SiliaBond® Functionalised Silica Gels: silica-bound reagents

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Silica-Bound Reagents

“Although we now have some excellent methods to effect the construction of target molecules with an ever increasing level of complexity, there is a need to find new, strategically important processes which are environmentally cleaner, more efficient and which lead to greater structural variation in a shorter period of time”

S. V. Ley et al., J. Chem. Soc., Perkin Trans. 1, 2000, 3815

What is special about solid-supported reagents?

Solid-supported reagents provide an attractive and practical means of expediting organic synthesis. The advantages of using bound (i.e. insoluble) reagents instead of their solution phase counterparts in organic synthesis are as follows:

Toxic or difficult to remove reagents and by-products are immobilised and can be separated from the product by a simple filtration
Purification protocols including chromatography and liquid-liquid extractions, which are time consuming and difficult to scale up, are not required
A large excess of reagent can be used, thus driving the reaction to completion
One-pot multiple step reactions are easier to carry out
They are suitable for use in flow-through applications and automated synthesis

The advantages of functionalised silica over polymer-supported equivalents

Silica-bound reagents are a class of modified silica gels that possess reactive moieties and the capacity to conduct chemical transformations. As illustrated in Figure 1, these materials are produced via surface functionalisation of the polar silanol (Si-OH) groups of regular silica.

Figure 1 – Surface functionalisation of regular silica gel, followed by end-capping

Silica-supported reagents and scavengers have a number of distinct advantages over their polymeric counterparts:

Fast Kinetics: since the silica particles are surface functionalised, the rate of reaction is not controlled by diffusion in and out of the polymer. Most SiliaBond® scavengers exhibit reaction times of less than 60 minutes.
Solvent Independent: Silica neither shrinks nor swells in any solvent and, because it is end-capped, it does not partially dissolve in any solvent either.
Easy to use: Silica does not carry a static charge; it is free flowing and thus easy to weigh out and handle. Its high density makes it suitable for small volume work, it does not require extensive washing for high recoveries and it won't stick to glassware!
Thermally Stable: Most SiliaBond® reagents and scavengers can withstand temperatures of over 200 °C and are suitable for use in microwave synthesisers.
Flexible Formats: Since it does not swell, silica can be packed into flow through systems including HPLC columns, Flash & SPE cartridges and 96 well plates.

SiliaBond® reagents for organic synthesis

SiliCycle Inc. is a pioneer in the development of functionalised silica gels, gathered under the name SiliaBond®, for use in synthesis and purification. The backbone of all SiliaBond® products is stationary phase silica gel having particle size 40 – 63 µm and pore size 60 Å.

The following table provides information on the SiliaBond® reagents. All reagents and scavengers are available in Flash, SPE and 96 well plate format. Please contact us with your enquiry or to request a quote.

Manufacturer	SiliCycle® Inc.
Availability	from 10 g to 25 kg
Particle Size	40 - 63 µm (mesh 230 - 400)
Pore Size	60 Å
Specific surface area	500 m²/g

