- Synthesis of Dicarbonyl(η4-tricarbonylcobaltacyclopentadiene)cobalt Complexes from Co2(CO)8. A General Route to Intermediates in Cobalt Carbonyl Mediated Alkyne Trimerization
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We have shown that cobaltacyclopentadiene complexes, derived from cobalt carbonyl and two alkyne molecules and long believed to be intermediates in cyclotrimerization as well as in the formation of the (three-alkyne-derived) flyover complexes, can be isolated in selected cases if the mono(alkyne)-Co2(CO)6 complexes are treated at room temperature with just 1 equiv of alkyne in the presence of trimethylamine N-oxide. The complex (PhC=CHCMe= CMe)Co2(CO)5 has been characterized by X-ray crystallography.
- Baxter, R. John,Knox, Graham R.,Pauson, Peter L.,Spicer, Mark D.
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p. 197 - 205
(2008/10/08)
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- Carbonylative cyclization of alkynes using cobalt carbonyl species prepared via reduction of CoBr2 with Zn under a carbon monoxide atmosphere
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Alkyne-Co2(CO)6 complexes prepared in situ using CoBr2, Zn, and CO give the corresponding cycloentenones or cyclopentadienones on heating in toluene or in CH2Cl2 at 25°C in the presence of DMSO or amines.
- Rajesh, Thotapally,Periasamy, Mariappan
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p. 5709 - 5712
(2008/10/08)
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- Alkylidyne-alkyne coupling reactions. Reactions of Mo2Co(CO)7Cp2(μ3-CH) with EtC2Et and PhC2Ph
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The reaction of Mo2Co(CO)7Cp2(μ3-CH) with EtC2Et has yielded two isomeric products Mo2Co-(CO)5Cp2[μ3-OCC(Et)C(Et)CH] (2a, 3%, 2b, 18%). Both products were characterized crystallographically and were found to contain triply bridging OCC(Et)C(Et)CH ligands formed by the coupling of the methylidyne ligand to one EtC2Et molecule and one CO ligand. The CO group bridges the face of a Mo2Co triangular cluster with the oxygen atom coordinated to one of the molybdenum atoms, Mo-O = 2.142 (5) A? in 2a and 2.150 (4) A? in 2b. The isomers were equilibrated as 1.0/1.7 2a/2b at 52°C in 7 days. The reaction of 1 with PhC2Ph yielded two products Mo2Co(CO)2Cp2[μ 3-C(Ph)C(H)C(Ph)C(Ph)](μ3-CPh) (3, 18%) and Mo2Co(CO)2Cp2(μ 3-CO)(μ-PhC2Ph)[μ3-C(H)C(Ph)C(Ph)] (4, 30%). Compound 3 contains a dimetallatriphenylbutadiene ligand and a triply bridging benzylidyne ligand. These were formed by the coupling of two PhC2Ph molecules to the methylidyne ligand and the splitting off of one CPh group. Compound 4 contains a triply bridging dimetalladiphenylallyl ligand formed by the coupling of one PhC2Ph molecule to the methylidyne ligand. Compounds 3 and 4 are both electron deficient and both contain Mo2Co clusters with unusually short Mo-Mo bonds. Compound 3 also contains an unusual agostic phenyl interaction. Crystal Data: for 2a, space group = P21/a, a = 15.035 (3) A?, b = 9.373 (4) A?, c = 16.494 (3) A?, β = 100.65 (1)°, Z = 4, 1659 reflections, R = 0.029; for 2b, space group = Pbca, a = 16.966 (3) A?, b = 25.777 (5) A?, c = 10.310 (1) A?, Z = 8, 2349 reflections, R = 0.027; for 3, space group = C2/c, a = 34.08 (2) A?, b = 11.436 (4) A?, c = 18.80 (1) A?, β= 118.62 (4)°, Z = 8, 2254 reflections, R = 0.040; for 4, space group = C2/c, a = 35.896 (9) A?, b = 13.243 (5) A?, c = 16.899 (3) A?, β = 96.62 (2)°, Z = 8, 2535 reflections, R = 0.048.
- Adams, Richard D.,Belinski, Judy A.
