Variable Temperature 13C NMR Studies Research Articles

Photophysical and Theoretical Insights on Fullerene/Zincphthalocyanine Supramolecular Interaction in Solution

The present article reports photophysical studies on supramolecular interaction of a zinc phthalocyanine derivative, namely, zinc-2,9,16,23-tetra-tert-butyl phthalocyanine (1) with C(60) and C(70) in solvents having varying polarity, i.e., toluene and 1,2-dichlorobenzene (DCB). The interesting feature of the present work is the observation of charge transfer (CT) absorption bands of the fullerene/1 complexes in DCB. Utilizing the CT transition energy, many important physicochemical parameters like vertical ionization potential of 1, degrees of CT, oscillator strength, transition dipole moment, and resonance energy of interaction have been determined in the present case. The influences of 1 on the UV-vis spectral characteristics of C(60) and C(70) have been explained using a theoretical model that takes into account the interaction between electronic subsystems of 1 with fullerenes. Steady state fluorescence experiment elicits efficient quenching of the fluorescence intensity of 1 in the presence of both C(60) and C(70). The average binding constants of the C(60) and C(70) complexes of 1 (estimated by UV-vis and steady state fluorescence measurements) are determined to be 18,330 dm(3)·mol(-1) (12,595 dm(3)·mol(-1)) and 19,160 dm(3)·mol(-1) (15,292 dm(3)·mol(-1)) in toluene (DCB), respectively. Lifetime experiment yields a larger magnitude of charge separated rate constant for the C(70)/1 species. The faster charge recombination of the fullerene/1 systems observed in more polar solvent results from solvent reorganization energies. Quantum chemical calculations by the ab initio method explore the geometry and electronic structure of the supramolecules and testify the significant redistribution of charge between fullerenes and 1 during fullerene/1 interaction. A variable temperature (13)C NMR study nicely demonstrates that the end-on orientation of C(70) is very much responsible for the low selectivity in binding between C(60)/1 and C(70)/1 systems. Free energy of charge recombination and free energy of radical ion-pair formation signify that electron transfer from the excited 1 to C(60) and C(70) in the C(60)/1 and C(70)/1 complexes, respectively, is an unlikely process. Finally, transient absorption measurements in the visible region establish that energy transfer from (T)C(60*) (and (T)C(70*)) to 1 occurs predominantly in both toluene and DCB, which is subsequently confirmed by the consecutive appearance of the triplet state of 1.

ChemInform Abstract: Dimethylmethoxyborane: Vibrational Assignment, Conformational Stability, ab initio Calculations and Barriers to Internal Rotation.

Abstract The infrared (4000-50 cm−1) and Raman spectra (3500-10 cm−1) have been recorded for dimethylmethoxyborane, (CH3)2BOCH3, in both the gaseous and solid states. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Only one conformation has been found in all three physical states and, on the basis of the polarized nature of the Raman band assigned as the BC2 antisymmetric stretch, this conformer is identified as being the “planar” form with Cs molecular symmetry. A complete vibrational assignment is proposed based on the depolarization data, infrared gas phase band contours, and group frequencies. Additionally, variable temperature 13C NMR studies have been carried out and the barrier to rotation about the BO bond has been determined as 8.9 kcal mol−1. Structural parameters have been obtained from ab initio Hartree—Fock gradient calculations employing 3-21G and 6-31G* basis sets. The results are compared with the rα values obtained earlier from an electron-diffraction study. Potential-surface calculations have been carried out to determine the conformational stability and barriers to internal rotation. Frequencies and potential-energy distributions for the normal modes have been calculated utilizing the 3-21G basis set. All results are compared to the corresponding data for some other organoboranes.

