also been observed for tris (trimethylsilyl) ethylenediamine. This compound condenses to a previously known compound, l,3-bis(trimethylsilyl ) -2,2-dimethyl-2-silaimidazolidine. Dr. Ishikawa and Dr. West point out that this new condensation reaction is remarkable in that a C-Li compound is formed from an N-Li compound, even though the N-Li bond is much more stable. The driving force for the condensation reaction, the Wisconsin chemists say, must be the formation of the highly stable N-Si-NSi structure in the imidazolidine compound. The condensation reaction may provide ways of synthesizing novel Si-N-Si polymers, Dr. West says, and such reactions are now under study.
Pt complex catalyzes novel hydrogénation
GAS CHROMATOGRAM. Dr. Mitsuo Ishikawa (right) and Dr. Robert West examine gas chromatogram for traces of reaction products. The technique was used to separate silylethylenediamines
served if the two nitrogens are attached to an aromatic ring, as in Nphenyl-N,N'-bis ( trimethylsilyl ) -ophenylenediamine. According to Dr. Ishikawa and Dr. West, other 1,4anionic rearrangements have been observed previously, but none in which substituents moved between nitrogen atoms. They believe, however, as in hydrazine rearrangement, that the movement of an organosilicon substituent is especially favored because the silicon atom can use a 3d orbital to form a low-energy, pentacovalent transition state. When they used methylethylenediamine instead of a phenylethylenediamine as the starting material, rearrangement did not take place at room temperature. However, at higher temperatures (65° C. in tetrahydrof uran ), N-metnyl-N,N'-bis- ( trimethylsilyl ) ethylenediamine underwent a totally unexpected condensation reaction. In that reaction, a methyl group from one of the silicon atoms was eliminated as methyllithium, and the compound formed silicon imidazolidine, a five-membered ring compound. The structure of this new product, Dr. West says, was established by NMR and IR spectroscopy. It isn't known how general the new condensation reaction is, but it has
Certain complexes of platinum, palladium, and nickel catalyze the hydrogénation of all but one double bond of methyl linoleate and linolenate. The hydrogénations may occur either with elemental hydrogen or with methanol. In work at the University of Illinois, Dr. John C. Bailar, Jr., and Dr. Hiroshi Itatani (now at Ube Industries in Japan) found that the hydrogénation of linoleate is preceded by conversion of cis double bonds to trans and by migration of the double bonds to form a conjugated system. The transition metal complexes may also cause the cistrans isomerization of methyl oleate. In a typical experiment, they hydrogenated methyl linoleate with dichlorob i s ( t r iphenylphosphine ) platinum ( II ) alone and found the reaction yields 4 . 1 % monoenate and no conjugated diene. Adition of tin (II) chloride, however, increased the yield of monoenate to 14.4% and of conjugated diene to 43.2% [J. Am. Chem. Soc, 89, 1592 (1967)]. The discovery and isolation of transition metal complexes containing the hydrido ligand permit the study of their relationship to catalytic hydrogénation. This catalytic activity is associated with the low-lying unfilled or f orbitals in the metal which can form weak bonds with the hydride ion by accepting electrons from it. In a solvent mixture of methanol and benzene, platinum complexes of this type catalyze isomerization reactions as well as hydrogénation, under either nitrogen or hydrogen pressure. The methanol in the mixture sometimes is the hydrogen source. Similar complexes of palladium and nickel also act as catalysts. The hydrogénations in the Illinois
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— — ~ After hydrogénation Monoenoate
Oienoate
SOYBEAN OIL. Gas chromatogram of soybean oil methyl ester from 2 0 % diethyleneglycol succinate verifies highly specific catalytic activity of some metal complexes. After hydrogénation, the trienoate is gone, the dienoate almost so, while the monoenate has greatly increased
50 Time, minutes Source: J. Am. Oil Chemists' Soc.r 44, 147 (1967)
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experiments were usually carried out under high pressures of hydrogen (about 39 atm.). However, when the reactions were at atmospheric pressure (either nitrogen or hydrogen), the platinum and palladium catalysts caused isomerization and migration of the double bonds, but not hydrogénation. The catalysts used by Dr. Bailar and Dr. Itatani were of the type (R 3 Q) MX 2 , where R represents an alkyl or aryl group; Q represents phosphorus, arsenic, or antimony; M represents platinum, palladium, or nickel; and X represents a halogen or halogenoid. In general, a compound of the type M'X 2 or M'X 4 (M' represents silicon, germanium, tin, or lead) was then added. This converts one (or perhaps more) of the X ligands in the hard metal complex to an M'X 8 or similar ligand. Dr. Bailar says the M'X 3 group is simply an electrophilic ligand which modifies the M—H bond to such an extent that the complex can react with double bonds. Two of the catalysts in the platinum series studied are mixtures of tin (II) chloride and dichlorobis (triphenylarsine) platinum (II) and a mixture of tin (II) chloride and dichlorobis (triphenylphosphine ) platinum ( II ). Benzene and methanol mixtures are suitable solvents for the reductions with platinum and palladium. But they are not suitable for nickel complexes, which are unstable in these solvent systems. If an alcohol higher than methanol is used, extensive ester exchange may take place. Not all the platinum or palladium complexes studied are effective as catalysts. However, addition of tini l l ) chloride enhances the reactivity of dichlorobis ( triphenylphosphine ) platinum (II) or the analogous palladium complex. Tin chloride has no effect on the nickel complexes. Mixtures of tin (II) chloride with
dichlorobis (triphenylarsine) platinum (II) or potassium tetrachloroplatinate(II) are effective catalysts, but mixtures of tin (II) chloride with dichlorobis ( triphenylarsine ) palladium( II ) or potassium tetrachloropalladate(II) are not. Both dicyanobis( triphenylarsine) palladium (II) and dicyanobis (triphenylphosphine) palladium (II) alone are effective catalysts, but the dicyanoplatinum analogs are not. Dr. Bailar found that under some conditions, a mixture of potassium tetrachloroplatinate(II) and tin (II) chloride dihydrate is also an effective agent for hydrogénation of linoleate and isomerization of oleate. This catalyst is not effective unless elemental hydrogen is present. As might be expected, Dr. Bailar says, the selective hydrogénation reaction depends on the temperature and concentration of the catalyst. In one case, doubling the concentration of catalyst increased the formation of monoene from 14.6 to 65.4%. The formation of small amounts of stéarate in some of the experiments was probably due to the catalytic action of a small amount of platinum black formed during the hydrogénation. The transition metal catalysts could be re-used, proving their stability. In another series of experiments, Dr. Bailar and Dr. Itatani studied the catalytic effects of bistriphenylphosphine nickel halides in benzene and in tetrahydrofuran ( T H F ) . They found that hydrogénation with hydrogen gas goes more rapidly in benzene than in THF. But hydrogénation with methanol proceeds more rapidly in T H F than in benzene. Methyl oleate is converted to trans isomers but not to stéarate under hydrogen pressure using these catalysts. However, methyl oleate is not affected in the absence of hydrogen.
