Coupling dehydrogenative

Dehydrogenative Coupling of Hydride Functional Silanes. The autocouphng of dihydridosilanes was first observed usiag Wilkinson s catalyst (128). A considerable effort has been undertaken to enhance catalyst turnover and iacrease the molecular weight of polysilane products (129) because the materials have commercial potential ia ceramic, photoresist, and conductive polymer technology. 

With the stable donor adducts of silylene complexes, valuable model compounds are now available for reactive intermediates which otherwise cannot be observed directly. For example, a side reaction occurring in the hydrosilation process [61 -63], is the dehydrogenative coupling of silanes to disilanes. This reaction could be explained in terms of a silylene transfer reaction with a coordinated silylene as the key intermediate. 

Recent investigations have been concerned with the reactivities observed with secondary silanes R2SiH2. In these cases, a dehydrogenative coupling of silanes to disilanes is observed as a side reaction of the hydrosilation. However, the hydrosilation can be totally suppressed if the olefins are omitted. The key intermediate in the coupling reaction has been identified as a silylene complex (sect. 2.5.4). 

The dehydrogenative coupling of silanes does not stop at the stage of disilanes in the coordination sphere of early transition metals like Zr and Hf, but chain polymers of low molecular weight are formed. As reactive intermediates in this reaction, silylene complexes are also assumed. However, alternative mechanisms have been discussed (sect. 2.5.4). 

Hydride species were also formed in the dehydrogenative coupling of hydrosilanes with DMF [45]. The catalytic system is applicable to tertiary silanes, which are known to be difficult to be converted into disiloxanes (Fig. 17). The catalytic reaction pathway involves the intermediacy of a hydrido(disilyl)iron complex... 

Itazaki M, Ueda K, Nakazawa H (2009) Iron-catalyzed dehydrogenative coupling of tertiary silanes. Angew Chem Int Ed 48 3313-3316... 

I J Hydroboration, Diboration, Silylboration and Stannylboration Tab. 1-5 Dehydrogenative Coupling giving 1 -Alkenylboronates... 

In the course of studying the reactions of Si-H compounds with dialkyltitanocenes, with a view to the synthesis of new hydridosilyltitanocene complexes, we adventitiously discovered that phenylsilane undergoes facile, quantitative dehydrogenative coupling to a linear poly(phenylsilylene) under the catalytic influence of dimethyltitanocene. The ease with which this reaction proceeds initially induced us to underestimate the significance of the observation. 

Further studies quickly revealed that the rapid dehydrogenative coupling of primary organosilanes to oligomers and the slower coupling of secondary silanes to dimers can be effected under ambient conditions with compounds of the type CP2MR2 (M = Ti, R = alkyl M = Zr, R = alkyl or H)(11,12,13). None of the other metallocenes, metallocene alkyls, or metallocene hydrides of groups 4, 5 or 6 have shown any measurable activity for polymerization... 

The principle of forming novel polymeric materials by dehydrogenative coupling is of considerable generality. The... 

More recently, it was the seminal work of Aitken, Harrod and Samuel which showed that Group IV metallocene compounds catalyzed the dehydrogenative coupling of primary silanes, RSiH3, to give polysilanes of relatively low molecular weight, [RSiH] [8], that attracted many others into the silicon/transition metal chemistry field [9],... 

Polysilazanes that can serve as precursors for silicon carbonitride have been prepared using a Ru3(CO)i2-catalyzed Si-H/N-H dehydrogenative coupling process by workers at SRI [21]. Thus the ammonolysis product of CH3SiHCl2, whose composition approximates [CH3Si(H)NH]n, could be crosslinked by heating at 40 °C with a catalytic quantity of Ru3(CO)i2. Other polysilazanes were prepared by this procedure ... 

Mannich-type chemistry and cross-dehydrogenative couplings between t/i3-C-H and t/i-G-H bonds can be mediated by copper catalysis (Equations (43) and (44)).49,49a It is to be noted that the nitrogen atom mediates the... 

A number of transition metal complexes will catalyze the dehydrogenative coupling of organotin tin hydrides, R SnI I, to give the distannanes, RjSnSnRj.443 These metals include palladium,449 gold,450, hafnium,451 yttrium, and ruthenium.452 The catalyst that is most commonly used is palladium, often as Pd(PPh3>4, and the most active catalysts appear to be the heterobimetallic Fe/Pd complexes, in which both metals are believed to be involved in the catalysis.443... 

Among the various synthetic procedures for polysilanes is the Harrod-type dehydrogenative coupling of RSiH3 in the presence of Group 4 metallocenes (Reaction 8.1) [5,6]. One of the characteristics of the product obtained by this procedure is the presence of Si—H moieties, hence the name poly(hydrosilane)s. Since the bond dissociation enthalpy of Si—H is relatively weak when silyl groups are attached at the silicon atom (see Chapter 2), poly(hydrosilane)s are expected to exhibit rich radical-based chemistry. In the following sections, we have collected and discussed the available data in this area. 

The properties of siloxide as ancillary ligand in the system TM-O-SiRs can be effectively utilized in molecular catalysis, but predominantly by early transition metal complexes. Mono- and di-substituted branched siloxy ligands (e.g., incompletely condensed silsesquioxanes) have been employed as more advanced models of the silanol sites on silica surface for catalytically active centers of early TM (Ti, W, V) that could be effectively used in polymerization [5], metathesis [6] and epoxidation [7] of alkenes as well as dehydrogenative coupling of silanes [8]. 

The dehydrogenative coupling of primary alcohols to indoylamides was effected by TPAP/NMO/PMS/CH3CN, e.g. of 3-phenyl-1-propanol with pratosine and hippadine [504]. 

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