28 research outputs found
Capacitance Performance of Subā2 nm Graphene Nanochannels in Aqueous Electrolyte
Molecular
dynamics simulations were used to explain the origin
and properties of electrical double-layer capacitance in short graphene
nanochannels with width below 2 nm. The results explain the previously
reported experimental result on the nonmonotonic dependence of the
capacitance with the channel width. The mechanism for the anomalous
increase of the capacitance in sub-1 nm in pore diameter is attributed
here to the width-dependent radial location of counterions in the
nanochannels and the restricted number of co-ions. Decrease of the
channel width lowers the number of co-ions and positions the counterions
closer to the channel walls. For nanochannels with width ranging from
1 to 2 nm, co-ions are allowed to enter the nanochannel, and both
types of ions assume alternating layered distributions leading to
the decrease of the capacitance. Voltage is another control parameter
which allows understanding capacitance in graphene nanochannels. As
the voltage increases, due to limited space near the charged surface,
more counterions need to be located in the center of the nanochannel,
resulting in further capacitance decrease
Intramolecular CāH Bond Activation in Bridged Dicyclopentadienyl Dimethyl Dinuclear Complexes
Photolysis
of the doubly bridged dicyclopentadienyl dimethyl dinuclear
complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀM<sub>2</sub>(CO)<sub>4</sub>Me<sub>2</sub> (M = Ru, R = H (<b>2a</b>), <sup><i>t</i></sup>Bu (<b>2b</b>); M = Fe, R = H (<b>2c</b>)) in benzene
yields the corresponding methylene-bridged complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀM<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)Ā(Ī¼-CH<sub>2</sub>) (<b>3a</b>ā<b>c</b>) and the MāM-bonded
complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀM<sub>2</sub>(CO)<sub>4</sub> (<b>1a</b>ā<b>c</b>). Irradiation of the analogous diethyl
complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀRu<sub>2</sub>(CO)<sub>4</sub>Et<sub>2</sub> (<b>4</b>) affords only <b>1a</b>. Unlike the
case for the doubly bridged complexes, photolysis of the singly bridged
dicyclopentadienyl dimethyl diruthenium complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(EMe<sub>2</sub>)]ĀRu<sub>2</sub>(CO)<sub>4</sub>Me<sub>2</sub> (E = C (<b>5a</b>); E
= Si (<b>5b</b>)) in benzene yields the corresponding ātwistedā
ruthenium methyl complexes with a cyclopentadienylāRu Ļ
bond (Ī·<sup>5</sup>,Ī·<sup>5</sup>:Ī·<sup>1</sup>-C<sub>5</sub>H<sub>4</sub>(EMe<sub>2</sub>)ĀC<sub>5</sub>H<sub>3</sub>)Ā[RuĀ(CO)<sub>2</sub>]Ā[RuĀ(CO)<sub>2</sub>Me] (<b>6a</b>,<b>b</b>) and
the similar phenyl complexes (Ī·<sup>5</sup>,Ī·<sup>5</sup>:Ī·<sup>1</sup>-C<sub>5</sub>H<sub>4</sub>(EMe<sub>2</sub>)ĀC<sub>5</sub>H<sub>3</sub>)Ā[RuĀ(CO)<sub>2</sub>]Ā[RuĀ(CO)<sub>2</sub>Ph] (<b>7a</b>,<b>b</b>), from reaction with the benzene solvent.
Plausible mechanisms for the formation of the different types of products
are proposed involving intramolecular CāH bond activation.
