Mixed-Metal Cluster Chemistry. 31. Reactions of Dimolybdenum

Mar 7, 2012 - Reactions of the tetrahedral clusters Mo2Ir2(μ-CO)3(CO)7(η5-L)2 (L = C5H5, C5HMe4) with the molybdenum alkylidyne complex ...
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Mixed-Metal Cluster Chemistry. 31.1 Reactions of Dimolybdenum− Diiridium Clusters with Alkylidyne Complexes Michael D. Randles,† Rian D. Dewhurst,‡ Marie P. Cifuentes,*,† and Mark G. Humphrey*,† †

Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 0200, Australia Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

‡

S Supporting Information *

ABSTRACT: Reactions of the tetrahedral clusters Mo2Ir2(μ-CO)3(CO)7(η5-L)2 (L = C5H5, C5HMe4) with the molybdenum alkylidyne complex Mo(CC6H4OMe4)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} afford the pentanuclear clusters Mo3Ir2(μ4-C)(μ3CC 6 H 4 OMe-4)(μ-O)(CO) 6 {(N 2 C 3 H 3 ) 3 BH-κ 3 N,N′,N″}(η 5 -C 5 H 5 ) 2 (1; 62%) and Mo 3 Ir 2 (μ 3 -CC 6 H 4 OMe-4)(μ 3 -η 2 -CO)(μ-CO)(CO) 6 {(N 2 C 3 H 3 ) 3 BH-κ 3 N,N′,N″}(η 5 C5Me4H)2 (2; 65%), respectively, while the reaction of Mo2Ir2(μ-CO)3(CO)7(η-C5H5)2 with W(CCCSiMe3)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} yields the butterfly cluster Mo 2 Ir 2 (μ 4 -η 2 -SiMe 3 C 2 CW(CO) 2 {(N 2 C 3 H 3 ) 3 BH-κ 3 N,N′,N″})(μ-CO) 4 (CO) 4 (η 5 C5H5)2 (3; 60%). The identities of 1−3 have been confirmed by single-crystal X-ray diffraction studies. Cluster 1 contains μ4carbido and μ-oxido ligands resulting from CO cleavage. Cluster 2, with sterically more encumbering tetramethylcyclopentadienyl ligands that arrest CO cleavage, possesses a μ3-η2-CO ligand with a weak CO bond (1.272(7), 1.257(7) Å). Cluster 2 could not be converted into an analogue of cluster 1. The reaction with alkyne is more facile than the reaction with alkylidyne; cluster 3 results from addition of the CC bond (rather than the WC bond) across the Mo−Mo vector.

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tris(pyrazolyl)borato ligands6 and the syntheses and structural studies of pentanuclear cluster products, demonstrating CO activation and cleavage, and a tetranuclear cluster, confirming preferential reaction at the alkyne rather than the alkylidyne linkage.

here has been longstanding interest in the field of metal carbonyl clusters.2 Initial studies that demonstrated, inter alia, (i) the existence of unsupported metal−metal linkages, (ii) main-group atoms in interstitial sites and within bonding distance of transition-metal atoms only, (iii) unprecedented substrate transformations employing multimetallic activation, and (iv) high-nuclearity clusters offering the tantalizing prospect of progression from molecular to metallic behavior all provided strong stimuli to the development of the field. While efficient methodologies for the preparation of lownuclearity mixed-metal clusters have been developed, the area of medium- and high-nuclearity cluster chemistry is still dominated by homometallic examples. The most broadly applicable route to the synthesis of mixed-metal clusters was developed by Gordon Stone and co-workers: namely, the reactions of metal alkylidene or alkylidyne complexes with bimetallic complexes or metal clusters, leading to an enormous number of “chain” and “star” clusters as well as more condensed species.3 This general procedure has not been employed for the syntheses of molybdenum−iridium clusters and has only been used once for tungsten−iridium cluster synthesis, the reaction of W(CC6H4Me-4)(CO)2(η5-C5H5) with IrCl(CO)(η2-C8H14)2 to afford W2Ir{μ3-η2-C2(C6H4Me4) 2 }Cl(CO) 4 (η 5 -C 5 H 5 ) 2 and W 2 Ir(μ 3 -CC 6 H 4 Me-4)(μCC6H4Me-4)Cl(CO)4(η5-C5H5)2.4 It has also mainly been used with cyclopentadienyl-containing reagentsalkylidyne complexes with sterically demanding ligands are comparatively less well explored, one notable exception being Stone’s metallacarborane alkylidyne complexes.3g,5 We report herein reactions of dimolybdenum−diiridium clusters with selected metal alkylidyne complexes containing sterically encumbering © 2012 American Chemical Society

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EXPERIMENTAL SECTION

General Considerations. Reactions were performed under an atmosphere of nitrogen using standard Schlenk techniques, with no precautions to exclude air during the workup. Solvents used in reactions were AR grade; CH2Cl2 (CaH2) and toluene (sodium benzophenone ketyl) were distilled under nitrogen, and other solvents were used as received. Petroleum ether refers to a fraction of boiling range 60−80 °C. Preparative and analytical thin-layer chromatography was carried out using 20 × 20 cm glass plates and aluminum sheets coated with 0.5 and 0.25 mm Merck GF254 silica gel, respectively. Diphenylacetylene (Aldrich) was used as received. Literature procedures were used to prepare Mo2Ir2(μ-CO)3(CO)7(η5-C5HR4)2 (R = H, 7 Me 8 ), Mo(CC 6 H 4 OMe-4)(CO) 2 {(N 2 C 3 H 3 ) 3 BHκ 3 N,N′,N″}, 9 and W(CCCSiMe 3 )(CO) 2 {(N 2 C 3 H 3 ) 3 BHκ3N,N′,N″}.10 Instrumentation. Infrared spectra were recorded on a PerkinElmer System 2000 FT-IR using CaF2 cells and were used to monitor the progress of reactions. 1H NMR spectra (300 MHz) were recorded on a Varian Gemini-300 spectrometer in CDCl3. Unit- and highresolution ESI mass spectra were recorded on a Micromass-Waters LC-ZMD single-quadrupole liquid chromatograph−MS instrument and are reported as m/z (assignment, relative intensity). Microanalyses Special Issue: F. Gordon A. Stone Commemorative Issue Received: October 31, 2011 Published: March 7, 2012 2582

