Alkynyl selenolate complexes of iron, nickel, and molybdenum

Article abstract of DOI:10.1021/om100694f

The successive treatment of terminal alkynes, HC≡CR (R = C ₆H₄Me-4, SiMe₃), with ⁿBuLi and gray selenium affords LiSeC≡CR, which in turn reacts with [FeCl(CO) ₂(η-C₅H₅)], [NiCl(P

Full text of DOI:10.1021/om100694f

6350 Organometallics 2010, 29, 6350–6358
DOI: 10.1021/om100694f
Alkynyl Selenolate Complexes of Iron, Nickel, and Molybdenum
Lorraine M. Caldwell,† Anthony F. Hill,*,† Alexander G. Hulkes,‡
Caitlin M. A. McQueen,† Andrew J. P. White,‡ and David J. Williams‡
†Research School of Chemistry, Institute of Advanced Studies, Australian National University, Canberra,
Australian Capital Territory, Australia, and ‡Imperial College of Science, Technology and Medicine,
London SW1W 9QU, United Kingdom
Received July 15, 2010
The successive treatment of terminal alkynes, HCtCR (R = C6H4Me-4, SiMe3), with nBuLi and
gray selenium affords LiSeCtCR, which in turn reacts with [FeCl(CO)2(η-C5H5)], [NiCl(PPh3)-
(η-C5H5)], and [MoI(CO)3(η-C5H5)] to afford the alkynylselenolato complexes [Fe(SeCtCR)-
(CO)2(η-C5H5)], [Ni(SeCtCR)(PPh3)(η-C5H5)], and [Mo(SeCtCR)(CO)3(η-C5H5)], two examples
of which have been structurally characterized. When [MoI(CO)3{HB(pz)3}] (pz = pyrazol-1-yl) was
however employed as the electrophile, low yields of the selenoketenyl complex [Mo(η2-C,C0-
SeCCR)(CO)2{HB(pz)3}] were obtained via the presumed intermediacy of the alkynylselenolato
complex [Mo(σ-SeCtCR)(CO)3{HB(pz)3}], which is perhaps destabilized relative to the seleno-
ketenyl complex by the octahedral enforcer character of the HB(pz)3 ligand.
Introduction
multiple bond, an arrangement that may be described as a
selenoketenyl (η2-C,C0). The vast majority of ketenyl ligands
arise from the coupling of carbonyl and carbyne ligands,5
and given that selenocarbonyl complexes are rare, and none
to date also possess carbyne ligands, this approach is unat-
tractive for the general synthesis of selenoketenyls. We chose
an alternative synthetic strategy,2 which involved conversion
of a preformed ketenyl complex with Woollins’ reagent
(Ph2P2Se4, obtained from PhPCl2 and Li2Se).7 This reagent
has emerged as an effective selenating agent.8
With these two disparate coordination modes firmly
established, in addition to the recent isolation of the first
isoselenocarbonyls,9 which might also be described as alkyli-
dynylselenolates (Scheme 2), we were eager to establish if these
two modes were interconvertible. Ketenyl ligands may in some
instances adopt a monodentate coordination mode; however
this is generally through the carbon atom rather than oxygen,6
e.g., in the complex [W{σ-C-C(dCdO) R1}(CO)(PMe3)2(η-
C5H5)],10 obtained from [W{η2-C,C0-OCCR1}(CO)(PMe3)2-
(η-C5H5)] and excess PMe3. We have therefore investigated
further examples of alkynylselenolates based on nickel (d8),
iron (d6), and molybdenum (d4) metal centers including one
We have previously reported the first examples of transi-
tion metal complexes of the alkynylselenolate ligand
‘”SeCtCR” in two different coordination modes via dis-
parate routes (Scheme 1).1,2
The first approach involved the generation of the alkynyl-
selenolate anion via the reaction of lithium alkynyls with
gray selenium followed by treatment with Vaska’s complex,
[IrCl(CO)(PPh3)2], to afford [Ir(SeCtCR1)(CO)(PPh3)2]
(R1=C6H4Me-4). The alkynylselenolate ligand in this com-
plex is coordinated solely through the selenium (σ-Se) atom
despite the coordinative unsaturation of the d8-square-
planar iridium(I) center and is in many respects akin to more
conventional selenolate ligands. In the interim other groups
have provided further examples of this class of ligand accessed
via this route,3-5 and these are summarized in Chart 1.
It is noteworthy that in all cases the alkynylselenolato
ligand coordinates in the σ-Se manner. By way of contrast,
we have also described the synthesis of complexes in which
the “SeCCR” group coordinates side-on through the C-C
*To whom correspondence should be addressed. E-mail: a.hill@anu.
edu.au.
(1) Bedford, R. B.; Dyson, P. J.; Hill, A. F.; Hulkes, A. G.; Yates,
C. J. Organometallics 1998, 17, 4117.
(2) Baxter, I.; Hill, A. F.; Malget, J. M.; White, A. J. P.; Williams,
D. J. J. Chem. Soc., Chem. Commun. 1997, 2049.
(3) (a) Beswick, M. A.; Raithby, P. R.; Steiner, A.; Vallat, J. C.;
Verhorevoot, K. L.; Wright, D. S. J. Chem. Soc., Dalton Trans. 1996,
2183. (b) Beswick, M. A.; Harmer, C. N.; Raithby, P. R.; Steiner, A.; Tombul,
M.; Wright, D. S. J. Organomet. Chem. 1999, 573, 267.
(4) (a) Sunada, Y.; Hayashi, Y.; Kawaguchi, H.; Tatsumi, K. Inorg.
Chem. 2001, 40, 7072. (b) Sugiyama, H.; Hayashi, Y.; Kawaguchi, H.;
Tatsumi, K. Inorg. Chem. 1998, 37, 6773.
(7) (a) Hill, A. F.; Malget, J. M. J. Chem. Soc., Chem. Commun. 1996,
1177. (b) Hill, A. F.; Malget, J. M.; White, A. J. P.; Williams, D. J. J. Chem.
Soc., Chem. Commun. 1996, 721.
(8) (a) Hua, G.; Woollins, J. D. Angew. Chem., Int. Ed. 2009, 48, 1368.
(b) Gray, I. P.; Woollins, J. D. Main Group Chem. 2005, 4, 69. (c) Foreman,
M. R. St. J.; Woollins, J. D. Dalton Trans. 2000, 1533.
(9) (a) Caldwell, L. M.; Hill, A. F.; Wagler, J.; Willis, A. C. Dalton
Trans. 2008, 3538. (b) Caldwell, L. M.; Hill, A. F.; Rae, A. D.; Willis, A. C.
Organometallics 2008, 27, 341. (c) Cade, I. A.; Hill, A. F.; McQueen,
C. M. A. Organometallics 2009, 28, 6639.
(10) (a) Sheridan, J. B.; Pourreau, D. B.; Geoffroy, G. L.; Rheingold,
A. L. Organometallics 1988, 7, 289. (b) Eberl, K.; Uedelhoven, W.; Karsch,
H. H.; Kreissl, F. R. Chem. Ber. 1980, 113, 3377. (c) Kreissl, F. R.; Eberl, K.;
Uedelhoven, W. Chem. Ber. 1977, 110, 3782. (d) Kreissl, F. R.; Frank, A.;
Schubert, U.; Lindner, T. L.; Huttner, G. Angew. Chem. 1976, 88, 649.
(5) (a) Schaefer, S.; Moser, C.; Tirree, J. J.; Nieger, M.; Pietschnig, R.
€
Inorg. Chem. 2005, 44, 2798. (b) Pietschnig, R.; Merz, K.; Schafer, S.
Heteroat. Chem. 2005, 16, 169.
