Rhodium(I) catalysed diboration of (E)-styrylboronate esters: Molecular structures of (E)-p-MeO-C6H4-CH = CH-B(1,2-O2C6H4) and p-MeO-C6H4-CH2C {B(1,2-O2C<su

Article abstract of DOI:10.1016/S0022-328X(02)01310-4

Diboration of the styrylboronate esters (E)-p-R-C₆H₄-CH=CH-Bcat (1) (R = H, (1a) MeO (1b); cat = 1,2-O₂C₆H₄), with B₂cat₂ in the presence of a variety of rhodium phosphine cataly

Full text of DOI:10.1016/S0022-328X(02)01310-4

Journal of Organometallic Chemistry 652 (2002) 77ꢀ85
/
www.elsevier.com/locate/jorganchem
Rhodium(I) catalysed diboration of (E)-styrylboronate esters:
molecular structures of (E)-p-MeOꢀC6H4ꢀCHÄCHꢀB(1,2-O2C6H4)
and p-MeOꢀC6H4ꢀCH2C{B(1,2-O2C6H4)}3
/
/
/
/
/
/
Paul Nguyen a, R. Benjamin Coapes b, Alden D. Woodward a, Nicholas J. Taylor a,
Jacquelyn M. Burke b, Judith A.K. Howard b, Todd B. Marder a,b,
*
a Department of Chemistry, University of Waterloo, Waterloo, Ont., N2L 3G1, Canada
b Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Received 29 October 2001; received in revised form 28 January 2002; accepted 29 January 2002
Abstract
Diboration of the styrylboronate esters (E)-p-Rꢀ
B2cat2 in the presence of a variety of rhodium phosphine catalysts gives predominantly either p-Rꢀ
contains three boronate ester groups on one carbon atom, or its isomer p-RꢀC6H4ꢀCH(Bcat)CH(Bcat)2 (3). The formation of 2
apparently involves regiospecific insertion of the vinylboronates into a RhꢀB bond followed by b-hydride elimination, another
regiospecific insertion of the 2,2-vinyl bis(boronate) into the remaining RhꢀB bond followed by CꢀH reductive elimination leading
/
C6H4ꢀ
/
CHÄ
/
CHꢀ
/
Bcat (1) (Rꢁ
/
H, (1a) MeO (1b); catꢁ
/
1,2-O2C6H4), with
/
C6H4ꢀCH2C(Bcat)3 (2), which
/
/
/
/
/
/
to 2,2-diboration and a 2,1-hydrogen shift. Wilkinson’s catalyst (7) gives the highest yields of 2 with 75 and 71% yields from 1a and
1b, respectively, while [Rh(COE)2(m-Cl)]2 (10) with two equivalents of P(o-tol)3 gave 3 in highest yield with 50 and 49% from 1a and
1b, respectively. The crystal structure of (E)-p-MeOꢀ
phenyl ring twisted slightly out of the plane. The tris(boronate) p-MeOꢀ
/
C6H4ꢀ
/
CHÄ
/
CHꢀ
/
Bcat shows the molecule to be essentially planar, with the
/
C6H4ꢀCH2C(Bcat)3 crystallises with two independent
/
molecules in the unit cell, which differ in the rotational orientation of the phenyl ring in relation to the catecholate groups; the latter
are arranged in a propeller-like fashion. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Boron; Diboration; Rhodium; Vinylboronate ester; Diborane (4); tris(Boronate) ester
1. Introduction
phosphine-free Pt-catalyst precursors [12,13], and for
the unstrained internal alkenes cis- and trans-stilbene
and trans-b-methylstyrene using an in situ prepared
zwitterionic rhodium complex [16] [Rh(dppm)(h6-catB-
cat)]. The difficulty with alkene diborations arises from
competing b-hydride elimination and reductive elimina-
tion processes which can occur subsequent to alkene
Transition metal catalysed diboration [1,2] of unsa-
turated organic compounds is a new tool in the arsenal
of synthetic chemists. Platinum-catalysed alkyne dibora-
tion is now a well understood [3ꢀ10] process which
/
involves a mono-phosphine [5,6,10] complex as the
active species. The reactions provide the syn-addition
product exclusively and new high-efficiency catalysts
have been reported [10]. In contrast, the 1,2-addition
insertion into an Mꢀ
elimination leads to accompanying dehydrogenative
borylation [17ꢀ27] and hydroboration [28ꢀ30] pro-
/
B(OR)2 bond. The b-hydride
/
/
[11ꢀ
/
15] of diborane compounds B2cat2 or B2pin2 (catꢁ
/
cesses. For example, we have observed [1,11] up to
nine products arising from the metal-catalysed addition
of B2cat2 to 4-vinylanisole, with yields of up to ca. 25%
1,2-O2C6H4; pinꢁOCMe2CMe2O) to alkenes remains a
challenge, with clean reactions being observed for
/
terminal and strained internal alkenes only using
of the unusual tris(boronate) ester 4-MeOꢀ
/
C6H4CH2C(Bcat)3 (2,2,2-TBE). Compounds such as
(2,2,2-TBE), containing three or even four boronate
* Corresponding author. Tel.: ꢂ
384-4737.
