Preparation of benzylstannanes by zinc-mediated coupling of benzyl bromides with organotin derivatives. Physicochemical characterization and crystal structures

Article abstract of DOI:10.1021/om9507742

Benzyltrialkyl- (1-13) and benzyltriphenylstannanes (16-22) have been easily prepared in a one-pot synthesis via coupling reaction of benzyl bromide derivatives (C₆H₅CH₂Br and XYC₆H₃CH₂Br, X = H, Y = o-, m-, p-CH₃, o-, m-, p-F, o-, m-Cl, and p-Br; X = o-F, Y = p-Br) with R₃SnCl compounds (R = Et, Pr, Bu, and Ph) in THF/H₂O (NH₄Cl) medium mediated by zinc powder. Such coupling also occurs with (Bu₃Sn)₂O. Dibenzyldibutylstannane (15) is prepared by reaction of benzyl bromide with Bu₂SnCl₂ or (Bu₂SnCl)₂O, and (2-naphthylmethyl)tributylstannane (14) by reaction of 2-(bromomethyl)naphthalene with Bu₃SnCl. ¹³C-and ¹¹⁹Sn-NMR data are reported for all compounds, and M?ssbauer data for benzyltributylstannanes 10 and 11 and benzyltriphenylstannanes 16-18 and 20-22. The crystal structures of Ph₃SnBn, with Bn = o- (17) and m-ClC₆H₄CH₂ (18) and o- (20) and m-FC₆H₄-CH₂ (21) have been determined.

Full text of DOI:10.1021/om9507742

Organometallics 1996, 15, 1645-1650
1645
P r ep a r a tion of Ben zylsta n n a n es by Zin c-Med ia ted
Cou p lin g of Ben zyl Br om id es w ith Or ga n otin
Der iva tives. P h ysicoch em ica l Ch a r a cter iza tion a n d
Cr ysta l Str u ctu r es
Daniele Marton, Umberto Russo, Diego Stivanello, and Giuseppe Tagliavini*
Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Universita´ di Padova,
Via Marzolo 1, I-35131 Padova, Italy
Paolo Ganis
Dipartimento di Chimica, Universita´ di Napoli, Via Mezzocannone 4, I-80134 Napoli, Italy
Giovanni Carlo Valle
Centro di Studi sui Biopolimeri del CNR, Via Marzolo 1, I-35131 Padova, Italy
Received September 29, 1995X
Benzyltrialkyl- (1-13) and benzyltriphenylstannanes (16-22) have been easily prepared
in a one-pot synthesis via coupling reaction of benzyl bromide derivatives (C6H5CH2Br and
XYC6H3CH2Br, X ) H, Y ) o-, m-, p-CH3, o-, m-, p-F, o-, m-Cl, and p-Br; X ) o-F, Y ) p-Br)
with R3SnCl compounds (R ) Et, Pr, Bu, and Ph) in THF/H2O (NH4Cl) medium mediated
by zinc powder. Such coupling also occurs with (Bu3Sn)2O. Dibenzyldibutylstannane (15)
is prepared by reaction of benzyl bromide with Bu2SnCl2 or (Bu2SnCl)2O, and (2-naphthyl-
methyl)tributylstannane (14) by reaction of 2-(bromomethyl)naphthalene with Bu3SnCl. 13C-
and 119Sn-NMR data are reported for all compounds, and Mo¨ssbauer data for benzyltribu-
tylstannanes 10 and 11 and benzyltriphenylstannanes 16-18 and 20-22. The crystal
structures of Ph3SnBn, with Bn ) o- (17) and m-ClC6H4CH2 (18) and o- (20) and m-FC6H4-
CH2 (21) have been determined.
In tr od u ction
method based on a Wurtz-type coupling reaction medi-
ated by zinc powder, as shown in eqs 1 and 2, respec-
tively.
The considerable development over recent decades in
the use of organotin compounds as reagents or inter-
mediates in organic synthesis1 has prompted the prepa-
ration of many new organotin compounds and the
development of new rapid and convenient synthetic
procedures, some of which are based on the use of water
or water-cosolvent media. In particular, water has
been successfully used as reaction medium in preparing
tribenzyltin chlorides in a one-pot synthesis by reacting
at 100 °C benzyl halide derivatives with tin powder2,3
and trialkyltin chlorides from dialkyltin dichlorides and
tin powder at 100 °C.4 Recently,5 we have successfully
used water-cosolvent media for the direct synthesis
under mild conditions of allyl- and allenylstannanes as
well as hexaaryldistannanes through a new preparative
nRBr + R′4-nSnXn cosolvent/H O (salt)/Zn8 R′4-nSnRn (1)
2
r.t., stirring
R ) allyl or allyl-like group, propargyl;
R′ ) Bu, Ph; X ) Cl, I, OH; n ) 1, 2
2R′3SnX THF/H O (NH Cl)/Zn8 R′3Sn-SnR′3
(2)
2
4
r.t., stirring
R′ ) Ph, m- and p-Tol; X ) Cl, I, OH
As an extension of this last method, we have prepared
several mixed benzylorganostannanes (1-22) by stirring
benzyl bromides with tri- and diorganotin derivatives
in a heterogeneous medium such as THF/H2O (NH4Cl)/
Zn at ambient temperature. Most of the synthesized
compounds are new, and 13C- and 119Sn-NMR as well
as some Mo¨ssbauer data have been collected. The
crystal structures of the compounds Ph3SnBn where Bn
) o-Cl- (17), m-Cl- (18), o-F- (20), and m-FC6H4CH2-
(21) have been determined.
