Synthesis and chemistry of the aryliridium(III) fluorides Cp'Ir(PMe3)(Aryl)F: High reactivity due to surprisingly easy Ir-F ionization

Article abstract of DOI:10.1021/ja00155a012

This paper reports the synthesis and chemistry of the unusual late metal fluoride complexes, Cp'Ir(PMe₃)(Aryl)F [Cp' = Cp* (C₅Me₅), Aryl = Ph (1a); Cp' = Cp*, Aryl = p-tolyl (1b); Cp' = Cp(Et) (C₅Me₄Et), Aryl = Ph (1c)]. The solid-state structure of 1c has been determined: crystals of 1c are monoclinic, space group P2₁/c, with a = 9.235(2) ?, b = 12.667(2) ?, c = 17.129(3) ?, β = 104.547(16)°, and Z = 4; R = 3.98%, wR = 4.65% for 2859 data for F² > 3σ(F²). These complexes exhibit reactivity that is substantially different from that of related Cl, Br, and I species because of the greater propensity of fluoride ion to dissociate from the Ir center, even in nonpolar solvents. For example, in solution at room temperature, fluoride is slowly displaced from complexes 1 by Lewis bases such as pyridines and phosphines (L); the resulting salts [Cp'Ir(PMe₃)(Aryl)(L)]F (2) exist in equilibrium with the covalent starting materials. This equilibrium lies well to the left for pyridines and phosphines under anhydrous conditions, but both the rate of establishment and the magnitude of K(eq) are increased dramatically by the addition of H₂O. In aqueous THF the aquo species [Cp*Ir(PMe₃)(Ph)(OH₂)]F·xH₂O (2e) is formed much more rapidly than the [Cp'Ir(PMe₃)(Aryl)(L)]F salts. This, and the rapid further reactivity of 2e, enables the aquo species to serve as an intermediate in the water-catalyzed substitution of fluoride by L. Treatment of 1a with mixtures of water and other entering ligands and monitoring these reactions over time reveals that the kinetic affinity of these ligands for the Ir center is exactly the reverse of their thermodynamic affinity: kinetically, H₂O > pyridines > phosphines; thermodynamically, phosphines > pyridines > H₂O. Addition of BPh₃ to [Cp'Ir(PMe₃)(Aryl)(L)]F (2) in nonaqueous media leads to irreversible formation of the borate complexes, [Cp'Ir(PMe₃)(Aryl)(L)]BPh₃F. The lability of the fluoride ligand in complexes 1 is also demonstrated by mixing Cp*Ir(PMe₃)(Ph)F with Cp*Ir(PMe₃)(p-tolyl)X [X = Cl, Br, OTf, OPh] in C₆D₆, which leads to solutions containing four species identifiable as the two starting materials and the two exchange products Cp*Ir(PMe₃)(Ph)X and Cp*Ir(PMe₃)(p-tolyl)F. Organic halides participate in exchange as well; reaction of 1a with PhCH₂Br, Me₃SiCl, MeCOCl, and even CH₂Cl₂ results in complete replacement of fluoride by bromide or chloride in 1a. The labile fluoride ion also leads to other novel reactivity. For example, addition of dimethyl acetylenedicarboxylate to complexes 1 gives iridacyclopentadiene complexes (5) and reaction of 1a and 1c with (1-trimethylsilyl)imidazole provides Cp'Ir(PMe₃)(Ph)(imidazolate) complexes (7) and Me₃SiF. Treatment of 1 with silanes HSiMe₂R [R = Ph, Me] leads to the formation of Cp'Ir(PMe₃)(R)(SiMe₂F) complexes (8); excess HS-p-tolyl reacts with either 1a or 1b to provide Cp*Ir(PMe₃)(S-p-tolyl)₂ (10).