Organic and Organometallic Catalysts for Aqueous Nitrile Hydration and Carbon-Carbon Bond Forming Reactions

Abstract

This dissertation investigates the ability of the phosphine 1,3,5-triaza-7-phosphaadamantane (PTA) and derivatives to serve as either organocataysts or ancillary ligands coordinated to transition metal catalysts. PTA and "upper rim" modified PTA derivatives were evaluated as organocatalysts for the Morita-Baylis-Hillman reaction and Henry (nitroaldol) reaction. Transition metal complexes were utilized as water soluble catalysts in the aqueous or aqueous biphasic hydration of nitriles or Suzuki cross-coupling of aryl bromides with phenyl boronic acid. In many cases the metal catalysts were synthesized in situ. Molybdenum and tungsten pentacarbonyl complexes [Mo(CO)₅{P(CH₂NH₂)₃}] (<bold>12</bold>) and [W(CO)₅{P(CH₂NH₂)₃}] (<bold>13</bold>) were synthesized and characterized by <super>1</super>H, <super>13</super>C{<super>1</super>H}, <super>31</super>P{<super>1</super>H} NMR spectroscopy, Infared spectroscopy, and ESI-MS. Insight into the electronic characteristics of P(CH₂NH₂)₃ (<bold>5</bold>) were obtained by comparison of the A₁ (CO) stretching frequencies with known phosphine complexes of the form M(CO)₅L, M = Mo, W. P(CH₂NH₂)₃ (<bold>5</bold>) is a strong &#963; donor ligand with an A₁ &#957;(CO) of 2069 cm<super>-1</super> similar to PTA and trimethylphosphine. Ruthenium arene complexes of P(CH₂NH₃Cl)₃ (<bold>4</bold>) and PTA were also synthesized and characterized by <super>1</super>H, <super>13</super>C{<super>1</super>H}, <super>31</super>P{<super>1</super>H} NMR spectroscopy, ESI-MS, and single crystal X-ray crystallography. These complexes are the first examples of P(CH₂NH₃Cl)₃ (<bold>4</bold>) and P(CH₂NH₂)₃ (<bold>5</bold>) coordinated to a metal center.Generation of a nitrile hydration catalyst in situ by reacting RuCl₃ and PTA was evaluated and compared with [RuCl₂PTA₄]. These catalysts were evaluated for nitrile hydration in water under air at 100°C. Both systems were tolerant of electron rich, electron neutral, and electron deficient aryl nitriles and aliphatic nitriles. When the pH was varied from acidic to basic the rate of reaction increased for both catalyst systems; At highly basic pH the buffer solution catalyzes the reaction. A pH of 6.8 was chosen for the reaction and used in all experiments. [RuCl₂PTA₄] was observed to be a more efficient catalyst relative to the in situ generated catalyst. Ruthenium arene complexes with P(CH₂NH₃Cl)₃ (<bold>4</bold>) and PTA were also evaluated as catalysts for the hydration of nitriles in water in air at 100°C. Conversion of nitrile to amide was modest to fair in water with good to excellent conversions (57-99%) at pH 6.8.Palladium in situ generated complexes of PTA and PTA derivatives were examined as Suzuki cross-coupling catalysts in water and acetonitrile at 80°C. Poor to excellent coupling of phenyl boronic acid with bromobenzene was observed with the best catalyst obtained from the reaction of PdCl₂ with ring open PTA (<bold>19</bold>). Compound <bold>19</bold> was observed to be tolerant of electron rich, electron neutral, and electron deficient aryl bromides. However, <bold>19</bold> was unable to couple the pseudo aliphatic bromide (2-bromoethyl)benzene with phenyl boronic acid.PTA and "upper rim" PTA derivatives (1 and 2) were observed to catalyze the MBH reaction of acrylates with electron deficient aryl aldehydes at room temperature. Good yields (64-82%) were obtained with electron deficient aldehydes. No reaction was observed when electron neutral aryl aldehydes were evaluated. These phosphines were also capable of catalyzing the Henry (nitroaldol) reaction of electron rich, electron neutral, and electron deficient aryl aldehydes with nitromethane in poor to excellent yields (28-97%). Electron rich aryl aldehydes were the least reactive while electron deficient aryl aldehydes were the most reactive. PTA derivatives 1 and 2 were also evaluated as enantioselective MBH catalysts with poor enantiomeric excess (10%) observed.