Synthesis and structural characterization of the first trialkylguanidinate and hexahydropyramidopyramidinate complexes of tin

Article abstract of DOI:10.1016/S0277-5387(01)01018-X

The first guanidinate complexes of tin have been prepared using N,N′,N″-trialkylguanidinates ([(RN)₂C(NRH)]-; R = cyclohexyl; isopropyl) and 1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyramidinate (hpp^-) as ligands. The direct reaction between triisopropylguanidine and SnCl₄ provided the complex {[ⁱPrN]₂C[NHⁱPr]}SnCl₃ (1) along with concomitant formation of the guanidinium salt {C[NHⁱPr]₃}+[SnCl₅(THF)]^- (2). The Sn(II) guanidinate complexes {(C₆H₁₁N)₂C [NH(C₆H₁₁)]}₂Sn (3) and {CN[N(CH₂)₃]₂}₂Sn (4) were prepared through metathesis reactions between 0.5 equiv. SnCl₂ and (C₆H₁₁N)₂C[NH (C₆H₁₁)]Li or hppLi, respectively. Complex 4 is the first reported mononuclear complex of this ligand. In contrast, the reaction of hppLi with 1 equiv. SnCl₂ afforded a bridging dinuclear species, {CN[N(CH₂)₃]₂SnCl}₂ (5). A second mononuclear complex of the hppligand, {CN[N(CH₂)₃]₂}₂SnCl₂ (6), was the product obtained from the reaction of 2 equiv. of hppLi with SnCl₄. The full structural details of compounds 1 and 3-6 are reported. In the case of compounds 1 and 3 these results revealed a distinctly unsymmetrical bonding mode for the bidentate guanidinate ligand and suggest variable degrees of π delocalization with the ligand. The geometries of the Sn centers in 3, 4 are derived from distorted trigonal bipyramidal coordination with a stereochemically active lone pair occupying one coordination site. In contrast, complex 5 displayed a geometry derived from a tetrahedral ligand array with one vertex occupied by a lone pair of electrons. Complex 6 is six coordinate and possesses 2 equiv. chelating bidentate hpp^- ligands and two cis-chloro groups.

Full text of DOI:10.1016/S0277-5387(01)01018-X

Polyhedron 21 (2002) 619–627
www.elsevier.com/locate/poly
Synthesis and structural characterization of the first
trialkylguanidinate and hexahydropyramidopyramidinate complexes
of tin
Stephen R. Foley, Glenn P.A. Yap, Darrin S. Richeson *
Department of Chemistry, Uni6ersity of Ottawa, Ottawa, Ont., Canada K1N 6N5
Received 28 June 2001; accepted 7 December 2001
Abstract
The first guanidinate complexes of tin have been prepared using N,N%,N%%-trialkylguanidinates ([(RN)2C(NRH)]−; R=cyclo-
hexyl; isopropyl) and 1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyramidinate (hpp−) as ligands. The direct reaction between
triisopropylguanidine and SnCl4 provided the complex {[iPrN]2C[NHiPr]}SnCl3 (1) along with concomitant formation of the
guanidinium salt {C[NHiPr]3}+[SnCl5(THF)]− (2). The Sn(II) guanidinate complexes {(C6H11N)2C[NH(C6H11)]}2Sn (3) and
{CN[N(CH2)3]2}2Sn (4) were prepared through metathesis reactions between 0.5 equiv. SnCl2 and (C6H11N)2C[NH(C6H11)]Li or
hppLi, respectively. Complex 4 is the first reported mononuclear complex of this ligand. In contrast, the reaction of hppLi with
1 equiv. SnCl2 afforded a bridging dinuclear species, {CN[N(CH2)3]2SnCl}2 (5). A second mononuclear complex of the hpp−
ligand, {CN[N(CH2)3]2}2SnCl2 (6), was the product obtained from the reaction of 2 equiv. of hppLi with SnCl4. The full structural
details of compounds 1 and 3–6 are reported. In the case of compounds 1 and 3 these results revealed a distinctly unsymmetrical
bonding mode for the bidentate guanidinate ligand and suggest variable degrees of p delocalization with the ligand. The
geometries of the Sn centers in 3, 4 are derived from distorted trigonal bipyramidal coordination with a stereochemically active
lone pair occupying one coordination site. In contrast, complex 5 displayed a geometry derived from a tetrahedral ligand array
with one vertex occupied by a lone pair of electrons. Complex 6 is six coordinate and possesses 2 equiv. chelating bidentate hpp−
ligands and two cis-chloro groups. © 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Guanidinate; 1,3,4,6,7,8-Hexahydro-2H-pyramido[1,2-a]pyramidinate; Tin; Mononuclear; Dinuclear
NCy)2SnꢀS and (CyNC(tBu)NCy)2GeꢀE (Cy=C6H11;
E=S, Se), were prepared by oxidative addition of
1. Introduction
styrene sulfide or elemental selenium to the correspond-
Amidinates are versatile ligands that have been used
to stabilize fundamentally interesting and catalytically
active complexes of tin and germanium. For example,
ing M(II) precursors, (CyNC(tBu)NCy)2M (M=Ge,
Sn) [1,2]. An unusual cyclotetrasulfido complex,
[CyNC(Me)NCy]Sn[N(SiMe3)2]S4, was prepared with
the terminal chalcogenido complexes, (CyNC(tBu)-
an amidinate supporting ligand [3]. Many of these
complexes function as excellent catalysts for the rapid
and selective cyclotrimerization of aryl isocyanates to
yield isocyanurates [3,4]. Additional variation of the
central NꢁCꢁN ligand framework can be achieved by
employing guanidinate ligands (Chart 1). Guanidinate
ligands should offer all of the coordination flexibility of
amidinates and may provide added steric and electronic
Chart 1.
variability. For example, the presence of a third nitro-
gen center in these species allows for variation of the
substitution pattern to give di-, tri-, or tetrasubstituted
ligands. The main resonance contributions for
* Corresponding author.
E-mail address: darrin@science.uottawa.ca (D.S. Richeson).
