The first structurally characterized homoleptic aryl-manganese(III) compound and the corresponding isoleptic and isoelectronic chromium(II) derivative

Article abstract of DOI:10.1021/om050206e

The homoleptic organochromium(II) compound [Mg(THF)₆] [Cr ^IIC₆F₅)₄] (1) was obtained as an extremely air-sensitive solid by reaction of [CrC]₂(THF)] with C ₆F₅MgBr. The arylation of MnBr₂ under similar conditions proceeded with oxidation of the metal center to give [Mg(THF) ₆][Mn^III(C₆F₅)₄] ₂ (2). The crystal structures of 1 and 2 (X-ray diffraction) contain the anions [Cr(C₆F₅]^2- and [Mn(C ₆F₅)₄]^-, respectively, both with approximate square-planar (SP-4) geometry around the metal center. In the solid state there is no sign of any covalent interaction or ion-pairing between these anions and the virtually octahedral (OC-6) [Mg(THF)₆]²⁺ cations. The average Mn^III-C distance in 2, 2.068(4) A, is slightly shorter than the mean Cr^II-C bond length in 1, 2.158(6) A, a fact that can be attributed mainly to the different oxidation states of the metal centers in each case. The use of 2 as an initiator itself and as a weakly coordinating anion in Pd-catalyzed polymerization processes of strained olefins has also been assayed.

Full text of DOI:10.1021/om050206e

3266
Organometallics 2005, 24, 3266-3271
The First Structurally Characterized Homoleptic
Aryl-Manganese(III) Compound and the Corresponding
Isoleptic and Isoelectronic Chromium(II) Derivative
Juan Fornie´s,* Antonio Mart´ın, L. Francisco Mart´ın, and Babil Menjo´n
Instituto de Ciencia de Materiales de Arago´n, Facultad de Ciencias, Universidad de
Zaragoza-CSIC, C/Pedro Cerbuna 12, E-50009 Zaragoza, Spain
Hongshi Zhen, Andrew Bell, and Larry F. Rhodes
Promerus LLC, 9921 Brecksville Road, Brecksville, Ohio 44141
Received March 18, 2005
The homoleptic organochromium(II) compound [Mg(THF)6][CrII(C6F5)4] (1) was obtained
as an extremely air-sensitive solid by reaction of [CrCl2(THF)] with C6F5MgBr. The arylation
of MnBr2 under similar conditions proceeded with oxidation of the metal center to give [Mg-
(THF)6][MnIII(C6F5)4]2 (2). The crystal structures of 1 and 2 (X-ray diffraction) contain the
anions [Cr(C6F5)4]2- and [Mn(C6F5)4]-, respectively, both with approximate square-planar
(SP-4) geometry around the metal center. In the solid state there is no sign of any covalent
interaction or ion-pairing between these anions and the virtually octahedral (OC-6) [Mg-
(THF)6]2+ cations. The average MnIII-C distance in 2, 2.068(4) Å, is slightly shorter than
the mean CrII-C bond length in 1, 2.158(6) Å, a fact that can be attributed mainly to the
different oxidation states of the metal centers in each case. The use of 2 as an initiator itself
and as a weakly coordinating anion in Pd-catalyzed polymerization processes of strained
olefins has also been assayed.
Introduction
different stoichiometries, nuclearities, and global charges,
such as [MnR2] [R ) CH2CMe3,6 CH2(adamant-1-yl),7
C(SiMe3)3,8 C6H2(CMe3)3-2,4,69], [Mn2R4] (R ) CMe2-
Ph),5 [Mn3R6] (R ) C6H2Me3-2,4,6),10 [Mn4R8] (R ) CH2-
CMe3),6 [{MnR2}n] (R ) CH2SiMe3),5 [MnR3]- (R ) Me,11
Et,12 nBu,12 C6H2Me3-2,4,613,14), [Mn2R6]2- (R ) Ph),13
The inorganic and coordination chemistry of Mn is
dominated by chemical species with the metal in oxida-
tion state II.1 This oxidation state is not uncommon in
organomanganese chemistry either; however most or-
ganoderivatives of Mn contain the metal in lower
oxidation states: 1, 0, or negative values.2,3 This is
mainly due to extensive and continued research carried
out for several decades on the chemistry of Mn carbonyl
compounds related directly or, at least, formally with
the prototypical species [Mn2(CO)10].3 The preparation4
of [MnCp2] marked a milestone in organomanganese-
(II) chemistry, but it was the seminal work of G.
Wilkinson and co-workers on homoleptic alkyl manga-
nese(II) compounds that made a real breakthrough in
this area.5 A good number of homoleptic σ-organoman-
ganese(II) compounds are currently available, showing
n
and [MnR4]2- (R ) Me,5,15,16 Et, Bu, CH2CH2CMe3,16
CH2SiMe3,5,16 CH2NC5H10,17 Ph,16 C6H4Me-2,18 alky-
nyl19). In contrast to this well-developed chemistry, the
corresponding homoleptic σ-organomanganese(III) de-
rivatives are extremely rare. The only representative
of this kind of compound for which the molecular
geometry has been unambiguously established is, as far
(6) [Mn(CH2CMe3)2] was found to be mononuclear in the gas
phase: Andersen, R. A.; Haaland, A.; Rypdal, K.; Volden, H. V. J.
Chem. Soc., Chem. Commun. 1985, 1807. For a preliminary account
on the tetrameric structure found in the solid state by single-crystal
X-ray diffraction, [Mn4(CH2CMe3)8], see ref 5a.
(7) Bochmann, M.; Wilkinson, G.; Young, G. B. J. Chem. Soc., Dalton
Trans. 1980, 1879.
* To whom correspondence should be addressed. E-mail:
juan.fornies@unizar.es.
(8) Buttrus, N. H.; Eaborn, C.; Hitchcock, P. B.; Smith, J. D.;
Sullivan, A. C. J. Chem. Soc., Chem. Commun. 1985, 1380.
(9) Wehmschulte, R. J.; Power, P. P. Organometallics 1995, 14, 3264.
