105736-81-0Relevant articles and documents
Synthesis, characterization, and electrochemical properties of a family of dinuclear rhodium complexes containing two terminal hydride ligands and two hydride (or chloride) bridges. Stoichiometric and catalytic hydrogenation reactions of alkynes and alkenes
Bianchini, Claudio,Meli, Andrea,Laschi, Franco,Ramirez, José A.,Zanello, Piero,Vacca, Alberto
, p. 4429 - 4435 (2008/10/08)
Protonation by strong acids and thermal decomposition in solution are two routes by which the trihydride (triphos)RhH3 (1) [triphos = MeC(CH2PPh2)3] is used to synthesize the tetrahydrido complexes [(triphos)RhH(μ-H)2HRh(triphos)](BPh4)2 (2) and [(triphos)RhH(μ-H)2HRh(triphos)] (3), respectively. The bis(μ-chloro) dihydride [(triphos)RhH(μt-Cl)2HRh(triphos)](BPh4)2 (6) can be prepared either by protonation of (triphos)RhCl(C2H4) followed by NaBPh4 addition or by H/Cl exchange between 2 and CH2Cl2. Interestingly, 6 exists in solution as a 1:1 mixture of two geometric isomers. The electrochemical behavior of the tetrahydride derivatives in nonaqueous solvents shows that they can reversibly undergo one-electron-redox changes with no change of the primary geometry. By contrast, 6 is unable to reversibly accept or lose electrons. Electrochemical techniques have been used to generate the paramagnetic [(triphos)RhH(μ-H)2HRh(triphos)]+ derivative, which is not directly obtainable by chemical methods. All of the compounds have been fully characterized by IR, NMR, and ESR techniques. Both the mononuclear trihydride 1 and the dimeric tetrahydride 2 are able to straightforwardly transfer hydrogen atoms to unsaturated substrates such as 3,3-dimethylbut-1-ene, dimethyl maleate (DMMA), or dimethyl acetylenedicarboxylate (DMAD). The effectiveness of 2 and 6 to catalytically hydrogenate DMAD and DMMA is investigated and compared to that shown by the mononuclear species [(triphos)Rh(π-DMAD)]BPh4 and [(triphos)Rh(π-DMMA)]BPh4 as well as a family of homo- and heterobimetallic (μ-H)3 complexes of formula [(triphos)Rh(μ-H)3M(triphos)]n+ (M = Rh, Co; n = 3, 2). All of the compounds prove active catalysts or catalyst precursors for hydrogenation reactions of DMAD and DMMA. The catalyzed alkyne hydrogenation yields largely the olefin. In the catalytic cycles some of the binuclear compounds are resistant to fragmentation and are responsible for the catalysis.
