Reaction of Tin Porphyrins with Vicinal Diols

Article abstract of DOI:10.1021/ic035123+

Reactions of tin porphyrins with vicinal diols were investigated. Treatment of (TTP)Sn(C≡CPh)₂ or (TTP)Sn(NHtolyl)₂ with pinacol and 2,3-diphenylbutane-2,3-diol afforded diolato complexes (TTP)Sn[OC(Me)₂C(Me)₂O]

Full text of DOI:10.1021/ic035123+

Inorg. Chem. 2004, 43, 2379−2386
Reaction of Tin Porphyrins with Vicinal Diols
Guodong Du, Arkady Ellern, and L. Keith Woo*
Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011-3111
Received September 24, 2003
Reactions of tin porphyrins with vicinal diols were investigated. Treatment of (TTP)Sn(CtCPh)2 or (TTP)Sn(NHtolyl)2
with pinacol and 2,3-diphenylbutane-2,3-diol afforded diolato complexes (TTP)Sn[OC(Me)2C(Me)2O] (1) and (TTP)-
Sn[OC(Ph)(Me)C(Ph)(Me)O] (2), respectively. Both complexes underwent C−C cleavage reactions to give (TTP)-
II
Sn and ketones. Reaction of (TTP)Sn(CtCPh)2 with 1 equivalent of o-catechol generated (TTP)Sn(Ct
CPh)(OC H OH) (3), which subsequently transformed into (TTP)Sn(OC H O) (4). With excess catechol, disubstituted
6
4
6 4
(TTP)Sn(OC H OH)2 (5) was obtained. (TTP)Sn(CtCPh)(OCHRCHROH) (R ) H, 6; R ) Ph, 8) and (TTP)Sn-
6
4
(OCHRCHROH)2 (R ) H, 7; R ) Ph, 9) were obtained analogously by treatment of (TTP)Sn(CtCPh)2 with
appropriate diols. In the presence of dioxygen, tin porphyrin complexes were found to promote the oxidative cleavage
of vicinal diols and the oxidation of R-ketols to R-diketones. Possible reaction mechanisms involving diolato or
enediolato intermediates are discussed. The molecular structure of (TTP)Sn(CtCPh)(OC H OH) (3) was determined
6
4
by X-ray crystallography.
Introduction
ed bisalkynyl complex, trans-(TTP)Sn(CtCPh)2.5 Quite sur-
prisingly, the same reaction with (TTP)TiCl2 resulted in oxi-
dative coupling of the acetylides and formation of a Ti(II)
alkyne adduct, (TTP)Ti(1,2-η2-PhCtCCtCPh).6
In continuing our investigation of group 4 metalloporphyin
diolato complexes,7 efforts were extended to reactions of tin
porphyrins with various diols. Although chelated diolato
complexes are invariably obtained for titanium porphyrins,
tin porphyrin-diol complexes show more structural diversity
with trans bisalkoxo substituted species being regularly
obtained. Both titanium and tin complexes are able to
promote the oxidative cleavage of diols with molecular
dioxygen.
The structural and physical similarities between the highest
oxidation state chemistry of the early transition metals (group
n) and the corresponding main group elements (group n +
10) were originally observed during Mendeleev’s time. This
analogy still retains utility. Thus, vanadyl (VdO) complexes,
which have shown promise as insulin mimics, are proposed
to function as PdO analogues.1 Considerable analogies are
also observed between the chemistry of organoscandium and
organoaluminum complexes.2
We have been interested in the chemistry of group 4
metalloporphyrins3 as well as tin (group 14) porphyrins.4
Although some chemical similarities exist, significant dif-
ferences are often observed. For example, treatment of
(TTP)SnCl2 with lithium phenylacetylide generated a σ-bond-
Experimental Section
General Procedures. All manipulations were performed under
a nitrogen atmosphere using a Vacuum Atmospheres glovebox
equipped with a model MO40-1 Dri-Train gas purifier, unless noted
otherwise. Toluene and hexane were dried by passage through
columns of activated alumina and supported copper redox catalyst
(Q-5) as described in the literature.8 Benzene-d6 and THF were
freshly distilled from purple solutions of sodium benzophenone,
degassed with several freeze-pump-thaw cycles, and brought into
* Author to whom correspondence should be addressed. E-mail: kwoo@
iastate.edu.
(1) (a) Elberg, G.; Li, J.; Shechter, Y. In Vanadium in the EnVironment
Part 2: Health Effects; Nriagu, J. O., Ed.; Wiley: New York, 1998;
Chaper 14. (b) Tsiani, E.; Bogdanovic, E.; Sorisky, A.; Nagy, L.;
Fantus, I. G. Diabetes 1998, 47, 1676.
(2) Piers, W. E.; Shapiro, P. J.; Bunel, E. E.; Bercaw, J. E. Synlett 1990,
74.
(3) (a) Thorman, J. L.; Young, V. G., Jr.; Boyd, P. D. W.; Guzei, I. A.;
Woo, L. K. Inorg. Chem. 2001, 40, 499. (b) Thorman, J. L.; Guzei, I.
A.; Young, V. G., Jr.; Woo, L. K. Inorg. Chem. 2000, 39, 2344. (c)
Thorman, J. L.; Guzei, I. A.; Young, V. G., Jr.; Woo, L. K. Inorg.
Chem. 1999, 38, 3814.
(5) Chen, J.; Woo, L. K. Inorg. Chem. 1998, 37, 3269.
(6) Chen, J.; Guzei, I. A.; Woo, L. K. Inorg. Chem. 2000, 39, 3715.
(7) Du, G.; Woo, L. K. Organometallics 2003, 22, 450.
(8) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(4) (a) Berreau, L. M.; Woo, L. K. J. Am. Chem. Soc. 1995, 117, 1314.
(b) Wang, X.; Gray, S. D.; Chen, J.; Woo, L. K. Inorg. Chem. 1998,
37, 5.
10.1021/ic035123+ CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/04/2004
Inorganic Chemistry, Vol. 43, No. 7, 2004 2379

Du et al.
the drybox without exposure to air. CH2Cl2 was dried with P2O5,
degassed with several freeze-pump-thaw cycles, and brought into
the drybox after trap-to-trap vacuum distillation. (TTP)SnCl2,9
(TTP)Sn(CtCPh)2,5 (TTP)Sn(OH)2,10 and (TTP)Sn4b were prepared
according to literature procedures. A d,l mixture of 2,3-diphenylbu-
tane-2,3-diol was obtained using a previously reported procedure.11
1H and 13C NMR data were acquired on Varian VXR (300 MHz,
20 °C) or Bruker DRX (400 MHz, 25 °C) spectrometers. Chemical
shifts are referenced to proton solvent impurities (C6D5H, δ 7.15;
CHCl3, δ 7.24). UV-vis data were recorded on a HP8453 diode
array spectrophotometer and reported as λmax in nm (log ꢀ). Fourier
transform infrared spectra were recorded on a FT-DL spectrometer.
