The N—H stretching vibrations and conformations of trialkylthioureas

The ν(N-H) vibrations of trialkylthioureas observed in the dilute solutions are interpreted in relation to the trans—out isomerism. Occurrence of the out form is discussed from the point of view of steric hindrance. The two forms are characterized by the behavior of ν(N—H) vibrations at several concentrations. Solid DiPTUtB and DcHTUtB exhibited one sharp band at the same position as the ν(N—H) band in solution. This indicates that they are in the out form in the solid state as well as in solution.     

Conformational studies by nuclear magnetic resonance—IV: Restricted rotation in vinylogous thioamides

Enamino -thial and -thiones R¹C(S)CH?CHNR (R¹ = H or alkyl; R² = Me or Et) have been shown by NMR spectra to exist in two rotational forms, s-cis and s-trans, the populations of the latter being approximately the same as in the case of the parent oxa analogues. An increase of the order of 2 to 4 Kcal/mole in the heights of C? C and C? N rotation barriers (ΔG*) was found on comparing the title compounds with their oxa analogues. IR spectra failed as a tool to establish the rotational equilibrium. IR absorption bands of the ν_{C? C}, ν_{C? H} (in the NMe₂ group) and γ_HC?CH vibrations have been found, but the ν_C?S band could not be assigned unambiguously. Anomalies concerning the frequency and intensity of the ν_C?C band are discussed.     

Polymorphism in 2‐(4‐hydroxy‐2,6‐dimethylanilino)‐5,6‐dihydro‐4H‐1,3‐thiazin‐3‐ium chloride

Details of the structures of two conformational polymorphs of the title compound, C₁₂H₁₇N₂OS⁺·Cl⁻, are reported. In form (I) (space group P), the two N—H groups of the cation are in a trans conformation, while in form (II) (space group P2₁/c), they are in a cis arrangement. This results in different packing and hydrogen‐bond arrangements in the two forms, both of which have extended chains lying along the a direction. In form (I), these chains are composed of centrosymmetric R₄²(18) (N—H...Cl and O—H...Cl) hydrogen‐bonded rings and R₂²(18) (N—H...O) hydrogen‐bonded rings. In form (II), the chains are formed by centrosymmetric R₄²(18) (N—H...Cl and O—H...Cl) hydrogen‐bonded rings and by R₄²(12) (N—H...Cl) hydrogen‐bonded rings.     

Conformations of N,N'-diphenyl-N-ethylthiourea and its related compounds in the solid state

The conformations of the related compounds RPhTUPh, RPhUPh and DRTUPh, DRUPh have been determined in the solid state by studying their v(N-H) vibrations and comparison with the conformations in solution. Only EPhTUPh in the solid state is observed to exhibit both cis and transv(N-H) bands. The coexistence of the cis and trans forms is suggested to take place with a balance between Ph-Ph interaction and hydrogen bond formation. In this balance the steric effect of the R group on the CS group plays an important role. For DRTUPh and DRUPh out-trans isomerism is discussed. The importance of hydrogen bond formation is emphasized as a factor determining conformations in the solid state.     

(1R,3R,4S)‐1‐Benzyl‐3‐(tert‐butyldimethylsilyloxy)‐4‐(hydroxymethyl)pyrrolidine–borane: novel B—H...H—O hydrogen bonding

The absolute configuration of the title cis‐(1R,3R,4S)‐pyrrolidine–borane complex, C₁₈H₃₄BNO₂Si, was confirmed. Together with the related trans isomers (3S,4S) and (3R,4R), it was obtained unexpectedly from the BH₃·SMe₂ reduction of the corresponding chiral (3R,4R)‐lactam precursor. The phenyl ring is disordered over two conformations in the ratio 0.65:0.35. The crystallographic packing is dominated by the rarely found donor–acceptor hydroxy–borane O—H...H—B hydrogen bonds.     

