Tetranuclear Complexes Containing Quadruply Bonded Dimolybdenum Units Joined by μ-Hydride Ions

Two tetranuclear complexes of the type
[Mo2(DArF)3]2(μ-H)2,
DArF = N,N‘-diarylformamidinate,
Ar = p-tolyl (1) and p-anisyl
(2), have been prepared by reaction of
Mo2(DArF)3Cl2 and
NaHBEt3. The cores
are similar and show two quadruply bonded dimolybdenum units joined by
two hydrogen atoms. These are
the first structurally characterized tetranuclear molecules with
localized quadruple bonds and also the first
molecules with two independent M−(μ-H)−M units, in which each
metal atom is also bonded to another M
atom. It is remarkable that in each case the compound resists
hydrolysis by water but will react with HCl.
The δ → δ* transitions, which are normally the lowest energy
bands in the visible region of the electronic
absorption spectra, appear as shoulders at 449 and 444 nm for
1 and 2. However, each compound also
shows
two more transitions at lower energy (ca. 505 and 728 nm). These
bands have been assigned to transitions
involving the three center−two electron Mo−H−Mo
bridges.