0277-5387/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)01018-X

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S.R. Foley et al. / Polyhedron 21 (2002) 619–627
Given the general lack of guanidinate complexes of
main group metals and of tin in particular, application
of these ligands to group 14 metals is warranted and we
now report the first Sn(II) and Sn(IV) complexes with
guanidinate ligands employing both monoanionic
N,N%,N%%-trialkylguanidinates and the pyramidinate an-
ion (hpp−). These include the first examples of
mononuclear complexes displaying chelating hpp−
ligand.
Chart 2.
2. Experimental
Chart 3.
2.1. General procedure
N,N%,N%%-trisubstituted guanidinate anions are summa-
rized in Chart 2. The zwitterionic structure I does not
have an analogy for amidinate ligands.
All manipulations were carried out in either a Vac-
uum Atmospheres drybox or under nitrogen using stan-
dard Schlenk-line techniques. Diethyl ether, toluene
and THF were sparged with nitrogen then dried by
passage through column of activated alumina using an
apparatus purchased from Anhydrous Engineering.
CH2Cl2 and CDCl3 were distilled under nitrogen from
CaH2. Deuterated benzene was distilled under nitrogen
from Na/K alloy. 1,3,4,6,7,8-Hexahydro-2H-pyrim-
ido[1,2-a]pyrimidine (Hhpp), SnCl2, SnCl4 and MeLi
(1.4 M in diethyl ether) were purchased from Aldrich
and used without further purification.
Guanidinates have received relatively limited atten-
tion as ligands in comparison with amidinates, with
only three reports for main group metal complexes of
N,N%,N%%-trisubstituted guanidinate anions appearing in
the literature. These consist of the lithium salts
Li2(C(NPh)3) [5], Li2(C(NtBu)3) [6], Li(C(NtBu)2-
(N(H)tBu)) [6] and the only p-block element complex,
[(iPrN)2C(NHiPr)][(iPrN)2C(NiPr)]Sb [7].
An interesting variation on the guanidinate frame-
work, in tetrasubstituted form, is provided by the anion
of
1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyrami-
NMR spectra were recorded on a Varian Gemini 200
MHz spectrometer with deuterated benzene or CDCl3
as a solvent and internal standard. All elemental analy-
ses were run on a Perkin–Elmer PE CHN 4000 elemen-
tal analysis system. All melting points were determined
on a Gallenkamp Melting Point Apparatus in sealed
capillary tubes.
dine (hpp−) (Chart 1). The steric bulk as well as the
orientation of the N lone pairs of this heterobicyclic
system is substantially restricted by the tethering of the
N centers. For example, it has been suggested that the
tying back of the N–R groups and the resultant projec-
tion of the s donor orbitals in a parallel direction
(Chart 3) is a critical difference between this species and
the amidinate anion and is one of the reasons that
hpp− promotes the formation of bridged dinuclear
transition metal complexes [8]. The restrictions of the
bicyclic framework should enhance the correct orienta-
tion for p-overlap of the central C center with all three
N centers and may stabilize resonance structure I and
Y-conjugation within the ligand.
2.2. Preparation of
{[(CH3)2CHN]2C[NHCH(CH3)2]}SnCl3 (1) and
{[(CH3)2CHNH]3C}SnCl5(THF) (2)
To a solution of 0.500 g N,N%,N%%-triisopropyl-
guanidine (2.70 mmol) in toluene (50 ml) was added 1
equiv. SnCl4 (0.703 g, 2.70 mmol). The reaction mixture
was stirred for 12 h and then was filtered to remove
complex 2 as an insoluble solid. Complex 1 was isolated
by removal of the reaction solvent under vacuum.
White crystals of 1 were obtained from diethyl ether at
The only reported main group metal complex of
hpp− is [(m-hpp)AlMe2]2 (II) [9]. As with all of the
reported transition metal complexes, this aluminum
complex adopts a dimeric structure in which the hpp−
ligands bridge two AlMe2 moieties.
1
−34 °C (0.54 g, 49% yield). H NMR (C6D6, ppm):
3.20, (br, overlapping signals CH, 3H); 3.19 (br, NH,
1H); 1.20 (d, JHH=6.6 Hz, CH3, 12H); 0.62 (d, JHH
=
6.0 Hz, CH3, 6H). 13C NMR (C6D6, ppm): 160.1 (s,
NCN); 48.2 (s, C(CH3)2); 46.4 (s, C(CH3)2); 23.4 (s,
CH3); 23.2 (s, CH3). 119Sn NMR (C6D6, ppm vs.
SnMe4): −356.9. Anal. Found: C, 29.76; H, 5.55; N,
9.81. Calc. for C10H22Cl3N3Sn: C, 29.34; H, 5.42; N,
10.26%. m.p. 54–56 °C.

S.R. Foley et al. / Polyhedron 21 (2002) 619–627
621
Solid 2 that was isolated from the above filtration
2.4. Preparation of {CN[N(CH2)3]2}2Sn (4)
was washed with toluene (3×5 ml) and dried. White
crystals of 2 were obtained from CH2Cl2 at −34 °C
(0.46 g, 35% yield). H NMR (CDCl3, ppm): 5.18 (d,
To a solution of 0.300 g Hhpp (2.16 mmol) in THF
(35 ml) was added 1.54 ml of MeLi (1.4 M, 2.16 mmol).
Gas evolution was observed during the addition. The
solution was stirred for 2 h then 0.5 equiv. SnCl2 (0.204
g, 1.08 mmol) was added. The solution was stirred for
an additional 24 h, filtered to remove LiCl and the
solvent removed under vacuum. White crystals of 4
were obtained from THF at −34 °C (0.31 g, 73%
1
JNH=7.8 Hz, NH, 3H); 4.37 (br, THF, 4H); 3.88 (br,
CH, 3H); 2.01 (br, THF, 4H); 1.33 (d, JHH=6.4 Hz,
CH3, 18H). 13C NMR (CDCl3, ppm): 152.1 (s, NCN);
45.3 (s, C(CH3)2); 22.7 (s, CH3). Anal. Found: C, 30.62;
H, 5.85; N, 7.51. Calc. for C10H24Cl5N3SnTHF: C,
30.44; H, 5.47; N, 7.61%. m.p. 133–134 °C.
