Yu- Chang

Diphenyl-2-pyridylphosphine as a bidentate ligand in the coordination of dicobalt octacarbonyl; X-ray crystal structures of Co2(CO)4(μ-P,N-PPh2py){μ-HCCSiMe3}, and Co4(CO)10(μ-P,N-PPh2py)

Abstract Under mild conditions, the reaction of Co 2 (CO) 8 with HCCSiMe 3 in the presence of PPh 2 py gave a binuclear cobalt carbonyl complex, Co 2 (CO) 4 (η 2 -μ 2 -HCCSiMe 3 )(μ-PPh 2 py) ( 1a ), which has both zero-valent cobalt centers coordinated by a bidentate ligand, PPh 2 py. PPh 2 py is also an effective ligand in promoting the yield of 2,5-bis(trimethylsilanyl)cyclopenta-2,4-dien-1-one. A cobalt cluster complex, Co 4 (CO) 10 (μ- P , N -PPh 2 py) ( 9 ) was obtained when two equivalents of Co 2 (CO) 8 were reacted with PPh 2 py at a higher temperature. The phosphorus and nitrogen atoms of the ligand coordinate to cobalt in the basal and apical positions, respectively. These two compounds, 1a and 9 were characterized by spectroscopic means as well as X-ray crystal structure determination.

Synthesis and structural characterization of novel palladium complexes chelated by bulky cobalt-containing phosphine ligands: unusual palladium–cobalt bond formation

The reaction of a bulky phosphine, [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 1 with P(OMe)3 gave a phosphite substituted tetracobalt-complex, [Co2(CO)4{P(OMe)3}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 5. Further reaction of 5 with (COD)PdCl2 yielded a 5 -coordinated palladium complex, [Co2(CO)4{P(OMe)3}}{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl27. Similar results were obtained for the reaction of 1 with (COD)PdCl2, which yielded [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)3(μ-CO){μ-P-(μ-PPh2CCPPh2)}]PdCl26. Likewise, reaction of another bulky phosphine [(μ-Ph2PCH2PPh2)Co2(CO)4(μ-PPh2CCP(O)Ph2)] 3 with (COD)PdCl2 yielded [{μ-P,P-PPh2CH2PPh2}Co2(CO)3(μ-CO){μ-PPh2CCP(O)Ph2}]PdCl28. The X-ray structural studies of 6, 7 and 8 reveal that unusual palladium–cobalt bonds were formed. A Suzuki type reaction employing complexes 6, 7 and 8, as catalysts in the reaction of 2-bromothiophene with boronic acid did not show encouraging signs.

Preparation and characterization of an unusual tetracobalt-complex; X-ray crystal structure of [Co2(CO)5{μ-P,P(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}]

Abstract The reaction of bis(diphenylphosphino)acetylene(DPPA) with Co2(CO)8 in toluene at 80 °C for 24 h resulted in an alkyne-bridged, diphosphine-chelated tetracobalt-complex, [Co2(CO)5{μ-P,P-(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}] 3. The X-ray structural studies of 3 reveals that it can be regarded as a dimerized form of two DPPA bridged dicobalt complex, [Co2(CO)6(μ-PPh2CCPPh2)] 1.

Nucleophilic substitution reactions of acetylides on substituted tricarbonyl(η6-fluoroarene)chromium and reactions of tricarbonyl[η6-(2-trimethylsilylethynyl)toluene]chromium and tricarbonyl[η6-(p-ethynyl-phenylethynyl)benzene]chromium with dicobalt octacarbonyl

Abstract Nucleophilic substitution reactions of various acetylides on substituted tricarbonyl(η6-fluoroarene)chromiums were pursued. The reaction presumably underwent a more complicated mechanism rather than the direct substitution on the fluorine-bearing carbon. The organometallic compounds (η6-C6H3R1R2R3)Cr(CO)3 (R1: CC–C6H4CH3, R2: o-Me, R3: H (5a), R1: CC–C6H4CH3, R2: o-OMe, R3: H (6a), R1: CC–C6H4CH3, R2: m-OMe, R3: H (6b), R1: CCPh, R2: o-Me, R3: o-OMe (8b), R1: CCPh, R2: m-Me, R3: m-OMe (8c), R1: CCSiMe3, R2: o-Me, R3: H (9a), R1: CC–C6H4CCH, R2: H, R3: H (12), R1: CC–C6H4CCH, R2: o-Me, R3: H (13)) as well as the organometallic dimmer [{(η6-o-Me-C6H4)Cr(CO)3(di-ethynyl)] (di-ethynyl: CC–C6H4CC (14)) have been synthesized from nucleophilic substitution reactions of tricarbonyl(η6-fluoroarene)(chromium) compounds with suitable acetylides. The products have been characterized by spectroscopic means. In addition, (8b) and (8c) were characterized by X-ray diffraction studies. Further reactions of (9a) and (12) with appropriate amount of Co2(CO)8 yielded μ-alkyne bridged bimetallic complexes, Co2(CO)6{μ-Me3SiCC–(o-tolueneCr(CO)3} (10) and (Co2(CO)6)2{μ-HCC–C6H4–CC–(benzene)Cr(CO)3)}(15), respectively. Both (10) and (15) were characterized by spectroscopic means as well as single crystal X-ray crystallography. The core of these molecules is quasi-tetrahedron containing a Co2C2 unit. A two-dicobalt-fragments coordinated di-enyls complex, (Co2(CO)6)2{μ-HCC–C6H4–CC–H} (17), was synthesized from the reaction of 1,3-diethynylbenzene with Co2(CO)8. Crystallographic studies of (17) also show that it exhibits a distorted Co2C2 quasi-tetrahedral geometry.

A novel approach to the synthesis of azobenzene using dicobalt carbonyl

Reaction of Co2(CO)8 with HCCC6H4NH2 in THF at 55 °C for 4 hours gave an unusual complex {[Co2(CO)6(μ-HCC)]C6H4N}22 in reasonable yield; the crystal structure of 2 reveals that it can be regarded as two alkyne-bridged dicobalt fragments joined by a diazene-based ligand; a mechanism for the formation of 2 is proposed.