Terphenyl ligand stabilized lead(II) derivatives of simple organic groups: Characterization of Pb(R)C6H3-2,6-Trip2 (R = Me, t-Bu, or Ph; Trip = C6H2-2,4,6-i-Pr3), {Pb(μ-Br)C6H3-2,6-Trip2}2, py·Pb(Br)C6H3-2,6-Trip2 (py = pyridine), and the bridged

Article abstract of DOI:10.1021/om0001624

The reaction between 1 equiv of the sterically encumbered lithium terphenyl Et₂O·LiC₆H₃-2,6-Trip₂ and PbBr₂ in diethyl ether afforded the organolead(II) halide compound {Pb(μ-Br)C₆H₃-2,6-Trip₂}₂ (1) as orange crystals. Treatment of 1 with a stoichiometric amount of pyridine (py) gave the complex py·Pb(Br)C₆H₃-2,6-Trip₂ (2) as yellow needles. The addition of 1 equiv of methylmagnesium bromide, tert-butyllithium, or phenyllithium to 1 resulted in the diorganolead(II) compounds Pb(R)C₆H₃-2,6-Trip₂ (R = Me, 3; t-Bu, 4; or Ph, 5) in good yield. The compounds 3 and 5 are the first stable, monomeric lead(II) derivatives involving the simplest alkyl and aryl groups Me and Ph. Reaction of 1 with W(CO)₅THF did not yield the expected plumbylene complex (CO)₅W{Pb(Br)C₆H₃-2,6-Trip₂}. Instead, the bridged plumbylyne species [{W(CO)₄}₂(μ-Br)(μ-Pb-C₆H₃-2,6-Trip₂)Ρ B (6) was obtained in low yield. All compounds were characterized by X-ray crystallography, ¹H and ¹³C NMR, IR, and UV-vis spectroscopy. ²⁰⁷Pb NMR spectra of 3-5 were also obtained. The results demonstrate the effectiveness of the terphenyl ligand in creating a protected cavity at a site in which normally unstable moieties are stabilized against decomposition reactions.

Full text of DOI:10.1021/om0001624

2874
Organometallics 2000, 19, 2874-2881
Ter p h en yl Liga n d Sta bilized Lea d (II) Der iva tives of
Sim p le Or ga n ic Gr ou p s: Ch a r a cter iza tion of
P b(R)C6H3-2,6-Tr ip 2 (R ) Me, t-Bu , or P h ; Tr ip )
C6H2-2,4,6-i-P r 3), {P b(µ-Br )C6H3-2,6-Tr ip 2}2,
p y‚P b(Br )C6H3-2,6-Tr ip 2 (p y ) P yr id in e), a n d th e Br id ged
P lu m bylyn e Com p lex
[{W(CO)4}2(µ-Br )(µ-P bC6H3-2,6-Tr ip 2)]
Lihung Pu, Brendan Twamley, and Philip P. Power*
Department of Chemistry, University of California, Davis, One Shields Avenue,
Davis, California 95616
Received February 18, 2000
The reaction between 1 equiv of the sterically encumbered lithium terphenyl Et2O‚LiC6H3-
2,6-Trip2 and PbBr2 in diethyl ether afforded the organolead(II) halide compound {Pb(µ-
Br)C6H3-2,6-Trip2}2 (1) as orange crystals. Treatment of 1 with a stoichiometric amount of
pyridine (py) gave the complex py‚Pb(Br)C6H3-2,6-Trip2 (2) as yellow needles. The addition
of 1 equiv of methylmagnesium bromide, tert-butyllithium, or phenyllithium to 1 resulted
in the diorganolead(II) compounds Pb(R)C6H3-2,6-Trip2 (R ) Me, 3; t-Bu, 4; or Ph, 5) in
good yield. The compounds 3 and 5 are the first stable, monomeric lead(II) derivatives
involving the simplest alkyl and aryl groups Me and Ph. Reaction of 1 with W(CO)5THF did
not yield the expected plumbylene complex (CO)5W{Pb(Br)C6H3-2,6-Trip2}. Instead, the
bridged plumbylyne species [{W(CO)4}2(µ-Br)(µ-Pb-C6H3-2,6-Trip2)] (6) was obtained in low
1
yield. All compounds were characterized by X-ray crystallography, H and 13C NMR, IR,
and UV-vis spectroscopy. 207Pb NMR spectra of 3-5 were also obtained. The results
demonstrate the effectiveness of the terphenyl ligand in creating a protected cavity at a site
in which normally unstable moieties are stabilized against decomposition reactions.
In tr od u ction
of PbR2 species (R ) σ-bonded alkyl or aryl group),
which may exist either as monomers or weakly associ-
ated metal-metal bonded dimers in the solid.6,7 The
latter, since they are formally analogous to alkenes,
have attracted considerable attention owing to the
current interest in the nature of the Pb-Pb bonding
interaction.7 Closely related to these are the heterolep-
tic, σ-bonded organolead(II) derivatives in which one of
the organic substituents is replaced by either a halide8-10
or a transition metal fragment.11 The halide compounds,
in particular, are potentially useful since they can be
easily derivatized by substitution of the halide, which
allows access to an expanded range of organolead(II)
species. For example, the recently described metal-
loplumbylenes11 (η5-C5H5)(CO)3MPbC6H3-2,6-Trip2 (M
) Cr, Mo, or W; Trip ) C6H2-2,4,6-i-Pr3), which feature
Organolead chemistry is primarily concerned with
compounds of lead in the oxidation state IV. In contrast,
the chemistry of Pb(II) tends to be dominated by
compounds with inorganic ligands, and bivalent orga-
nolead compounds are relatively rare and their chem-
istry is poorly explored.1,2 The first well-characterized
organolead(II) species was the bent sandwich complex
Pb(η5-C5H5)2,3 and this has been supplemented by a
number of related derivatives that have a variety of
substituents at the cyclopentadienyl ring.4 For many
years, however, Pb{CH(SiMe3)2}2 was the only stable
σ-bonded organolead(II) compound.5 More recent work
has resulted in the isolation of several further examples
(1) Harrison, P. G. Comprehensive Organometallic Chemistry; Per-
gamon: Oxford, 1984; Vol. 2, Chapter 12. Harrison, P. G. Comprehen-
sive Organometallic Chemistry II; Elsevier: Amsterdam, 1995; Vol. 2,
Chapter 7.
(2) Kaupp, M.; Schleyer, P. v. R. J . Am. Chem. Soc. 1993, 115, 1061.
(3) Fischer, E. O.; Grubert, H. Z. Anorg. Allg. Chem. 1956, 286, 237.
(4) J utzi, P.; Burford, N. Chem. Rev. 1999, 99, 969.
(5) (a) Davidson, P. J .; Lappert, M. F. J . Chem. Soc., Chem.
Commun. 1973, 317. (b) Davidson, P. J .; Harris, D. H.; Lappert, M. F.
J . Chem. Soc., Dalton Trans. 1976, 2268. (c) A much higher yield (95%)
synthesis of Pb{(CH(SiMe3)2}2 has also been reported in: Burton, N.
