Chlorocarbene complex

Iron(II) porphyrins react readily with haloalkanes in the presence of reducing agents, e.g., excess iron powder, to give chlorocarbene complexes 15,32). With the insecticide DDT [2,2-bis(4-chlorophenyl)-1,1,1 -trichloro-ethane, (C1C6H4)2CHCC13], the reaction proceeds one step further, by elimination of HC1 from the carbene complex, to give diarylvinylidene complexes 33) ... 

Chloride abstraction 5.8.2.16.3 Reaction with chlorocarbene complexes ... 

Trichloromethyl thioalkyl compounds of formula RSCXClj (a, b, X = Cl, R = Ph or CHjPh) as well as dichloromethyl benzyl thioether react with iron(II) tetraphenylporphyrin (TPP) (233), in the presence of a reducing agent (iron powder or Na2S204), to produce chlorocarbene complexes of type 234 (158). 

Fig. 3.34. Synthesis of [Ir(TpMs )N2>] and formation of a chlorocarbene complex upon cleavage of C-H and C-Cl in CH2CI2.

Chloride absU-action 12, 5.8.2.16.3 Fluorination agent 3, 2.5.12.3.4 Reaction with chlorocarbene complexes 12,... 

Somewhat more unusual is the recently described formation of the chlorocarbene complex 576, obtained via the fragmentation of CH2CI2 by the dinitrogen complex (K -iV,iV, A",C,C -Tp Tr(N2) (577), which is in turn generated photolytically from 578 (Scheme 60). " The identity of 576 was determined spectroscopically, its hydrolytic instability precluding isolation in analytical purity. Nonetheless, treating 576 with one equivalent of 3-mesitylpyrazole cleanly converted it to the pyrazolylcarbene complex 579, which was isolated and crystallographically characterised. 

The carbyne complex W(CO)2(CNEt2)Cp adds HCl so forming the chlorocarbene complex WCl(CO)2[CH(NEt2 ) ]Cp. ... 

Moreover, ab initio calculations indicate that additions of chlorocarbenes to ethylene or TME lead to cyclopropanes either without the intermediacy of CACs,39 or via broad shallow wells for complexes that might occur in the reaction enthalpy profile but are not minima on the free energy surface.40 More recent calculations confirm these conclusions CACs are not predicted to be im-... 

Abstraction of chloride anion from a chlorocarbene ligand by a strong halide acceptor is another route to carbyne complexes ... 

A number of reactions of organothiols with complexes of alkoxycar-benes, isocyanides, or thiocarbonyls, leading to thiocarbene complexes, have been reviewed (4,125,126). Further related examples include the conversion of a chlorocarbene to a dithiocarbene by reaction of the ruthenium complex 154 with RSH (R = Me, p-tolyl) or HSCH2CH2SH to give the dithiocarbene compounds 155 and 156 (82). 

The osmium carbyne complex 115 reacts with elemental sulfur, selenium, and tellurium to afford the complexes 135 in which the element atoms "bridge the metal-carbon triple bond [Eq. (123)] (56). Complex 115 also reacts with transition metal Lewis acids such as AgCl or Cul to give dinuclear compounds with bridging carbyne ligands. Reaction with elemental chlorine results in addition across the metal-carbon triple bond to generate the chlorocarbene osmium complex 136 [Eq. (124)]. 

Ir(TpMs )(N2)]5 which contains a pentadentate, doubly metalated 3-mesityl substituted tris(pyrazolyl)borate ligand, was obtained according to the reaction scheme depicted in Fig. 3.34. The compound induces the cleavage of C-H and C-Cl bonds of CH2CI2 to yield a highly electrophilic chlorocarbene Ir=C(H)Cl complex.176... 

Krogh-Jespersen, K., Yan, S., and Moss, R. A. "Ab Initio Electronic Structure Calculations on Chlorocarbene-Efhylene and Chlorocarbene-Benzene Complexes." /. Am. Chem. Soc., 121, 6269-6274 (1999),... 

Although the COC mechanism can explain the experimental observations, there are two problems that have not been resolved. First, a carbene-olefin complex has never been experimentally detected. Second, modem ab initio calculations do not predict free energy minima corresponding to COCs in the reaction of chlorocarbenes with olefins. They do, however, predict thermally stable Jt—complexes between benzene and carbenes, indicating that a COC mechanism might be operative if reactions are rim in aromatic solvents. ... 

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