Tin-magnesium transmetallation reactions

Article abstract of DOI:10.1016/S0022-328X(02)01430-4

Sulfur-functionalized methyltin compounds nBu₃SnCH₂S(O)_iR (i = 0, 1, 2; R = Me, Ph) underwent transmetallation with Grignard compounds MgR′X (R′ = Me, nBu, Ph; X = Cl, Br, I) and diorganomagnesium compounds MgR′R″ (R′/R″ =

Full text of DOI:10.1016/S0022-328X(02)01430-4

Journal of Organometallic Chemistry 655 (2002) 111ꢀ114
/
www.elsevier.com/locate/jorganchem
Tinꢀ
/
magnesium transmetallation reactions
Rushdi I. Yousef, Tobias Ruffer, Harry Schmidt, Dirk Steinborn *
¨
Institut fur Anorganische Chemie, Martin-Luther-Universitat Halle-Wittenberg, Kurt-Mothes-Strasse 2, 06120 Halle, Germany
¨ ¨
Received 24 January 2002
Abstract
Sulfur-functionalized methyltin compounds nBu3SnCH2S(O)iR (iꢁ
Grignard compounds MgR?X (R?ꢁMe, nBu, Ph; XꢁCl, Br, I) and diorganomagnesium compounds MgR?Rƒ (R?/Rƒꢁ
nBuꢀsBu) to provide Sn(nBu)3R and Mg[CH2S(O)iR]X and Mg[CH2S(O)i R]Rƒ, respectively. Analogously, the reaction of
nBu3SnCH2P(O)Ph2 with Mg(nBu)Br afforded quantitatively Mg[CH2P(O)Ph2]Br and Sn(nBu)4. Transmetallations between
nBu3SnCH2YMe2 (YꢁN, P) and MgMe2 proceeded only in the presence of catalytic amounts (10ꢀ20 mol%) of LinBu yielding
Mg(CH2YMe2)Me and Sn(nBu)3Me/Sn(nBu)4. # 2002 Elsevier Science B.V. All rights reserved.
/
0, 1, 2; Rꢁ/Me, Ph) underwent transmetallation with
/
/
/Me/Me,
/
/
/
Keywords: Transmetallation reactions; Organotin compounds; Organomagnesium compounds; Functionalized methyl carbanions
1. Introduction
In 1941 Gilman [1] discovered that SnR4 (Rꢁ
reacts with butyllithium yielding LiR and SnBu4. Since
then organotin compounds rank amongst the most
potent and versatile reagents for transmetallation reac-
tions according to Scheme 1 both in stoichiometric
reactions to prepare other organometallics and in
2. Results and discussion
/aryl)
Diorganomagnesium and Grignard reagents were
found to react with sulfur-functionalized methyltin
compounds nBu3SnCH2S(O)iR (iꢁ
ratio yielding sulfur-functionalized methylmagnesium
compounds (Scheme 2). These SnÃMg transmetallation
reactions were performed in THF, THFꢀEt2O or THFꢀ
/
0, 1, 2) in 1:1 molar
/
/
/
heptane at room temperature. Results are shown in
Table 1. The transmetallation reactions of sulfinyl-
catalytic CÃ
/
C bond formation reactions using them as
starting materials. Since the 1970s, SnÃLi transmetalla-
tions have been broadly applied for the preparation of
/
methyl- (iꢁ
/
1) and sulfonylmethyltin compounds (iꢁ
/
2) were complete within 1 h. On the other hand,
sulfanylmethyltin compounds nBu3SnCH2SR reacted
functionalized methyllithium compounds LiCH2YRn
(YRn ꢁ
/
NR2, OR, SR, . . .) [2]. Surprisingly, SnÃ
/Mg
within 9ꢀ12 days to a small extent only, except for
/
transmetallations were described only very recently,
namely those of tetraalkynylstannanes with Grignard
reactions of nBu3SnCH2SPh with MgMeX and MgMe2
(entries 2 and 8). In these cases, the degree of conversion
reagents [3]. Here, we report on a broader scope SnÃ
transmetallation reactions of functionalized methyltin
compounds nBu3SnCH2Y(O)iRx (Y(O)iRx ꢁSR,
S(O)R, S(O)2R, P(O)Ph2) and of nBu3SnCH2YMe2
(YꢁP, N) using LinBu as precatalyst.
/Mg
amounts to ꢀ/85% within 9 days. Interestingly, use of
/
/
Scheme 1.
* Corresponding author. Tel.: ꢂ
27028.
E-mail address: steinborn@chemie.uni-halle.de (D. Steinborn).
/
49-345-55-25620; fax: ꢂ49-345-55-
/
Scheme 2.
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 4 3 0 - 4

