(3h)J((15)N-(31)P) spin-spin coupling constants across N[bond]H....O[bond]P hydrogen bonds

Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) calculations have been performed to evaluate three-bond (15)N-(31)P coupling constants ((3h)J(N[bond]P)) across N[bond]H....O[bond]P hydrogen bonds in model cationic and anionic complexes including NH(4)(+):OPH, NH(4)(+):OPH(3), NH(3):(-)O(2)PH(2), NFH(2):(-)O(2)PH(2), and NF(2)H:(-)O(2)PH(2). Three-bond coupling constants can be appreciable when the phosphorus is P(V), but are negligible with P(III). (3h)J(N[bond]P) values in complexes with cyclic or open structures are less than 1 Hz, a consequence of the nonlinear arrangement of N, H, O, and P atoms. For complexes with these structures, (3h)J(N[bond]P) may not be experimentally measurable. In contrast, complexes in which the N, H, O, and P atoms are collinear or nearly collinear have larger values of (3h)J(N[bond]P), even though the N[bond]P distances are longer than N[bond]P distances in cyclic and open structures. In linear complexes, (3h)J(N[bond]P) is dominated by the Fermi-contact term, which is distance dependent. Therefore, N[bond]P (and hydrogen-bonding N[bond]O) distances in these complexes can be determined from experimentally measured (15)N-(31)P coupling constants.     

Observation of (31)P-(31)P Indirect Spin-Spin Coupling in Copper-Bis(phosphine) Complexes by Two-Dimensional Solid-State NMR

The first observations of (31)P-(31)P indirect spin-spin (J) coupling in copper(I) phosphine complexes are reported for solid Cu(PPh(3))(2)X (X = NO(3)(-), BH(4)(-)). Values of (2)J((31)P,(31)P), 157 +/- 5 and 140 +/- 5 Hz for Cu(PPh(3))(2)NO(3) and Cu(PPh(3))(2)BH(4), respectively, have been obtained from two-dimensional (2D) J-resolved (31)P NMR spectra obtained under slow magic-angle spinning (MAS) conditions. In both complexes, the two phosphine ligands are crystallographically equivalent; thus, the two (31)P nuclei have identical isotropic chemical shifts. Under rapid sample spinning conditions, the (31)P MAS NMR spectra exhibit relatively sharp overlapping asymmetric quartets arising from (1)J((63/65)Cu,(31)P) and residual (63/65)Cu-(31)P dipolar interactions. No evidence of (2)J((31)P,(31)P) is apparent from the spectra obtained with rapid MAS; however, under slow MAS conditions there is evidence of homonuclear J-recoupling. Peak broadening due to heteronuclear dipolar interactions precludes measurement of (2)J((31)P,(31)P) from standard 1D (31)P MAS NMR spectra. It is shown that this source of broadening can be effectively eliminated by employing the 2D J-resolved experiment. For the two copper(I) phosphine complexes investigated in this study, the peak widths in the f(1) dimension of the 2D J-resolved (31)P MAS NMR spectra are about three times narrower than those found in the corresponding 1D (31)P MAS NMR spectra.     

Trans-hydrogen-bond (h2)J(NN) and (h1)J(NH) couplings in the DNA A-T base pair: natural bond orbital analysis

Natural bond orbital (NBO) analysis described here demonstrates that trans-hydrogen-bond (trans-H-bond) NMR J couplings in the DNA A-T base pair, h2JNN and h1JNH, are determined largely by three terms: two Lewis-type contributions (the single-orbital contribution from the adenine lone pair and the contribution from the sigmaN3H3 natural bond orbital of the thymine ring) and one contribution from pairwise delocalization of spin density (between the lone pair in adenine and the sigma* antibonding orbital linking N3 and H3 of thymine). For h2JNN coupling, all three contributions are positive, whereas for h1JNH coupling, the delocalization term is negative, and the other two terms are positive, resulting in a small net positive coupling constant. This result rationalizes the experimental findings that the two-bond coupling (h2JNN approximately 9 Hz) is larger than the one-bond coupling (h1JNH approximately 3 Hz) and demonstrates that the same hyperconjugative and steric mechanisms that stabilize the H-bond are involved in the transmission of J coupling information. The N1...H3-N3 H-bond of the DNA A-T base pair is found to exhibit significant covalent character, but steric effects contribute almost equally to the trans-H-bond coupling.     

