Organometallics 1983, 2, 686-687
686
system 3. Interestingly, while 3 is found to be less airsensitive than 2, preliminary data show that 3 is thermally labile, converting completely to 2 and the reactive blue (CpCoCO), (C6H6,100 OC, 22 h). The latter has been prepared previou~ly,'~ but never cleanly and/or efficiently, and the present route offers a potential entry into the exploratory chemistry of this compound. In summary, this work reports a new method for the preparation of dinuclear butadiene cobalt complexes16and the structural and some preliminary chemical details of 3, the parent compound in the series.
Scheme I
2a,2b
-
x
* H
Acknowledgment. This work was supported by the NSF (Grant CHE-82-00049). K.P.C.V. is a Camille and Henry Dreyfus Teacher-Scholar (1978-1983). Scheme I1
R e g i s t r y No. 1, 12078-25-0;2, 1271-08-5; 3, 84802-74-4; Co,
7440-48-4. S u p p l e m e n t a r y M a t e r i a l Available: An experimental description of the structure determination, a listing of observed and calculated structure factors, and tables of positional and thermal parameters and bond lengths and angles (20 pages). Ordering information is given on any current masthead page.
1
R
j
R=CH,CICH,l,
i
(16)This method appears to be general also for substituted systems: J. A. King, Jr., and K. P. C. Vollhardt, in preparation.
R
R N
c C
' PD
RNC-Rh-CNR ti'
Preparatlon and Reactlons of New Isocyanlde Complexes of Rhodium and Their Role in Carbon-Hydrogen Bond Actlvatlon
C6D6
$ C' ,D, R
CNR
N
C
I PD RNC-Rh-C63,
'H N R
William D. Jones* and Frank J. Feher Department of Chemistry, University of Rochester Rochester, New York 14627 Received September 7, 1982
Summary: The compounds [ C5(CH3),] Rh[CNCH,C(CH,),]X, (X = CI, Br) can be mono arylated with Grignard reagents to give [C,(CH,),]Rh[CNCH,C(CH,),](p CBH4CH,)X or, after addition of NH4X, the carbenes [C,(CH,),] Rh(C@-C,H,CH,)[ NHCH,C(CH,),] ]X2. Facile isocyanide insertion into the rhodium-tolyl bond occurs upon addition of PMe,. Reduction of [C,(CH,),] Rh[CNCH,C(CH,)] I, in the presence of isocyanide gives [C5(CH3)5]Rh[CNCH,(CH,),] which produces the imine C,H,CHNCH,C(CH,), upon irradiation in benzene.
,,
There has been a recent resurgence of activity in the activation of carbon-hydrogen bonds by homogeneous transition-metal complexes. While most of these reports involve intermolecular oxidative addition of C-H bonds to metal centers.l some also include the functionalization
(1)(a) Janowicz, A. H.; Bergman, R. G. J.Am. Chem. SOC. 1982,104, 352. (b) Green, M. L. Pure Appl. Chem. 1978,50,27-35.(c) Rausch, M. D.; Gastinger, R. C.; Gardner, S. A.; Brown, R. K.; Wood, J. S. J. Am. Chem. SOC.1977,99, 7870-7876. (d) Crabtree, R. H.; Mellea, M. F.; Mihelcic, J. M.; Quirk, J. M. Ibid. 1982,104,107-113. (e) Grebenik, P. D.; Green, M. L. H.; Izquierdo, A. J. Chem. SOC.,Chem. Commun. 1981, 1981, 103, 186-187. (0 Gell, K. I.; Schwartz, J. J. Am. Chem. SOC. 2687-2695. (g) Bradley, M. G.; Roberts, D. A,; Geoffroy, G. L. Ibid. 1981, (h) Baudry, D.; Ephritikhine, M.; Felkin, H. J. Chem. SOC., 103,379-384. Chem. Commun. 1980,1243-1244. (i) Hoyano, J. K.; Graham, W. A. G. J. Am. Chem. SOC.1982,104, 3723-3725.
