Evidence for ? Bonding in the Boron-Thiolate Compounds (2,4,6-Me3C6H2)2B(SPh) and (2,4,6-i-Pr3C6H2)B(SPh)2

Article abstract of DOI:10.1039/DT9940002113

The use of the bulky aryl substituent groups 2,4,6-Me3C6H2 and 2,4,6-i-Pr3C6H2 has allowed the structural characterization of two monomeric boron-sulfur compounds (2,4,6-Me3C6H2)2B(SPh) 1 and (2,4,6-i-Pr3C6H2)B(SPh)2 2.The crystal structures of 1 and 2 show a close alignment between the boron and sulfur p orbitals that is consistent with a ? interaction.Furthermore, the B-S distances in 1 <1.790(6)> and 2 <1.801(6) Angstroem> are slightly shorter than the sum of the covalent radii (with allowance made for ionic effects) of boron and sulfur.Variable-temperature 1H and 13C NMR data for 2 indicate an average barrier to rotation around the B-S bond of ca. 12 kcal mol^-1.This value is significantly less than the 18.4 kcal mol^-1 reported earlier for 1.The lower rotational barrier observed in 2 is consistent with the delocalization of the B-S ? bond over the three atom BS2 ? system which has a similar electronic arrangement to that of an allyl anion.Crystal data at 130 K: 1, triclinic, space group P<*>, a = 7.851(5), b = 11.685(6), c = 13.096(7) Angstroem, α = 63.52(2), β = 73.93(2), γ = 74.54(2) deg, Z = 2, R = 0.073; 2, monoclinic, space group P2₁/c, a = 18.373(3), b = 12.713(2), c = 10.844(2) Angstroem, β = 99.96(1) deg, Z = 4, R = 0.072.

Full text of DOI:10.1039/DT9940002113

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