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.