Tin and mercury compounds supported by a bulky organometallic ligand incorporating a pendant guanidine functionality

Article abstract of DOI:10.1071/CH14255

The structure of a triclinic form of the organolithium derivative LiR, R≤C(SiMe3)2(SiMe2{hpp}) (1) (hppH≤1,3,4,6,7,8,-hexahydro-2H-pyrimido[1,2- a]pyrimidine) comprises dimers [1]2 held together by Li··· H3C interactions like those in the polymeric structure [1]∞ of the previously described orthorhombic form. Compound 1 reacts with the chlorides MCl2 (M≤Hg or Sn) to give compounds HgRCl (2) or SnRCl (3), which have been characterised by NMR spectroscopy and X-ray crystallography. The structural parameters and conformations of the metallacycles MRLn are compared with those in related compounds containing bulky organosilicon ligands with pendant nitrogen donors. Compound 3 reacts with Li[P{H}Ar*] (Ar*≤2,4,6- tBu3C6H2) to give the crowded phosphanide SnR(P{H}Ar*) (4). CSIRO 2014.

Full text of DOI:10.1071/CH14255

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 1071–1080
Full Paper
http://dx.doi.org/10.1071/CH14255
Tin and Mercury Compounds Supported by a Bulky
Organometallic Ligand Incorporating a Pendant
Guanidine Functionality*
A
B
C E
,
Salima M. El-Hamruni, Sebnem E. Sozerli, J. David Smith,
¨
D
C
Martyn P. Coles, and Peter B. Hitchcock
A
Department of Chemistry, Faculty of Science, Tripoli University, PO Box 13203,
Tripoli, Libya.
B
Department of Chemistry, Faculty of Arts and Sciences, Celal Bayar University,
Manisa, Turkey.
C
Department of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, UK.
D
School of Chemical and Physical Sciences, Victoria University of Wellington,
PO Box 600, Wellington 6012, New Zealand.
E
Corresponding author. Email: j.d.smith@sussex.ac.uk
The structure of a triclinic form of the organolithium derivative LiR, R ¼ C(SiMe3)2(SiMe2{hpp}) (1) (hppH ¼
1,3,4,6,7,8,-hexahydro-2H-pyrimido[1,2-a]pyrimidine) comprises dimers [1]2 held together by LiꢀꢀꢀH3C interactions like
those in the polymeric structure [1]N of the previously described orthorhombic form. Compound 1 reacts with the
chlorides MCl2 (M ¼ Hg or Sn) to give compounds HgRCl (2) or SnRCl (3), which have been characterised by NMR
spectroscopy and X-ray crystallography. The structural parameters and conformations of the metallacycles MRLn are
compared with those in related compounds containing bulky organosilicon ligands with pendant nitrogen donors.
Compound 3 reacts with Li[P{H}Ar*] (Ar* ¼ 2,4,6-tBu3C6H2) to give the crowded phosphanide SnR(P{H}Ar*) (4).
Manuscript received: 24 April 2014.
Manuscript accepted: 28 May 2014.
Published online: 3 July 2014.
Introduction
and an unusual tin(II) phosphanide derivative SnR(PHAr*)
(4, Ar* ¼ 2,4,6-tBu3C6H2).
The reactivity of organometallic reagents can be fine-tuned by
varying the metal, the size and nucleophilicity of the organic
fragment, and the bulk and basicity of the donorsolvents inwhich
reagentsarepreparedand used. Oneway inwhichtheinterplay of
these factors has been studied is by the synthesis of compounds in
which carbanionic and N-, O-, or P-donor atoms are incorporated
into a single ligand. For example, as well as compounds con-
taining the bulky carbanions (Me3Si)3Cꢁ or (Me2PhSi)3Cꢁ,[1]
derivatives of ligands (Me3Si)2(Me2{X}Si)Cꢁ, where X is a
donor such as NMe2,[2] 2-pyridyl,[3] OMe,[4] or CH2PPh2,[5] have
been reported.
In an extension to this area of chemistry, we have recently
described compounds of the electropositive elements lithium,[6]
potassium,[6] calcium,[7] and zinc[8] containing the ligand
(Me3Si)2(Me2{hpp}Si)Cꢁ (R), in which hpp is a bicyclic
guanidinato fragment (hppH ¼ 1,3,4,6,7,8,-hexahydro-2H-
pyrimido[1,2-a]pyrimidine).[9] In this paper we report the
synthesis and structures of derivatives 2 and 3 of the less
electropositive metals mercury and tin (Fig. 1), and compare
the metal–carbon and metal–nitrogen bonds with those in
previously characterised compounds. We also report the
crystal structure of a triclinic form of the lithium compound 1,
Results and Discussion
The Lithium Compound 1
In a previous paper we described the synthesis of the solvent-
free lithium compound Li[C(SiMe3)2(SiMe2{hpp})], 1, which
crystallised in the orthorhombic crystal system (space group
P212121).[6] The molecules formed a weakly coordinated poly-
mer through LiꢀꢀꢀC interactions to a SiMe3 group of an adjacent
molecule, propagating as a chain along the b-axis to form [1]N
(Tables 1 and 2). As this compound was a valuable reagent for
the synthesis of derivatives of other metals we prepared
numerous samples. In one case we noticed that the crystals
appeared to be different from those previously studied, and
when we examined them by X-ray crystallography we found that
they were of a less symmetrical triclinic polymorph, presumably
formed by crystallisation under conditions different from those
used in the earlier study.
ꢀ
The triclinic polymorph (space group P1) crystallises as the
dimer [1]2 linked in the solid-state by two LiꢀꢀꢀCMe3Si interac-
tions (Fig. 2). The intermolecular lithiumꢀꢀꢀcarbon distances
*Dedicated to the memory of our friend and colleague, Professor Michael Lappert FRS, who pioneered the use of bulky silicon-containing ligands in
organometallic chemistry.
