Isotope-induced Chemical Shifts Research Articles

Synthesis, NMR spectroscopic characterization and structure of a divinyldisilazane-(triphenylphosphine)platinum(0) complex: observation of isotope-induced chemical shifts 1 Δ12/13 C(195 Pt)

Tetramethyldivinyldisilazane-(triphenylphosphine)platinum(0) was prepared, characterized in solid state by X-ray crystallography and in solution by multinuclear magnetic resonance spectroscopy ((1)H, (13)C, (15)N, (29)Si, (31)P and (195)Pt NMR). Numerous signs of spin-spin coupling constants were determined by two-dimensional heteronuclear shift correlations (HETCOR) and two-dimensional (1)H/(1)H COSY experiments. Isotope-induced chemical shifts (1)Δ(12/13)C((195)Pt) were measured from (195)Pt NMR spectra of the title compound as well as of other Pt(0), Pt(II) and Pt(IV) compounds for comparison. In contrast to other heavy nuclei such as (199)Hg or (207)Pb, the "normal" shifts of the heavy isotopomers to low frequencies are found, covering a range of >500 ppb.

29/28, 30/28Silicon, 34/32sulfur and 80/77selenium isotope-induced fluorine chemical shifts through two bonds.

Isotope effects on fluorine chemical shifts induced by heteroatoms bonded covalently to a carbon atom bearing fluorine atoms were studied. For each compound, the isotope-induced chemical shifts 2delta19F(X) through two bonds were measured for the heteroatom (X = 29/28Si, 30/28Si, 34/32S and 80/77Se). The 1delta19F(13/12C) values for the carbon bonded to the fluorine atoms were also recorded. Examination of the 19F NMR data showed homogeneity of the isotope-induced chemical shifts along the rows of the periodic table and regularity down the columns (from 10 to 15 ppb per mass unit for the second row to 0.4 ppb for the fourth row). It became negligible for atoms of the fifth row.

Application of 207Pb NMR Parameters

AbstractFor Abstract see ChemInform Abstract in Full Text.

Isotope‐induced chemical shifts 2Δ10/11B(29Si) in alkenylsilanes containing three‐ and four‐coordinate boron. A new tool for studying weak intramolecular boron–element bonds

AbstractNumerous alkenylsilanes with silyl and boryl groups in cis ‐positions at the CC bond were studied for the first time by 29Si NMR with regard to isotope‐induced chemical shifts Δ10/11B(29Si). Such effects are transmitted across an Si—X—B bridge (X = H, OR, SR, Cl) most efficiently if the interactions in this bridge are weak. In the absence of an Si—X—B bridge, 3Δ10/11B(29Si) effects were not observed. In such cases, where, depending on the substituents, both weak and strong B—X bonding are possible, the 2Δ10/11B(29Si) effects were readily observed only for weak B—X interactions (except for X = Cl), whereas for strong B—X bonding the effects were small or not detectable. Thus, the 2Δ10/11B(29Si) values provide another tool for probing weak interactions which are not clearly reflected by other NMR data. Copyright © 2002 John Wiley & Sons, Ltd.

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

AbstractThe 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 1Δ15/14N(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

Precise measurements of 115/117/119Sn NMR frequencies and first observation of isotope-induced chemical shifts 1Δ117/119Sn( 15N), 1Δ115/119Sn( 15N), and 2Δ117/119Sn( 29Si) in N-trimethylstannyl amines

Tris(trimethylstannyl)amine 1 and trimethylsilyl-bis(trimethylstannyl)amine 2 (both ca. 13% 15N labelled) were studied by 115/117/119Sn-, 15N-, and 29Si NMR spectroscopy. Precise measurements of the Sn NMR frequencies of the respective Sn/ 15N isotopomers did not reveal any appreciable primary isotope effect, in agreement with the previous results. The standard frequencies Ξ( 119Sn) and Ξ( 117Sn), determined for tetramethyltin more than 30 years ago, were found to be very accurate, and Ξ( 115 Sn)=32.718781 MHz was measured in this work. In the 15N NMR spectra, small secondary isotope effects 1 Δ 117/119Sn( 15N) and 1 Δ 115/119Sn( 15N) could be detected for the first time, the 15N nucleus in the heavier isotopomer being more shielded. In the 29Si NMR spectrum of 2, the expected isotope-induced chemical shift 1 Δ 14/15N( 29Si) is shown, and in addition the so far unknown effect over two bonds 2 Δ 117/119Sn( 29Si) is visible.

