A novel metal-chain extension reaction: Synthesis of (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br, I; n = 1, 2, 3)

Article abstract of DOI:10.1139/v02-016

Complexes of formula (X)[Os(CO)₃(CN-t-Bu)]_nMn(CO)₅ (X = Cl, Br, I; n = 1, 2, 3) have been prepared by the reaction of Os(CO)₄(CN-t-Bu) with Mn(CO)₅(X) in hexane at room temperature. The characterization of the complexes included the crystal structures of compounds with X = I, n = 1, 3 and X = Cl, Br, n = 2 (2ClA and 2BrB). The trinuclear products were isolated as two isomers. The major isomer (2XA) has an isocyanide ligand attached to each osmium atom, whereas the minor isomer (2XB) has both of these ligands bound to the terminal Os atom. The structures contain Os_nMn chains with unbridged Os-Mn bonds (range of lengths are 2.870(1)-2.9245(8) A) and for compounds with n = 2 or 3 Os-Os bonds (range of lengths are 2.8812(4)-2.8928(5) A). The mechanism of formation is believed to involve replacement of a CO ligand with the 18e^- ligand Os(CO)₄(CN-t-Bu) at the metal with the coordinated halide, followed by a rearrangement in which the halide ligand migrates to the donor Os atom with concomitant migration in the reverse direction of a carbonyl ligand. The preparation of (OC)₄(t-BuNC)OsMn(CO)₄(Cl) with an Os-Mn dative bond is also reported along with the (OC)₄(t-BuNC)OsRe(CO)₄(X) analogues.

Full text of DOI:10.1139/v02-016

281
A novel metal-chain extension reaction: synthesis
of (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br, I; n =
1, 2, 3)
Faming Jiang, Hilary A. Jenkins, David F. Green, Glenn P.A. Yap, and
Roland K. Pomeroy
Abstract: Complexes of formula (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br, I; n = 1, 2, 3) have been prepared by
the reaction of Os(CO)4(CN-t-Bu) with Mn(CO)5(X) in hexane at room temperature. The characterization of the com-
plexes included the crystal structures of compounds with X = I, n = 1, 3 and X = Cl, Br, n = 2 (2ClA and 2BrB). The
trinuclear products were isolated as two isomers. The major isomer (2XA) has an isocyanide ligand attached to each
osmium atom, whereas the minor isomer (2XB) has both of these ligands bound to the terminal Os atom. The struc-
tures contain OsnMn chains with unbridged Os—Mn bonds (range of lengths are 2.870(1)–2.9245(8) Å) and for com-
pounds with n = 2 or 3 Os—Os bonds (range of lengths are 2.8812(4)–2.8928(5) Å). The mechanism of formation is
believed to involve replacement of a CO ligand with the 18e– ligand Os(CO)4(CN-t-Bu) at the metal with the coordi-
nated halide, followed by a rearrangement in which the halide ligand migrates to the donor Os atom with concomitant
migration in the reverse direction of a carbonyl ligand. The preparation of (OC)4(t-BuNC)OsMn(CO)4(Cl) with an Os–
Mn dative bond is also reported along with the (OC)4(t-BuNC)OsRe(CO)4(X) analogues.
Key words: manganese–osmium, rhenium–osmium, dinuclear, metal chain, dative metal–metal bond.
Résumé : On a préparé des complexes de formule (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br, I; n = 1, 2, 3) par
réaction du Os(CO)4(CNB-t-Bu) avec du Mn(CO)5(X), dans l’hexane, à la température ambiante. La caractérisation des
complexes a impliqué la détermination des structures cristallines des composés pour lesquels X = I avec n = 1 ou 3 et
X = Cl ou Br et n = 2 (2ClA et 2BrB). On a isolé deux formes isomères des produits trinucléaires. L’isomère princi-
pal (2XA) comprend un ligand isocyanure attaché à chaque atome d’osmium alors que, dans l’isomère minoritaire
(2XB), chacun de ces deux ligands est attaché à l’atome d’osmium terminal. Les structures comportent des chaînes
OsnMn dans lesquelles on retrouve des liaisons Os—Mn qui ne sont pas pontées (longueurs des liaisons allant de
2,870(1) à 2,9245(8) Å) et, dans les cas où n est égal à 2 ou 3, on rencontre aussi des liaisons Os—Os (longueurs des
liaisons allant de 2,8812(4) à 2,8928(5) Å). On croit que le mécanisme de formation implique premièrement le rempla-
cement, au niveau du métal coordiné à l’halogène, d’un ligand CO par le ligand à 18e– Os(CO)4(CN-t-Bu), suivi d’un
réarrangement dans lequel le ligand halogène migre vers l’atome d’osmium donneur avec une migration concomitante
d’un ligand carbonyle dans la direction inverse. On rapporte aussi la préparation du (OC)4(t-BuNC)OsMn(CO)4(Cl)
comportant une Os–Mn liaison dative ainsi que celles de ses analogues (OC)4(t-BuNC)OsRe(CO)4(X).
Mots clés : manganèse–osmium, rhénium–osmium, dinucléaire, chaîne de métaux, liaison dative métal–métal.
[Traduit par la Rédaction] Jiang et al. 291
Introduction
tional ligand such as PPh3 (1–7). Typical examples of mole-
cules of this type are (OC)5OsOs(CO)3(GeCl3)(Cl) (1),
(L)(OC)4OsM(CO)5 (M = Cr, Mo, W; L = PR3 (2), CN-t-Bu
(3)), and (R3P)(OC)4M′Ru(CO)3(SiCl3)2 (M′ = Ru, Os, but
not Fe) (4). These complexes contain an unbridged dative
bond between two transition metal atoms and are rare (8);
complexes with dative metal–metal bonds supported by
bridging ligands are, however, more common (9). There has
also been renewed interest in complexes with unbridged da-
tive bonds between a transition metal and a main-group
metal (10).
In some of our earliest studies, it was observed that iso-
merization often occurred for complexes with unbridged da-
tive metal–metal bonds that also contained a halide or
(especially) a hydride ligand coordinated to the acceptor
metal atom (11, 12). The isomerization involved migration
of the halide (or hydride) ligand to the donor atom with
Much of the past work from this laboratory has described
complexes in which an 18-electron organometallic com-
pound acts as a 2-electron donor ligand to a 16-electron
organometallic fragment in much the same way as a conven-
Received 16 October 2001. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 20 March 2002.
F. Jiang, D.F. Green, and R.K. Pomeroy.1 Department of
Chemistry, Simon Fraser University, Burnaby, BC V5A 1S6,
Canada.
H.A. Jenkins. Department of Chemistry, Saint Mary’s
University, Halifax, NS B3H 3C3, Canada.
