2D HETCOR Research Articles

Kraft Lignin Periodate Oxidation for Biobased Wood Panel Resins

The development of biobased resins with high-bonding performance has gained considerable attention in the wood industry. In this study, we developed biobased novolacs phenol-formaldehyde (BNPF) resins by partially replacing petroleum-based phenol and formaldehyde with lignin derived from kraft biorefinery and modified kraft biorefinery-derived lignin, respectively. We first performed a mild and efficient chemical modification of the lignin through the periodate oxidation process. Sodium periodate was used to oxidize the hydroxyl functional groups present in the interunit linkages (β-O-4 bond) in the lignin structure and convert lignin partly to quinones. This was assessed by Fourier-transform infrared spectroscopy, elemental analysis, solid-state 1H–13C 2D HETCOR NMR, and aldehyde content analysis. We synthesized a series of BNPF resins by replacing phenol with lignin, then by replacing formaldehyde with oxidized lignin, and finally by replacing both phenol and formaldehyde with lignin and oxidized lignin. The structural characterization results of the NPF resins revealed the formation of methylene linkages in the phenolic rings. Before application as wood adhesives, we studied the curing behavior of the formulated adhesive via differential scanning calorimetry. The adhesion strength of the adhesive was determined using the tensile shear strength analysis. The bonding performance tests indicated that BNPF resin adhesives have high adhesion strengths (>0.7 MPa). The outcome of this research provides a promising perspective to utilize natural polymers such as lignin for the synthesis of biobased wood adhesives.

NMR investigation of proton transport in polybenzimidazole/polyphosphoric acid membranes prepared via novel synthesis route

Here we present a molecular-level view of the structural changes in polybenzimidazole (PBI) membranes doped with phosphoric acid (PA) generated by a novel membrane fabrication technique. The modified PA doped membranes displayed unprecedented ionic conductivity at elevated temperatures, comparable to the starting PBI gel membranes prepared by the commonly used PPA process, while also exhibiting enhanced mechanical properties. To elucidate the cause of these effects, we used multi-nuclear (1H, 13C, 31P) 1D PFG, MAS and CPMAS, and 2D HETCOR magnetic resonance (NMR) techniques to characterize the structure and dynamics of the modified film and the original gel PBI membranes. 1H diffusivity measurements show significantly enhanced proton diffusivity, both in magnitude and in lower activation energy, which were consistent with its high ionic conductivity despite the lower PA content compared to the original gel membrane. CPMAS experiments further substantiated that the location of these distinct phosphate environments as being close to the polymer network. Finally, the phosphate groups in the modified membrane were revealed to be strongly bounded to each other and to the PBI polymer backbone in contrast to the combination of weakly and strongly bounded groups of the original gel membrane.

2D HETCOR Solid-State NMR Spectroscopy for Multiphase Materials with Mobility Contrast

2D HETCOR Solid-State NMR Spectroscopy for Multiphase Materials with Mobility Contrast

Facile synthesis of 5-Isopropyl-2,3-dimethylbenzene-1,4-diol by Friedel-Crafts and Determination of Partition Coefficient in n- Octanol/Water

The wide therapeutic effect of quinone-based drugs has received considerable interest for a long time. In this research, Friedel-Crafts performed a facile synthesis of quinone derivatives using the mixture of Brønsted acid. Reflux of 2,3-dimethylhydroquinone (1), isopropanol, glacial acetic acid, and H2SO4 for 15 minutes gave yellow oil product of 5-isopropyl-2,3-dimethylbenzene-1,4-diol (2) as a major product. Characterization using Nuclear Magnetic Resonance (NMR) revealed the methine proton splitting for isopropyl at δ 3.13 ppm, which has a cross-coupling with aromatic carbon at δ 119.6 ppm suggested the substitution of a proton on quinone ring with isopropyl group. Analysis Fourier Transform Infra-Red (FT-IR) showed the broad spectrum of –OH, the vibration of CH sp3, and isopropyl groups. The minor products identified as 5-isopropyl-2,3-dimethylcyclohexa-2,5-diene-1,4-dione (3), 5-isopropyl-2,3-dimethyl-1,4 phenylene diacetate (4), and 2,3-dimethylbenzene-5,6-isopropyl-1,4-diol (5) confirmed from 2D HETCOR and MS analysis. The partition coefficient (log P) of compound 2 showed a higher solubility by 1.9-fold compared to hydroquinone 1. It is suggested that an additional methyl group increased the partition into the organic phase.