Elemental analyses (C, H, N) were performed by Iowa State
University Instrument Services.
Synthesis of (TTP)Sn(CtCPh)(OC6H4OH) (3). A solution of
(TTP)Sn(CtCPh)2 (31 mg, 0.031 mmol) and catechol (3.5 mg,
0.032 mmol) in toluene (ca. 8 mL) was stirred for 24 h at ambient
temperature and reduced to dryness in vacuo. The residue was taken
up in toluene (1 mL), layered with hexane (3 mL), and placed in
a freezer at -25 °C for 23 h. The dark green microcrystalline
product 3 was collected by filtration and dried under vacuum. This
compound could be stored with air over weeks. Yields: 24 mg
(77%). 1H NMR (C6D6, 400 MHz): δ 9.18 (s, 8H, â-H), 8.02 (m,
8H, meso-C6H4CH3), 7.25 (d, 8H, J ) 8.4 Hz, meso-C6H4CH3),
6.13 (t, 1H, J ) 7.6 Hz, p-C6H5), 5.97 (t, 2H, J ) 7.6 Hz, m-C6H5),
5.78 (t, 1H, J ) 7.2 Hz, OC6H4OH), 5.71 (d, 1H, J ) 6.0 Hz,
OC6H4OH), 5.44 (m, 3H, o-C6H5 and OC6H4OH), 2.38 (s, 12H,
meso-C6H4CH3), 1.67 (d, 1H, J ) 7.2 Hz, OC6H4OH), 0.57 (s, 1H,
OC6H4OH). IR (KBr): 3440 (OH), 2129 (CtC) cm-1. UV-vis
(toluene): 412 (sh, 4.71), 433 (5.67), 531 (3.68), 571 (4.25), 613
(4.25). MS (EI): m/z 897 (M+ - CtCPh), 787 ((TTP)Sn+). The
molecular structure of this complex was solved by X-ray crystal-
lography (vide infra).
Synthesis of (TTP)Sn(NHtolyl)2. To a stirred solution of (TTP)-
SnCl2 (183 mg, 0.213 mmol) in 16 mL of toluene at -25 °C was
added LiNHtolyl (85 mg, 0.75 mmol). The solution was warmed
to ambient temperature and stirred for 18 h. After filtering the
mixture through a coarse frit, the filtrate was dried in vacuo,
triturated with hexane, and filtered. Removal of solvent from the
filtrate under reduced pressure afforded a dark green product.
Yield: 101 mg, 47%. 1H NMR (CDCl3, 400 MHz): δ 8.97 (s, 8H,
â-H), 8.03 (d, 8H, J ) 7.8 Hz, meso-C6H4CH3), 7.58 (d, 8H, J )
7.8 Hz, meso-C6H4CH3), 5.40 (d, 4H, J ) 7.8 Hz, m-NHC6H4-
CH3) 2.72 (s, 12H, meso-C6H4CH3), 1.81 (d, 4H, J ) 7.8 Hz,
o-NHC6H4CH3), 1.69 (s, 6H, NHC6H4CH3), -5.08 (s, 2H, NHC6H4-
CH3). The 1H NMR spectrum (C6D6) of (TTP)Sn(NHtolyl)2
prepared by an amine exchange reaction5 has been reported.
Synthesis of (TTP)Sn[OC(Me)2C(Me)2O] (1). To a solution
of (TTP)Sn(NHtolyl)2 (32 mg, 0.032 mmol) in toluene (3 mL) was
added a solution of pinacol (8 mg, 0.06 mmol) in toluene (3 mL).
The mixture was stirred at ambient temperature for 1.5 h as the
color changed from green to dark red. After the removal of solvent
under reduced pressure, the residue was taken up in toluene (1 mL),
layered with hexane (3 mL), and placed in a freezer at -25 °C for
6 d. The resulting dark red product was collected by filtration.
Generation of (TTP)Sn(OC6H4O) (4) from 3. An NMR tube
equipped with a Teflon stopcock was charged with (TTP)Sn(Ct
CPh)(OC6H4OH) (3) (1.4 mg, 1.4 µmol) and C6D6. After 12 d of
heating in a sand bath (∼120 °C), (TTP)Sn(CtCPh)(OC6H4OH)
(3) was consumed, and a new species (TTP)Sn(OC6H4O) (4) was
1
observed by H NMR spectroscopy. This species could be stored
in air over months without noticeable change. 1H NMR data for 4:
δ 9.15 (s, 8H, â-H), 8.02 (m, 4H, meso-C6H4CH3), 7.87 (m, 4H,
meso-C6H4CH3), 7.25 (d, 8H, J ) 8.4 Hz, meso-C6H4CH3), 5.65
(m, 2H, OC6H4O), 5.38 (m, 2H, OC6H4O), 2.38 (s, 12H, meso-
C6H4CH3). UV-vis (CH2Cl2): 427 (Soret), 561, 602 nm. Free
PhCtCH (1 equiv) was also observed.
Synthesis of (TTP)Sn(o-OC6H4OH)2 (5). A solution of (TTP)-
Sn(NHtolyl)2 (22 mg, 0.022 mmol) and catechol (7.6 mg, 0.069
mmol) in toluene (ca. 6 mL) was stirred for 6 h at ambient
temperature. The mixture was filtered, and the filtrate was reduced
to 3 mL in vacuo. Then it was layered with hexane (2 mL) and
placed in a freezer at -25 °C for 14 h. The brown-red product was
collected by filtration and dried under vacuum. Yield: 18 mg (80%).
1H NMR (CDCl3, 400 MHz): δ 9.14 (s, 8H, â-H), 8.07 (d, 8H, J
) 8.0 Hz, meso-C6H4CH3), 7.59 (d, 8H, J ) 7.6 Hz, meso-C6H4-
CH3), 5.63 (td, 2H, OC6H4OH), 5.31 (dd, 2H, OC6H4OH), 5.16
(td, 2H, OC6H4OH), 2.72 (s, 12H, meso-C6H4CH3), 1.37 (dd, 2H,
OC6H4OH), 0.01 (s, 2H, OC6H4OH). IR (KBr): 3455 (OH). UV-
vis (toluene): 426 (5.26), 523 (3.52), 563 (3.95), 603 (3.79).
Synthesis of (TTP)Sn(CtCPh)(OCH2CH2OH) (6). A mixture
of (TTP)Sn(CtCPh)2 (37 mg, 0.037 mmol) and ethylene glycol
(25 mg, 0.40 mmol) in toluene (ca. 8 mL) was stirred at ambient
temperature for 14 h and reduced to dryness in vacuo. The residue
was taken up in THF (1 mL), layered with hexane (3 mL), and
placed in a freezer at -25 °C for 8 h. The purple product was
collected in two crops by filtration and dried under vacuum.
