Syntheses and reactions of coordinatively unsaturated silyl, aryl osmium(II) complexes and the crystal structures of Os[Si(OEt)3]R(CO)(PPh3)2 and Os[Si(OEt)3]R(CO)2(PPh3)2 (R=phenyl or o-tolyl)

Article abstract of DOI:10.1016/S0022-328X(00)00899-8

Reaction between OsPhCl(CO)(PPh₃)₂ and HSi(OEt)₃ gives the five-coordinate complex, Os[Si(OEt)₃]Cl(CO)(PPh₃)₂ (1), the crystal structure of which reveals a square pyramidal geometry with the triethoxysilyl ligand at the apical site and the two triphenylphosphine ligands arranged mutually trans. Addition of CO gives the six-coordinate complex, Os[Si(OEt)₃]Cl(CO)₂(PPh₃)₂ (2), but this addition is thermally reversible. The chloride ligand in 1 is replaced easily and reaction with LiR gives the stable, five-coordinate complexes, Os[Si(OEt)₃]R(CO)(PPh₃)₂ (3a, R=phenyl; 3b, R=o-tolyl). Crystal structure determinations for 3a and 3b reveal a coordination geometry almost unchanged from that of 1 with Cl replaced by phenyl and o-tolyl, respectively. Addition of CO to 3a and 3b gives the six-coordinate complexes, Os[Si(OEt)₃]R(CO)₂(PPh₃)₂ (4a, R=phenyl) (4b, R=o-tolyl). Crystal structure determinations for 4a and 4b confirm octahedral geometry for each compound. Despite having adjacent aryl and silyl ligands neither 3a, 3b nor 4a, 4b show any tendency to undergo reductive elimination of RSi(OEt)₃. IR, ¹H-, ¹³C- and ²⁹Si-NMR data for all new complexes are presented.

Full text of DOI:10.1016/S0022-328X(00)00899-8

Journal of Organometallic Chemistry 625 (2001) 77–85
www.elsevier.nl/locate/jorganchem
Syntheses and reactions of coordinatively unsaturated silyl, aryl
osmium(II) complexes and the crystal structures of
Os[Si(OEt)3]R(CO)(PPh3)2 and Os[Si(OEt)3]R(CO)2(PPh3)2
(R=phenyl or o-tolyl)
Markus Albrecht, Clifton E.F. Rickard, Warren R. Roper *, Alex Williamson,
Scott D. Woodgate, L. James Wright
Department of Chemistry, The Uni6ersity of Auckland, Pri6ate Bag 92019, Auckland, New Zealand
Received 25 September 2000; accepted 7 November 2000
Abstract
Reaction between OsPhCl(CO)(PPh3)2 and HSi(OEt)3 gives the five-coordinate complex, Os[Si(OEt)3]Cl(CO)(PPh3)2 (1), the
crystal structure of which reveals a square pyramidal geometry with the triethoxysilyl ligand at the apical site and the two
triphenylphosphine ligands arranged mutually trans. Addition of CO gives the six-coordinate complex, Os[Si(OEt)3]-
Cl(CO)2(PPh3)2 (2), but this addition is thermally reversible. The chloride ligand in 1 is replaced easily and reaction with LiR gives
the stable, five-coordinate complexes, Os[Si(OEt)3]R(CO)(PPh3)2 (3a, R=phenyl; 3b, R=o-tolyl). Crystal structure determina-
tions for 3a and 3b reveal a coordination geometry almost unchanged from that of 1 with Cl replaced by phenyl and o-tolyl,
respectively. Addition of CO to 3a and 3b gives the six-coordinate complexes, Os[Si(OEt)3]R(CO)2(PPh3)2 (4a, R=phenyl) (4b,
R=o-tolyl). Crystal structure determinations for 4a and 4b confirm octahedral geometry for each compound. Despite having
adjacent aryl and silyl ligands neither 3a, 3b nor 4a, 4b show any tendency to undergo reductive elimination of RSi(OEt)3. IR,
1H-, 13C- and 29Si-NMR data for all new complexes are presented. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Silyl complexes; Aryl complexes; Osmium; X-ray crystal structures
complexes of osmium [6], we have recently demon-
strated that when an aryl ligand is incorporated into the
1. Introduction
complex, and is adjacent to the boryl ligand, as in
Os(Bcat)R(CO)(PPh3)2 and cis-Os(Bcat)R(CO)2(PPh3)2,
a very facile reductive elimination reaction occurs pro-
C–Si bond formation, from reductive elimination of
adjacent alkyl and silyl ligands in an alkyl, silyl–metal
species, is widely postulated as the product-forming
ducing the borane R–BR2 [7]. To examine whether or
step in metal-catalyzed hydrosilation [1]. There have
not, in a comparable coordination environment but
been studies of this process, both theoretical [2] and
with a silyl ligand replacing the boryl ligand, a similarly
experimental, using isolable alkyl, silyl–platinum [3]
facile reductive elimination of the silane R–SiR3 would
and alkyl, silyl–palladium [4] complexes. Fewer studies
occur, we needed to prepare suitable complexes incor-
have been made with octahedral metal complexes, but
porating both silyl and aryl ligands. We have previously
an important result was the demonstration that C–H
described numerous five-coordinate silyl complexes of
and C–Si reductive elimination could be competitive
osmium(II) from reaction between OsPhCl(CO)(PPh3)2
for an iridium(III) complex containing hydride, alkyl,
and the appropriate silane [8]. For this work we chose
and silyl ligands [5]. In our studies of boryl (BR2)
the triethoxysilyl ligand, introduced by reaction with
HSi(OEt)3, because it is a tightly bound ligand and
therefore offered a good chance for successful isolation
of the sought after aryl, silyl–osmium complexes. In
* Corresponding author. Tel.: +64-9-3737999, ext. 8320; fax: +
64-9-3737422.
