The complex trans-[(2,9-dipyridyl-1,10phenanthroline)(CH 3 CN) 2 Ru](OTf) 2 was synthesized and tested as a homogeneous hydrodeoxygenation catalyst for the conversion of biomass-derived furfuryl alcohol and furfuryl acetate to 1,4pentanediol (as the primary target compound) and cyclopentanol (formed by the competing Piancatelli rearrangement) in aqueous reaction medium at elevated temperature (150−200 °C) and hydrogen pressure (800 psi = 5.12 MPa). Catalytic reactions using furfuryl alcohol as a substrate were limited by the formation of solid resins with the product yields showing a strong negative correlation with increasing substrate concentration and maximum yields of 1,4-pentanediol and cyclopentanol being 23 and 41%, respectively. A two-level full factorial design of experiments study with four independent input variables (temp., time, [cat.],[substrate]) and a center point was carried out for the conversion of furfuryl acetate, showing good reproducibility between replicates and no humin formation. This enabled a full statistical analysis of the input variable impact on product distribution and yield. The maximum yields of 1,4-pentanediol and cyclopentanol using furfuryl acetate as a substrate are 68 and 35%, respectively. The decreased self-reactivity of furfuryl acetate versus furfuryl alcohol dramatically increases the yields of target products but still shows a strong negative correlation of the yield of the desired products with increasing substrate concentration.

The ruthenium complexes [Ru(H3CC(CH2PPh2)3-κ3-P)(NCCH3)3](OTf)2 (1, (H3CC(CH2PPh2)3 = triphos) and [Ru(N(CH2PPh2)3-κ3-P)(NCCH3)3](OTf)2 (2, N(CH2PPh2)3 = N-triphos) have been evaluated as homogeneous ionic hydrogenation catalysts for the catalytic hydrodeoxygenation of furfuryl alcohol and furfuryl acetate to 1,4-pentanediol and cyclopentanol in aqueous media reaction mixtures. For furfuryl alcohol, only marginal yields of 1,4-pentanediol could be achieved with mass balance deficiencies due to humin formation ranging from 67% to 90%. Attempts to improve the catalytic activity of 2 by enhancing its water solubility by nitrogen protonation and (or) methylation failed. Employing the less self-reactive furfuryl acetate as the substrate substantially diminishes humin formation, yielding up to 43% of 1,4-pentanediol and 19% of cyclopentanol (via Piancatelli rearrangement) with 1 and up to 33% of 1,4-pentanediol and 5% of cyclopentanol with 2. A design of experiments study was used to determine and compare the yield responses of the multiple parallel reaction channels with 1,4-pentanediol, cyclopentanol, and humins as a function of reaction temperature, time, catalyst load, and substrate concentration. This explores the correlations between these parameters and their impact on the reaction outcome and suggests an extremely complex overall reaction cascade of interdependent pathways of both acid- and metal-catalyzed steps with some significant differences emerging between the two catalysts.

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