2 research outputs found
“Chiral-at-Metal” Hemilabile Nickel Complexes with a Latent d<sup>10</sup>-ML<sub>2</sub> Configuration: Receiving Substrates with Open Arms
Complexes with highly reactive stereogenic metal centers
are of
great interest to asymmetric synthesis. Thus, by reacting [Ni(COD)<sub>2</sub>] with 2 equiv of the P-alkene ligand (<i>S</i>)-<b>5</b> ((<i>S</i>)-(+)-<i>N</i>-(3,5-dioxa-4-phosphacyclohepta[2,1-<i>a</i>;3,4-<i>a</i>′]dinaphthalen-4-yl)dibenz[<i>b</i>,<i>f</i>]azepine) or (<i>S</i><sub><i>P</i></sub><i>,S</i><sub><i>C</i></sub>)<i>-</i><b>6</b> ((2<i>S</i>,5<i>S</i>)-(-)-<i>N</i>-(aza-3-oxa-2-phosphabicyclo[3.3.0]octan-4-on-2-yl)dibenz[<i>b</i>,<i>f</i>]azepine), the diastereomerically and
enantiomerically pure tetrahedral complexes (Δ,<i>S,S</i>)-[Ni(<b>5</b>-κ<i>P</i>,η<sup>2</sup>-alkene)<sub>2</sub>] (<b>2a</b>) and (Δ,<i>S</i><sub>P</sub><i>,S</i><sub>C</sub><i>,S</i><sub>P<i>′</i></sub><i>,S</i><sub>C<i>′</i></sub>)-[Ni(<b>6</b>-κ<i>P</i>,η<sup>2</sup>-alkene)<sub>2</sub>] (<b>2b</b>) were
obtained in almost quantitative yields on multigram scales. The Ni
atoms showed in both cases stable Δ configurations. Even though
these Ni(0) complexes were air stable in the solid state, once dissolved,
complex <b>2a</b> readily activated CS<sub>2</sub>, alkynes,
and enones as the formal d<sup>10</sup>-ML<sub>2</sub> fragment [Ni(<b>5</b>-κ<i>P</i>)<sub>2</sub>] (<b>4</b>)
to form adducts <b>8</b>–<b>11</b>. This is possible
thanks to the decoordination of the hemilabile alkene arms of the
P-alkene ligands, and the X-ray crystal structures of the CS<sub>2</sub> and 4-ethynyltoluene adducts confirmed the η<sup>2</sup> coordination
modes of the substrates and the concomitant opening up of the alkene
arms of ligand <b>5</b>. The coordination of α,β-unsaturated
carbonyl compounds in complexes <b>11a</b>–<b>c</b> was reversible
“Chiral-at-Metal” Hemilabile Nickel Complexes with a Latent d<sup>10</sup>-ML<sub>2</sub> Configuration: Receiving Substrates with Open Arms
Complexes with highly reactive stereogenic metal centers
are of
great interest to asymmetric synthesis. Thus, by reacting [Ni(COD)<sub>2</sub>] with 2 equiv of the P-alkene ligand (<i>S</i>)-<b>5</b> ((<i>S</i>)-(+)-<i>N</i>-(3,5-dioxa-4-phosphacyclohepta[2,1-<i>a</i>;3,4-<i>a</i>′]dinaphthalen-4-yl)dibenz[<i>b</i>,<i>f</i>]azepine) or (<i>S</i><sub><i>P</i></sub><i>,S</i><sub><i>C</i></sub>)<i>-</i><b>6</b> ((2<i>S</i>,5<i>S</i>)-(-)-<i>N</i>-(aza-3-oxa-2-phosphabicyclo[3.3.0]octan-4-on-2-yl)dibenz[<i>b</i>,<i>f</i>]azepine), the diastereomerically and
enantiomerically pure tetrahedral complexes (Δ,<i>S,S</i>)-[Ni(<b>5</b>-κ<i>P</i>,η<sup>2</sup>-alkene)<sub>2</sub>] (<b>2a</b>) and (Δ,<i>S</i><sub>P</sub><i>,S</i><sub>C</sub><i>,S</i><sub>P<i>′</i></sub><i>,S</i><sub>C<i>′</i></sub>)-[Ni(<b>6</b>-κ<i>P</i>,η<sup>2</sup>-alkene)<sub>2</sub>] (<b>2b</b>) were
obtained in almost quantitative yields on multigram scales. The Ni
atoms showed in both cases stable Δ configurations. Even though
these Ni(0) complexes were air stable in the solid state, once dissolved,
complex <b>2a</b> readily activated CS<sub>2</sub>, alkynes,
and enones as the formal d<sup>10</sup>-ML<sub>2</sub> fragment [Ni(<b>5</b>-κ<i>P</i>)<sub>2</sub>] (<b>4</b>)
to form adducts <b>8</b>–<b>11</b>. This is possible
thanks to the decoordination of the hemilabile alkene arms of the
P-alkene ligands, and the X-ray crystal structures of the CS<sub>2</sub> and 4-ethynyltoluene adducts confirmed the η<sup>2</sup> coordination
modes of the substrates and the concomitant opening up of the alkene
arms of ligand <b>5</b>. The coordination of α,β-unsaturated
carbonyl compounds in complexes <b>11a</b>–<b>c</b> was reversible