Reactivity of IrCl(PPh3)3 with diphenylacetylene - A direct route to 1-iridaindene

Article abstract of DOI:10.1139/V08-119

The 1-iridaindene complex, Ir[C₈H₅(Ph-2)]Cl(PPh ₃)₂ (2), has been prepared from the reaction of IrCl(PPh₃)₃ with PhC≡CPh by a novel direct cycloiridation reaction. A plausible mechanistic p

Full text of DOI:10.1139/V08-119

183
Reactivity of IrCl(PPh3)3 with diphenylacetylene —
A direct route to 1-iridaindene1
Joyanta Choudhury, Sanjay Pratihar, Arnab Kumar Maity, and Sujit Roy
Abstract: The 1-iridaindene complex, Ir[C8H5(Ph-2)]Cl(PPh3)2 (2), has been prepared from the reaction of IrCl(PPh3)3
with PhCϵCPh by a novel direct cycloiridation reaction. A plausible mechanistic pathway has been suggested involving
π-coordination assisted ortho- C–H activation and subsequent alkyne hydroiridation reaction to provide the five-member
iridacycle.
Key words: iridium, diphenylacetylene, C–H activation, cyclometallation, metallacycle.
Résumé : On a préparé le complexe du 1-iridaindène, Ir[C8H5(ph-2)]Cl(PPh3)2 (2), par réaction du IrCl(PPh3)3 avec le
PhCϵCPh par une nouvelle réaction de cycloiridation directe. On propose une voie mécanistique plausible impliquant
une activation du C–H en ortho qui serait assistée par une coordination π et qui serait suivie par une réaction
d’hydroiridation de l’alcyne conduisant à la formation de l’iridacycle à cinq chaînons.
Mots-clés : iridium, diphénylacétylène, activation d’une liaison C–H, cyclométallation, métallacycle.
[Traduit par la Rédaction] Choudhury et al. 187
Introduction
cently, Wright and co-workers (30) reported a transmetalla-
tion route for the synthesis of a substituted 1-iridaindene
Ir[C8H5(Ph-3)]Cl(PPh3)2 (1) from the corresponding organo-
mercury compound Hg(CH=CPh2)2 and IrHCl2(PPh3)3
(Scheme 1a). Earlier, they isolated 1 as a side product from
the reaction of Hg(CH=CPh2)2 and IrCl(CS)(PPh3)2 in only
20% yield (Scheme 1b) (31).
Metallacycles are important synthons as well as interme-
diates in many catalytic organic and organometallic
reactions (1–12). Iridaindene motifs can be viewed as
metallacyclopentadienes that are intermediates in metal-
mediated [2+2+2] cyclotrimerization of alkynes to provide
aromatic six-membered rings (13–18). There are also exam-
ples of [2+2+1] cyclotrimerization reactions with the
intermediacy of metallacyclopentadienes (19–25). Moreover,
the metallacyclopentadiene complexes are utilized for the
synthesis of metallabenzenes, which are interesting struc-
tural units, compared with simple aromatics (26–28). To our
knowledge, a direct and unassisted route for the preparation
of such metallacycles by the activation of organic precursors
with appropriate metal complexes is hitherto unknown. The
more common routes involve (i) an indirect transmetallation
method, which commonly uses organomercury compounds
and (ii) carbon monoxide assisted cyclocarbonylation using
alkynes or allenes leading to metallacyclopentadienones.
With specific reference to iridium, an iridaindene complex
Ir[C8H5(Ph-2)](C5H5)(PiPr3) was prepared earlier from
Ir(PhCϵCPh)(C5H5)(PiPr3) via the formation of a vinyl com-
plex Ir(PhC=CHPh)(OCOCF3)(C5H5)(PiPr3) by CF3COOH
and subsequent reaction with NH4PF6 in methanol (29). Re-
Our recent interest in iridium chemistry, particularly on
the activation and coupling of organic functionalities (32–
37) led us to investigate the activation of alkynes. Herein we
report the first example of a direct cycloiridation from the
reaction of IrCl(PPh3)3 with PhCϵCPh, leading to a new air-
stable 1-iridaindene complex, Ir[C8H5(Ph-2)]Cl(PPh3)2 (2).
We also describe the structural characterization of 2 by sin-
gle crystal X-ray diffraction and propose a plausible mecha-
nism involving C–H activation followed by ring closure.
