The steric influence of β-diketiminato ligands on the coordination chemistry of lead(II)

Article abstract of DOI:10.1016/j.poly.2014.08.004

Three new β-diketiminatolead(II) chlorides have been synthesised, including [(BDI_DMP)PbCl], [(BDI_IPP)PbCl] and [(BDI_Ph)PbCl] (BDI_DMP = [N{(2,6-Me₂C₆H₃)C(Me)}₂CH], BDI<

Full text of DOI:10.1016/j.poly.2014.08.004

Polyhedron 85 (2015) 284–294
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
The steric influence of b-diketiminato ligands on the coordination
chemistry of lead(II)
1
,1
⇑
Eric C.Y. Tam, Martyn P. Coles , J. David Smith, J. Robin Fulton
Department of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new b-diketiminatolead(II) chlorides have been synthesised, including [(BDIDMP)PbCl], [(BDIIPP)-
PbCl] and [(BDIPh)PbCl] (BDIDMP = [N{(2,6-Me2C6H3)C(Me)}2CH], BDIIPP = [N{(4-iPrC6H4)C(Me)}2CH] and
BDIPh = [N{(C6H5)C(Me)}2CH]). Addition of sodium or potassium-alkoxide salts to [(BDIIPP)PbCl] or
[(BDIPh)PbCl] resulted in the unexpected formation of bis(b-diketiminato)lead(II) complexes, [(BDIIPP)2Pb]
and [(BDIPh)2Pb], whereas addition to [(BDIDMP)PbCl] led to the expected lead alkoxo complex, [(BDIDMP)-
PbOtBu]. The lead(II) triflate complex, [(BDIDMP)PbOTf], was synthesised by treatment of [(BDIDMP)PbCl]
with AgOTf.
Received 23 June 2014
Accepted 2 August 2014
Available online 11 August 2014
Keywords:
Lead
Group 14
Pb
Ó 2014 Elsevier Ltd. All rights reserved.
b-deketiminate
Homoleptic
1. Introduction
2. Results
A wide variety of b-diketiminatolead(II) complexes have been
generated over the past five years [1–7], with the ligand of choice
the ubiquitous [{N(2,6-iPr2C6H3)C(Me)}2CH] (BDIDIPP). The advan-
tage of this ligand is its ability to stabilise low-coordinate metal cen-
tres as the bulky isopropyl groups on the aryl substituent prevent
coordination of more than one ligand [8]. Other reported lead com-
pounds bearing a b-diketiminato ligand are the bis(b-diketimina-
2.1. Ligand synthesis
The condensation of acetylacetone with 2,6-diisopropylaniline
in the presence of concentrated hydrochloric acid and ethanol
under reflux reliably gives (BDIDIPP)H (1a) in good yield [15]. How-
ever, this approach gave poor yields for other substituted anilines.
Moderate yields of (BDIPh)H (1b), (BDIIPP)H (1c) and (BDIDMP)H (1d)
(78%, 51% and 42%, respectively) were obtained from performing
the reaction in concentrated hydrochloric acid without ethanol at
room temperature [16,17]. b-Diketimines 1b and 1d were obtained
as white solids that were purified by washing with cold methanol.
In contrast, (BDIIPP)H (1c) was obtained as a viscous brown oil. The
NMR spectrum of the oil showed a minimal amount of impurity,
hence it was used without further purification. The known com-
pounds 1b and 1d, and the newly synthesised b-diketimine 1c,
were characterised by 1H-and 13C NMR spectroscopy [16,17]. The
1H NMR spectra show two distinctive singlet resonances, corre-
to)lead(II) complexes, [(PhBDITMS)2Pb]
(
PhBDITMS = [{N(SiMe3)
C(C6H5)}2CH]), [(tBuBDIMes)2Pb] tBuBDIMes = [{N(2,4,6-Me3C6H2)
(
C(tBu)}2CH]), as well as the related lead chlorido complex
[(tBuBDIMes)PbCl], and a lead amido complex bearing a bifunctional
b-diketiminato
ligand,
[(BDICO)Pb{N(SiMe3)2}]
(BDICO
=
[{N(2-MeO)C6H4)C(Me)}2CH]) [9–11]. There are a few examples of
monomeric germanium(II) – and tin(II) complexes supported by
b-diketiminato ligands with less sterically encumbering N-aryl
groups, e.g. [(N{(C6H5)C(Me)}2CH}2)GeR] (R = Me or Cl) and
[(N{(2,6-Me2C6H3)C(Me)}2CH)SnOiPr] [12–14]. To examine the
influence of the b-diketiminato N-aryl group on the coordination
geometry of the lead(II) complexes, we focused our attention on
the synthesis of b-diketiminatolead(II) complexes with ligands with
less sterically encumbering N-aryl groups than BDIDIPP: viz [N{(2,6-
sponding to the N–H (dH ꢁ 12.7 ppm) and the –H (dH ꢁ 4.8 ppm)
c
protons. In (BDIIPP)H (1c), the tertiary proton of the isopropyl group
is shown by a septet at dH 2.87 ppm with an integration of two pro-
tons. A downfield resonance at dC 159.7 ppm, is assigned to the b-C.
This is consistent with the signal at dC 161.4 ppm in the b-diketi-
mine (BDIDIPP)H (1a).
Me2C6H3)C(Me)}2CH]ꢀ
(BDIDMP)ꢀ,
[N{(4-iPrC6H4)C(Me)}2CH]ꢀ
(BDIIPP
)
ꢀ and [N{(C6H5)C(Me)}2CH]ꢀ (BDIPh)ꢀ.
2.2. Synthesis of b-diketiminatolead(II) chlorides
⇑
Corresponding author. Tel.: +64 (0)4 463 9799.
E-mail address: j.robin.fulton@vuw.ac.nz (J.R. Fulton).
Present address: School of Chemical and Physical Sciences, Victoria University of
1
The b-diketiminatolead(II) chlorides 2b–2d were synthesised in
moderate yield (46–65%) by the lithiation of the b-diketimine with
Wellington, Wellington 6012, New Zealand.
http://dx.doi.org/10.1016/j.poly.2014.08.004
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
285
n-BuLi, followed by addition of the generated lithium b-diketimi-
nate to a THF slurry of lead dichloride (Eq. (1)).
obtained from an NMR tube fitted with a Young’s tap, containing
C6D6 as solvent after 48 h at room temperature. Ironically, this
compound was islated as the toluene solvate, presumably from
small amounts of toluene within the reaction mixture. In contrast,
single crystals of [(BDIDMP)PbCl] (2d) were easily obtained from a
concentrated solution in of toluene and n-hexane (1:1) at ꢀ30 °C.
ORTEP drawings of 2b are shown in Figs. 1 and 2. Selected bond
lengths and bond angles are listed in Table 1 and selected crystal-
lographic parameters in Table 2. The geometry around the lead
atom is pyramidal with the sum of bond angles around the metal
centre 261.0°, corresponding to a degree of pyramidalisation (DP)
of 110% [22]. The bond angles around lead are slightly more acute
than those in other b-diketiminatolead(II) halides. For example, in
[(BDIDIPP)PbCl] (2a), the sum of bond angles around the metal cen-
tre is 267.2 (DP = 103%) [1]. The PbꢀCl bond length is 2.8081(11) Å,
which is significantly longer than PbꢀCl bond lengths in 2a
(2.5653(7) Å), Smith’s [PbCl{C(SiMe3)2(SiMe2C5H4N-2)}] (2.647
(3) Å) and Leung’s [Pb{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}Cl]
(2.599(3) Å) [1,23,24]. The lead atom in 2b is only 0.110 Å from
the least squares plane defined by the b-diketiminate NCCCN back-
bone. This gives a dihedral angle between the mean NCCCN back-
bone plane and plane defined by NPbN atoms of 176.2°. In contrast,
the lead atom in 2a is 0.683 Å from the mean plane of the ring
(with a dihedral angle between the NCCCN and NPbN planes of
156.9°) and in other tri-coordinated b-diketiminatolead(II) com-
plexes, it is between 0.25 and 1.25 Å [1,4,25]. Delocalisation of
the NCCCN fragment does not extend to the N-aryl rings as shown
by the angles between the NCCCN backbone and the aromatic N-
aryl rings (c.f. 125.9° and 54.4°, Fig. 1). However, less torsion is
observed in 2b than in 2a, in which the angles between the N-aryl
aromatic groups and the NCCCN plane 72° and 78°. The solid-state
structure of compound 2b comprises a ‘polymeric-chain’ (Fig. 2).
