Dedicated to Vludimir Prelog on the occasion of his 85th birthday (25. X. 91)The chiral tris-and pentakis(bipyridine) ligand strands 3a and 4 were synthesised, each in optically pure form with (S,S)-configuration. Ligand 3a yielded substituted double-helical metal complexes, derived from the parent trihelicate structure 2, with Cu' and Ag' ions. The spectral data, in particular the 'H-NMR spectra and the large positive Cotton effect, indicate that helicate formation occurs with very high induction of helicity. Together with consideration of the steric effects in the two possible helical diastereoisomers (P)-1 and (M)-1 that may be formed, the data favour the preferential generation of the right-handed double helicate (P)-1 from the tris(bipyridine) strand 3a of (S,S)-configuration,

Nach der Röntgenstrukturanalyse von [C6H5CH2Li · N(CH2CH2)3N]∞ durch Patterman, Karle und Stucky37 sowie der von [C6H5CH2Li·OEt2]∞; durch Beno, Hope, Olmstead und Power42 präsentieren wir eine weitere Benzyllithium‐Strukturuntersuchung, nämlich die von η1‐C6H5CH2Li · THF · TMEDA (1). Im Gegensatz zu den früheren liegt bei 1 eine monomere Benzyllithium‐Verbindung vor. Außerdem ist Lithium lediglich an das benzylische C‐Atom koordiniert, dessen pyramidale Konfiguration erstmals ermittelt werden Konnte. Die Molekulargewichtsbestimmung von C6H5CH2Li in THF, die ein Monomer ergab 61, und Kernresonanzuntersuchungen in THF, die auf ein pyramidales, benzylisches C‐Atom bei 1 (und C6H5CH2Li53,54) hinweisen, entsprechen der Festkörperstruktur von 1. Die in den drei Festkörperstrukturen beobachteten verschiedenen Koordinationen des Lithium‐Kations an das Benzyl‐Anion sind wie die pyramidale Konfiguration des benzylischen C‐Atoms in 1 mit quantenmechanischen Rechnungen (auch anderer Autoren45–50) in Einklang. Die pyramidale Konfiguration des benzylischen C‐Atoms in 1 läßt vermuten, daß ähnliche stereochemische Verhältnisse zur hohen Retention beitragen, die bei der Haller‐Bauer‐Spaltung optisch aktiver Benzylphenylketone beobachtet wird62e–g.

Deprotonierung von Trimethylsilylacetonitril (1) entweder mit zwei Moläquivalenten n‐Butyllithium oder mit zwei Moläquivalenten Lithium‐diisopropylamid in Ether/Hexan führt zum „Dianion”︁ Li2(Me3SiCCN) (2), das aus dieser Lösung als [(2)12(Et2O)6(C6H14)] auskristallisiert. Zwölf „Dianionen”︁ bilden ein Aggregat mit einem kristallographischen Inversionszentrum. Sechs Ether‐Moleküle (drei pro asymmetrische Einheit) koordinieren mit den Li‐Atomen. Ein Molekül Hexan cokristallisiert außerhalb dieses Aggregats. Es gibt drei verschiedene „Dianion”︁‐Gruppen, die sich in der Anzahl ihrer NLi‐ und CLi‐Kontakte unterscheiden. Die Festkörperstruktur des Dilithionitrils [(2)12(Et2O)6(C6H14)] unterscheidet sich wesentlich von den Festkörperstrukturen von Monolithionitrilen.

atoms as in 4 and 5 was first observed quite recently in the complex ion [Co,Se,(PPh3),le.[' O1 One could alternatively consider the structure of the Ni, cluster consisting of four Ni, triangles (Nil, Ni2, Ni8; Ni9, NilO, Nill ; Ni12, Ni13, Ni14; and Ni4, Ni5, Ni6). The Ni-Ni distances in the outer rings (Nil, Ni2, Ni8 and Ni4, Ni5, Ni6) are very long (368-378 pm), and in the inner rings (Ni9, NilO, Nill, Ni12, Ni13, Ni14) they are 258.5-283.0 pm, i s . in the range for Ni-Ni bonds. The cluster core is completed by the atoms Ni3, Ni7 and Ni15.If it is assumed that Se2' and Cp'' hgands are present in 4, and SeZQ, C P '~ and Cle ligands in 5, then the Ni,, clusters in 4 and 5 have the formal charges + 28 and + 30, respectively. Moreover, assuming that the Ni-Ni bonds depicted in Figure 3 are single bonds, it is surprising to note that the valence-electron concentration (226e) in 4 (236e) and 5 (234e) predicted according to the 18-electron rule is relatively well fulfilled. The 18-electron rule is rigidly fulfilled in the case of 5, even if the long Ni-Ni distances in the central Ni, ring (282-294 pm) are interpreted as non-bonding contacts.Also other authors have already reported on the synthesis of multinuclear nickel complexes with Cp ligands. Examples of such compounds are INi,Cp,]"@ (n = 0, + l), [Ni,Cp,S,] and [Ni,Cp,S,].[' Investigations currently under way, however, clearly demonstrate that a direct variation of the Cp ligands can lead to metal-rich cluster compounds with novel structures. Experimental ProcedureA solution of [NiCp'(CO)], (2.2 g, 6.63 mmol) in 35 mL of diethyl ether was treated with 0.34 mL (6.60 mmol) of Br, at -80°C. After 30 min, a solution of 1.41 mL (6.60 mmol) of Se(SiMe,) in 10 mL of diethyl ether was added dropwise. Evolution of CO was observed, and at the same time a black crystalline precipitate separated out which consisted of a mixture of 2.3 and 4. After 24 h the residue was filtered off and the filtrate was allowed to stand for several days. A mixture of 2 (black needles), 3 (black hexagons) and 4 (black rhombuses) crystallized from the filtrate. When the reaction described above was carried out in the presence of 0.2 g of solid NiCI,, 5 (black columns) was also formed.Yields: 30 YO 2, 20 % 3. 20 % 4, and 30 % 5.

Crystal Structure of α‐(Trimethylsilyl)benzyllithium·Tetramethylethylendiamin [C6H5CH(SiMe3)Li·TMEDA] und α‐(Phenylthio)‐benzyllithium·3 Tetrahydrofuran [C6H5CH(SPh)Li – (THF)3] – Two Benzyllithium Compounds with Central Chirality The crystal structure analyses of [C6H5CH(SiMe3)Li·TMEDA] (6) and of [C6H5CH(SPh)Li·(THF)3] (7, in which the positions of the benzylic hydrogen atoms have been determined experimentally, reveal compounds with pyramidal benzylic carbon atoms. In 6 lithium is λ2‐bound to Cipso and α of the substituted benzylic anion which leads, together with the TMEDA molecule, to a tetra‐coordinated lithium atom. In 7 only one Li – C bond is formed, namely that to Cα. Additional coordination with three THF molecules results also in a tetracoordinated lithium atom, The extent of the pyramidalization in 6 and 7 is qualitatively in agreement with quantum‐mechanical ab initio calculations [G86, MP2/6‐311+ + G(d,p)].