Hydroformylation of Monoterpenic Polyenes: Effect of the Conjugation of Double Bonds on Reactivity

Abstract

Rhodium-catalyzed hydroformylation of a series of monoterpenic polyenes, i.e., myrcene (1), R-terpinene (2), γ-terpinene (3), terpinolene (4), and limonene (5), was studied in the presence of various monophosphines. Effects of reaction variables, such as the ligand to rhodium ratio, ligand basicity, and partial pressures of reacting gases were evaluated for each reactive substrate. The hydroformylation of conjugated olefins 1 and 2 results in two main aldehydes in each case with excellent combined selectivities and can be performed under mild conditions (80 °C, 80 atm) using a large excess of PPh 3 (P/Rh ) 20-40). The hydroformylation of 1 follows the trends opposite to those usually observed with simple olefins: the increase in the concentration of the phosphorus ligand, ligand basicity, and pressure of both hydrogen and CO strongly accelerates the reaction showing that the most critical step is a conversion of η 3 -allylrhodium intermediates into much more reactive η 1 -complexes. The hydroformylation of 2 does not seem to occur through the formation of η 3complexes and at low P/Rh ratios and in systems with more bulky ligands than PPh 3 , such as PBz 3 and PCy 3 , is strongly complicated by the hydrogenation of the substrate. Nonconjugated olefins 3 and 4 show an extremely low reactivity toward hydroformylation under similar conditions, whereas in substrate 5, only a terminal exocyclic double bond reacts with rhodium to give a corresponding aldehyde in near quantitative yield. Thus, the endocyclic double bond in p-menthane dienes 2-5 can be hydroformylated at a reasonable rate under relatively mild conditions only if it is conjugated with another double bond. All obtained aldehydes have a pleasant scent and can be useful as components of synthetic fragrances.

Myrcene as a Natural Base Chemical in Sustainable Chemistry: A Critical Review

“…[270] Recently, effects of reaction variables, such as ligand to rhodium ratio, ligand basicity, and partial pressures of the synthesis gas were evaluated showing that the hydroformylation of myrcene follows trends opposite to those usually observed with simple olefins: the increase in the concentration of the phosphorous ligand, ligand basicity, and pressure of hydrogen and CO strongly accelerates the reaction. [271] 6.5 Dimerization and co-dimerization Dimerization with other olefinic compounds ("co-dimerization") or myrcene itself ("dimerization") permits an atom-economical route to higher unsaturated olefins, > C 10. Depending on the number and the substitution pattern of the double bonds, often a complex product mixture is observed comprising the desired linear co-dimers as well as adducts from Diels-Alder reaction.…”

Hidroformilação do oleato de metila catalisada por complexos de ródio

“…Alguns autores sugerem que a presença de ligantes fosforados suprima espécies que levem à isomerização e/ou à hidrogenação do substrato. [17][18][19] Influência da proporção de gás de síntese O efeito da proporção de CO e H 2 sobre o desempenho do sistema catalítico foi estudado comparando-se as reações 8 e 10. Observouse que a maior quantidade de CO no meio reacional promove uma melhora na conversão da reação.…”

“…Os autores atribuem este resultado à diminuição da taxa de isomerização e, consequentemente, um aumento na taxa de hidroformilação. 1,[17][18][19] Frankel e colaboradores verificaram que a extensão da migração da ligação dupla é inversamente proporcional à concentração de fosfina no meio reacional. 5 Muilwijk e colaboradores verificaram que o excesso de fosfina inibe a isomerização posicional e, também, a isomerização geométrica da ligação dupla.…”

An Electrostatically-Anchored Rhodium(I) Catalyst for the Hydroformylation and Tandem Hydroformylation/Acetalization of Biorenewable Allyl Benzenes

“…Rhodium-catalyzed hydroformylation is also employed for fine chemicals syntheses, 1 as showed in a recent review. 2 In the last years our group has been interested in the hydroformylation of naturally occurring olefins, such as monoterpenes [2][3][4][5][6][7][8][9][10] and allyl benzenes. 11 The hydroformylation of allyl benzenes (1a-c) and propenyl benzenes (2a-c) (Scheme 1) represents a potential route to fragrance ingredients.…”