The PbꢀCl0 bond length (2.9928 (11) Å) is longer than the PbꢀCl
bond length (2.8081(11) Å) within a monomeric unit and the Cl–
Pb–Cl0 and Pb–Cl–Pb0 bond angles are 167.42(2) and 120.00(4) Å,
respectively. The elongated Pb–Cl bonds of 2b, taken with solubil-
ity properties reminiscent to that of the isolated [(BDIDIPP)Pb]+ cat-
ion [6], lead to the conclusion that [(BDIPh)PbCl] (2b) has a
significantly higher ionic character than that of [(BDIDIPP)PbCl]
(2a).
ð1Þ
The lead(II) chlorides are air-, moisture- and light sensitive.
[(BDIPh)PbCl] (2b) and [(BDIIPP)PbCl] (2c) are virtually insoluble
in common aromatic or non-polar organic solvents, but are readily
soluble in chlorinated solvents. Hence, purification can be conve-
niently achieved by washing with pentane, which removes unre-
acted 1b or 1c and their lithium derivatives from the crude solid.
In contrast, [(BDIDMP)PbCl] (2d) is relatively soluble in common
aprotic organic solvents. Purification of complex 2d is achieved
by washing the crude solid with cold pentane and crystallisation
from a concentrated toluene solution at ꢀ30 °C. The 1H resonance
for the c–H in the b-diketiminate backbone is at dH 4.87, 4.84 and
4.89 ppm for compounds 2b, 2c and 2d, respectively. These values
are similar to those in compounds 1b–1d (dH ꢁ 4.8 ppm). In com-
pound 2c, a septet at dH 2.68 ppm is found for the proton on the
tertiary carbon of the isopropyl group.
The 1H NMR spectrum of [(BDIDMP)PbCl] (2d) displays a broad
resonance at dH 2.31 ppm, assigned to the methyl group at the
ortho-position of the N-substituted aryl fragment, indicative of a
restricted rotation about the nitrogen-aryl bond [18,19]. This broad
signal is in contrast to the sharp singlet resonance observed for the
ortho-methyl groups in two previously reported b-diketiminato
heavy group 14 chlorides [(BDIMes)MCl] (BDIMes = [{N(2,4,6-Me3C6-
H2)C(Me)}2CH]; M = Ge or Sn) [20]. However, the broad signal of 2d
is similar to that of the ortho-methyl substituents in the 1H NMR
spectrum of the b-diketiminatomagnesium iodide [(BDIMES)-
MgI(THF)] [21]. No explanation was provided for the broadness
of the resonance in the magnesium compound.
The restricted rotation about the nitrogen-aryl bond in 2d was
investigated by a variable-temperature (VT) 1H NMR spectroscopic
study. With decreasing temperature, the ortho-methyl resonance
becomes broad at ꢀ10 °C and is then resolved into two singlets
The solid-state structureof [(BDIDMP)PbCl](2d) is shownin Figs. 3
and 4. Selected bond lengths and bond angles are listed in Table 1
and selected crystallographic parameters in Table 2. As with other
b-diketiminatolead(II) complexes, the ligands are coordinated in
pyramidal geometry around the lead atom with a sum of bond
angles of 272.3° (DP = 97.4%). The metal centre is 0.110 Å from the
mean NCCCN plane in the b-diketiminate backbone (dihedral angle
with NCN plane = 176.6°). The N-aryl substituents are not deloca-
lised to the NCCCN ring in the b-diketiminato ligand as shown by
the dihedral angles between the NCCCN plane and the N-aryl rings
(78.7° and 85.2°). The Pb–Cl bond distance (2.5757(11) Å) is similar
to that in 2a (2.5653(7) Å). The structurein the solid-state is dimeric;
at dH 2.66 and 1.96 ppm with
D
dH 296 Hz at ꢀ80 °C. At 60 °C,
sharpening of the broad signal at dH 2.28 ppm, indicates the
approach to a fast-exchange limit. From the coalescence tempera-
ture (ꢀ10 °C), the barrier to NꢀC bond rotation is estimated to be
D
Gà = 50 kJ molꢀ1
The
.
c
-C resonance is found at dC 100.5, 105.4 and 103.7 ppm for
the lead(II) chlorides 2b, 2c and 2d respectively, i.e. downfield from
signals in the parent protonated b-diketiminato ligands (dC 97.6,
97.1 and 93.6 ppm for (BDIPh)H (1b), (BDIIPP)H (1c) and (BDIDMP)H
(1d), respectively). This suggests that the NCCCN framework is
delocalised in the b-diketiminato ligand. A single lead resonance
at dPb 1227, 1220 and 1388 ppm for 2b, 2c and 2d respectively, is
found in their 207Pb NMR spectra. These resonances are similar to
that at dPb 1413 ppm for [(BDIDIPP)PbCl] (2a) [4].
The poor solubility in common organic solvents and extreme
air- and moisture-sensitivity of [(BDIPh)PbCl] (2b) and [(BDIIPP)-
PbCl] (2c) made the isolation of single crystals for X-ray crystallo-
graphic studies difficult. Although single crystals of compounds 2b
and 2c can be obtained from concentrated dichloromethane solu-
tions at ꢀ30 °C, none of these crystals from several different sam-
ples gave well-defined diffraction patterns. This may be due to
immediate decomposition upon removal of crystals from the
mother liquor. However, single crystals of 2b were adventitiously
Fig. 1. ORTEP diagram of [(BDIPh)PbCl] (2b). H atoms are omitted for clarity. The
ellipsoid probability is shown at 30%.

286
E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
Fig. 2. Molecular diagram depicting the polymeric chain of [(BDIPh)PbCl] (2b). H atoms are omitted for clarity.
Table 1
Selected bond lengths (Å) and relevant angles (°) for 2a, 2b and 2d.
[(BDIDIPP)PbCl] (2a)a
[(BDIPh)PbCl] (2b)
[(BDIDMP)PbCl] (2d)
Bond lengths
Pb–N(1)
Pb–N(2)
Pb–Cl
Pb–Cl0
N(1)–C(6)
N(2)–C(12)
Pb–NCCCNplane
Pb–aryl centre
2.290(2)
2.280(2)
2.5653(7)
2.279(3)
2.285(4)
2.8081(11)
2.9928(11)
1.425(5)
1.419(5)
0.110
2.288(3)
2.306(3)
2.5757(11)
1.439(5)
1.429(5)
0.110
0.683
3.486
Angles
N(1)–Pb–N(2)
N(1)–Pb–Cl
82.77(7)
91.13(5)
93.27(5)
84.68(12)
90.52(9)
85.78(9)
120.00(4)
82.10(9)
83.40(9)
167.42(2)
261.0
82.54(12)
93.49(8)
96.29(9)
N(2)–Pb–Cl
Pb–Cl–Pb0
N(1)–Pb–Cl0
N(2)–Pb–Cl0
Cl–Pb–Cl0
Sum of Pb angles
267.2
103%
272.34
97.4
Degree of pyramidalizationb
110%
Dihedral angles
NCCCNplane–NPbNplane
NCCCNplane–/Aryl 1
NCCCNplane–/Aryl 2
156.9
72.1
78.1
176.2
125.9
54.4
176.6
78.7
85.2
For 2a: Aryl 1, C(6)–C(7)–C(8)–C(9)–C(10)–C(11); Aryl 2, C(18)–C(19)–C(20)–C(21)–C(22)–C(23). For 2b: Aryl 1, C(6)–C(7)–C(8)–C(9)–C(10)–C(11); Aryl 2, C(12)–C(13)–
C(14)–C(15)–C(16)–C(17). For 2d: Aryl 1, C(6)–C(7)–C(8)–C(9)–C(10)–C(11); Aryl 2, C(14)–C(15)–C(16)–C(17)–C(18)–C(19). The Values in italics are from Ref. [1].
a
Ref. [1]
Ref. [22].
b
the lead atom in any one molecule interacts with an aryl group from
a white precipitate, were obtained (Eq. 2). These reactions are
reproducible, and the bis species can be obtained upon addition
of 2b or 2c to a wide range of alkoxide salts, such as sodium tert-
butoxide, potassium isopropoxide or sodium 2-methyl-3-buten-
2-oxide. However, treatment of [(BDIPh)PbCl] (2b) with potassium
methoxide did not give the bis(b-diketiminato)lead(II)] complex
3b, instead white precipitate and the protonated b-diketiminate
precursor, 1b, were obtained.
a neighbouring unit, with the the Pbꢂ ꢂ ꢂarylcentre distance 3.486 Å
(Fig. 4). The reported distances for g
6-interaction between heavy
group 14 metals and arene rings fall in the range of 2.69–3.20 Å
[26–28]. This interaction is rare in lead chemistry; only one example,
[(g g
6-1,2-Me2C6H4)Pb(AlCl4)2] (Pb ( 6-aryl) = 2.858 Å), is known at
the time of writing [27], although some potential longer range
aryl-lead interactions were observed in the crystal structure of
[Pb(DBM)2] (DBM-H = 1,3-diphenyl-propane-1,3-dione) [29]. The
weaker Pbꢂ ꢂ ꢂarylcentre interaction in the lead(II) chloride 2d may be
attributed to crowding from the b-diketiminato ligand and the for-
mally neutral lead(II) centre.
