Complexes of heteroscorpionate trispyrazolylborate ligands. Part XII. Variable hapticity of hydrobis(3-phenyl-5-isopropylpyrazolyl)(3,5- dimethylpyrazolyl)borate in its rhodium(I) complexes with COD and NBD

Article abstract of DOI:10.1016/j.poly.2003.11.010

The structure of Tp″Rh(NBD) complex was determined by X-ray crystallography (Tp″=hydrobis(3-phenyl-5-isopropylpyrazolyl)(3,5- dimethylpyrazolyl)borate, NBD=2,5-norbornadiene). The Tp″ was found to be κ³ coordinated to rhodium(I). Two independent molecules of Tp″Rh(NBD) were found in triclinic crystals with Rh-N(pz) distances in the region of 2.113(3)-2.307(3) A?. On the other hand the same Tp″ ligand was demonstrated to be coordinated in κ² fashion in Tp″Rh(COD) (COD=1,5-cyclooctadiene) by variable temperature 1-D and 2-D ¹H NMR measurements. The intramolecular exchange between coordinated and uncoordinated 3-phenyl-5-isopropylpyrazolyl residues occurs with ΔG^≠=42.2 kJ/mol as it was calculated from the ¹H NMR studies.

Full text of DOI:10.1016/j.poly.2003.11.010

Polyhedron 23 (2004) 219–223
www.elsevier.com/locate/poly
Complexes of heteroscorpionate trispyrazolylborate ligands.
Part XII. Variable hapticity of hydrobis
(3-phenyl-5-isopropylpyrazolyl)(3,5-dimethylpyrazolyl)
borate in its rhodium(I) complexes with COD and NBD
a
Tomasz Ruman , Zbigniew Ciunik , Stanisław Wołowiec
b
a,
*
a
Faculty of Chemistry, Rzeszꢀow University of Technology, 6 Powstaꢀncꢀow Warszawy Ave., 35-959 Rzeszꢀow, Poland
Faculty of Chemistry, University of Wrocław, 14 Joliot-Curie Str., 50-383 Wrocław, Poland
b
Received 11 May 2003; accepted 14 August 2003
Abstract
The structure of Tp00Rh(NBD) complex was determined by X-ray crystallography (Tp00 ¼ hydrobis(3-phenyl-5-isopropylpyraz-
olyl)(3,5-dimethylpyrazolyl)borate, NBD ¼ 2,5-norbornadiene). The Tp00 was found to be j3 coordinated to rhodium(I). Two inde-
00
ꢁ
pendent molecules of Tp Rh(NBD) were found in triclinic crystals with Rh–N(pz) distances in the region of 2.113(3)–2.307(3) A. On the
other hand the same Tp00 ligand was demonstrated to be coordinated in j2 fashion in Tp00Rh(COD) (COD ¼ 1,5-cyclooctadiene) by
variable temperature 1-D and 2-D 1H NMR measurements. The intramolecular exchange between coordinated and uncoordinated 3-
phenyl-5-isopropylpyrazolyl residues occurs with DG ¼ 42:2 kJ/mol as it was calculated from the 1H NMR studies.
¼
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Polypyrazolylborate; Rhodium(I); Cyclooctadiene; Norbornadiene; Structure; NMR
1. Introduction
orates and ancillary ligands (LL) other than mentioned:
TpMeRh(NBD) [10], TpMe2Rh(PEt3)(C2H4) [11], TpRh
(PPh3)[(CCOOCH3)2] [12], and TpiPr2Rh(NBD) [13], in
which the N(pz)–Rh bond lengths fall into the region of
Heteroscorpionate trispyrazolylborates (Tp00) are tri-
podal anionic ligands of potentially Cs symmetry [1].
The symmetry of the ligands can be preserved in their
metal ion complexes, when Tp00s are coordinated in j3
fashion. The j3 hapticity resulting in effective Cs sym-
metry of the complexes was observed in the series of
high-spin cobalt(II) complexes of the general formula
Tp00Co(NCS) [2–8].
