Unusual η1 Ligands Formed by an Unusual Reaction - American

Feb 11, 2011 - Fachbereich Chemie, Universit¨at Konstanz, Fach 727, 78457 Konstanz, Germany. Received December 10, 2010. The reaction of the ...
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Organometallics 2011, 30, 1215–1223 DOI: 10.1021/om101163j

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Amino-Substituted Butatrienes: Unusual η1 Ligands Formed by an Unusual Reaction† Bernhard Reichmann, Matthias Drexler, Bernhard Weibert, Normen Szesni, Tobias Strittmatter, and Helmut Fischer* Fachbereich Chemie, Universit€ at Konstanz, Fach 727, 78457 Konstanz, Germany Received December 10, 2010

The reaction of the bis(amino)allenylidene complex [(CO)5WdCdCdC(NMe2)2] with diethyldiazomethane yields two products, a cyclic carbene complex (2) by 1,2-addition of Et2C-N2 to the CR-Cβ bond of the allenylidene ligand and the η1-butatriene complex [(CO)5W{C[C(NMe2)2]d CdCEt2}] (3). Complex 2 slowly eliminates N2 and rearranges into 3. In contrast, only η1-butatriene complexes, [(CO)5M{C[C(NMe2)XR]dCdC(R0 )2}], are isolated from the reaction of diazoalkanes (R0 )2C-N2 (R0 = Me, Et, nPr) with alkoxy(amino)allenylidene complexes [(CO)5MdCd CdC(NMe2)OR] (M = Cr, W; R = Me, Et, (-)-menthyl) or with the (alkylthio)(amino)allenylidene complex [(CO)5WdCdCdC(NMe2)SnPr]. These new η1-butatriene complexes are related to CR phosphine adducts of allenylidene complexes such as [(CO)5W{C(PMe3)dCd C(NMe2)Ph}] (17) and might be regarded as CR carbene adducts. However, the PMe3 substituent in 17 is not replaced when 17 is treated with an N-heterocyclic carbene. Vice versa, the “carbene” substituent “C(NMe2)OEt” in the η1-butatriene complex [(CO)5Cr{C[C(NMe2)OEt]dCdCEt2}] is not replaceable by PMe3. Free N-heterocyclic carbenes do not add to the CR atom of the allenylidene complex [(CO)5WdCdCdC(C6H4NMe2-p)2] but instead to the Cγ atom, giving the dipolar neutral alkynyl complexes [(CO)5W-CtCC(C6H4NMe2-p)2L] (L = SIMe, SIMes). DFT calculations on the reaction mechanism indicate that a cyclic carbene complex and two isomeric η2-butatriene complexes are intermediates in the reaction pathway to form η1-butatriene complexes. The structure of two representative examples of η1-butatriene complexes and of one Cγ carbene adduct has been established by X-ray structure analyses.

Introduction The MC3 fragment in the allenylidene complexes [LnMd CRdCβdCγ(R1)R2]1 is characterized by a sequence of electrophilic and nucleophilic centers. The HOMO is predominantly localized at the metal and at the Cβ atom and the LUMO at CR and Cγ of the chain.2 Such a constellation allows for a multitude of reaction possibilities. Simple electrophiles are expected to add to the Cβ atom and nucleophiles to add to either the CR or the Cγ atom. The preferred site of nucleophilic attack is controlled by the substituents R1 and

R2, the type of nucleophile, the metal-ligand fragment, and in some cases also by the solvent.1 The addition of protic nucleophiles HX to the CR atom is usually followed by formation of vinylcarbene complexes.1 The addition of HX to the Cγ atom to form alkynyl complexes can be succeeded by substitution of X for one or both Cγ substituents.3-5 The reaction of allenylidene complexes with diprotic dinucleophiles will lead to different products, depending on the initial site of attack (Scheme 1). The R,γ sequence gives, via vinylcarbene complexes, new carbene complexes containing a

Dedicated to Professor J€urgen Heck on the occasion of his 60th birthday. *To whom correspondence should be addressed. E-mail: helmut. [email protected]. Tel: þ49-7531-882783. Fax: þ49-7531883136. (1) For reviews see: (a) Bruce, M. I.; Swincer, A. G. Adv. Organomet. Chem. 1983, 22, 59. (b) Bruce, M. I. Chem. Rev. 1991, 91, 197. (c) Doherty, S.; Corrigan, J. F.; Carty, A. J.; Sappa, E. Adv. Organomet. Chem. 1995, 37, 39. (d) Werner, H. J. Chem. Soc., Chem. Commun. 1997, 903. (e) Bruce, M. I. Chem. Rev. 1998, 98, 2797. (f) Touchard, D.; Dixneuf, P. H. Coord. Chem. Rev. 1998, 178-180, 409. (g) Cardierno, V.; Gamasa, M. P.; Gimeno, J. Eur. J. Inorg. Chem. 2001, 571. (h) Winter, R. F.; Z alis, S. Coord. Chem. Rev. 2004, 248, 1565. (i) Rigaut, S.; Touchard, D.; Dixneuf, P. H. Coord. Chem. Rev. 2004, 248, 1585. (j) Cadierno, V.; Gamasa, M. P.; Gimeno, J. Coord. Chem. Rev. 2004, 248, 1627. (k) Fischer, H.; Szesni, N. Coord. Chem. Rev. 2004, 248, 1659. (l) Cadierno, V.; Crochet, P.; Gimeno, J. In Metal Vinylidenes and Allenylidenes in Catalysis; Bruneau, C., Dixneuf, P. H., Eds.; Wiley-VCH: Weinheim, Germany, 2008; p 61 ff.

(2) For MO calculations on allenylidene complexes see: (a) Berke, H.; Huttner, G.; von Seyerl, J. Z. Naturforsch. 1981, 36B, 1277. (b) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Gonzalez-Cueva, M.; Lastra, E.; Borge, J.; Garcia-Granda, S.; Perez-Carreno, E. Organometallics 1996, 15, 2137. (c) Re, N.; Sgamellotti, A.; Floriani, C. Organometallics 2000, 19, 1115. (d) Baya, M.; Crochet, P.; Esteruelas, M. A.; Gutierrez-Puebla, E.; L opez, A. M.; Modrego, J.; O~ nate, E.; Vela, N. Organometallics 2000, 19, 2585. (e) Winter, R. F.; Klinkhammer, K.-W. Organometallis 2001, 20, 1317. (f) Marrone, A. M.; Re, N. Organometallics 2002, 21, 3562. (g) Marrone, A.; Coletti, C.; Re, N. Organometallics 2003, 23, 4952. (h) Auger, N.; Touchard, D.; Rigaut, S.; Halet, J.-F.; Saillard, J.-Y. Organometallics 2003, 22, 1638. (3) (a) Fischer, H.; Szesni, N.; Roth, G.; Burzlaff, N.; Weibert, B. J. Organomet. Chem. 2003, 683, 301. (b) Szesni, N.; Drexler, M.; Weibert, B.; Fischer, H. J. Organomet. Chem. 2005, 690, 5597. (c) Szesni, N.; Weibert, B.; Fischer, H. Inorg. Chim. Acta 2005, 358, 1645. (4) Drexler, M.; Haas, T.; Yu, S.-M.; Beckmann, H.; Weibert, B.; Fischer, H. J. Organomet. Chem. 2005, 690, 3700. (5) Szesni, N.; Weibert, B.; Fischer, H. Inorg. Chim. Acta 2006, 359, 617.

r 2011 American Chemical Society

Published on Web 02/11/2011

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pubs.acs.org/Organometallics

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Organometallics, Vol. 30, No. 5, 2011 Scheme 1

Reichmann et al. Scheme 2

the carbonyl oxygen atom to the CR-Cβ bond of the allenylidene ligand.13 We now report on the unusual reaction of diazoalkanes with amino-substituted allenylidene complexes leading to unprecedented η1-butatriene complexes.

