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

Symmetrically disubstituted bis(3-hydroxyalkynyl) complex [TpRu{C=CCPh2(OH)}(2)(NO)] (1) (Tp = BH(pyrazol-1-yl)(3)) and unsymmetrically mixed (arylalkynyl)(3-hydroxyalkynyl) congener [TpRu(C=CC6H4Me){C= CCPh2(OH)}(NO)] (2) were newly prepared. Treatment of I or 2 with p-toluenesulfonic acid monohydrate was carried out to give unusual four-membered metallacyclic complexes [TpRu{C(=C=CPh2)C(O)C(=CPh2)}(NO)] (3) and [TpRu{C=C=CPh2)- C(O)CH(C6H4Me)}(NO)] (5), respectively, as major products. Formation mechanism of 3 and 5 would involve insertion of the generated allenylidene group (Ru=C=C=CPh2) 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(==CPh2)C(O)CH=CPh2}(NO)] (7) and [TpRuCl{C=C=CPh2)C(O)CH2(C6H4Me))(NO)] (8). On the other hand, the use of CH2Cl2 and THF as the reaction solvent gave another type of one-HCl adducts [TpRu{CH(C(Cl)=CPh2)C(O)C(=CPh2)}(NO)] (9 a/9 b) and [TpRu{CH(C(Cl)=CPh2)C(O)CH(C6H4Me)}(NO)] (11a/11b) as diastereomeric pairs, still retaining the four-membered ring structure. Moreover, their kinetically controlled products 9b and 11b were treated with aq. HCl to afford the ring-opened two-HCl adducts [TpRuCl{C(C(Cl)=CPh2)(H)C(O)CH=CPb2}(NO)] (10) and [TpRuCl{CH(C6H4Me)C(O)CH2(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.