Synthesis and Se-Se bond breaking of polyselenides containing pendant diphosphine complexes of manganese(I)

Article abstract of DOI:10.1021/om100229q

Reaction of [Mn(CO)₄{(PPh₂)₂CH}] (1) with half an equivalent of dipiperidinotetraselane affords the tetraselenide compound [(CO)₄Mn{(PPh₂)₂C-Se₄-C(PPh ₂)₂}M

Full text of DOI:10.1021/om100229q

3058 Organometallics 2010, 29, 3058–3061
DOI: 10.1021/om100229q
Synthesis and Se-Se Bond Breaking of Polyselenides Containing Pendant
Diphosphine Complexes of Manganese(I)†
,†
Javier Ruiz,* Rene Arauz, Mario Ceroni, Marilı
†
†
´
n Vivanco,† Juan F. Van der Maelen,‡
ꢀ
ꢀ
and Santiago Garcı
´
a-Granda‡
†
‡
Departamento de Quımica Organica e Inorganica and, Departamento de Quımica Fısica y Analıtica,
´
Facultad de Quımica, Universidad de Oviedo, 33006 Oviedo, Spain
ꢀ
ꢀ
´
´
´
´
Received March 25, 2010
Summary: Reaction of [Mn(CO)4{(PPh2)2CH}] (1) with half an
equivalent of dipiperidinotetraselane affords the tetraselenide com-
pound [(CO)4Mn{(PPh2)2C-Se4-C(PPh2)2}Mn(CO)4] (2-Se4),
which, upon treatment with KOH, is transformed into the corres-
ponding triselenide and diselenide derivatives 2-Se3 and 2-Se2. Full
or partial protonation of the methanide carbon atoms can be
accomplished by reaction of the above compounds with HBF4,
whereas treatment of 2-Se2 with I2 gives rise to the formation of the
selenelyl iodide derivative [Mn(CO)4{(PPh2)2C-Se-I}] (5).
regioselective selenation reaction at the central carbon atom of
the bis(diphenylphosphino)methanide ligand in the neutral com-
plex[Mn(CO)4{(PPh2)2CH}].5 The dinuclear complexes formed
are closely related to those containing polysulfide chains pre-
viously described by our group.6 Apart from elemental sele-
nium,4b,7 a few selenating reagents have been developed in
organoselenophosphorus chemistry.8 Thus, Woollins’ reagent,8a
which contains a phosphorus-selenium ring, has proven to be
very useful for the synthesis of P-Se heterocycles and for intro-
ducing selenium into organic compounds. Also it is worth
mentioning the role of phosphine selenides, which have been
used as selenium-transferring reagents for the conversion of
phosphite triesters and H-phosphonate diesters into phosphoro-
selenoates under mild conditions.8b In relation with this, here
we have found that dipiperidinotetraselane9 can be conveniently
employed as a selective selenating reagent to introduce a tetra-
selenium chain as bridging backbone in manganese(I) dipho-
sphine complexes, as we will show throughout this paper.