Results and Discussion saturated cyclic carbene ligand,6 whereas the γ,R sequence affords, via initial substitution, complexes with an unsaturated carbene ligand.7,8 Finally, γ,γ addition yields, by double substitution, new allenylidene complexes Cγ now being part of a heterocycle.4,5 Dipolar substrates such as ynamines or imines, e.g. i PrNdC(H)Ph, add either to the CR-Cβ bond, giving isolable cyclic carbene complexes,9 or to the Cβ-Cγ bond, yielding initially new vinylidene complexes, Cβ of the vinylidene ligand being part of a cyclobutene ring. Formation of the cyclobutene ring is immediately followed by cycloreversion, affording new allenylidene complexes.5,10,11 Both reactions (R,β and β,γ addition) compete and may occur simultaneously, the product ratio then strongly depending on the solvent and the substitution pattern of both the allenylidene complex and the ynamine.10 Diazomethane was found to add to the CR atom. Elimination of dinitrogen gave η2-bound butatriene complexes, the butatriene initially being bonded to the metal via the terminal CdC bond (kinetically controlled reaction product). Isomerization finally gave complexes with the butatriene coordinated via the central CdC bond.12 The reaction of ethyl diazoacetate with [Ru(η5-Cp)(CdCdCPh2)(CO)(PiPr3)]BF4 gave a complex with an oxacyclopentylidene ligand formed by addition of the diazo carbon atom and

(6) Roth, G.; Fischer, H. J. Organomet. Chem. 1996, 507, 125. (7) Szesni, N.; Hohberger, C.; Mohamed, G. G.; Burzlaff, N.; Weibert, B.; Fischer, H. J. Organomet. Chem. 2006, 691, 5753. (8) For the formation of cyclic ligands by reaction of allenylidene complexes with nucleophiles see also: (a) Esteruelas, M. A.; Gomez, A. V.; L opez, A. M.; O~ nate, E. Organometallics 1998, 17, 3567. (b) Esteruelas, M. A.; Gomez, A. V.; L opez, A. M.; Olivan, M.; O~ nate, E.; Ruiz, N. Organometallics 2000, 19, 4. (c) Bernad, D. J.; Esteruelas, M. A.; L opez, A. M.; Olivan, M.; O~ nate, E.; Puerta, M. C.; Valerga, P. Organometallics 2000, 19, 4327. (d) Bertolasi, V.; Mantovani, N.; Marvelli, L.; Rossi, R.; Bianchini, C.; de los Rios, I.; Peruzzini, M.; Akbayeva, D. N. Inorg. Chim. Acta 2003, 344, 207. (9) Fischer, H.; Roth, G.; Reindl, D.; Troll, C. J. Organomet. Chem. 1993, 454, 133. (10) Roth, G.; Reindl, D.; Gockel, M.; Troll, C.; Fischer, H. Organometallics 1998, 17, 1393. (11) (a) Conejero, S.; Dı´ ez, J.; Gamasa, M. P.; Gimeno, J.; Garcı´ aGranda, S. Angew. Chem. 2002, 114, 3589; Angew. Chem., Int. Ed. 2002, 41, 3439. (b) Conejero, S.; Dı´ ez, J.; Gamasa, M. P.; Gimeno, J. Organometallics 2004, 23, 6299. (c) Dı´ ez, J.; Gamasa, M. P.; Gimeno, J.; Lastra, E.; Villar, A. J. Organomet. Chem. 2006, 691, 4092. (12) (a) Werner, H.; Laubender, M.; Wiedemann, R.; Windm€ uller, B. Angew. Chem. 1996, 108, 1330; Angew. Chem., Int. Ed. Engl. 1996, 35, 1237. (b) Werner, H.; Wiedemann, R.; Laubender, M.; Windm€ uller, B.; Steinert, P.; Gevert, O.; Wolf, J. J. Am. Chem. Soc. 2002, 124, 6966. (13) Esteruelas, M. A.; G omez, A. V.; L opez, A. M.; Puerta, M. C.; Valerga, P. Organometallics 1998, 17, 4959.

Preparative Results. In contrast to the reactions of trans[Cl{PiPr3}2RhdCdCdC(Ph)Y] (Y = Ph, CF3, tBu) with diazomethane,12 the reaction of the bis(dimethylamino)allenylidene complex 1 with freshly prepared excess diethyldiazomethane, Et2C-N2, in THF/Et2O (1:2) at room temperature proceeded slowly and was complete only after about 1 day. In the course of the reactions the color of the solutions changed from orange to red-brown. Chromatographic separation of the reaction mixture afforded essentially two compounds. Elution of both compounds required strongly polar solvents. The mass spectrum of the minor compound (2) isolated in only 5% yield indicated that 2 is composed of both starting compounds in a 1:1 ratio. From the ν(CO) absorptions in the IR spectrum and the NMR data it followed that 2 is the cyclic carbene complex shown in Scheme 2. Complex 2 was formed by cycloaddition of diethyldiazomethane to the CR-Cβ bond of the allenylidene ligand presumably initiated by nucleophilic attack of the dizoalkane at CR of 1. The structure of 2 was expected on the basis of previous results of the reactions of allenylidene pentacarbonyl complexes with ynamines.10 In tetrahydrofuran complex 2 slowly (1 h at 50 °C, then 15 h at ambient temperature) transformed into the second complex (3). The infrared spectra of complex 3, composed of 1 and the “Et2C” fragment of the diazoalkane and isolated in 24% yield, confirmed that the pentacarbonyl fragment had remained intact, implying coupling of “Et2C” with the allenylidene ligand. From the ν(CO) absorptions at rather low energy it further followed that the newly formed ligand is an even better donor than the π-donor-substituted allenylidene ligand in the starting complex 1 and that 3 exhibits considerable dipolar character. This fact was inconsistent with π bonding of the new ligand to the “(CO)5M” fragment. For olefinic type bonding a shift of the ν(CO) absorptions toward higher wavenumbers was to be expected. Exclusion of π bonding was also supported by a comparison of the 13C NMR data with those reported by Werner et al. for η2-butatriene rhodium complexes12 on the one hand and with those of pentacarbonyl olefin complexes on the other hand.14 The 13C NMR data, however, are related to (14) See e.g.: (a) Parlier, A.; Rudler, M.; Rudler, H.; Daran, J. C. J. Organomet. Chem. 1987, 323, 353. (b) Fischer, H.; Bidell, W.; Hofmann, J. Chem. Commun. 1990, 858. (c) Toma, J. M. D. R.; Toma, P. H.; Fanwick, P. E.; Bergstrom, D. E.; Byrn, S. R. J. Crystallogr. Spectrosc. Res. 1993, 23, 41. (d) Grevels, F.-W.; Jacke, J.; Klotzbucher, W. E.; Mark, F.; Skibbe, V.; Schaffner, K.; Angermund, K.; Kruger, C.; Lehmann, C. W.; Ozkar, S. Organometallics 1999, 18, 3278. (e) Gorski, M.; Kochel, A.; Szymanska-Buzar, T. Organometallics 2004, 23, 3037. (f) Gorski, M.; Kochel, A.; Szymanska-Buzar, T. Inorg. Chem. Commun. 2006, 9, 136.

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Figure 1. Structure of complex 3 in the crystal (hydrogen atoms omitted for clarity). Selected bond lengths (A˚), bond angles (deg), and torsion angles (deg): W1-C5 = 1.989(5), W1-CO(cis) (av) = 2.031(5), W1-C6 = 2.318(5), C6-C7 = 1.303(7), C7-C8 = 1.325(7), C6-C13 = 1.482(6), C13-N1 = 1.353(6), C13-N2 = 1.330(6); W1-C6-C7 = 124.6(3), W1-C6-C13 = 114.8(3), C6-C7-C8 = 173.6(5), C7-C6-C13 = 120.5(4), C6-C13-N1 = 119.4(4), C6-C13-N2 = 121.4(4); W1-C6C13-N1 = 75.5(5), C1-W1-C6-C7 = -37.2(4).