E-mail address: todd.marder@durham.ac.uk (T.B. Marder).
/
44-191-374-3137; fax: ꢂ44-191-
/
groups on a single carbon atom [31ꢀ
/
33], are relatively
rare but are very interesting due to their documented
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 3 1 0 - 4

78
P. Nguyen et al. / Journal of Organometallic Chemistry 652 (2002) 77ꢀ85
/
reactivity arising from the stabilisation of a carbanion
centre by the a-boronate ester moieties. Previous routes
to these compounds, developed [31ꢀ33] by Matteson
/
and co-workers, required reactions of RCCl3 with
ClB(OR?)2 and lithium metal (Scheme 1), and these
could prove difficult to control. More recently, Siebert
et al. reported [34] the syntheses of tris(boronate) esters
via hydroboration of alkynylboronates using HBCl2
(Scheme 1). We report herein a catalytic route to the
tris(boronate)esters in good yield under mild conditions
and in a single step from readily accessible vinylbor-
onates (VBEs).
Equation (1). ‘BH3’ promoted hydroboration of ethynylarenes.
2. Results and discussion
The styrylboronate esters (VBEs) were prepared in
high yields via conventional hydroboration [35,6] of the
corresponding ethynylbenzenes with HBcat, Eq. (1).
While this reaction would typically [35,36] require a
temperature of ca. 80 8C, the use of HBcat containing a
small amount of ‘BH3’ impurity, resulting from the
redistribution [37ꢀ
allowed the reaction to proceed rapidly at ambient
temperature in the absence of solvent [40ꢀ43]. Com-
/39] of HBcat to B2cat3 and BH3,
/
pounds 1a and 1b were subsequently reacted with B2cat2
in the presence of 1 mol% catalyst and heated to 58 8C
for 12 h using THF as solvent. The products obtained
are shown in Scheme 2, and product distributions,
determined by high-field 1H-NMR spectroscopy, are
given Table 1. In general, there is a similarity in the
product distributions resulting from the diboration of
either 1a or 1b. The catalyst precursor [Rh(PPh3)3Cl] (7),
gave the highest yield of 2, 75 and 71% for 1a and 1b,
respectively, with the reactions essentially going to
completion. Yields of 3, 4 and 5 were between 5 and
15%. The use of 7 in the presence of ten equivalents of
Scheme 2. Products resulting from the diboration of 1.
PPh3 again gave predominantly 2, but proved slightly
less selective than 7 alone, giving 62 and 70% yields with
1a and 1b, respectively. The zwitterionic catalysts
[Rh(dppb)(h6-catBcat)] (8) and [Rh(dppm)(h6-catBcat)]
(9), formed as shown in Eq. (2), also yielded 2
predominantly (63 and 67% for 8, 66 and 74% for 9,
for 1a and 1b, respectively). Reactions with 8 were 87ꢀ
94% complete in 12 h but reaction with 9 only achieved
67ꢀ79% completion in this time. The 74% yield of 2b
/
/
using 9, however, was the highest obtained for this
substrate.
The use of [Rh(COE)2(m-Cl)]2 (10) in the presence of
two equivalents of P(o-tol)3, one equivalent per Rh as
shown in Eq. (3), gave the highest yields of 3 of 50 and
49% for 1a and 1b, respectively, with completions of at
least 96%.
