Crystal structures, semiempirical PM3 calculations and NMR studies of trimesityllead bromide and dimesityllead dibromide

Article abstract of DOI:10.1016/S0277-5387(98)00367-2

Trimesityllead bromide has been synthesized by the reaction of mesityllithium with lead(II) chloride in tetrahydrofuran (THF). As a side product, dimesityllead dibromide was formed. The structures of both compounds were determined by single-crystal X-ray diffraction analysis. Both Mes₃PbBr and Mes₂PbBr₂ were characterized by NMR (¹H, ¹³C and ²⁰⁷Pb) and other spectroscopic methods. ²⁰⁷Pb-¹H and ²⁰⁷Pb-¹³C coupling constants were determined. The experimentally obtained X-ray data were compared with those calculated at the semiempirical PM3 level.

Full text of DOI:10.1016/S0277-5387(98)00367-2

Polyhedron 18 (1999) 839–844
Crystal structures, semiempirical PM3 calculations and NMR studies of
trimesityllead bromide and dimesityllead dibromide
*
¨
¨
¨
¨
Thomas M. Klapotke , Jorg Knizek, Heinrich Noth, Burkhard Krumm, Claudia M. Rienacker
Institute of Inorganic Chemistry, University of Munich, Meiserstrasse 1, D-80333 Munich, Germany
Received 5 June 1998; accepted 9 October 1998
Abstract
Trimesityllead bromide has been synthesized by the reaction of mesityllithium with lead(II) chloride in tetrahydrofuran (THF). As a
side product, dimesityllead dibromide was formed. The structures of both compounds were determined by single-crystal X-ray diffraction
analysis. Both Mes3PbBr and Mes2PbBr2 were characterized by NMR (1H, 13C and 207Pb) and other spectroscopic methods. 207Pb–1H
and 207Pb–13C coupling constants were determined. The experimentally obtained X-ray data were compared with those calculated at the
semiempirical PM3 level.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Trimesityllead bromide; Dimesityllead dibromide; Crystal structure; 207Pb NMR
˚
1. Introduction
was stored over 3 A molecular sieves. Lead(II) chloride
(Merck) was used without any manipulation.
The mesityl group [Mes52,4,6-(CH3)3C6H2], being a
relatively bulky substituent, has been widely used in the
chemistry of silicon and germanium in order to stabilize
and isolate new types of compounds, for example, dis-
ilenes and digermenes [1–7]. In contrast, there are few
reports of mesityl derivatives of lead, such as Mes4Pb [8],
Mes3PbCl and Mes3PbI [9,10]. The reaction of
mesitylmagnesium bromide with lead(II) bromide in the
presence of bromine produced dimesityllead dibromide
[11]. The brief note on the preparation of trimesityllead
bromide in the same article is questionable.
Infrared spectra were recorded as KBr pellets on a
Nicolet 520 Fourier transform infra-red (FT-IR) spec-
trometer. Raman spectra were recorded on a Spectrum
2000R NIR FT-Raman spectrometer. 1H, 13Ch1Hj and
207Pbh1Hj NMR spectra were obtained on Jeol GSX270
and EX400 Delta NMR instruments, and chemical shifts
are reported with respect to (CH3)4Si (1H, 13C) and
(CH3)4Pb (207Pb). The elemental analysis was done with a
C, H, N-Analysator Elementar Vario EL. Mass spectra
were obtained with a Finnigan MAT 95Q spectrometer.
The only synthesized and isolated diorganolead(II)
species reported up to now are [(Me3Si)2CH]2Pb [12] and
[2,4,6-(CF3)3C6H2]2Pb [13]. In addition, the preparation
of (PhSiMe2)3CPbCl has been reported recently [14].
In this report, we wish to present our results obtained
from the attempted preparation of mesityllead(II) chloride.
The resulting products were thoroughly characterized.
2.1. Preparation of mesityllithium [25]
Into a mixture, consisting of lithium pieces (96 mg,
13.82 mmol) in 10 mL of Et2O, mesityl bromide (1.25 g,
6.28 mmol) dissolved in 10 mL of Et2O was added.
During the addition, the reaction vessel was kept in an
ultrasonic bath. After the addition was completed, the
reaction mixture was treated for 3 h more with ultrasound.
The mixture was used for the next reaction without further
manipulation.
2. Experimental
All solvents were pre-dried over KOH (Et2O, THF,
acetone) or P4O10 (methylcyclohexane) and distilled from
Na before use (except acetone). Mesityl bromide (Aldrich)
2.2. Preparation of trimesityllead bromide and
dimesityllead dibromide
A mixture of the above-prepared mesityllitium in Et2O
was dissolved in 20 mL of THF and added dropwise to a
*
Corresponding author.
0277-5387/99/$ – see front matter
PII: S0277-5387(98)00367-2
1999 Elsevier Science Ltd. All rights reserved.