Introduction
Organoselenium compounds have attracted attention from
the scientific community owing to their versatile reactivity1 and
their unique role in biochemical systems.2 In the specific field of
organoselenophosphorus chemistry, phosphine and dipho-
sphine selenides are well known, as their synthesis, reactivity,
and coordination chemistry have been reported,3 but dipho-
sphines containing selenium in the backbone are only episodi-
cally encountered in the literature.4 This paper deals with the
metal-assisted formation of bridging tetraphosphine ligands con-
taining polyselenide chains of different lengths in manganese(I)
carbonyl complexes of general formula [(CO)4Mn{(PPh2)2-
C-Sen-C(PPh2)2}Mn(CO)4], their controlled protonation reac-
tions, and the reversible selenium-selenium bond breaking
and formation therein. The experimental approach involves
Results and Discussion
We first explored the reactivity of the diphosphinomethanide
complex [Mn(CO)4{(PPh2)2CH}] (1) with commercial gray
selenium, but no reaction was found even under forcing condi-
tions. By contrast, the molecular form of selenium Se810 readily
reacted with 1 in dichloromethane at room temperature, afford-
ing a mixture of polyselenide derivatives of general formula
[(CO)4Mn{(PPh2)2C-Sen-C(PPh2)2}Mn(CO)4] (2-Sen), contai-
ning selenium chains of variable length, together with the dppm
(bis(diphenylphosphino)methane) parent complex [Mn(CO)4-
(dppm)]þ. The last was removed from the reaction mixture by
column chromatography, but separation of the different poly-
selane compounds was not feasible owing to their similar solu-
bility in organic solvents. Fortunately, the treatment of 2-Sen
with PPh3 or KOH acting as selenium abstractors yielded 2-Se2
as the sole product. The above results can be compared with
those found in the reaction of Li[HC(PPh2)2] with elemental
selenium, leading to selenation of the phosphorus atoms to
†
ꢀ
ꢀ
Dedicated to the memory of Professor Jose Manuel Concellon.
*To whom correspondence should be addressed. E-mail: jruiz@uniovi.es.
(1) (a) Wirth, T. Organoselenium Chemistry: Modern Developments in
Organic Synthesis (Topics in Current Chemistry), 1st ed.; Springer:
Heidelberg, 2000. (b) Ogawa, A.; Somoda, N. In Comprehensive Organic
Synthesis; Trost, B. M.; Fleming, I., Eds.; Pergamon Press: Oxford, 1991;
Vol. 6, p 461. (c) Dell, C. P. In Comprehensive Organic Functional Group
Transformations; Katritzky, A. R.; Meth-Cohn, O.; Rees, C. W., Eds.;
Pergamon: Oxford, 1995; Vol. 5, p 565. (d) Krief, A. In Comprehensive
Organometallic Chemistry; Abel, W. W.; Stone, F. G. A.; Wilkinson, G.,
Eds.; Pergamon: Oxford, 1995; Vol. 11, p 515.
(2) (a) Metanis, N.; Keinan, E.; Dawson, P. E. J. Am. Chem. Soc.
2006, 128, 16684. (b) Mugesh; G.; du Mont, W.-W.; Sies, H. Chem. Rev.
2001 101, 2125, and references therein.
(3) (a) Gimeno, M. C.; Laguna, A. In Comprehensive Coordination
Chemistry II; Mc Cleverty, J. A.; Meyer, T. J.; Fenton, D. E., Eds.; Pergamon:
Oxford, 2004; Vol. 6, p 1069. (b) Cauzzi, D.; Graiff, C.; Lanfranchi, M.;
Predieri, G.; Tiripicchio, A. J. Chem. Soc., Chem. Commun. 1995, 2443.
(c) Cauzzi, D.; Graiff, C.; Predieri, G.; Tiripicchio, A.; Vignali, C. J. Chem.
Soc., Dalton Trans. 1999, 237. (d) Konu, J.; Chivers, T.; Tuononen, H. M.
Inorg. Chem. 2006, 45, 10678. (e) Kahn, S. L.; Breheney, M. K.; Martinak,
S. L.; Fosbenner, S. M.; Seibert, A. R.; Kassel, W. S.; Dougherty, W. G.;
Nataro, C. Organometallics 2009, 28, 2119.
(5) Ruiz, J.; Riera, V.; Vivanco, M.; Garcıa-Granda, S.; Garcıa-
´ ´
ꢀ
Fernandez, A. Organometallics 1992, 11, 4077.
(6) Ruiz, J.; Ceroni, M.; Quinzani, O. V.; Riera, V.; Vivanco, M.;
Garcıa-Granda, S.; Van der Maelen, F.; Lanfranchi, M.; Tiripicchio, A.
´
Chem.;Eur. J. 2001, 7, 4422.
(7) Lindh, I.; Stawinski, J. J. Org. Chem. 1989, 54, 1338.