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

1072
S. M. El-Hamruni et al.
˚
in [1]2 (2.451(3) A) are longer than those joining the molecules
˚
N2 [deviation d1 ¼ 0.033(6) A] with the CN3-core of the
guanidine twisted out of this plane [torsion y ¼ 32.2(2)8]. In
contrast, in the triclinic polymorph (Fig. 3b), Si1 is displaced by
˚
in the chain form (2.387(3) A) and in related structures [LiMe]4
[10]
˚
and LiBMe4 (both 2.36(1) A),
between the molecules is weak.
suggesting that interaction
˚
d1 ¼ 0.847(4) A from the mean plane, and y ¼ 10.48(3)8. The
Although the bond lengths in the two structures for 1
(Table 2) are not significantly different, the conformations of
the six-membered LiCSiNCN-metallacycles in the polymorphs
are dissimilar. The sums of internal angles are 6918 and 6798 for
the triclinic and orthorhombic structures, respectively. In the
orthorhombic structure (Fig. 3a), the silicon atom of the SiMe2
unit lies close to the least-squares plane defined by C8, Li, and
most notable differences in bond angle occur at the coordinated
nitrogen atom N2 (DLiNC ¼ 8.28), and in the bite angle of the
ligand (DCLiN ¼ 2.88), indicating considerable flexibility in the
chelating ligand.
Hirshfield surface (HS) analysis is a convenient tool for the
quantification and visualisation of intermolecular interactions.
The HS defines the three-dimensional space inside which more
than half of the electron density comes from the molecule. The
surface is colour-coded to highlight close contacts to atoms of
neighbouring molecules in the crystal, with white corresponding
to distances equal to the sum of the van der Waals radii, and red
and blue indicating distances shorter and longer the this sum,
respectively. This analysis has been useful in the comparison of
polymorphic molecular crystal structures,[11] prompting us to
examine the lithium salt LiR 1 using this tool.
N
N
N
N
CI
N
N
Hg
Li
Me2Si
Me2Si
C
C
SiMe3
SiMe3
Me3Si
Me3Si
The HS maps of the monomeric units of each polymorph of 1
are shown in Fig. 4. The general shapes of the surface are
similar, with the small differences reflecting the different
conformations of the metallacycle (Fig. 3). In both cases the
HS clearly illustrates the ‘pocket’ in which the lithium atom is
located, and the deep-red colour indicates that this atom is
involved in strong intermolecular interactions. Also clearly
indicated are the high dnorm values located in the area corre-
sponding to the different methyl groups that participate in the
intermolecular CHꢀꢀꢀLi interactions. Thus for the orthorhombic
polymorph, the ‘hot-spot’ on the HS is associated with C14,
whereas for the triclinic polymorph the contact is indicated at
C13, adjacent to the lithium atom. No other significant contacts
are indicated.
1
2
tBu
N
N
tBu
Sn
N
N
N
N
Sn
CI
P
tBu
Me2Si
Me2Si
C
C
H
SiMe3
SiMe3
Me3Si
Me3Si
3
4
Fig. 1. Compound-labelling scheme.
Table 1. Crystal structure and refinement data for the triclinic polymorph of Li[C(SiMe3)2(SiMe2{hpp})] (1-triclinic),
Hg[C(SiMe3)2(SiMe2{hpp})]Cl (2), Sn[C(SiMe3)2(SiMe2{hpp})]Cl (3), and Sn[C(SiMe3)2(SiMe2{hpp})](P{H}Ar*) (4)
Parameter
1-triclinic
2
3
4A
Empirical formula
Mr
C16H36LiN3Si3
361.69
C16H36ClHgN3Si3
590.79
C16H36ClN3Si3Sn
508.89
C34H66N3PSi3Sn
750.83
Crystal size [mm3]
Crystal system
Space group
˚
a [A]
˚
b [A]
0.40 ꢂ 0.40 ꢂ 0.25
0.25 ꢂ 0.20 ꢂ 0.20
0.25 ꢂ 0.05 ꢂ 0.05
Monoclinic
C2/c (No. 15)
16.6688(2)
8.9930(1)
0.25 ꢂ 0.20 ꢂ 0.10
Orthorhombic
P212121 (No. 19)
9.3359(2)
Triclinic
ꢀ
P1 (No. 2)
Triclinic
ꢀ
P1 (No. 2)
9.2176(2)
9.2210(2)
10.5323(3)
11.9456(3)
68.393(1)
10.6074(2)
12.3984(2)
103.117(1)
93.997(1)
18.9321(4)
22.7406(5)
90
˚
c [A]
32.7659(10)
90
a [deg.]
b [deg.]
g [deg.]
86.409(2)
103.058(1)
90
90
89.340(2)
93.360(1)
90
3
˚
V [A ]
1076.02(5)
2
1174.72(4)
2
4784.68(10)
8
4019.36(15)
4
Z
Dcalc. [Mg mꢁ3
]
1.12
1.67
1.41
1.24
Absorption coefficient [mmꢁ1
]
0.22
6.82
1.34
0.79
y range [deg.]
