Synthesis and Functionalization of Hexacoordinate (Arenediolato)bis(polypyridyl)silicon(IV) Complexes

Abstract

Hexacoordinate (arenediolato)silicon(IV) complexes that contain two additional 2,2′‐bipyridine or 1,10‐phenanthroline ligands are surprisingly stable against aqueous hydrolysis and therefore constitute attractive and novel templates for the design of bioactive compounds. In this article, we report the synthesis of (arenediolato)bis(polypyridyl)silicon(IV) complexes, including a case of diastereoselective synthesis of a nonracemic hexacoordinate (binaphtholato)silicon(IV) complex, and methods for their post‐coordinative functionalization with halides, nitro, and carbonyl groups. Several X‐ray crystal structures are provided and demonstrate the octahedral coordination of silicon in these complexes.

Exploring the structure and redox activity of hexacoordinate bis(bipyridyl)silicon(IV) complexes

“…Species 5 had a poorly defined E pa wave at +1.2 V (versus Fc + /Fc) with no clear E pc . This very positive oxidation potential is consistent with a previously reported unsuccessful attempt to oxidize Si(bpy) 2 (cat) +2 with lead(IV) oxide, in which only starting material was recovered [7]. The difficulty in oxidizing the catechol ligand in this silicon complex contrasts with the ruthenium analog, Ru(bpy) 2 (cat), which exhibits a reversible semiquinolate/catecholate wave at À0.73 V [13] (versus Fc + /Fc, converted from published SCE referenced data assuming Fc + /Fc is at +0.400 V versus SCE [14]).…”

“…5) were crystallized as the hexafluorophosphate salts following a metathesis reaction. A crystal structure was previously reported for [Si(bpy) 2 (cat)](PF 6 ) 2 containing disordered CH 3 CN solvent molecules in the unit cell as triclinic with a P 1 space group [7], but we find that the non-solvated [Si(bpy) 2 (cat)](PF 6 ) 2 complex crystallizes in an orthorhombic unit cell with space group Pbca.…”

“…The complexes described in this study were synthesized from the di-iodo precursor, [Si(bpy) 2 I 2 ]I 2 [7,11]. SiI 4 can be combined with excess bipyridine in CHCl 3 or CH 2 Cl 2 to form [Si(bpy) 2 I 2 ]I 2 nearly quantitatively, and further reaction to form [Si(bpy) 3 ]I 4 does not occur in CHCl 3 or CH 2 Cl 2 .…”

“…Hexacoordinate bis(bipyridyl)silicon(IV) complexes have also been investigated recently, and it is likely that these complexes will demonstrate similar biological activity [7]. Currently, only five hexacoordinate bis(bipyridyl)silicon(IV) complexes appear in the Cambridge Structural Database: [Si(bpy) 2 (catecholato)] (PF 6 ) 2 [7], [Si(bpy) 2 (binolato)] (PF 6 ) 2 [7], [Si(bpy) 2 Cl 2 ]I 2 [8], [Si(bpy) 2 (OH) 2 ]I 2 [9], and Na[Si(bpy) 2 (dpcat-H)](ClO 4 ) 4 (dpcat-H = protonated dipyidocatecholate) [10]. In this paper we explore the electrochemical and structural properties of five bis(bipyridyl)silicon(IV) complexes: [Si(bpy) 2 (OMe) 2 ] 2+ (1), [Si(bpy) 2 (-OCH 2 CH 2 O-)] 2+ (2), [Si(bpy) 2 (OPh) 2 ] 2+ (3), [Si(bpy) 2 (bph)] 2+ (4), and [Si(bpy) 2 (cat)] 2+ (5), (bpy = 2,2 0 -bipyridine, cat = 1,2-benzenediolato, bph = 2,2 0 -biphenolato ligand).…”

“…In a subsequent study Meggers demonstrated DNA mismatch recognition using a hexacoordinate bis(phenanthroline)silicon(IV) sandwich complex with a ruthenium center [6]. Hexacoordinate bis(bipyridyl)silicon(IV) complexes have also been investigated recently, and it is likely that these complexes will demonstrate similar biological activity [7]. Currently, only five hexacoordinate bis(bipyridyl)silicon(IV) complexes appear in the Cambridge Structural Database: [Si(bpy) 2 (catecholato)] (PF 6 ) 2 [7], [Si(bpy) 2 (binolato)] (PF 6 ) 2 [7], [Si(bpy) 2 Cl 2 ]I 2 [8], [Si(bpy) 2 (OH) 2 ]I 2 [9], and Na[Si(bpy) 2 (dpcat-H)](ClO 4 ) 4 (dpcat-H = protonated dipyidocatecholate) [10].…”