C.; Cardin, C. J .; Cardin, D. J .; Twamley, B.; Zubavichus, Y. Organo-
metallics 1995, 14, 5708. (d) The structure of Pb{CH(SiMe3)2}2 shows
that it is weakly dimerized in the solid with Pb-Pb ) 4.129 Å; data
cited in: Stu¨rmann, M.; Weidenbruch, M.; Klinkhammer, K. W.;
Lissner, F.; Marsmann, H. Organometallics 1998, 17, 4425.
(6) Kano, N.; Tokitoh, N.; Okazaki, R. J . Synth. Org. Chem. J pn.
1998, 56, 919.
(7) Weidenbruch, M. Eur. J . Inorg. Chem. 1999, 373. Stu¨rmann, M.;
Saak, W.; Marsmann, H.; Weidenbruch, M. Angew. Chem., Int. Ed.
Engl. 1999, 38, 187.
(8) Heteroleptic organolead halide derivatives with cyclopentadienyl
ligands have been known for over 20 years, see in: Holliday, A. K.;
Makin, P. H.; Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 1976,
435; J utzi, P.; Dickbreder, R.; No¨th, H. Chem. Ber. 1989, 122, 865.
(9) Eaborn, C.; Izod, K.; Hitchcock, P. B.; So¨zerli, S. E.; Smith, J . D.
J . Chem. Soc., Chem. Commun. 1995, 1829.
(10) Eaborn, C.; Hitchcock, P. B.; Smith, J . D.; So¨zerli, S. E.
Organometallics 1997, 16, 5653.
(11) Pu, L.; Power, P. P.; Boltes, I.; Herbst-Irmer, R. Organometallics
2000, 19, 352.
10.1021/om0001624 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 06/23/2000

Terphenyl-Stabilized Lead(II) Derivatives
Organometallics, Vol. 19, No. 15, 2000 2875
2 days to give 2 as yellow crystals: yield 0.91 g, 79.8%; mp
110-112 °C dec; 1H NMR (C6D6) δ 1.12 (12H, o-CH(CH3)2),
a bent, two-coordinate lead geometry and a stereo-
chemically active lead lone pair, were synthesized by
the treatment of Na[M(η5-C5H5)(CO)3]12 (M ) Cr, Mo
or W) with Pb(Br)C6H3-2,6-Trip2. The latter compound,
which was generated in situ from PbBr2 and Et2O‚
LiC6H3-2,6-Trip2, is a potentially useful transfer agent
for the “PbR” moiety. It was decided therefore to
characterize this aryl lead halide both spectroscopically
and structurally and to investigate some of its reaction
chemistry. In particular it was hoped that the presence
of the extremely large -C6H3-2,6-Trip2 substitutent13
would allow, for the first time, the isolation of Pb(II)
species with bonds to the simplest alkyl (i.e., CH3) and
aryl (i.e., C6H5) groups. The results of these investiga-
tions are now described.
3
3J HH ) 6.8 Hz; 1.21 (d, 12H, o-CH(CH3)2), J HH ) 7.2 Hz; 1.42
3
(d, 12H, p-CH(CH3)2), J HH ) 6.8 Hz; 2.76 (sept, 2H, p-
3
CH(CH3)2), J HH ) 6.8 Hz; 3.36 (sept, 4H, o-CH(CH3)2), J HH
)
3
4
6.8 Hz; 6.38 (t of t, 2H, m-C5H5N), J HH ) 6.2 Hz, J HH ) 1.6
Hz; 6.73 (t of t, 1H, p-C5H5N), J HH ) 7.8 Hz, J HH ) 1.2 Hz;
7.11 (s, 4H, m-Trip); 7.29 (tr, 1H, p-C6H3), J HH ) 7.6 Hz; 7.78
3
4
3
4
(d of d, 2H, m-C6H3), J HH ) 7.4 Hz; J HH ) 1.6 Hz; 7.98 (br,
2H, o-C5H5N); 13C{1H} NMR (C6D6) δ 23.56 (o-CH(CH3)2); 24.29
(o-CH(CH3)2); 26.39 (p-CH(CH3)2); 30.75 (o-CH(CH3)2); 34.53
(p-CH(CH3)2); 120.97 (m-Trip); 124.25 (m-C5H5N); 125.30 (p-
C6H3); 136.42 (p-C5H5N, i-Trip); 137.42 (m-C6H3); 147.32 (o-
Trip); 147.90 (p-Trip); 148.63 (o-C6H3); 149.49 (o-C5H5N). Anal.
Calcd for C41H53BrNPb: C, 58.18; H, 6.31. Found: C, 57.97;
H, 6.34. UV-vis (hexane): λmax 417 nm, ꢀ ) 1760 L M-1 cm-1
.
P b(Me)C6H3-2,6-Tr ip 2 (3). A diethyl ether solution of CH3-
MgBr (0.77 mL, 2.31 mmol) was added to a solution of 1 (1.77
g, 1.15 mmol) in diethyl ether (25 mL) at ca. 0 °C with constant
stirring. The reaction mixture, which had assumed a red color,
was stirred until the ice bath had thawed to room temperature.
The solvent was removed under reduced pressure, and the
purple residue was extracted with hexane (50 mL). After
filtering through Celite, the red solution was reduced to
incipient crystallization and stored in a ca. 4 °C refrigerator
to give 3 as red crystals: yield 1.22 g, 75.3%; mp 202-203 °C;
1H NMR (C6D6) δ 0.08 (s, 3H, CH3), 2J Pb-H ) 40 Hz; 1.14 (12H,
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were carried out
by using modified Schlenk techniques under an atmosphere
of N2 or in a Vacuum Atmospheres HE-43 drybox. All solvents
were distilled from Na/K alloy and degassed twice before use.
The lithium aryls Et2O‚LiC6H3-2,6-Trip2 and LiPh15 were
14
prepared according to literature procedures. The compounds
PbBr2, W(CO)6, t-BuLi (1.5 M in n-pentane), and CH3MgBr
(3.0 M in Et2O) were purchased commercially and used as
received. Pyridine (py) was dried by distillation from CaH2.
1H and 13C NMR data were recorded on a Bruker 300 MHz or
Varian 400 MHz instrument and referenced to the deuterated
solvent. Infrared data were recorded on a Perkin-Elmer PE-
1430 instrument. UV-vis data were recorded on a Hitachi-
1200 instrument.
3
3
o-CH(CH3)2), J HH ) 6.8 Hz; 1.18 (d, 12H, o-CH(CH3)2), J HH
) 6.8 Hz; 1.39 (d, 12H, p-CH(CH3)2), 3J HH ) 7.2 Hz; 2.77 (sept,
3
2H, p-CH(CH3)2), J HH ) 6.8 Hz; 3.35 (sept, 4H, o-CH(CH3)2),
3J HH ) 6.8 Hz; 7.18 (s, 4H, m-Trip); 7.41 (tr, 1H, p-C6H3), 3J HH
3
) 7.6 Hz; 7.76 (d, 2H, m-C6H3), J HH ) 7.2 Hz; 13C{1H} NMR
(C6D6): δ 1.438 (Pb-CH3; J Pb-C ) 248 Hz; δ 23.67 (o-CH-
(CH3)2); 24.21 (o-CH(CH3)2); 26.58 (p-CH(CH3)2); 30.86 (o-CH-
(CH3)2); 34.69 (p-CH(CH3)2); 114.70 (Pb-CH3); 121.26 (m-Trip);
124.75 (p-C6H3); 135.26 (i-Trip); 136.42 (m-C6H3); 145.60 (o-
Trip); 147.20 (p-Trip); 148.65 (o-C6H3); 256.85 (i-C6H3); 207Pb{1H}
NMR (C6D6) δ 7420. Anal. Calcd for C37H52Pb: C, 63.13; H,
7.44. Found: C, 63.69; H, 7.61. UV-vis (hexane): λmax (nm);
ꢀ (L M-1 cm-1), 466 (710), 332 (610).