3.49 to 26.02
14721
3.46 to 26.05
18729
3.43 to 26.04
29633
3.44 to 26.02
28147
Reflections collected
Independent reflections
Reflections with I . 2s(I)
Data/restraints/parameters
Final R indices [I . 2s(I)]
Final R indices (all data)
GOOF on F2
4190 [Rint ¼ 0.036]
3813
4625 [Rint ¼ 0.041]
4460
4709 [Rint ¼ 0.055]
4146
7872 [Rint ¼ 0.067]
6207
4190/0/224
R1 ¼ 0.031, wR2 ¼ 0.092
R1 ¼ 0.034, wR2 ¼ 0.095
1.145
4625/0/226
R1 ¼ 0.024, wR2 ¼ 0.061
R1 ¼ 0.025, wR2 ¼ 0.062
1.075
4709/0/217
R1 ¼ 0.030, wR2 ¼ 0.075
R1 ¼ 0.037, wR2 ¼ 0.079
1.036
7872/0/379
R1 ¼ 0.043, wR2 ¼ 0.076
R1 ¼ 0.069, wR2 ¼ 0.085
1.032
ꢁ3
˚
Largest diff. peak/hole [e A
]
0.36 and ꢁ0.33
1.32 and ꢁ1.89
1.16 and ꢁ0.45(near Sn)
0.60 and ꢁ0.5
AAbsolute structure parameter ¼ ꢁ0.07(2).

Tin and Mercury Guanidinato Compounds
1073
The two-dimensional ‘fingerprint’ (FP) representations of
the HS are a plot of di against de, where these values represent the
closest internal and external contacts on the HS, respectively.[12]
These plots summarise the frequency of each combination of de
and di across the surface and allow the visualisation of which
intermolecular contacts are present and the area of the surface
corresponding to each type of contact. Each point on the FP plot
is a unique (di, de) pair, with the colour corresponding to the
relative area of the surface with that (di, de) value (white ¼ no
contribution; range blue through green to red with increasing
contribution).
The molecules of 2 are located about an inversion centre in
the crystal and are considered as weakly associated dimers [2]2
that form centrosymmetric Hg2Cl2 rings in the solid-state. This
motif is known for neutral organomercury(II) compounds of
formula [Hg(R0)(m-Cl)]2 with a range of HgꢀꢀꢀCl distances. For
example, the values for derivatives with R0 ¼ Z1-cyclopentadie-
nyl vary from 3.035(1) to 3.460(1) A,[13] and the two indepen-
˚
dent molecules in the unit cell of the k-C,N-complex Hg(dpp)Cl
(Hdpp ¼ 2,9-diphenyl-1,10-phenanthroline)[14] have HgꢀꢀꢀCl
The relative contribution of the HS due to the different types
of intermolecular interaction (HꢀꢀꢀH, HꢀꢀꢀLi, HꢀꢀꢀN, and HꢀꢀꢀC) is
shown in Table 3. The percentages for each polymorph are quite
similar, with the dominant contribution coming from HꢀꢀꢀH
contacts. The LiꢀꢀꢀH contacts account for ,4 % of the HS in
each case, with the remainder being due to minor HꢀꢀꢀN and
HꢀꢀꢀC interactions. Two-dimensional FP plots for each poly-
morph are shown in Fig. 5, showing the same basic features.
Comparison of the full FP plots indicate that the voids (upper di
and de values) are more compact in the triclinic form, indicating
more efficient packing in the dimer than in the polymer. The
main LiꢀꢀꢀH interactions (#) are present as broad, diffuse
features, with similar di/de values indicative of similar LiꢀꢀꢀH
distances. The blue colour of these features in consistent with
their low overall contribution to the intermolecular interactions.
Si3
Liꢀ
C13
Si2
C8
Si1
C13ꢀ
Li
N1
N2
C1
N3
The Organomercury and Organotin Chlorides
The halides HgRCl 2 or SnRCl 3 were obtained by reactions of
the lithium compound 1 (usually prepared in situ from RH and
methyllithium in Et2O) with HgCl2 or SnCl2 in THF. Both were
isolated in good yields as colourless crystals, which gave clean
NMR spectra in C6D6. Their structures are shown in Figs 6 and
7, and selected bond lengths and angles in Table 2.
Fig. 2. Thermal ellipsoid plot of [1]2 (30 % ellipsoids, H-atoms omitted).
Symmetry generated atoms: ꢁx þ 1, ꢁy þ 1, ꢁz.
˚
Table 2. Selected bond lengths (A) and angles (deg.) for 1, 2, 3, and 4
Bond
LiR (triclinic)A
LiR (orthorhombic)B
HgRClC
SnRClD
SnR(P{H}Ar*)E
M–C8
2.090(3)
1.921(3)
2.094(3)
1.926(3)
2.150(3)
2.409(3)
1.381(5)
1.310(5)
1.365(5)
1.783(3)
99.22(11)
–
2.285(3)
2.213(3)
1.368(4)
1.326(4)
1.351(4)
1.793(3)
93.77(9)
–
2.314(4)
2.239(4)
1.378(6)
1.318(6)
1.351(6)
1.791(4)
93.31(15)
–
M–N2
C1–N1
1.3751(19)
1.3134(19)
1.3724(18)
1.8040(13)
113.05(13)
119.09(13)
124.22(13)
127.51(13)
119.70(13)
122.87(10)
115.03(6)
92.92(9)
1.375(2)
C1–N2
1.310(2)
C1–N3
1.371(2)
N1–Si1
1.8050(13)
115.91(14)
113.95(14)
130.08(15)
119.26(14)
118.89(13)
119.23(11)
112.99(6)
93.07(10)
109.47(12)
99.16(11)
115.24(8)
117.38(8)
117.41(8)
C8–M–N2
N2–MꢀꢀꢀCn
C8–MꢀꢀꢀCn
M–N2–C1
N2–C1–N1
C1–N1–Si1
N1–Si1–C8
Si1–C8–M
Si2–C8–M
Si3–C8–M
Si1–C8–Si2
Si1–C8–Si3
Si2–C8–Si3
–
–
–
120.3(2)
118.4(3)
119.6(2)
114.01(15)
102.59(15)
108.04(15)
102.15(15)
114.09(17)
114.03(17)
114.27(17)
130.47(18)
119.1(3)
118.39(19)
108.38(12)
105.05(12)
100.81(12)
110.09(13)
112.80(14)
114.70(14)
112.18(14)
128.9(3)
117.6(4)
116.6(3)
112.03(17)
105.35(18)
103.56(19)
110.2(2)
111.7(2)
112.4(2)
112.9(2)
106.69(10)
104.78(10)
116.06(7)
116.07(7)
116.16(7)
A
0
0
˚
LiꢀꢀꢀCn (n ¼ 13 ) ¼ 2.451(3) A.
