Bond Cleavage Reactions in Oxygen and Nitrogen Heterocycles by a

William D. Jones, Lingzhen Dong, and Andrew W. Myers .... Karl A. Pittard, Thomas R. Cundari, T. Brent Gunnoe, Cynthia S. Day, and Jeffrey L. Petersen...
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Organometallics 1996, 14, 855-861

855

Bond Cleavage Reactions in Oxygen and Nitrogen Heterocycles by a Rhodium Phosphine Complex William D. Jones,* Lingzhen Dong, and Andrew W. Myers Department of Chemistry, University of Rochester, Rochester, New York 14627 Received June 7, 1994@

The reactions of (CsMes)Rh(PMes)PhH with furan, 2,5-dimethylfuran, 2,3-dihydrofuran, dibenzofuran, pyrrole, 1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,54rimethylpyrrole, carbazole, 9-methylcarbazole, pyrrolidine, pyridine, 3,5-lutidine, 2,4,6-collidine, pyrazole, 3-methylpyrazole, and piperidine have been investigated. While the oxygen heterocycles give only C-H activation, the nitrogen heterocycles yield C-H and N-H insertion products. The chloro derivative (C5Mes)Rh(PMe3)[2-(l-methylpyrrole)]Cl was found to crystallize in the monoclinic space group CYc with a = 13.753 (6) b = 9.665 (5) c = 30.14 (2) /I = 99.77 (5)",2 = 8, and V = 3949 (4.1) A3 while (C~Mes)Rh(PMe3)[2-(3,5-lutidine)]Cl was found to crystallize in the monoclinic space group P21h with a = 14.976 (8) b = 8.613 (5) c = 17.12 (2) /I = 101.90 (6)",2 = 4, and V = 2160 (5.2) A3.

A,

A,

Introduction An alluring prospect of investigating the chemistry of homogeneous transition metal complexes with heterocycles is the potential for insight into many important industrial processes and catalytic cycles. Studies of the interaction between transition metals and N-, 0-, or S-containing heterocyclic compounds have provided both structural models for intermediates (i.e., coordination and bonding m ~ d e s ) l -and ~ mechanistic models which may be applied to critical industrial processes such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodeoxygenation (HD0h6-10 The development of new synthetic methodologies for heterocycles has also been demonstrated with transition metal-mediated systems.l' In particular, recent studies on N-H activation have yielded information on such processes as the hydroamination of olefins and alternate synthetic routes toward insecticides and other organic nitrogen-containing molecules.12-20 The complex (CsMes)Rh(PMes)PhHhas been shown t o behave as a thermal precursor for the generation of

* Abstract published in Advance ACS Abstracts, December 1,1994.

(1) Kvietok, F.; Allured, V.; Carperos, V.; Rakowski DuBois, M. Organometallics 1994, 13, 60-68, and references within. (2) Kershner, D. L.; Basolo, F. Coord. Chem. Rev. 1987, 79, 279292. (3) Rauchfuss, T. B. In Progress in Inorganic Chemistry; Lippard, S. J., Ed.; Wiley: New York, 1991; pp 259-329. (4) Myers, W. H.; Koontz, J . I.; Harman, W. D. J . Am. Chem. SOC. 1992,114,5684-5692. (5) (a) Neithamer, D. R.; Parkanyi, L.; Mitchell, J. F.; Wolczanski, P. T. J. Am. Chem. SOC.1988, 110, 4421-4423. (b) Covert, K. J.;

Neithamer, D. R.; Zonnevylle, M. C.; LaPointe, R. E.; Sclialler, C. P.; Wolczanski, P. T. Inorg. Chem. 1991,30,2494-2508. (6) Angelici, R. J. Acc. Chem. Res. 1988,21, 387-394. (7) Baralt, E.; Smith, S. J.; Hurwitz, J.; Horvath, I. T.; Fish, R. H. J . Am. Chem. SOC.1992,114,5187-5196. ( 8 ) Laine, R. M. New J . Chem. 1987, 11,543-547. (9) Erker, G.; Petrenz, R.; Kriiger, C.; Lutz, F.; Weiss, A.; Werner, S. Organometallics 1992, 11, 1646-1655. (10)Bohringer, W.; Schulz, H. Bull. SOC.Chim. Belg. 1991, 100, 831-840. (11)Bryndza, H. E.; Fultz, W. C.; Tam, W. Organometallics 1985, 4.939-940. -> ---

(12)Bergman, R. G.: Walsh, P. J.; Hollander, F. J. J . Am. Chem. SOC.1988,110, 8729-8733. (13) Rothwell, I. P.; Hill, J. E.; Profilet, R. D.; Fanwick, P. E. Angew. Chem., Int. Ed. Engl. 1990,29, 664-665. (14) Bercaw, J. E.: Hillhouse, G. L. J . Am. Chem. SOC.1984,106, 5472-5478.

A, A,

A, A,

the unsaturated fragment [(CsMes)Rh(PMe3)1,which is active toward the oxidative addition of a variety of C-H bonds.21 In addition, this fragment has been found to cleave a wide variety of thiophene C-S bonds, giving a six-membered-ring insertion product.22 In examining the effects of aromatization on C-H vs q2-coordination23 in a variety of heterocycles, we discovered different chemical reactions for furan, pyrrole, pyridine, and their derivatives.

Results and Discussion Reactions of (Caea)Rh(PMes)(Ph)H with Wan and Derivatives. Thermolysis of (CsMedRh(PMe3)PhH (1) in the presence of furan a t 60 "C in hexane solution results in the formation of a single organometallic compound. The lH NMR spectrum exhibits a four-line resonance centered at 6 -12.825 (dd, J = 45.0, 30.6 Hz) and three proton resonances in the aromatic region consistent with its formulation as a furanyl hydride complex. A lH COSY NMR spectrum showed that the C-H bond activation occurs a t the a-position of the furan to form the 2-furanyl hydride (Scheme 1). This hydride reacts with CHCl3 to produce the cor(15) (a) Roundhill, D. M.; Hedden, D. Inorg. Chem. 1986,25,9-15. (b) Roundhill, D. M.; Hedden, D.; Park, S. Organometallics 1986, 5 , 2151-2152. (c) Roundhill, D. M.; Rauchfuss, T. B. J.Am. Chem. SOC. 1974,96,3098-3105. (d)Roundhill, D. M. Inorg. Chem. 1970,9,254258. (16) Merola, J. S.; Ladipo, F. T. Inorg. Chem. 1990,29,4172-4173. (17) Landis, C. R.; Schaad, D. R. J . Am. Chem. Soc. 1990,112,16281629.

