Reactions of alkynes with cis-RuCl2(dppm)2: exploring the interplay of vinylidene, alkynyl and η3-butenynyl complexes

Abstract

Reactions of cis-RuCl₂(dppm)₂ with various terminal alkynes, of the type HCCC₆H₄-4-R (1 equiv.), in the presence of TlBF₄ have resulted in the formation of cationic vinylidene complexes trans-[RuCl(CCHC₆H₄-4-R)(dppm)₂]BF₄ ([1]BF₄). These complexes can be isolated, or treated in situ with a suitable base (Proton Sponge, 1,8-bis(dimethylamino)naphthalene) to yield the mono-alkynyl complexes trans-RuCl(CCC₆H₄-4-R)(dppm)₂ (2). Through similar reactions between cis-RuCl₂(dppm)₂ with 2 equiv. of alkyne, TlBF₄ and base, trans-bis(alkynyl) complexes, trans-Ru(CCC₆H₄-4-R)₂(dppm)₂ (3), can be isolated when R is an electron withdrawing substituent (R = NO₂, COOMe, CCSiMe₃), whereas reactions with alkynes bearing electron donating substituents (R = OMe and Me) form cationic η³-butenynyl complexes [Ru(η³-{HC(C₆H₄-4-R)CCCC₆H₄-4-R})(dppm)₂]⁺ ([4]⁺). This work highlights the importance of the electronic character of the alkyne in influencing product outcome.