A facile access to CpCr (acac)Cl and related systems

Article abstract of DOI:10.1016/S0022-328X(97)00122-8

CpCr(acac)Cl has been prepared by reacting CpCr(THF)Cl₂ with sodium acetylacetonate. Related Cr compounds containing the C₅Me₅ group and ethylacetoacetate have also been studied. Catalysts active for the polymerization of ethylene are obtained by treating these compounds with aluminium alkyls while the title compound reacts with Et₂AlCl or Et₃Al to give [CpCr(μ-Cl)Et]₂.

Full text of DOI:10.1016/S0022-328X(97)00122-8

Journal of Organometallic Chemistry 553 Ž1998. 477–479
Preliminary communication
ž
/
A facile access to CpCr acac Cl and related systems
)
Oliver Heinemann, Peter W. Jolly , Carl Kr u¨ ger, Glenn P.J. Verhovnik
Max-Planck-Institut f u¨ r Kohlenforschung, D-45466 M u¨ lheim an der Ruhr, Germany
Received 28 November 1996; received in revised form 29 January 1997
Abstract
CpCrŽacac.Cl has been prepared by reacting CpCrŽTHF.Cl2 with sodium acetylacetonate. Related Cr compounds containing the
C Me group and ethylacetoacetate have also been studied. Catalysts active for the polymerization of ethylene are obtained by treating
5
5
these compounds with aluminium alkyls while the title compound reacts with Et AlCl or Et Al to give wCpCrŽm-Cl.Etx . q 1998 Elsevier
2
3
2
Science S.A.
Keywords: Chromium; Cyclopentadienyl; Ethylene; Polymerization
3
0 years ago it was shown that CpCr
Ž
acac
.
Br in the
to give the compound as blue–green, metallic flakes
which were isolated and dried under high vacuum.
Crystals suitable for X-ray structural analysis were ob-
presence of aluminium alkyls is active for the catalytic
polymerization of ethylene w1x. As far as we are aware,
this system has received no further attention – presum-
ably because of the relative inaccessibility of the Cr
compound, which is formed in low yield as a side
tained from toluene. CpCr
70% . Satisfactory C, H, Cl and Cr analyses were
acac Cl 1 yield 9.05 g
Ž . Ž .
Ž
.
found for this and the other compounds reported. MS
q
q
product of the reaction between Cr
Ž
acac
.
and CpMgBr
Ž
100 8C
.
: mre 251
Ž
M , 75%
.
, 216
Ž
M yCl, 100%
.
,
3
w2,3x, and because of the modest activity of the catalyst.
186, 152. IR
Ž
KBr
.
: n 3100s, 1570s, 1520s, 1360s,
1
As part of an investigation of the Cr-catalyzed
1350s, 1020s, 1005s, 935s, 835s. H NMR
300 K : d 41.5 Cp , 30.6 CH, acac , y32.0
acac . Magnetic susceptibility m , Evans method,
Ž
toluene-d8,
oligomerization of alkenes w4x, we were interested in
.
Ž
.
Ž
.
Ž
Me,
preparing compounds of this type and report here a
more facile synthesis and discuss the reaction with
aluminium alkyls.
.
Ž
eff
toluene-d , 300 K
1
.
: 3.78 m . Crystal structure: see Fig.
8
B
)
Ž
a
.
. Cp Cr
Ž
acac
.
Cl
Ž
2
.
, blue rhombic crystals, yield
)
)
)
CpCr
Ž
acac
.
Cl
Ž
1
.
and Cp Cr
Ž
acac
.
Cl
Ž
2, Cp s
78%. From wCp CrCl x and sodium acetylacetonate in
2
2
q
q
C Me5. may be prepared in excellent yield by reacting
THF. MS
93% , 151, 135. IR
1360s, 935s, 805s. Magnetic susceptibility
method, toluene-d , 300 K : 3.4 m . Crystal structure:
Ž
70 8C
.
: mre 321
Ž
M , 73%
.
, 285
Ž
M yCl,
5
the appropriate dichloride with sodium acetylacetonate
in THF. A related compound 3 is the product of the
.
Ž
KBr
.
: n 2919s, 1570s, 1520s,
Ž
m , Evans
eff
reaction with sodium ethylacetoacetate
Typical experiment: CpCr THF
1.5 mmol was suspended in THF
to y30 8C. Sodium acetylacetonate
suspended in THF 100 ml
reaction mixture then stirred at room temperature for
5 h. The reaction mixture was evaporated to dryness
Ž
.