The use of four equivalents of P(o-tol)3 (two equiva-
lents per Rh) gave very similar product distributions and
hence it would appear that only one P(o-tol)3 binds to
Rh. This was confirmed by the reaction of
[Rh(COE)2(m-Cl)]2 with one equivalent P(o-tol)3 per
Rh which gave rise to one doublet at d 50.7 (JPꢀRh
ꢁ
/
190 Hz) in the 31P{1H}-NMR spectrum; addition of two
equivalents per Rh resulted in the same doublet and also
Scheme 1. Published routes to tetra and tris boronate esters.
a singlet at d ꢃ28.7 due to free P(o-tol)3. Using 10 in
/

Table 1
Product distributions for the diboration of 1a and 1b with different rhodium catalysts
a
Catalyst
Substrate ArCH2C(Bcat)3 (2)
ArCH(Bcat)CH(Bcat)2 (3)
ArCH(Bcat)CH2(Bcat) (4)
ArCH2CH(Bcat)2 (5)
ArCHꢁ/C(Bcat)2 (6)
Completion
[Rh(PPh3)3Cl] (7)
1a
1b
1a
1b
1a
1b
1a
1b
1a
1b
1a
1b
1a
1b
1a
1b
1a
1b
1a
1b
75
71
62
70
63
67
66
74
3
9
15
13
17
6
6
5
6
4
1
91
96
93
91
87
94
79
67
96
99
98
98
77
76
84
87
100
100
98
100
7
[Rh(PPh3)3Cl] (7)ꢂ
/10PPh3
10
9
7
2
14
3
7
[Rh(dppb)(h6-catBcat)] (8)
[Rh(dppm)(h6-catBcat)] (9)
[Rh(COE)2(m-Cl)]2 (10)
10
8
7
b
5
15
5
Trace
5
b
17
15
50
49
47
48
7
5
8
3
8
0
0
32
35
31
33
23
22
15
16
7
15
5
ꢂ
/
2P(o-tol)3
[Rh(COE)2(m-Cl)]2 (10)
4P(o-tol)3
[Rh(COE)2(m-Cl)]2 (10)
2PPh2(o-tol)
[Rh(COE)2(m-Cl)]2 (10)
11
1
0
21
11
14
16
4
ꢂ/
8
0
49
47
30
38
70
73
3
8
ꢂ/
7
9
45
37
6
5
ꢂ
/
2PCy3
4
6
[Rh(dppb)(h6-catBcat)] (8)
11
11
0
6
c
ꢂexcess B2cat2
/
8
6
2
[Rh(COE)2(m-Cl)]2 (10)
4P(o-tol)3ꢂexcess B2cat2
53
51
35
36
9
c
ꢂ/
/
7
0
7
a
b
c
Completion was calculated as the percentage of boron-containing products relative to the sum of products plus any unreacted (1).
Generated in situ as shown in Eq. (2).
A threefold excess of B2cat2 relative to 1 was used.

80
P. Nguyen et al. / Journal of Organometallic Chemistry 652 (2002) 77ꢀ85
/
mediate enhances the rate of b-hydride elimination
leading to 6. This then reinserts into the RhꢀB bond
of the [Rh(H)(Bcat)] intermediate with the same regio-
/
chemistry to give a 2,2,2-trisboronate-h3-benzyl com-
plex, with no remaining b-hydrogen, and hence Cꢀ
/H
reductive elimination leads to 2. Thus, the overall
catalytic process involves both diboration and a 1,2-
hydrogen shift. The high yield of 2 in particular is a
Equation (2). Formation of [RhL2(h6-catBcat)].
combination with two equivalents of the less bulky
phosphines PPh2(o-tol) or PCy3 (i.e. P:Rhꢁ1:1), gave
yields of 3 which were lower than those found for P(o-
tol)3. Thus, PPh2(o-tol) gave mainly 2 (Â50%), whereas
result of the tendency of alkylꢀ
boryl groups to undergo rapid b-hydride elimination. If
6 were to insert into the RhꢀB bond of a [Rh(Bcat)2]
/
Rh complexes with b-
/
/
/
intermediate, this would lead to a tetra(boronate)
product which we have not yet identified, vide infra.
