Synthesis and characterization of a tin(II) bis(phosphinoyl)methanediide complex: A stannavinylidene derivative

Article abstract of DOI:10.1039/b922377k

The reaction of [CH₂(PPh₂=NSiMe₃)(PPh ₂=S)] (1) with two equivalents of [Sn{N(SiMe₃) ₂}₂] in refluxing toluene afforded novel tin(II) bis(phosphinoyl)methanediide complex 3. The structure of compound 3 has been determined by X-ray crystallography and DFT calculations. The topological analysis of the electron densities of compound 3 was performed. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b922377k

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Synthesis and characterization of a tin(II) bis(phosphinoyl)methanediide
complex: a stannavinylidene derivativew
Jiayi Guo,a Kai-Chung Lau,b Hong-Wei Xi,c Kok Hwa Limc and Cheuk-Wai So*a
Received (in Cambridge, UK) 27th October 2009, Accepted 26th January 2010
First published as an Advance Article on the web 9th February 2010
DOI: 10.1039/b922377k
The reaction of [CH2(PPh2QNSiMe3)(PPh2QS)] (1) with two
equivalents of [Sn{N(SiMe3)2}2] in refluxing toluene afforded
novel tin(II) bis(phosphinoyl)methanediide complex 3. The
structure of compound 3 has been determined by X-ray crystallo-
graphy and DFT calculations. The topological analysis of the
electron densities of compound 3 was performed.
together with a small amount of 3. It is suggested that
compound 2 was dehydroaminated by [Sn{N(SiMe3)2}2] in
refluxing toluene to form 3. In contrast, the reaction of
[CH2(PPh2QNSiMe3)2] with [Sn{N(SiMe3)2}2] afforded the
1,3-distannacyclobutane [Sn{m2-C(PPh2QNSiMe3)2}]2.5
Compounds 2 and 3 were isolated as highly air- and
moisture-sensitive colorless and yellow crystalline solids,
respectively. Compound 2 is soluble in Et2O and toluene,
while compound 3 is soluble in CH2Cl2 and THF only. They
have been characterized by NMR spectroscopy and X-ray
crystallography. The 1H NMR spectra of 2 and 3 display
resonances for the SiMe3 and phenyl protons. It is noteworthy
that the 13C NMR signal for the carbenic carbon in 3 is not
observed. Similarly, there is no 13C NMR resonance for the
Compounds containing a double bond between carbon and
heavier group 14 elements (4MQCo; M = Si, Ge, Sn) have
attracted much attention in the past 20 years, and have been
the focus of several reviews.1 It was found that the thermal
stability of the MQC bond is intrinsically low, and it can
undergo oligomerization readily. Nevertheless, stable silenes
(4SiQCo),2 germenes (4GeQCo)3 and stannenes
(4SnQCo)4 can be synthesized by incorporating sterically
hindered substituents at both carbon and heavier group 14
elements. In contrast, stable heavier group 14 vinylidene
analogues (:MQCo) are scarcely known. Because of lacking
bulky substituents at the low-coordinate metal(II) center, they
are expected to oligomerize more readily. Until now, only one
example of a bisgermavinylidene [(Me3SiNQPPh2)2CQGe-
GeQC(PPh2QNSiMe3)2] containing a weak Ge–Ge inter-
action has been reported and structurally characterized.5 The
existence of the monomeric germavinylidene intermediate
‘‘{(Me3SiNQPPh2)2CQGe:}’’ in solution has been demonstrated
by the trapping reactions of bisgermavinylidene with various
transition metal complexes.6
carbenic carbon in the bisgermavinylidene.5 The 31P NMR
2
0
signals of 3 [d 20.5, 27.4 ppm (d, JP–P = 17.5 Hz)] show an
2
upfield shift compared with those of 2 [d 30.2 (t, JSn–P
=
2
0
73.7 Hz), 34.7 ppm (t, JSn–P = 39.0 Hz)]. Comparing the
119Sn NMR signal of 3 [d 132.1 ppm (dd, 2JSn–P = 177.1 Hz)]
with that of 2 (d ꢀ19.3 ppm), the 1,3-distannacyclobutane in
[2-{Sn{C(i-Pr2PQNSiMe3)}}-6-{Sn{CH(i-Pr2PQNSiMe3)}Cl}-
C5H3N]2 (d ꢀ10.96 ppm)9 and the 6-stannapentafulvene
[(Tbt)(Mes)SnQCR2] (Tbt
= 2,4,6-{CH(SiMe3)2}3C6H2,
Mes = 2,4,6-Me3C6H2, CR2 = fluorenylidene) (d 270 ppm),4d
it is suggested that compound 3 exists as a tin(II) bis-
(phosphinoyl)methanediide complex and does not undergo
oligomerization in solution.