Complexes olefiniques du ruthenium : IV. Etude des complexes [RuClH(diène)(amine)2], structure cristalline de [RuClH(cod)(pipéridine)2]

The polymer [RuCl₂(diene)]_n undergoes bridge cleavage reaction with amines giving, at temperatures dependant on the nature of the diene moiety, the monomer [RuClH(diene)(amine)₂]. The crystal structure of the compound [RuClH(cod)(pip)₂] has been determined from three dimensional X-ray data.The complex crystallizes in space group Pmcn of the orthorhombic system, a 16.808(4), b 11.520(2), c 9.744(2) Å D_m 1.44 D_c 1.46 g cm^?3; Z 4. The structure was solved by standard heavy atom methods and has been refined by least squares to a conventional R factor of 0.039 based on 3280 refections. The complex has a crystallographically C_s imposed symmetry. The coordination geometry around the ruthenium atom is octahedrally distorted with cis amine ligands, the chloro and the hydrido ligands being trans to each other and the cyclooctadiene moiety bound through the two double bonds. The CC distances of the olefinic bonds are longer (1.394(4) Å) than was to be expected according to the Dewar—Chatt—Duncanson model. Principal bond lengths are: RuH 1.57(4); RuCl 2.555(1) (demonstrating a high structural trans influence of the hydrido ligand); RuN, 2.240(2) Å. An order of increasing structural trans influence for RuCl distances is proposed. In the IR spectrum ν(RuH) was observed at 2040 cm^?1. Decomposition of the complexes in chlorinated solvents prevented NMR studies.     

NMR study of cis3̄trans isomerism in N-methylated lactams with 11- and 13-membered rings

From ¹H-NMR spectra of 1-methyl-azacyclo-undeca-2-one and 1-methyl-azacyclo-trideca-2-one, the bands corresponding to the cis and trans forms have been assigned and analyzed; based on this analysis, conformational structures about the C-C bond next to nitrogen are proposed. By analysis of the relative areas and shapes of the N-methyl bands measured for the two lactams in 1,1,2,2-tetrachloroethane-d₂, over a broad temperature range, the equilibrium and thermodynamic parameters characterizing the cis—trans isomerism of the amide bond in these lactams have been determined. Peaks corresponding to the cis and trans forms in the ¹³C-NMR spectra of these lactams have also been assigned.     

trans‐Di­chloro­tetrakis(4‐methylpyrimidine‐N1)­ruthenium(II)

The title compound, trans‐[Ru^IICl₂(N¹‐mepym)₄] (mepym is 4‐methylpyrimidine, C₅H₆N₂), obtained from the reaction of trans,cis,cis‐[Ru^IICl₂(N¹‐mepym)₂(SbPh₃)₂] (Ph is phenyl) with excess mepym in ethanol, has fourfold crystallographic symmetry and has the four pyrimidine bases coordinated through N¹ and arranged in a propeller‐like orientation. The Ru—N and Ru—Cl bond distances are 2.082 (2) and 2.400 (4) Å, respectively. The methyl group, and the N³ and Cl atoms are involved in intermolecular C—H?N and C—­H?Cl hydrogen‐bond interactions.     

Electronic spectra of α,β-unsaturated carbonyl compounds—II : An evaluation of increments characteristic of structural features of β-oxy-α,β-unsaturated ketones

By comparing UV spectra of β-alkoxy-α,β-unsaturated ketones of established steric structure, spectral constants characteristic of the cis/trans configuration change and s-cis/s-trans and O-s-cis/O-s-trans conformation changes have been evaluated. These are: Δλ^cis_trans = 0, Δλ^s-cis_s-trans = 8 nm and Δλ^O-s-trans_O-s-cis = 6 nm. A comparison of cis-s-cis enol ethers with the parent enols yielded the increment for the intramolecular (“chelating”) H-bond, Δγ_chel = 24 nm. The methanol-induced bathochromic shift has been found to depend strongly on s-cis/s-trans isomerism. The substituent increments have been shown to be dependent on the degree of substitution in the reference molecule. The results obtained have been summarized in a set of spectral increments complementing the basic system of Woodward and the Fiesers.     

Organophosphine ligands in PtPX<Subscript>2</Subscript>Y and PtPXYZ complexes; structural aspects

This review covers over ninety platinum complexes with PtPX₂Y and PtPXYZ inner coordination spheres, in which the P-donor ligands are organomonophosphines. These complexes crystallize in four crystal systems: tetragonal (×3), orthorhombic (×17), triclinic (×20) and monoclinic (×56). Complexes with the PtPX₂Y chromophore exist in cis- as well as trans-configurations; however, the latter prevails. There are four types of ligands which create such chromophores: monodentate (H, OL, NL, CO, BL, Cl, SL, Br, SeL and I); homobidentate (O₂L, N₂L, S₂L, Se₂L and As₂L); heterobidentate (O/N, O/S, N/S, N/Se and N/Te); and heterotridentate (O/O/N, N/N/S, N/N/Se, O/S/S, Se/N/Se and O/N/S). The chelating ligands create four-, five- and six-membered metallocycles, and the effects of both steric and electronic factors can be seen from the values of the L–Pt–L bite angles. The structural parameters are analyzed and discussed, with particular attention to trans-effects. Three types of isomerism are identified, namely cis–trans, distortion and ligands.     

