Nuclear magnetic resonance and the conformation of some derivatives of Michler's ketone

¹H NMR spectra are reported for Michler's ketone and twenty of its derivatives, along with ¹³C chemical shifts for five of the compounds. ¹H chemical shifts show only small changes with increasing substitution at the sterically hindered 2-position. Estimates of the dihedral angle between the benzene ring and C? CO? C planes have been obtained from the chemical shifts of C?O and 4-C for ketones 1, 3, 5, 15 and 16 . These angles are both internally consistent and very similar to dihedral angles determined by other methods for corresponding compounds in the benzophenone series.     

Vibrational spectra of σ-allylmanganese pentacarbonyl

The vibrational spectra of σ-(C₃H₅)Mn(CO)₅ are reported. Assignment of bands is made and carbonyl force constants are calculated. The results indicate that the Mn(CO)₅ moiety has C_4ν symmetry. The calculated angle between the axial and equatorial carbonyl groups is approximately 95°. The bonding in this compound is very similar to that in (CH₃)Mn(CO)₅.

In the far-infrared region, seven bands are expected in C_4ν symmetry (3A₁ + 4E), and all are observed.     

Structures and Mössbauer spectra of phosphido-bridged heterobimetallic complexes CpFe(CO)2(μ-PPh2)W(CO)5 and CpFe(CO)(μ-CO)(μ-PPh2)W(CO)4

Structures of non metal-metal bonded phosphido-bridged heterobimetallic complexes, including CpFe(CO)₂(μ-PPh₂)W(CO)₅ (1-W) and metal-metal bonded CpFe(CO)(μ-CO)(μ-PPh₂)W(CO)₄ (2), were determined by a single crystal X-ray diffraction study. In 1-W, the long distance between Fe and W indicates no metal-metal bond to exist. In 2, a Fe---W bond with bond length 2.851 Å and a semibridging carbonyl with W---C---O angle 153° were observed. Mössbauer spectra of 1-W and 2 were taken at 77 K. Isomer shifts of 1-W and 2 were − 0.0203 mm s⁻¹ and 0. 1917 mm s⁻¹ respectively.     

Double bond shifts induced by reaction of hex-5-en-2-one with triosmium clusters

Carbon---hydrogen bond cleavage at the terminal 6-position occurs when hex-5-en-2-one (CH₂=CHCH₂CH₂COMe) oxidatively adds to [Os₃(CO)₁₀(MeCN)₂] to give [Os₃H(μ-CH=CHCH₂CH₂COMe)(CO)₁₀], which is completely analogous to the simple vinyl complex [Os₃H(μ-CH=CH₂)(CO)₁₀]. A minor product from the reaction is [Os₃(CH₃CH=CHCH₂COMe)(CO)₁₀], an isomer in which double-bond migration has occurred to give the βγ-unsaturated ketone; stabilisation occurs through chelation and ketone coordination. [Os₃H₂(CO)₁₀] reacts with CH₂=CHCH₂CH₂COMe in refluxing cyclohexane to give a third isomer, [Os₃H(CH₃CH₂C=CHCOMe)(CO)₁₀], in which further double bond migration has occurred to give the β-unsaturated ketone. Metallation at the β-site gives an Os---C bond as part of a 5-membered chelate ring. Thermolysis of each of the three isomeric decarbonyl species in refluxing cyclohexane or heptane leads to the elimination of an Os(CO)₄ group to give the dinuclear compound [Os₂H(EtC=CHCOMe)(CO)₆] in varying yield. Pathways from γδ to the βγ and finally the β unsaturated ketones may be mapped out.     

Altered selectivity of reduction of steroidal carbonyls

The reduction of steroidal ketones in different solvents yielded different products. These conditions which altered the normal path, yielded a selective reduction of the Δ⁴-3 carbonyl without the concomitant reduction of the C-17 or C-20 ketones; this permitted a one step partial synthesis of 3β-hydroxy-Δ⁴-pregnen-20-one (I), 3β-hydroxy-5-pregnan-20-one (II), and of 3β,11β-dihydroxyandrostan-17-one (IV).     

