Fourth generation scorpionates: Coordination behavior of a new class of conformationally flexible mixed-donor (pyrazol-1-yl)borates

Article abstract of DOI:10.1021/ic100104t

The coordination behavior, the conformational flexibility, and the stability of the novel (pyrazol-1-yl)borate ligands [Ph(pz)B(μ-N(Me))(μ- pz)B(pz)Ph]- ([L¹]-), [Ph(pz)B(μ-O)(μ-pz)B(pz)Ph]- ([L2]-), and [Ph(pz)B(μ-O)(μ-OB(Ph)O)B(Pz)Ph]^2- ([L³] ² ) have been experimentally assessed by investigating the following compounds: [Ll(thf)L¹], [Li(thf)L²], [Mg(CI)(thf) _xL¹], [Mg(CI)(thf)₂L²], [Mn(CO) ₃L²], K(thf)[Mn(CO)₃L³], [CoCI ₂(HL¹)], [L¹Co(μ-CI)2CoL¹], [Zn(Br)L¹], [Cu(CI)L¹], [Cu(CI)L²]. The L-complexes were prepared from a mixture of HL¹ and the appropriate metal salt by addition of a base. HCl elimination from [CoCI₂(HL ¹)], which gives [L¹Co(μ-CI)2CoL¹], does not necessarily require the assistance of a base, but happens spontaneously when a solution of the complex Is stored at room temperature for several days. K(thf)[Mn(CO)₃L³] was obtained via in situ hydrolysis of HL¹[Mn(CO)₅Br] in the presence of K₂CO ₃. In some other cases, formation of the coordination compounds proceeded with decomposition of a part of the ligand molecules and yielded pyrazole (e.g., [Zn(CI)(Hpz)L²]) or pyrazolide (e.g., [L ²Co(μ-CI)(μ-pz)CoL²]) complexes. As evidenced by the crystal structure analyses of [Zn(Br)L¹l/[Mg(CI)(thf) ₂L²]/[Mn(CO)₃L²] on the one hand and [L¹ Mg(μ-CI)₂Mg(thf)L¹]-[Cu(CI)L ¹]-[Cu(CI)L²]₂ on the other, [L¹]- and [L²]- are able to adopt both a facial and a meridional conformation. Moreover, while many of the established design principles of scorplonate chemistry are still valid for [L¹]-, [L²]-, and [L³]²-, the bonding situation of the central donor moiety (N(Me) in [L¹]-; O in [L²]-, [L³] ^2-) is distinctly different from the way the pyrazolyl rings are attached to the molecule, so that donor scrambling is not an issue in these [N,N,N] and [N,O,N] mixed-donor ligands. 2010 American Chemical Society.

Full text of DOI:10.1021/ic100104t

3540 Inorg. Chem. 2010, 49, 3540–3552
DOI: 10.1021/ic100104t
Fourth Generation Scorpionates: Coordination Behavior of a New Class of
Conformationally Flexible Mixed-Donor (Pyrazol-1-yl)borates
Elena V. Mutseneck, Susanne Bieller, Michael Bolte, Hans-Wolfram Lerner, and Matthias Wagner*
€
Institut fu€r Anorganische und Analytische Chemie, Goethe-Universitat Frankfurt, Max-von-Laue-Strasse 7,
D-60438 Frankfurt (Main), Germany
Received January 18, 2010
The coordination behavior, the conformational flexibility, and the stability of the novel (pyrazol-1-yl)borate ligands
[Ph(pz)B(μ-N(Me))(μ-pz)B(pz)Ph]- ([L1]-), [Ph(pz)B(μ-O)(μ-pz)B(pz)Ph]- ([L2]-), and [Ph(pz)B(μ-O)(μ-OB-
(Ph)O)B(pz)Ph]2- ([L3]2-) have been experimentally assessed by investigating the following compounds: [Li(thf)L1],
[Li(thf)L2], [Mg(Cl)(thf)xL1], [Mg(Cl)(thf)2L2], [Mn(CO)3L2], K(thf)[Mn(CO)3L3], [CoCl2(HL1)], [L1Co(μ-Cl)2CoL1],
[Zn(Br)L1], [Cu(Cl)L1], [Cu(Cl)L2]. The L1-complexes were prepared from a mixture of HL1 and the appropriate metal
salt by addition of a base. HCl elimination from [CoCl2(HL1)], which gives [L1Co(μ-Cl)2CoL1], does not necessarily
require the assistance of a base, but happens spontaneously when a solution of the complex is stored at room
temperature for several days. K(thf)[Mn(CO)3L3] was obtained via in situ hydrolysis of HL1/[Mn(CO)5Br] in the
presence of K2CO3. In some other cases, formation of the coordination compounds proceeded with decomposition of a
part of the ligand molecules and yielded pyrazole (e.g., [Zn(Cl)(Hpz)L2]) or pyrazolide (e.g., [L2Co(μ-Cl)(μ-pz)CoL2])
complexes. As evidenced by the crystal structure analyses of [Zn(Br)L1]/[Mg(Cl)(thf)2L2]/[Mn(CO)3L2] on the one
hand and [L1Mg(μ-Cl)2Mg(thf)L1]/[Cu(Cl)L1]/[Cu(Cl)L2]2 on the other, [L1]- and [L2]- are able to adopt both a facial
and a meridional conformation. Moreover, while many of the established design principles of scorpionate chemistry are
still valid for [L1]-, [L2]-, and [L3]2-, the bonding situation of the central donor moiety (N(Me) in [L1]-; O in [L2]-,
[L3]2-) is distinctly different from the way the pyrazolyl rings are attached to the molecule, so that donor scrambling is
not an issue in these [N,N,N] and [N,O,N] mixed-donor ligands.
Introduction
Thus, to stabilize ML(X)-type complexes and to be able to
influence the ligands’ cone and wedge angles, “second gen-
eration scorpionates” with bulky substituents (e.g., Ph, tBu)
on the 3-positions of their pyrazolyl rings have been devel-
oped and are nowadays widely used.3
Finally, the term “third generation scorpionates” was coined
to designate poly(pyrazol-1-yl)borates (and methanes) that
are specifically functionalized at the non-coordinating, “back”
position.4 Such modifications can help, for example, to influ-
ence the crystal packing of scorpionate complexes and thereby
to bring about cooperative solid-state behavior,4 or to create
oligotopic scorpionate ligands as scaffolds for oligonuclear
metal complexes.5-20
Poly(pyrazol-1-yl)borates (“scorpionates”) of the general for-
mula [R0R00B(Rpz)2]- are extremely versatile ligands with appli-
cations ranging from cluster chemistry, bioinorganic chemistry,
and homogeneous catalysis to materials sciences (Rpz = (sub-
stituted) pyrazol-1-yl; R0, R00 = H, alkyl, aryl, Rpz).1,2
Already the first generation of scorpionates, which con-
sisted merely of species [H2B(Rpz)2]-, [HB(Rpz)3]-, and
[RpzB(Rpz)3]- bearing pyrazol-1-yl or 3,5-dimethylpyrazol-
1-yl donor groups, enjoyed tremendous interest because of
their relationship to the highly popular β-diketonate and
cyclopentadienyl ligands. However, because the coordina-
tion chemistry of first generation scorpionates is dominated
by the formation of unreactive ML2 (instead of ML(X))
complexes,3 the application range of the new ligand class in
homogeneous catalysis soon turned out to be limited.
A further extension of the scope of scorpionate ligands
requires (i) control not only over their steric demand but also
(4) Reger, D. L.; Gardinier, J. R.; Gemmill, W. R.; Smith, M. D.; Shahin,
A. M.; Long, G. J.; Rebbouh, L.; Grandjean, F. J. Am. Chem. Soc. 2005, 127,
2303–2316.
*To whom correspondence should be addressed. E-mail: matthias.wagner@
chemie.uni-frankfurt.de.
(1) Trofimenko, S. Scorpionates - The Coordination Chemistry of Poly-
pyrazolylborate Ligands; Imperial College Press: London, 1999.
(2) Pettinari, C. Scorpionates II: Chelating Borate Ligands; Imperial
College Press: London, 2008.
€
(5) Fabrizi de Biani, F.; Jakle, F.; Spiegler, M.; Wagner, M.; Zanello, P.
Inorg. Chem. 1997, 36, 2103–2111.
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Zanello, P.; Wagner, M. Inorg. Chem. 2001, 40, 4928–4936.
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(3) Trofimenko, S.; Calabrese, J. C.; Thompson, J. S. Inorg. Chem. 1987,
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r
pubs.acs.org/IC
Published on Web 03/03/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3541
over their ligand field strength and (ii) the design of conforma-
tionally more flexible frameworks that are able to support meri-
dional in addition to the common facial coordination modes.
The first problem has already been tackled by various
research groups who developed, “non-pyrazolyl scorpio-
nates” [R0B(Do)3]- possessing functional groups Do with
donor atoms other than N (e.g., P,21,22 S23-28). For a
systematic tuning of metal complex properties, it is, however,
desirable to possess complete homogeneous series of closely
-
related ligands of the form [R0B(Do1)x(Do2)3-x
]
(x = 0
to 3). Unfortunately, this is where scorpionate chemistry
exhibits its weaknesses because (i) the selective preparation of
a specific mixed-donor borate is often difficult to achieve, and
(ii) borate ions have a tendency for substituent scrambling.
At this point, we became interested in the question how the
architecture of classic poly(pyrazol-1-yl)borates can be mod-
ified further to meet current challenges of homogeneous
catalysis. Compounds of the type HL1/[L1]- and [Li(thf)L2]
(Figure 1) appeared to be particularly attractive, because they
present a mixed-donor set to the metal ion, and the bite angle
between the two pyrazolyl moieties should be sufficiently
large to make meridional binding a realistic option.
Figure 1. Two fourth generation scorpionates: HL1 and [Li(thf)L2].
Figure 2. Three experimentally observed isomers HL1, HL1A, and
HL1
The purpose of this paper is to explore the coordination
behavior, the conformational flexibility, and the stability of
HL1/[L1]- and [Li(thf)L2], for which we suggest the name,
“fourth generation scorpionates”.
.
B
the reaction of (i) the borazine derivative (B(Ph)N(Me))3 with
Hpz (1:3) in refluxing hexane or (ii) the diborylamine derivative
(Me2N(Ph)B)2NMe with Hpz (1:2.85) in refluxing Et2O.
We preferred the second route, which gives higher yields;
however, we modified the published synthesis protocol29 in
the following way: (i) The key compound (Me2N(Ph)B)2-
NMe was prepared from Me2N(Ph)BBr31,32 (instead of
Me2N(Ph)BCl) and (Me3Si)2NMe (pentane, -78 °C).33
(ii) The reaction time in the final step of synthesis sequence
was reduced from 25 to 12 h.
Results and Discussion
Both compounds, HL1 and [Li(thf)L2] (Figure 1), have al-
ready been described in the literature.29,30 HL1 is accessible via
(8) Zhang, F.; Bolte, M.; Lerner, H.-W.; Wagner, M. Organometallics
2004, 23, 5075–5080.
(9) Bieller, S.; Bolte, M.; Lerner, H.-W.; Wagner, M. Inorg. Chem. 2005,
44, 9489–9496.
(10) Haghiri Ilkhechi, A.; Mercero, J. M.; Silanes, I.; Bolte, M.; Scheibitz,
M.; Lerner, H.-W.; Ugalde, J. M.; Wagner, M. J. Am. Chem. Soc. 2005, 127,
10656–10666.
(11) Reger, D. L.; Watson, R. P.; Smith, M. D.; Pellechia, P. J. Organo-
metallics 2005, 24, 1544–1555.
(12) Casado, M. A.; Hack, V.; Camerano, J. A.; Ciriano, M. A.; Tejel, C.;
Oro, L. A. Inorg. Chem. 2005, 44, 9122–9124.
(13) Reger, D. L.; Watson, R. P.; Smith, M. D. Inorg. Chem. 2006, 45,
10077–10087.
(14) Reger, D. L.; Watson, R. P.; Gardinier, J. R.; Smith, M. D.;
Pellechia, P. J. Inorg. Chem. 2006, 45, 10088–10097.
(15) Reger, D. L.; Watson, R. P.; Smith, M. D.; Pellechia, P. J. Organo-
metallics 2006, 25, 743–755.
As already reported,29 the crude product of the synthesis of
HL1 consists of a mixture of three isomers (HL1, HL1A, and
HL1B; Figure 2) in a stoichiometric ratio of approximately
8:1:2. After recrystallization from hexane/benzene, only the
more abundant mirror-symmetric isomer HL1 was left,
1
together with HL1 (approximate ratio = 4:1; H NMR
B
spectroscopic control).
The X-ray crystal structure analysis of HL1 (Figure 3;
Table 1) revealed that the methyl group of the bridging N(H)-
Me moiety points toward the two phenyl rings, whereas the H-
atom is obviously engaged in intramolecular hydrogen bonds
(16) Zhang, F.; Morawitz, T.; Bieller, S.; Bolte, M.; Lerner, H.-W.;
Wagner, M. Dalton Trans. 2007, 4594–4598.
˚
with the pyrazolyl substituents (N(1) N(12) = 2.850(4) A,
3 3 3
€
(17) Ruth, K.; Tullmann, S.; Vitze, H.; Bolte, M.; Lerner, H.-W.;
˚
N(1) N(22) = 2.825(4) A; N(1)-H(1)-N(12) = 121(2)°,
Holthausen, M. C.; Wagner, M. Chem.;Eur. J. 2008, 14, 6754–6770.
(18) Morawitz, T.; Zhang, F.; Bolte, M.; Bats, J. W.; Lerner, H.-W.;
Wagner, M. Organometallics 2008, 27, 5067–5074.
3 3 3
N(1)-H(1)-N(22) = 119(2)°). We assume this bifurcated
hydrogen bond to be one reason why isomer HL1 is formed in
€
(19) Qin, Y.; Cui, C.; Jakle, F. Macromolecules 2008, 41, 2972–2974.
higher amount than HL1A and HL1 . This view is consistent
B
(20) Reger, D. L.; Foley, E. A.; Watson, R. P.; Pellechia, P. J.; Smith, M.
D.; Grandjean, F.; Long, G. J. Inorg. Chem. 2009, 48, 10658–10669.
(21) Barney, A. A.; Heyduk, A. F.; Nocera, D. G. Chem. Commun. 1999,
2379–2380.
with the fact, that the synthesis of [Li(thf)L2] does not suffer
from isomer formation, most likely because of a structure-
directing template effect of the Liþ ion.
(22) Betley, T. A.; Peters, J. C. Inorg. Chem. 2003, 42, 5074–5084.
(23) Ge, P.; Haggerty, B. S.; Rheingold, A. L.; Riordan, C. G. J. Am.
Chem. Soc. 1994, 116, 8406–8407.
(24) Ohrenberg, C.; Ge, P.; Schebler, P.; Riordan, C. G.; Yap, G. P. A.;
Rheingold, A. L. Inorg. Chem. 1996, 35, 749–754.
€
(29) Bielawski, J.; Das, M. K.; Hanecker, E.; Niedenzu, K.; Noth, H.
Inorg. Chem. 1986, 25, 4623–4628.
(25) Ohrenberg, C.; Riordan, C. G.; Liable-Sands, L.; Rheingold, A. L.
Coord. Chem. Rev. 1998, 174, 301–311.
(26) Schebler, P. J.; Riordan, C. G.; Guzei, I. A.; Rheingold, A. L. Inorg.
Chem. 1998, 37, 4754–4755.
(27) Kimblin, C.; Bridgewater, B. M.; Hascall, T.; Parkin, G. J. Chem.
Soc., Dalton Trans. 2000, 1267–1274.
(28) Ibrahim, M. M.; Seebacher, J.; Steinfeld, G.; Vahrenkamp, H. Inorg.
Chem. 2005, 44, 8531–8538.
(30) Bieller, S.; Bolte, M.; Lerner, H.-W.; Wagner, M. Chem.;Eur. J.
2006, 12, 4735–4742.
(31) Barfield, P. A.; Lappert, M. F.; Lee, J. J. Chem. Soc. A 1968, 554–559.
(32) Brown, C.; Cragg, R. H.; Miller, T. J.; Smith, D. O. J. Organomet.
Chem. 1983, 244, 209–215.
(33) To obtain decent yields (60-65%), it is essential to strictly maintain a
stoichiometric ratio Me2N(Ph)BBr/(Me3Si)2NMe of 2:1 and to use carefully
dried (Me3Si)2NMe.

