Reactions of Modified Intermolecular Frustrated P/B Lewis Pairs with Dihydrogen, Ethene, and Carbon Dioxide

In this contribution, we discuss the reactivity of different phosphanes (XPhos (<b>1a</b>), <i>^t</i>BuXPhos (<b>1b</b>), and Mes₂PEt (<b>1c</b>)) and tris­(pentafluorophenyl)­borane (and in one case, EtB­(C₆F₅)₂) against small molecules. <b>1a</b>/B­(C₆F₅)₃, <b>1b</b>/B­(C₆F₅)₃, and <b>1c</b>/B­(C₆F₅)₃ split dihydrogen heterolytically to yield the phosphonium borate salts <b>2a</b>, <b>2b</b>, and <b>2c</b>, respectively. Control experiments with D₂ gave the respective deuterated phosphonium borates <b>2a</b>-D₂, <b>2b</b>-D₂, and <b>2c</b>-D₂. The FLP systems <b>1b</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ underwent 1,2-addition reactions with ethene, resulting in the generation of the ethylene-bridged phosphonium borates <b>3b</b> and <b>3c</b>. As well, the Lewis pair EtB­(C₆F₅)₂ and Mes₂PEt reacted with ethene to yield the corresponding 1,2-addition product <b>3d</b>. At low temperature, the FLP systems <b>1a</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ coordinated carbon dioxide (<b>4a</b>, <b>4c</b>). The new compounds <b>2a</b>, <b>2b</b>, <b>3b</b>, <b>3c</b>, <b>3d</b>, <b>4a</b>, and <b>4c</b> were characterized by X-ray crystal structure analyses

Reactions of Modified Intermolecular Frustrated P/B Lewis Pairs with Dihydrogen, Ethene, and Carbon Dioxide

In this contribution, we discuss the reactivity of different phosphanes (XPhos (<b>1a</b>), <i>^t</i>BuXPhos (<b>1b</b>), and Mes₂PEt (<b>1c</b>)) and tris­(pentafluorophenyl)­borane (and in one case, EtB­(C₆F₅)₂) against small molecules. <b>1a</b>/B­(C₆F₅)₃, <b>1b</b>/B­(C₆F₅)₃, and <b>1c</b>/B­(C₆F₅)₃ split dihydrogen heterolytically to yield the phosphonium borate salts <b>2a</b>, <b>2b</b>, and <b>2c</b>, respectively. Control experiments with D₂ gave the respective deuterated phosphonium borates <b>2a</b>-D₂, <b>2b</b>-D₂, and <b>2c</b>-D₂. The FLP systems <b>1b</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ underwent 1,2-addition reactions with ethene, resulting in the generation of the ethylene-bridged phosphonium borates <b>3b</b> and <b>3c</b>. As well, the Lewis pair EtB­(C₆F₅)₂ and Mes₂PEt reacted with ethene to yield the corresponding 1,2-addition product <b>3d</b>. At low temperature, the FLP systems <b>1a</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ coordinated carbon dioxide (<b>4a</b>, <b>4c</b>). The new compounds <b>2a</b>, <b>2b</b>, <b>3b</b>, <b>3c</b>, <b>3d</b>, <b>4a</b>, and <b>4c</b> were characterized by X-ray crystal structure analyses

Reactions of a Cationic Geminal Zr⁺/P Pair with Small Molecules

The metallocene cation complex [Cp*₂ZrCH₃]⁺[B­(C₆F₅)₄]⁻ inserts the phosphino-substituted alkyne Ph–CC–PPh₂ into the [Zr]-CH₃ bond to form the internally phosphane-stabilized cation [Cp*₂Zr–C­(CMePh)­PPh₂]⁺ (<b>10</b>). Complex <b>10</b> adds alkyl isocyanides as well as pivalonitrile at a lateral site at the bent metallocene wedge with retention of the Zr–P bond. Complex <b>10</b> acts as a reactive frustrated Lewis pair toward heterocumulenes, undergoing Zr⁺/P addition reactions to the carbonyl groups of an alkyl isocyanate and of carbon dioxide to form the respective five-membered metallaheterocyclic adducts <b>13</b> and <b>14</b>. With mesityl azide complex <b>10</b> undergoes a Zr⁺/P FLP N,N-addition reaction at the terminal azide nitrogen atom to form the four-membered FLP cycloadduct <b>15</b>. The Zr⁺/P FLP is a reactive hydrogen activator. In a stoichiometric reaction it generates a hydridozirconocene cation that subsequently serves as a hydrogenation catalyst for various olefinic or acetylenic substrates. The Zr⁺/P pair <b>10</b> undergoes selective 1,4-addition reactions to conjugated enones and to a conjugated ynone to give the corresponding seven-membered metallacyclic Zr⁺/P FLP addition products. Many compounds of this study were characterized by X-ray diffraction

Reactions of Modified Intermolecular Frustrated P/B Lewis Pairs with Dihydrogen, Ethene, and Carbon Dioxide

