A novel linear hybrid tris-bidentate neutral ligand having 2,2'-bipyridine and two terminal triazolylpyridine coordination sites (L) was efficiently synthesized and explored in the synthesis of trinuclear triple-stranded homometallic side-by-side helicates L3Fe3(OTf)6 (1) and L3Zn3(OTf)6 (2), in which the three metal centers display alternating Λ and Δ configurations. Selective formation of the analogous heterometallic side-by-side helicate L3Fe2Zn(OTf)6 (3) was achieved from a mixture of L, Fe(CH3CN)2(OTf)2, and Zn(OTf)2 (1:1:1) in acetonitrile at room temperature. Various analytical techniques, i.e., single-crystal X-ray diffraction and NMR and UV/vis spectroscopy, were used to elucidate the sequence of the metal atoms within the heterometallic helicate, with the Zn(2+) at the central position. The formation of 3 was also achieved starting from either L3Zn3(OTf)6 or L3Fe3(OTf)6 by adding Fe(CH3CN)2(OTf)2 or Zn(OTf)2, respectively. ESI-MS and (1)H NMR studies elucidated different transmetalation mechanisms for the two cases: While a Zn(2+)-to-Fe(2+) transmetalation occurs by the stepwise exchange of single ions on the helicate L3Zn3(OTf)6 at room temperature, this mechanism is almost inoperative for the Fe(2+)-to-Zn(2+) transmetalation in L3Fe3(OTf)6, which is kinetically trapped at room temperature. In contrast, dissociation of L3Fe3(OTf)6 at higher temperature is required, followed by reassembly to give L3Fe2Zn(OTf)6. The reassembly follows an interesting mechanistic pathway when an excess of Zn(OTf)2 is present in solution: First, L3Zn3(OTf)6 forms as the high-temperature thermodynamic product, which is then slowly converted into the thermodynamic heterometallic L3Fe2Zn(OTf)6 product at room temperature. The temperature-dependent equilibrium shift is traced back to significant entropy differences resulting from an enhancement of the thermal motion of the ligands at high temperature, which destabilize the octahedral iron terminal complex and select zinc in a more stable tetrahedral geometry.

The reaction of the beta-diketiminato coordinated aluminum dihydride, [{HC[C(Me)N-C(6)H(5)](2)}AlH(2)] (1) with bis(trimethylsilyl)methyllithium afforded the monoalkylaluminum derivative [{HC[C(Me)N-C(6)H(5)](2)}Al(H)-CH(SiMe(3))(2)] (2) by the precipitation of lithium hydride. Interestingly, treatment of 2 with tert-butyl hydrogenperoxide did not result in the formation of the simple oxidation product containing a hydroxo or alkoxo group, instead, elemental hydrogen was released and the hydrido ligand attached to aluminum was replaced by an intact tert- butylperoxo group. The Al-C bond, which normally is extremely sensitive towards an attack of oxygen, was not affected. Hence, the product exhibits quite conflicting chemical properties in a close proximity: a strongly reducing Al-C bond beside an oxidizing peroxo group.

No abstract

A new class of cyclopentadiene-bis(oxazoline) compounds and their piano-stool-type organometallic complexes have been prepared as catalysts for hydroamination of aminoalkenes. The two compounds MeC(Ox Me2 ) 2 C 5 H 5 (Bo M CpH; Ox Me2 = 4,4-dimethyl-2-oxazoline) and MeC-(Ox Me2 ) 2 C 5 Me 4 H (Bo M Cp tet H) are synthesized from C 5 R 4 HI (R = H, Me) and MeC(Ox Me2 ) 2 Li. These cyclopentadienebis(oxazolines) are converted into ligands that support a variety of metal centers in piano-stool-type geometries, and here we report the preparation of Mg, Tl, Ti, and Zr compounds. Bo M CpH and Bo M Cp tet H react with MgMe 2 (O 2 C 4 H 8 ) 2 to give the magnesium methyl complexes {Bo M Cp}MgMe and {Bo M Cp tet }MgMe. Bo M CpH and Bo M Cp tet H are converted to Bo M CpTl and Bo M Cp tet Tl by reaction with TlOEt. The thallium derivatives react with TiCl 3 (THF) 3 to provide [{Bo M Cp}TiCl(μ-Cl)] 2 and [{Bo M Cp tet }TiCl(μ-Cl)] 2 , the former of which is crystallographically characterized as a dimeric species. Bo M CpH and Zr(NMe 2 ) 4 react to eliminate dimethylamine and afford {Bo M Cp}Zr(NMe 2 ) 3 , which is crystallographically characterized as a monomeric four-legged piano-stool compound. {Bo M Cp}Zr(NMe 2 ) 3 , {Bo M Cp}MgMe, and {Bo M Cp tet }MgMe are efficient catalysts for the hydroamination/cyclization of aminoalkenes under mild conditions.