112
R.I. Yousef et al. / Journal of Organometallic Chemistry 655 (2002) 111ꢀ114
/
Mg(nBu)sBu in 1:1 molar ratio (entries 9 and 10)
resulted in the transfer of the n-butyl group that was
sometimes accompanied by a transfer of the s-butyl
group to a small extent (B
compound (nBu3SnCH2S(O)iR : Mg(nBu)sBuꢁ
1) a further transmetallation yielding Mg[CH2S(O)iR]2
took place*if to any*to a small extent only.
/
10%). Using an excess of tin
/
2ꢀ3 :
/
Scheme 3.
/
/
Analogous reactions were carried out with other
heteroatom-functionalized methyltin compounds using
n-butylmagnesium halides as organomagnesium re-
agents. Aminomethyltin compounds nBu3SnCH2NR2
able to undergo SnÃ
/
Mg transmetallation due to en-
hanced carbanionoid character of the methyl groups [5].
Dimethylmagnesium, prepared by the ‘dioxane
method’ [6], contained 1ꢀ
a corresponding amount of the organolithium com-
pound was deactivated in metathesis reaction
(MgRXꢂLiR?0MgRR?ꢂLiX). Thus, the amount of
/5% residual halide. Therefore,
(NR2ꢁ
/
NMe2, NMePh, NPh2) did not undergo SnÃ
/Mg
transmetallation (10 h, r.t.). Phosphinomethyltin com-
pounds nBu3SnCH2PPh2 and nBu3SnCH2PMe2 reacted
a
/
/
/
to an extent of 5ꢀ
/
10% and 1ꢀ3% (10 h, r.t.), respec-
/
LinBu to be added has to exceed the halide content.
Entry 5 in Table 2 makes clear that a content of about 2
mol% of active organolithium compound is sufficient to
tively. Under the same reaction conditions, the phos-
phinoylmethyl compound nBu3SnCH2P(O)Ph2 was
found to react quantitatively with Mg(nBu)Br yielding
Sn(nBu)4 and Mg[CH2P(O)Ph2]Br.
catalyze the SnÃ
/
Mg transmetallation reaction.
All SnÃMg transmetallation reactions described here
/
As shown for dimethylamino- and dimethylphosphi-
are in accordance with the general trend for transme-
tallations in Scheme 1, that the more electronegative
ligand tends to be bound to the more electropositive
metal [2a,7]. Thus, dipole stabilized carbanions [8]
nomethyltin compounds nBu3SnCH2YMe2 (Yꢁ
SnÃMg transmetallation can be enforced by addition of
substoichiometric amounts of n-butyllithium (Scheme 3,
Table 2): At first, to these tin compounds 10ꢀ20 mol%
of LinBu (entries 1ꢀ4) was added forming the corre-
/N, P),
/
ꢃCH2Y(O)iRx (iꢁ
than those without such dipole stabilization (iꢁ
/1, 2) are significantly more reactive
/
/0). In
/
the latter case the transmetallation may be enforced to
proceed by adding catalytic amounts of organolithium
compounds. Further investigations are in progress to
elaborate the synthetic potential of these new transme-
tallation reactions.
sponding amounts of Sn(nBu)4 and LiCH2YMe2. The
following addition of equimolar amounts of MgMe2
resulted in complete conversion of the remained
nBu3SnCH2YMe2 yielding Sn(nBu)3Me and Mg(CH2Y-
Me2)Me within 1 day (Yꢁ
/
N) and 4 days (Yꢁ
/P).
The mechanism of these SnÃ/Mg transmetallations
catalyzed by organolithium compounds has not been
investigated yet. As experimentally proved by 119Sn-
NMR spectroscopy and described in lit. [4], the first step
3. Experimental
is a SnÃ
(Scheme 4, a). Then, the reaction could proceed via
MgÃLi (b) and SnÃLi transmetallations (c). On the
other hand, LiCH2YMe2 could form with MgMe2
/
Li transmetallation yielding LiCH2YMe2
3.1. General comments
/
/
Functionalized methyltin compounds nBu3SnCH2-
a
Y(O)iRx (Yꢁ/S, P, N) were prepared according to
magnesate complex Li[MgMe2(CH2YMe2)] being cap-
published procedures and in analogy to that [4,9].
Table 1
a
Degree of conversion (in%) and reaction time at room temperature for SnÃMg transmetallation reactions according to Scheme 2
Entry
R
nBu3SnCH2SR
12 days 9 days
10ꢀ30
nBu3SnCH2S(O)R
nBu3SnCH2S(O)2R
Reaction time
1 h
1 h
1
2
MgMeX (XꢁCl, Br, I)
Me
Ph
/
ꢀ95
ꢀ95
85ꢀ/95
ꢀ95
ꢀ95
ꢀ95
ꢀ95
ꢀ95
3
Mg(nBu)X (XꢁCl, Br)
MgPhX (XꢁCl, Br)
MgMe2
Me
Ph
B5
B5
10
80ꢀ
90ꢀ
95
80ꢀ
/
95
4
B10
B5
/95
5
Me
Ph
6
/90
7
Me
Ph
ꢀ95
ꢀ95
ꢀ95
ꢀ95
8
ꢀ95
B5
9
10
Mg(nBu)sBu
Me
Ph
B5
a
Determined by 119Sn-NMR spectroscopy.

