A utility for organoleads: Selective alkyl and aryl group transfer to tin

Article abstract of DOI:10.1039/c7dt04520d

Me₄Pb and Ph₄Pb readily transfer methyl or phenyl groups to an equivalent molar ratio of tin(iv) chlorides in the order SnCl₄ > MeSnCl₃ > Me₂SnCl₂ > Me₃SnCl, often in a selective manner. Me₃PbCl and Ph₃PbCl specifically transfer a single methyl/phenyl group under the same reaction conditions to produce recovered yields in >75%. Specific transfer of 2 methyl groups from PbMe₄ can be achieved at elevated temperatures and/or a 2:1 molar ratio Pb:Sn.

Full text of DOI:10.1039/c7dt04520d

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Efficient extraction of sulfate from water using
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A Utility for Organoleads: Selective Alkyl and Aryl Group Transfer to Tin
Renzo N. Arias-Ugarte,a Keith H. Pannell*a
Department of Chemistry, University of Texas at El Paso, El Paso, TX. 79968-
0513, USA
Me4Pb and Ph4Pb readily transfer methyl or phenyl groups to an equivalent molar ratio of tin (IV) chlorides in the
order SnCl4>MeSnCl3>Me2SnCl2>Me3SnCl, often in a selective manner. Me3PbCl and Ph3PbCl specifically transfer
a single methyl/phenyl group under the same reaction conditions to produce recovered yields in >75%. Specific
transfer of 2 methyl groups from PbMe4 can be achieved at elevated temperatures and/or a 2:1 molar ratio Pb:Sn.
Introduction
The study, and utility, of organotin and organolead chemistry has been relatively limited since the
discovery of the various health issues resulting from the wide-spread environmental dissemination
of both elements. Organotins have exhibited utility in a variety of societal uses e.g. as PVC
stabilizers,1 antifouling agents,2 medicinal and biocidal materials,3 tin oxide film deposition,4 and
as “green” catalytic reagents.5 Furthermore, and quite remarkably, elemental tin itself has been
promoted as a Pb substitute for non-toxic bullets!6 However, organotin materials can have
significant deleterious impact upon life forms. For example, and very relevant to the reader, they
can have a marked negative impact upon the functioning and efficacy of human natural killer cells.7
The early use of tetraethyl lead as an “anti-knock” agent in gasoline, and various pigments in
household paints, ceramics, etc. caused a wide dissemination of the lead into the environment and
much effort has been undertaken to understand the major health risks that result from the element.
Indeed a location mere yards from our laboratory was the focus of the first major study, and
definitive results, that illustrated the acute negative impact upon children of lead emissions from a
copper/lead smelter.8 An apparent resurgence in the use of “organolead” perovskite materials in

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solar cells is misleading since the lead compound used is generally CH3NH3PbX3, X = Cl, Br, I, a
material that contains no lead carbon bond.
There have been suggestions that rather than call for the elimination of organotin
compounds from such materials as marine hull paints, where they reduce mollusk growth and
hence dramatically decrease economic transportation costs, the search for structural modifications
that maintain utility, but reduce unwanted biocidal concerns, would be a fruitful endeavour.2 Our
interest in organotins has been associated with stabilizing tetravalent systems via intramolecular
Sn-O, S, Se interactions to hopefully alter some of their biological properties and outcomes.9 To
this end we recently illustrated an example of this notion by synthesizing materials where a butyl
group is replaced by a methylthiopropyl group, CH3SCH2CH2CH2-. Thus, whereas Bu2SnCl2
reduced natural killer cell function by >70%, (MeSCH2CH2CH2)2SnCl2 has little or no impact and
still maintains, for example, excellent properties as a trans-esterification catalyst.10 In this area of
study we had need for mixed aryl/alkyl organotins, R2R’SnCl, RR’SnCl2 etc. and their synthesis
often involved multiple steps and suffered from a lack of selectivity, a need for excess reagent,
and difficult separation/purification procedures.9, 11 To possibly overcome some of these issues we
have investigated a new synthetic approach using organolead materials.
Our limited prior interest in organolead materials was our observation illustrating the
lability of tetravalent Pb-C bonds in transition metal lead complexes as typified by the chemistry
outlined in equation 1 involving a methyl group transfer from Pb to Fe.12a
hv
Fe-PbMe3
Fe-Me
(1)
C
C
O
O
C
O
C
O

