Condensation of diphenylsilane diol through organostannoxane catalysis: a case study

Article abstract of DOI:10.1021/om990970z

Small amounts of [Ph₂(OH)Sn]₂CH₂ effectively catalyze the condensation of Ph₂Si(OH)₂ to give cyclo-(Ph₂SiO)₄ in good yield. The reaction proceeds under remarkably mild conditions

Full text of DOI:10.1021/om990970z

3272
Organometallics 2000, 19, 3272-3279
Articles
Con d en sa tion of Dip h en ylsila n e Diol th r ou gh
Or ga n osta n n oxa n e Ca ta lysis: A Ca se Stu d y†
J ens Beckmann,‡ Klaus J urkschat,*,‡ Stephanie Rabe,‡ Markus Schu¨rmann,‡
Dainis Dakternieks,§ and Andrew Duthie§
Lehrstuhl fu¨r Anorganische Chemie II der Universita¨t Dortmund, D-44221 Dortmund,
Germany, and Centre for Chiral and Molecular Technologies, Deakin University,
Geelong 3217, Australia
Received December 7, 1999
Small amounts of [Ph2(OH)Sn]2CH2 effectively catalyze the condensation of Ph2Si(OH)2
to give cyclo-(Ph2SiO)4 in good yield. The reaction proceeds under remarkably mild conditions.
In contrast, the reaction of [Ph2(OH)Sn]2CH2 with Ph2Si(OH)2 in a stoichiometric ratio
quantitatively gives the six-membered stannasiloxane ring cyclo-Ph2Si(OSnPh2)2CH2 (1).
Compound 1 reacts slowly and irreversibly with Ph2Si(OH)2 to provide the eight-membered
stannasiloxane ring cyclo-O(Ph2SiOSnPh2)2CH2 (2) and [Ph2(OH)Sn]2CH2. The driving force
for this reaction is attributed to the release of ring strain in 1. Condensation of [Ph2(OH)Sn]2-
CH2 with diphenylsiloxanols HO(Ph2SiO)nH (n ) 2-4), t-Bu2Si(OH)2, and t-Bu2Ge(OH)2,
respectively, provides the metallastannoxane rings cyclo-O(Ph2SiOSnPh2)2CH2 (2), cyclo-
Ph2Si(OSiPh2OSnPh2)2CH2 (3), cyclo-O(Ph2SiOPh2SiOSnPh2)2CH2 (4), cyclo-t-Bu2Si(OSnPh2)2-
CH2 (5), and cyclo-t-Bu2Ge(OSnPh2)2CH2 (6). The molecular structures of 2 and 5 were
determined by X-ray diffraction.
In tr od u ction
organotin catalysts for instant mixtures with long pot-
lives in which the catalysts are activated by heat prior
to use.3
During the course of our studies on polystannasilox-
anes,4 we found that small amounts of [Ph2(OH)Sn]2-
CH2 catalyze the condensation of Ph2Si(OH)2 to give
cyclo-(Ph2SiO)4. Further investigations on this reaction
revealed the involvement of stannasiloxanes along the
reaction pathway.
The reactions described within this work can be
regarded as a case study on the condensation of orga-
nosilanols catalyzed by organostannoxanes, which, in
general, is relevant for the industrial curing of silicone
elastomers.
Among various industrial applications, organotin
compounds serve as catalysts for the curing of silicone
elastomers.1 The benefits of organotin catalysts, namely,
diorganotin dicarboxylates, are their high efficiency
under virtually neutral and mild conditions and their
low cost and comparatively low toxicity. Despite the
importance of the curing process, little attention has
been paid to the role of the catalysts. We are aware of
only two publications dealing with kinetic studies on
model curing reactions.2 Although stannasiloxanes were
assumed to be intermediates in these reactions, so far
there is no experimental proof for this assumption. More
recent works were focused on the preparation of latent
Resu lts a n d Discu ssion
† This work contains part of the Ph.D. thesis of S. Rabe, Dortmund
University, 1999.
The reaction in acetone of Ph2Si(OH)2 with catalytic
amounts of [Ph2(OH)Sn]2CH2 (10 mol % at 60 °C for 20
h) provided cyclo-(Ph2SiO)4 as a colorless precipitate in
good yield (eq 1).
‡ Universita¨t Dortmund.
§ Deakin University.
(1) (a) Evans, C. J . Tin Its Uses 1971, 89, 5. (b) van der Weij, F. W.
Makromol. Chem. 1980, 181, 2541. (c) Karpel, S. Tin Its Uses 1984,
142, 6. (d) Emblem, H. G.; J ones, K. Trans. J . Brit. Ceram. Soc. 1984,
79, 56. (e) Evans, C. J .; Karpel, S. Organotin Compounds in Modern
Technology. J . Organomet. Chem. Libr. 1985, 16, and patent literature
cited there.
(2) (a) Martyakova, N. I.; Dogloplosk, S. B.; Kagan, E. G.; Kostikyan,
T. S.; Petrukhno, L. A. J . Gen. Chem. (USSR) 1974, 44, 283. (b) Fierens,
P.; Vandendunghen, G.; Segers, W.; van Elsuwe, R. React. Kinet. Catal.
Lett. 1978, 8, 179.
(3) (a) J ousseaume, B.; Gouron, V.; Maillard, B.; Pereyre, M.
Organometallics 1990, 9, 1330. (b) J ousseaume, B.; Guillou, V.; Noiret,
N.; Pereyre, M.; France`s, J .-M. J . Organomet. Chem. 1993, 450, 97.
(c) J ousseaume, B.; Noiret, N.; Pereyre, M.; Saux, A. Organometallics
1994, 13, 1034.
The identity of cyclo-(Ph2SiO)4 was established by its
29Si NMR chemical shift (CDCl3) of -42.7 ppm and by
(4) (a) Beckmann, J .; J urkschat, K.; Schollmeyer, D.; Schu¨rmann,
M. J . Organomet. Chem. 1997, 543, 229. (b) Beckmann, J .; J urkschat,
K.; Mahieu, B.; Schu¨rmann, M. Main Group Metal Chem. 1998, 21,
113. (c) Beckmann, J .; Biesemans, M.; Hassler, K.; J urkschat, K.;
Martins, J . C.; Schu¨rmann, M.; Willem, R. Inorg. Chem. 1998, 37, 4891.
