Neutral and cationic alkylmanganese(II) complexes containing 2,6-bisiminopyridine ligands

Article abstract of DOI:10.1002/chem.201001428

Manganese alkyl complexes stabilised by 2,6-bis(N,N'-2,6-diisopropyl- phenyl)acetaldiminopyridine (^iPrBIP) have been selectively prepared by reacting suitable alkylmanganese(II) precursors, such as homoleptic dialkyls [(MnR₂)_n

Full text of DOI:10.1002/chem.201001428

DOI: 10.1002/chem.201001428
Neutral and Cationic Alkylmanganese(II) Complexes Containing
2,6-Bisiminopyridine Ligands
Carmen M. Pꢀrez,[a] Antonio Rodrꢁguez-Delgado,[a] Pilar Palma,[a] Eleuterio ꢂlvarez,[a]
Enrique Gutiꢀrrez-Puebla,[b] and Juan Cꢃmpora*[a]
Abstract: Manganese alkyl complexes
stabilised by 2,6-bis(N,N’-2,6-diisoprop-
yl-phenyl)acetaldiminopyridine (iPrBIP)
have been selectively prepared by re-
acting suitable alkylmanganese(II) pre-
cursors, such as homoleptic dialkyls
[(MnR2)n] or the corresponding THF
pound slowly evolves to the corre-
sponding MnI monoalkyl derivative. A
detailed study of this reaction provides
insights on its mechanism, showing that
it proceeds through successive alkyl mi-
grations, followed by spontaneous de-
hydrogenation. Protonation of [Mn-
ternatively, the same complex can be
produced by reaction of the pyridine
complex [{Mn
the protonated ligand salt [HiPrBIP]+
[BAr’4]À. This last reaction allows the
ACHTUNGTNER(NNUG CH2SiMe3)2(Py)}2] with
AHCTUNGTRENNUNG
synthesis
alkylmangaACTHUNGTRENNUNG
of
nese(II) derivatives, when
precursors of type [MnR2ACHTUNGTRENNUNG
(iPrBIP)] are
analogous
cationic
adducts [{MnR
N
A
U
tioned ligand. For R=CH2CMe2Ph or
CH2Ph, formally MnI derivatives are
produced, in which one of the two R
groups migrates to the 4-position of the
central pyridine ring in the iPrBIP
ligand. In contrast, a true dialkyl com-
E
not available. Treatment of these neu-
tral and cationic iPrBIP alkylmanganese
derivatives with a range of typical co-
catalysts (modified methylaluminoxane
(MMAO), BACTHNUTRGNE(UNG C6F5)3, trimethyl or triiso-
butylaluminum) does not lead to active
ethylene polymerisation catalysts.
CTHUNGTRENNUNG
A
ACHTUNGTRENNUNG
Keywords: bis
manganese
polymerization · tridentate ligands
G
·
·
N
·
plex [MnR2ACHTUNGTRENNUNG
(iPrBIP)] can be isolated for
R=CH2SiMe3. In solution, this com-
Introduction
that while similar BIP complexes of vanadium[3] or chromi-
um[4] are also catalysts for ethylene polymerisation, analo-
gous manganese derivatives are essentially inactive.[5] In the
interim, it has been increasingly recognised that the BIP
complexes compose a promising class of homogenous cata-
lysts, not limited to ethylene polymerisation or oligomerisa-
tion, but capable of catalysing other reactions as well.[6]
The cause of the catalytic inactivity of Mn–BIP complexes
in olefin polymerisation remains unknown. Although it has
been suggested that it could be the inefficient activation of
In the last ten years, interest in 2,6-bisACTHNUTRGNEUNG(imino)pyridine (BIP)
complexes has grown steadily. Several examples of such
compounds have been known since the 1970s,[1] but wide in-
terest was triggered in 1998, by simultaneous reports from
Brookhart[2a] and Gibson[2b] on the capability of iron– and
cobalt–BIP complexes, upon treatment with alumoxanes, to
catalyse ethylene polymerisation. It was soon discovered
[MnX
ACHTUNGTRENNUNG
2ACHTUNGTRENN(UNG BIP)] complexes with organoaluminum com-
[a] Dr. C. M. Pꢀrez, Dr. A. Rodrꢁguez-Delgado, Dr. P. Palma,
Dr. E. ꢂlvarez, Dr. J. Cꢃmpora
pounds,[5a] it could also be linked to the unique properties of
this element in its +2 oxidation state.[7,8] The often unusual
structure and behaviour of MnII organometallic compounds
are due to the special stability of their high spin d5 configu-
ration, which renders the half-filled 3d orbitals nearly un-
available.[8] In contrast, access to empty d orbitals is possible
for BIP complexes of other transition metals, owing to the
existence of low-lying intermediate spin electronic configu-
rations.[9]
Instituto de Investigaciones Quꢁmicas
Departamento de Quꢁmica Inorgꢃnica
Universidad de Sevilla-Consejo Superior
de Investigaciones Cientꢁficas
Avenida Amꢀrico Vespucio 49, 41092 Sevilla (Spain)
Fax : (+34)954460565
E-mail: campora@iiq.csic.es
[b] Dr. E. Gutiꢀrrez-Puebla
Instituto de Ciencia de Materiales de Madrid
Consejo Superior de Investigaciones Cientꢁficas
Cantoblanco s/n, 28049 Madrid (Spain)
Several research groups have investigated the reactions of
BIP complexes of V, Cr, Mn, Fe and Co with alkyllithiums
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FULL PAPER
or Grignard reagents to synthesise alkyl complexes relevant
to the mechanism of olefin polymerisation.[10–13] These stud-
ies unveiled the fascinating reactivity associated to BIP li-
gands. The outcome of such reactions is usually complex,
and straightforward transmetallations are rather exception-
ed to expand the chemistry of dialkylmanganese complexes
that can be used as starting materials for ligand exchange re-
actions. In this paper, we provide a complete account of the
investigation we have carried out on the synthesis of Mn
alkyl complexes stabilised by the iPrBIP ligand, with the final
aim of establishing whether these compounds can be con-
verted in active catalysts for olefin polymerisation.