The molecular structures of <b>2a</b>,<b>c</b>, <b>3a</b>,<b>c</b>, <b>4</b>, <b>5a</b>, <b>6a</b>, and <b>7b</b>, determined by X-ray diffraction,
are also presented
Effect of user mobility and channel fading on the outage performance of UAV communications
Many wireless networks operate in a mobile environment with randomly moving user terminals. This letter analytically characterizes the impact of ground user mobility, propagation environment and channel fading on the outage performance of unmanned aerial vehicle (UAV) communications. Closed-form expressions for the outage probability using the random waypoint model for ground user mobility, UAV channel models for different propagation environments and the Nakagami- {m} model for fading channels are derived. Furthermore, the outage analysis takes into account the effect of co-channel interference by both the stationary and mobile users. Numerical results are presented to demonstrate the interplay between the communication performance and the system parameters
Intramolecular CāH Bond Activation in Bridged Dicyclopentadienyl Dimethyl Dinuclear Complexes
Photolysis
of the doubly bridged dicyclopentadienyl dimethyl dinuclear
complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀM<sub>2</sub>(CO)<sub>4</sub>Me<sub>2</sub> (M = Ru, R = H (<b>2a</b>), <sup><i>t</i></sup>Bu (<b>2b</b>); M = Fe, R = H (<b>2c</b>)) in benzene
yields the corresponding methylene-bridged complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀM<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)Ā(Ī¼-CH<sub>2</sub>) (<b>3a</b>ā<b>c</b>) and the MāM-bonded
complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀM<sub>2</sub>(CO)<sub>4</sub> (<b>1a</b>ā<b>c</b>). Irradiation of the analogous diethyl
complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub>R)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀRu<sub>2</sub>(CO)<sub>4</sub>Et<sub>2</sub> (<b>4</b>) affords only <b>1a</b>. Unlike the
case for the doubly bridged complexes, photolysis of the singly bridged
dicyclopentadienyl dimethyl diruthenium complexes [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(EMe<sub>2</sub>)]ĀRu<sub>2</sub>(CO)<sub>4</sub>Me<sub>2</sub> (E = C (<b>5a</b>); E
= Si (<b>5b</b>)) in benzene yields the corresponding ātwistedā
ruthenium methyl complexes with a cyclopentadienylāRu Ļ
bond (Ī·<sup>5</sup>,Ī·<sup>5</sup>:Ī·<sup>1</sup>-C<sub>5</sub>H<sub>4</sub>(EMe<sub>2</sub>)ĀC<sub>5</sub>H<sub>3</sub>)Ā[RuĀ(CO)<sub>2</sub>]Ā[RuĀ(CO)<sub>2</sub>Me] (<b>6a</b>,<b>b</b>) and
the similar phenyl complexes (Ī·<sup>5</sup>,Ī·<sup>5</sup>:Ī·<sup>1</sup>-C<sub>5</sub>H<sub>4</sub>(EMe<sub>2</sub>)ĀC<sub>5</sub>H<sub>3</sub>)Ā[RuĀ(CO)<sub>2</sub>]Ā[RuĀ(CO)<sub>2</sub>Ph] (<b>7a</b>,<b>b</b>), from reaction with the benzene solvent.
Plausible mechanisms for the formation of the different types of products
are proposed involving intramolecular CāH bond activation.
