Silyl–Thioether Multidentate Ligands – Synthesis of Rh^III Complexes via Rh^I/Rh^III Mixed‐Valent and Cyclooctenyl Intermediates

Abstract

The preparation and characterization of a dimeric RhIII complex containing two SSi ligands on each rhodium fragment is reported. {Rh[SiMe2(o‐C6H4SMe)]2Cl}2 (1) was obtained by reaction of thioether–silane SiMe2H(o‐C6H4SMe) (L1) with [Rh(cod)Cl]2. Mixed‐valent RhI/RhIII complex {(cod)Rh(μ‐Cl)2Rh[SiMe2(o‐C6H4SMe)]2} (2), which is an intermediate in the formation of 1, was isolated. Furthermore, 1H NMR spectroscopic monitoring revealed the formation of cyclooctenyl intermediates. The tridentate pincer proligand, SiMeH(o‐C6H4SMe)2 (L2), reacts with [Rh(cod)Cl]2 to yield a robust cyclooctenyl RhIII complex, {Rh(η3‐cyclooctenyl)[SiMe(o‐C6H4SMe)2]Cl} (3). Complexes 1–3 were characterized by X‐ray crystallography.

Dehydrogenative Coupling of a Tertiary Silane Using Wilkinson's Catalyst

“…The NMR chemical shift for the disilane is similar to that observed for the monomer L1 [δ = -31.1 (d, J H-Si = 198 Hz)]. [21] ESI-MS shows the ion [L2 -H] + (579.16 m/z). The IR spectrum of L2 lacks the presence of ν(SiO) (around 1000 cm -1 ), and serves to discard the formation of the disiloxane (o-C 6 H 4 SMe) 2 MeSi-O-SiMe(o-C 6 H 4 SMe) 2 .…”

“…In the 29 Si NMR spectrum of L2 a broad signal at δ = –31.0 ppm is observed. The NMR chemical shift for the disilane is similar to that observed for the monomer L1 [ δ = –31.1 (d, J H‐Si = 198 Hz)] . ESI‐MS shows the ion [ L2 – H] + (579.16 m/z ).…”

“…CH 2 Cl 2 , CD 2 Cl 2 and CDCl 3 , were distilled from CaH 2 , degassed by successive freeze‐pump‐thaw cycles and stored over molecular sieves (3 Å). [Rh(PPh 3 ) 3 Cl] and SiMeH( o ‐C 6 H 4 SMe) 2 (L1) was prepared as described previously. NMR spectra were recorded on Bruker AVD 500 and 400 MHz spectrometers at room temperature unless otherwise stated.…”

“…Herein, we report an efficient method for the dehydrogenative coupling of a tertiary silane using Wilkinson's catalyst and propose an active catalytic species and a deactivation process based on stoichiometric evidences. This is made possible because the silane used as substrate is also a tridentate pro‐ligand (Scheme ).…”

Steric Effects in the Catalytic Tandem Isomerization‐Hydrosilylation Reaction

“…Silane‐thioether bidentate proligands [SiMe 2 H( o ‐C 6 H 4 SR)] (R= i Bu, pentyl, benzyl, neopentyl, a ‐ d ) containing different substituents on the sulfur atom were synthesized following synthetic procedures analogue to the one already described for the methylated derivative e (Scheme 2). [36] These compounds and their precursors were characterized by 13 C{ 1 H} and 1 H NMR spectroscopy (see Experimental Section and Supporting Information). As expected, the 1 H NMR spectra show similar signals in the aromatic region, a septuplet around 4.6 ppm (due to Me 2 Si–H proton), and the characteristic signals of the corresponding substituent ( a , i Bu; b , pentyl; c , benzyl; d , neopentyl).…”