Tricarbonylchromium Complexes Research Articles

(Arene)tricarbonylchromium(0) complexes in the synthesis of metal-containing polymers based on vinyl monomers

(Arene)tricarbonylchromium(0) complexes in the synthesis of metal-containing polymers based on vinyl monomers

Meta, para and meta, ortho double exo nucleophilic additions of trimethylsilylester enolates derived from saturated and unsaturated carboxylic acids to tricarbonylchromium complexes of aryl ethers: dearomatizing cyclization to lactones

Potassium enolates derived from saturated and unsaturated bis(trimethylsilyl) ketene acetals react with tricarbonylchromium complexes of anisole and diphenylether to give, in addition to α-arylcarboxylic acids, the mono adducts, lactones, arising from a double exo nucleophilic addition. The latter were not observed in the case of benzenetricarbonylchromium. The intermediate dienol ethers could be isolated and fully characterized by X-ray crystallography. The influence of the nature of the substituents on the ketene acetals, of the nature of the oxidant, and of the nature of the ester enolates on the course of the reaction has been established and will be discussed.

Intramolecular Pd-catalyzed carbocyclization, Heck reactions, and aryl-radical cyclizations with planar chiral arene tricarbonyl chromium complexes.

(o-butenylhalobenzene)Cr(CO)(3) complexes were synthesized by diastereoselectve allylmetal additions to o-halo benzaldehyde complexes. The addition of allylZnBr proved particularly convenient and clean. The complexes undergo intramolecular Pd-catalyzed cyclizations (Heck reactions) without decomplexation and/or alkene isomerization. In complexes with a benzylic stereogenic center, the diastereoselectivity of the alkene carbopalladation is governed by the planar chirality of the complex rather than by the benzylic stereogenic center in the side chain. This reaction outcome can be rationalized by the geometry of the arene plane vs that of the Pd coordination plane in the transition step of the alkene carbopalladation step. An alternative cyclization procedure involves the generation of a Cr(CO)(3)-coordinated arene radical from the bromo and iodo complexes. Intramolecular aryl-radical cyclization affords indan complexes. The transition metal arene pi-bond remains intact during this process.

Tricarbonyl(h6-Arene)Chromium(0) Complexes as Chiral Auxiliaries: Asymmetric Synthesis of b-Lactones

The optically pure tricarbonyl(η6-2-substituted benzaldehydes)chromium are used as chiral auxiliaries in the condensation with a series of doubly lithiated carboxylic acids. The intramolecular ring closure of the obtained Cr(CO)3 complexed β-hydroxyacids affords the optically pure β-lactones in satisfactory yield.

Neighboring Group Participation by Chromium in Substitution Reactions of (η6-Arene)tricarbonylchromium Complexes

(η6-Arene)tricarbonylchromium complexes with leaving groups at the β- or γ-positions undergo nucleophilic substitution reactions with net retention of stereochemistry via neighboring group participation from the coordinatively saturated chromium atom.

ChemInform Abstract: Asymmetric Synthesis of Planar Chiral (Arene)tricarbonylchromium Complexes via Enantioselective Deprotonation by Conformationally Constrained Chiral Lithium‐Amide Bases.

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Chiral Ancillaries in the Benzannulations of Alkoxy and Amino Carbene Complexes with Alkynes