G.P.A. Yap. Department of Chemistry, University of Ottawa,
Ottawa, ON K1N 6N5, Canada.
1Corresponding author (e-mail: pomeroy@sfu.ca).
Can. J. Chem. 80: 281–291 (2002)
DOI: 10.1139/V02-016
© 2002 NRC Canada

282
Can. J. Chem. Vol. 80, 2002
Scheme 1.
concomitant migration of a carbonyl ligand to the acceptor
atom (Scheme 1; in this and other schemes presented here
the carbonyl ligands not involved in the isomerization have
been omitted.) If the halogen ligand is considered a one-
electron donor ligand, then the isomerization process results
in the conversion of the dative metal–metal bond to a
nondative bond.
:
X
X
X
Os
Os
Os
M
M
M
C
O
C
O
C
O
X = Cl, Br, I (H)
It is well-known that the presence of a halide ligand in a
metal-carbonyl complex often labilizes the carbonyls to
ligand substitution (13, 14). The possibility, therefore, exists
for further substitution–isomerization reactions on the
binuclear compound to yield complexes with extended metal
chains. Several previous attempts to exploit this strategy to
the synthesis of polynuclear compounds were unsuccessful.
Here we report the partial realization of the method in the
synthesis of (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br,
I; n = 1, 2, 3) complexes that contain chains of up to four
metal atoms. The tetranuclear complex has been the subject
of a communication (15).
Preparation of (OC)3(t-BuNC)(I)OsMn(CO)5 (1I)
To a Carius tube was added Os(CO)4(CN-t-Bu) (39 mg,
0.10 mmol), Mn(CO)5(I) (32 mg, 0.10 mmol), and hexanes
(10 mL); the solution was degassed as before and the reac-
tion tube covered with aluminum foil. The mixture was
stirred under vacuum at room temperature. An IR spectrum
after 2 days indicated the starting compounds were still pres-
ent. The vessel was resealed and the solution degassed as be-
fore. After a further 5 days of stirring an IR spectrum
indicated that only (OC)3(t-BuNC)(I)OsMn(CO)5 (1I) was
present. The resulting yellow solution was transferred into a
Schlenk tube, concentrated, and stored at –27°C to give 1I
as yellow crystals (49 mg, 73%). A second preparation un-
der ambient light resulted in the same product plus traces of
2IA that were separated by chromatography as described be-
low. The chloro and bromo analogues (1Cl and 1Br) were
prepared in a similar manner, that is, under ambient light
with a reaction period of 5 days.
Experimental
Unless otherwise stated, manipulations of starting materi-
als and products were carried out under a nitrogen atmo-
sphere with the use of standard Schlenk techniques.
Hydrocarbon solvents were heated to reflux over potassium,
distilled, and stored over molecular sieves before use. Di-
chloromethane was dried in a similar manner except that P2O5
was employed as the drying agent. The precursory com-
pounds Mn(CO)5(X) (X = Cl, Br, I) (16), [Re(µ-X)(CO)4]2
(17), and Os(CO)4(CN-t-Bu) (3) were prepared by literature
procedures. The reaction vessels were Carius tubes of vol-
umes between 25–50 mL and each were fitted with a Teflon
valve. NMR spectra were recorded on a Bruker AMX 400
spectrometer at the appropriate operating frequencies for the
1H, 13C{1H}, and 31P{1H} NMR spectra. Samples of the
complexes used for 13C{1H} NMR spectra were enriched to
~30% 13CO. The samples were prepared from more highly
13CO-enriched M(CO)5(X) (M = Mn, Re), which in turn was
prepared by stirring the M(CO)5(X) in hexane (or toluene)
under 13CO (99%; 2 atm) at room temperature for 24 h (13).
It was found that the 13CO was scrambled equally over all
CO sites in the products. Analytical and spectroscopic data
for the new compounds are given in Tables 1–3.
Preparation of (OC)6(t-BuNC)2(I)Os2Mn(CO)5 (2IA and
2IB)
A solution of Os(CO)4(CN-t-Bu) (60 mg, 0.15 mmol) and
Mn(CO)5(I) (24 mg, 0.075 mmol) in hexanes (10 mL) was
degassed as described above and the reaction vessel sealed
under vacuum. The mixture was stirred at room temperature.
Compounds Os(CO)4(CN-t-Bu) 1I and 2I were present after
2 days as indicated by IR spectroscopy. An IR spectrum of
the reaction solution after 7 days indicated the presence of
the desired product plus traces of 1I. The resulting yellow
solution was concentrated and subjected to chromatography
on a silica gel column (12 × 1 cm). Elution of the column
with hexanes–CH2Cl2 (8:1) gave two yellow bands; the first
contained 1I, the second 2IA. The second fraction was col-
lected, concentrated, and stored at –27°C to give 2IA
(41 mg, 53%) as yellow crystals. Further elution of the col-
umn with hexanes–CH2Cl2 (4:1) yielded a third yellow band
from which 2IB (5 mg, 6%) as yellow crystals was isolated
in a manner similar to that for 2IA. The chloro (2ClA and
2ClB) and bromo (2BrA and 2BrB) analogues were synthe-
sized in an analogous fashion; yields are given in Table 1. It
was verified on a small scale that the trinuclear complexes
could be also prepared from similar reactions of
Os(CO)4(CN-t-Bu) and 1X in a 1:1 molar ratio.
Preparation of (OC)4(t-BuNC)OsMn(CO)4(Cl) (1)
A solution of Os(CO)4(CN-t-Bu) (30 mg, 0.078 mmol)
and Mn(CO)5(Cl) (17 mg, 0.074 mmol) in hexanes (15 mL)
was cooled to –196°C and the solution was degassed with
three cycles of freeze-pump-thaw; the vessel was covered
with aluminum foil. The mixture was stirred under vacuum
at room temperature for 20 h. A bright yellow precipitate re-
sulted. The solvent was removed from the precipitate, which
was washed with hexane (3 × 2 mL) and then dried on the
vacuum line. The product was analytically pure; further pu-
rification was prevented by its instability in solution at room
temperature. Reaction of Mn(CO)5(X) (X = Br, I) under simi-
lar conditions gave the isomerized products (1X; see below).
Preparation of (OC)9(t-BuNC)3(Br)Os3Mn(CO)5 (3Br)
A degassed solution of Os(CO)4(CN-t-Bu) (58 mg,
0.15 mmol) and Mn(CO)5(Br) (14 mg, 0.05 mmol) in hex-
anes (8 mL) was stirred under vacuum at room temperature
for ~40 h, during which time a yellow precipitate formed.
