Exchange of boryl ligand substituents in Os[B(OEt)2]Cl(CO)(PPh3)2

Article abstract of DOI:10.1016/j.jorganchem.2004.02.011

Reaction between Os[B(OEt)₂]Cl(CO)(PPh_{3 2} and 1,2-ethanediol in the presence of Me₃SiCl (1 equivalent) leads to the tethered boryl complex, Cl(CO)(PPh_{3 2} (1), in which one ethoxy substituent on the boryl ligand is exchanged with one hydroxy group of the 1,2-ethanediol leaving the other OH group available to coordinate to osmium, so giving a six coordinate complex. This formulation is confirmed by crystal structure determination. The same reactants, but with 2 equivalents of Me₃SiCl, lead to the yellow, coordinatively unsaturated complex, Os Cl(CO)(PPh₃)₂ (2). Complex (2) adds CO to give Os Cl(CO)₂ (PPh₃)₂ (3). Crystal structure determinations of 2 and 3 reveal a very marked difference in the Os-B distances found in the five coordinate complex 2 (2.043(4) ?) and the six coordinate complex 3 (2.179(7) ?). In a reaction similar to that used for forming 2 but with 1,3-propanediol replacing 1,2-ethanediol, the product is Os Cl(CO)(PPh_{3 2} (4). The crystal structure for 4 is also reported.

Full text of DOI:10.1016/j.jorganchem.2004.02.011

Journal of Organometallic Chemistry 689 (2004) 1609–1616
www.elsevier.com/locate/jorganchem
Exchange of boryl ligand substituents in Os[B(OEt)2]Cl(CO)(PPh3)2
*
*
Clifton E.F. Rickard, Warren R. Roper , Alex Williamson, L. James Wright
Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand
Received 15 December 2002; accepted 2 February 2004
Abstract
Reaction between Os[B(OEt)2]Cl(CO)(PPh3)2 and 1,2-ethanediol in the presence of Me3SiCl (1 equivalent) leads to the tethered
Os[B(OEt)(OC H OH)]
boryl complex,
Cl(CO)(PPh3)2 (1), in which one ethoxy substituent on the boryl ligand is exchanged with one
2
4
hydroxy group of the 1,2-ethanediol leaving the other OH group available to coordinate to osmium, so giving a six coordinate
complex. This formulation is confirmed by crystal structure determination. The same reactants, but with 2 equivalents of Me3SiCl,
(BOC H O)
lead to the yellow, coordinatively unsaturated complex, Os
(BOC H O)
Cl(CO)(PPh3)2 (2). Complex (2) adds CO to give
Cl(CO)2 (PPh3)2 (3). Crystal structure determinations of 2 and 3 reveal a very marked difference in the Os–B distances
2
4
Os
found in the five coordinate complex 2 (2.043(4) A) and the six coordinate complex 3 (2.179(7) A). In a reaction similar to that used
2
4
ꢀ
ꢀ
(BOC H O)
for forming 2 but with 1,3-propanediol replacing 1,2-ethanediol, the product is Os
structure for 4 is also reported.
Cl(CO)(PPh3)2 (4). The crystal
3
6
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Boryl complex; Boron; Osmium; X-ray crystal structure
1. Introduction
described that Os[B(OEt)2]Cl(CO)(PPh3)2 can be re-
crystallised unchanged from methanol and is not hy-
drolysed by moist solvents [3]. The availability of this
simple and thoroughly characterised bis(ethoxy)boryl
complex, led us to explore conditions under which
exchange processes might occur. In this paper we re-
port: (i) that exchange of the ethoxy groups in
Os[B(OEt)2]Cl(CO)(PPh3)2 with 1,2-ethanediol or 1,3-
propanediol takes place in the presence of Me3SiCl to
Transition metal-boryl complexes, LnM–BR2, have
been widely studied in the past decade both because of
their fundamental interest and because of their role as
important intermediates in the metal-catalyzed synthe-
ses of boron-functionalised organics. These develop-
ments have been extensively reviewed [1]. An interesting
class of reactions, which some metal-boryl complexes
undergo, is substitution of the boryl substituents with-
out interference with the M–B bond. Such reactions
have been observed for chloro-boryl ligands [2–5]. In
organoboron chemistry, borate esters, B(OR)3, readily
undergo exchange reactions with other alcohols. Inter-
estingly, this exchange process has not been reported for
LnM–B(OR)2 complexes and indeed, we have recently
give the cyclic boryl complexes, Os
(PPh ) (2) or Os
Cl(CO)
(BOC2H4O)
Cl(CO)(PPh ) (4), respec-
(BOC3H6O)
3 2
3 2
tively, (ii) that in the case of 1,2-ethanediol it is possible
to isolate and structurally characterise an intermediate
in which only one ethoxy group is replaced,
Os[B(OEt)(OC2H4OH)]Cl(CO) (PPh3)2 (1), (iii) a struc-
tural comparison between the coordinatively unsatu-
rated boryl complex Os
Cl(CO)(PPh ) (2)
3 2
(BOC2H4O)
and the corresponding coordinatively saturated boryl
complex Os Cl(CO) (PPh ) (3), and (iv) a
* Corresponding authors. Tel: +64-9-373-7999x8320; fax: + 64-9-
373-7422.
