_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

General reactions of transition metal complexes
SiR 3
L __ 1 _.H
',_ 1 r ---
oc/J"'-L
X
Fig. 5.17 Additions to Vaska's compound and related complexes. L = PPh, or similar.
X= CI, Br. I.
ethanol with formaldehyde in the presence of excess triphenylphosphine. The
formaldehyde also is the source of the carbonylligand. The metal centre is basic.
Thecomplex isprotonated, even by carboxylic acids, which form octahedral derivatives
in which H and OCOR are trans to each other. This suggests a two stage
reaction, initial protonation being followed by coordination of the anion:
L, X
---.lr'/ + H-Yoc~
"L
The equilibrium constant (K) for the addition of benzoic acid to Vaska's type
compounds depends on the electron density at iridium. Thus electron attracting
ligands lower the basicity and electron donating ones raise it (Order of K where
X= I > Br >CI; L = Me,P > Me 2 PPh > MePPh 2 > PPhJ
Vaska's compound forms adducts with the Lewis acids BF 1 , BCI, and BBr,.
With HgC1 2 and SnCl 4 adducts may be formed initially, but transfer of chlorine to
iridium occurs and the final products are octahedral (Fig. 5.17).
Evidence on the reactions with methyl halides is consistent with S,) attack by
iridium at carbon. The reactions are first order each in CH,X and Ir(CO)XL 2 • The
most basic iridium complexes react fastest. In non-polar solvents trans addition
products result; this is consistent with the mechanism:
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