Tricarbonyl Unit Research Articles

Molybdenum tricarbonyl complex functionalised with a molecular triazatriangulene platform on Au(111): surface spectroscopic characterisation.

Transition metal complexes form the basis for small molecule activation and are relevant for electrocatalysis. To combine both approaches the attachment of homogeneous catalysts to metallic surfaces is of significant interest. Towards this goal a molybdenum tricarbonyl complex supported by a tripodal phosphine ligand was covalently bound to a triazatriangulene (TATA) platform via an acetylene unit and the resulting TATA-functionalised complex was deposited on a Au(111) surface. The corresponding self-assembled monolayer was characterised with scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS). The vibrational properties of the surface-adsorbed complexes were investigated with the help of infrared reflection absorption spectroscopy (IRRAS), and the frequency/intensity changes with respect to the bulk spectrum were analysed. A full vibrational analysis was performed with the help of DFT.

Photochemical CO2 Reduction Catalyzed by Phenanthroline Extended Tetramesityl Porphyrin Complexes Linked with a Rhenium(I) Tricarbonyl Unit.

A series of heterodinuclear complexes (M-1-Re) based on a phenanthroline (phen) extended tetramesityl porphyrin ligand (H2-1) has been prepared. The phen moiety of this ligand selectively coordinates a Re(I) tricarbonyl chloride unit, whereas the metal in the porphyrin moiety has been varied: namely, Cu, Pd, Zn, Co, or Fe was used. These dinuclear complexes were fully characterized by standard analytical methods. Additionally, a crystal structure of Cu-1-Re·5.5(C7H8)·0.5(C6H6) could be obtained, and extended time-resolved emission lifetime measurements were conducted. Furthermore, their ability to catalyze the photochemical reduction of CO2 to CO was investigated. Light-driven CO2 reduction experiments were performed in dimethylformamide (DMF) using triethylamine (TEA) as the sacrificial electron donor. The TONs (turnover numbers) of CO were determined and revealed a surprising catalytic activity that is obviously independent from the redox activity of the porphyrin metal. We have recently shown that the parent M-1 compounds are active photocatalysts, but the catalytic activity was dependent on the redox activity of the porphyrin metal. In the case of the new heterodinuclear complexes M-1-Re reported in this study, the catalytic active center seems to be the Re(I) moiety and not the porphyrin. Surprisingly, Zn-1-Re proved to be the most active compound in this series showing a TONCO of 13 after 24 h of illumination using a >375 nm cutoff filter while all other compounds showed minimal activity under this condition.

Nickelacyclopentadienylchromium tricarbonyl unit as a bulky pseudohalogen in cyclopentadienylchromium complexes leading to low-energy high-spin structures.

Recent studies, particularly from the laboratory of Buchalski and co-workers, have resulted in the syntheses of nickelacyclopentadienyl and nickelafluorenyl metallacycles that can function as pentahapto ligands in transition-metal complexes, similar to the ubiquitous cyclopentadienyl ligand. The structures and energetics of the neutral binuclear chromium carbonyls (CpNiC4H4)2Cr2(CO)n (n = 6, 5, 4, 3; Cp = η(5)-C5H5) containing the unsubstituted nickelacyclopentadienyl ligand have been investigated by density functional theory. The lowest energy (CpNiC4H4)2Cr2(CO)n (n = 6, 4) structures are similar to the corresponding experimentally characterized Cp2Cr2(CO)n structures with predicted Cr-Cr distances of ∼3.22 and ∼2.27 Å corresponding to the formal single and triple bonds, respectively. This gives the chromium atoms, as well as the nickel atoms, the favored 18-electron configuration. These species appear to be promising synthetic targets. However, the lowest energy (CpNiC4H4)2Cr2(CO)n (n = 5, 3) structures, as well as two (CpNiC4H4)2Cr2(CO)4 structures ∼10 to 12 kcal/mol in energy above the global minimum, can be dissected into a discrete pseudohalogen (CpNiC4H4)Cr(CO)3 unit and a (CpNiC4H4)Cr(CO)n-3 unit linked by a Cr-Cr bond flanked by one to three generally weakly semibridging CO groups. In most cases, the chromium atoms in the (CpNiC4H4)Cr(CO)n-3 units of these structures have 14-16-electron configurations rather than the favored 18-electron configuration. This leads to triplet and even quintet spin states in the lowest energy structures.

