Amidines catalytic effects

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]. 

Catalytic reduction of nitro-substituted 1,1-enediamines 174 gives the aminomethyl amidines 238 in good yields. Apparently, reduction of the nitro group gives the triamine intermediates 237 which undergo a rapid prototropic shift to afford 238 (equation 97) . Attempts to reduce the benzoyl-substituted 1,1-enediamines 8 were unsuccessful . These results are not unexpected, since the double-bond character in 8 is reduced due to the strong conjugation effect. 

Catalytic hydrogenation of oximes to amines requires conditions resembling those for catalytic hydrogenation of nitro compounds and nitriles.20d The catalyst should be as active as possible, e.g., Raney nickel101 (if necessary, platinized), platinum oxide,102 palladium-charcoal,103 palladium-barium sulfate,104 or rhodium-alumina.105 This rhodium catalyst also serves for reduction of an amidoxime to the amidine.106 Hydrogenation may be effected under pressure, but the temperature should be kept as low as possible to avoid formation of secondary amines. 

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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