dehydrogenative coupling of silanes

Titanocene and related their complexes are typical catalysts. A typical reaction involves phenylsilane:{{cite journal

| last1 =Aitken | first1 =C.

| last2 =Harrod| first2 =J. F.

| last3 =Gill | first3 =U. S.

| title =Structural studies of oligosilanes produced by catalytic dehydrogenative coupling of primary organosilanes | journal = Can. J. Chem.

| volume =65

| year =1987

| pages =1804–1809 | doi =10.1139/v87-303

}}

{{cite journal

|last1= Corey | first1=J.Y. | last2= Zhu | first2=X.H. | last3= Bedard |first3 =T.C. |last4= Lange | first4 = L.D.

|title =Catalytic Dehydrogenative Coupling of Secondary Silanes with Cp₂MCl₂

|journal=Organometallics | volume =10 | issue =4 | page = 924 | year = 1991 | doi = 10.1021/om00050a024

}}

:n PhSiH₃ → [PhSiH]_n + n H₂

Para- and meta-substituted phenylsilanes polymerize readily but ortho-substituted polymers were failed to form. Polymers white/colorless, tacky and soluble in organic solvents. Crosslinking was not observed.{{cite journal

| last1 =Banovetz | first1 =John P. | last2 =Suzuki | first2= Hiroshi | last3 =Waymouth | first3 =Robert M.

| title =Dehydrogenative coupling of substituted phenylsilanes synthesis of poly[((trifluoromethyl)phenyl)silanes] |volume =12 | issue =11 | year =1993 | pages =4700–4703 | doi =10.1021/om00035a070 | journal = Organometallics}}

Using Cp₂Ti(OPh)₂ as a catalyst, the dehydrogenative coupling of phenylsilane in the presence of vinyltriethoxysilane produces a polysilane terminated with a triethoxysilylvinyl group.{{cite journal|last1=Garcia|first1=Julien|last2=Meyer|first2=Daniel J.M.|last3=Guillaneux|first3=Denis|last4=Moreau|first4=Joël J.E.|last5=Wong Chi Man|first5=Michel|title=Investigation of titanium-catalysed dehydrogenative coupling and hydrosilylation of phenylhydrogenosilanes in a one-pot process|journal=Journal of Organometallic Chemistry|date=July 2009|volume=694|issue=15|pages=2427–2433|doi=10.1016/j.jorganchem.2009.03.018}}

The nickel(I) complex [(dippe)Ni(μ-H)]₂ promotes the dehydrogenative coupling of some silanes.{{cite journal

| last1 = Smith | first1 = Erin E.

| last2 = Du | first2 = Guodong

| last3 = Fanwick | first3 = Phillipe E.

| last4 = Abu-Omar |first4 = Mahdi M.

| title = Dehydrocoupling of Organosilanes with a Dinuclear Nickel Hydride Catalyst and Isolation of a Nickel Silyl Complex| journal = Organometallics | volume =29 | year =2010 | issue =23 | page =6529 | doi =10.1021/om100887v

}}

While catalysts for dehydrogenative coupling reactions generally tend to be transition metal complexes, magnesium oxide and calcium oxide promote the dehydrogenation of phenylsilane. Being a heterogeneous process, the products are easily separated from the catalyst.{{cite journal

| last1 =Itoh | first1 =M.

| last2 =Mitsuzuka | first2 =M.

| last3 =Utsumi | first3 =T.

| last4 =Iwata | first4 =K.

| last5 =Inoue | first5 =K.

| title =Dehydrogenative coupling reactions between hydrosilanes and monosubstituted alkynes catalyzed by solid bases | journal =Journal of Organometallic Chemistry | volume =476

| year =1994

| pages =C30-C31 | doi =10.1016/0022-328X(94)87091-8

}}

Dehydrogenative coupling of primary silanes using Wilkinson's catalyst is slow and dependent on the removal of H₂ product. This conversion proceeds by oxidative addition of the Si-H bond and elimination of dihydrogen.{{cite journal

| last1 =Rosenberg | first1 =Lisa

| last2 =Kobus | first2 =Danielle N.

| title =Dehydrogenative coupling of primary alkyl silanes using Wilkinson's catalyst | journal =Journal of Organometallic Chemistry | volume =685 | issue =1-2 | year =2003 | pages =107–112 | doi =10.1016/S0022-328X(03)00712-5 }}

