Platinum-catalysed 1,4-diboration of 1,3-dienes

Article abstract of DOI:10.1039/a800108a

The chiral diborane(4) compounds B₂[R,R-O₂CH(CO₂Me)CH(CO₂Me)] ₂, B₂(S,O₂CH₂CHPh)₂, B₂(R,R-O₂-CHPhCHPh)₂ and B₂(O

Full text of DOI:10.1039/a800108a

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Platinum-catalysed 1,4-diboration of 1,3-dienes
William Clegg,a Thorsten R. F. Johann,b Todd B. Marder,c Nicholas C. Norman,*,†,b
A. Guy Orpen,b Torren M. Peakman,b Michael J. Quayle,b Craig R. Riceb and Andrew J. Scotta
a The University of Newcastle, Department of Chemistry, Newcastle upon Tyne, UK NE1 7RU
b The University of Bristol, School of Chemistry, Bristol, UK BS8 1TS
c The University of Durham, Department of Chemistry, Science Laboratories, South Road,
Durham, UK DH1 3LE
The chiral diborane(4) compounds B2[R,R-O2CH(CO2Me)CH(CO2Me)]2, B2(S-O2CH2CHPh)2, B2(R,R-O2-
CHPhCHPh)2 and B2(O2C20H12)2 (O2C20H12 = 1,7Ј-bi-2-naphtholate) have been synthesized. All four
compounds have been characterised by X-ray crystallography, the latter as a racemate. The B᎐B bond oxidative-
addition reactions of the first three compounds with [Pt(PPh3)2(η-C2H4)] resulted in the platinum() bis(boryl)
complexes cis-[Pt(PPh3)2{B[R,R-O2CH(CO2Me)CH(CO2Me)]}2], cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2] and cis-
[Pt(PPh3)2{B(R,R-O2CHPhCHPh)}2]; the former two were also characterised by X-ray crystallography. The
platinum-catalysed diborations of a range of prochiral 1,3-dienes with the compounds B2[R,R-O2CH(CO2Me)-
CH(CO2Me)]2, B2(S-O2CH2CHPh)2 and B2(R,R-O2CHPhCHPh)2 were studied. Although these reactions were
clean and quantitative, observed product d.e.s (measured by 1H NMR spectroscopy) were low or non-existent
indicating that chirality transfer from the diborane(4) diolate groups to the diene diboration product is not
efficient in these cases.
The platinum-catalysed addition of diborane(4) compounds to
the C᎐C/C᎐O multiple bonds present in alkenes,1 alkynes,2 1,3-
dienes3 and α,β unsaturated ketones4 (diboration) is now well
established with key intermediates in these reactions thought to
be platinum() bis(boryl) complexes formed by oxidative add-
ition of the B᎐B bond of the diborane(4) compound to a
platinum(0) centre;1–5 many examples of complexes with the
general formula cis-[Pt(BR2)2(PRЈ3)2] have now been isolated
and structurally characterised.2b,c,e,6–8 As an extension to this
work, we have recently sought to carry out asymmetric dibor-
ation reactions using enantiomerically pure diborane(4) com-
pounds and have had limited success using alkene substrates.9
Herein we report on our attempts to diborate prochiral 1,3-
dienes asymmetrically using platinum phosphine catalyst pre-
cursors, and include full details of the synthesis and structural
characterisation of a range of chiral diborane(4) compounds.
Fig. 1 Molecular structure of compound 1 (one of two independent
molecules) with key atoms labelled. Non-hydrogen atoms are drawn as
ellipsoids to enclose 50% probability density
Results and Discussion
MeO2C
MeO2C
CO2Me
CO2Me
Ph
The chiral diborane(4) compounds B2[R,R-O2CH(CO2Me)-
CH(CO2Me)]2 1, B2(S-O2CH2CHPh)2 2, B2(R,R-O2CHPh-
CHPh)2 3 and B2(O2C20H12)2 4 (O2C20H12 = binaphthalenolate
or binolate) were prepared as described in the Experimental
section from B2(NMe2)4 and the corresponding diol according
to established literature procedures;10 4 was prepared as a
racemate.
O
O
O
O
O
O
O
O
B
B
B
B
Ph
1
2
Compounds 1–4 were characterised by normal spectroscopic
and analytical methods as well as by X-ray crystallography.
Their molecular structures are shown in Figs. 1–4 respectively
with an additional view of 4 in Fig. 5. Selected bond lengths
and angles are presented in Table 1 and crystallographic data in
Table 3. The structures of 1–3 are largely unexceptional and
similar to those of the many diborane(4) bis(diolates) which
have previously been structurally characterised.11–13 Com-
pounds 1 and 2 crystallise with two molecules per asymmetric
unit and 3 has crystallographic C2 symmetry. Since all three
were prepared from enantiomerically pure diol, they all crystal-
lise in chiral space groups (Table 3). The B᎐B bond distances
Ph
Ph
Ph
Ph
O
O
O
O
O
O
O
O
B
B
B
B
3
4
(Table 1) are within the range previously established for this
type of compound,11,13 and we note that the torsion angles
about the B᎐B bond, i.e. that defined by the interplanar angle
between the two adjacent boron trigonal planes, are 28.1 and
26.8Њ for 1, 4.5 and 5.0Њ for 2 and 34.7Њ for 3, which, in the
cases of 1 and 3, are somewhat larger than the corresponding
angles found in most other diborane(4) bis(diolate) structures.
† E-Mail: N.C.Norman@Bristol.ac.uk
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Table 1 Selected bond lengths (Å) and angles (Њ) for compounds 1–4
1
2
B(1)᎐B(2)
B(1)᎐O(1)
B(1)᎐O(2)
B(2)᎐O(7)
B(2)᎐O(8)
B(3)᎐B(4)
B(3)᎐O(13)
B(3)᎐O(14)
B(4)᎐O(19)
B(4)᎐O(20)
1.701(4)
1.373(3)
1.369(3)
1.363(3)
1.366(3)
1.688(4)
1.368(3)
1.365(3)
1.377(3)
1.352(3)
B(1)᎐B(2)
1.695(3)
1.370(2)
1.358(2)
1.362(2)
1.368(2)
1.694(3)
1.360(2)
1.373(2)
1.366(2)
1.371(2)
B(1)᎐O(11)
B(1)᎐O(12)
B(2)᎐O(21)
B(2)᎐O(22)
B(3)᎐B(4)
B(3)᎐O(31)
B(3)᎐O(32)
B(4)᎐O(41)
B(4)᎐O(42)
Fig. 2 Molecular structure of compound 2 (one of two independent
molecules). Details as in Fig. 1
B(2)᎐B(1)᎐O(1)
B(2)᎐B(1)᎐O(2)
O(1)᎐B(1)᎐O(2)
B(1)᎐B(2)᎐O(7)
B(1)᎐B(2)᎐O(8)
O(7)᎐B(2)᎐O(8)
B(4)᎐B(3)᎐O(13)