E-mail address: w.roper@auckland.ac.nz (W.R. Roper).
(BOC2H4O)
2
3 2
crystal structure determination of Os
Cl(CO)(PPh3)2 (4).
(BOC3H6O)
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.02.011

1610
C.E.F. Rickard et al. / Journal of Organometallic Chemistry 689 (2004) 1609–1616
2. Results and discussion
centre by coordination of the free hydroxy function. The
structure also revealed that the crystalline solid was an
ethanol solvate, the ethanol O atom associating with the
coordinated OH function in 1.
2.1. Reaction of Os[B(OEt)2]Cl(CO)(PPh3)2 with 1,2-
ethanediol in the presence of Me3SiCl and the structures
of
Os
Cl(CO)(PPh ) (1) and
3
The molecular geometry of 1 is shown in Fig. 1 and
the arrangement of the hydrogen-bonded ethanol is
shown in Fig. 2. Crystal data pertaining to this structure
and other structures reported in this paper are presented
in Table 1. Selected bond lengths and angles for 1 are
collected in Table 2. The overall geometry about os-
mium is octahedral with the two triphenylphosphine li-
gands mutually trans and the tethered boryl ligand
occupying two adjacent sites with B trans to Cl and the
coordinated OH group trans to CO. The Os–B distance
Os[B(OEt)(OC2H4OH)]
Cl(CO)(PPh ) (2)
2
(BOC2H4O)
3
2
Treatment of a solution of Os[B(OEt)2]Cl(CO)
(PPh3)2 with 1,2-ethanediol in the presence of one
equivalent of Me3SiCl leads to a fading of the yellow
colour and a cream-coloured solid can be isolated (see
Scheme 1). This proves to be a mixture of three com-
pounds:
(where only one ethoxy group has exchanged with 1,2-
ethanediol), Os Cl(CO)(PPh ) (2) (where
Cl(CO)(PPh )
(1)
Os[B(OEt)(OC2H4OH)]
3 2
ꢀ
is 2.107(4) A. This is longer than the Os–B distance
found in the five coordinate boryl complexes,
(BOC2H4O)
3 2
both ethoxy groups have exchanged and a cyclic boryl
ligand is formed), and unreacted starting material. Al-
though a bulk sample of pure 1 could not be obtained, it
was possible to separate spectral data for 1 (from data
for 2 and starting material) and also to grow a single
crystal of 1 for X-ray analysis. The m(CO) for compound
1 is observed at 1916 cmꢀ1 (cf. 1906 cmꢀ1 for
ꢀ
Os(Bcat)Cl(CO)(PPh3)2 (cat ¼ 1,2-O2C6H4) (2.019(3) A,
ꢀ
Cl(CO)(PPh ) (2) (2.043(4) A,
[6]) and Os
see below). It is, however, shorter than is observed when
(BOC2H4O)
3 2
the boryl ligand is located trans to the p-acceptor CO in
ꢀ
cis-Os(Bcat)I(CO)2(PPh3)2 (2.145(5) A, [7]) and closely
similar to the distance found when trans to I in trans-
ꢀ
Os(Bcat)I(CO)2 (PPh3)2(2.090(3) A, [7]). The Os–Cl
ꢀ
bond distance in 1 (2.5499(8) A) is comparable to the
Os[B(OEt)2]Cl(CO)(PPh3)2) and m(OH) at 3369 cmꢀ1
.
The pale colour suggests that 1 is not a coordinatively
unsaturated compound and indeed this was confirmed
by the crystal structure determination which confirmed
the presence of a boryl ligand tethered to the osmium
Os–Cl bond distances in the related compounds
where chloride is trans to the boryl ligand,
ꢀ
Cl(CO) (PPh ) (2.5606(7) A [5]),
Os[B(OH)(NHC5H4N)]
3 2
ꢀ
Cl(CO)(PPh3)2, (2.5653(6) A
Bu)(OC H N)]
Os[B(NHn-
[4]) and all three are at the long end limit of the observed
5
4
PPh3
H
Os
ꢀ
range for Os–Cl (mean ¼ 2.389, SD 0.067 A [8]). Once
Cl
O
HOC2H4OH
OC
B
O
Me3SiCl (1 eq.)
(a mixture of 1
and 2 is
produced in
this reaction)
PPh3
OEt
(1)
PPh3
Os
Cl
B
HOC2H4OH
O
OC
Me3SiCl (2 eq.)
