Ernst G. Hoffmann

Transition metal allyls ☆: III. The (η3-allyl)2M complexes of nickel, palladium and platinum: structural considerations

Abstract The structures of a series of (η 3 -allyl) 2 M complexes of nickel, palladium and platinum have been investigated with the help of 13 C NMR, 1 H NMR and Raman spectroscopy. The crystal structure of (η 3 -cyclooctatrienyl) 2 Ni has been determined by X-ray methods; the two nickel-bonded η 3 -allyl groups are mutually trans .

Ir- und 1H-NMR-spektroskopische untersuchungen an zirkon und hafniumallylen : I. Übergangsmetallallyle

Abstract A general scheme, utilizing both energetic and kinetic data, has been derived for the classification of allylmetals. On the basis of IR spectral data, three categories 1–3 may be formulated. These may be subdivided into a and b on the basis of their 1 H NMR spectra and hence 6 different types may be distinguished π-, σ-, π- and σ-dynamic or static. The spectra of allyl-zirconium and -hafnium compounds (MA 4 , COTMA 2 , COTMMet 2 , COTMCrot 2 , M = Zr, Hf; A = allyl; Met = methylallyl; Crot = crotyl; COT = cyclooctatetraene) are discussed and the compounds classified according to the above scheme.

Structure, thermal stability and decomposition of bis-allyl-zinc compounds

Abstract The structure, thermal stability and decomposition of solutions of diallylzinc (I), bis(2-methylallyl)zinc (II), bis(3-methylallyl)zinc (III) and bis(3,3-dimethylallyl)zinc (IV) in deuterated solvents, have been investigated by1H NMR and by kinetic measurements at temperatures between −125 and +180°C. At room temperature I, II, III and IV are dynamic systems and are best described as being rapidly equilibrating mixtures of all isomeric σ-allyl forms; the NMR spectra are averages weighted according to the relative concentrations of the respective forms. I displays a1H NMR spectrum of a static σ-allyl system only below −125°C and II only below −115°C. At temperatures above 100°C the thermal decomposition of I–IV results in coupling of the allyl groups, decomposition via radicals being the major process. The coupled products exhibit CIDNP, in which the multiplet polarisations confirm a decomposition via randomly diffusing allyl radicals. In the allyl radicals CH2CR1CR2R3 an alternating spin density was proved experimentally. The thermal stability decreases in the order I > II > III > IV.

1H NMR study of the fluxional behaviour of tetraallylhafnium and cyclooctatetraenediallylzirconium

Abstract The thermodynamic data for the syn—anti rearrangement in tetra-η3-allylhafnium and cyclooctatetraenedi-η3-allylzirconium have been calculated by line shape analysis of the temperature dependent 1H NMR spectra.