Compounds containing B-O-X bonds (X=Si, Ge, Sn, Pb): Part 5. Synthesis of chain borosilicates containing B:Si ratios of 2:1, 2:2, 2:3 and 2:4. Crystal structure of (O-CMe2CH2CHMe-O-B-O)2SiBut 2

Article abstract of DOI:10.1016/S0277-5387(99)00235-1

Twelve borosilicates with the general formula O-Y-O-B-O-(SiPh₂O)_n-B-O-Y-O (where n=1, 2, 3 or 4; Y=one of the organic groups CMe₂CMe₂, CMe₂CH₂CHMe, CMe₂CH₂CMe₂ or CHPrⁱCMe₂CH₂) were prepared. Three synthetic routes were investigated, including a one-pot self-assembly reaction of two equivalents each of boric acid, silanediol and organic diol. The probable sequence for this reaction is discussed. The borosilicates were either solids or viscous liquids and were colourless. They formed cyclosiloxane species when thermally decomposed or reacted with either water or potassium trimethylsilanolate. They were unreactive to triethylamine, di-iso-propylamine, pyridine or ethylenediamine. The di-tert-butyl species (O-CMe₂CH₂CHMe-O-B-O)₂SiBu^t ₂ was prepared and structurally characterised using X-ray techniques. The parameters associated with the B-O-Si bonds were a B-O-Si angle of 141.5(2)° and B-O and Si-O distances of 1.360(4) and 1.625(2) A, respectively. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00235-1

Polyhedron 18 (1999) 3135–3146
www.elsevier.nl/locate/poly
Compounds containing B–O–X bonds (X5Si, Ge, Sn, Pb)
Part 5. Synthesis of chain borosilicates containing B:Si ratios of 2:1, 2:2,
%%%%%%%%%%%%%%%%%%
4
%
4
2:3 and 2:4. Crystal structure of (O–CMe2CH2CHMe–O–B–O)2SiBu2t q
b,1
Brian J. O’Learya, Trevor R. Spaldinga , , George Ferguson
*
aChemistry Department, University College, Cork, Ireland
bSchool of Chemistry, The University, St. Andrews, Fife KY16 9ST, Scotland, UK
Received 7 June 1999; accepted 10 August 1999
Abstract
%4
%%
%4
%4 %%%4
Twelve borosilicates with the general formula O–Y–O–B–O–(SiPh2O)n –B–O–Y–O (where n51, 2, 3 or 4; Y5one of the organic
groups CMe2CMe2, CMe2CH2CHMe, CMe2CH2CMe2 or CHPriCMe2CH2) were prepared. Three synthetic routes were investigated,
including a one-pot self-assembly reaction of two equivalents each of boric acid, silanediol and organic diol. The probable sequence for
this reaction is discussed. The borosilicates were either solids or viscous liquids and were colourless. They formed cyclosiloxane species
when thermally decomposed or reacted with either water or potassium trimethylsilanolate. They were unreactive to triethylamine,
%4 %%%%%%%%%%4
di-iso-propylamine, pyridine or ethylenediamine. The di-tert-butyl species (O–CMe2CH2CHMe–O–B–O)2SiBut2 was prepared and
structurally characterised using X-ray techniques. The parameters associated with the B–O–Si bonds were a B–O–Si angle of 141.5(2)8
˚
and B–O and Si–O distances of 1.360(4) and 1.625(2) A, respectively.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Borosilicate; Silyl borate; Synthesis; X-ray crystallography
1. Introduction
Borosilicate materials have found important uses in
many areas. As an example of their current significance,
one may cite their use as interlayer dielectrics in micro-
electronics manufacture [2]. However, relatively little is
known about the chemistry, and, in particular, the structur-
al chemistry of molecular borosilicates. A research pro-
gramme has been initiated [1] to investigate these com-
pounds. We now report the syntheses and properties of
some borosilicates with B–O–(Si–O)n –B linked struc-
tures. The compounds studied are of the general type
shown in the diagram below where n51, 2, 3 or 4, Y is
one of the organic groups CMe2CMe2, CMe2CH2CHMe,
CMe2CH2CMe2 or CHPriCMe2CH2, and R5Ph or But.
Three synthetic routes to these compounds were used.
These may be described as: (a) dehydration reactions
between silanediols, boric acid and organic diols, e.g.
reactions (1) (3) and (5), (b) dehydration reactions be-
tween silanediols and either a 1,3,2-dioxaborolan-2-ol or a
borinan-2-ol, e.g. reaction (7), and (c) dehydrochlorination
reactions between dichlorosilanes and either a 1,3,2-diox-
aborolan-2-ol or a borinan-2-ol, e.g. reactions (8) and (9).
The compounds 1–13 which were prepared are shown in
Table 1.
2. Experimental
qD. Murphy, J.P. Sheehan, T.R. Spalding, G. Ferguson, A.J. Lough,
J.F. Gallagher, J. Mater. Chem. 3 (1993) 1275.
*Corresponding author. Tel.: 1353-21-902-602; fax: 1353-21-274-
097.
E-mail address: t.r.spalding@ucc.ie (T.R. Spalding)
1On sabbatical leave from the University of Guelph, Guelph, Ontario,
Canada.
All reactions were initially carried out in an inert
atmosphere. Work-up of products was carried out in air.
Solvents (Aldrich or Merck) were dried and distilled before
use. Water was doubly distilled and deionised. The follow-
ing reagents were used as supplied by Aldrich Chemical
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00235-1
1999 Elsevier Science Ltd. All rights reserved.

3136
B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
Table 1
Borosilicates prepared in the present work
Compound
no.
Structure
1
2
3
4
5
6
7
8

B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
3137
Table 1. Continued
Compound
no.
