Heterometallic Derivatives of the Unsaturated Methyl-Bridged

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Organometallics 2010, 29, 904–916 DOI: 10.1021/om900961u

Heterometallic Derivatives of the Unsaturated Methyl-Bridged Complex [Mo2(η5-C5H5)2(μ-CH3)(μ-PCy2)(CO)2]. Photochemical Generation of Methylidyne-Bridged Clusters M. Angeles Alvarez, M. Esther Garcı´ a, M. Eugenia Martı´ nez, and Miguel A. Ruiz* Departamento de Quı´mica Org anica e Inorg anica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain Received November 3, 2009

The photochemical reactions of the methyl-bridged complex [Mo2Cp2(μ-CH3)(μ-PCy2)(CO)2] (1) (Cp = η5-C5H5) with the carbonyl complexes [M(CO)6] (M = Cr, Mo, W) and [MnCp0 (CO)3] (Cp0 = η5-C5H4CH3) give the corresponding electron-precise methylidyne-bridged derivatives [MMo2Cp2(μ3CH)(μ-PCy2)(CO)7] (Mo-Mo = 2.9340(13) A˚ for M = W) and [MnMo2Cp2Cp0 (μ3-CH)(μ-PCy2)(CO)4] (Mo-Mo = 2.9678(6) A˚) in good yields. Under similar conditions, the reaction of 1 with [Ru3(CO)12] gives the 46-electron methylidyne-bridged cluster [Mo2RuCp2(μ3-CH)(μ-PCy2)(CO)5] (Mo-Mo = 2.6824(7) A˚), along with a small amount of the methoxy-bridged analogue [Mo2RuCp2(μ3-OCH3)(μPCy2)(CO)5]. A related iron species [FeMo2Cp2(μ3-OCH3)(μ-PCy2)(CO)5] (Mo-Mo = 2.667(1) A˚) can be prepared in moderate yield from the reaction of the 30-electron methyl complex [Mo2Cp2(μ-κ1:η2CH3)(μ-PCy2)(μ-CO)] and [Fe2(CO)9]. Compound 1 reacts with [Fe2(CO)9] at room temperature to give the acetyl-bridged cluster [FeMo2Cp2{μ3-κ1:η2:κ1-C(O)CH3}(μ-PCy2)(CO)5] (Mo-Mo = 2.8474(5) A˚) in high yield, which undergoes full cleavage of the acetyl C-O bond under thermal or photolytic activation to give the oxoethylidyne derivative [FeMo2Cp2(μ3-CCH3)(μ-PCy2)(O)(CO)4] (Mo-Mo = 2.8469(4) A˚). Under photochemical conditions, however, compound 1 reacts with [Fe2(CO)9] to give the methylidyne-bridged compound [Fe2Mo2Cp2(μ4-CH)(μ-PCy2)(CO)8] (Mo-Mo = 2.8351(7) A˚) as major species. This 60-electron cluster displays a butterfly Mo2Fe2 core with no agostic interactions of the methylidyne ligand.

Introduction Recently we reported the preparation, structure, and bonding of the unsaturated methyl-bridged complex [Mo2Cp2(μ-CH3)(μ-PCy2)(CO)2] (1), which revealed that in the solid state the methyl ligand is involved in a very weak agostic interaction with the dimetal center. This interaction is retained in solution, but there the agostic form A probably coexists with small amounts of the nonagostic form B (Chart 1), only slightly higher in energy (as computed for the analogous benzyl complex).1 Because of the weakness of the C-H 3 3 3 Mo interaction in the agostic form, the real unsaturation of the dimetal center in both structures is likely to be essentially the same and close to that expected for a triply bonded molecule. In any case, compound 1 provides an excellent opportunity to examine the chemistry of a bridging methyl ligand at a highly unsaturated dimetal site at the molecular level. Alkyl-bridged complexes are species of general interest for several reasons: they serve as models both for intermediates in alkyl-transfer processes and for adsorbates in several heterogeneously catalyzed reactions *To whom correspondence should be addressed. E-mail: mara@ uniovi.es. (1) (a) Garcı´ a, M. E.; Ramos, A.; Ruiz, M. A.; Lanfranchi, M.; Marchio, L. Organometallics 2007, 26, 6197. (b) García, M. E.; Melon, S.; Ramos, A.; Riera, V.; Ruiz, M. A.; Belletti, D.; Graiff, C.; Tiripicchio, A. Organometallics 2003, 22, 1983. pubs.acs.org/Organometallics

Published on Web 01/15/2010

Chart 1

such as the Fischer-Tropsch synthesis, and they are also implied as catalysts or precursors of the homogeneous catalysts used in the polymerization of olefins.2,3 Although (2) (a) Braunstein, P.; Boag, N. M. Angew. Chem., Ed. Int. 2001, 40, 2427. (b) Marks, T. J. Acc. Chem. Res. 1992, 25, 57. (3) For some recent work on alkyl-bridged complexes see, for example: (a) Bryliakov, K. P.; Talsi, E. P.; Semikolenova, N. V.; Zakharov, V. A. Organometallics 2009, 28, 3225. (b) Li, S.; Miao, W.; Tang, T.; Dong, W.; Zhang, X.; Cui, D. Organometallics 2008, 27, 718. (c) Bryliakov, K. P.; Talsi, E. P.; Voskoboynikov, A. Z.; Lancaster, S. J.; Bochmann, M. Organometallics 2008, 27, 6333. (d) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. J. Am. Chem. Soc. 2006, 128, 15005. (e) Dietrich, H. M.; Grove, H.; T€ornroos, K. W.; Anwander, R. J. Am. Chem. Soc. 2006, 128, 1458. (f) Weng, Z.; Teo, S.; Koh, L. L.; Hor, T. S. A. Chem. Commun. 2006, 1319. r 2010 American Chemical Society

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a large number of such binuclear complexes have been reported so far, only some of them display metal-metal bonds, these generally exhibiting an agostic interaction with one of the metal atoms. The reactivity reported so far for the alkyl ligands in the latter complexes includes the oxidative addition of the agostic C-H bond at trimetal centers,4 rearrangement of the ligand to a terminal coordination mode,5 deprotonation,6 reductive elimination with other ligands,7 and insertion of CO.5c,d,8 Among all the alkylbridged complexes described so far, however, only a few of them display multiple intermetallic bonding,9 and the reactivity of the latter unsaturated species has not been explored. In a preliminary study on the chemical behavior of the methyl-bridged complex 1 we found that, while a molecule of CO could be removed photochemically to yield the carbonyl derivative [Mo2Cp2(μ-κ1:η2-CH3)(μ-PCy2)(μ-CO)] (2), having a strengthened agostic interaction (Chart 1), the photochemical treatment of 1 in the presence of [Mo(CO)6] or [Fe2(CO)9] gave methylidyne-bridged heterometallic clusters, thus revealing the occurrence of easy dehydrogenation steps in these reations.10 This is an unusual evolution of a bridging agostic methyl ligand. Actually, we can quote only a couple of precedents of related μ-CH3/μ-CH transformations involving agostic ligands, these reported to occur at room temperature at Ru2 (through dehydrogenation)11 and Fe3 (through double oxidative addition of C-H bonds) metal centers.4b In addition, related μ-CH2R/μ-CH/μ-CR transformations (R = CH2Ph) were reported recently to occur at 120 °C in a Ru3 cluster.12 Besides this we note that (4) (a) Calvert, R. B.; Shapley, J. R. J. Am. Chem. Soc. 1977, 99, 5225. (b) Dutta, T. K.; Vites, J. C.; Jacobsen, G. B.; Fehlner, T. P. Organometallics 1987, 6, 842. (5) (a) Samant, R. G.; Trepanier, S. J.; Wigginton, J. R.; Xu, L.; Bierenstiel, M.; McDonald, R.; Ferguson, M. J.; Cowie, M. Organometallics 2009, 28, 3407. (b) Wigginton, J. R.; Trepanier, S. J.; McDonald, R.; Ferguson, M. J.; Cowie, M. Organometallics 2005, 24, 6194. (c) Rowsell, B. D.; McDonald, R.; Cowie, M. Organometallics 2004, 23, 3873. (d) Trepanier, S. J.; McDonald, R.; Cowie, M. Organometallics 2003, 22, 2638. (6) (a) Davies, D. L.; Gracey, B. P.; Guerchais, V.; Knox, S. A. R.; Orpen, A. G. J. Chem. Soc., Chem. Commun. 1984, 841. (b) Casey, C. P.; Fagan, P. J.; Miles, W. H. J. Am. Chem. Soc. 1982, 104, 1134. (c) Dawkins, G. M.; Green, M.; Orpen, A. G.; Stone, F. G. A. J. Chem. Soc., Chem. Commun. 1982, 41. (7) (a) Carlucci, L.; Proserpio, D. M.; D’Alfonso, G. Organometallics 1999, 18, 2091. (b) Noh, S. K.; Sendlinger, S. C.; Janiak, C.; Theopold, K. H. J. Am. Chem. Soc. 1989, 111, 9127. (8) (a) Samant, R. G.; Trepanier, S. J.; Wigginton, J. R.; Xu, L.; Bierenstiel, M.; McDonald, R.; Ferguson, M. J.; Cowie, M. Organometallics 2009, 28, 3407. (b) Gao, Y.; Jennings, M. C.; Puddephatt, R. J. Organometallics 2001, 20, 1882. (c) Jeffery, J. C.; Orpen, A. G.; Stone, F. G. A.; Went, M. J. J. Chem. Soc., Dalton Trans. 1986, 173. (9) Apparently only a few complexes (all dichromium ones) have been reported to have methyl bridges over multiple metal-metal bonds: (a) Horvath, S.; Gorelsky, S. I.; Gambarotta, S.; Korobkov, I. Angew. Chem., Int. Ed. 2008, 47, 1. (b) Heintz, R. A.; Ostrander, R. L.; Rheingold, A. L.; Theopold, K. H. J. Am. Chem. Soc. 1994, 116, 11387. (c) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. Organometallics 1994, 13, 1646. (d) Andersen, R. A.; Jones, R. A.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1978, 446. (10) Alvarez, M. A.; Garcı´ a-Viv o, D.; Garcı´ a, M. E.; Martı´ nez, M. E.; Ramos, A.; Ruiz, M. A. Organometallics 2008, 27, 1973. (11) Connelly, N. G.; Forrow, N. J.; Gracey, B. P.; Knox, S. A. R.; Orpen, A. G. J. Chem. Soc., Chem. Commun. 1985, 14. (12) Temjimbayashi, R.; Murotani, E.; Takemori, T.; Takao, T.; Suzuki, H. J. Organomet. Chem. 2007, 692, 442. (13) (a) Cho, H.-G.; Lester, A. J. Phys. Chem. A 2006, 110, 3886, and references therein. (b) Marsh, A. L.; Becraft, K. A.; Somorjai, G. A. J. Phys. Chem. B 2005, 109, 13619, and references therein. (c) Maitlis, P. M.; Zanotti, V. Chem. Commun. 2009, 1619. (d) Maitlis, P. M. J. Organomet. Chem. 2004, 689, 4366. (e) Maitlis, P. M. J. Mol. Catal. A 2003, 204-205, 55. (f) Dry, M. E. Catal. Today 2002, 71, 227.

Organometallics, Vol. 29, No. 4, 2010

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Chart 2

methylidyne clusters are relatively scarce molecules related to the surface species following methane activation by metal atoms and surfaces and to those involved in relevant heterogeneously catalyzed industrial processes such as the Fischer-Tropsch synthesis.13 Moreover only a few heterometallic methylidyne clusters containing molybdenum have been reported previously, these displaying MoCo2,14 Mo2Co,15 MoCoRu,16 and Mo2Ru4 metal cores.17 We thus decided to study in more detail the reactions of the methyl complex 1 with different metal-carbonyl substrates as a likely rational route to heterometallic clusters bridged by methylidyne or related ligands. As it will be shown below, the reactions of 1 with 16-electron metal carbonyl fragments has allowed us to prepare in good yields new methylidynebridged clusters having trinuclear Mo2M (M=Cr, Mo, W, Mn, Fe, Ru) and tetranuclear Mo2Fe2 metal skeletons. In contrast, those reactions with metal-metal bonded dimers of type [M2Cp2(CO)2n] or [M2(CO)2n] led to no new products (M=Mo, Co, Mn) or complex mixtures of products (M= Fe, Ni) that could not be characterized.