PPh3
O
(2)
PPh3
Os
CO
Cl
OC
B(OEt)2
PPh3
PPh3
Os
OC
OC
Cl
B
O
PPh3
(3)
O
PPh3
Os
Cl
B
HOC3H6OH
O
Me3SiCl (2 eq.) OC
PPh3
(4)
O
Os[B(OEt)(OC H OH)]
Cl(CO)
Scheme 1. Reactions of Os[B(OEt)2]Cl(CO)(PPh3)2 with 1,2-ethane-
diol and 1,3-propanediol.
Fig. 1. Molecular geometry of Os
(PPh3)2 (1).
2
4

C.E.F. Rickard et al. / Journal of Organometallic Chemistry 689 (2004) 1609–1616
1611
bonded ethanol (see Fig. 2). The O(2)–O(5) distance is
ꢀ
2.626 A and this lies within the range observed for O–
ꢀ
H. . .O hydrogen bonding interactions (2.48–2.90 A) [9].
The B–O bond lengths and associated angles about
boron are as expected.
Treatment of a solution of Os[B(OEt)2]Cl(CO)
(PPh3)2 with 1,2-ethanediol in the presence of two
equivalents of Me3SiCl leads directly to the yellow, five-
coordinate complex,
Cl(CO)(PPh ) (2).
3 2
Os(BOC2H4O)
Here, both ethoxy groups have been exchanged with the
difunctional 1,2-ethanediol producing the cyclic boryl
ligand (see Scheme 1). The m(CO) for compound 2 is
observed at 1912 cmꢀ1 (cf. 1906 cmꢀ1 for
Os[B(OEt)2]Cl(CO)(PPh3)2). The 1H NMR spectrum
shows a singlet at 3.72 ppm integrating for four protons
which is assigned to the ethylene bridging group of the
cyclic boryl ligand. The 11B NMR spectrum shows a
signal at 27.8 ppm. This is significantly shielded with
respect to the coordinatively saturated counterpart of 2,
viz., complex 3, the product of CO addition to 2.
Complex 3 has a 11B NMR signal at 45.0 ppm. This
difference may be associated with greater Os–B p-
backdonation in 2, a conclusion supported by the
structural data discussed below.
Fig. 2. The hydrogen-bond interaction between 1 and an ethanol
molecule in the crystalline state.
The crystal structure of 2 was determined and the
molecular geometry is shown in Fig. 3. Selected bond
lengths and angles for 2 are collected in Table 3. The
overall geometry about osmium is square pyramidal with
the two triphenylphosphine ligands mutually trans and
again it is clear that boryl ligands exert a pronounced
trans influence. An interesting feature revealed by the
crystal structure of 1 is the presence of the hydrogen-
Table 1
Data collection and processing parameters for 1–4
1 ꢁ EtOH
2
3
4
Formula
C41H40BClO4OsP2 ꢁ C2H5OH
C39H34BClO3OsP2
849.06
Monoclinic
C40H34BClO4OsP2
877.07
Monoclinic
C40H36BClO3OsP2
863.09
Monoclinic
Molecular weight
Crystal system
Space group
895.13
Monoclinic
P21=n
P21
P21=c
P21
ꢀ
a (A)
12.1904(1)
16.0736(2)
20.7912(1)
96.425(1)
4048.32(6)
4
9.6950(1)
14.6804(1)
13.1693(1)
109.820(1)
1763.31(3)
2
19.9431(1)
10.1890(1)
19.8028(2)
116.853(1)
3589.99(4)
4
9.5836(1)
14.9694(1)
13.1142(1)
109.273(1)
1775.93(3)
2
ꢀ
b (A)
ꢀ
c (A)
b (°)
V (A )
3
ꢀ
Z
Dcalc (g cmꢀ3
F ð000Þ
)
1.543
1884
3.34
1.599
840
3.82
1.623
1736
3.76
1.614
856
3.79
l (mmꢀ1
Crystal size (mm)
)
0.23 ꢂ 0.10 ꢂ 0.09
1.6–27.4
24,190
0.55 ꢂ 0.20 ꢂ 0.05
1.6–27.4
10,627
0.44 ꢂ 0.20 ꢂ 0.03
2.1–26.4
19,904
0.60 ꢂ 0.50 ꢂ 0.03
1.6–26.4
10,571
h (min–max) (°)
Reflections collected
Independent reflections (Rint
)
8894 (0.0273)
7450
6583 (0.018)
6326
7327 (0.060)
5260
6229 (0.056)
5794
Observed reflections, I > 2rðIÞ
A (min–max)
Goodness of fit on F2
R (observed data)a
0.514–0.753
1.065
0.227–0.832
0.869
0.288–0.895
0.989
0.209–0.895
0.934
R1 ¼ 0:0290
wR2 ¼ 0:0553
R1 ¼ 0:0416
WR2 ¼ 0:0602
1=2
R1 ¼ 0:0212
wR2 ¼ 0:0464
R1 ¼ 0:0223
wR2 ¼ 0:0468
R1 ¼ 0:0399
wR2 ¼ 0:0776
R1 ¼ 0:0728
wR2 ¼ 0:0889
R1 ¼ 0:0402
wR2 ¼ 0:0989
R1 ¼ 0:0424
wR2 ¼ 0:1002
R (all data)
P
P
2
2
wR2 ¼ f ½wðFo2 ꢀ Fc2Þ ꢃ= ½wðFo2Þ ꢃg
.