The IR spectra revealed the solution contained small
amounts of 2Br, whereas the solid was mainly 3Br. The so-
lution was removed from the solid, which was then
recrystallized from toluene–hexanes to furnish 3Br (28 mg,
© 2002 NRC Canada

Jiang et al.
Table 1. Analytical H NMR data and yields for complexes 1–3X.
283
1
Compound
Yield (%)
%C (calcd.)
%H (calcd.)
%N (calcd.)
1H NMR (δ)a
1
1Cl
1Br
1I
2ClA
2BrA
2IA
2ClB
2BrB
2IB
3Cl
3Br
3I
65
67
41
73
71
32
53
15
11
6
41
41
26
39
27
44
26.31 (26.56)
26.62 (26.56)
24.85 (24.69)
23.08 (22.99)
26.97 (26.68)
25.68 (25.48)
24.62 (24.33)
26.90 (26.68)
25.59 (25.48)
24.45 (24.33)
26.96 (26.74)
25.91 (25.86)
25.07 (24.99)
21.80 (21.71)
20.91 (20.45)
19.39 (19.26)
1.46 (1.54)
1.60 (1.54)
1.30 (1.43)
1.35 (1.34)
2.06 (1.92)
1.94 (1.83)
1.80 (1.75)
2.07 (1.92)
1.93 (1.83)
1.74 (1.75)
2.21 (2.09)
1.97 (2.02)
2.08 (1.95)
1.23 (1.26)
1.33 (1.19)
1.05 (1.12)
2.14 (2.38)
2.33 (2.38)
2.11 (2.22)
2.09 (2.06)
2.89 (2.92)
2.75 (2.83)
2.63 (2.70)
2.81 (2.96)
2.81 (2.83)
2.63 (2.70)
3.02 (3.23)
3.02 (3.12)
2.98 (3.01)
1.95 (1.95)
1.87 (1.83)
1.66 (1.73)
1.52b
1.64
1.62
1.60
1.61, 1.50
1.59, 1.50
1.57, 1.51
1.58
1.57
1.55
1.62, 1.47
1.61, 1.47
1.58, 1.48
1.52b
1.52b
1.53b
1ReCl
1ReBr
1ReI
aUnless otherwise stated, NMR spectra were recorded in CDCl3 at room temperature.
bRecorded in CD2Cl2 at – 40°C.
Table 2. IR spectra (in hexane) of the new complexes.
Compound
ν(CO) (cm–1)
ν(CN) (cm–1)
1a
1Cl
1Br
1I
2ClA
2ClB
2BrA
2BrB
2IA
2IB
3Cl
2118(m), 2053(s), 2043(sh), 2013(w), 1977(s), 1924(m)
2217(m)
2211(m)
2209(w-m)
2205(m)
2099(m), 2063(s), 2037(s), 2021(m), 2004(s), 1986(sh), 1983(s), 1970(m)
2098(m), 2063(s), 2036(s), 2021(w-m), 2004(s), 1984(s), 1971(m-s)
2096(m-s), 2063(s), 2034(s), 2020(w), 2004(s), 1985(s), 1972(m)
2088(m), 2064(s), 2034(m), 2022(s), 2002(s), 1989(s), 1983(m), 1966(m)
2101(w), 2064(w), 2047(w), 2036(m), 2002(s), 1996(s), 1969(m), 1963(w)
2087(m), 2064(s), 2034(w), 2022(s), 2002(s), 1989(s), 1983(w), 1966(m)
2102(w), 2064(w), 2040(w, sh), 2036(m), 2002(s), 1996(s), 1971(m), 1963(w)
2086(m), 2062(s), 2034(m), 2019(s), 2002(s), 1990(s), 1984(w), 1967(m)
2101(m), 2062(w), 2040(m), 2034(s), 2002(s), 1997(s), 1972(m), 1964(w)
2079(vw), 2064(m), 2041(w), 2020(w), 2015(m), 1994(s), 1987(w, sh), 1961(m)
2080(w), 2065(s), 2039(w), 2019(w, sh), 2013(m), 1991(vs), 1956(m)
2079(w), 2064(m-s), 2041(w), 2021(w), 2015(m), 1994(s), 1987(w, sh), 1961(m)
2080(w), 2064(s), 2039(m), 2020(w, sh), 2013(m), 1991(vs), 1956(m)
2079(w), 2061(m), 2040(w), 2021(w), 2013(m), 1994(s), 1987(w, sh), 1962(m)
2079(w), 2062(m), 2039(w), 2019(w, sh), 2010(m), 1991(vs), 1956(m)
2119(m), 2074(s), 2039(vs), 1978(s), 1914(s)
2207(w), 2188(m)
2204(vw), 2178(m)
2205(w), 2187(m)
2206(vw), 2176(m)
2202(w), 2185(m)
2206(vw), 2176(m)
2202(w), 2183(w), 2171(w)
2205(w), 2171(m)
2201(w), 2184(w), 2171(w)
2204(w), 2171(m)
2198(w), 2181(w), 2168(w)
2201(w), 2171(m)
2217(w)
3Br
3I
1ReCla
1ReBra
1ReIa
2118(m), 2073(s), 2040(vs), 1980(s), 1915(s)
2118(m), 2070(s), 2040(vs), 1978(s), 1917(s)
2219(w)
2218(w)
aIn CH2Cl2.
41%) as a yellow crystalline solid. The chloro (3Cl) and
iodo (3I) congeners were synthesized similarly. It was also
verified that the 2X complexes react with excess
Os(CO)4(CN-t-Bu) under the same conditions to give the
corresponding 3X compounds.
BuNC)(OC)4OsRe(CO)4(Cl) (30 mg, 39% yield). The bromo
and iodo analogues were prepared in a similar manner.
X-ray structural determination of 1I, 2ClA, 2BrB, and 3I
The structures of 1I, 2ClA, and 2BrB were determined at
St. Mary’s University, whereas that of 3I was carried out at
the University of Ottawa. The determinations followed the
same general procedure. A single (yellow) crystal of suitable
size was grown from hexane or hexane–CH2Cl2, and
mounted on a glass fiber. Data were collected at –50°C for
1I, 2ClA, and 2BrB, and at –70°C for 3I; a Bruker
(Siemens) SMART/CCD diffractometer was used in each
case. Crystal data refinement parameters are summarized in
Table 4, and selected interatomic distances and angles are
Preparation of (OC)4(t-BuNC)OsRe(CO)4(Cl)
A degassed solution of Os(CO)4(CN-t-Bu) (44 mg,
0.11 mmol) and [Re(µ-Cl)(CO)4]2 (36 mg, 0.054 mmol) in
toluene (15 mL) was stirred under nitrogen at 45°C for
~20 h, during which time a yellow precipitate formed. The
mother solution was removed and the precipitate washed
with hexanes; the precipitate was then recrystallized from to-
luene–hexanes at –40°C to afford yellow crystals of (t-
© 2002 NRC Canada

284
Can. J. Chem. Vol. 80, 2002
Table 3. 13C NMR data for selected derivatives.
