Studies of organotin(IV)-orthoquinone systems

Article abstract of DOI:10.1016/S0022-328X(97)00538-X

The primary process in the reaction of hexaphenylditin with various substituted orthoquinones (Q) is shown to involve attack by the quinone at a phenyl ligand. The intermediate thus formed decomposes to yield Ph₃Sn(SQ^·), where S(Q^·-) is the corresponding semiquinonate. Rearrangement of these species in solution gives rise to biradicals, while intramolecular electron transfer may lead to the formation and precipitation of Ph₂Sn(CAT), where CAT^2- is the corresponding substituted catecholate. The identification of these processes depends in part on electron paramagnetic resonance spectroscopy. The reaction of Ph₃SnCl or Ph₂SnCl₂ with Na(TBSQ^·) (TBSQ^·- = 3,5-di-tert-butyl-orthobenzosemiquinonate) results in the formation of Ph₂Sn(TBSQ^·), which can undergo redistribution and intramolecular electron transfer, so that the solution chemistry of these latter systems is similar to that of the products of the Sn₂Ph₆ + Q reaction.

Full text of DOI:10.1016/S0022-328X(97)00538-X

Ž
.
Journal of Organometallic Chemistry 550 1998 165–172
1
ž /
Studies of organotin IV -orthoquinone systems
2
)
Martyn A. Brown, Bruce R. McGarvey, Andrzej Ozarowski , Dennis G. Tuck
Department of Chemistry and Biochemistry, UniÕersity of Windsor, Windsor, Ontario, Canada, N9B 3P4
Received 5 February 1997
Abstract
Ž .
The primary process in the reaction of hexaphenylditin with various substituted orthoquinones Q is shown to involve attack by the
P
Py
Ž
.
Ž
.
is the corresponding
quinone at a phenyl ligand. The intermediate thus formed decomposes to yield Ph3Sn SQ , where S Q
semiquinonate. Rearrangement of these species in solution gives rise to biradicals, while intramolecular electron transfer may lead to the
2
y
Ž
.
formation and precipitation of Ph2Sn CAT , where CAT
is the corresponding substituted catecholate. The identification of these
P
Ž
.
processes depends in part on electron paramagnetic resonance spectroscopy. The reaction of Ph3SnCl or Ph2SnCl2 with Na TBSQ
Py
P
Ž
.
Ž
.
TBSQ s3,5-di-tert-butyl-orthobenzosemiquinonate results in the formation of Ph2Sn TBSQ , which can undergo redistribution and
intramolecular electron transfer, so that the solution chemistry of these latter systems is similar to that of the products of the Sn2Ph6qQ
reaction. q 1998 Elsevier Science S.A.
Keywords: Orthoquinones; Hexaphenylditin; Intramolecular electron transfer reactions; Ligand redistribution
Ž .
quinone X4C6O2-o; XsCl, Br , the final product was
1. Introduction
Ž
.
the unusual organotellurium IV
w x
catecholate
w
Ž
.
x
In a number of recent investigations, we have
demonstrated that the oxidation of Main Group ele-
ments, or compounds of those elements in low oxida-
tion states, by orthoquinones involves a sequence of one
electron transfer processes 1 . Preparative, spectro-
scopic and crystallographic results all support this con-
X4C6O2 TeC6 H5 2O 4 .
The present work began as an extension of these
Ž
.
investigations to the formally tin III compound
hexaphenylditin. The subsequent inclusion of te-
traphenyltin, and of the species formed in the metatheti-
w x
Ž .
cal reactions of semiquinonate salts and organotin IV
w x
clusion 2 , which is at odds with earlier assumptions
halides, reflects a common solution chemistry in these
systems, involving both ligand redistribution processes
and intramolecular electron transfer reactions.
about the nature of the redox reactions of such
molecules. It has also been shown that nucleophilic
attack by a substituted o-quinone can be an important
3
primary step in these processes. With some elements,
the oxidation of organic derivatives has also been stud-
ied, and in the particular case of diphenyl ditelluride,
the presence of semiquinone species in the reaction
mixture confirmed the importance of one-electron trans-
2. Experimental section
2.1. General
w x
fer 3 . When the oxidant was tetrahalogeno-o-benzo-
Hexaphenylditin, tetraphenyltin, organotin halides
and substituted orthoquinones were used as supplied
Aldrich . Solvents were dried and carefully degassed
before use. All experimental work was carried out in an
atmosphere of dry nitrogen, using conventional vacuum
line techniques.
Infrared spectrum of samples in KBr discs were
recorded on a Nicolet 3-DX instrument. Electron para-
Ž
.
)
Corresponding author.
1 Dedicated to Professor Ken Wade on the occasion of his 65th
Birthday in recognition of his outstanding contributions to Main
Group Chemistry.
