Desert Analytical Laboratory, Tucson, AZ,and National Chemical Consulting, Inc., Tenafly, NJ.
Instrumentation. 'H NMR spectra were recorded at 300 MHz and 13CNMR spectra at 75.4 MHz on a Varian VXR-300 NMR spectrometer. Chemical shifts, given in ppm, were referenced to TMS by using the solvent signal as a secondary reference. 31P NMR spectra were recorded at 75.4 MHz on this instrument using phosphoric acid as an external standard. Mass spectra were obtained on a VG Analytical 7070 EQ-HF mass spectrometer. 3-Nitrobenzyl alcohol was used as a matrix for the FAB spectra. The COSY spectra were collected by use of 1024 points in t z that were collected over the bandwidth necessary to include the desired resonances with 512 tl blocks and 1024 scans per block. These were zero filled t o 1024 t 2 x 1024 ti. Solution pH measurements were taken with an Orion Research Model 701A digital ionalyzer. Electrochemical mea-
~~
(18)Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. Inorg. Synth. 1982,21, 74.
(19)Ganja, E. A.; Rauchfuss, T. B.; Stern, C. L. Organometallics 1991,10, 270.
Organometallics, Vol. 14,No. 3, 1995 1229
Indole a n d Indolyl Complexes of (Cymene)Ru(II) surements were obtained on a Cypress Systems CYSY-1 analytical system. The cell consisted of a platinum working electrode, platinum auxiliary electrode, and copper reference electrode, Cyclic voltammograms were run in acetonitrile solutions of -0.1 M tetrabutylammomium hexafluorophosphate or tetrabutylammonium perchlorate at scan rates of 100 mV1s. Ferrocene was used as a n internal reference for all potentials. [(qe-p-Cymene)Ru(q6-indole)l [OW2 (3a). [@-Cymene)RuCl& (0.315 g, 0.515 mmol) was suspended in 30 mL of EtzO. To the red suspension was added AgOTf (0.60 g, 2.3 mmol), and the orange solution was stirred under N2 for 3 h. The resulting solution of [(p-cymene)Ru(OTf)& was filtered away from the white solids into a flask containing indole (0.135 g, 0.1.15 mmol). A yellow precipitate formed immediately. After 20 min, the clear supernatant was decanted and the yellow solid was washed with Et2O. The crude product, which contained free indole, was recrystallized from THF (10 mL)/ Et20 (30 mLj to give a tan solid, which was dried under vacuum. Yield: 0.266 g, 40%. MS (FAB+):mle 852 (853 calcd 352 (M - H - 20Tf). for the [Ru(cymene)(indolyl)l~[OTfl+), MS (FAB-): m l e 799 (M OTf - H), 650 (M - H). Anal. Calcd for C ~ O H ~ I N O ~ S ~ Fc,~ R36.92; U : H, 3.25; N, 2.15. Found: C, 36.61; H, 3.09; N, 2.15. The procedures for the syntheses of the indole derivatives 3b-d were similar t o that described for 3a. [(qe-p-Cymene)Ru(qe-l-methylindole)l[OTf12 (3b) yield: 0.198 g, 48%. I3C NMR (CDsCN): 6 148.6 (9, OTf); 6 129.6, 117.6, 114.1, 108.6, 103.2, 102.2, 92.7, 91.7, 89.9, 89.8, 88.2,87.6, 79.0,67.6 (aromatic quat C and CH); 6 34.2 ("3); 6 31.1 (CHCH3); 6 21.9, 21.4, 17.0 (CH3). Cyclic voltammetry: E,, = -1.49 v (irrev). Anal. Calcd for C2&3NF&,S2Ru: C, 37.95; H, 3.49; N, 2.11. Found: C, 37.70; H, 3.46; N, 2.32. X-ray Diffraction Study of [(Cymene)Ru(l-methylindole)](OTf)z (3b). Single crystals of 3b were grown by slow diffusion of Et20 into a THF solution of the compound. The structure was solved by Patterson techniques on a Siemens P3/F diffractometer using the SHELXTL PLUS program package. The non-hydrogen atoms were included in ideal positions. One of the CF3S03 anions was disordered and was refined with