A Structural and Spectroscopic Investigation of Octahedral Platinum Bis(dithiolene)phosphine Complexes: Platinum Dithiolene Internal Redox Chemistry Induced by Phosphine Association
journal contribution
posted on 2014-09-02, 00:00 authored by P. Chandrasekaran, Angelique
F. Greene, Karen Lillich, Stephen Capone, Joel T. Mague, Serena DeBeer, James P. DonahueThe
complexes [Pt(mdt)2] (4; mdt = methyldithiolene,
[Me2C2S2]n−), [Pt(adt)2] (5; adt = p-anisyldithiolene, [(MeO-p-C6H4)2C2S2]n−), and [Pd(adt)2] (10) have been prepared
in yields of ≥90% via transmetalation reactions with the corresponding
[R2Sn(S2C2R′2)]
complexes (R = nBu, R′ = Me; R
= Me, R′ = −C6H4-p-OMe, 3). Intraligand C–S and C–Cchelate bond lengths (∼1.71 and ∼1.40 Å,
respectively) obtained by X-ray crystallography show these compounds
to be comprised of radical monoanions mdt•– and adt•–. The six-coordinate octahedral
adducts [Pt(adt)2(dppe)] [6; dppe = 1,2-bis(diphenylphosphino)ethane], trans-[Pt(adt)2(PMe3)2]
(8), and trans-[Pt(mdt)2(PMe3)2] (9) have also been prepared, and
crystal structures reveal dithiolene ligands that are fully reduced
ene-1,2-dithiolates (C–S and C–Cchelate =
∼1.77 and 1.35 Å, respectively). Reduction of the dithiolene
ligand thus occurs to accommodate the +IV oxidation state typical
of octahedral six-coordinate platinum. The cyclic voltammogram of 5 shows two fully reversible reductions at −0.11 and
−0.84 V in CH2Cl2 (vs Ag/AgCl), attributed
to successive (adt•– + e– → adt2–) processes, and a reversible oxidation
at +1.01 V. The cyclic voltammogram of 9 shows two reversible
oxidations at +0.38 and +0.86 V, which are assigned as successive
(adt2– → adt•– +
e–) oxidations. Consistent with their formulation
as having fully reduced dithiolene ligands, the UV–vis spectra
for 6, 8, and 9 show no low-energy
absorptions below 700 nm, and the S K-edge XAS spectra of 6 and 8 show dithiolene sulfur that is reduced relative
to that in 5. The introduction of PMe3 to 10 did not produce the palladium analogue of 8 but rather [Pd(adt)(PMe3)2] (11). The reaction of [PdCl2(PPh3)2] with Li2(mdt) produced a mixture of [Pd(mdt)(PPh3)2] (12, 20%) and [(Ph3P)Pd(μ-1,2-mdt-S,S′:S)2Pd(PPh3)] (13, 28%),
with the latter having C2 symmetry with
a Pd2S2 core structure folded along the S···S
axis.