ꢁ
2.12–2.27 A. Here we report on the structure of another
complex, in which the Tp00 ligand bearing two sterically
demanding 3-phenyl substituents is coordinated in j3
fashion in Tp00Rh(NBD), while j2 hapticity is found
in Tp00Rh(COD) analogue as can be concluded on the
1
basis of variable temperature 1-D and 2-D H NMR
experiments.
In case of Tp00Rh(LL) complexes (where LL ¼ (CO)2
or COD), the Tp00 ligands are coordinated in j2 fashion
[9]. Fluxional behavior of those complexes was studied in
1
detail by variable-temperature H NMR spectroscopy.
2. Experimental
The homoscorpionate Tp00 ligands are in most cases j2-
bonded in their Tp00Rh(LL) complexes ([9] and references
[6–16] cited therein). However, there are three examples of
j3 hapticity in rhodium complexes with trispyrazolylb-
2.1. Syntheses
The sodium salt of hydrobis(3-phenyl-5-isopropylpy-
razolyl)(3,5-dimethylpyrazolyl)borate (NaTp00) was syn-
thesized as before [7]. The Tp00Rh(NBD) (1) and
Tp00Rh(COD) (2) complexes were synthesized upon
* Corresponding author. Tel.: +17-865-1657; fax: +17-854-3655.
E-mail address: sw@prz.rzeszow.pl (S. Wołowiec).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.11.010

220
T. Ruman et al. / Polyhedron 23 (2004) 219–223
addition of 120 mg of NaTp00 dissolved in toluene into
the equimolar amounts of [(COD)RhCl)]2 [14] or
[(NBD)RhCl)]2 [15] in toluene. The reaction mixtures
were stirred at room temperature for 4 h under atmo-
sphere of nitrogen, filtrated by passing through short bed
of celite, the solvent was partially removed, the solutions
layered with heptane and allowed to stand at 4 °C until
formation of yellow crystals of 1 (yield 85%) or 2 (yield
80%).
Table 1
Crystal data and structure refinement
Empirical formula
Formula weight
T (K)
C36H42BN6Rh
672.48
100(2)
0.71073
ꢁ
k (A)
Crystal system
Space group
triclinic
ꢂ
P1
ꢁ
a (A)
12.197(2)
15.876(3)
17.120(3)
102.42(3)
102.73(3)
90.88(3)
3151.1(10)
4
ꢁ
b (A)
ꢁ
c (A)
a (°)
b (°)
c (°)
2.2. Analytical data
3
ꢁ
V (A )
1: Elemental analysis: Calc. for C36H42N6BRh (MW
672.48): C, 64.30; H, 6.29; N, 12.50. Found: C, 64.55; H,
6.16; N, 12.43%.
1H NMR (toluene-d8, 298 K): 8.01 (4H, m, o-H(3-Ph));
7.25 (4H, m, m-H(3-Ph)); 7.16 (2H, m, p-H(3-Ph)); 6.31
(2H, s, 4-H(3-Ph,5-iPrpz)); 5.58 (1H, s, 4-H(3,5-diMepz));
3.33 (6H, septet + broad singlet, CH(5-iPr) + 20, 30, 50, 60-
H(NBD)); 2.94 (2H, s, 10, 40 –H(NBD)); 2.31 (3H, s, 3(5)-
Z
Dcalc (Mg mꢁ3
)
1.418
0.578
l (mmꢁ1
F ð000Þ
)
1400
0.17 ꢀ 0.15 ꢀ 0.15
Crystal size (mm)
h Range for data collection (°) 3.43–28.41
Ranges of h, k, l
)15 to 16, )20 to 20, )22 to 21
21 925
Reflections collected
Independent reflections
Data/parameters
13 848 (0.0561)
13 848/806
0.952
CH3); 2.14 (3H, s, 5(3)-CH3); 1.29 (6H, d, J
Hz, 2ꢀCH3(5-iPr)); 1.21(6H, d, J
¼ 6:6
ðCH3–CHÞ
ðCH3–CHÞ
Goodness-of-fit (F 2)
Final R1=wR2 indices
(I > 2rðIÞ)
¼ 6:6 Hz,
2ꢀCH3(5-iPr)); 0.59 (2H, s, 70-H(NBD)).
