Mn(CO)2 complexes of cyclopentadienyl/scorpionate hybrid ligands

Article abstract of DOI:10.1021/om700450j

Rare examples of complexes featuring a chelating cyclopentadienyl/ scorpionate hybrid ligand are reported. The compounds are obtained by photolytic decarbonylation of K[(OC)₃ Mn(C₅ H₄ -B(Pz)(R)R′)] (1: R = R′ = Me; 2: R = Me, R′ = pz; 3: R = R′ = pz; pz = pyrazol-1-yl), which leads to the constrained-geometry complexes K[p(OC)₂ Mn(C₅ H₄ -B(μ-Pz)(R)R′)] (4-6) in quantitative yields. In 4-6, the Mn-coordinating pyrazolyl ring is tethered to the cyclopentadienyl ligand via a borate bridge. According to X-ray crystallography, the molecular frameworks of 4-6 are largely unstrained. The ligand scaffold is thus well adapted to the coordination requirements of the Mn(I) ion. The crystal lattices of 2, 3, and Li[(OC)₃Mn(C₅ H₄ -BPha₃ )] (7) contain dimeric aggregates held together by K⁺-OC σ adducts, K⁺-pz σ adducts, and K⁺-pz n interactions (2, 3) as well as Li⁺-OC σ adducts and Li⁺-phenyl π interactions (7). In none of these cases does the π-electron cloud of the cymantrenyl substituent take part in alkali metal ion complexation.

Full text of DOI:10.1021/om700450j

Organometallics 2007, 26, 4663-4672
4663
Mn(CO)2 Complexes of Cyclopentadienyl/Scorpionate Hybrid
Ligands
Kerstin Kunz, Hannes Vitze, Michael Bolte, Hans-Wolfram Lerner, and Matthias Wagner*
Institut fu¨r Anorganische Chemie, J.W. Goethe-UniVersita¨t Frankfurt, Max-Von-Laue-Strasse 7,
D-60438 Frankfurt (Main), Germany
ReceiVed May 7, 2007
Rare examples of complexes featuring a chelating cyclopentadienyl/scorpionate hybrid ligand are
reported. The compounds are obtained by photolytic decarbonylation of K[(OC)3Mn(C5H4-B(pz)(R)R′)]
(1: R ) R′ ) Me; 2: R ) Me, R′ ) pz; 3: R ) R′ ) pz; pz ) pyrazol-1-yl), which leads to the
constrained-geometry complexes K[(OC)2Mn(C5H4-B(µ-pz)(R)R′)] (4-6) in quantitative yields. In 4-6,
the Mn-coordinating pyrazolyl ring is tethered to the cyclopentadienyl ligand via a borate bridge. According
to X-ray crystallography, the molecular frameworks of 4-6 are largely unstrained. The ligand scaffold
is thus well adapted to the coordination requirements of the Mn(I) ion. The crystal lattices of 2, 3, and
Li[(OC)3Mn(C5H4-BPh3)] (7) contain dimeric aggregates held together by K+-OC σ adducts, K+-pz σ
adducts, and K+-pz π interactions (2, 3) as well as Li+-OC σ adducts and Li+-phenyl π interactions (7).
In none of these cases does the π-electron cloud of the cymantrenyl substituent take part in alkali metal
ion complexation.
compounds range from dinuclear metallamacrocycles15 to metal-
containing polymers and ferrocene-based multiple-decker sand-
wich complexes.21
Introduction
Cyclopentadienyl derivatives1,2 and poly(pyrazol-1-yl)borates
(“scorpionates”)3,4 are among the most important ligands in
transition metal chemistry. In the field of metallocene com-
plexes, particularly interesting perspectives were opened by the
introduction of bridged cyclopentadienyl systems, which give
access either to oligonuclear complexes5,6 and polymeric materi-
als (e.g., [-(C5H4)Fe(C5H4)-SiMe2-]n)7 or to mononuclear
ansa-compounds (e.g., Me2Si(C5H4)2ZrCl2).8,9 Bridged scorpi-
onate ligands are known with a direct B-B bond10-12 as well
as with meta-phenylene, para-phenylene,13-15 and 1,1′-ferro-
cenylene16-21 linkers. Structural motifs accessible with these
Given this rich chemistry of oligo(cyclopentadienyl) and
oligo(scorpionate) systems, it is an interesting challenge to
combine both functionalities within the same ligand molecule
and thereby to create novel cyclopentadienyl/scorpionate hybrid
ligands. Two different coordination modes can be envisaged
for these kinds of donor molecules: They may either adopt a
bridging position between two different metal centers M1 and
M2 (A, Figure 1) or, alternatively, bind to the same metal atom
M via the Cp ring and one or two of their pyrazolyl substituents
(B, Figure 1). Type A compounds A1, A2, and A3 (Figure 1)
are well established in the literature.16-18,22-24 In contrast, only
few examples (B1, B2; Figure 1) of type B metal complexes
have been described and structurally characterized up to now.
These are the multiple-decker sandwich complexes B1 (M )
Li+-Cs+)21 and the samarium complex B2, which forms in a
unique rearrangement reaction upon thermolysis of the precursor
compound Sm[HB(pz3,5-Me)3]2(Cp) at 165 °C in the solid state.25
Recently, the free cyclopentadienyl/scorpionate hybrid ligands
[(C5Me4H)B(pz3-Me)3]- and [(9-fluorenyl)Bpz3]- have been
* Corresponding author. Fax: +49 69 798 29260. E-mail:
Matthias.Wagner@chemie.uni-frankfurt.de.
(1) Long, N. J. Metallocenes; Blackwell Science: London, 1998.
(2) Togni, A.; Halterman, R. L. Metallocenes: Synthesis-ReactiVity-
Applications; Wiley-VCH: New York, 2006.
(3) Trofimenko, S. Chem. ReV. 1993, 93, 943-980.
(4) Trofimenko, S., Scorpionates-The Coordination Chemistry of Poly-
pyrazolylborate Ligands; Imperial College Press: London, 1999.
(5) Yu, Y.; Bond, A. D.; Leonard, P. W.; Vollhardt, K. P. C.; Whitener,
G. D. Angew. Chem., Int. Ed. 2006, 45, 1794-1799.
(6) Wagner, M. Angew. Chem., Int. Ed. 2006, 45, 5916-5918.
(7) Manners, I. AdV. Organomet. Chem. 1995, 37, 131-168.
(8) Bajgur, C. S.; Tikkanen, W. R.; Petersen, J. L. Inorg. Chem. 1985,
24, 2539-2546.
(9) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
(10) Brock, C. P.; Das, M. K.; Minton, R. P.; Niedenzu, K. J. Am. Chem.
Soc. 1988, 110, 817-822.
(11) Harden, N. C.; Jeffery, J. C.; McCleverty, J. A.; Rees, L. H.; Ward,
M. D. New J. Chem. 1998, 661-663.
(17) Fabrizi de Biani, F.; Ja¨kle, F.; Spiegler, M.; Wagner, M.; Zanello,
P. Inorg. Chem. 1997, 36, 2103-2111.
(18) Guo, S. L.; Peters, F.; Fabrizi de Biani, F.; Bats, J. W.; Herdtweck,
E.; Zanello, P.; Wagner, M. Inorg. Chem. 2001, 40, 4928-4936.
(19) Ma, K.; Scheibitz, M.; Scholz, S.; Wagner, M. J. Organomet. Chem.
2002, 652, 11-19.
(20) Haghiri Ilkhechi, A.; Bolte, M.; Lerner, H.-W.; Wagner, M. J.
Organomet. Chem. 2005, 690, 1971-1977.
(12) Armaroli, N.; Accorsi, G.; Barigelletti, F.; Couchman, S. M.;
Fleming, J. S.; Harden, N. C.; Jeffery, J. C.; Mann, K. L. V.; McCleverty,
J. A.; Rees, L. H.; Starling, S. R.; Ward, M. D. Inorg. Chem. 1999, 38,
5769-5776.
(21) 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.
(13) Bieller, S.; Zhang, F.; Bolte, M.; Bats, J. W.; Lerner, H.-W.; Wagner,
M. Organometallics 2004, 23, 2107-2113.
(22) Herdtweck, E.; Peters, F.; Scherer, W.; Wagner, M. Polyhedron
1998, 17, 1149-1157.
(14) Zhang, F.; Bolte, M.; Lerner, H.-W.; Wagner, M. Organometallics
2004, 23, 5075-5080.
(23) Guo, S. L.; Bats, J. W.; Bolte, M.; Wagner, M. J. Chem. Soc., Dalton
Trans. 2001, 3572-3576.
(15) Bieller, S.; Bolte, M.; Lerner, H.-W.; Wagner, M. Inorg. Chem.
2005, 44, 9489-9496.
(24) Haghiri Ilkhechi, A.; Guo, S. L.; Bolte, M.; Wagner, M. Dalton
Trans. 2003, 2303-2307.
