5 research outputs found
Synthesis and Characterization of Palladium(II) and Nickel(II) Alcoholate-Functionalized NHC Complexes and of Mixed Nickel(II)–Lithium(I) Complexes
No full textThe
synthesis of Pd(II) and Ni(II) alcohol-functionalized N-heterocyclic
carbene (NHC) complexes was explored to examine the possible influence
of the functional arm attached to the NHC backbone on their structure
and reactivity and, in the case of a Ni(II) complex, on its catalytic
properties in ethylene oligomerization. Starting from the alcohol-functionalized
imidazolium salt [ImDiPP(C<sub>2</sub>OH)]Cl (<b>2</b>), the
new functionalized NHC palladium(II) complex [PdCl(acac){ImDiPP(C<sub>2</sub>OH)-<i>C</i><sub>NHC</sub>}] (<b>3</b>) was
synthesized and fully characterized. Two byproducts, [PdCl{μ-ImDiPP(C<sub>2</sub>O)-<i>C</i><sub>NHC</sub><i>,O</i>}]<sub>2</sub> (<b>4</b>) and <i>trans</i>-[PdCl<sub>2</sub>{ImDiPP(C<sub>2</sub>OH)-<i>C</i><sub>NHC</sub>}<sub>2</sub>] (<b>5</b>), formed during the synthesis of <b>3</b>, were also fully characterized. Acids promoted the transformation
of <b>3</b> into the new C<sub>NHC</sub>-bound complex [PdCl(μ-Cl){ImDiPP(C<sub>2</sub>OH)-<i>C</i><sub>NHC</sub>}]<sub>2</sub> (<b>6</b>), unveiling the lability of the acac ligand and the resistance
of the Pd–NHC bond to acids. Complex <b>6</b> reacted
with a base to afford complex <b>4</b>, in which alkoxide coordination
to Pd(II) has occurred to generate a C<sub>NHC</sub>,O chelate. The
stability of <b>3</b> was also assessed under basic conditions,
and the new complex [Pd(acac){ImDiPP(C<sub>2</sub>O)-<i>C</i><sub>NHC</sub><i>,O</i>}] (<b>7</b>) was characterized.
The new nickel(II) alcoholate-functionalized NHC complex [NiCl{μ-ImDiPP(C<sub>2</sub>O)-<i>C</i><sub>NHC</sub><i>,O</i>}]<sub>2</sub> (<b>8</b>) was synthesized by the reaction of the imidazolium
salt <b>2</b> with <i>n</i>-BuLi and [NiCl<sub>2</sub>(dme)]. The reaction of <b>8</b> with HCl regenerates the imidazolium
and alcohol functions to give [ImDiPP(C<sub>2</sub>OH)]<sub>2</sub>[NiCl<sub>4</sub>] (<b>9</b>). The mixed-metal Ni(II)–Li(I)
complexes [Ni<sub>2</sub>{μ-ImDiPP(C<sub>2</sub>O)-<i>C</i><sub>NHC</sub>,μ<i>-O</i>}<sub>4</sub>Li]BF<sub>4</sub> (<b>10</b>), [Ni<sub>2</sub>{μ-ImDiPP(C<sub>2</sub>O)-<i>C</i><sub>NHC</sub>,μ<i>-O</i>}<sub>4</sub>Li]Cl
(<b>11</b>), and [Ni{ImDiPP(C<sub>2</sub>O)-<i>C</i><sub>NHC</sub>,μ-<i>O</i>}<sub>2</sub>LiBr] (<b>12</b>) were isolated and characterized. However, it was not possible
to synthesize a Ni(II) alcohol-functionalized NHC complex in high
yield. Small amounts of the square-planar complex [NiCl<sub>2</sub>{ImDiPP(C<sub>2</sub>OH)-<i>C</i><sub>NHC</sub>}<sub>2</sub>] (<b>13</b>) could be isolated, and this complex was characterized
by single-crystal X-ray diffraction. In <b>13</b>, only the
C<sub>NHC</sub> atom of the alcohol-functionalized NHC ligand is bound
to the metal. The structures of the imidazolium salt <b>2</b>·2H<sub>2</sub>O and of the complexes <b>3</b>, <b>4</b>, <b>4-polymorph</b>, <b>5</b>, <b>6</b>·CH<sub>2</sub>Cl<sub>2</sub>, and <b>8</b>–<b>13</b> were established by single-crystal X-ray diffraction
Bis(ether-functionalized NHC) Nickel(II) Complexes, <i>Trans</i> to <i>Cis</i> Isomerization Triggered by Water Coordination, and Catalytic Ethylene Oligomerization
No full textThe
new nickel(II) complexes containing NHC ligands N-substituted
by a CH<sub>2</sub>CH<sub>2</sub>OR ether group (R = Me or Ph) [NiCl<sub>2</sub>{ImMes(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>6</b>), [NiCl<sub>2</sub>{Im<i>n-</i>Bu(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>7</b>), [NiBr<sub>2</sub>{ImDiPP(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>8</b>), [NiBr<sub>2</sub>{ImMes(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>9</b>), [NiBr<sub>2</sub>{Im<i>n-</i>Bu(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>10</b>), NiBr<sub>2</sub>{ImMes(C<sub>2</sub>OPh)}<sub>2</sub>] (<b>18</b>), [NiI<sub>2</sub>{ImDiPP(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>21</b>),
[NiI<sub>2</sub>{ImMes(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>22</b>), and [NiI<sub>2</sub>{Im<i>n-</i>Bu(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>23</b>) were synthesized in good yields and fully
characterized by NMR spectroscopy and X-ray diffraction analysis.
