Cationic Boranes for the Complexation of Fluoride Ions in Water below the 4 ppm Maximum Contaminant Level

In search of a molecular receptor that could bind fluoride ions in water below the maximum contaminant level of 4 ppm set by the Environmental Protection Agency (EPA), we have investigated the water stability and fluoride binding properties of a series of phosphonium boranes of general formula [p-(Mes2B)C6H4(PPh2R)]+ with R = Me ([1]+), Et ([2]+), n-Pr ([3]+), and Ph ([4]+). These phosphonium boranes are water stable and react reversibly with water to form the corresponding zwitterionic hydroxide complexes of general formula p-(Mes2(HO)B)C6H4(PPh2R). They also react with fluoride ions to form the corresponding zwitterionic fluoride complexes of general formula p-(Mes2(F)B)C6H4(PPh2R). Spectrophotometric acid−base titrations carried out in H2O/MeOH (9:1 vol.) afford pKR+ values of 7.3(±0.07) for [1]+, 6.92(±0.1) for [2]+, 6.59(±0.08) for [3]+, and 6.08(±0.09) for [4]+, thereby indicating that the Lewis acidity of the cationic boranes increases in following order: [1]+ 2]+ 3]+ 4]+. In agreement with this observation, fluoride titration experiments in H2O/MeOH (9:1 vol.) show that the fluoride binding constants (K = 840(±50) M−1 for [1]+, 2500(±200) M−1 for [2]+, 4000(±300) M−1 for [3]+, and 10 500(±1000) M−1 for [4]+) increase in the same order. These results show that the Lewis acidity of the cationic boranes increases with their hydrophobicity. The resulting Lewis acidity increase is substantial and exceeds 1 order of magnitude on going from [1]+ to [4]+. In turn, [4]+ is sufficiently fluorophilic to bind fluoride ions below the EPA contaminant level in pure water. These results indicate that phosphonium boranes related to [4]+ could be used as molecular recognition units in chemosensors for drinking water analysis

Cationic Boranes for the Complexation of Fluoride Ions in Water below the 4 ppm Maximum Contaminant Level

In search of a molecular receptor that could bind fluoride ions in water below the maximum contaminant level of 4 ppm set by the Environmental Protection Agency (EPA), we have investigated the water stability and fluoride binding properties of a series of phosphonium boranes of general formula [p-(Mes2B)C6H4(PPh2R)]+ with R = Me ([1]+), Et ([2]+), n-Pr ([3]+), and Ph ([4]+). These phosphonium boranes are water stable and react reversibly with water to form the corresponding zwitterionic hydroxide complexes of general formula p-(Mes2(HO)B)C6H4(PPh2R). They also react with fluoride ions to form the corresponding zwitterionic fluoride complexes of general formula p-(Mes2(F)B)C6H4(PPh2R). Spectrophotometric acid−base titrations carried out in H2O/MeOH (9:1 vol.) afford pKR+ values of 7.3(±0.07) for [1]+, 6.92(±0.1) for [2]+, 6.59(±0.08) for [3]+, and 6.08(±0.09) for [4]+, thereby indicating that the Lewis acidity of the cationic boranes increases in following order: [1]+ 2]+ 3]+ 4]+. In agreement with this observation, fluoride titration experiments in H2O/MeOH (9:1 vol.) show that the fluoride binding constants (K = 840(±50) M−1 for [1]+, 2500(±200) M−1 for [2]+, 4000(±300) M−1 for [3]+, and 10 500(±1000) M−1 for [4]+) increase in the same order. These results show that the Lewis acidity of the cationic boranes increases with their hydrophobicity. The resulting Lewis acidity increase is substantial and exceeds 1 order of magnitude on going from [1]+ to [4]+. In turn, [4]+ is sufficiently fluorophilic to bind fluoride ions below the EPA contaminant level in pure water. These results indicate that phosphonium boranes related to [4]+ could be used as molecular recognition units in chemosensors for drinking water analysis

Cationic Boranes for the Complexation of Fluoride Ions in Water below the 4 ppm Maximum Contaminant Level

In search of a molecular receptor that could bind fluoride ions in water below the maximum contaminant level of 4 ppm set by the Environmental Protection Agency (EPA), we have investigated the water stability and fluoride binding properties of a series of phosphonium boranes of general formula [p-(Mes2B)C6H4(PPh2R)]+ with R = Me ([1]+), Et ([2]+), n-Pr ([3]+), and Ph ([4]+). These phosphonium boranes are water stable and react reversibly with water to form the corresponding zwitterionic hydroxide complexes of general formula p-(Mes2(HO)B)C6H4(PPh2R). They also react with fluoride ions to form the corresponding zwitterionic fluoride complexes of general formula p-(Mes2(F)B)C6H4(PPh2R). Spectrophotometric acid−base titrations carried out in H2O/MeOH (9:1 vol.) afford pKR+ values of 7.3(±0.07) for [1]+, 6.92(±0.1) for [2]+, 6.59(±0.08) for [3]+, and 6.08(±0.09) for [4]+, thereby indicating that the Lewis acidity of the cationic boranes increases in following order: [1]+ 2]+ 3]+ 4]+. In agreement with this observation, fluoride titration experiments in H2O/MeOH (9:1 vol.) show that the fluoride binding constants (K = 840(±50) M−1 for [1]+, 2500(±200) M−1 for [2]+, 4000(±300) M−1 for [3]+, and 10 500(±1000) M−1 for [4]+) increase in the same order. These results show that the Lewis acidity of the cationic boranes increases with their hydrophobicity. The resulting Lewis acidity increase is substantial and exceeds 1 order of magnitude on going from [1]+ to [4]+. In turn, [4]+ is sufficiently fluorophilic to bind fluoride ions below the EPA contaminant level in pure water. These results indicate that phosphonium boranes related to [4]+ could be used as molecular recognition units in chemosensors for drinking water analysis

