3996
Organometallics 1996, 14, 3996-4003
Os(C0)4(q2-C2Me2)-PromotedCoupling of Alkynes and CO: Formation of (q4-C4Me2R2CO)Os(CO)3(R = Me, Et, nPr)and Catalytic Activity of (q4-C4R&O)Os(CO)3 (R = Me, Ph) John Washington, Robert McDonald,: and Josef Takats" Department of Chemistry and Structure Determination Laboratory, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Naim Menashe, Dvora Reshef, and Youval Shvo" School of Chemistry, Raymond and Beverly Sackler School of Exact Sciences, Tel Aviv University, Tel Aviv, Israel 69978 Received May 9, 1995@ Low-temperature photolysis of OS(CO)~ in the presence of excess 2-butyne gives os(Co)4(y2-C2Me2)(1)in moderate yield. Complex 1 undergoes facile alkyne-CO coupling with a n additional alkyne ligand under mild thermal activation to give the cyclopentadienonecontaining species (r4-C4Me2R2CO)Os(CO)3 (R = Me (2a),E t (2d),"Pr (2e)). Isolation of the alkyne-carbonyl complex is not necessary to effect the transformation; in situ generated M(C0)4(y2-C2R2)provides a convenient method for the synthesis of (q4-C4R4CO)M(C0)3(M = Ru, Os; R = Me, Et, "Pr). On the basis of these observations, the proposed mechanisms for the formation of (q4-C4R4CO)M(C0)3 complexes are discussed and evaluated. The solidstate structure of 2d was determined and compared to the tetraphenyl analogue, (q4-C4Ph4CO)Os(CO)3 (4). Compound 2d crystallizes in the monoclinic space group P21/c with a = 8.336(1) A, b = 15.334(2) c = 12.849(2) /3 = 108.78(2)", 2 = 4,R = 0.040, and R, = 0.046. The use of 2a and 4 a s catalyst precursors for both Tishchenko and hydrogenation reactions was investigated and compared to the analogous ruthenium complex (q4-C4Ph4CO)Ru(C0)3.
A,
A,
Introduction The concept of alkyne coupling at a transition metal center is well documented in the 1iterature.l Hubel contributed much to the early work in the field, studying the reactions of alkynes with iron carbonyl compounds.1a~2 The reactions are complex and yield a myriad of products, with an often isolated component the wellknown (cyc1opentadienone)tricarbonyliron complexes, (r4-CPD)Fe(C0)3 (CPD = substituted cyclopentadie n ~ n e ) . Recent ~ ? ~ interest in CPD complexes has been heightened by the discovery that (v4-C4Ph4C0)Ru(C0)3 is a useful catalyst precursor for a number of organic '' To whom inquiries regarding X-ray crystallographic results should be made. Abstract published in Advance ACS Abstracts, June 15, 1995. (1)(a) Hiibel, W. Organic Syntheses uia Metal Carbonyls; Wender, I., Pino, P., Eds.; Wiley: New York; 1968;p 273. (b) Schore, N. E. Chem. Reu. 1988,88,1081. (cj Efraty, A. Chem. Reu. 1977,7,691.(dj Nicholas, K.M.; Nestle, M. 0.;Seyferth, D. Transition Metal Organometallics in Organic Synthesis, Alper, H., Ed.; Academic Press: New York; 1978; Vol. 2, Chapter 1. (e) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.; Wiley: New York; 1992;Chapter 8. (DDavidson, D. L. Reactions of Coordinated Ligands; Braterman, P. S., Ed.; Plenum Press: New York, 1986;pp 825-895. (g) Winter, M. J. The Chemistry ofthe Metal-Carbon Bond; Hartley, F. R., Patai, S., Eds.; Wiley: New York, 1985;Vol. 3, Chapter 5. (h) Otsuka, S.; Nakamura, A. Adu. Organomet. Chem. 1975,14, 245. (2)(a)Hiibel, W.; Braye, B. H. J . Inorg. Nucl. Chem. 1969,10,250. (b)Hiibel, W.; Braye, E. H.; Clauss, A.; Weiss, E.; Kriierke, D.; Brown, D. A.; King, G. S. D.; Hoogzand, C. J . Inorg. Nucl. Chem. 1959,9,204. (3)(a) Formals, D.; Pericas, M. A,; Serratosa, F.; Vinaixa, J.; FontAltaba, M.; Solans, X. J . Chem. SOC.,Perkin Trans. I 1987,2749. (b) Krespan, C.G. J . Org. Chem. 1975,40, 261. (cj Boston, J. L.; Sharp, D. W. A.; Wilkinson, G. J . Chem. SOC.1962,3488. (d) Wilcox, C.; Breslow, R. Tetrahedron Lett. 1980,3241.
transformation^,^ and in conjunction with the work of Pearson on the reactions of Fe(C015 with ~ , o - d i y n e s . ~ The presence of Fe(C0)4(v2-RCCR)species along the reaction pathway to (v4-CPD)Fe(C0)3complexes has been postulated. However, these intermediates have not been detected, much less isolated. Indeed, although we have reported6 a convenient synthesis for several M(C0)4(v2-C2R2)(M = Ru, Os; R = H, CF3, SiMe3) species, only one iron analogue, the bis(trimethylsily1)acetylene derivative Fe(C0)4{v2-C2(SiMe&),is The Ru and Os complexes undergo interesting addition reactions with nucleophilic metal centers,6a-b,8yet no facile alkyne coupling reactions have been observed with these species. Here, we report the synthesis of Os(C0)4(y2-C2Me2) (1) and its reaction with electron-rich alkynes to yield (v4-CPD)Os(C0)3 complexes. In addition, a general (4)( a )Abed, M.; Goldbeg, Z.; Shvo, Y. Organometallics 1988,7,2054. (b)Shvo, Y.; Czarkie, D. J . Organomet. Chem. 1989,368,357.(c)Blum, Y.; Shvo, Y. Isr. J . Chem. 1984,24, 144. (d) Shvo, Y.; Czarkie, D.; Rahamim, Y. J . A m . Chem. SOC.1986,108,7400.(e)Shvo, Y.; Czarkie, D. J . Organomet. Chem. 1986,315,C25. (0 Menashe, N.; Shvo, Y. Organometallics 1991,10, 3885. (5)( a )Pearson, A. J.; Shively, R. J. Organometallics 1994,13,578. (b)Pearson, A. J.; Shively, R. J.;Dubbert, R. A. Organometallics 1992, 11, 4096. ( c ) Pearson, A. J.; Dubbert, R. A. J . Chem. Soc., Chem. Commun. 1991,202. (6)( a ) Burn, M.J.; Kiel, G.-Y.; Seils, F.; Takats, J.; Washington, J. J . A m . Chem. SOC.1989,111, 6850. (b) Gagne, M. R.; Takats, J. Organometallics 1988,7 , 561. ( c ) Ball, R. G.; Burke, M. R.; Takats, J. Organometallics 1987,6, 1918. (7)Pannell, K.H.; Crawford, G. M. J . Coord. Chem. 1973,2,251. (8)Takats, J.;Washington, J.;Santarsiero, B. Organometallics 1994, 13,1078.