¨
T.M. Klapotke et al. / Polyhedron 18 (1999) 839–844
840
suspension of lead(II) chloride (1.747 g, 6.28 mmol) in 30
mL of THF at 258C. The reaction mixture was stirred for
12 h at 258C after the addition was completed. The
solvents were removed under vacuum and the residue was
extracted with methylcyclohexane (50 mL). The solvent of
the extract was evaporated under vacuum and the remain-
ing solid was recrystallized from acetone. Yield: 0.6 g
(44% referring to MesLi) of colorless crystals, which were
identified as Mes3PbBr. Some yellow crystals of the minor
component Mes2PbBr2 could be isolated by hand-selection
out of the crystals of Mes3PbBr.
2.5. X-ray crystallography
2.5.1. Data collection and processing for Mes3PbBr and
Mes2PbBr2
All data were collected on a Siemens P4 diffractometer
with a SMART area detector; using graphite monochro-
˚
mated Mo–Ka radiation (l50.71073 A). The crystals
were mounted in perfluorpolyether oil at 183 K.
Mes3PbBr: 6938 independent measured reflections (Rint5
0.0255), 5492 observed [F.4s (F)]. Absorption correc-
tions were made with SADABS. Mes2PbBr2: 2057 in-
dependent measured reflections (Rint50.0301), 1755 ob-
served [F.4s (F)]. Absorption corrections were made
with SADABS.
2.3. Mes3PbBr
IR (KBr) n in cm21: 3436 s, 3019 s, 2967 vs, 2923 vs,
2865 m, 2733 w, 2594 w, 2411 w, 1712 m, 1691 sh, 1625
w, 1608 w, 1593 m, 1561 m, 1534 sh, 1402 m, 1377 m,
1291 vs, 1262 m, 1240 w, 1223 w, 1175 w, 1094 m, 1027
s, 1004 s, 945 w, 926 w, 879 w, 848 vs, 804 m, 696 m,
661 w, 578 m, 539 vs, 334 m and 303 m.
2.5.2. Structure solution and refinement for Mes3PbBr
and Mes2PbBr2
Crystallographic calculations were carried out using the
SHELXS-97 [26] and SHELXL-97 program systems [27].
Raman (100 mW) n in cm21: 3017 (23), 2917 (49),
1595 (13), 1562 (10), 1449 (10), 1390 (19), 1339 (6),
1294 (39), 1006 (12), 945 (15), 699 (10), 583 (21), 542
(100), 337 (19), 308 (11), 225 (11), 161 (97) and 89 (66).
MS hEI, 70 eV, m/e [Irel (%)]j: 565 (26) M1–Br; 525
(18) M1–Mes; 445 (8) [Mes2Pb–H]1; 404 (24)
[MesPbBr–2H]1; 327 (100) MesPb1; 287 (4) PbBr1, 208
(42) Pb1, 119 (30) Mes1 and 105 (60) [Mes–CH2]1.
Elemental analysis (%) C27H33BrPb [644.66] Calc.: C,
50.31; H, 5.17. Found: C, 50.61; H, 5.10.
3. Results and discussion
The reaction of mesityllithium (prepared from mesityl
bromide, see below) with lead(II)chloride in tetrahydro-
furan (THF) results in the unexpected formation of tri-
mesityllead bromide, Mes3PbBr. Its structure as well as the
structure of the side product, dimesityllead dibromide
(Mes2PbBr2), was confirmed by X-ray crystallography.
The desired product, mesityllead(II) chloride, MesPbCl,
Melting point: 179–1828C; Literature value: 145–1468C
[11].
2.4. Mes2PbBr2
IR (KBr) n in cm21: 3451 m, 3041 sh, 3011 m, 2975 s,
2916 s, 2843 w, 2740 w, 1723 w, 1587 w, 1563 s, 1521 w,
1448 vs, 1403 sh, 1378 s, 1294 vs, 1243 m, 1203 vw, 1174
m, 1035 s, 1025 sh, 997 vs, 942 m, 925 w, 886 w, 850 vs,
688 s, 579 w, 538 s, 525 w, 514 w, 491 w, 324 w and 301
s.
Raman (100 mW) n in cm21: 3017 (21), 2919 (49),
2733 (5), 1595 (12), 1534 (18), 1449 (11), 1389 (19),
1294 (38), 1270 (14), 1209 (7), 1005 (12), 945 (15), 698
(8), 582 (21), 543 (89), 339 (19), 312 (13), 224 (13), 194
(25), 162 (100) and 89 (65).
MS hEI, 70 eV, m/e [Irel (%))]j: 565 (9) [Mes3Pb]1; 525
(20) M1–Br; 406 (25) [MesPbBr]1; 327 (49) MesPb1;
287 (12) PbBr1, 208 (50) Pb1, 119 (35) Mes1 and 105
(100) [Mes–CH2]1.
Elemental analysis (%) C18H22Br2Pb [605.38] Calc.: C,
35.71; H, 3.67. Found: C, 35.82; H, 3.41.
Melting point: 183–1858C (dec.); Literature value: 198–
1998C [11].
Fig. 1. ORTEP view of Mes3PbBr (25% probability, H atoms are omitted
for clarity).