2 Present address: Department of Chemistry, University of Califor-
nia, Davis, CA.
3 D.L. Boucher, M.A. Brown, B.R. McGarvey, D.O. Tuck, unpub-
lished results.
Ž
.
magnetic resonance EPR spectra were run on a Bruker
ESP-300E spectrometer, using techniques described
0022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

(
)
166
M.A. Brown et al.rJournal of Organometallic Chemistry 550 1998 165–172
w x
previously 1 . Mass spectroscopy involved heated sam-
ples in a Shimadzu 14-B spectrometer operating in the
E.I. mode, with Sun Sparc software. Elemental analysis
was by Canadian Microanalytical Services. 119Sn NMR
spectra were recorded on a Bruker AC 200 instrument
operating at 74 MHz; chemical shifts are relative to
Ž
.
Sn CH3 4 s0.
In this paper, as elsewhere, we use the symbolism
Q§™SQPy§™CAT2y to identify the o-quinone
§™semiquinonate§™ catecholate sequence of lig-
ands, with appropriate prefixes.
2.2. Hexaphenylditin q 3,5-di-tert-butyl-1,2-benzo-
(
)
quinone TBQ
Ž
.
A solution of Sn2 Ph6 0.31 g, 0.45 mmol in n-
Ž
.
hexane 20 ml was heated with a suspension of TBQ
0.1 g, 0.45 mmol in the same solvent 20 ml . The
Ž
.
Ž
.
reaction mixture immediately became brown–black and
a colourless solid precipitated. This was collected,
Ž
washed and dried, and identified as tetraphenyltin melt-
ing pt. 223–2298C; cf. lit. value 228–2308C. 119Sn
Ž
.
w x
NMR CHCl3 dsy137 ppm; cf. lit. value 5 y137
Ž
..
"2 ppm C2 H3Cl3 . Identical phenomena were ob-
served when TBQ was dissolved in dichloromethane
Ž
.
10 ml , and when the TBQ: Sn2 Ph6 ratio was in-
creased to 2:1 or 4:1. On cooling, the reaction mixture
deposited additional quantities of Ph4Sn; further cooling
Fig. 1. EPR spectra of solution, in n-hexane, for the reaction of
and evaporation of solvent gave a dark grey solid,
Ž .
P
Sn2 Ph6 with 3,5-di-tert-butyl-benzoquinone.
Ž .
A Dilute solution at
Ž
.
identified as Ph3Sn TBSQ . Anal. Calcd. for
C32 H35O2 Sn: C 67.4, H 6.19. Found: C 67.6, H 5.93.
After the removal of Ph4Sn, the EPR of the filtrate
Ž
.
room temperature; B Frozen solution spectrum 77 K showing half
field transition and evidence of three biradical species Ds251,
Ž
236, and 172=10y4 cmy1
.
.
Ž
.
Fig. 1a established the presence of a free radical
Ž
.
species S s 1r2 , identified subsequently as
P
Ž
. Ž
.
Ph3Sn TBSQ see Section 3 . The g-value and hyper-
fine coupling constants for this and related species are
presented in Table 1; the coupling constants were de-
rived by simulating the experimental spectra, using the
program Simfonia. In addition, low temperature spectra
P
Ž
.
species. The
2
to increase relative to the Ph2 Sn TBSQ
g-value for the Ss1r2 signal changed only slightly
after irradiation, with gs1.992 at 238C, and 2.0061 at
77 K.
Ž
identified the presence of three biradical species Fig.
1b . With increasing TBQ:Sn2 Ph6 ratios, the biradical
.
(
)
2.3. Hexaphenylditinq9,10-phenanthrenequinone PQ
spectrum increased in intensity relative to the Ss1r2
signal, but was otherwise unchanged. The D-values
derived from this spectrum are also given in Table 1.
In a subsequent experiment, the filtrate was irradiated
Ž
.
When a solution of PQ 1.00 g, 4.80 mmol and
Ž
.
Ž
.
Sn2 Ph6 2.8 g, 4.0 mmol in dichloromethane 20 ml
was refluxed for 1 h, the product was a brown solution
from which a brown solid precipitated on the addition
of n-hexane, followed by cooling. This solid was identi-
Ž
.
with UV 480-W lamp, 1 h . The concentration of the
Ž
.
presumed Sn–Sn biradicals see Section 2.3 appeared
Table 1
Ž
.
Ž
.
EPR parameters g, aSn , aH for Ph3Sn SQ species, and D for related biradical species
Q
g
aSn
aH G
D cmy1 =10y4
Ž .
G
Ž .a
Ž
.
