Anion coordination polymers

Another bis-bisurea ligand 48 featuring a 1,5-naphthylene-bridged spacer was also synthesized by Wu and co-workers. This rigid bis-bidentate ligand could act as a linker to afford ID anion coordination polymers (ACPs) and dinuclear complexes, depending on the anions complexed [100]. 

In studying two-component polymerization catalysts, beginning with Feldman and Perry (161), a radioactive label was introduced into the growing polymer chain by quenching the polymerization with tritiated alcohols. The use of these quenching agents is based on the concept of the anionic coordination mechanism of olefin polymerization occurring... 

This review deals with the chemistry and coordination complexes of isoelectronic analogues of common oxo-anions of phosphorus such as PO3, POl", RPOl" and R2POy. The article begins with a discussion of homoleptic systems in which all of the 0x0 ligands are replaced by imido (NR) groups. This is followed by an account of heteroleptic phosphorus-centered anions, including [RN(E)P(/<-NR )2P(E)NR]2-, [EP(NR)3]3-, [RP(E)(NR)2] and [R2P(E)(NR )] (E=0,S, Se, Te). The emphasis is on the wide variety of coordination modes exhibited by these poly-dentate ligands, which have both hard (NR) and soft (S, Se or Te) centers. Possible applications of their metal complexes include new catalytic systems, coordination polymers with unique properties, and novel porous materials. 

Other Fe(II) btr coordination polymers with monovalent anions have been obtained [9, 67, 68]. [Fe(btr)3](CF3S03)2 is a HS compound. The stabilisation of the HS state is presumably due to the large size of the trifluo-romethanesulfonate anion, which could increase the size of the cavities and, by mechanical influence, the Fe-N bond lengths, precluding the thermal spin crossover [9]. X-ray investigations should clarify this behaviour. Iron(II) btr compounds with BF4 and PF6 anions exhibit incomplete TSCO, with Ti/2 150 K and 170 K, respectively. Interestingly, the 3D architecture of [Fe(btr)3](Cl04)2 is not retained in these derivatives as water molecules are detected in the coordination sphere of some Fe species [68]. 

Two general types of polymer electrolytes have been intensively investigated, polymer-salt complexes and polyelectrolytes. A typical polymer-salt complex consists of a coordinating polymer, usually a polyether, in which a salt, e.g. LiC104, is dissolved. Fig. 5.1(a). Both anions and cations can be mobile in these types of electrolytes. By contrast, polyelectrolytes contain charged groups, either cations or anions, covalently attached to the polymer. Fig. 5.1(h), so only the counterion is mobile. 

Excluding polymerizations with anionic coordination initiators, the polymer molecular weights are low for anionic polymerizations of propylene oxide (<6000) [Clinton and Matlock, 1986 Boileau, 1989 Gagnon, 1986 Ishii and Sakai, 1969 Sepulchre et al., 1979]. Polymerization is severely limited by chain transfer to monomer. This involves proton abstraction from the methyl group attached to the epoxide ring followed by rapid ring cleavage to form the allyl alkoxide anion VII, which isomerizes partially to the enolate anion VIII. Species VII and VIII reinitiate polymerization of propylene oxide as evidenced... 

Chain transfer to monomer is much less prevalent for polymerizations with most of the anionic coordination initiators and higher polymer molecular weights have heen obtained [Bots et al., 1987]. 

The mechanism for the stereoselective polymerization of a-olefins and other nonpolar alkenes is a Ti-complexation of monomer and transition metal (utilizing the latter s if-orbitals) followed by a four-center anionic coordination insertion process in which monomer is inserted into a metal-carbon bond as described in Fig. 8-10. Support for the initial Tt-com-plexation has come from ESR, NMR, and IR studies [Burfield, 1984], The insertion reaction has both cationic and anionic features. There is a concerted nucleophilic attack by the incipient carbanion polymer chain end on the a-carbon of the double bond together with an electrophilic attack by the cationic counterion on the alkene Ti-electrons. 

When nonpolar solvents are employed, polymerization proceeds by an anionic coordination mechanism. The counterion directs isotactic placement of entering monomer units into the polymer chain. The extent of isotactic placement increases with the coordinating power of the counterion (Li > NaK. Cs). The small lithium ion has the greatest coordinating power and yields the most stereoselective polymerization. Increased reaction temperature decreases the isoselectivity. 

The flexible ligand 4 can adopt different eonformations when it reacts with metal salts [51], For instance, ligand 4 reaeted with varied zinc(II) salts ZnX [X = (BF4)2, SO4, CI2, Br2,12] to afford a series of eoordination polymers with different structures. Coordination polymer [Zn(4)2](BF4)2 n (22) has an infinite 2D eationic double layered structure in which the ligand 4 has cis, cis, cw-eonformation, and the tetrafluoroborate anions are loeated in the voids of... 

A number of cyano-bridged coordination polymers with Prussian Blue-related structures, in which extended linear Ag(CN)2 or AufCNH bridges take the place of the OT bridges of the prototype, show 3-fold interpenetration [1]. A typical example is that of Rb[Cd Ag(CN)2)3] consisting of Rb+ cations and a 3-fold interpenetrating polymeric anion, whose structure is shown in Figure 31. 

The zincates K [ZnR(tBuNCH=CHN Bu)] contain the diazabutadiene fragment. They have been made, via a series of radical-anion complexes, from the alkylation of B uN = CHCH = N Bu by potassium in the presence of organozinc compounds, and characterized as THF and Et20 adducts, 70 and 71, respectively. Each forms linear coordination polymers comprising alternate potassium cations and zincate anions held together... 

POLYALLOMER RESINS. These are block copolymers prepared by polymerizing monomers in the presence of anionic coordination catalysts. The polymer chains in polyallomers are composed of homopolymerized segments of each of the monomers employed. The structure of a typical polyallomer can be represented as ... 

Figure 10.93 A coordination polymer Borromean weave containing water guests in the open cavities and supported by saturated hydrogen bonding to nitrate anions.113...

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