The photochemical and thermal reactions of a triosmium cluster carrying a γ-pyrone ligand with alkynes

Article abstract of DOI:10.1016/j.jorganchem.2003.09.022

The reaction of the cluster Os₃(CO)₁₀(μ-H) (μ-γ-C₅H₃O₂) (1) with a number of alkynes under thermal or visible light irradiation conditions, afforded in most cases the dinuclear complexes Os₂(CO)₆(μ-γ-C₅ H₃O₂)(μ-LH) (L=PhCCPh, ^tBuCCH, ^tBuCCMe or EtCCEt) (2) or the trinuclear chain complexes Os₃(CO)₉(μ-H)(μ-γ-C₅ H₃O₂)(μ-RCCHC₆H₄) (R=H, Ph) (3). In the case of PhCCPh, a new isomer of Os₃(CO)₈(PhCCPh)₂, viz., Os₃(CO)₈(μ-PhCCPh)(μ-PhCCHC₆ H₄) (7) has been isolated and characterised.

Full text of DOI:10.1016/j.jorganchem.2003.09.022

Journal of Organometallic Chemistry 689 (2004) 25–34
www.elsevier.com/locate/jorganchem
The photochemical and thermal reactions of a triosmium
cluster carrying a c-pyrone ligand with alkynes q
*
Qi Lin, Weng Kee Leong , Lu Gao
Department of Chemistry, National University of Singapore, Kent Ridge 119260, Singapore
Received 19 August 2003; accepted 17 September 2003
Abstract
The reaction of the cluster Os3(CO)10(l-H)(l-c-C5H3O2) (1) with a number of alkynes under thermal or visible light irradiation
t
t
conditions, afforded in most cases the dinuclear complexes Os2(CO)6(l-c-C5H3O2)(l-LH) (L ¼ PhCCPh, BuCCH, BuCCMe or
EtCCEt) (2) or the trinuclear chain complexes Os3(CO)9(l-H)(l-c-C5H3O2)(l-RCCHC6H4) (R ¼ H, Ph) (3). In the case of PhCCPh,
a new isomer of Os3(CO)8(PhCCPh)2, viz., Os3(CO)8(l-PhCCPh)(l-PhCCHC6H4) (7) has been isolated and characterised.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Osmium; Clusters; Pyrones; Alkynes
1. Introduction
ers, the reactions with alkynes proceed with retention of
the triangulo trinuclear framework, with the exception
of the reaction with DMAD (which gave an open chain
product) and the reaction of the triruthenium with 2-bu-
tyne (which gave also a diruthenium product) [1a].
The reactivity of clusters carrying a ligand other than
carbonyl or hydride continues to be of great interest.
These additional ligands may act as ancillary ligands to
stabilise and affect the reactivity of the cluster [1], or may
themselves act as substrates for reaction with the alkynes
[2]. Thus in the triiron and triruthenium l3-phenylimido
clusters M3(l3-NPh)2(CO)9 and H2M3(l3-NPh)(CO)9
(M¼ Fe, Ru), reactions with alkynes generally led to di-
nuclear complexes for the iron analogues and tetranuclear
complexes for the ruthenium analogues [2a]. In the imin-
ium-bridged triosmium cluster Os3(CO)10(l-H)(l-
H2CNMe2), the reaction with DMAD led to trinuclear
products, both with triangular arrangement as well as an
open chain, of the osmium core. However, it is clear that
the reactivity in this case is driven primarily by the active
CH2 group on the iminium, leading to C–C coupling and/
or rearrangement of the iminium [2b]. In the imidoyl
triruthenium and triosmium systems Ru3(l3-MeC¼
NEt)(l-H) and M3(l3-C¼ N(CH2)3)(CO)9 that have
been extensively investigated by Rosenberg and cowork-
In an earlier paper, we have reported our investigations
into the binding of pyrones onto a triosmium cluster [3].
The simple pyrones generally bind to the triosmium
framework via the exocyclic oxygen and an orthometal-
lation, for example, c-pyrone gave the cluster
Os3(CO)10(l-H)(l-c-C5H3O2) (1). These clusters are
among a very few triosmium clusters known that contain
an O-heterocyle [4], and unlike the clusters involving N-
donor ligands mentioned above, the reactivity of this class
of clusters has not been studied to any great extent. Fur-
thermore, pyrones are known to exhibit interesting pho-
tochemistry, for instance, photochemical activation of
c-pyrone can result in rearrangement and intramolecular
½2 þ 2ꢀ cycloaddition reactions [5]. We were therefore in-
terested to study the reactivity of cluster 1, and our in-
vestigations into its reactivity with alkynes is reported here.
2. Results and discussion
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.jorganchem.2003.09.022.
* Corresponding author. Tel.: +65-68745131; fax: +65-67791691.
E-mail address: chmlwk@nus.edu.sg (W.K. Leong).
Cluster 1 is thermally and photochemically quite
stable; refluxing a toluene solution or photolysis
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.09.022

26
Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
with UV or visible light led to the recovery of unreacted
1.
[6,7]. Both 2a and 3a have been characterised by single
crystal X-ray crystallographic studies; their ORTEP dia-
grams are given in Figs. 1 and 2, respectively.
2.1. Reactions with PhCBCPh
Interestingly, when the photolysis was carried out by
maintaining the reaction vessel at 10 °C over a similar
period of time, only 3a was isolated, in 12% yield.
Photolysis of 3a also did not afford 2a. The results of the
photochemical reactions are summarised in Scheme 1.
When 1 was heated with two equivalents of PhCCPh
at 100 °C, three major cluster products were isolated,
together with hexaphenylbenzene. The cluster products
were the two previously reported clusters 4 and
Os3(CO)8(l-H)(l-PhCCPhCPhCC6H4) (6) [8], and a
novel red cluster Os3(CO)8(l-PhCCPh)(l-PhCCHC6H4)
(7). Trace amounts of 5 and another known cluster,
Os3(CO)7(PhCCPh)3 (8) were also identified spectro-
scopically. Single crystal X-ray crystallographic studies
have been carried out on 6 and 7. The single crystal X-
ray structure of 6 has already been reported earlier [8a];
the one characterised here is a dichloromethane solvate
and the structural features are essentially similar. The
ORTEP diagram of 7, together with selected bond pa-
rameters, is given in Fig. 3.