B(4)᎐B(3)᎐O(14)
122.6(2)
124.9(2)
112.5(2)
124.8(2)
121.3(2)
113.9(2)
124.1(2)
123.0(2)
B(2)᎐B(1)᎐O(11)
B(2)᎐B(1)᎐O(12)
O(11)᎐B(1)᎐O(12) 113.3(2)
B(1)᎐B(2)᎐O(21)
B(1)᎐B(2)᎐O(22)
O(21)᎐B(2)᎐O(22) 113.3(2)
B(4)᎐B(3)᎐O(31)
B(4)᎐B(3)᎐O(32)
O(31)᎐B(3)᎐O(32) 113.0(2)
124.4(2)
122.4(2)
125.2(2)
121.5(2)
123.8(2)
123.2(2)
O(13)᎐B(3)᎐O(14) 112.9(2)
B(3)᎐B(4)᎐O(19)
B(3)᎐B(4)᎐O(20)
O(19)᎐B(4)᎐O(20) 112.8(2)
122.3(2)
124.8(2)
B(3)᎐B(4)᎐O(41)
B(3)᎐B(4)᎐O(42)
O(41)᎐B(4)᎐O(42) 113.1(2)
123.4(2)
123.5(2)
3
4
B(1)᎐B(2)
B(1)᎐O(1)
B(2)᎐O(2)
1.700(5)
1.359(2)
1.361(2)
B(1)᎐B(2)
B(1)᎐O(2)
B(1)᎐O(3)
B(2)᎐O(1)
B(2)᎐O(4)
1.715(5)
1.377(4)
1.372(4)
1.375(4)
1.367(4)
Fig. 3 Molecular structure of compound 3. Details as in Fig. 1
B(2)᎐B(1)᎐O(1)
O(1)᎐B(1)᎐O(1A)
B(1)᎐B(2)᎐O(2)
O(2)᎐B(2)᎐O(2A)
123.37(13)
113.3(3)
123.21(13)
113.6(3)
B(2)᎐B(1)᎐O(2)
B(2)᎐B(1)᎐O(3)
O(2)᎐B(1)᎐O(3)
B(1)᎐B(2)᎐O(1)
B(1)᎐B(2)᎐O(4)
O(1)᎐B(2)᎐O(4)
123.6(3)
122.5(2)
113.8(3)
123.6(3)
122.5(2)
113.8(3)
Fig. 5 Alternative view of the molecular structure of compound 4
attached such that they bridge the B᎐B bond. Compound 4 is
therefore an example of a 1,2 rather than the 1,1 isomer
observed for all previous diborane(4) bis(diolates).11,13 Such a
structure presumably results from the eight-membered B2O2C4
ring being more stable than the alternative seven-membered
BO2C4 ring which would be present in the 1,1 isomer and the
similarity of the B᎐O lengths and B᎐B᎐O and O᎐B᎐O angles in
4 as compared with 1–3 indicates that the 1,2-isomer form in 4
is essentially unstrained. Unlike compounds 1–3, 4 was pre-
pared from the racemic diol and both enantiomers of the par-
ticular conformational form adopted in the solid state, which
have approximate (non-crystallographic) D2 symmetry, are
present in the crystal (centrosymmetric space group P21/n); the
torsion angles between the naphthalene planes are 76.5 and
Fig. 4 Molecular structure of compound 4. Details as in Fig. 1
However, the barrier to rotation about the B᎐B bond is likely to
be very low such that these torsion angles would be expected to
vary widely as a result of crystal packing forces especially when
markedly non-planar diolate groups are present as is the case
here.
The structure of compound 4 (Figs. 4 and 5), which crystal-
lises as a toluene solvate, has a relatively long B᎐B bond
[1.715(5) Å], although still within the range observed for
diborane(4) compounds,11 and an angle between the boron
trigonal planes of 37.6Њ similar to the corresponding angle in 3.
However, the most notable feature is that the diolate groups are
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Table 2 Selected bond lengths (Å) and angles (Њ) for the complexes
cis-[Pt(PPh3)2{B[R,R-O2CH-
(CO2Me)CH(CO2Me)]}2]
cis-[Pt(PPh3)2{B(S-O2CH2-
CHPh)}2]
Pt᎐B(1)
Pt᎐B(2)
Pt᎐P(1)
Pt᎐P(2)
B(1)᎐O(3)
B(1)᎐O(4)
B(2)᎐O(1)
B(2)᎐O(2)
2.065(5)
2.054(7)
2.368(2)
2.341(2)
1.385(8)
1.417(9)
1.398(9)
1.387(9)
Pt᎐B(1)
Pt᎐B(2)
Pt᎐P(1)
Pt᎐P(2)
B(1)᎐O(1)
B(1)᎐O(2)
B(2)᎐O(3)
B(2)᎐O(4)
2.070(3)
2.054(4)
2.3456(9)
2.3505(9)
1.389(4)
1.383(4)
1.378(5)
1.375(6)
B(1)᎐Pt᎐B(2)
B(1)᎐Pt᎐P(1)
B(1)᎐Pt᎐P(2)
B(2)᎐Pt᎐P(1)
B(2)᎐Pt᎐P(2)
P(1)᎐Pt᎐P(2)
Pt᎐B(1)᎐O(3)
Pt᎐B(1)᎐O(4)
O(3)᎐B(1)᎐O(4)
Pt᎐B(2)᎐O(1)
Pt᎐B(2)᎐O(2)
O(1)᎐B(2)᎐O(2)
73.3(4)
91.5(3)
165.0(3)
163.7(2)
92.4(2)
103.14(6)
127.3(5)
123.3(5)
109.5(4)
119.6(5)
130.5(6)
109.9(6)
B(1)᎐Pt᎐B(2)
B(1)᎐Pt᎐P(1)
B(1)᎐Pt᎐P(2)
B(2)᎐Pt᎐P(1)
B(2)᎐Pt᎐P(2)
P(1)᎐Pt᎐P(2)
Pt᎐B(1)᎐O(1)
Pt᎐B(1)᎐O(2)
O(1)᎐B(1)᎐O(2)
Pt᎐B(2)᎐O(3)
Pt᎐B(2)᎐O(4)
O(3)᎐B(2)᎐O(4)
75.5(2)
164.7(2)
91.7(2)
89.63(12)
166.16(13)
102.75(3)
125.2(2)
124.3(2)
110.5(3)
127.3(3)
122.4(3)
110.2(3)
Fig. 6 Molecular structure of cis-[Pt(PPh3)2{B[R,R-O2CH(CO2Me)-
CH(CO2Me)]}2] with key atoms labelled; PPh3 hydrogen atoms are
omitted for clarity. Non-hydrogen atoms are drawn as ellipsoids to
enclose 50% probability density
86.2Њ. A more detailed look at the structure of 4 reveals that the
two eight-membered B2O2C4 rings have boat conformations
and that, for a given enantiomer, the chirality of the two binol
groups is the same. The use of models indicates that an altern-
ative twist-boat conformation for the rings is also possible. For
the twist-boat/twist-boat isomer, the binol groups must also
both have the same chirality (for a given enantiomer) but for a
boat/twist-boat isomer the binol group chiralities are opposite.
There are, therefore, three possible diastereomeric conform-
ational forms for 4, although NMR studies indicate that only
one of these (presumably the one found in the crystal structure)
is present in solution.
Compounds 1–3, but not 4, reacted cleanly and quanti-
tatively with [Pt(PPh3)2(η-C2H4)] affording the platinum() bis-
(boryls) cis-[Pt(PPh3)2{B[R,R-O2CH(CO2Me)CH(CO2Me)]}2],
cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2] and cis-[Pt(PPh3)2{B(R,R-
O2CHPhCHPh)}2], consistent with previously established
routes to this class of compound,2,6,7 and were characterised
by normal spectroscopic and analytical methods. In addition,
the first two were characterised by X-ray crystallography, the
results of which are shown in Figs. 6 and 7; selected bond
lengths and angles are given in Table 2 and crystallographic
data in Table 3.
Fig. 7 Molecular structure of cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2].
Details as in Fig. 6
within previously observed limits.2b,c,e,6,7 A discussion of these
structural features is given in ref. 6 and will not be reiterated
here.
