Allylic alkylation of complexed cyclo-octatetraene (cot)via the reaction of [Fe{P(OMe)3}(NO)2(η3-allyl)]+ with [M(CO)3(η4-cot)](M = Fe or Ru) derivatives; X-ray structure of [Ru(CO)2(PPh3)(η2,η3-C8H8R)][PF6]·0.5CH2Cl2[R = CH2C(Me)CH2]

Abstract

The reaction of [Fe{P(OMe)₃}(NO)₂(η³-allyl)][PF₆][1; allyl = CH₂CHCH₂ or CH₂C(Me)CH₂] with [Ru(CO)₂L(η⁴-cot)](L = CO or PPh₃, cot = cyclo-octatetraene) gives [Ru(CO)₂L(η²,η³-C₈H₈R)][PF₆][2; R = CH₂CHCH₂ or CH₂C(Me)CH₂] whereas that of (1; allyl = CH₂CHCHMe) yields [2; R = CH(Me)CHCH₂], as a mixture of two diastereomers, and (2; R = CH₂CHCHMe). The X-ray structure of [2; R = CH₂C(Me)CH₂] shows that the addition of the 2-methylallyl group to the C₈ ring yields the exo isomer, and confirms that the resulting cyclo-octatrienyl ligand is η²,η³-co-ordinated to ruthenium. The η²-alkene unit is trans to the PPh₃ ligand, and the η³-allyl moiety is transoid to the two carbonyl ligands. Complex (1) and [Fe(CO)₂(CNBu^t)(η⁴-cot)] give [Fe(CO)₂(CNBu^t)(η⁵-C₈H₈R)][PF₆] as a mixture of cyclo-octatrienyl (3) and bicyclo[5.1.0]octadienyl (4) isomers, the former showing rotamerism of the Fe(CO)₂(CNBu^t) group with respect to the η⁵-bound hydrocarbon; diastereomerism is observed for [3; R = CH(Me)CHCH₂]. The cationic iron and ruthenium complexes (2)–(4) are deprotonated by NEt₃ in CH₂Cl₂ to give the allyl-substituted cot complexes [M(CO)₂L(η⁴-C₈H₇R)][5; M = Fe, L = CNBu^t, R = CH₂CHCH₂, CH₂C(Me)CH₂, CH(Me)CHCH₂, or CH₂CHCHMe; M = Ru, L = PPh₃, R = CH₂C(Me)CH₂] which undergo two dynamic processes in solution, namely rotamerism (M = Fe) and oscillation of the M(CO)₂L unit with respect to the η⁴-bound hydrocarbon. The compounds [Fe(CO)₂(CNBu^t)(η⁴-C₈H₇R)][R = CH₂CHCH₂orCH₂C(Me)CH₂] react sequentially with [1; R = CH₂CHCH₂ or CH₂C(Me)CH₂] and NEt₃ to give the difunctionalised cyclo-octatetraene derivatives [Fe(CO)₂(CNBu^t)(η⁴-C₈H₆R₂)][6; R = CH₂CHCH₂ or CH₂C(Me)CH₂]. The substituted cyclo-octatetraenes C₈H₇[CH₂C(Me)CH₂] and C₈H₆[CH₂C(Me)CH₂]₂ are detached from the appropriate iron complexes, (5) or (6), on reaction with ONMe₃·2H₂O.