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CH2Cl2/petroleum ether (3/2) afforded three bands. The contents of the first band (Rf = 0.61, orange) were extracted with CH2Cl2 and reduced in volume to afford an orange-red solid, identified as unreacted Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 (1.7 mg, 1.7 μmol, 8%). The contents of the second band (Rf = 0.44, brown-green) were extracted with CH2Cl2 and reduced in volume to afford a green solid, identified as 3 (20.7 mg, 12.5 μmol, 60%). IR (CH2Cl2): ν(CO) 2070 vs, 2043 vs, 2018 m, 2000 m, 1962 m, 1878 s, 1813 s, 1770 m cm−1. 1H NMR: δ 8.10 (m, 1H, (N2C3H3)3BH), 8.08 (m, 1H, (N2C3H3)3BH), 7.79 (m, 1H, (N2C3H3)3BH), 7.71 (m, 1H, (N2C3H3)3BH), 7.63 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 7.60 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 6.51 (m, 1H, (N2C3H3)3BH), 6.27 (m, 1H, (N2C3H3)3BH), 6.17 (t, JHH = 2 Hz, 1H, (N2C3H3)3BH), 5.57 (s, 5H, C5H5), 4.90 (s, 5H, C5H5), 0.51 (s, 9H, SiMe3). MS (ESI): calcd for C35H29BIr2Mo2N6O10SiW, 1493 ([M]+); found, 1516 ([M + Na]+, 9), 1493 ([M]+, 44), 1465 ([M − CO]+, 100), 1437 ([M - 2CO]+, 28), 1409 ([M − 3CO]+, 26), 1381 ([M − 4CO]+, 79), 1353 ([M − 5CO] + , 24), 1325 ([M − 6CO] + , 9). Anal. Calcd for C35H29BIr2Mo2N6O10SiW: C, 28.16; H, 1.96; N, 5.63. Found: C, 28.24; H, 2.12; N, 5.11. The contents of the third band were obtained in trace amounts and were not identified. X-ray Crystallographic Studies. General Considerations. The crystal and refinement data for compounds 1−3 are summarized in ref 11. Crystals suitable for the X-ray structural analyses were grown by liquid diffusion of ethanol into a dichloromethane solution (1, 3) or liquid diffusion of ethanol into a chloroform solution (2) at 277 K. A single crystal of each species was mounted on a fine glass capillary, and data were collected on a Nonius Kappa CCD diffractometer at 200 K using graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). The unit cell parameters were obtained by least-squares refinement of the reflections. The reduced data were corrected for absorption using numerical methods implemented from within maXus;12 equivalent reflections were merged. The structures were solved by direct methods and refined with the use of the CRYSTALS software package.13 Compound 1. The crystallographic asymmetric unit contains one cluster and a dichloromethane solvent molecule. All non-hydrogen atoms of the cluster were refined with anisotropic displacement parameters. Hydrogen atoms were included at idealized positions and allowed to ride on the atoms to which they are bonded, before being refined independently. The largest peaks in the final difference electron map are located near the iridium atoms. Compound 2. The unit cell contains two cluster units and four chloroform solvent molecules. The four chloroform molecules were found to be disordered over two locations. In three of the chloroform molecules, one of the chlorine atoms was split over two sites and refined with isotropic displacement parameters, which were constrained to be equal for each pair; the relative populations were refined to 0.624(5):0.376(5), 0.636(7):0.364(7), and 0.602(8):0.398(8). Within the other chloroform solvate, one chlorine and the carbon atom were found to be disordered over two sites, the relative populations of which were refined to 0.510(7):0.490(7). The cluster molecules were well-behaved. Hydrogen atoms were included at idealized positions and allowed to ride on the atoms to which they are bonded. The largest peaks in the final difference electron map are located near the iridium atoms. Compound 3. The crystallographic asymmetric unit contains one cluster and a dichloromethane solvent molecule. All non-hydrogen atoms of the cluster were refined with anisotropic displacement parameters. Hydrogen atoms were included at idealized positions and allowed to ride on the atoms to which they are bonded, before being refined independently. The largest peaks in the final difference electron map are located near the iridium and tungsten atoms.

