[38465-86-0] · C34H38F6IrP3 · (1,5-Cyclooctadiene)bis(methyldiphenylphosphine)iridium(I) Hexafluorophosphate · (MW 845.81)
Physical Data: mp 236 °C (dec); 1H NMR (CD2Cl2) d 1.78 (d, JHP = 8 Hz, PMePh2), 2.19 (m, CH2 of cod), 4.36 (=CH of cod), 7.3-7.9 (ov m, PMePh2); conductivity 135 &OOmega;-1 cm2 mol-1.
Solubility: sol CH2Cl2; insol diethyl ether and hexanes.
Form Supplied in: red crystalline solid; commercially available.
Preparative Methods: to a suspension of [Ir(m-Cl)(1,5-cod)]2 (0.2 g) in 10 mL of ethanol is added methyldiphenylphosphine (0.2 g) in ethanol. The mixture is stirred for ca. 10 min until the original suspension has dissolved. To this is added excess NH4PF6 in ethanol. After cooling to 0 °C the precipitate is filtered, washed with ethanol and then ether to give the title reagent (0.36 g) as red prisms.3
Handling, Storage, and Precautions: the dry solid is moderately air-stable.
Cationic iridium complexes such as [Ir(1,5-cod)(PR3)2]+ catalyze the homogeneous hydrogenation of cyclooctadiene to give predominant formation of cyclooctene along with minor amounts of cyclooctane and 1,3-cyclooctadiene (formed by isomerization of the starting material). Slower rates of hydrogenation are observed in comparison to reactions employing complexes of the type [Ir(1,5-cod)(PR3)py]+ as catalyst precursor.4 A number of iridium complexes, including [Ir(1,5-cod)(PMePh2)2]PF6 (1), are also active catalysts for the hydrogenation of soybean and other vegetable oils.5
Addition of dihydrogen to (1) produces a very active catalyst for the isomerization of allyl ethers to the corresponding trans-propenyl ethers (eq 1). This reaction proceeds with high stereoselectivity (trans/cis > 30) and under mild conditions.
While substituted allylic ethers can be isomerized (eq 2), the reaction appears to be limited to primary allyl ethers. Complex (1) also catalyzes the isomerization of allyl ethers of glycerol or glucose having various protecting groups.6 The corresponding propenyl ethers thus formed are converted into free hydroxy compounds by treatment with Mercury(II) Chloride/Mercury(II) Oxide.7 In a related study, (1) is used to catalyze the isomerization of allylic alcohols to aldehydes and ketones.8
Hydrogen-activated (1) is used to isomerize the allyl group in carbohydrates as part of a two-step deallylation procedure.9 Initial isomerization is followed by treatment with catalytic amounts of Osmium Tetroxide and Trimethylamine N-Oxide to cleave the trans-1-propenyl group in the presence of an azide group at C-2 (eq 3).10 This method avoids the formation of intramolecular 1,3-dipolar cycloaddition products which are formed using other deallylation procedures. Unlike many other metal catalysts, cationic iridium complexes are able to perform this isomerization in the absence of elevated temperatures.
Stephen A. Westcott
University of North Carolina, Chapel Hill, NC, USA