The asymmetric benzannulation of chiral Fischer car- bene complexes were investigated with a series of complexes bear- ing either chiral alcohols or chiral amines at the heteroatom stabilizing substituent. A set of seven alkenyl complexes and one aryl complex were prepared from five chiral alcohols; (1S,2R,5S)- (+)-menthol, (1R,2S)-(−)-trans-2-phenylcyclohexanol, (±)-trans-2- methylcyclopentanol, (±)-isoborneol, and (−)-8-phenylmenthol. The reaction of all seven of the alkenyl complexes with pent-1-yne and 3,3-dimethylbut-1-yne gave (arene)chromium tricarbonyl com- plexes with very low asymmetric inductions (0−20% de). The phe- nyl carbene complex derived from (+)-menthol gave good asymmetric induction with 3,3-dimethylbut-1-yne as had been pre- viously reported, but the reaction with pent-1-yne gave lower induc- tion and a much lower chemical yield. Alkenyl complexes bearing prolinol derivatives as the heteroatom stabilizing substituent also gave very low induction in reactions with pent-1-yne and this held true for both E- and Z-isomers of these complexes. An alkenyl car- bene complex derived from the C-2 symmetrical amine, 3,5-dime- thylmorpholine, reacted with pent-1-yne to give moderate yields of the (arene)chromium tricarbonyl complex but only in 10% de. High asymmetric inductions were observed for the cyclohexadienone an- nulation of atropisomeric 2-(N-methyl-3-methylindolyl) carbene complexes prepared from the chiral auxiliary, (4R,5S)-5-phenyl-4- methylimidazolidinone. Each atropisomer gives a single and differ- ent diastereomer of the same 4H-carbazol-4-one where it is the chiral axis of each atropisomer that controls the sense of induction and not the chirality of the auxiliary. Thus it is likely that these com- plexes, unlike all of the others examined in this work, react with acetylenes in a process in which the chiral auxiliary is not free to ro- tate about the carbene carbon in any of the reaction intermediates leading to product formation.

Heterometallic metal carbonyl compounds derived from (η6-arene)tricarbonylchromium bearing propargyl units

The compounds [Co2(CO)8] and [Mo2Cp2(CO)4] readily react with (η6-arene)tricarbonylchromium complexes containing propargyl (prop-2-ynyl) 1a–c units to give new heterotrimetallic complexes [Cr{(η6-C6H5CCC(H)(R)Y)Co2(CO)6}(CO)3] (2a, R = Me and Y = NMe2; 2b, R = H and Y = NMe2; 2c, R = H and Y = OH) and [Cr{(η6-C6H5CCCH2NMe2)Mo2(Cp)2(CO)4}(CO)3] 3 in moderate to good yield (51–80%). Compounds 2a and 3 have been characterised by X-ray crystallography. Structural data reveal that the Cr(CO)3 unit adopts a nearly staggered conformation in 2a and eclipsed in 3.

Multiple substitutions on (η6-arene)tricarbonylchromium(0) complexes

The treatment of representative (η6-arene)tricarbonylchromium(0) complexes 1a–c and 4 with 3 equivalents of LiTMP followed by an electrophilic quench with Me3SiCl provided a series of trisilylated complexes 2a–c and 5a. The use of Me3SnCl and Ph2PCl as electrophile also yielded unusual trisubstituted complexes 13a and 13b. The X-ray crystallographic structure of complex 13b is reported. Deuteration studies using deuteroacetic acid as the electrophile led to the observation of a trideuterated species presumably derived from a trianionic species formed during the reaction. Efficient disubstitution was observed when complexes 7, 9 and 11 were treated with 3 equivalents of LDA followed by an electrophilic quench with Me3SiCl

Molecular design using electrostatic interactions. Part 3: Synthesis and properties of chromium tricarbonyl complexes of cationic mono-, di- and tripodands

Water soluble polycationic arene host systems have been prepared, using DABCO as the source of the cationic charge, in which the arene group is complexed to chromium tricarbonyl. Association constants for two salts were determined by NMR methods and the role of IR carbonyl band of the Cr(CO) 3 moeity as reporter group explored. The different properties of the salts in the solid state, in water and, where possible, organic solvents were examined and it was found that the nature of the anion had no effect on the carbonyl IR band in water, although it did in the solid state.