It is clear from Table 1 that the presence of bulkier
phosphines in the catalyst precursor produces signifi-
cantly larger quantities of 5 in relation to 4 and, with
P(o-tol)3, no 4 is produced at all. This phosphine also
provides the highest yield of 3. Thus, with the bulkiest
PCy3 gave a nearly even split in distributions of both 2
and 3. It is clear, therefore, that cone angle, and possibly
basicity, of the phosphine are important factors in the
product distributions obtained.
Commercially available [Pt(COD)Cl2], which has
been shown to diborate alkenes,[15] failed to diborate
1a and 1b but considerable reaction with the THF
solvent was observed. Repeating the reaction in benzene
showed no diboration to have taken place.
phosphine, our results suggest that insertion of CÄ
/
C(Bcat) into the RhꢀB bond in a [Rh(Bcat)2] inter-
/
mediate may take place with either of the two possible
regiochemistries. If it inserts as discussed above to give
the h3-benzyl intermediate, b-hydride elimination again
Two reactions were conducted using a threefold
excess of B2cat2, relative to 1, with catalyst 8, which
had given predominantly 2, and catalyst 10ꢂ4P(o-tol)3,
/
gives 6ꢂ[Rh(H)(Bcat)] whereas reductive elimination
/
which had given predominantly 3. In both cases, the
product distributions were similar to those obtained in
reactions employing one equivalent of B2cat2. In the
former case, a small increase in the yield of 2 was
observed whereas in the latter case, the yield of 3 was
slightly increased. In both cases the reactions went to
completion indicating some rate dependence on B2cat2
concentration.
would give 3. However, if it inserts the other way around
giving [Rh(Bcat)(CH(Bcat)CH(Bcat)Ar)], which should
be favoured on steric grounds, reductive elimination of
the Bꢀ
hydride elimination. Likewise, insertion of VBE into the
RhꢀH bond of any [Rh(H)(Bcat)] present would likely
lead to [Rh(Bcat)(CH(Bcat)CH2Ar)], again on steric
grounds, giving 5 after BꢀC reductive elimination.
/
C bond yielding 3 is rapid compared with b-
/
/
A plausible schematic catalytic cycle is shown in
Scheme 3. In this, oxidative addition of B2cat2 to the
Rh centre forms an unsaturated bis-boryl complex, of
which [RhCl(Bcat)2(PPh3)2] is representative [44,45].
Coordination of 1 is followed by insertion of the alkene
The significance of the experiments conducted in the
presence of excess B2cat2 is as follows. If the mechanism
involved a Rh(I) mono-boryl [Rh(Bcat)] species which
inserts CÄ
/
C(Bcat) to give e.g. [RhI(CHArCH(Bcat)2)],
we could envisage reaction of this species with B2cat2 to
give [RhIII(Bcat)2(CHArCH(Bcat)2)] which would yield
3 by reductive elimination regenerating [RhI(Bcat)]. This
would compete with b-hydride elimination to give
linkage into a Rhꢀ
/
B bond. Reductive elimination of the
BꢀC bond yields 3. Alternatively, b-hydride elimination
/
gives 6, and an [Rh(H)(Bcat)] species. Subsequent
addition of HBcat, via this complex, to 1 gives 4 or 5,
and addition to 6 yields 2.
[RhI(H)]ꢂ
6. One would have expected this partitioning
/
to be dependent strongly on the concentration of B2cat2.
In fact, we see a small rise in the formation of 2 with
catalyst 8 for which 2 already predominated, and a rise
As discussed previously [18,46] the regiochemistry of
compound 2 is consistent with insertion of the styryl CÄ
/
C unit into a RhꢀB bond, in such a fashion as to give an
/
in formation of 3 with catalyst (10ꢂ4P(o-tol)3) for
/
h3-benzyl intermediate. The presence of two Bcat
groups on the terminal carbon of the h3-benzyl inter-
which 3 already predominated. Thus, our results do not
support a Rh(I) boryl pathway to be operating here.
Clearly, the reaction is rather complex and a detailed
mechanistic interpretation is not yet possible although
some of the basic features have been identified.
As discussed above, products 2 and 3 result from the
diboration of 1 by B2cat2. The formation of 6 generates
HBcat, which reacts with 1 to give 4 and 5. The fact that
the total amount of 4 and 5 is always greater than the
amount of 6, however, indicates that there is either an
excess of hydrogen or a deficiency of boron in the
Equation (3). Reaction of [Rh(COE)2(m-Cl)]2 with P(o-tol)3.