3542 Inorganic Chemistry, Vol. 49, No. 7, 2010
Mutseneck et al.
Somewhat surprisingly, the B-N bonds to the four-
coordinate central nitrogen atom are only slightly longer
than those to the sp2-hybridized nitrogen atoms of the
reaction with MeMgCl in THF resulted in the formation
of the corresponding magnesium complex [Mg(Cl)-
(thf)xL1] (Scheme 1), which is extremely sensitive to
air and moisture. Interestingly, [Mg(Cl)(thf)xL1] cannot
be prepared from [Li(thf)L1] by salt metathesis, since
the addition of anhydrous MgCl2 to a solution of
the lithium compound in THF (stoichiometric ratio =
1:1) causes decomposition of the (pyrazol-1-yl)borate
ligand (1H NMR spectroscopic control). In contrast,
we were able to synthesize [Mg(Cl)(thf)2L2] from the
[N,O,N] ligand [Li(thf)L2] and MgCl2 in 88% yield
(Scheme 1).
˚
bridging pyrazolyl ring (av. values: 1.600(4) A vs 1.586(4)
˚
A). For the B-N bonds to the dangling pyrazolyl substitu-
ents, however, we find significantly shorter lengths (av. value:
˚
1.542(4) A). This observation indicates that the pyrazolide
backbone might be slightly too short to create a strain-free
ligand framework.
Main Group Metal Complexes of [L1]- and [L2]-:
[Li(thf)L1], [Mg(Cl)(thf)xL1], and [Mg(Cl)(thf)2L2]. Treat-
ment of HL1 in tetrahydrofuran (THF, thf) with 1 equiv
of n-BuLi in hexane at -78 °C gives [Li(thf)L1] in essen-
tially quantitative yield (Scheme 1). The analogous
Even though the samples of HL1 used in these syntheses
were mixtures of two isomers (HL1 and HL1B), the NMR
spectra of [Li(thf)L1] and [Mg(Cl)(thf)xL1] did not show
resonances attributable to (deprotonated) HL1B. Given
the reproducibly high yields, we come to the conclusion
that the contaminant has not simply been removed in the
recrystallization step. We rather assume that deprotona-
tion of HL1 induces a rearrangement of the molecular
B
framework, because now the central N(Me) fragment can
act as π-electron donor toward the boron atoms and
thereby facilitate the dissociation of a terminal pyrazolyl
ring. In the subsequent reassociation step, the template
Scheme 1. Synthesis
[Mg(Cl)(thf)2L2]a
of
[Li(thf)L1],
[Mg(Cl)(thf)xL1],
and
Figure 3. Molecular structure of HL1. Displacement ellipsoids are
˚
drawn at the 50% probability level. Selected bond lengths [A],
˚
atom atom distances [A], angles [deg], and dihedral angles [deg]:
3 3 3
B(1)-N(1) 1.599(4), B(1)-N(11) 1.539(4), B(1)-N(31) 1.583(4), B-
(2)-N(1) 1.601(4), B(2)-N(21) 1.545(4), B(2)-N(32) 1.589(4), N-
(1)-C(1) 1.493(4), N(1) N(12) 2.850(4), N(1) N(22) 2.825(4);
3 3 3
3 3 3
B(1)-N(1)-B(2) 110.5(2), N(1)-B(1)-N(31) 96.9(2), N(1)-B(2)-N-
(32) 96.6(2), C(1)-N(1)-B(1) 116.5(2), C(1)-N(1)-B(2) 115.6(2),
N(1)-H(1)-N(12) 121(2), N(1)-H(1)-N(22) 119(2); N(1)B(1)B(2)//
B(1)B(2)N(31)N(32) 31.5.
a (i) THF/hexane, -78 °C; (ii) THF, -78 °C; (iii) THF, r.t. (room
temperature).
Table 1. Selected Crystallographic Data of HL1, [Li(thf)L1], and [L1Mg(μ-Cl)2Mg(thf)L1]
compound
HL1
[Li(thf)L1]
[L1Mg(μ-Cl)2Mg(thf)L1] C5H12
3
formula
fw
color, shape
C22H23B2N7
407.09
colorless, block
173(2)
monoclinic
P21/n
9.8415(12)
12.8740(10)
16.9876(18)
90
94.607(9)
90
2145.4(4)
4
1.260
C26H30B2LiN7O
485.13
colorless, block
173(2)
monoclinic
P21
10.1477(6)
19.4929(12)
14.3962(8)
90
109.867(4)
90
2678.2(3)
4
1.203
C53H64B4Cl2Mg2N14
1075.94
colorless, block
173(2)
triclinic
O
temperature (K)
crystal system
space group
P1
˚
a (A)
10.3916(5)
11.3166(7)
25.0748(14)
80.102(4)
79.144(4)
80.988(4)
2829.2(3)
2
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Dcalcd. (g cm-3
F(000)
)
1.263
1132
856
0.078
1024
0.075
μ (mm-1
)
0.189
0.32 ꢀ 0.30 ꢀ 0.27
crystal size (mm3)
0.24 ꢀ 0.23 ꢀ 0.14
0.30 ꢀ 0.30 ꢀ 0.16
no. of rflns collected
no. of indep rflns (Rint
data/restraints/parameters
GOF on F2
17392
36111
36341
)
3784 (0.1104)
3784/0/285
0.964
5210 (0.0721)
5210/1/667
1.026
10976 (0.0423)
10976/37/685
1.031
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
largest diff peak and hole (e A
0.0589, 0.1127
0.1173, 0.1311
0.337, -0.209
0.0452, 0.1093
0.0548, 0.1141
0.338, -0.326
0.0508, 0.1435
0.0584, 0.1496
0.888, -0.721
-3
˚
)

