Experimentally, 14r and 15r have similar energies as indicated by broadened
peaks indicating dynamic exchange in the in situ
1 H and
31 P NMR spectra (90 psig,
30% water/d 6 -acetone) shown in Fig. 12. The
1 H NMR of the hydride region at
60
C only shows a single broadened resonance at À10.7 ppm, consistent with a
dynamic exchange between these 14r and 15r. Although we propose that dicationic
11r and 11r* are also present, the hydride resonances for these around À7.8 ppm
are not observed, most likely because their concentrations are too low or the
resonance is broadened out due to exchange via deprotonation.
Note that there is only a small amount of bimetallic catalyst fragmentation
occurring to form the monometallic complex [RhH 2 (κ
4 -rac-et,ph-P4)]
+ , 12r, and
no observable double-P4 ligand complex 13rr. The
31 P NMR at 25
C also shows a
symmetrical pattern consistent with a dynamic exchange between 14r and 15r.
Fig. 12
1
H and
31
P NMR spectra of [Rh 2 (nbd) 2 (rac-et,ph-P4)]
2+ in 30% water/d 6 -acetone producing an exchanging mixture of the monocationic dirhodium species 14r and 15r
Bimetallic Homogeneous Hydroformylation
19