253432-84-7Relevant academic research and scientific papers
Reactions of H2, silanes, and olefins with superelectrophilic cationic rhenium complexes: Heterolytic cleavage of H2 and relation to the structure and function of hydrogenases
Huhmann-Vincent, Jean,Scott, Brian L.,Kubas, Gregory J.
, p. 240 - 254 (2008/10/08)
The reaction of cis-Re(CO)4(PR3)Me (R = Ph, Cy) with the Lewis acid B(C6F5)3 was studied by NMR spectroscopy, and was found to provide an equilibrium mixture of the solvent-coordinated complex [cis-Re(CO)4(PR3)(ClCH2Cl)][MeB(C 6F5)3] and the reactants. Reaction of [cis-Re(CO)4(PR3)Me with HX (X = H, SiEt3) in the presence of B(C6F5)3 at low temperature yielded the σ-bonded complexes [cis-Re(CO)4(PR3)(η2-HX)][MeB(C 6F5)3] which decomposed at room temperature via intramolecular heterolytic cleavage of the X-H bond to produce MeX and the hydride-bridged dimer [cis-Re(CO)4(PR3)]2(μ-H)]{MeB(C 6F5)3}. The unstable H2 binding and cleavage on this and other highly electrophilic organometallic complexes that contain strong π-acceptor CO ligands can be related to the structure and function of metalloenzymes such as Fe-containing hydrogenases that catalyze H2?2H+ + 2e-. The latter contain dinuclear organometallic-like active sites with CO ligands, which would promote binding and heterolytic cleavage of molecular H2 in biological systems. The Fe-Fe and Ni-Fe bonds in hydrogenases are likely sites for protonation to form a bridging hydride as the initial step in the mechanism of H2 formation, and electrophilic fragments such as [Re(CO)4(L)]+ strongly prefer to form bridging rather than terminal hydrides. The reaction of olefins and Et3SiH with the [cis-Re(CO)4(PR3)(ClCH2Cl)][BArF] (BArF = B[3,5-(CF3)2(C6H3)4 -]) system was also investigated, and the X-ray crystal structure of the dimer {[cis-Re(CO)4(PPh3)]2(μ-H)}{BArF} was determined.
Steric and electronic effects on atom transfer reactions of Re(CO)4L· radicals with organic halides and HSn(n-C4H9)3
Hanckel, John M.,Lee, Kang-Wook,Rushman, Paul,Brown, Theodore L.
, p. 1852 - 1856 (2008/10/08)
Re(CO)4L·(L = CO, P(OR)3, PR3, AsEt3) radicals, generated by laser flash photolysis of L(CO)4Re-Re(CO)4L, react with halogen atom donors (CH2Br2, CHCl3, CCl4) or hydrogen atom donors (HSn(n-Bu)3) in solution to produce cis-Re(CO)4LX (X = H, Cl, Br). Bimolecular rate constants for halogen and hydrogen atom transfers to Re(CO)4L·were measured by following the decay of the transient Re(CO)4L·absorbance in the 550-nm region. The rate constants for both the halogen and hydrogen atom transfer processes are influenced by steric and electronic properties of the substituent L. Both bromine and chlorine atom transfer processes depend to a similar extent on the electronic properties of L. The bromine atom transfer reactions show a slightly greater steric dependence than the chlorine atom transfer reactions. The steric dependence of the hydrogen atom transfer reaction is similar to that of the halogen atom transfers, but the dependence on the electronic properties of L is smaller. Increasing electron density at the metal center enhances the rate of atom transfer; polar effects are more evident in the halogen atom transfer. Rate constants for both atom transfer reactions fit a two-parameter free energy relationship, wherein electronic and steric effects of L are represented.