(8) (a) Hua, G.; Woollins, J. D. Angew. Chem., Int. Ed. 2009, 48, 1368.
(b) Bollmark, M.; Stawinski, J. Chem. Commun. 2001, 771. (c) Stawinski, J.;
Thelin, M. J. Org. Chem. 1994, 59, 130.
(9) (a) Foss, O.; Janickis, V. J. Chem. Soc., Chem. Commun. 1977,
833. (b) Foss, O.; Janickis, V. J. Chem. Soc., Dalton Trans. 1980, 620.
(10) Foss, O.; Janickis, V. J. Chem. Soc., Chem. Commun. 1977, 834.
(4) (a) Appleby, T.; Woollins, J. D. Coord. Chem. Rev. 2002, 235, 121.
(b) Nguyen, C. Q.; Adeogun, A.; Afzaal, M.; Malik, M. A.; O'Brien, P. Chem.
Commun. 2006, 2179.
r
pubs.acs.org/Organometallics
Published on Web 06/08/2010
2010 American Chemical Society

Note
Organometallics, Vol. 29, No. 13, 2010 3059
Scheme 1. Reaction of Complex 1 with Dipiperidinotetraselane to Afford Complex 2-Se4 and Subsequent Selenium Abstraction to Give
2-Se3 and 2-Se2
Table 1. Selected Spectroscopic Data for Compounds 2-5
31P{1H} NMR,b
1H NMR,b
(δ ppm, J Hz)
77Se NMRb
(δ ppm)
13C{1H} NMRb,c
(δ ppm, J Hz)
compd
IRa ν(CO), cm-1
(δ ppm)
2-Se4
2072 (s), 1999 (sh)
1991 (vs), 1966 (s)
2071 (s), 1997 (sh)
1991 (vs), 1963 (s)d
2070 (s), 1997 (sh)
1991 (vs), 1962 (s)
2094 (s), 2035 (m)
2012 (vs)
2094 (s), 2035 (m)
2011 (vs)d
2093 (s), 2035 (m)
2009 (vs)
2092 (s), 2076 (s)
2032 (m), 2009 (vs)
1994 (s), 1975 (m)
2077 (s), 2006 (sh)
1996 (vs), 1973 (s)e
17.6 (br)
17.1 (br)
14.0 (br)
40.2 (br)
41.2 (br)
33.1 (br)
726.8, 817.0
32.7 (t, 1JPC = 42)
31.1 (t, 1JPC = 42)
31.9 (t, 1JPC = 41)
50.7 (t, 1JPC = 10)
51.1 (t, 1JPC = 10)
47.8 (t, 1JPC = 11)
2-Se3
2-Se2
3-Se4
3-Se3
3-Se2
4-Se2
663.6 (2Se)
888.6 (1Se)
635.2
6.29
(t, 2JPH = 11.4)
6.44
558.3, 825.6
581.7 (2Se)
769.8 (1Se)
462.8
(t, 2JPH = 11.1)
7.27
(t, 2JPH = 7.9)
6.05
21.5 (br)
36.4 (br)
607.7, 718.4
1209.9f
37.3 (t, 1JPC = 39)
45.7 (t, 1JPC = 14)
(t, 2JPH = 11.1)
5
26.2 (br)f
58.8 (t, 1JPC = 34)f
a CH2Cl2 unless noted otherwise. b CD2Cl2 unless noted otherwise. c P2C signal. d Sample enriched in the complex. e THF. f D2O capillary/THF.