(18)(a)Casalnuovo, A. L.; Calabrese, J. C.; Milstein, D. J. Am. Chem. SOC.1988,110,6738-6744. (b) Casalnuovo, A. L.; Calabrese, J. C.; Milstein, D. Inorg. Chem. 1987,26, 971-973. (19)(a) Gagne, M. R.; Marks, T. J. J. Am. Chem. SOC.1989, 111, 4108-4109. (b) Gagne, M. R.; Nolan, S. P.; Marks, T. J. Organometallics 1990, 9, 1716-1718. (20) Hsu, G. C.; Kosar, W. P.; Jones, W. D. Organometallics 1994, 13,385-396. (21) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91-100. (22) (a) Jones, W. D.; Dong, L. J . Am. Chem. SOC.1991,113,559564. (b) Dong, L.; Duckett, S. B.; Ohman, K. F.; Jones, W. D. J . Am. Chem. SOC.1992,114, 151-160. (23) (a) Chin, R. M.; Dong, L.;Duckett, S. B.; Partridge, M. G.; Jones, W. D.; Perutz, R. N. J. Am. Chem. SOC.1993, 115, 7685-7695. (b) Chin, R. M.; Dong, L.; Duckett, S. B.; Jones Organometallics 1992, 11,871-876, (c) Jones, W. D.; Dong, L. J . A m . Chem. SOC.1989,111, 8722-8723.

0276-733319512314-0855$09.OO/O 0 1995 American Chemical Society

856 Organometallics, Vol. 14,No.2, 1995

*

Jones et al.

Scheme 1. Reactions with Furans

Thermolysis of 1 with dibenzofuran a t 67 "C leads to C-H activation of the aromatic ring. lH NMR experiments indicate the site of activation as the 1 or 4 position,26consistent with results obtained in the reacMe?P/qh""'H ~~ tion of (CsMes)Rh(PMes)PhHwith b i ~ h e n y l e n e .Further heating of l with dibenzofuran resulted in decomposition to (CsMedRh(PMe3)z. The above reactions indicate that the aromaticity of the furan ring induces reactivity similar to that observed previously for monocyclic aromatics so that C-H cleavage occurs rather than y2-coordination.28 Reaction of 1 with F'yrrole and other Nitrogen Heterocycles. The reaction of (CsMes)Rh(PMes)PhH with pyrrole was examined. Pyrrole has stronger pnpn overlap than furan and substantial aromatic character. The object of this study was to see whether C-H bond activation (or y2-coordination) can occur in the presence of an N-H bond. Upon heating 1 with excess pyrrole in hexane solution at 60 "C, a single product was observed with a hydride resonance at 6 -11.523 H25.1 Hz). This hydride (dd, Jp-H = 50.4, J ~ - = resonance is -2 ppm downfield from those of the C-H bond activation products described above, and J R h - H is significantly smaller than for the C-H activation products (typically, J R h - H = 30-32 Hz). A Cp* resonance responding halide derivative, (CsMes)Rh(PMe3)(2-furis observed at 6 1.595 (s, 15 H) and a PMe3 resonance any1)Cl. Activation of the a-C-H bond is in agreement at 6 0.820 (d, J = 9.7 Hz, 9 H) in the lH NMR spectrum. with results found by Selnau and Merola, who obtained In addition, there is a broad peak at 6 6.729 that crystallographic evidence for the product of an iridium corresponds to four protons, suggesting a symmetrical phosphine complex with furan.24 Guerchais has also environment consistent with bonding of the N atom to seen a-activation of furan with C P ~ W H ~ . ~ ~ the metal center (Scheme 2). The 31PNMR spectrum Upon heating a hexane solution of 1 containing a of this complex shows a downfield doublet with a small mixture of benzene and furan (1:l molar ratio) at 50 "C coupling constant (6 9.15, d, Jm-p = 143.9 Hz), consisfor 48 h, two species were observed in a ratio of 1:15 tent with the formulation of the product as a Rh(II1) which were identified as (CsMes)Rh(PMes)PhH and N-H oxidative addition adduct. (CsMes)Rh(PMe3)(2-furanyl)H. Since the half-life for The N-H bond activation adduct (CsMes)Rh(PMes)arene exchange is 6.1 h under these conditions, the equi(l-pyrrolyl)(H) is apparently the thermodynamically librium constant can be calculated as Keg = 15 (eq 1). preferred product in this reaction (vide infra). The Rh-N bond is expected to be stronger than the Rh-C bond since nitrogen is a more electronegative element and the a-bonding mode takes electron density away from metal. Therefore, the metal center is less electron rich, which affects both chemical shifts (more downfield) The related and coupling constants (smaller &-PI. electron-rich coordinatively unsaturated fragment The reaction of 1 with 2,5-dimethylfuran a t 60 "C in Ru(DMPE)2 (generated by loss of naphthalene from hexane solution yields the related 3-furanyl hydride (6 Ru(DMPE)n(naphthyl)(H))interacts with pyrrole to give -13.315, dd, J = 48.5, 29.9 Hz) as the only organoa N-H bond activation p r o d ~ c t . N-H ~ ~ , ~addition ~ has metallic complex, since the a-positions are blocked by also been seen in the reaction of pyrrole with methyl groups in this substrate. The chloride deriva[Ir(PMe3)3(COD)lC116and C P ~ W H ~ . ~ ~ tive was isolated by reaction of the air-sensitive hydride A C-H bond activation product can be obtained by with CHCl3 to give (CsMes)Rh(PMe3)(3-(2,5-dimethylthe reaction of 1 with 1-methylpyrrole, blocking the furany1))Cl. In contrast, the thermal reaction of 1 with N-H position with a methyl group. The lH NMR dihydrofuran gives only the y2-C4H60complex, despite the fact that the strength of the vinylic C-H bond is (26)Numbering scheme for dibenzofuran is the same as the one that was broken in furan. In this 6 5 4 case, no resonance energy is lost upon y2-coordination, and thus, the n-complex is lower in energy than the 9 I C-H activation product. With furan, the v2-complex was not observed because q2-coordination greatly disrupts the aromatic character of the ring, raising the free (27)(a) Perthuisot, C.;Jones, W. D. J.Am. Chem. SOC.1994,116, energy of this species. 3647-3648. (b) Perthuisot, C.Ph.D. Thesis, University of Rochester,

0

/

:a:

(24)Selnau, H.E.;Merola, J. S. Organometallics 1993,12, 15831591. (25)Samat, A.;Sala-Pala, J.; Guglielmetti, R.; Guerchais, J. Nouu. J . Chem. 1978,2,13-14.

Rochester, NY,1994. (28)Belt, S.T.; Dong, L.; Duckett, S. B.; Jones, W. D.; Partridge, M. G.; Perutz, R. N. J. Chem. SOC.,Chem. Commun. 1991,266. (29)Hsu, G. C. Ph.D. Thesis, University of Rochester, Rochester, NY,1991.

