Rhodium versus Iridium Catalysts in the Controlled Tandem Hydroformylation-Isomerization of Functionalized Unsaturated Fatty Substrates

The hydroformylation of 10-undecenitrile (1) and related unsaturated fatty substrates (H2CCH(CH2)(7)CH2R; R=CO2Me, CH2Br, CHO) has been studied with rhodium, iridium, ruthenium, and palladium biphephos catalysts. The reactions proceeded effectively with all four systems, with high selectivities for the linear aldehyde (ratio of linear/branched aldehydes=99:1). The biphephos-bis[chloro(cyclooctadiene)iridium] system showed a non-optimized hydroformylation turnover frequency (TOFHF) of 770h(-1) that was only approximately 5times lower than that of the rhodium-based system (TOFHF=3320h(-1)); the palladium and ruthenium biphephos systems were less active (TOFHF=210 and 310h(-1), respectively). Upon recycling, remarkable productivities were achieved in both cases (TON approximate to 58000mol(1/1-int)mol(Ir)(-1) and 250000mol(1/1-int)mol(Rh)(-1), in which int=internal olefin). Competitive isomerization of terminal to internal olefins occurred with these catalysts. Iridium biphephos systems allowed slightly better control of the distribution of the internal isomers than the rhodium biphephos catalyst, with higher ratios of 9-/8-undecenitrile (1-int).