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p. 2114 - 2120
(2008/10/08)
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- Cluster Synthesis. 28. New platinum-cobalt carbonyl cluster complexes and products obtained from their reactions with alkynes
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The reaction of Pt(COD)2, COD = 1,5-cyclooctadiene, with Co2(CO)8 in cyclohexane solvent at 25°C has yielded the new compounds PtCo2(CO)7(COD) (1, 3%) and Pt2Co2(CO)8(COD) (2, 31%) and the known compound Co4(CO)12 (3, 14%). Compounds 1 and 2 were characterized by single-crystal X-ray diffraction analyses. Compound 1 contains a triangular cluster of one platinum and two cobalt atoms with a carbonyl ligand bridging the Co-Co bond. Compound 2 consists of a tetrahedral cluster of two platinum atoms and two cobalt atoms. The Pt-Pt bond is weak, 2.9546 (6) A?. Compound 2 reacts with EtC2Et to yield the new complex Pt2Co2(CO)8(μ3-EtC 2Et)2 (4, 8%), and it reacts with PhC2Ph to yield the new complex Pt3Co2(CO)6(COD)2(μ 3-PhC2Ph)2 (5, 22%). Compounds 4 and 5 were characterized crystallographically. Compound 4 contains a butterfly cluster of two cobalt and two platinum atoms. The two platinum atoms occupy the hinge positions and are joined by a short Pt-Pt bond, 2.4945 (7) A?. Triply bridging EtC2Et ligands bridge the two Pt2Co triangles. Compound 5 contains a bow-tie cluster of three platinum and two cobalt atoms with a platinum atom in the center. Triply bridging PhC2Ph ligands bridge the two Pt2Co triangular groupings. Crystallographic parameters for 1: space group Pbca, a = 15.076 (3) A?, b = 16.298 (3) A?, c = 14.547 (5) A?, Z = 8, R = 0.033, and Rw = 0.033 for 2149 reflections. For 2: space group P21/n, a = 8.835 (2) A?, b = 14.573 (2) A?, c = 15.377 (2) A?, β = 100.69 (1)°, Z = 4, R = 0.024, and Rw = 0.027 for 2140 reflections. For 4: space group P21/n, a = 9.430 (2) A?, b = 14.915 (4) A?, c = 17.931 (3) A?, β = 99.11 (2)°, Z = 4, R = 0.022, and Rw = 0.023 for 2236 reflections. For 5: space group C2/c, a = 34.905 (8) A?, b = 15.106 (4) A?, c = 19.028 (3) A?, β = 102.39 (2)°, Z = 8, R = 0.064, and Rw = 0.076 for 3760 reflections.
- Adams, Richard D.,Chen, Gong,Wu, Wengan,Yin, Jianguo
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p. 4208 - 4214
(2008/10/08)
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- Ligand Lability in an Electron Transfer of +; Cyclotrimerisation of Alkynes and Synthesis, Structure, and Properties of (η6-C6Ph6)Co(η2-C2Ph2) (py=pyridine)
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In pyridine the ionic CoI complex (py=pyridine) catalyses the cyclotrimerisation of but-2-yne and hex-1-yne at room temperature; under the same conditions, diphenylacetylene promotes an irreversible disproportionation of the Co
- Biagini, Paolo,Funaioli, Tiziana,Fachinetti, Giuseppe,Laschi, Franco,Zanazzi, Pier Francesco
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p. 405 - 407
(2007/10/02)
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- SYNTHESIS AND SPECTROSCOPIC STUDY OF A SERIES OF DIARYLACETYLENE DICOBALT HEXACARBONYL COMPLEXES
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A series of methyl, methoxy and trimethylsilyl substituted diphenylacetylenes was reacted with Co2(CO)8, giving the corresponding (diarylacetylene) Co2(CO)6 complexes.The predominance of the steric effect of the substituents in these reactions was established.The complexes were studied by IR, MS, 13C NMR, 1H NMR and UV-visible spectroscopy.
- Pepermans, Henri,Willem, Rudolph,Hoogzand, Cornelis
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p. 563 - 574
(2007/10/02)
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- Electron transfer in organometallic clusters. 10. Mechanism and solvent effects in ETC reactions of PhCCo3(CO)9 with phosphine ligands
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The mechanism of the electron-transfer chain catalyzed (ETC) reactions of PhCCo3(CO)9 with PPh3, dppm, dppe, and tpme was elucidated by using coulometric and transient electrochemical techniques. The catalytic efficiency for the attachment of one phosphorus atom to the cluster is independent of the ligand (?0.01 F mol-1 in CH2Cl2), but the rate of reaction is solvent-dependent. The subsequent step to PhCCo3(CO)7L2 or PhCCo3(CO)7(L-L) is much slower and of short chain length. Evidence is presented to show that dangling complexes PhCCo3(CO)8(L-L) are the initial ETC products but that a rapid EC reaction takes place to give [PhCCo3(CO)8]2(L-L) or PhCCo3(CO)7(L-L) depending on the bite of the ligand. A simplified kinetic scheme is used to evaluate a first-order rate constant for the primary dissociative step for PhCCo3(CO)9 as k1 = 3.2 mol-1 s-1 in CH2Cl2. The behavior of RCCo3(CO)9 (R = Ph, Me) under ETC conditions is also described; in CH3CN the derivatives RCCo3(CO)8NCCH3 are produced, and in CH2Cl2 carbyne coupling occurs to give R2C2Co4(CO)10.
- Downard, Alison J.,Robinson, Brian H.,Simpson, Jim
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p. 1140 - 1149
(2008/10/08)
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