R
O
Ph3P
Ph3P
B
R′
O
O
Having established routes to chiral diborane(4) compounds
and shown that these compounds (in the case of 1–3) reacted
with [Pt(PPh3)2(η-C2H4)] to afford platinum() bis(boryls), we
were interested to see whether or not we could effect a
platinum-catalysed, asymmetric diboration of prochiral 1,3-
dienes. Miyaura and co-workers3
Pt
R
B
O
R′
R = R′ = CO2Me; R = Ph, R′ = H; or R = R′ = Ph
were the first to report
platinum-catalysed diene diboration reactions. These workers
had shown that [Pt(PPh3)4] would catalyse the addition of B2-
(O2CMe2CMe2) to buta-1,3-diene, isoprene and 2,3-dimethyl-
buta-1,3-diene in either toluene or dmf (dmf = dimethylform-
amide) affording 1,4-diborated products in high yields (toluene
giving the best product yields) as single, Z isomers. Interest-
ingly, however, if the phosphine-free platinum species [Pt(dba)2]
(dba = dibenzylideneacetone) was used the diborated products
were those resulting from diene dimerisation.3
The compound cis-[Pt(PPh3)2{B[R,R-O2CH(CO2Me)CH-
(CO2Me)]}2] crystallises as a toluene solvate and cis-[Pt-
(PPh3)2{B(S-O2CH2CHPh)}2] as
a CH2Cl2 solvate. Both
adopt structures now well established for this class of com-
pound,2b,c,e,6,7 a key feature being the cis arrangement of the
boryl ligands about the square-planar platinum centre. Other
features are also unexceptional with the Pt᎐B distances and
P᎐Pt᎐P and B᎐Pt᎐B angles (Table 2) all falling within or close
to observed ranges for these parameters, and the angles between
the boryl boron trigonal planes and the platinum mean square
plane [86.4 and 62.4Њ and 84.5 and 81.1Њ respectively] also being
As our first attempt we studied the reaction between com-
pounds 1–3 and trans-penta-1,3-diene (Scheme 1), using 5 mol %
[Pt(PPh3)2(η-C2H4)] as catalyst in toluene at 80 ЊC for 1 d. In all
J. Chem. Soc., Dalton Trans., 1998, Pages 1431–1438
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[Pt(P)2(C2H4)]
–C2H4
[Pt]
+
B2(diolate)2
(diolate)B
B(diolate)
5 diolate = R,R-O2CH(CO2Me)CH(CO2Me)
6 diolate = S-O2CH2CHPh
7 diolate = R,R-O2CHPhCHPh
B
B
B
B
[Pt(P)2]
P
P
B
B
P
P
Pt
B
Pt
[Pt]
+
Et
B2(diolate)2
(diolate)B
B(diolate)
B
B
Et
9 diolate = S-O2CH2CHPh
10 diolate = R,R-O2CHPhCHPh
11 diolate = 1,2-O2C6H4
P
+ P
Pt
P
B
P
Pt
B
[Pt]
G
+
B2(diolate)2
(diolate)B
B(diolate)
B
I
B
P
12 diolate = S-O2CH2CHPh
Pt
B
H
[Pt]
+
B2(diolate)2
(diolate)B
B(diolate)
Scheme 2 P = PPh3
where the boron diolate group contains a single chiral centre
with an S configuration (as is the case in 14), the possible iso-
mers are C–F (C and D are a meso form and therefore the same
in this case although they would differ for an unsymmetrically
substituted cyclohexadiene), C/D (the meso form) having a syn
configuration with respect to the boryl groups and E/F having
an anti configuration.
13 diolate = R,R-O2CH(CO2Me)CH(CO2Me)
14 diolate = S-O2CH2CHPh
15 diolate = R,R-O2CHPhCHPh
16 diolate = 1,2-O2C6H4
Scheme 1
cases, spectroscopic data were consistent with the formation
of the expected 1,4-diboration products 5–7, but it was clear,
particularly from the H NMR data, that the two possible
1
diastereomers [A(S) and B(R) shown below] were formed in
approximately equal amounts, the highest d.e. (20%) being
seen for 5 (product d.e.s here and throughout this paper were
estimated from 1H NMR integrations).
(S-diolate)B
B(S-diolate) (S-diolate)B
B(S-diolate)
C, S,R,S,S
D, S,S,R,S
(diolate)B
B(diolate)
(diolate)B
B(diolate)
(S-diolate)B
B(S-diolate) (S-diolate)B
B(S-diolate)
A(S)
B(R)
E, S,R,R,S
F, S,S,S,S
The analogous reactions between trans-hexa-1,3-diene and 2
or 3 were also examined, as was a reaction using the achiral
diborane(4) compound B2(1,2-O2C6H4)2 8, resulting in the
products 9–11 (Scheme 1). Spectroscopic data revealed that
these three reactions also afforded the expected products after
similar reaction times and with similar yields, but as with 5–7
the observed d.e.s for 9 and 10 were poor.
The NMR data for compound 16 displayed a 2H singlet at
δ 6.05 for the alkene hydrogens (᎐CH) of the cyclohexene ring
indicating that only one diastereomer was present, although it
was not possible to determine whether this was the syn or anti
form. Such a determination was possible in principle, however,
in the case of 13–15 since the syn diastereomer (C/D) would be
᎐
O
O
O
O
expected to give rise to a mutually coupled pair of alkene ᎐CH
᎐
B
B
doublets whereas each anti diastereomer (E and F) should give
rise to a singlet as a result of the C2 symmetry axis present in
these forms. For each of 13–15 what was observed was a pair of
mutually coupled doublets of equal intensity consistent with
the exclusive presence of the meso syn isomer in each case.
A possible mechanism for 1,3-diene diboration (in line with
previously postulated alkyne and alkene mechanisms, and that
proposed for diene diboration by Miyaura and co-workers3) is
shown in Scheme 2. In the case of the acyclic dienes, initial co-
ordination of the s-cis-diene conformer (intermediate G) and
subsequent hindered rotation about the 2,3-C᎐C bond due to
co-ordination of the remaining diene double bond to the plat-
inum centre (not explicitly shown) in intermediates H and I
(and G) would account for the fact that the resulting alkene
product has a Z or cis configuration rather than the alternative
E or trans configuration. For cyclohexadiene, the constraints of
the ring require that the diboration product be the Z or cis
8
In the case of the reaction between compound 2 and trans-2-
methylpenta-1,3-diene, spectroscopic data were consistent with
the formation of the expected product 12 (Scheme 1) but, as
well as a poor observed d.e., reaction times were considerably
longer than for 5–7 and 9–11.
In contrast, the reactions between 1–3 or 8 and cyclohexa-
1,3-diene proceeded much more rapidly affording the diborated
compounds 13–16 (Scheme 1), although the product stereo-
chemistry was now more complicated since cyclohexa-1,3-diene
contains two prochiral centres. In the case of 16, for which the
boron diolate group is achiral, the possible isomers are simply
the expected diastereomerically related pairs of enantiomers
R,R/S,S and the meso R,S/S,R. In the case of 13–15, the same
situation arises since, although the boron diolate group is now
chiral, only one enantiomer is present. For a particular case
isomer with respect to the C᎐C double bond, but the formation
of syn diboration isomers (i.e. both borons added to one face of
᎐
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the diene) would also follow from co-ordination of the second
double bond in intermediates H and I (and G).
