Hexaethylbenzene complexes of ruthenium and manganese — X-ray crystal structures and NMR spectra of [(HEB) 2 Ru 2 (µ-Cl) 3 ][C 5 (CO 2 Me) 5 ], [(HEB)Ru(H 2 O) 3 ][BF 4 ] 2 , (HEB)RuCl 2 [P(OMe) 3 ], trans -RuCl 2 (PMe 3 ) 4 , and (HEB)Mn(CO) 2 Br

Hexaethylbenzene (HEB) and [(p-cymene)RuCl 2 ] 2 react in the melt to yield [(HEB)RuCl 2 ] 2 (6), the NMR spectra of which reveal the presence of [(HEB) 2 Ru 2 (µ-Cl) 3 ]Cl in solution. In [(HEB) 2 Ru 2 (µ-Cl) 3 ][C 5 (CO 2 Me) 5 ] (7), the cation has D 3 h symmetry with alternating proximal and distal ethyl groups. Bridge cleavage of 6 with trimethyl phosphite or with trimethylphosphine gives (HEB)RuCl 2 [P(OMe) 3 ] (9) or (HEB)RuCl 2 (PMe 3 ) (10), respectively. The latter reaction also yields RuCl 2 (Me 3 P) 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) 2 Ru] 2+ gave instead [(HEB)Ru(H 2 O) 3 ](BF 4 ) 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) 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.