Complexes demetallation

Iron cyclopentadienyl complexes of 3-(2-chlorophenyl)propanones are cyclized with hydrazine into 1,4-dihydrocinnoline complexes, demetalated with sodium amide to give 3- or 3,4-disubstituted cinnolines (70-80%) (Scheme 29) (88JHC1107). 

By far the most detailed thermodynamic studies have been made by Berezin, who has looked at the equilibria existing in concentrated sulfuric acid. Linstead s group were the first to observe that some of the metal phthalocyanines were demetallated in concentrated sulfuric acid, whereas others appeared indefinitely stable (10). It was shown that all phthalocyanines which resisted attack were of metals whose radii were of the right size to fit nicely into the space available at the center of the ligand. Berezin has since put these observations on a more quantitative basis (19, 21, 26). Labile complexes (i.e., those which are demetallated instantly or fairly rapidly in concentrated sulfuric acid) include those of the alkali metals, alkaline earth metals, Be, Mg, Cd, Hg, Sb(III), Pb, Sn(II), Mn(II), and Fe(III). Stable complexes (demetallated very slowly in acid) include those of Zn, Al, Cl2Sn(IV), OV(IV), Co(II), Rh(II), Os(IV), Ni(II), Pd(II), Pt(II), and Cu(II). The actual rates of decomposition vary widely thus, while calcium and magnesium phthalocyanines are demetallated very rapidly, silver and lead phthalocyanines react fairly slowly (19). The rates of decomposition in 1 M sulfuric acid increase in the sequence (19) Fe(III)... 

The metallation-demetallation reaction of tin tetra(4-pyridyl) porphyrin in Na-hectorite has been investigated (153). UV-vis and luminescence spectra revealed that the adsorbed complex demetallated to the tetra(4-pyridyl) porphyrin dication upon dehydration. This process was reversible, however, indicating that the Sn4 + ion remains in the vicinity of the porphyrin upon demetallation. 

Among complexes of the first row transition metals most often used as templates, copper(II) macrocyclic complexes demetallate least readily as the energy of vacant d-orbitals decreases along the d, d , d, d, d ion series [4, 44], In this case, reductive transmetallation may be used [4,44]. Thus, by treatment of the copper] II) complexes with metallic zinc or zinc amalgam, it is possible to replace Cu by Zn [52] (Scheme 1.4). 

Most mordant dyes are monoazo stmctures. The most important feature of this class of dyes is excellent fastness to light and washing. Mordant dyes are available ia aU shades of the spectmm with the exceptioa of bright violets, blues, and greens. To be useful, the metal complexes must be stable, ie, must not demetallize when subjected to dyebath conditions and aU aftertreatment processes, especially repeated washings. Chromium forms stable chelate rings with mordant dyes which are not affected by treatment with either weak acid or alkaU (see Coordination compounds). 

Arenes, on complexdQon with Cr, Fe, Mn, and so forth, acquire strongly electrophilic character, such complexes m reactions with nucleophiles behave as electrophilic tutroarenes. Synthesis of aromatic tutnles via the temporary complexanon of rutroarenes to the catiotuc cyclopentadienyhron moiety, cyarude addition, and oxidative demetalation v/ith DDQ has been reported fEq. 9.43 ... 

An approach to isobacteriochlorins1 ln-e makes use of Pd(II) or metal-free bilatrienes 1 as starting materials. Cyclization of the corresponding bilatriene derivatives is induced by base in the presence of palladium(II) or zinc(II) which exercise a template effect. Zinc can be readily removed from the cyclized macrotetracycles by acid whereas palladium forms very stable complexes which cannot be demetalated. Prior to the cyclization reaction, an enamine is formed by elimination of hydrogen cyanide from the 1-position. The nucleophilic enamine then attacks the electrophilic 19-position with loss of the leaving group present at the terminal pyrrole ring. 

Complexation and demetalation reactions of porphyrins. D. K. Lavallee, Comments Inorg. Chem., 1986,5,155 (45). 

Sandwich complexes nickel. 5, 35 Sapphyrins, 2, 888 demetallation, 2, 891 metallation, 2, 891 reactions, 2, 891 synthesis, 2, 889 Sarcoplasmic reticulum calcium/magnesium ATPase, 6, 566 skeletal muscle... 

The use of a stereogenic carbon centre allowed an efficient asymmetric induction in the benzannulation reaction towards axial-chiral intermediates in the synthesis of configurationally stable ring-C-functionalised derivatives of al-locolchicinoids [51]. The benzannulation of carbene complex 52 with 1-pen-tyne followed by oxidative demetalation afforded a single diastereomer 53 (Scheme 33). 

Merlic developed a new variation of the thermally induced benzannulation reaction. The dienylcarbene complex 132 was reacted with isonitrile to give an orf/zo-alkoxyaniline derivative 135 [76] (Scheme 56). This annulation product is regiocomplementary to those reported from photochemical reaction of chromium dienyl(amino)carbene complexes. The metathesis of the isocyanide with the dienylcarbene complex 132 generates a chromium-complexed di-enylketenimine intermediate 133 which undergoes electrocyclisation. Final tau-tomerisation and demetalation afford the orf/zo-alkoxyaniline 135. 

The preparation and characterization of the silver(II) complex [AgL] (where H2L = tetraneopentoxyphthalocyanine) has been reported. Electrochemical studies show that oxidation to stable [AginL]+ occurs followed by further oxidation to the radical cation [AgL]2+. Reduction to [AgrL]- leads to demetallation on the electrochemical time scale.207... 

One of the main concerns for resid HDT catalysts is the life cycle, since it is shorten by the deactivating reactions (formation of ammonia, from HDN coke from poor hydrogenation, and metals accumulation from demetallization, etc.) and the complexity of the... 

A mechanistic picture which reconciles the experimental results is given in Scheme 24. It is assumed that both the heteroatom and the double bond of the allyl halide compete for an electrophilic metal carbene. Heteroatom attack yields a metalated ylide 129, which may go on to ylide 131 by demetalation and/or to allylmetal complex 130. Symmetry-allowed [2,3] rearrangement of 131 accounts for product 132, and metal elimination from 130 gives rise to products 132 and 133, corresponding to [2,3] and [1,2] rearrangement, respectively, as well as haloacetate (if R3 = CHc ). 

The magnesium(II) complexes have been relatively little studied as PDT sensitizers, probably because they are rather sensitive to demetalation under mildly acidic conditions (Table 1) and to oxidation (Table 8). 

Because of its ionic size, cadmium(II) does not fit well into the coordination site of the porphyrin nucleus (N-centre distance 200 pm), and the complexes are readily demetalated (stability group IV, Tables land 2). The complexes can be prepared, of course, but zinc(II) compounds have been overwhelmingly favored for PDT purposes. 

Several additional conclusions concerning the nature of the chemisorbed layer can be drawn from the Hall effect measurements (33, 34) The chemisorbed species, together with the surface metal atoms, represent complexes analogical to the ordinary chemical compounds and, consequently, one might expect that the metal atoms involved in these complexes will contribute to lesser extent or not at all to the bulk properties of the metal. Then we should speak about the demetallized surface layer (41). When the Hall voltage was measured as a function of the evaporated film thickness... 

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