13 research outputs found
4-Phosphino-Substituted N-Heterocyclic Carbenes (NHCs) from the Abnormal Reaction of NHCs with Phosphaalkenes
The activation of the Pî—»C bond of phosphaalkenes
with N-heterocyclic
carbenes (NHCs) offers a convenient means to introduce new functionality
at the 4-position of an NHC. Treatment of MesPCRR′
(<b>2a</b>: R = R′ = Ph; <b>2b</b>: R = Ph, R′
= 2-C<sub>5</sub>H<sub>4</sub>N; <b>2c</b>: R = R′ =
4-C<sub>6</sub>H<sub>4</sub>F) with 1,3-dimesitylimidazol-2-ylidene
[:CÂ(NMesCH)<sub>2</sub>, IMes, Mes = 2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>] affords 4-phosphino-2-carbenes :CÂ(NMes)<sub>2</sub>CHCÂ(PMesCHRR′)NMes
[<b>1a</b>: R = R′ = Ph; <b>1b</b>: R = Ph, R′
= 2-C<sub>5</sub>H<sub>4</sub>N; <b>1c</b>: R = R′ =
4-C<sub>6</sub>H<sub>4</sub>F]. Significantly, these functional NHCs
retain the parent carbene functionality and, in addition, contain
a phosphine moiety. The preparation and spectroscopic characterization
of the complexes [(<b>1a</b>)ÂMÂ(cod)ÂCl] (<b>4</b>) and <i>cis</i>-[(<b>1a</b>)ÂMÂ(CO)<sub>2</sub>Cl] (<b>5</b>) (M = Ir, Rh) are reported. The average CO stretching frequencies
(ν̅<sub>CO</sub><sup>av</sup>) for <b>5<sub>M=Ir</sub></b>, <b>5<sub>M=Rh</sub></b>, and authentic samples of <i>cis</i>-[(IMes)ÂMÂ(CO)<sub>2</sub>Cl] (M = Ir, Rh) are presented as a means to evaluate the
donor properties of 4-phosphino-2-carbene <b>1a</b>. The average
CO stretching frequency is lower energy for <b>5<sub>M=Ir</sub></b> than for <i>cis</i>-[(IMes)ÂIrÂ(CO)<sub>2</sub>Cl] <b>(</b>Δν̅<sub>CO</sub><sup>av</sup> = −2 cm<sup>–1</sup>), whereas
the opposite is observed between <b>5<sub>M=Rh</sub></b> and <i>cis</i>-[(IMes)ÂIrÂ(CO)<sub>2</sub>Cl] <b>(</b>Δν̅<sub>CO</sub><sup>av</sup> = 2 cm<sup>–1</sup>). The molecular structures are reported for <b>1a</b>, <b>1b</b>, <b>1c</b>, <b>4<sub>M=Ir</sub></b>, and <b>5<sub>M=Ir</sub></b>
Addition-Isomerization Polymerization of Chiral Phosphaalkenes: Observation of Styrene–Phosphaalkene Linkages in a Random Copolymer
These studies provide
the first evidence for styrene–phosphaalkene
connectivities in a phosphaalkene copolymer. The synthesis and structural
characterization of new phosphaalkene–oxazolines, ArPî—»CÂ(Ph)Â(3-C<sub>6</sub>H<sub>4</sub>Ox) [<b>1a</b>,<b>b</b>, Ar = Mes
(<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCHÂ(<sup><i>i</i></sup>Pr)ÂCH<sub>2</sub>], are reported. The radical-initiated
homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional polyÂ(methyleneÂphosphine) (<b>4a</b>: <i>M</i><sub>n</sub> = 5300 g mol<sup>–1</sup>, PDI = 1.2) and polyÂ(methyleneÂphosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i><sub>n</sub> = 4000
g mol<sup>–1</sup>, PDI = 1.1). Multinuclear NMR spectroscopic
analyses of <b>4a</b> and <b>5a</b> provided evidence
for the predominance of an addition-isomerization mechanism for the
radical polymerization of <b>1a</b>. In addition, signals could
be assigned to CHPh–PÂ(CHPhAr) (i.e., S–<b>1a</b>) and ArCH<sub>2</sub>–CH<sub>2</sub> (i.e., <b>1a</b>–S) linkages in copolymer <b>5a</b>. With a monomer