Exploring the chemistry of free CI3+: reactions with the weak Lewis bases PX3 (X = Cl–I), AsI3 and Et2O

What is the preferred coordination site of CI3+? Recent computational work suggested the iodine atoms of the Lewis acid CI3+ to be more electrophilic than the classically expected carbon atom, e.g. the complex with water is of type I2C-I...OH2+ and not the classically expected I3C-OH2+. If this structure is correct, one may also anticipate reactions of CI3+ as an I+ donor. Thus, we were interested in investigating the chemistry of CI3+ in the room-temperature stable salt [CI3]+[pftb](-) ([pftb](-) = [Al(OC(CF3)3)4]-) with weak nucleophiles that i) mimic water (OEt2) or ii) are electronically deactivated weak nucleophiles (PX3, X = Cl-I; AsI3). One question was: is it possible to obtain iodine-coordinated Lewis acid-base adducts of the CI3+ cation? With Et2O as a base, the cation behaves as a strong Lewis acid and cleaves the ether to give I3C-OEt, C2H4 and [H(Et2O)2]+. By contrast PX3 and AsI3 coordinate to the CI3+ cations and the adducts have classical, carbon-bound ethane-like structures, as proven by X-ray single-crystal diffraction, IR, UV-Vis and NMR spectroscopy. From variable temperature 13C NMR studies, it followed for the I3C-AsI3+ salt that the equilibrium between CI3+ and AsI3 is reversible and temperature dependent in solution. The I3C-PI3+ salt decomposes at room temperature giving PI4+ and C2I4, likely through an iodine coordinated I2C-I[dot dot dot]PI3+ intermediate. Thus CI3+ may also act as an I+ donor. All reactions are in agreement with ab initio quantum chemical calculations at the MP2/TZVPP level and assignments of experimental spectra were aided by quantum chemistry.

First Spectroscopical Evidence of a Dioxomethylene Intermediate in the Reaction of CO2 with Cp2Zr(H)Cl: A 13C NMR Study

An in situ variable-temperature 13C NMR study on the mechanism of the reaction of Schwartz's reagent, Cp2Zr(H)Cl, with labeled 13CO2 was performed. In the course of the investigations, for the first time the long postulated μ-η1-O,O‘ gem-diolate species Cp2Zr(Cl)OCH2OZr(Cl)Cp2 was observed.

Conformational analysis. Part 36. A variable temperature 13C NMR study of conformational equilibria in methyl substituted cycloalkanes

The conformational equilibria in six methylcycloalkanes have been investigated using the temperature dependence of the 13C chemical shifts at temperatures above the coalescence point. Using conformationally homogeneous compounds as standards the temperature dependence was analysed to give the conformer energy differences ΔH (ax–eq). These were for methylcyclohexane 1.92 kcal mol−1, 2- and 3-methylcyclohexanone 1.58 and 1.35 kcal mol−1, 3-methyltetrahydropyran 1.50 kcal mol−1 and 2- and 4-methylpiperidine >2.6 and 2.30 kcal mol−1. These values are compared with previous literature values and theoretical values from molecular mechanics and ab initio calculations. They are in very good agreement with previous literature values and the ab initio values, but the values from MM calculations show larger differences. The only exceptional case is 2-methylcyclohexanone in which the ab initio value of 2.38 kcal mol−1 is much larger than the energy difference in chloroform solution determined here (1.58 kcal mol−1) which is in good agreement with previous literature data in solution. Sterically hindered solvation in the equatorial conformer is the most likely cause of this difference. It is concluded that this technique represents a novel and useful approach to conformational analysis.

The Search for Persistent Cyclobutylmethyl Cations in Superacidic Media and Observation of the Cyclobutyldicyclopropylmethyl Cation1a

Primary and secondary cyclobutylmethyl cations were found to be elusive in superacidic media even at low temperatures. They give thermodynamically more stable rearrangement products, i.e., the dimeric bicyclo[4.4.0]dec-1-yl cation and substituted cyclopentyl cations, respectively. In the search for a persistent cyclobutylmethyl cation, the more stabilized cyclobutyldicyclopropylmethyl cation was prepared from its corresponding alcohol in FSO3H/SO2ClF at −90 °C. Using variable-temperature 13C NMR studies and theoretical calculations, the ion was shown to exist preferentially in its bisected conformation at −80 °C. The ion is predominantly classical, with expected significant delocalization into the neighboring cycloalkyl rings.