were carried out by the Microanalysis Service Unit in the Research School of Chemistry, ANU. S y n t h e s i s of M o 3 I r 2 ( μ 4 - C ) ( μ 3 - C C 6 H 4 O M e - 4 ) ( μ - O ) (CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5H5)2 (1). Mo(CC6H4OMe4)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} (7.0 mg, 14.5 μmol) was added to an orange solution of Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 (13.4 mg, 13.6 μmol) in toluene (10 mL), and the resultant mixture was heated at reflux for 15 min. The solution was taken to dryness in vacuo, the crude residue was dissolved in the minimum amount of CH2Cl2, and this solution was applied to preparative silica TLC plates. Elution with CH2Cl2 afforded three bands. The contents of the first band (Rf = 0.90, orange) were extracted with CH2Cl2 and reduced in volume to afford an orange-red solid, identified as unreacted Mo(CC6H4OMe4)(CO)2{(N2C3H3)3BH-κ3N,N′,N″}. The contents of the second band (Rf = 0.83, orange) were extracted with CH2Cl2 and reduced in volume to afford an orange-red solid, identified as unreacted Mo2Ir2(μCO)3(CO)7(η5-C5H5)2 (2.9 mg, 2.9 μmol, 21%). The contents of the third band (Rf = 0.14, red-brown) were extracted with CH2Cl2 and reduced in volume to afford a brown solid, identified as 1 (11.2 mg, 8.4 μmol, 62%). IR (CH2Cl2): ν(CO) 2029 s, 2002 vs, 1975 m, 1952 m, 1896 m, 1790 m cm−1. 1H NMR: δ 8.52 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 7.77 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 7.75 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 7.69−7.64 (m, 2H, (N2C3H3)3BH), 7.55 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 6.69−6.59 (m, 4H, C6H4), 6.36 (t, JHH = 2 Hz, 1H, (N2C3H3)3BH), 6.23 (t, JHH = 2 Hz, 1H, (N2C3H3)3BH), 6.14 (t, JHH = 2 Hz, 1H, (N2C3H3)3BH), 5.94 (s, 5H, C5H5), 5.44 (s, 5H, C5H5), 3.79 (s, 3H, OCH3). MS (ESI): calcd for C34H27BIr2Mo3N6O8, 1331 ([M]+); found, 1331 ([M]+, 100), 1303 ([M − CO]+, 60), 1275 ([M − 2CO]+, 17). Anal. Calcd for C34H27BIr2Mo3N6O8: C, 30.69; H, 2.05; N, 6.32. Found: C, 30.62; H, 2.18; N, 6.07. Synthesis of Mo 3 Ir 2 (μ 3 -CC 6 H 4 OMe-4)(μ 3 -η 2 -CO)(μ-CO)(CO) 6 {(N 2 C 3 H 3 ) 3 BH-κ 3 N,N′,N″}(η 5 -C 5 Me 4 H) 2 (2). Mo( CC6 H4OMe-4)(CO) 2{(N 2C3 H3) 3BH-κ3N,N′,N″} (7.1 mg, 14.7 μmol) was added to an orange solution of Mo2Ir2(μ-CO)3(CO)7(η5C5HMe4)2 (16.5 mg, 15.0 μmol) in toluene (10 mL), and the resultant mixture was heated at reflux for 15 min. The solution was taken to dryness in vacuo, the crude residue was dissolved in a minimum amount of CH2Cl2, and this solution was applied to preparative silica TLC plates. Elution with CH2Cl2/petroleum ether (11/9) afforded two bands. The contents of the first band (Rf = 0.62, orange) were extracted with CH2Cl2 and reduced in volume to afford an orange-red solid, identified as unreacted Mo2Ir2(μ-CO)3(CO)7(η5-C5HMe4)2 (3.6 mg, 3.3 μmol, 22%). The contents of the second band (Rf = 0.49, purple) were extracted with CH2Cl2 and reduced in volume to afford a purple solid, identified as 2 (14.4 mg, 9.8 μmol, 67%). IR (CH2Cl2): ν(CO) 1995 vs, 1959 s, 1935 m, 1916 m, 1880 w, 1843 w, 1794 w cm−1. 1H NMR: δ 8.80 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 8.00 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 7.70 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 7.67 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 7.45 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 6.35 (t, JHH = 2 Hz, 1H, (N2C3H3)3BH), 6.29 (t, JHH = 2 Hz, 1H, (N2C3H3)3BH), 6.18−6.03 (m, 4H, C6H4), 6.02 (d, JHH = 2 Hz, 1H, (N2C3H3)3BH), 5.61 (t, JHH = 2 Hz, 1H, (N2C3H3)3BH), 5.21 (s, 1H, η5-C5HMe4), 5.02 (s, 1H, η5-C5HMe4), 3.60 (s, 3H, OCH3), 2.49 (s, 3H, η5-C5HMe4), 2.32 (s, 3H, η5C5HMe4), 2.26 (s, 3H, η5-C5HMe4), 1.90 (s, 3H, η5-C5HMe4), 1.67 (s, 3H, η5-C5HMe4), 1.65 (s, 3H, η5-C5HMe4), 1.10 (s, 3H, η5-C5HMe4), 0.94 (s, 3H, η5-C5HMe4). MS (ESI): calcd for C43H43BIr2Mo3N6O9, 1471 ([M]+); found, 1510 ([M + K]+, 5), 1494 ([M + Na]+, 24), 1471 ([M] + , 100), 1443 ([M − CO] + , 5). Anal. Calcd for C43H43BIr2Mo3N6O9: C, 35.11; H, 2.95; N, 5.71. Found: C, 34.87; H, 3.11; N, 5.96. Synthesis of Mo2Ir2(μ4-η2-SiMe3C2CW(CO)2{(N2C3H3)3BHκ 3 N,N′,N″})(μ-CO) 4 (CO) 4 (η 5 -C 5 H 5 ) 2 (3). W(CCCSiMe 3 )(CO)2{(N2C3H3)3BH-κ3N,N′,N″} (14.5 mg, 25.8 μmol) was added to an orange solution of Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 (20.7 mg, 21.0 μmol) in CH2Cl2 (10 mL), and the resultant mixture was heated at reflux for 24 h. The solution was taken to dryness in vacuo, the crude residue was dissolved in the minimum amount of CH2Cl2, and this solution was applied to preparative silica TLC plates. Elution with

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RESULTS AND DISCUSSION Syntheses and Spectroscopic Characterization. The isolobal analogy relates organometallic fragments to (generally better understood) organic counterparts and was employed 2583

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Scheme 1. Syntheses of 1−3

Figure 1. ORTEP plot and atomic numbering scheme for Mo3Ir2(μ4-C)(μ3-CC6H4OMe-4)(μ-O)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5H5)2 (1). Displacement ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å): Mo3− Mo4 = 2.5481(12), Ir1−Ir2 = 2.6716(6), Ir1−Mo3 = 2.8880(10), Ir1−Mo4 = 2.7496(9), Ir1−Mo5 = 3.0222(9), Ir2−Mo3 = 2.7023(10), Ir2−Mo5 = 2.8707(9), Ir2−Mo4 = 3.1902(9).

