Novel five-coordinate organoiridium(I) complexes of the type Ir(R)(CO)(chel-P3) (chel-P3=PhP(CH2CH2CH2PPh2)2: R = CH2CMe3, CH2SiMe3; chel-P3 = MeP-(CH2CH2CH2PPh2)2: R = CH2SiMe3; chel-P3PhP(CH2CH2PPh2)2; R = CH2SiMe3, 4-MeC6H4) have been prepared from Ir(R)(CO)(PPh3)2 and the respective triphosphine. According to 31P NMR, these compounds are stereochemically rigid at normal temperatures. The reaction