A new approach to coordination chemistry involving phosphorus-selenium based ligands. Ring opening, deselenation and phosphorus-phosphorus coupling of Woollins' Reagent

Article abstract of DOI:10.1016/j.ica.2010.11.034

The facile reaction of [CpCr(CO)₃]₂ (1) with an equivalent of 2,4-bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide or Woollins' Reagent (WR) at ambient temperature gave mainly [CpCr(CO) ₂]₂Se (3) as the main product. A similar reaction with an excess of 1 gave 3 (58%) and trans-[CpCr(CO)₂(SePPh)]₂ (5, 25%). However reaction with an equivalent of the triply bonded congener Cp ₂Cr₂(CO)₄ (2) at 60 °C took 3 h to complete and led to the isolation of trans-[CpCr(CO)₂(SePPh)]₂ (5, 3%), CpCr(CO)₂(SeP(H)Ph) (4, 18%) and [CpCr(Se₂P(O)Ph)] ₂ (6, 2%). The ring-opening reaction of WR via an initial homolytic P-Se bond cleavage by CpCr(CO)_n· (n = 2 (2A) or 3 (1A)) depicts a new approach to coordination chemistry involving P-Se based ligands. A mechanistic pathway was proposed according to the evidences obtained from thermolysis, NMR and mass spectra studies. All the products of 4, 5 and 6 have been structurally characterized by single-crystal X-ray diffraction analysis.

Full text of DOI:10.1016/j.ica.2010.11.034

Inorganica Chimica Acta 366 (2011) 350–356
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
A new approach to coordination chemistry involving phosphorus-selenium
based ligands. Ring opening, deselenation and phosphorus–phosphorus coupling
of Woollins’ Reagent
⇑
Richard C.S. Wong , Mei Lee Ooi
Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 August 2010
Received in revised form 12 November 2010
Accepted 18 November 2010
Available online 5 December 2010
The facile reaction of [CpCr(CO)3]2 (1) with an equivalent of 2,4-bis(phenyl)-1,3-diselenadiphosphetane-
2,4-diselenide or Woollins’ Reagent (WR) at ambient temperature gave mainly [CpCr(CO)2]2Se (3) as the
main product. A similar reaction with an excess of 1 gave 3 (58%) and trans-[CpCr(CO)2(SePPh)]2 (5, 25%).
However reaction with an equivalent of the triply bonded congener Cp2Cr2(CO)4 (2) at 60 °C took 3 h to
complete and led to the isolation of trans-[CpCr(CO)2(SePPh)]2 (5, 3%), CpCr(CO)2(SeP(H)Ph) (4, 18%) and
[CpCr(Se2P(O)Ph)]2 (6, 2%). The ring-opening reaction of WR via an initial homolytic P–Se bond cleavage
by CpCr(CO)nꢀ (n = 2 (2A) or 3 (1A)) depicts a new approach to coordination chemistry involving P–Se
based ligands. A mechanistic pathway was proposed according to the evidences obtained from thermol-
ysis, NMR and mass spectra studies. All the products of 4, 5 and 6 have been structurally characterized by
single-crystal X-ray diffraction analysis.
Keywords:
Woollins’ Reagent
Congener
Ring-opening
Bond cleavage
Mechanistic pathway
Thermolytic studies
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
For the last two decades, mixed pnicogen–chalcogen ligands
have attracted a lot of attention from organometallic chemists.
Transition metals especially those at low oxidation states are stabi-
lized by the presence of both pnicogen–chalcogen soft donors in
these mixed ligands [1,2]. For example, ligands containing
arsenic–sulfur [3–7], phosphorus–sulfur [8–14] and phosphorus–
selenium [15–22] have been associated with interesting chemistry
due to their inherent potential liability and strong residual nucle-
ophilicity. Mixed ligands especially organo-phosphorus–chalcogen
heterocycles such as (p-methoxyphenyl)-thionophosphine sulfide
(LR, Lawesson’s reagent) [23,24] and 2,4-bis(p-tolylthio)1,
3-dithia-2,4-diphosphetane-2,4-disulfide (DR, Davy’s Reagent)
[25,26] have proven to be versatile ligands for novel metal-
complex formation. Another such ligand is Woollins’ Reagent
[27–32], whose reactivity with Group 6 organomolybdenum metal
is relatively unexplored. With this background we embarked on
the study of the reactivity of [CpCr(CO)n]2 (n = 2 or 3) towards
Woollins’ Reagent.