29Si-29Si and 29Si-13C Indirect Nuclear Spin-Spin Coupling, and Isotope-Induced Chemical Shifts 1Δ 12/13C(29Si) and 1Δ 28/29Si(13C), Determined for Silenes Stabilized by Intramolecular N-Si Coordination

Abstract Silicon, Silenes Two intramolecularly donor-stabilized silenes, l-(8-dimethylamino-l-naphthyl)-l,2,2-tris-(trimethylsilyl)silene (1), and l-[bis-2 ,6 -(dimethylaminomethyl)phenyl]-l,2 ,2 -tris(trimethyl-silyl)silene 2, were studied by 2 9 Si and C NMR spectroscopy, using polarization transfer techniques in order to determine coupling constants V (2 9 Si,2 9 Si) in = 1,2, 3) and '/ (2 9 Si,l3 C) together with isotope-induced chemical shifts 1 zA12/l3 C(2 9 Si) and Z\2 8 / ~9 Si(C).

1-Boraadamantane: reactivity towards di(1-alkynyl)silicon and -tin compounds: first access to 7-metalla-2,5-diboranorbornane derivatives.

1-Boraadamantane (1) reacts with di(1-alkynyl)silicon and -tin compounds 2 (Me2M(C...CR)2: M=Si; R=Me (a), tBu (b), SiMe3 (c); M=Sn, R=SiMe3 (e)) in a 1:1 ratio by intermolecular 1,1-alkylboration, followed by intramolecular 1,1-vinylboration, to give siloles 5a-c and the stannole 5e, respectively, in which the tricyclic 1-boraadamantane system is enlarged by two carbon atoms. Owing to the high reactivity of 1, a second fast intermolecular 1,1-alkylboration competes with the intramolecular 1,1-vinylboration as the second major step in the reaction if the substituent R at the C...C bond is small (2a) and/or if the M-C... bond is also highly reactive, as in 2d (M=Sn, R= Me) and 2e (M=Sn, R=SiMe3). This leads finally to the novel octacyclic 7-metalla-2,5-diboranorbornane derivatives 8a, 8d, and 8e, of which 8e was characterized by X-ray analysis in the solid state. 1,1,2,2-Tetramethyldi(1-propynyl)disilane, MeC...C-SiMe2SiMe2-C...CMe (3), reacts with 1 to give mainly a 1,2-dihydro-1,2,5-disilaborepine derivative 9 and the octacyclic compound 11, which is analogous to 8a but with an Me4Si2 bridge. All new products were characterized in solution by 1H, 11B, 13C, 29Si, and 119Sn NMR spectroscopy. For 8 and 11, highly resolved 29Si and 119Sn NMR spectra revealed the first two-bond isotope-induced chemical shifts, 2delta10/11B(29Si) and 2delta10/11B(119Sn) respectively, to be reported.

Rigid five-coordinate diorganotin derivatives of oxalic acid diamides, studied by 119Sn-NMR and X-ray structural analysis

Bis(2-hydroxy-3,5-di- tert-butyl-phenylanilido) oxalic acid reacts with diorganotin dichlorides, R 2SnCl 2, in the presence of triethylamine to give the polycyclic bis(diorganotin) derivatives 1, in which the surroundings of each tin atom correspond to a distorted trigonal bipyramid with one nitrogen and two carbon atoms in the equatorial and two oxygen atoms in the axial positions. The solid state structure was established for 1a (R=Me) by X-ray analysis, and the agreement between the 119Sn chemical shift in the solid state and in solution suggests that this structure is retained in solution. It was possible for the first time to determine isotope-induced chemical shifts 1Δ 12/13C( 119Sn) for five-coordinate tin nuclei at natural abundance of 13C. A positive sign of 1Δ 12/13C( 119Sn) was found for R=Me ( 1a), Bu ( 1b) and Ph ( 1c).

NMR study of spirophosphoranes derived from 2-aminophenols

Multinuclear magnetic resonance experiments were performed (1H, 13C, 31P, and 15N) for P-H phosphoranes derived from 2-aminophenol, 4-tert-butyl-2-aminophenol, and 4,6-di-tert-butyl-2-aminophenol. Selective heteronuclear 1H{15N} double resonance experiments and two-dimensional 15N/1H HETCOR experiments enabled us to determine various signs of coupling constants (e.g., 2J(31P, N, 1H) > 0; 1J(31P, 15N) < 0). The 1H-coupled 15N NMR spectrum recorded by the INEPT pulse sequence shows the splitting due to 1J(31P, 15N) and 2J(15N, P, 1H). The latter value is useful for polarization transfer experiments from 1H to 15N, once the hydrogen atoms of the N-H functions are replaced by other groups. Isotope-induced chemical shifts 1Δ14/15N(31P) were measured by using the INEPT-HEED pulse sequence. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:11–15, 2000