TBQb
PQ
2.000389
2.0037
2.00375
2.0348
2.00393
2.00389
10.2
11.51
8.50
11.2
10.4
10.2
3.03, 0.46, 0.36
1.93, 0.46
251, 236, 172
104, 63
not detected
147
NQa
Br4Q
5.3, 1.4 2 , 1.1
Ž .
Ž
.
Ž .
2.95, 0.33 9 , 0.5
Ž .
3.03, 0.46, 0.36 9
Ph3SnClqNa TBSQ
Ph2 SnCl2 qNa TBSQ
299, 278, 204
Ž
.

(
)
M.A. Brown et al.rJournal of Organometallic Chemistry 550 1998 165–172
167
P
Ž
.
fied as Ph3Sn PSQ . Anal. Calcd. for C32 H23O2 Sn: C
68.9, H 4.15. Found: C 68.9, H 4.34. Yield 1.20 g.
Predominant peaks in the mass spectrum at mres558,
q
q
q
197 SnC6 Hq5
Ž
.
Ž
.
M , 351 Sn C6 H5 3 , 274 Sn C6 H5
2
and 120 Snq, are in keeping with this formulation.
The filtrate was EPR-active, with strong mono- and
biradical signals. Slow evaporation of this solution gave
small quantities of crystals identified crystallographi-
P
w x
Ž
.
cally and analytically 6 as Ph2 Sn PSQ 2; the D-val-
ues for this compound have been reported elsewhere as
63 and 104=10y4 cmy1. In addition to this biradical,
Ž
.
the solution also yielded the compound Ph2 Sn PCAT .
Anal. Calcd. for C26 H18O2 Sn: C 64.9, H 3.77. Found:
C 65.3, H 4.13. Mass spectral peaks were detected at
mres493, Mq. When the mole ratio PQ:Sn2 Ph6 in
the initial reaction mixture was 2:1, this diolate was the
only product identified.
(
)
2.4. Hexaphenylditin and 1,2-naphthoquinone NQ
Ž
.
Stirred solutions of NQ 0.32 g, 2.02 mmol and
Ž
.
Ž
Sn2 Ph6 0.70 g, 1 mmol in dichloromethane total
volume 40 ml were mixed, with the immediate precipi-
.
tation of a black solid which was insoluble in all
common organic solvents other than dimethylsulph-
oxide. This solid was collected, dried and characterized
P
Ž
.
as Ph3Sn NSQ . Anal. Calcd for C28 H21O2 Sn: C 66.2,
H 4.17. Found: C 66.1, H 4.35. Prominent mass special
q
q
q
Ž
.
Ž
.
ions were at 508 M , 351 Sn C6 H5 3 , 274 Sn C6 H5 ,
2
Fig. 3. EPR spectra of a dichloromethane solution from the reaction
197 SnC6 Hq5 , 120 Snq. This solid was EPR active. The
green filtrate from this reaction showed a well-resolved
Ž .
of Sn2 Ph6 and tetrabromo-o-benzoquinone.
A
Dilute solution at
Ž .
room temperature. Simulation gives gs2.00348, aSn s11.2 G; B
Frozen solution spectrum 77 K showing half field transition for a
Ž
.
room temperature EPR spectrum, corresponding to
y4
biradical species Ds147=10 cmy1
.
Ž
.
P
Ž
.
Ph3Sn NSQ , with only a weak biradical component
Ž
.
Fig. 2 . No sensible D-values could be derived from
this system.
2.5. Hexaphenylditin and tetrahalogeno-o-quinone
(
)
BrQ, ClQ
Ž
.
A solution of Sn2 Ph6 1.40 g, 2 mmol and BrQ
Ž
.
Ž
.
1.70 g, 4 mmol in dichloromethane 20 ml was
refluxed for 5 h. The resultant deep brown solution was
Ž
EPR active; biradical signals were also detected Fig.
.
3a,b . Addition of n-hexane followed by cooling gave a
P
Ž
.
red precipitate of Ph3Sn BrSQ . Anal. Calcd. for
C24 H15O2 Br4Sn: C 37.3, H 1.95. Found: C 37.3, H
1.91. Mass spectral peaks at 774 Mq, 620 M-
Ä
q
Ž
.
4q
Ž
.
Ž
.
2 C6 H5 , 351, Sn C6 H5 3 , 274 Sn C6 H5 , 197
SnC6 H5, 120 Snq, were in keeping with this formula-
tion.
A similar procedure was used for the chloro ana-
Ž
.
logue. When the quinone 1.23 g, 5 mmol was refluxed
Ž
.
in toluene or dichloromethane 50 ml with
Ž .
a solution of Ph3Sn NSQ in
Fig. 2. EPR spectrum of
Ž
.
hexaphenylditin 1.75 g, 2.5 mmol , the deep red solu-
tion which had a very strong EPR signal. The frozen
solution showed an intense central transition with zero
Ž
dichloromethane at room temperature NSQs1,2-naphthaquinonate
.
