Reversible methyl group migration between osmium and tin in reactions of osmium trimethylstannyl complexes

Article abstract of DOI:10.1039/a902938i

Treatment of the coordinatively unsaturated osmium trimethylstannyl complex, Os(SnMe₃)Cl(CO)(PPh₃)₂ 1, with either pyridine (py) or sodium acetate results in methyl migration from tin to osmium, giving the structurally cha

Full text of DOI:10.1039/a902938i

Reversible methyl group migration between osmium and tin in reactions of
osmium trimethylstannyl complexes
Clifton E. F. Rickard, Warren R. Roper,* Timothy J. Woodman and L. James Wright*
Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
E-mail: w.roper@auckland.ac.nz
Received (in Cambridge, UK) 13th April 1999, Accepted 10th May 1999
L
L
Treatment of the coordinatively unsaturated osmium trime-
thylstannyl complex, Os(SnMe3)Cl(CO)(PPh3)2 1, with ei-
ther pyridine (py) or sodium acetate results in methyl
migration from tin to osmium, giving the structurally
Cl
Cl
OC
OC
CO
Os
Os
OC
SnMe3
SnMe3
L
1
L
characterised
complexes,
Os(Me)(SnClMe2)(py)-
pyridine
NaOAc
CO
(CO)(PPh3)2 2 or Os(Me)(SnMe2OC[Me]O)(CO)(PPh3)2 3,
respectively: the methyl migration is reversible and treat-
ment of Os(Me)(SnClMe2)(py)(CO)(PPh3)2 with CO gives
the trimethylstannyl complex, Os(SnMe3)Cl(CO)2(PPh3)2.
Me
C
L
L
N
O
Me
OC
Me
OC
NaOAc
O
Os
Os
SnMe2
SnMe2Cl
L
3
L
2
(L = PPh3)
Scheme 1
a-Migration, as shown in eqn. (1), is an established feature of
organometallic chemistry.1 In the closely related metal silyl
complex chemistry many transformations have been observed
which imply the intermediacy of metal silylene complexes
generated by 1,2-migration of an R group as in eqn. (2).2 In one
instance, when R = H, reversible 1,2-migration has been
reported for a platinum silyl complex.3 Since there is a
substantial number of well characterised stannylene complexes4
it can be envisaged that the type of interconversion represented
in eqn. (3) might play a part in understanding the reactions
by a crystal structure determination.‡ The structure of 2 is
shown in Fig. 1, along with selected bond lengths and angles.
The osmium–tin bond distance of 2.6741(4) Å does not differ
substantially from the corresponding distances found in other
osmium stannyl complexes. The osmium–bound methyl group
is found to lie trans to the tin atom, with the angle C–Os–Sn at
175.30(12)°. The osmium–methyl bond length of 2.249(5) Å is
similar to that observed in both Os(Me)(H)(CO)2(PPri3)2
[2.198(17) Å]8 and Os(Me)(I)(CO)2(PMe3)2 [2.174(15) Å].9
The geometry around the tin centre is quite symmetrical with
the angles Os–Sn–C(3), Os–Sn–C(4) and Os–Sn–Cl(1), all
close to 120°.
Remarkably, when compound 2 is treated with CO, pyridine
is displaced but the compound formed is not ‘Os(Me)(Sn-
Me2Cl)(CO)2(PPh3)2’. Instead, the trimethylstannyl complex,
Os(SnMe3)Cl(CO)2(PPh3)2, is obtained in 80% isolated yield,
where the methyl group has migrated back to the tin atom and
chloride has returned to osmium. It may be significant for this
CR2
LnM CHR2
LnM SiR3
LnM SnR3
LnM
LnM
LnM
(1)
(2)
(3)
H
SiR2
R
SnR2
R
undergone by metal stannyl and metal stannylene complexes.