Complexes formed by Zn II, Cd II and Hg IIin the presence of the octadentate ligand 1,4,7,10-tetrakis(pyrazol-1-ylmethyl)-1,4,7,10-tetraazacyclododecane. X-ray structure of the cadmium complex

The potentially octadentate ligand 1,4,7,10-tetrakis(pyrazol-1-ylmethyl)-1,4,7,10-tetraazacyclododecane (L 1) yields with cadmium(II) compounds of formula [CdL 1]Y 2 (Y = BPh 4, ClO 4, PF 6) in which the metal ion is coordinated by the eight nitrogen donor atoms of the ligand. The crystal structure of [CdL 1] (BPh 4) 2 has been determined by X-ray diffraction. With zinc(II) and mercury(II) L 1 affords the compounds [ML 2]Y 2 [L 2 = 1,7-bis(pyrazol-1-ylmethyl)-1,4,7,10-tetraazacyclododecane. M = Zn; Y = ClO 4, PF 6. M = Hg; Y = PF 6] where the ligand L 2 originates from L 1 by loss of the methylpyrazole groups from two pendant arms of the macrocycle in trans positions. The compounds have been characterized by 1H and 13C NMR data. A variable temperature 13C NMR study on [CdL 1](PF 6) 2 suggests that the cation undergoes rearrangements in solution between two geometric isomers

Coordination chemistry of mono- and di-nitriles in [Ru 3(CO) 12− n(RCN) n] ( n = 1–3): influence of the CO/nitrile ratio on fluxionality

The clusters [Ru 3(CO) 12− n (RCN) n ] ( n = 1–3; RCN = acetonitrile, adiponitrile, phenylenediacetonitrile) have been prepared in dichloromethane solution by reaction of [Ru 3(CO) 12] with Me 3NO in the presence of the desired nitrile. The number of coordinated nitriles depends on the nitrile concentration and to a lesser extend on the Me 3NO/Ru 3 ration. The new cluster [Ru 3(CO) 9(MeCN) 3] is prepared and isolated in high yield. Spectroscopic IR and 13C NMR investigations in solution indicate that the dinitriles remain monocoordinated but only in a concentrated medium (1M <[RCN] < 4M). Spectroscopic data suggest axial coordination of the nitriles, one on each ruthenium atom, and equatorial bridging carbonyl groups. For [Ru 3(CO) 7( μ 2−CO) 3(MeCN) 2], the two nitriles are located on each side of the triruthenium plane, whereas for [Ru 3(CO) 6( μ 2−CO) 3(MeCN) 3], two MeCN are located on one side of the triruthenium plane with the third lying on the other side. Variable-temperature 13C NMR study reveals a fluxionality of the carbonyls around the trimetal core. The first fluxional motion involves in-plane carbonyl exchange with activation energies depending on the degree of substitution n. The influence of ligand substitution in the axial position on the mobility of the carbonyls is attributed to an increase of the π back-donation from the cluster to each of the remaining carbonyls with increasing substitution.

Synthesis and Characterization of Organic Materials with Conveniently Accessible Supercooled Liquid and Glassy Phases: Isomeric 1,3,5-Tris(naphthyl)benzenes

1,3,5-Tris(1-naphthyl)benzene (1), 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (2), and 1-(1-naphthyl)-3,5-bis(2-naphthyl)benzene (3) easily supercool and form glasses on cooling from the melt. We synthesized 1, 2, and 3 using Suzuki's conditions to effect the cross-coupling reactions of 1,3,5-tribromobenzene with 1-naphthylboronic acid and/or 2-naphthylboronic acid. Variable-temperature 13C NMR studies of 1 establish a barrier of ca. 12 kcal/mol for rotation about the aryl−aryl bond; this value displays good agreement with the barrier of 13 kcal/mol computed using molecular mechanics calculations (MM2). This relatively low rotational barrier is inconsistent with the previously held notion that 1,3,5-tris(1-naphthyl)benzene (1) exists as a mixture of noninterconverting rotational isomers (atropisomers) in solution at room temperature. Variable-temperature 13C NMR studies of 2 establish barriers of ca. 12 kcal/mol for rotation about the 1-naphthyl−aryl bond and <9 kcal/mol for rotation about the 2-naphthyl−a...