(d) Beckmann, J .; Mahieu, B.; Nigge, W.; Schollmeyer, D.; Schu¨rmann,
M.; J urkschat, K. Organometallics 1998, 17, 5697. (e) Beckmann, J .;
J urkschat, K.; Kaltenbrunner, U.; Pieper, N.; Schu¨rmann, M. Orga-
nometallics 1999, 18, 1586. (f) Beckmann, J .; J urkschat, K.; Mu¨ller,
D.; Rabe, S.; Schu¨rmann, M. Organometallics 1999, 18, 2326.
10.1021/om990970z CCC: $19.00 © 2000 American Chemical Society
Publication on Web 07/28/2000

Condensation of Diphenylsilane Diol
Organometallics, Vol. 19, No. 17, 2000 3273
Sch em e 1
addition of an authentic sample of cyclo-(Ph2SiO)4. Trace
amounts of cyclo-(Ph2SiO)3 were identified (δ 29Si 33.5
ppm, CDCl3) as byproduct in the mother liquor from
which cyclo-(Ph2SiO)4 had been filtered off. In the
absence of [Ph2(OH)Sn]2CH2, a solution of Ph2Si(OH)2
treated under the same conditions remained unchanged.
It is worth mentioning that the hydrolysis of Ph2SiCl2
affords mixtures of diphenylsil(ox)anediols HO(SiPh2O)nH
(n ) 1, 2, 3) and diphenylsiloxanes cyclo-(Ph2SiO)m (m
) 3, 4).5
Obviously, the condensation of Ph2Si(OH)2 is a mul-
tistep reaction, which makes kinetic investigations
concerning the mechanistic pathway difficult. However,
the following experiments allow us to suggest certain
intermediate species likely to be involved in the con-
densation reaction.
F igu r e 1. General view (SHELXTL-PLUS) of a molecule
of 2a showing 30% probability displacement ellipsoids and
the atom numbering. The other conformer 2b, being
slightly different from 2a , is not shown.
The reaction in CDCl3 or toluene at 60 °C for 30 min
of equimolar quantities of Ph2Si(OH)2 and [Ph2(OH)Sn]2-
CH2 gave a clear solution, the 29Si and 119Sn NMR
spectra of which displayed single resonances at -34.0
latter was isolated as a colorless crystalline solid and
has been completely characterized by NMR spectroscopy
and X-ray analysis (Figure 1).
(2J (29Si-O-117/119Sn) ) 25 Hz) and -34.7 ppm ((2J (119
-
Sn-C-117Sn) ) 512 Hz), respectively. The 29Si chemical
shift, the 2J (29Si-O-117/119Sn) coupling, and the signal-
to-satellite integral ratio of the latter support the
exclusive presence of the six-membered stannasiloxane
ring, cyclo-Ph2Si(OSnPh2)2CH2 (1). In a previous paper
we have shown that these NMR data are very sensitive
to the ring size of cyclo-stannasiloxanes.4d Within
several days at room temperature or 2 days at 60 °C,
or upon evaporation of this solution even in vacuo, the
six-membered stannasiloxane ring 1 is converted into
[Ph2(OH)Sn]2CH2 and the eight-membered stannasilox-
ane ring, cyclo-O(Ph2SiOSnPh2)2CH2 (2) (Scheme 1). The
The formation of 2 can be explained by a combination
of kinetically and thermodynamically controlled reac-
tions. Although the six-membered stannasiloxane ring
1 is rapidly formed, it is still in equilibrium with the
starting compounds; that is, even in the presence of
traces of moisture there is a steady state concentration
of Ph2Si(OH)2, which slowly reacts with the six-
membered stannasiloxane ring 1 to give compound 2,
[Ph2(OH)Sn]2CH2, and water (Scheme 1).
Although no kinetic studies were performed, the rapid
formation of the six-membered stannasiloxane ring 1
suggests the presence of the same compound in the
condensation of Ph2Si(OH)2 catalyzed by [Ph2(OH)Sn]2-
CH2.
(5) (a) Kipping, F. S. J . Chem. Soc. 1912, 101, 2125. (b) Kipping, F.
S.; Robinson, R. J . Chem. Soc. 1914, 105, 484. (c) Kipping, F. S. J .
Chem. Soc. 1927, 2728. (d) Burkhard, C. A. J . Am. Chem. Soc. 1945,
67, 2173. (e) Hyde, J . F.; Frevel, L. K.; Nutting, H. S.; Petrie, P. S.;
Purcel, M. A. J . Am. Chem. Soc. 1947, 69, 488. (f) Young, C. W.;
Servais, P. C.; Currie, C. C.; Hunter, M. J . Am. Chem. Soc. 1948, 70,
3758. (g) Behbehani, H.; Brisdon, B. J .; Mahon, M. F.; Molloy, K. C. J .
Organomet. Chem. 1993, 463, 41.
Compound 2 was also obtained in good yield by the
reaction of [Ph2(OH)Sn]2CH2 with O(Ph2SiOH)2 (Scheme
2).

3274 Organometallics, Vol. 19, No. 17, 2000
Beckmann et al.
Sch em e 2
The molecular structure of 2 is shown in Figure 1,
and selected geometrical data are given in Table 1. The
unit cell of 2 contains two individual molecules, 2a and
2b, which differ only slightly in their bond lengths and
bond angles. The two tin atoms in each of these
conformers are nonequivalent, as also reflected in the
119Sn MAS NMR spectrum of 2, which contains four
resonances (δ -18.8, -25.5, -30.7, and -31.8 ppm). The
Si-O, Si-C, Sn-O, and Sn-C bond lengths are as
expected and comparable with those of other cyclo-
stannasiloxanes.4
The eight-membered stannasiloxane ring 2 can for-
mally be regarded as derived from cyclo-(Ph2SiO)4, in
which one (Ph2SiOSiPh2) unit has been replaced by a
(Ph2SnCH2SnPh2) fragment. Thus, the C-Si-C, C-Si-
O, and O-Si-O bond angles of 2 are very close to the
values reported for the parent compound, whereas the
Si-O-Si bond angles of 138.3(2)° (2a ) and 140.4(2)° (2b)
are significantly smaller than the average Si-O-Si
bond angle of 160.4(4)° reported for cyclo-(Ph2SiO)4.6 The
high flexibility of the Si-O-Sn bond angles is demon-
strated by the chemically equivalent Si(1)-O-Sn(2) and
Si(2)-O-Sn(1) bond angles in 2a and 2b, which differ
by 30.8(2)° and 24.8(2)°, respectively. The Sn-C-Sn
bond angles in 2a of 120.4(2)° and 2b of 118.0(2)° can
be best compared with the corresponding angles of
116.8(6)° and 117.9(7)° measured for the cyclo-1,3,5,7-
tetrastannaoctane derivative, cyclo-(Me2SnCH2)4.7 Ac-
cording to a classification scheme recently introduced
for the conformations of eight-membered germasiloxane
rings8 and extended for stannasiloxane rings,4d both
conformers 2a and 2b adopt G-type conformations
(Figure 3).
