Dinuclear complexes cobalt

Figure 26.2 O2 bridges in dinuclear cobalt complexes (a) peroxo (02 ) bridge, and (b) superoxo (02 ) bridge.

Love and coworkers have reported a series of dinuclear cobalt complexes derived from a rigid binucleating macrocycle H4L 18 as shown in Fig. 26 (150). The synthesis of the dicobalt complex [Co2(L18)] (36) was achieved by an anaerobic transamination reaction between H4L18 and [Co(thf) N(SiMe3)2 2] in THF. The unsaturated species 36 forms a bis(pyridine) adduct, 36 py2 (py — pyridine), which has a cleft-like structure reminiscent of pacman diporphyrin complexes (151,152). Both cobalt ions are square pyramidal, with Col and Co2 displaced out of the N4-basal planes by 0.17 and 0.18 A, respectively. The apical sites are occupied by pyridine nitrogen atoms that are exo and endo to the cleft. Interestingly the endo pyridine is canted and reflects the... 

Dinuclear clusters ferrous site distortion, 38 175 spin ladder, 38 182-183 Dinuclear cobalt complex, 45 291-293 Dinuclear complexes osmium, electrochemistry, 37 321-323 quadruply bridged, 40 187-235 axial ligand substitution properties, 40 232-234... 

Apart from the unambiguous and useful classification of the dinuclear cobalt complexes as /i-peroxo or /i-superoxo species, we shall not use formal oxidation states frequently in this review, and we limit the discussion here to the following points ... 

Polynuclear The dinuclear cobalt complex. Co fCO) (Fig. 15. ) represents a large number of... 

Varieties of dinuclear cobalt complexes are known with two phosphido bridges. Those so far reported with the di-terf-butylphosphido ligand have two pseudotetrahedral 18-electron Co atoms linked by a metal-metal bond formally of order 2. Tetracarbonylbis(ii-di-terf-butylphosphido)-dicobalt( -t-1) can be prepared from the reaction of Co(CO)4l (generated in situ) with Li(r-Bu2P) in THE We describe here a simplified, high yield synthesis of this dimer via the interaction of Co2(CO)g with r-Bu2PH in toluene. The complex should prove to be a useful starting material for further reactivity studies. 

Binuclear complexes of naphthalene (VIII) and of benzene (IX) with [Os(NH3)5]2+ and [Ru(NH3)5]2+ moieties were reported by Taube et al. (19), in which anti- //-1,2-rj2 3,4- 2) coordination of the arene is present. This bonding mode was first observed by Pasman et al. (20) in the binuclear Rhenium complex X. Wolczanski et al. (21) obtained complex XI from the mononuclear complex [Ta(0—Si Bu3)3 2-(N,C)-pyridine ] and benzene. Each tantalum atom is bound unsymmetrically to one C=C bond of benzene with a weak interaction to a third carbon atom the bonding may be described as a distorted tj3-enyl. In the dinuclear cobalt complex XII, the xylene functions as a bis(enyl)-ligand (12,22). 

Photolysis of the dinuclear cobalt complex (59) in low-temperature matrices has been investigated using IR spectroscopy. The primary process is loss of CO... 

Two different binuclear copperdi) complexes have been prepared recently, one with a bridging phenoxy ligand having two bis-benzi-midazole arms (12, Fig. 14), and the second having a bis-cyclen-naphthalene ligand (13, Fig. 15) (352, 353). Both of them show bimetallic cooperativity for the hydrolysis of phosphate diesters, contrary to studies with the dinuclear cobalt complex (354). The pseudo-first-order rate constants for hydrolysis of the para-nitrophenylphosphate ester of propylene glycol by bis-benzimidazole-based copper complexes... 

There have been two reports of fluxional dinuclear cobalt complexes. The first concerns the complexes [Co2(CO)4(/it-R2PCH2PR2)2] (R = Me, Ph). These exist in solution as equilibrium mixtures of CO bridged and nonbridged isomers which can be distinguished by variable-temperature NMR. The AG values for the process were 41.5 (R = Me) and 47.0 (R = Ph) kJ mol" in contrast to the very rapid fluxionality of [Co2(CO)g] for which AG is estimated to be ca 27 kJ mol from studies in a hexane matrix. The binuclear cobalt complexes are of type [ (i -Cp)Co 2(/it2- i -QHxSe)] (x = 6, 10, 12). The fluxional process... 

In an atmosphere of dioxygen, the catalytic oxidation of 1,2-diaminobenzene takes place in the presence of the dinuclear cobalt complex of the 24-member macrocyclic ligand OBISDIEN In water at 25°C the only oxidation product is 2,3-diaminophenazine, which is formed via a complex mechanism involving o-benzoquinonediimine and a p.-peroxo complex as intermediates. The mechanism shown in Figure 50 has been proposed to interpret the observed kinetic behavior. 

Nevertheless, refinement of a structural model to fit the observed intensity data gives distances that can be reliable to within 0.01 A. In the study of the dinuclear cobalt complex [CpCoPPh2l2 [73] the Co—C, Co—P and Co-Co distances obtained were 2.034(4), 2.169(19) and 2.572(9) A, respeetively. These are in good agreement with values of 2.046(20), 2.16(1) and 2.56(1) A found by single-crystal X-ray crystallography. In this case, little new information has been obtained, but in the same paper parameters are also presented for... 

Reaction of [S(CCPh)2] with [Co2(CO)g] afforded 2 jhe crystallographically characterised adduct [(PhCC)S Co2(CO)6(Ti2-CCPh) ] which, on treatment with further [Co2(CO)g] afforded [S Co2(CO)6(Tl2-CCPh) 2l. The reaction of pentacarbonyl allyloxy((4-methylphenyl)ethynyl)carbene) chromium and tungsten complexes with dicobalt octacarbonyl afforded 63 tpe alkyne complexes (62) (M = Cr, W), which failed to undergo intramolecular Pauson-Khand reactions instead, at room temperature, a 1,2-elimination occurs, regenerating the metal hexacarbonyl with predominant formation of dinuclear cobalt complexes (63) - (65). 

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