(10) Solari, E.; Musso, F.; Gallo, E.; Floriani, C.; Re, N.; Chiesi-Villa,
A.; Rizzoli, C. Organometallics 1995, 14, 2265. Gambarotta, S.;
Floriani, C.; Chiesi-Villa, A.; Guastini, C. J. Chem. Soc., Chem.
Commun. 1983, 1128.
(1) McAuliffe, C. A.; Godfrey, S. M.; Watkinson, M. In Encyclopedia
of Inorganic Chemistry; King, R. B., Ed.; John Wiley & Sons: Chich-
ester, UK, 1994; Vol. 4, pp 2075-2085.
(2) Sweigart, D. A. In Encyclopedia of Inorganic Chemistry; King,
R. B., Ed.; John Wiley & Sons: Chichester, UK, 1994; Vol. 4, pp 2085-
2101.
(11) Beermann, C.; Clauss, K. Angew. Chem. 1959, 71, 627.
(12) Reimschneider, R.; Kassahn, H.-G.; Schneider, W. Z. Natur-
forchs., Teil B 1960, 15, 547.
(3) Treichel, P. M. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier Science
Ltd.: Oxford, UK, 1995; Vol. 6, Chapter 1, pp 1-19.
(4) Wilkinson, G.; Cotton, F. A.; Birmingham, J. M. J. Inorg. Nucl.
Chem. 1956, 2, 95. Wilkinson, G.; Cotton, F. A. Chem. Ind. (London)
1954, 307.
(5) (a) Andersen, R. A.; Carmona-Guzma´n, E.; Gibson, J. F.; Wilkin-
son, G. J. Chem. Soc., Dalton Trans. 1976, 2204. (b) Andersen, R.;
Carmona-Guzma´n, E.; Mertis, K.; Sigurdson, E.; Wilkinson, G. J.
Organomet. Chem. 1975, 99, C19.
(13) Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Shoner, S. C.
Organometallics 1988, 7, 1801.
(14) Seidel, W.; Bu¨rger, I. Z. Chem. 1977, 17, 31.
(15) Morris, R. J.; Girolami, G. S. J. Am. Chem. Soc. 1988, 110, 6245.
(16) Morris, R. J.; Girolami, G. S. Organometallics 1989, 8, 1478.
(17) Steinborn, D. Z. Chem. 1976, 16, 328.
(18) Morris, R. J.; Girolami, G. S. Organometallics 1991, 10, 799.
(19) Nast, R.; Griesshammer, H. Chem. Ber. 1957, 90, 1315.
10.1021/om050206e CCC: $30.25 © 2005 American Chemical Society
Publication on Web 05/24/2005

Homoleptic Aryl-Manganese(III) Compound
Organometallics, Vol. 24, No. 13, 2005 3267
Table 1. Summary of Crystallographic Data and
as we know, the square-planar (SP-4) anion
[MnIIIMe4]-.20 A square-pyramidal (SPY-5) structure
Structure Refinement for 1‚2THF and 2‚3C4H8O2
has been suggested for the anion [MnIIIMe5]2- 15,20
while
,
1‚2THF
2‚3C4H8O2
we are not aware of any structural proposal having been
put forward for the metallacyclic anions [MnIII(CH2-
CH2CH2CH2-κC1,κC4)2]- and [MnIII(C6H4OC6H4-κC2,
κC2′)2]-.21,22 This paucity has been related with the lack
of suitable synthetic precursors20 and, on the other
hand, with the tendency of many MnIII compounds to
undergo disporportionation into MnII and MnIV species.
We report now on a reasonably stable tetraarylmanga-
nate(III) salt together with the corresponding isoleptic
and isoelectronic chromium(II) derivative.
empirical formula
fw
C56H64CrF20MgO8 C84H72F40MgMn2O12
1321.38
71.073
monoclinic
C2/c
2167.60
71.073
triclinic
P1h
λ (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
15.848(2)
16.147(2)
22.643(2)
90
98.751(2)
90
13.212(1)
13.281(1)
14.499(1)
111.854(2)
108.778(2)
92.750(2)
2195.0(4)
1
5727(1)
4
Z
dc (g cm-3
F(000)
)
1.533
1.640
Results and Discussion
2720
2188
0.440
µ (mm-1
)
0.330
Synthesis. The low-temperature reaction of [CrCl2-
(THF)] with C6F5MgBr in a 1:1 mixture of Et2O and
THF takes place under full arylation of the metal center
(eq 1). Addition of 1,4-dioxane to the reaction medium
does not produce the expected removal of the magne-
sium ions in an efficient way, since the salt [Mg(THF)6]-
[CrII(C6F5)4] (1) still remains dissolved at -30 °C. From
these solutions, complex 1 can be isolated as an ex-
tremely air- and moisture-sensitive green solid in
moderate yield.
θ range (deg)
1.81-25.08
-17 e h e 18
-19 e k e 12
-26 e l e 25
15 263
1.80-25.06
-15 e h e 11
-15 e k e 15
-12 e l e 17
12 971
index range
no. of reflns
collected
no. of unique reflns 5044 (Rint
)
7637 (Rint )
0.0496)
0.0356)
refinement method
final R indices
[I > 2σ(I)]a
full-matrix least-squares on F2
R1 ) 0.0546,
wR2 ) 0.1125
R1 ) 0.1024,
wR2 ) 0.1218
1.037
R1 ) 0.0604,
wR2 ) 0.1004
R1 ) 0.1067,
wR2 ) 0.1086
1.031
R indices (all data)
[CrCl2(THF)] + C6F5MgBr THF/Et O8
2
GOFb on F2
a R1 ) ∑(|Fo| - |Fc|)/∑|Fo|; wR2 ) [∑w(Fo2 - Fc )2/∑w(Fc )2]1/2; w
2
2
[Mg(THF)6][Cr(C6F5)4]
(1)
) [σ2(Fo2) + (g1P)2 + g2P]-1; P ) (1/3)‚[max{Fo2,0} + 2Fc ].
2
1
2
2
b Goodness-of-fit ) [∑w(Fo - Fc )2/(nobs - nparam)]1/2
.
