Halostibines SbMeX₂ and SbMe₂X: Lewis Acids or Lewis Bases?

Abstract

Alkylhalostibines have been shown to behave either as Lewis acids toward appropriate neutral ligands or as Lewis bases to low-valent metal fragments. The boundaries of their Lewis acid and Lewis base behavior have been determined, and the structural and spectroscopic consequences of the different behaviors probed. [SbMeX 2 (L−L)] (L−L = 2,2′-bipyridyl, 1,10-phenanthroline) and [SbMeX 2 (L) 2 ] (L = OPMe 3 , OPPh 3 ) are five-coordinate, distorted squarepyramidal monomers with the Me group axial, with the bond distances little affected by coordination. Significant changes in the bonding within the group 6 carbonyl complexes [M(CO) 5 (L′)] are evident, with L′→M σ-donation decreasing across the series L′ = SbMe 3 → SbMe 2 Br → SbMeBr 2 , and an increase in M→L′ π-acceptance within the same series. Intermolecular interactions are a major feature within these systems, ranging from weak, MCO•••Sb interactions in [M(CO) 5 (SbMe 2 Br)] and [M(CO) 5 (SbMeBr 2 )] to remarkably strong O•••Sb hypervalent bonds in [Mn(CO) 5 (SbMe 2 Br)][CF 3 SO 3 ] and [Mn(CO) 3 (SbMe 2 Br) 3 ][CF 3 SO 3 ], the latter involving the triflate anions. These lead to large changes in the geometry at Sb and represent very rare examples in which the antimony exhibits significant Lewis acid and Lewis base behavior simultaneously. The coordinated alkylhalostibines are alkylated cleanly with MeLi or n BuLi.

Lewis base complexes of methyldihalobismuthines BiMeX2 (X = Cl or Br)

“…The products are relatively stable in air and the BiÀMe units less fragile than in the parent halobismuthines. The same bases bring about disproportionation in BiMe 2 X, the reaction being driven by complexation of the BiMeX 2 produced; similar behaviour occurs with SbMe 2 X and diimines [14]. The group 6 metal carbonyl reagents [M(CO) 5 (thf)] (M ¼ Cr or W) also promote disproportionation of BiMe 2 Br, in this case the BiMe 3 that is produced complexes with the metal centre to form [M(CO) 5 (BiMe 3 )].…”

“…The group 6 metal carbonyl reagents [M(CO) 5 (thf)] (M ¼ Cr or W) also promote disproportionation of BiMe 2 Br, in this case the BiMe 3 that is produced complexes with the metal centre to form [M(CO) 5 (BiMe 3 )]. In contrast, SbMe 2 Br functions as a Lewis base towards the same metal carbonyls forming stable [M(CO) 5 (SbMe 2 Br)] adducts [14].…”

“…In contrast to [BiMeCl 2 (2,2 0 -bipy)] [10], the bromo-complexes show no intermolecular contacts out to 5 Å. The corresponding [SbMeBr 2 (diimine)] are also discrete square pyramidal molecules [14]. Bismuth trihalides are stronger Lewis acids than the halobismuthines and a wide range of BiX 3 complexes with 2,2 0 -bipyridyl and 1,10-phenanthroline have been described [20e24].…”

“…During this study we prepared several methylhalobismuthines, BiMeX 2 and BiMe 2 X (X ¼ Cl or Br) as synthons for the introduction of Bi-containing donor groups into the ligands. We have also undertaken a detailed comparison of methylhalostibines as Lewis acids toward N-or Odonor ligands and as Lewis bases towards low-valent metal carbonyl species [14]. Here we report the synthesis and structures of BiMe 2 Br and five methyldihalobismuthine complexes with N-donor bidentate ligands, and the results of attempted complexation of BiMe 2 Br with [M(CO) 5 (thf)] (M ¼ Cr or W) and [Mn(CO) 5 (CF 3 SO 3 )].…”

Neutral organoantimony(III) and organobismuth(III) ligands as acceptors in transition metal complexes – Role of substituents and co-ligands

“…We have recently made an effort to draw the boundaries of these behaviours, 28 and have found that the mixed alkylhalostibines prove a fertile ground for unusual coordination chemistry in which both behaviours are often observed …”