Stannaacetylene (RSn≡CR′) Showing Carbene-like Reaction Mode

Article abstract of DOI:10.1021/ja0389974

Photolysis of diazomethylstannylene 2 (ArSn?C(N₂)Si(i-Pr)₃, Ar = C₆H₃-2,6-Tip₂ (Tip = C₆H₂-2,4,6-(i-Pr)₃)) generated formal stannaacetylene 1 as a reactive intermediate, which was evidenced by the formation of cyclic arylalkylstannylene 4 via an intramolecular carbene insertion to a CH bond of isopropyl groups. The structures of the compounds 2 and 4 were fully characterized by X-ray crystallography. Stannaacetylene 1 was directly observed by laser flash photolysis of 2; λ_max = 355 nm, τ = 50 ms at room temperature. No triplet ESR signals were observed during the photolysis of 2 in 3-methylpentane glass matrix at 77 K, indicating the singlet nature of 1. Theoretical calculations for the parent stannaacetylene suggest that the stannaacetylene is characterized as a Sn≡C triple-bonded compound with a significant contribution of stannylene?(doubly excited)carbene structure. Copyright

Full text of DOI:10.1021/ja0389974

Published on Web 02/13/2004
Stannaacetylene (RSntCR′) Showing Carbene-like Reaction Mode
Wataru Setaka,†,‡ Katsuyuki Hirai,§ Hideo Tomioka,§ Kenkichi Sakamoto,*,†,‡ and Mitsuo Kira*,†
Department of Chemistry, Graduate School of Science, Tohoku UniVersity, Aoba-ku, Sendai 980-8578, Japan,
Photodynamics Research Center, RIKEN (The Institute of Physical and Chemical Research), 519-1399, Aoba,
Aramaki, Aoba-ku, Sendai 980-0845, Japan, and Chemistry Department for Materials, Faculty of Engineering and
Instrumental Analysis Center, Mie UniVersity, Tsu, Mie 514-8507, Japan
Received October 10, 2003; E-mail: mkira@si.chem.tohoku.ac.jp
Many experimental and theoretical studies have been devoted
to the chemistry of triple-bonded compounds of heavy group 14
elements.1 Among them, silaisocyanide,2a silanitrile,2b silaacetylene,2c
germaisocyanide,2d and disilaacetylene2e-g,3 have been evidenced
as short-lived species by various spectroscopic and trapping
experiments. Only three acetylene analogues of heavy group 14
elements, [(2,6-Tip2-C6H3)Pb-Pb(C6H3-2,6-Tip2), (Tip ) 2,4,6-i-
Pr3-C6H2-)]4a , [(2,6-Dipp2-C6H3)Sn-Sn(C6H3-2,6-Dipp2), (Dipp )
2,6-i-Pr2-C6H3-)],4b (2,6-Dipp2-C6H3)Ge-Ge (C6H3-2,6-Dipp2),4c,d
have been isolated as stable compounds recently by Power et al.
Metallaacetylenes (RMtCR′, M ) Si, Ge, and Sn) are interesting
because they are expected to have the carbene character perturbed
electronically by a neighboring divalent heavy group 14 element
through the resonance forms shown in Chart 1. Although a number
of theoretical studies have been performed about metallaacetylenes,5
Figure 1. Molecular structure of aryldiazomethylstannylene 2 determined
by X-ray crystallography (ORTEP, 30% thermal probability ellipsoid).
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg): Sn1-C1 2.184(9); Sn1-C37 2.063(11); Si1-C37 1.858-
(10); C37-N1 1.287(11); N1-N2 1.164(10); C1-Sn1-C37 99.2(3); C37-
N1-N2 177.3(11); Sn1-C37-N1 119.8(7); Si1-C37-N1 115.5(8).
their carbene character has been discussed very rarely. Couret and
co-workers have succeeded in the generation of a germaacetylene
by the photolysis of a diazomethylgermylene.6 The germaacetylene
was trapped by alcohols, but no evidence was obtained for its
carbene character.
lithium8 as thermally stable but air- and moisture-sensitive red
crystals in 18% yield (Scheme 1).9,10 The molecular structure of 2
in the solid state is shown in Figure 1. Notably, the much shorter
Sn-C(dN2) bond length (2.063(11) Å) than the Sn-Car bond length
(2.184(9) Å) as well as the rather high 119Sn NMR resonance (1323
ppm) is suggestive of the significant electron-donating effects of
the diazomethyl substituent.
