Organometallics
COMMUNICATION
Scheme 2. Synthesis of MAP Species
Figure 2. Thermal ellipsoid drawing of 9b. Ellipsoids are displayed at
the 50% probability level. Hydrogen atoms are omitted. Selected
distances (Å) and angles (deg): W(1)ꢀN(1) = 2.0540(18), W(1)ꢀN-
(2) = 1.7571(19), W(1)ꢀO(1) = 1.9797(14), W(1)ꢀC(1) = 2.049(2),
W(1)ꢀC(3) = 2.077(2), C(61)ꢀC(81) = 3.405; W(1)ꢀN(2)ꢀC(61)
= 164.32(16), N(2)ꢀW(1)ꢀO(1) = 173.29(7), W(1)ꢀO(1)ꢀC(11)
= 157.73(14).
limited by bimolecular decomposition of intermediate methyli-
dene species to give an ethylene complex, a type of reaction that
has been documented under other circumstances.8 For example,
treatment of a sample of 8a with ethylene leads to formation
of W(NAr00)(CH2)(2,5-Me2pyr)(OHIPT) (10), according
to proton NMR spectra (see the Supporting Information).
Crystals of the metallacyclopentane species W(NAr00)(C4H8)-
(2,5-Me2pyr)(OHIPT) (11) were isolated from an NMR sample
of 10 after the sample stood for 2 months at ꢀ35 °C. An X-ray
structural study (see the Supporting Information) shows 11 to be
approximately a square pyramid with the imido group in the
apical position; this stucture is analogous to that of a related
tungstacyclopentane complex in the literature.9 Facile bimole-
cular decomposition is likely to be a consequence of the relatively
small size of the 3,5-dimethylimido group. There is little to no Z
selectivity for the homocoupling of 1-hexene with 9b at room
temperature (entry 3) or at 0 °C (entry 4) as a consequence of
the lower steric demand of the OTPP ligand compared to that of
the OHIPT ligand.
The speed and conversion of homocoupling can be improved
by performing the reaction in neat substrate (Table 2). 1-Hexene,
1-octene, and methyl 10-undecenoate are homocoupled in
45ꢀ89% yield with Z selectivities of >99%. We propose that
the substrates listed in entries 4ꢀ6 yield product with a lower Z
content as a consequence of the greater steric hindrance that is
required in the R,β-disubstituted molybdacyclobutane inter-
mediates. All homocouplings performed at elevated tempera-
tures led to relatively low yields of product as a consequence of
catalyst decomposition.
Figure 1. Thermal ellipsoid drawing of 9a. Ellipsoids are displayed at
the 50% probability level. Hydrogen atoms are omitted. Selected
distances (Å) and angles (deg): W(1)ꢀN(1) = 1.7617(18), W(1)ꢀN-
(2) = 2.0536(16), W(1)ꢀO(1) = 1.9713(13), W(1)ꢀC(81) =
2.0697(19), W(1)ꢀC(82) = 2.353(2), W(1)ꢀC(83) = 2.0428(19);
W(1)ꢀN(1)ꢀC(51) = 176.83(16), W(1)ꢀO(1)ꢀC(1) = 160.80(13),
N(1)ꢀW(1)ꢀC(81) = 91.28(8), N(1)ꢀW(1)ꢀC(83) = 94.32(8),
C(81)ꢀW(1)ꢀC(83) = 83.91(8).
A variety of bispyrrolide species (7aꢀc) could be prepared
from 6, as shown in Scheme 2. Tungsten MAP species (8a,b) are
generated in good yields, while two species of type 8 were turned
into the more crystalline and readily isolated metallacyclobutane
complexes (9) by exposing a solution of 8 to an ethylene atmosphere.
X-ray structural studies of 9a (Figure 1) and 9b (Figure 2)
show each to have the expected TBP geometry with the imido
and aryloxide ligands in apical positions. Bond distances and
angles are similar to those found for W(NAr)(C3H6)(pyr)-
(OHIPT) (Ar = 2,6-i-Pr2C6H3).4a The WꢀOꢀCipso angle is
relatively large (160.80(13)°) in 9a, consistent with significant
steric demands for the HIPTO ligand. The WꢀOꢀCipso angle
in 9b is slightly smaller (157.73(14)°), as one might expect for
the less sterically demanding OTPP ligand. In the solid state, the
3,5-dimethylphenyl and mesityl rings in 9b show an interdigi-
tated π-stacking; the C(61) C(81) distance is 3.405 Å,
3 3 3
and the W(1)ꢀN(2)ꢀC(61) angle (164.32(16)°) is reduced
from what it is in 9a (176.83(16)°) in response to the π-stacking
interaction.
Resistance of the Z double bond in the homocoupled products
toward isomerization to E for the first three substrates in Table 2
suggests that it should be possible to homocouple terminal
olefins in the presence of an internal (E)-CdC bond. This is
shown to be the case for the substrate shown in eq 1; the triolefin
product is obtained in 60% yield (eq 1) as a single E,Z,E isomer.
Formation of a high percentage of Z homocoupled products in
the presence of (E)-olefins elsewhere in the molecule has never
been observed, to the best of our knowledge.
Results for the homocoupling of 1-hexene in benzene are
shown in Table 1. W(NAr00)(C3H6)(pyr)(OHIPT) (9a) cata-
lyzes the homocoupling of 1-hexene to >99% (Z)-5-decene at
room temperature (entry 1). (Reactions were monitored until no
further change was observed.) When 8a was employed (entry 2),
a slight decrease in the Z content was observed. Conversion is
1781
dx.doi.org/10.1021/om200150c |Organometallics 2011, 30, 1780–1782
Marinescu, Smaranda C.