Tris(pentafluorophenyl)borane (B(C₆F₅)₃)) is yet another catalyst for the dehydrogenative coupling of tertiary silanes. This system has the useful characteristic of being selective for Si-H bonds vs Si-Si bonds, leading to fewer branches and more linear polymers. This catalyst is particularly useful in reactions involving thiols and tertiary silanes or disilanes.{{cite journal

| last1 =Harrison | first1 =D. J.

| last2 =Edwards | first2 =D. R.

| last3 =McDonald | first3 =R.

| last4 =Rosenberg | first4 =L.

| title =Toward selective functionalisation of oligosilanes: borane-catalysed dehydrogenative coupling of silanes with thiols| journal = Dalton Trans. | volume =26 | year =2008

| pages =3401–3411 | doi =10.1039/b806270f }}

As well as being coupled to each other, tertiary silanes can be coupled with carboxylic acids to form silyl esters. Ru₃(CO)₁₂/EtI is a good catalyst for this. This reaction applies to a wide range of silanes and acids.{{cite journal|last=Liu|first=G.|author2=Zhao, H.|title=Ru-catalyzed dehydrogenative coupling of carboxylic acids and silanes - a new method for the preparation of silyl esters|journal=Beilstein Journal of Organic Chemistry|year=2008|volume=4|issue=27|doi=10.3762/bjoc.4.27|pmc=2511026}} The complex [Cu(PPh₃)₃Cl] can also be used to produce silyl esters.{{cite journal

| last1 =Liu | first1 =G. -B.

| last2 =Zhao | first2 =H. -Y.

| last3 =Thiemann | first3 =T.

| title =Two New Catalysts for the Dehydrogenative Coupling Reaction of Carboxylic Acids with Silanes - Convenient Methods for an Atom-Economical Preparation of Silyl Esters| journal = Synthetic Communications | volume =37 | year =2007

| pages =2717–2727 | doi =10.1080/00397910701465669

}}

Tertiary silanes may also be dehydrogenatively coupled to aromatic rings with the use of the catalyst Tp^Me2Pt(Me)₂H (Tp^Me2 = hydrido tris(3,5-dimethylpyrazolyl)borate). For example, this platinum catalyst can be used to react triethyl silane with benzene to produce phenyltriethylsilane, with the elimination of hydrogen gas. This is a terrific catalyst because it eliminates the need for a hydrogen acceptor, something which is normally required for the silation of a C-H bond. This reaction may also be done intramolecularly to produce five- or six-membered silicon-containing rings fused to a phenyl ring. In addition, tributylsilane can be converted into the corresponding cyclic organosilane via the same process. A drawback to this catalyst, however, is that it requires rather harsh reaction conditions (typically 200 °C for 24 hours for the intermolecular reaction, 48 – 72 hours for the intramolecular ones). It is also not particularly regioselective, so starting materials containing substituted benzene would result in a mixture of products.{{cite journal|last=Tsukada|first=N.|author2=Hartwig, J. F.|title=Intermolecular and intramolecular, platinum-catalyzed, acceptorless dehydrogenative coupling of hydrosilanes with aryl and aliphatic methyl C-H bonds|journal=Journal of the American Chemical Society|year=2005|issue=127|pages=5022–5023|doi=10.1021/ja050612p}}

File:Intra.gif

Some methods used to produce polysilanes are polymerization of masked dislenes,{{cite journal

| last1 = Sakomto | first1 = Kenkichi | last2 = Yoshida | first2 = Masaru | last3 = Sakurai | first3 = Hideki

| title = Highly ordered high-molecular weight alternating polysilylene copolymer prepared by anionic polymerization of masked disilene | journal = Macromolecules | volume =23 | year =1990 | issue =20 | pages=4494–4496 | doi =10.1021/ma00222a031

}}

electroreduction of dichlorosilanes,{{cite journal

|last1=Shono |first1=T. |last2=Ishifune|first2=S. |last3=Nishida|first3=R. | title =Electroreductive synthesis of some functionalized polysilanes and related polymers |journal =Tetrahedron Letters | volume=38 | issue =36 | year =1997 | pages = 4607–4610 | doi =10.1016/S0040-4039(97)00987-8

}}

¹H and ²⁹Si NMR spectroscopy can sometimes be used to help identify and characterize products from these reactions.

Infrared spectroscopy may also be useful as it can indicate whether or not the product is a tertiary silane. The stretch for Si-H is seen at around 2100 and 910 cm⁻¹. In the case of tertiary silanes however, the peak at 910 cm⁻¹ is not seen. The shift or change in these peaks will be affected by the size of the polymer.

Category:Silanes