Synthesis, Structure, and Protonation Studies of
Cp*MH<sub>3</sub>(dppe) (M = Mo, W). Pseudo-Trigonal-Prismatic
vs Pseudo-Octahedral Structures for Half-Sandwich
Group 6 M(IV) Derivatives
Brett Pleune
Rinaldo Poli
James C. Fettinger
10.1021/om961002o.s003
https://acs.figshare.com/articles/dataset/Synthesis_Structure_and_Protonation_Studies_of_Cp_MH_sub_3_sub_dppe_M_Mo_W_Pseudo-Trigonal-Prismatic_vs_Pseudo-Octahedral_Structures_for_Half-Sandwich_Group_6_M_IV_Derivatives/3779145
The compounds Cp*MH<sub>3</sub>(dppe) (M = Mo,
<b>1</b>; W, <b>2</b>) are accessible in good yields from
reacting
the corresponding compound Cp*MCl<sub>4</sub> and LiAlH<sub>4</sub>
in toluene/Et<sub>2</sub>O followed by methanolysis.
The X-ray structure of <b>1</b> shows a
pseudo-trigonal-prismatic geometry which is unprecedented
for half-sandwich CpML<sub>5</sub>-type compounds. Protonation
with HBF<sub>4</sub>·Et<sub>2</sub>O in Et<sub>2</sub>O at
low
temperature affords
[Cp*MH<sub>4</sub>(dppe)]<sup>+</sup>BF<sub>4</sub><sup>-</sup>
salts (M = Mo, <b>3</b>; W, <b>4</b>). While
<b>3</b> spontaneously
decomposes, even at low temperatures, in coordinating solvents and
CH<sub>2</sub>Cl<sub>2</sub>, <b>4</b> is stable
at
room temperature in MeCN. An X-ray structure of <b>4</b> is
consistent with a classical
tetrahydrido species with a distorted pseudo-pentagonal-bipyramidal
structure. The low-temperature NMR properties, <i>J</i><sub>HD</sub> ≤ 1 Hz for
<b>4</b>-<i>d</i><sub>3</sub>, and the
<i>T</i><sub>1(min)</sub> value for the hydride
resonance are also consistent with this structural assignment.
Decomposition of <b>3</b> in MeCN
at room temperature selectively affords
[Cp*MoH<sub>2</sub>(MeCN)(dppe)]<sup>+</sup>BF<sub>4</sub><sup>-</sup>,
<b>5</b>. The NMR
properties of this complex indicate a fluxional structure with
inequivalent H and P nuclei
and are consistent with a pseudo-trigonal-prismatic structure analogous
to that of the
precursor <b>1</b>. Further protonation of <b>5</b> in
MeCN or direct protonation of <b>1</b> with excess
acid
in MeCN affords two isomers of complex
[Cp*MoH(MeCN)<sub>2</sub>(dppe)](BF<sub>4</sub>)<sub>2</sub>,
<b>6</b> and <b>7</b>. Thermal
treatment in MeCN slowly converts <b>7</b> into <b>6</b>
initially, but both isomers further transform
into a third isomer, <b>8</b>, upon prolonged heating. The
structure of <b>6</b> has been elucidated by
X-ray crystallography and consists of a highly distorted
pseudo-octahedral geometry with
relative <i>trans</i> MeCN ligands. The structures of
<b>7</b> and <b>8</b> and mechanisms of the
interconversions between the various isomeric structures are proposed on the
basis of the solution
NMR studies.
1997-04-15 00:00:00
HBF
dppe
BF 4
compound
trans MeCN ligands
HD
solution NMR studies
Mo
Et 2 O
Cp
CH 2 Cl 2
NMR properties
room temperature