MECHANISM OF ALKYNE INSERTION INTO THE RU-C BONDS OF ORTHORUTHENATED COMPOUNDS FEATURING SIMILARITY OF THE RU(II) AND PD(II) REACTIONS

The pseudo-first-order rate constants k(obs) for the reaction between the ring-substituted orthoruthenated N,N-dimethylbenzylamines [Ru-II(e ta(G)-C6H6)(o-C(6)H(3)RCH(2)NMe(2))Cl] (R = 4,5-(MeO)(2), 5-Me, H, 5-F ), and alkynes R'C drop CR'' (R'/R'' = Ph/Ph, Ph/C6H4CF3-3, Ph/C6H4NO2 -4, Et/Et, CO(2)Me/CO(2)Me) to afford the isoquinolinium cations coord inated to the [Ru-0(eta(6)-C6H6)] moiety are a linear function of [R'C drop CR''] in methanol at 20.0-40.0 degrees C in accord with the rate -determining insertion of alkyne into the Ru-C bond. The latter was co nfirmed by the observation that the electron-donating groups R at the dimethylbenzylamine ruthenocycle favor the insertion and the slope of the corresponding Hammett plot equals -1.6 against sigma(+). The elect ron-poor alkynes react slower than the electron-rich ones. An X-ray st ructural investigation of the product of the MeO(2)CC drop CCO(2)Me re action with the related ruthenocycle [(3-MeC(5)H(3)N-2-C6H4)Ru(mu-I)(C O)(2)](2) demonstrates that the alkyne inserts into the Ru-C bond. Add ition of LiCl retards the insertion markedly indicative of the importa nce of the ionization of the coordinated chloride. The major reaction pathway involves the solvento species II(eta(6)-C6H6)(o-C(6)H(3)RCH(2) NMe(2))(MeOH)](+), the existence of which was confirmed by the spectro photometric study of the starting compound in the presence of LiCl. Al l the observations reported show that the d(6) system under study is v ery mechanistically similar to the insertion, of alkynes into the dinu clear d(8) Pd-II complexes [Pd(o-C(6)H(3)RCH(2)NMe(2))mu-Cl)](2), the key difference being the ways of creation of a coordinative site readi ly accessible by alkyne. These are the ionization of the Ru-CI bond an d the cleavage of the [Pd(mu-Cl)(2)Pd] bridge in the ruthenium and pal ladium cases, respectively.