ACHTUNGTRENNUNG
al.[11a,13] More often, products arising from apparent reduc-
tion of the metal center,[3,4a,5a,13] or from some alteration of
the BIP ligand (such as deprotonation,[4a,11e,14] addition of
the alkylating reagent to the imine or pyridine moi-
eties[3,4a,11e] or coupling of two ligands to afford dimeric com-
plexes[3,11e,15]) have been observed. In consequence, high-
Results and Discussion
valent alkyl derivatives of type [MR
(BIP)] (n>1; M=tran-
Neutral MnI and MnII alkyl complexes: As shown in
Scheme 1, reaction of [{Mn(CH2CMe2Ph)2}2] with iPrBIP af-
fords a burgundy red product that has been identified as
monoalkyl complex, 1a.[19] A analogous product, 1b, was
similarly obtained from the reaction of the THF adduct of
sition metal) have been rare until recently. Early studies by
Gambarotta showed that manganese is no exception to this
behaviour.[3,5a] The treatment of [MnCl
2ACTHNUTRGNE(NUG BIP)] derivatives
with organolithium or organomagnesium reagents leads to
mixtures of products, including MnI or Mn0 derivatives, as
dibenzylmanganese, [{MnACTHNUTRGENNUG(CH2Ph)2ACHTUGNTREN(NNGU thf)}2], with the same
À
well as dimeric complexes, arising from intermolecular C C
coupling of the imine functionality.
ligand. The structures of these compounds were established
on the basis of analytical data, magnetometry and degrada-
tion experiments. Thus, while elemental analyses are consis-
In our previous work, we have found that ligand exchange
reactions provide an efficient mean for the synthesis of vari-
ous transition metal alkyl complexes. These reactions avoid
complications related to potentially reactive ancillary li-
gands, such as imines. A key requirement for this approach
is the availability of suitable alkylmetal precursor com-
plexes. For example, Ni and Pd alkyl derivatives containing
a-diimine ligands can be prepared in high yields from the
corresponding pyridine dialkyl derivatives [MR2(Py)2].[16]
Similarly, we reported that alkyliron complexes of the type
tent with the composition [MnR2ACTHNUTRGNEUNG
(iPrBIP)], their magnetic
moments, 4.9 (1a) and 4.8 mB (1b) (298 K), are too low for
typical high-spin MnII centers, pointing out the presence of
only four unpaired electrons. These properties resemble
those of the structurally characterised monomethyl complex
[MnMeACHTNUGRTNEUNG
(iPrBIP)], described by Gambarotta.[5a] Both com-
pounds react rapidly with methanol, selectively affording
the corresponding 4-alkyl BIP derivatives, 2a and 2b. Fur-
thermore, careful measurements showed that 1a reacts with
exactly one equivalent of methanol, releasing one equivalent
of the 4-substituted ligand and one of tert-butylbenzene,
which becomes [D1]tBuPh when CD3OD is used. These re-
sults confirm that compounds 1 contain a single alkyl group
bound to the metal center, whilst the other alkyl has been
transferred to the pyridine ring of the BIP ligand, as shown
in Scheme 1. Analogous monoalkyl derivatives of Fe and Co
have also been described in the literature, which according
to DFT calculations should be considered metal(II) com-
plexes containing an antiferromagnetically coupled BIP
anion radical, rather than true metal(I) compounds.[9,22] This
is probably the case for 1a and 1b as well.
[Fe
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(CH2SiMe3)2ACHTUNGTRENNUNG(BIP)] can be prepared from [Fe-
moleptic alkyls of the type [(MnR2)n] are known, which are
excellent starting materials for this class of reactions. Copꢀr-
et has studied the reaction of the bis(neopentyl)manganese
with bidentate diimine ligands.[18] Interestingly, these reac-
tions did not afford the expected dialkylMnII complexes, but
monoalkylmanganese(II) complexes, arising from alkyl
transfer from Mn to the imine ligand. Some time later, we
communicated that the reaction of [{Mn(CH2CMe2Ph)2}2]
with 2,6-bis(N,N’-2,6-diisopropylpropylphenyl)acetaldimino-
pyridine (iPrBIP) also takes place with the selective transfer
of one alkyl group to the pyridine ring,[19] affording a MnI
complex displaying a neophyl substituent at the 4-position
of the pyridine ring (see Scheme 1). This reaction is remark-
ably selective and general and we have been able to use it
as part of a practical method for the synthesis of 4-alkyl-BIP
ligands. Recently, our group[20] and others[21] have contribut-
The presence of a silyl group in the b-position of the R
group can enhance the stability of the transition-metal alkyl
complexes of the BIP ligands, as compared with analogous
derivatives that lack such substituents. For instance, while
(BIP)] complexes are stable,[11,17] similar
[FeACHTUNGTRENNUG(CH2SiMe3)2AHCUTNGTRENNGUN
À
neopentyl derivatives undergo spontaneous Fe C homolysis
affording monoalkyliron com-
plexes.[17f] Thus, in order to
throw some light on the mecha-
nism that lead to the formation
of complexes 1, we undertook
the synthesis of related trime-
thylsilylmethyl
derivatives
(Scheme 2). Both the homolep-
tic
A
alkyl
[{Mn-
Scheme 1.
(CH2SiMe3)2}n][20,23] and its THF
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13835

J. Cꢃmpora et al.
unit and exchanges the two halves of the molecule. Its gen-
eral configuration resembles that of its Fe analogue, report-
ed by Chirik.[12] In both compounds, the axial M C bond
À
length is somewhat longer than that of the basal one, al-
though the difference is more significant in the Mn deriva-
À
tive (2.169 vs. 2.133 ꢅ). This suggests that the apical M C
bond could be weak, and this would be consistent with the
À
observed tendency of one of the two M C bonds to leave
À
the metal center. In addition, some of the Mn N distances
À
are remarkably long. For example, the Mn N
A
are 2.4181(12) ꢅ, which are significantly longer than those
in the related [MnCl2ACTHNUTRGNEUNG
(iPrBIP)] complex (2.342(3) ꢅ, av),[5a]
Scheme 2.
and are probably in the limit of what could be considered a
À
covalent Mn N interaction.
adduct [{Mn(CH2SiMe3)
N
On standing at room temperature for 72 h, the dark blue
solutions of 3 gradually turn to burgundy-red. A new com-
pound, 1c, was isolated from the purple solution in about
20% yield. Its colour and magnetic moment (4.8 mB) are
similar to those of 1a and 1b. As shown in Scheme 2, meth-
anolysis of 1c affords the corresponding 4-trimethylsilyl-
methyl substituted BIP ligand 2c. These observations con-
firm that, like 1a and 1b, 1c arises from migration of one of
the alkyl groups to the 4-position of the BIP pyridine ring.
From this conclussion it is reasonable inferring that, in gen-
eral, formation of compounds of type 1 involves the initial
iPrBIP in toluene, affording compound 3 as a dark blue solid.