Results and Discussion Reactions of Compound 1 with [M(CO)6] (M=Cr, Mo, W). The photolysis of toluene solutions of 1 and the hexacarbonyls [M(CO)6] (M=Mo, W) using visible-UV light gives the trinuclear methylidyne clusters [MMo2Cp2(μ3-CH)(μ-PCy2)(CO)7] [M = Mo (3a), W (3b)] in good yield (Chart 2). No reaction took place, however, when using tetrahydrofuran (THF) as solvent. In the same line, our attempts to prepare (14) (a) Zhang, W.; Watson, W. H.; Richmond, M. G. J. Chem. Crystallogr. 2008, 38, 437. (b) Watson, W. H.; Poola, B.; Richmond, M. G. J. Organomet. Chem. 2006, 691, 5567. (c) Zhang, W. Q.; Zhu, B. H.; Hu, B.; Zhang, Y. H.; Zhao, Q. Y.; Ying, Y. Q.; Sun, J. J. Organomet. Chem. 2004, 689, 714. (d) Beurich, H.; Vahrenkamp, H. Chem. Ber. 1982, 116, 2385. (15) Duffy, D. N.; Kassis, M. M.; Rae, A. D. J. Organomet. Chem. 1993, 460, 97. (16) Schacht, H. T.; Vahrenkamp, H. Chem. Ber. 1989, 122, 2239. (17) Adams, H.; Gill, L. J.; Morris, M. J. Organometallics 1996, 15, 4182.

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Alvarez et al. Table 1. Selected Bond Lengths and Angles for Compounds 3a10 and 3b

Figure 1. ORTEP diagram (30% probability) of compound 3b, with Cy rings (except the C1 atoms) and H atoms (except H8) omitted for clarity.

these clusters through the thermal reaction of 1 with the adducts [M(CO)5(THF)] were also unsuccessful, suggesting that the methyl complex 1 lacks the electron-donor ability needed to displace the coordinated THF molecule. Unlike the above reactions with [Mo(CO)6] and [W(CO)6], the photolytic reaction of 1 with [Cr(CO)6], under the same conditions, gives a mixture of three isomeric methylidyne derivatives, [CrMo2Cp2(μ3-CH)(μ-PCy2)(CO)7] (3c, 4) and [CrMo2Cp2(μ-CH)(μPCy2)(CO)7] (5), differing in the relative positioning of the bridging (and even carbonyl) ligands (Chart 2). These products were found to interconvert in solution, with the equilibrium ratio being 1:15:5, respectively, in CD2Cl2 solution, as shown by NMR measurements (see Experimental Section). Moreover, the ratio 4/5 increases to 4:1 in C6D6 solution (3c being present only in trace amounts here), whereas compound 4 is the unique isomer present in acetone-d6 solution. We should finally note that, although the formation of the methylidyne complexes 3 to 5 from the methyl complex 1 requires the elimination of hydrogen at some intermediate stage, to be discussed later on, we have been unable to characterize any intermediate species in these reactions. Solid-State and Solution Structure of Compounds 3. The structure of the trimolybdenum compound 3a was determined by X-ray diffraction methods in our preliminary study.10 We have now determined that of the Mo2W compound 3b, which is very similar (Figure 1 and Table 1). In both cases the molecule can be viewed as resulting from the addition of a M(CO)5 fragment (M = Mo, W) to the unsaturated dimetal center of a dehydrogenated molecule of 1 (thus transformed into a methylidyne-bridged substrate) opposite the dicyclohexylphosphide ligand. This is accompanied by a trans to cis rearrangement of the Mo2Cp2(CO)2 moiety, not unexpected under photochemical conditions,18 while the M(CO)5 fragments display octahedral geometry, with the sixth coordination position roughly pointing to the center of the Mo2C(8) triangle. The Mo-Mo separation of ca. 2.93 A˚ is significantly shorter than the Mo-W ones (ca. 3.10 A˚). Yet, all these values can be considered consistent with the presence of single intermetallic bonds and are comparable to the intermetallic lengths found for the electron-precise (48-electron) clusters [MMo2(μ3-S)(CO)12][PPN]2 (M=Mo, W).19 Although the M(CO)5 fragments can be isolobal-related to either CH3þ or (18) (a) Alvarez, C. M.; Garcı´ a, M. E.; Ruiz, M. A.; Connelly, N. G. Organometallics 2004, 23, 4750. (b) Bitterwolf, T. E.; Scallorn, W. B.; Li, B. H. Organometallics 2000, 19, 3280. (19) Darensbourg, D. J.; Zalewski, D. J.; Sanchez, K. M.; Delord, T. Inorg. Chem. 1988, 27, 821.

3a (M = Mo)

3b (M = W)

Mo(1)-Mo(2) Mo(1)-M Mo(2)-M Mo(1)-C(8) Mo(2)-C(8) M-C(8) Mo(1)-P Mo(2)-P C(8)-H(8)

2.9283(3) 3.1245(3) 3.0938(3) 2.040(3) 2.053(3) 2.316(3) 2.410(1) 2.425(1) 0.99(3)

2.934(1) 3.113(1) 3.086(1) 2.06(1) 2.06(1) 2.32(1) 2.410(3) 2.422(3) 1.02(13)

Mo(1)-M-Mo(2) Mo(1)-Mo(2)-C(2) Mo(2)-Mo(1)-C(1) Mo(2)-P-Mo(1) Mo(1)-C(1)-O(1) Mo(2)-C(2)-O(2) Mo(1)-C(8)-Mo(2) Mo(1)-C(8)-H(8) Mo(2)-C(8)-H(8) P-Mo(1)-C(8) P-Mo(2)-C(8)

56.2(1) 87.0(1) 86.7(1) 74.5(1) 170.9(2) 170.5(2) 91.4(1) 129(2) 126(2) 79.0(1) 78.4(1)

56.5(1) 87.6(3) 86.6(3) 74.8(1) 171(1) 172(1) 90.8(4) 129(8) 127(7) 78.5(3) 78.0(3)

CH2 depending on the partner,20 the above intermetallic distances suggest a methylenic behavior of this fragment in compounds 3a,b so as to render an electron-precise cluster. In contrast, we have previously found that in the related hydridebridged cluster [WMo2Cp2(μ3-H)(μ-PCy2)(CO)7], having two fewer cluster electrons, the W(CO)5 fragment acts essentially as an acceptor group (CH3þ-like behavior), then exhibiting quite large Mo-W lengths (ca. 3.35 A˚), as expected for a 3c-2e interaction.21 We finally note the largely asymmetric coordination of the methylidyne ligand in 3b, strongly bound to the Mo atoms, as indicated by the short Mo-C lengths of ca. 2.05 A˚, but more weakly bound to the W(CO)5 fragment (M-C ca. 2.30 A˚). The above Mo-C lengths are comparable to those measured for the trimolybdenum compounds [Mo3Cp3(μ3CH)(CO)6]22 and [Mo3Cp*3(μ3-CH)(μ-CH2)(μ-O)2].23 Spectroscopic data in solution for compounds 3a,b are consistent with the structure found in the solid state for these molecules, but only limited data are available for compound 3c due to its low proportion in the corresponding mixture of isomers. The IR spectra for 3a,b display a strong band at ca. 2040 cm-1, characteristic of the presence of M(CO)5 fragments (M = Cr, Mo, W).24 As for the 31P NMR spectra, these complexes exhibit resonances ranging from 164 to 173 ppm. These chemical shifts are somewhat lower than the values of ca. 170-210 ppm previously found by us for the unsaturated clusters derived from the complexes [Mo2Cp2(μ-H)(μ-PCy2)(CO)2]21 and [Mo2Cp2(μ-COMe)(μ-PCy2)(μ-CO)]25 and are thus consistent with the formulation of compounds 3 as electron-precise molecules. Their 1H NMR spectra display in each case a single cyclopentadienyl resonance, indicative of the (20) (a) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711. (b) Stone, F. G. A. Angew. Chem., Int. Ed. Engl. 1984, 23, 89. (21) Alvarez, C. M.; Alvarez, M. A.; Garcı´ a, M. E.; Ramos, A.; Ruiz, M. A.; Graiff, C.; Tiripicchio, A. Organometallics 2007, 26, 321. (22) (a) Akida, M.; Noda, K.; Moro-oka, Y. Organometallics 1994, 13, 4145. (b) Akida, M.; Noda, K.; Takahashi, Y.; Moro-oka, Y. Organometallics 1995, 14, 5209. (23) Guzyr, O. I.; Prust, J.; Roesky, H. W.; Lehman, C.; Teicher, M.; Cimpoesu, F. Organometallics 2000, 19, 1549. (24) Braterman, P. S. Metal Carbonyl Spectra; Academic Press: London, U.K., 1975. (25) (a) Garcı´ a, M. E.; Garcı´ a-Viv o, D.; Ruiz, M. A. Organometallics 2009, 28, 4385. (b) García, M. E.; García-Vivo, D.; Ruiz, M. A. Organometallics 2008, 27, 169.

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Table 2. Selected IRa and NMRb Data for New Compounds ν(CO)a

compound [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7] (3a) [Mo2WCp2(μ3-CH)(μ-PCy2)(CO)7] (3b) [CrMo2Cp2(μ3-CH)(μ-PCy2)(CO)7] (3c) [CrMo2Cp2(μ3-CH)(μ-PCy2)(CO)7] (4) [CrMo2Cp2(μ2-CH)(μ-PCy2)(CO)7] (5) [MnMo2Cp2Cp0 (μ3-CH)(μ-PCy2)(CO)4] (6) [Mo2RuCp2(μ3-CH)(μ-PCy2)(CO)5] (7) [Mo2RuCp2(μ3-OCH3)(μ-PCy2)(CO)5] (8d) [FeMo2Cp2(μ3-OCH3)(μ-PCy2)(CO)5] (8e) [FeMo2Cp2{μ3-C(O)CH3}(μ-PCy2)(CO)5] (9) [FeMo2Cp2(μ-CCH3)(μ-PCy2)(O)(CO)4] (10) [Fe2Mo2Cp2(μ4-CH)(μ-PCy2)(CO)8] (11) [FeMo2Cp2(μ2-CH)(μ-PCy2)(CO)5] (12)

2042 (s), 1949 (s, sh), 1935 (vs), 1825 (w) 2041 (s), 1963 (m, sh), 1945 (s, sh), 1932 (vs), 1917 (m, sh), 1890 (w, sh), 1815(w) 2006 (m, sh), 1999(m), 1979 (w, sh), 1962 (vs), 1932 (s), 1897 (s), 1868 (m, sh)c 1927 (vs), 1862 (w), 1813 (w), 1773 (w) 2039 (vs), 1978 (s), 1949 (m), 1901 (w), 1870 (w)d 2040 (vs), 1979 (s), 1949 (m), 1900 (w), 1850 (w)e 2007 (vs), 1943 (s), 1920 (m) 1995 (vs), 1945 (s), 1906 (m), 1600 (w) 2002 (vs), 1933 (s), 1818 (w) 2022 (s), 1984 (m, sh), 1972 (vs), 1944 (s), 1911 (m), 1870 (w) 1986 (vs), 1928 (vs), 1858 (w)

δ(P)b

δ(CH)b

δ(CH)b

172.8 169.7

12.26[5] 12.05[5]

244.7[21]

164.2 272.9

11.67[14] 13.47

273.5[3]

147.7 144.9 180.9 179.1 179.1 154.1 182.6 164.2

9.47[14] 12.79[7] 13.59

270.6[2]

4.24[2]

234.3[11]

244.8

15.47

330.0[7]