The molecular structure of 2 is shown in Fig. 1.10 In the
asymmetric unit, there are two independent molecules with
slightly different bond distances and angles. Only one of
them is discussed here for clarity. The methanide ligand is
bonded in a C,N0-chelate fashion to the tin center and displays
a trigonal pyramidal geometry. The thiophosphinoyl group of
the ligand remains uncoordinated. The sum of the bond angles
In this communication, we report the synthesis and charac-
terization of a novel tin(II) bis(phosphinoyl)methanediide
complex, which is regarded as a stannavinylidene (:SnQCo)
derivative.
The reaction of [CH2(PPh2QNSiMe3)(PPh2QS)] (1)7 with
two equivalents of [Sn{N(SiMe3)2}2] in refluxing toluene afforded
compound 3 (Scheme 1).8 Similar reaction of 1 with two
equivalents of [Sn{N(SiMe3)2}2] in toluene at room tempera-
ture gave [HC{(PPh2QNSiMe3)(PPh2QS)}SnN(SiMe3)2] (2)
a Division of Chemistry and Biological Chemistry,
School of Physical and Mathematical Sciences,
Nanyang Technological University, 637371 Singapore.
E-mail: CWSo@ntu.edu.sg; Fax: +65 6791 1961;
Tel: +65 6513 2730
b Department of Biology and Chemistry, City University of Hong Kong,
Tat Chee Avenue, Kowloon, Hong Kong
c Division of Chemical and Biomolecular Engineering,
School of Chemical and Biomedical Engineering,
Nanyang Technological University, 637459 Singapore
w Electronic supplementary information (ESI) available: Selected
theoretical calculation data for 3. CCDC 751809 (2) and 761168 (3).
For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/b922377k
Scheme 1 Synthesis of 2 and 3.
ꢁc
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Fig. 2 Molecular structure of 3. Hydrogen atoms are omitted for
clarity. Selected bond distances (A) and angles (1): Sn(1)–C(1)
2.2094(9), Sn(1)–N(1) 2.2554(8), Sn(1)–S(1) 2.6926(2), P(1)–N(1)
1.6158(8), C(1)–P(1) 1.7071(9), C(1)–P(2A) 1.6870(9), P(2)–S(1)
2.0390(3); C(1)–Sn(1)–S(1) 96.34(2), N(1)–Sn(1)–S(1) 91.12(2),
C(1)–Sn(1)–N(1) 70.62(3), Sn(1)–N(1)–P(1) 94.15(3), N(1)–P(1)–C(1)
101.89(4), P(1)–C(1)–P(2A) 137.44(5), Sn(1)–C(1)–P(2A) 119.62(5),
Sn(1)–C(1)–P(1) 93.26(4).
Fig. 1 Molecular structure of 2. One of two independent molecules in
the asymmetric unit is shown. Hydrogen atoms and solvent atoms are
omitted for clarity. Selected bond distances (A) and angles (1):
Sn(2)–C(47) 2.384(4), Sn(2)–N(3) 2.152(4), Sn(2)–N(4) 2.275(3),
P(3)–C(47) 1.776(4), P(4)–C(47) 1.780(4), P(3)–N(4) 1.612(3),
P(4)–S(2) 1.960(2); C(47)–Sn(2)–N(3) 98.8(1), N(3)–Sn(2)–N(4)
106.6(1), C(47)–Sn(2)–N(4) 67.8(1), Sn(2)–N(4)–P(3) 96.0(2),
N(4)–P(3)–C(47) 100.2(2), P(3)–C(47)–P(4) 123.4(2).