Product Code	Name	Structure
R74530B	SiliaBond® Aluminium Chloride (nec)
Catalyst for Friedel-Crafts acylations and alkylations^1-3, and for the synthesis of ethers (SiliCycle 2008 catalogue, page 71) In comparison to free AlCl₃, the silica-bound equivalent offers milder acidity, superior shelf-life and the ability to conduct non-aqueous work-ups^4,5 Loading: 1.6 mmol/g; compatible with all organic solvents
R52030B R52130B	SiliaBond® Amine SiliaBond® Amine (nec)
Solid-supported primary amine base; can be used as a catalyst for Knoevenagel condensations⁶ and Claisen rearrangements⁷ Useful as: a stationary phase for the separation of peptides, metabolites, steroids, cholesterols, triglycerides and sugars; a weak anion exchanger for the purification of strong acids; and as a supported scavenger of electrophiles & metal complexes Loading: 1.6 mmol/g; compatible with all solvents (aqueous and organic)
R70530B	SiliaBond® Carbodiimide
Used in amide and Weinreb amide syntheses (SiliCycle 2008 catalogue, pages 64 and 84); also applicable in acylsulfonamide synthesis (SiliCycle 2008 catalogue, page 81) and in esterification reactions including synthesis of activated esters Loading: 1.0 mmol/g; not compatible with protic solvents
R66030B	SiliaBond® Carbonate
Solid-supported tetraalkyl ammonium base, used to free base amines in their ammonium salt form⁸ (SiliCycle 2008 catalogue, page 67) Also useful as a scavenger of acids and acidic phenols including HOBt,⁹ which is commonly used in amide coupling reactions (SiliCycle 2008 catalogue, page 77) Loading: 0.7 mmol/g; compatible with all solvents (aqueous and organic)
R66730B	SiliaBond® Cyanoborohydride
Silica-bound equivalent of sodium cyanoborohydride, used in: reductive aminations (SiliCycle 2008 catalogue, page 73 ); the reduction of imines and aldehydes; and the reduction of α,β-unsaturated carbonyl compounds Loading: 1.0 mmol/g; compatible with all solvents (aqueous and organic)
R52230B	SiliaBond® Dichlorotriazine
Silica-bound equivalent of 2,4,6-trichloro-1,3,5-triazine Used in the synthesis of amides, Weinreb amides (SiliCycle 2008 catalogue, pages 85 and 86) and acylsulfonamides (SiliCycle 2008 catalogue, page 81) Loading: 0.7 mmol/g; compatible only with anhydrous aprotic solvents
R76530B	SiliaBond® Diethylamine
Can be used as a solid-supported tertiary amine base for Knoevenagel and Michael reactions (the by-products are immobilised and easily removed by filtration) Also useful as a stationary phase for ion-exchange chromatography and as a weak anion exchanger for solid phase extraction (SPE) and HPLC Loading: 1.2 mmol/g; compatible with all solvents (aqueous and organic)
R45030B	SiliaBond® Dimethylamine
Can be used as a solid-supported tertiary amine base for the catalysis of Michael¹⁰ and Knoevenagel¹¹ reactions ; also applicable in alkane oxidations¹² Unlike polystyrene-based equivalents, the silica-bound amine is not susceptible to cleavage by electrophiles Loading: 1.4 mmol/g; compatible with all solvents (aqueous and organic)
R39030B	SiliaBond® Diphenylphosphine
Can be used as a linker for the immobilisation of catalysts including Pd(PPh₃)₄ for metal catalysed coupling reactions (SiliCycle 2008 catalogue, page 83) Loading: 0.9 mmol/g; requires degassed solvents
R75530B	SiliaBond® DMAP
Silica-bound equivalent of 4-dimethylaminopyridine, used as a catalyst in numerous transformations including acylations, amidations and acetylations Unlike its free counterpart, SiliaBond® DMAP can be removed from the crude reaction mixture by filtration Loading: 0.8 mmol/g; compatible with all organic solvents
R60030B	SiliaBond® Piperazine
Deprotecting and scavenging agent for Fmoc¹³ and Bsmoc¹⁴ protecting groups; also used as a solid-supported catalyst for Knoevenagel reactions According to published research, silica-supported piperazine works more effectively than the polystyrene-based equivalent¹³ Loading: 0.8 mmol/g; compatible with all solvents (aqueous and organic)
R23030B	SiliaBond® Potassium Permanganate (nec)
