Other Ligands

Other Ligands.—Reactions of platinum(n) complexes PtHX(PR3 2 with azides, which give amido-complexes, may proceed by attack at the co-ordinated hydride. In Friedel-Crafts sulphination of Fe(butadiene)-(CO)s, attack is both at the metal and at the diene ligand, for an X-ray study has revealed that the structure of the intermediate is (49).  

Electrophilic attack at the co-ordinated ligand has been demonstrated for acetylacetone complexes of platinum and of palladium. Several reactions 

Many other species have been employed as ligands, including amines and nitrogen heterocycles, sulfides and sulfoxides, halides, alkoxides and nitriles. Dienes, such as 1,5-cyclooctadiene, are commonly used as ligands. 

Is cone angle still adequate to describe the increasingly complex phosphine ligands, and the new NHC ligands that are far from cone shaped New quantifiers are being proposed.  

The vast majority of the transition-metal catalysed reactions in this book use transition-metal species that are soluble in the reaction medium. These are often well-defined and characterized complexes. It does not have to be this way. Sources of transition metals that are insoluble in the reaction medium, especially heterogeneous sources of palladium, can be very effective. Palladium on inert supports, such as carbon, has been employed for many decades for hydrogenation reactions. They can also be employed for carbon-carbon bond-forming reactions. Other heterogeneous sources, such as perovskites, which are better known as components of car exhaust systems, have also been used. Catalysts of this type may act as sources of palladium, releasing palladium as complexes or nanoparticles into the reaction medium, then reclaiming it. Often, these systems leave less residual metal contamination in the final product and, therefore, are particularly useful industrially. 

Other types of homodonor and heterodonor phosphorus ligands have also been developed for application in asymmetric hydroformylation. 

In this context, several diphosphine ligands have been applied to this catalytic process. However, they do not achieve ee s as high as that obtained in the Rh system, with diphosphite or BINAPHOS. For example, in the Rh-catalyzed hydroformylation 

Although thiol ligands are the most widely used as stabilizers in the synthesis of Au NPs, other organic ligands bearing amine, phosphine, phosphine oxide, carboxylate or other functional groups have been employed alone or in mixtures. 

The modification to the Brust-Schiffrin method through the addition of lauryla-mine (LAM) or octadecylamine (ODA) instead of thiols to colloidal gold particles 

Using amine chemistry for reduction and for surface stabilization at the same time, gold nanoparticles can be prepared in water directly by addition of oleyl amine (O LA) to a solution of AuCI4. The XRD measurements show the peaks that confirm the face centered cubic (fee) lattice of gold. The analysis of the obtained nanoparticles displays narrow size distributions and, for example, when high concentrations of oleyl amine are used an average core size of 10 0.6 nm is achieved [79]. 

A one-pot method for the synthesis of amine-stabilized gold nanoparticles using 

A combination of octylamine (OA) and hexadecylamine (HDA) has been used for the synthesis of gold nanoparticles using the organometallic complex 

Treatment of the carbene complex [Cr C(OMe)Ph (CO)6] with certain alkenes yields cyclopropanes by transfer of the carbene entity. The reaction of diethyl fumarate with (- )-(/ )-methyIphenylpropylphosphine(phenylmethoxycarbene)tetracarbonyl-chromium produces the optically active cyclopropane (19), the formation of which demonstrates that no free carbene is involved in the mechanism for the reaction.  

PDA vesicles have been used to screen small molecules that are known to interact with membranes. Screening of almost 40 compounds against PDA/DMPC liposomes 

Liposomes prepared from diacetylene hydrazide 7 undergo chromatic transitions in response to pH changes (Jonas et al. 1999). Liposomes of 7, which form only in 

The reactions of co-ordinated isocyanide in Pt(CNEt)2(PMeaPh)a with ethanol, aniline, benzyl mercaptan, or similar compounds occur by 1,2-m-addition to the carbon-nitrogen bond, to give carbene compounds of the type (12). Addition of methylamine to co-ordinated methyl isocyanide in [Fe(CNMe)e] is thought to occur by attack of methyl-amine-N at isocyanide-C, to give initially (13).  

There have been three reports of reactions involving Cr(CO)6(carbene) compounds. The rate law for reaction of Cr(CO)5 C(OMe)Ph with primary amines in a variety of solvents is 

Tolson, J. Weaver, D. C. Wood, and P. Woodward, Chem. Comm., 1971, 222. 

The first step is attack at the carbene-C to form Cr(CO)5 C(N3)-2-furyl. This can lose dinitrogen and rearrange either in a concerted or a two-stage manner. The latter would have a transient nitrene intermediate. As the authors had no success in trapping any such nitrene the former, concerted, mechanism is preferred.  