ð2Þ
2.3. Reactivity of b-diketiminatolead(II) chlorides
We attempted to synthesise a series of b-diketiminatolead(II)
alkoxides containing different substituents in the b-diketiminato
ring for comparison with those previously reported [5]. However,
treatment of [(BDIPh)PbCl] (2b) or [(BDIIPP)PbCl] (2c) with potas-
sium tert-butoxide at room temperature did not give the corre-
sponding lead(II) alkoxides. Instead bis(b-diketiminato)lead(II)
complexes [(BDIPh)2Pb] (3b) and [(BDIIPP)2Pb] (3c), in addition to
Although the identity of the white precipitate in these reactions
was not ascertained, in an 1H NMR study of the reaction between
[(BDIPh)PbCl] (2b) and potassium tert-butoxide, a singlet at dH
1.39 ppm was observed. As this resonance was not observed in

E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
287
Table 2
Crystal structure and refinement data for 2b, 2d, 3b and 3c.
[(BDIPh)PbCl] (2b)a
[(BDIDMP)PbCl] (2d)b
[(BDIPh)2Pb] (3b)
[(BDIPh)2Pb] (3c)
Chemical formula
Formula weight
T (K)
C
17H17ClN2Pbꢂ0.5(C7H8)
2(C21H25ClN2Pb)ꢂ(C7H8)
1188.28
173(2)
C34H34N4Pbꢂ(C7H8)
798.01
173(2)
C46H58N4Pb
874.15
173(2)
538.03
173(2)
Wavelength (Å)
Crystal size (mm)
Crystal system
Space group
a (Å)
0.71073
0.2 ꢃ 0.04 ꢃ 0.04
monoclinic
C 2/c (No.15)
23.4501(5)
10.0070(2)
16.7676(4)
90
106.434(1)
90
3774.02(14)
8
0.71073
0.71073
0.71073
0.15 ꢃ 0.07 ꢃ 0.05
0.20 ꢃ 0.09 ꢃ 0.06
0.20 ꢃ 0.14 ꢃ 0.12
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1 (No.2)
P1 (No.2)
P1 (No.2)
8.3126(3)
12.5001(4)
12.9418(4)
112.537(2)
94.850(2)
104.513(1)
1177.65(7)
1
10.3923(2)
11.5345(4)
17.0319(5)
104.310(1)
96.037(2)
113.289(2)
1769.24(9)
4
10.9335(3)
12.1290(2)
16.9989(4)
85.690(2)
73.900(1)
74.641(1)
2088.50(8)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
pc (Mg mꢀ3
)
1.89
9.09
1.68
7.289
1.50
4.80
1.39
4.07
Absorption coefficient (mmꢀ1
)
h Range for data collection (°)
Measured/independent reflections/
Rint
3.40–27.10
29205/4164/0.061
3.40–26.76
15979/4989/0.056
3.49–27.09
31069/7797/0.0548
3.42–26.72
30594/8825/0.051
Reflections with I > 2
r(I)
3591
4563
7106
8166
Data/restraints/parameters
4164/0/206
1.009
4989/0/239
1.038
7797/0/420
0.837
8825/0/464
1.210
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.027, wR2 = 0.056
R1 = 0.027, wR2 = 0.060
R1 = 0.029,
wR2 = 0.069
R1 = 0.037,
wR2 = 0.073
0.91 and ꢀ1.44
R1 = 0.034,
wR2 = 0.079
R1 = 0.039,
wR2 = 0.080
1.12 and ꢀ1.49
R indices (all data)
R1 = 0.037, wR2 = 0.059
R1 = 0.032, wR2 = 0.062
Largest difference in peak and hole
(e Å3)
1.95 and ꢀ0.94 (near disordered
1.77 and ꢀ1.03 (near disordered
toluene)
toluene)
a
The toluene solvate has unresolved disorder.
The toluene solvate lies on an inversion centre and was modeled as a rigid body with common thermal displacement parameters and all carbon atoms isotropic.
b
Fig. 3. ORTEP diagram of [(BDIDMP)PbCl] (2d). H atoms and toluene solvate are
omitted for clarity. The ellipsoid probability is shown at 30%.
the isolated bis(b-diketiminato)lead(II) complex 3b, it was tenta-
tively assigned to [Pb(
for the formation of this species, but Buhro’s [Pb3(
a single resonance at dH 1.43 ppm, which is similar to that in our
l
-Cl)(OtBu)]2. We have no further evidence
Fig. 4. Molecular diagram depicting dimer unit of [(BDIDMP)PbCl] (2d). H atoms are
omitted for clarity. (‘ = 1 ꢀ x, 1 ꢀ y, 2 ꢀ z).
l
-OtBu)6] shows
product [30].
weeks without decomposition. The1H NMR spectrum of [(BDIPh)2Pb]
[(BDIPh)2Pb] (3b) is also accessible by treatment of lead dichlo-
ride with two equivalents of the lithium b-diketiminate [(BDIPh)Li]
(generated in situ) at room temperature. The 1H and 13C NMR spec-
tra of the product were identical to those of the product from equa-
tion 2. Previous attempts to synthesise [(BDIDIPP)2Pb] by treatment
of lead dichloride with two equivalents of [(BDIDIPP)Li] were unsuc-
cessful, suggesting that substituents at the ortho-position of the N-
substituted aryl fragments cause congestion between neighbour-
ing b-diketiminato ligands, and prevent the formation of the
bis(b-diketiminato)lead(II) [(BDIDIPP)2Pb].
3b shows resonances at dH 1.85 and 4.85 ppm for the b-Me and
protons in the b-diketiminato ligand. The 13C NMR spectrum shows
resonances at dC 162.2 and 100.7 ppm for the b- and -carbon atoms,
c-H
c
respectively. These results show that the two b-diketiminato ligands
are equivalent in solution. Similar observations can be found in
Lappert’s [(PhBDITMS)2Pb] as well as other bis(b-diketiminato) transi-
tion metal complexes, such as Schulz’s [(BDIMes)2Zn] and Song’s
[(BDIPh)2Pd] [31,32]. A lead resonance at dPb 454 ppm is obtained in
the 207Pb NMR spectrum of [(BDIPh)2Pb] (3b), upfield from that in
the lead(II) chloride 2b (dPb 1228 ppm).
The bis(b-diketiminato)lead(II) complexes 3b and 3c are soluble
incommonaproticorganic solvents. Theyarestablein thesolid-state
and can be stored in an inert environment at ꢀ30 °C for several
Similarly, the 1H NMR spectrum of [(BDIIPP)2Pb] (3c) shows
singlets at dH 1.92 and 4.90 ppm, for b-Me and c-H protons, respec-

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E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
tively, in the b-diketiminato ligand. The 13C NMR spectrum also
shows resonances at dC 162.2 and 103.4 ppm for b- and -carbon
Table 3
Selected bond lengths (Å) and relevant angles (°) for 3b and 3c.
c
atoms, respectively. These resonances are similar to those found
in the spectra of 3b. The isopropyl groups at the para-position of
the N-substituted aryl fragments in compound 3c give a septet at
dH 2.76 ppm and a doublet at dH 1.19 ppm assigned to the tertiary
and methyl protons, respectively. The spectra are similar to those
of Roesky’s bis(b-diketiminato)zinc(II) complex [(BDIMOP)2Zn]
(BDIMOP = [{N(4-(MeO)C6H4)C(Me)}2CH]), which shows the para-
oxymethyl substituents on the N-substituted aryl group are chem-
ically equivalent [33]. In the 13C NMR spectrum, signals at dC 34.4
and 24.9 ppm are observed for the tertiary and methyl isopropyl
carbons of [(BDIIPP)2Pb] (3c). The lead resonance at dPb 476 ppm
is obtained from the 207Pb NMR spectrum; the shift is similar to
that from [(BDIPh)2Pb] (3b, dPb 454 ppm).