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3543
of the B-O-B bridge by a B-N(Me)-B fragment causes
an increase in the N(12)-Li(1)-N(22) angle by 11.6°
([Li(thf)L1]: N(12)-Li(1)-N(22) = 127.5(3)°).
Lithiation of HL1 significantly flattens the envelope
conformation of the N(1)B(1)B(2)N(31)N(32) ring; the
corresponding dihedral angles N(1)B(1)B(2)//B(1)B(2)N-
(31)N(32) are 31.5° in HL1, but only 8.1° in [Li(thf)L1].
Moreover, the average B-N(Me) bond length shrinks by
1
˚
˚
˚
0.071 A from a value of 1.600(4) A in HL to 1.529(4) A in
[Li(thf)L1]. This shortening of the B-N(Me) bonds is
accompanied by a significant increase in the mean
B(1)-N(11)/B(2)-N(21) distances upon going from
1
1
˚
˚
HL (1.542(4) A) to [Li(thf)L ] (1.584(4) A). In contrast,
the B-N(μ-pz) bond lengths remain the same (1.586(4) A
in HL ; 1.588(4) A in [Li(thf)L ]). This observation is in
˚
1
1
˚
line with previous findings of negative hyperconjugation
in amino-substituted pyrazaboles R2N(R0)B(μ-pz)2B-
35,36
(R0)NR2
and lends support to our suggestion that
deprotonation of HL1B promotes dissociation of terminal
pyrazolyl groups and thus ultimately causes a rearrange-
ment to [Li(thf)L1] (see above).
The magnesium complex [Mg(Cl)(thf)xL1], which was
crystallized from pentane/THF, forms chloride-bridged
dinuclear aggregates [L1Mg(μ-Cl)2Mg(thf)L1] in the solid
state (Figure 5; Table 1).
Figure 4. Molecular structure of [Li(thf)L1]. The H-atoms are omitted for
clarity; displacement ellipsoids are drawn at the 50% probability level.
˚
Selected bond lengths [A], angles [deg], and dihedral angles [deg]: Li(1)-N-
The Mg(1) ion is five-coordinate by the donor atoms
N(1), N(12), and N(22) of [L1]- and by the two bridging
chloride ions. According to the structure parameter τ5 =
0.44,37 the configuration of the ligand environment is
intermediate between trigonal-bipyramidal and square-
pyramidal. In contrast to Mg(1), the Mg(2) ion bears an
additional thf ligand and thus possesses a slightly dis-
torted octahedral donor environment. Most importantly,
[L1]- acts as meridionally coordinating tridentate chela-
tor toward Mg(2), the angle N(62)-Mg(2)-N(72) =
158.5(1)° being even more obtuse than N(12)-Mg(1)-
N(22) = 139.3(1)°.
(1) 2.093(6), Li(1)-N(12) 2.015(6), Li(1)-N(22) 1.993(6), Li(1)-O(61)
1.923(5), B(1)-N(1) 1.530(4), B(1)-N(11) 1.593(4), B(1)-N(31) 1.587(4),
B(2)-N(1) 1.528(4), B(2)-N(21) 1.574(4), B(2)-N(32) 1.589(4), N(1)-C-
(1) 1.465(4); N(1)-Li(1)-N(12) 89.7(2), N(1)-Li(1)-N(22) 90.4(2), N-
(1)-Li(1)-O(61) 126.4(3), N(12)-Li(1)-N(22) 127.5(3), B(1)-N(1)-
B(2) 113.2(2), N(1)-B(1)-N(31) 101.1(2), N(1)-B(2)-N(32) 100.5(2);
N(1)B(1)B(2)//B(1)B(2)N(31)N(32) 8.1.
effect of the Liþ or Mg2þ ion likely leads to [L1]- forma-
tion.
The 1H NMR spectra of [Li(thf)L1] and [Mg(Cl)(thf)x-
L1] show similar characteristics as the spectrum of HL1:
One signal for the NMe protons, two sets of signals for
terminal and bridging pyrazolyl rings (integral ratio =
2:1, respectively), as well as signals for the phenyl moieties
With regard to the key structure parameters of the
ligand backbone, we note that the average B-N(Me)
1
(integral ratio pz/Ph = 9:10). The H NMR spectra of
1
1
˚
bond length (1.546(2) A) in [L Mg(μ-Cl)2Mg(thf)L ] lies
[Mg(Cl)(thf)xL1] and [Mg(Cl)(thf)2L2] are also pretty
much alike, apart from the fact that the NMe resonance
is missing in the latter case.
between the average B-N(Me) distances in HL1 (1.600(4)
A) and [Li(thf)L ] (1.529(4) A). The same is true for the
1
˚
˚
1
˚
mean terminal B-N(pz) bond lengths (HL : 1.542(4) A,
The 11B NMR resonances of [Li(thf)L1], [Mg(Cl)(thf)x-
L1], and [Mg(Cl)(thf)2L2] appear at 6.7 ppm, 5.3 ppm,
and 5.4 ppm, respectively, thereby testifying to the
presence of four-coordinate boron nuclei in all three
compounds.34
1
1
1
˚
[L Mg(μ-Cl)2Mg(thf)L ]: 1.572(2) A, [Li(thf)L ]: 1.584(4)
˚
A). This comparison leads to the conclusion that the
negative hyperconjugation from the central amino group
into the B-N(pz) σ* orbitals is less pronounced in the
magnesium complex than in the lithium species, which is
most likely due to the higher Lewis acidity of the Mg2þ
ion compared to that of the Liþ ion.
The molecular structure of the lithium complex was
determined by X-ray crystallography. The compound,
which is monomeric in the solid state, crystallizes with
two crystallographically independent molecules in the
asymmetric unit ([Li(thf)L1] and [Li(thf)L1]A). Since the
key geometric parameters of both molecules are the same
within the experimental error margins, only the structure
of [Li(thf)L1] is discussed here (Figure 4; Table 1).
As in the [N,O,N] complex [Li(thf)L2],30 the Liþ center
in [Li(thf)L1] possesses a coordination number of four:
[L1]- acts as tridentate ligand, the fourth coordination
site is occupied by a THF molecule. However, replacement
Crystals of [Mg(Cl)(thf)2L2] have been grown from a
pentane/THF mixture (cf. the Supporting Informa-
tion for an ORTEP-plot and a compilation of key struc-
ture parameters of [Mg(Cl)(thf)2L2]). In contrast to
€
(35) Jakle, F.; Priermeier, T.; Wagner, M. Organometallics 1996, 15,
2033–2040.
€
(36) Herdtweck, E.; Jakle, F.; Opromolla, G.; Spiegler, M.; Wagner, M.;
Zanello, P. Organometallics 1996, 15, 5524–5535.
(37) For five-coordinate complexes, the geometry index τ5 = (θ - j)/60°
provides a quantitative measure of whether the ligand sphere more closely
approaches a square-pyramidal (τ5 = 0) or a trigonal-bipyramidal geometry
(τ5 = 1; θ, j are the two largest bond angles and θ g j): Addison, A. W.;
Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton
Trans. 1984, 1349–1356.
€
(34) Noth, H.; Wrackmeyer, B. Nuclear Magnetic Resonance Spectro-
scopy of Boron Compounds. In NMR Basic Principles and Progress; Diehl,
P., Fluck, E., Kosfeld, R., Eds.; Springer: Berlin, 1978.

3544 Inorganic Chemistry, Vol. 49, No. 7, 2010
Mutseneck et al.
Figure 5. Molecular structure of [L1Mg(μ-Cl)2Mg(thf)L1]. The H-atoms are omitted for clarity; displacement ellipsoids are drawn at the 50% probability
˚
level. Selected bond lengths [A] and angles [deg]: Mg(1)-Cl(1) 2.384(1), Mg(1)-Cl(2) 2.443(1), Mg(2)-Cl(1) 2.563(1), Mg(2)-Cl(2) 2.531(1), Mg(1)-N(1)
2.268(2), Mg(1)-N(12) 2.078(2), Mg(1)-N(22) 2.074(2), Mg(2)-N(2) 2.293(2), Mg(2)-N(62) 2.098(2), Mg(2)-N(72) 2.099(2), Mg(2)-O(111) 2.258(1),
B(1)-N(1) 1.549(2), B(1)-N(11) 1.569(3), B(2)-N(1) 1.550(3), B(2)-N(21) 1.570(2), B(3)-N(2) 1.541(2), B(3)-N(61) 1.577(2), B(4)-N(2) 1.542(2),
B(4)-N(71) 1.573(2); Cl(1)-Mg(1)-Cl(2) 89.4(1), Cl(1)-Mg(2)-Cl(2) 83.6(1), Mg(1)-Cl(1)-Mg(2) 93.8(1), Mg(1)-Cl(2)-Mg(2) 93.2(1), Cl(1)-
Mg(1)-N(1) 105.1(1), Cl(2)-Mg(1)-N(1) 165.5(1), N(12)-Mg(1)-N(22) 139.3(1), Cl(1)-Mg(2)-N(2) 177.8(1), Cl(2)-Mg(2)-N(2) 97.9(1),
N(62)-Mg(2)-N(72) 158.5(1).
[L1Mg(μ-Cl)2Mg(thf)L1], [Mg(Cl)(thf)2L2] forms dis-
crete mononuclear complexes in the crystal lattice.
The distorted octahedral ligand sphere of the Mg2þ
ion in [Mg(Cl)(thf)2L2] is composed of [L2]-, one Cl-
ion, and two thf ligands. A striking difference between
[L1Mg(μ-Cl)2Mg(thf)L1] and [Mg(Cl)(thf)2L2] lies in the
fact that [L2]- is clearly facially coordinating (N(pz)-
Mg-N(pz)0 = 90.5(1)°).
Scheme 2. Synthesis of [Zn(Br)L1], [Zn(Br)(Hpz)L2], and [Cu(Cl)L1]a
Investigation into the Conformational Flexibility of
[L1]- and [L2]-: [Zn(Br)L1], [Zn(Br)(Hpz)L2], and [Cu-
(Cl)L1]. Since classic tridentate poly(pyrazol-1-yl)borates
are restricted to facial binding modes, the meridional
coordination of [L1]- in [L1Mg(μ-Cl)2Mg(thf)L1] promp-
ted us to begin a systematic investigation into the con-
formational flexibility of fourth generation scorpionates.
For our studies, we selected the following target com-
plexes: [Zn(Br)L1], [Zn(Br)L2], and [Cu(Cl)L1] ([Cu(Cl)-
L2] has already been described by our group).30 The rati-
onale behind this selection was that four-coordinate ZnII
complexes are usually tetrahedral, which should force
[L1]-/[L2]- into a fac-like conformation, while four-
coordinate CuII complexes tend to adopt square-planar
coordination geometries and thus should promote a mer-
like conformation of [L1]-/[L2]-.
a (i) THF, r.t.; (ii) THF/hexane, -78 °C.
adding 2 equiv of pyrazole to the mixture of starting
materials. Indeed, this time [Zn(Br)(Hpz)L2] formed al-
most quantitatively (1H, 11B NMR spectroscopic con-
trol). It should, however, be noted, that other N-donors
like pyridine or 2,6-lutidine do not prevent ligand degra-
dation. For example, reaction of [Li(thf)L2] with ZnBr2 in
the presence of pyridine gave [Zn(Br)(Hpz)L2] in the same
yield as has been obtained without added base. Replace-
ment of ZnBr2 by ZnCl2 also had no decisive effect on the
course of the reaction because again only the pyrazole
adduct [Zn(Cl)(Hpz)L2] was generated (details of the
synthesis of [Zn(Cl)(Hpz)L2] and [Zn(Br)(Hpz)L2] are
given in the Supporting Information).
Complex [Zn(Br)L1] was prepared in a two-step se-
quence: First, HL1 was treated with 1 equiv of ZnBr2 in
THF. The mixture was stirred for 2 h to achieve pre-
coordination of ZnBr2 to HL1. In the second step, 1 equiv
of n-BuLi in hexane was added at -78 °C which resulted
in deprotonation of the central amino group, accompa-
nied by elimination of LiBr and formation of the target
compound (Scheme 2).
The deep blue CuII complex [Cu(Cl)L1] was synthesized
by adding 1 equiv of n-BuLi to a dark green mixture of
HL1 and CuCl2 in THF at -78 °C (Scheme 2).
The NMR data of [Zn(Br)L1] nicely compare to those
of [Li(thf)L1] and [Mg(Cl)(thf)xL1] and will thus not be
discussed further. Similarly, the NMR spectra of [Zn(Br)-
(Hpz)L2] agree with those of [Mg(Cl)(thf)2L2], apart from
the resonances of the pyrazole ligand, which appear
at 6.33 ppm (HpzH-4), 7.28/8.09 ppm (HpzH-3,5), and
12.29 ppm (NH).
Attempts to prepare the related complex [Zn(Br)L2]
from the [N,O,N] ligand [Li(thf)L2] and ZnBr2 reprodu-
cibly resulted in the formation of the pyrazole adduct
[Zn(Br)(Hpz)L2] (Scheme 2). The compound was isolated
by crystallization in yields of about 30%. Given that the
pyrazole ligand obviously originates from degradation of
[L2]-, we tried to increase the yield of [Zn(Br)(Hpz)L2] by
The molecular structures of [Zn(Br)L1] and [Cu(Cl)L1]
are juxtaposed in Figure 6; key crystallographic data are
compiled in Table 2 (cf. the Supporting Information for

