Synthesis and reactivity of tin amide complexes

Article abstract of DOI:10.1016/j.ica.2010.12.009

A terminal tin amide and a terminal tin anilide complex, (BDI)SnN(iPr ₂) and (BDI)SnN(H)Ar (Ar = 2,6-ⁱPr₂C ₆H₃), respectively, have been synthesized utilizing the bulky β-diketiminate ligand, [{N(2,6-

Full text of DOI:10.1016/j.ica.2010.12.009

Inorganica Chimica Acta 369 (2011) 97–102
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and reactivity of tin amide complexes
⇑
Lisa A.-M. Harris, Martyn P. Coles, J. Robin Fulton
Department of Chemistry, University of Sussex, 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:
Available online 9 December 2010
A terminal tin amide and a terminal tin anilide complex, (BDI)SnN(iPr2) and (BDI)SnN(H)Ar (Ar =
2,6-iPr2C6H3), respectively, have been synthesized utilizing the bulky b-diketiminate ligand,
[{N(2,6-iPr2C6H3)C(Me)}2CH]ꢀ, or BDI, to stabilize the low coordinate divalent tin metal center. Only
(BDI)SnN(iPr2) reacts with phenylacetylene to yield (BDI)SnCCPh, but both species react with methyl tri-
flate to give (BDI)SnOTf and carbon dioxide, resulting in the formation of (BDI)SnOC(O)N(iPr2) and
(BDI)SnOC(O)N(H)Ar.
Dedicated to Robert G. Bergman.
Keywords:
Tin
Amide
Ó 2010 Elsevier B.V. All rights reserved.
b-Diketiminate
Carbon dioxide
1. Introduction
Ar
N
N
Ar
N
N
M
X
Divalent b-diketiminate group 14 complexes have been the
subject of several recent studies, including the synthesis and reac-
tivity of germanium and tin hydrides [1,2], synthesis and reactivity
of lead alkoxides [3,4], and the generation of unusual molecules
such as a tin hydroxide stabilized by Fe(CO)4 [5], and germanium
and lead phosphides [6,7]. By far the most common b-diketiminate
ligand used is [{N(2,6-iPr2C6H3)C(Me)}2CH]ꢀ, or BDI. The geometry
of the ligands around the BDI-bound group 14 metal center,
(BDI)MX, is always trigonal pyramidal, presumably due to the pres-
ence of a stereochemically active lone pair. The metal center for
these neutral molecules lies outside the plane consisting of the
BDI back-bone (NCCCN plane). This is consistent with four-
coordinate BDI-metal complexes, furthering the hypothesis that
the presence of a stereochemically lone pair is influencing the
geometry of the complex. However, the overall solid state geometry
of the complex takes two different forms; one in which the metal
center and X ligand are on the same side of the NCCCN plane, the
X ligand lies in between the two N-aryl groups of the BDI ligand
and the M–X bond is at an approximately 90° angle from the NCCCN
plane (‘‘endo’’ configuration) and the other configuration in which
the metal center lies above the NCCCN plane and the X ligand points
away from the (BDI)-M core (‘‘exo’’ configuration, Fig. 1).
M
X
Ar
Ar
"endo"
"exo"
Fig. 1. The two different configurations of (BDI)MX complexes, where M = Ge(II),
Sn(II), Pb(II).
[9,10] and the reactivity of the latter towards electrophiles and
weak acids has been examined [11]. This study aims to expand
the reactivity of tin-amide complexes towards a wider variety of
electrophiles as well as heterocumulenes.
2. Experimental
2.1. General considerations
All manipulations were carried out under an atmosphere of dry
nitrogen using standard Schlenk techniques or in an inert-atmo-
sphere glovebox. Solvents were dried from the appropriate drying
agent, distilled, degassed and stored over 4 Å sieves. The 1H, 13C
and 119Sn NMR spectra were recorded on a Varian 400, 500 or
600 MHz spectrometer. All spectrometers were equipped with
X{1H} broadband-observe probes. The 1H and 13C NMR spectros-
copy chemical shifts are given relative to residual solvent peaks
and the 119Sn signals were externally referenced to SnMe4.
(BDI)SnCl (1) was prepared according to literature procedure [12],
other reagents were purchased from Acros or Aldrich and purified
according to standard procedures. Carbon dioxide was used as
received (BOC, 100.000%).
