Amino and Alkyl B‑Substituted P‑Stabilized Borenium Salts

The ability of the phosphino-naphthyl moiety to stabilize amino- and alkylborenium cations has been studied. Surprisingly, the phosphine–aminochloroborane precursor <b>2</b> was found to exist in neutral open form (without P→B 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>3′</b>. The phosphine group of <b>2</b> remains available for external reactivity, as shown by the ready formation of the corresponding phosphine gold­(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>3′</b>, and <b>4</b>–<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 → B Interactions

Three naphthyl-bridged phosphine-borane derivatives <b>2</b>-BCy₂, <b>2</b>-BMes₂, 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 → B interactions have been assessed experimentally and theoretically. The naphthyl linker was found to enforce the P → 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 → B Interactions

Three naphthyl-bridged phosphine-borane derivatives <b>2</b>-BCy₂, <b>2</b>-BMes₂, 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 → B interactions have been assessed experimentally and theoretically. The naphthyl linker was found to enforce the P → 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>Bu₂PCH₂BPh₂

In this work, we explored the coordination properties of the geminal phosphinoborane <i>t</i>Bu₂PCH₂BPh₂ (<b>2</b>) toward different gold­(I) precursors. The reaction of <b>2</b> with an equimolar amount of the sulfur-based complex (Me₂S)­AuCl resulted in displacement of the SMe₂ ligand and formation of linear phosphine gold­(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 gold­(I) metal precursor to the phosphorus-based complex, (Ph₃P)­AuCl impacted the coordination behavior of ligand <b>2</b>. Namely, the reaction of ligand <b>2</b> with (Ph₃P)­AuCl led to the heterolytic cleavage of the gold–chloride bond, which is favored over PPh₃ 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 gold–chloride 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>Bu₂PCH₂BPh₂

In this work, we explored the coordination properties of the geminal phosphinoborane <i>t</i>Bu₂PCH₂BPh₂ (<b>2</b>) toward different gold­(I) precursors. The reaction of <b>2</b> with an equimolar amount of the sulfur-based complex (Me₂S)­AuCl resulted in displacement of the SMe₂ ligand and formation of linear phosphine gold­(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 gold­(I) metal precursor to the phosphorus-based complex, (Ph₃P)­AuCl impacted the coordination behavior of ligand <b>2</b>. Namely, the reaction of ligand <b>2</b> with (Ph₃P)­AuCl led to the heterolytic cleavage of the gold–chloride bond, which is favored over PPh₃ 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 gold–chloride bond. The coordination chemistry of <b>2</b> was further analyzed by density functional theory calculations

A Significant but Constrained Geometry Pt→Al Interaction: Fixation of CO₂ and CS₂, Activation of H₂ and PhCONH₂

Reaction of the geminal PAl ligand [Mes₂PC­(CHPh)­Al<i>t</i>Bu₂] (<b>1</b>) with [Pt­(PPh₃)₂(ethylene)] affords the T-shape Pt complex [(<b>1</b>)­Pt­(PPh₃)] (<b>2</b>). X-ray diffraction analysis and DFT calculations reveal the presence of a significant Pt→Al interaction in <b>2</b>, despite the strain associated with the four-membered cyclic structure. The Pt···Al distance is short [2.561(1) Å], the Al center is in a pyramidal environment [Σ­(C–Al–C) = 346.6°], and the PCAl framework is strongly bent (98.3°). Release of the ring strain and formation of X→Al interactions (X = O, S, H) impart rich reactivity. Complex <b>2</b> reacts with CO₂ to give the T-shape adduct <b>3</b> stabilized by an O→Al interaction, which is a rare example of a CO₂ adduct of a group 10 metal and actually the first with η¹-CO₂ coordination. Reaction of <b>2</b> with CS₂ affords the crystalline complex <b>4</b>, in which the PPtP framework is bent, the CS₂ molecule is η²-coordinated to Pt, and one S atom interacts with Al. The Pt complex <b>2</b> also smoothly reacts with H₂ and benzamide PhCONH₂ via oxidative addition of H–H and H–N bonds, respectively. The ensuing complexes <b>5</b> and <b>7</b> are stabilized by Pt–H→Al and Pt–NH–C­(Ph) = O→Al 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 H₂ has been thoroughly analyzed, and the role of the Lewis acid moiety has been delineated. These results generalize the concept of constrained geometry TM→LA 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