Synthesis and reactions of manganese(II) dialkyl complexes containing monodentate and bidentate nitrogen ligands

Article abstract of DOI:10.1021/om100190g

In this paper we describe the synthesis of Mn(II) dialkyl compounds and their adducts with THF and pyridine. These compounds are useful precursors for the preparation of Mn complexes relevant to catalysis, such as dialkylmanganese(II) derivatives containing chelating nitrogen ligands. In contrast with previously known manganese(II) dialkyls, dibenzylmanganese can not be prepared from MnCl₂ and benzylmanganese chloride due to the formation of insoluble mixed manganesemagnesium compounds. Homoleptic manganese(II) dialkyls are highly sensitive and often quite insoluble owing to their polymeric structure. However, adducts of type MnR₂L or MnR ₂L₂ (L = THF, pyridine) are soluble in hydrocarbon solvents and more readily isolated and stored than the homoleptic alkyls compounds. Manganese dialkyls as well as their THF or pyridine adducts react instantly with 2,2'-bipyridyl to afford the corresponding MnR₂(bipy) complexes. Thus, the stabilized dialkylmanganese(II) THF or Py adducts represent a practical alternative to the more reactive but less easily handled homoleptic dialkyl precursors for synthetic purposes. In addition, the reactivity of MnR₂(bipy) derivatives with O₂ and the protic acid [H(OEt₂)][BAr'₄] (Ar' = 3,5-C₆H ₃(CF₃)₂) are described. The former reaction leads to the formation of a mixed-valence Mn(II)/Mn(III) alkyl complex containing a tetranuclear [Mn₄O₂] core.

Full text of DOI:10.1021/om100190g

2960 Organometallics 2010, 29, 2960–2970
DOI: 10.1021/om100190g
Synthesis and Reactions of Manganese(II) Dialkyl Complexes Containing
Monodentate and Bidentate Nitrogen Ligands
,†
†
†
Juan Campora,* Pilar Palma, Carmen M. Perez, Antonio Rodrı
´
guez-Delgado,†
ꢀ
ꢀ
Eleuterio Alvarez, and Enrique Gutierrez-Puebla
†
‡
ꢀ
ꢀ
†
´
ꢀ
Instituto de Investigaciones Quımicas, CSIC-Universidad de Sevilla, C/ Amerivo Vespucio, 49, 41092,
Sevilla, Spain, and ‡Instituto de Ciencia de Materiales, CSIC, Cantoblanco s/n, 28049 Madrid, Spain
Received March 11, 2010
In this paper we describe the synthesis of Mn(II) dialkyl compounds and their adducts with THF
and pyridine. These compounds are useful precursors for the preparation of Mn complexes relevant
to catalysis, such as dialkylmanganese(II) derivatives containing chelating nitrogen ligands. In
contrast with previously known manganese(II) dialkyls, dibenzylmanganese can not be prepared
from MnCl2 and benzylmanganese chloride due to the formation of insoluble mixed manganese-
magnesium compounds. Homoleptic manganese(II) dialkyls are highly sensitive and often quite
insoluble owing to their polymeric structure. However, adducts of type MnR2L or MnR2L2 (L =
THF, pyridine) are soluble in hydrocarbon solvents and more readily isolated and stored than the
homoleptic alkyls compounds. Manganese dialkyls as well as their THF or pyridine adducts react
instantly with 2,20-bipyridyl to afford the corresponding MnR2(bipy) complexes. Thus, the stabilized
dialkylmanganese(II) THF or Py adducts represent a practical alternative to the more reactive but
less easily handled homoleptic dialkyl precursors for synthetic purposes. In addition, the reactivity
of MnR2(bipy) derivatives with O2 and the protic acid [H(OEt2)][BAr04] (Ar0 = 3,5-C6H3(CF3)2) are
described. The former reaction leads to the formation of a mixed-valence Mn(II)/Mn(III) alkyl
complex containing a tetranuclear [Mn4O2] core.
Introduction
nowadays achieved a degree of development comparable to
that of any other transition element, it is still largely limited
to compounds in low oxidation states (-1, 0, þ1) containing
carbonyl or other strongly π-acceptor ligands. Organome-
tallic derivatives in þ2 or higher oxidation states continue to
be relatively rare, with the exception of manganocene
derivatives.5 Manganese(II) alkyls have found many appli-
cations in organic synthesis as in situ generated reagents,6 but
their study has been hampered by their paramagnetic, NMR-
silent character and their extreme sensitivity to air. Simple
Mn(II) dialkyls[MnR2]n (R=CH2SiMe3 (1),CH2CMe2Ph (2),
CH2CMe3),7 as well as their adducts with phosphines,8
were first reported by Wilkinson between 1976 and 1983.
Partial X-ray diffraction data for the homoleptic derivatives
showed that these compounds have unusual alkyl-bridged
structures, polymeric in the case of 1 and dimeric for 2. Very
recently, Mulvey and co-workers have provided full char-
acterization data for 1, confirming Wilkinson’s proposal.9
Discrete molecular dialkyls are obtained with large R groups.
Owing to its central position in the first transition row of
the periodic table, manganese is an element with many
singular properties.1 Perhaps because of this circumstance,
development of its organometallic chemistry has been slower
than that of its congener transition elements.2 Thus,
although organomanganese(II) alkyls were first prepared
in solution by Gilman in the decade of 1930,3 these com-
pounds remained uncharacterized for a long time. Another
example of such delay is dimanganese heptacarbonyl, one of
the main starting materials in modern organomanganese
chemistry, which was not fully characterized until 1954.4
Although the organometallic chemistry of manganese has
*To whom correspondence should be addressed. E-mail: campora@
iiq.csic.es.
(1) Layfield, R. A. Chem. Soc. Rev. 2008, 37, 1096.
(2) Treichel, P. M. Manganese. In Comprehensive Coordination
Chemistry, Vol. 4; Wilkinson, G.; Stone, F. G. A.; Abel, E. W., Eds.;
Pergamon Press: Oxford, 1982.
(3) (a) Gilman, H.; Bailie, J. C. J. Org. Chem. 1937, 2, 84. (b) Gilman,
H.; Kirby, R. H. J. Am. Chem. Soc. 1941, 63, 2046.
(4) Brimm, E. O.; Lynch, M. A.; Sesny, W. J. J. Am. Chem. Soc. 1954,
76, 3831.
(5) (a) Girolami, G. S.; Morris, R. J. High-Valent Organomanganese
Compounds. In Comprehensive Organometallic Chemistry II, Vol. 6;
Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Casey, C. P., Vol. Ed.;
Pergamon: London, 1995. (b) Sheridan, J. B. Manganese Organometallics
without CO or Isocyanides. In Comprehensive Organometallic Chemistry III,
Vol. 7; Crabrtree, R.; Mingos, M., Eds.; Theopold, K. H., Vol. Ed.;
Elsevier: London, 2007.
(6) Cahiez, G.; Duplais, C.; Buendia, J. Chem. Rev. 2009, 109, 1434.
(7) Andersen, R. A.; Carmona-Guzman, E.; Gibson, J. F.; Wilkinson,
G. J. Chem. Soc., Dalton Trans. 1976, 2204.
ꢀ
(8) (a) Davies, J. I.; Howard, C. G.; Skapski, C.; Wilkinson, G.
J. Chem. Soc., Chem. Commun. 1982, 1077. (b) Howard, C. G.; Wilkinson,
G.; Thornton-Pett, M.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans.
1983, 2025. (c) Howard, C. G.; Girolami, G. S.; Wilkinson, G.; Thornton-
Pett, M.; Hursthouse, M. J. Chem. Soc., Dalton Trans. 1983, 2631.