A number of tin complexes, (BDI)SnX, have been generated. For
instance, Gibson synthesized
complexes and investigated them as potential catalysts for the
polymerization of rac-lactide [8,9]. Only two (BDI)Sn-amide com-
plexes have been synthesized, (BDI)SnN(SiMe3)2 and (BDI)SnNMe2
a
series of (BDI)Sn-alkoxide
⇑
Corresponding author. Tel.: +44 (0) 1273 873170; fax: +44 (0) 1273 876687.
E-mail address: j.r.fulton@sussex.ac.uk (J.R. Fulton).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.12.009

98
L.A.-M. Harris et al. / Inorganica Chimica Acta 369 (2011) 97–102
2.2. Synthesis of [{N(2,6-iPr2C6H3)C(Me)}2CH}SnN(CH{CH3}2)2], 2
2.5. Synthesis of [{N(2,6-iPr2C6H3)C(Me)}2CH}SnOCON(C{CH3}2)2], 6
Lithium diisopropylamide (2 M, 175 L, 0.350 mmol) was
l
Compound 2 (0.2 g, 0.315 mmol) was dissolved in toluene
(5 mL) and loaded into an ampule. The reaction vessel was con-
nected to a Schlenk line and a cylinder of high-purity CO2. The ves-
sel was submerged in a dry ice/acetone bath, and after three pump/
refill cycles, CO2 was introduced at a pressure of 1.5 and the mix-
ture was stirred for 3 days at room temperature. The yellow solu-
tion was concentrated in vacuo and stored at ꢀ30 °C yielding 6
(14%, first crop) as colorless crystals. 1H NMR (C6D6, 293 K): d
7.13 (s, 1H, ArH), 7.12 (s, 1H, ArH), 7.11 (s, 1H, ArH), 7.05 (d, 1H,
J = 2.7 Hz, ArH), 7.04 (d, 1H, J = 2.7 Hz, ArH), 4.96 (s, 1H, middle
CH), 3.91 (septet, 2H, J = 6.7 Hz, CHMe2), 3.67 (septet, 2H,
J = 6.8 Hz, CHMe2), 3.14 (septet, 2H, J = 6.9 Hz, CHMe2), 1.58 (s,
6H, NCMe), 1.43 (d, 6H, J = 6.7 Hz, CHMe2), 1.26 (d, 6H, J = 6.8 Hz,
CHMe2), 1.18 (d, 12H, J = 6.8 Hz, CHMe2), 1.15 (d, 6H, J = 6.9 Hz,
CHMe2), 1.08 (d, 6H, J = 6.8 Hz, CHMe2). 13C{1H} NMR (C6D6,
293 K): d 164.85 (NCMe), 161.75 (OCO), 144.59 (ipso-C), 142.86
and 142.18 (ortho-C), 126.59 (para-C), 124.46 and 123.69 (meta-
C), 99.71 (middle CH), 45.34 (CHMe2), 28.58 and 27.66 (CHMe2),
26.23, 24.82 (CHMe2), 24.13 and 23.37 (CHMe2), 21.19 (NCMe).
119Sn NMR (C6D6, 293 K): d ꢀ394. IR (Nujol, cmꢀ1) 1595 (s), 1575
(s), 1552 (s), 1524 (s), 1337 (s), 1262 (s), 1097 (s), 1050 (s), 1019
(s) 791 (s). Anal. Calc. for C36H55N3O2Sn: C, 63.53; H, 8.15; N,
6.17. Found: C, 63.59; H, 8.26; N, 5.98%.
added to a solution of (BDI)SnCl (1) (0.200 g, 0.350 mmol) in tolu-
ene (5 mL), resulting in an immediate color change to an orange
solution, and the mixture was stirred for 1 h at room temperature.