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Similar chemistry was illustrated for chromium, molybdenum, tungsten, and manganese
complexes containing direct Pb-metal bonds, and always resulted in transfer of the organic radical,
Me, Et, Ph, to the metal with concomitant elimination of divalent lead.12 In the case of R = Me,
the divalent Pb material leads to the formation of Me4Pb and Pb. There are reports concerning the
utility of alkylleads as alkyl transfer/exchange reagents to main group elements such as B,13a Al,13b
Sb,13c and there is even a report of a metal-catalyzed transfer to C in the form of acyl halides,
aldehydes and carbamates.14
In a single line at the end of an article associated with the formation of CF3 derivatives of
Sn and Pb using Hg(CF3)2, Eujen and Lagow noted: When PbMe3CF3 was allowed to warm up
slowly with an excess of SnCl4 an immediate reaction occurred with SnMeCl3 as the major
product.15 They also noted a series of unidentified Sn materials containing a CF3 group but no
experimental detail was provided. Coupling this observation to the fact that Pb(acetate)4 reacts
with Bu3PhSn to form Bu3Sn(acetate) and PhPb(acetate)3 in the presence of Hg(II) catalyst,16 we
initiated, and now report, a study on the reactions of organolead materials with tetravalent
organotin halides, RnSnCl4-n, n = 0-3.
Results and Discussion
Our initial study involved the room temperature reaction between equimolar amounts of PbMe4
(1) and SnCl2 in the hope that we could form a Pb-Sn bond via the oxidative addition of a Pb-C
bond to form Me3PbSnMeCl2 following some literature evidence for such chemistry.17 However,
in CDCl3 at 60 C, the reaction led to an efficient methyl group transfer from Pb to Sn resulting in
the clean formation of Me4Sn (2) and PbCl2, eq. 2; Table 1, entry 1; Figure 1.
60 C
Me4Pb + SnCl2
Me4Sn + PbCl2
(2)

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We could observe transient amount of Me3SnCl (3) and Me3PbCl (4), but after 8 hours the
reaction was complete, Figure 1.
1
S
S
t = 0.2 h
2
t = 8 h
Figure 1: 13C NMR spectroscopic monitoring of the reaction between Me4Pb and SnCl2 in CDCl3 at 60C showing the disappearance
of Me4Pb, 1, (-4.1 ppm) and the appearance of Me4Sn, 2 (-10.0 ppm).at. Traces of diethyl ether solvent, S, (66.0 and 16.0 ppm))
are present. The presence of this solvent has no impact upon the outcome of the experiments, vide infra
When performed in C6D6 the reaction was less efficient and a mixture of products Me3SnCl
and Me4Sn was obtained as a ~50/50 mixture, even at 60 C, Table 1, entry 2.
Table 1: Reaction between Me4Pb (1) and organotin chloridesa
Item Method
Conditions
60 C
60 C/ C6D6
RT/C6D6
RT
RT
RT
RT/C6D6
60 C/C6D6
100 C/C6D6
RT
80 C
80 C
Ratio
1:1
1:1
1:1
1:1
1:1
1:1
2:1
2:1
2:1
1:1
1:1
1:1
1:1
Products(ratio)b
Me4Sn
Me3SnCl+Me4Sn (1:1)
Me2SnCl2, MeSnCl3 (1.5/1)
Me2SnCl2, MeSnCl3 (1:3)
Me2SnCl2+Me3SnCl (1/1)
Me3SnCl
Me2SnCl2
Me3SnCl
Me4Sn
Me3SnCl
Time(h) Yieldc
1
1+SnCl2
8
8
(100)68
-
2
1+SnCl2
3
1+SnCl4
0.2
0.2
0.2
24
0.2
1
12
0.6
4
-
-
-
4
1+SnCl4
5
6
7
8
1+SnMeCl3
1+SnMeCl3
1+SnMeCl3
1+SnMeCl3
1+SnMeCl3
1+SnMe2Cl2
1+SnMe3Cl
1+SnPh3Cl
1+SnPh2Cl2
1+SnPh2Cl2
(100)75
(100) 55
(100)
(95)
(100)
(100)
(100)
(100)70
(100)70
9
10
11
12
13
14
Me4Sn
MePh3Sn
MePh2SnCl
16
2
2
RT
RT
2.2:1 Me2Ph2Sn
a: All reactions were performed in a sealed NMR tube in CDCl3, otherwise indicated. b: Ratio based in 1H NMR.
c: (Conversion of PbMe4 by (NMR Spectroscopy) recovered yield.
The use of Me4Pb to methylate tetravalent tin chlorides was also successful and thus at
varying temperatures Me3SnCl (3), Me2SnCl2 (5), MeSnCl3 (6), and SnCl4, were each transformed