(9) Alberola, A.; Blair, B. L.; Carrella, L. M.; Clegg, W.; Kennedy,
A. R.; Mulvey, R. E.; Newton, S.; Rentschler, E.; Russo, L. Organo-
metallics 2009, 28, 2112.
r
pubs.acs.org/Organometallics
Published on Web 06/16/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 13, 2010 2961
For example, monomeric Mn(II) dialkyls, displaying linear
R-M-R arrangements, have been observed for very bulky
alkyl groups (R = CH(SiMe3)2,10 C(SiMe3)311). Furthermore
polymeric MnR2 molecules of simple alkyls such as 1 can be
broken down into readily soluble THF adducts that are
convenient starting materials in organometallic synthesis.12
However, apart from these results, further work on the
chemistry of simple Mn(II) dialkyls have only sparsely been
reported.1,5
Recent progress on olefin polymerization catalysis has
generated a renewed interest in the chemistry of transition
metal alkyls and their role in polymerization catalysis.13 As
previously noted, manganese is in many aspects exceptional
when compared to other transition elements. This is also true
with regard to its behavior in polymerization catalysis. Very
few examples of manganese catalysts for olefin polymeriza-
tion have been reported,14 in contrast with other first-row
transition elements. For example, 2,6-bisiminopyridine com-
plexes of cobalt, iron, chromium, and vanadium give rise to
very active ethylene polymerization catalysts on activation
with alkylaluminum cocatalysts, but the corresponding
manganese complexes do not.15 Clarifying the reasons for
such behavior would contribute to a better understanding of
polymerization mechanism, but this task is thwarted by the
difficulty of synthesizing suitable alkylmanganese complexes
from such ligands.15a,16 Most post-metallocene polymeriza-
tion complexes are based on classic σ-donor imine-based
ligands. The synthesis of alkyl complexes containing such
ligands is frequently complicated by the tendency of the
latter to undergo side reactions with strongly basic or
nucleophilic transmetalation reagents.17 We found that these
problems can be avoided to a large extent if, instead of
resorting to classic transmetalation reactions involving pre-
built metal halocomplexes containing the ligand of interest,
these ligands are reacted with appropriate alkylmetal pre-
cursors capable of delivering the “MRn” fragment. Alkyl
complexes supported by labile secondary ligands, such as the
pyridine derivatives MR2Py2 (M = Ni or Pd,18 Fe19), have
Figure 1. ORTEP view of compound 2. Selected bond distances
(A) and angles (deg): Mn1-C1, 2.255(2); Mn1-C10, 2.327(2);
Mn1-C11, 2.118(2); Mn1-C5, 2.7284(16); Mn1-C10: 2.6389(17);
Mn1-Mn10: 2.7286(6); C11-Mn1-C1, 127.73(7); C11-Mn1-C1:
120.01(7); C10-Mn1-C1: 106.92(6); Mn1-C1-Mn10, 73.08(6);
Mn1-C1-C2, 121.00(13); Mn10-C1-C2, 104.84(11). Symme-
try transformations used to generate equivalent atoms (0): -x,
-yþ1, -z.
proven very useful for this purpose. Manganese homoleptic
dialkyls or weakly ligated dialkyl complexes also appear to
be ideal precursors for the synthesis of organometallic com-
plexes with reactive nitrogen ligands. In this paper, we
describe the synthesis and characterization of different types
of manganese dialkyl complexes and preliminary work on
their use in the preparation of derivatives containing mono-
dentate and bidentate nitrogen ligands, such as pyridine and
bipyridine. In addition, we present some results on the reacti-
vity of MnR2(bipy) complexes.
Results and Discussion
Homoleptic Manganese(II) Dialkyls and THF Adducts.
The homoleptic trimethylsilymethyl (1) and neophyl (R =
CH2CMe2Ph, 2) dialkyls were prepared as described by
Wilkinson, by reaction of MnCl2 with the suitable Grignard
reagents in diethyl ether (eq 1).7 Attempts to extend this
procedure to the synthesis of dibenzylmanganese led to the
formation of a highly insoluble colorless material. However,
a pyrophoric yellowish product, sparingly soluble in hot
toluene, was isolated in up to 33% yield when, instead of
using Mg(CH2Ph)(Cl), the reaction was carried out with
Mg(CH2Ph)2 (prepared by addition of 1,4-dioxane to the
latter). The IR spectrum of this product shows exclusively
absorptions assigned to the benzyl group, while character-
istic ν(C-O-C) bands of coordinated dioxane or diethyl
ether (ca. 1000-1200 cm-1) are absent, and therefore we
propose that this compound is dibenzylmanganese, 3 (eq 2).
Compound 3 is only sparingly soluble in hydrocarbon
solvents, and this, combined with its extreme sensitivity to
air, prevented us from advancing in its characterization. The
insolubility of this compound suggests that it has a polymeric
structure in the solid state, as previously shown for 1.7a,20
(10) Andersen, R. A.; Berg, D. J.; Fernholt, L.; Faegri, K.; Green,
J. C.; Haaland, A.; Lappert, M. F.; Leung, W.-P.; Rypdal, K. Acta
Chim. Scand. Ser. A 1988, 42, 554.
(11) Buttrus, N. H.; Eaborn, C.; Hitchcock, P. B.; Smith, J. D.;
Sullivan, A. C. Chem. Soc., Chem. Commun. 1985, 1380.
(12) (a) Crewdson, P.; Gambarotta, S.; Yap, G. P. A.; Thompson,
L. K. Inorg. Chem. 2003, 42, 8579. (b) Hitchcock, P. B.; Lappert, M. F.;
Leung, W. P.; Buttrus, N. H. J. Organomet. Chem. 1990, 394, 57.
(13) (a) Takeuchi, D. Dalton Trans. 2010, 39, 311. (b) Metal Catalysts
in Olefin Polymerization; Topics in Organometallic Chemistry, Vol. 26;
Zhibin, G., Ed., 2009. (c) Special issues of Chem. Rev. dedicated to olefin
polymerization: 2000, 100 (4), “Frontiers in Olefin Polymerization”;
2009, 109 (11), “Frontiers in Polymer Synthesis”. (d) Gibson, V. C.;
Spitzmesser., S. K. Chem. Rev. 2003, 103, 283.
€
€ €
(14) (a) Yliheikkila, K.; Axenov, K.; Raisanen, M.; Klinga, T. M.;
€
Lankinen, M. P.; Kettunen, M.; Leskela, M.; Repo, T. Organometallics
2007, 26, 980. (b) Nabika, M.; Seki, Y.; Miyatake, T.; Ishikawa, Y.; Okamoto,
K.-I.; Fujisawa, K. Organometallics 2004, 23, 4335. (c) Nabika, M.; Kiuchi,
S.; Miyatake, T.; Okamoto, K.-I.; Fujisawa, K. J. Mol. Catal. A: Chem.
2007, 269, 163.
(15) (a) Reardon, D; Aharonian, G; Gambarotta, S; Yap, G. P. A.
Organometallics 2002, 21, 786. (b) Gibson, V. C.; McTavish, S.; Redshaw,
C.; Solan, A. S.; White, A. J.; Williams, D. J. Dalton Trans. 2003, 221.
(16) Sugiyama, H.; Aharonian, G.; Gambarotta, S.; Yap, G. P. A.;
Budzelaar, P. H. M. J. Am. Chem. Soc. 2002, 124, 12268.
(17) Knijnenburg, Q.; Gambarotta, S.; Buzelaar, P. H. M. Dalton
Trans. 2006, 5442.
ꢀ
ꢀ
(18) Campora, J.; Conejo, M. M.; Mereiter, K.; Palma, P.; Perez,
C. M.; Reyes, M. L.; Ruız, C. J. J. Organomet. Chem. 2003, 683, 220.
(19) Campora, J.; Perez, C. M.; Rodrıguez-Delgado, A.; Naz, M.;
Palma, P.; Alvarez, E. Organometallics 2007, 26, 1104.
(20) (a) Davies, J. I.; Howard, C. G.; Skapski, C.; Wilkinson, G.
J. Chem. Soc., Chem. Commun. 1982, 1077. (b) Howard, C. G.; Wilkinson,
G.; Thornton-Pett, M.; Hurstohouse, M. B. J. Chem. Soc., Dalton Trans.
1983, 2025.
´
ꢀ
´
ꢀ

ꢀ
Campora et al.
2962 Organometallics, Vol. 29, No. 13, 2010
In contrast with 1 and 3 compound 2 is readily soluble in
hydrocarbon solvents, and this facilitates its isolation as a
crystalline solid in good yields (ca. 50%). Although the struc-
ture of this compound has been described,7 full crystallo-
graphic data were not provided, and for this reason we
completed the characterization of this interesting molecule
(Figure 1). Our results are in full agreement with the previous
description. The molecule is a dimer containing two MnR2
units, bridged by one of the alkyl groups, while the other is
coordinated in a terminal fashion. A crystallographic inver-
sion center relates the two MnR2 fragments. The distance
between the manganese atoms, 2.7286(6) A, is significantly
smaller than in some other structurally related Mn(II) di-
meric compounds (see below) and even shorter than some
typical Mn-Mn bonds (e.g., in Mn2(CO)10, 2.903 A); there-
fore a Mn-Mn covalent interaction cannot be easily ruled
out. The low magnetic susceptibility (μeff = 3.1 μB per Mn
atom at 293 K) measured for this compound could be argued
in favor of such a metal-metal bonding interaction, but
probably this is best explained by a strong antiferromagnetic
interaction, as Gambarotta12a and Mulvey9 have found for
related dimeric Mn(II) and polymeric alkyl compounds.
spite of the larger covalent radius of Pd. The weakness of the
Mn π-arene interaction is further confirmed by the nearly
planar geometry of the MnC3 fragment formed by the metal
atom and the three σ-bonded carbons, C1, C10, and C11,
which is in contrast with the tetrahedral arrangement nor-
mally observed in four-coordinated Mn centers. The sum of
the three C-Mn-C bonds amounts to 354,7ꢀ, equivalent to a
pyramidalization degree of only 18.4% in a scale going from
0% for a perfectly planar MnC3 unit to 100% for a pyramid
with three perfectly tetrahedral C-Mn-C angles of 109.5ꢀ.
