Chromium Tricarbonyl Research Articles

Investigations into the hydrogenation of diolefins and prochiral olefins employing the “Daniphos”-type ligandsDedicated to the memory of Professor Noel McAuliffe.

A number of enantiopure, planar chiral diphosphines of the Daniphos-type have been synthesized in good chemical yields and excellent stereochemical outcome according to a modular, straightforward synthetic method based on an arene–chromium–tricarbonyl scaffold. They were readily converted to their rhodium complexes, two of which have been characterized by X-ray crystallography. Their catalytic performance has been assessed by carrying out hydrogenations of dienes and prochiral olefins, taking the Josiphos ligand as a reference system for comparison. Interesting influences of the substitution patterns and solvents were found. Reaction rates of the hydrogenations of diolefins were also found to be strongly dependent on the respective substituents.

Photoinduced reactions of Cr(CO)3-coordinated N-cyanoazepine: [6 + 4] cycloaddition with conjugated dienes

The tricarbonyl(N-cyanoazepine)chromium(0) complex (2) is formed when (MeCN)3Cr(CO)3 is treated photochemically with N-cyanoazepine (1). U.v photolysis of Cr(CO)3(η6-N-cyanoazepine)chromium(0) (2) and conjugated dienes [1,3-butadiene (3), trans-1,3-pentadiene (4), trans,trans-2,4-hexadiene (5)] in PhMe give the [6 + 4]cycloadducts, tricarbonyl{η4:2-11-N-cyano-11-azabicyclo[4.4.1]-undeca-2,4,8-triene}chromium(0) complexes (6–8). The π-complex (2) and these new bicyclic compounds (6–8) were purified by chromatography, recrystallized, isolated as analytically pure crystalline solids in moderate yields and characterized by mass, i.r. and n.m.r. spectroscopy. The heterobicyclotrienes, 11-N-cyano-11-azabicyclo[4.4.1]undeca-2,4,8-triene (9–11), were isolated from the complexes (6–8) by heating in PhMe, and their structures were assigned by the same spectroscopic methods.

Cis selectivity of mixed catalyst systems in canola oil hydrogenation

Two mixed catalyst systems were investigated for their suitability to produce partially hydrogenated canola oils with low levels of trans fatty acids. Each system included a homogeneous catalyst paired with a heterogeneous catalyst. Cl 2(CO) 2(PPh 3) 2Ru(II) was combined with Ni, while methyl benzoate chromium tricarbonyl [MeBeCr(CO) 3] was paired with Pd. The effect of changing the catalysts’ molar ratios and the reaction conditions on activity, specific isomerization index, linoleate and linolenate selectivities and fatty acid compositions was evaluated in an effort to identify synergies related to differences in the hydrogenation reaction mechanisms of the two components. Only the Ru and Ni combination proved to be advantageous. At 110 °C and 5.2 MPa, the activities of the Ni/Ru mixtures were higher than the activities of the catalysts used individually, and low levels of trans isomers (∼9%), characteristic of the Ru catalyst, were observed.

Conformational Studies ofortho-Substituted Benzaldehyde Chromium Tricarbonyl Complexes

The syn/anti conformational equilibrium of o-substituted benzaldehyde chromium tricarbonyl complexes was studied by CD and 1H NMR (NOE). The preferred conformation of the o-methyl-, o-methoxy-, and o-iodobenzaldehyde complexes is anti, while those of the o-trimethyltin and o-trimethylsilyl benzaldehyde complexes is syn. The optical rotation values of (o-trimethylsilyl benzaldehyde)Cr(CO)3 ((1S)-2d) vary from -174 (in ethanol) to +108 (in chloroform).

Synthesis of chiral chromium tricarbonyl labeled thymine PNA monomers via the Ugi reaction.

[reaction: see text] Ugi condensation was used to synthesize the first examples of chiral racemic Ar.Cr(CO)(3) labeled peptide nucleic acid (PNA) monomers bearing the organometallic moiety linked to the alpha-carbon of the glycine unit.

Stereocontrolled [3 + 2] Annulations with Arene Chromium Tricarbonyl Complexes: Construction of Spirocyclic Compounds Related to Fredericamycin A.

AbstractFor Abstract see ChemInform Abstract in Full Text.

An approach to serrulatane diterpenes via endo-selective conjugate nucleophilic addition to arene-Cr(CO)3 complexes.

