125591-75-5Relevant articles and documents
Interaction of monohydrido complexes of rhodium(I) with 1-alkynes. Experimental study on deceptively simple reactions
Bianchini, Claudio,Meli, Andrea,Peruzzini, Maurizio,Vizza, Francesco,Frediani, Piero
, p. 1146 - 1155 (1990)
The reaction of HC≡CR (R = CO2Et, Ph, n-C3H7, n-C5H11, SiMe3) with the Rh(I) monohydrides [(NP3)RhH] (1) and [(PP3)RhH] (2) in THF is influenced by a number of factors, including stoichiometry, alkyne substituent, and temperature (NP3 = N(CH2CH2PPh2)3; PP3 = P(CH2CH2PPh2)3). At room temperature, HC≡CCO2Et and HC≡CPh react with an equimolar amount of 1, yielding mixtures of the trigonal-bipyramidal complexes [(NP3)Rh(C≡CR)] and [(NP3)Rh{(E)-CH≡C(H)R}] (R = CO2Et, Ph). The σ-acetylide compounds form via C(alkyne)-H oxidative addition to rhodium, followed by H2 elimination. For R = alkyl and SiMe3, no reaction occurs even when a 10-fold excess of 1-alkyne is used. In contrast, by treatment of 1 with an excess of HC≡CCO2Et, the σ-acetylide complex selectively forms together with ethyl acrylate. At reflux temperature, 1 reacts with a 10-fold excess of 1-alkynes to give σ-acetylide derivatives (R = SiMe3, CO2Et) or σ-acetylide/σ-alkenyl mixtures (R = alkyl, Ph). A variety of organic products is also formed, including as the major products 1,3,5- and 1,2,4-trisubstituted benzenes, 1,4-butadiynes, and butenynes. The only 1-alkyne that stoichiometrically reacts with 2 in THF at room temperature is HC≡CCO2Et. As a result, the σ-alkenyl[(PP3)Rh{gem-C(CO2Et)=CH2}] is obtained. The σ-acetylide complexes [(PP3)Rh(C≡CR)] (R = CO2Et, Ph) are synthesized by reacting 2 with a 10-fold excess of the corresponding 1-alkyne. No reaction is observed for R = alkyl and SiMe3. When performed in refluxing THF, the reactions between 2 and an excess of 1-alkyne lead to the formation of σ-acetylide complexes regardless of the alkyne substituent. Again, the reactions are catalytic and cause extensive conversion of 1-alkynes to a variety of linear and cyclic oligomers. The product distribution is essentially similar to that observed for the NP3 hydride 1. The stereospecific addition of 1-alkynes to either 1 or 2 is interpreted in terms of a concerted mechanism.