Yield: 27 mg (75%). Samples for combustion analysis were
obtained by layering a CH2Cl2 (1 mL) solution with hexane (2 mL),
allowing the mixture to stand at -25 °C, filtering, and drying the
1
Yield: 15 mg (53%). H NMR (C6D6, 400 MHz): δ 9.19 (s, 8H,
â-H), 8.31 (br, 4H, meso-C6H4CH3), 7.97 (br, 4H, meso-C6H4CH3),
7.29 (m, 8H, meso-C6H4CH3), 2.38 (s, 12H, meso-C6H4CH3), -1.07
(s, 12H, OCMe2). UV-vis (toluene): 406 (4.73), 429 (5.44), 488
(3.86), 565 (3.96), 603 (3.68). MS (EI): m/z 904 (M+), 787 ((TTP)-
Sn+). Anal. Found: C, 72.32; H, 5.90; N, 5.85. Calcd for
C54H48N4O2Sn: C, 71.77; H, 5.35; N, 6.20.
Synthesis of (TTP)Sn[OC(Me)(Ph)C(Me)(Ph)O] (2). To a
solution of (TTP)Sn(NHtolyl)2 (32 mg, 0.032 mmol) in CH2Cl2 (5
mL) was added a solution of 2,3-diphenylbutane-2,3-diol (16 mg,
0.066 mmol) in CH2Cl2 (5 mL). The mixture was stirred at ambient
temperature for 40 min during which the color changed from green
to dark red. After the solvent was removed under reduced pressure,
the residue was taken up in toluene and filtered. The filtrate was
dried under vacuum, redissolved in CH2Cl2 (1 mL), layered with
hexane (3 mL), and placed in a freezer at -25 °C for 3 d. Filtration
provided the desired product (TTP)Sn[OC(Me)(Ph)C(Me)(Ph)O].
1
Yield: 16 mg (48%). H NMR (C6D6, 400 MHz): δ 9.24 (s, 8H,
â-H), 8.25 (br, 4H, meso-C6H4CH3), 8.05 (br, 4H, meso- C6H4-
CH3), 7.26 (d, 8H, J ) 7.6 Hz, meso- C6H4CH3), 6.68 (m, 6H,
p,m-C6H5), 5.88 (m, 4H, o-C6H5), 2.40 (s, 12H, meso-C6H4CH3),
-1.69 (s, 6H, OCCH3). UV-vis (toluene): 410 (sh), 430 (Soret),
490, 564, 604 nm. The presence of (TTP)Sn (∼8%) was observed
1
solid in vacuo. H NMR (C6D6, 400 MHz): δ 9.18 (s, 8H, â-H),
8.03 (m, 8H, meso-C6H4CH3), 7.24 (d, 8H, meso-C6H4CH3), 6.14
(t, 1H, p-C6H5), 5.99 (t, 2H, m-C6H5), 5.41 (d, 2H, o-C6H5), 2.38
(s, 12H, meso-C6H4CH3), 0.61 (m, 2H, OCH2CH2OH), -1.65 (m,
1H, OCH2CH2OH), -1.95 (m, 2H, OCH2CH2OH). IR (KBr): 3432
(OH), 2123 (CtC). UV-vis (toluene): 414 (4.59), 434 (5.56), 532
(3.47), 572 (4.08), 613 (4.12). MS (EI): m/z 888 (M+ - OCH2-
CH2OH), 787 ((TTP)Sn+). Anal. Found: C, 70.87; H, 5.53; N, 5.37.
Calcd. for C58H46N4O2Sn‚CH2Cl2: C, 70.92; H, 4.84; N, 5.61.
1
by its H NMR â-H signal at 9.19 ppm.
(9) O’Rourke, M.; Curran, C. J. Am. Chem. Soc. 1970, 92, 1501.
(10) Arnold, D. P. J. Chem. Educ. 1988, 65, 1111.
(11) Khurana, J. M.; Sehgal, A. J. Chem. Soc., Chem. Commun. 1994, 571.
2380 Inorganic Chemistry, Vol. 43, No. 7, 2004

Reaction of Tin Porphyrins with Vicinal Diols
Table 1. Crystal Data and Structure Refinement for Complex 3
Synthesis of (TTP)Sn(OCH2CH2OH)2 (7). A mixture of (TTP)-
Sn(CtCPh)2 (28 mg, 0.028 mmol) and ethylene glycol (110 mg,
1.77 mmol) in toluene (ca. 6 mL) was heated at ∼80 °C for 18 h.
The resulting mixture was filtered and reduced to dryness in vacuo.
The residue was triturated with hexane (2 mL), then filtered. The
solid was dried under vacuum. Yield: 10 mg (40%). Samples for
combustion analysis were obtained by layering a CH2Cl2 (1 mL)
solution with hexane (2 mL), allowing the mixture to stand at -25
empirical formula
fw
C62H46N4O2Sn
997.72
temperature
173(2) K
wavelength
0.71073 Å
cryst syst
space group
monoclinic
P21/c
a
b
c
10.594(3) Å
32.673(9) Å
15.814(4) Å
90°
1
°C, filtering, and drying the solid in vacuo. H NMR (C6D6, 400
R
MHz): δ 9.16 (s, 8H, â-H), 8.03 (d, 8H, J ) 8.0 Hz, meso-C6H4-
CH3), 7.25 (d, 8H, J ) 8.0 Hz, meso-C6H4CH3), 2.38 (s, 12H, meso-
C6H4CH3), 0.61 (m, 4H, OCH2CH2OH), -1.54 (m, 2H, OCH2-
CH2OH), -1.95 (m, 4H, OCH2CH2OH). UV-vis (toluene): 409
(4.69), 429 (5.65), 523 (3.67), 563 (4.25), 603 (4.18), 624 (3.88).
Anal. Found: C, 67.21; H, 5.62; N, 5.78. Calcd. for C52H46N4O4-
Sn‚0.25CH2Cl2: C, 67.42; H, 5.03; N, 6.02.
â
98.477(5)°
γ
90°
volume
5414(2) Å3
4
Z
density (calculated)
absorption coefficient
data/restraints/parameters
goodness-of-fit on F2
final R indicesa [I > 2σ(I)]
R indices (all data)
largest diff. peak and hole
1.224 mg/m3
0.517 mm-1
6589/0/622
1.090
R1 ) 0.0864, wR2 ) 0.2083
R1 ) 0.1255, wR2 ) 0.2308
1.348 and -1.359 e‚Å-3
Reaction of (TTP)Sn(CtCPh)2 with meso-Hydrobenzoin. An
NMR tube equipped with a Teflon stopcock was charged with
(TTP)Sn(CtCPh)2 (0.8 mg, 0.8 µmol), meso-hydrobenzoin (0.7
mg, 3.3 µmol), Ph3CH (1.2 mg, 4.9 µmol), and ∼0.5 mL of C6D6.