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to methylated products. Regardless of the solvent, CDCl3 or C6D6, the reaction between PbMe4
and SnCl4 resulted in a mixture of products MeSnCl3 and Me2SnCl2. Table 1, entries 3 and 4. The
room temperature reaction between equimolar amounts of MeSnCl3 and Me4Pb in CDCl3 leads to
the initial formation of a mixture of Me2SnCl2 and Me3SnCl but after 24 hours final tin product of
Me3SnCl was observed and isolated, Table 1, entries 5 and 6, Figure 2, eq. 3.
4
S
S
5
3
t = 0.2 h
t = 24 h
Figure 2: 13C NMR spectroscopic monitoring in CDCl3 of Me4Pb (1) + MeSnCl3 (6) at RT,
indicating immediate absence of 1 and 6 and formation of Me2SnCl2 (5), Me3SnCl (3) and
Me3PbCl (4) after 15 min. and complete formation of Me3SnCl (3) after 24h.
During the process the formation of Me3PbCl (4) was observed as a transient material, clearly
suggesting that it was also capable of transferring a methyl group to the tincentre. This was initially
demonstrated by performing the room temperature reaction in C6D6 where Me3PbCl precipitates
upon formation resulting only in the specific formation of Me2SnCl2, eq. 4; Table 1, entry 7. Trace
amounts of both Me4Sn (-10 ppm) and MeCl (26 ppm) are observed at the end of the reaction.
CDCl3
Me3SnCl + Me2PbCl2 (3)
Me4Pb + MeSnCl3
Me2SnCl2 + Me3PbCl
RT
C6D6
Me4Pb + MeSnCl3
Me2SnCl2 + Me3PbCl
(4)
RT

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At elevated temperatures, and using a 2:1 mixture of Me4Pb/MeSnCl3, the reaction in C6D6
can lead to further methylation quantitatively, entries 8, 9. Similar chemistry may be observed with
the other methyl chlorostannanes. As expected single methylation is observed under the
appropriate conditions for Me2SnCl2 and Me3SnCl Table 1, entries 10, 11. For the bulkier, and less
Lewis acidic Me3SnCl, higher temperatures are needed for the reaction to proceed.
Equimolar reactions between Me4Pb and Ph3SnCl (7) or Ph2SnCl2 (8), produced high yields
of mono-methylation products, at an elevated temperature in the case of Ph3SnCl. For Ph2SnCl2
subsequent methylation of the initially formed Ph2MeSnCl to produce Ph2Me2Sn was observed, in
the reaction with a 2:1 Pb:Sn molar ratio, Table 1, entries 12, 13, 14.
Because of the transient intermediacy of Me3PbCl noted above we examined its properties
to discern possible superior selectivity of product formation. Typical results are outlined in Table
2. In contrast to the results with Me4Pb where methylation of equimolar ratios of the various
organotin chlorides generally led initially to multiple methylations, the use of Me3PbCl always
resulted in a mono-methylation reaction, although at a slower rate than with Me4Pb, e.g. Figure 3.
5
4
t = 0.2h
3
t = 24h
Figure 3: 13C NMR spectroscopic monitoring in CDCl3 (60C) of the reaction between
Me3PbCl (4) and Me2SnCl2 (5), showing the selective formation of trimethyltin chloride
(3). The secondary product PbMe2Cl2 is insoluble and precipitates out of solution.