The solvent was filtered and the solution was slowly evaporated in
vacuo and stored at ꢀ30 °C for 24 h yielding 2 (0.34 g, 32%, first
crop) as orange crystals. 1H NMR (C6D6, 293 K): d 7.14 (d, 2H,
J = 1.9 Hz, m-H), 7.10 (s, 2H, p-H), 7.07 (d, 2H, J = 2.0 Hz, m-H),
4.85 (s, 1H, middle CH), 3.82 (septet, 2H, J = 6.9 Hz, CHMe2), 3.75
(septet, 2H, J = 6.5 Hz, CHMe2), 3.25 (septet, 2H, J = 6.7 Hz, CHMe2),
1.57 (s, 6H, NCMe), 1.36 (d, 6H, J = 6.7 Hz, CHMe2), 1.28 (d, 6H,
J = 6.8 Hz, CHMe2), 1.19 (d, 6H, J = 6.7 Hz, CHMe2), 1.15 (s, 6H,
CHMe2), 1.12 (d, 12H, J = 6.8 Hz, CHMe2). 13C{1H} NMR (C6D6,
293 K): d 166.61 (NCMe), 143.93 (ipso-C), 143.80 and 143.71
(ortho-C), 126.02 (para-C), 124.19 and 124.14 (meta-C), 98.36 (mid-
dle CH), 50.90, 28.48 and 27.76 (CHMe2), 27.53, 25.87, 24.99, 24.63
(CHMe2), 24.40 (NCMe), 24.37 (CHMe2). 119Sn NMR (C6D6, 293 K): d
ꢀ224 ppm. IR (Nujol, cmꢀ1) 1623 (s), 1552 (s), 1316 (s), 1169 (s),
1100 (s), 934 (s). Anal. Calc. for C35H55N3Sn: C, 66.04; H, 8.71; N,
6.60. Found: C, 65.98; H, 8.64; N, 6.52%.
2.3. Synthesis of [{N(2,6-iPr2C6H3)C(Me)}2CH}SnNH(iPr2C6H3)], 3
Lithium 2,6-diisopropylanilide (0.064 g, 0.35 mmol) was added
to a solution of (BDI)SnCl (1) (0.200 g, 0.350 mmol) in toluene
(5 mL) and the mixture was stirred for 1 h at room temperature.
The solvent was removed under vacuum and the residue was
extracted with pentane (2 ꢁ 2 mL). The combined extracts were fil-
tered and the resulting orange solution was slowly evaporated in
vacuo and stored at ꢀ30 °C for 24 h yielding 3 (0.095 g, 38%, first
crop) as yellow crystals. 1H NMR (C6D6, 293 K): d 7.12–7.02 (8H,
ArH), 6.78 (t, 1H, J = 7.6, p-H), 5.54 (s, 1H, NH), 4.96 (s, 1H, middle
CH), 3.40 (septet, 2H, J = 6.8 Hz, CHMe2), 3.28 (septet, 4H, J = 6.7 Hz,
CHMe2), 1.61 (s, 6H, NCMe), 1.21 (d, 6H, J = 6.9 Hz, CHMe2), 1.20 (d,
12H, J = 6.4 Hz, CHMe2), 1.10 (d, 6H, J = 6.8 Hz, CHMe2), 0.92 (d, 6H,
J = 6.8 Hz, CHMe2), 0.90 (d, 6H, J = 6.7 Hz, CHMe2). 13C{1H} NMR
(C6D6, 293 K): d 164.49 (NCMe), 147.52, 145.09 (ipso-C), 142.55,
142.20 and 134.19 (ortho-C), 126.82 (meta-C), 124.60 (para-C),
123.72 and 122.98 (meta-C), 115.84 (para-C), 96.57 (middle CH),
28.81, 28.39 and 28.12 (CHMe2) 25.70, 24.29, 24.25, 23.93, 23.54
(CHMe2), 23.40 (NCMe). 119Sn NMR (C6D6, 293 K): dꢀ745. IR (Nujol,
cmꢀ1) 1623 (s), 1589 (s), 1552 (s), 1520 (s), 1283 (s), 1170 (s), 1098
(s), 935 (s), 841 (s), 793 (s), 747(s). Anal. Calc. for C41H59N3Sn: C,
69.10; H, 8.34; N, 5.90. Found: C, 69.16; H, 8.50; N, 5.90%.
