2786
Organometallics 1989,8, 2786-2792
312 (16,M+ - C04(CO)12),297 (100,M+ - CH&o,(CO),,). Anal. "C; IR (hexane, cm-') u ( C ~ 02081,2047,2020,2000,1950; ) 'H Calcd for CzaHzaO14Si4Cor: C, 32.59;H, 2.73. Found: C, 32.18; NMR (CC,, 6) 0.7 (12 H, s), 4.8 (10 H, 8 ) . Anal. Calcd for H, 3.03. Complex 28 was added to a solution containing 0.8 g (15 CzsHpOl,,SizFezCo2:C, 40.03; H, 2.84. Found C, 40.04; H, 2.67. mM) of ceric ammonium nitrate in 10 mL of acetone and stirred Methanolysis of Complex 15. At 0 "C, a solution containing until the black color disappeared. The solvent then was removed 1.3 g (40mM) of methanol in 50 mL of hexane was added to a and the residue extracted with pentane. Crystallization afforded solution of 10.0 g (20mM) of the chloro complex 15 in 50 mL of 0.24 g (57%) of colorless crystals of compound 29: mp 110-112 hexane. The solution then was stirred for 12 h at 25 "C. The "C; IR (CCl,, cm-') u(Si-C) 1258,u(Si-0) 1060; 'H NMR (CC,, mixture was pumped to dryness and the residue extracted with hexane. After the filtrate was cooled, 9.0 g of black crystals of 6) 0.02 (8); 13CNMR (CDC13,6) 1.87,112.88,mass spectrum, mle (re1 int, assignment) 312 (50, M+),297 (100,M+ - CH3). complex 9 (90%),identical with the sample previously described, Reaction of Complex 27 with Oxalyl Chloride. A solution was obtained. of 0.55 mL (6.5mM) of oxalyl dichloride in 60 mL of pentane Ammonolysis of Complex 15. Gaseous ammonia, previously was added at -20 OC to a solution containing 3.0 g (6.5mM) of dried by passing though KOH pellets, was bubbled at -20 OC into diamino complex 27 and 1.6 mL (20mM) of triethylamine in 60 a solution containing 5.0 g (10mM) of complex 15 in 100 mL of mL of pentane. The mixture was stirred for 12 h at room tempentane. After an hour, the reaction mixture was filtered and perature and filtered. Evaporation of the pentane, followed by pumped to dryness. Extraction of the residue with hexane and extraction of the residue with hexane, led to the isolation of 0.5 crystallization at -20 OC afforded 3.2 g of red-black crystals of g (15% yield) of black crystals of complex 3 0 mp 150 O C dec; diamino complex 27 (70% yield): mp 163-165 OC; IR (CCL, cm-') IR (CCl,, cm-') v(N-H) 3340,u ( C 4 ) 2080,2042,2016,u ( C 4 ) vN-H) 3485,3410,u(C..O) 2086,2047,2019; 'H NMR (CCl,, 6) 1680;'H N M R (CDCl,, 6) 0.65 (12H, e) 1.35 (2H, s). And Calcd 0.35 (12H, s) 0.75 (2H, 8); mass spectrum, mle (re1 int, assignfor Cl4Hl4O&+3i2C&: C, 32.82;H, 2.75. F o w d C, 32.85;H, 3.06. ment), 430 (1,M+ - CO), 403 (1,M+ - 2 CO), 374 (1,M+ - 3 CO), 346(1,M+-4CO),318(1,M+-5CO),290(10,M+-6CO),231 Reaction of Complex 27 with Dimethyldichlorosilane. A solution of dimethyldichlorosilane (0.86mL, 7.2 mM) in 70 mL (3,M+ - Co(CO),), 171 (1,M+ - Co,(CO),). Anal. Calcd for C12H1606N2Si2C02: C, 31.45;H, 3.51. Found: c , 31.64;H, 3.40. of hexane was added at 0 "C to a solution containing 3.3 g (7.2 mM) of complex 27 and 1.6 mL (20mM) of triethylamine in 70 Formation of Cyclosiloxanes and Silazanes. Hydrolysis mL of hexane. The mixture was stirred at room temperature for of Complex 15. A solution of 5 g (10mM) of dichloro complex 12 h and filtered, and the solvent was evaporated. The residue 15 and 10 mL of water in 50 mL of acetone was stirred for 10 h was extracted with hexane and crystallization afforded 0.60 g at room temperature. After solventswere removed in vacuo, the (17%) of black crystals of complex 31: mp 192.193 "C dec; IR residue was dissolved in 100 mL of hexane and heated to 60 "C (CCl,, cm-') u(N-H) 3320, u ( C e ) 2080,2040,2019;'H NMR for 2 h. The mixture was filtered, concentrated, and cooled at (CCl,, 6) 0.3( 8 ) ; % ' ' NMR (CDC13,6) 1.56,5.39;mass spectrum, -20 "C to give 1.25 g (28%) of complex 28 as black crystals: mp m l e (re1 int, assignment) 514 (4,M+),486 (6,M+ - CO), 458 (8, 137-138 OC; IR (CC,, cm-') u(C=O) 2096,2058, 2028,u(Si-0) M+- 2 CO), 430 (13,M+ - 3 CO), 402 (1,M+ - 4 CO), 374 (4,M+ 1075; 'H NMR (CC,, 6) 0.4 ( 8 ) ; mass spectrum, m l e (re1 int, - 5 CO), 346 (4,M+ - 6 CO), 287 (1,M+ - Co(CO)&,228 (1,M+ assignment) 744 (0.5, M+ - 5 CO), 660 (2,M+ - 8 CO), 604 (1, M+-10CO),576(1,M+-11CO),548(1,M+-12CO),489(1;- Co2(CO),), 213 (2,M+ - CH&o,(CO),). Anal. Calcd for C14H2006N2Si3C02: C, 32.68;H, 3.91. Found: C, 32.45;H, 3.74. M+ - CO(CO)12),430 (3,M+- CO~(CO)~~), 371 (4,M+ - C03(C0)12),
Molybdenum Carbyne, Vinylidene, and Ketenyl Complexes with Hydrotris(3,5-dimethylpyrazolyI)borate Ligands Douglas C. Brower, Michaela Stoll, and Joseph L. Templeton" Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290 ReceivedMay 16, 1989
Treatment of Tp'(CO),Mo[q2-C(0)R] #-acyl complexes with excess sodium ethoxide in refluxing ethanol affords carbyne complexes TP'(CO)~MO(CR)(Tp' = hydrotris(3,5-dimethylpyrazolyl)borate; R = methyl, ethyl). The carbyne complexes can be deprotonated at low temperature to form anionic vinylidene complexes that are susceptible to electrophilic attack by methyl iodide or ethyl iodide at the vinylidene @-carbon. Photochemical carbonyl substitution occurs in acetone or acetonitrile solvent for the methyl carbyne complex, but the known phenyl analogue undergoes photochemical carbonyl-carbyne coupling to form an q2-ketenyl complex under these conditions. Transition-metal carbyne complexes can be prepared by a number of routes,' including the classic Fischer preparation involving abstraction of alkoxide from alkoxycarbene complexes,2 abstraction of a-hydrogen from Schrock-type alkylidene ~ o m p l e x e sand , ~ rearrangement of u-vinyl c o m p l e x e ~ .T~ h e formal abstraction of oxide, (1) Kim, H. P.; Angelici, R. J. Ado. Organomet. Chem. 1987,27, 51. (2) Fischer. E. 0.: Schubert. U. J. Oraanomet. Chem. 1976,100. 59. (3) (a) Guggenberger, L. J.; Schrock, R. R. J. Am. Chem. soc. 1975, 97,2935. (b) Wengrovius, J. H.; Sancho, J.; Schrock, R. R. J.Am. Chem. SOC.1981, 103,3932.