The contrast between its colour and the burgundy-red hue
of complexes 1a and 1b immediately suggested that 3 would
be a different kind of compound. Its magnetic moment at
298 K, 5.3 mB, is higher than those of complexes 1 and fully
consistent with high-spin MnII derivative. In addition, unal-
tered iPrBIP is recovered when 3 is treated with an excess of
methanol, indicating that no alkyl migration had taken place
in this case. These observations suggested that this com-
pound might be a genuine MnII dialkyl complex, which was
ultimately confirmed by its crystal structure, shown in
Figure 1.
formation of dialkyls [MnR2ACTHNUTRGENUGN(BIP)], which are too unstable
to be detected when the alkyl group lacks stabilising a-silyl
substituents.
The process leading to the formation of formally MnI spe-
cies 1 can be decomposed in two more basic steps: 1) migra-
tion of the alkyl group from the metal center to the aromat-
ic ring, and 2) loss of one hydrogen atom. The latter takes
place spontaneously in solution, but it is relatively slow at
room temperature. Previous investigations[19] showed that
when [MnR2] complexes (R=neophyl, benzyl or allyl) are
reacted with BIP ligands and the resulting reaction mixtures
are directly quenched with MeOH, not only the 4-alkyl-BIP
ligands, but also the corresponding 4-alkyl-2,6-diimino-1,4-
dihydropyridine derivatives are obtained. In some cases,
such dihydropyridines can represent as much as 80% of the
products. The availability of the stable MnII dialkyl 3 gave
us the opportunity to investigate this transformation in
more detail, in order to provide some insights on its mecha-
nism. Thus, we carried out a series of experiments in which
solutions of 3 were allowed to evolve over different reaction
times and temperatures. The products were then quenched
with MeOH, and the resulting organic species were analysed
Figure 1. Crystal structure of compound 3·C7H8 (solvent molecule not
shown). Selected bond lengths (ꢅ) and angles (8): Mn-C21, 2.169(2);
1
À
À
À
À
Mn C18 2.133(2); Mn N1, 2.2279(17); Mn N2, 2.4181(12); C1 C4,
by H NMR spectroscopy. In the first experiment, we repro-
À
À
1.490(2); C4 N2, 1.277(2); C4 C5, 1.504(2); C18-Mn-C21, 120.93(10);
N1-Mn-C18, 133.90(9); N1-Mn-C21, 105.17(7); N2-Mn-N2’, 135.16(6);
N1-Mn-N2, 69.16(3).
duced the conditions that led to the isolation of 1c by allow-
ing a toluene solution of 3 to stand at room temperature for
four days. Quenching the resulting burgundy solution afford-
ed a mixture of four organic products (Scheme 3). The
1H NMR spectrum of this mixture displays signals of two fa-
miliar compounds: unaltered iPrBIP, and the expected 4-tri-
methylsilylmethyl BIP derivative 2c, each one representing
20% of the mixture. The other products, 4 and 4’, were iden-
Complex 3 has a square-pyramidal coordination environ-
ment around the Mn atom, with one of the alkyl groups sit-
ting on the apical site, while the other shares the base with
the iPrBIP nitrogen atoms. The molecule has a crystallo-
graphically imposed mirror plane that contains the MnR2
1
tified with help of their 2D H COSY and NOESY spectra.
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Coordination Chemistry
FULL PAPER
after treatment with methanol.
The disappearance of 4 and 4’
suggests that the corresponding
precursor complexes, 5 and 5’,
are intermediates in the forma-
tion of 1c, as shown in the
upper part of Scheme 3. Ac-
cordingly, the alkyl group mi-
grates sequentially from the
metal centre to the 2-position
in the heterocyclic ring, and
then to the 4-position. This
would be similar to alkyl migra-
tions observed by Copꢀret for
the reaction of dineopentyl-
manganese with a-diimines.[18]
The process concludes with hy-
drogen loss and aromatisation,
producing the final product, 1c.
As discussed previously, it is
reasonable to assume that this
mechanism operates in the for-
mation of compounds of the
Scheme 3.
type 1 on a general basis. Al-
though in our previous studies,
The major component (35%) of the mixture, 4’, gives rise to
a diagnostic multiplet at d=3.62 ppm, corresponding to the
4-C(R)-H signal of a 1,4-dihydropyridine derivative. This
signal is coupled to both the alkyl CH2 and to the 3,3’-pyri-
dine protons, which produce a single resonance at d=
5.09 ppm, as expected for a symmetric 1,4-dihydropyridine.
In contrast, the central ring of 4 is a non-symmetric 1,2-dihy-
dropyridine derivative with the alkyl ring bound to one of
the heterocyclic a-carbon atoms. Consistently, this com-
pound gives rise to a set of three mutually coupled resonan-
ces at d=5.32, 5.40 and 5.99 ppm, and two different acetal-
dimino (Me-C=N(Ar)) signals. The absence of couplings in
the Me3SiCH2 methylene signal confirms that it is bound to
a quaternary carbon atom. While iPrBIP and 2c are evidently
formed by the methanolysis of 3 and from 1c, compounds 4
and 4’ must originate from the MnII–dihydropyridinate(À1)
complexes 5 and 5’ (Scheme 3, top), although these have not
been isolated from the reaction mixture, probably due to
their high solubility. Notice that this result is consistent with
the isolated yield of complex 1c (ca. 20%), and implies that
the alkyl transfer does not proceed to completion under the
conditions of this experiment.
When a solution of 3 is heated at 608C, the characteristic
colour change from blue to burgundy takes place within a
few minutes. After heating for 30 min, methanolysis afford-
ed compounds 4, 4’ and 2c in a relative ratio of 3:6:2, but
not iPrBIP, showing that alkyl transfer to the ring is now
complete. Thus, under these conditions, migration of the tri-
methylsilylmethyl group to the pyridine ring is fast, but the
intermediates 4 and 4’ still survive for some time. However,
these two products disappear when the heating is extended
for four days, leaving compound 2c as the only product
1,4-dihydropyridines of the type 4’ were obtained in high
yields, while analogues of 4 were not observed, this is proba-
bly due to the low stability of intermediates of type 5. It is
also possible that the full reaction sequence might involve a
sequence of elemental 1,2- rather than 1,3-shifts, but the cor-
responding intermediates are too unstable to be trapped. It
is worth noting here that the migration of the CH2CMe2Ph
group that leads to 1a rules out the participation of free rad-
icals, because the neophyl radical is known to rapidly rear-
ranged to the more stable 1,1-dimethyl-2-phenylethyl,[24] and
the corresponding 4-R-BIP derivative has not been detect-
ed. This consideration supports further the intramolecular
nature of the alkyl migration mechanism, although more
complex mechanisms involving intermolecular alkyl transfer
cannot be entirely ruled out.
