Zn-Co-DMC

Scheme 1.1 Schematic Representation of a Zn-Co-DMC with tert-Butanol and ROH as Complexing and Co-Complexing Agents, Respectively.

Additionally, the catalytic activity of Zn-Co-DMCs in this reaction was found to increase upon the addition to the synthesis mixture of excess ZnClj [14], generally regarded as the most... 

It is clear from the numerous accounts in literature that DMCs can efficiently catalyze the copolymerization of CO2 and epoxides. DMCs can however also be used to develop systems that selectively catalyze the CO2 cycloaddition rather than the copolymerization (Scheme 1.4) as is illustrated by the work of Dharman et al. [20]. By itself, a Zn-Co-DMC is an efficient catalyst for the copolymerization reaction. However, the addition of a quaternary ammonium salt to the reaction mixture switches the selectivity of the catalytic system toward the exclusive formation of the cyclic carbonate. The quaternary ammonium ion plays two important roles in the catalytic system it accelerates the diffusion of CO2 into the reaction mixture and it favors a backbiting mechanism. As such, it hinders the growth of the polymer chain and it enables the selective cyclic carbonate production. Although most zinc-containing catalysts for this reaction are very sensitive toward water, Wei et al. have shown that, for example, the combination of Zn-Co-DMC with CTAB (cetyltrimethylammonium bromide) could even use water-contaminated epoxides as an epoxide feed [21]. 

Finally, the catalytic activity of DMCs in esterification reactions can be readily combined with their catalytic activity in epoxide ring-opening polymerizations, as was reported by Suh et al. [35]. This study showed that the copolymerization of propylene oxide with cyclic acid anhydrides such as succinic, maleic, or phthalic anhydride, catalyzed by a Zn-Co-DMC, afforded polyester polyols characterized by a moderate molecular weight and narrow polydispersity index. 

The catalytic activity was shown to vary greatly with metal combination, starting metal salts, (co-)CA, and synthesis procedure. Overall, the most active DMC for this reaction was a Zn-Co-DMC synthesized using ZnCl2 as a Zn source and poly(tetramethylene ether) glycol as a co-CA, although DMCs synthesized in the absence of CAs and co-CAs also had a considerable catalytic activity. 

As the pore size of these DMCs is too small to accommodate the reactant molecules, the catalytic activity of these materials is confined to the outer surface of the particles. The synthesis of nanoparticles using a reverse emulsion technique, therefore, further increased the catalytic activity of the materials. Comparison of these Zn-Co-DMC materials with the Ztf -exchanged zeolite H-p as a reference material moreover showed that DMC materials were both more active and selective catalysts. 

Furthermore, this follow-up study also illustrated the broad applicability of DMCs for the hydroamination of various substrate molecules [37]. Zn-Co-DMCs could catalyze the hydroamination reaction of both aromatic and aliphatic alkynes with aromatic as well as aliphatic amines, a rare trait in heterogeneous hydroamination catalysts. 

PO 50 6.7 50 73 34700 2.0 Reaction carried out using nano lamellar Zn-Co DMC catalyst contains 98 ppm water in the system 277... 

Highly active catalysts with reduced induction periods are obtained by adding a polyether, poly (butane-1,4-diol), as a co-complexing agent or using CaCl2-modified Zn-Co(III) DMC. The resulting poly(POx) shows a very low unsaturation level (0.003-0.006 mequiv. g ) and a narrow molar mass distribution (D= 1.02-1.04). 

Double metal cyanides (DMCs), also known as Prussian blue analogues, are a class of molecular salts built up of a crystalline metal cyanide framework [1], As their name suggests, DMCs feature two different metal centers, one coordinating via the carbon atom of the CN ligand and the other via the nitrogen atom. DMCs have a general structural formula M [M (CN) Jv A typical selection of M metals is Zn(II), Fe(II), Co(II), or Ni(II), whereas Co(ni), Fe(n), Fe(in), Cr(in), or Ir(III) is often used as M [2]. Typical u-v combinations... 

Later that year, the same groups reported the use of DMCs as catalysts for the production of biodiesel and biolubricants from vegetable oils (Scheme 1.7) [25]. Various M-Fe(II)-DMCs (M = Ztf+, Cu +, Ni +, Co " ) and one Zn-Fe(III)-DMC were characterized and closely examined for their catalytic activity in transesterification reactions. A Zn-Fe(II)-DMC synthesized in the presence of both CAs (tert-butanol) and co-CAs (preferably of high molecular weight) showed the highest catalytic activity. The cataljdic activity of the material could again be attributed to coordinatively unsaturated Zn ions in the structure of the catalyst and the number of these sites could be maximized using surfactant molecules in the catalyst synthesis. 

Co-Ni DMC catalyst, Co-Pd DMC catalyst, Co-R DMC catalyst, Estimated by H NMR. Carbonate linkage (%) = carbonate linkage/[carbonate linkage + ether linkage] x 100), Turn over frequency (TOP) = moles of epoxide consumed per mole of Zn per hour, Obtained from GPC analysis, PO = propylene oxide. CHO = cyclohexene oxide, VCHO = 4-vinyl 1-cyclohexene 1,2-epoxide, CPO = Cyclopentene oxide. 

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