stability of 2-4 to the reduced ring strain as compared
to the six-membered stannasiloxane ring 1. In addition
to elemental analysis, NMR spectroscopy, and mass
spectrometry (see Experimental Section) the identity of
the 12-membered stannasiloxane ring 4 was also es-
tablished by single-crystal X-ray diffraction. However,
the structure could not be satisfactorily refined because
of disorder of the silicon and tin atoms.
If the cyclo-stannasiloxanes 2-4 are involved in the
[Ph2(OH)Sn]2CH2-catalyzed condensation of Ph2Si(OH)2
to give cyclo-(Ph2SiO)4 as the major product, then
compounds 2, 3, and 4, respectively, should react with
Ph2Si(OH)2, which is present in large excess in the
condensation reaction described above.
The corresponding reactions described below were
monitored by 29Si and 119Sn NMR spectroscopy, and
integration of the 119Sn resonances are given. The
reaction of cyclo-O(Ph2SiOSnPh2)2CH2 (2) with Ph2Si-
(OH)2 in CDCl3 (60 °C, 20 h) gave the 10-membered
stannasiloxane ring 3 (integral 41), unreacted eight-
membered stannasiloxane ring 2 (integral 48), and
small amounts of the six- and 12-membered stannasi-
loxane rings 1 (integral 4.5) and 4 (integral 5.7),
respectively. The diphenylsiloxanediols Ph2Si(OSiPh2-
OH)2 and O(SiPh2OSiPh2OH)2 as well as trace amounts
of cyclo-(Ph2SiO)3 were also formed. The identity of the
three latter compounds was unambiguously established
by addition of authentic samples to the reaction mixture.
In addition there are unassigned signals of very low
intensity at δ 29Si -37.1, -45.6 (approximately 2% of
the major signals).
The reaction mixture of the 10-membered stannasi-
loxane ring cyclo-O(Ph2SiOPh2SiOSnPh2)2CH2 (3) with
Ph2Si(OH)2 in CDCl3 (60 °C, 20 h) showed the presence
of the 12-membered stannasiloxane ring 4 (integral 47)
as well as unreacted 10-membered stannasiloxane ring
3 (integral 42), eight-membered stannasiloxane ring 2
(integral 4), and six-membered stannasiloxane ring 1
(integral 7). In addition, the 29Si NMR spectrum indi-
cated the presence of O(SiPh2OSiPh2OH)2 (δ 29Si -36.9,
-45.4).
The condensation of [Ph2(OH)Sn]2CH2 with diphenyl-
siloxanediols HO(Ph2SiO)nH (n ) 3-4) provided the 10-
and 12-membered stannasiloxane rings 3 and 4 (Scheme
2). Unlike the six-membered ring 1, these larger rings
show no tendency to rearrange in toluene at 60 °C and
are stable against moisture. We attribute the higher
(6) Braga, D., Zanotti, G. Acta Crystallogr. 1980, B36, 950.

Condensation of Diphenylsilane Diol
Organometallics, Vol. 19, No. 17, 2000 3275
Ta ble 1. Selected Bon d Len gth s (Å), Bon d An gles
(d eg), a n d Tor sion An gles (d eg) for 2a , 2b, a n d 5
2a
2b
5
Sn(1)-O(2)
1.983(6)
Sn(1)-O(3)
1.978(3)
2.126(4)
2.107(5)
2.108(5)
1.942(3)
2.130(4)
2.101(6)
2.107(6)
1.585(3)
1.631(3)
1.842(7)
1.844(6)
1.612(3)
1.596(3)
1.853(5)
1.983(3)
2.124(4)
2.105(6)
2.103(5)
1.952(3)
2.115(5)
2.090(7)
2.115(5)
1.600(3)
1.631(3)
1.850(5)
1.860(5)
1.619(3)
1.596(3)
1.859(5)
1.850(5)
Sn(1)-C(1)
2.135(8)
2.140(7)
2.146(7)
1.975(6)
2.136(9)
2.145(8)
2.138(8)
1.627(6)
1.605(6)
1.910(9)
1.909(8)
Sn(1)-C(11)
Sn(1)-C(21)
Sn(2)-O(1)
Sn(2)-C(1)
Sn(2)-C(31)
Sn(2)-C(41)
Si(1)-O(1)
Si(1)-O(2)
Si(1)-C(51)
Si(1)-C(61)
Si(2)-O(2)
Si(2)-O(3)
Si(2)-C(71)
Si(2)-C(81)
O(2)-Sn(1)-C(1)
O(2)-Sn(1)-C(11)
O(2)-Sn(1)-C(21)
O(3)-Sn(1)-C(1)
O(3)-Sn(1)-C(11)
O(3)-Sn(1)-C(21)
C(1)-Sn(1)-C(11)
C(1)-Sn(1)-C(21)
C(11)-Sn(1)-C(21)
O(1)-Sn(2)-C(1)
O(1)-Sn(2)-C(31)
O(1)-Sn(2)-C(41)
C(1)-Sn(2)-C(31)
C(1)-Sn(2)-C(41)
C(31)-Sn(2)-C(41)
O(1)-Si(1)-O(2)
O(1)-Si(1)-C(51)
O(1)-Si(61)-C(61)
O(2)-Si(1)-C(51)
O(2)-Si(1)-C(61)
C(51)-Si(1)-C(61)
O(3)-Si(2)-O(2)
O(2)-Si(2)-C(71)
O(2)-Si(2)-C(81)
O(3)-Si(2)-C(71)
O(3)-Si(2)-C(81)
C(71)-Si(2)-C(81)
Sn(2)-O(1)-Si(1)
Sn(1)-O(2)-Si(1)
Si(1)-O(2)-Si(2)
Sn(1)-O(3)-Si(2)
Sn(1)-C(1)-Sn(2)
105.7(3)
109.0(3)
101.4(3)
110.21(16) 109.62(15)
102.28(18) 104.16(17)
105.48(16) 101.12(19)
114.81(19) 109.2(2)
110.6(2)
112.7(2)
F igu r e 2. General view (SHELXTL-PLUS) of a molecule
of 5 showing 30% probability displacement ellipsoids and
the atom numbering.