Metal-assisted reactions—12 : Unusual selectivity in the reduction of ketones with zinc or cadmium bis-tetrahydroborate/dimethylformamide complex

Zinc bis-tetrahydroborate forms a solid complex with dimethylformamide (DMF) of composition, Zn(BH₄)₂ 1.5DMF. Unlike zinc bis-tetrahydroborate itself, the complex with DMF can be stored as a solid at room temperature. Ketones and aldehydes are reduced to the corresponding alcohols by the complex but the mechanism of reduction appears to be different from that using zinc bis-tetrahydroborate itself and from other tetrahydroborates in that only one hydride equivalent from each BH₄⁻ unit is utilized and not four. Further, although saturated aliphatic ketones are reduced rapidly to alcohols, aromatic ketones react much more slowly and ,β-unsaturated ketones react very slowly so that the complex appears to have selective reducing potential with regard to different classes of ketones. It is also apparent that the zinc bis-tetrahydroborate/DMF complex reduces sterically hindered saturated ketones much more slowly than it does unhindered ketones. An analogous cadmium bis-tetrahydroborate/DMF complex can be prepared in solution and reacts with ketones similarly to the zinc complex.     

Reactions of the cationic diruthenium carbonyl complex [Ru2(μ-dppm)2(CO)4(μ,η-O2CMe)] with bidentate ligands; intramolecularly assisted stereospecific synthesis via the second-sphere face-to-face π–π stacking interactions

The reactions of the diruthenium carbonyl complexes [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]X (X=BF₄⁻ (1a) or PF₆⁻ (1b)) with neutral or anionic bidentate ligands (L,L) afford a series of the diruthenium bridging carbonyl complexes [Ru₂(μ-dppm)₂(μ-CO)₂(η²-(L,L))₂]X_n ((L,L)=acetate (O₂CMe), 2,2′-bipyridine (bpy), acetylacetonate (acac), 8-quinolinolate (quin); n=0, 1, 2). Apparently with coordination of the bidentate ligands, the bound acetate ligand of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ either migrates within the same complex or into a different one, or is simply replaced. The reaction of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ (1) with 2,2′-bipyridine produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)₂] (2), [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-bpy)]⁺ (3), and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-bpy)₂]²⁺ (4). Alternatively compound 2 can be prepared from the reaction of 1a with MeCO₂H–Et₃N, while compound 4 can be obtained from the reaction of 3 with bpy. The reaction of 1b with acetylacetone–Et₃N produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-acac)] (5) and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-acac)₂] (6). Compound 2 can also react with acetylacetone–Et₃N to produce 6. Surprisingly [Ru₂(μ-dppm)₂(μ-CO)₂(η²-quin)₂] (7) was obtained stereospecifically as the only one product from the reaction of 1b with 8-quinolinol–Et₃N. The structure of 7 has been established by X-ray crystallography and found to adopt a cis geometry. Further, the stereospecific reaction is probably caused by the second-sphere π–π face-to-face stacking interactions between the phenyl rings of dppm and the electron-deficient six-membered ring moiety of the bound quinolinate (i.e. the N-included six-membered ring) in 7. The presence of such interactions is indeed supported by an observed charge-transfer band in a UV–vis spectrum.     

C NMR spectra of cyclomercurated ferrocenylimines: Substituent effects and conformations in the ferrocenes

Three series of cyclomercurated ferrocenylimines (2-chloromercurio-ferrocenylimines) have been studied using ¹³C NMR spectroscopy. Good to excellent linear relationships have been found to exist between the chemical shifts of the carbon atoms in the ferrocenyl moiety and normal Hammett substituent constants σ_m and σ_p. The δ values of the iminyl carbon atoms show excellent linear correlations with the σ values. In three series of the ferrocenes, the sensitivity of the carbon atoms to the substituent effect is different, which is discussed in terms of the twist angle between the N-phenyl ring and the C---C=N---C plane. The relative sensitivity of the chemical shifts on different positions in ferrocenyl moiety to the substituent effect has also been presented.     

Monodentate and bidentate trifluoroacetato ligands in bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato)thallium(III)—a new dynamic 4:3 piano stool seven-coordinate geometry

