Halogen exchange and expulsion: ligand stabilized dihalogen silicon dications

Abstract

The first ligand stabilized SiCl 2 2ϩ dications were synthesized using N-methylimidazole as co-ordinating ligand. The compounds SiCl 4 , SiBr 2 Cl 2 , and SiH 2 Cl 2 form six-co-ordinated dicationic compounds of almost octahedral symmetry with similar structures which were investigated by single crystal X-ray analysis and density functional calculations. The structures exhibit particularly short dative Si-N bonds of about 1.90 Å. Complexes crystallized from the same solvent are isostructural. A different solvent, though, leads to geometrical variations. It was also discovered that the halogen exchange process among mixed silicon tetrahalides occurs under much milder conditions than previously thought and proceeds with considerable speed even without a catalyst.

Complexes of mixed silicon halides with 4-picoline

“…The structures presented in this paper are isostructural with trans-tetrachlorobis(4-methylpyridine)titanium (Hensen et al, 1999). The presence of an aromatic base during the reaction to synthesize these compounds did not considerably stimulate the halogen exchange, a fact that has already been observed (Hensen et al, 2000). As a result of that, no dismutation could be detected and each of the reaction products could be recrystallized.…”

“…Several complexes of silicon halides are already known, but only little is known about adducts of mixed silicon halides, because exchange reactions have to be taken into account. This kind of exchange reaction between silicon tetrahalides at high temperatures and pressures has been described by Forbes & Anderson (1944) and was recently proved (Hensen et al, 2000) at ambient conditions. Furthermore, it was presumed (Wannagat et al, 1954) that pyridine or comparable ligands catalyze halogen exchange reactions of silicon halides.…”

“…In recent years the extension of the coordination sphere of silicon in complexes with organic nitrogen bases has been the subject of numerous studies (Bechstein et al, 1990;Chuit et al, 1993;Kane et al, 1998;Hensen et al, 1998Hensen et al, , 2000. Several complexes of silicon halides are already known, but only little is known about adducts of mixed silicon halides, because exchange reactions have to be taken into account.…”

Hydrosilylation in Aryliminopyrrolide‐Substituted Silanes

“…The obtained knowledge of the conditions favoring and disfavoring the imine hydrosilylation reaction complements existing approaches in which the imine moiety is passivated by incorporation in a conjugated π‐system; that is, aromatic heterocycles and amidinate/guanidinate compounds . This is anticipated to aid in the controlled synthesis of N‐substituted silicon compounds as precursors for silicon(II) ligands.…”

cis-Bis(2,2′-bipyridyl-N,N′)dichlorosilicon diiodide

“…The two chloro ligands are arranged cis with respect to each other. The two SiÐCl bonds are rather short compared with similar ionic complexes (Hensen et al, 2000), where these bonds are in the range 2.184 (1)±2.207 (1) A Ê . The SiÐN bond lengths are in the usual range, but they are signi®cantly different from each other.…”