112.8(3)
114.04(19) 113.7(3)
117.6(3)
113.2(3)
106.04(16) 103.29(14) 106.3(3)
102.3(2) 103.0(2) 106.1(3)
102.54(18) 106.91(17) 104.5(3)
possible, and consequently the catalytic cycle is closed
by reaction of the 12-membered stannasiloxane ring 4
with Ph2Si(OH)2 to give six-membered stannasiloxane
1 and the organosiloxanol O(SiPh2OSiPh2OH)2. The
organosiloxanols generated in steps III and IV (Scheme
3) are then transformed into cyclo-(Ph2SiO)3 and cyclo-
(Ph2SiO)4, respectively.
In analogy with compound 1, the synthesis of the six-
membered metallastannoxane rings, cyclo-t-Bu2Si-
(OSnPh2)2CH2 (5) and cyclo-t-Bu2Ge(OSnPh2)2CH2 (6),
was achieved by condensation of [Ph2(OH)Sn]2CH2 with
t-Bu2Si(OH)2 and t-Bu2Ge(OH)2, respectively (eq 2).
Compounds 5 and 6 show no tendency to rearrange to
give larger rings, which is to be expected when consid-
ering the stability toward self-condensation of t-Bu2Si-
(OH)2 and t-Bu2Ge(OH)2.9
114.6(2)
116.5(3)
112.7(3)
115.2(3)
112.35(18) 113.5(3)
114.6(3) 114.6(3)
111.0(4)
110.77(18) 111.58(17) 113.2(3)
109.2(2)
109.9(3)
105.9(3)
108.8(3)
112.3(3)
108.8(2)
110.1(2)
107.8(2)
106.8(2)
111.8(2)
107.7(4)
105.7(3)
106.4(4)
107.8(4)
116.3(4)
112.52(19) 113.44(17)
106.2(2)
107.6(3)
108.9(3)
110.5(2)
111.2(3)
171.5(2)
107.5(2)
107.8(2)
107.6(2)
109.5(2)
111.1(2)
163.1(2)
134.6(4)
136.4(3)
138.3(2)
140.71(19) 138.82(17)
140.4(2)
120.4(2)
O(1)-Sn(2)-C(1)-Sn(1) 39.6(3)
118.0(2)
41.0(3)
77.4(7)
-64.6(7)
-20.5(4)
113.9(4)
-32.1(5)
14.8(6)
9.9(6)
C(1)-Sn(2)-O(1)-Si(1)
O(2)-Si(1)-O(1)-Sn(2)
O(1)-Si(1)-O(2)-Si(2)
O(1)-Si(1)-O(2)-Sn(1)
O(3)-Si(2)-O(2)-Si(1)
O(2)-Si(2)-O(3)-Sn(1)
C(1)-Sn(1)-O(3)-Si(2)
-10.5(17)
35.8(18)
-40.3(4)
-18.0(6)
-21.0(4)
94.0(3)
-28.7(4)
-26.8(4)
90.9(3)
-23.5(3)
-65.1(3)
O(3)-Sn(1)-C(1)-Sn(2) -57.1(3)
Si(1)-O(2)-Sn(1)-C(1)
O(2)-Sn(1)-C(1)-Sn(2)
-1.8(6)
27.5(5)
Interestingly, neither the 14-membered stannasilox-
ane ring cyclo-Ph2Si(OSiPh2OSiPh2OSnPh2)2CH2 nor
open-chain stannasiloxanes were formed in these reac-
tions.
From these results, one possible reaction sequence for
the [Ph2(OH)Sn]2CH2-catalyzed condensation of Ph2Si-
(OH)2 is proposed in Scheme 3. In a kind of growth
reaction, the initially formed six-membered stannasi-
loxane ring 1 reacts with Ph2Si(OH)2 to give the eight-
membered stannasiloxane ring 2, which in turn reacts
with further Ph2Si(OH)2 to give the 10-membered stan-
nasiloxane ring 3. The latter, however, reacts with Ph2-
Si(OH)2 to give the 12-membered ring 4 as well as the
six-membered ring 1 and the organosiloxanol Ph2Si-
(OSiPh2OH)2. Further ring enlargment seems to be not
The molecular structure of 5 is shown in Figure 2,
and selected geometrical data are given in Table 1. The
two tin atoms in 5 are nonequivalent, which is also
(7) (a) Ku¨hn, S. Ph.D. Thesis, Dortmund University, 1997. (b) Ku¨hn,
S.; Hummeltenberg, R.; Schu¨rmann, M.; J urkschat, K. Phosphorus,
Sulfur, Relat. Elem. 1999, 150-151, 333.
(8) Akkurt, M.; Ko¨k, T. R.; Faleschini, P.; Randaccio, L.; Puff, H.;
Schuh, H. J . Organomet. Chem. 1994, 470, 59.
(9) (a) Sommer, L. H.; Tyler, L. J . J . Am. Chem. Soc. 1954, 76, 1030.
(b) Weidenbruch, M.; Pesel, H.; Hieu, D. V. Z. Naturforsch. 1980, 35b,
31. (c) Puff, H.; Reuter, H. J . Organomet. Chem. 1989, 364, 57. (b)
Puff, H.; Reuter, H. J . Organomet. Chem. 1989, 368, 173.

3276 Organometallics, Vol. 19, No. 17, 2000
Beckmann et al.
F igu r e 3. Ring conformations (SHELXTL-PLUS) of cyclo-stannasiloxanes 2a , 2b, and 5.
Sch em e 3
reflected by two 119Sn MAS NMR resonances (-34.2 and
-35.2 ppm).
cyclo-stannasiloxanes 2, 3, and 4, respectively (Table 3).
