摘要:
Two tungsten-substituted phospholes were prepared by reaction of CpW(CO)3Na with 1-cyano-3,4-dimethylphosphole and 1-bromo-2,5-diphenylphosphole, respectively. According to a X-ray crystal structure analysis, the 3,4-dimethyl-substituted compound is more planar and displays a higher electronic delocalization than an ordinary phosphole such as 1-benzylphosphole. In both cases, the lone pair at phosphorus retains a substantial nucleophilicity, with oxidation, sulfurization, and quaternization being easily achieved. Reaction with carboxylic acids leads to a tungsten-substituted 2,5-dihydrophosphole oxide via an initial protonation at phosphorus followed by a [1,5]-sigmatropic shift of hydrogen. [4 + 2] cycloadditions with N-phenylmaleimide are possible with the phosphole oxides or sulfides. The reaction with dimethyl acetylenedicarboxylate yields a spirocyclic compound containing a P-C=C-C(O)-W ring whose structure was established by X-ray analysis. The thermolysis of the 3,4-dimethyl-substituted phosphole leads to a normal mu-phosphido P2W2 dimer by loss of CO, whereas the more congested 2,5-diphenyl derivative gives a mu-phosphido, mu-hydrido complex with a W-W bond.