02-,from metal acyl precursors5 with strong Lewis acids has been developed by Mayr6 into a n efficient approach to group VI carbynes (eq 1). Stone and co-workers' have applied this protocol to prepare a series of Cp(CO),M(CAr) (4) Green, M. J. Organomet. Chem. 1986, 300, 93.
(5) (a) Fischer, H.;Fischer, E. 0. J. Organomet. Chem. 1974,69, C1. (b) Himmelreich, D.; Fischer, E. 0. 2. Naturforsch. 1982, 3 7 4 1218. (6) McDermott, G. A.; Domes, A. M.; May,A. Organometallics 1987, 6, 925.
(7) Doasett, S. J.; Hill, A. F.; Jeffery, J. C.; Marken, F.; Sherwood, P.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1988, 2443.
0276-7333/89/2308-2786$01.50/00 1989 American Chemical Society
Organometallics, Vol. 8, No. 12, 1989 2787
Molybdenum Carbyne, Vinylidene, and Ketenyl Complexes 0 (CO)+Io--C L
II
+ (CF3CO)zO
-7s 4:
b H 3
J
( C F ~ C O Z ) ( C ~ ) ~ M O E C+C HCF3COT ~
+
CO (1)
complexes (Cp = q5-C5H5;Ar = substituted phenyl; M = Cr, Mo, W) as well as a complex bearing the T p ligand, Tp(CO)2W(C-TOl) (Tp = v3-HB(C3H3N2)3;To1 = p-tolyl). Carbyne complexes containing the TP’(CO)~Mfragment (M = Mo, W) have encompassed a broad class of carbyne substituents, including halide, substituted chalcogenide, and amine groups.8 We describe here the preparation of related carbynes with alkyl substituents. Greeng has reported carbyne deprotonation and alkylation in a Cp-based system (eq 2), and conversion of neutral vinylidene complexes t o cationic carbynes by electrophilic attack has been observed previously.1° Lalor CpLzM-CCHzBu
(1)BuLi
(2) RX
C ~ L ~ M O ~ C C H R ~(2)B U
has isolated anionic carbon-substituted vinylidene complexes that are nucleophilic a t CP3’ The photochemical properties of carbyne complexes have also attracted attention.” Bocarsly, Mayr, and coworkers12 found that complexes of the type X(CO)2L2W(CPh) (X = C1, Br; L = phosphine, pyridine, TMEDA) luminesce in solution at room temperature, due to metal-to-carbyne charge transfer. However, this MLCT band is absent when the carbyne substituent is tert-butyl. Mayrl3 and Geoffroy14 have established that carbonylcarbyne coupling is an important photochemical reaction pathway in some systems. Both 7’-ketenyl and $-ketenyl products can be prepared. Geoffroy14 has described the formation of $--ketenyl complexes by photolysis of Cp(C0)2W(C-Tol) in the presence of PMe, or PPh, (eq 3).
Cp(C0)zWECCHs
k
P R3
/t
Cp(CO)(PR3)W\\
(3)
To1
Mayrl3 has deduced the presence of q2-ketenyl intermediates in the photoassisted isomerization of complexes of the type X(CO),L,M(CPh) (eq 4: X = C1, Br; L = PMe,, PPh,; M = Mo, W). An interesting 7’-ketenyl complex, W(.rl’-PhCCO)Cl(CO)(PhCCH)(PMe,),, has also been prepared photochemically by Mayr13 from the reaction of (8) (a) Halides: Desmond, T.; Lalor, F. J.; Ferguson, G.; Parvez, M. J. Chem. Soc., Chem. Commun. 1983,457. (b) Chalcogenides: Desmond, T.; Lalor, F. J.; Ferguson, G.; Parvez, M. J.Chem. SOC.,Chem. Commun. 1984,75. (c) Amine: Kim, H. P.; Angelici, R. J. Organometallics 1986, 5, 2489. (9) (a) Baker, P. K.; Barker, G. K.; Green, M.; Welch, A. J. J. Am. Chem. SOC.1980, 102, 7811. (b) Gill, D. S.; Green. M. J. Chem. SOC., Chem. Commun. 1981,1037. (c) Beevor, R. G.; Freeman, M. J.; Green, M.; Morton, C. E.; Orpen, A. G. J. Chem. SOC.,Chem. Commun. 1985, 68. (10) (a) Beevor, R. G.; Green, M.; Orpen, A. G.; Williams, I. D. J. Chem. SOC.,Chem. Commun. 1983,673. (b) Birdwhistell, K. R.; Burg1983,105,7789. (c) mayer, s.J. N.; Templeton, J. L. J. Am. Chem. SOC. Mayr, A.; Schaefer, K. C.; Huang, E. Y. J. Am. Chem. SOC.1984,106, 1517. (11) (a) Vogler, A.; Kisslinger, J.; Roper, W. R. 2.Naturforsch. 1983, 38,1506. (b) Fischer, E. 0.; Friedrich, P. Angew. Chem., Int. Ed. Eng. 1979, 18, 327. (12) Bocarsly, A. B.; Cameron, R. E.; Rubin, H.-D.; McDermott, G. A.; Wolff, C. R.; Mayr, A. Inorg. Chem. 1985,24, 3976. (13) Mayr, A.; Kjelsberg, M. A,; Lee, K. S.; Asaro, M. F.; Hsieh, T.-C. Organometallics 1987, 6, 2610. (14) Sheridan, J. B.; Pourreau, D. B.; Geoffroy, G. L.; Rheingold, A. L. Organometallics 1988, 7, 289.