The reaction of MnBr2 with C6F5MgBr under similar
conditions proceeds not only with full arylation but also
with oxidation of the metal center (eq 2). From the
reaction medium, the salt [Mg(THF)6][MnIII(C6F5)4]2 (2)
could be isolated as a brown solid in moderate yield.
Table 2. Selected Interatomic Distances (Å) and
Angles (deg) and Their Estimated Standard
Deviations for 1‚2THF
Anion
Cr-C(1)
2.157(4)
2.158(6)
2.162(5)
1.352(5)
1.368(4)
1.391(5)
1.365(4)
1.367(5)
1.372(4)
1.371(5)
1.372(4)
C(1)-Cr-C(1′)
C(1)-Cr-C(7)
C(1′)-Cr-C(7)
C(1)-Cr-C(11)
C(1′)-Cr-C(11)
C(7)-Cr-C(11)
Cr-C(1)-C(2)
Cr-C(1)-C(6)
C(2)-C(1)-C(6)
Cr-C(7)-C(8)
C(8)-C(7)-C(8′)
Cr-C(11)-C(12)
C(12)-C(11)-C(12′)
179.6(2)
89.8(1)
Cr-C(7)
Cr-C(11)
C(1)-C(2)
C(2)-F(2)
C(1)-C(6)
C(6)-F(6)
C(7)-C(8)
C(8)-F(8)
C(11)-C(12)
C(12)-F(12)
89.8(1)
MnBr2 + C6F5MgBr THF/Et O8
2
90.2(1)
90.2(1)
[Mg(THF)6][Mn(C6F5)4]2
(2)
180.000(1)
122.2(3)
125.3(3)
112.5(3)
124.1(3)
111.7(5)
123.7(2)
112.5(5)
2
The preparation of MnIII derivatives starting from
lower-valent precursors (typically MnII compounds) is
well documented. The most common oxidant in such
processes is molecular oxygen,18 but some other oxida-
tion mechanisms have also been reported, such as the
reductive coupling of ethylene to give the 1,4-butanediyl
ligand present in the oily species [K(THF)x][MnIII(CH2-
CH2CH2CH2-κC1,κC4)2] or in its pyridine adduct [K(py)2]-
[MnIII(CH2CH2CH2CH2-κC1,κC4)2(py)].21 The formation
of the MnIII complex 2 could also be due to dispropor-
tionation of some nondetected perfluorophenyl-manga-
nese(II) intermediate species. In any case, the nature
of the oxidation agent enabling eq 2 to proceed is still
unclear.
Cation
Mg-O(1)
2.093(2)
2.077(2)
2.103(3)
1.462(4)
1.466(4)
1.463(4)
1.453(4)
1.462(5)
1.467(4)
O(1)-Mg-O(2)
O(1)-Mg-O(2′)
O(1)-Mg-O(3)
O(1)-Mg-O(3′)
O(2)-Mg-O(3)
O(2)-Mg-O(3′)
Mg-O(1)-C(15)
Mg-O(1)-C(18)
C(15)-O(1)-C(18)
Mg-O(2)-C(19)
Mg-O(2)-C(22)
C(19)-O(2)-C(22)
Mg-O(3)-C(23)
Mg-O(3)-C(26)
C(23)-O(3)-C(26)
90.20(9)
89.80(9)
89.62(9)
90.38(9)
90.9(1)
Mg-O(2)
Mg-O(3)
O(1)-C(15)
O(1)-C(18)
O(2)-C(19)
O(2)-C(22)
O(3)-C(23)
O(3)-C(26)
89.1(1)
126.0(2)
126.3(2)
107.6(2)
124.1(2)
127.2(2)
108.6(3)
125.0(2)
127.1(2)
107.8(3)
Characterization. Compounds 1 and 2 were identi-
fied by analytical and spectroscopic methods. Their
crystal and molecular structures were also established
by X-ray diffraction methods on single crystals of
1‚2THF and 2‚3C4H8O2, respectively (crystal data given
in Table 1). A selection of interatomic distances and
angles for 1 and 2 are collected in Tables 2 and 3,
respectively. The crystal lattices of both 1‚2THF and 2‚
3C4H8O2 are made of separate ions [Mg(THF)6]2+ and
(20) Morris, R. J.; Girolami, G. S. Organometallics 1991, 10, 792.
(21) Jonas, K.; Ha¨selhoff, C.-C.; Goddard, R.; Kru¨ger, C. Inorg. Chim.
Acta 1992, 198-200, 533. Jonas, K.; Burkart, G.; Ha¨selhoff, C.; Betz,
P.; Kru¨ger, C. Angew. Chem., Int. Ed. Engl. 1990, 29, 322.
(22) Drevs, H. Z. Chem. 1975, 15, 451.

3268 Organometallics, Vol. 24, No. 13, 2005
Fornie´s et al.
Table 3. Selected Interatomic Distances (Å) and
Angles (deg) and Their Estimated Standard
Deviations for 2‚3C4H8O2
Anions
Mn(1)-C(1)
Mn(1)-C(7)
C(1)-C(2)
2.072(4) Mn(2)-C(13)
2.061(4) Mn(2)-C(19)
1.372(6) C(13)-C(14)
1.354(5) C(14)-F(14)
1.365(5) C(13)-C(18)
1.350(5) C(18)-F(18)
1.386(5) C(19)-C(20)
1.354(5) C(19)-C(24)
1.371(6) C(20)-F(20)
1.353(5) C(24)-F(24)
2.078(4)
2.061(4)
1.374(5)
1.366(5)
1.366(5)
1.358(4)
1.367(5)
1.373(5)
1.367(4)
1.369(4)
C(2)-F(2)
C(1)-C(6)
C(6)-F(6)
C(7)-C(8)
C(8)-F(8)
C(7)-C(12)
C(12)-F(12)
C(1)-Mn(1)-C(7)
89.7(2)
C(13)-Mn(2)-C(19) 87.5(2)
C(13)-Mn(2)-C(19′) 92.5(2)
C(1)-Mn(1)-C(7′) 90.3(2)
Mn(1)-C(1)-C(2) 129.3(4)
Mn(1)-C(1)-C(6) 116.2(3)
Mn(2)-C(13)-C(14) 124.9(3)
Mn(2)-C(13)-C(18) 121.3(3)
C(14)-C(13)-C(18) 113.6(4)
Mn(2)-C(19)-C(20) 128.3(3)
Mn(2)-C(19)-C(24) 117.7(3)
C(20)-C(19)-C(24) 113.7(4)
C(2)-C(1)-C(6)
114.5(4)
Figure 1. Thermal ellipsoid diagram (50% probability) of
the [CrII(C6F5)4]2- anion in 1‚2THF.