In this contribution, we discuss the reactivity of different phosphanes (XPhos (<b>1a</b>), <i>^t</i>BuXPhos (<b>1b</b>), and Mes₂PEt (<b>1c</b>)) and tris­(pentafluorophenyl)­borane (and in one case, EtB­(C₆F₅)₂) against small molecules. <b>1a</b>/B­(C₆F₅)₃, <b>1b</b>/B­(C₆F₅)₃, and <b>1c</b>/B­(C₆F₅)₃ split dihydrogen heterolytically to yield the phosphonium borate salts <b>2a</b>, <b>2b</b>, and <b>2c</b>, respectively. Control experiments with D₂ gave the respective deuterated phosphonium borates <b>2a</b>-D₂, <b>2b</b>-D₂, and <b>2c</b>-D₂. The FLP systems <b>1b</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ underwent 1,2-addition reactions with ethene, resulting in the generation of the ethylene-bridged phosphonium borates <b>3b</b> and <b>3c</b>. As well, the Lewis pair EtB­(C₆F₅)₂ and Mes₂PEt reacted with ethene to yield the corresponding 1,2-addition product <b>3d</b>. At low temperature, the FLP systems <b>1a</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ coordinated carbon dioxide (<b>4a</b>, <b>4c</b>). The new compounds <b>2a</b>, <b>2b</b>, <b>3b</b>, <b>3c</b>, <b>3d</b>, <b>4a</b>, and <b>4c</b> were characterized by X-ray crystal structure analyses

Reactions of Modified Intermolecular Frustrated P/B Lewis Pairs with Dihydrogen, Ethene, and Carbon Dioxide

In this contribution, we discuss the reactivity of different phosphanes (XPhos (<b>1a</b>), <i>^t</i>BuXPhos (<b>1b</b>), and Mes₂PEt (<b>1c</b>)) and tris­(pentafluorophenyl)­borane (and in one case, EtB­(C₆F₅)₂) against small molecules. <b>1a</b>/B­(C₆F₅)₃, <b>1b</b>/B­(C₆F₅)₃, and <b>1c</b>/B­(C₆F₅)₃ split dihydrogen heterolytically to yield the phosphonium borate salts <b>2a</b>, <b>2b</b>, and <b>2c</b>, respectively. Control experiments with D₂ gave the respective deuterated phosphonium borates <b>2a</b>-D₂, <b>2b</b>-D₂, and <b>2c</b>-D₂. The FLP systems <b>1b</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ underwent 1,2-addition reactions with ethene, resulting in the generation of the ethylene-bridged phosphonium borates <b>3b</b> and <b>3c</b>. As well, the Lewis pair EtB­(C₆F₅)₂ and Mes₂PEt reacted with ethene to yield the corresponding 1,2-addition product <b>3d</b>. At low temperature, the FLP systems <b>1a</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ coordinated carbon dioxide (<b>4a</b>, <b>4c</b>). The new compounds <b>2a</b>, <b>2b</b>, <b>3b</b>, <b>3c</b>, <b>3d</b>, <b>4a</b>, and <b>4c</b> were characterized by X-ray crystal structure analyses

Reactions of Modified Intermolecular Frustrated P/B Lewis Pairs with Dihydrogen, Ethene, and Carbon Dioxide

In this contribution, we discuss the reactivity of different phosphanes (XPhos (<b>1a</b>), <i>^t</i>BuXPhos (<b>1b</b>), and Mes₂PEt (<b>1c</b>)) and tris­(pentafluorophenyl)­borane (and in one case, EtB­(C₆F₅)₂) against small molecules. <b>1a</b>/B­(C₆F₅)₃, <b>1b</b>/B­(C₆F₅)₃, and <b>1c</b>/B­(C₆F₅)₃ split dihydrogen heterolytically to yield the phosphonium borate salts <b>2a</b>, <b>2b</b>, and <b>2c</b>, respectively. Control experiments with D₂ gave the respective deuterated phosphonium borates <b>2a</b>-D₂, <b>2b</b>-D₂, and <b>2c</b>-D₂. The FLP systems <b>1b</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ underwent 1,2-addition reactions with ethene, resulting in the generation of the ethylene-bridged phosphonium borates <b>3b</b> and <b>3c</b>. As well, the Lewis pair EtB­(C₆F₅)₂ and Mes₂PEt reacted with ethene to yield the corresponding 1,2-addition product <b>3d</b>. At low temperature, the FLP systems <b>1a</b>/B­(C₆F₅)₃ and <b>1c</b>/B­(C₆F₅)₃ coordinated carbon dioxide (<b>4a</b>, <b>4c</b>). The new compounds <b>2a</b>, <b>2b</b>, <b>3b</b>, <b>3c</b>, <b>3d</b>, <b>4a</b>, and <b>4c</b> were characterized by X-ray crystal structure analyses

Frustrated Lewis Pair vs Metal–Carbon σ‑Bond Insertion Chemistry at an <i>o</i>‑Phenylene-Bridged Cp₂Zr⁺/PPh₂ System