Organometallics, Vol. 14, No. 2, 1995 857

Bond Cleavage Reactions in 0 and N Heterocycles

Scheme 2. Reactions with Pyrroles and F'yridines

+ meta + para

Figure 1. ORTEP drawing of (CsMes)Rh(PMes)[2-( 1methylpyrro1e)lCl. Ellipsoids are shown at the 50% probability level.

Table 1. Summary of Crystallographic Data for (C~Me~)Rh(PMe3)[2-(l-methylpyrroIe)]Cl and (CsMes)Rh(PMe,)[2-(3,5-lutidine)]Cl [Rh](2-( 1-methylpyrrole)} [Rh]{2 43S-lutidine)}

spectrum shows a hydride resonance a t 6 -12.947 (dd, J = 49.4, 30.4 Hz). Homonuclear decoupling experiments and a J-resolved lH NMR experiment indicate that the product is (C5Mes)Rh(PMe3)[2-(l-methylpyrrolyll(H), in which C-H bond activation has occurred at the 2 position of the ring. The aromaticity of 1-methylpyrrole plays an important role in formation of the C-H activation adduct just as it did in furan and benzene. An X-ray crystal structure of the chloro derivative was obtained after reacting the air-sensitive hydride with CHCl3. Figure 1 shows an ORTEP drawing illustrating activation of the a-C-H bond. Data collection parameters and select bond distances and angles are listed in Tables 1 and 2, respectively. To probe the reactivity of substituted pyrroles further, 2,5-dimethylpyrrole and 1,2,54rimethylpyrrole were examined. Upon heating 1with 2,5-dimethylpyrrole a t 67 "C for 25 h, a single hydride was observed by lH NMR spectroscopy at 6 -12.71 (dd, J = 53.2, 23.1 Hz). 31PNMR data are consistent with an N-H inserted complex exhibiting a resonance at 6 6.87 (d, J = 146.0 Hz). Attempts to isolate the N-H activated product by quenching with CHBr3 failed. Five minutes after the addition of 1 equiv of CHBr3, 31P NMR spectroscopy showed two new products a t 6 6.43 (d, J = 145.2 Hz) and 4.05 (d, J = 138.2 Hz). The resonance a t 6 6.43 was assigned as the N-Br adduct, which was observed to quickly decompose as the resonance at 6 4.05, (CsMes)Rh(PMe~)Brz,increased. Decomposition to (CsMes)Rh(PMe& was seen when 1 was heated with 1,2,5-trimethylpyrrole. Reaction of 1 with pyrrolidine resulted in decomposition. (C&les)Rh(PMea)z was found as the major product and a small amount of (CsMedRh(PMe3)Hzwas also produced. No N-H or C-H bond activation reactions occurred. Competitive N-H and C-H activation was seen in the reaction of 1 with carbazole. Thermolysis at 67 "C for 3 days gave two products in a 2:l ratio, observed by

chemical formula formula weight cryst syst space group (No.)

2 a, 8,

b, 8, C, 8,

b dT3 vol, ecalcr g cm-3

Crystal Parameters RhClPNClsH3o 429.78 monoclinic C21C

8 13.753(6) 9.665(5) 30.14(2) 99.77(5) 3949 (4.1) 1.45

Measurement of Intensity Data Mo, 0.710 73 8, radiation (monochrom) (graphite) scan rate, degmin 2- 16.5 0.7 0.35 tan e scan range, deg 28 range, deg 4-50 data collected +h,+k,fE no. of data collected 7479 no. of unique data 2746 FL '3u(FL) no. of params varied 199 p , cm-I 10.76 systematic absences hkl, h k odd OM), k odd h01,l odd differential abs cor range of trans factors 0.62-1.00 0.03376 R(FJ 0.04125 Rw(Fo) goodness of fit 1.557

+

+

RhClI"C3oHsz 455.81 monoclinic P211~(NO. 14) 4 14.976(8) 8.613(5) 17.12(2) 101.90(6) 2160 (5.2) 1.40 Mo, 0.710 73 8, (graphite) 2-16.5 0.7 0.35 tan e 4-50 fh,+k,kl 4241 1536

+

217 9.78 OM), k odd

h01,l odd

differential 0.69-1.21 0.0616 0.0591 1.394

lH NMR spectroscopy at 6 -11.23 (dd, J = 52.1, 24.2 Hz) and -13.28 (dd, J = 49.9, 32.4 Hz), respectively. The 31PNMR spectrum agreed with assignment of the major product as an N-H insertion complex, 6 6.64 (d, J = 143.1 Hz, 67%), and the minor product as a C-H activation complex, 6 9.19 (d, J = 148.6 Hz, 33%). The N-H insertion complex was found to be the more thermodynamically stable product as seen by the disappearance of the C-H activation complex upon further heating and the appearance of more of the N-H

Jones et al.

858 Organometallics, Vol. 14, No. 2, 1995 Table 2. Selected Bond Distances (A) and Angles (deg) for (CsMes)Rh(PMe~)[2-( 1-methy1pyrrole)lCl Bond Lengths 2.439(1) ~(1)-~(5) 2.271(1) c(2)-c(3) 2.068(5) C(3)-C(4) 1.423(7) C(4)-C(5) 1.393(6) c1-Rh-P Cl-Rh-C(S) P-Rh-C(S) C(l)-N( 1)-C(2) C(1)-N( 1)-C(5) C(2)-N( 1)-C(5)

Bond Angles 85.36(5) N(l)-C(2)-C(3) 99.6(1) C(2)-C(3)-C(4) 87.1(1) C(3)-C(4)-C(5) 122.3(5) Rh-C(S)-N(l) 128.0(4) Rh-C(5)-C(4) 109.4(5) N(l)-C(5)-C(4)

1.374(6) 1.359(8) 1.400(7) 1.370(6)

108.7(5) 105.5(5) 111.2(5) 124.9(4) 129.0(4) 122(2)