Mn(1)-C(7)-C(8) 124.4(3)
Mn(1)-C(7)-C(12) 121.1(3)
C(8)-C(7)-C(12) 114.4(4)
this difference of unknown origin, the vibrational be-
havior of compounds 1 and 2 is quite similar.
Cation
O(1)-Mg-O(2)
Mg-O(1)
2.085(3)
2.085(3)
2.099(3)
1.451(5)
1.462(5)
1.458(4)
1.456(5)
1.460(5)
1.461(4)
89.5(1)
90.5(1)
The structure of the mononuclear anion [CrII(C6F5)4]2-
as found in 1‚2THF is shown in Figure 1. The CrII
coordination environment can be described as square-
planar (SP-4) with no perceptible interligand angular
distortions and four virtually identical Cr-C distances
(Table 2). The small departure of the CrII first coordina-
tion sphere from ideal SP-4 geometry is evidenced by
the very low value of continuous shape measure ob-
tained,26 S(SP-4) ) 0.005.27 The molecule has crystal-
lographically imposed C2 symmetry along the C(7)-Cr-
C(11) vector, which also comprises the C(10)-F(10) and
C(14)-F(14) segments. The Cr-C(sp2) average value,
2.158(6) Å, is shorter than the mean Cr-C(sp3) distance
found in the mononuclear species [Li(TMEDA)]2[CrII-
Me4] [2.208(5) Å].28 Strong cation/anion interactions
were observed in the latter compound, where each
methyl group is, in fact, acting as an electron-deficient
bridge between the Cr center and one of the Li+ ions.
This bridging function as well as the different hybrid-
ization at the C atom could well justify the longer Cr-C
distances observed in this case. In this context, it is
interesting to note that the only crystallographically
independent Cr-C(sp2) bond distance in the related
mononuclear aryl species [CrII(C6Cl5)4]2- was found29 to
be also significantly longer [2.208(3) Å] than in 1,
despite both kinds of C-donor atoms having now the
same hybridization. Moreover, the four C6F5 groups in
1 are roughly perpendicular to the molecular plane (tilt
Mg-O(2)
O(1)-Mg-O(2′)
O(1)-Mg-O(3)
O(1)-Mg-O(3′)
O(2)-Mg-O(3)
O(2)-Mg-O(3′)
Mg-O(1)-C(25)
Mg-O(1)-C(28)
C(25)-O(1)-C(28)
Mg-O(2)-C(29)
Mg-O(2)-C(32)
C(29)-O(2)-C(32)
Mg-O(3)-C(33)
Mg-O(3)-C(36)
C(33)-O(3)-C(36)
Mg-O(3)
89.2(1)
O(1)-C(25)
O(1)-C(28)
O(2)-C(29)
O(2)-C(32)
O(3)-C(33)
O(3)-C(36)
90.7(1)
90.7(1)
89.3(1)
126.2(3)
125.8(2)
108.0(3)
125.6(2)
126.2(2)
108.2(3)
127.5(2)
125.3(2)
107.2(3)
[M(C6F5)4]q- (1, M ) Cr, q ) 2; 2, M ) Mn, q ) 1) in
the appropriate stoichiometric ratio in each case to-
gether with interstitial solvent molecules. The six
oxygen atoms of the THF ligands in the [Mg(THF)6]2+
cation define a virtually octahedral (OC-6) environment
for the Mg2+ ion. Angles between cis-coordinating
oxygen atoms do not significantly deviate from 90°, and
those between trans-coordinating oxygen atoms are
exactly 180° because of crystallographically imposed
symmetry (inversion center). All the Mg-O distances
are in a very narrow range, 2.077(2)-2.103(3) Å, similar
to those found in other salts containing the solvated
cation [Mg(THF)6]2+ 23
. The IR spectra of 1 and 2 contain
absorptions of medium to strong intensity assignable
to the stretching vibrations of the C-O-C ether link
corresponding to the Mg-coordinated THF ligands.24
Standard patterns are observed for the vibrations
associated with the C6F5 groups,25 although no absorp-
tion could be unambiguously assigned to the X-sensitive
vibration modes in the IR spectrum of 2. In contrast, a
band of medium intensity at 765 cm-1 was observed in
the IR spectrum of 1, which can be attributed to the
referred C6F5 X-sensitive vibration mode. Aside from
angles: 74.8-88.8°), while in the anion [CrII(C6Cl5)4]2-
,
(26) For the definition and use of the continuous shape measure, S,
as a parameter quantifying the reliability with which a real coordina-
tion entity can be described by means of a given regular geometric
polyhedron, see: (a) Pinsky, M.; Avnir, D. Inorg. Chem. 1998, 37, 5575.
(b) Casanova, D.; Llunell, M.; Alemany, P.; Alvarez, S. Chem. Eur. J.
2005, 11, 1479. (c) Cirera, J.; Alemany, P.; Alvarez, S. Chem. Eur. J.
2004, 10, 190. (d) Casanova, D.; Alemany, P.; Bofill, J. M.; Alvarez, S.
Chem. Eur. J. 2003, 9, 1281. (e) Alvarez, S.; Avnir, D.; Llunell, M.;
Pinsky, M. New J. Chem. 2002, 996. (f) Alvarez, S.; Llunell, M. J.
Chem. Soc., Dalton Trans. 2000, 3288. The smaller the value of S, the
better the agreement between the real molecule and the suggested
model, being S ) 0 for perfect coincidence.
(23) See for instance: Bond, A. D.; Layfield, R. A.; MacAllister, J.
A.; McPartlin, M.; Rawson, J. M.; Wright, D. S. Chem. Commun. 2001,
1956, where the X-ray structure of [Mg(THF)6][Mn(η2-Cp)3]‚2THF is
reported.