Compound
M–CO
Os–CO
t-Bu–C
1a
1I
2ClAb
221.2 (1C), 220.8 (2C), 219.2 (1C)
219.8 (4C), 215.6 (1C)
222.9 (4C), 218.3 (1C)
182.4 (2C), 177.3 (1C), 163.0 (1C)
177.4 (1C), 171.8 (1C), 162.4 (1C)
193.4 (1C),c 191.9 (1C),c 189.7 (1C),
183.3 (1C), 174.4 (1C), 164.1 (1C)
191.9 (4C), 175.1 (1C), 166.3 (1C)
194.8 (2C),d 194.3 (1C),e 192.3 (1C),e
191.1 (1C), 191.0 (1C), 185.6 (1C),
176.3 (1C), 166.0 (1C)
60.8, 29.5
59.8, 30.1
59.7, 58.6, 30.0
2ClBb
3Clb
223.8 (4C), 217.8 (1C)
223.8 (4C), 218.9 (1C)
59.1, 30.2
59.1, 58.2, 58.0,
29.8, 29.7 (2Me)
1ReCla
1ReBra
1ReIa
194.0 (2C), 188.8 (1C), 186.0 (1C)
192.7 (2C), 188.5 (1C), 185.3 (1C)
190.4 (2C), 188.1 (1C), 184.2 (1C)
180.2 (2C), 175.7 (1C), 164.2 (1C)
180.3 (2C), 176.0 (1C), 163.6 (1C)
180.7 (2C), 176.4 (1C), 162.7 (1C)
29.5
29.5
29.5
aIn CD2Cl2 at – 40°C.
bIn CDCl3 at – 40°C.
2
cTrans, JC,C = 31.3 Hz.
dDegenerate singlets.
2
eTrans, JC,C = 31.6 Hz.
Table 4. Details of the crystal structure determinations of 1I, 2ClA, 2BrB, and 3I.
1I
2ClA
2BrB
3I
Compound
Formula weight
Crystal system
T (°C)
C13H9IMnNO8Os
679.25
Monoclinic
–50
C21H18ClMnN2O11Os2
945.16
Monoclinic
–50
C21H18BrMnN2O11Os2
989.62
Triclinic
–50
C29H27IMnN2O4Os3
1393.98
Monoclinic
–70
Space group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
Cell volume (Å3)
Z
P21/c
P21/n
P1
P21/c
15.0686(8)
11.2590(6)
12.0421(7)
12.2794(8)
16.5412(11
14.3631(10)
9.0783(5)
9.8272(6)
17.621(1)
102.530(1)
100.984(1)
95.273(1)
1491.9(2)
2
11.503(1)
12.394(1)
29.959(3)
108.245(1)
91.870(1)
99.894(2)
1940.3(2)
4
2915.8(3)
4
4207.6(7)
4
Dcalcd. (mg m–3)
Abs. coeff (mm–1)
Unique data
(I > 2σ)
2.325
8.820
3428
2.153
9.266
5134
2.203
10.305
5198
2.201
10.116
7166
Ra
0.0313
0.0817
0.0315
0.0723
0.0342
0.0822
0.0329
0.0478
wRb
aR = Σ|(|Fo| – |Fc |)|/Σ|Fo|.
2
bwR = [Σ (w(|Fo| – |Fc |)2)/Σ(wFo2 )]1/2. w = [σ2(Fo)2 + kFo ]–1.
given in Tables 5–7.2 Unit-cell parameters were calculated
from reflections obtained from 60 data frames collected at
different sections of the Ewald sphere. A statistical measure-
ment of intensity data indicated the space group, and this
was borne out by successful refinement of the structure.
Semiempirical absorption corrections were applied using re-
dundant data. Full-matrix least-squares refinement on F2
was performed after solving using Patterson methods and
the solution package SHELXTL v. 5.10 (18). Anisotropic
thermal parameters were applied to all non-hydrogen atoms;
hydrogen atoms were generated at ideal positions and their
positions were updated with each refinement cycle. The fol-
lowing disorders in the structures were encountered: (i) for
1I: O(2), O(11), and O(13) were each disordered over two
positions; all were refined satisfactorily with 0.5 occupancy
factors. (ii) For 2ClA: CO(15) and Cl were disordered and
modeled with occupancy factors of 53:47. (iii) For 2BrB:
CO(22) and Br were disordered with an occupancy factor of
88:12. Rotational disorder (50%) was also observed for the
methyl groups within the t-BuNC ligands of 2BrB.
2 Supplementary material may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada. For information on obtaining material electronically go to http://www.nrc.ca/cisti/irm/unpub_e.shtml.
Crystallographic information has also been deposited with the Cambridge Crystallographic Data Centre. Copies of the data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2002 NRC Canada

Jiang et al.
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Table 5. Selected bond lengths (Å) and angles (deg) of 1I.
Bond lengths (Å)
Os—Mn
Os—I
Os—C(1)
Os—C(2)
Os—C(3)
Os—C(4)
2.9245(8)
2.7734(4)
1.895(6)
1.940(7)
1.924(6)
2.029(5)
Mn—C(11)
Mn—C(radial)
O—C(Os)
O—C(Mn)
N—C(4)
1.818(7)
1.840(7)–1.857(6)
1.06(3)–1.23(3)
1.09(4)–1.22(4)
1.160(7)
N—C(5)
1.448(7)
Bond angles (deg)
I-Os-Mn
95.38(2)
89.14(15)
170.1(2)
172.6(5)
92.8(3)–93.9(3)
87.9(3)–93.4(3)
91.3(2)–94.2(2)
C(11)-Mn-Os
C(3)-Os-Mn
C(4)-Os-I
179.9(2)
174.98(18)
85.6(2)
C(4)-Os-Mn
C(2)-Os-C(4)
N-C(4)-Os
C(11)-Mn-C
cis-C-Mn-C(radial)
cis-C-Os-C
Os-Mn-C(radial)
Mn-Os-C(radial)
86.0(2)–87.30(18)
81.2(2)–89.1(2)
Table 6. Selected bond lengths (Å) and angles (deg) for 2ClA and 2BrB.
