Bis(diphenylphosphino)acetylene as Bifunctional Ligand in Dicobalt Carbonyl Complexes

Abstract

Treatment of bis(diphenylphosphino)acetylene (DPPA) with a bis(diphenylphosphino)methylene (DPPM)-bridged dicobalt complex, [{µ-P,P-PPh 2 CH 2 PPh 2 }Co 2 (CO) 6 ], 3, yielded a DPPA-bridged dicobalt compound, [{µ-P,P-PPh 2 CH 2 PPh 2 }Co 2 (CO) 4 {µ-PPh 2 CtCPPh 2 }], 5. Two oxidized complexes, [{µ-P,P-PPh 2 CH 2 PPh 2 }Co 2 (CO) 4 {µ-PPh 2 CtCP(dO)Ph 2 }], 6, and [{µ-P,P-PPh 2 CH 2 PPh 2 }Co 2 (CO) 4 {µ-P(dO)Ph 2 CtCP(dO)Ph 2 }], 7, were obtained along with 5 during the chromatographic separation process. Further reaction of 5 with selenium powder in THF at 25 °C produced [{µ-P,P-PPh 2 CH 2 PPh 2 }Co 2 (CO) 4 {µ-P(dO)Ph 2 CtCP(dSe)Ph 2 }], 8, a compound with two phosphorus atoms of 5 oxidized by oxygen and selenium, respectively. The 31 P-77 Se coupling constant of the Se-P bond is 723 Hz. The reaction of 5 with Mo(CO) 6 in toluene at 110 °C yielded [{µ-P,P-PPh 2 CH 2 PPh 2 }Co 2 (CO) 4 {µ-P,P-PPh 2 CtCPPh 2 }Mo(CO) 4 ], 9.Compounds 5-9 were characterized by spectroscopic means as well as by X-ray diffraction studies. Crystal structures of 6-8 reveal that the distance between the oxide and the adjacent methylene proton is within the range of an intramolecular hydrogen bond. The structure of 9 reveals that 5 behaves as a diphosphine chelating ligand toward the Mo(CO) 4 fragment. The fluxional behavior of the DPPM ligands in 5 and 9 were examined by variabletemperature 1 H NMR experiments. The calculated activation energies for the fluxional processes are 19.2 and 7.1 kcal/mol for 5 and 9, respectively.

Experimental and DFT Study of the Tautomeric Behavior of Cobalt‐Containing Secondary Phosphine Oxides

“…7 a and 7 a': A solution of [Co 2 (CO) 6 A C H T U N G T R E N N U N G (dppm)] (2, 1.340 g, 2.000 mmol) and PhCCPA C H T U N G T R E N N U N G (tBu)A C H T U N G T R E N N U N G (NEt 2 ) (5 a, 0.523 g, 2.000 mmol) in THF (15 mL) was stirred at 70 8C for 16 h. Then the solvent was removed under reduced pres- sure, and the resulting dark red residue was separated by CTLC. A dark red band was eluted with hexanes/CH 2 Cl 2 (1:1).…”

“…Keywords: density functional calculations · Heck reaction · P ligands · palladium · tautomerism these newly made compounds as assisting ligands in reactions catalyzed by palladium complexes were thoroughly explored. [6] In most cases, the phosphorus atoms of these ligands are electron-rich and, unfortunately, prone to oxidation. Oxidized ligands lose their coordination capabilities toward low-valent transition metals such as Pd II or Pd 0 , and this results in greatly reduced catalytic performance.…”

“…A solution of PhCCP(=O)(H)A C H T U N G T R E N N U N G (tBu) (6 a, 0.412 g, 2.000 mmol) in THF (5 mL) was added to [Co 2 (CO) 6 A C H T U N G T R E N N U N G (dppm)] (2, 1.340 g, 2.000 mmol) and THF (10 mL). The mixture was stirred for 24 h at room temperature.…”

“…It was identified as 8 a (1.246 g, 1.520 mmol, 76.0 % yield). A similar procedure was used for the preparation of 8 b: A solution of [Co 2 (CO) 6 A C H T U N G T R E N N U N G (dppm)] (2, 1.340 g, 2.000 mmol) and PhCCP(Ph)A C H T U N G T R E N N U N G (NEt 2 ) (6 b, 0.563 g, 2.000 mmol) in THF (15 mL) was stirred at 50 8C for 8 h and then worked up. The solvent was removed under reduced pressure, and the resulting dark red residue was purified by CTLC.…”

Preparation and Characterization of Trimethylsilylpyridylacetylene Bridged, Dicobalt Carbonyl Complexes Containing Bis(diphenylphosphino)methylene or Bis(diphenylphosphino)ethylene Ligand

“…Our previous work described the preparation of a new type of bulky bidentate phosphine ligand, [(mPh2PCH2PPh2)Co2(CO)4(m-PPh2CºCPPh2)] 1, prepared from the reaction of a bi-functional ligand bis(diphenylphosphino)acetylene (DPPA) with one equivalent of Co2(CO)6(mPh2PCH2PPh2). 6 Compound 1 can also be regarded as one member of the alkyne-bridged dicobalt complexes family. Interestingly, during its chromatographic process, two complexes, [{m-P,P-PPh2CH2PPh2}Co2(CO)4{m-PPh2CºCP(=O)-Ph2}] 2 with one phosphorus atom oxidized and [{m-P,PPPh2CH2PPh2}Co2(CO)4{m-P(=O)Ph2CºCP(=O)Ph2}] 3 with two phosphorus atoms oxidized, along with 1, were obtained.…”