Treatment of cerous Cp R 3 Ce(thf) (Cp R = C 5 H 4 R; R = H, Me) with the halogenating reagents C 2 Cl 6 , TeBr 4 , and I 2 afforded the ceric halides Cp R 3 CeX (X = Cl, Br, I) in high yield. Subsequent salt metathesis with sodium alkoxides and siloxides led to a series of alkoxy and siloxy derivatives. Compounds Cp R 3 CeOR′ with R′ = Me, Et, CH 2 tBu, iPr, tBu, SiMe 3 , SiEt 3 , Si(iPr) 3 SiPh 3 (and Si(OtBu) 3 ) have been isolated and characterized by 1 H, 13 C, and 29 Si NMR and DRIFT spectroscopy, magnetic measurements, X-ray structure analyses, cyclic voltammetry, and elemental analyses. The ceric complexes Cp R 3 CeX and Cp R 3 CeOR′ are isostructural, featuring terminal ligands X and OR′. The magnetic measurements revealed temperature-independent paramagnetism (TIP), with positive magnetic susceptibilities in the range χ 0 (1.53−3.9) × 10 −4 emu/mol. Cyclic voltammetry indicated two types of redox processes: (a) chemical and electrochemical reversibility for halide and siloxide complexes and (b) EC-or ECE-type mechanisms for the alkoxides (chemical reversibility at high scan rates). In all cases formal potentials could be determined ranging from −0.583 V vs Fc/Fc + for Cp 3 CeI to −1.259 V vs Fc/Fc + for Cp Me 3 Ce(OEt). The electrochemical data revealed an increase in stabilization with respect to reduction of the cerium(IV) center in the series I < Br < Cl < siloxy < alkoxy ligand and a better stabilization with Cp Me in comparison to Cp ligands by approximately 0.05−0.1 V. As a result, an improved stabilization of Ce(IV) was observed for more strongly electron donating ligands.
Binuclear complexes of copper, silver, and gold bearing a 2,2′-bipyridine analogue, the pyridazine annelated bis(N-heterocyclic carbene) ligand (vegi) 1, were prepared and structurally characterized. They all feature the shortest metal− metal distances that have been measured so far in complexes with this structural motif bearing neutral bidentate ligands, indicative of d 10 −d 10 interactions. While in the silver complex the linear coordination of each silver atom with two carbene ligands results in a planar complex, the ligand planes are twisted by 70°in the Cu complex 4 and by 31°in the gold complex 3. The copper complex shows a solvent-dependent equilibrium between the [Cu 2 L 2 ] 2+ complex and a [Cu 2 L 3 ] 2+ complex along with solvated CuPF 6 .
During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe 4 ) 3 , have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln
Bimetallic rare-earth-metal imide complexes Ln 2 (μ 2 -Ndipp)(μ 3 -Ndipp)[(μ 2 -Me) 2 AlMe](AlMe 4 ) 2 (3-Ln; Ln = Y, La, Ce, Nd; dipp = 2,6-diisopropylphenyl) have been obtained from the reaction of Ln(AlMe 4 ) 3 (1-Ln) with Li(NHdipp) (2). X-ray diffraction studies of toluene-soluble 3-Ln revealed an unusual Ln[{(μ 2 -Me) 2 AlMe}(μ 3 -Ndipp)]Ln moiety as the most striking feature. Facile salt-metathetical exchange of the tetramethylaluminato ligands in 3-Ln with K(L) (L = N(SiMe 3 ) 2 , Cp′) allowed for the isolation of Ln 2 (Ndipp) 2 [N(SiMe 3 ) 2 ] 2 (AlMe 3 ) (4-La), partially exchanged Ln 2 (Ndipp) 2 (Cp′)(AlMe 4 )(AlMe 3 ) (5-La, Cp′ = C 5 Me 4 SiMe 3 ), and Ln 2 (Ndipp) 2 (Cp′) 2 (AlMe 3 ) (6-La). Attempted cleavage of the AlMe 3 moiety in 3-Ln with THF led to C−H bond activation of one of the isopropyl methine moieties to produce Ln 2 (μ 2 -Ndipp)[(μ 3 -NC 6 H 3 -2-CMe 2 -6-iPr)Al(μ 2 -Me) 2 ](AlMe 4 ) 2 (7-La). Selective cleavage of the bridging AlMe 3 "cap" was achieved by addition of DMAP (DMAP = 4-dimethylaminopyridine) to produce [Ln(μ 2 -Ndipp)(AlMe 4 )(DMAP)] n (8-Ln; Ln = La, Ce) and concomitantly DMAP•AlMe 3 . The organoaluminum-free compounds [Ln(μ 2 -Ndipp){N(SiMe 3 ) 2 }(DMAP)] 2 (9-Ln; Ln = La, Ce), [Ln(μ 2 -Ndipp)(Cp′)(DMAP)] 2 (10-La), and [Ln(μ 2 -Ndipp)(OAr)(DMAP)] 2 (11-Ln; Ln = La, Ce; Ar = 2,6-di-tert-butyl-4-methylphenyl) were obtained via reactions of 8-Ln with K(L) (L = Cp′, N(SiMe 3 ) 2 , OAr). In the presence of activators [Ph 3 C][B(C 6 F 5 ) 4 ] and [PhNMe 2 H][B(C 6 F 5 ) 4 ], AlEt 2 Cl complexes 3-Ln, 5-Ln, and 7-Ln initiate the polymerization of isoprene to yield PIPs with narrow molecular weight distributions, involving new imido-supported bimetallic catalysts.
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