Structure
9
10
11
12
13
Co.: boric acid, diphenylsilanediol, 2,3-dimethyl-2,3-
butanediol, 2,4-dimethyl-2,4-pentanediol, 2,2,4-trimethyl-
1,3-pentanediol, dichlorodiphenylsilane, triethylamine,
pyridine, di-iso-propylamine, ethylenediamine, potassium
trimethylsilanolate, di-tert-butyldichlorosilane; aniline
(Merck) and 2-methyl-2,4-pentanediol (BDH) were dis-
tilled prior to use and 1,3-dichloro-1,1,3,3-tetra-
phenyldisiloxane (Fluorochem) was used as supplied. The
substituted 1,3,2-dioxaborolan-2-ol (Y5CMe2CMe2) and
-borinan-2-ols (Y5CMe2CH2CHMe, CMe2CH2CMe2,
CHPriCMe2CH2) were prepared according to literature
methods [4]. The 1,1,3,3-tetraphenyldisiloxane-1,3-diol,
1,1,3,3,5,5-hexaphenyltrisiloxane-1,5-diol and 1,1,3,3,5,5-
7,7-octaphenyltetrasiloxane-1,7-diol were prepared by li-
terature methods [5].
13C NMR spectra were recorded in CDCl3 solvent at
ambient temperature on a JEOL FT NMR GSX-270
spectrometer using SiMe4 as standard. Mass spectra were
recorded on a Kratos Profile mass spectrometer in EI
mode. Melting points were recorded on an Electrothermal
IA 9000 apparatus and are uncorrected. Elemental analyses
were carried out on a Perkin-Elmer 240C analyser by the
Microanalytical Laboratory, University College, Cork.
2.1. Synthesis of compounds 1–4 and 6–13 from an
organic diol, boric acid and appropriate silanediol in
2:2:1 ratio
2.1.1. Compounds 1–4: Eq. (1)
Infrared spectra in the range 4000–4500 cm21 were
recorded on a Perkin-Elmer Paragon 1000 FT spectrometer
(As identical procedures were followed for the prepara-
tions of 1–4, a detailed description is given only for 1).
Compound 1 has been reported previously [3].
1
as KBr discs or thin films between NaCl plates. All H and

3138
B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
2.1.1.4. Compound 4
Compound 4 was prepared on a 7.88-mmol scale: yield
85.2%. Mp 54–568C. Found: C, 64.01; H, 7.99; B, 3.83%.
C28H42B2O6Si requires: C, 64.14; H, 8.07; B, 4.12%. IR
(KBr disc), nmax /cm21
: 1410(s), 1382(vs), 1299(s),
(1)
1209(s), 1179(s), 1125(s), 844(s), 664(s). 1H NMR
(CDCl3): 7.78–7.65 [m, 4H, C6H5]; 7.41–7.24 [m, 6H,
where Y5CMe2CMe2, CMe2CH2CHMe, CMe2CH2CMe2
]
C6H5]; 3.65–3.31 [m, 6H, 4CH2 and 2CHPri]; 1.91–1.69
or CHPriCMe2CH2.
]
]
]
]
[m, 2H, CHMe2]; 1.17–0.66 [m, 24H, CH3]. 13C NMR
]
(CDCl3): 134.70, 129.89, 127.43 [all C6H5]; 84.53 [CH2 –
]
]
O]; 74.32 [CHPri]; 34.92, 29.47, 23.50, 22.64 [all CH3];
2.1.1.1. Compound 1
]
]
18.95 [CH(CH3)2]; 17.40 [C(CH3)2]. MS (EI), m/z: 524
A mixture of 2,3-dimethyl-2,3-butanediol (0.745 g, 6.30
mmol), boric acid (0.390 g, 6.31 mmol) and
diphenylsilanediol (0.681 g, 3.15 mmol) was added to 50
ml toluene and the solution was refluxed for 8 h in a
Dean–Stark apparatus. Removal of solvent on a rotary
evaporator afforded a viscous liquid which was redissolved
in hexanes. The solution was filtered to remove small
amounts of insoluble powder, concentrated (to ¯8 ml) on
a rotary evaporator and cooled to 2228C. After a few
hours, compound 1 formed as a colourless solid (1.328 g,
90.1%). Mp 42–458C. Found: C, 61.73; H, 7.40; B, 4.92%.
C24H34B2O6Si requires: C, 61.56; H, 7.32; B, 4.62%. IR
(KBr disc), nmax /cm21: 2974(s), 1380(br, vs), 1307(vs),
1212(s), 1178(s), 1121(s), 841(s), 663(s), 510(s). 1H NMR
]
]
[(M)1].
2.1.2. Compounds 6–9: Eq. (2)
(2)
2.1.2.1. Compound 6
Prepared on a 2.96-mmol scale: yield 93.4%. Mp 74–
768C. Found: C, 65.16; H, 6.56; B, 3.11%. C36H44B2O7Si2
requires: C, 64.87; H, 6.65; B, 3.24%. IR (KBr disc),
nmax /cm21: 1428(vs), 1379(s), 1317(vs), 1154(s), 1125(s),
1101(vs), 955(s), 858(s), 803(s), 718(s), 518(vs). 1H NMR
(CDCl3): 7.73–7.67 [d, 4H, C6H5]; 7.50–7.29 [m, 6H,
]
C6H5]; 1.25 [s, 24H, CH3]. 13C NMR (CDCl3): 134.25,
]
]
133.32, 130.36, 127.75 [all C6H5]; 82.91 [C(CH3)2];
]
]
24.51 [CH3]. MS (EI), m/z: 468 [(M)1].
(CDCl3): 7.70–7.66 [d, 8H, C6H5]; 7.38–7.23 [m, 12H,
]
]
C6H5]; 1.26 [s, 24H, CH3]. 13C NMR (CDCl3): 134.99,
]
]
134.21, 130.44, 128.08 [all C6H5]; 83.39 [C(CH3)2];
]
]
24.81 [CH3]. MS (EI), m/z: 666 [(M)1].
2.1.1.2. Compound 2
]
Compound 2 was prepared on a 4.66-mmol scale: yield
86.7%. Mp 41–448C. Found: C, 61.69; H, 7.42; B, 4.40%.