P
P
a R ¼ jjFoj ꢀ jFcjj= jFoj.

1612
C.E.F. Rickard et al. / Journal of Organometallic Chemistry 689 (2004) 1609–1616
Table 2
Table 3
ꢀ
ꢀ
Selected bond lengths [A] and angles [°] for 1
Selected bond lengths [A] and angles [°] for 2
Os–C(1)
Os–B
1.817(4)
Os–C(10)
Os–C(1)
Os–B
1.762(9)
2.107(4)
2.180(2)
2.3694(9)
2.3739(9)
2.5499(8)
1.370(5)
1.399(5)
1.164(4)
1.417(5)
1.420(5)
1.424(4)
1.379(7)
1.489(6)
1.764(7)
2.043(4)
2.3661(9)
2.3751(10)
2.447(3)
2.484(3)
1.171(9)
1.139(10)
1.379(5)
1.390(5)
1.454(5)
1.449(5)
1.479(8)
Os–O(2)
Os–P(2)
Os–P(1)
Os–Cl
Os–P(1)
Os–P(2)
Os–Cl
B–O(4)
B–O(3)
Os–Cl0
O(1)–C(1)
O(10)–C(10)
B–O(3)
O(1)–C(1)
O(2)–C(2)
O(3)–C(3)
O(4)–C(4)
C(2)–C(3)
C(4)–C(5)
B–O(2)
O(2)–C(2)
O(3)–C(3)
C(2)–C(3)
C(1)–Os–B
C(1)–Os–O(2)
B–Os–O(2)
C(1)–Os–P(2)
B–Os–P(2)
87.56(16)
174.92(13)
87.36(13)
89.47(12)
90.98(11)
90.70(7)
89.89(12)
91.27(11)
90.13(7)
177.64(3)
104.00(11)
168.43(12)
81.08(7)
89.57(3)
88.38(3)
112.4(3)
122.1(3)
125.4(3)
123.7(2)
C(1)–Os–B
C(1)–Os–P(1)
B–Os–P(1)
90.9(3)
88.3(3)
91.31(12)
90.6(3)
C(1)–Os–P(2)
B–Os–P(2)
88.48(12)
178.92(3)
160.0(3)
109.03(15)
89.45(6)
91.62(6)
177.7(8)
110.1(3)
124.7(3)
125.3(3)
O(2)–Os–P(2)
C(1)–Os–P(1)
B–Os–P(1)
P(1)–Os–P(2)
C(1)–Os–Cl
B–Os–Cl
O(2)–Os–P(1)
P(2)–Os–P(1)
C(1)–Os–Cl
B–Os–Cl
P(1)–Os–Cl
P(2)–Os–Cl
O(1)–C(1)–Os
O(3)–B–O(2)
O(3)–B–Os
O(2)–B–Os
O(2)–Os–Cl
P(2)–Os–Cl
P(1)–Os–Cl
O(4)–B–O(3)
O(4)–B–Os
O(3)–B–Os
C(2)–O(2)–Os
the cyclic boryl ligand occupying the apical position. The
ꢀ
Os–B distance is 2.043(4) A. This can be compared with
the Os–B distances in the related five-coordinate com-
ꢀ
plexes, Os[B(OEt)2]Cl(CO)(PPh3)2 (2.081(5) A [3]) and
ꢀ
Os(Bcat)Cl(CO)(PPh3)2 (2.019(3) A [6]). The Os–B dis-
tance in Os
Cl(CO)(PPh ) (2) is longer than
3 2
(BOC2H4O)
the corresponding distance in Os(Bcat)Cl(CO)(PPh3)2
which is consistent with a competitive p-donation situa-
tion where Os–B p-donation is relatively stronger in the
Bcat complex, and O–B p-donation is relatively stronger
in the
complex. Further support for this idea
is that the two B–O distances in 2 are 1.379(5) and 1.390(5)
(BOC2H4O)
ꢀ
A whereas the two B–O distances found in Os(Bcat)Cl
ꢀ
(CO)(PPh3)2 are 1.411(4) and 1.406(4) A. The observed
Os–Cl distances in 2 (disorder between Cl and CO) are
ꢀ
2.447(3) and 2.484(3) A, and are similar to other five-co-
ordinate osmium boryl complexes where Cl is trans to CO.