co
I .&
X-M=C-Ph
(4)
/LO
C1(C0)2(PMe3)2W(CPh)with excess phenylacetylene at low temperature. We now report syntheses of carbyne complexes [Tp’(CO),Mo(CR) (l)]by the formal abstraction of an oxygen atom, “0”,from +-acyl precursors of the type Tp’(CO),Mo[ $-C( O)R]15J6(Tp’ = hydrotris( 3,5-dimethylpyrazoly1)borate; R = methyl, ethyl). In this reaction, formation of the carbyne product occurs without a change in the overall charge of the metal-containing species-thus corresponding to formal removal of atomic oxygen. Both Tp’(CO),Mo(CCH,) (la) and Tp’(C0)2Mo(CCH2CH3)(lb) are susceptible to deprotonation by strong bases at the carbyne @-carbon. Electrophiles such as methyl iodide readily add to these anions at the vinylidene @-carbonto generate elaborate carbyne ligands. We also report that photolysis of an acetonitrile solution of TP’(CO)~MO(CPh)8b produces an v2-ketenyl complex while Tp’(C0)2Mo(CMe)loses carbon monoxide under these conditions rather than undergoing carbonyl-carbyne coupling.
Experimental Section General Conditions, Reagents, and Instrumentation. All reactions were performed under a blanket of dry nitrogen gas unless otherwise noted. Solvents were purified and distilled under nitrogen by conventional means.17 KTp’’* and TP’(CO)~MO[$2(O)R] (R = CH3, CH2CH3)lswere prepared by literature methods. Other reagents were obtained from commercial sources and used as received. Infrared spectra were obtained either from a Beckman IR4250 spectrophotometer or a Mattson Polaris Fourier transform spectrophotometer. NMR spectra were obtained from a Varian XL400 spectrometer. Elemental analyses were performed by Galbraith Laboratories, Knoxville, TN. Cyclic voltammograms were obtained on a Bioanalytical Systems Model CV-27 instrument using acetonitrile solutions containing 0.10 M [NEt4][Clod]as the supporting electrolyte. The voltammograms were obtained at a scan rate of 100 mV/s, and Ellz values [(E,, + Ep,,)/2]were recorded with the ferrocene/ferrocenium couple employed as an internal standard.lg The electrode array consisted of a saturated sodium calomel reference electrode and platinum-bead working and auxiliary electrodes. Potentials were uncorrected for junction effects. Tp’(CO),Mo(CR) [R = Me (la), Et (lb)]. A Schlenk tube was charged with T ~ ’ ( C O ) , M O ( ~ ~ - C ( O(2.0 ) M ~g,)4.0 ~ ~ mmol), NaOEt (2.8 g, 40 mmol), and 40 mL of absolute ethanol. The vessel was placed in an oil bath and heated to reflux with vigorous stirring. Over 30 min, the orange starting material dissolved and its color was discharged from the solution. Upon cooling to room temperature, small quantities of a yellow precipitate formed. Additional precipitate was obtained by slow addition of 5 mL of water to the solution followed by chilling in an ice bath. The solid was collected by filtration through a medium glass frit. A second crop of crude product was obtained by adding more water to the (15) (a) Trofimenko, S. J . Am. Chem. SOC.1969,91,588. (b) Curtis, M. D.; Shiu, K.-B.; Butler, W. M. J. Am. Chem. SOC.1986,108,1550. (c) Desmond, T.; Lalor, F. J.; Ferguson, G.; Ruhl. B.; Parvez. M. J. Chem. Soc., Chem. Commun. 1983,5?1. (16) (a) Rusik, C. A.; Collins, M. A,; Gamble, A. S.; Tonker, T. L.; Templeton, J. L. J. Am. Chem. SOC.1989,111, 2550. (b) Rusik, C. A.; Tonker, T. L.; Templeton, J. L. J. Am. Chem. SOC.1986, 108, 4652. (17) Gordon, Arnold, J.; Ford, Richard, A. The Chemist’s Companion; Wiley-Interscience: New York, 1972. (18) Trofimenko, S. J. Am. Chem. SOC.1967,89,6288. (19) Gagne, R. R.; Koval, C. A,; Lisensky, G. C. Inorg. Chem. 1980,19, 2855.