(6) Mayr, A.; Bastos, C. M. Prog. Inorg. Chem. 1992, 40, 1.
r
pubs.acs.org/Organometallics
Published on Web 11/01/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 23, 2010 6351
Scheme 1. Synthetic Routes to Alkynylselenolate1 and
Scheme 2. Synthesis of an Isoselenocarbonyl/Alkylidynyl-
selenolate Complex8
Selenoketenyl2 Complexes
Chart 2. Resonance Descriptions for (a) the Alkynylselenolate
Anion and (b) Positively Mesomeric Heteroatom (D:)-Substituted
Alkynes
Chart 1. Further Examples of Alkynylselenolate Complexes3-5
Results and Discussion
The reaction of alkynyl lithium reagents (LiCtCR) with
elemental (gray) selenium proceeds via the presumed forma-
tion of the lithium alkynylselenolate (LiSeCtCR), which
although not isolated, may be inferred through the nature of
products obtained via subsequent reactions with electro-
philes.11 The alkynylselenolate anion is an ambidentate
nucleophile (Chart 2), the behavior of which may be ratio-
nalized by two resonance contributors, which suggest that
both the selenium and the β-carbon may be prone to electro-
philic attack. The potential nucleophilicity of Cβ is most
clearly demonstrated in the case of protonation, which does
not provide the selenohydryl acetylene RCtCSeH (though
reversible kinetic protonation of the heteroatom should not
be discounted), but rather heterocycles that may be viewed
as forming via the highly reactive selenoketene (SedCd
CHR).12 Selenoketenes are at present hypothetically inferred
intermediates and due to their high reactivity are likely to
remain so in condensed phases. However, selenoketenes
have been assembled as ligands within the protective envi-
ronment of transition metal coordination spheres.13 We shall
return to the question of electrophilic attack at Cβ subse-
quently; for the work to immediately follow, attack at the
example where it was indeed possible to infer the interconver-
sion of σ-Se and η2-C,C0 bonding modes, affording a new route
to chalcoketenyl complexes.
(11) (a) Shafiee, A.; Fanaii, G. Synthesis 1984, 512. (b) Shafiee, A.;
Lalezari, I.; Savabi, F. Synthesis 1977, 765. (c) Koketsu, M.; Kanoh, M.;
Ishihara, H. Synlett. 2002, 805. (d) Raubenheimer, H. G.; Kruger, G. J.;
Linford, L.; Marais, C. F.; Otte, R.; Hattingh, J. T. Z.; Lombard, A. J. Chem.
Soc., Dalton Trans. 1989, 1565. (e) Raubenheimer, H. G.; Kruger, G. J.;
Marais, C. F. J. Chem. Soc., Chem. Commun. 1984, 634. (f) Raubenheimer,
H. G.; Kruger, G. J.; Marais, C. F.; Otte, R.; Hattingh, J. T. Z. Organome-
tallics 1988, 7, 1853. (g) Pietschnig, R.; Merz, K.; Schaefer, S. Heteroat.
(12) (a) Malek-Yazdi, F.; Yalpani, M. J. Org. Chem. 1976, 41, 729. (b)
Ghandehari, M. H.; Davalian, D.; Yalpani, M.; Partovi, M. H. J. Org. Chem.
1974, 39, 3906. (c) Lalezari, I.; Shafiee, A.; Yalpani, M. J. Org. Chem. 1973,
38, 338.
(13) (a) Werner, H.; Weinand, R.; Knaup, W.; Peters, K.; Von
Schnering, H. G. Organometallics 1991, 10, 3967. (b) Werner, H.;
Weinand, R.; Knaup, W.; Peters, K.; Von Schnering, H. G. Organometallics
1991, 10, 967. (c) Weinand, R.; Werner, H. J. Chem. Soc., Chem. Commun.
1985, 1145. (d) Wolf, J.; Zolk, R.; Schubert, U.; Werner, H. J. Organomet.
Chem. 1988, 340, 161. (e) Werner, H.; Paul, W.; Knaup, W.; Wolf, J.; Mueller,
G.; Riede, J. J. Organomet. Chem. 1988, 358, 95. (f) Werner, H.; Wolf, J.;
Zolk, R.; Schubert, U. Angew. Chem. 1983, 95, 1022.
€
Chem. 2005, 16, 169. (h) Pietschnig, R.; Schafer, S.; Merz, K. Org. Lett.
2003, 5, 1867. (i) Brandsma, L.; Wijers, H. E.; Arens, J. F. Recl. Trav. Chim.
Pays-Bas 1962, 81, 583. (j) Johannsen, I.; Henriksen, L.; Eggert, H. J. Org.
Chem. 1986, 51, 1657.

6352 Organometallics, Vol. 29, No. 23, 2010
Caldwell et al.
The formulation of 1 was confirmed in the solid state by a
crystallographic study, the results of which are summarized
in Figure 1. Geometric parameters associated with the “Ni-
(PPh3)(η-C5H5)” unit are unremarkable, conform to prece-
dent for chalcogenolato complexes of this fragment,16,17 and
do not call for further comment. Structural data associated
with the previously reported nickel selenolate complex
[Ni(SePh)(PPh3)(η-C5H5)]17 include Ni-Se and Ni-P bond
lengths of 2.301(1) and 2.136(1) A with P-Ni-Se and
Ni-Se-C angles of 91.4(1)° and 107.9(1)°. Thus the Ni-Se
bond length of 2.3056(16) A found for 1 is within the
experimental accuracy, identical to that for the phenylsele-
nolate example, while the Ni-Se-C angle of 105.0(3)° is also
very similar. The C1tC2 bond length of 1.216(14) A is
somewhat longer than found for hydrocarbon alkynes, but
within the range typical of alkynes bearing positively meso-
meric (π-donor) heteroatom substituents (Chart 2b). Struc-
tural data for conventional acyclic alkynylselenoethers are
somewhat sparse18 but typically span the ranges 1.17-1.21 A
(CtC) and 1.81-1.85 A (C-Se), within which those for
1 fall.
Figure 1. Molecular structure of 1 in a crystal of 1 (CHCl3)2.
3
Selected bond lengths (A) and angles (deg): Ni-Se 2.3056(16),
Ni-P 2.145(3), Se-C(1) 1.831(10), Se-Ni-P 91.71(7), Ni-
Se-C(1) 105.0(3), Se-C(1)-C(2) 171.9(9), C(1)-C(2)-C(3)
177.2(11), P-Ni-Se-C(1) -157.6(3).
Scheme 3. Synthesis of Alkynylselenolato Complexes of
Nickel(II) and Iron(II)
The reactions of LiSeCtCR (R=R1, SiMe3) with [FeCl-
(CO)2(η-C5H5)]19 provide in high yield khaki-olive green
compounds formulated as the monomeric species [Fe-
(SeCtCR)(CO)2(η-C5H5)] (R = C6H4Me-4 2a, SiMe3 2b).
The compounds appear to be stable in solution (aerobic
dichloromethane, 36 h, TLC, IR). The infrared spectrum of
2b includes peaks at 2034 and 1990 cm-1 due to the cis
carbonyl ligands and one weaker absorption at 2061 cm-1
that we attribute to the alkynyl group. The former may be
compared with those for the selenolato complex [Fe(SePh)-
(CO)2(η-C5H5)] (cyclohexane: 2026, 1984 cm-1 20
for the alkynylthiolato complex [Fe(SCtCtBu)(CO)2-
(η-C5H5)] (THF: 2032, 1987 cm-1 21
described previously by
Delgado.
) and those
)
selenium appears to be the preferred mode for transition
metal electrophiles.
The molecular structure of 2a in the solid state is depicted
in Figure 2, and selected geometric parameters for alkynyl-
selenolate complexes are collated in Table S1 (Supporting
Information). The geometry of the “Fe(CO)2(η-C5H5)”
moiety is unexceptional, with OC-Fe-Se and OC-Fe-CO
angles close to 90° [87.7(3)-94.7(4)°] and the Fe-Se bond
length of 2.4072(14) A being close to that found for
[Fe(SePh)(CO)2(η-C5H5)] (2.413(3) A)22 and other mono-
nuclear 18-electron iron(II) selenolates.23 The features of the
Fe-Se-CtC spine (Se-C1=1.834(9), CRC=1.188(13) A)
Treating a solution of 4-ethynyltoluene (hereafter HCt
CC6H4Me-4=HCtCR1) in tetrahydrofuran with gray sele-
nium provides a solution of LiSeCtCR1, which was used
without isolation. Treating this solution with [NiCl(PPh3)-
(η-C5H5)]14 results in the clean formation of a red-brown
compound formulated as the alkynylselenolato complex
[Ni(SeCtCR1)(PPh3)(η-C5H5)] (1) (Scheme 3) on the basis
of spectroscopic, elemental microanalytical, and crystallo-
graphic data (Figure 1). The infrared spectrum includes a
single absorption at 2131 cm-1, which may be assigned to the
1
alkynyl group. The H and 13C NMR spectra feature the
(17) (a) Darkwa, J.; Moutloali, R. M.; Nyokong, T. J. Organomet.
Chem. 1998, 564, 37. (b) Darkwa, J. Organometallics 1994, 13, 3743.
