Chemistry of a novel family of tridentate alkoxy tin(II) clusters

Article abstract of DOI:10.1021/ja0202309

The chemical interconversions observed for a novel family of trihydroxymethyl ethane (THME-H₃) ligated Sn(II) compounds have been determined using single-crystal X-ray and ¹¹⁹Sn NMR experiments. (μ-THME)₂Sn₃ (1) was isolated from the reaction of 3 equiv of [Sn(NR₂)₂]₂ (R = SiMe₃) with 4 equiv of THME as a unique trinuclear species capped above and below the plane of Sn atoms by two THME ligands. Upon reaction with Sn(NR₂)₂ , compound 1 rearranged to yield another novel molecule [μ-THME)Sn₂- (NR₂)]₂ (2). Compound 2 could also be formed directly from the stoichiometric mixture of THME-H₃ and [Sn(NR₂)₂]₂. Further studies revealed that 1 would also rearrange in the presence of Sn(OR)₂ to form [(μ-THME)Sn₂(μ-OR = OMe (3), OCH₂Me (4), OCH₂CH(Me)CH₂CH₃ (5), OCH₂CMe₃ (6, ONep), OC₆H₅ (7, not structurally characterized), OC₆H₄Me-3 (8), OC₆H₄Me-2 (9), OC₆H₃(Me)₂-2,6 (10), OC₆H₃(CHMe₂)₂-2,6 (11). Additionally, 3-11 could by synthesized from the reaction of 2 and the appropriate H-OR. ¹¹⁹Sn solution NMR studies of 2-11, in THF-d₈, indicate that an equilibrium between the parent complex and its disassociation products (1 and the free parent Sn alkoxy or amide precursor) exists at room temperature. This is a likely reason behind the ease of interconversion observed for 1. The generality of this exchange was further verified through the reaction of 1 with [Ti(μ-ONep)(ONep)₃]₂, which led to the isolation of (μ- ONep)₂Sn₃-THME)₂Ti(ONep)₂ (12). For 12, the solid-state structure was maintained in solution with no indication of an equilibrium.

Full text of DOI:10.1021/ja0202309

Published on Web 05/23/2002
Chemistry of a Novel Family of Tridentate Alkoxy Tin(II)
Clusters
Timothy J. Boyle,* Judith M. Segall, Todd M. Alam, Mark A. Rodriguez, and
Jessica M. Santana
Contribution from the Sandia National Laboratories, AdVanced Materials Laboratory,
1001 UniVersity BouleVard SE, Albuquerque, New Mexico, 87106
Received February 14, 2002
Abstract: The chemical interconversions observed for a novel family of trihydroxymethyl ethane (THME-
H3) ligated Sn(II) compounds have been determined using single-crystal X-ray and 119Sn NMR experiments.
(µ-THME)2Sn3 (1) was isolated from the reaction of 3 equiv of [Sn(NR2)2]2 (R ) SiMe3) with 4 equiv of
THME as a unique trinuclear species capped above and below the plane of Sn atoms by two THME ligands.
Upon reaction with “Sn(NR2)2”, compound 1 rearranged to yield another novel molecule [(µ-THME)Sn2-
(NR2)]2 (2). Compound 2 could also be formed directly from the stoichiometric mixture of THME-H3 and
[Sn(NR2)2]2. Further studies revealed that 1 would also rearrange in the presence of Sn(OR)2 to form [(µ-
THME)Sn2(µ-OR)]2 [OR ) OMe (3), OCH2Me (4), OCH2CH(Me)CH2CH3 (5), OCH2CMe3 (6, ONep), OC6H5
(7, not structurally characterized), OC6H4Me-3 (8), OC6H4Me-2 (9), OC6H3(Me)2-2,6 (10), OC6H3(CHMe2)2-
2,6 (11). Additionally, 3-11 could by synthesized from the reaction of 2 and the appropriate H-OR. 119Sn
solution NMR studies of 2-11, in THF-d8, indicate that an equilibrium between the parent complex and its
disassociation products (1 and the free parent Sn alkoxy or amide precursor) exists at room temperature.
This is a likely reason behind the ease of interconversion observed for 1. The generality of this exchange
was further verified through the reaction of 1 with [Ti(µ-ONep)(ONep)3]2, which led to the isolation of (µ-
ONep)2Sn3(µ-THME)2Ti(ONep)2 (12). For 12, the solid-state structure was maintained in solution with no
indication of an equilibrium.
optoelectronic devices,3,19,20 phosphors,21 and anodes of Li+
batteries.22-24 Metal alkoxides (M(OR)x) are excellent precursors
Introduction
Tin oxide (SnOx) ceramic materials have demonstrated utility
in such varied applications as glass coatings,1,2 flat panel
displays,3 reversible thermoelectric converters,4 solar cells,5,6
gas sensors (NOx, COx, HOR, CH4),1,3,7-16 LED instruments,17,18
to ceramic materials due to their high solubility, high volatility,
low decomposition temperatures, ease of modification, and
commercial availability.25-29 The hydrolysis and condensation
rates of the M(OR)x are often altered through the introduction
of modifying ligands to optimize the properties of the final
material. Since the characteristics of the metal alkoxide precur-
sors greatly affect the properties of the final ceramic material,25-30
it is critical to know the structural aspects of these compounds,
* To whom correspondence should be sent. E-mail: tjboyle@Sandia.gov.
(1) Koh, S. K.; Jung, H. J.; Song, S. K.; Choi, W. K.; Choi, D.; Jeon, J. S.
U.S. Patent US598990, 1999.
(2) Clough, T. J.; Gosvenor, V. L.; Pinsky, N. U.S. Patent US5756192, 1998.
(3) Martel, A.; Caballero-Briones, F.; Fandino, J.; Castro-Rodriguez, R.;
Bartolo-Perez, P.; Zapata-Navarro, A.; Zapata-Torres, M.; Pena, J. L. Surf.
Coat. Technol. 1999, 122, 136.
(4) Yater, J. C.; Yater, J. A.; Yater, J. E. U.S. Patent US5889287, 1999.
(5) Veluchamy, P.; Tsuji, M.; Nishio, T.; Aramoto, T.; Higuchi, H.; Kumazawa,
S.; Shibutani, S.; Nakajima, J.; Arita, T.; Ohyama, H. Sol. Energy Mater.
Sol. Cells 2001, 67 (MAR), 179.
(17) Ishikawa, H.; Lippey, B.; Kobayashi, T.; Oshima, Y.; Mitsuhashi, S.;
Yamashita, M.; Honjo, Y.; Kaneko, K. U.S. Patent US6284382, 2001.
(18) Forrest, S.; Thompson, M. E.; Burrows, P. E.; Sapochak, L. S.; McCarty,
D. M. U.S. Patents US5757026, 1998; US5721160, 1998; and US5707745,
1998.
(6) Amin, N.; Isaka, T.; Yamada, A.; Konagai, M. Sol. Energy Mater. Sol.
Cells 2001, 67 (MAR), 195.
(19) Gamard, A.; Jousseaume, B.; Toupance, T.; Campet, G. Inorg. Chem. 1999,
38, 4671.
(7) Abbas, M. N.; Moustafa, G. A.; Gopel, T. V. Anal. Chim. Acta 2001, 4331,
181.
(20) Jimenez, V. M.; Espinos, J. P.; Caballero, A.; Contreras, L.; Fernandez,
A.; Justo, A.; Gonzalez-Elipe, A. R. Thin Solid Films 1999, 353, 113.
(21) Chadha, S. S.; Alwan, J. J. U.S. Patent US5695809, 1997.
(22) Nam, S. C.; Yoon, Y. S.; Cho, W. I.; Cho, B. W.; Chun, H. S.; Yun, K. S.
Electr. Commun. 2001, 3, 6.
(23) Nam, S. C.; Yoon, Y. S.; Cho, W. I.; Cho, B. W.; Chun, H. S.; Yun, K. S.