Synthesis, Structures, and Ethylene Dimerization Reactivity of Palladium Alkyl Complexes That Contain a Chelating Phosphine–Trifluoroborate Ligand

The chemistry of palladium alkyl complexes that incorporate the phosphine–trifluoroborate ligand ortho-(Ph2P)C6H4(BF3–) (PF–) is described. The reaction of the pinacol borane ortho-(Ph2P)C6H4(Bpin) with K[HF2] yields ortho-(Ph2P)C6H4(BF3K) (K[PF], 1). Crystallization of 1 from Et2O/THF in the presence of 18-crown-6 yields [K-(18-crown-6)][PF]·0.5THF (2·0.5THF). In the solid state, the phosphine–borate anion of 2 is ion-paired with the [K-(18-crown-6)] cation through weak contacts with the phosphorus and two fluorine atoms. 1 reacts with (COD)PdMeCl in the presence of 18-crown-6 to form [K-(18-crown-6)][(PF)PdMeCl] (3) and with (COD)PdMeCl and 2,4,6-collidine (col) to yield (PF)PdMe(col) (4). The PF– ligands in 3 and 4 are bound to Pd in a κ2 mode through the phosphine and one fluorine of the −ArBF3– unit. The other two fluorines are weakly bound to the K(18-crown-6)+ cation in 3. NMR studies show that the Pd–F interactions in 3 and 4 are maintained in solution and that, for 4, the three fluorine atoms undergo fast site exchange on the NMR time scale. 4 reacts with excess pyridine to yield (κ1-P-PF)PdMe(py)2 (6), in which the −ArBF3– unit has been completely displaced by pyridine. 4 slowly dimerizes ethylene to 1-butene (36 t.o./h, 23 °C, CH2Cl2, 400 psi ethylene). The catalyst resting state is (PF)PdEt(col) (7). Addition of [H(OEt2)2][B(3,5-(CF3)2-C6H3)4] traps the collidine as [collidinium] [B(3,5-(CF3)2-C6H3)4] and results in a 10-fold increase in the ethylene dimerization rate (385 t.o./h, 23 °C, CD2Cl2, 150 psi ethylene)

Cationic Boranes for the Complexation of Fluoride Ions in Water below the 4 ppm Maximum Contaminant Level

In search of a molecular receptor that could bind fluoride ions in water below the maximum contaminant level of 4 ppm set by the Environmental Protection Agency (EPA), we have investigated the water stability and fluoride binding properties of a series of phosphonium boranes of general formula [p-(Mes2B)C6H4(PPh2R)]+ with R = Me ([1]+), Et ([2]+), n-Pr ([3]+), and Ph ([4]+). These phosphonium boranes are water stable and react reversibly with water to form the corresponding zwitterionic hydroxide complexes of general formula p-(Mes2(HO)B)C6H4(PPh2R). They also react with fluoride ions to form the corresponding zwitterionic fluoride complexes of general formula p-(Mes2(F)B)C6H4(PPh2R). Spectrophotometric acid−base titrations carried out in H2O/MeOH (9:1 vol.) afford pKR+ values of 7.3(±0.07) for [1]+, 6.92(±0.1) for [2]+, 6.59(±0.08) for [3]+, and 6.08(±0.09) for [4]+, thereby indicating that the Lewis acidity of the cationic boranes increases in following order: [1]+ 2]+ 3]+ 4]+. In agreement with this observation, fluoride titration experiments in H2O/MeOH (9:1 vol.) show that the fluoride binding constants (K = 840(±50) M−1 for [1]+, 2500(±200) M−1 for [2]+, 4000(±300) M−1 for [3]+, and 10 500(±1000) M−1 for [4]+) increase in the same order. These results show that the Lewis acidity of the cationic boranes increases with their hydrophobicity. The resulting Lewis acidity increase is substantial and exceeds 1 order of magnitude on going from [1]+ to [4]+. In turn, [4]+ is sufficiently fluorophilic to bind fluoride ions below the EPA contaminant level in pure water. These results indicate that phosphonium boranes related to [4]+ could be used as molecular recognition units in chemosensors for drinking water analysis

Cationic Boranes for the Complexation of Fluoride Ions in Water below the 4 ppm Maximum Contaminant Level

