Transition metal complexes thermolysis

Attempts have been made to catalyze the arrangement of 3-oxaquadricyclane to oxepins with transition-metal complexes.1 32 1 35 When dimethyl 2,4-dimethyl-3-oxaquadricyclane-l,5-dicarboxylate is treated with bis(benzonitrile)dichloroplatinum(II) or dicarbonylrhodium chloride dimer, an oxepin with a substitution pattern different from that following thermolysis is obtained as the main product. Instead of dimethyl 2,7-dimethyloxepin-4,5-dicarboxylate, the product of the thermal isomerization, dimethyl 2,5-dimethyloxepin-3,4-dicarboxylate (12), is formed due to the cleavage of a C O bond. This transition metal catalyzed cleavage accounts also for the formation of a 6-hydroxyfulvene [(cyclopentadienylidene)methanol] derivative (10-15%) and a substituted phenol (2-6%) as minor products.135 The proportion of reaction products is dependent on solvent, catalyst, and temperature. 

As the ladder frameworks are highly strained, the Si-Si bonds are easily cleaved by thermolysis, photolysis, and the action of electrophiles and transition metal complexes. 

Certain transition metal complexes catalyze the decomposition of diazo compounds. The metal-bonded carbene intermediates behave differently from the free species generated via photolysis or thermolysis of the corresponding carbene precursor. The first catalytic asymmetric cyclopropanation reaction was reported in 1966 when Nozaki et al.93 showed that the cyclopropane compound trans- 182 was obtained as the major product from the cyclopropanation of styrene with diazoacetate with an ee value of 6% (Scheme 5-56). This reaction was effected by a copper(II) complex 181 that bears a salicyladimine ligand. 

Certain transition metal complexes catalyze the decomposition of diazo compounds, where the metal-bound carbene intermediates behave differently from the free species generated by their photolysis or thermolysis. 

A reaction that may be characteristic of T 2- and q1-complexes formed from transition metals is thermolysis with cleavage of one CO bond resulting in the loss of CO and formation of an oxo compound. 

Lappert developed the thermolysis of an electron-rich olefin in the presence of a transition metal complex as another way to synthesise these compounds [4], When, in 1975, Clarke and Taube published their findings on carbon coordinated purine transition metal complexes [5], transition metal NHC complexes with functionalised NHC made their debut in biochemistry. The chemistry of carbenes from natural products became firmly established following the discovery that the catalytic activity of thiamine (vitamin Bl) is based on the intermediate formation of a carbene derived from thiazole [6-9] (see Figure 1.2). 

Chloro(methoxy)- and chloro(phenoxy)carbenes, which are generated from the diazirine precursors, behave as ambiphiles in additions to alkenes, exhibiting high reactivities toward both electron-poor and electron-rich olefins. Methoxy(phenyl)- and ferrocenyl(methoxy)methylenes have been transferred in a stereospecific manner from transition metal complexes of these species to electron-deficient alkenes. Irradiation of benzocyclobutanedione with UV light induces a rearrangement of the cyclic a-diketone to 17, which has been trapped by alkenes in good yields " . Thermolysis of 18 gives rise to nucleophilic dimethoxycarbene, which has been intercepted by electron-deficient olefins or by styrene derivatives. 

The complex [Ph2BiMn(CO)5] was synthesized by Whitmire and Cassidy " as a candidate single-source precursor for the alloy MnBi, which has interesting magnetic properties. Unfortunately no thermolysis data were presented. Some bismuth-transition metal complexes are surprisingly stable, e.g. " . 

Thermolysis rates are enhanced substantially by the presence of certain Lewis acids (e.g. boron and aluminum halides), and transition metal salts (e.g. Cu ", Ag1).46 There is also evidence that complexes formed between azo-compounds and Lewis acids (e.g. ethyl aluminum scsquichloridc) undergo thermolysis or photolysis to give complexed radicals which have different specificity to uncomplexed radicals.81 83... 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Metal alkyls of late transition metals readily undergo decomposition by /3-hydrogen elimination.31 In principle, it should therefore be possible to prepare aryne complexes of dw metals by thermolysis of appropriately substituted late transition-metal aryl complexes. However, in practice this... 

Figure 1.12 Transition metal NHC complexes via thermolysis of electron-rich olefins or isocyanide template synthesis.

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