Probing interactions through space using spin–spin coupling

Abstract

A series of eight 5-(TeAr)-6-(SePh)acenaphthenes (Ar = aryl) were prepared and structurally characterised by X-ray crystallography, solution and solid-state NMR spectroscopy and DFT/B3LYP calculations.

Sterically Restricted Tin Phosphines, Stabilized by Weak Intramolecular Donor–Acceptor Interactions

“…0.18 computed for these separations indicate a significant degree of covalency between the peri-substituents in these systems, and under appropriate geometric conditions this can be traced back to weak donor-acceptor type interactions and the onset of 3-center-4-electron (3c4e) bonding. 20,22,[25][26][27][28] Similar weak donor-acceptor interactions were observed during a recent study of sterically crowded bromine-tin derivatives (E Figure1), which became more prevalent with the increasing Lewis acidity of the tin centre as a result of contrasting substituent effects. 24 In conjunction with X-ray structural data, indirect spin-spin coupling constants (SSCCs) present a convenient method for analyzing the extent of chemical bonding between two atoms.…”

“…Such, attractive, interactions which lead to peri-distances significantly shorter than the sum of van der Waals radii (1 3.2511(19) Å, 2 2.815(3) Å, 3 2.912(3) Å,4 2.8721(10) Å; r vdW (SnP) 3.97 Å), 6 have been shown to partially counterbalance steric repulsion between heavier congeners in peri-substituted systems and thus play an important role in controlling their fine structures (G-dependence). 8,[20][21][22][25][26][27][28] The steric and electronic effects of substituents (Y) attached to the peri-atoms must also be considered however, as subtle changes to the size and donor/acceptor properties of Y can greatly influence the underlying bonding situation and thus the particular conformations that ensue (Y-dependence). This is aptly demonstrated by comparing the contrasting size of the peri-distance in triphenyltin derivative 1 (3.2511(19) Å) with the much smaller distances exhibited by triorganotin chlorides 2-4 (2.815(3) Å-2.912(3) Å), indicative of much stronger donor-acceptor interactions in the latter as a result of replacing a phenyl group with a highly electronegative chlorine atom, subsequently increasing the Lewis acidity of the tin centre.…”

“…[20][21][22][25][26][27][28] Each Sn-Y/P-C iPr substituent bond is designated as either type A (perpendicular), B (coplanar) or C (intermediate) depending upon the relative alignment with respect to the mean acenaphthene plane. 8 The absolute conformation of the peri-substituents is determined from C-C-Z-Y torsion angles θ, which define the degree of rotation around the Z-C Acenap bonds (Table S3).…”

“…19 During our own investigations it emerged that in systems containing pnictogen and chalcogen moieties in the peri-positions, steric repulsion can be partly counterbalanced by attractive intramolecular interactions. [20][21][22][23][24][25][26][27][28] In particular, with heavier congeners such as tellurium occupying the proximal positions (K-O Figure 1), 20.22,25-28 but still formally nonbonded "across-the-bay", distances significantly shorter than the sum of the van der Waals radii were achieved. Wiberg bond indices (WBIs) 29 of up to ca.…”

“…25 Even larger SSCCs are observed in the neutral mixed tellurium-selenium (N 688-748 Hz) and bis-tellurium (O 2110-3398 Hz) systems. 22,[25][26][27][28] The question now arises, how much of the observed spin-spin coupling in these sterically restrained systems is transmitted via the overlapping lone-pairs and how much is due to the polarized electrons in the succession of bonds that link the interacting nuclei. A good illustration of the through-space contribution to the overall coupling in these systems is found by comparing the 4 J( 31 P, 77 Se) coupling constant of phosphine I (391 Hz), in which the lone-pair on phosphorus is free to interact, with the value observed for equivalent phosphine oxides of type J (19)(20)(21)(22)(23)(24) where the lone-pair is now taken up in the P=E double bond (E = S/Se).…”