Terphenyl ligand stabilized lead(II) derivatives: Steric effects and lead-lead bonding in diplumbenes

Article abstract of DOI:10.1021/ic049174y

The reaction of PbBr₂ with the lithium reagents LiC ₆H₃-2,6-(C₆H₃-2,6-Pr ⁱ₂)₂ (LiArPrⁱ₂) and Et₂O·LiC₆H₃-2,6-(2,6-Pr ⁱ-4-Bu¹C₆H₂)₂ (Et ₂O·LiArPrⁱ₂Bu^t) furnished the bromide bridged organolead(II) halides {Pb(μ-Br)ArPrⁱ ₂}₂ (1) and {Pb-(μ-Br)ArPrⁱ ₂Bu^t}₂ (2) as orange crystals. Treatment of 1 with a stoichiometric amount of methylmagnesium bromide resulted in the "diplumbene" Prⁱ₂Ar(Me)PbPb(Me)ArPr ⁱ₂ (3). The addition of 1 equiv of 4-tert- butylphenylmagnesium bromide to 1 afforded the feebly associated, Pb-Pb bonded species {Pb(C₆H₄-4-Bu^t)ArPrⁱ ₂}₂ (4), whereas the corresponding reaction of tert-butylmagnesium chloride and 1 afforded the monomer Pb(Bu ^t)ArPrⁱ₂ (5). The reaction of the more crowded aryl lead(II) bromide {Pb(μ-Br)ArPrⁱ₃}₂ (Ar* = C₆H₃-2,6(C₆H₂-2,4,6- Prⁱ₃)₂) with 4-isopropylbenzylmagnesium bromide or LiSi(SiMe₃)₃ yielded the monomers 6, [Pb(CH ₂C₆H₄-4-Prⁱ)ArPrⁱ ₃], or 7, [Pb(Si(SiMe₃)₃)-ArPrⁱ ₃]. All compounds were characterized with use of X-ray crystallography, ¹H, ¹³C, and ²⁰⁷Pb NMR (3-7), and UV-vis spectroscopy. The dimeric Pb-Pb bonded (Pb-Pb = 3.1601(6) A) structure of 3 may be contrasted with the previously reported monomeric structure of Pb(Me)ArPrⁱ₃, which differs from 3 only in that it has para Prⁱ substituents on the flanking aryl rings. The presence of these groups is sufficient to prevent the weak Pb-Pb bonding seen in 3. The dimer 4 displays a Pb-Pb distance of 3.947(1) A, which indicates a very weak lead-lead interaction, and it is possible that this close approach could be caused by packing effects. The monomeric structures of 6 and 7 are attributable to steric effects and, in particular, to the large size of ArPrⁱ₃.

Full text of DOI:10.1021/ic049174y

Inorg. Chem. 2004, 43, 7346−7352
Terphenyl Ligand Stabilized Lead(II) Derivatives: Steric Effects and
Lead Lead Bonding in Diplumbenes
−
Shirley Hino, Marilyn Olmstead, Andrew D. Phillips, Robert J. Wright, and Philip P. Power*
Department of Chemistry, UniVersity of California, DaVis, One Shields AVenue,
DaVis, California 95616
Received June 24, 2004
The reaction of PbBr2 with the lithium reagents LiC6H3-2,6-(C6H3-2,6-Pri2)2 (LiArPri2) and Et2O
‚
LiC6H3-2,6-(2,6-Pri-
-Br)ArPri2
(1) and Pb-
} (2) as orange crystals. Treatment of 1 with a stoichiometric amount of methylmagnesium bromide
2
4-ButC6H2)2 (Et2O
-Br)ArPri2But
‚
LiArPri2But) furnished the bromide bridged organolead(II) halides
{Pb(
µ
}
2
{
(
µ
resulted in the “diplumbene” Pri2Ar(Me)PbPb(Me)ArPri2 (3). The addition of 1 equiv of 4-tert-butylphenylmagnesium
bromide to 1 afforded the feebly associated, Pb Pb bonded species (4), whereas the
Pb(C6H4-4-But)ArPri2
corresponding reaction of tert-butylmagnesium chloride and 1 afforded the monomer Pb(But)ArPri2 (5). The reaction
of the more crowded aryl lead(II) bromide Pb( (Ar*
-Br)ArPri3 C6H3-2,6(C6H2-2,4,6-Pri3)2) with 4-isopropyl-
benzylmagnesium bromide or LiSi(SiMe3)3 yielded the monomers 6, [Pb(CH2C6H4-4-Pri)ArPri3], or 7, [Pb(Si(SiMe3)3)-
ArPri3]. All compounds were characterized with use of X-ray crystallography, 1H, 13C, and 207Pb NMR (3
7), and
UV vis spectroscopy. The dimeric Pb Pb bonded (Pb Pb 3.1601(6) Å) structure of 3 may be contrasted with
the previously reported monomeric structure of Pb(Me)ArPri3, which differs from 3 only in that it has para Pri
substituents on the flanking aryl rings. The presence of these groups is sufficient to prevent the weak Pb Pb
bonding seen in 3. The dimer 4 displays a Pb Pb distance of 3.947(1) Å, which indicates a very weak lead lead
−
{
}
2
{
µ
}
2
)
−
−
−
−
)
−
−
−
interaction, and it is possible that this close approach could be caused by packing effects. The monomeric structures
of 6 and 7 are attributable to steric effects and, in particular, to the large size of ArPri3.
Introduction
bonded dimers, R2PbPbR2,8,9 or as a trimer (PbR2)3,10 which
features a unique Pb3 ring. The lead-lead bonding in the
“diplumbene” dimers, R2PbPbR2, is of considerable relevance
to the debate on multiple bonding in the heavier main group
Since their discovery in the 1970s, diorganolead(II)
compounds, PbR2,1 (R ) variety of bulky groups) have
received less attention than the corresponding silicon,2,3
germanium,3-6 and tin6-8 species. Currently, ca. 40 examples
are known. They exist mainly as PbR2, monomers,6,8 weakly
(4) Tokitoh, N.; Kishikawa, K.; Okazaki, R.; Sasamori, T.; Nakata, N.;
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Barrau, J.; Rima, G. Coord. Chem. ReV. 1998, 178-180, 593.
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and Lead Compounds; Rappoport, Z., Ed.; Wiley: Chichester, 2002;
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of Organic Germanium, Tin and Lead Compounds; Rappoport, Z.,
Ed.; Wiley: Chichester, 2002; Vol. 2, Part 1, Chapter 13. (c)
Weidenbruch, M. Main Group Met. Chem. 2001, 24, 621-631.