At this point it should be noted that our result is quite in-
teresting because the 16-electron iridium(I) complex
IrCl(PPh3)3 was reported earlier to react with various al-
kynes. With terminal alkynes, the oxidative addition prod-
ucts resulted (38). But in the case of diphenylacetylene, the
π-complex, IrCl(PhCϵCPh)(PPh3)2 (3), was reported to be
1
formed (vide H NMR and IR) with the substitution of one
phosphine ligand (Scheme 2a) (38). The complex 3 was also
synthesized as yellow crystals by the reaction of
IrCl(N2)(PPh3)2 with diphenylacetylene (Scheme 2b) (39).
Received 5 April 2008. Accepted 31 May 2008. Published on
the NRC Research Press Web site at canjchem.nrc.ca on
9 September 2008.
Results and discussion
J. Choudhury, S. Pratihar, A. Kumar Maity and S. Roy.2
Organometallics and Catalysis Laboratory, Chemistry
Department, Indian Institute of Technology, Kharagpur
721302, India.
The reaction of IrCl(PPh3)3 with diphenylacetylene in
refluxing benzene was accompanied by a gradual color
change from yellow to red, which is noticeable to the naked
eye within 4–6 h. Ex-situ UV–vis monitoring of the solution
in benzene showed the appearance of a new peak at 510 nm.
After reflux for 18 h, evaporation of the solvent in vacuum
and subsequent recrystallization of the resulting solid resi-
1This article is part of a Special Issue dedicated to Professor
Richard J. Puddephatt.
2Corresponding author (e-mail: sroy@chem.iitkgp.ernet.in).
Can. J. Chem. 87: 183–187 (2009)
doi:10.1139/V08-119
© 2008 NRC Canada

184
Can. J. Chem. Vol. 87, 2009
Scheme 1.
Fig. 1. ORTEP representation for the molecular structure of
2·CHCl3 (50% thermal ellipsoids). H atoms have been omitted
for clarity. Selected bond lengths (Å) and angles (°): Ir(01)–P(1),
2.349(4); Ir(01)–P(2), 2.341(4); Ir(01)–Cl(01), 2.411(4); Ir(01)–
C(01), 2.00(2); Ir(01)–C(08), 2.035(15); C(06)–C(07), 1.42(3);
C(01)–C(06), 1.40(2); C(07)–C(08), 1.36(3); pP(1)-Ir(01)-P(2),
176.73(16); pCl(01)-Ir(01)-C(01), 133.1(5); pCl(01)-Ir(01)-C(08),
149.6(6); pC(01)-Ir(01)-C(08), 77.3(8).
Scheme 2.
Scheme 3.
due from chloroform/ethanol or dichloromethane/ethanol af-
forded 2 as deep red block-like air-stable crystals, the 1st
crop yield being 45%–65% (Scheme 3).
the phenyl group at the 2 position is slightly tilted away
from the plane. In the five-membered iridacycle, the two Ir–
C bond lengths are 2.00(2) and 2.035(15) Å, which signify
some degree of multiple bond nature instead of single bond
character. The other three C–C bond lengths within this ring
are 1.42(3) Å (C06–C07), 1.40(2) Å (C01–C06), and
1.36(3) Å (C07–C08), indicating little delocalization within
the ring. The two triphenylphosphine ligands are mutually
trans with Ir–P distances of 2.349(4) and 2.341(4) Å. The
Ir–Cl distance is 2.411(4) Å.
To gain some insight into the plausible mechanistic path-
way of this cycloiridation process, the aliquots from a 1:1
reaction mixture of IrCl(PPh3)3 and PhCϵCPh in C6D6 at 30,
60, and 90 °C (oil-bath temperature) were subjected to
1H NMR spectral analysis. The formation of complex 2 was
observed only under reflux conditions, as revealed from the
appearance of new and characteristic peaks at 5.50, 5.84,
5.98, 6.25, and 6.37 ppm due to the iridaindene fragment.
These characteristic peaks were observed at slightly
downfield region in CDCl3 solution of 2 (see the Experimen-
tal section). The temperature effect suggests that sufficient
thermal energy was required for the C–H activation–
cycloiridation to take place.