P. Nguyen et al. / Journal of Organometallic Chemistry 652 (2002) 77ꢀ
/85
81
Scheme 3. Plausible schematic catalytic cycle for the diboration of 1.
observed product mixture. One possibility is that small
amounts of highly boronated organic species are pre-
sent, such as ArCH(Bcat)C(Bcat)3 (11) or ArC(Bcat)Ä
/
C(Bcat)2 (12), which result from the diboration and
dehydrogenative borylation of 6 respectively. Both
would be virtually undetectable by NMR spectroscopy
in the complex product mixtures, for Arꢁ
difficult to assign unambiguously for Arꢁ
/
Ph, and very
MeOC6H4.
/
Thus 11 would give only a weak singlet in the region d 3-
4, probably obscured by 2, and an MeO singlet for 11b.
Complex 12a would contain only aromatic hydrogens
and 12b an additional MeO singlet. Both 11 and 12
would also be undetectable by GC/MS under conditions
we typically employ. It is also possible that some B2cat3
is being formed as a decomposition product. Although
rigorous techniques are employed to avoid the presence
of any water, the possibility of small amounts of surface
Fig. 1. Molecular structure of 1b. Ellipsoids shown at 50% probability
for non-H atoms, with H atoms shown as circles of arbitrary radius.
phenyl ring out of the plane of the molecule. This twist is
due presumably to a packing effect, resulting from an
intermolecular p-interaction between catecholate and
adjacent phenyl groups in an asymmetric manner. The
sum of the angles around the boron atom is 360.0(1)8.
Bond lengths and angles are comparable to the literature
values for 1a [47]. Compound 2b crystallises in space
ꢀOH on glass vessels cannot be ignored as a source of H
/
in these small scale reactions. Additionally, there is
evidence for the formation of THF-oligomers in reac-
tions using [Rh(COE)2(m-Cl)]2/nPR3 catalyst precursors,
and it is possible that these could be partially boronated
in some way.
The molecular structures of 1b and 2b are shown in
Figs. 1 and 2, respectively, and important bond lengths
and angles are listed in Table 2. In the solid state, 1b is
essentially planar with a slight twist (ca. 108) of the
group P/1 with two unique molecules in the crystal-
lographic asymmetric unit. The two molecules differ
predominantly in the rotational orientation of the
MeOC6H4 moiety with respect to the catecholate
groups; the latter are arranged in a propeller-like
fashion. Bond lengths are comparable to analogous
values in CH3C(Bcat)3 [34], which crystallises with three
THF solvent molecules in the unit cell.

82
P. Nguyen et al. / Journal of Organometallic Chemistry 652 (2002) 77ꢀ85
/
3. Conclusion
The catalysed diboration of styrylboronate esters
provides a novel route to 2 and 3 under mild conditions
using readily available boron reagents, with selectivity
between the two isomeric products depending on the
catalyst used. Whilst 3 represents 1,2-addition of the two
borons to the CÄ
/
C double bond, formation of 2 involves
a 1,2-hydrogen shift and addition of both borons to a
single carbon centre.
4. Experimental
All reactions were carried out under a dry nitrogen
atmosphere using standard Schlenk techniques or an
Innovative Technology, Inc. System 1 glove box. Glass-
ware was oven dried before transfer into the glove box.
THF was dried over sodium/benzophenone and CDCl3
was dried over calcium hydride; both were distilled
under nitrogen. B2cat2 was prepared by established
Fig. 2. Molecular structure of one of the two independent molecules in
the asymmetric unit of 2b. Ellipsoids shown at 50% probability for
non-H atoms, with H atoms shown as circles of arbitrary radius.
