PYRAZOLYL-BRIDGED IRIDIUM DIMERS .16. THE ATROPISOMERIC (C-2) SYSTEM [IR(CO)(PPH(3))(MU-PZ)](2) - SYNTHESIS OF HOMOLOGOUS DIASTEREOMERIC COMPLEXES THAT UNDERGO SLOW STEREOMUTATION BY RING INVERSION OF THE BRIDGING FRAMEWORK - MECHANISTIC IMPLICATIONS FOR BIMETALLIC SUBSTRATE ACTIVATION

The diiridium(I) complex [Ir(P{OR}Ph(2))(Co)(mu-pz)](2) (R*=Bor, 4a,b , OBor=(1S)-endo-(-)-bornoxy) exists as two diastereomers (63:37 ratio , IH and (31)p NMR) that are found to cocrystallize, providing a sourc e of 4a,b in nonequilibrium distribution. NMR measurements show that M el adduct formation to give the diastereomeric pair of diiridium(II) a dducts 7a,b is orders of magnitude faster than ring inversion that int erconverts 4a and 4b and that 7a,b equilibrate much more slowly than t he 4a-4b interconversion in a manner that implicates reductive elimina tion of MeI.