2.1. General procedures
All reactions were carried out using conventional Schlenk tech-
niques under an inert atmosphere of argon in a Vacuum Atmo-
sphere Dribox equipped with a Model HE 493 Dri-train. 1H, 13C
and 31P NMR spectra were measured on JEOL Lambda and ECA
400 MHz spectrometers. 1H and 13C chemical shifts were refer-
enced to residual C6H6 in C6D6 and 31P chemical shifts to 85% aque-
ous H3PO4 (external standard) for 31P {1H}. IR spectra in Nujol
mulls were measured in the range of 4000–400 cmꢁ1 by means
of a Perkin–Elmer 2000 FTIR instrument. Elemental analyses were
performed by the in-house microanalytical laboratory using a Per-
kin–Elmer 2400 Series II CHNS/O System. Mass spectrometric mea-
surements, performed by direct injection using electrospray
ionization (ESI), were made on an Agilent 6230 LCMS instrument.
Electrospray (high resolution) mass spectrometric measurements
were obtained on an Accurate Mass Q-Tof spectrometer. All sol-
vents were distilled of sodium/benzophenone under nitrogen prior
to use. Silica gel (Merck Kieselgel 60, 35–70 mesh) and Celite (Flu-
ka AG) were activated at 140 °C overnight before chromatographic
use. 1,3,2,4-Dithiadiphosphetane 2,4-diselenides (Woollins’ Re-
agent) was purchased from Sigma–Aldrich. [CpCr(CO)3]2 was syn-
thesized as described by Manning and co-workers [33] from
chromium hexacarbonyl (99% purity from Sigma).
⇑
Corresponding author. Tel.: +60 379674260; fax: +60 379674193.
E-mail addresses: richard@um.edu.my, richardwongcheeseng@gmail.com (R.C.S.
Wong).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.11.034

R.C.S. Wong, M.L. Ooi / Inorganica Chimica Acta 366 (2011) 350–356
351
2.2. Reaction of Cp2Cr2(CO)6 (1) with an equivalent of Woollins’
reagent at ambient temperature
[CpCr(CO)2(SePPh)]2, 691 [Cp2Cr2(CO)3(SePPh)2], 664
[Cp2Cr2(CO)2(SePPh)2], 633 [Cp2Cr2(CO)(SePPh)2)], 589
[Cp2Cr2(CO)2(SePPh)(SeP)], 533 [Cp2Cr2(SePPh)(SeP)],
502 [Cp2Cr2(Se2PPh)(Se)], 451 [Cp2Cr2(CO)(SePPh)], 413
[CpCr(Se2(O)PPh)(O)], 401 [CpCr(Se2(O)PPh)], 385
[CpCr(Se2PPh)], 359 [CpCr(CO)2(SePPh)], 331 [CpCr(CO)(SeP-
Ph)], 303 [CpCr(SePPh)], 273 [CpCrSe2], 228 [CpCrSeP]. Anal.
Calc. for C26H20Cr2O4P2Se2: C, 43.21; H, 2.77; Cr, 14.40; O,
8.86; P, 8.59; Se, 22.16. Found: C, 43.37; H, 2.89; Cr, 14.67;
O, 8.45; P, 8.62; Se, 22.45%.
A
deep green suspension of Cp2Cr2(CO)6 (1) (200 mg,
0.497 mmol) in toluene (ꢂ15 mL) was added WR (264 mg,
0.497 mmol) and the mixture stirred at ambient temperature. A
dark orange brown suspension was obtained after ca. 5 min. The
reaction mixture was allowed to continue stirring for 0.5 h. The
resultant dark orange brown solution was filtered through celite
and the filtrate was concentrated to ca. 3–4 mL before loading onto
a silica gel column (2 cm ꢃ 9 cm) prepared in n-hexane. Elution
gave three fractions:
A deep bluish green ring was remained unmoved on top of the
column.
