Syntheses of four-membered metallacyclic complexes with nitrosylruthenium and their ring-opening upon HCl addition

Symmetrically disubstituted bis(3-hydroxyalkynyl) complex [TpRu{C[triple chemical bond]CCPh(2)(OH)}(2)(NO)] (1) (Tp = BH(pyrazol-1-yl)(3)) and unsymmetrically mixed (arylalkynyl)(3-hydroxyalkynyl) congener [TpRu(C[triple chemical bond]CC(6)H(4)Me){C[triple chemical bond]CCPh(2)(OH)}(NO)] (2) were newly prepared. Treatment of 1 or 2 with p-toluenesulfonic acid monohydrate was carried out to give unusual four-membered metallacyclic complexes [TpRu{C(=C=CPh(2))C(O)C(=CPh(2))}(NO)] (3) and [TpRu{C(=C=CPh(2))C(O)CH(C(6)H(4)Me)}(NO)] (5), respectively, as major products. Formation mechanism of 3 and 5 would involve insertion of the generated allenylidene group (Ru=C=C=CPh(2)) into the other Ru--C(alkynyl) bond, followed by hydration of the resulting alpha-alkynyl--allenyl fragment. With regards to the chemical reactivity of their four-membered metallacycles, treatment with aq. HCl in MeOH afforded the ring-opened one-HCl adducts, [TpRuCl{C(=C=CPh(2))C(O)CH=CPh(2)}(NO)] (7) and [TpRuCl{C(=C=CPh(2))C(O)CH(2)(C(6)H(4)Me)}(NO)] (8). On the other hand, the use of CH(2)Cl(2) and THF as the reaction solvent gave another type of one-HCl adducts [TpRu{CH(C(Cl)=CPh(2))C(O)C(==CPh(2))}(NO)] (9 a/9 b) and [TpRu{CH(C(Cl)=CPh(2))C(O)CH(C(6)H(4)Me)}(NO)] (11 a/11 b) as diastereomeric pairs, still retaining the four-membered ring structure. Moreover, their kinetically controlled products 9 b and 11 b were treated with aq. HCl to afford the ring-opened two-HCl adducts [TpRuCl{C(C(Cl)=CPh(2))(H)C(O)CH=CPh(2)}(NO)] (10) and [TpRuCl{CH(C(6)H(4)Me)C(O)CH(2)(C(Cl)=CPh(2))}(NO)] (12), respectively. In 10 and 12, each one Ru--C bond is cleaved at mutually different positions in the ring. Protonation on the carbonyl group would trigger the formation of 7-12.