those complexes obtained by addition of phosphines to the CR atom of [(CO)5MdCdCdC(aryl)2],15 [(CO)5WdCd CdCd(NMe2)Ph] (16, see below), or of other transition metals,16 indicating strongly dipolar character of the new compounds and η1 coordination of the new ligand as shown in Scheme 2. The structure of the new complex 3 was finally established by an X-ray structure analysis (Figure 1). The butatriene ligand in 3 is η1 bound through that central carbon atom of the C4 chain that is adjacent to the heteroatom-substituted carbon atom and that constituted the Cβ atom of the former allenylidene ligand. Therefore, formation of the new complex involves a 1,2-shift of the pentacarbonylmetal fragment. In contrast, the butatriene ligand in Werner’s complexes12 is π coordinated via either one of the terminal CdC bonds (that formed by addition of “CH2” to the CR atom of the allenylidene ligand, kinetic product) or the central CdC bond (thermodynamic product). (15) Fischer, H.; Reindl, D.; Troll, C.; Leroux, F. J. Organomet. Chem. 1995, 490, 221. (16) (a) Kolobova, N. E.; Ivanov, L. L.; Zhvanko, O. S.; Khitrova, O. M.; Batsanov, A. S.; Struchkov, Yu. T. J. Organomet. Chem. 1984, 265, 271. (b) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; L opez-Gonzalez, M. C.; Borge, J.; Garcı´ a-Granda, S. Organometallics 1997, 16, 4453. (c) Esteruelas, M. A.; G omez, A. V.; Modrego, J.; O~ nate, E. Organometallics 1998, 17, 5434. (d) Peruzzini, M.; Barbaro, P.; Bertolasi, V.; Bianchini, C.; de los Rios, I.; Mantovani, N.; Marvelli, L.; Rossi, R. Dalton Trans. 2003, 4121. (e) Jimenez-Tenorio, M.; Palacios, M. D.; Puerta, M. C.; Valerga, P. J. Organomet. Chem. 2004, 689, 2776. (17) Roth, G.; Fischer, H. Organometallics 1996, 15, 1139. (18) (a) Casey, C. P.; Polichnowski, S. W.; Tuinstra, H. E.; Albin, L. D.; Calabrese, J. C. Inorg. Chem. 1978, 17, 3045. (b) Darensbourg, D. J.; Bauch, C. G.; Rheingold, A. L. Inorg. Chem. 1987, 26, 977. (c) Darensbourg, D. J.; Joyce, J. A.; Rheingold, A. L. Organometallics 1991, 10, 3407. (19) (a) Aumann, R.; Fr€ ohlich, R.; Prigge, J.; Meyer, O. Organometallics 1999, 18, 1369. (b) Barluenga, J.; Tomas, M.; Rubio, E.; LopezPelegrin, J. A.; Garcia-Granda, S.; Priede, M. P. J. Am. Chem. Soc. 1999, 121, 3065. (c) Rudler, H.; Martin-Vaca, B.; Nicolas, M.; Audouin, M.; Vaissermann, J. Organometallics 1998, 17, 361. (d) Rudler, H.; Audouin, M.; Parlier, A.; Martin-Vaca, B.; Goumont, R.; Durand-Reville, T.; Vaissermann, J. J. Am. Chem. Soc. 1996, 118, 12045. (e) Aumann, R.; Heinen, H.; Dartmann, M.; Krebs, B. Chem. Ber. 1991, 124, 2343. (f) Rudler, H.; Alvarez, C.; Denise, B.; Parlier, A.; Vaissermann, J. J. Organomet. Chem. 2003, 684, 105. (g) Rudler, H.; Parlier, A.; Durand-Reville, T.; Martin-Vaca, B.; Audouin, M.; Garrier, E.; Certal, V.; Vaissermann, J. Tetrahedron 2000, 56, 5001.

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The W-CO(trans) distance is significantly longer than the average of the W-CO(cis) distances, confirming the pronounced donor capacity of the butatriene ligand already deduced from the IR spectra. The W-C6 bond (2.318(5) A˚) is considerably longer than in the starting complex 1 (2.185(8) A˚)17 but is significantly shorter than the corresponding W-C bonds in [(CO)5W(olefin)] complexes (2.37-2.53 A˚)14 and slightly shorter than in anionic alkyl pentacarbonyl complexes (2.31-2.40 A˚)18 or neutral dipolar [(CO)5W-L] complexes with an W-C(sp3) bond (2.32-2.40 A˚).19 The W1 3 3 3 C7 and W1 3 3 3 C13 distances are 3.241 and 3.233 A˚, respectively. Therefore, a bonding interaction between W1 and C7 or C13 can be excluded. The atoms C6, C8, C13, and N2 are planar coordinated (sum of angles between 359.6 and 360°). Both terminal CR2 groups are nearly perpendicular with respect to the coordination plane formed by the atoms W, C6, C7, C8, and C13 (torsion angles: W-C6-C8-C11 = 85.3°; W-C6-C13-N1 = 75.5°), as expected for a butatriene. However, the CR2 groups are not coplanar but tilted against each other by 53.6°. The bonds C6-C7 and C7-C8 are short, C7-C8 being slightly longer than C6-C7. Both distances compare well with those in the PPh3 adduct [(CO)5Crh-C(PPh3)þdCdCPh2]20 and in allenyl complexes.21 A shortening of the CRdCβ bond with respect to the terminal CβdCγ bond is usually observed in allenyl complexes. In contrast to these bonds, C6-C13 is rather long and corresponds to a C(sp2)-C(sp2) single bond.22 In turn, the C13-N bonds are very short, indicating double-bond character. These bond lengths agree well with those in the starting allenylidene complex 1 (1.348 (6) A˚).17 When all these structural features are considered, complex 3 is best described as an adduct of a π-donor-stabilized carbene to the CR atom of the allenylidene ligand, comparable to CR phosphine adducts.14,20 Surprisingly, no reaction was observed when the chromium analogue of complex 1 was treated with diethyldiazomethane. In contrast, the allenylidene complex 4 (Scheme 3), related to 1 but Cγ being incorporated into a heterocycle, reacted significantly faster with Et2C-N2 in THF/Et2O (1:2) than did 1. From the reaction mixture the allenylidene complex 5 was isolated. Instead of a complex analogous to 2 or 3, complex 5 was formed by insertion of “Et2C” into both N-H bonds. Obviously, insertion into the N-H bond is much faster than nucleophilic addition to the CR atom. Replacing one terminal amino substituent in 1 by an alkoxy group led to an increase in the reaction rate. The reactions with diazoalkanes in Et2O were already complete within several hours and, in contrast to the chromium analogue of complex 1, the corresponding alkoxy(amino)allenylidene (20) Drexler, M. Ph.D. Thesis, Universit€at Konstanz, 2009. (21) (a) Matsuzaka, H.; Koizumi, H.; Takagi, Y.; Nishio, M.; Hidai, M. J. Am. Chem. Soc. 1993, 115, 10396. (b) Wiedemann, R.; Steinert, P.; Gevert, O.; Werner, H. J. Am. Chem. Soc. 1996, 118, 2495. (c) Blenkiron, P.; Corrigan, J. F.; Taylor, N. J.; Carty, A. J.; Doherty, S.; Elsegood, M. R. J.; Clegg, W. Organometallics 1997, 16, 297. (d) Bohanna, C.; Callejas, B.; Edwards, A. J.; Esteruelas, M. A.; Lahoz, F. J.; Oro, L. A.; Ruiz, N.; Valero, C. Organometallics 1998, 17, 373. (e) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann, W.; Spannenberg, A.; Rosenthal, U. Chem. Eur. J. 2000, 6, 81. (f) Blosser, P. W.; Calligaris, M.; Schimpff, D. G.; Wojcicki, A. Inorg. Chim. Acta 2001, 320, 110. (g) Arikawa, Y.; Ikeda, K.; Asayama, T.; Nishimura, Y.; Onishi, M. Chem. Eur. J. 2007, 13, 4024. (h) Takahashi, Y.; Tsutsumi, K.; Nakagai, Y.; Morimoto, T.; Kakiuchi, K.; Ogoshi, S.; Kurosawa, H. Organometallics 2008, 27, 276. (22) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; A. Orpen, G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.

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Scheme 3

Scheme 4

Figure 2. Structure of complex 12a in the crystal (hydrogen atoms omitted for clarity). Selected bond lengths (A˚), bond angles (deg), and torsion angles (deg): Cr1-C5 = 1.848(2), Cr1-CO(cis) (av) = 1.899(2), Cr1-C6 = 2.226(2), C6-C7 = 1.304(3), C7-C8 = 1.319(3), C6-C13 = 1.447(3), C13-N1 = 1.317(2), C13-O6 = 1.330(2); Cr1-C6-C7 = 125.5(2), Cr1C6-C13 = 111.4(1), C6-C7-C8 = 174.1(2), C7-C6-C13 = 123.2(2), C6-C13-N1 = 123.7(2), C6-C13-O6 = 123.0(2); Cr1-C6-C13-N1 = 87.0(2), C1-Cr1-C6-C7 = -120.6(2). Scheme 5

chromium complexes likewise reacted with the diazo compounds. η1-Butatriene complexes (Scheme 4) were exclusively isolated in yields ranging from 8 to 43%. Generally, the yields decreased in the series R0 = Me, Et, nPr. Complexes analogous to 2 could not be detected. The new complexes have been characterized by ν(CO) absorptions at rather low energy and by resonances for the butatriene carbon atoms in the ranges δ 82-95 (W-C2 and C4) and δ 178-201 (C1 and C3). The structure of complex 12a was additionally established by an X-ray structure analysis (Figure 2). The structural features of 12a correspond to those of 3; angles and distances are very similar. In addition to bis(amino)allenylidene and alkoxy(amino)allenylidene complexes, the (alkylthio)(amino)allenylidene complex 14 (obtained by thiolysis of complex 6b) reacted with diethyldiazomethane in Et2O in a similar way. After chromatography, the η1-butatriene complex 15 (Scheme 5) was isolated in 35% yield. In contrast, addition of diethyldiazomethane to a solution of the palladium allenylidene complex trans-[Br(PPh3)2PddCdCdC(OEt)NMe2][BF4]23 led to immediate N2 evolution. The reaction was complete within a few seconds; however, no complex related to 3 could be isolated. Instead, the starting complex was recovered almost completely. GC analysis of the reaction mixture after chromatography indicated that the Pd complex had acted as a catalyst for the dimerization of the Et2C fragment of the diazoalkane to form Et2CdCEt2. The spectroscopic data of 9-13 and 15 agree well with those of complex 3 and are similar to those of the PMe3 adduct 17 formed on treatment of allenylidene complex 16 with PMe3 in THF (Scheme 6). The similarity of the IR spectroscopic data and of the 13C resonances of the W-C3 unit of the new η1-butatriene (23) Kessler, F.; Szesni, N.; P~ ohako, K.; Weibert, B.; Fischer, H. Organometallics 2009, 28, 348.