X Abstract published in Advance ACS Abstracts, February 15, 1996.
(1) For general reviews, see: Davies, A. G.: Smith, P. J . In
Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G.
A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982. Pereyre, M.;
Quintard, J . P.; Rahm, A. In Tin in Organic Synthesis; Butterworths:
London, 1987; p 185. Yamamoto, Y. Acc. Chem. Res. 1987, 20, 243.
Wardell, J . L. In Chemistry of Tin; Harrison, P. G., Ed.; Blackie:
Glasgow, Scotland, 1989; p 315.
(2) Sisido, K.; Takeda, W.; Kinugawa, Z. J . Am. Chem. Soc. 1961,
83, 538.
Resu lts a n d Discu ssion
(3) Sisido, K.; Kozima, S.; Hanada, T. J . Organomet. Chem. 1967,
9, 99.
(4) Sisido, K.; Kozima, S. J . Organomet. Chem. 1968, 11, 503.
(5) Carofiglio, T.; Marton, D.; Tagliavini, G. Organometallics 1992,
11, 2961. Gyldenfeldt, F.; Marton, D.; Tagliavini, G. Organometallics
1994, 13, 906.
P r ep a r a tion of Ben zylsta n n a n es. Reactions be-
tween R3SnCl (R ) Et, Pr, Bu and Ph), (Bu3Sn)2O, Bu2-
SnCl2 and (Bu2SnCl)2O and various benzyl bromide
derivatives have been carried out in a three-phase THF/
0276-7333/96/2315-1645$12.00/0 © 1996 American Chemical Society

1646 Organometallics, Vol. 15, No. 6, 1996
Marton et al.
Ta ble 1. P r ep a r a tion of Mixed Ben zylsta n n a n es fr om Tr i- a n d Dior ga n otin Der iva tives a n d Ben zyl
Br om id es In THF /H2O/Zn Med iu m a
reagent
entry
no.
amt,
g
amt,
g
product amt,
g (yield, %)
anal.: calcd (found) for
C, H, halogen (%)
organotin
Et3SnCl
RBr (R)
product (no.)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
7.4 C6H5CH2
7.4 p-CH3C6H4CH2
8.7 C6H5CH2
8.7 m-CH3C6H4CH2
8.7 p-CH3C6H4CH2
10.0 C6H5CH2
10.5 C6H5CH2SnEt3 (1)
12.0 p-CH3C6H4CH2SnEt3 (2)
10.5 C6H5CH2SnPr3 (3)
12.0 m-CH3C6H4CH2SnPr3 (4)
12.0 p-CH3C6H4CH2SnPr3 (5)
10.5 C6H5CH2SnBu3 (6)
10.3 (85)
5.6 (58)
7.3 (70)
6.3 (59)
8.0 (74)
10.3 (86)
9.3 (80)
8.5 (70)
8.8 (72)
7.0 (58)
11.1 (87)
10.1 (80)
12.4 (88)
14.1 (91)
53.48 (53.82), 5.87 (5.70)
54.95 (55.24), 6.26 (6.05)
56.67 (56.61), 8.32 (8.40)
57.82 (57.33), 8.56 (8.64)
57.82 (58.38), 8.56 (8.64)
59.87 (59.73), 8.99 (9.08)
Pr3SnCl
Bu3SnCl
(Bu3Sn)2O
Bu3SnCl
9.2 C6H5CH2
10.5
6
10.0 o-CH3C6H4CH2
10.0 m-CH3C6H4CH2
10.0 p-CH3C6H4CH2
10.0 o-ClC6H4CH2
10.0 m-ClC6H4CH2
10.0 p-BrC6H4CH2
12.0 o-CH3C6H4CH2SnBu3 (7)
12.0 m-CH3C6H4CH2SnBu3 (8)
12.0 p-CH3C6H4CH2SnBu3 (9)
12.6 o-ClC6H4CH2SnBu3 (10)
12.6 m-ClC6H4CH2SnBu3 (11)
15.4 p-BrC6H4CH2SnBu3 (12)
60.78 (60.65), 9.18 (9.29)
60.78 (60.89), 9.18 (9.25)
60.78 (61.03), 9.18 (9.09)
54.91 (54.77), 8.00 (7.95), 8.53 (8.46)
54.91 (55.00), 8.00 (8.08), 8.53 (8.48)
49.59 (49.83), 7.23 (7.30), 10.74 (10.68)
47.73 (46.85), 6.74 (7.03), 3.97 (3.87),b
16.73 (16.90)c
64.36 (64.06), 7.98 (8.00)
63.95 (63.99), 7.32 (7.38)
10.0 o-F-, p-BrC6H3CH2 16.5 o-F-, p-BrC6H3CH2SnBu3 (13)
d
15
16
17
18
19
20
21
22
23
24
10.0 C10H7CH2
9.5 C6H5CH2
8.5 C6H5CH2
13.6 C10H7CH2SnBu3e (14)
21.4 (C6H5CH2)2SnBu2 (15)
15.7 15
10.5 C6H5CH2SnPh3 (16)
12.6 o-ClC6H4CH2SnPh3 (17)
12.6 m-ClC6H4CH2SnPh3 (18)
15.4 p-BrC6H4CH2SnPh3 (19)
11.6 o-FC6H4CH2SnPh3 (20)
11.6 m-FC6H4CH2SnPh3 (21)
11.6 p-FC6H4CH2SnPh3 (22)
8.8 (67)
10.4 (81)
8.1 (63)
9.4 (69)
13.0 (89)
8.8 (60)
13.9 (75)
10.3 (73)
10.0 (71)
8.2 (58)
Bu2SnCl2
(Bu2SnCl)2O
Ph3SnCl
11.8 C6H5CH2
68.07 (67.96), 5.03 (4.97)
11.8 o-ClC6H4CH2
11.8 m-ClC6H4CH2
11.8 p-BrC6H4CH2
11.8 o-FC6H4CH2
11.8 m-FC6H4CH2
11.8 p-FC6H4CH2
63.14 (63.02), 4.45 (4.39), 7.45 (7.30)
63.14 (63.10), 4.45 (4.49), 7.45 (7.50)
57.73 (57.94), 4.07 (4.01), 15.38 (15.03)
65.40 (65.67), 4.61 (4.70), 4.14 (4.30)
65.40 (65.35), 4.61 (4.70), 4.14 (4.19)
65.40 (65.48), 4.61 (4.65), 4.14 (4.09)
a
Except for entries 7, 16 and 17, all runs have been performed with the following amounts of components: 30.7 mmol of organotin,
