Mononuclear coordination with

N40 donor set ligands with pyridyl and phenolic arms form mononuclear complexes with approximately trigonal-bipyramidal coordination geometries.888... 

Hydrido-(l-pyrazolyl)borates [H4 B(C3H3N2) ]-, in short [H4 B(pz) ], often with more or less bulky substituents in 3- and/or 5-positions of the pz ring, have been used for the preparation of mononuclear complexes with controlled coordination sphere about a metal.195 With Cd as a metal center different coordination numbers and geometries can be realized, depending on the pyrazolylborate used, but also on the co-ligands. 

The reactions of mercury(II) salts with oligo-amines afford informative examples for the fact that counterions induce the formation of a distinct complex or select a distinct complex in an equilibrium to crystallize with. Thus, Hg11 acetate with dien under exactly the same reaction conditions, in the presence of C104- or PF6-, yields the dinuclear complex [Hg2(dien)3](C104)4 or the mononuclear species [Hg(dien)(H20)](PF6)2, respectively, both characterized by IR, H, and 13C NMR spectrometries, by fast-atom bombardment (FAB) MS, cyclovoltammetry, and X-ray structure analyses.209 In the first compound Pna2, Z = 4), one Hg adopts five-coordination with one tridentate and one bidentate dien ligand, which with the remaining N-donor binds to the... 

These observations, coupled with the findings of Muetterties et al. that none of a large number of mononuclear coordination catalysts examined showed any activity for the H2/CO reaction (53), lend further support to the idea that more than one metal center is necessary for the catalytic formation of hydrocarbon products from synthesis gas. 

We now describe some results obtained with the extended CNDO formalism concerning preferred conformations and related parameters within the field of mononuclear coordination derivatives. 

The preparation of a novel mononuclear iron(III)-t-butylperoxo-complex, end-on coordinated, with bis(6-pivalamido-2-pyridylmethyl)(2-pyridylmethyl)amine, bppa = (206), to Fe, " was followed by the isolation of a similar complex containing hydroperoxide. The latter reacts by O—O bond cleavage and a [(bppaH2)Fe —O ] intermediate." ... 

The selective S3mthesis of tri- and dichlorotitanium complexes 140-142 bearing chiral tridentate Schiff base ligands derived from (lf ,25)-( )-l-aminoindanol (Fig. 20) has been recently reported. X-ray structural studies of these complexes revealed a mononuclear feature with an octahedral coordination sphere at the metal center, and a meridional occupation of the Schiff base. Surprisingly, though these complexes lack the typical ROP-initiating units such as aUcoxides or amides, they are effective catalysts for the controlled ROP of L-lactide, as evidenced by the linearity of the molecular weight versus [l-LA] [Ti] ratio as well as the narrow PDIs (1.17-1.33) [127]. 

Species (A) and (B) constitute the main class of unsaturated carbenes and play important roles as reactive intermediates due to the very electron-deficient carbon Cl [1]. Once they are coordinated with an electron-rich transition metal, metal vinylidene (C) and allenylidene (D) complexes are formed (Scheme 4.1). Since the first example of mononuclear vinylidene complexes was reported by King and Saran in 1972 [2] and isolated and structurally characterized by Ibers and Kirchner in 1974 [3], transition metal vinylidene and allenylidene complexes have attracted considerable interest because of their role in carbon-heteroatom and carbon-carbon bond-forming reactions as well as alkene and enyne metathesis [4]. Over the last three decades, many reviews [4—18] have been contributed on various aspects of the chemistry of metal vinylidene and allenylidene complexes. A number of theoretical studies have also been carried out [19-43]. However, a review of the theoretical aspects of the metal vinylidene and allenylidene complexes is very limited [44]. This chapter will cover theoretical aspects of metal vinylidene and allenylidene complexes. The following aspects vdll be reviewed ... 

A large number of studies devoted to metal-sulfur centers are motivated by the occurrence of such arrangements at the active site of various metalloenzymes [1-13]. Mononuclear complexes with Mo=0 func-tion(s) and possessing sulfur ligands in their coordination sphere have been extensively investigated since they can be seen as models of the active site of enzymes such as nitrate- and DM SO reductases or sulfite- and xanthine oxidases [1-4]. On the other hand, a large variety of mono-, di-, and polynuclear Mo—S centers have been synthesized in order to produce functional models of the Mo-nitrogenase since the exact nature (mono-, di- or polynuclear) of the metal center, where N2 interacts within the iron-molybdenum cofactor (FeMo—co) of the enzyme is still unknown [4-8]. 

The acyl radical formed from acrolein, maintaining its coordination with a catalyst, may react preferably with oxygen, rather than decompose to produce carbon monoxide, though it is generally believed that a free acyl radical is formed after the abstraction of aldehyde hydrogen by a metal. In such a case, the catalyst metal is considered as behaving as a mononuclear, not a binuclear complex. The molecular weight of the catalyst recovered from the oxidation solution was measured (Table V). 

Octahedrally coordinated mononuclear complexes with S- and P-donor atoms (9) and (10) have also been reported.108,109... 

Names for Mononuclear Coordination Compounds with Monodentate Ligands... 

Werner apparently did not realize that the polynuclear complexes which he investigated so extensively95 constituted a transition between the usual mononuclear coordination compounds and the infinite structure of the crystal lattice. It remained for Paul Pfeiffer, Paul Niggli (1888—1953) and others to point out that crystal structures were in beautiful agreement with his coordination theory, as revealed by the then new experimental technique of X-ray diffraction.96... 

The phosphines with one P-donor atom reveal properties close to those of amines and form mononuclear coordination compounds 574 or binuclear structures 239 (Sec. 2.2.4.3) and 575 (3.14) ... 

Use of a flexible aminosubstituted cyclopentadienyl ligand afforded a mononuclear species with the bulky silox ligand as alkoxide component. Only one donor arm is required to achieve a sterically saturated 8-coordinated neodymium center (Fig. 30, Table 14) [207]. 

Most coordination catalysts have been reported to be formed in binary or ternary component systems consisting of an alkylmetal compound and a protic compound. Catalysts formed in such systems contain associated multinuclear species with a metal (Mt)-heteroatom (X) active bond ( >Mt X Mt—X > or — Mt—X—Mt—X— Mt = Al, Zn, Cd and X = 0, S, N most frequently) or non-associated mononuclear species with an Mt X active bond (Mt = Al, Zn and X = C1, O, S most frequently). Metal alkyls, such as triethylaluminium, diethylzinc and diethylcadmium, without pretreatment with protic compounds, have also been reported as coordination polymerisation catalysts. In such a case, the metal heteroatom bond active in the propagation step is formed by the reaction of the metal-carbon bond with the coordinating monomer. Some coordination catalysts, such as those with metal alkoxide or phenoxide moieties, can be prepared in other ways, without using metal alkyls. There are also catalysts consisting of a metal alkoxide or related compound and a Lewis acid [1]. 

Prussian blue, Fe4[Fe(CN)6]3xH20, consists of a cubic lattice of alternating Fe2+ and Fe3+ ions connected with cyanide bridges (Figure 8.3). The [Fe(CN)6]4 sites are 75 % occupied and the exposed Fe3+ ions are coordinated with H2O. Dehydration and hydration by moisture is reversible hence, Prussian blue is a porous solid albeit one with very small pores. To increase pore size, the [Fe(CN)6]4 complexes were replaced with octahedral [Rer TeACNAJ4 clusters (Figure 8.4). This cluster displays an octahedral array of N donors on a sphere about 4 A larger in diameter than the mononuclear complex. Reaction of Fe3+ with the cluster in... 

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