Scheme 1
Cl2 13.39 g,
200 ml and cooled
6.26 g, 51.3 mmol
.
.
.
8
B
Ž
Ž
see Fig. 1
Ž
b
.
. CpCr
Ž
MeCOCHCO Et
.
Cl
THF
75 8C : mre 281
, 197, 161, 152. IR
Ž
3
.
, blue,
Cl2 and
2
5
.
Ž
Ž
.
metallic flakes, yield 30%. From CpCr
sodium ethylacetoacetate in THF. MS
Ž
.
.
,
Ž
.
q
q
Ž
.
, was added over 2 h and the
Ž
Ž
M , 43%
KBr
.
, 246
Ž
M yCl, 12%
.
.
: n 1591s, 1515s, 1286s, 1177s, 1064s, 1019s,
1
821m. Magnetic susceptibility
toluene-d , 300 K : 3.68 mB.
Ž
m , Evans method,
eff
and the residue extracted with boiling acetone. The
.
8
extract was concentrated to 200 ml and cooled to y70 8C
Compounds 1–3 are blue–green crystalline solids
which are stable at room temperature and the crystal
structures of both 1 and 2 have been established by
)
Corresponding author.
X-ray diffraction Fig. 1 .
Ž .
0
022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

4
78
O. Heinemann et al.rJournal of Organometallic Chemistry 553 (1998) 477–479
The same compound can be prepared yield 41% by
Ž .
reacting CpCr
Ž
acac
.
Cl with Et Al in toluene at y30 8C.
3
)
)
wCp Cr
.2 mmol
molar solution in toluene, 13.6 mmol
y30 8C to room temperature as described above to give
the compound as a blue powder. Yield 1.55 g 97%
w6x.
The crystal structure of 4 has been confirmed by X-ray
diffraction Fig. 2 m-
and is related to that of wCpCr
Cl
Mex which has been reported to be the product of
Ž
m-Cl
.
Clx . Cp Cr
Ž
acac
.
Cl
Ž
1.99 g,
2
6
.
was reacted with Et AlCl
Ž
2.0 ml of a 0.68
in toluene at
2
.
Ž
.
Ž
.
Ž
.
2
Scheme 1.
Crystal data for CpCr acac Cl 1 : C H ClCrO ,
Ž . Ž .
10 12 2
triclinic, space group P1, a s 6.592
Ž
1
.
A˚ , b s
8, b s
8, Vs545.3 A˚ , Zs2, D
s
9
9
1
.122
Ž
Ž
1
.
1
A˚ , c s 9.673
8, gs91.11
Ž . Ž .
1 1
A˚ , a s 108.03
3
8.79
.
Ž
1
.
calc
y3
.53 Mg m , 2633 measured reflections, 2483 unique
used in
reflections, 2228 reflections with IG2s
I
Ž .
refinement, structure solved by direct methods, Rs
2
0
.031, R s0.041 wws1rs
Ž
F
.
x, EOFs1.87, resid-
w
o
y3
)
˚
Ž
.
Ž .
ual electron density 0.27 e A . For Cp Cr acac Cl 2 :
C H ClCrO , monoclinic, space group P2 ra, as
1
5
22
2
1
Ž
2
1
.
A˚ , bs8.439 A˚ , cs14.195 A˚ , bs
Ž . Ž .
1 2
1
1
9
4
4.069
07.73
3 y3
Ž
.
8, Vs1605.3 A˚ , Zs4, D s1.33 Mg m
,
calc
594 measured reflections, 5569 unique reflections,
148 reflections with IG2s used in refinement,
I
Ž .
structure solved by direct methods, Rs0.050, R s
w
2
0
.060 wws1rs
Ž
F
.x, EOFs2.34, residual electron
o
y3
˚
density 0.44 e A . The structures were solved by
SHELX-86 and refined anisotropically for non-hydrogen
atoms with H-atoms isotropic, Sw
Ž .
F yF minimized.
o c
For the final refinement the program GFMLX was used.
The similarity between the two structures is surpris-
)
ing: presumably the larger size of the Cp group
Ž
com-
pared to the Cp group
bond to the metal atom w5x.
Nevertheless, the two compounds react differently
.
compensates for the stronger
with aluminium alkyls: 1 reacts with Et AlCl
Ž
or Et Al
.
.
2
3
to give the dinuclear species wCpCr
Ž
m-Cl
.
Etx
Ž
4
2
)
whereas 2 reacts with Et AlCl to give wCp Cr
Ž
m-Cl
.
