Hexaethylbenzene complexes of ruthenium and manganese--X-ray crystal structures and NMR spectra of [[(HEB).sub.2][Ru.sub.2][(μ-Cl).sub.3]] [[C.sub.5][(C[O.sub.2]Me).sub.5]], [(HEB)Ru[([H.sub.2] O).sub.3]][[B[F.sub.4]].sub.2], (HEB)Ru[Cl.sub.2][P[(OMe).sub.3]], trans-Ru[Cl.sub.2][(P[Me.sub.3]).sub.4], and (HEB)Mn[(CO).sub.2] [Br.sup.1]

Hexaethylbenzene (HEB) and [(p-cymene)Ru[Cl.sub.2] react in the melt to yield [[(HEB)Ru[Cl.sub.2]].sub.2] (6), the NMR spectra of which reveal the presence of [[(HEB).sub.2][Ru.sub.2][(μ-Cl).sub.3]]Cl in solution. In [[(HEB).sub.2][Ru.sub.2][(μ-Cl).sub.3]][[C.sub.5][(C[O.sub.2]Me).sub.5]] (7), the cation has [D.sub.3h] symmetry with alternating proximal and distal ethyl groups. Bridge cleavage of 6 with trimethyl phosphite or with trimethylphosphine gives (HEB)Ru[Cl.sub.2] [P[(OMe).sub.3]] (9) or (HEB)Ru[Cl.sub.2](P[Me.sub.3]) (10), respectively. The latter reaction also yields Ru[Cl.sub.2][([Me.sub.3]P).sub.4] (11), whose structure represents a relatively rare example of a crystallographically characterized trans isomer of this type. In 9, five of the ethyl ligands are distal, whereas in 10 all six substituents are distal. Attempts to prepare the sandwich dication [[[(HEB).sub.2]Ru].sup.2+] gave instead [(HEB)Ru[([H.sub.2]O).sub.3]][(B[F.sub.4]).sub.2] (8), whose NMR and X-ray data reveal the 1,3,5-distal-2,4,6-proximal arrangement of ethyls both in the solid state and in solution. (HEB)Mn[(CO).sub.2]Br (13) likewise adopts the 1,3,5-distal-2,4,6-proximal structure in the solid state but, surprisingly, there is no evidence for slowed ethyl rotation in solution. Key words: hexaethylbenzene conformations, hindered rotations, crystallography, NMR, ruthenium, manganese. L'hexaethylbenzene (HEB) et le [[(p-cymene)Ru[Cl.sub.2]].sub.2] reagissent a l'etat fondu pour conduire a la formation de [[(HEB)Ru[Cl.sub.2]].sub.2] (6) dont le spectre RMN en solution revele la presence de [[(HEB).sub.2][Ru.sub.2] [(μ-Cl).sub.3]]Cl. Dans le [[(HEB).sub.2][Ru.sub.2][(μ-Cl).sub.3]][[C.sub.5] [(C[O.sub.2]Me).sub.5]] (7), le cation est de symetrie [D.sub.3h] avec, en alternance, des groupes ethyles de type distal et proximal. Le clivage du pont du compose 6 avec du phosphite de trimethyle ou avec de la trimethylphosphine conduit, selon le cas, au (HEB)Ru[Cl.sub.2] [P[(OMe).sub.3]] (9) ou au (HEB)Ru[Cl.sub.2](P[Me.sub.3]) (10). La derniere reaction fournit aussi du Ru[Cl.sub.2][([Me.sub.3]P).sub.4] (11) dont la structure correspond a un rare exemple d'un isomere trans de type a etre caracterise par cristallographie. Dans le compose 9, cinq sur six ligands sont de type distal alors que dans le compose 10 les six ligands sont tous de type distal. Des essais en vue de preparer le dication sandwich [[[(HEB).sub.2]Ru].sup.2+] on plutot conduit a la formation de [(HEB)Ru[([H.sub.2]O).sub.3]][(B[F.sub.4]).sub.2] (8) dans lequel, selon les donnees de la RMN et de la diffraction des rayons X, on observe un arrangement 1,3,5-distal-2,4,6-proximal des groupes ethyles tant 5 l'etat solide qu'en solution. La structure du (HEB)Mn(C[O.sub.2])Br (13) adopte aussi une structure 1,3,5-distal-2,4,6-proximal a l'etat solide, mais il est surprenant d'observer que, en solution, on n'observe aucune donnee laissant croire a un ralentissement de la rotation des groupes ethyles. Mots cles : conformation de l'hexaethylbenzene, rotations empechees, cristallographie, RMN, ruthenium, manganese. [Traduit par la Redaction]
Introduction Hexaethylbenzene (HEB) is a conformationally versatile ligand! When bonded to organometallic fragments, such as Cr[(CO).sub.3] (1), [[Fe([C.sub.5][H.sub.5])].sup.+] (2), or [[Mo[(CO).sub.3]Cl].sup.+] (3), the ethyl groups can adopt a variety of [...]