J. Electrochem. Soc. 2001, 148 (MAR), A220.
(24) Mohamedi, M.; Lee, S. J.; Takahashi, D.; Nishizawa, M.; Itoh, T.; Uchida,
I. Electrochem. Acta 2001, 46, 1161.
(25) Hubert-Pfalzgraf, L. G. New J. Chem. 1987, 11, 663.
(26) Chandler, C. D.; Roger, C.; Hampden-Smith, M. J. Chem. ReV. 1993, 93,
1205.
(27) Bradley, D. C. Chem. ReV. 1989, 89, 1317.
(28) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides; Academic
Press: New York, 1978.
(8) Chaudhary, B. A.; Mulla, I. S.; Vijayamohanan, K.; Hegde, S. G.; Srinivas,
D. J. Phys. Chem. B 2001, 105, 2565.
(9) Hellegouarc’h, F.; Arefi-Khonsari, F.; Planade, R.; Amouroux, J. Sens.
Actuators, B 2001, 73, 27.
(10) Gregory, O. J.; Luo, Q. Sens. Actuators, A 2001, 88, 234.
(11) Tarabek, J.; Wolter, M.; Rapta, P.; Plieth, W.; Maumy, M.; Dunsch, L.
Macromol. Symp. 2001, 164, 219.
(12) Yoshimi, Y.; Ohdira, R.; Iiyama, C.; Sakai, K. Sens. Actuators, B 2001,
73, 49.
(13) Koh, S. K.; Jung, H. J.; Song, S. K.; Choi, W. K.; Choi, D.; Jeon, J. S.
U.S. Patent US6059937, 2000.
(14) Chou, J. C.; Chung, W.-Y.; Hsiung, S.-K.; Sun, T.-P.; Liao, H.-K. U.S.
Patent US6218208, 2001.
(15) Chang, S.-C. U.S. Patent US4169369, 1979.
(16) Sangaletti, L.; Depero, L. E.; Dieguez, A.; Marca, G.; Morante, J. R.;
Romano-Rodriguez, A.; Sberveglieri, G. Sens. Acutators, B 1997, 44, 268.
(29) Bradley, D. C.; Mehrotra, R. C.; Rothwell, I. P.; Singh, A. Alkoxo and
Aryloxo DeriVatiVes of Metals; Academic Press: San Diego, CA, 2001.
9
6904
J. AM. CHEM. SOC. 2002, 124, 6904-6913
10.1021/ja0202309 CCC: $22.00 © 2002 American Chemical Society

A Novel Family of Tridentate Alkoxy Tin(II) Clusters
A R T I C L E S
both in solution and in the solid sate, to fully exploit them. On
the basis of the diverse applications of cassiterite thin films, it
is surprising that only a few simple tin alkoxide (Sn(OR)x)
Me2-2,6 (DMP, 10), and OC6H3(CHMe2)2-2,6 (DIP, 11)]. To
explore the generality of this structural incorporation, the early
transition metal alkoxide, [Ti(µ-ONep)(ONep)3]2,40 was reacted
with 1 and the unique mixed metal species to yield (µ-
ONep)2Sn3(µ-THME)2Ti(ONep)2 (12). The synthesis of this
unique family of compounds, 1-12, the various interexchanges
these compounds undergo, and exploitable physical properties
are presented.
species have been crystallography characterized, including [Sn-
31,32
(OR)4(HOR)]2 (OR ) OCHMe2
or OCH2C(H)Me233),
[Sn(OCH2Ph)4(HN(CH3)2)]2,34 [Sn(OC(CH3)2-C6H4)2]2,34 Sn-
(OCMe3)4,31 [Sn(OCMe3)2]2,35,36 Sn(OCH(CF3)2)4‚HNMe2,37
and Sn(OCH(CF3)2)2‚HNMe2.38 Additional Sn(II) and Sn(IV)
aryloxide species have also been characterized as mono- or
dinuclear complexes based on the steric bulk of the ring
substituent.34 This small number of Sn(OR)x precursors, with
limited geometrical arrangements, greatly limits the properties
of final ceramic materials that can be obtained.
Experimental Section
All compounds described were handled with rigorous exclusion of
air and water, using standard Schlenk line and glovebox techniques.
All solvents [hexanes (hex), toluene (tol), tetrahydrofuran (THF),
pyridine (py), dioxane (diox)], as well as, H-OMe and H-OEt, were
freshly distilled from the appropriate drying agent,50 immediately prior
to use. The following chemicals were used as received (Aldrich): SnCl2,
LiNR2 (R ) Me, SiMe3), THME-H3, H-OBuMe, H-ONep, H-oMP,
H-DMP, H-DIP, and H-DBP. The appropriate “Sn(NR2)2” was syn-
thesized from the reaction of SnCl2 and 2 equiv of LiNR2 in THF.51
The Sn(OR)2 precursors were synthesized from Sn(NMe2)2 and ∼2
equiv of the appropriate HOR (HOR ) H-OMe, H-OEt, HONep,
H-OBuMe, H-OPh, H-mMP, H-oMP, H-DMP, H-DIP). [Ti(µ-ONep)-
(ONep)3]2 was prepared as reported in the literature.40 For additional
information concerning the analytical data collection methodologies
see the Supplemental Information.
We have been investigating the structural aspects of metal
alkoxide compounds using mono-, di-, and tridentate ligands.39-48
Recently, through the introduction of the monodentate neopen-
toxide (ONep ) OCH2CMe3) ligand, we isolated the unusual
polymeric Sn(II) species [Sn(µ-ONep)2]∞.45,47 By using bidentate
carboxylic acids, several Sn(II) oxo, alkoxy carboxylate struc-
tures have been characterized; however, due to esterification,
control over the structure of the resultant complexes has been
limited.47 This was not the case for the tridentate ligated Sn-
(OR)x system, wherein the introduction of the tridentate ligand
tris(hydroxymethyl)ethane (H3CC(CH2OH)3 ) THME-H3) ligand
was used as a means to generate a family of structurally
controlled molecules (Scheme 1).
(THME)2Sn3 (1). THME-H3 (7.23 g, 64.4 mmol) was added to a
solution of [Sn(N(SiMe3)2]2 (20.0 g, 96.6 mmol) in hex (30 mL) with
stirring, which formed a white precipitate over time. The reaction was
stirred for an additional 12 h and then warmed (60 °C) for 1 h to ensure
completeness of the reaction. The volatile material was removed by
rotary evaporation to yield an off-white powder. This material was
washed with a minimal amount of hex and dried again. Crystals were
grown from hot solutions of 1 in hex (1a), tol (1b), THF (1c), py (1d),
and diox (1e) which were either concentrated and allowed to sit at
glovebox temperatures or cooled to -35 °C until crystals formed. Yield
15.4 g (81.2%, from hexanes). 119Sn (149.1 MHz, THF-d8) δ -330.
Anal. Calcd for C6H18Sn3: 20.34, C; 3.07, H. Found: 20.42, C; 3.03,
H. FTIR (KBr, cm-1) 951(m), 2923(m), 2900(m), 2833(m), 2787(m),
2731(m), 2672(m), 1458(m), 1397(s), 1130(s), 1043(s), 595(s), 450-
(s).
The syntheses of THME-modified Sn(OR)2 compounds led
to the isolation and characterization of a unique Sn(II) com-
pound,49 (µ-THME)2Sn3 (1a-e). Further studies on chemical
modification of this compound led to the characterization of
[(µ-THME)Sn2(N(SiMe3)2)]2 (2) and [(µ-THME)Sn2(µ-OR)]2
[OR ) OMe (3), OCH2Me (OEt, 4), OCH(Me)CH2CH3 (OBuMe
,
5), ONep (6), and OC6H5 (OPh, 7, not structurally character-
ized), OC6H4Me-3 (mMP, 8), OC6H4Me-2 (oMP, 9), OC6H3-
(30) Boyle, T. J.; Tyner, R. P.; Alam, T. M.; Scott, B. L.; Ziller, J. W.; Potter,
B. G. J. J. Am. Chem. Soc. 1999, 121, 12104.
(31) Hampden-Smith, M. J.; Wark, T. A.; Rheingold, A.; Huffman, J. C. Can.