Clx
2
2
w6x.
wCpCr
Ž
m-Cl
.
Etx
Ž
4
.
. CpCr
50 ml
2.3 ml of a 1.87 molar solution
.
. The reaction mixture was stirred
Ž
acac
Cl 0.81 g, 3.2 mmol
. Ž .
2
was suspended in toluene
dropwise with Et AlCl
Ž
.
at y30 8C and treated
Ž
2
in toluene, 4.3 mmol
for 15 h at room temperature. The resulting red solution
was evaporated to dryness and the residue extracted
with pentane. The combined extract was concentrated to
Fig. 1. The molecular structure of Ža. CpCrŽacac.Cl Ž1. and Žb.
)
5
ml and cooled to y30 8C to give the compound as
dark violet prisms which were recrystallized from pen-
tane 5 ml at y30 8C to remove a highly viscous
impurity. Yield 0.26 g 45% . MS 40 8C : mre 333
, 305, 182, 152, 117. Magnetic sus-
: 3.5 m . Crystal structure: see Fig. 2.
Cp CrŽacac.Cl Ž2.. Selected interatomic distances Ž A˚ . and angles Ž8.:
1
1
, Cr–D 1.882, Cr–Cl 2.299Ž1., Cr–OŽ1. 1.944Ž1., OŽ1.–CŽ2.
.278Ž2., CŽ1.–CŽ2. 1.502Ž3., CŽ2.–CŽ3. 1.391Ž3., D–Cr–Cl 123.2,
Ž
.
D–Cr–OŽ1. 123.3, OŽ1.–Cr–OŽ2. 90.9Ž1., CŽ1.–CŽ2.–CŽ3. 119.9Ž2.;
, Cr–D 1.885, Cr–Cl 2.307Ž1., Cr–OŽ1. 1.967Ž2., OŽ1.–CŽ2.
Ž
.
Ž
.
2
q
Ž
M yC H , 16%
.
2
4
m
1.281Ž3., CŽ1.–CŽ2. 1.502Ž3., CŽ2.–CŽ3. 1.381Ž3., D–Cr–Cl 123.5,
D–Cr–OŽ1. 120.3, OŽ1.–Cr–OŽ2. 90.0Ž1., CŽ1.–CŽ2.–CŽ3. 119.9Ž2..
ceptibility
Ž
.
eff
B

O. Heinemann et al.rJournal of Organometallic Chemistry 553 (1998) 477–479
479
2
1
822m, 1437m, 1418m, 1385w, 1356w, 1262w, 1115w,
016m, 1003s, 802s.
1
Ž .
This behavior should be compared with that of
m-Cl
wCpCr Mex which has been shown to react further
in toluene at 60 8C to give the trinuclear species
m-CH
wCpCrClx3 w7x.
Treatment of 1 and 2 with aluminium alkyls
Et AlCl, MAO gives catalysts for the polymerization
of ethylene which are considerably more active than
w x
Ž
.
2
Fig. 2. The molecular structure of wCpCrŽm-Cl.Etx Ž4.. Selected
2
interatomic distances Ž A˚ . and angles Ž8.: Cr–D 1.910, Cr–Cl 2.343Ž1.,
Ž
.
)
Cr –Cl 2.360Ž1., Cr–CŽ6. 2.082Ž7., CŽ6.–CŽ7. 1.44Ž1., D–Cr–Cl
24.9, D–Cr–Cl 123.6, Cl–Cr–Cl 91.5Ž1., Cr–Cl–Cr) 88.5Ž1..
)
)
Ž
Et Al,
3
1
.
2
the reaction between MeCr THF
Ž .Cl and TlCp w7x. The
2
Ž
.
CpCr acac Br 1 . The most active system is
˚
Cr–Cr distance of 3.28 A indicates that 4 does not
)
Cp Cr
3 8C with an initial ethylene pressure of 50 bar this
acac ClrEt Al Cr:Al 1:300 and in toluene at
Ž . Ž .
3
contain a direct metal–metal bond and the magnetic
3
susceptibility
tiferromagnetically coupled dimer.
Crystal data for wCpCrEt .x Ž .
m-Cl 4 : C H Cl Cr ,
2 14 20 2 2
Ž
m s3.5 mB. is characteristic of an an-
4
eff
system has an activity of 4.2 = 10 mol PE mol
Cr
out in a 200 ml steel autoclave containing a solution of
y1 y1
h
. wThe polymerization reactions were carried
Ž
A˚ , bs
A˚ , b s 96.10
Ž .