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Our results illustrate that Me3PbCl is the preferred and selective methylation reagent rather than
the molecule we expected to be more useful, M4Pb. The total specificity exhibited for the
methylation of SnCl4 is important since formation of such RSnCl3 materials is difficult due to
secondary alkylations.11
Table 2: Reaction between PbMe3Cl (4) and organotin chloridesa
Item
1
Method
4+SnCl4
4+MeSnCl3
4+Me2SnCl2
4+Me3SnCl
Conditions
RT
RT
60 C
100 C
Products
MeSnCl3
Me2SnCl2
Me3SnCl
Me4Sn
Time(h)
0.2
3
24
120
Yieldc
(100)70
(100)70
(95)68
(100)
2
3b
4
a: All the reactions were performed in a 1:1 ratio in a sealed NMR tube in CDCl3. b: Traces of MeCl and Me4Sn. c: (NMR yield)
recovered yield.
The data in Table 2 also illustrates very clearly that increasing Lewis acidity of the tin
species facilitates the methylation process as observed by both the time and temperature needed
for complete reaction to occur in the order Me3SnCl>Me2SnCl2>MeSnCl3 >SnCl4.
We also investigated the capacity of Pb-Ph containing species to be involved in phenylation
reactions with the various tin halides. The results, presented in Table 3, are remarkably similar to
those using Me4Pb and Me3PbCl as methylation reagents. Tetraphenyllead, (9) in equimolar
reactions, is a rapid and selective reagent for SnCl4 forming PhSnCl3 in >70% recovered yield at
room temperature, eq. 5; Table 3, entry 1. It is not selective in its reaction with MeSnCl3, indeed
no reaction is observed until the temperature is raised to 80 C under which conditions a mixture of
products is observed, eq. 6; Table 3, entry 2. This distinction reflects reduced Lewis acidity of
MeSnCl3, cf. SnCl4. The selectivity for mono-phenylation of SnCl4 is an important observation.11
RT
Ph4Pb + SnCl4
PhSnCl3
(5)
80 C
Ph4Pb + MeSnCl3
PhMeSnCl2 + Ph2MeSnCl
(6)
If the relative amount of Ph4Pb is increased to a 2:1 ratio at 80 C, only Ph2MeSnCl (10)
can be formed in high yield; Table 3, entry 5. However, that is a wasteful type of chemistry using