Diastereoselective Transformation of Arenes into Highly Enantiomerically Enriched Substituted Cyclohexadienes

Sequential addition of a C-nucleophile and a C-electrophile to enantiomerically pure arene tricarbonyl chromium complexes 3a,b, 6, and 8b, containing aryl bound chiral oxazoline, SAMP-hydrazone and chiral imine auxiliaries affording substituted cyclohexadienes. C-Nucleophiles included alkyl-, vinyl-, and phenyl-lithium reagents. C-Electrophiles included methyl iodide, allyl bromide, benzyl bromide, and propargyl bromides. The 1,3-cylohexadienes were obtained with a 1,5,6-substitution pattern. The results are consistent with a diastereoselective exo-nucleophilic addition to an ortho position of the complexed arene, followed by addition of the electrophile to the metal center. With allyl, ben-zyl, and propargyl groups, direct reductive elimination then yielded trans-5,6-substituted products. With methyl iodide, reductive elimination was preceded by CO insertion and acetyl cyclohexadienes were formed exclusively whose in situ deprotonation/alkylation gave products in which three C-substituents had been added across an arene double bond with complete regio- and stereocontrol. The two path-ways reflect migratory aptitude to carbonylation. An X-ray structure determination of the phenyl oxazoline complex 3a allowed a rationalization of observed diastereoselectivity. Asymmetric induction was very high with the oxazoline and the SAMP-hydrazone complexes (>90% de) whereas the chiral benzaldehyde imine complex 8b afforded the substituted diene aldehydes in moderate enantiomeric purity (34-58% ee). Changing the reaction medium from THF to toluene in reactions with 8b resulted in products of the opposite chirality.

Enantioselective Synthesis of Novel Enantiopure Phosphines via Reaction of a Tricarbonyl(η6-arene)chromium Complex with a Chiral Lithium Amide Base

A range of novel phosphorus-containing tricarbonyl(η6-arene)chromium complexes has been synthesised via the enantioselective ortho-metallation approach using a chiral lithium amide base. Initial asymmetric reaction of a phosphine oxide complex allows the preparation of silyl- or stannyl-substituted products in ca. 73% ee, which then allows the preparation of other phosphine derivatives in very high ee (>95%) following phosphine reduction and enantiomeric enrichment.

Asymmetric synthesis based on chiral (arene)tricarbonylchromium acetal complexes. Addition reactions to the ortho-formyl complex

The addition reactions of organolithium and Grignard reagents to chiral, enantiomerically pure ortho-formyl (arene)tricarbonylchromium acetal complex (2) have been studied. The diastereoselectivity of the addition process is fair in the absence of an additional Lewis acid, and good in the presence of Ti(OiPr)4. The nature of the newly formed chiral centre, and studies on the possible nature of the nucleophilic species suggest that the Lewis acid acts through monodentate coordination to the aldehyde carbonyl, and thereby alters the carbonyl rotamer population more heavily in favour of the s-trans conformation. Nucleophilic attack then occurs on the face anti- to that bearing the Cr(CO)3 unit.Key words: (arene)tricarbonylchromium complexes, asymmetric synthesis, carbonyl additions, Lewis acids.

π-Arene complexes.: Part 12. Synthesis of chromiumtricarbonyl complexes of quinoline and N-methylindoles and selected metallation reactions

The lithiation of indole, using a slight excess of n-butyl lithium in THF, followed by methylation and reaction with [Cr(CO) 6] in refluxing dibutyl ether, resulted in the formation of [Cr(η 6- N-methylindole)(CO) 3] ( 1a) and [Cr(η 6- N-methyl-2-methylindole)(CO) 3] ( 1b). In contrast, lithiation of quinoline in THF, silylation and the subsequent reaction with [Cr(CO) 6] under similar reaction conditions, afforded [Cr(η 6- N-trimethylsilyl-2-butyl-1,2-dihydroquinoline)(CO) 3] ( 2) and [Cr(η 6-{2-butyl-1,2,3,4-tetrahydroquinoline})(CO) 3] ( 3). The formation of [Cr(η 6-2,2′-bis{ N-methylindolyl})(CO) 3] ( 4) implied lithiation at the 2-position of 1a. However, metallation at the 7-position was also indicated during the same reaction. In the presence of [Mn(CO) 5Br], product 4 and the transmetallation product [Cr(η 6-{7-( N-methylindolyl)Mn(CO) 5})(CO) 3] ( 5) were isolated. Reaction with titanocene dichloride gave [Cr(η 6-{2-( N-methylindolyl)TiCp 2Cl})(CO) 3] ( 6), which slowly converted into [TiCp 2{Cr(η 6-2-( N-methylindolyl)(CO) 3} 2] ( 7).