B
C
˚
LiꢀꢀꢀCn (n ¼ 14 ) ¼ 2.387(3) A.
˚
˚
Hg–Cl 2.4340(8) A; HgꢀꢀꢀCl 3.0230(8) A; Hg–ClꢀꢀꢀHg 96.98(3)8; N2–Hg–Cl 101.19(8)8; C8–Hg–Cl 151.94(9)8.
D
˚
Sn–Cl 2.5277(8) A; N2–Sn–Cl 88.82(7)8; C8–Sn–Cl 100.77(7)8.
E
˚
˚
Ar* ¼ 2,4,6-tBu3C6H2; Sn–P 2.698(2) A; P–C17 1.856(4) A; N2–Sn–P 98.49(12)8; C8–Sn–P 104.76(11)8.

1074
S. M. El-Hamruni et al.
(a)
Table 3. Relative contributions of the different intermolecular con-
tacts to the Hirshfield surface for the polymorphic structures of LiR (1)
Si2
Intermolecular contact
LiR (orthorhombic)
LiR (triclinic)
N3
N1
Li
C1
N2
HꢀꢀꢀH
LiꢀꢀꢀH
NꢀꢀꢀH
CꢀꢀꢀH
94.8 %
3.9 %
0.6 %
0.7 %
95.5 %
3.8 %
0.4 %
0.4 %
C8
Si1
Si3
˚
The Hg atom in 2 lies 0.321(2) A above the plane defined by
C8, Cl, and N2 so coordination at Hg is almost planar (sum of
bond angles 3528). The Hg–Cl and Hg–C bond lengths
˚
˚
(2.150(3) A and 2.4340(8) A, respectively) are slightly longer
than those in the related species A–C (ranges: Hg–C 2.092(9) to
˚
˚
2.124(3) A; Hg–Cl 2.320(3) to 2.3466(9) A). The bonding of the
nitrogen in the six-membered metallacycle is stronger than that
in the five-membered ring of C, as shown by the Hg–N bond
(b)
Si2
˚
lengths of 2.409(3) and 2.611(3) A, respectively. This is also
reflected in the C–Hg–Cl angle in 2 (151.94(9)8), which is
significantly narrower than the corresponding angles in
A (171.0(3)8 and 171.3(3)8), B (R ¼ H, 174.5(4)8; R ¼ Me
174.9(3)8), and C (173.43(9)8). The sum of the angles at C8
(SC) is 3428 (cf. 3488 or 3508 in 1) showing that less negative
charge is delocalised from the metal on to silicon in 2 than in 1.
The molecular structure of 3 contains a three-coordinate
tin(II) atom with kC,N-bidentate coordination for the ligand R
and a terminal chloride (Fig. 7). Compounds D[18] and E[19]
(Fig. 9) adopt similar monomeric structures, whereas the related
species F and G[20] dimerise in the solid-state via a central
Sn2Cl2 metallacycle. The sum of angles at tin (SSn) decreases
within the series of monomeric compounds SnR0Cl, containing
six- (3, SSn ¼ 2838), five- (D, SSn ¼ 2748), and four-
(E, SSn ¼ 2548 av.) membered stannacycles; this is accompa-
nied by a reduction in the bite angle of the ligand (C–Sn–N:
3 93.77(9)8; D 85.57(13)8; E 61.6(6) av.). The SC value of 3408
in 3 shows only weak delocalisation of carbanionic charge on
to the Si3 system.
N3
C1
Li
C8
N2
N1
Si3
Si1
Fig. 3. Projection of the structures of (a) [1]N (orthorhombic) and (b) [1]2
(triclinic) looking along the C–Li–N plane.
Orthorhombic
Li
Triclinic
Li
C13
The Sn–N distance in 3 is significantly shorter than that in
D and E but the Sn–C bond is intermediate between that found in
the other two compounds (Fig. 9). A similar pattern is apparent
in comparisons of hpp and 2-pyridyl derivatives of lithium[6] and
zinc,[8] for which the nitrogen of the ligand (Me3Si)2(Me2{hpp}
Si)Cꢁ binds more strongly to the metal than that in (Me3Si)2
(Me2{C5H4N}Si)Cꢁ. These parameters reflect both electronic
and steric effects. Thus hppMe (pKa ¼ 25.4)[21] is a stronger
base than pyridine (pKa ¼ 12.3)[22] in MeCN and a six-
membered chelate ring is less strained than a five-membered
one. These data strengthen our conclusion[8] that ligand R is
more bulky than previously studied ligands but still forms strong
metal–nitrogen bonds.[8]
C14
∗ ꢁ C13
Polymer
Li
∗
Li
#
# ꢁ C14
Dimer
The ligand (Me3Si)2(Me2hppSi)Cꢁ is thus a versatile bulky
bidentate ligand for a wide range of metals. Table 4 shows that as
the metal becomes less electropositive the bond to the imine
nitrogen becomes weaker relative to the bond to the carbanion
centre; i.e. the ligand tilts away from bidentate coordination, and
the ligation becomes closer to k-C-monodentate.
Fig. 4. Thermal ellipsoid figures (50 % ellipsoids) and corresponding
Hirshfield surface plots (normalised contact distance, dnorm) for the ortho-
rhombic (left, range: ꢁ0.63 to þ1.68) and triclinic (right, range: ꢁ0.59 to
þ1.42) polymorphs of LiR (1) in two orientations (top and middle).