Reactions of MnCl2 with alkylmagnesium reagents in
Et2O are in general very slow, and this combined with the
low solubility of the products (particularly in the cases of 1
and 3) led us to examine the use of THF as solvent (eq 3).
Judging from the changes in the appearance of the mixtures,
these reactions proceed more rapidly and are completed
within a few hours. The binuclear THF adduct of bis-
(trimethylsilyl)manganese, 4, was readily isolated as orange
crystals in good yield. Although the reaction is apparently
also rapid and complete for R = neophyl and benzyl, the
products formed are exceedingly soluble in hydrocarbon
solvents and reluctant to crystallize. Only after very careful
removal of THF under vacuum was a small amount of
compound 5, the neophyl analogue of 4, obtained. The
corresponding benzyl derivative, 6, could not be isolated in
the same way, but was obtained by a somewhat different
procedure (see below). The IR spectra of these compounds
display intense absorptions at ca. 1020 and 870 cm-1 that are
absent in those of the corresponding homoleptic derivatives
and hence can be assigned to coordinated THF C-O stretch-
ing bands. Crystalline samples of these compounds are
moderately soluble in hexane; therefore the difficulties for
product isolation when R = neophyl or benzyl suggest that
the use of THF as solvent favors the formation of very
soluble products, perhaps THF-stabilized monomeric com-
plexes. The crystal structures of 4, 5, and 6 are shown in
Figure 2, and Table 1 collects selected bond distances and
angles. Although the crystal structure of 4 has been reported
previously,12 we have determined it independently and con-
sidered worthwhile including our data here because of their
relation with other compounds in this work. As can be seen,
the three THF adducts have closely related alkyl-bridged
binuclear structures. Effective magnetic moments measured
at room temperature (293 K) are 5.2-5.3 μB per manganese
atom, larger than that found for homoleptic 2 but still
slightly below 5.9, the spin-only value for five electrons that
would be expected for high-spin Mn(II). As pointed out by
MgðClÞR
MnCl2
½MnR2ꢀn þ MgCl2
R ¼ CH2SiMe3, ¥ ¼ ð1Þ;
CH2CMe2Ph, n ¼ 2 ð2Þ
ð1Þ
Et2O
MgðCH2PhÞ2
MnCl2
½MnðCH2PhÞ2ꢀn þ MgCl2 ð2Þ
Et2O
3
The Mn2C2 ring has a trapezoidal shape, with two differ-
ent Mn-C bond lengths (2.327(2) and 2.255(2) A). The
coordination geometry of the bridging carbon atoms can
be compared to a square pyramid, with both manganese
centers and the two hydrogen atoms placed on the base and
the CMe2Ph fragment in the apex. This configuration causes
the H atoms of the bridging CH2 to come in close contact
with the closest Mn center (ca. 2.2 A), hinting at the existence
of agostic interactions, as previously suggested for [MnR2-
(PR03)]2 complexes.20 The configuration of the bridging alkyl
groups allows secondary interactions between the pendant
phenyl rings and each of the manganese atoms. Short con-
tacts are observed between Mn and carbons ipso (C5,
2.7284(16) A) and ortho (C10, 2.6389(17) A), and thus the
interaction is best described as a η2-arene bond. These
2MgðRÞCl
Mn C bond distances are very similar to those measured
3 3 3
MnCl2
½MnR2ðTHFÞnꢀ þ MgCl2
in the zinc π-adduct Zn(C6F5)2(η2-C6H8), 2.784(2) and
2.6847(15) A.21 The π-arene interaction is also reminiscent
of that observed in a family of three-coordinated neutral and
cationic Pd-neophyl complexes, where a π-interaction alle-
viates the coordinative unsaturation of the metal center.22
However, this interaction appears to be significantly weaker
in the Mn complex than in the Pd derivatives, as the Pd-
C(ipso) distances (2.34-2.39 A) are significantly shorter, in
THF
ð3Þ
R ¼ CH2SiMe3 ð4Þ; CH2CMe2Ph ð5Þ; CH2Ph ð6Þ
Gambarotta for 4, this is due to the noticeable antiferro-
magnetic coupling of the manganese centers.12a
Compounds 4-6 feature two symmetrical Mn(μ-R)(R)-
(THF) units related by a crystallographic inversion center.
As found for 2, Mn2C2 cores have rhomboidal shapes with
obtuse CBr-Mn-CBr and acute Mn-CBr-Mn0 angles (CBr
denotes the bridging carbon) and two slightly unequal
Mn-CBr distances. The Mn centers occupy a distorted
tetrahedral environment, configured by the two bridging
and the terminal C atoms and completed by the THF ligand.
As compared with 2, the MnC3 fragments are less planar in
(21) Guerrero, A.; Martin, E.; Hughes, D.; Kaltsoyannis, N.; Bochmann,
M. Organometallics 2006, 25, 3311.
ꢀ
ꢀ
(22) (a) Campora, J.; Lopez, J. A.; Palma, P.; Valerga, P.; Spillner, E.;
ꢀ
Carmona, E. Angew. Chem., Int. Ed. 1999, 38, 147. (b) Campora, J.;
ꢀ
ꢀ
Gutierrez-Puebla, E.; Lopez, J. A.; Monge, A.; Palma, P.; del Río, D.;
Carmona, E. Angew. Chem., Int. Ed. 2001, 40, 3641.

Article
Organometallics, Vol. 29, No. 13, 2010 2963
Figure 2. Crystal structures of compounds 4 (left), 5 (center), and 6 (right). See Table 1 for selected bond distances and angles.
Symmetry transformations used to generate equivalent atoms (0): 4, -x, yþ1/2, -zþ1/2; 5, -xþ2, -y, -zþ1; 6, -xþ1, -yþ1, -z.
Table 1. Selected Bond Distances and Angles for Binuclear Alkyls
[MnR2L]2
Figure 3. Schematic representation of the bridging alkyl con-
figurations found in compounds 2, 4, 5, and 6.
4
5
6
8
symmetrical fashion, with one of the two H atoms eclipsing
the “long” Mn-C bond. Although at first sight the geome-
tries of the CBr center appear rather unusual for carbon, it
can be readily seen that the “short” Mn-C bond is never too
far from the normal “tetrahedral” disposition with respect to
the H and C/Si substituents. The different configurations of
the bridging carbon can be viewed as a result of the relative
orientation of the farthest Mn atom with regard to the
“short” Mn-C(R)(H)(H) group, as schematically repre-
sented in Figure 3. This interpretation suggests that the
Distances (A)
Mn Mn0
2.7792(11) 2.8416(4) 2.7136(3) 2.7927(5)
3 3 3
Mn-CBr
2.203(4)
2.352(4)
2.127(4)
2.184(4)
2.2158(15) 2.2753(10) 2.1991(18)
2.4615(14) 2.3182(10) 2.3711(7)
2.1478(15) 2.1460(11) 2.124(2)
2.1773(11) 2.1206(8) 2.2251(14)
0
Mn-CBr
Mn-Ct
Mn-O or N
Angles (deg)
75.12(14) 74.61(4)
104.88(14) 105.39(4) 107.59(3) 104.77(5)
Mn-CBr-Mn00
CBr-Mn-CBr
Ct-Mn-CBr
72.41(3)
75.23(5)
127.5(2)
115.9(2)
130.12(6) 123.06(4) 124.36(8)
113.58(5) 113.87(4) 115.42(8)
107.64(9) 103.63(6) 106,65(9)
166.55(11) 124.44(7) 178,07(11)
124.76(10) 111.48(7) 121.76(10)
104.21(5) 111.28(4) 109,51(8)
secondary (“long”) Mn C interaction lacks directional
0
3 3 3
Ct-Mn-CBr
character, which is not too surprising considering the highly
ionic character of Mn(II)-C bonds.1 The relative disposition
of the two Mn centers is probably dictated by steric factors
or by the influence of the secondary π-interactions as in the
case of 2.
Mn-CBr-(Si or C) 105.6(2)
Mn0-CBr-(Si or C) 176.0(3)
Mn-Ct-(Si or C)
O or N-Mn-Ct
121.6(2)
108.4(2)
the THF adducts but still rather flat, with pyramidalization
degrees of 37%, 34%, and 49% for 4, 5, and 6, respectively.