A plausible route for the formation of 2 is suggested in
Scheme 4, invoking prior dissociation of a phosphine ligand
from IrCl(PPh3)3 in solution, followed by the π coordination
of the alkyne ligand forming the complex A. This proximal
π-alkyne coordination in A adopts one of the alkyne phenyl
rings, such that the iridium center can access the ortho C–H
bond for the purpose of orthometallation. Though alkyne is
less well-known to serve such a role of tethering for
orthometallation, compared with other donor groups such as
carbonyl, halide, or amine (40, 41), recently Hill et al. (42)
The IR spectrum of 2 in KBr discs shows no characteristic
peak for coordinated alkyne. The νCϵC frequency in IR of
2
the known η -alkyne complex 3 appears within 1850–
1865 cm–1 (31, 32). In the 1H NMR spectrum of 2, there is a
clean signature for the resonances of the iridaindene frag-
ment. The sharp singlet at 5.65 ppm is assigned to the reso-
nance of the CH of the five-membered iridacycle. The
remaining four protons of the iridaindene six-membered ring
resonate as an unresolved doublet of doublet at 5.99 ppm
(JH-H= 7.2, 7.6 Hz), a doublet at 6.10 ppm (JH-H = 7.2 Hz),
an apparent triplet at 6.43 ppm (formally doublet of doublet,
JH-H = 7.2, 7.2 Hz), and a doublet at 6.91 ppm (JH-H
=
7.6 Hz), respectively. In the 13C NMR spectrum, the signals
of two carbon atoms bonded to iridium, viz., vinyl-C(Ph)Ir
and aryl-CIr appear as unresolved triplets at 133.9 and
145.9 ppm, respectively. The assignment is made according
to a literature comparison (31). The carbon atoms of the
iridaindene six-membered ring and phenyl substituent of
iridaindene resonate separately as singlets between 120.1
and 133.0 ppm. The 31P NMR signal appears at 22.78 ppm.
A single crystal of 2 suitable for an X-ray diffraction
study was obtained by slow diffusion of ethanol into a chlo-
roform solution of the compound at room temperature. The
solid-state molecular structure of 2 is illustrated in Fig. 1.
The structure contains a CHCl3 molecule as solvent of crys-
tallization. The geometry around the iridium atom is trigonal
bipyramidal with axial phosphines (∠P1-Ir01-P2
=
176.73(16)°), while the equatorial plane is occupied by the
chlorine atom and the two carbon atoms (∠Cl01-Ir01-C01 =
133.1(5)°, ∠Cl01-Ir01-C08 = 149.6(6)°, ∠C01-Ir01-C08 =
77.3(8)°). The iridaindene ring is found to be planar, while
© 2008 NRC Canada

Choudhury et al.
185
2
Scheme 4.
plexes of the type D having a pendent dead η -alkyne moiety
(40). The observation of selective ortho C–H activation may
be due to the driving force of the subsequent ring-closure re-
action to a stable product, whereas the insertion into meta or
para C–H bonds would be reversible.
The possibility of catalysis in the presence of traces of
acid impurity (29) in our reaction mixture was also consid-
ered. We ruled out this possibility because even in the pres-
ence of 1 equiv. of Na2CO3, the reaction of IrCl(PPh3)3 with
diphenylacetylene proceeded well, leading to the formation
of the desired iridacycle 2.
In summary, we have demonstrated here
a direct
cycloiridation reaction leading to an iridaindene molecule
that is poised towards further functionalization of the acti-
vated indene moiety to useful organic end-product(s). A
plausible mechanistic pathway has also been suggested in-
volving π-coordination assisted ortho C–H activation and
subsequent alkyne hydroiridation reaction to provide the
five-membered iridacycle. Work is underway to explore the
generality of the reaction, the reactivity of the iridacycle,
and deducing the mechanism.
Scheme 5.
Experimental
General
All preparations and manipulations have been performed
under a dry, oxygen-free argon atmosphere using standard
vacuum lines and Schlenk techniques. All solvents have
been dried and distilled by standard methods and previously
1
deoxygenated in the vacuum line. H (400 MHz), 13C NMR
(100 MHz), and 31P NMR (162 MHz) spectra were recorded
on Bruker Avance II 400 MHz spectrometer at 300 K.