1
yield). H NMR (CDCl3, ppm): 3.25, (br, CH2, 16H);
2.3. Preparation of {[(C6H11)N)2C[NHC(C6H11)]}2Sn
(3)
1.85 (br, CH2, 8H). The low solubility of 4 prevented us
from obtaining a 13C NMR spectrum. Anal. Found: C,
42.01; H, 6.10; N, 20.85. Calc. for C14H24N6Sn: C,
42.56; H, 6.12; N, 21.27%. m.p. 154–156 °C.
To a solution of 0.500 g N,N%,N%%-tricyclohexyl-
guanidine (1.64 mmol) in diethyl ether (40 ml) was
added 1 equiv. MeLi (1.17 ml, 1.4 M, 1.64 mmol). The
solution was stirred for 30 min followed by addition of
0.5 equiv. SnCl2 (0.155 g, 0.82 mmol). The reaction
mixture was stirred for an additional 12 h, filtered to
remove the LiCl precipitate and the solvent was re-
moved under vacuum. Crystals of 3 were obtained from
2.5. Preparation of {CN[N(CH2)3]2SnCl}2 (5)
Dropwise addition of 1.54 ml of MeLi (1.4 M, 2.16
mmol) to a THF (35 ml) solution of 0.300 g Hhpp (2.16
mmol) resulted in gas evolution and formation of a pale
yellow solution. This solution was stirred for 2 h then 1
equiv. SnCl2 (0.408 g, 2.15 mmol) was added. The
reaction mixture was stirred for an additional 24 h,
filtered to remove LiCl and the solvent removed under
vacuum. White crystals of 5 were obtained from
CH2Cl2 at −34 °C (0.40 g, 63% yield). 1H NMR
(CDCl3, ppm): 3.40, (br, CH2, 8H); 3.20 (br, CH2, 8H);
1.94 (br, CH2, 8H). 13C NMR (CDCl3, ppm): 144.9 (s,
NCN); 47.4 (s, CH2); 40.9 (br, CH2); 23.6 (br, CH2).
Anal. Found: C, 27.02; H, 4.23; N, 12.58. Calc. for
C14H24Cl2N6Sn2(CH2Cl2): C, 26.91; H, 3.91; N, 12.55%.
m.p. 175 °C (dec.).
1
diethyl ether at −34 °C (0.47 g, 78% yield). H NMR
(C6D6, ppm): 3.95, (br, C6H11, 2H); 3.40 (br d, JNH=11
Hz, NH, 2H); 3.10 (br, C6H11, 2H); 2.90 (br, C6H11,
2H); 2.19–0.74 (m, C6H11, 60H). 13C NMR (C6D6,
ppm): 148.4 (s, NCN); 55.0, 52.0, 49.2, 35.9, 34.7, 34.0,
26.8, 26.6, 25.9, 25.6, 25.3 (11s, C6H11, intensity ra-
tio:1:1:1:2:2:2:1:1:1:4:2). Anal. Found: C, 62.29; H,
9.56; N, 11.11. Calc. for C38H68N6Sn: C, 62.72; H, 9.42;
N, 11.55%. m.p. 163–164 °C.
2.6. Preparation of {CN[N(CH2)3]2}2SnCl2 (6)
Table 1
Crystal data and structure refinement for {[iPrN]2C[NHiPr]}SnCl3 (1)
and {[CyN)2C[NHCy]}2Sn (3)
Dropwise addition of 2.56 ml of MeLi (1.4 M, 3.58
mmol) to a THF (50 ml) solution of 0.500 g Hhpp (3.59
mmol) resulted in gas evolution and formation of a pale
yellow solution. This solution was stirred for 30 min
then 0.5 equiv. SnCl4 (0.470 g, 1.80 mmol) was added.
The reaction mixture was stirred for an additional 24 h,
filtered to remove LiCl and the solvent removed under
vacuum. White crystals of 6 were obtained from THF
at −34 °C (0.40 g, 48% yield). 1H NMR (CDCl3,
ppm): 3.22, (br, CH2, 8H); 3.10 (br, CH2, 8H); 1.91 (br,
CH2, 8H). 13C NMR (CDCl3, ppm): 155.4 (s, NCN);
46.2 (s, CH2); 40.4 (br, CH2); 23.7 (br, CH2). Anal.
Found: C, 36.50; H, 5.56; N, 17.74. Calc. for
C14H24Cl2N6Sn: C, 36.08; H, 5.19; N, 18.03%.
1
3
Empirical formula
Formula weight
Temperature (K)
C
10H22Cl3N3Sn
C38H68N6Sn
719.61
298(2) K
0.71073
C2/c
409.35
203(2) K
0.71073
P21/c
,
u (A)
Space group
,
a (A)
13.980(1)
10.501(1)
11.828(1)
90
97.041(2)
90
1723.2(3)
4
1.578
17.542(7)
12.284(7)
18.584(9)
90
93.36(1)
90
3998(3)
4
1.196
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (g cm−3
)
2.7. Structural determinations for 1, 3, 4, 5 and 6
v (mm−1
R1
)
1.934
0.0307
0.0605
0.671
0.0626
0.1185
Single crystals were mounted on thin glass fibers
using viscous oil and then cooled to the data collection
temperature. Crystal data and details of the measure-
wR2
2 1/2
R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ. wR2=(Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwꢀFoꢀ )
.

622
S.R. Foley et al. / Polyhedron 21 (2002) 619–627
Scheme 1.
ments are summarized in Tables 1 and 4. Data were
collected on a Bruker AX SMART 1k CCD diffrac-
tometer using 0.3° ꢀ-scans at 0°, 90°, and 180° in ƒ.
Unit-cell parameters were determined from 60 data
frames collected at different sections of the Ewald
sphere. Semi-empirical absorption corrections based on
equivalent reflections were applied. The structures were
solved by direct methods, completed with difference
Fourier syntheses and refined with full-matrix least-
squares procedures based on F2. All non-hydrogen
atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were treated as ideal-
ized contributions. All scattering factors and anoma-
lous dispersion factors are contained in the SHELXTL
5.1 program library.