0276-733319512314-3996$09.00/0 0 1995 American Chemical Society
(r4-C4Me2R&O) Os(C0)s method utilizing in situ generated M(C0)4(r2-C2R2)for the synthesis of a number of (r4-C4R4CO)M(C0)3(M = Ru, Os; R = Me, Et, nPr)compounds is presented. The solid-state X-ray structure of (y4-C4Me2Et2CO)Os(CO)3 (2d) was determined and a comparison made to the related (r4-C4Ph4CO)Os(C0)3 (4). In addition, 2a and 4 were evaluated as possible catalyst precursors in both Tishchenko and hydrogenation reactions, and the results of these studies are reported.
Experimental Section General Procedures. All synthetic procedures were carried out under purified nitrogen or argon atmospheres using standard Schlenk techniques. Pentane was stirred over concentrated HzS04 for several cycles, then washed with distilled water, and finally dried over sodium sulfate before distillation from CaH2. Other solvents were distilled before use from appropriate drying agents. 2-Butyne, 3-hexyne, and 4-octyne were purchased from Aldrich Chemical Co. and used without further purification. R U ~ ( C O )and I Z ~OS3(C0)1zgb ~ were prepared by published procedures as were (q4-C4Ph&O)Ru(C0)31°a and (q4-C4Ph4CO)Os(C0)3.'ObSlight modifications were made to the reported procedures for the synthesis of Ru(CO)511aand O S ( C O ) ~Specifically, .~~~ Ru(CO)S was prepared by external photolysis (1 2 370 nm) of a pentane suspension of R u ~ ( C O )under ~ Z > 1 atm of CO. Also, in a typical experiment, 2.02 g of O S ~ ( C Owas ) ~ ~ placed in a high-pressure autoclave under 200 atm of CO and heated to 280 "C for 9 h. The yield of OS(CO)~ was 0.87 g along with 1.05 g of recovered Os3(CO)12. The catalytic studies were carried out at Tel Aviv University, Tel Aviv, Israel. Infrared spectra were recorded on Bomem MB-100 or Nicolet 205 Fourier transform spectrometers over the range 2200-1600 cm-'. NMR tubes were septa sealed under an inert atmosphere. The NMR spectra were collected on Bruker WP-400, WM-360, or WH-200 spectrometers. The mass spectra were obtained on AEI-12 (EI, 16 eV) or VG AUTOSPEC M-250 (FAB,35 KV) mass spectrometers. Elemental analyses were carried out by the Microanalytical Laboratory at the University of Alberta (Department of Chemistry) or at The Hebrew University, Jerusalem, Israel. Preparation of 0~(CO)~(q~-CzMed (1). A 100 mL immersion well fitted with a GWV (Glaswerk Vertheim, 2 2 370 nm) cut-off filter was charged with a pentane solution containing os(co)5 (127.0 mg, 0.385 mmol) and excess 2-butyne (1.0 mL). The temperature of the solution was maintained at -60 "C with a Lauda Klein-Kryomat circulating bath. The solution was photolyzed using a Philips HPK 125 W mercury vapor lamp, and the reaction was monitored using FT-IR spectroscopy. The reaction was complete in ca. 2 h after which time no O s ( c 0 ) ~( Y C O 2035, 1994 cm-'1 was present. An infrared spectrum taken at this time shows only bands due to (q4-C4Me&O)Os(CO)s (2a) ( V C O 2071, 2006, 1988 cm-'; VC-o 1676 cm-') as a result of a facile thermal reaction between os(co)4(q2-C2Me2) (1)and excess 2-butyne. The characterization of 1 is possible once excess alkyne is removed (vide infra). The solution was transferred by cannula to a flask precooled to -78 "C. The solvent and excess 2-butyne were removed in vacuo at -78 "C, and the product, Os(C0)4(q2-C2Mez) (1) was sublimed at ca. -20 "C to a dry ice cooled probe. The white, waxy solid was washed off the cold finger with cold pentane t o yield a thermally sensitive, colorless solution. A yield of (9)(a)Bruce, M. I.; Jensen, C. M.; Jones, N. L. Inorg. Synth. 1989, 26, 259. (b) Johnson, B. F. G.; Lewis, J.; Kilty, P. A. J . Chem. SOC.A 1968, 2859. (10)(a) Bruce, M. I.; Knight, J. R. J . Organomet. Chem. 1968,12, 411. (b) Burke, M.; Funk, T.; Takats, J. Organometallics 1994,13, 2109. (11)(a) Johnson, B. F. G.; Lewis, J.; Twigg, M. V. J. Organomet. Chem. 1974,67,C75. (b) Rushman, P.; van Buuren, G. N.; Shiralian, M.; Pomeroy, R. K. Organometallics 1983,2, 693.
Organometallics, Vol. 14,No. 8,1995 3997 Table 1. Mass Spectral Data ( d e ) and Elemental Analyses (%) for Complexes 2,3, 7, and 8 mass spectrum (EI,16 eVP compd M+ 2a
2b 2~
2d 2e 3a 3b 3~ 7
8 a
412 468 524 440 468 322 378 434 126F 633c
%*
M+-nCO
90.7 43.6 36.9 23.4 62.8 24.8 29.6 24.5 100 45
0-4 0-4 0-4 0-4 0-4 0-4 0-4 0-4
found
calcd
formula
C
H
C12H1~040s 35.12 2.95 Ci6H20040S 41.19 4.32 CzoHzs040~ 45.96 5.40 CidH16040S 38.34 3.68 C16Hz0040s 41.19 4.32 ClzH1204Ru 44.86 3.76 C ~ ~ H ~ O O50.92 ~RU 5.34 CzoHzs04Ru 55.41 6.51 C62H4006OS2 59.05 3.17 C3iH22030~ 58.84 3.48
C
H
35.28 41.30 46.23 38.33 41.27 45.15 50.91 55.57 58.86 59.17
2.68 4.42 5.12 3.60 4.14 3.60 5.43 6.68 2.99 3.52
130-180 "C. b Relative intensity. FAB, 35 KV, M+ - H.
61% (82.3 mg, 0.231 mmol) was obtained based upon titration with Cp*Rh(CO)z. In further reactions absorption coefficients (€1 of the two strong terminal carbonyl bands were used to prepare pentane solutions of Os(C0)4(q2-CzMez)of known concentration. MS (ca. -20 "C, 16 eV) [ m l e (abundance)]: M+ (358, 17.2%),M+ - CzMez (304, 1.3%),M+ - nCO (n = 0-4). IR (pentane, cm-'): v(C0) 2106 (w), 2020 (vs) ( E = 7.9 x lo3 M-'*cm-'), 1988 (m) ( E = 5.0 x lo3 M-km-'). 'H NMR (400 MHz, toluene-&, -70 "C, 6): 2.03 (CH3). I3C NMR (100.6 MHz, toluene-&, -70 "C, 6): 69.7 (C-CH3), 14.8 (CH3). Elemental analysis of this thermally sensitive compound could not be obtained. Preparation of (q4-CPD)M(C0)3 Compounds. The mass spectral data and elemental analyses for compounds 2-3 are listed in Table 1;IR and selected 13CNMR data are collected in Table 4. The designation "inner" and "outer" refers to the following diagram:
For 2-3, NMR spectra were recorded in CDC13 at 23 "C with the IH NMR spectra acquired at 360 MHz and the NMR spectra obtained at 90.5 MHz. (q4-C&le4CO)Os(CO)3(2a). (a) Using Isolated Os(CO)4(q2-C2Med (1). A round-bottomed flask, precooled to -78 "C, was charged with a pentane solution containing 78.0 mg (0.219 mmol) of Os(C0)4(q2-CzMez)(1). An excess of 2-butyne (0.5 mL, 6.38 mmol) was added via syringe and the flask transferred to an ice bath. The solution was stirred at low temperature for 1 h and then a t room temperature for an additional 0.5 h. The solvent and excess alkyne were removed in vacuo and the solid material extracted with pentane (2 x 10 mL). The volume of solvent was reduced to ca. 10 mL and the solution cooled to -80 "C. The off-white, air stable precipitate was isolated and washed with 3 mL of cold pentane; the yield was 73.3 mg. Concentration of the mother liquor followed by crystallization at -80 "C gave an additional 3.9 mg of 2a for a total yield of 77.2 mg (0.188 mmol, 86%). 'H NMR NMR (6): 2.35 (6H, S, i-CH3), 1.92 (6H, S, O-CH3). (6): 10.1 (i-CH31, 8.9 (o-CH~). (b) Using in Situ Generated Os(CO)4(q2-C2Me2) (1). A pentane solution containing O s ( c 0 ) (88.0 ~ mg, 0.266 mmol) and excess 2-butyne (0.5 mL) was photolyzed (1 z 370 nm, -60 "C) until no IR bands due to Os(c0)s were visible (ca. 2 h). The solution was transferred from the immersion well t o a flask at 0 "C and stirred for 1 h. The solvent and 2-butyne were removed in vacuo, and the solid product was extracted with pentane (2 x 10 mL). The filtered extracts were combined and the volume reduced using an Ar stream until precipitation occurred. A small volume of pentane was then added to redissolve the precipitate and the solution placed in a -80 "C freezer overnight. The resulting off-white solid was
3998 Organometallics,
Vol.14,No.8,1995
Washington et al.