The photolysis of a benzene solution of 2 without any trapping
reagent using a 500-W high-pressure mercury arc lamp at room
temperature gave red crystals of cyclic stannylene 4 in 70% yield
(Scheme 2).11,12 The 119Sn resonance appearing at δ 1426 is a little
Chart 1
We report herein the first evidence for the successful generation
of a stannaacetylene [1, Ar ) 2,6-Tip2-C6H3-, R′′ ) i-Pr in Scheme
1] via the photolysis of the corresponding diazomethylstannylene
2. Interestingly, stannaacetylene 1 thus generated showed a singlet
carbene-like reaction mode.
Scheme 2
Scheme 1
higher field than that of a known alkyl(aryl)stannylene [(C6H3-2,6-
Tip2)(t-Bu)Sn: δ 1904],13,14 probably due to the π coordination of
a benzene ring to the divalent tin atom in 4. The molecular structure
of 4 with a twist-crown stannacyclooctadiene ring is shown in
Figure 2. The photoreaction is highly stereoselective to give only
cyclic stannylene 4 with cis arrangement between methyl and
triisopropylsilyl substituents on the stannacyclooctadiene ring; no
trans isomer was detected in the reaction mixture.
Diazomethylstannylene 2 was synthesized by the substitution of
the corresponding arylchlorostannylene 37 with silyldiazomethyl-
† Tohoku University.
‡ Photodynamics Research Center, RIKEN.
§ Mie University.
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J. AM. CHEM. SOC. 2004, 126, 2696-2697
10.1021/ja0389974 CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
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16, 310. (b) Karni, M.; Apeloig, Y. Silicon Chem. 2002, 1, 61 and
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119, 11705.
Figure 2. Molecular structure of 4 in the unit cell (ORTEP, 30% thermal
probability ellipsoid). Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and bond angles (deg): Sn1-C1 2.201(7); Sn1-C37 2.231-
(8); C20-C37 1.557(11); C1-Sn1-C37 94.4(3); Sn1-C37-Si1 111.2-
(4); Sn1-C37-C20 115.0(6).
(8) (a) Bertrand, G. In Organosilicon Chemistry III: From Molecules to
Materials; Auner, N., Weis J., Eds.; Wiley-VCH: Weinheim, 1998; pp
223. (b) Aoyama, T.; Inoue, S.; Shioiri, T. Tetrahedron. Lett. 1984, 25,
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(9) 2: mp 169-172 °C dec. 1H NMR (300 MHz, C6D6, 298 K) δ 0.87 (d, J
) 7.2 Hz, 18 H), 1.03 (septet, J ) 7.2 Hz, 3 H), 1.23 (d, J ) 6.9 Hz, 12
H), 1.47-1.50 (m, 12 H), 2.79 (septet, J ) 6.9 Hz, 2 H), 3.3-3.5 (m, 4
H), 7.18 (s, 4 H), 7.2-7.4 (m, 3 H); 13C NMR (75 MHz, C6D6, 298 K)
δ 12.4 [Si(CH(CH3)2)3], 18.8 [Si(CH(CH3)2)3], 23.1 [p-CH(CH3)2], 24.2
[o-CH(CH3)2], 27.3 (CN2), 31.0 [p-CH(CH3)2], 34.7 [o-CH(CH3)2], 121.6
(m-CH), 128, 130.4, 135.2, 146.0, 149.1, 176.9; 29Si NMR (59 MHz, C6D6,
298 K) δ 5.4; 119Sn NMR (112 MHz, C6D6, 298 K) δ 1323; MS (EI, 70
eV) m/z 798 (M+, 20), 601 (100), 481 (10). See the Supporting Information
for the details of the synthesis of 2.
The formation of 4 by the photolysis of 2 is explained
straightforwardly by the intermediacy of stannaacetylene 1 followed
by the intramolecular insertion of the carbene moiety of 1 to a
proximate methyl C-H bond in an isopropyl group as shown in
Scheme 2. The stereoselective formation of 4 is consistent with
the severe steric repulsion between the triisopropylsilyl group and
a triisopropylphenyl ring caused during the formation of the trans
isomer. The present results afford the evidence not only for the
generation of 1 but also for its high carbene-like reactivity.