{P b(Br )C6H3-2,6-Tr ip 2}2 (1). Et2O‚LiC6H3-2,6-Trip214 (2.40
g, 4.26 mmol) in diethyl ether (25 mL) was added to a
suspension of PbBr2 (1.56 g, 4.26 mmol) in diethyl ether (10
mL) at ca. 0 °C with constant stirring. The reaction mixture,
which became an orange color, was stirred at ca. 0 °C for 20
min and for a further 24 h at room temperature. The solvent
was removed under reduced pressure, and the orange residue
was extracted with hexane (30 mL). After filtering through
Celite, the orange filtrate was reduced to incipient crystal-
lization and stored in a ca. -20 °C freezer for 24 h to afford 1
as orange crystals: yield 2.09 g, 64%; mp 217-219 °C; 1H NMR
P b(t-Bu )C6H3-2,6-Tr ip 2 (4). A pentane solution of tert-
butyllithium (1.17 mL of a 1.5 M solution) was added to a
rapidly stirred solution of 1 (1.35 g, 0.88 mmol) in diethyl ether
(30 mL) with cooling to ca. -78 °C. The reaction mixture,
which had assumed a violet color, was stirred for 1 h and then
allowed to warm to room temperature. The solvents were
removed under reduced pressure, and the violet residue was
extracted with hexane (30 mL). The violet solution was
separated from the white precipitate (LiBr) by decanting. The
volume of the solution was reduced to incipient crystallization
and stored in a ca. 4 °C refrigerator to give the product 4 as
violet crystals: yield 1.07 g, 81.7%; mp 129-130 °C; 1H NMR
3
(C6D6) δ 1.07 (d, 12H, p-CH(CH3)2), J HH ) 6.6 Hz; 1.29 (d,
3
12H, o-CH(CH3)2), J HH ) 6.9 Hz; 1.34 (d, 12H, o-CH(CH3)2),
3J HH ) 6.9 Hz; 2.84 (sept, 2H, p-CH(CH3)2), J HH ) 6.9 Hz;
3
3.11 (sept, 4H, o-CH(CH3)2); 7.15 (s, 4H, m-Trip); 7.29 (tr, 1H,
3
3
p-C6H3), J HH ) 7.5 Hz; 7.97 (d, 2H, m-C6H3), J HH ) 7.5 Hz;
13C{1H} NMR (C6D6) δ 23.69 (o-CH(CH3)2); 26.43 (p-CH(CH3)2);
30.74 (o-CH(CH3)2); 34.87 (p-CH(CH3)2); 121.23 (m-Trip);
125.72 (p-C6H3); 137.07 (i-Trip); 137.33 (m-C6H3); 147.62 (o-
Trip); 148.54 (p-Trip); 148.78 (o-C6H3); 169.10 (i-C6H3); 287.88
(i-C6H3). Anal. Calcd for C72H98Br2Pb2: C, 56.24; H, 6.42.
Found: C, 56.68; H, 6.59. UV-vis (hexane): λmax 416.5 nm, ꢀ
3
(C6D6) δ 1.13 (12H, o-CH(CH3)2), J HH ) 6.6 Hz; 1.20 (d, 12H,
3
3
o-CH(CH3)2), J HH ) 6.9 Hz; 1.44 (d, 12H, p-CH(CH3)2), J HH
3
) 6.3 Hz; 2.78 (sept, 2H, p-CH(CH3)2), J HH ) 6.9 Hz; 3.35
3
(sept, 4H, o-CH(CH3)2), J HH ) 6.9 Hz; 3.75 (s, 9H, C(CH3)3);
) 1580 L M-1 cm-1
.
7.19 (s, 4H, m-Trip); 7.47 (tr, 1H, p-C6H3), 3J HH ) 7.6 Hz; 7.86
(d, 2H, m-C6H3,), J HH ) 7.5 Hz; 13C{1H} NMR (C6D6) δ 23.48
3
p y‚P b(Br )C6H3-2,6-Tr ip 2 (2). Pyridine (0.14 mL, 1.75
mmol) was added to 1 (1.04 g, 0.68 mmol) in hexane (35 mL)
at ca. 0 °C with constant stirring. The reaction mixture became
a yellow color and was stirred at ca. 0 °C for 20 min and for a
further 2 h at room temperature. The yellow solution was
separated from the small amount of white precipitate by
decanting. The volume of the yellow solution was reduced to
incipient crystallization and stored in a ca. -20 °C freezer for
(C(CH3)3), 24.20 (o-CH(CH3)2); 24.62 (o-CH(CH3)2); 27.29 (p-
CH(CH3)2); 31.16 (o-CH(CH3)2); 34.78 (p-CH(CH3)2); 121.49 (m-
Trip); 124.41 (m-C6H3); 128.16 (p-C6H3), 137.26 (i-Trip); 145.65
(p-Trip); 147.29 (o-Trip); 148.74 (o-C6H3); 171.49 (i-C6H3);
171.49 (C(CH3)3); 262.33 (i-C6H3); 207Pb{1H} NMR (C6D6) δ
7853. Anal. Calcd for C40H58Pb: C, 64.40; H, 7.84. Found: C,
65.11; H, 8.01. UV-vis (hexane): λmax 470 nm, ꢀ ) 720 L M-1
cm-1
.
(12) Braunstein, P.; Bender, R.; J ud, J . Inorg. Synth. 1989, 26, 341.
(13) Twamley, B. T.; Haubrich, S. T.; Power, P. P. Adv. Organomet.
Chem. 1999, 44, 1.
(14) Schiemenz, B.; Power, P. P. Organometallics 1996, 15, 958.
(15) Schlosser, M.; Ladenberger, V. J . Organomet. Chem. 1967, 8,
193.
P b(P h )C6H3-2,6-Tr ip 2 (5). The solution of phenyllithium
(0.139 g, 0.88 mmol) in diethyl ether (20 mL) was added to a
rapidly stirred solution of 1 (0.68 g, 0.44 mmol) in diethyl ether
(10 mL) with cooling to ca. -78 °C. The reaction mixture
became a red color and was stirred for 1 h and then allowed

2876 Organometallics, Vol. 19, No. 15, 2000
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p ou n d s 1-6
Pu et al.
