Synthesis of syn-facial (Cr,Mn) benzyl complexes by the stereoselective thermolytic coupling of unsymmetric diazomethanes with cyclomanganated (η-arene)tricarbonylchromium complexes

The heat-promoted reaction of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene with cyclomanganated 2-[tricarbonyl(η⁶-phenyl)chromium]pyridine afforded, upon departure of a molecule of CO, a new stable manganese alkylidene complex in which, according to X-ray diffraction analyses, the heterocyclic ligand is anti-facial with respect to the Cr(CO)₃ moiety. Similar heat-promoted reactions of unsymmetrically substituted diazoalkanes such as (Me₃Si)(H)CN₂, (Ph)(Me)CN₂, (Ph)(t-Bu)CN₂ and (Ph)(FcCH₂CH₂)CN₂, which are precursors of more electrophilic alkylidenes, with cyclomanganated 2-[tricarbonyl(η⁶-phenyl)chromium]pyridine derivatives afforded new syn-facial heterobimetallic benzyl complexes. The stereoselectivity of these reactions depends on the steric demand of the substituents at the diazoalkane. A phenyl substituent at the diazoalkane favors the formation of syn-facial heterobimetallic benzyl complexes with the Ph group in the endo position. Combining this “phenyl directing effect” to the steric effect operated by a bulky group at the phenyldiazoalkane, like noticed with (Ph)(t-Bu)CN₂, led to total stereoselectivity. This study discloses four new X-ray structures of syn-facial Cr,Mn benzyl complexes, which all present the same short Cr-to-Mn distance of ca. 3.04 Å.     

Theoretical study of solvent and substituent effects on the structure, <Superscript>14</Superscript>N NQR and electronic spectra of [Cr(CO)<Subscript>5</Subscript>py]

The structure, ¹⁴N NQR parameters, electronic spectra, and hyperplarizability of [Cr(CO)₅py] in seven different solvents were theoretically computed with MPW1PW91 method based on Polarizable Continuum Model (PCM). The substituent effects in para- substituted Cr(CO)⁵–pyridine complexes have been evaluated. The results indicate that both polarity of solvents and the substituents have played a significant role on the structures and properties of complexes. The study also shows that the structural and solvent modification change the NLO properties.     

The crystal structures of m-trifluoromethylphenylsilatranone and p-fluorophenylsilatranone

The crystal structures of two silatranone derivatives are reported. The close N → Si approach (2.106(3) Å in m-trifluoromethylphenyl-, and 2.129(3) Å in p-fluorophenyl-silatranone) indicates strong dative acceptor bonds. For various silatrane derivatives and inverse relation has been revealed between the mean group electronegativity of the substituent R attached to silicon and the N → Si dative bond distance. In both structures there are long (1.72 Å) SiO bonds in the SiOCO moiety. The m-trifluoromethylphenyl derivative contains a disordered CF₃ group.     

Antiferromagnetic complexes involving metalmetal bonds IV. Synthesis,molecular structure and magnetic properties of the heterotrinuclear cluster, (C5H5Cr)2(μ2-SCMe3)(μ3-S)2Fe(CO)3, with direct and indirect exchange between CrIII and FeI centers

The photochemical reaction between the antiferromagnetic complex (C₅H₅-CrSCMe₃)₂S (I) (containing a CrCr bond 2.689 Å long) and Fe(CO)₅ results in the elimination of two carbonyl groups and one tert-butyl radical to give (C₅H₅Cr)₂(μ²-SCMe₃)(μ³-S)₂ · Fe(CO)₃ (III). As determined by X-ray diffraction, III contains a CrCr bond of almost the same length as in I (2.707 Å), together with one thiolate and two sulphide bridges. The latter are also linked with the Fe atom of the Fe(CO)₃ moiety (average FeS bond length 2.300 Å). Fe also forms a direct bond, 2.726 Å long, with one of the Cr atoms, whereas its distance from the other Cr atom (3.110 Å) is characteristic for non-bonded interactions. Complex III is antiferromagnetic, the exchange parameter, ?2J, values for CrCr, Cr(1)Fe and Cr(2)…Fe are 380, 2600 and 170 cm^?1, respectively. The magnetic properties of III are discussed in terms of the “exchange channel model”. The contributions from indirect interactions through bridging ligands are shown to be insignificant compared with direct exchange involving metalmetal bonds. The effects of steric factors and of the nature of the M(CO)_n fragments on the chemical transformations of (C₅H₅CrSCMe₃)₂S · M(CO)_n are discussed.     