61.4 mmol of organic bromide, and 61.4 mmol (4.01 g) of Zn powder (325 mesh, from Aldrich) in the molar ratio 1:2:2, respectively, in 25
mL of THF and 50 mL of H2O saturated with NH4Cl; for entry 7, 15.35 mmol of organotin, 61.4 mmol of organic bromide, and 61.4 mmol
(4.01 g) of Zn in the molar ratio 1:4:4, respectively; for entry 16, 31.25 mmol of organotin, 125.1 mmol of organic bromide, and 125.1 mmol
(8.18 g) of Zn in the molar ratio 1:4:4, respectively; for entry 17, 15.35 mmol of organotin, 92.0 mmol of organic bromide, and 92.0 mmol
b
d
(6.01 g) of Zn in the molar ratio 1:2:2 respectively. F (%). c Br (%). 2-Naphthylmethyl. e (2-Naphthylmethyl)trimethylstannane.
H2O(NH4Cl saturated)/Zn medium. This direct proce-
dure is very simple and rapid if compared with those
dealing with known, customary methods.6-10 In fact,
the products are obtained under mild reaction conditions
in air and at ambient temperature. Table 1 shows the
experimental data and results for benzylorganostan-
nanes 1-22, most of which have been prepared here
for the first time in yields in the range 58-90%.
All coupling reactions have been performed using
benzyl bromides, which gave better results than the
corresponding chlorides. Use of a cosolvent has been
limited to THF because workup in the case of cyclohex-
ane and other solvents previously used for allylations5
produced poor results. The coupling reactions of benzyl
bromides and organotin derivatives behave similarly to
those of allyl bromides.5 These between benzyl bro-
mides and R3SnCl compounds to form benzylstannanes
are accompanied by side reactions such as dimerization
of R3Sn and benzyl species and the reduction of the
bromides to toluene derivatives.12
We believe that the mechanistic aspects of the tin
benzylation are analogous to those proposed in the case
of allylation.5 Radical ions pairs [C6H5CH2Br]-• Zn+•
are formed by single-electron transfer (SET) from zinc
metal to the organic bromide. Subsequently, the radical
ions [C6H5CH2Br]-• adsorbed on the metal surface are
trapped by R3SnX molecules to form benzylstannanes.
Side reactions, such as coupling and reduction of benzyl
species, can be ascribed to the formation of free radicals
[C6H5CH2]• adsorbed on the metal surface or freely
diffused in solution13 after desorption. Some chemical
evidence14 suggests the presence also of R3Sn radical
species under these experimental conditions.
Many reactions are characterized by high exother-
micity and are completed in the short time (5-10 min)
required for the addition of the organic bromide to the
system THF/H2O (NH4Cl)/Zn/organotin compound. Com-
plete disappearance of zinc powder is observed after this
time. Through this method there is no need to prepare
the organotin lithium or benzyllithium species as, for
instance, in the case of benzyltriphenylstannane (16),
which was prepared previously by reaction of triphenyl-
tin lithium and benzyl chloride8 in 22% yield (compare
with 69% of entry 18), and of (2-naphthylmethyl)-
tributylstannane (14), obtained by reaction of (2-naph-
thylmethyl)lithium with chlorotributylstannane11 in
57% yield (compare with 67% of entry 15). In addition,
dibenzyldibutylstannane (15) is easily obtained by
coupling either Bu2SnCl2 (entry 16) or (Bu2SnCl)2O
(entry 17) with benzyl bromide in the ratio 1:4 and 1:6,
respectively. In the case of Bu2SnCl2, benzyldibutyltin
chloride is formed as an intermediate which can be
recovered in 50-75 % yield together with dibenzyldibu-
tyltin when 1:2 and 1:1 molar ratios are employed.
(12) In THF/H2O (NH4Cl), zinc powder reacts with benzyl bromide
to give both dibenzyl (about 20%) and toluene (80%).
(13) Garst, J . F. Acc. Chem. Res. 1991, 24, 95.