J. Chem. 1991, 69, 121.
(32) Reuter, H.; Kremser, M. Z. Anorg. Allg. Chem. 1991, 598/599, 259.
(33) Chandler, C. D.; Caruso, J.; Hampden-Smith, M. J.; Rheingold, A. L.
Polyhedron 1995, 14, 2491.
(34) Smith, G. D.; Visciglio, V. M.; Fanwich, P. E.; Rothwell, I. P. Organo-
metallics 1992, 11, 1064.
(35) Fjeldberg, T.; Hitchcock, P. B.; Lappert, M. F.; Smith, S. J.; Thorne, A. J.
Chem. Commun. 1985, 939.
(36) Veith, M.; Hobein, P.; Rosler, R. Z. Naturforsch., Teil B 1989, 44, 1067.
(37) Suh, S.; Hoffman, D. M.; Atagi, L. M.; Smith, D. C.; Liu, J.-R.; Chu, W.-
K. Chem. Mater. 1997, 9, 730.
[(THME)Sn2(NR2)]2 (2). To a vial of [Sn(N((SiMe3)2)2]2 (1.00 g,
1.14 mmol) dissolved in THF (∼7 mL) was added THME-H3 (0.137
g, 1.14 mmol) with stirring. The reaction was heated to a boil, allowed
to cool with stirring over 12 h, heated to a boil again, and allowed to
cool to room temperature. The volatile material was removed by rotary
evaporation to yield a pale yellow powder. This material was washed
with hexanes, heated in THF, and allowed to cool to room temperature
whereupon crystals were isolated. Crystalline yield 0.250 g (22.0%).
119Sn (149.1 MHz, THF-d8) δ +12, -331, -451. Anal. Calcd for
C22H54N2O6Si4Sn4: 54.60, C; 5.29, H; 2.72, N. Found: 37.50, C; 7.96,
H; 6.24, N. FTIR (KBr, cm-1) 2950(s), 1459(m), 1400(m), 1245(m),
1130(m), 1052(s), 941(m), 835(m), 670(m), 601(m), 454(w).
(38) Suh, S.; Hofman, D. M. Inorg. Chem. 1996, 35, 6164.
(39) Boyle, T. J.; Schwartz, R. W.; Doedens, R. J.; Ziller, J. W. Inorg. Chem.
1995, 34, 1110.
(40) Boyle, T. J.; Alam, T. M.; Mechenbeir, E. R.; Scott, B.; Ziller, J. W. Inorg.
Chem. 1997, 36, 3293.
(41) Boyle, T. J.; Alam, T. M.; Dimos, D.; Moore, G. J.; Buchheit, C. D.; Al-
Shareef, H. N.; Mechenbier, E. R.; Bear, B. R. Chem. Mater. 1997, 9,
3187.
General Syntheses of [(µ-THME)2Sn2(µ-OR)]2 (3-11). To a
solution of 1 in tol (∼7 mL) was added the appropriate Sn(OR)2 with
stirring, which resulted in a clear solution. After 12 h, the reaction
was warmed for 1 h, the volume of the reaction mixture was drastically
reduced by rotary evaporation, and the mixture was cooled to -35 °C
or it was allowed to set loosely sealed at glovebox temperature until
crystals formed. Full synthesis and analytical data for 3-11 are listed
in the Supporting Information. For the representative compounds shown
in this paper, the full details are listed below.
(42) Boyle, T. J.; Pedrotty, D. M.; Scott, B.; Ziller, J. W. Polyhedron 1997, 17,
1959.
(43) Boyle, T. J.; Alam, T. M.; Tafoya, C. J.; Scott, B. L. Inorg. Chem. 1998,
37, 5588.
(44) Boyle, T. J.; Gallegos, J. J., III; Pedrotty, D. M.; Mechenbier, E. R.; Scott,
B. L. J. Coord. Chem. 1999, 47, 155.
(45) Boyle, T. J.; Alam, T. M.; Rodriguez, M. A.; Zechmann, C. A. Inorg. Chem.
2002, 41, 2574.
(46) Boyle, T. J.; Alam, T. M.; Peter, K. P.; Rodriguez, M. A. Inorg. Chem.
2002, 40, 6281.
(47) Boyle, T. J.; Jackson, N.; Miller, J.; Segall, J. M.; Alam, T. M.; Zechmann,
C. A.; Rodriguez, M. A. Abstracts of Papers; 221st National Meeting of
the American Chemical Society April 1, 2001; American Chemical
Society: Washington, DC, 2001; Abstract U748.
(48) Zechmann, C. A.; Boyle, T. J.; Pedrotty, D. M.; Alam, T. M.; Lang, D. P.;
Scott, B. L. Inorg. Chem. 2001, 40, 2177.
(49) Boyle, Timothy J. U.S. Patent US6307078, 2001.
(50) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals,
3rd ed.; Pergamon Press: New York, 1988.
(51) Harris, D. H.; Lappert, M. F. Chem. Commun. 1974, 895.
9
J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002 6905

A R T I C L E S
Boyle et al.
Scheme 1. Reaction Pathway for THME-Modified Sn(OR)2
[(µ-THME)Sn2(µ-ONep)]2 (6). Sn(ONep)2 (0.50 g, 1.7 mmol) and
1 (1.0 g, 1.7 mmol) in THF (∼5 mL) were used. Crystalline yield 1.3
g (84%). Anal. Calcd for C20H40O8Sn4: 27.20, C; 4.53, H. Found:
27.45, C; 4.43, H. 119Sn (149.1 MHz, THF-d8) δ -330 (0.66 Sn), -366
(1.0 Sn), -377 (2.0 Sn), -387 (1.0 Sn). FTIR (KBr, cm-1) 2949(m),
2923(sh,m), 2829(m), 2798(m), 2705(m), 2675(m), 1474(sh,m) 1458-
(m), 1406(sh, m), 1356(m), 1120(s), 1038(s), 1012(sh,s), 907(w), 608-
(m), 557(sh,m), 445(m), 432(sh,m).
to set loosely sealed at glovebox temperature until crystals formed.
Crystalline yield 0.92 g (55%). FT-IR (KBr, cm-1) 2951(s), 2864(s),
2825(s), 2745(m), 2681(m), 1287(w), 1260(w), 1561(w), 1544(w),
1509(w), 1476(m), 1460(m), 1450(w), 1439(w), 1403(m), 1390(m),
1361(m), 1260(m),1215(m), 1128(s), 1109(s,sh), 1054(s), 1020(s), 932-
(w), 899(w), 809(w), 751(w), 671(m), 658(s), 620(m), 583(m), 513-
(s), 465(s), 438(w). Anal. Calcd for C30H62O10Sn3Ti: 36.52, C; 6.33,
H. Found: 36.83, C; 6.12, H. 119Sn (149.1 MHz, THF-d8) δ -358 (1
Sn), -403 (2 Sn).
[(µ-THME)Sn2(µ-DIP)]2 (11). Sn(DIP)2 (0.80, 1.7 mmol) and 1 (1.0
g, 1.7 mmol) in THF (∼5 mL) were used. Crystalline yield 0.89 g
(55%). FTIR (KBr, cm-1) 2957(m), 1459(m), 1431(m), 1382(m), 1361-
(w,sh), 1313(m), 1258(m), 1179(m), 1118(m), 1041(s), 932(sh,w), 825-
(m), 799(w), 755(w), 732(w), 489(w). Anal. Calcd for C34H52O8Sn4:
38.40, C; 4.93, H. Found: 38.86, C; 5.21, H. 119Sn (149.1 MHz, THF-
d8) δ -208, -309, -339, -390, -403.