C24H34B2O6Si requires: C, 61.56; H, 7.32; B, 4.62%. IR
(KBr disc), nmax /cm21: 2976(s), 1385(br, vs), 1302(vs),
1210(s), 1177(s), 1122(s), 842(s), 662(s), 511(s). 1H NMR
2.1.2.2. Compound 7
Compound 7 was prepared on a 2.89-mmol scale: yield
90.7%. Mp 100–1028C. Found: C, 64.66; H, 6.61; B,
3.39%. C36H44B2O7Si2 requires: C, 64.87; H, 6.65; B,
3.24%. IR (KBr disc), nmax /cm21: 1429(s), 1395(vs),
1372(vs), 1303(s), 1125(vs), 1101(s), 838(s), 720(s), 698(s),
(CDCl3): 7.75–7.70 [m, 4H, C6H5]; 7.41–7.25 [m, 6H,
]
C6H5]; 4.26–4.17 [m, 2H, CH(CH3)]; 1.76–1.65 [m, 4H,
]
]
]
518(s). 1H NMR (CDCl3): 7.71–7.65 [m, 8H, C6H5];
CH2]; 1.53–1.17 [m, 18H, CH3]. 13C NMR (CDCl3):
]
]
7.40–7.23 [m, 12H, C6H5]; 4.23–4.10 [m, 2H, CH(CH3)];
134.72, 130.18, 129.69, 127.46 [all C6H5]; 72.15
]
]
]
]
]
1.61–1.51 [m, 4H, CH2]; 1.42–1.06 [m, 18H, CH3]. 13C
[C(CH3)2]; 65.94 [CH(CH3)]; 45.63 [CH2]; 31.12, 27.66,
]
]
]
23.07 [all CH3]. MS (EI), m/z: 468 [(M)1].
NMR (CDCl3): 134.77, 129.94, 129.57, 127.49 [all
]
C6H5]; 72.22 [C(CH3)2]; 65.93 [CH(CH3)]; 45.45 [CH2];
]
]
]
]
30.94, 27.35, 22.89 [all CH3]. MS (EI), m/z: 666 [(M)1].
]
2.1.1.3. Compound 3
2.1.2.3. Compound 8
Compound 3 was prepared on a 2.19-mmol scale: yield
79.2%. Bp decomp. at 1908C (3 mmHg). Found: C, 62.66;
H, 7.68; B, 4.15%. C26H38B2O6Si requires: C, 62.92; H,
7.72; B, 4.36%. IR (thin film), nmax /cm21: 2975(s),
1369(br, vs), 1303(s), 1209(vs), 1126(s), 718(s), 700(s),
Compound 8 was prepared on a 3.62-mmol scale: yield
82.6%. Bp decomp. at 1758C (1.5 mmHg). Found: C,
65.86; H, 6.97; B, 3.33%. C38H48B2O7Si2 requires: C,
65.71; H, 6.97; B, 3.11%. IR (thin film), nmax /cm21
:
1
2975(s), 1369(br, vs), 1210(s), 1123(s), 1097(vs), 861(s),
502(s). H NMR (CDCl3): 7.72–7.13 [m, 10H, C6H5];
]
718(s), 699(s), 511(vs). 1H NMR (CDCl3): 7.60–7.09 [m,
1.73 [s, 4H, CH2]; 1.15 [s, 24H, CH3]. 13C NMR (CDCl3):
]
]
]
20H, C6H5]; 1.69 [s, 4H, CH2]; 1.18 [s, 24H, CH3]. 13
C
135.06, 134.28, 130.03, 127.67 [C6H5]; 72.42 [C(CH3)2];
]
]
]
]
48.42 [CH2]; 31.45 [CH3]. MS (EI), m/z: 496 [(M)1].
NMR (CDCl3): 135.00, 134.19, 130.09, 127.75 [all
]
]

B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
3139
C6H5]; 72.33 [C(CH3)2]; 48.88 [CH2]; 31.41 [CH3]. MS
2.1.4. Compounds 12 and 13: Eq. (4)
]
]
]
]
(EI), m/z: 694 [(M)1].
2.1.2.4. Compound 9
(4)
Compound 9 was prepared on a 3.62-mmol scale: yield
83.1%. Bp decomp. at 1858C (2 mmHg). Found: C, 66.26;
H, 7.19; B, 2.78%. C40H52B2O7Si2 requires: C, 66.48; H,
7.25; B, 2.99%. IR (thin film), nmax /cm21: 1422(s),
1402(s), 1384(vs), 1343(vs), 1126(s), 718(s), 699(s), 518(s).
where Y5CMe2CMe2 or CMe2CH2CHMe.
2.1.4.1. Compound 12
Prepared on a 2.12-mmol scale: yield 78.5%. Bp de-
comp. at 1758C (2 mmHg). Found: C, 67.55; H, 6.11; B,
1.84%. C60H64B2O9Si4 requires: C, 67.79; H, 6.07; B,
2.03%. IR (thin film), nmax /cm21: 1428(vs), 1379(vs),
1315(s), 1127(s), 1070(vs), 858(s), 719(s), 698(s), 524(s).
1H NMR (CDCl3): 7.68–7.66 [m, 8H, C6H5]; 7.38–7.23
]
[m, 12H, C6H5]; 3.59–3.31 [m, 6H, 4CH2 and 2CHPri];
]
]
]
]
]
1.92–1.74 [m, 2H, CHMe2]; 1.03–0.67 [m, 24H, CH3].
]
13C NMR (CDCl3): 134.98, 129.93, 127.54 [all C6H5];
84.60 [CH2 –O]; 74.29 [CHPri]; 34.93, 29.48, 23.75, 22.66
1H NMR (CDCl3): 7.57–6.95 [m, 40H, C6H5]; 1.13 [s,
]
]
]
24H, CH3]. 13C NMR (CDCl3): 134.52, 133.94, 129.92,
[all CH3]; 18.95 [CH(CH3)2]; 17.25 [C(CH3)2]. MS (EI),
]
]
]
]
m/z: 722 [(M)1].
127.52 [all C6H5]; 82.87 [C(CH3)2]; 24.44 [CH3].
]
]
]
2.1.4.2. Compound 13
Prepared on a 2.12-mmol scale: yield 74.9%. Bp de-
comp. at 1758C (2 mmHg). Found: C, 67.89; H, 5.99; B,
2.22%. C60H64B2O9Si4 requires: C, 67.79; H, 6.07; B,
2.03%. IR (thin film), nmax /cm21: 1429(s), 1398(s),
1372(vs), 1309(vs), 1126(vs), 1072(vs), 718(s), 699(s),
2.1.3. Compounds 10 and 11: Eq. (3)
1
522(s). H NMR (CDCl3): 7.70–7.05 [m, 40H, C6H5];
]
(3)
4.35–3.96 [m, 2H, CH(CH3)]; 1.56–1.42 [m, 4H, CH2];
]
]
1.29–1.01 [m, 18H, CH3]. 13C NMR (CDCl3): 135.20,
]
where Y5CMe2CMe2 or CMe2CH2CHMe.