A quantum chemistry study of ruthenabenzene complexes

The electronic structure and properties of the ruthenabenzenes and substituted ruthenabenzenes have been explored using the hybrid density functional B3LYP theory. Systematic studies on the substituent effect in para-substituted ruthenabenzenes complexes have been studied. The following substituents were taken into consideration: H, NO₂, CN, CHO, COOH, F, CH₃, OH, and NH₂. Basic measures of aromatic character were derived from the structure and nucleus-independent chemical shift (NICS). The NICS calculations indicate a correlation between NICS(1.5) and the hardness in all species. The atoms in molecule analysis indicates a correlation between r(Ru-C) bonds and the electron density of bond critical point in all species.     

Boron‐Metallated Borirenes and Bis(Borirenes)

Heating the metalloborylene complex [{(η⁵‐C₅Me₅)Fe(CO)₂}(μ‐B){Cr(CO)₅}] with alkynes and diynes leads to the formation of B‐metallated borirenes and a bis(B‐metallated borirene) through formal transfer of the metalloborylene moiety [(η⁵‐C₅Me₅)(OC)₂Fe(B:)]. By using this protocol, a range of B‐metallated borirenes with electron‐donating and electron‐withdrawing substituents are prepared, and these are studied spectroscopically, structurally, and computationally. The yellow‐orange color of the complexes is additionally explained through time‐dependent density functional theory calculations.     

The mutual influence of the imine substituents of terephthal-bis-imines concerning their reactivity towards Fe2(CO)9

The reaction of terephthal-bis-imines with Fe₂(CO)₉ proceeds via a C---H activation reaction in the ortho position with respect to one of the imine functions. The corresponding hydrogen atom is shifted towards the former imine carbon atom producing a methylene group instead. The dinuclear iron complexes formed by this reaction sequence and showing no coordination of the second imine group were isolated from reactions of bis-imines with both phenyl and cyclohexyl substituents at the imine nitrogen atoms. In addition, we observed three different reaction pathways of the second imine substituent of the starting material which is obviously thus influenced by the fact that the first one is coordinating an Fe₂(CO)₆ moiety. If the organic substituent at the imine nitrogen atoms is a phenyl group the formation of a trinuclear complex is achieved in which an additional Fe(CO)₃ group is coordinating the CN double bond and one of the carbon---carbon bonds of the central phenyl ring in an η⁴-fashion. The same reaction leads to the isolation of a tetranuclear iron---carbonyl compound in which both imine substituents were transformed via the pathway described above, each building up dinuclear subunits. In contrast to this the reaction of a bis-imine with cyclohexyl groups at the imine nitrogen and thus an enhanced nucleophilicity leads to the formation of a tetranuclear complex in which only one imine group reacts under C---H activation with subsequent hydrogen migration towards the former imine carbon atom. The second imine substituent also shows a C---H activation reaction in the ortho position with respect to the imine group but the corresponding hydrogen atom is transferred to one of the aromatic carbon atom of the central phenyl ring of the ligand. The C=N double bond remains unreacted and only coordinates the second Fe₂(CO)₆ moiety via the nitrogen lone pair.     

Correlations of 95Mo NMR chemical shifts with ligand basicity in substituted pyridine pentacarbonylmolybdenum(O) complexes

Molybdenum-95 NMR chemical shifts are reported for a series of Mo(O) compounds of the type Mo(CO)₅L (L = pyridine derivatives). A good correlation is found between the δ(⁹⁵Mo) values and the Hammett sigma constant of the pyridine substituent or the pK_a of the substituted pyridine. The chemical shift values, which range from −1366 ppm (3-CN, σ = 0.62, pK_a = 1.35) to −1433 ppm (4-NMe₂, σ = −0.83, pK_a = 9.61), directly reflect the electronic properties of the pyridine derivatives even though the substituent is four or five bonds away from the molybdenum atom.     

A quantum chemical study of Cr(CO)3(B3N3H6 ? n F n ) (n = 1–3) complexes

The electronic structure and properties of Cr(CO)₃(B₃N₃H_{6 ? n} F _n ) (n = 1?C3) complexes have been explored using hybrid density functional B3LYP theory. Calculations indicate B-fluorinated isomers are more stable, and less polarizable, than N-fluorinated isomers. The aromatic natures of the borazine rings have been analyzed by nucleus independent chemical shift (NICS). The atoms in molecules (AIM) analysis indicates that Cr-C and Cr-N bonds distance is well correlated with the electron density of critical point (??_cp) in all species.     

