24554-70-9Relevant academic research and scientific papers
Rhodium - Hydrogen - Tin three-center bonds. NMR (1H, 31P, 103Rh, 119Sn) study of [Rh(Cl)(H)(SnPh3)(PPh3)(py)] and related compounds
Carlton, Laurence
, p. 4510 - 4519 (2000)
The complex trans-[Rh(NCBPh3)(H)(SnPh3)(PPh3)2] (1) reacts with pyridine and substituted pyridines (L) in dichloromethane at 22 °C to give [Rh(NCBPh3)(H)(SnPh3)(PPh3)(L)] (2a) and at -25 °C to give trans-[Rh(NCBPh3)(H)(SnPh3)(PPh3)2(L)] (3a). These complexes and numerous analogues can be prepared (the majority in solution only) by the reactions of [Rh(X)(PPh3)3] (X = NCBPh3 (a), N(CN)2 (b), NCS (c), N3 (d), NCO (e), O2CCF3 (f), Cl (g)) with Ph3SnH in solutions containing pyridines (4-Rpy; R = CO2Me, H, NMe2), 1-methylimidazole (1-Meim), and benzonitriles (4-RC6H4CN; R = COMe, H, NMe2) (L). NMR data for the series of complexes 2 in which ligands X, L, and, for X = Cl, the phosphine P(4-C6H4R)3 (R = F, H, Me) were varied independently show systematic changes in the parameters δ(119Sn), δ(103Rh), J(119Sn-1H), and J(103Rh119Sn), which are related to the electron-donating properties of X, L, and the phosphine. Plots of J(119Sn-1H) against δ(119Sn), δ(103Rh), and J(103Rh-119Sn) are approximately linear and show δ(103Rh) and J(103Rh-119Sn) increasing with J(119Sn-1H) and δ(119Sn) decreasing. Complexes 3 give higher values of J(119Sn-1H) and lower values of δ(119Sn) than found for the less electron-rich 2, with data for 3 continuing the trends in J(119Sn-1H) and δ(119Sn) observed for 2. Values of δ(103Rh) and J(103Rh-119Sn) for 3 do not match the pattern found for 2; nor do data for an isomeric form of 3, cis-[Rh(Cl)(H)(SnPh3)(PR3)2(L)] (L = benzonitriles) (4). The plot of J(119Sn-1H)/δ(119Sn) for 3 shows discontinuities at high values of J(119Sn-1H), with the trend in δ(119Sn) toward more negative values (as the ligands become more nucleophilic) being transformed into an increase and changes in J(119Sn-1H) becoming smaller. These patterns of NMR data are interpreted in terms of the weakening of an Rh-(H-Sn) three-center interaction and changes in the coordination geometry of tin as the electron density on rhodium is increased.
Irreversible cleavage of a carbene-rhodium bond in Rh-N-heterocyclic carbene complexes: Implications for catalysis
Allen, Daryl P.,Crudden, Cathleen M.,Calhoun, Larry A.,Wang, Ruiyao
, p. 3203 - 3209 (2004)
Despite the generally accepted belief that carbene-metal bonds are strong and do not dissociate, the reaction of Rh-N-heterocyclic carbene complexes with triphenylphosphine in dichloroethane was determined to take place via cleavage of the Rh-carbene bond. The products of this reaction are Wilkinson's catalyst and a bisimidazolium salt derived from reaction between dichloroethane and two equivalents of the carbene. The implications of this reaction for catalysis are significant since the carbene complex shows lower activity than Wilkinson's catalyst in hydrogenation reactions. In non-halogenated solvents, the catalyst shows higher stability, such that the rate of exchange with free phosphine could be measured, and was determined to be ca. 10 times slower than in Wilkinson's catalyst.
Regioselectivity in the rhodium catalysed 1,4-hydrosilylation of isoprene. Aspects on reaction conditions and ligands
Gustafsson, Magnus,Frejd, Torbj?rn
, p. 438 - 443 (2007/10/03)
The regioselectivity in the Rh catalysed 1,4-hydrosilylation of isoprene was investigated. Variation of solvents and temperature did not significantly affect the isomer distribution between tail-product (I) and head-product (II). The choice of ligands had
Synthesis, structure, and ligand-promoted reductive elimination in an acylrhodium ethyl complex
Suggs, J. William,Wovkulich, Michael J.,Cox, Sherman D.
, p. 1101 - 1107 (2008/10/08)
8-Quinolinecarboxaldehyde and [(C2H4)2RhCl]2 reacted to give a polymeric acylrhodium ethyl compound which was solubilized by pyridine to give chloroethyl(8-quinolinecarbonyl-C,N)(pyridine)rhodium. This compound was stable in the presence of amine ligands, but phosphine ligands caused rapid reductive elimination. Intermediates in the reductive elimination were observed at -40°C by using 1H, 13C, and 31P NMR in the case of the ligand PPh3. In the first-formed intermediate PPh3 displaced pyridine. The resulting five-coordinated Rh(III) complex reductively eliminated (with an observed first-order rate constant of 3.7 × 10-4 s-1 at -40°C) to give an η2-ketone Rh(I) intermediate. With excess phosphine RhCl(PPh3)3 and 8-quinolinyl ethyl ketone were the final products. Recrystallization of the starting pyridine complex from pyridine-ether gave Cl(C2H5)Rh(C10H6NO)(C 5H5N)2·1/2C 4H10O (chloroethyl(8-quinolinecarbonyl-C,N)bis(pyridine)rhodium-hemi(diethyl ether)), whose structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the triclinic space group P1 with two molecules in the unit cell a = 8.933 (3) A?, b = 17.573 (8) A?, c = 7.760 (2) A?, α = 97.57 (3)°, β = 98.04 (2)°, and γ = 79.98 (3)°. The least-squares refinement with anisotropic thermal parameters for all non-hydrogen atoms converged at RF = 0.046 (RwF = 0.055) for 2595 observed reflections and 262 parameters refined.
NMR AND THERMODYNAMIC INVESTIGATION OF THE REACTION OF SQUARE-PLANAR RHODIUM (I) COMPOUNDS WITH H2.
Drago,Miller,Hoselton,Farris,Desmond
, p. 444 - 449 (2007/10/02)
The reaction of square-planar rhodium(I) complexes of the general formula P(4-tolyl)//3)//2RhClB with H//2 has been investigated where B is P(4-tolyl)//3, pyridine, or tetrahydrothiophene. NMR studies confirm that in all cases the product geometry has the
