Salicylaldehyde derivatives and related β-hydroxo aldehydes CHO-CR=CR′-OH react with CoMe(PMe3)4 via oxidative substitution to form low-spin d6 complexes mer-CoH(CO-CR=CR-O)(PMe3)3. Reductive elimination of acyl and hydride functions from cis positions at the metal is less favourable than in carbonyl cobalt intermediates through a pronounced stabilization by neutral phosphane σ-donor and dianionic acylenolato chelate ligands. Reactions of the hydride complexes with iodomethane or with protic acids HX afford octahedral molecular complexes mer-CoX(CO-CR=CR′-O)(PMe3)3 (X =I, OAc) and mer-CoX(CO-CR=CR′-O)(PMe3)2 (X = OAc, O-CR′=CR-CHO) without opening of the acylenolato chelate ring.
Complexes raer-CoH(CO-CR=CR'-0)(PMe3)3 react with haloalkanes RX (X = Br, I) or with acids HX (X = Cl, Br) under elimination of dihydrogen. In both reactions a change of configu ration at the metal is brought about by directional steering through the hard/soft (acyl)enolato chelate ligands to form octahedral complexes raer-CoX(CO-CR=CR'-C))(PMe3)3 or sterically crowded ionic compounds [Co(CO-CR=CR'-0)(PMe3)4(3)]+ X-(X = C104) without opening of the (acyl)enolato chelate ring.
Einleitung
A correlation between spontaneous polarisation and the chirality index of the constituent molecules, multiplied by the molecular transverse dipole, has been considered for five series of ferroelectric smectic C* liquid crystals. A good correlation has been found within each series, and it has been shown that the scaled chirality index may be used to estimate the spontaneous polarisation in a series of smectic C* mesogens with small systematic changes of the molecular structure. At the same time one cannot expect any significant correlation between the polarisation and the chirality index for smectic C* materials of sufficiently different structure because the spontaneous polarisation may be significantly effected by some details of the molecule's structure including the orientation of the transverse dipole with respect to the primary short molecular axis.
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