In search of a molecular receptor that could bind fluoride ions in water below the maximum contaminant level of 4 ppm set by the Environmental Protection Agency (EPA), we have investigated the water stability and fluoride binding properties of a series of phosphonium boranes of general formula [p-(Mes2B)C6H4(PPh2R)]+ with R = Me ([1]+), Et ([2]+), n-Pr ([3]+), and Ph ([4]+). These phosphonium boranes are water stable and react reversibly with water to form the corresponding zwitterionic hydroxide complexes of general formula p-(Mes2(HO)B)C6H4(PPh2R). They also react with fluoride ions to form the corresponding zwitterionic fluoride complexes of general formula p-(Mes2(F)B)C6H4(PPh2R). Spectrophotometric acid−base titrations carried out in H2O/MeOH (9:1 vol.) afford pKR+ values of 7.3(±0.07) for [1]+, 6.92(±0.1) for [2]+, 6.59(±0.08) for [3]+, and 6.08(±0.09) for [4]+, thereby indicating that the Lewis acidity of the cationic boranes increases in following order: [1]+ 2]+ 3]+ 4]+. In agreement with this observation, fluoride titration experiments in H2O/MeOH (9:1 vol.) show that the fluoride binding constants (K = 840(±50) M−1 for [1]+, 2500(±200) M−1 for [2]+, 4000(±300) M−1 for [3]+, and 10 500(±1000) M−1 for [4]+) increase in the same order. These results show that the Lewis acidity of the cationic boranes increases with their hydrophobicity. The resulting Lewis acidity increase is substantial and exceeds 1 order of magnitude on going from [1]+ to [4]+. In turn, [4]+ is sufficiently fluorophilic to bind fluoride ions below the EPA contaminant level in pure water. These results indicate that phosphonium boranes related to [4]+ could be used as molecular recognition units in chemosensors for drinking water analysis

Synthesis, Structures, and Ethylene Dimerization Reactivity of Palladium Alkyl Complexes That Contain a Chelating Phosphine–Trifluoroborate Ligand

The chemistry of palladium alkyl complexes that incorporate the phosphine–trifluoroborate ligand ortho-(Ph2P)C6H4(BF3–) (PF–) is described. The reaction of the pinacol borane ortho-(Ph2P)C6H4(Bpin) with K[HF2] yields ortho-(Ph2P)C6H4(BF3K) (K[PF], 1). Crystallization of 1 from Et2O/THF in the presence of 18-crown-6 yields [K-(18-crown-6)][PF]·0.5THF (2·0.5THF). In the solid state, the phosphine–borate anion of 2 is ion-paired with the [K-(18-crown-6)] cation through weak contacts with the phosphorus and two fluorine atoms. 1 reacts with (COD)PdMeCl in the presence of 18-crown-6 to form [K-(18-crown-6)][(PF)PdMeCl] (3) and with (COD)PdMeCl and 2,4,6-collidine (col) to yield (PF)PdMe(col) (4). The PF– ligands in 3 and 4 are bound to Pd in a κ2 mode through the phosphine and one fluorine of the −ArBF3– unit. The other two fluorines are weakly bound to the K(18-crown-6)+ cation in 3. NMR studies show that the Pd–F interactions in 3 and 4 are maintained in solution and that, for 4, the three fluorine atoms undergo fast site exchange on the NMR time scale. 4 reacts with excess pyridine to yield (κ1-P-PF)PdMe(py)2 (6), in which the −ArBF3– unit has been completely displaced by pyridine. 4 slowly dimerizes ethylene to 1-butene (36 t.o./h, 23 °C, CH2Cl2, 400 psi ethylene). The catalyst resting state is (PF)PdEt(col) (7). Addition of [H(OEt2)2][B(3,5-(CF3)2-C6H3)4] traps the collidine as [collidinium] [B(3,5-(CF3)2-C6H3)4] and results in a 10-fold increase in the ethylene dimerization rate (385 t.o./h, 23 °C, CD2Cl2, 150 psi ethylene)

Synthesis and Anion Affinity of a Bidendate Sulfonium Fluorosilane Lewis Acid

The cationic fluorosilane [1-Ant2FSi-2-Me2S-(C6H4)]+ (2+) readily complexes fluoride ions to afford the corresponding zwitterionic difluorosilicate complex 1-Ant2F2Si-2-Me2S-(C6H4) (2-F) with a binding constant in CHCl3 of 7 (±1) × 106 M−1. Structural and computational results indicate that the high fluorophilicity of 2+ arises from both Coulombic and cooperative effects reflected by the formation of a Si−F→S bridge with a F→S distance of 2.741(3) Å

Synthesis and Anion Affinity of a Bidendate Sulfonium Fluorosilane Lewis Acid

The cationic fluorosilane [1-Ant2FSi-2-Me2S-(C6H4)]+ (2+) readily complexes fluoride ions to afford the corresponding zwitterionic difluorosilicate complex 1-Ant2F2Si-2-Me2S-(C6H4) (2-F) with a binding constant in CHCl3 of 7 (±1) × 106 M−1. Structural and computational results indicate that the high fluorophilicity of 2+ arises from both Coulombic and cooperative effects reflected by the formation of a Si−F→S bridge with a F→S distance of 2.741(3) Å