Scheme 6

complexes with those of CR-PR3 adducts (such as 17 and those reported earlier) indicate that 3, 9-13, and 15 might be regarded as CR-carbene adducts of allenylidene complexes. The donor/acceptor properties of N-heterocyclic carbenes were found to be similar to those and even exceed those of tertiary phosphines.24 Attempts to replace the “C(OEt)NMe2” unit in 12a by PMe3 failed. Complex 12a reacted with PMe3 in excess very slowly. After 2 days at room temperature only the product of substitution of the complete butatriene ligand, [(CO)5CrPMe3], was detected. The free butatriene was not observed by GC/MS. Attempts to carry out the reverse process ; replacing PR3 in CR-PR3 adducts such as 17 by heterocyclic carbene ; likewise failed. No reaction was observed when the PPh3 adduct of allenylidene complex 18 (or its chromium analogue) was treated with the heterocyclic carbene 1,3dimesitylimidazolin-2-ylidene.25 (24) For reviews see e.g.: (a) Scott, N. M.; Nolan, S. P. Eur. J. Inorg. Chem. 2005, 1815. (b) Dı´ ez-Gonzalez, S.; Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874. (25) Arduengo, A. J., III; Krafczyk, R.; Schmutzler, R.; Craig, H. A.; Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55, 14523.

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Scheme 7

However, carbene adducts, albeit Cγ adducts, were obtained when allenylidene tungsten complex 18 was added to solutions in THF of in situ generated 1,3-dimethylimidazolin-2-ylidene26 and 1,3-dimesitylimidazolin-2-ylidene,25 respectively. The complexes 19 and 20 (Scheme 7) were isolated in 57% and 53% yields. The corresponding chromium complex also added the carbenes; however, these adducts turned out to be very labile. Therefore, they could not be isolated in a pure form. In contrast, the aminoallenylidene complex 6a did not react with these carbenes, presumably due to the strong π-donor capacity of the heteroatom substituents at Cγ that considerably reduces the electrophilicity of CR and Cγ. From the IR spectra of 19 and 20 a very strong donor potential of the new ligands was deduced. The ν(CO) absorptions (a) are observed at even lower energy than those of the CR phosphine adducts and of the complexes 3, 9-13, and 15 and (b) are found at only slightly higher energy than those of anionic tungsten alkynyl complexes such as Li[(CO)5W-CtCC(NMe2)2Ph].27 Complex 19 was additionally characterized by an X-ray structure analysis (Figure 3). As expected for an alkynyl complex, the W-CtC-C fragment is nearly linear (W1-C6-C7 = 176.5(5)°, C6-C7-C8 = 174.1(6)°) and the W-C6 bond (2.184(6) A˚) corresponds to a single bond (W-CR3 = 2.187 A˚).28 The bond W-C6 in 19 is significantly shorter than in 3. The shortening is expected when considering that W-C6 in 19 is a W-C(sp) and in 3 it is a W-C(sp2) bond. The length of 1.207(8) A˚ for C6-C7 is in agreement with the average value for a triple bond.22 All these data compare well with those of the anion [(CO)5W-CtCC(dO)NMe2]-,20 precursor of complex 6b. The Cγ atom (C8) is tetrahedrally coordinated, C-C8-C bond angles varying between 105.9(4) and 112.1(4)°. The C8-C bonds compare well with those expected for C(sp3)-C(sp2) and C(sp3)-C(sp) bonds, respectively. To avoid unfavorable steric interactions, the three planar rings at C8 adopt a propeller-type arrangement; the angles between the planes are 72.3, 83.3, and 85.5°. These Cγ carbene adducts proved to be quite stable. It was not possible to transform them thermally into the isomeric CR adduct or photochemically, via CO elimination and carbene migration, into allenylidene carbene tetracarbonyl complexes. DFT Calculations and Reaction Mechanism. Formation of the new η1-butatriene complexes involves transfer of the CR2 moiety of the diazoalkane to the allenylidene ligand and 1,2migration of the pentacarbonylmetal fragment. To elucidate the most likely reaction pathway, DFT calculations have been carried out on the reaction of complex 6a with (26) Benac, B. L.; Burgess, E. M.; Arduengo, A. J., III Org. Synth. 1986, 64, 92. (27) Dede, M. Ph.D. Thesis, Universit€at Konstanz, 2004. (28) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.

Figure 3. Structure of complex 19 in the crystal (hydrogen atoms omitted for clarity). Selected bond lengths (A˚) and bond angles (deg): W1-C5 = 2.000(6), W1-CO(cis) (av) = 2.036(6), W1-C6 = 2.184(6), C6-C7 = 1.207(8), C7-C8 = 1.484(8), C8-C9 = 1.526(7), C8-C21 = 1.559(7), C8-C31 = 1.545(8); W1-C6-C7 = 176.5(5), C6-C7-C8 = 174.1(6), C7-C8-C9 = 109.1(4), C7-C8-C21 = 105.9(4), C7-C8-C31 = 112.0(5). Scheme 8

dimethyldiazomethane, Me2C-N2. Several pathways have been taken into consideration, including direct attack of the diazoalkane at the Cγ atom. The most likely reaction mechanism, on the basis of these DFT calculations, is shown in Scheme 8; the energy profile is given in Figure 4. The reaction is initiated by the approach of the diazoalkane perpendicular to the allenylidene plane. The diazoalkane carbon atom interacts nucleophilically with the CR atom of the allenylidene ligand and the terminal nitrogen atom electrophilically with the allenylidene Cβ atom. Initially, the nucleophilic interaction dominates, as indicated by the

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Organometallics, Vol. 30, No. 5, 2011

Figure 4. Gibbs free energy profile for the reaction of 6a with dimethyldiazomethane. The states marked with an apostrophe include free molecular N2.

calculated distances Me2C 3 3 3 CR (2.22 A˚) and N 3 3 3 Cβ (2.68 A˚) in the transition state B. Ring closure leads to the zwitterionic complex C. The reaction A f C proceeds with an activation barrier of ΔGq = þ108 kJ/mol. The reaction is exergonic, and the free reaction enthalpy for A f C is ΔG = -43 kJ/mol. The next step involves elimination of N2 and migration of chromium to the newly formed Cdiazoalkane-CR bond. The activation barrier ΔGq for this reaction step (C f E) is 49 kJ/ mol. Due to the formation of molecular nitrogen the free reaction enthalpy is relatively large (ΔG = -98 kJ/mol). The calculated distances Cr-C(sp2) and Cr-C(sp) in E are 2.48 and 2.72 A˚, respectively. The subsequent migration of the metal carbonyl fragment to the central CdC bond (E f F f G) is slightly endergonic (ΔG = þ18 kJ/mol); the activation barrier ΔGq is small (36 kJ/mol). In G, both Cr-C(sp) distances are almost equal: 2.25 and 2.32 A˚, respectively. Finally, η2-butatriene complex G is transformed into the η1-butatriene I (equal to complex 9a). The activation barrier for the final step (G f H f I) is very low (ΔGq = 16 kJ/mol), and the free reaction enthalpy ΔG is -51 kJ/mol. The overall reaction is strongly exergonic with a reaction enthalpy of ΔGtotal = -174 kJ/mol. Complex C corresponds to complex 2 (see Scheme 2). Intermediate E is related to the kinetically controlled and structure G to the thermodynamically controlled η2-butatriene complexes of rhodium formed in the reaction of allenylidene rhodium complexes with diazomethane.12 In agreement with this reaction mechanism, complex 2 (Scheme 2) slowly reacts in solution at slightly elevated temperature to form complex 3. The calculated distances and angles in I (9a) agree reasonably well with those of 12a determined by the X-ray diffraction method. The HOMO in 9a is predominantly localized at the Cr-CO(trans) unit and at C3 (the central carbon atom of the CdCdC fragment) (see the Supporting Information). The LUMO is essentially composed of contributions from the C(O)N fragment and to a lesser degree from the Cr[C(cis)]4 fragment. From the natural population analysis it follows that the (CO)5Cr part of the molecule is negatively charged (-0.38), whereas the “C(OMe)NMe2” moiety is positively charged (þ0.68). This charge distribution supports the interpretation of the new η1-butatriene complexes as carbene adducts of allenylidene complexes.

