Alkyneselenolate vs Selenoketenyl Coordination: Synthesis and reactivity of [Ir(SeC≡CC6H4Me-4)(CO)(PPh3)2]

Article abstract of DOI:10.1021/om980268n

The reaction of [IrCl(CO)(PPh₃)₂] with LiSeC≡CR (R = C₆H₄Me-4) provides [Ir(SeC≡CR)(CO)-(PPh₃)₂] (1), which undergoes oxidative addition reactions with oxygen, methyl iodide, benzeneselenenyl chloride and bis(4-tolylethynyl)mercury to provide the complexes [Ir(SeC≡CR)(η-O₂)(CO)(PPh₃)₂] (2), [Ir(CH₃)-(SeC≡CR)I(CO)(PPh₃)₂] (3), [Ir(CH₃)I₂(CO)(PPh₃)₂] (4), [IrCl(SePh)(SeC≡CR)(CO)(PPh₃)₂] (5), and [Ir(C≡CR)-(HgC≡CR)(SeC≡CR)(CO)(PPh₃)₂] (6). The complexes 1-3, and 5, and 6 each contain the alkyneselenolate ligand bound to iridium in a monodentate manner through selenium.

Full text of DOI:10.1021/om980268n

Organometallics 1998, 17, 4117-4120
4117
Alk yn eselen ola te vs Selen ok eten yl Coor d in a tion :
Syn th esis a n d Rea ctivity of
[Ir (SeCtCC6H4Me-4)(CO)(P P h 3)2]
Robin D. Bedford, Paul J . Dyson,*,1 Anthony F. Hill,*,1 Alexander G. Hulkes, and
Christopher J . Yates
Centre for Chemical Synthesis, Department of Chemistry, Imperial College of Science,
Technology and Medicine, London SW7 2AY, U.K.
Received April 7, 1998
Sch em e 1. Syn th esis of Selen ok eten yl Com p lexes
of Tu n gsten a n d Molybd en u m (R ) C6H4Me-4; ML
) WP P h 3, WP Me2P h , MoP P h 3; Tp )
Summary: The reaction of [IrCl(CO)(PPh3)2] with
LiSeCtCR (R ) C6H4Me-4) provides [Ir(SeCtCR)(CO)-
(PPh3)2] (1), which undergoes oxidative addition reac-
tions with oxygen, methyl iodide, benzeneselenenyl chlo-
ride and bis(4-tolylethynyl)mercury to provide the
complexes [Ir(SeCtCR)(η2-O2)(CO)(PPh3)2] (2), [Ir(CH3)-
(SeCtCR)I(CO)(PPh3)2] (3), [Ir(CH3)I2(CO)(PPh3)2] (4),
[IrCl(SePh)(SeCtCR)(CO)(PPh3)2] (5), and [Ir(CtCR)-
(HgCtCR)(SeCtCR)(CO)(PPh3)2] (6). The complexes
1-3, and 5, and 6 each contain the alkyneselenolate
ligand bound to iridium in a monodentate manner
through selenium.
Hyd r otr is(p yr a zolyl)bor a te2)
alkylidynes of the late transition metals are not appar-
ently prone to coupling reactions with carbonyl coli-
gands,8 we reasoned that if ketenyl (or chalcoketenyl)
ligands could be introduced into the coordination sphere
of late transition metals, decoupling into alkylidyne and
chalcocarbonyl ligands might actually be facile. Despite
notable recent advances,9 routes to late transition metal
alkylidynes remain rare8 providing impetus for develop-
ing new approaches to such complexes.
Weigand has reported that the reaction of [RuCl-
(PPh3)2(η-C5H5)] with LiSCtCR (R ) CMe3, cyclohexyl,
Ph) provides the alkynethiolato complexes [Ru(σ-SCt
CR)(PPh3)2(η-C5H5)], wherein the organosulfur ligand
is bound only through sulfur as a conventional thiolate
(A, Chart 1).10 One phosphine ligand in [Ru(σ-SCt
CPh)(PPh3)2(η-C5H5)] is clearly labile, as indicated by
its replacement with carbon monoxide; however the
presumed 16 electron intermediate does not appear to
rearrange to a thioketenyl ligand (B, Chart 1).
