Tripod-Type Ligands

Different metal oxidation states can be involved with the same trigonal bipyramidal arrangement of the ligands as, for example, in Co+ P(CH2CH2PPh2)3H PF and Co P(CH2CH2PPh2)3H. 

Trigonal bipyramidal (8.156a) and octahedral (8.156b) complexes of tris (diphenyl-phosphino-methyl)ethane are known, as well as octahedral complexes of tris(di-phenylphosphinoethyl) amine (8.156c). 

Dinitrogen is easily lost from triphos complexes (8.157) and the -AuPPh3 ligand is easily substituted (8.158) [75]. 

2Mo(N2 )2 (triphos)(PPh3) -F 8HBr 2MoBr3 (triphos)+2NH4Br+3N2 + 2PPh3 (8.157) 

Ligand (8.153a) can also act as a tetradentate ligand in octahedral arrangements such as (8.159a), where X = CO, N2, PPhj. Condensation of the dinitrogen compound produces (8.159b). 

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Batten et al. <2004AXCm311> have reported an Fe(n) complex using a tris(heterocycle)tripod-type ligand with phosphorus at the bridgehead. Compound 23 was fully characterized using X-ray crystallography. 

In addition to the bidentate ligands depicted in Table 6.15, there are tripod-type ligands (below) and many other multidentate poly(phosphine) ligands which can form complexes. Those based on phenyl groups seem to be the most popular (Chapter 6.17). Poly(phosphine) ligands are useful in stabilising metal cluster complexes (above) and cyclic and acyclic P units. 

In order to construct new types of binding and activating models of dioxygen molecules, Jitsukawa, Masuda and their co-workers have synthesized a novel group of tripodal tetradentate ligands and successfully utilized them in the formation of mononuclear copper(II) complexes with novel structural features (complexes (473)-(488)).395-403 This group of ligands has four... 

Most of this section is devoted to derivatives containing CO and Cp-type ligands. An exception is a family of coordinatively unsaturated, silyl complexes LFeSiR2R involving the tripodal ligand [PhB(CH2PPr 3)3]-.170... 

Figure 7.2 Different types of coordination complexes with the tripodal amide ligand. Type A and type C are adapted from [29] and [30],...

Increasing the number of ligating sites greatly increases the stmctural possibilities both of the ligand and of the complexes. Tridentate ligands may be either linear R2P(CH2) P(R)(CH2)mPR2, or of the so-called tripod type... 

Dendrimer-type ligand (32) serves as a lanthanide container to exhibit on-off switchable luminescence upon lanthanide complexation in response to external anions [56]. Because of the presence of two classes of coordination sites for the lanthanide cations at the inner and outer spheres, the dendrimer 32 exhibits two different binding modes to afford on-off lanthanide luminescence, in which outer complexation at the tetradentate tripod site offers the on luminescence state upon quinoline excitation whereas, inner complexation at the multidentate core site corresponds to the off luminescence state. Upon complexation of 32 with Yb(CF3 SO3 )3, the quite weak NIR luminescence from the Yb(III) center suggests that the Yb(III) ion is most probably located at the inner coordination sites and apart from the excited quinoline moieties. Nevertheless, addition of SCN anion to the 32-Yb(CF3803)3 system induced remarkable spectral changes around the quinoline absorption band and about ninefold enhancement in luminescence intensity at around 980 nm. As the intense Yb luminescence appeared upon quinoline excitation, the employed SCN anion promoted the tripod-Yb +... 

A tripod-type Schiff-base ligand, (127), was prepared by a 3 1 condensation reaction of 2-phenyl-4-formylimidazole in methanol.204 In two nickel(II) complexes, the screw coordination arrangement of the tripod ligand (127) around the metal ion induces chirality, resulting in a A (clockwise) or a A (anticlockwise) enantiomer.204 A multifunctional tripodal ligand possessing two different functionalities, such as pyridine and cyano moieties, (128), has been prepared by the reaction of 2-aminomethylpyridine, excess acrylonitrile, and glacial acetic acid. 

Some rigid tripodal ligands have been synthesized for the construction of various novel cage- or box-like complexes, and have demonstrated their potential use in supramolecular chemistry. The relatively flexible amide-type ligand (136) was prepared by the replacement reaction of 1,1,1-tris(p-tosyloxymethyl)propane and /V-benzylsalicylamide.217... 

A different type of tripodal triamido ligand is based on rA,m-l, 3,3-triaminocyclohexanc. Several ligands of this type with different peripheral (V-substituents have been employed to synthesize a series of organometallic zirconium... 

Most of the tetradentate tripod-like ligands of the type A—C... 

Of the molecular hydrogen complexes that were first synthesized, none were the d ML4(H2) type. This is not at all surprising because it is well known that d ML4 systems yield oxidative addition with formation of a dihydride. Application by Bianchini et al of the novel tripodal phosphine ligand to the rhodium atom led to the synthesis of the first compound in this class, the [Rh(P(CH2CH2PPh2)3(H2)] complex [24]. 

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