(i) A dark purplish orange fraction was eluted with n-hexane
(65 mL) which when concentrated to dryness gave fine dark
orange brown crystalline solids of [CpCr(CO)2]2Se (3)
(70 mg, 0.165 mmol, 33.2% yield) [34,35], identified its 1H
NMR in benzene-d6 [d(Cp) 4.36] and TLC against an authen-
tic sample [Rf = 0.64 in 6:3:1 n-hexane/toluene/ether as elu-
ent] together with a trace amount of CpCr(CO)2(SeP(H)Ph)
(4).
(ii) A dark orange brown fraction was eluted with toluene
(48 mL) which when concentrated to dryness gave a dark
brown oily precipitate (189 mg, 60%). Analyses via TLC
showed it consisted of a mixture of [CpCr(CO)2]2Se (3),
trans-[CpCr(CO)2(SePPh)]2 (5) and CpCr(CO)2(SeP(H)Ph) (4)
in ratio of 8:1:1. Attempts to separate the mixture resulted
in failure.
2.4. Reaction of Cp2Cr2(CO)4 (2) with Woollins’ reagent at 60 °C
A
deep green suspension of Cp2Cr2(CO)4 (2) (300 mg,
0.867 mmol) in toluene (ꢂ15 mL) was added WR (461 mg,
0.867 mmol) and stirred at 60 °C for 3 h. The resultant dark brown-
ish green reaction mixture was concentrated to ca. 10 mL left and
was filtered through a sintered-glass funnel to remove a deep
green residue (361 mg). The filtrate was concentrated to ca. 3 mL
left and absorbed onto silica gel (ꢂ1 g). The dark brownish green
slurry was evacuated to dryness under vacuo and chromato-
graphed onto a silica gel column (1.5 cm ꢃ 9 cm) prepared in n-
hexane. Elution under slight pressure gave four fractions:
(i) A greyish brown eluant in n-hexane–toluene (1:2) (45 mL)
when which was concentrated to dryness gave dark brown
crystalline solids of 5 (18 mg, 0.022 mmol, 3% yield).
(iii) An uncharacterized green fraction was eluted with THF
(60 mL) which when concentrated to dryness gave a green
residue (162 mg).
(ii) A dark pinkish purple eluant in n-hexane–toluene (1:1,
15 mL) and when concentrated to dryness, gave dark pinkish
purple crystalline solids of CpCr(CO)2(SeP(H)Ph) (4) (55 mg,
0.152 mmol, 18% yield). Anal. Found: 1H NMR (benzene-d6):
d 4.26 (s, Cp); d 5.72 (s, P–H); d 6.68–7.37 (m, C6H5); 13C
NMR (benzene-d6): d 89.53 (Cp), d 132.71, 132.59, 131.37,
129.67, 129.62 and 129.50 (C6H5), 249.79, 254.22 (CO). 31P
NMR (benzene-d6: proton coupled): d 45.84, 48.26 (d,
A deep bluish green ring was remained unmoved on top of the
column.
