Addition of Ligands

Beyond those rather complicated amine ligands, other common bases are applied as ligands as weU. Lutidine, pyridine and amino acids like histidine and proline have been tested as rate-accelerating additives. 

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While inference has been made in a few cases as to the order of addition of ligands in prethermal reactions, no generalization can yet be made. When only one type of ligand is present, it is clear that the same ligand type may... 

The addition of metal ions to the mobile phase frequently yields Improved separations of solutes capable of forming complexes (conversely the addition of ligands to the mobile phase may allow the separation of metal ions based on differences in the distribution constants of the complexes between the mobile phase and, stationary phase) [353-355]. A number of important... 

Spectroscopists also saw the potential of reacting ligands with transition metal under matrix isolation conditions. Photolysis of metal carbonyls in organic (383 or inert gas matrices (39) had already been done, but atoms offered the possibility of step-wise addition of ligands. DeKock (40), Turner (41 ), and Moskovits and Ozin (42) made early contributions, but the work of the last two became dominant (32). By 1972, there were the two distinct branches in transition metal atom chemistry, the preparative and matrix spectroscopic studies. 

In this section, we start by describing the main features of the photolytic chemistry of iron pentacarbonyl and related species, focusing on the experimental data. We then describe our and other people s computational work aimed at understanding the reactivity of the fragments formed upon photolysis, with a focus on the spin-forbidden steps. We consider, in turn, the addition of ligands to Fe(CO)4, Fe(CO)3, and Fe(CO)3L (where L is a ligand such as H2 or ethene). For some of the reactions, we include some new computational results as well as a review of existing work. 

In this scheme, M <1 and K equilibrium constants. Direct binding experiments have confirmed the generality of this scheme for nicotinic receptors. Thus, distinct conformational states govern the different temporal responses that ensue upon addition of a ligand to the nicotinic receptor. No direct energy input or covalent modification of the receptor channel is required. 

Equilibrium constant for cumulative addition of ligand in mononuclear complexes... 

Otsuka and coworkers—addition of ligands to Pt and Rh complexes to facilitate water activation. Most researchers in the water-gas shift field focused their research primarily on the activation of CO through coordination that facilitated the nucleophilic attack by OH- or H20. In addition to this, Ostuka and coworkers28,40,47,55,56 added a new approach. It was based on a strategy that induces two-electron transfer from a low valent metal compound to a H20 molecule that leads to a hydrido-hydroxo-metal species, M + H20 <-> MH(OH). In so doing, they predicted that nucleophilic attack by the OH- on the coordinated CO would be more facile relative to the neutral H20 molecule. 

One possible criterion for designating a compound complex , that the ligand is exclusively held by one metal, is too restrictive because it excludes the / -complexes. However, it is reasonable to state that if all anions contact more than three cations the solid does not contain complexed cations. Compounds made by addition of ligands to M(I)... 

It should be recognized that the stability of cobalt complexes under carbon monoxide can be enhanced by the addition of ligands, as is the case for phosphine-modified cobalt hydroformylation catalysts (57, 58). The stability will also probably depend on properties of the solvent employed. Nevertheless, the plot shown in Fig. 4 appears to be quite useful for assessing long-term cobalt stability under H2/CO in the absence of strongly coordinating solvents or ligands. 

Sc(OR)3(tppo) are prepared by direct addition of ligand to Sc(OR)3 in benzene at 20 °C. The bridged compound is obtained together with Sc(OR)3(THF) by reaction of NaOR-THF on ScCl3 followed by appropriate work-up. These compounds are soluble in hydrocarbons and of course very easily hydrolyzed. Single crystal X-ray data are available for Sc(OR)3 the coordination is trigonal planar (O—Sc—O = 123.3°+120.1°+115.1° = 358.5°) with Sc—0 = 1.854-1.889 A. Sc—O—C is not quite linear, averaging 168.40.94... 

Structurally these complexes (Fig. 16.59) are clearly related to IRe ClJ. the only difference being (for the rhenium complexes) the addition of ligands to overlap wiih the metal dp hybrid orbitals which were nonbonding in [RevCl )2. ... 

Addition of ligand names to a central atom name hexaaquanickel(ll) ion... 

Methyl-2-diphenylphosphino-3-(l -isoquinolyl)indole with pallada-cycle derived from dimethyl-1-naphthyl ethylamine and potassium hexa-fluorophosphate yields chelate 310 (97T4035). With [(r)3-PhCH = CH = CHPh)Pd( j.-Cl)]2, allyl 311 follows in the presence of silver tetrafluor-oborate. Addition of ligands 312 (R = R1 = H, Me) to [(r 3-PhCHCHCHPh)Pd (Cl) ]2 under conditions of allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate leads to the formation of P,N-chelates 313 (R = R1 = H, Me), the active species of the catalytic reaction (00T(A)4753). 

Uson and collaborators described an A-frame PdPt complex [C6F5Pd (p-C=N-p-tolyl)(p,-dppa)2PtC6F5] (75),85 and more recently, [XPd(p,-dppm)2 (p-C=N-R)Pt(CN-R)]+ (76-78) and [ClPd(p,-dppm)2(p,-C=N-R)PtCl] (79-81) were reported by Knorr and collaborators86-88 (Fig. 32). In the bis(isonitrile) heterobimetallics 76—78, a site selectivity in the second CNR ligand coordination (Pd vs. Pt) was noticed. The additional isocyanide is systematically coordinated on the Pt site.86,88 This distinct selectivity between Pd and Pt was explained by the greater lability of the Cl- ion on the Pt center as well as a better stabilization of the positive charge on the electron-rich Pt1 center.88 The question arises as to why the addition of ligand isocyanide sometimes produces the A-frame compound whereas under similar conditions, a d9-d9 isocyanide... 

The addition of ligands in the hydroformylation of camphene influenced the reaction to endo product, while without ligands, an equal ratio between the exo and the endo product was observed. The selectivity for the two linear isomers was 100%. 

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