E-mail address: w.roper@auckland.ac.nz (W.R. Roper).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00899-8

78
M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
this paper we describe (i) the synthesis of five- and
six-coordinate triethoxysilyl complexes of osmium(II)
with a crystal structure of the five-coordinate complex,
(ii) the introduction of aryl groups (phenyl and o-tolyl)
into these complexes through reaction with lithium
aryls, (iii) structural studies of both the five- and six-co-
ordinate mixed silyl, aryl complexes, and (iv) prelimi-
nary observations of the reactivity of these compounds
towards reductive elimination reactions.
[Si(OEt)3]Cl(CO)(PPh3)2 (1) (see Scheme 1) as a yellow
crystalline solid. The IR spectrum of 1 (see Table 1)
shows a strong absorption at 1914 cm−1 (w(CO)) and
another at 1099 cm−1 characteristic of the triethoxysi-
1
lyl ligand. The H-NMR spectrum (see Table 2) of 1
reveals a triplet at 0.93 ppm (3JHH=7.0 Hz) which is
assigned to the methyl protons of the three ethyl
groups. A quartet at 3.33 ppm (3JHH=7.0 Hz) is
assigned to the corresponding methylene groups. The
13C-NMR spectrum (see Table 3) includes resonances
for the ethyl groups at 17.7 and 57.9 ppm, as well as a
triplet for the carbonyl carbon resonance at 182.1 ppm
(2JCP=9 Hz). The 29Si-NMR spectrum (see Table 4)
shows a triplet at −61.1 ppm (2JCP=11 Hz), with
coupling to two magnetically equivalent phosphorus
nuclei. The 31P{1H} spectrum (see Table 5) shows a
broad singlet at 23.6 ppm. All of the above spectro-
scopic data is compatible with the geometry depicted
for 1 in Scheme 1, and to confirm this and to provide a
point of reference for the structures to be discussed
later in this paper, a crystal structure determination of
1 was completed.
2. Results and discussion
2.1. Preparation and crystal structure of
Os[Si(OEt)3]Cl(CO)(PPh3)2 (1)
The reaction between OsPhCl(CO)(PPh3)2 and
HSi(OEt)3 proceeds smoothly to produce Os-
The molecular geometry of 1 is illustrated in Fig. 1,
while selected interatomic distances and bond angles
are tabulated in Table 7. The structure has four inde-
pendent molecules in the asymmetric unit. Like other
five-coordinate silyl complexes of osmium(II) which we
have studied [8] this compound has a square pyramidal
geometry with the silyl group at the apical position.
,
The Os–Si distance (2.319(2) A, average of the four
independent molecules) is identical to the distance
found for Os[Si(OH)3]Cl(CO)(PPh3)2 [8b] and very
close to the value found for the silatranyl complex
,
Os(silatranyl)Cl(CO)(PPh3)2 [8f] (2.326(2) A). Other
structural features for 1 are unremarkable.
2.2. Preparation of the six-coordinate triethoxysilyl
complex, Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2)
Scheme 1. Syntheses of aryl, triethoxysilyl complexes of osmium(II).
A solution of the unsaturated five-coordinate com-
plex 1 decolourised rapidly when treated with carbon
monoxide (see Scheme 1). The IR spectrum of the
resulting colourless complex, Os[Si(OEt)3]Cl(CO)2-
(PPh3)2 (2), shows w(CO) bands at 2013 and 1947
Table 1
IR data for osmium silyl complexes
1
cm−1. The H- and 13C-NMR spectra of 2 are very
Complex
w(CO) (cm−1) Other bands
(cm−1
similar to those of 1 but the 29Si-NMR spectrum (see
Table 4) reveals a triplet at −19.5 ppm (2JSiP=18 Hz),
considerably shifted to higher frequency and with a
larger coupling constant, relative to compound 1. The
values are, however, very close to those recorded for
Os[Si(OH)3]Cl(CO)2(PPh3)2 (−10.6 ppm, t, 2JSiP=18
Hz) [9]. Surprisingly, and in marked contrast to the
aryl, silyl derivatives described below, the CO addition
is readily reversible both in solution and in the solid
state. Solutions of 2 at room temperature over several
hours become yellow with the formation of 1.
)
Os[Si(OEt)3]Cl(CO)(PPh3)2 (1)
Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2)
1914
2013, 1947
1099, 1070, 941
1040, 936
Os[Si(OEt)3](Ph)(CO)(PPh3)2 (3a) 1914
1108, 1094, 1073,
937
Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2 1916
(3b)
1116, 1103, 1093,
1073, 938
Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a) 2015, 1950
1116, 1101, 1090,
1070, 929
Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2 2005, 1945
(4b)
1115, 1101, 1088,
1070, 938

M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
79
Table 2
1H-NMR data for osmium silyl complexes
Complex
1H, l (ppm)
Os[Si(OEt)3]Cl(CO)(PPh3)2 (1)
Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2)
Os[Si(OEt)3](Ph)(CO)(PPh3)2 (3a)
0.93 (t, J=7.0 Hz, 9H, OCH2Me), 3.33 (q, J=7.0 Hz, 6H, OCH2Me), 7.36–7.96 (m, 30H, PPh3).
0.91 (t, J=7.0 Hz, 9H, OCH2Me), 3.46 (q, J=7.0 Hz, 6H, OCH2Me), 7.33–7.71 (m, 30H, PPh3).
0.91 (t, J=6.8 Hz, 9H, OCH2Me), 3.53 (q, J=6.8 Hz, 6H, OCH2Me), 6.56 (br s, 3H, Ph),
7.18–7.31 (m, 32H, 2H Ph, 30H PPh3).
Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2 (3b)
Isomer 1: 0.34 (s, 3H, C6H4Me), 0.88 (t, J=6.9 Hz, 9H, OCH2Me), 3.36 (q, J=6.9 Hz, 6H,
OCH2Me), 6.03 (d, J=7.1 Hz, 1H, C6H4Me), 6.61 (t apparent, J=7.1 Hz, 1H, C6H4Me), 6.67
(t apparent, J=7.1 Hz, 1H, C6H4Me). Isomer 2: 0.95 (t, J=6.8 Hz, 9H, OCH2Me), 1.56
(s, 3H, C6H4Me), 3.59 (q, J=6.8 Hz, 6H, OCH2Me), 4.93 (d, J=7.2 Hz, 1H, C6H4Me), 5.98
(t apparent, J=7.2 Hz, 1H, C6H4Me), 6.45 (t apparent, J=7.2 Hz, 1H, C6H4Me). Overlapping
resonances of both isomers: 7.18–7.35 (m, PPh3). Fourth phenyl proton obscured.
0.89 (t, J=6.8 Hz, 9H, OCH2CH3), 3.36 (q, J=6.8 Hz, 6H, OCH2CH3), 6.27 (t apparent, J=7.2
Hz, 2H, Ph), 6.60 (t apparent, J=7.2 Hz, 1H, Ph), 7.16–7.41 (m, 32H, 2H Ph, 30H PPh3).
Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a)
Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2 (4b) 0.90 (t, J=7.0 Hz, 9H, OCH2Me), 1.53 (s, 3H, C6H4Me), 3.33 (q, J=7.0 Hz, 6H, OCH2Me),
6.00 (t apparent, J=7.1 Hz, 1H, C6H4Me), 6.46 (d, J=7.1 Hz, 1H, C6H4Me), 6.57 (t apparent,
J=7.1 Hz, 1H, C6H4Me), 7.14 (m, 12H, PPh3), 7.21 (m, 6H, PPh3), 7.40 (m, 12H, PPh3), 7.82
(d, J=7.1 Hz, 1H, C6H4Me).
Table 3
13C-NMR data for osmium silyl complexes
Complex
13C, l (ppm)
Os[Si(OEt)3]Cl(CO)(PPh3)2 (1)
Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2)
17.7 (OCH2Me), 57.9 (OCH2Me), 127.8 (t% [11], 2,4JCP=9 Hz, o-PPh3), 129.8 (s, p-PPh3), 132.5
(t%, 1,3JCP=50 Hz, i-PPh3), 134.8 (t%, 3,5JCP=11 Hz, m-PPh3), 182.1 (t, 2JCP=9 Hz, CO).
17.9 (OCH2Me), 58.1 (OCH2Me), 127.5 (t%, 2,4JCP=9 Hz, o-PPh3), 129.7 (s, p-PPh3), 134.2 (t%,
3,5JCP=11 Hz, m-PPh3), 134.7 (t%, 1,3JCP=52 Hz, i-PPh3), 178.3 (t, 2JCP=9 Hz, CO), 178.7 (t,
2JCP=8 Hz, CO).
Os[Si(OEt)3](Ph)(CO)(PPh3)2 (3a)
18.0 (OCH2Me), 58.4 (OCH2Me), 121.2 (br s, Ph), 127.6 (t%, 2,4JCP=10 Hz, o-PPh3), 129.4 (s,
p-PPh3), 133.5 (t%, 1,3JCP=48 Hz, i-PPh3), 134.7 (t%, 3,5JCP=11 Hz, m-PPh3), 178.3 (t, 2JCP=12
Hz, CO), 193.8 (t, 2JCP=8 Hz, i-Ph). 2 signals for OsPh not detected.
Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2 (3b)
Isomer 1: 17.9 (OCH2Me), 23.3 (C6H4Me), 58.5 (OCH2Me), 121.4 (C6H4Me), 125.4 (C6H4Me),
127.3 (t%, 2,4JCP=9 Hz, o-PPh3), 128.3 (C6H4Me), 129.1 (s, p-PPh3), 134.9 (t%, 3,5JCP=11 Hz,
m-PPh3), 141.8 (C6H4Me), 144.0 (C6H4Me), 178.6 (t, 2JCP=12 Hz, CO), 194.4 (t, 2JCP=9 Hz,
i-C6H4Me). ipso-PPh3 not detected. Isomer 2: 17.9 (OCH2Me), 26.5 (C6H4Me), 58.8 (OCH2Me),
119.8 (C6H4Me), 121.9 (C6H4Me), 127.3 (t%, 2,4JCP=9 Hz, o-PPh3), 129.3 (s, p-PPh3), 130.4
(C6H4Me), 131.4 (C6H4Me), 134.9 (t%, 3,5JCP=11 Hz, m-PPh3), 149.2 (C6H4Me), 179.7 (t,
2JCP=14 Hz, CO), 193.7 (t, 2JCP=8 Hz, i-C6H4Me). Ipso-PPh3 not detected.
18.0 (s, OCH2CH3), 58.4 (s, OCH2CH3), 121.0 (s, Ph), 125.9 (s, Ph), 127.0 (t%, 2,4JCP=10 Hz,
o-PPh3), 129.1 (s, p-PPh3), 134.6 (t%, 3,5JCP=10 Hz, m-PPh3), 134.8 (t%, 1,3JCP=52 Hz, i-PPh3),
140.3 (t, 2JCP=12 Hz, i-Ph), 148.4 (s, Ph), 182.7 (t, 2JCP=8 Hz, CO), 185.4 (t, 2JCP=7 Hz,
CO).
Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a)
Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2 (4b)
17.9 (OCH2Me), 31.8 (C6H4Me), 58.5 (OCH2Me), 122.1 (C6H4Me), 123.7 (C6H4Me), 126.9 (t%,
2,4JCP=9 Hz, o-PPh3), 127.5 (C6H4Me), 129.0 (s, p-PPh3), 134.6 (t%, 3,5JCP=10 Hz, m-PPh3),
135.1 (t%, 1,3JCP=52 Hz, i-PPh3), 146.7 (t, 2JCP=12 Hz, i-C6H4Me), 149.0 (C6H4Me), 152.9
(C6H4Me), 183.7 (t, 2JCP=8 Hz, CO), 183.7 (t, 2JCP=9 Hz, CO).
Table 4
29Si-NMR data for osmium silyl complexes
Likewise, when solid 2 is heated at 125°C under vac-
uum CO is slowly lost and 1 is reformed.
Complex
29Si, l (ppm)
2.3. Preparation and crystal structures of
Os[Si(OEt)3]R(CO)(PPh3)2 (3a, R=Ph; 3b,
R=o-tolyl)
Treatment of 1 with RLi (R=Ph, o-tolyl) results in
displacement of the labile chloride ligand affording the
five-coordinate silyl, aryl complexes, Os[Si(OEt)3]-
R(CO)(PPh3)2 (3a, R=Ph; 3b, R=o-tolyl) (see Scheme
Os[Si(OEt)3]Cl(CO)(PPh3)2 (1)
Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2)
Os[Si(OEt)3](Ph)(CO)(PPh3)2 (3a)
−61.1 (t, OsSi, 2JSiP=11)
−19.5 (t, OsSi, 2JSiP=18)
−68.1 (t, OsSi, 2JSiP=14)
Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2 (3b) −66.7 (t, OsSi, 2JSiP=14),
−73.5 (t, OsSi, 2JSiP=15)
Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a)
−22.5 (t, OsSi, 2JSiP=24)
Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2 (4b) −26.5 (t, OsSi, 2JSiP=23)

80
M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
Table 5
31P-NMR data for osmium silyl complexes
Complex
31P{1H}, l (ppm)
Os[Si(OEt)3]Cl(CO)(PPh3)2 (1)
Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2)
Os[Si(OEt)3](Ph)(CO)(PPh3)2 (3a)
Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2 (3b)
23.6 (bs, OsP)
−12.4 (bs, OsP)
23.9 (bs, OsP)
22.7 (bs, OsP), 25.2
(bs, OsP)
Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a)
−3.2 (s, OsP), with
satellites (d, 2JPSi=24 Hz)
Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2 (4b) −5.3 (s, OsP), with
satellites (d, 2JPSi=23 Hz)
Fig. 1. Molecular geometry of Os[Si(OEt)3]Cl(CO)(PPh3)2 (1).
1) in good yield. The analogous transformations also
occur readily for the corresponding boryl complex,
Os(Bcat)Cl(CO)(PPh3)2 [7]. 3a and 3b are bright orange
crystalline solids with good stability both in the solid
state and in solution. In the IR spectra of both of these
compounds the w(CO) values (see Table 1) are almost
unchanged from the value found for 1. The NMR
spectroscopic data (see Tables 2–5) for 3a are as ex-
pected, however all NMR data for 3b is indicative of
the presence of two isomers. This same phenomenon
Table 6
Data collection and processing parameters
1
3a
3b
4a
4b
Formula
Molecular weight
T (K)
C43H45ClOsP2Si
941.47
200
C49H50O4OsP2Si
983.12
150
C50H52O4OsP2Si
997.15
200
C50H50O5OsP2Si
1011.13
150
C51H52O5OsP2Si
1025.16
200
,
Wavelength (A)
0.71073
Triclinic
0.71073
Monoclinic
P21/c
10.7412(2)
32.0669(6)
13.2119(3)
0.71073
Monoclinic
P21/c
19.6526(2)
12.5130(1)
20.7190(1)
0.71073
Orthorhombic
P212121
12.3458(1)
15.7999(2)
22.8179(3)
0.71073
Monoclinic
P21/n
13.9740(1)
22.4592(1)
14.3258(1)
Crystal system
Space group
(
P1
,
a (A)
10.3380(2)
22.1043(4)
37.0723(8)
78.025(1)
82.736(1)
88.803(1)
8220.6(3)
8
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
106.918(1)
117.600(1)
94.240(1)
3
,
V (A )
4353.72(15)
4
1.500
1984
3.07
4515.16(5)
4
1.467
2016
2.96
4450.19(9)
4
1.509
2040
3.01
4483.78
4
1.519
2072
Z
Dcalc (g cm−3
F(000)
)
1.521
3776
3.32
v (mm−1
)
2.990
Crystal size mm
2q (min–max) (°)
h, k, l range
0.42×0.20×0.12
1.0–28.2
−135h513,
0.16×0.14×0.12
1.7–26.3
−135h512,
047×0.40×0.35
1.2–27.4
−255h522,
0.60×0.12×0.08
1.6–27.1
−155h515,
0.36×0.16×0.14
1.7–25.0
−165h516, 05k526,
05l517
−275k527, 05l548 05k540, 05l516 05k516, 05l525 05k519, 05l528
Reflections collected 80912
24945
8784 Rint=0.0283
41889
10023
26961
9452 Rint=0.0264
50098
7881 Rint=0.0328
Independent
reflections
36062 Rint=0.0418
Rint= =0.0228
A (min–max)
0.336, 0.692
0.639, 0.709
Sw(F2o−F2c)2
1.103
0.336, 0.423
Sw(F2o−F2c)2
1.122
0.265, 0.795
Sw(F2o−F2c)2
1.045
0.412, 0.679
Sw(F2o−F2c)2
1.149
Function minimised Sw(F2o−Fc2)2
Goodness-of-fit on 1.089
F2
R (observed data) a R1=0.0544,
wR2=0.1157
R (all data)
R1=0.0272,
wR2=0.0569
R1=0.0337,
wR2=0.0594
+1.15, −0.71
R1=0.0283,
wR2=0.0607
R1=0.0342,
wR2=0.0641
+1.36, −0.65
R1=0.0243,
wR2=0.0519
R1=0.0299,
wR2=0.0545
+1.05, −0.89
R1=0.0378,
wR2=0.0854
R1=0.0535,
wR2=0.0958
+2.15, 1.10
R1=0.0788,
wR2=0.1263
+2.96, −1.75
Diff. map
(min–max)
−3
,
(e A
)
a R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ, wR2={S[w(F2o−Fc2)2]/S[w(Fo2)2]}1/2
.