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3545
Scheme 3. Synthesis of [CoCl2(HL1)] and [L1Co(μ-Cl)2CoL1]a
a (i) THF, r.t., subsequent recrystallization from CH2Cl2/hexane at
r.t.; (ii) CH2Cl2/hexane, 7 d; (iii) THF/hexane, -78 °C.
N(Me) occupying the axial position, we would expect
an angle sum of 360.0° in the basal plane. In line with
that, the geometry index τ438 of [Zn(Br)L1] has a value of
0.82, typical of a (distorted) trigonal-pyramidal config-
uration.
X-ray crystallography on [Cu(Cl)L1] reveals a mono-
meric compound with a four-coordinate CuII center, in
contrast to the solid-state structure of the related [N,O,N]
complex [Cu(Cl)L2],30 which consists of chloro-bridged
dimeric entities [Cu(Cl)L2]2 containing five-coordinate
CuII ions. The geometry of the ligand environment in [Cu-
(Cl)L1] is largely square-planar, with N(pz)-Cu-N(pz)0
and Cl-Cu-N(Me) angles of 161.5(2)° and 165.8(1)°, res-
pectively. When these values are compared to the corres-
Figure 6. Comparison of the molecular structures of [Zn(Br)L1] and
[Cu(Cl)L1] in the solid state.
ponding angles of [Zn(Br)L1] (N(pz)-Zn-N(pz)0
=
127.2(3)°, Br-Zn(1)-N(Me) = 117.7(2)°), an astonishing-
ly high degree of conformational flexibility of ligand [L1]-
becomes immediately apparent.
Table 2. Selected Crystallographic Data of [Zn(Br)L1] and [Cu(Cl)L1]
compound
[Zn(Br)L1] 2C4H8O
[Cu(Cl)L1]
3
Importantly, the different coordination modes are not
accompanied by any major changes in the bond lengths
and angles of the central NB2N2 five-membered ring.
With regard to octahedral complexes, we may therefore
safely assume, that [L1]- is able to bind both in a facial
and in a meridional manner.
formula
fw
color, shape
C30H38B2BrN7O2Zn C22H22B2ClCuN7
695.57
505.08
colorless, block
173(2)
triclinic
P1
dark blue, block
173(2)
triclinic
temperature (K)
crystal system
space group
P1
˚
a (A)
11.951(2)
12.826(3)
13.559(3)
69.40(3)
63.85(3)
62.23(3)
1622.4(6)
2
10.8061(11)
12.8424(14)
18.620(2)
73.420(8)
74.722(8)
87.420(8)
2387.8(4)
4
Ligand Properties of HL1 versus [L1]-: [CoCl2(HL1)]
and [L1Co(μ-Cl)2CoL1]. In the course of the synthesis of
[Zn(Br)L1] and [Cu(Cl)L1] it has become apparent that
treatment of a mixture of the respective metal salt and
HL1 with n-BuLi leads to better results than the reaction
between the same metal salt and [Li(thf)L1]. However, we
have not yet been able to isolate the likely intermediates
of the sequential protocol, that is, [ZnBr2(HL1)] and
[CuCl2(HL1)].
This situation changed when CoCl2 was employed. The
products of both synthesis steps, the protonated species
[CoCl2(HL1)] and the deprotonated complex [L1Co(μ-
Cl)2CoL1], are described in this paragraph.
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Dcalcd. (g cm-3
F(000)
)
1.424
716
1.405
1036
μ (mm-1
)
2.027
0.31 ꢀ 0.28 ꢀ 0.22
1.051
0.25 ꢀ 0.22 ꢀ 0.22
crystal size (mm3)
no. of rflns collected
no. of indep rflns (Rint
data/restraints/parameters 5722/0/389
22313
18290
)
5722 (0.0913)
8877 (0.0927)
8877/0/595
1.042
GOF on F2
1.081
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
largest diff peak and
0.0689, 0.1763
0.0806, 0.1941
1.265, -1.554
0.0649, 0.1668
0.0859, 0.1799
0.732, -1.124
[CoCl2(HL1)] readily forms from CoCl2 and HL1 in
THF (Scheme 3). Deep blue crystals of [CoCl2(HL1)] were
grown from CH2Cl2/hexane. After these crystals had been
stored in the mother liquor for a period of several days,
we discovered that the color of the entire crop had
changed from blue to violet. Subsequent X-ray crys-
tallography revealed the complete conversion of [CoCl2-
(HL1)] into [L1Co(μ-Cl)2CoL1]. As to be expected, this
process can be accelerated by adding 1 equiv of n-BuLi to
-3
˚
hole (e A
)
ORTEP plots and a compilation of important bond
lengths and angles of [Zn(Br)L1] and [Cu(Cl)L1]; the
X-ray crystal structure analysis of [Zn(Cl)(Hpz)L2] and
[Zn(Br)(Hpz)L2] are also given in the Supporting In-
formation).
The Zn(1) center in [Zn(Br)L1] is surrounded by the
[L1]- ligand and one Br- ion. The sum of the bond angles
Br-Zn-N(pz), Br-Zn-N(pz)0, and N(pz)-Zn-N(pz)0
is 355.8°. If the ligand configuration about Zn was an
ideal tetrahedron, the corresponding value would have to
be 328.5°; in the case of an ideal trigonal pyramid with
(38) For four-coordinate complexes, the geometry index τ4 = {360° -
(θþj)}/141° provides a quantitative measure of whether the ligand sphere
more closely approaches a tetrahedral (τ4 = 1) or a trigonal-pyramidal
geometry (τ4 = 0.85; θ, j are the two largest bond angles): Yang, L.; Powell,
D. R.; Houser, R. P. Dalton Trans. 2007, 955–964.

3546 Inorganic Chemistry, Vol. 49, No. 7, 2010
Mutseneck et al.
Figure 8. Molecular structure of [L1Co(μ-Cl)2CoL1]. The H-atoms are
omitted for clarity; displacement ellipsoids are drawn at the 50% prob-
˚
ability level. Selected bond lengths [A] and angles [deg]: Co(1)-Cl(1)
2.515(1), Co(1)-Cl(1A) 2.329(1), Co(1)-N(1) 2.228(2), Co(1)-N(12)
1.995(2), Co(1)-N(22) 1.993(2), B(1)-N(1) 1.550(4), B(1)-N(11)
1.572(4), B(2)-N(1) 1.552(4), B(2)-N(21) 1.576(4); Cl(1)-Co(1)-Cl-
(1A) 87.1(1), N(12)-Co(1)-N(22) 132.1(1), B(1)-N(1)-B(2) 110.6(2).
Symmetry transformation used to generate equivalent atoms: A: -x þ 1,
-y þ 1, -z.
Figure 7. Molecular structure of [CoCl2(HL1)]. The H-atoms are omitted
for clarity (except H(1) on the N(Me) bridge); displacement ellipsoids are
hand, the N(1)B(1)B(2)N(31)N(32) ring in [CoCl2(HL1)]
was found to be rather flat (N(1)B(1)B(2)//B(1)B(2)N-
(31)N(32) = 8.9°), which is similar to [Li(thf)L1] (8.1°),
but different from HL1 (31.5°).
˚
drawn at the 50% probability level. Selected bond lengths [A],atom atom
3 3 3
˚
distances [A], angles [deg], and dihedral angles [deg]: Co(1)-Cl(1) 2.264(1),
Co(1)-Cl(2) 2.257(1), Co(1)-N(12) 2.024(2), Co(1)-N(22) 2.035(2), Co-
(1) N(1) 3.179(2), Cl(1) H(1) 2.45(4), B(1)-N(1) 1.617(4), B(1)-N-
(11) 1.553(4), B(2)-N(1) 1.623(4), B(2)-N(21) 1.559(4); Cl(1)-Co(1)-
Cl(2) 116.0(1), N(12)-Co(1)-N(22) 112.8(1), B(1)-N(1)-B(2) 110.5(2);
N(1)B(1)B(2)//B(1)B(2)N(31)N(32) 8.9.
3 3 3
3 3 3
Deprotonation of [CoCl2(HL1)] is accompanied by the
formation of a third Co-N bond (Co(1)-N(1) =
2.228(2) A) and loss of one chloro ligand (Figure 8;
˚
Table 3. Selected Crystallographic Data of [CoCl2(HL1)] and [L1Co(μ-Cl)2CoL1]
Table 3). In the solid state, the new complex exists as
centrosymmetric dimer [L1Co(μ-Cl)2CoL1] with five-
coordinate CoII ions in a distorted trigonal-bipyramidal
environment (τ5 = 0.6337). The average Co-N(pz) bond
[L1Co(μ-Cl)2CoL1]
CH2Cl2
3
compound
[CoCl2(HL1)]
formula
fw
color, shape
C22H23B2Cl2CoN7 C45H46B4Cl4Co2N14
1
1
˚
length is smaller in [L Co(μ-Cl)2CoL ] (1.994(2) A) as
536.92
blue, plate
173(2)
1085.86
violet, plate
173(2)
1
˚
compared to [CoCl2(HL )] (2.030(2) A), but the N(12)-
temperature (K)
crystal system
space group
Co(1)-N(22) angle is more obtuse by almost 20°.
triclinic
P1
monoclinic
P21/c
The X-ray crystal structure analysis of [CoCl2(HL1)]
reveals why HCl abstraction does not necessarily require
an external base, but happens spontaneously: The proton
on N(1) is directed toward the midpoint of the Co(1)-
˚
a (A)
9.2228(9)
9.9006(9)
14.4611(13)
96.443(7)
105.370(7)
96.724(8)
1250.2(2)
2
10.1326(6)
22.9453(11)
11.8089(8)
90
110.323(5)
90
2574.6(3)
2
1.401
1112
0.899
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
Cl(1) bond and the distance Cl(1) H(1) amounts to
˚
only 2.45(4) A. An intramolecular proton shift from N(1)
3 3 3
3
˚
V (A )
Z
to Cl(1) can therefore easily take place.
In view of the successful synthesis of [L1Co(μ-
Cl)2CoL1], we also tried to prepare the corresponding
complex [L2Co(μ-Cl)2CoL2] from CoCl2 and [Li(thf)L2].
However, this reaction always proceeded with degrada-
tion of some of the [N,O,N] ligands and yielded com-
pound [L2Co(μ-Cl)(μ-pz)CoL2] which possesses a bridg-
ing pyrazolide ring (cf. the Supporting Information for
the synthesis and X-ray crystal structure analysis of
[L2Co(μ-Cl)(μ-pz)CoL2]).
Dcalcd. (g cm-3
F(000)
)
1.426
550
0.925
μ (mm-1
)
crystal size (mm3)
0.22 ꢀ 0.18 ꢀ 0.09 0.27 ꢀ 0.19 ꢀ 0.11
no. of rflns collected
no. of indep rflns (Rint
data/restraints/parameters 4688/0/311
18031
37037
)
4688 (0.0719)
5168 (0.0833)
5168/0/316
1.025
GOF on F2
0.932
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
largest diff peak and
0.0385, 0.0810
0.0609, 0.0881
0.470, -0.549
0.0481, 0.1258
0.0655, 0.1329
0.715, -1.243
Investigation into the Chemical Stability of [L1]- and
[L2]-: [Mn(CO)3L2], K(thf)[Mn(CO)3L3], and [L2Co(μ-
pz)2CoL2]. The above-mentioned formation of the pyr-
azole and μ-pyrazolide complexes [Zn(Cl,Br)(Hpz)L2]
and [L2Co(μ-Cl)(μ-pz)CoL2] poses questions regarding
the general chemical stability of [L1]- and [L2]-. In the
past, we had observed similar ligand degradation reac-
tions when trying to prepare [(R2Bpz2)Mn(CO)4] com-
plexes from classic bis(pyrazol-1-yl)borates and [Mn-
(CO)5Br].18 Thus, to gather more information about
the stability limits of fourth generation scorpionates, we
-3
˚
hole (e A
)
the THF solution of [CoCl2(HL1)] prior to workup
(Scheme 3).
Complex [CoCl2(HL1)] is a monomeric compound
featuring one CoII center in a distorted tetrahedral
environment (Figure 7; Table 3; the hydrogen atom
H(1) has been located in the electron density map).
˚
The average B-N(Me) bond length of 1.620(4) A is
similar to that of HL (1.600(4) A), but almost 0.1 A
1
˚
˚
1
longer than that of [Li(thf)L ] (1.529(4) A). On the other
˚