2.1.3.1. Compound 10
134.71, 129.82, 127.77 [all C6H5]; 72.15 [C(CH3)2];
66.00 [CH(CH3)]; 45.53 [CH2]; 30.91, 27.45, 22.88 [all
]
]
]
]
CH3].
]
Prepared on a 3.39-mmol scale: yield 75.2%. Bp de-
comp. at 1908C (1.5 mmHg). Found: C, 66.34; H, 6.35; B,
2.78%. C48H54B2O8Si3 requires: C, 66.66; H, 6.29; B,
2.50%. IR (thin film), nmax /cm21: 1428(vs), 1379(s),
1315(s), 1127(vs), 1075(vs), 858(s), 719(s), 699(s). 1H
2.2. Synthesis of compounds 6–9 from an organic diol,
boric acid and diphenylsilanediol in a 1:1:1 ratio on a
¯3-mmol scale
NMR (CDCl3): 7.73–7.08 [m, 30H, C6H5]; 1.21 [s, 24H,
]
CH3]. 13C NMR (CDCl3): 135.24, 134.37, 130.04, 127.54
]
[all C6H5]; 82.71 [C(CH3)2]; 24.47 [CH3]. MS (EI), m/z:
]
]
]
864 [(M)1].
(5)
Compounds 6–9 were identified by elemental analysis (C,
H, B), infrared spectroscopy, mass spectrometry and, for 6
and 7, by melting point. The yields of 6, 7, 8 and 9 were
88.8, 87.1, 77.0 and 80.0%, respectively.
2.1.3.2. Compound 11
Prepared on a 2.12-mmol scale: yield 77.3%. Bp de-
comp. at 1908C (1.5 mmHg). Found: C, 66.78; H, 6.32; B,
2.29%. C48H54B2O8Si3 requires: C, 66.66; H, 6.29; B,
2.50%. IR (thin film), nmax /cm21: 1429(s), 1399(vs),
1372(vs), 1304(vs), 1126(vs), 1075(vs), 838(s), 718(s),
2.3. Synthesis of 12 and 13 from an organodiol, boric
acid and 1,1,3,3-tetraphenyldisiloxane-1,3-diol in a 1:1:1
ratio on a ¯3-mmol scale
1
699(s), 523(s). H NMR (CDCl3): 7.70–7.08 [m, 30H,
C6H5]; 4.58–4.00 [m, 2H, CH(CH3)]; 1.72–1.49 [m, 4H,
]
]
]
CH2]; 1.33–1.01 [m, 18H, CH3]. 13C NMR (CDCl3):
]
135.24, 134.66, 129.98, 127.59 [all C6H5]; 72.16
]
[C(CH3)2]; 65.92 [CH(CH3)]; 45.55 [CH2]; 30.93, 27.61,
]
]
]
22.88 [all CH3]. MS (EI), m/z: 864 [(M)1].
(6)
]

3140
B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
Table 2
Both compounds 12 and 13 were identified by elemental
analysis (C, H, B), IR spectroscopy and H NMR spec-
troscopy. The yields of 12 and 13 were 68.7 and 65.3%,
respectively.
1
Summary of crystal data, data collection, structure solution and refine-
ment details for 5
(a) Crystal data
Empirical formula
Molar mass
C20H42B2O6Si
428.25
Color, habit
Colorless, block
0.3830.3830.36
Monoclinic
19.346(3)
10.1974(10)
16.859(2)
127.810(10)
2627.6(6)
C2/c
Crystal size, mm
Crystal system
2.4. Synthesis of 1–5 from a 1,3,2-dioxaborolan-2-ol or
1,3,2-borinan-2-ol and the appropriate diorganosilane-
diol in a 2:1 ratio on a ¯4.65-mmol scale
˚
a, A
˚
b, A
˚
c, A
b, 8
V, A
3
˚
Space group
Molecular symmetry
Z
Two-fold
4
F(000)
936
1.083
0.118
(7)
dcalc, g cm23
m, mm21
The synthesis of 5 is given as an example; 1–4 were
prepared similarly in yields of 88.1, 86.9, 78.4 and 85.0%,
respectively. A mixture of 4,4,6-trimethyl-1,3,2-diox-
aborinan-2-ol (0.818 g, 5.68 mmol) and di-tert-
butylsilanediol (0.501 g, 2.84 mmol) was refluxed for 10 h
in toluene (40 ml) in a Dean–Stark apparatus. Removal of
solvent gave a viscous liquid which was dissolved in
toluene (¯8 ml) and cooled to 2248C. Large colourless
crystals of 5 formed after ¯1 day (1.003 g, 82.4%). Mp
51–538C. Found: C, 56.20; H, 9.92; B, 4.83%.
C20H42B2O6Si requires: C, 56.09; H, 9.89; B, 5.05%. IR
(b) Data acquisitiona
Temperature, K
294(1)
10.4–16.2
25
Unit-cell reflections (u range, 8)
Max. u (8) for reflections
hkl range of reflections
Decay in 3 standard reflections
Reflections measured
Unique reflections
222 to 18; 0 to 12; 0 to 20
5.4%
2374
2296
0.009
1330
Rint
Reflections with I.2s(I)
(c) Structure solution and refinementb
Refinement on
F2
(KBr disc), nmax /cm21
: 1407(s), 1382(vs), 1299(s),
Solution method
Direct methods
Riding
132
1208(s), 1179(s), 878(s), 844(vs), 769(s), 662(s). 1H NMR
H-atom treatment
No. of variables in L.S.
Weights:
(CDCl3): 4.25–4.17 [m, 2H, CH(CH3)]; 1.78–1.46 [m,
]
4H, CH2]; 1.41–1.21 [m, 18H, CH3 of dioxaborinane
]
]
k in w 5 1/(s2F2o 1 k)
[P 5 (F2o 1 2F2c )/3]
R, Rw, gof
(0.1120P)210.1060P
rings]; 1.01 [s, 18H, CH3 of tert-butyl groups]. 13C NMR
]
(CDCl3): 72.71 [C(CH3)2]; 66.69 [CH(CH3)]; 46.52
]
]
0.067, 0.205, 1.08
[CH2]; 32.07, 28.30, 24.08, 21.13 [all CH3]. MS (EI),
Density range in
final D-map, e A
]
]
m/z: 371 [(M)1–But].