In tr od u ction
We have recently reported the first examples of
selenoketenyl ligands which result from the reaction of
ketenyl complexes with Woollins’ reagent (Scheme 1).2
These results follow from our earlier studies on the
related reactions of ketenyl complexes with Lawesson’s
thiating agent which provide analogous thioketenyl
complexes.3 Thioketenyl complexes had been previously
reported by Mayr via the presumed coupling of thiocar-
bonyl and alkylidyne ligands on tungsten centers,4
although we have recently had reason to reinterpret the
mechanism of such processes.5 Furthermore, Weiss has
invoked thioketenyl intermediates in rationalizing the
products of various coupling reactions of high-valent
tungsten alkylidynes with alkyl isothiocyanates and
related heterocumulenes.6 In our studies of thio- and
selenoketenyls of group 6 we have never encountered
the decoupling of such a ligand into the notional
alkylidyne and chalcocarbonyl constituents, even though
such processes are often facile for ketenyls themselves,
as is the reverse process whereby the majority of known
ketenyl complexes have been prepared.7 Given that
(7) For a review of ketenyl complexes, see: Mayr, A.; Bastos, C. M.
Prog. Inorg. Chem. 1992, 40, 1.
(8) For reviews of late transition metal alkylidynes, see: (a) Hill,
A. F. In Comprehensive Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K., 1995;
Vol. 7. (b) Roper, W. R. NATO ASI Series C.; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1993; Vol. 392, p 155. (c)
Roper, W. R. J . Organomet. Chem. 1986, 300, 167. (d) Gallop, M. A.;
Roper, W. R. Adv. Organomet. Chem. 1986, 25, 121.
(1) E-mail: a.hill@ic.ac.uk, p.dyson@ic.ac.uk.
(2) Baxter, I.; Hill, A. F.; Malget, J . M.; White, A. J . P.; Williams,
D. J . J . Chem. Soc., Chem. Commun. 1997, 2049.
(3) Hill, A. F.; Malget, J . M. J . Chem. Soc., Chem. Commun. 1996,
1177.
(4) Lee, T. Y.; Mayr, A. J . Am. Chem. Soc. 1994, 116, 10300; Angew.
Chem., Int. Ed. Engl. 1993, 32, 1726.
(9) (a) Espuelas, J .; Esteruelas, M. A.; Lahoz, F. J .; Oro, L. A.; Ruiz,
N. J . Am. Chem. Soc. 1993, 115, 4683. (b) Bourgault, M.; Castillo, A.;
Esteruelas, M. A.; On˜ate, E.; Ruiz, N. Organometallics 1997, 16, 636.
(c) Esteruelas, M. A.; Lopez, A. M.; Ruiz, N.; Tolosa, J . I. Organome-
tallics 1997, 16, 4657. (d) Weber, B.; Steinert, P.; Windmuller, B.; Wolf,
J .; Werner, H. J . Chem. Soc., Chem. Commun. 1994, 2595. (e) LaPointe,
A. M.; Schrock, R. R.; Davis, W. H. J . Am. Chem. Soc. 1995, 117, 4802.
(f) LaPointe, A. M.; Schrock, R. R. Organometallics 1993, 12, 3379. (g)
Trammel, S.; Sullivan, B. P.; Hodges, L. M.; Harman, W. D.; Smith,
S. R.; Thorp, H. H. Inorg. Chem. 1995, 34, 2791. (h) Hodges, L. M.;
Sabat, M.; Harman, W. D. Inorg. Chem. 1993, 32, 371. (i) Anderson,
S.; Hill, A. F. J . Organomet. Chem. 1990, 394, C24. (j) Anderson, S.;
Hill, A. F. Organometallics 1995, 14, 1562.
(5) Hill, A. F.; Malget, J . M.; White, A. J . P.; Williams, D. J . Inorg.
Chem. 1998, 37, 598.
(6) (a) Goller, R. Doctorate Thesis, University of Bayreuth, 1988.
