Self-Activation of a Cluster-Bound Alkyne toward
Carbon−Carbon Bond Forming Reactions
Soa Rivomanana
Carole Mongin
Guy Lavigne
10.1021/om950835w.s001
https://acs.figshare.com/articles/journal_contribution/Self-Activation_of_a_Cluster-Bound_Alkyne_toward_Carbon_Carbon_Bond_Forming_Reactions/3776751
The methanol-catalyzed elimination of Cl<sup>-</sup> from the
“activated” anionic species
[PPN][Ru<sub>3</sub>(μ-Cl)(μ-PhCCPh)(CO)<sub>9</sub>] (<b>1</b>) in the
presence of bis(diphenylphosphino)methane (dppm)
constitutes a rational high-yield route (>90%) to either the unique
unsaturated 46-e (alkyne)triruthenium cluster,
Ru<sub>3</sub>(μ-PhCCPh)(CO)<sub>7</sub>(dppm)
(<b>2</b>), or its 48-e CO adduct,
Ru<sub>3</sub>(μ-PhCCPh)(CO)<sub>8</sub>(dppm) (<b>3</b>). Whereas the CO-induced
conversion of <b>2</b> into <b>3</b> is complete within
few
seconds at 25 °C under 1 atm of CO, the reverse transformation takes
1 h at 80 °C. The
X-ray structure analysis of <b>2</b> is reported, revealing a
perpendicular conformation of the alkyne
relative to the metal triangle. The high reactivity of
<b>2</b> is substantiated by a high chemical
reactivity toward 2-e donors. Its reaction with 1 equiv of dppm
(25 °C, 3 h) leads to the
bis-dppm-substituted complex,
Ru<sub>3</sub>(μ-PhCCPh)(CO)<sub>6</sub>(dppm)<sub>2</sub>
(<b>4</b>) (53% yield). Reaction of
<b>2</b>
with hydrogen gas (1 atm, 25 °C, 10 min) yields the dihydrido
species,
Ru<sub>3</sub>(μ-H)<sub>2</sub>(μ-PhCCPh)(CO)<sub>7</sub>(dppm) (<b>5</b>) (89% yield) existing as a
mixture of two isomers differing in the orientation
of the alkyne relative to the edge-bridging dppm ligand. Complex
<b>2</b> reacts with a terminal
alkyne like phenylacetylene under mild conditions to afford a mixture
of the “fly-over” type
compound
Ru<sub>3</sub>{μ-HCC(Ph)C(O)(Ph)CCPh}(dppm)(CO)<sub>6</sub>
(<b>6</b>) (57% yield) and the diruthenacyclopentadiene derivative
Ru<sub>2</sub>{μ-HCC(Ph)(Ph)CCPh}(μ-dppm)(CO)<sub>4</sub>
(<b>7</b>) (20% yield). The
structure of <b>6</b> reveals the occurrence of a disymmetric
edge-bridging dialkenyl ketone ligand
HCC(Ph)C(O)(Ph)CCPh, resulting from regioselective
coupling between the two alkynes
and a carbonyl group. The formal unsaturation of <b>6</b> is
masked by a weak interaction between
the terminal C−Ph bond of the organic chain and one of the metal
centers. Facile loss of
this interaction is induced by mild thermolysis of <b>6</b>.
As a consequence, free rotation of the
organic moiety around the metal−metal edge brings the opposite end of
the organic chain
(i.e., the C−H bond) close to the opposite face, thereby favoring CH
activation to convert
the alkenyl end into a vinylidene. This leads to quantitative
formation of the vinylidene
alkenyl ketone derivative,
Ru<sub>3</sub>(μ-H){μ-CC(Ph)C(O)(Ph)CCPh}(dppm)(CO)<sub>6</sub>
(<b>8</b>) (94% yield).
The X-ray structure of <b>8</b> is reported. Unsuccessful
attempts to release the organic moiety
from the cluster core are described. The reaction of a THF
solution of <b>6</b> with CO in a reactor
[<i>P</i>(CO) = 10 atm, <i>T</i> = 80 °C] leads to the
new binuclear “fly-over” species
Ru<sub>2</sub>{μ-HCC(Ph)C(O)(Ph)CCPh}(CO)<sub>6</sub> (<b>9a</b>), thereby
indicating that elimination of the edge-bridging dppm and
cluster fragmentation are more favorable than elimination of a free
ketone from the intact
cluster. The X-ray structure of
Ru<sub>2</sub>{μ-HCC(C<sub>3</sub>H<sub>7</sub>)C(O)(Ph)CCPh}(CO)<sub>6</sub>
(<b>9b</b>) (resulting from
the coupling between diphenylacetylene and 1-pentyne) is reported.
1996-02-20 00:00:00
Ru
metal triangle
Unsuccessful attempts
chemical reactivity
dppm
THF solution
carbonyl group
10 min
vinylidene alkenyl ketone
HC
cluster core
dihydrido species
9 b
PhCCPh
HCC
Complex 2
1 atm
3 h
CO
1 equiv
terminal alkyne
1 h
CH activation
10 atm
PPN
metal centers
cluster fragmentation
alkenyl end
Facile loss