Reactions of (Me3SiCH2)2AsSiMe3 with gallium halides. Crystal structure and dynamic NMR study of the dimer {[(Me3SiCH2)2As]2GaBr}2

Article abstract of DOI:10.1021/om00153a012

(Me₃SiCH₂)₂AsSiMe₃ reacted with the gallium halides GaBr₃, MeGaCl₂, and PhGaCl₂ to produce the (arsino)gallanes [(Me₃SiCH₂)₂AsGaBr₂]₃, {[(Me₃SiCH₂)₂As]₂GaBr}₂, [(Me₃SiCH₂)₂AsGaMeCl]_n (n = 2, 3), and [(Me₃SiCH₂)₂AsGaClPh]_n (n = 2, 3), which were characterized by elemental analysis (C and H), ¹H and C NMR spectroscopy, and cryoscopic molecular weight determinations. A single-crystal X-ray diffraction study of {[(Me₃SiCH₂)₂As]₂GaBr}₂ was carried out. Crystal data are as follows: triclinic, space group P1, a = 11.892 (2) ?, b = 12.492 (2) ?, c = 11.515 (1) ?, α = 98.24 (1)°, β = 113.57 (1)°, γ = 84.21 (1)°, V = 1549.9 ?³, Z = 1. The centrosymmetric, dimeric molecule crystallizes in the trans configuration, with unequal endocyclic Ga-As distances [2.513 (1) ? and 2.521 (1) ?] and very significantly different bond angles [84.37 (1)° and 95.63 (2)°, respectively, at Ga and As] in the planar (Ga-As)₂ ring. The Ga-exo-As distance of 2.437 (1) ? is the shortest yet measured in an organogallium-arsenic compound. A ¹³C{¹H} dynamic NMR study of {[(Me₃SiCH₂)₂As]₂GaBr}₂ revealed that both an interchange of the (Me₃SiCH₂)₂As groups [ΔH? = 18.7 ± 0.3 kcal/mol; ΔS? = 4.5 ± 1.0 cal/(mol K)] and a trans-cis isomerization [ΔH? = 17.4 ± 0.7 kcal/mol; ΔS? = -2.2 ± 2.1 cal/(mol K)] take place.