Antiferromagnetic complexes involving metal---metal bonds IV. Synthesis, molecular structure and magnetic properties of the heterotrinuclear cluster, (C5H5Cr)2(μ-SCMe3)(μ-S)2Fe(CO)3, with direct and indirect exchange between Cr and Fe centers

The photochemical reaction between the antiferromagnetic complex (C₅H₅-CrSCMe₃)₂S (I) (containing a Cr---Cr bond 2.689 Å long) and Fe(CO)₅ results in the elimination of two carbonyl groups and one tert-butyl radical to give (C₅H₅Cr)₂(μ²-SCMe₃)(μ³-S)₂ · Fe(CO)₃ (III). As determined by X-ray diffraction, III contains a Cr---Cr bond of almost the same length as in I (2.707 Å), together with one thiolate and two sulphide bridges. The latter are also linked with the Fe atom of the Fe(CO)₃ moiety (average Fe---S bond length 2.300 Å). Fe also forms a direct bond, 2.726 Å long, with one of the Cr atoms, whereas its distance from the other Cr atom (3.110 Å) is characteristic for non-bonded interactions. Complex III is antiferromagnetic, the exchange parameter, −2J, values for Cr---Cr, Cr(1)---Fe and Cr(2)…Fe are 380, 2600 and 170 cm⁻¹, respectively. The magnetic properties of III are discussed in terms of the “exchange channel model”. The contributions from indirect interactions through bridging ligands are shown to be insignificant compared with direct exchange involving metal---metal bonds. The effects of steric factors and of the nature of the M(CO)_n fragments on the chemical transformations of (C₅H₅CrSCMe₃)₂S · M(CO)_n are discussed.     

13C and 19F NMR substituent chemical shifts (SCS) of some bridgehead-substituted phenyl- and fluorophenylbicyclo [2.2.2] octyltricarbonylchromium(O) derivatives: nature of aryl 19F NMR polar field effects in the Cr(CO)3-complexed benzene ring system

A number of Cr(CO)₃ complexes of bridgehead-substituted phenylbicyclo[2.2.2]octanes and (m- and p-)fluoropheylbicyclo[2.2.2]octanes have been synthesized and their ¹³C and ¹⁹F NMR spectra have been recorded, respectively. The substituent chemical shifts (SCS) of these stereochemically well-defined model systems permit an unambiguous evaluation of polar factors governing ¹³C and ¹⁹F SCS in arene-Cr(CO)₃ complexes. The dual nature of ¹⁹F NMR polar field effects is reaffirmed and the coefficient (A) of the Buckingham equation for linear electric field effects on C(sp²)F bonds in fluoroarene-Cr(CO)₃ complexes has been calculated. A re-examination and re-interpretation of the ¹⁹F chemical shifts of m- and p-substituted fluorophenyltricarbonylchromium derivatives is also reported. New substituent parameters (σ_I and σ^o_R) for C₆H₅ · Cr(CO)₃ as a substituent in the neutral ground state arepresented.     

Modeling of the structure and IR spectra of boron difluoride acetylacetonate and its halogen-substituted derivatives

The infrared spectra of the complexes of boron difluoride acetylacetonate and its halogen-substituted derivatives F₂B(aaX) (X = H, Cl, Br, I) in the crystalline state are studied. The substituent effect on the geometry and force field of molecules is revealed from DFT/B3LYP quantum chemical calculations with the 6-311G(d,p) basis set. The detailed assignment of IR absorption bands is performed based on the calculations of normal modes (NMs) and the potential energy distribution (PED). The bands most sensitive to the substituent nature belong to vibrations with prevalent involvement of ring CC and CO bonds and some low-frequency noncharacteristic NMs involving the Х atom. In support of the single crystal XRD data, intermolecular interactions have the strongest effect on the characteristic bands of the BF₂ moiety in the ranges 1280-1220 cm^–1 and 875-835 cm^–1; the sequences of IR band frequency shifts in a series of substituents corresponding to these interactions are reported.     