Irradiation of a cyclohexane solution of 1 and excess
PhCCPh with a tungsten lamp for 2 d afforded four
products, viz., the novel complexes Os2(CO)6(l-c-C5H3-
O2)(l-PhCCHPh) (2a) and Os3(CO)9(l-H)(l-c-C5H3-O2)
(l-PhCCHC6H4) (3a) and the previously known clusters
Os3(CO)8(PhCCPh)2 (4) and Os3(CO)9-(PhCCPh)2 (5)
Cluster 7 was not among the products in the original
report on the thermal reaction between Os3(CO)12 and
PhCCPh [7]. Its structure shows that one of the alkyne
ligand is orthometallated and that an alkyne has been
formally reduced to an alkenyl. This alkenyl C@C bond
length is also longer than the other, formally a CBC
ꢀ
triple bond (1.407(7) and 1.363(7) A, respectively), al-
though both are elongated as expected.
Fig. 1. ORTEP diagram of 2a (50% probability thermal ellipsoids;
aromatic and pyrone hydrogens omitted).
ꢀ
Fig. 2. ORTEP diagram (50% probability thermal ellipsoids; aromatic and pyrone hydrogens omitted) and selected bond lengths (A) and angles (°)
of 3a. Os(1)–Os(2) ¼ 2.9809(4); Os(1)–Os(3) ¼ 2.8535(4); Os(1)–O(7) ¼ 2.139(4); Os(1)–C(102) ¼ 2.330(6); Os(1)–C(101) ¼ 2.363(6); Os(2)–C(102) ¼
2.118(6); Os(2)–C(112) ¼ 2.129(6); Os(3)–C(3) ¼ 2.129(6); O(1)–C(6) ¼ 1.351(8); O(1)–C(2) ¼ 1.355(8); O(7)–C(4) ¼ 1.260(7); C(2)–C(3) ¼ 1.361(8);
C(3)–C(4) ¼ 1.466(9); C(4)–C(5) ¼ 1.424(8); C(5)–C(6) ¼ 1.319(9); C(101)–C(102) ¼ 1.393(9); C(101)–C(111) ¼ 1.480(8); C(102)–C(121) ¼ 1.513(8);
Os(3)–Os(1)–Os(2) ¼ 111.707(10); O(7)–Os(1)–Os(3) ¼ 80.61(10); C(3)–Os(3)–Os(1) ¼ 81.20(17).

Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
27
1
+ PhCCPh
h
ν
, ~35 oC
Ph
Ph
Ph
C
Ph
O
C
C
C
O
O
Os
C
O
Os
Os
H
C
Os
Os
C
Os
C
Os
Os
H
Os
Os
C
H
C
C
Ph
C
Os
Ph
Ph
Ph
Ph
Ph
Ph
3a (9%)
2a (9%)
4
(6.4%)
5
(10%)
Scheme 1.
ꢀ
Fig. 3. ORTEP diagram (50% probability thermal ellipsoids; aromatic hydrogens omitted) and selected bond lengths (A) and angles (°) of 7. Os(1)–
Os(2) ¼ 2.7298(3); Os(2)–Os(3) ¼ 2.7985(3); Os(1)–C(1) ¼ 2.252(4); Os(1)–C(2) ¼ 2.328(5); Os(1)–C(101) ¼ 2.303(5); Os(1)–C(102) ¼ 2.334(5);
Os(2)–C(102) ¼ 2.095(5); Os(2)–C(2) ¼ 2.107(5); Os(2)–C(3) ¼ 2.232(5); Os(2)–C(4) ¼ 2.259(5); Os(3)–C(3) ¼ 2.066(5); Os(3)–C(4) ¼ 2.078(5); C(1)–
C(2) ¼ 1.407(7); C(3)–C(4) ¼ 1.363(7); C(1)–C(101) ¼ 1.440(7); C(2)–C(201) ¼ 1.487(6); C(3)–C(301) ¼ 1.484(6); C(4)–C(401) ¼ 1.476(7); Os(1)–Os(2)–
Os(3) ¼ 155.056(9); C(4)–C(3)–C(301) ¼ 140.3(4); C(3)–C(4)–C(401) ¼ 140.2(4).
Clusters 4, 6 and 7 are isomers. A comparison of the
reported structure of 4 [6], with those of 6 and 7 here
show that the essential structural differences among
these three clusters are: (i) both 4 and 6 contain a tri-
angular Os3 framework while 7 comprises a triosmium
chain, (ii) orthometallation of a phenyl ring of an alkyne
has occurred in 6 and 7 but not in 5, and (iii) there is no
coupling of the two alkynes in 4 and 7, while in 6 a C–C
bond has been formed between the two alkynes.
5 and 6 (by IR and 1H NMR spectroscopy), while
heating a sample of 7 in d8-toluene (in a Carius) at 100
°C showed that it was converted completely to another
unidentified compound (mCO 2078m, 2045s, 2015vs,
2002s, 1990w, 1983w, 1971w, 1967w, 1957vw cmꢁ1) af-
ter 40 h. We have also carried out the reaction between
Os3(CO)10(NCCH3)2 and PhCCPh at room tempera-
ture, which gave only 4 and 5 but no 7. Thus these re-
sults show that 4 is the precursor to 5 (the formation of
5, and 8, from 4 have been reported [7,18]) and 6 but not
to 7, and that the formation of 7 may be activated by the
c-pyrone ligand. However, we have also found that the
reaction of 3a with excess PhCCPh at 110 °C did not
give 7, indicating that 3a is not a precursor to 7 in the
thermal reaction of 1 with PhCCPh. The results also
We have monitored the reaction between 1 and
1
PhCCPh at 130 °C in d8-toluene (in a Carius) via H
NMR spectroscopy, and found that compound 6 was
formed after a few hours but was slowly consumed; 5
was also detected although not isolated. Heating a
sample of 4 at 100 °C for 4 h resulted in the formation of

28
Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
Ph
h
P
H
h
P
C
C
Ph
C
C
C
Os
C Ph
6
6
s
O
O
s
Os
s
s
O
O
C
C
C
Ph
Ph
h
P
4
7
h
P
C
Ph
C
C
+
5 + 8
C
Os
h
P
s
O
s
O
H
Scheme 2.
indicate that 2a does not arise from the photochemical
or thermal decomposition of 3a. This is also corrobo-
rated by the different products obtained here compared
to the case for Os3(CO)12 [6,9]. Thus the reaction
pathway for 1 with PhCCPh is as depicted in Scheme 2.