2.6. Synthesis of [{N(2,6-iPr2C6H3)C(Me)}2CH}SnOCONH(iPr2C6H3)], 7
Compound 3 (0.2 g, 0.280 mmol) was dissolved in toluene
(5 mL) and loaded into an ampule. The reaction vessel was con-
nected to a Schlenk line and a cylinder of high-purity CO2. The ves-
sel was submerged in a dry ice/acetone bath, and after three pump/
refill cycles, CO2was introduced at a pressure of 1.5 and the mix-
ture was stirred for 4 h at room temperature. The yellow solution
was concentrated in vacuo and stored at ꢀ30 °C yielding 7. 1H
NMR (C6D6, 293 K): d 7.14 (d, 1H, J = 1.5 Hz, m-H), 7.13 (s, 1H,
ArH), 7.11 (t, 2H, J = 4.1 Hz, p-H), 7.08 (d, 1H, J = 3.1 Hz, m-H),
7.05 (s, 1H, ArH), 7.03 (s, 2H, ArH), 7.01 (s, 1H, ArH), 5.91 (s, 1H,
NH), 4.85 (s, 1H, middle CH), 3.61 (septet, 2H, J = 6.8 Hz, CHMe2),
3.29 (septet, 2H, J = 6.8 Hz, CHMe2), 3.11 (septet, 2H, J = 6.9 Hz,
CHMe2), 1.57 (s, 6H, NCMe), 1.31 (d, 6H, J = 6.7 Hz, CHMe2), 1.24
(d, 6H, J = 6.8 Hz, CHMe2), 1.17 (d, 6H, J = 6.9 Hz, CHMe2), 1.10 (d,
12H, J = 6.8 Hz, CHMe2), 1.06 (d, 6H, J = 6.8 Hz, CHMe2). 13C{1H}
NMR (C6D6, 293 K): d 165.23 (NCMe), 161.59 (OCO) 145.25 (ipso-
C), 142.52 (ipso-C), 141.67 (ortho-C), 133.36 and 126.82 (ortho-C),
126.48 (meta-C), 124.48 (para-C) 123.77 and 122.96 (meta-C)
115.84 (para-C), 99.01 (middle CH), 28.75 (CHMe2), 28.32 and
27.82 (CHMe2) 25.75 (CHMe2), 24.87 (CHMe2), 24.32, 24.23 and
23.76 (CHMe2) 23.70 (NCMe). 119Sn NMR (C6D6, 293 K): d ꢀ398.
IR (Nujol, cmꢀ1) 3413 (s), 1624 (s), 1554 (s), 1526 (s), 1517 (s),
1238 (s), 1172 (s), 1099 (s), 1058 (s), 1022 (s), 891 (s), 793 (s).
2.4. Synthesis of [{N(2,6-iPr2C6H3)C(Me)}2CH}SnCC-(C6H3)], 4
Phenyl acetylene (35 lL, 0.315 mmol) was added to a solution
of (BDI)Sn(NiPr2) (2) (0.2 g, 0.315 mmol) in toluene (5 mL), and
the mixture was stirred for 6 days at 70 °C. The solvent was filtered
and the solution was slowly evaporated in vacuo and stored at
ꢀ30 °C yielding 4 (0.19 g, 96%, first crop) as colorless crystals. 1H
NMR (C6D6, 293 K): d 7.53 (dd, 2H, J = 7.53 Hz, 1.3 Hz, ortho-C),
712–6.92 (m, 9H, ArH), 5.01 (s, 1H, middle CH), 4.04 (septet, 2H,
J = 6.8 Hz, CHMe2), 3.35 (septet, 2H, J = 6.8 Hz, CHMe2), 1.61 (s,
6H, NCMe), 1.41 (d, 6H, J = 6.7 Hz, CHMe2), 1.25 (d, 6H, J = 7.0 Hz,
CHMe2), 1.25 (d, 6H, J = 7.0 Hz, CHMe2) 1.12 (d, 6H, J = 6.8 Hz,
CHMe2). 13C{1H} NMR (C6D6, 293 K): d not found (CC), 166.28
(NCMe), 145.67, 142.60, 142.44, 131.64, 128.13, 126.68, 124.57,
123.97, 123.70 (Ar-C), 106.10 (CC), 99.97 (middle CH), 28.75,
27.85 (CHMe2), 27.77, 24.47, 24.17, 23.73 (CHMe2), 23.56 (NCMe).
119Sn NMR (C6D6, 293 K): d ꢀ206. IR (Nujol, cmꢀ1) 1523 (s), 1316
(s), 1203 (s), 1171 (s), 1100 (s), 934 (s). Anal. Calc. for C37H46N2Sn:
C, 69.71; H, 7.27; N, 4.39. Found: C, 69.99; H, 7.32; N, 4.33%.
2.7. X-ray data
Data collection parameters for complexes 2, 3, 4 and 6 are listed
in Table 1. Crystals were covered in an inert oil and suitable single
crystals were selected under a microscope and mounted on a Kap-
pa CCD diffractometer. The structures were refined with SHELXL-97
[13] Details specific to individual datasets are outlined below:
Compound 2. A residual peak of 1.90 electrons is present close to
the Sn atom.