Saturation of the Mn centers by the THF ligand results in the
disappearance of any secondary interactions with the alkyl
chain. Thus, in contrast with bis(neophyl)manganese 2, the
phenyl rings of the THF adduct 5 are removed far away from
the metal center. Another difference between 2 and 5 is
observed in the more open structure of the latter, as eviden-
We have mentioned that the dibenzylmanganese THF
adduct 6 could not be isolated from the reaction mixture
obtained by treating MnCl2 with the benzyl Grignard re-
agent in diethyl ether. However, while studying the synthesis
of [Mn(CH2Ph)2] from dibenzylmagnesium and MnCl2 in
Et2O, we observed that extraction in toluene is greatly helped
by the addition of a small amount of THF. This procedure
led to the isolation of two products, 6 and a new compound
of composition [MnMg(CH2Ph)Cl3(THF)2], 7, in 11% and
25% yield, respectively. The crystal structure of 7 is shown in
Figure 4. This compound could be described as an adduct of
the (chloro)benzylmanganese “Grignard” Mn(CH2Ph)Cl
with magnesium chloride. The molecule is dimeric, compris-
ing two crystallographically equivalent “Mn(CH2Ph)Mg-
(THF)2Cl3” units. Each pair of manganese and magnesium
atoms is bridged by two chlorine ligands. The manganese
atoms are found in a slightly distorted tetrahedral environ-
ment formed by three Cl atoms and the terminal benzyl
group, while the octahedral coordination of magnesium is
completed by two mutually cis molecules of THF. The
molecule resembles a prism lacking two opposite vertexes
ced by the significantly longer Mn Mn distance (2.7286(6)
3 3 3
A in 2 vs 2.8416(4) A in 5), probably as a consequence of the
increased steric hindrance. However, the most striking dis-
similarity between the structures of 2, 4, 5, and 6 is the
different coordination geometries of the bridging carbon
atom. As noted by Gambarotta,12a the silyl group of com-
pound 4 is almost perfectly aligned with one of the Mn atoms
(Mn0-CBr-Si = 176.0(3)ꢀ), giving rise to a bipyramidal-
trigonal geometry at the CBr center, with the two H atoms
and the other Mn atom occupying the equatorial positions.
A similar but not as precise alignment is observed in 5 (Mn0-
CBr-C = 166.55(11)ꢀ). In 6, the coordination polyhedron of
the bridging carbon is more akin to that in 2, although in less

ꢀ
Campora et al.
2964 Organometallics, Vol. 29, No. 13, 2010
THF is converted into 7 in high yield (see Experimental
Section).
Pyridine and Bipyridine Mn(II) Dialkyl Complexes. As
anticipated, both the homoleptic dialkyls and their THF
adducts serve as excellent starting materials for the prepara-
tion of different derivatives containing the MnR2 fragment.
Due to our previous results in related chemistry of Ni, Pd,
and Fe alkyls, in the first place we were interested in the
corresponding pyridine adducts.16,17 These compounds can
be readily prepared adding pyridine to “MnR2(THF)n”
solutions, as shown in Scheme 2. This procedure led to the
isolation of trimethylsilylmethyl (8) and neophyl (9) adducts
as orange- and red-colored solids, respectively. Pyridine-
stabilized complexes are less sensitive than the correspond-
ing THF adducts and can be stored for long periods of time
without signs of decomposition. Analytical data for these
two compounds indicate different pyridine contents: while 8
contains one equivalent of pyridine per manganese, 9 has
two. This suggests that 9 is a monomer, and 8 is a dimer
displaying a hydrocarbyl-bridged structure analogous to that
of 4. The crystal structure of the latter, shown in Figure 5,
confirmed this proposal. Selected bond distances and angles
are included in Table 1. For 9, formation of a dimeric
structure probably reflects the somewhat low ability of the
comparatively bulky neophyl group to bridge two Mn(II)
centers. Wilkinson observed a similar trend for the dialkyls
MnR2(PR03)2: These compounds spontaneously lose one
phosphine ligand, converting into the corresponding binuc-
lear species [MnR2(PR03)]2, except in the case of the neophyl
derivatives.25 In this light, the formation of the monomeric
trimethylsilylmethyl complex Mn(CH2SiMe3)2Py2 from 1
and pyridine, recently reported by Mulvey,18 is not too sur-
prising and suggests that also in this case monomeric and
dimeric species are readily exchangeable species.
The structure of compound 8 is very similar to that of the
THF adduct 4. The disposition of the bridging alkyl is the
same in the two compounds, and analogous bond distances
and angles are very close. The sum of the three C-Mn-C
angles is slightly smaller in 8, leading to a larger degree of
pyramidalization of the MnC3 fragment as compared to 4.
Together with the PMe3 adduct, described by Wilkinson,8a,b
4 and 8 constitute a series of isostructural complexes of
composition [Mn(CH2SiMe3)2L]2, with L = THF, Py, and
PMe3. The donor capability of L exerts a small but notice-
able influence in the pyramidalization degree of the MnC3
fragment, which increases along the series in the order THF
(37%) < Py (49%) < PMe3 (53%).
Figure 4. Crystal structure of compound 7. Selected bond
lengths (A) and angles (deg): Mn1-C1, 2.1225(14); Mn1-Cl1,
2.4074(4); Mn1-Cl2, 2.4954(4); Mn1-Cl3, 2.4201(4); Mg1-
Cl1, 2.4816(6); Mg1-Cl2, 2.5785(6); Mg1-O1, 2.0480(11);
Mg1-O2, 2.0311(11); Cl1-Mn1-Cl2, 91.559(13); Cl1-Mn1-
Cl3, 101.571(14); Cl2-Mn1-Cl3, 90.076(13); C1-Mn1-Cl1,
122.33(5); C1-Mn1-Cl2, 115.01(4); C1-Mn1-Cl3, 126.73(5);
Mn1-C1-C2, 108.00(10). Symmetry transformations used to
generate equivalent atoms (0): -xþ1, -y, -z.
and is strongly reminiscent of the dimeric ethylmagnesium
compound [Mg2EtCl3(THF)3]2, reported by Toney and
Stucky in 1971.23 In fact, the distances Mn-Cl and Mg-Cl
are very similar, resulting in a very harmonious and symme-
trical structure. The effective magnetic moment per manga-
nese atom in this compound at room temperature (5.8 μB) is
very close for the spin-only value for five unpaired electrons,
suggesting that magnetic interactions are weak or nonexist-
ing. In spite of the great relevance of “Grignard”-type mono-
alkylmanganese derivatives in organic synthesis,8 only a few
derivatives of this kind containing extremely bulky alkyl
ligands of the type tris(trialkylsilyl)-methyl have been char-
acterized so far.24 The formation of compounds 6 and 7 in 1:2
ratio suggests that in the reaction of manganese dichloride
withMg(Cl)CH2PhinEt2O aninsoluble, possibly a polymeric
The reactivity of homoleptic manganese alkyls toward
ꢀ
product of composition “Mn(R)(Cl) MgCl2” is strongly
chelating nitrogen ligands has been seldom explored. Coperet
3
favored over the dialkyl MnR2, as shown in Scheme 1.
Because the use of the dibenzylmagnesium reagent limits
the amount of chloride available for the formation of this
adduct, a fraction of the starting material can be converted
into dibenzylmangnese (3), and upon treatment with a near-
stoichiometric amount of THF, the two products are con-
verted into the soluble products 6 and 7. Accordingly, the
reaction of MnCl2 with Mg(CH2Ph)(Cl) in diethyl ether
essentially leads, as previously mentioned, to the insoluble
has studied the reaction of bis(neopentyl)manganese, showing
that the initially formed MnR2(N-N) complexes undergo
migration of one metal-bound alkyl to the imine ligand.26 We
obtained a similar result in the case of reaction of bis-
(neophyl)manganese 6 with 2,6-bis(imino)pyiridine ligands,
which takes place with selective migration of one alkyl group
to the pyridine ring, to afford formally Mn(I) alkyl com-
plexes.19 2,20-Bipyridyl is a highly stabilizing ligand and
probably less prone than imine derivatives to accept alkyl
migrations, but to the best of our knowledge, MnR2(bipy)
material “Mn(R)(Cl) MgCl2”, which on treatment with
3
(23) Toney, J.; Stucky, G. D. J. Organomet. Chem. 1971, 28, 5.
(24) (a) Al-Juaid, S. S.; Eaborn, C; El-Hamruni, S. M.; Hitchcock,
P. B.; Smith, J. D.; Can, S. E. S. J. Organomet. Chem. 2002, 649, 121. (b)
Eaborn, C.; Hitchcock, P. B.; Smith, J. D.; Sullivan, A. C. Chem. Commun.
1985, 534.
(25) Howard, C. G.; Girolami, G. S.; Wilkinson, G.; Thornton-Pett,
M.; Hursthouse, M. J. Chem. Soc., Dalton Trans. 1983, 2631.
(26) Riollet, V.; Coperet, C.; Basset, J.-M.; Rousset, L.; Bouchu, D.;
ꢀ
Grosvalet, L.; Perrin, M. Angew. Chem., Int. Ed. 2002, 41, 3025.