Recorded in dichloromethane solution, ν in cm-1. b Recorded in CD2Cl2 solutions at 290 K and 121.50 (31P) or 100.63 (13C) MHz, δ in ppm relative to internal TMS (13C) or external 85% aqueous H3PO4 (31P); coupling constants to 31P for the methyne resonances are shown in square brackets and are given in Hz. c Bands corresponding to a mixture of compounds 3c, 4, and 5 in a 1:15:5 ratio. d Recorded in petroleum ether solution. e Estimated from mixtures 7/8d in petroleum ether solution. a

retention of the cisoid geometry of the Mo2Cp2(CO)2 moiety in solution, and a strongly deshielded methylidyne resonance at ca. 12 ppm. This chemical shift is comparable to those measured for different molecules displaying CH ligands symmetrically bridging three metal atoms,15,22,23,26 thus suggesting that compounds 3 in solution might display a more symmetrical coordination of the CH ligand over the trimetal triangle, compared to the solid state. In line with this, the methylidyne ligand of 3a gives rise to a relatively shielded 13C NMR resonance (δ 244.7 ppm), as usually found for μ3-CH ligands. This spectrum also exhibits three resonances for the Mo(CO)5 fragment in agreement with the static structure, this being indicative of the absence of fast rotation of this fragment, which in turn is consistent with its strong binding in the cluster (carbene-like behavior). Solution Structure of Compounds 4 and 5. The IR spectra of the mixture of the chromium isomers 4 and 5 (recall that the isomer 3c is present only in very small amounts) lack the high-frequency band at ca. 2050 cm-1 characteristic of M(CO)5 fragments (Table 2). Thus we propose that a CO ligand has been transferred from chromium to the Mo atoms in these isomers, leaving Cr(CO)4, Mo(CO)2, and Mo(CO) fragments in both cases (Chart 2). In agreement with this, the cyclopentadienyl ligands are inequivalent in both cases (see Experimental Section). The major isomer 4 displays methylidyne resonances (δH 13.47 ppm, δC 270.6 ppm) comparable to those of the ruthenium complex [Mo2RuCp2(μ-CH)(μPCy2)(CO)5] (7) to be discussed later (Table 2), this being indicative of a rather symmetrical coordination of the CH ligand over the metal triangle. However, its 31P{1H} NMR spectrum exhibits a strongly deshielded resonance at 272.9 ppm, which we take as indicative of its coordination to the lighter chromium atom.27 For instance, the 13P chemical shifts of the complexes [M2Cp2(μ-H)(μ-PEt2)(CO)4] are (26) (a) Kolis, J. W.; Holt, E. M.; Shriver, D. F. J. Am. Chem. Soc. 1983, 105, 7307. (b) Vites, J. C.; Jacobsen, G.; Dutta, T. K.; Fehlner, T. P. J. Am. Chem. Soc. 1985, 107, 5563. (27) Carty, A. J.; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH: Deerfield Beach, FL, 1987; Chapter 16. (28) Weng, Z.; Leong, W. K.; Vittal, J. J.; Goh, L. Y. Organometallics 2002, 21, 5287. (29) Garcı´ a, M. E.; Riera, V.; Ruiz, M. A.; Saez, D. Organometallics 2002, 21, 5515.

237.4 ppm (Cr)28 and 179.8 ppm (Mo), respectively.29 In agreement with all this, the carbonyl ligands bound to chromium exhibit a 5 to 15 Hz P-C coupling, not observed in the structures of type 3 (see Experimental Section), and two of the Mo-bound carbonyls exhibit no P-C coupling at all. As for the isomer 5, it exhibits a relatively shielded 31P NMR resonance at 147.7 ppm, close to that of the electronprecise cluster [MnMo2Cp2Cp0 (μ3-CH)(μ-PCy2)(CO)4] (6), to be discussed later (Table 2), and to those of the isoelectronic methoxycarbyne complexes [MnMo2Cp2L(μ3-COMe)(μ-PCy2)(CO)4] (ca. 142 ppm, L=Cp, Cp0 ).25 We take this as indicative that the phosphide ligand in 5 still bridges the Mo-Mo edge (as in isomers 3). To balance the electronic distribution of the cluster, we propose that the methylidyne ligand should act as an essentially edge-bridging ligand connecting the Cr(CO)4 and Mo(CO) fragments (Chart 2). Unfortunately we could not locate the methylidyne resonance of this minor isomer in the 13C{1H} NMR spectrum of the mixture of isomers, so as to check the proposed change in the coordination mode of this ligand. Reaction of Compound 1 with [MnCp0 (CO)3]. The photolysis of toluene solutions of 1 and [MnCp0 (CO)3] using visible-UV light gives the trinuclear methylidyne cluster [MnMo2Cp2Cp0 (μ3-CH)(μ-PCy2)(CO)4] (6) in good yield (Chart 1). This electron-precise cluster can be viewed again as resulting from the addition of a 16-electron MnCp0 (CO)2 fragment to the unsaturated dimetal center of a dehydrogenated molecule of 1. The molecular structure of 6 in the crystal (Figure 2 and Table 3) displays a metal triangle made up of two MoCp(CO) fragments and a MnCp0 (CO)2 fragment, with a dicyclohexylphosphide ligand bridging the Mo atoms and a methylidyne ligand bridging the metal triangle rather symmetrically, if we allow for the ca. 0.1 A˚ difference in the covalent radii of Mo and Mn. The Mn-bound carbonyls are involved in bent-semibridging interactions with the Mo atoms (Mo(1)-C(4)=2.468(6) A˚, Mo(2)-C(3)=2.527(6) A˚), thus balancing the electron densities at the Mo and Mn atoms. Actually, the structure of 6 is very similar to that of the isoelectronic methoxycarbyne cluster [MnMo2Cp3(μ3-COMe)(μ-PCy2)(CO)4] recently reported by us,25 and no further discussion is therefore needed. We just note that the Mo-Mo length of 2.9678(6) A˚ is comparable to those measured in the

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Scheme 1

Figure 2. ORTEP diagram (30% probability) of compound 6, with Cy rings (except the C1 atoms) and H atoms (except H5) omitted for clarity. Table 3. Selected Bond Lengths (A˚) and Angles (deg) for Compound 6 Mo(1)-Mo(2) Mo(1)-Mn(1) Mo(2)-Mn(1) Mo(1)-C(5) Mo(2)-C(5) Mn(1)-C(5) Mo(1)-P(1) Mo(2)-P(1) Mo(1)-C(1) Mo(2)-C(2) C(1)-Ο(1) C(2)-O(2) Mo(1)-C(4) Mo(2)-C(3) Mn(1)-C(4) Mn(1)-C(3) C(3)-O(3) C(4)-O(4) C(5)-H(5)

2.9678(6) 2.840(1) 2.843(1) 2.074(5) 2.063(5) 1.970(5) 2.422(1) 2.428(1) 1.966(6) 1.971(6) 1.154(7) 1.152(7) 2.468(6) 2.527(6) 1.808(6) 1.809(6) 1.173(7) 1.184(7) 0.96(2)

Mo(1)-Mn(1)-Μο(2) Mo(1)-P(1)-Mo(2) Mo(1)-Μο(2)-C(2) Mo(2)-Mo(1)-C(1) Mo(1)-C(1)-O(1) Mo(2)-C(2)-Ο(2) Mo(1)-C(5)-Mo(2) Mo(1)-C(5)-Mn(1) Mo(2)-C(5)-Mn(1) P(1)-Mo(1)-C(5) P(1)-Mo(2)-C(5) P(1)-Mo(1)-C(1) P(1)-Mo(2)-C(2) Mn(1)-C(4)-O(4) Mn(1)-C(3)-C(3) Mo(1)-Mn(1) -C(4) Mo(2)-Mn(1) -C(3)

62.9(1) 75.5(1) 87.4(1) 86.6(2) 171.4(5) 171.4(5) 91.7(2) 89.2(2) 89.6(2) 77.8(1) 77.8(1) 86.94(17) 86.94(17) 155.1(5) 155.5(5) 59.28(19) 61.09(19)

48-electron clusters 3a,b, as expected, while the relatively short Mo-Mn distances (ca. 2.84 A˚) can be related to the presence of small-sized C-donor bridging ligands, notably the triply bridging methylidyne ligand, but also the carbonyl ligands acting as semibridging groups.25 Spectroscopic data in solution for compound 6 are consistent with the structure found in the crystal and are very similar to those of the methoxycarbyne-bridged Mn2Fe cluster mentioned above;25 therefore a detailed analysis is not needed. We just note the retention in solution of the semibridging interactions of the carbonyl ligands, as indicated by the presence of a low-frequency (1773 cm-1) C-O stretching band in the IR spectrum. The presence of the triply bridging methylidyne ligand in 6 is denoted by the appearance of a strongly deshielded resonance at 12.79 ppm in its 1 H NMR spectrum, a position comparable to those of the clusters 3 and 5. Reactions of Compound 1 with Group 8 Metal Carbonyls. The photolysis of toluene solutions of 1 and [Ru3(CO)12] using visible-UV light gives the 46-electron methylidynebridged cluster [Mo2RuCp2(μ3-CH)(μ-PCy2)(CO)5] (7) in good yield, along with small and variable amounts of the methoxy-bridged analogue [Mo2RuCp2(μ3-OMe)(μ-PCy2)(CO)5] (8d) (Chart 3). Although these compounds could not be separated from each other using chromatographic procedures, crystallization of these mixtures allowed the

purification of the major product 7. The formation of 8d is obviously originated from trace amounts of oxygen during photolysis, although we have not investigated this side reaction in detail. The formation of 7 could be viewed again as resulting from the addition of a 16-electron fragment (Ru(CO)4 in this case) to the unsaturated dimetal center of a dehydrogenated molecule of 1, then followed by further decarbonylation of the resulting 48-electron cluster thus generated. In an attempt to prepare a related iron species, we examined the room-temperature reaction of 1 with [Fe2(CO)9], the latter acting as a source of the Fe(CO)4 fragment in the absence of light. However, this reaction instead gives the acetyl-bridged cluster [FeMo2Cp2{μ3-κ1:η2:κ1-C(O)Me}(μ-PCy2)(CO)5] (9), derived from CO insertion into the Mo-Me bond possibly after the incorporation of the iron fragment, as it will be discussed later. Since compound 9 displays an acetyl ligand C,O,O-bound over the metal triangle, we were interested in determining whether a full C-O bond cleavage could be induced, as had previously been shown by Shapley et al. in the tetranuclear cluster [WOs3Cp{μ3-C(O)CH2(p-tol)}(CO)11].30 Indeed, separate experiments revealed that compound 9 can be transformed into the corresponding oxoethylidyne derivative [FeMo2Cp2(μ3-CMe)(μ-PCy2)(O)(CO)4] (10) in refluxing toluene, although a more selective transformation is achieved upon photolysis at 288 K (Scheme 1). The above results suggest that the dehydrogenation steps leading to methylidyne derivatives most likely require photolytic conditions even if a 16-electron metal fragment can be added thermally to the unsaturated dimetal center present in 1. In line with this, the photolysis of toluene solutions of 1 in the presence of [Fe2(CO)9] gave the tetranuclear methylidyne cluster [Fe2Mo2Cp2(μ4-CH)(μ-PCy2)(CO)8] (11) as a major product, along with small and variable amounts of the oxo complex 10 and the trinuclear methylidyne cluster [FeMo2Cp2(μ-CH)(μ-PCy2)(CO)5] (12) (Chart 4). The major product 11 could be fully purified by column chromatography and characterized completely. However, the minor (30) (a) Shapley, J. R.; Park, J. T; Churchill, M. R.; Zieller, J. W.; Beanan, L. R. J. Am. Chem. Soc. 1984, 106, 1144. (b) Churchill, M. R.; Zieller, J. W.; Beanan, L. R. J. Organomet. Chem. 1985, 287, 235. (c) Park, J. T.; Chi, Y.; Shapley, J. R.; Churchill, M. R.; Zieller, J. W. Organometallics 1994, 13, 813.