2.3. Reaction of excess Cp2Cr2(CO)6 (1) with Woollins’ Reagent at
ambient temperature
A
deep green suspension of Cp2Cr2(CO)6 (1) (101 mg,
J = 387.6 Hz). IR: m(CO) at 1954.93vs, 1942.23vs, 1871.60vs,
0.251 mmol) in toluene (ꢂ10 mL) was added in 0.125 equivalent
of WR (16 mg, 0.031 mmol). The color of the reaction mixture
changed to orange brown immediately. The reaction mixture was
stirred at ambient temperature. After 1 h, no more color change
was observed and the resultant dark orange brown reaction mix-
ture was filtered through a sintered-glass funnel. The filtrate was
concentrated to ca. 3 mL and loaded onto a silica gel column pre-
pared in n-hexane (1.5 cm ꢃ 11.5 cm). Three fractions were eluted:
1853.25sh, and 1847.43sh cmꢁ1 and other peaks at
1159.72m, 1110.70m, 1093.53m, 1067.03m, 1055.44m,
1014.44m, 921.75m, 912.90m, 846.61m, 823.99m,
748.56m, 727.74w, 706.84vw, 690.43m, 685.54m,
639.48m, 590.79m, 550.25 m cmꢁ1 (nujol). HR-MS ESI+
(m/z): (52Cr, 80Se): 362.2380 [CpCr(CO)2(SeP(H)Ph)], 723
[Cp2Cr2(CO)4(SePPh)2], 695 [Cp2Cr2(CO)3(SePPh)2], 666
[Cp2Cr2(CO)2(SePPh)2], 633 [Cp2Cr2(CO)(SePPh)2], 451
[Cp2Cr2(CO)(SePPh)],
[CpCr(SePPh)(O)],
413
362
[CpCr(Se(O)PPh)(O)],
[CpCr(CO)2(SeP(H)Ph)],
401
331
(i) A dark orange brown fraction with n-hexane (10 mL) which
upon evaporation to dryness gave a black crystalline solid 3
(62 mg, 0.146 mmol, 58.2% yield).
(ii) A dirty green fraction was eluted with n-hexane/toluene
mixture (4: 1) (18 mL) which upon evaporation to dryness
gave green crystalline solids of unreacted Cp2Cr2(CO)6 (1)
(17 mg, 0.042 mmol, 16.7% recovery).
(iii) A greyish brown fraction was eluted with toluene (36 mL)
which upon evaporation to dryness gave the dark brown
crystalline solids of trans-[CpCr(CO)2(SePPh)]2 (5) (45 mg,
0.062 mmol, 24.7% yield). Anal. Found: 1H NMR (benzene-
d6): d 4.01 (s, Cp); d 7.02–7.72 (m, C6H5). 13CNMR (ben-
zene-d6): d 90.4 (Cp), d 126.02, 128.89, 129.65, 130.56,
[CpCr(CO)(SePPh)], 303 [CpCr(SePPh)], 273 [CpCrSe2]. Anal.
Calc. for C13H10CrO2PSe: C, 43.09; H, 2.76; Cr, 14.36; O,
8.84; P, 8.56; Se, 22.10. Found: C, 43.37; H, 2.58; Cr, 14.39;
O, 8.68; P, 8.47; Se, 22.54%.
(iii) A dark green eluant in ether (9 mL) which when concen-
trated to dryness gave dark brownish green crystalline solids
of Cp2Cr2(Se2P(O)Ph)2 (6) (14 mg, 0.018 mmol, 2% yield).
Anal. Found: 1H NMR (toluene-d8): d 5.04 (s, Cp); d 6.82–
7.08 (m, C6H5). 13C NMR (benzene-d6): d 126.02 (Cp), d
129.67, 130.56, 132.46, 138.20 and 138.63 (C6H5); 31P NMR
(benzene-d6): d ꢁ123.34. I.R:
m at 1157.67w, 1106.17m,
1084.11m, 1058.96m, 1026.21m, 998.64m, 815.55m,
138.23 and 138.65 (C6H5), d 249.79, 254.22 (CO). IR:
m
(CO)
741.12w, 728.43sh, 686.71w cmꢁ1 (nujol). HR-MS ESI+ (m/
at 1962.47vs, 1951.77vs, 1899.03vs cmꢁ1; other peaks at
1086.72m, 1063.01m, 1016.07m, 860.22vw, 844.94vw,
828.13w, 803.69w, 741.04w, 690.62w, 664.64vw cmꢁ1
z):
[CpCr(Se2(O)PPh)(O)],
(
52Cr, 80Se): 801.5744 [Cp2Cr2(Se2P(O)Ph)2], 413
401
[CpCr(Se2P(O)Ph)],
385
[CpCr(Se2PPh)], 303 [CpCr(Se2P)], 273 [CpCrSe2]. Anal. Calc.
for C20H20Cr2O2P2Se4: C, 29.93; H, 2.49; Cr, 12.97; O, 3.99;
(nujol). HR-MS ESI+ (m/z):
(
52Cr, 80Se): 722.4748

352
R.C.S. Wong, M.L. Ooi / Inorganica Chimica Acta 366 (2011) 350–356
P, 7.73; Se, 39.90. Found: C, 29.62; H, 2.54; Cr, 12.88; O, 3.96;
P, 7.45; Se, 39.46%.