2788 Organometallics, Vol. 8, No. 12, 1989 filtrate. The combined solids were purified by reprecipitation from hot ethanol/water (0.39 g, 20%). Tp'(CO),Mo(CMe) (la): IR (KBr) 1982, 1889 cm-' (vco); 'H NMR (CD2Clz)6 5.81, 5.70 (s, 2:1, Tp' CH),2.51 (br s, 9H, two Tp' CCH,, and carbyne CH,), 2.37, 2.33, 2.30 (s, 3:6:3, Tp' CCH,); '%{'HI NMR (CD2C12)6 304.0 (carbyne carbon), 225.0 (carbonyl), 152.0, 151.4, 145.7, 145.3 (1:21:2,Tp' CCH,), 106.4,106.3(1:2, Tp' C-H),36.5 (carbyneCH,), 15.7, 14.6, 12.8, 12.7 (2:1:2:1, Tp' CH,). Anal. Calcd for Cl@,BMoN8O2: C, 47.92; H, 5.29; N, 17.65; Mo, 20.15. Found: C, 47.97; H, 5.55; N, 17.30; Mo, 19.86. Tp'(CO),Mo(CEt) (lb): IR (KBr) 1980, 1885 cm-' (vco); 'H NMR (CD2C1,) 6 5.86, 5.75 (s, 2:1, Tp' CH), 2.71 (9, J = 7 Hz, carbyne CH,CH,), 2.50, 2.38, 2.35, 2.32 (s, 6:3:6:3, Tp' CCHJ, 1.26 (t, J = 7 Hz, carbyne CH,CHJ; lsC('H}NMR (CD,Cl,) 6 310.6 (carbyne carbon), 225.6 (carbonyl), 151.8, 151.3, 145.7, 145.3 (1:2:1:2, Tp' CCH,), 106.4, 106.3 (1:2, Tp' CH),43.51 (carbyne CHZCH,), 15.9, 14.6,12.8,12.7 (2:1:2:1, Tp' CCH,), 11.4 (carbyne CH,CH,). Anal. Calcd for C&27BM~N602:C, 49.00; H, 5.55; N, 17.14; Mo, 19.57. Found: C, 48.59; H, 5.45; N, 17.03; Mo, 19.24. Reactivity Studies of Tp'(CO)zMo(q,2-C(0)CH3). A. A slurry of the q2-acylcomplex in absolute ethanol was heated to reflux for 12 h. No reaction was observed. B. The $-acyl was heated to reflux for 30 min in isopropanol solvent with an excess of sodium isopropoxide. l a was isolated in a 2% yield following chromatography on an alumina support with hexanes as eluent. No starting material was recovered; other colored species were observed on the column but were not identified. C. The $-acyl was heated to reflux with 10 equiv of t-BuOK in t-BuOH. No carbyne product was isolated or observed in the infrared spectrum of the solution. D. The $-acyl was heated to reflux in toluene with an excess of tributylphosphine or triphenylphosphine. No reaction was observed. E. The $-acyl was heated to reflux in tetrahydrofuran solvent with excess sodium methoxide. Tp'(CO),Mol- was the only metal carbonyl-containing product evident in IR spectra of the reaction solution. Reactivity Studies of Tp'(C0),Mo(CCH3) (la). A. Complex l a was heated to reflux for 40 min in absolute ethanol with 10 equiv of NaOEt. No change in the infrared spectrum of the solution was observed after this time, nor after standing at room temperature overnight. B. Complex l a was heated to reflux with excess triethylphosphine in 2-methoxyethanol solution. No reaction was observed after 1 day. Tp'(CO),Mo(CR) [R = Me ( l a ) , P h (IC)]. Solutions of (CF,CO,)(CO),Mo(CR) were prepared by the method of Mayre and treated at -78 "C with 1 equiv of KTp' dissolved in a minimum of methanol. The crude reaction solution was evaporated to an oil and chromatographed on alumina with 5:l v/v hexanes/methylene chloride as eluent. The first yellow fraction (R = Me) or orange fraction (R = Ph) was collected and dried. Residual Mo(CO)~ was removed by sublimation. Yield based on starting MO(CO)~: la, 15%; IC, 18%. Tp'(CO),Mo(CPh): IR (KBr) 1979, 1890 cm-' (vco); 'H NMR (CD,Cl,) 6 7.2-7.7 (m, 5 H, C&Is), 5.92,5.82 (e, 2:1, Tp' CH), 2.50,2.42, 2.40, 2.37 (s,6:363, Tp' CH,); 13C(lH}NMR (CD,C12)6 288.8 (carbyne carbon), 226.2 (carbonyl), 151.9, 151.7, 146.0, 145.5 (1:2:1:2, Tp' CCHJ, 146.2 (phenyl ipso), 127-129 (phenyl), 106.7,106.5 (1:2, Tp' CH), 16.0, 14.7, 12.9, 12.8 (2:1:2:1, Tp' CCH,). Anal. Calcd for C2,H2,BMoN802: C, 53.55; H, 5.06. Found: C, 51.81; H, 5.01. Li[Tp'(CO),Mo=CYH,] (2). A Schlenk tube was charged with l a (0.10 g, 0.20 mmol) and 10 mL of tetrahydrofuran (THF) was added. The yellow solution was chilled to -78 "C and ether or hexane solutions of methyllithium or butyllithium were syringed into the flask with stirring. A red solution formed immediately. When excess base was present, it was possible to obtain roomtemperature infrared spectra of the reaction solution. It was not possible to isolate the product. IR (THF): 1871,1698cm-' (strong, sharp, vco), 1607 cm'l (br, weak, V M ~ ~ H J . Na[Tp'(CO)zMo=C=CH,], NMR Detection. An NMR tube was charged with l a (0.025 e. 0.052 mmol) and NalN(SiMeA1 (0.025g, 6.14 mmol). The tuce was chilled to -78 "C:and 1.5 mE of THF-d, was added, giving a red solution. The 'H and '% NMFt spectra, recorded at -65 "C, indicated complete conversion of l a to Na[Tp'(CO)2Mo=C=CH,J. When the experiment was repeated with 1equiv of Na[N(SiMe&], approximately half of the metal reagent was observed to react, as determined by NMR integration: 'H NMR (C,D,O, -65 "C) 6 5.64 (s,3 H, Tp' CH),