One possible explanation for this reversed trend is the
assumption of monomer-dimer equilibria in solutions
of 1 and 5, the population of dimers being sufficient to
influence the 119Sn chemical shift. Upon dimerization,
the coordination number at tin becomes 5, which usually
causes considerable high-field shifts in 119Sn NMR
spectroscopy.4d These equilibria are fast on the 119Sn
NMR time scale. Given the ring strain in the six-
membered cyclo-stannasiloxanes 1 and 5, their endocy-
clic C-Sn-O bond angles are smaller than those of the
larger rings 2-4, and thus the tin atoms are more
affected by the dimerization. A comparison of the solid
state and solution 119Sn NMR spectra of the eight-
membered stannasiloxane ring 2 (low strain) and six-
membered stannasiloxane ring 5 (high strain) shows
that the signals in the solid state are high-frequency
shifted by 3.1 and 8.1 ppm, respectively. The observed
The six-membered stannasiloxane ring 5 can formally
be regarded as derived from cyclo-(t-Bu2SiO)310 in which
one (t-Bu2SiOSit-Bu2) unit is replaced by a (Ph2SnCH2-
SnPh2) fragment. As a consequence of the six-membered
ring structure of 5, the Si(1)-O(1)-Sn(2), Si(1)-O(2)-
Sn(1), and Sn(1)-C(1)-Sn(2) bond angles of 134.6(4)°,
136.4(3)°, and 113.9(4)°, respectively, are smaller than
the corresponding angles of the eight-membered stan-
nasiloxane ring 2 (Table 1). The ring conformation of 5
(Figure 3) is almost planar, with C(1) showing the
largest deviation from the plane (-0.622(9) Å).
1
The H and 13C NMR spectra (Experimental Section)
of compounds 2-6 are fully consistent with their
proposed structures in solution. The 29Si NMR chemical
shifts of the stannasiloxane rings 1-5 exhibit the
expected dependence on the ring size (Table 3).4d
Surprisingly the 119Sn NMR chemical shifts show a
reverse dependence on the ring size. Usually, the 119Sn
chemical shifts of smaller rings appear at higher
frequency than those of larger rings.4d Here, the 119Sn
NMR signals of the six-membered cyclo-stannasiloxanes
1 and 5 at -34.7 and -42.8 ppm, respectively, are more
low-frequency shifted than the signals at -29.8, -26.1,
and -26.9 ppm of the eight-, 10-, and 12-membered
2
2J (119Sn-O-117Sn) and J (29Si-O-119Sn) couplings in
the cyclo-stannasiloxanes 1-5 show no systematic trend
related to the ring size, which is in sharp contrast to
other cyclo-stannasiloxanes.4d
The presence of monomer-dimer equilibria is further
supported by electrospray mass spectroscopy. To iden-
tify ionic species related to the parent compounds, we
measured electrospray mass spectra (negative mode) of

Condensation of Diphenylsilane Diol
Organometallics, Vol. 19, No. 17, 2000 3277
Ch a r t 1
Ta ble 2. Cr ysta llogr a p h ic Da ta for 2 a n d 5
with Ph2Si(OH)2. The mass clusters and the proposed
structures are depicted in Chart 1. For all compounds
the mass peak plus chloride was detected. In addition,
compounds 1 and 5 exhibit a dimer mass peak plus
chloride. An equimolar mixture of 1 and 5 shows the
presence of both the homodimers plus chloride and the
heterodimer plus chloride. In all solutions a mass cluster
consistent with the anionic four-membered stannoxane
A was observed.
2
5
formula
fw
C
49H42O3Si2Sn2
C33H40O2SiSn2
734.12
972.39
cryst syst
cryst size, mm
space group
a, Å
triclinic
triclinic
0.15 × 0.10 × 0.10 0.26 × 0.16 × 0.06
P1h
P1h
10.434(1)
15.493(1)
29.220(1)
95.570(1)
91.011(1)
106.169(1)
4510.3(5)
4
10.713(4)
12.7321(9)
13.387(2)
102.225(4)
107.37(2)
100.61(1)
1642.2(7)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Con clu sion
Z
F
F
The [Ph2(OH)Sn]2CH2-catalyzed condensation of Ph2-
Si(OH)2 to give cyclo-(Ph2SiO)4 appears to be initiated
by the formation of the six-membered cyclo-stannasi-
loxane Ph2Si(OSnPh2)2CH2 (1). Very likely, the eight-,
10-, and 12-membered stannasiloxane rings 2-4 are
also involved in the condensation pathway.
Unlike these three latter stannasiloxane rings, the
six-membered cyclo-stannasiloxane 1 is unstable in
solution and reacts with water present in the reaction
mixture to give the eight-membered cyclo-stannasilox-
ane 2 and [Ph2(OH)Sn]2CH2.
calcd, Mg/m3
meas, Mg/m3
1.432
1.4388(4)
1.200
1.485
1.5537(8)
12.638
µ, mm-1
F(000)
1952
736
θ range, deg
index ranges
2.56-23.22
-10 e h e 10
-17 e k e 16
-32 e l e 32
48 237
94.6
12 208/0.041
5831
3.61-74.77
-12 e h e 13
-15 e k e 15
-16 e l e 0
7033
99.7
6731/0.1026
5465
no. of reflns collcd
completeness to θmax
no. of indep reflns/Rint
no. of reflns obsd with
(I > 2σ(I))
abs corr
max/Tmin
n.m.