Determination of (3)J((1)H3'-(31)P) couplings in a DNA oligomer with enhanced sensitivity employing a constant-time TOCSY difference experiment

A constant-time TOCSY difference experiment for the determination of (3)J((1)H3'-(31)P) coupling constants in non-isotope-labelled DNA oligonucleotides is presented. The method is tested on a DNA octamer and compared with the established constant-time NOESY difference method. Each (3)J((1)H3'-(31)P) coupling constant is determined from amplitude changes caused by phosphorous decoupling, which are observable on multiple cross-peaks, thus leading to a high accuracy of the value of the (3)J((1)H3'-(31)P) coupling constant. The new experiment delivers up to three times the sensitivity compared with previously reported methods.     

A polarization propagator analysis of the geminal 31P-31P coupling in bis(difluorophosphino)amine⋆

Inner projections of the polarization propagator (IPPP) are used to decompose in through-space and through-bond contributions the two-bond P-P coupling in PF₂-NH-PF₂. This study is carried out using a ground state INDO wavefunction. Results for a phosphorus sp and spd atomic basis sets are compared. Several experimental trends are correctly reproduced using either of them. It is concluded that the overlap of the lone pair of both P atoms constitutes a very efficient pathway for transmitting through-space the spin information associated to the Fermi contact term.Part of a PhD thesis (H.O.G.) to be presented to the University of Buenos AiresFellow of the Argentine National Research Council (CONICET)Member of the Argentine National Research Council (CONICET)     

The through-space transmission of 31P-31P coupling constants

Inner projections of the polarization propagator (IPPP) are used to study several features of the throughspace transmission of ³¹P-³¹P coupling constants. Cis-1,2-diphosphinoethylene is chosen as a model compound. INDO ground state wave functions are used, including two different second-row parameterizations. Results obtained with a phosphorus spd basis set are also presented. It is found that the overlap of phosphorus lone-pairs constitute an efficient coupling pathway. Results are discussed in terms of experimental values for similar compounds taken from the literature. Theoretical predictions are in line with experimental trends.     

31P-{1H} NMR spectra of some o-tolylbis (triphenylphosphine)nickel derivatives

Conclusion ³¹P NMR spectroscopy was used to show that o-tolylbis(triphenylphosphine)nickel carboxylates may exist in solution in two forms. A study of the exchange reactions of these complexes with triphenylphosphine indicated that the difference between these forms is a consequence of the chelation or lack of chelation of the nickel atom with the carboxylate group oxygen.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1028–1031, May, 1988.     

31P-, 119Sn- and 195Pt-NMR. Studies of Trichlorostannate Complexes of Pt(II) and Pd(II). 2J(119Sn, 117Sn)-Values

The synthesis and solution structures of new four- and five-coordinate phosphine and arsine complexes of Pt and Pd containing the trichlorostannate ligand are described. Complexes containing two and three SnCl^?₃-ligands have been identified from their ³¹P-, ¹¹⁹Sn- and ¹⁹⁵Pt-NMR. spectra. The complexes trans-[M (SnCl₃)₂L₂] (M = Pt, L-PEt₃, PPr₃, AsEt₃; M = Pd, L = AsEt₃) show unexpectedly large ²J(¹¹⁹Sn, ¹¹⁷Sn)-values (34,674–37,164 Hz) with the trans-orientation of these spins playing an important role. The heteronuclear coupling constant ²J(¹¹⁹Sn, ³¹P) in the five-coordinate cationic complexes [Pt(SnCl₃)(P(o-AsPh₂? C₆H₄)₃)]⁺ and [Pt(SnCl₃)(As(o-PPh₂? C₆H₄)₃)]⁺ also shows a geometric dependence. New five-coordinate anionic complexes of type [M (SnCl₃)₃L₂]^? (M = Pd, Pt; L = PEt₃, AsEt₃) may be prepared via addition of three mol-equiv. of SnCl₂ and one mol-equiv. of (PPN)Cl to [MCl₂L₂] in acetone.     