M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
81
Table 7
Selected bond lengths (A) and bond angles (°) for 1
Table 8
,
,
Selected bond lengths (A) and bond angles (°) for 3a
Molecule 1 Molecule 2 Molecule 3 Molecule 4
Bond lengths
Os–C(1)
Os–C(2)
Os–Si
Os–P(2)
Os–P(1)
Si–O(3)
Si–O(4)
Si–O(2)
1.899(4)
2.147(3)
2.3218(9)
2.3577(8)
2.3796(8)
1.643(2)
1.650(3)
1.666(3)
Bond lengths
Os–C(1)
Os–Si
Os–P(1)
Os–P(2)
Os–Cl
Si–O(2)
Si–O(3)
Si–O(4)
1.924(7)
2.3311(18) 2.317(2)
1.939(7)
1.922(7)
2.3166(18)
1.910(7)
2.312(2)
2.3787(17)
2.3630(16)
2.431(3)
1.627(6)
1.642(5)
1.685(6)
2.3778(17) 2.3823(17) 2.3835(16)
2.3666(17) 2.3850(17) 2.3889(17)
2.433(3)
1.652(5)
1.655(5)
1.651(5)
2.423(3)
1.617(7)
1.652(5)
1.657(7)
2.438(3)
1.629(6)
1.651(5)
1.657(5)
Bond angles
C(1)–Os–C(2)
C(1)–Os–Si
171.21(13)
87.35(10)
101.24(9)
91.23(10)
89.70(8)
96.10(3)
89.93(10)
87.22(8)
Bond angles
C(1)–Os–Si
94.7(3)
95.0(3)
90.1(2)
93.0(2)
159.0(3)
96.52(7)
96.36(7)
94.1(3)
89.6(2)
92.6(2)
160.2(3)
95.15(6)
95.36(6)
90.9(2)
86.7(2)
91.8(2)
163.7(2)
97.77(7)
97.15(7)
105.32(9)
86.73(7)
90.52(8)
165.03(6)
C(2)–Os–Si
C(1)–Os–P(1) 86.7(2)
C(1)–Os–P(2) 91.7(2)
C(1)–Os–Cl 163.5(3)
Si–Os–P(1)
Si–Os–P(2)
Si–Os–Cl
Cl–Os–P(1)
Cl–Os–P(2)
P(1)–Os–P(2) 164.31(6)
C(1)–Os–P(2)
C(2)–Os–P(2)
Si–Os–P(2)
C(1)–Os–P(1)
C(2)–Os–P(1)
Si–Os–P(1)
98.34(6)
97.34(6)
101.78(8)
89.91(7)
87.17(7)
105.96(10) 105.71(8)
96.90(3)
166.98(3)
85.84(7)
86.59(7)
166.44(6)
86.91(7)
87.45(7)
169.10(6)
P(2)–Os–P(1)
Table 9
,
Selected bond lengths (A) and bond angles (°) for 3b
Bond lengths
Os–C(1)
Os–C(2)
Os–Si
Os–P(1)
Os–P(2)
Si–O(3)
Si–O(2)
Si–O(4)
Si–O(3)%
1.879(3)
2.161(3)
2.3258(9)
2.3671(8)
2.3782(8)
1.616(5)
1.643(3)
1.649(3)
1.698(6)
Bond angles
C(1)–Os–C(2)
C(1)–Os–Si
169.88(14)
87.37(10)
102.76(11)
91.33(10)
88.00(9)
C(2)–Os–Si
Fig. 2. Molecular geometry of Os[Si(OEt)3](Ph)(CO)(PPh3)2 (3a).
C(1)–Os–P(1)
C(2)–Os–P(1)
Si–Os–P(1)
93.14(3)
C(1)–Os–P(2)
C(2)–Os–P(2)
Si–Os–P(2)
88.64(10)
89.85(8)
99.27(3)
P(1)–Os–P(2)
167.58(3)
restricted rotation of the o-tolyl ligand. It is worth
noting that the chemical shifts for the o-tolyl methyl
protons are quite different in the two rotamers (0.34
and 1.56 ppm) reflecting very different environments
for these methyl groups. The 13C-NMR data reveals
that in both isomers the two triphenylphosphine ligands
are mutually trans and the chemical shifts for the CO
ligands are closely similar. Both these observations
support rotational rather than stereo-isomers. Further-
Fig. 3. Molecular geometry of Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2 (3b).
was also observed for the five-coordinate o-tolyl, boryl
complex, Os(Bcat)(o-tolyl)(CO)(PPh3)2 [7]. We believe
the two isomers are rotational isomers arising from
more,
no
isomers
are
observed
for
the
six-coordinate di-carbonyl derivative, Os[Si(OEt)3]-
(o-tolyl)(CO)2(PPh3)2 (4b), where restricted rotation of

82
M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
Table 10
the o-tolyl ligand is less likely because of the increased
Os–Si, Os–P, and Os–C(o-tolyl) distances (see Tables
9 and 11 and discussion of the structures below).
