Organic chemistry of subvalent transition metal complexes. 12. Hydrodesulfurization of organosulfur heterocycles by metal hydride-nickel(0) complexes: accelerated single-electron transfer in carbon-sulfur bond cleavage

Nickel(II)‐Carbene Intermediates in Reactions of Geminal Dihaloalkanes with Nickel(0) Reagents and the Corresponding Carbene Capture as the Phosphonium Ylide

“…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 13 C NMR spectroscopic data, been found to have the zwitterionic structure Ph 4 Cp --+ PEt 3 as its paramount resonance contributor.…”

“…As to the first anomaly, a detailed study has shown that no trace of octaphenylfulvalene was formed. As to the second anomaly, the R 2 C fragment could be trapped by the carbonyl reagents only in reactions involving (Et 3 P) 4 Ni, but not in reactions with (Cod) 2 Ni. This finding compels one to conclude that the carbonyl reagent is capturing the Wittig reagent, R 2 C=PEt 3 , and not R 2 C=Ni 0 .…”

“…The oxidative addition of nickel(0) complexes (L n Ni, 1) into σ-covalent bonds between carbon and a wide variety of heteroatoms or even another carbon [2; E = X, O (of epoxide ring or allylic ether), N, C, S, P, Al] [2,3] produces organonickel intermediates (3) pivotal in olefin isomerization, [3] olefin and diolefin oligomerization, [3] desulfurization of aromatic sulfur heterocycles, [4] epoxide deoxygenation [5] and the Kumada carbon-carbon cross coupling [6] [Equation (1)]. (1) A recent study of nickel(0)-induced α-eliminations from geminal disubstituted alkanes 4 leading directly to carbon-aldehyde or benzophenone).…”

“…We have tried to detect and identify all possible by-products and side products. Most of all, we have striven to explain the anomalous course of the attempted carboncarbon π-bond coupling of 5,5-dibromotetraphenylcyclo- Scheme 5. pentadiene (19) by tetrakis(triethylphosphane)nickel(0), (Et 3 P) 4 Ni (20). Instead of dimerizing to octaphenylfulvalene (21), the corresponding phosphonium ylide or Wittig reagent 22c was formed in high yield [7] (Scheme 4).…”

Ullmann Reaction Optimization within Bitolyl and Decafluorobiphenyl Synthesis

“…Water and organic layers are separated. Heptane is stripped, while the deposit is vacuum-distilled through water-jet pump to collect the fraction of 155-180 °C/15-20 mm Hg (lit 12 153-155 °C/18 mm Hg).…”