(16) Ja¨kle, F.; Polborn, K.; Wagner, M. Chem. Ber. 1996, 129, 603-
606.
(25) Lopes, I.; Lin, G. Y.; Domingos, A.; McDonald, R.; Marques, N.;
Takats, J. J. Am. Chem. Soc. 1999, 121, 8110-8111.
10.1021/om700450j CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/01/2007

4664 Organometallics, Vol. 26, No. 18, 2007
Kunz et al.
Scheme 1. Synthesis of the Cymantrenylmono-,
Cymantrenylbis-, and Cymantrenyltris(pyrazol-1-yl)borate
Salts 1-3a
Figure 1. Bridging (A) and chelating (B) coordination mode of
cyclopentadienyl/poly(pyrazol-1-yl)borate hybrid ligands; repre-
sentative examples A1-B2 for which these coordination modes
have been realized. B2: CH3 groups in the 3 and 5 positions of all
pyrazolyl rings are omitted for clarity.
a Cym ) cymantrenyl, pz ) pyrazol-1-yl; (i) toluene/THF, -78 °C
to rt; (ii) toluene, rt; (iii) toluene/THF, -78 °C to rt; (iv) THF, 0 °C.
prepared, but their ligand properties are still largely unex-
plored.26,27
created the complexes 4-6 with chelating cyclopentadienyl/
scorpionate hybrid ligands (Scheme 2). Complexes 4-6 also
form when the precursor compounds 1-3 are exposed to
daylight in THF over a period of several days. Under these
conditions, the transformation is fastest for 1 and slowest for
3. Single crystals of 4(18-c-6)-6(18-c-6) were grown from
toluene or toluene/THF solutions of 4-6 to which excess 18-
crown-6 had been added.
The purpose of this paper is to describe the synthesis and
molecular structure of B-type Mn(CO)2 complexes that are
readily available from cymantrenylpoly(pyrazol-1-yl)borates (cf.
A3, M ) K+) by replacement of one CO ligand with a pyrazolyl
nitrogen atom.
Results and Discussion
An X-ray crystal structure analysis of the THF adduct of 3
revealed that the K+ ions are bound to some of the pyrazolyl
substituents via their nitrogen lone pair and to others via their
electron π system (see below). The π faces of the cyclopenta-
dienyl rings, however, do not contribute to K+ coordination.
This is in contrast to the behavior of the alkali metal salts of
analogous ferrocenyl scorpionate ligands, which tend to establish
multiple-decker sandwich structures in the solid state.20,21,29,30
We have synthesized the lithium cymantrenylborate 7 in order
to investigate whether a M+-η5-(C5H4R)Mn(CO)3 arrangement
can be brought about when (i) K+ is replaced by the more
strongly π coordinating Li+ ion21 and (ii) no Lewis basic
nitrogen donor sites are present that could compete with the
cyclopentadienyl ring for Li+ binding. Compound 7 is access-
Synthesis. The cymantrenylmono(pyrazol-1-yl)borate 1 was
obtained from Kpz and CymBMe228 via B-N adduct formation
(Scheme 1; pz ) pyrazolide; Cym ) cymantrenyl).
The corresponding bis(pyrazol-1-yl)borate 2 (Scheme 1)
readily formed upon treatment of CymB(NMe2)Me with an
equimolar mixture of Kpz and Hpz. One equivalent of HNMe2
is liberated in the course of the reaction.
Finally, deprotonation of the free acid H[CymBpz3]23 with
KOtBu gave the potassium tris(pyrazol-1-yl)borate 3 in almost
quantitative yield (Scheme 1).
Irradiation of THF solutions of 1-3 in borosilicate glass
vessels with a high-pressure mercury lamp (λmax ) 510 nm)
led to the replacement of CO by a pyrazolyl ring and thus
28
ible from CymBBr2 and a solution of PhLi in dibutyl ether.
Li[BPh4] was formed as a byproduct irrespective of the reaction
conditions applied.
(26) Roitershtein, D.; Domingos, A.; Marques, N. Organometallics 2004,
23, 3483-3487. For a related bis(pyrazol-1-yl)methane ligand see: Otero,
A.; Ferna´ndez-Baeza, J.; Antin˜olo, A.; Tejeda, J.; Lara-Sa´nchez, A.;
Sa´nchez-Barba, L.; Rodr´ıguez, A. M.; Maestro, M. A. J. Am Chem. Soc.
2004, 126, 1330-1331.
(27) Bieller, S.; Bolte, M.; Lerner, H.-W.; Wagner, M. J. Organomet.
Chem. 2005, 690, 1935-1946.
(28) Renk, T.; Ruf, W.; Siebert, W. J. Organomet. Chem. 1976, 120,
1-25.
(29) Haghiri Ilkhechi, A.; Scheibitz, M.; Bolte, M.; Lerner, H.-W.;
Wagner, M. Polyhedron 2004, 23, 2597-2604.
(30) Kaufmann, L.; Vitze, H.; Bolte, M.; Lerner, H.-W.; Wagner, M.
Organometallics 2007, 26, 1771-1776.

Mn(CO)2 Complexes of Hybrid Ligands
Organometallics, Vol. 26, No. 18, 2007 4665
the presence of tetracoordinated boron atoms.31,32 In both series
1-3 and 4(18-c-6)-6(18-c-6), a continuous downfield shift of
the 11B resonance is observed upon replacement of methyl
substituents for more electronegative pyrazolyl rings; there are
no significant differences between the 11B resonances of an
open-chain species and its corresponding chelate complex [cf.
δ(11B) ) -8.7 (1), -1.1 (2), 0.1 (3); -8.1 (4(18-c-6)), -2.0
(5(18-c-6)), -0.1 (6(18-c-6))]. In line with these arguments, the
tetraorganylborate 7 [δ(11B) ) -9.5] possesses the most
shielded 11B nucleus of all complexes 1-7.
Scheme 2. Synthesis of the Mn(CO)2 Complexes 4-6 with
Chelating Cyclopentadienyl/Scorpionate Hybrid Ligands;
Synthesis of Lithium Cymantrenyltris(phenyl)borate 7 and
of the Pyrazole Complex 8a
1
In the H NMR spectrum of 1, the cymantrenyl substituent
gives rise to two resonances for the R and â protons (4.45 ppm,
4.46 ppm). Moreover, three signals at 5.94, 7.24, and 7.46 ppm
can be assigned to the three chemically nonequivalent protons
1
of the pyrazolyl ring. The H NMR spectra of 2 and 3 are
characterized by similar signal patterns and chemical shift
values. However, the integral ratio between the cymantrenyl
and pyrazolyl resonances is no longer 4:3 as in 1, but 4:6 (2)
and 4:9 (3), in agreement with the presence of bis- and tris-
(pyrazol-1-yl)borate moieties. As to be expected, complex 7
shows two signals in the cyclopentadienyl range and one set of
three resonances for the three chemically equivalent phenyl rings
(integral ratio C5H4:Ph ) 4:15).
Upon going from 1 to 4(18-c-6), one of the cymantrenyl
proton signals experiences an upfield shift of almost 1 ppm
(δ(1H) ) 3.53), whereas the second signal appears at signifi-
cantly lower field (δ(1H) ) 4.93). Similarly increased shift
differences between the R and â proton resonances are also
evident for 5(18-c-6) and 6(18-c-6). Most importantly, the two
R protons as well as the two â protons of 5(18-c-6) are not
chemically equivalent but give rise to a total number of four
resonances (integral ratio 1:1:1:1). This feature can easily be
explained by the fact that the boron atom of 5(18-c-6) becomes
a chiral center once one of the two pyrazolyl substituents gets
attached to the Mn(I) ion. In accordance with this interpretation,
1
the H NMR spectrum of 5(18-c-6) gives clear evidence for
the presence of two chemically inequivalent pyrazolyl rings (six
resonances, each integrating 1H, in the chemical shift range
between 5.84 and 7.31 ppm). As to be expected, the proton
NMR spectrum of the more symmetrical tris(pyrazol-1-yl)borate
6(18-c-6) is characterized by only two cymantrenyl proton
resonances as well as by two sets of pyrazolyl signals with an
integral ratio Cym:pz:pz* ) 4:6:3.
The 13C NMR spectra of 1-7 fully support the interpretation
outlined above; signals for the ipso-carbon atoms of the
cyclopentadienyl rings are broadened beyond detection due to
1
quadrupolar relaxation and JCB coupling.
a
(i) THF, UV irradiation; (ii) toluene/Bu2O, -78 °C to rt; (iii) Et2O,
In the IR spectrum, parent cymantrene has CO vibrations at
2035 cm-1 (A1) and 1949 cm-1 (E) compared to values ν˜(CO)
) 2004 cm-1/1910 cm-1, 2009 cm-1/1920 cm-1, and 2006
cm-1/1921 cm-1 for 1, 2, and 3, respectively (KBr pellets). This
leads to the conclusion that a (pyrazol-1-yl)borate substituent
increases the charge density on the Mn(I) ion, thereby leading
to more extensive metal-to-carbonyl π back-bonding (cf. also
7: ν˜(CO) ) 2000 cm-1/1911 cm-1). A related effect has been
observed in the case of numerous different ferrocenyl deriv-
atives [Fc-BR3]0/-, which are easier to oxidize than ferro-
cene itself.20,21,33-36 In the half-sandwich chelate complexes
4-6, the CO bands exhibit a further red shift and appear
UV irradiation.