(iv) A green eluant in THF (25 mL) which when concentrated to
dryness gave an uncharacterized deep green crystalline pre-
cipitate (361 mg).
2.5.3. Thermolysis of Cp2Cr2(Se2P(O)Ph)2 (6)
A green solution of 6 (22 mg, 0.013 mmol) was thermolyzed for
14 h. The resultant dark green solution consists of some uncharac-
terized dark brown precipitates.
2.5.4. Co-thermolysis of CpCr(CO)2(SeP(H)Ph) (4) and Woollins’
reagent
2.5. NMR tube reactions
A
purple mixture of CpCr(CO)2(SeP(H)Ph) (4) (20 mg,
The following thermolysis experiments were carried out in tol-
uene-d8 (ꢂ0.6 mL) in a 5 mm septum-capped NMR tube at 110 °C
and monitored via 1H NMR at specified time intervals for 14 h or
otherwise stated. The final product composition from each ther-
molysis study is tabulated in Table 1.
0.055 mmol) with an equivalent of WR (29 mg, 0.055 mmol) was
thermolyzed for 14 h. The resultant dark brown solution consists
of 4 (19%), 5 (6%) and 6 (31%) together with some uncharacterized
dark brown precipitates.
2.6. Structural studies of 4, 5 and 6
2.5.1. Thermolysis of CpCr(CO)2(SeP(H)Ph) (4)
A purple solution of 4 (20 mg, 0.055 mmol) was thermolyzed for
14 h. The resultant dark brown solution consists of 5 (38%) and 6
(11%) together with some uncharacterized dark brown precipitates.
Diffraction-quality single crystals were obtained from the solu-
tion at ambient temperature. Compound 4 was obtained as dark
purple crystals from n-hexane/THF at room temperature after 2–
3 days. Complexes 5 was obtained as dark brown crystals and 6
as dark brownish green crystals in THF at ꢁ28 °C after 1 week
and 2 weeks, respectively. The crystals are mounted on quartz fi-
bers. Details of crystal parameters, data collection and structure
refinement are tabulated in Table 2. The data were corrected for
Lorentz and polarization effects with SMART suite of programs [36]
and for absorption effects with the SHELXTL suite of programs [37].
2.5.2. Thermolysis of trans-[CpCr(CO)2(SePPh)]2 (5)
A greyish brown solution of 5 (13 mg, 0.018 mmol) was ther-
molyzed for 5 h. The resultant dark green solution consists of 4A
(10%) and 6 (70%) together with some uncharacterized dark brown
precipitates.
Table 1
Time dependent variation of product composition.a
3. Results and discussion
Reaction
Products (% yield)
4A
4
5
6
3.1. Products isolation
Thermolysis of 4/14 h
Thermolysis of 5/5 h
Co-thermolysis of 4 and Woollins’ reagent/14 h
–
10
–
–
–
19
38
–
6
11
70
31
The facile reaction of [CpCr(CO)3]2 (1) with one mole equivalent
of WR at ambient temperature completed in 0.5 h had led to the
isolation of Cp2Cr2(CO)4Se (3) as main product together with a
trace amount of [CpCr(CO)2(SePPh)]2 (5), CpCr(CO)2{SeP(H)Ph}
a
Product yields obtained by integration of Cp resonances in 1H NMR spectrum of
product mixture.
Table 2
Data collection and processing parameters of trans-[CpCr(CO)2(SePPh)]2 (5), CpCr(CO)2(SeP(H)Ph) (4) and Cp2Cr2(Se2P(O)Ph)2 (6).
