6 research outputs found
Amino and Alkyl BâSubstituted PâStabilized Borenium Salts
The
ability of the phosphino-naphthyl moiety to stabilize amino-
and alkylborenium cations has been studied. Surprisingly, the phosphineâaminochloroborane
precursor <b>2</b> was found to exist in neutral open form (without
PâB interaction) in benzene solution and in the solid state
but to ionize spontaneously in chloroform to generate the P-stabilized
borenium salt <b>3</b>. Addition of gallium trichloride shifts
the process forward and affords the corresponding tetrachlorogallate
borenium salt <b>3â˛</b>. The phosphine group of <b>2</b> remains available for external reactivity, as shown by the
ready formation of the corresponding phosphine goldÂ(I) chloride complex <b>4</b>. The P-stabilized cyclohexylborenium cation <b>6</b> has also been prepared by reacting the corresponding bromoborane <b>5</b> with gallium tribromide. Compound <b>6</b> is a very
rare example of an alkyl-substituted borenium salt. The structures
of <b>2</b>, <b>3â˛</b>, and <b>4</b>â<b>6</b> have been unambiguously ascertained by multinuclear NMR
spectroscopy and X-ray crystallography
Phosphino-Boryl-Naphthalenes: Geometrically Enforced, Yet Lewis Acid Responsive P â B Interactions
Three
naphthyl-bridged phosphine-borane derivatives <b>2</b>-BCy<sub>2</sub>, <b>2</b>-BMes<sub>2</sub>, and <b>2</b>-BFlu,
differing in the steric and electronic properties of the boryl moiety,
have been prepared and characterized by spectroscopic and crystallographic
means. The presence and magnitude of the P â B interactions
have been assessed experimentally and theoretically. The naphthyl
linker was found to enforce the P â B interaction despite steric
shielding, while retaining enough flexibility to respond to the Lewis
acidity of boron
Phosphino-Boryl-Naphthalenes: Geometrically Enforced, Yet Lewis Acid Responsive P â B Interactions
Three
naphthyl-bridged phosphine-borane derivatives <b>2</b>-BCy<sub>2</sub>, <b>2</b>-BMes<sub>2</sub>, and <b>2</b>-BFlu,
differing in the steric and electronic properties of the boryl moiety,
have been prepared and characterized by spectroscopic and crystallographic
means. The presence and magnitude of the P â B interactions
have been assessed experimentally and theoretically. The naphthyl
linker was found to enforce the P â B interaction despite steric
shielding, while retaining enough flexibility to respond to the Lewis
acidity of boron
Gold(I) Complexes of the Geminal Phosphinoborane <i>t</i>Bu<sub>2</sub>PCH<sub>2</sub>BPh<sub>2</sub>
In this work, we
explored the coordination properties of the geminal
phosphinoborane <i>t</i>Bu<sub>2</sub>PCH<sub>2</sub>BPh<sub>2</sub> (<b>2</b>) toward different goldÂ(I) precursors. The
reaction of <b>2</b> with an equimolar amount of the sulfur-based
complex (Me<sub>2</sub>S)ÂAuCl resulted in displacement of the SMe<sub>2</sub> ligand and formation of linear phosphine goldÂ(I) chloride <b>3</b>. Using an excess of ligand <b>2</b>, bisligated complex <b>4</b> was formed and showed dynamic behavior at room temperature.