1.54 mmol) in Et2O (5 cm3) was added to a solution of S-1-
phenylethane-1,2-diol (0.430 g, 3.12 mmol) in Et2O (10 cm3)
and the reaction mixture stirred for 18 h. After this time a
solution of HCl (7.6 cm3 of a 1.0  solution in Et2O) was added
and the reaction mixture stirred for 2 h. Subsequent filtration
followed by removal of all volatiles from the filtrate by vacuum
afforded crude compound 2 as a white solid. Recrystallisation
from hexane afforded pure 2 as a white crystalline solid (yield
In conclusion, we have shown that chiral diborane(4) com-
pounds can be readily prepared from easily available, enantio-
merically pure diols and that these compounds, with the excep-
tion of 4, react with [Pt(PPh3)2(η-C2H4)] to afford platinum
bis(boryls) in line with previous observations.2,6,7 Moreover, 1,4-
diboration of 1,3-dienes also occurs readily, consistent with the
previous report from Miyaura and co-workers,3 but in the sys-
tems studied here no significant asymmetric induction was
observed although it is possible that other chiral diborane(4)
compounds might afford better results in this regard. In any
event, the stoichiometric use of the chiral reagent could be con-
sidered somewhat wasteful and an alternative approach might
be to make the metal centre chiral by the use of suitable chiral
phosphines. Most such systems in the literature, however,
involve the use of a chiral chelating diphosphine,14 but it is
known from related studies dealing with alkyne diboration2e
that chelating diphosphines cause a dramatic reduction in reac-
tion rates presumably because the active catalytic species con-
tains only one phosphine. This problem might be alleviated by
using enantiomerically pure chiral monodentate phosphines. In
situations where phosphine catalyst precursors are ineffective
however, such as in platinum-catalysed alkene diboration, the
use of chiral diborane(4) compounds provides the only means
of controlling the product chirality, an area in which we have
had modest success.9
1
0.270 g, 60%). NMR (CDCl3): H, δ 7.35 (m, 10 H, Ph), 5.50
3
2
(dd, 2 H, CH, JHH = 8.6), 4.60 (dd, 2 H, CH2, JHH = 8.6,
3JHH = 8.6) and 4.10 (dd, 2 H, CH2, JHH = 8.6, JHH = 8.6 Hz);
13C-{1H}, δ 141.7 (ipso-C of Ph), 128.8 (o-C of Ph), 128.9 (m-C
of Ph), 126.0 (p-C of Ph), 78.9 (CH) and 72.9 (CH2); 11B-{1H},
δ 28.9 (br s). Mass spectrum: m/z 294 (Mϩ, 100%); high reso-
lution, C16H16B2O4 requires 294.123, found 294.124 (Found: C,
64.4; H, 6.0. C8H8BO2 requires C, 65.4; H, 5.5%). [α]D20 = 6.81
(c = 0.0048, CH2Cl2).
2
3
B2(R,R-O2CHPhCHPh)2 3. A solution of B2(NMe2)4 (0.280
g, 1.4 mmol) in Et2O (10 cm3) was added to a suspension of
R,R-1,2-diphenylethane-1,2-diol (0.606 g, 12.8 mmol) in Et2O
(10 cm3) and the reaction mixture stirred for 18 h. After this
time a solution of HCl (7.5 cm3 of a 1.0  solution in Et2O) was
added and the reaction mixture stirred for 6 h resulting in the
formation of a white precipitate. The reaction mixture was then
filtered, the residual solid being washed with Et2O (2 × 5 cm3)
affording a colourless filtrate from which all volatiles were
removed by vacuum affording crude compound 3 as a white
solid. Washing with acetonitrile (3 × 3 cm3) and recrystallis-
ation from CH2Cl2–hexane mixtures afforded 3 as large colour-
Experimental
General procedures
1
less crystals (yield = 0.311 g, 50%). NMR (CDCl3): H, δ 7.35
(m, 20 H, Ph) and 5.30 (s, 4 H, CH); 13C-{1H}, δ 139.8 (ipso-C
of Ph), 128.8 (m-C of Ph), 128.4 (o-C of Ph), 126.1 (p-C of Ph)
and 86.8 (CH); 11B-{1H}, δ 29.4 (br s). Mass spectrum: m/z 446
(Mϩ, 60%); high resolution, C28H24B2O4 requires 446.186,
found 446.187 (Found: C, 74.9; H, 5.6. C14H12BO2 requires C,
75.4; H, 5.4%). [α]D20 = 2.21 (c = 0.0022, CH2Cl2).
All reactions were performed using standard Schlenk or glove-
box techniques under an atmosphere of dry, oxygen-free
dinitrogen. All solvents were distilled from appropriate dry-
ing agents immediately prior to use (sodium for toluene and
hexanes and sodium–benzophenone for Et2O and thf). Micro-
analytical data were obtained at The University of Bristol.
Proton, 13C, 31P and 11B NMR spectra were recorded on a JEOL
GX 400 spectrometer and referenced to SiMe4, SiMe4, 85%
H3PO4 and BF3ؒEt2O respectively. Mass spectra (high and
low resolution) were obtained in EI mode (unless otherwise
stated) on a VG Micromass Autospec spectrometer. Optical
rotation measurements were obtained on a Perkin-Elmer 141
polarimeter.
B2(O2C20H12)2 4. A solution of B2(NMe2)4 (0.210 g, 1.0
mmol) in Et2O (10 cm3) was added to a suspension of ( )-1,1Ј-
bi-2-naphthol (0.600 g, 2.1 mmol) in Et2O (10 cm3) and the
reaction mixture stirred for 18 h. After this time HCl (7.5 cm3
of a 1.0  solution in Et2O) was added and the reaction mixture
stirred for 6 h. All volatiles were then removed from the reaction
mixture by vacuum and the resulting white solid extracted with
warm toluene (3 × 5 cm3). Evaporation and recrystallisation
from toluene afforded compound 4 as colourless crystals, one
of which was used for X-ray diffraction which showed the pres-
ence of toluene of crystallisation (yield 0.410 g, 65%). NMR
(CDCl3): 1H, δ 7.94 (dd, 8 H, C10H6, 3JHH = 8.5), 7.43 (dd, 4 H,
All starting materials were procured commercially and used
without further purification unless otherwise stated; B2-
(NMe2)4,15 [Pt(PPh3)2(η-C2H4)]16 and R,R-1,2-diphenylethane-
1,2-diol17 were prepared by literature methods.
3
3
C10H6, JHH = 8.5), 7.23 (dd, 4 H, C10H6, JHH = 8.5), 7.05 (d, 4
Preparations
3
3
H, C10H6, JHH = 8.5) and 6.93 (d, 4 H, C10H6, JHH = 8.5 Hz);
13C-{1H}, δ 152.4, 134.1, 131.0, 130.8, 128.0, 127.0, 126.4,
125.2, 120.5 and 120.4 (C10H6); 11B-{1H}, δ 30.9 (br s). Mass
spectrum: m/z 591 (Mϩ, 100%); high resolution, C40H24B2O4
requires 590.186, found 590.187 (Found: C, 82.1; H, 4.4.
C40H24B2O4ؒC7H8 requires C, 82.7; H, 4.7%).
(a) Diborane(4) compounds. B2[R,R-O2CH(CO2Me)CH-
(CO2Me)]2 1. A solution of dimethyl -tartrate (0.600 g, 3.4
mmol) in thf–Et2O (1:1, 15 cm3) was added to a solution of
B2(NMe2)4 (0.303 g, 1.53 mmol) in Et2O (10 cm3) and the reac-
tion mixture stirred for 12 h resulting in a white precipitate. A
solution of HCl (7.6 cm3 of a 1.0  solution in Et2O) was then
added and the suspension stirred for 12 h during which time
most of the solid product dissolved. After this time the reaction
solution was filtered any residual solid being washed with Et2O
(2 × 5 cm3). Removal of all volatiles from the filtrate by vacuum
afforded crude compound 1 as a colourless oil. Pure samples of
1 as a white crystalline solid were obtained after recrystallis-
(b) Platinum bis(boryls). cis-[Pt(PPh3)2{B[R,R-O2CH-
(CO2Me)CH(CO2Me)]}2]. A solution of [Pt(PPh3)2(η-C2H4)]
(0.100 g, 0.10 mmol) in toluene (5 cm3) was added to a solution
of compound 1 (0.050 g, 0.10 mmol) in toluene (5 cm3) and the
resulting reaction mixture stirred for 2 h. After this time the
solvent volume was reduced to about 5 cm3 and an overlayer of
hexane (10 cm3) was added. Cooling to Ϫ30 ЊC for 2–3 d
afforded 5 as a colourless crystalline solid which was filtered off
and washed with hexane (2 × 5 cm3) (yield 0.060 g, 40%). One
of the crystals present was used for X-ray diffraction. NMR
([2H8]toluene): 1H, δ 7.36 (m, 12 H, PPh3), 7.08 (m, 18 H, PPh3),
4.95 (s, 4 H, CHCO2Me) and 3.45 (s, 12 H, CHCO2Me); 13C-
{1H}, δ 171.3 (CO2Me), 135.9 (t, o-C of PPh3), 135.2 (t, ipso-C
of PPh3), 129.4 (s, p-C of PPh3), 128.5 (t, m-C of PPh3), 78.0
1
ation from toluene (yield 0.305 g, 53%). NMR (CDCl3): H,
δ 4.95 (s, 4 H, CHCO2Me) and 3.80 (s, 12 H, CO2Me); 13C-
{1H}, δ 170.3 (CO2Me), 78.6 (CHCO2Me) and 53.8 (CO2Me);
11B-{1H}, δ 29.0 (br s). Mass spectrum: m/z 374 (Mϩ, 30%); high
resolution, C12H16B2O12 requires 374.083, found 374.083
(Found: C, 39.0; H, 4.6. C6H8BO6 requires C, 38.5; H, 4.3%).