The effectiveness of Me3SiCl in promoting the above
exchange reactions could be attributed simply to acid-
catalysis by HCl (liberated through alcoholysis of the
Me3SiCl), however, attempted exchange reactions in the
presence of introduced HCl in place of Me3SiCl were
not successful. An alternative explanation could be that
Me3SiCl converts the B–O bonds in the B(OEt)2 ligand
to B–Cl bonds which would be expected to undergo
rapid alcoholysis. We were, however, unable to detect
any transient chloroboryl complexes.
(BOC H O)
Fig. 3. Molecular geometry of Os
Cl(CO)(PPh3)2 (2).
2
4

C.E.F. Rickard et al. / Journal of Organometallic Chemistry 689 (2004) 1609–1616
1613
Table 4
2.2. Reaction of Os
Cl(CO)(PPh ) (2)with
3 2
(BOC2H4O)
CO and the structural comparison of Os
ꢀ
Selected bond lengths [A] and angles [°] for 3
Cl
(BOC2H4O)
Cl(CO) (PPh )
3 2
Os–C(1)
Os–C(2)
Os–C(20)
Os–B
1.970(6)
(CO)(PPh ) (2) and Os
3
(BOC2H4O)
2
2
1.857(12)
1.874(16)
2.179(7)
2.3946(15)
2.3982(16)
2.433(4)
2.485(7)
1.385(7)
1.371(7)
1.143(7)
1.192(15)
0.981(16)
1.447(7)
1.441(7)
1.508(8)
(3)
As depicted in Scheme 1 the coordinatively unsatu-
rated complex 2 readily takes up CO to give the col-
ourless dicarbonyl complex, Os
(PPh3)2 (3). The IR spectrum of 3 shows two m(CO)
bands at 2031, 1945 cmꢀ1, indicating that the CO li-
gands are arranged mutually cis. To permit a compari-
son between a five-coordinate and a six-coordinate boryl
complex where the boryl ligands are identical, an X-
ray crystal structure determination of complex 3 was
undertaken.
Os–P(2)
Os–P(1)
Os–Cl
Cl(CO)
2
(BOC2H4O)
Os–Cl0
B–O(3)
B–O(4)
O(1)–C(1)
O(2)–C(2)
O(20)–C(20)
O(3)–C(3)
O(4)–C(4)
C(3)–C(4)
The molecular geometry of 3 is shown in Fig. 4. Se-
lected bond lengths and angles for 3 are collected in
Table 4. The overall geometry about osmium is octa-
hedral with the two triphenylphosphine ligands mutu-
ally trans and with the cyclic boryl ligand trans to CO.
C(1)–Os–C(2)
C(1)–Os–C(20)
C(1)–Os–B
92.4(4)
87.8(5)
177.0(3)
90.2(4)
89.7(5)
C(2)–Os–B
C(20)–Os–B
C(1)–Os–P(2)
C(2)–Os–P(2)
C(20)–Os–P(2)
B–Os–P(2)
ꢀ
The Os–B distance is 2.179(7) A which is considerably
93.56(19)
92.4(4)
91.3(6)
ꢀ
longer than the corresponding distance in 2 (2.043(4) A)
where there is no ligand trans to the boryl ligand. One
factor which must contribute to this lengthening, is the
presence of a competitive p-acceptor ligand (CO) trans
the boryl ligand. Significantly, the Os–CO distance for
84.86(19)
96.53(19)
86.4(4)
C(1)–Os–P(1)
C(2)–Os–P(1)
C(20)–Os–P(1)
B–Os–P(1)
89.9(6)
ꢀ
this trans CO ligand is 1.970(6) A, considerably longer
than the Os–CO distance for the cis CO ligand (disor-
85.10(19)
169.88(5)
87.5(2)
P(2)–Os–P(1)
C(1)–Os–Cl
C(1)–Os–Cl0
C(2)–Os–Cl
C(20)–Os–Cl0
B–Os–Cl
ꢀ
dered, 1.857(12) and 1.874(16) A).
89.4(2)
179.8(5)
174.8(6)
89.83(19)
93.2(2)
B–Os–Cl0
P(2)–Os–Cl
P(2)–Os–Cl0
P(1)–Os–Cl
P(1)–Os–Cl0
O(3)–B–O(4)
O(3)–B–Os
O(4)–B–Os
87.76(8)
93.21(14)
93.44(8)
86.13(14)
111.7(5)
124.2(4)
124.1(4)
2.3. Reaction of Os[B(OEt)2]Cl(CO)(PPh3)2 with 1,3-
propanediol in the presence of Me3SiCl and the structure
of Os
Cl(CO)(PPh ) (4)
3 2
(BOC3H6O)
Os[B(OEt)2]Cl(CO)(PPh3)2 reacts with 1,3-propane-
diol in the presence of two equivalents of Me3SiCl in just
the same way as it does with 1,2-ethanediol to give the
expected five-coordinate complex with the six-membered
cyclic boryl ligand, Os
Cl(CO)(PPh ) (4) (see
3 2
(BOC3H6O)
Scheme 1). The IR spectrum of this yellow compound
shows a m(CO) band at 1904 cmꢀ1, significantly lower
than the m(CO) (1912 cmꢀ1) for the previously described
compound from reaction with 1,2-ethanediol,
Os
Cl(CO)(PPh ) (2). This suggests that the
3 2
(BOC2H4O)
(BOC H O)
Fig. 4. Molecular geometry of Os
Cl(CO)2(PPh3)2 (3).