(b) Weiss, K.; Goller, R.; Denzner, M.; Lo¨ssel; and Ko¨del, J . In
Transition Metal Carbyne Complexes; Kreissl, F. R., Ed.; NATO ASI
Series C; Kluwer Academic Publishers: Dordrecht, The Netherlands,
1993; Vol. 392, p 55. (c) Goller, R.; Schubert, U.; Weiss, K. J .
Organomet. Chem. 1993, 459, 229. (d) Schrock, R. R.; Schubert, U.;
Weiss, K. Organometallics 1986, 5, 359.
(10) (a) Weigand, W. Z. Naturforsch., B 1991, 46, 1333. (b) Weigand,
W.; Robl, C. Chem. Ber. 1993, 126, 1807. (c) Weigand, W.; Weishaupl,
M.; Robl, C. Z. Naturforsch., B 1996, 51, 501.
S0276-7333(98)00268-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 08/12/1998

4118 Organometallics, Vol. 17, No. 18, 1998
Notes
°C): 1H, δ 2.18 [s, 3 H, CH3], 6.04, 6.69 [(AB)2, 4 H, C6H4,
J (HAHB) ) 7.92 Hz], 7.34-7.88 [m, 30 H, C6H5] ppm; 13C{1H},
175.8 [t, IrCO, J (PC) ) 25.0], 135.0 [tv, C2,6(C6H5), J (PC) )
6.3], 131.2 [tv, C1(C6H5), J (PC) ) 19.7 Hz], 130.3 [s, C4(C6H5)],
127.8 [tv, C3,5(C6H5), J (PC) not resolved], 122.4 [C4(C6H4)]
(remaining C6H4 resonances obscured by those for C6H5
groups), 94.9 [CCt], 68.0 [SeCt], 21.3 [CH3] ppm; 31P{1H}, δ
27.9 ppm. FAB-MS: m/z ) 940 [M]+, 712 [M - CO]+, 796 [M
- CO - CCR]+, 745 [Ir(CO)(PPh3)2]+, 715 [Ir(PPh3)2]+, 453
[IrPPh3]+, 263 [HPPh3]+. Anal. Found: C, 59.0; H, 4.0. Calcd
for C46H37IrOP2Se: C, 58.8; H, 4.0.
Ch a r t 1. Coor d in a tion Mod es for Alk yn yl
Ch a lcogen ola tes a n d Alk yn yl Ch a lcoeth er s
P r ep a r a tion of [Ir (SeCtCR)(η2-O2)(CO)(P P h 3)2] (2). A
solution of [Ir(SeCtCR)(CO)(PPh3)2] (1) (0.100 g, 0.11 mmol)
in dichloromethane (20 mL) was stirred under air for 12 h
(quantitative conversion by FT-IR). The solvent was removed
under reduced pressure and the residue crystallized by addi-
tion of diethyl ether. Yield: 0.055 g (54%). IR: CH2Cl2, 2035
[ν(CO)] cm-1; Nujol, 2132 [ν(CtC)], 1982 [ν(CO)], 852 [ν(IrO2)],
815 [δ(C6H4)] cm-1. NMR (CDCl3, 25 °C): 1H, δ 2.29 [s, 3 H,
CH3], 6.96, 7.03 [(AB)2, 4 H, C6H4, J (HAHB) ) 7.92 Hz], 7.30-
7.93 [m, 30 H, C6H5] ppm; 13C{1H}, 168.8 [t, IrCO, J (PC) )
9.5], 134.7 [tv, C2,6(C6H5), J (PC) ) 5.3], 132.2 [tv, C1(C6H5)],
131.0 [s, C4(C6H5)], 128.2 [tv, C3,5(C6H5), J (PC) 4.5 Hz], 122.7
[C4(C6H4)] (remaining C6H4 resonances obscured by those for
C6H5 groups), 89.4 [CCt], 75.7 [SeCt], 21.5 [CH3] ppm; 31P-
{1H}, δ 5.6 ppm. FAB-MS: m/z ) 971 [M]+, 940 [M - O2]+,
712 [M - O2 - CO]+, 796 [M - CO - O2 - CCR]+, 745 [Ir-
(CO)(PPh3)2]+, 715 [Ir(PPh3)2]+, 453 [IrPPh3], 263 [HPPh3]+.