Infrared spectra and configuration of N,N'-diaryl-thioureas

The conformation of the —NH—CS—NH— grouping in a series of N,N'-diarylthioureas some of which possess a marked anti-viral activity is studied using IR spectral data. The results indicate that in organic solvents (CCl₄, CHCl₃, C₂C1₄, CH₂C1₂) the compounds studied participate in an equilibrium between several isomeric forms arising from the possibility of a cis or trans structure of the —CS—NH— groups. The increased solvent polarity favours the cis conformation.     

Monomeric and polymeric structures of oxovanadium(IV) complexes with Schiff base ligands derived from (R,R)-2,4-pentanediamine: Synthesis and crystal structure

New tetradentate Schiff base–oxovanadium(IV) complexes which have electron donating or withdrawing groups at the 5-position of the salicylaldehyde moieties, [VO{Xsal-(R,R)-2,4-ptn}] (H₂{Xsal-(R,R)-2,4-ptn}: N,N′-di-Xsalicylidene-(R,R)-2,4-pentanediamine; X=5-MeO (methoxy), 5-Br, and 5-NO₂) were prepared. The structures and redox potentials for the V(V)/V(IV) couple of the complexes were compared with those of other [VO{Xsal-(R,R)-2,4-ptn}] (X=3-EtO (ethoxy), 3-MeO, and H). The 5-MeO substituted complex which has electron donating groups at the 5-position of the salicylaldehyde moieties forms a monomeric structure in the solid state. The 3-EtO substituted complex has both monomeric and polymeric structures. On the other hand, the other [VO{Xsal-(R,R)-2,4-ptn}] (X=H, 3-MeO, 5-Br, 5-NO₂) complexes have only polymeric structures. X-ray crystal structure analysis of [VO{5-MeOsal-(R,R)-2,4-ptn}]⋅CH₃OH (1) was carried out. Complex 1 has a monomeric five-coordinate square–pyramidal structure. The six-membered N–N chelate ring forms a distorted flattened boat form with two methyl groups in the axial positions.     

The infrared spectra (500-150 CM−1) of the complexes cis- and trans-[Pt(pyridine)2X2] (X = Cl,Br, I,SCN)

The IR spectra of cis- and trans-[Pt(pyridine)₂X₂] (X = Cl, Br, I, SCN) are discussed. Distinction between the vPt—N and vPt—X bands is based on their relative sensitivities to ¹⁵N-labelling and deuteration of the pyridine ring, to halogen substitution and to ¹⁵NCS-labelling. Two vPt—N and two vPt—X bands are observed in the cis-complexes as required for C_2v symmetry. The D_2h symmetry of the trans-complexes requires one vPt-N and one vPt—X band but additional bands are observed and are ascribed to coupling between vPt—N and vPt—X.     

A series of hydridoplatinum(II) complexes stabilized with tribenzylphosphines: their preparation,and an empirical approach to the mutual influence of ligands

The preparation, IR and NMR spectra of 123 platinum hydrides of the general formula, trans-PtHX(PBz₃)₂ or trans-PtHL(PBz₃)₂BPh₄ (X = a uninegative anionic ligand, L = a neutral donor molecule, Bz = benzyl), are described. Neutral platinum hydrides have been synthesized by the reduction of trans-PtCl₂-(PBz₃)₂ with NaBH₄, by the Michaelis—Arbuzov rearrangement, or by metathesis. Cationic hydridoplatinum(II) complexes are obtained from the reaction of trans-PtHX(PBz₃)₂ (X = Cl or NO₃) with a donor molecule (L) in the presence of NaBPh₄, or by coordinating a donor molecule through use of PtH(PBz₃)₂BPh₄ · $\text{1}\text{2}$CH₂Cl₂. The observed trends in ν(PtH), τ(H), ¹J(PtH) and ¹J(PtP) in a series of the hydridobenzylphosphineplatinum(II) complexes are discussed in terms of “trans- or cis-influences”, defined as the ability of a ligand to weaken the bond trans or cis to itself. The data support the view that a donor atom trans to the hydridic ligand is important in determining the strength of the PtH bond in this series. Some remarks on the distinctive characteristics of some complexes, e.g., dissociation of coordinated cycloalkanone from platinum(II) or stereochemical non-rigidity of the sym-dimethylurea ligand, are included. Tricyclohexylphosphine analogs also have been prepared for comparison.     