Further confirmation of the connectivity of 1 comes
from a single crystal X-ray diffraction study (Table 1).
The resultant structure with atom labeling scheme is
shown in Fig. 1 and corresponding values for bond
distances and angles are given in Table 2. These results
confirm the pseudotrigonal bipyramidal coordination
environment for the Sn(IV) center consisting of one
chelating bidentate guanidinate ligand spanning axial/
equatorial sites and three chloride ligands. The pseudo-
equatorial plane is defined by N(1) of the guanidinate
ligand and Cl(1) and Cl(2) (S angles=357°). The
pseudo-axial vector defined by Cl(3)ꢁSnꢁN(2) exhibits
an angle of 159.76(7)°.
While the sum of the angles around the central
carbon, C(7), and N(2) of the NCN framework indicate
planarity, the sum of angles around N(1) is only 349°,
possibly indicating that it retains some sp3 character.
As a result, the ligand does not yield a planar four-
membered ring with the Sn center. Further asymmetry
is observed in the ligand with the N(1)ꢁC(7) distance
3. Results and discussion
3.1. N,N%,N%%-Trialkylguanidinate complexes of tin
,
(1.361(4) A) being slightly longer than the N(2)ꢁC(7)
The reaction of N,N%,N%%-triisopropylguanidine with
SnCl4 proceeded smoothly at room temperature as de-
picted in Scheme 1 to give complexes 1 and 2. In this
case, we envisage the parent guanidine functioning as
the base to generate the guanidinate anion bonded to 1
and the guanidinium cation of compound 2 [10]. The
two products of this reaction were easily separated due
to their differences in solubility and we were able to
propose formula for each species on the basis of NMR
spectroscopic and microanalytical characterization. The
1H and 13C NMR spectra of complex 1 show two sets
of isopropyl resonances in a ratio of 2:1 consistent with
formation of a monoanionic ligand with rapid rotation
of the N(H)iPr group at room temperature. The most
obvious change in the 13C NMR for the guanidine
upon deprotonation and coordination is a shift for the
central sp2 carbon, CN3, from 148 to 160 ppm. This is
in accord with the formulation for 1 as a monoanionic
guanidinate complex [11]. Complex 1 was stable in
solution at temperatures up to 125 °C.
,
distance (1.341(3) A). The third guanidinate nitrogen,
N(3), lies in the plane of the ligand (SnꢁC(7)ꢁN(3)
179.1(2)°) and the C(8)ꢁN(3)ꢁC(7) angle of 127.3(3)°
suggests sp2 hybridization about N(3). The short
,
N(3)ꢁC(7) distance of 1.339(4) A indicates a degree of
multiple bonding between these centers. For conjuga-
tion of the p orbital of an sp2 N(3) with the p system of
Complex 2, [(iPrNH)3C+][SnCl5(THF)−], is appar-
ently derived from the reaction of guanidinium hydro-
chloride, the byproduct in the formation of 1, with
SnCl4. The 1H and 13C NMR spectra of 2 are consistent
with formation of guanidinium cation and clearly show
Fig. 1. Molecular structure and atom numbering scheme for
{[iPrN]2C[NHiPr]}SnCl3 (1). Hydrogen atoms have been omitted for
clarity.
i
only one set of resonances for the equivalent Pr groups
of this species [12].

S.R. Foley et al. / Polyhedron 21 (2002) 619–627
623
Table 2
the N(1)ꢁC(7)ꢁN(2) group, the plane defined by
C(8)ꢁN(3)ꢁC(7) should be coincident with the plane
defined by N(1)ꢁC(7)ꢁN(2). The observed angle be-
tween these two planes of 32.9° allows some degree of
p bonding between N(3) and C(7). On the basis of these
results it appears that all three C(7)ꢁN bonds of the
guanidinate have some degree of double bond character
with resonance contributors II and III being particu-
larly important in a bonding description for 1.
,
Selected bond distances (A) and angles (°) for complex 1
Bond distances
SnꢁN(1)
SnꢁN(2)
SnꢁCl(1)
SnꢁCl(2)
SnꢁCl(3)
SnꢁC(7)
N(1)ꢁC(7)
N(1)ꢁC(1)
N(2)ꢁC(7)
2.091(2)
2.137(2)
2.3188(9)
2.3221(9)
2.3897(9)
2.564(3)
1.361(4)
1.485(4)
1.341(3)
N(2)ꢁC(4)
N(3)ꢁC(7)
N(3)ꢁC(8)
C(1)ꢁC(2)
C(1)ꢁC(3)
C(4)ꢁC(6)
C(4)ꢁC(5)
C(8)ꢁC(9)
C(8)ꢁC(10)
1.474(4)
1.339(4)
1.465(4)
1.515(4)
1.525(4)
1.512(4)
1.523(5)
1.524(5)
1.531(5)
Bond angles
N(1)ꢁSnꢁN(2)
N(1)ꢁSnꢁCl(1)
N(2)ꢁSnꢁCl(1)
N(1)ꢁSnꢁCl(2)
N(2)ꢁSnꢁCl(2)
63.48(9)
121.87(7)
96.13(7)
124.81(7)
97.18(7)
C(7)ꢁN(2)ꢁSn
C(4)ꢁN(2)ꢁSn
92.11(17)
140.87(19)
127.3(3)
110.9(3)
111.1(3)
111.1(3)
108.4(3)
112.1(3)
111.9(3)
124.2(3)
124.9(3)
110.8(3)
179.1(2)
56.38(15)
54.49(14)
109.5(3)
110.2(3)
110.6(3)
C(7)ꢁN(3)ꢁC(8)
N(1)ꢁC(1)ꢁC(2)
N(1)ꢁC(1)ꢁC(3)
C(2)ꢁC(1)ꢁC(3)
N(2)ꢁC(4)ꢁC(6)
N(2)ꢁC(4)ꢁC(5)
C(6)ꢁC(4)ꢁC(5)
N(3)ꢁC(7)ꢁN(2)
N(3)ꢁC(7)ꢁN(1)
N(2)ꢁC(7)ꢁN(1)
N(3)ꢁC(7)ꢁSn
N(2)ꢁC(7)ꢁSn
N(1)ꢁC(7)ꢁSn
N(3)ꢁC(8)ꢁC(9)
N(3)ꢁC(8)ꢁC(10)
C(9)ꢁC(8)ꢁC(10)
In contrast to the above reaction of SnCl4, direct
reaction of guanidine and SnCl2 was not a successful
method for generating a guanidinate complex of Sn(II).