(18) (a) Husebye, S.; Meyers, E. A.; Zingaro, R. A.; Braga, A. L.;
Comasseto, J. V.; Petragnani, N. Acta Crystallogr., Sect. C: Cryst.
Struct. Commun. 1986, 42, 1789. (b) Werz, D. B.; Gleiter, R.; Rominger, F.
J. Org. Chem. 2002, 67, 4290. (c) Terent'eva, N. A.; Petrov, M. L.; Potekhin,
K. A.; Galishev, V. A.; Struchkov, Y. T. Russ. J. Org. Chem. 1994, 30, 1471.
(d) Yamane, K.; Hayashi, S.; Nakanishi, W.; Sasamori, T.; Tokitoh, N.
Polyhedron 2008, 27, 2478. (e) Yamane, K.; Hayashi, S.; Nakanishi, W.;
Sasamori, T.; Tokitoh, N. Polyhedron 2008, 27, 3557.
expected signatures of the cyclopentadienyl, tolyl, and phos-
phine groups, while the chemical shifts of the alkynyl unit
[δC=92.6 (CCt), 84.9 (SeCt)] are consistent with those for
more conventional alkynylselenoethers.15 FAB-mass spec-
trometric data suggest that the complex is monomeric.
(14) Hernandez, E.; Royo, P. J. Organomet. Chem. 1985, 291, 387.
(15) Cook, D. J.; Hill, A. F.; Wilson, D. J. J. Chem. Soc., Dalton
Trans. 1998, 1171.
(19) Piper, T. S.; Cotton, F. A; Wilkinson, G. J. Inorg. Nucl. Chem.
1955, 1, 165.
(16) (a) Darkwa, J.; Bothata, F.; Koczon, L. M. J. Organomet. Chem.
1993, 55, 23.5. (b) Nevondo, F. A.; Crouch, A. M.; Darkwa, J. J. Chem. Soc.,
Dalton Trans. 2000, 43. (c) Darkwa, J.; Milius, W. Acta Crystallogr., Sect.
C: Cryst. Struct. Commun. 1996, 52, 2159. (d) Hsieh, C.-K.; Lo, F.-C.; Lee,
G.-H.; Peng, S.-M.; Liaw, W.-F. J. Chin. Chem. Soc. 2000, 47, 103. (e)
Tsipis, C.; Manoussakis, G. E.; Kessissoglou, D. P.; Huffman, J. C.; Lewis,
L. N.; Adams, M. A.; Caulton, K. G. Inorg. Chem. 1980, 19, 1458. (f)
Shimoi, M.; Ouchi, A.; Sato, S.; Saito, Y. Bull. Chem. Soc. Jpn. 1982, 55,
2083. (g) Moloto, M. J.; Nelana, S. M.; Moutloali, R. M.; Guzei, I. A.;
Darkwa, J. J. Organomet. Chem. 2004, 689, 387.
(20) (a) Rosenbuch, P.; Welcman, N. J. Chem. Soc., Dalton Trans.
1972, 1963. (b) Schermer, E. D.; Baddley, W. H. J. Organomet. Chem. 1971,
27, 83.
(21) (a) Delgado, E.; Donnadieu, B.; Garcıa, S.; Zamora, F.
´
J. Organomet. Chem. 2002, 649, 21. (b) Cabrera, A.; Delgado, E.; Pastor,
C.; Maestro, M. A.; Zamora, F. Inorg. Chim. Acta 2005, 358, 1521. (c)
Delgado, E; Alcalde, M. I; Donnadieu, B; Hernandez, E.; Sanchez-Nieves, J.
Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, E59, m207. (d) Ara,
I.; Delgado, E.; Fornies, J.; Hernandez, E.; Lalinde, E.; Mansilla, N.; Moreno,
M. T. J. Chem. Soc., Dalton Trans. 1998, 3199.

Article
Organometallics, Vol. 29, No. 23, 2010 6353
arrangement of the carbonyl and selenolate donors. The
13C{1H} NMR spectrum would appear to suggest the latter
(CDCl3: δC = 235.3, 222.9); however the infrared data are
too numerous by one for this to be a simple case (2036, 1973,
1960, 1944 cm-1). We suggest that perhaps there exist
rotamers with respect to the Cp-Mo-Se-C spine that
interconvert on the 13C NMR time scale but are apparent
on the IR time scale. The alkynyl group however gives rise to
a single infrared absorption (CHCl3: 2137 cm-1).
Seven-coordinate geometry is common for complexes of
the form [MoL4(η-C5H5)], designating the cyclopentadienyl
as a facial pseudotridentate ligand. The hydrotris(pyra-
zolyl)borate ligand in contrast has been described as an
octahedral enforcer.27-29 This would appear to be the case
with respect to the reaction of LiSeCtCR1 with [MoI-
(CO)3{HB(pz)3}], which proceeds distinctly from that invol-
ving the cyclopentadienyl analogue. Selenolates of the form
[Mo(SeR)(CO)3(η-C5H5)] are well known,25 as are binuclear
species [M2(μ-SeR)2(CO)x(η-C5H5)2] (x = 2, 4).26,30 Within
the poly(pyrazolyl)borate series, Templeton has described
the thiolate complexes [M(SR)(CO)2{HB(pzMe2)3}], which
are stable monomeric, paramagnetic species,31 while Young
has more generally considered group 6 poly(pyrazolyl)-
borates with a variety of chalcogen donors within the broader
context of the biomimetic modeling of molybdenum and
tungsten enzyme active sites.32
Treating the complex [MoI(CO)3{HB(pz)3}]33 with one
equivalent of LiSeCtCR1 at -40 °C afforded in poor
yield (ca. 10%) after cryogenic anaerobic chromatography
(-30 °C, silica gel) a red compound formulated as the
selenoketenyl complex [Mo(η2-SeCCR1)(CO)2{HB(pz)3}]
(4) on the basis of spectroscopic, (FAB) mass spectrometric,
and elemental microanalytical data. Unfortunately, succes-
sive attempts to obtain crystallographic grade crystals from
the trace amounts of product obtained were unsuccessful.
Intermediate species could be observed spectroscopically
(IR: νCO =1984, 1752, 1725, 1688 cm-1) with a collective
intense purple color. However, all attempts to intercept these
species, including workup at -20 °C, failed to provide useful
Figure 2. Molecular structure of 2a in a crystal. Selected bond
distances (A) and angles (deg.): Fe-Se 2.4072(14), Se-C(1)
1.834(9), C(1)-C(2) 1.188(13), Fe-Se-C(1) 103.0(2), Se-Fe-
C(15) 92.7(3), Se-Fe-C(16) 87.7(3), Se-C(1)-C(2) 176.3(8),
C(1)-C(2)-C(3) 178.4(8), C(15)-Fe-Se-C(1) 29.4(4), C(16)-
Fe-Se-C(1) -65.2(4).
are comparable to those observed for 1. The iron(II) center
being d6-pseudo-octahderal has little inclination for any
π-dative capacity on the part of the selenium center. Accord-
ingly, the positively mesomeric influence of the selenium is
rather directed toward the alkynyl group, which is lengthened
toward the long end of the norms discussed above. The steric
profile of the “Fe(CO)2(η-C5H5)” group is modest, and ac-
cordingly the angle at selenium [103.0(2)°] is also comparable
to that for 1.
The reaction of [MoI(CO)3(η-C5H5)]24 with LiSeCtCR1
affords the anticipated complex [Mo(SeCtCR1)(CO)3(η-
C5H5)] (3) by analogy with the reported reactions25 of [MoX-
(CO)3(η-C5H5)] (X=Cl, Br, I) with RSe-, although the more
common entry into the selenolate chemistry of the molybde-
num cyclopentadienyl unit is typically via the reactions of
[Mo2(CO)x(η-C5H5)2] (x = 4, 6) with diselenides.26 Alkynyl
diselenides (RCtCSeSeCtCR), though a potentially inter-
esting class of compounds, are not yet synthetically avail-
able, precluding the latter approach. Our choice of [MoI-
(CO)3(η-C5H5)] as the preferred substrate was based on the
proclivity of the corresponding chloride to undergo outer-
sphere single electron transfer reactions with strong reducing
agents, including chalcogenolates, to provide [Mo2(CO)6(η-
C5H5)2]. The complex [MoI(CO)3(η-C5H5)] performed well
in this respect, with no indication (TLC, IR) for the forma-
tion of [Mo2(CO)6(η-C5H5)2].
(27) Curtis, M. D.; Shiu, K. B.; Butler, W. M. Organometallics 1983,
2, 1475.