2ClA
2BrB
2ClA
2BrB
Bond lengths (Å)
Os(1)—Mn
Os(1)—Os(2)
Os(2)—X
2.900(1)
2.8812(4)
2.58(1) (2.51(1))a
1.798(7)
2.884(1)
2.8895(4)
2.568(2) (2.44(2))a
1.808(8)
Os(1)—C(9)
Os(2)—C(17)
Os(2)—C(23)
Os(2)—C(24)
Os —C(O)
2.012(7)
2.033(7)
2.005(7)
2.003(7)
1.877(7)–1.95 (1)b
Mn—C(1)
Mn—C(radial)
Bond angles (deg)
Os(2)-Os(1)-Mn
Os(1)-Mn-C(1)
1.820(8)–1.847(9)
1.83(1)–1.85 (1)
1.921(8)–1.950(8)
176.87(2)
179.2(3)
177.54(3)
177.9(2)
176.8(2)
Os-Mn-C(radial)
Mn-Os(1)-C
Os(1)-Os(2)-C(radial)
83.3(3)–85.0(2)
90.1(2)–92.4(2)
86.1(2)–87.6(5)
(89.9(7))a
83.1(3)–86.0(3)
91.1(3)–91.9(3)
87.9(2)–88.6(2)
(92(2))a
C(ax)-Os(2)-Os(1) 178.1(2)
Os(1)-Os(2)-X
87.6 (3) (88.6 (3))a
91.15 (2) (89.1 (6))a
aDisorder present.
bOs(2)—C(21).
Scheme 2.
Results and discussion
25°C, 7 d
(OC)3(X)(L)OsMn(CO)5 + CO
Binuclear OsMn complexes
Os(CO)4(L) + Mn(CO)5(X)
hexane
A bright yellow precipitate resulted when Os(CO)4(CN-t-
Bu) and Mn(CO)5(Cl) in a 1:1 molar ratio in hexanes was
stirred in the dark overnight. From its 13C NMR spectrum at
–40°C in CD2Cl2 and its IR spectrum it is formulated as
(OC)4(t-BuNC)OsMn(CO)4(Cl) (1) with a donor–acceptor
OsMn bond and with both noncarbonyl ligands cis to the
metal–metal bond (eq. [1]).
:
X
X
Os
X
L = CNBut
Os
Os
Mn
Mn
Mn
L
L
C
O
L
C
O
C
X = Cl, Br, I
O
1
1X
Cl
is characteristic of this type of complex and is assigned to
the carbonyl trans to the dative metal–metal bond (1–3, 7).
The chemical shift of this resonance in (OC)4(t-
BuNC)Os[Acc] (Acc = 16e– acceptor fragment) complexes
may be a measure of the acceptor strength of the 16e– frag-
ment (19). The shift of this resonance in 1 may be compared
with δ 165.1 and 159.3, the shifts found in (OC)4(t-
BuNC)OsCr(CO)5 and (OC)4(t-BuNC)OsOs(CO)3(GeCl3)(Cl),
respectively (3, 19).
Compound 1 was insoluble in hexane at room tempera-
ture; warming 1 in hexane caused it to decompose. Although
1 was stable in CD2Cl2 at –40°C, it decomposed in CH2Cl2
at room temperature over ~90 min. Two decomposition
25°C
Os
Os(CO)4(L) + Mn(CO)5(Cl)
L = CNBut
Mn
+ CO
[1]
hexane
L
1
In 1 the 18e– compound Os(CO)4(CN-t-Bu) acts as a two-
electron donor ligand towards the 16e– Mn(CO)4(Cl) moiety.
The 13C NMR spectrum of 1 has a 1:2:1 pattern in the Mn–
CO region around δ 220, and a 2:1:1 pattern in the Os–CO
region (δ 160–185). The latter pattern is typical of com-
plexes such as (OC)4(t-BuNC)OsCr(CO)5 in which the 18e–
Os(CO)4(CN-t-Bu) compound acts as a ligand (3). In partic-
ular, the high field resonance in the spectrum of 1 at δ 163.0
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Table 7. Selected bond lengths (Å) and angles (deg) of 3I.
Bond lengths (Å)
Os(1)—Mn
2.870(1)
Mn—C(11)
1.80(1)
Os(1)—Os(2)
Os(2)—Os(3)
Os(3)—I
2.8894(5)
2.8928(5)
2.7768(7)
Mn—C(radial)
Os—C(CO)
Os—C(CNBu)
1.81(1)–1.87(1)
1.89(1)–1.96(1)
2.01(1)–2.026(9)
Bond angles (deg)
Os(1)-Os(2)-Os(3)
Mn-Os(1)-Os(2)
Os(1)-Mn-C(1)
Os(2)-Os(3)-C(14)
Os(2)-Os(3)-I
177.60(2)
177.04(3)
179.5(4)
178.5(3)
92.63(2)
Os-Mn-C(radial)
Mn-Os(1)-C
Os(1)-Os(2)-C
82.7(3)–84.9(3)
90.0(2)–93.5(3)
88.1(2)–91.5(3)
83.2(2)–87.8(2)
Os(2)-Os(3)-C(radial)
Fig. 2. Molecular structure of (OC)3(CI)(CN-t-Bu)OsOs(CO)3-
(CN-t-Bu)OsMn(CO)5 (2C1A).
Fig. 1. Molecular structure of (OC)3(I)(t-BuNC)OsMn(CO)5 (1I).
products were identified as Os(CO)4(CN-t-Bu) and
Mn(CO)5(Cl) by IR spectroscopy. Dissociation in solution
of complexes with weak dative metal–metal bonds has been
observed previously (6, 11). Furthermore, in some cases
these complexes react with CH2Cl2 (20).
metal bond lengths reported for Mn2(CO)10 (2.9038(6) Å)
(23) and Os3(CO)12 (average = 2.887 Å) (24) one can esti-
mate the length of an unbridged Mn—Os bond to be ~2.895
Å. The Os–Mn distance in 1I is, therefore, somewhat longer
than expected; it is also significantly longer than the three
other Os–Mn lengths reported below.
When the reaction of Os(CO)4(CN-t-Bu) and Mn(CO)5(Cl)
in hexanes was carried out for 7 days in ambient light under
vacuum, a second product, which was also analyzed as
MnOs(CO)8(CN-t-Bu)(Cl) (1Cl), was obtained. The reaction
with Mn(CO)5(X) (X = Br, I) and Os(CO)4(CN-t-Bu) gave
the corresponding MnOs(CO)8(CN-t-Bu)(X) (1Br, 1I) deriv-
atives; there was no evidence in the latter reactions for a
complex analogous to that of 1. The crystal structure of 1I
(reported below) revealed that these compounds should be
formulated as (OC)3(t-BuNC)(X)OsMn(CO)5 (X = Cl, Br, I)
(Scheme 2). Since the Mn(CO)5 and Os(CO)3(CN-t-Bu)(X)
fragments are 17e– species, the Mn–Os bonds in these mole-
cules are considered nondative metal–metal bonds.