Accelerating the acquisition of high-resolution quadrupolar MQ/ST-HETCOR 2D spectra under fast MAS via 1H detection and through-space population transfers

Recently, we established an experimental setup protocol to perform the population transfer from half-integer quadrupolar spin to 1H nuclei under fast MAS in the context of MQ-HETCOR experiments. In this article, we further develop the high-resolution 2D HETCOR methods by ST-based approaches, making use of the sensitivity advantage of STMAS over its MQMAS counterpart. In a similar manner to the previous work, which utilized CP and RINEPT for the population transfer, we also demonstrate the experimental setup protocol for PRESTO. Using {23Na}-1H and {27Al}-1H spin systems of powder samples, we compare a series of MQ/ST-HETCOR 2D spectra to discuss the pros and cons of the distinct MQ/ST-based approaches for spin 3/2 and 5/2 nuclei, respectively. We also incorporate two experimental tricks to reduce the experimental time of such long 2D experiments, the Optimized Rotor-Synchronization (ORS) and the Non-Uniform Sampling (NUS), in the context of high-resolution spectra of half-integer quadrupolar spin nuclei.

2D Solid-State HETCOR 1H-13C NMR Experiments with Variable Cross Polarization Times as a Tool for a Better Understanding of the Chemistry of Cellulose-Based Pyrochars—A Tutorial

The chemistry and nature of biochars are still far from being well understood. In the present work, solid-state 2D HETCOR 1H-13C NMR spectroscopy is introduced for an improved characterization of the aromatic network in biochars. To that end, a pyrochar obtained from the pyrolysis of cellulose at 350 °C for 1 h was used as an example. Variation of the contact time during cross polarization from 50 µs, to 200 µs and 1000 µs gave information about the protonation degree of the different C groups and their interactions. We demonstrated that carbohydrates did not survive the used pyrolysis conditions. Therefore, O-alkyl C was assigned to ethers. Phenols were not identified to a higher extent suggesting that furan and benzofuran-type units determine the O-functionality of the aromatic domains. The latter are directly connected to alkyl chains. Those features are expected to affect chemical but also physical properties of the biochar. Based on our results, we developed a new concept describing the nature of the aromatic network in the studied cellulose-based pyrochars. The latter contrasts common views about the chemical nature of biochar, possibly because pyrolysis temperatures > 350 °C are required for achieving advanced condensation of the aromatic domains.

Characterization of the fullerene derivative [60]PCBM, by high-field carbon, and two-dimensional NMR spectroscopy, coupled with DFT simulations

High-resolution (600 MHz) 1H and 13C chemical shift and 2D HETCOR NMR spectra of [60]PCBM were recorded. Resonances from every carbon atom of the ester, phenyl and cyclo-fullerenyl groups, were fully accounted. Assignments of the fullerene cyclopropa-ring, and all phenyl and ester carbons to their respective resonances were based on a HETCOR 2D NMR spectrum. Remaining fullerene assignments were made to a high level of confidence with the aid of an ωB97X hybrid HF/DFT simulation of the 13C NMR spectrum employing a triple zeta Dunning-type basis set. The best result was obtained with the range-separation parameter ω set effectively to zero. This indicates that the fraction of HF in the HF/DFT hybrid at very short range is the dominant factor in achieving good NMR results, that ωB97X with its 15.77% HF fraction at rij = 0 seems very well suited, and that allowing the HF fraction to increase with range is not particularly beneficial. The resulting spectrum had a remarkable qualitative agreement with experiment with a very low mean absolute error for fullerene carbons of 0.09 ppm, which was considerably lower than the 0.28 ppm of the more commonly used B3LYP/6-31G(d,p) method.

Evaluation of chitosan crystallinity: A high-resolution solid-state NMR spectroscopy approach

We propose a novel approach relied on high-resolution solid-state 13C NMR spectroscopy to quantify the crystallinity index of chitosans (Ch) prepared with variable average degrees of acetylation (DA¯) from 5% to 60 % and average weight molecular weight (M¯w) ranged in 0.15 × 106 g mol−1–1.2 × 106 g mol−1. The Dipolar Chemical Shift Correlation (DIPSHIFT) curve of the C(6)OH segment revealed increased mobility dynamic, which induced different distribution from trans-to-gauche conformations in relation to C(4). Indeed, 1H-13C Heteronuclear Correlation (2D HETCOR) showed that distinguished C4 chemical shifts correlates with the same aliphatic protons. The short-range ordering can be assigned to C4/C6 signals on 13C CPMAS and, for our case, the deconvolution procedure between disordered and ordered phases revealed increasing crystallinity with DA¯, as confirmed by SVD multivariate analysis. This work extended the knowledge regarding the use of 13C CPMAS technique to predict the crystallinity of chitosans without the use of amorphous standards.