1
Tetramethylsilane was used as internal reference for H and
13C, while H3PO4 was used as external reference for
31P NMR. FT-IR (4000-500 cm–1; using KBr pellets) spectra
were obtained using a PerkinElmer FTIR Spectrometer
(Spectrum RX-I). UV–vis spectra were recorded in a
Chemito Spectroscan UV 2600 spectrophotometer using
HPLC-grade benzene. Elemental analyses were performed
on PerkinElmer Instruments 2400 Series II CHNS/O Ana-
lyzer. IrCl(PPh3)3 was prepared according to literature pro-
cedure (47). Diphenylacetylene (Lancaster, 99%) either used
directly or after recrystallization from ethanol, yielded iden-
tical results. All other chemicals were obtained commer-
cially and used without further purification.
proposed such a phenomenon during the formation of a
ruthenaindenone complex. Accordingly, in our proposal the
iridium-hydride intermediate B resulting from the ortho C–H
activation then undergoes alkyne hydroiridation to generate
the iridacycle 2. At this stage we cannot rule out another al-
2
ternative mechanism (Scheme 5), involving the η alkyne as
dead-end, with the coordination of iridium to phenyl group
leading to the hypothetical intermediate C. The latter, upon
ortho C–H insertion, would produce intermediate D, which
subsequently converts to the iridacycle 2. Complexes featur-
ing the binding of a phenyl group of diphenylacetylene to
Synthesis and characterization details of 23
2
6
the metal in a η - or η -fashion (as in intermediate C, vide
Scheme 5) have precedents in the literature. Examples from
In a typical example, IrCl(PPh3)3 (0.1 mmol, 101 mg) and
diphenylacetylene (0.3 mmol, 54 mg) were placed in a
Schlenk flask under argon. Following dissolution in dry ben-
zene (3 ml), the solution was refluxed for 18 h. The color of
the solution gradually changed from yellow to deep red. Af-
ter this period, the solvent was removed under vacuum at
300 K, and the resulting solid residue was recrystallized
2
late transition metal complexes include [Os(NH3)5(η -C6H5C
6
ϵCPh)](OTf)2 (43) and [CpRu(η -C6H5CϵCPh)](OTf) (44).
6
Two examples of η -bound diphenylacetylene complexes of
6
early transition metals are [(CO)3Cr(η -C6H5CϵCPh)] (45)
6
and [(CO)3Mo(η -C6H5CϵCPh)] (46). Recently, Legzdins
and co-workers reported the formation of tungsten com-
3 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of Un-
published Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3810. For more in-
formation on obtaining material refer to cisti-icist.nrc-cnrc.gc.ca/cms/unpub_e.shtml. CCDC 652721 contains the crystallographic data for
this manuscript. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2008 NRC Canada

186
Can. J. Chem. Vol. 87, 2009
from chloroform/ethanol to give iridaindene 2 as deep red
block-like crystals (68 mg, 65%), mp 282–284 °C (dec).
UV–vis (benzene) λmax (nm) (ε (mol/L)–1cm–1)): 364
(10 000), 510 (640). IR (KBr, cm–1): 694 (s), 743(s),
1094(s), 1435(s), 1483(s). 1H NMR (400 MHz, CDCl3, ppm)
δ: 7.10–7.57 (m, P(C6H5)3, and 3H′s of C6H5, 33H), 6.96–
7.02 (m, 2H′s of C6H5, 2H), 6.91 (d, JH-H= 7.6 Hz, H05,
References
1. I. Omae. Coord. Chem. Rev. 248, 995 (2004).
2. M. Catellani, G.P. Chiusoli, and M. Costa. J. Organomet.
Chem. 500, 69 (1995).
3. G.P. Chiusoli. J. Mol. Catal. 41, 75 (1987).
4. J. Dehand and M. Pfeffer. Coord. Chem. Rev. 18, 327 (1976).
5. M.E. van der Boom and D. Milstein. Chem. Rev. 103, 1759
(2003).
1H), 6.43 (dd, JH-H= 7.2, 7.2 Hz, H03, 1H), 6.10 (d, JH-H
=
7.2 Hz, H02, 1H), 5.99 (dd, JH-H= 7.2, 7.6 Hz, H04, 1H),
6. V. Ritleng, C. Sirlin, and M. Pfeffer. Chem. Rev. 102, 1731
(2002).
5.65 (s, H07, 1H). 13C{1H} NMR (100 MHz, CDCl3, ppm)
2,4
δ: 127.4 (t, JCP= 5.1 Hz, o-C6H5P), 129.3–129.8 (m, i-
7. G. Dyker. Angew. Chem. Int. Ed. 38, 1698 (1999).
8. P.R. Sharp. J. Organomet. Chem. 683, 288 (2003).
9. J.R. Bleeke. Acc. Chem. Res. 40, 1035 (2007).
10. U. Rosenthal, V.V. Burlakov, M.A. Bach, and T. Beweries.
Chem. Soc. Rev. 36, 719 (2007).