Compound 3. The hydrogen atom on N3 was located and
refined; all others were placed in calculated positions.
Compound 4. The unit cell contains a toluene solvate molecule
which has been treated as diffuse contribution to the overall

L.A.-M. Harris et al. / Inorganica Chimica Acta 369 (2011) 97–102
99
Table 1
Crystallographic data for 3, 4, 5 and 6.
(BDI)SnN(iPr)2 (2)
35H55N3Sn
636.51
173(2)
(BDI)SnNH(Ar) (3)
(BDI)SnCCPh (4)
(BDI)Sn{OC(O)N(iPr2)] (6)
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal size (mm3)
Crystal system
Space group
a (Å)
C
C41H59N3Sn
712.60
173(2)
C37H46N2SnꢃC7H8
729.58
173(2)
C36H55N3O2Sn
680.54
173(2)
0.71073
0.71073
0.71073
0.71073
0.28 ꢁ 0.22 ꢁ 0.08
P 21/c (no. 14)
monoclinic
10.3140(2)
20.2436(4)
17.9140(3)
90
114.056(1)
90
3415.45(11)
4
0.19 ꢁ 0.13 ꢁ 0.10
0.20 ꢁ 0.20 ꢁ 0.16
I 4/m (no. 87)
tetragonal
18.4398(4)
18.4398(4)
21.2276(6)
90
90
90
7217.9(3)
8
1.34
0.29 ꢁ 0.20 ꢁ 0.14
ꢀ
triclinic
P1 (no. 2)
ꢀ
triclinic
P1 (no. 2)
9.2335(2)
11.4858(3)
13.1637(4)
13.4152(4)
91.601(2)
107.273(2)
114.822(4)
1730.45(11)
4
b (Å)
c (Å)
11.4606(2)
19.1522(4)
100.622(1)
102.355(1)
99.208(1)
1903.40(7)
2
1.24
a
(°)
b (°)
c
(°)
V (Å3)
Z
qc (Mg mꢀ3
)
1.24
0.77
1.31
0.772
Absorption coefficient (mmꢀ1
)
0.70
0.74
h range for data collection (°)
Measured/independent reflections/R(int)
3.53–26.74
37 640/6909/0.065
5886
3.44–27.10
30 546/8358/0.055
7414
3.45–26.73
11 847/3941/0.036
3335
3.45–27.50
25 911/7847/0.044
7182
Reflections with I > 2 (I)
r
Data/restraints/parameters
6909/0/366
1.052
8358/0/412
1.028
3941/0/173
1.082
7847/0/381
1.070
Goodness-of-fit on (GOF) F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.036, wR2 = 0.080
R1 = 0.048, wR2 = 0.085
1.90 and ꢀ0.80
R1 = 0.031, wR2 = 0.064
R1 = 0.039, wR2 = 0.066
0.42 and ꢀ0.55
R1 = 0.038, wR2 = 0.104
R1 = 0.048, wR2 = 0.108
0.80 and ꢀ0.77
R1 = 0.0326, wR2 = 0.078
R1 = 0.037, wR2 = 0.081
3.17 and ꢀ0.86
Largest difference in peak and hole (e Å3)
scattering without specific atom positions by SQUEEZE/PLA-
TON. The phenyl group of the acetylide ligand is disordered
across a mirror plane and was refined as a rigid body with
atoms at half occupancy and isotropic carbon atoms.
Compound 6. There is residual electron density of ꢂ3 electrons
located at the inversion center. This is believed to be an artifact
of the data.
length of 2.070(2) Å is slightly longer than the Sn–N bond length
of the (BDI)SnNMe2 complex (2.038(6) Å), but shorter than the
Sn–N bond length of the (BDI)SnN(SiMe3)2 complex (2.159 Å).