We attribute this to the reduced acidity of Sn(II) rela-
tive to Sn(IV). Therefore, an alternative metathetical
route for introduction of guanidinate anions was inves-
tigated that employed the lithium salt of N,N%,N%%-tricy-
clohexylguanidinate in reaction with SnCl2. Following
the pathway shown in Scheme 2, [(CyN)2C(HNCy)]2Sn
(3) (Cy=C6H11) was isolated in 78% yield. When the
reaction is performed with an equimolar ratio of
guanidinate and SnCl2, in an attempt to generate a
monoguanidinato tin(II) chloride species, only complex
3 and unreacted SnCl2 were isolated.
Cl(1)ꢁSnꢁCl(2) 110.74(4)
N(1)ꢁSnꢁCl(3)
N(2)ꢁSnꢁCl(3)
Cl(1)ꢁSnꢁCl(3)
Cl(2)ꢁSnꢁCl(3)
N(1)ꢁSnꢁC(7)
N(2)ꢁSnꢁC(7)
Cl(1)ꢁSnꢁC(7)
Cl(2)ꢁSnꢁC(7)
Cl(3)ꢁSnꢁC(7)
96.34(7)
159.76(7)
93.47(4)
96.01(4)
31.98(9)
31.51(8)
111.18(7)
114.65(7)
128.27(7)
C(7)ꢁN(1)ꢁC(1) 122.4(2)
C(7)ꢁN(1)ꢁSn
C(1)ꢁN(1)ꢁSn
93.53(17)
132.95(18)
C(7)ꢁN(2)ꢁC(4) 123.8(2)
1
The H and 13C NMR spectra of 3 displayed three
independent cyclohexyl groups of equal intensity and
are consistent with a rigid geometry derived from a
trigonal bipyramid with an equatorial site occupied by
a lone pair of electrons. One signal arises from a pair of
unique NCy groups which occupy a pseudoequatorial
position, another from the pair that resides in the
pseudoaxial position, and the two noncoordinated
N(H)Cy groups provide a third resonance.
Scheme 2.
In order to confirm the geometry of 3 and clarify the
structural details for the guanidinate ligand, an X-ray
diffraction study was performed (Table 1). From Fig. 2,
it is clear that the environment about the Sn(II) center
consists of two chelating bidentate guanidinate anions
and that the geometry of 3 is consistent with the
spectroscopic data. The two ligands are made equiva-
lent by a crystallographic C2 axis. Selected bond dis-
tances and angles for 3 are provided in Table 3.
The pseudoaxial vector for
3
is defined by
N(1)ꢁSnꢁN(1A), with an angle of 140.4(3)° is heavily
distorted from linearity due to the restricted bite angle
(58.1(2)°) of the ligands. This bite angle is typical of
both amidinates and guanidinates [1,11,13]. Like com-
plex 1, the guanidinate ligands in 3 are non-planar;
while the sum of the angles around N(2) is 360°, the
angles around N(1) only sum to 344°. The N(1)ꢁC(19)
Fig. 2. Molecular structure and atom numbering scheme for
{[CyN)2C[NHCy]}2Sn (3). Hydrogen atoms have been omitted for
clarity.

624
S.R. Foley et al. / Polyhedron 21 (2002) 619–627
Table 3
,
distance (1.306(9) A) is shorter than that of N(2)ꢁC(19)
,
Selected bond distances (A) and angles (°) for complex 3
,
(1.344(8) A), suggesting a degree of localization of the p
bond between N(1) and C(19). While the noncoordi-
nated guanidinate nitrogen, N(3), lies in the plane of
the ligand and the C(8)ꢁN(3)ꢁC(7) angle of 118.3(6)°
suggests sp2 hybridization for N(3), the N(3)ꢁC(19)
Bond distances
SnꢁN(2)
SnꢁN(2A)
SnꢁN(1)
SnꢁN(1A)
N(1)ꢁC(19)
2.152(6)
2.152(6)
2.424(6)
2.424(6)
1.306(9)
N(1)ꢁC(6)
N(2)ꢁC(19)
N(2)ꢁC(12)
N(3)ꢁC(19)
N(3)ꢁC(18)
1.453(8)
1.344(8)
1.429(8)
1.435(9)
1.473(9)
,
distance of 1.435(9) A indicates little p interaction
between these centers. Consistent with this is the ob-
served angle of 57.3° between the plane defined by
C(18)ꢁN(3)ꢁC(19) and that defined by N(1)ꢁ
C(19)ꢁN(2).
Bond angles
N(2)ꢁSnꢁN(2A)
N(2)ꢁSnꢁN(1)
N(2A)ꢁSnꢁN(1)
N(2)ꢁSnꢁN(1A)
N(2A)ꢁSnꢁN(1A)
N(1)ꢁSnꢁN(1A)
C(19)ꢁN(1)ꢁC(6)
99.4(3)
58.1(2)
95.1(2)
95.1(2)
58.1(2)
140.4(3)
121.8(6)
C(19)ꢁN(1)ꢁSn
C(6)ꢁN(1)ꢁSn
C(19)ꢁN(2)ꢁC(12)
C(19)ꢁN(2)ꢁSn
C(12)ꢁN(2)ꢁSn
C(19)ꢁN(3)ꢁC(18)
86.3(5)
136.1(5)
122.8(7)
97.4(5)
139.8(5)
118.2(6)
3.2. Hexahydro-2H-pyramido[1,2-a]pyramidinate
complexes of tin
The lithium salt of hpp− was readily prepared by
reaction of Hhpp with 1 equiv. MeLi. Subsequent
reaction with SnCl2 follows one of two paths depending
on the reaction stoichiometry (Scheme 3). Addition of
0.5 equiv. SnCl2 resulted in the formation of a mononu-
clear complex (hpp)2Sn (4) in 73% yield while a stoi-
chiometric ratio of 1:1 produced complex 5 in 63%
yield.
