346
P
-l-H +
- H
~b
÷
(a)
(b)
Fig. 6. Molecular structures of [H2Os6(CO)IsPPh2C6H4]- (a) and [H3Os6(CO)IsPPh~C6H4] (b).
reaction with MeaNO produces, in addition to the expected anion
[HOs6(CO)16PPh3]-, a mixture of other anionic species of which a brown product is
the major component. The IR spectrum of this product, as the Et4N+ salt, is similar
to that of [HOs6(CO)16PPh3]-, however, the 1H NMR spectrum shows two broad
hydride signals at 8 8.83 and 8 13.52. On cooling to 260 K, these signals are
resolved into a singlet and a doublet (J(alP-1H)= 9.5 Hz) resonance respectively.
In the phenyl region of the spectrum, a set of three coupled resonances each
integrating for one proton, as well as a complex multiplet integrating for eleven
protons is observed. The coupled phenyl resonances resemble part of the ABCD
spin pattern expected for protons in an asymmetrically ortho-substituted C6H4 ring.
Assuming that the fourth resonance for the C~H4 ring proton is concealed by the
multiplet due to the other phenyl protons (as the integration of the phenyl region
suggests) the ~H NMR spectrum of this compound is consistent with its formulation
as the orthometallated anionic species [H2Os6(CO)ls(PPh2C6H4)]-. This species,
which is isoelectronic with [Os6(CO)lTPPh3] and the orthometallated species,
[HOs6(CO)16(C6H4N)], is proposed to have the bicapped tetrahedral structure
shown in Fig. 6a. The hydrido positions shown in the figure have not been
established with certainity; however, comparison with the structure of
[HOs6(CO)16(C6H4N)] leads us to suggest that shown in 6a. Such a structure is
consistent with our reported data.
Acidification of this anion with HBF4• Et20 produces a neutral red compound
which is formulated as [HaOs6(CO)ls(PPh2C6H4)] [Fig. 6b] on the basis of its
spectroscopic data (Table 1). Again, the precise location of the hydrido ligands has
not been established and their location in 6b follows from the proposed structure of
the dihydrido species 6a and is again consistent with our recorded data. Similar
orthometallated compounds are also obtained on reaction of [Os6(CO)I7L] (L-~
PPh2Me, AsPh3, As(p-tol)3 or SbPh3) with MeaNO (1:2) in CH2C12, in addition
to the expected anion [HOs6(CO)16L]-.
Fluxional behaviour and the proposed structure of the anion [HOsn(CO)/aL] - in
solution
The 1H NMR spectrum of [HOs6(CO)16P(OMe)3]- shows a broad hydride
resonance (linewidth ca. 30 Hz) at 8 - 9.62 at room temperature which, on cooling
to 260 K, is resolved into a sharp doublet with two pairs of doublet lSTOs satellites
[J(187Os-lH) ---- 32.2 Hz, 52.30 Hz]. This low temperature spectrum is consistent
Johnson, Brian F. G.