Single crystals of [(BDIPh)2Pb] (3b) suitable for an X-ray crystal-
lographic study were obtained from toluene at ꢀ30 °C. ORTEP
drawings of [(BDIPh)2Pb] (3b) are shown in Fig. 5. Selected bond
lengths and bond angles are listed in Table 3 and selected crystal-
lographic parameters in Table 2. The ligands are arranged in a dis-
torted pseudo-trigonal bipyramidal geometry around the metal
centre with an empty coordination site, reminiscent of a hemi-
directed geometry common in four-coordinate divalent lead com-
plexes [34]. Both Pb–N(1) (2.482(3) Å) and Pb–N(4) (2.466(3) Å)
are longer than Pb–N(2) (2.363(3) Å) and Pb–N(3) (2.338(3) Å).
The N(1)–Pb–N(4) bond angle (151.05(11)°) is significantly wider
than the N(2)–Pb–N(3) bond angle (89.87(11)°). The coordination
is similar to that in Lappert’s [(PhBDITMS)2Pb], in which there are
two different Pb–N bond lengths (ca. 2.609 and 2.314 Å) and N–
Pb–N bond angles of ca. 166.2° and 96.9° [9]. However, the exterior
bond angles of Jones’ [(tBuBDIMes)2Pb] are much more obtuse
(203.8° and 103.1°), presumably due to the presence of tert-butyl
groups on the b-diketiminato backbone in addition to methyl
groups in the 2,4,6-position of the N-aryl groups [10]. Density func-
tional theory calculations on four-coordinated gas-phase lead(II)
complexes performed by Glusker et al. suggest that the longer
Pb–N bonds (2.620 Å), associated with a wider N–Pb–N angles
(203.2°), have more s-character than the shorter Pb–N bonds
(2.446 Å) with a smaller N–Pb–N angle (91.6°) [34]. The two
NCCCN planes of two the b-diketiminato ligands in [(BDIPh)2Pb]
[(BDIPh)2Pb] (3b)
[(BDIIPP)2Pb] (3c)
Bond lengths
Pb–N(1)
Pb–N(2)
Pb–N(3)
2.482(3)
2.363(3)
2.338(3)
2.466(3)
2.632
2.333(4)
2.446(4)
2.456(5)
2.348(4)
1.425(5)
2.553
2.790
0.991
0.947
Pb–N(4)
C(11)–H(11)ꢂ ꢂ ꢂarylcentre
C(16)–H(16)ꢂ ꢂ ꢂarylcentre
C(34)–H(34)ꢂ ꢂ ꢂarylcentre
Pb–NCCCNplane1
Pb–NCCCNplane2
Pb–Aryltoluene
2.647
1.202
1.167
3.616
Angles
N(1)–Pb–N(2)
N(3)–Pb–N(4)
N(1)–Pb–N(3)
N(1)–Pb–N(4)
N(2)–Pb–N(3)
N(2)–Pb–N(4)
73.44(10)
75.40(10)
85.01(10)
151.05(11)
89.87(11)
85.22(10)
75.10(13)
76.71(13)
87.03(13)
90.33(13)
87.13(13)
155.86(12)
Dihedral angles
NCCCNplane1-NPbNplane
NCCCNplane1-/Aryl 1
NCCCNplane1-/Aryl 2
NCCCNplane2-NPbNplane
NCCCNplane2-/Aryl 3
NCCCNplane2-/Aryl 4
1
2
142.4
49.9
97.7
142.7
49.1
91.3
149.0
65.0
65.6
150.4
103.7
58.8
For 3b: NCCCNplane1, N(2)–C(3)–C(2)–C(1)–N(1); NPbNplane 1, N(2)–Pb–N(1); Aryl 1,
C(12)–C(13)–C(14)–C(15)–C(16)–C(17); Aryl 2, C(6)–C(7)–C(8)–C(9)–C(10)–C(11);
NCCCNplane2, N(3)–C(18)–C(19)–C(20)–N(4), NPbNplane 2, N(3)–Pb–N(4); Aryl 3,
C(23)–C(24)–C(25)–C(26)–C(27)–C(28); Aryl 4, C(29)–C(30)–C(31)–C(32)–C(33)–
C(34). For 3c: NCCCNplane1, N(2)–C(3)–C(2)–C(1)–N(1); NPbNplane 1, N(2)–Pb–N(1);
Aryl 1, C(15)–C(16)–C(17)–C(18)–C(19)–C(20); Aryl 2, C(6)–C(7)–C(8)–C(9)–C(10)–
C(11); NCCCNplane2, N(3)–C(24)–C(25)–C(26)–N(4); NPbNplane 2, N(3)–Pb–N(4);
Aryl 3, C(29)–C(30)–C(31)–C(32)–C(33)–C(34); Aryl 4, C(38)–C(39)–C(40)–C(41)–
C(42)–C(43).
H(1)ꢂ ꢂ ꢂarylcentre = 2.632 Å and C(34)–H(34)ꢂ ꢂ ꢂarylcentre = 2.647 Å,
are within the range for reported CꢀHꢂ ꢂ ꢂ
p distances (<2.90 Å), for
example in Harder’s [(BDIDIPP)2Ca] (avg. CꢀHꢂ ꢂ ꢂarylcentre = 2.696 Å)
and [(BDIDIPP)2Sr] (avg. CꢀHꢂ ꢂ ꢂarylcentre = 2.761 Å) [35]. The lead
atom is solvated by a toluene molecule which coordinates in an
g6 fashion with the metal centre (Pbꢂ ꢂ ꢂtoluenecentre = 3.616 Å) in
3b. This is slightly longer than the Pbꢂ ꢂ ꢂaryl interaction observed
for [(BDIDMP)PbCl] (2d) and significantly longer than that in Frank’s
(3b) are not parallel. In addition, there may be weak CꢀHꢂ ꢂ ꢂ
p inter-
actions between the ortho-hydrogen of the N-substituted aryl
group and the aryl ring from the other ligand (dotted lines in
[(
g
g
6-1,2-Me2C6H4)Pb(AlCl4)2] (Pbꢂ ꢂ ꢂ( 6-aryl) = 2.858 Å) [27].
Fig. 5). Two CꢀHꢂ ꢂ ꢂp interactions, with distances of C(11)–
ORTEP drawings of [(BDIIPP)2Pb] (3c) are shown in Fig. 6.
Selected bond lengths and bond angles are listed in Table 3 and
selected crystallographic parameters in Table 2. In the bis(b-dike-
timinato)lead(II) complexes 3b and 3c, the ligands are coordinated
in a distorted pseudo-trigonal bipyramidal geometry around the
metal centre, with N(2) and N(3) axial. The two NCCCN planes of
the b-diketiminato ligands are not parallel (Fig. 6). Two different
sets of bond lengths are found. Pb–N(2) (2.446(4) Å) and Pb–N(3)
(2.456(5) Å) are longer than both Pb–N(1) (2.333(4) Å) and Pb–
N(4) (2.348(4) Å). Likewise, the bond angle of N(2)–Pb–N(3)
(155.86(12)°) is significantly wider than N(1)–Pb–N(4)
(90.33(13)°). Two C–Hꢂ ꢂ ꢂ
(2.553 Å) and C(34)–H(34)ꢂ ꢂ ꢂarylcentre (2.790 Å) are observed (dot-
inter-
p
interactions, C(16)ꢀH(16)ꢂ ꢂ ꢂarylcentre
ted lines in Fig. 6). These distances are similar to the C–Hꢂ ꢂ ꢂ
p
actions found in 3b (avg. C–Hꢂ ꢂ ꢂarylcentre = 2.640 Å). There is no
Pbꢀtoluenecentre interaction as in 3b, possibly because the isopro-
pyl groups in the para-position in the N-substituted aryl groups
hinder access of solvent to the metal atom.
In contrast to the less sterically encumbered lead chloride com-
plexes (2b and 2c), treatment of [(BDIDMP)PbCl] (2d) with potassium
tert-butoxide at room temperature gave the b-diketiminatolead(II)
alkoxide [(BDIDMP)PbOtBu] (4d) in 72% yield (equation 3). There is
Fig. 5. ORTEP diagram of [(BDIPh)2Pb] (3b). H atoms are omitted for clarity. C–Hꢂ ꢂ ꢂ
p
and Pbꢂ ꢂ ꢂtoluene interactions are shown. The ellipsoid probability is shown at 30%.

