A heterotopically chelated low-valent lead amide

Article abstract of DOI:10.1021/om0501677

The solid-state structure and NMR parameters of the heavier carbene analogue [Pb{Ph₂PC(H)Py}-{N(SiMe₃)₂}] (1), obtained in the reaction of the phosphane Ph₂P(CH₂Py) with [Pb{N(SiMe₃)₂}₂], are discussed.

Full text of DOI:10.1021/om0501677

3576
Organometallics 2005, 24, 3576-3578
Notes
A Heterotopically Chelated Low-Valent Lead Amide1
Alexander Murso, Michal Straka, Martin Kaupp, Ru¨diger Bertermann, and
Dietmar Stalke*
Institut fu¨r Anorganische Chemie, Universita¨t Wu¨rzburg,
Am Hubland, 97074 Wu¨rzburg, Germany
Received March 9, 2005
Summary: The solid-state structure and NMR param-
eters of the heavier carbene analogue [Pb{Ph2PC(H)Py}-
{N(SiMe3)2}] (1), obtained in the reaction of the phos-
phane Ph2P(CH2Py) with [Pb{N(SiMe3)2}2], are discussed.
Plumbylenes usually occur as reactive intermediates
in the preparation of plumbanes R4Pb and undergo
polymerization and/or disproportionation in the absence
of stabilizing groups at the lead(II) center.2 Thus, only
a few examples of low-valent plumbylenes have been
reported so far,3 although the first diamino- and dialkyl-
plumbylenes were already described by Lappert et al.
in the 1970s.4 Recently, some heteroleptic plumbylenes
with a dimeric structure in the solid state were pub-
lished.5 In this paper a low-valent lead(II) complex, sta-
bilized by sidearm donation, is communicated. This hea-
vier carbene analogue is one of the rare examples of
heterotopically chelated monomeric lead(II) complexes.
The reaction of Ph2P(CH2Py)6 with [Pb{N(SiMe3)2}2]4c
in a 1:1 ratio gives the phosphanamide [Pb{Ph2PC(H)-
Py}{N(SiMe3)2}] (1). One amide anion of the starting
material deprotonates the phosphane at the CR-position,
while the other remains coordinated to the lead(II) cat-
ion. A heteroleptic lead(II) complex is formed (Scheme
1).
Figure 1. Solid-state structure of [Pb{Ph2PC(H)Py}-
{N(SiMe3)2}] (1). Only one of the two molecules in the
asymmetric unit is shown. Anisotropic displacement pa-
rameters are depicted at the 50% probability level. Selected
bond lengths [pm] and angles [deg]: Pb-P 275.01(7), Pb-
N1 236.32(19), Pb-N2 223.31(18), P-C1 173.9(2), C1-C2
139.4(3), C2-N1 138.4(3), av. P-CPh 182.3; P-C1-C2
122.46(17), P-Pb-N1 73.78(5), N1-Pb-N2, 100.37(7),
P-Pb-N2 93.30(5).
Scheme 1. Synthesis of
[Pb{Ph2PC(H)Py}{N(SiMe3)2}] (1) by
Deprotonation of Ph2P(CH2Py) with
[Pb{N(SiMe3)2}2]
Dissolving 1 in various solvents results in decomposi-
tion and formation of elemental Pb0. However, dark red
* To whom correspondence should be addressed. Fax: +49-551-39-
3373. Tel: +49-551-39-3000. E-mail: dstalke@chemie.uni-goettin-
gen.de.
(1) Dedicated to Professor Johann Weis on the occasion of his 60th
birthday.
(2) (a) Rivie`re, P.; Rivie`re-Baudet; M.; Satge´, J. In Comprehensive
Organometallic Chemistry; Pergamon: New York, 1982; Vol. 2, p 670.
(b) Harison, P. G. In Comprehensive Coordination Chemistry; Perga-
mon: Oxford, U.K., 1987; Vol. 3, p 185. (c) Harison, P. G. In
Comprehensive Organometallic Chemistry II; Pergamon: New York,
1995; Vol. 2, p 305.