(µ-ONep)2Sn3(µ-THME)2Ti(ONep)2 (12). To a solution of 1 (1.0
g, 1.7 mmol) in tol (∼7 mL) was added [Ti(ONep)4]2 (0.67 g, 0.85
mmol) with stirring, which resulted in a clear solution. After 12 h, the
reaction was warmed for 1 h, the volume of the reaction mixture was
drastically reduced by rotary evaporation, and the mixture was allowed
X-ray Crystal Structures.52 Tables 1- 3 list the data collection
parameters for 1a-e, 2-6, and 8-12, respectively. All crystals were
mounted onto a thin glass fiber from a pool of Fluorolube and placed
immediately under a liquid N2 stream on a Bruker AXS diffractometer.
Structural solutions were performed by using the following software:
SMART Version 5.054, SAINT+ 6.02 (7/13/99), SHELXTL 5.1 (10/
29/98), XSHELL 4.1 (11/08/2000), and SADABS within the SAINT+
package.52 Each structure was solved by using direct methods, yielding
(52) The listed versions of SAINT, SMART, XSHELL, and SADABS Software
from Bruker Analytical X-ray Systems Inc., 6300 Enterprise Lane, Madison,
WI 53719, were used in this analysis.
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6906 J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002

A Novel Family of Tridentate Alkoxy Tin(II) Clusters
A R T I C L E S
yields and purity of 1 were greatly improved when hexanes and
the appropriate 3:2 stoichiometry was used (eq 1). Compound
1 was found to be soluble in (a) hex, (b) tol, (c) THF, (d) py,
or (e) diox and X-ray quality crystals were isolated from each
but with different unit cell dimensions and number of formula
units per unit cell. The elemental analyses of the bulk powder
of 1 isolated from the initial hexanes wash, and prior to
crystallization, were in agreement with the solid-state crystal
structure.
Compound 1 was found to be relatively air/water stable as
determined by no change in the FTIR spectrum of a sample of
1 that had been exposed to atmospheric conditions for several
hours. Investigation of the thermal properties of 1 by DSC
revealed a melt occurred at ∼227 °C with a complete loss of
material at 353 °C (∆H ) -165 J/g), which is indicative of
sublimation. TGA/DTA analysis of 1 revealed that this com-
pound was stable up to ∼170 °C under an O2 atmosphere but
at higher temperatures an ∼5% weight increase accompanied
by an exotherm in the DTA was recorded. The melting point
of 1 was found to be ∼200 °C. These characteristics imply that
1 may be useful as a metalloorganic chemical vapor deposition
(MOCVD) precursor.
When the original 3:1 Sn:THME reaction mixture was heated,
[(µ-THME)Sn2(NR2)]2 (2) was isolated and is shown in Figure
2. Improved yields were obtained for a heated 2:1 reaction
mixture. Interestingly, it was also discovered that compound 2
could be synthesized from a heated mixture of 1 and [Sn-
(N(SiMe3)2)2]2 or “Mg(N(SiMe3)2)2”, as verified by single-
crystal X-ray and 119Sn NMR studies. Attempts to use smaller,
less sterically demanding amides (i.e., Sn(NMe2)2) did not yield
analogues to 2, instead 1 was isolated. Elemental analyses of
the bulk powder and the presence of NR2 and THME stretches
in the FTIR spectrum of 2 were consistent with the ligands
present in the crystal structure.
Figure 1. Thermal ellipsoid plot of (THME)2Sn3 (1). Thermal ellipsoid
plots are drawn at the 30% level.
the Sn, O, and some of the C atoms, with subsequent Fourier synthesis
yielding the remaining C atom positions. The hydrogen atoms were
fixed in positions of ideal geometry and refined within the XSHELL
software.52 The final refinement of each compound included anisotropic
thermal parameters on all non-hydrogen atoms. See the appropriate
table or Supporting Information for additional details.
Results and Discussion
As was noted for [(µ-THME)Ti2(OPri)5]2,39 [(µ-THME)Zr2-
(OPri)5]2,39 and [(µ-THME)Nb(OEt)2]2,41 the introduction of the
tridentate THME ligand reduces the number of accessible
terminal alkoxides which garners greater control over the
condensation and hydrolysis (i.e., cross-linking) behavior of
metal alkoxides. While a number of cationic and mixed halide
THME ligated species for a variety of systems have been
reported,53-62 before this work there was an absence of
information concerning THME-modified Sn(OR)x. The reaction
pathways developed for this novel family of compounds49 (1-
11) are illustrated in Scheme 1 with the details of the synthesis
and characterization of these compounds presented below.
Synthesis. Initial synthetic strategies focused on generating
the fully Sn-substituted THME complex; however, with a 3:1
Sn:THME stoichiometry, the temperature of the reaction mixture
dictated the final product formed. When the reaction mixture
was not heated, a unique, fully Sn-substituted THME ligand
was isolated as (µ-THME)2Sn3 (1), shown in Figure 1. The
The ease with which the central core of 1 was rearranged
with M(NR2)2 suggested that modifications, such as Sn(OR)2
(eq 2) would be possible. The alcohols used were selected to
study the effect of steric bulk on the overall structure.
Independent of the steric bulk of the alcohol, 1 rearranges to
incorporate the Sn(OR)2 in what appears to be a side-on-
addition, forming a tetranuclear species, [(µ-THME)Sn2(µ-OR)]2
where OR ) OMe (3), OEt (4), OBuMe (5), ONep (6), OPh
(7), mMP (8), oMP (9), DMP (10), and DIP (11). The thermal
ellipsoid plots of the alkoxide (6) and aryloxide (11) representa-
tives are shown in Figures 3 and 4, respectively. While well-
formed crystals of 7 could be grown from toluene and other
solvents, the solid-state structure could not be established by
single-crystal X-ray diffraction. Therefore, the mMP ligand was
selected as a model to the OPh, since it has no steric bulk in
the ortho position, as with the OPh, but offered a methyl group
on the ring to alter the crystallization behavior. The structure
solved for the mMP derivative, 8, was consistent with the other
compounds and based on the similarity of the steric bulk of the
ortho position of the ring implies that the OPh also adopts a
similar structure. Attempts to go beyond the steric bulk of the
(53) Chen, Q.; Zubieta, J. Coord. Chem. ReV. 1992, 107.
(54) Mckee, V.; Wilkins, C. J. J. Chem. Soc., Dalton Trans. 1987, 523.
(55) Hegetschweiler, K.; Schmalle, H.; Streit, H. M.; Schneider, W. Inorg. Chem.
1990, 29, 3625.
(56) Sillanp, R.; Leskel, M.; Hiltunen, L. Acta Crystallogr. 1982, B38, 1591.
(57) Chang, Y.; Chen, Q.; Khan, M. I.; Salta, J.; Zubieta, J. J. Chem Soc., Chem.
Commun. 1993, 1872.
(58) Chen, Q.; Goshorn, D. P.; Scholes, C. P.; Tan, X.; Zubieta, J. J. Am. Chem.
Soc. 1992, 114, 10058.
(59) Wilson, A. J.; Robinson, W. T.; Wilkins, C. J. Acta Crystallogr. 1983,
C39, 54.
(60) Cornia, A.; Gatteschi, D.; Hegetschweiler, K.; HausherrPrimo, L.; Gramlich,
V. Inorg. Chem. 1996, 35, 4414.
(61) Crans, D. C.; Jiang, F.; Chen, J.; Anderson, O. P.; Miller, M. M. Inorg.
Chem. 1997, 36, 1038.
(62) Jiang, F. L.; Anderson, O. P.; Miller, S. M.; Chen, J.; MahroofTahir, M.;
Crans, D. C. Inorg. Chem. 1998, 37, 5439.
9
J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002 6907

A R T I C L E S
Boyle et al.
Figure 2. Thermal ellipsoid plot of [(THME)Sn2(NR2)]2, (2). Thermal ellipsoid plots are drawn at the 30% level.
Figure 4. Thermal ellipsoid plot of [(µ-THME)Sn2(OC6H3(CHMe2)2-2,6)]2,
(11). Thermal ellipsoid plots are drawn at the 30% level.