Reichmann et al.

In summary, aminoallenylidene pentacarbonyl complexes, [(CO)5MdCdCdC(NMe2)R] (R = NMe2, OR, SR), react with diazoalkanes (R0 )2C-N2 to form butatriene complexes. In contrast to the η2-butatriene complexes previously synthesized, the butatriene ligand in the new complexes is bound in an unprecedented η1 mode via the former Cβ atom of the allenylidene ligand. According to the DFT calculations, the formation of the new complexes proceeds in a multistep process involving nucleophilic addition, ring closure, N2 elimination, and (CO)5M migration. A heterocyclic carbene complex and (although not detected until now) two η2butatriene complexes are likely intermediates. The yields significantly decrease with increasing chain length of R0 presumably for steric reasons. For R0 = nBu a reaction was no longer observed. To be isolable, the η1-butatriene complexes seem to require two strong π-donor substituents at C1 (Cγ of the starting allenylidene complex) such as amino, alkoxy, and alkylthio groups. When an amino(phenyl)- (R = Ph) or amino(phosphino)allenylidene complex (R = PPh2) was treated with diethyldiazomethane, a rapid reaction was observed; however, η1-butatriene complexes could not be detected. The same was true for bis(aryl)allenylidene pentacarbonyl complexes. The rate of the reaction of allenylidene complexes with diazoalkanes increases with decreasing π-donor capacity of the substituents at Cγ of the allenylidene complex, whereas the stability of the resulting η1-butatriene complexes decreases. Increasing the back-bonding potential of the L5M moiety through replacing one CO ligand in [(CO)5 CrdCdCdC(NMe2)OMe] by PPh3 led to a reaction failure. Likewise, no reaction was observed when phenyldiazomethane or ethyl diazoacetate was employed instead of dialkyldiazomethanes. Obviously, a high nucleophilicity of the diazoalkane carbon atom is necessary for the reaction to proceed. Although the spectroscopic data of the η1-butatriene complexes indicate that these compounds are best regarded as adducts of aminocarbenes at the CR atom of allenylidene complexes, N-heterocyclic carbenes do not add to CR. Instead, they add to the Cγ atom, affording dipolar neutral alkynyl pentacarbonyl complexes. Thus, CR as well as Cγ carbene adducts are accessible but require different reaction pathways.

Experimental Section All reactions were performed under a nitrogen atmosphere using standard Schlenk techniques. Solvents were dried by distillation from CaH2 (CH2Cl2), LiAlH4 (petroleum ether), and sodium (THF, Et2O). The silica gel used for chromatography (Roth, silica for flash chromatography) was nitrogen saturated. The yields refer to analytically pure compounds and are not optimized. Instrumentation: 1H NMR and 13C NMR spectra were recorded with a Jeol JNX 400 or a Varian Inova 400 spectrometer at ambient temperature. Chemical shifts are reported relative to the residual solvent peaks. IR: Biorad FTS 60. UV-vis: Hewlett-Packard diode array spectrophotometer 8453. MS: Finnigan MAT 312. Elemental analysis: Elementar vario EL or Elementar vario Micro Cube. GC: Thermo Finnigan Trace GC. Dimethyldiazomethane,29 diethyldiazomethane,29 di-npropyldiazomethane,29 1,3-dimethylimidazolin-2-ylidene,26 1,3dimesitylimidazolin-2-ylidene,25 and the complexes 1,3a 6a,3a (29) Day, A. C.; Raymond, P.; Southam, R. M.; Whiting, M. C. J. Chem. Soc. C 1966, 467.

Article 6b,3a 7a,3a 8b,5 16,3a and 1830 were prepared according to literature procedures. Complex 4 was synthesized by γ,γ double substitution from 6b and ethylenediamine, as described in ref 4. HgO (yellow, Fluka), 3-pentanone (Acros), and 4-heptanone (Aldrich) were commercial products and were used without further purification. Reaction of Complex 1 with Diethyldiazomethane. A solution of 1 mmol of the allenylidene complex 1 in 5 mL of THF was added at room temperature to a solution of diethyldiazomethane (5 mmol, 10 mL, 0.5 M solution in Et2O). The progress of the reaction was followed by monitoring the ν(CO) absorption in the IR spectra. The reaction was complete after 24 h. The solvent was removed in vacuo. The residue was chromatographed at -20 °C on silica gel. First, complex 3 was eluted with petroleum ether/ethyl acetate (ratio decreasing from 1:1 to 0:1) and then complex 2 with acetone. Pentacarbonyl((5,5-diethylpyrazol-3-ylidene)tetramethylmethanediamine)tungsten (2). Yellow solid. Yield: 0.03 g (5%). IR (THF): ν(CO) 2049 w, 1950 vw, 1915 vs, 1897 vs cm-1. 1H NMR (d6-acetone): δ 0.43 (t, 3JHH = 7.4 Hz, 6H, CH2CH3), 2.08 (m, 2H, CH2CH3), 2.50 (m, 2H, CH2CH3), 3.18, 3.55 (br, 12H, NCH3). 13C NMR (d6-acetone): δ 8.7 (CH2CH3), 29.8 (CH2CH3), 114.2 (CC(NCH3)2), 169.6 (CCH2CH3), 199.6 (JWC = 120.9 Hz, cis-CO), 202.0 (trans-CO), 207.0 (CC(NCH3)2), 290.4 (CR). FAB-MS: m/z (%) 546 (5) [Mþ], 519 (3) [(M - CO)þ], 491 (5) [(M - 2CO)þ], 461 (56) [(M - 3CO)þ], 403 (26) [(M - 5CO)þ]. Due to the small amount of complex available (very low yield!) an elemental analysis could not be performed. Pentacarbonyl[η1,KC2-1,1-bis(dimethylamino)-4-ethylhexa-2,3dien-2-yl]tungsten (3). Yellow solid. Yield: 0.12 g (24%). Mp: 84-87 °C. IR (THF): ν(CO) 2052 w, 1958 w, 1907 vs, 1879 m cm-1. 1H NMR (d6-acetone): δ 1.06 (t, 3JHH = 7.4 Hz, 6H, CH2CH3), 2.06 (m, 4H, CH2CH3), 3.29 (s, 12H, NCH3). 13C NMR (d6-acetone): δ 13.0 (CCH2CH3), 24.7 (CCH2CH3), 42.4 (NCH3), 91.3 (CCH2CH3), 92.9 [C(W)], 178.8 [C(N{CH3}2)], 199.3 (dCd), 200.8 (JWC = 126.4 Hz, cis-CO), 203.1 (trans-CO). FAB-MS: m/z (%) 518 (6) [Mþ], 490 (7) [(M - CO)þ], 462 (51) [(M - 2 CO)þ], 404 (21) [(M - 4 CO)þ], 376 (41) [(M - 5 CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 386 nm (3.152). Anal. Calcd for C17H22N2O5W (518.22): C, 39.40; H, 4.28; N, 5.41. Found: C, 39.47; H, 4.44; N, 5.34. Pentacarbonyl[2-(1,3-diisopropylimidazolidine)propa-1,2-dienylidene]tungsten (5). A solution of 1 mmol of the allenylidene complex 4 in 5 mL of THF was added at room temperature to a solution of diethyldiazomethane (5 mmol, 10 mL, 0.5 M solution in Et2O). The progress of the reaction was followed by monitoring the ν(CO) absorptions in the IR spectra. The reaction was complete after 5 h. The solvent was removed in vacuo. The residue was chromatographed at -20 °C on silica gel with petroleum ether/CH2Cl2 (ratio decreasing from 3/1 to 2/1) as the eluant. Yellow powder. Yield: 0.24 g (43%). Mp: 107-110 °C. IR (THF): ν(CO), 2090 vw, 1972 vw, 1924 vs, 1897 m cm-1; ν(CCC), 2024 w cm-1. 1H NMR (d6-acetone): δ 0.94 (t, 3JHH = 6.6 Hz, 6H, CHCH2CH3), 1.64 (q, 3JHH = 7.0 Hz, 4H, CHCH2CH3), 3.82 (s, 2H, CH2), 4.14 (br, 1H, CHCH2). 13C NMR (d6-acetone): δ 11.9 (CHCH2CH3), 26.6 (CHCH2CH3), 42.5 (CHCH2), 97.6 (Cβ), 150.6 (Cγ), 165.3 (CR), 199.3 (cisCO), 203.0 (trans-CO). FAB-MS: m/z (%) 558 (57) [Mþ], 530 (80) [(M - CO)þ], 502 (100) [(M - 2CO)þ], 430 (14) [(M CHEt2)þ], 418 (65) [(M - 5CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 382 nm (4.269). Anal. Calcd for C20H26N2O5W (558.29): C, 43.03; H, 4.69; N, 5.02. Found: C, 42.66; H, 4.65; N, 4.99. General Procedure for the Synthesis of the Complexes 9-13. At room temperature a solution of the diazo compound (5 mmol, 10 mL, 0.5 M solution in Et2O) was added to 1 mmol of the solid allenylidene complex (6a, 0.30 g; 6b, 0.44 g; 7a, (30) Fischer, H.; Reindl, D.; Roth, G. Z. Naturforsch. 1994, 49b, 1207.