feed ratio of <b>1a</b>:S (1:2, 33 mol % <b>1a</b>) the
inverse gated <sup>13</sup>CÂ{<sup>1</sup>H} NMR spectrum suggested
an incorporation of 19 mol % <b>1a</b> in copolymer <b>5a</b>. Polymers <b>4a</b> and <b>5a</b> were further functionalized
to AuÂ(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i><sub>n</sub> = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i><sub>n</sub> = 7500, PDI = 1.1]
Addition-Isomerization Polymerization of Chiral Phosphaalkenes: Observation of Styrene–Phosphaalkene Linkages in a Random Copolymer
These studies provide
the first evidence for styrene–phosphaalkene
connectivities in a phosphaalkene copolymer. The synthesis and structural
characterization of new phosphaalkene–oxazolines, ArPî—»CÂ(Ph)Â(3-C<sub>6</sub>H<sub>4</sub>Ox) [<b>1a</b>,<b>b</b>, Ar = Mes
(<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCHÂ(<sup><i>i</i></sup>Pr)ÂCH<sub>2</sub>], are reported. The radical-initiated
homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional polyÂ(methyleneÂphosphine) (<b>4a</b>: <i>M</i><sub>n</sub> = 5300 g mol<sup>–1</sup>, PDI = 1.2) and polyÂ(methyleneÂphosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i><sub>n</sub> = 4000
g mol<sup>–1</sup>, PDI = 1.1). Multinuclear NMR spectroscopic
analyses of <b>4a</b> and <b>5a</b> provided evidence
for the predominance of an addition-isomerization mechanism for the
radical polymerization of <b>1a</b>. In addition, signals could
be assigned to CHPh–PÂ(CHPhAr) (i.e., S–<b>1a</b>) and ArCH<sub>2</sub>–CH<sub>2</sub> (i.e., <b>1a</b>–S) linkages in copolymer <b>5a</b>. With a monomer
feed ratio of <b>1a</b>:S (1:2, 33 mol % <b>1a</b>) the
inverse gated <sup>13</sup>CÂ{<sup>1</sup>H} NMR spectrum suggested
an incorporation of 19 mol % <b>1a</b> in copolymer <b>5a</b>. Polymers <b>4a</b> and <b>5a</b> were further functionalized
to AuÂ(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i><sub>n</sub> = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i><sub>n</sub> = 7500, PDI = 1.1]
Addition-Isomerization Polymerization of Chiral Phosphaalkenes: Observation of Styrene–Phosphaalkene Linkages in a Random Copolymer
These studies provide
the first evidence for styrene–phosphaalkene
connectivities in a phosphaalkene copolymer. The synthesis and structural
characterization of new phosphaalkene–oxazolines, ArPî—»CÂ(Ph)Â(3-C<sub>6</sub>H<sub>4</sub>Ox) [<b>1a</b>,<b>b</b>, Ar = Mes
(<b>1a</b>), Mes* (<b>1b</b>), Ox = CNOCHÂ(<sup><i>i</i></sup>Pr)ÂCH<sub>2</sub>], are reported. The radical-initiated
homo- and copolymerization of <b>1a</b> with styrene affords <i>P</i>-functional polyÂ(methyleneÂphosphine) (<b>4a</b>: <i>M</i><sub>n</sub> = 5300 g mol<sup>–1</sup>, PDI = 1.2) and polyÂ(methyleneÂphosphine-<i>co</i>-styrene) (<b>5a</b>: <i>M</i><sub>n</sub> = 4000
g mol<sup>–1</sup>, PDI = 1.1). Multinuclear NMR spectroscopic
analyses of <b>4a</b> and <b>5a</b> provided evidence
for the predominance of an addition-isomerization mechanism for the
