Metal derivatives, thermal stability

Colored forms of 5, 8 -disulfonate derivatives of 33 chelate with divalent metal ions, e.g., Ca2+, Cu2+, and Pb2+, causing blueshift.85 The order of blueshift and thermal stability of the chelated photomerocyanine is as follows Ca2+ < Cu2+ < Pb2+. 5 -Methoxy derivative of 33 also gives Ni2+ complexes. This chelation significantly stabilizes photomerocyanine, compared with the nonchelating colored form. In contrast to sulfonate derivatives, chelation of 5 -methoxy derivatives with Ni2+ causes redshift (ca. 40 nm), but their structures are not clear. 

Silver(I) /3-diketonate derivatives have received significant attention due to the ease with which they can be converted to the elemental metal by thermal decomposition techniques such as metal organic chemical vapor deposition (MOCVD).59 The larger cationic radius of silver(I) with respect to copper(I) has caused problems in achieving both good volatility and adequate stability of silver(I) complexes for the use in CVD apparatus. These problems have been overcome with the new techniques such as super critical fluid transport CVD (SFTCVD), aerosol-assisted CVD (AACVD), and spray pyrolysis, where the requirements for volatile precursors are less stringent. 

Syntheses of aryl organometallics other than polyhalogenoaryls by thermal decarboxylation are comparatively rare. There are several reasons for this. For transition elements, the thermal stability of simple aryls is often low, especially by comparison with polyhalogenoaryl derivatives, thereby excluding syntheses at elevated temperatures. Electron-withdrawing substituents frequently aid thermal decarboxylation (Section III,A-D), and their absence inhibits major mechanistic paths to both transition metal and main group element derivatives, e.g., SEi (carbanionic) and oxidative addition (Section II). In thermal decomposition of... 

The fe-ester derivatives of trithiophosphinic acids, RP(S)(SR )2, have also been studied and, similar to the metal and ammonium salts, show enhanced thermal stability compared to their parent acids. Trithiophosphonic acid Zj zA (tr im e t lr y 1 s i 1 y 1) esters have been synthesised from organo-/u.v(trim-ethylsilyl)phosphanes with elemental sulfur in toluene (Equation 40).53 These 6z,s(silyl esters) can be readily converted into the parent trithiophosphinic acid by a very slow, controlled reaction with water or methanol.53... 

Since group 4 derived species are of particular interest as catalysts for olefin polymerization and epoxidation reactions, the thermal stability of surface metal-alkyl species, as weU as their reactivity towards water, alcohols and water, deserve some attention. On the other hand, mono(siloxy) metaUiydrocarbyl species can be converted into bis- or tris(siloxy)metal hydrides by reaction with hydrogen [16, 41, 46-48]. Such species are less susceptible to leaching and can be used as pre-catalysts for the hydrogenolysis of C-C bonds, alkane metathesis and, eventually, for epoxidation and other reactions. 

The 18-electron rale is not obeyed as consistently by these types of oiganome-tank compounds a by the carbonyl and nitrosyl complexes and their derivatives. For example, in addition to ferrocene. M(i 5-CsHs)2 compounds are known for most of the other elements of the first transition series (M — V, Cr, Mn.Co, Ni) and these cannot obey ihe 18-electron rule. However, only ferrocene shows exceptional thermal stability (stable to 500 C) and is not oxidized by air. Furthermore, cobaltocene, a 19-electron species, is readily oxidized to the 18-electron cobaltocenium ion. (Co(ip-CsH )3)4 , which reflects much of the thermal stability of ferrocene. Mixed cyclopentadienyl carbonyl complexes are common K -CjHjMCO) ]. [(if-CjH )-Cr(CO), . [( -CjHOMnCCOjJ, [(>r-C,H,>Fe(CO ,, . [fo -CjiyCoCoy. and (ip-CsH,)Ni(CO) 2. Of interest is the fact that among these compounds, the odd-atomic-number elements (V. Mn, and Co) form monomers and the even-atomic-number elements (Cr. Fe. and Ni) Ibrm dimers, which is in direct contrast to the behavior shown by the simple carbonyl complexes. Cyclopentadienyl derivatives are now known for every main group and transition metal of the periodic table and for most of the -block metals.89... 

The discovery of hexamethyltungsten by Shortland and Wilkinson (259, 260) has prompted an interest in the synthesis and physical properties of alkylated transition metal compounds. The relatively high thermal stability of these derivatives is plausibly ascribed to the lack of a low-energy decomposition pathway. This is particularly true in the case of ligands such as Me3SiCH2 — and Me3 CCH2 for which /3-hydrogen transfer is precluded (43, 282). 

The M(OR) derivatives are known now for almost all the elements of the Periodic Table (including the transuranium elements and Xenon). They are formal analogs of hydroxides but possess much higher thermal stability. Their properties are determined not only by the electronegativity of the metal atom but also by the nature of the radical — its ramification and the acidity of the corresponding alcohol, which provides their various properties. From this point of view they can be subdivided into the following groups of compounds ... 

Derivatives of alkaline, alkaline earth metals and phenols, naphtols, an-troles, etc. (pK> 10). These compounds are salts in their nature and, as the salts of strong bases and moderately weak acids, can exist in water solutions. They are soluble only in polar solvents (water, liquid ammonia), are prone to form adducts with phenols, water, etc., have high thermal stability and cannot be transferred into the gas phase. 

The molecular derivatives of platinum group metals are usually rather well soluble in organic solvents and volatile in vacuum. At normal pressure they demonstrate very low thermal stability and easily decompose producing fine metal powders. This decomposition occurs more easily for the derivatives of branched radicals as it is based on a P-hydrogen elimination process. An important feature of the chemical behavior of these alkoxide complexes is their rather high stability to hydrolysis. Some derivatives can even form outer sphere hydrates when reacted with water in organic solvents. This stability to hydrolysis can at least partially be due to the kinetic inertness of the complexes of this group. 

Both H2Pc and its derivatives exhibit high thermal stability. For example, CuPc can be sublimed without decomposition at 500-580°C under inert gas and normal pressure [7], In vacuum, stability up to 900 °C has been reported [44], Polychloro CuPc is thermally stable up to 600°C in vacuum. At higher temperature it decomposes without sublimation. CuPc decomposes vigorously at 405-420°C in air. In nitrogen, sublimation and decomposition occur simultaneously at 460-630 °C [45,46], Generally all metal Pc s are more stable thermally in N2 than in 02. CuPc changes from the a- to the (3-form at 250-430°C [47],... 

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