13C n.m.r. spectroscopy of diethyl alkyl- and benzyl-phosphonates. A study of phosphorus–carbon spin–spin coupling constants over one to seven bonds

¹³C chemical shifts and ³¹P? ¹³C spin–spin coupling constants are reported for 10 alkyl-, 20 benzyl- and 3 (naphthylmethyl)-phosphonates. While in saturated aliphatic chains P–C couplings over more than four bonds cannot be resolved, couplings over up to seven bonds are observed in the benzyl type systems. Conformational and substituent effects on J(PC) are studied and discussed. ⁿJ(PF) (n = 4, 5, 6) are reported for the isomeric (fluorobenzyl)phosphonates and ⁿJ(PP) (n = 5, 6, 7) were obtained from the ¹³C satellites in the ³¹P n.m.r. spectra of the isomeric diphosphonates, C₆H₄[CH₂P(O)(OEt)₂]₂. Comparison of those ¹³C absorptions of the latter, which represent the X parts of ABX or AA′X spin systems, with the spectra of the corresponding (methylbenzyl)phosphonates, CH₃C₆H₄CH₂P(O)(OEt)₂, yielded the relative signs of ⁿJ(PC) (n = 2–6).     

1H n.m.r. spectra of N-phenylmaleimide in isotropic and nematic phases

¹H n.m.r. spectra of N-phenylmaleimide have been investigated in isotropic as well as nematic phases; the chemical shifts, the direct dipolar and the indirect spin–spin coupling constants have been determined. The direct dipolar coupling constants are consistent with rapidly interconverting energetically equivalent twisted conformations of C₂ symmetry. Under the assumption that only two such conformers are predominantly present, the angle between the phenyl and the maleimide planes is determined as 52.9±0.9°.     

Organic chemistry of dinitrogen and related ligands. Part 2. Non-radical acylation of ligating dinitrogen

Summary Ligating dinitrogen, in the complexes,trans-M(N₂)₂(Ph₂PCH₂CH₂PPh₂)₂ (where M=Mo or W) may be acylated by trifluoroacetic anhydride, to give trifluoroacetyldiazenido complexes in high yield. Unlike corresponding reactions with acyl halides, trifluoroacetylation proceeds under nonradical conditions, and a mechanism analogous to that of protonation is suggested.Dinitrogen-derived ligands may also be acylated by (CF₃CO)₂O, so that the methyldiazenido ligand is converted into a methyl (trifluoroacetyl) hydrazido (2-) ligand, and the acetyldiazenido ligand undergoes transacylation to give a trifluoroacetyl diazenido derivative.New complexes were characterised by i.r.,¹⁹F and¹H n.m.r. spectra, and by elemental analysis.Part 1 is ref. 10     

Solution <Superscript>1</Superscript>H n.m.r. of paramagnetic Co<Superscript>2+</Superscript>complexes with dioxobis(carboxymethyl)tetraazamacrocycles

Paramagnetic shifts in the ¹H n.m.r. spectra were observed for high-spin Co²⁺ complexes with 12--14-membered tetraazamacrocycles incorporating two amide groups and two pendant carboxymethyl groups. The pseudocontact term due to the dipolar interaction between the metal ion and the resonant protons was calculated on the basis of X-ray structures, and the Fermi contact term due to spin delocalization was determined. The ethylenediamine moiety of the ligand molecule is coordinated in an unsymmetric manner, even in solution, and internal motion (involving conformational change of the macrocyclic frame and exchange of coordinate bonds) is much slower than the n.m.r. observation frequency. In the 12-membered macrocyclic complex Co(L12), three of the eight CH₂ groups fix their orientation in the n.m.r. time scale; in Co(L13) only one CH₂ group fixes its orientation; in Co(L14) all CH₂ groups undergo a rapid reorientation. The facility in internal motion increases with the ring size, and shows a correlation with the chemical stabilities of these Co²⁺ complexes against oxidation; to atmospheric oxygen, Co²⁺(L12) is the most resistant and Co²⁺(L14) is the most susceptible.     