Methyl anion abstraction from (<i>o</i>-diphenylphosphino)­phenyl­(methyl)­zirconocene by trityl tetrakis­(pentafluorophenyl)­borate gives the <i>o</i>-phenylene-bridged Zr⁺/P system <b>10</b>. It behaves toward a variety of reagents as a typical Zr⁺/P frustrated Lewis pair (FLP). It undergoes cooperative 1,4-addition reactions to some chalcone derivatives and adds in a 1,2-fashion to a variety of organic carbonyls and to several heterocumulenes. The reactive Zr–C σ bond of the FLP <b>10</b> remains intact in these reactions. Complex <b>10</b> splits dihydrogen, but subsequently the Zr–C σ bond is protonolytically cleaved in this case. Only a few special reagents, among them carbon monoxide, undergo the usual insertion reaction into the Zr–C­(aryl) σ-bond of the Zr⁺/P system <b>10</b>

Reactions of a Cationic Geminal Zr⁺/P Pair with Small Molecules

The metallocene cation complex [Cp*₂ZrCH₃]⁺[B­(C₆F₅)₄]⁻ inserts the phosphino-substituted alkyne Ph–CC–PPh₂ into the [Zr]-CH₃ bond to form the internally phosphane-stabilized cation [Cp*₂Zr–C­(CMePh)­PPh₂]⁺ (<b>10</b>). Complex <b>10</b> adds alkyl isocyanides as well as pivalonitrile at a lateral site at the bent metallocene wedge with retention of the Zr–P bond. Complex <b>10</b> acts as a reactive frustrated Lewis pair toward heterocumulenes, undergoing Zr⁺/P addition reactions to the carbonyl groups of an alkyl isocyanate and of carbon dioxide to form the respective five-membered metallaheterocyclic adducts <b>13</b> and <b>14</b>. With mesityl azide complex <b>10</b> undergoes a Zr⁺/P FLP N,N-addition reaction at the terminal azide nitrogen atom to form the four-membered FLP cycloadduct <b>15</b>. The Zr⁺/P FLP is a reactive hydrogen activator. In a stoichiometric reaction it generates a hydridozirconocene cation that subsequently serves as a hydrogenation catalyst for various olefinic or acetylenic substrates. The Zr⁺/P pair <b>10</b> undergoes selective 1,4-addition reactions to conjugated enones and to a conjugated ynone to give the corresponding seven-membered metallacyclic Zr⁺/P FLP addition products. Many compounds of this study were characterized by X-ray diffraction

Metal-Free Carbonylation Route to a Reactive Borataepoxide System

Hydroboration of <i>N</i>-allyl-<i>cis</i>-2,6-dimethylpiperidine with HB­(C₆F₅)₂ gave the trimethylene-bridged frustrated N/B Lewis pair <b>7</b>. It featured a <i>trans</i>-2,6-dimethyl substitution pattern at the piperidine unit which indicated preceding equilibration with its iminium cation/hydridoborate isomer <b>6</b> by means of an internal hydride transfer. In situ generated compound <b>6</b> is essential for the reaction with CO/HB­(C₆F₅)₂ to give the borataepoxide product <b>12</b> at the [N]–(CH₂)₃–[B] framework. The borataepoxide <b>12</b> reacts rapidly with CO₂, cleaves the acidic C–H bond of a terminal alkyne, splits dihydrogen, and reacts with nitriles and benzaldehyde. Most products were characterized by X-ray diffraction

Reaction of Diphenylphosphanylacetylene with RB(C₆F₅)₂ Reagents: Evidence for a Remarkable Sequence of Synergistic Frustrated <i>Lewis</i> Pair Addition Reactions

Diphenylphosphanylethyne (<b>3a</b>) reacts with tris­(pentafluorophenyl)­borane at room temperature by a typical frustrated <i>Lewis</i> pair (FLP) reaction. It undergoes a sequential series of 1,2-phosphane/borane additions to the alkyne unit in an overall 2:2 molar ratio to selectively form the dimeric product <b>5a</b>. Product <b>5</b> features a pentafulvene-reminiscent structure with a pair of phosphonium units in the ring and B­(C₆F₅)₃ substituents at the periphery. At elevated temperature, the reaction becomes less selective, now favoring the formation of cis- and trans-1,1-carboboration products from a 1:1 stoichiometry. After photolytic trans/cis isomerization, the vicinal FLP <b>6a</b> becomes the major product, featuring an intramolecular P···B interaction. The reaction of <b>3a</b> with H₃CB­(C₆F₅)₂ also gives a heterocyclic dimer (<b>11</b>), except that here a substituent H/CH₃ exchange by an addition/elimination pathway has taken place. In the B­(C₆F₅)₃-derived system, we were able to trap an alleged intermediate of this rearrangement reaction by adding <i>n</i>-butyl isocyanide. Five products in the Ph₂P- and (<i>p</i>-tolyl)₂P-derived systems were characterized by X-ray diffractio