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

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.