Synthesis of new o-alkyl substituted arylalkylphosphanes: study of their molecular structure and influence on rhodium-catalyzed propene and 1-hexene hydroformylation

Iridium-phosphine ligand complexes as an alternative to rhodium-based catalysts for the efficient hydroformylation of propene

Expensive rhodium (Rh)-based catalysts have been widely used for the hydroformylation of propene. To find a cheaper and effective alternative to these Rh-based catalysts, herein, a series of phosphine ligands were used to coordinate with iridium, and their catalytic reactivities for the hydroformylation of propene were systematically investigated in this study. The effects of different phosphine ligands, pressures, temperatures, and catalyst dosages on the hydroformylation of propene were investigated. Tripyridyl phosphine iridium Ir2(cod)2Cl2-P(3-py)3 (Ir(I)-L5) and its derivatives exhibit the highest catalytic reactivity. Surprisingly, the catalytic reactivity of Ir(I)-L5 is higher than that of Rh2(cod)2Cl2-P(3-py)3 (Rh(I)-L5). When the Ir(I)-L5 complex is used as the catalyst, reactions performed in a polar solvent gave higher turnover number (TON) values than those in a non-polar solvent. Up to a TON of 503 can be obtained. Different n-butyraldehyde/iso-butyraldehyde (n/i) ratios can be obtained by adjusting the phosphine ligands or the proportion of gas pressure. The catalyst showed good reusability in five recycling experiments. Furthermore, based on DFT theoretical calculations, a probable reaction mechanism was proposed. It is reliable that an Ir-based catalyst can be considered as a highly effective catalyst for the hydroformylation of propylene with CO.

Au⋅⋅⋅H-C Hydrogen Bonds as Design Principle in Gold(I) Catalysis

Secondary ligand-metal interactions are decisive in many catalytic transformations. While arene-gold interactions have repeatedly been reported as critical structural feature in many high-performance gold catalysts, we herein report that these interactions can also be replaced by Au⋅⋅⋅H-C hydrogen bonds without suffering any reduction in catalytic performance. Systematic experimental and computational studies on a series of ylide-substituted phosphines featuring either a PPh3 (Ph YPhos) or PCy3 (Cy YPhos) moiety showed that the arene-gold interaction in the aryl-substituted compounds is efficiently compensated by the formation of Au⋅⋅⋅H-C hydrogen bonds. The strongest interaction is found with the C-H moiety next to the onium center, which due to the polarization results in remarkably strong interactions with the shortest Au⋅⋅⋅H-C hydrogen bonds reported to date. Calorimetric studies on the formation of the gold complexes further confirmed that the Ph YPhos and Cy YPhos ligands form similarly stable complexes. Consequently, both ligands showed the same catalytic performance in the hydroamination, hydrophenoxylation and hydrocarboxylation of alkynes, thus demonstrating that Au⋅⋅⋅H-C hydrogen bonds are equally suited for the generation of highly effective gold catalysts than gold-arene interactions. The generality of this observation was confirmed by a comparative study between a biaryl phosphine ligand and its cyclohexyl-substituted derivative, which again showed identical catalytic performance. These observations clearly support Au⋅⋅⋅H-C hydrogen bonds as fundamental secondary interactions in gold catalysts, thus further increasing the number of design elements that can be used for future catalyst construction.

Chemistry of transition-metal complexes containing functionalized phosphines: synthesis and structural analysis of rhodium(I) complexes containing allyl and cyanoalkylphosphines

A series of related acetylacetonate–carbonyl–rhodium compounds substituted by functionalized phosphines has been prepared in good to excellent yields by the reaction of [Rh(acac)(CO)2] (acac is acetylacetonate) with the corresponding allyl-, cyanomethyl- or cyanoethyl-substituted phosphines. All compounds were fully characterized by 31P, 1H, 13C NMR and IR spectroscopy. The X-ray structures of (acetylacetonato-κ2 O,O′)(tert-butylphosphanedicarbonitrile-κP)carbonylrhodium(I), [Rh(C5H7O2)(CO)(C8H13N2)] or [Rh(acac)(CO)(tBuP(CH2CN)2}] (2b), (acetylacetonato-κ2 O,O′)carbonyl[3-(diphenylphosphanyl)propanenitrile-κP]rhodium(I), [Rh(C5H7O2)(C15H14N)(CO)] or [Rh(acac)(CO){Ph2P(CH2CH2CN)}] (2h), and (acetylacetonato-κ2 O,O′)carbonyl[3-(di-tert-butylphosphanyl)propanenitrile-κP]rhodium(I), [Rh(C5H7O2)(C11H22N)(CO)] or [Rh(acac)(CO){tBu2P(CH2CH2CN)}] (2i), showed a square-planar geometry around the Rh atom with a significant trans influence over the acetylacetonate moiety, evidenced by long Rh—O bond lengths as expected for poor π-acceptor phosphines. The Rh—P distances displayed an inverse linear dependence with the coupling constants J P-Rh and the IR ν(C[triple-bond]O) bands, which accounts for the Rh—P electronic bonding feature (poor π-acceptors) of these complexes. A combined study from density functional theory (DFT) calculations and an evaluation of the intramolecular H...Rh contacts from X-ray diffraction data allowed a comparison of the conformational preferences of these complexes in the solid state versus the isolated compounds in the gas phase. For 2b, 2h and 2i, an energy-framework study evidenced that the crystal structures are mainly governed by dispersive energy. In fact, strong pairwise molecular dispersive interactions are responsible for the columnar arrangement observed in these complexes. A Hirshfeld surface analysis employing three-dimensional molecular surface contours and two-dimensional fingerprint plots indicated that the structures are stabilized by H...H, C...H, H...O, H...N and H...Rh intermolecular interactions.