11. C.W. Landorf and M.M. Haley. Angew. Chem. Int. Ed. 45,
3914 (2006).
12. L.J. Wright. Dalton. Trans. 1821 (2006).
13. J.P. Collman, J.W. Kang, W.F. Little, and M.F Sullivan. Inorg.
Chem. 7, 1298 (1968).
3,5
C6H5P and p-C6H5P), 134.9 (t, JCP= 5.1 Hz, m-C6H5P),
120.1, 121.8, 122.1, 126.4, 127.1, 127.8, 133.0 (all singlet
signals are for CH of iridaindene six-membered ring and Ph
2
substituent of iridaindene); 133.9 (unresolved t, JCP=
7.9 Hz, iridaindene C2Ph), 139.5 (s, iridaindene C3H), 144.5
2
(s, quat. C), 145.9 (unresolved t, JCP= 6.9 Hz, iridaindene
1
CIr), 160.3 (s, quat. C). N.B. in H and 13C NMR spectra,
peaks due to the solvated CHCl3 appeared at 7.27 and
77.0 ppm, respectively. 31P NMR (162 MHz, CDCl3, ppm)
δ: 22.78. Anal. calcd. for C50H40ClP2Ir.CHCl3: C 58.35, H
3.94; found: C 57.82, H 4.36.
14. T. Takahashi, Z. Xi, A. Yamazaki, Y. Liu, K. Nakajima, and
M. Kotora. J. Am. Chem. Soc. 120, 1672 (1998).
15. T. Takahashi, R.Y. Tsai, Y. Li, K. Nakajima, and M. Kotora. J.
Am. Chem. Soc. 121, 11093 (1999).
X-ray structure determination of 2·CHCl3
16. R.J. Baxter, G.R. Knox, P.L. Pauson, and M.D. Spicer.
Single crystals of 2 suitable for X-ray diffraction study
were obtained from slow diffusion of ethanol into a solution
of 2 in chloroform or dichloromethane at room temperature.
A suitable deep-red blocklike crystal of the complex 2 ob-
tained from CHCl3/EtOH solution was subjected to an Enraf
Nonius Turbo CAD4 diffractometer with Graphite
monochromated Mo Kα (λ= 0.710 73 Å). Unit cell parame-
ters were obtained from a least-square refinement of 25 re-
flections. The structure was solved by SHELXS-97 and
refined by full-matrix least squares on F2 with SHELXL-97
methods (48, 49). The non-hydrogen atoms were refined
anisotropically. All calculations were performed using
WinGX crystallographic software package (50). Crystallog-
raphic data as well as structure solution and refinement
details for 2: C50H40Cl1P2Ir1.CHCl3; triclinic, P-1; a =
10.3295(15) Å, b = 12.4243(19) Å, c = 17.544(3) Å; α =
94.005(11)°, β = 98.539(13)°, γ = 98.581(12)°; V = 2191.9(6) Å3;
Organometallics, 18, 197 (1999).
17. R. Diercks, B.E. Eaton, S. Gurtzgen, S. Jalisatgi, A.J. Matzger,
R.H. Radde, and K.P.C. Vollhardt. J. Am. Chem. Soc. 120,
8247 (1998).
18. N. Agenet, V. Gandon, K.P.C. Vollhardt, M. Malacria, and C.
Aubert. J. Am. Chem. Soc. 129, 8860 (2007).
19. J.M. O’Connor, K. Hiibner, R. Merwin, P. Gantzel, A.L.
Rheingold, and B.S. Fong. J. Am. Chem. Soc. 119, 3631 (1997).
20. E.S. Johnson, G.J. Balaich, P.E. Fanwick, and I.P. Rothwell. J.
Am. Chem. Soc. 119, 11086 (1997).
21. H.J. Kim, N.S. Choi, and S.W. Lee. J. Organomet. Chem. 616,
67 (2000).
22. G. Moran, M. Green, and A.G. Orpen. J. Organomet. Chem.
250, C15 (1983).
23. J. Moreto, K. Maruya, P.M. Bailey, and P.M. Maitlis. J. Chem.
Soc. Dalton Trans. 1341 (1982).
24. W.S. Han and S.W. Lee. Organometallics, 24, 997 (2005).
25. E. Becker, K. Mereiter, M. Puchberger, R. Schmid, K. Kirchner,
A. Doppiu, and A. Salzer. Organometallics, 22, 3164 (2003).
26. E. Álvarez, M. Paneque, M.L. Poveda, and N. Rendón. Angew.
Chem. Int. Ed. 45, 474 (2006).
