STERICALLY CONTROLLED DOUBLE NUCLEOPHILIC-ADDITION REACTIONS OF (ETA(6)-ARENE)(ETA(6)-[2.2]PARACYCLOPHANE)RUTHENIUM(II) COMPLEXES AND REACTIONS TO FORM HIGHLY FLUXIONAL AGOSTIC CYCLOHEXENYLS

Action of the hydride source Na[BH4] on the (eta6-arene)(eta6-[2.2]paracyclophane)ruthenium(II) complexes [Ru(eta6-C16H16)(eta6-arene)][BF4], (arene = benzene 1a, p-cymene 1b, 1,2,4,5-tetramethylbenzene 1c, pentamethylbenzene 1d or hexamethylbenzene 1e) results exclusively in the addition of two hydride nucleophiles to the non-cyclophane arene ring, giving the neutral (1,3-diene)ruthenium(o) complexes [Ru(eta6-C16H16)(eta4-diene)] (diene = C6Me6H2 4, C6Me5H3 6, C6Me4H4 7 or MeC6H6CHMe2 8). Complex 4 is the 1,3-diene isomer of the previously reported 1,4-diene compound [Ru(eta6-C16H16)(eta4-3,6-C6Me6H2)] 2 (formed in the reduction of 1e by Red-Al {Na[AlH2(OCH2CH2OMe)2]}). In complexes 1a-1e, attack on the [2.2]paracyclophane ligand is not observed, implying that nucleophilic additions to these compounds are not charge controlled. This contrasts with previously reported related reactions which give bis-(cyclohexadienyl) complexes. Attempts to prepare functionalised diene complexes derived from 1a and 1e were largely unsuccessful although the functionalised cyclohexadienyl compounds [Ru(eta6-C16H16)-(eta5-C6R6X)] [BF4] 9-11 (R = H or Me; X = Me or OMe) are prepared. Deprotonation of the hexamethylbenzene complex le results in the formation of the exo-methylene species [Ru(eta6-C16H16){eta5-C6Me5(CH2)}][BF4] 12 and [Ru(eta6-C16H16){eta4-C6Me4(CH2)2}] 13. Complexes 4, 6 and 7 react with HBF4 to generate agostic cyclohexenyl compounds [Ru(eta6-C16H16)(eta3-C6MenH9-n)][BF4] (n = 6 16, 5 20 or 4 21). However, reaction of 2 with HBF4 gives the exocyclic agostic complex [Ru(eta6-C16H16){eta3-(HCH2)(CH2)C6Me4H4}][BF4] 18. In 16 the agostic cyclohexenyl ligand is bound via an endocyclic allylic functionality whereas in the isomer, 18, the metal is bound externally to the ring. Deprotonation of 18 with LiBu(n) results in the abstraction of the agostic proton to generate (Ru(eta6-C16H16)-{eta4-(CH2)2C6Me4H4}] 19, which is isomeric with 2 and 4 and contains a saturated C6Me4H4(CH2)2 ring bound to the metal centre by two exocyclic olefinic functionalities. The mechanisms for the formation of these compounds have been probed by deuteriation studies and their extensive dynamic behaviour investigated by variable-temperature H-1 NMR spectroscopy.