(24) Barrow, G. M.; Searles, S. J. Am. Chem. Soc. 1953, 75, 1175.
Bellamy, L. J. The Infra-Red Spectra of Complex Molecules, 3rd ed.;
Chapman and Hall, Ltd.: London, UK, 1975; Vol. 1, Chapter 7, pp
129-140.
(25) Uso´n, R.; Fornie´s, J. Adv. Organomet. Chem. 1988, 28, 219.
Maslowsky, E., Jr. Vibrational Spectra of Organometallic Compounds;
John Wiley & Sons: New York 1977; pp 437-442.
(27) Llunell, M.; Casanova, D.; Cirera, J.; Bofill, J. M.; Alemany,
P.; Alvarez, S.; Pinsky, M.; Avnir, D. SHAPE (version 1.1); Universitat
de Barcelona (Spain) and The Hebrew University of Jerusalem (Israel).
(28) Hao, S.; Gambarotta, S.; Bensimon, C. J. Am. Chem. Soc. 1992,
114, 3556.
(29) Alonso, P. J.; Fornie´s, J.; Garc´ıa-Monforte, M. A.; Mart´ın, A.;
Menjo´n, B.; Rillo, C. Chem. Eur. J. 2002, 8, 4056.

Homoleptic Aryl-Manganese(III) Compound
Organometallics, Vol. 24, No. 13, 2005 3269
anion [MnIIIMe4]- [mean MnIII-C length: 2.078(5) Å].20
In these examples, the MnIII-C bond length appears to
be quite insensitive to the hybridization of the C-donor
atoms and to the coordination number. In contrast with
the virtually regular SP-4 geometry observed for the
[MnIII(C6F5)4]- anion in 2, the [MnIIIMe4]- anion showed
a significant tetrahedral distortion, as evidenced by the
fairly large value of the continuous shape measure
parameter, S(SP-4) ) 2.641.27 This distortion follows a
B2u vibrational mode of the ideal square plane, resulting
in a D2d spread symmetry.26c The structural differences
found in the homoleptic organomanganate(III) deriva-
tives [MnIIIR4]- (R ) Me or C6F5) cannot be assigned to
the steric requirements of the organic group. Methyl is
usually considered as a nearly spherical substituent
with a global33 van der Waals radius of 2.0 Å and a
specific value of rvdW(Caliph) ) 1.70 Å for the aliphatic C
atom.30 Aryl rings, in contrast, are highly anisotropic
groups with an effective thickness of 3.4-3.7 Å.33 The
van der Waals radius assigned to an aromatic C atom
is rvdW(Carom) ) 1.77 Å.30 Hence, it can be concluded that
steric repulsions arising between adjacent Me or per-
pendicularly arranged aryl groups in SP-4 metal com-
plexes might be comparable in magnitude.34 On the
other hand, the different polarity expected for the
MnIII-R bond considering the markedly different elec-
tron-withdrawing characters of the Me and C6F5 organic
groups might well play an important role in deciding
the most energetically favored ground-state molecular
geometry in each case. In this context it is interesting
Figure 2. Thermal ellipsoid diagram (50% probability) of
oneofthetwocrystallographicallyindependent[MnIII(C6F5)4]-
anions in 2‚3C4H8O2.
the more sterically demanding C6Cl5 groups show a
higher tilt angle with respect to the molecular plane
(68.7°). Both the longer Cr-C distance and the more
tilted perhalophenyl groups in [CrII(C6Cl5)4]2- can be
reasonably ascribed to the considerably larger size of
Cl vs F given by their corresponding effective van der
Waals radii (rvdW) in haloaryl compounds: rvdW(F) ) 1.47
Å vs rvdW(Cl) ) 1.77 Å.30 Shorter Cr-C6Cl5 bonds and
less tilted C6Cl5 rings would probably entail energeti-
cally unaffordable Cl‚‚‚Cl nonbonding interactions be-
tween adjacent ortho-Cl atoms belonging to neighboring
rings.31 The significance of avoiding such repulsive
interactions between ortho-substituents for tuning the
M-C distance in aryl-metal derivatives can be further
illustrated by comparing the Cr-C distances in the
homoleptic arylchromate(II) species: [Li(THF)2]2-
[CrII(C6H2Me3-2,4,6)4] [2.255(5) Å] vs [Li(THF)2]2[CrII-
Ph4] [mean Cr-C distance: 2.178(3) Å].32 Note that the
Cr-C distance in the later compound bearing unsub-
stituted phenyl rings is quite similar to that found in
our pentafluorophenyl derivative 1 regardless of the
sharply different degrees of cation/anion association
observed in each case.
The unit cell of 2‚3C4H8O2 contains two crystallo-
graphically independent [MnIII(C6F5)4]- anions, one of
which is depicted in Figure 2. The structural features
of these anions are very similar to those just discussed
for the isoleptic and isoelectronic [CrII(C6F5)4]2- anion
with also negligible angular distortions with respect to
the ideal SP-4 geometry. Continuous shape measure
values, S(SP-4), of 0.001 and 0.048 are obtained respec-
tively for the two crystallographically independent
metal centers Mn(1) and Mn(2).27 The average MnIII-C
distance in 2, 2.068(4) Å, is shorter by ca. 0.09 Å than
the mean CrII-C bond length in 1, 2.158(6) Å, an
observation that can be related to the different oxidation
states of the metal centers. On the other hand, similar
MnIII-C distances were found in the heteroleptic five-
coordinate species [Mn(C6H2Me3-2,4,6)Br2(PMe3)2] [2.089-
(8) Å],18 as well as in the permethylmanganate(III)
to note that the four S-donor atoms in the [MnIII
-
(toluene-3,4-dithiolato)2]- anion also define a virtually
regular SP-4 geometry around the metal center35 with
a value of continuous shape measure, S(SP-4) ) 0.000.27
No tendency to dimerize giving metal-metal bonded
units was observed either in the [MnIII(C6F5)4]- or in
the [CrII(C6F5)4]2- anions, both of them having d4
electron configuration. This observation can be at-
tributed, at least in the case of CrII, to the shielding
effect of the sterically demanding C6F5 groups, which
would preclude two metal centers from approaching a
sufficiently short distance to establish a bonding inter-
action.