Changing the goldÂ(I) metal precursor to the phosphorus-based complex,
(Ph<sub>3</sub>P)ÂAuCl impacted the coordination behavior of ligand <b>2</b>. Namely, the reaction of ligand <b>2</b> with (Ph<sub>3</sub>P)ÂAuCl led to the heterolytic cleavage of the goldâchloride
bond, which is favored over PPh<sub>3</sub> ligand displacement. To
the best of our knowledge, <b>2</b> is the first example of
a P/B-ambiphilic ligand capable of cleaving the goldâchloride
bond. The coordination chemistry of <b>2</b> was further analyzed
by density functional theory calculations
Gold(I) Complexes of the Geminal Phosphinoborane <i>t</i>Bu<sub>2</sub>PCH<sub>2</sub>BPh<sub>2</sub>
In this work, we
explored the coordination properties of the geminal
phosphinoborane <i>t</i>Bu<sub>2</sub>PCH<sub>2</sub>BPh<sub>2</sub> (<b>2</b>) toward different goldÂ(I) precursors. The
reaction of <b>2</b> with an equimolar amount of the sulfur-based
complex (Me<sub>2</sub>S)ÂAuCl resulted in displacement of the SMe<sub>2</sub> ligand and formation of linear phosphine goldÂ(I) chloride <b>3</b>. Using an excess of ligand <b>2</b>, bisligated complex <b>4</b> was formed and showed dynamic behavior at room temperature.
Changing the goldÂ(I) metal precursor to the phosphorus-based complex,
(Ph<sub>3</sub>P)ÂAuCl impacted the coordination behavior of ligand <b>2</b>. Namely, the reaction of ligand <b>2</b> with (Ph<sub>3</sub>P)ÂAuCl led to the heterolytic cleavage of the goldâchloride
bond, which is favored over PPh<sub>3</sub> ligand displacement. To
the best of our knowledge, <b>2</b> is the first example of
a P/B-ambiphilic ligand capable of cleaving the goldâchloride
bond. The coordination chemistry of <b>2</b> was further analyzed
by density functional theory calculations
A Significant but Constrained Geometry PtâAl Interaction: Fixation of CO<sub>2</sub> and CS<sub>2</sub>, Activation of H<sub>2</sub> and PhCONH<sub>2</sub>
Reaction of the geminal
PAl ligand [Mes<sub>2</sub>PCÂ(îťCHPh)ÂAl<i>t</i>Bu<sub>2</sub>] (<b>1</b>) with [PtÂ(PPh<sub>3</sub>)<sub>2</sub>(ethylene)]
affords the T-shape Pt complex [(<b>1</b>)ÂPtÂ(PPh<sub>3</sub>)] (<b>2</b>). X-ray diffraction analysis
and DFT calculations reveal the presence of a significant PtâAl
interaction in <b>2</b>, despite the strain associated with
the four-membered cyclic structure. The Pt¡¡¡Al distance
is short [2.561(1) Ă
], the Al center is in a pyramidal environment
[ÎŁÂ(CâAlâC) = 346.6°], and the PCAl framework
is strongly bent (98.3°). Release of the ring strain and formation
of XâAl interactions (X = O, S, H) impart rich reactivity.
Complex <b>2</b> reacts with CO<sub>2</sub> to give the T-shape
adduct <b>3</b> stabilized by an OâAl interaction, which
is a rare example of a CO<sub>2</sub> adduct of a group 10 metal and
actually the first with Ρ<sup>1</sup>-CO<sub>2</sub> coordination.
Reaction of <b>2</b> with CS<sub>2</sub> affords the crystalline
complex <b>4</b>, in which the PPtP framework is bent, the CS<sub>2</sub> molecule is Ρ<sup>2</sup>-coordinated to Pt, and one
S atom interacts with Al. The Pt complex <b>2</b> also smoothly
reacts with H<sub>2</sub> and benzamide PhCONH<sub>2</sub> via oxidative
addition of HâH and HâN bonds, respectively. The ensuing
complexes <b>5</b> and <b>7</b> are stabilized by PtâHâAl
and PtâNHâCÂ(Ph) = OâAl bridging interactions,
resulting in 5- and 7-membered metallacycles, respectively. DFT calculations
have been performed in parallel with the experimental work. In particular,
the mechanism of reaction of <b>2</b> with H<sub>2</sub> has
been thoroughly analyzed, and the role of the Lewis acid moiety has
been delineated. These results generalize the concept of constrained
geometry TMâLA interactions and demonstrate the ability of
Al-based ambiphilic ligands to participate in TM/LA cooperative reactivity.
They extend the scope of small molecule substrates prone to such cooperative
activation and contribute to improve our knowledge of the underlying
factors