[formula: see text] Starting from a nonracemic planar-chiral arene tricarbonyl chromium complex, the serrulatane diterpenoid (+)-20-methoxy-serrulat-14-en-7,8-diol was synthesized in a highly stereoselective fashion. The key step of the synthesis is an endo-selective conjugate nucleophilic addition of lithio-methylphenyl sulfone to a 1-ethylidene-tetralin-Cr(CO)3 derivative. By employing different substrates and nucleophiles it was shown that the surprising and rather general endo selectivity must result from a unique complex induced proximity effect under participation of the Cr(CO)3 moiety.

Synthesis and Characterization of Chromium Tricarbonyl Complexes of 1-Phenylgermatrane and 1-Phenylazagermatrane. Crystal Structure of [N(CH2CH2O)3GeC6H5]Cr(CO)3

The reaction of 1-phenylgermatrane (1) and 1-phenylazagermatrane (2) with Cr(CO)6 affords chromium tricarbonyl complexes [N(CH2CH2O)3GeC6H5]Cr(CO)3 (6) and [N(CH2- CH2NH)3GeC6H5]Cr(CO)3 (7). In contrast, the same reaction of Cr(CO)6 with 1-(9-anthracenyl) germatrane (3) does not proceed. Composition and structures of the 6 and 7 were established by elemental analyses, 1H and 13C NMR spectroscopy and mass spectrometry. The crystal structure of 6 is reported

Organometallic radical-initiated cleavage of the metal chelate and thiazole rings in a cyclopentadienylchromium complex.

Extensive ring cleavage in the mercaptobenzothiazole chromium complex CpCr(CO)2(SCSN(C6H4)) (2), initiated by cyclopentadienyl chromium tricarbonyl, produced novel polynuclear complexes 3-5.

Synthesis and Properties of a Novel Series of Organometallic Merocyanines Combining the Potent Electron-Donating [(CpFeCO)2(μ-CO)(μ-C=CH−)] Fragment with Tropylium-Type Acceptors

The potent electron-donating group [(CpFeCO)2(µ-CO)(µ-C=CH−)] was combined with different tropylium-based acceptors yielding the push-pull complexes [(CpFeCO)2(µ-CO)(µ-C=CH−CH=A)][BF4] where =A represents [=CH−(η7-C7H6)Cr(CO)3]+ (5), [={C10H7}]+ (azulenylium) (7) [={C10H4Me2iPr}]+ (guaiazulenylium) (8). Crystal structures of the precursor complexes [(CpFeCO)2(µ-CO)(µ-C=CH−CH=CH−C7H7)] (3), [(CpFeCO)2(µ-CO){µ-C=CH−CH=CH−(η6-C7H7)Cr(CO)3}] (4) and the push-pull derivative 5 are presented. Whereas complexes 3 and 4 demonstrate localised carbon−carbon double and single bonds in the π-bridge between the diiron moiety and the seven-membered ring a small but distinct π-bond delocalisation can be observed in the π-linker of the cationic derivative 5. From the NMR spectroscopic results a correlation between the 13C NMR shift of the bridging carbon atom µ-C of the diiron unit and the coupling constant J(1H-1H) of the β- and γ-protons of the π-bridge was found. This correlation indicates an increased π-bond delocalisation throughout the conjugated bridge with respect to the electron-accepting capability in the order tricarbonyl(η7-cycloheptatrienylium)chromium < guaiazulenylium < azulenylium implying a predominantly charge-delocalised form in the case of the azulenylium complex 7. Considerably large first hyperpolarisabilities β were determined for 5 and 8 by means of hyper-Rayleigh scattering. Based on the two-level model β0 values were calculated and related to the bond-length alternation in the π-linker. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Tricarbonyl(3-methoxybenzocyclobutenedione)chromium: Regioselective Nucleophilic Addition Reactions, Dianionic Oxy-Cope Rearrangements, Regioselective Intramolecular Aldol Additions, and a Rare Case of an Anionic 1-Vinylcyclobutenol−Cyclohexadienol Rearrangement

Tricarbonyl(3-methoxybenzocyclobutenedione)chromium (rac-3) has a lower symmetry than the corresponding unsubstituted benzocyclobutenedione complex. This has consequences for reaction sequences involving both ketone functionalities. The relative electrophilicity of the two ketone functions was evaluated by partial reduction of rac-3 and by a partial hydrolysis of the bis(ethylene acetal), the precursor of rac-3. In addition, monovinyl Grignard addition was performed. All three experiments indicated a higher electrophilicity of C-1 than of C-2, in agreement with the resonance formulas that can be drawn. Dianionic oxy-Cope rearrangements, followed by intramolecular aldol addition, occurred with remarkable regioselectivity: in five of six cases investigated only one of two expected reaction products was obtained. As an explanation of this remarkable selectivity we considered a chelation effect of the intermediate bis(enolate) involving the 3-methoxy substituent. This causes a rare, if not the first, case of differentiation of two enolate moieties present in the cyclooctane ring. Addition of 2-lithio-3,4-dihydro-2H-pyran did not give rise to a dianionic oxy-Cope rearrangement but instead to a rare example of an anionic 1-vinylcyclobutenol−cyclohexadienol rearrangement. Five compounds presented in this publication have been characterized by crystal structure analyses. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Chromium tricarbonyl complexes with biphenylene as η 6 ligand: synthesis, structure, dynamic behaviour in solid state and thermal η 6,η 6-haptotropic rearrangements. Experimental (NMR) and theoretical (DFT) studies