Indeed, free, stable stannylenes have been inserted into metal–
halogen bonds.4 A further observation relevant to this idea is
that Ru[Sn(C6H4Me-p)3]Cl(CO)(PPh3)2 readily decomposes in
solution to Ru(C6H4Me-p)Cl(CO)PPh3)2.5 We describe herein
new reactions undergone by the osmium trimethylstannyl
complex, Os(SnMe3)Cl(CO)(PPh3)2 1, in which (i) a methyl
group migrates to osmium and this is accompanied by either a
chloride transfer to tin forming a chlorodimethylstannyl ligand,
or by formation of a bridging acetatodimethylstannyl ligand, (ii)
an example of reverse migration of a methyl group from
osmium to tin to reform the trimethylstannyl ligand, and (iii) the
crystal structures of the two products of methyl migration to
osmium, Os(Me)(SnClMe2)(py)(CO)(PPh3)2 2 (py = pyridine)
and Os(Me)(SnMe2OC[Me]O)(CO)(PPh3)2 3.
Os(SnMe3)Cl(CO)(PPh3)2 1, when treated with CO,
CNC6H4Me-p, or sodium dimethyldithiocarbamate, gives the
expected six coordinate trimethylstannyl complexes, Os(Sn-
Me3)Cl(CO)2(PPh3)2,
Os(SnMe3)Cl(CO)(CNC6H4Me-p)-
(PPh3)2, or Os(SnMe3)(h -S2CNMe2)(CO)(PPh3)2.6,7 We now
report that reaction of 1 with pyridine (Scheme 1) leads not to
the expected six-coordinate complex, ‘Os(SnMe3)Cl(py)-
(CO)(PPh3)2’, but rather to the colourless, methyl-migrated
product, Os(Me)(SnClMe2)(py)(CO)(PPh3)2 2 in 64% isolated
yield. That methyl group migration has occurred in the
2
1
formation of 2 is revealed by the H NMR spectrum which
Fig. 1 Crystal structure of 2. Selected bond lengths (Å) and angles (°): Os–
Sn 2.6741(4), Os–C(1) 2.249(5), Os–N(1) 2.251(4), Sn–Cl(1) 2.422(2), Os–
Sn–C(3) 123.47(11), Os–Sn–C(4) 120.9(2), Os–Sn–Cl(1) 119.17(6), C(3)–
Sn–C(4) 99.5(3), C(1)–Os–Sn 175.30(12).
shows the osmium-bound methyl group as a triplet at d 0.15
(3JHP 6.62 Hz) (syntheses and other data for 2 and 3 are given
in footnote †). This structural assignment was fully confirmed
Chem. Commun., 1999, 1101–1102
1101

(1.00 g, 5.23 mmol) in a mixture of benzene (18 mL) and toluene (18 mL)
and heated to reflux under nitrogen. The mixture was then photolysed with
a 1000 W tungsten/halogen lamp held 10 cm from the flask, the heat of the
lamp being sufficient to maintain reflux. After 7 min the photolysis was
stopped. The resulting red solution of Os(SnMe3)Cl(CO)(PPh3)2 1 was
cooled to 0 °C in an ice bath and pyridine (2 mL) was added. The red colour
changed rapidly to pale yellow. The reaction was maintained at room
temperature for 30 min and then the solvent was removed in vacuo.
Recrystallisation from dichloromethane–ethanol gave 2 as a white micro-
crystalline solid in 63.8% yield. nmax(Nujol mull)/cm21: 1878 (CO);
dH(CDCl3, 400.133 MHz, 300 K) 0.15 [t, 3H, OsCH3, 3J(PH) 6.62 Hz], 0.24
[s, 6H, SnCH3, 2J(SnH) 21.0 Hz), 6.95–7.60 (m, 35H, PPh3 and pyridine);
2
dSn(CDCl3, 149.144 MHz, 300 K) 186.63 [t, J(SnP) 110.4 Hz]. Calc. for
C
45H44NOClP2OsSn: C, 52.93; H, 4.34; N, 1.37. Found: C, 53.52; H, 4.32;
N, 1.26%.