N-Heterocyclic carbene complexes of palladium(II) and rhodium(I) with pendant ferrocenylmethyl groups: synthesis and electrochemistry

1-Ferrocenylmethyl-3-benzylimidazolidinium iodide and 1-ferrocenylmethyl-3-(2,4,6-trimethylbenzyl)imi-dazolidinium iodide were prepared in good yields by boiling, under reflux, a solution of (ferrocenylmethyl)- trimethylammonium iodide and the appropriate N-alkyl-2-imidazoline in MeCN. From the 1-ferrocenylmethyl-3-ben- zylimidazolidinium iodide salt, N-heterocylic carbene complexes of Pd^II and Rh^I were synthesized by in situ deprotonation and subsequent trapping. The new compounds were characterized by C, H, N analyses, ¹H-n.m.r., ¹³C-n.m.r. and by cyclic voltammetry. The n.m.r. properties of the complexes are compared with those of non-ferrocenylated carbene derivatives. The c.v.'s of these compounds show a number of resolved redox processes, indicating that CH₂Fc substituents are electronically isolated from the remaining molecular framework.     

Synthesis and Spectroscopic Characterisation of Six-Coordinate Complexes of Oxovanadium(V)

Complexes of the types VO(L)(R-deaH), VO(R-dea)(LH), and VO(L)(OGOH)[L = deprotonated form of N-(1-hydroxyethyl) naphthaldimine; R-dea = deprotonated form of a N-substituted diethanolamine, with R = H or Ph; G = CH₂CH₂, CHMeCHMe, CMe₂CMe₂, CHMeCH₂CMe₂, CMe₂CH₂CH₂CMe₂] have been prepared by the equimolar reactions of VO(OPr ⁱ )₃, LH₂, and an appropriate diethanolamine or glycol in benzene. All of these coloured solid complexes have been characterised by elemental (C, H, N, and V) analyses and by spectroscopic (i.r., electronic, ¹H-, ⁵¹V-n.m.r) studies. The relative lability of the hydroxy group(s) of N-(1-hydroxyethyl)naphthaldiamine, diethanolamine, and glycol has also been investigated.     

1H N.m.r. Chemical shifts and hydrogen exchange rates oftrans-[Co(en)2XY]n+ complexes in liquid ammonia

Summary ¹H n.m.r. spectra of coordinated ethylenediamine HN< hydrogens for 23trans-[Co(en)₂XY]ⁿ⁺ complexes and¹H-²H exchange rates for some selected compounds are reported in the solvent liquid ammonia. Assignments are presented for asymmetric complexes. These are based on the chemical shift order of the symmetric complexes. The assignments are confirmed by independent experimental findings including the effect of specific ion-association and the observed exchange rates. The exchange rates follow the relation k_obsd=k⁰+k¹ [N²H₄ClO₄]^–1, illustrative of general base-catalysis; in this case rate-determining proton abstraction by N²H₃ and N²H ₂ ^– , respectively. Chemical shifts and exchange rates in liquid ammonia follow the published order of the aqueous parameters.     

Borchelate und Bormetallchelate, 4. Mitt.

The i.r., u. v.,¹H n.m.r.,¹³C n.m.r., and¹¹B n.m.r. spectra of several substituted diphenylboron chelates derived from salicylaldehyde azomethines were compared with respect to the influence of the amine substituentR. O–B–N-6-ring constitution of the chelates29–32 [R=OH, NH₂, NHC₆H₅, N(CH₃)₂] can be deduced from the spectra.

Als 3. Mitt. gilt:F. Umland undE. Hohaus mit Beiträgen vonW. Riepe, K. Brodte, C. Schleyerbach undD. Szonn. Untersuchungen über borhaltige Ringsysteme vom Chelattyp. Forschungsbericht des Landes Nordrhein-Westfalen Nr. 2538. Opladen: Westdeutscher Verlag. 1976.     