Cationic alkyl complexes: Cationic alkyl complexes play an
important role in most olefin polymerisation catalyst sys-
tems, and it is believed that this is the case for BIP-contain-
ing catalysts as well. Some years ago, Chirik studied the re-
action of the dialkyl complex [Fe
the protic acid [PhNMeH2]
+A[BPh4]À, which led to the isola-
tion of complexes of type [Fe(CH2SiMe3)(L)
(iPrBIP)]+.[11]
(CH2SiMe3)2iPrBIP] with
ACHTUNGTRENNUNG
CTHUNGTRENNUNG
A
ACHTUNGTRENNUNG
When L is diethyl ether, the cationic iron alkyl behaves as a
single-component catalysts for ethylene polymerisation. We
decided to prepare similar cationic manganese derivatives,
containing pyridine as ancillary ligand (L). For this purpose,
have used two different approaches converging in the same
type of product (Scheme 4). The first one is analogous to
Chirikꢆs route for cationic alkyliron complexes, and consists
in reacting 3 with the pyridinium salt [H(Py)2]
(Ar’=3,5-C6H3A(CF3)2) as a protic acid. The second method
CHTUNGTRENNUNG
+A[BAr’4]À
CTHUNGTRENNUNG
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13837

J. Cꢃmpora et al.
bon solvents, expected for an
ionic compound. The second
route is more general and
allows the preparation of stable
cationic MnII derivatives con-
taining “normal” alkyl groups
without
stabilising
b-silyl
groups. Thus, complex 6, the
neophyl analogue of 7, was ob-
tained in 40% yield as violet
Scheme 4.
involves the reaction of the pyridine complex [{Mn-
A
crystals
from
(CH2SiMe3)2(Py)}2] with the protonated ligand [HiPrBIP]+
[Mn(CH2CMe2Ph)2(Py)2]. Magnetic susceptibilities mea-
sured in solution for compounds 6 and 7 at 258C provide
values of meff of 5.9 and 6.1 mB, respectively, in good agree-
ment with their formulation as high-spin MnII species. The
identity of 6 was confirmed by its crystal structure, shown in
Figure 3.
ACHTUNGTRENNUNG
A
CHTUNGTRENNUNG
CHTUNGTRENNUNG
Figure 2. Crystal structure of [HiPrBIP]+[BAr’4]À. Selected bond lengths
Figure 3. Crystal structure of compound 6 (cationic part). Selected bond
À
À
À
(ꢅ) and angles (8): N3 H3, 0.950(4); H3 N1, 2.04(5); H3 F2, 2.22(5);
À
À
lengths (ꢅ) and angles (8): Mn1 C34, 2.1257(18); Mn1 N4, 2.2122(15);
À
À
N3···N1, 2.619(4); N3···F2, 2.906(4); C40 N3, 1.289(4); C34 N2, 1.278(4);
N3-H3-N1, 117(2); N3-H3-F2, 128(2).
À
À
À
À
Mn1 N2, 2.2323(14); Mn1 N1, 2.3519(14); Mn1 N3, 2.4243(15); C1 C7,
À
À
À
1.495(2); C5 C6, 1.489(2); C6 N1, 1.285(2); C7 N3, 1.283(2); C34-Mn1-
N2, 141.35(6); N2-Mn1-N4, 98.20(5); N1-Mn1-N4, 97.56(5); N3-Mn1-N4,
96.66(5); N1-Mn1-N3, 138.60(5)
imonium proton was located bound to nitrogen atom N3, in-
dicating that the imine functionality behaves as a stronger
base than the pyridine ring. The neutral C34=N2 group is
The cationic fragment of compound 6 exhibits a penta-
coordinated manganese atom in approximate square-pyra-
midal coordination environment, with the iPrBIP ligand and
one of the alkyls occupying three basal positions, as ob-
served for 3, and the pyridine ligand at the apex. In spite of
the positive charge of 6, metal–ligand bond lengths in the
neutral and cationic species are very similar. Thus, the basal
À
antipleriplanar with regard to the pyridine C38 N1 bond,
which is the preferred configuration of imine groups in free
BIP ligands. In contrast, the protonated imine adopts the
opposite configuration with the NH facing the pyridine N1
atom, because this allows hydrogen-bonding stabilisation.
The imonium proton forms an additional hydrogen bond
with F2, one of the fluorine atoms of the tetraarylborate
anion. This interaction is probably rather weak, but illus-
À
Mn C bond is only marginally shorter in 6 (2.133(2) ꢅ for 3
vs. 2.1257(18) ꢅ for 6), and the bond to the central pyridine
atom (N2) is even slightly longer in the cation. In contrast
with 3, coordination of the iPrBIP ligand is rather unsymmet-
À
trates the capability of the BAr’4 ion for weak interactions
with H-bond donors.
À
À
As expected, the two reactions described in Scheme 4
converge in the formation of the same substance, cationic
complex 7, in 76% and 81% yields, respectively. This com-
pound was isolated as violet material, insoluble in hydrocar-
rical in 6, with one of the two Mn NACHNUTGTRENNUNG
being almost as long as that of 3, while the other (Mn N1)
À
À
is 0.072 ꢅ shorter. The shortest Mn N distance in 6 corre-
sponds to the apical pyridine ligand. Interestingly, in the
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Coordination Chemistry
FULL PAPER
analogous Fe derivatives [Fe(R)(L)iPrBIP]+ (R=CH2SiMe3,
L=Et2O or THF)[11b] the alkyl group and the neutral L
ligand invert their relative positions, with the lying in the
basal position and the former occupying the apex.
1,3- or 1,2-alkyl shifts), followed by spontaneous hydrogen
loss and aromatisation, has been proposed. Compounds 1a
and 1b are most likely formed through analogous mecha-
nisms, but the corresponding dialkylmanganese intermedi-
ates are too unstable to be detected. This behavior resem-
bles the chemistry of the analogous Fe complexes, and thus
the ability of the trimethylsilylmethyl group to stabilise
high-valent BIP–alkyl complexes appears to be a common
feature among first-row transition metal elements.
Attempted ethylene polymerisation: We have shown that
complexes of type [FeACHTNUGTRENNU(G CH2SiMe3)2ACHUTNGTRENN(UNG BIP)] become active eth-
ylene polymerisation catalysts in the presence of very mild
activators, such as trimethylaluminum (AlMe3) or triisobutyl-
aluminum (TIBA) or even Al(Me)(O-2,4,6-C6H2-tBu3)2.[20]
The availability of an array of alkylmanganese iPrBIP com-
plexes provided new opportunities for testing the potential
activity of this kind of compounds in olefin polymerisation.