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3547
Scheme 4. Synthesis of [Mn(CO)3L2] and K(thf)[Mn(CO)3L3]a
from Li[Li(thf)L3]39 and [Mn(CO)5Br] in THF. However,
this synthesis protocol, which has been shown to work
faithfully for the preparation of [(p-cymene)RuL3],39
failed for the manganese compound because we only
isolated [Mn2(CO)10], the product of a MnIfMn0 reduc-
tion, from the reaction mixture.
In contrast to HL1, [Li(thf)L2] reacts with 1 equiv of
[Mn(CO)5Br] (THF, reflux, 8 h) without degradation so
that the target compound [Mn(CO)3L2] is obtained in
70% yield (Scheme 4). Recrystallization of [Mn(CO)3L2]
from Et2O led to yellow crystals suitable for X-ray
analysis. The compound is relatively air-stable, even in
solution (Et2O, CH2Cl2), but rapidly decomposes on a
silica gel chromatography column.
The 11B NMR spectrum of K(thf)[Mn(CO)3L3] is char-
acterized by two signals at about 31 ppm (h1/2 ≈ 1100 Hz,
1B) and 6.1 ppm (2B), which confirm that the molecule
contains three- and four-coordinate boron atoms.34 The
1H NMR spectrum is consistent with the presence of
two magnetically equivalent pyrazolyl rings (δ(1H) =
6.24 (pzH-4), 7.65, 7.81 (pzH-3,5)) as well as three phenyl
groups, two of them being again magnetically equivalent.
Compound [Mn(CO)3L2] gives rise to one resonance at
δ(11B) = 6.0. Two sets of 1H (13C) signals can be assigned
to one symmetrically bridging pyrazolyl ring on the one
hand and two metal-coordinating pyrazolyl substituents
on the other.
a (i) THF, reflux temperature, 8 h.
The IR spectrum of [Mn(CO)3L2] exhibits one sharp
and one broad band in the typical region of CO stretching
vibrations. The corresponding wavenumbers (ν~ (CO) =
2033 cm-1, 1930 cm-1; KBr) compare well with those of
Mn(CO)3 complexes of classic tris(pyrazol-1-yl)borate
ligands.18,40,41 In contrast to [Mn(CO)3L2], three sharp
absorptions at ν~ (CO) = 2026 cm-1, 1929 cm-1, and 1891
cm-1 are resolved in the IR spectrum (KBr) of K(thf)-
[Mn(CO)3L3].
decided to treat also [L1]- and [L2]- with the manganese
carbonyl reagent.
Attempts at the synthesis of [Mn(CO)3L1] from an
equimolar mixture of [Li(thf)L1] and [Mn(CO)5Br] in
THF at reflux temperature met with failure because the
ligand framework does not persist under these conditions.
In an alternative approach and similar to the preparation
of [Zn(Br)L1] and [L1Co(μ-Cl)2CoL1], we used HL1 and
performed the experiment in the presence of a base
(n-BuLi, NEt3, K2CO3). None of these reactions gave
evidence for the formation of [Mn(CO)3L1]. However, in
the case where K2CO3 (2 equiv) was employed, we iso-
lated an interesting other product in moderate yield
(i.e., K(thf)[Mn(CO)3L3]; Scheme 4). This compound
contains a new ligand, [L3]2-, featuring a three-atom
O-B(Ph)-O backbone instead of a two-atom μ-pyr-
azolide bridge. K(thf)[Mn(CO)3L3] is relatively air-
stable in the solid state, but its THF and CH2Cl2
solutions are air-sensitive.
The cyclic voltammograms of complexes [Mn(CO)3L2]
and K(thf)[Mn(CO)3L3] show irreversible MnIfMnII
oxidation waves at Epa = 0.69 and 0.86 V, respectively
(vs FcH/FcHþ, CH2Cl2, NBu4PF6; see the Supporting
Information for the CV plots). Thus, the negatively
charged species [Mn(CO)3L3]- is more resistant to oxida-
tion than neutral [Mn(CO)3L2]. The electrochemical be-
havior of [Mn(CO)3L2] and K(thf)[Mn(CO)3L3] may be
compared with that of the related cyclopentadienyl com-
plex [CpMn(CO)3], which undergoes reversible one-elec-
tron oxidation at a potential value of E1/2 = 0.89 V (vs
FcH/FcHþ, CH2Cl2, NBu4PF6).42,43
In a previous publication, we have already reported on
a related system, that is, [(p-cymene)RuL3], which has
been synthesized from [(p-cymene)RuCl2]2 and [Li(thf)-
L2] in the presence of TlPF6 (1:2:4 equiv, respectively).39
In the case of [(p-cymene)RuL3], two pathways can be
The molecular structures of [Mn(CO)3L2] and K(thf)-
[Mn(CO)3L3] are presented in Figures 9 and 10, respec-
tively (see also Table 4).
In both complexes, the MnI ion is located in a distorted
octahedral environment composed of three facially co-
ordinating carbonyl ligands and the [N,O,N] donor set of
the respective chelate ligand. The Mn-CO bonds of
envisaged for the formation of the boroxine ligand [L3]2-
:
(i) a rearrangement reaction of [L2]- and (ii) hydrolysis
of [L2]- by adventitious traces of water. In the case of
K(thf)[Mn(CO)3L3], however, water (probably originat-
ing from the hygroscopic K2CO3) must be the key factor,
because it is the only plausible source of oxygen atoms in
the entire setup.
(40) Joachim, J. E.; Apostolidis, C.; Kanellakopulos, B.; Maier, R.;
€
Marques, N.; Meyer, D.; Muller, J.; de Matos, A. P.; Nuber, B.; Rebizant,
J.; Ziegler, M. L. J. Organomet. Chem. 1993, 448, 119–129.
(41) Haghiri Ilkhechi, A.; Guo, S.; Bolte, M.; Wagner, M. Dalton Trans.
2003, 2303–2307.
(42) Atwood, C. G.; Geiger, W. E.; Bitterwolf, T. E. J. Electroanal. Chem.
1995, 397, 279–285.
(43) Laws, D. R.; Chong, D.; Nash, K.; Rheingold, A. L.; Geiger, W. E. J.
Am. Chem. Soc. 2008, 130, 9859–9870.
The serendipitous discovery of K(thf)[Mn(CO)3L3] led
us to attempt a targeted synthesis of the anionic complex
€
(39) Mutseneck, E. V.; Reus, C.; Schodel, F.; Bolte, M.; Lerner, H.-W.;
Wagner, M. Organometallics 2010, 29, 966-975.

3548 Inorganic Chemistry, Vol. 49, No. 7, 2010
Mutseneck et al.
Figure 10. Molecular structure of K(thf)[Mn(CO)3L3]. The H-atoms are
omitted for clarity; displacement ellipsoids are drawn at the 50% probability
˚
level. Selected bond lengths [A] and angles [deg]: Mn(1)-O(1) 2.079(1),
Mn(1)-N(12) 2.029(2), Mn(1)-N(22) 2.035(2), Mn(1)-C(4) 1.829(2),
Mn(1)-C(5) 1.793(2), Mn(1)-C(6) 1.794(2), K(1)-O(2) 2.693(1), K(1)-
O(6A) 2.898(2), K(1)-C(41) 3.198(2), K(1)-C(42) 3.119(2), K-
Figure 9. Molecular structure of [Mn(CO)3L2]. The H-atoms are omitted
for clarity; displacement ellipsoids are drawn at the 50% probability level.
Selected bond lengths [A] and angles [deg]: Mn(1)-O(4) 2.091(1),
Mn(1)-N(12) 2.038(1), Mn(1)-N(22) 2.055(1), Mn(1)-C(1) 1.820(2),
Mn(1)-C(2) 1.803(2), Mn(1)-C(3) 1.825(2), B(1)-O(4) 1.486(2),
B(2)-O(4) 1.490(2), B(1)-N(11) 1.563(2), B(1)-N(31) 1.566(2), B(2)-N-
(21) 1.560(2), B(2)-N(32) 1.573(2); N(12)-Mn(1)-N(22) 87.3(1).
˚
(1) COG(Ph(31A)) 2.986, B(1)-O(1) 1.473(2), B(1)-O(3) 1.459(3), B-
3 3 3
(2)-O(1) 1.484(2), B(2)-O(2) 1.469(3), B(3)-O(2) 1.365(3), B(3)-O(3)
1.348(3), B(1)-N(11) 1.595(3), B(2)-N(21) 1.575(3); N(12)-Mn(1)-N-
(22) 88.7(1), B(1)-O(1)-B(2) 121.1(2). COG(Ph(31A)) = centroid of the
phenyl ring containing C(31A). Symmetry transformation used to generate
equivalent atoms: A: x - 1/2, -y þ 1/2, z - 1/2.
[Mn(CO)3L2] involving carbonyl ligands trans to the
˚
pyrazolyl rings are slightly longer (1.820(2) A, 1.825(2)
Table 4. Selected Crystallographic Data of [Mn(CO)3L2] and K(thf)[Mn(CO)3L3]
˚
˚
A) than the Mn(1)-C(2) bond trans to O(4) (1.803(2) A).
This leads to the conclusion that the oxygen atom acts not
only as σ-, but also as π-donor. A similar effect is visible in
the boroxine derivative K(thf)[Mn(CO)3L3] (Mn(1)-
compound
[Mn(CO)3L2]
K(thf)[Mn(CO)3L3]
formula
fw
color, shape
C24H19B2MnN6O4 C31H29B3KMnN4O7
532.01
yellow, block
173(2)
696.05
yellow, block
173(2)
˚
˚
C(4) = 1.829(2) A vs Mn(1)-C(5) = 1.793(2) A; C(6)O-
(6) is not taken into account here, because it bridges
Mn(1) and K(1A)). The Mn-O and average Mn-N bond
temperature (K)
crystal system
space group
monoclinic
P21/c
monoclinic
P21/n
3
˚
lengths of K(thf)[Mn(CO)3L ] (Mn-O = 2.079(1) A,
˚
a (A)
10.8977(6)
19.1699(7)
12.8863(6)
90
11.4093(3)
17.8054(6)
17.0313(5)
90
˚
Mn-N = 2.032(2) A) are a little shorter than those of
˚
b (A)
2
˚
[Mn(CO)3L ] (Mn-O = 2.091(1) A, Mn-N = 2.047(1)
A), most likely because of a higher electrostatic attraction
˚
c (A)
˚
R (deg)
β (deg)
γ (deg)
of the dianionic ligand [L3]2- compared to the mono-
anionic (pyrazol-1-yl)borate [L2]-.
111.739(4)
90
105.180(2)
90
3
˚
K(thf)[Mn(CO)3L3] forms heterobimetallic coordina-
tion polymers in the solid state (cf. the Supporting Infor-
mation for a plot of the extended structure). The con-
necting Kþ ions bind to the boroxine oxygen atom O(2)
and the phenyl carbon atoms C(41)/C(42) of one [Mn-
(CO)3L3]- complex and at the same time to the phenyl
ring (η6-mode) and the carbonyl oxygen atom O(6A) of a
second [Mn(CO)3L3]- anion.44 The coordination sphere
of each Kþ ion is completed by one thf ligand.
The structure parameters of the chelate ligands in
[Mn(CO)3L2] and [Mn(CO)3L3]- nicely fit to those in
[Mg(Cl)(thf)2L2] and [(p-cymene)RuL3]39 and thus do not
merit further discussion.
V (A )
Z
2500.6(2)
4
1.413
3339.14(17)
4
1.385
Dcalcd. (g cm-3
F(000)
)
1088
0.571
1432
0.571
μ (mm-1
)
crystal size (mm3)
0.41 ꢀ 0.36 ꢀ 0.33 0.28 ꢀ 0.26 ꢀ 0.25
no. of rflns collected
no. of indep rflns (Rint
data/restraints/parameters 5750/0/335
38051
43379
)
5750 (0.0462)
6804 (0.0535)
6804/26/421
1.061
GOF on F2
1.032
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
largest diff peak and
0.0308, 0.0807
0.0354, 0.0832
0.324, -0.399
0.0424, 0.1043
0.0498, 0.1084
0.551, -0.452
-3
˚
hole (e A
)
The unexpected formation of K(thf)[Mn(CO)3L3]
prompted us to unveil important factors governing the
assembly of [L3]2-. In the absence of Kþ and [Mn(CO)5-
Br], hydrolysis ofHL1 gives the bridged pyrazabolePhB(μ-
pz)2(μ-OB(Ph)O)BPh.29 In the presence of both, Kþ ions
(44) For more examples of LnM-CO Kþ bonding interactions, see: (a)
3 3 3
Wink, D. J.; Fox, J. R.; Cooper, N. J. J. Am. Chem. Soc. 1985, 107, 5012–
5014. (b) Himmel, D.; Seitz, M.; Scheer, M. Z. Anorg. Allg. Chem. 2004, 630,
1220–1228. (c) Kirin, V.; Roesky, P. W. Eur. J. Inorg. Chem. 2004, 1045–1050.
(d) Aldridge, S.; Baker, R. J.; Coombs, N. D.; Jones, C.; Rose, R. P.; Rossin, A.;
Willock, D. J. Dalton Trans. 2006, 3313–3320. (e) Kunz, K.; Vitze, H.; Bolte, M.;
Lerner, H.-W.; Wagner, M. Organometallics 2007, 26, 4663–4672.
and [Mn(CO)5Br], a pyrazolide-boroxine diadduct ([L3]2-
)
is formed. To see the effect of Kþ ions alone, we kept a
mixture of HL1 and K2CO3 (stoichiometric ratio = 1:5) in