After 6 h at ambient temperature, 1H NMR spectroscopy revealed
the formation of a major product, (TTP)Sn(CtCPh)[OCH(Ph)CH-
(Ph)OH] (8). 1H NMR (C6D6, 400 MHz): 9.15 (s, 8H, â-H), 8.06
(t, 8H, J ) 9.2 Hz, meso-C6H4CH3), 7.27 (t, 8H, J ) 9.2 Hz, meso-
C6H4CH3), 6.46 (t, 1H, J ) 7.6 Hz, p-C6H5), 6.42 (t, 1H, J ) 7.2
Hz, p-C6H5), 6.33 (t, 2H, J ) 7.6 Hz, m-C6H5), 6.12 (m, 3H, m-C6H5
and p-CCC6H5), 5.97 (t, 2H, J ) 8.0 Hz, m-CCC6H5), 5.42 (d, 2H,
J ) 8.0 Hz, o-CCC6H5), 4.97 (d, 2H, J ) 7.6 Hz, o-C6H5), 3.69
(d, 2H, J ) 7.2 Hz, o-C6H5), 2.39 (s, 12H, meso-C6H4CH3), 1.60
(m, CHPhOH), -1.11 (d, 1H, J ) 6.8 Hz, CHPhOH), -1.88 (d,
1H, J ) 3.2 Hz, OCHPh). UV-vis (toluene): 412 (sh), 435 (Soret),
531, 571, 612 nm. Heating over a sand bath (∼120 °C) for 3 h
resulted in the production of (TTP)Sn[OCH(Ph)CH(Ph)OH]2 (9)
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo| and wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2
]}1/2
.
(2.4 mg, 9.8 µmol), and ∼0.5 mL of C6D6. The tube was sealed
after exposure to air. Heating the tube in a sand bath (∼120 °C)
for 22 h resulted in the consumption of benzoin and the production
of benzil (87% yield) and a small amount of benzaldehyde (8.7%
1
yield), as determined by H NMR spectroscopy.
Adipoin Oxidation Mediated by (TTP)Sn(CtCPh)2. An NMR
tube equipped with a Teflon stopcock was charged with (TTP)Sn-
(CtCPh)2 (1.8 mg, 1.8 µmol), adipoin (4.0 mg, 35 µmol), Ph3CH
(2.4 mg, 9.8 µmol), and ∼0.5 mL of C6D6. The tube was sealed
after exposure to air. Heating the tube in a sand bath (∼120 °C)
for 35 h resulted in 69% conversion of adipoin and the production
of 1,2-cyclohexanedione (31% yield) in its enol form, as determined
1
as the major product. H NMR (C6D6, 400 MHz): 9.09 (s, 8H,
1
1
by H NMR spectroscopy. H NMR of 1,2-cyclohexanedione in
its enol form (C6D6, 400 MHz): δ 6.17 (s, 1H, OH), 5.73 (t, 1H,
J ) 4.6 Hz, vinyl-H), 1.95 (t, 2H, COCH2), 1.60 (q, 2H, CHCH2),
1.22 (quintet, 2H, COCH2CH2). 1H NMR in CDCl3 (400 MHz): δ
6.13 (t, 1H, J ) 4.6 Hz, vinyl-H), 5.95 (s, 1H, OH), 2.52 (t, 2H,
COCH2), 2.38 (q, 2H, CHCH2), 1.99 (quintet, 2H, COCH2CH2).12
EI-MS: m/z 112 (M+, base peak), 97, 83, 70, 55.
â-H), 8.09 (d, 8H, J ) 8.0 Hz, meso-C6H4CH3), 7.30 (d, 8H, J )
7.6 Hz, meso-C6H4CH3), 6.45 (m, 8H, m,p-C6H5), 6.17 (t, 4H, J )
7.2 Hz, m-C6H5), 5.22 (d, 4H, J ) 7.6 Hz, o-C6H5), 3.95 (d, 4H, J
) 7.2 Hz, o-C6H5), 2.42 (s, 12H, meso-C6H4CH3), 1.64 (m, 2H,
CHPhOH), -0.73 (d, 2H, CHPhOH), -1.62 (d, 2H, OCHPh). UV-
vis (toluene): 409 (sh), 430 (Soret), 562, 602, 626 nm. Further
heating decomposed the bisalkoxo complex 9, with (TTP)Sn
observed as one of the products.
X-ray Crystallography. A dark purple crystal with approximate
dimensions 0.3 × 0.3 × 0.3 mm3 was mounted on a glass fiber.
The crystal evaluation and data collections at 173 K were performed
on a BRUKER SMART 1000 CCD-based diffractometer with Mo
KR radiation (0.71073 Å), using the full-sphere routine. The datasets
were corrected for Lorentz and polarization effects. The absorption
correction was based on fitting a function to the empirical
transmission surface as sampled by multiply equivalent measure-
ments13 using SADABS software.14 Details of the X-ray structure
determination are summarized in Table 1.
The systematic absences in the diffraction data were consistent
for the monoclinic space group P21/c. The position of Sn atom
was found by the Patterson method. The remaining non-hydrogen
atoms were located in an alternating series of least-squares cycles
and difference Fourier maps, and their positions were refined in a
full-matrix anisotropic approximation. All hydrogen atoms were
placed at calculated positions and refined using a riding model.
Diol Oxidation Mediated by Tin Porphyrin Complexes. In a
typical experiment, diol (35 µmol), tin(IV) porphyrin (4-6 mol
%), Ph3CH (2.5 mg, 10 µmol, internal standard), and C6D6 (∼0.5
mL) were placed in a NMR tube equipped with a Teflon stopcock.
The tube was sealed and heated in a sand bath (∼120 °C). The
1
reaction was monitored via H NMR spectroscopy. The yields of
products were determined by appropriate NMR signal integration
relative to the internal standard.
Reaction of (TTP)Sn with Ethylene Glycol. An NMR tube
equipped with a Teflon stopcock was charged with (TTP)Sn (0.9
mg, 1 µmol), ethylene glycol (3.2 mg, 52 µmol), Ph3CH (1.7 mg,
7.0 µmol), and ∼0.6 mL of C6D6. Heating the mixture in a sand
1
bath (∼120 °C) over 30 h resulted in no change in the H NMR
signals for the porphyrin. The NMR tube was then flushed with
air and capped. Another 3 h of heating resulted in the color of the
1
solution changing from dark green to purple-red. The H NMR
spectrum revealed the total consumption of (TTP)Sn and the
quantitative generation of (TTP)Sn(OCH2CH2OH)2 (7).