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Chart 4

methylidyne cluster 12 could not be separated from the oxo complex 10, and therefore it was not isolated as a pure material. To gain complementary information on the formation of the above iron derivatives of 1, we also examined the thermal reaction of the monocarbonyl methyl complex [Mo2Cp2(μ-η1:κ2-CH3)(μ-PCy2)(μ-CO)] (2) with [Fe2(CO)9]. Unfortunately, this reaction gave a mixture of products, with the major one being the methoxy-bridged cluster [FeMo2Cp2(μ3-OMe)(μ-PCy2)(CO)5] (8e), isostructural with the ruthenium compound 8d. As we noted in our preliminary report, the triply bonded compound 2 is extremely air-sensitive,10 so it seems that 2 first reacts with trace amounts of oxygen, and the formation of 8e then follows from the addition of the Fe(CO)4 fragment to the major oxoderivatives of 2, yet to be investigated. Solid-State and Solution Structure of Compound 7. The molecular structure of this Mo2Ru cluster (Figure 3 and Table 4) can be derived from that of 6, after replacing the MnCp0 (CO)2 fragment with a Ru(CO)3 fragment. This, however, removes two electrons from the system, then leaving an unsaturated (46-electron) cluster. This unsaturation seems to be localized on the Mo2 center, since the short Mo-Mo length of 2.6824(7) A˚ is consistent with the presence of a double metal-metal bond. In fact, the structure of 7 is very similar to that of the isoelectronic methoxycarbyne-bridged cluster [FeMo2Cp2(μ3-COMe)(μ-PCy2)(CO)5] (Mo-Mo = 2.688(3) A˚) recently reported by us,25a and therefore a detailed analysis is not needed here. We just note that the intermetallic lengths in 7 are also comparable to those measured in the unsaturated clusters [Mo2RuCp2{μ-η3RCC(R’)CPh}{μ3-η3-HCC(Ph)CH}(μ3-S)(CO)2] (R = Ph, H; R0 = H, Ph; Mo-Ru ca. 2.83 A˚ and Mo-Mo ca. 2.68 A˚).31 Another structural feature of 7 is the absence of semibridging carbonyls and a change in the conformation of the Mo-bound carbonyls (when compared to that in 6), since now these ligands are directed toward the ruthenium atom in a very incipient semibridging interaction (Ru 3 3 3 C separations of ca. 2.75 A˚) so as to partially balance the electron densities at the Ru and Mo atoms. This effect was also observed in the mentioned methoxycarbyne-bridged Mo2Fe cluster.25a Such conformational modification (compared to that in the electron-precise cluster 6) is accompanied by a change of the phosphide position, which moves away from the bridging carbyne ligand, this implying an increase in the P-Mo-C(carbyne) angles from ca. 78° to 103°. The IR spectrum of compound 7 exhibits five C-O stretching bands in the region of terminal carbonyls, when recorded in petroleum ether solution. The three bands of higher frequency and intensity are characteristic of pyramidal M(CO)3 fragments24 and are comparable to those observed for the mentioned clusters [MMo2Cp2(μ3-COMe)(μ-PCy2)(CO)5] (31) Adams, R. D.; Babin, J. E.; Tasi, M.; Wang, J. G. Organometallics 1988, 7, 755.

Figure 3. ORTEP diagram (30% probability) of compound 7, with Cy rings (except the C1 atoms) and H atoms (except H6) omitted for clarity. Table 4. Selected Bond Lengths (A˚) and Angles (deg) for Compound 7 Mo(1)-Mo(2) Mo(1)-Ru(1) Mo(2)-Ru(1) Mo(1)-C(6) Mo(2)-C(6) Ru(1)-C(6) Mo(1)-P(1) Mo(2)-P(1) Mo(1)-C(1) Mo(2)-C(2) Ru(1)-C(3) Ru(1)-C(4) Ru(1)-C(5) C(6)-H(6)

2.6824(7) 2.8793(7) 2.8789(7) 2.091(6) 2.089(6) 2.012(7) 2.401(2) 2.398(2) 1.986(7) 1.970(7) 1.884(7) 1.895(8) 1.960(7) 0.98(2)

Mo(1)-Ru(1)-Μο(2) Mo(1)-P(1)-Mo(2) Mo(1)-Μο(2)-C(2) Mo(2)-Mo(1)-C(1) Ru(1)-Μο(2)-C(2) Ru(1)-Mo(1)-C(1) Mo(1)-C(1)-O(1) Mo(2)-C(2)-Ο(2) Mo(1)-C(6)-Mo(2) Mo(1)-C(6)-Ru(1) Mo(2)-C(6)-Ru(1) P(1)-Mo(1)-C(6) P(1)-Mo(2)-C(6) P(1)-Mo(1)-C(1) P(1)-Mo(2)-C(2)

55.5(1) 68.0(1) 91.3(2) 91.9(2) 65.9(2) 67.7(2) 168.8(6) 166.4(5) 79.9(2) 89.1(3) 89.2(3) 102.6(2) 102.8(2) 90.1(2) 91.1(2)

(M = Fe, Ru).25 We note that the Mo-bound carbonyls give rise to very weak bands, an effect also observed in the above methoxycarbyne clusters and in compounds 3a,b. As expected, the methylidyne ligand in 7 gives rise to quite deshielded 1H and 13C NMR resonances (δH 13.59 ppm, δC = 270.6 ppm), and the low value of the P-C coupling in the latter (2 Hz) is consistent with the conformation found in the crystal, implying P-Mo-C angles (ca. 103°) substantially larger than those in the electron-precise clusters 3 and 6 (ca. 78°, JPC = 21 Hz for 3a). Besides this, the relative deshielding of the 13C carbyne and 31P resonances in 7 (compared to those in the clusters 3) is attributed to the unsaturation of the cluster. We finally note that the Ru(CO)3 fragment in this molecule gives rise to a single 13C resonance at room temperature, which is indicative of the occurrence of a fast fluxional process effectively exchanging the carbonyl positions, a feature commonly found for pyramidal M(CO)3 fragments in cluster compounds.32 Solid-State and Solution Structure of Compounds 8. The crystal structure of compound 8e (Figure 4 and Table 5) is essentially identical to that of the isoelectronic methylidyne cluster 7, after replacing Ru by Fe and the methylidyne by a methoxy ligand, and no detailed comments are therefore needed. We just note that the Mo-Mo length (2.667(1) A˚) is even shorter than that in 7, thus indicating that the unsaturation of the cluster also is essentially localized at the Mo2 edge. As for the methoxy ligand, the M-O separations are (32) Orrel, K. G.; Sik, V. Ann. Rep. NMR 1987, 19, 79.

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Figure 4. ORTEP diagram (30% probability) of compound 8e, with Cy rings (except the C1 atoms) and H atoms omitted for clarity.

Figure 5. ORTEP diagram (30% probability) of compound 9, with Cy rings (except the C1 atoms) and H atoms omitted for clarity.

Table 5. Selected Bond Lengths (A˚) and Angles (deg) for Compound 8e

Table 6. Selected Bond Lengths (A˚) and Angles (deg) for Compound 9

Mo(1)-Mo(2) Mo(1)-Fe(1) Mo(2)-Fe(1) Mo(1)-O(6) Mo(2)-O(6) Fe(1)-O(6) Mo(1)-P(1) Mo(2)-P(1) Mo(1)-C(1) Mo(2)-C(2) Fe(1)-C(1) Fe(1)-C(2) Fe(1)-C(3) Fe(1)-C(4) Fe(1)-C(5) O(6)-C(6)

2.667(1) 2.766(2) 2.799(2) 2.20(2) 2.25(2) 1.88(1) 2.409(3) 2.390(3) 1.99(1) 1.97(1) 2.60(1) 2.90(1) 1.81(1) 1.75(1) 1.78(1) 1.40(2)

Mo(1)-Fe(1)-Μο(2) Mo(1)-P(1)-Mo(2) Mo(1)-Μο(2)-C(2) Mo(2)-Mo(1)-C(1) Mo(1)-C(1)-O(1) Mo(2)-C(2)-Ο(2) Mo(1)-O(6)-Mo(2) Mo(1)-O(6)-Fe(1) Mo(2)-O(6)-Fe(1) P(1)-Mo(1)-C(1) P(1)-Mo(2)-C(2) P(1)-Mo(1)-O(6) Fe(1)-Mo(1)-C(1) Fe(1)-C(3)-O(3) Fe(1)-C(4)-O(4) Fe(1)-C(5)-C(5)

57.3(1) 67.5(1) 90.2(3) 91.2(3) 165(1) 170.8(9) 73.7(6) 84.9(6) 84.8(6) 100.6(3) 91.3(4) 104.1(4) 63.7(4) 175(1) 178(1) 179(1)

comparable to those measured for other clusters having μ3-OMe groups.33 However, the Mo-O lengths are ca. 0.35 A˚ longer than the Fe-O separation of 1.88(1) A˚, exceeding the ca. 0.2 A˚ difference in the covalent radii of these metal atoms.34 This is suggestive of a stronger binding of the methoxy ligand to the iron atom, surely to balance the relative deficiency of that metal center. Spectroscopic data for compounds 8d,e are consistent with the structure found for 8e in the solid state and are also very similar to those of either 7 or the mentioned methoxycarbyne clusters [MMo2Cp2(μ3-COMe)(μ-PCy2)(CO)5] (M=Fe, Ru);25 therefore a detailed discussion is not needed. We just note that the 1H resonances for the methoxy ligands appear at 3.32 and 3.65 ppm, respectively, these being values comparable to those reported for other clusters displaying triply bridging methoxy ligands.33 Solid-State and Solution Structure of Compound 9. The molecular structure of this compound in the crystal (Figure 5 and Table 6) can be derived from that of 8 after replacing the bridging methoxy group by an acetyl ligand bridging the Mo2Fe triangle, so that the C atom spans one of the Mo-Fe (33) (a) Litos, C.; Terzis, A.; Raptopoulou, C.; Rontoyianni, A.; Karaliota, A. Polyhedron 2006, 25, 1337. (b) Adrian, R. A.; Yaklin, M. M.; Klausmeyer, K. K. Organometallics 2004, 23, 1252. (c) Villanneau, R.; Delmont, R.; Proust, A.; Gouzerh, P. Chem.;Eur. J. 2000, 6, 1184. (34) Cordero, B.; G omez, V.; Platero-Prats, A. E.; Reves, M; Echeverrı´ a, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008, 2832.

Mo(1)-Mo(2) Mo(1)-Fe(1) Mo(2)-Fe(1) Mo(1)-O(6) Mo(2)-O(6) Mo(1)-C(6) Fe(1)-C(6) Mo(1)-P(1) Mo(2)-P(1) Mo(1)-C(1) Mo(2)-C(2) C(1)-Ο(1) C(2)-O(2) Fe(1)-C(3) Fe(1)-C(4) Fe(1)-C(5) Fe(1)-C(1) C(6)-O(6) C(6)-C(7)

2.8474(5) 2.7417(8) 2.7603(8) 2.139(3) 2.121(3) 2.131(5) 1.935(5) 2.445(1) 2.434(1) 1.972(5) 2.000(6) 1.168(6) 1.154(6) 1.736(6) 1.796(6) 1.805(6) 2.518(6) 1.386(6) 1.507(7)

Mo(1)-Fe(1)-Μο(2) Mo(1)-P(1)-Mo(2) Mo(1)-Μο(2)-C(2) Mo(2)-Mo(1)-C(1) Mo(1)-C(1)-O(1) Mo(2)-C(2)-Ο(2) Mo(1)-O(6)-Mo(2) Mo(1)-C(6)-Fe(1) Fe(1)-C(6)-C(7) Fe(1)-C(6)-O(6) O(6)-C(6)-C(7) P(1)-Mo(1)-C(1) P(1)-Mo(2)-C(2) P(1)-Mo(1)-O(6) Fe(1)-Mo(1)-C(1) Fe(1)-C(3)-O(3) Fe(1)-C(4)-O(4) Fe(1)-C(5)-O(5)

62.3(1) 71.4(1) 95.4(1) 79.1(2) 160.8(4) 176.4(4) 83.9(1) 84.7(2) 129.3(4) 114.2(3) 112.0(4) 93.0(1) 86.1(1) 76.6(1) 62.1(2) 177.2(5) 177.9(5) 178.7(5)

edges and the O atom bridges the molybdenum atoms. This coordination mode of the acetyl ligand is comparable to that found in other acyl-bridged clusters such as [Fe2WCp{μ3-C(O)CH2(p-tol)}(μ-PPh2)2(CO)5],35 [Os3W{μ3C(O)CH2(p-tol)}(CO)11],36 [NEt4][Fe3{μ3-C(O)Me}(CO)9],37 and [Fe3(μ-H){μ3-C(O)Me}(CO)9].38 The large C(6)-O(6) length of 1.386(6) A˚ in 9, almost identical to the single C-O bond length of the methoxy group in 8e (1.40(2) A˚), along with the short C(6)-M and O(6)-Mo lengths, in the range of the corresponding single-bond figures, indicates a strong binding of the acetyl ligand over the metal triangle, therefore to be considered essentially as a five-electron donor group. This renders a saturated (48-electron) cluster, as opposed to the unsaturated nature of its methoxycarbyne-bridged isomer [FeMo2Cp2(μ3-COMe)(μ-PCy2)(CO)5],25 or the complexes 7 and 8. In agreement with this, the Mo-Mo length of (35) (a) Jeffery, J. C.; Lawrence-Smith, J. G. J. Chem. Soc., Chem. Commun. 1985, 275. (b) Jeffery, J. C.; Lawrence-Smith, J. G. J. Chem. Soc., Dalton Trans. 1990, 1063. (36) Park, J. T.; Shapley, J. R.; Churchill, M. R.; Bueno, C. Inorg. Chem. 1983, 22, 1579. (37) Wong, W. K.; Wilkinson, G.; Galas, A. M.; Hursthouse, M. B.; Thornton-Pett, M. J. Chem. Soc., Dalton Trans. 1981, 2496. (38) Wong, W. K.; Chiu, K. W.; Wilkinson, G.; Galas, A. M. R.; Thornton-Pett, M.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1983, 1557.