Anal. Found: C, 56.5; H, 3.9. Calcd for C46H37IrO3P2Se: C,
56.9; H, 3.8.
In pursuit of alternative routes to selenoketenyl
complexes we have investigated the reactions of Vaska’s
complex [IrCl(CO)(PPh3)2] with LiSeCtCC6H4Me-4, the
results of which are reported herein.
Exp er im en ta l Section
Gen er a l Com m en ts. All manipulations were carried out
under anaerobic conditions using conventional Schlenk and
vacuum line techniques. Solvents as received from commercial
sources were distilled from a suitable drying agent and purged
with nitrogen prior to use. Vaska’s complex was prepared
according to a published procedure,11 with the exception that
hexachloroiridic acid was used in place of iridium(III) chloride
with no substantial compromise in yield. All other reagents
were used as received from commercial sources. 1H, 13C{1H},
and 31P{1H} NMR spectra were recorded with a J EOL J NM
EX270 NMR spectrometer and calibrated against internal
SiMe4 (1H), internal CDCl3 (13C) or external H3PO4 (31P)
references. “tv” indicates a virtual triplet arising from the
trans-bis(phosphine) arrangement, with “apparent” couplings
given. Infrared spectra were recorded both as dichloromethane
solutions, and Nujol mulls, using Perkin-Elmer 1720-X or
Mattson Series 1 FT-IR spectrometers. Characteristic “fin-
gerprint” bands for PPh3 are omitted. FAB-mass spectrometry
was carried out using an Autospec Q instrument with 3-ni-
trobenzyl alcohol as a matrix. Compositional assignments are
based on simulation of isotopic distributions. Elemental
analysis was carried out by the University of North London
Microanalytical Service.
P r ep a r a t ion of [Ir (CH3)(SeCtCR )I(CO)(P P h 3)2] (3)
a n d [Ir (CH3)I2(CO)(P P h 3)2] (4). [Ir(SeCtCR)(CO)(PPh3)2]
(1) (0.100 g, 0.11 mmol) was stirred in iodomethane (3 mL)
for 16 h. Diethyl ether (15 mL) was added and the resulting
precipitate filtered off to provide pale yellow microcrystals of
3. Yield: 0.035 g (30%). The filtrate was diluted with ethanol
(20 mL) and the solvent volume reduced slowly to afford
fibrous crystals of 4. Yield: 0.070 g (69%). The complex could
be recrystallized from a mixture of dichloromethane and
ethanol as a CH2Cl2 hemisolvate.
(a ) Da ta for (3). IR (Nujol): 2134 [ν(CtC)], 2049 [ν(CO)]
cm-1. NMR (CDCl3, 25 °C): 1H, δ 0.66 [t, 3 H, IrCH3, J (PH)
) 5.1], 2.33 [s, 3 H, C-CH3], 7.03, 7.19 [(AB)2, 4 H, C6H4,
J (HAHB) ) 7.92 Hz], 7.32, 7.89 [m × 2, 30 H, C6H5] ppm; 31P-
{1H}, δ -21.1 ppm. FAB-MS: m/z )1078 [M]+, 887 [M -
SeCCR]+. Anal. Found: C, 50.5; H, 4.0. Calcd for C47H40
-
IIrOP2Se‚0.5CH2Cl2: C, 50.7; H, 3.7.
(b) Da ta for 4. IR (CH2Cl2): 2044 [ν(CO)] cm-1
. IR
(Nujol): 2028 [ν(CO)], 1241 [ν(IrCH3)] cm-1. NMR (CDCl3, 25
°C): 1H, δ 1.14 [t, 3 H, IrCH3, J (PH) ) 5.2 Hz], 7.19-8.01 [m,
30 H, C6H5] ppm; 31P{1H}, δ -25.4 ppm. FAB-MS: m/z ) 1015
[HM]+, 887 [M - I]+, 859 [M - I - CO]+. Anal. Found: C,
44.9; H, 3.3. Calcd for C38H33I2IrOP2: C, 45.0; H, 3.3.
