Activation of acetonitrile in [Cp*Ir(eta(3)-CH2CHCHPh)(NCMe)(+): Crystal structures of iridium-amidine, imino-ether, amido, and amide complexes

Abstract

Reactions of [Cp*Ir(eta(3)-CH2CHCHPh)(NCMe)]OTf (1) with protic amines, alcohols, and water produce amidine complexes [Cp*Ir(eta(3)-CH2CHCHPh)(NH=C(NR2)Me)]OTf (2) (R-2 = (Me)(2) (a), (Me)(H) (b), (i-Pr)(H) (c), (-CH2(CH2)(3)CH2-) (d)), imino-ether complexes [Cp*Ir-(eta(3)-CH2CHCHPh)(NH=C(OR')Me)]OTf (4) (R' = Me (a), Et (b), i-Pr (c)), and amido complex Cp*Ir(eta(3)-CH2CHCHPh)(NHC(=O)Me) (5-K), respectively. The keto form amido complex 5-K undergoes tautomerization to give the enol form complex Cp*Ir(eta(3)-CH2CHCHPh)(N=C(OH)Me) (5-E) in polar solvents. Tertiary amines (NMe3, NEt3) react with 1 in chlorinated solvents (XCl) to give the chloro complex Cp*IrCl(eta(3)-CH2CHCHPh) (3) and quaternary ammonium salts [R3NX]OTf(R = Me, Et and ii = CH2Cl, CH3, CHCl2, CCl3, PhCH2). Crystal structures of 2a, 4a, 5-K, and [Cp*Ir(NH=C(OH)Me)(OH2)(PPh3)]OTf2 (6) have been determined by single-crystal X-ray diffraction analysis, which lead us to suggest hybrid structures, Ir--NH-C(=N+Me2)Me (2a') for 2a and Ir--NH-C(=O+Me)Me (4a') for 4a to some extent. Complexes 2 and 4 react with PPh3 to give an iridium(III) complex [Cp*Ir(eta(3)-CH2CHCHPh)(PPh3)]OTf (7) and the free amidines NH=C(NR2)Me (8) and imino-ethers NH=C(OR')Me (9), respectively. Nitrile complexes I and [Cp*Ir(eta(3)-CH2CHCHPh)(NCCH=CHMe)]OTf(10) catalyze the hydration of the nitriles in the presence of Na2CO3 to produce amides, and the benzonitrile complex [Cp*Ir(eta(3)-CH2CHCHPh)(NCPh)]OTf(ll) catalyzes the methanolysis of benzonitrile in the presence of Na2CO3 to produce NH=C(OMe)Ph. Plausible mechanisms for these catalytic reactions are suggested with the amido and imino-ether complexes such as 4 and 5 being involved.