Dioximato complexes

A series of chiral bis-dioximato complexes of Fe11, Co11, Ni11 and Pd11 have been described from three geometrical isomers ( , j8 and 3) of D-camphorquinone dioxime (Hcqd) and two (fi and <5) of L-nopinoquinone dioxime (Hnqd).41 Opposite Cotton effects around 20000 cm-1 have been observed for Co(a-cqd)2-H20 and Co(<5-nqd)2 H20 indicating their quasi-enantiomeric stereochemistries.. , ... 

What should we do to observe a three-dimensional template effect First, we should choose a reaction type that we know to be effective for the formation of macrocyclic ligands and extend the methodology to a kinetically inert cP or d6 metal centre. Let us reconsider the reaction, that we first encountered in Fig. 6-11. In this reaction, a dioximato complex reacted with BF3 to give the nickel(n) complex of a dianionic macrocycle (Fig. 7-1). 

Figure 7-1. The reaction of a nickel(n) dioximato complex with BF3 gives the nickel(n) complex of a new dianionic, macrocyclic ligand. Note that in the interests of clarity, throughout this chapter we use simple lines to represent co-ordinate bonds...

A well-established complex of NiIV is the diacetylpyridine dioximato complex... 

Pt—O distances between the platinum atoms and the out-of-plane hgands are 1.98(2)-2.02(2) A, which are within a normal range for Pt—O distances. Pt—N distances range from 2.09(2) to 2.17(2) A and are somewhat longer than those in a mononuclear platinum dioximato complex ( 2.00 A) (56). The elongation arises from a trans influence from the Pt—Pt bonds, which was observed in Pt4 clusters (see Section II,B). 

Nickel is an important component in many thin-film materials. Precursors for the growth of nickel metal films have been recently summarized in a review. Recently reported precursors for the CVD growth of nickel-containing materials include Ni(tmhd)2, Ni(hfac)2(en), a series of nickel dioximato complexes, Ni(02CCF3)2(dmen)2, Ni(C5H5)2, and Ni(tBuNC(CH3)NtBu)2. Single-source... 

The a-diketone precursors used to prepare the dithiolene complexes discussed above can be used for the preparation of other potential ligands such as dioximes. Such ligands are directly obtained by the reaction of the corresponding benzil species with hydroxylamine chloride. Dioximato complexes with cf metals crystallize in columnar stacks with the formation of a chain of metals orthogonal to the molecular planes, and as such are potentially interesting candidates for the design of discotic systems with low-dimensional semiconducting properties. Ohta et al. reported a... 

References to studies of complexes of the type // a/i -[Co(dioxime)2LX] + (X=leaving group) are collected in Table 9. A review of substitution reactions of dioximato-complexes has appeared (Introduction, ref. 9). 

Co(LLLL)(L)X] + and [Co(LLLLL)X] + Complexes. Included in this section are studies in which the non-leaving group is an open-chain or cyclic quadridentate (LLLL) or quinquedentate (LLLLL) ligand. Excluded are the complexes of edta and related ligands discussed earlier and the dioximato-complexes covered in the next section. 

Dioximato-complexes. References to studies of complexes of the type trans-[Co-(dioxime)a(L)X] + are collected in Table 10. When L is an S -bonded sulphinato-ligand, RSOa" (R = Me or p-MeC6H4), the trans effect is greater than that of iodide... 

Table 10 References to studies of dioximato-complexes of the type trans-[Co-(dioxime)2LX] +(X = leaving group)...

Solvent Variation.—References to the aquation of cobalt(iii) complexes in mixed aqueous-organic solvents will be found in earlier sections. The aquation of the [Co(NH3)sDMSO] + ion and the equilibrium between Cl and [Co(NH3)50H2] ions have been investigated in ethanol-water mixtures, and references to a few studies of the solvolysis of dioximato-complexes in mixed non-aqueous solvents are given in Table 10. The effect of solvent variation is the subject of Chapter 5. 

Two studies of the base hydrolysis of dioximato-complexes of the type trans-[Co(dmgH)2(amine)X] (amine = NH3, PhNHg, or py, X = Cl, Br, or I) and tra 5-[Co(dioxime)2(OH2)X] (dioxime = methyl-, methylethyl-, a-benzyl-, or a-furfuryl-dioxime, X = Cl, Br, or occasionally I) have appeared. The latter study shows that the rates increase with the inductive effect of the dioximato-substituents in the order Et< MeSteric effects are also apparent since the... 

Table 28 References to studies of the rates of formation of trans-[Co(dmgH)g(X)(Y)] and other dioximato-complexes of cobalt (ja) (X andY are unidentate ligands)...

As in previous volumes, the remainder of this section will be subdivided into parts dealing first with the [Co(en)aLX] + ions, then the [CoL4XJ + complexes, and finally dioximato-complexes. 

Dioximato-complexes. Studies of dioximato-complexes continue to be extensive probably because of their close similarity to the cobalamins and vitamin B12. Dissociative (often Z>) mechanisms are most commonly observed for the aquation reactions as well as for formations and for ligand exchange. Since these reactions are so similar most of the results will be collected together in this section. References to kinetic studies of aquation,ligand-exchange, and anation reactionsof neutral and anionic complexes of the type /ra 5-[Co(dioxime)2AX] dioxime = [HON=C(R )C(R )=NO] where R and R are alkyl groups are collected in Table 7. 

Table 7 Kinetic studies of aquation and formation of neutral and anionic dioximato-complexes, trans-[Co(dioxime)2AX] (dioxime =... 

One further reference on formation at rhodium(III), in binary aqueous solvents, will be found in Section 5.8.9 on dioximato complexes. 

A comparison of Co and Rh dioximato-complexes has been made for the aquation of /ra/w-[M(L)g(N02)Cl] (L=methylglyoximate, dmgH, or dioximate), and for the reverse (anation) reactions. The aquation rate increases as the electron-donating ability of L increases. Also, for trfl 5-[Co(L)2(S03)(am)] the rate of loss of am (am=py or NH3) varies with L in the order dmgH > methylglyoximate > diphenylglyoximate, and NH3 is lost more rapidly than py. ... 

Recent examples of investigations of kinetics of aquation of dioximato-complexes [Co(LLH)2X2) include those of anions with LLH2 = dmgHg and X = NO2, NCS,i° or NCSe, and with LLHg = 1,2-cyclopentadione... 

Other complexes for whose aquation in mixed aqueous solvents kinetic parameters have been obtained include [Co(RNH2)6Cl] + in aqueous dioxan, and of c -[Co(NH2CH2CH20H)(en)2Cl] + (ref. 19) and several dioximato-complexes [Co(LLH)2(S03H)Cl] (refs. 35—37) in several aqueous organic mixed solvents. Activation parameters are collected together in Table 5. As an extension of the dioximato-complex aquation work, one might add that the kinetics of thermal decomposition of some of these complexes have been studied in the solid state. ... 

Dioximato-complexes. Kinetic parameters for aquation of a range of... 

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