bond distance constraints.20 Information on the crystal data, experimental conditions, and solution and refinement procedures are given in Table 4, and full details are given in the supplementary material. [(qe-p-Cymene)Ru(q6-2,3-dimethylindole)l[OW~ (3c). Yield: 0.284 g, 87%. The cyclic voltammogram of 3c showed an irreversible reduction (Epc)at -1.22 V and a quasireversible couple with E,,2 = -1.60 V (AE,= 260 mV). A plot of the peak current of the cathodic wave at -1.73 V vs the square root of the scan rate between 50 and 500 mV1s was linear. MS (FAB+): m l e 380 (M - 20Tf); 909 ([(cymene)Ru(2,3-dimethylindolyljl~OTf+). Anal. Calcd for CzzH25NO6S2F6Ru: C, 38.94; H, 3.71; N, 2.06. Found: C, 38.69; H, 3.53; N, 1.93. [(q6-p-Cymene)Ru(q8-2-methylindole~l[O~~ (3d). Yield: 0.154 g, 44%. MS (FAB+): m l e 366 (M - H - 20Tf). MS (FAB-): mle 814 (M + OTf), 664 (M - H). [(q6-p-Cymene)Ru(~e-l,2,3-trimethylindole)l[OTfl~ (3e). To a red solution of 4c (see below) (0.137 g, 0.259 mmol) in 20 mL of CHzCl2 was added MeOTf (0.050 mL, 0.44 mmol). The solution immediately turned yellow. After 1 h, solvent was evaporated to give a yellow sticky solid, which was washed with Et20 and dried under vacuum. [(qep-Cymene)Ru(~e-indolyl)l[OTfl (4a). Complex 3a was prepared in CHzClz solution, and the crude product was chromatographed on a neutral alumina column. Elution with CH&N defined a slow moving yellow band which was then
+
(20) The bond distance constraints, given a s distances in angstroms (ESDs), are a s follows: CF3S03-, S-0 = 1.43(20), S-C = 1.80(12), C-F = 1.33(19), and F-F = 2.17.
Table 4. Selected Crystallographic and Data Collection (3b) Parameters for [(Cymene)Ru(l-methrlindole)l(OTD~ formula Fw,a m u color, habit crystal system crystal dimens, mm space group a, A b, A c. A f J 9 deg
v,A 3
Z Dcalcd, g/cm3 p, mm-' F(OO0) radiation temp, "C 28 range, deg scan type scan speed scan range
total no. of reflectns no. of obsd reflectns
R,R w goodness of fit largest difference peak, e-/A3 largest difference hole, e-/Ao3
C~IH~~N~~F~SZRU 664.6 yellow, parallelpiped monoclinic 0.1 x 0.2 x 0.4 P2dn 16.180(3) 9.028(2) 18.827(4) 109.54(2) 2591.7(9) 4 1.703 0.825 1336 Mo K a (A = 0.710 73 Aj 22-24 3.0-50.0 8-28 variable; 4.00-60.0O0/min to from 1.00" below 28 for 1.OO" above 28 for & 5535 2166 ( F > 4.0o(F)j 0.0528, 0.0589 1.27 0.55 -0.35
moved quickly down the column with EtOH. Solvent was evaporated to give an orange-yellow oily solid, which was dried under vacuum. Yield: 0.049 g, 52%. MS (FAB+): m l e 852 352 (M - H (853 calcd for the [Ru(cymene)(indolyl)l~[OTfl+); - 20Tf). MS (FAB-1: m l e 799 (M + OTf - H), 650 (M - H). [(qs.p-Cymene)Ru(2~-dimethylindolyl)l[0 (4c). Complex 3c was prepared in CHzCl2 solution. The crude product was washed with Et20 and then loaded onto a neutral alumina column with CH2C12. Upon contact with the alumina, it underwent a color change from yellow to red. About 500 mL of CHzCl2 was passed through the column to remove any remaining 2,3-dimethylindole. The red band was then eluted with EtOH, and solvent was evaporated to give a red oily solid, which was dried under vacuum. Yield: 0.534 g, 88%. Attempts to recrystallize the triflate salt from CH2Clat20, CH2Cldhexane, CH3CN/Et20, and THFfEt20 were unsuccessful. The product was stored at -18 "C, at which it remained stable for up to 3 days. MS (FAB+): mle 380 (M - OW. A fragment at m l e 909 (M + 2,3-dimethylindolyl)) was