The molecular structures of <b>2a</b>,<b>c</b>, <b>3a</b>,<b>c</b>, <b>4</b>, <b>5a</b>, <b>6a</b>, and <b>7b</b>, determined by X-ray diffraction,
are also presented
Reactions of SnMe<sub>2</sub>-Bridged Bis(cyclopentadienes) with Iron Pentacarbonyl: Migration of the SnMe<sub>2</sub> Group
In reactions of the singly bridged bisĀ(cyclopentadiene)
(SnMe<sub>2</sub>)Ā(<sup><i>t</i></sup>BuC<sub>5</sub>H<sub>4</sub>)<sub>2</sub> (<b>1</b>) or the doubly bridged bisĀ(cyclopentadienes)
(SiMe<sub>2</sub>)Ā(SnMe<sub>2</sub>)Ā(RC<sub>5</sub>H<sub>3</sub>)<sub>2</sub> (R = H (<b>2</b>), R = <sup><i>t</i></sup>Bu (<b>3</b>)) with FeĀ(CO)<sub>5</sub> in refluxing xylene,
the bridging SnMe<sub>2</sub> group migrates from the ligand to the
iron atoms to give compounds (<b>5</b>, <b>7</b>, <b>9a</b>,<b>b</b>) containing the FeāSnāFe units,
together with the corresponding destannylated products (<b>6</b>, <b>8</b>, <b>10a</b>,<b>b</b>); the bridging
SiMe<sub>2</sub> group (in <b>2</b> and <b>3</b>) does
not migrate. However, in the reaction of the doubly bridged ligand
(GeMe<sub>2</sub>)Ā(SnMe<sub>2</sub>)Ā(C<sub>5</sub>H<sub>4</sub>)<sub>2</sub> (<b>4</b>) with FeĀ(CO)<sub>5</sub>, the SnMe<sub>2</sub> group undergoes a similar migration to produce the complex GeMe<sub>2</sub>[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)<sub>2</sub>]<sub>2</sub>SnMe<sub>2</sub> (<b>12</b>), containing
the FeāSnāFe unit, both SnMe<sub>2</sub> and GeMe<sub>2</sub> groups migrate from the ligand to the iron atoms to yield
the product [(GeMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)<sub>2</sub>]Ā[(SnMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)<sub>2</sub>] (<b>11</b>),
containing one FeāGe bond and one FeāSn bond, or the
SnMe<sub>2</sub> group is cleaved to afford the destannylation product
GeMe<sub>2</sub>[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)]<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>13</b>). The stability
of complexes <b>5</b>, <b>7</b>, and <b>12</b> containing
the FeāSnāFe unit toward heat and light was also studied.
The molecular structures of <b>9a</b>,<b>b</b>, <b>11</b>, and <b>12</b> were determined by X-ray diffraction
Direction Dependence of Resistive-Pulse Amplitude in Conically Shaped Mesopores
Conically
shaped pores such as glass pipets as well as asymmetric
pores in polymers became an important analytics tool used for the
detection of molecules, viruses, and particles. Electrokinetic or
pressure driven passage of single particles through a single pore
causes a transient change of the transmembrane current, called a resistive-pulse,
whose amplitude is the measure of the particle volume. The shape of
the pulse reflects the pore topography, and in a conical pore, resistive
pulses have a shape of a tick point. Passage of particles in both
directions was reported to produce pulses of the same amplitude and
shapes that are mirror images of each other. In this manuscript we
identify conditions at which the amplitude of resistive-pulses in
a conical mesopore is direction dependent. Neutral particles entering
the pore from the larger entrance of a conical pore, called the base,
block the current to a larger extent than the particles traveling
in the opposite direction. Negatively charged particles on the other
hand size larger when being transported in the direction from tip
to base. The findings are explained via voltage-regulated ionic concentrations
in the pore such that for one voltage polarity a weak depletion zone
is formed, which increases the current blockage caused by a particle.
For the opposite polarity, an enhancement of ionic concentrations
was predicted. The findings reported here are of crucial importance
for the resistive-pulse technique, which relates the current blockage
with the size of the passing object