¨
T.M. Klapotke et al. / Polyhedron 18 (1999) 839–844
841
Fig. 2. ORTEP view of Mes2PbBr2 (25% probability).
Table 1
Crystal data, structure solution and refinement for Mes3PbBr and Mes2PbBr2
Compound name
Chemical formula
Molecular weight
T (K)
Mes3PbBr
C27H33BrPb
644.66
Mes2PbBr2
C18H22Br2Pb
605.38
183(2)
183(2)
Crystal system, space group
Triclinic, P21
8.2082(2)
16.8041(2)
19.5006(2)
93.594(1)
96.588(1)
90.756(1)
2666.33(8)
2
1.606
Orthorhombic, Pbcn
11.2264(2)
9.4887(2)
17.4281(4)
90.00
90.00
90.00
1856.51(7)
4
2.166
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
Volume (A )
Z
Density (calc.) (mg/m3)
Absorption coefficient (mm21
F(000)
)
7.836
1248
13.384
1128
Crystal color
Colorless
Yellow
Crystal size (mm)
Scan type
2u range for data collection (8)
0.330.230.2
Hemisphere
13.62 to 49.42
29#h#7, 219#k#19,
222#I#22
12 923
0.3230.2530.22
Hemisphere
4.68 to 58.62
214#h#14, 213#k#10,
222#I#22
9893
2057
0.0301
Index ranges (maximum)
Reflections collected
Independent reflections
Rint
2938
0.0255
Observed reflections
Max. and min. transmission
Structure solution
Refinement method
5492
1755
0.336 and 0.183
Heavy-atom method
Full-matrix least-squares
on F2
0.1567 and 0.0996
Heavy-atom method
Full-matrix least-squares
on F2
Weighting scheme
w215s2Fo21(0.1260P)21
3.8784P
w215s2Fo21(P)21P
where P5(Fo212 Fc2)/3
where P5(Fo212Fc2)/3
6938/12/541
R150.0466, wR250.1329
0.153 and 0.009
2.222
Data/restraints/parameters
Final R indices [F.4s (F)]
2057/0/99
R150.0318, wR250.0731
0.011 and 0.000
0.926
Largest and mean D/s
Largest difference peak (e A
Largest difference hole (e A
23
˚
˚
)
)
23
23.016
21.763