Ž .
anion . Simulation gives gs2.00375, aSn s8.50 G, aH s5.3 G 1 ,
Ž . Ž .
1.4 G 2 , 1.1 G 1 .

(
)
168
M.A. Brown et al.rJournal of Organometallic Chemistry 550 1998 165–172
field splitting, and an intense half field transition. The
zero-field splitting indicated the presence of more than
one biradical. Tetraphenyltin precipitated after some
time, and was removed by filtration. The filtrate was
evaporated to give a viscous red syrup which failed to
crystallize or solidify under a variety of conditions;
analysis Found: C, 55.17; H, 5.21 , suggested that this
was a mixture of compounds, which could not be
separated.
was followed. The EPR spectrum of the filtrate obtained
after removal of these solids was that of a monoradical,
but no evidence was obtained for the presence of diradi-
cals.
(
)
2.9. Reaction of diphenyltin dichloride with Na TBSQ
Ž
.
The experimental procedures followed those for the
P
Ž
.
Ph3SnCl-Na TBSQ system. With a 1:1 mole ratio of
P
Ž
.
Ph2 SnCl2 and Na TBSQ , the initial brown solution
Ž
.
2.6. Tetraphenyltin and 3,5-di-tert-butyl-o-benzo-
quinone
had a strong EPR spectrum Fig. 5 , which showed
presence of diradicals through a very weak feature at
half-field. It was not possible to derive any values for
the D-parameter from these results. For the monoradical
Ž
.
A
solution of TBQ 0.22 g,
1
mmol in
Ž
.
Ž
.
Ž
.
dichloromethane 10 ml was added to a stirred solution
component, gs2.0043 RT and 2.0031 77 K . The
Ž
.
Ž
of Ph4Sn 0.21 g, 0.5 mmol in the same solvent 10
only solids obtained from the reaction mixture were
.
Ž
.
ml . The mixture immediately became deep brown. The
Ph4Sn and Ph2 Sn TBC .
EPR spectrum of this mixture at room temperature was
that of a single free radical species, essentially identical
to the Ss1r2 region of the spectrum obtained from
With a mole ratio of 1:2, the EPR spectrum appeared
to be that of a mixture of two mono-radical species,
Ž
.
Sn2 Ph6 qTBQ Table 1 .
2.7. Diphenylmercury and 3,5-di-tert-butyl-o-quinone.
Ž
A solution containing equimolar quantities ca. 2
.
mmol of these substance in chloroform was refluxed
for 1 d, but no evidence of a reaction was obtained, in
that there was no perceptible change of colour, and no
EPR activity was detected
(
)
2.8. Reaction of triphenyltin chloride with Na TBSQ
In this work, and that with diphenyltin dichloride,
P
Ž
.
deep blue solutions of Na TBSQ in n-hexane were
prepared by the reaction of 3,5-di-tert-butyl-catechol
Ž
w x
.
with sodium hydride cf. Ref. 1 .
P
Ž
. Ž
.
4.5 mmol in n-hexane
A solution of Na TBSQ
Ž
.
Ž
.
20 ml , and a dichloromethane 10 ml solution of
Ž
.
triphenyltin chloride 1.7 g, 4.41 mmol , were stirred
together at room temperature. The resultant green mix-
ture deposited NaCl 0.24 g, 4.10 mmol, 93% . When
the filtrate was cooled after the removal of this precipi-
tate, a colourless diamagnetic solid was thrown down.
Mass spectrometry and IR spectroscopy suggested that
this was a mixture of Ph4Sn and Ph2 Sn TBC . The
former was dissolved in acetone, leaving a residue of
Ph2 Sn TBC . Anal. Calcd. for C26 H30O2 Sn: C 63.3, H
Ž
.
Ž
.
Ž
.
6. 13. Found: C 63.5, H 6.16. Mass spectrum, mres
q
Ž
.
494 M . Repeated attempts to recrystallize this sub-
stance from various solvents yielded only te-
traphenyltin, leaving a solution which was strongly EPR
Fig. 4. EPR spectra of a n-hexane of products of the reaction of
Ž
.
active. The spectra Fig. 4a,b showed the presence of
Ž
.
Ž
Ph 3 SnCl with Na TSBQ
TBSQ s 3,5-di-tert-butyl-o-
Ž
.
both mono- and diradical species Table 1 .
. Ž .
benzosemiquinonate anion . A Dilute solution at room temperature.
P
Ž
.
In a later experiment, the Na TBSQ : Ph3SnCl mole
ratio was 2:1, and again Ph4Sn and Ph2 Sn TBC were
the solid products identified when the above procedure
Ž .