E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
289
Fig. 6. ORTEP diagram of [(BDIIPP)2Pb] (3c). H atoms are omitted for clarity. C–Hꢂ ꢂ ꢂ
p
interactions are shown. The ellipsoid probability is shown at 30%.
Fig. 7. ORTEP diagram of [(BDIDMP)PbOtBu] (4d). H atoms are omitted and the BDI C
atoms minimised for clarity. The ellipsoid probability is shown at 30%.
no evidence for the formation of the bis(b-diketiminato)lead(II)
complex [(BDIDMP)2Pb] from the reaction. Attempts to generate this
complex by addition of two equivalents of [(BDIDMP)Li] to lead
dichloride only yielded 2d.
Treatment of [(BDIDMP)PbCl] (2d) with silver trifluoromethane-
sulfonate (AgOTf) in toluene at room temperature gave the b-dike-
timinatolead(II) triflate [(BDIDMP)PbOTf] (5d) in 61% yield (Eq. 4).
ð3Þ
ð4Þ
The b-diketiminatolead(II) tert-butoxide 4d is soluble in com-
mon aprotic organic solvents, such as toluene and hexane. It has
a characteristic singlet at dH 1.05 ppm in the 1H NMR spectrum,
assigning to the terminal tert-butoxide ligand. This is similar to
the tert-butoxide resonance (dH 0.88 ppm) found in [(BDIDIPP)PbOt-
Bu] (4a) [5]. Two singlets at dH 2.67 and 2.16 ppm in the 1H NMR
spectrum, and also at dC 20.5 and 19.2 ppm in the 13C NMR spec-
trum, correspond to the methyl groups at the ortho-position of
the N-substituted aryl fragment. This suggests that the barrier to
rotation about the N–C bond is higher than that observed in 2d.
The 207Pb NMR spectrum of lead(II) tert-butoxide 4d shows a single
resonance at dPb 1513 ppm, which is within the range found in
other b-diketiminatolead(II) alkoxides (dPb ꢁ 1500–1700 ppm)
[2,5].
The 1H NMR spectrum of the lead(II) triflate 5d in CDCl3 shows
singlets at dH 5.14 and 1.84 ppm for the c-H and the methyl pro-
tons at the ortho-position of the N-substituted aryl groups, respec-
tively. This indicates that the methyl groups are chemically
equivalent and there is free rotation about the N–aryl bond. A res-
onance at dC 124.5 ppm (CDCl3) is found in the 13C NMR spectrum,
and assigned to the CF3 group. This shift is similar to that for the
CF3 fragment (dC 120.9 ppm in C6D6) in Driess’ [(BDIDIPP)GeOTf]
[37,38]. A single resonance at dF ꢀ78.0 ppm (CDCl3) is found in
the 19F NMR spectrum of compound 5d, which is similar to that
in Roesky’s [(BDIDIPP)PbOTf] (dF ꢀ76.5 ppm in C6D6) [4]. The 207Pb
NMR spectrum shows a single upfield resonance at dPb 1154 ppm
(CDCl3) for [(BDIDMP)PbOTf] (5d).
Single crystals of 5d suitable for an X-ray crystallographic study
were obtained from THF at ꢀ30 °C. The ORTEP drawings of com-
pound 5d are shown in Figs. 8 and 9. Selected bond lengths and
bond angles are listed in Table 4 and selected crystallographic
parameters are listed in Table 5. The ligands are coordinated with
pyramidal geometry around the lead atom with the sum of bond
angles around the metal centre of 262.7° (DP = 108%). The mole-
cules are linked into a polymeric chain by triflate fragments
(Fig. 9). In the monomeric unit of compound 5d, the Pb–O(1) bond
length (2.593(3) Å) is significantly longer than the Pb–O bond dis-
tance found in [(BDIDMP)PbOtBu] (4d) (2.154(3) Å); however, it is
similar to the Pb–O bond length in Roesky’s [(BDIDIPP)Pb(OTf)]
complex (ave = 2.591 Å), which also forms a polymeric chain [4].
The Pb–O(2)0 bond distance (2.733(3) Å) and the O(1)ꢀPbꢀO(2)0
bond angle (165.50(9)°) are similar to those in [(BDIDIPP)PbOTf]
(2.624 Å and 168.2°, respectively). Similar to the elongated bonds
of [(BDIPh)PbCl] (2b), the elongated Pb-O bonds of the triflate com-
plexes are indicative of relatively more ionic bond as compared to
other b-diketiminatolead(II) alkoxides.
Single crystals of [(BDIDMP)PbOtBu] (4d) suitable for an X-ray
crystallographic study were obtained by crystallisation from pen-
tane at ꢀ30 °C. The ORTEP drawings are shown in Fig. 7. Selected
bond lengths and bond angles are listed in Table 4 and selected
crystallographic parameters are listed in Table 5. The ligands are
coordinated in a pyramidal geometry around the lead atom with
the sum of bond angles around the metal centre 267.4°
(DP = 103%). In sharp contrast to other known b-diketiminato-
lead(II) alkoxide complexes such as [(BDIDIPP)PbOtBu] (4a) in which
the alkoxide ligand points away from the Pb–NCCCN core (exo con-
formation), the alkoxide ligand of 4d lies below the NCCCN plane in
an endo conformation [5,36]. In addition, the lead atom lies
essentially within the mean b-diketiminate NCCCN plane
(Pb–NCCCNplane = 0.001 Å) in contrast to the lead centre of 4a
(Pb–NCCCNplane = 1.021 Å). Similar to the lead chloride examples
(ie 2a and 2d, vide supra), this is due to a relief of crowding from
the N-substituted aryl fragments around the metal centre in 4d
[5], effectively providing additional space to accommodate the lead
atom in the NCCCN plane of the b-diketiminato ligand. The Pb–O
bond distance, 2.154(3) Å, is similar to the Pb–O bond length
(2.126(3) Å) in 4a [5].

290
E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
Table 4
Selected bond lengths (Å) and relevant angles (°) for 4d, 5d and 6c.
[(BDIDMP)PbOtBu] (4d)a
[(BDIDMP)PbOTf] (5d)
[(BDIIPP)PbI] (6c)
Bond lengths
Pb–N(1)
Pb–N(2)
Pb–X
O–C(22)
Pb–O(2)0
Pb–I0
2.311(3) [2.301(3)]
2.322(3) [2.318(3)]
2.154(3) [2.146(3)]
1.426(5) [1.419(5)]
2.266(3)
2.282(3)
2.593(3)
2.284(3)
2.275(3)
3.1928(3)
2.733(3)
3.5079
0.229
Pb–NCCCNplane
Angles
0.001 [0.286]
0.606
N(1)–Pb–N(2)
N(1)–Pb–X
N(2)–Pb–X
81.32(11) [80.63(11)]
94.17(11) [91.06(12)]
91.92(11) [92.79(11)]
121.2(2) [123.4(3)]
82.88(10)
91.94(10)
87.90(9)
120.00(4)
91.86(10)
106.45(10)
165.50(9)
83.11(11)
92.28(8)
88.47(8)
Pb–O–C(22)
N(1)–Pb–O(2)0
N(2)–Pb–O(2)0
O(1)–Pb(2)–O(2)0
N(1)–Pb–I0
98.97(9)
97.49(8)
167.809(9)
263.9
N(2)–Pb–I0
I–Pb–I0
Sum of Pb angles
Degree of pyramidalizationb
Dihedral angles
NCCCNplane–NPbNplane
NCCCNplane-/Aryl 1
NCCCNplane-/Aryl 2
267.4 [264.5]
103% [106%]
262.7
108
107
179.8 [170.9]
89.0 [81.5]
84.4 [79.4]
159.6
89.3
76.4
172.3
70.7
106.7
For 4d, molecule 1: Aryl 1, C(6)–C(7)–C(8)–C(9)–C(10)–C(11); Aryl 2, C(14)–C(15)–C(16)–C(17)–C(18)–C(19); For 4d, molecule 2: Aryl 1, C(31)–C(32)–C(33)–C(34)–C(35)–
C(36); Aryl 2, C(39)–C(40)–C(41)–C(42)–C(43)–C(44). For 5d: Aryl 1, C(6)–C(7)–C(8)–C(9)–C(10)–C(11); Aryl 2, C(14)–C(15)–C(16)–C(17)–C(18)–C(19). For 6c: Aryl 1, C(15)–
C(16)–C(17)–C(18)–C(19)–C(20); Aryl 2, C(6)–C(7)–C(8)–C(9)–C(10)–C(11).
a
The numbers in brackets correspond to the second molecule in the unit cell.
