Kelley C.B. Oliveira

Chemical Plants: High-Value Molecules from Essential Oils

As society faces a future of dwindling petrochemical supplies at increasing cost, much attention has been focused on methods to degrade biomass into renewable commodity-chemical building blocks. Reported here is a powerful complementary approach that amplifies the complexity of molecular structures present in plant materials. Essential-oil phenylpropenoids are transformed via acrylate cross-metathesis into potent antioxidants that are widely used in perfumery and cosmetics, and in treating disorders associated with oxidative damage.

Rhodium-catalyzed hydroformylation of allylbenzenes and propenylbenzenes: effect of phosphine and diphosphine ligands on chemo- and regioselectivity

Abstract Various allylbenzenes and propenylbenzenes have been hydroformylated with a 97–99% chemoselectivity using bis[(μ-acetate)(1,5-cyclooctadiene)rhodium(I)] as a catalyst precursor. Regioselectivity of the hydroformylation can be controlled by the nature of phosphorus auxiliary ligands. The Rh-NAPHOS (2,2′-bis[(diphenylphosphino)methyl]-1,1′-binaphthyl) system promotes the hydroformylation of allylbenzenes into linear aldehydes in near 95% selectivity and propenylbenzenes into branched aldehydes with a formyl group in α-position to phenyl ring in near 90% selectivity, while the Rh-dppp (1,3-bis(diphenylphosphino)propane) system gives branched aldehydes with a formyl group in β-position in near 70% selectivity starting from allylbenzenes. The regioselectivity of Rh-diphosphine systems correlates with a ligand bite angle. Both the rate and regioselectivity of the hydroformylation are largely influenced by the basicity of monophosphine auxiliary ligands, however, no correlation between their steric characteristics and the regioselectivity has been observed.

Rhodium Nanoparticles as Precursors for the Preparation of an Efficient and Recyclable Hydroformylation Catalyst

Despite all the advances in the application of nanoparticle (NP) catalysts, they have received little attention in relation to the hydroformylation reaction. Herein, we present the preparation of a hydroformylation catalyst through the immobilization of air‐stable rhodium NPs onto a magnetic support functionalized with chelating phosphine ligands, which serves as an alternative to air‐sensitive precursors. The catalyst was active in hydroformylation and could be used in successive reactions with negligible metal leaching. The interaction between the rhodium NPs and the diphenylphosphine ligand was evidenced by an enhancement in the Raman spectrum of the ligand. Changes occurred in the Raman spectrum of the catalyst recovered after the reaction, which suggests that the rhodium NPs are precursors of active molecular species that are formed in situ. The supported catalyst was active for successive reactions even after it was exposed to air during the recycling runs and was easily recovered through magnetic separation.

Support Functionalization with a Phosphine‐Containing Hyperbranched Polymer: A Strategy to Enhance Phosphine Grafting and Metal Loading in a Hydroformylation Catalyst

We present the design of a hydroformylation catalyst through the immobilization of air‐stable Rh nanoparticles (NPs) on a magnetic support functionalized with a hyperbranched polymer that bears terminal phosphine groups. The catalyst modification with the hyperbranched polymer improved the metal–support interaction, the metal loading, and the catalytic activity. The catalyst was active for the hydroformylation of natural products, such as estragole, and could be used in successive reactions with negligible metal leaching. The phosphine grafting played a key role in the recyclability of Rh NPs under hydroformylation conditions. The catalytic activity was maintained in successive reactions, even if the catalyst was exposed to air during each recovery procedure. The modification of the support with hyperbranched polyester allowed us either to increase the number of Rh active species or to obtain more active Rh species on the catalyst surface.

Synthesis of fragrance compounds from renewable resources: the aqueous biphasic hydroformylation of acyclic terpenes

The rhodium-catalyzed hydroformylation of acyclic terpenic compounds, i.e., β-citronellene, linalool and nerolidol, was performed in a water/toluene biphasic system. The addition of the cationic surfactant cetyltrimethylammonium chloride remarkably increased the reaction rates, with the surfactant effect being substrate dependent. A water-soluble phosphine ligand was used to immobilize the rhodium catalyst in water, an environmentally benign solvent, whereas non-polar products were collected in the organic phase. A complete phase separation was easily achieved by switching the magnetic stirrer off and cooling the mixture to room temperature. Linalool and nerolidol gave cyclic hemiacetals with excellent stereoselectivity, whereas the hydroformylation of β-citronellene resulted in two isomeric aldehydes with a linear-to-branched product ratio of approximately 85/15. Several fragrance compounds with pleasant sweet floral and woody scents were obtained in high yields through a simple and green one-pot procedure starting from the substrates easily available from natural bio-renewable resources.

Rhodium catalyzed hydroformylation of nerolidol

The rhodium-catalyzed hydroformylation of nerolidol, a biorenewable substrate with strong therapeutic potential available from various essential oils, was studied in toluene and ethanol solutions in the presence of PPh3 or P(O-o-tBuPh)3 ligands. In toluene, the reaction gave with high chemo- and stereoselectivity a cyclic hemiacetal, which formally arises from the intramolecular cyclization of the primarily formed hydroxy aldehyde. In ethanol, hydroformylation gave a corresponding cyclic acetal in excellent yields even without additional acid co-catalysts. In the absence of phosphorous ligands, nerolidol was resistant to hydroformylation probably due to binding with rhodium through both the double bond and the hydroxyl group to form stable chelates. The P(O-o-tBuPh)3 ligand exerted a remarkable effect on the substrate reactivity accelerating the reaction by five to ten times as compared to the system with PPh3. All isolated products have a pleasant sweet floral and woody scent and can be useful as components of synthetic fragrances.