(28) Trofimenko, S. Scorpionates: The Chemistry of Pyrazolylbo-
rates; Imperial College Press: London, 1999.
Complex 3, being of the four-legged piano-stool variety,
has the option of two possible ligand arrangements, a local
C3v-Mo(CO)3 arrangement of the three carbonyls, capped
by the selenolato ligand, or alternatively a square-pyramidal
(29) For recent reviews of organometallic chemistry supported by
poly(pyrazolyl)borate coligands see: (a) Caldwell, L. M. Adv. Organo-
met. Chem. 2008, 56, 1. (b) Lail, M.; Pittard, K. A.; Gunnoe, T. B. Adv.
Organomet. Chem. 2008, 56, 95. (c) Becker, E.; Pavlik, S.; Kirchner, K. Adv.
Organomet. Chem. 2008, 56, 155. (d) Crossley, I. R. Adv. Organomet.
Chem. 2008, 56, 199. (e) Crossley, I. R. Adv. Organomet. Chem. 2010,
58, 107.
(22) Liaw, W.-F.; Horng, Y.-C.; Ou, D.-S.; Ching, C.-Y.; Lee, G.-H.;
Peng, S.-M. J. Am. Chem. Soc. 1997, 119, 9299.
(30) (a) Shi, Y.-C.; Song, L.-C. J. Coord. Chem. 2004, 57, 731. (b)
Song, L.-C.; Shi, Y.-C.; Zhu, W.-F. Polyhedron 1999, 18, 2163. (c) Song,
L.-C.; Shi, Y.-C.; Hu, Q.-M.; Du, F.; Mao, X.-A. Polyhedron 1999, 18, 19. (d)
Song, L.-C.; Wang, J.-Q.; Hu, Q.-M.; Sun, J. J. Coord. Chem. 1997, 42, 63.
(23) (a) El-Khateeb, M. Polyhedron 2006, 25, 1386. (b) El-Khateeb, M.
Inorg. Chim. Acta 2004, 357, 4341. (c) El-Khateeb, M.; Roller, A. Poly-
hedron 2007, 26, 3920. (d) El-Khateeb, M.; Gorls, H.; Weigand, W. Inorg.
Chim. Acta 2007, 360, 705. (e) Liaw, W.-F.; Lai, C.-H.; Lee, C.-K.; Lee,
G.-H.; Peng, S.-M. J. Chem. Soc., Dalton Trans. 1993, 2421. (f) Liaw,
W.-F.; Ou, D.-S.; Horng, Y.-C.; Lai, C.-H.; Lee, G.-H.; Peng, S.-M. Inorg.
Chem. 1994, 33, 2495. (g) Liaw, W.-F.; Chen, C.-H.; Lee, C.-M.; Lin, G.-Y.;
Ching, C.-Y.; Lee, G.-H.; Peng, S.-M. J. Chem. Soc., Dalton Trans. 1998,
353.
€
(e) Jones, P. G.; Laube, J.; Thone, C. Inorg. Chem. 1997, 36, 2097. (f)
Schollhammer, P.; Petillon, F. Y.; Pichon, R.; Poder-Guillou, S.; Talarmin, J.;
Muir, K. W.; Manojlovic-Muir, L. Organometallics 1995, 14, 2277. (g)
Rakoczy, H.; Schollenberger, M.; Nuber, B.; Ziegler, M. L. J. Organomet.
Chem. 1994, 467, 217. (h) Jaitner, P.; Winder, W. Inorg. Chim. Acta 1987,
128, L17. (i) Grobe, J.; Haubold, R. Z. Anorg. Allg. Chem. 1985, 522, 159.
(j) Jaitner, P.; Wohlgenannt, W. Inorg. Chim. Acta 1985, 101, L43. (k)
Jaitner, P. J. Organomet. Chem. 1982, 233, 333.
(31) (a) Philipp, C. C.; Young, C. G.; White, P. S.; Templeton, J. L.
Inorg. Chem. 1993, 32, 5437. (b) Trofimenko, S. Inorg. Chem. 1971,
10, 504.
(24) Piper, T. S.; Wilkinson, G. Naturwissenschaften 1955, 42, 625.
€
(25) (a) Thone, C. Phosphorus, Sulfur, Silicon 1998, 136-138, 645. (b)
€
Jones, P. G.; Laube, J.; Thone, C. Inorg. Chem. 1997, 36, 2097. (c) Davidson,
J. L.; Holz, B.; Leverd, P. C.; Lindsell, W. E.; Simpson, N. J. J. Chem. Soc.,
€
Dalton Trans. 1994, 3527. (d) Eikens, W.; Kienitz, C.; Jones, P. G.; Thone, C.
(32) (a) Enemark, J. H.; Young, C. G. Adv. Inorg. Chem. 1994, 40, 1.
(b) Young, C. G.; Wedd, A. G. Chem. Commun. 1997, 1251. (c) Young, C. G.
J. Biol. Inorg. Chem. 1997, 2, 810.
J. Chem. Soc., Dalton Trans. 1994, 3329.
(26) Baddley, W. H.; Schermer, E. D.; Tillay, E. W. Inorg. Chem.
1968, 7, 1925.
(33) Curtis, M. D.; Shiu, K. B. Inorg. Chem. 1985, 24, 1213.

6354 Organometallics, Vol. 29, No. 23, 2010
Caldwell et al.
Scheme 4. Synthesis of Alkynylselenolato and Selenoketenyl
Complexes of Molybdenum(II)a
The two carbon resonances for the few known examples of
selenoketenyl ligands appear within a narrow range in the
13C{1H} NMR spectrum,; for example, the complex [Mo(η2-
SeCCR1)(CO)(PPh3){HB(pz)3}] gives rise to two closely
spaced resonances at 238.8 and 234.8 ppm.2 On the basis of
the intensity of the single broad absorption observed for 4 at
234.0 ppm relative to that observed at 215.1 ppm for the two
carbonyl ligands, it would appear that the former corresponds
to two overlapping resonances, presumably for the two carbon
nuclei of a η2-C,C0-selenoketenyl ligand.
As to the nature of the intensely purple intermediate(s),
three possibilities to consider include (i) the monodentate
σ-Se alkynylselenolate complex [Mo(SeCtCR1)(CO)3{HB-
(pz)3}] (5a); (ii) the monodentate selenoketenyl complex
[Mo{σ-C-C(dCdSe)R1}(CO)3{HB(pz)3}] (5b), and (iii)
the trihapto η3-Se,C,C0 alkynylselenolate complex [Mo(η3-
SeCtCR1)(CO)2{HB(pz)3}] (5c). We doubt that the last of
these would be a persistent species since the barrier to
rearrangement to 4 would involve little energy expenditure
or atom reorganization. The possibility of electrophilic
attack by molybdenum at Cβ would seem to be sterically
disfavored, leaving us with the first option, an alkynylsele-
nolate complex akin to 1, 2, and 3 as the most plausible
formulation. Selenolate complexes of the form [Mo(SeR)-
(CO)3{HB(pz)3}] are presently unknown;28,29 however the
complexes [W(SR)(CO)2{HB(pzMe2)3}]31 have been reported
to be exceptionally stable both thermally and aerobically. The
reason for the apparent instability of 5a relative to the stable
cyclopentadienyl analogue 4 may presumably be traced to the
predilection of tris(pyrazolyl)borates toward octahedral
geometry,27 with higher coordination numbers being disfa-
vored. For the HB(pz)3 ligand, this is primarily an electronic
argument (metal orbitals more orthogonally hybridized than
for M(η-C5H5)), while the inclusion of 3,5-pyrazolyl substitu-
ents introduces an additional steric component.
a R1 = C6H4Me-4; Tp = HB(pz)3. Complexes 5a-c (indicated by an
asterisk) are alternative mechanistic postulates, none of which were
isolated. The formulation of 4 rests on spectroscopic and analytical data.
results. In the absence of crystallographic data the formula-
tion of 4 rests on spectroscopic and elemental microana-
lytical data, the interpretation of which is however sub-
stantiated by sparse data available for other selenoketenyl
complexes of group 6 metals.2 The dicarbonyl formulation
follows from the observation of two νCO absorptions (Nujol:
1952vs, 1861vs cm-1) in the infrared spectrum, the relative
intensities of which are consistent with a cis-M(CO)2 unit in
close to octahedral geometry. The spectrum is however
devoid of any further absorptions that might be attributable
to a (free) alkynyl group. We tentatively assign the absorp-
tion at 1049 cm-1 to a predominantly νCSe mode; however
the spectrum in this area is cluttered with fingerprint bands
associated with the HB(pz)3Mo cage, precluding more con-
fident assignment. Complexes of carbon diselenide, in which
one CdSe bond coordinates side-on leaving one exocyclic
CdSe bond, have some topological similarity to selenokete-
nyl ligands, and the limited data available for such complexes
suggest that the exocyclic CdSe stretch appears in the region
1000-1050 cm-1, though again, many of these complexes
have extraneous coligand absorptions in this region.
