134882-80-7Relevant academic research and scientific papers
Thermal and photochemical C-H bond activation reactions at iridium. π-Coordination vs C-H cleavage of ethene, styrene, and phenylacetylene
Bianchini, Claudio,Barbaro, Pierluigi,Meli, Andrea,Peruzzini, Maurizio,Vacca, Alberto,Vizza, Francesco
, p. 2505 - 2514 (2008/10/08)
Thermolysis of [(triphos)Ir(H)2(C2H5)] (1) in various solvents (benzene, THF, MeCN, DMF) results in formation of the 16-electron fragment [(triphos)IrH] and ethane. The reactive intermediate is capable of insertion into the C-H bonds of either solvents or appropriate substrates (1-alkynes, ethene), generally affording σ-organyl dihydrides of the formula [(triphos)Ir(H)2(σ-organyl)] (organyl = C6H5, CH2CN, C≡CPh, C≡CCO2Et, CH=CH2). The hydride carbonyl [(triphos)IrH(CO)] and dimethylamine are produced by reaction with N,N-dimethylformamide. Thermolysis of 1 in THF at 66°C in the presence of ethene (1-4 atm) gives the vinyl hydride [(triphos)Ir(H)2(CH=CH2)] (8) and the π-complex [(triphos)IrH(C2H4)] (7) in a kinetic product ratio showing that π-complexation is not a precursor for C-H insertion. Under the same reaction conditions, styrene gives selectively the π-complex [(triphos)IrH(CH2=CHPh)] (9). UV irradiation of 7 and 9 in either benzene or THF at 20°C promotes insertion of iridium into the C-H bonds to give 8 and a 1:1 mixture of the E and Z styryl complexes [(triphos)Ir(H)2(CH=CHPh)] (11, 12), respectively. Secondary photolysis on either 8 or 11 and 12 results in photoejection of ethene and dihydrogen, respectively. In the case of the vinyl complex, the reactive intermediate is trapped by the solvent, whereas the styryl dihydrides are converted to the stable π-alkyne hydride [(triphos)IrH(HC≡CPh)]. The latter complex is also obtained by photolysis of [(triphos)Ir(H)2(C≡CPh)] in THF at 20°C. Both the vinyl dihydride and the styryl dihydrides are thermodynamically unstable and convert to the corresponding π-olefin complex in refluxing THF. Irradiation of 1 in either THF or benzene at 20°C produces several metal products and gases (C2H6, C2H4, and H2) due to the occurrence of both primary and secondary photolysis reactions. Irradiation of the trihydride [(triphos)Ir(H)3] in benzene results in formation of the phenyl dihydride [(triphos)Ir(H)2(Ph)] and evolution of H2. Possible mechanisms for the thermal and photochemical reactions are discussed.
Assembling ethylene, alkyl, hydride, and CO ligands at iridium
Barbara, Pierluigi,Bianchini, Claudio,Meli, Andrea,Peruzzini, Maurizio,Vacca, Alberto,Vizza, Francesco
, p. 2227 - 2238 (2008/10/08)
The iridacyclopropane complex [(tripos)Ir(Cl)(C2H4)] is the starting point to synthesize a number of stable iridium complexes containing various combinations of participative ligands such as hydride, ethylene, alkyls and heteroalkyls, alkynes, and carbon monoxide: Ir(H)(C2H4), Ir(H)2(C2H4), Ir(C2H5)(C2H4), Ir(CO)2, Ir(H)(C2H5)(CO), Ir(H)2(CO), Ir(H)2(CH2CH2PEt3), Ir(H)3, Ir(H)2(C2H5), Ir(H)2(C3H7), Ir(C2H4)2, Ir(RC≡CR), IrH(μ-H)2HIr, and IrH(μ-Cl)2HIr. Due to the tripodlike structure of the ligand MeC(CH2PPh2)3 (triphos), all the complexes invariably exhibit a facial arrangement of the phosphorus and non-phosphorus ligands. The contemporaneous availability of so many related species has allowed a comparative experimental study on several important reactions. These include (i) reductive elimination of C-H and H-H bonds from dihydride alkyl complexes, (ii) reductive elimination of H-H bonds vs hydride migration in dihydride ethylene species, (iii) nucleophilic additions to coordinated double bonds, (iv) phosphine arm dissociation in triphos complexes, and β-H elimination vs C-H bond reductive elimination in hydride alkyl complexes. In most instances, such reactions are characterized by stereo- and chemoselectivity. Valuable information on the role played by the nature of the metal and of the phosphine ligands in determining the reactivity has been provided by a comparison among strictly related Rh and Ir complexes containing either triphos or three comparable monophosphines.
