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.     

19F nuclear magnetic resonance spectra of some trisubstituted metal trifluorophosphine complexes. Examples of [AX3]3 nuclear spin systems

The ¹⁹F NMR spectra of π-allyl-tris(trifluorophosphine)rhodium(I), [A], benzene-tris(trifluorophosphine)chromium(0), [B], and nitrosyl-tris(trifluorophosphine) rhodium(-I), [C], are presented. These are examples of [AX₃]₃ nuclear spin systems (A = phosphorus, X = fluorine). The spectra of [A] and [B] have been completely analysed to afford values of ¹J(PF), ²J(PP′), ³J(PF′) and ⁴J(FF′).     

13C-NMR relaxation studies of alkali metal cryptate complexes

The ¹³C spin-lattice relaxation times (T₁'s) of cryptands [2.1.1], [2.2.1] and [2.2.2] as well as those of the corresponding cryptate complexes with Li⁺, Na⁺, and K⁺ in CDCl₃ and CH₃OH:D₂O (90:10) were measured and the results are interpreted in terms of molecular compression and desolvation effects.     

13C13C spin spin coupling constants in azulenes

[4-¹³C]- Azulene and [4-¹³C]-4-methylazulene have been synthesized. The ¹³C¹³C spin coupling constants have been measured and interpreted in terms of πMO theory.     

13C NMR spectrum of coumarin

Summary The positions of the signals from the C₃, C₅, C₆, and C₇ carbon atoms in the¹³C NMR spectrum of coumarin have been established with the aid of information obtained from the¹³C NMR spectra of [3-D]-, [4-D]-, and 7-methoxycoumarins and by the use of an additive calculation based on the increments of the methoxy group in the¹³C NMR spectrum of anisole.M. V. Lomonosov Moscow State University Scientific-Research Institute of Pharmacology, Academy of Medical Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 458–462, July–August, 1975.     

Oxidative addition reactions of [Pt(CN)4]2−; A 13C and 195Pt NMR study

¹³C and ¹⁹⁵Pt NMR measurements show that complexes of the type trans-[Pt(CN)₄X₂]^2? are formed on addition of X₂ (X = Br, Cl, I) to M₂[Pt(CN)₄] (M = K or NBu₄) in aqueous and chloroform solution respectively. Addition of ICN to K₂[Pt(CN)₄] (60% ¹³CN^?) in aqueous solution results in the formation of potassium pentacyanoiodoplatinate(IV) with complete¹³CN^?/¹²CN^?scrambling. The reaction of equi-molar amounts of trans-[PtX₂(CN)₄]^2? (X = Br and Cl), which was previously claimed to result in complete transformation into trans-[PtBrCl(CN)₄]^2?, is instead shown to result in an approximately statistical redistribution of halogens. A progressive shift of δ_Pt to high field is observed on successive replacement of ¹²CN^? by ¹³CN^? in [Pt(CN)₄]^2?.     

Trends in 19F-19F and 29Si-19F coupling constants in organosilicon derivatives containing SiF2 and Si2F4 units

Consideration of ¹⁹F-¹⁹F and ²⁹Si-¹⁹F coupling constants in a series of organosilicon derivatives containing SiF₂ and Si₂F₄ units reveals a number of trends which are useful for structural and stereochemical assignments. For example the vicinal ¹⁹F-¹⁹F coupling constants in a number of CSiF₂SiF₂C- derivatives (including straight chain compounds, disilacyclobutanes and disilacyclohexanes) show an apparent linear dependence on dihedral angle, varying in magnitude from near zero for small values of φ up to ca. 19 Hz for φ ～ 180°. This is particularly useful for stereochemical assignments [1,2]. In addition ²⁹Si-¹⁹F coupling constants appear to fall in quite distinct ranges (¹J_SiF > 300 Hz, 29 Hz < ²J_SiF < 55 Hz, ³J_SiF < 10 Hz). This is quite useful for structural assignments [1,6]. Reaction of SiF₂ with 1,3-cyclohexadiene gives two new silicon fluorine compounds: a disilabicyclo[2,2,2]octene and an HSi₂F₅-substituted cyclohexadiene.     

1H and 13C NRM and infrared spectral studies on mixed ligand complexes of the type cis-[Co(en)2(Im)Cl]Cl2

A number of mixed ligand complexes of the type [Co(en)₂(Im)Cl]Cl₂ (Im = imidazole or a substituted imidazole) have been synthesized by reaction of trans-[Co(en₂Cl₂]Cl with the imidazole ligands. Electrical conductivity measurements support the ionic (1:2) formulation of the compounds, the electronic spectra is in agreement with an octahedral stereochemistry, and the IR and NMR (¹H and ¹³C) spectra strongly favour the cis configuration for the isolated complexes, [Co(en)₂(Im)Cl]Cl₂.Trans-[Co(en)₂Cl₂]Cl reacts with KNCS to form cis-[Co(en)₂(NCS)₂Cl, the crystal structure of which is briefly reported. This lends additional support in favour of the probable cis configuration of the above complexes.     