Brower et al. 3.73 (s, 2 H, vinylidene CH,), 2.49,2.36,2.33 (s,3:12:3, Tp' CCH3); 13CNMR (C4DD,0, -65 "C) 6 349.6 (s, vinylidene Mo=C=CH2), 240.2 (s, carbonyl), 151.5, 150.4, 142.7, 142.0 (each a multiplet, 1:2:1:2, Tp' CCH,), 105.2, 105.1 (each a d , 'JcH = 170 Hz, 1:2, Tp' CH), 91.4 (t, l J C H = 153 Hz, vinylidene M d = C H 2 ) , 16.1 15.9, 13.1, 12.9 (each a q, 2:1:2:1, 'JCH = 125 Hz, Tp' CCH,). Tp'(CO),Mo(CR) [R = CHzCH3 (lb), CHzCHzCH3 (ld), CH(CH,), (le)]. The procedure described is for Id, which is typical of the series. A Schlenk flask was charged with la (0.90 g, 1.9 mmol) and 40 mL of THF. Approximately 2 equiv of butyllithium in hexane was added dropwise to the solution at -78 "C with stirring. To the cold solution was added 5 equiv (1.0 mL) of ethyl iodide. The red color of the vinylidene anion was discharged in 1 h. The cold bath was removed, and the reaction solution was stirred at room temperature overnight. The solution was filtered, reduced to an oil, and chromatographed on alumina with hexanes as eluent. The first yellow fraction was collected and the solvent evaporated. The crude product was purified by precipitation from hot ethanol/water, resulting in a yellow powder: yield 0.40 g, 42%; IR (KBr) 1977, 1882 cm-' (uco); 'H NMR (CD2C1,) 6 5.88, 5.78 (s, 2:1, Tp' CH), 2.71 (t, 2 H, carbyne CH,CH,CH,), 2.52, 2.38,2.35, 2.33 (s,63:63,Tp'CCH3), 1.80 (m, 2 H, carbyne CH,CH,CH,), 1.02 (t,3 H, carbyne CH,CH,CH,); l3C{lH)NMR (CD2C12)6 310.5 (carbyne carbon), 225.8 (carbonyl), 150.9, 150.6, 144.9, 144.5 (1:2:1:2, Tp' CCH,), 105.6, 105.5 (1~2, Tp' CH),51.6 (carbyne CH2CH,CH3), 20.4 (carbyne CH,CH,CHJ, 13.5(carbyne CH2CH2CH3),15.1,13.8,12.0,11.9 (21:21, Tp' (333). Anal. Caicd for C21H&MoN802: C, 50.02; H, 5.80. Found: C, 49.81; H, 5.87. When methyl iodide was employed in place of ethyl iodide in this procedure, the vinylidene anion was immediately consumed and complex l b was obtained in 75% yield. Complex le was obtained in 12% yield from lb, butyllithium, and methyl iodide. Tp'(CO),Mo(CH(CH,),): IR (KBr) 1980, 1885 cm-' (vco);'H NMR (CD,Cl,) 6 5.85, 5.74 (s, 2:1, Tp' CH), 2.86 (septet, 1 H, carbyne CH(CH,),), 2.51, 2.36, 2.33, 2.29 (8, 6:3:6:3, Tp' CCH,), 1.25 (d, 6 H, carbyne CH(CH,),); l3C('H] NMR (CD2Cl,) 6 314.4 (carbyne carbon), 226.1 (carbonyl), 151.8, 151.3, 145.7, 145.4 (1:2:1:2, Tp' CCH,), 106.5, 106.3 (1:2, Tp' CH), 48.6 (carbyne CH(CH3)2),20.4 (carbyne CH(CH3)2),16.1,14.6, 12.9, 12.7 (21:21, Tp' CCH,). Anal. Calcd for CZlH@MoNBO2:C, 50.03; H, 5.79. Found C, 49.24; H, 5.47. Tp'(CO)(CH,CN)Mo($-OCCPh)(3). An orange acetonitrile solution of IC (0.50 g, 1.0 mmol, dissolved in 100 mL of solvent) was photolyzed through a Pyrex filter for 30 min at 0 "C with a Hanovia 750-W medium-pressure Hg arc lamp. A continuous nitrogen purge was maintained through the solution. The resultant green solution was fdtered, reduced to an oil, and triturated with diethyl ether. The ether wash contained some residual IC reagent, as shown by the color of the solution and its infrared spectrum. The blue-green product 3 was recrystallized from methylene chloride/diethyl ether solution: yield 0.35 g, 66%; IR (CH2C1,) 1884 ( ~ ~ 01758 1 , ~ m - q',-(;) 'H NMR (CDZClJ 6 7.3-7.1 (m, 5 H, phenyl), 5.93, 5.75,5.67 (s,each 1H, Tp' CH), 2.72, 2.50, 2.46, 2.38, 2.32, 1.46, 1.30 (s, each 3 H, CH3CN and Tp' CCH,); l3C NMR (CD,C12) 6 232.1 (t, ,JCH = 8 Hz, ketenyl Ca), 230.8 (s, carbonyl), 209.5 (s, ketenyl Cp),153.9, 151.2,150.7, 145.8,145.7, 144.8 (each a m, Tp' CCH,), 143.2(4, 'JcH = 10Hz,CHaCN), 140.2 (t, 'JCH = 8 Hz, phenyl ipso), 128.6,127.9, 125.6 (phenyl), 106.7, 106.5 (each a d , 'JCH = 170 Hz, 21, Tp' CH),15.2,13.6, 13.2, 12.9 (overlapping q, ~ J c H= 122-129 Hz, 21:1:2, Tp' CCH,), 5.1 (q, 'JCH = 138 Hz, CH,CN). Anal. Calcd for C,HGMoN,O2: C, 53.90; H, 5.22. Found: C, 53.66; H, 5.18. [ T ~ ' ( C O ) ( C H , C N ) M O ( P ~ C C O C H , ) ~ [ ~ ~ ~ C (4). FJ~X~~C~~ Complex IC (0.50 g, 0.93 mmol) was dissolved in 100 mL of acetonitrile and photolyzed at 0 "C for 40 min. The residue after solvent evaporation and trituration with diethyl ether was dissolved in 20 mL of methylene chloride and filtered into a 100-mL round-bottom flask. The solution was chilled to -78 "C, and a solution of methyl triflate (1.0 mL, 0.80 mmol, dissolved in 5 mL of methylene chloride) was added dropwise until the infrared spectrum of the reacting solution indicated that no $-ketenyl complex remained. Solvent was removed at room temperature, and the green oil was triturated with 5 mL of diethyl ether. The lime powder that resulted was recrystallized from methylene chloride/diethyl ether: yield 0.48 g, 62%. The presence of co-