The solid state geometries of 3a and 3b, obtained by
X-ray crystallography, are depicted in Figs. 2 and 3,
and selected bond lengths and bond angles are pre-
sented in Tables 8 and 9, respectively. The geometries
of both are closely similar to that of 1 with phenyl or
o-tolyl replacing the chloride ligand. It is interesting
that in these complexes, where there are two ligands,
aryl and silyl, of recognised strong |-bonding/trans
influence character, it is the silyl ligand which domi-
nates and which adopts the apical site of the square
pyramid. The phenyl and o-tolyl ligands are approxi-
mately coplanar with the plane through the Os, Si, and
C(1) atoms and the Si–Os–C(2) angles are effectively
the same (3a, 101.24(9)°; 3b, 102.76(11)°). The Si–Os–
C(1) angles are also identical and slightly less than 90°
(3a, 87.35(10)°; 3b, 87.37(10)°). The Os–Si distances are
also very similar and little changed from the value in 1
(3a, 2.3218(9)°; 3b, 2.3258(9)°). The same is true of the
Os–P and Os–C distances (see Tables 8 and 9).
,
Selected bond lengths (A) and bond angles (°) for 4a
Bond lengths
Os–C(1)
Os–C(2)
Os–C(9)
Os–P(2)
Os–P(1)
Os–Si
Si–O(3)
Si–O(4)
Si–O(5)
1.921(3)
1.934(3)
2.175(3)
2.4058(8)
2.4079(8)
2.4906(10)
1.659(3)
1.660(3)
1.676(3)
Bond angles
C(1)–Os–C(2)
C(1)–Os–C(9)
C(2)–Os–C(9)
C(1)–Os–P(2)
C(2)–Os–P(2)
C(9)–Os–P(2)
C(1)–Os–P(1)
C(2)–Os–P(1)
C(9)–Os–P(1)
P(2)–Os–P(1)
C(1)–Os–Si
91.26(14)
178.20(13)
86.97(14)
92.45(12)
91.73(10)
87.28(10)
92.30(12)
88.33(10)
87.98(10)
175.25(4)
88.76(10)
178.16(10)
93.01(9)
C(2)–Os–Si
C(9)–Os–Si
P(2)–Os–Si
90.11(3)
P(1)–Os–Si
89.83(3)
Table 11
,
Selected bond lengths (A) and bond angles (°) for 4b
Bond lengths
Os–C(1)
Os–C(2)
Os–C(9)
Os–P(1)
Os–P(2)
Os–Si
Si–O(4)
Si–O(3)
Si–O(5)
1.904(6)
1.947(6)
2.220(5)
2.4109(13)
2.4145(13)
2.4804(14)
1.649(4)
1.658(4)
1.661(4)
Fig. 4. Molecular geometry of Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a).
Bond angles
C(1)–Os–C(2)
C(1)–Os–C(9)
C(2)–Os–C(9)
C(1)–Os–P(1)
C(2)–Os–P(1)
C(9)–Os–P(1)
C(1)–Os–P(2)
C(2)–Os–P(2)
C(9)–Os–P(2)
P(1)–Os–P(2)
C(1)–Os–Si
90.4(2)
177.1(2)
92.1(2)
91.60(15)
86.85(15)
90.03(13)
89.24(15)
96.46(15)
89.00(13)
176.58(5)
86.81(16)
174.89(16)
90.88(14)
88.97(5)
87.77(4)
C(2)–Os–Si
C(9)–Os–Si
P(1)–Os–Si
P(2)–Os–Si
Fig. 5. Molecular geometry of Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2 (4b).

M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
83
2.4. Preparation and crystal structures of Os[Si(OEt)3]-
R(CO)2(PPh3)2 (4a, R=Ph; 4b, R=o-tolyl)
pyramidal geometry is still retained and if so which of
these two strong trans influence ligands, silyl or aryl,
occupies the apical site. Structural study confirms that
it is the silyl ligand. Unlike the mixed boryl, aryl
complexes of osmium(II), neither Os[Si(OEt)3]-
R(CO)(PPh3)2 nor Os[Si(OEt)3]R(CO)2(PPh3)2 undergo
ready reductive elimination of R–Si(OEt)3.
Both 3a and 3b react readily with CO to form the
corresponding colourless, six-coordinate, di-carbonyl
complexes, Os[Si(OEt)3]R(CO)2(PPh3)2 (4a, R=Ph; 4b,
R=o-tolyl) (see Scheme 1). Whereas addition of CO to
1 is reversible, neither 4a nor 4b show any tendency to
lose CO. The mutually cis arrangement of the two CO
ligands is confirmed by the appearance of two w(CO)
4. Experimental
1
bands in the IR spectra. The H- and 13C-NMR spec-
troscopic data are as expected and there is no evidence
for the existence of isomers for the o-tolyl complex, 4b.
The 29Si resonances of the five-coordinate complexes 1,
3a, and 3b, all move to higher frequency on addition of
CO to form 2, 4a, and 4b, respectively, whereas the 31P
resonances move to lower frequency.
The solid state geometries of 4a and 4b, obtained by
X-ray crystallography, are depicted in Figs. 4 and 5,
and selected bond lengths and bond angles are pre-
sented in Tables 10 and 11, respectively. Both com-
pounds have regular octahedral geometry about
osmium with mutually trans triphenylphosphine ligands
and mutually cis CO ligands. All bond lengths to
osmium increase upon changing from the five-coordi-
nate geometry of 3a and 3b to the six-coordinate ge-
ometry of 4a and 4b. The most striking increase
involves the Os–Si distances which increase by up to
4.1. General procedures and instruments
Standard laboratory procedures were followed as
have been described previously [11]. The compound
OsPhCl(CO)(PPh3)2 was prepared according to the lit-
erature method [10].