˚
values of 3.240(8) and 3.121(9) A. As the intermolecular HgꢀꢀꢀCl
˚
In the mercury compound 2 the conformation of the
HgCSiNCN ring is almost identical to that in the orthorhombic
structure of RLi [1]N, with the sum of internal angles 6748,
distance in [2]2 is 3.0230(8) A the association is stronger than
that in the related silyl-substituted compounds A[15] and B[16]
(Fig. 8). The 2-pyridyl analogue HgCl[C(SiMe3)2
(SiMe2{C5H4N})] (C)[17] is best considered as monomeric as
˚
torsion angle y ¼ 38.0(2)8 and Si1 displacement d1 ¼ 0.023(5) A
˚
(see Fig. S1, Supplementary Material). The bite angle in 2 is
all intermolecular distances to mercury are . 4 A.

Tin and Mercury Guanidinato Compounds
1075
Orthorhombic
Triclinic
de
de
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
Full FP
Full FP
di
di
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
de
de
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
#
#
#
#
...
...
Li H only
Li H only
di
di
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Fig. 5. Fingerprint (FP) plots for the orthorhombic and triclinic polymorphs of LiR. The LiꢀꢀꢀH contacts are highlighted in the
lower figures, with the major interactions labelled #.
N3
Si2
C1
N2
N1
N3
Cl
N1
Hgꢀ
C8
Si1
C1
Si1
Hg
Clꢀ
Si3
Si3
C8
Sn
N2
Si2
Cl
Fig. 6. Thermal ellipsoid plot of [2]2 (30 % ellipsoids, H-atoms omitted).
Symmetry generated atoms: 1 – x, 1 – y, –z.
Fig. 7. Thermal ellipsoid plot of 3 (30 % ellipsoids, H-atoms omitted).
16.78 narrower than in [1]N and the Si1–C8–Hg angle larger by
9.58. The metallacycle conformation in the tin compound 3 is
closer to that in the triclinic [1]2 polymorph. These results show
that there is considerable flexibility in the large group R attached
to both more electropositive and less electropositive metals. In
both 2 and 3 the conformation of the hpp group is similar to that
The 1H, 13C, 29Si, 199Hg, and 119Sn NMR spectra show that
the structures found in the solid-state are preserved in solution;
assignments are given in the Experimental section. The 1H and
13C NMR spectra of 2 show singlets for the SiMe2 and SiMe3
resonances, indicating that on the NMR timescale the two sets of
methyl groups are equally distributed above and below the plane
in [1]N
.

1076
S. M. El-Hamruni et al.
of the metallacycle. In contrast the pyramidal geometry of the tin
atom in 3 is shown by two signals for both SiMe2 and SiMe3
resonances in 1H and 13C NMR spectra and two resonances for
the silicon atoms of the SiMe3 groups at dSi ꢁ5.5 and ꢁ5.3 ppm.
The 199Hg NMR spectrum of compound 2 showed a reso-
nance of dHg ꢁ761 ppm, similar to those in A (dHg ꢁ888 ppm)
and B (dHg ꢁ814). We were not able to detect the signal for the
CSi3 carbon in the 13C{1H} NMR spectrum. The presence of the
A
C
ꢁ
ꢁ
3
Hg–C bond was inferred in solution, however, from JHgC
coupling to both the SiMe2 (71 Hz) and SiMe3 (65 Hz) groups.
Although it is not common to observe three bond coupling
between mercury and carbon, the coupling constants for
2 are close to those reported for 1,4-bis(methylmercury)-2-
methylbutane determined by two-dimensional 13C,199Hg corre-
lation experiments (77 and 98 Hz),[23] but lower than those
found in organomercury compounds with the aryl-bound
‘pincer’ ligand, 2,6-[O(CH2CH2)2NCH2]2C6H3] (3JHgC: 109,
115 Hz for the methylene groups; 180, 185 Hz for the m-carbons
of the aromatic ring).[24]
B
[2]2
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
The 119Sn chemical shift for 3 (dSn 196 ppm) is at a lower
frequency than that recorded for the similar [Sn(R0)(m-Cl)]n
compounds D (dSn 378 ppm), E (dSn 351 ppm), F (dSn 469 ppm),
and G (dSn 777 ppm), illustrating the large range of chemical
shifts observed in these systems. The CSi3 resonance was
observed at dC 28.7 ppm in the 13C{1H} NMR experiment, with
1J119SnC 407 Hz. The data may be compared with those for D (dC
28.6 ppm, 1J119SnC 434 Hz), G (dC 37.1 ppm, 1J119SnC 420 Hz),
or F (dC 32.7 ppm, 1J119SnC 348 Hz).
Fig. 8. Associated dimers (A and B, n ¼ 2) and monomers (C, n ¼ 1) of
organomercury compounds [Hg(R0)(m-Cl)]n in which R0 ¼ a silyl-substituted
alkyl ligand.
The Organotin Phosphanide
3
D
E
In a parallel investigation we have recently described the
synthesis of SnII derivatives containing the bulky bidentate
ligand, Sn(BDI)(PR02), [BDI ¼ CH{C(Me)NAr}2] (Ar ¼ 2,6-
iPr2C6H3), from reactions of Sn(BDI)Cl with LiPR02 (R0 ¼ Ph,
Cy, SiMe3).[25] The conformations of the chelate ring[26] and the
orientations of the phosphanide substituents are constrained by
the steric requirements of both the BDI ligand and the organic
groups attached to phosphorus. To examine the extent to which
substituents attached to tin were similarly restricted in com-
pounds containing the ligand (Me3Si)2(Me2{hpp}Si)Cꢁ, we
made a preliminary study of the reaction between 3 and the
lithium salt of the crowded phosphane Ar*PH2 (Ar* ¼ 2,4,6-
tBu3C6H2). This gave the compound SnR(P{H}Ar*) 4, which
we characterised by elemental analysis, NMR spectroscopy, and
an X-ray crystallographic study.