Molybdenum Carbyne, Vinylidene, and Ketenyl Complexes crystallized CHzClzwas indicated’by NMR spectroscopy; slow exchange of coordinated and free acetonitrile was also observed in CD3CNsolvent. In CDzClzsolvent, the bound acetonitrilewas slowly displaced from the coordination sphere of the metal by the triflate anion. The degree of substitution was dependent on temperature, and the reaction was readily monitored by ‘H NMR spectroscopy (see text below): ‘H NMR (CD2C12)6 7.4-7.2 (m, 3 H, phenyl), 6.66 (m, 2 H, phenyl), 5.98, 5.90, 5.74 (s, each 1 H, Tp’ CH), 4.77 (s, 3 H, alkyne OCH,), 2.59, 2.57, 2.54, 2.52, 2.42, 1.49,1.38 (s, each 3 H, CH,CN and Tp’ CCHJ; 13CNMR (CD2ClJ 6 227.8 (q, ,JCH = 5 Hz, alkyne COCH,), 224.6 (s, carbonyl), 215.2 (t, , J C H = 5 Hz, alkyne CC6H5),153.1, 152.4, 150.2, 147.8, 147.3, 145.9 (each a m, Tp’ CCH,), 147.1 (q, 2Jm= 10 Hz, CH,CN), 136.1 (phenyl ipso), 130.4, 128.8, 128.4 (1:2:2, phenyl), 121.2 (q, lJcF = 322 Hz, 03SCF3),108.2 (overlappingsignals, Tp’ CH), 68.8 (q, l J C H = 149 Hz, OCH,), 10-18 (overlapping q, ‘JCH = 125-130 Hz, Tp’ CCH,), 5.2 (q, ~ J C =H 132 Hz, CH3CN). Anal. Calcd for C ~ H ~ B C ~ ~ M O NC, , O42.05; ~ S : H, 4.26. Found: C, 42.32; H, 4.34. Tp’(CO)(CD,CN)Mo(CCH,) (5a). Complex l a (0.05 g, 0.1 mmol) was dissolved in 1.5 mL of CD3CNand sealed in an NMR tube. The solution was photolyzed for 30 min at 0 “C. Effervescence in the NMR tube indicated loss of CO from the solution. The ‘H NMR spectrum of the reaction solution indicated about 35% of la remained ‘H NMR (CD3CN)6 5.97,5.89,5.87 (s, each 1 H, Tp’ CH), 2.67,2.60,2.47, 2.45,2.43,2.41 (s,333:633, Tp’ CH, and carbyne CH,); 13C(’H}NMR (CD,CN) 6 291.9 (carbyne carbon),248.6 (carbonyl),152.2,151.7,151.5,145.9,145.6, 145.3 (Tp’ CCH,), 106.4,106.5 (overlapping signals, 1:2, Tp’ CH), 36.2 (carbyne CH,), 15.9, 14.8, 14.1, 13.1, 12.6, 12.5 (Tp’ CH,). Separate signals due to coordinated acetonitrile were not observed. Tp’(CO)(CH,CN)Mo(CCH,) (5b). Complex l a (0.50 g, 1.0 mmol) was dissolved in 100 mL of CH3CN and photolyzed for 40 min at 0 “C. The IR spectrum of the red solution indicated that only traces of l a remained at this time: IR (CH,CN) 1840 cm-’ (vc0). Evaporation of the solvent resulted in a red oil. Attempts to isolate the product by chromatography or trituration resulted in decomposition. Tp’(CO)(PMe,)Mo(CMe) (6). Complex l a (0.30 g, 0.63 “01) was dissolved in 60 mL of acetone and photolyzed for 40 min at 0 “C. The infrared spectrum of the reaction solution indicated that only traces of la remained. The red solution was reduced to 5 mL, a solution of trimethylphosphine (1.0 mL, 10 mmol, dissolved in 10 mL of methylene chloride) was added, and the solution was stirred overnight. The cloudy solution was filtered, reduced to an oil, and chromatographed on alumina with 5:l hexanes/methylene chloride as the eluent. A thin yellow band eluted first and was identified as l a from its infrared spectrum. The second orange band, containing 6, was collected and evaporated to dryness, giving a yellow powder: yield 0.050 g, 15%; IR (KBr) 1841 (vco); ‘H NMR (CD2C12)6 5.80, 5.67, 5.65 (s, each 1 H, Tp’ CH), 2.51, 2.35, 2.32, 2.30, 2.27, 2.16 (8, each 3 H, Tp’ = 5 Hz, carbyne CH,), 1.24 (d, = 7 Hz, CCH,), 2.29 (d, 4JHp P(CH,),); ‘%(lH)NMR (CD2C12)6 288.1 (d, VCp= 20 Hz, carbyne carbon), 243.0 (d, 2Jcp= 10 Hz, carbonyl), 151.4,151.2,150.8,145.5, 145.4, 144.4 (Tp’CCH,), 106.5,106.4,105.2 (Tp’CH), 34.9 (carbyne CH3), 20.9 (d, ‘Jcp = 20 Hz, P(CH,),), . . 16.8, 16.0, 15.7, 13.1, 13.0, 12.9 (Tp’ CCH3).Thermodynamic Study. 4 was dissolved in CDzClzand sealed in an NMR tube. The tube was immersed in a flask containing a convenient solvent, and the solvent was heated to reflux. The tube was removed from the bath periodically, and the NMR spectrum was obtained; heating continued until successive spectra showed no further changes. Equilibrium constants were obtained from well-separated signals representing the acetonitrile-coordinated and triflate-coordinated species. Electrochemical Studies. A. A solution of Tp’(CO),Mo(tl2-C(0)CH3) was cooled to -20 “C, and the cyclic voltammogram was obtained. A single reversible wave was recorded with Ell2 = +0.30 V. At room temperature, cyclic voltammograms of this solution presented additional features indicative of sample decomposition following passage through the +0.30-V couple. The resting potential of the solution was -0.10 V. B. A solution of Tp’(C0)2Mo(CCH3)was cooled to -20 “C, and the cyclic voltammogram was obtained. A reversible wave was recorded with ElI2= +0.68 V. The resting potential of the solution was -0.12 V.