Ref. [22].
b
Table 5
Crystal structure and refinement data for 4d, 5d and 6c.
[(BDIDMP)PbOtBu] (4d)a
[(BDIDMP)PbOTf] (5d)
[(BDIIPP)PbI] (6c)b
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal size (mm)
Crystal system
Space group
a (Å)
C25H34N2OPb
585.73
173(2)
C22H25F3N2O3PbS
661.69
173(2)
C23H29IN2Pbꢂ(C6H6)
745.69
173(2)
0.71073
0.71073
0.71073
0.20 ꢃ 0.18 ꢃ 0.13
0.15 ꢃ 0.13 ꢃ 0.13
monoclinic
P 21/c (No.14)
11.4124(2)
11.5990(3)
20.5159(6)
90
0.22 ꢃ 0.06 ꢃ 0.04
monoclinic
C 2/c
28.2581(5)
9.9106(2)
20.1416(3)
90
triclinic
ꢀ
P1 (No.2)
12.0429(4)
12.2155(4)
18.6440(5)
70.951(2)
b (Å)
c (Å)
a
(°)
b (°)
73.482(2)
88.626(1)
2478.36(13)
4
1.57
117.144(2)
90
2416.63(10)
4
1.82
7.116
90.889(1)
90
5640.07(17)
8
1.76
7.10
c
(°)
V (Å3)
Z
pc (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
)
6.824
range for data collection (°)
Measured/independent reflections/Rint
3.44–26.76
30981/10379/0.057
8521
3.49–26.72
25271/5100/0.056
4472
3.50–27.10
44103/6196/0.074
5147
Reflections with I > 2 (I)
r
Data/restraints/parameters
10379/0/535
1.000
5100/0/295
1.046
6196/78/328
1.084
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.030, wR2 = 0.067
R1 = 0.042, wR2 = 0.072
0.73 and ꢀ1.62
R1 = 0.028, wR2 = 0.053
R1 = 0.031, wR2 = 0.055
0.54 and ꢀ1.05
R1 = 0.031, wR2 = 0.056
R1 = 0.045, wR2 = 0.059
0.72 and ꢀ0.87
R indices (all data)
Largest difference in peak and hole (e Å3)
a
There are two essentially equivalent molecules in the unit cell.
There are two ½-molecules of benzene solvate located at special positions; one of the Pr groups is disordered and was refined over two positions.
b
i
2.4. Reactions of bis(b-diketiminato)lead(II) complexes
trifluoromethanesulfonate, an intractable mixture of products
were observed. Treatment of [(BDIIPP)2Pb] (3c) with methyl iodide
in C6D6 gave an intractable mixture of products at room tempera-
ture. However, single crystals of one of them were obtained adven-
titiously from the mixture after 48 h.
Preliminary studies on the reaction of the bis(b-diketimina-
to)lead(II) complexes with aliphatic electrophiles were investi-
gated. When [(BDIPh)2Pb] (3b) was treated with methyl

E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
291
Fig. 10. ORTEP diagram of [(BDIIPP)PbI] (6c). H atoms are omitted for clarity. The
ellipsoid probability is shown at 30%.
polymeric, whereas a dimeric structure is found for [(BDIDMP)PbCl]
(2d) in the solid-state. These results contrast with other b-diketim-
inato heavy group 14 metal halides, such as our [(BDIDIPP)PbX]
(X = Cl, Br or I) and Barrau’s [(BDIPh)MCl] (M = Ge or Sn), which
show no significant intermolecular interactions in the solid-state
[1,12,14].
The lead(II) chloride complexes reported in this study show
essentially planar skeletons in the solid-state; that is, the lead
atom lies close to the mean NCCCN plane, in contrast to the non-
planar ring observed with [(BDIDIPP)PbCl] (2a). Computational
studies on [(BDIPh)PbCl] (2b) predicted a distance between lead
and the least-squares plane defined by N(1)–C(1)–C(3)–N(2)
(NC2N) is 0.550 Å [41]. Although we incorporate the entire NCCCN
plane in our measurements for consistency with our earlier
reports, our experimental results reveal that the lead atom is dis-
placed by 0.110 Å from either definitions defining the b-diketimi-
nate plane. The difference between the computational and
experimental results for [(BDIPh)PbCl] (2b) could be attributed to
the polymeric nature of the structure, leading to lengthening of
the Pb–Cl bond and a more cationic metal centre, which have been
shown to lie in the NCCCN plane [6]. However, this does not
explain the relative planarity of [(BDIDMP)PbCl] (2d), with a Pb–
NCCCN distance also of 0.110 Å (or, using Rosas-García’s NC2N
Fig. 8. ORTEP diagram of [(BDIDMP)PbOTf] (5d). H atoms are omitted and the BDI C
atoms minimised for clarity. The ellipsoid probability is shown at 30%.
An X-ray crystallographic study revealed that the product was
[(BDIIPP)PbI] (6c) as illustrated in Figs. 10 and 11. Selected bond
lengths and bond angles are listed in Table 4 and selected crystal-
lographic parameters are listed in Table 5. Ligands are coordinated
in a pyramidal geometry around the lead atom with the sum of
bond angles around the metal centre of 263.9° (DP = 107%). The
lead atom deviates from the mean b-diketiminate NCCCN plane
by
a
distance of 0.229 Å, in contrast to [(BDIDIPP)PbI]
(PbꢀNCCCNplane = 0.846 Å) [1]. The differences can be explained
by the reduced crowding around the metal centre due to the
absence of ortho-substitutents on the N-substituted aryl groups.
The lead(II) iodide 6c has a polymeric structure, with Pb–I bonds
comprising the polymeric chain (Fig. 11). Each lead atom is bound
to two iodide atoms, with one Pb–I bond (3.5079(4) Å) longer than
the other (3.1928(3) Å). Both Pb–I bond lengths are longer than the
sum of covalent radii of lead and iodine (2.58 Å), indicating that the
bonding has a strong electrostatic component [39]. The bonds are
also longer than the Pb–I bond found in [(BDIDIPP)PbI] (Pb–
plane, 0.062 Å, which indicates a slight puckering at the c-carbon
atom). Although there are some long distance Pb-aryl interactions,
the simplest explanation for the planarity of the b-diketiminate
metallacyle is that the methyl groups on the N-aryl ligand of
[(BDIDMP)PbCl] (2d) exert less steric influence than the isopropyl
groups on [(BDIDIPP)PbCl] (2a). The influence of the N-aryl moeity
is exemplified in the b-diketiminatolead(II) tert-butoxide com-
plexes, [(BDIDIPP)PbOtBu] (4a) and [(BDIDMP)PbOtBu] (4d). In the
complex, 4a, an exo conformation is adopted in which the tert-
butoxide ligand points away from the metallacyle and the metal
centre is displaced from the NCCCN plane by 1.021 Å. In contrast,
an endo conformation is observed in the less sterically encumbered
[(BDIDMP)PbOtBu] (4d), and the lead atom lies close to the NCCCN
plane (Pb–NCCCNplane = 0.001 Å).
I = 2.9531(5) Å)
and
Filippou’s
[{Pb(2,6-Trip2C6H3)I}2]
(Trip = 2,4,6-iPr3C6H2) (avg. Pb–I = 3.1132 Å) [1,40].
3. Discussion
We have synthesised several lead(II) complexes containing a
series of b-diketiminato ligand. X-ray crystallographic studies on
[(BDIPh)PbCl] (2b) and [(BDIIPP)PbI] (6c) show both structures are
Fig. 9. Molecular diagram depicting the polymeric chain of [(BDIDMP)PbOTf] (5d). H atoms are omitted for clarity.

292
E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
Fig. 11. Molecular diagram depicting the polymeric chain of [(BDIIPP)PbI] (6c). H atoms are omitted for clarity.
Although previous work demonstrated that treatment of
sieves. (BDIPh)H (1b), (BDIDMP)H (1d) and [(BDIPh)Li] were prepared
by slight modifications to known procedures [16,17]. Potassium
alkoxide salts were prepared by the slow addition of the relevant
alcohol (dried and distilled) to a suspension of potassium hydride.