Combining fast magic angle spinning dynamic nuclear polarization with indirect detection to further enhance the sensitivity of solid-state NMR spectroscopy

Dynamic nuclear polarization (DNP) and indirect detection are two commonly applied approaches for enhancing the sensitivity of solid-state NMR spectroscopy. However, their use in tandem has not yet been investigated. With the advent of low-temperature fast magic angle spinning (MAS) probes with 1.3-mm diameter rotors capable of MAS at 40 ​kHz it becomes feasible to combine these two techniques. In this study, we performed DNP-enhanced 2D indirectly detected heteronuclear correlation (idHETCOR) experiments on 13C, 15N, 113Cd and 89Y nuclei in functionalized mesoporous silica, CdS nanoparticles, and Y2O3 nanoparticles. The sensitivity of the 2D idHETCOR experiments was compared with those of DNP-enhanced directly-detected 1D cross polarization (CP) and 2D HETCOR experiments performed with a standard 3.2-mm rotor. Due to low CP polarization transfer efficiencies and large proton linewidth, the sensitivity gains achieved by indirect detection alone were lower than in conventional (non-DNP) experiments. Nevertheless, despite the smaller sample volume the 2D idHETCOR experiments showed better absolute sensitivities than 2D HETCOR experiments for nuclei with the lowest gyromagnetic ratios. For 89Y, 2D idHETCOR provided 8.2 times better sensitivity than the 1 D89Y-detected CP experiment performed with a 3.2-mm rotor.

Exploring water-soluble organic aerosols structures in urban atmosphere using advanced solid-state 13C NMR spectroscopy

Abstract Water-soluble organic matter (WSOM) in air particles has profound effects on climate and human health. At the heart of this environmental significance of WSOM lies a complex set of compounds, of which a major fraction still often remains undeciphered. Yet, not all environmental problems require delving into the molecular-level identification of WSOM constituents. Understanding the contribution of different functional groups to whole aerosol WSOM composition offers a highly important structural dataset that enables a better representation of WSOM in climate studies. For the first time, advanced solid-state 13C nuclear magnetic resonance (NMR) techniques, including nearly quantitative 13C multiple cross polarization/magic angle spinning (multiCP/MAS), multiCP/MAS with dipolar dephasing, multiCP/MAS with 13C chemical shift anisotropy filter, and two-dimensional 1H–13C heteronuclear correlation (2D HETCOR), are applied to acquire an accurate quantitative structural description of whole aerosol WSOM collected in an urban atmosphere. Two urban aerosol WSOM samples collected in two short periods of time, under different wintry weather conditions, were investigated. NMR data successfully pinpointed the variability of whole aerosol WSOM composition, allowing to suggest source-specific structural characteristics for each sample in two short periods of time. A new structural model of urban aerosol WSOM was build based on this compositional data, showing the presence of three independent classes of compounds that vary both in content and molecular diversity within short periods of time: heteroatom-rich aliphatic (either chain or branched), carbohydrate-like moieties, and highly substituted aromatic units. These findings establish advanced solid-state NMR as a promising tool for probing the chemical structures of inhomogeneous aerosol WSOM in rapidly changing atmospheric conditions, allowing to resolve discrepancies between modeled and measured aerosol WSOM.

Hyperpolarised 1H–13C Benchtop NMR Spectroscopy

Benchtop NMR spectrometers with sub-ppm spectral resolution have opened up new opportunities for performing NMR outside of the standard laboratory environment. However, the relatively weak magnetic fields of these devices (1–2 T) results in low sensitivity and significant peak overlap in 1H NMR spectra. Here, we use hyperpolarised 13C{1H} NMR to overcome these challenges. Specifically, we demonstrate the use of the signal amplification by reversible exchange (SABRE) parahydrogen-based hyperpolarisation technique to enhance the sensitivity of natural abundance 1D and 2D 13C{1H} benchtop NMR spectra. We compare two detection methods for SABRE-enhanced 13C NMR and observe an optimal 13C{1H} signal-to-noise ratio (SNR) for a refocused INEPT approach, where hyperpolarisation is transferred from 1H to 13C. In addition, we exemplify SABRE-enhanced 2D 13C benchtop NMR through the acquisition of a 2D HETCOR spectrum of 260 mM of 4-methylpyridine at natural isotopic abundance in a total experiment time of 69 min. In theory, signal averaging for over 300 days would be required to achieve a comparable SNR for a thermally polarised benchtop NMR spectrum acquired of a sample of the same concentration at natural abundance.

