89530-44-9Relevant academic research and scientific papers
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 (2008/10/08)
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.
Rhodium Complexes with Tripodal Polyphosphines as Excellent Precursors to Systems for the Activation of H-H and C-H Bonds
Bianchini, Claudio,Masi, Dante,Meli, Andrea,Peruzzini, Maurizio,Zanobini, Fabrizio
, p. 6411 - 6423 (2007/10/02)
The trigonal-bipyramidal (TBP) Rh(I) complexes (1) and (2) are protonated by strong acids to give, after addition of NaBPh4, the octahedral (OCT) cis-(chloride)hydrides BPh4 (3) and BPh4 (4) which, by reaction with NaBH4, yield the cis-dihydride BPh4 (6) and the monohydride (8), respectively .By treatment of 6 in acetone with an excess of NaBH4, the monohydride (7) is obtained.Protonation of 8 with HOSO2CF3 followed by addition of NaBPh4 affords the Rh(III) OCT complex BPh4 (9) for which the dichotomy η2-H2 versus cis-dihydride as a function of temperature has been demonstrated.Metathetical reactions of 2 with organolithium reagents give the ?-organyl complexes (11) and (12) which react with CO to give the corresponding ?-acyl derivatives (13) and (14).Decoordination of a phosphine arm of PP3 is a necessary step for the insertion reaction.The monohydride 7 undergoes electrophilic attack by MeSO3CF3 in THF to give CH4 and the ortho-metalated hydride RhH>(SO3CF3) (15) through the intramolecular activation of a phenyl C-H bond.The structure of the iodide derivative RhI>BPh4*C6H6*0.5CH3COCH3 (17a) was determined by X-ray crystallography.When the methylation of 7 is carried out in THF/benzene mixtures both 15 and the cis-(phenyl)hydride (SO3CF3) (22) are obtained.Decreasing the temperature or increasing the concentration of benzene favors intermolecular C-H activation over cyclometalation.Methylation of 7 in THF followed by addition of an excess of α,α,α-trifluorotoluene gives the cis-(trifluorotolyl)hydride (SO3CF3) (23) regardless of the temperature.The reductive elimination of the metalated phenyl from 15 is easily promoted by monodentate ligands such as hydride, halides, pseudohalides, pyridine, and CO to form Rh(I) TBP complexes of the formula n+ (n = 0, 1).OCT complexes of rhodium(III), in which the two additional coligands are disposed in mutually cis positions, are obtained by reacting solutions of 15 with a plethora of addenda such as H2, Cl2, and CS2.As a result, cis-dihydride, cis-dichloride, and η2-CS2 derivatives are obtained.Dihydrogen elimination from 9, protonation of 11, as well as methylation of 8 give (24) which exists in two isomeric forms.The + system neither intramolecularly inserts across a C-H bond from a phenyl ring nor intermolecularly activates aromatic C-H bonds.The factors that may be responsible for such a behavior are discussed.Compound 24 reacts with neutral or anionic monodentate ligands affording TBP Rh(I) complexes or oxidatively adds HSO3CF3 to give, after addition of NaBPh4, the OCT Rh(III) cis-(triflate)hydride BPh4 (25).