29Si and 13C NMR spectra of chloro- and fluoro-substituted linear permethylpolysilanes

²⁹Si and ¹³C NMR spectra are reported for the three halopolysilane series Me(SiMe₂)_nCl, Cl(SiMe₂)_nCl and F(SiMe₂)_nF, where n = 2 to 6. Except for the dihalodisilanes (XSiMe₂)₂, data for all of the compounds fit linear relationships based on substituent constants for chlorine or fluorine atoms in the α, β and γ positions. The effects of halogen substitution on ²⁹Si and ¹³C chemical shifts are rapidly attenuated along the polysilane chain, becoming negligible four atoms away from the halogen. The NMR data provide no evidence for long-range electronic transmission from chlorine or fluorine in halopermethylpolysilanes of the type suggested by other workers [1].     

Complexation of [2.2]paracyclophane with an (η5-cyclopentadienyl)iron+ moity: mono- and di-cations

The reaction of [2.2]paracyclophane with ferrocene in the presence of AlCl₃ and Al/powder gives the new compounds [1-6-η-[2.2]paracyclophane- (η⁵-cyclopentadienyl)iron]⁺[PF₆] and [1-6-η; 9-14-η-[2.2]paracyclophane- [(η⁵-cyclopentadienyl)iron]₂]²⁺[PF₆]₂ in high yields. The species have been characterized by elemental analysis, and by ¹H and ¹³C NMR spectroscopy.     

Application des spectrographies RMN 13C et 1H a l'etude de derives cycliques du silicium et germanium,interactions pπdπ

The properties of 1-sila- and 1-gemma-cyclopent-2-(or -3-)enes with various substituents have been investigated by ¹³C and ¹H NMR spectroscopies. Values of chemical shifts and coupling constants in olefinic cyclic systems and in aromatic or ethylenic substituents attached to the hereto atom suggest the presence of a mesomeric p_πd_π interaction, particularly for the silicon atom. Studies at low temperatures given conformational data, which have been compared with data from the literature.     

NMR (1H, 13C, 29Si) study of some allylhalogenosilanes

¹H, ¹³C and ²⁹Si NMR spectra of the allylchlorosilanes (CH₂CH-CH₂-)_xSiCl_4?x and of triallylbromosilane have been analysed. Results are discussed in terms of inductive and steric effects and of contributions of diamagnetic anisotropy. There is no conclusive evidence for (p-d)π conjugation.     

The conformational dependence of 15n13c spin spin coupling constants

2-Azabicyclo(2.2.2)octan-3-One 1, N-isopropylpivaloylamide 2 and 4-azatricyclo(4.3.1.1^3,8)undecan-5-one 3 have been prepared with a ¹⁵N label. The amides were reduced to the corresponding amines 2-azabicy-clo(2.2.2)octane 4, N-isopropyl-N-neopentylamine 5 and 4-azatricyclo(4.3.1.1^3,8)undecane 6. The ¹³C spectra of these compounds and their hydrochlorides were measured and the ¹⁵N¹³C spin coupling constants interpreted in terms of their conformational dependence.     

19F substituent chemical shifts (SCS) of 4-substituted bicyclo[2.2.2]oct-1-yl flourides

The results of a linear multiple regression analysis indicate that the ¹⁹F SCS of 4-substituted bicyclo[2.2.2]oct-1-yl fluorides are essentially a manifestation of electric field and electronegativity effects.     

NMR isotope shifts in the 2-methyl-2-bicyclo[2.1.1]hexyl cation and related systems

NMR isotope shifts at ¹³C nuclei due to deuteriation in the 2-methyl-2-bicyclo[2.1.1]hexyl cation are reported. Comparisons are made to the 2-methyl-2-bicyclo[2.2.1]heptyl and 2-methyl-2-bicyclo[2.2.2]octyl cations, and also to neutral molecules containing the bicyclo[2.1.1]hexyl framework. The combination of isotope effects with temperature dependence of ¹³C chemical shifts allows predictions of the shapes of the energy surfaces along the bending coordinate corresponding to bridging in these cations.     

The solid state 13C-NMR and 19F-NMR spectra of some graphite fluorides

The solid state ¹³C nuclear magnetic resonance spectra of fluorinated graphites show two resonances, one of which is assigned to aromatic carbon and the other to aliphatic carbon. The resonances are very broad with the high-field resonance centered at about 35 ppm below tetramethylsilane (TMS) and a low-field resonance centered at about 160 ppm below tetramethylsilane. The high-field resonance is typical of an sp³-like carbon and the low-field resonance is assigned to sp²-like carbons. It is found that the aromatic resonance in graphite decreases with an increase in fluorination of the graphite fluorides examined in this study. The ¹⁹F nuclear magnetic resonance spectra of C₄F and CF₁ each show one resonance. The fluorine resonance in C₄F is 180 ppm above CFCI₃ whereas the fluorine resonance in CF₁ is 55 ppm above CFCI₃. These peaks are in the range for fluorine bonded to aromatic and aliphatic carbons, respectively.     

Metalloidalmethyl substituent effects by 13C and 19F NMR : electron release in the neutral ground state.