0276-7333/83/2302-0686$01.50/0
of the carbon attached to the metal centera2 We wish to report here the preparation of new isocyanide complexes of rhodium(II1) and their reduction to rhodium(1) species capable of activating arene C-H bonds under photolytic conditions. The bridging halide complexes I [C5(CH3),]RhX),(p-X), (X = C1, Br, I)3can be easily cleaved by addition of 1equiv of CNCH2C(CH3),in CH2C12solution, producing air-stable, monomeric [C&CH3)5]Rh[CNCH2C(CH3)3]X2 (la, X = C1; l b , X = Br; IC, X = I)4 in >95% yield after recrystallization from CH2C12/hexane. Addition of 1 equiv of p CH3Cd-14Lior p-CH3C6H4MgBrto a 0.025 M THF solution of l b produces quantitatively (NMR) a new species whose 'H NMR spectrum (THF-$, 400 MHz) shows singlets at 6 1.643 (15 H), 0.999 (9 H), and 2.179 (3 H) and doublets at 6 6.697 (J= 8 Hz, 2 H) and 7.301 (J= 8 Hz, 2 H). The compound exhibits a terminal isocyanide stretch at 2190
(2)(a) Parshall, G. W. Acc. Chem. Res. 1976,8, 113-117. (b) Gustavson, W. A.; Epstein, P. S.; Curtis, M. D. Organometallics 1982,1, 884-885. (c) Diamond, W. E.; Szalkiewicz, A,; Mares, F. J.Am. Chem. SOC.1979,101, 490-491. (d) Horino, H.; Inoue, N. Tetrahedron Lett. 1979,26, 2403-2406. (e) Fujiwara, Y.;Kawauchi, T.; Taniguchi, H. J. Chem. SOC., Chem. Commun. 1980,220-221. (3)Kang, J. W.; Moseley, K.; Maitlis, P. M. J.Am. Chem. SOC.1969, 91, 5970-5977. (4)All NMR spectra were recorded at 400 MHz. For la: 'H NMR (CBDB) S 0.728,(s,9 H), 1.438 (E, 15 H), 2.662 (E, 2 H); IR (CHCl3) 2221 cm-'. Anal. Calcd for CleH,C12NRh C, 47.31;H, 6.45;N, 3.45. Found C, 47.25;H, 6.58;N, 3.36. For I b 'H NMR (C&) 6 0.700 ( 8 , 9 H); 1.541 (8, 15 H), 2.521 (B, 2 H); IR (CHC18)2216 cmd. For IC: 'H NMR (C&) 6 0.710(8, 9 H), 1.767 (a, 15 H), 2.579 (a, 2 H); IR (CHC13)2210 cm-'. Cf. Faraone, F.; Marsala, V.; Tresoldi, G. J. Organomet. Chem. 1978,152, 337-345.
0 1983 American Chemical Society
Organometallics, Vol. 2, No. 5, 1983 687
Communications cm-' (THF) and can be assigned the structure [C,(CH3)5]Rh[CNCH2C(CH3)3](p-C6H4CH3)Br, 2b., Its extreme air sensitivity has thus far precluded its isolation in analytically pure form. Treatment of a THF solution of 2a or 2b with saturated aqueous NH4C1or NH,Br, respectively, produces the new carbene complexes [C5(CH3)5]Rh(C(p-C6H,CH3)[NHCHzC(CH3)3])Xz(3a, X = C1; 3b, X = Br) in 90% yield after preparative thin-layer chromatography (Si02, 2% THF/CH2CI2)and recrystallization from benzene/ hexane. The complexes are believed to form by insertion of the isocyanide into the rhodium-tolyl bond, protonation of the iminoacyl nitrogen, and coordination of halide ion to the vacant Rh(II1) site (Scheme I)??' Further evidence for the facile insertion of the isocyanide into a rhodiumtolyl bond was obtained by treating a 0.025 M soIution of 2b with 1 equiv of PMe3 at room temperature. An immediate reaction produces the iminoacyl species [C5(CH3)5IRh[WCH3)31[C(p-C6H4CH3)NCH2C(CH3)31Br, 4, identified on the basis of its NMR, IR, mass spectrum and elemental analysis.s Reduction of IC with 0.47% Na/Hg in 2:l THF/benzene (v:v) or with sodium napthalide in THF produces a deep blue solution from which dark blue crystals of a complex assigned structure 5 are ~ b t a i n e d . ~
fN
t
Similar reductions of la and l b lead to decomposition. However, reduction of IC in the presence of excess CNCH2(CH3)3leads to the mononuclear complex [C5(CH3),]6, obtained as air-sensitive red-orange Rh[CNCH2(CH3)3]2, crystals in >85% isolated yield after recrystallization from hexane at -78 OC.l0
Compound 6 is stable to thermolysis in C6D6at 200 "C for 3 h. However, UV irradiation of 6 in C6D6results in the formation of traces ( N 1%) of the imine C6D5CD=NCH2C(CH3),at the expense of 6. Irradiation of 6 in the presence of 2 equiv of CNCH2(CH3),increases the yield of imine to 26% (GC) as all of 6 is consumed (eq 1). lH NMR and mass spectral analysis of the imine reveals a 1:l ratio of d, and d6 imine.