2.2. Reactions with other alkynes
Similar reactions were also carried out with a number
of other alkynes. Thus the photolysis of 1 with tBuCCH,
tBuCCMe and EtCCEt gave the corresponding dinu-
clear complexes Os2(CO)6(l-c-C5H3O2)(l-L) (where
L ¼ tBuCHCH (2b), tBuCHCMe (2c) or EtCHCEt (2d))
in good yields. These reactions yet again contrast with
those of Os3(CO)12 [10]. There are minor differences in
behaviour with each alkyne; for instance, EtCCEt gave
the same product (2d) using the thermal route, while
the photochemical reaction with PhCCH afforded only
the trinuclear species Os3(CO)9(l-H)(l-c-C5H3O2)(l-
HCCHC6H4) (3b) and the thermal reaction (at 100 °C)
did not proceed. The clusters have all been characterised
spectroscopically and analytically, and in the case of 2b,
2d and 3b, also by single crystal X-ray crystallography.
The structures of 2a and 2d are similar, while 2b has a
different orientation of the alkyne substituents relative
to the pyrone; the ORTEP diagram of 2b is shown in
Fig. 4. Thus the alkyne is twisted such that the sub-
stituent on the l2 alkyne carbon (C(31)) in 2a or 2d is
pointing away from the pyrone, while the H atom on
that carbon in 2b is pointing towards the pyrone. A
Fig. 4. ORTEP diagram of 2b (50% probability thermal ellipsoids;
methyl and pyrone hydrogens omitted).
common atomic numbering scheme and selected bond
parameters for clusters 2 are given in Table 1.
The Os–Os bond lengths in these complexes are ra-
ther short, although this appears to be a feature com-
mon to most of the relatively small number of diosmium
complexes reported [11]. The variations in C–O and
C–C bond distances for the c-pyrone are consistent with

Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
29
Table 1
Common cluster numbering scheme and selected bond lengths (A) and
ꢀ
bond angles (°) for 2a, 2b and 2d
2a
2b
2d
ꢀ
Bond length (A)
Os(1)–Os(2)
Os(1)–C(3)
Os(2)–O(4)
Os(1)–C(31)
Os(1)–C(32)
Os(2)–C(31)
O(1)–C(6)
O(1)–C(2)
O(4)–C(4)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(31)–C(32)
2.76411(19)
2.167(3)
2.112(2)
2.358(3)
2.343(3)
2.112(3)
1.340(4)
1.366(4)
1.272(4)
1.347(4)
1.445(4)
1.426(5)
1.335(5)
1.393(5)
2.7723(6)
2.163(12)
2.111(8)
2.7732(3)
2.152(5)
2.132(4)
2.327(5)
2.333(4)
2.229(5)
1.314(7)
1.348(7)
1.283(7)
1.355(7)
1.447(7)
1.412(8)
1.350(9)
1.368(7)
2.286(10)
2.423(12)
2.087(11)
1.310(17)
1.347(15)
1.285(13)
1.326(17)
1.423(17)
1.434(17)
1.339(19)
1.309(17)
Fig. 5. ORTEP diagram (50% probability thermal ellipsoids; aromatic
ꢀ
and pyrone hydrogens omitted) and selected bond lengths (A) and
angles (°) of 3b. Os(1)–Os(2) ¼ 2.9855(4); Os(2)–Os(3) ¼ 2.8805(4);
Os(1)–C(41) ¼ 2.113(6); Os(1)–C(44) ¼ 2.140(8); Os(2)–O(4) ¼ 2.144(5);
Os(2)–C(41) ¼ 2.220(6);
Os(2)–C(42) ¼ 2.457(7);
Os(3)–C(3) ¼
2.141(7); O(1)–C(6)¼1.330(9); O(1)–C(2)¼1.362(10); O(4)–C(4)¼1.274(9);
C(2)–C(3)¼1.364(10); C(3)–C(4)¼1.429(10); C(4)–C(5)¼1.428(10);
C(5)–C(6)¼1.315(11); Os(3)–Os(2)–Os(1)¼109.914(11); O(4)–Os(2)–
Os(3)¼83.48(14); C(3)–Os(3)–Os(2)¼82.8(2).
As 1 is stable both photochemically and thermally, it
would appear that formation of the dinuclear com-
pounds 2 occurs via fragmentation of a trinuclear cluster
in which the alkyne has already been incorporated. That
such an intermediate species is plausible is exemplified
Bond angle (°)
O(4)–Os(2)–Os(1)
C(3)–Os(1)–Os(2)
85.16(6)
82.98(8)
86.1(2)
83.7(3)
84.88(10)
83.39(14)
t
retention of the pyrone character of that ligand, while
ꢀ
the C(31)–C(32) distances (1.309(17)–1.393(5) A) sug-
by the reaction with BuCCMe, for which the trinuclear
cluster Os3(CO)8(l-CO)(l-c-C5H3O2)(tBuCHCHCH2)
(9) was also isolated from the photochemical reaction, in
8% yield. From the same reaction was also isolated a
trace amount of Os3(CO)12, and two unidentified com-
plexes A and B; the latter decomposed during attempts
at TLC separation. Similar products were obtained
when the irradiation was carried out with UV light.
The spectroscopic data assignable to A suggests that
it is a carbonyl cluster containing c-pyrone and an allyl
group. The carbonyl ligands are indicated in the IR
spectrum; the c-pyrone is indicated in the 1H resonances
comprising of a singlet and two doublets at d 7.99 ppm
(1H), 7.67 ppm (1H) and 6.06 ppm (1H), corresponding
to H2, H6 and H5, respectively, and the allyl group by
three doublets and a doublet of triplets at d 6.06 ppm
(1H), 3.53 ppm (1H), 2.96 ppm (1H) and 4.71 ppm (1H),
gest that the alkyne bond order has been reduced to
somewhere between that of a C–C single and a C@C
double bond [12]. As has already been observed for 1 [3],
the carbonyl ligand trans to the O-donor atom of the
pyrone is closer to the Os, consistent with an increase in
p-back bonding into the carbonyl; this is also true for
clusters 3.