Table 2. Summary of Crystallographic Data for isolated and washed (2 x 5 mb) with cold pentane. The yield 2d of (q4-C4Me4CO)Os(C0)3(2a) was 60% (65.6 mg, 0.160 mmol) based on os(co)5. formula C14H16040S (q4-C4Et4CO)Os(C0)3(2b). Using method b, Os(CO)5(76.5 fw 438.48 mg, 0.232 mmol) and 3-hexyne (0.5 mL) gave (q4-C4Et4CO)cryst size, mm 0.29 x 0.21 x 0.05 cryst system monoclinic Os(CO)3 (2b) in 56% yield (61.1 mg, 0.131 mmol). 'H NMR space group P21lc (6): 2.53 (4H, m, i-CHzCH3),2.31 (2H, m, o-CH~CH~), 1.94 (2H, 8.336(1) a, A NMR ( 6 ) : 18.7 m, o - C H ~ C H ~1.19 ) , (12H, m, CH2CH3). b, 8, 15.334(2) (i-CHzCH31, 18.3 ( o - C H ~ C H ~16.8 ) , (i-CHzCH31, 16.4 (0c, A 12.849(2) CH2CH3). I%deg 108.78(2) (q4-C4nPr4CO)Os(CO)s(2c). Using method b, o s ( c o ) 5 v, A3 1555.0 (72.8 mg, 0.220 mmol) and 4-octyne (0.5 mL) gave (q4-ChnPr4z 4 CO)Os(CO)3(2c)in 83% yield (95.2 mg, 0.182 mmol). 'H NMR temp, "C 21 Deale,g c m 4 1.873 ( 6 ) : 2.43 (4H, m, i-CH2CH2CH31,2.19 (2H, m, o - C H ~ C H ~ C H ~ ) , p , cm-1 82.17 1.82 (2H, m, o - C H ~ C H ~ C H1.79 ~ ) ,(2H, m, i-CH2CH&H3), 1.52 radiation (A) i, Mo Ka (0.710 73) (2H, m, i-CH2CH2CH3), 1.46 (2H, m, O - C H ~ C H ~ C1.22 H ~ (2H, , reflcns measd 2849 (&h,k,L) m, o - C H ~ C H ~ C H1.01 ~ ) , (6H, m, i-CH2CHzCH31, 0.98 (6H, m, 1528 with I > 3 d I ) reflcns used o - C H ~ C H ~ C HI3C ~ ) .NMR ( 6 ) : 27.8 (i-CHzCH2CH3), 27.7 (0variables 172 CH&H2CH3),25.9 (i-CHzCH2CH3),25.5 (o-CH~CH~CH~), 14.8 R" 0.040 (i-CH2CH2CH31,14.7 ( o - C H ~ C H ~ C H ~ ) . Rwb 0.046 (q4-C&le2Et2CO)Os(CO)3(2d). Using method a, OS(CO)~R = C l F o l - IFCIIEIFOI. Rw = (Cw(lFOI- lFc/)2E~Fo2)1'2. (T~~-C~ (20.3 M ~mg, Z ) 0.057 mmol) and 3-hexyne (0.5 mL) gave (q4-C4Me2Et2CO)Os(C0)3(2d) in 78% yield (19.4 mg, 0.044 at -50 "C, and the solution was photolyzed using a Philips mmol). 'H NMR (6): 2.52 (2H, m, i-CH2CH3), 2.36 (3H, s, HPK 125 W mercury vapor lamp. The reaction was complete i-CH3), 2.31 ( l H , m, o-CHZCH~), 2.02 ( l H , m, o - C H ~ C H ~1.94 ), in ca. 1.5 h after which time only bands due to OS(CO)~(?]~NMR (6): 18.7 (i(3H, s, o-CH~),1.15 (6H, m, CHzCH3). CH2CH3), 18.1(o-CH~CH~), 16.8 (i-CHzCH3),15.5 (o-CH~CH~), C2Ph2) (YCO 2117, 2037, 2024, 1991 cm-l) were present. The solution was transferred from the immersion well and filtered, 10.1 (i-CH3), 9.1 (O-CH3). at low temperature, to a precooled (-78 "C) flask. The pentane (q4-C&le2"Pr&O)Os(C0)3(2e). Using method a, OS(CO)~was removed at -50 "C, and the residue was redissolved in a (q2-C2Me2)(34.4 mg, 0.097 mmol) and 4-octyne (0.5 mL) gave hexane solution containing additional (91.4 mg, 0.513 mmol) (q4-C4Me2"Pr2CO)Os(C0)3(2e) in 69% yield (31.1 mg, 0.067 diphenylacetylene. The resulting solution was warmed to mmol). 'H NMR (6): 2.46 (2H, m, i-CHzCH&H3), 2.35 (3H, room temperature. After 4 h only minimal amounts of (q4-C4s, i-CH31, 2.19 (lH, m, O-CH~CH~CHS), 1.92 (3H, s, O-C&), 1.89 Ph&O)Os(CO)a (4) were detected by FT-IR spectroscopy. The (lH, m, o - C H ~ C H ~ C H1.72 ~ ) , (lH, m, i-CH2CH&H3), 1.51 ( l H , complete preparation and characterization of Os(CO)4(q2-C2m, i-CH2CHzCH3), 1.48 ( l H , m, O - C H ~ C H ~ C1.27 H ~ ,( l H , m, Ph2) will be detailed in a forthcoming publication. o - C H ~ C H ~ C H1.00 ~ ) , (3H, m, i-CH&HzCH3), 0.97 (3H, m, o - C H ~ C H ~ C H ~ ) .NMR ( 6 ) : 27.7 (L-CH~CHZCH~), 27.5 (0Preparation of (Tetraphenylcyclopentadieny1)osmium CH~CH~CHS), 25.9 (i-CH2CHzCH3),24.5 ( o - C H ~ C H ~ C H 14.8 ~), Complexes. The mass spectral data and elemental analyses (i-CH&H2CH3), 14.3 (o-CH~CH~CH~), 10.5 (i-CH3),9.1 (O-CH3). for compounds 7 and 8 are listed in Table 1. The IR and 'H Preparation of (q4-CPD)Ru(C0)3Compounds. Due to and NMR data for 7 and 8, along with the data for 5 and the instability of Ru(C0)4(q2-C2R2),complexes 3a-c were 6,are listed in Table 6. prepared exclusively via the in situ method b. (q5-C4Ph40)2(lr-H)20s2(C0)4 (7). A solution containing (q4(q4-C&le4C0)Ru(C0)3 (3a). The immersion well was C4Ph&O)Os(C0)3 (4) (140 mg, 0.212 mmol), sodium carbonate maintained at -5 "C, and Ru(C0)s(82.1 mg, 0.340 mmol) and (300 mg), and water (1.0 mL) in THF (20 mL) was heated in excess 2-butyne (0.5 mL) gave (q4-C4Me4CO)Ru(C0)3(3a) in a closed bomb under nitrogen a t 110 "C for 4 h. After cooling, 29% yield (31.3 mg, 0.097 mmol). lH NMR ( 6 ) : 2.13 (6H, s, the solvent was removed in uacuo and the residue extracted i-CH3), 1.87 (6H, S, O-CH3). 