Synthesis of Os(Me)(SnMe2OC[Me]O)(CO)(PPh3)2 3: to the red solution
of Os(SnMe3)Cl(CO)(PPh3)2 1 produced as described above but cooled
only to 40 °C, was added NaO2CMe (0.080 g, 0.975 mmol) dissolved in a
mixture of ethanol (10 mL) and water (5 mL). The colour of the solution
changed from deep red to pale yellow over 10 s. The reaction mixture was
then stirred at room temp. for 30 min. Solvent removal in vacuo provided a
pale yellow solid which was recrystallised from dichloromethane–ethanol
to give colourless microcrystals of 3 in 76.4% yield, mp 167–171 °C.
nmax(Nujol mull)/cm21: 1881 (CO), 1535 (O2CMe); dH(CDCl3, 400.133
MHz, 300 K) 20.19 [s, 6H, Sn·CH3, 2J(SnH) 21.4 Hz], 0.25 [t, 3H, OsCH3,
3J(PH) 7.12 Hz], 0.71 (s, 3H, O2CCH3), 7.25–7.70 (m, 30H, PPh3);
dSn(CDCl3, 149.144 MHz, 300) 392.94 [t, 2J(SnP) 119.4 Hz]. Calc. for
C42H42O3P2SnOs: C, 52.24; H, 4.38%. Found: C, 53.53; H, 4.38%.
‡ Crystal data: 2·CH2Cl2: crystals were grown from dichloromethane–
ethanol. C45H44ClNOP2OsSn·CH2Cl2, M = 1106.02, triclinic, space group
P1, a = 9.6249(1), b = 12.5510(2), c = 19.6568(3) Å, a = 96.708(1), b
Fig. 2 Crystal structure of 3. Selected bond lengths (Å) and angles (°): Os–
Sn 2.6766(4), Os–C(2) 2.183(5), Os–O(2) 2.183(4), Sn–O(3) 2.143(4), Os–
Sn–C(5) 131.22(19), Os–Sn–C(6) 129.70(18), C(5)–Sn–C(6) 98.2(3),
C(2)–Os–Sn 158.77(15).
transformation that solutions of 2 are red suggesting that partial
pyridine dissociation occurs to give a coordinatively un-
saturated species in solution.
= 97.968(1), g = 107.02(1)°, U = 2217.36(5) Å3, F(000) = 1088, Dc
=
1.657 g cm23, Z = 2, m(Mo-Ka, l = 0.71073 Å) = 3.714 mm21. Intensity
data were collected to a q limit of 27.45° on a Siemens ‘SMART’
diffractometer10 at 203(2) K and corrected for absorption.11 The structure
was solved using Patterson methods12 and refined by full-matrix least
squares analysis on F2 employing SHELXL97.13 All non-hydrogen atoms
were allowed to assume anisotropic motion, except C(3) which was refined
isotropically. Hydrogens were placed in calculated positions and refined
using a riding model. Refinement converged to 0.0384 (Rw = 0.0944) for
9304 reflections for which I > 2s(I).
Treatment of 1 with sodium acetate also gives a methyl-
migrated product, Os(Me)(SnMe2OC[Me]O)(CO)(PPh3)2
3
(Scheme 1). The same compound is accessible from a reaction
1
between 2 and sodium acetate. The H NMR spectrum of 3
shows the osmium-bound methyl group as a triplet at d 0.25
(3JHP 7.12 Hz). The structure was confirmed by a crystal
structure determination.‡ The molecular geometry of 3 is shown
in Fig. 2, along with selected bond lengths and angles. The
acetate bridges across the osmium–tin bond forming a five-
membered chelate ring. The osmium–tin bond distance of
2.6766(4) Å does not differ substantially from the correspond-
ing distances found in other osmium stannyl complexes. The
osmium–methyl bond length is 2.183(5) Å, and the osmium-
bound methyl group is found to lie trans to the tin atom, with the
angle C–Os–Sn at 158.77(15)°. This considerable deviation
from linearity is no doubt a consequence of the small O–Os–Sn
angle required by the bridging acetate ligand. The osmium
atom, the osmium-bound methyl, the carbonyl, the tin atom and
the acetate ligand are all coplanar. The geometry around the tin
centre is far from tetrahedral with C(5), C(6), Sn, and Os almost
coplanar. The sum of the angles made by the two methyl groups
and the osmium atom about tin is 359.1°, with the tin atom lying
only 0.127(3) Å from the plane through C(5), C(6) and Os. The
acetate oxygen, O(3), is bound to tin at a distance of 2.143(4) Å
and the O(3)–Sn bond is perpendicular to the Os, Sn, C(5), C(6)
plane. These structural parameters are compatible with some
base-stabilised stannylene character in the bonding of the tin
ligand. The tin resonance found in the 119Sn NMR spectrum of
3 is a triplet signal at d 392.94 (2JSnP 119.4 Hz).
