THE SELECTIVE REDUCTION OF BENZENE TO CYCLOHEXENE MEDIATED BY PLATINUM METAL COMPLEXES: X-RAY CRYSTAL STRUCTURE OF 5-C5Me5)Ir(η5-C6H6CH2NO2)>

DOI: 10.1039/DT9840001747

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 1747 - 1754 (1984)

Update date:2022-08-29

Topics:

Authors:

Grundy, Stephen L.

Smith, Arnold J.

Adams, Harry

Maitlis, Peter

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Article abstract of DOI:10.1039/DT9840001747

The dicationic η⁶-benzene complexes <(C_nMe_n)M(C6H6)>(2+) 5-cyclohexadienyl complexes <(C_nMe_n)M(C6H7)>(1+) (3) which are further reduced to the η⁴-cyclohexadiene complexes <(C_nMe_n)M(C6H8)> (4).Reaction of complexes (4) with acid gives cyclohexene with 100percent selectivity; when the reaction is carried out with tetrafluoroboric acid in benzene, the initial benzene complexes (2) are regenerated.The overall reaction consists of addition of two hydrides followed by two protons to co-ordinated benzene, and a cycle catalytic in the platinum metal can be constructed.The efficiency of the overall reduction of benzene to cyclohexene decreases in the order Ir> Ru> Rh.The reaction is compared to the reduction of benzene to cyclohexane mediated by rhodium, iridium, and ruthenium trichloride hydrates and tetrahydroborate in ethanol.Other nucleophyles also attack the benzene ring in (2b): these include methyl-lithium (which gives two dimethylcyclohexadiene complexes from which isomeric dimethylcyclohexenes can be obtained with acid), methoxide (which gives the methoxycyclohexadienyl and, with an excess, two dimethoxycyclohexa-1,3-diene complexes), and nitromethane which in the presence of base gives the nitromethylcyclohexadienyl complex <(C5Me5)Ir(C6H6CH2NO2)> (9).The single-cristal X-ray structure determination of (9) shows the C5Me5 and The C6 ring both to be η⁵-bonded, and the CH2NO2 substituent to be in the exo position on the η⁵-cyclohexadienyl ring.Analysis of the highfield 1H n.m.r.spectra of the complexes showed that exo attack on the C6 ring occured with all the nucleophiles.In the presence of base, (9) reacted further with (2b) to give <<(C5Me5)Ir(C6H6)>2CHNO2>(2+).These reactions show the versatility of the reduction procedure.