Silane Complexes of Electrophilic Metal Centers

Abstract

Photolysis of solutions of M(CO)6 (M = Cr, Mo, and W) in the presence of Et3SiH affords the silane complexes Cr(CO)5(eta2-HSiEt3), Mo(CO)5(eta2-HSiEt3), and W(CO)5(eta2-HSiEt3). Observed values of J(SiH) in these complexes are consistent with modest elongation of the Si-H bond. With Ph3SiH, complexes of Cr(CO)5 and W(CO)5 were obtained, but no complex with Mo was observed. When Ph2SiH2 was employed, only one Si-H bond interacts with the metal center. A dynamic exchange process observable on the magnetic resonance time scale exchanges the pendant and coordinated Si-H bonds of the coordinated diphenylsilane. Silanes bound to M(CO)5 are activated with respect to reaction with nucleophiles. With methanol, catalytic methanolysis of HSiEt3 has been observed in the presence of Cr(CO)5(eta2-HSiEt3), affording Et3SiOMe.

Investigation of the Stability of the M‐H‐B Bond in Borane σ Complexes [M(CO)5(η1‐BH2R⋅L)] and [CpMn(CO)2(η1‐BH2R⋅L)] (M=Cr, W; L=Tertiary Amine or Phosphine): Substituent and Lewis Base Effects

“…Although this species is unstable, it can be observed by NMR at low temperature. [37] Moreover, their lifetimes at ambient temperature have been measured by a fast spectroscopy method by Brown and coworkers. [24] In this system, despite its excellent p-accepting character, silanes with electron-releasing substituents form more stable complexes in contrast to other many silanemetal adducts.…”

Electrophilic Activation of Silicon–Hydrogen Bonds in Catalytic Hydrosilations

“…However, these early studies provided only limited details of the electrophilic silicon intermediates involved in catalysis. [57][58][59][60] Subsequent improvements in synthetic techniques (e.g. use of fluorinated aryl borate or carborane anions) and analytical techniques (e.g.…”

“…[57] However, there are some examples in which this type of mechanism was implicated for neutral metal complexes such as 14 [58] and 15. [59] For the neutral Ni(II) based catalyst 14, it was noted that Si-H oxidative addition was unlikely since the ligand used was not expected to stabilize the unfavorable Ni(IV) oxidation state. [58] Other neutral electrophilic catalysts (e.g.…”

“…Cr(CO)5 (15)) involve relatively low oxidation states for their respective metal centers. [59] In these examples, electrophilic character of the metal center and resistance to oxidative addition can be attributed to the presence of several electron withdrawing carbonyl ligands. [60] Scheme 21.…”

The UV‐Light Initiated Reaction of Organosilanes with Tungsten Hexacarbonyl: Formation of an Organosilylene Complex and Organosilylium Salts

“…Associated with this is the desire to get more insight into the mechanism of Si-H bond activation by transition metal compounds [20][21][22][23][24][25][26][27][28][29] which in turn is relevant even for the topic of C-H bond activation [30] as well as for the understanding of transition metal-catalyzed oligo-and polysilane formation [31].…”