also observed. Cyclic voltammetry: E,, = -1.72 V (irrev). High-resolution MS (FAB+): calcd m l e 380.0952, found m l e 380.0988. The tetraphenylborate salt [@-cymene)Ru(2,3-dimethylindolyl)l[BPh41was prepared by adding 1 equiv NaBPhr to an ethanol solution of 4c. The product precipitated out of solution as a red solid. After stirring for 1 h, the air-stable solid was collected by filtration, washed with ethanol, and dried under vacuum. Anal. Calcd for C44H44NBRu: C, 75.64; H, 6.35; N, 2.00. Found: C, 75.26; H, 6.50; N, 2.02. [(qs-p-Cymene)Ru(2-methylindolyl)l[OW (4d). Complex 3d was synthesized in CH2Clz solution, washed with EkO, and loaded onto a neutral alumina column with CHzCl2 as the elutant. About 400 mL of CHzCl2 was eluted through the column to remove any free 2-methylindole. The solvent was then changed to ethanol, which eluted an orange-yellow band down the column. Solvent was evaporated to give an orangeyellow oil, which was dried under vacuum. The product could be stored in the drybox at -18 "C for up to 4 days. Reaction of 3c with Sodium Hydroxide. Complex 3c (0.15 g, 0.22 mmol) was added t o a 0.015 M solution of NaOH (30 mL, 0.45 mmol) t o form an orange-red solution, which was stirred under N2 for 1h. The solvent was evaporated to give a mixture of red and black solids, which were dried under vacuum for 40 min. The red solid was redissolved in CH3CN
1230 Organometallics, Vol. 14, No. 3, 1995
Chen et al.
and filtered away from the black solid. Solvent was evaporated from the red filtrate. 'H NMR spectroscopy showed that the red product was the monocationic complex 4c. Reaction of 4c with Triflic Acid. Complex 4c (0.035 g, 0.066 mmol) was dissolved in 8 mL of CHzClz t o form a red solution. Triflic acid (0.006 mL, 0.07 mmol) was added via syringe, causing an immediate color change from red to yellow. The solution was stirred for 20 min before the solvent was evaporated. The yellow solid was washed with Et20 and dried under vacuum. The 'H NMR spectrum of the yellow product showed that i t was the dicationic complex 3c. Determination of pK. Values for 3a, c, and d. An aqueous solution of 3c (25.0 mL of 0.001 50 M) was titrated with 0.00 170 M NaOH. The solution slowly changed color from yellow to orange-red. The pH of the solution was measured after every 2 mL of NaOH was added. Complex 3d (25.0 mL of 0.004 97 M) was titrated with 0.005 95 M NaOH in a similar fashion, and the pH was measured every 1-2 mL of NaOH added. The pKa of 3a was determined by titrating an aqueous solution of the deprotonated derivative 4a (10.0 mL of 0.0300 M) with 0.0107 M HCl. The pKa of each complex was determined at the half-equivalence point of each titration curve. The pKa of 3a was found t o be 7.71 (10.06), that of 3c was 8.15 (f0.05),and that of 3d was 8.02 (10.04). The errors in the pKa values are based on calculations of pKa at individual points on the titration curves. PdCl2(CHsCN)(PPh& To a yellow solution of PdC12(NCCH3)z(0.302 g, 0.116 mmol) in 30 mL of CHzC12 was added PPh3 (0.306 g, 0.116 mmol) . The solution turned orangeyellow in color. After stirring under Nz for 30 min, solvent was evaporated to give an orange-yellow solid, which was washed with Et20 and dried under vacuum. Yield: 0.477 g, 85%. 'H NMR (CDC13): 6 7.66-7.74 (m, 6H, m-H of PPhs), 7.53-7.54 (m, 3H, p-H of PPhs), 7.40-7.47 (m, o-H of PPh3), 1.23 (s,3H, CH3CN). 31PNMR (DMSO-&): 6 32.0.