radical polymerization of <b>1a</b>. In addition, signals could
be assigned to CHPh–PÂ(CHPhAr) (i.e., S–<b>1a</b>) and ArCH<sub>2</sub>–CH<sub>2</sub> (i.e., <b>1a</b>–S) linkages in copolymer <b>5a</b>. With a monomer
feed ratio of <b>1a</b>:S (1:2, 33 mol % <b>1a</b>) the
inverse gated <sup>13</sup>CÂ{<sup>1</sup>H} NMR spectrum suggested
an incorporation of 19 mol % <b>1a</b> in copolymer <b>5a</b>. Polymers <b>4a</b> and <b>5a</b> were further functionalized
to AuÂ(I)-containing macromolecules [<b>4a</b>·AuCl: <i>M</i><sub>n</sub> = 13 000, PDI = 1.2; <b>5a</b>·AuCl: <i>M</i><sub>n</sub> = 7500, PDI = 1.1]
Copper(I) Complexes of Pyridine-Bridged Phosphaalkene-Oxazoline Pincer Ligands
The synthesis of enantiomerically
pure pyridine-bridged phosphaalkene-oxazolines
ArPî—»CÂ(Ph)Â(2,6-C<sub>5</sub>H<sub>3</sub>NOx) (<b>1</b>, Ar = Mes/Mes*, Ox = CNOCHÂ(<i>i</i>-Pr)ÂCH<sub>2</sub>/ÂCNOCHÂ(CH<sub>2</sub>Ph)ÂCH<sub>2</sub>) is reported.
This new ligand forms a κÂ(P), κ<sup>2</sup>(NN) dimeric
complex with copperÂ(I) (<b>7</b>) that dissociates into a cationic
κ<sup>3</sup>(PNN) monomeric complex upon addition of a neutral
ligand {[<b>1a</b>·CuL]ÂOTf (<b>8a</b>–<b>e</b>): L = PPh<sub>3</sub> (<b>a</b>), PÂ(OPh)<sub>3</sub> (<b>b</b>), 2,6-lutidine (<b>c</b>), 4-DMAP (<b>d</b>), 1-methylimidazole (<b>e</b>)}. The P–Cu bond lengths
in <b>8</b> are influenced by the π-accepting/σ-donating
properties of L, and this can be observed by changes in the δ<sup>31</sup>P<sub>PC</sub> NMR shift. The donor–acceptor
properties in complexes of type <b>8</b> have also been investigated
by UV/vis spectroscopy and density functional theory calculations
Reaction of an Enantiomerically Pure Phosphaalkene-Oxazoline with MeM Nucleophiles (M = Li and MgBr): Stereoselectivity and Noninnocence of the P‑Mesityl Substituent
The addition of alkyl
nucleophiles (MeM, M = Li, MgBr) across the
Pî—»C bond of an enantiomerically pure phosphaalkene-oxazoline
followed by protonation of the C anion affords phosphines with three
chirality centers. The formation of palladiumÂ(II) complexes of the
resultant phosphines permitted structural characterization of the
products by X-ray diffraction. The choice of nucleophile has a profound
effect on the product distributions. For instance, the Grignard reagent
adds in a diastereoselective manner to give one major phosphine product
with P- and C-stereocenters. In contrast, addition of methyllithium
has proven not only to be less stereoselective but also affords a
fascinating cyclic phosphine product. Both the Grignard and RLi reactions
involve proton transfer from the <i>o</i>-Me of the P-Mes
substituent even though the products are quite different in each case
Copper(I) Complexes of Pyridine-Bridged Phosphaalkene-Oxazoline Pincer Ligands
The synthesis of enantiomerically
pure pyridine-bridged phosphaalkene-oxazolines
ArPî—»CÂ(Ph)Â(2,6-C<sub>5</sub>H<sub>3</sub>NOx) (<b>1</b>, Ar = Mes/Mes*, Ox = CNOCHÂ(<i>i</i>-Pr)ÂCH<sub>2</sub>/ÂCNOCHÂ(CH<sub>2</sub>Ph)ÂCH<sub>2</sub>) is reported.