Article
Organometallics, Vol. 29, No. 13, 2010 2965
Scheme 1
complexes have not been reported before. Thus, in order to
gauge of the potential of different types of alkylmanganese
compounds as precursors for the synthesis of stable dialkyl-
manganese derivatives containing chelating nitrogen ligands,
we compared the reactivity of MnR2 and their THF or
pyridine adducts toward bipyridyl (Scheme 3). These reac-
tions proceed in a straightforward manner, affording the
bipyridine complexes 10 and 11 in good yields (50-65%,
isolated), as dark blue solids. The use of the more reactive
precursors such as homoleptic 6 or the THF adduct 4 provides
no significant advantage over the pyridine derivatives 8 and 9,
which are more easily stored and handled. Actually, isolated
yields were slightly improved with the latter. The crystal
structure of 11, shown in Figure 6, confirms that this complex
is mononuclear with the bipyridyl ligand and the alkyl groups
arranged in an approximately tetrahedral structure. The
molecule has no symmetry elements, and small differences
are observedinthetwo Mn-C bonds, as well as in the Mn-N.
On average, these distances are ca. 2.150 and 2.216 A,
respectively, which can be considered normal for a high-spin
Mn(II) center.
Figure 5. Crystal structure of compound 8. See Table 1 for
selected bond distances and angles. Symmetry transformations
used to generate equivalent atoms (0): -xþ2, -y, -z.
In general, alkylmanganese(II) complexes are extremely
sensitive to air, but stable products resulting from their reac-
tions with oxygen have not been reported so far. Wilkinson
mentions that samples of bis(neophyl)manganese 2 are
often stained to a green hue, and he attributed this to an
impurity formed by reaction with traces of oxygen. This
impurity was detected by ESR, but could not be isolated.7
In the course our efforts for growing X-ray quality crystals of
10, we isolated a brown crystalline material, 12. Its structure is
shown in Figure 7. It is a tetranuclear oxo-bridged alkyl
complex displaying two Mn(R)(bipy) and two MnR2 units
bridged by two μ3-oxo units. A large number of inorganic
polynuclear complexes containing [Mn4(μ3-O)2] cores have
been synthesized and characterized.27 These compounds have
attracted much interest because of their relevance as bioinor-
ganic models for the active center for water oxidation in
Figure 6. Crystal structure of compound 11. Selected bond
lengths (A) and angles (deg): Mn1-C11, 2.1518(15); Mn1-C21,
2.1490(17); Mn1-N1, 2.2214(12); Mn1-N2, 2.2099(12); C11-
Mn1-C21, 125.19(6); N1-Mn1-N2, 73.60(4).
Scheme 2
photosystem II28 and their behavior as molecular magnets.29
However, this is the first time that such an array is observed in
an organometallic structure, and it is interesting that this
compound has been formed as result of a “natural” oxidation
with atmospheric oxygen. Because of the potential interest of
Scheme 3
(27) Aromı, G.; Brechin, E. K. Struct. Bond. 2006, 122, 1.
´
(28) Mukhopadhyay, S.; Mandal, S. K.; Bhaduri, S.; Armstrong,
W. H. Chem. Rev. 2004, 104, 3981.
(29) (a) Wieghardt, K. Angew. Chem., Int. Ed. Engl. 1989, 28, 1153. (b)
R€uttinger, W.; Dismukes, G. C. Chem. Rev. 1997, 97, 1. (c) Christou, G. Acc.
Chem. Res. 1989, 22, 328.

ꢀ
Campora et al.
2966 Organometallics, Vol. 29, No. 13, 2010
Figure 7. Top and side views of the crystal structure of compound 12. Selected distances (A) and angles (deg): Mn1-C11, 2.142(4);
Mn2-C15, 2.070(3); Mn2-C19, 2.068(4); Mn1-O1, 1.959(2); Mn2-O1, 1.932(2); Mn2-O10, 1.923(2); Mn1-N1, 2.240(3); Mn1-N2,
2.246(3); C15-Mn2-C19, 92.14(14); C11-Mn1-O1, 121.41(12); N1-Mn1-N2, 73.33(10); O1-Mn2-O10, 84.92(10); Mn2-O1-
Mn20, 95.08(10); Mn1-O1-Mn2, 126.65(13); Mn1-O1-Mn20, 136.89(12); Mn2-Mn20, 2.8443(11). Symmetry transformations used
to generate equivalent atoms (0): -xþ2, -yþ1, -z.
Scheme 4
this process, we sought a reproducible method for the synth-
esisof this compoundbycontrolledreactionof10withoxygen
(eq 4). After a number of attempts, we found that a brown
material with the correct elemental analysis is obtained when
the latter compound (generated in situ from 8 and bipy) is
exposed to a stoichiometric amount of O2 (0.25 O2 per
manganese atom) at -80 ꢀC. The IR spectrum of this
substance shows typical absorptions for bipyridyl (1597,
1567 cm-1) and SiMe3 (1233 and 893 cm-1).
1=4 O2
MnðCH2SiMe3Þ2ðbipyÞ ð10Þ
½Mn2ðCH2SiMe3Þ3ðμ-OÞðbipyÞꢀ2ð12Þ
ð4Þ
The molecule of 12 contains two symmetrical halves
related by a crystallographic inversion center. The four
manganese atoms are strictly coplanar, but due to the slightly
pyramidal geometry of the bridging O atoms (pyramidali-
zation degree 4.3%), these fall a little above and below the
plane. The geometry of the terminal Mn1 is approximately
tetrahedral, while Mn2 is intermediate between tetrahedral
and square planar. The average oxidation state of manga-
nese atoms is þ2.5, but comparison of bond lengths at the
Mn1 and Mn2 centers shows significant differences, which
suggest that these have well-defined oxidation states of þ2
and þ3, respectively. Thus, the Mn1-C11 bond length
(2.148 A) is similar to the analogous distances in the Mn(II)
derivative 11, but Mn2-C15 and Mn2-C19 are appreciably
shorter (2.070 and 2.068 A, respectively), consistent with a
smaller covalent radius of Mn2. The Mn2-O1 distances are
also somewhat shorter than Mn1-O1. Other metric para-
meters of the Mn1 center (Mn1-N distances and bond
angles in general) also resemble those in 11, while the
flattened tetrahedral geometry of Mn2 is precisely as ex-
pected for a high-spin tetracoordinated d4 center.30 The
effective magnetic moment measured in solution for this mole-
cule is very low, 1.6 μB per Mn atom at 298 K, which indicates
that the four Mn centers have strong antiferromagnetic
couplings, as is usually observed in polynuclear manganese
complexes with high S numbers.27,31
Due to our interest in olefin polymerization and oligo-
merization, we decided to attempt the synthesis of poten-
tially active catalysts based on alkylmanganese complexes
displaying a coordinative unsaturation or a readily dissoci-
able ligand. Bipyridyl dialkylmanganese complexes pro-
vide a good starting point for this purpose, and therefore
we investigated the reaction of 11 with protic acids contain-
ing the anion [BAr04]- (Ar0 = 3,5-C6H3(CF3)2) (Scheme 4).
We anticipated that its reaction with [H(OEt)2]þ[BAr04]-
would lead to the coordinatively unsaturated cation
[Mn(CH2CMe2Ph)(bipy)]þ, and we desired to ascertain
whether such species could be stabilized by a weak intra-
molecular π-arene interaction similar to that observed in 2.
When a solution of 11 in Et2O was treated with an
equimolar amount of the acid at -60 ꢀC, a rapid color
change from blue to red was observed. However, on
stirring the mixture at room temperature, the color chan-
ged again to pale orange. The only product isolated from
this solution was a paramagnetic colorless compound,
identified as the ionic complex [Mn(bipy)3]2þ{[BAr04]-}2
on the basis of its crystal structure (Figure 8). The structure
cation [Mn(bipy)3]2þ, typical for a high-spin Mn(II) octa-
hedral complex, has been reported in the literature as a
ꢀ
(30) Cirera, J.; Ruiz, E.; Alvarez, S. Inorg. Chem. 2008, 47, 2871.
(31) Stamatatos, Th. C.; Christou, G. Philos. Trans. R. Soc. A 2008,
366, 113.

Article
Organometallics, Vol. 29, No. 13, 2010 2967
obtained from the reaction of MnCl2 and Mg(CH2Ph)Cl,
affording the cage-shaped manganese “Grignard” compound
[Mn(CH2Ph)Cl MgCl2(THF)2]2. Homoleptic dialkyls and
3
their THF adducts display alkyl-bridged binuclear structures.
These bridges are not symmetrical: they display “short” and
“long” Mn-C distances, and the geometry at the pentacoor-
dinated carbon center varies from approximately square
pyramidal to bipyramidal trigonal. This can be described as
the result of a nondirectional interaction between a “normal”
tetrahedral carbon at a Mn-C(R)(H)(H) unit with a second
Mn atom. When the dialkyls are reacted with pyridine, the
products can be either binuclear complexes, analogous to the
THF adducts, or mononuclear MnR2Py2 derivatives. Homo-
leptic complexes and their THF or pyridine derivatives have a
large potential for the synthesis of new organometallic man-
ganese compounds that is still largely underdeveloped. They
all react readily with bipyridyl to afford MnR2(bipy) com-
pounds in similarly good yields. Compared to homoleptic
alkyls and their THF adducts, pyridine derivatives have some
advantage in practice because of their higher stability, which
facilitates handling and allows longer storage periods.