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0.32 g; 8b, 0.56 g). The progress of the reaction was followed by monitoring the ν(CO) absorption in the IR spectra. When the starting allenylidene complex could no longer be detected, the solvent was removed in vacuo. The residue was chromatographed on silica gel at -20 °C using petroleum ether/CH2Cl2 (ratio decreasing from 3/1 to 2/1) as the eluant. Pentacarbonyl[η1,KC2-1-(dimethylamino)-1-methoxy-4-methylpenta-2,3-dien-2-yl]chromium (9a). Yellow oil. Yield: 0.07 g (19%). IR (THF): ν(CO) 2045 vw, 1964 vw, 1917 vs, 1888 m cm-1. 1H NMR (d6-acetone): δ 1.67 (s, 6H, CCH3), 3.26, 3.39 (s, 6H, NCH3), 4.16 (s, 3H, OCH3). 13C NMR (d6-acetone): δ 19.7 (CCH3), 37.7, 41.7 (NCH3), 59.9 (OCH3), 82.3 (CCH3), 93.5 [C(Cr)], 179.9 [C(OCH3)], 198.2 (dCd), 220.7 (cis-CO), 225.9 (trans-CO). FAB-MS: m/z (%) 345 (16) [Mþ], 289 (42) [(M 2CO)þ], 261 (70) [(M - 3CO)þ], 233 (100) [(M - 4CO)þ], 204 (85) [(M - 5CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 391 nm (3.237). Anal. Calcd for C14H15NO6Cr (345.27): C, 48.70; H, 4.38; N, 4.06. Found: C, 48.58; H, 4.40; N, 4.03. Pentacarbonyl[η1,KC2-1-(dimethylamino)-1-methoxy-4-methylpenta-2,3-dien-2-yl]tungsten (9b). Yellow solid. Yield: 0.21 g (43%). IR (THF): ν(CO) 2056 w, 1963 w, 1916 vs, 1885 m cm-1. 1H NMR (d6-acetone): δ 1.70 (s, 6H, CCH3), 3.27, 3.39 (s, 6H, NCH3), 4.18 (s, 3H, OCH3). 13C NMR (d6-acetone): δ 19.7 (CCH3), 37.9, 42.2 (NCH3), 60.4 (OCH3), 84.4 (CCH3), 91.0 [C(W)], 180.3 [C(OCH3)], 201.2 (dCd), 201.7 (JWC = 126.8 Hz, cis-CO), 204.4 (JWC = 154.9 Hz, trans-CO). FAB-MS: m/z (%) 477 (11) [Mþ], 449 (16) [(M - CO)þ], 421 (100) [(M - 2CO)þ], 393 (12) [(M - 3CO)þ], 365 (56) [(M - 4CO)þ], 337 (69) [(Mþ 5CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 384 nm (3.369). Anal. Calcd for C14H15NO6W (477.13): C, 35.24; H, 3.17; N, 2.94. Found: C, 35.62; H, 3.55; N, 2.92 (these data show that this compound is not analytically pure but are presented nonetheless to inform the reader of the best results obtained to date). Pentacarbonyl[η1,KC2-1-(dimethylamino)-1-methoxy-4-ethylhexa-2,3-dien-2-yl]chromium (10a). Yellow oil. Yield: 0.14 g (37%). IR (THF): ν(CO) 2046 w, 1965 w, 1916 vs, 1888 m cm-1. 1H NMR (d6-acetone): δ 1.10 (t, 3JHH = 7.4 Hz, 6H, CCH2CH3), 2.04 (q, 3JHH = 7.4 Hz, 4H, CCH2CH3), 3.29, 3.46 (s, 6H, NCH3), 4.22 (s, 3H, OCH3). 13C NMR (d6-acetone): δ 13.1 (CH2CH3), 25.0 (CH2CH3), 36.6, 41.0 (NCH3), 59.2 (OCH3), 86.7 (CCH2CH3), 93.8 [C(Cr)], 178.8 [C(OCH3)], 196.3 (dCd), 219.4 (cis-CO), 224.4 (trans-CO). FAB-MS: m/z (%) 373 (5) [Mþ], 346 (3) [(M - CO)þ], 317 (16) [(M - 2CO)þ], 289 (29) [(M - 3CO)þ], 261 (73) [(M - 4CO)þ], 233 (75) [(M 5CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 390 nm (2.954). Anal. Calcd for C16H19NO6Cr (373.33): C, 51.48; H, 5.13; N, 3.75. Found: C, 51.60; H, 5.16; N, 3.78. Pentacarbonyl[η1,KC2-1-(dimethylamino)-1-methoxy-4-ethylhexa-2,3-dien-2-yl]tungsten (10b). Yellow oil. Yield: 0.24 g (46%). IR (THF): ν(CO) 2056 w, 1963 w, 1913 vs, 1886 m cm-1. 1H NMR (CDCl3): δ 1.00 (t, 3JHH = 7.4 Hz, 6H, CH2CH3), 1.99 (q, 3JHH = 7.4 Hz, 4H, CH2CH3), 3.10, 3.26 (s, 6H, NCH3), 4.09 (s, 3H, OCH3). 13C NMR (CDCl3): δ 13.1 (CH2CH3), 24.7 (CH2CH3), 25.0 (CCH2CH3), 36.8, 41.2 (NCH3), 59.0 (OCH3), 86.3 (CCH2CH3), 93.6 [C(W)], 178.5 [C(OCH3)], 197.9 (dCd), 200.0 (cis-CO), 202.9 (trans-CO). EI-MS: m/z (%) 505 (24) [Mþ], 449 (11) [(M - 2CO)þ], 365 (49) [(M - 5CO)þ]. Anal. Calcd for C16H19NO6W (505.18): C, 38.04; H, 3.79; N, 2.77. Found: C, 38.27; H, 3.88; N, 2.79. Pentacarbonyl[η1,KC2-1-(dimethylamino)-1-methoxy-4-propylhepta-2,3-dien-2-yl]tungsten (11b). Dark yellow oil. Yield: 0.04 g (8%). IR (THF): ν(CO) 2056 w, 1962 w, 1914 vs, 1886 m cm-1. 1H NMR (d6-acetone): δ 0.82 (t, 3JHH = 7.3 Hz, 6H, CCH2CH2CH3), 1.40 (m, 4H, CCH2CH2CH3), 1.89 (t, 3JHH = 7.8 Hz, 4H, CCH2CH2CH3), 3.14 (s, 3H, NCH3), 3.30 (s, 3H, NCH3), 4.09 (s, 3H, OCH3). 13C NMR (d6-acetone): δ 14.4 (CCH2CH2CH3), 22.1 (CCH2CH2CH3), 34.4 (CCH2CH2CH3), 34.6 (CCH2CH2CH3), 37.1, 41.6 (NCH3), 59.7 (OCH3), 85.4 (CCH2CH2CH3), 89.9 [C(W)], 179.3 [C(OCH3)], 199.9 (dCd), 200.8 (JWC = 130.3 Hz, cis-CO), 203.9 (trans-CO).