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3549
Scheme 5. Synthesis of [K(thf)2L4]a
Scheme 6. Reaction Between HL1, K2CO3, and CoCl2 with Forma-
tion of [L2Co(μ-pz)2CoL2]a
a (i) THF, r.t., 12 h.
Given that replacement of N(Me) by O in the central
part of the ligand framework requires a considerable
degree of bond breaking and reforming, it can be con-
cluded that [L1]- and [L2]- possess substantial self-
healing forces, as long as the amount of water is limited,
and pyrazolide ions are not trapped by transition metal
Lewis acids.
Rearrangement of the [N,O,N] pyrazolylborate [L2Ph]-.
As already stated in the introductory paragraph, a major
advantage of classic tris(pyrazol-1-yl)borate donors lies
in the fact that it is conveniently possible to tune their
steric demand by introducing bulky substituents into the
3-positions of the pyrazolyl rings (i.e., [HB(3Rpz)3]-).
With the aid of these so-called, “second generation scor-
pionates”, even highly reactive metal complex fragments
can be kinetically stabilized.1 Sometimes, however, such
regiochemically pure scorpionate ligands have been ob-
served to undergo ring-flip isomerization to [HB(5Rpz)n-
a (i) THF, reflux temperature, 8 h.
THF for 8 h at reflux temperature. After workup, colorless
crystals were obtained.
The H NMR spectrum of the sample in THF-d8 is
1
characterized by few broad signals indicating dynamic
behavior of the species in solution.
(
3Rpz)3-n]- during complex formation.1
According to X-ray crystallography, the crystals con-
sist of the potassium salt of a phenylboroxine-pyrazolide
monoadduct (i.e., [K(thf)2L4]; Scheme 5), which crystal-
lizes in the form of dimers [K(thf)2L4]2 (cf. the Supporting
Information for more details of the synthesis and the
molecular structure of [K(thf)2L4]2).
Also in the case of our ligand systems, the selective
synthesis of 3-substituted derivatives has been achieved
(e.g., [Li(thf)L2Ph]; Scheme 7).30 This immediately raises
questions into the configurational stability of these ligands
when strong transition metal Lewis acids are present.
Given this background, it is revealing to compare the
outcome of the reaction between FeCl3 and [Li(thf)L2] on
the one hand and [Li(thf)L2Ph] on the other.
These results lead to the conclusion that Kþ ions are
able to shift the course of HL1 hydrolysis from pyrazabole
to boroxine formation. However, [K(thf)2L4] contains
only one pyrazolide donor per boroxine ring, which is
consistent with the view that 1:1 adducts, but not 1:2
adducts, between boroxine and amines are thermodyna-
mically favorable.45-49 In the case of K(thf)[Mn(CO)3-
L3], a driving force for the generation of the boroxine-
pyrazolide diadduct is most likely provided by Mn(CO)3
chelation (note: the lithium salt Li[Li(thf)L3] also features
a boroxine-pyrazolide diadduct, and, similar to K(thf)-
[Mn(CO)3L3], the Liþ ion is chelated by the two pyrazolyl
rings and one boroxine oxygen atom).39
We find it noteworthy in this context, that partial
hydrolysis of only the B-N(Me)-B fragment, but not
the B-(μ-pz)-B backbone, has been observed upon treat-
ment of HL1 with K2CO3 (1.5 equiv) in the presence of
CoCl2 (1 equiv). The resulting complex [L2Co(μ-pz)2-
CoL2] (Scheme 6) was isolated in almost 25% yield (cf.
the Supporting Information for more details of the syn-
thesis procedure and an X-ray crystal structure analysis).
In the first case, the expected compound [FeCl2L2] was
obtained in 71% yield after recrystallization.30 In the sec-
ond case, however, we isolated complex [FeCl2(3PhpzH)-
L5] (Scheme 7). The compound was characterized by
X-ray crystallography (cf. the Supporting Information
for details of the synthesis and the X-ray crystal structure
analysis of [FeCl2(3PhpzH)L5]).
[FeCl2(3PhpzH)L5] contains an FeIII ion in a slightly dis-
torted octahedral coordination environment. The (pyra-
zol-1-yl)borate [L5]- acts as facially coordinating triden-
tate ligand. The remaining three coordination sites are
occupied by two chloride ions and one 3-phenylpyrazole
molecule (Scheme 7). [FeCl2(3PhpzH)L5] is remarkable in
several respects: (i) B-N(3Phpz) bonds have been broken
so that free 3-phenylpyrazole is available for iron coordi-
nation. (ii) A 3-phenylpyrazolyl ring has moved from a
terminal to the sterically more encumbered bridging
position. (iii) The ratio 3Phpz:pz of 2:1 in [Li(thf)L2] has
changed to 1:2 in [L5]-. [L5]- is therefore not just the
product of intraligand pyrazole shuffling, but it must
have been assembled from the fragments of at least two
[L2]- molecules.
(45) Beckmann, J.; Dakternieks, D.; Duthie, A.; Lim, A. E. K.; Tiekink,
E. R. T. J. Organomet. Chem. 2001, 633, 149–156.
(46) Perttu, E. K.; Arnold, M.; Iovine, P. M. Tetrahedron Lett. 2005, 46,
8753–8756.
These observations indicate [L2Ph -
to be a rather
]
dynamic molecule in solution because it readily under-
goes B-N dissociation and reassociation. The same
might even be true for the parent ligand [L2]-, for which
such equilibria are harder to detect, because the com-
pound possesses only one sort of pyrazolyl rings. The
(47) Iovine, P. M.; Gyselbrecht, C. R.; Perttu, E. K.; Klick, C.; Neuwelt,
A.; Loera, J.; DiPasquale, A. G.; Rheingold, A. L.; Kua, J. Dalton Trans.
2008, 3791–3794.
(48) Kua, J.; Iovine, P. M. J. Phys. Chem. A 2005, 109, 8938–8943.
(49) Kua, J.; Fletcher, M. N.; Iovine, P. M. J. Phys. Chem. A 2006, 110,
8158–8166.

