Agostic NSiH⋅⋅⋅Mo Complexes: From Curiosity to Catalysis

Abstract

All manipulations were carried out using conventional inert atmosphere glove-box and Schlenk techniques. Dry ether, toluene and hexanes were obtained, using Grubbs-type purification columns, other solvents were dried by distillation from appropriate drying agents.NMR spectra were obtained with a Bruker DPX-300 and Brucker DPX-600 instruments ( 1 H: 300 and 600 MHz; 13 C: 75.5 and 151 MHz; 29 Si: 59.6 and 119.2 MHz; 31 P: 121.5 and 243 MHz). IR spectra were measured on a Perkin-Elmer 1600 FT-IR spectrometer.(ArN) 2 Mo(PMe 3 ) 3 (Ar = 2,6-( i Pr) 2 C 6 H 3 ) was prepared by a literature procedure. [ was prerared by a literature procedure from SiCl 4 and corresponding Grignard reagent. 2 All catalytic and NMR reactions were done under nitrogen atmosphere using NMR tubes equipped with Teflon valves. The structures and yields of all hydrosilated products were determined using NMR analysis. Preparation of (ArN)(PMe 3 )(PhH 2 Si)Mo(η 3 -NAr-SiHPh-H) (3)PhSiH 3 (0.37 mL, 3.0 mmol) was added to a solution of (ArN) 2 Mo(PMe 3 ) 3 (1.01 g, 1.5 mmol) in 100 mL of hexane at room temperature. After the addition of PhSiH 3 , the colour of reaction mixture immediately turned from dark-green to brown, and the formation of a brown precipitate was observed. The reaction mixture was purged with N 2 under stirring at room temperature for 30 min., concentrated and left in a freezer (-30°C) overnight. More crystalline brown precipitate formed. The cold precipitate was filtered off, washed with cold hexane (10 mL) and dried in vacuum to give a fine brown powder of 3. Yield: 0.7 g, 77 %.

Unusual Structure, Fluxionality, and Reaction Mechanism of Carbonyl Hydrosilylation by Silyl Hydride Complex [(ArN)Mo(H)(SiH2Ph)(PMe3)3]

“…Indeed, silyl hydride complex 3 was found to be a much better catalyst than hydrido chloride 1 (Table 2). For example, the hydrosilylation of benzaldehyde by PhSiH 3 catalyzed by compound 1 11a requires 3 h at 50 °C, whereas the complex 3 catalyzed reaction takes only 15 min at room temperature (Table 2).…”

“…No further conversion of acetonitrile was observed over 24 h. At the same time, the hydrosilylation of benzonitrile selectively gives the mono(addition) product PhH 2 SiNCHPh in 20 % yield (Table 2, entry 9). Catalytic mono(hydrosilylation) of nitriles into imines has only been observed in a few cases 11a,b,e,f. 41–43…”

“…In contrast to the reaction with acetone, the treatment of complex 3 with excess PhHCO (about 4 equiv and more) leads, after 5 min at room temperature, to the elimination of the hydrosilylation product, PhHSi(OBn) 2 ,11a,e, 49 and to the formation of bis(aldehyde) complex [ trans ‐(ArN)Mo( η 2 ‐PhHCO) 2 (PMe 3 ) 2 ] ( 23 , Scheme ) 50. The product is highly fluxional, even at −20 °C.…”

Chemoselective Catalytic Hydrosilylation of Nitriles

“…[9,10] These methods either require drastic reactions conditions or are very slow and give low yields, and in no case was the selectivity towards functional groups established. A handful of examples of stoichiometric monoSiÀH additions to nitriles have been published.…”

Dehydrosilylation of ArNHSiH3 with Ytterbium(II) Amide: Formation of a Dimeric Ytterbium(II) Silanimine Complex

“…A few metal hydrosilylamido complexes can be converted into the corresponding silanimine complexes by either SiH σ‐bond metathesis or oxidative addition to the metal centers 6a. f These unsaturated silicon complexes, although very rare in number, have been shown to display interesting structural features and reactivity 6. Inspired by these findings, we became interested in the investigation of primary aminosilanes with an HNSiH 3 linkage in lanthanide chemistry, as the elimination of hydrogen may take place to give lanthanide silanimine complexes.…”