P r ep a r a tion of [Ir (SeCtCC6H4Me-4)(CO)(P P h 3)2] (1).
A solution of 4-ethynyltoluene (0.037 g, 0.32 mmol) in diethyl
ether (10 mL) was cooled to -20 °C and then treated with
nBuLi (0.16 mL, 2.0 mol L-3, 0.32 mmol) and the mixture
stirred for 20 min. The solution was allowed to warm to room
temperature, and then gray selenium (0.030 g) was added and
the mixture stirred for a further 30 min or until all the
selenium had dissolved. The resulting (air-sensitive) solution
was transferred by cannula to a flask containing [IrCl(CO)-
(PPh3)2] (0.25 g, 0.32 mmol) in tetrahydrofuran (25 mL). The
mixture was stirred for 15 min (darkens somewhat) and then
transferred by filter cannula to a second Schlenk tube. The
total solvent volume was reduced in vacuo to ca. 5 mL and
then diluted with diethyl ether (20 mL) resulting in the
precipitation of a bright yellow solid which was recrystallized
from a mixture of dichloromethane and diethyl ether. Yield:
0.20 g (67%). IR: CH2Cl2, 1957 [ν(CO)] cm-1; Nujol, 2142 [ν-
P r ep a r a tion of [Ir Cl(SeP h )(SeCtCR)(CO)(P P h 3)2] (5).
A solution of [Ir(SeCtCR)(CO)(PPh3)2] (1) (0.10 g, 0.11 mmol)
in tetrahydrofuran (15 mL) was treated with benzeneselenenyl
chloride (0.022 g, 0.11 mmol) and the mixture stirred for 15
min. The solvent volume was reduced in vacuo to ca. 10 mL
and then diluted with diethyl ether (15 mL) to provide an
orange solid which was recrystallized from a mixture of
dichloromethane and diethyl ether. Yield: 0.098 g (75%). IR
(CH2Cl2): 2134 [ν(CtC)], 2059 [ν(CO)] cm-1. IR (Nujol): 2130
[ν(CtC)], 2049 [ν(CO)], 815 [δ(C6H4)] cm-1. NMR (CDCl3, 25
°C): 1H, δ 2.15 [s, 3 H, CH3], 6.49, 6.68 [(AB)2, 4 H, C6H4,
J (HAHB) ) 7.92 Hz], 6.8-8.2 [m, 35 H, C6H5] ppm; 31P{1H}, δ
-26.4 ppm. FAB-MS: m/z ) 1130 [M]+, 1094 [M - Cl]+, 1066
[M - Cl - CO]+, 1017 [M - CCR]+, 937 [M - SePh]+, 937 [M
- Cl - SePh]+, 910 [M - Cl - CO - SePh]+. Anal. Found:
C, 51.4; H, 3.8. Calcd for C52H42ClIrOP2Se2‚1.5CH2Cl2: C,
51.1; H, 3.6.
(CtC)], 1959 [ν(CO)], 817 [δ(C6H4)] cm-1
. NMR (CDCl3, 25
(11) Vrieze, K.; Collman, J . P.; Sears, C. T., J r.; Kubota, M. Inorg.
Synth. 1986, 11, 101.

Notes
P r ep a r a tion of [Ir (CtCR)(HgCtCR)(SeCtCR)(CO)-
Organometallics, Vol. 17, No. 18, 1998 4119
Sch em e 2. Syn th esis a n d Rea ction s of
[Ir (SeCtCR)(CO)(P P h 3)2] (R ) C6H4Me-4, L )
P P h 3)
(P P h 3)2] (6). A solution of [Ir(SeCtCR)(CO)(PPh3)2] (1) (0.10
g, 0.11 mmol) in tetrahydrofuran (15 mL) was treated with
solid bis(4-tolylethynyl)mercury(II) (0.046 g, 0.11 mmol) and
the mixture stirred for 1 h. The solvent volume was reduced
in vacuo to ca. 5 mL and then diluted with diethyl ether (20
mL) to provide a yellow solid which was recrystallized from a
mixture of dichloromethane and diethyl ether. Yield: 0.055
g (36%). IR (thf): 2130 [ν(CtC)], 2042 [ν(CO)] cm-1
(Nujol): 2125 [ν(CtC)], 2034 [ν(CO)], 815 [δ(C6H4)] cm-1
. IR
.