Clusters 3a and 3b have a bent triosmium chain, and
like 2, they also differ in the relative orientation of the
alkyne and pyrone ligands; the ORTEP diagram of 3b,
together with selected bond parameters, is given in
Fig. 5.
As can be clearly discerned, a phenyl ring of the al-
kynes is orthometallated; in 3a, the orthometallated ring
is on the same side of the triosmium plane as the pyrone,
while in 3b, it is on the opposite side. As may be ex-
pected, this imposes steric strains in 3a, which is mani-
fested in the twisting of the pyrone ring w.r.t the Os–Os
bond which it bridges; the torsion angle between the
pyrone and this Os–Os edge (C(4)C(3)Os(3)Os(1)) is
26.5° compared to 12.2° (for C(4)C(3)Os(3)Os(2)) in 3b.
Interestingly, the two C(alkyne) to central Os bond
lengths are very different for 3b (2.220(6) and 2.457(7)
t
corresponding to the allylic hydrogens BuCHCHCH2,
t
t
tBuCHCHCH H, BuCHCHCHH and BuCHCHCH2,
respectively, as well as a singlet at d 1.15 ppm (9H) for
the t-butyl group.
The structure of 9 has been characterised by an X-ray
cystallographic study; the ORTEP diagram is presented
in Fig. 6, together with selected bond parameters.
Cluster 9 contains an allyl ligand, presumably formed
via migration of the metal hydride onto the alkyne;
ꢀ
A), while that for 3a are more equal.

30
Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
ꢀ
Fig. 6. ORTEP diagram (50% probability thermal ellipsoids; aromatic hydrogens omitted) and selected bond lengths (A) and angles (°) of 9. Os(1)–
Os(2) ¼ 2.8863(4); Os(1)–Os(3) ¼ 2.8543(4); Os(2)–Os(3) ¼ 2.8559(4); Os(1)–C(12) ¼ 1.854(7); Os(1)–C(11) ¼ 1.893(7); Os(1)–O(4) ¼ 2.124(5);
Os(1)–C(13) ¼ 2.248(7); Os(1)–C(14) ¼ 2.260(7); Os(1)–C(15) ¼ 2.312(7); Os(3)–C(3) ¼ 2.129(7); Os(3)–C(11) ¼ 2.605(7); O(1)–C(6) ¼ 1.326(10);
O(1)–C(2) ¼ 1.368(9); O(4)–C(4) ¼ 1.262(8); C(13)–C(14) ¼ 1.385(9); C(14)–C(15) ¼ 1.394(10); C(15)–C(16) ¼ 1.543(10); C(2)–C(3) ¼ 1.355(10); C(3)–
C(4) ¼ 1.440(10); C(4)–C(5) ¼ 1.437(9); C(5)–C(6) ¼ 1.353(11); Os(3)–Os(1)–Os(2) ¼ 59.666(9); Os(3)–Os(2)–Os(1) ¼ 59.610(9); Os(1)–Os(3)–
Os(2) ¼ 60.723(9); O(4)–Os(1)–Os(3) ¼ 83.93(13); C(3)–Os(3)–Os(1) ¼ 83.0(2).
carrying out the photochemical reaction in the presence
of H2 gave a similar yield of 9. Although allyl-substi-
tuted triosmium clusters are well documented, those
with the allyl ligand coordinated to only one osmium
centre are rare; the only examples reported so far are the
linear clusters Os3Br(CO)10(NCR)(g3-C3H5) (R ¼ Pr,
PhCH2CH2) [13], and the cationic, triangular cluster
[Os3(CO)11(g3- C3H5)]þBFꢁ4 [14]. Another striking fea-
ture of 9 is the presence of a semi-bridging carbonyl
1H NMR of the irradiation of a CDCl3 solution of 9
showed that unknown B was formed, but not A, C nor
2c, thus ruling out cluster 9 as a precursor to A, C or 2c.
3. Conclusion
The reactions of cluster 1 with various alkynes show a
tendency towards metal–metal bond scission. Photo-
chemical activation appears to lead generally to reten-
tion of the pyrone ligand with metal–metal bond
scission, resulting in the formation of dinuclear or tri-
nuclear chain products. On the other hand, the thermal
reactions are more varied, ranging from no reaction to
affording similar dinuclear products as the photochem-
ical reaction. In the case of PhCCPh, however, cleavage
of the c-pyrone from the cluster is favoured. Further-
more, we have not observed any change in bonding
mode of, or reaction directly involving, the pyrone.
These are in contrast to the reactivities observed for the
clusters containing N-donor bridging ligands, such as
the imidoyl or iminium systems.
ꢀ
(Os(1)–C(11) ¼ 1.893(7) A and Os(3)–C(11) ¼ 2.605(7)
ꢀ
A), an uncommon feature among osmium clusters.
Semi-bridging carbonyl groups are better p-acceptors
than terminal carbonyls [15]; the strongly electron do-
nating allyl group may be responsible for the adoption
of a semi-bridging carbonyl in 9.
That 9 is formed only photochemically and not
thermally is corroborated by the observation that the
t
reaction between 1 and BuCCMe carried out at 110 °C
for 16 h resulted in the formation of 2c (56%), a trace
amount of Os3(CO)12, and a low yield of another un-
identified product C. Although the structure of C has
not been determined, its IR spectroscopic data suggests
a cluster compound. Its 1H NMR spectrum contains
three doublets and a doublet of triplets at d 3.78 ppm
(1H), 3.70 ppm (1H), 2.23 ppm (1H) and 5.17 ppm (1H),
assignable to the allylic hydrogens tBuCHCHCH2,
4. Experimental
t
t
tBuCHCHCHH, BuCHCHCHH and BuCHCHCH2,
respectively, and a singlet at d 1.23 ppm (9H) assignable
to the t-butyl group. These resonances, together with the
absence of any resonances assignable to a pyrone, sug-
gest that it is an alkyne carbonyl cluster. Monitoring by
4.1. General procedures
All reactions and manipulations were carried out
under nitrogen by using standard Schlenk techniques.