ψ-scan
1.000/0.655
352
T
no. of refined params
1010
0.761
Exp er im en ta l Section
GooF (F2)
1.059
The starting compounds t-Bu2Si(OH)2,11a t-Bu2Ge(OH)2,8c
[Ph2(OH)Si]2O,5g [Ph2(OH)SiO]2SiPh2,5g [Ph2(OH)SiOSiPh2]2O,4f
and [Ph2(OH)Sn]2CH211b were prepared according to literature
methods. Ph2Si(OH)2 was supplied by Fluka and used as
received. Solution state NMR spectra were recorded in CDCl3
on a Bruker DRX 400 spectrometer at 400.13 MHz (1H), 100.62
MHz (13C{1H}), 79.49 MHz (29Si{1H}), and 149.21 MHz (119Sn-
{1H}) using Me4Si and Me4Sn as external references. Solid
state 119Sn{1H} NMR spectra were recorded on a Bruker MSL
400 spectrometer at 149.21 MHz using cross polarization (CP)
and magic angle spinning techniques (MAS) (recycle delay 4.0
s, 90° pulse 5.0 µs, contact time 3.5 ms) at spinning frequencies
of 8 and 10 kHz, respectively. Tetracyclohexyltin was used as
R1(F) (I > 2σ(I))
wR2(F2) (all data)
(∆/ σ)max
0.0331
0.0564
<0.001
0.0649
0.1998
<0.001
1.750/-2.729
largest diff peak/hole, e/Å3 0.244/-0.223
Ta ble 3. Selected 119Sn a n d 29Si NMR P a r a m eter
for 1-6 in CDCl3
δ(119Sn) 2J (119Sn-C-117Sn)
δ(29Si)
2J (29Si-O-117/119Sn)
1
2
3
4
5
6
-34.7
-29.8
-26.1
-26.9
-42.8
-38.3
512
535
474
551
508
508
-34.0
-41.0
-42.2, -46.8
-42.1, -47.5
-13.5
25
36
33
33
39
(10) Clegg, W. Acta Crystallogr. 1982, B38, 1648.
(11) (a) Weidenbruch, M.; Pesel, H.; Hieu, D. V. Z. Naturforsch.
1980, 35b, 31. (b) Gielen, M.; J urkschat, K. J . Organomet. Chem. 1984,
273, 303.
acetonitrile/dichloromethane solutions (1:1) of 1-3 and
5, respectively, and of a mixture of 1 and 5. The solution
of 1 was prepared in situ by reacting [Ph2(OH)Sn]2CH2

3278 Organometallics, Vol. 19, No. 17, 2000
Beckmann et al.
a
second reference (-97.35 ppm against Me4Sn) and to
1,1,3,3,5,5,7,7,9,9-Deca p h en yl-4,6,8,10-tetr a oxa -1,3-d is-
optimize Hartmann-Hahn matching conditions. Mass spectra
were measured on a Finnigan MAT 8230 spectrometer. Elec-
trospray mass spectra were obtained with
ta n n a -5,7,9-tr isila cyclod eca n e (3). Yield: 2.32 g, 1.98 mmol,
1
79%; mp 115 °C. H NMR (CDCl3) δ: 7.7-7.1 (50 H, m; Ph),
0.95 (2H, s, 2J (119Sn-1H) ) 59 Hz; SnCH2Sn). 13C{1H} NMR
(CDCl3) δ: 139.9 (SnPhCi), 137.6 ((SiO)2SiPhCi), 135.9 (SnO-
SiPhCi), 135.8 (SnPhCo), 134.7 ((SiO)2SiPhCo), 134.5 (SnO-
SiPhCo), 129.6 (SnPhCp), 129.4 ((SiO)2SiPhCp), 129.1 (SnO-
SiPhCp), 128.5 (SnPhCm), 127.3 ((SiO)2SiPhCm), 127.2 (SnOSi-
PhCm), -5.91 (SnCH2Sn). 29Si{1H} NMR (CDCl3) δ: -42.2
(2J (29Si-O-117/119Sn) ) 33 Hz; SnOSi), -46.8 ((SiO)2Si). 119Sn-
{1H} NMR (CDCl3) δ: -26.1 (2J (119Sn-C-117Sn) ) 474 Hz,
a Micromass
Platform II single quadrupole mass spectrometer using an
acetonitrile mobile phase. Acetonitrile/dichloromethane solu-
tions (1:1; c ) 1 × 10-3 mol L-1) of the compounds were injected
directly into the spectrometer via a Rheodyne injector equipped
with a 50 µL loop. A Harvard 22 syringe pump delivered the
solutions to the vaporization nozzle of the electrospray ion
source at a flow rate of 10 µL min-1. Nitrogen was used both
as a drying gas and for nebulization with flow rates of
approximately 200 and 20 mL min-1 respectively. Pressure
in the mass analyzer region was usually about 4 × 10-5 mbar.
Typically 10 signal-averaged spectra were collected. Ions
showed the expected isotopic pattern. Elemental analyses were
performed on an instrument from Carlo Erba Strumentazione
(model 1106). The density of single crystals was determined
using a Micromeritics Accu Pyc 1330.
2J (119Sn-O-29Si) ) 33 Hz). MS m/z (%): 896 (8) [M+ - C12H10
-
Sn], 696 (4) [M+ - C25H22SiSn], 636 (13) [M+ - C30H20O3Si3],
594 (32) [M+ - C25H22OSn2]. Anal. Calcd for C61H52O4Si3Sn2
(1170.81): C, 62.58; H, 4.48. Found: C, 62.6; H, 4.5.
1,1,3,3,5,5,7,7,9,9,11,11-Dod eca p h en yl-4,6,8,10,12-p en -
ta oxa -1,3-d ista n n a -5,7,9,11-tetr a sila cyclod od eca n e (4).
1
Yield: 2.51 g, 1.85 mmol, 74%; mp 182 °C. H NMR (CDCl3)
2
δ: 7.7-7.1 (60H, m; Ph). 0.94 (2H, s; J (119Sn-1H) ) 63 Hz;
SnCH2Sn). 13C{1H} NMR (CDCl3) δ: 141.2 (SiPhCi), 139.5
(SiPhCi), 137.1 (SiPhCi), 137.8 (SnPhCo), 136.7 (SiPhCo), 136.6
(SiPhCo), 131.7 (SiPhCp), 131.6 (SiPhCp), 131.2 (SnPhCp), 130.5
5 (SnPhCm), 129.5 (SiPhCm), 129.4 (SiPhCm), -2.04 (SnCH2-
Sn). 29Si{1H} NMR (CDCl3) δ: -42.1 (2J (29Sn-O-117/119Sn) )
33 Hz; SnOSi), -47.5 ((SiO)2Si). 119Sn{1H} NMR (CDCl3) δ:
-26.9 (2J (119Sn-C-117Sn) ) 551 Hz, 2J (119Sn-O-29Si) ) 33
Ca ta lytic Con d en sa tion of Dip h en ylsila n d iol. A mix-
ture of [Ph2(OH)Sn]2CH2 (1.19 g, 2.00 mmol) and Ph2Si(OH)2
(4.32 g, 20.0 mmol) in acetone (50 mL) was heated at 60 °C.