Preliminary reactivity studies on the complexes 1 and 2
have been carried out. First, complex 2a, while thermally
stable, was found to undergo photochemical carbonyl ligand
substitution by triphenylphosphine to provide the complex
[Fe(SeCtCR1)(CO)(PPh3)(η-C5H5)] (6, Scheme 5). The
characterisational data for 6 do not call for comment, and
superficially, this would appear to be a rather mundane
reaction. However, the simplicity of the reaction outcome
hides a significant point. Ketenyl complexes are prevalent
within group 6, arising from thermally, photochemically, or
nucleophile-induced coupling of carbyne and carbonyl
ligands.6 Because this ligand coupling depletes the metal
center of two valence electrons (Chart 3), the transient 16-
electron ketenyl intermediates are typically not observed, but
are rather inferred from the nature of products obtained
(34) (a) Werner, H.; Ebner, M.; Otto, H. J. Organomet. Chem. 1988,
350, 257. (b) Werner, H.; Ebner, M.; Bertleff, W. Z. Naturforsch. 1985, 40B,
1351. (c) Kolb, O.; Werner, H J. Organomet. Chem. 1984, 268, 49. (d)
Roper, W. R.; Town, K. G. J. Organomet. Chem. 1983, 252, C97. (e)
Brothers, P. J.; Headford, C. E. L.; Roper, W. R. J. Organomet. Chem. 1980,
195, C29. (f) Collins, T. J.; Grundy, K. R.; Roper, W. R.; Wong, S. F.
J. Organomet. Chem. 1976, 107, C37. (g) Bianchini, C.; Masi, D.; Mealli,
C.; Meli, A.; Sabat, M.; Vizza, F. Inorg. Chem. 1988, 27, 3716. (h) Bianchini,
C.; Mealli, C.; Meli, A.; Sabat, M.; Silvestre, J.; Hoffmann, R. Organome-
tallics 1986, 5, 1733. (i) Bianchini, C.; Mealli, C.; Meli, A.; Sabat, M. J. Am.
Chem. Soc. 1985, 107, 5317. (j) Bianchini, C.; Mealli, C.; Meli, A.; Sabat, M.
J. Chem. Soc., Chem. Commun. 1984, 1647. (k) Kawakami, K.; Ozaki, Y.;
Tanaka, T. J. Organomet. Chem. 1974, 69, 151. (l) Jensen, K. A.;
Huge-Jensen, E. Acta Chem. Scand. 1973, 27, 3605.
The remaining spectroscopic data associated with the
“HB(pz)3(CO)2Mo” are either unremarkable or uninforma-
tive other than to note that the 13C{1H} NMR spectrum
indicates one pyrazolyl environment on this time scale. This
is, however, not unusual in that complexes of the form [Mo(η2-
XY)(CO)2{HB(pz)3}] are often fluxional, despite the low (Cs)
symmetry of the ground state. The key spectroscopic data
associated with the ligand of interest are somewhat equivocal.
(35) (a) Cook, D. J.; Hill, A. F. Organometallics 2003, 22, 3502. (b)
Anderson, S.; Cook, D. J.; Hill, A. F. Organometallics 2001, 20, 2468.

Article
Scheme 5. Reactivity of an Iron Alkynylselenolatea
Organometallics, Vol. 29, No. 23, 2010 6355
Chart 3. Interconversion of Carbyne and Ketenyl Ligands
complex [FeI(CO)2(η-C5H5)]. Support for this mechanism is
provided by the reaction of 2a with MeOTf, which affords the
marginally more stable salt 8 OTf, in which the triflate coun-
3
teranion less readily replaces the alkynylselenoether. Never-
theless, the salt 8 OTf was also not isolated in pure form due to
3
slow decomposition. It could however be spectroscopically
characterized based on data obtained from a sample generated
in situ. Thus treating a solution of 2a in CDCl3 with excess
MeOTf affords a complex with a resonance at δH=2.80 ppm
attributable to the selenoether methyl group (upfield of
MeOTf, δH=4.18) and a cyclopentadienyl resonance appear-
a R1 = C6H4Me-4.
ing at 5.47 ppm. The 13C{1H} NMR spectrum of 8 OTf in-
3
when an extraneous ligand is provided. In contrast, mono-
nuclear complexes of ketenyl ligands are rare for the later
transition metals,36 and none arise from carbyne-carbonyl
coupling. It therefore remains to be seen if coordinatively
unsaturated late transition metal ketenyls might serve as
synthetic intermediates en route to carbyne complexes.
However for the moment this remains conjecture.
The formation of 6 via photolysis of 2a presumably
proceeds via conventional carbonyl photoejection to afford
a coordinatively unsaturated alkynylselenolate complex,
and the failure of this complex to evolve to an observable
selenoketenyl complex [Fe(η2-SeCCR1)(CO)(η-C5H5)] (“7”)
is therefore noteworthy. Notably, [Mo(SePh)(CO)3(η-C5-
H5)] and [Fe(SePh)(CO)2(η-C5H5)] both undergo photo-
chemical CO dissociation to provide the selenolate-bridged
binuclear species [Mo2(μ-SePh)2(CO)4(η-C5H5)2] and [Fe2-
(μ-SePh)2(CO)2(η-C5H5)2], respectively.37 While the possibi-
lity that “7” represents a perhaps reversible means of stabi-
lizing the coordinative unsaturation, this would appear
unlikely, given that dihapto ketenyls are on (rare) occasion
opened by strong nucleophiles (e.g., PMe3)10 to provide σ-C-
coordinated ketenyls.6
cluded resonances at δC=103.6 and 64.4 (cf. 85.7, 75.0 for 2a).
While these data alone might not allow us to exclude formation
of the alkyne salt [Fe(η2-MeSeCtCR1)(CO)2(η-C5H5)]OTf,
the absorption at 2169 cm-1 in the infrared spectrum is most
consistent with the presence of a noncoordinated alkynyl group.
The alkynyl character of the alkynylselenolate ligand in 2a
was investigated with recourse to the classical addition of
“Co2(CO)6” (from [Co2(CO)8]) across a CtC triple bond.
Alkynylselenoethers have been previously shown to undergo
this reaction,38 as does 2a, to afford the dicobaltatetrahe-
drane [Fe(SeC{Co2(CO)6}CR1)(CO)2(η-C5H5)], 9 (Scheme 5).
While the spectroscopic signatures (1H, 13C NMR) for the
cyclopentadienyl and 4-tolyl groups are only marginally shifted
from those for 2a, the resonances due to the alkynyl group are
shifted markedly (δC = 103.3, 90.4 ppm) from those for 2a
(δC=85.7, 85.4 ppm), indicating that this is the site of adduct
formation, rather than coordination to the selenium center.
Remaining data for 9 conform where applicable to the copious
precedent for dicobaltatetrahedranes of the general form
[Co2(μ-RCCR)(CO)6].39
Concluding Remarks. The reactions of 2a discussed above
point to the alkynylselenolate ligand functioning as both a
conventional selenolate and a conventional heteroatom-
substituted alkyne. In contrast, the failure to isolate an alky-
nylselenolate complex [Mo(σ-SeCCR1)(CO)n{HB(pz)3}] (n =
2, 3; cf. [Mo(SeCtCR1)(CO)3(η-C5H5)] (3)) in favor of the
formation of the selenoketenyl complex [Mo(η2-SeCCR1)-
(CO)2{HB(pz)3}] (4) points toward a unique reactivity relying
The nucleophilicity of the selenium atom in 2a was in-
vestigated through reactions with iodomethane and methyl
trifluoromethane sulfonate (MeOTf). In the case of iodo-
methane, loss of the alkynylselenolate was observed with
formation of [FeI(CO)2(η-C5H5)]. Presumably, this occurs
via Se-alkylation to provide the iodide salt (8 I) of the labile
3
selenoether complex [Fe{σ-Se(Me)CtCR1}(CO)2(η-C5H5)]þ
(8þ), which evolves via selenoether dissociation to the neutral
(38) (a) Lang, H.; Keller, H.; Imhof, W.; Martin, S. Chem. Ber. 1990,
123, 417. (b) Werz, D. B.; Schulte, J. H.; Rausch, B. J.; Gleiter, R.; Rominger,
F. Eur. J. Inorg. Chem. 2004, 2585.
(39) (a) Kemmitt, R. D. W.; Russell, D. R. In Comprehensive
Organometrallic Chemistry; Wilkinson, G.; Stone, F. G. A.; Abel, E. W.,
Eds.; Pergamon Press, 1982; Vol. 5, Chapter 34, pp 916-201. (b) Pauson,
P. L.; Khand, I. U. Ann. N.Y. Acad. Sci. 1977, 295, 2. (c) Dickson, R. S.;
Fraser, P. J. Adv. Organomet. Chem. 1974, 12, 323.
