Homogeneous CO Hydrogenation: Ligand Effects on the Lewis Acid ...

spectrum showed 1.01:1.00 18-crown-6:formyl, and the concentration of Re was determined to
be 17.5 mM. Aliquots of a 1.0 M solution of t Bu(CH 2) 2B(C 8H 14) in THF-d 8 were then added:
0.13, 0.33, 0.89, 1.33, and 1.68 equiv. The chemical shift change of the formyl was recorded at
each concentration of borane, and a Benesi-Hildebrand-type analysis 12 gave a linear plot of 1/Δδ
vs. 1/[ t Bu(CH 2) 2B(C 8H 14)] (Figure S11), providing an estimate of the equilibrium constant of
Scheme S1, K eq = 100 M -1 favoring adduct formation. A correction was made for the background
equilibrium of THF binding the borane, as less borane would be available to interact with the
formyl.
PPh3 OC <strong>CO</strong>
Re H
OC C
PPh3 O
+ B
PPh3 OC <strong>CO</strong>
Re
OC C
H
Scheme S1.
Figure S11. Benesi-Hildebrand plot.
PPh3 O
B
S14