Ar
Ar
Sn
toluene
1h
N
N
+
LiN(iPr)2
N(iPr)2
N
Ar
N
Ar
Sn
Cl
Ar = 2,6-iPr2-C6H3
2
3. Results and discussion
1
ð1Þ
3.1. Synthesis of tin-amide complexes
Tin anilide 3 was generated by treating a toluene solution of tin
chloride 1 with lithium-(2,6-di-isopropyl)anilide (Eq. (2)). The 1H
NMR spectrum revealed the presence of three septets in a 1:1:1
ratio, corresponding to the isopropyl CH protons; two of these cor-
respond to the BDI ligand, the other correspond to the (2,6-di-
isopropyl)anilide ligand. A single 119Sn spectroscopic signal was
observed at d ꢀ745 ppm, significantly upfield to the tin amide
complexes. The solid state structure reveals the expected trigonal
pyramidal arrangement of the ligands around the metal center,
with the tin atom displaced from the NCCCN plane by 0.721 Å,
and a Sn–N bond length of 2.1000(17) Å (Fig. 3, Table 2). The latter
is slightly shorter than the terminal anilide tin complex, {(MA-
Addition of a lithium diisopropylamide solution to (BDI)SnCl (1)
results in an immediate color change to an orange solution of tin
diisopropyl amide 2 (Eq. (1)). The 1H NMR spectrum of isolated
tin-amide 2 revealed three resonances in a 1:1:1 ratio, correspond-
ing to three different isopropyl CH environments, two from the BDI
N-aryl isopropyl groups, and one from the N-diisopropyl ligand. A
119Sn NMR spectroscopic signal was observed at d ꢀ224 ppm,
which is only slightly upfield to that found for (BDI)SnNMe2 (d
ꢀ172 ppm) [9], but significantly upfield to that of (BDI)Sn{N
(SiMe3)2} (d 112 ppm) [10]. X-ray quality crystals were grown by
cooling a saturated toluene solution of tin amide 2 to ꢀ30 °C. The
ORTEP diagram is shown in Fig. 2 and selected bond lengths and
angles are listed in Table 2. As with most other (BDI)-Sn complexes,
the ligands around the metal center are in a pyramidal arrange-
ment, presumably due to the presence of a stereochemically active
lone pair. The tin metal center is displaced from the N(1)–C(1)–
C(2)–C(3)–N(2) (NCCCN) plane by 1.359 Å, significantly further
than any other (BDI)Sn complex reported. This is presumably due
to the inability of the bulky N-isopropyl ligand to lie in between
the two N-aryl groups of the BDI ligand (endo configuration); in-
stead, this planar N-isopropyl ligand must point away from the rest
of the molecule (exo configuration). This is in contrast to both
(BDI)SnNMe2 and (BDI)Sn{N(SiMe3)2}; the trigonal planar amide li-
gands of these latter structures lie in between the N-aryl groups of
the BDI ligand, and one of the N-Me or N-SiMe3 groups lies directly
below the NCCCN plane (endo configuration). The Sn–N bond
NH)Sn-(
l
-HN-MA)2Liꢃ2THF} (MA = 2-MeO-C6H4) of 2.118(8) Å and
the terminal anilide ligands of Sn2{N(H)Ar}4 (Ar = 2,6-iPr2C6H3)
(2.117(3) and 2.120(4) Å) [14,15]. An endo configuration of the
complex is found, presumably due to smaller bulk at the N-aryl
nitrogen relative to the amide ligand of 2. No evidence of hin-
dered rotation around the Sn–N3 bond was found by 1H NMR
spectroscopy.
Ar
Ar
toluene
1h
N
N
+
LiNHAr
N
Ar
N
Ar
Sn
Cl
Sn
NHAr
Ar = 2,6-iPr2-C6H3
3
1
ð2Þ

100
L.A.-M. Harris et al. / Inorganica Chimica Acta 369 (2011) 97–102
Fig. 2. ORTEP diagram of tin amide 2, showing two different orientations of the complex; ‘‘front-view’’ (left), with H atoms omitted and ‘‘side-view’’ (right) with H atoms
omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%.
ꢀ206 ppm, upfield to that observed for Roesky’s (BDI)SnCC(-
Table 2
Selected bond lengths and angles for compounds 2 and 3.
CO2Et) complex (d 187 ppm).
(BDI)SnN(iPr)2 (2)
(BDI)SnNH(Ar) (3)
Ar
Ar
Sn
M–N(1)
2.227(2)
2.290(2)
2.070(2)
1.458(4)
1.477(4)
2.2143(17)
2.2250(17)
2.1000(17)
1.403(3)
N
N
N(iPr)2
+
PhCC
H
M–N(2)
M–N(3)
N
Ar
N
Ar
Sn
Ph
N(3)–C(30)
N(3)–C(33)
N(3)–H
N(1)–M–N(2)
N(1)–M–N(3)
N(2)–M–N(3)
M–N(3)–C(30)
M–N(3)–C(33)
C(30)–N(3)–C(33)
Ar = 2,6-iPr2-C6H3
2
4
81.28(8)
99.27(8)
104.59(9)
127.81(18)
117.27(18)
114.9(2)
83.72(6)
86.08(7)
94.17(7)
131.85(15)
ð3Þ
Both tin amide and anilide complexes, 2 and 3, exhibit reactivity
with methyl triflate (Eq. (3)). However, divergent reactivity was
observed with these systems; for instance, addition of methyl tri-
flate to anilide 3 results in 100% conversion to known (BDI)SnOTf
(5); however with amide 2, a complex mixture of products is
formed. Addition of the less reactive electrophile, methyl iodide,
to the tin amide 2 results in the formation of a complex mixture
of products after 1 day at room temperature, and the tin-anilide
complex 3 does not react with methyl iodide, even upon heating
to 75 °C for several days.