The crystal structure of bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato) thallium(III), Tl(N---Me---tpp)(CF₃CO₂)₂ (2), was established and the coordination sphere around the Tl³⁺ ion is described as 4:3 tetragonal base–trigonal base piano stool seven-coordinate geometry in which the two cis CF₃CO₂ ⁻ groups occupy two apical sites. The plane of the three pyrrole nitrogen atoms [i.e. N(2), N(3) and N(4)] strongly bonded to Tl³⁺ is adopted as the reference plane 3N. The pyrrole N(1) ring bearing the methyl group [i.e. C(45)H₃] is the most deviated one from the 3N plane making a dihedral angle of 23.3° whereas smaller angles of 9.9, 2.7 and 4.7° occur with pyrroles N(2), N(3), and N(4), respectively. Because of the larger size of the thallium(III) ion, Tl is considerably out of the 3N plane; its displacement of 1.02 Å is in the same direction as that of the two apical CF₃CO₂ ⁻ ligands. The intermolecular trifluoroacetate exchange process for 2 in CD₂Cl₂ solvent is examined through ¹⁹F and ¹³C NMR temperature-dependent measurements. In the slow-exchange region, the CF₃ and carbonyl (CO) carbons of the CF₃CO₂ ⁻ groups in 2 are separately located at δ 114.3 [¹J(C–F)=290 Hz, ³J(Tl–C)=411 Hz] and 155.1 [²J(C–F)=37 Hz, ²J(Tl–C)=204 Hz], respectively, at −106 °C. In the same slow-exchange region, the fluorine atoms of 2, Tl(N---Me---tpp)(CF₃CO₂)⁺ and the free CF₃CO₂ ⁻ are located at δ −73.76 [⁴J(Tl–F)=44 Hz], −73.30 [⁴J(Tl–F)=22 Hz], and −76.15 ppm at −97 °C, respectively.     

Syntheses, X-ray structures, and reactions of ruthenium carbonyl complexes containing 1,1-dithiolates

Treatment of [Ru₂(CO)₄(MeCN)₆][BF₄]₂ or [Ru₂(CO)₄(μ-O₂CMe)₂(MeCN)₂] with uni-negative 1,1-dithiolate anions via potassium dimethyldithiocarbamate, sodium diethyldithiocarbamate, potassium tert-butylthioxanthate, and ammonium O,O′-diethylthiophosphate gives both monomeric and dimeric products of cis-[Ru(CO)₂(η²-(SS))₂] ((SS)⁻=Me₂NCS₂⁻ (1), Et₂NCS₂⁻ (2), ^tBuSCS₂⁻ (3), (EtO)₂PS₂⁻ (4)) and [Ru(CO)(η²-(Me₂NCS₂))(μ,η²-Me₂NCS₂)]₂ (5). The lightly stabilized MeCN ligands of [Ru₂(CO)₄(MeCN)₆][BF₄]₂ are replaced more readily than the bound acetate ligands of [Ru₂(CO)₄(μ-O₂CMe)₂(MeCN)₂] by thiolates to produce cis-[Ru(CO)₂(η²-(SS))₂] with less selectivity. Structures 1 and 5 were determined by X-ray crystallography. Although the two chelating dithiolates are cis to each other in 1, the dithiolates are trans to each other in each of the {Ru(CO)(η²-Me₂NCS₂)₂} fragment of 5. The dimeric product 5 can be prepared alternatively from the decarbonylation reaction of 1 with a suitable amount of Me₃NO in MeCN. However, the dimer [Ru(CO)(η²-Et₂NCS₂)(μ,η²-Et₂NCS₂)]₂ (6), prepared from the reaction of 2 with Me₃NO, has a structure different from 5. The spectral data of 6 probably indicate that the two chelating dithiolates are cis to each other in one {Ru(CO)(η²-Et₂NCS₂)₂}fragment but trans in the other. Both 5 and 6 react readily at ambient temperature with benzyl isocyanide to yield cis-[Ru(CO)(CNCH₂Ph)(η²-(SS))₂] ((SS)=Me₂NCS₂⁻ (7) and Et₂NCS₂⁻ (8)). A dimerization pathway for cis-[Ru(CO)₂(η²-(SS))₂] via decabonylation and isomerization is proposed.     

The stereochemistry at silicon of an iron to cyclopentadienyl ligand silyl group migration in (η-C5H5)Fe(CO)2SiR3

The silyl group migration observed upon treating (R)(+)-(η⁵-C₅H₅)Fe(CO)₂-SiMePh(1-Np) with n-BuLi occurs with retention of configuration at silicon. The anion resulting from the migration, (η⁵-C₅H₄SiMePh(1-Np))Fe(CO)₂Li, is alkylated with MeI to give (R)-(−)-(η⁵-C₅H₄SiMePh(1-Np))Fe(CO)₂Me (II). Compound II is independently prepared from (η⁵-C₅H₅)Fe(CO)₂Me. A concerted mechanism for the migration involving frontside nucleophilic attack at silicon is suggested.     