Solvents were purified, dried, distilled and stored under

Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
31
nitrogen prior to use. IR spectra were recorded as hex-
ane solutions unless otherwise stated. NMR spectra
were recorded on a Bruker ACF-300 FT-NMR spec-
trometer as CDCl3 solutions unless otherwise stated. 1H
chemical shifts reported are referenced against the re-
sidual proton signals of the solvents. ESI spectra were
obtained on a Finnigan MAT LCQ, with a spray volt-
age of 4.5 kV and capillary temperature of 353 K, as
CH3CN solutions. FAB mass spectra were recorded on
a Finnigan MAT 95XL-T Mass Spectrometer in an m-
nitrobenzyl alcohol matrix. EI spectra were obtained on
a Macromass VG7035, at 70 eV. Microanalyses were
carried out by the microanalytical laboratory at the
National University of Singapore. The preparation of
Os3(CO)10(l-H)(c-C5H3O2) (1) has been described pre-
viously [3]. The cluster Os3(CO)10(NCCH3)2 was pre-
pared according to a literature method [16]. All other
reagents were from commercial sources and used as
supplied. TLC separations were on silica plates of 0.25
or 0.5 mm thickness and extracted with dichlorome-
thane. In photochemical reactions, irradiation with vis-
ible light was performed with an OSRAM or a
Tungsraflex 60 W lamp. NMR-scale experiments were
carried out in an NMR tube fitted with a Teflon valve,
purchased from Kontes.
H60), 7.35 (2H, t, H30 and H50), 7.25 (1H, d, H300), 7.19
(1H, t, H40), 7.00 (1H, d, H600), 6.84 (1H, t, H500), 6.74
(1H, t, H400), 4.99 (1H, d, H6), 4.15 (1H, s, ¼ CH), )13.3
(1H, s, OsHOs). Calc. for C28H14O11Os3: C, 30.65; H,
1.29. Found: C, 30.59; H, 1.28%.
A similar reaction of 1 (21.8 mg, 0.023 mmol) with
PhCBCPh (20.5 mg, 0.11 mmol) in cyclohexane at 10 °C
for 44 h gave unreacted 1 (1.9 mg) and 3a (3.0 mg, 12%).
t
4.2.2. With BuCBCH
A similar reaction of 1 (42.6 mg, 0.045 mmol) with
tBuCBCH (5 drops) in CH2Cl2 (5 ml) for 3 d, followed
by a similar work up, gave colourless crystals of
Os2(CO)6(l-c-C5H3O2)(l-tBuCHCH) (2b) (Rf ¼ 0:35,
yield 20.0 mg, 61%). IR mCO 2081m, 2046s, 2003vs,
1
1986w, 1971w, 1965m(sh); H NMR d 7.85 (1H, s, H2),
3
7.71 (1H, d, J56 ¼ 5:2 Hz, H6), 6.42 (1H, d, H5), 4.97
3
(1H, d, JHH ¼ 15 Hz, tBuCHCH), 3.33 (1H, d,
t
tBuCHCH), 1.09 (9H, s, Bu). Calc. for C17H14O8Os3:
C, 28.10; H, 1.94. Found: C, 28.19; H, 2.02%.
4.2.3. With PhCBCH
A similar reaction of 1 (46.4 mg, 0.049 mmol) with
PhCBCH (8 drops) in hexane (25 ml) for 3 d gave, after
work up, unreacted 1 (Rf ¼ 0:45, 27.0 mg) and yellow
Os3(CO)9(l-H)(l-c-C5H3O2)(l-HCCHC6H4) (3b) (Rf ¼
0:24, yield 2.6 mg, 5.2%). IR mCO 2121m, 2077m, 2047m,
4.2. Photochemical reactions of 1
1
2035vs, 2018m, 2003s, 1993m(sh), 1958m; H NMR d
4.2.1. With PhCBCPh
7.95 (1H, s, H2), 7.77 (1H, d, 3J56 ¼ 5:4 Hz, H6), 6.7–6.9
(4H, m, aromatic), 6.26 (1H, d, H5), 4.07 (1H, s,@CH),
)12.4 (1H, s, OsHOs). Calc. for C22H10O11Os3: C,
25.88; H, 0.99. Found: C, 26.12; H, 0.88%.
A solution of 1 (22.0 mg, 0.023 mmol) and PhCBCPh
(42.0 mg, 0.24 mmol) in cyclohexane (16 ml) was placed
in a Carius tube, degassed by three freeze–pump–thaw
cycles and irradiated with visible light at 35 °C for 2 d.
The solvent was removed under reduced pressure and the
residue chromatographed on silica TLC plates. Elution
with hexane/CH2Cl2 (4/1, v/v) gave four major bands.
Band 1 (Rf ¼ 0:54) gave red crystalline samples of the
known cluster Os3(CO)8(PhCCPh)2 (4) (1.7 mg, 6.4
mmol) as identified by its IR spectrum [6].
Band 2 (Rf ¼ 0:46) gave purple crystalline samples of
Os3(CO)9(PhCCPh)2 (5) (2.7 mg, 10%): IR mCO 2114m,
2058vs, 2043s, 2036m(sh), 2012s, 1999m, 1988w(sh),
1974m, 1930m (lit.: [7] 2113m, 2057vs, 2042s, 2037sh,
2011s, 1998m, 1990sh, 1972m).
Band 3 (Rf ¼ 0:27) gave pale yellow crystalline
Os2(CO)6(l-c-C5H3O2)(l-PhCCHPh) (2a) (5.7 mg, 30%):
IR mCO 2079m, 2062vw, 2047s, 2000s, 2000s, 1990m(sh),
1972m, 1964w(sh); 1H NMR d 8.17 (1H, s, H2), 7.83 (1H,
d, 3J56 ¼ 5:0 Hz, H6), 7.3–6.9 (10H, m, phenyl), 6.33 (1H,
d, H5), 4.15 (1H, s, @CH). Calc. for C25H14O8Os2: C,
36.49; H, 1.71. Found: C, 36.81; H, 1.63%.
t
4.2.4. With BuCBCMe
A similar reaction of 1 (38.6 mg, 0.041 mmol) with
tBuCBCMe (0.2 ml) in CH2Cl2 for 6 h gave, after
workup, a trace amount of Os3(CO)12 (identified by its
IR spectrum), an unstable compound B which decom-
posed during the TLC separation (as judged spectro-
scopically), and the following three bands:
Band 1 (Rf ¼ 0:60) gave red crystalline Os3(CO)8(l-
CO)(l-c-C5H3O2)(tBuCHCHCH2) (9) (3.3 mg, 8.0%): IR
mCO 2093m, 2047vs, 2017vs, 2002s, 1991m, 1984m(sh),
1967w; 1H NMR d 7.93 (1H, s, H2), 7.62 (1H, d, 3J56 ¼ 5:0
3
Hz, H6), 6.11 (1H, d, H5), 5.10 (1H, d, JHH ¼ 7:4 Hz,
3
t
tBuCHCHCH2), 4.86 (1H, dt, JHH ¼ 12 Hz, BuCHC
t
t
HCH2), 3.56 (2H, d, BuCHCHCH2), 1.34 (9H, s, Bu).