NMR (CDCl3, 25 °C): 1H, δ 2.28, 2.30, 2.31 [s × 3, 3 H × 3,
CH3 × 3], 6.8-7.2 [(AB)2 × 3, 12 H, C6H4 × 3], 7.34, 8.08 [m
× 2, 30 H, C6H5] ppm; 13C{1H}, 173.8 [t, IrCO, J (PC) ) 6.5 ],
146.4, 137.5, 135.5 [C4(C6H4) × 3], 134.5 [tv, C1(C6H5), J (PC)
) 21.9], 133.9 [tv, C2,6(C6H5), J (PC) ) 4.9], 131.9, 131.5, 130.3,
128.9, 128.8 [C2,3,5,6(C6H4)], 130.6 [C4(C6H5)], 128.4 [tv, C3,5(C6H5),
J (PC) ) 5.4], 125.0, 123.2, 120.8 [C1(C6H4) × 3], 115.7 [IrC≡C],
101.4 [HgCtC], 86.8 [SeCtC], 80.6 [t, IrCt, J (PC) ) 17.2 Hz],
79.4 [HgCt], 68.1 [SeCt], 21.6, 21.5, 21.4 [CH3 × 3] ppm; 31P-
{1H}, δ -18.6 [J (PSe) ) 27.8, J (PHg) ) 233.7 Hz] ppm. FAB-
MS: m/z ) 1252 [M - CCR]+, 1175 [M - SeCCR]+, 1055 [M
- HgCCR]+, 975 [M - Hg - SeCCR]+, 947 [M - Hg - SeCCR
- CO]+, 860 [M - HgCCR - SeCCR]+, 831 [M - HgCCR -
SeCCR - CO]+, 745 [Ir(CO)(PPh3)2]+, 715 [Ir(PPh3)2]+, 559
[IrPPh3]+. Anal. Found: C, 56.2; H, 3.9. Calcd for C64H51
HgIrOP2Se: 56.1; H, 3.8.
-
Resu lts a n d Discu ssion
A solution of LiSeCtCC6H4Me-4 was prepared by
first deprotonating 4-ethynyl toluene with nBuLi, fol-
lowed by treatment with elemental selenium12 (Scheme
2). Treating a tetrahydrofuran solution of [IrCl(CO)-
(PPh3)2] with this solution leads to the formation of a
bright yellow solution from which the complex [Ir(SeCt
CR)(CO)(PPh3)2] (1) (hereafter R ) C6H4Me-4) may be
isolated in 66% yield. Solutions of complex 1 must be
manipulated under total exclusion of air due to facile
formation of the dioxygen adduct [Ir(SeCtCR)(η2-O2)-
(CO)(PPh3)2] (vide infra); however, it is indefinitely
stable in the absence of air and may be handled briefly
in air as a solid.
The gross formulation of 1 follows from elemental
microanalytical data and FAB-mass spectrometry. The
latter includes an isotopic distribution attributable to
the molecular ion in addition to fragmentations due to
loss of the alkyneselenolate and/or carbonyl ligands. The
infrared spectrum reveals absorptions assignable to the
carbonyl ligand (Nujol: 1959 cm-1) and the free alkynyl
group [ν(CtC) ) 2142, δ(C6H4) ) 817 cm-1]. No band
could be identified due to ν(C-Se); however, these are
typically weak and buried within the phosphine finger-
print. The 1H NMR spectrum of 1 is unremarkable;
however, the 13C{1H} NMR spectrum is more informa-
tive. The appearance of a triplet resonance for the
carbonyl ligand [175.8 ppm, J (PC) ) 25.0 Hz] confirms
the trans-bis(phosphine) stereochemistry at iridium, and
this is further supported by a singlet 31P{1H} NMR
resonance being observed at 27.9 ppm. The alkynyl
group gives rise to two resonances at 94.9 and 68.0 ppm.
