1085561-73-4Relevant articles and documents
Well-Defined and Robust Rhodium Catalysts for the Hydroacylation of Terminal and Internal Alkenes
Prades, Amparo,Fernández, Maitane,Pike, Sebastian D.,Willis, Michael C.,Weller, Andrew S.
, p. 8520 - 8524 (2015)
A Rh-catalyst system based on the asymmetric ligand tBu2PCH2P(o-C6H4OMe)2 is reported that allows for the hydroacylation of challenging internal alkenes with β-substituted aldehydes. Mechanistic studies point to the stabilizing role of both excess alkene and the OMe-group.
Intermolecular hydroacylation: High activity rhodium catalysts containing small-bite-angle diphosphine ligands
Chaplin, Adrian B.,Hooper, Joel F.,Weller, Andrew S.,Willis, Michael C.
supporting information; experimental part, p. 4885 - 4897 (2012/05/04)
Readily prepared and bench-stable rhodium complexes containing methylene bridged diphosphine ligands, viz. [Rh(C6H5F)(R 2PCH2PR'2)][BArF4] (R, R' = tBu or Cy; ArF = C6H3-3,5- (CF3)2), are shown to be practical and very efficient precatalysts for the intermolecular hydroacylation of a wide variety of unactivated alkenes and alkynes with β-S-substituted aldehydes. Intermediate acyl hydride complexes [Rh(tBu2PCH 2PtBu2)H{κ2(S,C)-SMe(C 6H4CO)}(L)]+ (L = acetone, MeCN, [NCCH 2BF3]-) and the decarbonylation product [Rh(tBu2PCH2PtBu2)(CO) (SMePh)]+ have been characterized in solution and by X-ray crystallography from stoichiometric reactions employing 2-(methylthio) benzaldehdye. Analogous complexes with the phosphine 2-(diphenylphosphino) benzaldehyde are also reported. Studies indicate that through judicious choice of solvent and catalyst/substrate concentration, both decarbonylation and productive hydroacylation can be tuned to such an extent that very low catalyst loadings (0.1 mol %) and turnover frequencies of greater than 300 h-1 can be achieved. The mechanism of catalysis has been further probed by KIE and deuterium labeling experiments. Combined with the stoichiometric studies, a mechanism is proposed in which both oxidative addition of the aldehyde to give an acyl hydride and insertion of the hydride into the alkene are reversible, with the latter occurring to give both linear and branched alkyl intermediates, although reductive elimination for the linear isomer is suggested to have a considerably lower barrier.
Intermolecular alkene and alkyne hydroacylation with β-S-substituted aldehydes: Mechanistic insight into the role of a hemilabile P-O-P ligand
Moxham, Gemma L.,Randell-Sly, Helen,Brayshaw, Simon K.,Weller, Andrew S.,Willis, Michael C.
supporting information; experimental part, p. 8383 - 8397 (2009/09/28)
A straightforward to assemble catalytic system for the intermolecular hydroacylation reaction of β-S-substituted aldehydes with activated and unactivated alkenes and alkynes is reported. These catalysts promote the hydroacylation reaction between β-S-substituted aldehydes and challenging substrates, such as internal alkynes and 1-octene. The catalysts are based upon [Rh(cod)(DPEphos)][ClO4] (DPE-phos = bis(2-diphenylphosphinophenyl) ether, cod = cyclooctadiene) and were designed to make use of the hemilabile capabilities of the DPEphos ligand to stabilise key acyl-hydrido intermediates against reductive decarbonylation, which results in catalyst death. Studies on the stoichiometric addition of aldehyde (either ortho-HCOCH2CH 2SMe or ortho-HCOC6H4SMe) and methylacrylate to precursor acetone complexes [Rh(acetone)2(DPEphos)][X] [X = closo-CB11H6Cl6 or [BAr4 F] (ArF = 3,5-(CF3)2C 6H3)] reveal the role of the hemilabile DPEphos ligand. The crystal structure of [Rh(acetone)2(DPEphos)][X] shows a cis-coordinated diphosphine ligand with the oxygen atom of the DPEphos distal from the rhodium. Addition of aldehyde forms the acyl hydride complexes [Rh(DPEphos)(COCH2CH2SMe)H][X] or [Rh(DPEphos)(COC 6H4SMe)H][X], which have a trans-spanning DPEphos ligand and a coordinated ether group. Compared to analogous complexes prepared with dppe (dppe = 1,2-bis(diphenylphosphino)ethane), these DPEphos complexes show significantly increased resistance towards reductive decarbonylation. The crystal structure of the reductive decarbonylation product [Rh(CO)(DPEphos) (EtSMe)][closo-CB11H6I6] is reported. Addition of alkene (methylacrylate) to the acyl-hydrido complexes forms the final complexes [Rh(DPEPhOs)(η1-MeSC2H4- η1-COC2H4CO2Me)][X] and [Rh-(DPEphos)(η1-MeSC6H4-η1- COC2H4-CO2Me)][X], which have been identified spectroscopically and by ESIMS/MS. Intermediate species in this transformation have been observed and tentatively characterised as the alkyl-acyl complexes [Rh(CH2CH2CO2Me)-(COC2H 4SMe)(DPEphos)][X] and [Rh(CH2CH2CO 2Me)(COC6H4SMe)-(DPEphos)][X]. In these complexes, the DPEphos ligand is now cis chelating. A model for the (unobserved) transient alkene complex that would result from addition of alkene to the acyl-hydrido complexes comes from formation of the MeCN adducts [Rh(DPEphos)(MeSC2H4CO)H(MeCN)] [X] and [Rh(DPEphos)(MeSC6-H4CO)H(MeCN)][X]. Changing the ligand from DPEphos to one with a CH2 linkage, [Ph2P(C 6H4)]2CH2, gave only decomposition on addition of aldehyde to the acetone precursor, which demonstrated the importance of the hemiabile ether group in DPEphos. With [Ph2P(C 6H4)]2S, the sulfur atom has the opposite effect and binds too strongly to the metal centre to allow access to productive acetone intermediates.