Benzoin Oxidation Mediated by (TTP)Sn(CtCPh)2. An NMR
tube equipped with a Teflon stopcock was charged with (TTP)Sn-
(CtCPh)2 (1.2 mg, 1.2 µmol), benzoin (5.0 mg, 22 µmol), Ph3CH
(12) Amon, C. M.; Banwell, M. G.; Gravatt, G. L. J. Org. Chem. 1987,
52, 4851.
(13) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
(14) All software and sources of the scattering factors are contained in the
SHELXTL (version 5.1) program library. Sheldrick, G., Brucker
Analytical X-ray Systems, Madison, WI.
Inorganic Chemistry, Vol. 43, No. 7, 2004 2381

Du et al.
Results
Synthesis of Tin Porphyrin Diolato Complexes. Tin
(TTP)Sn[OC(Me)(Ph)C(Me)(Ph)O] (2) decomposed par-
tially (∼40%) to (TTP)SnII and 2 equiv acetophenone at
ambient temperature over 14 h. Appreciable decomposition
was noticed even in the solid state. Isolation of analytically
pure 2 was thus precluded. On heating in C6D6, the
decomposition of 2 was much faster, as indicated by the rapid
color change from a deep red of 2 to the green color of
(TTP)SnII over 30 min (eq 2). The decomposition of (TTP)-
porphyrins have high affinity for oxygen donor ligands.15
This is reflected in the reactions of MeOH with (TTP)Sn-
(CtCPh)2 that sequentially afforded (TTP)Sn(CtCPh)-
(OMe) and then (TTP)Sn(OMe)2.5 Replacement of MeOH
with vicinal diols in these reactions was expected to generate
chelated diolato complexes, analogous to titanium porphyrin
chemistry.7 Surprisingly, the reactions of vicinal diols with
tin porphyrins are somewhat diol-dependent. Thus, treatment
of (TTP)Sn(CtCPh)2 with dl-2,3-diphenylbutane-2,3-diol led
to the formation of the diolato complex (TTP)Sn[OC(Me)-
(Ph)C(Me)(Ph)O] (2) in ∼50% yield. The bis substituted
complex, (TTP)Sn[OC(Ph)(Me)C(Ph)(Me)OH]2 was ob-
served in only ∼40% yield even when a large excess of diol
was used in the reaction. With the more labile bisamido tin
porphyrin complex, (TTP)Sn(NHtolyl)2, clean formation of
(TTP)Sn[OC(Me)(Ph)C(Me)(Ph)O] (2) was observed, but
required more than 1 equiv of diol to complete this
conversion. The same was true with pinacol (eq 1). The
reaction of pinacol with (TTP)Sn(NHtolyl)2 yielded the
Sn[OC(Me)2C(Me)2O] (1) proceeded similarly, yielding
(TTP)SnII and 2 equiv of acetone, although the process was
much slower. Upon exposure with air, diolato complex 1
reacted with moisture to release free pinacol. The porphyrin
1
product was identified as (TTP)Sn(OH)2 by its H NMR
spectrum,10 although the signal for the OH group was not
observed.
Reaction of Tin Porphyrins with o-Catechol. (TTP)Sn-
(CtCPh)2 and (TTP)Sn(NHtolyl)2 react readily with excess
o-catechol, resulting in the formation of a bis catecholato
complex, (TTP)Sn(OC6H4OH)2 (5), with two pendant -OH
groups. This complex is sparingly soluble in nonpolar
solvents such as C6D6, but readily soluble in polar CDCl3.
The axial catecholato ligands adopt a trans geometry, as
indicated by the appearance of the o-protons of the meso-
tolyl groups as an 8H doublet in its 1H NMR spectrum. This
is in contrast to the reaction of o-phenylenediamine with
(TTP)Sn(NHPh)2, where a chelating diamido complex,
(TTP)Sn(o-C6H4(NH)2), formed readily.5 The trans substi-
tuted complex with pendant amines was not observed.
The reaction of (TTP)Sn(CtCPh)2 with o-catechol pro-
ceeded presumably in a stepwise manner. Indeed, treatment
of (TTP)Sn(CtCPh)2 with 1 equivalent of catechol afforded
an unsymmetrically substituted complex (TTP)Sn(CtCPh)-
(OC6H4OH) (3). In the 1H NMR spectrum of 3, the o-protons
of the meso-tolyl groups appear as a multiplet and not as a
doublet observed for symmetrical trans metalloporphyrin
complexes. The IR spectrum for 3 showed the presence of
both CtC (2129 cm-1) and OH (3440 cm-1) functional
groups, thus verifying its formulation. On heating in C6D6
(∼120 °C), this complex slowly transformed to a new
diolato complex (TTP)Sn[OC(Me)2C(Me)2O] (1) in good
yield. In the reaction of (TTP)Sn(CtCPh)2 with excess
pinacol (∼10 equiv), complex 1 was afforded as a major
product, as well as mono- and bis-substituted complexes,
(TTP)Sn(CtCPh)[OC(Me)2C(Me)2OH] (1a) and (TTP)Sn-
[OC(Me)2C(Me)2OH]2 (1b), as monitored by 1H NMR
spectroscopy. However, attempts to isolate either 1a or 1b
under a variety of conditions proved unsuccessful. Treatment
of (TTP)Sn(CtCPh)2 with benzopinacole at ambient tem-
perature in C6D6 resulted in the consumption of diol and the
generation of benzophenone, but no diolato species was
observed during the reaction. Treatment of the disodium salt
of pinacol with (TTP)SnCl2 or (TTP)Sn(OTf)2 resulted in
the formation of a complex mixture in which diolato complex
1 was a minor component. Other products could not be
identified.
The tin porphyrin diolato complexes (TTP)Sn[OC(Me)2C-
(Me)2O] (1) and (TTP)Sn[OC(Me)(Ph)C(Me)(Ph)O] (2)
1
species, as monitored by H NMR spectroscopy. The â-H
signal for (TTP)Sn(CtCPh)(OC6H4OH) (3) at 9.18 ppm
diminished while a new signal at 9.15 ppm increased over a
period of 12 days. This new species was assigned as the
chelated diolato complex, (TTP)Sn(OC6H4O) (4) (Scheme
1). The presence of two broad 4H multiplets for the o-protons
of the meso-tolyl groups was similar to that observed for
the Ti(TTP) analogue and other diolato complexes7,16 and
indicated an enforced cis-ligation by the chelating catecholato
ligand. IR spectroscopy revealed the loss of the CtC and
1
share similar H NMR characteristics. The presence of two
broad resonances for the o-protons of the meso tolyl groups
on the porphyrin ring is consistent with the enforced cis
geometry of the chelating diolato ligands. The upfield shifted
signals of the diolato ligands, due to the large porphyrin
current effect, are also comparable to their titanium ana-
logues.7
(15) (a) Kim, H.-J.; Bampos, N.; Sanders, J. K. M. J. Am. Chem. Soc.