The reaction of biphenylene ( 1) with Cr(CO) 3Py 3/BF 3·OEt 2 at 25 °C gives a mixture of two known isomeric complexes: tricarbonyl(1-4,4a,8b-η 6-biphenylene)chromium ( 2) (yield 62%) and hexacarbonyl(μ-η 6:η 6-biphenylene)bis-chromium ( 3) (yield 4%). Complexes 2 and 3 were separated by thin layer chromatography on silica and characterised by 1H and 13C, as well as 13C CP MAS-NMR. X-ray structure analysis for 3 proved trans-orientation of the chromium tricarbonyl groups. A novel regioselective method for the synthesis of (η 6-biphenylene)chromium tricarbonyl complexes bearing a substituent R (D ( 4), CH 3 ( 5)) in position 1 of the coordinated ring was proposed. The kinetics of η 6,η 6-inter-ring haptotropic rearrangement (IRHR) for 4 in inert, noncoordinating C 6F 6 was investigated by 2H–{ 1H}-NMR spectroscopy. Density function theory (DFT) calculations for ground, intermediate and transition states were done and fitted well with experiment.

Stereocontrolled [3 + 2] Annulations with Arene Chromium Tricarbonyl Complexes: Construction of Spirocyclic Compounds Related to Fredericamycin A

[reaction: see text] An efficient method has been developed for the stereocontrolled construction of polycyclic and spirocyclic compounds, including the spirocyclic core of the antitumor agent fredericamycin A. The strategy involves a one-pot aldol addition/Brook rearrangement/cyclization sequence beginning from arene chromium tricarbonyl complexes and can formally be described as a [3 + 2] annulation.

Synthesis and properties of conjugated copolymers having a tricarbonyl(arene)chromium and thiophene units in the main chain

Palladium-catalyzed polymerization of η 6-(1,4-diethynylbenzene)tricarbonyl chromium (1) with 3-alkyl-2,5-dibromothiophene (2a-c) was carried out to give the corresponding alternating conjugated copolymers (5a-c) in good yields. The structures of the polymers were supported by 1H NMR and IR spectra. The polymers obtained were soluble in common solvents such as THF, CH2Cl2, CHCl3 and toluene. The molecular weights of the polymers were determined by GPC. Their thermal, optical and electrical properties were investigated in detail.

Intermolecular Interactions in (Arene)chromium Carbonyl Compounds: Prediction of Chiral Crystal Packing from Racemate Structure

Six X-ray crystal structures are reported, all containing substituted triphenylmethanol derivative 4 either alone or as its mono or bis(chromium tricarbonyl) complexes. All four chromium complexes studied crystallize with two independent molecules in the crystallographic asymmetric unit. It is demonstrated that from the X-ray crystal structure of the acentric racemic (+/-)-(1pR,1' 'R)(1pS,1' 'S)-[Cr(CO)(3)(eta(6)-t-BuC(6)H(3)(CMeOMe)CPh(2)OH)], (+/-)-3, it is possible to deduce the 4-fold helical structure of the chiral (-)-(1pR,1' 'R) isomer, (-)-3. The bimetallic derivatives demonstrate the ability to control intermolecular interactions by the positioning of relative stereochemistry.