The reaction conditions were optimized and further applied to thioether
or nonfunctionalized NHC ligands, affording [NiBr<sub>2</sub>{ImDiPP(C<sub>2</sub>SPh)}<sub>2</sub>] (<b>19</b>) and [NiBr<sub>2</sub>{ImDiPP(<i>n-</i>Bu)}<sub>2</sub>] (<b>20</b>), respectively.
Equilibria involving <i>syn/anti</i> isomers were unveiled
for complexes [NiCl<sub>2</sub>{ImDiPP(C<sub>2</sub>OMe)}<sub>2</sub>] (<b>5</b>), <b>6</b>–<b>10</b>, and <b>18</b>–<b>23</b>. Reactions of <b>6</b> and <b>20</b> with a halide abstractor afforded the dicationic aquo complexes <i>cis</i>-[Ni{ImMes(C<sub>2</sub>OMe)}<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>][PF<sub>6</sub>]<sub>2</sub> (<b>27</b>) and <i>cis</i>-[Ni{ImDiPP(<i>n-</i>Bu)}<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>][PF<sub>6</sub>]<sub>2</sub> (<b>28</b>), in which a <i>cis</i> arrangement of the carbene ligands
is evidenced, which contrasts with that in their precursors. These
molecules represent rare examples of nickel aquo NHC complexes and
of complexes with two <i>cis</i> monodentate NHC ligands.
The new complexes reported in this work (15 crystal structures) displayed
moderate activities as precatalysts for ethylene oligomerization and
favored dimerization
New Boron-Containing Molybdenum Imido Alkylidene Complexes for Linear Olefin Homometathesis
No full textThe new molybdenum imido alkylidene
complex Mo(N(2,6-<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>))(CHCMe<sub>2</sub>Ph)(NC<sub>4</sub>H<sub>2</sub>Me<sub>2</sub>)(OB(Mes)<sub>2</sub>) (<b>1</b>;<b> </b>Mes =
2,4,6-MePh) containing both boroxide and pyrrolide
ligands is reported. Its formation results from the reaction between
bis(mesityl)borinic acid ((Mes)<sub>2</sub>BOH) and the bis-pyrrolide
Schrock-type precursor Mo(N-2,6-<i>i</i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)(CHCMe<sub>2</sub>Ph)(NC<sub>4</sub>H<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>. The complex was fully characterized
by <sup>1</sup>H, <sup>13</sup>C, <sup>11</sup>B, and <sup>95</sup>Mo NMR spectroscopy, X-ray diffraction, and elemental analysis. Complex <b>1</b> proved to be active for homometathesis reactions of 1- and
2-octene at 0.1 mol % loading. The synthesis of mixed pyrrolide boroxide
imido molybdenum alkylidene complexes was extended to other borinic
acids. The catalytic activity of these new complexes was evaluated
in the homometathesis of linear olefins
Straightforward Access to Stable, 16-Valence-Electron Phosphine-Stabilized Fe<sup>0</sup> Olefin Complexes and Their Reactivity
No full textThe use of the dialkene divinyltetramethyldisiloxane
(dvtms) allows
easy access to the reactive 16-valence-electron complexes [Fe<sup>0</sup>(L-L)(dvtms)] (L-L = dppe (1,2-bis(diphenylphosphino)ethane; <b>1</b>), dppp (1,2-bis(diphenylphosphino)propane; <b>2</b>), pyNMeP(<sup>i</sup>Pr)<sub>2</sub> (<i>N</i>-(diisopropylphosphino)-<i>N</i>-methylpyridin-2-amine; <b>4</b>), dipe (1,2-bis(diisopropylphosphino)ethane; <b>5</b>)) and [Fe<sup>0</sup>(L)<sub>2</sub>(dvtms)] (L = PMe<sub>3</sub>; <b>3</b>) by a mild reductive route using AlEt<sub>2</sub>(OEt) as reducing agent. In contrast, by the same methodology,
the 18-valence-electron complexes [Fe<sup>0</sup>(L-L)<sub>2</sub>(ethylene)] (L-L = dppm (1,2-bis(diphenylphosphino)methane; <b>6</b>), dppa (1,2-bis(diphenylphosphino)amine; <b>7</b>),
dppe (<b>8</b>)) were obtained, which do not contain dvtms.
In addition, a combined DFT and solid-state paramagnetic NMR methodology
is introduced for the structure determination of <b>5</b>. A
comparative study of the reactivity of <b>1</b>, <b>2</b>, <b>4</b>–<b>6</b>, and <b>8</b> with 3-hexyne
highlights emerging mechanistic implications for C–C coupling
reactions using these complexes as catalysts