These compare well with those reported for PhSeCt
CR (103.2, 68.2 ppm).13 These data taken together
indicate that the organoselenium ligand adopts the η1-
Se mode of coordination, previously established for
alkynethiolates10 but which is novel for selenium. It is
noteworthy that this is despite the alternative η2-C,C′
mode offering the possibility of providing 3 valence
electrons to iridium and is clearly a feature of the
favorable and ubiquitous 16-electron d8-ML4 square
planar geometry.
The selenolate clearly serves as a potent donor, as
indicated by the significant increase in the propensity
of 1 to coordinate dioxygen irreversibly cf Vaska’s
complex. Thus, the orange dioxygen adduct forms
rapidly in solution at room temperature. Spectroscopic
data for [Ir(σ-SeCtCR)(η2-O2)(CO)(PPh3)2] (2) are di-
rectly comparable to those of the precursor, with the
exception that an infrared absorption attributable to the
IrO2 group is noted at 857 cm-1. This oxidation of the
iridium center is accompanied by an increase in ν(CO)
to 1982 cm-1 and a shift in the value of δ(31P) to 5.7
ppm. The effect of halide replacement upon the facility
and reversibility of dioxygen binding in the complexes
[IrX(CO)(PPh3)2] has long been established by Roper,14
and the present result is entirely consistent with the
established trends.
F u r th er Oxid a tive Ad d ition Rea ction s. The oxi-
dative addition of methyl iodide to Vaska’s complex
provides [IrCl(CH3)I(CO)(PPh3)2]15 and is a sufficiently
fundamental process that it features in most organo-
(12) Raucher, S.; Hansen, M. R.; Colter, M. A. J . Org. Chem. 1978,
43, 4885.
(14) Reed, C. A.; Roper, W. R. J . Chem. Soc., Dalton Trans. 1973,
1370.
(13) Cook, D. J .; Hill, A. F.; Wilson, D. J . J . Chem. Soc., Dalton
Trans. 1998, 1171.
(15) Collman, J . P.; Roper, W. R. Adv. Organomet. Chem. 1968, 7,
53.

4120 Organometallics, Vol. 17, No. 18, 1998
Notes
metallic textbooks. The reaction of 1 with methyl iodide
proceeds initially in a completely analogous manner to
provide [Ir(CH3)I(SeCtCR)(CO)(PPh3)2] (3); however,
with longer reaction times and excess CH3I the ultimate
product is [Ir(CH3)I2(CO)(PPh3)2] (4) and presumably
MeSeCtCR, although this was not identified. The
complex 4 has been described previously as resulting
from an alternative route.16 Thus, secondary alkylation
of the alkyneselenolate appears to be followed by
dissociation of the alkynyl selenoether and replacement
by iodide. Complexes of alkynyl selenoethers remain
rare,2,17,18 although Angelici’s elegant studies on the
synthetic versatility of alkynyl thioether complexes19
presages a similarly rich chemistry for selenium. The
apparent lability of the MeSeCtCR group is consistent
with the generally accepted weak coordination of sele-
noethers. It should thus be emphasized that the known
complexes of alkynyl selenoethers involve either η2-C,C′
coordination through the alkyne group (C, Chart 1)2,17
or are of the dicobaltaterahedrane form (D, Chart 1),18
again involving coordination through the alkynyl group
rather than the selenoether. We have previously shown
that the alkylation of [M(η2-SeCCR)(CO)(PPh3){HB-
(pz)3}] (M ) Mo, W; pz ) pyrazol-1-yl) with methyl
iodide provides [M(η2-MeSeCtCR)(CO)(PPh3){HB-
(pz)3}]I.2 Hence, perhaps unsurprisingly, the process
of alkylation is dependent upon the mode of coordination
of the “SeCCR” ligand and the metal center involved.
