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 HC≡CC6H4-4-R (1 equiv.), in the presence of TlBF4 have resulted in the formation of cationic vinylidene complexes trans-[RuCl(=C=CHC6H4-4-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(C≡CC6H4-4-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(C≡CC6H4-4-R)2(dppm)2 (3), can be isolated when R is an electron withdrawing substituent (R = NO2, COOMe, C≡CSiMe3), whereas reactions with alkynes bearing electron donating substituents (R = OMe and Me) form cationic η(3)-butenynyl complexes [Ru(η(3)-{HC(C6H4-4-R)=CC≡CC6H4-4-R})(dppm)2](+) ([4](+)). This work highlights the importance of the electronic character of the alkyne in influencing product outcome.

Iron(II) Bis(acetylide) Complexes as Key Intermediates in the Catalytic Hydrofunctionalization of Terminal Alkynes

“…Catalyst initiation starting from 1b ( A ACT in the calculations) proceeds via a three-step sequence with an overall barrier of 16.3 kcal/mol (see Figure S4 in the Supporting Information). Analogous to traditional ruthenium-based systems, , our calculations unveiled a classical acetylene–vinylidene mechanism outlined by the simplified catalytic cycle in Scheme . In particular, an incoming acetylene substrate undergoes a 1,2-H shift ( II ), yielding a vinylidene intermediate which suffers nucleophilic attack from the neighboring acetylide ligand ( III ), resulting in the formation of an alkynyl vinyl complex.…”

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure–Property Relationships and Applications

“…To synthesize Ru-acetylide, a similar type of reaction has been reported by Low and co-workers. 152 Ren and co-workers 153 reported a new synthetic method to synthesize Co(III) cyclam bis-alkynyls (cyclam = 1,4,8,11tetraazacyclotetradecane) under aerobic and weakly basic conditions. The symmetrical 91(OTf) (OTf = trifluoromethanesulfonate, Scheme 18) and unsymmetrical 92(OTf) (Scheme 18) bis-alkynyl Co(III) cyclam complex were realized in high-yield from the judiciously selected doubly charged solvento intermediate 90(OTf) 2 .…”

“…When a metal-acetylide 87 was treated with trimethylstannyl acetylides 88 , a series of symmetrical/unsymmetrical bis-acetylides 89 , containing Ru/Os were obtained (Scheme ) . To synthesize Ru-acetylide, a similar type of reaction has been reported by Low and co-workers …”

Syntheses and Structures of trans‐bis(Alkenylacetylide) Ruthenium Complexes

“…Perhaps unsurprisingly, due to the strongly electron withdrawing nature of the trans ‐allenylidene ligand which, as noted above, reduces the lability of the chloride ligand, attempts at the formation of bis(allenylidene) complexes from further reaction of [ 1 a – e ]OTf with A – E were unsucccessful, even in the presence of strong halide abstractors such as TlBF 4 or AgPF 6 (Scheme 6). However, deprotonation of the allenylidene complexes [ 1 a – e ]OTf to their alkenylacetylide counterparts 1 a – e increases the trans ‐effect and hence the lability of the chloride ligand, and permitted substitution by propargylic alcohols in the presence of TlBF 4 (CARE–Thallium salts are highly toxic) [7,25] . These purple reaction mixtures, presumably contain the mixed acetylide/allenylidene species [{R(Me)C=C=C}Ru{C≡CC(=CH 2 )R}(dppe) 2 ]BF 4 ([ 2 a–e ]BF 4 ), evidenced by key 31 P{ 1 H} NMR resonances at 44.0 ppm and ν(C=C=C) and very weak ν(C≡C) IR bands at ca.…”

“…In turn, these interests have prompted detailed examination of the electronic structures of these species [3f,i,5] . Structurally, trans ‐bis(alkynyl) and closely related trans ‐bis(polyynyl) complexes of the form [Ru{(C≡C) n R} 2 L n ] may be described in modular terms as a function of their ancillary supporting ligands (comprised of homogenous or heterogenous ligand sets L 4 =(dppe) 2 , [2a] (dmpe) 2 , [6] (dppm) 2 , [7] (P(OEt) 3 ) 4 , [8] (CO) 2 (PEt 3 ) 2 , [9] 1,5,9,13‐tetramethyl‐1,5,9,13‐tetra‐azacyclohexadecane (16‐TMC) [10] etc. ), the number of C≡C repeat units (n) and the terminal substituents (R) (Figure 1).…”