Pentacarbonyl chromium

Structural analogues of the /]4-vinylketene E were isolated by Wulff, Rudler and Moser [15]. The enaminoketene complex 11 was obtained from an intramolecular reaction of the chromium pentacarbonyl carbene complex 10. The silyl vinylketene 13 was isolated from the reaction of the methoxy(phenyl)-carbene chromium complex 1 and a silyl-substituted phenylacetylene 12, and -in contrast to alkene carbene complex 7 - gave the benzannulation product 14 after heating to 165 °C in acetonitrile (Scheme 6). The last step of the benzannulation reaction is the tautomerisation of the /]4-cyclohexadienone F to afford the phenol product G. The existence of such an intermediate and its capacity to undergo a subsequent step was validated by Wulff, who synthesised an... 

Triethylamine (8) Ethanamine, N,N-diethyl- (9) (121-44-8) Pentacarbonyl[phenyl(methoxy)chromium]carbene Chromium, pentacarbonyl(a-methoxybenzylidene)- (8) ... 

Diethyl-1,3,2-dithiagermolane (336) reacts with the chromium pentacarbonyl complex of dichlorogermylene (in the form of solvate with THF) to give a cyclic germylene complex (337) which can be further stabilized with an additional nitrone ligand <87JOM(33i)ii>. 

Simple alkenes, norbomene and styrene do not undergo cyclopropanation or insertion reactions with cyclopropyl(methoxy)carbene chromium pentacarbonyl complex. However, the conjugated 1-vinylcyclopentene is cyclopropanated under the reaction conditions at the terminal double bond, affording an isomeric mixture (trans cis = 40 60), in 66% yield (equation 72). 

When cyclopropylidenemethy](ethoxy)carbene chromium pentacarbonyl is treated with diphenylacetylene in THF, a mixture of products is obtained, from which only the tricarbonyl(5-ethoxy-6,7-diphenylbenzofuran)chromium complex could be isolated, in... 

The rearrangement exhibits some stereochemical preference for c/s-vinyl carbene complex (with respect to the metal) compared to the //ww-isomer. Thus, 2-methyl-2-m-vinyl cyclopropyl (methoxy) carbene chromium pentacarbonyl rearranges to 5-methyl-5-vinyl-2-methoxycyclopentenone approximately 4 times faster (THF, 52 °Q than the trans-isomer, which in turn rearranges faster than phenyl derivatives. This suggests that vinyl complexes undergo initial Cope-type rearrangement to form metallacycloheptadienes, which then rearrange to jt-allyl complexes. Subsequent CO insertion and reductive elimination leads to the vinylcyclopentenones (equation 89)150. 

Methyl) (methoxy)carbene] jentacarbonyl chromium(O) Chromium, pentacarbonyl(1-methoxyethylidene)-, (8) Chromium, pentacarbonyl(1-methoxyethylidene)-, (OC-6-21)-, (9) (20540-69-6)... 

The doubly charged Mn(II) cation is paramagnetic and isoelectronic with vanadium hexacarbonyl and neutral chromium pentacarbonyl iodide. These are examples of some of the few carbonyl compounds which contravene the rare gas formalism (/, 57). 

The Group VI metals would not be expected to form binary metal carbonyl cations, but they do form some substituted cations with nitrogen and phosphorus ligands. The paramagnetic monomeric and dimeric chromium pentacarbonyl iodides react in liquid ammonia with iodide expulsion. 

Fischer and co-workers have prepared several novel carbene derivatives of chromium pentacarbonyl and have confirmed the molecular formulas by mass spectrometry (5, 6, 73, 74, 77, 128, 147). The spectra show the expected stepwise loss of the five carbonyl groups giving the ions [Ligand Cr(CO) ]+ (w = 0-5). The compounds for which spectral data have been reported are given in Table III. The selenium derivative (XXIX) shows... 

Preparation of b/s(5-bromopentyl)zinc and its reaction with chromium pentacarbonyl THF preparation of pentacarbonyl ((5-bromopentyl)methoxycarbene) chromium(O)6... 

Universitat in Miinchen (for his studies on arene chromium tricarbonyls see Chap. 5) prepared the diaminocarbene chromium pentacarbonyl 9 from the imidazolium salt 8 by heating the starting material at 120°C [13]. Although Wanzlick s and Ofele s results received considerable attention, the opportunity to isolate stable carbenes was missed. 

The first report of a perfluorocarbon as a solvent for synthesis pre-dates Horvath and Rabai s fluorous biphase paper by 14 years. Kelly [70] investigated the flash photolysis of chromium hexacarbonyl in perfluoroheptane where the chromium pentacarbonyl (generated during photolysis) was shown to be more reactive in perfluorocarbon solvents than in hydrocarbon solvents. This effect, presumably, arises from the weak solvation of the unsaturated metal centre by the perfluorocarbon. 

The nitrogen atom in a-ferrocenylalkylamines generally shows the same reaction pattern as that in other amines alkylation and acylation do not provide synthetic problems. Due to the high stability of the a-ferrocenylalkyl carbocations, ammonium salts readily lose amine and are, therefore, important synthetic intermediates. Acylation of primary amines with esters of formic acid gives the formamides, which can be dehydrated to isocyanides by the standard POClj/diisopropylamine technique (Fig. 4-16) [92]. Chiral isocyanides are obtained from chiral amines without any racemization during the reaction sequence. The isocyanides undergo normal a-addition at the isocyanide carbon, but could not be deprotonated at the a-carbon by even strong bases. This deviation from the normal reactivity of isocyanides prompted us to study the electrochemistry of these compounds, but no abnormal redox behaviour, compared with that of other ferrocene derivatives, was detected [93]. The isocyanides form chromium pentacarbonyl complexes on treatment with Cr(CO)s(THF) (Fig. 4-16) and electrochemistry demonstrated that there is no electronic interaction between the two metal centres. 

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