Degradation processes in the cellulose/<Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide system studied by HPLC and ESR. Radical formation/recombination kinetics under UV photolysis at 77 K

Degradation processes of N-methylmorpholine-N-oxide monohydrate (NMMO), cellulose and cellulose/NMMO solutions were studied by high performance liquid chromatography (HPLC) and electron spin resonance (ESR) spectroscopy. Kinetics of radical accumulation processes under UV (λ = 248 nm) excimer laser flash photolysis was investigated by ESR at 77 K. Beside radical products of cellulose generated and stabilized at low temperature, radicals in NMMO and cellulose/NMMO solutions were studied for the first time in those systems and attributed to nitroxide type radicals ∼CH₂–NO^•–CH₂∼ and/or ∼CH₂–NO^•–CH₃∼ at the first and methyl ^•CH₃ and formyl ^•CHO radicals at the second step of the photo-induced reaction. Kinetic study of radicals revealed that formation and recombination rates of radical reaction depend on cellulose concentration in cellulose/NMMO solutions and additional ingredients, e.g., Fe(II) and propyl gallate. HPLC measurements showed that the concentrations of ring degradation products, e.g., aminoethanol and acetaldehyde, are determined by the composition of the cellulose/NMMO solution. Results based on HPLC are mainly maintained by ESR that supports the assumption concerning a radical initiated ring-opening of NMMO.     

Nitrogen-15 n.m.r. studies of 13C, 15N labeled arginine

¹⁵N n.m.r. spectra of [¹³C-2, 3-¹⁵N₂-guanidino]arginine and [¹³C, ¹⁵N₂] urea were obtained in D₂O and H₂O at a variety of pH values both with and without proton decoupling. The effects of the proton exchange rate are readily observable in the proton coupled ¹⁵N spectra. When the guanidino group is deprotonated (pK = 12.5), the terminal nitrogens give a single resonance 6.6 ppm downfield of the protonated species, indicating a rapid tautomeric exchange. The observed NH and CN couplings are compared with calculated values, and good agreement is found for ¹J(CN) using a Blizzard–Santry type calculation. The ramifications of the proton exchange on ¹⁵N n.m.r. spectra of amino acids and peptides are discussed.     

Nickel(II) Complexes of Pentadentate N5 Ligands as Catalysts for Alkane Hydroxylation by Using m‐CPBA as Oxidant: A Combined Experimental and Computational Study

A new family of nickel(II) complexes of the type [Ni(L)(CH₃CN)](BPh₄)₂, where L=N‐methyl‐N,N′,N′‐tris(pyrid‐2‐ylmethyl)‐ethylenediamine (L1, 1 ), N‐benzyl‐N,N′,N′‐tris(pyrid‐2‐yl‐methyl)‐ethylenediamine (L2, 2 ), N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐(6‐methyl‐pyrid‐2‐yl‐methyl)‐ethylenediamine (L3, 3 ), N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐(quinolin‐2‐ylmethyl)‐ethylenediamine (L4, 4 ), and N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐imidazole‐2‐ylmethyl)‐ethylenediamine (L5, 5 ), has been isolated and characterized by means of elemental analysis, mass spectrometry, UV/Vis spectroscopy, and electrochemistry. The single‐crystal X‐ray structure of [Ni(L3)(CH₃CN)](BPh₄)₂ reveals that the nickel(II) center is located in a distorted octahedral coordination geometry constituted by all the five nitrogen atoms of the pentadentate ligand and an acetonitrile molecule. In a dichloromethane/acetonitrile solvent mixture, all the complexes show ligand field bands in the visible region characteristic of an octahedral coordination geometry. They exhibit a one‐electron oxidation corresponding to the Ni^II/Ni^III redox couple the potential of which depends upon the ligand donor functionalities. The new complexes catalyze the oxidation of cyclohexane in the presence of m‐CPBA as oxidant up to a turnover number of 530 with good alcohol selectivity (A/K, 7.1–10.6, A=alcohol, K=ketone). Upon replacing the pyridylmethyl arm in [Ni(L1)(CH₃CN)](BPh₄)₂ by the strongly σ‐bonding but weakly π‐bonding imidazolylmethyl arm as in [Ni(L5)(CH₃CN)](BPh₄)₂ or the sterically demanding 6‐methylpyridylmethyl ([Ni(L3)(CH₃CN)](BPh₄)₂ and the quinolylmethyl arms ([Ni(L4)(CH₃CN)](BPh₄)₂, both the catalytic activity and the selectivity decrease. DFT studies performed on cyclohexane oxidation by complexes 1 and 5 demonstrate the two spin‐state reactivity for the high‐spin [(N5)Ni^II?O^.] intermediate (ts1_hs, ts2_doublet), which has a low‐spin state located closely in energy to the high‐spin state. The lower catalytic activity of complex 5 is mainly due to the formation of thermodynamically less accessible m‐CPBA‐coordinated precursor of [Ni^II(L5)(OOCOC₆H₄Cl)]⁺ ( 5 a ). Adamantane is oxidized to 1‐adamantanol, 2‐adamantanol, and 2‐adamantanone (3°/2°, 10.6–11.5), and cumene is selectively oxidized to 2‐phenyl‐2‐propanol. The incorporation of sterically hindering pyridylmethyl and quinolylmethyl donor ligands around the Ni^II leads to a high 3°/2° bond selectivity for adamantane oxidation, which is in contrast to the lower cyclohexane oxidation activities of the complexes.     