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Scheme 2. Fluxional Process Proposed for Compound 9 in Solutiona

a

Mo = MoCp(CO); Fe = Fe(CO)3; P = PCy2.

2.8474(5) A˚ in 9 is substantially higher than the values found for the mentioned unsaturated clusters (ca. 2.68 A˚), although still somewhat shorter than those in the electron-precise clusters 3a,b and 6 (ca. 2.94 A˚). We finally note the presence of a very incipient semibridging interaction between one of the Mo-bound carbonyls and the iron atom (C(1) 3 3 3 Fe ca. 2.52 A˚), surely to balance the electron densities at the Mo and Fe atoms. The spectroscopic data for 9 in solution are essentially consistent with the structure found in the crystal, but reveal the presence of dynamic effects. The IR spectrum exhibits just three strong C-O stretching bands corresponding to the Fe(CO)3 moiety, as observed for the isomeric methoxycarbyne clusters [MMo2Cp2(μ-COMe)(μ-PCy2)(CO)5] (M=Fe, Ru),25 although the very weak bands arising from the Mo2(CO)2 unit can be appreciated when the spectrum is recorded in a Nujol mull (see Experimental Section). In addition, the spectrum also displays a weak band at 1600 cm-1 (1575 cm-1 in Nujol mull) corresponding to the C-O stretch of the acetyl ligand. This suggests that the corresponding C-O bond might retain substantial multiplicity, not revealed by the geometric parameters discussed above. In contrast, the 31 P{1H} NMR spectrum of 9 exhibits a resonance at 154.1 ppm, a shift close to those measured for the 48-electron clusters 6 and [MnMo2Cp3(μ3-COMe)(μ-PCy2)(CO)4],25 therefore consistent with a five-electron contribution of the acetyl ligand to cluster binding. The 1H NMR and 13C{1H} NMR spectra of 9 reveal the occurrence of two fluxional processes in solution. In the first place, there is a single cyclopentadienyl resonance at room temperature, which is inconsistent with the absence of any symmetry elements in the static structure. On lowering the temperature, this resonance broadens and eventually splits into two resonances of the same intensity, as expected. From the coalescence temperature of the proton resonances (Tc = 263 ( 1 K) we can estimate39 a free energy of activation of 55.5 ( 0.5 kJ mol-1 for the corresponding process, proposed to involve the migration of the bridgehead carbon atom of the acetyl ligand between both Fe-Mo edges (Scheme 2). This also implies the averaging of the Mo-bound carbonyl sites, in agreement with the presence of a single and broad resonance at 251.2 ppm for these ligands in the roomtemperature 13C NMR spectrum, which splits into separated resonances below 243 K (see Experimental Section). At room temperature, however, the ligands of the Fe(CO)3 fragments give rise also to just a single 13C resonance, with this requiring the existence of an additional exchange process within this pyramidal fragment analogous to that proposed for compound 7. Both dynamic processes are slowed down enough at 208 K to allow the observation of three separated Fe-CO resonances. Finally we note that the bridgehead (39) Calculated using the modified Eyring equation ΔG# = unter, H. NMR Spectros19.14Tc[9.97 þ log(Tc/Δν)] (J mol-1). See: G€ copy; John Wiley: Chichester, U.K., 1980; p 243.

Figure 6. ORTEP diagram (30% probability) of compound 10, with Cy rings (except the C1 atoms) and H atoms omitted for clarity. Table 7. Selected Bond Lengths (A˚) and Angles (deg) for Compound 10 Mo(1)-Mo(2) Mo(1)-Fe(1) Mo(2)-Fe(1) Mo(1)-C(5) Mo(2)-C(5) Fe(1)-C(5) Mo(2)-O(5) Mo(1)-P(1) Mo(2)-P(1) Mo(1)-C(1) Fe(1)-C(1) Fe(1)-C(2) Fe(1)-C(3) Fe(1)-C(4) C(5)-C(6)

2.8469(4) 2.7560(5) 2.6609(5) 1.972(3) 2.478(3) 1.865(3) 1.702(2) 2.369(1) 2.463(1) 1.965(3) 2.650(4) 1.788(4) 1.766(4) 1.781(3) 1.509(4)

Mo(1)-Fe(1)-Μο(2) Mo(1)-P(1)-Mo(2) Mo(1)-Μο(2)-O(5) Mo(2)-Mo(1)-C(1) P(1)-Mo(1)-C(5) P(1)-Mo(2)-C(5) P(1)-Mo(1)-C(1) Mo(1)-C(1)-O(1) Fe(1)-Mo(1)-C(1) Mo(1)-C(5)-Mo(2) Mo(1)-C(5)-Fe(1) Mo(2)-C(5)-Fe(1) Fe(1)-C(2)-O(2) Fe(1)-C(3)-O(3) Fe(1)-C(4)-O(4)

63.4(1) 72.2(2) 108.8(1) 78.7(1) 102.0(1) 86.4(1) 95.6(1) 166.6(3) 65.8(1) 78.6(1) 91.8(1) 74.1(1) 177.7(3) 177.0(3) 179.5(3)

acetyl carbon atom gives rise to a relatively shielded resonance at 199.9 ppm, not far from the figure reported for the cluster [Fe2WCp{μ3-C(O)(p-tol)}(μ-PPh2)(CO)5] (ca. 197 ppm).35,36 These are values considerably lower than those measured recently for several binuclear derivatives of 1 having μ2-acetyl ligands (δC ca. 275 ppm).40 Solid-State and Solution Structure of Compound 10. The molecular structure of this oxo complex (Figure 6 and Table 7) can be viewed as resulting from the removal of a Mo-bound carbonyl ligand from 9 and cleavage of the acetyl C-O bond, thus yielding a bridging ethylidyne and an oxo ligand, the latter being coordinated to the decarbonylated metal atom in a terminal fashion, on the same side of the intermetallic plane as the carbyne group. This oxygen atom is strongly bound to the Mo(2) atom, as usually found in organomalybdenum oxo complexes,41 with the corresponding Mo-O length of 1.702(2) A˚ being comparable to those measured in the binuclear complexes [Mo2Cp2(μ-PPh2)(μ-CHCHPh)(O)(CO)], [Mo2Cp2(μ-PPh2)2(O)(CO)], and [W2Cp2(μ-PPh2)(μ-CH2PPh2)(O)(CO)].42 We have shown recently that the oxo ligand can be thus described as a (40) Alvarez, M. A.; Garcı´ a, M. E.; Martı´ nez, M. E.; Ramos, A.; Ruiz, M. A. Organometallics 2009, 28, 6293. (41) Bottomley, F.; Sutin, L. Adv. Organomet. Chem. 1988, 28, 339. (42) (a) Endrich, K.; Korswagen, R.; Zhan, T.; Ziegler, M. L. Angew. Chem., Int. Ed. Engl. 1982, 21, 919. (b) Adatia, T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby, P. R. J. Chem. Soc., Dalton Trans. 1989, 1555. (c) Alvarez, M. A.; García, M. E.; Riera, V.; Ruiz, M. A.; Falvello, L. R.; Bois, C. Organometallics 1997, 16, 354.

912


four-electron donor in this sort of complexes,43 and this would lead to the formulation of compound 10 as an electron-precise molecule. In any case, this oxo ligand has a significant labilizing effect on the remaining ligands there present, such as the phosphide ligand (ca. 0.1 A˚ closer to Mo(1)) and the carbyne ligand, essentially edge-bridging the opposite Mo(1)-Fe bond (C(5) 3 3 3 Mo(2)=2.478(3) A˚). The latter ligand seems to be more strongly bound to the Mo(1) atom, since the Mo(1)-C(5) length of 1.972(3) A˚ is shorter than the corresponding distances in compounds 3a,b (almost edge-bridging the Mo atoms, Mo-C ca. 2.05 A˚), while the C(5)-Fe length of 1.865(3) A˚ is slightly longer than that measured in the triply bridged methoxycarbyne complex [FeMo2Cp2(μ3-COMe)(μ-PCy2)(CO)5] (1.82(3) A˚).25 The intermetallic distances, however, are somewhat shorter than the single-bond lengths expected for an electron-precise cluster, a circumstance also found for the acetyl precursor 9, as discussed above. Yet, the more striking feature in the structure of 10 is perhaps the fact that the shorter intermetallic length (Fe-Mo(2) = 2.6609(5) A˚) corresponds to the metal edge lacking any bridging ligand and involving the metal atom bearing the oxygen ligand. Currently we cannot offer a satisfactory explanation for this structural feature. The IR spectrum of 10 in CH2Cl2 solution exhibits two strong C-O stretching bands corresponding to the Fe(CO)3 fragment and a weak band at 1818 cm-1 arising from the Mo(CO) moiety. The 13C NMR spectrum displays a strongly deshielded carbyne resonance at 401.5 ppm, a chemical shift significantly higher than those measured in the triply bridged clusters [Mo2Ru(μ3-CR)(μ-PPh2)(CO)5] (R=Me, Et; δC ca. 350 ppm),44 this being suggestive that the carbyne ligand retains in solution the almost edge-bridging coordination found in the crystal. Besides, the Fe-bound carbonyls give rise to a single resonance at room temperature, with this indicating the operation of a fast fluxional process within the Fe(CO)3 fragment, as found for the clusters 7 and 9. Solid-State and Solution Structure of Compound 11. The molecular structure of this tetranuclear cluster (Figure 7)10 can be viewed as derived from the addition of two Fe(CO)3 moieties to a dehydrogenated molecule of 1, which still holds the bridging dicyclohexylphosphide ligand and a transoid arrangement of the Cp and CO ligands. Unexpectedly, this 60-electron cluster does not display a tetrahedral structure, but a “butterfly” one with the CH ligand bridging the four metal atoms in a rather symmetrical way; therefore the molecule must be considered electronically unsaturated. In agreement with this, the intermetallic lengths are 0.1-0.2 A˚ shorter than the corresponding single-bond lengths of reference, this indicating a delocalization of such an unsaturation. It is interesting noting that only a few similar “butterfly” methylidyne clusters, [Fe4(μ-CH)(μ-H)(CO)12]45 and [MFe3(μ-CH)(CO)x]n (M = Cr, W, Mn, Rh; x = 12, 13; n = 0, -1),46 have been reported previously. These, however, display CH ligands involved in agostic C-H-M interactions, therefore (43) (a) Garcı´ a, M. E.; Garcı´ a-Viv o, D.; Mel on, S.; Ruiz, M. A.; Graiff, C.; Tiripicchio, A. Inorg. Chem. 2009, 48, 9282. (b) García, M. E.; Mel on, S.; Ramos, A.; Ruiz, M. A. Dalton Trans. 2009, 8171. (44) Adams, H.; Bailey, N. A.; Gill, L. J.; Morris, M. J.; Sadler, N. D. J. Chem. Soc., Dalton Trans. 1997, 3041. (45) (a) Tachikawa, M.; Muetterties, E. L. J. Am. Chem. Soc. 1980, 102, 4541. (b) Beno, M. A.; Williams, J. A.; Tachikawa, M.; Muetterties, E. L. J. Am. Chem. Soc. 1980, 102, 4542. (c) Wadepohl, H.; Braga, D.; Grepioni, F. Organometallics 1995, 14, 24. (46) Hriljac, J. A.; Harris, S.; Shriver, D. F. Inorg. Chem. 1988, 27, 816.