A detailed study defining the extent of preorganization of an aza macrocycle containing the phenyldinaphthomethane subunit (a three bladed propeller) using dynamic NMR and molecular dynamics

The aza-propeller crown 4,7,10-tritosyl-4,7,10-triaza-1,13-dioxacyclooctadecane 1 has been examined by variable temperature 13C NMR studies, and the movement of each segment of the molecule (ArOCCN, NCCN, propeller) was determined kinetically. Several sets of coalescences were found to occur at the same activation energy, which was also that found for the flip of the propeller segment. This movement of the macrocycle as a whole is a relatively slow process (ms scale) compared to the torsional movements round the crown ether ring (ps scale). These torsional movements were explored by molecular dynamics (MD) modelling; the macrocyclic ring is mobile when simulated at 200 K. The tosyl groups are in permanent motion although none twists by more than a few degrees round the N–S torsion. The segments next to the propeller (which are both gauche in the crystal structure) converted from gauche to anti, while the TsNCCNTS segments remained anti throughout.

Intramolecular exchange between square antiprismatic enantiomers of the pendant arm macrocyclic ligand complex N,N′,n″,n‴-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecanelead(II)

Variable temperature 13C NMR studies of the pendant arm macrocyclic complex N,N′,N″,N‴-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecanelead(II) and its cadmium(II) and mercury(II) analogues in [2H4]-methanol indicate that these complexes undergo rapid intramolecular exchange between two square antiprismatic enantiomers.

Variable temperature 13C NMR study of some L(CO) 3FeH(SiR 3) (L = CO, P(OPh) 3; R = Ph, Me, Cl) species. X-ray crystal structure of P(OPh) 3(CO) 3Fe(H)SiPh 3

Intramolecular rearrangement of (CO) 4FeH(SiPh 3) ( I), (CO) 4FeH(SiMe 3) ( II), (CO) 4FeH(SiCl 3) ( III) and P(OPh) 3(CO) 3Fe(H)SiPh 3 ( IV), as studied by variable temperature 13C NMR spectroscopy, yielded activation enthalpies (kcal mol −1): 10.3±0.1, 10.4±0.4, 17.4±0.1 and 10.9±0.03, respectively, and activation entropies (cal deg −1 mol −1): −1.8 ± 0.5, −2.21 ± 0.1, 0.7 ± 0.5 and −2.2 ± 0.2, respectively. Crystal structure data for IV: C 39H 31FeO 6PSi, OC-6-23-tricarbonylhydrido(triphenylphosphite)(triphenylphosphine)iron(II), triclinic, P 1 , a = 11.509(2), b = 14.403(3), c = 11.153(4) Å, α = 108.04(2), β = 95.10(2), γ = 92.55(2)°, Z = 2, V = 1746(1) Å 3, final R factor 0.030. The structure is a highly distorted octahedron.

Dimethylmethoxyborane: vibrational assignment, conformational stability, ab initio calculations and barriers to internal rotation

The infrared (4000-50 cm −1) and Raman spectra (3500-10 cm −1) have been recorded for dimethylmethoxyborane, (CH 3) 2BOCH 3, in both the gaseous and solid states. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Only one conformation has been found in all three physical states and, on the basis of the polarized nature of the Raman band assigned as the BC 2 antisymmetric stretch, this conformer is identified as being the “planar” form with C s molecular symmetry. A complete vibrational assignment is proposed based on the depolarization data, infrared gas phase band contours, and group frequencies. Additionally, variable temperature 13C NMR studies have been carried out and the barrier to rotation about the BO bond has been determined as 8.9 kcal mol −1. Structural parameters have been obtained from ab initio Hartree—Fock gradient calculations employing 3-21G and 6-31G* basis sets. The results are compared with the r α values obtained earlier from an electron-diffraction study. Potential-surface calculations have been carried out to determine the conformational stability and barriers to internal rotation. Frequencies and potential-energy distributions for the normal modes have been calculated utilizing the 3-21G basis set. All results are compared to the corresponding data for some other organoboranes.

Chromium, tungsten, iron, and ruthenium complexes of the 4-membered ring diazene 3,4-diazatricyclo[4.2.1.0 2,5]non-3-ene