27. C.S. Chin and H. Lee. Chem. Eur. J. 10, 4518 (2004).
28. C.S. Chin, H. Lee, and M.-S. Eum. Organometallics, 24, 4849
(2005) and refs. cited therein.
Z = 2; T = 293(2) K; λ (Mo K α) = 0.710 73 Å; Dcalc
=
1.591 mg/m3; µ = 3.398 mm–1; F(000) = 1044; Θ (min–max) =
1.18–25.00°; independent reflection = 6440; Rint = 0.0201; T
(min, max) = 0.6124, 0.7727; data, restraints, parameters =
6440, 0, 524; final R indices (I>2σ(I)) R1 = 0.0711, wR2 =
0.1693; R indices (all data) R1 = 0.1339, wR2 = 0.2386; GOF
on F2 = 1.137.
29. H. Werner and A. Höhn. J. Organomet. Chem. 272, 105 (1984).
30. A. Bierstedt, G.R. Clark, W.R. Roper, and L.J. Wright. J.
Organomet. Chem. 691, 3846 (2006).
Acknowledgements
31. G.-L. Lu, W.R. Roper, L.J. Wright, and G.R. Clark. J.
Organomet. Chem. 690, 972 (2005).
SR thanks the Department of Science and Technology
(DST), New Delhi, for research grant inclusive of a post-
doctoral fellowship to JC. Financial assistance from Council
of Scientific and Industrial Research (CSIR) (fellowship to
SP) and University Grants Commission (UGC) (fellowship
to AKM) is also acknowledged. While submitting this work
to this special issue of CJC, SR likes to fondly express his
gratitude to Dick for the cheerful years spent at the RJP lab
two decades ago.
32. J. Choudhury, S. Podder, and S. Roy. J. Am. Chem. Soc. 127,
6162 (2005).
33. M. Banerjee and S. Roy. J. Mol. Catal. A, 246, 231 (2006).
34. J. Choudhury and S. Roy. J. Organomet. Chem. 692, 5614
(2007).
35. S. Podder, J. Choudhury, U.K. Roy, and S. Roy. J. Org. Chem.
72, 3100 (2007).
36. S. Podder, J. Choudhury, and S. Roy. J. Org. Chem. 72, 3129
(2007).
© 2008 NRC Canada

Choudhury et al.
187
37. J. Choudhury and S. Roy. J. Mol. Catal. A, 279, 37 (2008).
38. M.A. Bennett, R. Charles, and P. J. Fraser. Aust. J. Chem. 30,
1213 (1977).
39. J.P. Collman and J.W. Kang. J. Am. Chem. Soc. 89, 844 (1967).
40. J.Y.K. Tsang, M.S.A. Buschhaus, P. Legzdins, and B.O. Pat-
rick. Organometallics, 25, 4215 (2006).
45. S.P. Tunik, A.V. Vlasov, A.B. Nikol’skii, G.L. Starova, S. Ooi,
H. Nakai, and T. Sato. J. Organomet. Chem. 464, 71 (1994).
46. A.N. Nesmeyanov, V.V. Krivykh, V.S. Kaganovich, and M.I.
Rybinskaya. J. Organomet. Chem. 102, 185 (1975).
47. R. Acharyya, F. Basuli, R-Z. Wang, T.C.W. Mak, and S.
Bhattacharya. Inorg. Chem. 43, 704 (2004).
41. X. Li, P. Chen, J.W. Faller, and R.H. Crabtree. Organo-
48. G.M. Sheldrick. SHELXS-97 [computer program]. University
metallics, 24, 4810 (2005).
of Göttingen, Göttingen, Germany, 1997.
42. A.F. Hill, M. Schultz, and A.C. Willis. Organometallics, 23,
5729 (2004).
49. G.M. Sheldrick. SHELXL-97 [computer program]. University
of Göttingen, Göttingen, Germany, 1997.
43. W.D. Harman, J.F. Wishart, and H. Taube. Inorg. Chem. 28,
2411 (1989).
44. B. Chaudret, X. He, and Y. Huang. J. Chem. Soc. Chem.
Commun. 1844 (1989).
50. L.J. Farrugia. J. Appl. Cryst. 32, 837 (1999) (WinGX Version
1.70.00. An integrated system of Windows programs for the
solution, refinement, and analysis of single crystal X-ray dif-
fraction data).
© 2008 NRC Canada