This new ligand forms a κÂ(P), κ<sup>2</sup>(NN) dimeric
complex with copperÂ(I) (<b>7</b>) that dissociates into a cationic
κ<sup>3</sup>(PNN) monomeric complex upon addition of a neutral
ligand {[<b>1a</b>·CuL]ÂOTf (<b>8a</b>–<b>e</b>): L = PPh<sub>3</sub> (<b>a</b>), PÂ(OPh)<sub>3</sub> (<b>b</b>), 2,6-lutidine (<b>c</b>), 4-DMAP (<b>d</b>), 1-methylimidazole (<b>e</b>)}. The P–Cu bond lengths
in <b>8</b> are influenced by the π-accepting/σ-donating
properties of L, and this can be observed by changes in the δ<sup>31</sup>P<sub>PC</sub> NMR shift. The donor–acceptor
properties in complexes of type <b>8</b> have also been investigated
by UV/vis spectroscopy and density functional theory calculations
Homo- and Heteropolynuclear Complexes Containing Bidentate Bridging 4‑Phosphino-N-Heterocyclic Carbene Ligands
The
abnormal reaction of phosphaalkenes with N-heterocyclic carbenes (NHC)
offers a convenient method to introduce new functionality at the backbone
of an NHC. The 4-phosphino-substituted NHC (<b>1a</b>) derived
from 1,3-dimesitylimidazol-2-ylidene (IMes) and MesPî—»CPh<sub>2</sub> is shown to be an effective bifunctional ligand for AuÂ(I)
and PdÂ(II). Several new complexes are reported: <b>2a</b>: <b>1a</b>·Au<sub><i>C</i></sub>Cl, <b>3a</b>: <b>1a</b>·(AuCl)<sub>2</sub>, <b>4a</b>: [(<b>1a</b>)<sub>2</sub>Au<sub><i>C</i></sub>]ÂCl, <b>5a</b>: [(<b>1a</b>·Au<sub><i>P</i></sub>Cl)<sub>2</sub>Au<sub><i>C</i></sub>]ÂCl], and <b>6a</b>: <b>1a</b>·(Pd<sub><i>C</i></sub>) (Au<sub><i>P</i></sub>Cl). The reaction of 4-phosphino-NHC <b>1b</b>, derived
from 1,3-diÂ(cyclohexyl)Âimidazol-2-ylidene (ICy) and MesPî—»CÂ(4-C<sub>6</sub>H<sub>4</sub>F)<sub>2</sub>, with (tht)ÂAuCl (2 equiv, tht
= tetrahydrothiophene) affords the fascinating tetranuclear <b>5b</b> [(<b>1b</b>·Au<sub><i>P</i></sub>Cl)<sub>2</sub>Au<sub><i>C</i></sub>]Â[AuCl<sub>2</sub>]. The molecular
structure of <b>5b</b> features a close Au···Au
contact (3.0988(4) Ã…) between the bisÂ(carbene)ÂgoldÂ(I) cation
and the dichloroaurateÂ(I) anion. The buried volumes (%<i>V</i><sub>bur</sub>) and Tolman cone angles for representative 4-phosphino-NHCs
calculated from structural data are compared to related carbenes and
phosphines. The molecular structures are reported for complexes <b>3a</b>, <b>4a</b>, <b>5b</b>, and <b>6a</b>
Poly(<i>p</i>‑phenylenediethynylene phosphine)s and Related π‑Conjugated Phosphine–Diyne Polymers: Synthesis, Characterization and Photophysical Properties
Despite
the considerable synthetic challenge, polymers that incorporate
phosphorus atoms within or adjacent to a π-conjugated backbone
framework are of interest due to the ability to modulate the photophysical
properties of the polymer based on the chemical environment at phosphorus.