reactions of the molybdenum-containing tetranuclear cluster and its tetramethylcyclopentadienyl-containing analogue with selected alkylidyne complexes. Thus, reactions between Mo(CC 6 H 4 OMe-4)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} and Mo2Ir2(μCO)3(CO)7(η5-C5HR4)2 (R = H, Me) in refluxing toluene afforded Mo3Ir2(μ4-C)(μ3-CC6H4OMe-4)(μ-O)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5H5)2 (1) in 62% yield and Mo3Ir2(μ3-CC6H4OMe-4)(μ3-η2-CO)(μ-CO)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5Me4H)2 (2) in 65% yield (Scheme 1), both complexes being characterized by IR and 1H NMR spectroscopy, ESI mass spectrometry, satisfactory

extensively by Gordon Stone and co-workers to rationalize and direct the syntheses of a vast array of mixed-metal cluster complexes.3f,g,14 A particularly useful isolobal connection proved to be that between alkynes (RCCR) and alkylidyne complexes (LnMCR), especially between the ligated metal fragments LnM and the alkylidyne units CR. We have previously noted the facile reactivity of M 2 Ir 2 (μCO)3(CO)7(η5-C5H5)2 (M = Mo, W) and analogues bearing other cyclopentadienyl ligands toward alkynes, products of composition M2Ir2(μ4-η2-RC2R)(μ-CO)4(CO)4(η5-C5H5)2 corresponding to formal insertion of the alkyne into the M−M bond generally being observed.15 We have now investigated 2584

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Figure 2. ORTEP plot and atomic numbering scheme for Mo3Ir2(μ3-CC6H4OMe-4)(μ3-η2-CO)(μ-CO)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5C5Me4H)2 (2). Displacement ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å): Ir1−Ir2 = 2.6845(3), 2.6865(3), Ir1−Mo3 = 2.7066(5), 2.7114(5), Ir1−Mo4 = 2.7851(5), 2.7968(5), Ir1−Mo5 = 2.8293(5), 2.8481(5), Ir2− Mo3 = 2.7481(5), 2.7541(5), Ir2−Mo4 = 2.7730(5), 2.7850(6), Mo3−Mo4 = 2.8140(7), 2.7946(7).

containing clusters19 have all afforded edge-bridging oxo-ligandcontaining clusters, as have reactions of clusters with water20 and trimethylamine N-oxide,21 and indeed derivatization of preexisting μ-oxo-containing clusters22 has been successfully effected. The formation of coordinated carbide and oxo ligands by cleavage of a coordinated carbonyl ligand, as in the present case, is comparatively rare, although there are mixed-metal precedents.23 The Mo3−Mo4 bond distance of 2.5481(12) Å is considerably shorter than the “typical” Mo−Mo distance of 3.10 Å;8 it is longer than the MoMo distances found in {Mo(CO) 2 (η 5 -C 5 H 5 )} 2 (2.448(1) Å), 16 {Mo(CO) 2 (η 5 C 5 Me 5 )} 2 (2.488(3) Å), 24 and {Mo(CO) 2 (η 5 -C 9 H 7 )} 2 (2.500(1) Å)25 and similar to the MoMo distances in {Mo(CO)2(η5-C5Me4Ph)}2 (2.5374(10) Å), {Mo(CO)2(η5C5Me4C6H4-4-Cl)}2 (2.5286(5) Å), and {Mo(CO)2(η5C5Me4C6H4-4-Me)}2 (2.5253(5) Å).26 Oxo-bridged Mo−Mo linkages are rare in organometallic clusters,27 the analogous distance in Mo2Ru4(μ6-C)(μ-O)(CO)12(η5-C5H5)2 being 2.9052(12) Å.27 There are also a number of long and short Ir−Mo bonds present in cluster 1, in comparison to the “normal” bond range (2.86 ± 0.05 Å);8 bonds Ir1−Mo5 and Ir2−Mo4 are long at 3.022(9) and 3.1902(9) Å, respectively, while Ir1−Mo4 and Ir2−Mo3 are short at 2.7496(9) and 2.7023(10) Å, respectively. All other metal−metal bonds fall within previously established ranges. Assuming the oxido ligand in 1 is a four-electron donor, the cluster is EAN precise with 74 CVE (3 × 6 (Mo) + 2 × 9 (Ir) + 4 (C) + 3 (CR) + 4 (O) + 6 × 2 (CO) + 5 (Tp) + 2 × 5 (Cp)), which corresponds to the expected polyhedral electron count for a tetrahedron (Ir1, Ir2, Mo3, Mo4) (60 CVE) fused to a butterfly (Ir1, Ir2, Mo4, Mo5) (62 CVE) through a common triangular face (−48 CVE). The metal core of 2 adopts a spiked-tetrahedral geometry; as with 1, η 5 -cyclopentadienyl groups ligate two of the molybdenum atoms and a tris(pyrazolyl)borate group ligates the third. The structure contains six terminally bound carbonyls, a bridging carbonyl, a μ3-η2-bound carbonyl, and a