A facile synthetic route to (η-benzoyleyclopentadienyl) metal compounds

A reaction between cyclopentadienylsodium and ethyl benzoate in refluxing THF produces (benzoylcyclopentadienyl)sodium (4) in 70–80% yield. Subsequent treatment of 4 in ethanol solution with thallium ethoxide affords (benzoyleyclopentadienyl)thallium (3) in nearly quantitative yield. Reactions of 3 with Mn(CO)₅Br, Re(CO)₅Br, [Rh(CO)₂Cl]₂ or FeCl₂ lead to the respective η⁵-benzoylcyclopentadienyl derivatives of these metals, and demonstrate the utility of 3 in organometallic syntheses. Reactions of several of these organometallic ketones with cymantrenyllithium [(η⁵-C₅H₄Li)Mn(CO)₃] provide a useful new route to bimetallic compounds.     

Photochemical synthesis and structural characterization of (η-C5Me5)3Mo3(CO)4(μ2-H)(μ3-O): an unprecedented 46-electron trimolybdenum cluster containing a localized monoprotonated Mo---Mo double bond

Irradiation of the 30-electron Mo₂(η⁵-C₅Me₅)₂(CO)₄ and Re₂(CO)₁₀ in toluene solution (containing H₂O) afforded (in 1–2% yields) a novel triangular metal cluster, (η⁵-C₅Me₅)₃Mo₃(CO)₄(η₂-H)(η₃-O) (1), which was characterized by a single-crystal X-ray diffraction study. Compound 1, of pseudo C_s-m symmetry, has a triangulo-Mo₃(η₃-O) core with composite Mo---H---Mo and Mo---Mo electron-pair bonds along one unusually short edge (2.660(1) Å) and Mo--- electron-pair bonds along the other two edges (2.916(1) and 2.917(1) Å). The edge-bridged hydride ligand, which displays a characteristic high-field proton NMR resonance at δ −17.79 ppm, was not found from the crystallographic determination but was located via a quantitative potential-energy-minimization method. This procedure unambiguously established that the optimized hydrogen position, which corresponds to a distinct coordination site with identical Mo---H distances of 1.85 Å, is the only one that can be sterically occupied by a metal-bound hydride ligand. This 46-electron species is the first electron-deficient trimolybdenum cluster containing a monoprotonated Mo---Mo double bond; its existence is attributed to ligand overcrowding due to the bulky pentamethylcyclopentadienyl rings. Black (η⁵- C₅Me₅)₃Mo₃(CO)₄(η₂-H)(η₃-O) · 1/2THF crystallizes with two formula species in a triclinic unit cell of P1 symmetry with a 8.603(4), b 11.115(4), c 19.412(11) Å, 80.69(4)°, β 101.10(4)°, and γ 98.88(3)° at −40° C. Least-squares refinement (RAELS with 221 variables) of one independent Mo₃ molecule and a centrosymmetrically-disordered THF molecule converged at R₁(F) 5.62%, R₂(F 6.88% for 8460 independent diffractometry data (I₀ ρ 3σ(I₀ collected at −40° C with Mo-K radiation     

A new entry of highly nucleophilic CHBr3–TiCl4–Mg system for the stereoselective synthesis of 1-alkenyl bromides

This TiCl₄–Mg promoted coupling of CHBr₃ with various aldehydes and ketones, especially in sterically hindered or enolizable ketones, provides a simple, practical, and stereoselective carbonyl–bromomethylenation leading primarily to (E)-vinyl bromides.     

Preparation and structure of (η-cyclopentadienyl)(η-tetraphenylcyclobutadiene) cobalt coordinated by four Cr(CO)3 units at the phenyl rings

The reaction of (η⁵-cyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt (1) with excess Cr(CO)₆ yielded several heterometallic compounds: 2, 3 (3′ and 3″), 4 and 5 with, respectively, one, two, three and four phenyl rings complexed with Cr(CO)₃ fragment(s). These compounds were characterized by mass, infrared, ¹H and ¹³C NMR spectra. The crystal structure of 5 was determined. In 5 the four Cr(CO)₃ fragments are on the same side of the CpCo fragment; whereas, the two Cr(CO)₃ fragments of 3′, the precursor of 5, are pointed in a different direction from the CpCo fragment. The cyclopentadienyl ring shows a static disorder around the axis that passes through the cobalt and the centre of the ring.     