1999, 121, 8120. (b) Maiya, B. G.; Bampos, N.; Kumar, A. A.; Feeder,
N.; Sanders, J. K. M. New. J. Chem. 2001, 25, 797. (c) Webb, S. J.;
Sanders, J. K. M. Inorg. Chem. 2000, 39, 5920.
(16) Dawson, D. Y.; Sangalang, J. C.; Arnold, J. J. Am. Chem. Soc. 1996,
118, 6082.
2382 Inorganic Chemistry, Vol. 43, No. 7, 2004

Reaction of Tin Porphyrins with Vicinal Diols
Scheme 1
Figure 1. ORTEP representation of the structure of (TTP)Sn(CtCPh)-
(OC6H4OH) (3).
Scheme 2
OH functional groups. Unlike (TTP)Sn[OC(Me)2C(Me)2O]
(1) and (TTP)Sn[OC(Ph)(Me)C(Ph)(Me)O] (2), this species
was very inert to heating at 120 °C. Alternative routes to 4
were attempted. Reaction of (TTP)SnCl2 with the dilithium
salt of catechol did not afford the expected diolato complex.
Treatment of (TTP)Sn(NHtolyl)2 with 1 equiv of catechol
in toluene resulted in no reaction; whereas with more than 2
equiv of catechol, the disubstituted product (TTP)Sn(OC6H4-
OH)2 (5) was obtained.
Reaction of (TTP)Sn(CtCPh)2 with Other Diols. As
observed in the reaction of catechol, (TTP)Sn(CtCPh)2
generally reacts with other diols in a stepwise manner. In
the first step, the substitution of one acetylide ligand by an
alkoxide generated the unsymmetrically substituted tin por-
phyrin complexes. A number of such complexes, (TTP)Sn-
(CtCPh)(OCHRCHROH) (R ) H, 6; R ) Ph, 8), can be
observed in NMR tube reactions and/or isolated (Scheme
2). This step is facile and is usually complete within hours.
The second substitution, however, is more difficult, and often
requires a longer reaction time and/or heating. Nevertheless,
bis alkoxo complexes (TTP)Sn(OCHRCHROH)2 (R ) H,
7; R ) Ph, 9) can be obtained cleanly.
When pure (TTP)Sn(CtCPh)(OCH2CH2OH) (6) was
heated in C6D6 in a sealed NMR tube, the generation of a
diolato complex was observed, as indicated by the appearance
of two broad signals at aromatic region around 8 ppm.
However, this reaction was not clean and (TTP)Sn (â-H:
9.19 ppm) was observed as well as other unidentifiable
species.
Structure of (TTP)Sn(CtCPh)(OC6H4OH) (3). The
molecular structure of (TTP)Sn(CtCPh)(OC6H4OH) (3) is
one of the few examples of tin porphyrins with a Sn-C bond
(Figure 1) structurally characterized by X-ray diffraction.
Selected bond lengths and bond angles are listed in Table 2.
The central Sn atom possesses a pseudooctahedral coordina-
tion geometry with phenylacetylide and catecholato ligands
at mutually trans positions. The porphyrin ring adopts a
planar conformation. The RMS deviation for the N4 plane
is 0.015 and the Sn atom is displaced 0.116(4) Å toward the
acetylide group. The Sn-C bond distance is 2.139(12) Å
and is noticeably shorter than the Sn-C distances observed
in other tin porphyrin complexes (2.167(2) Å in (TTP)Sn-
The 1H NMR spectra of (TTP)Sn(CtCPh)(OCH2CH2OH)
(6) and (TTP)Sn(CtCPh)[OCH(Ph)CH(Ph)OH] (8) are
typical for unsymmetrically substituted trans metalloporphy-
rins. The o-protons of the tolyl groups resonate as multiplets
due to the loss of mirror symmetry along the porphyrin plane.
With symmetric disubstitution, the mirror symmetry is
regained and these signals appear as regular 8H doublets in
bis alkoxo complexes 7 and 9. Compared to monoalkoxo
1
complexes 6 and 8, the H NMR signals of alkoxo ligands
in complexes 7 and 9 are shifted downfield. In addition, it
is observed that in (TTP)Sn(CtCPh)(OCH2CH2OH) (6), the
alkoxo ligand is more labile than -CtCPh toward water,
as HOCH2CH2OH was detected within days upon exposure
with air, while the acetylide ligand remained bound.
Inorganic Chemistry, Vol. 43, No. 7, 2004 2383

Du et al.
Table 2. Selected Bond Lengths [Å] and Bond Angles [°] for
Complex 3
Table 3. Vicinal Diol Cleavage Mediated by Tin Porphyrinsa
Sn(1)-N(1)
Sn(1)-N(3)
Sn(1)-O(1)
C(55)-C(56)
O(1)-C(49)
2.090(9)
2.101(9)
2.083(7)
1.194(15) C(56)-C(57)
1.311(12) O(2)-C(54)
Sn(1)-N(2)
Sn(1)-N(4)
Sn(1)-C(55)
2.100(8)
2.102(9)
2.139(12)
1.434(16)
1.381(15)
time
(h)
conv
(%)
yield
(%)
entry
1
R1
Ph
R2
catalyst
O(1)-Sn(1)-N(1)
O(1)-Sn(1)-N(2)
O(1)-Sn(1)-N(3)
O(1)-Sn(1)-N(4)
N(1)-Sn(1)-N(3)
O(1)-Sn(1)-C(55)
86.7(3)
83.6(3)
86.1(3)
90.9(3)
172.8(3)
175.2(4)
C(55)-Sn(1)-N(1)
89.8(4)
93.1(3)
97.4(4)
92.4(4)
174.5(3)
127.3(6)
Me
(TTP)Sn(CCPh)2
44
85
15
190
36
188
42
46
60
100
28
50
52
42
55
97
C(55)-Sn(1)-N(2)
C(55)-Sn(1)-N(3)
C(55)-Sn(1)-N(4)
N(2)-Sn(1)-N(4)
C(49)-O(1)-Sn(1)
2
3
4
Ph
Me
Ph
Ph
Me
H
(TTP)Sn(CCPh)2
(TTP)Sn(CCPh)2
(TTP)Sn(CCPh)2
16
4.3
8.8b
11c
28
C(56)-C(55)-Sn(1) 168.5(10) C(55)-C(56)-C(57) 177.1(12)
5
6
tolyl
Ph
H
Me
(TTP)Sn(CCPh)2
(TTP)SnII
90
32
38
83
41
83
18
51
36
60
100
83
46
35
53
86
(CtCPh)2,5 2.212(4) and 2.196(4) Å in trans-(TPP)SnPh2(CH2-
Cl2), 2.210(7) and 2.193(7) Å in cis-(TBPP)SnPh216) while
still in the normal range observed for Sn-C single bonds.