Figure 3. Thermal ellipsoid plot of [(µ-THME)Sn2(OCH2CMe3)]2, (6).
Thermal ellipsoid plotsare drawn at the 30% level.
bisisopropyl substituent in the 2,6 ring of 11 by using 2,6-bis-
(dibutyl)phenoxide yielded only insoluble materials which could
not be redissolved in a variety of solvents at elevated temper-
atures. This implies a change in structure but due to its low
solubility, crystallographic analyses of these compounds were
precluded.
Compounds 3-11 were found to be soluble in hexanes,
toluene, THF, and py. Elemental analyses of the crystals of these
compound were in agreement with the solid-state structures.
The IR spectra of 3-11 revealed similar M-O regions;28
however, the pendant hydrocarbon chains of the various
modifiers dominated the spectra of the individual components.
Compounds 3-11 could also be synthesized form the reaction
of 2 and the respective HOR. These reactions were run on small
scale so that the yields were not optimized; however, the
conversions were verified by 119Sn NMR analyses.
To explore the generality of the substitution of the core of 1
by metal alkoxides, we chose to investigate if the previously
characterized early transition metal alkoxide [Ti(µ-ONep)-
Figure 5. Thermal ellipsoid plot of (µ-ONep)2Sn3(µ-THME)2Ti(ONep)2,
(12). Thermal ellipsoid plots are drawn at the 30% level.
40
(ONep)3]2 would also substitute as noted for the main group
Sn(OR)2. Under similar conditions as noted for 3-11, [Ti(µ-
identified as (µ-ONep)2Sn3(µ-THME)2Ti(ONep)2 (12) and is
shown in Figure 5. Elemental analysis was consistent with the
ONep)(ONep)3]240 was reacted with 1. The product isolated was
9
6908 J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002

A Novel Family of Tridentate Alkoxy Tin(II) Clusters
A R T I C L E S
Table 1. Data Collection Parameters for 1a-e
1a‚hex
1b
1c‚THF
1d‚py
1e‚diox
chemical formula
formula weight
temp (K)
C56H100O30Sn15
3033.70
168(2)
C80H144O48Sn24
4722.51
168(2)
P2(1)2(1)2(1)
orthorhombic
21.4033(14)
24.3825(15)
24.4347(15)
C24H44O13Sn6
1252.73
168(2)
C35H59NO18Sn9
1850.04
168(2)
C24H44O14Sn6
1268.73
168(2)
space group
C2/c
Pbca
Pnma
C2/c
monoclinic
23.508(3)
12.1330(14)
31.393(14)
109.602(2)
8435.0(16)
4
2.389
4.426
3.49
7.27
orthorhombic
12.3788(19)
22.642(3)
25.337(4)
orthorhombic
22.278(4)
10.0634(16)
23.648(4)
monoclinic
30.379(4)
10.4956(15)
12.4140(18)
113.638(2)
3626.1(9)
4
2.324
4.128
1.78
4.34
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
12751.6(14)
4
2.460
4.680
4.33
7.52
6.95
7101.5(19)
8
2.343
4.212
2.05
4.38
3.06
5301.7(15)
4
2.318
4.228
2.34
5.38
3.22
D
calcd (Mg/m3)
µ, (Mo KR) (mm-1
R1a (%)
)
wR2b (%)
R1a (all data, %)
wR2b (all data, %)
5.73
7.84
2.07
4.43
8.01
4.66
5.70
a R1 ) Σ |Fo| - |Fc|/Σ|Fo| × 100. b wR2 ) [Σ w(Fo - Fc )2/Σ(w|Fo| )2]1/2 × 100.
Table 2. Data Collection Parameters for 2-6
2
2
2
2
3
4
5
6
chemical formula
formula weight
temp (K)
C22H54N2O6Si4Sn4
1029.79
168(2)
P2(1)
monoclinic
6.834(3)
C12H24O8Sn4
771.07
168(2)
C14H28O8Sn4
799.12
168(2)
P1h
triclinic
8.845(3)
10.630(3)
12.957(4)
98.746(5)
101.834(5)
106.563(5)
1113.8(6)
2
2.383
4.467
3.43
8.93
4.06
9.36
C20H40O8Sn4
883.28
168(2)
C20H40O8Sn4
883.28
168(2)
space group
P2(1)/c
P2(1)/c
P1h
monoclinic
14.226(3)
9.1780(18)
15.553(3)
monoclinic
15.051(2)
12.1069(18)
15.607(2)
triclinic
11.0984(16)
11.9361(17)
12.1199(17)
109.963(2)
100.248(2)
99.461(2)
1440.3(4)
2
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
17.680(7)
15.981(6)
101.050(5)
95.867(3)
92.027(3)
1895.1913)
2
1.805
2.765
3.95
8.90
4.49
2019.9(7)
4
2.536
4.922
2.32
5.33
2.98
2842.2(7)
4
2.064
3.512
2.67
6.06
3.12
D
calcd (Mg/m3)
2.037
3.465
3.19
8.12
4.37
8.86
µ, (Mo KR) (mm-1
R1a (%)
)
wR2b (%)
R1a (all data, %)
wR2b (all data, %)
9.21
5.54
6.25
a R1 ) ∑||Fo| - |Fc||/∑|Fo| × 100. b wR2 ) [∑w(Fo - Fc )2/∑(w|Fo| )2]1/2 × 100.
2
2
2
solid-state structure. The FTIR spectrum of 12 was similar to
that of the other species but the M-O stretches were shifted to
higher energies due to the influence of the Ti atoms.
approximated by a square base pyramidal (SBP) geometry. Both
arrangements force the electron pairs to reside externally.
Since there was very little difference in the metrical data
between the individual species present in the crystal structures
of 1 or between the various crystallized species (1a-e) only
1b will be discussed. The Sn metal centers of 1b are separated
by an average of 3.46 Å with an average Sn-O distance of
2.20 Å. The [-Sn-O]2 central cores possess very regular
geometries with an average Sn-(µ-O)-Sn of 104.5 °, an
average (µ-O)-Sn-(µ-O) from the same THME ligand of 78.7
°, and average (µ-O)-Sn-(µ-O) internal angle of 66.4 °. The
shape of the molecule approximates an ellipsoid of ∼10 × 5 Å
in size. The packing diagrams of 1a-e, however, reveal that
there is a great deal of flexibility in the arrangement of these
subunits, the orientations of which are greatly dependent upon
the solvent of crystallization.
Compound 2 (Figure 2) is a symmetric molecule consisting
of a plane of four Sn cations in the trapezoidal arrangement.
Two of the metal centers adopt a trigonal (TRI) and two adopt
a PYD arrangement through the coordination of two THME
and two NR2 ligands. On each side of the plane of Sn atoms,
each oxygen of the THME ligands is bound to each Sn metal
center forming three [-Sn-O-]2 moieties. The basal PYD-
coordinated Sn cations are from THME oxygens only, whereas
Solid State. The identities of the compound discussed above
were determined by single-crystal X-ray diffraction investiga-
tions. Tables 1-3 list the data collection parameters for 1a-e,
2-6, and 8-12, respectively. Full listing of the metrical data,
thermal ellipsoid plots, and syntheses of 1-12 can be found in
the Supporting Information. The consistency of the bulk powder
with the observed structures was investigated by using solid-
state NMR experiments. Table 4 lists the chemical shifts of the
13C and 119Sn MAS NMR spectra for these compounds.
Structures. While numerous arrangements were isolated for
1a-e based upon the choice of crystallization solvent, the same
basic subunit was found for each. The structure of 1 is the first
THME-ligated Sn compound reported to date with the thermal
ellipsoid plot shown in Figure 1 (structure shown is from 1c).
It is in a unique arrangement, consisting of three Sn atoms joined
solely by the oxygens of the THME ligands. The THME ligands
cap the Sn atoms above and below the plane of the metals
forming a C3h center of symmetry. Each Sn atom formally
adopts a pyramidal (PYD) geometry; however, if the free
electrons are included in the discussion, the geometry is best
9
J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002 6909

A R T I C L E S
Boyle et al.