activation complex. Formation of the decomposition product (CsMes)Rh(PMe& was observed after continued heating at 75 "C. N-H activation was eliminated in the reaction of 1 with 9-methylcarbazole. Thermolysis in CsD12 led to a small amount of C-H activation but mostly decomposition to (C5MedRh(PMe3)2. The reactivity of pyridine and several substituted pyridines was also examined. Thermal reaction of 1 with pyridine gave three Rh(II1) products in a 8:4:2 ratio, as identified by 31PNMR spectroscopy. The major product appeared at d 11.91 (d, J = 158.0 Hz, 57%)and was assigned as the C-H insertion complex at the ortho carbon. The increased electronegativity of nitrogen would be expected to produce a downfield chemical shift for this isomer. Confirmation of this assignment was found through lH (COSY) NMR and homonuclear decoupling experiments. The other two products were formulated as C-H activation products at the para and meta sites of the pyridine ring with resonances in the 31P spectrum at 6 7.28 (d, J = 154.0 Hz, 28%) and 7.71 respectively. These assignments (d, J = 156 Hz, E%), were also confirmed by lH (COSY) NMR and homonuclear decoupling experiments. The chloro derivatives were isolated by reaction with CHC13. A single C-H activation product was found when 1 was reacted with 3,5-lutidine at 70 "C for 7 h. The presence of two distinct proton resonances at 6 6.82 (s, 1H) and 7.93 (s, 1H) identified the product as insertion into the C-H bond a t o N, as insertion into the para position would yield a single proton resonance for a symmetrically bound heterocycle. Agreement was found in the 31PNMR spectrum with one resonance observed at 6 13.77 (d, J = 156.0 Hz). Quenching the product with CHC13 resulted in the disappearance of the hydride resonances in the 'H NMR and the appearance of a new doublet in the 31P NMR at d 13.28 ( J = 155.9 Hz). Orange crystals formed at -30 "C in hexanes allowed single-crystal X-ray structure determination of the chloro derivative, (C5Me5)Rh(PMe3)[2-(3,5-lutidine)lCl. An ORTEP drawing is shown in Figure 2, data collection parameters are listed in Table 1, and selected bond distances and angles in Table 3. The a-sites in pyridine were blocked in the reaction of 1 with 2,4,6-collidine. The methyl substituents deactivate the ring, and thermolysis led only to decomposition to (C5Me5)Rh(PMe&. Thermal reaction of 1 with pyrazole was conducted at 52 "C. A 31PNMR spectrum revealed the presence of two products in a ratio of 2:l a t d 8.24 (d, J = 140.4 Hz, 67%) and 7.63 (d, J = 141.2 Hz, 33%),respectively. 'H NMR analysis was used to assign the major product as the N-H activation product (C~Me5)Rh(PMes)(l-

'd C16 Figure 2. ORTEP drawing of (CsMes)Rh(PMe3)[2-(3,51utidine)lCl. Ellipsoids are shown at the 50%probability level. Table 3. Selected Bond Distances (A) and Angles (deg) for

(C~Mes)Rh(PMe3)[2-(3,5-lutidine)]Cl Rh-c1 Rh-P Rh-C(11) N(l)-C(11) N( 1)-C(17) C(l1)-C(12) Cl-Rh-P Cl-Rh-C(11) P-Rh-C(l1) C( 11)-N(1)-C(l7) Rh-C(1l)-N( 1) Rh-C(11)-C(12) N(l)-C(ll)-C(l2) C( 1l)-C(12)-c(13)

Bond Lengths 2.40 l(4) C(12)-C(13) 2.264(5) C(12)-C(15) 2.02(2) C( 13)-C( 14) 1.33(2) C(14)-C(16) 1.34(2) C(14)-C(17) 1.42(2) Bond Angles 86.0(2) C(ll)-C(l2)-C(l5) 95.6(5) C(13)-C(12)-C(15) 84.1(5) C( 12)-C( 13)-C( 14) 122(2) C( 13)-C(14)-C(16) 117(1) C(13)-C(14)-C(17) 127(1) C(16)-C(14)-C(17) 116(1) N(l)-C(l7)-C(l4) 120(2)

1.38(2) 1.53(2) 1.39(2) 1.50(2) 1.35(2)

123(2) 117(2) 122(2) 122(2) 114(2) 124(2) 126(2)

pyrazo1yl)H based on the downfield chemical shift of the hydride resonance and its small Rh-H coupling constant (6 -11.815, dd, J = 48.1, 25.0 Hz). The second component was assigned as the C-H activation product (C5Me5)Rh(PMe3)(5-pyrazolyl)H based on its upfield hydride resonance chemical shift and Rh-H coupling constant (6 -13.069, dd, J = 45.8, 30.6 Hz). The remainder of the lH NMR data were consistent with these assignments. Upon introduction of a second nitrogen into the pyrrole ring, both the N-H and C-H activation products are thermodynamically comparable, as the product ratio does not change with further heating. Reaction of 1 with 3-methylpyrazole was also examined. A 'H NMR spectrum for the products revealed the presence of four hydrides [A, 6 -11.468 (dd, J = 48.6, 24.8 Hz, 28%); B, 6 -11.662 (dd, J = 50.9, 26.7 Hz, 26%);C, 6 -12.814 (dd, J = 45.1, 30.2 Hz, 42%);D, d -13.442 (dd, J = 40.7, 29.1 Hz, 4%)1. The corresponding 31PNMR data were as follows: A, 6 8.51 (d, J = 140.1 Hz); B, 6 10.41 (d, J = 138.0 Hz); C, 6 7.44 (d, J = 139.4 Hz); D, 6.54 (d, J = 151.0 Hz). Complexes A and B were assigned as N-H activation products based

Bond Cleavage Reactions in 0 and N Heterocycles Scheme 3. Reaction with 3-Methylpyrazole RhVH

'

A/B

t

H

B/A

t

H

H

on the fact that (1)the chemical shifts of A and B were shifted downfield (by about 1-3 ppm for the 31P resonances and -2 ppm for hydride resonances) and (2) ) the coupling of the hydride to rhodium ( J ~ - Hwas smaller in the 'H NMR spectrum (A,J = 24.8 Hz; B,J = 26.7 Hz; in contrast to C-H activation complexes, J = 30-32 Hz). While there is only a single N-H bond in 3-methylpyrazole, the N-H activation products A and B can be assigned to activation of the tautomers of 3-methylpyrazole (Scheme 3). The possibility of two distinct rotamers was deemed unlikely since rotamers are not observed with aryl hydride complexes. Complexes C and D can be similarly assigned to the tautomeric a-C-H activation adducts, since a preference for a-activation is seen with furan and pyrrole.

Conclusions Aromatic heterocycles tend to undergo C-H activation a t the site adjacent t o the heteroatom. N-H activation is a facile and thermodynamically preferable site of reaction. r,Acomplexes are only observed with nonaromatic heterocycles, and in no case were the simple a-donor complexes of the heteroatom observed. Experimental Section General Procedures. All manipulations were carried out under an Nz atmosphere or on a high-vacuum line using Schlenk techniques. All solvents were distilled from dark purple solutions of sodium benzophenone ketyl under a nitrogen atmosphere. Reagent grade furan,2,5-dimethylfuran, 2,3-dihydrofuran,dibenzofuran,pyrrole, 1-methylpyrrole,2,5dimethylpyrrole, 1,2,5-trimethylpyrrole,carbazole, 9-methylcarbazole, pyrrolidine, pyrazole, 3-methylpyrazole, pyridine, 3,5-lutidine, and 2,4,6-collidine were purchased from Aldrich Chemical Co. and were used without further purification, although each liquid was freeze-pump-thaw degassed (three cycles) prior to use. IH (400 MHz), 31P(162 MHz), and 13C (100 MHz) NMR spectra were recorded on a Bruker AMX-400 spectrometer.All chemical shifts are reported in ppm (6) relative to tetramethylsilane and referenced to the chemical shifts of residual solvent resonances (CsHs, 6 7.15; C&2, 6 1.38). 31PNMR chemical shifts were measured in ppm relative to 30% H3P04 (6 0.0). Analyses were performed by Desert Analytics. An