1
2‚0.5C6H12
3
4
5
6
formula
fw
color, habit
cryst syst
space group
a, Å
C
72H98Pb2Br2
C44H55.5PbBrN
855.49
yellow, needle
monoclinic
P21/c
C37H52Pb
703.98
dichroic red/pink, block
orthorhombic
Pbcm
10.9737(8)
12.0562(8)
25.3639(17)
C40H58Pb
746.05
purple, block
monclinic
C2/c
C42H54Pb
766.04
red, block
monoclinic
P21/c
C44H49PbW2O8Br
1360.63
orange plate
orthorhombic
Pnma
15.2672(7)
18.6878(9)
15.4719(7)
1537.70
orange, block
monoclinic
P21/c
18.330(2)
14.184(2)
26.215(3)
91.760(10)
6812.5(14)
4
17.4582(12)
14.4136(10)
17.3971(12)
97.3830(10)
4341.4(5)
4
32.3169(17)
9.5877(5)
24.7261(13)
106.8590(10)
7332.0(7)
8
12.6017(8)
18.2376(11)
16.5121(10)
105.5330(10)
3656.3(4)
4
b, Å
c, Å
â, deg
V, Å3
3355.7(4)
4
1.393
4414.3(4)
4
2.047
Z
d
calc, Mg/m3
1.499
1.355
1.352
1.392
θ range, deg
µ, mm-1
obs data I >2σ(I)
R1
1.11-2.500
1.84-31.51
1.86-25.00
2.22-27.50
2.02-31.53
1.71-31.49
6.174
4.833
5.049
4.626
4.640
9.958
6340
10 017
2031
0.0424
0.0955
2933
7520
5604
0.0290
0.0586
0.0685
0.0475
0.0606
0.0352
wR2
0.1092
0.1149
0.1201
0.0573
to come to room temperature. Diethyl ether was removed
under reduced pressure, and the red residue was extracted
with benzene (20 mL). After filtering through Celite, the red
solution was reduced to incipient crystallization and stored
in a ca. 4 °C refrigerator to give 5 as red crystals: yield 0.47
g, 70%; mp 197 °C (dec); 207Pb{1H} NMR (C6D6) δ 6657; 1H
NMR (C6D6) δ 1.09 (12H, o-CH(CH3)2), 3J HH ) 7.2 Hz; 1.10 (d,
1 was mounted on a glass fiber using epoxy resin. Data for 1
were collected at 293 K, 2-5 at 90 K, and 6 at 93 K using a
Bruker SMART 1000 system (Mo ΚR (λ ) 0.70173 Å) radiation
and a CCD area detector). The Bruker SHELXTL 5.1 program
package17 was used for the structure solutions and refinement.
An absorption correction was applied using the program
SADABS.18 The crystal structures were solved by direct
methods and refined by full-matrix least-squares procedures.
All non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were included in the refinement at calculated
positions using a riding model included in the SHELXTL
program. An isopropyl group in 5 was subject to a disorder
which could be modeled successfully using partial occupancies
for the disordered atoms as described in the Supporting
Information. Hydrogen atoms associated with the disordered
atom sites were determined geometrically and fixed in position.
The structure of 2 contains a six-atom fragment, which was
modeled as a methylcyclopentane molecule with 50% oc-
cupancy. This six-carbon species, of formula C6H12, is a 10%
contaminant in the hexanes solvent. Anomalous electron
densities were observed in the neighborhood of the heavy atom
sites in 1-6. These were attributed to uncorrected absorption
effects. Some details of the data collection and refinement are
given in Table 1. Further details are provided in the Support-
ing Information. Selected bond distances and angles for 1-6
are listed in Table 2.
3
12H, o-CH(CH3)2), J HH ) 6.8 Hz; 1.14 (d, 12H, p-CH(CH3)2),
3
3J HH ) 6.8 Hz; 2.68 (sept, 2H, p-CH(CH3)2), J HH ) 6.8 Hz;
3
3.35 (sept, 4H, o-CH(CH3)2), J HH ) 6.8 Hz; 7.10 (s, 4H,
3
m-Trip); 7.40 (tr, 1H, p-C6H3), J HH ) 7.2 Hz; 7.67 (t, 2H,
3
3
m-Ph), J HH ) 7.6 Hz; 7.82 (d, 2H, m-C6H3), J HH ) 8.0 Hz;
8.65 (d of d, 2H, o-Ph), J HH ) 7.6 Hz, J HH ) 1.2 Hz; 13C{1H}
NMR (C6D6) δ 23.27 (o-CH(CH3)2); 24.14 (o-CH(CH3)2); 26.89
(p-CH(CH3)2); 31.15 (o-CH(CH3)2); 34.66 (p-CH(CH3)2); 121.40
(m-Trip); 124.84 (p-C6H3); 127.42 (p-Ph); 132.78 (m-Ph); 134.54
(i-Trip); 137.66 (m-C6H3); 139.71 (o-Ph); 146.11 (o-Trip); 147.63
(p-Trip); 148.95 (o-C6H3); 259.85 (i-Ph); 275.25 (i-C6H3). Anal.
Calcd for C41H54Pb: C, 65.85; H, 7.1. Found: C, 66.01; H, 7.21.
3
3
UV-vis (hexane): λmax 460 nm, ꢀ ) 350 L M-1 cm-1
.
[{W(CO)4}2(µ-Br )(µ-P bC6H3-2,6-Tr ip 2)] (6). A solution of
W(CO)6 (0.53 g, 1.15 mmol) in THF (45 mL), irradiated by UV
light for 8 h, was added to the solution 1 (0.87 g, 0.57 mmol)
in hexane (15 mL) at room temperature. The reaction mixture
became a brown color and was stirred for a further 16 h. The
solvent was then removed under reduced pressure, and the
brown residue was extracted with hexane (20 mL). After
filtering through Celite, the brown solution was concentrated
under reduced pressure to incipient crystallization and stored
in a ca. -20 °C freezer to give 6 as orange crystals: yield 0.11
Discu ssion
Th e Ha lid e Der iva tives {P b(Br )C6H3-2,6-Tr ip 2}2
(1) a n d p y‚P b(Br )C6H3-2,6-Tr ip 2 (2). The aryllead
halide compound 1 was synthesized in a straightforward
manner, and in over 60% yield, by treatment of an
diethyl ether suspension of lead(II) bromide with a
diethyl ether solution of Et2O‚LiC6H3-2,6-Trip2.14 It was
isolated as orange crystals, which were stable up to their
melting point of 217-219 °C. Lead(II) bromide was used
in preference to the other lead(II) halides since it was
found that the product 1 could be more readily dissolved
in and crystallized from hexane solvent. Both the 1H
and 13C NMR (including the ipso-carbon signal of the
C6H3 moiety) spectra of 1 are readily obtainable in C6D6,
but no 207Pb NMR resonance could be observed. It is
possible that the difficulty in detecting this signal is
associated with the large anisotropies expected for the
three diagonal components of the chemical shift tensor.