0.0549/0.0738
IR (KBr): m(BH) 2534, 2474 cmꢁ1
.
Extinction coefficient
Largest diffraction peak/hole
0.00015(10)
0.569/)0.734
2: Elemental analysis: Calc. for C37H46N6BRh (MW
688.53): C, 64.54; H, 6.73; N, 12.21. Found: C, 64.62; H,
6.86; N, 12.13%.
ꢁ3
ꢁ
(e A
)
1H NMR (toluene-d8, 273 K): 8.10 (4H, m, o-H(3-
Ph)); 7.25 (4H, m, m-H(3-Ph)); 7.10 (2H, m, p-H(3-Ph));
6.45 (2H, s, 4-H(3-Ph,5-iPrpz)); 5.56 (1H, s, 4-H(3,5-
diMepz)); 4.10 (4H, s, 10, 20, 50, 60-H(COD)); 3.19 (2H,
septet, CH(5-iPr)), 2.34 (3H, s, 5-CH3); 2.22 (3H, s, 3-
CH3); 1.87 (4H, s, 30, 40, 70, 80-Hexo (COD)); 1.39 (6H, d,
the Oxford Diffraction (Poland) Sp. z o.o (formerly
Kuma Diffraction Wrocław, Poland) programs. The
structure was solved by direct methods (program
SHELXS-97 [17]) and refined by the full-matrix least-
squares method on all F 2 data using the SHELXL-97 [17]
programs. Non-hydrogen atoms were refined with an-
isotropic displacement parameters; hydrogen atoms
were included from geometry of molecules and Dq maps.
During refinement they were fixed.
J
J
) ¼ 6.6 Hz, 2ꢀCH3(5-iPr)); 1.20 (10H, d,
ðCH3–CHÞ
ðCH3–CHÞ
) ¼ 6.6 Hz, 2ꢀCH3(5-iPr) + overlapped s, 30, 40,
70, 80-Hendo (COD)).
IR (KBr): m(BH) 2478 cmꢁ1
.
2.3. Methods
3. Results and discussion
The 1H NMR spectra were recorded with Bruker
AMX 300 spectrometer. Standard COSY and NOESY
experiments were performed with repetition time 1.0 and
mixing time 0.3 s (NOESY).
The heteroscorpionate ligand used in these studies,
composed of two 3-phenyl-5-isopropylpyrazolyl and 3,5-
dimethylpyrazolyl residues ([HB(3-Ph,5-iPrpz)2(3,5-
diMepz)]ꢁ) is more sterically demanding in comparison
with homoscorpionates TpMe [10], Tp [11], or TpMe2 [12],
which coordinate in j3 fashion to the rhodium(I) metal
ion in their Tp0Rh(LL) complexes. On the other hand it is
probably slightly less demanding than TpiPr2, which
forms Tp00Rh(diene) complexes with j3 hapticity, when
dien ¼ NBD and j2 hapticity in case of diene ¼ COD
[13]. Other sterically demanding Tp0 ligands, like TpPh
[18] and Tp4-OMePh [19], as well as [HB(pz)4]ꢁ [20] coor-
dinate in j2 fashion in their Tp0Rh(diene) complexes. We
have synthesized two compounds: [HB(3-Ph,5-iPrpz)2
(3,5-diMepz)]Rh(NBD) (1) and [HB(3-Ph,5-iPrpz)2(3,5-
Crystal data are given in Table 1, together with re-
finement details. All measurements of crystal were per-
formed at low temperature using an Oxford Cryosystem
device on a Kuma KM4CCD j-axis diffractometer with
graphite-monochromated Mo Ka radiation. The crystal
was positioned 65 mm from the CCD camera. 612
frames were measured at 0.75° intervals with a counting
time of 20 s. Accurate cell parameters were determined
and refined by least-squares fit of 5950 of the strongest
reflections. The data were corrected for Lorentz and
polarization effects. No absorption correction was ap-
plied. Data reduction and analysis were carried out with

T. Ruman et al. / Polyhedron 23 (2004) 219–223
221
diMepz)]Rh(COD) (2) in which the coordination mode
of Tp00 ligand is j3 and j2, respectively.
