Simple N-Donor Ligands

Since most Ni1 species with simple N-donor ligands are prone to disproportionation into Ni° and Ni11, relatively few Ni1 complexes with nonmacrocyclic N-donor ligands have been reported. Formation of Ni1 species is in most cases proposed on the basis of electrochemical data, although ligand-centered redox processes have to be considered. The ligands usually contain imine donor atoms or aromatic N-heterocycles, which because of their 7r-acceptor ability favor stabilization of lower oxidation states. 

Modes through which bridging between two different metals can arise, illustrated for simple N-donor ligands. 

The readily available oxazolines (L19) are used in the cross-coupling of arylboronic acids with aryl bromides, including nonactivated ones in the system (Pd(OAc)2/L, Cs2C03, dioxane, 80 °C). It is notable that the system works well at 1 1 Pd L ratio.442 A simple sulfide complex showed similar activity (PdCl2(SEt2)2, K3P04, DMF, 130°C).18 A series of bidentate N,N-donor ligands... 

N-Donor Ligands. The full account of the crystal structure of [Mo02(8-hydroxyquinolate)2] has been published. The dimensions of the M0O2 unit are O—Klo—O = 104.C and Mo—O = 171(2) pm. The electrochemistries of this and the related molybdenum(v) complex. [ MoO(8-hydroxyquino-late)2 2 0], have been investigated as simple models of molybdenum-fluoro-protein enzymes (p. 146). Reduction of the molybdenum(vi) complex occurs in two one-electron steps with solvent attack of the reduced intermediates and displacement of the 8-hydroxyquinolato-groups. ... 

Nitric Oxide Adducts of Other Complexes. Simple nitrosyl complexes containing a-N donor ligands are rare, as these hard bases do not allow the appreciable d-7t interaction required to stabilize the Fe-NO group. As a result, nitric oxide... 

A method that has recently been introduced to the study of diiron model complexes involves self-assembly reactions using bulky carboxylate ligands (Scheme 6). The steric bulk is employed about the carboxylate group to control nuclearity. In this approach, simple nonchelating N-donor ligands are employed as ancillary ligands. This method... 

A simple synthetic method for Cr1 complexes, based on the reaction of CrCl2 with Ag1 complexes, has been proposed (it is believed that EtOH, used as a solvent, also acts as a reductant).1213 Formation of [CrL3]+ complexes (where L is a bidentate N-donor ligand) has been supported by magnetic measurements (/j.en 1.9 ps at 298 K) and cyclic voltammetry.1213 Studies of the... 

The second major problem in studying simple iron porphyrins is the preference of the metal for six-coordination. For example, in solution containing strongly coordinating N-donor ligands, six-coordination is favoured over five-coordination, i.e., for the equilibria in Eq. 9, K2 > Kj (K2/K1 = 10-30 in aprotic solvent at 25 "0) In benzene at 25 °C, the... 

Simple alkyl and aryl cr-bonded complexes are conveniently prepared by reaction of an alkylating reagent with a halocobalt(II) precursor. All-alkyl systems are rare, but the penta-methylcobaltate(II) anion is known.197 More typically, the coordination sphere of the metal contains additional co-ligands, particularly with P, S, or N donors. Some examples that reflect the style of reactions extant appear below. 

The variety and extent of research devoted to ligands carrying both O- and N-donors is simply immense. The type of cobalt(III) systems extant include amino acids, amino alcohols, amino ethers, amino phosphates, amino phenolates, as well as amide and imine analogs of these. These are met as simple chelates or more elaborate polydentates. Here, we highlight a strictly limited selection of examples to illustrate the type of systems reported no attempt at exhaustive review has been made. 

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