Unexpectedly different reactions of [(arene)Mn(CO)3]+ cations (arene = trindane, indane, tetralin, or dibenzosuberane) with potassium t-butoxide — C-H insertions, haptotropic shifts, dimerization, or elimination

Abstract

[(η6-Trindane)Mn(CO)3][BF4] (1) reacts with tert-BuOK in THF in the presence of alkyl halides (CH2=CHCH2Br, CH3I) to yield the corresponding (η6-C15H18)Mn(CO)2X, where X = Br (3) or I (4). In contrast, 1 and tert-BuOK react, in the presence of a donor ligand, to generate (η5-C15H15)Mn(CO)2L, where L = CO (7), P(OMe)3 (8), or PPh3 (9), in which the metal has migrated from the central ring onto a peripheral ring that has lost three hydrogens; [(η6-indane)Mn(CO)3][BF4] behaves similarly. A mechanism is proposed in which the initially formed (η6-trindane)Mn(CO)2CO2-tert-Bu suffers the loss of CO2 and isobutene to yield the hydride, (η6-trindane)Mn(CO)2H, that in turn undergoes three successive C-H insertions with concomitant loss of two molecules of dihydrogen. In contrast, [(η6-tetralin)Mn(CO)3][PF6] (17) and [(η6-dibenzosuberane)Mn(CO)3][BF4] (23) each suffer deprotonation at a benzylic site. In the first case, the zwitterion formed attacks its progenitor to yield a tetralenyl-substituted (η5-cyclohexadienyl)Mn(CO)3 complex (21); however, for the dibenzosuberane complex (23) the elimination product (28) is stable. X-ray crystal structures are reported for 3, 4, 7, 8, 23, 28, and for the phosphite complexes [(η6-trindane)Mn(CO){P(OMe)3}2][BF4] (15) and [(η6-tetralin)Mn(CO)2{P(OMe)3}][PF6] (20).Key words: arene-manganese, organometallic cations, deprotonations, X-ray crystallography.