17523-24-9Relevant academic research and scientific papers
Nickel(II)-carbene intermediates in reactions of geminal dihaloalkanes with nickel(0) reagents and the corresponding carbene capture as the phosphonium ylide
Eisch, John J.,Qian, Yun,Rheingold, Arnold L.
, p. 1576 - 1584 (2008/02/06)
In a previous study of geminal bond cleavages of substrates of the type R2CE2 [E2 = X2, O, S, Li(SO 2Ph)] by nickel(0) reagents [LnNi, Ln = (Cod)2, (Et4P)4], leading to R 2C=CR2 as products, the tentative hypothesis had been proposed that such reactions likely proceed via nickel(0)-carbene intermediates (J. J. Eisch, Y. Qian, M. Singh, J. Organomet. Chem. 1996, 512, 207). Because such proposed nickel(0)-carbenes do not satisfactorily account for reactions encountered with such α-eliminations, a detailed reexamination of the reaction of these nickel(0) reagents with geminal dihalides has been undertaken. For example, two reactions of such presumed nickel(0)-carbenes remained anomalous: (1) the failure of 5,5-dibromotetraphenylcyclopentadiene to form its expected dimer, octaphenylphenylfulvalene and instead the formation of triethylphosphonium tetraphenylcyclopentadienide in its reaction with (Et 3P)4Ni; and (2) the presumed capture of intermediate R2C=Ni0 in presence of the trapping agent (benzaldehyde or benzophenone). As to the first anomaly, a detailed study has shown that no trace of octaphenylfulvalene was formed. As to the second anomaly, the R 2C fragment could be trapped by the carbonyl reagents only in reactions involving (Et3P)4Ni, but not in reactions with (Cod)2Ni. This finding compels one to conclude that the carbonyl reagent is capturing the Wittig reagent, R2C=PEt3, and not R2C=Ni0. Based upon all present data, the mechanism of such C=C bond dimerizations is best explicable in terms of nickel(II)-carbenes. The triethylphosphonium tetraphenylcyclopentadienide formed here has by single-crystal X-ray structure determination, complemented by 13C NMR spectroscopic data, been found to have the zwitterionic structure Ph 4Cp--+PEt3 as its paramount resonance contributor. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
Preparation of Four-membered Phosphonickelocycles. Unusual Facile Stabilization of Five-co-ordinate Complexes
Font-Bardia, Merce,Gonzalez-Platas, Javier,Muller, Guillermo,Panyella, David,Rocamora, Merce,Solans, Xavier
, p. 3075 - 3084 (2007/10/02)
Three different types of organometallic compounds (R = Ph 1 or Et 1'), (R = Ph 2 or Et 2') and (R = Ph 3 or Et 3') have been obtained from 1 equivalent of PR2(C6Cl5) (R = Ph or Et), (cod = cis,cis-cycloocta-1,5-diene), and L = PMe2Ph a, PEt3 b, P(CH2Ph)3 c or PPh3 d.Complexes 2 evolve in solution, either to 1 and , or to 3 by breaking of the Ni-P bond of the four-membered ring by free phosphine.The selective preparation of compounds 1 or 3 can be achieved by performing the oxidative-addition reaction in the absence or with 2 equivalents of L respectively.When 1 equivalent of a diphosphine was used in the oxidative-addition reaction a mononuclear five-co-ordinate complex was obtained, 4 .However, dppm (Ph2PCH2PPh2) acts as a monodentate ligand to give the five-co-ordinate compound .Complexes 2, 2' show preferentially a cis geometry, 1' is trans, and 3, 3' have the L ligands in trans position.Insertion of CO or alkynes into the Ni-C bond was not observed.Compounds 1 and 1' in the presence of neutral ligands L = CO or PR3 (PR3 = PMe2Ph a or PEt3 b) gave five-co-ordinate complexes without cleavage of the Ni-P bond of the ring.Stabilization of the four-membered ring is achieved when two bidentate ligands are present or in the five-co-ordinate compound .Two bidentate ligands are also needed to stabilize the formation of five-co-ordinate complexes.The molecular structures of complexes 1', 3b, and were determined by single-crystal X-ray diffraction.
Reactions of Dialkylnickel(II) Complexes NiR2L2 with Alkyl (or Aryl) Halides, R'COY (Y=Cl, Br, OPh, OCOPh), and CS2
Yamamoto, Takakazu,Kohara, Teiji,Osakada, Kohtaro,Yamamoto, Akio
, p. 2147 - 2153 (2007/10/02)
Reactions of Ni(CH3)2(bpy) (1), Ni(C2H5)2(bpy) (2) (bpy=2,2'-bipyridine), trans-Ni(CH3)2(triethylphosphine)2 (3), Ni(CH3)2(1,2-bis(diphenylphosphino)ethane) (4), and Ni(CH3)2(1,3-bis(diphenylphosphino)propane) (5) with alkyl or aryl halides, R'COY (Y=Cl, Br, OC6H5, OCOC6H5), and CS2 have been investigated.The reactions of NiR2L2 with alkyl or aryl halides are classified into three types of reactions by their reaction products: Type A: NiR2L2 + R'X ->NiX(R')L2 + R-R, Type B: NiR2L2 + R'X -> alkane (RH) + olefin (R'(-H)), and Type C: NiR2L2 + R'X -> NiR(X)L2 + R-R'.Complexes 1 and 2 undergo mainly Type A reaction.Complex 3 gives Type A reaction product on treatment with C6H5Br, but it gives Type B reaction product on treatment with C2H5Br.On the other hand, 4 undergoes Type C reaction on interaction with C6H5Cl.The reactions with R'COY (Y=Cl, Br, OPh, OCOPh) are classiffed into two types of reactions by their reaction products: Type D: NiR2L2 + R'COY -> NiY(R)L2 + RCOR' and Type E: NiR2L2 + R'COY -> NiY(R')L2 + RCOR.Complexes 1-3 undergo mainly Type D reaction, whereas complexes 4 and 5 mainly Type E reaction.The diffrence in the reaction route is discussed on the basis of presence or absence of vacant coordination site for attack by R'COY.The reaction of 4 with CS2 affords Ni(CS2)(1,2-bis(diphenylphoshino)ethane) with evolution of a reductive elimination product, ethane, whereas the reaction of 3 with CS2 gives a 1:1 adduct of 3 and CS2.