(14) As previously reported,5 ditin compounds are thought to arise
from the trapping of radical ions [R3SnCl]-• adsorbed on the zinc
surface with R3SnCl molecules. However, also [R3Sn]• radicals could
form ditin compounds. We have ascertained that Bu3SnCl reacts with
several alkyl iodides RI (R ) Me, Et, Pr, Bu, Pent) in THF/H2O (NH4-
Cl)/Zn powder to give mixtures of Bu3SnR and Bu3SnI. The former
may be formed from the coupling of the two reagents, while the latter
could arise from the following free-radical halogen abstraction:15 RI +
Bu3Sn• f Bu3SnI + R•.
(6) Kraus, C. A.; Bullard, R. H. J . Am. Chem. Soc. 1926, 48, 2136.
(7) Kipping, F. B. J . Chem. Soc. 1928, 131, 2365.
(8) Gilman, H.; Rosenberg, S. D. J . Am. Chem. Soc. 1952, 74, 531.
(9) Peddley, J . B.; Skinner, H. Trans. Faraday Soc. 1959, 55, 544.
(10) Gilman, H.; Rosenberg, S. D. J . Org. Chem. 1953, 18, 1554.
(11) Tius, M. A.; Gomez-Galeno, J . Tetrahedron Lett. 1986, 27, 2571.

Preparation of Benzylstannanes
Organometallics, Vol. 15, No. 6, 1996 1647
Ta ble 2. P h ysicoch em ica l Da ta for Ben zyltr ia lk yl- (1-13), (2-Na p h th ym eth yl)tr im eth yl- (14), a n d
Dibu tyld iben zyl-sta n n a n es (15)a
119Sn-b and 13C-NMRc chem shifts, ppm (1J (119Sn-13C), Hz)
compd
no.
bp,
°C/mm Hg
Sn
C(4) C(3) C(2)
C(1)
C(1′)
C(2′) C(3′) C(4′) C(5′) C(6′) C(7′) C(8′) C(9′) C(10′) C(11′)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
88-90/0.06d
94-96/0.07
107-109/0.05 -15.8
107-108/0.04 -16.5
112-116/0.05 -17.7
130-131/0.04 -12.5 13.4 27.4 29.1
132-135/0.04 -12.8 13.7 27.5 29.2
136-139/0.05 -13.4 13.8 27.6 29.3
131-136/0.04 -13.9 13.8 27.6 29.3
-2.8e
-3.9
11.0f 0.7 (323) 17.1 (234) 143.2 127.0 128.4 123.2 128.4 127.0
11.0 0.6 (322) 16.5 (230) 139.8 127.0 129.1 131.9 129.1 127.0 20.9
19.0 20.5 12.4 (317) 18.4(216) 143.1 127.0 128.3 123.1 128.3 127.0
19.0 20.5 12.4 (316) 18.3 (-)g
142.9 127.8 137.2 124.0 128.2 124.2 21.4
19.0 20.5 12.4 (314) 17.7 (216) 139.8 126.8 129.0 131.8 129.0 126.8 20.9
9.2 (316) 18.2 (245) 143.1 126.9 128.2 123.0 128.2 126.9
9.8 (313) 16.2 (298) 141.4 132.8 129.8 123.1 126.0 127.4 20.2
9.4 (316) 18.2 (248) 142.9 127.8 137.1 123.9 128.2 124.2 21.4
9.4 (315) 17.7 (256) 139.8 127.0 129.0 131.8 129.0 127.0 20.9
133-137/0.04 -7.5 13.7 27.5 29.1 10.1 (319) 17.2 (227) 142.0 131.8 129.1 124.2 126.5 128.5
135-137/0.04 -9.4 13.7 27.5 29.2
175-180/0.2 -11.0 13.7 27.4 29.1
156-160/0.07 -6.7 13.7 27.4 29.1
9.5 (319) 18.2 (228) 143.9 127.1 134.2 123.1 129.3 125.0
9.4 (319) 17.7 (239) 142.5 128.5 131.1 116.2 131.1 128.5
9.7 (322) 10.6 (-)g
130.2 159.6 118.3 116.0 127.0 130.0
h
-11.1i 13.7 27.5 29.2
9.5 (315) 18.7 (202) 140.9 127.1 126.7 125.7 123.8 127.6 127.8 123.8 134.3 130.9
9.8 (319) 18.5 (248) 142.5 127.0 128.3 123.2 128.3 127.0
155-158/0.04 -17.0 13.7 27.3 28.8
8′
CH3
a
Carbon identification: for compounds 1-13 and 15:
Carbon identification for compound
3′ 4′
4
3
2
1
1′
2′
5′
C–C–C–C–Sn–C
6′
7′
3′
4′
4
3
2
1
1′
10′
11′
b
d
δ values refer to TMT as external standard. c δ values refer to TMS as internal standard. Bp 115
2′
9′
14:
C–C–C–C–Sn–C
5′
6′
8′
7′
°C/4 mmHg; see ref 16. e δ(119Sn) in CCl4 (saturated solution): -6.0 ppm; see ref 17. f δ(13C) 10.7, 0.5, 16.9, 143.1, 126.8, 128.2, 122.9,
g
h
i 4
128.2, 126.8; see ref 16. Not determined. Heavy oil. | J (119Sn-C-C-C-19F)| ) 14.7 Hz.
