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

Diazoalkane complexes [Os((5)-C5Me5)(N(2)CAr1Ar2)(PPh3){P(OR)(3)}]BPh4 (1, 2) [R = Me (1), Et (2); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b); Ar1Ar2 = C12H8 (fluorenyl) (c)] were prepared by reacting bromo-compounds OsBr((5)-C5Me5)(PPh3){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((5)-C5Me5)((1)-?N?NC(C12H8)CH?C?H)(PPh3){P(OR)(3)}]BPh4 (6, 7) [R = Me (6), Et (7)] whereas reactions with terminal alkynes R1C?CH (R1 = Ph, p-tolyl, COOMe) gave vinylidene derivatives [Os((5)-C5Me5){?C?C(H)R1}(PPh3){P(OR)(3)}]BPh4 (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((5)-C5Me5)((2)-O-2)(PPh3){P(OR)(3)}]BPh4 (10, 11) [R = Me (10), Et (11)]. Allenylidene [Os]?C?C?CR1R2 (12-14) [R1 = R2 = Ph (12, 13); R1 = Ph, R2 = Me (14)], vinylvinylidene [Os]?C?C(H)C(Ph)?CH2 (15) and 3-hydroxyvinylidene [Os]?C?C(H)C(H)R2(OH) (16, 17) [R2 = Ph (16), H (17)] derivatives were also prepared. The vinylidene complex [Os((5)-C5Me5)(?C?CH2)(PPh3){P(OMe)(3)}]BPh4 (8a) reacted with PPh3 to afford the alkenylphosphonium derivative [Os((5)-C5Me5){(1)-C(H)?C(H)PPh3}(PPh3){P(OMe)(3)}]BPh4 (18) whereas vinylidene complexes 8 and 9 reacted with water leading to the hydrolysis of the alkyne and the formation of carbonyl complexes [Os((5)-C5Me5)(CO)(PPh3){P(OR)(3)}]BPh4 (19, 20). The complexes were characterised by spectroscopic data (IR and NMR) and by X-ray crystal structure determination of [Os((5)-C5Me5){?C?C(H)p-tolyl}(PPh3){P(OEt)(3)}]BPh4 (9c), [Os((5)-C5Me5)((2)-O-2)(PPh3){P(OMe)(3)}]BPh4 (10) and [Os((5)-C5Me5)(CO)(PPh3){P(OMe)(3)}]BPh4 (19).