Methyl iodide was freshly dried and distilled before use. All other
reagents were used as received. 1H and 13C NMR spectra were
recorded on Varian 400 and 500 MHz spectrometers. The 207Pb
NMR spectra were recorded on a Varian 400 MHz spectrometer
that was equipped with a X{1H} broadband-observe probe. All
spectra were recorded in C6D6 at 300 K, unless stated otherwise.
The 1H and 13C NMR chemical shifts are given relative to SiMe4,
19F signals were externally referenced to CFCl3 and 207Pb signals
were externally referenced to PbMe4. The data for the X-ray struc-
tures were collected at 173 K on a Nonius Kappa CCD diffractome-
[(BDIDIPP)PbCl] (2a) with potassium alkoxides gave the correspond-
ing b-diketiminatolead(II) alkoxides, the analogous reactions of
[(BDIPh)PbCl] (2b) or [(BDIIPP)PbCl] (2c) led to the formation of
bis(b-diketiminato)lead(II) complexes 3b and 3c. Similarly, Theo-
pold and co-workers found that reaction between [(BDIPh)CrIII
Cl2(THF)2] and lithium alkyls led to the formation of bis(b-diketim-
inato)chromium(II) complex [42]. In a study on substituent effects
in the b-diketiminato ligands, Itoh co-workers suggested that the
steric influence of substituents at the ortho-position of the N-
substituted aryl group played an important role in control of the
formation of monomeric or dimeric b-diketiminatocopper(II) com-
plexes [43]. Although there has been no systemic study of such
effects in heavy group 14 chemistry, the present work suggests
that they are apparent also in b-diketiminatolead(II) complexes.
Preliminary studies on the reactions of bis(b-diketimina-
to)lead(II) complexes with aliphatic electrophiles are intriguing.
At present, we do not have further evidence to suggest the lead
atom is the primary reaction centre for these reactions, which pro-
ceeded with substitution rather than oxidative addition. Further
studies are ongoing towards understanding the reactions of
bis(b-diketiminato)lead(II) complexes with other substrates and
the reaction mechanisms involved.
ter [k (Mo, Ka) 0.71073 Å] and refined using the SHELXL-97 software
package [44].
5.2. Synthesis of [CH{(CH3)CN-4-iPrC6H4}2H], (BDIIPP)H, (1c)
Concentrated HCl (5.1 mL) was added dropwise to a mixture of
4-isopropylaniline (13.5 g, 100 mmol) and acetylacetone (5.00 g,
50 mmol) at 0 °C. The mixture was stirred and allowed to warm
gradually to room temperature. A yellow precipitate was observed
after 24 h. The mixture was filtered and washed with cold hexanes.
The residue was dissolved in dichloromethane (15 mL) and satu-
rated sodium carbonate solution (250 mL). The aqueous layer
was extracted with dichloromethane (3 ꢃ 30 mL) and the com-
bined organic layer was dried with magnesium sulfate. The vola-
tiles were removed under vacuum to leave a brown oil. Yield:
8.54 g, 51%. 1H NMR (399.50 MHz, 303 K): d 12.70 (s, 1H, NH),
7.16 (d, J = 8.0 Hz, 4H, o-H), 6.88 (d, J = 7.6 Hz, 4H, m-H), 4.84 (s,
4. Conclusion
The sterics of the b-diketiminato ligand affects the coordination
properties of divalent lead complexes, from influencing how the
divalent lead centre lies in the metallocycle plane, to determining
the nature of the bonding interactions (ie the unusual ionic bond-
ing observed in [(BDIPh)PbCl] (2b)) as well as the stability of the
complexes themselves. The diverse reactivity with potassium alk-
oxide salts revealed that the larger ligands are less prone to ligand
rearrangement than the less sterically encumbered ligands.
Whether this is due to the complexes themselves, or due to the sta-
bility of reactive intermediates, has yet to be determined.
1H, c-CH), 2.87 (septet, J = 6.4 Hz, 2H, CHMe2), 1.99 (s, 6H, NCMe),
1.24 (d, J = 6.8 Hz, 12H, CHMe2). 13C{1H} NMR (100.46 MHz, 303 K):
d 159.7 (NCMe), 144.0 (ipso-C), 143.6 (p-C), 126.8 (o-C), 122.9 (m-
C), 97.1 (c-CH), 33.7 (CHMe2), 24.3 (CHMe2), 21.0 (NCMe).
5.3. Synthesis of [CH{(CH3)CN-C6H5}2PbCl], [(BDIPh)PbCl], (2b)
5. Experimental
(BDIPh)H (1b) (1.95 g, 7.75 mmol) was dissolved in THF (30 mL)
and n-BuLi in n-hexane (3.2 mL of 2.7 M solution, 7.75 mmol)
added dropwise. The mixture was stirred for 30 min at room tem-
perature, then transferred slowly to a THF (10 mL) slurry of PbCl2
(2.16 g, 7.75 mmol) via cannula. The mixture was stirred at room
temperature for a further 20 h. Volatiles were removed under vac-
uum and the residue was extracted with dichloromethane
(3 ꢃ 40 mL). The solvent was removed from the extract in vacuo
5.1. General
All manipulations were carried out under an inert atmosphere
of dry nitrogen using standard Schlenk techniques or in an inert-
atmosphere glove-box. Solvents were dried over the appropriate
drying agent, distilled, degassed and stored over 4 Å molecular

E.C.Y. Tam et al. / Polyhedron 85 (2015) 284–294
293
and the crude solid was washed with pentane (5 ꢃ 10 mL). Yellow
crystals of [(BDIPh)PbCl] (2b) were obtained by crystallisation from
dichloromethane at ꢀ30 °C. Yield: 1.83 g, 46%. 1H NMR
(499.91 MHz, 303 K): d 7.10 (m, 7H, Ar–H), 6.93 (m, 2H, Ar–H),
dissolved in toluene. Yellow crystals of [(BDIPh)2Pb] (3b), suitable
for X-ray crystallographic study were obtained at ꢀ30 °C. Yield:
0.14 g, 48%. 1H NMR (399.50 MHz, 303 K): d 7.09 (t, J = 14.0 Hz,
8H, o-H), 6.92 (t, J = 14.8 Hz, 4H, p-H), 6.52 (d, J = 7.2 Hz, 8H, m-
4.74 (s, 1H,
c
-CH), 1.72 (s, 6H, NCMe). 13C{1H} NMR (125.72 MHz,
H), 4.85 (s, 2H,
(100.46 MHz, 303 K): d 162.2 (NCMe), 151.3 (ipso-C), 128.2 (o-C),
126.4 (m-C), 124.1 (p-C), 100.7 (
-CH), 24.8 (NCMe). 207Pb NMR
c
-CH), 1.85 (s, 12H, NCMe). 13C{1H} NMR
303 K): d 163.8 (NCMe), 148.5 (ipso-C), 130.1 (o-C), 128.7 (o-C),
128.5 (p-C), 128.3 (m-C), 126.0 (m-C), 100.5 (
c
-CH), 24.6 (NCMe).
c
207Pb NMR (83.83 MHz, 303 K): d 1228. IR (Nujol, v/cmꢀ1): 1530
(s), 1262 (s), 1166 (s), 1018 (s), 912 (s). Anal. Calc. For C17H17N2PbCl
(491.98): C, 42.64; H, 3.98; N, 5.53. Found: C, 41.54; H, 3.56; N,
5.38%.
(83.83 MHz, 303 K): d 454. Anal. Calc. For C34H34N4Pb (705.86): C,
57.87; H, 4.82; N, 7.94. Found: C, 57.92; H, 4.94; N, 7.89%.
5.7. Alternative synthesis of [(BDIPh)2Pb] (3b)
5.4. Synthesis of [CH{(CH3)CN-4-iPrC6H4}2PbCl], [(BDIIPP)PbCl], (2c)
A suspension of (BDIPh)Li (0.31 g, 1.17 mmol) in toluene was
added to PbCl2 (0.16 g, 0.58 mmol). The mixture was stirred at
room temperature for 20 h. Purification of the mixture was as
above. Yield: 0.34 g, 82%.
(BDIIPP)H (1c) (2.15 g, 6.43 mmol) was dissolved in THF (20 mL)
and n-BuLi in n-hexane (2.73 mL of 2.37 M solution, 6.43 mmol)
was added dropwise. The mixture was stirred at room temperature
for 30 min then transferred slowly via cannula to a THF (10 mL)
slurry of PbCl2 (1.79 g, 6.43 mmol). The mixture was stirred at
room temperature for 20 h, and volatiles were removed in vacuo.