F
G
Fig. 9. Organotin compounds [Sn(R0)(m-Cl)]n (3, D, and E, n ¼ 1; F and G,
n ¼ 2) in which R0 ¼ a silyl-substituted alkyl ligand.
The structure of monomeric 4 in the solid-state is shown in
Fig. 10. The position of the hydrogen-atom on the phosphorus
could not be confidently assigned, and is omitted from the
refinement. The bulky ligands attached to tin and phosphorus
can be accommodated with only minor changes in the molecular
parameters of the RSn metallacycle. Replacement of Cl by the
P{H}Ar* fragment results in a flattening of the bonds at tin (sum
of bond angles increased from 2838 to 2968) and in a small but
significant lengthening of the Sn–C and Sn–N bonds (Table 2).
As both bonds are elongated to a similar extent the change is
attributed to crowding rather than to a change in the effective
˚
Table 4. Comparison of M–C and M–N bond lengths (A) with electro-
negativity values in [MR] fragments
˚
M–C [A]
Metal
Electronegativity
(Pauling)
M–N
˚
[A]
Reference
KA
Ca
Li
0.8
1.0
1.0
3.173
2.668
2.094
2.090
2.043
2.285
2.169
2.210
2.150
2.718
2.373
1.926
1.921
2.018
2.213
2.142
2.309
2.409
[6]
[7]
[6]
This paper
[8]
Zn
1.65
1.8
SnII
InIII
SnIV
Hg
This paper
B
˚
Lewis acidity of the tin centre. The Sn–P bond in 4 (2.698(2) A)
1.78
2.0
is significantly longer than that found in the only other com-
pound in the CCDC database containing the SnP{H}C fragment,
[{SnPAr*}2(m-NMe2)(SnP{H}Ar*)], for which the terminal
B
2.0
This paper
Sn–P length is 2.640(2) A.[27] It is also longer than those found
˚
APolymeric in the solid-state.
BCrystal structure data (.cif files) for InRCl2 and SnRMe2Cl have been
in three-coordinate Sn(BDI)(PR02) species (range 2.5526(7) to
deposited with the CCDC (numbers 995412 and 995413, respectively).
2.6612(12) A),[25] possibly reflecting the bulk of the ligand R.
˚

Tin and Mercury Guanidinato Compounds
1077
The M–P–C angle associated with metal bound P{H}Ar*
ligands is extremely sensitive to the size and shape of the metal-
containing fragment. For example, substitution of the cyclo-
pentadienyl ligands in ZrCp2Cl(P{H}Ar*}[28] by bulkier Cp*
(Cp* ¼ C5Me5) to give ZrCp*2Cl(P{H}Ar*),[29] increases this
angle by ,108, from 128.4(2)8 to 138.8(8)8. At the other
extreme, acute M–P–C angles (97.7(2)8 to 101.9(6)8) are
observed in the three- and four-coordinate gallium phosphanides
Ga(tBu)(P{H}Ar*)2,[30] and [Ga(tBu)(P{H}Ar*)(m-Cl)]2.[31]
The Sn–P–C17 angle in 4, 95.77(14)8, is one of the most acute
M–P–Ar* angles to be crystallographically characterised. The
only examples of smaller angles are in the series [M(P{H}Ar*)
(18-crown-6)] where M ¼ K (85.57(7)8),[32] Rb (78.85(11)8),[32]
or Cs (62.4(2)8/56.0(2)8 for two independent molecules),[33]
where Mꢀꢀꢀaryl interactions contribute to the reduced angles in
the Rb and Cs derivatives. The Sn atom in 4 is displaced
towards one side of the C6-ring of the phosphanide (Fig. 11),
˚
with SnꢀꢀꢀC17 and SnꢀꢀꢀC22 distances of 3.24 and 3.76A,
˚
respectively. The SnꢀꢀꢀC32 bond distance is 3.60A, although it
is noted that there is disorder in the position of the methyl groups
of this tBu substituent. These distances are, for the most part,
longer than for the p-bound aryl groups in [(Z6-C6HnMe6 – n
)
[34]
˚
SnCl(AlCl4)]4 (n ¼ 0, range 2.897(5) to 3.110(5) A;
n ¼ 3,
[35]
˚
range 2.883(3) to 3.189(3)A;
n ¼ 5, range 2.975(3) to
3.347(2) A[36]) suggesting that any interaction in 4 is weak.
The C6-ring of the Ar* group of the phosphanide is significantly
distorted from planarity. The ipso-carbon C17 is displaced
˚
Si2
˚
0.24 A ‘above’ the plane of the remaining five carbon atoms,
with the CMe3 carbon atoms C23 and C31 located 0.26 and
Si1
C8
˚
0.39 A ‘below’ this plane, respectively (Fig. 11b).
N1
The coupling between Sn, P, and H was examined by multi-
nuclear NMR spectroscopy. The PH resonance in 4 appears as a
doublet in the expected region (dH 4.62 ppm), with 1JPH 186 Hz
(Fig. 12). The magnitude of this coupling is less than in the
parent phosphane Ar*PH2 (207 Hz), which appears as a minor
decomposition product. It is also less than the 1JPH values (range
203–269 Hz) in other terminal P{H}Ar* phosphanides cited in
this manuscript.