Alvarez et al.

Figure 7. ORTEP diagram (30% probability) of compound 11 (reproduced from ref 1b), with Cy rings (except the C1 atoms) and H atoms (except H9) omitted for clarity. Selected bond lengths (A˚): Mo(1)-Mo(2) = 2.835(1), Mo(1)-Fe(1) = 2.725(1), Mo(1)-Fe(2) = 2.707(1), Mo(2)-Fe(1) = 2.770(1), Fe(1)-Fe(2) = 2.537(1), Mo(1)-C(9) = 2.144(6), Mo(2)-C(9) = 2.113(6), Fe(1)-C(9) = 1.906(6), Fe(2)-C(9) = 2.001(6), Mo(1)-P(1) = 2.476(2), Mo(2)-P(1) = 2.392(1).

yielding electron-precise (62-electron) “butterfly” structures. In contrast, the methylidyne ligand in 11 is not involved in agostic interactions, as indicated by the large values of the closest M 3 3 3 H approaches (ca. 2.6 A˚) and the normal value (not elongated) of the C-H distance (0.84(9) A˚). The IR spectrum of cluster 11 is consistent with the structure just described, since it exhibits five strong- to medium-intensity C-O stretching bands, which can be assigned as arising from an asymmetric Fe2(CO)6 oscillator, and a weak band at 1870 cm-1 probably originating from the Mo2(CO)2 oscillator. In agreement with this, the 13C NMR spectra display independent resonances for the inequivalent pairs of Cp ligands and Mo-bound carbonyls, as expected. However, the six carbonyl ligands bound to iron atoms give a single resonance at 215.1 ppm at room temperature, thus suggesting the occurrence of a fast exchange process involving the six Fe-CO ligands. This process is slowed down enough at 213 K to yield independent resonances for all these ligands, in agreement with the static structure. Although we have not studied this rearrangement in detail, we note that these exchange processes are common in trinuclear iron carbonyl clusters.47 The coordination mode of the methylidyne ligand of compound 11 in solution might be slightly different from that found in the crystal. For instance, its proton shift (4.24 ppm) is substantially higher than those measured for the mentioned agostic methylidyne clusters (δH in the range þ2 to -2 ppm),45,46 but still much lower than all other methylidyne complexes reported in this work (δH in the range 10 to 15 ppm, Table 2). Therefore it can be proposed that, in solution, the methylidyne ligand in compound 11 might be involved in weak agostic interactions with the iron atoms. In line with this, the methylidyne carbon (δC = 243.8 ppm) exhibits a reduced C-H coupling of 143 Hz. Although this value is certainly higher than those measured for the mentioned agostic clusters (JCH ≈ 105 Hz), it is significantly lower than a “normal” coupling in a methylidyne-bridged cluster (i.e., JCH = 162 Hz for 3a). (47) Mann, B. E. J. Chem. Soc., Dalton Trans. 1997, 1457.

Article Scheme 3. Reaction Pathways in the Formation of Compounds 3-12a

a

Mo = MoCp; P = PCy2.

Solution Structure of Compound 12. The IR spectrum of this trinuclear cluster in CH2Cl2 solution exhibits just two strong C-O bands, corresponding to the Fe(CO)3 moiety, as found for 10, and a weaker band at 1858 cm-1 probably arising from the Mo2(CO)2 oscillator. The number of carbonyls and lack of symmetry of the molecule is denoted by the appearance, in the room-temperature 13C NMR spectrum, of two Mo-CO and three Fe-CO resonances (see Experimental Section). This asymmetry is attributed to the presence of the bridging phosphide ligand over a Fe-Mo edge, rather than the original positioning between the Mo atoms. This is also suggested by the strong deshielding of the corresponding phosphorus resonance (δP = 244.8 ppm), comparable to that of the isomer 4 and much higher than those of all other compounds here reported with PCy2 bridges over Mo2 edges (Table 2). As for the methylidyne ligand, it gives rise to very deshielded NMR resonances (δH = 15.47 ppm; δC = 330.1 ppm), with the high chemical shift of the 13C resonance being taken as an indication of its positioning over a Mo-Fe edge, rather than over the Mo2Fe face. All this would substantially increase the crowding around the iron atom, thus explaining the unusual rigid behavior of the Fe(CO)3 fragment on the NMR time scale. Reaction Pathways in the Formation of the Heterometallic Clusters 3-12. Leaving apart the formation of the methoxybridged compounds 8, obviously derived from the presence of trace amounts of oxygen in the reaction media, the formation of all other heterometallic clusters 3-12 reported in the present work can be rationalized by assuming a common initial step, the addition of a thermally (Fe) or photochemically generated 16-electron metal fragment ML(CO)n (M = Cr, Mo, W, Mn, Ru, Fe; L = CO, Cp0 ; n = 2-4) to the unsaturated dimolybdenum center in 1 to give a heterometallic intermediate A possibly having a terminal methyl ligand (Scheme 3). This intermediate then might evolve in three likely ways. First, in the absence of photochemical activation (thermal reaction with [Fe2(CO)9]), the intermediate A might evolve by CO insertion into the


913

Mo-CH3 bond (or CH3 migration to CO) to give an acetyl ligand, this allowing the electronic saturation of the cluster after rearrangement of the latter ligand into a face-bridging position. The resulting cluster 9 may afterward experience thermally or photochemically induced decarbonylation, this triggering the cleavage of the C-O bond of the acetyl ligand to yield oxo and carbyne ligands, thus preserving the electron count of the molecule. Under photochemical activation, however, the intermediate A would preferentially undergo dehydrogenation. This reaction cannot occur at an earlier stage (i.e., directly from 1) since separate experiments indicate that 1 does not experience any dehydrogenation under photolytic conditions, but just decarbonylation to give the methyl-bridged agostic complex 2.10 In addition, our results suggest that dehydrogenation of A might occur in two different ways. First, the simple dehydrogenation (surely involving several elemental steps in turn) would be the dominant reaction path for the group 6 and 7 metal fragments, this leading to the electronprecise clusters 3 and 6, after rearrangement of the so-formed methylidyne ligand into a face-bridging position. The observed equilibrium relating the methyl, hydride-methylidene, and dihydride-methylidyne tautomers in the iron cluster [Fe3(CO)9CH4]4b is an attractive model of the elementary steps that might connect the intermediate A with our methylidyne derivatives, thus explaining the need to incorporate at least one more metal atom to the unsaturated compound 1, to achieve the dehydrogenation of the methyl ligand. Incidentally, under this scheme the minor chromium product 3c would thus be the kinetic product in the corresponding reaction, although further rearrangement of the phosphide and methylidyne ligands would then rapidly occur so as to reach an equilibrium mixture of isomers 3c-5. When the heterometal in the intermediate A is ruthenium or iron, however, the dehydrogenation process is accompanied by further decarbonylation (we do not know which of these elementary steps would take place first), this leading to a 46-electron cluster that would be stable only for ruthenium (compound 7). The corresponding iron species would be an unstable intermediate B that might evolve either through rearrangement of the bridging ligands, to give a more stable isomer 12, or by the addition of a second Fe(CO)4 fragment and further decarbonylation to give the tetranuclear cluster 11. Separate experiments revealed that compound 12 does not react further with [Fe2(CO)9] under photolytic conditions. Moreover, an electron-precise cluster [FeMo2Cp2(μCH)(μ-PCy2)(CO)6] also seems an unlikely intermediate in the formation of 11, since the isoelectronic cluster 3a failed to react under photolytic conditions with [Fe2(CO)9] to yield a hypothetical Mo3Fe analogue of 11, according to independent experiments. All this gives indirect support to the hypothesis that the precursor of the tetranuclear cluster 11 must be a 46-electron isomer of compound 12.

Concluding Remarks The methyl complex 1 reacts with different metal carbonyl complexes under conditions in which the corresponding 16-electron metal fragments ML(CO)n (M = Cr, Mo, W, Mn, Ru, Fe; L = CO, Cp0 ; n = 2-4) can be generated to a significant extent. The reaction seems to involve in all cases the addition of the corresponding fragment to the unsaturated dimetal center in 1 to give a trinuclear intermediate that can evolve in different ways, depending on the nature of the

914


metal and the reaction conditions. Under thermal conditions, no dehydrogenation of the methyl ligand can take place, only CO insertion into the Mo-CH3 bond to give an acetyl-bridged cluster. Under photolytic conditions, dehydrogenation of the methyl ligand to give a methylidynebridged cluster occurs in all cases at the corresponding trinuclear intermediate. When M is a metal of the group 6 or 7, this leads directly to stable 48-electron clusters. When M is a metal of the group 8, the dehydrogenation process is accompanied by further decarbonylation to yield unsaturated 46-electron clusters that are stable only for ruthenium, but are able to add a further metal fragment in the case of iron, now to yield a 60-electron tetranuclear cluster with a butterfly Mo2Fe2 metal core.

Experimental Section General Procedures and Starting Materials. All manipulations and reactions were carried out under a nitrogen (99.995%) atmosphere using standard Schlenk techniques. Solvents were purified according to literature procedures and distilled prior to use.48 Petroleum ether refers to that fraction distilling in the range 338-343 K. The compounds [Mo2Cp2(μ-CH3)(μ-PCy2)(CO)2] (1) and [Mo2Cp2(μ-κ1:η2-CH3)(μ-PCy2)(μ-CO)] (2) were prepared as described previously.1,10 All other reagents were obtained from the usual commercial suppliers and used as received. Photochemical experiments were performed using jacketed quartz or Pyrex Schlenk tubes, cooled by tap water (ca. 288 K). A 400 W mercury lamp placed ca. 1 cm away from the Schlenk tube was used for all the experiments. Chromatographic separations were carried out using jacketed columns cooled by tap water (ca. 288 K). Commercial aluminum oxide (Aldrich, activity I, 150 mesh) was degassed under vacuum prior to use. The latter was mixed under nitrogen with the appropriate amount of water to reach the activity desired. IR stretching frequencies were measured in solution or Nujol mulls and are referred as ν (solvent) or ν (Nujol), respectively. Nuclear magnetic resonance (NMR) spectra were routinely recorded at 400.13 (1H), 121.50 (31P{1H}), or 100.63 MHz (13C{1H}) at 290 K in CD2Cl2 solutions unless otherwise stated. Chemical shifts (δ) are given in ppm, relative to internal tetramethylsilane (1H, 13C) or external 85% aqueous H3PO4 (31P). Coupling constants (J) are given in Hz. Preparation of [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7] (3a). A toluene solution (4 mL) of compound 1 (0.025 g, 0.042 mmol) and [Mo(CO)6] (0.018 g, 0.068 mmol) was irradiated in a Pyrex Schlenk tube with visible-UV light under a gentle N2 (99.9995%) purge for 5 h to give a greenish-brown solution. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethane-petroleum ether (1:8) yielded a brown fraction. Removal of solvents under vacuum from this fraction gave compound 3a as a brown microcrystalline solid (0.028 g, 80%). The crystals used in the X-ray study were grown by slow diffusion of petroleum ether into a dichloromethane solution of the complex at 253 K. Anal. Calcd for C30H33Mo3O7P: C, 43.71; H, 4.03. Found: C, 43.55; H, 3.85. 1H NMR (300.13 MHz): δ 12.26 (d, JPH = 5, JCH = 162, 1H, CH), 5.25 (d, JPH = 1, 10H, Cp), 2.34-1.13 (m, 22H, Cy). 13C{1H} NMR (75.49 MHz): δ 244.7 (d, JCP = 21, CH), 244.1 (d, JCP = 9, 2CO), 222.0 (s, 2CO), 213.8 (s, 2CO), 201.6 (s, CO), 90.6 (s, Cp), 52.5 [d, JCP = 18, C1(Cy)], 44.8 [d, JCP = 7, C1(Cy)], 32.5 [d, JCP = 4, C2(Cy)], 31.0 [s, C2(Cy)], 28.0, 27.7 [2d, JCP = 10, C3(Cy)], 26.7, 26.4 [2s, C4(Cy)].

