A Dinuclear Palladium(I) Ethynyl Complex: Synthesis, Structure, and Dynamics

The reaction of Pd(η3-C3H5)2 with PiPr3 at −30 °C affords yellow crystals of the PdII complex
(iPr3P)Pd(η3-C3H5)(η1-C3H5) (1). At 20 °C 1 transforms into the dinuclear PdI complex
{(iPr3P)Pd}2(μ-C3H5)2 (2) due to oxidative C−C coupling of two allyl groups with elimination
of 1,5-hexadiene. Heating 1 or 2 in 1,6-heptadiene to 80 °C produces the Pd0 complex
(iPr3P)Pd(η2,η2-C7H12) (3). {(η3-C3H5)PdCl}2 reacts with iPr3P to give (iPr3P)Pd(η3-C3H5)Cl
(4b), from which further derivatives (iPr3P)Pd(η3-C3H5)X (X = OSO2CF3 (4a), C⋮CH (5a),
CH3 (5b)) are obtained by replacement reactions. The mononuclear PdII-acetylide 5a and
complex 3 combine to give the dinuclear PdI derivative {(iPr3P)Pd}2(μ-C3H5)(μ2-η2-C2H) (6).
The Pd−Pd bond in 6 is unsymmetrically bridged by a π-allyl and a σ−π-ethynyl group, as
determined by X-ray structure analysis. The structures of 1, 4a,b, and 6 are dynamic in
solution, with 1 undergoing an exchange of the binding modes of the π- and σ-coordinated
allyl groups and 4a,b displaying a π/σ-allyl group rearrangement, and in 6 the C⋮CH
substituent oscillates in its π-coordination from one PdI atom to the other.