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* To whom correspondence should be addressed. E-mail: pppower@
ucdavis.edu.
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7346 Inorganic Chemistry, Vol. 43, No. 23, 2004
10.1021/ic049174y CCC: $27.50
© 2004 American Chemical Society
Published on Web 10/09/2004

Terphenyl Ligand Stabilized Lead(II) DeriWatiWes
elements, since they comprise, along with the neighboring
dibismuthenes11 (RBidBiR), the heaviest homonuclear mul-
tiple bonds. However, the divalent lead compounds differ
from their bismuth counterparts in that they generally
dissociate in solution according to the following equilibrium:
Experimental Section
General Procedures. All manipulations were carried out by
using modified Schlenk techniques under an argon atmosphere or
in a Vacuum Atmospheres HE-43 drybox. All solvents were
distilled from Na/K alloy and degassed twice before use. The
lithium aryls and silyls, LiArPri2,16 Pri3ArLi‚OEt2,16 ButPri2ArLi‚
OEt2,17 and LiSi(SiMe3)3,18 were prepared according to literature
procedures. The compounds PbBr2, CH3MgBr (3.0 M in Et2O), and
ButMgCl (20 wt % in THF) were purchased commercially and used
as received. 4-Pri-C6H4-CH2MgBr and 4-But-C6H4MgBr were
freshly prepared prior to use. H, 13C, and 207Pb NMR data were
1
recorded on a Varian 300 MHz or Varian 400 MHz instrument
and referenced to the deuterated solvent and 1 M Pb(NO3)2 in
D2O.19
Furthermore, the observed lead-lead bond distances8,9
(2.903-3.527 Å) are generally longer than single bonds in
tetravalent diplumbanes, R3PbPbR3, which range from ca.
2.84 to 2.97 Å.12 Their tendency to dissociate and the long
Pb-Pb distances indicate weak metal-metal bonding. This
is a consequence of the requirement to use very stable 6s
electrons in bonding if a full fledged Pb-Pb double bond is
to be observed. We have previously shown that terphenyls
are useful ligands for the stabilization of a variety of low
valent and multiply bonded group 14 species.13 In the case
of lead, simple monomers of formula Pb(R)ArPri3 (R ) Me,
Ph, But; ArPri3 ) -C6H3-2,6-(2,4,6-C6H2-Pri3)2)14 have been
prepared and characterized. Also, the ArPri3 ligand has been
used in the isolation of a “diplumbyne”,15 Pri3ArPbPbArPri3,
which has a long single Pb-Pb 3.1881(1) Å bond rather than
a triple one. The stabilization of these molecules results from
the protecting character of the ArPri3 ligand (see graphic),
which carries flanking aryl rings that have isopropyl sub-
stituents at the ortho and para positions. We now show that
elimination of the para substituents of the flanking rings, to
give the slightly less crowded ligand ArPri2 (ArPri2 ) -C6H3-
2,6(2,6-C6H3-Pri2)2), enables a dimeric diplumbene com-
pound Pri2Ar(Me)PbPb(Me)ArPri2 to be observed. In addi-
tion, the effects of altering the coligands on the structure
and spectroscopy of the compounds are described.
{Pb(µ-Br)ArPri2}2, 1. The lithium aryl LiArPri2 (4.805 g, 11.88
mmol) was dissolved in diethyl ether (45 mL), and the solution
was added dropwise over 40 min to a suspension of PbBr2 (4.73 g,
12.88 mmol) in diethyl ether (10 mL) with cooling in an ice bath.
The solution was allowed to warm to room temperature and stirred
overnight. The diethyl ether was removed under reduced pressure,
and the orange solid was extracted with toluene (100 mL) and
filtered through Celite. The orange filtrate was concentrated to
incipient crystallization (ca. 20 mL) and stored in a ca. -20 °C
freezer to afford 1 as orange crystals. Yield: 5.70 g, 70%. Mp:
201-206 °C. Anal. Calcd for C30H3BrPb: C, 52.62; H, 5.45.
Found: C, 51.88, H, 5.52. 1H NMR (C6D6): δ 1.02 (d, 12H, o-CH-
3
3
(CH3)2) JHH ) 6.60 Hz; 1.34 (d, 12H, o-CH(CH3)2) JHH ) 6.90
3
Hz; 3.09 (sept, 4H, o-CH(CH3)2) JHH ) 6.90 Hz; 7.13 (d, 4H,
m-C6H3Pri2) 3JHH ) 2.10 Hz; 7.22 (t, 2H, p-C6H3Pri2) 3JHH ) 6.00
3
Hz; 7.28 (t, 1H, p-C6H3) JHH ) 6.00 Hz; 7.91 (d, 2H, m-C6H3)
3JHH ) 4.80 Hz. 13C{1H} NMR (C6D6): δ 23.74 (o-CH(CH3)2);
26.28 (o-CH(CH3)2); 30.77 (o-CH(CH3)2); 123.52 (m-C6H3Pri2);
125.59 (p-C6H3); 138.80 (i-C6H3Pri2); 145.63 (p-C6H3Pri2); 147.80
(o-C6H3Pri2); 147.85 (o-C6H3); 286.77 (i-C6H3). UV-vis (hex-
ane): λmax 416.0 nm, ꢀ 740 M-1 cm-1
.
{Pb(µ-Br)ArPri2But}2, 2. In a similar manner, the reagent
ArPri2‚OEt2 (1.35 g, 2.28 mmol) was reacted with PbBr2 (1.20 g,
3.25 mmol). Workup, as described for 1, afforded 2 as orange
crystals. Yield: 1.00 g, 55%. Mp: 250-256 °C. 1H NMR (C6D6):
δ 1.11 (d, 12H, o-CH(CH3)2) 3JHH ) 6.80 Hz; 1.37 (d, 12H, o-CH-
3
(CH3)2) JHH ) 6.80 Hz; 1.38 (s, 18H, C(CH3)3); 3.16 (sept, 4H,
o-CH(CH3)2) 3JHH ) 6.80 Hz; 7.32 (s, 1H, p-C6H3)3JHH ) 7.2 Hz;
7.36 (s, 4H, m-C6H2Pri2But); 8.03 (d, 2H, m-C6H3) 3JHH ) 7.2 Hz.
13C{1H} NMR (C6D6): δ 23.79 (o-CH(CH3)2); 26.52 (o-CH(CH3)2);
30.93 (o-CH(CH3)2); 31.74 (C(CH3)3); 35.10 (C(CH3)3); 119.20 (m-
C6H2Pri2But); 120.04 (m-C6H3); 129.26 (p-C6H2Pri2But); 137.37 (i-
(16) (a) Schiemenz, B.; Power, P. P. Angew. Chem., Int. Ed. 1996, 35,
2150. (b) Schiemenz, B.; Power, P. P. Organometallics 1996, 15, 958.