The pyrazole complex 8 (Scheme 2) was structurally char-
acterized in order to be able to compare the Mn-N(pz) bond
lengths of the constrained-geometry complexes 4(18-c-6)-6(18-
c-6) with the corresponding bond length in a closely related
unbridged species. Even though irradiation of a 1:1 mixture of
cymantrene and pyrazole in diethyl ether with a high-pressure
mercury lamp (λmax ) 510 nm; 50 h) did not lead to complete
conversion, we were able to isolate a few single crystals of 8
that were suitable for X-ray crystallography.
Spectroscopic Characterization. Note: In the cases of the
complexes 4-6 we are reporting the NMR data of their crown
ether adducts 4(18-c-6)-6(18-c-6) because here the signal
resolution is least affected by cation/anion association-dis-
sociation equilibria.
(31) No¨th, H.; Wrackmeyer, B. Nuclear Magnetic Resonance Spectros-
copy of Boron Compounds. In NMR Basic Principles and Progress; Diehl,
P., Fluck, E., Kosfeld, R., Eds.; Springer: Berlin, 1978.
(32) Mason, J. Multinuclear NMR; Plenum Press: New York, 1987.
(33) Fontani, M.; Peters, F.; Scherer, W.; Wachter, W.; Wagner, M.;
Zanello, P. Eur. J. Inorg. Chem. 1998, 1453-1465.
The 11B NMR signals of the complexes 1-6(18-c-6) appear
in the interval between 0.1 and -8.7 ppm, which testifies to

4666 Organometallics, Vol. 26, No. 18, 2007
Kunz et al.
Table 1. Selected Crystallographic Data for CymBBr2, (2THF)2, (3THF)2, 4(18-c-6), 5(18-c-6), and 6(18-c-6)
CymBBr2
(2THF)2
(3THF)2
formula
fw
C8H4BBr2MnO3
373.68
light yellow, block
173(2)
Mo KR, 0.71073 Å
orthorhombic
Pbca
13.6364(13)
12.0796(11)
13.9393(11)
90
90
90
2296.1(4)
8
2.162
C38H42B2K2Mn2N8O8
948.50
light yellow, plate
173(2)
Mo KR, 0.71073 Å
monoclinic
P2/c
11.8591(11)
8.2372(5)
23.1905(19)
90
C21H21BKMnN6O4
526.29
yellow, block
173(2)
Mo KR, 0.71073 Å
triclinic
color, shape
temp (K)
radiation
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
P1h
9.7794(11)
11.5583(14)
12.2180(16)
105.250(10)
109.593(9)
101.044(9)
1194.3(3)
2
100.310(7)
90
2228.8(3)
2
Z
D
calcd (g cm-3
)
1.413
1.463
F(000)
1408
8.090
976
0.811
540
0.767
µ (mm-1
)
cryst size (mm3)
no. of rflns collected
no. of indep rflns (Rint
0.17 × 0.15 × 0.09
0.31 × 0.27 × 0.13
0.51 × 0.48 × 0.35
15 920
11 899
9394
)
2159 (0.0915)
2159/0/136
1.084
4147 (0.0394)
4147/20/292
1.024
4382 (0.0493)
4382/0/327
1.049
no. of data/restraints/params
GOOF on F2
R1, wR2 (I > 2σ(I))
0.0618, 0.1048
0.0979, 0.1148
0.609, -0.706
0.0373, 0.0951
0.0491, 0.0997
0.631, -0.290
0.0493, 0.1330
0.0550, 0.1370
0.743, -1.192
R1, wR2 (all data)
largest diff peak and hole (e Å-3
)
4(18-c-6)
5(18-c-6)
6(18-c-6)
formula
fw
C24H37BKMnN2O8
586.41
red, block
173(2)
Mo KR, 0.71073 Å
triclinic
C26H37BKMnN4O8 × C7H8
C28H37BKMnN6O8
690.49
orange, plate
173(2)
Mo KR, 0.71073 Å
monoclinic
P21/n
13.0269(7)
16.1183(9)
15.9486(10)
90
730.58
color, shape
temp (K)
radiation
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
orange, needle
173(2)
Mo KR, 0.71073 Å
triclinic
P1h
P1h
10.8194(7)
11.6661(7)
13.3634(9)
115.469(5)
91.690(5)
106.515(5)
1437.38(16)
2
10.3349(7)
10.4943(7)
18.0340(12)
82.379(6)
76.520(5)
76.384(5)
1842.3(2)
2
96.974(5)
90
3324.0(3)
4
Z
D
calcd (g cm-3
)
1.355
1.317
1.380
F(000)
616
0.650
768
0.524
1440
0.578
µ (mm-1
)
cryst size (mm3)
no. of rflns collected
no. of indep rflns (Rint
0.50 × 0.40 × 0.20
0.54 × 0.10 × 0.09
0.27 × 0.24 × 0.12
24 723
27 445
30 917
)
5369 (0.0460)
5369/0/335
1.038
7482 (0.0537)
7482/31/433
1.018
6242 (0.0809)
6242/0/407
1.014
no. of data/restraints/params
GOOF on F2
R1, wR2 (I > 2σ(I))
0.0267, 0.0674
0.0296, 0.0689
0.257, -0.292
0.0470, 0.1202
0.0608, 0.1274
1.146, -0.543
0.0407, 0.0956
0.0620, 0.1021
0.780, -0.362
R1, wR2 (all data)
largest diff peak and hole (e Å-3
)
at ν˜(CO) ) 1891 cm-1/1817 cm-1, 1890 cm-1/1813 cm-1
,
pyrazole complex 8 is characterized by ν˜(CO) values of 1913
and 1837 cm-1
and 1902 cm-1/1824 cm-1, respectively (KBr pellets). These
values are considerably lower than those measured for the
neutral complex dicarbonyl[η5-(8-quinolyl)cyclopentadienyl]-
manganese(I) (ν˜(CO) ) 1928 cm-1/1864 cm-1; toluene solu-
tion)37 but agree well with the CO stretching frequencies
reported for several (C5H4R)Mn(CO)2 complexes featuring
chelating (pyrazol-1-yl)methyl sidearms R.38-42 The neutral
.
In the electronic spectrum, cymantrene has a well-defined
ultraviolet transition maximizing near 330 nm (ꢀ ) 1100
L‚mol-1‚cm-1).43 The corresponding absorption maximum of
the tris(pyrazol-1-yl)borate 3 is also observed at λmax ) 330
nm (ꢀ ) 1110 L‚mol-1‚cm-1). The UV/vis spectrum of the
complex 6 is characterized by two bands in the UV region (λmax
) 280 nm (ꢀ ) 2990 L‚mol-1‚cm-1), 312 nm (ꢀ ) 2770
L‚mol-1‚cm-1)) and an additional extremely broad absorption
with an onset at about 550 nm (ꢀ(400 nm) ) 390 L‚mol-1‚cm-1).
(34) Scheibitz, M.; Winter, R. F.; Bolte, M.; Lerner, H.-W.; Wagner,
M. Angew. Chem., Int. Ed. 2003, 42, 924-927.
(35) Scheibitz, M.; Bolte, M.; Bats, J. W.; Lerner, H.-W.; Nowik, I.;
Herber, R. H.; Krapp, A.; Lein, M.; Holthausen, M. C.; Wagner, M. Chem.-
Eur. J. 2005, 11, 584-603.
(36) Scheibitz, M.; Heilmann, J. B.; Winter, R. F.; Bolte, M.; Bats, J.
W.; Wagner, M. Dalton Trans. 2005, 159-170.
(37) Enders, M.; Kohl, G.; Pritzkow, H. J. Organomet. Chem. 2001, 622,
66-73.
(38) Ro¨der, J. C.; Meyer, F.; Kaifer, E. Angew. Chem., Int. Ed. 2002,
41, 2304-2306.
(39) Ro¨der, J. C.; Meyer, F.; Winter, R. F.; Kaifer, E. J. Organomet.
Chem. 2002, 641, 113-120.
(40) Ro¨der, J. C.; Meyer, F.; Hyla-Kryspin, I.; Winter, R. F.; Kaifer, E.
Chem.-Eur. J. 2003, 9, 2636-2648.
(41) Sheng, T.; Dechert, S.; Hyla-Kryspin, I.; Winter, R. F.; Meyer, F.
