Second-order rate coefficients and activation parameters are reported for the reaction in solution of triphenylphosphine with a series of diazoalkanes (Ar,CN,) having two aromatic groups attached to the diazo-carbon atom, 9-diazofluorene (DAF), dJcycloheptene (DBSE), its 10,ll -dihydro analogue (DBSA), and diazodiphenylmethane (DDM). Although the product phosphazine Ar,CNN PPh, arises formally by nucleophilic attack of phosphorus on the terminal nitrogen atom of the diazoalkane, the pattern of reactivity approximates to that for proton transfer from acetic acid to the diazoalkane under similar conditions, highlighting the biphilic nature of the reaction. The results can be rationalised in terms of qualitative FMO theory taking into account both HOMO( Ph3P)-LUMO (Ar, CN,) and HOMO(Ar,CN,)-LUMO (Ph3P) interactions. This is lent qualified support by MNDO calculations on Ar,CN, based on molecular parameters from the X-ray crystal structure of DAF itself and of the ketones corresponding to DBSE, DBSA, and DDM.The reactivity of DDM and the effect of 4,4'-disubstitution by CH30-, CH3-, and CI-, which gives rise to a U-shaped Hammett po correlation, is not easily interpreted within the FMO framework. Conformational changes which affect the interacting orbitals as the reactants are transformed into transition states offer an alternative interpretation.

9-Diazofluorene, on treatment with stoichiometric or substoichiometric amounts of quaternary ammonium hydroxide or methoxide or of potassium t-butoxide in solution in aqueous or alcoholic dimethyl sulfoxide or acetonitrile at 30 degrees C, decomposes with evolution of nitrogen to yield fluorenone azine [bis(fluorenylidene)hydrazine] in almost quantitative yield. Studies are reported of the identity of the minor by-products, together with an examination of the kinetics of the reactions and additional spectroscopic experiments. The general rate equation is v = k[FIN2]3/2[Nu-]1/2, where Nu- represents the nucleophile. It is concluded that the oxyanions, most probably after nucleophilic attack on 9-diazofluorene under these basic conditions to generate a new anionic species, are capable of transferring an electron to the diazo-compound. This initiates decomposition of further diazo-molecules in a process of electron-transfer chain catalysis that bears some similarities to, but has also some differences from, that encountered using cathodic initiation. In support of this interpretation it is found that reactions can be accelerated by the introduction of carbon acids (fluorene, 9-phenylfluorene) into the reaction mixtures. The nature of the initiation, propagation and termination steps of the chain mechanism are discussed.

No abstract