In addition, this work has addressed some aspects of the
chemisty of monomuclear MnR2(bipy) compounds. Reac-
tion of the trimethylsilyl derivative with oxygen under con-
trolled conditions provides an organometallic example of
the mixed-valence Mn(II)/Mn(III) compound displaying a
Mn4O2 core. However, attempts to prepare cationic com-
plexes MnR(bipy)þ were unsuccessful, apparently due to
their tendency to diproportionate, leading to the formation
of the [Mn(bipy)3]þ cation.
Figure 8. Crystal structure of 13 (cationic part).
component of several ionic compounds.32 The color
changes observed suggested that the targeted cationic
species is in fact generated, but π-bonding does not suffice
to stabilize it at room temperature. Therefore, we decided
to synthesize a cationic complex of type [Mn(R)(bipy)(Py)]þ
containing a relatively strong co-ligand such as pyridine. With
this aim, we explored two alternative methods: treating bipyr-
idine dialkyl 11 with pyridinium tetraarylborate, and the
reaction of the bis(pyridine) bis(neophyl)manganese 9 with
bipyridinium tetraarylborate, as shown in Scheme 4 (right
side). Neither of these methods afforded the expected cationic
alkyl, but the same product 13 in 51% and 32% yield,
respectively. No other products could be isolated from the
reaction mixtures. As expected, 13 is obtainedþin good to
excellent yields by reacting 2, bipy, and [H(OEt)2] [BAr04]- in
the correct stoichiometric ratio (1:3:2). Again, these results
suggest that, although the sought cationic alkylmanganese
complexes might have been formed as intermediates in these
reactions, they are in fact thermally unstable and sponta-
neously disproportionate in solution to afford 13 and dialkyl-
manganese species.
Experimental Section
All manipulations were carried out under oxygen-free argon
atmosphere, using conventional Schlenck techniques or a nitro-
gen-filled glovebox. Solvents were rigorously dried and de-
gassed before using. Microanalyses were performed by the
Microanalytical Service of the Instituto de Investigaciones
Quımicas (Sevilla, Spain). Infrared spectra were recorded on a
´
Bruker Vector 22 spectrometer, and NMR spectra on Bruker
1
DRX 300, 400, and 500 MHz spectrometers. The H and 13C-
{1H} resonances of the solvent were used as the internal stan-
dard, but the chemical shifts are reported with respect to TMS.
Magnetic susceptibilities were measured at 298 K by Evans’
method.33 Magnetic moments have been calculated from the
average values of two independent measurements of the mag-
netic susceptibility and were corrected for the diamagnetic
contributions estimated from Pascal’s constants.34
Conclusions
Homoleptic dialkylmanganese compounds [MnR2]n and
their adducts with labile monodentate ligands such as THF
or pyridine constitute very useful reagents for the synthesis of
organomanganese(II) derivatives containing other types of co-
ligands. In this paper we have described the synthesis of some
of these compounds and evaluated their synthetic potential for
the preparation of bipyridylmanganese(II) alkyl derivatives.
In general, homoleptic alkyls [MnR2]n are prepared by
reaction of Mn(II) chloride with alkylmagnesium reagents in
diethyl ether, but for R = CH2Ph this reaction is complicated
by the formation of a highly insoluble material, possibly a
MnCl2 was purchased from Aldrich Chemical Co. and rigor-
ously dried following a literature method.35 Pyridine was refluxed
over Na, distilled, and stored in an gastight ampule under Ar pro-
tected from the light. Stock solutions of the Grignard reagents
Mg(R)Cl (R = CH2SiMe3, CH2CMe2Ph, and CH2Ph) were
prepared according to conventional procedures. The reagent
Mg(CH2Ph)2 was obtained by addition of 1,4-dioxane
(1 equiv) to a solution of Mg(CH2Ph)Cl in Et2O, followed by
removal ofþthe resulting precipitate by centrifugation. The acid
[H(Et2O)2] [BAr0]- was obtained as described in the literature.36
[Mn(CH2CMe2Ph)(μ-CH2CMe2Ph)]2, 2. To a vigorously
stirred 40 mL Et2O suspension of MnCl2 (0.63 g, 5 mmol) at
polymeric adduct of composition Mn(Cl)(CH2Ph) MgCl2.
3
Reaction of the manganese dialkyls with THF or pyridine
leads to the formation of binuclear complexes [Mn(R)(μ-
R)(THF)]2. THF also solubilizes the polymeric material
(33) Luchinat, C; Parigi, G.; Bertini, I. Solution NMR of Para-
magnetic Molecules; Elsevier Science: Amsterdam, 2001.
(34) Bain, G. A.; Berry, J. F. J. Chem. Educ. 2008, 85, 532.
(35) So, J.-H.; Boudjouk, P. Inorg. Chem. 1990, 29, 1592.
(36) Brookhart, M.; Grant, F.; Volpe, F., Jr. Organometallics 1992,
11, 3920.
(32) (a) Yu, X.-L.; Tong, Y.-X.; Chen, X.-M-; Mak, T. C. M.
J. Chem. Cryst. 1997, 27, 441. (b) Chen, X. M.; Wang, R. Q.; Xu, Z.-T.
Acta Crystallogr. Sect. C.: Cryst. Struct. Commun. 1995, 51, 820. (c)
ꢀ
Fernandez, G.; Corbella, M.; Alfonso, M.; Stoeckli-Evans, H.; Castro, I.
Inorg. Chem. 2004, 43, 6684.

ꢀ
Campora et al.
2968 Organometallics, Vol. 29, No. 13, 2010
-60 ꢀC was added dropwise 10 mL (10 mmol) of a 1 M Et2O
solution of Mg(CH2CMe2Ph)Cl. After 5 min, the mixture was
allowed to reach room temperature and the stirring was main-
tained for 48 h at room temperature. Solvents and volatiles were
then evaporated at reduced pressure. The residue was extracted
with hexane (3 ꢁ 50 mL), and after filtration, the green solution
was concentrated to five-sixths of its volume. Compound 2
formed pale yellow crystals after cooling to -30 ꢀC, which were
collected by filtration, washed with cold hexane, and dried under
vacuum. Yield: 0.86 g (53%). Anal. Calcd for C40H52Mn2: C,
74.76; H, 8.01. Found: C, 74.03; H, 7.92. IR (Nujol mull, cm-1):
3080, 3055, 3010 (ν C-H arom); 2790, 2715 (νs and νas CH2);
1595, 1575 (Ph). μeff: 3.1 μB.
[Mn(CH2Ph)2]n, 3. To a suspension of MnCl2 (0.38 g, 3 mmol)
in 40 mL of Et2O, vigorously stirred at -60 ꢀC, was added
dropwise 5.7 mL (3 mmol) of a 0.53 M Et2O solution of
Mg(CH2Ph)2. After 5 min, the cold bath was removed and the
pale green mixture was stirred for 48 h at room temperature.
Volatiles were then removed under reduced pressure. The
resulting brown oily residue was washed with 20 mL of hexane
and extracted with 100 mL of hot toluene (90 ꢀC). Upon
filtration, the solution was stored at 4 ꢀC and a pale yellow solid
precipitated. After filtration and drying, compound 3 was iso-
lated as a yellow-green solid. Yield: 0.12 g (17%). IR (Nujol
mull, cm-1): 3059, 2740, 1590, 1271, 1078, 1037, 793, 750, 700.
[Mn(CH2SiMe3)(μ-CH2SiMe3)(THF)]2, 4. A 0.5 M solution
of Mg(CH2SiMe3)Cl in Et2O (12 mL, 6 mmol) was added to a
stirred suspension of MnCl2 (0.38 g, 3 mmol) in 30 mL of THF,
and the mixture stirred at room temperature for 4 h. The solvent
was removed under vacuum, and the residue was extracted with
hexane (2 ꢁ 30 mL). After filtration, the combined extracts were
concentrated and cooled overnight at -30 ꢀC. Compound 4 was
isolated as orange crystals in 94% yield (0.85 g). Anal. Calcd for
C24H60Mn2O2Si4: C, 47.81; H, 10.03. Found: C, 47.27; H, 9.58.
IR (Nujol mull, cm-1): 1237 (δsym Si-Me); 1029, 864 (ν C-O-C,
THF); 824 (δ Si-CH3). μeff: 5.3 μB.