Studies in negative ion mass spectrometry: XIV—Electron attachment reactions of a series of η6-arenetricarbonylchromium(O) complexes

Electron attachment reactions of a series of (η⁶-arene)tricarbonylchromium(O) complexes have been examined in the gas phase. The electron capture process has been shown to be influenced by the structure of the η⁶-arene ligand and its substituents. Whereas (η⁶-benzene)- and (η⁶-mesitylene)tricarbonylchromium(O) undergo dissocative electron capture, or reductive decarbonylation, yielding [M? CO]^?˙ ions of highest abundance in their negative ion mass spectra, [η⁶-(2,2-dimethylindan-1,3-dione)]tricarbonylchromium(O) forms a molecular negative ion which undergoes sequential CO eliminations and finally a demetallation to give the arene radical ion. A localization of charge on the coordinated arene ligand is proposed for the formation of [M]^?˙ in this case. (η⁶-Methylbenzoate)tricarbonylchromium(O) also forms a molecular negative ion by secondary electron attachment which decomposes by simultaneous and consecutive eliminations of up to four CO molecules. The elucidation of a mechanism and sequence for these CO eliminations has been achieved by synthesizing and examining the negative ion mass spectrum of [η⁶-(C₆H₅·¹³CO₂Me)]Cr(CO)₃. The first CO loss in the principal fragmentation pathway occurs solely from the –Cr(CO)₃ group of [M]^?˙. The effect of para substituent groups on the stabilities of molecular negative ions and their fragmentations has been ascertained using a series of para-substituted (η⁶-methylbenzoate)tricarbonylchromium(O) compounds containing the groups NH₂, OH, OCH₃, CL and COOMe. The stabilities of the [M]^?˙ ions have been rationalized in terms of the Hammett and Taft parameters σ_P, σ_I, σ_R^P, σ_P^O and σ_R^O. The overall electronic substituent effect transmitted to the carbonyl groups of the –Cr(CO)₃ unit involves both resonance and inductive components. In this series of compounds the stability of [M]^?˙ decreases as the electron withdrawing capacities of the para substituents increase.     

A dichromium(II) compound with an elongated metal-metal bond: Cr2(oxindolate)4(oxindole)2

The title compound has been prepared by reaction of (C₅H₅)₂Cr with oxindole (indole with CO in place of CH₂ at the 2-position). Red single crystals belong to space group P2₁/c with a = 10.107(4) Å, b = 22.496(7) Å, c = 9.210(3) Å, β = 93.26(3)°, V = 2091(2), and Z = 2. The centrosymmetric molecule has a CrCr distance of 2.495(4) Å. The mean CrO and CrN distances for the bonds to bridging oxindolate anions are 2.024(7) and 2.065(8) Å, respectively. There is an oxindole molecule bound at each end with a CrO axial bond of length 2.341(8) Å and a hydrogen bond from the oxindole NH group to an equatorial oxygen atom of length 2.83(1) Å. The significance of this compound with respect to CrCr bonding is discussed.     

Structure-reactivity correlations on the kinetics of substituted 2-phenylethyl m-nitrobenzenesulfonates with substituted pyridines

The rates of the substituted 2-phenylethyl m-nitrobenzenesulfonate(2-PNS) with pyridines were determined in acetonitrile. The reaction was accelerated by an electron - donating substituent on both substrate and nucleophlie. Substitutent effects 2-PNS and pyridine are correlated by Brønsted and Hammett equations, respectively. The sensitivity parameters, β and ϱ, obtained from the free-energy relationships, are inter-related and are themselves sensitive to the reactivity of the system. Thus, β varies from 0.246 for p-MeO 2-PNS to 0.284 for p-NO₂PNS, and are linearly related to the α values for 2-PNS substituents. Likewise the ϱ_z (Z is a substituent of substrate) values are linearly related to pKa of the pyridines and ϱ_y (Y is a substituent of pyridine) values are also correlated to the β values. These data show that electron-withdrawing substituents in 2-PNS increse bond formation between C and N atoms and such subsituents in the pyridines also lead to increased bond formation relatively to bond breaking in the transition state. The More O'Ferral and Swain, Thornton, and Harris approaches were applied for the prediction of substituent effects on above interpretation.     

NMR study of (C6H5)3-nPXn (X = Cl,Br, I; n = 0-3) and (C6H6)3-n PXnCr(CO)5 compounds

The ³¹P chemical shift of the (C₆H₅)_3-nPX_n ligands (X = Cl, Br, I; n = 0–3) is dominated by the electronegativity of the substituents. π bonding is only important for derivatives with three strongly electronegative substituents. The ³¹P chemical shift of the corresponding complexes (C₆H₅)_3-nPX_nCr(CO)₅ is governed by the simultaneous effects of the electronegativity, steric hindrance and π bonding. The resonance parameter, δ', indicates an increasing (p_ring → d_p)π and (d_cr→ d_p)π electron delocalization with halogen substitution.     

