C–P vs C–H Bond Cleavage of Triphenylphosphine at Platinum(0): Mechanism of Formation, Reactivity, Redox Chemistry, and NMR Chemical Shift Calculations of a μ-Phosphanido Diplatinum(II) Platform
Andreas Berkefeld, Marc Reimann, Gerald Hörner, Martin Kaupp, Hartmut Schubert
Abstract
Transition-metal phosphanides M–PR2 are key intermediates in catalytic C–P bond functionalization. M–PR2 formation from tertiary phosphines through P–C bond cleavage widens the scope beyond P–H functionalized substrates, but mechanistic understanding of this reaction still is fragmentary. Starting from a defined coordination complex has allowed monitoring the reaction of a Pt-PPh3 moiety and Pt(0) by NMR spectroscopy. Initial Pt(0) transfer is rate-limiting and leads to products from PPh3-borne ortho-C–H and C–P bond cleavage along kinetically distinct pathways. Albeit kinetically favored, the reversibility of C–H bond cleavage eventually leads to thermodynamically preferred C–P bond scission. This pathway affords a robust [Pt(μ-PPh2)Pt] core structure whose redox chemistry and reactivity toward external ligands are reported. Organometallic products have been substantiated by a combination of magnetic resonance and absorption spectroscopies, X-ray diffraction, and DFT computations.