Proton NMR spectra of 4 and 5 showed only broad
signals which were of little help in assigning the struc-
tural features of this species. The presence of single
quaternary signal at 144.9 ppm for the central C of the
hpp− ligand in the 13C NMR spectrum of 5 as well as
observation of only three signals for the CH2 groups is
indicative of equivalent environments for the two lig-
ands of 5. In order to determine the structural details of
these species, single crystals of 4 and 5 were subjected
to an X-ray diffraction study (Table 4). The molecular
structures of these two complexes are shown in Figs. 3
and 4 with corresponding values for selected bond
distances and angles provided in Tables 5 and 6.
Contrary to all previously reported structures involv-
ing the hpp− anion, the Sn(II) complex 4 is mononu-
clear with two chelating bidentate ligands. The
geometry of the Sn center in 4 is similar to that of 3 and
can be derived from a distorted trigonal bipyramidal
geometry with an equatorial site occupied by a lone
pair of electrons [1]. Again, we attribute the distortion
of the pseudoaxial angle (N(7)ꢁSnꢁN(17)=129.6(3)°)
to the restricted bite angle of the ligand
(N(2)ꢁSnꢁN(1)=58.1(2)°).
Scheme 3.
Table 4
Crystal data and structure refinement for {CN[N(CH2)3]2}2Sn (4),
{CN[N(CH2)3]2SnCl}2 (5) and {CN[N(CH2)3]2}2SnCl2 (6)
4
5
6
Empirical
formula
Formula weight 395.08
Temperature (K) 203(2)
C
14H24N6Sn {(C7H12ClN3Sn) C14H24Cl2N6Sn
·(CH2Cl2)}2
754.52
238(2)
0.71073
C2/c
17.270(2)
13.821(1)
23.395(2)
90
105.361(2)
90
5385(1)
8
·(THF)
538.09
238(2)
0.71073
C2/c
12.354(3)
13.778(3)
14.123(4)
90
110.900(3)
90
2246(1)
4
,
u (A)
0.71073
Pbca
8.282(3)
16.129(6)
23.783(8)
90
Space group
,
a (A)
,
b (A)
,
c (A)
The sum of angles around all three nitrogen centers
of the ligand varies only slightly over a range of 356–
358°, suggesting sp2 character for these atoms. The
three C(central, sp2)ꢁN bond distances on each ligand
h (°)
i (°)
k (°)
90
90
3
,
V (A )
Z
3177(2)
8
1.652
1.613
0.0496
0.0981
,
vary from 1.30–1.37 A. These features indicate that all
Dcalc (g cm−3
)
1.861
2.467
0.0428
0.1006
1.591
1.397
0.0316
0.0731
three nitrogen atoms of the ligand participate to some
degree in p bonding to the central carbon [C(6) or
C(16)] and suggest, in comparison with 3, that the
tethering of the N centers has increased the degree of p
delocalization within the ligand.
v (mm−1
R1
)
wR2
R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ. wR2=(Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwꢀFoꢀ )
.
2 1/2

S.R. Foley et al. / Polyhedron 21 (2002) 619–627
625
In contrast to the mononuclear complex 4, complex 5
displayed a dinuclear structure with two hpp− ligands
bridging the two Sn atoms (Fig. 4). Two independent
molecules, each lying on a crystallographic inversion
center, were found in the unit cell with only marginal
differences in their bond lengths and angles. Within
each molecule the three NꢁC(central, sp2) distances are
,
equivalent (1.34–1.35 A) within experimental error and
correspond to a degree of NC p bonding. The SnꢁN
,
distances are equivalent at 2.21 A. In this case the
Sn(II) centers have pyramidal geometries derived from
a distorted tetrahedron in which one vertex is occupied
by a stereochemically active lone pair of electrons. The
lone pairs on the Sn centers appear to be oriented in
orthogonal directions, thus precluding any interaction
between them.
Fig. 3. Molecular structure and atom numbering scheme for
{CN[N(CH2)3]2}2Sn (4). Hydrogen atoms have been omitted for
clarity.
A similar metathetical route can be used to prepare a
Sn(IV) complex of the hpp− ligand. Addition of 2
equiv. of in situ prepared hppLi to SnCl4 in THF gave
a new complex that was formulated as the mononuclear
Sn(IV) complex (hpp)2SnCl2 (6) (Scheme 4) on the basis
of what appeared to be a single ligand environment in
the 1H and 13C NMR spectra and on our previous
experience with similar formamidinate/amidinate com-
plexes [13].
A single crystal X-ray diffraction analysis confirmed
the structural features of 6 (Table 4). As seen in Fig. 5,
complex 6 is a mononuclear Sn(IV) species with a
coordination environment consisting of two chelating
bidentate hpp− ligands along with two chloride ligands.
Values for selected bond distances and angles are pro-
Fig. 4. Molecular structure and atom numbering scheme for one of
the unique molecules of {CN[N(CH2)3]2SnCl}2 (5) in the unit cell.
Hydrogen atoms have been omitted for clarity.