Reactions of SnMe<sub>2</sub>-Bridged Bis(cyclopentadienes) with Iron Pentacarbonyl: Migration of the SnMe<sub>2</sub> Group
In reactions of the singly bridged bisĀ(cyclopentadiene)
(SnMe<sub>2</sub>)Ā(<sup><i>t</i></sup>BuC<sub>5</sub>H<sub>4</sub>)<sub>2</sub> (<b>1</b>) or the doubly bridged bisĀ(cyclopentadienes)
(SiMe<sub>2</sub>)Ā(SnMe<sub>2</sub>)Ā(RC<sub>5</sub>H<sub>3</sub>)<sub>2</sub> (R = H (<b>2</b>), R = <sup><i>t</i></sup>Bu (<b>3</b>)) with FeĀ(CO)<sub>5</sub> in refluxing xylene,
the bridging SnMe<sub>2</sub> group migrates from the ligand to the
iron atoms to give compounds (<b>5</b>, <b>7</b>, <b>9a</b>,<b>b</b>) containing the FeāSnāFe units,
together with the corresponding destannylated products (<b>6</b>, <b>8</b>, <b>10a</b>,<b>b</b>); the bridging
SiMe<sub>2</sub> group (in <b>2</b> and <b>3</b>) does
not migrate. However, in the reaction of the doubly bridged ligand
(GeMe<sub>2</sub>)Ā(SnMe<sub>2</sub>)Ā(C<sub>5</sub>H<sub>4</sub>)<sub>2</sub> (<b>4</b>) with FeĀ(CO)<sub>5</sub>, the SnMe<sub>2</sub> group undergoes a similar migration to produce the complex GeMe<sub>2</sub>[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)<sub>2</sub>]<sub>2</sub>SnMe<sub>2</sub> (<b>12</b>), containing
the FeāSnāFe unit, both SnMe<sub>2</sub> and GeMe<sub>2</sub> groups migrate from the ligand to the iron atoms to yield
the product [(GeMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)<sub>2</sub>]Ā[(SnMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)<sub>2</sub>] (<b>11</b>),
containing one FeāGe bond and one FeāSn bond, or the
SnMe<sub>2</sub> group is cleaved to afford the destannylation product
GeMe<sub>2</sub>[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀFeĀ(CO)]<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>13</b>). The stability
of complexes <b>5</b>, <b>7</b>, and <b>12</b> containing
the FeāSnāFe unit toward heat and light was also studied.
The molecular structures of <b>9a</b>,<b>b</b>, <b>11</b>, and <b>12</b> were determined by X-ray diffraction
Reactions of Doubly SiMe<sub>2</sub>-Bridged Bis(cyclopentadienyl) Complexes of Molybdenum and Iron Carbonyls: Competitive Ring-to-Metal Migrations of Hydrogen and SiMe<sub>2</sub>
Reaction of the doubly bridged bisĀ(cyclopentadiene) (C<sub>5</sub>H<sub>4</sub>(SiMe<sub>2</sub>))<sub>2</sub> (<b>1</b>) with
MoĀ(CO)<sub>6</sub> in refluxing xylene gave the corresponding dinuclear
molybdenum carbonyl complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>3</b>) and the desilylated product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>6</b>), together with the singly
SiMe<sub>2</sub>SiMe<sub>2</sub>-bridged dinuclear molybdenum product
[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>SiMe<sub>2</sub>)]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>5</b>) and the novel complex [(SiMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀMoĀ(CO)<sub>3</sub>]<sub>2</sub> (<b>4</b>) containing two MoāSi bonds. This diversity of products is
caused by similar ring-to-metal migrating abilities of the hydrogen
and SiMe<sub>2</sub> groups and their competitive migration during
the reactions. Reaction of the dihydride <i>cis</i>-[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀMo<sub>2</sub>(CO)<sub>6</sub>(H)<sub>2</sub> (<b>7c</b>) in refluxing xylene also afforded the above products except <b>4</b>, which suggests that <b>7c</b> might be intermediate
precursor to <b>3</b>, <b>5</b>, and <b>6</b>. Similar
treatment of substituted doubly bridged bisĀ(cyclopentadiene) (C<sub>5</sub>H<sub>3</sub><sup><i>t</i></sup>BuĀ(SiMe<sub>2</sub>))<sub>2</sub> (<b>2</b>) with MoĀ(CO)<sub>6</sub> provided
the corresponding derivatives (<b>8</b>ā<b>10</b>) of the above products and the product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub><sup><i>t</i></sup>Bu)ĀMoĀ(CO)<sub>3</sub>]<sub>2</sub> (<b>11</b>), in which both SiMe<sub>2</sub> groups