Polymerization. Vinyl addition norbornene poly-
mers are typically made using transition metal cata-
lysts.36 Over the years, we have developed two types of
vinyl addition norbornene polymerization initiators:
neutral nickel and cationic nickel and palladium com-
plexes. Neutral nickel initiators include complexes
containing electron-withdrawing halogenated aryl and
labile solvent ligands such as [Ni(η6-C6H5Me)(C6F5)2]
and [Ni{C6H2(CF3)3-2,4,6}2(dme)].37 Cationic nickel and
palladium catalysts include η3-allyl complexes balanced
by weakly coordinating anions such as [PF6]-, [SbF6]-,
(33) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; Section 7.12, pp 257-264.
(34) We are indebted to one of the reviewers for suggesting this
viewpoint.
(35) Henkel, G.; Greiwe, K.; Krebs, B. Angew. Chem., Int. Ed. Engl.
1985, 24, 117.
(36) Janiak, C.; Lassahn, P. G. J. Mol. Catal. A: Chem. 2001, 166,
193.
(30) Bondi, A. J. Phys. Chem. 1964, 68, 441. It must be stressed
that van der Waals volumes and radii are parameters belonging to
the intermolecular domain. Their use in the intramolecular realm
should just help as a criterion enabling qualitative comparisons.
(31) Alvarez, S.; Alemany, P.; Avnir, D. Chem. Soc. Rev. 2005, 34,
313.
(37) Barnes, D. A.; Benedikt, G. M.; Goodall, B. L.; Huang, S. S.;
Kalamarides, H. A.; Lenhard, S.; McIntosh, L. H., III; Selvy, K. T.;
Shick. R. A.; Rhodes, L. F. Macromolecules 2003, 36, 2623.
(32) Edema, J. J. H.; Gambarotta, S.; van Bolhuis, F.; Smeets, W.
J. J.; Spek, A. L.; Chiang, M. Y. J. Organomet. Chem. 1990, 389, 47.

3270 Organometallics, Vol. 24, No. 13, 2005
Table 4. Polymerization Resultsa of Norbornene-Type Monomers Using 2
Fornie´s et al.
experiment
monomer
complex
activator
yield
Mw
Mw/Mn
1
2
3
4
5
tBuEsNB
tBuEsNB
tBuEsNB
TESNB
[Ni(η6-C6H5Me)(C6F5)2]
90%
0%
18 800
1.85
2
2
HBArF
LiFABA
2
0%
trans-[Pd(OAc)2(PiPr3)2]
trans-[Pd(OAc)2(PiPr3)2]
95%
33%
TESNB
190 000
2.50
a See Experimental Section for details.
and [B(C6F5)4]-.38 In addition, we have found that
neutral palladium phosphine complexes in the presence
of salts of weakly coordinating anions are excellent
initiators for norbornene vinyl addition polymeriza-
tion.39
Despite their electron-deficient nature, the reluctance
of the [MnIII(C6F5)4]- or the [CrII(C6F5)4]2- anions to
dimerize suggested that these new transition metal
anions would not initiate the vinyl addition polymeri-
zation of strained olefins themselves. However, they
might serve as weakly coordinating anions in the Pd-
catalyzed vinyl addition polymerization processes of
strained olefins considering their obvious relationship
with the widely used tetrahedral (T-4) [B(C6F5)4]- anion.
We decided to test this theory for one of the two
anions synthesized, namely, [MnIII(C6F5)4]-. First the
ability of the anion itself to polymerize a norbornene-
type monomer was examined (Table 4). In experiments
1-3, 5-norbornene carboxylic acid tert-butyl ester
(tBuEsNB) was chosen as a typical norbornene func-
tional monomer. As a control, [Ni(η6-C6H5Me)(C6F5)2]
was used to initiate the polymerization of the ester
functional monomer. Under the conditions employed, a
90% yield of polymer was obtained (experiment 1).
When the polymerization was repeated but with 2
instead of the nickel complex, no polymer is isolated
(experiment 2). An attempt to activate the polymeriza-
tion by addition of [H(OEt2)2][B{C6H3(CF3)2-3,5}4]
(HBArF)40 also failed (experiment 3). This experiment
was carried out in hopes that protonation of the C6F5
ligands would occur, eliminating pentafluorobenzene,
creating a reactive “Mn(C6F5)n” species in situ akin to
[Ni(η6-C6H5Me)(C6F5)2].
electron) species [CrII(C6F5)4]2- and [MnIII(C6F5)4]-,
which have been isolated as their corresponding [Mg-
(THF)6]2+ salts. Both anions, in which the metal centers
have d4 electron configuration, show rather regular SP-4
geometries. The structural comparison is especially
reliable because of the absence of significant cation/
anion covalent interactions in any of the crystal lattices.
This point was not fulfilled in the related permethyl
derivatives [CrIIMe4]2- and [MnIIIMe4]-, since different
degrees of cation/anion association have always been
observed for the methylchromate(II) anion in the dif-
ferent salts for which the molecular structure has been
established.28,41 These often disregarded cation/anion
interactions seem to be, at least in the case of CrII, so
important as to determine the formation or breaking of
a quadruple metal-metal bond.28 In the absence of
significant cation/anion interactions in the crystal lat-
tices of 1‚2THF and 2‚3C4H8O2, the structures of the
[M(C6F5)4]q- anions (M ) Cr, q ) 2; M ) Mn, q ) 1) are
thought to accurately reflect the preferred ground-state
geometries in each case. The anion [MnIII(C6F5)4]- was
shown to be effective as a weakly coordinating anion in
the palladium-catalyzed vinyl polymerization of TESNB.
Experimental Section
The second set of experiments (4, 5) employed 2 as a
weakly coordinating anion in the polymerization of
5-triethoxysilyl-2-norbornene (TESNB). As a control,
[Li(OEt2)2.5][B(C6F5)4] (LiFABA) was used in conjunction
with trans-[Pd(OAc)2(PiPr3)2]. Under these conditions,
a 95% yield of poly(5-triethoxysilyl-2-norbornene) was
isolated. When 2 was employed instead of LiFABA, a
33% yield of polymer was obtained.