The structure of 1 was elucidated crystallographi-
cally. There are two independent molecules of 1. The
views of the molecules are shown in Fig. 1 together with
relevant bond lengths and angles around metal ion. The
Rh–N(pz) distances fall into the region of 2.113(3)–
throughout broad range of temperature (down to 193
K) indicating the effective Cs symmetry of the molecule.
Thus, the ligand remains coordinated in j3 fashion in
solution or is in fast exchange between j2 and j3 mode.
The resonances from methyl groups of 5-ispopropyl
substituents are diastereotopically split into two dou-
blets due to local chirality in 1. The mutual rotation of
Tp00 and NBD ligands in 1 is fast at the time-scale of the
1H NMR even at the lowest temperature available in
toluene-d8 solvent as can be concluded from the pres-
ence of three resonances from NBD throughout the
studied temperature range.
ꢁ
ꢁ
2.307(3) A (average value 2.24 A), which is typical for
other j3-Tp00Rh(NBD) complexes [10–13] and appar-
ently longer in comparison with those for j2-
Tp00Rh(NBD) ones (average value of Rh–N(pz) is equal
ꢁ
2.08 A) [18–20].
1
The H NMR spectrum of 1 (Fig. 1(b)) is composed
of two 4-H(pz) resonances of relative 2:1 intensity ratio
The crystals of 2 suitable for X-ray analysis could not
be obtained. Therefore, the detailed analysis of the
(a)
C36
C72
C71
C32
C35
C67
C68
C69
C66
C70
C34
C33
C30
C31
Rh1
Rh2
N12
N11
N10
N9
N6
N2
N1
N4
N3
N8
N7
N5
B1
B2
(b)
CH3(5-iPr)
3,5-CH3
*
H(5-iPr) + NBD
4-H(3-Ph-5-iPrpz)
NBD
4-H(3,5-diMepz)
NBD
8
7
6
5
4
3
2
1
[ppm]
δ
ꢁ
Fig. 1. (a) View of two independent molecules of 1. Selected bond lengths (A) and angles (°): Rh(1)–N(2), 2.299(3); Rh(1)–N(4), 2.290(3); Rh(1)–N(6),
2.113(3); Rh(1)–C(30), 2.169(4); Rh(1)–C(31), 2.157(4); Rh(1)–C(33), 2.078(4); Rh(1)–C(34), 2.069(4); N(4)–Rh(1)–N(2), 88.15(12); N(6)–Rh(1)–
N(4), 83.26(13); N(6)–Rh(1)–N(2), 83.59(12); C(34)–Rh(1)–C(31), 79.34(16); C(33)–Rh(1)–C(30), 79.55(17) and Rh(2)–N(8), 2.307(3); Rh(2)–N(10),
2.282(4); Rh(2)–N(12), 2.136(3); Rh(2)–C(66), 2.087(4); Rh(2)–C(67), 2.082(4); Rh(2)–C(69), 2.166(4); Rh(2)–C(70), 2.177(4); N(10)–Rh(2)–N(8),
87.26(12); N(12)–Rh(2)–N(8), 85.07(12); N(12)–Rh(2)–N(10), 83.35(13); C(67)–Rh(2)–C(70), 79.44(17); C(66)–Rh(2)–C(69), 79.85(17). (b) 1H NMR
spectrum of 1 in toluene-d8 at 298 K. The residual peak from solvent (q, CHD2) is labeled with asterisk. The peaks from norbornadiene are labeled as
NBD.

222
T. Ruman et al. / Polyhedron 23 (2004) 219–223
variable temperature 1H NMR experiments was per-
formed for 2 in toluene-d8. The spectrum of 2 at ambient
temperature reflects the effective Cs symmetry of 2.
However, the spectrum changes dramatically upon de-
crease of temperature; the coalescence point observed at
223 K clearly indicates that a chemical exchange be-
tween coordinated and uncoordinated pyrazolyl resi-
dues becomes slow at the time-scale of the method.