theory (DFT)16 B3LYP17 as implemented in the Gaussian
03 program.18 To account for the relativistic effect on the tin
atoms and hypervalent bonds, one augmented LanL2DZ
basis set with the d, p polarization functions (denoted
as LanL2DZ(d,p))19 is adopted in the calculation. Compound
3A was fully optimized with Ci symmetry and confirmed
as a stable molecular structure. The calculated structural
parameters (A, 1) (Sn(1)–C(1): 2.217, Sn(1)–N(1): 2.205,
P(1)–C(1): 1.722, P(1)–N(1): 1.658, P(2A)–C(1): 1.717,
P(2)–S(1): 2.062, Sn(1)–S(1): 2.796; C(1)–Sn(1)–N(1):
70.6, Sn(1)–N(1)–P(1): 96.4, N(1)–P(1)–C(1): 98.2) are in
good agreement with the crystallographic data. Each
‘‘(PH2QNH)(PH2QS)CSn:’’ moiety in compound 3A almost
locates at the same plane which is slightly different from the
X-ray structure of 3. The natural bond orbital (NBO)20
analysis shows that the Sn(1) atom is almost non-hybridized
(Table S1, ESIw). The Sn(1)–C(1) s bond is formed by p-rich
hybrids on the tin atom (s0.25p2.00) and sp2.00 hybrids on the
carbon atom. The Sn(1)–C(1) p bond is formed by pure p
orbitals on both atoms. The electron density of the Sn(1)–C(1)
s and p bonds are mostly occupied by the C(1) atom (85.3%
electron density of s bond and 96.9% electron density of
p bond). Thus, the NBO bond order by the natural-resonance-
theory (NRT)21 analysis shows that the Sn(1)–C(1) bond is
highly polar (19.5% covalent character, 82.0% ionic character).
The lone pair electrons at the tin center are high in s-character
with some directionality (sp0.18, occupancy: 1.98). It is
suggested that the Sn(1)–C(1) bond has a 4CQSn: skeleton.
The reactive Sn(1)–C(1) bond is stabilized by the lone pair of
electrons on the N(1) and S(1) atoms. The Wiberg bond index
(WBI)22 of the P–C (1.105, 1.109), P–N (0.979) and P–S bonds
(1.077) shows that the charge distributions on the ligand
at the tin center is 273.31, which is significantly smaller
than that of 337.71 in the tetra-coordinated stannylene
[Sn{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}2].11 This geometry
is consistent with a stereoactive lone pair at the tin center.
The Sn(2)–C(47) (2.384(4) A), Sn(2)–N(3) (2.152(4) A) and
Sn(2)–N(4) (2.275(3) A) bonds in 2 are comparable with those
of [{C5H4N-2-C(SiMe3)2}Sn{N(SiMe3)2}] (Sn–C: 2.356(8) A,
Sn–Namide: 2.144(5) A, Sn–Npyridine: 2.299(5) A), respectively.12
The molecular structure of 3 is shown in Fig. 2.10 It is sym-
metric and comprised of two ‘‘(PPh2QNSiMe3)(PPh2QS)CSn:’’
moieties bonded together in a head-to-head manner. The tin
atom Sn(1) is bonded to the methanediide carbon atom C(1),
one nitrogen and one sulfur atom of each ligand. Therefore,
the geometry around the tin atom is trigonal pyramidal. The
sum of the bond angles at the tin atom is 258.081, which is
comparable with that of 2 (273.31). This geometry is con-
sistent with a stereoactive lone pair at the tin center. The
C(1)–Sn(1) bond (2.2094(9) A) in 3 is significantly shorter
than that of 2 (2.384(4) A) and the 1,3-distannacyclobutane
[Sn{m2-C(PPh2QNSiMe3)2}]2 (average 2.322 A).5 This demon-
strates some double bond character in the C(1)–Sn(1) bond.