Simulation gives gs2.00393, aSn s10.4 G, aH s2.87 G 1 , 0.33
Ž
.
Ž . Ž .
Ž
.
G 9 ; B Frozen solution spectrum 77 K showing half field transi-
tion for biradical species Ds299, 278, 204=10 cmy1
.
y4
Ž
.

(
)
M.A. Brown et al.rJournal of Organometallic Chemistry 550 1998 165–172
169
w x
We have recently shown 9 that o-quinones will
oxidise the phenyl group of LiPh by the processes
LiC6 H5 qQ™LiqSQPyqC6 HP5
2C HP ™ C H
1
Ž .
2
Ž .
Ž
.
6
5
6
5
2
and the attack of o-quinone at a phenyl group of
Ph6Sn2 is therefore the most probable initiating pro-
cess. Whether this is a cooperative process involving
two neighbouring phenyl groups is not clear, although
Ž
.
the absence of reaction with HgPh2 C–Hg–Cs1808
suggests such a mechanism. Leaving this aside, the
proposed reaction sequence is:
QqSn2 Ph6 ™ SQP PhP Ph SnSnPh
Ž
.
2
3
x
Fig. 5. EPR spectrum of n-hexane solution resulting from the
Ž
.
reaction of Ph2 SnCl2 and Na TSBQ at room temperature. Simula-
Ž . Ž .
P
SQP SnPh q SnPh
3
Ž .
Ž
.
3
3
tion gives gs2.00389, aSn s10.2 G, aH s3.03 G 1 , 0.46 G 1 ,
Ž .
0.36 G 9 .
followed by
2PSnPh3 ™Sn2 Ph6
or
4
Ž .
Ž
.
with no evidence for biradicals; g;2.0045 RT , 1.980
77 K .
Ž
.
P
Qq SnPh ™Ph Sn SQP
5
Ž .
Ž
.
3
3
The comparable sequence for Ph4Sn is:
QqPh Sn™SQP PhP SnPh ™Ph Sn SQP qPhP
3. Results and discussion
Ž
.
Ž
.
4
3
3
3.1. Reaction of hexaphenylditin and o-quinones
The behaviour of Sn–Sn bonded organotin com-
pounds has been reviewed by Sawyer 7 . Especially
relevant to the present work is the thermal stability of
Sn2 Ph6, which was recovered in almost quantitative
6
Ž .
This last process is exactly analogous to that proposed
w
x
w x
by Davies and Hawari 10 for the reaction of organotin
compounds with 3,6-di-tert-butyl-1,2-benzoquinone.
Ž .
3
Ž .
6 is the
The common feature of Eqs.
formation of Ph3Sn TBSQ and in the case of the
reaction of TBQ with both Sn2 Ph6 and Ph4Sn, the EPR
and
P
Ž
.
Ž
yield after 21 h in refluxing tetrahydrofuran boiling pt.
.
668C . The compound is unaffected by undiluted oxy-
parameters of the monoradical formed are identical. The
gen. Reaction with iodine yields Ph3SnI quantitatively,
and a cyclic intermediate has been proposed. Oxidation
P
Ž
.
identification of this radical as Ph3Sn TBSQ depends
in part on the similarity in the hyperfine constants for
this molecule and the analogous product identified by
Ž
.
by organic peroxides R2O2 produces Ph3SnOR, and
free radical species may be involved in such reactions.
We have recently shown that o-quinones coordinate
to halides of Main Group elements, and that with SnCl4
in particular a stable QSnCl4 species can be crys-
w x
Davies and Hawari 8 , who reported aSn s12.0 G,
aH s3.7 G. We assign the aH values given in Table 1
Ž
.
Ž
.
Ž
.
to H4 3.03 G , H6 0.46 G and t-C4 H9 0.36 G ,
2
partly by comparison with results from earlier work on
tallised. In order to test the possibility that Sn2 Ph6
w
x
w
x
Ž
.
TBQqSnX2 , 11 and TBQqInX 12 XsCl, Br, I ,
might act as a Lewis acid towards such ligands, we
investigated mixtures of Sn2 Ph6 and a variety of mono-
and bidentate nitrogen bases in chloroform, using 119Sn
NMR. The chemical shifts ppm , with line widths Hz
in parentheses, for solutions containing excess base,
partly by analogy with the work of Davies and Hawari
w
x
10 , and partly on the basis of the simulation procedure.
Ž
.
Ž
.
It follows that the remaining values in Table 1 refer
P
Ž
.
to the analogous Ph3Sn SQ species derived from the
reactions described in Section 2. There seems to be no
method of rationalising the specific results in terms of
the detailed structure of the semiquinone in question.
The more important point is that all these reactions
involve the same initiating processes.