CLOPPA-IPPP analysis of electronic mechanisms of intermolecular (1h)J(A,H) and (2h)J(A,D) spin-spin coupling constants in systems with D-H...A hydrogen bonds

The electronic origin of intermolecular (2h)J(A,D) and (1h)J(A,H) couplings is discussed by means of the CLOPPA-IPPP approach in several model complexes with D-H...A hydrogen bonds. It is found that the origin of these couplings is mainly due to the interaction between the acceptor sigma lone pair and vacant molecular orbitals localized in the D-H...A moiety, regardless of the donor and acceptor nuclei. The problem of the larger absolute value of (2h)J(A,D) compared to (1h)J(A,H) is also addressed.     

Application of P-31 NMR to the Study of Phosphorylated/Cellulose and Lignocellulosic Materials(Wood)

Phosphorylation of cellulose and wood(also named as lignocellulosic material) is one of the potential methods for chemical modification of these natural polymers. In this research, α-cellulose and wood meals (extracts free) were mixed with certain organophosphoryl chloride compounds, producing the corresponding phosphorylated derivatives. A series of model chemicals (e.g. ethylene glycol, glucose, cellobiose, phenols,guaiacol, etc.) were converted to the same derivatives as references. The phosphorylated products were examined by using P-31 NMR spectroscopy to analyze their structural characteristics.     

Internuclear (31)P-(51)V distance measurements in polyoxoanionic solids using rotational echo adiabatic passage double resonance NMR spectroscopy

We report the first results establishing rotational echo adiabatic passage double resonance (REAPDOR) experiments for distance measurements between a spin-1/2 (31P) and spin-7/2 (51V) pair in a series of vanadium-substituted polyoxoanionic solids from the Keggin and Wells-Dawson families. We have quantitatively measured 31P-51V distances in monovanadium substituted K4PVW11O40, 1-K7P2VW17O62, and 4-K7P2VW17O62. Numerical simulations of the experimental data yield very good agreement with the averaged P-W/P-V distances determined from the X-ray diffraction measurements in the same or related compounds. REAPDOR is therefore a very sensitive P-V distance probe anticipated to be especially useful in the absence of long-range order. Our results suggest that REAPDOR spectroscopy could be broadly applicable for interatomic distance measurements in other spin-7/2-spin-1/2 nuclear pairs.     

Long-Range 31P-31P Spin Coupling Constants in the 31P NMR Spectra of Phosphite Triesters

Abstract

Data are presented on the magnitudes of ⁵ J _pp and ⁶ J _PP spin-spin coupling constants in the ³¹P NMR spectra of a variety of novel polyphosphite triesters.     

Reactions of alkynes with bis(triphenylphosphine)platinum-ethylene: A 31P-{1H} NMR study

Internally consistent assignments of the ³¹P-{¹H} NMR parameters of the complexes [Pt(RCCR′)(PPh₃)₂] are proposed, based on the premise that the magnitude of ¹J(PtP) depends mainly on the nature of the moiety CR trans to P. For a given R, ²J(PP) correlates with ¹J(PtP) for thebond trans to CR. The alkynes PhCCSnEt₃, PhCCSnPh₃, Me₃SiCCCl, Me₃SiCCBr, Et₃SiCCI and MeCCI undergo oxidative addition reactions with [Pt(C₂H₄)(PPh₃)₂]; the intermediate alkyne complex was detected for PhCCSnEt₃, Me₃SiCCCl and Me₃CCBr. The triyne Me(CC)₃Me forms platinum(0) complexes by coordination with the central or terminal CC bond and appears also to give a platinum(II) complex by oxidative addition.     

P-31 MR Spectroscopic Analysis of Human Colon Cancer

Abstract

Phosphatic metabolic profiles of nineteen malignant and normal human colon specimens were analyzed by techniques of perchloric acid extraction and ³¹P MR spectroscopy at 202.4 MHz. Thirty-one individual phosphorus-containing intermediaries of metabolism were identified and their relative concentrations in mole-percentages of phosphorus were computed. Metabolic indices representing ratios and sums of individual or grouped metabolites were concurrently computed. The individual metabolite concentrations and metabolic indices were statistically compared revealing significant differences between malignant and normal tissues (see table). Malignant tissues demonstrate significant increases in the phosphomonoesters and diesters along with corresponding decreases in the high-energy phosphate compounds. While these changes may be relative, the increases in the PME and PDE bands most likely represent an increase in cell membrane activity ind P-lipid metabolism. P-31 MR is effective in differentiating malignant from normal tissues.     