Inorg. Chem. 2005, 44, 3863-3874.
(42) Sheng, T.; Dechert, S.; Stu¨ckl, A. C.; Meyer, F. Eur. J. Inorg. Chem.
2005, 1293-1302.

Mn(CO)2 Complexes of Hybrid Ligands
Organometallics, Vol. 26, No. 18, 2007 4667
Table 2. Selected Crystallographic Data for (7OBu2)2 and 8
(7OBu2)2
8
formula
fw
C34H37BLiMnO4
582.33
light yellow, plate
173(2)
Mo KR, 0.71073 Å
triclinic
C10H9MnN2O2
244.13
orange, block
173(2)
Mo KR, 0.71073 Å
monoclinic
P21/n
7.8006(10)
9.3963(8)
14.4520(18)
90
color, shape
temp (K)
radiation
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
P1h
10.8317(13)
13.0141(16)
13.2055(15)
109.377(9)
114.001(9)
96.173(8)
1539.4(3)
2
90.860(10)
90
1059.2(2)
4
Z
D
calcd (g cm-3
)
1.256
1.531
F(000)
612
0.464
496
1.225
µ (mm-1
)
cryst size (mm3)
no. of rflns collected
no. of indep rflns (Rint
no. of data/restraints/
params
0.28 × 0.14 × 0.04
0.23 × 0.22 × 0.18
Figure 2. Structure of CymBBr2 in the crystal. Thermal ellipsoids
are drawn at the 50% probability level. Selected bond lengths (Å)
and angles (deg): B(1)-Br(1) ) 1.940(10), B(1)-Br(2) ) 1.935-
(8), B(1)-C(11) ) 1.510(12), C(11)-C(12) ) 1.428(11), C(12)-
C(13) ) 1.422(12), C(13)-C(14) ) 1.441(13), C(14)-C(15) )
1.410(13), C(11)-C(15) ) 1.451(10); Br(1)-B(1)-Br(2) ) 116.4-
(5), C(11)-B(1)-Br(1) ) 122.1(5), C(11)-B(1)-Br(2) ) 121.5-
(6), R* ) 11.4.
14 175
13 952
)
5734 (0.0861)
5734/0/370
1979 (0.0930)
1979/0/136
GOOF on F2
0.955
1.142
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
largest diff peak and
0.0662, 0.1489
0.1179, 0.1700
0.856, -0.524
0.0425, 0.0934
0.0499, 0.0964
0.377, -0.491
hole (e Å-3
)
coordinated in a trigonal-planar fashion. (ii) Each BBr2 group
is bent out of the plane of its cyclopentadienyl ring toward the
Mn(I) center by a dip angle R* of 11.4° in CymBBr2 and 12.3°
in CymMeBBr2 (R* ) 180° - R; R is the angle between the
geometric center of the carbon atoms constituting the substituted
cyclopentadienyl ring, the ipso carbon atom, and the boron
atom). (iii) There is a characteristic C-C bond length alternation
within the cyclopentadienyl rings, giving the Br2B-C5H4
moieties some borafulvene character. This effect manifests itself
in higher reliability in the case of CymMeBBr2, for which the
bond lengths have been determined with lower error margins.44
Similar structural peculiarities as in the cymantrenyl(dibromo)-
boranes are evident in the cation [(Ph2C-C5H4)Mn(CO)3]+,
which bears an exo methylene group instead of the BBr2
substituent and has been described as a η5-diphenylfulvene
complex (dip angle: 6.6°).45 In spite of these remarkable
similarities of the molecular frameworks, there appear to be
important differences in the electronic structures of [(Ph2C-
C5H4)Mn(CO)3]+ and the cymantrenylboranes. For example, the
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salt of [(Ph2C-
C5H4)Mn(CO)3]+ is a deep blue compound, whereas CymBBr2
and CymMeBBr2 are yellow colored.
It is known that the low-energy region of the electronic
absorption spectra of pyridine complexes (C5H5)Mn(CO)2py is
dominated by a Mn(I) f π*-pyridine CT absorption.43 We
therefore tentatively assign the band at λmax ≈ 400 nm in the
UV/vis spectrum of 6 to a Mn(I) f π*-pyrazolyl CT transition.
Electrochemical Investigation. The formal electrode poten-
tials E1/2 (vs FcH/FcH+) for the Mn(I)/Mn(II) redox transitions
of 4(18-c-6), 5(18-c-6), and 6(18-c-6) are -0.82, -0.72, and
-0.63 V, respectively (THF solutions, [NBu4][PF6] (0.1 mol‚L-1)
as supporting electrolyte; for electrochemical data of related
complexes see refs 38-42). These redox transitions are chemi-
cally reversible, as evidenced by the following criteria: the
current ratios ipc/ipa are constantly equal to 1, the current
functions ipa/V1/2 remain constant, and the peak-to-peak separa-
tions ∆E are very close to the value found for the internal
ferrocene standard (∆E ) 109 mV for 4(18-c-6), 104 mV for
5(18-c-6), 99 mV for 6(18-c-6); V ) 0.1 V s-1). We note a
pronounced influence of the substituents at boron on the redox
potentials of our compounds. Replacement of one methyl group
by an electronegative pyrazolyl ring leads to an anodic shift of
about 0.1 V.
The potassium bis(pyrazol-1-yl)borate 2 crystallizes together
with 1 equivalent of THF in the form of C2-symmetric dimers
with bridging scorpionate ligands ((2THF)2; Figure 3). Each of
these two ligands binds to one potassium cation via two
pyrazolyl rings and to the other via one pyrazolyl ring: The
N(31)-pyrazolyl substituent acts as a σ donor toward K(1)
(K(1)-N(32) ) 2.826(2) Å). The N(41)-pyrazolyl ring binds
to K(1) in an η5 manner (K(1)‚‚‚COG(pz) ) 3.121 Å) and to
K(1#) via the nitrogen lone pair (K(1#)-N(42) ) 2.805(2) Å).
The coordination sphere of each K+ ion is completed by one
THF molecule and two carbonyl oxygen atoms (intradimer
contact: K(1)-O(3#) ) 3.133(3) Å; interdimer contact: K(1)-
O(2*) ) 2.925(2) Å).
X-ray Crystal Structure Determination. Crystal data and
structure refinement details for CymBBr2 and (2THF)2-8 are
compiled in Tables 1 and 2.
Even though cymantrenyl(dihalo)boranes were first prepared
more than 30 years ago,28 their crystal structures remained
unknown until very recently. This is mainly due to the fact that
they are normally isolated as oily products. In 2006, Braun-
schweig et al. determined the solid-state structure of (methyl-
cymantrenyl)(dibromo)borane (CymMeBBr2).44 Our group now
succeeded in growing single crystals of the parent compound
CymBBr2 from hexane (Figure 2; Cym ) cymantrenyl). As to
be expected, the molecules of CymMeBBr2 and CymBBr2
possess very similar structures in the solid state. The most
important features are the following: (i) Each boron atom is
Single crystals of the potassium tris(pyrazol-1-yl)borate 3
were grown from THF/pentane (1:1). Similar to the potassium
(43) Giordano, P. J.; Wrighton, M. S. Inorg. Chem. 1977, 16, 160-166.
(44) Braunschweig, H.; Kraft, M.; Schwarz, S.; Seeler, F.; Stellwag, S.
Inorg. Chem. 2006, 45, 5275-5277.
(45) Volland, M. A. O.; Kudis, S.; Helmchen, G.; Hyla-Kryspin, I.;
Rominger, F.; Gleiter, R. Organometallics 2001, 20, 227-230.

4668 Organometallics, Vol. 26, No. 18, 2007
Kunz et al.
Figure 3. Structure of (2THF)2 in the crystal. Hydrogen atoms
are omitted for clarity; thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths (Å), atom‚‚‚atom distances
(Å), angles (deg), and torsion angles (deg): B(1)-C(4) ) 1.618-
(3), B(1)-C(11) ) 1.625(4), B(1)-N(31) ) 1.580(3), B(1)-N(41)
) 1.577(3), K(1)-N(32) ) 2.826(2), K(1)-N(42) ) 3.166(2),
K(1#)-N(42) ) 2.805(2), K(1)-O(3#) ) 3.133(3), K(1)-O(2*)
) 2.925(2), K(1)‚‚‚COG(pz) ) 3.121, K(1)‚‚‚K(1#) ) 4.460(1);
N(31)-B(1)-N(41) ) 104.9(2); B(1)-N(31)-N(32)-K(1) )
-8.8(3), B(1)-N(41)-N(42)-K(1#) ) 21.6(4). COG(pz): center
of gravity of the N(41)-pyrazolyl ring. Symmetry transformations
used to generate equivalent atoms: -x+1, y, -z+3/2 (#), x-1, y,
z (*).
