Organometallic reactivity patterns in fluorocarbons and implications for catalysis: Synthesis, structure, solubility, and oxidative additions of a fluorous analogue of Vaska's complex, trans-Ir(CO)(Cl)[P(CH2CH2(CF2) 5CF3)3]2Academic Article
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The reaction of [Ir(Cl)(cod)]2, P(CH2CH2(CF2)5CF3) 3, and CO (1 atm) gaves the title comnound (2, 97%). Tri(n-octyl)phosphine (3) and rhodium (4) analogues are similarly prepared. Crystal structures of 2 and 4 show anti CCCC conformations m the six perfluoroalkyl groups (average torsion angle 169), with four chains (two per phosphorus) in parallel coplanar arrays that define ca. 21 6 "rafts". The other two chains extend on a common side of the raft, which pack back-to-back in stacks, maximizing parallel chains in every dimension. DSC shows one phase transition (melting, 2/4 75/79C) prior to thermal decomposition (> 200C). The IR vCO values (2/3/4 1975/1942/1979 cm-1) show that the CH2-CH2 spacers do not completely insulate the metals from the perfluoroalkyl groups. Both 2 and 4 are soluble in CF3C6F11, CF3C6H5, ether, THF, and acetone but insoluble in hexane toluene, CHCl3, and CH2Cl2 (CF3C6F11/THF partition coefficient >99.7:<0.3). Reactions of 2 with RI, H2, and 3O2 or 1O2 in (CF3C6F11 give Ir(CO)(Cl)(R)(I)[P(CH2CH2(CF2) 5CF3)3]2 (R = CH2CH2(CF2)7 CF3 (5), CH3 (6), CH(CH3)CH2CH3 (7), 70-84%), Ir(CO)(Cl)(H)2[P(CH2CH2-(CF2) 5CF3)3]2 82%), and Ir(CO)(Cl)(O2)[P(CH2CH2(CF2) 5CF3)3]2 (9, 67%), respectively Additions of RI occur by free-radical chain mechanisms (inhibition by duroquinone; slower dark reactions; rates 7 > 5 > 6) with no evidence for polar pathways. Complex 9 forms more rapidly in THF, indicating that (relative to THF) 2 and 3O2 are stabilized by CF3C6F11 more than the transition state.