23
˚
20.29, 10.43
Final shift/error ratio
0.00
a Data collection on an Enraf Nonius CAD4 diffractometer with
˚
graphite monochromatised Mo-Ka radiation (l50.71073 A).
2.4.1. X-ray crystallography
b Calculations were done on a Dell Inspiron 3200 laptop computer
system with the NRCVAX system of programs (E.J. Gabe, Y. Le Page, J.-P.
Charland, F.L. Lee, P.S. White, J. Appl. Crystallogr. 22 (1989) 384–389)
[6] for data reduction and with SHELXL-93 (Sheldrick, 1993) [7] for
refinement with all data on F2.
Crystal data, data collection, structure solution and
refinement details for 5 are summarised in Table 2. Fig. 1
was prepared with the aid of published crystallographic
programmes [6–8]. Full crystallographic details have been
deposited in CIF format with the Cambridge Crystallo-
graphic Data Centre and are also available directly from
the authors.
2.5. Synthesis of 1–4 from a 1,3,2-dioxaborolan-2-ol or
-borinan-2-ol and dichlorodiphenylsilane
(8)
(Only the synthesis of 1, Y5CMe2CMe2, is described in
detail. Compounds 2–4 were prepared similarly). The
yields of 2, 3 and 4 were 79.5, 69.3 and 78.8%, respective-
ly.
2.5.1. Compound 1
Triethylamine (0.820 g, 8.10 mmol) in 20 ml ether was
added dropwise to a solution of 4,4,5,5-tetramethyl-1,3,2-

B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
3141
2.7. Attempted synthesis of 10 and 11 from organodiol,
boric acid and diphenylsilanediol in a 2:2:3 mol ratio
(10)
The attempted synthesis of compound 10 by reaction (10)
afforded hexaphenyltrisiloxane, (Ph2SiO)3 (0.210 g,
31.3% based on diphenylsilanediol) and 6 (i.e. a two-
silicon chain silyl borate), 1.90 g, 84%. Similar results
were obtained when 2-methyl-2,4-pentanediol was used in
the attempted synthesis of 11. In this case, the yield of 7
was 82%.
2.8. Thermal decomposition reactions of the
borosilicates 1–4 and 6–13
Fig. 1. A general view of 5 showing the atom numbering scheme.
Hydrogen atoms are omitted for clarity.
The liquid chain borosilicates 3 and 8–13 decomposed
prior to their distillation temperatures affording dark brown
decomposition products which solidified at room tempera-
ture. Attempted fractional recrystallisation of these solids
was unsuccessful. However, their IR spectra contained
significant bands in the region 1100–1040 cm21, con-
sistent with the presence of Si–O–Si bonds [9]. Examina-
tion of these spectra suggested the presence of (Ph2SiO)3,
14, as the predominant siloxane product when one- or
three-silicon borosilicate compounds were decomposed
and (Ph2SiO)4, 15, when two- or four-silicon compounds
were decomposed. Supporting evidence was obtained in
the mass spectra of the decomposition products hparent
ions at m/z5594 and 792 for 14 and 15, respectivelyj. The
IR spectra of decomposition products also contained peaks
in the region 1400–1375 cm21 which may be attributed to
B–O(–C) stretching [3] and near 3400 cm21 due to B–
O(–H) stretching [4].
dioxaborolan-2-ol (1.138 g, 7.90 mmol) and dich-
lorodiphenylsilane (1.001 g, 3.95 mmol) in 40 ml ether. A
white precipitate of [Et3NH]Cl (1.071 g, 98.4%) (IR)
formed immediately. This was removed after 12 h. Remov-
al of solvent afforded a cloudy viscous liquid which was
dissolved in hexanes and the solution filtered. The re-
sulting clear solution was concentrated (to ¯10 ml) and
cooled to 2218C. After 1 day, 1 formed as colourless
crystals (1.566 g, 84.6%).
2.6. Synthesis of 6–9 from a 1,3,2-dioxaborolan-2-ol or
-borinan-2-ol and 1,3-dichloro-1,1,3,3-tetraphenyldisi-
loxane
(Only 6, Y5CMe2CMe2, is described. Compounds 7–9
were prepared similarly).
Similar results were obtained for the thermal decomposi-
tions of the solid compounds 1, 2 and 4–7. Solid samples
were heated to 3008C in a melting point apparatus and
cooled to room temperature. The brown solid products had
the same IR spectral features as those of the products from
decomposition of the liquid borosilicates.
(9)
2.6.1. Compound 6
2.9. Reactions of 1–4 and 6–13 with water
Triethylamine (0.260 g, 2.57 mmol) in 20 ml ether was
added dropwise to a solution of 4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-ol (0.697 g, 4.84 mmol) and 1,3-dichloro-
1,1,3,3-tetraphenyldisiloxane (1.093 g, 2.42 mmol) in 40
ml ether. After 12 h, the colourless precipitate of
[Et3NH]Cl was removed by filtration (0.660 g, 99.0%).
Removal of solvent afforded a colourless solid which was
recrystallised from hot cyclohexane affording 6 as colour-
less crystals (1.415 g, 87.7%).
Compounds 7–9 were isolated in yields of 85.1, 74.0
and 75.9%, respectively.
(11)

3142
B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
Y5CMe2CMe2 or CMe2CH2CHMe, n51, 2, 3 or 4, x53
or 4.
silyl borates, a second solid was isolated and identified as
unreacted silyl borate by IR spectroscopy.
3. Results and discussion
Two borosilicates which contain O2B–OSiPh2O–BO2
units have been previously reported [3]. One was com-
pound 1, a 1,3,2-dioxaborolane derivative (Table 1) and
the other was the 2-methyl-1,3,2-dioxaborinane derivative.
The present work reports the first examples of chain
disilatrioxy-, trisilatetroxy- and tetrasilapentoxy-bridged
1,3,2-dioxaborolanes and -borinanes (Table 1). Com-
pounds 1–4 were prepared by the three different reactions
shown in Eqs. (1,7,8). Reaction (1) involved heating a
toluene solution of a mixture of two equivalents of the
particular organic diol (HO–Y–OH) with two equivalents
of boric acid and one equivalent of diphenylsilanediol at
reflux temperature in a Dean–Stark apparatus for 8 h.
