Assembling ethylene, alkyl, hydride, and carbon monoxide ligands at iridium

The iridacyclopropane complex [ (triphos)Ir(C1)(CzH4)]is the starting point to synthesize a number of
stable iridium complexes containing various combinations of participative ligands such as hydride, ethylene,
alkyls and heteroalkyls, alkynes, and carbon monoxide: Ir(H)(CzH4)I,r (H),(C2H4)I, r(CzHs)(CzH$,I r(CO)z,
Ir(H)(C&d(CO), ~(H)z(COI)r,( H)z(CHzCH$Eb), Ir(HI3, Ir(H)2(CzHs)I,r (H)z(C3H7)I,r (C2H&, Ir(RC=CR),
IrH(p-H)zHIr,a nd IrH(p-C1)zHIr. Due to the tripodlike structure of the ligand MeC(CHzPPhz)3( triphos),
all the complexes invariably exhibit a facial arrangement of the phosphorus and non-phosphorus ligands.
The contemporaneous availability of so many related species has allowed a comparative experimental study
on several important reactions. These include (i) reductive elimination of C-H and H-H bonds from
dihydride akyl complexes, (ii) reductive elimination of H-H bonds vs hydride migration in dhydride ethylene
species, (iii) nucleophilic additions to coordinated double bonds, (iv) phosphine arm dissociation in triphos
complexes, and &H elimination vs C-H bond reductive elimination in hydride alkyl complexes. In most
instances, such reactions are characterized by stereo- and chemoselectivity. Valuable information on the
role played by the nature of the metal and of the phosphine ligands in determining the reactivity has been
provided by a comparison among strictly related Rh and Ir complexes containing either triphos or three
comparable monophosphines.