This is particularly true for 1, and to a lesser extent 2,
1
g, 7.2%; mp 183-185 °C; H NMR (C6D6) δ 1.01 (12H, o-CH-
3
3
(CH3)2), J HH ) 6.8 Hz; 1.06 (d, 12H, o-CH(CH3)2), J HH ) 6.8
3
Hz; 1.55 (d, 12H, p-CH(CH3)2), J HH ) 6.8 Hz; 2.56 (sept, 2H,
p-CH(CH3)2), 3J HH ) 6.8 Hz; 3.39 (sept, 4H, o-CH(CH3)2), 3J HH
3
) 6.8 Hz; 7.14 (s, 4H, m-Trip), 7.35 (tr, 1H, p-C6H3), J HH
)
7.6 Hz; 8.02 (d, 2H, m-C6H3), J HH ) 7.6 Hz; 13C{1H} NMR
(C6D6) δ 23.39 (o-CH(CH3)2); 24.42 (o-CH(CH3)2); 27.00 (p-CH-
(CH3)2); 31.13 (o-CH(CH3)2); 34.43 (p-CH(CH3)2); 122.62 (m-
Trip); 128.11 (p-C6H3); 132.39 (i-Trip); 138.97 (m-C6H3); 143.42
(o-Trip); 147.64 (p-Trip); 151.00 (o-C6H3); 190.43 (CO); 191.09
(CO); 193.10 (CO); 201.47 (CO); IR (Nujol mull, cm-1) ν
2050(m), 2018(s), 1978(s), 1965(sh), 1958(s), 1907(s), 1899(s),
1600(vw), 1572(s), 1360(sh), 1260(m), 1100(m), 880(w), 800(m),
720(m), 560(s), 475(vw), 425(vw), 355(m). Anal. Calcd for
3
C
44H49BrO8PbW2: C, 38.84; H, 3.63. Found: C, 38.10; H, 3.53.
UV-vis (hexane): λmax 344 nm, ꢀ ) 6050 L M-1 cm-1
.
X-r a y Cr ysta llogr a p h ic Stu d ies. The crystals were re-
moved from the Schlenk tube under a stream of N2 and
immediately covered with a layer of hydrocarbon oil. A suitable
crystal was selected, attached to a glass fiber, and immediately
placed in the low-temperature nitrogen stream.16 Compound
(17) SHELXTL version 5.1; Bruker AXS, Madison, WI, 1998.
(18) SADABS, an empirical absorption correction program part of
the SAINTPlus NT version 5.0 package; BRUKER AXS: Madison, WI,
1998.
(16) Hope, H. Prog. Inorg. Chem. 1995, 41, 1.

Terphenyl-Stabilized Lead(II) Derivatives
Organometallics, Vol. 19, No. 15, 2000 2877
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d An gles (d eg) for Com p ou n d s 1-6
1
2
3
Pb(1)-C(1)
Pb(2)-C(37)
Pb(1)-Br(1)
Pb(1)-Br(2)
Pb(2)-Br(1)
Pb(2)-Br(2)
2.329(11)
2.306(13)
2.7892(16)
3.0157(17)
2.9902(17)
2.7841(16)
85.07(4)
85.64(4)
94.83(4)
94.37(4)
95.4(3)
Pb(1)-C(1)
Pb(1)-Br(1)
Pb(1)-N(1)
C(1)-Pb(1)-Br(1)
C(1)-Pb(1)-N(1)
N(1)-Pb1)-Br(1)
C(2)-C(1)-Pb(1)
C(6)-C(1)-Pb(1)
C(2)-C(1)-C(6)
2.322(4)
2.7063(6)
2.502(4)
92.39(11)
103.81(13)
90.45(9)
130.9(3)
111.3(3)
118.5(4)
Pb(1)-C(1)
2.272(9)
2.274(15)
101.4(4)
121.9(4)
117.4(8)
Pb(1)-C(20)
C(1)-Pb(1)-C(20)
C(2)-C(1)-Pb(1)
C(2)-C(1)-(2A)
Br(1)-Pb(1)-Br(2)
Br(1)-Pb(2)-Br(2)
Pb(1)-Br(1)-Pb(2)
Pb(1)-Br(2)-Pb(2)
C(1)-Pb(1)-Br(1)
C(37)-Pb(2)-Br(2)
C(2)-C(1)-Pb(1)
C(6)-C(1)-Pb(1)
C(2)-C(1)-C(6)
98.0(3)
133.2(9)
108.6(8)
118.0(11)
109.8(9)
133.0(10)
117.1(2)
C(38)-C(37)-Pb(2)
C(42)-C(37)-Pb(2)
C(38)-C(37)-C(42)
4
5
6
Pb(1)-C(1)
2.289(11)
2.329(14)
100.5(5)
118.9(7)
122.8(8)
117.1(10)
Pb(1)-C(1)
2.321(3)
2.264(3)
95.64(11)
111.7(2)
128.2(2)
119.6(3)
123.9(2)
118.2(3)
117.4(3)
W(1)-Pb(1)
2.7517(3)
Pb(1)-C(37)
Pb(1)-C(37)
W(2)-Pb(1)
2.7423(3)
2.6341(6)
2.6534(6)
2.183(5)
C(1)-Pb(1)-C(37)
C(2)-C(1)-Pb(1)
C(6)-C(1)-Pb(1)
C(2)-C(1)-C(6)
C(1)-Pb(1)-C(37)
C(2)-C(1)-Pb(1)
C(6)-C(1)-Pb(1)
C(2)-C(1)-C(6)
C(38)-C(37)-Pb(1)
C(42)-C(37)-Pb(1)
C(42)-C(37)-C(38)
W(1)-Br(1)
W(2)-Br(1)
Pb(1)-C(1)
Br(1)-W(1)-Pb(1)
Br(1)-W(2)-Pb(1)
W(1)-Br(1)-W(2)
W(2)-Pb(1)-W(2)
108.379(15)
108.094(15)
73.350(16)
70.177(8)
where in addition to the very low local symmetry at lead,
the aryl and bromine substituents are quite different
electronically. Since large chemical shift anisotropies
result in short T1 and T2 relaxation times,19 very broad
and difficult to detect isotropic signals are often the
result. In addition, the presence of the very large
terphenyl substituent could slow the molecular tumbling
rates required to average the three anisotropic shift
components. The presence of the quadrupolar nuclei
79Br or81Br bound to the lead atom could also be a
factor in broadening of the 207Pb NMR signal.20 The
difficulty in obtaining 207Pb NMR signals for 1 and 2
is consistent with the observations of Eaborn, Smith,
and co-workers on the organolead chlorides [Pb(µ-Cl)-
{C(SiMe2Ph)3}]2,9,10 [Pb(µ-Cl){C(SiMe3)3}]3,10 and
{Pb(µ-Cl)C(SiMe3)2(SiMe2OMe)}2;10 a solution signal
was obtained only in the case of the latter species.
F igu r e 1. Thermal ellipsoidal (30%) plot of 1. H atoms
are not shown for clarity. Selected bond distances and
angles are given in Table 2.
