Solid-state metathesis reactions

Wallace C H, Rao L, Kim S-H, Heath J R, Nicol M and Kaner R B 1998 Solid-state metathesis reactions under pressure a rapid route to crystalline gallium nitride Appl. Phys. Lett. 72 596... 

The chemistry of lanthanide nitridoborates was developed by the more flexible and more efficient solid-state metathesis route by using nitridoborate salts and a lanthanide trichloride, at reaction temperatures as low as 600 °C. This type of reaction has been previously established and studied in some detail for reactions, such as the synthesis of lanthanide nitrides (LnN). Following this concept, lanthanum nitridoborates are obtained from reactions of lanthanum trichloride and lithium nitridoborate (or calcium nitridoborate), performed in a salt-balanced manner with respect to the formation of the co-produced liCl ... 

In contrast, less is known about La-(CNx) compounds. The composition La2(CN2)3 was reported many years ago [43], without any structural information. Solid-state metathesis reactions of lanthanum chloride with Li2(CN2) or Zn(CN2) have recently brought up three series of the lanthanide compounds Ln2(CN2)3 [44], LnCl(CN2) [45], and Ln2Cl(CN2)N [46], Syntheses routes for Ln-(CNx) compounds containing new anions such as [C2N4] are to be developed, as well as for compounds in the La-B-C-N system (Fig. 8.15). 

Brus and co-workers produced nanoparticles of CdSe from the pyrolysis of the single-molecular cadmium selenate precursor [Cd(SePh)2].392 The similar metal(benzylthiolate) compounds [M(SCH2C6i Is)2] (M = Zn, Cd) were also used in the solid-state preparation of ZnS and CdS particles and produced mixtures of the hexagonal and cubic phases of the crystallites, with sizes of 5nm, on thermolysis between 200 °C and 400 °C under nitrogen.393 The bis(trialkylsilyl)chalco-genides [(Me3SiE)2Cd] (E = S, Se), prepared by heterocumulene metathesis as in Equation (11), were used to produce nanoparticles. If the reactions are carried out in TOPO, TOPO-passivated CdE nanoparticles can be obtained although there was little control over particle size 394... 

The exact nature of the alkylidenes formed on various oxide surfaces is still uncertain, as is the nature of the alkylidenes responsible for the often observed metathesis activity. Mo(N)(CH2CMe3)3 also has been employed as a precursor to a surface-bound species believed to be of the type Mo(NH)(CHCMe3)(CH2CMe3) (Osurf) [115]. Although the alkylidene carbon atom could not be observed in solid state NMR spectra, which is typical of surface supported alkylidenes, reaction with acetone to give 2,4,4-trimethylpent-2-ene quantitatively confirmed the presence of the reactive neopentylidene complex. Such species would initiate various metathesis reactions when prepared on partially dehydroxylated silica. 

An unusual synthetic approach to PF copolymers was demonstrated by Bunz and coworkers [370], who prepared poly(fluorene ethynylene) 281a-e by metathesis polymerization reaction (Scheme 2.44) [370], The aggregation of polymers 281 in concentrated solutions and in solid state is manifested in slight (up to 10-20 nm) red shift of the absorbance and emission peaks, although solutions and films emit pure blue light. 

Combustion Synthesis. Besides solid-state reactions requiring heating even for several days at high temperatures to be completed, fast reactions are also known which give their products in minutes or seconds. Several nearly equivalent names are used for these reactions such as solid-state combustion, combustion synthesis, self-propagating (self-sustained) high-temperature synthesis. Solid state direct combinations and solid-state metathesis have been described. 

Solid-state metathesis reactions. For a number of compounds, solid-state metathesis (exchange) reactions have the advantages of a rapid high-yield method that starts from room-temperature solids and needs little equipment. The principle behind these reactions is to use the exothermicity of formation of a salt to rapidly produce a compound. We may say that for instance a metal halide is combined with an alkali (or alkaline earth) compound of a /7-block element to produce the wanted product together with a salt which is then washed away with water or alcohol. Metathesis reactions have been used successfully in the preparation of several crystalline refractory materials such as borides, chalcogenides, nitrides. 

Solid-state metathesis reactions as an effective synthetic route to 13-15 compounds have been discussed by Treece et al. (1993). The reaction scheme ... 

A solid-state modification of the ring-closing metathesis reaction has also been reported in the preparation of the tetrahydroazepine derivative 189 <1999S138> and of the lactams 190 (e.g., 190, R1 Ph, R2 = H, R3 = NHBOC 36% overall yield) <1998TL2667>. 

The second attempt to synthesize Mg(BH4)2 has been made in our laboratory by the mechano-chemical activation synthesis (MCAS) (or solid state metathesis reaction) [175] according to the reaction of (3.37b). The starting powder mixture of as-received NaBH4 (98% purity) and anhydrous MgCI2 (99% purity) were mixed together in the 2 1 stoichiometric ratio with the objective of initiating the following metathesis reaction... 

Figure 1 XRD analysis of Pf -(Cys)/nAu + reaction. 0.5 - 2.0 eq. of added to 1.0 eq. of Pt -(Cys), precipitated, and scanned on a Scintag Xj 0/0 automated powder diffractometer with a Cu target, a peltier-cooled solid-state detector, and zero background Si (510) sample support. Both line sets of standard diffractions are included for fee Pt (red lines) and Au (blue lines). Reaction sc heme for metathesis/transmetallation reaction between Pt -(Cys)/Au...

Grubbs reported an unexpected reaction, which may be at play during the course of the synthesis of the second-generation olefin metathesis catalyst (264) (equation 46). The product (265), air stable both in solution and in the solid state, results from the C-H activation of one ortho methyl of the mesityl group. Unfortunately, no explanation was proposed for the mechanistic pathway leading to (265). 

---