Metal complexes preparation

Metal complexes prepared by reacting less than one mole of an alkan olamine with an excess of a polyhydric alcohol, such as polyethylene glycol 200—400 or glycerol, reportedly impart a greater degree of thixotropy to systems containing protective organic coUoids (501). 

Ziegler-Natta catalysts-—there are many different formulations—are organometallic transition-metal complexes prepared by treatment of an alkyl-aluminum with a titanium compound. Triethylaluminum and titanium tetrachloride form a typical preparation. 

In preliminary studies various metal salts such as PdCl2 were attached to the ligands and the complexes characterized by NMR spectroscopy and X-ray crystallography. Typical examples are the palladium complexes (32)—(44) (Scheme 9).66 The catalytic profiles of these and other transition metal complexes prepared by this method still need to be defined. Moreover, solid-phase synthetic versions would be advantageous, and this may well be possible via the (protected) phenol function. 

A number of capped cyclodextrins which are able to bind a metal ion at one end of their cavity, together with an organic guest in the cavity, have been synthesized. Such species parallel in several respects the family of completely synthetic vaulted transition-metal complexes prepared by Busch and coworkers and already discussed in Chapter 3 (section 3.5). 

It should be recalled that one of the principal properties of transition metals is their aptitude to accede to multiple oxidation states. Thus, the main scope of an electrochemical study is to ascertain whether a metal complex, prepared in a certain oxidation state, is stable also in different oxidation states, or whether the lifetimes of these oxidation states are too short to observe stable products. Whenever stable oxidation states are identified, the chemist might be able to prepare and fully characterize these new complexes. 

Covalent coupling A pre-existing metal complex is coupled covalently with den-drons and is thus surrounded by a dendritic shell. Appropriate examples are the redox-active metallodendrimers of Kaifer et al. [117] or the dendritic porphyrin/ metal complexes prepared and characterised by Diederich et al. [118] and Aida et al. [119]. 

The first successful syntheses utilizing trifluoromethyl iodide in transition metal chemistry were reported by Stone and his students. Stone reasoned that if CF3I would not react with transition metal anions to form trifluoromethyl derivatives [see Eq. (3)] then perhaps compounds containing perfluoroalkyl substituents could be generated by the oxidative addition of perfluoroalkyl halides to low valent transition metal substrates (9,10). The first reported trifluoromethyl-substi-tuted transition metal complex prepared by this route is shown in Eq. (4) (41). 

Similar trends are observed for the metal complexes prepared in the present study. The mode of coordination of cyclophosphazenes to transition metal ions mainly depends upon the ring size and the nature of the substituent. The rigid six-membered cyclotri-phosphazenes have low propensity for forming metal complexes and clearly steric effects predominate. 

Krocher, O., Koppel, R.A., Froba, M. and Baiker, A. (1998) Silica hybrid gel catalysts containing group(VIII) transition metal complexes preparation, structural, and catalytic properties in the synthesis of N, N-dimethylformamide and methyl formate from supercritical carbon dioxide. Journal of Catalysis, 178, 284-298. 

Bulky Cp Metal Complex preparation Characterization Comments Ref. 

Metal complexes prepared from derivatives of salen ligands (Fig. 29) have enjoyed wide utility as constituents of CPs (127-136). Because of the ease of modification of salen ligands and their propensity to adopt a square-planar coordination mode, salen complexes can exhibit at least two types of secondary coordination modes, as illustrated in Fig. 30. Most often the salen complex itself acts as a metal node, for example, by the coordination of abridging cyanide ligand (131,135,136) or other moiety (128,129,134) to the axial positions of the central... 

We list in Table 2 a few of the systems that have been reported in the recent literature to show metal complexes supported on amorphous, non-porous oxides. We also include a few recent reports on the decorating of mesoporous supports with metal complexes. Complexes have also been introduced into porous, crystalline oxides as well as placed on organic supports." We reported the use of metal complexes as templates for forming familiar crystalline solids and new crystalline materials, some of them adopting the chirality of the metal complex. " Preparations have appeared recently using dinuclear Pd(II) complexes [Pd2Me2Cl2(dppm)2] as the precursor and these were reacted with a silica surface to produce the grafted dinuclear Pd complex with the elimination of methane from the complex. ... 

Anchoring of metal complexes through interaction with surface hydroxyl groups of inorganic supports continues to be of interest. Studies with catalysts prepared with allyl, carbonyl, chloride, and ethoxy ligands have been reported. Kuznetsov and co-workers conclude that the precursors of metathesis-active centres of surface metal complexes, prepared by anchoring allyl and ethoxy compounds of Mo, W, and Re to silica, are co-ordinatively unsaturated metal ions with oxidation number +4. Metathesis activity of the surface species depends on the ligand environment of the metal ion. 

The number and diversity of transition metal phosphine complexes is vast and a wide range have been used as catalysts for synthetic organic transformations for many years. It therefore comes as little surprise that the preparation of polymer-supported metal phosphine complexes and assessment of their catalytic activity has attracted much attention. Supported phosphine ligands and their metal complexes prepared from 1981 to 2001 can be found in a review published in 2002. Discussed here are examples in the literature from 1996 to the present together with a selected number of those from 1981 to 1996 where particularly notable synthetic methods have been used or where key points should be raised. 

The abbreviation Salen (A/.A -bis(3,5-di-rer/-butylsalycilidene)-l,2-cyclohexanediamine) was expanded on a wide class of achiral and chiral compounds originating from 1,2-diamines and salycilaldchyde derivatives. Chiral metal-salcn complexes arc attractive for catalyst design, due to the proximity of the stcrcogcnic centers to the coordinated metal and the simplicity of the metal complexes preparation [ 1 ]. 

Until recently, only diphosphines with different chain lengths of saturated carbon-carbon linkages have been studied. In 1965, Hansen and Aguiar prepared a saturated diphosphine containing an ether link in the chain, namely fois(2-diphenylphosphinomethyl)ether, Ph2PCH20CH2PPh2, (abbreviation ppme). This paper reports the preparation, spectral, magnetic, and conductance measurements of some of the metal complexes prepared with this ligand. Two types of complexes have been studied ... 

Other examples of metal complexes prepared by salt metathesis are 23 and 24. The disodium salt was unstable at room temperature, but it could be in situ generated and transferred to [MCl4(THF)2] (M = Ti, Zr) (Equation (6.7)). ... 

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