The X-ray crystal structure of 1 (Figure 1) shows that
the molecule is dimerized through bridging of the metal
centers by the bromides. The dimeric structure of 1 thus
differs from the mononuclear structures21 observed for
Ge(Cl)C6H3-2,6-Trip2 and Sn(I)C6H3-2,6-Trip2. This is
probably a result of the reduction in steric congestion
owing to the larger size of the lead. The Pb2Br2C(1)C-
(37) array almost possesses a center of symmetry, and
the Pb2Br2 parallelogram core is essentially perfectly
planar with internal angles near 85.5° at the lead atoms
and 94.5° at the bromides. There are two pairs of Pb-
Br distances, one averaging 2.79 Å and the other near
3.00 Å. The Pb-C distances 2.329(11) and 2.306(13) Å
differ by only two standard deviations. It is difficult to
compare the Pb-Br distances in 1 with those found in
other crystal structures where the coordination number
of the Pb(II) center is much higher (generally six or
greater). For instance, an X-ray study of [NH4][Pb2Br5]22
features two bromides 2.89(5) Å distant from the lead,
two bromides at 3.16(2) Å, and four at 3.35(5) Å. On
the other hand, an electron diffraction study of PbBr2
vapor,23 where the lead is two-coordinate, afforded a
much shorter Pb-Br length of 2.60(3) Å. The latter
value is somewhat less than the sum of the metallic
radius of lead, 1.54 Å,24 and the covalent radius of
bromine, 1.14 Å.25 However, the ionic character of the
Pb-Br bond leads to the expectation of some shortening
in the bond. Although bonding to lead often shows
effects that are not normally observed in its lighter
congeners,2 it is possible to say that in 1 the shorter
(19) Poole, C. P.; Farach, H. A. Relaxation in Magnetic Resonance;
Academic Press: New York, 1971; p 75.
(20) Sebald, A.; Harris, R. K. Organometallics 1990, 9, 2096.
(21) Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics 1998,
17, 5602.
(22) Powell, H. M.; Tasker, H. S. J . Chem. Soc. 1937, 119.
(23) Lister, M. W.; Sutton, L. E. Trans Faraday Soc. 1941, 37, 406.
(24) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 257.

2878 Organometallics, Vol. 19, No. 15, 2000
Pu et al.
pyramidally coordinated (∑°Pb ) 286.65°) by the C(1)
of the aryl, the pyridine nitrogen, and a bromine. The
pyridine nitrogen lone pair is obviously coordinated
through the “empty” 6p-orbital on lead. However, the
N-C(para) vector deviates 10° from the line of the
Pb(1)-N(1) bond toward the less crowded side of the
molecule. The large size of the aryl ligand is also
reflected in the over 13° difference in the N(1)-Pb-
Br(1) ) 90.45(9)° and N(1)-Pb-C(1) ) 103.81(3)°
angles. Similar to 1, there is also a very large difference,
ca. 19°, in the external angles at the C(1) (i.e., ipso)
carbon atom, but there is very little deviation of the
Pb(1)-C(1) bond from the plane of the central ring
(angle ) 2.3°). The Pb(1)-C(1) bond length is essentially
identical to that in 1, while the Pb(1)-Br(1) bond
(2.7063(6) Å) is ca. 0.08 Å shorter than the short pair
of bridging Pb-Br distances in the dimer 1. This
contraction is consistent with the terminal nature of the
Pb-Br moiety. The Pb-N bond distance 2.502(4) Å may
be compared to the 2.59(4) or 2.60(2) Å seen in the PbBr2
complexes28 {(4-MeH4C5N)2‚PbBr2}n and {(3-MeH4C5N)2‚
PbBr2}n that feature infinite chains in which the
six-coordinate lead atoms are bridged by bromides.
In addition there are complexes29 such as {(1,10-
F igu r e 2. Thermal ellipsoidal (30%) plot of 2. H atoms
are not shown for clarity. Selected bond distances and
angles are given in Table 2.
Pb-Br distances (2.79 Å) seem to be in keeping with
the three-coordination at the metal, whereas the longer
Pb-Br distances near 3.00 Å are more consistent with
a higher coordination number. We also note that
Pb-Br distances of 2.623(1) and 2.656(7) Å were ob-
served in the sterically crowded Pb(IV) molecules
PbBr2(Tbt)2 (Tbt ) C6H2-2,4,6-{CH(SiMe3)2}3)26 and
Pb(Br)(CMe2C6H3-2,5-t-Bu2)3,27 which are close to the
2.60(3) Å observed for the vapor phase structure of
PbBr2. The longer Pb-Br distances in the dimer 1 may
suggest that dissociation might occur in solution, al-
though there is no direct evidence for this. The observa-
tion of a 0.21 Å difference in the bridging lead-halogen
phenanthroline)‚PbBr2}n (also with six-coordinate Pb2+
)
that have Pb-N distances as short as 2.521(7) Å. At
the other end of the Pb-N distance scale are the
recently reported30 complexes TMEDA‚Pb(η5-C5H5)2 and
4,4′-Me2bipyridyl‚Pb(η5-C5H5)2, which have Pb-N dis-
tances of 2.879(3) and 2.702(5) Å, which are dissociated
in solution. The longer Pb-N bonds in these complexes
reflect the higher formal eightfold coordination of lead,
if the η5-C5H5 ligand is considered to occupy three
coordination sites.
Th e Dior ga n olea d (II) Com p ou n d s P b(R)C6H3-
2,6-Tr ip 2 (R ) Me, 3; t-Bu , 4; P h , 5). The diorgano
compounds 3-5 were synthesized by the reaction of 2
with 1 equiv of CH3MgBr, Li(t-Bu), or LiPh. The
reactions proceed smoothly and in moderate yield to
afford the products as thermally robust red or purple
dichroic crystals. The stability of these derivatives is
attributable to the almost unique steric properties of
the -C6H3-2,6-Trip2 substituent, which creates a rela-
tively sheltered (by the ortho-Trip substituents) cavity
in which the Pb-C bond to the smaller organo substitu-
ent is less prone to further reaction. The high steric
protection of the -C6H3-2,6-Trip2 ligand is supported
by the fact that attempts to substitute a second -C6H3-
2,6-Trip2 group at the lead have so far failed.31 None-
theless, it is possible to synthesize the compound
Pb{C6H3-2,6-Mes2}2,32 which features somewhat less
bulky terphenyl groups. Attempts10 to synthesize Pb-
(Ph){C(SiMe2Ph)3}, via the reaction of [Pb(Cl){C(SiMe2-
Ph)3]2 with LiPh, did not afford the desired product but
a mixture of species that contained the lead-lead
bonded compound Ph3PbPbPh3.
distances in 1 is consistent with the structures of the
9,10
dimers [Pb(µ-Cl){C(SiMe2Ph)3}]2
(Pb-Cl ) 2.729(3)
10
and 2.962(3) Å) and [Pb(µ-Cl){C(SiMe3)2SiMe2OMe}]2
(Pb-Cl ) 2.680(5) and 2.868(5) Å), where the Pb-Cl
distances differ by ca. 0.24 and 0.19 Å, respectively. It
is also notable that, on the basis of the ca. 0.15 Å differ-
ence25 in the radius of chlorine and bromine, the Pb-
Br distances in 1 are ca. 0.04-0.1 Å shorter than
expected. The average Pb-C bond length in 1, ca. 2.32
Å, is also shorter than the 2.435(10) and 2.37(2) Å values
9,10
in [Pb(µ-Cl){C(SiMe2Ph)3}]2
or {Pb(µ-Cl)C(SiMe3)2-
SiMe2OMe}2.10 Taken together, the above data suggest
that -C(SiMe2Ph)3 and -C(SiMe3)2SiMe2OMe ligands
are more sterically crowding than the -C6H3-2,6-Trip2
ligand. However, there are very large differences (ca.