Alternatively, a 1,3,2-dioxaborolan-2-ol or -borinan-2-ol
was synthesised initially then reacted with diphenylsilane-
diol, reaction (7), to give the borosilicate. As the yields
from reaction (7) were almost identical to those from
reaction (1), the borosilicates 1–4 were more efficiently
prepared according to reaction (1), as it is a one-pot
reaction. This is an example of an unusual self-assembly
reaction involving five separate molecules. The implications
of this and some related reactions are discussed below.
The possibility of obtaining the borosilicates 1–4 from
dichlorodiphenylsilane was also investigated (Eq. (8)).
This reaction involved the addition of two equivalents of
triethylamine to an ether solution containing one equiva-
lent of dichlorodiphenylsilane and two equivalents of the
particular 1,3,2-dioxaborolan-2-ol or -borinan-2-ol. The
yields from reaction (8) were 5–10% lower than for
reactions of the type shown in Eqs. (1) and (7). It is also
noteworthy that the pinacol derivative 1, which was
previously reported to be a viscous liquid [3], was obtained
in the present work as a solid melting at 42–458C.
Apart from melting points/boiling points, compounds
1–4 were characterised by elemental analysis (C, H and
B), IR spectroscopy, 1H and 13C NMR spectroscopy, and
mass spectrometry. The IR spectra of 1–4 exhibited strong
absorptions corresponding to the B–O(–Si) stretch
[3,10,11] at 1307, 1302, 1303 and 1299 cm21, respective-
ly. The mass spectra of 1–4 showed the parent ions at
m/z5468, 468, 496 and 524, respectively. Peaks arising
from the loss of methyl and phenyl groups were common
to all four spectra. No unusual 1H or 13C NMR signals
were observed in the spectra of 1–4. Unfortunately,
crystals of the solid compounds 1, 2 and 4 suitable for
X-ray crystallographic analysis could not be obtained.
The synthesis and characterisation of the disilatrioxy-
bridged borosilicates 6–9 were achieved in an exactly
analogous manner to 1–4. Compounds 6–9 were obtained
(12)
Y5CMe2CH2CMe2 or CHPriCMe2CH2, n51 or 2, x53
or 4.
2.9.1. Y5CMe2CMe2 or CMe2CH2CHMe, n51–4,
reaction (11)
Solutions of the borosilicates in water/acetone (3:1 v/v)
were heated at reflux for 3 h. The solvent was removed
affording a colourless solid. Fractional crystallisation gave
solids which were identified by mp, IR and mass spectra as
(Ph2SiO)3 (when n51 or 3), or (Ph2SiO)4 (when n52 or
4). The yields of the cyclosiloxanes were quantitative.
From each reaction a second colourless solid was isolated
and identified by IR and mp as 4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-ol or 4,4,6-trimethyl-1,3,2-dioxaborinan-2-
ol [4]. The yields of these compounds were quantitative.
2.9.2. Y5CMe2CH2CMe2 or CHPriCMe2CH2 , n51,2:
reaction (12)
Solutions of the silyl borates in water/acetone (3:1 v/v)
were heated at reflux for 3 h. The solvent was removed
leaving sticky solids. Ether was added and a powder
formed. This was identified as boric acid by IR spec-
troscopy. The filtrate was concentrated and layered with
cyclohexane. Colourless crystalline solids formed which
were identified as (Ph2SiO)3 when n51 or 3, or, as
(Ph2SiO)4 when n52 or 4. The solvent was removed from
the remaining solution to leave a viscous clear liquid
which was identified as either HOCMe2CH2CMe2OH or
HOCHPriCMe2CH2OH by IR spectroscopy. The yields of
boric acid, cyclosiloxane and organic diol obtained from
hydrolysis reactions (12) were almost quantitative.
2.10. Reactions of 1–4 and 6–13 with potassium
trimethylsilanolate
One equivalent of chain silyl borate and one equivalent
of K[OSiMe3] were stirred in dichloromethane solution for
8 h. Removal of solvent left sticky solids or viscous liquids
containing suspended solid particles. Fractional crystallisa-
tion of these residues from CH2Cl2 /cyclohexane solutions
afforded either (Ph2SiO)3 (from reactions of compounds
containing one or three silicon atoms) or (Ph2SiO)4 (from
compounds with two or four silicon atoms). The yields of
cyclosiloxanes were greater than 90%. In the case of solid

B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
3143
from either of the routes shown in Eqs. (2) and (9) hwhere
Y was CMe2CMe2, CMe2CH2CHMe, CMe2CH2CMe2 or
CHPriCMe2CH2, respectivelyj. The yields of compounds
6–9 from reaction (2) were in the range 93–83%. Reaction
(9) gave slightly worse results by 5–10%.
An alternative route to 6–9 which involved assembling
six reagent molecules was developed and is shown as
reaction (5). One advantage of reaction (5) over reaction
(2) is that it does not require the use of 1,1,3,3-tetra-
phenyldisiloxane-1,3-diol, which must first be synthesised
from 1,3-dichloro-1,1,3,3-tetraphenyldisiloxane or from
dichlorodiphenylsilane. Yields from reaction (5) were in
the range 89–77%.
The infrared spectra of 6–9 showed the B–O(–Si)
stretch at 1317, 1303, 1302 and 1343 cm21, respectively.
Absorptions of medium to very strong intensity between
¯1100 and 1090 cm21, which are not observed in the
mono-silicon compounds 1–4, are assigned to Si–O–Si
stretching vibrations in 6–9 [9]. The mass spectra of 6–9
showed parent ion peaks and fragmentation patterns large-
ly analogous to those for the single silicon species 1–4.
Compounds 10 and 11 were prepared in yields of 75 and
77%, respectively, according to reaction (3) hY5
CMe2CMe2 or CMe2CH2CHMej.
Bearing in mind that in the dehydration reactions, e.g.
Eqs. (1) and (5), either five or six molecules, respectively,
are assembled to form the borosilicate product in high
yield, some comments on the possible sequence of re-
actions affording the borosilicates are necessary. The most
probable sequence is shown in Scheme 1 below. Initially,
the 1,3,2-dioxaborolan-2-ol or 1,3,2-dioxaborinan-2-ol is
formed from boric acid and the organic diol (Eq. (13)).
