Ligand, Bis

The stability of the phosphine adducts is notable as is the fact that thioethers readily form such adducts whereas ethers do not. Bis-ligand adducts of moderate stability play an important role in activating decaborane for several types of reaction to be considered in moie detail in subsequent paragraphs, e.g. ... 

Pyridyl functionalized tris(pyrazolyl)borate ligands show some interesting properties including the formation of polynuclear zinc complexes.23,1 Some of these contain extensive H bonding and have potential as models for multinuclear zinc enzymes such as phospholipase C or PI nuclease.235 A bis-ligand complex of the hydrotris(5-methyl-3-(3-pyridyl)pyrazolyl)borate ligand (23) shows octahedral coordination of all six pyrazole nitrogen donors despite the steric bulk. 

The above results justify a simple ligand field model for the bis(ligand) metal species which is based on the assumption of pseudoaxial symmetry (40). This model allowed a consistent reinterpretation of an early ESR study of Co(C5H5BPh)2 (13) (42) the reinterpretation was later confirmed by additional and more sophisticated ESR work on 13 (43,44). 

As mentioned already, Curtis reported the first (Curtis, 1960) of a number of pioneering template reactions for macrocyclic systems which were published in the period 1960 to 1965. In the Curtis synthesis, a yellow crystalline product was observed to result from the reaction of [Ni(l,2-diaminoethane)3]2+ and dry acetone. This product was initially thought to be a bis-ligand complex of the diimine species (58). However, the stability of the product in the presence of boiling acid or alkali was... 

Figure 4.4. Structure of the bis-ligand potassium complex of benzo-15-crown-5. The complex shown is cationic (Mallinson Truter, 1972).

Metal complexes of pinene-fused boratabenzene ligands, analogous to chiral metallocenes that have found application in catalysis and enantioselective synthesis, have been prepared.122-124 With late transition metals such as Mn and Fe, the complexes are obtained as mixtures of diastereomers (e.g., 97) with the sterically less congested exo form predominating, but the bis(ligand) Zr complex 98 was obtained as the pure exo,exo product.124 A lithium... 

Hemochromes are the symmetrical bis(ligand) adducts of the Fe11 porphyrins, e.g. the bis(imidazole) moiety [11] presumably occurring in reduced cytochrome a or bs (1, 47). The bis(pyridine) hemochromes Fe(P)Py2 are all rather labile in solution the same is true for the corresponding hemichrome derivatives, [Fe(P)Py2] , which are the cationic oxidation products of the hemochromes. Reliable spectral and other physicochemical data on these species can only be obtained in solution when an excess of L is present to suppress the dissociation equilibrium (5) (M = Fe) (20, 24), which is the origin of subsequent oxidation (n = 0) or solvolysis reactions (n = 0 or 1). 

The structures of the bis-ligand iron(II) complexes of the tripodal ligands tiis(pyiidin-2-yl)methane and tris(pyridin-2-yl)phosphine oxide have been determined." " The tetradentate tripodal ligand... 

The structures of the bis-ligand iron(II) complexes of the tripodal ligands tris(pyrazol-l-yl)methane and bis(pyrazol-l-yl)(pyridin-2-yl)methane have been determined the former is a spin cross-over complex." " Polybis(pyrazolateiiron(II) has a ID chain structure with the Fe " " ions doubly bridged by pyrazolates the Fe + ions (-S = 2) are weakly antiferromagnetically coupled. ... 

The hydrotris(triazolyl)borate (httazb, (133)) ligand gives a bis-ligand iron(II) complex [Fe-(httazb)2] 6H20, whose structure consists of layers of complex molecules separated by layers of water molecules. ... 

The triazacyclononane ligand with o-aminophenylmethyl pendant arms (140) forms a bis-ligand complex with Fe +, isolated as its perchlorate. Aerial oxidation of this salt gives an uncharged iron(III) complex containing the ligand in triply-deprotonated form. ... 

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