The detailed fate of the metal in these irradiations is not exactly known, but we suspect that a photoprocess in which the C5(CH3),ring is cleaved from the metal is occurring. The isolation of 2,3,4,5-tetramethylful~ene~~ and Rh2[CNCH2C(CH3)3]6:37, from the photolysis solution in yields similar to that of the imine supports this hypothesis. Other workers have also proposed a decrease in hapticity of q5-coordinatedcyclopentadienyl rings upon irradiati~n.'~ A possible mechanism accounting for these observations is shown in Scheme 11. Simple loss of isocyanide followed by oxidative addition of a benzene C-D bond does not appear to be occurring here. Irradiation of 6 in toluene produces a 2:l mixture of the meta- and para-methylsubstituted imines in low yield ( N 1 %), consistent with a step involving arene C-H oxidative addition to a low valent metal center.', Further work investigating the chemistry of complex 7 and its role in C-H bond activation is under way.
Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American (5) For the chloro derivative [Cs(CH3)s]Rh[CNCHzC(CH3)3](p-Chemical Society, and to the Camille and Henry Dreyfus CeH4CH3)Cl,2a: 'H NMR (CDCld 6 1.555 (s, 15 H), 0.629 (s,9 H), 2.489 Foundation for support of this research. We also wish to (a, 2 H), 2.289 (s, 3 H), 7.059 (d, J = 8 Hz, 2 H), 7.787 (d, J = 8 Hz, 2 H); thank Johnson Matthey, Inc., for a generous loan of rhoIR (THF) 2180 cm-'. In contrast to Adams studies: we do not observe dium trichloride. an $-iminoacyl species.
(6) Cf. Adams, R. D.; Chodosh, D. F. J. Am. Chem. SOC. 1982, 99, 6544-6550. (7) For 3a: 'H NMR (CDCl,) 6 0.939 ( s , 9 H) 1.371 ( 8 , 15 H), 2.406 ( 8 , 3 H), 3.192 (d, J = 6 Hz, 2 H), 7.224 (d, J = 8 Hz, 2 H), 7.307 (d, J = 8 Hz, 2 H), 11.389 (br s, 1 H) (coupled to 6 3.192 resonance); IR (CHCl,) 3155 (m), 1573 (s), 1562 (ah) cm-'. Anal. Calcd for C23H&lzNRh C, 55.43; H, 6.82; N, 2.81. Found: C, 54.99; H, 6.98; N, 2.86. For 3b: 'H NMR (CeDe)6 0.787 (a, 9 H), 1.293 (s, 15 H), 2.035 (s, 3 H), 2.838 (d, J = 6 Hz, 2 H), 6.903 (d, J = 8 Hz, 2 H), 7.377 (d, J = 8 Hz, 2 H), 11.625 (br s, 1 H) (coupled to 6 2.838 resonance); I3C NMR (CDCl3) 6 9.35 (q, J = 129.0 Hz), 21.19 (q, J = 126.7 Hz), 27.68 (q, J = 123.8 Hz), 32.30 (s), 61.74 (t, J = 145.0 Hz), 97.89 (d, J = 6.6 Hz), 124.72 (d, J = 160.8 Hz), d 128.21 (d, J = 158.2 Hz), 138.74 (s), 139.77 (s), 233.84 (d, J = 39.7 Hz); IR (CHCl,) 3160 (m), 1568 (sh), 1558 ( 8 ) cm-'; mans spectrum (75 eV), m/e 585, 587, 589 (M+).Anal. Calcd for CZ3HaBr2NRh C, 47.04; H, 5.84; N, 2.39. Found C, 46.87; H, 5.82; N, 2.45. An X-ray structure determination of 3a is in progress. (8) For 4 'H NMR (CeDe) d 1.056 (8, 9 H), 1.346 (dd, J 11, 1 Hz, 9 H), 1.583 (d, J = 3 Hz, 15 H), 2.144 ( 8 , 3 H), 2.961 (dd, J = 14, 3 Hz, 1 H), 3.347 (d, J = 14 Hz, 1 H); 7.120 (d, J = 8 Hz, 2 H), 61962 (d, J = 8 Hz. 2 H): IR ITHF) 1560 cm-': mans mectrum (75 eV). m/e 505. 