(3) (a) Driess, M.; Gru¨tzmacher, H. Angew. Chem., Int. Ed. Engl.
1996, 35, 827. (b) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000,
210, 251.
(4) (a) Harris, D. H.; Lappert, M. F. J. Chem. Soc., Chem. Commun.
1974, 895. (b) Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem.
Soc., Dalton Trans. 1976, 2268. (c) Gyane, M. J. S.; Harris, D. H.;
Lappert, M. F.; Power, P. P.; Rivie`re, P.; Rivie`re-Baudet, M. J. Chem.
Soc., Dalton Trans. 1977, 2004.
(5) (a) Stu¨rmann, M.; Weidenbruch, M.; Klinkhammer, K. W.;
Lissner, F.; Marsmann, H. Organometallics 1998, 17, 4425. (b)
Klinkhammer, K. W.; Fa¨ssler, T. F.; Gru¨tzmacher, H. Angew. Chem.,
Int. Ed. 1998, 37, 124. (c) Stu¨rmann, M.; Saak, W.; Marsmann, H.;
Weidenbruch, M. Angew. Chem., Int. Ed. 1999, 38, 187. (d) Stu¨rmann,
M.; Saak, W.; Weidenbruch, M.; Klinkhammer, K. W. Eur. J. Inorg.
Chem. 1999, 579.
blocks of crystalline [Pb{Ph2PC(H)Py}{N(SiMe3)2}] (1)
could be grown from a solution of 1 in hexane at -24
°C.
The asymmetric unit contains two independent mol-
ecules of 1. As the structural parameters of the two
molecules are almost identical within their estimated
standard deviations (esd’s), the bond lengths and angles
given in the caption of Figure 1 are averages; the esd’s
are maxima. The molecular structure of 1 is depicted
in Figure 1. In [Pb{Ph2PC(H)Py}{N(SiMe3)2}] (1), the
central cation is 3-fold coordinated. The [Ph2PC(H)-
Py]- anion (P,N)-chelates the metal, forming a five-
membered planar metallacycle. The cation is displaced
only by 1.8 pm from the best plane of the anion. The
10.1021/om0501677 CCC: $30.25 © 2005 American Chemical Society
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Notes
Organometallics, Vol. 24, No. 14, 2005 3577
[N(SiMe3)2]- anion, completing the coordination sphere
of the central metal ion, is arranged almost perpendicu-
lar to the five-membered metallacycle (P-Pb-N2: 93.30-
(5)°; N1-Pb-N2: 100.37(7)°). The sum of the angles at
the cation of 267.45° illustrates the pyramidal coordina-
tion sphere and the presence of a stereochemically active
lone pair at the lead(II) atom.
nucleus resonates quite unexpectedly at δ ) 61.17. The
observed lead satellites give a coupling constant of
1J
P ) 2679.5 Hz, which is quite large in compari-
207Pb,31
son to other plumbylenes, e.g., in [Pb{HC(PPh2)2}2]
(1J
(1J
) 1970 Hz),8 [(THF)Li(µ2-PtBu2)Pb(PtBu2)]
P
207Pb,31
207Pb,31
P ) 1770 Hz),16 or [Pb{SiMe3C(Ph2P)2}2] (1J
207Pb,31
P
) 1510 Hz).8b The single proton at the CR atom gives
rise to a doublet at δ ) 4.56; the coupling constant is
The P-C1-C2 angle of 122.46(17)° indicates sp2-
hybridization of the C1 atom. The sum of the angles at
C1 of 360° ascertains the planar coordination sphere.