Further decrease of temperature results in decrease of
symmetry of the spectrum consistent with slow exchange
between coordinated and uncoordinated 3-Ph-5-iPrpz
residues. Three resonances of 4-H(pz) and four reso-
nances from olefinic COD hydrogens are observed at
193 K (resonances a–d at lower trace at Fig. 2).
signals in COSY spectrum and concomitant EXSY cross-
peaks between the same diagonal peaks in NOESY
spectrum clearly confirm that effective C1 symmetry of the
1H NMR spectrum of 2 at 193 K is consistent with slow
exchange between coordinated and uncoordinated 3-
Ph,5-iPrpz residues. For this interconversion the
¼
DG ¼ 42:2 kJ/mol has been calculated. The obtained
value of energy of activation is very close to those found in
other similar systems, in which the coordinated and un-
coordinated 3-Ph,5-Mepz residues interchanged with
¼
DG ¼ 41:1 kJ/mol in case when third, slowly exchanging
¼
pyrazolyl residue was 3,5-diEtpz and DG ¼ 43:2 kJ/mol
in case of 3-Me,5-Phpz as third, coordinated pyrazolyl
moiety [9].
These features were already observed in case of other
heteroscorpionate complexes: [HB(3-Ph,5-Mepz)2(3-
Me,5-Phpz)]Rh(COD) and [HB(3-Ph,5-Mepz)2(3,5-
diEtpz)]Rh(COD) [9], in which the Tp00 ligands are
coordinatedin j2 fashion, andattributed toslow exchange
between coordinated and uncoordinated 3-Ph,5-Mepz
moiety. The 1H-1H COSY and NOESY experiments
showed the cross-peaks within a () b and c () d
pairs of olefinic protons of COD, similarly as it was found
for [HB(3-Ph,5-Mepz)2(3-Me,5-Phpz)]Rh(COD) and
[HB(3-Ph,5-Mepz)2(3,5-diEtpz)]Rh(COD) [9]. Thus, the
scalar coupling within a () b and c () d pairs of
The
heteroscorpionate
[HB(3-Ph,5-iPrpz)2(3,5-
diMepz)]ꢁ ligand serves a borderline example of steric
demand towards the Rh(diene) counterpart, similar to
homoscorpionate TpiPr2 [13]. The hapticity of Tp00 de-
pends on the rhodium-centered diene cone angle. Tp00
coordinates in j2 fashion in case of diene ¼ COD (average
value of a for Tp00Rh(COD) complexes is 93.4° [9]), while
j3 coordination mode occurs for diene ¼ NBD (a ¼ 79:5°
in 1) in solid state at 100 K. However, it should be em-
phasized that according to the IR spectral criterion pro-
posed by Akita et al. [21] based on the position of m(BH)
the presence of two distinct bands at 2534 and 2474 cmꢁ1
(of relative intensity about 2:1 both in KBr and in chlo-
roform solution) for 1 suggests that at ambient tempera-
ture the [HB(3-Ph,5-iPrpz)2(3,5-diMepz)]ꢁ ligand is
coordinated in two ways: j3 and j2 mode, while in case of
2 (one m(BH) band at 2478 cmꢁ1) the ligand remains co-
ordinated in j2 mode both in solid state and in solution
throughout the entire range of temperatures.
4-H(3-Ph,5-iPrpz)
4-H(3,5-diMepz)
Hol(COD)
CH(5-iPr)
4. Supplementary data
Crystallographicdataforthestructures reportedinthis
paper (excluding structure factors) have been deposited
withtheCambridgeCrystallographicDataCentre,CCDC
No. 209564. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union Road,
Cambridge 1EZ, UK (fax: +44-1223-336033; deposit@
ccdc.cam.ac.uk or www.ccdc.cam.ac.uk).
4-H(3-Ph,5-iPrpz)
4-H(3,5-diMepz)
CH(5-iPr)
Acknowledgements
d
a b
c
4
The authors thank KBN (Poland) for the Grant No.
3 T09A 05219.
10
8
6
[ppm]
δ
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Fig. 2. The relevant fragments of 1H NMR spectra of 2 in toluene-d8
taken at temperature (from top to bottom): 273, 253, 223, and 193 K,
respectively. The resonances labeled with Hol(COD) (top trace) and a,
b, c, d (bottom trace) belong to 10, 20, 50, and 60 H(COD).
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