24°) in the external (Pb-C-C) angles at the C(1) and
C(37) ipso-carbons in 1, which suggest the presence of
some steric congestion in this molecule, although this
is not supported by other distortions such as a deviation
of the Pb(1)-C(1) bond from the plane of the central
aryl ring (angle ) 2.3°).
The addition of pyridine to a hexane solution of 1
results in cleavage of the bridged structure and the
1
formation of a 1:1 monomeric complex 2. The H and
13C NMR spectra of 2 were readily obtainable, but, as
in the case of 1, a 207Pb NMR signal was not observed.
In the X-ray crystal structure (Figure 2), the lead is
(28) Engelhardt, L. M.; Patrick, J . M.; Whitaker, C. R.; White, A.
H. Aust. J . Chem. 1987, 40, 2107.
(29) Bowmaker, G. A.; Harrowfield, J . M.; Miyamae, H.; Shand, T.
M.; Skelton, B. M.; Doudi, A. A.; White, A. H. Aust. J . Chem. 1996,
49, 1089.
(25) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Oxford,
1984; p 286.
(26) Kano, N.; Tokitoh, N.; Okazaki, R. Organometallics 1997, 16,
(30) Beswick, M. A.; Cromhout, N. L.; Harmer, C. N.; Raithby, P.
R.; Russell, C. A.; Smith, J . S. B.; Steiner, A.; Wright, D. S. Chem.
Commun. 1996, 1977.
2748.
(31) Pu, L.; Power, P. P. Unpublished work.
(32) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organo-
metallics 1997, 16, 1920.
(27) Okazaki, R.; Shibata, K.; Tokitoh, N. Tetrahedron Lett. 1991,
32, 6601.

Terphenyl-Stabilized Lead(II) Derivatives
Organometallics, Vol. 19, No. 15, 2000 2879
5.7°. The same angles in 5 differ by 16.5°, and the
torsion angle between the lead coordination plane and
the plane of the phenyl ring is 21.4°. The Pb-C(phenyl)
bond is also shorter (by ca. 0.06 Å) than the Pb-C6H3-
2,6-Trip2 bond. These features suggest the existence of
an interaction between the p-orbital on lead and the
π-electrons of the phenyl group.
The main structural and spectroscopic (207Pb NMR)
features of 3-5 may also be compared with those of the
known monomeric diorganolead(II) species.5d,32-35 These
data are presented in Table 3. For the previously
published complexes the range of Pb-C distances is
2.327(13)-2.476(14) Å. Thus, five of the six Pb-C
distances in the derivatives 3-5 fall below this range,
and the remaining distance 2.329(14) Å is essentially
identical to the shortest of the previously published
values. The C-Pb-C angles in 3-5 (none wider than
101.4(4)°) are also in the lower third of the known range
of C-Pb-C angles (Table 3). These data illustrate the
differences in the steric characteristics of the terphenyl
ligand, whose effectiveness is associated with the cre-
ation of a protected space surrounding the central atom,
whereas for most bulky alkyl or aryl groups, protection
is achieved by the occupation of the space in immediate
proximity to the central atom. In the latter case, the
steric crowding near the protected center is often
sufficient to produce lengthening of the bonds and a
widening of the angles. This may be the most likely
explanation for the longer Pb-C bond distances seen
in the previously published compounds. Such differences
however should not obscure the fact that the Pb(II)-C
bond lengths in all the compounds are generally longer
than those observed in lead(IV) organo compounds (cf.
2.19(3) Å in PbPh4,36 2.238(9) Å in PbMe437). Nonethe-
less, “long” Pb(IV)-C bonds can also be observed in very
crowded molecules such as PbBr2(Tbt)2, which has very
distorted tetrahedral coordination and Pb-C ) 2.274(6)
Å.26
F igu r e 3. Thermal ellipsoidal (30%) plot of 3. H atoms
are not shown for clarity. Selected bond distances and
angles are given in Table 2.
F igu r e 4. Thermal ellipsoidal (30%) plot of 4. H atoms
are not shown for clarity. Selected bond distances and
angles are given in Table 2.
The 207Pb NMR spectroscopic data for 3-5 display a
strong downfield shift, which is consistent with the low
coordination number.38 The values of 3-5 are well
within the range (4878-10 050 ppm) previously ob-
1
served for two-coordinate species. The H NMR spectra
of 3 and 4 also display features of interest. For instance
the lead methyl resonance in 3 is (not unexpectedly)
near 0 ppm, whereas the t-Bu resonance in 4 appears
well downfield at 3.75 ppm. Possibly, the proximity of
the t-Bu hydrogens to the aromatic rings of the ter-
phenyl ligands could produce this anomalous shift. The
coupling between the 207Pb nucleus and the Pb-CH3
hydrogens is 40 Hz. This is significantly less than the
60 Hz observed in PbMe4.39 In contrast the J (207Pb-
13C) coupling is 248 Hz, which is almost identical to the
F igu r e 5. Thermal ellipsoidal (30%) plot of 5. H atoms
are not shown for clarity. Selected bond distances and
angles are given in Table 2.
The structures of 3-5 are illustrated in Figures 3-5.
The lead centers have two-coordinate, V-shaped geom-
etries in the three molecules. It can be seen from Table
2 that the Pb-C distances fall within the narrow range
of 2.264(3)-2.329(14) Å. These distances are similar to
those reported (2.278(9)-2.294(4) Å) for the metal-
loplumbylenes (η5-C5H5)(CO)3MPbC6H3-2,6-Trip2 (M )
Cr, Mo, or W).11 The C-Pb-C angles in the two alkyl
derivatives 3 and 4 are within 0.5° of 101°, whereas the
angle in the diaryl compound 5 is ca. 5° narrower,
95.64(11)°. As in 1 and 2, the deviation of the Pb-C(1)
bonds from the plane of the C(1) aryl ring are relatively
small: 10° for 3, 8.4° for 4, and 4° for 5. However, in
contrast to what is observed in 1 and 2, the Pb-C(ipso)-
C(ortho) angles in 3 are identical (owing to the existence
of a plane of symmetry) and those of 4 differ by only
(33) Brooker, S.; Buijink, J .-K.; Edelmann, F. T. Organometallics
1991, 10, 25.
(34) Eaborn, C.; Ganicz, T.; Hitchcock, P. B.; Smith, J . D.; So¨zerli,
S. E. Organometallics 1997, 16, 5621.
(35) Kano, N.; Shibata, K.; Tokitoh, N.; Okazaki, R. Organometallics
1999, 18, 2999.
(36) Busetti, V.; Mammi, M.; Signor, A.; Del Pra, A. Inorg. Chem.
Acta 1967, 1, 424.
(37) Oyamada, T.; Iijima, T.; Kimura, M. Bull. Chem. Soc. J pn. 1971,
44, 2638.
(38) Wrackmeyer, B.; Horchler, K. Ann. Reports on NMR Spectros-
copy 1990, 22, 249.
(39) Fritz, H. P.; Scharzhous, K. J . Organomet. Chem. 1964, 1, 297.