The C(1)–Sn(1) bond is longer than that of the stannaethene
[{(Me3Si)2CH}2SnQC{(Bt-Bu)2C(SiMe3)2}] (2.025(4) A)4a and
the 6-stannapentafulvene [(Tbt)(Mes)SnQCR2] (2.016(5) A)4d
due to the lower oxidation state of the tin atom in 3. The
Sn(1)–N(1) bond (2.2554(8) A) in 3 is comparable with that
of 2 (2.275(3) A), while it is longer than the terminal Sn–N
s-bond in [:Sn{N(SiMe3)2}2] (2.096(1) A).13 The Sn(1)–S(1)
bond (2.6926(2) A) is longer than the terminal Sn–S s-bond in
[:Sn(SAr)2] (Ar = C6H2-2,4,6-t-Bu3) (2.435(1) A),14 but it is
comparable with that of the aryltin(II) dithiocarboxylate
[:Sn(Ar){S2CAr}] (average 2.659 A).15
In order to understand the bonding nature in 3, a simple
derivative [:SnQC(PH2QNH)(PH2QS)]2 (3A) (Fig. S1, ESIw)
was investigated by means of quantum chemical calculations.
The calculations were performed by the density functional
backbone are consistent with
a resonance structure A
(Fig. 3), which is an extreme case. One lone pair of electrons
on the N(1) atom form p–p conjugation with the p orbital of
the Sn(1)–C(1) bond (second-order perturbation stabilizing
ꢁc
This journal is The Royal Society of Chemistry 2010
1930 | Chem. Commun., 2010, 46, 1929–1931

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This work was supported by the Academic Research Fund
Tier 1 (RG 47/08) (C.-W. S.), (RG 28/07) (K. H. L.) and by a
Strategic Research Grant from City University of Hong Kong
(Project No. 7002285) (K.-C. L.).
Fig. 3 The charge distributions on the ligand backbone A.
Notes and references
energy: 6.65 kcal molꢀ1), while another lone pair of electrons
donates strongly to the vacant p-rich hybrids (sp23.23 (95.9%
p-character), occupancy: 0.22) of the Sn(1) atom (second order
perturbation stabilizing energy: 80.05 kcal molꢀ1). One lone
pair of electrons on the S(1) atom delocalize to the p* orbital
of the Sn(1)–C(1) bond (second-order perturbation stabilizing
energy: 42.07 kcal molꢀ1).
1 (a) A. G. Brook and M. A. Brook, Adv. Organomet. Chem., 1996,
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, C. Couret,
The topological analysis of the electron densities of com-
pound 3 according to Bader’s quantum theory of atoms in
molecules (QTAIM) was performed.23 Compound 3 is optimized
at the B3LYP17 level with the cc-pVTZ-PP basis set24 for Sn
and the 6-31G(d) basis set for other atoms. The Laplacian of
´
¨
4 See ESIw for complete citation.
5 W.-P. Leung, Z.-X. Wang, H.-W. Li and T. C. W. Mak, Angew.
Chem., Int. Ed., 2001, 40, 2501.
6 (a) W.-P. Leung, C.-W. So, J.-Z. Wang and T. C. W. Mak, Chem.
Commun., 2003, 248; (b) W.-P. Leung, C.-W. So, K.-W. Kan,
H.-S. Chan and T. C. W. Mak, Inorg. Chem., 2005, 44, 7286;
(c) W.-P. Leung, C.-W. So, K.-W. Kan, H.-S. Chan and T. C.
W. Mak, Organometallics, 2005, 24, 5033.
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4617.
8 See ESIw for the complete experimental procedures and spectro-
scopic data of 2 and 3.
2
electron density r r and the total energy density H at the
(3,ꢀ1) bond critical point (BCP) show that the Sn–C bonds in
3, [:Sn(CH3)H] and [:SnQCH2] are polar and covalent
(Table 1). The bond nature of the Sn–C bond in 3 is in
between that of the :Sn–C bond in [:Sn(CH3)H] and that of
the :SnQC bond in [:SnQCH2]. As there may be substantive
p-electron delocalization along the Sn–C bond in compound 3,
it is unsurprising to find that the Sn–C bonds in compound 3
may have little double bond character compared with the :SnQC
bond in [:SnQCH2].
