Diazoacetates polymerization

Proline-derived Rh(I) catalyst (36) has been involved in ethyl diazoacetate polymerization.36 The poly(ethyl 2-ylideneacetate) polymers obtained are syndiotactic and have polydispersities slighter higher than 2. Interestingly, switching from rhodium to iridium leads to dimerization, no polymer being observed. 

Allylruthenium(IV) complexes such as 23 convert into highly performing metathesis catalysts on treatment with ethyl diazoacetate (Fig. 3) [17]. Again,the structure of the active species is unknown and only applications to polymerization reactions have been reported so far. 

Over the last few years it has become clear that rhodium(II) acetate is more effective than the copper catalysts in generating cyclopropenes.12 126 As shown in Scheme 28,12S a range of functionality, including terminal alkynes, can be tolerated in the reaction with methyl diazoacetate. Reactions with phenyl-acetylene and ethoxyacetylene were unsuccessful, however, because the alkyne polymerized under the reaction conditions. 

The importance of the substituents at the electron-deficient alkene is illustrated by the reactions between ethyl diazoacetate and acrylaldehyde, to give 15, followed by polymerization, 2-chloro-acrylaldehyde, to give cis- and tran -cyclopropanes 16, and 2-methylacrylaldehyde, to give cis-and tra/ii-cyclopropanes 17, together with byproducts. ... 

The catalytic activity of low-valent ruthenium species in carbene-transfer reactions is only beginning to emerge. The ruthenium(O) cluster RujCCO), catalyzed formation of ethyl 2-butyloxycyclopropane-l-carboxylate from ethyl diazoacetate and butyl vinyl ether (65 °C, excess of alkene, 0.5 mol% of catalyst yield 65%), but seems not to have been further utilized. The ruthenacarborane clusters 6 and 7 as well as the polymeric diacetatotetracarbonyl-diruthenium (8) have catalytic activity comparable to that of rhodium(II) carboxylates for the cyclopropanation of simple alkenes, cycloalkenes, 1,3-dienes, enol ethers, and styrene with diazoacetic esters. Catalyst 8 also proved exceptionally suitable for the cyclopropanation using a-diazo-a-trialkylsilylacetic esters. ... 

A screening of ruthenium(II) carboxylates and several ruthenium(II) chloride complexes has identified tetrakis(trifluoroacetato)diruthenium as an excellent catalyst for the cyclo-propanation of cyclooctene with ethyl diazoacetate (60°C, excess of alkene, 0.75 mol% of catalyst yield of ethyl bicyclo[6.1,0]nonane-9-carboxylate 99% endojexo 1.65)." With several other ruthenium(II) complexes, ring-opening metathesis polymerization of cyclooctene competes strongly with the cyclopropanation reaction. 

Ethyl diazoacetate (228 mg, 2.0 mmol) was added at a controlled rate over a 6-8 h period to a stirred mixture of the alkene (20.0 mmol) or diene (10.0 mmol) and the catalyst (0.01 -0,02 mmol) under and ordinarily at 25 C. For copper(I) triflate catalyzed reactions with enol ethers, the diazo ester dissolved in the enol ether w as added to copper(II) triflate in EtjO in order to minimize polymerization of the enol ether. Alkenes were generally purified by distillation prior to their use. The initial solubility of the transition metal compound was dependent on the alkene employed, and, with the exception of Rhg(CO)jg, bis(acetylacetonato)copper(II), and copper bronze, homogeneous solutions were obtained prior to or immediately after the initial addition of ethyl diazoacetate. 1 h after addition was complete, EtjO was added, the resulting solution was washed twice with sat. aq NaHC03 dried (MgSOJ. EtjO and excess alkene were distilled under reduced pressure. The desired cyclopropanes were obtained either by fractional bulb-to-bulb distillation or by preparative GC (Table 8). 

Another type of polymer-supported chiral catalyst for asymmetric cyclopropanation was obtained by electropolymerization of the tetraspirobifluorenylporphyrin ruthenium complex [143]. The cyclopropanation of styrene with diazoacetate, catalyzed by the polymeric catalyst 227, proceeded efficiently at room temperature with good yields (80-90%) and moderate enantioselectivities (up to 53% at -40 °C) (Scheme 3.75). PS-supported versions of the chiral ruthenium-porphyrin complexes 231 (Scheme 3.76) were also prepared and used for the same reaction [144]. The cyclopropanation of styrene by ethyl diazoacetate proceeded well in the presence of the polymeric catalyst to give the product in good yields (60-88%) with high stereoselectivities (71-90% ee). The highest ee-value (90%) was obtained for the cyclopropanation of p-bromostyrene. 

First of all we compared the behaviour of these catalysts in the benchmark reaction of ethyl diazoacetate (1) with styrene (2) (Scheme 1) using equimol amounts of both reagents or even a twofold excess of diazoacetate (Table 1). Under these conditions the selectivity with regard to diazoacetate was low and did not depend on the catalyst. This result was not unexpected because this reagent has a great tendency to dimerize and polymerize so a large excess of alkene is generally used. 

The reagent is generated in situ by dehydrochlorination of ethoxyacetyl chloride with triethylamine at —78°. It appears to be fairly stable at this temperature but slowly polymerizes at room temperature. It is also formed to some extent by photochemical Wolff rearrangement of ethyl diazoacetate. 

Similar studies involving metal-mediated carbene polymerization using diazocarbonyl monomers were reported in 2006 by de Brain. These showed that rhodium-based catalysts could be used for the stereoselective polymerization of carbenes generated from alkyl diazoacetates (Figure 31.5) [26]. Indeed, such catalysts were the first to produce high-molecular-weight, functionalized polymethylene 3, and demonstrated the first use of a mononuclear Rh(I) species (4 and 5) for carbene transfer reactions. The resulting poly(alkyl 2-ylideneacetate)s displayed... 

Optically active ruthenium porphyrins have also been recently reported [184]. It was decided to target porphyrins bearing spirobifluorenyl groups to allow polymerization and chiral groups for asymmetric induction, as monomers (Scheme 16). As a second example of carbene transfer catalyzed by chiral ruthenium porphyrin polymers, intramolecular cyclopropanation of trans-cinnamyl diazoacetate (Scheme 17) was found to proceed with good enantios-electivity (85%) and high product turnover munbers [186]. 

Instead of a conventional polymerization reaction, Demonceau et al. [65] observed ring-opening metathesis polymerization of norbornene, which was initialized by ethyl diazoacetate or trimethyl-silyldiazomethane (Scheme 22.18). The used ruthenium complexes 62 and 63 gave moderate yields of the polymer (Figure 22.22, Table 22.27). 

For aromatic molecules of intermediate size these hydrophobic interactions seem to be more important than electrostatic charge effects, as has been concluded from work on soluble polymers [33]. However, it is also possible for hydrophobic interactions to become so strong that substrate and product molecules block the polymeric catalyst, and some observations of decreasing activity of catalyst with progressing reaction have been ascribed to this cause [1]. It has been noted that a similar effect may be caused by degradation (desulphonation) of the polysulphonic acid [1] or, as in Noller and Gruber s study of the decomposition of ethyl diazoacetate [19], by the accumulation of bubbles of a gaseous reaction product in the pores of the resin. 

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