Studies on the γ-effects. Part 3. Variations in the γ-effects ofN-substituted benzylamines,o-aminomethylphenols and 3,4-dihydro-2H-1,3-benzoxazines against theE s ′ substituent constants

The magnitude of the -effects on¹³C chemical shifts was studied as function of theN-substitution [Me, Et, Bu, CH₂C₆H₅, CH₂CH₂C₆H₅, Prⁱ, Bu^t, Bu^s, c-C₆H₁₁, CH(CH₃)C₆H₅, Bu^t, or Ph] for several benzylamines,o-aminomethylphenols and 3,4-dihydro-2H-1,3-benzoxazines. A correlation between the _c-values and the steric substituent constants (E _s ) of theN-substituents proved useful in characterizing the variation of the -effects along with the conformational factors. The diastereospecificity of the -effects is discussed for purposes of configurational assignments.For part 2, see Ref. 1. This paper is also Part 5 in the series Studies on the Benzoxazine Series.     

Carbon-13 isotope effect on proton decoupled 13C and 31P n.m.r. spectra of bis(diphenylphosphino)acetylene

High resolution proton decoupled ¹³C and ³¹P n.m.r. spectra of bis(diphenylphosphino)acetylene in (CD₃)₂SO and CDCl₃ are analysed as ABX spectra to give the relative chemical shifts of the ¹³C and ³¹P nuclei as well as the spin–spin coupling constants ³J(PP) and ⁿJ(PC). The differences in ³¹P shieldings are due to secondary ¹³C isotope effects which have been observed to be negligible over more than two bonds.     

Proton lability in the amino ligand of and the1H-n.m.r. spectra oftrans-dichloro(diethylamine)(π-ethene)platinum and related complexes

Summary The NCH ₂CH₃ region of the¹H-n.m.r. spectrum oftrans-PtCl₂(-C₂H₄)(NHEt₂) has been investigated and shown to contain inequivalent protons. A study has also been made in related amine complexes of the conditions under which Pt-N-CH ₂ protons are equivalent, NH-CH coupling takes place and¹⁹⁵Pt-N-CH coupling occurs.The lability of the N-H bond intrans-olefin-amine, carbonyl-amine, ethanide-amine and phosphine-amine complexes is also investigated and compared with that of the platinum-amine link.Trans-labilizing powers of-C₂H₄, CO, CH₂¯CH₂ and Ph₃P are compared.     

13C n.m.r. spectra of some polychloroalkenes

¹³C n.m.r. spectra have been measured for thirty-two polychloroalkenes including (i) monosubstituted compounds CH₂?CHCCl_nH_2?nX, where ? X stands for ? H, ? Cl, alkyl, and trisubstituted alkenes CCl₂?CHAlk, none of which form geometric isomers; (ii) disubstituted compounds RCH?CHR′; (iii) and (iv) trisubstituted compounds of the types RCCl?CHR′ and CHCl?CClR, respectively. Compounds (ii) to (iv) represent either individual isomers or mixtures of the Z and E forms. In the case of compounds (ii) and (iii), the ordering of chemical shifts is δ_E > δ_Z for the sp²-carbon atoms and δ_E < δ_z for the adjacent tetrahedral ones. On the contrary, the signals of the sp²-carbon atoms of compounds (iv) obey the rule δ_E < δ_z. The effect of vinyl and allyl groups as substituents on the ¹³C chemical shifts of chlorine-containing groups is discussed. The dependence of the sp²-carbon spin–spin coupling constants J(¹³C? ¹H) on the number of chlorinated substituents in the molecule is also considered.     