procedures (see, for example, Refs. [48ꢀ50]) and
/
checked for purity by NMR spectroscopy and GC/MS
techniques. The catalyst precursors [Rh(PPh3)3Cl]
[51,52], [Rh(COE)2(m-Cl)]2 [53], [Rh(dppb)(acac)] [54]
and [Rh(dppm)(acac)] [16,54] were prepared using
published procedures and checked for purity by NMR
spectroscopy. Phosphines were purchased from Aldrich
or Strem and were checked for purity by 1H- and
Table 2
˚
Selected bond lengths (A) and bond angles (8) for 1b and 2b
1b
2b
a
Molecule A
Molecule B
1.549(4)
1
31P{1H}-NMR spectroscopy before use. H-NMR ex-
˚
Bond lengths (A)
C(1)ꢀ
C(1)ꢀ
B(1)ꢀ
B(1)ꢀ
/
C(2)
1.340(2)
1.532(2)
1.557(5)
periments were performed on Varian Inova 500 and
Varian C 500 spectrometers and were referenced to
residual protio-solvent resonances. 31P{1H}-NMR ex-
periments were performed on either Varian Unity 200 or
a Varian VXR-400 instruments and were referenced to
external 85% H3PO4. 11B{1H}-NMR experiments were
performed on a Bruker AC200 instrument and were
/B(1)
/O(1)
1.3954(19)
1.3937(19)
1.3848(17)
1.470(2)
/O(2)
C(11)ꢀ
C(2)ꢀC(21)
B(11)ꢀ
B(21)ꢀ
B(31)ꢀ
B(11)ꢀ
B(11)ꢀ
B(21)ꢀ
B(21)ꢀ
B(31)ꢀ
B(31)ꢀ
/
O(1)
/
/C(2)
1.557(5)
1.577(5)
1.561(5)
1.390(5)
1.380(5)
1.385(4)
1.376(4)
1.380(5)
1.381(4)
1.561(5)
1.572(5)
1.565(5)
1.393(5)
1.388(5)
1.378(4)
1.391(5)
1.386(4)
1.374(4)
/C(2)
/C(2)
referenced to external BF3×
/
OEt2. Coupling constants
/
O(11)
O(12)
O(21)
O(22)
O(31)
O(32)
are reported in Hertz (Hz).
/
/
/
4.1. Synthesis of (E)-p-Rꢀ
/
C6H4ꢀ
/
CHÄ
/
CHꢀBcat
/
/
/
The compounds phenyl acetylene or 4-methoxyphe-
nylethyne (0.0196 mol) and HBcat containing ‘BH3’
impurity (2.35g, 0.0196 mol) in a round-bottom flask
were stirred at ambient temperature for 1 h, after which
an orange solid resulted. Successive recrystallisations
Bond angles (8)
O(1)ꢀ
O(1)ꢀ
O(2)ꢀ
O(11)ꢀ
O(21)ꢀ
O(31)ꢀ
B(11)ꢀC(2)ꢀ
B(11)ꢀC(2)ꢀ
B(21)ꢀC(2)ꢀ
C(1)ꢀC(2)ꢀ
C(1)ꢀC(2)ꢀ
C(1)ꢀC(2)ꢀ
/
B(1)ꢀ
B(1)ꢀ
B(1)ꢀ
/
O(2)
C(1)
C(1)
111.32(13)
123.98(14)
124.70(14)
/
/
/
/
/
B(11)ꢀ
B(21)ꢀ
B(31)ꢀ
/O(12)
110.6(3)
111.2(3)
111.2(3)
106.0(3)
112.8(3)
103.9(3)
112.5(3)
110.3(3)
110.9(3)
110.4(3)
111.8(3)
110.3(3)
103.9(3)
111.2(3)
103.8(3)
113.1(3)
110.3(3)
113.6(3)
/
/O(22)
from Et2Oꢂ
white solid (Â
Refs. [21,44,47].
/
hexane (50:50) at ꢃ
/
30 8C gave pure 1 as a
/
/O(32)
/83% yield). For spectroscopic data see
/
/
B(21)
B(31)
B(31)
/
/
/
/
/
/
B(11)
B(21)
B(31)
4.2. General procedure for the catalysed diboration of
styrylboronate esters
/
/
/
/
a
A solution of B2cat2 (54 mg, 0.23 mmol), styrylbor-
onate ester (0.23 mmol) and catalyst precursor (0.0023
Compound 2b contains two independent molecules in the asym-
metric unit. Equivalent atoms in molecule B are primed.