afford the anion [HC(PPh2Se)2]-.11 In our case, coordination
of the diphosphinomethanide ligand [HC(PPh2)2]- through the
phosphorus atoms to manganese prevents selenation from
taking place on these atoms, allowing regioselective selenation
at the central carbon atoms of the diphosphinomethanide
moiety. A more convenient and clean procedure to prepare
these kinds of polyselenide derivatives in a controlled manner is
by using dipiperidinotetraselane as selenating reagent. Thus,
when complex 1 was treated with half an equivalent of C5H10N-
Se4-NC5H10, the tetraselenide compound [(CO)4Mn{(PPh2)2-
C-Se4-C(PPh2)2}Mn(CO)4] (2-Se4) was formed after 20 min of
stirring at room temperature in dichloromethane, with simulta-
neous generation of two equivalents of piperidine as a bypro-
of this mixture with KOH afforded 2-Se2, which was isolated
in good yield. The IR spectra of compounds 2-Se4, 2-Se3, and
2-Se2 in the ν(CO) region are almost identical; also the broad
singlet signal observed in the 31P{1H} NMR spectra, corres-
ponding to the diphosphino groups, appears at very similar
chemical shifts for the three complexes (Table 1). This means
that the shortening of the selenium chain has little electronic
effect on the two pendant octahedral manganese(I) complexes.
However, the 77Se NMR chemical shifts were found to be quite
sensitive to the selenium atom environment, and hence to the
selenium chain length. Thus, a singlet at 635.2 ppm was ob-
served for the diselenide compound 2-Se2, two singlets at 663.5
and 888.6 ppm in a 2:1 ratio, respectively, for the triselenide
2-Se3, and two singlets of equal intensity at 726.8 and 817.0 ppm
for the tetraselenide derivative 2-Se4.12
Reaction of 2-Se2 or 2-Se4 with an excess of an strong acid
(HBF4 or HClO4) immediately afforded the cationic complexes
[(CO)4Mn{(PPh2)2C(H)-Sen-C(H)(PPh2)2}Mn(CO)4]2þ (3-Se2,
n=2; 3-Se4, n=4) (Scheme 2), as a result of the protonation of
both methanide carbon atoms, which were isolated as yellow
solids and fully spectroscopically characterized. Protonation
of the above-mentioned mixtures of complexes 2-Se2, 2-Se3,
1
duct, as detected by H NMR spectroscopy (Scheme 1). As
shown in Scheme 1, the reaction pathway should involve for-
mation of the intermediate adduct I and further proton transfer
from the P2C(H)Se- group to the amide moiety to eliminate
piperidine. The tetraselenium chain in 2-Se4 slowly loses a
selenium atom by treatment with KOH in CH2Cl2, giving the
triselenide compound 2-Se3, but formation of a small amount of
the diselenide derivative 2-Se2 begins before the starting com-
plex 2-Se4 has been consumed, thus precluding isolation of 2-Se3
as a pure sample. This is made evident by the 77Se NMR spec-
trum of the reaction mixture, which showed signals correspond-
ing to the three complexes (see below). The prolonged treatment
(12) For references on 77Se NMR chemical shifts in polyselenium
compounds see: (a) Maaninen, T.; Chivers, T.; Laitinen, R.; Schatte, G.;
Nissinen, M. Inorg. Chem. 2000, 39, 5341. (b) Bates, C. M.; Morley, C. P. J.
Organomet. Chem. 1997, 533, 193. (c) Sekar, P.; Ibers, J. A. Inorg. Chem.
€
€
(11) Konu, J.; Tuononen, H. M.; Chivers, T. Inorg. Chem. 2009, 48,
11788.
2004, 43, 5436. (d) Rotter, C.; Schuster, M.; Kidik, M.; Schon, O.; Klapotke,
T. M.; Karaghiosoff, K. Inorg. Chem. 2008, 47, 1663.

3060 Organometallics, Vol. 29, No. 13, 2010
Scheme 2. Protonation Reactions of Complexes 2-Sen (n = 2-4) at the Methanide Carbon Atoms
Ruiz et al.
and 2-Se4 also allowed spectroscopic characterization of
the triselenide complex [(CO)4Mn{(PPh2)2C(H)-Se3-C(H)-
(PPh2)2}Mn(CO)4]2þ (3-Se3). Naturally, the νCO bands in
the IR spectra undergo a substantial change to high frequencies
on going from the neutral to the cationic complexes (Table 1).