microanalyses, and single-crystal X-ray diffraction studies. The solution IR spectrum of 1 in CH2Cl2 contains six ν(CO) bands, four corresponding to terminally bound carbonyls (2029−1952 cm−1) and two to bridging modes (1896 and 1790 cm−1), while that of 2 contains seven ν(CO) bands, four corresponding to terminally bound carbonyls (1995−1916 cm−1) and three to bridging modes (1880−1794 cm−1). The 1H NMR spectrum of 1 contains two resonances at δ 5.94 and 5.44 assigned to the cyclopentadienyl groups, as well as resonances corresponding to the tris(pyrazolyl)borate ligand and the 4-methoxyphenylalkylidyne group, while that of 2 contains 9 and 10 separate resonances for the tris(pyrazolyl)borate and tetramethylcyclopentadienyl ligands, respectively. The ESI mass spectrum of 1 displays a molecular ion peak at m/z 1331 and fragmentation peaks corresponding to the loss of one and two carbonyl ligands, while that of 2 shows sodium and potassium adducts at m/z 1510 and 1494, respectively, in addition to the molecular ion at m/z 1471 and fragmentation by loss of a carbonyl ligand. The molecular structures of 1 (Figure 1) and 2 (Figure 2) were determined by single-crystal X-ray diffraction studies. The metal core of 1 adopts an edge-bridged tetrahedral geometry with η5-cyclopentadienyl groups coordinated to two of the molybdenum atoms and a tris(pyrazolyl)borate group κ3ligating the third. The structure contains a μ3-coordinated alkylidyne ligand, along with an edge-bridging oxido ligand and μ4-bound carbido ligand. One of the six terminally bound carbonyl ligands (CO25) is formally semibridging (asymmetry parameter16 α = 0.26). The carbide ligand sits in a butterfly cleft defined by Ir1, Ir2, Mo4, and Mo5, displaced slightly toward Mo4 (distances to carbide C124 (Å): Mo4, 1.972(10); Mo5, 2.046(10); Ir1, 2.119(9); Ir2, 2.068(9)); Mo4−C124− Mo5 is close to linearity (∠166.1(5)°). The edge-bridging oxo ligand is somewhat unsymmetrically disposed (Mo3−O34 = 1.881(8) Å, Mo4−O34 = 1.998(8) Å). This specific ligand coordination mode is not unusualreactions of monometallic oxo complexes,17 μ-acyl clusters,18 and terminal oxo-ligand2585

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μ3-bound 4-alkylidyne group. The bridging carbonyl is asymmetrically disposed toward Mo4 (asymmetry parameter16 α = 0.31). The μ3-η2-CO bond distance in 2 (1.272(7), 1.257(7) Å) is long; cluster activation of CO in similar mixedmetal environments has afforded C−O distances up to 1.286 Å.28 Assuming that μ3-η2-CO is a four-electron donor, the cluster possesses 72 CVE ((3 × 6 (Mo)) + (2 × 9 (Ir)) + 3 (CR) + 4 (μ3-η2-CO) + 2 (μ-CO) + (6 × 2 (CO)) + 5 (Tp) + (2 × 5 (Cp))), which is 4 electrons less than the expected polyhedral electron count for a spiked (Ir1, Mo5) tetrahedron (Ir1, Ir2, Mo3, Mo4) (34 CVE + 60 CVE − 18 CVE). However, this may be ameliorated to some extent by the fact that a number of the metal−metal bonds are short compared to “normal” Ir−Mo bond lengths (2.86 ± 0.05 Å), namely Ir1− Mo3 (2.7066(5), 2.7114(5) Å), Ir1−Mo4 (2.7851(5), 2.7968(5) Å), Ir2−Mo3 (2.7481(5), 2.7541(5) Å), and Ir2− Mo4 (2.7730(5), 2.7850(6) Å), while the Mo−Mo distance in 2 (2.8140(7), 2.7946(7) Å) is also short and indeed similar to the MoMo bond length in {Mo(CO)2(η5-C5H5)}2(μ-η1C13H8) (2.798(1) Å).23 Stone has previously explored the use of propargylidyne complexes M(CCCBut)(CO)2L (M = Mo, W; L = η5C5H5, (N2C3H3)3BH-κ3N,N′,N″, (N2C3HMe2)3BH-κ3N,N′,N″) in the bridge-assisted synthesis of low-nuclearity clusters,29 from which it was concluded that the coordination of extraneous metal fragments to either the metal−carbon or carbon−carbon triple bonds could occur. For cyclopentadienyl derivatives, attack at the MC bond predominated, while the steric encumbrance imposed by inclusion of poly(pyrazolyl)borate coligands directed metal addition to the CC bond. The proclivity of M2Ir2(μ-CO)3(CO)7(η5-C5H5)2 (M = Mo, W) to bind alkynes coupled with the extension to alkylidynes discussed above therefore suggested an opportunity to explore the reactions of propargylidynes, with a view toward the synthesis of higher nuclearity clusters, via the reaction of W( CCCSiMe 3 )(CO) 2 {(N 2 C 3 H 3 ) 3 BH-κ 3 N,N′,N″} with Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 (Scheme 1). This reaction proceeded smoothly in refluxing dichloromethane to afford Mo2Ir2(μ4-η2-SiMe3C2CW(CO)2{(N2C3H3)3BHκ3N,N′,N″})(μ-CO)4(CO)4(η5-C5H5)2 (3) in 60% yield. The solution IR spectrum of 3 is analogous to those of other Mo2Ir2(μ4-η2-RC2R)(μ-CO)4(CO)4(η5-C5H5)2 examples,15d−f with additional carbonyl bands at 1962 and 1878 cm−1 corresponding to the tungsten-bound carbonyl ligands. In addition to the expected resonances for the tris(pyrazolyl)borate ligand and trimethylsilyl group, the 1H NMR spectrum contains two resonances assigned to the cyclopentadienyl ligands at δ 5.57 and 4.90. Molecular ion peaks and sodium adduct peaks are seen in the ESI mass spectrum, along with fragment ion peaks corresponding to the loss of one to six carbonyl ligands. The X-ray structural study (Figure 3) confirms that 3 adopts a butterfly geometry in which the iridium atoms form the hinge, with μ4-η2-coordination of the alkyne to the Mo2Ir2 core, a structure seen in similar products from reactions between Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 and alkynes.15a,c−f The propargylidyne precursor has been crystallographically characterized;10b while the WC distances are equivalent within experimental error, the CC linkage is lengthened on complexation, as expected (WC, W(CC CSiMe3)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} 1.844(6) Å, cf. 3 1.874(11) Å; CC, W(CCCSiMe3)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} 1.236(9) Å, cf. 3 1.510(12) Å). Cluster 3 possesses 60 CVE ((2 × 6 (Mo)) + (2 × 9 (Ir)) + 4

