104453-08-9Relevant articles and documents
1H- and 2H-T1 relaxation behavior of the rhodium dihydrogen complex [(triphos)Rh(η2-H2)H2]+
Bakhmutov, Vladimir I.,Bianchini, Claudio,Peruzzini, Maurizio,Vizza, Francesco,Vorontsov, Evgeny V.
, p. 1655 - 1660 (2008/10/08)
Protonation of the classical trihydride [(triphos)RhH3] (2) at 210 K in either THF or CH2Cl2 by either HBF4·OMe2 or CF3SO2OH gives the nonclassical η2-H2 complex [(triphos)Rh(η2-H2)H2]+ (1) [triphos = MeC(CH2PPh2)3]. Complex 1 is thermally unstable and highly fluxional in solution. In THF above 230 K, 1 transforms into the solvento dihydride complex [(triphos)Rh(η1-THF-d8)H2]+ (5) that, at room temperature, quickly converts to the stable dimer trans-[{(triphos)RhH}2(μ-H)2]2+ (trans-6). In CH2Cl2, 1 is stable up to 240 K. Above this temperature, the η2-H2 complex begins to convert into a mixture of trans- and cis-6, which, in turn, transform into the bridging-chloride dimers trans- and cis-[{(triphos)RhH}2(μ-Cl)2]2+ at room temperature. Complex 1 contains a fast-spinning H2 ligand with a T1(min) of 38.9 ms in CD2Cl2 (220 K, 400 MHz). An NMR analysis of the bis-deuterated isotopomer [(triphos)RhH2D2]+ (1-d2) did not provide a J(HD) value. At 190 K, the perdeuterated isotopomers [(triphos)RhD3] (2-d3) and 1-d4 show T1(min) values of 16.5 and 32.6 ms (76.753 MHz), respectively, for the rapidly exchanging deuterides. An analogous 2-fold elongation of T1(min) is also observed on going from [(triphos)IrD3] to [(triphos)Ir(η2-D2)D2]+. A rationale for the elongation of T1(min) in nonclassical polyhydrides is proposed on the basis of both the results obtained and recent literature reports.
Synthesis and Reactivity of the Labile Dihydrogen Complex [{MeC(CH2PPh2)3}Ir(H2)(H) 2]BPh4
Bianchini, Claudio,Moneti, Simonetta,Peruzzini, Maurizio,Vizza, Francesco
, p. 5818 - 5825 (2008/10/09)
The novel Ir(III) nonclassical tetrahydrido complex [(triphos)Ir(H2)(H)2]BPh4 (4BPh4) has been prepared by hydrogenation of the ethene dihydride complex [(triphos)Ir(C2H4)(H)2]BPh4 in either the solid state (PH2 ≥ 1 atm) or CH2Cl2 solution (PH2 ≥ 3 atm) [triphos = MeC(CH2PPh2)3]. Complex 4BPh4 is very labile in solution and can be isolated in the solid state exclusively from solid-gas reactions. Characterization of 4BPh4 in solution can be achieved by high-pressure NMR and IR spectroscopies, however. Various deuterated isotopomers of [(triphos)Ir(H2)(H)2]+ have been obtained in CD2Cl2 solution at low temperature by treatment of the trihydride [(triphos)IrH3] with DOSO2CF3. On the basis of a variety of NMR experiments, the complex cation [(triphos)Ir(H2)(H)2]+ is assigned an octahedral structure where two terminal hydride ligands and a dihydrogen molecule are trans to the phosphorus atoms of a facial triphos ligand. Complex 4BPh4 dissolves in THF at room temperature yielding [(triphos)IrH3], BPh3, and benzene; a similar reaction occurs in acetone, whereas in C2HCl2 the complex loses H2 converting to the dimers cis- and trans-[(triphos)IrH(μ-H)2HIr(triphos)](BPh4) 2.
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.