The Pb‚‚‚C1 distance of 348.0 pm clearly shows that the
cation is not interacting with the deprotonated “car-
banionic” atom. The P-CPh distances in 1 (av 182.3 pm)
are identical within their esd’s and in the range
normally quoted for standard P-C single bonds (185
pm).7 However, the P-C1 bond length of 173.9(2) pm
is substantially shorter. This distance is similar to those
observed in [Pb{HC(PPh2)2}]2 (171.3-175.9 pm).8 Also
the C1-C2 distance in 1 of 139.4(3) pm is shorter than
a formal C(sp2)-C(sp2) single bond (146 pm).7 Therefore,
the C2-N2 distance (138.4(3) pm) in the pyridyl sub-
stituent is ca. 5.2 pm longer than in the related
Ph2P(CH2Py)(NSiMe3) (133.17 pm).9 These structural
parameters are consistent with a delocalization of the
negative charge over the [P-C(H)-Py] moiety and
charge transfer into the electron-deficient pyridyl sub-
stituent observed in the related zinc and iron com-
plexes.10 Thus, the short P-C1 and C1-C2 distances
in 1 originate from high electrostatic contributions and
polarization effects.9 In 1, the Pb-N1 distance of 236.32-
(19) pm is ca. 13 pm longer than the Pb-N2 bond
(223.31(18) pm), indicating that the Pb-N1 interaction
is weaker due to charge delocalization in the [P-C(H)-
Py)]- residue. In the lead amide [Pb{N(SiMe3)2}2] the
Pb-N distances are 226.0 pm.11 A good example for
PbrNPy donor interactions is [(C5H5N)Pb{2,6-(2,4,6-
iPr-C6H2)C6H3}Br], with a Pb-N distance of 250.2
pm.12 For the lead organic complex [Pb(o-C6H4PPh2-
NSiMe3)2] a much longer PbrN bond length of 263.6
pm is observed.13 Thus, in 1 the Pb-N2 bond is in the
range for lead amides and the Pb-N1 interaction has
a considerable amidic character, which is in accordance
with a charge transfer toward the pyridyl nitrogen atom
N1. The Pb-P bond in 1 is 275.01(7) pm long. Interest-
ingly, this value is in the range found for Pb-P
interactions in lead phosphanides with a tricoordinated
lead(II) atom as in 1. For example the Pb-P distances
in [Pb(PtBu2)2]2 are 278.1 and 281.2 pm;14 those in [Pb2-
{P(SiMe3)2}4], 269.4 and 279.7 pm.15
2
31P
1
J H, ) 6.4 Hz. This signal shows satellites with a
3
207
1
coupling constant of J
) 33.0 Hz. The 15N spec-
Pb, H
1
troscopical shifts were obtained from a H,15N-HMBC
experiment. They reflect clearly the different bonding
environment of the two nitrogen nuclei. Whereas the
nitrogen atom of the [N(SiMe3)2]- moiety resonates
upfield at δ ) -268.0, the resonance for the pyridyl
nitrogen atom is shifted to lower field at δ ) -145.3.
The resonance for the pyridyl nitrogen atom is located
∆δ ) 83.3 upfield in comparison to the starting material
Ph2P(CH2Py) (δ ) -62.0),17 consistent with an amidic
character for this atom and in accordance with the
observed structural parameters. To verify the experi-
mental findings, the 31P and 15N shifts were calculated
by density functional methods that include scalar
relativistic effects on lead via an effective-core potential
(ECP) and additionally spin-orbit (SO) corrections by
a triple perturbation SO-ECP approach.18 The scalar
relativistically obtained 31P shift of 19 ppm is moved to
60 ppm by large deshielding SO corrections, to give the
computed shifts an excellent agreement with the ex-
perimental ones. Final SO-corrected 15N shifts are -129
ppm for the pyridyl nitrogen atom and -256 ppm for
the [(Me3Si)2N]- moiety, again in good agreement with
the experiment. These values include more moderate
deshielding SO corrections of ca. +12 ppm and ca. +11
ppm, respectively. The lesser importance of SO effects
for the nitrogen nuclei compared to phosphorus is
consistent with a relatively low nitrogen s-character in
the Pb-N bonds.19 The more deshielded character of the
pyridyl nitrogen atom reflects incorporation into an
unsaturated π-system.
In summary, the [Ph2PC(H)Py]- anion in 1 should
be regarded as an amide, although the Pb-P distance
matches those of phosphanides and the Pb-N distance
is considerably longer than that of the [(Me3Si)2N]-
ligand. This view is further substantiated by the ex-
perimental and theoretical NMR shifts.
