Dehydrocoupling

In recent years, dehydrocoupling reactions catalysed by early transition metal complexes have become an increasingly important method for generating catenated species of the p-block elements. In addition to producing cyclic oligomers, this approach is used to prepare linear oligomers and polymers such as polysilanes and polystannanes of the type H(MR2) H (M = Si, Sn) (see Section 10.1.4).  

The zirconium hydride catalyst [Cp2Zr(H)Cl] is very effective for the high-yield synthesis of cyclotetrastibines (ArSb)4 from arylstibines ArSbH2 [eqn (2.11)].  

Catalytic dehydrocoupling can also be used for the efficient generation of heterocyclic systems by use of a suitable precursor incorporating a hetero-nuclear bond between two p-block elements. For example, the thermal dehydrocoupling of Ph2PH BH3 at 170 °C yields a mixture of the cyclic trimer (Ph2PBH2)3 (2.7) and tetramer (Ph2PBH2)4 (2.8) in an 8 1 ratio. The same two 

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A significant problem is the dehydrocoupling reaction, which proceeds only at low yields per pass and is accompanied by rapid deactivation of the catalyst. The metathesis step, although chemically feasible, requires that polar contaminants resulting from partial oxidation be removed so that they will not deactivate the metathesis catalyst. In addition, apparendy both cis- and /ra/ j -stilbenes are obtained consequendy, a means of converting the unreactive i j -stilbene to the more reactive trans isomer must also be provided, thus complicating the process. 

Corey, Joyce Y., Dehydrocoupling of Hydrosilanes to Polysilanes and Silicon... 

Dehydrocoupling A General Strategy for the Formation of Element-Element... 

With diphosphanes recently Stephan et al. reported an intriguing Al and P based macrocyclic structure [37]. A zirconium based catalyst precursor first was employed in the catalytic dehydrocoupling of the primary bidentate phosphane to give the tetraphosphane 6, (Scheme 4). The function of 6 as a molecular building block has been demonstrated by its reaction with MMe3(M = Al, Ga). Although, the gallium derivative 7 has not been... 

For the amino-borane dehydrocoupling using [Rh(l,5-cod)(p-Cl)]2 as starting catalyst, an induction period and a sigmoid-shaped kinetic curve (plot of substrate conversion versus time) were also observed, consistent with metal-particle formation. But, for Ph2PH BH3... 

Recently, Manners and co-workers have found another type of reaction, the inorganic process corresponding to Rh-catalysed dehydrocoupling of borane adducts, which is homogeneous or heterogeneous catalysed depending on the substrate, in particular the nature of the Lewis base, phosphine or amine respectively [15]. 

The latter part of the chapter focusses on catalyzed dehydrocoupling reactions as a route to polysilazanes. 

Si-N bonds can also be formed by a dehydrocoupling reaction catalyzed by alkali (6-11) or transition metals (12) ... 

None of the above described ring opening polymerization methods has, as yet, proved useful for the formation of polysilazane preceramic polymers. However, Si-N bond cleavage and reformation, as it occurs in reaction (13), is probably responsible in part for the curing or thermoset step in transition metal catalyzed dehydrocoupling polymerization of hydridosilazanes (31), as described below. 

Catalytic dehydrocoupling, as shown in reaction (3), was pioneered by Fink (6-10) and later studied by Andrianov et al (43). Although Fink described the synthesis of the first polysilazanes, (9) reaction (23), this route to oligo- and polysilazanes remained unexplored... 

Transition Metal Catalyzed Dehydrocoupling Polymerization Reactions... 

Transition metal catalyzed dehydrocoupling, reaction (27), offers an alternative to the alkali metal dehydrocyclizatlon process... 

There appear to be considerable steric demands involved in formation of the Si-N bond in reaction (28). Support for the importance of steric constraints in dehydrocoupling comes from studies on the synthesis of oligosilazanes from PhSiHj and NH3. When reaction (29) is run at 60°C, NMR and elemental analysis... 

The following reactions were performed to demonstrate the utility of transition metal dehydrocoupling for the synthesis of different types of polysilazanes and a novel polysiloxazane ... 

We have also explored the use of the dehydrocoupling reaction for the synthesis of preceramlc polysilazanes starting from the precursor MeNH-[H2SlNMe]x-H. As described above, MeNH-[H2SlNMe]X H Is produced by aminolysis of H2SiCl2 with MeNH2 under conditions where x 18-20 (Mn - 1150). 

Mono- and bis(silyl)platinum(II) complexes are believed to play important catalytic roles in hydrosilylation, dehydrocoupling, and double silylation reactions with disilanes and hydrosilanes. A stable, mono(silyl)platinum(II) complex has been prepared by the oxidative addition reaction of the sterically hindered, primary arylsilane 2,6-Mes2C6H3SiH3 (Mes = 2,4,6-trimethylbenzene) to the platinum(O) species [Pt(PPr3)3] in hexane solution at room temperature.133 The colorless product m-[PLl 1(2,6-Mes2C6II3(11 )2Si)(PPr3)2] (21) was isolated as the OPPr3 adduct, and its... 

Gauvin, Franjois, Harrod, John F., and Woo, Flee Gweon, Catalytic Dehydrocoupling A General Strategy for the Formation of Element—Element Bonds. .. 42 363... 

IV Facile Preparation of Organoboron Polymer Electrolytes via Dehydrocoupling Reaction of 9-Borabicyclo[3.3.1]nonane... 

Mw = 56,170, PDI = 1.67). The electron-withdrawing nature of the fluorinated aryl substituents appeared to have had an important influence on the reactivity, as the dehydrocoupling process was observed to occur efficiently at the mildest temperatures observed with such polymerizations to date.49... 

Since the initial cross-linking reactions do not permit applications requiring a thermoplastic polymer, further studies have been devoted to the control of the dehydrocoupling reaction, in particular between the already established chains. For this purpose, Sneddon et al. demonstrated that the preparation of dialkylamine-modified... 

This feature can be explained by intermolecular chain transfer, giving branched macromolecules with high molecular weight or by the occurrence of dehydrocoupling cross-linking reactions, such as described previously for polyborazylene (scheme 1). 

IV. FACILE PREPARATION OF ORGANOBORON POLYMER ELECTROLYTES VIA DEHYDROCOUPLING REACTION OF 9-BORABICYCLO[3.3.1JNONANE AND... 

The synthesis of comblike organoboron polymer was examined (see scheme 2) by dehydrocoupling polymerization of hydroborane monomers bearing an... 

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