The hydroformylation of 10-undecenitrile (1), a route towards polyamide-12, has been studied using Ru-diphosphite catalysts. The reactions proceeded effectively by in situ combination of chloro precursors such as RuCl2(PPh3)(3) and RuCl2(DMSO)(4) with Biphephos. High productivities (TON up to 15,000 mol(aldehyde)mol(Ru)-1) were achieved by carrying the reactions at low catalyst loading ([1](0)/[Ru] = 20,000), at 120 degrees C in toluene or acetonitrile under 20 bar CO/H-2 (1:1), with 20 equiv of Biphephos vs. Ru. Up to 75% chemoselectivity for the aldehydes and very high regioselectivities for the linear aldehyde (l/b = 99:1) were reached under such optimized conditions. Lower loadings of Biphephos (down to 2.5 equiv. vs. Ru) did not affect the chemo- and regioselectivities but the activity. The Ru-Biphephos combinations showed a non-optimized hydroformylation TOFHF of ca. 2-7 min(-1), that is ca. 1-2 order of magnitude lower than that of analogous Rh-based systems (TOFHF =ca. 80 min(-1)). These Ru-Biphephos systems are, however, incapable, under the conditions suitable for selective hydroformylation, to promote isomerization of internal olefins, and hence to achieve a tandem isomerization-hydroformylation process. (C) 2016 Elsevier B.V. All rights reserved.