Selective Carbon–Carbon Bond Activation of Oxirane by a Bisphosphine Pt(0) ComplexA Theoretical Study

Platinum­(0) complexes with the chelate
ligand bis­(di-tert-butylphosphino)­methane, tBu2P-CH2-PtBu2 (dtbpm),
generated in solution from
appropriate precursors, are the only known transition metal species
that selectively activate epoxides (oxiranes) by inserting the Pt
fragment into their carbon–carbon bond. The mechanism of this
unprecedented reaction is studied theoretically using the random phase
approximation. We find that the reaction is kinetically controlled
and is caused by the formation of a monocoordinate (dtbpm-κ1P)­Pt­(0) fragment rather than a (dtbpm-κ2P)­Pt­(0) chelate complex. Insertion into epoxide
C–C bonds occurs without energy barrier. Conceivable competing
reactions, oxirane C–O and C–H activation, both proceed
via formation of a σ-complex, followed by small but significant
barriers for insertion steps. A reversible formation of the σ-complexes
would perfectly explain the observed reactivity. For an irreversible
formation, we find that intramolecular rearrangement of these σ-complexes
toward C–C activation products is faster than both C–O
and C–H activation. In principle, the same reactivity should
be expected for other monocoordinated platinum(0) phosphine complexes.
However, only the specific properties of dtbpm cause the subsequent,
rapid, and irreversible closing of the chelate ligand yielding stable,
square-planar Pt­(II) C–C activation products.