1.2- Diaminobenzene complexes

Which of the following isomers of diaminobenzene can form chelating complexes Explain. 

To conclude the present section, it is noted that closed-chain Mn4 complexes have been also prepared. This is, for example, the case of [Mn404(tpdp)2]4+ (the electrochemical behaviour of which has not been examined)81 or that of [Mn4in(salmphen)6], (salmphen = 7V,A -disalicy-lidene-l,3-diaminobenzene), Figure 56.82... 

Treatment of RuCl3 xH20 with Hacac gives tra i-[Ru(acac)2Cl2] (the first trani-bis(acac) complex to have been made). The complex anion is a precursor to a range of Ru, Ru, and Ru tra 5 -bis(acac) complexes including tra w-[Ru (acac)2L2] where L = MeCN or pyrazine (pyz) the cis analogs result from direct reaction between [Ru(acac)3] and MeCN or pyz (see also Section 5.5.3.4.1). The reaction of [Ru(acac)3] with molten 1,3-diaminobenzene yields complexes (8)-(10). Their formation involves Ru-mediated oxidative di- and trimerization of 1,3-diaminobenzene. Structural data for [Ru(acac)3] and [Ru(3-Bracac)3] (H-3-Bracac = 3-bromopentane-2,4-dione)... 

The diimines (38) and (39) formed by the condensation of benzil with en or 1,2-diaminobenzene, respectively, have been shown to form the tetrahedral complexes [CdL].352... 

Ligands such as aniline (an), 1,2-diaminobenzene (dab, o-phenylenediamine) and 2,2 -dia-minobiphenyl886 887 are classed separately, not because their ability to bind to a central metal is any less than the ligands discussed previously, but because of their potential non-innocent behavior888 with respect to internal redox reactions. Indeed, the dark blue complex isolated from the air oxidation of Con/dab in aqueous ethanol (a conventional route to yellow Co(diamine)3+ systems) has been shown to have structure (117) with five-coordinate Co11.888 Related diimine complexes have been reported for Ni11889 as well as the conventional Ni(dab)(+,890 Co(dab)3+ 891 and Pt(dab) + 892 systems. 

Template reactions between malonaldehydes and diamines in the presence of copper(II), nickel(II) or cobalt(II) salts yield neutral macrocyclic complexes (equation 15).99-102 Both aliphatic102 and aromatic101 diamines can be used. In certain cases, non-macrocyclic intermediates can be isolated and subsequently converted into unsymmetrical macrocyclic complexes by reaction with a different diamine (Scheme ll).101 These methods are more versatile and more convenient than an earlier template reaction in which propynal replaces the malonaldehyde (equation 16).103 This latter method can also be used for the non-template synthesis of the macrocyclic ligand in relatively poor yield. A further variation on this reaction type allows the use of an enol ether (vinylogous ester), which provides more flexibility with respect to substituents (equation 17).104 The approach illustrated in equation (15), and Scheme 11 can be extended to include reactions of (3-diketones. The benzodiazepines, which result from reaction between 1,2-diaminobenzenes and (3-diketones, can also serve as precursors in the metal template reaction (Scheme 12).101 105 106 The macrocyclic complex product (46) in this sequence, being unsubstituted on the meso carbon atom, has been shown to undergo an electrochemical oxidative dimerization (equation 18).107... 

Monoiminophosphines. As illustrated in Scheme II, PCHO condenses with a wide variety of simple and functionalized monoamines. Studies of the Mo(O) derivatives of several of these ligands demonstrate that they efficiently displace CO from Mo(CO)e affording (chel)Mo(CO)4 or fac-(chel)Mo(CO)3 derivatives (4). Similar, but bimetallic, complexes can be obtained from the ligands prepared by condensations with nonchelating diamines such as m- or p-diaminobenzene. 

Figure 6-41. The reaction of 2,6-diacetylpyridine with 1,2-diaminobenzene gives a complex product 6.42. Steric interactions prevent 6.43 from being formed.