The oxidative addition of benzeneselenenyl chloride
to 1 takes a more conventional route to provide [IrCl-
(SePh)(SeCtCR)(CO)(PPh3)2] (5), a complex with two
different selenolate ligands. Although only one isomer
is formed (31P NMR), the stereochemistry at iridium
does not follow unambiguously from spectroscopic data.
It is however reasonable to assume that a two-step
process occurs to deliver the two components to opposite
faces of the substrate providing the stereochemistry
shown in Scheme 2.
complex would provide the unusual situation wherein
alkynyl groups were bound to three different elements,
viz. [Ir(CtCR)(HgCtCR)(SeCtCR)(CO)(PPh3)2] (6).
This anticipation follows from Collman’s synthesis of [Ir-
(CtCPh)Cl(HgCtCR)(CO)(PPh3)2] from Vaska’s com-
plex and bis(phenylethynyl)mercury20 and our own
observation that such processes are involved in the
catalytic demercuration of bis(alkynyl)mercurials by the
analogous rhodium complex [RhCl(CO)(PPh3)2].21 The
spectroscopic data clearly identify the nature of 6:
Although no molecular ion is observed, the FAB mass
spectrum features a substantial peak due to loss of one
alkynyl group in addition to further fragmentations
involving loss of “SeCCR” and (less abundantly) “HgC-
CR” groups. Notably no peak is observed due to the sole
loss of mercury, although in solution such a process is
facile for [Ir(CtCPh)Cl(HgCtCR)(CO)(PPh3)2]. The
comparatively high value of ν(CO) (thf: 2042 cm-1
)
suggests that this ligand is trans to the ligand with the
lowest Lewis basicity toward the metal, i.e., the alkynyl
group. Infrared spectroscopy fails to adequately resolve
the three ν(CtC) absorptions occurring around 2130
cm-1; however, three distinct alkynyl environments are
1
evident in the H and 13C NMR spectra. The 31P NMR
spectrum consists of a singlet resonance (δ -18.6 ppm)
showing satellite resonances arising from coupling to
selenium [J (SeP) ) 27.8 Hz ] and mercury [J (HgP) )
233.7 Hz], further confirming the proposed stereochem-
istry.
In conclusion, the preliminary results discussed above
show that (i) alkyneselenolate ligands may be intro-
duced by simple metal halide metathesis, (ii) the
coordination mode of the “SeCCR” fragment is depend-
ent on the metal center involved, (iii) the alkynyl
selenolate ligand can support simple oxidative addition
reactions on iridium(I) allowing the preparation of
mixed bis(selenolate) complexes, and (iv) the coordina-
tion mode of the “SeCCR” group affects the outcome of
alkylation reactions.
Finally, the reaction of 1 with bis(4-tolylethynyl)-
mercury was investigated. Our motives for such an
investigation were purely aesthetic, as the desired
Ack n ow led gm en t. We are grateful to the EPSRC
(U.K.) for financial support and the award of a student-
ship (to A.G.H.) and to J ohnson Matthey Ltd. for a
generous loan of iridium salts. A.F.H. gratefully ac-
knowledges the award of a Senior Research Fellowship
by the Leverhulme Trust and The Royal Society. P.J .D.
gratefully acknowledges the support of the Royal Society
in the form of a University Research Fellowship.
(16) Chock, P. B.; Halpern, J . J . Am. Chem. Soc. 1966, 88, 3511.
(17) Plate, M.; Dehnicke, K.; Abram, S.; Abram, U. Z. Naturforsch.,
B 1996, 51, 1049.
(18) Lang, H.; Keller, H.; Imhof, W.; Martin, S. Chem. Ber. 1990,
123, 417.
(19) Miller, D. C.; Angelici, R. J . Organometallics 1991, 10, 79; 1991,
10, 89.
(20) Collman, J . P.; Kang, J . W. J . Am. Chem. Soc. 1967, 89, 844.
(21) Bedford, R. B.; Hill, A. F.; Thompsett, A. R.; White, A. J . P.;
Williams, D. J . J . Chem. Soc., Chem. Commun. 1996, 1059.
OM980268N