13C NMR ( 6 ) : 10.8 (i-CH3), 9.3 with methylene chloride. Following drying (MgS04) and (O-CH3). evaporation, the residue was chromatographed on a silica (q4-C4Et4CO)Ru(CO)3(3b). The immersion well was column, using CHzClz-petroleum ether (3:l) as eluant, to give maintained at -60 "C, and Ru(C0)5 (93.0 mg, 0.386 mmol) 7 as yellow platelets in 19% yield (25.0 mg, 0.020 mmol), mp and 3-hexyne (0.5 mL) gave ( T ~ ~ - C ~ E ~ ~ C O ) (3b) R U (inC53% O)~ 270-277 "C (dec). The second complex eluted (75 mg, 56%) yield (77.3 mg, 0.204 mmol). 'H NMR (6): 2.44 (4H, m, i-CHz), was found to be identical with 8. 2.30 (2H, m, o-CH~),1.98 (2H, m, o-CH~), 1.19 (6H, m, i-CH3), (qS-C4Ph&OH)Os(C0)2H (8). A solution containing (q41.16 (6H, m, O - C H 3 ) . 13C NMR ( 6 ) : 19.1 (i-CH2CH3), 17.6 (oC*Ph&O)Os(C0)3 (4) (70 mg, 0.106 mmol), sodium carbonate CH2CH3), 16.9 (i-CHzCH3), 15.7 (o-CH~CH~). (150 mg), and water (0.5 mL) in THF (10 mL) was heated in (q4-C4"Pr4CO)Ru(CO)3(3c). The immersion well was a closed bomb under nitrogen at 110 "C for 1h. After cooling, maintained at -60 "C, and Ru(CO)5 (91.1 mg, 0.378 mmol) the solvent was removed in uacuo and the residue extracted and 4-octyne (0.5 mL) gave (q4-C4"Pr4CO)Ru(CO)3 (3c) in 63% with methylene chloride, which, after drying (MgS04) and yield (103.4 mg, 0.238 mmol). 'H NMR (6): 2.34 (4H, m, i-CH2evaporation, was chromatographed on a silica column (CHzCHzCHd, 2.15 (2H, m, o - C H ~ C H ~ C H1.85 ~ ) , (2H, m, o-CH2Cl2 eluant). Complex 8 was recovered as a white solid in 83% CHzCHd, 1.78 (2H, m, i-CH2CH2CH31, 1.53 (2H, m, i-CH2CH2yield (56 mg, 0.088 mmol) which gave a single TLC spot CHd, 1.46 (2H, m, o-CH~CH~CH~), 1.28 (2H, m, o-CH2CH2CH3), (silica-methylene chloride), mp 200 "C (dec). 1.01 (6H, m, i-CH2CH2CH31, 0.98 (6H, m, o - C H ~ C H ~ C H13C ~). X-ray Crystal Structure Analysis of (q4-C4Me&t2CO)NMR (6): 28.3 (i-CH2CH&H3), 27.1 ( o - C H ~ C H ~ C H 26.1 ~ ) ,(iCH2CH&H3),24.9 ( o - C H ~ C H ~ C H 14.8 ~ ) ,(i-CH&H2CH3), 14.7 os(co)3(2d). A colorless, X-ray-quality crystal of 2d, grown (o-CH~CH~CH~). by cooling a hexane solution of 2d to -5 "C, was mounted on the goniometer of a Enraf-Nonius CAD4 diffractometer. The Generation of Os(C0)4(q2-CzPh2)and Attempted Thercrystal data and general conditions of data collection and mal Reaction with C2Ph2. A 100 mL immersion well fitted structure refinement are given in Table 2. Three intensity Iz 370 nm) cut-off filter with a GWV (Glaswerk Vertheim, , was charged with a pentane solution containing OS(CO)~ (90.0 and orientation standards were checked after every 120 min mg, 0.273 mmol) and excess diphenylacetylene (155.0 mg, of exposure time and showed no appreciable decay. The 0.870 mmol). The temperature of the solution was maintained position of the Os atom was determined using the direct
Organometallics, Vol. 14, No. 8, 1995 3999
(~4-C&fe~R&O)OsCCO)3 Table 3. Positional ( x 10s) and Isotropic Thermal ( x 102) Parameters"for Non-Hydrogen Atoms of 2d atom
os 01 06 07 08
c1
c2 c3 c4 c5 C6 c7 C8 C11 C21 C31 C32 C41 C42
X
Y
z
u,A2
52.72(6) 53( 1) 28(2) 34% 1) -230(1) -88(1) -40(2) 145(2) 199(1) 57(1) 44(2) 228(2) -120(2) -269(2) -154(2) 253(2) 296(2) 378(2) 422(2)
-329.64(4) -174.5(6) -151.5(7) -393.7(9) -409.8(8) -304.6(7) -393.3(9) -394.4(9) -305.3(9) -249.5(8) -221.39)
-98.56(4) -300.2(7) -9(1) 95.4(9) -26.5(9) -274.6(9) -263(1) -220(1) -212(1) -268(1) -41(2) 24(1) -48(1) -326( 1) -298( 1) -20% 1) -309(1) - 185(1) -116(2)
4.73(1) 6.2(3) 11.8(6)
-371(1) -380(1) -273(1) -471(1) -474(1) -494(1) -276(1) -194( 1)
10.4(5) 10.0(5) 4.1(4) 6.1(53 6.0(5) 5.2(5) 4.7(4) 8.8(7) 7.6(6) 7.1(6) 7.6(6) 9.3(7) 9.2(7) 12.2(8) 10.1(8) 12.3(9)
Numbers in parentheses are the estimated standard deviations in the last significant digit. methods program SHELXS-86,12 and the remaining nonhydrogen atoms were located i n difference Fourier m a p s after l e a s t s q u a r e s refinement. Reflection data were corrected for absorption using t h e method of Walker and Stuart;13 t h e minimum and m a x i m u m correction coefficients were 0.5077 and 1.5019. All H a t o m s were included at their idealized positions (calculated by assuming C-H = 0.95 A and sp3 geometry) and constrained to "ride" w i t h the attached C atom. The H atom were assigned fixed, isotropic thermal parameters 1.2 times those of the p a r e n t C atom. T h e final atomic coordinates are given i n Table 3.