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2 equivalents of the Pb reagent to transfer 2 phenyl groups. We observed no indication for
tetraorganotin products, Me4-nPhn, under any conditions we have used involving phenyl transfer;
this is distinct from the reactivity of Me4Pb with Ph2SnCl2 which does form Ph2Me2Sn: compare
entry 14 Table 1 and entry 10 Table 3.
Table 3: Reaction between Ph4Pb (9), or Ph3PbCl (11), with organotin chloridesa
Item Method
Conditions
RT
80 C
80 C-100 C 1:1
80 C/C6D6
100 C
60 C -100 C 1:1
RT
80 C/C6D6
Ratio Products(ratio)b
Time(h) Yieldc
1
9+SnCl4
1:2
1:1
PhSnCl3
0.2
(100)71
-
2
3
4
5
9+MeSnCl3
9+MeSnCl3
9+MeSnCl3
9+MeSnCl3
9+SnCl2
MePhSnCl2+ MePh2SnCl (2:1) 12
MePhSnCl2+MePh2SnCl (1:2) 72
-
1.5:1 MePhSnCl2
2.2:1 MePh2SnCl
1
3
(100)71
(100)60
-
(100)84
(100)75
(100)
(100)
(100)95
(100)90
6
Ph3SnCl
96
0.2
12
24
12
3
7
11+SnCl4
1:1
1:1
PhSnCl3
MePhSnCl2
8
11+MeSnCl3
9
11 +Me2SnCl2 100 C
11+Me2SnCl2 80 C
11+Me2SnCl2 100 C/C6D6 1:1
11 +Ph2SnCl2 80 C 1:1
1:1.2 Me2PhSnCl
10
11
12
2:1
Me2PhSnCl
Me2PhSnCl
Ph3SnCl
12
1
a: All the reaction were performed in a sealed NMR tube in CDCl3, otherwise indicated. b: Ratio of product based H NMR
spectroscopy. c: Prolonged heating to higher temperatures promotes decomposition >100 C.
As with the utility of Me3PbCl, the use of Ph3PbCl (11) as the phenylating reagent was
uniformly excellent in equimolar reactions with all of the tin chlorides we studied, always resulting
in a single mono-phenylation reaction, Table 3, entries 7, 8, 9,11. In each case recovered yields,
which we made no attempt to optimize, were very good.
From the above results it is clear than the lead bi-product from the reactions of R3PbCl, i.e.
Me2PbCl2 and Ph2PbCl2, are not useful methyl/phenyl transfer agents under our conditions,
primarily because they precipitate from solution. Indeed in reactions where MePbCl3 would be the
expected lead product we obtained PbCl2 and, via NMR could observe the formation of
methylchloride, 13C, 26 ppm, 1H, 2.9 ppm.
As noted in Table 2, the Lewis acidity of the tin centre facilitates the organic group transfer
reaction. Therefore, we studied the halide effect at tin in the expectation of observing decreasing

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reaction rates in the order Cl>Br>I. For this study we chose Me2SnX2 as a model substrate, X =
Cl, Br, I in CDCl3 with a 1:1 ratio with Me4Pb, see Table 4.
Table 4: Reaction between PbMe4 (1) and Me2SnX2 (X = Cl, Br, I) a
Item
Method
Conditions
RT
RT
Products(ratio)b
Me3SnCl
Me3SnBr
Time(h)
0.75
3
Yieldc
(100)
(100)
(95)
2
3
4
1+Me2SnCl2
1+Me2SnBr2
1+Me2SnI2
60 C
Me3SnI
6
a: All reactions were performed in a sealed NMR in CDCl3 in a 1:1 ratio and monitored by NMR Spectroscopy. b: Ratio calculated
by 1H NMR spectroscopic analysis. c: NMR yield.
From the results noted in Table 4 we do observe the order predicted based upon the
electronegativity of the halogen, Cl>Br>I, being indicative of the relative Lewis acidity of the
organotin materials. The impact of changing the halogen was smaller than the impact of the various
amount of chloro substituents on tin as recorded in Table 2. The organotin reagent Me2SnF2 was
too insolublein the solvents used in our study to enable a relative reactivity to be cleanly observed.
Overall, the chemistry reported herein is an extension of the so-called Kocheshkov
redistribution reaction,18 a reaction first observed by Buckton some 50 years earlier.19 The initial
interaction between the Pb and Sn moieties presumably involves a bridging transition state, or
unstable intermediate, as depicted in Scheme 1.
R'
Pb
R'
R
R'
X
Sn
R
R'3PbX + R3R'Sn
R'4Pb + R3SnX
R'
R
Scheme 1. Possible bridging transition state/intermediate for the exchange process
The need for a lone pair on a halogen to initiate the exchange is evident since no chemistry
is observed for a mixture of Me4Sn and Ph4Pb under any reaction conditions employed in this
study. The increasing reactivity as a function of increasing Lewis Acidity of the tin centre,
reinforces this suggestion. We have also performed a limited solvent variation to test this