ChemInform Abstract: Synthesis of Axially Chiral Anilides by Enantioselective Desymmetrization of Tricarbonyl(N‐methyl, N‐aroyl 2,6‐dimethylaniline)chromium Complexes.

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The first examples of ester enolate addition across a chiral (alkoxybenzene)–chromium complex π-bond with a remarkable degree of 1,5-asymmetric induction

The first examples are described wherein addition of an ester enolate to an alkoxy-substituted arene–chromium tricarbonyl complex, to afford a substituted cyclohexenone in high enantiomeric excess.

ChemInform Abstract: Asymmetric Functionalization of Tricarbonylchromium(0) Complexes of Arenes by Non-racemic Chiral Bases

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Asymmetric Synthesis of Planar Chiral (Arene)tricarbonylchromium Complexes via Enantioselective Deprotonation by Conformationally Constrained Chiral Lithium-Amide Bases

Enantioselective lithiation/electrophile addition reactions with eight chiral Li-amide bases, 1 - 8, and five [Cr(arene)(CO)3] complexes, 9 - 13, were investigated. Restriction of conformational freedom in the chiral Li-amide base Li-1, in general, did not result in an increase in asymmetric induction. A new route to enantiomerically enriched (75 - 92%) planar chiral ortho-substituted benzaldehyde complexes via enantioselective lithiation of benzaldimine complexes 16 and 17 is reported. Within the (1S)-enantiomer series of o-substituted benzaldehyde complexes 18a - d, the sign of the specific rotation, [a], is found to be positive, except for the trimethylstannyl derivative 18b. This is interpreted in terms of a reversed conformation of the aldehyde group.

Synthesis and photochromic properties of tricarbonylchromium complexes of 2H‐η6‐benzochromenes

Synthesis and photochromic properties of tricarbonylchromium complexes of 2H‐η6‐benzochromenes

Novel synthesis of indazoles from (η 6-arene)tricarbonylchromium complexes

Indazole chromium complexes and some of its derivatives were synthesised by two strategies: (1) by cyclisation of [η 6-2-(2′-phenylhydrazine)-1,3-dioxolane]tricarbonylchromium ( 2) in acidic conditions which was converted into σ-complex ( 11); (2) by thermolysis of Cr(CO) 6 with 1-bis(trimethylsilyl)methylindazole ( 3) and 2-bis(trimethylsilyl)methyl-3-trimethyl-silylindazole ( 4), using bulky protecting groups at N(1) or simultaneously at N(2) and C(3), to afford [η 6-1-bis(trimethylsilyl)methylindazole]tricarbonylchromium ( 14) and [η 6-2-bis(trimethylsilyl)methyl-3-trimethylsilylindazole]tricarbonylchromium ( 15), respectively. The deprotonation of complex 14 followed by electrophilic quench occurs at the C(4) and C(7) positions in a ratio of 3:1 and with complex 15 the deprotonation was completely regioselective at the C(7) position. The position of this substitution was confirmed by n.O.e. difference spectroscopy and X-ray crystal structure determination of the [η 6-2-bis(trimethylsilyl)methyl-7-methyl-3-trimethylsilylindazole]tricarbonylchromium ( 5). These complexes were decomplexed to produce new substituted indazole derivatives in good yield.