1 8, V s
monoclinic, space group C2rc, as12.487
Ž
1
.
0
3
.0035 mmol of the chromium compound and 100 to
00 equiv. of the aluminium alkyl in 20 ml toluene with
A˚ , c s 15.989
Ž
.
8
1
.082
Ž
2
.
˚
1
3
y3
604.4 A , Zs4, D s1.50 Mg m , 2572 measured
calc
an initial pressure of 50 bar of ethylene at RT. After 1 h
the polymerization was quenched with 200 ml ethanol
and the polymer was filtered off, washed with ethanol
reflections, 2339 unique reflections, 1793 reflections
with IG2s
I
Ž .
used in refinement, structure solved by
direct methods, R s 0.045, R s 0.056 ww s
w
x
Ž
.
and dried under vacuum. Interestingly, CpCr acac Cl
2
1
0
rs
Ž
F
.
x, EOF s 2.15, residual electron density
o
Ž .
rEt AlCl Cr:Al 1:300 and CpCr m-Cl Et
. x
Ž
.
w
Ž
1
y3
2
2
˚
.58 e A . The structures were solved by SHELX-86 and
Ž
Ž
4 rEt AlCl Cr:Al 1:300 show comparable activity
. Ž .
2
refined anisotropically for non-hydrogen atoms with
H-atoms isotropic, Sw F yF minimized. For the
final refinement the program GFMLX was used.
m-Cl
Whereas solutions of wCpCr Etx in toluene re-
3
y1 y1
5=10 mol PE mol Cr
h
.
and the far-reaching
Ž
.
c
o
suggestion that dinuclear species play a role is being
explored further. The product of the polymerization is
Ž
.
2
Ž
.
in all cases linear polyethylene crystallinity 65–70%
act further at 60 8C to give Cp Cr and wCpCrCl x , in
2
2 2
having a melting point of ca. 130 8C.
the solid a slow rearrangement occurs at room tempera-
ture to give a red–violet dinuclear species, which is
provisionally
adequate for a structure determination
Cp Cr2Žm-Cl. Žm-Et. Ž . ŽEq. .. from the mass spec-
tral data and a comparison of the IR spectroscopic data
Ž
we are still attempting to grow crystals
References
.
identified as
5
Ž
1
2
2
w1x Y. Tajima, K. Tani, S. Yuguchi, J. Polym. Sci., Polym. Lett. 3B
Ž1965. 529.
)
with those for wCp Cr
Ž
m-Et
.
x2 whose structure has been
w x
2 J.C. Thomas, Chem. Ind. London 1956 1388.
Ž
. Ž
.
established by X-ray diffraction w8x.
w3x J.C. Thomas, US Patent 3,030,399, du Pont, 1962; Chem. Abstr.
5
7 Ž1962. 13802g.
Ž
CpCr. Žm-Cl. Žm-Et. Ž
5
.
: wCpCr
Ž
m-Cl
.
Etx
Ž
0.18 g,
2
2
.
2
w4x P.W. Jolly, Acc. Chem. Res. 29 Ž1996. 544.
w5x F.G. Bordwell, M.J. Bausch, J. Am. Chem. Soc. 105 Ž1983.
0
.5 mmol
was stored under argon for 2 months at room
temperature during which time the crystals changed
color from violet to blue. The solid was dissolved in
pentane to give a blue solution which was filtered and
cooled to y30 8C to give the compound as red–violet
plates which were washed with pentane at y78 8C and
6
188.
6
w x
F.H. K o¨ hler, J. Lachmann, G. M u¨ ller, H. Zeh, H. Brunner, J.
Pfauntsch, J. Wachter, J. Organomet. Chem. 365 Ž1989. C15;
D.S. Richeson, J.F. Mitchell, K.H. Theopold, Organometallics 8
Ž1989. 2570.
w7x D.S. Richeson, S.-W. Hsu, N.H. Fredd, G. Van Duyne, K.H.
dried under high vacuum. Yield 0.13 g
Ž
79%
.
. MS
Theopold, J. Am. Chem. Soc. 108 Ž1986. 8273.
q
q
Ž
40 8C
.
: mre 332
Ž
M yH, 9%
.
, 304
Ž
M yEt, 18%
.
,
w8x R.A. Heintz, R.L. Ostrander, A.L. Rheingold, K.H. Theopold, J.
Am. Chem. Soc. 116 Ž1994. 11387.
1
82, 152, 117. IR
Ž
KBr
.
: n 3101m, 2919m, 2851m,