[α]D20 = Ϫ0.25 (c = 0.0032, CH2Cl2).
B2(S-O2CH2CHPh)2 2. A solution of B2(NMe2)4 (0.305 g,
J. Chem. Soc., Dalton Trans., 1998, Pages 1431–1438
1435

View Article Online
3
(CHCO2Me) and 51.9 (CHCO2Me); 11B-{1H}, δ 48.1 (br s);
31P-{1H}, δ 29.7 (t, 2P, 1JPtP = 1634 Hz) (Found: C, 51.2; H, 3.6.
C48H46B2O12P2Pt requires C, 52.7; H, 4.2%). Crystals were
shown by X-ray diffraction to be a toluene solvate but this
solvent was readily lost on vacuum pumping, the calculated
analytical data being quoted for the unsolvated material.
(dd, 1 H ᎐CHCHMe, JHH = 10.5, 9.0 Hz), 5.20 (m, 2 H,
᎐
PhCHO), 4.31 (m, 2 H, CH2O), 4.00 (m, 2 H, CH2O), 2.81 (ddq,
1 H, CHMe, 3JHH = 9.0, 7.1, 4JHH = 4.0), 2.35 (d, 2 H, ᎐CHCH ,
᎐
2
3JHH = 4.1) and 1.55 (d, 3 H, Me, JHH = 7.1 Hz); 13C-{1H},
3
δ 142.1, 142.0 (ipso-C of Ph), 132.6 (CH CH᎐), 128.8, 128.7
(o-C of Ph), 125.7, 125.6 (m-C of Ph), 123.5 (p-C of Ph), 123.4
᎐
2
cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2].
A
solution of [Pt-
(᎐CHCHMe), 78.5, 78.4 (PhCHO), 73.0, 72.9 (CH O) and 16.4
᎐
2
(PPh3)2(η-C2H4)] (0.130 g, 0.17 mmol) in toluene (5 cm3) was
added to a solution of compound 2 (0.050 g, 0.17 mmol) in
toluene (5 cm3) and the resulting reaction mixture stirred for
2 h. After this time the solvent volume was reduced to about 5
cm3 and an overlayer of hexane (10 cm3) was added. Cooling to
Ϫ30 ЊC for 2–3 d afforded the complex as a colourless crystal-
line solid which was filtered off and washed with hexane (2 × 5
cm3) (yield 0.088 g, 40%). X-Ray-quality crystals were obtained
by slow diffusion of hexane into a CH2Cl2 solution. NMR
(Me); 11B-{1H}, δ 32.4 (br s). Mass spectrum (EI): m/z 347
(Mϩ Ϫ CH3, 70%).
Compound 7: reaction time 12 h, yield 80%, d.e. 10%. NMR
(C6D6): (major isomer), 1H, δ 7.30 (m, 20 H, Ph), 5.71 (m, 1 H,
᎐CH), 5.60 (m, 1 H, ᎐CH), 5.14 (s, 2 H, PhCHO), 5.12 (s, 2 H,
᎐
᎐
PhCHO), 2.55 (m, 1 H, CHMe), 2.07 (m, 2 H, CH2) and 1.29 (d,
3 H, CHMe, 3JHH = 7.2 Hz); 13C-{1H}, δ 140.6, 140.3 (ipso-C of
Ph), 132.5 (᎐CH), 128.7 (o-C of Ph), 128.2 (m-C of Ph), 125.8,
᎐
125.7 (p-C of Ph), 123.0 (᎐CH), 86.6 (PhCHO), 86.5 (PhCHO)
᎐
1
1
([2H8]toluene): H, δ 7.25 (m, 40 H, PPh3), 4.95 (dd, 2 H, CH,
and 16.2 (Me); 11B-{1H}, δ 32.3 (br s); (minor isomer), H,
3JHH = 8.1), 4.07 (dd, 2 H, CH2, 2JHH = 8.1, 3JHH = 8.1) and 3.70
δ 7.30 (m, 20 H, Ph), 5.71 (m, 1 H, ᎐CH), 5.60 (m, 1 H, ᎐CH),
᎐
᎐
2
3
(dd, 2 H, CH2, JHH = 8.1, JHH = 8.1 Hz); 13C-{1H}, δ 142.7
(ipso-C of Ph), 134.8 (t, o-C of PPh3), 134.8 (t, ipso-C of PPh3),
127.6 (p-C of PPh3), 127.5 (o-C of Ph), 126.4 (m-C of PPh3),
125.2 (m-C of Ph), 124.4 (p-C of Ph), 75.9 (CH) and 70.6
(CH2); 11B-{1H}, δ 48.2 (br s); 31P-{1H}, δ 30.8 (t, 2P,
1JPtP = 1578 Hz) (Found: C, 62.1; H, 4.8. C52H46B2O4P2Pt
requires C, 61.6; H, 4.6%). Crystals were shown by X-ray
diffraction to be a CH2Cl2 solvate but this solvate was readily
lost on vacuum pumping, the calculated analytical data being
quoted for the unsolvated material.
5.14 (s, 2 H, PhCHO), 5.13 (s, 2 H, PhCHO), 2.55 (m, 1 H,
3
CHMe), 2.07 (m, 2 H, CH2), 1.28 (d, 3 H, CHMe, JHH = 7.3
Hz); 13C-{1H}, δ 140.6, 140.3 (ipso-C of Ph), 132.3 (᎐CH), 128.7
᎐
(o-C of Ph), 128.2 (m-C of Ph), 125.7, 125.6 (p-C of Ph),
122.7 (᎐CH), 86.4 (PhCHO), 86.3 (PhCHO) and 16.1 (Me);
᎐
11B-{1H}, δ 32.3 (br s). Mass spectrum (CI, CH4): m/z 352
(Mϩ ϩ H, 40%); high resolution, C33H32B2O4 requires 514.249,
found 514.248.
Compound 9: reaction time 4 d, yield 55%, d.e. 10%. NMR
(CDCl3): (major isomer), 1H, δ 7.36 (m, 10 H, Ph), 5.65 (m, 1 H,
cis-[Pt(PPh3)2{B(R,R-O2CHPhCHPh)}2]. This complex was
prepared in a manner analogous to that described above,
although it was not isolated and was characterised in solution in
situ by 11B and 31P NMR spectroscopy. NMR (C6D6): 11B-{1H},
δ 47.3 (br s); 31P-{1H}, δ 29.7 (t, 2P, 1JPtP = 1584 Hz).
CH CH᎐), 5.45 (m, 1 H, ᎐CHCHEt), 5.40 (m, 2 H, PhCHO),
᎐ ᎐
2
4.50 (m, 2 H, CH2O), 4.00 (m, 2 H, CH2O), 2.21 (m, 1 H,
3
CHEt), 1.89 (d, 2 H, ᎐CHCH , JHH = 7.4 Hz), 1.71 (m, 1 H,
᎐
2
CH2Me), 1.55 (m, 1 H, CH2Me) and 0.95 (t, 3 H, Me, 3JHH = 7.2
Hz); 13C-{1H}, δ 141.3, 141.1 (ipso-C of Ph), 130.6 (CH CH᎐),
᎐
2
128.6 (o-C of Ph), 128.1 (m-C of Ph), 125.4, 125.3 (p-C of Ph),
(c) Diene diboration. A representative procedure for the
platinum-catalysed diene diboration reactions is given below.