All the synthetic manipulations and operations were carried
out under an inert atmosphere (Ar) using Schlenk techniques.
Polymerizations were carried out under nitrogen atmosphere
using typical drybox techniques. Solvents for synthesis were
dried by standard methods. Anhydrous grade solvents were
used for polymerization after sparging with nitrogen. Anhy-
drous MnBr2 (Riedel-de Hae¨n), TESNB (Gelest), and tBuEsNB
(Promerus LLC) were obtained from commercial suppliers and
used as received. [CrCl2(THF)],42 [Ni(η6-C6H5Me)(C6F5)2],37
trans-[Pd(OAc)2(PiPr3)2],39a HBArF,40 and Et2O solutions of
C6F5MgBr43 were prepared according to literature procedures.
The 1H NMR spectra were recorded on a Bruker AMX-500
NMR spectrometer. Chemical shifts were referenced to inter-
nal residual protio solvent resonances and are reported relative
to SiMe4. Polymer molecular weights were determined by GPC
according to the following procedure. Approximately 50-60 mg
of polymer was dissolved in THF (20 cm3) containing 250 mg
of BHT. The solution was filtered through a 0.2 µm Teflon
disposable syringe filter and then injected into the chromato-
graph. The mobile phase used was THF stabilized with 250
Concluding Remarks
A similar structural behavior has been observed for
the highly unusual pair of isoleptic and isoelectronic (12-
(38) (a) Goodall, B. L. In Late Transition Metal Polymerization
Catalysis; Rieger, B., Saunders Baugh, L., Kacker, S., Striegler, S.,
Eds.; Wiley-VCH: Weinheim, Germany, 2003; pp 101-154. (b) Lipian,
J.; Mimna, R. A.; Fondran, J. C.; Yandulov, D.; Goodall, B. L.; Rhodes,
L. F.; Shick, R. A.; Huffman, J. C. Macromolecules 2002, 35, 8969. (c)
Lipian, J.; Rhodes, L. F.; Goodall, B. L.; Bell, A.; Mimna, R. A.;
Fondran, J. C.; Jayaraman, S.; Hennis, A. D.; Elia, C. N.; Polley, J.
D.; Sen, A. U.S. Patent 6455650, 2002.
(39) (a) Chun, S.-H.; Kim, W.-K.; Yoon, S.-C.; Lim, T.-S.; Kim, H.;
Kim, K.-H. WO 2004007564, 2004. (b) Kim, K. H.; Han, Y.-K.; Lee, S.
U.; Chun, S.-H.; Ok, J. H. J. Mol. Modeling 2003, 9, 304. See also ref
38c.
(40) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920.
(41) Krausse, J.; Marx, G.; Scho¨dl, G. J. Organomet. Chem. 1970,
21, 159. For a redetermination of this structure, see: Hao, S.; Song,
J.-I.; Berno, P.; Gambarotta, S. Organometallics 1994, 13, 1326.
(42) Ko¨hler, F. H.; Pro¨ssdorf, W. Z. Naturforsch., Teil B 1977, 32,
1026.
(43) Nield, E.; Stephens, R.; Tatlow, J. C. J. Chem. Soc. 1959, 166.

Homoleptic Aryl-Manganese(III) Compound
Organometallics, Vol. 24, No. 13, 2005 3271
ppm BHT. The measurements were run on a PL-GPC 50
integrated GPC system from Polymer Laboratories at 40 °C,
with a Midas 830 autosampler. The column set used was 2
PLgel 5 µm Mixed C, plus 1 PL 5 µm guard column. The data
for analysis were acquired using PL Cirrus software, version
2.0. Calibration was obtained using EasiCal polystyrene
standards from Polymer Laboratories. The calibration range
was 7.5 × 106 to 580 Da. Elemental analyses were carried out
with a Perkin-Elmer 2400-Series II microanalyzer. IR spectra
of KBr disks were recorded on a Perkin-Elmer Spectrum One
(4000-350 cm-1) spectrophotometer.
4 h. The reaction did not yield any polymer after addition of
the reaction mixture to MeOH.
Polymerization of TESNB. (a) To a solution of TESNB
(4.0 g, 15.6 mmol) in toluene (10 cm3) were added trans-[Pd-
(OAc)2(PiPr3)2] (8.5 mg, 0.016 mmol) and LiFABA (68.0 mg,
0.078 mmol). The glass vial was sealed and then placed in an
oil bath at 65 °C. After stirring for 22 h, the reaction mixture
was cooled to ambient temperature and then added dropwise
to an excess of MeOH. The precipitated polymer was collected
by filtration, washed, and dried at 50 °C for 20 h. Yield: 3.8
g (95%). Poly(5-triethoxy-2-norbornene): Mn(GPC): 76 000;
Mw(GPC): 190 000; Mw/Mn: 2.50. 1H NMR (o-dichlorobenzene-
d4): δ 4.2-3.7 [b, 6H, Si(OCH2CH3)3] and 3.0-0.5 [b, 18 H,
Si(OCH2CH3)3 and aliphatic norbornene protons].
Synthesis of [Mg(THF)6][CrII(C6F5)4] (1). A suspension
of [CrCl2(THF)] (1.87 g, 9.61 mmol) in THF (50 cm3) was slowly
added to a freshly prepared Et2O solution (50 cm3) of C6F5-
MgBr (ca. 48 mmol) precooled at -78 °C. The temperature of
the mixture was allowed to rise to 0 °C and further stirred for
3 h at that temperature. After the addition of 1,4-dioxane (30
cm3), the reaction medium was allowed to stand at -30 °C for
2 days. A white precipitate formed, which was removed by
filtration. Vacuum evaporation of the solvent from the filtrate
gave a green solid, which was identified as 1 (3.4 g, 2.89 mmol,
30% yield). Anal. Calcd (%) for C48H48CrF20MgO6: C 49.0, H
4.1. Found: C 48.5, H 3.75. IR (KBr): ν˜max/cm-1 2982 (m), 2905
(m), 1633 (w), 1536 (m), 1505 (vs), 1443 (vs), 1255 (m), 1061
(s), 1045 (s), 953 (vs; C6F5: C-F),25 863 (s; THF: C-O-C),24
765 (m; C6F5: X-sensitive vibr.),25 717 (w), 677 (m), 605 (m),
579 (m) and 482 (m).