Results and Discussion Synthesis and Characterization of 0s(CO)4(q2C2Med (1). The synthesis of Os(C0)4(v2-C2Mez)is similar to that previously described for other osmiumalkyne compounds.6a-CSpecifically,excess 2-butyne and L 370 nm, -60 "C) to OS(CO)~were photolyzed (,I generate Os(C0)4(v2-C2Mez)(1) in moderate yield (eq 1). Low temperatures are required as 1 is thermally
1
The FT-IR spectrum of 1 in the carbonyl region shows three bands, a characteristic high-frequency, lowintensity band due to the symmetrical stretch of the axial carbonyls at 2106 cm-l and two strong bands at 2020 and 1984 cm-l. For Os(C0)4(y2-alkyne)complexes with CpUsymmetry, four terminal carbonyl bands are expected and often observed.6a-c In compound 1, the band at 2020 cm-l is likely comprised of two overlapping IR-active bands. The lH NMR and 13C NMR spectra for 1 in toluened8 (-70 "C) show methyl signals at 2.03 and 14.8 ppm, respectively, which are 0.50 and 11.6 ppm downfield of those of free 2-butyne. Coordination of an alkyne to a metal center reduces the C-C triple bond character of the alkyne, and this is usually reflected in a downfield 13C NMR shift of the coordinated alkyne carbons.14 Indeed, Templeton has reported an empirical relationship that correlates the number of electrons donated by an alkyne and its 13C NMR chemical shift.14" The 13C NMR results obtained for Os(C0)4(v2-C2Me2) are not in accord with these expectations as the alkyne carbons in 1 (6 = 69.7 ppm) are shifted upfield compared to those in free 2-butyne (6 = 74.6 ppm). However, within the series of Os(C0)4(v2-alkyne)complexes that we have prepared, there are precedents for such unusual results. For Os(CO)4(v2-C2(SiMe3)2), an upfield coordination shift is observed,6cand Os(C0)4(v2-HCCH)undergoes only a small downfield coordination shift of 1.6 ppm.6a The unusual 13C NMR chemical shifts may be related to a four-electron repulsive interaction between the coordinated alkyne and the d8 transition metal center.15 Thermal Reaction of M(C0)4(q2-C2R2) with Alkynes: Preparation of (q4-CPD)M(C0)3 (M = Os (21, Ru (3)). The observation that Os(C0)4(q2-C2Me2) reacts with alkynes was first noticed as an anomaly during infrared monitoring of the photochemical preparation of Os(C0)4(v2-C2Me2).As the reaction proceeded, only a decrease in the concentration of Os(COI5coupled with an increased concentration of a species with three strong terminal carbonyl bands was observed in the FTIR spectra at room temperature; bands due to 1 were not detected. Later it was discovered that a thermal reaction occurs in the IR cell between 1 and an additional molecule of 2-butyne to produce (v4-C4Me4CO)(2a). This was verified by deliberate reaction OS(CO)~ of 2-butyne with isolated 1 (eq 2). O S ( C O ) ~ ( T $ Q M ~ )+ CzMq 1
unstable and will decompose t o unidentified products at temperatures exceeding -25 "C. Owing to its unstable nature only spectroscopic data on 0s(CO)4(v2-C2Me2) were obtained. The mass spectrum of Os(C0)4(y2-C2Me2),obtained at ca. -20 "C, shows a peak due t o the molecular ion, Os(C0)4(v2-C2Me2)+, at 358 amu followed by signals due to the successive loss of four carbonyl ligands. The fragment Os(CO)4+is also observed, representing the loss of 2-butyne from 1. Similar observations were made in the mass spectra of Os(C0)4(v2-HCCH) and Os(C0)4(q2-C2(SiMe3)~}.6a,c (12)Sheldrick, G. M.SHELXS-86. A Program for Crystal Structure Determination. Institiit fur Anorganische Chemie der Universitat Gottingen, 1986. (13)Walker, N.;Stuart, D. Acta Crystallogr. 1983,A39, 158.
(q'-C~Me4CO)Os(CO~ (2) 2n
The spectral characteristics of 2a are in accord with previously reported (q4-CPD)M(C0)3c o m p o ~ n d s . ~ J ~ J ~ The IR spectrum consists of four carbonyl bands, three strong terminal carbonyl bands at 2071,2006, and 1988 cm-l and a weak signal at 1676 cm-' due to the ketonic carbonyl. In the lH NMR spectrum, two singlets of equal intensity are observed. Similarly, two 13C NMR resonances are observed for the methyl carbons. The (14) (a) Templeton, J . L. Adu. Organomet. Chem. 1989,29, 1. ib) Chisholm, M.H.; Clark, H. C.; Manzer, L. E.; Stothers, J. B. J . A m . Chem. SOC.1972,94,5087. (15) Marinelli, G.; Streib, W. E.; Huffman, J. C.; Caulton, K. G.; Gagne, M. R.; Takats, J.; Dartiguenave, M.; Chardon, C.; Jackson, S. A,; Eisenstein, 0. Polyhedron 1990,9,1867. (16)(a)Sappa, E.; Centini, G.; Gambino, 0.;Valle, M. J . Organomet. Chem. 1969,20,201. (b) Sears, C. T.; Stone, F. G. A. J . Organomet. Chem. 1968,11,644.
Washington et al.
4000 Organometallics, Vol. 14, No. 8, 1995
Table 4. FT-IR and
lSC
NMR Data for M(q4-C&CO)(CO)~ (M= Ru, Os) Complexes I3C NMR (23 “C, d, ppm)“
IR (pentane, cm-’) compd
V(C0)
2a 2b 2c 2d 2e 3a 3b 3c
2071 (s), 2006 ( s ) , 1988 (s) 2070 (s), 2004 (SI, 1987 (s) 2069 (s), 2004 (SI, 1987 (SI 2070 (SI, 2005 (SI, 1988 (s) 2071 (s), 2005 (SI, 1988 (SI 2073 (SI, 2016 (SI, 1996 (s) 2072 (s), 2015 (SI, 1996 (SI 2071 (SI, 2014 (SI, 1995 (s) 2079 ( s ) , 2015 (sj, 1997 (SI’
4h
v(C-0)
outer (C,j
inner (C,)
c=o
M(C0)
1676 (w) 1669 (w) 1669 (w) 1672 (wj 1673 (w) 1670 (w) 1663 (w) 1662 (w) 1677 (wIc
71.9 80.7 79.5 73.4,b 80.5‘ 73.0,b 79.2f 77.5 85.4 84.2 78.4
97.1 101.1 100.1 96.4: 101.4e 96.6: 100.3 101.2 105.6 104.6 102.0
175.7 177.0 177.3 175.2 176.4 175.4 176.3 176.3 173.9
176.1 175.4 175.4 175.2 175.6 196.0 195.6 195.7 173.6
Recorded at 90.5 MHz; chemical shifts relative to TMS in CDC13. “Inner” and “outer” refer to t h e carbon atoms that belong to the closed and oDen ends of the 1,3-dienes. C,-Me. C,-Et. d C,-Me. e C,-Et. fC,-”Pr. g C,-”Pr. Burke, M.; Funk, T.; Takats, J. Organometaliics 1994,13, 2109. Recorded in cyclohexane.
three terminal carbonyls give rise to a single 13C NMR resonance down to -60 “C, indicating rapid carbonyl group scrambling,17 consistent with previous work.lob Finally, two 13C NMR resonances are observed at 71.9 and 97.1 ppm which can be assigned to the CPD carbons and are in the region associated with coordinated dienetype s t r u c t u r e ~ . ~ ~ ~ J ~ J ~ The discovery of the facile alkyne coupling to produce (r4-C4Me4CO)Os(C0)3 led to the development of a general synthesis for compounds of the type (v4-C4R4CO)M(C0)3 (M = Ru, Os; R = Me, Et, nPr).19This general method involves the low-temperature photolysis of M(C0)s (M = Ru, Os) in the presence of an excess amount of the appropriate alkyne (CzR2, R = Me, Et, “Pr). After the photolysis is complete, as judged by the disappearance of M(COI5, the solutions are warmed to 0 “C. This results in relatively clean conversions to the corresponding cyclopentadienone species in modest yields (eq 3).