A view of 1I is shown in Fig. 1; selected bond lengths and
angles for the molecule are listed in Table 5. As can be seen
from the figure, the Mn–Os bond is unbridged. There do not
appear to be any structures of complexes with unbridged
Mn–Os bonds with which to compare the Mn—Os length in
1I of 2.9245(8) Å. In CpMnOs3(µ2-CHCHPh)(µ-H)(µ-
CO)(CO)11 the Os—Mn length is 2.765(4) Å (21); in the
MnOs3(µ4-C)(CO)13 the Os—Mn lengths range from
2.7797(9) to 2.8271(7) Å (22). From the (unbridged) metal–
The formation of complexes of type 1X involves an iso-
merization in which the halide X migrates from the Mn to
the Os atom in (OC)4(t-BuNC)OsMn(CO)4(X) with concom-
itant migration of a carbonyl ligand from Os to Mn as shown
in Scheme 2. As mentioned in the Introduction, we have previ-
ously observed this type of migration in (Me3P)(OC)4-
OsRu(CO)3(SiCl3)(Br) (11). A similar migration is presumably
also involved in the formation of (Me3P)(OC)3(H)OsRe(CO)5
from Re(CO)5(H) and Os(CO)4(PMe3), although the inter-
mediate with a dative Os–Re bond is not observed (12).
Because of the donor–acceptor character of the metal–
metal bond in molecules such as 1 there is expected to be a
greater charge separation in these molecules compared with
the isomerized derivatives (e.g., 1Cl). Consistent with this
view is that the C—O stretches in 1 (with a dative Os—Mn
bond) span the range 1924–2118 cm–1, whereas in 1Cl the
range is 1970–2099 cm–1. It may be the relief of this charge
separation that is the driving force for the isomerization. The
nondative Os–Re bond in (Me3P)(OC)3(Br)OsRe(CO)5 is
slightly shorter than the dative Os–Re bond in the closely re-
lated (Me3P)(OC)4OsRe(Br)(CO)4, an observation consistent
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Jiang et al.
287
Fig. 3. The 13C NMR spectrum (CO region) of 2C1A (13CO enriched) in CH2Cl2–CD2Cl2 (4:1) at – 40°C. The assignment of the sig-
nals is given in the inset.
O
f
L
L
d'
CO
C
CO
CO
g
OC
Os
CO
Os
Mn
a
OC
b
Cl
OC
d
e
c
C
O
C
C
O
O
(L = ButNC)
with the view that nondative metal–metal bonds are somewhat
stronger than similar dative metal–metal bonds (4, 12, 25).
the Os–Mn bond (see below). The apparent strengthening of
the Os–Mn bond in 2ClA compared with that in 1I is tenta-
tively assigned to more extensive delocalization and hence
stabilization of the metal–metal bonding electrons in 2ClA.
Trinuclear OsMn complexes
The Os—Os distance in 2ClA of 2.8812(4) Å, may be
Halide ligands in metal carbonyl complexes such as
M(CO)6–n(X)n (M = Mn (26), Re (27), n = 1; M = Fe (28),
Ru, Os (29), n = 2; X = Cl, Br, I) usually activate the com-
plex to carbonyl substitution. It was, therefore, reasoned that
the 1X complexes might undergo further carbonyl substitu-
tion by Os(CO)4(CN-t-Bu) at the osmium atom and this pos-
sibility was found to be correct.
compared with the average Os—Os length (2.887(3) ) in
Å
Os3(CO)12 (24). The Os–Os distances in linear Os3 chains
are, however, somewhat longer than the distance in the trian-
gular cluster. For example, the Os—Os lengths in
-
,
Os (CO) (I)2 (30), Os3(CO)12(SiCl3)2 (31), and Os (CO)10
[P(3OMe)12] (Br) (32) are 2.935(2), 2.912(1), and 2.9316(2)
Å
2
respectiv3el2y. In (OC)3[MeC(CH2O)3P]2OsOs(CO)4W(CO)5
(33), (OC)4(CN-t-Bu)OsOs(CO)3(CN-t-Bu)W(CO)5 (34), and
(Ph3Sb)(OC)4OsOs(CO)4Os(CO)3(Br)2 (35), the Os—Os
(dative) bond lengths are 2.940(1), 2.907(2), 2.8882(5), and
2.9308 Å, respectively. The Os–Os length in 2ClA, there-
fore, appears to be significantly shorter than most compara-
ble unbridged Os–Os distances in noncluster complexes
reported in the literature.
Reaction of 1X with Os(CO)4(CN-t-Bu) in a 1:1 ratio, or
the reaction of Mn(CO)5(X) and Os(CO)4(CN-t-Bu) in a 1:2
ratio, readily affords complexes of formula MnOs2(CO)12-
(CN-t-Bu)2(X) (2X) according to Scheme 3. Two isomers of
this formula were isolated by column chromatography. The
major isomer in each case (2XA) is formulated with an
MnOs2 backbone with an isocyanide ligand coordinated to
each osmium atom. The halide ligand is placed on the termi-
nal Os atom at a site that is both cis to the Os–Os bond and
the t-BuNC ligand (Scheme 3). This is based on the crystal
structure and the 1H and 13C NMR data of 2ClA. The bromo
The 13C NMR spectrum of 2ClA in the CO region (Fig. 3)
has the expected 1:4 pattern in the Mn–CO region due to the
axial and radial carbonyls of the Mn(CO)5 unit; these signals
are broadened due to the quadrupole moment of 5/2 of 55Mn.
There are six resonances each of intensity 1 in the δ 160–195
region (the region where the resonances of Os–CO group-
ings normally appear (2, 3, 7, 36)). Such a spectrum is con-
sistent with the solid-state structure when it is realized that
the terminal Os atom is chiral because it has four different
ligands with three unique ligands occupying a face of the
octahedron. The trans-carbonyl ligands attached to the cen-
tral Os atom (labeled d/d′ in Fig. 3) are, therefore, chemi-
cally distinct. This is similar to the AB pattern exhibited by
protons of a CH2 unit adjacent to a chiral center in organic
1
and iodo analogues have similar H NMR and IR spectra to
2ClA.
A view of 2ClA is shown in Fig. 2; selected bond lengths
and angles are given in Table 6. The Os—Mn length in
2ClA of 2.900(1) Å is significantly shorter than the Os—Mn
length in 1I (2.9245(8) ). This is unexpected because in 1I
Å
the ligands trans to the Os–Mn bond are π-acceptor carbonyl
ligands, whereas in 2ClA one of the trans ligands is
Os(CO)3(L)(Cl), which is probably a π-donor ligand (7). The
latter property would be expected to increase the dπ–dπ in-
teractions across the metal–metal bond and hence weaken
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Can. J. Chem. Vol. 80, 2002
Scheme 3.