Infrared spectra (4000–400 cm−1) were recorded as
Nujol mulls between KBr plates on a Perkin–Elmer
Paragon 1000 spectrometer. NMR spectra were ob-
tained on a Bruker DRX 400 at 25°C. H-, 13C-, 31P-
1
and 29Si-NMR spectra were obtained operating at 400.1
(1H), 100.6 (13C), 162.0 (31P), and 79.5 (29Si) MHz,
1
respectively. Resonances are quoted in ppm and H-
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 (77.0 ppm), 31P-NMR spectra to 85% or-
thophosphoric acid (0.0 ppm) as an external standard,
and 29Si-NMR spectra to tetramethylsilane (0.0 ppm).
Mass spectra were recorded using the fast atom bom-
bardment technique with a Varian VG 70-SE mass
spectrometer. Elemental analyses were obtained from
the Microanalytical Laboratory, University of Otago.
,
0.17 A (3a, 2.3218(9), 4a, 2.4906(10); 3b, 2.3258(9), 4b,
2.4804(14)). Increases in the Os–P and Os–C distances
are less but still significant (see Tables 10 and 11).
4a and 4b are thermally robust as solids and in
solution. In contrast to the cis-boryl, aryl complexes,
Os(Bcat)R(CO)2(PPh3)2 [7], which readily undergo re-
ductive elimination of R–Bcat in solution with accom-
panying formation of ‘Os(CO)2(PPh3)2’ (as the
ortho-metallated isomer), complexes 4a and 4b are re-
luctant to eliminate R–Si(OEt)3 even under forcing
conditions (see Section 4). Thus, 4a and 4b do not
model the Si–C bond-forming step proposed in metal
catalysed hydrosilation.
4.2. Preparation of Os[Si(OEt)3]Cl(CO)(PPh3)2 (1)
OsCl(Ph)(CO)(PPh3)2 (200 mg, 0.234 mmol) and
HSi(OEt)3 (52 ml, 0.28 mmol) were heated under a
nitrogen atmosphere in toluene (25 ml) for 2 h. The
solvent was removed in vacuo, and the resulting yellow
residue was dissolved in dichloromethane (25 ml). This
solution was filtered through a Celite pad and ethanol
(10 ml) was added. The dichloromethane was removed
on the rotary evaporator to yield bright-yellow crystals
that were recrystallised from dichloromethane:ethanol
(25:10 ml) to give pure 1 (193 mg, 86%). m/z 905.2184;
3. Conclusions
Five-coordinate mixed silyl, aryl complexes of
osmium(II) have been prepared by treating Os-
[Si(OEt)3]Cl(CO)(PPh3)2 with lithium aryls. In previous
studies we have shown that the five-coordinate
complexes, Os(BR2)Cl(CO)(PPh3)2 [7], Os(SiR3)Cl(CO)-
(PPh3)2 [8], and OsRCl(CO)(PPh3)2 [10] adopt a square
pyramidal geometry with the boryl, silyl, and R groups,
respectively, in the apical position. In this study the
accessibility of Os(SiR3)R(CO)(PPh3)2 presents the
opportunity to examine whether or not the square
C43H45O4OsP2Si [M+ −Cl] requires 905.2147. Anal.
’
Calc. for C43H45ClO4OsP2Si: C, 54.85; H, 4.82. Found:
C, 54.15; H, 5.03%.
4.3. Preparation of Os[Si(OEt)3]Cl(CO)2(PPh3)2 (2)
Os[Si(OEt)3]Cl(CO)(PPh3)2 (200 mg, 0.212 mmol)
was dissolved in dichloromethane (20 ml), and the

84
M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
solution introduced to a Fischer–Porter bottle and
treated with carbon monoxide (4 atm.). Ethanol (10 ml)
was added to the resulting colourless solution and the
dichloromethane was removed to yield colourless crys-
tals of pure complex 2 (183 mg, 89%). m/z 935.2130;
4.7. Preparation of Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2
(4b)
A stream of CO gas was passed through a solution of
Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2 (100 mg, 0.100 mmol)
in benzene (12 ml) for 20 s, generating a pale yellow
solution. Concentration of the solution in vacuo to
about 1 ml followed by addition of hexane gave a white
precipitate which was collected on a glass frit and
washed with EtOH and hexane. This product was
recrystallised from CH2Cl2/EtOH to give pure 4b (91
mg, 89%). Anal. Calc. for C51H52O5OsP2Si: C, 59.75; H,
5.11. Found: C, 59.70; H, 5.23%.
C44H45O5OsP2Si [M+ −Cl] requires 935.2126. Anal.
’
Calc. for C44H45ClO5OsP2Si: C, 54.50; H, 4.67. Found:
C, 54.06; H, 4.94%.
4.4. Preparation of Os[Si(OEt)3](Ph)(CO)(PPh3)2 (3a)
To a yellow solution of Os[Si(OEt)3]Cl(CO)(PPh3)2
(108 mg, 0.115 mmol) in benzene (15 ml) at 5°C was
added a solution of LiPh in Et2O (0.83 M, 0.17 ml, 0.14
mmol), giving a bright orange, cloudy solution. The
mixture was allowed to warm up to room temperature
and was stirred for a further 30 min. Concentration of
the solution in vacuo to about 3 ml and addition of
hexane gave a bright orange precipitate of pure 3a
which was collected on a glass frit and washed with
EtOH and hexane (65 mg, 58%). Anal. Calc. for
C49H50O4OsP2Si: C, 59.86; H, 5.13. Found: C, 59.82; H,
5.24%.
4.8. Thermolysis of Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a)
and Os[Si(OEt)3](o-tolyl)(CO)2(PPh3)2 (4b)
Unchanged 4a was recovered in high yield from
solutions of 4a in toluene which had been heated to
75°C for 2 h. At higher temperatures in toluene some
decomposition occurred over two hours but neither
PhSi(OEt)3 nor ortho-metallated ‘Os(CO)2(PPh3)2’
could be detected amongst the products.