FAB-MS m=z 1015.9 [M]þ. Exact mass fragments at
1014.943, 1015.947 and 1016.947 matched C21H16O11Os3.
Band 2 (Rf ¼ 0:52) gave a yellow compound A, which
could not be completely separated from 2c. IR mCO 2095m,
1
Band
4
(Rf ¼ 0:16) gave yellow crystalline
2077w, 2023w, 2014s, 1992s, 1982m, 1966w, 1928m; H
NMR d 7.99 (1H, s, H2), 7.67 (1H, d, 3J56 ¼ 5:8 Hz, H6),
Os3(CO)9(l-H)(l-c-C5H3O2)(l-PhCCHC6H4) (3a) (2.2
mg, 9%): IR mCO 2111m, 2078m, 2044m, 2034vs, 2020m,
3
6.06 (1H, d, H5), 4.72 (1H, dt, JHH ¼ 7:4, 12 Hz,
1
2005s, 1996m(sh), 1960w; H NMR d 7.67 (1H, s, H3),
tBuCHCHCH2), 3.53 (1H, d, tBuCHCHCH2), 2.96 (2H,
d, tBuCHCHCH2), 1.15 (9H, s, tBu).
7.64 (1H, d, J56 ¼ 5:4 Hz, H5), 7.81 (2H, d, H20 and
3

32
Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
1
Band
3
(Rf ¼ 0:49) light yellow Os2(CO)6(l-c-
1960w(sh); H NMR d 8.12 (1H, s, H2), 7.78 (1H, d,
3J56 ¼ 5:0 Hz, H6), 6.18 (1H, d, H5), 3.1 (2H, m, CH2),
2.84 (1H, m, CH), 2.5 (1H, m, CHH), 2.1 (1H, m,
C5H3O2)(l-tBuCHCMe) (2c) (16.6 mg, 55%): IR mCO
2077m, 2043s, 1998s, 1989w(sh), 1982m, 1974m, 1966m;
1H NMR d 8.11 (1H, s, H2), 7.77 (1H, d, 3J56 ¼ 5:0 Hz,
H6), 6.18 (1H, d, H5), 3.38 (3H, s, Me), 2.97 (1H, s,
3
CHH), 1.40 (3H, t, JHH ¼ 7:4 Hz, CH3), 1.02 (3H, t,
CH3). FAB-MS ðm=zÞ 728 [M]þ, 698 [M ) CO]þ, 670
[M ) 2CO]þ, 644 [M ) 3CO]þ, 614 [M ) 4CO]þ, 584
[M ) 5CO]þ, 556 [M ) 6CO]þ. Calc. for C17H14O8Os2:
C, 28.10; H, 1.94. Found: C, 28.85; H, 2.08%.
tBuCH), 1.15 (9H, s, Bu). FAB-MS m=z 742 [M]þ, 713
t
[M ) CO]þ, 686 [M ) 2CO]þ, 656 [M ) 3CO]þ, 627
[M ) 4CO]þ, 600, [M ) 5CO]þ.
t
4.3. Thermal reactions of 1
4.3.3. With BuCBCMe
A similar reaction of 1 (27.3 mg, 0.029 mmol) and
EtCBCEt (0.05 mL) gave, after workup as above, a
trace amount of Os3(CO)12 (2c) (12.0 mg, 56%), and an
unidentified yellow compound C (Rf ¼ 0:05, yield 1.1
mg): IR mCO 2099m, 20772s, 2062m, 2051m, 2043w,
2026s, 2004s, 1988s, 1972w(sh); 1H NMR d 5.17 (1H, dt,
3JHH ¼ 7:0, 12 Hz, tBuCHCHCH2), 3.78 (1H, d,
3JHH ¼ 6:6 Hz, tBuCHCHCH2), 3.70 (1H, d, tBuC-
4.3.1. With PhCBCPh
A solution of 1 (29.5 mg, 0.031 mmol) and PhCBCPh
(11.1 mg, 0.062 mmol) in cyclohexane (10 ml) was
placed in a Carius tube and degassed by three freeze–
pump–thaw cycles. After being heated at 100 °C for 44
h, the solvent was removed under reduced pressure and
the residue re-dissolved in the minimum volume of di-
chloromethane for chromatographic separation on TLC
plates to afford five bands.
t
HCHCHH), 2.23 (1H, d, BuCHCHCHH), 1.23 (9H, s,
tBu).
Band 1 (Rf ¼ 0:68) gave red crystalline 4 (yield 3.8
mg, 11%) which was identified spectroscopically [6].
Band 2 (Rf ¼ 0:58) gave red crystalline samples of the
previously reported compound Os3(CO)8(l-H)(l-
PhCCPhCPhCC6H4) (6) (6.5 mg, 18%): IR mCO 2095m,
2057m, 2033s, 2019w, 2011w(sh), 1996w, 1988vw(sh),
1976w. (Lit.: [7] (CCl4) 2096s, 2058s, 2033vs, 2020m,
2012m, 1997m, 1990sh, 1977m); 1H NMR d 7.9–5.8
(16H, m, aromatic), )14.9 (1H, s, OsHOs).
4.4. Reaction of Os3(CO)10 (NCCH3)2 with PhCBCPh
A solution of Os3(CO)10(NCCH3)2 (32.4 mg, 0.035
mmol) and PhCBCPh (6.2 mg, 0.035 mmol) in CH2Cl2
(15 ml) was degassed in a Carius tube by three freeze–
pump–thaw cycles and then stirred at RT for 13 h.