(h4-Dibenzylideneacetone)pentamethylcyclopentadienylrhodium(I)

dibenzylideneacetone can act as a 1,4-diene in bonding to a single metal atom and this has been shown by the synthesis of (h⁴-dibenzylideneacetone)pentamethylcyclopentadienylrhodium(I).     

P-31 Solid State Nuclear Magnetic Resonance Investigations on Cyclophosphazenes

Abstract

The present study deals with solid state NMR investigations on cyclophosphazeaes wah the following substituents: -NH₂, -OMe, -F, -Cl, -Br, at which the substituent atoms are elements of the 2^nd period (N, O, and F) or elements of the 7^th main group (F, Cl, and Br). The NMR spectra were obtained by a BRUKER MSL 300 spectrometer using a resonance frequenacy of 121.496 MHz. With each compound a static powder spectrum, a hgh speed MAS spectrum, and several side band spectra were recorded.     

Aminophosphanes with bulky amino groups: Molecular structure,coupling constants 1J(31P, 15N) and 2J(31P, 29Si), and isotope‐induced chemical shifts 1Δ14/15N(31P)

The preferred conformation of aminophosphanes with bulky amino groups ( 1–20 ) was determined by NMR spectroscopy in solution, in two cases in the solid state ( 11,17 ) and in one case ( 11 ) by X‐ray crystallography. Trimethylsilylaminodiphenylphosphanes Ph₂PN(R)SiMe₃ (R = Bu ( 1 ), Ph ( 2 ), 2‐pyridyl ( 3 ), 2‐pyrimidyl ( 4 ), Me₃Si ( 5 )), amino(chloro)phenylphosphanes Ph(Cl)PNRR′ (R = Bz, R′ = Me ( 6 ), R = Bz, R′ = ^tBu ( 7 ), R = Et, R′ = Ph ( 8 )), amino(chloro)tert‐butylphosphanes ^tBu(Cl)PNRR′ (R = R′ = ⁱPr ( 9 ), R = Me, R′ = ^tBu ( 10 ), R = Bz, R′ = ^tBu ( 11 ), R = H, R′ = ^tBu ( 12 ), R = Et, R′ = Ph ( 13 ), R = ⁱPr, R′ = Ph ( 14 ), R = Bu, R′ = Ph ( 15 ), R = Bz, R′ = Ph ( 16 ), R = R′ = Ph ( 17 ), R = R′ = Me₃Si ( 18 )), 3‐tert‐butyl‐2‐chloro‐1,3,2‐oxazaphospholane ( 19 ), and benzyl(tert‐butyl)aminodichlorophosphane ( 20 ) were studied by ¹H, ¹³C, ¹⁵N, ²⁹Si, and ³¹P NMR spectroscopy. In all cases, the more bulky substituent at the nitrogen atom prefers the syn‐position with respect to the assumed orientation of the phosphorus lone pair of electrons. Many of the derivatives studied adopt this preferred conformation even at room temperature. Numerous signs of coupling constants ¹J(³¹P, ¹⁵N), ²J(³¹P, ¹³C), and ²J(³¹P, ²⁹Si) were determined. Low temperature NMR spectra were measured for derivatives for which rotation about the P N bond at room temperature is fast, showing the presence of two rotamers at low temperature. The respective conformation of these rotamers could be assigned by ¹³C, ¹⁵N, and ³¹P NMR spectroscopy. Isotope‐induced chemical shifts ¹Δ^15/14N(³¹P) were determined for all compounds at natural abundance of ¹⁵N by using Hahn‐echo extended polarization transfer experiments. The molecular structure of 11 in the solid state reveals pyramidal surroundings of the nitrogen atom and mutual trans‐positions of the tert‐butyl groups at phosphorus and nitrogen. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:667–676, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10084