Ž
.
Ž
.
were for pyridine y142.5 35 , g-picoline y144.2 32 ,
X
X
Ž
.
2,2 -bipyridine y144.1 30 and N,N,N,N -tetramethyl-
Ž
.
ethanediamine y142.8 38 . The mean value is y143.4
Ž
.
Ž
.
"0.7 34 , to be compared with y143.6 31 for a solu-
tion of Ph6Sn2 in the same solvent. We conclude that
nucleophilic attack of the o-quinone at a tin centre of
Ph6Sn2 is unlikely to be the primary process in the
systems studied in this work. Tetraphenyltin also lacks
3.2. Related reactions
w x
acceptor properties 8 , and a coordinative mechanism
can also be ruled out for this substance.
The striking features of the Sn2 Ph6rTBQ system are
the precipitation of Ph4Sn and formation of biradical

(
)
170
M.A. Brown et al.rJournal of Organometallic Chemistry 550 1998 165–172
Ž
.
Ž
.
w x
species Table 1 . and the precipitation of Ph4Sn. The
experimental evidence for these latter include a reso-
nance for the frozen solution at magnetic field half that
and r C–O distances 6 . The zero-field parameters of
this molecule are similar to these discussed in the last
Ž .
paragraph. It is reasonable to ask whether Eq. 7 can be
Ž
.
of the corresponding monoradical e.g., Figs. 3 and 4 ,
and weak features adjacent to the central resonance.
e.g., Fig. 1 . In favourable circumstances, these may
lead to measurement of the zero-field parameters D and
E, which in turn may allow estimates of the effective
distance between the radical sites in a molecule. In the
case of phenanthrenequinone, we also identified the
mononuclear biradical Ph2 Sn PSQ 2 , and the cate-
cholate Ph2 Sn CAT , but with naphtha- and tetrabromo-
o-quinones, the only product recovered was the mono-
radical Ph3Sn SQ . The significance of these differ-
ences presumably lies in
strength of the o-quinone or semiquinones involved,
and ii the solubility of the various species in question.
For TBQ, we suggest that the explanation of the
formation of these products requires both intramolecular
electron transfer, and solution redistribution processes.
The latter are related to the known tendency of organ-
otin IV halides, and other species, to undergo ligand
redistribution in solution, as evidenced by a number of
extended to other redistribution products such as
P
P
Ž
.
Ž .
PhSn TBSQ
and Sn TBSQ 4. We find no evidence
3
Ž
.
for such tri- or tetraradical species, which might require
seven- and eight-coordination at tin, and therefore con-
fine the discussion to Eq. 7 .
Table 1 shows that the frozen reaction solution con-
tains three biradical species, which cannot be ade-
quately accounted for by Eq. 7 . Following arguments
Ž .
P
Ž
.
Ž .
Ž
.
w
x
used elsewhere 1,11 involving intramolecular electron
transfer, we propose the processes:
P
Ž
.
Ph Sn TBSQP |Ph Sn TBSQP
Q
8
Ž .
Ž
.
Ž
. Ž
.
2
2
2
Ž .
i the different oxidising
Ph Sn TBSQP Q |Ph Sn TBSQP qQ
9
Ž .
Ž
. Ž
.
Ž
.
2
2
Ž .
2Ph Sn TBSQP ™Ph TBSQP SnSn TBSQP Ph
Ž
.
2 Ž
.
Ž
.
2
2
10
Ž
.
This sequence results in tin–tin bonded species, and
again the earlier work shows that two stereoisomers of
such analogous molecules are possible Scheme 1 .
In the case of the analogous Cl2 TBSQ SnSn-
TBSQ Cl2 species identified in studies of the
Ž
.
Ž
.
P
Ž
.
119
P
w
x
Sn NMR studies 13 . We therefore suggest that the
formation of Ph3Sn TBSQ Eq. 6 is followed by:
Ž
.
P
Ž
. Ž
Ž ..
SnCl2rQ system, the zero-field parameters of 228 and
65=10y4 cmy1 were assigned on the basis of calcula-
2Ph Sn TBSQP |Ph SnqPh Sn TBSQP
7
Ž .
Ž
.
Ž
.
2
3
4
2
w
x
tions to the cis- and trans-isomers respectively 10 .
Since Ph4Sn is almost insoluble in either n-hexane or
dichloromethane, Eq. 7 will be displaced to the right
hand side by the precipitation of Ph2 Sn, resulting in the
formation of the biradical Ph2 Sn TBSQ
Ž
.
In one case Sn 2 Ph 6 q PQ the product
Ž .
Ž
.
Ph2 Sn PCAT was identified, and although this was the
only reaction involving Sn2 Ph6 to yield such a product,
similar diphenyltin catecholates were found in the reac-
P
Ž
.
in solution.
