The use of the bulky aryl substituent groups 2,4,6-Me₃C₆H₂ and 2,4,6-Prⁱ₃C₆H₂ has allowed the structural characterization of two monomeric boron-sulfur compounds (2,4,6-Me₃C₆H₂)₂B(SPh)1 and (2,4,6-Prⁱ₃C₆H₂)B(SPh)₂2. The crystal structures of 1 and 2 show a close alignment between the boron and sulfur p orbitals that is consistent with a π interaction. Furthermore, the B–S distances in 1[1.790(6)] and 2[1.801(6)Å] 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 π bond over the three atom BS₂π 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)Å, α= 63.52(2), β= 73.93(2), γ= 74.54(2)°, Z= 2, R= 0.073; 2, monoclinic, space group P2₁/c, a= 18.373(3), b= 12.713(2), c= 10.844(2)Å, β= 99.96(1)°, Z= 4, R= 0.072.