Anion, noncoordinating

Transition metal complexes containing the pyrazolate group as anionic noncoordinating ligand, although rare, have been reported (5). They are undoubtedly of lesser importance and will not be further discussed. 

D.ii.c. Cationic Pd(II) Complexes. The most preferred coordination number for Pd(II) complexes is four. When more than two neutral ligands coordinate to a divalent palladium, the complex becomes cationic. Anions snch as hahde can be potential ligands, which may replace the coordinating neutral hgands. To prevent the counteranions from coordination, weakly coordinating anions (noncoordinating anions) such as Bp4 are frequently employed for these complexes. 

Apparently, a palladium carbamate is formed that is able to attack the triple bond, thus forming a vinylpalladium bond that undergoes carbonylation in the presence of carbon monoxide.f The main product is an oxazolidinone containing a c -(methoxycar-bonyl)methylene chain. The product is accompanied by a secondary compound, which is the trans isomer. This has been traced to partial attack on the triple bond by the carbamate anion, noncoordinated to palladium, which occurs with opposite stereochemistry (Scheme 38). 

The duoroborate ion has traditionally been referred to as a noncoordinating anion. It has shown Httie tendency to form a coordinate—covalent bond with transition metals as do nitrates and sulfates. A few exceptional cases have been reported (13) in which a coordinated BF was detected by infrared or visible spectroscopy. 

Noncoordination anions with extensive charge delocalization have been very suc-cesful in enhancing the performance of dry polymer electrolytes. Examples of these are given in Table 1. 

In recent years ionic liquids have also been employed as media for reactions catalyzed both by isolated enzymes and by whole cells, and excellent reviews on this topic are already available [47]. Biocatalysis has been mainly conducted in those room-temperature ionic liquids that are composed of a 1,3-dialkylimidazolium or N-alkylpyridinium cation and a noncoordinating anion [47aj. 

The Au anion distance of [Au2(dcpm)2][Au(CN)2]2 lies between those with noncoordinating (C104 or PFg ) anions and that of the I salt. The visible emission of the [Au2(dcpm)2] [Au(CN)2]2 solid at 7, = 515 nm is more intense than the visible emission of solid samples of C104 and PF salts of [Au2(dcpm)2] at 564 and 505 nm... 

Giitlich et al. [4, 6] have studied SCO in solid [Fe(2-pic)3]Cl2-EtOH (2-pic = 2-picolylamine), particularly the influence of dilution with Zn and Co, the nature of noncoordinated anions and crystal solvent, the HID and isotope effect,... 

Reactions of P-halogen-NHPs with Lewis acids leading to halide abstraction, or metathetic replacement of the halide by a nucleofugic, noncoordinating anion form by far the most important routes to access phosphenium ions in general [51, 52] and also 1,3,2-diazaphospholenium cations in particular. As Lewis acid assisted P-X... 

Anions of the type [M(C2B9H11)2] (M = Fe, Cp, Ni) were also used as noncoordinating anions with [Cp2ZrMe] +, which are active for the polymerization and copolymerization of ethylene and oc-olefins in non-polar solvents such as toluene and hexane [54]. By using the same anions, cationic actinide complexes have also been prepared [110]. 

Noncontact printing, in microarray fabrication, 16 386 Noncoordinating anions, 16 95 Noncovalent carbon nanotube functionalization, 17 53 Noncovalent fluorescence labeling, 20 519... 

The first hydration step was promoted by Bronsted acids containing weakly or noncoordinating anions. In the second step, an intramolecular hydrogen transfer in the secondary alcohol was catalyzed by ruthenium(III) salts with chelating bipyridyl-type ligands. The possible complexation of the latter with the diene did not inhibit its catalytic activity in the allylic rearrangements, under acid-catalyzed hydration conditions. 

Vicentini and coworkers have reported the complexes of DPPA with lanthanide perchlorates 224), hexafluorophosphates 225), chlorides and nitrates 226). The anions in the perchlorate and hexafluorophosphate complexes are noncoordinated and hence the complexes are six coordinated. Conductance data for the nitrate complexes indicate that the coordination interaction between the lanthanide ion and the nitrate ion decreases along the lanthanide series 226). 

How can these bulky, extremely weakly coordinating anions prevent catalyst deactivation A comparative kinetic study of catalysts with different anions provided a plausible answer [19]. With PFg as a counterion, the rate dependence on olefin concentration was first order, whereas the rate order observed for the corresponding BArp complex was close to zero. This striking difference may be explained by the stronger coordination of PFs or formation of a tight anion pair, which slows down the addition of the olefin to the catalyst to such an extent that it becomes rate-limiting. In contrast, the essentially noncoordinating BArp ion does not interfere with olefin coordination, and the catalyst remains saturated with olefin even at low substrate concentration. The slower reaction of the PFg salt with the olefin could... 

Metallocenes are of low activity unless they are used with a noncoordinating anion such as a methylalumoxane or borate. This noncoordinating anion can be anchored to a silica surface. 

They are often composed of weakly coordinating anions, e.g. BF4 and PFg and, hence, have the potential to be highly polar yet noncoordinating solvents. They can be expected, therefore, to have a strong rate-enhancing effect on reactions involving cationic intermediates. 

The bulky methylaluminoxane anion stabilizes the coordinatively unsaturated metal cation. Stabilization by noncoordinating anions such as carbosilane dendrimers is also viable.571 Aluminoxanes, however, are required to be used in large excess to be effective. Alternatively, the active catalyst can also be prepared by reacting a metal dialkyl with fluorinated boranes, borate salts or aluminate salts. 

Treatment of HAuC14, NaAuCl4, or AuBr3 with isonitriles gives (132, 133) complexes of the type [AuX(CNR)]. Such complexes have also been prepared by displacement of dimethyl sulfide from [AuX(SMe2)] (134). In the presence of free isonitrile, and with a noncoordinating anion, ionic complexes of the type [Au(CNR)2]+X are obtained (132, 133). 

When an isonitrile ligand containing a suitable hydroxyl group was reacted with AUCI4, it underwent isomerization (147) via a carbene complex (Scheme 1). With CN(CH2)3OH, in the presence of a noncoordinating anion, the bis(carbene)gold(I) complex [Au tO(CH2)3l(jH 2]+BPhJ was formed. 

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