Chromium complexes ylide

The configuration of these complexes were established on the basis of IR and H-NMR spectra (62). When triphenylarsine was reacted with sulfoxonium ylide complex, pentacarbonyl triphenylarsonium ylide-chromium complex was obtained (95). 

Iminocarbene complexes of chromium and tungsten are useful isolable synthetic equivalents to nitrile ylides having the advantage that the range of 1,3-dipo-larophiles is not limited to electron-acceptor substrates and can be extended to electronically neutral as well as to electron-rich systems [56] (Scheme 18). 

Photolysis or thermolysis of heteroatom-substituted chromium carbene complexes can lead to the formation of ketene-like intermediates (cf. Sections 2.2.3 and 2.2.5). The reaction of these intermediates with tertiary amines can yield ammonium ylides, which can undergo Stevens rearrangement [294,365,366] (see also Entry 6, Table 2.14 and Experimental Procedure 2.2.1). This reaction sequence has been used to prepare pyrrolidones and other nitrogen-containing heterocycles. Examples of such reactions are given in Figure 2.31 and Table 2.21. 

The imino carbene complexes of tungsten and chromium (e.g., 81) also serve as nitrile ylide synthons (40). The mngsten complexes gave higher yields of the adducts and were strongly regioselective for product 82. For example, for 81 (M=W R = Me, Ph R = Pr, Ph R" = H), the pyrrole 82 was produced in yields of 65-75% with <1% of 83. This route to pyrroles thus has clear advantages over... 

The metal-free eyclobutane-1,2-dioxime can be generated by oxidative displacement. It is interesting to note that, unlike ketene dimerization, head-to-head dimerization takes place here. The chromium ketenimine complex 20 is prepared by reaction of the Fischer-type chromium carbene complex with alkyl isocyanides.60 A cyclobutane-1,2,3,4-tetraimine 24 has been reported from the reaction of the ketenimine phosphonium ylide 22.61 Bisimine 23 has been proposed as the intermediate in this transformation. 

In a third class of 7t-cyclopentadienyl complexes, compounds of type LVIII are bound to a transition metal via the lone pair at the germanium atom. The first compounds in this series, the pentacarbonyl-[chloro(pentamethylcyclopentadienyl)germylene]chromium(0) (LIXa) and -tungsten(O) (LIXb) were synthesized by alkylation of the ylide complexes (CO)5M—GeCl2 THF according to Eq. (22) (201). Nucleophilic substitution reactions of LIXb lead to the alkyl- and amino-substituted complexes LIXc-e [Eq. (23)] (202). 

The synthesis of tricarbonylchromium(O) complexes of mono-, di- and tri-substituted cyclopropanes, e.g. 150, has been accomplished through the reaction of tricarbonyl(styrene) chromium(O) complexes 151 with phosphorus and sulfur ylides. ... 

Similarly, the [cyclopropylmethyl(methyl)amino]carbene system reacted to give a cyclopropyl-methyl-substituted pyrrolinone. This cyclopropane-containing aminocarbene complex of chromium underwent alkyne insertion and formation of a heterocyclic ylide. Further rearrangements gave dihydro pyrrolones 17 and 18 with cyclopropylmethyl substituents. ... 

The reaction of 3,3-dichloro-l,2-diphenylcyclopropene (1) with disodium peiitacarbonyl-chromate or disodium pentacarbonylmolybdatc afforded pentacarbonyl(2,3-diphenylcyclo-prop-2-enylidene)chromium (2, M = Cr) or the corresponding molybdenum complex 2 (M = Mo). which reacted with pyridinium ylides to give the 2//-pyran-2-ylidenc complexes 3. The structure of 2 (M = Cr) was determined by X-ray crystallography. ... 

Homogeneous ylide-nickel systems were combined with heterogeneous surface chromium(II) catalysts. Both separate catalyst systems work in the absence of aluminum alkyl co-catalysts. In this process the nickel complex is supported on the chromium contact, resulting in a new heterogeneous catalyst, which is active in the ediylene polymerization and where two different catalytic centers co-operate [14a, b]. 

CO)sCr=C(OR)R complexes allenes/ Photolysis of a mixture of the chromium carbenc I and the stabilized phosphorus ylide 2 under CO gives the allenc 3 in 60% > icld. Hydrolysis of 3 with HjO+ in ether provides the /3-substituted (Z)-enone 4. The jllcnc 3 rearranges to a (Z)-l,3-diene (5). Pyridinium p-toluenesulfonamidc is an effective catalyst for this rearrangement. 

The reactions of chromium carbenes has received considerable attention. Such complexes appear to be useful to solve some tricky synthetic problems and have been applied to the stereospecific cyclo-propanation of unsaturated esters and ethers [96, 97], to vinyl type reactions with phosphonium ylides[98]. 

Photochemical Reactions with Alkoxychromium Carbene Complexes. Photolysis of chromium alkoxycarbene complexes in the presence of tosylmethylene phosphorane [or ester stabilized ylides such as (methoxycarbonylmethylene)-triphenylphosphorane] under an atmosphere of carbon monoxide produced aflenes. Such reactive allenes (EWG at C1 and electron donating group at C3) hydrolyzed to give y-keto-a. -unsaturated sulfones with. stereoselectivity (eq 6). ... 

A short review addresses the use of chromium aminocarbenes in organic synthesis32S and a second review concerns aminocarbene complexes of Cr and Mo as initiators for cascade reactions with alkynes leading to new heterocyclic compounds via nitrogen ylides.334... 

Reactions.—1-Methyl-3,5-diphenylthiabenzene 1-oxide is a novel sulphur ylide ligand in tricarbonyl-chromium, -molybdenum, and -tungsten complexes (14),... 

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