Macrocyclic ligands nickel complexes

A new family of bis(macrocyclic ligand) nickel complexes of type 10 has been synthesized (34). The procedure involved electrophillic substitution of 9 or its 14-membered analogue (35) at their respective y carbons, using two difunctional electrophiles, terephthaloyl chloride or isophthaloyl chloride. This procedure was based on a previous study describing electrophillic attack by benzoyl chloride on the above starting complexes (36). 

Macrocyclic N-donor ligands. Nickel complexes of macrocyclic ligands have been studied by cyclic voltammetry, and the irreversible or quasi-reversible couples Ni" L Ni L Ni L have been established. The structure of (124) has been reported and the co-ordination is essentially square-planar with a slight tetrahedral distortion. The reaction of [Ni(pn)3] with... 

Tinnemans et al.132 have examined the photo(electro)chemical and electrochemical reduction of C02 using some tetraazamacrocyclic Co(II) and Ni(II) complexes as catalysts. CO and H2 were the products. Pearce and Pletcher133 have investigated the mechanism of the reduction of C02 in acetonitrile-water mixtures by using square planar complexes of nickel and cobalt with macrocyclic ligands in solution as catalysts. CO was the reduction product with no significant amounts of either formic or oxalic acids... 

The third class of metal catalysts includes nickel and cobalt complexes of Schiff bases and nitrogen macrocyclic ligands, which can form on electroreduction cobalt(I) and nickel(I) reactive intermediates for the activation of organic halides. 

Ligand (119) yields nickel complexes of type [Ni2L](BF4)4 (low spin) and [Ni2L(NCS)4].2H20 (high spin). For each of these complexes, physical studies indicate that the macrocycle circumscribes the two nickel ions such that each ion is surrounded by four sulfur donors in a planar array. 

Table 6.1 summarizes the thermodynamic parameters relating to the macrocyclic effect for the high-spin Ni(n) complexes of four tetraaza-macrocyclic ligands and their open-chain analogues (the open-chain derivative which yields the most stable nickel complex was used in each case) (Micheloni, Paoletti Sabatini, 1983). Clearly, the enthalpy and entropy terms make substantially different contributions to complex stability along the series. Thus, the small macrocyclic effect which occurs for the first complex results from a favourable entropy term which overrides an unfavourable enthalpy term. Similar trends are apparent for the next two systems but, for these, entropy terms are larger and a more pronounced macrocyclic effect is evident. For the fourth (cyclam) system, the considerable macrocyclic effect is a reflection of both a favourable entropy term and a favourable enthalpy term. 

The S-oxygenation of the hexaamine-dithiophenolate macrocycles should provide a potential entry into the novel class of binucleating polyamine-disulfonate and -disulfinate macrocycles. Indeed, such ligands can be prepared by the oxidation of dinuclear nickel complexes of the parent hexaaza-dithiopheno-late macrocycles followed by the decomposition of the oxidation products in acidic solution. The dinuclear nickel complexes [Nin2(L36)(L )]+ (L = Cr (70) and OAc (71)) of the hexaaza-diphenylsulfonate ligand (L36)2- (Fig. 38) are obtained by... 

The electrochemical processes involving cobalt complexes have already been thoroughly investigated [62, 66], Additional results have been reported with cobalt complexes different from vitamin Bxj and also with nickel ligated to tetradentated macrocyclic ligands. Both series of complexes lead to radicals. 

The reaction of planar Ni ([14]aneN4) + represented as shown in (2.10) with a number of bidentate ligands (XY) to produce c -octahedral Ni ([14]aneN4) XY + is first-order in nickel complex and [OH ] and independent of the concentration of XY.In the preferred mechanism, the folding of the macrocycle (base-catalyzed tmns — cis isomerization) is rate determining, and this is followed by rapid coordination of XY ... 

Macrocyclic Fi-donor ligands and vitamin Bj, analogues. The free amine [(97) tet] can be prepared from the previously reported nickel complex. Cobalt-fin) complexes have been prepared with both planar (bcde octahedral) and folded (abed octahedral) co-ordination. Derivatives of the three ligand configurations arising from restricted inversion at the four chiral co-ordinated secondary amino-groups have been prepared (see Scheme 2) and their stabilities and configurations discussed. ... 

Complexes of the strained macrocyclic ligand (134) have been prepared. The complex [NiL(N03)2],- H20 is octahedral however, [NiLCl2],fH,0 and [NiLCl](C10J,H20 [L = (134)] are the first nickel(ii) complexes containing... 

A complete series of nickel(ii) complexes (136)—(139) has been produced wherein the macrocyclic ligands contain four N-donors and vary stepwise from containing one to four unsaturated N atoms. All the complexes are formally obtained by hydrogenation or oxidative-dehydrogenation of Ni(CR) (138). The complexes of (CR) and (CR -f- 4H) have been reported earlier. [(CR -h 2H)-... 

Steric constraints dictate that reactions of organohalides catalysed by square planar nickel complexes cannot involve a cw-dialkyl or diaryl Ni(iii) intermediate. The mechanistic aspects of these reactions have been studied using a macrocyclic tetraaza-ligand [209] while quantitative studies on primary alkyl halides used Ni(n)(salen) as catalyst source [210]. One-electron reduction affords Ni(l)(salen) which is involved in the catalytic cycle. Nickel(l) interacts with alkyl halides by an outer sphere single electron transfer process to give alkyl radicals and Ni(ii). The radicals take part in bimolecular reactions of dimerization and disproportionation, react with added species or react with Ni(t) to form the alkylnickel(n)(salen). Alkanes are also fonned by protolysis of the alkylNi(ii). 

The square-planar Ni(II) complex of an anionic macrocyclic ligand, 21, was prepared from the template reaction of 3,3 -(ethylenebis(imino-methylidene)bis(2,4-pentanedionato)nickel(II) with 1,3-diamino-2-pro-panol [Eq. (10)]. The uncoordinated -OH group reacted smoothly with acylating agents, resulting in -COPh and -COCH3 (28). 

Electronic Absorption Spectral Data for Five-Coordinate Nickel(I) Complexes with Macrocyclic Ligands... 

Most of the nickel(l) complexes are four-coordinate, either tetrahedral (phosphine and arsine complexes) or square planar (macrocyclic and dithiolene complexes), but five-coordinate complexes are also easily formed in the presence of tetradentate tripodal ligands. 

The field of nickel complexes with macrocydic ligands is enormous and continuous interest in this area in recent years has resulted in innumerable publications. A number of books and review articles are also available covering the general argument of the bonding capability of the various macrocydic ligands towards transition and non-transition metals. 22 2627 Synthetic procedures for metal complexes with some tetraaza macrocycles have been reported.2628 Kinetics and mechanism of substitution reactions of six-coordinate macrocydic complexes have also been reviewed.2629... 

---