Chromium compounds tricarbonylchromium complexes

Arylation of N, N-dimethylhydrazone 77 with ( fl-chlorobenzene)tricarbonylchromium complex lb can be achieved in 64 % yield. The copper lithium azaenolate 78 is trapped with the chromium complex at 70 °C to give a-phenyl ketone 80 as a result of an ipso substitution (Scheme 35) [59]. This represents an easy access to a-aryl carbonyl compounds, some of which may exhibit anti-inflammatory properties. 

It is well known that the tricarbonylchromium-complexed benzylic anions and cations are stabilized due to overlapping between d-orbital of the chromium and p-orbital of the benzylic carbon [1]. Tricarbonylchromium complexes of a-te-tralone and a-indanone having a carbonyl group at the side chain underwent a deprotonation of the exo-benzylic protons by treatment with base to give the stereo-controlled tricyclic compounds (Eqs. 1 and 2) [2]. In these cases, Robinson annulation products were formed in less than 10% yield. Also, base treatment of benzyl ether chromium complex having a chlorine at the side chain 3 gave cyclization product as a diastereomeric mixture (Eq. 3) [3]. 

Planar chiral ortho substituted benzaldehyde chromium complexes are useful compounds for a variety of asymmetric reactions. For example, planar chiral tricarbonylchromium complexes of o-substituted benzaldehydes were reacted with Danishefsky s diene in the presence of Lewis acid at room temperature to afford the chromium-complexed 2,3-dihydro-4-pyranones 25 with high dias-tereoselectivity (Eq. 15) [14]. The high diastereoselectivity of the formation of cycloaddition products 25 is also contributed to an exo-side approach of the diene to anti-oriented carbonyl oxygen of the planar chiral ortho substituted benzaldehyde chromium complexes. When the reaction takes place at lower temperature, aldol-type condensation product 26 was obtained along with the formation of pyranones. The open intermediate 26 was easily transformed to the corresponding cycloaddition product after stirring at room temperature [14]. 

Fourteen new tricarbonylchromium complexes of benzodiazaboroles, phenyl-boranes and related compounds have been prepared and characterired. In all compounds n.m.r. data indicate that the Cr(CO)8 moiety is bonded to the benzo and phenyl rings. New types of co-ordination compounds of chromium, molybdenum, and tungsten with phosphino-aminoboranes of general formula (COsMPRSBRS, (CO)4M(PRia)aBR , and (CO)3M(PRS)B have been synthesized. Suitably substituted carbonyl compounds of the same metals reportedly react with l-phenyl-4,5-dihydroborepin (35) to yield stable complexes in which the boron atom apparently participates in metal-ligand bonding. "... 

The optically pure tricarbonyl chromium(O) complexes 116 have proven to offer an effective shielding of one of the faces of the alkene. Complex 116 was subjected to a 1,3-dipolar cycloaddition with the sterically crowded nitrile oxide 117 (Scheme 12.39) (172). The reaction proceeds at room temperature to give a 70% yield of 118. After removal of the tricarbonylchromium moiety by a light induced oxidation with air, compound 119 was obtained with an optical purity of 98% enantiomeric excess (ee). 

Compounds containing chromium directly linked to a cyclosilanyl ring are not known so far. From hexacarbonylchromium and mono- or diphenylcyclopenta- and hexasilanes, however, the corresponding tricarbonylchromium r/ -phenyl complexes have recently been synthesized106 (Scheme 28). 

Activation of aromatic compounds by transition-metal complexes was initially studied with Cr(CO)3 complexes. Nucleophilic addition of 2-lithio-l,3-dithianes to arene-chromium(O) complexes 185 followed usually by iodine-promoted decomplexation affords the corresponding 2-arylated 1,3-dithianes 186. The reaction of //-(toluene)- and (anisole)tricarbonylchromium (185) with compound 161 gave mixtures (52 46 and 10 90, respectively) of ortho and meta substituted derivatives (186) (Scheme 54)244. The meta directing effect was also observed (mainly better than 95%) with amino and fluoro substituted complexes245. 

For the alkylation of enolates, chromium tricarbonyl complexes of aromatic compounds (benchrotrenes) are useful, as they make simple aromatic compounds chiral. Thus, enantiomer-ically pure (indanone)tricarbonylchromium (2R)-25 has been prepared by resolution of the racemic benchrotrene derivative with cinchonidine and oxidation of the alcohol to the ketone with manganese dioxide60. The chiral ketone is alkylated diastereoselectively via the enolate, leading to the f.vo-2-methyl derivative (2/ )-25 which has been used in enolate alkylations and annulation reactions (Section D.1.5.2.4.). If necessary, complete isomerization to the endo-methyl compound can be achieved by treatment with base. 

The chromium complexes of styrene and the related arenes can be susceptible to nucleophilic addition at the p-position of the double bond. The conjugate addition of nucleophiles at the p-position generates the tricarbonylchromium-stabilized benzylic carbanion and the generated benzylic carbanion could be further trapped with electrophiles. An intramolecular cyclization to the chromium complexed styrene double bond gave tricyclic compound (Eq. 4) [4]. 

The reaction of the iron-carbene complex [[Bu C CC(OEt)=)Fe(CO)4] with 1,3-cyclohexadiene afforded223 (32), which was characterised by X-ray diffraction. The addition of the anionic derivatives of i-(diphenylmethane)-il-fluorene- and ii-(9,10-dihydroanthracene)-bis tricarbonylchromium to the hydrocarbon moiety (alkene, benzene, cyclohexadienyl, cycloheptadienyl and cycloheptatrienyl) in various cationic compounds of manganese, rhenium, iron, chromium, molybdenum, tungsten and cobalt was reported224 to provide a new route to hydrocarbon-bridged heteronuclear species such as (33). 

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