木质素模化物键离解能的理论研究

采用密度泛函理论B3P86方法,在6-31G(d,p)基组水平上,对木质素结构中的6种连接方式(β-O-4、α-O-4、4-O-5、β-1、α-1、5-5)的63个木质素模化物的醚键(C-O)和C-C键的键离解能E_B进行了理论计算研究。分析了不同取代基对键离解能的影响以及键长与键离解能的相关性。计算结果表明,C-O键的键离解能通常比C-C键的小,在各种醚键中C_α-O键的平均键离解能最小,为182.7 kJ/mol;其次是β-O-4连接中的C_β-O键,苯环和烷烃基上的取代基对醚键的键离解能有较强的弱化作用,C-O键的键长和键离解能的相关性较差。与C-O键相比,C-C键的键离解能受苯环上取代基的影响很小,而烷烃基上的取代基对C-C键的键离解能有较大的影响,C-C键的键离解能和键长之间存在较强的线性关系,C-C键的键长越长,其键离解能越小。     

Theoretical study on the interactions of halogen‐bonds and pnicogen‐bonds in phosphine derivatives with Br2, BrCl,and BrF

The MP2 ab initio quantum chemistry methods were utilized to study the halogen‐bond and pnicogen‐bond system formed between PH₂X (X = Br, CH₃, OH, CN, NO₂, CF₃) and BrY (Y = Br, Cl, F). Calculated results show that all substituent can form halogen‐bond complexes while part substituent can form pnicogen‐bond complexes. Traditional, chlorine‐shared and ion‐pair halogen‐bonds complexes have been found with the different substituent X and Y. The halogen‐bonds are stronger than the related pnicogen‐bonds. For halogen‐bonds, strongly electronegative substituents which are connected to the Lewis acid can strengthen the bonds and significantly influenced the structures and properties of the compounds. In contrast, the substituents which connected to the Lewis bases can produce opposite effects. The interaction energies of halogen‐bonds are 2.56 to 32.06 kcal·mol^?1; The strongest halogen‐bond was found in the complex of PH₂OH???BrF. The interaction energies of pnicogen‐bonds are in the range 1.20 to 2.28 kcal·mol^?1; the strongest pnicogen‐bond was found in PH₂Br???Br₂ complex. The charge transfer of lp(P) ? σ*(Br? Y), lp(F) ? σ*(Br? P), and lp(Br) ? σ*(X? P) play important roles in the formation of the halogen‐bonds and pnicogen‐bonds, which lead to polarization of the monomers. The polarization caused by the halogen‐bond is more obvious than that by the pnicogen‐bond, resulting in that some halogen‐bonds having little covalent character. The symmetry adapted perturbation theory (SAPT) energy decomposition analysis showes that the halogen‐bond and pnicogen‐bond interactions are predominantly electrostatic and dispersion, respectively.     

Synthesis of tetrahydropyrido[2,3-b]pyrazine scaffolds from 2,3,5,6-tetrafluoropyridine derivatives

Reactions between N,N′-dimethylethylene diamine and a range of 2,3,5,6-tetrafluoropyridine derivatives provided ready access to the corresponding tetrahydropyrido[2,3-b]pyrazine systems if the substituent located at the 4-position of the pyridine ring was either hydrogen or an electron withdrawing substituent. In contrast, the presence of electron donating substituents at the 4-position made the formation of ring-fused products much more difficult. The two-step sequential nucleophilic substitution procedures from pentafluoropyridine gave convenient and adaptable methodology for the synthesis of polyfunctional tetrahydropyrido[2,3-b]pyrazine scaffolds of interest to the life science discovery arenas.     

Pentacarbonyl(4‐phenylpyridine)­tungsten(0) and pentacarbonyl(2‐phenylpyridine)chromium(0)

In penta­carbonyl(4‐phenyl­pyridine)­tungsten(0), [W­(C₁₁H₉N)(CO)₅], the mol­ecules have mm site symmetry and the pyridine ligand, with m symmetry, is completely planar. In penta­carbonyl(2‐phenyl­pyridine)­chromium(0), [Cr(C₁₁­H₉N)(CO)₅], the mol­ecules are in general positions and the phenyl and pyridine rings of the ligand are twisted by 67.7 (3)° with respect to one another by rotation about the C—C bond joining them. In both compounds, the axial M—C_carbonyl bond trans to the M—N_ligand bond is significantly shorter than the equatorial M—C_carbonyl bonds.