five-membered cyclic boryl ligand is a better p-acceptor
2
4

1614
C.E.F. Rickard et al. / Journal of Organometallic Chemistry 689 (2004) 1609–1616
midal with the two triphenylphosphine ligands mutually
trans and the cyclic boryl ligand occupying the apical
ꢀ
position. The Os–B distance is 2.062(9) A. This can be
compared with the value for the Os–B distance of
ꢀ
2.043(4) A found for 2. The longer distance found for the
six-membered cyclic boryl ligand in 4 is compatible with
there being a weaker p-component to the Os–B bond as
suggested by the IR data. Consistent with this interpre-
tation it can also be noted that the B–O distances in 4
ꢀ
(1.374(10), 1.374(12) A) are shorter than the B–O dis-
ꢀ
tances in 2 (1.390(5), 1.379(5) A). Another structural
feature worth noting is that the O–B–O angle in the six-
membered ring is 120.9(7)°, allowing almost perfect tri-
gonal planarity about B, whereas the corresponding an-
gle in the five-membered cyclic boryl ligand is restrained
to 110.1(3)°. This smaller angle implies greater p-char-
acter in the B–O bonds and correspondingly greater s-
character in the Os–B bond which would also be a factor
contributing to the shorter Os–B bond observed in 2.
Fig. 5. Molecular geometry of Os(BOC3H6O)Cl(CO)(PPh3)2 (4).
3. Conclusions
Although the OEt groups in Os[B(OEt)2]Cl(CO)
(PPh3)2 do not exchange with alcohols under neutral
conditions, we demonstrate here that such exchanges take
place readily in the presence of Me3SiCl. By using one
equivalent of Me3SiCl in the reaction with 1,2-ethanediol
it is possible to obtain, as one of several products, a com-
pound in which there has been exchange of only one OEt
group (complex 1). However, with two equivalents of
Me3SiCl both OEt groups react forming the five-coordi-
than the six-membered cyclic boryl ligand. This in turn
suggests that the Os–B distance in complex 4 should be
greater than that in complex 2 and to ascertain whether
or not this prediction is true a crystal structure determi-
nation of complex 4 was undertaken.
The molecular geometry of 4 is shown in Fig. 5. Se-
lected bond lengths and angles for 4 are collected in Table
5. The overall geometry about osmium is square pyra-
nate, cyclic boryl complex, Os
Cl(CO)(PPh ) .
3 2
(BOC2H4O)
Table 5
A structural comparison of five- and six-coordinate com-
plexes with this cyclic boryl ligand reveals a pronounced
elongation of the Os–B bond when the p-accepting ligand
CO is introduced trans to the boryl ligand. A further
structural comparison of the five coordinate complexes,
ꢀ
Selected bond lengths [A] and angles [°] for 4
Os–C(10)
Os–C(1)
Os–B
1.736(13)
1.737(14)
2.062(9)
Os–P(1)
Os–P(2)
Os–Cl
2.3653(18)
2.3673(18)
2.446(5)
Os
Cl(CO)(PPh ) and Os
3 2
Cl(CO)
(BOC3H6O)
(BOC2H4O)
(PPh3)2 which contain, respectively, five- and six-mem-
bered cyclic boryl ligands reveals a shorter Os–B bond
associated with the five-membered cyclic boryl ligand. An
explanation is offered in terms of the significance of both
the r- and p-components of the Os–B bond.
Os–Cl0
2.454(5)
B–O(3)
B–O(2)
O(2)–C(2)
O(3)–C(4)
1.374(10)
1.374(12)
1.442(10)
1.455(10)
C(1)–Os–B
C(1)–Os–P(1)
B–Os–P(1)
C(1)–Os–P(2)
B–Os–P(2)
P(1)–Os–P(2)
C(1)–Os–Cl
B–Os–Cl
93.3(6)
88.7(5)
4. Experimental
91.4(2)
90.2(5)
88.3(2)
4.1. General procedures and instruments
178.89(6)
158.9(6)
107.7(3)
89.82(12)
91.29(12)
120.9(7)
119.3(6)
119.8(6)
Standard laboratory procedures were followed as
have been described previously [10]. The compound
Os[B(OEt)2]Cl(CO)(PPh3)2 [3] was prepared according
to the literature method.