(48) Armarego, W. L. F.; Chai, C. Purification of Laboratory Chemicals, 5th ed.; Butterworth-Heinemann: Oxford, U.K., 2003.

Alvarez et al. Preparation of [Mo2WCp2(μ3-CH)(μ-PCy2)(CO)7] (3b). A toluene solution (4 mL) of compound 1 (0.025 g, 0.042 mmol) and [W(CO)6] (0.027 g, 0.076 mmol) was irradiated in a quartz Schlenk tube with visible-UV light under a gentle N2 (99.9995%) purge for 10 h to give a greenish-brown solution. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethane-petroleum ether (1:9) yielded a yellowishgreen fraction. Removal of solvents under vacuum from this fraction gave compound 3b as a brown microcrystalline solid (0.025 g, 64%). The crystals used in the X-ray study were grown by slow diffusion of petroleum ether into a dichloromethane solution of the complex at 253 K. Anal. Calcd for C30H33Mo2O7PW: C, 39.50; H, 3.65. Found: C, 39.55; H, 3.70. 1H NMR (300.13 MHz): δ 12.05 (d, JPH = 5, JWH = 4, 1H, CH), 5.26 (d, JPH = 1, 10H, Cp), 2.04-1.16 (m, 22H, Cy). Reaction of 1 with [Cr(CO)6]. A toluene solution (4 mL) of compound 1 (0.020 g, 0.034 mmol) and [Cr(CO)6] (0.018 g, 0.034 mmol) was irradiated in a Pyrex Schlenk tube with visible-UV light under a gentle N2 (99.9995%) purge for 4.5 h to give a brown solution. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethane-petroleum ether (1:9) yielded a yellowish-brown fraction. Removal of solvents under vacuum from the latter fraction gave 0.020 g (75%) of a mixture of the isomers 3c, 4, and 5 in a ratio 1:15:5. The 4/5 equilibrium ratio, as measured by 1H NMR, was somewhat dependent on the solvent, it being 3 in CD2Cl2 and 4 in C6D6; however, when acetone-d6 was used as solvent, only signals attributable to the isomer 4 were observed. Anal. Calcd for C30H33CrMo2O7P: C, 46.17; H, 4.26. Found: C, 45.85; H, 4.05. Spectroscopic data for 3c: 1H NMR: δ 11.67 (d, JPH =14, 1H, CH), 5.25 (d, JPH =1, 10H, Cp), 2.98-1.00 (m, 22H, Cy). Spectroscopic data for 4: 1H NMR: δ 13.47 (s, JCH =161, 1H, CH), 5.48, 5.16 (2s, 2 5H, Cp), 2.98-1.00 (m, 22H, Cy). 13C{1H} NMR: δ 273.5 (d, JCP = 3, CH), 242.3 (d, JCP = 14, MoCO), 232.9 (d, JCP = 15, CrCO), 230.4 (s, MoCO), 229.2 (d, JCP = 5, CrCO), 228.4 (s, MoCO), 225.8 (d, JCP = 8, CrCO), 220.7 (d, JCP = 6, CrCO), 94.1, 92.9 (2s, Cp), 55.5 [d, JCP = 14, C1(Cy)], 55.1 [d, JCP = 9, C1(Cy)], 36.4 [d, JCP = 6, C2(Cy)], 36.4 [d, JCP = 5, C2(Cy)], 34.8 [s, 2C2(Cy)], 29.0 [d, JCP = 11, C3(Cy)], 28.7 [d, JCP = 9, C3(Cy)], 28.6, 28.5 [2d, JCP = 11, C3(Cy)], 26.8, 26.5 [2s, C4(Cy)]. Spectroscopic data for 5: 1H NMR: δ 9.47 (d, JPH =14, 1H, CH), 5.37, 5.15 (2s, 2 5H, Cp), 2.98-1.00 (m, 22H, Cy). 13C{1H} NMR: δ 94.3, 93.0 (2s, Cp), 50.2 [d, JCP = 11, C1(Cy)], 45.2 [d, JCP = 5, C1(Cy)], 35.6 [s, C2(Cy)], 33.9, 33.7 [2d, JCP = 5, C2(Cy)], 33.1 [s, C2(Cy)], 26.7 [s, C4(Cy)] ppm. Other resonances of this isomer were obscured by those from the major isomer. Preparation of [MnMo2Cp2Cp0 (μ3-CH)(μ-PCy2)(CO)4] (6). A toluene solution (4 mL) of compound 1 (0.025 g, 0.042 mmol) and [MnCp0 (CO)3] (20 μL, 0.127 mmol) was irradiated in a quartz Schlenk tube with visible-UV light under a gentle N2 (99.9995%) purge for 3.5 h to give an orange solution, which was filtered using a canula. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethanepetroleum ether (1:1) yielded a pink fraction. Removal of solvents under vacuum from this fraction gave compound 6 as a pink microcrystalline solid (0.015 g, 45%). The crystals used in the X-ray study were grown by slow diffusion of petroleum ether into a dichloromethane solution of the complex at 253 K and were found to contain two dichloromethane molecules per molecule of complex. Anal. Calcd for C33H40MnMo2O4P: C, 50.92; H, 5.18. Found: C, 50.74; H, 5.21. 1H NMR: δ 12.79 (d, JPH = 7, 1H, CH), 5.00 (d, JPH = 1, 10H, Cp), 4.32, 4.11 (2 false t, apparent JPH = 2, 2 2H, C5H4), 2.16 (s, 3H, Me), 2.32-1.09 (m, 22H, Cy).

Article Preparation of [Mo2RuCp2(μ3-CH)(μ-PCy2)(CO)5] (7). A toluene solution (4 mL) of compound 1 (0.025 g, 0.042 mmol) and [Ru3(CO)12] (0.031 g, 0.048 mmol) was irradiated in a Pyrex Schlenk tube with visible-UV light under a gentle N2 (99.9995%) purge for 2 h 30 min to give a greenish-brown solution, which was filtered using a canula. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethane-petroleum ether (1:8) yielded a brown fraction. Removal of solvents under vacuum from this fraction gave 0.028 g of compound 7 containing variable amounts of [Mo2RuCp2(μ3-OCH3)(μ-PCy2)(CO)5] (8d). Further purification was achieved by the slow diffusion of petroleum ether into a toluene solution of the impure product at 253 K, this yielding compound 7 as black crystals suitable for X-ray diffraction (0.020 g, 69%). Spectroscopic data for 7: Anal. Calcd for C28H33Mo2O5PRu: C, 43.48; H, 4.30. Found: C, 43.30; H, 4.19. 1H NMR (300.13 MHz): δ 13.59 (s, 1H, CH), 5.15 (s, 10H, Cp), 2.77-0.86 (m, 22H, Cy). 13C{1H} NMR (75.48 MHz): δ 270.6 (d, JCP = 2, CH), 256.8 (d, JCP = 7, 2MoCO), 201.9 (s, 3RuCO), 89.4 (s, Cp), 48.0 [d, JCP = 23, C1(Cy)], 43.8 [d, JCP = 15, C1(Cy)], 34.2, 32.7 [2s, C2(Cy)], 28.2 [d, JCP = 12, 2C3(Cy)], 26.8, 26.6 [2s, C4(Cy)]. Spectroscopic data for 8d: 1H NMR (300.13 MHz): δ 5.19 (s, 10H, Cp), 3.56 (s, 3H, OCH3), 2.77-0.86 (m, 22H, Cy). 13C{1H} NMR (75.48 MHz): δ 255.6 (d, JCP = 7, 2MoCO), 202.4 (s, 3RuCO), 90.8 (s, Cp), 47.3 [d, JCP = 23, C1(Cy)], 42.5 [d, JCP = 16, C1(Cy)], 32.5, 32.0 [2s, C2(Cy)]; other resonances were obscured by those of the major reaction product. Preparation of [FeMo2Cp2(μ3-OCH3)(μ-PCy2)(CO)5] (8e). Solid [Fe2(CO)9] (0.031 g, 0.085 mmol) was added to a toluene solution (4 mL) of compound 2, prepared in situ from compound 1 (0.025 g, 0.042 mmol), and the mixture was stirred for 1 h to give a brown solution. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethane-petroleum ether (1:6) yielded an orange fraction. Removal of solvents under vacuum from this fraction gave compound 8e as a brown microcrystalline solid (0.015 g, 48%). The crystals used in the X-ray study were grown by slow diffusion of petroleum ether into a dichloromethane solution of the complex at 253 K. Anal. Calcd for C28H35FeMo2O6P: C, 45.06; H, 4.72. Found: C, 45.13; H, 4.67. 1 H NMR (300.13 MHz): δ 5.16 (d, JPH = 1, 10H, Cp), 3.65 (s, 3H, OMe), 2.72-0.78 (m, 22H, Cy). Preparation of [FeMo2Cp2{μ3-K1:η2:K1-C(O)CH3}(μ-PCy2)(CO)5] (9). A toluene solution (8 mL) of compound 1 (0.050 g, 0.085 mmol) was stirred at room temperature for 16 h while adding solid [Fe2(CO)9] (0.031 g, 0.085 mmol) every two hours to give an orange solution. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethanepetroleum ether (1:5) yielded an orange fraction. Removal of solvents under vacuum from this fraction gave compound 9 as an orange microcrystalline solid (0.054 g, 84%). The crystals used in the X-ray study were grown by slow diffusion of petroleum ether into a toluene solution of the complex at 253 K. Anal. Calcd for C29H35FeMo2O6: C, 45.93; H, 4.65. Found: C, 45.77; H, 4.57. ν(CO) (Nujol): 1990 (vs), 1934 (s), 1889 (s), 1800 (w), 1575 (w). 1H NMR: δ 5.17 (d, JPH = 1, 10H, Cp), 2.39 (s, 3H, Me), 2.34-0.98 (m, 22H, Cy). 1H NMR (248 K): δ 5.26, 5.16 (2s, 2 5H, Cp), 3.38 (s, 3H, Me), 2.34-0.98 (m, 22H, Cy). 13 C{1H} NMR: δ 251.2 (s, br, 2MoCO), 216.5 (s, br, 3FeCO), 199.9 [s, C(O)Me], 91.0 (s, Cp), 45.9 [d, JCP = 21, C1(Cy)], 40.8 [s, C1(Cy)], 40.0 (s, CH3), 33.4, 31.9 [2s, C2(Cy)], 28.3, 27.8 [2d, JCP = 11, C3(Cy)], 26.6, 26.4 [2s, C4(Cy)]. 13C{1H} NMR (248 K): δ 253.2 (s, MoCO), 251.0 (d, JCP = 10, MoCO), 199.7 [s, C(O)Me], 93.2, 89.0 (2s, Cp), 45.3 [d, JCP = 21, C1(Cy)], 40.2 [d, JCP = 6, C1(Cy)], 40.1 (s, CH3), 33.8, 32.5, 32.4, 30.5 [4s,


