Ligand displacement reactions

Three approaches have been tested, as already described above for inorganic supports. The first attempts concern the direct reaction of transition metal carbonyls with unmodified organic polymers like poly-2-vinyl-pyridine.61 62 However, this kind of anchoring is restricted to only a few complexes. Various polymers have been functionalized with donor groups 63-72 ligand displacement reactions using these afforded the corresponding immobilized complexes. Finally, tests with modified complexes and unmodified polymers are scarce because of the low stability of these complexes under the conditions of reactions. 

Ligand displacement reactions for [MX]+ and [MX2]+ ions may be used as a measure of ligand strength for a wide variety of donor molecules. The M-O bond in the [MO]+ ion varies from very strong for the groups 3 (IIIB), 4 (IVB), and 5 (VB) metals to weak in the later transition metals. 

A number of systems have been studied where a formal ligand displacement reaction is followed by an isomerization process. One recently described example involves the cleavage of a Pt-C(alkyl) cr-bond in complexes of the type cis-[Pt(R)(R )(PEt3)2] to produce cis-[Pt(R)(PEt3)2(MeOH)]+ and R H, which subsequently isomerizes to nms-[Pt(R)(PEt3)2(MeOH)]+ (90). The first protonolysis reaction is characterized by significantly negative volumes of activation between... 

R. J. Watts, J. S. Harrington, and J. Van Houten, A stable monodentate 2,2-bipyridine complex of iridium (III) A model for reactive intermediates in ligand displacement reactions of tris 2,2-bipyridine metal complexes, J. Am. Chem. Soc. 99, 2179-2187 (1977). 

VO(oxine)2] (138) and [VO(oxine)2py]-C6H6 (140), prepared by a ligand displacement reaction (equation 61), had v(V==0) = 963 and 945 cm and pcS = 1.75 and 1.64 BM, respectively. When 8-quinolinol is replaced by 2-methyl-8-quinolinol in reaction (61), [VO(2-Me-oxine)2] is obtained, with v(V=0) = 970 cm-1. Complexes (138) and (140) react readily with 02 and a diamagnetic dinuclear pi-oxo Vv species [(oxine)2—OV—O—VO(oxine)2] is produced.826 Nitrobenzene and 2-nitrosobiphenyl also react in a similar manner in THF giving the same complex. With p-benzoquinone a dinuclear diamagnetic Vv complex [(oxine)2OVOC6H4OVO(oxine)2] is obtained. 

Although dithiolenes are stable compounds, many of which do not react with strong acids or bases, they are nevertheless reactive enough to undergo ligand displacement reactions as well as... 

Mononuclear a-complexes of group VIb carbonyls are conveniently prepared by ligand displacement reactions.44-48) As in the case of iron carbonyls the reaction... 

Otsuka, Nakamura et al.112 prepared the first complexes containing side-on coordinated diazo compounds by ligand displacement reactions [Eqs. (2—4)]. The... 

Besides the elimination of alkali halides in the reaction between the silyl and metal reagents, several types of reactions in which other simple molecules are liberated have been widely employed. These methods, which include elimination of hydrogen, oxidative eliminations and ligand displacement reactions, are often interrelated. 

A series of ligand displacement reactions has been investigated in which a phosphine replaces a carbonyl group, the ease of reaction depending on both M and the silyl residue. Triphenyl or trialkyl phosphine can remove only one CO molecule in Mn, Re, Co, and Fe complexes, even under forced conditions,... 

When the divalent compound is stable, the complexes are synthesized by ligand displacement reactions such as those shown in Eqs. (47) (52), (48) (78, 100), and 49 (78). 

There are literally thousands of chromium(III) complexes that, with a few exceptions, are hexacoordinate and octahedral. An important characteristic of these complexes in aqueous solutions is their relative kinetic inertness. Ligand displacement reactions of Cr111 complexes are only 10 times faster than those of Co111, with half-times in the range of several hours. It is largely because of this kinetic inertness that so many complex species can be isolated as solids and that they persist for relatively long periods of time in solution, even under conditions of marked thermodynamic instability. 

This interpretation, however, faces a new problem If the low frequency bands are not due to bridging species, what is the explanation of the distinct downward shift of the vco bands upon CO addition and also of their strong intensity Authors of quoted works [48,53,54,77,99] have probably solved this contradiction. The surface process depicted is not a simple hgand insertion into a pre-existing coordinative vacancy, but more likely a ligand displacement reaction of the type reported in Eq. 2 ... 

H. Werner Fortschr. Chem. Ring ligand displacement reactions 41 ... 

The bulky stable silylenes described in Section 3 may be used as ligands in a range of transition metal complexes. The complexes are formed mostly via simple ligand displacement reactions as shown in Scheme 73 although in some cases reactions occur involving reduction of halogenometal complexes. ... 

The -acyl derivatives of transition metals undergo the ligand displacement reaction (o) ... 

This section covers only transition-metal complexes which are directly formed during the synthesis of the heterocycles, or such which result from ligand displacement reactions with suitable metal complexes. Chemical transformations at the metal-bound three-membered ring with metal complexes whereby the structural integrity of the diphosphirene moiety is destroyed is considered in Section 1.16.5.2 in more detail. 

The coordination chemistry of boron was reviewed some time ago and the structure and properties of compounds of the general formula BX3 L, where X and L can be one of a wide variety of substituents and electron pair donors, respectively (15). Indeed, the reactions of tricoordinate boron compounds in general are thought to proceed via addition of the reaction partner in a Lewis acid-base reaction to yield a tetracoord-inate intermediate that then undergoes further reaction. Stable tetra-coordinate boron compounds are subject to ligand displacement reactions for which a variety of mechanisms obtain (16). The coordination chemistry of transition metals is vast and includes not only structimal facts (17) but considerable information on the mechanistic behavior of these species as well (18). In our brief comparison we will restrict ourselves to low oxidation state chemistry and group 16 metals (19). 

A report of cationic, mixed-ligand complexes of iron(III) containing dithiocarbamate ligands appeared recently (277). The complexes, [FeLiRidtclj] (L = CNR, diphos, or PPhs) were obtained by reaction of L with [Fe(R2dtc>3]+, involving a ligand-displacement reaction (277). 

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