(36) (a) Pandolfo, L.; Paiaro, G.; Ganis, P.; Valle, G.; Traldi, P. Inorg.
Chim. Acta 1993, 210, 39. (b) Paiaro, G.; Pandolfo, L.; Ganis, P.; Valle, G.
Organometallics 1991, 10, 1527. (c) Akita, M.; Chung, M.-C.; Terada, M.;
Miyauti, M.; Tanaka, M.; Moro-oka, Y. J. Organomet. Chem. 1998, 565, 49.
(37) Baddley, W. H.; Schermer, E. D. J. Organomet. Chem. 1971,
27, 83.

6356 Organometallics, Vol. 29, No. 23, 2010
Caldwell et al.
on both components of the “SeCtCR” unit. A further feature,
yet to be explored, which may impinge on the reactivity profile
of alkynylselenolates is the fragility of alkynylselenoether
linkages in combination with transition metal centers. The
facile rearrangement of alkynylselenoethers to selenatovinyli-
dene ligands upon coordination to ruthenium(II) has been
previously demonstrated.40 Alkynylselenolatoalkylidyne com-
plexes have been shown to react with zerovalent platinum via
insertion of platinum into the alkynyl-selenoether linkage to
afford isoselenocarbonyls.9 Furthermore, Tatsumi has demon-
strated the insertion of zirconocene into the tC-Se bond of the
alkynylselenolate complex [Ru(SeCtCPh)(PPh3)2(η-C5H5)].4
These observations, taken together, suggest that alkynylsele-
nolate complexes represent an intriguing class of compound for
further study.
the desired product from hexane in which the small amount of
[Mo(CO)6] remains dissolved: A mixture of [Mo(CO)6] (10.00 g,
37.9 mmol) and NaC5H5 dme (6.75 g, 38.0 mmol) in tetrahy-
3
drofuran (100 mL) was heated under reflux for 12 h to afford a
solution of Na[Mo(CO)3(η-C5H5)]. The mixture was cooled in
an ice bath and treated with one equivalent of iodine (9.64 g, 38.0
mmol) in one portion, causing a color change to deep red-
purple. The solution was warmed to room temperature and
diluted with hexane (50 mL). The precipitated NaI was removed
by filtration, and the filtrate diluted with further hexane (50 mL)
was concentrated on a rotary evaporator to precipitate the
product as a red-purple crystalline solid. Yield: 11.51 g (82%,
30.9 mmol). The material, as formed, was spectroscopically pure
(IR) and used without further purification. Spectroscopic data
were comparable to those previously published.24,41
Synthesis of [Ni(SeCtCC6H4Me-4)(PPh3)(η-C5H5)] (1). A
solution of 4-ethynyltoluene (0.271 g, 2.33 mmol) in tetrahy-
drofuran (20 mL) was cooled to 0 °C, treated dropwise with a
solution of nBuLi in hexane (1.46 mL, 1.60 M, 2.33 mmol), and
allowed to warm to room temperature and then recooled to 0 °C.
Gray selenium (0.192 g, 2.41 g-atom) was added, and the
mixture stirred until all the selenium had dissolved. The resulting
yellow solution was cooled to -20 °C and transferred by filter
cannula to a second vessel containing a solution of [NiCl(PPh3)(η-
C5H5)] (1.00 g, 2.40 mmol) in tetrahydrofuran (25 mL), which was
also precooled to -20 °C. The mixture was allowed to warm slowly
to room temperature, during which time it changed in color from
purple to deep red-brown. After approximately 30 min stirring at
room temperature, the solution was reduced in volume to ca. 15
mL under reduced pressure, resulting in the precipitation of the
crude product. The supernatant was removed via filter cannulation
to afford a red-brown powder that was washed with diethyl ether
and then recrystallized from a mixture of dichloromethane and
hexane to give 1 in an analytically pure form. Yield: 0.57 g (41%,
Experimental Section
General Procedures. All manipulations, unless otherwise sta-
ted, were carried out under an atmosphere of dry prepurified
dinitrogen using conventional Schlenk, vacuum line, and glove-
box techniques. Solvents were purified, when necessary, by
distillation from an appropriate drying agent (ethers and par-
afins from sodium/potassium alloy with benzophenone as in-
dicator; halocarbons from CaH2). Petroleum ether refers to that
fraction of petroleum of boiling range 40-60 °C. 1H and 31P{1H}
NMR spectra were recorded at 25 °C on JEOL JMX-270
(1H: 270.0 MHz, 31P{1H}: 121.5 MHz), Varian Gemini 300, or
Mercury 300 (1H: 300.1 MHz, 31P{1H}: 121.469 MHz) spectrom-
eters. 13C{1H} spectra were recorded on Varian INOVA 300
(13C{1H}: 75.42 MHz) or Varian INOVA 500 (13C{1H}: 125.7
MHz) spectrometers. 1H and 13C{1H} NMR chemical shifts are
reported relative to δ(SiMe4) = 0, internally referenced against
deuterated (13C) orresidual protiated(1H) solvent peaks. 31P{1H}
NMRchemical shiftsarereportedrelativetoanexternalstandard
(D3PO4). Elemental microanalytical data were obtained from the
ANU Research School of Chemistry or University of North
London microanalytical services. FAB mass spectrometry was
performed by the Imperial College mass spectrometry service
with samples prepared in nitrobenzyl matrices. Electrospray
mass spectrometry (ESI) was performed by the Research
School of Chemistry mass spectrometry service. Samples for
ESI were prepared by dissolving a solid in a small amount
of CH2Cl2 and diluting with either acetonitrile or methanol.
Mass spectrometric assignments were substantiated by simula-
tion of isotopic distributions. IR spectra were recorded in the
solid state (Nujol mulls) and in solution (CH2Cl2). Only bands
associated with the chromophores of interest are reported. The
complexes [NiCl(PPh3)(η-C5H5)],14 [FeCl(CO)2(η-C5H5)],19
and [MoI(CO)3{HB(pz)3)3]41 were prepared according to
published procedures. The complex [MoI(CO)3(η-C5H5)]
has been described previously,24 but was in this instance
prepared by the procedure outlined below. Caution: heavy
metal alkynyls have on occasion been found to spontaneously
detonate.42
0.98 mmol). Crystals of the solvate 1 (CHCl3)2 suitable for X-ray
3
diffraction analysis were grown by slow cooling of a concentrated
chloroform solution of 1. IRCH2Cl2: 2131 cm-1 νCꢀC. Nujol: 2127
cm-1 νCꢀC. NMR (CDCl3, 25 °C): 1H: δH 2.30 (s, 3 H, CH3), 5.25
3
(s, 5 H, C5H5), 7.03, 7.25 [(AB)2, 4 H, C6H4, JAB = 6.7 Hz),
7.30-7.9 (m, 15 H, C6H5). 13C{1H}: δC 136.1 [C1(C6H4)], 133.9 [d,
2
1
C
2,6(C6H5), JPC=11.2], 132.5 [d, C1(C6H5), JPC=24.0], 131.5
[C3,5(C6H4)], 130.5 [C4(C6H5)], 128.8 [C2,6(C6H4)], 128.4 [d, C3,5
-
(C6H5)], JPC = 10.0 Hz], 123.2 [C4(C6H4)], 95.1 (C5H5), 92.6
3
(CCt), 84.9 (SeCt), 21.5 (CH3). 31P{1H}: δP 40.1 ppm. FAB-MS
(þve ion, nba matrix): m/z 580 [M]þ, 515 [M - C5H5]þ, 465 [M -
CCR1]þ, 400 [M - C5H5 - CCR1]þ, 385 [M - SeCCR1]þ. Anal.