915

C2(Cy)], 28.2 [d, JCP = 13, C3(Cy)], 28.0 [d, JCP = 8, C3(Cy)], 27.6 [d, JCP = 10, 2C3(Cy)], 26.4, 26.3 [2s, C4(Cy)]. 13C{1H} NMR (208 K): δ 254.0, 251.1 (2s, MoCO), 221.0, 217.8, 211.7 (3s, FeCO), 199.7 [s, C(O)Me], 93.2, 89.0 (2s, Cp), 44.8, 39.8 [2s, br, C1(Cy)], 40.2 (s, CH3); other resonances in this spectrum were too broad to be unambiguously assigned. Preparation of [FeMo2Cp2(μ-CCH3)(μ-PCy2)(O)(CO)4] (10). A toluene solution (3 mL) of compound 9 (0.020 g, 0.026 mmol) was irradiated in a Pyrex Schlenk tube with visible-UV light under a gentle N2 (99.9995%) purge for 30 min to give an orange solution. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethane-petroleum ether (1:5) yielded a pink fraction. Removal of solvents under vacuum from the latter fraction gave compound 10 as a pink microcrystalline solid (0.015 g, 84%). The crystals used in the X-ray study were grown by the slow evaporation of a concentrated petroleum ether solution of the complex at room temperature. Anal. Calcd for C28H35FeMo2O5P: C, 46.05; H, 4.83. Found: C, 46.25; H, 5.15. 1H NMR (300.13 MHz): δ 5.91 (s, 5H, Cp), 5.54 (d, JPH = 1, 5H, Cp), 2.86 (d, JPH = 1, 3H, Me), 2.57-0.45 (m, 22H, Cy). 13 C{1H} NMR (75.48 MHz): δ 401.5 (d, JCP = 5, CMe), 241.4 (d, JCP = 8, MoCO), 218.1 (s, 3FeCO), 102.5, 91.0 (2s, Cp), 46.8 [d, JCP = 20, C1(Cy)], 46.7 (s, CH3), 39.8 [d, JCP = 13, C1(Cy)], 34.5 [s, C2(Cy)], 34.1 [d, JCP = 3, C2(Cy)], 32.6 [d, JCP = 5, C2(Cy)], 29.5 [d, JCP = 3, C2(Cy)], 28.2 [d, JCP = 10, C3(Cy)], 28.1 [d, JCP = 14, C3(Cy)], 27.7 [d, JCP = 10, C3(Cy)], 27.4 [d, JCP = 14, C3(Cy)], 26.5, 26.1 [2s, C4(Cy)]. Preparation of [Fe2Mo2Cp2(μ4-CH)(μ-PCy2)(CO)8] (11). A toluene solution (4 mL) of compound 1 (0.025 g, 0.042 mmol) and [Fe2(CO)9] (0.020 g, 0.127 mmol) was irradiated in a Pyrex Schlenk tube with visible-UV light under a gentle N2 (99.9995%) purge for 3.5 h to give a greenish-brown solution, which was filtered using a canula. The solvent was then removed under vacuum, and the residue was dissolved in a minimum of dichloromethane and chromatographed through an alumina column (activity IV) at 288 K. Elution with dichloromethane-petroleum ether (1:5) yielded a greenish-brown fraction. Removal of solvents under vacuum from this fraction gave compound 11 as a greenishbrown microcrystalline solid (0.025 g, 68%). Elution with dichloromethane-petroleum ether (1:5) yielded an orange fraction. Removal of solvents under vacuum from the latter fraction gave ca. 0.008 g of a mixture of compound 10 and [FeMo2Cp2(μ3CH)(μ-PCy2)(CO)5] (12) in variable amounts. The crystals used in the X-ray study of compound 11 were grown by the slow diffusion of petroleum ether into a toluene solution of the complex at 253 K. Spectroscopic data for 11: Anal. Calcd for C31H33Fe2Mo2O8P: C, 42.89; H, 3.83. Found: C, 42.51; H, 3.97. 1 H NMR: δ 5.46, 5.00 (2s, 2 5H, Cp), 4.24 (d, JPH = 2, 1H, CH), 2.18-0.83 (m, 22H, Cy). 13C{1H} NMR: δ 243.8 (d, JCP = 14, MoCO), 239.4 (d, JCP = 12, MoCO), 234.3 (d, JCP = 11, CH), 215.1 (s, 6FeCO), 92.4, 91.1 (2s, Cp), 50.0 [d, JCP = 17, C1(Cy)], 44.6 [d, JCP = 10, C1(Cy)], 34.4 [d, JCP = 4, C2(Cy)], 32.9 [d, JCP = 3, C2(Cy)], 32.4 [d, JCP = 4, C2(Cy)], 31.6 [s, C2(Cy)], 28.8 [d, JCP = 11, C3(Cy)], 28.2 [d, JCP = 10, C3(Cy)], 28.0 [d, JCP = 12, C3(Cy)], 27.1 [d, JCP = 11, C3(Cy)], 26.5 [s, 2C4(Cy)]. 13C{1H} NMR (213 K): δ 243.9 (d, JCP = 19, MoCO), 240.0 (d, JCP = 14, MoCO) 232.6 (d, JCP = 13, CH), 225.2, 224.0, 217.3 (3s, FeCO), 215.5 (s, 2FeCO), 213.8 (s, FeCO), 92.3, 90.8 (2s, Cp), 48.8 [d, JCP = 17, C1(Cy)], 43.0 [s, br, C1(Cy)], 33.8, 33.4, 31.3, 30.7 [4s, C2(Cy)], 28.5 [d, JCP = 11, C3(Cy)], 27.7 [d, JCP = 15, C3(Cy)], 27.6 [d, JCP = 16, C3(Cy)], 26.5 [d, JCP = 13, C3(Cy)], 26.2, 26.1 [2s, C4(Cy)]. 13C NMR: δ 234.3 (d, JCH = 143, CH). Spectroscopic data for 12: 1H NMR (300.13 MHz, CDCl3): δ 15.47 (s, 1H, CH), 5.73, 5.52 (2s, 2 5H, Cp), 2.55-0.52 (m, 22H, Cy). 13C{1H} NMR: δ 330.1 (d, JCP = 7, CH), 241.1 (s, MoCO), 232.0 (s, MoCO), 229.2 (s, FeCO), 223.8, 213.4 (2s, br, 2FeCO), 93.4, 92.7 (2s, Cp), 46.1 [d, JCP = 18, C1(Cy)], 45.8 [d, JCP = 11, C1(Cy)], 33.5 [d, JCP = 2, C2(Cy)], 32.9, 32.6, 31.9 [3s,

916


Alvarez et al. Table 8. Crystal Data for New Compounds

3b

6 3 2CH2Cl2

7

8e

9

10

)

C30H33Mo2C35H44Cl4C28H33Mo2C28H35C29H35C28H35O7PW MnMo2O4P O5PRu FeMo2O6P FeMo2O6P FeMo2O5P mol wt 912.26 948.29 773.46 746.26 758.27 730.26 cryst syst monoclinic monoclinic triclinic monoclinic monoclinic monoclinic P21/c P1 P21/c P21/c P21/c space group P21/c radiation (λ, A˚) 0.71073 1.54184 0.71073 0.71073 0.71073 0.71073 a, A˚ 10.0848(3) 14.1100(2) 9.8055(2) 9.7313(3) 10.2670(2) 8.4495(2) b, A˚ 15.5653(3) 15.5049(1) 10.1325(3) 20.2819(7) 18.5240(4) 16.7274(2) c, A˚ 19.2321(6) 17.9623(2) 15.6350(4) 16.6023(6) 15.1115(4) 20.1560(4) R, deg 90 90 92.550(2) 90 90 90 β, deg 95.862(1) 111.979(1) 90.460(2) 118.749(1) 91.566(1) 100.350(1) γ, deg 90 90 116.682(1) 90 90 90 3003.13(14) 3644.08(7) 1385.93(6) 2872.87(17) 2872.92(11) 2802.46(9) V, A˚3 Z 4 4 2 4 4 4 -3 2.018 1.728 1.853 1.725 1.753 1.731 calcd density, g cm 4.742 11.749 1.523 1.453 1.455 1.485 absorp coeff, mm-1 temperature, K 100(2) 100(2) 100(2) 100(2) 100(2) 100(2) θ range (deg) 2.13-25.24 3.38-73.87 1.3-25.24 2.33-25.24 2.27-25.24 1.59-25.24 index ranges (h, k, l) -11, 11; 0, -17, 16; -18, -11, 11; -12, -11, 11; -24, -12, 12; 0, -10, 9; 0, 18; 0, 23 16; -19, 21 12; 0, 18 0; -19, 10 22; 0, 18 20; 0, 24 no. of reflns collected 27 503 19 519 19 070 5629 22 464 20 196 5267(0.0575) 6984(0.0347) 4980(0.0248) 5061(0.0581) 5181(0.0493) 5061(0.0320) no. of indep reflns (Rint) reflns with I > 2σ(I) 4371 5871 4189 3533 3860 4416 R1 = 0.0522 R1 = 0.044 R1 = 0.0471 R1 = 0.0735 R1 = 0.0393 R1 = 0.0317 R indexes [data with I > 2σ(I)]a wR2 = 0.117c wR2 = 0.1316d wR2 = 0.1902e wR2 = 0.0967f wR2 = 0.0884g wR2 = 0.1416b R indexes (all data)a R1 = 0.0666 R1 = 0.0559 R1 = 0.0581 R1 = 0.1064 R1 = 0.0621 R1 = 0.0386 wR2 = 0.1283c wR2 = 0.1537d wR2 = 0.2239e wR2 = 0.1115f wR2 = 0.1068g wR2 = 0.1637b GOF 1.217 1.076 1.236 1.121 1.134 1.276 no. of restraints/params 0/374 1/429 1/338 0/344 0/353 0/335 2.792, -2.674 0.948, -1.181 2.412, -2.082 1.622, -1.649 0.843, -0.856 1.068, -1.483 ΔF(max., min.), e A˚-3 P P P P a R= Fo| - |Fc / |Fo|. wR = [ w(|Fo|2 - |Fc|2)2/ w|Fo|2]1/2. w = 1/[σ2(Fo2) þ (aP)2 þ bP] where P = (Fo2 þ 2Fc2)/3. b a = 0.0741, b = 46.0162. c d e a = 0.0512, b = 26.8266. a = 0.0843, b = 4.6921. a = 0.0993, b = 28.3430. f a = 0.0561, b = 1.7199. g a = 0.0607, b = 1.6420. )

mol formula

C2(Cy)], 28.3 [d, JCP = 12, C3(Cy)], 28.1 [d, JCP = 11, C3(Cy)], 27.5 [d, JCP = 10, 2C3(Cy)], 26.5, 26.4 [2s, C4(Cy)]. X-ray Structure Determination of Compounds 3b, 7, 8e, 9, and 10. Data collection for these compounds was performed on a Nonius Kappa CCD single diffractometer, using graphitemonochromated Mo KR radiation. Images were collected at 29 to 65 mm fixed crystal-detector distance, using the oscillation method, with 1° to 1.7° oscillation and 2 to 120 s exposure time per image, depending on the particular compound. Data collection strategy was calculated with the program Collect.49 Data reduction and cell refinements were performed with the programs HKL Denzo and Scalepack.50 Semiempirical absorption corrections were applied using the program SORTAV.51 Using the program suite WinGX,52 the structures were solved by Patterson interpretation and phase expansion and refined with full-matrix least-squares on F2 with SHELXL97.53 All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were geometrically placed, except the methylidyne hydrogen in compounds 3b and 7, which were located in the Fourier maps and refined. They all were given an overall isotropic thermal parameter. A restraint on the methylidyne C-H bond length (0.95(2) A˚) had to be applied for 7; in that case, the largest residual electron density was located around the ruthenium atom. Further details of the data collection and refinements are given in Table 8. (49) (50) (51) (52) (53)

Collect; Nonius BV: Delft, The Netherlands, 1997-2004. Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307. Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33. Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837. Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.

X-ray Structure Determination of Compound 6. Data collection was performed on an Oxford Diffraction Xcalibur Nova single-crystal diffractometer, using Cu KR radiation. Images were collected at a 65 mm fixed crystal-detector distance, using the oscillation method, with 1° oscillation and variable exposure time per image (2-8 s). Data collection strategy was calculated with the program CrysAlis Pro CCD.54 Data reduction and cell refinement were performed with the program CrysAlis Pro RED.54 An empirical absorption correction was applied using the SCALE3 ABSPACK algorithm as implemented in the program CrysAlis Pro RED.54 Using the program suite WinGX,52 the structure was solved by Patterson interpretation and phase expansion and refined with full-matrix least-squares on F2 using SHELXL97.53 This compound was found to crystallize with two molecules of dichloromethane. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were geometrically placed, except the methylidyne hydrogen H(5), which was located in the Fourier maps and refined with a restraint on the C-H bond length (0.95(2) A˚). All hydrogen atoms were given an overall isotropic thermal parameter. Further details of the data collection and refinements are given in Table 8.

Acknowledgment. We thank the DGI of Spain for financial support (project CTQ2006-01207/BQU). Supporting Information Available: A CIF file giving the crystallographic data for the structural analysis of compounds 3b, 6, 7, 8e, 9, and 10. This material is available free of charge via the Internet at http://pubs.acs.org. (54) CrysAlis Pro; Oxford Diffraction Ltd.: Oxford, U.K., 2006.

Heterometallic Derivatives of the Unsaturated Methyl-Bridged

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