The Sn-O bond distance (2.083(7) Å) is in good accord
with data for six-coordinate tin complexes.17 The acetylenic
bond distance of 1.194(15) Å is in the range of CtC triple
bonds and is consistent with the IR signal observed at 2129
cm-1.
7
Ph
Me
(TTP)Sn(OH)2
8
9
Ph
Ph
Ph
Ph
(TTP)Sn(OH)2
(TTP)SnCl2
96
71
a For reaction conditions, see Experimental Section. b Other products were
also observed: benzyl alcohol (0.5-0.8%), benzil (9.4-17%). c Other
products were also observed: p-methyl benzyl alcohol (5.4%), dimethyl
benzil (29%).
conditions with a turnover number of 2.3 after 8 days of
heating (entry 3). Diolato complexes (TTP)Sn[OC(Me)2C-
(Me)2O] (1) and (TTP)Sn[OC(Me)(Ph)C(Me)(Ph)O] (2) were
observed in these reactions, respectively, by 1H NMR
spectroscopy. When the less substituted hydrobenzoin was
subjected to the same reaction conditions, up to 10% yield
of benzaldehyde was obtained. Benzyl alcohol (∼0.8%) and
benzil (∼16%) were also detected (entry 4). With trans-1,2-
cyclohexanediol, only a trans-bisalkoxo complex (TTP)Sn-
(OC6H10OH)2 was observed without the formation of oxi-
dation products.
A number of other tin porphyrin complexes were found
to mediate the oxidative cleavage of vicinal diols as well.
In the presence of catalytic amounts of (TTP)Sn or (TTP)-
Sn(OH)2, 2,3-diphenylbutane-2,3-diol was oxidized to ac-
etophenone in similar yields (entries 6 and 7). With
(TTP)SnCl2, which possesses robust Sn-Cl bonds, the
cleavage of benzopinacole to benzophenone was observed,
although it was substantially slower compared to reactions
with other tin porphyrins (entry 9).
Given the ability of (TTP)TidO to catalyze the oxidation
of R-ketols to R-diketones, we further examined the utility
of tin porphyrin complexes in this transformation. Heating
an aerobic C6D6 solution of benzoin in the presence of 5.5
mol % (TTP)Sn(CtCPh)2 in an NMR tube resulted in the
smooth conversion of benzoin to benzil. After total con-
sumption of benzoin within 22 h, benzil was obtained in 87%
NMR yield, as well as a small amount of benzaldehye
(8.7%). Similarly, 2-hydroxy cyclohexanone (adipoin) was
oxidized to cyclohexan-1,2-dione under identical conditions
with 70% conversion, although the yield of cyclohexan-1,2-
dione was low (31% after 35 h), as determined by 1H NMR
spectroscopy.
The most notable feature in the structure of (TTP)Sn(Ct
CPh)(OC6H4OH) is large voids of 218.4 Å3 found in the
lattice that could capture organic solvents with up to 9 non-
hydrogen atoms. However, the SQUEEZE routine from the
PLATON package18 found only three “unaccounted” elec-
trons per cell. The negative and positive residuals are almost
equal (1.348 and -1.359 eÅ-3), therefore the existence of
diffuse solvent in this structure is very unlikely. Such sieves-
like lattices were obtained in other tin porphyrin complexes,19
holding promise for new types of porous materials.20
Oxidation of Vicinal Diols and r-Ketols Mediated by
Tin Porphyrins. We have shown that (TTP)TidO is able
to catalyze the oxidative cleavage of vicinal diols to carbonyl
compounds and the oxidation of R-ketols to R-diketones,
probably via the formation of titanium porphyrin diolato or
enediolato intermediates.21 Similar reactivity is observed in
tin porphyrin chemistry, i.e., the formation of diolato
complexes from tin porphyrin precursors and the decomposi-
tion of diolato complexes to (TTP)SnII and carbonyl com-
pounds. This prompted us to investigate oxidative transfor-
mations mediated by tin porphyrin complexes. Selected
results are summarized in Table 3. Heating (∼120 °C) an
aerobic C6D6 solution of 2,3-diphenylbutane-2,3-diol and 5.7
mol % (TTP)Sn(CtCPh)2 in a sealed NMR tube resulted in
the conversion of diol to acetophenone in modest yield (55%,
entry 1). Benzopinacole was converted into benzophenone
in high yield (97%, entry 2) within 15 h. With unactivated
diols, this cleavage reaction proceeded very slowly. For
example, pinacol was cleaved to acetone under similar
(17) Denmark, S. E.; Su, X. Tetrahedron 1999, 55, 8727.
(18) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool, Utrecht
University, Utrecht, The Netherlands, 2003.
(19) Fallon, G. D.; Lee, M. A.-P.; Langford, S. J.; Nichols, P. J. Org. Lett.
2002, 4, 1895.
(20) (a) LeCours, S. M.; DiMagno, S. G.; Therien, M. J. J. Am. Chem.
Soc. 1996, 118, 11854. (b) Knapp, S.; Vasudevan, J.; Emge, T. J.;
Arison, B. H.; Petenza, J. A.; Schugar, H. J. Angew. Chem., Int. Ed.
1998, 37, 2368. (c) Lin, K. J. Angew. Chem., Int. Ed. 1999, 38, 2730.
(21) Du, G.; Woo, L. K. Manuscript in preparation.
Discussion
Reaction of Tin Porphyrins with Diols. The structure
and coordination geometry of metal diolato complexes have
2384 Inorganic Chemistry, Vol. 43, No. 7, 2004

Reaction of Tin Porphyrins with Vicinal Diols
Scheme 3
been shown to be influenced greatly by the type of diolato
moiety.22 Although chelated diolato complexes were invari-
ably obtained for Ti porphyrins,7 the outcome of reactions
between (TTP)Sn(CtCPh)2 or (TTP)Sn(NHtolyl)2 and vici-
nal diols was dependent on the diols employed. Highly
substituted vicinal diols tended to yield diolato chelate
complexes, whereas less substituted diols preferred to form
mono- and bisalkoxo complexes. With pinacol and 2,3-
diphenylbutane-2,3-diol, the diolato chelate complexes 1 and
2 were readily obtained. In contrast, attempts to prepare
chelated diolato complexes from ethylene glycol and hy-
drobenzoin in a similar manner proved to be elusive. Only
mono- and/or bisalkoxo complexes were observed. Higher
temperatures and longer reaction times appeared to favor the
production of diolato complex 1 in the pinacol reaction.
