Monohalocarbene complexes

This is the principal method of synthesis. In the special case when X = F 

A derived Ru(II) CF3 complex, Ru(CF3)Cl(CO)(MeCN)(PPh3)2, is a good substrate for generation of a CF2 complex using either anhydrous HC1 gas (22) or Me3SiCI as fluoride-abstracting reagents, 

When Cd(CF3)2 is used instead of Hg(CF3)2 to introduce a CF3 group the reaction proceeds a step further producing a zero-valent CF2 complex (21). 

The simple oxidative addition product Ru(CF3)(CdCF3)(CO)2(PPh3)2 is a likely intermediate in this reaction. Several stable, zero-valent CF2 complexes have been isolated using Cd(CF3)2, and they are included in Table VII (see Section V,C,2,b). 

The suggested intermediate Ru(CCl3)Cl(CO)2(PPh3)2 could not be detected. 

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Dihalo- and Monohalocarbene Complexes Some Structural Parameters... 

Halide addition to a cationic carbyne complex, [L M=CR]+, or halogen oxidation of a low oxidation state carbyne complex are both potential routes to monohalocarbene species. Examples of the first process are well known for carbyne complexes from Groups 6 and 7 of the periodic table (120), e.g.,... 

Modification of a Complex-Already Incorporating a Monohalocarbene Ligand... 

The first carbene compound to be well characterized was prepared in 1966 and was one of many Fischer-Type Carbene Complexes to be reported (see equation 7). Fischer carbenes are characterized by heteroatom substituents at the carbene carbon, stabilization by a low-valent metal center, and a partial positive charge at the carbene carbon. In contrast, Schrock-Type Carbene Complexes, or alkylidenes," that have alkyl substituents, are found on metal centers in higher oxidation states, and are nucleophihc at carbon. Many Fischer carbenes are known for chromium, whereas chromium alkylidenes are much less common. Monohalocarbenes of chromium, for example, (OC)5Cr=C(F)NEt2, have also been extensively investigated." Two carbene reactions of note for their application to organic synthesis are the cycloaddition of alkenes with carbene complexes and the reaction of aromatic carbenes with aUcynes to yield complexed naphthols (the Dotz reaction ). ... 

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