1
The most characteristic signal in the H NMR spectra is that
corresponding to the P2CH proton, which appears as a triplet at
7.27, 6.44, and 6.29 ppm for complexes 3-Se2, 3-Se3, and 3-Se4,
respectively. Note that this signal is significantly shifted down-
field in complex 3-Se2 compared with that in the other two
polyselenide derivatives, 3-Se3 and 3-Se4. Furthermore, the 2JPH
coupling constant is appreciably lower for 3-Se2 (7.9 Hz) than
for 3-Se3 (11.1 Hz) and 3-Se4 (11.4 Hz). Also of note is the
chemical shift of the signal corresponding to the phosphorus
atoms of the diphosphine in the 31P{1H} NMR spectra, which is
notably lower for complex 3-Se2 (33.1 ppm) than for complexes
3-Se3 (41.2 ppm) and 3-Se4 (40.2 ppm). These data suggest that
in the diselenide complex 3-Se2 there is a unique electronic
interaction between the diselenide chain and the P2CH groups
that is not present, or at least not to the same extent, in the other
two polyselenide complexes, 3-Se3 and 3-Se4. A similar situation
was observed in the polysulfide counterparts previously re-
ported by our group.6 In order to gain insight into the structural
disposition of the tetraphosphine ligand (PPh2)2C(H)-Se2-
C(H)(PPh2)2 in the cationic complex 3-Se2, an X-ray analysis
of the corresponding perchlorate salt was carried out. Crystals
of [3-Se2](ClO4)2 suitable for X-ray diffraction were grown by
slow diffusion of hexane into a dichloromethane solution of the
compound. A view of the complex cation is shown in Figure 1
together with a selection of bond distances and angles. The
molecular cation contains two almost identical halves, which are
twisted around the Se-Se segment (C9-Se1-Se2-C10 torsion
angle 104.2(3)°). The Se-Se and C-Se bond lengths are similar
to those found in dimethylselane (2.326(4) and 1.954(5) A, res-
pectively).13 The C-H10 Se1 (3.27(5) A) and C-H9 Se2
Figure 1. Structure of the dication 3-Se2 (50% thermal ellipsoids).
Phenyl groups have been omitted for clarity. Selected interato-
mic distances (A) and angles (deg): Mn1-P1 2.298(2), Mn1-P2
2.331(2), P1-C9 1.853(6), P2-C9 1.851(7), C9-Se1 1.982(6),
Se1-Se2 2.318(1), Se2-C10 1.977(6), C10-P3 1.853(6), C10-P4
1.860(6), Mn2-P3 2.305(2), Mn2-P4 2.329(2), H9 Se2 3.12(5),
3 3 3
H10 Se1 3.27(5); P2-Mn1-P1 71.54(7), P1-C9-P2 93.9(3),
3 3 3
Se1-C9-P1 108.9(3), Se1-C9-P2 113.2(3), C9-Se1-Se2
99.0(2), Se1-Se2-C10 99.1(2), Se2-C10-P3 108.5(3), Se2-
C10-P4 113.2(3), P3-C10-P4 94.2(3), P3-Mn2-P4 71.87(7),
C9-H9 Se2 88(3), C10-H10 Se1 99(3).
3 3 3 3 3 3
containing C-H Se hydrogen bonds are very rare;15 for a
3 3 3
comparison, values such as 2.92 A and 101.7° for intramolecular
C-H Se interactions have been reported.15a In our case, an
3 3 3
additional cooperative effect could exist as the two proposed
hydrogen bonds are interconnected.16 Despite this, HMQC
measurements showed that the JSeH value in complex 3-Se2 is
low (7.2 Hz), which seems to rule out the existence of typical
C-H Se hydrogen bonds in this complex.15a
3 3 3
In order to clarify the existence of an apparently special elec-
tronic interaction in the C(H)-Se-Se-C(H) core, theoretical elec-
tron density calculations within the framework of the quantum
theory of atoms in molecules (QTAIM)17 were performed for
complex 3-Se2 as well as for the disulfide counterpart [(CO)4-
Mn{(PPh2)2C(H)-S2-C(H)(PPh2)2}Mn(CO)4]2þ (3-S2).6 Delo-
calization indices for the nonbonding interactions of the central
C(H)-S-S-C(H) and C(H)-Se-Se-C(H) cores are listed in Table 2.