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FAB-MS: m/z (%) 533 (6) [Mþ], 479 (57) [(M - 2 CO)þ], 391 (29) [(M - 5 CO)þ]. Due to the small amount of complex available (oil, very low yield!), an elemental analysis could not be performed. Pentacarbonyl[η1,KC2-1-(dimethylamino)-1-ethoxy-4-ethylhexa-2,3-dien-2-yl]chromium (12a). Yellow solid. Yield: 0.14 g (35%). Mp: 69-71 °C. IR (THF): ν(CO) 2045 w, 1964 w, 1916 vs, 1887 m cm-1. 1H NMR (d6-acetone): δ 1.07 (t, 3JHH = 7.5 Hz, 3H, CCH2CH3), 1.09 (t, 3JHH = 7.5 Hz, 3H, CCH2CH3), 1.41 (t, 3 JHH = 7.1 Hz, 3H, OCH2CH3), 2.02 (q, 3JHH = 7.0 Hz, 4H, CCH2CH3), 3.27, 3.42 (s, 6H, NCH3), 4.54 (q, 3JHH = 7.0 Hz, 1H, OCH2CH3), 4.62 (q, 3JHH = 7.2 Hz, 1H, OCH2CH3). 13C NMR (d6-acetone): δ 13.7, 15.6 (CCH2CH3), 25.6, 26.2 (CCH2CH3), 37.3, 41.6 (NCH3), 69.6 (OCH2CH3), 85.4 (CEt2), 94.4 [C(Cr)], 179.2 [C(OCH3)], 196.4 (dCd), 220.1 (cis-CO), 225.2 (trans-CO). FAB-MS: m/z (%) 387 (6) [Mþ], 359 (10) [(M - CO)þ], 331 (4) [(M - 2CO)þ], 303 (6) [(M - 3CO)þ], 275 (4) [(M - 4CO)þ], 247 (18) [(M - 5CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 400 nm (3.212). Anal. Calcd for C17H21CrNO6 (387.35): C, 52.71; H, 5.46; N, 3.62. Found: C, 52.51; H, 5.58; N, 3.67. Pentacarbonyl{η1,KC2-1-(dimethylamino)-1-[(-)-menthyloxy]4-ethylhexa-2,3-dien-2-yl}tungsten (13b).

Yellow oil. Yield: 0.08 g (13%). IR (THF): v(CO) 2055 w, 1959 w, 1911 vs, 1886 m cm-1. 1H NMR (d6-acetone): δ 0.92-1.01 (m, 10H, H3, H7, H9, H10), 1.09-1.13 (m, 8H, H5, CCH2CH3), 1.61-1.68 (m, 1H, H6), 1.76-1.80 (m, 3H, H2, H8), 1.92-2.02 (m, 2H, H4), 2.08-2.14 (m, 2H, CCH2CH3), 2.18-2.29 (m, 2H, CCH2CH3), 3.29, 3.45 (s, 6H, NCH3), 4.69 (td, 3JHH = 10.5 Hz, 2JHH = 4.7 Hz, 1H, H1). 13C NMR (d6acetone): δ 13.9 (CCH2CH3), 17.3 (C7), 22.6 (C9), 23.0 (C10), 24.9 (C5), 26.9 (CCH2CH3), 27.6 (C8), 33.0 (C3), 35.3 (C4), 38.1 (C2), 42.1, 42.6 (NCH3), 49.7(C6), 84.9 (C1), 87.0 (CCH2CH3), 91.9 [C(W)], 179.8 (CO-menthyl), 201.1 (dCd), 201.8 (cis-CO), 203.6 (trans-CO), C(OC1) not detected. FAB-MS: m/z (%) 629 (18) [Mþ], 574 (44) [(M - 2CO)þ], 518 (14) [(M - 4CO)þ], 489 (9) [(M - 5CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 384 nm (3.531). Anal. Calcd for C25H35NO6W (629.41): C, 47.71; H, 5.81; N, 2.23. Found: C, 47.60; H, 5.80; N, 2.68. Pentacarbonyl[3-(dimethylamino)-3-(propylthio)-1,2-propadienylidene]tungsten (14). A solution of 1.1 mmol of BuLi in hexane (0.69 mL, 1.6 M) was added dropwise at -80 °C to a solution of n-propanethiol in 10 mL of THF. The solution was stirred at -80 °C for 30 min. A solution of 6b in 10 mL of THF was added. The solution was warmed to room temperature, and then stirring was continued for 1 h. The solvent was removed in vacuo. The residue was chromatographed at -20 °C on silica gel with petroleum ether/CH2Cl2 (ratio decreasing from 1/1 to 0/1) as the eluant. Orange solid. Yield: 0.21 g (44%). Mp: 87-90 °C. IR (THF): ν(CO) 2081 vw, 1929 vs, 1907 m cm-1; ν(CCC) 1997 m cm-1. 1H NMR (d6-acetone): δ 1.08 (t, 3JHH = 7.3 Hz, 3H, SCH2CH2CH3), 1.83-1.89 (m, 2H, SCH2CH2CH3), 3.42 (t, 3 JHH = 7.3 Hz, 2H, SCH2CH2CH3), 3.45, 3.70 (s, 6H, NCH3). 13 C NMR (d6-acetone): δ 14.2 (SCH2CH2CH3), 24.4 (SCH2CH2CH3), 39.8 (SCH2CH2CH3), 42.2, 47.1 (NCH3), 110.4 (Cβ), 162.1 (Cγ), 190.3 (CR), 198.1 (JWC = 124.5 Hz, cisCO), 203.8 (JWC = 131.0 Hz, trans-CO). FAB-MS: m/z (%) 479 (67) [Mþ], 452 (100) [(M - CO)þ], 423 (48) [(M - 2 CO)þ], 339 (31) [(M - 5 CO)þ]. UV-vis: λmax (log ε) [solvent] 474 nm (4.331) [pentane]; 438 nm (4.315) [CH2Cl2]; 414 nm (4.202) [DMF]. Anal. Calcd for C13H13NO5SW (479.16): C, 32.59; H, 2.73; N, 2.92. Found: C, 32.57; H, 2.88; N, 2.99.

