Surprising Insights in the Various Molecular Structures of Hypercoordinate Bis(oxinato)silicon Complexes

Abstract

The syntheses of two cyclic diorganosilicon enamines =CH2) [R = Ph (2a), Me (2b)] are described. These compounds react with 8-oxyquinoline leading to bis(oxinato)silicon complexes RPhSi(oxinate)2 [R = Ph (5a), Me (5b)]. Their X-ray structures reveal hexacoordination of the Si atom with the monodentate substituents in cis-positions and N atoms as well as O atoms in trans-positions.In crystalline dimethylbis(oxinato)silicon, Me2Si(oxinate)2 (7), the silicon atom is only bicapped tetrahedrally coordinated, while for dichlorobis(oxinato)silicon, Cl2Si(oxinate)2 (8), there is an octahedral coordination of the Si atom with chlorine atoms in trans-positions. This conclusion is based on the results of spectroscopic analysis (IR, 29Si CP/MAS NMR) as well as quantum chemical calculations. The first example of a silicon-bis-oxinate with the N→Si dative bonds in a trans-arrangement has been detected in the hexacoordinate silicon tris-chelate (oxinate)2Si(PhN-CH2CH2-NPh) (11). Its configuration was proven by X-ray structure analysis. Thus, for hexacoordinate bis(oxinato)silicon compounds three new architectures were found which complement the previously established building pattern of the N,N’-cis-O,O’-trans-bis(oxinato)silicon complexes.The mer-tris(oxinato)siliconium cation (9+) (its configuration being proven by 1H and 13C NMR spectroscopy) features at least three coordination patterns with (O,O;N,N)-cis,cis-, -cis,trans- as well as -trans,cis-arrangements of two oxinate ligands.

Pentacoordinate Silicon Complexes with N‐(2‐pyridylmethyl)­salicylamide as a Dianionic (ONN′) Tridentate Chelator

“…The decreased axial angle in 2f is accompanied by a notable shortening of the bond Si1–N2 [1.993(1) Å in 2f ], which ranges between 2.041(1) Å and 2.069(1) Å in compounds 2a – 2e . The pyridine donor trans ‐influenced bond O1–Si1 [lengths in the range of 1.720(1) Å to 1.750(1) Å] is notably longer than the related Si–O bond of 1.648(1) Å in the pyridine donor free molecule 3c depicted in Scheme 9a. The Si1–N1 bonds [lengths in the range of 1.794(1) Å to 1.802(1) Å in 2a – 2f ] are affected by the pyridine donor action to a similar extent, thus being also notably longer than the Si–N bond in the reference molecule 3c in Scheme [1.720(2) Å].…”

Novel hexacoordinate organosilicon(IV) complexes of diethylenetriamine Schiff base with SiO2N3 skeleton

“…The limited literature on computational studies of hypercoordinated silicon is due to large size of these molecules which restricts these studies to semi empirical methods [19][20][21] . The IR frequencies were obtained by using structures optimized with PM3 methods and 29 Si NMR shifts were calclulated by Density Functional Theory calculations performed at 3-21+G* basis set and the results were compared with experimental data.…”

2‐Acylpyrroles as Mono‐anionic O,N‐Chelating Ligands in Silicon Coordination Chemistry

“…Thus, the herein reported compound [L 1 3 Si][GaCl 4 ] ⋅ MeCN is the first crystallographically characterized silicon tris‐chelate of that kind which comprises five‐membered chelate rings. For the cationic tris‐oxinato silicon complex,16 which also comprises five‐membered chelate rings, we also found mer ‐configuration of the Si coordination sphere, but crystallographic evidence for this configuration in the solid state could not be obtained.…”