Organometallics, Vol. 14, No. 2, 1995 859 Enraf-Nonius CAD4 dieactometer was used for X-ray crystal structure determination. Preparationof (C&fedRh(PMes)(2-furanyl)H. A sample of (C&fes)Rh(PMes)PhH(25 mg, 0.0637 mmol) was dissolved in 4 mL of hexane. To this solution was added 5 equiv of furan (217 mg, 0.32 "01). The mixed solution was placed in an ampule equipped with a Teflon stopcock and stirred at 60 "C for 23 h. The reaction was cooled in an ice-water bath and the solvent removed in vacuo. A IH NMR spectrum showed that a single complex was produced in quantitative yield. The acproduct was formulated as (C~Mes)Rh(PMe3)(2-fanyl)H cording to lH COSY NMR spectroscopy. NMR (CeDs): 6 -12.825 (dd, J = 45.0, 30.6 Hz, 1H), 0.953 (d, J = 10.1 Hz, 9 H), 1.840 (s, 15 H), 6.206 (d, J = 2.6 Hz, 1H), 6.513 (dd, J = 2 . 3 , 2 . 3 H z , l H ) , 7 . 8 0 9 ( d , J = 1 . 3 H z , l H ) .31PNMR: 69.37 (d, J = 151.0 Hz). 13CNMR 6 10.76 ( 8 , CsMes), 19.03 (d, J = 33.0 Hz, PMes), 97.90 (t,J = 3.5 Hz, C&fes), 110.98 (s,2 CH), 117.32 (s, CH), 167.64 (dd, J = 47.0, 25.0 Hz, RhC). Preparation of (C&fe6)Rh(PMes)(2-furanyl)Cl.To a CsHe (0.5 mL) solution of (CsMes)Rh(PMe3)(2-furanyl)H(31 mg, 0.081 mmol) was added an excess of CHCl3 (2 equiv, 0.16 mmol) at 0 "C. The yellow solution rapidly turned orange. After standing at room temperature for a few minutes a lH NMR spectrum was recorded, showingthe formation of a new product. lH COSY and homonuclear decoupling experiments confirmed that the produced complex was (CaMea)Rh(PMe& (2-furanyl)C1(28mg, 84%). lH NMR (CeDe): 6 1.047 (d, J =

10.7Hz,9H),1.453(d,J=2.9Hz,15H),6.552(dd,J=2.9, 1.8Hz,lH),6.774(d,J=2.9Hz,lH),7.698(d,J=l.lHz, 1H). 31PNMR: 6 10.59 (d, J = 143.0 Hz).Anal. Calcd for C17H2,ClOPRh: C, 49.00; H, 6.53. F o n d : 48.90; H, 6.55. Preparation of (CaMedRh(PMe~)i3-(2,S-dimethylfuranyl)]H. 2,fi-Dimethylfuran (0.12 mL, 1.10 mmol) was added by syringe to a hexane (3 mL) solution of 1 (20 mg, 0.051 "01). Reaction was carried out at 61 "C for 19 h, after which the resulting solution was evaporated t o dryness under vacuum. Both IH and 31P NMR data were consistent with the formulationof (CsMes)Rh(PMe3)[3-(2,5-dimethyl)furanyllH. 'H NMR (C&j): 6 -13.315 (dd, J = 48.5,29.9 Hz, 1H), 0.936 (d, J = 9.9 Hz, 9 H), 1.836 ( 8 , 15 H), 2.350 (s,3 H), 2.614 (9, 3 H), 5.733 ( 8 , 1H). 31PNMR (C&): 6 8.59 (d, J = 150.2 Hz). Preparation of (C&Ie&)Rh(PMes)[3-(2,&dimethylfuranyl)]Cl. To a hexane (2.5 mL) solution of (CsMe5)Rh(PMe3)(3-(2,5-dimethylfuranyl)H (30 mg, 0.067 mmol) was added a slight excess of CHCls (2 equiv, 0.13 mmol) at 0 "C. The brown solution rapidly turned orange. After standing at room temperature for a few minutes a 'H NMR spectrum was recorded, showing the formation of a new product. lH COSY and homonuclear decoupling experiments confirmed that the produced complex was (CsMes)Rh(PMea)(3-(2,5-dimethylfuranyl)Cl(15.5 mg, 52%). 'H N M R (C6Ds): 6 1.130 (d, J = 10.0 Hz,9 H), 1.390 (d, J = 2.8 Hz, 15 H), 2.331 ( 8 , 3 H), 2.857 ( 8 , 3 H), 5.470 ( 8 , 1H). 31PNMR: 6 8.96 (d, J = 147.0 Hz). Anal. Calcd for C19H31ClOPRh: C, 51.31; H, 7.02. Found: C, 50.61; H, 7.18. Preparation of iC&Ies)Rh(PMes)(2,3-pa.dihydrofuran). Complex 1 (20 mg, 0.0510 mmol) in hexane solution was treated with excess of dihydrofuran (0.10 mL, 1.32 mmol). The solution was then heated in an ampule at 50 "C for 24 h. The solvent removed under vacuum, and the resulting yellow solid was characterized as (CsMea)Rh(PMea)(2,3-92-dydrofuran) by 1D and COSY NMR spectroscopy (95%). For (CsMedRh(PMe3)(q2-dihydrofuran),IH NMR (csD12): 6 1.004 (d, J = 8.2 Hz, 9 H), 1.774 (s, 15 H), 1.673 (m, 1 H), 2.010 (br m, 1 H), 2.208 (br m, 1H), 3.483 (9, J = 7.7 Hz, 1H),3.829 (4, J = 8.3 Hz, 1 H), 4.942 (m, 1 H). 31P NMR (C6D12): 6 2.54 (d, J = 208.0 Hz). Preparation of (CaMe5)Rh(PMea)(dibenzofuran)H. Dibenzofuran (7 mg, 0.04 mmol) was added to a C6DlZ (0.5 mL) solution of 1 (10 mg, 0.026 "01). The sample was heated for 3 days at 67 "C in a resealable NMR tube equipped with a Teflon stopcock. lH and 31PNMR spectra show the formation

860 Organometallics, Vol. 14,NO.2, 1995

Jones et al.

