Mechanistic Investigation of the Hydration Reaction of [Cr(η6-silabenzene)(CO)3]: Hydrido(silacyclohexadienyl)chromium Complex as an Intermediate

Abstract

A key intermediate for the hydration reaction of [Cr(η6-silabenzene)(CO)3], hydrido(η5-silacyclohexadienyl)chromium complex, was successfully synthesized by the reaction of silabenzene complex with 2 mol equiv of H2O. X-ray diffraction study revealed that the hydroxy group on the central silicon atom is located at the endo position to the metal moiety. The treatment of the endo adduct with excess of D2O resulted in the stereoselective formation of 1-silacyclohexa-2,4-diene bearing a deuterium atom at the methylene position.

Iron(II) Complex with a Silacycle-Bridged Biaryl-Based Ligand

“…The dihedral angle between the two phenyl rings in the biaryl moiety was ∼43° with a Si–C (1) bond distance of 1.862 (3) Å; these values are comparable to those in the previously reported, structurally similar 10-methyl-5-phenyl-5,6-dihydrodibenzo­[ b , d ]­siline (dihedral angle: ∼39°; Si–C = 1.866 (2) Å) . It is noteworthy that the reactions of anionic sila-cyclohexadienyl reagents with transition-metal precursors generally lead to the formation of metal complexes in which the sila-cyclohexadienyl skeleton is coordinated to the metal center in an η 5 -fashion; , thus, to the best of our knowledge, 3 is the first example of a complex that features an η 1 (C)-coordinated silacyclohexadienyl framework.…”

Novel silacyclohexadienyl chromium and iron complexes bearing a bulky substituent on the central silicon atom

“…In the 13 C NMR spectrum of 6, the signals of three carbons in the carbonyl ligands were observed equivalently at 230.4 ppm, suggesting the existence of rapid rotation of Cr(CO) 3 unit around axis through Cr and centroid in the SiC 5 ring with agostic interaction. In the IR spectrum of 6, the wavenumbers of the carbonyl stretchings (2002,1929, and 1897 cm -1 ) are higher than those observed for the related complex 2 bearing a hydroxyl group on the silicon atom (1991,1910, and 1888 cm -1 ) [6]. This result indicates that the electron-donating ability of the η 5 -1-chloro-1-silacyclohexa-2,4-dienyl ligand is smaller than that of the η 5 -1-hydroxy-1-silacyclohexa-2,4-dienyl ligand and that electronic properties of silacyclohexadienyl ligands were controllable by changing a substituent on the silicon atom.…”

“…We previously reported that silacyclohexadienyl complex 2 exists as an equilibrated mixture in benzene, as depicted in Scheme 2 [6,7]. This equilibrium suggests that silacyclohexadienyl complex is obtainable using the reaction of silacyclohexadiene with Cr(0) complex having three replaceable ligands such as a solvent molecule.…”

“…One is hydration of silabenzene complex, as shown in Scheme 1 [6]. The other is the formal insertion reaction of Cr(0) to C-H or Si-H bond of silacyclohexadiene (Schemes 3 and 4).…”

“…An issue of reviews and research papers based on lectures presented at the 13 th International Symposium on Novel Aromatic Compounds (ISNA-13), 19-24 July 2009, Luxembourg City, Luxembourg on the theme of aromaticity. ‡ Corresponding author [(H)(η 5 -silacyclohexadienyl)Cr(CO) 3 ] (2) was isolated as a key intermediate in the hydration reaction of [Cr(η 6 -silabenzene)(CO) 3 ] (1) (Scheme 1) [6]. Herein, we report the syntheses and structures of novel chromium and iron complexes bearing a silacyclohexadienyl ligand.…”