Fig. 4. Molecular structure of (OC)2(Br)(CN-t-Bu)OsOs(CO)4-
OsMn(CO)5 (2BrB).
25 °C
CO +
Os(CO)4(L) + (OC)3(X)(L)OsMn(CO)5
hexane
1X
(OC)4(L)OsOs(CO)2(X)(L)OsMn(CO)5
2
:
X
X
Os Os
Os Os
Mn
Mn
L
L
L
2XA
L
2
X
L
Os Os
Mn
L = CNBut
X = Cl, Br, I
L
2XB
molecules (37). The signals due to these carbonyls also ex-
hibit 13C–13C coupling as expected for chemically different
carbonyls that are mutually trans to each other (38) and the
level of 13C enrichment of the sample (~30%).
ample, the sample used for the spectrum shown in Fig. 3
was prepared from 13CO-enriched Mn(CO)5(Cl) and unen-
riched Os(CO)4(CN-t-Bu). It is evident from the spectrum
that the label is scrambled over all carbonyl sites in the mol-
ecule. Similar isomers to 2A and 2B are found for Os2(CO)7-
(CN-t-Bu)2W(CO)5, but in this case the isomers are not in
equilibrium in solution at room temperature (34). The migra-
tion of the noncarbonyl ligand to the terminal osmium atom in
2BrB is also reminiscent of the migration observed in the for-
mation of (OC)3[MeC(CH2O)3P]2OsOs(CO)4OsW(CO)5 from
the addition of Os(CO)4[P(OCH2)3CMe] to [MeC(CH2O)3
P](OC)4OsW(CO)5 at 90°C (33). The trinuclear complex in
this case contains two dative metal–metal bonds in tandem
and has both P ligands coordinated to the terminal Os atom,
in a trans configuration. This type of migration results in the
more bulky noncarbonyl ligand moving to a less sterically
hindered site, although the radial site on the terminal Os
atom is even less sterically hindered. The trans arrangement
of the noncarbonyl ligands, which are poorer π-acceptor lig-
ands than CO, would not be expected to be the electronically
preferred structure. It is usually found that poor π-acceptor
ligands prefer sites trans to carbonyl ligands. We have re-
cently argued that there is an electronic preference to have a
strong π-acceptor ligand (e.g., CO) trans to the metal–metal
bond in binuclear complexes. This is because it will reduce
the repulsive dπ–dπ interactions across the metal–metal
bond (7).
From their spectroscopic properties, the minor isomers
(2XB) are formulated with a similar structure to 2XA, but
with both isocyanide ligands on the terminal osmium atom
in a mutually trans orientation (Scheme 3). In each case, the
1H NMR spectrum consists of a singlet that indicates, in the
absence of chemical exchange, that both isocyanide ligands
are chemically equivalent. The IR spectrum has one very
weak and one strong C–N stretch consistent with the view
that these ligands are in mutually trans sites on the same os-
mium atom. The 13C NMR spectrum of 2ClB in CH2Cl2–
CD2Cl2 exhibits two signals in a ratio of 4:1 in the Mn–CO
region and three signals in a 4:1:1 ratio in the Os–CO re-
gion, as expected.
The structure of 2BrB was confirmed by X-ray crystallog-
raphy. A view of the molecule is given in Fig. 4; selected
bond lengths and angles are presented in Table 6. The Os—
Mn and Os—Os lengths are 2.884(1) and 2.8895(4) Å, re-
spectively, and may be compared with the other Os–Mn and
Os–Os lengths discussed above. That the Os–Mn length in
2BrB is somewhat shorter than that in 2ClA may reflect
fewer steric interactions between the radial ligands on the
Mn and Os(1) atoms in 2BrB.
A solution of pure 2IA in hexane was stirred under vac-
uum at room temperature for 90 h. An IR spectrum of the
solution at this stage indicated the presence of 2IA, along
with significant amounts of Mn2(CO)10 and trace amounts of
2IB. Likewise, a solution of 2BrB in hexane was stirred un-
der vacuum at room temperature for 90 h and an IR spec-
trum then taken of the solution. The spectrum indicated the
presence of 2BrA, significant amounts of Mn2(CO)10, but
little or no starting complex (2BrB). In each case there were
C–O stretching bands due to unidentified products. These
preliminary results indicate that the A and B forms of 2X are
present in equilibrium in hexane at room temperature. They
also show that the complexes are unstable under these condi-
tions and decompose to Mn2(CO)10 and other unidentified
products. It may be that decomposition proceeds mainly via
form B.
Tetranuclear OsMn complexes
Reaction of Mn(CO)5(X) and Os(CO)4(CN-t-Bu) in a 1:3
ratio in solution at room temperature readily gave products
that analyzed as MnOs3(CO)14(CN-t-Bu)3(X) (3X; eq. [2]);
it was also established on a small scale that the same prod-
ucts could be formed from 2X and with an excess of
Os(CO)4(CN-t-Bu) under the same conditions. The X-ray
crystal structure of 3I was determined at –70°C and a view
of the molecule is given in Fig. 5; structural parameters are
listed in Table 7. The structure consists of an essentially lin-
ear Os3Mn chain with an isocyanide ligand attached to each
Os atom. The halide is coordinated, once again, to the termi-
nal Os atom in a site that is cis to both the Os–Os bond and
a t-BuNC ligand.
There is ample evidence that migration of carbonyl lig-
ands across dative metal–metal is facile (2, 3, 5, 6). For ex-
© 2002 NRC Canada

Jiang et al.
289
Fig. 5. Molecular stucture of (OC)3(I)(CN-t-Bu)OsOs(CO)3(CN-t-
Bu)Os(CO)3(CN-t-Bu)OsMn (CO)5 (31).
Fig. 6. The 13C NMR spectrum (CO region) of (OC)4(t-BuNC)-
OsRe(CO)4 (Br) (13CO enriched) in CH2Cl2–CD2Cl2 (4:1) at
–40°C. The assignment of the signals is given in the inset (L =
t-BuNC).
X
25 °C
3Os(CO)4(L) + Mn(CO)5(X)
Os
Os
Os
Mn
+ CO
[2]
hexane
L
L
L
(or 2X)
L = CNBut
3X
X = Cl, Br, I
The Os—Mn distance in 3I at 2.870 (1) Å is the shortest
of the four Os—Mn lengths determined in this study and
some 0.05 Å shorter than that in 1I. The Os—Os lengths
2.8894(5) and 2.8928(5) Å in 3I are not significantly differ-
ent from the Os—Os lengths in 2ClA and 2BrB, and compa-
rable to the Os—Os lengths in Os3(CO)12. From a ground
state point of view, therefore, the metal–metal bonds in 3I
appear strong.
sulted in only 3X being formed. Carrying out the same
reactions at elevated temperatures resulted in decomposition.