After 20 h a colorless precipitate of cyclo-(Ph2SiO)4 was filtered
(2.53 g, 3.19 mmol, 64%). 29Si{1H} NMR (CDCl3) δ: -42.7.
Anal. Calcd for C48H40O4Si4 (793.19): C, 72.69; H, 5.08.
Found: 72.6; H, 5.1.
In Situ Syn th esis of 1,1,3,3,5,5-Hexa p h en yl-4,6-d ioxa -
1,3-d ista n n a -5-sila cycloh exa n e (1). A mixture of [Ph2(OH)-
Sn]2CH2 (29.7 mg, 0.05 mmol) and Ph2Si(OH)2 (10.8 mg, 0.05
mmol) in CDCl3 (300 µL) was heated at 60 °C for 30 min,
resulting in a clear solution. 119Sn and 29Si NMR spectroscopy
showed the exclusive formation of 1. 29Si{1H} NMR (CDCl3)
δ: -34.0 (2J (29Si-O-117/119Sn) ) 25 Hz. 119Sn{1H} NMR (CDCl3)
δ: -34.7 (2J (119Sn-C-117Sn) ) 512 Hz, 2J (119Sn-O-29Si) ) 25
Hz). Then the mixture was heated again at 60 °C for 2 days.
During this period the solution was investigated by 119Sn and
29Si NMR spectroscopy, which revealed increasing amounts
of 2. After a short time a colorless precipitate was observed,
which was not filtered.
The above reaction was repeated on a preparative scale
using [Ph2(OH)Sn]2CH2 (1.48 g, 2.50 mmol) and Ph2Si(OH)2
(0.54 g, 2.50 mmol) in toluene (25 mL): The precipitate was
filtered. It consisted exclusively of [Ph2(OH)Sn]2CH2, which
was identified by elemental analysis and by comparison of its
IR spectrum with that of an authentic sample. The filtrate
was evaporated in vacuo ,and the solid residue was crystallized
from hexane/dichloromethane, affording 2 (0.86 g, 0.88 mmol,
35%, mp 110 °C).
Syn th esis of th e cyclo-Meta lla sta n n oxa n es 2-6. A
mixture of [Ph2(OH)Sn]2CH2 (1.49 g, 2.5 mmol) and 2.5 mmol
of the corresponding silanol (1.04 g [Ph2(OH)Si]2O for 2, 1.53
g [Ph2(OH)SiO]2SiPh2 for 3, 2.03 g [Ph2(OH)SiOSiPh2]2O for
4, and 0.44 g t-Bu2Si(OH)2 for 5) or germane diol (0.55 g t-Bu2-
Ge(OH)2 for 6), respectively, in toluene (25 mL) was heated at
60 °C in an open flask, resulting in a clear solution. The solvent
was removed in vacuo, and the solid residue was crystallized
from hexane/dichloromethane (1:1) to give the cyclo-metal-
lastannoxanes 2-6.
Hz). MS m/z (%): 890 (16) [M+ - C18H15OSi], 813 (7) [M+
-
-
C
C
24H20OSi], 637 (48) [M+ - C42H35O5Si4), 558 (28) [M+
48H40O5Si4]. Anal. Calcd for C73H62O5Si4Sn2 (1357.10): C,
63.72; H, 4.60. Found: C, 64.2; H, 4.6.
1,1,3,3-Tetr a p h en yl-5,5-d i-ter t-bu tyl-4,6-d ioxa -1,3-d is-
ta n n a -5-sila cycloh exa n e (5). Yield: 1.75 g, 2.38 mmol, 95%;
1
mp 148 °C. H NMR (CDCl3) δ: 7.6-7.20 (20H, m; Ph), 0.96
(2H, s, 2J (1H-119Sn) ) 53 Hz; SnCH2Sn), 0.85 (18H, s; SiCMe3).
13C{1H} NMR (CDCl3) δ: 140.1 (SnPhCi), 135.4 (SnPhCo),
129.4 (SnPhCp), 128.2 (SnPhCm), 27.8 (SiCMe3), 21.0 (SiCMe3),
-8.1 (SnCH2Sn). 29Si{1H} NMR (CDCl3) δ: -13.5 (2J (29Si-O-
117/119Sn) ) 39 Hz). 119Sn{1H} NMR (CDCl3) δ: -42.8 (2J (119Sn-
C-117Sn) ) 551 Hz, 2J (119Sn-O-29Si) ) 39 Hz). 119Sn{1H} MAS
NMR δ: -34.2, -35.2. MS m/z (%): 676 (100) [M+ - C4H9],
634 (30) [M+ - C5H12], 556 (27) [M+ - C10H17]. Anal. Calcd for
C
33H40O2SiSn2 (734.24): C, 53.98; H, 5.49. Found: C, 54.0; H,
5.9.
1,1,3,3-Tetr a p h en yl-5,5-d i-ter t-bu tyl-4,6-d ioxa -1,3-d is-
ta n n a -5-ger m a cycloh exa n e (6). Yield: 1.60 g; 2.05 mmol,
82%; mp 117 °C. 1H NMR (CDCl3) δ: 7.7-7.2 (20H, m; Ph),
1.05 (2H, s, SnCH2Sn), 1.13 (18H, s, SiCMe3). 13C{1H} NMR
(CDCl3) δ: 141.6 (SnPhCi), 135.8 (SnPhCo), 129.5 (SnPhCp),
128.7 (SnPhCm), 30.1 (GeCMe3), 28.1 (GeCMe3), -7.0 (SnCH2-
Sn). 119Sn{1H} NMR (CDCl3) δ: -38.3 (2J (119Sn-C-117Sn) )
508 Hz). 119Sn{1H} MAS NMR δ: -30.2, -33.7, -37.4, -40.8.
MS m/z (%): 721 (92) [M+ - C4H9], 664 (10) [M+ - C8H18],
577 (45) [M+ - C8H18Ge], 499 (10) [M+ - C14H23Ge], 421 (8)
[M+ - C20H28Ge]. Anal. Calcd for C33H40O2GeSn2 (778.78): C,
50.90; H, 5.18. Found: C, 50.9; H, 5.2.
In Situ Rea ction of cyclo-O(P h 2SiOSn P h 2)2CH2 (2) a n d
cyclo-P h 2Si(OP h 2SiOSn P h 2)2CH 2 (3) w it h P h 2Si(OH )2.