Figure 4. Structure of (3THF)2 in the crystal. Hydrogen atoms
are omitted for clarity; thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths (Å), atom‚‚‚atom distances
(Å), angles (deg), and torsion angles (deg): B(1)-C(11) ) 1.623-
(3), B(1)-N(21) ) 1.554(3), B(1)-N(31) ) 1.553(3), B(1)-N(41)
) 1.567(3), K(1)-N(22#) ) 2.912(2), K(1)-N(32) ) 2.924(2),
K(1)-N(42) ) 3.186(2), K(1)-N(42#) ) 2.738(2), K(1)-O(3#)
) 3.009(2), K(1)-O(1*) ) 2.969(2), K(1)‚‚‚COG(pz) ) 3.069,
K(1)‚‚‚K(1#) ) 4.749; N(21)-B(1)-N(31) ) 106.6(2), N(21)-
B(1)-N(41) ) 113.1(2), N(31)-B(1)-N(41) ) 105.7(2); B(1)-
N(21)-N(22)-K(1#) ) 70.8(2), B(1)-N(31)-N(32)-K(1) )
12.6(3), B(1)-N(41)-N(42)-K(1) ) -105.9(2), B(1)-N(41)-
N(42)-K(1#) ) -7.1(4). COG(pz): center of gravity of the N(41)-
pyrazolyl ring. Symmetry transformations used to generate equiva-
lent atoms: -x+1, -y+1, -z+2 (#), x, y-1, z (*).
bis(pyrazol-1-yl)borate 2, the crystal lattice of 3 consists of
dimeric units ((3THF)2; Figure 4). However, in contrast to
(2THF)2, the two halves of each dimer of (3THF)2 are related
by an inversion center rather than by a 2-fold rotation axis.
Irrespective of that, the main structural motifs of both com-
pounds are largely the same ((3THF)2: K(1)-N(32) ) 2.924-
(2) Å, K(1)‚‚‚COG(pz) ) 3.069 Å, K(1#)-N(42) ) 2.738(2)
Å; intradimer contact K(1)-O(3#) ) 3.009(2) Å; interdimer
contact K(1)-O(1*) ) 2.969(2) Å). The additional N(21)-
pyrazolyl ring of 3 coordinates K(1#) at a bond length
K(1#)-N(22) of 2.912(2) Å with a torsion angle B(1)-N(21)-
N(22)-K(1#) of 70.8(2)°. This indicates the K+ ion to interact
not only with the lone pair of N(22) but also with its p orbital.
Interestingly, the structure of (3THF)2 closely resembles the
structure of the dimeric ferrocenyl scorpionate {[K(THF)][FcB-
(Me)pz2]}2.20 Here, a methyl group replaces the cymantrenyl
substituent, while the C5H4 ring of the ferrocenyl fragment takes
the place of the N(21)-pyrazolyl ring and acts as a π donor
toward K(1#). π-Coordination of ferrocene to main-group metal
ions is not an uncommon phenomenon.21,29,30,46-52 We thus find
it interesting to see that in (2THF)2 and (3THF)2 the cyclopen-
tadienyl rings do not engage in this kind of behavior, which
may be attributed to the facts that the Mn(CO)3 fragment is
electron-withdrawing and provides three Lewis basic carbonyl
oxygen atoms as alternative donor sites.
B(1)-N(11)-N(12) ) 120.9(1)°, and N(11)-N(12)-Mn(1) )
120.0(1)° of the mono(pyrazol-1-yl)borate side arm are close
to the ideal values of 109° for an sp3-hybridized B atom and
120° for an sp2-hybridized N atom (torsion angle C(21)-B(1)-
N(11)-N(12) ) 1.8(2)°). Moreover, the B-C5H4 bond pos-
sesses the same length as in the open-chain species (4(18-c-6):
1.626(2) Å, (3THF)2: 1.623(3) Å), and the Mn-pz bond length
of 2.026(1) Å in 4(18-c-6) is identical to the corresponding value
in the pyrazole complex CpMn(CO)2pzH (8: Mn(1)-N(11) )
2.024(2) Å; cf. also dicarbonyl[η5-(8-quinolyl)cyclopentadienyl]-
manganese(I): Mn-N ) 2.014(1) Å;37 the Mn-N bonds of
several related complexes (C5H4R)Mn(CO)2 with chelating
(pyrazol-1-yl)methyl side arms R lie in the range of Mn-N )
2.006(2)-2.066(3) Å38-40,42). The B-pz bond is elongated by
0.048 Å in 4(18-c-6) (1.606(2) Å) with respect to (3THF)2 (mean
value: 1.558(3) Å). It is revealing to compare the average
Mn-C and C-O bond lengths of the Mn(I) carbonyl fragments
in CymBBr2, (3THF)2, and 4(18-c-6) (Mn-C: 1.820(8), 1.796-
(3), and 1.769(2) Å; C-O: 1.142(9), 1.159(4), and 1.175(2)
Å). Along this series, we find a continuous decrease of the
Mn-C bond lengths accompanied by an increase of the C-O
bond lengths. This trend is in accord with an increasing degree
of MnfCO π back-bonding upon going from a derivative
bearing a BBr2 π-acceptor substituent at the cyclopentadienyl
Single crystals of complex 4(18-c-6) were grown from toluene
after the addition of excess 18-crown-6 (Figure 5). The three
relevant internal bond angles C(21)-B(1)-N(11) ) 103.2(1)°,
(46) Scholz, S.; Green, J. C.; Lerner, H.-W.; Bolte, M.; Wagner, M.
Chem. Commun. 2002, 36-37.
(47) Honeyman, G. W.; Kennedy, A. R.; Mulvey, R. E.; Sherrington,
D. C. Organometallics 2004, 23, 1197-1199.
(48) Jones, J. N.; Moore, J. A.; Cowley, A. H.; Macdonald, C. L. B.
Dalton Trans. 2005, 3846-3851.
(51) Sarazin, Y.; Kaltsoyannis, N.; Wright, J. A.; Bochmann, M.
Organometallics 2007, 26, 1811-1815.
(52) Morris, J. J.; Noll, B. C.; Honeyman, G. W.; O’Hara, C. T.;
Kennedy, A. R.; Mulvey, R. E.; Henderson, K. W. Chem.-Eur. J. 2007,
13, 4418-4432.
(49) Sa¨nger, I.; Heilmann, J. B.; Bolte, M.; Lerner, H.-W.; Wagner, M.
Chem. Commun. 2006, 2027-2029.
(50) Sarazin, Y.; Hughes, D. L.; Kaltsoyannis, N.; Wright, J. A.;
Bochmann, M. J. Am. Chem. Soc. 2007, 129, 881-894.

Mn(CO)2 Complexes of Hybrid Ligands
Organometallics, Vol. 26, No. 18, 2007 4669
Figure 5. Structure of 4(18-c-6) in the crystal. Hydrogen atoms
and [K(18-crown-6)]+ ion are omitted for clarity; thermal ellip-
soids are drawn at the 50% probability level. Selected bond lengths
(Å), angles (deg), torsion angles (deg), and dihedral angles (deg):
B(1)-C(3) ) 1.636(2), B(1)-C(4) ) 1.630(2), B(1)-C(21) )
1.626(2), B(1)-N(11) ) 1.606(2), Mn(1)-N(12) ) 2.026(1),
K(1)-O(1) ) 2.684(1); C(21)-B(1)-N(11) ) 103.2(1), B(1)-
N(11)-N(12) ) 120.9(1), N(11)-N(12)-Mn(1) ) 120.0(1), COG-
(Cp)-C(21)-B(1) ) 170.1; C(21)-B(1)-N(11)-N(12) ) 1.8(2);
C5H5//C3H3N2 ) 83.1. COG(Cp): center of gravity of the cyclo-
pentadienyl ring.
Figure 7. Structure of 6(18-c-6) in the crystal. Hydrogen atoms
and [K(18-crown-6)]+ ion are omitted for clarity. Thermal ellipsoids
are drawn at the 50% probability level. Selected bond lengths (Å),
angles (deg), torsion angles, and dihedral angles (deg): B(1)-C(21)
) 1.614(3), B(1)-N(11) ) 1.569(3), B(1)-N(31) ) 1.564(3),
B(1)-N(41) ) 1.532(3), Mn(1)-N(12) ) 2.017(2), K(1)-N(32)
) 2.872(2); C(21)-B(1)-N(11) ) 106.0(2), B(1)-N(11)-N(12)
) 118.2(2), N(11)-N(12)-Mn(1) ) 120.1(1), COG(Cp)-C(21)-
B(1) ) 167.7; C(21)-B(1)-N(11)-N(12) ) 15.1(3); C5H5//
C3H3N2 ) 83.3. COG(Cp): center of gravity of the cyclopentadienyl
ring.
