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Silapentadienyl−Iridium−Phosphine Chemistry

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journal contribution
posted on 09.06.2008, 00:00 by John R. Bleeke, Todsapon Thananatthanachon, Nigam P. Rath
A series of η1-silapentadienyl−iridium complexes have been synthesized by reacting (η2-cyclooctene)(X)Ir(PMe3)3 (X = Cl or Me) with butadienyldimethylsilanes, and the reactivity of these species has been investigated. Treatment of (η2-cyclooctene)(Cl)Ir(PMe3)3 wi th E- or (Z-butadienyl)dimethylsilane produces, via Si−H bond activation, (η1-E-dimethylsilapentadienyl)(H)(Cl)Ir(PMe3)3, 1E. Similarly, treatment of (η2-cyclooctene)(Me)Ir(PMe3)3 with E- or (Z-butadienyl)dimethylsilane produces η1-E- or (η1-Z-dimethylsilapentadienyl)(H)(Me)Ir(PMe3)3, 2E or 2Z. Upon heating in benzene at 100 °C (under pressure), 2E decomposes, but 2Z loses methane and coordinates the terminal double bond of the silapentadienyl ligand, producing (η12-dimethylsilapentadienyl)Ir(PMe3)3, 3. Treatment of (η2-cyclooctene)(Cl)Ir(PMe3)3 with (E-2,3-dimethylbutadienyl)dimethylsilane produces (η1-E-2,3,5,5-tetramethylsilapentadienyl)(H)(Cl)Ir(PMe3)3, 4E. In acetone, this species isomerizes via 2,3-dimethylbutadienyl migration from silicon to iridium, leading ultimately to production of (η1-E-2,3-dimethylbutadienyl)(H)(SiMe2Cl)Ir(PMe3)3, 5. Treatment of (η2-cyclooctene)(Cl)Ir(PMe3)3 with the Z isomer of (2,3-dimethylbutadienyl)dimethylsilane produces transient (η1-Z-2,3,5,5-tetramethylsilapentadienyl)(H)(Cl)Ir(PMe3)3, 4Z, which also rearranges. In this case, hydride first migrates from iridium to C2 of the silapentadienyl ligand, and then the resulting butenyl group migrates from silicon to iridium, forming an iridacyclopentene product, 6. The reactions of (η2-cyclooctene)(Me)Ir(PMe3)3 with E- or (Z-2,3-dimethylbutadienyl)dimethylsilane generate η1-E- or (η1-Z-2,3,5,5-tetramethylsilapentadienyl)(H)(Me)Ir(PMe3)3, 7E or 7Z. Heating these compounds in toluene or benzene (under pressure) leads to methane loss, followed by C−H bond activation. In the case of 7E, a silapentadienyl methyl group is activated, producing an iridasilacyclopentene product, 8. In the case of 7Z, a C−H bond on the end of the silapentadienyl chain is activated, producing the first example of an iridasilacyclohexadiene, 9. X-ray crystal structures of (η2-cyclooctene)(Me)Ir(PMe3)3, 5-acetone, 6, and 7E are reported here, while structures of 1E and 3 were reported in a prior communication.1