3·CH2Cl2: crystals were grown from dichloromethane–ethanol.
C42H42O3OsP2Sn·CH2Cl2, M = 1050.51, triclinic, space group P1, a =
9.8487(1), b = 11.9753(2), c = 18.5656(3) Å, a = 95.559(1), b =
101.214(1), g = 103.598(1)°, U = 2064.36(5) Å3, F(000) = 1032, Dc
=
1.690 g cm23, Z = 2, m(Mo-Ka, l = 0.71073 Å) = 3.924 mm21. Intensity
data were collected to a q limit of 27.40° on a Siemens ‘SMART’
diffractometer10 at 203(2) K and corrected for absorption.11 The structure
was solved by direct methods12 and refined by full-matrix least-squares
analysis on F2 employing SHELXL97.13 All non-hydrogen atoms were
allowed to assume anisotropic motion. Hydrogens were placed in calculated
positions and refined using a riding model. Refinement converged to 0.0401
(Rw = 0.0721) for 7401 reflections for which I > 2s(I).
CCDC 182/1258. See http://www.rsc.org/suppdata/cc/1999/1101/ for
crystallographic files in .cif format.
1 R. H. Crabtree, The Organometallic Chemistry of the Transition Metals,
Wiley, New York, 2nd edn., 1994, p. 176.
2 K. H. Pannell and H. K. Sharma, Chem. Rev., 1995, 95, 1351; T. D.
Tilley, Comments Inorg. Chem., 1990, 10, 37.
3 G. P. Mitchell and T. D. Tilley, J. Am. Chem. Soc., 1998, 120, 7635.
4 M. F. Lappert and R. S. Rowe, Coord. Chem. Rev., 1990, 100, 267.
5 G. R. Clark, K. R. Flower, W. R. Roper and L. J. Wright,
Organometallics, 1993, 12, 259.
6 P. D. Craig, K. R. Flower, W. R. Roper and L. J. Wright, Inorg. Chim.
Acta, 1995, 240, 385.
7 C. E. F. Rickard, W. R. Roper, T. J. Woodman and L. J. Wright, Chem.
Commun., 1999, 837.
8 M. A. Esteruelas, F. J. Lahez, J. A. Lopez, L. A. Oro, C. Schlünken, C.
Valero and H. Werner, Organometallics, 1992, 11, 2034.
9 G. Bellachioma, G. Cardaci, A. Macchioni and P. Zanazzi, Inorg.
Chem., 1993, 32, 547.
We have as yet no mechanistic information regarding these
methyl group migrations. However, from the observations
depicted in Scheme 1 and discussed herein, it is clear that
methyl migration occurs only when a coordinatively un-
saturated osmium stannyl species is accessible. It is possible
that such a species is in an equilibrium of the type shown in eqn.
(3).
10 SMART and SAINT, Siemens Analytical Instruments Inc., Madison,
WI, 1994.
T. J. W. is grateful to the Royal Society (London) for the
award of a postdoctoral fellowship.
11 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
12 SHELXTL, Siemens Analytical Instruments Inc., Madison, WI, USA,
1994.
13 G. M. Sheldrick, SHELXS-97, Program for the Solution of Crystal
Structures, Universität Göttingen, Germany, 1997.
Notes and references
† Synthesis of Os(Me)(SnClMe2)(py)(CO)(PPh3)2 2: OsHCl(CO)(PPh3)3
(1.00 g, 0.960 mmol) was added directly to a solution of trimethylvinyltin
Communication 9/02938I
1102
Chem. Commun., 1999, 1101–1102