Transition metal complexes coordination structure

The free electron pair(s) in the concave pyridines 3 (Table 1), 13 (s. Scheme 3) and 29 (s. Scheme 5) and especially in the concave 1,10-phenanthrolines 11 (s. Scheme 2) and 21 (Structures 3) are not only able to bind a proton, they may also be used to coordinate a metal ion. For concave 1,10-phenanthrolines 11 and 21, transition metal complexes 87 (Structure 11) have already been generated [18, 55]. They form readily in acetonitrile solution with binding constants of 10 10 and larger. Of great importance is the nature of the chains X in the concave 1,10-phenanthrolines 21 (Structures 3). Pure aliphatic chains lead to smaller association constants than polyether chains. 

Transition Metal Complexes Related to the Simon test is a family of color-producing reactions based on transition metal complexes (coordination complexes) and tightly associated ion pairs. Coordination complexes arise from a Lewis acid-base interaction between a metal cation, such as cobalt, and an atom with unshared electrons, such as water or, in the case of drugs, basic nitrogen found in alkaloids and amines. Metals that have been used in these reagents include copper, vanadium, bismuth, and cobalt Cobalt, as part of two common reagents (cobalt thiocyanate and Dilli-Koppanyi) is perhaps the most versatile. Cobalt has an electron structure of 3d 4s, while ttie cation has a 3d (2 ) or 3d (3 ") structure. 

A number of transition-metal complexes of RNSO ligands have been structurally characterized. Three bonding modes, r(A,5), o-(5)-trigonal and o (5 )-pyramidal, have been observed (Scheme 9.1). Side-on (N,S) coordination is favoured by electron-rich (et or j °) metal centers, while the ff(S)-trigonal mode is preferred for less electron-rich metal centres (or those with competitive strong r-acid co-ligands). As expected ti (N,S)... 

The solvated sulfenamides [Li2( BuNSC6H4Me-4)2(THF)n] (n = 2,4) have dimeric structures with a central Li2N2 ring. The coordination mode is determined by the extent of solvation of the Li" ions monosolvation allows for rj -N,S coordination whereas disolvation restricts the coordination mode to // -M Variable temperature NMR studies indicated that a dynamic exchange between these two structural types occurs in THF solution (Scheme 10.10). The dihapto coordination mode is observed exclusively in transition-metal complexes and the... 

The dominant features which control the stoichiometry of transition-metal complexes relate to the relative sizes of the metal ions and the ligands, rather than the niceties of electronic configuration. You will recall that the structures of simple ionic solids may be predicted with reasonable accuracy on the basis of radius-ratio rules in which the relative ionic sizes of the cations and anions in the lattice determine the structure adopted. Similar effects are important in determining coordination numbers in transition-metal compounds. In short, it is possible to pack more small ligands than large ligands about a metal ion of a given size. 

The finding of preparatively available iminoboranes RB = NR some years ago opened exciting new possibilities not only in B—N chemistry, but also in coordination chemistry. The first examples of iminoborane-transition-metal complexes have now been published. The structurally completely characterized t-BuB = NBu-t adds, like its alkyne analog, to the 03(00)5 fragment as a bridging ligand. When Co2(CO)g and t-BuB = NBu-t are dissolved in pentane at 0°C, warming to RT and evaporation of unreacted iminoborane yields (t-BuBNBu-t)Co2(CO)5 (86%) as a black solid, which can be recrystallized from ether-nitromethane (1 3) ... 

Metal complexes of ligands containing a sulfur donor in conjunction with nitrogen, oxygen or a second sulfur have been reviewed in the past [11-13]. For example, reviews of the coordination compounds of dithiophosphates [14], dithiocarbamates [15, 16], dithiolates [17], dithiodiketonates [18], and xanthates [16] have appeared. The analytical aspects [19] and the spectral and structural information of transition metal complexes of thiosemicarbazones [20, 21] have been reviewed previously. Recent developments in the structural nature of metal complexes of 2-heterocyclic thiosemicarbazones and S-alkyldithiocarbazates, depicted below, are correlated to their biological activities. 

In this chapter, synthesis, structure, and reactions of various classes of diazaphospholes have been reviewed. Recently used synthetic methods and variations for obtaining diversely substituted diazaphospholes have been discussed. On account of the cycloadditions on P=C bond of [1,4,2]- and [l,2,3]diazaphospholes, a number of organophos-phorus compounds incorporating a bridgehead phosphorus atom have become accessible. Recently reported complexation reactions of diazaphospholes, illustrate their capability to form transition metal complexes via different coordination modes. 

Related to tertiary stibines is the (Me3Si)3Sb ligand. Recent studies of this ligand comprise coordination on transition metal and main group element centers. An example for a transition metal complex with a known crystal structure is [(CO)5CrSb(SiMe3)3],5° the structure of which is depicted in Fig. 2. 

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