Equimolar quantities of Ph2Si(OH)2 (19 mg, 0.088 mmol) and
cyclo-O(Ph2SiOSnPh2)2CH2 (2) (85.6 mg, 0.088 mmol) (case A)
or cyclo-Ph2Si(OPh2SiOSnPh2)2CH2 (3) (103 mg, 0.088 mmol)
(case B) were dissolved in CDCl3 to give clear solutions. From
these solutions, 29Si and 119Sn NMR spectra were recorded,
the results of which are given below.
1,1,3,3,5,5,7,7-Octa p h en yl-4,6,8-tr ioxa -1,3-d ista n n a -5,7-
d isila cycloocta n e (2). Yield: 1.96 g, 2.02 mmol, 81%; mp 110
°C. 1H NMR (CDCl3) δ: 7.7-7.1 (40H, m; Ph), 0.87 (2H, s,
2J (1H-119Sn) ) 55 Hz; SnCH2Sn). 13C{1H} NMR (CDCl3) δ:
139.9 (SnCi), 138.2 (SiCi), 135.8 (SnCo), 134.4 (SiCo), 129.7,
(SnCp), 129.0 (SiCp), 128.6, (SnCm), 127.3 (SiCm), -5.22 (SnCH2-
Sn). 29Si{1H} NMR (CDCl3) δ: -41.0 (2J (29Si-O-117/119Sn) )
36 Hz). 119Sn{1H} NMR (CDCl3) δ: -29.8 (2J (119Sn-C-117Sn)
Case A: 3 (δ 119Sn -26.1, 2J (119Sn-C-117Sn) 474 Hz,
integral 41; δ 29Si -42.2, 2J (29Si-O-117/119Sn) 33 Hz, δ 29Si
2
-46.8), 2 (δ 119Sn -29.8, J (119Sn-C-117Sn) 535 Hz, integral
2
) 535 Hz, J (119Sn-O-29Si) ) 36 Hz). 119Sn{1H} MAS NMR
δ: -18.8, -25.5, -30.7, -31.8. MS m/z (%): 816 (14) [M+
-
48; δ 29Si -41.0, 2J (29Si-O-117/119Sn) 36 Hz), 1 (δ 119Sn -34.7,
integral 4.5; δ 29Si -34.0, 2J (29Si-O-117/119Sn) 25 Hz), 4 (δ 119Sn
C
12H10], 697 (12) [M+ - C25H22SiSn], 637 (12) [M+ - C18H15O3-
2
Si3], 594 (26) [M+ - C25H22OSn2]. Anal. Calcd for C49H42O3-
Si2Sn2 (972.51): C, 60.52; H, 4.35. Found: C, 60.5; H, 4.4.
-26.9, integral 5.7; δ29Si -42.1 J (29Si-O-117/119Sn) 33 Hz, δ
29Si -47.5), Ph2Si(OSiPh2OH)2 (δ 29Si -36.1, -44.2), O(SiPh2-

Condensation of Diphenylsilane Diol
Organometallics, Vol. 19, No. 17, 2000 3279
OSiPh2OH)2 (δ 29Si -36.9, -45.3), cyclo-(Ph2SiO)3 (δ 29Si
-33.6), unidentified signals at δ 29Si -37.1, -45.6.12
were solved by direct methods using SHELXS9712a and suc-
cessive difference Fourier syntheses. Refinements applied full-
matrix least-squares methods, SHELXL97.12b The H atoms
were placed in geometrically calculated positions using a riding
model and refined with common isotropic temperature factors
for different C-H types (C-Hprim. 0.96 Å, C-Hsec. 0.97 Å, Uiso
0.114(11) Å2; C-Haryl 0.93 Å, Uiso 0.112(11) Å2 (5); Uiso 0.123-
(3) Å2 (2).
Case B: 4 (δ 119Sn -26.9, integral 47; δ29Si -42.1 2J (29Si-
O-117/119Sn) 33 Hz, δ29Si -47.5), 3 (δ 119Sn -26.1, 2J (119Sn-
C-117Sn) 474 Hz, integral 42; δ 29Si -42.2, 2J (29Si-O-117/119Sn)
33 Hz, δ 29Si -46.8), 2 (δ 119Sn -29.8, integral 4; δ 29Si -41.0,
2J (29Si-O-117/119Sn) 36 Hz), 1 (δ 119Sn -34.7, integral 7),
O(SiPh2OSiPh2OH)2 (δ 29Si -36.9, -45.4).
Cr ysta llogr a p h y. Intensity data for the colorless crystals
were collected on a Nonius CAD4 (5) and KappaCCD (2)
diffractometer with graphite-monochromated Cu KR (5) and
Mo KR (2) radiation at 291 K. Three standard reflections were
recorded every 60 min (5), and an anisotropic intensity loss
up to 10.0% (5) was detected during X-ray exposure. The data
collections for 2 covered the sphere of reciprocal space with
360 frames via ω-rotation (∆/ω ) 1°) at two times 30 s per
frame. The crystal-to-detector distance was 2.9 cm (2). Crystal
decay was monitored by repeating the initial frames at the
end of data collection. Analyzing the duplicate reflections
showed there was no indication of any decay (2). The structures
Atomic scattering factors for neutral atoms and real and
imaginary dispersion terms were taken from International
Tables for X-ray Crystallography.12c The figures were created
by SHELXTL-Plus.12d Crystallographic data are given in Table
2; selected bond lengths, angles, and torsion angles are listed
in Table 1.
Ack n ow led gm en t. We thank the Deutsche Fors-
chungsgemeinschaft, the Fonds der Chemischen Indus-
trie, Wacker Chemie GmbH, and the Australian Re-
search Council (ARC) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of all coor-
dinates, anisotropic displacement parameters, and geometric
data for compounds 2 and 5. This material is available free of
charge via the Internet at http://pubs.acs.org.
(12) (a) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467. (b)
Sheldrick, G. M. SHELXS97; University of Go¨ttingen, 1997. (c)
International Tables for Crystallography; Kluwer Academic Publish-
ers: Dordrecht, 1992; Vol. C. (d) Sheldrick, G. M. SHELXTL-PLUS.
Release 4.1; Siemens Analytical X-ray Instruments Inc., 1991.
OM990970Z