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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 20, Number 1
BKCSDE 20(1)
January 20, 1999 

Selective Deprotonation and Decarbonylation from Hydridocarbonyl-iridium(Ⅲ) Compounds with Trimethylamine N-oxide
Chong Shik Chin, Moonhyun Oh, Gyongshik Won, Haeyeon Cho, Dongchan Shin
Me3NO selectively abstracts the proton from [IrH(CO)(PPh3)2L(A)]0.1+,2+ (1) (A: -CCPh, Cl-, CH3CN and L: CH3CN, Cl-, C1O4-) to give the trans-elimination products, Ir(CO)(PPh3)2(A) (2). The reductive elimination of H+ and Cl- from Ir(H)Cl2(CO)(PPh3)2 (lb) to give IrCl(CO)(PPh3)2 (2b) is first order in both lb and Me3NO. The rate law d[2b]/dt=kobs[lb]=k2[lb][Me3NO] suggests the formation of (PPh3)2(CI)2(CO)Ir-H-ON+Me3 in the rate determining step (k2) followed by the fast dissociation of both H-ON+Me3 and the trans ligand Cl-. The rate significantly varies with the cis liaand A and the trans ligand L and is slower with both A and L being Cl- than other ligands. Me3NO selectively eliminates CO from [Ir(H)2(CO)(PPh3)2L]0,+ (3) (L=CH3CN, C1O4-) to produce [Ir(H)2(PPh3)2L'(CH3CN)]+ (4) (L'=CH3CN, PPh3) in the presence of L. Me3NO does not readily remove either H+ or CO from cis, trans- and trans, trans-lr(H)(-CCPh)2(CO)(PPh3)2 and cis, trans-Ir(H)2Cl(CO)(PPh3)2. The choice whether hydridocarbonyls, 1 and 3 undergo the deprotonation or decarbonylation may be understood mostly in terms of thermodynamic stability of the products and partly by kinetic preference of Me3NO on proton and CO.
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