Trioxaphosphocanes-1,3,6,2, etude par R.M.N. (13C, 1H, 31P et stereochimie

The stereochemistry of several 2-R-1,3,6,2-trioxaphosphocanes (R = Cl, OCH₃, CH₃, N(CH₃)₃ has been investigated by ¹H, ¹³C and ³¹P n m r spectroscopy.     

COMPLEXES OF BINUCLEATING LIGANDS. XIII. SOLUBLE COMPLEXES OF A LIGAND WITH A BRIDGING THIOPHENOXIDE COMPONENT AND PERIPHERAL n-OCTYL SUBSTITUENTS

Abstract

The trianionic binucleating ligands formally derived from the condensation products of S-n-octyldithiocarbazate with either 2-hydroxy- or 2-mercapto-5-methylisophthalaldehyde (hereafter (L″)^3- and L^3- respectively) gave the binuclear complexes L″Ni₂ (CH₃ O), L″Ni₂ (C₆ H₅ CH₂ O), LNi₂ (C₃ H₃ N₂), LCu₂ (C₃ H₃ N₂) and LNi₂ (SR) where R=C₈H_{1 7} of CH₃.C₆ H₄ and C₃ H₃ N₂ ^?=the pyrazolate anion. These complexes were soluble in chloroform and ¹H n.m.r. data for some of them are presented. There was no evidence for significant magnetic exchange within LCu₂ (C₃ H₃ N₂). Attempts to generate LNi₂ (X) where X^?=Cl^?, Br^? or I^? gave L₂ Ni₃ in which L^3- fails to impose the intended molecular arrangement. Attempts to generate L(Pd(II))₂ (X) unexpectedly gave materials containing additional palladium, i.e. LPd₄ (CH₃ CO₂) and LPd₄ (C₃ H₃ N₂).     

New N-nitrosoamines. 1. Synthesis and nitrosative cleavage of the Mannich bases derived from nitrogen-containing heterocycles and primary aliphatic amines

The reactions of isatin, benzotriazole, and succinimide with formaldehyde and methylamine yield monoamines RCH₂N(Me)CH₂R and methylenediamines RCH₂N(Me)CH₂N(Me)CH₂R. The use of ethylenediamine as the amino component affords N,N"-disubstituted imidazolidines, while the reactions with 3-aminopropan-1-ol give N-substituted tetrahydro-1,3-oxazines. RCH₂NBuⁱ ₂ was obtained from succinimide, formaldehyde, and diisobutylamine. Nitrosative cleavage of the amines obtained was studied; it was shown that monoamines and methylenediamines give N-nitrosoamines RCH₂N(NO)Me, which were structurally characterized by X-ray diffraction analysis. RCH₂NBuⁱ ₂ affords diisobutylnitrosamine, while imidazolidines transform into dinitroso compounds RCH₂N(NO)CH₂CH₂N(NO)CH₂R.     

The effect of molecular geometry on the fragmentation of methyl esters of cyclobut-3-ene-1,2-dicarboxylic acids

Elimination of CH₃OH from the molecular ions of the methyl esters of cyclobut-3-ene-1, 2-dicarboxylic acids under electron-impact occurs to a much greater extent in stereoisomers having a trans configuration than in the cis analogues. Deuterium labelling shows that this process takes place via different mechanisms in the stereoisomeric esters. The abundance ratio [M ? CH₃OH]^˙+/[M ? CH₃O]+ is suggested as the most sensitive criterion for the deduction of configuration in this system. Determination of the geometry of the cyclobutene esters by n.m.r. spectroscopy as well as by pyrolysis to corresponding isomeric muconates is also discussed.