Complexes
trans-[CpCr(CO)2(SePPh)]2 (5)
26H20Cr2O4P2Se2
720.28
223(2)
CpCr(CO)2{SeP(H)Ph} (4)
[CpCr(Se2P(O)Ph)]2 (6)
Empirical formula
Formula weight
T (K)
C
C13H10CrO2PSe
360.14
243(2)
C22H20Cr2O2P2Se4
399.08
223 (2)
k (Å)
0.71073
monoclinic
P2(1)/c
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21/n
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
7.9095(8)
18.688(2)
9.2154(10)
90
6.3855(6)
18.3404(17)
11.3791(11)
90
9.6596(6)
8.0501(5)
17.2372(11)
90
a
(°)
b (°)
104.246(2)
90
1320.3(2)
2
1.812
3.733
95.489(2)
90
1326.5(2)
4
1.803
3.715
103.2300(10)
90
1304.80(14)
4
2.032
6.553
c
(°)
V (Å3)
Z
Dcalc (Mg mꢁ3
)
Absorption coefficient (mmꢁ1
F(0 0 0)
)
708
708
764
Crystal size (mm)
h range for data collection
Limiting indices
0.16 ꢃ 0.10 ꢃ 0.10
2.18–25.00
ꢁ9 6 h 6 9
ꢁ22 6 k 6 21
ꢁ10 6 l 6 10
7378/2329 [R(int) = 0.0452]
2329/0/163
1.165
0.12 ꢃ 0.06 ꢃ 0.03
2.11–27.50
ꢁ76h68
0.64 ꢃ 0.18 ꢃ 0.14
2.17–27.50
ꢁ11 6 h 6 12
ꢁ10 6 k 6 9
ꢁ22 6 l 6 20
9000/3002 [R(int) = 0.0316]
3002/0/145
1.026
ꢁ22 6 k 6 23
ꢁ14 6 l 6 14
9213/3048 [R(int) = 0.0531]
3048/0/163
1.159
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices (I > 2
r
(I))
R1 = 0.0561
wR2 = 0.1268
R1 = 0.0720
wR2 = 0.1317
1.828 and ꢁ0.533
R1 = 0.0592
wR2= 0.1152
R1 = 0.0785
wR2 = 0.2105
0.676 and ꢁ0.472
R1 = 0.0321
wR2 = 0.0791
R1 = 0.0395
wR2 = 0.0820
0.658 and ꢁ0.372
R indices (all data)
Largest different peak and hole (e Åꢁ3
)

R.C.S. Wong, M.L. Ooi / Inorganica Chimica Acta 366 (2011) 350–356
353
(4) and an uncharacterized insoluble green residue believed to be
decomposed WR.
hydrogen since the 1H chemical shifts for 4 are d 4.26 (Cp) and d
5.72 (P–H) (route v). The formation of this phosphinoselenoylidene
product, 4A, is believed to be the common intermediate species
which acts as a precursor to the formation of 5 and 6. This postu-
lation agrees with the NMR tube thermolysis study of 4 at 110 °C
for 14 h which gave 5 (38% yield) and 6 (11% yield) and also the
ESI mass spectrum of 4 which shows the presence of trans-
[CpCr(CO)2(SePPh)]2 (m/e = 722). These observations suggest that
the thermally unstable 4 is likely to be the primary product which
slowly converts to the secondary product 5 via 4A (route iv and vi).
Under similar condition, cothermolysis of 4 with WR gave unre-
acted 4 (19% recovered), 5 (6% yield), 6 (31% yield) and some
uncharacterized Cp-containing compounds. As expected, in the
presence of WR more Se atoms will be available for the formation
of 6, hence prolonged thermolysis ultimately resulted in the isola-
tion of the eight-membered ring complex [CpCr(Se2P(O)Ph)]2 (6) as
the final thermolytic product (route vii).