Therefore, we carried out a set of ethylene polymerisation
tests using neutral 3 and cationic 6 complexes under similar
Cationic MnII alkyl complexes of type [Mn(R)(Py)-
AHCTUNGTRENNUNG
(iPrBIP)]+ (complexes 6 and 7) can be prepared either by
protonation of [Mn
tetraarylborate, or by reaction of the salt [H
[BAr’4]À with dialkyl precursors [{MnR2(Py)}2]. In contrast
with the neutral dialkyl MnII complexes, these cationic
monoalkyls are thermally stable, even for R groups without
ACHTUTGNRENNUG(CH2SiMe3)2ACTHUNGTRENNNUG
(iPrBIP)] (3) with pyridinium
(iPrBIP)]+
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
conditions,
employing
modified
methylaluminoxane
ACHTUNGTRENNUNG
(MMAO), AlMe3 or B
N
stabilising b-silyl groups.
lytic activity was detected in any of these experiments.
Monoalkyl complexes 1 are formally MnI derivatives, and
thus isoelectronic with catalytically active FeII derivatives.
The 4-alkyl groups in the central ring of these compounds
are not expected to perturb their catalytic activity, since the
presence of such substituents has no significant effects on
the activity of FeII or CoII catalysts.[25] Thus, they might be
promising candidates to generate active ethylene polymeri-
sation catalysts. However, no activity was detected when
compound 1b was tested in the presence of MMAO, AlMe3
Attempts to generate active ethylene polymerisation cata-
lysts from either neutral Mn dialkyl 3 or from cationic MnII
dialkyl 6 and typical activation agents such as MMAO,
AlMe3 or BACHTUNTRGNEUNG(C6F5)3 have been unsuccessful. It is striking
that, in spite of the remarkable analogies in the structure
and chemical behaviour of the BIP alkyl derivatives of Fe
and Mn, the former give rise to highly active catalysts, while
the latter are essentially inactive. The failure of the Mn
complexes to catalyse ethylene polymerisation could be due
to the high stability of the d5 electronic configuration of the
high-spin MnII ion, which renders intermediate spin states
with empty d orbitals energetically unavailable. This situa-
tion prevents the coordination of the olefin monomer and
frustrates migratory insertion, the essential step in coordina-
tion olefin polymerisation. In spite of being isoelectronic
with the FeII–BIP catalysts, the formally MnI complex 1a
proves also inactive in the presence of the above-mentioned
co-catalysts. It is very likely that this class of monoalkyl
compounds are actually MnII complexes containing a mono-
anionic BIP radical ligand, and therefore it is not too sur-
prising that, similarly to 3, 6 or 7, they are also catalytically
inactive.
or AlACHTUNGTRENNUNG(iBu)3 as cocatalysts. This would not be too surprising
since if, as previously mentioned, compounds like 1 are ac-
tually MnII complexes containing a monoanionic BIP radical
ligand.
Conclusion
In this article we have addressed the questions of whether
MnII alkyl complexes stabilised by BIP ligands are isolable
compounds, and whether they can give rise to active olefin
polymerisation catalysts. The reaction of suitable dialkyl-
manganese complexes ,such as homoleptic dialkyls
[(MnR2)n] or [{MnR2ACTHNURGTNE(UNG thf)}2], with BIP ligands is an efficient
methodology for this purpose. Specifically, we investigated
the reactions of the iPrBIP ligand with neophyl
(CH2CMe2Ph), benzyl and trimethylsilylmethyl manganese
alkyls. Only in the last case does this method afford the ex-
Experimental Section
All manipulations were carried out under oxygen-free argon atmosphere,
using conventional Schlenck techniques or a nitrogen filled glove box.
Solvents were rigorously dried and degassed before using. Methanol was
refluxed over sodium methoxide, distilled and kept in a glass ampoule
over activated molecular sieves under inert atmosphere. Microanalyses
were performed by the Microanalytical Service of the Instituto de Inves-
tigaciones Quꢁmicas. Infrared spectra were recorded on a Bruker Vector
22 spectrometer, and NMR spectra on Bruker 300, 400 and 500 MHz
spectrometers. The 1H and 13C{1H} resonances of the solvent were used
as the internal standard, but the chemical shifts are reported with respect
to TMS. Magnetic susceptibilities were measured at 298 K by Evansꢆ
method.[26] Magnetic moments have been calculated from the average
values of two independent measurements of the magnetic susceptibility
and are corrected for the diamagnetic contributions estimated from
Pascal constants.[27]
pected MnII dialkyl, [Mn (iPrBIP)] (3), while in
ACHTUNGRTENN(UG CH2SiMe3)2ACHUTNGTRENNUGN
the other two, it leads to the formation of formally MnI
monoalkyl complexes 1a and 1b, in which one of the R
groups, originally bound to the metal center, has been trans-
ferred to the 4-position of the pyridine ring of the BIP
ligand. Compound 3 also undergoes this alkyl transfer pro-
cess, although much more slowly, leading to the monoalkyl-
manganese derivative 1c. Detailed studies on this particular
transformation allowed the identification of 1,2- and 1,4-di-
hydropyridinate(À1) complexes 4 and 4’ as intermediates in
the alkyl migration process. Accordingly, an intramolecular
mechanism involving elemental alkyl migration steps (either
Chem. Eur. J. 2010, 16, 13834 – 13842
ꢄ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13839

J. Cꢃmpora et al.
MnCl2 was purchased from Aldrich Chemical Co. and rigorously dried
following a literature method.[28] Pyridine was refluxed over Na, distilled
and stored in a gastight ampoule under Ar protected from the light.
Stock solutions of the Grignard reagents Mg(R)Cl (R=CH2SiMe3,
CH2CMe2Ph and CH2Ph) were prepared according to conventional pro-
Methanolysis of 3: Compound 3 (0.100 g, 0.14 mmol) was dissolved in tol-
uene (15 mL). MeOH (5 mL) was added to the dark blue solution at
room temperature. The resultant mixture turned brown and a precipitate
of the same colour was formed. The suspension was filtered and the re-
sulting dark yellow solution was passed through an Et3N-doped silica
column. The resultant yellow solution was evaporated to dryness, leading
to the recovery of 0.060 g (0.12 mmol, 88%) of iPrBIP.
