Rare‐Earth Complexes Coordinated by ansa‐Bis(amidinate) Ligands with m‐Phenylene, 2,6‐Pyridinediyl, and SiMe₂ Linkers

Abstract

The salt-metathesis reactions of anhydrous LnCl 3 (Ln = Y, Er) with [1,3-C 6 H 4 {NC(Ph)NSiMe 3 } 2 Li 2 (thf ) 2 ] 2 (1; thf = tetrahydrofuran) in a 2:1 molar ratio in thf afford tris(amidinate) (3) and [(1,3-C 6 H 4 {NC(Ph)NSiMe 3 } 2 ) 3 Er 2 (μ-Cl)Li(thf ) 3 ] (4), which feature bridging coordination of the amidinate ligands to two Ln 3+ ions. The reactions of the dilithium derivative of the related bis(amidine) with a 2,6-pyridinediyl linker, [2,6-C 5 H 3 N-{NC(tBu)N(2,6-Me 2 C 6 H 3 )} 2 ] 2-, with LnCl 3 (Ln = Y, Er) result in the formation of mononuclear chlorido bis(ligand) ate complexes [{(2,

Ligands with Two Monoanionic N,N‐Binding Sites: Synthesis and Coordination Chemistry

“…The catalytic activity of the mononuclear type F complexes in the ring‐opening polymerization of ϵ ‐caprolacton was found to be lower than the activity of the respective dinuclear homoleptic complexes of type I (see further below). For the sake of completeness, it is worthy to note that with a 2,6‐pyridylene‐bridged bis(amidine) another type of mononuclear complexes has been reported for erbium and yttrium ( IX , M=Y; Figure ), in which two bis(amidine)s chelate one metal center involving coordination of the pyridyl nitrogen …”

“… Molecular structure of IX in the solid state . Hydrogen atoms except those of the NH groups, counter ions and solvent molecules are omitted for clarity.…”

“…Although further general conclusions remain elusive due to the limited sample set, it appears that the product yield is more affected by the electronic and steric properties of both the imidoylchloride and the primary diamine, rather than the experimental protocol, that is performing the reaction with or without triethylamine as an HCl scavenger. Notably, a 2,6‐pyridylene bridged bis(amidine) was obtained in 66 % yield starting from dilithiated 2,6‐diaminopyridine and the respective imidoylchloride . In conclusion, both routes appear to be suitable and the preference for one over the other is most likely due to the synthetic aim: for ligand libraries with varying terminal (R) or backbone (R′) substituents, the use of bis(imidoylchloride)s through route ii ) is more convenient, whereas aiming for a ligand set with various linker groups, route iii ) is of benefit.…”

“…The coordination number of the two metal centers within complexes of type I , in which three bis(amidinate) ligands are heteroleptically bound to two metals (Er, Y, and Yb), is strongly affected by the rigidity of the bridging group (Figure ). For the flexible 1,3‐propylene linker, the purely homoleptic homodinuclear complex X with coordination number 6 ( m = n =0) for each yttrium is obtained, whereas using a more rigid 1,3‐phenylene bridge yields the heterobimetallic complex XI , in which the two metals possess a coordination number of 7 ( m = n =1) due to the additional complexation of one THF molecule and one Cl ion bridging the second yttrium and the lithium counterion, respectively . Although the purely homoleptic yttrium and ytterbium complexes bearing a 1,3‐propylene linker show higher activities in the ring‐opening polymerization of ϵ ‐caprolacton than the respective mononuclear type F complexes, they yield polymers with rather broad molecular‐weight distributions, most likely because of several active lanthanide amidinate bonds.…”

“… Molecular structures of a) X and b) XI in the solid state . Hydrogen atoms and noncoordinated solvent molecules are omitted for clarity.…”