Figure 3. ORTEP plot and atomic numbering scheme for Mo2Ir2(μ4η2-SiMe3C2CW(CO)2{(N2C3H3)3BH-κ3N,N′,N″})(μCO)4(CO)4(η5-C5H5)2 (3). Displacement ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å): Ir1−Ir2 = 2.6889(5), Ir1−Mo3 = 2.8380(9), Ir1−Mo4 = 2.8471(10), Ir2−Mo3 = 2.8120(9), Ir2−Mo4 = 2.8312(9).

(RC2R′) + (4 × 2 (μ-CO)) + 94 × 2 (CO)) + (2 × 5 (Cp))), 2 electrons less than the expected electron count for a cluster with a butterfly core geometry; however, the alkyne carbons should be considered as core atoms in a pseudo-octahedral cluster core, for which the polyhedral skeletal electron pair theory predicts 7 skeletal electron pairs, as observed (1/2((2 × 6 (Mo)) + (2 × 9 (Ir)) + (2 × 4 (C)) + (8 × 2 (CO)) + (2 × 5 (Cp)) + (2 × 1 (alkyne substituents)) − (4 × 12 (M)) − (2 × 2 (C)))).

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DISCUSSION When the dimolybdenum−diiridium cluster has been reacted with a molybdenum alkylidyne reagent bearing a bulky tris(pyrazolyl)borate ligand, the reaction outcomes have been shown to depend strongly on the nature of the cluster-bound cyclopentadienyl ligands. Employing sterically demanding tetramethylcyclopentadienyl ligands afforded spiked-tetrahedral 2; the MoC bond has cleaved and the alkylidyne ligand now caps a MoIr2 face of the tetrahedron, and four CO ligands are lost, but the integrity of the remaining COs is maintained (although the μ3-η2-CO ligand is lengthened considerably). Using smaller cyclopentadienyl ligands permits further condensation to occur, affording edge-bridged tetrahedral 1; the alkylidyne now caps a Mo2Ir face of the tetrahedron, and five CO ligands are lost and another cleaved. The CO cleavage is noteworthy; clusters containing both oxo and carbide ligands derived from coordinated CO are uncommon,30 and the 2586

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present example is unique in presenting exposed oxo and carbide ligands. Similarly, while clusters containing both carbido and alkylidyne ligands are extant,28 we are not aware of alkylidyne−carbido−oxido cluster precedents. There is at present no evidence for the intermediacy of an analogue of 2 en route to 1; thermolysis of 2 did not afford an analogue of 1. Monitoring the syntheses of 1 and 2 by TLC and solution IR revealed that reaction proceeds in refluxing toluene, lower temperatures and other solvents proving insufficient. In contrast, previous studies with Mo2Ir2(μ-CO)3(CO)7(η5C5 H5 ) 2 and W 2Ir2(CO) 10(η 5 -C 5 H5 ) 2 had revealed that reactions with alkynes proceed in refluxing dichloromethane. The reaction of W(CCCSiMe3)(CO)2{(N2C3H3)3BHκ3N,N′,N″} with Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 to afford 3 confirms this reactivity discrimination, the alkyne inserting into the Mo−Mo bond with a residual pendant tungsten alkylidyne. The aforementioned studies by Stone and co-workers revealed a similar reactivity preference at the alkyne when the sterically encumbered M(CCCBu t )(CO) 2 {(N 2 C 3 HR 2 ) 3 BHκ3N,N′,N″} (M = W, R = H; M = Mo, R = Me) was reacted with Co2(CO)8, but as mentioned above, Stone noted that addition occurred at the alkylidyne linkage when the sterically less demanding M(CCCBut)(CO)2(η5-C5H5) was employed.29 Heating cluster 3 did not afford any tractable products from further condensation. Clusters 1 and 2 result from MoC cleavage at the elevated reaction temperature. Heating W2Ir2(CO)10(η5-C5H5)2 with excess diphenylacetylene in refluxing dichloromethane affords not only the W−W insertion product W2Ir2(μ4-η2-PhC2Ph)(μCO) 4 (CO) 4 (η 5 -C 5 H 5 ) 2 but also W 2 Ir 2 (μ 3 -CPh)(μ 3 -η 3 CPhCPhCPh)(μ-CO)2(CO)4(η5-C5H5)2, corresponding to CC cleavage and addition of one of the resultant CPh units to another acetylene; a W−Ir bond of the precursor tetrahedral cluster has cleaved, giving a planar butterfly in which the C1 and C3 fragments cap the resultant triangular faces.32 Heating W2Ir2(CO)10(η5-C5H5)2 with the ethynediyl complex (η5-C5H5)(CO)2Ru(CC)Ru(CO)2(η5-C5H5) in refluxing tetrahydrofuran gives W2RuIr2{μ4-η2-(C2CC)Ru(CO)2(η5C5H5)}(μ-CO)2(CO)6(η5-C5H5)3 as the major product (but in only 7% yield);33 the product possesses a Ru-capped W2Ir2 butterfly core resulting from W−Ir cleavage. In contrast, the present alkylidyne chemistry proceeds with retention and embellishment of the tetrahedral core geometry.

