Interet de la deuteriation des molecules organostanniques en RMN de 119Sn

Karplus‐Type Dependence of Vicinal 119Sn‐13C and 119Sn‐1H Spin‐Spin Couplings in Organotin(IV) Derivatives: A DFT Study

“…Kitching and co-workers, starting from a small set or rigid polycyclic organotin(IV) compounds, proposed a Karplus-type equation which correlates the 3 J( 119 Sn-C-C-13 C) with the dihedral angle, φ; [15,16] they also pointed out that the occurrence of more than one conformer in solution for flexible cyclic systems must be taken into account when structural assignments are inferred from the vicinal coupling constants. [17] A similar equation was derived by Quintard and coworkers for 3 J( 119 Sn-C-C-D) [18] from which it is possible to obtain the corresponding 3 [20] Conformational studies of organotin derivatives can greatly benefit from the use of Karplus-type equations: for example, weak tin-donor interactions, mainly of van der Waals nature, rather than true coordination bonds, have been highlighted by applying the above Karplus-type relationships to 3 J( 119 Sn, 13 C) and 3 J( 119 Sn, 1 H) in gem-bis(tributylstannyl) compounds. [21] Three-bonds coupling constants 3 J( 119 Sn, X) are influenced by the kind of atoms in the bonding path and possibly by the substituent groups bound to them.…”

Identification of Chiral cis‐ and trans‐2‐Stannyloxazolidines by Their NMR Spectra and Solid‐State Structures

“…J( 119 SnϪCϪCϪD), [15] 3 J( 119 SnϪCϪCϪ 31 P) [16] or 3 J( 119 SnϪCϪCϪ 119 Sn) [17] in saturated systems and have been used for identification of geometrical isomers such as vinyl and dienyltins, for example. [18] When a heteroelement has been introduced into the linkage Ϫ as in 3 J(HϪSiϪCϪH) [19] or 3 …”

“…[15] Accordingly, in the present case, for a homogeneous series, a more reliable way to evaluate dihedral angles would be to examine 3 J( 119 SnϪCϪN(PG)Ϫ 13 C) values (for PG ϭ Ts and PG ϭ CO 2 R) and 3 J( 119 SnϪCϪOϪ 13 C) values after measurement of these 3 J values in compounds with a dihedral angle close to 180°(anti relationship). As these curves are likely to follow Karplus-type variations as a function of the relative spatial orientation of Sn and Cγ, these experimentally determined values for a 180°dihedral angle should reflect the modification of the electron spin density by the presence of the heteroatom in the linkage with subsequent effects on the 3 J(Sn, C) values.…”

“…[12,13] This means that a similar curve with a decrease in values of coupling constants by about 10Ϫ15% should be observed in tributylstannyl series if one refers to the effect of substituents on tin for 3 J( 119 SnϪCϪCϪ 13 C) [24,25] or 3 J( 119 SnϪCϪCϪD) values. [15,26,27] The effect of N(PG) in the transmission of couplings for 3 J( 119 SnϪCϪN(PG)Ϫ 13 C) can be broadly taken into account with this type of evaluation. The observation of a 3 J value of 11.8 Hz made recently by Gawley for a 120°dihedral angle in a SnϪCϪNϪC linkage is not in good agreement with these curves, but it should be taken into account that this observation was made on a strained isoquinuclidine skeleton with subsequent alteration of the electron density due to a modification of the s character of the bonding.…”

“…[8] The NMR spectroscopic data for unsubstituted 2-stannyloxazolidines 3 and 13 (analogues of perhydroxazines 4 and 14) in N-Ts and N-CO 2 Me derivatives, respectively, are given in Table 2 and Table 3 for comparison, as examples of more flexible systems. The last available parameter, the 119 Sn chemical shift, though highly sensitive for discrimination between very similar organostannanes, [15,26,30] is almost useless for primary identification because of its extreme sensitivity to steric effects, [27] to solvation and to chelation effects. [31] …”