For each reaction discussed in the text full spectroscopic data
are given together with details on reaction time, yield and d.e.
(calculated on the basis of 1H NMR integrations).
To a Young’s tap tube charged with compound 3 (0.050 g,
0.11 mmol) and [Pt(PPh3)2(η-C2H4)] (5 mol %), toluene (5 cm3)
was added and the reaction allowed to stand for 15 min. After
this time cyclohexadiene (16 µl, 0.17 mmol) was added by
syringe and the reaction was then placed in an oil-bath at 80 ЊC
for 2 d. All volatiles were then removed by vacuum affording a
crude product as a pale red oil. Extraction into hexane and
subsequent removal of the solvent by vacuum gave the product
as a colourless oil (yield = 0.049 g, 75%).
123.6 (᎐CHCHEt), 78.3, 78.2 (PhCHO), 72.8, 72.7 (CH O),
᎐
2
24.3 (CH2CH3) and 13.8 (CH2CH3); 11B-{1H}, δ 32.3 (br s);
(minor isomer), 1H, δ 7.36 (m, 10 H, Ph), 5.65 (m, 1 H,
CH CH᎐), 5.45 (m, 1 H, ᎐CHCHEt), 5.40 (m, 2 H, PhCHO),
᎐
᎐
2
4.50 (m, 2 H, CH2O), 4.00 (m, 2 H, CH2O), 2.21 (m, 1 H,
3
CHEt), 1.89 (d, 2 H, ᎐CHCH , JHH = 7.4), 1.71 (m, 1 H,
᎐
2
CH2Me), 1.55 (m, 1 H, CH2Me) and 0.95 (t, 3 H, Me, 3JHH = 7.2
Hz); 13C-{1H}, δ 141.3, 141.1 (ipso-C of Ph), 130.6 (CH CH᎐),
᎐
2
128.6 (o-C of Ph), 128.1 (m-C of Ph), 125.4, 125.3 (p-C of Ph),
123.6 (᎐CHCHEt), 78.3, 78.2 (PhCHO), 72.9, 72.6 (CH O),
᎐
2
24.3 (CH2CH3) and 13.8 (CH2CH3); 11B-{1H}, δ 32.3 (br s).
Mass spectrum (EI): m/z 375 (Mϩ Ϫ H, 20%); high resolution,
C22H25B2O4 requires 375.194, found 375.194.
Compound 10: reaction time 48 h, yield 90%, d.e. 0%. NMR
Compound 5: reaction time 12 h, yield 70%, d.e. 20%. NMR
(CDCl3): (major isomer), 1H, δ 7.30 (m, 20 H, Ph), 5.77 (ddd, 1
(C D ): (major isomer), 1H, δ 5.88 (m, 1 H, HC᎐), 5.75 (m, 1 H,
H, CH CH᎐, J = 10.5, 7.2, 6.2), 5.56 (dd, 1 H, ᎐CHCHEt,
3
᎐
᎐
᎐
6
6
2
HH
᎐CH), 5.02 (s, 2 H, CHCO Me), 4.98 (s, 2 H, CHCO Me), 3.31
3JHH = 10.5, 7.6), 5.13 (s, 2 H, PhCHO), 5.12 (s, 2 H, PhCHO),
2.42 (ddd, 1 H, CHEt, JHH = 7.6, 6.8, 3.4), 2.12 (dd, 1 H,
᎐
2
2
3
(s, 12 H, CO2Me), 2.60 (m, 1 H, CHMe), 2.15 (m, 2 H, CH2)
and 1.45 (d, 3 H, Me); (minor isomer), 1H, δ 5.88 (m, 1 H, HC᎐),
CH CH᎐, JHH = 13.4, JHH = 7.2), 2.05 (dd, 1 H, CH CH᎐,
᎐ ᎐
2 2
3 2
2
3
᎐
5.75 (m, 1 H, ᎐CH), 5.01 (s, 2 H, CHCO Me), 4.98 (s, 2 H,
2JHH = 13.4, JHH = 6.2), 1.83 (ddq, 1 H, CH2CH3, JHH = 13.4,
᎐
2
2
CHCO2Me), 3.31 (s, 12 H, CO2Me), 2.60 (m, 1 H, CHMe), 2.15
(m, 2 H, CH2) and 1.42 (d, 3 H, Me). Mass spectrum (CI, NH3):
m/z 460 (Mϩ ϩ NH4); high resolution, C17H25B2O12 requires
442.145, found 442.144.
3JHH = 7.3, 6.8), 1.63 (ddq, 1 H, CH2CH3, JHH = 13.4,
3JHH = 7.3, 3.4) and 1.07 (t, 3 H, CH2CH3, 3JHH = 7.3 Hz); 13C-
{1H}, δ 140.6, 140.3 (ipso-C of Ph), 130.8 (CH CH᎐), 128.8,
᎐
2
128.7 (o-C of Ph), 128.2, 128.2 (m-C of Ph), 125.7, 125.6 (p-C
Compound 6: reaction time 48 h, yield 60%, d.e. 0%. NMR
of Ph) 123.8 (᎐CHCHEt), 86.5, 86.4 (PhCHO), 24.6 (CH CH )
᎐
2 3
1
(C6D6): (isomer a), H, δ 7.40 (m, 10 H, Ph), 6.15 (ddt, 1 H,
and 13.9 (CH2CH3); 11B-{1H}, δ 32.1 (br s); (minor isomer), 1H,
δ 7.30 (m, 20 H, Ph), 5.76 (ddd, 1 H, CH CH᎐, 3JHH = 10.5, 7.2,
3
4
CH CH᎐, JHH = 10.5, 4.1, JHH = 4.0), 5.94 (dd,
1 H,
᎐
᎐
2
2
᎐CHCHMe, 3JHH = 10.5, 9.0), 5.20 (m, 2 H, PhCHO), 4.31 (m,
6.2), 5.56 (dd, 1 H, ᎐CHCHEt, JHH = 10.5, 7.6), 5.13 (s, 2 H,
3
᎐
᎐
2 H, CH2O), 4.00 (m, 2 H, CH2O), 2.81 (ddq, 1 H, CHMe,
PhCHO), 5.11 (s, 2 H, PhCHO), 2.42 (m, 1 H, CHEt), 2.12 (dd,
4
3
3JHH = 9.0, 7.1, JHH = 4.0), 2.35 (d, 2 H, ᎐CHCH , JHH = 4.1
1 H, CH CH᎐, 2JHH = 13.4, 3JHH = 7.2), 2.05 (dd, 1 H, CH CH᎐,
᎐
᎐
᎐
2
2
2
3
Hz) and 1.55 (d, 3 H, Me, JHH = 7.1 Hz); 13C-{1H}, δ 142.2,
2JHH = 13.4, 3JHH = 6.2), 1.83 (m, 1 H, CH2CH3), 1.63 (m, 1 H,
142.0 (ipso-C of Ph), 132.7 (CH CH᎐), 128.8, 128.7 (o-C of
CH2CH3) and 1.07 (t, 3 H, CH2CH3, 3JHH = 7.3 Hz); 13C-{1H},
᎐
2
Ph), 125.6, 125.5 (m-C of Ph), 123.5 (p-C of Ph), 123.4
δ 140.6, 140.3 (ipso-C of Ph), 130.6 (CH CH᎐), 128.7, 128.6
᎐
2
(᎐CHCHMe), 78.4, 78.3 (PhCHO), 73.0, 72.9 (CH O) and 16.4
(o-C of Ph), 128.2, 128.1 (m-C of Ph), 125.7, 125.6 (p-C of Ph),
᎐
2
1
(Me); 11B-{1H}, δ 32.4 (br s); (isomer b), H, δ 7.40 (m, 10 H,
