3 research outputs found
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>
Aminoborane σ Complexes: Significance of Hydride Co-ligands in Dynamic Processes and Dehydrogenative Borylene Formation
Systems of the type [(<i>p</i>-cym)ÂRuÂ(PR<sub>3</sub>)Â(H)Â(H<sub>2</sub>BN<sup><i>i</i></sup>Pr<sub>2</sub>)]<sup>+</sup> (R = Cy, Ph) can be synthesized
from (<i>p</i>-cym)ÂRuÂ(PR<sub>3</sub>)ÂCl<sub>2</sub> and
H<sub>2</sub>BN<sup><i>i</i></sup>Pr<sub>2</sub>/NaÂ[BAr<sup><i>f</i></sup><sub>4</sub>] and are best formulated as
(hydrido)ruthenium κ<sup>1</sup>-aminoborane complexes. VT-NMR
measurements have been used to probe
the σ-bond metathesis process leading to Ru–H/H–B
exchange, yielding an activation barrier of Δ<i>G</i><sup></sup><sup>⧧</sup> = 7.5 kcal mol<sup>–1</sup> at 161 K. Moreover, in contrast to the case for related non-hydride-containing
systems, reactivity toward alkenes constitutes a viable route to a
metal borylene complex via sacrificial hydrogenation
Aminoborane σ Complexes: Significance of Hydride Co-ligands in Dynamic Processes and Dehydrogenative Borylene Formation
Systems of the type [(<i>p</i>-cym)ÂRuÂ(PR<sub>3</sub>)Â(H)Â(H<sub>2</sub>BN<sup><i>i</i></sup>Pr<sub>2</sub>)]<sup>+</sup> (R = Cy, Ph) can be synthesized
from (<i>p</i>-cym)ÂRuÂ(PR<sub>3</sub>)ÂCl<sub>2</sub> and
H<sub>2</sub>BN<sup><i>i</i></sup>Pr<sub>2</sub>/NaÂ[BAr<sup><i>f</i></sup><sub>4</sub>] and are best formulated as
(hydrido)ruthenium κ<sup>1</sup>-aminoborane complexes. VT-NMR
measurements have been used to probe
the σ-bond metathesis process leading to Ru–H/H–B
exchange, yielding an activation barrier of Δ<i>G</i><sup></sup><sup>⧧</sup> = 7.5 kcal mol<sup>–1</sup> at 161 K. Moreover, in contrast to the case for related non-hydride-containing
systems, reactivity toward alkenes constitutes a viable route to a
metal borylene complex via sacrificial hydrogenation