[Mn(CH2CMe2Ph)(μ-CH2CMe2Ph)(THF)]2, 5. A suspension
of MnCl2 (0.41 g, 3.3 mmol) in THF (40 mL) was cooled to
-78 ꢀC. A 1.0 M solution Mg(CH2CMe2Ph)Cl in Et2O (7.5 mL,
2 equiv), cooled to 0 ꢀC, was slowly added. The suspension
immediately turned pale green, evolving to pale brown within a
few minutes. The cold bath was removed after 10 min. Follow-
ing the intial darkening, the solution turned again nearly color-
less after 15 min of stirring at room temperature. Stirring was
continued for 16 h at room temperature, and no further changes
were observed. Solvents and volatiles were evaporated, and the
residue was kept under vacuum during 12 h. The oily residue was
treated with hexane (60 mL) and centrifuged. The solution was
concentrated to one-fourth of its original volume and stored at
-20 ꢀC. After 24 h, some orange cubic crystals were observed,
which were separated and used directly for X-ray diffraction. IR
(Nujol mull, cm-1): 3195, 3085, 3055, ν(C-H); 2770, 2760 (νs
and νas CH2); 1600, 1580 (Ph); 1030, 870 (THF).
[Mn(CH2Ph)(μ-CH2Ph)(THF)]2, 6. To a vigorously stirred
and cold (-78 ꢀC) suspension of MnCl2 (0.38 g, 3 mmol) in
Et2O (40 mL) was added dropwise 1 equiv (5.7 mL, 3 mmol) of
a 0.53 M Et2O solution of Mg(CH2Ph)2. The mixture was
stirred for 48 h at room temperature, and the color turned pale
green over this time. The volatiles were evaporated under
vacuum, and the brown oily residue was washed with 20 mL
of hexane. The resulting solid was filtered and suspended in
40 mL of toluene, and 0.5 mL (6 mmol) of THF was added. The
color turned immediately dark green, and after 15 min stirring,
the mixture was filtered. The solution was concentrated and
stored at -30 ꢀC. Two crops of crystalline solids were obtained
by fractional crystallization. The first crop contained 0.12 g of
orange crystals corresponding to compound 6 (11% yield). The
second fraction consisted of 0.32 g of colorless crystals of 7
(25% yield). A slightly modified procedure led to an increased
yield of 6. In this case, the reaction time was extended to 4 days,
and the residue was treated with approximately half the
amount of THF (0.3 mL, ca. 1 Equiv). The above-described
workup procedure produced 0.35 g (38%) of crystals of 6. IR
(Nujol mull, cm-1): 1020, 860 (ν C-O-C, THF). μeff: 5.2 μB.
[Mn(CH2Ph)(Cl) MgCl2(THF)2]2, 7. MnCl2 (0.38 g, 3 mmol)
3
was suspended in 40 mL of Et2O, and the mixture was treated
with 6 mL of Mg(CH2Ph)(Cl) 0.5 M in Et2O (3 mmol). The
mixture was stirred for 48 h at room temperature and turned
pale yellow. Volatiles were removed under vacuum, and the oily
brown residue was washed with hexane (20 mL). The resulting
solid was filtered and suspended in 30 mL of toluene, and 0.5 mL
(6 mmol) of THF were added. The mixture turned dark purple.
After stirring for 15 min, the solution was filtered off, concen-
trated, and cooled to -30 ꢀC. Compound 7 was obtained as
colorless crystals (0.95 g, 75% yield). Anal. Calcd for C30H46-
Cl6Mg2Mn2O4: C, 43.80; H, 5.51. Found, C, 43.40; H, 5.85. IR
(Nujol mull, cm-1): 1025, 880 (ν C-O-C, THF). μeff: 5.8 μB.
[Mn(CH2SiMe3)py)2]2, 8. A 1.4 M Et2O solution (7.14 mL,
10 mmol) of Mg(CH2SiMe3)Cl was added to a suspension of
MnCl2 (0.63 g, 5 mmol) in 40 mL of THF. The mixture was
stirred for 4 h at room temperature. Solvent and volatiles were
evaporated, and the resultant residue was extracted with hot
toluene (40 mL). The suspension was centrifuged, and the
solution was treated with 0.4 mL (5 mmol) of dry pyridine.
The mixture was stirred for 15 min at the ambient temperature,
during which time a yellow precipitate was formed. After solvent
removal, the yellow oily residue was extracted with hexane (3 ꢁ
30 mL). After filtration, the combined extracts were concentrated
to approximately one-half of their original volume and cooled at
-30 ꢀC. Orange crystals 8 were formed after 48 h, yielding 0.94 g
(61%). Anal. Calcd for C26H54Mn2N2Si4: C, 50.62; H, 8.82; N,
4.54. Found: C, 50.31; H, 8.59; N, 4.49. IR (Nujol mull, cm-1):
1600 (pyridine), 1235 (δ Si-Me), 816 (δ Si-CH3). μeff: 6.0 μB.
[Mn(CH2CMe2Ph)2(py)2], 9. To a vigorously stirred and cold
(-60 ꢀC) suspension of MnCl2 (0.63 g, 5 mmol) in THF (50 mL)
were added 10 mL of a 1 M solution of Mg(CH2CMe2Ph)Cl
(10 mmol) in Et2O. The resultant suspension was stirred for
5 min before the cold bath was removed. The stirring was
continued for 48 h at room temperature. Solvents and volatiles
were removed at reduced pressure. The residue was treated with
40 mL of toluene, and the resulting suspension was centrifuged.
The solution was then treated with 0.8 mL (10 mmol) of dry
pyridine. The mixture became dark red, and it was stirred for
20 min at room temperature and taken to dryness. The residue was
extracted with hexane (2 ꢁ 50 mL), filtered, and concentrated.
Cooling the solution at -30 ꢀC for 16 h afforded 1.04 g of 9 as a
crystalline red solid (43% yield). Anal. Calcd for C30H36MnN2: C,
75.14; H, 7.57; N, 5.84. Found: C, 74.44; H, 7.54; N, 5.55. IR
(Nujol mull, cm-1): 1595 (py). μeff: 5.9 μB.
[Mn(CH2SiMe3)2(bipy)], 10. Method A, from Compound 4. A
solution of compound 4 (0.45 g, 1.50 mmol) in 15 mL of toluene
was added dropwise to a solution of 2,20-bipyridyl (0.23 g,
1.50 mmol) in 15 mL of toluene, stirred at -30 ꢀC. The resulting
deep blue mixture was stirred for 5 min at the same temperature,
and then the cooling bath was removed. Stirring was continued
for 30 min at room temperature, and the solvent was evaporated
under vacuum. The dark blue solid residue was washed with
15 mL of hexane and then extracted with 15 mL of Et2O. The
solution was filtered and hexane was added until a slight per-
sistent turbidity was developed. On cooling to -30 ꢀC, the
product crystallizes as a dark blue solid (0.30 g, 51% yield).
Method B, from Compound 8. To a solution of 2,20-bipyridyl
(0.29 g, 1.85 mmol) in 15 mL of toluene, stirred at -30 ꢀC was
added dropwise a solution of compound 8 (0.61 g, 1.99 mmol) in
15 mL of the same solvent, turning immediately dark blue. The
same workup procedure used in method A was applied to obtain
0.480 g of 10 (65% yield). Anal. Calcd for C18H30MnN2Si2: C,
56.07; H, 7.84; N, 7.27. Found: C, 55.40; H, 7.47; N, 7.50. IR
(Nujol mull, cm-1): 1595, 1575 (bipyridine); 1237 (δ SiMe3), 855
(δ Si-CH3). μeff: 5.8 μB.

Article
[Mn(CH2CMe2Ph)2(bipy)], 11. Method A, from Compound
Organometallics, Vol. 29, No. 13, 2010 2969
2. A solution of compound 2 (0.48 g, 1.50 mmol) in 15 mL of
toluene was added dropwise to a solution of 2,20-bipyridyl
(0.22 g, 1.40 mmol) in 15 mL of toluene, stirred at -30 ꢀC.
The resulting deep blue mixture was stirred for 5 min at the same
temperature, and then the cooling bath was removed. Stirring
was continued for 30 min at room temperature, and then the
solvent was evaporated under vacuum. The solid residue was
washed with 10 mL of hexane and then extracted with 10 mL of
Et2O. The solution was filtered and hexane was added until a
slight persistent turbidity developed. On cooling to -30 ꢀC, the
product crystallizes as a dark blue solid (0.400 g, 60% yield).
Method B, from Compound 9. To a solution of 2,20-bipyridyl
(0.18 g, 1.16 mmol) in 15 mL of toluene, stirred at -30 ꢀC, was
added dropwise a solution of compound 9 (0.63 g, 1.26 mmol) in
15 mL of the same solvent, turning immediately dark blue. The
same workup procedure used in method A was applied, to
obtain 0.350 g of 11 (63% yield). Anal. Calcd for C30H34MnN2:
C, 75.45; H, 7.18; N, 5.87. Found: C, 75.42; H, 6.91; N, 6.00. IR
(Nujol mull, cm-1): 1595, 1575 (bipyridine). μeff: 6.0 μB.