Oxidises methyl- and alcohol-functionalised molecules to the corresponding carboxylic acids, while the manganese by-product stays adsorbed onto the silica Solid-supported KMnO₄ increases recoveries, facilitates work-up and expands the scope of the chemistry because it can be carried out in non-aqueous solvents¹⁵ Loading: 20% wt/wt, adsorbed onto silica; not compatible with alcohol-, aldehyde- and ketone-functionalised solvents
R51230B	SiliaBond® Propylsulfonic Acid
Silica-bound sulfonic acid that is used as a general acid catalyst and solid-supported base scavenger Can be used to provide an acidic work-up in the absence of aqueous conditions Loading: 1.0 mmol/g; compatible with all solvents (aqueous and organic)
R43030B	SiliaBond® Pyridine
Can be used as a solid-supported tertiary amine base, as a scavenger of acidic molecules and as a Cu²⁺anchor in the oxidation of hydroquinones¹⁶ Loading: 1.3 mmol/g; compatible with all solvents (aqueous and organic)
R24030B	SiliaBond® Pyridinium Chlorochromate (nec)
Versatile solid-supported oxidant^17-20; used in the general oxidation of alcohols to carbonyl compounds, selective oxidation of allylic and benzylic alcohols, organometallic oxidations, oxidative transpositions, oxidative cleavages, allylic and benzylic oxidations, and oxidative cyclisation reactions The use of immobilised pyridinium chlorochromate provides anhydrous conditions that disfavour side-reactions and increase yields; moreover, it facilitates removal of chromium by-products and is compatible with acid-sensitive protecting groups^21,22 When used in conjunction with ultrasound technology, the kinetics are increased and the amount of oxidant required to complete the reaction is reduced^23-25 Loading: 20% wt/wt, adsorbed onto silica; compatible with anhydrous CH₂Cl₂
R24530B	SiliaBond® Pyridinium Dichromate (nec)
Used as an alternative to SiliaBond® pyridinium chlorochromate in nucleoside and carbohydrate oxidation reactions, particularly for fragile molecules²⁶; also used in conjunction with tert-butylhydroperoxide for a variety of oxidative transformations²⁷ Solid-supported pyridinium dichromate is a convenient and effective reagent for the oxidation of allylic and benzylic alcohols, as well as saturated primary and secondary alcohols; moreover, it is compatible with acid-sensitive groups such as ketals²⁸ Loading: 20% wt/wt, adsorbed onto silica; compatible with anhydrous CH₂Cl₂
R68530B	SiliaBond® TBD
Versatile solid-supported base, catalyst and reagent^29,30 It is sufficiently basic to deprotonate moderately acidic hydrogens and has been used in Michael reactions, Knoevenagel condensations, Robinson annulations and nucleophilic epoxidations As a reagent it can be used in the alkylation of phenols (Williamson ether synthesis) and amines, esterification of carboxylic acids by use of alkyl halides, alkylation of activated methylene-containing compounds, dehalogenation of organic halides and synthesis of aryl triflates Loading: 0.9 mmol/g; compatible with all solvents (aqueous and organic)
R72530B	SiliaBond® Tin Hydride
Versatile, clean and selective solid-bound reagent^31,32; the silica support allows toxic and difficult-to-remove organotin by-products to be separated via filtration It is used in a variety of transformations including reduction or dehalogenation of alkyl halides³³ (SiliCycle 2008 catalogue, page 72), ring enlargement of cyclohexa-dienones, Barton-McCombie deoxygenation of alcohols and Giese reactions Loading: 0.6 mmol/g; compatible only with anhydrous and degassed solvents
R60530B	SiliaBond® Tosic Acid
Silica-bound sulfonic acid that is used as a general acid³⁴ catalyst and solid-supported base scavenger Can be used to provide an acidic work-up in the absence of aqueous conditions Loading: 0.8 mmol/g; compatible with all solvents (aqueous and organic)
R44030B	SiliaBond Tosyl Chloride
Reacts with alcohols to yield the bound tosylate, which is used in the synthesis of amines and oxazolines (SiliCycle 2008 catalogue, page 80) Loading: 1.0 mmol/g; compatible with anhydrous aprotic solvents, but is not stable in dimethylformamide (DMF)