Experimental Section
Preparation of [Pb{Ph2PC(H)Py}{N(SiMe3)2}] (1). To
a suspension of 0.50 g (1.80 mmol) of Ph2PCH2Py in 40 mL of
hexane was added 0.95 g (1.80 mmol) of [Pb{N(SiMe3)2}2] in
In the 31P NMR spectrum of 1, the phosphorus
(6) Alvarez, M.; Lugan N.; Mathieu, R. J. Chem. Soc., Dalton Trans.
1994, 2755.
(7) Rademacher, P. In Strukturen Organischer Moleku¨le; VCH:
Weinheim, 1987.
(16) Arif, A. M.; Cowley, A. H.; Jones, R. A.; Power, J. M. J. Chem.
Soc., Chem. Commun. 1986, 1446.
(8) (a) Balch A. L.; Oram, D. E. Organometallics 1986, 5, 215. (b)
Balch A. L.; Oram, D. E. Inorg. Chem. 1987, 26, 1906.
(9) Kocher, N.; Leusser, D.; Murso, A.; Stalke, D. Chem. Eur. J.
2004, 10, 3622.
(10) Murso, A.; Stalke, D. Dalton Trans. 2004, 2563.
(11) Fjeldberg, T.; Hope, H.; Lappert, M. F.; Power P. P.; Thorne,
A. J. J. Chem. Soc., Chem. Commun. 1983, 639.
(12) Pu, L.; Twamley B.; Power, P. P. Organometallics 2000, 19,
2874.
(13) Wingerter, S.; Gornitzka, H.; Bertermann, R.; Pandey, S. K.;
Rocha, J.; Stalke, D. Organometallics 2000, 19, 3890.
(14) Cowley, A. H.; Giolando, D. M.; Jones, R. A.; Nunn, C. M.;
Power, J. M. Polyhedron 1988, 7, 1909.
(15) Goel, S. C.; Chiang, M. Y.; Rauscher, D. J.; Buhro, W. E. J.
Am. Chem. Soc. 1993, 115, 160.
(17) Assigned unambigiously in a 1H,15N-HMBC NMR experiment.
(18) Vaara, J.; Malkina, O. L.; Stoll, H.; Malkin, V. G.; Kaupp, M.
J. Chem. Phys. 2001, 114, 61 (see this work for more computational
details). Scalar relativistic shifts were calculated at the BP86-IGLO
level, and SO corrections were computed with a common gauge on lead
and a finite perturbation of λ ) 0.001 au. A four-valence-electron ECP
with (5s5p2d/4s4p2d) valence basis and matching SO-ECP was used
on lead (Ku¨chle, W.; Dolg, M.; Stoll, H.; Preuss, H. Mol. Phys. 1991,
74, 1245), with an IGLO-III basis on P, Si, and N (Kutzelnigg, W.;
Fleischer, U.; Schindler, M. NMR-Basic Principles and Progress;
Springer: Heidelberg, 1990; Vol. 23, p 165) and a DZVD basis set on
all other atoms (Godbout, N.; Salahub, D. R.; Andzelm, J.; Wimmer,
E. Can. J. Chem. 1992, 70, 560).
(19) Kaupp, M.; Malkina, O. L.; Malkin, V. G.; Pyykko¨, P. Chem.
Eur. J. 1998, 4, 118.