Table 5
Table 6
,
,
Selected bond distances (A) and angles (°) for complex 4
Selected bond distances (A) and angles (°) for complex 5
Bond distances
Bond distances
SnꢁN(11)
SnꢁN(1)
SnꢁN(7)
SnꢁN(17)
N(1)ꢁC(6)
N(1)ꢁC(2)
N(5)ꢁC(6)
2.171(8)
2.204(7)
2.327(8)
2.394(7)
1.302(12)
1.462(12)
1.373(11)
C(4)ꢁN(5)
N(5)ꢁC(10)
C(6)ꢁN(7)
N(11)ꢁC(16)
N(15)ꢁC(16)
C(16)ꢁN(17)
1.458(12)
1.456(12)
1.331(12)
1.350(11)
1.343(12)
1.324(11)
Sn(1)ꢁN(1)
2.208(4)
2.213(4)
2.5293(15) N(3)ꢁC(7)
2.214(4)
2.217(4)
N(2)ꢁC(7)
N(2)ꢁSn(1)c1
1.352(6)
2.213(4)
1.344(6)
1.341(6)
1.344(6)
2.217(4)
1.347(6)
Sn(1)ꢁN(2)c1
Sn(1)ꢁCl(1)
Sn(2)ꢁN(4)
Sn(2)ꢁN(5)c2
Sn(2)ꢁCl(2)
N(1)ꢁC(7)
N(4)ꢁC(14)
N(5)ꢁC(14)
2.5316(14) N(5)ꢁSn(2)c2
1.350(6) N(6)ꢁC(14)
Bond angles
Bond angles
N(11)ꢁSnꢁN(1)
N(11)ꢁSnꢁN(7)
N(1)ꢁSnꢁN(7)
N(11)ꢁSnꢁN(17)
N(1)ꢁSnꢁN(17)
N(7)ꢁSnꢁN(17)
C(6)ꢁN(1)ꢁC(2) 123.7(8)
C(6)ꢁN(1)ꢁSn
C(2)ꢁN(1)ꢁSn
C(6)ꢁN(5)ꢁC(10) 120.3(9)
C(6)ꢁN(5)ꢁC(4) 119.0(9)
C(10)ꢁN(5)ꢁC(4) 116.9(8)
N(1)ꢁC(6)ꢁN(7) 113.9(9)
N(1)ꢁC(6)ꢁN(5) 122.9(9)
N(7)ꢁC(6)ꢁN(5) 123.2(10)
102.2(3)
88.8(3)
58.2(3)
57.9(3)
90.5(3)
129.6(3)
C(6)ꢁN(7)ꢁC(8)
C(6)ꢁN(7)ꢁSn
C(8)ꢁN(7)ꢁSn
120.6(9)
89.9(6)
144.7(7)
121.0(9)
99.0(7)
138.2(7)
120.8(9)
118.3(9)
118.8(8)
112.2(11)
125.5(10)
122.2(10)
119.7(9)
89.8(7)
N(1)ꢁSn(1)ꢁN(2)c1 92.50(14) C(14)ꢁN(4)ꢁC(8)
117.0(4)
106.7(3)
127.5(3)
114.3(4)
N(1)ꢁSn(1)ꢁCl(1) 91.71(11) C(14)ꢁN(4)ꢁSn(2)
N(2)c1ꢁSn(1)ꢁCl(1) 91.96(11) C(8)ꢁN(4)ꢁSn(2)
N(4)ꢁSn(2)ꢁN(5)c2 92.84(14) C(14)ꢁN(5)ꢁC(11)
C(16)ꢁN(11)ꢁC(12)
C(16)ꢁN(11)ꢁSn
C(12)ꢁN(11)ꢁSn
C(16)ꢁN(15)ꢁC(14)
C(16)ꢁN(15)ꢁC(20)
C(14)ꢁN(15)ꢁC(20)
N(17)ꢁC(16)ꢁN(11)
N(17)ꢁC(16)ꢁN(15)
N(11)ꢁC(16)ꢁN(15)
C(16)ꢁN(17)ꢁC(18)
C(16)ꢁN(17)ꢁSn
C(18)ꢁN(17)ꢁSn
N(4)ꢁSn(2)ꢁCl(2)
89.27(11) C(14)ꢁN(5)ꢁSn(2)c2 111.0(3)
N(5)c2ꢁSn(2)ꢁCl(2) 92.01(10) C(11)ꢁN(5)ꢁSn(2)c2 122.4(3)
C(7)ꢁN(1)ꢁC(1)
C(7)ꢁN(1)ꢁSn(1)
C(1)ꢁN(1)ꢁSn(1)
C(7)ꢁN(2)ꢁC(4)
116.2(4)
108.1(3)
126.0(3)
116.0(4)
C(14)ꢁN(6)ꢁC(10)
C(14)ꢁN(6)ꢁC(13)
C(10)ꢁN(6)ꢁC(13)
N(3)ꢁC(7)ꢁN(1)
N(3)ꢁC(7)ꢁN(2)
N(1)ꢁC(7)ꢁN(2)
N(4)ꢁC(14)ꢁN(5)
N(4)ꢁC(14)ꢁN(6)
N(5)ꢁC(14)ꢁN(6)
123.1(4)
122.3(4)
114.6(4)
122.4(4)
122.8(4)
114.8(4)
115.2(4)
121.8(4)
123.0(4)
96.5(6)
135.6(6)
C(7)ꢁN(2)ꢁSn(1)c1 107.3(3)
C(4)ꢁN(2)ꢁSn(1)c1 127.5(3)
C(7)ꢁN(3)ꢁC(3)
C(7)ꢁN(3)ꢁC(6)
C(3)ꢁN(3)ꢁC(6)
122.5(4)
122.4(4)
114.9(4)
147.0(7)

626
S.R. Foley et al. / Polyhedron 21 (2002) 619–627
Table 7
,
Selected bond distances (A) and angles (°) for complex 6
Bond distances
SnꢁN(2)
SnꢁN(2A)
SnꢁN(1)
SnꢁN(1A)
SnꢁCl
SnꢁClA
SnꢁC(7)
SnꢁC(7A)
2.104(4)
2.104(4)
2.191(4)
2.191(4)
2.4202(14) N(3)ꢁC(7)
2.4202(14) N(3)ꢁC(3)
N(1)ꢁC(7)
N(1)ꢁC(1)
N(2)ꢁC(7)
N(2)ꢁC(6)
1.326(6)
1.448(6)
1.326(6)
1.456(6)
1.344(6)
1.455(7)
1.453(6)
2.582(5)
2.582(5)
N(3)ꢁC(4)
Scheme 4.
