Proligands

The facile insertion of carbodiimides into a Ti-CMe bond of (CsRslTiMes (R = FI, Me) (cf. Section 1II.B.2) has been extended to the insertion of optically pure (R,R)- and meso-(R,S)-1.3-bis(l-phenylethyl)carbodiimide. Treatment of Cp M(NMe2)3 (M = Zr, FFf) with both achiral and optically pure aminooxazoline proligands ITL yielded metastable aminooxazoline half-sandwich diamide... 

The reaction of Ni11 perchlorate with (740a) gave the complex (741), in which the imine bond of the proligand had undergone hydrolysis. In the resulting dimeric Ni2 structure with a Ni Ni distance of 3.088 A, both metal ions are in octahedral coordination environment. When (740b) was used,... 

The metal is chelated by an ene-1,2-dithiolate (dithiolene) of the dihydropyran ring which is fused to a partially reduced pteridine 178. The syntheses of these molybdopterin-related proligands were described as model compounds for verification of the stability in vitro <2001CC 123>. The proligand 179 is a relatively stable compound however, after several weeks, the pyran ring opened and oxidation to the diol derivatives 180 was observed (Scheme 35). 

Figure 6 The trithiol proligands (a) l,4,7-tris(4-sulfanylbenzoyl)-l,4,7-triazacyclono-nane, H3L and (b) l,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(4-tolylthio)-benzene, H3LS3.

Scheme 11 Reactions of rhenium complexes with silylated phosphine proligands...

The imidazolium protons and the alcohol and amino protons are sufficiently acidic that monoprotonated proligands can be used in transamination reactions to afford f-element functionalised-NHC adducts. 

In this way, the indenyl tethered NHC complexes of yttrium, lutetiiim and scandium were synthesised [135] each still bearing two potentially reactive trimethylsilylmethyl substituents. The potential as single component or cationic (after activation with MAO) catalysts for the polymerisation of olefins was pointed out by the authors, but no studies have as yet been reported. The same can of course be said about the corresponding early transition metal complexes of titanium, zirconium, vanadium and chromium [134,136] where the synthesis of the proligands and the transition metal complexes were reported, but no catalytic studies performed. 

This arises when the counterion in a complex salt is a proligand and can, in principle, displace a ligand which can then become the counterion. An example is provided by the ionization isomers [Co(NH3)5SOJBr and [Co(NH3)5Br](S04). 

As with any other chemical reaction, the formation of a metal complex from a metal ion and a set of proligands can be described by an equilibrium constant. In its simplest form, a complexation reaction might involve the reaction of unsolvated metal ions in the gas phase with gas phase proligands to form a complex. In practice it is difficult to study such reactions in the gas phase and complex formation is normally studied in solution, often in water. This introduces the complication that the solvent can also function as a ligand, so that complex formation will involve the displacement of solvent from the metal coordination sphere by the proligand. 

In complexation reactions the solvent is normally present in large excess so that its concentration is essentially constant. Thus, in cases where the reactivity of the coordinated solvent is not an issue, it is possible to simplify considerations of complex formation by omitting the solvent from the description of the equilibrium. In such cases the formation of a metal complex from a metal ion and one or more proligands, L, according to equation 5.4 can be described by the simplified... 

When a solvated metal ion reacts with a proligand, which could be poly-dentate, to form a complex, several things must happen. Firstly, coordinated solvent must be removed from the metal ion coordination sphere to create a space for the incoming ligand, and the solvation shell around the metal must be reorganized to accommodate the new structure. This will require an energy input A similar process will occur around... 

Transitions of this type are associated with polyatomic ligands which have electronic spectra in their own right. As an example, the tris(3,5-dimethylpyrazolyl)borate (tp 2-) proligand (Figure 4.2) exhibits a tc 7C transition in the ultraviolet region at about 230 nm, which is also observed in its transition metal complexes. Usually, such absorptions do not reveal much about the metal centre and so they are of less interest to transition metal chemists than the remaining types of absorption which directly involve the metal centre. 

This section deals with a series of phosphor-1,1-dithiolates, which includes dithiophosphinates, M(S2PR2) , dithiophosphates, M[S2P(OR)2] , and dithiophosphonates, MIS R OR2)] Alternative names are phosphinodithioates, phosphorodithioates, and phosphonodithioates, respectively. The parent acids (proligands), (l)-(3) are shown in Scheme 1. ... 

The preparation methods of dithiophosphoric acid diesters, (RO)2P(S)SH, which are the proligands for dithiophosphato complexes, use almost exclusively the reaction of alcohols with tetra-phosphorus decasulfide ... 

In 2003, O Shaughnessy and Scott reported the first example of rare-earth metal complexes supported by biaryl diamide ligands as the catalysts for the hydroamination reactions [159]. A series of C2 symmetric secondary diamine proligands L37-L40 were prepared by arylations of (7 )-2,2 -diamino-6,6 -dimethybiphenyl under palladium catalysis. L37 reacted with complexes [Ln N(SiHMe2)2 3(THF)2] to form the biaryl diamide complexes [Ln(L37) N(SiHMe2)2 (THF)2] (Ln = Y (190), La (191), Sm (192)). Deprotonation... 

When we utilized the chiral proligand in an identical reaction, we... 

Deprotonation of the racemic or enantiopure salen proligand featuring a trans cyclohexyldiamine backbone (ONNO) and subsequent salt metathesis with indium trichloride and sodium ethoxide in a three-step process involving an indium chloride intermediate yields racemic or enantiopure indium ethoxide complex [(ONNO) In(p-OEt)j2 (2) (Figure 34). 2" ... 

Scheme 1 Modular one-step proligand syntheses ensure that steric bulk and electronic properties can be easily varied...

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