cedures. Mg
solution of Mg
precipitate by centrifugation. The manganese alkyl precursors [Mn-
(CH2SiMe3)2A(thf)], [Mn(CH2SiMe3)2(Py)], [{Mn(CH2CMe2Ph)2}2],
[Mn(CH2CMe2Ph)2(Py)2], and [{Mn(CH2Ph)2A(thf)}2], as well as the acid
[H(Py)2]
+A[BAr’4]À were prepared as described in a precedent publica-
tion.[20] The homoleptic trimethylsilylmethyl derivative [Mn-
(CH2SiMe3)2][29] and the acid [H +A[BAr’4]À[30] were obtained as de-
(Et2O)2]
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
[Mn
(0.4 mmol) in toluene (30 mL), directly prepared from [Mn
AHCTUNGTRENNUNG
(thf)] and iPrBIP was stirred for 72 h at room temperature. During this
ACHUTGTNERN(NUG CH2SiMe3){4-ACTHUNGTRENNNUG
AHCTUNGTRENNUNG
A
N
ACHTUNGTRENNUNG
A
CHTUNGTRENNUNG
time, the colour gradually changed from blue to purple. The solution was
taken to dryness, and the oily residue was extracted in hexane (25 mL),
filtered, concentrated to about 2/3 of its original volume and stored at
À308C. The product precipitates as a powdery purple solid, which was fil-
tered out and dried in vacuo. Yield 0.860 g, 29%; elemental analysis
calcd (%) for C41H64MnN3Si2 C 69.35, H 9.08, N 5.92; found: C 68.82, H
9.44, N 5.93; IR (Nujol mull): n˜ =1625, 1590 (4-R-iPrBIP), 1250, 852 cmÀ1
CHTUNGTRENNUNG
A
R
CHTUNGTRENNUNG
scribed in literature. The synthesis and spectroscopic properties of com-
pounds 1a, 2a and 2b have been reported before.[18]
Methanolysis of compound 1a: Compound [{Mn(CH2CMe2Ph)2}2][17]
(0.280 g, 0.03 mmol) was dissolved in dry C6D6 (0.6 mL). To this solution,
dry methanol (3 mL, 2 equiv) was added and a brown precipitate ap-
peared. The volatile components of the mixture were transferred under
(nACHTUNGTRENUNG(Si-C)); meff =4.8 mB.
Methanolysis of compound 1c—formation of 4-(Me3SiCH2)iPrBIP (2c):
Compound 1c (0.180 g, 0.25 mmol) was treated as described for the
methanolysis of 2, affording 0.12 g of 2c (84 % yield). 1H NMR (C6D6,
298 K, 300 MHz): d=À0.11 (s, 9H; CH2SiMe3), 1.18 (d, 3JHH =6.7 Hz,
12H; CHMe), 1.24 (d, 3JHH =6.9 Hz, 12H; CHMeꢀ), 1.85 (s, 2H;
CH2SiMe3), 2.34 (s, 6H; CH3C=NAr), 2.97 (sept, 4H; CHMe2), 7.17–7.24
(m, 6H; CHar), 8.45 ppm (s, 2H; 3-CHar(py)); 13C{1H}-NMR (C6D6, 298 K,
125 MHz): d=À2.8 (s, CH2SiMe3), 16.8 (s, CH3C=NAr), 23.1, 22.5 (s,
CHMe2), 27.0 (s, CH2SiMe3), 28.6 (s, CHMe2), 122.1 (s, CHar), 123.2 (s,
CHar), 123.9 (s, CHar), 135.5 (s, Car), 146.9 (s, Car), 151.1 (s, Car), 155.0 (s,
Car), 166.8 ppm (s, CH3C=NAr). ESI MS: m/z: 590.4 [M+Na]+.
1
vacuum into a cold trap, and analysed by H, 13C NMR, GC and GC-MS,
which showed the presence of equimolar amounts of tBu-Ph and
CH3OH. This indicates that only one equivalent of the latter had been
consumed in the reaction. The dry residue was extracted in C6D6, filtered
and analysed by 1H and 13C NMR spectroscopy, showing the presence of
4-(PhCMe2CH2)-iPrBIP (2a)[18] as the only detectable organic component.
The same experiment using only one equivalent of CH3OH led to similar
results, but the volatile fraction did not contain significant amounts of
the alcohol.
A
similar experiment was carried out using CD3OD. In this case,
Monitoring the transformation of 3 into 1c: A dark blue toluene solution
of compound 3 (12.7 mmol, 9.0 mg) was stirred in a Youngꢇ Teflon tap
sealed glass ampoule. After 96 h, the solution, which had turned purple,
was treated with excess of anhydrous methanol. Solvents and volatiles
were removed from the resultant red-orange solution. An orange oil was
isolated, which was then extracted in hexane (3ꢈ25 mL), leading, after
solvent evaporation, to yellow-orange oily residue This was dissolved in
C6D6 and analysed by 1H NMR spectroscopy, showing the presence of
four compounds (together with trace amounts (ca. 5%) of related com-
pounds of unknown structure). The identified compounds are: iPrBIP
(25%), 4-alkyl-bisiminopyridine (2c 21%), 4-alkyl-bisimino-1,2 dihydro-
pyridine (4; 21%) and 4-alkyl-bisimino-1,4 dihydropyridine (4’; 33%).
PhCMe2CH2D was detected in the volatile fraction, while the solid resi-
due contained 2a.
(CH2Ph)(4-PhCH2-iPrBIP)] (1b): A solution of [{Mn
[MnACHTUNGTRENNUNG ACHTUNRTEG(NGNNU CH2Ph)2ACHTNUGRTEN(NUGN thf)}2]
(0.34 g, 1.1 mmol)[18] in toluene (15 mL) was added to a solution of iPrBIP
(0.48 g, 1 mmol) in toluene (10 mL) that was being stirred at À408C. The
colour of the mixture turned to dark red within seconds. The stirring was
continued for 5 min at this temperture and then for 45 min at room tem-
perature. Volatiles were removed and the resultant oily residue was ex-
tracted in hexane (15 mL). The solution was filtered and cooled at
À308C. A purple microcrystalline precipitate (1b) was formed, which
was collected by filtration and dried under vacuum. Yield, 0.23 g, 31%;
elemental analysis calcd (%) for C47H56MnN3: C 78.63, H 7.86, N 5.85;
found: C 78.52, H 7.99, N 5.84; IR (Nujol mull): n˜ =3060, 1588, 1566,
Data for 4: 1H NMR (C6D6, 298 K, 500 MHz): d=À0.10 (s, 9H;
CH2SiMe3), 0.99 (d, 3JHH =8.5 Hz, 12H; CHMe2), 1.02 (d, 3JHH =8.5 Hz,
12 H; CHMe2ꢆ), 1.85 (m, 2H; CH2SiMe3), 1.63 (s, 3H; CH3C=NAr), 1.57
1492, 1401, 1325, 1309, 1267, 1094, 1057. 971, 790, 744, 698 cmÀ1; meff
4.8 mB
=
3
(s, 3H; CH3C=NAr), 2.83 (sept, 4H; CHMe2), 5.32 (d, JHH =8.0 Hz, 1H;
3
3,5-CHar(py)), 5.40 (d, 3JHH =11.0 Hz, 1H; 3,5-CHar(py)), 5.99 (dd, JHH
=
Methanolysis of compound 1b: Compound 1b (0.033 g) was reacted with
two equivalents of methanol as described for the methanolisis of 1a.
