Synthesis and Structural Studies of Platinum Complexes Containing Monodentate, Bridging, and Chelating Formamidine Ligands

The reactions of K2PtCl4 with
N,N‘-diphenylformamidine (HDPhF) and
N,N‘-di-p-tolylformamidine
(HDTolF)
produce the trans square-planar compounds
PtCl2(HDPhF)2, 1a, and
PtCl2(HDTolF)2, 1b.
Compound 1a crystallizes
as yellow parallelepipeds in the space group
P21/c with two independent molecules
in the asymmetric unit and
unit cell dimensions a = 23.427(7) Å, b
= 16.677(6) Å, c = 12.980(4) Å, and β =
96.10(2)°. These compounds
are soluble in common organic solvents and have been used as starting
materials for the preparation of diplatinum
compounds. Treatment of 1a and 1b with NaOMe
and the halide abstraction reagent TlPF6 produces the
compounds
Pt2(μ-DArF)2(η2-DArF)2,
Ar = Ph (2a) and Tol (2b), respectively.
Compound 2a crystallizes as yellow rods in
the space group P1̄ with unit cell dimensions
a = 12.296(3) Å, b = 12.310(4) Å,
c = 15.374(4) Å, α = 90.75(2)°,
β = 91.02(2)°, and γ = 110.20(2)°. Compound
2b crystallizes with a molecule of THF, as yellow rods in
the
space group P21/c with a
= 17.883(3) Å, b = 14.517(3) Å, c
= 22.581(3) Å, and β = 98.17(1)°. These
compounds
contain two cis bridging formamidinato ligands and two formamidinato
ligands that are chelated to separate Pt
centers. Upon heating, they further react to give the tetrabridged
compounds Pt2(μ-DArF)4, Ar = Ph
(3a), Tol
(3b). Compound 3a crystallizes as orange
cubes in the cubic space group I432 with a =
19.671(1) Å. On going
from the bis-bridged, bis-chelate structure in 2a to the
tetrabridged structure in 3a, the metal−metal
separation
decreases from 2.910(1) to 2.649(1) Å. Both 2b
and 3b have been oxidized to give the
PtII−PtIII compound
Pt2(μ-DTolF)4(PF6),
4. Compound 4 crystallizes as cubes in the
tetragonal space group P4/ncc with a
= 14.392(1)
Å and c = 14.436(1) Å. The Pt−Pt distance in
4 is 2.5304(6) Å.