C1
Si3
N3
N2
Sn
P
Additional coupling to Sn is observed in the 1H NMR
2
spectrum of 4, with JSnH 57 Hz. Although the magnitude of
C17
this coupling is similar to that for the terminal Sn–H in three-
coordinate Sn(BDI)H (1JSnH 64 Hz),[37] it is considerably less
than is observed in the terphenyl compounds [Ar0Sn(m-H)]2
(87–95 Hz) [Ar0 ¼ C6H2-4-X-2,6-(C6H3-2,6-iPr2)2, X ¼ H, OMe,
tBu, SiMe3],[38] highlighting the range of values associated
with a one-bond Sn–H coupling. A wide range of two-bond
coupling to the methyl group has also been noted for a series
of compounds SnMen(X)4 – n (X ¼ Cl, Br, I or Ph) (2JSnH
Fig. 10. Thermal ellipsoid plot of 4 (20 % ellipsoids, H-atoms omitted).
1
56–101.5 Hz).[39] The value of JSnP in 4 (1002 Hz) is greater
(a)
(b)
Si1
Si2
Si1
C8
C8
P
N1
N1
Si3
Sn
C32
C1
N3
C33
N2
C1
Sn
C17
N2
C31
C23
C22
C34
P
C17
C23
C31
Fig. 11. Views of the core of 4, (a) highlighting the displacement of the Sn atom towards one side of the aromatic ring and (b)
showing the curvature of the Ar* group.

1078
S. M. El-Hamruni et al.
1H NMR
1JSnP
119Sn NMR
400, 500, and 600 MHz spectrometers. Chemical shifts were
referenced to residual solvent peaks or external standards and
are given relative to SiMe4, H3PO4, SnMe4, or HgMe2. Spectra
at lower temperatures were recorded in toluene solution. Com-
pound 1 was made according to our previously published
procedure.[6]
1
186 Hz
JPH
1002 Hz
320 310 300 290 280 270 260 250
Hg[C(SiMe3)2(SiMe2{hpp})]Cl (2)
†
2
57 Hz
4.6
JSnH
1
A solution of MeLi (0.91 mL of a 1.6 M solution in Et2O,
1.46 mmol) was added slowly to a stirred solution of HC
(SiMe3)2(SiMe2hpp) (0.52 g, 1.46 mmol) in THF (20 mL) at
room temperature. The mixture was stirred for 6 h, and then
added drop-wise to a stirred solution of HgCl2 (0.40 g,
1.45 mmol) in THF (15 mL) at ꢁ1108C. The mixture was
allowed to warm to room temperature overnight and the solvents
were removed under vacuum to leave a solid that was extracted
with toluene (3 ꢂ 15 mL). The extract was filtered, its volume
reduced to 10 mL, and the solution allowed to stand at room
temperature to give colourless crystals suitable for an X-ray
structure determination. Mp 125.6–126.28C. Yield 0.55 g
(64 %).
Anal. Calc. for C16H36ClHgN3Si3: C 32.53, H 6.14, N 7.11.
Found: C 32.65, H 5.99, N 7.21 %. dH (399.5 MHz, C6D6) 0.26
(s, 18H, SiMe3), 0.36 (s, 6H, SiMe2), 1.23, 1.52, 2.40, 2.45, 2.74,
3.54 (m 2H, hpp-CH2). dC (100.5 MHz, C6D6) 5.8 (3JHgC 65,
1JSiC 53, SiMe3) 5.9 (3JHgC 71, 1JSiC 58, SiMe2) 23.5, 24.4, 42.0,
42.3, 48.0, 48.5 (hpp-CH2), 155.3 (hpp-CN3). The quaternary
(SiC3) carbon signal was not identified. dSi (79.5 Hz, C6D6) 38.9
(SiMe3), 43.4 (SiMe2). dHg (107.3 MHz, C6D6) ꢁ761. m/z (EI)
591 (20 %, [Mþ]) 576 (20, [M ꢁ Me]þ), 354 (80, [hppSiMe2C
(SiMe3)2]þ) 324 (40, [hppSiMe2C(SiMe2)2]þ), 196 (hppSiMe2)þ,
138 (hppþ), 73 (SiMeþ3 ). The identity of the molecular ion was
confirmed by the isotope pattern.
207 Hz
JPH
4.9
4.8
4.7
4.5
4.4
4.3
4.2
4.1
4.0
1
Fig. 12. Main: H NMR spectrum (C6D6, 298 K, 600 MHz) of the P{H}
Ar* region of 4 (y PH2Ar* decomposition product). Inset: 119Sn{1H} NMR
spectrum (C6D6, 298 K, 223 MHz) of 4.
than that observed for [{SnPAr*}2(m-NMe2)(SnP{H}Ar*)]
(800 Hz),[27] but similar to the values observed for Sn(BDI)
(PR02) (R0 ¼ Ph, 978 Hz; R ¼ Cy, 964 Hz).[25] These data rule
out firm conclusions about the exact nature of the Sn–P–H
bonding in 4 in solution and, given the limitations associated
with the precise location of hydrogen atoms by X-ray diffrac-
tion, we are at present reluctant to claim a P–H agostic-type
interaction in 4.
The NMR spectra of 4 (benzene or toluene solutions) also
suggest that conformations different from that found in the
crystal may be present in dynamic equilibrium, so that the
chemical shifts and coupling constants in the Experimental
section represent average values. For example, at 258C a broad
peak is observed in the 31P{1H} NMR spectrum at dP ꢁ76.0
ppm. When the sample is cooled to ꢁ408C this signal separates
into two peaks, each with 119Sn satellites (dP ꢁ77.1 ppm, 1JSnP
1007 Hz; dP ꢁ97.3, 1JSnP 719 Hz) with relative intensities ,3 to
1 (Fig. S2, Supplementary Material). Temperature-dependent
splittings in spectra of ZrCp2(P{H}Ar*)X (X ¼ Cl, P{H}Ar*)
have been attributed to inversion at phosphorus and rotation
about the P–C bond,[40] and it is possible that similar conforma-
tion changes account for the spectra of 4. Further splittings of
some of the peaks are observed when samples are cooled below
ꢁ408C. These probably reflect restricted rotations resulting
from steric interactions between the bulky ligands.