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Article

AUTHOR INFORMATION

Corresponding Author

*M.G.H.: tel, +61 2 6125 2927; fax, +61 2 6125 0750; e-mail, [email protected]. M.P.C.: tel, +61 2 6125 4293; fax, +61 2 6125 0750; e-mail, [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Australian Research Council (ARC) for financial support. M.D.R. was the recipient of an Australian Postgraduate Award, M.P.C. thanks the ARC for an Australian Research Fellowship, and M.G.H. thanks the ARC for an Australian Professorial Fellowship.

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DEDICATION Dedicated to the memory of Professor Gordon Stone, a Colossus in cluster chemistry. REFERENCES

(1) Part 30: Randles, M. D.; Lucas, N. T.; Cifuentes, M. P.; Humphrey, M. G.; Smith, M. K.; Willis, A. C.; Samoc, M. Macromolecules 2007, 40, 7807. (2) (a) Braunstein, P.; Oro, L. A.; Raithby, P. R. Metal Clusters in Chemistry; Wiley-VCH: Weinheim, Germany, 1999. (b) Shriver, D. F.; Kaesz, H. D.; Adams, R. D., The Chemistry of Metal Cluster Complexes; Wiley-VCH: Weinheim, Germany, 1990. (3) (a) Baumann, F. E.; Howard, J. A. K.; Musgrove, R. J.; Sherwood, P.; Ruiz, M. A.; Stone, F. G. A. J. Chem. Soc., Chem. Commun. 1987, 1881. (b) Baumann, F. E.; Howard, J. A. K.; Musgrove, R. J.; Sherwood, P.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1988, 1891. (c) Byers, P. K.; Carr, N.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1990, 3701. (d) Byers, P. K.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1990, 3499. (e) Fernandez, J. R.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1988, 3035. (f) Stone, F. G. A. Angew. Chem., Int. Ed. Engl. 1984, 23, 89. (g) Stone, F. G. A. Pure Appl. Chem. 1986, 58, 529. (4) Jeffery, J. C.; Ruiz, M. A.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1988, 1131. (5) (a) Stone, F. G. A. Adv. Organomet. Chem. 1990, 31, 53. (b) Brew, S. A.; Stone, F. G. A. Adv. Organomet. Chem. 1993, 35, 135. (6) Caldwell, L. R. Adv. Organomet. Chem. 2008, 56, 1. (7) Lucas, N. T.; Humphrey, M. G.; Hockless, D. C. R. J. Organomet. Chem. 1997, 535, 175. (8) Lucas, N. T.; Blitz, J. P.; Petrie, S.; Stranger, R.; Humphrey, M. G.; Heath, G. A.; Otieno-Alego, V. J. Am. Chem. Soc. 2002, 124, 5139. (9) Cook, D. J.; Hill, A. F. Organometallics 2003, 22, 3502. (10) (a) Schwenzer, B.; Schleu, J.; Burzlaff, N.; Karl, C.; Fischer, H. J. Organomet. Chem. 2002, 641, 134. (b) Dewhurst, R. D.; Hill, A. F.; Willis, A. C. Chem. Commun. 2004, 2826. (11) Crystal data are as follows (a) 1·CH2Cl2: C35H28BCl2Ir2Mo3N6O8, formula wt 1414.62, size 0.16 × 0.05 × 0.01 mm, dark red, plate, triclinic, P1̅, a = 11.6240(3) Å, b = 12.8133(5) Å, c = 13.7322(5) Å, α = 78.7340(16)°, β = 85.573(2)°, γ = 89.436(2)°, V = 1999.87(12) Å3, Z = 2, Dcalc = 2.349 g cm−3, μ = 7.74 mm−1, θmin = 3.0°, θmax = 27.6°, Ncollected = 41 718, Nunique = 9201, Nobs = 5930 (I > 2.0σ(I)), absorption correction integration, Tmin, Tmax = 0.544, 0.926, 514 parameters, R (=∑||Fo| − |Fc||/∑|Fo|) = 0.038, Rw (=[(∑w(|Fo| − |Fc|)2/∑wFo2)]1/2) = 0.142, S = 0.87, (Δ/ρ)min = 2·2CHCl 3 : −2.14 e Å −3 , (Δ/ρ) max = 2.01 e Å −3 . (b) C90H88B2Cl12Ir4Mo6N12O18, formula wt 3417.33, size 0.36 × 0.27 × 0.23 mm, dark purple, block, triclinic, P1̅, a = 14.1283(2) Å, b = 17.1504(2) Å, c = 23.2541(3) Å, α = 81.7881(6)°, β = 88.8624(7)°, γ = 78.6851(5)°, V = 5468.25(12) Å3, Z = 2, Dcalc = 2.075 g cm−3, μ = 5.87 mm−1, θmin = 3.0°, θmax = 30.1°, Ncollected = 135 159, Nunique = 31 923, Nobs = 24 602 (I > 2.0σ(I)), absorption correction integration, Tmin, Tmax = 0.237, 0.342, 1274 parameters, R = 0.044, Rw = 0.114, S =

ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic details for Mo3Ir2(μ4-C)(μ3CC 6 H 4 OMe-4)(μ-O)(CO)6 {(N 2 C 3 H 3 ) 3 BH-κ 3 N,N′,N″}(η 5 C 5 H 5 ) 2 (1), Mo 3 Ir 2 (μ 3 -CC 6 H 4 OMe)(μ 3 -η 2 -CO)(μ-CO)(CO) 6 {(N 2 C 3 H 3 ) 3 BH-κ 3 N,N′,N″}(η 5 -C 5 Me 4 H) 2 (2), and Mo2Ir2(μ4-η2-SiMe3C2CW(CO)2{(N2C3H3)3BHκ3N,N′,N″})(μ-CO)4(CO)4(η5-C5H5)2 (3), including complete numbering schemes, thermal ellipsoid figures, positional and thermal parameters, bond lengths, and bond angles. This material is available free of charge via the Internet at http:// pubs.acs.org. The crystallographic data for 1 (CCDC 848809), 2 (CCDC 848807), and 3 (CCDC 848808) may also be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request.cif. 2587