Ta ble 3. P h ysicoch em ica l Da ta for Ben zyltr ip h en ylsta n n a n esa
119Sn-b and 13C-NMRc chem shifts, ppm (1J (119Sn-13C), Hz)
compd
no.
mp, °C
Sn
C(4)
C(3,5) C(2,6)
C(1)
C(1′)
C(2′)
C(3′)
C(4′)
C(5′)
C(6′)
C(7′)
16
17
18
19
20
21
22
90-90.5d
65.5-66
40-40.5
-117.1e
-115.1
-115.0
128.9
128.8
129.4
129.8
128.4
128.3
128.4
128.4
128.5
128.5
128.5
137.0
136.7
136.8
136.8
136.8
136.9
137.0
138.2 (496) 20.0 (333) 140.5 127.8 128.4 123.8 128.4 127.8
138.1 (503) 19.2 (319) 139.2 132.1 126.6 125.1 129.0 132.1
137.5 (510) 19.7 (319) 142.8 127.6 133.9 123.8 129.4 125.7
64.5-65.5 -117.1
137.6 (-)f
138.0 (-)f
137.7 (-)f
138.0 (-)f
19.4 (-)f
139.7 129.3 131.2 117.2 131.2 129.3
58-58.5
96-96.5
94.5-95
-113.6g 128.9
12.8 (313) 127.3 159.8 114.9 125.4 123.8 128.7
20.1 (322) 143.5 114.4 162.3 129.5 110.7 123.4
-116.0h 129.1
-116.9i
128.7
18.9 (-)f
136.0 129.4 115.1 160.1 115.1 129.4
3
2
3′ 4′
Y
a
b
Carbon identification:
CDCl3 solution, δ values refer to TMT as external standard. c CDCl3 solution, δ
1′
Sn–C
1
2′
4
5′
6′
5
6
7′
d
g 4
values refer to TMS as internal standard. Mp 90-91 °C; see ref 8. e δ(119Sn): -118 ppm; see ref 18. f Not determined. | J (119Sn-C-
C-C-19F)| ) 20.2 Hz. | J (119Sn-C-C-C-C-19F)| ) 11.0 Hz. | J (119Sn-C-C-C-C-C-19F)| ) 25.7 Hz.
h
5
i 6
P h ysicoch em ica l Da ta . Physicochemical data for
compounds 1-15 and 16-22 are listed in Tables 2 and
3, respectively. Among these, only compounds 1 and
16 have been characterized previously.8,16-18
tylbenzene; a similar behavior is observed in benzyl-
stannanes 1, 3, 6, and 16 . This is in line with the
pronounced hyperconiugative, electron-releasing ability
of the CH2SnR3 substituents.20 Moreover, the δ(13C)
values of the benzyl carbons are consistent with
the theoretical substituent-induced chemical shift
The 119Sn-NMR chemical shifts range from -2.7 to
-17.7 ppm for compounds 1-14 and from -113.6 to
-117.1 ppm for 16-22. The single values are strongly
dependent upon the nature and the position of the
substituents on the benzyl ring as well as upon the other
three organic groups bonded to tin. As an example, the
δ(119Sn) values for benzyltributylstannanes 6-13 clearly
become more negative the lower the electron-with-
drawing ability of the substituent (e.g., compare the
values of 7, 10, and 13).
1
values. The values of both J (119Sn-13Calkyl or phenyl) and
1J (119Sn-13Cbenzyl) coupling constants are in the range
expected for four-coordinate tin compounds.19,21 If the
former constants show no significant change on varying
the nature and the position of the benzyl substituent,
the latter exhibit a noticeable increase on the increasing
of the electron-donating ability of the substituent. This
behavior, albeit observed to a lesser extent, has been
described previously for trimethylphenylstannanes.19
As already reported for benzyltrimethylstannanes,19
the 13C-NMR resonance lines of C(5′) move to upfield
with respect to that of the analogue carbon in neopen-
4
The low | J (119Sn-C-C-C-19F)| values for 14 and 20
(14.7 and 20.2 Hz, respectively) exclude any coordinative
interaction between the metal and F in the ortho-
position.22
(15) Ingold, K. U.; Lusztyck, J .; Scaiano, J . C. J . Am. Chem. Soc.
1984, 106, 343. Neumann, W. P. Synthesis 1987, 665.
(16) Steinborn, D.; Buthge, M.; Taube, R.; Radeglia, R.; Schlothauer,
K.; Nowak, K. J . Organomet. Chem. 1982, 234, 277.
(17) McFarlane, W.; Maire, J . C.; Delmas, M. J . Chem. Soc., Dalton
Trans. 1972, 1862.
(18) Gielen, M. Bull. Soc. Chim. Belg. 1983, 92, 409.
(19) For benzyltrimethylstannanes and related compounds, see:
Doddrell, D.; Bullpitt, M. L.; Moore, C. J .; Fong, C. W.; Kitching, W.;
Adcock, W.; Gupta, B. D. Tetrahedron Lett. 1973, 665.
Mo1ssba u er Da ta . Some of the compounds (10, 11,
16-18, and 20-22) have been examined by Mo¨ssbauer
(20) Hanstein, W.; Berwin, H. J .; Traylor, T. G. J . Am. Chem. Soc.
1970, 92, 7476.
(21) Mitchell, T. H. J . Organomet. Chem. 1973, 59, 189.
(22) Kroth, H. J .; Schumann, H.; Kuivila, H. G., Schaeffer, C. D.,
J r.; Zuckerman, J . J . J . Am. Chem. Soc. 1975, 97, 1754.

