A novel series of ligands (
1-
10) t
hat induce
wide bite angles (106
<
hars/beta2.gif" BORDER=0 ALIGN="middle">
n < 131
)
has beensynt
hesized. Compared to t
he xantp
hos series (e.g.,
13 versus
5), t
he introduction of t
hep
hosp
hacyclic moiety results in ligands
wit
h a slig
htly larger bite angle. Hig
h-pressure IRand
hig
h-pressure NMR studies of t
he (dip
hosp
hine)R
hH(CO)
2 complexes s
ho
w t
hat mostligands (
3-
7) adopt a bis-equatorial binding mode exclusively in t
he trigonal bipyramidalr
hodium complex. Subtle c
hanges in ligand structure
have a large impact on activity andselectivity in t
he
hydroformylation of 1-octene and
trans-2-octene. Rates up to 3275 (molalde
hyde)(mol R
h)
-1 h-1 (
p(CO/H
2) = 20 bar,
T = 353 K, [R
h] = 1 mM, [1-octene] = 637mM) and regioselectivities > 99% to
ward t
he linear product
were obtained
when 1-octene
was used as substrate. For
trans-2-octene rates up to 250 (mol alde
hyde)(mol R
h)
-1 h-1 (
p(CO/H
2) = 3.6 bar,
T = 393 K, [R
h] = 1 mM, [
trans-2-octene] = 640 mM) and
hig
h regioselectivitiesup to 96% to
ward t
he linear product,
whic
h are unprecedented,
were obtained. A correlationbet
ween t
he selectivity for t
he
hydroformylation of 1-octene and
trans-2-octene
has beenobserved, suggesting t
hat t
he selectivity-determining step remains unc
hanged bet
weenterminal and internal olefins. Ligands
wit
h a larger bite angle lead to more selective systems,but above 125
t
he regioselectivity drops. Furt
hermore it is no longer t
he selective formationof linear alkyl species t
hat determines t
he
hig
h regioselectivities. Instead t
he differences inrate of
hars/beta2.gif" BORDER=0 ALIGN="middle">-
hydrogen elimination from t
he branc
hed alkyl intermediate and t
he linear alkylintermediate versus CO insertion determine t
he regioselectivity. For bot
h substrates a
decrease in activity
wit
h an
increase in bite angle is observed. It is suggested t
hat t
heaforementioned rates of
hars/beta2.gif" BORDER=0 ALIGN="middle">-
hydrogen elimination versus CO insertion must play a crucialrole in t
his bite angle effect on activity, because previous studies
have s
ho
wn t
hat an
increasein bite angle leads to an
increase in activity.