As an extension of the successful Strecker reaction under high pressure [83], a heterocyclic version of this reaction was investigated by us but met with very limited success. For example, 1 equivalent of 1,2-diacetylbenzene (152) with 1,2-diaminobenzene (153) and TMSCN (2.4 equivalents) afforded 5,6,11,12-tetrahydro-6,11 -dimethyldibenzo[b,f][ 1,4]diazo-cine-6,ll-dicarbonitrile (154), albeit only in 17% yield in one step. A similar reaction of cyclohexane-1,2-dione (155) with 153 produced 1,2,3,4,5,10-hexahydrophenazine-4a,10a-dicarbonitrile (156) in 13% yield along with the aromatized product, 1,2,3,4-tetrahydrophenazine (157) (Scheme 42). However, similar attempts with other diketones, such as 2,5-hexanedione, 2,3-butadiene, and 9,10-phenanthrenequinone, met with failure, either giving a complex mixture of products or well known and commercially available product possessing a pyrazine skeleton [100]. 

Hall and Polis 7 prepared a series of polyarylamines using an aromatic nucleophilic substitution-reduction sequence (Scheme 4.20). Hence, 2,4-dinitrofluorobenzene 66 was treated with />-diaminobenzene to afford tetranitro 67, which was reduced to give the corresponding first generation, diamine 68. Repetition of this sequence afforded the second generation tetradecaamine 69. These starburst polyarylamines were complexed with iodine to form semiconducting materials and were the first dendrimers to be examined by cyclic voltammetry. 

A broad spectrum of multidentate ligand—Th(TV) complexes have been isolated and characterized. The simplest bidentate ligands utilized are diaminoalkanes, H2N(CH2)kNH2, where n = 2-4, eg, ThBr4(H2N(CH JSIH H20, where y = 2, x = 3 or 4, or y = 4, x = 3. Diaminoarenes, diaminobenzene, benzidine, 0-tolidine, and 0-dianisidine have also been found to coordinate to Th(IV) halides and nitrates. The chlorides have been isolated with all of the aforementioned ligands in the form of ThQ4L2, and the nitrates have been identified as complex salts, eg,... 

The majority of U(VI) coordination chemistry has been explored with the trans-dioxo uranyl cation, U02+2. The simplest complexes are ammonia adducts, of importance because of the ease of their synthesis and their versatility as starting materials for other complexes. In addition to ammonia, many of the ligand types mentioned in the introduction have been complexed with U(VI) and usually have coordination numbers of either 6 or 8. As a result of these coordination environments a majority of the complexes have an octahedral or hexagonal bipyramidal coordination environment. Examples include U02X2Lw (X = halide, OR, N03, RC02, L = NH3, primary, secondary, and tertiary amines, py, n = 2-4), U02(N03)2Lk (L = en, diaminobenzene n = 1, 2). The use of thiocyanates has lead to the isolation of typically 6 or 8 coordinate neutral and anionic species, ie, [U02(NCS)J2 xj H20 (x = 2-5). 

Solutions of 26 were found to catalyze the oxidation of N,N,N, N -tetramethyl-l,2-diaminobenzene (TMPD) to TMPD+ in the presence of dioxygen. Control experiments with 25 showed lower catalytic activity, whereas the activity of the mononuclear complex Fe(ibz)Cl3, 27, (ibz is N,N-bis(2-benzimidazolyl-methyl)amine) was minimal. The authors proposed that the active species arose from the interaction of 26 with dioxygen. This interaction is not possible if the formulation of 26 as a diferric species is correct. However, if either dioxygen or 26 is reduced by a solution component or by TMPD, the redox catalysis can be explained. 

This copolymer can be obtained from a polydimethylsiloxane that has aminoalkyl end groups in a reaction with the polyetherimide formed from the reaction of a bis(ether anhydride) with diaminobenzene. The material is fire resistant and is used in cable insulations. Among other more complex copolymers with practical applications are poly[2,2-propanebis(4-phenyl)-carbonate]-b/ock-poly(dimethylsiloxane)] and a silicone phenol formaldehyde copolymer obtained in two steps, the first being the heating of a polydimethylsiloxane that has reactive end groups with glycerol, and the second step being the reaction with a phenol formaldehyde resin. 

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