1.569(3) Å) and that the torsion angles C(21)-B(1)-N(11)-
N(12) are slightly larger (5(18-c-6): -21.7(3)°, 6(18-c-6): 15.1-
(3)°) in the bis- and tris(pyrazol-1-yl)borate derivatives. A
concluding glimpse at the crystal lattices reveals a bond between
the [K(18-crown-6)]+ cation and the carbonyl oxygen atom O(1)
in the case of 4(18-c-6) (2.684(1) Å), polymer chains with short
K(1)-O(1) ) 2.960(2) Å and K(1#)-N(32) ) 2.919(2) Å
contacts in 5(18-c-6), and a K+-pyrazolyl bond in 6(18-c-6)
(K(1)-N(32) ) 2.872(2) Å).
The lithium cymantrenyltris(phenyl)borate 7 crystallizes as
a dibutyl ether adduct and forms centrosymmetric dimers in
the solid state ((7OBu2)2; Figure 8). In contrast to (2THF)2 and
(3THF)2, the dimers of (7OBu2)2 are held together not by
bridging (pyrazol-1-yl)borate ligands but by bridging cyman-
trenyl fragments. Thus, two of the three carbonyl ligands of
each cymantrenyl substituent take part in Li+ coordination
(Li(1)-O(1) ) 1.976(9) Å, Li(1#)-O(2) ) 2.045(8) Å). In
addition to two carbonyl oxygen atoms, each Li+ ion binds one
dibutyl ether ligand and coordinates to the π face of one phenyl
substituent (the other two phenyl rings of each borate moiety
remain uncomplexed). The Li+ ion is significantly shifted away
from a position above the center of gravity of the six-mem-
bered ring toward the carbon atom C(43) (Li(1)-C(43) ) 2.482-
(10) Å).
Figure 6. Structure of 5(18-c-6) in the crystal. Hydrogen atoms
and [K(18-crown-6)]+ ion are omitted for clarity; thermal ellipsoids
are drawn at the 50% probability level. Selected bond lengths (Å),
angles (deg), torsion angles, and dihedral angles (deg): B(1)-C(3)
) 1.602(4), B(1)-C(21) ) 1.616(4), B(1)-N(11) ) 1.583(3), Mn-
(1)-N(12) ) 2.030(2), K(1)-O(1) ) 2.960(2), K(1#)-N(32) )
2.919(2); C(21)-B(1)-N(11) ) 103.1(2), B(1)-N(11)-N(12) )
119.6(2), N(11)-N(12)-Mn(1) ) 118.8(2), COG(Cp)-C(21)-
B(1) ) 168.4; C(21)-B(1)-N(11)-N(12) ) -21.7(3); C5H5//
C3H3N2 ) 74.0. COG(Cp): center of gravity of the cyclopentadienyl
ring. Symmetry transformation used to generate equivalent atoms:
x+1, y-1, z (#).
The molecular structure of 8 (Figure 9) was determined in
order to be able to compare the Mn-N bond lengths in the
complexes 4(18-c-6)-6(18-c-6) with the corresponding value
in a related unstrained system. Our results show that the
Mn(1)-N(11) distance of 2.024(2) Å in 8 is the same as in the
other three molecules even though the dihedral angle between
the planes of the cyclopentadienyl ring and the pyrazolyl ligand
is 30.2° in 8, but 83.1° in 4(18-c-6), 74.0° in 5(18-c-6), and
83.3° in 6(18-c-6).
ring to a species in which one of three electron-withdrawing
CO ligands has been replaced by a strong σ donor.
The structural parameters of the core frameworks of 5(18-
c-6) and 6(18-c-6) (Figures 6, 7) do not deviate significantly
from those of 4(18-c-6), except for the fact that the B(1)-N(11)
bonds are somewhat shorter (5(18-c-6): 1.583(3) Å, 6(18-c-6):

4670 Organometallics, Vol. 26, No. 18, 2007
Kunz et al.
6(18-c-6) clearly reveal the respective anionic moieties to be
largely unstrained and, consequently, that the cyclopentadienyl/
mono(pyrazol-1-yl)borate chelate ligand is well designed to meet
the coordination requirements of a [Mn(CO)2]+ complex frag-
ment. This interpretation is further supported by the 1H and 13
C
NMR spectra of 4-6 (d8-THF), which do not give an indication
either for dissociation of the chelating pyrazolyl tether or for
the formation of a solvent-stabilized open form. In contrast to
comparable constrained-geometry species like half-sandwich
amido, imido, or alkoxy complexes, the pyrazolyl sidearm is
merely a σ donor with less ability to provide additional
π-electron density to the metal ion.
The cyclopentadienyl/scorpionate hybrid system opens up
interesting perspectives for further development: (i) The steric
and/or electronic properties of the ligand scaffold can be
modified at will using well-established poly(pyrazol-1-yl)borate
synthesis protocols. (ii) (Hetero)bimetallic complexes can be
prepared by using the remaining two pyrazolyl substituents of
K[(OC)2Mn(C5H4-B(µ-pz)pz2)] (6) for the chelation of a second
metal ion.
Figure 8. Structure of (7OBu2)2 in the crystal. Hydrogen atoms
are omittied for clarity; thermal ellipsoids are drawn at the 30%
probability level. Selected bond lengths (Å), atom‚‚‚atom distances
(Å), and angles (deg): B(1)-C(11) ) 1.659(6), B(1)-C(21) )
1.658(6), B(1)-C(31) ) 1.648(6), B(1)-C(41) ) 1.650(7), Li-
(1)-C(42) ) 2.578(11), Li(1)-C(43) ) 2.482(10), Li(1)-C(44)
) 2.732(9), Li(1)-COG(Ph) ) 2.450, Li(1)-O(1) ) 1.976(9), Li-
(1)-O(2#) ) 2.045(8), Li(1)‚‚‚Li(1#) ) 7.029; C(21)-B(1)-C(31)
) 109.9(4), C(21)-B(1)-C(41) ) 107.0(3), C(31)-B(1)-C(41)
) 110.9(3). COG(Ph): center of gravity of the C(41)-phenyl ring.
Symmetry transformation used to generate equivalent atoms:
-x+1, -y+1, -z+1 (#).
Moreover, we are currently trying to broaden the scope of
our hybrid ligand system by preparing complexes of metal ions
other than Mn(I).
Experimental Section
General Remarks. All reactions were carried out under a
nitrogen atmosphere using Schlenk tube techniques. Solvents were
freshly distilled under argon from Na/benzophenone (toluene, C6D6,
THF, d8-THF) and Na/Pb alloy (pentane, hexane) prior to use.
NMR: Bruker AM 250, Avance 250, Avance 300, and Avance
400. Chemical shifts are referenced to residual solvent signals (1H,
13C{1H}) or external BF3‚Et2O (11B{1H}). Abbreviations: s )
singlet, d ) doublet, vtr ) virtual triplet, mult ) multiplet, n.r. )
multiplet expected in the 1H NMR spectrum but not resolved, n.o.
) signal not observed, br ) broad. Bridging pyrazolyl substituents
are denoted with an asterisk (pz*). The compounds CymBBr2,
CymBMe2, CymB(NMe2)2,28 and H[CymBpz3]23 were synthesized
according to published procedures.
Synthesis of CymB(NMe2)Br. To a solution of CymB(NMe2)2
(0.98 g, 3.25 mmol) in toluene (15 mL) was added dropwise with
stirring at rt a solution of CymBBr2 (1.21 g, 3.25 mmol) in toluene
(15 mL). The reaction mixture was stirred overnight at rt, and the
solvent was removed in Vacuo. CymB(NMe2)Br was obtained in
the form of yellow crystals. Yield: 2.05 g (93%). IR (toluene,
cm-1): ν˜(CO) 2022 (s), 1935 (s). 11B{1H} NMR (96.3 MHz,
1
C6D6): δ 33.5 (h1/2 ) 160 Hz). H NMR (300.0 MHz, C6D6): δ
2.31, 2.59 (2 × s, 2 × 3H, NMe2), 4.11, 4.69 (2 × vtr, 2 × 2H,
4
3JHH ) JHH ) 1.9 Hz, C5H4). 13C{1H} NMR (75.4 MHz, C6D6):
δ 40.3, 43.3 (NMe2), 84.7, 93.0 (C5H4), 224.9 (CO), n.o. (CB).
Synthesis of CymB(NMe2)Me. To a solution of CymB(NMe2)-
Br (8.78 g, 26.00 mmol) in toluene (70 mL) was added dropwise
with stirring at -78 °C a solution of MeMgCl in THF (8.67 mL,
26.00 mmol, 3 mol/L). The reaction mixture was slowly warmed
to rt and stirred overnight. After a colorless precipitate had been
removed by filtration, the clear filtrate was evaporated in Vacuo.
The resulting yellow oil was stirred overnight with hexane (50 mL).