Isotope-induced chemical shifts1?12/13C(29Si) and57Fe NMR of organosubstituted 2,5-dihydro-1,2,5-azasilaboroles, a silole and their tricarbonyliron complexes

2,5-Dihydro-1,2,5-azasilaboroles (1) (cyclic heterodienes) readily form tricarbonyliron complexes (3) and both are compared with a silole (2) and its tricarbonyliron complex (4). The compounds 1–4 were studied with respect to isotope-induced chemical shifts 1Δ12/13C(29Si). The data set indicates that the interpretation of 1Δ12/13C(29Si) is not straightforward. Although there may be a crude correlation between 1Δ12/13C(29Si) and the magnitude of |1J(29Si,13C| within each class of compounds [e.g., in the series Me4 −nSi(CCMe)n (n = 0, 1, 2, 3, 4)], a direct relationship between different classes is not apparent, even for different Me groups linked to the same silicon atom (3, 4). 57Fe NMR (16.2 MHz) measurements are reported for the first time, using standard NMR equipment and ca 0.5 M solutions in 5 mm tubes. The 57Fe nuclear shielding in the heterodiene complexes is reduced by 500–600 ppm with respect to that of the silole complex (δ57Fe = +241.2). Copyright © 2000 John Wiley & Sons, Ltd.

N-Triorganostannyl‐substituted pyrroles and indoles and N-trimethylstannylcarbazole: determination of signs of coupling constants and isotope‐induced chemical shifts 1Δ1415N(119Sn)

N-Triorganostannyl (R3Sn)-substituted pyrroles (1) and indoles (2) [R=Me (a), Et (b), tBu (c)], N-trimethylstannyl-carbazole (3), N-trimethylstannyl-2,5-dimethylpyrrole (1d), the corresponding silicon and lead derivatives [1d(Si) and 1d(Pb)] and N-trimethylstannyl-2-methylindole (2d) were prepared and studied by multinuclear magnetic resonance (1H, 13C, 15N, 29Si, 119Sn and 207Pb NMR). The absolute signs of numerous coupling constants nJ(119Sn,13C) and 1J(119Sn,15N) (<0) were determined by appropriate 2D heteronuclear shift correlations of the type 13C/1H and 15N/1H. Precise measurement of the coupling constants 1J(119Sn,15N) from 119Sn NMR spectra by using Hahn-echo extended (HEED) polarization transfer pulse sequences enabled one to obtain isotope-induced chemical shifts 1Δ14/15N(119Sn) at natural abundance of 15N. The 1Δ14/15N(119Sn) data become more negative with increased branching of the substituent R at the tin atom and with stronger steric interactions. The latter effect is also evident from δ119Sn values and changes in the magnitude of the coupling constants 1J(119Sn,13C) or 1J(119Sn,15N). © 1998 John Wiley & Sons, Ltd.

Coupling Sign Determination and Isotope-Induced Chemical Shifts1Δ15/14N(29Si),1Δ15/14N(119Sn) and1Δ29/28Si(15N): Multinuclear Magnetic Resonance Study ofN-Trimethylsilyl-, -stannyl- and -plumbyl-Substituted 2-Aminopyridines, 2,6-Diaminopyridines and Analogous 2-Picolines

2-Aminopyridines (1), 2-amino-3-methylpyridines (2) and 2,6-diaminopyridines (3), bearing N-trimethylsilyl, -stannyl or -plumbyl groups, and analogously substituted 2-picolines (4) were studied by 1H, 13C, 15N, 29Si, 119Sn and 207Pb NMR spectroscopy. Intramolecular N—Sn coordination became evident in the case of N,N-trimethylsilyl(trimethylstannyl)-2-aminopyridine (1e) and N,N-trimethylsilyl(trimethylstannyl)-N-trimethylsilyl-2,6-diaminopyridine (3f), in particular from their δ15N(amine) and δ119Sn data. Numerous coupling constants J(M,15N) and J(M,13C) (M = 29Si, 119Sn, 207Pb) were measured and, in the case of 2-[trimethylsilyl(trimethylstannyl)]methylpyridine (4e), absolute signs of nJ(119Sn,13C) and n+1J(119Sn,1H) were determined by appropriate 2D 13C/1H heteronuclear shift correlations. Isotope-induced chemical shifts 1Δ15/14N(29Si) (range -9 to -16 ppb) and 1Δ15/14N(119Sn) (range -32 to -55 ppb) were measured at natural abundance of 15N by using Hahn-echo extended polarization transfer pulse sequences. 1Δ29/28Si(15N) values (range of -2.4 to -6.0 ppb) were measured from 15N NMR spectra.