Table 3. Data Collection Parameters for 8-12
8
9
10
11
12
chemical formula
formula weight
temp (K)
C24H32O8Sn4
923.26
168(2)
C24H32O8Sn4
923.26
168(2)
C26H36O8Sn4
951.31
168(2)
C34H52O8Sn4
1063.52
168(2)
C30H62O10Sn3Ti
986.77
168(2)
space group
Pbca
Pbca
P2(1)/c
monoclinic
19.4460(14)
8.3861(6)
18.4826(13)
92.6900(10)
3010.7(4)
4
2.099
3.324
3.31
5.76
Pbca
P2(1)/c
monoclinic
17.174(10)
18.681(11)
13.090(7)
106.920(10)
4018(4)
4
1.631
2.081
7.25
12.76
orthorhombic
22.209(6)
8.843(2)
29.053(8)
orthorhombic
20.967(4)
8.9897(15)
29.726(5)
orthorhombic
16.066(4)
17.328(4)
28.081(6)
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
5706(3)
8
5603.1(16)
8
2.189
3.569
3.56
6.53
5.76
6.99
7818(3)
8
D
calcd (Mg/m3)
2.150
3.505
3.16
6.66
4.77
7.06
1.807
2.571
3.84
5.93
9.09
6.83
µ, (Mo KR) (mm-1
R1a (%)
)
wR2b (%)
R1a (all data, %)
wR2b (all data, %)
6.81
6.47
19.98
15.87
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo| × 100. b wR2 ) [∑w(Fo - Fc )2/∑(w|Fo| )2]1/2 × 100.
Table 4. NMR Data for Selected Species
compd
119Sn (THF-d8)
119Sn MAS
13C MAS
1
2
-330
+12, -331, -451
-252
118, 94, -371, -382
78.4 (OCH2)3CMe, 39.6 (OCH2)3CMe, 18.7 (OCH2)3CMe
78.6, 74.8, 73.8, 71.6, 70.5, 69.4 (OCH2)3CMe, 42.7, 42.3,
39.7 (OCH2)3CMe, 42.7, 42.3, 39.7 (OCH2)3CMe, 8.8, 7.2,
5.8 N(Si(CH3)3)2
3
4
5
6
-330(1.25 Sn), -347(1.0 Sn),
-372(2.0 Sn), -397(1.0 Sn).
-330 (0.4 Sn), -351(1.0 Sn),
-373 (2.1 Sn), -394 (1.0 Sn).
-330(0.7 Sn), -366(1.0 Sn),
-379(2.0 Sn), -391(1.0 Sn)
-330(0.7 Sn), -366(1.0 Sn),
-377(2.0 Sn), -387(1.0 Sn)
-186, -208, -214, -230
-190, -197, -213, -222
-203, -210, -218, -237
-196, -241, -248
75.7 (CH3C(CH2O)3), 52.3, 51.4 (OCH3), 41.8, 41.1
(CH3C(CH2O)3), 20.5 (CH3C(CH2O)3).
76.5, 75.6, 75.0 (CH3C(CH2O)3), 57.0, 56.3 (OCH2CH3),
40.9 (CH3C(CH2O)3), 21.9, 20.4 (CH3C(CH2O)3), 18.9 (OCH2CH3)
76.6, 74.8 (CH3C(CH2O)3), 41.2, 39.2 (CH3C(CH2O)3), 27.8,
19.6, 17.5, 16.1, 14.1 (OCH2C(CH3)CH2CH3, CH3C(CH2O)3)
74.8, 74.5 (CH3C(CH2O)3), 71.6, 70.9 (OCH2CMe3), 41.2.
40.5 (CH3C(CH2O)3), 34.8 (OCH2CMe3), 30.7, 28.9
(OCH2CMe3), 20.1, 19.0 (CH3C(CH2O)3).
7
-330(2.0 Sn), -390(1.0 Sn),
-421(2.0 Sn), -464(1.0 Sn)
-330(0.25 Sn), -389(1.0 Sn),
-420(2.0 Sn), -462(1.0 Sn)
-126 (broad), -241, -280
-232, -242, -294
159.9, 130.4, 123.0, 120.8 (OC6H5), 76.1, 74.8
(CH3C(CH2O)3), 41.3 (CH3C(CH2O)3), 21.0 (CH3C(CH2O)3).
160.7, 159.6, 139.3, 131.9, 130.5, 122.6, 121.5, 120.8, 119.2
(OC6H4(Me)-3), 75.9, 74.3, 72.8 (CH3C(CH2O)3), 41.7, 41.5
(CH3C(CH2O)3), 23.3 (OC6H4(Me)-3), 20.6, 19.2 (CH3C(CH2O)3)
130.8, 130.1, 129.4, 128.7, 125.8, 120.3, 119.3
(OC6H3(Me)2-2,6), 77.4, 76.3, 74.6 (CH3C(CH2O)3), 40.7,
40.1 (CH3C(CH2O)3), 23.8, 23.1, 22.4 (OC6H3(Me)2-2,6),
19.2, 18.4 (CH3C(CH2O)3)
8
10
11
-335(1.8 Sn), -372(1.0 Sn),
-398(2.0 Sn), -417(1.0 Sn).
-220, -226, -257
-208, -309, -339,
-390, -403
-294, -324, -344, -361
155.6, 153.2, 142.7, 140.8, 138.9, 137.9, 125.8, 124.3, 118.6
(OC6H3(CHMe2)2-2,6), 76.1, 74.6, 73.1, 72.6
(CH3C(CH2O)3), 56.2, 54.9, 49.3 (OC6H3(CHMe2)2-2,6),
40.3 (CH3C(CH2O)3), 30.1, 29.7, 28.5, 27.8, 26.4, 25.6, 24.3
(OC6H3(CHMe2)2-2,6), 19.1, 18.3 (CH3C(CH2O)3)
83.7, 84.6, 85.5, 86.8 (OCH2CMe3), 79.7, 74.8, 76.5
(CH3C(CH2O)3), 39.1, 38.5 (CH3C(CH2O)3, 35.7, 35.3 34.8,
34.3(CH3C(CH2O)3), 29.7, 29.2, 28.8, 27.8 (OCH2CMe3),
19.0, 17.9(CH3C(CH2O)3)
12
-358(1.0 Sn), -403(2.0 Sn)
-370, -403
the apical TRI-coordinated Sn atoms bind an NR2 ligand to
complete their coordination. The electrons of the apical Sn atoms
point inward and the basal Sn atoms point outside from the
molecule. The tridentate nature of the THME ligands forces
the molecule into a cup shape that is open in comparison to 1.
In the literature, only two other crystallographically characterized
Sn(OR)(NR2) species have been reported, Sn(N(SiMe3)2)-
(OC6H2(CMe3)2-2,6,Me-4)63 and [Sn(N(SiMe3)2)(µ-OBu)]2.64
The basal Sn atoms of 2 are separated by ∼3.43 Å wherein the
apical Sn atoms are separated by ∼5.97 Å. The average Sn-N
distances of 2.11 Å and the average Sn-OR distances of 2.20
Å are consistent with literature reports. The [-Sn-O]2 central
cores possess very regular geometries with Sn-(µ-O)-Sn that
average 104.9 °, (µ-O)-Sn-(µ-O) that range from 67.6 to 121.5
°, and (µ-O)-Sn-N angles that average 92.8 Å. The distances
of 2 are within agreement of those of the [Sn(N(SiMe3)2)(µ-
OBu)]2 dimer.64
Because of the similarity of the general constructs of 3-11,
the structures of these compounds will be discussed collectively.
Each compound consists of a ring of four [-Sn-(µ-OR)2-Sn]
squares linked by Sn atoms. Six of the eight coordination sites
of the four Sn cations are filled by the oxygen atoms of the
THME ligands and two from the appropriate OR ligand. The
(63) Braunschweig, H.; Chorley, R. W.; Hitchcock, P. B.; Lappert, M. F. J.