2880 Organometallics, Vol. 19, No. 15, 2000
Pu et al.
Ta ble 3. Im p or ta n t Sp ectr oscop ic a n d Str u ctu r a l P a r a m eter s for Mon om er ic Dior ga n olea d (II) Com p ou n d s
In clu d in g 3-5
compound
Pb-C (Å)
C-Pb-C (deg)
207Pb NMR (δ)
UV-vis (nm)
33
Pb{C6H2-2,4,6-(CF3)3}2
Pb{C6H3-2,6-Mes2}2
2.361(4), 2.371(4)
2.334(12)
94.5(1)
114.5(6)
4878
32
8844a
526
34
PbC(SiMe)2SiMe2CH2CH2SiMe2C(SiMe3)2
2.397(6), 2.411(5)
2.357(4), 2.376(4)
2.344(9), 2.476(14)
2.327(13)
117.1(2)
103.04(13)
94.8
10050
6927
5067
9751
8888
8873
8884
9112
7420
7853
6657
610
490
406
610
550
560
531
5d
Pb(C6H-2,3,5-Me3-6-t-Bu)2
PbMes*(CH2CMe2C6H2-2,5-t-Bu)2
5d,b
35,b
Pb(Tbt)2
116.3(7)
Pb(Tbt)Trip35,b
Pb(Tbt){C6H2-2,4,6-(CH2SiMe3)3}35
Pb(Tbt){CH(SiMe3)2}35
c
Pb{CH(SiMe3)2}2
Pb(Me)C6H3-2,6-Trip2 (3)
Pb(t-Bu)C6H3-2,6-Trip2 (4)
Pb(Ph)C6H3-2,6-Trip2 (5)
2.272(9), 2.274(15)
2.289(11), 2.329(14)
2.321(3), 2.264(3)
101.41(4)
100.5(5)
95.64(11)
466
570
460
a
b
Newly recorded value; the value previously given in ref 32 was in error. Mes* ) C6H2-2,4,6-t-Bu3; Tbt ) C6H2-2,4,6-{CH(SiMe3)2}3.
c Data cited in ref 38, p 293.
250 Hz found for PbMe4.40 The 13C NMR spectra of 1
and 3-5 are also notable in that the chemical shift of
the carbon atoms attached directly to lead appear at
extremely low field (generally >250 ppm). The UV-vis
spectra of 3-5 are characterized by absorbances that
appear below 500 nm. These absorbances are usually
thought to arise from an n-p electronic transitions.37
Since the energy difference between these two levels is
expected to decrease with increasing the interligand
angle at lead, a longer absorption wavelength would be
expected for the wider angle. It can be seen that,
although longer wavelengths are often found to cor-
respond to the wider angle, the correlation is not a
strong one and the wavelength of the absorption is
obviously influenced by other factors as well.
Th e Br id ged P lu m bylyn e Com p lex [{W(CO)4}2-
(µ-Br )(µ-P bC6H3-2,6-Tr ip 2}] (6). This unusual complex
was synthesized in low (ca. 7%) yield by the reaction
between W(CO)5THF and 1. It was hoped that this
reaction would result in the formation of the plumbylene
complex (OC)5W{Pb(Br)C6H3-2,6-Trip2}. However 6 was
the only crystalline product isolated from the reaction
mixture. The other components of this mixture included
W(CO)6, the arene 1,3-Trip2C6H4, lead metal, and PbBr2.
Possibly, 6 results from the oxidative addition of 1 to
W(CO)5THF or W(CO)6 to yield (OC)4(Br)WPb{C6H3-2,6-
Trip2}, which may react further with W(CO)6 or
W(CO)5THF to give 6 with CO or THF elimination. An
X-ray crystal structure determination of the orange
crystals of 6 showed that the molecules (Figure 6) were
characterized by a plane of symmetry that includes the
W2PbBr core in addition to four of the carbonyls and
the ipso and para carbons of the central aryl ring of the
terphenyl group. Formally, the structure may be de-
scribed as consisting of two edge-bridged octahedra in
which the lead and bromine atoms define the common
edge, with the other apexes of the octahedra being
occupied by eight carbonyl ligands.
F igu r e 6. Thermal ellipsoidal (30%) plot of 6. H atoms
are not shown for clarity. Selected bond distances and
angles are given in Table 2.
to the metals such that each tungsten-centered unit has
seventeen electrons. An 18-electron configuration is then
attained by forming a W-W single bond. The PbC6H3-
2,6-Trip2 moiety, since it employs three electrons for
bonding to the metals, may therefore be properly
regarded as a plumbylyne moiety. This is in accord with
the geometry at lead, which is planar as crystallo-
graphically required. The trigonal geometry at lead is
very distorted, however, with an acute W(1)-Pb(1)-
W(2) angle (70.177(8)°) and two wide W-Pb-C angles
that differ by ca. 10°. The two Pb-W bonds are very
similar at 2.7517(3) and 2.7423(3) Å, and these are a
good deal shorter than the ca. 3.0 Å recently observed
for the structure of (η5-C5H5)(CO)3WPbC6H3-2,6-Trip2.11
Since tungsten and molybdenum are of almost equal
size, a structural comparison may also be made with
the metalloplumbylene THF‚Pb{Mo(η5-C5Me5)(CO)3}2,42
which also has three-coordinate lead and Pb-Mo dis-
tances of 2.989(2) and 3.019(2) Å. The Pb-C(1) distance
in 6, 2.183(5) Å, is also short, and a comparison with
the structures of 1-5 shows that it is ca. 0.1-0.14 Å
shorter than the corresponding Pb-C bonds in those
compounds. The Pb-C shortening can be attributed to
The structure resembles that found for {W(CO)4(µ-
I)}2,41 in which two iodine atoms form the common edge
of the two octahedra. It was found to have a W-W single
bond of 3.155 Å, which is very close to the 3.158(2) Å
observed in 6. In the bonding model of the iodide
derivative, each bridging ligand supplies three electrons
(40) McFarlane, W. Mol. Phys. 1967, 13, 587.
(41) Schmid, G.; Bo¨se, R. Chem. Ber. 1976, 109, 2148.
(42) Hitchcock, P. B.; Lappert, M. F.; Michalczyk, M. J . J . Chem.
Soc., Dalton Trans. 1987, 2635.

Terphenyl-Stabilized Lead(II) Derivatives
Organometallics, Vol. 19, No. 15, 2000 2881
the geometrical changes at lead, which have resulted
in a planar geometry and a change in the σ-orbital
composition in the bonding to carbon. These also imply
that there is an “empty” p-orbital at the lead, which
could interact with the tungsten d-orbitals in a back-
bonding fashion. However, the CO stretching frequen-
cies of 6 are similar to those43 found in {W(CO)4(µ-I)}2,
which suggests limited back-bonding by the plumbylyne
ligand.
Ack n ow led gm en t. We are grateful to the National
Science Foundation for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables giving full
details of the crystallographic data and data collection param-
eters, atom coordinates, bond distances, bond angles, aniso-
tropic thermal parameters, and hydrogen coordinates for 1-6.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(43) Schmid, G.; Boese, R.; Welz, E. Chem. Ber. 1975, 108, 260.
OM0001624