FLUORINATED ISOCYANIDES - MORE THAN LIGANDS WITH UNUSUAL PROPERTIES

The substitution of hydrogen by fluorine in organic compounds usually results in drastic changes in their properties. For isocyanides, for which fluorinated examples have only recently become available in preparative quantities, this substitution leads to a significantly increased reactivity and a tendency to polymerize, which, on one hand, makes their handling more difficult. On the other hand, this high reactivity makes the fluorinated isocyanides useful building blocks for the synthesis of compounds like N‐trimethylformamide. Energetically favorable π* orbitals bestow excellent π‐acceptor properties towards low‐valent transition metal complexes, especially on the ligand trifluoromethyl isocyanide. The pronounced tendency of this ligand to bridge two metal atoms enables the formation of structural types that are not accessible with other π‐acceptor ligands. Thus it was possible to prepare [(Os3(CO)11(μ2‐CNCF3)2] (a) derivative of the hypothetical [Os(CO)13]) which may be considered as a model for an associative mechanism of ligand substitution at carbonyl clusters. In contrast to the well‐studied chemistry of trifluoromethyl isocyanide, that of the few other known fluorinated isocyanides is only now receiving attention. In particular the only recently synthesized trifluorovinyl isocyanide promises a rich chemistry as a result of its difunctionality. Copyright © 1994 by VCH Verlagsgesellschaft mbH, Germany