Publisher Summary The chapter focuses on carbene andcarbyne complexes. If one of the hydrogen atoms in an alkane hydrocarbon, such as ethane, is formally replaced by a metal atom, an organometallic compound in which the organic entity is bonded to the metal by a σ-bond is obtained. If a system with 2 carbon atoms bonded to each other by a double bond, i.e., an alkene molecule, is considered, a number of separate paths leading to organometallic derivatives are recognized. One path involves the replacement of a substituent by a metal atom and leads to σ compounds that are exemplified by vinyl-lithium derivatives. If molecules with a carbon-carbon triple bond of the type that exists in alkynes are considered, then it is realized that there also are three possible paths to metal-containing derivatives. The chapter discusses various properties of transition metal-carbene complexes such as preparation of the first carbene complexes, bonding concepts, and spectroscopic findings. It also presents various properties of transition metal-carbyne complexes such as preparation of the first carbyne complexes and x-ray structural analyses.

On the Way to Carbene and Carbyne Complexes

Preparation de catenates dimetalliques par reaction assistee et dont la decomplexation donne les catenandes correspondants

https://pubs.acs.org/doi/pdf/10.1021/ja00307a049

Synthesis of biscopper(I) [3]-catenates: multiring interlocked coordinating systems.

Chromium aminocarbene complexes in organic synthesis

Natrium-hydrogentetracarbonylferrat (4) reagiert mit 1.4-Dimethyl-tetrazolium-tetrafluoroborat (5) zu einem Gemisch von (1.4-Dimethyl-tetrazolium)-carbonylferraten (6). Diese spalten Wasserstoff und Stickstoff ab, wobei (1.4-Dimethyl-tetrazolinyliden)- (7) und [Bis-(methylamino)carben]-tetracarbonyl-eisen(0) (8) entstehen. Struktur und Bindungsverhaltnisse dieser neuen Komplexe werden anhand spektroskopischer Daten diskutiert, Vergleiche mit (1.3-Dimethyl-imidazolinyliden)-tetracarbonyl-eisen(0) (10) und N.N' -Dimethyl-harnstoff (9) werden angestellt. Die Bildungsmechanismen von 7 und 8 werden diskutiert.



(1.4-Dimethyltetrazolium)carbonylferrates, Starting Products for (1.4-Dimethyltetrazolinylidene)- and Bis(methylamino)carbene Complexes



Sodium hydrogen(tetracarbonyl)ferrate (4) reacts with 1.4-dimethyltetrazolium tetrafluoroborate (5) to yield a mixture of 1.4-dimethyltetrazolium carbonylferrates (6). These split off hydrogen and nitrogen under formation of (1.4-dimethyltetrazolinylidene)- (7) and [bis-(methylamino)carbene]tetracarbonyliron(0) (8). Structures and bonding properties of these new complexes are discussed by means of spectroscopic data, comparisons are made with (1.3-dimethylimidazolinylidene)tetracarbonyliron(0) (10) and N.N' -dimethylurea (9). The mechanisms of formation of 7 and 8 are discussed.

(1.4-Dimethyl-tetrazolium)-carbonylferrate, Ausgangsprodukte für (1.4-Dimethyl-tetrazolinyliden)- und Bis(methylamino)carben-Komplexe

Publisher Summary This chapter deals with the chemistry of the Fischer-type complexes. The key to the rich chemistry of the Fischer carbene complexes is that they can undergo reactions at several sites; they include modification of the carbene fragment, reaction on the side chain or the metal, and insertion of unsaturated organic molecules into the metal–carbon bond. After such elaborations of the carbene complex, removal of the metal to complete the synthesis of the target organic molecule is usually a simple task. The most prominent systems studied so far are the Fischer carbene complexes of the Group 6 metals. The chapter discusses nucleophilic substitution process, for example, the replacement of the MeO group by a group with a different heteroatom, such as an amino or thioalkyl group. This reaction proceeds via a tetrahedral intermediate and is similar to nucleophilic substitutions on carboxylic esters. Another common reaction based on the acidity of the α-carbon proton—that is, the carbon attached to the carbene carbon—has also been discussed in detail. The carbanion that results from the deprotonation of the α-carbon can act as a nucleophile and react with a variety of electrophiles, especially in the presence of Lewis acid catalysis, to form many different products.

The Physical Organic Chemistry of Fischer Carbene Complexes

The preparation of a series of aminocarbenepentacarbonylchromium complexes of the type (CO)5CrC(Me)NR1R2 is reported. The influence of steric and of substituent effects upon the physical properties of the complexes has been investigated. Attention is drawn to elimination reactions which may occur during the preparation of aminocarbene complexes with secondary amines.

J. A. Connor

Papers

Transition-metal carbene complexes. Part XII. Substituent and steric effects in aminocarbene complexes of chromium