Metal−Metal Multiply-Bonded Complexes of Technetium. 3. Preparation and Characterization of Phosphine Complexes of Technetium Possessing a Metal−Metal Bond Order of 3.5

Two new ditechnetium complexes possessing Tc−Tc bonds with a
formal bond order of 3.5 have been prepared
in high yield. Mild chemical oxidation of
Tc2Cl4(PMe2Ph)4
with ferrocenium hexafluorophosphate in acetonitrile
produces
[Tc2Cl4(PMe2Ph)4][PF6]
(1) in 82% yield. One-electron oxidation of
Tc2Cl4(PMe2Ph)4
by ferrocenium
hexafluorophosphate in the presence of ppnCl (ppn =
bis(triphenylphosphine)iminium) yielded the
neutral
compound
Tc2Cl5(PMe2Ph)3
(2) in 89% yield. Both species are paramagnetic, as
evidenced by EPR spectroscopy,
and possess a σ2π4δ2δ*
ground state electronic configuration on the basis of structural and
spectroscopic data.
The solid state structures of three forms of 1 have
been investigated by X-ray crystallography together with
the
structure of 2. The crystallographic parameters for
these structures are as follows: 
[Tc2Cl4(PMe2Ph)4][PF6]
(1a,
orthorhombic form), C2221 with a =
9.448(1) Å, b = 24.299(1) Å, c =
18.231(1) Å, V = 4185.4(6) Å3, and
Z
= 4;
[Tc2Cl4(PMe2Ph)4][PF6]
(1b, monoclinic form),
P21/n with a =
12.799(4) Å, b = 18.254(2) Å, c =
17.945(5) Å, β = 96.39(1)°, V = 4166(2)
Å3, and Z = 4;
[Tc2Cl4(PMe2Ph)4][PF6]·1/2THF
(1·1/2THF),
P21/c with a
=
10.580(3) Å, b = 33.327(3) Å, c =
13.861(5) Å, β = 111.04(2)°, V =
4562(1) Å3, and Z = 4;
Tc2Cl5(PMe2Ph)3
(2), P21/c with
a = 11.134(1) Å, b = 14.406(1) Å,
c = 19.501(5) Å, β = 98.144(6)°,
V = 3096.3(7) Å3, and
Z
= 4. The cation in 1 is the 1,3,6,8-isomer, and the
molecule in 2 is the 1,3,6-isomer. The Tc−Tc bond
lengths
for 1a, 1b,
1·1/2THF, and 2
(2.1092(9), 2.106(1), 2.1073(8), and 2.1092(4) Å,
respectively) are slightly shorter
than those of the corresponding
Tc2Cl4(PR3)4
complexes, consistent with the removal of one electron from a
δ*
orbital. Electrochemical studies reveal that both compounds are
capable of undergoing a one-electron oxidation
and a one-electron reduction to yield the respective
Tc26+ and Tc24+
dinuclear cores. IR, EPR, and UV−vis
spectroscopic data are presented for compounds 1 and
2.