Chem. Soc., Chem. Commun. 1992, 1311.
(64) McGeary, M. J.; Folting, K.; Caulton, K. G. Inorg. Chem. 1989, 28, 4051.
9
6910 J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002

A Novel Family of Tridentate Alkoxy Tin(II) Clusters
A R T I C L E S
geometry around the metal centers approximates a SBP if the
free electrons are included in the geometrical consideration. The
OR ligands are bound to the same Sn atom and bridge to
different Sn atoms in a trans arrangement. The remainder of
the molecule consists of the bound THME ligands above and
below the plane of Sn atoms. This results in one Sn atom with
four µ-OTHME, two with three µ-OTHME and one µ-OR, and one
with two µ-OTHME and two µ-OR oxygens atoms. The simplest
mechanism for the formation of this arrangement is the side-on
addition of the Sn(OR)s from the disruption of two Sn-OTHME
bonds. The free electrons, as observed for 1, are pointed
externally for these molecule.
13C MAS NMR the representative ligand resonances are
observed but are present as multiplets. The 119Sn MAS NMR
spectrum reveals four types of Sn metal centers: two around
+105 ppm and two centered at -375 ppm. The ideal symmetry
of 2 is disrupted in the solid state by intra- and interpacking
inequivalancies. The four 119Sn resonances may reflect the two
types of Sn present (i.e., those bound by THME only ligands
and those bound by THME and NR2 ligands).
For 3-12, each molecule possesses a C2 axis of rotation
which equates the THME and OR ligands and, therefore, one
complete set of THME and OR ligand resonances is expected
in the 13C MAS NMR. The appropriate 13C resonances are
clearly present for each sample but many were duplicated, which
can be attributed to many complications when looking at solid-
state structures, including solid-state packing forces such as
inequivalent pendant ligand groups, unit cell moieties (see Table
1-3), unit cell solvent inclusion, intermolecular generated
packing inequivalancies, and/or asymmetry introduced by the
OR groups which are not free to equilibrate in the solid state.
Since an asymmetric molecule was observed in the 13C MAS
NMR, the 119Sn MAS NMR should reveal four unique Sn peaks
for 3-11 and three for 12. The modification of 1 with an Sn-
(OR)2 or Ti(OR)4 causes a significant change in the 119Sn
chemical shift as evidenced by a more than 100 ppm shift from
1 (see Table 4). For 3-5 and 11, the expected four 119Sn
resonances were observed, but for 6 and 7-10, three peaks were
observed, each of which had a resonance around -240 ppm.
For 12, only two 119Sn resonances were observed. The lower
than expected number of 119Sn MAS NMR peaks may be due
to coincidental overlap of similar Sn environments. Considering
the elemental analyses and infrared and solid-state NMR data
in toto, the bulk powders of 1-12 appear to be consistent with
the solid-state structure. It is of note that for every sample there
was no 119Sn peak observed that was consistent with compound
1 (i.e., compound 1 was not present).
Metrical data of the alkoxide and aryloxide derivatives are
all similar. The Sn- - -Sn distances were on average 3.55 Å for
3-6 and 3.57 Å for 8-11 which are substantially longer than
those noted for 1, reflecting the expansion of the original
molecule. The Sn-(µ-THME) distances for the Sn-(µ-OR) and
the Sn-(µ-OAr) species were ∼2.16 Å, independent of the OR
group. The Sn-(µ-OR) distances systematically increase as the
steric bulk around the metal center increases (av. 2.23 Å, 3;
2.24 Å, 4; 2.25 Å, 5; 2.27 Å, 6; 2.30 Å, 8; 2.34 Å, 10; 2.36 Å,
11). The angles for the Sn-(µ-OR)-Sn range from ∼102.6 to
106.6 ° for 3-6 and ∼99.8 to 102.4 ° for 8-11. In contrast,
the Sn-(µ-THME)-Sn angles are much broader ranging, from
∼106.9 to 112.5 ° for 3-6 and ∼106.6 to 114.6 ° for 8-11,
due to the steric constraints invoked by the tridentate ligand.
For 12, the central core resembles those of 3-11. Observable
by the presence of the hetero Ti atom, the µ-ONep ligands have
rearranged and appear on the opposite side, not bound to the
Ti metal center. Therefore, the assumption that simple expansion
of the coordination sphere by a side-on addition noted for 3-11
is incorrect and a significant amount of ligand rearrangement
must occur. The Ti uses four of the two THME ligands and
two terminal ONep ligands to complete its octahedral geometry.
Again the Sn atoms are PYD, using both THME and µ-ONep
ligands. The Sn- - -Sn distance of 12 (av. 3.53 Å) is slightly
shorter than what was noted for 3-11, but the Sn- - -Ti distances
are significantly shorter, at av. 3.44 Å. The Sn-O distances
are within the range noted for 3-11 and the Ti-O distances
are in agreement with the distances noted for [Ti(µ-ONep)-
(ONep)3]2.40 The angles around the Ti metal center are only
slightly distorted from ideal octahedral angles. The geometry
around the Sn cations is in agreement with those observed for
3-11. On the basis of these data, the introduction of the Ti-
(OR)4 in comparison to the Sn(OR)2 appears to have only subtly
altered the basic constructs of the central core; therefore, it may
be possible to add a wide range of metal alkoxides to yield a
systematic method for production of mixed metal alkoxides.
Solution State. Due to the known dynamic behavior of metal
alkoxides in solution, it was necessary to discern whether the
solid-state structures of 1-12 were retained upon dissolution.
Solution behaviors of 1-12 were investigated through the
redissolution of crystals in THF-d8. Samples were made as
concentrated as possible without leaving any insoluble material
in the NMR tubes, otherwise it is difficult to observe the 119Sn
signal.
1
The H and 13C NMR spectra of 1 in THF revealed three
resonances consistent with the moieties of the THME ligand
(methyl, quaternary, and methylene). A number of smaller peaks
are present which are consistent with Sn- - -C J-coupling. The
119Sn NMR spectrum indicates that the structure of 1 was
retained in solution since only one peak was observed at δ -330
ppm. Therefore, the free electron pair on each Sn atom of 1 are
still accessible in solution, which will allow for it to be used in
a wide variety of applications, such as base catalyst (vide supra).
Solid-State NMR. In an effort to verify that the bulk powders
were consistent with the crystal structures, solid-state 13C and
119Sn MAS NMR investigations were undertaken. Crystalline
material of each compound was packed into a rotor under an
atmosphere of argon immediately prior to obtaining a spectrum.
Table 4 lists the NMR data obtained on these compounds. The
solid-state 119Sn and 13C MAS NMR spectra collected on the
bulk powder of 1 are consistent with the symmetry observed
for the single-crystal structures wherein a single 119Sn MAS
resonance and one set of THME 13C resonances were observed.
1
For each of the remaining samples (2-12), the H and 13C
NMR spectra revealed multiple THME resonances and the
respective OR or NR2 resonances. These data were very
complicated due to multiple overlapping resonances and did not
significantly aid in interpretation of the solution behavior of
the various compounds. In general, the 119Sn NMR data were
the most useful in clarifying the behavior of these compounds
in solution.
The symmetry of 2 leads to two equivalent THME and
N(SiMe3)2 ligands and two types of Sn metal centers. For the
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J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002 6911

A R T I C L E S
Boyle et al.
The solid-state structure of 2 has two types of Sn atoms but
the solution-state 119Sn NMR spectrum revealed three peaks,
one of which was consistent with compound 1 (δ -330 ppm).
It has been reported that as the coordination number increases,
the chemical shift is found further upfield.65 Therefore, we
assigned the upfield resonance (δ 451 ppm) to the 4-coordianted
and the downfield resonance (δ +10) to the 3-coordinated Sn
metal centers of 2. Since the solid-state NMR data indicated
that there was no 1 impurity present, this spectrum either must
represent a decomposition of 2 in solution or an equilibrium
must exist between 2 and its constituent parts (1 and Sn-
(N(SiMe3)2)2).