Reversible Cross-Linking and De-Cross-Linking System of Polystyrenes Bearing the Monohydrate Structure of Vicinal Tricarbonyl Group through Water–Alcohol Exchange Reactions at Ambient Conditions

We describe in this paper reversible cross-linking and de-cross-linking system based on a polystyrene derivative bearing monohydrate structure of vicinal tricarbonyl groups with 1,6-hexanediol utilizing the direct water–alcohol exchange reactions on the vicinal tricarbonyl groups. By employing diphenylpropanetrione as a unit model compound for the polymer, we have demonstrated that the water–alcohol exchange reactions could be carried out reversibly in both directions by changing solvents. Notably, the water–alcohol exchange reactions proceeded without any catalysts and under mild conditions. For example, an equimolar mixture of the hydrate of diphenylpropanetrione and benzyl alcohol in chloroform (0.5 M) reached equilibrium after standing at ambient temperature within 48 h, where the content ratio of the benzyl alcohol adduct increased up to 49%. The reaction rate and the position of the equilibrium were highly affected by the concentrations of the substrates as well as the reaction temperature. By virtue of the above characteristic features of the water–alcohol exchange reactions, the polystyrene derivative bearing monohydrate structure of vicinal tricarbonyl group (2.0 M) was cross-linked with 1,6-hexanediol (0.2 equiv of OH group to the tricarbonyl unit) in acetone at ambient temperature for 5 days to afford the networked polymer in almost quantitative yield. On the other hand, the networked polymer was treated with an excess of water at ambient temperature for 3 days to afford the original linear polymer in high yield as a result of de-cross-linking through the water–alcohol exchange reaction. The cross-linking and de-cross-linking behavior was also evidenced by SEC analysis of the reaction mixture.

ChemInform Abstract: A New Synthesis of Triphenylhosphorane Ylide Precursors to α‐Keto Amide/Ester and Tricarbonyl Units via Horner—Wadsworth—Emmons Reaction.

AbstractNewly developed Horner—Wadsworth—Emmons reagents (III) readily condense with various carbonyl compounds to afford the corresponding β,γ‐unsaturated α‐keto triphenylphosphoran ylides of type (V) or (VIII) which can easily be reduced to the corresponding β,γ‐saturated α‐keto triphenylphosphoran ylides of type (VI) or (IX).

A New Synthesis of Triphenylphosphorane Ylide Precursors to α-Keto Amide/Ester and Tricarbonyl Units via Horner-Wadsworth-Emmons Reaction

Newly developed Horner-Wadsworth-Emmons (HWE) reagents 5 having triphenylphosphorane ylide subunits readily condensed with various carbonyl compounds under mild reaction conditions to afford <TEX>$\beta,\gamma$</TEX>-unsaturated <TEX>$\alpha$</TEX>-keto triphenylphorane ylides in good to excellent yields, which were hydrogenated over Pd-C (10%)/<TEX>$H_2$</TEX> (1 atm) to give the corresponding <TEX>$\alpha$</TEX>-keto triphenylphorane ylides in quasi-quantitative yields. These triphenyphosphorane ylides have been utilized as the precursors to <TEX>$\alpha$</TEX>-keto amide/ester and vicinal tricarbonyl units in Wasserman's synthetic protocols, and have previously been prepared only from carboxylic acids/acid chlorides. Our new approaches provide excellent alternatives for the synthesis of triphenylphosphorane ylide precursors to <TEX>$\alpha$</TEX>-keto amide/ester and vicinal tricarbonyl units directly from carbonyl compounds in good to excellent yields.