No critical points or bond paths were found for these weak inter-
actions from the QTAIM calculations, which is consistent with
3 3 3
3 3 3
(3.12(5) A) distances are similar to the sum of van der Waals
radii of hydrogen and selenium atoms (3.25 A), which could
allow a weak hydrogen bond interaction,14 although the
the rather low values obtained for each δ(A B) index. Never-
C-H Se angle is too close (94° in average). Compounds
3 3 3
3 3 3
theless, δ(Se H), δ(Se C), δ(S H), and δ(S C) indices
3 3 3
3 3 3
3 3 3
3 3 3
are not negligible at all but comparable to other values for non-
bonding interactions found in organometallic compounds.18
(13) Hargittai, I.; Rozsondai, B. In The Chemistry of Organic Sele-
nium and Tellurium Compounds; Patai, S.; Rappoport, Z., Eds.; John Wiley
& Sons: Chichester, 1986; Vol. 1, p 83.
(14) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48.
(15) (a) Iwaoka, M.; Tomoda, S. J. Am. Chem. Soc. 1994, 116, 4463.
(b) Michalczyk, R.; Schmidt, J. G.; Moody, E.; Li, Z.; Wu, R.; Dunlap, R. B.;
Odom, J. D.; Silks, L. A., III. Angew. Chem., Int. Ed. 2000, 39, 3067. (c)
Zade, S. S.; Panda, S.; Singh, H. B.; Sunoj, R. B.; Butcher, R. J. J. Org.
Chem. 2005, 70, 3693. (d) Narayanan, S. J.; Sridevi, B.; Chandrashekar,
T. K.; Vij, A.; Roy, R. Angew. Chem., Int. Ed. 1998, 37, 3394.
(16) Steiner, T. J. Chem. Soc., Chem. Commun. 1997, 727.
(17) Bader, R. F. W. Atoms in Molecules: A Quantum Theory;
Clarendon: Oxford, 1990.
´
(18) (a) Cabeza, J. A.; Van der Maelen, J. F.; Garcıa-Granda, S.
Organometallics 2009, 28, 3666. (b) Macchi, P.; Sironi, A. Coord. Chem.
Rev. 2003, 238, 383.

Note
Organometallics, Vol. 29, No. 13, 2010 3061
Table 2. Delocalization Indices for Nonbonded Interactions in
3-S2 and 3-Se2
Scheme 3. Reversible Selenium-Selenium Bond Breaking and
Formation in Complex 2-Se2
Se
S
H
H
S
C
3 3 3
3 3 3
3 3 3
Se
C
C
H
H
H
C
C total
3 3 3
3 3 3
3 3 3
3 3 3
3-S2 δ (A B) 0.061
0.091
0.085
0.002
0.001
0.001
0.001
0.006 0.31
0.005 0.29
3 3 3
3-Se2 δ (A B) 0.058
3 3 3
It is worth noting the almost equal results obtained for the
same interactions in the two different complexes. The only
reason for not finding critical points for these weak interac-
oxidative scission of the Se-Se chain with formation of a new
Se-I bond has taken place. Consequently, the IR spectrum in
the νCO region shows bands at higher frequencies (8 cm-1 on
average, Table 1) than those for the disulfide derivative 2-Se2,
and the signal corresponding to the diphosphino group in the
31P{1H} NMR spectrum is shifted 12 ppm downfield with
respect to compound 2-Se2. Selenenyl iodide compounds are
scarce in the literature, owing to their very favored dispropor-
tionation to the corresponding diselenide and iodine,23 and they
can be isolated in a few cases only by introducing highly
demanding alkyl substituents24 or internally chelating groups.25
Nevertheless, organoselenenyl iodides are relevant molecules in
biochemical systems, as they play a crucial role in thyroid
hormone action; in fact an enzyme selenenyl iodide complex is
formed in the deiodination of thyroxine by the selenocysteine
active site of iodothyronine deiodinase to afford the biologically
active hormone triiodothyronine.26 In view of this, formation of
new molecules containing Se-I bonds appears to be an inter-