3550 Inorganic Chemistry, Vol. 49, No. 7, 2010
Mutseneck et al.
Scheme 7. Ligand Rearrangement upon Treatment of [Li(thf)L2Ph
with FeCl3
]
with the metallic component and in a second step n-BuLi was
added as a base.
a
Using CoCl2, it was possible to isolate and fully character-
ize both the intermediate [CoCl2(HL1)] and the final product
[L1Co(μ-Cl)2CoL1] of the reaction sequence. Interestingly,
HCl elimination from [CoCl2(HL1)] does not necessarily
require the assistance of a base, but happens spontaneously
when a solution of the complex is stored at room temperature
for several days. Similar to the case of ZnII, attempts to
prepare CoII complexes of [L2]- were accompanied by ligand
decomposition and gave the pyrazolyl-bridged dinuclear
compound [L2Co(μ-Cl)(μ-pz)CoL2].
Efforts to synthesize the MnII complex [Mn(CO)3L1] from
[Mn(CO)5Br] and either [Li(thf)L1] or HL1 in the presence of
a base (n-BuLi, NEt3, K2CO3) all met with failure. With
K2CO3, however, we isolated the compound K(thf)[Mn-
(CO)3L3] from the reaction mixture. K(thf)[Mn(CO)3L3]
features another example of a fourth generation scorpionate,
that is, the boroxine-based [N,O,N] derivative [Ph(pz)B(μ-
O)(μ-OB(Ph)O)B(pz)Ph]2-([L3]2-). [L3]2- is undoubtedly a
hydrolysis product of [L1]-; we believe that the source of
water was the hygroscopic K2CO3. The fact, that the borox-
ine adduct [L3]2- is assembled under reaction conditions that
otherwise lead to the degradation of HL1 underlines the high
stability of [L3]2- and suggests to employ this ligand delib-
erately in future studies (Li2[L3] is easily accessible from
2 Lipz and (B(Ph)O)3).39 In contrast to [Mn(CO)3L1], the
[N,O,N] congener [Mn(CO)3L2] forms from [Mn(CO)5Br]
and [Li(thf)L2] in excellent yields.
As evidenced by the crystal structure analyses of the
complexes [Zn(Br)L1]/[Mg(Cl)(thf)2L2]/[Mn(CO)3L2] on
the one hand and [L1Mg(μ-Cl)2Mg(thf)L1]/[Cu(Cl)L1]/[Cu-
(Cl)L2]2 on the other, [L1]- and [L2]- are able to adopt both a
fac and a mer conformation, which is a unique feature in
scorpionate chemistry.
a (i) THF, r.t., 10 h.
structural fluxionality of L2-type compounds can be
rationalized by considering the π-donor ability of the
central oxygen atom which helps to stabilize three-
coordinate boron intermediates generated by B-N dis-
sociation.
Finally, we discovered that the ligand framework of [L1]-
and [L2]- has a tendency to undergo B-N association/
dissociation equilibrium reactions, most likely because the
bridging N(Me) or O atom is able to stabilize three-coordi-
nate boron intermediates by N/O-B π interactions. How-
ever, once chelation of a transition metal ion has been
achieved, the resulting complexes are reasonably stable, in
many cases even toward air and moisture.
Conclusion
This paper deals with the coordination properties of fourth
generation scorpionates, that is, mixed-donor (pyrazol-1-yl)-
borates with potentially large bite angles. We started our
investigation with the [N,N,N]/[N,O,N] ligands [Ph(pz)B(μ-
N(Me))(μ-pz)B(pz)Ph]- ([L1]-)/[Ph(pz)B(μ-O)(μ-pz)B(pz)-
Experimental Section
General Considerations. All reactions were carried out under
nitrogen using standard Schlenk techniques. All solvents were
dried and distilled prior to use. Ligand [Li(thf)L2] was prepared
as published in the literature.30 1H, 11B{1H}, and 13C{1H} NMR
spectra were recorded on Bruker AMX 300 or Avance 400
spectrometers at room temperature. Abbreviations: s = singlet,
d = doublet, t = triplet, vt = virtual triplet, dd = doublet of
doublets, m = multiplet, n.r. = multiplet not resolved, br =
broad, Me = methyl, Ph = phenyl, pz = pyrazol-1-yl. IR:
Jasko FT-IR 4200 spectrometer. Cyclic voltammograms were
recorded using an EG&G Princeton Applied Research 263A
potentiostat. Elemental analyses were performed by the micro-
analytical laboratory of the Goethe University Frankfurt.
Synthesis of HL1. A mixture of (Me2N(Ph)B)2NMe (1.61 g,
5.49 mmol) and Hpz (0.90 g, 13.22 mmol) was refluxed in Et2O
(20 mL) for 12 h. The colorless precipitate formed was isolated
by filtration, washed with Et2O (3 ꢀ 10 mL), dried under
vacuum and recrystallized from hexane/benzene. Yield: 1.36 g
(76%; note: the sample still contained about 20% of HL1B).
Ph]-([L2]-) and included main group metal ions (Liþ, Mg2þ
)
as well as middle (MnI, CoII) and late transition metal ions
(CuII, ZnII) into the study.
Liþ and Mg2þ complexes are accessible with both ligands
(i.e., [Li(thf)L1], [Li(thf)L2], [Mg(Cl)(thf)xL1], [Mg(Cl)(thf)2-
L2], and the same is true for CuII ([Cu(Cl)L1], [Cu(Cl)L2]). In
contrast, ZnII ions undergo clean complexation only with
[L1]- ([Zn(Br)L1]), while the reactions between ZnX2 (X =
Cl, Br) and [Li(thf)L2] proceeded with decomposition of a
part of the ligand molecules and yielded the pyrazole com-
plexes [Zn(X)(Hpz)L2].
We noted on several occasions that treatment of [L1]- with
certain metal reagents led to ligand degradation (e.g., with
MgCl2) or unwanted redox reactions (e.g., with [Mn(CO)5-
Br]). In some of these cases, the problem could be solved by
applying a sequential protocol: First, the acid HL1 was mixed

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3551
Crystals of HL1 suitable for X-ray analysis were obtained from a
hexane/benzene mixture. 1H NMR (300.0 MHz, CDCl3): δ 2.28
(d, 3H, 3JHH = 5.7 Hz; NMe), 6.30 (vt, 2H; pzH-4), 6.57 (t, 1H,
3JHH = 2.4 Hz; μ-pzH-4), 7.04-7.07, 7.12-7.20 (2 ꢀ m, 4H, 6H;
(μ-pzC-4), 127.4 (PhC-m), 127.6 (PhC-p), 131.0 (μ-pzC-3,5),
133.4 (PhC-o), 135.0, 139.3 (pzC-3,5). Anal. Calcd for
C22H22B2BrN7Zn [551.35] ꢀ 0.33 C4H8O [72.11]: C, 48.70; H,
4.32; N, 17.04. Found: C, 48.81; H, 4.45; N, 17.03 (note: the
relative amount of THF was confirmed by H NMR spectro-
scopy).
1
PhH), 7.44 (m, 4H; μ-pzH-3,5, pzH-3 or 5), 7.82 (d, 2H, 3JHH
=
1.2 Hz; pzH-3 or 5), 8.40 (br, 1H; NH). 11B{1H} NMR (96.3
Synthesis of [Cu(Cl)L1]. HL1 (284 mg, 0.70 mmol) and CuCl2
(94 mg, 0.70 mmol) were stirred in THF (5 mL) at room
temperature for 2 h. The dark green solution formed was cooled
to -78 °C. A 1.6 M solution of n-BuLi in hexane (0.45 mL, 0.72
mmol) was added, whereupon the color of the mixture changed
to deep blue. The mixture was allowed to warm to room
temperature, stirred for 2 h and then layered with hexane
(20 mL). Dark blue X-ray quality crystals formed, which were
collected on a frit, rinsed with hexane, and dried under vacuum.
Yield: 95 mg (27%). Anal. Calcd for C22H22B2ClCuN7 [505.08]:
C, 52.32; H, 4.39; N, 19.41. Found: C, 52.06; H, 4.50; N, 19.18%.
Synthesis of [CoCl2(HL1)]. A mixture of HL1 (204 mg, 0.50
mmol) and CoCl2 (65 mg, 0.50 mmol) was stirred in THF
(10 mL) overnight. The resulting deep blue solution was evapo-
rated to dryness, and the residue was extracted into CH2Cl2. The
extract was concentrated to a volume of 3 mL and layered with
hexane (20 mL). Blue crystals (suitable for X-ray analysis)
formed, which were isolated by filtration, rinsed with hexane
and dried under vacuum. Note: The blue crystals should be
isolated soon after they appear. Prolonged storage of the
crystals in the mother liquor results in their transformation into
crystals of [L1Co(μ-Cl)2CoL1]. Yield: 215 mg (80%). Anal.
Calcd for C22H23B2Cl2CoN7 [536.92] ꢀ 0.75 CH2Cl2 [84.93]:
C, 45.49; H, 4.11; N, 16.32. Found: C, 45.32; H, 4.38; N, 16.76.
The identity of the entire sample with the material used for single
crystal X-ray analysis was further confirmed by X-ray powder
diffraction.
Synthesis of [L1Co(μ-Cl)2CoL1]. A mixture of HL1 (204 mg,
0.50 mmol) and CoCl2 (65 mg, 0.50 mmol) was stirred in THF
(10 mL) for 2 h. The resulting dark blue solution was cooled to
-78 °C, and a 1.6 M solution of n-BuLi in hexane (0.33 mL, 0.53
mmol) was added. The reaction mixture was allowed to warm to
ambient temperature and stirred overnight. A black precipitate
formed, which was removed by filtration. The violet filtrate was
concentrated to a volume of 2 mL and layered with hexane
(20 mL). Violet crystals (suitable for X-ray analysis) formed,
which were collected on a frit, rinsed with hexane, and dried
under vacuum. Yield: 105 mg (39%). Anal. Calcd for C44H44B4-
Cl2Co2N14 [1000.93] ꢀ CH2Cl2 [84.93]: C, 49.78; H, 4.27; N,
18.05. Found: C, 50.41; H, 4.28; N, 18.43.
MHz, CDCl3): δ 3.2.
Synthesis of [Li(thf)L1]. A stirred solution of HL1 (420 mg,
1.03 mmol) in THF (5 mL) was treated at -78 °C with a 1.6 M
solution of n-BuLi in hexane (0.63 mL, 1.01 mmol). The mixture
was allowed to warm to room temperature and stirred over-
night. Gas-phase diffusion of pentane into the solution led to
colorless X-ray quality crystals within one week. The mother
liquor was decanted and the crystals dried under vacuum. Yield:
470 mg (96%). 1H NMR (300.0 MHz, THF-d8): δ 1.99 (s, 3H;
3
NMe), 6.22 (dd, 2H, JHH = 1.8, 2.3 Hz; pzH-4), 6.42 (t, 1H,
3JHH = 2.2 Hz; μ-pzH-4), 6.96-7.08 (m, 10H; PhH), 7.43 (d,
2H, 3JHH = 2.2 Hz; μ-pzH-3,5), 7.48 (dd, 2H, 4,3JHH = 0.6, 2.3
Hz; pzH-3 or 5), 7.55 (dd, 2H, 4,3JHH = 0.6, 1.8 Hz; pzH-3 or 5).
11B{1H} NMR (96.3 MHz, THF-d8): δ 6.7. 13C{1H} NMR (75.5
MHz, THF-d8): δ 33.2 (NMe), 105.4 (pzC-4), 109.2 (μ-pzC-4),
126.4 (PhC-p), 127.1 (PhC-m), 131.0 (μ-pzC-3,5), 134.0 (PhC-o),
134.7, 139.1 (pzC-3,5). Anal. Calcd for C26H30B2LiN7O
[485.13]: C, 64.37; H, 6.23; N, 20.21. Found: C, 64.57; H, 6.23;
N, 20.40.
Synthesis of [Mg(Cl)(thf)xL1]. A stirred solution of HL1 (177
mg, 0.43 mmol) in THF (5 mL) was treated at -78 °C with a 3 M
solution of MeMgCl in THF (0.14 mL, 0.42 mmol). The
reaction mixture was allowed to warm to room temperature
and stirred overnight. It was then concentrated to a volume of
2 mL under vacuum and layered with pentane, whereupon
colorless crystals formed that were suitable for X-ray analysis
([L1Mg(μ-Cl)2Mg(thf)L1]). The mother liquor was decanted,
and the crystals dried under vacuum. Yield: 220 mg (97%). 1H
NMR (300.0 MHz, CDCl3): δ 2.22 (s, 3H; NMe), 6.35 (vt, 2H;
3
pzH-4), 6.51 (t, 1H, JHH = 2.4 Hz; μ-pzH-4), 6.96-7.05,
7.09-7.15 (2 ꢀ m, 4H, 6H; PhH), 7.33 (d, 2H, 3JHH = 2.4 Hz;
μ-pzH-3,5), 7.48, 7.86 (d, n.r., 2 ꢀ 2H, 3JHH = 2.1 Hz; pzH-3,5).
11B{1H} NMR (96.3 MHz, CDCl3): δ 5.3.
Synthesis of [Mg(Cl)(thf)2L2]. A mixture of [Li(thf)L2] (113
mg, 0.24 mmol) and anhydrous MgCl2 (22 mg, 0.23 mmol) was
stirred in THF (10 mL) overnight. Gas-phase diffusion of
pentane into the solution led to colorless X-ray quality crystals
within 2 weeks. The mother liquor was removed using a syringe,
and the crystals were dried under vacuum. Yield: 121 mg (88%).
1H NMR (300.0 MHz, CDCl3): δ 6.38 (vt, 2H; pzH-4), 6.60 (t,
1H, 3JHH = 2.4 Hz; μ-pzH-4), 6.88-6.94, 7.02-7.14 (2 ꢀ m, 4H,
6H; PhH), 7.58 (dd, 2H, 4,3JHH = 0.6, 2.1 Hz; pzH-3 or 5), 7.68
(d, 2H, 3JHH = 2.4 Hz; μ-pzH-3,5), 8.01 (d, 2H, 3JHH = 1.8 Hz;
pzH-3 or 5). 11B{1H} NMR (96.3 MHz, THF-d8): δ 5.4. Anal.
Calcd for C29H35B2ClMgN6O3 [597.01]: C, 58.34; H, 5.91; N,
14.07. Found: C, 58.07; H, 5.96; N, 14.19.
Synthesis of K(thf)[Mn(CO)3L3]. A mixture of HL1 (194 mg,
0.48 mmol), [Mn(CO)5Br] (131 mg, 0.48 mmol), and K2CO3
(133 mg, 0.96 mmol) in THF (10 mL) was heated at reflux
temperature for 8 h. The resulting yellow suspension was cooled
to room temperature and filtered through a frit. The filtrate was
concentrated under reduced pressure to a volume of 3 mL and
layered with hexane (20 mL). Yellow X-ray quality crystals
formed, which were isolated by filtration and dried under vacuum.
Synthesis of [Zn(Br)L1]. A mixture of HL1 (230 mg, 0.56
mmol) and ZnBr2 (126 mg, 0.56 mmol) in THF (10 mL) was
stirred at room temperature for 2 h. The mixture was cooled to
-78 °C, a 1.6 M solution of n-BuLi in hexane (0.35 mL, 0.56
mmol) was added, the temperature was allowed to rise to room
temperature, and stirring was continued overnight (note: n-BuLi
can be replaced by NaN(SiMe3)2). The reaction mixture was
concentrated under reduced pressure to a volume of 2 mL and
layered with pentane, whereupon colorless crystals formed that
were suitable for X-ray analysis. The mother liquor was de-
canted, and the crystals were dried under vacuum. Yield: 190 mg
(59%). 1H NMR (300.0 MHz, CDCl3): δ 2.00 (s, 3H; NMe), 6.48
1
Yield: 104 mg (31% based on [Mn(CO)5Br]). H NMR (400.1
MHz, THF-d8): δ 6.24 (vt, 2H; pzH-4), 7.18 (m, 2H; PhH-p),
7.25-7.36 (m, 7H; PhH-m, PhH*-m,p), 7.65 (n.r., 2H; pzH-3 or 5),
3
7.73 (m, 4H; PhH-o), 7.81 (d, 2H, JHH = 1.6 Hz; pzH-3 or 5),
7.96-8.01 (m, 2H; PhH*-o). 1B{1H} NMR (128.4 MHz, THF-d8):
δ 6.1 (s, 2B), 31 (h1/2 ≈ 1100 Hz, 1B). 13C{1H} NMR (62.9 MHz,
THF-d8): δ 105.7 (pzC-4), 126.0 (PhC-p), 127.3 (PhC-m), 127.6
(PhC*-m), 129.3 (PhC*-p), 132.2 (pzC-3 or 5), 133.0 (PhC-o),
135.0 (PhC*-o), 138.8 (pzC-3 or 5). IR (KBr, cm-1): ν~ (CO) 2026,
1929, 1891. ESI-MS: m/z (%) 585.7 [M-(K(thf))]- (14), 529.6
[M-(K(thf))-2CO]- (12), 501.5 [M-(K(thf))-3CO]- (100). Anal.
Calcd for C31H29B3KMnN4O7 [696.05]: C, 53.49; H, 4.20; N, 8.05.
Found: C, 53.31; H, 4.20; N, 8.03.
3
(vt, 2H; pzH-4), 6.54 (t, 1H, JHH = 2.1 Hz; μ-pzH-4),
7.02-7.09, 7.20-7.25 (2 ꢀ m, 4H, 6H; PhH), 7.37 (d, 2H, 3JHH
=
2.1 Hz; μ-pzH-3,5), 7.62, 7.84 (2ꢀdd, 2ꢀ2H, 4,3JHH=0.6, 2.0/2.4
Hz; pzH-3,5). 1B{1H} NMR (96.3 MHz, CDCl3): δ 5.1. 13C{1H}
NMR (75.4 MHz, CDCl3): δ 39.1 (NMe), 108.2 (pzC-4), 110.6
Synthesis of [Mn(CO)3L2]. A mixture of [Li(thf)L2] (113 mg,
0.24 mmol) and [Mn(CO)5Br] (63 mg, 0.23 mmol) in THF