The mass spectral and elemental analytical data for
2-3 are listed in Table 1; the IR and 13C NMR data listed in Table 4. The only exception to the above synthetic strategy involves the reaction of Ru(CO15 with excess 2-butyne. The extreme thermal instability of Ru(C0)4(r2-CzMe2)necessitates that the photolysis reaction be carried out a t -5 “C so that any Ru(C0)4(r2-C2Me2) formed reacts immediately with excess 2-butyne in solution. In an effort to extend the method, Os(C0)4(~+CzMe2) was treated with different alkynes. Gratifyingly, 1 undergoes smooth copuling reactions with 3-hexyne and 4-octyne to yield the corresponding (r4-C4Me2R2CO)Os(CO)3complexes (eq 4). The structures shown are those -expected from simple alkyne-CO coupling. (17) Kruczynski, L.; Takats, J. Inorg. Chem. 1976, 15, 3140. 118) (a) Mann, B. E.; Taylor, B. F. 23CNMRData for Organometallic Compounds; Academic: New York, 1981. (b) Zobl-Ruh, S.; Von Philipsborn, W. Helu. Chim. Acta. 1980,63, 773. (c) Zobl-Ruh, S.;Von Philipsborn, W. Helu. Chim. Acta. 1981, 64, 2378. (d) Mann, B. E. Adu. Organomet. Chem. 1974,12, 135. (19)(a) The synthesis of (q4-C4Me4CO)Os(C0)3has been reported although the spectroscopic data are not consistent with our results: Bruce, M. I.; Cooke, M.; Green, M.; Westlake, D. J. J . Chem. SOC.A 1969, 987. (b)(q4-C4Et4C0)Ru(C0)3has been reported: ref 16b. (c) The synthesis of (q4-CPD)Ru(C0)3compounds with electron-withdrawing substituents (R = CF3, Ph) has been reported: ref loa.
0
R=Et.ld = ‘R.l e
It is interesting to note that, although Os(cO)4(y2CzPhz) can be cleanly generated by low-temperature photolysis of Os(CO)a and diphenylacetylene (DPA = CZPhz), thermal reaction is not the method of choice for the preparation of (q4-C4Ph4CO)Os(CO)3(4). Indeed, stirring Os(C0)4(q2-CzPhz) with excess DPA a t room temperature in hexane for several hours gives mostly unidentified decomposition products and only minimal amounts of (v4-C4Ph4CO)Os(C0)3 (4). The lack of thermally induced alkyne coupling is consistent with our previous observation that M(C0)4(v2-CF3C2CF3)(M = Ru, Os), containing the electron-deficient hexafluoro-2butyne, also do not undergo such a reaction. A convenient synthesis of (~4-C4Ph4CO)Os(CO)3 (4) is prolonged photolysis of Os3(CO)12 in the presence of excess DPA.lob The FT-IR, lH NMR, and 13CNMR data for 2d-3are consistent with their formulation as (q4-CPD)Os(C0)3 complexes (Tables 1and 4),and this was also confirmed by an X-ray crystal structure analysis of complex 2d.A perspective view of the molecule, with numbering scheme, is shown in Figure 1. Relevant bond distances and selected bond angles are listed in Table 5. The formation of the CPD ring from coupling of the 2-butyne and 3-hexyne units is clearly visible. The structure of 2d is consistent with other (y4-diene)M(C0)3 type complexes.10b,20The geometry around the Os center can be described as a tetragonal pyramid. The apical carbonyl, C6-06, occupies a site eclipsed by the ring ketone, C5-01. The other two carbonyls and the midpoints of the y4-coordinatedcyclopentadienone ring form the four basal coordination sites. The Os-C1, Os-C2, Os-C3, and Os-C4 distances are similar to those in related systems. Most notably, the solid-state structure of the tetraphenyl-substituted derivative (v4-C4Ph4CO)Os(C0)3 (4) has been determined.lob The M-C distances in 2d are essentially equal (range 2.19(2)-2.23(1) A), whereas the corresponding distances in 4 range from 2.20(1) to 2.27(1) A, with the Os-to-outer diene carbon distances being somewhat longer, as is commonly observed.lob The diene C-C distances in 2d are Cl-C2 = 1.41(2)A, C2(20) LiShingMan, L. K. K.; Reuvers, J. G. A,; Takats, J.;Deganello, G. Organometallics 1983,2 , 28 and references therein.
Organometallics, Vol.14,No.8,1995 4001
Scheme 1. Proposed Mechanism for Formation of 2d-e &(COk($-CzMcd
=
[Os(CO)dCaMct)l + CO A
C
Figure 1. ORTEP view of 2d. Probability ellipsoids are shown at the 50% level for non-hydrogen atoms. Table 5. Selected Bond Lengths and Angles for 2d os-c1 os-c2 OS-C~ OS-C~ OS-C~ OS-C~ OS-C~ 01-C5 c 2 -c 1- c 5 c2-c3-c4 c3-c4-c5 Cl-C5-C4 Cl-C2-C3
Bond Lengths (A). 2.22(1) Cl-C2 2.23(1) Cl-C5 2.19(2) C2-C3 2.21(1) c3-c4 1.83(1) c4-c5 1.88( 1) 06-C6 0 7 4 7 1.92(1) 1.22(2) 08-C8 Bond Angles (deg)CI 111(1) 01-C5-C1 107(1) 01-C5-C4 llO(1) Os-C6-06 102(1) Os-C7-07 106(1) Os-C8-08
1.41(2) 1.46(2) 1.46(2) 1.43(2) 1.45(2) 1.”) 1.15(2) 1.13(1) 127(1) 131(1) 175(1) 174(1) 175(1)
Esd’s given in parentheses.
