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

Abstract

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.

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

“…This requires highly symmetrical surroundings of the boron atom as in the cases of 'free' anions [BH 4 ] ( 1 H NMR), [BF 4 ] , also in some adducts of BF 3 ( 19 F NMR spectra) 1 or, as shown recently, for [B(CF 3 ) 4 ] [ 13 C NMR, and 19 F NMR for 2  10/11 B( 19 F)]. 2 Otherwise, the NMR signals of nuclei X linked to boron are usually broad owing to partially relaxed 11 B-X ( 11 B: I D 3/2) and 10 B-X ( 10 B: I D 3) scalar spin-spin coupling. Hence, most 1  10/11 B(X) data cannot be readily determined and, therefore, have received no attention.…”

Synthesis of 1-(2-aminopyridine)-4-phenyl-1-azabuta-1,3-diene and 1-(3-aminopyridine)-4-phenyl-1-azabuta-1,3-diene as heterodienes for iron carbonyl complexes

“…Although a large number of p-(1,3-diene) iron tricarbonyl complexes have been reported and their reactivity investigated [1], less is known of the corresponding heterodiene compounds. In such compounds, which may be regarded as derived from the basic butadiene unit by the replacement of one or more of the carbon atoms by the oxygen or nitrogen, the possibility arises that the lone pair of electrons of the heteroatom is involved with the metal-ligand bond [2][3][4][5].In this study we report the synthesis of two new Schiff bases derived from 2-aminopyridine, 3-aminopyridine and cinnamaldehyde.These compounds are potentially good ligands for iron carbonyl complexes.…”

57Fe NMR of Ferrocenes by 1H−57Fe INEPT Techniques

“…In this context, 57 Fe NMR spectroscopy 2 can provide useful data, as has been shown for ferrocene derivatives, [2][3][4][5] for CpFe half-sandwich compounds, [6][7][8][9] and for η 4 -diene iron complexes. 10,11 There is also increasing interest in applying 57 Fe NMR to the study of biologically relevant iron-containing systems. 12,13 Recently we have shown 5 that improvements in measuring 57 Fe NMR signals of ferrocenes directly by single-pulse techniques at natural abundance promise a brighter future of 57 Fe NMR as compared with the gloomy picture drawn originally.…”

“…Although the principal structural features of ferrocene derivatives are well-known, in particular in the solid state from X-ray structural analysis and in solution from 1 H, 13 C, and 31 P NMR (if appropriate) spectroscopy, more precise information on their electronic structures is still desirable. In this context, 57 Fe NMR spectroscopy can provide useful data, as has been shown for ferrocene derivatives, − for CpFe half-sandwich compounds, − and for η 4 -diene iron complexes. , There is also increasing interest in applying 57 Fe NMR to the study of biologically relevant iron-containing systems. , Recently we have shown 5 that improvements in measuring 57 Fe NMR signals of ferrocenes directly by single-pulse techniques at natural abundance promise a brighter future of 57 Fe NMR as compared with the gloomy picture drawn originally. − ,− These improvements can be traced to better NMR instrumentation (e.g., higher field strengths, B 0 , and improved hardware such as frequency generation, amplifiers, and probe head design) and also to optimized experimental parameters . Here we report on the application of polarization transfer (PT) techniques ( 1 H− 57 Fe) to ferrocenes ( 1 − 3 ).…”