P. Nguyen et al. / Journal of Organometallic Chemistry 652 (2002) 77ꢀ
/85
83
mmol Rh) in THF (1.5 ml) was heated to 58 8C under
Table 3
Crystal data and processing parameters for 1b and 2b
N2 in a ca. 10 ml tube sealed with a Young’s tap. After
12 h, the solution was allowed to cool to room
temperature and the solvent removed in vacuo. The
crude reaction mixture was then dissolved in CDCl3 and
1b
2b
Empirical formula
Formula weight
Temperature (K)
Diffractometer
C
15H13BO3
C27H21B3O7
489.9
180
1
252.1
105(2)
analysed by high field H-NMR spectroscopy.
Bruker SMART- Siemens R3m/v
CCD 1K
4.2.1. Selected NMR data (CDCl3) and elemental
analyses for boron containing products (see also Refs.
[21] and [44])
˚
Wavelength (A)
0.71073
Monoclinic
P21/n
0.71073
Triclinic
¯
P1
Crystal system
Space group
2a: d 3.83 (s, 2H, CH2C(Bcat)3), 7.02ꢀ
/
7.41 (ov. m,
phenyl H); 11B{1H} d 35.3; 13C{1H}
˚
a (A)
6.8374(8)
24.170(3)
7.4719(8)
90
9.607(3)
13.307(5)
20.485(7)
99.34(3)
90.65(3)
94.06(3)
2383.1(14)
1.365
17H, catecholateꢂ
/
˚
b (A)
d 33.6, 112.7, 122.9, 126.4, 128.7, 128.9, 141.4, 148.4.
The C(Bcat)3 resonance was not observed due to severe
quadrupolar broadening. Anal. Calc. C26H19B3O6: C,
67.91; H, 4.16. Found: C, 68.09; H, 4.37%.
2b [21]: d 3.67 (s, 3H, OCH3), 3.83 (s, 2H,
CH2C(Bcat)3), 6.66 (m, 2H, p-C6H4), 7.05-7.10 (ov. m.
˚
c (A)
a (8)
b (8)
g (8)
94.102(2)
90
3
˚
V (A )
1231.2(2)
1.360
Dcalc (Mg mꢃ3
)
Z
4
0.093
528
4
0.096
1016
m (Moꢀ
F(000)
/
Ka) (mmꢃ1
)
8H, catecholateꢂp-C6H4), 7.25 (m, 6H, catecholate H);
/
11B{1H} d 37.2; 13C{1H} 32.9, 55.2, 112.7, 113.9, 122.9,
129.8, 133.6, 148.4, 158.4. The C(Bcat)3 resonance was
not observed due to severe quadrupolar broadening.
u Range for data
collected (8)
1.69ꢀ/27.49
2.0ꢀ22.5
/
Reflections collected
Independent reflections 2822
Refinement method
12831
6284
6284
3a: d 2.75 (d, JHꢀH
JHꢀH 11.7, 1H, CHBcat).
3b: d 2.68 (d, JHꢀH 11.5, 1H, CH(Bcat)2), 3.69ꢀ
3.74 (ov. m, 4H, CHBcatꢂOCH3), 6.78 (m, 2H, p-
ꢁ
/
11.7, 1H, CH(Bcat)2), 3.69 (d,
ꢁ
/
Full-matrix least Full-matrix least squares
squares on F2
using 4099 data for
ꢁ
/
/
which F ꢀ
/
6.0s(F)
/
a
Goodness-of-fit on F2 1.066
1.92
R1ꢁ
wR2ꢁ
R1ꢁ0.0563,
wR2ꢁ0.0382
0.241 0.21 and ꢃ
C6H4), 7.01 (m, 2H, catecholate H), 7.14 (m, 2H,
catecholate H), 7.33 (m, 2H, p-C6H4); 11B{1H} d 23.8;
13C{1H} 13.6, 27.0, 55.2, 112.5, 112.6, 114.4, 122.7,
122.8, 129.0, 129.3, 140.0, 148.3, 158.1.
4a: d 1.93 (second-order dd, 1H, CH2Bcat), 2.19
(second-order dd, 1H, CH2Bcat), 3.36 (second-order dd,
b
c
Final R indices
R1ꢁ
wR2ꢁ
R1ꢁ0.0577,
wR2ꢁ0.0971
0.268 and ꢃ
/
0.0425
,
b
/
0.0371 ,
c
/
0.0906
/0.0369
R indices (all data)
/
/
/
/
Largest difference
˚
peak and hole (e A
/
/
0.17
ꢃ3
)
a
jFcj)2/(NOꢀ
/
NV)]1/2
.