¹³C and ¹⁹F chemical shift studies of a series of CH₂M(CH₃)₃ and CH₂M(C₆H₅)₃ (M  Si, Ge, Sn, Pb) - substituted aryl derivatives (phenyl; 1-naphthyl; 2-naphthyl) have established unambiguously that the order of hyperconjugative electron release in the neutral ground state is Pb>Sn>Ge>Si. This order is clearly at variance with the commonly accepted order(Pb>Sn>Ge>Si) based on studies of electron deficient substrates. The phenomenon is discussed in terms of current theories on σ-π interactions. In addition, substituent parameters (σ_I and σ_R^o) for the PB(CH₃)₃ group have been derived utilizing new data from the fluorophenyl tag. These new constants are compared with those previously reported.     

57Fe NMR Chemical shifts and 57fe, 13C coupling constants in α-ferrocenyl carbocations. Direct metal participation in the stabilization of metallocenyl carbocations

The ¹³C{⁵⁷Fe} double resonance method has been used to investigate ⁵⁷Fe-enriched samples of ferrocene derivatives, α-ferrocenyl carbocations and carbonyl complexes with various σ- and π-hydrocarbon ligands. In the α-ferrocenyl carbocations the ⁵⁷Fe resonances span a 1200 ppm range, being a sensitive tool of direct iron participation in the stabilization. The ⁵⁷Fe resonances in the carbocations [FcCH₂][HSO₄] (I), [FcCHMe][HSO₄] (II), [FcCHPh][HSO₄] (III), [FcCHC₅H₄ Mn(CO)₃][CF₃CO₂] (IV), [(Fc)₂CH][BF₄] (V), [FcCHC₅H₄RuC₅Hs][BF₄] (VI) and [FcCMe₂][HSO₄] (VII), ?523.6, ?219.3, 221.0, 368.7, 699.0, 405.0 and 288.5 ppm, respectively, relative to ferrocene, are interpreted in terms of rehybridization of the iron non-bonding d orbitals (shielding effect and the electron withdrawing effect of the substituent in the cyclic ligand (deshielding effect). The role of rehybridization of non-bonding iron orbitals in the low-frequency shift of the ⁵⁷Fe resonances, in addition to that in the previously investigated complex [(C₅H₅)₂FeH][BF₃OH] (?1109.3 ppm), has been demonstrated for bridge-substituted [3]ferrocenophanes, whose ring tilting induces a low-frequency shift of up to 340 ppm relative to their unbridged analogues.The ¹³C NMR spectra of carbocations V and VI reveal a temperature dependence due to the rotation around the C(1)C_α exocyclic bonds. In carbocation VI the ruthenium atom effectively competes with the iron atom to bond with C_α whereas in carbocation V two equivalent metal atoms possess the same ability for such bonding; as a result, complex V has a more pronounced “carbenium ion” nature than IV and VI, as indicated by the relative positions of the ¹³C_α resonances in carbocations IV, V and VI: δ 122.4, 147.2 and 116.9 ppm, respectively.The values of ⁵⁷Fe, ¹³C coupling constants for α-ferrocenyl carbocations exclude Fe-C_α σ-bonding and support a structure in which the iron atom is π-bonded with six carbon atoms of a fulvenoid ligand. According to the data on ⁵⁷Fe resonances and ⁵⁷Fe, ¹³C coupling constants in α-ferrocenyl carbocations the strength of FeC_α bonding is markedly influenced by the electronic effect of the substituent at C_α, being even lower in carbocation I than that of Fe-cyclopentadienyl carbon atoms.     

Coordination de la phosphine organo-fer [CpFeIIC6Me5CH2PPh2]+ au RhI et proprietes spectroscopiques,electrochimiques et catalytiques des complexes heterobinucleaires FeII-RhI

The reactions between the phosphine-organoiron [CpFe^II-η⁶-C₆Me₅CH₂PPh₂]⁺ PF₆^? (1) and [RhCl(η⁴-diolefin)(μ-Cl)]₂ in CH₂Cl₂ at reflux give the new heterobinuclear air-stable crystalline complexes [CpFe^II-η⁶-C₆Me₅CH₂)P(Ph)₂Rh(η⁴-diene)Cl]PF₆,(D'*-diene=cyclooctadiene (COD): 65%, 2; trimethylfluorobenzobicyclo[2.2.2]octadiene (Me₃TFB): 48%, 3). Complexes 2 and 3 have been studied by ¹H, ¹³C and ³¹P NMR spectroscopy and they are carbonylated (CO, 1 atm). Cyclic voltammetry experiments with addition of MeOH show electron transfer Fe^IRh^I → Fe^IIRh⁰, the presence of a catalytic wave Fe^I/Fe^II and the possible formation of Rh hydrides. Under normal conditions 2 is a catalyst for hydrogenation of cyclohexene, but it is less efficient than the known mononuclear Rh¹ analogues.     

13C nuclear magnetic resonance spectra of aflatoxin B1 derived from acetate

The labeling distribution of the fungal metabolite, aflatoxin B₁, produced from [1- or 2- ¹³C] acetate was determined by ¹³C FT NMR. The results support the polyketide hypothesis for aflatoxin biogenesis.