Jeffrey B. Hoke

Catalytic hydrodechlorination of chlorophenols

Abstract Feasibility studies have shown that complete destruction of chlorophenols by hydrodechlorination over palladium/carbon is possible under mild reaction conditions. When hydrogen was used as the reducing agent, all chlorophenols investigated could be cleanly hydrodechlorinated to phenol at 35°C and 35 psi (1 psi=6.895 kPa). In general, increasing the degree of chlorine substitution on the phenol ring decreased the rate of dechlorination. Base was required for the reaction to occur, and ammonium hydroxide was found to be superior to sodium hydroxide, sodium acetate, and triethylamine. Aging studies using 4-chlorophenol as substrate showed dramatic improvement in catalyst lifetime when a 50/50 mixture of ethanol/water was used as the reaction solvent instead of ethanol. In the case of 4-chlorophenol which has significant water solubility, hydrodechlorination also worked well when water was the solvent. When hydrazine (sulfate or hydrate) was used as the reducing agent, all chlorophenols investigated could be cleanly dechlorinated to phenol without the need for a pressure apparatus. Except for pentachlorophenol which required a higher reaction temperature (50°C), dechlorinations were accomplished at room temperature. Using 4-chlorophenol as substrate, both water and 50/50 ethanol/water were found to be superior reaction solvents to ethanol.

Catalytic asymmetric hydrogenation of β-ketoesters using new BINAP complexes of ruthenium

Abstract Two new, air-stable BINAP complexes of ruthenium(II), (RCp)Ru(S-(−)-BINAP)Cl (R=1cr; H, CH3) have been prepared in good yield from the reaction of (RCp)Ru(PPh3)2Cl with S-(−)-BINAP in refluxing toluene. The structure of the methylcyclopentadienyl analog has been determined by X-ray crystallography. Both complexes have been found to be effective homogeneous catalysts for the enantioselective hydrogenation of β-ketoesters.

Low-temperature vapour deposition of high-purity iridium coatings from cyclooctadiene complexes of iridium. Synthesis of a novel liquid iridium chemical vapour deposition precursor

High-purity, crystalline iridium coatings have been prepared by low-temperature chemical vapour deposition (CVD) from three volatile cyclooctadiene (COD) iridium precursors. One of these, (MeCp)Ir(COD)(MeCp = methylcyclopentadienyl), is a novel complex which melts at low temperature (40 °C) and therefore can be used as a liquid iridium source for CVD. When hydrogen is used as a carrier gas, iridium coatings containing < 1 atm % carbon are generated at ca. 120 °C using (MeCp)Ir(COD) and CpIr(COD)(Cp = cyclopentadienyl). Likewise, deposition under low oxygen pressure in partial vacuum also generates coatings free of carbon and oxygen. However, when the deposition is carried out in vacuo(no carrier gas), ca. 80% carbon is incorporated into the films. When [(COD)Ir(µ-OAc)]2(OAc = acetate) is used as the metal-organic CVD (MOCVD) precursor, films containing < 1% carbon and oxygen are obtained at ca. 250 °C in vacuo without the need for a carrier gas.

Synthesis of new bis(trimethylsilylcyclopentadienyl) complexes of hafnium

The new trimethylsilylcyclopentadienyl hafnocene complexes, (Me3SiCp)2Hf(Cl)(BH4), (Me3SiCp)2Hf(H)(BH4), (Me3SiCp)2HfMe2, (Me3SiCp)2Hf(OR)2 (R = Me and Et), and (Me3SiCp)2Hf(Cl)(OMe), have been prepared in good yield from the reactions of (Me3SiCp)2HfCl2 with LiBH4, MeLi, Et3N/ROH (R = Me and Et), or NaOMe. All were isolated as volatile, low melting solids or oils. In the reaction of (Me3SiCp)2HfCl2 with LiBH4 in hexane, either the borohydride-chloride complex, (Me3SiCp)2Hf(Cl)(BH4) or the borohydride-hydride complex, (Me3SiCp)2Hf(H)(BH4), was isolated depending on the reaction temperature. Although the expected bis(borohydride) complex, (Me3SiCp)2Hf(BH4)2, was not obtained, 11B NMR spectroscopy suggests that it may be formed as an intermediate which subsequently loses BH3 to form (Me3SiCp)2Hf(H)(BH4).

Low-temperature vapour deposition of high-purity copper coatings from bis[N-(fluoroalkyl)salicylaldiminato]copper chelates

High-purity copper coatings have been prepared by chemical vapour deposition at low temperature from two nove bis[N-(fluoroalkyl)salicylaldiminato] chelates of copper(II). When hydrogen is used as the carrier gas at ambient pressure, copper coatings containing < 1 atom.% carbon, oxygen, nitrogen, and fluorine are generated at 290 and 330 °C using Cu(NCH2CF2CF3-SAL)2 and Cu(NCH2CF2CF2CF3-SAL)2, respectively (SAL = salicylaldiminato). When the deposition is carried out in vacuo, ca. 6% carbon, 2% oxygen, and 3% fluorine are incorporated into the films using Cu(NCH2CF2CF3-SAL)2 as the copper source.