The treatment of the recently reported potassium salt (S)-N,N'-bis-(1-phenylethyl)benzamidinate ((S)-KPEBA) and its racemic isomer (rac-KPEBA) with anhydrous lanthanide trichlorides (Ln = Sm, Er, Yb, Lu) afforded mostly chiral complexes. The tris(amidinate) complex [{(S)-PEBA}(3)Sm], bis(amidinate) complexes [{Ln(PEBA)(2)(μ-Cl)}(2)] (Ln = Sm, Er, Yb, Lu), and mono(amidinate) compounds [Ln(PEBA)(Cl)(2)(thf)(n)] (Ln = Sm, Yb, Lu) were isolated and structurally characterized. As a result of steric effects, the homoleptic 3:1 complexes of the smaller lanthanide atoms Yb and Lu were not accessible. Furthermore, chiral bis(amidinate)-amido complexes [{(S)-PEBA}(2)Ln{N(SiMe(3))(2)}] (Ln = Y, Lu) were synthesized by an amine-elimination reaction and salt metathesis. All of these chiral bis- and tris(amidinate) complexes had additional axial chirality and they all crystallized as diastereomerically pure compounds. By using rac-PEBA as a ligand, an achiral meso arrangement of the ligands was observed. The catalytic activities and enantioselectivities of [{(S)-PEBA}(2)Ln{N(SiMe(3))(2)}] (Ln = Y, Lu) were investigated in hydroamination/cyclization reactions. A clear dependence of the rate of reaction and enantioselectivity on the ionic radius was observed, which showed higher reaction rates but poorer enantioselectivities for the yttrium compound.

Dedicated to Professor Herbert W. Roesky on the occasion of his 75th birthday b-hydrogen (b-H) elimination is a rarely documented phenomenon for transition-metal amido complexes (Scheme 1). [1] The first directly observable example of a b-H elimination involving a monomeric late-transition-metal amido complex, [Ir(PPh 3 ) 2 (CO){N(CH 2 Ph)Ph}] (1), was reported by Hartwig in 1996.[1a] Surprisingly, the b-H elimination in 1 occurs slowly (depending on the concentration of added phosphine) and requires relatively high temperatures (110 8C in toluene) to obtain stable N-phenyltoluenimine and the hydrido species [Ir(PPh 3 ) 3 (CO)H] (1 a).Hartwig concluded that "b-H elimination of late metal amides can be much slower than elimination of the corresponding alkyl complexes".[1a] In general, it is assumed that the potential energy surface (PES) of the b-H elimination process in transition-metal alkyl complexes involves intermediates in which b-agostic interactions occur.[2] Hence, the reduced b-H elimination activity in amido compared to alkyl complexes may be due to the enhanced ability of alkyl systems to form pronounced b-agostic interactions even in the ground state. This might explain "the different mechanistic features detected for amido, alkoxo and alkyl derivatives which makes it difficult to directly compare their tendencies to undergo b-elimination reaction"[1k] even in related complexes. Therefore, we have compared the structural and electronic characteristics of various d 0 alkyl and amido benchmark complexes exhibiting deformations resulting from b-agostic interactions in their ground-state structures (Figure 1). This study should provide further insight into the control parameters for elementary b-H elimination processes. (3) [3c] (dmpe = (CH 3 ) 2 PCH 2 CH 2 P(CH 3 ) 2 ) at 105 K. Alkyl complexes containing b-agostic interactions are typically characterized by acute ]MC a C b angles, [2c] while ]MN a C b angles smaller than the expected 1208 in combination with short M···H b distances have been suggested as indicators of amido groups involved in b-agostic interactions. [3a, 4] On the basis of these structural criteria, 2 reported by Pupi et al., [3a] has one of the smallest ]MN a C b angles and shortest M···H distances observed to date for an amido species with a b-agostic interaction (see the Supporting Information). The above geometrical definition of an agostic ]. CÀH distances were not refined as they were calculated from isolated CÀH stretching frequencies n is .

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To be able to correlate the catalytic properties of nanoparticles with their structure, detailed knowledge about their make-up on the atomic level is required. Herein, we demonstrate how atom-probe tomography (APT) can be used to quantitatively determine the three-dimensional distribution of atoms within a Au@Ag nanoparticle with near-atomic resolution. We reveal that the elements are not evenly distributed across the surface and that this distribution is related to the surface morphology and residues from the particle synthesis.

Enantiomerically pure lutetium complexes were synthesized as the first rare earth metal complexes containing a chiral amidinate ligand. The catalytic activity and the enantioselectivity in hydroamination reactions were studied.