The stereodivergent asymmetric synthesis of a range of 2-(1′-hydroxyalkyl)phenols

Abstract The use of the (S)-α-methylbenzyl group as a chiral auxiliary has allowed the diastereoselective ortho-deprotonation of a chromium tricarbonyl complexed phenoxy ring. When the resultant ortho-anion is treated with an aldehyde two diastereoisomeric complexes are formed, in relatively poor dr, which differ in the configuration of the newly formed benzylic stereogenic centre. However, both ortho-formylation followed by treatment with Grignard reagents and ortho-acylation followed by reduction with Super-Hydride® were found to be completely diastereoselective, giving access to either epimer of the corresponding benzylic alcohol complexes in >99:1 dr. Subsequent oxidative removal of the chromium tricarbonyl unit, followed by cleavage of the O-α-methylbenzyl chiral auxiliary gives enantiopure 2-(1′-hydroxyalkyl)phenols. Following this stereodivergent procedure, either enantiomer of the product may be accessed from a single antipode of [(α-methylbenzyloxy)benzene]Cr(CO)3.

(η5-C4H4S)Cr(CO)3 and (η5-C4H4Se)Cr(CO)3: A DFT Investigation of the Ground-State Singlet and Triplet Surfaces. New Insights into the Mechanism of C−S or C−Se Insertion Reactions

The singlet and triplet surfaces for the interaction of thiophene or selenophene with a chromium tricarbonyl unit were calculated using the B3LYP/LanL2DZ+p model chemistry. The singlet surfaces confirm that the (η5-C4H4E)Cr(CO)3 (E = S or Se) are the lowest energy species. The (η1(C2)-C4H4E)Cr(CO)3 and (κ2(E,C)-C4H4E)Cr(CO)3 species were also located in shallow energy minima. Reaction path modeling on the singlet surfaces provided activation energies for the endothermic insertion process of 172 and 160 kJ mol−1 for E = S or Se, respectively. The activation energy for the insertion process on the triplet surfaces is on the order of 70 kJ mol−1. A novel η3(E,C,C)-η1(C)-coordinated species was located as a transition state between the insertion species and (η5-C4H4E)Cr(CO)3 on the singlet surfaces and an intermediate on the triplet surface for E = S.

Chromium arene complexes in organic synthesis

The complexation of an arene to a chromium tricarbonyl unit changes its chemical behavior, giving rise to unprecedented transformations. The electron-withdrawing effect of the unit allows efficient nucleophilic attack (S(N)Ar and dearomatization reactions), stabilizes negative charges in benzylic positions and activates C(Ar)-halogen bonds for cross-coupling reactions. In addition, the Cr(CO)(3) moiety exerts great facial control so it can be used as an auxiliary that can easily be removed. The 1,2- and 1,3-unsymmetrically disubstituted complexes are planar chiral and there are various ways to prepare them in enantiomerically pure form. Planar chiral chromium complexes are becoming useful intermediates and ligands for asymmetric catalysis. This mature field of organometallic chemistry has given rise to several synthetic applications of chromium arene complexes in the synthesis of natural products. This chemistry is overviewed in this tutorial review, giving special attention to the most recent and outstanding contributions in the area.

Energy transfer pathways in pyridylporphyrin Re(I) adducts

Dimeric and pentameric adducts between a meso-4′ pyridylporphyrin core and either one or four rhenium(I) bipyridine tricarbonyl units, fac-[Re(CO) 3(bipy)(4′MPyP)][CF 3SO 3] and fac-[{Re(CO) 3(bipy)} 4(4′TPyP)][CF 3SO 3] 4(4′MPyP = 4′-monopyridylporphyrin, 4′TPyP = 4′-tetrapyridylporphyrin), respectively, were synthesized and their photophysical behaviors were investigated by emission and absorption time resolved experiments. The adducts exhibit distinctive supramolecular features, different from those of the molecular components. Upon excitation of the core, the typical porphyrin fluorescence is quenched. This effect is attributed to enhanced intersystem crossing in the porphyrin unit, owing to the heavy atom effect provided by the attached rhenium unit(s). Following excitation of rhenium fragments the typical rhenium MLCT emission is not observed while partial sensitization of the porphyrin fluorescence occurs, indicating that fast intercomponent energy and/or electron transfer processes take place in competition with the intersystem crossing in the rhenium unit.