are removed. Heating a mixture of <b>1</b> and FeĀ(CO)<sub>5</sub> in xylene yielded the normal dinuclear iron complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀFe<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>12</b>) and the desilylated product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)]ĀFe<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>14</b>), together
with the novel complex (SiMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)Ā(Ī·<sup>5</sup>:Ī·<sup>1</sup>-C<sub>5</sub>H<sub>3</sub>)Ā[(SiMe<sub>2</sub>)ĀFeĀ(CO)<sub>2</sub>]Ā[FeĀ(CO)<sub>2</sub>)] (<b>13</b>) containing one FeāSi bond. However,
similar treatment of <b>2</b> with FeĀ(CO)<sub>5</sub> provided
only the corresponding dinuclear complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub><sup><i>t</i></sup>Bu)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀFe<sub>2</sub>(CO)<sub>4</sub> (<b>15</b>), in which the FeāFe bond (2.8205(9) Ć
) is the longest
among all dimeric Cpā²<sub>2</sub>Fe<sub>2</sub>(CO)<sub>4</sub> analogues. A plausible mechanism for the formation of the different
types of products is proposed. Molecular structures of <b>4</b>, <b>9c</b>, <b>13</b>, and <b>15</b> determined
by X-ray diffraction are also presented
Reactions of Doubly SiMe<sub>2</sub>-Bridged Bis(cyclopentadienyl) Complexes of Molybdenum and Iron Carbonyls: Competitive Ring-to-Metal Migrations of Hydrogen and SiMe<sub>2</sub>
Reaction of the doubly bridged bisĀ(cyclopentadiene) (C<sub>5</sub>H<sub>4</sub>(SiMe<sub>2</sub>))<sub>2</sub> (<b>1</b>) with
MoĀ(CO)<sub>6</sub> in refluxing xylene gave the corresponding dinuclear
molybdenum carbonyl complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>3</b>) and the desilylated product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>6</b>), together with the singly
SiMe<sub>2</sub>SiMe<sub>2</sub>-bridged dinuclear molybdenum product
[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>SiMe<sub>2</sub>)]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>5</b>) and the novel complex [(SiMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀMoĀ(CO)<sub>3</sub>]<sub>2</sub> (<b>4</b>) containing two MoāSi bonds. This diversity of products is
caused by similar ring-to-metal migrating abilities of the hydrogen
and SiMe<sub>2</sub> groups and their competitive migration during
the reactions. Reaction of the dihydride <i>cis</i>-[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀMo<sub>2</sub>(CO)<sub>6</sub>(H)<sub>2</sub> (<b>7c</b>) in refluxing xylene also afforded the above products except <b>4</b>, which suggests that <b>7c</b> might be intermediate
precursor to <b>3</b>, <b>5</b>, and <b>6</b>. Similar
treatment of substituted doubly bridged bisĀ(cyclopentadiene) (C<sub>5</sub>H<sub>3</sub><sup><i>t</i></sup>BuĀ(SiMe<sub>2</sub>))<sub>2</sub> (<b>2</b>) with MoĀ(CO)<sub>6</sub> provided
the corresponding derivatives (<b>8</b>ā<b>10</b>) of the above products and the product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub><sup><i>t</i></sup>Bu)ĀMoĀ(CO)<sub>3</sub>]<sub>2</sub> (<b>11</b>), in which both SiMe<sub>2</sub> groups
are removed. Heating a mixture of <b>1</b> and FeĀ(CO)<sub>5</sub> in xylene yielded the normal dinuclear iron complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀFe<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>12</b>) and the desilylated product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)]ĀFe<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>14</b>), together
with the novel complex (SiMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)Ā(Ī·<sup>5</sup>:Ī·<sup>1</sup>-C<sub>5</sub>H<sub>3</sub>)Ā[(SiMe<sub>2</sub>)ĀFeĀ(CO)<sub>2</sub>]Ā[FeĀ(CO)<sub>2</sub>)] (<b>13</b>) containing one FeāSi bond. However,