¨
842
T.M. Klapotke et al. / Polyhedron 18 (1999) 839–844
Table 3
was not detected. We believe that the lead bromine bond
was formed via exchange of the Cl for Br (arising from the
precursor mesityl bromide). Initially formed plumbylenes,
Mes2Pb, MesPbCl or MesPbBr, which can be postulated as
being intermediates, then could react with mesityl bromide
to produce Mes3PbBr and Mes2PbBr2.
Both products, soluble in chloroform, dichloromethane
or acetone, are stable to air and moisture. Attempts to
prepare Mes3PbBr via reaction of MesMgBr with PbBr2
according to the literature method [11] also led to a
mixture of Mes3PbBr and Mes2PbBr2.
˚
Selected measured (X-ray) and computed (PM3) bond lengths [A] and
angles [8] for Mes2PbBr2a
X-ray
2.211(5)
2.211(5)
2.6028(6)
2.6027(6)
PM3
Pb1–C1A
Pb1–C1
Pb1–Br1A
Pb1–Br1
C1A–Pb1–C1
C1A–Pb1–Br1A
C1–Pb1–Br1A
C1A–Pb1–Br1
C1–Pb1–Br1
Br1A–Pb1–Br1
EPM3 (kcal mol21
NIMAG
2.087
2.087
2.602
2.5988
123.4(3)
120.8
100.51(13)
115.56(14)
115.56(14)
100.51(13)
99.26(3)
101.59
113.31
114.98
106.35
97.41
3.1. Crystallographic studies
)
24308.6
0
Single crystals of both compounds were obtained by
slow evaporation of the solvent of an acetone solution.
Mes3PbBr: The compound crystallizes as colorless prisms
in a triclinic system, and the space group is P21. The
molecular structure is shown in Fig. 1. There are two
independent molecules found in the unit cell.Mes2PbBr2:
The compound crystallizes as yellow prisms in an ortho-
rhombic system, and the space group is Pbcn. The
molecular structure is shown in Fig. 2.
a
Atomic labeling for the PM3 structure is analogous to the X-ray
structure.
PM3 level of theory is a reparametrization of AM1 [18–
21], which is based on the neglect of diatomic differential
overlap (NDDO) approximation. NDDO retains all one-
center differential overlap terms when Coulomb and
exchange integrals are computed.
Crystal data, structure solution and refinement for
Me3PbBr and Mes2PbBr2 are given in Table 1. Selected
bond lengths and angles, including those obtained from
PM3 calculations of Mes3PbBr, are listed in Table 2 and
those of Mes2PbBr2 are listed in Table 3.
The agreement between the experimentally observed
(X-ray) and quantum-chemically computed (PM3) struc-
tural parameters is reasonably good (Tables 2 and 3),
which indicates that the PM3 parameters are suitable even
for the prediction of organometallic heavy-element com-
pounds such as Mes3PbBr and Mes2PbBr2. The most
intriguing structural features are the bond angles at the
3.2. Semiempirical PM3 computations
Table 4
All calculations were carried out with the program
package HyperChem [15] at the semiempirical PM3
[16,17] level of theory using the VSTO-3G* basis set. We
chose PM3 (which differs from AM1 only in the values of
the parameters) since the parameters for PM3 were derived
by comparing a much larger number and a wide variety of
experimental versus computed molecular properties. The
NMR data for Mes3PbBr and Mes2PbBr2 (Mes52,4,6-(CH3)3C6H2)
Mes3PbBr
Mes2PbBr2
d (CDCl3) [ppm], J [Hz]
1H
CH, 2H
6.98
49.0
2.42
10.1
2.27
5.3
7.04
2.62
2.30
4JH–Pb
81.3
14.3
7.2
2,6-CH3, 6H
4JH–Pb
4-CH3, 3H
Table 2
6JH–Pb
˚
Selected measured (X-ray) and computed (PM3) bond lengths [A] and
13Ch1Hj
C-1 (Ar)
1JC–Pb
angles [8] for Mes3PbBra
160.8
481.1
143.5
78.9
139.2
19.2
161.7
142.0
141.1
130.9
24.0
X-ray
2.204(10)
2.241(11)
2.224(10)
2.6616(10)
PM3
647.7
109.0
27.5
C-2 (Ar)
Pb1–C10
Pb1–C19
Pb1–C1
Pb1–Br1
2.223
2.127
2.120
2.666
2JC–Pb
C-4 (Ar)
4JC–Pb
C-3 (Ar)
129.9
83.0
C10–Pb1–C19
C19–Pb1–C1
C1–Pb1–C10
C10–Pb1–Br1
C19–Pb1–Br1
C1–Pb1–Br1
EPM3 (kcal mol21
NIMAG
115.4(4)
120.8
3JC–Pb
128.2
96.0
116.7(4)
119.0(4)
96.7(3)
103.1(3)
100.2(3)
107.9
120.2
91.5
2,6-CH3
3JC–Pb
25.5
71.1
4-CH3
21.0
21.0
109.8
103.1
26358.92
0
5JC–Pb
12.5
19.2
)
207Pbh1Hj
Pb
297
2149
1JPb–C
481
Not resolved
650
aAtomic labeling for the PM3 structure is analogOUS to the X-ray
structure.
nJC–Pb
|80 (n52, 3)