We report the synthesis and characterization of polyÂ(<i>p</i>-phenylenediethlynylene phosphine)Âs, <b>1a</b>–<b>1e</b>, a new class of σ–π conjugated polymer.
Polymers <b>1a</b>–<b>1e</b> were prepared by a
Ni-catalyzed coupling of dialkynes with phenyldichlorophosphine in
the presence of excess triethylamine and have molecular weights (<i>M</i><sub>w</sub>) up to 12,000 g mol<sup>–1</sup> (vs.
polystyrene). While the polymers <b>1b</b>–<b>1e</b> are nonfluorescent, blue fluorescence is observed upon oxidation
of the phosphorus centers (Φ<sub>soln</sub> = 0.12–0.28).
Polymers <b>1b</b>·O–<b>1e</b>·O also
exhibit yellow/green fluorescence in the solid state (Φ<sub>solid</sub> = 0.04–0.08). These results introduce a fascinating
new class of main group-containing macromolecule and lay the groundwork
for their utilization in sensory applications and/or their incorporation
into optoelectrical devices
An Addition–Isomerization Mechanism for the Anionic Polymerization of MesPCPh<sub>2</sub> and <i>m</i>‑XylPCPh<sub>2</sub>
We
report that the anionic polymerization of P-mesityl and <i>m</i>-xylyl-substituted phosphaalkenes follows an unusual addition–isomerization
mechanism. Specifically, the polymerization of ArPî—»CPh<sub>2</sub> [Ar = Mes (<b>1a</b>), <i>m</i>-Xyl (<b>1b</b>)] involves the hindered nucleophilic anion intermediate,
Ⓟ–PÂ(Ar)–CPh<sub>2</sub><sup>–</sup>, which
undergoes a proton migration from the <i>o</i>-CH<sub>3</sub> of the Mes/<i>m</i>-Xyl moiety to the −CPh<sub>2</sub> moiety to afford a propagating benzylic anion. This mechanism
is supported by the preparation of model compounds MePÂ(CHPh<sub>2</sub>)-4,6-Me<sub>2</sub>C<sub>6</sub>H<sub>2</sub>–2-CH<sub>2</sub>–CPh<sub>3</sub> (<b>2a</b>) or MePÂ(CHPh<sub>2</sub>)-6-MeC<sub>6</sub>H<sub>3</sub>–2-CH<sub>2</sub>–CPh<sub>3</sub> (<b>2b</b>), which were both crystallographically characterized.
Polymerization of <b>1a</b> or <b>1b</b> in THF solution
using <i>n</i>-BuLi (2 mol %) revealed <sup>1</sup>H and <sup>13</sup>C NMR signals assigned to −CH<sub>2</sub>–
and −CHPh<sub>2</sub> groups consistent with an addition–isomerization
polymerization mechanism to afford polyÂ(methyleneÂphosphine) <b>3a</b> or <b>3b</b>. A large kinetic isotope effect (≤23)
was determined for the <i>n</i>-BuLi-initiated polymerization
of <b>1a</b>-<i>d</i><sub>9</sub> compared to <b>1a</b> in THF at 50 °C, consistent with C–H (or C–D)
activation as the rate-determining step. This C–H activation
step was modeled using DFT computations which revealed that the intramolecular
proton transfer from the <i>o</i>-CH<sub>3</sub> of the
Mes moiety to the −CPh<sub>2</sub> moiety has an activation
energy (<i>E</i><sub>a</sub> = +18.5 kcal mol<sup>–1</sup>). For comparison, this computational value was quite close to the
experimentally measured activation energy of propagation ArPCPh<sub>2</sub> in THF [<i>E</i><sub>a</sub> = 14.0 ± 0.9
kcal mol<sup>–1</sup> (<b>1a</b>), 15.6 ± 2.8 kcal
mol<sup>–1</sup> (<b>1b</b>)]