esting goal. In this sense complex 5 is a rare example of an
organometallic complex containing a selenenyl iodide function-
ality. Reduction of 5 with Na in THF readily regenerates the
selenium-selenium bond, affording the diselenide derivative
2-Se2. Curiously, this process is the opposite of that found in
the reaction of the carbodiphosphorane selenolate zwitterion
PPh3C(Se)PPh3 with iodine, which leads to the coupling of two
selenolate functions upon oxidation to afford the cation
ꢀ
tions is the Poincare-Hopf relationship applied to the
QTAIM theory, which restricts the number of bonds to the
strongest interactions, while the weakest ones may be recog-
nized only by their non-negligible δ(A B) values. More-
3 3 3
over, by adding up δ(A B) indices for all the Se H,
Se C, C C, and H H interactions in the central part
3 3 3
3 3 3
3 3 3 3 3 3 3 3 3
of 3-Se2 (and the corresponding interactions for 3-S2) a value
of 0.3 is found (Table 2), which is comparable to, and even
larger than, the ones found in bonding interactions such as
Zn-C in Zn2(η5-C5Me5)2 (0.23), Na-F in NaF (0.27),
Co-Co in Co2(CO)8 (0.46), and B-C in H3BCO (0.50).19
A correlation between spin-spin coupling and electron
delocalization measured by these delocalization indices is
well known.20 Then, it is fair to conclude that there exists a
collaborative multicenter delocalized interaction in the cen-
tral part of complexes 3-S2 and 3-Se2, which could well be
responsible for the NMR data observed.21
Protonation of just one methanide carbon atom of 2-Se2 can
be accomplished by controlled treatment of a dichloromethane
solution of this compound with an equivalent of HBF4, affording
the cationic complex [(CO)4Mn{(PPh2)2C(H)-Se2-C(PPh2)2}-
Mn(CO)4]þ (4-Se2) (Scheme 2). The IR spectrum of 4-Se2 in
the νCO region showed two groups of bands corresponding to
the two nonequivalent sides of the complex cation. Also two
broad resonances were present in the 31P{1H} NMR spectrum at
37 and 32 ppm due to the diphosphinomethane and diphos-
phinomethanide parts of the bridging ligand, respectively. As
expected, two singlet signals were observed in the 77Se NMR
spectrum (607.7 and 718.4 ppm), whereas the 13C{1H} NMR
spectrum showed two triplets at 45.7 (1JPC = 14 Hz) and 37.3
(1JPC = 39 Hz) ppm corresponding to P2C(H)Se and P2CSe
carbon atoms, respectively.
[(PPh3)2C-Se-Se-C(PPh3)2]2þ 27
.
Acknowledgment. This work was supported by the Span-
ꢀ
ish Ministerio de Ciencia e Innovacion (PGE and FEDER
funding, Project CTQ2009-11457). The authors thank Isabel
Merino for valuable help in the NMR measurements.
Supporting Information Available: Experimental details re-
garding the synthesis and characterization of compounds 2-5
and crystallographic data in CIF format of complex 3-Se2. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Complex 2-Se2 readily undergoes Se-Se bond breaking by
treatment with an equivalent of I2, yielding the selenenyl iodide
compound [Mn(CO)4{(PPh2)2C-Se-I}] (5) (Scheme 3), in a
similar way to that found in the disulfide counterpart.22 The
appearance of a very low field singlet (1209.9 ppm) in the 77Se
NMR spectrum of this complex clearly indicates that formal
(23) (a) du Mont, W.-W.; Martens, A.; Pohl, S.; Saak, W. Inorg.
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