To verify this phenomenon, a sample of 2 was diluted,
whereupon the ratio of the integration of the 1 to 2 resonances
was increased. Variable-temperature NMR experiments revealed
that at higher temperatures (>40 °C), the resonances associated
with 2 increased in intensity. Combined these results suggest
that for 2 the equilibrium discussed above exists (eq 3) in
from 22319,66 to 420-44031,65,67 to 610 Hz,65 was not observed
for any of these compounds. This phenomenon was also
previously reported for the similar Sn6O4(OSiMe3)4 compound68
and attributed to rapid ligand exchange. The equilibrium (eq 4)
described previously would account for the ligand scrambling
2
and thus prevent the observation of the 117-119Sn J-coupling.
For 12, two 119Sn resonances should be observed, but a
significant shift should also be expected due to the presence of
the Ti metal center and the sensitivity of the 119Sn resonances
to their environment. For 12 the chemical shift was shifted about
100 ppm further upfield in comparison to the other compounds.
There is no indication of the δ -330 ppm peak and 117Sn- - -
119Sn coupling was observed. This indicates that the structure
of 12 is maintained upon dissolution. The presence of the Ti
metal center with the increased Ti-O bond strengths and the
octahedral geometry demanded by the Ti must reduce the ability
to equilibrate. This stability would seem to favor the formation
of other mixed-metal alkoxide complexes and these investiga-
tions are underway.
Applications
Due to the unique structures observed for these compounds
in comparison to existing species, unusual properties are
expected. For instance, based on the geometrical arrangement
of 1 the free electron pairs on each of the metal centers point
outward and are readily accessible. Since 1 was found to be
relatively air stable and the solid-state structure was retained in
solution, the utility of 1 as a base catalyst was investigated. A
simple aldol condensation of acetaldehyde catalyzed by 1
revealed that greater than stoichiometric production of the
expected condensation products occurs as determined by GC-
MS experiments. Additional work to quantify this process with
benzaldehyde to assist in quantification of the catalyzed product
is currently underway.47 The introduction of an alternative metal
center into the framework of 1, such as 12, leads to the
possibility of multiple catalytically active structurally rigid metal
centers and/or single source MOCVD precursors.
Alternative to its catalytic nature, the DSC data for 1 indicated
that this molecule may also be useful as a MOCVD precursor.
Initial investigations of 1 with a simple vacuum MOCVD setup69
revealed that high substrate temperatures are necessary for
deposit (650 °C on a Pt/Si substrate), forming discrete uniform
Sn° spheres (ranging from ∼1 to 10 µm) instead of a SnOx
film.47,70 The ease that 1 was modified, as evidenced by 2-11
(the properties of these compounds as MOCVD reagents) may
be fine-tuned by introduction of alternative pendant ligands or
altered to include other metals (i.e., 12) for single-source
reagents. Additional work in developing these MOCVD precur-
sors is underway.
solution. However, no signal for Sn(N(SiMe3)2)2 (δ +76663 in
C6D6) was observed. A series of 119Sn NMR spectra of Sn-
(N(SiMe3)2)2 in THF-d8 at different concentrations displayed a
broad and weak signal that varied from δ -337 to -370 ppm.
Therefore, the lack of a signal for Sn(N(SiMe3)2)2 in the
proposed equilibrium of 2 is most likely due to its weak signal
and the small amount that would be generated. It is also of note
that, over time, two additional peaks (δ -504 and +10 ppm)
increased while the remaining resonances decreased, further
demonstrating the unstable nature of 2 in solution.
Solution 119Sn NMR data were also obtained for 3-11 and
the expected 1:2:1 ratios of peak intensities were observed.
However, for each sample, an additional signal at δ -330 ppm
was observed, which is consistent with what was previously
assigned to compound 1. Compound 1 was not present in any
of the solid-state MAS NMR spectra. Therefore, an equilibrium
must exist as noted for 2 (eq 4), wherein 3-11 respectively are
dissociated into 1 and the Sn(OR)2. The absence of a 119Sn signal
for the Sn(OR)2 is not surprising since these compounds lack a
sharp 119Sn signal and would only be present in a relatively
small amount.
In an attempt to quantify the proposed equilibrium for 3-11,
the dilution of a select set of samples was followed by variable-
temperature solution 119Sn NMR. Dilution of a sample of 6 and
10 revealed a change in the ratio of the various peaks and
variable-temperature NMR studies showed a broadening of the
-330 ppm peak as the other peaks grew for both of these
samples. This observation, and the fact that 1 was not observed
in the solid state for any of these samples, indicates that an
equilibrium as shown in eqs 3 or 4 must exist between these
species in solution. The modification of 1 therefore is not as
surprising as originally appeared since these molecules are
fluctional in solution. The 117-119Sn 2J-coupling normally
associated with Sn-O-Sn linkages, and that typically range
Summary and Conclusion
[Sn(N(SiMe3)2)2]2 was modified with the tridentate alkoxide
THME-H3 to yield a new family of compounds consisting of
several unique shaped metal alkoxides (1, 3- 11), alkoxy amide
(66) Lockhart, T. P.; Puff, H.; Schuh, W.; Reuter, H.; Mitchell, T. N. J.
Organomet. Chem. 1989, 366, 61.
(67) Boegeat, D.; Jousseaume, B.; Toupance, T.; Campet, G.; Fournes, L. Inorg.
Chem. 2000, 39, 3924.
(68) Sita, L. R.; Xi, R.; Yap, G. P. A.; Liable-Sands, L. M.; Rheingold, A. L.
J. Am. Chem. Soc. 1997, 119, 756.
(69) Gallegos, J. J. I.; Ward, T. L.; Boyle, T. J.; Francisco, L. P.; Rodriguez,
M. A. AdV. Mater. CVD 2000, 6, 21.
(70) Boyle, T. J.; De’Angeli, S. M.; Ward, T. L. Unpublished Results.
(65) Teff, D. J.; Minear, C. D.; Baxter, D. V.; Caulton, K. G. Inorg. Chem.
1998, 37, 2547.
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6912 J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002

A Novel Family of Tridentate Alkoxy Tin(II) Clusters
A R T I C L E S
(2), and unique early main group mixed metal alkoxide species
(12). Compound 1 appears by solid and solution state multi-
nuclear (119Sn, 13C) NMR to maintain its solid-state structural
arrangement in solution. Under relatively mild conditions, 1 can
be easily manipulated to expand its central core, incorporating
additional Sn(OR)2 (3-11) or Sn(NR2)2 (2). In solution, for
2-11, there appears to be an equilibrium between the solid-
state structure and compound 1 and the parent alkoxides or
amide. The exploitation of the expandability of 1 in both solution
and the solid state was shown to exist for more than just Sn-
(OR)2 through the introduction of a [Ti(µ-ONep)(ONep)3]2
forming 12, which does not display dynamic behavior upon
dissolution.
catalyst and MOCVD processes. Further investigations into the
chemistry and utility of this novel family of THME-ligated Sn
precursors (1-12)49 are currently underway.
Acknowledgment. For support of this research, the authors
would like to thank the Office of Basic Energy Sciences of the
Department of Energy and the United States Department of
Energy under contract DE-AC04-94AL85000. Sandia is a
multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin Company, for the United States Department
of Energy. The authors would also like to thank Dr. B. Cherry
for his technical assistance in obtaining the 13C and 119Sn MAS
spectra.
The introduction of the THME ligand has led to a versatile
family of controlled structures that potentially have a wide range
of applications. The transformation that 1 can undergo is well
established in both the solid and solution state and is now being
exploited as a stable scaffold to build larger more complex
molecules. These tailor-made compounds will find utility in a
variety of applications but currently are being explored as base
Supporting Information Available: X-ray crystallographic
files (CIF) for the structures 1-12 and experimental details
(PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
JA0202309
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J. AM. CHEM. SOC. VOL. 124, NO. 24, 2002 6913