2
tion between Ph3SnCl and NaSQP see Section 3.3 . In
the present system, we suggest that the isomerisation
The EPR properties of biradicals of the type
Ž
.
P
1
Ž
.
Ž
M TBSQ 2 L MsMg, Zn, Cd; Ls2,2 -bipyridine,
X
X
.
N,N,N ,N - tetramethylethanediamine have been dis-
Ph Sn PSQP |Ph Sn PCAT PQ
is followed by loss of o-quinone and precipitation of
Pb2 Sn PCAT , and this clearly depends on the prior
formation of the bis-semiquinone complex, only de-
tected in the particular case of phenanthrenequinone.
11
Ž
.
Ž
. Ž
.
Ž
.
2
2
2
w
x
cussed earlier 14 . The zero-field parameters obtained
experimentally were compared with those calculated for
various configurations, and the stereochemistries of the
complexes thereby identified. For such six-coordinate
complexes with bidentate ligands, the only possible
isomer is the cis-form, and reasonable agreement was
found between calculated and experimental values,
Ž
.
Ž
.
Isomerizations to Eq. 11 have been identified earlier
w x
1 .
which were in the range 150–250=10y4 cm 1 for
w x
P
Ž
. Ž
.
those elements. For the compound Si DBSQ DBC
2
P
Ž
DBSQ s 4,6-di-tert-butyl-1,2-benzosemiquinone an-
ion; DBC2yscorresponding catecholate , the D-value
.
y4
exptl. 15 is 301=10
cmy1. Given this range of
Ž
. w x
values, it is difficult to assign any one of the values in
P
Ž
.
Table 1 to Ph2 Sn TBSQ with any confidence; on the
2
other hand, the order of magnitude is clearly appropriate
Ž .
for such a molecule, and Eq. 7 is supported to that
extent.
Further confirmation comes from the recent crystal-
lographic characterisation of the diradical species
P
Ž
.
Ph2 Sn PSQ 2 , noted briefly above. The structure of
Ž
.
this six-coordinate tin IV complex confirms the pres-
ence of two semiquinonate ligands, with typical r Sn–O
Ž
.
Scheme 1.

(
)
M.A. Brown et al.rJournal of Organometallic Chemistry 550 1998 165–172
171
(
)
(
)
3.3. The reaction between Ph3 SnCl and Na TBSQ
3.4. The reaction between Ph2 SnCl2 and Na TBSQ
The original intent of this part of the study was to
As with Ph3SnCl, the 119Sn NMR spectrum of a
freshly prepared solution of Ph2 SnCl2 in dichloro-
methane-d2 showed a single resonance at y29.8 ppm
P
Ž
.
prepare Ph3Sn SQ compounds by metathesis, but the
P
Ž
.
experimental results for Ph3SnClqNa TBSQ showed
that the solution chemistry is more complicated than
expected. The near-quantitative elimination of NaCl
shows that the first reaction is indeed.
Ž
w x
cf. y32"0.8 ppm reported 5 for a solution in
.
CH2Cl2 . The initial reaction with a 1:1 mole ratio of
reactants gave a solution containing one monoradical,
Ž
.
and Pb4Sn and Ph2 Sn TBC as solids; a mole ratio of
Ph SnClqNa TBSQP ™Ph Sn TBSQP qNaCl
Ž
.
Ž
.
P
3
3
Ž
.
2:1 NaTBSQ :Ph2 SnCl2 gave a mixture of two mono-
radicals. A detailed analysis of the EPR spectra was not
possible.
The isolation of Ph4Sn and Ph2 Sn TBC suggests
that Ph3Sn TBSQ is one of the radicals formed in
these reactions. A large number of possible reactions
12
Ž
.
It is important to note that a freshly prepared solution of
Ž
.
Ž
.
Ph3SnCl in dichloromethane the reaction medium
showed only a single 119Sn NMR signal at y46.5 ppm
w x
P
Ž
.
Ž
.
cf. y48"11 ppm reported in the literature 5 , so that
can be constructed for this system, involving redistribu-
the presence of other possible redistribution products in
the starting solution can be ignored. This initial reaction
is followed by the precipitation of a mixture of Ph4Sn
P
Ž
.
Ž
molecules in solution xq
tion of Phx SnCly TBSQ
z
.
yqzs4 , and the evidence presently available does
not allow any single set of reactions to be identified.
Ž
.
Ž
.
and Ph2 Sn CAT . We suggest that Eq. 12 is followed
by the redistribution process Eq. 7 and an isomerisa-
tion corresponding to Eq. 11 , namely
Ž
Ž ..
3.5. General conclusions
Ž
.
Ph Sn TBSQP |Ph Sn TBC TBQ
13
Ž
.