1648 Organometallics, Vol. 15, No. 6, 1996
Marton et al.
Ta ble 4. Tin -119 Mo1ssba u er Sp ectr a l Da ta a t 80.0
K for Ben zyltr ibu tylsta n n a n es 10 a n d 11 a n d
Ben zyltr ip h en ylsta n n a n es 16-18 a n d 20-22
δ,a ∆EQ,
mm mm mm mm s-1
s-1 s-1 s-1 mmol-1 mp, °C
Γ,
A,b
compd
o-ClC6H4CH2SnBu3 (10) 1.60 0.57 0.99
m-ClC6H4CH2SnBu3 (11) 1.62 0.50 1.00
m-ClC6H4CH2SnPh3 (18) 1.52 0.29 0.85
0.323
0.431
0.501
0.498
0.563
0.639
40-40.5
58-58.5
65.5-66
90-90.5
94.5-95
96-96.5
o-FC6H4CH2SnPh3 (20)
1.51 0.29 0.88
o-ClC6H4CH2SnPh3 (17) 1.52 0.27 0.85
C6H5CH2SnPh3 (16)
p-FC6H4CH2SnPh3 (22)
1.51 0.30 0.87
1.53 0.33 0.80
m-FC6H4CH2SnPh3 (21) 1.53 0.28 0.87
a
b
Relative to room temperature, SnO2. Absorption area.
spectroscopy. The spectra of all the samples present a
single, slightly broad line, as expected for tetraorganotin
derivatives; however, a fitting to a symmetric doublet
gives better ø2 values and gives much narrower line
widths. The results obtained are reported in Table 4.
The quadrupole splitting values are obviously very small
and, at least in the case of the phenyl derivatives, in
good agreement with those calculated by means of the
point charge model (0.2 mms-1).23 The values for the
butyl derivatives 10 and 11 are somewhat larger,
probably as a consequence of slight deviations from the
ideal tetrahedral geometry. Moreover, the Mo¨ssbauer
spectra of 10 and 11 present also the highest line width,
due to structural disorder of the long and bulky butyl
groups. The isomer shift values are typical for this type
of compound and, within the butyl and phenyl series,
almost constant, within experimental error. As already
reported,24 strongly perturbing substituents on the
benzyl group do not appreciably affect the s-electron
density at the tin nucleus. The absorption area (see
Table 4) shows a linear positive dependence with the
melting points on going from 18 to 21.
F igu r e 1. Schematic view of the four molecular structures
down the Sn-C(1) axis (Sn overlaps C(1)). A refers to the
ortho- (20) and meta- (dotted) fluoro (21) derivatives; B
refers to the ortho-chloro derivative (17). For a given
configuration of the Ph3Sn group, C and D represent the
two stereoisomers of the meta-chloro derivative (18) present
in the crystal.
Cr ysta l Str u ctu r es. Single crystals of the o-chloro
(17), m-chloro (18), o-fluoro (20), and m-fluoro (21)
derivatives have been examined by X-ray analysis. The
molecular structures of these homologous compounds
are schematically shown in Figure 1 and, as an example,
in Figure 2 with the atom labeling. The relevant
geometrical parameters are given in Table 5.
The coordination about Sn is always consistent with
a virtually undistorted tetrahedral geometry, which
excludes any bond interaction between Sn and intra-
or intermolecular halogen atoms. Except for 17, all
these molecules show the expected staggered orientation
of the benzyl bond C(1)-C(2) with respect to the tri-
phenyltin group (σ ) C(2)-C(1)-Sn-C(20) ) -53 to
-68°). In all cases the plane of the benzyl ring forms
an angle æ of ca. 80° with the plane through Sn-C(1)-
C(2) (or -80° according to the left- or the right-handed
configuration of the usual propeller-shaped triphenyltin
group), which is in agreement with theoretical predic-
tions when π-π interactions are operating.25
F igu r e 2. ORTEP view of the ortho-fluoro derivative (20).
The atom labeling is the same for all the examined
compounds.
The ortho substitution of the halogen atom X seems
to be controlled by this angle. In fact, between the two
possible geometrically nonequivalent ortho-positions the
one is preferred which leads to the Sn‚‚‚X nonbonded
distance closest to the sum (Σ) of the corresponding van
der Waals radii. As an example, for 17 these distances
would be 3.7 and 4.28 Å, respectively; the former (ca.
0.25 Å shorter than Σ)26-28 is the one observed. The
orientation of the bond C(1)-C(2) found in this com-
pound, intermediate between staggered and eclipsed
(23) Parish, R. V. In Mo¨ssbauer Spectroscopy Applied to Inorganic
Chemistry; Long, G. J ., Ed.; Plenum Press: New York, 1987; Vol. 1,
Chapter 16.
(24) King, B.; Eckert, H.; Denney, D. Z., Herber, R. H. Inorg. Chim
Acta 1986, 122, 45.