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hypothesis. As can be noted in Figures 1 and 2, small amounts of Et2O were present, and in their
absence no change in the chemistry was noted. However, using a solvent which is a significantly
superior Lewis base dramatically retards the chemistry. Thus, in THF the reaction between
Me2SnCl2 and Me4Pb is only ~ 50% complete after 4 h compared to complete reaction after <1 h
in CDCl3. Separately, adding an equivalent of the well-established tin coordinating base Ph3P(O)
to the reaction between Me2SnCl2 and Me4Pb in CDCl3 similarly curtails the reaction. All these
observations are congruent with a process outlined in Scheme 1, where the tin halide can be
intercepted by the base, retarding the transfer chemistry.
The overall driving force for the reactions between the Pb and Sn species reflects the
relative Pb-C, Sn-C, Pb-X and Sn-X bond energies, Table 5.
Table 5: Selected Bond energies in KJ/Mol for the reaction Pb-C + Sn-X → Pb-X + Sn-C
X
Reactants
Energy KJoules
Products
Calculated
Energy
KJ/Mol
-18.0
-10.0
-1.0
Pb-C
130
130
130
Sn-X
323
130
205
Pb-X
243
201
142
Sn-C
192
192
192
Cl
Br
I
Reference: Huheey, pps. A-21 to A-34; T.L. Cottrell, "The Strengths of Chemical Bonds," 2nd ed., Butterworths, London, 1958;
B. deB. Darwent, "National Standard Reference Data Series," National Bureau of Standards, No. 31, Washington, DC, 1970; S.W.
Benson, J. Chem. Educ., 42, 502 (1965).
These data reflect the trend observed in the reactions of Me4Pb and Me2SnX2, Table 4.
Experimental
All manipulations were carried out under a nitrogen atmosphere using Schlenk or vacuum line
techniques. A solvents were used subsequent to drying by normal techniques. Tetramethyllead was
synthesized by small modification from PbCl2 and methyllithium 1.5M in hexanes and MeI.20
Trimethyllead chloride was synthesized using the procedure involving the reaction between
tetramethyllead and HCl in ether at -78 C in toluene and stored under nitrogen atmosphere.21 Tin
dichloride, tetraphenyl lead, and the various tin halides were obtained from Gelest Inc. and used

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without further purification. NMR spectra were recorded on a 300 MHz Bruker spectrometer in
C6D6 or CDCl3. All column chromatography was performed on small columns (5 x 60 mm) of
Silica Gel (Aldrich), 700-230 mesh, 60 Ao, Pore Volume 0.75 cm3/g. All the distillation were
performed is a small distillation set under for fractional distillation under nitrogen atmosphere.
Some typical reactions are outlined below. All solutions containing Pb and Sn materials were
appropriately disposed of via the University Environmental Health and Safety Division.
Reaction of PbMe4 with SnCl2
In a typical experiment, a Pyrex NMR tube was charged with 0.2 g (0.74 mmol) of PbMe4 and
0.14 g (0.74 mmol) of SnCl2 and 0.5 mL of CDCl3. The tube was sealed under vacuum and warmed
to 60 oC in an oil bath under which conditions the SnCl2 dissolved. Initially the reaction generated
an intense yellow color and then become colorless, with a clear white solid precipitated (PbCl2).
1
The reaction was monitored by 13C, H, 119Sn, and 207Pb NMR spectroscopy and after 8 h of
heating, the reaction was stopped at this stage and the NMR tube was opened and the solution was
filtered through an acrodisc filter to remove the PbCl2, and the solution was distilled at 60oC to
remove the solvent under nitrogen atmosphere, leaving behind the tetramethyl tin as an oily
compound in 68% (0.09g, 0.50 mmol).
Reactions between PbMe3Cl (PbPh3Cl and Ph4Pb) with SnCl4.
In a typical experiment, a Pyrex NMR tube was charged with 0.16 g. (0.56 mmol) of PbMe3Cl,
and 0.5 mL of CDCl3, then 0.14 g (0.56 mmol) of SnCl4 dissolved in 0.5ml of CDCl3 was added
dropwise and immediately a white insoluble solid was observed. The tube was sealed under
vacuum and mixed at room temperature for about 12 minutes. The reaction was stopped at this
stage and the NMR tube was opened and the solution was filtered through an acrodisc filter to
remove the insoluble white solid (PbMe2Cl2) formed in the process, and the solution was