Found: C, 66.11; H, 4.70. Calcd for C32H27PNiSe: C; 66.25, H;
4.69. Crystal data for 1: C32H27NiPSe (CHCl3)2, Mw = 818.91,
3
monoclinic, P21/c (no. 14), a = 14.164(6) A, b = 17.521(6) A, c =
15.348(10) A, β = 105.60(4)°, V = 3669(3) A3, Z = 4, Dc = 1.483
Mg m-3, μ(MoKR) = 2.024 mm-1, T= 203 K, orange-red plates,
Siemens P4 diffractometer; 4442 independent measured reflections
(Rint=0.0592), F2 refinement, R1(obs)=0.0660, wR2(all) = 0.1594,
2684 independent observed absorption-corrected reflections
[|Fo|>4σ(|Fo|), 2θmax=45°], 509 parameters. CCDC 784169.
Synthesis of [Fe(SeCtCC6H4Me-4)(CO)2(η-C5H5)] (2a). A
solution of 4-ethynyltoluene (2.00 g, 17.2 mmol) in tetrahydro-
furan (20 mL) was cooled to 0 °C and treated dropwise with a
solution of nBuLi in hexane (10.8 mL, 1.60 M, 17.3 mmol). The
mixture was then allowed to warm to room temperature and
stirred for 30 min before being recooled to 0 °C. Gray selenium
(1.36 g, 17.2 g-atom) was added in one portion, and the mixture
then stirred for 30 min, by which time all the selenium had
dissolved and reacted. The solution was cooled to -20 °C and
transferred dropwise by filter cannula to a precooled (-20 °C)
solution of [FeCl(CO)2(η-C5H5)] (3.67 g, 17.2 mmol) in diethyl
ether (50 mL). The mixture was allowed to warm to room
temperature with stirring, during which time, the color changed
from red to deep green. After approximately 30 min stirring at
room temperature, the solvent was removed in vacuo, and the
Synthesis of [MoI(CO)3(η-C5H5)]. The following procedure
is a minor modification of that described by Filippou.41 The
modifications are of a practical nature. Rather than employing
NaC5H5, which typically forms as a nonstoichiometric thf sol-
vate that is difficult to completely free of the solvent, the free-
flowing crystalline stoichiometric solvate NaC5H5 dme was
used. Unreacted [Mo(CO)6] was removed by precipitation of
3
(40) Hill, A. F.; Hulkes, A. G.; White, A. J. P.; Williams, D. J.
Organometallics 2000, 19, 371.
(41) Filippou, A. C.; Gruenleitner, W.; Herdtweck, E. J. Organomet.
Chem. 1989, 373, 325.
(42) Dewhurst, R. D.; Hill, A. F.; Smith, M. K. Organometallics 2006,
25, 2388.

Article
Organometallics, Vol. 29, No. 23, 2010 6357
residue was then extracted with dichloromethane (50 and 20 mL
portions). The combined, filtered extracts were concentrated to
ca. 20 mL and then diluted with light petroleum followed by
further concentration to afford the crude product (green
platelets), which was found to be slightly impure (IR, TLC).
This crude material was then recrystallized from a mixture of
diethyl ether and hexane to provide deep green platelets. Yield:
3.32 g (52%, 8.95 mmol). Crystals of 2a suitable for X-ray
diffraction analysis were grown by slow diffusion of hexane into
a concentrated solution of 1 in diethyl ether. IR Nujol: 2133
Subsequent elution with neat diethyl ether mobilized a broad,
red fraction. This was diluted with light petroleum, and the
solvent volume was reduced on a rotary evaporator until the
product precipitated as deep red crystals. These were collected
on a glass frit, washed with small portions of petroleum ether,
and dried in vacuo. Yield: 1.51 g (42%, 3.44 mmol). IR Nujol:
2134 νCtC, 2033, 1962, 1943 νCO cm-1. CHCl3: 2137 νCtC, 2050
(sh), 2036, 1976, 1960, 1934 (br) νCO cm-1. Hexane: 2142 νCꢀC
,
2036, 1973, 1960, 1944 (br) νCO cm-1. NMR (CDCl3, 25 °C): 1H:
H 2.32 (s, 3 H, CH3), 5.60 (s, 5 H, C5H5), 7.29, 7.55 [(AB)2, 4 H,
δ
ν
CꢀC, 2026, 1979 νCO cm-1. NMR (CDCl3, 25 °C): 1H: δH 2.30
C6H4, 3JAB=7.9 Hz]. 13C{1H}: δC 235.3 (CO), 222.9 (CO), 137.0
[C4(C6H4)], 131.8 [C2,6(C6H4)], 129.1 [C3,5(C6H4)], 121.8 [C1-
(C6H4)], 95.2 (C5H5), 92.1 (SeCt), 86.9 (CCt), 75.2 (SeC0t),
21.6 (CH3). Anal. Found: C, 46.31; H, 2.83. Calcd for
C17H12MoO3Se: C, 46.49; H, 2.75. FAB-MS (þve ion): m/z
438 [M - 2H]þ, 412 [M - CO]þ, 383 [M - 2CO - H]þ, 356 [M -
3CO]þ.
(s, 3 H, CH3), 5.00 (s, 5 H, C5H5), 7.03, 7.25 ((AB)2, 4 H, C6H4,
3JAB = 7.8 Hz). 13C{1H}: δC 212.9 (CO), 137.0 [C4(C6H4)], 131.7
[C2,6(C6H4)], 129.0 [C3,5(C6H4)], 122.3 [C1(C6H4)], 85.7 (CCt),
85.4 (C5H5), 75.0 (SeCt), 21.5 (CH3). FAB-MS (þve ion, nba
matrix): m/z 372 [M]þ, 316 [M - 2CO]þ. Anal. Found: C, 51.71;
H, 3.33. Calcd for C16H12O2FeSe: C, 51.79; H, 3.26. Crystal
data for 2a: C16H12FeO2Se, Mw=371.07, triclinic, P1 (no. 2),
a = 6.7194(5) A, b = 8.6243(11) A, c = 13.679(3) A, R =
105.948(10)°, β=97.141(11)°, γ=96.818(9)°, V=746.5(2) A3,
Z = 2, Dc=1.651 Mg m-3, μ(Cu KR)=10.865 mm-1, T = 293
K, orange prisms, Siemens P4 diffractometer; 2194 independent
measured reflections (Rint =0.0968), F2 refinement, R1(obs)=
0.0625, wR2(all)=0.1850, 1704 independent observed absorp-
tion-corrected reflections [|Fo| > 4σ(|Fo|), 2θmax = 120°], 183
parameters. CCDC 784170.
Synthesis of [Mo(η2-C,C0-SeCCC6H4Me-4)(CO2{HB(pz)3)]
(4). The reaction of LiSeCtCR1 with [MoI(CO)3{HB(pz)3}]. A
solution of LiSeCtCC6H4Me-4 was prepared as described
above by successive addition of nBuLi (2.40 mL, 1.6 M solution
in hexane, 3.84 mmol) and gray selenium (0.30 g, 3.80 g.atom) to
a solution of 4-ethynyltoluene (0.44 g, 3.91 mmol) in diethyl
ether (15 mL) at 0 °C. This solution was added dropwise over
15 min to a solution of [MoI(CO)3{HB(pz)3}] (2.00 g, 3.81
mmol) in THF maintained at -40 °C. The solution was allowed
to warm slowly to 0 °C, at which point all volatiles were removed
in vacuo. The resulting oil was redissolved in diethyl ether
and applied to a cryostatically cooled (-30 °C) silica gel
chromatography column (15 cm). Elution with diethyl ether
gave several minor unidentified yellow and brown fractions,
followed by a deep red fraction, which was collected, concen-
trated in vacuo, and further diluted with light petroleum to give a
red solid. Recrystallization from a mixture of dichloromethane
and hexane gave a deep red, microcrystalline solid. Yield: 0.22 g
(10%, 0.39 mmol). IR Nujol: 2479 (w) νBH, 1952, 1861 νCO, 1049
(m) νCdSe (tentative). NMR (CDCl3, 25 °C): 1H: δH 2.24 (s, 3 H,
CH3), 4.6 (s br, 1 H, BH), 6.0-8.6 (m, 13 H, C6H4 and pz).