Heating solid samples of 4b under vacuum at 125°C
for 24 h resulted in loss of CO only to give 3b quantita-
tively. Further heating of solid samples of 3b under
vacuum at 125°C for 48 h returned 3b unchanged.
4.5. Preparation of Os[Si(OEt)3](o-tolyl)(CO)(PPh3)2
(3b)
4.9. X-ray crystal structure determinations for complexes
1, 3a, 3b, 4a and 4b
To a yellow solution of Os[Si(OEt)3]Cl(CO)(PPh3)2
(298 mg, 0.317 mmol) in benzene (25 ml) at 5°C was
added a solution of Li-o-tolyl in Et2O (0.75 M, 0.55 ml,
0.413 mmol) giving a bright orange cloudy solution.
The mixture was allowed to warm up to room tempera-
ture and was stirred for a further 30 min. Concentra-
tion of the solution in vacuo to about 3 ml and addition
of hexane gave a bright orange precipitate of pure 3b
which was collected on a glass frit and washed with
EtOH and hexane (284 mg, 90%). Anal. Calc. for
C50H52O4OsP2Si: C, 60.22; H, 5.26. Found: C, 60.05; H,
5.16%.
X-ray data collection was on a Siemens SMART
diffractometer with
a CCD area detector, using
graphite monochromated Mo–Ka radiation (u=
,
0.71073 A). Data were integrated and Lorentz and
polarisation correction applied using SAINT [12] soft-
ware. Semi-empirical absorption corrections were ap-
plied based on equivalent reflections using SADABS [13].
The structures were solved by Patterson and Fourier
methods and refined by full-matrix least squares on F2
using programs SHELXS [14] and SHELXL [15]. All non-
hydrogen atoms were refined anisotropically and hy-
drogen atoms were included in calculated positions and
refined with a riding model with thermal parameter
20% greater than Uiso of the carrier atom. 1 has four
independent molecules in the unit cell. Some of these
show disorder in the phenyl carbon atoms consistent
with rotation about the P–C bond. Crystal data and
refinement details are given in Table 6.
4.6. Preparation of Os[Si(OEt)3](Ph)(CO)2(PPh3)2 (4a)
A stream of CO gas was passed through a solution of
Os[Si(OEt)3](Ph)(CO)(PPh3)2 (120 mg, 0.122 mmol) in
benzene (5 ml) for 30 s, generating a pale yellow
solution. Concentration of the solution in vacuo to
about 1 ml followed by addition of hexane gave a white
precipitate which was collected on a glass frit and
washed with EtOH and hexane. The product was re-
crystallised from benzene/hexane to give pure 4a (102
mg, 82%). Anal. Calc. for C50H50O5OsP2Si: C, 59.39; H,
4.98. Found: C, 59.35; H, 5.13%.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic

M. Albrecht et al. / Journal of Organometallic Chemistry 625 (2001) 77–85
85
[6] (a) G.J. Irvine, M.J.G. Lesley, T.B. Marder, N.C. Norman, C.R.
Rice, E.G. Robins, W.R. Roper, G.R. Whittell, L.J. Wright,
Chem. Rev. 98 (1998) 2685. (b) G.R. Clark, G.J. Irvine, C.E.F.
Rickard, W.R. Roper, A. Williamson, L.J. Wright, Boryl com-
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Hughes, T.B. Marder, K. Wade (Eds.), Contemporary Boron
Chemistry, Royal Society of Chemistry, Cambridge, 2000, p.
379.
Data Centre, CCDC nos. 149641–149645 for com-
pounds 1, 3a, 3b, 4a, 4b, respectively. Copies of this
information may be obtained from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44-1233-336033; e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk).
[7] (a) C.E.F. Rickard, W.R. Roper, A. Williamson, L.J. Wright,
Angew. Chem. Int. Ed. Engl. 38 (1999) 1110. (b) C.E.F. Rickard,
W.R. Roper, A. Williamson, L.J. Wright, Organometallics, 19
(2000) 4344.
Acknowledgements
[8] (a) G.R. Clark, C.E.F. Rickard, W.R. Roper, D.M. Salter, L.J.
Wright, Pure Appl. Chem. 62 (1990) 1039. (b) C.E.F. Rickard,
W.R. Roper, D.M. Salter, L.J. Wright, J. Am. Chem. Soc. 114
(1992) 9682. (c) C.E.F. Rickard, W.R. Roper, D.M. Salter, L.J.
Wright, Organometallics 11 (1992) 3931. (d) K. Hu¨bler, W.R.
Roper, L.J. Wright, Organometallics 16 (1997) 2730. (e) K.
Hu¨bler, P.A. Hunt, S.M. Maddock, C.E.F. Rickard, W.R.
Roper, D.M. Salter, P. Schwerdtfeger, L.J. Wright,
Organometallics 16 (1997) 5076. (f) M.T. Attar-bashi, C.E.F.
Rickard, W.R. Roper, L.J. Wright, S.D. Woodgate,
Organometallics 17 (1998) 504.
[9] W.R. Roper, D.M. Salter, L.J. Wright, unpublished work.
[10] C.E.F. Rickard, W.R. Roper, G.E. Taylor, J.M. Waters, L.J.
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[11] S.M. Maddock, C.E.F. Rickard, W.R. Roper, L.J. Wright,
Organometallics 15 (1996) 1793.
We thank the Marsden Fund, administered by the
Royal Society of New Zealand, for supporting this
work and for granting Postdoctoral Fellowships to AW
and MA. We also thank the University of Auckland
Research Committee for partial support of this work
through grants-in-aid and through the award of a Doc-
toral Scholarship to SDW.
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