-
addition to C4 in both indolyl ligands, and the other is the result of addition to C7 of both indolyl ligands of 6. (See Table 1for 'H NMR assignments.) MS (FAB+): 824 (M - OTf); 380 ( 4 -~ OTf). The above reaction was repeated with 6 equiv of LiAl(0-tBuI3H at -78 "C. After 6 h the yellow solution was placed in a n ice bath at 0 "C, and solvent was evaporated to give a brownish-yellow solid. Extraction with CHzClz followed by solvent evaporation gave a yellow solid which was dried under vacuum. The 'H NMR (in CD3CN) showed clean formation of the major isomer observed above, 7a,which was assigned to the C4 addition product. Reaction of [(Cymene)Ru(l-methylindole)l(OTf)~ with LiCH(COzEt)2. To a yellow solution of 3b (0.0227 g, 0.0341 mmol) in 30 mL of THF was added lithium diethyl malonate (0.0057 g, 0.034 mmol) a t -78 "C. The solution was stirred at this temperature for 2.5 h. The flask was then warmed to 20 "C, and solvent was evaporated. The crude product was extracted with CH2C12, and the resulting yellow solution was filtered away from green solids. Solvent was evaporated to give a yellow solid, The 'H NMR indicated that two major products were present in a 3:2 ratio. The following tentative assignments are based on 'H NMR integrations and coupling patterns given by the COSY spectrum. Chemical shifts for the major isomer: 6 7.17 (d, H4 or H7 of ind, J = 4.5 Hz), 7.15 (d, HZof ind, J = 2.7 Hz), 6.30 (m, 2H of cym), 5.77 (d, H3 of ind, J = 3.0 Hz), 5.47 (d, 1H of cym, J = 6.0 Hz), 5.29 (d, 1H of cym, J = 6.4 Hz), 4.71 (t, H5 or Hs of ind, J = 5.7 Hz), 3.62 (s, 3H, NCHs), 1.81 (s, 3H, PhCH3). Chemical shifts for the minor isomer: 6 7.10 (d, H2 of ind, J = 3.3 Hz), 6.75 (d, H4 or
H~ofind,J=5.1Hz),6.14(d,H3ofind,J=3.6Hz),6.04(d, 1H of cym, J = 5.7 Hz), 5.79 (d, 1H of cym, J = 6.6 Hz), 5.47 (d, 1H of cym, J = 6.0 Hz), 5.38 (d, 1H of cym, J = 6.0 Hz), 4.84 (t,H5 or He of ind, J = 5.4 Hz), 4.43 (t,H5 or Hs of ind, J = 6.6 Hz), 3.48 (s, 3H, NCH3), 1.88 ( s , 3H, PhCH3). The
remaining resonances were not assigned because of the [(p-Cymene)Ru(2,3-dimethylindolyl)Pd(PPh3)Clz] complexity of the spectrum in the regions 3.6-4.2, 2.2-2.4, [OTfl (5). To a mixture of complex 4 (0.232 g, 0.438 mmol) and 1.0-1.3 ppm. and ClzPd(PPh3)(NCCH3)(0.212 g, 0.441 mmol) was added 30 Reactions of 3 with Other Nucleophiles. Complex 3b mL of CHZC12. The solution gradually turned from red to (0.198 g, 0.298 mmol) was combined with LiAl(0-t-Bu)~H (0.48 orange. After stirring for 2 h, solvent was evaporated to give g, 1.8 mmol) in THF at -78 "C. After stirring for 7.5 h, the an orange solid, which was dried under vacuum. Yield: 0.338 yellow solution was warmed to 0 "C, and solvent was evapog, 80%. The air-stable product was recrystallized from CH2rated. The resulting green-yellow oil was redissolved in 20 C12/Et20. 31PNMR (DMSO-&): 6 27.6 (s). MS (FAB+): m l e and filtered under Nz, and the product was then U of P CHzClz ~: 818 (M - OTD. Anal. Calcd for C ~ ~ H ~ ~ N P S O ~ F ~C,C ~ ~ RmL eluted as a broad yellow band on a neutral alumina column. 48.38; H, 4.06; N, 1.45. Found: C, 48.17; H, 4.46; N, 1.48. This fraction was collected and solvent was removed to give a { [(qs-p-Cymene)Ru(2,3-dimethylindolyl)l~Cu}(Ol%~ (6). yellow oil. The 'H NMR spectrum suggested two major To a mixture of 4c (0.223 g, 0.422 "01) and [CU(OTf)lz(CsHs) products in approximately a 1:l ratio: 6 3.48,3.44 (2 s, NMe); (0.126 g, 0.250 mmol) was added 25 mL of CHzClz. The color 1.95, 1.93 (2 s, PhMe); 1.1to 1.3 (2 dd, CHMez). These two of the solution changed from red t o yellow-orange within 10 compounds may be the expected products of hydride addition min. After stirring for 1 h, the solution was filtered, and t o C4 and C7 of the 1-methylindole ligand. However, the lH solvent was evaporated from the filtrate to give a yellow solid. NMR spectrum was not clean enough t o allow for definite The product was dried under vacuum. Yield: 0.192 