The 4-membered ring diazene 3,4-diazatricyclo[4.2.1.0 2,5]non-3-ene (dtn) reacts with Cr and W carbonyls to give the complexes M(CO) 5(dtn))(Ia,b), [M(CO) 5] 2 (dtn) (IIa,b), M(CO) 4(dtn) 2 (IIIa,b), [M(CO) 4] 2(dtn) 2 (IVa,b), and [M(CO) 3] 2(dtn) 3 (Va,b) where a = Cr and b = W. 1H and 13C NMR provide evidence that compounds III-V each exist in the predicted two isomeric forms and full assignment of the resonances is made for all but the Va 13C spectrum. Fe 2(CO) 9 reacts with dtn to give Fe(CO) 4(dtn) (Ic) and Fe 3(CO) 9(dtn) (VIIIc). It is argued that steric effects from the hydrocarbon portion, notably C(9), of dtn prevents formation of the normally stable diiron complexes Fe 2(CO) 6(dtn) (VIc) and Fe 2(CO) 7(dtn) (VIIc). Ru 3(CO) 12 and dtn react to form only Ru 3CO) 9(dtn) (VIIId). Variable temperature 13C NMR studies reveal CO scramblingin VIIIc and VIIId at room temperature, which ceases at low temperature. Results for the dtn complexes are compared with results for another 4-membered ring diazene ligand as well as with results for 3−, 5−, and 6-membered ring diazenes.

Synthesis and spectroscopic properties of the binuclear pentacarbonylcyclopentadienylcycloheptatrienyl complexes [M(CO) 3(η-C 5R 5)M′(CO) 2(η-C 7H 7](M,M′  Mo or W; R  H or Me)

A series of metalmetal bonded complexes [M(CO) 3(η-C 5R 5 M′(CO) 2(η-C 7H 7)] ( 1: M  M′  Mo, R  H; 2: M  M′  Mo, R  Me; 3 M  M′  W, R  H; 4: M  W, M′  Mo, R  H) have been synthesized from the dicarbonylacetonitrile cations [M′(CO) 2(NCMe)(η-C 7H 7)][BF 4] (M′  Mo or W) and the appropriate anion Li[M(CO) 3(η-C 5H 5)] (M  Mo or W, R  H or Me). Infrared, electronic absorption, and NMR spectra of complexes 1 to 4 are discussed; variable temperature 13C NMR studies on 2 advocate an intermetallic carbonyl scrambling process.

ChemInform Abstract: Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part 1. Bromotri‐μ‐carbonyloctacarbonyltetrairidate(1‐)

A 2D and variable-temperature 13C-NMR study indicates that a CO-site exchange occurs in the title complex via several consecutive processes, the first being a ‘merry-go-round’ of the basal CO's, the second a switch of basal face not involving unbridged intermediates.

Acceleration of the pseudorotation rates in pentacoordinated phosphorus compounds. Conformational transmission versus hexacoordinated zwitterionic intermediates

A variable-temperature 13C NMR study, accompanied by a high-resolution 1H NMR conformational analysis study, on a series of monocyclic oxyphosphoranes is reported. The selected compounds enabled us to study the acceleration of the rates of intramolecular ligand reorganization on pentacoordinated phosphorus. It allowed us to determine whether the enhancement of the reorganization rates was brought about by accelerated pseudorotation due to the conformational transmission effect or by the involvement of hexacoordinated zwitterionic phosphorus intermediates. The results of the study further substantiate the findings that the involvement of such hexacoordinated intermediates is of no importance in the type of oxyphosphoranes studied.

Dynamic NMR studies on hydride and carbonyl fluxionality in triosmium-platinum cluster compounds. X-ray crystal structure of [Os3Pt(.mu.-H)3(CO)10(PCy3)]+BF4- (Cy = cyclohexyl)