(17) Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P. J. Am.
Chem. Soc. 2003, 125, 2667.
(18) (a) Gilman, H.; Smith, C. L. J. Organomet. Chem. 1967, 8, 245. (b)
Gutekunst, G.; Brook, A. G. J. Organomet. Chem. 1982, 225, 1. (c)
Heine, A.; Herbst-Irmer, R.; Sheldrick, G. M.; Stalke, D. Inorg. Chem.
1993, 32, 2694.
(11) (a) Tokitoh, N.; Arai, Y.; Sasamori, T.; Okazaki, R.; Nagase, S.;
Uekusa, H.; Ohashi, Y. J. Am. Chem. Soc. 1998, 120, 433. (b) Tokitoh,
N.; Arai, Y.; Okazaki, R.; Nagase, S. Science 1997, 277, 78.
(12) (a) Mallela, S. P.; Geanangel, R. A. Inorg. Chem. 1994, 33, 6357. (b)
Whittaker, S. M.; Cervantes-Lee, F.; Pannell, K. H. Inorg. Chem. 1994,
33, 6406-8. (c) Mallela, S. P.; Myrczek, J.; Bernal, I.; Geanangel, R.
A. J. Chem. Soc., Dalton Trans. 1993, 19, 2891. (d) Shibata, K.;
Tokitoh, N.; Okazaki, R. Tetrahedron Lett. 1993, 34, 1499. (e)
Okazaki, R.; Shibata, K.; Tokitoh, N. Tetrahedron Lett. 1991, 32, 6601.
(f) Kleiner, N.; Draeger, M. Polyplumbanes. I. J. Organomet. Chem.
1985, 293, 323.
(13) (a) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV. Organomet. Chem.
1999, 44, 1-65. (b) Clyburne, J. A. C.; McMullen, N. Coord. Chem.
ReV. 2000, 210, 73-99.
(14) Pu, L.; Twamley, B.; Power, P. P. Organometallics 2000, 19, 2874.
(15) Pu, L.; Twamley, B.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 3524.
(19) (a) The 207Pb NMR spectra of 3-7 in C6D6 were externally referenced
to Pb(NO3)2. The 207Pb chemical shift was converted to the Me4Pb
standard by adding 2961 ppm to the value obtained using Pb(NO3)2.
Thus, the 207Pb chemical shifts for 3, 4, 5, 6, and 7 are 5777, 4314,
5296, 5589, and 7784 relative to Pb(NO3)2, but are 8738, 7275, 8257,
8550, and 10745 relative to PbMe4. The data given in the Experimental
Section and Table 3 have been corrected to refer to PbMe4. (b)
Marsmann, H. C. In Chemistry of Organic Germanium, Tin and Lead
Compounds; Rappoport, Z., Ed.; Wiley: Chichester, 2002; Vol. 2,
Part 1, Chapter 6. (c) Wrackmeyer, B.; Horchler, K. Annu. Rep. NMR
Spectrosc. 1989, 22, 249.
Inorganic Chemistry, Vol. 43, No. 23, 2004 7347

Hino et al.
C6H2Pri2But); 146.38 (o-C6H3); 148.61 (o-C6H2Pri2But); 150.75 (p-
173.71 (o-C6H3); 262.70 (i-C6H3). 207Pb{1H} NMR (C6D6)}: 8257.
UV-vis (hexane): λmax 581.0 nm, ꢀ 740 M-1 cm-1
.
C6H3); 289.92 (i-C6H3). UV-vis (hexane): λmax 417.0 nm, ꢀ 760
M-1 cm-1
.
Pb(CH2C6H4-4-Pri)ArPri3, 6. Compound 6 was synthesized in
a manner similar to 4 with use of a freshly prepared 4-isopropyl-
benzylmagnesium bromide solution (5.75 mL, 0.189 M in THF)
and {Pb(µ-Br)ArPri3}2 (0.808 g, 0.525 mmol, 20 mL Et2O). The
reaction mixture became a deep purple color. The mixture was
allowed to warm to room temperature and stirred for 8 h. The
volatile solvent was removed under reduced pressure, and the
remaining residue was extracted with hexanes and filtered through
Celite. The solvent volume was reduced to incipient crystallization
and cooled in a ca. -20 °C freezer to afford 6 as dark red crystals.
Yield: 0.381 g, 46.5%. Mp: 176-178 °C. Anal. Calcd for C46H62-
Pb; C, 67.20; H, 760. Found: C, 67.91; H, 7.25. 1H NMR (C6D6):
δ 1.13 (d, 12H, p-CH(CH3)2) 3JHH ) 6.80 Hz; 1.16 (d, 6H, -CH2-
(C6H4)-CH(CH3)2) 3JHH ) 6.40 Hz; 1.26 (d, 12H, o-CH(CH3)2) 3JHH
{Pb(CH3)ArPri2}2, 3. Compound 1 (2.19 g, 0.80 mmol) was
dissolved in diethyl ether (45 mL) and cooled to ca. -30 °C. CH3-
MgBr (1.17 mL, 3.0 M in Et2O) was added via syringe. The solution
was allowed to warm to room temperature and stirred for 3 h, during
which time the solution became deep red. The diethyl ether was
removed under reduced pressure, and the red solid was extracted
with hexanes (60 mL) and filtered through Celite. The filtrate was
placed in a ca. -20 °C freezer. Dichroic, red-green crystals of 2
were obtained upon storage for 2 days. Yield: 0.64 g, 65%. Mp:
210-214 °C. Anal. Calcd for C31H40Pb: C, 60.01; H, 6.51.