13C{1H}: δC 234.0 (br, ModCCSe, ModCCSe), 215.1 (CO),
150-125 [C3,5(pz) and C6H4], 106.2 [C4(pz)], 21.4 (CH3). Anal.
Found: C, 43.07; H, 3.11; N, 15.05. Calcd for C20H17BMo-
N6O2Se: C, 42.97; H, 3.06; N, 15.03. FAB-MS (þve ion): m/z
504 [M - 2CO]þ, 467 [M - C7H7]þ, 388 [M - C7H7 - Se]þ.
Synthesis of [Fe(SeCtCC6H4Me-4)(CO)(PPh3)(η-C5H5)] (6).
A solution of [Fe(SeCtCC6H4Me-4)(CO)2(η-C5H5)] (2a: 0.25 g,
0.67 mmol) and triphenylphosphine (0.18 g, 0.69 mmol) in
diethyl ether (25 mL) was irradiated with a domestic tungsten
lamp, resulting in vigorous evolution of CO and a color change
to red-brown within 30 s. Irradiation was continued until the
complete consumption of 2a was indicated (IR, TLC). The
solution was diluted with hexane and reduced in volume on a
rotary evaporator to give the title compound as a red-brown
solid, which was recrystallized from a mixture of dichloro-
methane and hexane (-18 °C). Yield: 0.30 g (72%, 0.50 mmol).
Synthesis of [Fe(SeCtCSiMe3)(CO)2(η-C5H5)] (2b). A solu-
tion of ethynyltrimethylsilane (2.00 mL, d = 0.695 g mL-1
1.40 g, 14.1 mmol) in tetrahydrofuran (20 mL) was cooled to
,
n
0 °C and treated dropwise with a solution of BuLi in hexane
(8.84 mL, 1.60 M, 14.1 mmol). The pale yellow solution was
allowed to warm to room temperature (1 h) and then recooled to
0 °C. Gray selenium (1.125 g, 14.2 g-atom) was added in one
portion, which dissolved within 15 min to provide an orange
solution, which was then cooled (-60 °C). The solution was
transferred (filter cannula) to a cooled (-60 °C) suspension
of [FeCl(CO)2(η-C5H5)] (3.02 g, 14.2 mmol) in diethyl ether
(50 mL). The mixture was allowed to warm to room temperature
and stirred for 1 h with the development of an olive green color.
TLC (silica gel, CH2Cl2/hexane, 1:1) indicated the presence of
only one visible mobile component. The solvent was removed
under reduced pressure, the resulting residue was extracted with
dichloromethane (2 ꢁ 50 mL), and the combined extracts were
filtered through diatomaceous earth. Addition of petroleum
ether (40-60) to the filtrate and slow concentration provided
a khaki microcrystalline powder that was spectroscopically pure
(1H NMR, IR) and suitable for subsequent investigations. A
sample for elemental microanalysis was prepared by recrystalli-
zation of the mixture from a mixture of dichloromethane and
n-hexane at -18 °C. Yield: 4.35 g (87%, 12.3 mmol). IR CH2Cl2:
2061 νCꢀC, 2034, 1990 νCO cm-1. Nujol: 2062 νCꢀC, 2035, 1993
ν
CO cm-1. NMR 1H (C6D6): δ 3.94 (s, 5 H, C5H5), 0.25 (s, 9 H,
SiCH3) ppm. 13C{1H} (CDCl3): 212.5 (CO), 92.89, 92.78 (CtC),
85.34 (C5H5), 0.38 (SiCH3) ppm. MS (ESI high-res, þve ion,
MeCN): m/z 353.9286. Anal. Calcd 353.9282. Found: C, 40.67;
H, 4.20. Anal. Calcd for C12H14FeO2SeSi: C, 40.82; H, 4.00.
Synthesis of [Mo(SeCtCC6H4Me-4)(CO)3(η-C5H5)] (3). A
solution of LiSeCtCC6H4Me-4 (from 0.94 g of 4-ethynyl-
toluene, 1 equiv of 1.6 M BuLi, and 0.64 g of gray selenium as
described above) was added via a filter cannula to a solution of
[MoI(CO)3(η-C5H5)] (3.00 g, 8.10 mmol, prepared as described
above) in THF (25 mL), maintained at -40 °C. The mixture was
then allowed to warm slowly to room temperature with stirring,
during which time it changed slightly in color from red to purple-
red. After approximately 30 min stirring, the solvent was re-
moved in vacuo, and the resulting red oil was redissolved in
diethyl ether/light petroleum (4:1). The solution was applied to
the top of a cryostatically cooled (-30 °C) chromatography
column (silica gel/15 cm). Initial elution with the same solvent
combination removed traces of unreacted starting material.
IR CH2Cl2: 2129 νCꢀC, 1945 νCO cm-1. Nujol: 2122 νCꢀC
,
1945, 1933 νCO cm-1. NMR (CDCl3, 25 °C): 1H: δH 2.30 (s, 3
H, CH3), 4.55 (s, 5 H, C5H5), 7.01, 7.28 [(AB)2, 4 H, C6H4, 3JAB
= 7.0 Hz], 7.21-7.74 (m, 15 H, C6H5). 13C{1H}: δC 219.8 (d,
CO, 2JPC=34), 136.0 [C1(C6H4)], 135.0 [d, C1(C6H5), 1JPC
=
2
44], 133.4 [d, C2,6(C6H5), JPC=9.8], 131.6 [C3(C6H4)], 130.3
[C4(C6H5)], 128.8 [C2(C6H4)], 128.4 [d, C3,5(C6H5), 3JPC=9.9],
123.3 [C4(C6H4)], 84.7 (C5H5), 82.7 (CCtC), 79.4 (d, SeCtC,
3JPC =7.2 Hz), 21.6 (CH3). 31P{1H}: δP 71.2. FAB-MS (þve
ion, nba matrix) m/z 606 [M]þ, 578 [M - CO]þ, 513 [M - C5H5
- CO]þ, 463 [M - CO - CCR1]þ, 411 [M - SeCCR1]þ, 399
[FePPh3]þ, 383 [M - SeCCR1 - CO]þ, 316 [M - PPh3 - CO]þ.
Anal. Found: C, 65.52; H, 4.61. Calcd for C33H27OPFeSe: C,
65.48; H, 4.50.
Synthesis of [Fe(SeC{Co2(CO)6}CC6H4Me-4)(CO)2(η-C5H5)]
(8). To a solution of [Fe(SeCtCC6H4Me-4)(CO)2(η-C5H5)]

6358 Organometallics, Vol. 29, No. 23, 2010
Caldwell et al.
(2a: 0.30 g, 0.81 mmol) in diethyl ether (20 mL) was added
[Co2(CO)8] (0.28 g, 0.81 mmol) in one portion. Evolution of gas
was observed, which ceased after 1-2 min. The volatiles were
removed in vacuo, and the residue was redissolved in light petro-
leum and transferred via cannula filtration to a second Schlenk
vessel. The solvent volume was reduced, and cooling (dry ice/
propanone) gave the title compound as a deep green microcrystal-
line solid. Yield: 0.52 g (98%, 0.79 mmol). IR Nujol: 2080, 2048,
2028, 2003, 1978 νCO cm-1. NMR (CDCl3, 25 °C) 1H: δH 2.35 (s, 3
H, CH3), 5.03 (s, 5 H, C5H5), 7.19, 7.74 [s br ꢁ 2, 2 H ꢁ 2, C6H4,
3JHH not resolved). 13C{1H}: δC 213.2 (FeCO), 199.8 (br, CoCO),
137.7 [C4(C6H4)], 136.2 [C1(C6H4)], 128.9 [C2,6(C6H4)], 128.7
[C3,5(C6H4)], 103.3 (CCtC), 90.4 (SeCtC), 85.0 (C5H5), 21.5
(CH3) ppm. FAB-MS (þve ion, nba matrix): m/z 658 [M]þ,
followed by peaks for successive loss of 8 ꢁ CO. Anal. Found:
C, 40.33; H, 1.88. Calcd for C22H12O8Co2FeSe: C, 40.22; H, 1.84.
Acknowledgment. We gratefully acknowledge the fi-
nancial support of the Australian Research Council
(DP0556236).
Supporting Information Available: Full details of the crystal
structure determination of 1 (CHCl3)2 (CCDC 784169) and 2a
3
(CCDC 784170) in CIF format; ORTEP representations of the
molecular structures of 1 and 2a; Tables S1 collating geometric
parameters for alkynylselenolate complexes. This material is
available free of charge via the Internet at http://pubs.acs.org.