The next step is the reaction between one equivalent of
either the 1,3,2-dioxaborolan-2-ol or 1,3,2-dioxaborinan-2-
ol and one equivalent of the silanediol or siloxanediol to
produce B–O–Si bonded species which retain one Si–OH
moiety (Eq. (14)). The last steps are shown in Eqs. (15)
and (16). Evidence supporting the Scheme includes: (a) the
lack of any cyclic products containing –Si–O–B–O–Si–
units which might be expected if more than one reactive
B–OH site was available for reaction with the Si–OH
bonds, (b) that yields of products from reactions with
mixtures of boric acid and organic diol, or from preformed
1,3,2-dioxaborolan-2-ol or 1,3,2-dioxaborinan-2-ols, are
very similar, (c) the isolation of the same products when
either two equivalents of Ph2Si(OH)2 or one of
(HO)SiPh2OSiPh2(OH) was used (and likewise when two
HO(SiPh2O)2H or one HO(SiPh2O)4H was used), and (d)
the formation of two-silicon products 6 and 7, but not any
three-silicon product, when three equivalents of
Ph2Si(OH)2 were used (Eq. (10)).
Attempts to prepare 10 and 11 using three equivalents of
diphenylsilanediol, two of boric acid and two of the
organic diol in reactions analogous to (5) afforded only the
two-silicon compounds
6
and 7, respectively, and
The preference for Si–OH bonds to react with B–OH
rather than other silanol bonds during the self-assembly
reactions has been seen previously in the synthesis of the
17-membered cage compound [B(OSiPh2OSiPh2O)3B], 16
[12]. This compound can be prepared in almost identical
yields from two moles of boric acid and either six moles of
Ph2Si(OH)2 or three moles of HOSiPh2OSiPh2OH.
The stability of the chain borosilicates to atmosphere
and heat was assessed. The solid compounds 1, 2 and 4–7
were unchanged after exposure to atmosphere for 2
months. Liquid borosilicates 3 and 8–13 were less stable
to atmosphere and after exposure for ¯2 weeks, small
amounts of crystalline material began to form. These solids
were identified as the cyclosiloxane species (Ph2SiO)3
(from one- and three-silicon borosilicates) or (Ph2SiO)4
(from two- and four-silicon borosilicates).
All the liquid chain borosilicates decomposed when
vacuum distillation was attempted at ¯170–1908C and
1.5–3 mmHg. Infrared spectral analysis of the products of
decomposition indicated the presence of Si–O–Si groups
and suggested that the decomposition mixtures contained
cyclosiloxane species. Similarly, after the solid compounds
had been heated to 3008C, the resulting materials had IR
spectra suggestive of cyclosiloxane formation, possibly
(Ph2SiO)3 or (Ph2SiO)4.
(Ph2SiO)3. Both 10 and 11 were isolated from reaction (3)
as viscous liquids which decomposed when vacuum dis-
tillation (¯1908C, 1.5 mmHg) was attempted. Both com-
pounds were identified on the basis of elemental analysis
(C, H and B), IR, 1H and 13C NMR spectroscopy and mass
spectrometry. The infrared spectra of 10 and 11 contained
the B–O(–Si) stretch at 1315 and 1304 cm21, respectively.
The compounds showed parent ion peaks in their mass
spectra and the fragmentation patterns were analogous to
those of the two-silicon species, 6 and 7.
Compounds 12 and 13 were prepared in yields of 79 and
75%, respectively, according to reaction (4) hY5
CMe2CMe2 or CMe2CH2CHMej.
An alternative synthesis of 12 and 13 was also de-
veloped and is given in Eq. (6). The advantage of this
method is that it does not require the prior synthesis of the
tetrasiloxanediol 8. However, the yields of reaction (6)
were ¯10% lower than those from reaction (4). Com-
pounds 12 and 13 were isolated as viscous liquids which
decomposed when vacuum distillation (¯1758C, 2 mmHg)
was attempted. Both compounds were identified on the
basis of elemental analysis (C, H and B), IR which
contained the B–O(–Si) stretch at 1315 and 1309 cm21
,
1
respectively, and H and 13C NMR spectroscopy. Attempts
to prepare 12 and 13 using four equivalents of
diphenylsilanediol in reactions analogous to Eq. (5) af-
forded only the two-silicon analogues 6 and 7, respective-
ly, and (Ph2SiO)3.
All the borosilicates were decomposed in a refluxing
water/acetone (3:1 v/v) solution within 3 h. From com-
pounds containing CMe2CMe2 or CMe2CH2CHMe moi-
eties, the products were the corresponding 1,3,2-diox-

3144
B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
Scheme 1.
aborolan-2-ol, or borinan-2-ol, and cyclosiloxanes, viz.
(Ph2SiO)3 when n51 or 3, or (Ph2SiO)4 when n52 or 4
(Eq. (11)). For the chain compounds containing
CMe2CH2CMe2 or CHPriCMe2CH2 groups, further de-
composition occurred during the hydrolysis and the prod-
ucts were the organic diol reagent, boric acid and
(Ph2SiO)3 (for n51) or (Ph2SiO)4 (for n52) (Eq. (12)).
The tendency for the chain borosilicates 1–13 to de-
compose to siloxane species when exposed to heat or
moisture is not a new observation. For example, ‘ring-
reorganisation’ reactions of (PhBO)(Ph2SiO)2, 17, and
(PhBO)(Me2SiO)2, 18, have previously been reported
[13]. In the presence of acidic or basic initiators at elevated
temperatures, compounds 17 and 18 were converted to
siloxane polymers and (PhBO)3. The release of ring strain,
coupled with the formation of stable siloxane and boroxine
products, were the reasons suggested to explain these
observations [13]. In the cases of 1–13, the decomposi-
tions may be favoured by the formation of stable siloxane
species but the release of ring strain cannot be a factor.

B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
3145
Compounds 1–13 were surprisingly unreactive to the
following amines even under forcing conditions; triethyl-
amine, di-iso-propylamine, pyridine and ethylenediamine.