Chromatographic separation by TLC with hexane/
CH2Cl2 (4/1, v/v) as the mobile phase gave yellow 4
(Rf ¼ 0:52, yield 1.6 mg, 4.0%) [6] and dark purple
crystalline 5 (Rf ¼ 0:47, yield 13.3 mg, 32%) [7], both
identified by their IR spectra.
Band 3 (Rf ¼ 0:36) gave unreacted 1 (9.1 mg), iden-
tified spectroscopically.
Band 4 (Rf ¼ 0:22) gave red crystalline Os3(CO)8(l-
PhCCPh)(l-PhCCHC6H4) (7) (13.2 mg, 37%): IR mCO
2087s, 2056vs, 2025s, 2013s, 2002w, 2000w, 1977s,
1968m(sh); (CH2Cl2): 2089s, 2052s, 2025m, 2015m(sh),
1996w(sh), 1965m(br), 1908vw(br); 1H NMR d (CD2Cl2):
7.7–6.5 (m, aromatic). Calc. for C36H20-O8Os3: C, 37.56;
H, 1.75. Found: C, 37.32; H, 2.02%.
4.5. Crystal structure determinations
Crystals were grown from dichloromethane (or di-
bromomethane)/hexane solutions and mounted on
quartz fibres. X-ray data were collected on a Bruker
AXS APEX system, using Mo Ka radiation, with the
SMART suite of programs [19]. Data were processed and
corrected for Lorentz and polarisation effects with
SAINT [20], and for absorption effects with SADABS
[21]. Structural solution and refinement were carried out
with the SHELXTL suite of programs [22]. Crystal and
refinement data are summarised in Tables 2 and 3.
The structures were solved by direct methods to lo-
cate the heavy atoms, followed by difference maps for
the light, non-hydrogen atoms. Organic hydrogens were
placed in calculated positions, except for 2a and 3a in
which the H on the alkyne was located in the difference
map. All non-hydrogen atoms were generally given an-
isotropic displacement parameters in the final model
(but see below). Metal hydrides were placed in positions
calculated with XHYDEX [23] and refined with a fixed
isotropic thermal parameter and riding on one of the
osmium atoms it is attached to.
Band 5 (Rf ꢂ 0) gave colourless crystals of hexaphe-
1
nylbenzene, identified by H NMR and EI-MS [17].
A second set of the same reaction under similar
conditions afforded, in addition to the above, also trace
amounts of 5 and the previously reported compound
Os3(CO)7(PhCCPh)3 (8) [18], both identified spectro-
scopically.
4.3.2. With EtCBCEt
A solution of 1 (14.9 mg, 0.016 mmol) and EtCBCEt
(0.05 ml) in CDCl3 was prepared in an NMR tube fitted
with a Teflon valve and degassed by three freeze–pump–
thaw cycles. This was then heated at 110 °C for 16 h.
TLC separation with hexane/CH2Cl2 (4/1, v/v) as the
mobile phase afforded one major band (Rf ¼ 0:50) from
which light yellow crystalline Os2(CO)6(l-c-C5H3O2)(l-
EtCCHEt) (2d) (10.0 mg, 85%) was obtained: IR mCO
2078m, 2044s, 1998s, 1989w(sh), 1983m, 1975m, 1967m,

Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
33
Table 2
Crystal data for clusters 2a, 2b, 2d, 3a and 3b
Compound code
2a
2b
2d
3a
3b
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C25H14O8Os2
822.76
173(2)
C17H14O8Os2
726.68
223(2)
C17H14O8Os2
726.68
223(2)
C28H14O11Os3
1096.99
223(2)
C22H10O11Os3
1020.90
223(2)
Triclinic
ꢁ
Monoclinic
P21=n
9.2600(14)
13.5435(19)
15.333(2)
90
Triclinic
ꢁ
Monoclinic
P21=c
9.5336(4)
32.3465(15)
9.0914(4)
90
Triclinic
ꢁ
P1
P1
P1
ꢀ
a (A)
10.2401(4)
10.3457(4)
11.6577(5)
98.747(1)
94.815(1)
108.529(1)
1145.80(8)
2
9.4835(2)
9.5843(2)
10.9083(2)
80.941(1)
78.699(1)
87.297(1)
960.00(3)
2
8.9921(2)
10.8710(3)
12.8541(3)
102.237(1)
100.493(1)
97.515(1)
1188.54(5)
2
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
95.696(3)
90
101.575(1)
90
3
ꢀ
Volume (A )
1913.4(5)
4
2.523
2746.6(2)
4
2.653
Z
Density (calculated) (mg/m3)
Absorption coefficient (mmꢁ1
F ð000Þ
2.385
11.129
760
2.514
13.263
664
2.853
16.056
916
)
13.309
1328
13.907
1992
Crystal size (mm3)
0.32 ꢃ 0.18 ꢃ 0.16
2.11 to 31.46
18320
0.04 ꢃ 0.16 ꢃ 0.28
2.01 to 25.03
13023
0.32 ꢃ 0.28 ꢃ 0.15
1.93 to 29.34
7832
0.12 ꢃ 0.16 ꢃ 0.17
2.18 to 30.50
22502
0.18 ꢃ 0.26 ꢃ 0.28
2.23 to 29.97
10886
Theta range for data collection (°)
Reflections collected
Independent reflections
7023
3377
4650
8122
6585
[Rint ¼ 0:0366]
92.5 (31.46)
0.267 and 0.148
[Rint ¼ 0:0724]
100.0 (25.03)
0.496 and 0.212
[Rint ¼ 0:0302]
88.6 (29.34)
0.241 and 0.101
[Rint ¼ 0:0519]
96.9 (30.50)
0.266 and 0.175
[Rint ¼ 0:0284]
95.3 (29.97)
0.141 and 0.072
Completeness (%) (to theta (°))
Maximum and minimum
transmission
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices [I > 2rðIÞ]
7023/0/320
0.934
3377/0/247