Sum of angles
DOP
M–NCCCN plane
NR2–NCCCN
285.14
83.2
1.359
0.564
263.97
106.7
0.721
2.615
3.2. Reactivity of tin-amide complexes
There are only a few studies exploring the reactivity of terminal
tin amide complexes. For instance, Gibson examined the use of
(BDI)SnNMe2 as a potential catalyst for the polymerization of
rac-lactide [9]. Roesky performed a small reactivity study with
(BDI)SnNMe2 and found that this compound acts as a nucleophile
towards reactive ketones, such as 2-benzoylpyridine and 2,2,2-tri-
fluoroacetophenone, and deprotonates terminal acetylenes, such
as methyl- and ethyl propiolate, to yield terminal tin-acetylide
complexes [11].
Ar
Ar
N
N
+
MeOTf
Ar = 2,6-iPr2-C6H3
N
Ar
N
Ar
Sn
OTf
Sn
NHAr
3
5
ð4Þ
No reactivity was observed between the amide and anilide com-
plexes, 2 and 3, with benzophenone. Addition of benzaldehyde to
complexes 2 and 3 resulted in the formation of a complex mixture
of products in both cases. However, both tin complexes 2 and 3 do
react cleanly with one atmosphere of carbon dioxide to yield the cor-
responding metal carbamates 6 and 7 after four hours at room tem-
perature (Eq. (5)). The 13C NMR spectrum of N-diisopropyl
carbamate 6 shows a resonance at d 161.8 ppm, indicative of a carba-
mate carbon. The 119Sn spectroscopic signal shifts upfield to d
ꢀ394 ppm. The IR spectrum reveals a new stretch at 1595, 1575
and 1524 cmꢀ1; unfortunately, conclusive assignment of the IR
stretching frequencies was prevented due to overlap of the NCO2
moiety stretching frequencies with the b-diketiminate stretching
frequencies [16,17]. X-ray quality crystals were grown by slowly
cooling a pentane solution of 6 to ꢀ30 °C (Fig. 4, Table 4). Although
transitionmetal carbamates are not unusual, this is the first example
Tin amide 2 is generally more reactive than tin anilide 3. For
instance tin amide
2 reacts with phenylacetylene to form
(BDI)SnCCPh 4 after heating to 70 °C for 3 days; however, no reac-
tivity was observed between tin anilide 3 and phenylacetylene,
even after prolonged heating. X-ray quality crystals of acetylide 4
were grown by slow cooling a toluene solution of 4 to ꢀ30 °C
(Fig. 4, Table 3). The solid state structure reveals the typical pyra-
midal arrangement of the ligands around the metal center, and an
endo configuration of the complex. The Sn is displaced from the
NCCCN plane by 0.805 Å, and the acetylide ligand is perpendicular
to the NCCCN plane (Table 4). Both the Sn–C16 bond length of
2.196(4) Å and the C–C triple bond length of 1.190(6) Å are slightly
shorter than the Sn–C bond length of Roesky’s (BDI)SnCC(CO2Et)
complex of 2.214(2) Å and the C–C triple bond length of
1.213(3) Å. A 119Sn spectroscopic signal was observed at d

L.A.-M. Harris et al. / Inorganica Chimica Acta 369 (2011) 97–102
101
Fig. 3. ORTEP diagram of tin anilide 3, showing two different orientations of the complex; ‘‘front-view’’ (left), with H atoms omitted and ‘‘side-view’’ (right) with H atoms
omitted and BDI C atoms minimized for clarity. The ellipsoid probability is shown at 30%.
Table 4
Selected bond lengths and angles for compound 6.