Subsequently, insoluble material was removed by filtration. All
volatiles were removed from the filtrate in Vacuo to give CymB-
(NMe2)Me as a yellow oil. Yield: 4.72 g (67%). IR (toluene, cm-1):
ν˜(CO) 2017 (s), 1921 (s). 11B{1H} NMR (96.3 MHz, C6D6): δ
39.8 (h1/2 ) 131 Hz). 1H NMR (300.0 MHz, C6D6): δ 0.44 (s, 3H,
CH3), 2.38, 2.44 (2 × s, 2 × 3H, NMe2), 4.17, 4.43 (2 × vtr, 2 ×
Figure 9. Structure of 8 in the crystal. Thermal ellipsoids are drawn
at the 50% probability level. Selected bond lengths (Å), angles
(deg), and dihedral angles (deg): Mn(1)-N(11) ) 2.024(2), Mn-
(1)-C(1) ) 1.763(3), Mn(1)-C(2) ) 1.781(3), C(1)-O(1) )
1.169(4), C(2)-O(2) ) 1.174(4); C(1)-Mn(1)-C(2) ) 88.2(1),
C(1)-Mn(1)-N(11) ) 93.8(1), C(2)-Mn(1)-N(11) ) 96.7(1);
C5H5//C3H4N2 ) 30.2.
Conclusion
The constrained-geometry complexes K[(OC)2Mn(C5H4-B(µ-
pz)(R)R′)] (4-6) are readily accessible by photolytic decarbo-
nylation of cymantrenyl-substituted mono-, bis-, and tris(pyrazol-
1-yl)borates K[(OC)3Mn(C5H4-B(pz)(R)R′)] (1: R ) R′ ) Me;
2: R ) Me, R′ ) pz; 3: R ) R′ ) pz; pz ) pyrazol-1-yl).
X-ray crystal structure analyses of 4(18-c-6), 5(18-c-6), and
3
4
2H, JHH ) JHH ) 2.0 Hz, C5H4). 13C{1H} NMR (62.9 MHz,
C6D6): δ 4.4 (br, CH3), 40.4, 40.7 (NMe2), 84.2, 90.8 (C5H4), 225.9
(CO), n.o. (CB).

Mn(CO)2 Complexes of Hybrid Ligands
Organometallics, Vol. 26, No. 18, 2007 4671
Synthesis of 1. A suspension of Kpz (0.25 g, 2.36 mmol) in
THF (15 mL) was added dropwise with stirring at -78 °C to a
solution of CymBMe2 (0.58 g, 2.38 mmol) in toluene (40 mL).
The reaction mixture was slowly warmed to rt and stirred overnight.
After a small amount of colorless precipitate had been removed by
filtration, the clear filtrate was evaporated to dryness in Vacuo. The
resulting brown oil was stirred with pentane (15 mL) overnight,
whereupon it solidified. After filtration, the insoluble residue was
dried in Vacuo to give a solid foam. Yield of 1: 0.80 g (97%). IR
(KBr, cm-1): ν˜(CO) 2004 (s), 1910 (s). 11B{1H} NMR (96.3 MHz,
d8-THF): δ -8.7 (h1/2 ) 100 Hz). 1H NMR (300.0 MHz,
d8-THF): δ 0.00 (s, 6H, CH3), 4.45, 4.46 (2 × n.r., 2 × 2H, C5H4),
5.94 (n.r., 1H, pzH-4), 7.24, 7.46 (2 × n.r., 2 × 1H, pzH-3,5).
13C{1H} NMR (75.4 MHz, d8-THF): δ 14.0 (CH3), 81.7, 89.4
(C5H4), 102.6 (pzC-4), 132.5, 137.0 (pzC-3,5), 229.2 (CO), n.o.
(CB). Anal. Calcd for C13H13BKMnN2O3 (350.10): C, 44.60; H,
3.74; N, 8.00. Found: C, 43.79; H, 4.11; N, 7.29.
1H NMR (250.1 MHz, d8-THF): δ -0.17 (s, 6H, CH3), 3.53 (vtr,
2H, 3JHH ) 4JHH ) 1.7 Hz, C5H4), 3.61 (s, 24H, 18-c-6), 4.93 (vtr,
3
4
3
2H, JHH ) JHH ) 1.7 Hz, C5H4), 5.72 (vtr, 1H, JHH ) 2.0 Hz,
3
pz*H-4), 6.78, 6.94 (n.r., d, JHH ) 2.0 Hz, 2 × 1H, pz*H-3,5).
13C{1H} NMR (100.6 MHz, d8-THF): δ 71.2 (18-c-6), 78.1,
84.1 (C5H4), 104.1 (pz*C-4), 131.4, 142.6 (pz*C-3,5), n.o. (CB,
CO). Anal. Calcd for C12H13BKMnN2O2 (322.09) × C12H24O6
(264.32): C, 49.16; H, 6.36; N, 4.78. Found: C, 48.99; H, 6.40;
N, 4.70.
Synthesis of 5. A solution of 2‚THF (0.26 g, 0.55 mmol) in
THF (15 mL) was placed in a borosilicate glass vessel and irradiated
with a high-pressure mercury lamp (λmax ) 510 nm). After 6 h,
the transformation of 2 to 5 was quantitative (NMR spectroscopical
control). All volatiles were removed in Vacuo, and the remaining
orange residue was washed with pentane (20 mL), isolated by
filtration, and dried in Vacuo. Orange X-ray quality crystals of
5(18-c-6) formed at rt from a solution of 5 in toluene to which
excess 18-crown-6 had been added. IR (KBr, cm-1): ν˜(CO) 1890
(s), 1813 (s). 11B{1H} NMR (128.4 MHz, d8-THF): δ -2.0 (h1/2
) 100 Hz). 1H NMR (400.1 MHz, d8-THF): δ 0.32 (s, 3H, CH3),
3.65 (s, 24H, 18-c-6), 3.45, 3.65, 4.71, 4.97 (4 × n.r., 4 × 1H,
C5H4), 5.84, 5.89 (2 × n.r., 2 × 1H, pz*H-4, pzH-4), 6.95, 6.98,
7.23, 7.31 (4 × n.r., 4 × 1H, pz*H-3,5, pzH-3,5). 13C{1H} NMR
(100.6 MHz, d8-THF): δ 70.9 (18-c-6), 77.4, 79.0, 83.9, 86.1
(C5H4), 101.9, 105.1 (pz*C-4, pzC-4), 131.5, 133.6, 137.9, 144.2
(pz*C-3,5, pzC-3,5), n.o. (2 × CB, CO). Anal. Calcd for
Synthesis of 2. A mixture of Hpz (1.18 g, 17.33 mmol) and
Kpz (1.84 g, 17.33 mmol) in THF (25 mL) was added dropwise
with stirring at -78 °C to a solution of CymB(NMe2)Me (4.72 g,
17.29 mmol) in toluene (50 mL). The reaction mixture was slowly
warmed to rt and stirred overnight. After a small amount of colorless
precipitate had been removed by filtration, the clear filtrate was
evaporated to dryness in Vacuo. The resulting orange oil was stirred
with pentane (25 mL) overnight, whereupon it solidified. The
colorless microcrystalline solid was collected on a frit and dried in
Vacuo. Yield of 2‚THF: 6.96 g (85%). The solid material contained
light yellow single crystals of (2THF)2, which were suitable for
X-ray crystallography. IR (KBr, cm-1): ν˜(CO) 2009 (s), 1920 (s).
C14H13BKMnN4O2 (374.13)
(92.14): C, 54.25; H, 6.21; N, 7.67. Found: C, 54.71; H, 6.24; N,
7.57.
×
C12H24O6 (264.32)
×
C7H8
1
11B{1H} NMR (128.4 MHz, d8-THF): δ -1.1 (h1/2 ) 92 Hz). H
Synthesis of 6. A solution of 3‚THF (0.11 g, 0.21 mmol) in
THF (15 mL) was placed in a borosilicate glass vessel and irradiated
with a high-pressure mercury lamp (λmax ) 510 nm). After 6 h,
the transformation of 3 to 6 was quantitative (NMR spectroscopical
control). All volatiles were removed in Vacuo, and the remaining
orange residue was washed with pentane (20 mL), isolated by
filtration, and dried in Vacuo. Orange X-ray quality crystals of
6(18-c-6) formed at rt from a solution of 6 in toluene/THF to which
excess 18-crown-6 had been added. IR (KBr, cm-1): ν˜(CO) 1902
NMR (400.1 MHz, d8-THF): δ 0.55 (s, 3H, CH3), 4.55, 4.77 (2 ×
3
4
3
vtr, 2 × 2H, JHH ) JHH ) 1.8 Hz, C5H4), 6.00 (vtr, 2H, JHH
)
3
1.8 Hz, pzH-4), 7.30, 7.54 (n.r., d, 2 × 2H, JHH ) 2.0 Hz,
pzH-3,5). 13C{1H} NMR (100.6 MHz, d8-THF): δ 81.6, 92.3
(C5H4), 103.2 (pzC-4), 133.1, 138.8 (pzC-3,5), n.o. (2 × CB, CO).