The photolysis (λ > 330 nm) of 2 in a 3-methylpentane glass
matrix at 77 K showed new absorption maxima at 350 nm (strong)
and 453 nm (weak) assignable to 1.15 In accord with the result, a
similar transient absorption maximum was observed at 355 nm with
the lifetime of 50 ms during the laser flash photolysis (XeCl, 190
mJ, 308 nm) of 2 in benzene at room temperature.16 No triplet ESR
spectrum was observed during the photolysis of 2 in a low-
temperature glass matrix. In accord with the experimental results,
our preliminary calculations at the QCISD/3-21G* level have shown
that the singlet of HSnCH is 4.9 kcal mol-1 more stable than the
triplet and characterized as an SntC triple-bonded compound with
a significant stannylene-carbene character.17
(10) X-ray crystallographic analysis of 2: Diffraction data were collected from
single crystals of dimensions (0.2 mm × 0.2 mm × 0.1 mm) in sealed
glass capillaries on a Bruker SMART 1000 CCD system using graphite-
monochromatized Mo KR radiation (λ ) 0.71069 Å). Crystal data (120
K): C46H70N2SiSn, FW ) 797.82, monoclinic, space group P21/c, a )
12.384(5) Å, b ) 21.871(9) Å, c ) 16.751(7) Å, â ) 104.875(9)°, V )
4385(3) Å3, density (calcd) 1.209 Mg/m3, Z ) 4. Final R indices R1 )
0.0601 for 2547 reflections with I > 2σ(I), wR2 ) 0.1288 for all data,
4712 unique reflections.
(11) 4: 1H NMR (300 MHz, C6D6, 298 K) δ 0.96 (d, J ) 6.9 Hz, 18 H),
1.0-1.4 (m, 37 H), 2.68-2.85 (m, 3 H), 3.28 (septet, J ) 6.9 Hz, 2 H),
3.52-3.66 (m, 2 H), 3.84-3.92 (m, 1 H), 7.1-7.4 (m, 7 H); 29Si NMR
(59 MHz, C6D6, 298 K) δ 5.6; 119Sn NMR (112 MHz, C6D6, 298 K) δ
1426; MS (EI, 70 eV) m/z 770 (M+, 100). See the Supporting Information
for the 1H and 13C NMR data obtained by a 600 MHz NMR spectrometer.
(12) Diffraction data were collected from a single crystal of dimensions 0.4
mm × 0.3 mm × 0.2 mm. Crystal data for 4 (120 K): C46H70SiSn, FW
) 769.80, monoclinic, space group P21/n, a ) 16.407(4) Å, b ) 21.904-
(5) Å, c ) 24.092(5) Å, â ) 106.357(4)°, V ) 8308(3) Å3, density (calcd)
1.231 Mg/m3, Z ) 8. Final R indices (all data) R1 ) 0.0972, wR2 )
0.1676 for 9535 unique reflections.
(13) Eichler B. E.; Power, P. P. Inorg. Chem. 2000, 39, 5444.
(14) Stable arylstannylenes without donor stabilization, see: (a) Tokitoh, N.;
Saito, M.; Okazaki, R. J. Am. Chem. Soc. 1993, 115, 2065. (b)
Weidenbruch, W.; Schlaefke, J.; Scha¨fer, A.; Peters, K.; von Schnering,
H. G.; Marsmann, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 1846. (c)
Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics
1997, 16, 1920. (d) Pu, L.; Olmstead, M. M.; Power, P. P.; Schiemenz,
B. Organometallics 1998, 17, 5602. (e) Eichler B. E.; Phillips, B. L.;
Power, P. P.; Augustine, M. P. Inorg. Chem. 2000, 39, 5450. (f) Eichler,
B. E.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 8785. (g) Setaka, W.;
Sakamoto, K.; Kira, M.; Power, P. P. Organometallics 2001, 20, 4460.
(15) The two bands are tentatively assigned to two πfπ* transitions. Detailed
theoretical calculations for 1 will be required for the reasonable assignment
of these bands. See the Supporting Information.
Supporting Information Available: X-ray structural information
on 2 and 4 (CIF) and experimental details of the photolysis of 2 (PDF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
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(ground state)carbene structure. See the Supporting Information for the
details of the theoretical calculations.
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