Metal-benzene and metal-CO bond energies in neutral and ionic C6H6Cr(CO)3 studied by threshold photoelectron-photoion coincidence spectroscopy and density functional theory.

photoelectron-photoion coincidence spectroscopy and density functional theory calculations have been used to investigate the dissociation kinetics of the benzene chromium tricarbonyl ion, BzCr(CO)3+ (Bz = C6H6). The dissociation of the BzCr(CO)3+ ion proceeds by the sequential loss of three CO and benzene ligands. The first and third CO and the benzene loss reactions were associated with metastable precursor ions (lifetimes in the microsecond range). By simulating the resulting asymmetric time-of-flight peak shapes and breakdown diagram, the 0 K appearance energies of the four product ions were determined to be 8.33 +/- 0.05, 8.93 +/- 0.05, 9.97 +/- 0.06, and 11.71 +/- 0.06 eV, respectively. Combined with the ionization energy of BzCr(CO)3, 7.30 +/- 0.05 eV, the three successive Cr-CO bond energies in the BzCr(CO)3+ were found to alternate, with values of 1.03 +/- 0.05, 0.60 +/- 0.05, and 1.04 +/- 0.05 eV, respectively, and the Bz-Cr bond energy in BzCr+ is 1.74 +/- 0.05 eV, a trend confirmed by the density functional theory (DFT) calculations. Using the heats of formation of the fully dissociated products, C6H6, Cr+, and CO, the 298 K heats of formation the ionic BzCr(CO)n+ (n = 03) species were determined. By scaling the DFT calculated bond energies for the neutral molecules, the heats of formation of the neutral BzCr(CO)n (n = 03) were also obtained.

Analysis of vibrational spectra of naphthalene, deuterionaphthalenes, and chromium (η6-naphthalene)tricarbonyl based on density functional calculations

The vibrational frequencies and force constants for naphthalene (C10H8), 1,4,5,8- and 2,3,6,7-tetradeuterionaphthalenes (C10H4D4), octadeuterionaphthalene (C10D8), and chromium (η6-naphthalene)tricarbonyl were calculated by the DFT method using the PBE approximation in extended and split bases. The results calculated without the use of scaling factors are in good agreement with the IR and Raman experimental data. All vibrational frequencies for the free ligand and π-complex molecules were assigned. The influence of coordination to the transition metal on the frequencies and force field of the naphthalene molecule (both for the free ring and the ring coordinated to the transition metal) was discussed.

α-Arylation of 2-Arylacetates and Benzofuran-2-one with Tricarbonyl(fluoroarene)chromium Complexes

In order to synthesise fragments of the natural product diazonamide A, α-arylation of 2-arylacetates 3 and benzofuran-2-one with the aid of the tricarbonyl(fluoroarene)chromium complex rac-2 was investigated. After decomplexation of the products rac-4 and rac-6, it was possible to obtain 2,2-diarylacetates rac-5 and the 3-arylbenzofuran-2-one rac-7.

Metal π complexes of benzene derivatives: Part 56. (η 6-Fluoranthene)(tricarbonyl)chromium: isomerism and haptotropic equilibration

Reaction of fluoranthene with Cr(CO) 3Py 3/BF 3·OEt 2 at 25 °C affords a mixture of two isomeric complexes: traces of tricarbonyl(1-5,15-η 6-fluoranthene)chromium ( 3) (coordination to benzene) and, as the major product, tricarbonyl(1-4,15,16-η 6-fluoranthene)chromium ( 2) (coordination to naphthalene). The ratio 3: 2 is less than 0.05 according to 1H-NMR of crude product before crystallization. Complex 2 is thermodynamically less stable than 3: at 100 °C in decane or C 6D 6 for 8 h or at 90 °C in C 6F 6 for 100 h 2 rearranges irreversibly to 3 via an inter-ring haptotropic shift of the Cr(CO) 3 group from the naphthalene moiety to the benzene part of the fluoranthene ligand. NMR evidence for a degenerate reversible haptotropic shift within the naphthalene moiety is absent. The isomers 2 and 3 have been characterized by X-ray structural analysis.

Reactions of complex ligands: Part 94. Chromium-templated angular versus linear benzannulation of dibenzofuran and haptotropic metal migration in tetracyclic fused arenes

The chromium-templated [3+2+1]-benzannulation of dibenzofuryl(methoxy)carbene complex 1 with alkynes leads to hydroquinoid benzonaphthofurans. A competition of angular versus linear annulation affords angular-fused (η 6-1,2,3,4,4a,11c)-benzo[ b]naphtho[1,2- d]furan tricarbonyl chromium complexes 2– 6 along with considerable amounts of uncoordinated benzo[ b]naphtho[2,3- d]furans as linear annulation products 7– 9. As demonstrated for 2 and 6 the Cr(CO) 3 complexes undergo a thermally induced haptotropic metal migration along the tetracyclic heteroaromatic π-system to give (η 6-7a,8,9,10,11,11a)-benzonaphthofuran complexes 10 and 11 in which the chromium fragment is coordinated to the terminal unsubstituted benzoid ring. The molecular structures of both the kinetic annulation products and the thermodynamic rearrangement products were established by NMR spectroscopy and single crystal X-ray analysis.