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concentrated under vacuum and the remaining solid was sublimed at 50 C under high vacuum
giving the pure MeSnCl3 as white solid in 70% yield (0.09g, 0.39 mmol); m. pt. 46oC;
literature, 48oC.22
The related reactions between PbPh3Cl (0.16g, 0.34 mmol), and Ph4Pb (0.16g, 0.31 mmol) with
SnCl4 gave a insoluble material Ph2PbCl2 which was easily filtrated with an acrodisc filter and the
solution concentrated to give exclusively PhSnCl3, as a gummy white solid in high yields 84%
(0.086g, 0.28 mmol) and 71% (0.13g, 0.44 mmol) respectively.
Reaction between PbMe3Cl and MeSnCl3
In a typical experiment, a Pyrex NMR tube was charged with 0.10 g. (0.35 mmol) of PbMe3Cl
and 0.083 g (0.35 mmol) of MeSnCl3 and 0.5 mL of CDCl3. The tube was sealed under vacuum
13
1
and warmed to room temperature. The reaction was monitored by C, H, 119Sn, and 207Pb
NMR spectroscopy and 3h after mixing, the reaction was stopped. The NMR tube was opened,
the solution filtered through an acrodisc filter to remove the insoluble Me2PbCl2, and the
concentrated under vacuum, leaving Me2SnCl2 as a white colorless solid in 70% yield (0.054g,
0.24 mmol). Further purification can be obtained by sublimation at 60oC, 760 mm/Hg;
Me2SnCl2 m. pt. 104 C; literature, 107 C.23
Conclusions
We have found that alkyl and aryl lead (IV) compounds are useful methylation or
phenylation reagents for a variety of organotin halides in the reactivity order
SnCl4>MeSnCl3>Me2SnCl2>Me3SnCl, reflective of the Lewis acidity of the central tin atom. A
similar trend is observed when studying the methylation of Me2SnX2, X = Cl, Br, I where the
relative reactivity is in the order Cl > Br > I. The selectivity of mono-methylation or mono-

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phenylation vs di-methylation or di-phenylation using R4Pb reagents is often very specific
dependent upon the molar ratio of Pb:Sn, the reaction temperature or solvent used. For example,
the room temperature reactions of Me4Pb with equimolar amounts of the tin chlorides using C6D6
as solvent uniformly involve a single organic radical transfer to tin, since the concomitantly formed
Me3PbCl precipitates out of the solvent and no longer is available for chemistry. However, in
CDCl3, where Me3PbCl is soluble, further methyl transfer occurs. To observe multi methyl group
transfer in C6D6 excess Me4Pb, and/or elevated temperature, is required. The use of the related
R3PbCl, R = Me, Ph, reagents resulted in selectivity for the single methylation or phenylation with
excellent recovered product yields, although the overall reactions were somewhat slower than with
Me4Pb. The new chemistry will be extended to the transfer of organic radicals containing
potentially coordinating substituents which are of interest to us as noted in the introduction, e.g. -
(CH2)3ER, C6H4-CH2ER, CH2C6H4(ER), ER = SMe, OMe, NMe2, etc. It may be that such
functionalities themselves interact with the Lewis acidic tin centre thereby modifying the
observable chemistry. A series of competitive transfer studies is also planned using R2R’2Pb etc.
to ascertain the relative migratory aptitudes of the various organic radicals.
Conflicts of Interest
There are no conflicts of interest.
Acknowledgements
We thank the Welch Foundation for support of this research via grant # AH-0546.
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