Two trans‐4‐aminoazoxybenzenes

Two isomeric trans‐4‐amino­azoxy­benzenes, trans‐1‐(4‐amino­phenyl)‐2‐phenyl­diazene 2‐oxide (α, C₁₂H₁₁N₃O) and trans‐2‐(4‐amino­phenyl)‐1‐phenyl­diazene 2‐oxide (β, C₁₂H₁₁N₃O), have been characterized by X‐ray diffraction. The α isomer is almost planar, having torsion angles along the C_aryl—N bonds of only 4.9 (2) and 8.0 (2)°. The relatively short C_aryl—N bond to the non‐oxidized site of the azoxy group [1.401 (2) Å], together with the significant quinoid deformation of the respective phenyl ring, is evidence of conjugation between the aromatic sextet and the π‐electron system of the azoxy group. The geometry of the β isomer is different. The non‐substituted phenyl ring is twisted with respect to the NNO plane by ca 50°, whereas the substituted ring is almost coplanar with the NNO plane. The non‐oxidized N atom in the β isomer has increased sp³ character, which leads to a decrease in the N—N—C bond angle to 116.8 (2)°, in contrast with 120.9 (1)° for the α isomer. The deformation of the C—C—C angles (1–2°) in the phenyl rings at the substitution positions is evidence of the different character of the oxidized and non‐oxidized N atoms of the azoxy group. In the crystal structures, mol­ecules of both isomers are arranged in chains connected by weak N—H?O (α and β) and N—H?N (β) hydrogen bonds.     

Polymorphism and solvolysis of 2‐cyano‐3‐[4‐(N,N‐diethyl­amino)­phenyl]­prop‐2‐ene­thio­amide

Two new polymorph forms, (Ia) and (Ib), of the title compound, C₁₄H₁₇N₃S, and its solvate with aceto­nitrile, C₁₄H₁₇N₃S·0.25C₂H₃N, (Ic), have been investigated. Crystals of the two polymorphs were grown from different solvents, viz. ethanol and N,N‐di­methyl­form­amide, respectively. The polymorphs have different orientations of the thio­amide group relative to the CN substituent, with s‐cis and s‐trans geometry of the C=C—C=S diene fragment, respectively. Compound (Ic) contains two independent mol­ecules, A and B, with s‐cis geometry, and the solvate mol­ecule lies on a twofold axis. The core of each mol­ecule is slightly non‐planar; the dihedral angles between the conjugated C=C—CN linkage and the phenyl ring, and between this linkage and the thio­amide group are 13.4 (2) and 12.0 (2)° in (Ia), 14.0 (2) and 18.2 (2)° in (Ib), 2.3 (3) and 12.7 (4)° in molecule A of (Ic), and 23.2 (3) and 8.1 (4)° in molecule B of (Ic). As a result of strong conjugation between donor and acceptor parts, the substituted phenyl rings have noticeable quinoid character. In (Ib), there exists a very strong intramolecular steric interaction (H⋯H = 1.95 Å) between the bridging and thio­amide parts of the mol­ecule, which makes such a form less stable. In the crystal structure of (Ia), intermolecular N—H⋯N and N—H⋯S hydrogen bonds link mol­ecules into infinite tapes along the [10] direction. In (Ib), such intermolecular hydrogen bonds link mol­ecules into infinite (101) planes. In (Ic), intermolecular N—H⋯N hydrogen bonds link mol­ecules A and B into dimers, which are connected via N—H⋯S hydrogen bonds and form infinite chains along the c direction.     

Alkyl,hydrido and related compounds of ruthenium with trimethylphosphine and bis(1,2-dimethylphosphino)ethane. X-ray crystal structures of cis-hydridoethyltetrakis(trimethylphosphine)-ruthenium(II) and ethylene tetrakis-(trimethylphosphine)ruthenium(0)