Bond angles
N(2)ꢁSnꢁN(2A)
N(2)ꢁSnꢁN(1)
N(2A)ꢁSnꢁN(1)
N(2)ꢁSnꢁN(1A)
N(2A)ꢁSnꢁN(1A)
N(1)ꢁSnꢁN(1A)
N(2)ꢁSnꢁCl
164.1(2)
N(2)ꢁSnꢁC(7A)
136.64(16)
30.76(15)
101.35(15)
30.89(15)
122.62(12)
96.80(11)
123.0(2)
119.1(4)
91.1(3)
61.64(15) N(2A)ꢁSnꢁC(7A)
106.43(16) N(1)ꢁSnꢁC(7A)
106.43(16) N(1A)ꢁSnꢁC(7A)
61.64(15) ClꢁSnꢁC(7A)
92.2(2)
ClAꢁSnꢁC(7A)
99.11(12) C(7)ꢁSnꢁC(7A)
91.87(12) C(7)ꢁN(1)ꢁC(1)
93.50(12) C(7)ꢁN(1)ꢁSn
153.42(11) C(1)ꢁN(1)ꢁSn
91.87(12) C(7)ꢁN(2)ꢁC(6)
99.11(12) C(7)ꢁN(2)ꢁSn
153.42(11) C(6)ꢁN(2)ꢁSn
93.50(12) C(7)ꢁN(3)ꢁC(3)
N(2A)ꢁSnꢁCl
N(1)ꢁSnꢁCl
N(1A)ꢁSnꢁCl
N(2)ꢁSnꢁClA
N(2A)ꢁSnꢁClA
N(1)ꢁSnꢁClA
N(1A)ꢁSnꢁClA
ClꢁSnꢁClA
N(2)ꢁSnꢁC(7)
N(2A)ꢁSnꢁC(7)
N(1)ꢁSnꢁC(7)
N(1A)ꢁSnꢁC(7)
ClꢁSnꢁC(7)
148.8(3)
119.6(4)
95.0(3)
143.2(3)
120.8(4)
120.3(4)
118.9(4)
112.3(4)
123.6(4)
124.1(5)
54.3(2)
Fig. 5. Molecular structure and atom numbering scheme for
{CN[N(CH2)3]2}2SnCl2 (6). Hydrogen atoms have been omitted for
clarity.
92.88(7)
C(7)ꢁN(3)ꢁC(4)
30.76(15) C(3)ꢁN(3)ꢁC(4)
136.64(16) N(2)ꢁC(7)ꢁN(1)
30.89(15) N(2)ꢁC(7)ꢁN(3)
101.35(15) N(1)ꢁC(7)ꢁN(3)
96.80(11) N(2)ꢁC(7)ꢁSn
122.62(12) N(1)ꢁC(7)ꢁSn
177.6(4)
vided in Table 7. The geometry of 6 is based on a
cis-dichloro distorted octahedron with a crystallo-
graphic C2 bisecting the ClꢁSnꢁCl angle making the
two hpp− ligands equivalent. Complex 6 is reminiscent
of bis(amidinate) Sn(IV) dichloride species [13].
ClAꢁSnꢁC(7)
N(3)ꢁC(7)ꢁSn
58.0(2)
In 6 the hpp− ligand is bonded to Sn(IV) through
nitrogen atoms N(1) and N(2). The NꢁC(7) bond dis-
and Sn(IV) (6) are mononuclear with chelating biden-
tate ligands thus representing the first reported
mononuclear complexes of this ligand. Reducing the
coordination number and steric bulk about tin by
preparing a mono(hpp) Sn(II) complex resulted in the
formation of a dinuclear species with bridging hpp−
ligands, {CN[N(CH2)3]2SnCl}2 (5). Structural charac-
terization of the hpp− complexes suggests that the
tethering of the N centers may favor p delocalization
within the ligand. We are further investigating the
reactivity of the reported complexes and related species.
,
tances for N(1) and N(2) are the same at 1.326(6) A.
The sum of the angles around these two atoms is 359°
and 358°, suggestive of sp2 character. The sum of angles
around N(3) is 360° and the N(3)ꢁC(7) distance is
,
1.344(6) A. As with complex 4, this indicates that all
three nitrogen atoms within the ligand participate to
some degree in p bonding to C(7) and further suggests
that tethering of the N centers promotes p delocaliza-
tion between all three nitrogen atoms and the central
carbon.
In conclusion, we have demonstrated the utility
of guanidinate monoanions as ligands for complexes
of tin by reporting the first examples of Sn(II) and
Sn(IV) compounds of N,N%,N%%-trialkylguanidinates
([(RN)2C(NRH)]−; R=cyclohexyl; isopropyl) and
1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyramidinate
(hpp−). In the case of the trialkylguanidinate com-
plexes, structural analysis revealed a distinctly unsym-
metrical bonding mode for the bidentate ligand and
suggests a degree of p localization with the ligand. We
are investigating the role of this feature in the reactivity
of these species. The bis(hpp) complexes of Sn(II) (4)
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 166027 (1), 166026 (3),
166028 (4), 166029 (5), and 166030 (6). Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).

S.R. Foley et al. / Polyhedron 21 (2002) 619–627
627
[7] P.J. Bailey, R.O. Gould, C.N. Harmer, S. Pace, A. Steiner, D.S.
Wright, Chem. Commun. (1997) 1161.
5. Note added in proof
[8] For examples, see: (a) J.L. Bear, Y. Li, B. Hen, K.M. Kadish,
Inorg. Chem. 35 (1996) 1395;
An example of the chelating coordination mode for
the hpp anion appeared prior to publication of this
manuscript [14].
(b) F.A. Cotton, J.H. Matonic, C.A. Murillo, J. Am. Chem. Soc.
119 (1997) 7889;
(c) F.A. Cotton, L.M. Daniels, C.A. Murillo, D.J. Timmons, J.
Chem. Soc., Chem. Commun. (1997) 1449;
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Acknowledgements
This work was supported by the Natural Sciences
and Engineering Research Council of Canada.
[9] S.L. Aeilts, M.P. Coles, D.G. Swenson, R.F. Jordan, V.G.
Young, Organometallics 17 (1998) 3265.
[10] Alternative synthetic routes to 1, including reactions between
lithium guanidinate and SnCl4 or use of trialkylamines as a base,
have been explored. Thus far all such attempts have led to
complex reaction mixtures from which 1 cannot be cleanly
separated.
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