[Mn2(CH2SiMe3)3(bipy)(μ-O)]2, 12. A solution of compound
10 in toluene was generated from 8 (0.41 g, 1.34 mmol) and 2,20-
bipyridyl (0.21 g, 1.34 mmol), as described before. The dark
blue solution was allowed to stir 30 min at room temperature.
The glass stopper of the flask was replaced with a septum, the
argon inlet was closed, and the flask was cooled to -80 ꢀC.
Oxygen (7.5 mL, 0.33 mmol) was taken into a gastight syringe
fitted with a thin needle (i.d. = 0.7 mm) and injected through the
septum (partial vacuum inside the flask assisted the gas uptake).
The pore left by the needle was sealed with silicone paste and
covered with a piece of parafilm. After 5 min, the cooling bath
was removed, and the mixture was allowed to stir for 15 min at
room temperature. During this time, the color of the solution
changed to dark brown. The solvent was evaporated under
reduced pressure. Washing with 10 mL of hexane, the brown
oily residue solidified. This solid was extracted with 15 mL of
diethyl ether, the solution was filtered, and hexane was added
until a slight persisting turbidity developed. A brown powder
precipited upon cooling to -10 ꢀC overnight, which was col-
lected by filtration, washed with hexane, and dried under
vacuum. Yield: 0.180 g, 49%. Anal. Calcd for C44H82Mn4N4O2-
Si6: C, 48.60; H, 7.60; N, 5.15. Found: C, 48.69; H, 7.37; N, 5.25.
IR (Nujol mull, cm-1): 1595, 1575 (bipy); 1235, 860 (SiMe3).
Average μeff/Mn atom: 1.6 μB.
Pyridinium Tetrakis(3,5-bis(trifluoromethyl)phenyl)borate,
[HPy2]þ[BAr04]-. 2 mL of dry pyridne was added to solution of
[H(Et2O)2]þ[BAr04]- (0.70 g, 0.69 mmol) in 5 mL of diethyl ether
cooled at -20 ꢀC, and the mixture was the allowed to stir at
room temperature for 20 min. The solvent was eliminated under
reduced pressure. On treatment with 10 mL of hexane, the oily
residue converted into a beige solid. The latter was washed with
2 ꢁ 10 mL of hexane and dried under vacuum to afford 0.502 g
(71%) of the title compound as a beige powder. The 1H NMR
spectrum showed signals of the anion and the cation with
relative intensities corresponding to the formula. 1H NMR
(CD2Cl2. 400 MHz): δ 7.56 (s, 4H, p-H, Ar0); 7.73 (s, 8H, o-H,
Ar0); 7.89 (br s, 4H, H-3 Py); 8.24 (t, 3JHH = 7.4 Hz, 2H, H-4 Py);
8.84 (br s, 4H, H-2 Py).
Bipyridinium Tetrakis(3,5-bis(trifluoromethyl)phenyl)borate,
[Hbipy]þ[BAr04]-. A solution of [H(Et2O)2]þ[BAr04]- (1.14 g,
1.12 mmol) in 15 mL of diethyl ether was added to a cooled
(-30 ꢀC) solution of 2,20-bipyridyl (0.17 g, 1.12 mmol) in the
same amount of ether. The resulting orange mixture was stirred
5 min in the cooling bath and 30 min at room temperature. After
this time, the solvent was eliminated under vacuum, leaving an
orange solid residue that was taken up in a minimum amount
of ether. Hexane was added carefully until persistent turbidity.
The solution was filtered and cooled to -30 ꢀC to afford the
product as pale orange crystals. Yield: 0.830 g, 73%. IR (Nujol
mull, cm-1): 1630, 1605 (bipy); 1280, 1120, 890 (B-Ar0). 1HNMR

ꢀ
Campora et al.
2970 Organometallics, Vol. 29, No. 13, 2010
(CD2Cl2. 300 MHz): δ 7.56, (s, 4H, p-H, Ar0); 7.73 (over-
lapping signals, 10H, o-H, Ar0 and CH bipy); 8.28 (m, 4H,
4,40,5,50 CH bipy); 8.72 (d, 2H, 3JHH = 4.8 Hz, 6,60 CH bipy);
12.34 (br s, N-H).
turbidity was attained. Cooling to -10 ꢀC overnight afforded
colorless crystals of 13 in ca. 50% yield.
Reaction of Compound 9, [Hbipy]þ[BAr04]-. The reaction was
carried out similarly to the previous one, using equimolar
amounts of Mn(CH2CMe2Ph)2(Py)2 (9) and the bipyridinium
salt. Compound 13 was isolated in 32% yield.
[Mn(bipy)3]2þ{[BAr04]-}2, 13. Solutions of 2,20-bipyridyl
(0.16 g, 1.05 mmol) and compound 3 (0.110 g, 0.35 mmol) in 10
and 15 mL of Et2O, respectively, were mixed at room tempera-
ture, and the resulting dark blue mixture was stirred for 10 min
and then cooled to -60 ꢀC. The acid [H(Et2O)2]þ[BAr04]- (0.710
g, 0.70 mmol) was dissolved in 15 mL of Et2O, and this solu-
tion was added dropwise to the former mixture. The color
changed from dark blue to purple and then to pale orange.
Stirring was continued for 5 and 20 min more at room tempera-
ture. The solvent was evaporated, and the residue was washed
with hexane (10 mL). The resulting pale orange solid was recrys-
tallized from a 2:1 mixture of CH2Cl2 and hexane at -30 ꢀC. The
product was obtained as colorless needles. Yield: 0.550 g, 70%.
Anal. Calcd for C94H48B2F48MnN6: C, 50.18; H,2.15; N, 3.74.
Found: C, 50.21; H, 2.20; N, 3.82. IR (Nujol mull, cm-1): 1605,
1580 (bipy); 1280, 1120, 890 (B-Ar0). μeff: 6.1 μB.
X-ray Crystallography. Crystals coated with dry perfluoro-
polyether were mounted on a glass fiber and fixed in a cold
nitrogen stream (T = 100(2) K), and the intensity data were
collected on a Bruker-Nonius X8Apex-II CCD diffractometer
(2, 5, 6, 7, 11, 12, and 13). Compounds 4 and 8 were coated with
an epoxy polymer (T = 293(2) K), and data were collected on a
Bruker SMART Apex CCD diffractometer. Both diffracto-
meters were equipped with a Mo KR1 radiation (λ = 0.71073 A)
source and graphite monochromator. The data were reduced
(SAINT)37 andcorrectedfor Lorentz polarizationandabsorption
effects by the multiscan method (SADABS).38 The structure was
solved by direct methods (SIR-2002)37 and refined against all F2
data by full-matrix least-squares techniques (SHELXTL-6.12)40
2
2 2
minimizing w[Fo - Fc ] . All non-hydrogen atoms were re-
fined with anisotropic thermal parameters. Hydrogen atoms
were included in calculated positions and allowed to ride on the
attached carbon atoms with the isotropic temperature factors
(Uiso values) fixed at 1.2 times (1.5 times for methyl groups) the
Ueq values of the corresponding carbon atoms. Crystal and
refinement data for all compounds are summarized in Table 2.
Reactions of Compound 11 with [H(Z)2]þ[BAr04]- (Z = Et2O
or Py).þ A solution of 1 mmol of the corresponding acid
[H(Z)2] [BAr04]- (Z = Et2O, 1.01 g; Py, 1.02 g) in 15 mL of
Et2O was dropwise added to a solution of Mn(CH2CMe2Ph)2-
(bipy) (11) (0.49 g, 1.03 mmol) in 15 mL of Et2O, stirred at
-60 ꢀC. The color of the mixture gradually changed from blue to
red. After 5 min, the mixture was allowed to warm to room
temperature, and the stirring was continued for 15 min. The
solvent was evaporated under vacuum, leaving a orange foam,
which was washed with 10 mL of hexane. The resulting orange
solid was extracted with 10 mL of Et2O. The solution was
filtered, and hexane was added until a slight but persistent
Acknowledgment. Financial support from the DGI
(Project CTQ2009-11721), Junta de Andalucıa (Project
´
P09-FQM5074), and CSIC (PIF 08-017-1) is gratefully
acknowledged. C.M.P. thanks Repsol-YPF for a research
contract. A.R.-D. acknowledges a postdoctoral contract
ꢀ
from the Ministerio de Educacion y Ciencia (Ramon y
Cajal Program).
ꢀ
(37) SAINT 6.02; Bruker-AXS, Inc.: Madison, WI , 1997-1999.
(38) Sheldrick, G. SADABS; Bruker AXS, Inc.: Madison, WI, 1999.
(39) Burla, M. C.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.;
Giacovazzo, C.; Polidori, G.; Spagna, R. SIR2002: the program.
J. Appl. Crystallogr., 2003, 36, 1103
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
(40) SHELXTL 6.14; Bruker AXS, Inc.: Madison, WI, 2000-2003.