A convenient synthesis of Fe(CO)2(η-S2CNMe2)2 and Fe(η-S2CNMe2)2 from the monodentate dithiocarbamato derivative, [(η-C5H5)(CO)3W(η-SCSNMe2)] and Fe2(CO)9

A high yield synthesis of the carbonyl dithiocarbamato derivative Fe(CO)₂(η²-S₂CNMe₂)₂ and Fe(η²-S₂CNMe₂)₂ by photolysis with visible light of solutions containing Fe₂(CO)₉ or Fe₃(CO)₁₂ and [(η⁵-C₅H₅)(CO)₃W(η¹-SCSNMe₂)] is reported.     

Mixed-metal cluster chemistry Part 20. Syntheses, crystal structures and electrochemical studies of W2Ir2(μ-L)(CO)8(η-C5H4Me)2 (L=dppe, dppf)

The 60-electron tetrahedral clusters W₂Ir₂(μ-L)(CO)₈(η⁵-C₅H₄Me)₂ [L=dppe (2), dppf (3)] have been prepared from reaction between W₂Ir₂(CO)₁₀(η⁵-C₅H₄Me)₂ (1) and the corresponding diphosphine in 52 and 66% yields, respectively. A structural study of 2 reveals that three edges of a WIr₂ face are spanned by bridging carbonyls, that the iridium-ligated diphosphine coordinates diaxially and that the tungsten-bound methylcyclopentadienyls coordinate axially and apically with respect to the plane of bridging carbonyls. A structural study of 3 reveals that the dppf ligand bridges an Ir---Ir bond which is also spanned by a bridging carbonyl; tungsten-ligated methylcyclopentadienyl ligands and terminal carbonyls result in electronic asymmetry (17e and 19e iridium atoms) in the electron-precise cluster. Both clusters show two reversible one-electron oxidation processes and an irreversible two-electron reduction; the dppf-containing cluster 3 has a further, irreversible, one-electron oxidation process. UV–vis-NIR spectroelectrochemical studies of the 2→2⁺→2²⁺ progression reveal the appearance of a low-energy transition on oxidation to 2⁺ which persists on further oxidation to 2²⁺.     

Hydrogen-bonding effect on C NMR chemical shifts of amino acid residue carbonyl carbons of some peptides in the crystalline state

¹³C cross polarization-magic angle spinning NMR spectra were measured for a series of peptides containing -valine, -leucine and -aspartic acid residues, for which the crystal structures were already determined by X-ray diffraction, in order to investigate the relationship between hydrogen-bond lengths (R_N…O) and ¹³C chemical shifts of amide carbonyl carbons in the peptides. From these experimental results, it was found that the isotropic ¹³C chemical shifts (δ_iso) of the amino acid residues move linearly downfield with a decrease in R_N…O within the hydrogen-bonded length range considered here and also shown in our previous work on glycine and -alanine residues as expressed by δ_iso(ppm) = a − bR_N…O(Å) where a and b are 215.4 (ppm) and 14.2 (ppm Å⁻¹) for the -valine residue, 202.2 (ppm) and 10.0 (ppm Å⁻¹) for the -leucine residue, and 199.0 (ppm) and 9.6 (ppm Å⁻¹) for the -aspartic acid residue, respectively. Using these relations, the R_N…O values of some polypeptides in the crystalline state were determined through the observation of the amide carbonyl carbon chemical shifts. These values were compared with those determined by the X-ray diffraction method. Furthermore, quantum-chemical calculation of the ¹³C shielding constant for a model compound was carried out by the finite perturbation theory INDO method in order to ascertain the ¹³C shielding behavior in the formation of hydrogen bonds.     

Iron carbonyl complexes from 2-[2,3-diaza-4-(2-thienyl)buta-1,3-dienyl]thiophene: N---N bond cleavage and cyclometalation

When thienyl Schiff base 1, derived from 2-formylthiophene and hydrazine, reacted with Fe₂(CO)₉ in n-hexane, three major complexes were obtained: (1) a diironhexacarbonyl complex with two 2-thienylmethylideneamido bridging ligands 2, which resulted from the =N---N= bond cleavage of ligand 1; (2) a doubly cyclometalated di-μ-di-(η¹:η²-thienyl; η¹:η¹(N))bis(hexacarbonyldiiron) complex (3); and (3) a cyclometalated (μ-η¹:η²-thienyl; η¹:η¹(N))hexacarbonyldiiron complex (4). Molecular structures of compounds 1a, 1c, and 2a have been determined by single-crystal X-ray diffraction.