The Chemistry of Vicinal Tricarbonyls and Related Systems

AbstractFor Abstract see ChemInform Abstract in Full Text.

The chemistry of vicinal tricarbonyls and related systems.

In this Account, we survey our work on the chemistry of vicinal tricarbonyls and cyano analogues. Methods of preparing the vicinal functionalities are reviewed as well as the use in organic synthesis of these strongly electrophilic aggregates, readily available from carboxylic acids. By attaching neighboring electrophilic groups to the vicinal tricarbonyl, we have developed polyelectrophilic systems, which may be added to di- and trinucleophiles to create novel types of multistep reactivity. Application of tricarbonyl chemistry in synthesis is illustrated by the formation of various natural products or their precursors including fused-ring beta-lactams, indole alkaloids, marine metabolites, enzyme inhibitors containing alpha-keto amides, and bioactive depsipeptides incorporating hydrated tricarbonyl units.

The organometallic fac-[(CO)3Mn(H2O)3]+ aquaion: base-hydrolysis and kinetics of H2O-substitution.

The novel organometallic aqua complex [(CO)(3)Mn(H(2)O)(3)](+) (1(+)) was obtained through hydrolysis of the analogous acetone complex. IR [nu(CO) = 2051, 1944 cm(-)(1)] and (17)O NMR spectroscopy revealed the presence of a fac tricarbonyl unit. Potentiometric titrations established that the trimer [(CO)(3)Mn(3)(OH)(4)](-) was the principal condensation product in the pH range >6 prior to slow formation of the tetramer [[(CO)(3)Mn](OH)](4). Water exchange in 1(+), determined by NMR line broadening as k(ex) = 19 +/- 4 s(-)(1) at 298 K, is four orders faster than with the analogous Re complex. The activation volume DeltaV(++) = -4.5 +/- 0.4 cm(3) mol(-1) is indicative of an associatively activated (I(a)) process.

Re(I) sensitised near-infrared lanthanide luminescence from a hetero-trinuclear Re2Ln array.

The trinuclear complexes Re2Ln (Ln = Nd, Yb or Er) contain two Re(I) tricarbonyl units linked to a DTPA binding site via 2,2'-bipyridyl ligands; Ln(III)-centred emission is sensitised by the Re(I) MLCT excited states.

On the reactivity of ascomycin at the binding domain. Part 1: Liberation of the tricarbonyl portion of ascomycin

Within the binding domain, ascomycin features the unusual pattern of a masked tricarbonyl moiety, which potentially allows for high structural diversity via simple isomerisation events. Herein, methodologies, allowing the liberation of the tricarbonyl unit by blocking the 14-hydroxy group are reported.

Synthesis, isolation, and characterization of trisodium tricarbonyliridate (3-), Na3[Ir(CO)3]. Initial studies on its derivative chemistry and structural characterizations of trans-[Ir(CO)3(EPh3)2](-), E = Ge, Sn, and trans-[Co(CO)3(SnPh3)2](-1).

Reduction of Na[Ir(CO)4] by sodium metal in (Me2N)3PO, followed by treatment with liquid ammonia, provided high yields (ca. 90%) of unsolvated Na3[Ir(CO)3], a thermally stable, pyrophoric orange solid. This substance contains iridium in its lowest known formal oxidation state of -3 and has been characterized by IR spectroscopy, elemental analyses, and derivative chemistry, i.e., by its conversion to the triphenylgermyl and triphenylstannyl complexes, trans-[Ir(CO)3(EPh3)2](-), E = Ge, Sn. Single-crystal X-ray structures of the tetraethylammonium salts of these species, as well as [Co(CO)3(SnPh3)2](-), confirm the trigonal bipyramidal nature of the anions, originally predicted on the basis of their IR spectra in the carbonyl stretching frequency region. These structural characterizations provide important additional evidence for the presence of metal tricarbonyl units in Na3[M(CO)3], M = Co, Ir.