(BDI)Sn{OC(O)N(iPr2)] (6)
Sn–N(1)
Sn–N(2)
Sn–O(1)
O(1)–C(30)
C(30)–O(2)
Sn–O(2)
2.2051(18)
2.2012(19)
2.1346(16)
1.304(3)
1.238(3)
2.839
C(3)–N(3)
N(3)–C(31)
N(3)–C(34)
1.366(3)
1.474(3)
1.481(3)
84.78(7)
87.43(7)
87.41(7)
109.65(15)
121.7(2)
116.6(2)
121.7(2)
122.0(2)
120.2(2)
117.8(2)
259.62
N(1)–Sn–N(2)
N(1)–Sn–O(1)
N(2)–Sn–O(1)
Sn–O(1)–C(30)
O(1)–C(30)–O(2)
O(1)–C(30)–N(3)
O(2)–C(30)–N(3)
C(30)–N(3)–C(31)
C(30)–N(3)–C(34)
C(31)–N(3)–C(34)
Sum of angles
DOP
111.5
M–NCCCN plane
C(30)–NCCCN plane
0.546
2.514
of a group 14 metal carbonate bound through the oxygen atom of the
carbamate ligand [18]. The tin center is displaced from the NCCCN
plane by 0.546 Å, and an endo configuration is observed in which
the Sn–O bond is approximately 90° to the of the NCCCN plane.
The Sn–O(1) bond length of 2.1346(16) Å is longer than that of
Gibson’s (BDI)SnOiPr (2.000(5) Å) [8]. The Snꢃ ꢃ ꢃO(2) of 2.839 Å is
smaller than the sum of the van der Waals radii for oxygen and tin
(3.69 Å).
Fig. 4. ORTEP diagram of tin acetylide 4 (left) and tin carbamate 6 (right), with H
atoms omitted and BDI C atoms minimized for clarity. The ellipsoid probability is
shown at 30%.
Table 3
Selected bond lengths and angles for compound 4.
(BDI)SnCCPh (4)
Sn–N
Sn–C(16)
C(16)–C(17)
C(17)–C(18)
N–Sn–N’
2.179(2)
2.196(4)
1.190(6)
1.435(6)
86.42
Ar
Ar
N
N
+
CO2
Ar = 2,6-iPr2-C6H3
N
Ar
N
Ar
Sn
NRR'
Sn
O
N–Sn–C(16)
N’–Sn–C(16)
Sn–C(16)–C(17)
C(16)–C(17)–C(18)
Sum of angles
DOP
90.57(10)
90.57(10)
170.7(4)
174.2(4)
267.56
NRR'
2, RR' = iPr2
6, RR' = iPr2
O
3, R = H, R' = Ar
7, R = H, R' = Ar
ð5Þ
102.7
Sn–NCCCN plane
C(30)–NCCCN plane
0.805
2.724
Tin amide carbamate 6 is formed quantitatively as observed by
1H NMR spectroscopic analysis; however, tin anilide carbamate 7

102
L.A.-M. Harris et al. / Inorganica Chimica Acta 369 (2011) 97–102
only forms in 90% conversion and a second product is observed in
the 1H NMR spectrum. The 13C NMR spectrum of 7 shows a indic-
ative carbamate carbon resonance at d 161.6 ppm, and the 119Sn
NMR spectrum revealed a resonance at d 398 ppm, significantly
downfield to that of tin anilide 3. The IR spectrum shows a shift
of the stretching frequencies from the tin anilide complex 3 to
1554, 1526 and 1517 cmꢀ1. As with the carbamate 6, the b-diketi-
minate stretching frequencies overlap with that expected for the
NCO2 moiety, preventing conclusive assignment of the IR stretch-
ing frequencies [16,17]. Unfortunately, despite repeated attempts,
we have been unable to grow X-ray quality crystals of this species.
In contrast to what is observed for (BDI)-tin- and lead-alkoxides
[3,19], no reversion back to amide 2 or anilide 3 is observed, even
under reduced pressure.
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Two new tin-amide and -anilide complexes have been synthe-
sized and their reactivity was explored. The amide complex was
found to be more reactive than the anilide complex, a trend that
mirrors reactivity studies performed on transition metal analogs
[20], and is presumably due to the higher nucleophilic character
of the amide nitrogen versus the anilide nitrogen. Addition of car-
bon dioxide to both tin-amide and -anilide complexes 2 and 3 re-
sulted in insertion of carbon dioxide into the tin-nitrogen bond.
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.12.009.