Infrared spectra (4000–400 cmꢀ1) were recorded as
Nujol mulls between KBr plates on a Perkin–Elmer
P(1)–Os–Cl
P(2)–Os–Cl
O(3)–B–O(2)
O(3)–B–Os
O(2)–B–Os

C.E.F. Rickard et al. / Journal of Organometallic Chemistry 689 (2004) 1609–1616
1615
Paragon 1000 spectrometer. NMR spectra were ob-
1
4.4. Preparation of Os
Cl(CO) (PPh ) (3)
2 3 2
(BOC2H4O)
tained on a Bruker DRX 400 at 25 °C. H, 13C, 11B,
and31P NMR spectra were obtained operating at 400.1
(1H), 100.6 (13C), 128.0 (11B), and 162.0 (31P) MHz,
respectively. Resonances are quoted in ppm and 1H
NMR spectra referenced to either tetramethylsilane
(0.00 ppm) or the proteo-impurity in the solvent (7.25
ppm for CHCl3). 13C NMR spectra were referenced to
CDCl3 (77.00 ppm), 11B NMR spectra to BF3 ꢁ OEt2 as
an external standard (0.00 ppm), and 31P NMR spectra
to 85% orthophosphoric acid (0.00 ppm) as an external
standard. Elemental analyses were obtained from the
Microanalytical Laboratory, University of Otago.
An
approximately
1:1
Cl(CO)(PPh )
mixture
and
of
Os-
Os[B(OEt)(OC2H4OH)]
3 2
Cl(CO)(PPh ) which had been synthesised
3 2
(BOC2H4O)
from Os[B(OEt)2]Cl(CO)(PPh3)2 (100 mg, 0.114 mmol)
following the procedure described in Section 4.2 was
dissolved in THF (10 mL) and a stream of CO gas was
bubbled through the solution for 5 s, turning it colour-
less. The solvent was concentrated to a volume of ca. 1
mL in vacuo and addition of hexane gave pure 3 as a
white precipitate which was collected on a glass frit and
washed with EtOH and hexane (71 mg, 71%). Anal.
Calc. for C40H34BClO4OsP2: C, 54.77; H, 3.91. Found:
C, 54.51; H, 3.57%. IR (cmꢀ1): 2031 s, 1945 s m(CO);
Os[B(OEt)(OC H OH)]
4.2. Preparation of
(PPh3)2 (1)
Cl(CO)
2
4
1
1160 m, 1126 s, 1111 m, 941 w. H NMR (CDCl3, d):
3.24 (s, 4H, BO2C2H4), 7.34–7.39 (m, 18H, PPh3), 7.69–
A mixture of Os[B(OEt)2]Cl(CO)(PPh3)2 (101 mg,
0.115 mmol), 1,2-ethanediol (6 mL) and Me3SiCl (0.014
mL, 0.110 mmol) was stirred in THF (10 mL) for 11
min. The solvent was removed slowly in vacuo to pre-
cipitate a cream-coloured solid (70 mg) which was col-
lected on a glass frit and washed with EtOH and hexane.
The product obtained this way was always contami-
7.74 (m, 12H, PPh3). 13C NMR (CDCl3, d): 64.67
(BO2C2H4), 127.82 (t0,
J
¼ 10 Hz, o-C6H5), 129.97
CP
¼ 54 Hz, i-C6H5), 133.99 (t0,
2;4
1;3
(p-C6H5), 133.87 (t0,
J
CP
3;5
J
¼ 11 Hz, m-C6H5). CO not observed. 11B NMR
CP
(CDCl3, d): 45.0.
4.5. Preparation of Os
Cl(CO)(PPh ) (4)
3 2
(BOC3H6O)
nated with variable amounts of both Os
(BOC2H4O)
Cl(CO)(PPh3)2 and starting material. The ratios of
Os[B(OEt)2]Cl(CO)(PPh3)2, 1, and 2, appear to depend
on the time taken to remove the THF in vacuo from the
reaction mixture. Elemental analysis was not obtained
for the above reasons, however, a single crystal of 1 was
grown from a solution of the mixture so permitting
structure confirmation by X-ray crystallography. IR
(cmꢀ1): 1916 vs m(CO); 3369 br m(OH); 1225 m, 1211 m,
1162 m, 1030 m, 1016 m, 919 w, 878 w. 1H NMR
(CDCl3, d): 0.76 (t, 3H, 3JHH ¼ 7:0 Hz, OCH2Me), 1.88
A mixture of Os[B(OEt)2]Cl(CO)(PPh3)2 (99 mg,
0.113 mmol), 1,3-propanediol (6 mL) and Me3SiCl
(0.028 mL, 0.221 mmol) was stirred in THF (10 mL) for
15 min. The THF was removed in vacuo affording a
yellow precipitate which was collected on a glass frit and
washed with EtOH and hexanes. The product was re-
crystallised from CH2Cl2/hexane to give pure 4 (85 mg,
1
87%). H NMR spectroscopy showed 0.25 equivalents
of CH2Cl2 present as solvate. Anal. Calc. for
C46H37BClO3OsP2 ꢁ 0.25CH2Cl2: C, 54.66; H, 4.16.