123.6 (᎐CHCHEt), 86.5, 86.4 (PhCHO), 24.5 (CH CH ) and
᎐
2
3
Ph), 6.14 (ddt, 1 H, CH CH᎐, 3JHH = 10.5, 4.1, 4JHH = 4.0), 5.95
14.0 (CH2CH3); 11B-{1H}, δ 32.1 (br s). Mass spectrum (EI):
᎐
2
1436
J. Chem. Soc., Dalton Trans., 1998, Pages 1431–1438

View Article Online
Table 3 Crystallographic data for the structure determinations of compounds 1–3, 4ؒ1.0C6H5Me, cis-[Pt(PPh3)2{B[R,R-O2CH(CO2Me)-
CH(CO2Me)]}2]ؒ1.5 C6H5Me and cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2]ؒ2.0CH2Cl2
cis-[Pt(PPh3)2-
{B[R,R-O2CH(CO2-
Me)CH(CO2Me)]}2]ؒ
1.5C6H5Me
cis-[Pt(PPh3)2-
{B(S-O2CH2-
CHPh)}2]ؒ2.0CH2Cl2
1
2
3
4ؒ1.0C6H5Me
Crystal data
Empirical formula
M
C12H16B2O12
373.87
C16H16B2O4
587.82
C28H24B2O4
446.09
C47H32B2O4
682.35
C58.5H58B2O12P2Pt
1231.70
C54H50B2Cl4O4P2Pt
1183.39
Crystal system
Space group
a/Å
b/Å
c/Å
Orthorhombic
P212121 (no. 19)
9.0355(8)
16.9385(15)
22.3820(19)
Orthorhombic
P212121 (no. 19)
9.6718(12)
11.8885(12)
26.482(5)
Tetragonal
P41212 (no. 92)
12.731(2)
12.731(2)
14.653(4)
Monoclinic
P21/n (no. 14)
14.063(2)
10.8214(11)
24.853(5)
105.194(10)
3649.9(10)
4
Orthorhombic
P21212 (no. 18)
15.668(2)
28.485(3)
12.696(2)
Monoclinic
C2 (no. 5)
38.311(3)
12.1983(13)
11.1210(7)
94.350(7)
5180.9(8)
4
β/Њ
U/ÅϪ3
Z
3425.5(5)
8
0.129
3045.0(8)
8
0.089
2374.8(7)
4
0.081
5666.0(12)
4
2.593
µ/mmϪ1
0.077
3.021
Data collection and reduction
T/K
160(2)
21 864
8031
173(2)
19 284
6936
292(2)
3020
2083
173(2)
18 479
6411
173(2)
35 886
12 895
173(2)
16 962
11 487
Reflections collected
Unique reflections
with I > Ϫ3σ(I)
Rint
0.0400
0.0348
0.0350
0.0365
0.0631
0.0148
Solution and refinement
Absolute structure
parameter
Final R
Ϫ0.26(74)
Ϫ0.79(71)
0(2)
—
Ϫ0.010(7)
Ϫ0.021(3)
0.0512
0.0382
0.0384
0.0546
0.0442
0.0219
m/z 528 (Mϩ, 1%); high resolution, C34H34B2O4 requires 528.264,
found 528.265.
Compound 13: reaction time 4 h, yield 60%, d.e. n/a. NMR
1
3
(CDCl ): H, δ 5.82 (d, 1 H, ᎐CH, JHH = 10.0), 5.77 (d, 1 H,
᎐
3
Compound 11: reaction time 12 h, yield 70%, d.e. n/a. NMR
᎐CH, 3JHH = 10.0 Hz), 4.90 (s, 4 H, CHCO2Me), 3.83 (s, 12 H,
᎐
1
(CDCl3): H, δ 7.05 (m, 8 H, 1,2-O2C6H4), 5.80 (dddd, 1 H,
OMe), 2.05 (m, 2 H, ᎐CHCH) and 1.85 (m, 4 H, CH ); 13C-
᎐
2
3
4
CH CH᎐, JHH = 10.3, 16.0, 16.3, JHH = 5.7), 5.59 (dd, 1 H,
{1H}, δ 169.9 (C᎐O), 169.8 (C᎐O), 125.9 (᎐CH), 125.7 (᎐CH),
᎐
᎐
᎐
᎐
᎐
2
3
᎐CHCHEt, JHH = 10.3, 9.8), 2.57 (dddd,
1
H, CHEt,
77.5 (CHCO2Me), 77.4 (CHCO2Me), 53.1 (OMe), 53.0 (OMe)
and 23.4 (CH2); 11B-{1H}, δ 33.5 (br s). Mass spectrum (EI): m/z
454 (Mϩ, 20%); high resolution, C18H24B2O12 requires 454.145,
found 454.146.
᎐
3JHH = 8.9, 9.8, 13.9, JHH = 5.7), 2.34 (dd, 1 H, ᎐CHCH ,
4
᎐
2
2
3
2JHH = 8.0, JHH = 16.3), 2.23 (dd, 1 H, ᎐CHCH , JHH = 8.0,
᎐
2
3JHH = 16.0), 1.87 (ddq, 1 H, CH2CH3, JHH = 6.5, JHH = 13.9,
2
3
2
3
6.1), 1.67 (ddq, 1 H, CH2CH3, JHH = 6.5, JHH = 8.9, 6.1) and
1.01 (t, 3 H, CH2CH3, 3JHH = 6.1 Hz); 13C-{1H}, δ 148.2, 148.1
(C1,2 of 1,2-O C H ), 134.5 (᎐CHCHEt), 128.1 (CH CH᎐),
Compound 14: reaction time 12 h, yield 80%, d.e. n/a. NMR
(C D ): 1H, δ 7.20 (s, 10 H, Ph), 6.47 (d, 1 H, ᎐CH, 3JHH = 10.5),
᎐
6
6
3
6.45 (d, 1 H, ᎐CH, JHH = 10.5), 5.08 (dd, 1 H, PhCHO,
᎐
᎐
᎐
2
6
4
2
122.5, 122.4 (C4,5 of 1,2-O2C6H4), 122.3, 122.2 (C3,6 of 1,2-
O2C6H4), 24.1 (CH2CH3) and 13.7 (CH2CH3); 11B-{1H}, δ 32.4
(br s). Mass spectrum (EI): m/z 320 (Mϩ, 10%); high resolution,
C18H18B2O4 requires 320.139, found 320.139.
3JHH = 7.8, 4.2), 5.06 (dd, 1 H, PhCHO, JHH = 7.8, 4.2), 4.14
3
2
3
(dd, 2 H, OCH2, JHH = 7.8, JHH = 7.8), 3.81 (dd, 1 H, OCH2,
2JHH = 7.8, 3JHH = 4.2), 3.79 (dd, 1 H, OCH2, 2JHH = 7.8, 3JHH
=
4.2 Hz), 2.45 (m, 2 H, CH ), 2.35 (m, 2 H, ᎐CHCH) and 2.18
᎐
2
Compound 12: reaction time 10 d, yield 50%, d.e. 0%. NMR
(m, 2 H, CH2); 13C-{1H}, δ 142.1 (ipso-C of Ph), 128.7 (o-C of
Ph), 126.9 (᎐CH), 126.8 (᎐CH), 125.6 (m-C of Ph), 125.5 (p-C
(C6D6): (major isomer), 1H, δ 7.35 (m, 10 H, Ph), 5.34 (m, 2 H,
᎐
᎐
3
PhCHO), 5.19 (dq, 1 H, ᎐CH, JHH = 10.0, 1.5), 4.47 (m, 2
of Ph), 78.5 (PhCHO), 73.1 (OCH2), 73.0 (OCH2) and 24.5
(CH2); 11B-{1H}, δ 32.2 (br s). Mass spectrum (EI): m/z 374
(Mϩ, 5%); high resolution, C22H24B2O4 requires 374.186, found
374.185.