g, 72%. assignments. MS (FAB+): mle 1270 (M - e), 1208 (M + H - Cu), 1122 (M Reactions of 3b with MeLi at -78 "C and at room tempera+ H - OTf), 1058 (M - OTf - Cu), 908 (909 calcd for M - Cu ture, and with NaBH4 at room temperature, were also carried - 20T0, 530 (4c + H), 380 (4c - OTD. Anal. Calcd for out, but complex mixtures of products were formed in each C ~ ~ H ~ ~ N ~ S ~ O ~ C, F ~40.68; R U ZH;C3.81; U : N, 2.21. Found: C, 40.90; H, 3.77; N, 2.33. case, and these were not successfully separated or identified. Reactions of 3a with LiAl(0-t-Bu)sH at room temperature and { [(~e-Cymene)Ru(2,S-dimethylindolyl-H)]~Cu~ [OW (7). LiEt3BH at -78 "C also failed to give characterizable products. Complex 6 (0.0493 g, 0.0388 mmol) and LiAl(O-t-Bu)3H(0.0497 g, 0.195 mmol) were combined in a Schlenk flask, which was Reactions of [(Cymene)Ru(2,3-dimethylindolyl)l(OTf) cooled to -78 "C. To the solid mixture was added 25 mL of (4c) with Nucleophiles. A solid mixture of 4c (0.292 g, 0.553 THF, and the resulting orange solution was stirred at -78 "C mmol) and LiAl(O-t-Bu)aH(0.4463 g, 1.82 mmol) was cooled for 8 h. The flask was warmed t o 20 "C and solvent was t o -78 "C, and 30 mL of EtOH was added to form a light evaporated, leaving a mixture of yellow and white solids. orange solution. After 3 h, CHsCN (10 mL) was added t o Addition of 30 mL of CHzClz t o the solid mixture resulted in increase the solubility of 4c. After another 4 h at -78 "C, the a yellow solution, which was filtered away from the white soution was darker orange, and there appeared to be no solids. Solvent was evaporated from the filtrate, and the undissolved solids present. The solution was stirred at 0 "C resulting yellow solid was dried under vacuum. The lH NMR for 4 h and then warmed to 30 "C and solvent was evaporated, of the product (in CD3CN) showed resonances for two isomers leaving a mixture of brown-orange and white solids. The crude in a -151 molar ratio. Both isomers have incorporated two product was redissolved in 30 mL of CHzClz and filtered. The hydride equivalents. On the basis of coupling patterns given solvent was evaporated from the filtrate, and the brown-orange by the COSY spectrum, one isomer is the result of hydride solid was eluted on a neutral alumina column with CH3CN. A
Organometallics, Vol. 14, No. 3, 1995 1231
Indole and Indolyl Complexes of (Cymene)Ru(II) yellow band was collected and solvent evaporated to give a yellow oil. The lH NMR spectrum of the oil displayed resonances for free indole and three major new products which have not yet been identified. However, resonances characteristic of nucleophilic additon to indole were not observed. lH NMR (CD3CN): 6 5.4-7.2 (multiple resonances); 4.0-4.6 (3 d, J = 5 Hz); 2.32-2.06(7s,Me); 1.28,1.27 (2s, Me); 0.5-1.0 (3 d, CHMez). Reaction of 4c with Sodium Methoxide. Complex 4c (0.100g, 0.189mmol) was dissolved in 30 mL of MeOH to form a red solution. A solution of NaOMe was prepared by dissolving sodium metal (0.035 g, 1.4 mmol) in 15 mL of MeOH, and this was added to the solution of 4c. M e r stirring under Nz for 15 h, the solution was still red. The solvent was evaporated, and 30 mL of CHzClz was added to form an orange solution, which was filtered. Solvent was evaporated from the filtrate to give a n orange oil, which was dried under vacuum.
The lH NMR (in CDC13) displayed a complicated series of broad peaks throughout the spectrum suggesting decomposition, and there was no evidence for starting material (4c) remaining.
Acknowledgment. Support for this work by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U.S.Department of Energy, is gratefully acknowledged. Supplementary Material Available: Details of data collection and refinement and tables of bond distances and angles and positional and thermal parameters for 3b and for [(cymene)Ru(2,3-dimethylindolyl)lBPh~ (19pages). Ordering information is given on any current masthead page. OM940632S