C3 = 1.46(2) A, and C3-C4 = 1.43(2) A, while the corresponding C-C bond distances in 4 are 1.480(18), 1.428(15), and 1.456(17) A. The long-short-long alternation in 4, in contrast to the short-long-short alternation in 2d, implies a stronger Os-CPD backbonding interaction in 4 as compared to 2d. This is as expected from the nature of the substituents on the respective CPD rings and is consistent with the slightly larger bending of the ring carbonyl away from the planar 1,3-diene moiety in 4 (20.4”)compared to that in 2d (19.8”). Mechanism of Formation of (q4-CPD)Os(C0)3 Complexes: A Proposal. The observation that Os(C0)4(q2-C2Me2)can be used as a starting point in alkyne-carbonylation reactions is significant for the overall mechanism for the formation of cyclopentadienones. Iron carbonyl mediated alkyne-carbonyl coupling reactions are thought to proceed via undetected Fe(C0)4(r2-alkyne)intermediates; thus, the thermal C ~ Malkynes ~ ~ ) is an imreaction of O S ( C O ) ~ ( ~ ~ - with portant piece of the puzzle. Related alkyne coupling reactions at other ds metal centers are known.1f,21 Specifically, Britzinger and workers synthesized CpCo(r4-C4Ph4CO)from the photolysis of CpCo(C0)z in the presence of diphenylacetylene and suggested the intermediacy of CpCo(CO)(~2-C2Phz).21 Although there was this species could IR evidence for CpCo(C0)(y2-C2Ph2), not be isolated. The proposed scenario for the formation of compounds 2d-e, and by extension to the related (r4-CPD)M(C0)3 (M = Fe, Ru, Os) derivatives, is given in Scheme 1. The (21) Lee, W.-S.; Britzinger, H. H. J . Organomet. Chem. 1977, 127, 93.
R
2
km
D
initial step is dissociation of CO from complex 1. This is consistent with other work in o u r laboratories which has shown that CO loss from M(C0)4(q2-RCCR)(M = Ru, Os) species is a common initiation step in their reactions with nucleophiles.6a-b,s,22 To explain the lability of a CO ligand in M(C0)4(r2-RCCR)complexes, one may invoke the ground-state four-electron destabilization that exists between the alkyne ligand and the ds metal center.15 In addition, there is potential stabilization of the “Os(CO)3(C2Me2)”(A) intermediate with the alkyne ligand acting as a four-electron donor.15 In this regard, we note the recent isolation and structural where the two characterization of Os(PiPr3)2(CO)(C2Ph2) bulky, a-donating phosphine ligands stabilize the mole ~ u l e The . ~ ~isoelectronic Ir(PMe2Ph)3(DMAD)+(DMAD = C2(C02Me)2)complex of C, symmetry is stable, but it can add another DMAD ligand to yield the corresponding trigonal bipyramidal Ir(PMezPh)3(q2-DMAD)2+spec i e ~ . In ~ ~ contrast, , ~ ~ the Ir(triphos)+(triphos = MeC(CH2PPh2)s)fragment has been shown to initiate alkyne cyclotrimerization reactions.24 Related t o this, the formation of cobaltacyclopentadienes from the isoelectronic CpCo(alkyne):! species has been observed by Yasufuku and W a t a t ~ u k i . ~ ~ Coordination of a second alkyne molecule t o “OS(CO)~(C2Me2)”(A) is the proposed second step in the reaction. This finds precedent in the aforementioned iridium case.24 The presence of two alkyne ligands in the 18electron O~(C0)3(1;1~-CzMez)(r~-CzR2) (B;R = Et, nPr) complex should result in an even larger destabilizing effect than in the starting complex, 1,and provides the driving force for the next step. This could either be CO insertion into one of the Os(r2-alkyne)bonds t o give the (22) Washington, J . Ph.D. Thesis, University of Alberta, 1994. (23) Espuelas, J.; Estereulas, M. A,; Lahoz, F. J.; Lopez, A. M.; Oro, L. A.; Valero, C. J . Organomet. Chem. 1994, 468,223. (24) Bianchini, C.; Caulton, K. G.; Chardon, C.; Doublet, M.-L.; Eisenstein, 0.;Jackson, S. A,; Johnson, T. L.; Meli, A,; Peruzzini, M.; Streib, W. E.; Vacca, A,; Vizza, F. Organometallics 1994, 13, 2010. (25) (a) Yasufuku, K.; Hamada, A,; Aoki, K.; Yamazaki, H. J.Am. Chem. SOC.1980,102,4363. (b)Wakatsuki, Y.; Nomura, 0.;Kitaura, K.; Morokuma, K.; Yamazaki, H. J . Am. Chem. SOC.1983, 105, 1907.
4002 Organometallics, Vol. 14,No. 8, 1995
Washington et al.
Table 6. FT-IR, lH NMR, and 13CNMR Data for Tetraphenylcyclopentadienyl-Containing Os and Ru Complexes OH
I I
13C NMR (6, D,pm)d ~~
'H NMR (6, ppmY
compnd 5 (Ru)
6 (Ru) 7 (Os) 8 (Os) a
2040 (s), 2010 (m), 1980 (s), 1970 (sh)" 2014 (SI, 1955 ( s ) ~ 2032 (s), 1998 (m), 1968 (s), 1952 (sh)a 2000 (SI, 1940 (sib
7.10-7.73 7.35-7.60 6.69-7.50 7.05-7.46
(m, Ph), -17.7 (s, 1H) (m, Ph), -9.31 (s, 1H) (m, Ph), -21.5 (s, 1H) (m, Ph), -13.1 (s, 1H)
c1
c2.5
c3.4
Phenyl
M(CO)
154.3 137.3 157.1 134.5
87.8 92.2 84.5 88.4
103.5 104.8 99.4 101.5
132.0-127.0 133.6-128.4 132.0-127.0 134.5-125.9
200.8 202.6 181.3 183.1
Measured i n CH2C12. Measured in THF. Measured at 200.0 MHz i n CsD6. Measured at 50.3 MHz i n C6D6.