9 W.-P. Leung, Q. W.-Y. Ip, S.-Y. Wong and T. C. W. Mak,
Organometallics, 2003, 22, 4604.
10 Crystal data for 2, [C36H53N2O0.5P2SSi3Sn], M = 818.76, mono-
clinic, space group P21, a = 9.2762(3), b = 40.3235(12), c =
11.5632(3) A, b = 110.8640(10)1, V = 4041.6(2) A3, Z = 4, T =
103(2) K, m = 0.880 mmꢀ1, 46 207 measured reflections, 17 778
independent reflections [R(int) = 0.0429], 841 refined parameters,
R1 = 0.0367, wR2 = 0.0683 (I 4 2s(I)), Flack parameter
In conclusion, the first example of a tin(II) bis(phosphinoyl)-
methanediide compound 3, has been synthesized successfully
by the reaction of 1 with two equivalents of [Sn{N(SiMe3)2}2]
in refluxing toluene. It is suggested that the reaction proceeded
through the intermediate compound 2, which was further
dehydroaminated by [Sn{N(SiMe3)2}2] to form 3. X-Ray
crystallography shows that the Sn–C bond in compound 3
has some double character. DFT calculations show that the
Sn–C bond in 3 has a 4CQSn: skeleton which is stabilized by
the lone pair of electrons on the nitrogen and sulfur donors.
Topological analysis of the electron densities shows that the
Sn–C bond in 3 is polar and covalent and its bond nature is
between a single and double bond.
0.463(12). Crystal data for 3, [C56H58N2P4S2Si2Sn2],
M =
1240.60, monoclinic, space group P21/n, a = 10.6210(2), b =
12.6848(3), c = 20.9770(5) A, b = 101.344(1)1, V = 2770.9(1) A3,
Z = 2; T = 143(2) K, m = 1.174 mmꢀ1, 116 621 measured
reflections, 23 274 independent reflections [R(int) = 0.0343], 310
refined parameters, R1 = 0.0268, wR2 = 0.0667 (I 4 2s(I)).
11 W.-P. Leung, C.-W. So, Y.-S. Wu, H.-W. Li and T. C. W. Mak,
Eur. J. Inorg. Chem., 2005, 513.
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19 See ESIw for complete citation.
20 F. Weinhold and C. R. Landis, in Valency and Bonding: A Natural
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Table
1 Theoretical topological features at the BCP of 3,
[:SnH(CH3)] and [:SnQCH2]a
2
Bond
r
r r
G
H
|V|
3
Sn(1)–C(1)
C(1)–P(1)
P(1)–N(1)
C(1)–P(2A)
P(2)–S(1)
Sn(1)–N(1)
Sn(1)–S(1)
0.57
1.22
1.23
1.24
0.97
0.44
0.30
3.24
0.42
1.36
2.02
1.43
0.25
0.39
0.15
ꢀ0.20
ꢀ1.21
ꢀ0.98
ꢀ1.20
ꢀ0.64
ꢀ0.08
ꢀ0.06
0.62
2.57
3.00
2.63
0.89
0.47
0.21
2.22
14.88
3.25
ꢀ5.58
4.50
1.36
21 (a) E. D. Glendening and F. Weinhold, J. Comput. Chem., 1998,
19, 593; (b) E. D. Glendening and F. Weinhold, J. Comput. Chem.,
1998, 19, 610; (c) E. D. Glendening, J. K. Badenhoop and
F. Weinhold, J. Comput. Chem., 1998, 19, 628.
[:SnH(CH3)]
Sn–C
0.64
2.85
0.44
ꢀ0.24
0.67
1.28
[:SnQCH2]
Sn–C
22 K. B. Wiberg, Tetrahedron, 1968, 24, 1083.
0.87
6.52
0.87
ꢀ0.41
23 R. F. W. Bader, in Atoms in Molecules—A Quantum Theory,
Oxford University Press, New York, 1990.
24 K. A. Peterson, J. Chem. Phys., 2003, 119, 11099.
a
2
Units: r (e Aꢀ3); r r (e Aꢀ5); H, G, |V| (hartree Aꢀ3).
ꢁc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 1929–1931 | 1931