3578 Organometallics, Vol. 24, No. 14, 2005
Notes
10 mL of hexane at -10 °C. The resulting dark red solution
was stored at -24 °C, yielding 1.10 g (1.71 mmol, 95%) of 1 as
red blocks. The 1H, 13C, 15N, 29Si, and 31P solution NMR spectra
were recorded on a Bruker DRX-300 NMR spectrometer (1H,
300.1 MHz; 13C, 75.5 MHz; 15N, 30.4 MHz; 29Si, 59.6 MHz; 31P,
121.5 MHz). Toluene-d8 was used as solvent. Chemical shifts
[ppm] were determined relative to internal C6D5CHD2 (1H, δ
) 2.09; C7D8), C7D8 (13C, δ ) 20.4; C7D8), external formamide
(15N, δ ) -268.0; C7D8), external TMS (29Si, δ ) 0; C7D8), and
external 85% H3PO4 (31P, δ ) 0; C7D8). Analysis and assign-
ment of the 1H NMR data were supported by 1H,1H COSY,
13C,1H, 15N,1H, and 31P,1H correlation experiments. Assignment
of the 13C NMR data was supported by DEPT 135 experiments.
refined by full-matrix least-squares on F2 using SHELXL.21
The hydrogen atoms at the methylene bridges were taken from
the difference Fourier map and refined freely. All other
hydrogen atoms were refined using a riding model. All non-
hydrogen atoms were refined anisotropically. 1: C24H33N2-
PPbSi2, Mr ) 643.86 g/mol, triclinic, space group P1h, a )
859.44(15) pm, b ) 1748.2(3) pm, c ) 1841.1(3) pm, R )
102.425(3)°, â ) 96.536(3)°, γ ) 95.131(3)°, V ) 2.6652(8) nm-3
,
Z ) 4, Fcalcd ) 1.605 Mg m-3, µ ) 6.493 mm-1, F(000) ) 1264.
Data were collected from θ ) 2.29 to 28.28°. A total of 73 736
reflections were measured, from which 13 243 were unique,
R(int) ) 0.0266, wR2(all data) ) 0.0412, R1(I > 2σ(I)) )
0.0179, for 13 238 data and 561 parameters. Crystallographic
data of 1 have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publications no.
CCDC-234744. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: internat.) +44-1223/336-033, e-mail:
deposit@ccdc.cam. ac.uk].
2
1H NMR: δ 0.18 (s, 18H, SiMe3), 4.56 (d, J H, ) 6.4 Hz,
1
31
P
3
207
1
satellites, J
) 33.0 Hz, 1H, H-1), 5.62 (ddd, 1H, H-5),
H
Pb
,
6.53 (dddd, 1H, H-4), 6.74 (d, 1H, H-3), 7.14 (overlap with m-,
p-PhH, 1H, H-6), 7.07-7.46 (m, m-, p-PhH), 7.44-7.68 (m,
2
o-PhH). 13C NMR: δ 6.1 (s, SiMe3) 61.8 (d, J
P ) 55.6 Hz,
13 31
C,
C-1), 105.1 (s, C-5), 121.0 (d, C-3), 134.6 (s, C-4), 144.6 (d, C-6),-
2
13 31
172.6 (d, J
P ) 22.5 Hz, C-2), 127.5-129.8 (m, m-,p- PhH),
C,
132.8 (d, o-PhH). 1H,15N-HMBC NMR: δ -268.0 (N(SiMe3)2),
Acknowledgment. Continuous financial support of
the DFG (grants no. STA 334/8, KA 1187/5 and the
Graduiertenkolleg 690 Elektronendichte-Theorie und
Experiment) is kindly acknowledged.
-145.3 (NPy). 29Si NMR: δ -1.72 (s). 31P NMR: δ 61.17 (s,
1
207
31
satellites,
J
) 2679.5 Hz). Anal. CHN, found, (calcd)
P
Pb,
[%]: C 44.98 (44.77), H 5.13 (5.17), N 4.45 (4.35). Mp: 43 °C.
Crystal Structure of [Pb{Ph2PC(H)Py}{N(SiMe3)2}] (1).
The dataset was measured at 100(2) K20 using graphite-
monochromated Mo KR radiation (λ ) 71.073 pm) on a Bruker
D8 goniometer platform, equipped with a Smart Apex CCD
detector. The structure was solved using direct methods and
Supporting Information Available: Crystal data tables
for 1, including atomic coordinates, bond lengths and angles,
and anisotropic displacement parameters in cif file format are
available free of charge via the Internet at http://pubs.acs.org.
OM0501677
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