Ž
. Ž
.
Ž
.
2
The initial reaction of a series of substituted ortho-
2
2
quinones with Sn2 Ph6 yields the monoradical species
with subsequent loss of TBQ and precipitation of
P
Ž
.
Ph3Sn SQ . The nature of reaction products which
may be derived subsequently from these radicals ap-
pears to depend on the properties of the o-quinone, and
of the reaction conditions. Redistribution processes in
solution are an important feature of these systems, as
Ž
.
Ph2 Sn TBC .
In addition to the solid products just noted, the
filtrate contains biradicals, with D-values similar to
those found for the Ph6Sn2rTBQ reaction. These are
Ž . Ž
.
presumed to arise by Eqs. 8 – 10 . It will be clear that
we have postulated two possible competing processes
for the intramolecular electron transfer processes in
Ž
.
they are in other areas of tin IV chemistry. Reactions
involving Ph4Sn, and metathetical reactions between
P
Ž
.
Na TBSQ and Ph3SnCl or Ph2 SnCl2 , give related
products, and a common solution chemistry and intra-
molecular electron transfer processes underlies all these
systems.
Ž
.
Ph2 Sn TBSQ .
2
Ph Sn TBC q TBQ
.
Ž
.
Ž
2
|Ph Sn TBSQP
Ž
.
2
2
|Ph SnP TBSQ q TBQ
14
Ž
.
Ž
.
Ž
.
2
Acknowledgements
The left-hand product is the result of intraligand elec-
tron transfer
Ž
.
Prof. A.G. Davies University College, London, UK
is thanked for helpful discussions. Financial support
2TBSQPy|TBQqTBC2y
whilst the right-hand product arises from the oxidation
15
Ž
.
Ž
.
through research grants to BRM and DGT from the
Natural Sciences and Engineering Research Council of
Canada is acknowledged.
of TBSQPy by tin IV
SnIV qTBSQPy™SnIII qTBQ
As noted above, the analogue of Eq. 15 has been
Ž
.
16
Ž
.
Ž
.
References
w x
observed in indium chemistry 1
XIn TBSQP |XIn TBC TBQ
. Ž
17
w x
1
M.A. Brown, B.R. McGarvey, A. Ozarowski, D.G. Tuck, Inorg.
Ž
.
Ž
.
Ž
.
2
Ž
.
Chem. 35 1996 1560, and refs. therein.
w x
Ž
.
The relative importance of the competing processes in
2
D.G. Tuck, Coord. Chem. Rev. 112 1992 215.
w x
3
T.A. Annan, A. Ozarowski, Z. Tian, D.G. Tuck, J. Chem. Soc.,
Ž
.
Eq. 14 should depend, inter alia, on solvent and
temperature, to the extent that these parameters affect
Ž
.
Dalton Trans. 1992 2931.
w x
Ž
.
4
Z. Tian, D.G. Tuck, J. Organomet. Chem. 462 1993 125.
Ž
.
the solubility of Ph2 Sn TBC , and it is therefore reason-
able that different products are observed in solid and
solution phases.
w x
5
R.K. Harris, J.D. Kennedy, W. McFarlane, in: R.K. Harris, B.E.
Ž
.
Mann Eds. , AMR and the Periodic Table, Academic Press,
New York, 1978, p. 342 et seq.

(
)
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x
6
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Ž
.
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.
D.O. Tuck, Chem. Commun., 1997 699.
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w x
7
A.K. Sawyer, Organtin Compounds, Vol. 3, Marcel Dekker,
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w
x
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13 A.G. Davies, P.J. Smith, in: G. Wilkinson, F.G.A. Stone, E.W.
w x
8
Ž
.
M.A. Brown, B.R. McGarvey, A. Ozarowski, D.G. Tuck, J.
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Ž .
Chem. Soc. 113 1991 3288.
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Ž
.
Am. Chem. Soc. 118 1996 9691.
w x
9
w
x
A.G. Davies, P.J. Smith, in: G. Wilkinson, F.G.A. Stone, E.W.
Abel Eds. , Comprehensive Organometallic Chemistry, Vol. 2,
Pergamon, Oxford, 1982, Chap. 11, p. 535.
Ž
.
w
x
w
w
x
Ž
.
10 A.G. Davies, J.A.A. Hawari, J. Organomet. Chem. 231 1983
53.
I.S. Bebostotskaya, V.V. Ershov, M.I. Kabachnik, Dokl. Chem.
Ž
.
Ž
.
Engl. Trans. 234 1977 276.
x
11 T.A. Annan, B.R. McGarvey, A. Ozarowski, D.G. Tuck, R.K.
Ž
.
Chadha, J. Chem. Soc., Dalton Trans. 1989 439.