Investigation into the Effect of Heteroatom Content on Kerogen Structure Using Advanced 13C Solid-State Nuclear Magnetic Resonance Spectroscopy

To elucidate how different extreme heteroatom concentrations in oil shale kerogen may present and contribute to various structural features, three shale samples, containing kerogen with high oxygen content, low heteroatom content, and high sulfur content, were analyzed using advanced 13C solid-state nuclear magnetic resonance (NMR) techniques, including multiple cross-polarization/magic angle spinning (multiCP/MAS), dipolar dephasing (multiCP/DD), and 2D 1H–13C heteronuclear correlation (2D HETCOR). We found that oxygen in Estonian kukersite was present mostly in aromatic C–O structures and that nonprotonated aromatic carbons bonded to oxygen and alkyl chains led to more diverse aromatic signal distributions and structures in the kukersite organic matter than were observed in the other shales. The low-heteroatom kerogen present in Australian Glen Davis torbanite had the simplest structural pattern and the lowest aromaticity, despite having a lower atomic H/C ratio than the kerogens present in the other sh...

Structural, chemical and electrical characterization of organocyclotriphosphazene derivatives and their graphene-based composites

In the present work, new di-spiro and tetra-spiro organophosphazene compounds (DPP-Ant-1 and 2, BPP-Ant-1 and 2) were synthesized by interaction with conjugate anthracene-substituted chalcone compounds (Ant-1 and 2) with organocyclotriphosphazene compounds DPP and BPP. All the compounds were fully characterized and confirmed by elemental analysis, spectroscopic and thermal techniques such as DSC, TGA, mass, FT-IR, 1H, 13C-APT, 31P NMR and 2D HETCOR NMR. These organocyclotriphosphazes were designed and synthesized in order to investigate the changes in the conductive properties of graphene-based compounds. The graphene-based materials have a wide range of technological applications such as electronics, optics, thermal and mechanical properties. Graphene-based phosphazenes composites were prepared. The AC and DC conductivity of graphene-based phosphazene composites were measured. Dielectric measurements (dielectric constant, dielectric loss factors and conductivity) of organophosphazene compounds were measured against increasing frequency (range from 100 Hz to 20 kHz at 25 °C) at different temperature (between 298 and 348 K) using means of an impedance analyzer and then and compared with each other. Also, the activation energy profile of graphene/phosphazene composites was revealed by measuring DC conductivity of an individual composite material. The obtained graphene/phosphazene composites have been found that they have a semiconductor property according to the DC conductivity results.

Selective and sensitive fluorescent and colorimetric chemosensor for detection of CO32- anions in aqueous solution and living cells

A new colorimetric and fluorescent chemosensor for visual determination of carbonate ions was developed by the microwave assisted solvent free synthesis of 7,8-dihydroxy-3-(4-methylphenyl) coumarin (DHMC). The structural characterization of DHMC was confirmed by microanalysis and spectroscopy methods (MALDI-TOF, FT-IR, 1H NMR, 13C NMR, and 2D HETCOR). The binding behaviors of DHMC were investigated towards various anions by UV–vis and fluorescence spectroscopy. DHMC showed a selective and sensitive fluorometric and colorimetric responses towards carbonate ion over other anions. The detection limit of CO32- was found to be 1.03 µM. Moreover, the fluorescence imaging in living cells suggests that DHMC has a great potential in the biological imaging application. It has been demonstrated that DHMC can be used as a rapid and reliable sensor for the determination of carbonate anion in a variety of practical applications.

Proton detection of MAS solid-state NMR spectra of half-integer quadrupolar nuclei