᎐
H, CH2O), 3.95 (m, 2 H, CH2O), 2.19 (dq, 1 H, CHMe,
3JHH = 10.0, 7.3), 2.00 (d, 1 H, ᎐CMeCH , 2JHH = 15.5), 1.80 (d,
᎐
2
2
3
1 H, ᎐CMeCH , J = 15.5), 1.85 (d, 3 H, MeC᎐, JHH = 1.5)
᎐
᎐
2
HH
and 1.15 (d, 3 H, CHMe, JHH = 7.3 Hz); 13C-{1H}, δ 142.2,
Compound 15: reaction time 12 h, yield 75%, d.e. n/a. NMR
3
142.1 (ipso-C of Ph), 130.8 (MeC᎐), 128.3 (o-C of Ph), 128.3
(CDCl3): 1H, δ 7.30 (m, 20 H, Ph), 6.00 (d, 1 H, ᎐CH,
᎐
᎐
3
(m-C of Ph), 126.8 (᎐CH), 125.7, 125.6 (p-C of Ph), 78.5, 78.4,
3JHH = 10.5), 5.96 (d, 1 H, ᎐CH, JHH = 10.5 Hz), 5.18 (s, 2 H,
᎐
᎐
(PhCHO), 73.0, 72.9 (CH O), 26.2 (MeC᎐) and 16.7 (CHMe);
PhCHO), 5.17 (s, 2 H, PhCHO), 2.21 (m, 2 H, ᎐CHCH) and
᎐
᎐
2
11B-{1H}, δ 32.5 (br s); (minor isomer), 1H, δ 7.35 (m, 10 H, Ph),
2.04 (m, 4 H, CH2); 13C-{1H}, δ 140.5 (ipso-C of Ph), 128.8 (o-
3
5.34 (m, 2 H, PhCHO), 5.21 (dq, 1 H, ᎐CH, JHH = 10.0, 1.5),
C of Ph), 128.2 (m-C of Ph), 126.6 (᎐CH), 126.4 (᎐CH), 125.7
᎐
᎐ ᎐
4.47 (m, 2 H, CH2O), 3.95 (m, 2 H, CH2O), 2.23 (dq, 1 H,
(p-C of Ph), 86.6 (PhCHO), 86.5 (PhCHO), 24.1 (CH2) and
24.0 (CH2); 11B-{1H}, δ 31.8 (br s). Mass spectrum (EI): m/z 526
(Mϩ, 5%); high resolution, C34H32B2O4 requires 524.256, found
524.256.
CHMe, 3JHH = 10.0, 7.3), 2.00 (d, 1 H, ᎐CMeCH , 2JHH = 15.5),
᎐
2
2
1.89 (d, 1 H, ᎐CMeCH , J = 15.5), 1.85 (d, 3 H, ᎐CMe,
᎐
᎐
2
HH
3
3JHH = 1.5) and 1.16 (d, 3 H, CHMe, JHH = 7.3 Hz); 13C-{1H},
δ 142.2, 142.1 (ipso-C of Ph), 131.0 (MeC᎐), 128.3 (o-C of Ph),
Compound 16: reaction time 12 h, yield 90%, d.e. n/a. NMR
᎐
1
3
128.3 (m-C of Ph), 126.7 (᎐CH), 125.7, 125.5 (p-C of Ph), 78.5,
(CDCl3): H, δ 7.20 (dd, 4 H, H3,6 of 1,2-O2C6H4, JHH = 5.9,
᎐
3
78.3, (PhCHO), 72.8, 72.7 (CH O), 26.1 (MeC᎐) and 16.6
4JHH = 3.4), 7.05 (dd, 4 H, H4,5 of 1,2-O2C6H4, JHH = 5.9,
᎐
2
(CHMe); 11B-{1H}, δ 32.5 (br s). Mass spectrum (EI): m/z 375
(Mϩ Ϫ H, 20%); high resolution, C22H25B2O4 requires 375.194,
found 375.194.
4JHH = 3.4 Hz), 6.05 (s, 2 H, ᎐CH), 2.45 (m, 2 H, ᎐CHCH) and
᎐
᎐
2.05 (m, 4 H, CH2); 13C-{1H}, δ 148.1 (C1,2 of 1,2-O2C6H4),
126.1 (᎐CH), 122.6 (C4,5 of 1,2-O2C6H4), 112.4 (C3,6 of 1,2-
᎐
J. Chem. Soc., Dalton Trans., 1998, Pages 1431–1438
1437

View Article Online
O2C6H4) and 23.6 (CH2); 11B-{1H}, δ 32.3 (br s). Mass
spectrum (EI): m/z 318 (Mϩ, 100%); high resolution,
C18H16B2O4 requires 318.123, found 318.124.
References
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X-Ray crystallography
Details of the structure determination of compounds 1–3,
4ؒC6H5Me,
cis-[Pt(PPh3)2{B[R,R-O2CH(CO2Me)CH(CO2-
Me)]}2]ؒ1.5C6H5Me and cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2]ؒ
2.0CH2Cl2 are given in Table 3. All hydrogen atoms were
assigned isotropic thermal parameters and were constrained to
idealised geometries. Absorption effects were corrected for the
latter two structures on the basis of multiple equivalent reflec-
tions. An extinction parameter, x, of the form k[1 ϩ 0.001xFc2λ3/
sin(2θ)]Ϫ0.25 was refined to 0.0042(6) and 0.0032(6) for 1 and
4ؒC6H5Me, respectively. In 4ؒC6H5Me the bond lengths of the
toluene solvate were restrained to idealised geometry. In cis-
[Pt(PPh3)2{B[R,R-O2CH(CO2Me)CH(CO2Me)]}2]ؒ1.5C6H5Me
one toluene was disordered over a two-fold axis and this was
refined isotropically without any restraints. The second toluene
molecule was constrained to idealised geometry. Unresolved
disorder is probably present in one of the boryl ligands where
O(11) and C(66) of the terminal OMe group have large Uij
values. In cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2]ؒ2.0CH2Cl2 the
solvent molecules were disordered and each chlorine was
refined over two atomic positions. The first molecule,
C(96)Cl(1)Cl(2), lay on a general position and the chlorine
positions were refined in the occupancy ratio 73:27, whereas
two CH2Cl2 molecules which lay on two-fold axes were refined
in the occupancy ratio 50:50. Unresolved disorder is also
apparent as shown by large Uij values in both of the phenyl
groups of the boryl ligands. The absolute structure18 was con-
firmed by refinement for all compounds except 4. Refinements
converged to residuals given in Table 3.
CCDC reference number 186/915.
See http://www.rsc.org/suppdata/dt/1998/1431/ for crystallo-
graphic files in .cif format.
Acknowledgements
T. B. M. thanks Natural Sciences and Engineering Research
Council (NSERC) of Canada and N. C. N. thanks the EPSRC,
Laporte plc and The Royal Society for research support.
T. B. M. and N. C. N. also thank NSERC and The Royal
Society for supporting this collaboration via a series of Bilateral
Exchange Awards. Johnson Matthey Ltd. and E. I. Du Pont
De Nemours & Co., Inc. are thanked for generous supplies of
platinum salts.
16 M. Camalli, F. Caruso, S. Chaloupka, E. M. Leber, H. Rimml and
L. M. Venanzi, Helv. Chim. Acta, 1990, 73, 2263.
17 B. H. McKee, D. G. Gilheany and K. B. Sharpless, Org. Synth.,
1992, 70, 47.
18 H. D. Flack, Acta Crystallogr., Sect. A, 1983, 39, 876.
Received 5th January 1998; Paper 8/00108A
1438
J. Chem. Soc., Dalton Trans., 1998, Pages 1431–1438