Bouley Bailey S, Bae Dae Young, Chakrabarti Sagnik, Rosen Mari, Kennedy Robert D, Mirica Liviu M
Department of Chemistry, University of Illinois at Urbana-Champaign Urbana IL 61801 USA
Core R&D, The Dow Chemical Company Midland Michigan 48667 USA.
Chem Sci. 2025 Jul 21;16(34):15486-15498. doi: 10.1039/d5sc02171e. eCollection 2025 Aug 27.
The mechanism by which Pd precursors are reduced to catalytically active low-valent Pd species has been a subject of interest for developing better catalysts. This process is well understood for catalytic systems employing a combination of palladium(ii) acetate [Pd(OAc)] and tertiary phosphines. However, the mechanism of reduction of palladium(ii) acetylacetonate [Pd(acac)] in the presence of phosphines has not been thoroughly investigated. This is especially important in the context of the Pd-catalyzed butadiene telomerization process, which uses a combination of Pd(acac) and tertiary phosphines in methanol to produce the commercially valuable precursor 1-methoxyoctadiene (MOD-1). In this work, we elucidate the steps for generating the active Pd species for this reaction using a combination of Pd(acac) and triphenylphosphine (PPh). The investigations presented in this study provide the following key insights: (a) unification of the steps involved in the generation of the active precatalyst [Pd(acac)(PPh)]; (b) elucidation of the mechanism of reduction of the precatalyst to Pd without MOD-1, which parallels the chemistry of the Pd(OAc)/PPh system; and (c) the generation of Pd-octadienyl species from the reaction between the precatalyst and MOD-1, the product of the telomerization reaction. A reversible C-O bond cleavage process was identified that leads to the formation of the Pd π-octadienyl species as the active catalyst in the commercial telomerization process. These studies provide important insights into the reduction of Pd(acac) into active Pd species or Pd π-allyl species, which have wide implications for both cross-coupling catalysis as well as the telomerization reaction.
钯前驱体被还原为具有催化活性的低价钯物种的机制一直是开发更好催化剂的研究热点。对于采用醋酸钯（II）[Pd（OAc）]和叔膦组合的催化体系，这一过程已得到充分理解。然而，在膦存在下乙酰丙酮钯（II）[Pd（acac）]的还原机制尚未得到深入研究。这在钯催化的丁二烯端粒化过程中尤为重要，该过程在甲醇中使用Pd（acac）和叔膦的组合来生产具有商业价值的前体1-甲氧基辛二烯（MOD-1）。在这项工作中，我们阐明了使用Pd（acac）和三苯基膦（PPh）组合生成该反应活性钯物种的步骤。本研究中的调查提供了以下关键见解：（a）活性预催化剂[Pd（acac）（PPh）]生成过程中涉及步骤的统一；（b）阐明了预催化剂在没有MOD-1的情况下还原为钯的机制，这与Pd（OAc）/PPh体系的化学过程相似；（c）由预催化剂与端粒化反应产物MOD-1之间的反应生成钯-辛二烯基物种。确定了一个可逆的C-O键裂解过程，该过程导致形成Pd π-辛二烯基物种作为商业端粒化过程中的活性催化剂。这些研究为将Pd（acac）还原为活性钯物种或Pd π-烯丙基物种提供了重要见解，这对交叉偶联催化以及端粒化反应都具有广泛的意义。