Found: C, 60.81; H, 6.92. 1H NMR (C6D6): δ 0.10 (s, 3H, CH3);
3
1.08 (d, 12H, o-CH(CH3)2) JHH ) 6.90 Hz; 1.31 (d, 12H, o-CH-
(CH3)2) 3JHH ) 6.90 Hz; 3.30 (sept, 4H, o-CH(CH3)2) 3JHH ) 6.90
3
Hz; 7.13 (d, 4H, m-C6H3Pri2) JHH ) 6.75 Hz; 7.20 (t, 2H,
3
) 6.80 Hz; 1.38 (d, 12H, o-CH(CH3)2) JHH ) 6.80 Hz; 1.55 (s,
p-C6H3Pri2) 3JHH ) 6.75 Hz; 7.44 (t, 1H, p-C6H3) 3JHH ) 7.50 Hz;
3
2H, -CH2-(C6H4)-CH(CH3)2); 2.84 (sept, 2H, p-CH(CH3)2) JHH
3
7.75 (d, 2H, m-C6H3) JHH ) 7.20 Hz. 13C{1H} NMR (C6D6): δ
) 6.80; 2.91 (sept, 2H, -CH2-(C6H4)-CH(CH3)2) 3JHH ) 6.40; 3.33
1.59 (Pb-CH3); 23.48 (o-CH(CH3)2); 26.48 (o-CH(CH3)2); 30.73
(o-CH(CH3)2); 123.41 (m-C6H3Pri2); 125.70 (p-C6H3); 128.51 (o-
C6H3); 136.22 (i-C6H3Pri2); 137.29 (m-C6H3); 145.46 (o-C6H3Pri2);
147.10 (p-C6H3Pri2); 256.41 (i-C6H3). 207Pb{1H} NMR (C6D6): δ
8738. UV-vis (hexane): λmax 468.0 nm, ꢀ 3180 M-1cm-1; 343
3
(sept, 4H, o-CH(CH3)2) JHH ) 6.80 Hz; 6.02 (d, 2H, m-(C6H4)-
CH(CH3)2) 3JHH ) 8.40 Hz; 7.17 (d, 2H, o-(C6H4)-CH(CH3)2) 3JHH
) 8.40 Hz; 7.23 (s, 4H, m-C6H2Pri3); 7.44 (t, 1H, p-C6H3) 3JHH
)
7.60 Hz; 7.44 (d, 2H, m-C6H3) JHH ) 7.60 Hz. 13C{1H} NMR
(C6D6): δ 1.37 (CH2); 23.68 (o-CH(CH3)2); 24.41 (o-CH(CH3)2);
24.56 (CH2(C6H4)CH(CH3)2); 26.57 (p-CH(CH3)2); 30.88 (o-CH-
(CH3)2); 33.03 ((C6H4)CH(CH3)2); 34.780 (p-CH(CH3)2); 120.76
(o-C6H4); 121.59 (m-C6H2Pri3); 124.96 (o-C6H2Pri3); 125.05 (m-
C6H4); 128.75 (p-C6H3); 135.66 (i-C6H2Pri3); 135.95 (i-C6H4);
136.93 (m-C6H3); 145.11 (p-C6H4); 145.86 (o-C6H3); 147.20 (p-
C6H2Pri3); 263.68 (i-C6H3). 207Pb{1H} NMR (C6D6)}: 8550. UV-
vis (hexane): λmax 556.0 nm, ꢀ 860 M-1 cm-1; 391.0 nm, ꢀ 710
3
nm, ꢀ 870 M-1 cm-1
.
Pb(C6H4-4-But)ArPri2, 4. A freshly prepared solution of 4-tert-
butyl phenylmagnesium bromide (2.20 mL, 1.18 mmol, 0.54 M in
THF) was added to a rapidly stirred solution of 1 (0.727 g, 0.53
mmol) in THF (40 mL) with cooling to ca. 0 °C in an ice bath.
The reaction mixture became a red color and was allowed to warm
to room temperature and stirred overnight. The THF was removed
under reduced pressure and extracted with toluene (50 mL). The
solution was filtered through Celite, concentrated, and stored in a
ca. -20 °C freezer to give orange crystals of 4. Yield: 0.548, 70%.
Mp: 100-102 °C. 1H NMR (C6D6): δ 1.082 (d, 12H, o-CH(CH3)2)
3JHH ) 6.90 Hz; 1.09 (d, 12H, o-CH(CH3)2) 3JHH ) 6.90 Hz; 1.25
M-1 cm-1
.
Pb{Si(SiMe3)3}ArPri3, 7. {Pb(µ-Br)ArPri3}2 (0.769 g, 0.500
mmol, 25 mL Et2O) was cooled to -78 °C and added to a solution
of Li{Si(SiMe3)3} (0.463 g, 1 mmol, 10 mL Et2O). The mixture
was allowed to warm to room temperature and stirred overnight.
The volatile solvent was removed under reduced pressure, and the
remaining residue was extracted with hexanes (50 mL) and filtered
through Celite. The solvent volume was reduced to incipient
crystallization to afford teal crystals of 7. Yield: 0.52 g, 55.5%.
Mp: 120-122 °C. 1H NMR (C6D6): δ 0.228 (Si(Si(CH3)3); 1.111
(d, 12H, o-CH(CH3)2) 3JHH ) 6.80 Hz; 1.234 (d, 12H, o-CH(CH3)2)
3JHH ) 6.80 Hz; 1.418 (d, 12H, p-CH(CH3)2) 3JHH ) 6.80 Hz; 2.778
(sept, 2H, p-CH(CH3)2) 3JHH ) 6.80; 3.308 (sept., 4H, o-CH(CH3)2)
3JHH ) 6.80 Hz; 7.074 (s, 4H, m-C6H2Pri3); 7.315 (t, 1H, p-C6H3)
3
(s, 9H, C(CH3)3); 3.36 (sept, 4H, o-CH(CH3)2) JHH ) 6.90 Hz;
7.06 (d, 4H, m-C6H3Pri2) 3JHH ) 6.50 Hz; 7.17 (t, 2H, p-C6H3Pri2)
3JHH ) 6.50 Hz; 7.47 (t, 1H, p-C6H3) 3JHH ) 7.80 Hz; 7.76 (d, 2H,
3
3
o-C6H4) JHH ) 8.10 Hz; 7.89 (d, 2H, m-C6H3) JHH ) 7.80 Hz;
8.78 (d, 2H, m-C6H4) JHH ) 8.10 Hz. 13C{1H} NMR (C6D6): δ
3
1.37 (C(CH3)3); 23.13 (o-CH(CH3)2); 26.83 (o-CH(CH3)2); 31.02
(o-CH(CH3)2); 31.42 (C(CH3)3); 123.49 (m-C6H3Pri2); 124.74 (p-
C6H3Pri2); 128.83 (o-C6H3); 129.80 (o-C6H4But); 136.54 (i-
C6H3Pri2); 137.52 (m-C6H4But); 145.93 (o-C6H3Pri2); 147.49 (p-
C6H3Pri2); 150.17 (p-C6H4But); 260.26 (i-C6H4But); 276.16 (i-C6H3).
207Pb{1H} NMR (C6D6): 7275. UV-vis (hexane): λmax 462 nm, ꢀ
3
3JHH ) 7.50 Hz; 7.769 (d, 2H, m-C6H3) JHH ) 7.50 Hz. 13C{1H}
1020 M-1 cm-1
.