However, under these conditions the decomposition of 1 to
(TTP)Sn become significant and clean formation of 1 was
not achieved. On the other hand, it is possible to produce
the diolato complex (TTP)Sn(OC6H4O) (4) by heating a C6D6
solution of (TTP)Sn(CtCPh)(OC6H4OH) (3) over a long
period of time (12 d). This is in part due to the thermal
stability of the resulting diolato complex and in part due to
the inability of the pendant OH groups to form dimers or
oligomers with other tin porphyrin species. In contrast,
heating a (TTP)Sn(CtCPh)(OCH2CH2OH) (6) solution did
generate the diolato complex as a minor product, while
accompanied by the decomposition to (TTP)Sn (â-H: 9.19
ppm) and other uncharacterizable products.
The nature of the starting tin porphyrin complexes was
also important in the reaction outcome. In the reactions of
(TTP)Sn(CtCPh)2 with pinacol and 2,3-diphenylbutane-2,3-
diol, the formation of mono- and bisalkoxo complexes were
often observed. With a more labile diamido complex, (TTP)-
Sn(NHtolyl)2, the diolato complexes (TTP)Sn[OC(Me)2C-
(Me)2O] (1) and (TTP)Sn[OC(Ph)(Me)C(Ph)(Me)O] (2)
could be obtained in good yields with trace or no formation
of mono- or bisalkoxo species. However, the requirement
of excess diol was somewhat unexpected. Presumably the
formation of the diolato complexes proceeds through an
alkoxo-alkynyl-substituted intermediate, as demonstrated by
the generation of (TTP)Sn(OC6H4O) (4) from (TTP)Sn(Ct
CPh)(OC6H4OH) (3). Moreover, protic acids do not seem
to catalyze the conversion of a bisalkoxo species into a
chelated diolato complex. For example, heating a solution
of (TTP)Sn(OC6H4OH)2 (5) in the presence of 5% acetic
acid did not result in the formation of diolato complex 4.
The ease of dissociation of the amido group, relative to that
of the CtCPh group, greatly facilitates the formation of
diolato complexes from the intermediates mentioned above.
Surprisingly, the reaction of a labile tin porphyrin, (TTP)-
Sn(OTf)2, with disodium pinacolate did not produce the
desired diolato complex cleanly.
catalytic cycle for the tin porphyrin-mediated diol cleavage
is shown in Scheme 3. Sn(IV) complexes, such as (TTP)-
Sn(CtCPh)2, react with diols to form diolato intermediates,
which in turn undergo oxidative cleavage to release carbonyl
compounds and (TTP)SnII. This latter step was observed
independently in the decomposition of the diolato complexes
under N2. The SnII species is subsequently oxidized to (TTP)-
Sn(OH)2 by molecular oxygen in moist air, which is known
to be a very facile process.23 This was further supported by
the reaction of 2,3-diphenylbutane-2,3-diol in the presence
of (TTP)SnII. Under N2, no acetophenone production was
observed, whereas under air, the formation of the diolato
complex 2 was observed and acetophenone was produced
in a rate similar to that of the (TTP)Sn(CtCPh)2-mediated
reaction. Although (TTP)Sn(OH)2 is quite inert, it has been
known to react with an array of phenols and carboxylic acids
under mild conditions.10,24 We have shown here that (TTP)-
Sn reacted readily with ethylene glycol to afford (TTP)Sn-
(OCH2CH2OH)2 (7) upon exposure to air. Thus, the forma-
tion of diolato complexes from (TTP)Sn(OH)2 and diols
completes the catalytic cycle. We also found that (TTP)Sn-
(OH)2 was able to cleave diols oxidatively under catalytic
conditions (Table 3, entries 7 and 8).
To probe the reaction pathway of tin porphyrin-mediated
R-ketol oxidation, the reaction of benzoin with (TTP)Sn-
(CtCPh)2 under N2 was monitored by H NMR spectro-
1
scopy. The reaction proceeded stepwise, first yielding
monosubstituted (TTP)Sn(CtCPh)[OCH(Ph)COPh], then
disubstituted (TTP)Sn[OCH(Ph)COPh]2. (TTP)Sn and benzil
were produced very slowly after prolonged heating. This
behavior contrasts with the related oxotitanium porphyrin-
mediated reaction, where an enediolato species (TTP)Ti[OC-
(Ph)dC(Ph)O] was readily observed.21 We have also shown
that titanium(II) porphyrins react with benzil to afford the
enediolato complex (TTP)Ti[OC(Ph)dC(Ph)O]. Treatment
of (TTP)Sn(II) with benzil does not produce the analogous
tin(IV) product. Although the generation of such tin(IV)
porphyrin species has been elusive, non-porphyrin tin ene-
diolato complexes are known.25 Thus, by analogy with the
(TTP)TidO-mediated reaction, we believe an enediolato
(23) Barbe, J. M.; Ratti, C.; Richard, P.; Lecomte, C.; Gerardin, R.; Guilard,
R. Inorg. Chem. 1990, 29, 4126.
(24) (a) Hawley, J. C.; Bampos, N.; Abraham, R. J.; Sanders, J. K. M.
Chem. Commun. 1998, 661. (b) Langford, S. J.; Lee, M. A.-P.;
MacFarlane, K. J.; Weigold, J. A. J. Inclusion Phenom. Macrocyclic
Chem. 2001, 41, 135. (c) Reddy, D. R.; Maiya, B. G. J. Porphyrins
Phthalocyanines 2002, 6, 3.
Mechanistic Aspects of Tin Porphyrin-Mediated Diol
Cleavage and Ketol Oxidation. On the basis of analogous
studies with (TTP)TidO-mediated oxidations,21 a probable
(22) (a) Crans, D. C.; Felty, R. A.; Chen, H.; Eckert, H.; Das, N. Inorg.
Chem. 1994, 33, 2427. (b) Zechmann, C. A.; Huffman, J. C.; Folting,
K.; Caulton, K. G. Inorg. Chem. 1998, 37, 5856.
(25) (a) Mukaiyama, T.; Tsuzuki, R.; Kato, J.-i. Chem. Lett. 1985, 6, 837.
(b) Ichikawa, J.; Mukaiyama, T. Chem. Lett. 1985, 7, 1009.
Inorganic Chemistry, Vol. 43, No. 7, 2004 2385

Du et al.
intermediate is operative in the tin porphyrin-mediated
R-ketol oxidation. The presence of coordinating groups
(carbonyl CO or OH) vicinal to the alcohol group seems to
be crucial for these reactions. Simple alcohols such as
benzhydrol and p-methyl benzyl alcohol cannot be oxidized
under the same conditions.
the National Science Foundation for financial support of this
work.
Supporting Information Available: Tables of crystallographic
data for 3 including atomic coordinates, bond lengths and angles,
and anisotropic displacement parameters; and proton NMR spectra
for 1 and 6. Crystallographic information files for the studied
complexes (cif). This information is available free of charge via
the Internet at http://pubs.acs.org.
Acknowledgment. We thank the Petroleum Research
Fund, administered by the American Chemical Society, and
IC035123+
2386 Inorganic Chemistry, Vol. 43, No. 7, 2004