Organometallics, Vol. 8, No. 12, 1989 2789 Scheme I
7
H
t H3C H
/
Pa
c
T P ’ ( c o ) ~ M O ~ ~ ~
-HC(O)CH,
-OH-_ Tp’(CO)&io=CCH3
TP’(CO)*M;2cH ‘OH 3
Results and Discussion Synthesis of Carbyne Complexes. Under strongly alkaline conditions in alcohol solvent, molybdenum q2-acyl complexes are converted to molybdenum carbyne complexes in 20% yield (eq 5). No other products of this unusual reaction have been identified. Tp’(CO)nMcff0
EtOH, NaOEt
Tp’(C0),Mo=CCH3
(5)
A
The carbyne complexes 1 are characterized by two strong bands in the infrared spectrum, assigned to the terminal CO ligands, a t approximately 1980 and 1880 cm-’. The average of these bands is about 30 cm-’ higher in energy than the average CO stretching frequency of the starting q2-acyl complexes, consistent with the formation of the strongly .Ir-bonding carbyne ligand.20 Bands due to the Tp’ ligand can be identified near 2530 (B-H) and 1560 cm-l (C-N). The ‘HNMR spectra of complexes 1 exhibit resonances due to the carbyne substituent and the Tp’ ligand. The 2:l pattern of intensities observed for the Tp’ ligand protons is consistent with the presence of a plane of symmetry that contains the carbyne ligand and bisects the carbonyls. 13C NMR spectra display a low-field resonance at approximately 300 ppm, which is assigned to the carbyne carbon.’P2 Other resonances also appear in expected regions. Both base and protic solvent are required for the reaction to proceed: no carbyne product forms when tetrahydrofuran is employed or the base is absent. We have no mechanistic information. It may be that this reaction proceeds by attack of ethoxide at the metal center (Scheme I), followed by proton transfer to form a hydroxycarbene, release of acetaldehyde, and loss of hydroxide. Note that carbyne formation proceeds with greater difficulty for Tp’(CO)2Mo[q2-C(0)Et]than Tp’(C0),Mo[q2-C(O)Me] and that isopropanol/isopropoxideis a less effective promoter for the reaction than ethanol/ethoxide, perhaps due to steric congestion in the intermediates. The oxidation of primary and secondary alcohols to aldehydes and ketones is a common reaction effected by transition-metal reagents,21and seven-coordinate intermediates analogous to those in Scheme I have been suggested by Desmonds” to explain the formation of halogen-substituted carbynes of the type Tp’(CO),W(CX) from Tp’W(CO),1-. However, other mechanisms cannot be ruled out. McCleverty2?- has (20) Kostic, N. M.; Fenske,R. F.J . Am. Chem. SOC.1981,103,4677.
(21) Wilkinson, S.G. In Comprehensiue Organic Chemistry: Stoddart. J. F.,Ed.; Pergammon: Oxford, 1979; Vol. 1, p 579.
Brower et al.
2790 Organometallics, Vol. 8, No. 12, 1989 shown that one-electron reduction of Tp’(NO)Mo12 by alcohol solvent is the first step in ligand substitution reactions of this substrate. Thus, a role for ethoxide as a reductant toward Tp’(C0),M[q2-C(O)R] is plausible despite the lack of an accessible electrochemical reduction in aprotic solvent. The vinylidene anion, 2, prepared by deprotonating l a with excess Na[N(SiMe,),] in THF, can be detected at low temperature by NMR spectroscopy (eq 6). The vinylidene CH2group appears as a singlet at 3.74 ppm in the ‘H NMR spectrum. In the 13CNMR spectrum, a resonance at 349.6 Tp’(C0)2Mo=CCH3 la
+ Na[N(SiMe,),]
-18 ‘C
TP’(CO)~MO=C=CH,- (6) ll
L
ppm is assigned to the a-carbon of the vinylidene ligand, while the @-carbonresonates a t 91.4 ppm (t, lJcH = 153 Hz). When 1 equiv of base is employed, only half of carbyne l a is converted to vinylidene 2. Thus, the pKa of the methyl carbyne l a is approximately equal to the pKa of HN(SiMe3)2;23 the latter value is 25.8 in T H F solvent.% Ethylcarbyne complex l b can be similarly deprotonated, as shown by its successful use in the preparation of the isopropyl derivative, le. Conversion of carbyne ligands to vinylidene ligands via deprotonation has been investigated by Green? 13CNMR spectroscopy offers a simple means of identifying these species, since the chemical shifts of the a-carbon and the @-carbonof vinylidene ligands lie in reasonably well-defined regions of the spectrumaZ6 For complex 2, the @carbon resonates a t slightly higher field than typically observed (ca. 110-130 ppmZ5). However, its appearance as a triplet is conclusive-no other carbon atom in 2 is bound to two protons. The coupling information indicates that the @-carbonis sp2 hybridized as expected, and the negative charge in the complex is extensively delocalized. Complex 2 is susceptible to attack at the @-carbonof the vinylidene ligand by methyl iodide or ethyl iodide a t -78 “C, to regenerate a metal carbyne (eq 7). Nucleophilic behavior a t vinylidene C, has been observed in other W O ~ ~ ~ J Oand ~ ~ predicted ’ from molecular orbital calculationsaZ6 The vinylidene anion is quenched much less rapidly by ethyl iodide than by methyl iodide. Tp’(C0)2Mo=C=CH,RX TP’(CO)~MO=CCH~R X- (7)
+
4
+
Photolysis of methylcarbyne la in acetonitrile gives red solutions of Tp’(CO)(CH,CN)Mo(CCH,) ( 5 ) (eq 8). 13C NMR spectroscopy confirms that the carbyne linkage remains intact: a resonance at 291.9 ppm is assigned to the carbyne carbon. Compound 5 could not be isolated as a
hu
Tp’(C0)2Mo=CCH3 CH,CN la Tp’(CO)(CH&N)MeCCH,
-
+ CO
(8)
PMe,
Tp’(CO)(Me2CO)Mo=CCH, Tp’(CO)(PMe,)Mo=CCH,
by photolyzing l a in acetone and treating the resulting solution with excess trimethylphosphine (eq 9). An interesting feature of the ‘H NMR spectrum of 6 is the appearance of a doublet (4&p = 5 Hz) assigned to the methyl group of the carbyne ligand. In the 13C NMR spectrum, the carbyne carbon resonates a t 288.1 ppm, coupled to phosphorus by 20 Hz. The carbonyl carbon, a t 243.0 ppm, is coupled to phosphorus by 10 Hz. The coupling data are consistent with a metal-bound phosphine ligand. The presence of a single terminal CO absorption in the IR spectrum, at 1842 cm-l, and the lack of a ketonic absorption associated with a metal-bound ketenyl ligand completes the characterization of 6 as the product of simple CO substitution from la. The procedure employed by Stone’ to prepare Cp-based group VI carbyne complexes has been adapted to synthesize Tp’-based carbynes. Both la and IC were prepared this way. Compound l c was previously prepared by Desmond, et al.,8b by another route. They also encountered difficulty, as we did, in obtaining satisfactory analytical results for this compound. Formation of Tp’(CO ) (CH,CN) Mo (T$OCCP h) (3). In acetonitrile solvent, phenylcarbyne IC is photochemically converted to an $-ketenyl complex, Tp’(C0)(CH3CN)Mo(q2-OCCPh)(3), by coupling a carbonyl and the carbyne ligand (eq 10). The ketenyl complex is Tp’(C0)pMoECPh
hv
,.