For example, the borosilicates were recovered unchanged
after refluxing in NEt3, NHPri2, pyridine or ethyl-
enediamine for one day. The highly nucleophilic reagent,
K[OSiMe3], easily cleaved the B–O–Si bonds in com-
pounds 1–13. However, the reactions were not selective.
Reaction of any chain borosilicate with one equivalent of
K[OSiMe3] afforded either (Ph2SiO)3 or (Ph2SiO)4, some
unreacted borosilicate and an unidentified sticky colourless
solid.
interest are the cage compound [ButSihOB( p-
C6H4Br)Oj3SiBut], 21 [16], which contains B–O–Si(But)
linkages, and O–CMe2CH2CH(Me)–O–B–OSiPh3, 22
[17].
Crystals of 5 which were suitable for X-ray diffraction
studies were grown from toluene solution at 2248C.
Molecules of 5 lie on crystallographic two-fold axes with
two symmetry-related trigonal planar BO3-units bridged by
a tetrahedral But2SiO2-unit (Fig. 1).
Principal dimensions are given in Table 3. There were
no untoward intermolecular contacts. The two independent
B–O(C) distances in 5 are essentially identical (1.331(4)
%4 %%%%%%%%%%%%4
˚
and 1.330(5) A, Table 3), but the B–O(Si) distance is
t
˚
significantly longer (1.360(4) A). The B–O(SiBu2) dis-
tances in 19, 1.350(4) and 1.350(5) A [14], are similar to 5
3.1. Structural characterisation of 5
˚
but the distances in 20 are significantly smaller at 1.313(2)
t
Compound 5 was isolated in 82% yield as a colourless
solid with melting point 51–538C. The IR spectrum of 5
contained a strong peak corresponding to the B–O(–Si)
stretch at 1299 cm21. The EI mass spectrum of 5 did not
show the parent molecular ion, but the peak at highest
mass was at m/z5371, corresponding to the loss of one
butyl group.
˚
and 1.320(3) A [15]. The B–O(SiBu ) lengths in the cage
˚
compound 21 were in the range 1.345(9)–1.372(10) A
˚
[16]. The B–O(C) distances in 5 (1.330(5), 1.331(4) A)
are shorter than the corresponding distances in 22
˚
(1.347(5), 1.361(5) A) [17]. The Si–O distance in 5
˚
(1.625(2) A) is similar to the corresponding distances in
˚
19 [14] (1.630(3), 1.631(2) A) and 20 [15] (1.626(1),
Compound 5 is the third silyl borate containing the
B–O–Si(But)2 moiety to be studied using X-ray crys-
tallography. Previously, two cyclic compounds had been
˚
1.635(2) A).
The unique B–O–Si angle in 5 measures 141.5(2)8 and
lies within the range of reported values for such angles, i.e.
128.89(14)8 in (PhBO)(Ph2SiO)2, 17 [13], to 160.9(3)8 in
(PhBO)2(Ph2SiO)2, 23 [18]. The B–O–Si angle in
reported
(PhBO)2(But SiO)2,
19
[14],
and
%4 %%%%%%%%%%2%4
FBOSiBut2OSiMe2OSiBut2 O, 20 [15]. Other compounds of
%4 %%%%%%%%%%%%4
O–CMe2CH2CH(Me)–O–B–OSiPh3, 22, was 133.1(2)8
%4 %%%%%%%%%%%4
[17]. The B–O–Si(Bu2t ) angles in (PhBO)2(Bu2t SiO)2, 19
[14], and FBOSiBu2t OSiMe2OSiBut2 O, 20 [15], varied
from 149.1(3)8 in 19 to 159.8(2)8 in 20 and are sig-
nificantly larger than those in 5. The six B–O–Si(But)
angles in the cage compound [ButSihOB( p–
C6H4Br)Oj3SiBut], 21 [16], varied from 137.5(6)8 to
140.7(6)8.
Table 3
%4 %%%%%%% 4
Bond distance and angle data for (O–CMe2CH2CHMe–O–B–O)2SiBut2,
5
˚
˚
Bond
Bond length (A)
Bond
Bond length (A)
Si1–O1
Si1–C1
B1–O1
B1–O2
B1–O6
C3–O2
C5–O6
C1–C11
1.625(2)
1.867(4)
1.360(4)
1.331(4)
1.330(5)
1.443(4)
1.438(5)
1.524(5)
C1–C12
C1–C13
C3–C4
C3–C31
C3–C32
C4–C5
1.552(6)
1.549(5)
1.479(5)
1.507(6)
1.511(6)
1.399(6)
1.494(6)
The unique C3BO2 ring in 5 adopts a conformation
which is intermediate between a half-chair and a sofa and
has dimensions which are very similar to those for this ring
in 22 [17].
C5–C51
Bond angle
Degrees
Bond angle
O2–C3–C4
O2–C3–C31 105.4(3)
O2–C3–C32 107.0(3)
Degrees
109.4(3)
Supplementary data
O1–Si1–O1a 112.1(2)
O1–Si1–C1 107.75(14)
O1–Si1–C1a 105.51(14)
C1–Si1–C1a 118.3(3)
Si1–C1–C11 112.7(3)
Si1–C1–C13 111.4(3)
Si1–C1–C12 107.3(3)
Si1–O1–B1 141.5(2)
O1–B1–O2 117.6(3)
O1–B1–O6 118.7(3)
O2–B1–O6 123.6(3)
B1–O2–C3 121.3(3)
B1–O6–C5 120.5(3)
Supplementary data are available from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK, on request, quoting the deposition number
CCDC 118704.
O6–C5–C4
111.1(4)
O6–C5–C51 107.3(4)
C11–C1–C12 108.0(4)
C11–C1–C13 109.6(4)
C12–C1–C13 107.6(4)
C3–C4–C5
119.5(4)
Acknowledgements
C4–C3–C31 110.0(4)
C4–C3–C32 112.0(4)
C4–C5–C51 119.4(5)
C31–C3–C32 112.7(4)
BO’L thanks FORBAIRT (Ireland) for a postgraduate
grant.
a This superscript in an atom label refers to equivalent position 2 x, y,
1/2 2 z.

3146
B.J. O’Leary et al. / Polyhedron 18 (1999) 3135–3146
[10] E.W. Abel, A. Singh, J. Chem. Soc. (1959) 690.
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