J = 2.2 Hz, 15 H), 2.480 ( s , 6 H), 5.820 (s, 2 H). 31P NMR (CsDs): 6 6.87 (d, J = 146.0 Hz). Reaction of 1 with 1,2,5-l"ethylpyrrole. A C6Dl2 (0.5 mL) solution of 1 (10 mg, 0.025 mmol) was heated with 1,2,5trimethylpyrrole (0.16 g, 1.5 mmol) at 67 "C for 21 h. The pale yellow solution turned dark green. Removal of solvent revealed the decomposition product, (CsMes)Rh(PMe&,as the only product. 'H NMR (CsD12): 6 1.259 (d, J = 7.6 Hz, 9 HI, 1.889 (d, J = 1.7 Hz, 15 H). 31PNMR (CsDi2): 6 -5.68 (d, J = 218.0 Hz). No C-H activation was seen. Reaction of 1 with Carbazole. Thermolysis at 67 "C of 1 (10 mg, 0.025 mmol) and carbazole (0.012 g, 0.075 mmol) for 3 days gave two Rh(II1) products in a 2:l ratio. The major from product was assigned as (C5Mes)Rh(PMe3)(N-~arbazole)H, insertion into the N-H bond. 'H NMR (CsD12): 6 -11.232 (dd, J = 52.1,24.2 Hz, 1H), 0.922 (d, J = 10.1 Hz, 9 HI, 1.766 (d, J = 1.8 Hz, 15 Hz), aromatic resonances were not assigned due to overlap with other product and starting material resonances. 31PNMR (CsD12): 6 6.64 (d, J = 143.1 Hz). The minor product was formulated as a C-H activation product, (C~,Mes)Rh(PMe3)(carbazole)H.'H NMR (CsDs): 6 -13.28 (dd, J = 49.9, 32.4 Hz, 1H), 1.079 (d, J = 9.3 Hz, 9 HI, 1.807 (d, J = 1.8 Hz, 15 H), aromatic resonances and site of activation were not assigned due to complexity and overlap in aromatic region. 31P{1H}NMR (CsD6): 6 9.19 (d, J = 148.6 Hz). Reaction of 1with 9-Methylcarbazole. A CD12 (0.5 mL) solution of 1 (10 mg, 0.025 mmol) and 9-methylcarbazole (11 mg, 0.055 mmol) was heated at 67 "C for 17 h. Only the formation of (CsMee)Rh(PMe& was observed by 'H and 31P NMR spectroscopy. Reaction of 1 with Pyrrolidine. To a hexane (4 mL) solution of 1 (22 mg, 0.056 mmol) was added 40 mg of pyrrolidine (0.562 mmol). After stirring for 22 h at 61 "C, the pale yellow solution turned dark grey. Upon removal of the solvent, the decomposition product (CsMes)Rh(PMe& was found as the major product and a small amount of (CsMe5)Rh(PMe3)H2was also produced. No N-H bond activation or C-H bond activation reaction occurred. Reaction of 1 with Pyridine. Pyridine (0.196 g, 2.5 mmol) and 1 were heated in a C6Dl2 (0.5 mL) solution at 70 "C for 7 h. Three C-H activation products were identified. The major product (57%)was formulated as (CsMes)Rh(PMe& (2-pyridy1)H based on lH (COSY) NMR and homonuclear decoupling experiments. 'H NMR (C6D12): 6 -13.675 (dd, J = 48.0, 34.0 Hz, 1 H), 1.267 (d, J = 10.1 Hz, 9 H), 1.857 (d, J = 2.3 Hz, 15 H), 6.470 (td, J = 7.2, 1.5 Hz, 1H), 6.732 (td, J = 7.1, 2.3 Hz, 1H), 7.250 (dt, J =8.5, 1.4 Hz, 1H), 8.165 (dd, H),5.90l(dd,J=3.6,2.0Hz,lH),6.623(t,J=3.8Hz,lH), J = 5.7, 2.8 Hz, 1 H). 31P{1H)NMR (CsD12): 6 11.91 (d, J = 7.042 (br s , 1H). 31PNMR (CsDs): 6 10.37 (d, J = 142.8 Hz). 158.0 Hz). The second product (28%) was formulated as Preparation of (C&lea)Rh(PMes)[Z-(l-methyl)pyr(CsMes)Rh(PMe3)(4-pyridyl)H, the product of insertion into the rolylIC1. To a hexane solution of (CsMes)Rh(PMe3)[2-(1para C-H bond. 'H NMR (CsD12): 6 -13.490 (dd, J = 50.0, methylpyrroly1)H(40 mg, 0.093 mmol) was added to an excess 34.0Hz,1H),1.247(d,J=9.8Hz,9H),1.866(d,J=2.0Hz, of CHC13 (2 equiv, 186 mmol). The solution turned orange, 15 HI, 7.146 (d, J = 5.0 Hz, 2 H), 7.755 (d, J = 5.7 Hz, 2 H). and a new product was seen by 31P NMR. 'H NMR data 31P NMR (CsD12): 6 7.35 (d, J = 152.7 Hz). The third C-H agreed with the assignment as (CsMes)Rh(PMe3)[2-(l-meth- insertion product (15%)was assigned as activation at the meta ylpyrr~lyl)]Cl.'H NMR (CsDs): 6 1.128 (dd, J = 10.8,0.6 Hz, 'H NMR (CsD12): 6 1.236 site, (CsMe~)Rh(PMes)(3-pyridyl)H. 9 H), 1.341 (d, 3.0 Hz, 15 H), 3.932 (s, 3 H), 5.611 (dd, J = 3.2, (d, J = 8.6 Hz, 9 H), 1.899 (d, J = 1.72 Hz, 15 H), 6.571 (t,J 1.7 Hz, lH), 6.593 (t, J = 3.2 Hz, lH), 7.030 (m, 1 H). 31P = 7.1 Hz, 1H), 7.436 (d, J = 6.0 Hz, 1H), 7.957 (dd, J = 7.0, NMR (CsDs): 6 9.74 (d, 144.6 Hz). l3C{'H} NMR (CsDs): 6 2.0 Hz, 1H), 8.360 (s, 1H). The hydride for the third product 9.00 (s, C a e s ) , 14.98 (d, J = 33.6 Hz, PMe3), 39.00 ( s , NMe), was obscured. 31P NMR (CsD12): 6 7.71 (d, J = 153.3 Hz). 98.80 (t,J = 3.6 Hz, CsMes), 109.25 ( s ) , 115.00 (s), 125.25 (s), Preparation of Chloro Derivatives of Pyridine Prod159.58 (dd, J = 37.1, 18.3 Hz, RhC). Anal. Calcd for ucts. A slight excess (2 equiv, 0.164 mmol) of CHC13 was ClaHaoCINPRh: C, 50.30; H, 7.04; N. 3.26. Found: C, 49.34; added a t 0 "C to a hexane solution of a mixture of the three H, 7.03; N, 2.96. rhodium-pyridine products (35 mg, 0.0818 mmol). The dark Preparation of (CaMes)Rh(PMe,)[1-(2,5-dimethyl. orange solution was evaporated and then recrystallized in CsHs-hexanes to give dark orange crystals (23 mg, 67%). pyrro1e)lH. 2,5-Dimethylpyrrole (0.23 g, 2.5 mmol) was Anal. Calcd for ClsHz8C1NPRh: C, 50.54; H, 6.60; N, 3.27. added t o a CsDl2 (0.5 mL) solution of 1(10 mg, 0.025 mmol). Found: C, 50.41; H, 7.02; N, 2.37. Major product (ortho C-H The reaction was heated at 67 "C for 25 h, after which solvent activation): 'H NMR ((CD3)zCO): 6 1.302 (d, J = 11.1Hz, 9 was removed and fresh solvent condensed. 'H and 31P NMR H), 1.658 (d, J = 3.0 Hz, 15 H), 6.720 (br s, 1 H), 7.040 (d, J spectra were consistent with the formation of (CsMe5)Rh= 2.3 Hz, 1 H), 7.725 (d, J = 1.4 Hz, 1 H),8.207 (br s, 1 HI. (PMe3)[1-(2,5-dimethylpyrrole)lH.'H NMR (CsDs): 6 -12.710 31P{1H)NMR ((CD3)2CO):6 11.16 (d, J = 154.9 Hz). Second (dd, J = 53.2, 23.1 Hz, 1HI, 1.009 (d, 10.0 Hz, 9 HI, 1.703 (d,