Tp’(CO)(CH&N)Mo h(
(10)
CH3CN
IC
3
characterized by a single terminal CO absorption in the infrared spectrum at 1884 cm-l and by a broad, weak band at 1758 cm-’ that is assigned to the ketonic C = O moiety. NMR spectra of 3 confirm the loss of mirror symmetry in the complex, as shown by the unique set of resonances for each pyrazole ring of the Tp’ ligand. The a-carbon of the ketenyl ligand resonates a t 232.1 ppm and appears as a triplet (,JCH = 8 Hz). The ketenyl @-carbonis found at 209.5 ppm. These values are similar to those of other q2-ketenylcomplexes.n The bound acetonitrile resonates a t 143 ppm (CH3CNhZ8 The metal center in 3 is formally six-coordinate, considering the ketenyl group as occupying one coordination site, with a formal d4 configuration. A molecular orbital study has examined the preferred orientation of q2-ketenyl ligands in d4 octahedral environment^.^^ The a-system of the ketenyl ligand is not symmetrically distributed along the C-C-0 framework, due to the electronegative oxygen atom. As a result, if a competing a-acid such as CO is present in the coordination sphere, the ketenyl ligand maximizes a-overlap with the metal center when its oxygen atom lies proximal to the carbonyl. Structurally characterized monocarbonyl #-ketenyl complexes display this g e ~ m e t r y . ~By ’ this rationale, rotamer A would be more
(9)
6
Tp’(CO)(CH3CN)M I
Tp‘(CO)(CH3CN)Mdo I
pure solid, however. A stable analogue, 6, was obtained (22) McClevertv, J. A.; Murr, N. E. J. Chem. Soc., Chem. Commun. 1981,960. (23) This pK, value should be considered an ‘ion pair acidity”, as
others have pointed out: Crocco, G. L.; Gladysz, J. A. J.Am. Chem. SOC. 1988, 110, 6110, and references cited therein. (24) Fraser, R. R.; Mansour, T. S.; Savard, S. J. Org. Chem. 1985,50, 3232. (25) Bruce, M. I.; Swincer, A. G. Adu. Organomet. Chem. 1983,22,59. (26) Kostic, N. M.; Fenske, R. F. Organometallics 1982, 1, 974.
o& A
P ‘h
B
(27) (a) Fischer, E. 0.;Filippou, A. C.; Alt, H. G.; Ackermann, K. J. Oraanomet. Chem. 1983,254, C21. (b) Birdwhistell, K. R.; Tonker, T. L.rTempleton, J. L. J.Am. Chem. SOC.1985, 107, 4474. (c) Kreissl, F. R.; Friedrich, P.; Huttner, G. Angew. Chem., Int. Ed. Engl. 1977,16,102. (28) Fernandez, J. M.; Gladysz, J. A. Organometallics 1989, 8, 207. (29) Brower, D. C.; Birdwhistell, K. R.; Templeton, J. L. Organometallics 1986, 5 , 94.
Organometallics, Val. 8, No. 12, 1989 2791
Molybdenum Carbyne, Vinylidene, and Ketenyl Complexes Table I. Equilibrium Constants for Equation 12
T,“C 90
Kw
T,O C
14
57
Kw 3.5
42
1.8
78
9.5
65
5.0
stable than rotamer B. Steric repulsions between the phenyl group of the ketenyl ligand and the Tp’ ligand no doubt destabilize A, but the alkyne ligand in [Tp’(CO)(CH3CN)W (PhCCPh)] [BF4l3O adopts an orientation analogous to that proposed for the ketenyl ligand in 3-the phenyl substituent of the alkyne and the Tp’ ligand are accommodated in this case. NMR spectra indicate the presence of only one isomer of 3 a t room temperature. While population of isomer B by rotation of the ketenyl ligand cannot be ruled out by this result, the barrier to rotation is nevertheless likely to be high.29 Addition of Lewis acids to q2-ketenyl complexes is a facile route to alkoxyalkyne c ~ m p l e x e s . Accordingly, ~~ we find that 3 is readily alkylated by methyl triflate to give a cationic alkyne complex, 4 (eq 11). + CH30Tf
Tp’(CO)(CH3CN)Mo,
3
o ! .
,
.
I
.
I
-
I
‘
I
0.0027 0.0028 0,0029 0.0030 0.0031 0.0032 1I-r
Figure 1. Gibbs-Helmholtz plot of data from Table I. Scheme I1 Tp’(C0)pMoSCPh
I’
---c
-
