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Kuiper et al.
Scheme 1
2 Na(silox)
.31 Et20
- CI
12 h, 65C
3 Na(silox)
Et20 -3NaCI
12 h, 65C
CI
tBu 3SiO
Mo ~OSitBu3
tBu3SiO
15% CI + ........
CI 2-Mo
I-
60% pure
tu3SiO Mo -OsitBu3
tBu3SiO + .
CI 2-Mo
Na/Hg t
.........II', tBu3Si M
Et2 Mo ----SitBu3
- NaCI tBu3SiO 60%
(unoptimized)
- PMe3 4 h, 10-3 torr
100C
CI
PMe3
pentane
5 min, 23C
tBu3SiO,, I
Mo - OSitBu3
tBu3SiO/
precipitate
PMe3 IMoPMe
2-MoPMe3
THF
, CI THF
THF Mo CI 12 h, 60C
CI + -2 NaCI
THF 2 Na(silox)
third row complexes lowers the energy of 5dz2 to a greater
extent than 4dZ2 is similarly lowered in second-row transition-
metal complexes.
Similar metric parameters of 4d and 5d metals (i.e.,
covalent radii, bond distances, and angles, etc.) can often
belie reactivity patterns3-11 that derive from differences in
electronic structure in which ndz2/(n + 1)s mixing is critical.
For example, different rates of olefin dissociation in
(silox)3M(olefin) and association to (silox)3M (M = Nb, Ta;
silox = tBu3SiO) were traced to the higher density of states
of niobium versus tantalum.1'0 The stability of (silox)3Ta
relative to (silox)3Nb - a plausible species that has never
been directly observed - may stem from the relatively lower
energy of 5dz2, whose torus is attenuated from mixing with
the 6s. Investigations of oxygen atom transfer to d2 (silox)3M
(M = V, NbL (L = 4-picoline, PMe3), Ta revealed orbital
symmetry constraints in which the energy of the dz2 orbital
plays a prominent role."
Previous studies manifested reactivity trends that revealed
the importance of ndz2/(n + 1)s mixing, but evidence that
such electronic factors have an impact on ground-state
geometry was lacking. In three-coordinate molecules, changes
(3) (a) Poli, R.; Cacelli, I. Eur. J. Inorg. Chem. 2005, 12, 2324-2331. (b)
Petit, A.; Cacelli, I.; Poli, R. Chem.-Eur. J. 2006, 12, 813-823.
(4) (a) Carreon-Macedo, J.; Harvey, J. N.; Poli, R. Eur. J. Inorg. Chem.
2005, 12, 2999-3008. (b) Smith, K. M.; Poli, R.; Harvey, J. N.
Chem.-Eur. J. 2001, 7, 1679-1690.
(5) Carreon-Macedo, J. L.; Harvey, J. N. J. Am. Chem. Soc. 2004, 126,
5789-5797.
(6) (a) Poli, R. J. Organomet. Chem. 2004, 689, 4291-4304. (b) Poli, R.
Acc. Chem. Res. 1997, 30, 1861-1866.
(7) (a) Harvey, J. N.; Poli, R.; Smith, K. M. Coord. Chem. Rev. 2003,
238, 347-361. (b) Poli, R.; Harvey, J. N. Chem. Soc. Rev. 2003, 32,
1-8. (c) Harvey, J. N.; Poli, R. Dalton Trans. 2003, 4100-4106.
(8) (a) Harvey, J. N. Struct. Bonding 2004, 112, 151-183. (b) Harvey,
J. N. Phys. Chem. Chem. Phys. 2007, 9, 331-343. (corr. 541)
(9) Matsunaga, N.; Koseki, S. Rev. Comput. Chem. 2004, 20, 101-152.
(10) K. F., Hirsekorn.; E. B, Hulley.; P. T., Wolczanski.; T. R., Cundari.
J. Am. Chem. Soc. 2008, 130, 1183-1196.
(11) Veige, A. S.; Slaughter, L. M.; Lobkovsky, E. B.; Wolczanski, P. T.;
Matsunaga, N.; Decker, S. A.; Cundari, T. R. Inorg. Chem. 2003, 42,
6204-6224.
7140 Inorganic Chemistry, Vol. 47, No. 16, 2008
CI
112 OSitBu3 13-M
tBu3SiO weMo Mo 60%
tBu3SiOitu3
OSitBu3
in the torus of dz2 do not effect the general trigonal geometry
observed.10,11 In higher-coordinate species, the orbital is o*
and empty, and its filled, bonding counterpart is unlikely to
be the origin of a geometric difference. For example, in
coordination chemistry studies of biological relevance,
molybdenum and tungsten are often complementary in model
complexes in part because the metric parameters in relevant
5- and 6-coordinate compounds are so similar.12-14 In
4-coordinate species, second- and third-row complexes have
the capability of exhibiting substantial changes in geometry
due to the greater involvement of dz2 in bonding; it may be
filled in square planar systems and empty in pseudotetrahe-
dral arrangements, depending on the dn count. Cummins
observed a modest structural effect - a greater planarity for
tungsten versus molybdenum in M(enolate)4 species - that
hinted at the possibility of greater conformational deviations
between second- and third-row transition-metal complexes.15
Herein is described the synthesis and characterization of a
several (silox)3MoX/R and (silox)3WX/R compounds that
exhibit profound structural differences that can be traced to
ndz2/(n + 1)s mixing.
Results
Syntheses of (silox)3MCl,. 1. Molybdenum. As Scheme
1 illustrates, various molybdenum chlorides have been
prepared depending on stoichiometry and starting material.
Treatment of trans-(Et20)2MoC1416 with 2 equiv of Na(silox)
(12)
(13)
(14)
(15)
(16)
Enemark, J. H.; Cooney, J. J. A. Chem. Rev. 2004, 104, 1175-1200.
(a) Tenderholt, A. L.; Szilagyi, R. K.; Holm, R. H.; Hodgson, K.;
Hedman, B.; Solomon, E. J. Inorg. Biochem. 2007, 101, 1594-1600.
(a) Groysman, S.; Holm, R. H. Inorg. Chem. 2007, 46, 4090-4102.
(b) Wang, J. J.; Tessier, C.; Holm, R. H. Inorg. Chem. 2006, 45, 2979-
2988. (c) Wang, J. J.; Kryatova, O. P.; Rybak-Akimova, E. V.; Holm,
R. H. Inorg. Chem. 2004, 43, 8092-8101. (d) Partyka, D. V.; Staples,
R. J.; Holm, R. H. Inorg. Chem. 2003, 42, 7877-7886.
Soo, H. S.; Figueroa, J. S.; Cummins, C. C. J. Am. Chem. Soc. 2004,
126, 11370-11376.
Stoffelbach, F.; Saurenz, D.; Poli, R. Eur. J. Inorg. Chem. 2001, 2699-
2703.
OEt2
C
CI Mo-
CI
OEt2