Sn[C(SiMe3)2(SiMe2{hpp})]Cl (3)
A solution of MeLi (1.6 mL of a 1.6 M solution in Et2O,
2.56 mmol) was added to a solution of HC(SiMe3)2(SiMe2hpp)
(0.86 g, 2.42 mmol) in THF (15 mL) and the mixture was stirred
overnight at room temperature. A solution of SnCl2 (0.46 g,
2.42 mmol) in THF (15 mL) was added and the orange mixture
stirred for 7 h at room temperature. The solvent was removed
under vacuum and the residue extracted with hexane (15 mL).
The extract was filtered, concentrated, and kept at ꢁ258C to give
colourless crystals of Sn[C(SiMe3)2(SiMe2{hpp}]Cl. Yield
0.37 g (30 %).
Anal. Calc. for C16H36N3ClSi3Sn: C 37.72, H 7.07, N 8.25.
Found: C 37.64, H 7.06, N 8.18 %. dH (599.7 MHz, C6D6) 0.37
(s, 3H, SiMe2), 0.40 (s, 9H, SiMe3), 0.44 (s, 3H, SiMe2), 0.57
(s, 9H, SiMe3), 1.09 (m, 1H, hpp-CH2), 1.17 (m, 2H, hpp-CH2),
1.81, 2.23, 2.24, 2.33, 2.44, 2.84, 2.88, 3.04, 3.24 (m, 1H, hpp-
CH2). dC (150.8 MHz, C6D6) 5.0 (1JSiC 56, SiMe2), 5.0 (1JSiC 50,
SiMe3), 5.7 (1JSiC 59, SiMe2), 6.0 (1JSiC 50, SiMe3), 22.7, 23.4
(hpp-CH2), 28.7 (1JSiC 36, 1J119SnC 407, CSi3), 41.5, 45.3, 47.8
(hpp-CH2), 160.0 (hpp-CN3). dSi (119.1 MHz, C6D6) ꢁ5.5,
ꢁ5.3 (SiMe3), 1.2 (SiMe2). dSn (223.7 MHz, C6D6) 196.
Conclusions
The guanidinato compounds described in this and previous
papers form a series MC(SiMe2)2(SiMe2hpp)Ln, similar to the
series MC(SiMe2)2(SiMe2X)Ln (X ¼ NMe2 or C5H4N). The
structural parameters of the chelate rings are determined prin-
cipally by the number of atoms in the metallacycle, the basicity
of the N-donor atoms, and the Lewis acidity of the metal centre.
The compounds characterised so far have potential as reagents
for the synthesis of derivatives of other metals, including those
in unusual oxidation states. Complexes in which a chelate ring is
transiently opened in solution could be developed as catalytic
intermediates.
Experimental
Sn[C(SiMe3)2(SiMe2{hpp})](PH{2,4,6-tBu3C6H2}) (4)
General
Ar*PH2 (0.50 g, 1.79 mmol) was dissolved in THF (15 mL) and
cooled to ꢁ788C. nBuLi (0.72 mL of a 2.5 M solution,
1.79 mmol) was added and the mixture stirred for 1 h at ꢁ788C,
to give a cloudy yellow suspension. This suspension was added
to a cooled (ꢁ788C) solution of 3 (0.91 g, 1.79 mmol) in THF
Samples were prepared under a dry nitrogen atmosphere by
standard Schlenk-tube or glove-box techniques and solvents
were dried by standard methods. 1H, 13C, 29Si, 31P, 119Sn, and
199Hg NMR spectra were recorded in C6D6 at 300 K, on Varian

Tin and Mercury Guanidinato Compounds
1079
(20 mL). The mixture was allowed to attain room temperature,
during which time a deep red/orange solution was formed. The
volatiles were removed after 18 h at room temperature to
afford an orange solid. Extraction with toluene and crystal-
lisation from pentane afforded 4 as very fine yellow needles.
Yield 0.51 g (38 %).
Acknowledgements
The authors thank a reviewer for comments about the polymorphism of 1.
SME-H is grateful to Tripoli University for financial support.
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Anal. Calc. for C34H66N3PSi3Sn: C 54.30, H 8.85, N 5.59.
Found: C 54.20, H 8.78, N 5.53 %. dH (599.7 MHz, C6D6) 0.30
(s, 3H, SiMe2), 0.40, 0.54 (s, 9H, SiMe3), 0.59 (br s, 3H, SiMe2),
1.10 (br m, 4H, hpp-CH2), 1.38 (s, 9H, p-tBu), 1.81 (s, 18H,
o-tBu2), 2.21 (m, 1H, hpp-CH2), 2.26 (m, 2H, hpp-CH2), 2.38
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3
(p-CMe3), 31.9 (o-CMe3), 34.4 (d, JPC 7, o-CMe3), 34.5
3
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Li[C(SiMe3)2(SiMe2{hpp})]
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Sn[C(SiMe3)2(SiMe2{hpp})](P{H}Ar*)
The H-atom on the phosphorus could not be located from the
difference map, and was omitted from the solution. The C31 tBu
group was disordered and included with isotropic methyl C atom
positions.
HSs[42,43] and their associated FP plots[43,44] were generated
by use of CrystalExplorer (Version 3.1)[45] software from the
crystal structure coordinates supplied in the format of the
crystallographic information file (.cif).
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Crystallographic Data
CCDC numbers 995408 (1, triclinic), 995409 ([2]2), 995410 (3),
and 995411 (4). The .cif files for InRCl2 (995412) and
SnRMe2Cl (995413) have also been uploaded for reference
purposes. These data can be obtained free of charge via http://
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Supplementary Material
Overlay projections of the metallacycles of 1, 2, and 3, variable
temperature NMR data for 4, and thermal ellipsoid plots of
InRCl2 and SnRMe2Cl are available on the Journal’s website.

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