Halogenide Complexes

The syntheses discussed above can all be scaled up by at least a factor of 3 without significantly lowering the yield. The /ac-Mo(NH3)3X3 (X = CF3SO3, Cl, Br, I) compounds are very susceptible to oxidation by the atmospheric dioxygen and should only be handled in a protective atmosphere. The halogenide complexes can, however, be handled in air for shorter (<15min) periods of time. The compounds have all been characterized by UV-vis diffuse reflectance spectroscopy./ac-Mo(NH3)3(CF3S03)3 ... 

Halogenide complexes of heavy metals such as mercury bismuth, cadmium and antimony can be used in the titration of some basic heterocyclic nitrogen compounds < and among others, thiamineS > In this latter example, thiamine was titrated... 

Selective reaction of the complex-bounded A1C13 with alkali halogenides. 

In late 1975, Enders et al.156) started a research project directed towards the development of a new synthetic method for asymmetric carbon-carbon bond formation. A new chiral auxiliary, namely the (S)-proline derivative SAMP (137), was allowed to react with aldehydes and ketones to give the hydrazones (138), which can be alkylated in the a-position in an diastereoselective manner 157,158). Lithiation 159) of the SAMP hydrazones (138), which are formed in excellent yields, leads to chelate complexes of known configuration 160). Upon treatment of the chelate complexes with alkyl halogenides the new hydrazones (139) are formed. Cleavage of the product hydrazones (139) leads to 2-alkylated carbonyl compounds (140). 

The need to better control surface-initiated polymerization recently led to the development of controlled radical polymerization techniques. The trick is to keep the concentration of free radicals low in order to decrease the number of side reactions. This is achieved by introducing a dormant species in equilibrium with the active free radical. Important reactions are the living radical polymerization with 2,2,4,4-methylpiperidine N-oxide (TEMPO) [439], reversible addition fragment chain transfer (RAFT) which utilizes so-called iniferters (a word formed from initiator, chain transfer and terminator) [440], and atom transfer radical polymerization (ATRP) [441-443]. The latter forms radicals by added metal complexes as copper halogenides which exhibit reversible reduction-oxidation processes. 

Fig. 6. Rehm-Weller plots for halogenide and pseudohalogenide inhibitors of some uranyl complexes. Redrawn from Park et al. (1990).

Anion sensing using visible-emitting lanthanide probes has proven successful (Tsukube et al., 2006) and this work is now being extended to Ybm probes, particularly for the detection of thiocyanate. The latter is the principal metabolite of cyanide anion and exists in human serum, saliva, and urine. The luminescent probe is a complex of hexadentate tetrakis(2-pyridylmethyl)ethylenediamine (tpen, see fig. 119) which bears two water molecules, [Yb(tpen)(H20)2](0tf)3. In absence of anion coordination, the 980-nm luminescence is quenched, but the replacement of the water molecules with thiocyanate or other anions such as acetate, nitrate or halogenides removes the quenching, which makes the complex a responsive probe. The largest effect (a six-fold increase in luminescence) is obtained for thiocyanate, followed by acetate and nitrate (3.5-fold) and chloride (two-fold). 

Treatment of 1,3,2-dithiastannetane 72 with sulfur halogenides resulted in a cleavage of the four-membered ring and formation of a complex mixture of products (Scheme 9) <1996CB663>. 

A specific, greatly simplified form of the general scheme (79) is the initiation of 2-methylpropene polymerization [302]. It occurs in the presence of VC14 (Ti halogenides, etc.) and photons. The donor-acceptor complex of 2-methylpropene with VC14 forms an intermediate... 

These are halogenated adds, metallic halogenides or a mixture of both, forming complexes with aromatics, AIO —HCl, BF3—HF, etc. They act according to the following prindple ... 

An interesting variant is the in situ preparation of transition metal alkoxides from the corresponding halogenides and subsequent reaction with an azolium salt to form the NHC transition metal complex [69]. This works particularly well with rhodium, iridium and ruthenium where [(ii -cod)MCl]j (M = Rh, Ir) and [Cp RuCl]2 are readily available [57,58,71]. 

---