Analysis of the volatile components indicated the presence of equimolar
amounts of toluene and methanol, while the non-volatile fraction consist-
ed of 4-(PhCH2)iPrBIP, (2b).[18]
11.0, 8.0 Hz 1H; 4-CH 3,5-CHar(py)), 6.38 (s, 1H; N-H) 7.08–7.23 ppm (m,
6H; CHar); some coupling constants are not included, because they could
not be accurately calculated due to signal overlapping.
Data for 4’: 1H NMR (C6D6, 298 K, 300 MHz): d=0.10 (s, 9H;
CH2SiMe3), 1.11 (brd, 12H; CHMe2), 1.14 (brd, 12H; CHMe2ꢀ), 1.89 (s,
2H; CH2SiMe3), 1.74 (s, 6H; CH3C=NAr), 2.83 (sept, 4H; CHMe2), 3.58
(brq, 1H; 4-CH CHar(py)) 5.08–5.10 (m, 2H; 3,5-CHar(py)) 7.23–7.26 (m,
6H; CHar), 8.90 ppm (brs, 1H; N-H); some coupling constants are not in-
cluded, because they could not be accurately calculated due to signal
overlapping.
[Mn
Method A, from [{Mn
(CH2SiMe3)2}n] (0.30 g, 1.3 mmol) in toluene (15 mL) was added to a
A
E
iPrBIP)] (3)
(CH2SiMe3)2}n]:
U
A
suspension of [{Mn-
ACHTUNGTRENNUNG
stirred suspension of iPrBIP (0.580 g, 1.2 mmol) in toluene (10 mL) at
À408C. The colour of the mixture changed gradually from pale orange to
dark blue. After 5 min, the cold bath was removed, and the mixture
stirred for 30 min at room temperature. The solution was concentrated to
about 1/3 of the original volume, and stored at À308C. Blue crystals were
observed after 24 h. These were collected by filtration and dried in
vacuum to afford 0.490 g (57%) of product 3.
In a second experiment, a Youngꢇ Teflon tap sealed NMR tube contain-
ing a solution of compound 3 (12.7 mmol, 9.0 mg) in toluene (0.7 mL) was
heated at 608C in oil bath. The dark blue solution turned dark-red within
few minutes. The solution was quenched with an excess of methanol after
30 min at the said temperature. After the above-mentioned organic stan-
dard workup, the yellow residue was dissolved in C6D6 and analysed by
1H NMR spectroscopy, showing the presence of signals attributed to com-
pouns 4, 4’ and 2c in 26:57:17 ratio and total absence of unsubstituted bis-
Method B, from [{MnACHTUNGTENR(UNNG CH2SiMe3)2ACHTUNTGRNE(UNG thf)}2]: [{MnACHTUNGERTNN(GNU CH2SiMe3)2ACHTNUGRTEN(NUGN thf)}2]
(0.900 g, 3 mmol) was dissolved in toluene (15 mL) and reacted with an
equimolar amount of iPrBIP as described above. The same workup afford-
ed 1.210 g (61% yield) of 3. Elemental analysis calcd (%) for
C41H65MnN3Si2: C 69.25, H 9.21, N 5.91; found.: C 69.26, H 9.21, N 5.66;
IR (Nujol mull): n˜ =1635, 1590 (iPrBIP); 1260, 871 cmÀ1 (SiMe3); meff
5.9 mB.
iminopyridine
(608C) during 96 h, the only product observed is 2c.
Synthesis of [HiPrBIP]+A[BAr’4]À:
solution of [H
(1.010 g, 1 mmol) in of Et2O (10 mL) was added dropwise to a stirred
(
iPrBIP). When the same experiment was performed
=
C
A
ACHTUNGTREN(NUG Et2O)2]ACHTUNGTRENNUNG[BAr’]4
13840
www.chemeurj.org
ꢄ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 13834 – 13842

Coordination Chemistry
FULL PAPER
suspension of iPrBIP (0.480 g, 1 mmol) in Et2O (20 mL) at À308C. The re-
sulting orange solution was stirred for 5 min, and then for additional 1 h
at room temperature. The solvent was then evaporated under vacuum.
The yellow residue was recrystallised from a 2:1 mixture of diethyl ether
Table 1. Crystal and refinement data.
3·C7H8
[HBIP][BAr’4]
6
formula
Mr
C48H73MnN3Si2
803.21
C65H56BF24N3
1345.94
293(2)
C80H73BF24N4Mn
1612.17
100(2)
0.4ꢈ0.2ꢈ0.2
monoclinic
P21/c
12.5799(3)
19.7359(6)
30.8501(10)
90
90.5860(10)
90
7658.9(4)
4
1.398
0.277
1.22-30.52
48014
CTHNUGTRNENUG
and hexane, affording [HiPrBIP]+A[BAr’4]À as yellow crystals. Yield,
3
1.010 g, 75%; 1H NMR (CD2Cl2, 298 K, 300 MHz): d=1.16 (d, JHH
=
T [K]
173(2)
6.8 Hz, 12H; CHMe), 1.20 (d, 3JHH =6.9 Hz, 12H; CHMeꢀ), 2.52 (s, 6H;
CH3-C=NAr), 2.64 (sept, 3JHH =6.8 Hz, 4H; CHMe2), 7.33 (m, 6H;
CHar), 7.55 (s, 4H; CHar), 7.72 (brs, 8H; CHar), 8.43 (t, J=8.1 Hz, 1H; 4-
CH(py)), 8.63 (d, J=8.1 Hz, 2H; 3-CH(py)), 11.58 ppm (s, 1H; NH). IR
(Nujol mull): n˜ =1637, 1611, 1589 (HiPrBIP+) 1277, 1127, 890 cmÀ1
(BAr’4À); elemental analysis calcd (%) for C65H56BF24N3 C 58.00, H 4.19,
N 3.12; Found: C 58.04, H 4.00, N 3.13.