osmacyclobutenone(C) or alkyne coupling to generate the osmacyclopentadiene(D). The proposed intermediates, unsaturated at first glance, can be stabilized by four-electron donation from the alkyne in C or contribution from the metal1cyclopentatrieneZ6resonance form in D. Both sequences of events have been postulated in alkyne-CO coupling p r o c e ~ s e s . l g ~Formation ~,~~ of stable metallacyclopentadienes with x-acidic alkynes (DMAD and HFB; HFB = C2(CF&) are ~ e l l - k n o w n . ~ * 9 ~ ~ OH 0 As shown in a recent study by Lindner and co-workers, an ionic alkyne coupling mechanism is favored due to the presence of an electron-rich metal center concomitant with alkynes bearing electron-withdrawing substituents.28a These electron-withdrawing groups can stabilize the negative charge which forms on the acety6 6a lenic carbon in the proposed reaction pathway. An ionic best known catalyst for Tishchenko-type reactions. Its mechanism would be disfavored in the formation of 2 selectivity, rate, and turnover number allow the prepaand 3 as alkyl substituents are attached to the acetyration of esters from aldehydes on a substantial scale.4f lenic carbons. An oxidative alkyne coupling also seems The stability of 5, both in solution and in the solid state, to be unfavorable since, in a recent seminal paper, makes it a convenient reagent. The recent introduction Bianchini, Caulton, and Eisenstein, using extended of formic acid as a promoter further simplifies the Hiickel calculations, reported that the transformation performance of this reaction.4f We have found that the from the trigonal bipyramidal bis(a1kyne) complex key intermediate in the catalytic cycle of the Tishchenko Ir(PH3)3(q2-C2H&+,isoelectronic to our proposed interreaction,4f using 5 as the charged catalyst, as well as mediate B,to the corresponding metallacyclopentadiene hydrogenation reactions,4dis the mononuclear hydride is a symmetry-forbiddenprocess. We are thus left with 6. It was experimentally demonstrated that this catathe proposal that CPD ring formation with electron-rich lytic species transfers two hydrogen atoms to unsaturalkynes proceeds along the alkyne-CO insertion route. ated organic substrate^.^^ Complex 6 has never been Supporting this postulate, we have discovered that isolated, but spectroscopic data support the proposed CO insertion, promoted by bis(phosphines),into Os(CO)4structure rather than its tautomer 6a. Complex 6 (q2-HCCH) and Os(C0)4(q2-C2Me2)is a very facile reverts to 5 upon exposure to air but is stable in solution process.30 Our proposed mechanism is in accord with this whereby the putative trigonal bipyramidal o s ( C 0 ) ~ - under inert conditions. Thus, due to its key role in several catalytic reactions, (q2-C2Mez)(q2-C2Rz)(B; R = Et, nPr) intermediate, further insight into the structure and properties of 6 instead of alkyne coupling, undergoes a CO-insertion was desired. The isoelectronic Os complex (81, which process which is driven by two four-electron destabilizhas now been prepared from 4, was pursued as a way ing interactions. The formation of 2d-e is completed of achieving this goal (eq 5). Treatment of the osmium by insertion of the second alkyne ligand followed by compound 4, after 1 h of reaction time, gave 8 as the reductive coupling of the organic fragment.lf,h sole product. Further heating leads to the formation Catalytic Studies. The dimeric ruthenium tetof 7 as well. Complexes 7 and 8 can be separated by raphenylcyclopentadienyl complex, 5, is currently the column chromatography using silica gel. Refluxing an (26)Albers, M. 0.;deWaal, P. J. A.; Liles, D. C.; Robinson, D. J.; acetone solution of 8 exposed to air slowly forms the Singleton, E.; Wiege, M. B. J . Chem. SOC.,Chem. Commun. 1986, 1680. dimer 7, implying a sluggish oxidation process of the (27) Garlaschelli, L.; Malatesta, M. C.; Panzeri, S.; Albinati, A,; Ganazzoli, F. Organometallics 1987, 6, 63. hydride. Complex 8, in contrast to its ruthenium (28) ( a ) Lindner, E.; Kuhbauch, H.; Mayer, H. A. Chem. Ber. 1994, congener 6, is stable in solution and in the solid state 127, 1343. Lindner, E.; Kuhbach, H. J . Organomet. Chem. 1991,403, without the need for an inert atmosphere. The spectral C9. (c) Lindner, E.; Jansen, R.-M.; Mayer, H. A,; Hiller, W.; Fawzi, R. Organometallics 1989, 8, 2355. (d) Burke, M. R.; Takats, J. J . data for the new osmium complexes 7 and 8 as well as Organomet. Chem. 1986, 302, C25. their isoelectronic ruthenium complexes 5 and 6 are (29) Burt, R.; Cooke, M.; Green, M. J. Chem. SOC.A 1970, 2981. given in Table 6. (30) Mao, T.-F.; Takats, J . Manuscript in preparation.
Organometallics, Vol. 14, No. 8, 1995 4003
On the basis of the infrared carbonyl stretching frequencies, it may be concluded that 8 displays greater M-CO back-donation than 6. The same trend can also be observed in the osmium and ruthenium dimers 5 and 7 (Table 6). Also, all the ring C atoms of 8 resonate at higher field than those of 6,indicating a more extensive delocalization of the metal electronic charge into the CPD ring system in the osmium complex. Such phenomenon has been observed previously down the group VI11 triad.lob Complex 8 has greater polarization of the M-H bond; the metal hydride resonance in 8 (-13.1 ppm) is nearly 4 ppm upfield to that of 6 (-9.31 ppm). A similar trend is also observed for the Os and Ru dimers 5 and 7 (Table 6). Although formally the osmium atom in 8 has a d6 electronic configuration, the increased electron donation to the carbonyl ligands and the CPD ring as compared to 6 causes it to be an inferior reducing agent relative to the Ru atom in 6. The catalytic activity of 8 was examined. Attempted hydrogenation of cyclohexanone with hydrogen (47 atm) at 105 "C over a period of 4 h gave minimal conversion to the corresponding alcohol. A Tishchenko-type reaction with benzaldehyde with formic acid as a promoter was also attempted. Minimal product conversion, under toluene reflux, was seen over a 4 h period. Under the above conditions, the isoelectronic complex 6 catalyzes these reactions very e f f i ~ i e n t l y . In ~ ~ addition, the hydrogenation of benzaldehyde at 105 "C and 25 atm hydrogen gave only a low yield (30%)of benzyl alcohol after 96 h. Thus, not unexpectedly, 8 is a very sluggish hydrogenation catalyst compared to its Ru analogue. Subjecting (r4-C4Me4CO)Os(C0)3(2a)to the reaction conditions of eq 5 gave back 2a; no other complex could be detected in the reaction mixture by TLC and FT-IR analysis. This is in contrast to the facile formation of the isostructural complex 8 (eq 5) and must imply a diminished reactivity of the Os-bound CO groups in 2a toward nucleophilic attack of hydroxide ion. Inspection of the IR stretching frequencies of the CO groups of 2a and 4 (Table 4)reveals a shift to lower wavenumbers
in 2a relative to 4. This then implicates a stronger OsCO bond in 2a as a result of better Os-CO backdonation, consonant with the weaker n-acidity of tetramethylcyclopentadienone compared to tetraphenylcyclopentadienone. Summary. Facile thermal reaction of Os(CO)4(y2CzMez) (1) with excess alkyne offers an attractive method for the synthesis of (cyc1opentadienone)tricarbonylosmium complexes and provides insights into the mode of formation of these species. The increased reactivity of 1 is due t o a combination of enhanced CO lability and a weakly bound alkyne ligand, as compared to other Os(C0)4(y2-alkyne)species. We attribute this and subsequent facile alkyne coupling reactions involving 1 to the four-electron destabilization between 2-butyne and the d8 metal center. In addition, electron-rich alkynes such as 3-hexyne and 4-octyne may readily attack the pseudovacant coordination site left after CO loss from 1. These alkynes can disrupt the four-electron interaction that stabilizes the putative Os(CO)3(C2Me2) intermediate, and the dramatic rise in electron density following coordination of a second electron-rich alkyne provides the impetus for the formation of the cyclopentadienone complexes. These features provided by electron-rich alkynes can also be exploited to effect the synthesis of a number of aliphatically substituted (r4CPD)M(C0)3(M = Ru, Os) complexes. In addition, the synthesis of (q5-C4Ph4COH)Os(CO)2H ( 8 ) was also carried out and its catalytic activity was investigated. The increased thermal and air stability of this complex allowed for a more complete understanding of the role of the ruthenium analogue, 6,in several catalytic cycles. Not unexpectedly, the increased stability of 8 resulted in minimal catalytic activity. Attempts to increase the catalytic potential of the osmium-based systems by increasing the donor ability of the CPD ring were unsuccessful. Thus, although the Ru-based complexes are superior catalysts, the Os analogues allow for the isolation and complete characterization of a key intermediate in the ruthenium-catalyzed reactions.
Acknowledgment. We wish to thank the Natural Sciences and Engineering Research Council of Canada for financial support of this work and a graduate scholarship t o J.W. Support from the University of Alberta and Johnson-Mathey (loan of OSOS)is also gratefully acknowledged. Supporting InformationAvailable: Tables of anisotropic thermal parameters, least squares planes, torsional angles, and derived hydrogen atom positions and U values for 2d (5 pages). Ordering information is given on any current masthead page. OM9503331