Anal. Calcd for C15H13BKMnN4O3 (402.14) × OC4H8 (72.11): C,
48.12; H, 4.46; N, 11.81. Found: C, 48.00; H, 4.57; N, 11.89.
Synthesis of 3. A suspension of KOtBu (0.26 g, 2.32 mmol) in
THF (20 mL) was added dropwise with stirring at 0 °C to a solution
of H[CymBpz3]23 (0.95 g, 2.28 mmol) in THF (10 mL). The reaction
mixture was slowly warmed to rt and stirred overnight and the
resulting yellow solution evaporated to dryness in Vacuo. The
remaining yellow oil was stirred with pentane (15 mL) overnight,
whereupon it solidified. The colorless microcrystalline solid was
collected on a frit and dried in Vacuo. Yield of 3‚THF: 0.93 g
(78%). Yellow single crystals of (3THF)2 formed upon storing a
solution of 3 in THF/pentane (1:1) at -35 °C. IR (KBr, cm-1):
(s), 1824 (s). UV/vis (THF, c ) 7 × 10-4 mol‚L-1, nm): λmax
)
280 (ꢀ ) 2990 L‚mol-1‚cm-1), 312 (ꢀ ) 2770 L‚mol-1‚cm-1),
∼400 (v br, onset at ∼550, ꢀ(400 nm) ) 390 L‚mol-1‚cm-1). 11B-
{1H} NMR (96.3 MHz, d8-THF): δ -0.1 (h1/2 ) 70 Hz). 1H NMR
(300.0 MHz, d8-THF): δ 3.57 (s, 24H, 18-c-6), 3.57, 5.04, (1 ×
3
4
n.r., 1 × vtr, 2 × 2H, JHH ) JHH ) 1.9 Hz, C5H4), 5.88 (mult,
1H, pz*H-4), 5.96 (mult, 2H, pzH-4), 7.01 (n.r., 1H, pz*H-3 or 5),
3
7.17, 7.36 (2 × mult, 2 × 2H, pzH-3,5), 7.64 (d, 1H, JHH ) 2.1
Hz, pz*H-5 or 3). 13C{1H} NMR (75.4 MHz, d8-THF): δ 71.4
(18-c-6), 79.0, 86.9 (C5H4), 103.0 (pzC-4), 106.0 (pz*C-4), 133.6
(pzC-3 or 5), 136.8 (pz*C-3 or 5), 139.7 (pzC-5 or 3), 145.9
(pz*C-5 or 3), n.o. (CB, CO). Anal. Calcd for C16H13BKMnN6O2
(426.16) × C12H24O6 (264.32): C, 48.71; H, 5.40; N, 12.17.
Found: C, 48.70; H, 5.47; N, 12.20.
ν˜(CO) 2006 (s), 1921 (s). UV/vis (THF, c ) 7 × 10-4 mol‚L-1
,
nm): λmax ) 330 (ꢀ ) 1110 L‚mol-1‚cm-1). 11B{1H} NMR (128.4
MHz, d8-THF): δ 0.1 (h1/2 ) 80 Hz). 1H NMR (400.1 MHz,
3
4
d8-THF): δ 4.67, 4.82 (2 × vtr, 2 × 2H, JHH ) JHH ) 1.7 Hz,
C5H4), 6.08 (vtr, 3H, 3JHH ) 1.8 Hz, pzH-4), 7.32, 7.39 (d, 3JHH
)
2.0 Hz, n.r., 2 × 3H, pzH-3,5). 13C{1H} NMR (100.6 MHz,
d8-THF): δ 82.9, 91.6 (C5H4), 104.0 (pzC-4), 135.1, 139.7 (pzC-
3,5), 227.2 (CO), n.o. (CB). Anal. Calcd for C17H13BKMnN6O3
(454.17) × OC4H8 (72.11): C, 47.93; H, 4.02; N, 15.97. Found:
C, 48.09; H, 4.05; N, 16.25.
Synthesis of 7. To a solution of CymBBr2 (2.60 g, 6.96 mmol)
in toluene (25 mL) was added dropwise with stirring at -78 °C
PhLi in Bu2O (10.50 mL, 21.00 mmol, 2 mol/L). The reaction
mixture was slowly warmed to rt and stirred overnight. The reaction
mixture was filtered, and the filtrate was evaporated to dryness in
Vacuo. The resulting brown oil was contaminated with substantial
amounts of Li[BPh4], which could not be removed completely. A
few single crystals of (7OBu2)2 formed upon storing a solution of
Li[CymBPh3] in toluene/hexane (1:1) at -35 °C. IR (KBr, cm-1):
ν˜(CO) 2000 (s), 1911 (s). 11B{1H} NMR (128.4 MHz, C6D6): δ
Synthesis of 4. A solution of 1 (0.06 g, 0.17 mmol) in THF (15
mL) was placed in a borosilicate glass vessel and irradiated with a
high-pressure mercury lamp (λmax ) 510 nm). After 6 h, the
transformation of 1 to 4 was quantitative (NMR spectroscopical
control). All volatiles were removed in Vacuo, and the remaining
red-brown residue was washed with pentane (20 mL), isolated by
filtration, and dried in Vacuo. Red X-ray quality crystals of 4(18-
c-6) formed at rt from a solution of 4 in toluene to which excess
18-crown-6 had been added. IR (KBr, cm-1): ν˜(CO) 1891 (s), 1817
(s). 11B{1H} NMR (128.4 MHz, d8-THF): δ -8.1 (h1/2 ) 75 Hz).
1
-9.5 (h1/2 ) 14 Hz). H NMR (400.1 MHz, C6D6): δ 4.44, 4.60
(2 × n.r., 2 × 2H, C5H4), 7.02 (vtr, 3H, 3JHH ) 6.7 Hz, p-Ph), 7.22
(vtr, 6H, 3JHH ) 6.6 Hz, m-Ph), 7.61 (d, 6H, 3JHH ) 5.4 Hz, o-Ph).
13C{1H} NMR (62.9 MHz, C6D6): δ 85.3, 90.3 (C5H4), 123.9,

4672 Organometallics, Vol. 26, No. 18, 2007
Kunz et al.
127.1, 136.0 (Ph), 230.5 (CO), n.o. (2 × CB). A decent elemental
analysis of 7 was not obtained due to contamination of the sample
with Li[BPh4].
Synthesis of 8. To a solution of CymH (3.45 g, 16.9 mmol) in
diethyl ether (200 mL) was added Hpz (1.15 g, 16.9 mmol). The
(2THF)2 are disordered over two positions (occupancy factors
0.56(2) and 0.44(2) in both cases). 5(18-c-6): The asymmetric
unit contains one toluene molecule, which is not disordered.
CCDC reference numbers: 644558 (CymBBr2), 644559 ((2THF)2),
644560 ((3THF)2), 644561 (4(18-c-6)), 644562 (5(18-c-6)), 644563
(6(18-c-6)), 644564 ((7OBu2)2), and 644565 (8).
reaction mixture was irradiated using a UV lamp (TQ 150, λmax
)
510 nm) for 50 h, whereupon the yellow solution turned orange.
The solvent was removed in Vacuo and the resulting orange oil
stored at -35 °C. After 3 weeks, a few orange single crystals of 8
had formed, which were suitable for X-ray crystallography. IR (KBr,
Acknowledgment. M.W. is grateful to the “Deutsche
Forschungsgemeinschaft” (DFG) and the “Fonds der Chemi-
schen Industrie” (FCI) for financial support.
1
cm-1): ν˜(CO) 1913 (s), 1837 (s). H NMR (250.1 MHz, Et2O/
C6D6): δ 4.22 (s, 5H, C5H5), 5.94 (br, 1H, pzH-4), 7.29 (br, 2H,
pzH-3,5), 11.46 (br, 1H, NH).
Supporting Information Available: Crystallographic data of
CymBBr2, (2THF)2, (3THF)2, 4(18-c-6), 5(18-c-6), 6(18-c-6),
(7OBu2)2, and 8 in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
X-ray Crystal Structure Analysis of CymBBr2, (2THF)2,
(3THF)2, 4(18-c-6), 5(18-c-6), 6(18-c-6), (7OBu2)2, and 8. All
single crystals were analyzed with a STOE IPDS II two-circle
diffractometer with graphite-monochromated Mo KR radia-
tion. Empirical absorption corrections were performed using the
MULABS53 option in PLATON.54 The structures were solved by
direct methods using the program SHELXS55 and refined against
F2 with full-matrix least-squares techniques using the program
SHELXL-97.56 The coordinated THF molecules of (3THF)2 and
OM700450J
(53) Blessing, R. H. Acta Crystallogr. Sect. A 1995, 51, 33-38.
(54) Spek, A. L. Acta Crystallogr. Sect. A 1990, 46, C34.
(55) Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467-473.
(56) Sheldrick, G. M. SHELXL-97, A Program for the Refinement of
Crystal Structures; Universita¨t Go¨ttingen, 1997.