crystal size [mm]
crystal system
space group
a [ꢅ]
b [ꢅ]
c [ꢅ]
0.5ꢈ0.5ꢈ0.1
monoclinic
P21/m
9.2626(3)
14.4853(6)
18.5098(8)
90
0.5ꢈ0.3ꢈ0.1
triclinic
¯
P1
14.4268(7)
14.5529(8)
17.9210(9)
83.7840(8)
70.1920(9)
63.2210(10)
3163.7(3)
2
1.413
0.132
1.57-28.84
24866
16397
a [8]
b [8]
100.6570(10)
90
2440.65(17)
2
1.093
0.352
1.12–30.53
44726
7320
278
0.0444
[Mn(CH2CMe2Ph)(Py)
(
CTHUNGTERNNUNG
iPrBIP)]+A[BAr’4]À (6): The acid [HiPrBIP]+
g [8]
ACHTUNGTRENNUNG
[BAr’4]À (1.345 g, 1 mmol) was dissolved in diethyl ether (15 mL), and
V [ꢅ3]
Z
the
solution
was
added
dropwise
into
a
solution
of
[Mn(CH2CMe2Ph)2(Py)2][20] (0.500 g, 1.05 mmol) in diethyl ether (15 mL),
stirred at À608C. The colour of the mixture turned violet. After 5 min,
the bath was removed and the mixture was stirred for 30 min at the room
temperature. The solvent was removed under vacuum, leaving a violet-
coloured foam, which solidified upon washing with hexane (15 mL). This
was extracted in diethyl ether (15 mL). The suspension was filtered and
hexane was carefully added until slight turbidity. Violet crystals appeared
when the solution was allowed to rest at À108C. Yield: 0.620 g, 32%; ele-
mental analysis calcd (%) for C80H73BF24MnN4 C 59.60, H 4.56, N 3.48;
found: C 58.98, H 4.53, N 3.56; IR (Nujol mull): n˜ =1630, 1603, 1593
(BIP); 1280, 1129, 885 cmÀ1 (BAr’4); meff =6.1 mB.
1calcd [MgmÀ3
]
m [mmÀ1
q range [8]
]
reflns collected
reflns used
parameters
R1 [I>2s(I)]
wR2 (all data)
GOF
22959
1001
0.0518
0.1499
852
0.0729
0.2158
0.998
0.1082
1.025
1.048
[Mn
Route A, from compound 3:
ACHTUNGTRENNUNG(CH2SiMe3)(Py)ACHTUNGTRENNUNG( CHTUNGTRENNUNG
iPrBIP)]+A
[BAr’4]À (7)
X8Apex-II CCD diffractometer (6) or coated with an epoxy polymer
(T=293(2) K) were collected on a Bruker SMART Apex CCD diffrac-
tometer ([HBIP]ACHTUNGTRENGN[U BAr’4]), both equipped with a MoKa1 radiation (l=
A
fine suspension of [H(Py)2]ACTHNUTRGEN[UNG BAr’4]
(1.020 g, 1 mmol) in toluene (15 mL) was added dropwise to a solution of
3 (0.780 g, 1.10 mmol) in toluene (30 mL) stirred at À408C. The mixture
turned from dark blue to violet. The stirring was kept 5 min at À408C
and 25 min at room temperature. Solvents and volatiles were then re-
moved and the violet solid was washed with hexane (15 mL). The resul-
tant solid was taken up in Et2O (15 mL), filtered, and hexane was added
again to the solution until it became slightly turbid. Crystals of 7 ap-
peared after storing the solution overnight at À308C. Filtration and
drying yielded, 1.190 g, 76%.
0.71073 ꢅ) source and graphite monochromator. The data were reduced
(SAINT)[31] and corrected for Lorentz polarisation and absorption effects
by multiscan method (SADABS)[32]. The structure was solved by direct
methods (SIR-2002)[33] and refined against all F2 data by full-matrix least-
squares techniques (SHELXTL-6.12)[34] minimising w[F2oÀFc2]2. All non-
hydrogen atoms were refined with anisotropic thermal parameters. Hy-
drogen 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) those Ueq values
of the corresponding carbon atoms. Table 1 contains some more details
of the crystallographic measurements. CCDC-773733 (3), 773734
([HiPrBIP]+[BAr’4]À) and 773735 (6) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Route B, from [{Mn
ligand [HiPrBIP]+A[BAr’4]À (0.910 g, 0.68 mmol) in diethyl ether (15 mL)
was dropwise added to a stirred solution of [{Mn
(CH2SiMe3)2(Py)}2][21]
ACHTUNGTRENNUNG(CH2SiMe3)2(Py)}2]: A solution of the protonated
CHTUNGTRENNUNG
AHCTUNGTRENNUNG
(0.240 g, 0.39 mmol) in diethyl ether (15 mL), cooled at À608C. The
colour of the mixture first changed to dark blue and then to violet. Fol-
lowing the same workup described for Route A, 0.950 g (89%) of com-
pound
7
were obtained. Elemental analysis calcd (%) for
C74H71BF24MnN4Si: C 56.75, H 4.57, N 3.58; found: C 56.44, H 4.41, N
3.54; IR (Nujol mull): n˜ =1607, 1584 (iPrBIP); 1279 (SiMe3); 1280, 1129,
889 cmÀ1 (BAr’4); meff =6.0 mB.
Attempted ethylene polymerisation: All attempts were carried out in a
Fischer–Porter glass reactor equipped with a septum-capped and magnet-
ic stirring. The temperature was fixed at 308C with a thermostatic oil
bath, and the ethylene pressure was 4 bar. Ethylene consumption was
monitored continuously. The reactor was charged with toluene (50 mL),
purged with ethylene to displace the original N2 atmosphere and allowed
to stabilise at the working temperature and pressure. Once the toluene
was saturated with ethylene at the desired pressure, freshly made solu-
tions containing the catalyst (10 mmol in 2 mL of toluene) and the co-cat-
alyst were successively injected through the septum port. Complexes 3
and 7 were tested in combination with i) MMAO (400 or 1000 equiv); ii)
Acknowledgements
Financial support from the DGI, Junta de Andalucꢁa and European
Union (Projects CTQ2009-11721 Project FQM5074 and FEDER funds)
and CSIC (PIF 08-017-1) is gratefully acknowledged. C.M.P. thanks a re-
search contract from Repsol-YPF. A.R.-D. acknowledges a postdoctoral
contracts from the Ministerio de Educaciꢉn y Ciencia (Ramꢉn y Cajal
program).
BACHTUNGTRENNUNG
[1] a) E. C. Alyea, G. Ferguson, R. J. Restivo, Inorg. Chem. 1975, 14,
2491–2495; b) E. C. Alyea, P. H. Merrel, Inorg. Met.-Org. Chem.
1974, 4, 535–539; c) B. de Bruin, E. Bill, E. Bothe, T. Weyhermuller,
K. Wieghardt, Inorg. Chem. 2000, 39, 2936–2947.
[2] a) B. L. Small, M. Brookhart, A. A Bennett, J. Am. Chem. Soc.
1998, 120, 4049–4050; b) G. J. P. Britovsek, V. C. Gibson, B. S. Kim-
berley, P. J. Maddox, S. J. McTavish, G. A. Solan, A. J. P. White, D. J.
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AHCTUNGTRENNUNG
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Received: May 23, 2010
Published online: October 19, 2010
13842
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Chem. Eur. J. 2010, 16, 13834 – 13842