1H, CH(Bcat)2, 7.00ꢀ
/
7.08 (m, 4H, catecholate H),
7.41 (m, 5H,
GoFꢁ
/
[Sw(jFojꢃ
2s(I)].
[F ꢀ6s(F)].
/
b
c
[I ꢀ
/
7.13ꢀ
/
7.20 (m, 4H, catecholate H), 7.27ꢀ
/
phenyl H); 11B{1H} d 36.8. Anal. Calc. C20H16B2O4: C,
70.25; H, 4.72. Found: C, 70.12; H, 4.70%.
/
4b [21,44]: d 1.88 (second-order dd, 1H, CH2Bcat),
2.12 (second-order dd, 1H, CH2Bcat), 3.28 (second
order dd, 1H, CHBcat), 3.76 (s, 3H, OCH3), 6.85 (m,
several f-settings in such a way as to cover a sphere of
˚
data to a maximum resolution of 0.77 A. Cell para-
meters were determined and refined using the SMART
software [57] from the centroid values of 5356 reflections
with 2u values between 5 and 558. Raw frame data were
integrated using the SAINT program [58]. The structure
was solved using Direct Methods and refined by full-
matrix least squares on F2 using SHELXTL [59]. The
reflection intensities were corrected for absorption and
other effects by the multi-scan method [60] based on
multiple scans of identical and Laue equivalent reflec-
2H, p-C6H4), 7.00ꢀ
/
7.18 (ov. m, 8H, catecholate H), 7.33
(m, 2H, p-C6H4); 11B{1H} d 37.1.
5a: d 2.12 (t, JHꢀH
JHꢀH 7.8, 2H, CH2).
5b: d 2.12 (t, JHꢀH
JHꢀH 7.8, 2H, CH2).
6a [55] and 6b: d 8.40 (s, 1H, CH Ä
ꢁ
/
7.8, 1H, CH(Bcat)2), 3.69 (d,
ꢁ
/
ꢁ
/
7.8, 1H, CH(Bcat)2), 3.66 (d,
ꢁ
/
/C(Bcat)2).
4.3. Crystallography
tions, Tmax
ꢁ
/
0.995, Tmin
ꢁ0.973. All non-hydrogen
/
atoms were refined with anisotropic atomic displace-
ment parameters (adps). Hydrogen atoms were located
from difference Fourier maps and their coordinates and
isotropic adps refined.
A colourless crystal of 1b dimensions 0.30ꢄ
0.05 mm was used for the single crystal structure
determination. Data were collected using graphite
/
0.15ꢄ
/
monochromated Moꢀ
/
Ka radiation (lꢁ0.71073) on a
/
Data for 2b were collected from a colourless prism of
Bruker SMART-CCD 1K detector diffractometer
equipped with a Cryostream N2 flow cooling device
[56]. Series of narrow v-scans (0.38) were performed at
dimensions 0.29ꢄ
/
0.20ꢄ/0.44 mm mounted on a glass
fibre, using v scans with variable scan rates (2.93ꢀ
/
29.38

84
P. Nguyen et al. / Journal of Organometallic Chemistry 652 (2002) 77ꢀ85
/
minꢃ1). From a total of 6284 reflections, 4099 with F ꢀ
6.0s(F) were used in the structure solution and refine-
ment [61]. Data were collected for Lorentz and polar-
isation effects, and for absorption (face indexed
numerical method). The structure was solved by direct
methods and Fourier techniques and refined by full
matrix least squares. Hydrogen atoms were located in
difference maps and refined anisotropcially (riding
/
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/
was employed. Scattering factors and anomalous dis-
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Crystallographic data for the structural analysis have
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Data Centre, CCDC nos. 172402 and 172548. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
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Acknowledgements
T.B.M. thanks NSERC (Canada) and EPSRC (UK)
for funding, P.N. thanks NSERC for a postgraduate
scholarship, R.B.C. and J.M.B. thank EPSRC for
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for a Senior Research Fellowship. We also thank Dr
A.E. Goeta for assistance with the X-ray structures,
Johnson-Matthey Ltd. for a loan of rhodium chloride
and Dr R.T. Baker and Professors D. Matteson, R.B.
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