David L. Beach

A carbon-13 NMR study of some metal carbonyl compounds containing one-electron ligands

Carbon-13 NMR spectral data for complexes having the general formula CpM(CO)nX (Cp = η5-C5H5; M = Mo or W, n = 3; M = Fe, n = 2; X = halogen, methyl or acetyl) and their phosphine and isocyanide substitution products are reported. For CpM(CO)3X complexes two carbonyl resonances (1 : 2 ratio) are observed in all cases, consistent with the retention of the “piano-stool” geometries observed in the solid state. Substituted complexes CpM(CO)2(L)X (M = Mo or W; L = PR3 or cyclohexyl isocyanide) are unequivocally assigned cis or trans geometries on the basis of the number of observed carbonyl resonances and values of 2J(Pue5f8C) for the phosphine substituted derivatives. Spectral data for [M(CO)5X]− (M = Cr, Mo or W; X = Cl, Br or I) and η7-C7H7Mo(CO)2X and the halide derivatives above generally show an increase in the shielding for carbonyls adjacent to the halide ligand in the order Cl < Br < I. Carbonyl resonances are more shielded in isostructural complexes in the order Cr < Mo < W (triad effect).

Tertiary phosphine complexes of cyclopentadienylmolybdenum carbonyl halides. Stereoselective syntheses and isomer separations

Abstract Pure cis and trans isomers of CpMo(CO) 2 (L)X (Cp = η 5 -C 5 H 5 , L = PPh 3 or PBu 3 , X = Br, or I) have been separated by chromatography and characterized by infrared and proton NMR spectroscopy. The reactions of trans -CpMo(CO) 2 (L)CH 3 with HgX 2 (X = Cl, Br, I, SCN) afford cis -CpMo(CO) 2 (L)X in high yield. Both linkage isomers are obtained in the reaction with Hg(SCN) 2 , L = PPh 3 . The mercuric halides react with CpMo(CO) 2 (L)COCH 3 to form the metalue5f8metal bonded derivatives trans -CpMo(CO) 2 (L)HgX. Reactions of CpMo(CO) 2 (L)CH 3 or CpMo(CO) 2 (L)COCH 3 with bromine or iodine yield the halide complexes CpMo(CO) 2 (L)X (X = Br and I, respectively), the product mixtures containing high proportions of the trans isomers.

Isomerically pure cyclopentadienyl-molybdenum and -tungsten carbonyl halide complexes

Abstract Pure cis - and trans -(η 5 -C 5 H 5 )M(CO) 2 [P(C 6 H 5 ) 3 ]X (M = Mo, X = I or Br; M = W, X = I) have been separated by chromatographic methods. Stereochemical assignments are made on the basis of infrared and 1 H and 13 C NMR spectroscopy. Mechanistic implications of the cis/trans isomer ratios as a function of the method of preparation are discussed.

Linear dimerization of propylene and 1-butene catalyzed by (η3-4-cyclooctene-1-yl)- (1,1,1,5,5-hexafluoro-2,4-pentanedionato)nickel

Abstract The dimerization and oligomerization of propylene and 1-butene in the presence of homogeneous Group VIII transition metal catalysts has been extensively studied. In most cases the products obtained are mixtures of isomers in which branched species predominate, in accordance with preferred anti-Markownikov addition pathways. In what is perhaps the most well-defined catalyst system to date, a family of substituted fluoroacetylacetonate cyclooctenyl nickel complexes, 1-butene is oligomerized to up to 82% linear octenes. Propylene and 1-butene are dimerized to predominantly normal alkenes using homogeneous hydrocarbon solutions of (η3-4-cyclooctene-1-yl)(1,1,1,5,5,5-hexafluoro)-2,4-pentanedionato)nickel. Two disadvantages of this catalyst system are its relatively low activity and rapid deactivation on storage. In this paper, an improved synthesis of the catalyst is reported, in addition to a method of catalyst storage which virtually eliminates deactivation A comprehensive olefin dimerization reaction scheme is formulated on the basis of detailed gas chromatographic analyses of propylene and 1-butene dimers. The relative amounts of the materials identified allow conclusions to be drawn on relative rates for the competing olefin insertion, β-elimination pathways.

Rhodium catalyzed reactions of bicyclic hydrocarbons. products, mechanism, and the nature of the catalyst

Abstract The rhodium complexes Rh(PPh 3 ) 3 Cl and Rh(PPh 3 ) 2 (CO)Cl catalyze the ring opening of endo -6-carbomethoxybicyclo[3.1.0]hex-2-ene (I) forming the five possible isomeric carbomethoxycyclohexadienes II–VI. The rate of the reaction is dramatically accelerated by the presence of O 2 , and the dioxygen complex [Rh(PPh 3 ) 2 (Cl)O 2 ] 2 has been shown to be an active catalyst precursor for the reactions. A mechanism involving theintermediacy of cyclohexadienylrhodium hydride complexes accounts for the products formed and their subsequent interconversions.

Mechanism of thermolysis of tetramethylammonium μ-chlorobis(triethylaluminate)

Abstract The thermolysis of tetramethylammonium μ-chlorobis(triethylaluminate) has been investigated. In addition to the previously reported products, [Me4N][Clue5f8AlEt3] and (AlEt3)2, Me3N · AlEt3 is formed simultaneously in lesser amounts. A mechanism for the observed thermolysis reactions is presented which predicts formation of methyl chloride as a transient species which undergoes further reaction with (AlEt3)2 to ultimately produce methane and ethylene. The experimentally observed methane/ethylene ratio supports the proposed mechanism.

Rhodium catalyzed reactions of bicyclic hydrocarbons. : Substituent, stereochemical and ring size effects

Tris(triphenylphosphine)rhodium(I) chloride in the presence of oxygencatalyzes the rearrangement of bicyclo[3.1.O]hex-2-enes, producing cyclohexadienes. Rearrangement rates are increased by introduction of methyl or carboxymethyl substituents at C6, the effects being maximized when the methyl group is exo and/or the carboxymethyl group is endo. Bicyclo[4.1.O]hept-2-enes are less reactive but yield analogous products. Bicyclo[6.1.0]non-2-enes are unreactive under the reaction conditions even after two years.

Dissociative Phenomena in Triethylaluminum Complexes of Alkali Metal Halides and Pseudohalides

Abstract During the course of investigations into the stability of complexes derived from triethylaluminum and alkali metal halides and pseudohalides, we have discovered that 1–decene induces dissociation of A1Et3 from M[A12Et6X] complexes, where MX = KC1, KN3, NaN3, KSCN, NaCN and NaF. These results provide experimental evidence that an olefin-alkylaluminum π interaction can be sufficiently strong to promote cleavage of the A1−X sigma bond, X = halide or pseudohalide in these systems.