Ligand monomeric state

Aminocyclopentene-l-dithiocarbamic acid (LH) forms a series of complexes, MIjCM = Ni", Co", or Cu"), in which the ligands are S,S-bonded (427). Diethanoldithiocarbamic acid forms Cu[(HOC2H4)2-NCS2]2, which is a monomeric, planar, CUS4 chromophore in solution, but Cu - S interaction probably occurs between neighboring molecules in the solid state (428). 

Tris(ferf-butoxy)siloxide molecular precursors of V(IV) and V(V) can be prepared via simple silanolysis reactions. For example, OV[OSi(O Bu)3]3 was obtained in 85% yield by reaction of OVCI3 with excess HOSi(O Bu)3 in the presence of pyridine [79]. Although crystals of sufficient quality for an X-ray structural analysis of 0V[0Si(0 Bu)3]3 were not obtained, its identity was confirmed by various spectroscopic and analytical techniques. Additionally, ( BuO)3VOSi(O Bu)3 and ( BuO)2V[OSi(O Bu)3]2 were obtained via reaction of V(0 Bu)4 with 1 and 2 equiv of HOSi(O Bu)3, respectively, in toluene at 80 °C [80] (Eq. 5). Both (fBu0)3V0Si(0 Bu)3 and CBu0)2V[0Si(0 Bu)3]2 are monomeric in the solid state, and possess only monodentate siloxide ligands... 

In view of this, it is not surprising that dithiocarbamato compounds with copper in the oxidation state + 3 are stable instead it must be regarded as unexpected that Cu(I) dithiocarbamato complexes exist. The latter complexes are not simply monomeric, but they are tetrameric metal cluster compounds. Obviously, the stability must be attributed to the metal-metal bond rather than to the stabilising effect of the ligand. 

Fig. 12.4. Successive models of the transition state for Sharpless epoxidation. (a) the hexacoordinate Ti core with uncoordinated alkene (b) Ti with methylhydroperoxide, allyl alcohol, and ethanediol as ligands (c) monomeric catalytic center incorporating t-butylhydroperoxide as oxidant (d) monomeric catalytic center with formyl groups added (e) dimeric transition state with chiral tartrate model (E = CH = O). Reproduced from J. Am. Chem. Soc., 117, 11327 (1995), by permission of the American Chemical Society. 

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