Steric and electronic evaluations of P(o-tol)R2, where R is phenyl or cyclohexyl: crystal structures of SeP(o-tol)R2

The crystal structures of SeP(o-tol)R₂, where o-tol is ortho-tolyl (2-methylphenyl) and R is Ph (phenyl), namely (2-methylphenyl)diphenylphosphane selenide, C₁₉H₁₇PSe, or Cy (cyclohexyl), namely dicyclohexyl(2-methylphenyl)phosphane selenide, C₁₉H₂₉PSe, were determined to aid in the evaluation of the steric and electronic behaviour of these analogous phosphane compounds. The compounds crystallized in similar monoclinic crystal systems, but are differentiated in their unit cells by a doubling of the number of independent molecules for R = Cy (Z' = 2) and the choice of glide plane by convention. The preferred orientation for the o-tolyl substituent obtained from the X-ray structural analysis is gauche for R = Ph and anti for R = Cy (using the Se-P-C_ipso-C_ortho torsion angles as reference). Density functional theory (DFT) calculations showed both conformations to be equally probable and indicate that the preferred solid-state conformer is probably due to the minimization of repulsion energies, resulting in a packing arrangement primarily featuring weak C-H...Se interactions and additional C-H...π interactions in the R = Ph structure. A detailed electronic and steric analysis was conducted on both phosphanes using Se-P bond lengths, multinuclear NMR ¹J_Se-P coupling constants, theoretical topological evaluation and crystallographic and solid-angle calculations, and compared to selected literature examples. The results indicate that the use of the o-tolyl substituent increases both the electron-donating capability and the steric size, but is also dependent on whether the o-tolyl group adopts a gauche or anti conformation. The single-crystal geometrical data are unable to detect electronic differences between these two structures due to the somewhat large displacement parameters observed for the Se atom in the R = Cy structure.

Synthesis, structures and catalytic activity of cyclometalated rhenium complexes

Several five-membered cyclometalated rhenium complexes (1–5) were synthesized, and their photocatalytic activity on direct arylation of arenes with aryl halides was examined.

Bis(2,4-dimeth-oxy-phen-yl)(phen-yl)phosphine selenide

In the title mol­ecule, C₂₂H₂₃O₄PSe, the P atom has a distorted tetra­hedral environment formed by the selenide atom [P=Se = 2.1219 (5) Å] and three aryl rings. The orientations of the meth­oxy groups in the two 2,4-dimeth­oxy­phenyl ligands are distinct, as seen from the torsion angles: C—C—O—C = 14.7 (3) and 175.97 (17)° in one ligand, and −9.1 (2) and 5.1 (3)° in the other. In the crystal, weak inter­molecular C—H⋯Se inter­actions link the mol­ecules into zigzag chains propagated in [010].

Bis(2-meth-oxy-phen-yl)(phen-yl)phosphine selenide

The title compound, C(20)H(19)O(2)PSe or SePPh(2-OMe-C(6)H(3))(2), crystallizes with two distinct orientations for the meth-oxy groups. The Se=P bond is 2.1170 (7) Å and the cone angle is 176.0°. Intra-molecular C-H⋯Se inter-actions occur. In the crystal, mol-ecules are linked by inter-molecular C-H⋯Se inter-actions.

Nickel-catalyzed coupling of alkenes, aldehydes, and silyl triflates

A full account of two recently developed nickel-catalyzed coupling reactions of alkenes, aldehydes, and silyl triflates is presented. These reactions provide either allylic alcohol or homoallylic alcohol derivatives selectively, depending on the ligand employed. These processes are believed to be mechanistically distinct from Lewis acid-catalyzed carbonyl-ene reactions, and several lines of evidence supporting this hypothesis are discussed.

Highly selective coupling of alkenes and aldehydes catalyzed by [Ni(NHC){P(OPh)3}]: synergy between a strong sigma donor and a strong pi acceptor

Both a strong electron donor (IPr ) and a strong electron acceptor (P(OPh)3 ) are necessary for a highly selective, nickel-catalyzed coupling reaction between alkenes, aldehydes, and silyltriflates. Without the phosphite, catalysis is not observed and several side reactions are observed. The phosphite appears to suppress the formation of these byproducts and rescue the catalytic cycle by accelerating reductive elimination from an (IPr–Ni–H)(OTf) complex.