Monodentate neutral

The coordination abilities of A-heterocyclic thiols such as 2-thiopyridine, HSpy (66a), 2-mercapto-pyrimidine, Hspym (66b), or 2-mercaptothiazoline (67) with rhenium centers has already been described for oxorhenium(V) complexes is Section 5.3.2.3.L It has been outlined that ligands with five-membered rings preferably coordinate as monodentate neutral thiones whereas chelate formation is possible for mercaptopyridine or mercaptopyrimidine. Similar complex formation... 

Acetic acid by itself acts as a monodentate neutral ligand in the hexakis complex [Ni(HOCOMe)6](BF4)2.1718,1748 The Ni—O bond distances are similar to those observed in the acetate complex indicating that MeC02H is as strong a donor as its conjugate base. The hexakis acetic add complex dissolves in MeN02 without appredable dissociation. 

Nickel(II) complexes with either bidentate mononegative ligands, such as dithiocarbamates, phosphorodithioates and thiocarboxylates, or monodentate neutral and anionic ligands are generally square planar. Nickel(II) complexes with Se and Te donors are strictly similar to those with S donors. 

There are a few analogs of the bridged complexes described above which contain bidentate neutral ligands in place of the four monodentate neutral ligands. 

The most numerous complexes of this general type are those containing two bidentate neutral ligands, which are discussed in Section 48.6.3.7 below. These can easily be obtained by the oxidative addition of two anionic ligands to the numerous [Rh(LL)2]X complexes. There are, however, a considerable number of complexes which contain monodentate neutral ligands. These include the catalytically important [RhH2(PR3)2(solv)2]X complexes,1017-1019 and a number of dioxygen complexes.1030... 

There are many complexes containing one bidentate and two monodentate neutral ligands. A preliminary crystal study has been made on one of them.1034 It may finally be noted that the oxidative addition of sundry reagents to rhodium(I) complexes is not an infallible preparative method for complexes of this type. Nitronium tetrafluoroborate, for example, gives only a five-coordinate cation (equation 230).1035... 

Mechanisms for exchange of the monodentate neutral ligands has been extensively studied by dynamic NMR spectra and kinetic measurement using absorption spectra. The cationic methyl complex [PtMe(PPh3)(2,9-... 

In this chapter we review the interaction between rare-earth cations and both inorganic anions and simple, monodentate neutral molecules in anhydrous organic solutions. Some of the work in mixed solvents is also taken into account. The literature is surveyed until April 1994. 

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