Found: C, 54.85; H, 3.88%. IR (cmꢀ1): 1904vs m(CO);
1258 w, 1250 m, 1144 s, 1120 s, 1019 w. 1H NMR
3
(br), 2.25 (br), 3.13 (br), 3.38 (q, 2H, JHH ¼ 7:0 Hz,
OCH2Me), 3.52 (br), 7.37 (m, 18H, PPh3), 7.63–7.67 (m,
12H, PPh3).
3
(CDCl3, d): 1.30 (quin, 2H, JHH ¼ 5:5 Hz, BO2C3H6),
3
3.61 (t, 4H, JHH ¼ 5:5 Hz, BO2C3H6), 7.35–7.38 (m,
4.3. Preparation of Os
Cl(CO)(PPh ) (2)
3
18H, PPh3), 7.55–7.61 (m, 12H, PPh3). 13C NMR
(CDCl3, d): 27.66 (BO2C3H6), 62.01 (BO2 C3H6), 128.00
(t0, 2;4JCP ¼ 10 Hz, o-C6H5), 139.80 (p-C6H5), 133.04 (t0,
(BOC2H4O)
2
A mixture of Os[B(OEt)2]Cl(CO)(PPh3)2 (98 mg,
0.111 mmol), 1,2-ethanediol (6 mL) and Me3SiCl (0.028
mL, 0.221 mmol) was stirred in THF (10 mL) for 30
min. The solvent was removed slowly in vacuo to give
pure 2 as a yellow precipitate which was collected on a
glass frit and washed with EtOH and hexane (57 mg,
60%). Anal. Calc. for C39H34BClO3OsP2: C, 55.17; H,
4.04. Found: C, 55.30; H, 4.26%. IR (cmꢀ1): 1912 vs
m(CO); 1169 w, 1143 m, 1118 s, 1068 m, 940 w. 1H NMR
(CDCl3, d): 3.72 (s, 4H, BO2C2 H4), 7.36–7.39 (m, 18H,
1;3
3;5
J
¼ 49 Hz, i-C6H5), 134.57 (t0,
J
¼ 11 Hz, m-
CP
CP
C6H5). CO not observed. 11B NMR (CDCl3/CH2Cl2, d):
23.5. 31P NMR (CDCl3/CH2Cl2, d): 29.79 (s).
4.6. X-ray crystal structure determinations for complexes
1, 2, 3, and 4
Data were collected on a Siemens SMART CCD
diffractometer at 200 K with graphite-monochromated
PPh3), 7.56–7.61 (m, 12H, PPh3). 13C NMR (CDCl3, d):
Mo Ka radiation (k 0.71073 A) using x scans. Data
ꢀ
2;4
65.14 (BO2 C2H4), 128.17 (t0 [10],
J
J
¼ 10 Hz, o-
were corrected for Lorentz and polarisation effects and
absorption corrections applied using symmetry related
measurements [11]. The structures were solved using
SHELXS [12] and refined by full-matrix least squares
CP
1;3
C6H5), 130.00 (p-C6H5), 132.46 (t0,
¼ 51 Hz, i-
CP
C6H5), 134.45 (t0,
J
CP
¼ 12 Hz, m-C6H5). CO not
3;5
observed. 11B NMR (CDCl3, d): 27.8.

1616
C.E.F. Rickard et al. / Journal of Organometallic Chemistry 689 (2004) 1609–1616
using SHELXL [13] with anisotropic thermal parameters
for all non-hydrogen atoms. Hydrogen atoms were in-
cluded in calculated positions and refined with a riding
model. 2 and 4 are isostructural, even though 4 has an
additional methylene group in the cyclic boryl ligand.
Structures 2, 3, and 4 all have disorder between the
chlorine and carbonyl groups and these structures have
been refined with these two groups half-weighted in the
two alternate positions. In addition, the central carbon
atom of the bridging C3H6 group of the cyclic boryl li-
gand in 4 is disordered and has also been refined, half-
weighted, in two alternative sites. 2 and 4 are chiral and
coincidentally are opposite enantiomers, the absolute
structure parameters [14] being 0.010(4) and –0.016(9)
for 2 and 4, respectively. Crystal data and refinement
details for all three structures are given in Table 1.
and for granting a Post Doctoral Fellowship award to
A.W.
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Acknowledgements
We thank the Marsden Fund, administered by the
Royal Society of New Zealand, for supporting this work
€
€
structures, University of Gottingen, Gottingen, Germany, 1997.
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