NMR (C6D6): δ 8.359 (Si(SiCH3)3); 24.448 (o-CH(CH3)2); 24.757
(o-CH(CH3)2); 26.525 (p-CH(CH3)2); 31.416 (o-CH(CH3)2); 34.755
(p-CH(CH3)2); 120.723 (m-C6H2Pri3); 122.210 (o-C6H2Pri3); 128.315
(p-C6H3); 134.348 (i-C6H2Pri3); 139.424 (m-C6H3); 146.990 (p-
C6H3); 147.362 (o-C6H3); 148.610 (p-C6H2Pri3); 263.68 (i-C6H3).
29Si NMR (C6D6): δ 3.89 (Si(SiMe3)3; 185.32 (Si(SiMe3)3). 207Pb-
{1H} NMR (C6D6): δ 10745. IR (Nujol): ν˜ 1605 w, 1565 vw,
1365 w, 1240 m, 945 vw, 830 vs, 720 w, 680 m, 615 m, 245m.
UV-vis (hexane): λmax 725 nm, ꢀ 260 M-1 cm-1; 415 nm, ꢀ 270
Pb(But)ArPri2, 5. In a manner similar to 3, a THF solution of
ButMgCl (0.79 mL, 1.25 mmol, 20 wt % in THF) was added to a
solution of 1 (0.717 g, 0.26 mmol) in diethyl ether (25 mL) at ca.
0 °C with constant stirring. Workup was as described for 3 and
afforded 5 as dark purple crystals. Yield: 0.434 g, 63%. Mp: 115-
118 °C. Anal. Calcd for C34H46Pb: C, 61.69; H, 7.01. Found: C,
1
61.73; H, 7.47. H NMR (C6D6): δ 1.064 (d, 12H, o-CH(CH3)2)
3JHH ) 6.90 Hz; 1.365 (d, 12H, o-CH(CH3)2) 3JHH ) 6.90 Hz; 3.263
3
(sept, 4H, o-CH(CH3)2) JHH ) 6.90 Hz; 3.831 (s, 9H, C(CH3)3;
M-1 cm-1
.
7.133 (d, 4H, m-C6H3Pri2) 3JHH ) 3.90 Hz; 7.182 (t, 4H, p-C6H3Pri2)
3
3JHH ) 3.90 Hz; 7.441(t, 1H, p-C6H3) JHH ) 7.80 Hz; 7.825 (d,
Crystallographic Studies. Crystals of 1-7 were covered with
hydrocarbon oil under a rapid flow of argon, mounted on a glass
fiber attached to a copper pin, and placed in a N2 cold stream on
the diffractometer. X-ray data were collected on a Bruker SMART
1000 diffractometer at 90(2) K with use of Mo KR radiation (λ )
2H, m-C6H3) 3JHH ) 7.80 Hz. 13C{1H} NMR (C6D6): δ 23.44 (o-
CH(CH3)2); 24.73 (C(CH3)3); 26.16 (o-CH(CH3)2); 31.05 (o-CH-
(CH3)2); 123.68 (m-C6H3Pri2); 124.40 (p-C6H3); 137.24 (m-C6H3);
137.89 (i-C6H3Pri2); 145.49 (o-C6H3Pri2); 147.30 (p-C6H3Pri2);
7348 Inorganic Chemistry, Vol. 43, No. 23, 2004

Terphenyl Ligand Stabilized Lead(II) DeriWatiWes
Table 1. Crystallographic Data for Compounds 1-7
1
2‚2PhMe
3
4‚0.25n-hexane
5
6
7‚0.5n-hexane
formula
fw
color, habit
C60H74Br2Pb2
1369.40
orange, prism
C90H122Br2Pb2
1778.08
yellow, needles
C62H80Pb2
1239.64
dichroic
pink-green, blocks
orthorhombic
Pbca
15.668(2)
17.285(2)
20.011(3)
90.0
90.0
90.0
5419.4(12)
4
1.519
C41.5H53.5Pb
759.53
red, needles
C34H46Pb
661.90
royal blue,
needles
monoclinic
P21/n
9.666(2)
9.567(2)
32.913(7)
90.0
C46H62Pb
822.15
red, needles
C48H83PbSi4
979.69
light blue,
blocks
monoclinic
P21/c
19.6824(12)
15.9100(8)
16.9291(10)
90.0
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
monoclinic
P21/n
13.3164(2)
14.1792(2)
14.6144(2)
90.0
97.538(8)
90.0
2735.6(6)
2
triclinic
P1h
triclinic
P1h
monoclinic
P21/n
8.0428(5)
18.6486
27.0344
90.0
96.516(3)
90.0
4028.6(5)
4
14.230(2)
14.791(3)
20.433(4)
100.245(7)
94.306(6)
97.848(7)
4170.8(13)
2
13.477(3)
16.148(3)
19.017(4)
105.856(3)
106.890(3)
101.503(3)
3630.4(13)
4
95.306(4)
90.0
3030.6(11)
4
101.041(3)
90.0
5203.2(5)
4
Z
d
calc, Mg/m3
1.662
1.416
1.389
1.451
1.356
1.251
θ range, deg
1.95-26.00
1.42-27.5
2.03-25.25
1.80-25.35
2.30-30.00
1.33-27.5
1.77-25.25
µ, mm-1
7.643
5.031
6.241
4.673
5.586
4.217
3.363
obsd data I > 2σ(I)
R1 (obsd data)
wR2 (all data)
4780
0.0209
0.0560
13702
0.0343
0.0869
2550
0.0321
0.0987
9825
0.0385
0.0997
5618
0.0595
0.1300
7757
0.0276
0.0677
7625
0.0331
0.0644
0.71073 Å). Absorption corrections were applied using SADABS.20
The structures were solved with use of direct methods or the
Patterson option in SHELXS21 and refined by the full-matrix least-
squares procedure in SHELXL.21 All non-hydrogen atoms were
refined anisotropically, while hydrogens were placed at calculated
positions and included in the refinement by using a riding model.
Some details of the data collection and refinement are given in
Table 1. Further details are in the Supporting Information.
{Pb(µ-Cl)C(SiMe3)2(SiMe2OMe)}2, [Pb(µ-Cl){C(SiMe3-
Ph)3}2], and [Pb(µ-Cl){C(SiMe3)3}]3 as well as our previous
work on the related organolead bromides {Pb(µ-Br)ArPri3}2
14
and ArPri3Pb(py)Br.14 The reactions of compound 2 were
not further pursued due to the tendency of the products to
display crystallographic problems and the fact the bulky
ArPri3But ligand was unlikely to permit a Pb-Pb bond to
be observed.