3552 Inorganic Chemistry, Vol. 49, No. 7, 2010
Mutseneck et al.
(10 mL) was heated at reflux temperature for 8 h. The resulting
solution was cooled to room temperature, all volatiles were
removed under reduced pressure, and the crude product was
extracted into CH2Cl2 (10 mL). The extract was evaporated to
dryness under vacuum and the solid residue was recrystallized
from Et2O at -5 °C; the yellow crystals obtained were suitable
for X-ray analysis. Yield: 88 mg (70%). 1H NMR (400.1 MHz,
CDCl3): δ 6.35 (vt, 2H; pzH-4), 6.54 (t, 1H, 3JHH = 2.1 Hz; μ-
pzH-4), 7.21-7.25, 7.29-7.34 (2 ꢀ m, 4H, 6H, PhH), 7.56, 7.63
The crystal of [Zn(Br)L1] 2C4H8O was twinned (twin law: 1 0
3
0/1 -1 0/1 0 -1) with a ratio of 0.669(1)/0.331(1) for the two
twin components.
In [Zn(Br)(Hpz)L2] C4H8O 0.5 C6H14, one atom of a non-
3
3
coordinating THF molecule is disordered over two positions
with a site occupation factor of 0.65(2) for the major occupied
site.
For [Zn(Cl)(Hpz)L2] 2C4H8O, the absolute structure was
3
determined by refinement of the Flack-parameter: x =
0.03(3). One non-coordinating THF molecule in [Zn(Cl)-
3
(2 ꢀ d, 2 ꢀ 2H, 2 ꢀ JHH = 2.1 Hz; pzH-3 or 5, μ-pzH-3,5), 7.75
(d, 2H, 3JHH = 1.6 Hz; pzH-3 or 5). 1B{1H} NMR (128.4 MHz,
CDCl3): δ 6.0. 13C{1H} NMR (62.9 MHz, CDCl3): δ 107.8 (pzC-
4), 110.6 (μ-pzC-4), 127.6 (PhC-m), 128.1 (PhC-p), 131.0 (μ-pzC-
3,5), 131.7 (pzC-3 or 5), 132.4 (PhC-o), 140.5 (pzC-3 or 5). IR
(KBr, cm-1): ν~(CO) 2033, 1930. ESI-MS: m/z (%) 533.3
[MþH]þ (100). Anal. Calcd for C24H19B2MnN6O4 [532.01]: C,
54.18; H, 3.60; N, 15.80. Found: C, 54.23; H, 3.73; N, 16.25.
X-ray Crystal Structure Analyses. Single crystals were ana-
lyzed with a STOE IPDS II two-circle diffractometer with
(Hpz)L2] 2C4H8O is disordered over two positions with a site
3
occupation factor of 0.70(2) for the major occupied site.
In K(thf)[Mn(CO)3L3] the coordinating thf molecule is dis-
ordered over two positions with a site occupation factor of
0.608(8) for the major occupied site.
In [K(thf)2L4]2, two of the coordinating thf molecules show
one disordered C atom each. These atoms are disordered over
two positions with site occupation factors of 0.56(1) and 0.61(1)
for the respective major occupied site.
˚
graphite-monochromated MoKR (0.71073 A) radiation. Em-
pirical absorption corrections were performed for all structures
(except HL1 and [Li(thf)L1]) using the MULABS50 option in
PLATON.51 The structures were solved by direct methods using
the program SHELXS52 and refined against F2 with full-matrix
least-squares techniques using the program SHELXL-97.53 All
non-hydrogen atoms (except the disordered atoms of
[Zn(Br)(Hpz)L2] C4H8O 0.5 C6H14, K(thf)[Mn(CO)3L3], and
Acknowledgment. Financial funding by the Deutsche
Forschungsgemeinschaft (DFG) and the Fonds der Chemischen
Industrie (FCI) is acknowledged. The authors are grateful to
€
F. Schodel for cyclic voltammetric measurements.
Supporting Information Available: X-ray crystallographic files
in CIF format. ORTEP-plot, selected structure parameters and
crystallographic data of [Mg(Cl)(thf)2L2]. ORTEP plots and key
structure parameters of [Zn(Br)L1] and [Cu(Cl)L1]. Synthesis and
X-ray crystal structure analysis of [Zn(Cl)(Hpz)L2], [Zn(Br)-
(Hpz)L2], and [L2Co(μ-Cl)(μ-pz)CoL2]. Plot of the polymeric
structure of K(thf)[Mn(CO)3L3] in the solid state. Cyclic voltam-
mograms of complexes [Mn(CO)3L2] and K(thf)[Mn(CO)3L3].
Synthesis and X-ray crystal structure analysis of [K(thf)2L4]2,
[L2Co(μ-pz)2CoL2], and [FeCl2(3PhpzH)L5]. This material is avail-
able free of charge via the Internet at http://pubs.acs.org. Crystal-
lographic data of HL1 (CCDC-758004), [Li(thf)L1] (CCDC-
758003), [L1Mg(μ-Cl)2Mg(thf)L1] (CCDC-758005), [Mg(Cl)-
(thf)2L2] (CCDC-758000), [Zn(Br)L1] (CCDC-758007), [Zn(Br)-
(Hpz)L2] (CCDC-758002), [Zn(Cl)(Hpz)L2] (CCDC-757997),
[Cu(Cl)L1] (CCDC-758006), [CoCl2(HL1)] (CCDC-758008),
[L1Co(μ-Cl)2CoL1] (CCDC-758009), [L2Co(μ-Cl)(μ-pz)CoL2]
(CCDC-758001), [L2Co(μ-pz)2CoL2] (CCDC-758012), [Mn-
(CO)3L2] (CCDC-757999), K(thf)[Mn(CO)3L3] (CCDC-758010),
[K(thf)2L4]2 (CCDC-758011), and [FeCl2(3PhpzH)L5] (CCDC-
757998) in CIF format. These data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
3
3
[K(thf)2L4]2) were refined with anisotropic displacement para-
meters. The hydrogen atoms were geometrically positioned and
treated as riding on the carbon atoms; the amino H atoms were
freely refined.
In the absence of anomalous scatterers in [Li(thf)L1], the
Flack-x-parameter is meaningless. Therefore, Friedel pairs were
merged and the absolute structure was arbitrarily set.
In [L1Mg(μ-Cl)2Mg(thf)L1] C5H12, the bond lengths in the
3
ꢀ
˚
pentane molecule were restrained to 1.5(1) A, and the displace-
ment parameters of the C atoms were restrained to an isotropic
behavior.
The crystal lattice of [L2Co(μ-Cl)(μ-pz)CoL2] CH2Cl2 con-
3
tains void spaces. However, no significant electron density could
be found in these regions.
In [L1Co(μ-Cl)2CoL1] CH2Cl2 the C atom of the CH2Cl2
molecule is disordered over two equally occupied positions.
3
(50) Blessing, R. H. Acta Crystallogr. 1995, A51, 33–38.
(51) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.
(52) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467–473.
(53) Sheldrick, G. M. SHELXL-97. A Program for the Refinement of
€
€
€
Crystal Structures; Universitat Gottingen: Gottingen, Germany, 1997.