of one C-H activation product. 'H NMR (C6D12): 6 -13.367 (dd, J = 4 8 . 7 , 3 1 . 1 H z , l H ) , 1.144(d, J = 9 . 8 H z , 9 H ) , l . 8 1 3 (9, 15 H), 6.848 (m), 7.097 (t, 7.3 Hz, 1H), 7.196 (m), 7.367 (d, J = 7.2 Hz, 1H), 7.491 (m), 7.742 (d, 7.4 Hz, 1H).31PNMR (CsDi2): 6 6.75 (d, J = 151.0 Hz). Preparation of (CaMea)Rh(PMes)(dibenzofuran)Cl.To a hexane (0.5 mL) solution of (CSMes)Rh(PMe3)(dibenzofuran)H (40 mg, 0.0774 mmol) was added an excess of CHC13 (2 equiv, 0.155 mmol) at 0 "C. The yellow solution rapidly turned orange. After standing at room temperature for a few minutes a 'H NMR spectrum was recorded, showing the formation of a new product. The chloro derivative was isolated on a thinlayer silica chromatography plate with a 9 5 5 (v/v) solution of CHZClZ-THF. 'H resonances and decoupling experiments indicate activation of the C-H bond in the 1 or 4 position. Elemental analysis of the chloride was high in C and H due t o free dibenzofuran, which was difficult t o remove (16.4 mg, 41%). 'H NMR ((CD&CO): 6 1.401 (dd, J = 10.9, 0.8 Hz, 9 H), 1.601 (d, J = 2.9 Hz, 15 H), 7.019 (t, J = 7.5, Hz, 1 H), 7.290 (td, J = 7.6, 1.0 Hz, 1H), 7.394 (td, J = 8.1, 1.3 Hz, 1 H), 7.544 (dd, J = 8.0, 1.0 Hz, 1H), 7.565 (dd, J = 7.3, 1.0 Hz, 1 H), 7.927 (dd, J = 7.5, 1.1Hz, 1 H), 7.982 (dd, J = 7.0, 1.1 Hz, 1H). 31PNMR (CsDs): 6 4.05 (d, J = 148.7 Hz). 13C{'H} NMR (CsHs): 6 9.27 (s, C&fe5), 15.74 (d, J = 31.0 Hz, PMez), 98.83 (t, J = 5.1 Hz, CsMes), 110.43 (9, CHI, 115.04 (8, CHI, 120.82 ( s , CH), 121.16 (8,CH), 122.41 (s, CH), 122.86 (8, C), 123.68 ( s , C), 125.70 (9, CH), 127.05 (8, CHI, 129.78 (8, C), 140.49 (dd, J = 38.0, 20.1 Hz, RhC), 155.34 (5, CH). Preparation of (C~e5)Rh(PMes)(l-pyrrolyl)H.1 (20 mg, 0.051 mmol) was dissolved in 4 mL of hexane and 0.050 mL of pyrrole (0.70 mmol) added. The reaction mixture was placed into an ampule equipped with a Teflon stopcock and stirred at 61 "C for 22 h. The sample was cooled and evaporated to dryness t o give (CsMedRh(PMe3)(l-pyrrolyl)H as an orange solid. 'H NMR (C&): 6 -11.523 (dd, J = 50.4, 25.1 Hz, 1H), 0.820 (d, J = 9.7 Hz, 9 H), 1.595 ( s , 15 HI, 6.729 (br s, 4 H). 31PNMR (CsD.4: 6 9.15 (d, J = 143.9 Hz). Preparation of (C&Xe5)Rh(PMes)[2-(1-methyl)pyrrolyl]H. 1(15 mg, 0.0383 mmol) was reacted with 0.10 mL of 1-methylpyrrole (1.25 mmol) at 60 "C for 16 h. After cooling, vacuum evaporation afforded an orange solid. The complex (CsMes)Rh(PMe3)[2-(1-methy1)pyrrolylJHwas formed in quantitative yield and was characterized by 'H (lD, homonuclear decoupling, and JRES)NMR and 31PNMR experiments (29.2 mg, 73%). 'H NMR (CsDs): 6 -12.947 (dd, J = 49.4, 30.4 Hz, 1H), 0.921 (d, J = 10.4 Hz, 9 H), 1.862 (s, 15 H), 3.622 (8,3