Fast magic angle spinning (MAS) and proton detection has found widespread application to enhance the sensitivity of solid-state NMR experiments with spin-1/2 nuclei such as 13C, 15N and 29Si, however, this approach is not yet routinely applied to half-integer quadrupolar nuclei. Here we have investigated the feasibility of using fast MAS and proton detection to enhance the sensitivity of solid-state NMR experiments with half-integer quadrupolar nuclei. The previously described dipolar hetero-nuclear multiple quantum correlation (D-HMQC) and dipolar refocused insensitive nuclei enhanced by polarization transfer (D-RINEPT) pulse sequences were used for proton detection of half-integer quadrupolar nuclei. Quantitative comparisons of signal-to-noise ratios and the sensitivity of proton detected D-HMQC and D-RINEPT and direct detection spin echo and quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) solid-state NMR spectra, demonstrate that one dimensional proton detected experiments can provide sensitivity similar to or exceeding that obtainable with direct detection QCPMG experiments. 2D D-HMQC and D-RINEPT experiments provide less sensitivity than QCPMG experiments but proton detected 2D hetero-nuclear correlation solid-state NMR spectra of half-integer nuclei can still be acquired in about the same time as a 1D spin echo spectrum. Notably, the rarely used D-RINEPT pulse sequence is found to provide similar, or better sensitivity than D-HMQC in some cases. Proton detected D-RINEPT benefits from the short longitudinal relaxation times (T1) normally associated with half-integer quadrupolar nuclei, it can be combined with existing signal enhancement methods for quadrupolar nuclei, and t1-noise in the indirect dimension can easily be removed by pre-saturation of the 1H nuclei. The rapid acquisition of proton detected 2D HETCOR solid-state NMR spectra of a range of half-integer quadrupolar nuclei such as 17O, 27Al, 35Cl and 71Ga is demonstrated.

Design and fabrication of dioxyphenylcoumarin substituted cyclotriphosphazene compounds photodiodes

The present study introduces cyclotriphosphazene compounds substituted by dioxyphenylcoumarin as a photodiode application. Firstly, 7,8-dihydroxy-3-(3-methylphenyl)coumarin (1b) has been obtained by conventional as well as microwave assisted methods. Novel optoelectronic device characteristics for both mono and disubstituted dioxyphenylcoumarin bearing cyclotriphosphazene compounds (HCP-2 and HCP-4) have been synthesized from the reactions of cyclotriphosphazene containing dioxybiphenyl (HCP-1 and HCP-3) with compound 1b, respectively. The structures of compounds HCP 1–4 were identified by using elemental analysis, 1H, 13C-APT, 31P NMR and 2D HETCOR NMR and FT-IR spectroscopy methods. The Al/HCP-2/p-Si/Al and Al/HCP-4/-p-Si/Al photodiodes properties have been investigated from current-voltage (I−V) and capacitance-voltage (C−V) measurements. The electrical parameters of the prepared diodes such as ideality factor n and series resistance Rs were investigated in dark and at room temperature from (I−V) curve and Nord's method. As can be seen, the Al/HCP-2/p-Si/Al diode of high rectification ratio RR and with ideality factor greater than unity. The influence of light illuminations on the diode shows that the device can be used as photodiode with good efficiency. The barrier height ϕb and series resistance Rs have been calculated from the capacitance-voltage (C−V)and conductance-voltage (G−V) measurements under various applied frequencies from 10kHz to 1MHz. the high difference in the results of barrier height obtained from I-V and C-V calculations confirm the influence of series resistance and localized states on transport of charge carriers and the photodiode performance.

Application of 1H and 27Al magic angle spinning solid state NMR at 60 kHz for studies of Au and Au-Ni catalysts supported on boehmite/alumina

In this work for the first time we show the power of solid state NMR spectroscopy in structural analysis of alumina and catalysts supported on the alumina surface employing very fast (60kHz) magic angle spinning (MAS) technique. In the methodological part we demonstrate that under such MAS condition, cross-polarization (CP) from proton to aluminum is an efficient process when a very weak 27Al RF field is applied. The mechanism of CP transfer and the Hartmann-Hahn (H-H) matching conditions were tested for 27Al RF fields equal to 3.3 and 8.3kHz. It has been found that double quantum (DQ) CP/MAS is the best choice for H-H set with RF =3.3kHz. It has been also proved that the quality of 1H-27Al CP/MAS spectra strongly depends on 27Al carrier offset. Applied to γ-alumina, this method revealed that 1H-27Al CP/MAS at 60kHz is extremely useful for mapping the distribution of hydroxyl groups on the surface. Indeed, the AlV sites, which are not easily detected with Single Pulse Experiment (SPE), are clearly seen when 1H-27Al CP/MAS is applied. Utilizing 2D 1H-27Al CP/MAS HETCOR experiment it was possible to assign the proton positions and to correlate them with aluminum centers. Studies of mono- (Au) and bi- (Au-Ni) metallic catalysts supported on boehmite/alumina carrier employing 1D and 2D HETCOR experiments clearly show that distributions of hydroxyl groups for both systems are dramatically different.