507 (M+ 76):' An&. Cdcd for Cz6HilzBrNPRh:C, 53.61; H; 7.27; N, 2.42. N. -Foiind: C. -, 63.91: - - ._- , -H. -, 7.49: . . .- , . ., 2.36. (9) For 5: 'H NMR (c6Dd 8 1.259 (a, 18 H),1.663 (8, 30 H), 4.178 ( 8 , 4 H); 13C NMR (CDCI,) 6 11.31 (q, J 126 Hz), 28.31 (q, J = 127 Hz), 32.73 (s), 68.70 (t, J = 128 Hz), 100.14 (s), 234.95 (t, J = 53 Hz); IR (THF) 1690 cm-'. A structurally similar complex, CpzRhz(CO)z, has been reported Nutton, A.; Maitlis, P. M. J. Organomet. Chem. 1979, 166, c21-c22. (10) For 6: 'H NMR (C6D6)6 0.805 ( 8 , 18 H), 2.234 ( 8 , 15 H), 2.803 (d, J 1 Hz, 4 H); 13C NMR (CDC13) 6 11.84 (q, J 125 Hz), 26.73 (q, J = 127 Hz), 32.24 (s), 56.51 (t, J = 128 Hz), 97.66 (s), 166.92 (d, J = 82 Hz). IR (KBr) 2073(s), 1977(m) cm-'; mans spectrum (75 eV), m / e 432 (M+). Traces of 6 are also produced in the reductions of la, lb, and IC in the absence of added isocyanide.
Registry No. la, 85028-72-4; lb, 85028-73-5; IC, 85028-74-6; 2a, 85028-76-8; 2b, 85028-75-7; 3a, 85028-77-9; 3b, 85028-78-0; 4, 85028-79-1; 5, 85028-80-4; 6, 85028-81-5; 7, 85028-82-6; ( [C5(CH3),IRhC1)2(~-C1)2, 12354-85-7; ( [ C5CH3)5]RhBr)Z(p-Br)Z, 36484-11-4; ( [C,(CH,),]RhI)2(p-I)2, 67841-74-1; CBD&D=NCHZC(CH&,, 85028-83-7; CBD&H=NCHzC(CH3)3, 85028-84-8; 2,3,4,5-tetramethylfulveneP76089-59-3. (11)The imine wan identified by gas chromatographic coinjection with in. 5% SE-30/Chromosorb WAW an authentic sample on a 10 f t X column (125 "C, 20 mL/min), by ita mass spectrum (75 eV, m / e 180,lal), and by ita 'H NMR spectrum ((c&) 6 1.021 (s,9 H), 3.244 (a, 2 H), 7.999 (br s,0.5 H)). Irradiations were performed with a 500-W Hanovia lamp (no. 679A10) filtered through quartz at a distance of 15 cm. An air jet maintained the sample at 25 "C ( i 5 "C). (12) Identified by 'H NMR ((C6D6)6 1.683 ( 8 , 6 H), 1.845 (a, 6 H), 5.337 (s,2 H) and mass spectroscopy (75 eV, m / e 134) and by gas chromatographic coinjection with an authentic sample. (13) Rhz[CNCH2C(CH3)3]e can be recrystalliied from benzene/hexane: H NMR (C&) 6 2.529 (8, 4 H), 2.472 (a, 8 H), 0.694 (s, 36 H), 0.678 (s, 18 H); IR (KBr) 2214 (m), 2156 (vs), 2015 ( 8 ) cm-'. Traces of added isocyanide scramble the isocyanide resonances on the NMR time scale. The related palladium derivative [Pd2(CNR)6]2+has been reported Doonan, D. J.; Balch, A. L.; Goldberg, S. Z.; Eisenberg, R.; Miller, J. S. J.Am. Chem. SOC. 1975,97, 1961-1962. Goldberg, S. Z.; Eisenberg, R. Inorg. Chem. 1976,15,535-541. (14) Crichton, 0.;Rest, A. J.; Taylor, D. J. J. Chem. SOC.,Dalton Trans. 1980,167-173. Green, M. L. H. Pure Appl. Chem. 1978,50,27-35. (15) Cf. Jones, W. D.; Feher, F. J. J . Am. Chem. SOC.1982, 104, 4240-4242. Tolman, C. A.; Ittel, S.D.; English, A. D.; Jesson, J. P. Ibid. 1979,101, 1742-1751.
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