Results and Discussion
The plumbylene dimer, 3, was synthesized by reaction of
1 with 1 equiv of MeMgBr. The reaction proceeded smoothly
to give a moderate yield of the product as thermally robust,
red crystals. The 207Pb NMR spectrum for 3 displayed a
signal at 8738 ppm, which is very similar to that reported
(8750 ppm) for Pb(Me)ArPri314 for which a monomeric
structure has been already established. This indicates that
dissociation to monomers is essentially complete in solution
at room temperature.23 In addition, the UV-vis spectrum of
3 displayed absorption maxima at 343 and 468 nm, and these
values are very similar to those of Pb(Me)ArPri3, which has
maxima at 332 and 466 nm.
Synthesis and Spectroscopy. The aryl lead halides, {Pb-
(µ-Br)ArPri2}2 (1), and the related species {Pb(µ-Br)Ar Pri2-
But}2 (2) were synthesized by treating a diethyl ether
suspension of lead(II) bromide with a diethyl ether solution
of a stoichiometric quantity of ArPri2Li or ButPri2ArLi‚OEt2
(eq 1).
2Pri2ArLi
or
{Pb(µ-Br)ArPri2)2 1
or
{Pb(µ-Br)ArPri2But)2 2
(1)
Et2O
+ 2PbBr2
'
-2LiBr
2BuPri2ArLi‚OEt2
Orange crystals of 1 or 2 were isolated in good yield, and
these were stable up to their melting points of 201 or 256
°C, respectively. Both the 1H and 13C NMR spectra of 1 and
2 were easily obtained in C6D6, but no 207Pb NMR signal
could be observed. It is possible that the difficulty in
detecting this signal is associated with the large anisotropies
expected for the components of the chemical shift tensor.
Also, the presence of the quadrupolar nuclei 79Br and 81Br
linked to the lead atom could be a factor in broadening the
207Pb NMR signal beyond the limit of observation. The
difficulty associated with obtaining a 207Pb NMR signal for
1 and 2 is consistent with the previous reports of Eaborn,
Smith, and co-workers22 on the organolead chlorides
The weakly dimerized 4 and the monomers 5-7 were
synthesized by the reaction of the aryl lead bromide with
(23) The chemical shifts reported here for compounds 3-7 are consistent
with those previously reported for two coordinate organolead
compounds.19b,c An increase in the coordination number of lead from
two to three, which occurs upon association, is expected to result in
a large chemical shift change (>1000 ppm upfield) such as that
observed when the lead carbene adduct (NN)PbC(NN) (NN ) 1,2-
(ButCH2N)2C6H4) dissociates in solution.23a The consistency of the
shifts observed for 3-7 with those previously reported for two-
coordinate species led us to conclude that 3-7 were also two-
coordinate in solution at room temperature. The relatively low
solubility of 3 and 6 has so far prevented us from investigating the
monomer-dimer equilibrium for these species by VT 207Pb NMR
spectroscopy. (a) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Dalton
Trans. 2000, 3094.
(20) SADABS: Area-Detection Absorption Corrections; Bruker AXS
Inc.: Madison, WI, 1996.
(21) SHELXTL, PC version 5.03; Bruker AXS Inc.: Madison, WI, 1994.
(22) Eaborn, C.; Hitchcock, P. B.; Smith, J. D.; Soezerli, S. E. Organo-
metallics 1997, 16, 5653.
Inorganic Chemistry, Vol. 43, No. 23, 2004 7349

Hino et al.
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for Compounds 1-7
1
2
3
4
Pb(1)-C(1)
Pb(1)-Br(1)
Pb(1)-Br(1A)
C(1)-Pb(1)-Br(1)
C(1)-Pb(1)-Br(1A)
Br(1)-Pb(1)-Br(1A)
Pb(1)-Br(1)-Pb(1A)
C(2)-C(1)-C(6)
2.322(3)
2.8125(5)
3.0346(5)
91.23(8)
109.64(9)
89.014(10)
90.986(10)
119.5(3)
109.0(2)
131.4(3)
120.9(3)
Pb(1)-C(1)
Pb(1)-Br(1)
Pb(1)-Br(2)
Pb(2)-C(39)
Pb(2)-Br(2)
Pb(2)-Br(1)
2.338(5)
2.9202(7)
2.9191(7)
2.346(4)
2.8713(7)
2.9419(7)
108.02(11)
97.17(11)
86.75(2)
106.82(11)
98.41(10)
87.22(2)
92.26(2)
93.74(2)
118.6(4)
108.6(3)
132.7(3)
Pb(1)-C(31)
Pb(1)-C(1)
Pb(1)-Pb(1A)
C(1)-C(6)
C(31)-Pb(1)-C(1)
C(31)-Pb(1)-Pb(1A)
C(1)-Pb(1)-Pb(1A)
C(6)-C(1)-C(2)
2.280(6)
2.318(6)
3.1601(6)
1.386(8)
91.8(2)
109.35(16)
121.51(14)
119.8(5)
125.9(4)
114.2(4)
119.2(5)
Pb(1)-C(31)
Pb(1)-C(1)
Pb(1)-Pb(2)
C(31)-Pb(1)-C(1)
C(6)-C(1)-C(2)
C(6)-C(1)-Pb(1)
C(2)-C(1)-Pb(1)
2.275(6)
2.311(5)
3.927(1)
94.53(19)
120.0(5)
124.3(4)
115.1(4)
C(1)-Pb(1)-Br(2)
C(1)-Pb(1)-Br(1)
Br(2)-Pb(1)-Br(1)
C(39)-Pb(2)-Br(2)
C(39)-Pb(2)-Br(1)
Br(2)-Pb(2)-Br(1)
Pb(1)-Br(1)-Pb(2)
Pb(2)-Br(2)-Pb(1)
C(2)-C(1)-C(6)
C(2)-C(1)-Pb(1)
C(6)-C(1)-Pb(1)
C(3)-C(2)-C(1)
C(6)-C(1)-Pb(1)
C(2)-C(1)-Pb(1)
C(3)-C(2)-C(1)
C(2)-C(1)-Pb(2)
C(6)-C(1)-Pb(1)
5
6
7
Pb(1)-C(31)
Pb(1)-C(1)
C(31)-Pb(1)-C(1)
C(2)-C(1)-C(6)
C(2)-C(1)-Pb(1)
C(6)-C(1)-Pb(1)
C(3)-C(2)-C(1)
2.301(7)
Pb(1)-C(1)
2.294(3)
2.317(3)
97.64(11)
120.0(2)
120.14(19)
118.28(19)
C(1)-Pb(1)
2.296(3)
2.7230(11)
110.82(9)
2.301(6)
102.5(2)
119.3(6)
122.8(4)
116.6(4)
119.6(6)
Pb(1)-C(37)
Pb(1)-Si(1)
C(1)-Pb(1)-C(37)
C(6)-C(1)-C(2)
C(6)-C(1)-Pb(1)
C(2)-C(1)-Pb(1)
C(1)-Pb(1)-Si(1)
t
the Grignard reagents, 4-tBuC6H4MgBr, BuMgBr, 4-iPr-
C6H4-CH2-MgBr, or the lithium reagent, LiSi(SiMe3)3, as
shown in eqs 3 and 4:
Figure 1. Thermal ellipsoid plot of 3. H atoms are not shown for clarity.
