Metal amidinate complexes

Certain aspects of catalytic applications of transition metal amidinate complexes have already been summarized in review articles. The "Chemistry of... 

In 2007, Smolensky and Eisen published a review entitled "Design of organometallic group IV heteroallylic complexes and their catalytic properties for polymerizations and olefin centered transformations.In this article a strong emphasis was placed on various synthetic and catalytic aspects of group IV metal amidinate complexes. It was clearly pointed out that such amidinate... 

Several patents dealing with the use of volatile metal amidinate complexes in MOCVD or ALD processes have appeared in the literature.The use of volatile amidinato complexes of Al, Ga, and In in the chemical vapor deposition of the respective nitrides has been reported. For example, [PhC(NPh)2]2GaMe was prepared in 68% yield from GaMes and N,N -diphenylbenzamidine in toluene. Various samples of this and related complexes could be heated to 600 °C in N2 to give GaN. A series of homoleptic metal amidinates of the general type [MIRCfNROilnl (R = Me, Bu R = Pr, BuO has been prepared for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. The types of products are summarized in Scheme 226. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. 

In the presence of N,N,N, N",N"-pentamethyldiethylenetriamine ( = PMDETA), monomeric lithium complexes of bulky formamidinate ligands can be isolated. The compounds (Scheme 12) comprise a Li(PMDETA) center coordinated by a bulky formamidinate in either the E-syn- or E-anti-isomeric form. Two of the structures display coordination of the pendant amidinate imine, and can therefore be considered the first examples of if. r -C = N,N metal amidinate coordination. ... 

Titanium imido complexes supported by amidinate ligands form an interesting and well-investigated class of early transition metal amidinato complexes. Metathetical reactions between the readily accessible titanium imide precursors Ti( = NR)Cl2(py)3 with lithium amidinates according to Scheme 84 afforded either terminal or bridging imido complexes depending on the steiic bulk of the amidinate anion. In solution, the mononuclear bis(pyridine) adducts exist in temperature-dependent, dynamic equilibrium with their mono(pyiidine) homologs and free pyridine. 

Deprotonation of Group 4 mono(pentamethylcyclopentadienyl) metal acet-amidinates can be achieved in high yield using sterically encumbered bases (Scheme 103) to provide anionic enolate complexes as purple powders. These can subsequently be allowed to react with electrophiles (e.g., PhCH2Cl, CH2CI2, Me2SiCl2) to produce several new classes of metal amidinates that are not accessible by conventional routes (Scheme 104). ° ... 

Metathetical reactions between NbCl4(THF)2, NbCls, TaCls, [(Et2N)2TaCl3]2, or (R2N)3Ta(=NBu (R = Me, Et) with various amounts of lithium amidinates have been employed to synthesize the corresponding heteroleptic niobium and tantalum amidinate complexes. The products were investigated as potential precursors to metal nitrides (cf. Section VI) Carbodiimide insertion routes... 

Structurally related complexes are also active initiators for the living polymerization of carbo-diimides (which are isoelectronic to isocyanates).1003 The proposed intermediate for this polymerization process is a metal amidinate (Scheme 29), and the model complex (349) has been reported to be a highly efficient catalyst, polymerizing 500 equivalents of di- -hexylcarbodiimide in less than 10 s. A more hydrolytically robust series of initiators has also been developed, based upon copper(I) and copper(II) amidinates.1004... 

Bonds typically hydrolyzed include carboxylic and phosphoric esters, amides, acetals, amidines, as well as metal ion complexes. (When a nucleophilic substitution reaction uses the solvent as the nucleophile, the reaction is often referred to as solvolysis.)... 

The metal-bound RCN group is also activated on coordination towards nucleophilic attack by alcohols, thiols or amines to give stable N-bonded iminoether, iminothioether and amidine complexes respectively.332 Several cationic cyanobenzylpalladium(II) complexes have been prepared, and the reactivity of the CN group towards nucleophiles has been studied.333,334 The palladium complex (97) reacts with aromatic amines to give chelated amidino complexes (98) and the reaction has been studied kinetically.333 In this case intermediates with the nitrile group bonded side-on are considered to be involved. 

The reaction of a variety of liganded metal derivatives with carbodiimides give [1+2] or [2+2] cycloadducts or more complicated products resulting from rearrangement or reductive coupling reactions. Also, amidinate complexes, which are sometimes obtained in the reaction of metal complexes with carbodiimides, are included. 

The lithium amidinates are used as precursors for homoleptic lanthanide amidinates. Lanthanide amidinate complexes have a high catalytic activity in the polymerization of ethylene. They are also used in the manufacture of membranes. Lanthanide amidinate complexes 37 (La=Er, Y, Gd) are also obtained from alkyl metal complexes 36 and... 

Silver dinuclear and trinuclear amidinate complexes are also known. Also, bis-(amidinate) complexes are obtained by direct metallation of amidines. ... 

The use of amidinato catalyst systems for the polymerization of olefins has first been reported in a patent application by us in cooperation with BASF company [6,7,46]. Since then various other patents dealing with the use of amidinato metal complexes as catalysts for olefin polymerizations have appeared. However, the main focus of these studies was on the use of group 4 metal amidinates as these have been found... 

The ROP of TMC using the homoleptic lanthanide amidinate complexes [RC(NCy)2]3Ln (R = Me, Ph Ln = La, Nd, Sm, Yb) as single-component initiators was investigated in detail. It was found that the substituents on the amidinate ligands and the metal centers had a great effect on the catalytic activities of these complexes, that is, Me > Ph, and La > Nd > Sm > Yb. Thus, the lanthanum acetamidinate [MeC(NCy)2]3La showed the highest catalytic activity [64]. 

Tml2, Dyh and Ndh have also been used in an acetonitrile/amine coupling reaction, which produced amidines of general formula MeC (=NH)NR R R R2 = H, Me H, iPr H, fBu Et2). The reaction is sub-stoichiometric in rare-earth diiodide but not really catalytic since part of the produced amidine remained tightly held aroimd the rare-earth metal it could be liberated by heating a trivalent intermediate formulated as Rl2(amidine)4(amidinate) (R = Nd, Dy, Tm) imder vacuum, and the residue could be recycled to produce more amidine. This reaction is not specific of the divalent iodides since many rare-earth triiodides were also effective. In the case of dysprosium and diethylamine, an intermediate trivalent amidine complex has been isolated and structurally characterised in the form of the zwitterionic [Dy MeC(=NH)NEt2 4][(I)3] (Bochkarev et al., 2007) (Figure 9). 

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