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T.M. Klapotke et al. / Polyhedron 18 (1999) 839–844
843
Fig. 3. 207Pbh1Hj NMR of Mes3PbBr in CDCl3.
5
central Pb atom, which deviate substantially from the ideal
tetrahedral angle of 109.58. The C–Pb–C angles are about
115–1238 (both experimentally and PM3), and the C–Pb–
Br and Br–Pb–Br angles are reduced to 96–1158. These
findings are nicely in agreement with Bent’s rule, accord-
ing to which, more electronegative substituents prefer
hybride orbitals with lower s character and more elec-
tropositive substituents prefer hybride orbitals with higher
s character [22–24].
at 21.0 ppm, but, interestingly, not the value of JC–Pb
(12.5 19.2 Hz).
The 13C satellites for C-1 with J coupling are visible in
1
the 207Pb NMR spectra and confirm the values obtained
from the 13C NMR. The smaller couplings, J and 3J,
2
consisting of the satellites C-2, C-3 and 2,6-CH3, are also
present but cannot be resolved. Due to the greater number
of carbon atoms (six) coupling to Pb, the resonance is
significantly more intense than for the C(1)–Pb coupling.
A singlet pair of satellites with an average coupling of 80
Hz is observed. Fig. 3 shows the 207Pb NMR resonance of
Mes3PbBr containing 13C satellites.
3.3. NMR studies
The NMR data for both lead compounds are listed in
Table 4. All 1H and 13C resonances show sets of lead
satellites due to coupling with 207Pb (I51/2). A striking
feature in the comparison of Mes3PbBr with Mes2PbBr2 is
the significant increase (|40–60%) in the values of the
Acknowledgements
The authors gratefully acknowledge the University of
Munich and the Fonds der Chemischen Industrie for
financial support.
n
n
coupling constants JH–Pb (n54,6) and JC–Pb (n51–5)
from the bromide to the dibromide. Also, there is a low
field shift observed for the resonances of the dibromide
1
relative to the bromide in H and 13C, except for C-2 and
References
2,6-CH3. The influence of the change in the environment
at the lead atom for the 4-CH3 carbon resonance is
negligible; therefore, the chemical shift remains unchanged
[1] T. Tsumuraya, S.A. Batcheller, S. Masamune, Angew. Chem. Int.
Ed. Engl. 30 (1991) 902.

¨
T.M. Klapotke et al. / Polyhedron 18 (1999) 839–844
844
[2] R. West, Angew. Chem. Int. Ed. Engl. 26 (1987) 1201.
[15] HyperChem 4.0, Molecular visualization and simulation program
package, Hypercube, Waterloo, Ontario, 1994.
[3] R. West, M.J. Fink, J. Michel, Science 214 (1981) 1343.
[4] S. Collin, S. Murakami, H. Tobita, D.J. Williams, J. Am. Chem. Soc.
105 (1983) 7776.
[5] K.M. Baines, J.A. Cooks, Organometallics 10 (1991) 3419.
[6] M. Riviere-Baudet, A. Morere, J.F. Britten, M. Onyszchuk, J.
Organomet. Chem. 423 (1992) C5.
[16] J.J.P. Steward, J. Comp. Chem. 10 (1989) 209.
[17] J.J.P. Steward, J. Comp. Chem. 10 (1989) 221.
[18] M.J.S. Dewar, W. Thiel, J. Am. Chem. Soc. 99 (1977) 4499.
[19] M.J.S. Dewar, M.L. McKee, H.S. Rzepa, J. Am. Chem. Soc. 100
(1978) 3607.
[7] S. Masamune, in: E.R. Corey, J.Y. Corey, P.P. Gasper (Eds.), Silicon
Chemistry, Ellis Horwood, Chichester, 1988, p. 257.
[8] H. Gilman, J. Bailie, J. Am. Chem. Soc. 61 (1939) 731.
[9] H.K. Sharma, R.J. Villazana, F. Cervantes-Lee, L. Parkanyi, K.H.
Pannell, Phosphorus, Sulfur Silicon 87 (1994) 257.
[10] B.C. Pant, W.E. Davidson, J. Organomet. Chem. 39 (1972) 295.
[11] F. Glocking, K. Hooton, D. Kingston, J. Chem. Soc. A (1961) 4405.
[12] P.J. Davison, M.F. Lappert, J. Chem. Soc., Chem. Commun. (1976)
2612.
[20] M.J.S. Dewar, E.G. Zoebisch, E.F. Healy, J. Am. Chem. Soc. 107
(1985) 3902.
[21] M.J.S. Dewar, C.H. Reynolds, J. Comp. Chem. 2 (1986) 140.
[22] H.A. Bent, J. Chem. Educ. 37 (1960) 616.
[23] H.A. Bent, Chem. Rev. 61 (1961) 275.
[24] H.A. Bent, J. Chem. Phys. 33 (1960) 1258.
¨
[25] G. Bahr, R. Gelius, Chem. Ber. 91 (1958) 818.
[26] G.M. Sheldrick, SHELXS-97, Program for the solution of crystal
¨
structure, University of Gottingen, 1997.
[13] S. Brooker, J.-K. Buijink, F.T. Edelmann, Organometallics 10
(1991) 25.
[27] G.M. Sheldrick, SHELXL-97, Program for the refinement of crystal
¨
structure, University of Gottingen, 1997.
¨
[14] C. Eaborn, K. Izod, P.B. Hitchcock, S.E. Sozerli, J.D. Smith, J.
Chem. Soc. Chem. Commun. (1995) 1829.