(25) Hunter, C. A.; Sanders, J . K. M. J . Am. Chem. Soc. 1990, 112,
5525

Preparation of Benzylstannanes
Organometallics, Vol. 15, No. 6, 1996 1649
Ta ble 5. Selected Geom etr ica l P a r a m eter s for o-ClC6H4CH2Sn P h 3 (17), m -ClC6H4CH2Sn P h 3 (18),
o-F C6H4CH2Sn P h 3 (20), a n d m -F C6H4CH2Sn P h 3 (21)a
compd
17
18 (C)
18 (D)
20
21
Bond Lengths (Å)
2.187(4)
Sn-C(1)
Sn-C(8)
Sn-C(14)
Sn-C(20)
X-C(3)
2.150(9)
2.109(8)
2.118(9)
2.102(8)
1.660(9)b
2.161(5)
2.140(3)
2.148(3)
2.150(3)
2.166(6)
2.145(5)
2.139(5)
2.143(6)
1.363(8)c
2.168(9)
2.159(4)
2.155(4)
2.157(5)
2.140(3)
2.154(3)
2.159(3)
X-C(4)
1.704(3)b
1.315(8)c
X-C(6)
1.707(3)b
Bond Angles (deg)
110.9(4)
Sn-C(1)-C(2)
C(14)-Sn-C(1)
C(14)-Sn-C(8)
C(14)-Sn-C(20)
C(8)-Sn-C(1)
C(8)-Sn-C(20)
C(1)-Sn-C(20)
113.4(9)
107.2(5)
107.9(3)
111.0(3)
108.6(4)
106.2(4)
115.7(4)
115.7(4)
105.3(3)
108.2(2)
110.2(3)
113.9(3)
107.0(2)
112.7(2)
114.4(4)
105.0(3)
110.4(2)
111.0(2)
111.3(2)
106.2(3)
113.0(2)
113.1(5)
109.5(3)
109.2(3)
108.4(3)
113.0(3)
108.2(2)
108.3(3)
109.5(3)
109.3(2)
107.3(3)
110.3(3)
108.6(2)
111.8(2)
Torsion Angles (deg)
-60(1)
σ ) C(2)-C(1)-Sn-C(20)
æ ) C(3)-C(2)-C(1)-Sn
C(9)-C(8)-Sn-C(1)
C(15)-C(14)-Sn-C(1)
C(21)-C(20)-Sn-C(1)
-16(1)
78(1)
-128(1)
-119(1)
-145(1)
-68(1)
82(1)
-131(1)
-137(1)
-115(1)
-66(1)
80(1)
-141(1)
-157(1)
-106(1)
-54(1)
79(1)
-134(1)
-127(1)
-129(1)
94(1)
-137(1)
-130(1)
-126(1)
a
b
c
For labeling, see Figures 1 and 2. X ) Cl. X ) F.
conformation (σ ) 18°), arises from the necessity to
maintain the value of ca. 80° for the angle æ and to
relieve nonbonded interactions between Cl and phenyl
groups bonded to Sn. Actually, Cl is located at distances
from C(8) and C(14) of 4.37 and 3.81 Å, respectively;
for a staggered conformation they would be <3 and >5
Å, respectively. This does not occur in the case of the
o-fluoro derivative (20) owing to the much smaller steric
encumbrance of the fluorine atom.
In the meta-derivatives the halogen atoms are so far
away from Sn and its phenyl groups that the staggered
conformation of the benzyl ring, and the angle æ of ca.
80° as well, are retained. However, in these cases, for
a given configuration of the Ph3Sn group two meta-
stereoisomers of nearly the same internal conforma-
tional energy are theoretically predictable. As a matter
of fact, for the m-Cl derivative (18) we observe the
presence in the crystal of both the configurational
isomers (and their enantiomers) as individual structural
subunits. The crystals of the m-F derivative (21) here
examined contain only one stereoisomer, but the pos-
sibility of a second crystalline modification cannot be
excluded, even though not observed.
These findings are in some correlation with the
Mo¨ssbauer data. As reported above, they indicate an
almost regular increase of absorption area (see Table
4) on going from 18 to 21. Interestingly, 18 exhibits
the highest crystalline order (two different stereoiso-
mers arranged in the same crystal lattice) and 21 the
highest disorder as it derives from a presumably freer
libration of the benzyl group. The question arises
whether the Mo¨ssbauer absorption area can be assumed
to be a measure of the degree of order in the crystal.
Ta ble 6. Cr ysta l Da ta a n d Deta ils of In ten sity
Mea su r em en ts for o-ClC6H4CH2Sn P h 3 (17),
m -ClC6H4CH2Sn P h 3 (18), o-F C6H4CH2Sn P h 3 (20),
a n d m -F C6H4CH2Sn P h 3 (21)
compd
17
18
20
21
formula
C25H21ClSn C25H21ClSn C25H21FSn C25H21FSn
fw
475.58
8.046(1)
19.418(2)
6.987(1)
92.1(1)
101.7(1)
98.5(1)
1054.7
2
475.58
14.335(2)
16.750(2)
10.113(2)
95.1(1)
110.2(1)
75.3(1)
2204.3
4
459.13
9.829(2)
11.262(2) 11.604(2)
9.476(2)
92.2(1)
95.0(1)
82.3(1)
1035.2
2
459.13
10.645(2)
a/Å
b/Å
c/Å
9.945(1)
103.3(1)
111.3(1)
102.3(1)
1052.6
2
R/deg
â/deg
γ/deg
V/Å3
Z
dcalcd/g cm-3
F(000)
1.50
476
1.43
952
1.47
460
1.45
460
space group
cryst dimens/mm
T, K
P1h
P1h
P1h
P1h
ca. 0.3 × 0.3 × 0.3
298
radiation, λ/Å
graphite-monochromated Mo KR, 0.7107
µ/cm-1
12.29
11.76
11.17
11.19
scan speed/
deg min-1
take off angle/deg
2θ range/deg
unique reflns
reflns used for
refinementa
solution method
Rb (on Fo)
2.0 in the 2θ scan mode
3
3.0 e 2θ e 45
3725
1665
7746
5798
3654
3267
5079
3279
Patterson
0.050
0.052
1.263
0.032
0.037
0.820
0.46
0.044
0.053
1.247
0.63
0.048
0.051
1.160
0.95
c
Rw
GOFd
highest map resids 0.53
a
Fo2 > 2σ (Fo2). b R ) ∑||Fo| - |Fc||/∑|Fo|. c Rw ) [∑w(|Fo| - |Fc|)2/
∑w|Fo| ]1/2
.