Binuclear OsRe complexes
Complexes of formula (OC)4(t-BuNC)OsRe(CO)4(X) (i.e.,
with dative Os–Re bonds) were synthesized according to
eq. [3] as air-stable, yellow crystals. (It was found that the
dimeric rhenium precursor gave purer products than the
The 13C NMR spectrum of 13CO-enriched 3Cl (Table 3)
has two signals in a 4:1 ratio to low field of δ 215 assigned
to the carbonyls on manganese, and eight signals to high
field of δ 195 assigned to the carbonyls attached to the os-
mium atoms. The latter signals are of intensity 1 except that
at δ 194.8, which is of intensity 2. The spectrum is consis-
tent with the view that 3Cl has the same structure as found
for 3I in the solid state if two of the resonances are degener-
ate. As in the spectrum of 2ClA, because the terminal os-
mium atom is chiral each carbonyl attached to an osmium
atom is chemically different. The methyl resonances in both
[3]
+ [Re(µ-X)(CO) ]
4 2
2Os(CO)4(L)
X = Cl, Br, I
45° C
2(OC)4(L)OsRe(CO)4(X)
toluene
1ReX
corresponding Re(CO)5(X) complexes.) The formulation of
the products with a dative metal–metal bond is clearly indi-
cated by 13C NMR spectroscopy (e.g., Fig. 6). In particular,
the complexes exhibit three resonances in a 2:1:1 ratio in the
region δ 184–194 attributed to the carbonyls of the
Re(CO)4(X) moiety (Table 2). These signals show little
quadrupolar broadening presumably because of the large
field gradient through the molecule arising from the polar
nature of the dative Os–Re bond causing rapid quadrupolar
relaxation.
Attempts to isomerize the (OC)4(t-BuNC)OsRe(CO)4(X)
complexes by heating them in solution at 60°C only resulted
in decomposition. It has previously been found that, like
nondative metal–metal bonds, dative metal–metal bonds ap-
pear strongest when both metals are third-row transition ele-
ments (2, 4, 25). The increased strength of the Os–Re bond
would contribute to the barrier to the isomerization of the
1ReX complexes compared with that of the Mn analogues.
We point out here that although (Me3P)(OC)4(Br)OsRe(CO)5
is known it was not prepared by isomerizarion of
1
the H NMR spectra of 3X (and in 13C NMR spectrum of
3Cl) show two resonances in the ratio of 2:1. It is probable
that the signals due to the methyl groups of the CN-t-Bu
groups coordinated to the two internal osmium atoms are de-
generate.
Only one isomer of 3X was isolated and it can be as-
sumed to be the result of addition of Os(CO)4(CN-t-Bu) to
the major isomer of 2X (i.e., 2XA). The substitution of a
carbonyl ligand of the Os(CN-t-Bu)2(X)(CO)2 unit in 2XB
would be expected to be slower than in 2XA for both steric
and electronic reasons. The presence of an additional CN-t-
Bu ligand on the terminal Os atom would block the substitu-
tion and increase the strength of the remaining Os–CO bonds.
Attempts to prepare complexes with still longer metal
chains have so far been unsuccessful. Stirring Mn(CO)5(X)
in solution with a large excess of Os(CO)4(CN-t-Bu) re-
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Can. J. Chem. Vol. 80, 2002
Scheme 4.
rangement (11). Attempts to further exploit this reaction for
the preparation of complexes with still longer metal chains
are planned.
X
25 oC, hexane
- CO
Os
Mn
Os(CO)4(L) + Mn(CO)5(X)
L
C
O
Acknowledgments
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) and St. Mary’s University for
financial support.
X
X
References
Os(CO)4(L)
- CO
Os
Os
Mn
etc.
Os
Mn
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Chem. Soc. Chem. Commun. 854 (1983).
2. H.B. Davis, F.W.B. Einstein, P.G. Glavina, T. Jones, R.K.
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L
L
L
C
O
1X
(Os(CO)4(L))
X
Mn
Os
Os
Os
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L = ButNC; X = Cl, Br, I
L
L
L
3X
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(Me3P)(OC)4OsRe(Br)(CO)4, but rather by reaction of
(Me3P)(OC)4(H)OsRe(CO)5 with CBr4 (12).
Conclusions
We have previously observed the isomerization of (Me3P)-
(OC)4OsRu(CO)3(SiCl3)(Br) with a dative Os–Ru bond to
(Me3P)(OC)4(Br)OsRu(CO)3(SiCl3) with a nondative Os–Ru
bond (11). This type of migration has been exploited for the
synthesis of (X)[Os(CO)3(CN-t-Bu)Os]nMn(CO)5 complexes
with n = 1, 2, 3. It is believed that there is initial replace-
ment of CO in the Mn(CO)5(X) or Os(CO)3(CN-t-Bu)(X)
unit by the 18e– ligand Os(CO)4(CN-t-Bu). This is followed
by rearrangement to the isomer with a nondative metal–
metal bond by migration of the halogen ligand to the donor
Os atom with concomitant migration in the reverse direction
of a carbonyl ligand. This is summarized in Scheme 4.
There are a number of factors involved in the successful
synthesis of the OsnMn complexes. The 18e– Os(CO)4(L)
must be sufficiently basic to form the initial donor–acceptor
complex (Os(CO)5 does not undergo these reactions). The
noncarbonyl ligand (L) must be sterically undemanding so
that it does not block entry of an additional Os(CO)4(L)
ligand. With one exception, this reaction stops at the
binuclear derivative for Os(CO)4(PR3) ligands (2, 33). Fur-
thermore, in complexes such as (Me3P)(OC)4OsW(CO)5 and
(Me3P)(OC)4OsRu(CO)3(SiCl3)(Br) the major isomer has
the P ligand trans to the dative metal–metal bond (2, 12).
An additional requirement for the formation of the tri- and
tetranuclear species is that the dative bond in the intermedi-
ates should not be too strong. For example, the (OC)4(t-
BuNC)OsRe(CO)4(X) complexes do not isomerize. In addi-
tion, the 1e– ligand on the acceptor atom should readily al-
low the formation of the bridged intermediate. In previous
work, we have shown that for (Me3P)(OC)4OsRu(CO)3-
(SiCl3)(X) compounds isomerization occurs immediately for
X = H and slowly for X = halide. On the other hand,
(Me3P)(OC)4OsRu(CO)3(SiCl3)2 does not undergo this rear-
© 2002 NRC Canada

Jiang et al.
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