15631-52-4Relevant academic research and scientific papers
Rapid, reversible heterolytic cleavage of the Co-Rh bond in (CO)4Co-Rh(CO)(PEt3)2
Roberts, David A.,Mercer, William C.,Geoffroy, Gregory L.,Pierpont, Cortlandt G.
, p. 1439 - 1444 (2008/10/08)
The complex (CO)4Co-Rh(CO)(PEt3)2 (1) was prepared by the reaction of Na[Co(CO)4] with trans-RhCl(CO)(PEt3)2 and has been structurally characterized: P21/c, a = 8.294 (1) ?, b = 17.746 (6) ? c = 16.575 (3) ?, β = 104.37 (1)°, V = 2363.2 (8) ?3, Z = 4, R1 = 0.042 and R2 = 0.053 for 3209 reflections with F > 6σ(F). The Co center is ligated by four carbonyls in an approximately tetrahedral arrangement while the Rh center has a square-planar arrangement of trans phosphines, a carbonyl, and the Co atom. The Co-Rh distance of 2.676 (1) ? is consistent with a single bond between these metals although the structural parameters and the reactivity properties of 1 imply that this is a polar donor-acceptor metal-metal bond between formally Co(-I) and Rh(+I) centers. The Co-Rh bond is readily cleaved by nucleophiles, and for example, addition of [(Ph3P)2N]Cl to solutions of 1 gives immediate and quantitative formation of [(Ph3P)2N]Co(CO)4 and trans-RhCl(CO)(PEt3)2. Even CH3CN displaces this weak bond to form trans-[Rh(CO)(PEt3)2(CH3CN)]+ (4), and at low CH3CN concentrations, the equilibrium 1 + CH3CN ? 4 + [Co(CO)4]- is established. Variable-temperature NMR data indicate that the forward and reverse reactions in the above equilibrium are fast on the 31P NMR time scale. Computer simulation of the NMR spectra has given the thermodynamic parameters for this equilibrium as well as rate and kinetic parameters for both the forward and reverse reactions. For illustration, the second-order rate constants for the forward and reverse reactions at 20°C are 17 100 M-1 s-1 and 5.1 × 106 M-1 s-1, respectively, corresponding to a turnover number of ?13000/s for the equilibrium.
Preferential retainment of the cobalt-rhodium bond in some reactions of Co2Rh2(CO)12 and its triethylphosphine-substituted derivatives
Horváth, István T.
, p. 2333 - 2340 (2008/10/08)
Co2Rh2(CO)12 (1) reacts with PEt3 to give CoRh(CO)5(PEt3)2 (3); three intermediates, Co2Rh2(CO)11(PEt3) (4), Co2Rh2(CO)10(PEt3)2 (5), and CoRh(CO)6(PEt3) (6), were separately isolated and characterized by IR and NMR spectroscopy. 4 reacts with CO in a reversible reaction to give an equilibrium mixture of 4, CoRh(CO)7 (2), and 6. 5 undergoes facile and reversible fragmentation when treated with CO to give 6. Medium-pressure in situ IR studies have revealed that at higher CO pressure 6 is in equilibrium with CoRh(CO)7(PEt3) (7). 1 reacts with excess of MeCN to give CoRh(CO)6(MeCN) (8), which undergoes heterolytic metal-metal bond cleavage when treated with PEt3 to give [Rh(CO)(MeCN)(PEt3)2]+[Co(CO)4] -. The treatment of 1 with 2 equiv of [PPN]Cl or [N(CH2Ph)Et3]Cl gives PPN[CoRh(CO)6Cl] (9) and [N(CH2Ph)Et3][CoRh(CO)6Cl] (10), respectively. 9 reacts with 2 equiv of PEt3 to yield PPN[Co(CO)4] and ClRh(CO)(PEt3)2.