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0.99, (Δ/ρ)min = −2.53 e Å−3, (Δ/ρ)max = 3.21 e Å−3. (c) 3·CH2Cl2: C36H30BCl2Ir2MoN6O10SiW, formula wt 1576.64, size 0.23 × 0.08 × 0.03 mm, dark green, plate, monoclinic, P21/n, a = 17.4282(4) Å, b = 14.7952(3) Å, c = 17.9635(3) Å, β = 110.0194(12) deg, V = 4352.08(16) Å3, Z = 4, Dcalc = 2.406 g cm−3, μ = 9.50 mm−1, θmin = 3.0 deg, θmax = 27.5°, Ncollected = 85 532, Nunique = 9957, Nobs = 6824 (I > 2.0σ(I)), absorption correction integration, Tmin, Tmax = 0.324, 0.754, 550 parameters, R = 0.046, Rw = 0.185, S = 0.81, (Δ/ρ)min = −3.09 e Å−3, (Δ/ρ)max = 2.76 e Å−3. (12) Mackay, S.; Gilmore, C. J.; Edwards, C.; Tremayne, M.; Stewart, N.; Shankland, K. maXus; Nonius, MacScience, and The University of Glasgow, The Netherlands, Japan, and U.K., 2000. (13) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.; Cooper, R. I. CRYSTALS Issue 11, Chemical Crystallography Laboratory, Oxford, U.K.: 2001. (14) Stone, F. G. A. Philos. Trans. R. Soc. London, Ser. A 1982, 308, 87. (15) (a) Lucas, N. T.; Humphrey, M. G.; Healy, P. C.; Williams, M. L. J. Organomet. Chem. 1997, 545−546, 519. (b) Waterman, S. M.; Humphrey, M. G.; Tolhurst, V. A.; Bruce, M. I.; Low, P. J.; Hockless, D. C. R. Organometallics 1998, 17, 5789. (c) Lucas, N. T.; Humphrey, M. G.; Rae, A. D. Macromolecules 2001, 34, 6188. (d) Lucas, N. T.; Notaras, E. G. A.; Cifuentes, M. P.; Humphrey, M. G. Organometallics 2003, 22, 284. (e) Lucas, N. T.; Notaras, E. G. A.; Petrie, S.; Stranger, R.; Humphrey, M. G. Organometallics 2003, 22, 708. (f) Notaras, E. G. A.; Lucas, N. T.; Humphrey, M. G.; Willis, A. C.; Rae, A. D. Organometallics 2003, 22, 3659. (16) Klinger, R. J.; Butler, W. M.; Curtis, M. D. J. Am. Chem. Soc. 1978, 100, 5034. (17) Shiu, C.-W.; Chi, Y.; Carty, A. J.; Peng, S.-M.; Lee, G.-H. Organometallics 1997, 16, 5368. (18) Churchill, M. R.; Ziller, J. W.; Beanan, L. R. J. Organomet. Chem. 1985, 287, 235. (19) Chi, Y.; Wu, H.-L; Chen, C.-C.; Su, C.-J.; Peng, S.-M.; Lee, G.H. Organometallics 1997, 16, 2434. (20) Park, J. T.; Chung, J.-H.; Song, H.; Lee, K.; Lee, J.-H.; Park, J.R.; Suh, I.-H. J. Organomet. Chem. 1996, 526, 215. (21) Churchill, M. R.; Bueno, C.; Park, J. T.; Shapley, J. R. Inorg. Chem. 1984, 23, 1017. (22) (a) Chi, Y.; Shapley, J. R.; Ziller, J. W.; Churchill, M. R. Organometallics 1987, 6, 301. (b) Churchill, M. R.; Li, Y. J. J. Organomet. Chem. 1985, 294, 367. (23) (a) Su, C.-J.; Su, P.-C.; Chi, Y.; Peng, S.-M.; Lee, G.-H. J. Am. Chem. Soc. 1996, 118, 3289. (b) Adams, H.; Gill, L. J.; Morris, M. J. Organometallics 1996, 15, 464. (24) Huang, J. S.; Dahl, L. J. Organomet. Chem. 1983, 243, 57. (25) Greaney, M. A.; Merola, J. S.; Halbert, T. R. Organometallics 1985, 4, 2057. (26) Lin, J.; Gao, P.; Li, B.; Xu, S.; Song, H.; Wang, B. Inorg. Chim. Acta 2006, 359, 4503. (27) Lucas, N. T.; Humphrey, M. G.; Healy, P. C.; Williams, M. L. J. Organomet. Chem. 1997, 545, 519. (28) Notaras, E. G. A.; Lucas, N. T.; Humphrey, M. G. J. Organomet. Chem. 2001, 631, 139. (29) Hart, I. J.; Hill, A. F.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1989, 2261. (30) Chi, Y.; Peng, S.-M.; Lee, G.-H.; Su, C.-J. Organometallics 2001, 20, 1102 and references therein. (31) Hwang, S.-F.; Chi, Y.; Chiang, S.-J.; Peng, S.-M.; Lee, G.-H. Organometallics 2001, 20, 215 and references therein. (32) Shapley, J. R.; McAteer, C. H.; Churchill, M. R.; Biondi, L. V. Organometallics 1984, 3, 1595. (33) Dalton, G. T.; Viau, L.; Waterman, S. M.; Humphrey, M. G.; Bruce, M. I.; Low, P. J.; Roberts, R. L.; Willis, A. C.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H. Inorg. Chem. 2005, 44, 3261.

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