GOF ) [∑w(|Fo| - |Fc|)2/(ND - NV)2]1/2
.
2
d
mercially available, were used as received. All employed
organotin derivatives were purified before use by well-known
conventional procedures.
Exp er im en ta l Section
Elemental analyses and boiling and melting points for all
compounds prepared are listed in Tables 1-3, respectively.
Characterization was made by means of 119Sn (33.35 MHz) and
13C (22.49 MHz) nuclear magnetic resonance spectroscopy
All manipulations were carried out at room temperature,
in air. Solvents, salts, and zinc powder (325 mesh), com-
(26) Pauling, L. In The Nature of the Chemical Bond; Cornell Univ.
Press: Ithaca, New York, 1960.
(27) Bondi, M. J . Phys. Chem. 1964, 68, 441.
(28) Spackman, M. A. J . Chem. Phys. 1986, 85, 6587.

1650 Organometallics, Vol. 15, No. 6, 1996
Marton et al.
using a J eol FX90Q Fourier transform NMR spectrometer.
Spectra of the triphenyltin derivatives, as CDCl3 solutions, and
of neat trialkyltin derivatives were recorded using Me4Si and
Me4Sn as internal and external standards, respectively.
Mo¨ssbauer analysis was carried out in transmission geom-
etry by means of a standard spectrometer using a source of
Sn in BaSnO3 matrix and a variable-temperature cryostat. The
zero of the velocity scale was the centroid of a high-purity
crystalline SnO2 sample.The velocity scale was determined by
a pure iron foil spectrum at room temperature. A standard
least-squares minimization routine was used to fit the spectra
profiles to Lorentzian lines.
P r ep a r a tion of Tr i- a n d Dia lk ylben zylsta n n a n es (En -
tr ies 1-17). In a round-bottomed two-necked flask (200 mL)
equipped with a condenser and dropping funnel, the appropri-
ate organotin halide was added to a THF/H2O (NH4Cl satu-
rated) mixture and an excess of zinc powder (quantities are
given in Table 1). With magnetic stirring, the appropriate
benzyl bromide (generally in 1:1 stoichiometric ratio with
respect to zinc) was added dropwise at a rate sufficient to
maintain a gentle reflux due to the exothermicity of the
reaction. The addition lasts about 5-10 min, during which
time disappearance of the zinc powder was noted. The
heterogeneous mixture was stirred until it had cooled to room
temperature (about 30 min). The organic layer was separated
and the THF was removed by means of rotary evaporator,
leaving a heavy liquid residue. This was distilled under
vacuum to afford the pure benzyltin compound. Yields, listed
in Table 1, are based on the amounts of the pure distilled
products.
benzyl bromide. After removal of THF from the separated
organic layer by means of rotary evaporator, a heavy solid-
liquid residue was obtained. Initial crystallization from
petroleum ether (40-60 °C) or n-hexane allowed the separation
of the organic dimer and Ph6Sn2 when they were formed as
byproducts. Pure samples of benzylstannanes were obtained
by repeated crystallization from anhydrous ethanol. Yields
of the purified products are listed in Table 1.
Cr ysta llogr a p h ic An a lysis. Crystal data, intensity data
collection, and processing details are presented in Table 6. The
data were obtained with a Philips PW-100 four-circle diffrac-
tometer with graphite monochromator. Intensity data were
collected at 20 °C using the 2θ scan method. Two reference
reflections, monitored periodically, showed no significant
variation in intensity. Data were corrected for Lorentz and
polarization effects and an empirical absorption correction was
applied to the intensities (Ψ scan). The positions of the Sn
and Cl atoms were determined from the three-dimensional
Patterson functions. All the remaining atoms, including some
of the hydrogen atoms, were located from successive Fourier
maps using SHELX-76.29 Anisotropic thermal parameters
were used for all the non-hydrogen atoms. Blocked-cascade
least-squares refinements converged to the conventional R
indexes given in Table 6.
Ack n ow led gm en t. We gratefully acknowledge sup-
port of this work by the Consiglio Nazionale delle
Ricerche (CNR, Rome) and the Ministero dell’Universita´
e della Ricerca Scientifica e Tecnologica (MURST,
Rome).
P r ep a r a t ion of Tr ip h en ylb en zylst a n n a n es (E n t r ies
18-24). The mixing procedure was the same as that described
above. The reactions are exothermic, and the zinc powder
disappears during the time (5-10 min) of the addition of the
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
parameters, positional parameters of all atoms, thermal
parameters, and complete bond lengths and bond angles (60
pages). Ordering information is given on any current mast-
head page.
(29) Sheldrick, G. M. In SHELX-76, a Computer Program for Crystal
Structure Determination; University of Cambridge: Cambridge, U.K.,
1976.
OM9507742