The Chemistry of Vicinal Tricarbonyls: Total Syntheses of Elastase Inhibitors YM-47141 and YM-47142

We have completed the total syntheses of elastase inhibitors YM-47141 and YM-47142, the first natural products containing a vicinal tricarbonyl group. The work establishes the configuration at C(4) of the macrocyclic depsipeptide and demonstrates the generality of the phosphoranylidene-ylide activation and protection methodology employed earlier in syntheses of α-keto amides. Key steps involve the coupling of a carboxylic acid with a phosphorane to form a stable ylide intermediate, which contains the highly electrophilic carbonyl group in protected form. The tricarbonyl unit was unmasked at the final stage of the synthesis by oxidative cleavage of the C=P bond.

ジエン鉄カルボニル錯体を利用した立体制御反応

(Diene) Fe (CO) 3 complexes enjoy widespread use in organic synthesis, because they are synthetically equivalent to free dienes, yet are more stable and possess markedly different chemical properties. Complexation and decomplexation of diene Fe (CO) 3 compounds is readily accomplished and provides high yields in most cases. In addition, unsymmetrically substituted dienes are prochiral and, therefore, the corresponding Fe (CO) 3 complexes, are chiral. Considerable attention has been directed toward the efficient use of this temporally introduced chirality to construct neighboring stereogenic centers. Indeed, this is the main subject of Fe (CO) 3 complex chemistry, along with research on a practical method for synthesizing chiral (diene) Fe (CO) 3 complexes. Another fascinating aspect of these complexes is the mobility of the Fe (CO) 3 unit, which has received less attention than its stereodirecting ability. The Fe (CO) 3 moiety, which attaches to dienyl compounds by coordination, can move one carbon unit accompanied by isomerization of the diene via a η5 cation intermediate (1, 2-migration). This article presents the recent studies on iron tricarbonyl units to control the regio- and stereochemistry of nucleophilic addition to a neighboring C=X (X=O, N) double bond and η5- (pentadienyl) iron (+1) cation complex.

Synthesis of Monophasic Hybrid Organic−Inorganic Solids Containing [η6-(Organosilyl)arene]chromium Tricarbonyl Moieties

Silica gel containing benzenechromium tricarbonyl units have been obtained from molecular organosilicon precursors. The hydrolytic sol−gel polymerization of [η6-C6H5Si(OMe)3]Cr(CO)3 (1), [η6-1,4-C6H4RR‘]Cr(CO)3 [R = R‘ = Si(OMe)3 (2), R = R‘ = CH2Si(OMe)3 (3), R = R‘ = CH2CH2Si(OMe)3 (4)], {η6-1,3,5-C6H3[Si(OMe)3]3}Cr(CO)3 (5), under nucleophilic catalysis by fluoride ion (NH4F), have led quantitatively to new monophasic hybrid organic−inorganic silica gels. The derived xerogels X were characterized by FT IR, 13C and 29Si solid state CP MAS NMR spectroscopies. The silicon−carbon bond and the tricarbonylchromium ligand were retained within the gel. The major environment of the Si atoms corresponded to a T2:CSi(OR)(OSi)2 substructure for X2−X4, a T3:CSi(OSi)3 one for X1 and a Ts:CSi(OR)2(OSi) in the case of X5. In most cases, these were amorphous materials that exhibited low specific surface areas (∼10 m2 g-1). Upon heating the xerogels X1, X2, and X4 at 400 °C under an argon flow, weight losses corresponding to complete carbon monoxide elimination were obtained, leading to chromium in a low oxidation state within the solid.

Catalytic enantioselective synthesis of the second generation histamine antagonist cetirizine hydrochloride

The first enantioselective synthesis of cetirizine hydrochloride ( 1) has been developed using the highly stereospecific chiral oxazaborolidine (CBS) reduction of 4[ η 6-chromium tricarbonylbenzoyl]chlorobenzene to establish the benzhydryl stereocenter. The chromium tricarbonyl unit also served as stereocontroller to allow the stereospecific displacement of hydroxyl by amino at the benzylic stereocenter, as outlined in Scheme 1.