Organometallics, Vol. 14, No. 2, 1995 861

Bond Cleavage Reactions in 0 and N Heterocycles product (para C-H activation): 1H NMR ((CD&CO): 6 1.385 (d, J = 13.1 Hz, 9 H), 1.708 (d, J = 2.9 Hz, 15 H), 7.490 (d, J = 4.2 Hz, 1 H), 7.650 (d, J = 5.0 Hz,1 H), 7.801 (d, J = 5.0 Hz, 1H). 31P{1H)NMR ((CD3)zCO): S 8.46 (d, J = 156.3 Hz). Formation of (CaMes)Rh(PMes)C2-(3,5-lutidine)lH.A CsDlz (0.5 mL) solution of 1 (10 mg, 0.025 mmol) and 3,5-lutidine (94 mg, 0.8 mmol) was heated at 70 "C for 7 h. Both lH and 31PNMR data agree with the assignment of the single product as (C5Me5)Rh(PMe3)[2-(3,5-lutidine)]H, insertion into the C-H bond adjacent to N. I H NMR (CeD12): 6 -13.670 (dd, J = 50.0,34.0Hz, 1H), 1.106(d,J = 10.1 Hz, 9H), 1.748 (d, 1.6 Hz, 15 H), 2.048 (8,3 H), 2.252 (9, 3 H), 6.820 (8,1HI, 7.930 (s, 1H). 31PNMR (CsD12): 6 13.77 (d, 156.0 Hz). Preparation of (CaMe6)Rh(PMe~)[2-(3,5-lutidine)ICl. To a hexane solution of (C5Me5)Rh(PMe3)[2-(3,5-lutidine)lH (40 mg, 0.0949 mmol) was added 23 mg of CHC13 (2 equiv, 190 mmol). The solution turned orange, and a new product was seen by 3lP NMR. lH NMR data agreed with the assignment (19.5 mg, 45%). 'H as (CsMe5)Rh(PMe3)[2-(3,5-lutidine)lCl NMR (CsDs): 6 1.244 (d, J = 11.2 Hz, 9 H), 1.400 (d, J = 2.9 Hz, 15 H), 2.000 (8, 3 H, Me-5), 2.827 (8,3 H, Me-3), 6.890 (8, 1 H, H-4), 8.098 (s, 1 H, H-6). 31PNMR (CsDs): 6 13.28 (d, 155.9 Hz).Anal. Calcd for C2oH3zClNF'Rh C, 52.70; H, 7.08; N, 3.07. Found: C, 51.78; H, 7.12; N, 3.29. Reaction of 1 with 2,4,6-Collidine. 2,4,6-Collidine (91 mg, 0.76 mmol) and 1 (10 mg, 0.025 mmol) were heated in a CsDlz (0.5mL) solution at 65 "C for 3 days. A green solid was found after removal of the solvent which was identified by IH and 31P NMR as the decomposition product, (C&Ie5)Rh(PMe&. No C-H activation was observed. Reaction of 1 with Pyrazole. 1 (30 mg, 0.0765 mmol) and pyrazole (white crystals, 8 mg, 0.118 mmol) were stirred in hexane at 52 "C for 72 h. lH and 31PNMR analysis of the residue consisted of 66% (C5Me~)Rh(PMe3)(1-pyazolyl)H and 34% (CsMe5)Rh(PMe3)(5-pyrazolyl)H.For (CaMea)Rh(PMed(l-pyrazolyl)H,IH NMR (C&): 6 -11.815 (dd, J = 48.1,25.0 Hz, lH),0.749(d,J = 10.7Hz,9H), 1.426(s, 15H),6.255(~, 1 H), 7.248 (9, 1H), 7.755 (8, 1H). 31PNMR: 6 8.24 (d, J = 140.4 Hz). For (C5Me5)Rh(PMe3)(5-pyrazolyl)H,lH NMR (CsDs): 6 -13.069 (dd, J = 45.8, 30.6 Hz, 1 H), 0.608 (d, J = 9.8 Hz, 9 H), 1.545 (s, 15 H), 5.838 (8, 1H), 7.673 (8, 1H); the proton resonance for N-H was not observed. 31P NMR (CsDs): 6 7.63 (d, J = 141.2 Hz). Reaction of 1 with 3-Methylpyrazole. 1 (20 mg, 0.051 mmol) was reacted with 3-methylpyrazole (0.040 mL, 0.497 mmol) in hexane for 24 h at 60 "C. Upon removal of the solvent, the residue was analyzed by NMR spectroscopy. The lH NMR spectrum exhibited four hydrides: A, 6 -11.468 (dd, J = 48.6, 24.8 Hz), 28%; B, 6 -11.662 (dd, J = 50.9, 26.7 Hz), 26%; C, 6 -12.814 (dd, J = 45.1,30.2 Hz), 42%; D, 6 -13.442 (dd, J = 40.7,Zg.l Hz), 4%. The corresponding31PNMR data are as follows: A, 6 8.51 (d, J = 140.1 Hz); B, 6 10.41 (d, J = 138.0 Hz);C, 6 7.44 (d, J = 139.4 Hz); D, 6 6.54 (d, J = 151.0

Hz). Complexes A and B are assigned as N-H activation products. Similarly, complexes C and D are assigned t o tautomeric C-H activation products as described in the text. X-ray Structural Determination of (CaMedRh(PMes)[2-(l-methylpyrrole)lCl.Dark orange crystals formed from slow evaporation of benzene solvent at 25 "C. A single orange crystal was mounted with epoxy on a glass fiber. Lattice constants were obtained from 25 centered reflections with values of x between 5 and 70". Data were collected at -40 "C in accord with parameters in Table 1. The Molecular Structure Corp. TEXSAN analysis soRware package was used for data reduction and solution.30 Patterson map solution of the structure to locate the rhodium atom, followed by expansion of the structure with the program DIRDIF, revealed all nonhydrogen atoms. Following isotropic refinement, an absorption correction was applied by use of the program DIFABS. Full-matrix, least-squares anisotropic refinement of the nonhydrogen atoms (with hydrogens attached to carbons in idealized positions) was carried out t o convergence, with R1 = 0.0338 and R2 = 0.0413. Fractional coordinates are given in the supplementary material. X-ray Structural Determination of (CaMedRh(PMes)[2-(3,5-lutidine)lCl. Orange crystals of the compound were formed by slow diffision of hexanes into a saturated benzene solution at -30 "C. Data collection, solution, and refinement of the structure followed similarly to that of the pyrrole compound, except that the molecule crystallized in the monoclinic space group CWc with eight molecules per unit cell. Fullmatrix, least-squares anisotropic refinement of the nonhydrogen atoms (with hydrogens attached to carbons in idealized positions) was carried out to convergence, with R1 = 0.0616 and Rz = 0.0591. Fractional coordinates are given in the supplementary material.

Acknowledgment. This work was supported by the U S . Department of Energy Grant FG02-86ER13569. We also thank NATO for a travel grant. Supplementary Material Available: Tables of data collection parameters, bond lengths, bond angles, fractional atomic coordinates, and anisotropic thermal parameters for (C~Mes)Rh(PMe3)[2-(l-methylpyrrole)lCl (A) and (C5Me5)Rh(PMes)[2-(3,5-lutidine)]Cl(B)(12 pages). Ordering information is given on any current masthead page. OM9404339 (30)Rl = (ZIIFol - lFoll)&lFol, RZ = [ % ( P o l -, I F c ! ) 2 1 m @ 4 ~ 0 1 2 ~ where UI = [u2(Fo) (eF,,2)2Im for a nonPoisson contnbution weightmg scheme. The quantity minimized was C,(IF,I - lFc1)2. Source of scattering factors fo, f ', f ": Cromer, D. T.; Waber, J. T. International Tables for X-Ray Crystallography; The Kynoch Press: Birmingham, England, 1974;Vol. IV,Tables 2.2B, 2.3.1.

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