The residue was extracted with dichloromethane (3 ꢃ 20 mL).
The solvent was removed and the solid washed with pentane
(3 ꢃ 10 mL). Yellow crystals of [(BDIIPP)PbCl] (2c) suitable for X-
ray crystallographic study were obtained by crystallisation from
a minimum amount of dichloromethane at ꢀ30 °C. Yield: 2.01 g,
57%. 1H NMR (399.50 MHz, 303 K): d 7.08–7.19 (m, 4H, Ar-H),
5.8. Synthesis of [(CH{(CH3)CN-4-iPrC6H4}2)2Pb], [(BDIIPP)2Pb], (3c)
[(BDIIPP)PbCl] (2c) (0.14 g, 0.25 mmol) was dissolved in toluene
(10 mL) and added to a toluene suspension (5 mL) of potassium- or
sodium alkoxide (0.25 mmol). After the mixture was stirred at
room temperature for 15 h, the suspension was filtered through a
pad of Celite. The volatile was removed from the filtrate in vacuo
and the residue was washed with pentane. Yellow crystals of
[(BDIIPP)2Pb] (3c) suitable for X-ray crystallographic study was
obtained by crystallisation from a minimum amount of toluene
at ꢀ30 °C. Yield: 0.15 g, 71%. 1H NMR (399.50 MHz, 303 K): d
7.05 (d, J = 8.4 Hz, 8H, o-C), 6.53 (d, J = 8.4 Hz, 8H, m-H), 4.90 (s,
7.03 (d, J = 8.8 Hz, 4H, Ar–H), 4.77 (s, 1H, c-CH), 2.68 (septet, 2H,
J = 7.2 Hz, 2H, CHMe2), 1.77 (s, 6H, NCMe), 1.11 (d, J = 6.8 Hz,
12H, CHMe2). 13C{1H} NMR (100.46 MHz, 303 K): d 164.0 (NCMe),
146.5 (ipso-C), 146.2 (o-C), 125.7 (m-C), 105.4
(
c
-CH), 34.3
2H, c-CH), 2.76 (septet, J = 6.8 Hz, 4H, CHMe2), 1.92 (s, 12H, NCMe),
(CHMe2), 24.6 (CHMe2), 24.5 (NCMe). 207Pb NMR (83.83 MHz,
303 K): d 1220. IR (Nujol, v/cmꢀ1): 1559 (s), 1496 (s), 1378 (s),
1194 (s), 1053 (s), 856 (s). Anal. Calc for C23H29ClN2Pb (576.14):
C, 47.95; H, 5.07; N, 4.86. Found: C, 47.83; H, 4.97; N, 4.79%.
1.19 (d, J = 6.8 Hz, 24H, CHMe2). 13C{1H} NMR (100.46 MHz, 303 K):
d 162.2 (NCMe), 149.3 (ipso-C), 144.3 (o-C), 126.8 (p-C), 126.4 (m-
C), 103.4 (c
-CH), 34.4 (CHMe2), 24.9 (CHMe2), 24.8 (NCMe). 207Pb
NMR (83.83 MHz, 303 K): d 476.
5.5. Synthesis of [CH{(CH3)CN-2,6-Me2C6H3}2PbCl], [(BDIDMP)PbCl],
(2d)
5.9. Synthesis of [CH{(CH3)CN-2,6-Me2C6H3}2PbOtBu],
[(BDIDMP)PbOtBu], (4d)
(BDIDMP)H (1d) (1.87 g, 6.13 mmol) was dissolved in THF and n-
BuLi in n-hexane (2.6 mL of 2.37 M solution, 6.13 mmol) was added
dropwise. The mixture was stirred at room temperature for 30 min,
then transferred slowly via cannula to a THF (10 mL) slurry of PbCl2
(1.70 g, 6.13 mmol). The mixture was stirred at room temperature
for 20 h. Volatile material was removed under vacuum and the res-
idue was extracted with toluene (3 ꢃ 20 mL). The solvent was
removed in vacuo and the crude solid was washed with pentane
(3 ꢃ 10 mL). Light yellow crystals of [(BDIDMP)PbCl] (2d) suitable
for X-ray crystallographic study were obtained by crystallisation
from toluene at ꢀ30 °C. Yield: 2.19 g, 65%. 1H NMR (499.91 MHz,
303 K): d 6.97 (d, J = 7.5 Hz, 4H, m-H), 6.91 (t, J = 7.5 Hz, 2H, p-H),
[(BDIDMP)PbCl] (2d) (0.25 g, 0.46 mmol) in toluene (20 mL) was
added to
a suspension of potassium tert-butoxide (0.05 g,
0.46 mmol) in toluene (5 mL). The mixture was stirred at room
temperature for 15 h. The suspension was filtered through a pad
of Celite and volatile material from the filtrate was removed under
vacuum. The residue was washed with pentane and recrystallised
from toluene. Crystals suitable for an X-ray crystallographic study
were obtained at ꢀ30 °C. Yield: 0.19 g, 76%. 1H NMR (499.91 MHz,
303 K): d 7.10 (dd, J = 2.0, 7.0 Hz, 2H, p-H), 6.94–6.99 (m, 4H, m-H),
4.70 (s, 1H, c-CH), 2.67 (s, 6H, Ar-Me), 2.16 (s, 6H, Ar–Me), 1.64 (s,
6H, NCMe), 1.05 (s, 9H, OC(Me)3). 13C{1H} NMR (125.72 MHz,
303 K): d 163.2 (NCMe), 146.6 (ipso-C), 136.1 (o-C), 131.1 (o-C),
4.83 (s, 1H,
c
-CH), 2.31 (br, 12H, Ar–Me), 1.58 (s, 6H, NCMe).
129.7 (p-C), 128.8 (m-C), 125.7 (m-C), 99.4 (c-CH), 69.7 (OC(Me)3),
13C{1H} NMR (125,72 MHz, 303 K): d 163.9 (NCMe), 146.3 (ipso-
36.8 (OC(Me)3), 23.9 (NCMe), 20.5 (Ar-Me), 19.2 (Ar–Me). 207Pb
NMR (83.83 MHz, 303 K): d 1513. Anal. Calc. for C25H34N2OPb
(585.73): C, 51.24; H, 5.85; N, 4.78%. Found: C, 51.17; H, 5.77; N,
4.76%.
C), 129.7 (o-C), 128.9 (p-C), 126.3 (m-C), 103.7 (c-CH), 24.2 (Ar–
Me), 21.8 (Ar–Me), 19.7 (NCMe). 207Pb NMR (83.83 MHz, 303 K): d
1388. IR (Nujol, v/cmꢀ1): 1551 (s), 1522 (s), 1178.7 (s), 1093 (s),
1019 (s). Anal. Calc. For C21H25N2ClPb (548.09): C, 46.02; H, 4.60;
N, 5.11. Found: C, 46.18; H, 4.49; N, 4.91%.
5.10. Synthesis of [CH{(CH3)CN-2,6-Me2C6H3}2PbOSO2CF3],
[(BDIDMP)PbOTf], (5d)
5.6. Synthesis of [(CH{(CH3)CN-C6H5}2)2Pb], [(BDIPh)2Pb], (3b)
[(BDIDMP)PbCl] (2d) (0.20 g, 0.37 mmol) in toluene (10 mL) was
added to a suspension of AgOTf (0.09 g, 0.37 mmol) in toluene
(5 mL). The mixture was stirred at room temperature for 12 h
and the yellow precipitate was filtered off and washed with cold
pentane (3 ꢃ 3 mL). The yellow residue was crystallised from THF
and stored at ꢀ30 °C. Light yellow crystals of [(BDIDMP)PbOTf]
(5d) were obtained. Yield: 0.15 g, 61%. 1H NMR (399.50 MHz,
A solution of [(BDIPh)PbCl] (2b) (0.20 g, 0.41 mmol) in toluene
(10 mL) was added to a toluene suspension (5 mL) of potassium-
or sodium alkoxide (0.41 mmol). The mixture was stirred at room
temperature for 15 h. The suspension was filtered through a pad of
Celite and volatile material was removed from the filtrate under
vacuum. The residue was washed with cold pentane (5 mL) and

294
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ꢀ78.0. 207Pb NMR
Acknowledgements
We would like to thank the University of Sussex, School of
Chemical and Biological Sciences, for funding.
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