Selected bond distances and angles are given in Table 2.
in moderate yield. Its 207Pb NMR chemical shift, 8559 ppm,
is further downfield than the 5067 ppm value observed for
the previously reported benzyl derivative Pb(CH2CMe2C6H3-
But2)Mes*,9b where Mes* ) 2,4,6-But3-C6H2. The upfield
chemical shift may be attributed to the increased coordination
in the latter compound, where the tert-butyl groups assist in
the stabilization of the Pb center through CH-Pb interac-
tions. The UV-vis absorption maxima for 6 (556 nm)
resembles the other m-terphenyl lead alkyl complexes. The
silyl substituted plumbylene, Pb{Si(SiMe3)3}ArPri3, 7, was
synthesized by the reaction of {Pb(µ-Br)ArPri3}2 with 1 equiv
of LiSi(SiMe3)3. The reaction yielded X-ray quality, teal
crystals. The 207Pb NMR signal observed for 7 was similar
to that for the previously reported Pb{Si(SiMe3)3}ArMe3,24
where ArMe3 ) -C6H3-2,6-(C6H2-2,4,6-Me3)2.
Pb(C6H4-4-But)ArPri2, 4, was prepared as red-orange crystals
by the addition of 4-tert-butyl phenylmagnesium bromide
to a rapidly stirred solution of 1. The spectroscopic data
obtained are very similar to those found in Pb(Ph)ArPri3.14
For 4, the maximum absorption was at 462 nm, cf. 460 nm
for Pb(Ph)ArPri3.14 Compound 5 was obtained as royal blue
X-ray quality crystals. The 207Pb NMR signal and the UV-
vis spectrum were consistent with the monomeric Pb(But)-
ArPri3. The 207Pb NMR signal at 8257 ppm is close to that
reported for Pb(But)ArPri3 (8756 ppm). The UV-vis spec-
trum of 5 displays a maximum at 581 nm, cf. 571 nm for
Pb(But)ArPri3. Similarly, the reaction of 4-isopropyl-ben-
zylmagnesium bromide with a rapidly stirred solution of {Pb-
(µ-Br)ArPri3}2 in Et2O yielded 6, Pb(CH2C6H4-4-Pri)ArPri3,
7350 Inorganic Chemistry, Vol. 43, No. 23, 2004

Terphenyl Ligand Stabilized Lead(II) DeriWatiWes
Table 3. Spectroscopic and Structural Parameters for Selected Diorganolead Compounds Including 1-7
Pb-C (Å)
2.318(6)
2.311(5), 2.275(6)
2.301(6)
2.294(3)
2.296(4)
2.272(9), 2.274(15)
2.321(3), 2.264(3)
2.289(11), 2.274(15)
2.344(9), 2.476(14)
2.290(4)
2.33(1)
2.334(12)
2.335(3)
2.317(62)
2.322(3)
2.250(7)
Pb angle (deg)
91.8(2)
94.53(19)
102.5(2)
97.64(11)
110.8(3)
101.4(4)
95.64(11)
100.5(5)
94.8
109.17(11)
116.3(7)
114.5(6)
97.24(19), 108.08(19)
95.4(3), 98.0(3)
91.23(8), 109.64(9)
127.0(1)
207Pb NMR (δ)
UV-vis (nm)
ref
[Pb(Me)ArPri2]2 (3)
8738
7275
8257
8550
10745
8750
7987
8556
5067
10510
8971
8844
470; 340
462
520
860; 390
730; 420
446; 332
460
570
406
720; 399
610
526
this work
this work
this work
this work
this work
14
Pb(C6H4-4-But)ArPri2 (4)
Pb(But)ArPri2 (5)
Pb{CH2C6H4-4-Pri}ArPri3 (6)
Pb{Si(SiMe3)3}ArPri3 (7)
Pb(Me)ArPri3
Pb(Ph)ArPri3
14
14
9b
24
27
26
Pb(But)ArPri3
Pb{CH2CMe2C6H3But2}Mes*a
Pb{Si(SiMe3)3}ArMe3
Pb[C6H2-2,4,6-{CH(SiMe3)2}3]2
Pb{ArMe3}2
{Pb(µ-Br)ArPri2But}2 (2)
{Pb(µ-Br)ArPri3}2
420
420
420
430
this work
14
this work
28
{Pb(µ-Br)ArPri2}2 (1)
[Pb(C6H5CH3)ArPri3][MeB(C6F5)3]
8974
a Mes* ) -C6H2-2,4,6-But3; ArMe3 ) -C6H3-2,6-(2,4,6-Me3C6H2)2.
Table 4. Structural and Spectroscopic Parameters of Diplumbenes Including 3 and 4a
PbdPb
(Å)
PbsAr or
PbsR (Å)
ArsPbsR
(deg)
207Pb NMR
UV-vis
(nm)
δ
(deg)
γ
(deg)
(δ)
ref
9c
{PbTrip2}2
3.0515(3)
3.3549(6)
2.903(11)
2.899(5)
3.537(1)
3.33695(11)
3.1601(6)
3.947(1)
4.129
2.288(5),
2.293(5)
2.322(5),
2.304(6)
97.8(2),
102.3(2)
97.4
541, 385, 321
43.9, 51.2
71.0
[Mes2Pb{2MgBr2(THF)4}]2
[Pb{Si(SiMe3)3}Mes]2
[Pb{Si(SiMe3)3}Trip]2
[Pb{Si(SiMe3)3}ArF]2
[Pb{Si(SiMe3)3}Bmp]2
{Pb(Me)ArPri2}2 (3)
{Pb(C6H4-4-But)ArPri2}2 (4)
[Pb{CH(SiMe3}2]2
0
0
9d
2.314(10),
2.681(3) Si
2.296(4),
2.717(1) Si
2.369(7),
2.705(2) Si
2.37(2),
2.709(4) Si
2.318(6),
2.289(6)
102.5(3)
108.8(1)
96.7(2)
61.0
8
770, 591, 350
1025, 586
42.7
0
9e
40.8
0
9a
106.0(3)
91.8(2)
7545
8738
7275
9112
610, 341, 303
468, 343
46.5
0
9b
51.8
0
this work
this work
9b
2.275(6),
2.311(5)
94.53(19)
35.5, 3.9
74.2
34.2
a Trip ) 2,4,6-triisopropylphenyl; Mes ) 2,4,6-trimethylphenyl; Hyp ) Si(SiMe3)3; ArF ) C6H2-2,4,6-(CF3)3; Bmp ) 2-But-4,5,6-Me3C6H.
