Literature heterocyclic ligands

Many publications are devoted to the synthesis of nitrile complexes, carried out by the immediate (direct) interaction of RCN and MX , mostly in the absence of a solvent [10, p. 95]. A series of N-donors, N-containing heterocyclic donors, whose complexes frequently model biologically important objects (Sec. 2.2.42), should be mentioned apart. The following compounds belong to this type azoles 188, azines 189, and their amino derivatives 572. Their interaction with metal salts takes place usually without a solvent with the use of liquid heterocyclic ligands, for example pyridine [10, ch. 4, p. 107 11], in alcohol or alcohol-aqueous mediums in cases of crystalline ligands (3.10)—(3.12). The specific conditions are presented in the literature, cited in Sec. 2.2.4.2. 

This schematic overview of NHC ligands found in the literature shows that most are based on five-membered heterocyclic cores. The most common are listed in Section 1.1.3. 

Numerous examples of nucleophilic attack on coordinated nitrile ligands are found in the literature, particularly when the transition metal is platinum(II).224 The nucleophilic attack of two equivalents of CIO I2CII20 on the electrophilic nitrile carbon atoms of both nitrile ligands in cis-or /r<7H.v-[PtC12(RCN)2] (R = Et, Prn, Pr1, Bu p-CF3C6H4, p- and o-MeC6H4) affords the corresponding A2-l,3-oxazoline complexes ((76) and (77), respectively), in which the heterocycle acts as a... 

In more recent work by other researchers, sealed-vessel microwave technology has been utilized to access valuable medicinally relevant heterocyclic scaffolds or intermediates (Scheme 6.120) [240-245]. Additional examples not shown in Scheme 6.120 can be found in the most recent literature (see also Scheme 6.20) [246-249]. Examples of nucleophilic aromatic substitutions in the preparation of chiral ligands for transition metal-catalyzed transformations are displayed in Scheme 6.121 [106,108]. 

Aqueous two-phase hydrogenations are dominated by platinum group metal catalysts containing water-soluble tertiary phosphine ligands. The extremely stable and versatile N-heterocyclic carbene complexes attracted only limited interest, despite the fact that such complexes were described in the literature [62-65]. Recently, it was reported that the water-soluble [RuXY(l-butyl-3-methylimi-dazol-2-ylidene) ( 76-p-cymene)]n+ (X=Ch, H20 Y = C1-, H20, pta) complexes preferentially hydrogenated cinnamaldehyde and benzylideneacetone at the C = C double bond (Scheme 38.5) with TOF values of 30 to 60 h 1 in water substrate biphasic mixtures (80 °C, lObar H2) [66]. 

Undoubtedly, pyridine, C5H5N (2), is the best-known heterocyclic nitrogen ligand and its coordination chemistry has been studied in great detail, as have its simple derivatives bearing a non-coordinating substituent. For the physical properties, the reader is referred to the heterocyclic literature.1 3,5,9 The basic properties of pyridine have been mentioned above. Alkyl-substituted derivatives are slightly more basic [pA (base) values of about 5-7]. 

An inorganic photoconductor such as zinc oxide can be optically sensitized by treating it with a ligand that will form a colored zinc complex. The resulting material then responds to light of the wavelength where the complex absorbs. Suitable ligands are prepared by the condensation of heterocyclic hydrazines and heterocyclic aldehydes.235 Two examples of the more than 50 disclosed in the patent literature are (114) and (115). 

The heterocycle dmit2-, occasionally referred to as [0C-C3S5]2-, is one of the most important dithiolene ligands. The literature on dmit2- is vast, but an overview of the ligand chemistry including many useful experimental procedures is available (1) as are reviews on specific aspects of the coordination chemistry (2, 3, 90-92). Most studies on dmit2- are directed toward applications in materials chemistry, for example, the photonic or electronic properties (90,93). 

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