(b) Under the same conditions as in (a), 2 (94.7 mg, 0.050
mmol) was employed as a weakly coordinating anion instead
of LiFABA. Yield: 1.3 g (33%).
X-ray Structure Determinations. Crystal data and other
details of the structure analyses are presented in Table 1. All
diffraction measurements were made at 100 K on a Bruker
Smart CCD diffractometer using graphite-monochromated Mo
KR radiation. Unit cell dimensions were initially determined
from 2147 reflections for 1‚2THF and 888 reflections for 2‚
3C4H8O2. For each structure, a full hemisphere of reciprocal
space was scanned by 0.3° ω steps at φ 0°, 90°, and 180° with
the detector at 2θ ) 28°. The diffraction frames were inte-
grated using the SAINT package44 and corrected for absorption
with SADABS.45 Lorentz and polarization corrections were
applied.
The structures were solved by direct methods and refined
using the SHELXL-97 program.46 All non-hydrogen atoms
were assigned anisotropic displacement parameters. The
hydrogen atoms were constrained to idealized geometries and
assigned isotropic displacement parameters equal to 1.2 times
the Uiso values of their respective parent atoms. For 1‚2THF,
carbon atom C(17) belonging to the [Mg(THF)6]2+ cation is
disordered over two sets of positions, which were refined with
0.5 partial occupancy. The C-C bond distances involving these
two disordered atoms were restrained to be the same. For 2‚
3C4H8O2, weak interatomic distances restraints (SADI) were
applied on the dioxane solvent molecules. A common set of
thermal anisotropic parameters was used for the carbon atoms
of dioxane. Full-matrix least-squares refinement of these
models against F2 converged to final residual indices given in
Table 1. Final difference electron density maps showed no
features with significant electron density. CCDC reference
numbers: 266541 (1‚2THF) and 266542 (2‚3C4H8O2).
Single crystals suitable for X-ray diffraction purposes with
formula [Mg(THF)6][Cr(C6F5)4]‚2THF were obtained by slow
diffusion of an Et2O (5 cm3) layer into a solution of 30 mg of 1
in 2 cm3 of THF at -30 °C.
Synthesis of [Mg(THF)6][MnIII(C6F5)4]2 (2). A freshly
prepared Et2O solution (50 cm3) of C6F5MgBr (ca. 26 mmol)
was diluted with THF (50 cm3) and cooled to -78 °C. To this
solution was added solid MnBr2 (1.12 g, 5.22 mmol), and the
resulting suspension was allowed to reach room temperature
overnight and then filtered. 1,4-Dioxane (25 cm3) was added
to the filtrate, and by allowing this mixture to stand 3 days at
-30 °C, a white precipitate formed, which was removed by
filtration. Evaporation of the solvent from the filtrate under
vacuum gave a brown solid, which was identified as 2
(3.96 g, 2.08 mmol, 40% yield). Anal. Calcd (%) for C72H48F40-
MgMn2O6: C 45.4, H 2.5. Found: C 44.8, H 3.1. IR (KBr): ν˜max
/
cm-1 2985 (m), 2905 (w), 1634 (m), 1533 (m), 1503 (vs), 1462
(vs), 1368 (w), 1338 (m), 1258 (w), 1180 (w), 1063 (s), 1046 (s),
1016 (m), 955 (vs; C6F5: C-F),25 and 864 (m; THF: C-O-
C).24
Single crystals suitable for X-ray diffraction purposes with
formula [Mg(THF)6][Mn(C6F5)4]2‚3C4H8O2 were obtained by
slow diffusion of an Et2O (5 cm3) layer into a solution of 40
mg of 2 in 2 cm3 of THF at -30 °C.
Acknowledgment. This work has been supported
by the Spanish MCYT (DGI)/FEDER (Project BQU2002-
03997-CO2-02) and Promerus LLC. We are indebted to
Prof. Dr. S. Alvarez (Universitat de Barcelona) for
kindly providing values of continuous shape measure
as well as for sharing results prior to publication.
Polymerization of tBuEsNB. (a) To a solution of tBuEsNB
(2.0 g, 10.3 mmol) in toluene (5.4 cm3) was added [Ni(η6-C6H5-
Me)(C6F5)2] (0.10 g, 0.21 mmol). The glass vial was sealed.
After stirring at room temperature for 4 h, the reaction
mixture was added dropwise to an excess of MeOH. The
precipitated polymer was collected by filtration, washed with
MeOH, and dried at 50 °C for 20 h. Yield: 1.8 g (90%). Poly-
(5-norbornene carboxylic acid tert-butyl ester): Mn(GPC):
Supporting Information Available: Crystallographic
data of 1‚2THF and 2‚3C4H8O2 (CIF format). This material is
available free of charge via the Internet at http://pubs.acs.org.
1
10 200; Mw(GPC): 18 800; Mw/Mn: 1.85. H NMR (CDCl3): δ
1.5 [s, b, C(CH3)3] and 0.8-3.5 (b, aliphatic norbornene
protons).
OM050206E
(b) Under the same conditions as (a), 2 (0.25 g, 0.13 mmol)
t
was added to a toluene solution of BuEsNB instead of [Ni-
(44) SAINT, version 6.02; Bruker Analytical X-ray Systems: Madi-
son, WI, 1999.
(45) Sheldrick, G. M. SADABS empirical absorption program,
version 2.03; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(46) Sheldrick, G. M. SHELXL-97, Program for the refinement of
crystal structures from diffraction data; University of Go¨ttingen:
Go¨ttingen, Germany, 1997.
(η6-C6H5Me)(C6F5)2]. The reaction mixture was stirred for 4
h. No polymer was obtained after addition of the reaction
mixture to MeOH.
(c) Under the same conditions as (b), HBArF (0.41 g, 0.45
mmol) was added to the same mixture and allowed to stir for