Coumarin Based Highly Selective "off-on-off" Type Novel Fluorescent Sensor for Cu2+ and S2- in Aqueous Solution.

Solvent free synthesis of 6,7-dihydroxy-3-(3-chlorophenyl) coumarin (CFHC) was designed and obtained by the interaction of 2-(2,4,5-trimethoxyphenyl)-1-(3-chlorophenyl)acrylonitrile with pyridinium hydrochloride in the presence of silica gel by using microwave irradiation. The characterization of CFHC was confirmed by FT-IR, 1H, 13C, 13C-APT and 2D HETCOR spectroscopy methods. The optical behavior of CFHC towards metal ions was investigated by UV-visible and fluorescence spectroscopy. CFHC showed "on-off" type fluorescence response towards Cu2+ with high selectivity in aqueous solution (CH3CN/H2O, 9/1, v/v). Once binding with Cu2+, CFHC-Cu2+ complex also displayed high selectivity for sulfide, resulting in "off-on" type sensing of sulfide anion. Graphical abstract Visual fluorescence changes upon addition of various metal ions (5.0 eq.) to CFHC in CH3CN/H2O (90:10, v/v) under UV excitation (365 nm).

2D HETCOR NMR spectra and unequivocal assignments of (E)- and (Z)-1-ferrocenyl-2-phenylethene, and (1E,3E)- and (1Z,3E)-1-ferrocenyl-4-phenyl-1,3-butadiene, (E)-1,2-diferreocenylethene, and (1E,3E)-1,4-diferrocenyl-1,3-butadiene in 13C NMR spectra

Reaction of ferrocenecarbaldehyde with benzyltriphenylphosphorane and (E)-Cinnamyltriphenylphosphorane, respectively, afforded (E)- and (Z)-1-ferrocenyl-2-phenylethene ([(E)-5] and ([(Z)-5]), and (1E,3E)- and (1Z,3E)-1-ferrocenyl-4-phenyl-1,3-butadiene ([(1E,3E)-6] and [(1Z,3E)-6]), respectively, via the conventional Wittig reaction. An analogous reaction between (ferrocenylmethyl)triphenylphospphorane and (E)-1-ferrocenyl-2-formylethene 9 gave (1E,3E)-1,4-diferrocenyl-1,3-butadiene 8.From the 2D HETCOR, we observed that the C(3,4) of Cp ring (or C(para) of phenyl ring) resonates at a lower field than the C(2,5) of Cp ring (or C(ortho) of phenyl ring) in E isomers, whereas the C(2,5) (or C(ortho)) resonates at a lower field than the C(3,4) (or C(para)) in Z isomers. In the 1H NMR spectra, the H(2,5) (or H(ortho)) and the vinyl protons in E isomers resonate at a lower field than those of corresponding protons in Z isomers. The hypotheses to elucidate these data assignments are proposed.

Crystal structures of (η5-C5H4COC6H5)Cr(NO)2(X) (X = Cl, I), and unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of dicarbonyl(η5-cyclopentadienyl)nitrosylchromium, (η5-cyclopentadienyl)halodinitrosylchromium (halo = Cl, Br, I), bis(η5-cyclopentadienyl)iron, and tricarbonyl(η5-cyclopentadienyl)methyltungsten bearing a carbonyl substituent in 13C NMR spectra

Metallocenyl ketones (η5-C5H4COC6H5)Cr(NO)2(X) (X = Cl, 3b; X = I, 5b), (η5-C5H5)Fe[(η5-C5H4)CO(η5-C5H5)]Cr(NO)2(X)(X = Cl, 3c; X = I, 5c), and (η5-C5H5)Fe[(η5-C5H4)CO(η5-C5H5)]W(CO)3(CH3) 6c are synthesized. The structures of 3b and 5b are determined by X-ray diffraction studies. The exocyclic carbon of 5b bends toward the Cr atom with a θ value of 3.46°. The correlation between the magnitudes of nonplanarity of Cp-exocyclic carbon to π-acceptor carbonyl substituents and the twist angle of NO to Cp-exocyclic carbon are discussed. Based on the 2D HETCOR, C(2,5) resonating at a lower field than C(3,4) on the Cp(Cr) ring whereas C(3,4) resonating at a lower field than C(2,5) on the Cp(Fe) and the Cp(W) ring are revealed. The hypothesis to elucidate these data assignments has been proposed. The electron density distribution in the cyclopentadienyl ring has been discussed on the basis of 13C NMR data and compared with calculations using the density functional B3LYP exchange–correlation method for those with X-ray diffraction studies.