Amidine ligand

In addition to the substituents listed in Scheme 1, chiral groups may be introduced and unsymmetrically substituted amidinate anions are also possible. The amidinate anions may also contain additional functional groups, or two such anions can be linked with or without a suitable spacer unit. Yet another variety comprises the amidinate ligands being part of an organic ring system. All these aspects will be covered in the present review. 

This metathetical route was recently extended to the synthesis of amidinato complexes of Al, Ga, and In containing very bulky amidinate ligands with 2,6-Pr CgHs, adamantyl, m-terphenyl or 9-tiiptycenyl substituents at the central carbon atom. ... 

In a related study, sterically bulky amidinate ligands containing terphenyl substituents on the backbone carbon atoms have been utilized in organoalumi-num chemistry. Mono(amidinate) dialkyl complexes were generated as shown in... 

Gallium compounds that incorporate amidinate ligands have been studied because of their potential use as volatile precursors to nitride materials.The two most common classes of Ga amidinate compounds, however, are [RC(NR )2]GaX2 species, X = Cl, alkyl I in Scheme 32), in which one amidinate... 

The synthesis and characterization of the monomeric amidinato-indium(I) and thallium(I) complexes [Bu C(NAr)2]M[But(NAr(NHAr)] (M = In, Tl Ar = 2,6-Pr2CgH3) have been reported. Both compounds were isolated as pale yellow crystals in 72-74% yield. These complexes, in which the metal center is chelated by the amidinate ligand in an N, j -arene-fashion (Scheme 33), can be considered as isomers of four-membered Group 13 metal(I) carbene analogs. Theoretical studies have compared the relative energies of both isomeric forms of a model compound, In[HC(NPh)2]. ... 

Treatment of GaH3(quin) (quin = quinuclidine) with 1 equivalent of the sterically bulky formamidine as shown in Scheme 40 resulted in formation of a monomeric amido-gallane complex containing a monodentate amidinate ligand. Reaction of this species with a second equivalent of the amidine led to displacement of the quinuclidine ligand and formation of a five-coordinate monohydride complex, which could also be prepared directly by a one-pot reaction of GaHsfquin) with the free amidine in a molar ratio of 1 2 ... 

Different coordination modes of the amidinate ligands were observed when the mixed-ligand amidinato-amido complexes of Ge(II) and Sn(II) were treated... 

Tin amidinates display a rich coordination chemistry with the metal in both the di- and tetravalent oxidation states. The first results in this area were mainly obtained with N-silylated benzamidinate ligands. Typical reactions are summarized in Scheme 48. A stannylene containing unsymmetrically substituted amidinate ligands, [o-MeC6H4C(NSiMe3)(NPh)]2Sn, has been prepared accordingly and isolated in the form of colorless crystals in 75% yield. ... 

While ytterbium(II) benzamidinate complexes have been known for many years/ the synthesis of the first divalent samarium bis(amidinate) required the use of a sterically hindered amidinate ligand, [HC(NDipp)2l (Dipp = C6H3Pr2-2,6)/ As illustrated in Scheme 54, the dark green compound Sm(DippForm)2(THF)2 (DippForm = [HC(NDipp)2] ) can be prepared by three different synthetic routes. Structural data indicated that hexacoordinated... 

Titanium imido complexes supported by amidinate ligands form an interesting and well-investigated class of early transition metal amidinato complexes. Metathetical reactions between the readily accessible titanium imide precursors Ti( = NR)Cl2(py)3 with lithium amidinates according to Scheme 84 afforded either terminal or bridging imido complexes depending on the steiic bulk of the amidinate anion. In solution, the mononuclear bis(pyridine) adducts exist in temperature-dependent, dynamic equilibrium with their mono(pyiidine) homologs and free pyridine. 

The reaction of the coordinatively unsaturated ruthenium amidinates with [Cp RuCl]4 tetramer or [CpRufMeCNlsJPFg provides access to novel amidinate-bridged dinuclear ruthenium complexes (Scheme 146), which in turn can be transformed into cationic complexes or hydride derivatives. In these complexes, a bridging amidinate ligand perpendicular to the metal-metal axis effectively stabilizes the highly reactive cationic diruthenium species. 

Other amidinate anions normally form dinuclear copper(I) complexes with bridging amidinate ligands, although tetracopper(l) complexes have also been reported Silver(1) forms dimeric complexes with functionalized N,N -... 

Gold in the oxidation state +1 also tends to form dinuclear complexes with bridging amidinate ligands. A typical example is Au2[HC(NC6H3Me2-2,6)2]2 (cf. Section Oxidative addition of iodomethane to the dinuclear gold(I)... 

Tridentate amido-amidinate ligands have also been constructed starting from (lR,2R)-diaminocyclohexane (cf. Section IV.D). Scheme 181 illustrates the use of such ligand in the preparation of novel amidinato-titanium alkoxide com-plexes. ... 

In a related study the synthesis of half-sandwich cyclopentadienyl titanium f-butylimido complexes containing pendant-arm-functionalized amidinate ligands... 

The coordination chemistry of ancillary amidinate ligands with a pyridine functionality has been described. Magnesium, aluminum, zirconium, and lanthanum complexes have been prepared in which the amidinate anions act as tridentate, six-electron-donor ligands Amidinate ligands containing quinolyl substituents were constructed in the coordination sphere of lanthanide... 

Very recently, yet another interesting approach to novel-functionalized amidinate ligands has been reported. It involves the combination of amidinate... 

Oxalamidinate anions represent the most simple type of bis(amidinate) ligands in which two amidinate units are directly connected via a central C-C bond. Oxalamidinate complexes of d-transition metals have recently received increasing attention for their efficient catalytic activity in olefin polymerization reactions. Almost all the oxalamidinate ligands have been synthesized by deprotonation of the corresponding oxalic amidines [pathway (a) in Scheme 190]. More recently, it was found that carbodiimides, RN = C=NR, can be reductively coupled with metallic lithium into the oxalamidinate dianions [(RN)2C-C(NR)2] [route (c)J which are clearly useful for the preparation of dinuclear oxalamidinate complexes. The lithium complex obtained this way from N,N -di(p-tolyl)carbodiimide was crystallized from pyridine/pentane and... 

The crystal structure of a mono(cyclopentadienyl)zirconium complex containing a novel Me2Si-linked bis(amidinate) ligand was reported (Scheme 203). In this compound the central Zr atom is octahedrally coordinated with the bis(amidi-nate) acting as a tridentate ligand. ... 

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