The interaction of trans-RuCl₂(PMe₃)₄ with R₂Mg, depending on the reaction conditions and the alkyl groups gives either (C₂H₄)Ru(PMe₃)₄ or cis-Ru(H)(C₂H₅)(PMe₃)₄ for R = ethyl, and cis-Ru(H)(ⁿC₃H₇(PMe₃)₄ for R = n-propyl. The interaction of Et₂Mg with trans-RuX₂(dmpe)₂ (X = Cl, CO₂Me) gives either cis-Ru(Et₂)dmpe)₂ for X = Cl or trans-Ru(Et)₂(dmpe)₂ for X = CO₂Me. NMR data for (C₂H₄)Ru(PMe₃)₄ suggest that ethylene is bound in the η² or metallocyclopropane form, which is confirmed by a single-crystal X-ray diffraction study. This shows a relatively long carbon-carbon bond distance of 1.44(1)Å between the “ethylene” carbons. The structure of cis-Ru(H)(C₂H₅)(PMe₃)₄ has also been confirmed by a single-crystal X-ray diffraction study. Possible mechanisms for the observed reactivities are considered.     

Asymmetric oxidation catalyzed by myoglobin mutants

The sperm whale myoglobin active site mutants (L29H/H64L and F43H/H64L Mb) have been shown to catalyze the asymmetric oxidation of sulfides and olefins. Thioanisole, ethyl phenyl sulfide, and cis-β-methylstyrene are oxidized by L29H/H64L Mb with more than 95% enantiomeric excess (% ee). On the other hand, the F43H/H64L mutant transforms trans-β-methylstyrene into the trans-epoxide with 96% ee. The dominant sulfoxide product in the incubation of alkyl phenyl thioethers is the R isomer; however, the mutants afford dominantly the S isomer of aromatic bicyclic sulfoxides. The results help us to rationalize the difference in the preferred stereochemistry of the Mb mutant-catalyzed reactions. Furthermore, the Mb mutants exhibit an improvement in the oxidation rate up to 300-fold with respect to wild type.     

Theoretical study on coordination of methanol clusters to 3-methyl-4-pyrimidone

Density functional theory (DFT), MP2, and couple cluster ab initio methods were employed to investigate the microsolvation of 3-methyl-4-pyrimidone (3M4P) surrounded by methanol (MeOH) molecules. Structures are analyzed based on hydrogen bonds with a focus on relative energies, interaction energies, hydrogen bond cooperativity, hydrogen bonding geometries, and redshifts in the frequencies of O–H and C=O stretching modes. Our results show that there is no preferential orientation of MeOH attacks on the carbonyle site of 3M4P; both trans and cis 3M4P-MeOH complexes have same chance to be observed. cis 3M4P-MeOH and 3M4P-MeOH complex in which MeOH is located on N lie 0.56 and 3.11 kJ/mol at CCSD(T)/6-31+G(d,p) (0.63 and 1.67 kJ/mol at MP2/6-311++G(d,p)) above trans 3M4P-MeOH. MeOH dimers form more stable 3M4P-(MeOH)₂ complexes compare to 3M4P-(MeOH)₂ complexes in which individual MeOH molecules bind to carbonyl and N. Relative energies of 3M4P-(MeOH)₃ computed using various DFT methods point out the complex formed by linear MeOH trimer along methyl group of 3M4P (cis 3M4P-(MeOH)₃) as lowest. Carbonyl group is predicted as preferential site for hydrogen bond interaction. Besides O–H…O and O–H…N hydrogen bonds, 3M4P-(MeOH)₂ and 3M4P-(MeOH)₃ complexes are also stabilized by H–O…H–C weak interactions.     

Structure and packing of aminoxyl and piperidinyl acrylamide monomers

The closely related title compounds, 4‐acrylamido‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl, C₁₂H₂₁N₂O₂, (I), and N‐(2,2,6,6‐tetramethylpiperidin‐4‐yl)acrylamide monohydrate, C₁₂H₂₂N₂O·H₂O, (II), are important monomers in the preparation of redox‐active polymers. They comprise an acrylamide group of the usual s‐cis configuration appended to a 2,2,6,6‐tetramethyl‐substituted piperidine‐1‐oxyl radical or a piperidinyl chair, respectively. The adjacent amide and piperidinyl H atoms are approximately trans across the C—N bond. The packing in (I) is dominated by N—H...O hydrogen bonds; these are supported by C—H...O contacts to form an R₂¹(6) ring repeat, a motif which has been observed in other acrylamide structures. In (II), hydrogen bonds are again key to the packing arrangements. In this case, the incorporated solvent water molecule acts as an acceptor through its O atom and as a donor through both H atoms, binding three adjacent piperidinylacrylamide molecules into layers. In both structures, weak C—H...O contacts involving the piperidinyl methyl H atoms and a proximal acrylamide carbonyl O atom extend the structure in the third dimension.