1.015
4650/0/246
1.077
8122/0/382
0.894
6585/0/325
0.955
R1 ¼ 0:0227,
wR2 ¼ 0:0459
R1 ¼ 0:0285,
wR2 ¼ 0:0468
1.247 and )1.007
R1 ¼ 0:0493,
wR2 ¼ 0:1224
R1 ¼ 0:0583,
wR2 ¼ 0:1276
4.005 and )2.021
R1 ¼ 0:0276,
wR2 ¼ 0:0726
R1 ¼ 0:0311,
wR2 ¼ 0:0743
1.992 and )1.945
R1 ¼ 0:0361,
wR2 ¼ 0:0663
R1 ¼ 0:0531,
wR2 ¼ 0:0703
1.875 and )0.924
R1 ¼ 0:0375,
wR2 ¼ 0:0794
R1 ¼ 0:0472,
wR2 ¼ 0:0821
1.835 and )2.196
R indices (all data)
Largest difference peak and hole
ꢁ3
ꢀ
(e A
)
Table 3
Crystal data for clusters 6, 7 and 9
Compound code
6
7
9
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C36H20O8Os3.CH2Cl2
1236.05
223(2)
C36H20O8Os3
1151.12
193(2)
C21H16O11Os3
1014.94
223(2)
Monoclinic
P21=c
a ¼ 9:0099ð2Þ
b ¼ 22:1015ð5Þ
c ¼ 12:8932ð3Þ
b ¼ 106:773ð1Þ
2458.22(10)
4
Monoclinic
P21=n
Monoclinic
P21=n
ꢀ
a (A)
a ¼ 17:9706ð10Þ
b ¼ 8:9568ð5Þ
c ¼ 23:4649ð12Þ
b ¼ 106:479ð1Þ
3621.7(3)
a ¼ 10:7830ð6Þ
b ¼ 17:0255ð9Þ
c ¼ 17:8035ð9Þ
b ¼ 100:588ð1Þ
3212.8(3)
ꢀ
b (A)
ꢀ
c (A)
b (°)
Volume (A )
3
ꢀ
Z
4
2.267
4
2.380
Density (calculated) (mg/m3)
2.742
15.525
1832
Absorption coefficient (mmꢁ1
)
10.697
2280
11.888
2112
F ð000Þ
Crystal size (mm3)
0.40 ꢃ 0.30 ꢃ 0.28
2.36 to 30.57
31182
0.40 ꢃ 0.30 ꢃ 0.28
1.67 to 31.01
27361
0.24 ꢃ 0.17 ꢃ 0.08
2.36 to 30.01
21065
Theta range for data collection (°)
Reflections collected
Independent reflections
10872 [Rint ¼ 0:0327]
97.9 (30.57)
0.156 and 0.083
10,872/16/453
0.969
9817 [Rint ¼ 0:0394]
95.8 (31.01)
0.124 and 0.059
9817/0/424
6996 [Rint ¼ 0:0725]
97.6 (30.01)
0.336 and 0.163
6996/0/319
Completeness (%) (to theta (°))
Maximum and minimum transmission
Data/restraints/parameters
Goodness-of-fit on F 2
1.003
0.872
Final R indices [I > 2rðIÞ]
R1 ¼ 0:0318, wR2 ¼ 0:0678
R1 ¼ 0:0438, wR2 ¼ 0:0700
1.808 and )1.271
R1 ¼ 0:0303, wR2 ¼ 0:0679
R1 ¼ 0:0390, wR2 ¼ 0:0698
1.995 and )1.305
R1 ¼ 0:0377, wR2 ¼ 0:0697
R1 ¼ 0:0546, wR2 ¼ 0:0733
1.812 and )2.844
R indices (all data)
Largest difference peak and hole (e A
ꢁ3
ꢀ
)

34
Q. Lin et al. / Journal of Organometallic Chemistry 689 (2004) 25–34
[6] B.F.G. Johnson, R. Khattar, F.J. Lahoz, J. Lewis, P.R. Raithby,
J. Organomet. Chem. 319 (1987) C51.
A CH2Cl2 solvent molecule was found in 6. This was
modelled as disordered over three sites, with the occu-
pancies summed to 1.0. The carbon and chlorine atoms
were given a common isotropic thermal parameter each,
and the C–Cl distances restrained to be the same.
[7] (a) O. Gambino, G.A. Vaglio, R.P. Ferrari, G. Cetini,
J. Organomet. Chem. 30 (1971) 381;
(b) G. Ferraris, G. Gervasio, J. Chem. Soc., Dalton Trans. (1974)
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5. Supplementary material
(b) R.P. Ferrari, G.A. Vaglio, Trans. Metal Chem. 8 (1983)
155.
Crystallographic data (excluding structure factors)
for the structures in this paper have been deposited with
the Cambridge Crystallographic Data Centre as sup-
plementary publication numbers CCDC 217214–
217221. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44 1223 336033 or
e-mail: deposit@ccdc.cam.ac.uk).
[9] (a) M.R. Burke, T. Funk, J. Takats, V.W. Day, Organometallics
13 (1994) 2109;
(b) M.R. Burke, J. Takats, J. Organomet. Chem. 302 (1986) C25.
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Chim. Acta 12 (1975) 155;
(b) R.P. Ferrari, G.A. Vaglio, Gazz. Chim. Ital. 105 (1975)
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[11] (a) A.W. Herlinger, A.L. Rheingold, Acta Cryst. Sect. C C53
(1997) 285;
(b) N. Spetseris, J.R. Norton, C.D. Rithner, Organometallics 14
(1995) 603;
Acknowledgements
(c) A.A. Cherkas, N. Hadj-Bagheri, A.J. Carty, E. Sappa, M.A.
Pellinghelli, A. Tiripicchio, Organometallics 9 (1990) 1887;
(d) A.J. Deeming, N.P. Randle, M.B. Hursthouse, R.L. Short,
J. Chem. Soc., Dalton Trans. (1987) 2473;
This work was supported by the National University of
Singapore (Research Grant No. RP 010172) and one of us
(Q.L.) thanks the University for a Research Scholarship.
(e) A.A. Cherkas, A.J. Carty, E. Sappa, M.A. Pellinghelli, A.
Tiripicchio, Inorg. Chem. 26 (1987) 3201;
(f) G.L. Geoffroy, S. Rosenberg, A.W. Herlinger, A.L. Rhein-
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[1] (a) See for example S.E. Kabir, E. Rosenberg, L. Milone, R.
Gobetto, D. Osella, M. Ravera, T. McPhillips, M.W. Day, D. Carlot,
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