Exclusive Hydroformylation of Terminal Olefins: A Phosphorus-Free Ruthenium System for the Selective...

We report a paradigm shift in ruthenium-catalyzed hydroformylation using a remarkably simple, phosphorus-free system based on ruthenium carbonyl complexes and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The optimal catalytic system operates under mild conditions and exhibits an unprecedented "terminal-only" selectivity. It quantitatively discriminates between terminal and internal or multi-substituted double bonds, which has been a long-standing challenge in oxo synthesis. Traditional systems often trigger the isomerization of internal olefins, but our catalyst leaves them untouched, even within complex industrial feedstocks. Comprehensive mechanistic investigations, including in situ IR spectroscopy and high-pressure VT NMR spectroscopy, identify the tetranuclear ruthenium-hydride cluster [DBUH]₂ ⁺[H₂Ru₄(CO)₁₂]^2- as the pivotal active species. Isolating this cluster and successfully reapplying it confirms its role as the catalytic resting state. Combining low-cost, air-stable components with exceptional chemo- and regioselectivity provides this system with a robust, economically superior alternative to precious rhodium-phosphine catalysts for academic synthesis and large-scale industrial applications .