Torsional Angular Dependence of ¹J(Se,Se) and Fermi Contact Control of ⁴J(Se,Se): Analysis of ⁿJ(Se,Se) (n=1–4) Based on Molecular Orbital Theory

Abstract

(n)J(Se,Se) (n=1-4) nuclear couplings between Se atoms were analyzed by using molecular orbital (MO) theory as the first step to investigating the nature of bonded and nonbonded (n)J(Se,Se) interactions between Se atoms. The values were calculated by employing Slater-type triple xi basis sets at the DFT level, which were applied to structures optimized with the Gaussian 03 program. The contribution from each occupied MO (psi(i)) and psi(i)-->psi(a) (psi(a)=unoccupied MO) transition was evaluated separately. 1J(Se,Se) was calculated for the MeSeSeMe model compound, which showed a typical dependence on the torsion angle (phi(C(Me)SeSeC(Me))). This dependence explains the small values (< or =64 Hz) of 1Jobsd(Se,Se) observed for RSeSeR' and large values (330-380 Hz) of 1Jobsd(Se,Se) observed for 4-substituted naphtho[1,8-c,d]-1,2-diselenoles, which correspond to synperiplanar diselenides. The HOMO-->LUMO and HOMO-1-->LUMO transitions contribute the most to 1J(Se,Se) at phi=0 and 180 degrees to give large values of 1J(Se,Se), whereas various transitions contribute and cancel each other out at phi=90 degrees to give small values of 1J(Se,Se). Large 4Jobsd(Se,Se) values were also observed in the nonbonded Se...Se, Se...Se=O, and O=Se...Se=O interactions at naphthalene 1,8-positions. The Fermi contact (FC) term contributes significantly to 4J(Se,Se), whereas the paramagnetic spin-orbit (PSO) term contributes significantly to 1J(Se,Se). 2J(Se,Se) and 3J(Se,Se) were analyzed in a similar manner and a torsional angular dependence was confirmed for 3J(Se,Se). Depending on the structure, the main contribution to (n)J(Se,Se) (n=2, 3) is from the FC term, with a lesser contribution from the PSO term. Analysis of each transition enabled us to identify and clearly visualize the origin and mechanism of the couplings.

Intramolecular Nonbonded Interactions Between Divalent Selenium Centers with Donor and Acceptor Substituents

“…[30] In systems such as 1,8-bis(selanyl)naphthalene derivatives, in which both Se centers are forced into close proximity, considerably larger values of 4 J Se,Se have been reported. [31] Conformational Analysis of 1-3…”

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

“…The magnitude of throughspace coupling, which is dependent upon the spacial distribution of electron density between the coupling nuclei, thus provides a good indication of any covalent contributions to the intramolecular lone-pair bonding interaction. [30][31][32][33][34] For instance, the exceptionally large J( 19 F, 19 F) SSCCs observed in the series of peri-difluoronaphthalenes F (65-85 Hz) were attributed to a significant 19 F-19 F through-space interaction which was found to rely heavily on the internuclear separation. 32 Bis-phosphines of type G 33 and selenium derivatives of type H 34 exhibit similar lone-pair interactions across the peri-gap, with 4 J( 31 P, 31 P) coupling constants in the former (222-246 Hz) of the same magnitude as 1 J-couplings for conventional P-P bonds (cf.…”

Analysis of One‐Bond Se‐Se Nuclear Couplings in Diselenides and 1,2‐Diselenoles on the Basis of Molecular Orbital Theory: Torsional Angular Dependence, Electron Density Influence, and Origin in 1J(Se, Se)

“…How do 1 J obsd (Se, Se: 2 ) depend on the substituent Y in 2 ? 1 J (Se, Se) are analyzed on the basis of the MO theory, as the first step to investigate the nature of the bonded and nonbonded interactions between selenium atoms through n J (Se, Se) [18]. 1 J (Se, Se) are calculated for 1a and 2a – g .…”