Reichmann et al. Pentacarbonyl[η1,KC2-1-(dimethylamino)-1-(propylthio)-4ethylhexa-2,3-dien-2-yl]tungsten (15). Yellow oil. Yield: 0.11 g (19%). IR (THF): v(CO) 2055 w, 1961 w, 1912 vs, 1886 m cm-1. 1 H NMR (d6-acetone): δ 1.00-1.07 (m, 9H, C3CH2CH3, SCH2CH2CH3), 1.68-1.79 (m, 2H, SCH2CH2CH3), 2.03-2.08 (m, 4H, C3CH2CH3), 3.20-3.27 (m, 2H, SCH2CH2CH3), 3.44, 3.56 (s, 6H, NCH3). 13C NMR (d6-acetone): δ 14.4 (C3CH2CH3), 24.2 (C3CH2CH3), 25.6 (SCH2CH2CH3), 27.2 (SCH2CH2CH3), 38.3 (SCH2CH2CH3), 42.5, 46.0 (NCH3), 94.0 (CEt2), 98.4 [C(W)], 192.1 [C(SnPr)], 196.3 (dCd), 201.9 (JWC = 125.2 Hz, cis-CO), 204.3 (trans-CO). FAB-MS: m/z (%) 549 (4) [Mþ], 520 (9) [(M CO)þ], 465 (11) [(M - 3 CO)þ], 406 (16) [(M - 5 CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 384 nm (3.399). Anal. Calcd for C18H23NO5SW (549.29): C, 39.36; H, 4.22; N, 2.55. Found: C, 40.23; H, 4.19; N, 2.76 (these data show that this compound is not analytically pure but are presented nonetheless to inform the reader of the best results obtained to date). Pentacarbonyl[η1,KC1-3-(dimethylamino)-3-phenyl-1-(trimethylphosphonio)propa-1,2-dien-1-yl]tungsten (17). A solution of 5 equiv of PMe3 was added quickly to a solution of 1 mmol of complex 16 in 50 mL of THF. The reaction was followed by IR spectroscopy and was complete within 1 h. The solvent was removed in vacuo. The brown residue was recrystallized from pentane/CH2Cl2 (3/1) to afford yellow crystals. Yield: 0.54 g (97%). Mp: 133-134 °C. IR (THF): ν(CO) 2055 w, 1964 w, 1918 vs, 1905 s, 1882 m cm-1. 1H NMR (d6-acetone): δ 1.96 (d, 2 JPH = 12.9 Hz, 9H, PCH3), 2.53 (s, 6H, NCH3), 7.12 (m, 1H, Ph), 7.30 (m, 2H, Ph), 7.46 (m, 2H, Ph). 13C NMR (d6-acetone): δ 12.7 (d, 1JPC = 57.8 Hz, PCH3), 45.0 (NCH3), 76.9 (C3), 93.2 (C1), 127.1, 127.2, 129.6, 137.9 (m, Ph), 201.8 (d, 3JPC = 1.6 Hz, cis-CO), 204.1 (d, 3JPC = 2.1 Hz, trans-CO), 213.8 (d, 2JPC = 8.1 Hz, C2). 31P NMR (d6-acetone): δ 19.1. FAB-MS: m/z (%) 557 (31) [Mþ], 529 (26) [(M - CO)þ], 501 (68) [(M - 2 CO)þ], 473 (19) [(M - 3 CO)þ], 445 (22) [(M - 4 CO)þ], 417 (38) [(M - 5 CO)þ]. UV-vis (CH2Cl2): λmax (log ε): 375 nm (3.588). Anal. Calcd for C19H20NO5PW (557.20): C, 40.96; H, 3.62; N, 2.51. Found: C, 40.93; H, 3.47; N, 2.64. General Procedure for the Synthesis of the Complexes 19 and 20. At -80 °C, 0.5 mmol of 1,3-dimethylimidazolium iodide (or 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride), dissolved in 10 mL of THF, was deprotonated with 1 mmol of BuLi (0.62 mL, 1.6 M in hexane). Then, complex 18 (0.3 g, 0.5 mmol) was added as a solid. The solution turned from deep blue to greenblue. After 30 min the reaction was complete. The solution was filtered at -20 °C over a 2 cm layer of silica. The solvent was removed in vacuo. The residue was dissolved in a minimum amount of CH2Cl2. Crystallization of the products 19 and 20 was done by solvent layering (3/1) of hexane on the dichloromethane solution. Pentacarbonyl{3,3-bis[p-(dimethylamino)phenyl]-3-(N,N-dimethylimidazolyl)propynyl}tungsten (19). Green solid. Yield: 0.20 g (57%). Mp: 216-218 °C. IR (THF): ν(CO) 2043 w, 1951 vw, 1908 vs, 1869 m cm-1; ν(CtC) 2043 w cm-1. 1H NMR (d6-acetone): δ 2.95 (s, 12H, N(CH3)2), 3.49 (s, 6H, NCH3), 6.72, 7.38 (d, 8H, Ph), 7.53 (s, 2H, imidazole). 13C NMR (d6-acetone): δ 39.2 (NCH3), 40.6 (N(CH3)2), 106.8 (JWC = 109.0 Hz, CR), 110.2 (Cβ), 112.9, 124.7, 130.3, 130.5, 150.0, 151.3 (C6H4, imidazole C), 200.6 (JWC = 124.5 Hz, cis-CO), 203.1 (transCO), FAB-MS: m/z (%) 695 (9) [Mþ], 611 (9) [(M - 3 CO)þ]. UV-vis (CH2Cl2): λmax (log ε) 373 nm (3.572). Anal. Calcd for C29H28N4O5W (696.42): C, 50.02; H, 4.05; N, 8.05. Found: C, 49.92; H, 4.33; N, 7.76. Pentacarbonyl{3,3-bis[p-(dimethylamino)phenyl]-3-[N,N-bis(2 0 ,4 0 ,6 0 -trimethylphenyl)imidazolyl]propynyl}tungsten (20). Green solid. Yield: 0.25 g (53%). Mp: 171-174 °C. IR (THF): ν(CO) 1957 vw, 1909 vs, 1869 m cm-1; ν(CtC) 2042 w cm-1. 1H NMR (d6-acetone): δ 2.19 (s, 6H, Mes), 2.26 (s, 12H, Mes), 2.81 (s, 12H, NCH3), 6.28, 7.64 (m, 8H, Ph), 6.69 (s, 4H, Mes), 7.66 (s, 2H, imidazole). 13C NMR (d6-acetone): δ 20.3 (Μes), 40.8 (NCH3), 105.6 (CR), 112.1 (Cβ), 126.0, 129.9, 130.0, 130.5,

Article

Organometallics, Vol. 30, No. 5, 2011

Table 1. Crystal Data and Refinement Details for Compounds 3, 12a, and 19

formula Mr cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z F(calcd) (g/cm3) μ (mm-1) F(000) max 2θ (deg) index ranges no. of data no. of unique data no. of params R1(F), I > 2σ(I) wR2(F2), all data goodness of fit on F2 max, min ΔF (e/A˚3)

3

12a

19

C17H22N2O5W 518.22 triclinic P1 8.9841(18) 9.3610(19) 12.898(3) 96.62(3) 102.75(3) 112.00(3) 957.2(3) 2 1.798 6.062 504 53.62 -11 e h e 11 -11 e k e 11 -16 e l e 16 12 736 3978 226 0.0305 0.0651 1.040 2.024, -2.474

C17H20CrNO6 386.34 triclinic P1 9.1653(18) 9.910(2) 11.834(2) 89.59(3) 72.69(3) 66.44(3) 933.0(3) 2 1.375 0.644 402 57.9 -12 e h e 12 -12 e k e 13 -16 e l e 16 15 717 4878 226 0.0456 0.1075 1.036 0.641, -0.692

C29H28N4O5W 696.40 monoclinic P21/c 12.500(3) 16.028(3) 14.100(3) 90 95.04(3) 90 2814.1(10) 4 1.644 4.149 1376 52.44 -15 e h e 15 -19 e k e 19 -17 e l e 17 36 429 5647 352 0.0415 0.0741 1.024 1.182, -2.037

134.5, 135.7, 139.9, 150.8 (C6H4, imidazole C), 200.4 (cis-CO), 203.0 (trans-CO). FAB-MS: m/z (%) 903 (5) [Mþ], 846 (6) [(M 2 CO)þ], 820 (53) [(M - 3 CO)þ], 764 (78) [(M - 5 CO)þ]. UV-vis (CH2Cl2): λmax (nm) (log ε) 373 (3.632). Anal. Calcd for C45H44N4O5W 3 0.5CH2Cl2 (904.72): C, 57.70; H, 4.79; N, 5.92. Found: C, 57.96; H, 4.72; N, 6.03. X-ray Structure Analysis of 3, 12a, and 19. Single crystals of 3, 12a, and 19 suitable for X-ray structure analyses were obtained at 4 °C by slow diffusion of n-hexane into solutions of 3, 12a, and 19 in CH2Cl2. The measurements were performed with a crystal mounted on a glass fiber on a Stoe IPDS II diffractometer (graphite monochromator, Mo KR radiation, λ = 0.710 73 A˚). The structures were solved by direct methods using the SHELXTL-97 program package.31 The positions of the hydrogen atoms were calculated by assuming ideal geometry, and their (31) Sheldrick, G. M. SHELX-97, Programs for Crystal Structure Analysis; Universit€ at G€ ottingen, G€ ottingen, Germany, 1997.

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coordinates were refined together with those of the attached carbon atoms as riding models. All other atoms were refined anisotropically. For the crystallographic data and the refinement details see Table 1. Computational Details. All ab initio calculations were performed using Jaguar32 (version 5.5.016) running on Linux2.4.20-28.7smp on six Athlon MP 2400þ dual-processor workstations (Beowulf cluster) parallelized with MPICH 1.2.4. Initial structures were obtained by MMþ optimization using Hyperchem.33 Geometries were optimized using the LACVP* basis set (ECP for Cr, N31G6* for all other atoms)34 and the BP86 density functional.35 Calculation of the second derivatives ensured that true minima were found by showing no large negative frequencies. Transition states of reorganization reactions were obtained by using the QST (quadratic synchronous transit) method implemented in Jaguar, using an interpolated structure between starting compound and product as a transition state guess. After the second derivative was calculated, all transition states showed exactly one imaginary frequency in the direction of the reaction coordinate. All reported activation energies are Gibbs free activation energies at 298.15 K. Transition states of the nucleophilic attack were obtained by a stepwise reduction of the corresponding C-C bond distance. The maximum energy structures from these geometry scans were finally used as transition state guesses in standard LST (linear synchronous transit) calculations with Jaguar. Again, second derivatives were used for transition state validation. Supporting Information Available: CIF files, figures, and tables giving (a) the bond distances, bond angles, and torsion angles of the complexes 3, 12a, and 19, (b) the Cartesian coordinates and energies (at 298 K) of the starting compounds, the product complex 9a, the optimized minima, and the transition states, (c) the orbital contributions to the HOMO and LUMO of 9a, (d) a summary of the natural population analysis of 9a, and (e) representative UV-vis spectra for the various types of complexes. This material is available free of charge via the Internet at http://pubs.acs.org. (32) Jaguar 5.5; Schrodinger, LLC, Portland, OR, 2003. (33) Hyperchem (version 5); Hypercube Inc., Gainesville, FL, 32601. (34) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (35) (a) Slater, J. C. Quantum Theory of Molecules and Solids; McGraw-Hill: New York, 1974; Vol. 4 (The Self-Consistent Field for Molecules and Solids). (b) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (c) Perdew, J. P.; Zunger, A. Phys. Rev. B 1981, 23, 5048. (d) Perdew, J. P. Phys. Rev. B 1986, 33, 8822. (e) Perdew, J. P. Phys. Rev. B 1986, 34, 7406.