Structures. In both 1 and 2, the molecules are dimerized
through bridging of the lead centers by two bromides. The
bond distances and angles resemble those already reported
for {Pb(µ-Br)ArPri3}2,14 and for the three compounds, the
Pb-C and Pb-Br distances span the narrow ranges 2.322-
(3)-2.340(7) and 2.7841(16)-3.034(5) Å, respectively. The
X-ray structure of the “diplumbene” 3 shows that it has a
trans-pyramidal structure as illustrated in Figure 1 with a
Pb-Pb distance 3.1601(6) Å and an out-of-plane angle of
51.8°. These structural parameters can be compared with
those of the previously reported “diplumbenes” in Table 4.
The Pb-Pb bond length lies in the middle of the previously
known range (2.899(5)-3.537(1) Å); however, it should be
noted that even the shortest of these distances does not imply
strong Pb-Pb interaction or that the complex will remain
dimeric in solution. The 207Pb NMR spectrum clearly shows
that 3 is completely dissociated in benzene,23 and it may be
concluded that the Pb-Pb bond in 3 is weak and a relatively
small increase in crowding would be sufficient to dissociate
the bond. This is what happens in the closely related species
Pb(Me)ArPri3,14 which remains monomeric in the solid state.
The only difference between Pb(Me) and 3 is the absence
of Pri groups at the para positions of the flanking aryls in 3.
Inspection of the thermal ellipsoid plot of 3 clearly shows
that if the para Pri groups were present in the structure, they
would cause steric interference between each other across
the Pb-Pb bond which is sufficient to cause dissociation to
monomers in the crystal phase as observed in Pb(Me). A
similar relationship between monomeric and dimeric struc-
tures is observed when ArPri2 and ArPri3 ligands are
employed in the neighboring group 13 element derivatives
MArPri3 and Pri2ArMMArPri2 (M ) In or Tl),25 where their
use allows weakly dimerized structures for Pri2ArMMArPri2
to be observed,25c,d whereas dissociated one-coordinate
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5, 2531.
Inorganic Chemistry, Vol. 43, No. 23, 2004 7351

Hino et al.
The latter parameter underlines the lack of any multiple
character in the Pb-Pb bond. It seems probable that crystal
packing forces could account for the observed Pb-Pb
interaction as the packing arrangement for this structure
appears to be influenced by parallel relationships between
the aromatic substituents.
The structures 5-7 feature two-coordinate lead centers
with a V-shaped geometry. For 5, the Pb(1)-C(1) and the
Pb(1)-C(31) distances are 2.301(6) and 2.301(7) Å, respec-
tively. These distances are similar to those reported for Pb-
(But)ArPri3;14 however, there is a lengthening of the Pb-
C(ipso) bond and a shortening of the Pb-(But) bond in 5.
The X-ray crystallographic analysis of the benzylic derivative
6 (see Figure 3) revealed that the Pb-C(ipso) (2.294(3) Å)
and Pb-C(benzyl) (2.317(3) Å) are considerably shorter than
the corresponding distances in Pb(CH2CMe2C6H3-3,5-But)-
Mes* isolated by Weidenbruch and co-workers,9b where the
Pb-C(ipso) length is 2.344(9) Å and the Pb-C(alkyl) bond
is 2.476(14) Å. The extreme crowding in the Mes* derivative,
which caused its rearrangement to Pb(CH2CMe2C6H3-3,5-
But)Mes* in the first instance, accounts for the long Pb-C
distances. For the silyl substituted plumbylene, 7, the angle
at the two-coordinate lead, 110.8(3)°, is just 1° wider than
in Pb{Si(SiMe3)3}ArMe3 despite the use of the larger
substituent Ar*. The Pb-C bond and Pb-Si distances are
2.296(4) and 2.723 Å, respectively, which are also very
similar to those in Pb{Si(SiMe3)3}ArMe3.24
Figure 2. Thermal ellipsoid plot of 4. H atoms are not shown for clarity.
Selected bond distances and angles are given in Table 2.
Conclusion
The use of the terphenyl ligand ArPri2 which lacks para-
Pri groups on the flanking aryl rings has permitted examina-
tion of the weak Pb-Pb bonding in diplumbenes. In contrast
to the corresponding ArPri3 derivatives which are monomeric
in the solid state, the use of the slightly less crowding ArPri2
ligand permits weak Pb-Pb bonding to occur. Nonetheless,
solution spectroscopic data for all diorganolead derivatives
of the ArPri2 and ArPri3 ligands show that they are exclu-
sively monomeric in solution. The behavior of these lead-
(II) aryl derivatives, having simple methyl or phenyl groups
as coligands, is in marked contrast to those of the corre-
sponding tin(II) derivatives where disproportionation to tin(I)/
tin(III) compounds is observed.29
Figure 3. Thermal ellipsoid plot of 6. H atoms are not shown for clarity.
Selected bond distances and angles are given in Table 2.
monomeric structures are observed for MArPri325a,b in the
solid state.
An almost parallel situation is observed in the case of the
monomeric species Pb(Ph)ArPri314 and the weakly dimerized
4, which has a long Pb-Pb separation of 3.947(1) Å. Only
9b
Acknowledgment. The authors would like to thank the
National Science Foundation for financial support and Dr.
P. Bruins and E. Rivera for useful discussions and technical
assistance.
[Pb{CH(SiMe3)2}2]2 displays a longer Pb-Pb interaction
of 4.129 Å for a diplumbene dimer. The thermal ellipsoid
plot of 4 (Figure 2) shows that the p-tert-butyl groups on
the phenyl substituents contribute to steric interference which
may weaken the Pb-Pb bond. Unfortunately, attempts to
grow crystals of Pb(Ph)ArPri2 to test this hypothesis were
unsuccessful. Other features of the structures of 4 merit
comment. In particular, it is notable that Pb(1) (35.5°) and
Pb(2) (3.9°) possess different out-of-plane angles and the
twist angle between the two lead coordination planes is 74.2°.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC049174Y
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7352 Inorganic Chemistry, Vol. 43, No. 23, 2004