Hydrogen exchange with the a-carbon-protons of the co-ordinated amino-acids in [Mo(A -C6H5)2(amino-acid)] could involve a carbanion or an oxazolonium ion intermediate. Whereas benzyl thiocyanate 

Isocyanides when bonded to a transition metal have a strong tendency to react with amines or alcohols to form carbene complexes. Kinetic studies on the 

Norbornadiene reacts with bis-(cis-l,2-perfluoromethylethylene-l,2-di-thiolato)nickel (74) to give the 1,8-cycloaddition adduct (75). This oxidative cycloaddition reaction obeys second-order kinetics. In cyclohexane as solvent 

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When the water ligands around a cation are replaced by other ligands which are more strongly attached, the redox potential can change dramatically, for example for the cobalt(II)-cobalt(III) system we have... 

Anions of Oxygen. Oxygen is treated in the same manner as other ligands with the number of -oxo groups indicated by a suffix for example, SO, trioxosulfate. 

EDTA Must Compete with Other Ligands To maintain a constant pH, we must add a buffering agent. If one of the buffer s components forms a metal-ligand complex with Cd +, then EDTA must compete with the ligand for Cd +. For example, an NH4+/NH3 buffer includes the ligand NH3, which forms several stable Cd +-NH3 complexes. EDTA forms a stronger complex with Cd + and will displace NH3. The presence of NH3, however, decreases the stability of the Cd +-EDTA complex. 

The biochemical basis for the toxicity of mercury and mercury compounds results from its ability to form covalent bonds readily with sulfur. Prior to reaction with sulfur, however, the mercury must be metabolized to the divalent cation. When the sulfur is in the form of a sulfhydryl (— SH) group, divalent mercury replaces the hydrogen atom to form mercaptides, X—Hg— SR and Hg(SR)2, where X is an electronegative radical and R is protein (36). Sulfhydryl compounds are called mercaptans because of their ability to capture mercury. Even in low concentrations divalent mercury is capable of inactivating sulfhydryl enzymes and thus causes interference with cellular metaboHsm and function (31—34). Mercury also combines with other ligands of physiological importance such as phosphoryl, carboxyl, amide, and amine groups. It is unclear whether these latter interactions contribute to its toxicity (31,36). 

The diisopropoxy-bis-(triethanolamine)-titanate, TYZORTE [36673-16-2] is an excellent cross-linker for aqueous solutions of hydroxyl-containing polymers. The reaction product of TYZORTPT with a mixture of trialkano1 amines and dialkanolarnines or monoalkano1 amines can be used to cure polyester-based powder coatings (109). Other ligands of this type iaclude triisopropano1 amine [122-20-3] ... 

Three features of chelation chemistry are fundamental to most of the appHcations of the chelating agents. The first and probably the most extensively used feature is the control of free metal ion concentration by means of the binding—dissociation equiUbria. The second, often called the preparative feature, is that in which the special properties of the chelate itself provide the basis of the appHcation. The third feature comprises displacement reactions metal by other metal ions, chelant by chelant, and chelant by other ligands or ions. An appHcation may be termed defensive if an undesirable property in a process or product is mitigated, or aggressive if a new and beneficial property is induced. 

The two protons at C-1 are topologically nonequivalent, since substitution of one produces a product tiiat is stereochemically distinct fiom that produced by substitution of the other. Ligands of this type are termed heterotopic, and, because the products of substitution are enantiomers, the more precise term enantiotopic also applies. If a chiral assembly is generated when a particular ligand is replaced by a new ligand, the original assembly is prochiral. Both C-1 and C-3 of 1,3-propanediol are prochiral centers. 

Many other ligands (L) also give 1 1 and 1 2 adducts. 

Some of these reactions result, essentially, in the oxidative addition of N0" N03 to coordinatively unsaturated metal centres whereas in others ligand replacement by NO+ occurs — this is a favoured route for producing nitroprusside , i.e. nitrosylpentacyanoferrate(II) ... 

Other ligands containing sulfur as donor atom... 

Mixed complexes in which a metal is coordinated by a dithiolene and by other ligands such as CO, NO, R3P, etc., are also known. 

Numerous carbonyl halides, of which the best known are octahedral compounds of the type [M(C0)4X2] are obtained by the action of halogen on Fe(CO)5, or CO on MX3 (M = Ru, Os). Stepwise substitution of the remaining CO groups is possible by X or other ligands such as N, P and As donors. 

The bulk of derivatives are obtained by the displacement of CO by other ligands. These include phosphines and other group 15 donors, NO, mer-captans and unsaturated organic molecules such as alkenes, alkynes and cyclopentadienyls. 

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