Variable-temperature 13C NMR studies on Os3Pt(μ-H)2(CO)10(PCy3) (1) show three distinct carbonyl exchange processes. The lowest energy process (ΔG‡233 = 49.7 (5) kJ mol−1) involves localized scrambling in two Os(CO)3 groups, while a second process permutes all nine Os-bound CO ligands. A proposed mechanism involving rotation of the PtL2 fragment, coupled with facial hydride migration, accounts for both this latter process and the simultaneous mutual exchange of the hydride ligands (for which ΔG‡295 = 63.1 (5) kJ mol−1, ΔH‡ = 55 (1) kJ mol−1, ΔS‡ = −27 (3) J mol−1 K−1). Above 333 K a final mechanism results in total CO scrambling. Protonation of 1 with HBF4 affords the trihydrido salt [Os3Pt(μ-H)3(CO)10(PCy3)]+BF4− (2) in high yield. Crystal data for 2: monoclinic, space group Pn, a = 9.925 (2) A, b = 11.747 (3) A, c = 16.186 (4) A, β = 89.75 (2)°, V = 1887.1 (8) A3, Z = 2, final R (Rw) values of 0.032 (0.034) for 4087 independent observed data, I ≥ 3σ(I). 2 has a tetrahedral framework with the hydrido ligands bridging the Pt–Os(3) edge (2.845 (1) A) and the Os(1)–Os(3) and Os(1)–Os(2) edges (2.891 (1) and 2.747 (1) A, respectively), with the other metal-metal edges Pt–Os(1) = 2.812 (1), Pt–Os(2) = 2.819 (1), and Os(2)–Os(3) = 2.790 (1) A. The two Os(μ-H)Os hydrides, unambiguously assigned by using NOE difference spectra, are involved in mutual exchange (ΔG‡293 = 62.7 (5) kJ mol−1). The lower energy carbonyl exchange process, observed in magnetization transfer studies using DANTE, is compatible with the hydride fluxionality, and a higher energy carbonyl exchange is consistent with rotation of the PtH(CO)(PR3) moiety about the Os3 triangle. The butterfly adducts Os3Pt(μ-H)2(CO)10(PCy3)(L) (3, L = CO; 4, L = PCy3) show strikingly different fluxional behavior. A highly unusual and very low-energy six-site Pt–Os carbonyl exchange, involving a proposed closo transition state, is observed for 3. In contrast magnetization transfer and 13C 2D exchange correlation NOESY studies on complex 4 show only high-energy CO exchange between Pt and Os and suggest a novel flipping of the butterfly framework through a planar transition state. In both compounds the hydrides are nonfluxional at ambient temperature. 1J(187Os–13C) coupling constants in the range 98–117 Hz are reported for complexes 1–3.

Molecular structure and fluxional behaviour of the iron-rhodium methoxymethylidyne cluster complex Fe 2 Rh(μ-H)(μ 3-COCH 3)(CO) 7(η-C 5H 5)

The complex Fe 2Rh(μ-H)(μ 3-COCH 3)(CO) 7(η-C 5H 5) prepared by treatment of Fe 3(μ-H)(μ-COCH 3)(CO) 10 with Rh(CO) 2 (η-C 5H 5), has been examined by single crystal X-ray diffraction. The compound crystallises in the monoclinic space group C2/ c (No. 15) with a 25.409(2), b 8.129(1), c 17.044(1) Å, β 103.744(6)°, V 3419.6(6) Å 3 and D c 2.02 g cm −3 for Z = 8 and M = 519.8. Data were collected for 2° ⩽ θ ⩽ 30° with graphite monochromated X-radiation (Mo- K α) using an Enraf-Nonius CAD4-F diffractometer. The structure was refined to R = 0.025 ( R itw = 0.037) for 3557 observed [ I ⩾ 3(σ I)], absorption corrected data. The complex contains an asymmetrically bonded methoxymethylidyne ligand capping an Fe 2Rh triangular face (Fe(1)-C(8) 1.863(3), Fe(2)-C(8) 1.881(3), Rh-C(8), 2.211(3) Å). The terminal carbonyl ligand on the rhodium atom shows slight semi-bridging interactions with the two iron atoms (Fe(1) … C(7) 2.888(4), Fe(2) … C(7), 2.769(4) Å, Rh-C(7)-O(7) 169.1(4)°. The iron—iron vector is spanned by a (directly located) μ-hydride ligand. Variable temperature 13C NMR studies reveal fluxional behaviour, including a temperature dependence both of the alkylidyne carbon chemical shift (δ 323.5 at +80°C, δ 319.2 at −90°C) and its 103Rh coupling constant ( 1 J(Rh-C) 23 Hz at −90°C, 26 Hz at +80°C). These data suggest an increased interaction of the ‘semi-μ 3’ alkylidyne ligand with the rhodium centre at higher temperatures, primarily associated with the highest energy fluxional process. Extended Hückel MO calculations on this complex allow a rationalisation of the ‘semi-μ 3’ nature of the COCH 3 group.

The synthesis and structure of novel ferrocene bis-crown ethers

The synthesis of novel ferrocene bis-crown ethers is reported. Variable temperature 13C NMR studies on these compounds reveal a common intramolecular dynamic process involving rotation about the NCO bond.