similar treatment of <b>2</b> with FeĀ(CO)<sub>5</sub> provided
only the corresponding dinuclear complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub><sup><i>t</i></sup>Bu)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀFe<sub>2</sub>(CO)<sub>4</sub> (<b>15</b>), in which the FeāFe bond (2.8205(9) Ć
) is the longest
among all dimeric Cpā²<sub>2</sub>Fe<sub>2</sub>(CO)<sub>4</sub> analogues. A plausible mechanism for the formation of the different
types of products is proposed. Molecular structures of <b>4</b>, <b>9c</b>, <b>13</b>, and <b>15</b> determined
by X-ray diffraction are also presented
Reactions of Doubly SiMe<sub>2</sub>-Bridged Bis(cyclopentadienyl) Complexes of Molybdenum and Iron Carbonyls: Competitive Ring-to-Metal Migrations of Hydrogen and SiMe<sub>2</sub>
Reaction of the doubly bridged bisĀ(cyclopentadiene) (C<sub>5</sub>H<sub>4</sub>(SiMe<sub>2</sub>))<sub>2</sub> (<b>1</b>) with
MoĀ(CO)<sub>6</sub> in refluxing xylene gave the corresponding dinuclear
molybdenum carbonyl complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>3</b>) and the desilylated product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>6</b>), together with the singly
SiMe<sub>2</sub>SiMe<sub>2</sub>-bridged dinuclear molybdenum product
[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>SiMe<sub>2</sub>)]ĀMo<sub>2</sub>(CO)<sub>6</sub> (<b>5</b>) and the novel complex [(SiMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)ĀMoĀ(CO)<sub>3</sub>]<sub>2</sub> (<b>4</b>) containing two MoāSi bonds. This diversity of products is
caused by similar ring-to-metal migrating abilities of the hydrogen
and SiMe<sub>2</sub> groups and their competitive migration during
the reactions. Reaction of the dihydride <i>cis</i>-[(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀMo<sub>2</sub>(CO)<sub>6</sub>(H)<sub>2</sub> (<b>7c</b>) in refluxing xylene also afforded the above products except <b>4</b>, which suggests that <b>7c</b> might be intermediate
precursor to <b>3</b>, <b>5</b>, and <b>6</b>. Similar
treatment of substituted doubly bridged bisĀ(cyclopentadiene) (C<sub>5</sub>H<sub>3</sub><sup><i>t</i></sup>BuĀ(SiMe<sub>2</sub>))<sub>2</sub> (<b>2</b>) with MoĀ(CO)<sub>6</sub> provided
the corresponding derivatives (<b>8</b>ā<b>10</b>) of the above products and the product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub><sup><i>t</i></sup>Bu)ĀMoĀ(CO)<sub>3</sub>]<sub>2</sub> (<b>11</b>), in which both SiMe<sub>2</sub> groups
are removed. Heating a mixture of <b>1</b> and FeĀ(CO)<sub>5</sub> in xylene yielded the normal dinuclear iron complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀFe<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>12</b>) and the desilylated product [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)]ĀFe<sub>2</sub>(CO)<sub>2</sub>(Ī¼-CO)<sub>2</sub> (<b>14</b>), together
with the novel complex (SiMe<sub>2</sub>)Ā(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>)Ā(Ī·<sup>5</sup>:Ī·<sup>1</sup>-C<sub>5</sub>H<sub>3</sub>)Ā[(SiMe<sub>2</sub>)ĀFeĀ(CO)<sub>2</sub>]Ā[FeĀ(CO)<sub>2</sub>)] (<b>13</b>) containing one FeāSi bond. However,
similar treatment of <b>2</b> with FeĀ(CO)<sub>5</sub> provided
only the corresponding dinuclear complex [(Ī·<sup>5</sup>-C<sub>5</sub>H<sub>2</sub><sup><i>t</i></sup>Bu)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>]ĀFe<sub>2</sub>(CO)<sub>4</sub> (<b>15</b>), in which the FeāFe bond (2.8205(9) Ć
) is the longest
among all dimeric Cpā²<sub>2</sub>Fe<sub>2</sub>(CO)<sub>4</sub> analogues. A plausible mechanism for the formation of the different
types of products is proposed. Molecular structures of <b>4</b>, <b>9c</b>, <b>13</b>, and <b>15</b> determined
by X-ray diffraction are also presented