Pentamethylcyclopentadienyl osmium complexes that contain diazoalkane, dioxygen and allenylidene ligands: Preparation and reactivity

Abstract

Diazoalkane complexes [Os(η 5 -C 5 Me 5 )(N 2 CAr1Ar2)(PPh 3 ){P(OR) 3 }]BPh 4 (1, 2) [R = Me (1), Et (2); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b); Ar1Ar2 = C 12 H 8 (fluorenyl) (c)] were prepared by reacting bromo-compounds OsBr(η 5 -C 5 Me 5 )(PPh 3 ){P(OR) 3 } with an excess of diazoalkane in ethanol. The treatment of diazoalkane complexes 1 and 2 with acetylene under mild conditions (1 atm, RT) led to dipolar (3 + 2) cycloaddition affording 3H-pyrazole derivatives [Os(η 5 -C 5 Me 5 )(η 1 -NNC(C 12 H 8 )CHCH)(PPh 3 ){P(OR) 3 }]BPh 4 (6, 7) [R = Me (6), Et (7)] whereas reactions with terminal alkynes R1CCH (R1 = Ph, p-tolyl, COOMe) gave vinylidene derivatives [Os(η 5 -C 5 Me 5 ){CC(H)R1}(PPh 3 ){P(OR) 3 }]BPh 4 (8b-d, 9b-d) [R = Me (8), Et (9); R1 = Ph (b), p-tolyl (c), COOMe (d)]. Exposure to air of dichloromethane solutions of complexes 1 and 2 produced dioxygen derivatives [Os(η 5 -C 5 Me 5 )(η 2 -O 2 )(PPh 3 ){P(OR) 3 }]BPh 4 (10, 11) [R = Me (10), Et (11)]. Allenylidene [Os]CCCR1R2 (12-14) [R1 = R2 = Ph (12, 13); R1 = Ph, R2 = Me (14)], vinylvinylidene [Os]CC(H)C(Ph)CH 2 (15) and 3-hydroxyvinylidene [Os]CC(H)C(H)R2(OH) (16, 17) [R2 = Ph (16), H (17)] derivatives were also prepared. The vinylidene complex [Os(η 5 -C 5 Me 5 )(CCH 2 )(PPh 3 ){P(OMe) 3 }]BPh 4 (8a) reacted with PPh 3 to afford the alkenylphosphonium derivative [Os(η 5 -C 5 Me 5 ){η 1 -C(H)C(H)PPh 3 }(PPh 3 ){P(OMe) 3 }]BPh 4 (18) whereas vinylidene complexes 8 and 9 reacted with water leading to the hydrolysis of the alkyne and the formation of carbonyl complexes [Os(η 5 -C 5 Me 5 )(CO)(PPh 3 ){P(OR) 3 }]BPh 4 (19, 20). The complexes were characterised by spectroscopic data (IR and NMR) and by X-ray crystal structure determination of [Os(η 5 -C 5 Me 5 ){CC(H)p-tolyl}(PPh 3 ){P(OEt) 3 }]BPh 4 (9c), [Os(η 5 -C 5 Me 5 )(η 2 -O 2 )(PPh 3 ){P(OMe) 3 }]BPh 4 (10) and [Os(η 5 -C 5 Me 5 )(CO)(PPh 3 ){P(OMe) 3 }]BPh 4 (19).