Communications
Organometallics, Vol. 18, No. 8, 1999 1361
F igu r e 2. Treatment of CrCl3 with 3 gave 4 in 68% yield
(Ar ) 3,5-C6H3Me2, Ad ) 2-adamantylidene). (i) Compound
4 was found to react with pyridine to give 5 as blue needles
(81% yield). Other Lewis bases (triethylphosphine, tet-
rahydrothiophene) failed to react with 4.
F igu r e 3. Drawing of Cr(THF)(C[Ad]Ar)3 (4) (35% prob-
ability ellipsoids). Selected distances (Å) and angles (deg):
Cr(1)-O, 2.174(4); Cr(1)-C(1), 2.039(7); Cr(1)-C(2),
2.048(6); Cr(1)-C(3), 2.055(7); C(1)-Cr(1)-C(2), 104.7(3);
C(1)-Cr(1)-C(3), 112.3(3); C(2)-Cr(1)-C(3), 106.0(3);
C(1)-Cr(1)-O, 97.3(2); C(2)-Cr(1)-O, 130.4(2); C(3)-
Cr(1)-O, 105.6(2).
was sequentially brominated and dehydrohalogenated
to give the corresponding bromoolefin 2,9 which in turn
was converted to the Grignard reagent 3 upon refluxing
with magnesium turnings in THF. Grignard 3 was
isolated as a white powder consisting of a presumed
mixture of Mg(C[Ad]Ar)2(THF)x and Mg(C[Ad]Ar)(Br)-
(THF)x.10
netic moment of 3.67 µB, as measured by SQuID
magnetometry, indicative of a high spin d3 system. The
visible spectrum in C6H6 consists of a single broad band
at λ 590 nm (ꢀ 1300 M-1 cm-1).
The chromium trisalkenyl compound Cr(THF)(C[Ad]-
Ar)3 (4) was prepared by reaction of the Grignard
reagent 3 with anhydrous CrCl3 in diethyl ether (Figure
2). Addition of dioxane and filtration of the mixture,
followed by partial removal of volatile components,
provided 4 in 68% yield as blue crystals.11 The com-
pound is paramagnetic and exhibits a solid-state mag-
The solid-state structure of Cr(THF)(C[Ad]Ar)3 is
shown in Figure 3.12 The THF is located in a pocket
comprised of the three aryl rings. The Cr-C bond
lengths are 2.039(7), 2.048(6), and 2.055(7) Å. These
distances compare well with the value of 2.07(1) Å found
for Cr(CH[SiMe3]2)3.5 In comparing the Cr-C bond
lengths to those found in other chromium alkenyl
compouds, the bond lengths are similar to those in
Cr(C[CMe2]Ph)4 (2.049(12), 2.027(13), 2.032(13), and
2.033(11) Å)3 and shorter than the length found in the
much more electron-rich Cr(CMedCMeCH2CHdCH2 )-
(C3H5)(PMe3)2 (2.113(5) Å).13 The CdC bond lengths are
unexceptional and are 1.347(9), 1.323(8), and 1.349(9)
Å. The issue of donation of π electron density from the
double bond into empty metal orbitals, or conversely
π-backbonding, has previously been investigated by
comparison of the solid-state structures of Cr(C[CMe2]-
Ph)4 and Sn(C[CMe2]Ph)4. It was concluded that there
is a real, but statistically insignificant, lengthening of
the CdC double bonds in the chromium structure as
compared to the tin structure.3
(9) Synthesis of 2: olefin 1 (58.4 g, 0.23 mol) was dissolved in CH2-
Cl2 (500 mL). Br2 (13 mL, 40.7 g, 0.25 mol, 1.1 equiv) was dissolved in
CH2Cl2 to give a total volume of 100 mL. The bromine solution was
SLOWLY added to the stirring solution of 1. The reaction mixture was
stirred for 1.5 h, concentrated, and brought into the glovebox. Dry THF
(500 mL) was added, and the solution was chilled. To the chilled
solution was added KOtBu (32 g, 0.29 mol, 1.25 equiv), the flask was
closed, and the mixture was allowed to stir overnight under N2. The
reaction mixture was concentrated and added to a mixture of water
(400 mL) and diethyl ether (400 mL). The organic layer was then
washed with water (200 mL), and the combined aqueous layers were
washed with ether (100 mL). The combined organic extracts were dried
with MgSO4 and concentrated. The crude solid 2 was then recrystal-
lized from boiling methanol (2 L). The crystalline product was then
dried in vacuo overnight (59.6 g, 78%). 1H NMR (C6D6, 300 MHz): δ
1.5-1.9 (m, 12H, adamantyl H), 2.07 (s, 6H, aryl methyl), 2.85 (s, 1H,
adamantyl), 3.55 (s, 1H, adamantyl), 6.68 (s, 1H, aryl), 7.07 (s, 2H,
aryl).
(10) Synthesis of 3: bromide 2 (38.05 g, 0.114 mol) was dissolved
in dry THF (200 mL), and 10 mL of the solution was cannula-
transferred onto Mg turnings (6 g, 0.25 mol). The reaction mixture
was heated until initiation began, at which point the cannula transfer
was completed. The reaction mixture was refluxed for 1 h, cooled, and
brought into the glovebox. It was filtered through a Bu¨chner funnel
with additional THF (100 mL) and concentrated to yield a yellow oil.
The oil was slurried in pentane (100 mL) to give a white solid, which
was collected on a filter frit (52.05 g, 91%) One-pulse 1H NMR indicated
the product to be a mixture of Mg(C[Ad]Ar)(Br)(THF)x (δ 2.25 for aryl
methyl H) and Mg(C[Ad]Ar)2(THF)x (δ 2.31 for aryl methyl H).
(11) Synthesis of 4: Grignard 3 (12.9 g, 0.026 mol, 3.0 equiv) and
anhydrous CrCl3 (1.7 g, 0.011 mol, 1.25 equiv) were slurried in diethyl
ether (500 mL). The suspension was allowed to stir for 48 h. Dioxane
(10 mL) was added, the reaction mixture was allowed to stir for an
additional 2 h, and then the solid was allowed to settle. The mixture
was filtered through Celite, washed with diethyl ether (40 mL), and
concentrated to 100 mL. After standing for 2 h the mixture was once
again filtered to collect 4 as blue crytals (5.1 g, 68%). Anal. Calcd for
To address the question of Cr-C π-bonding in 4, we
performed density functional theory (DFT) calcula-
tions14 on the hypothetical molecule Cr(OMe2)(vinyl)3
(7) using the core bond angles found in the X-ray
structure for 4. These calculations, the results of which
are summarized in Table 1 (see also Figure 4), reveal
(12) Crystal Data. 4: C61H77CrO, Mw ) 878.23, triclinic P1h, a )
11.3534(10) Å, b ) 11.6451(10) Å, c 20.165(2) Å, R ) 76.556(2)°, â )
77.9370°, γ ) 73.5660(10)°, V ) 2457.5(4) Å3, Z ) 2, Dcalc ) 1.187 Mg/
m3, absorption coefficient 0.274 mm-1, F(000) ) 950, number of
reflections collected ) 7262, number of independent reflections ) 4531,
GOF ) 1.234, R ) 0.0762, wR2 ) 0.1372.
C
61H77CrO: C, 83.42; H, 8.84. Found: C, 83.33 H, 8.99. µeff (SQuID) )
(13) Betz, P.; J olly, P. W.; Kruger, C.; Zakrzewski, U. Organome-
tallics 1991, 10, 3520.
3.67 µB.