R.I. Yousef et al. / Journal of Organometallic Chemistry 655 (2002) 111ꢀ
/114
113
Table 2
SnÃMg transmetallation reactions in the presence of substoichiometric amounts of LinBu according to Scheme 3 (degree of conversionꢀ95%)
Entry
Y in nBu3SnCH2YMe2
[Sn]:[MgMe2]:[LinBu]
Solvent
[nBu3SnMe]:[Sn(nBu)4]
a
1
2
3
4
5
P
1:1:0.2
1:1:0.1
1:1:0.2
Hexaneꢀ
Hexaneꢀ
Hexaneꢀ
Hexaneꢀ
Hexaneꢀ
/
Et2O
Et2O
THF
THF
THF
0.8:0.2
0.9:0.1
0.8:0.2
0.9:0.1
0.93:0.07
a
P
/
b
P
/
b
N
N
1:1:0.1
1:1:0.07
/
b
/
a
MgMe2 contains ca. 1 mol% Brꢃ
MgMe2 contains ca. 5 mol% Clꢃ
.
.
b
3.3. SnÃ
/
Mg transmetallation reactions catalyzed by
LinBu (Table 2)
At ꢃ
/
78 8C, to nBu3SnCH2YMe2 (Yꢁ/N, P; 1.0
mmol) in n-hexane (5 ml) LinBu (0.07ꢀ/0.2 mmol) in
n-hexane was added. After stirring for 15 min at room
temperature (r.t.), MgMe2 (1.0 mmol) in THF or ether
was added at ꢃ
reaction mixture was allowed to warm to r.t. Reactions
were complete after 1 day (YꢁN) and 4 days (YꢁP).
Products were identified by 119Sn-NMR spectroscopy
and after hydrolysis with H2OꢀTHF (1/4) at ꢃ78 8C
by means of GCꢀMS.
/
78 8C. After stirring for 30 min, the
Scheme 4.
/
/
/
/
Grignard reagents (1ꢀ
/
3
M
in THF or Et2O),
/
Mg(nBu)sBu (1 M in n-heptane) and LinBu (1.6 M in
n-hexane) were commercially (Aldrich, Fluka) available.
MgMe2 in THF with a residual content of about 5 mol%
Clꢃ and in Et2O with a residual content of about 1
mol% Brꢃ, respectively, was prepared from Mg(Me)Cl
and Mg(Me)Br according to the ‘dioxane method’ [6].
NMR spectra were recorded on Varian NMR spectro-
meters (Gemini 2000, Unity 500) using SnMe4 (internal
reference) and H3PO4 (external reference) for 119Sn and
3.4. 119Sn chemical shifts
nBu3SnCH2SR: d ꢃ
(a). nBu3SnCH2S(O)Ph: d ꢃ
S(O)2R: d 15.8 (RꢁMe), ꢃ
nBu3SnCH2NR2: d ꢃ34.1 (R2ꢁMe2), ꢃ
MePh), ꢃ24.7 (R2ꢁPh2) (b). nBu3SnCH2PR2: d
73.3 Hz (R2ꢁMe2), d ꢃ10.2,
81.0 Hz (R2ꢁPh2) (b). nBu3SnCH2-
55.0 Hz (b). (a) Relative
/
17.6 (Rꢁ
20.1 (a). nBu3SnCH2-
12.7 (RꢁPh) (a).
20.7 (R2ꢁ
/
Me), ꢃ
/
12.5 (Rꢁ
/
Ph)
/
ꢃ
/
/
/
/
/
/
/
/
/
/
2
ꢃ
/
10.6, J119Sn,31P
2J119Sn,31P
P(O)Ph2: d ꢃ
ꢁ
/
/
/
31P measurements, respectively. GCꢀ
were carried out on an HP 5890 Series II/HP 5972
(HewlettꢀPackard).
/
MS investigations
ꢁ
/
/
2
/
6.4, J119Sn,31P
ꢁ
/
to SnMe4 as internal reference; solvent: THF accom-
panying the organomagnesium starting materials sol-
/
vent (diethyl etherꢀheptane). (b) Relative to SnMe4 as
/
external reference, solvent: CDCl3.
3.2. SnÃ/Mg transmetallation reactions (Table 1)
Reactions were performed in NMR tubes strictly
under anaerobic conditions. The NMR tubes were filled
in a Glove Box (Fa. M. Braun, Garching) with,
typically, nBu3SnCH2S(O)iR (0.2 mmol), magnesium
Acknowledgements
Financial support from the Deutsche Forschungsge-
meinschaft and Fonds der Chemischen Industrie as well
as gifts of chemicals by Merck (Darmstadt) are grate-
fully acknowledged.
reagent (0.2 mmol using 1ꢀ3 molar solutions), SnMe4 as
/
internal standard (ca. 0.08 mmol) and THF (0.5 ml).
Reactions were monitored by 119Sn-NMR spectroscopy.
No other signals were detected than those from the
(unreacted) starting compound (nBu3SnCH2S(O)iR)
References
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/
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/
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