Dedicated to Professor Wolfgang A. Herrmann on the occasion of his 60th anniversaryThe synthesis of multinuclear complexes, in particular systems with different metals, is an intensely studied branch of modern coordination chemistry.[1] Metal-metal bonds are of special interest in this regard, because their significance goes far beyond the borders of chemistry.[2] The variety of bonding phenomena among transition metals, which can range from strongly polar direct metal-metal bonds in heterodinuclear complexes [3] to quintuple bonds in homodinuclear complexes, [4] is in contrast to the one example [5] in which a direct bond between a lanthanoid metal and a transition metal is observed: [(thf)Cp 2 Lu-RuCp(CO) 2 ] (Cp = cyclopentadienyl). [6,7] The donor-acceptor bonds described by Roesky [8] and co-workers are also interesting in this regard, since they represent examples of direct bonds between maingroup metals and lanthanoids.[9] In our previous work, we were interested in metal-metal communication in heterodinuclear complexes in which lanthanoids and late transition metals were "held together" by virtue of coordinated bridging aminopyridinato ligands.[10] Herein we report that unsupported metal-metal bonds between transition metals and rare earth elements are accessible by alkane elimination.Heterobimetallic complexes in which lanthanoids and transition metals are bridged by hydride ligands have been prepared by H 2 elimination, [11] salt elimination, [12] and alkane elimination.[13] The alkane elimination route should be the most promising and efficient method for the stabilization of heterobimetallic complexes with direct metal-metal bonds, since the eliminated alkane is relatively inert, and a difficult workup procedure can be avoided. NMR spectroscopy supports the structural arrangement presented in Scheme 1 as well as the presence of three bridging hydride ligands. At ambient temperature a doublet with a coupling constant of J YH = 10.5 Hz is observed for these three hydride ligands. Cooling the sample results in line broadening, and at temperatures below 233 K two signals in the ratio 2:1 are registered. At d = À13.9 ppm a doublet (YRu bridging hydride ligands) with a coupling constant J YH = 15.4 Hz is observed, which is accompanied by a singlet at d = À15.4 ppm (Ru-Ru bridging hydride ligand).The molecular structure of 1 was determined by X-ray single crystal analysis and is presented in Figure 1.[16] The RuÀ Y separations amount to 3.0396(5) (to Ru1) and 3.0514 (5) (to Ru2) and the RuÀRu separation is 2.4881(5) . The positions of the three hydride ligands could not be determined despite the high quality of the crystal structure analysis. [17] The reaction of monohydride complexes, for example [Cp 2 ReH], [18] with lanthanoid monoalkyl complexes should lead to hydride-free bimetallic complexes. Especially promising are alkyl complexes of the type [Cp 2 LnR(thf)] (Ln = lanthanoid, R = alkyl). Both metal-complex components will be stabilized by the same ligands, and ligand transfer reactions that could l...

Die Umsetzung von Monohydridkomplexen später Übergangsmetalle mit Lanthanoidalkylen führt zu heterodimetallischen Verbindungen mit direkten Metall‐Metall‐Bindungen (siehe Schema). Diese kovalenten Bindungen sind stark polar und können als Donor‐Akzeptor‐Bindungen verstanden werden.

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The reaction of Grignard compounds of 1‐bromo‐2,4,6‐diisopropylbenzene (1) or 1‐bromo‐2,6‐dimethylbenzene (2), formed in situ, with 2,6‐dibromopyridine in the presence of a catalytic amount of [(dme)NiBr2] (dme = 1,2‐dimethoxyethane) and tricyclohexylphosphane (1:2 ratio) leads to the corresponding monoarylated bromopyridines. These bromopyridines undergo Pd‐catalysed aryl amination (Buchwald−Hartwig amination) with 2,6‐diisopropylaniline giving rise to (2,6‐diisopropylphenyl)[6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐yl]amine (Ap*H) and (2,6‐diisopropylphenyl)[6‐(2,6‐dimethylphenyl)pyridin‐2‐yl]amine (Ap′H) (Ap = aminopyridinate). Deprotonation of Ap*H in diethyl ether using BuLi results (after workup in hexane) in a colourless crystalline material. X‐ray structural analysis reveals it to be a monomeric three‐coordinate lithium aminopyridinate. In toluene solution, an equilibrium between [(Ap*Li)2] (in excess at room temperature) and [Ap*Li(OEt2)] (prominent at low temperature) is observed. Reaction of Ap′H with BuLi in diethyl ether gives rise to [Ap*LiAp*Li(OEt2)]. Deprotonation of Ap*H and Ap′H using KH leads to [Ap*K]n and [Ap′K]∞, respectively. [Ap′K]∞ is a rare example of a crystalline organometallic polymer, as determined by X‐ray analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The reaction of the carborane nido‐5,6‐C2B8H12 (1) with PCl3 in dichloromethane in the presence of a “proton sponge” [PS = 1,8‐bis(dimethylamino)naphthalene], followed by hydrolysis of the reaction mixture, resulted in the isolation of the eleven‐vertex nido‐phosphadicarbaboranes 7,8,9‐PC2B8H11 (2) and 10‐Cl‐7,8,9‐PC2B8H10 (10‐Cl‐2), depending on the ratio of the reactants. Both of these compounds can be deprotonated by PS to give the nido anions [7,8,9‐PC2B8H10]− (2−) and [10‐Cl‐7,8,9‐PC2B8H9]− (10‐Cl‐2−). The molecular geometries of all compounds were optimized by ab initio methods at a correlated level of theory [RMP2(fc)] using the 6‐31G* basis set and their correctness was assessed by a comparison of the experimental 11B NMR chemical shifts with those calculated by the GIAO‐SCF/II//RMP2(fc)/6‐31G* method. Moreover, the structure of 10‐Cl‐2− was determined by an X‐ray diffraction analysis. The anionic compounds 2− and 10‐Cl‐2− are analogs of the Cp (Cp = η5‐C5H5−) anion. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)