Si-H activation

It appeared to be a logical consequence to transfer this synthetic principle to more suitable metals like ruthenium and introduce bulky, kinetically stabilizing ligands at the metal. An interesting example for this approach is the complex 78. The latter is synthesized from Cp RuCl(PR3)2 with ClMgCH2SiMe2H through 77 by a thermal Si — H activation reaction. 

The TFTs are made on transparent glass substrates, onto which gate electrodes are patterned. Typically, the gate electrode is made of chromium. This substrate is introduced in a PECVD reactor, in which silane and ammonia are used for plasma deposition of SiN as the gate material. After subsequent deposition of the a-Si H active layer and the heavily doped n-type a-Si H for the contacts, the devices are taken out of the reactor. Cr contacts are evaporated on top of the structure. The transistor channel is then defined by etching away the top metal and n-type a-Si H. Special care must be taken in that the etchant used for the n-type a-Si H also etches the intrinsic a-Si H. Finally the top passivation SiN, is deposited in a separate run. This passivation layer is needed to protect the TFT during additional processing steps. 

Previous investigations of the photolysis reactions of 5 in the presence of various silanes only showed the products of Si-H activation [20], Metal silyl hydride formation, however, becomes the main reaction path with sterically less hindered silanes [21]. 

This reaction mode sheds new light on the mechanism of the Si-H activation reaction of the 16e complex [(7j5-H3CC5H4)Mn(CO)2 x THF] 6. 

Given the ability of 14 electron fragments [(dtbpm)Pt(O)] and [(dcpm)Pt(O)] to activate C-H and C-Si bonds of inert organosilanes under very mild reaction conditions, it was of course no big surprise that Si-H activation reactions of silanes are possible as well. Hydrido-silyl complexes were formed in practically quantitative reactions if 14 or IS were used as precursors for the [(dtbpm)Pt(O)] fragment. Examples of Si-H insertion products, all stable, isolable compounds which could be fully characterized, are 25 - 27, and others have been made. 

Figure 10 Proposed mechanism of Si-H activation by CpMn(CO)3. Inset UV-vis spectrum of CpMn(CO)3 in neat Et3SiH imder experimental conditions. (Reprinted with permission from Ref 127. 1999 American Chemical Society)...

Our thinking regarding the mechanism of Si-H activation was dramatically redirected by the appearance of the seminal communication by Vaska and DiLuzio in which they demonstrated the facile, reversible addition of H2 to a square planar Ir complex to give an octahedral Ir" dihydride... 

Some Si-Si activation involves initial Si-H activation followed by sily-lene migration. An example is the reaction between tetrahydrodimethyldisilane and a cis-platimun dihydride that gives [(dcpe)Pt]2(/r-SiHMe)2 (dope = 1,2-bis(dicyclohexylphosphino)ethane) via the intemediacy of a disilanylplatinum hydride (Eq. 2.75) [173]. The transformation of a disilanylplatinum hydride to bis(silyl)platinum complex seems to proceed via an intramolecular a-silylene migration. 

R=/ -Xyl, Mes, Tol) were photochemically generated in situ Interestingly, in the presence of EtsSiH, Si-H activation predominates over C H, affording exclusively Tp IrH(SiEt3)(CO) (437), which is isolable and stable. This greater thermodynamic stability is reiterated by the observation that in -pentane solution, the formation of 437 is competitive with that of 431, despite the silane being in much lower concentration. ... 

Alkane C-H activation by a cationic methyl-lr " complex oxidative addition (left side) rather than a-bond metathesis (right side). Related Si-H activation (by ortho-metallation) below goes to stable Ir. ... 

In a general paper the synthesis, structure and fluxionality of (p-diphenylsilyl-ene)(fulvalene)tetracarbonyldirhenium has been examined and a double Si-H activation is observed which led to the formation of the first fulvalene silylene,... 

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