This observation is comparable to the reaction of 1 with ele-
mental selenium [34,35] and mixed ligand P4Se3 [15–17] affording
3 as the main product. It is envisaged that the labile monomeric
species CpCr(CO)3ꢀ (1A) or CpCr(CO)2ꢀ (2A) [38–40] generated from
the dissociation of 1 reacts with excess WR resulting in its cleavage
and subsequent abstraction of Se atom to form 3 as depicted in
route (i) in Scheme 1. However, a similar reaction of 1 with
0.125 equivalent of WR gave Cp2Cr2(CO)4Se (58% yield), unreacted
Cp2Cr2(CO)6 (1) (17% recovery) and trans-[CpCr(CO)2(SePPh)]2 (5)
(25% yield). Here we noticed that the WR was completely con-
sumed since 1 was in excess and noticeably the uncharacterized
insoluble green residue was not formed.
The reaction of the triply bonded congener Cp2Cr2(CO)4 (2) with
an equivalent of WR required a longer time of 3 h and at an ele-
vated temperature of 60 °C to yield 4 (18%), 5 (3%), 6 (2%) and an
uncharacterized insoluble green precipitate (361 mg). It is worthy
to note that Cp2Cr2(CO)4Se (3) was not formed here which agrees
with previous reports involving selenation agents such as Se8
[34,35] and Ph2Se2 [41].
3.2. Mechanistic pathways
Similar to its sulfur analogue of LR [23], WR also underwent
P2Se2 ring opening mechanism with a propensity to give several
types of fragments as detected by mass spectrometry [42] (Scheme
2). The molecular structure of 4 suggested that its formation is
likely to result from the attack of CpCr(CO)nꢀ (n = 2 (2A) or 3
During the thermolysis of 5 which was monitored by 1H NMR at
110 °C, we noticed the emergence of a species at d 4.26 together
with the formation of 6 (d 5.04). We propose that this species (d
4.26) to be CpCr(CO)2(SePPh) (4A) resulting from the loss of a
-
-
17 e species
15 e species
OC
CO
CO
CO
CO
2
Cr Cr
2
Cr Cr
.
Cr
.
or
Cr
OC
OC
OC
OC
OC
OC
OC
OC
CO
1
OC
2
1A
(ii)
2A
Se
P
(i)
Se
P
H
- CO
Se
H
(iii)
OC
CO
Cr Se Cr
OC
CO
3
(iv)
Cr
Cr
2
Se
OC
Se
OC
OC
P
OC
P
H
4
4A
(v
i)
(v)
-H+
CO
CO
Se
Cr
P
Se
Cr
Se
Cr
Se
P
(vii)
rearrangement
O
O
P
Se
Se
6
CO
P
OC
Cr
5
Scheme 1. Proposed synthetic pathway for the formation of products 3, 4, 5 and 6.

354
R.C.S. Wong, M.L. Ooi / Inorganica Chimica Acta 366 (2011) 350–356
Se
P
Se
Se
Se
Se
M+ = 374
P
P
P
M+ = 454
Se
P
Se
Se
P
Se
Se
Se
Se
P
P
M+ = 268
M+ = 188
P
Se
P
M+ = 296
Scheme 2. Fragmentation of Woollins’ Reagent as detected by mass spectrometry.
(1A)) radical at the P2Se2 central ring of the WR to generate the
PhPSeꢀ fragment. Further interaction of 1A or 2A with a PhPSeꢀ
fragment followed by subsequent abstraction of H afforded 4
(route ii and iii). The source of hydrogen is believed to be the coor-
dinated Cp, as proposed by Goh and co-workers in a similar reac-
tion with LR [23] which explained the presence of several
unassigned peaks in the Cp region encountered in the product
solutions. Such observation was also present especially in reaction
mixtures of 1 and 2 with WR and some chromatographed fractions
as weak intensity Cp resonances between d 4.07 and 5.55. How-
ever, the unstable 4 underwent thermolytic degradation with the
loss of hydrogen to give 4A (route iv). From the thermolysis study,
we concluded that the formation of 5 is reversible which proceeds
with dimerization of 4A via P–P bond coupling and decoupling
(route v and vi). Similarities in both P–Se (2.1487(14) Å) and Cr–
Se (2.6389(9) Å) bond lengths for CpCr(CO)2(SeP(H)Ph) (4) as com-
pared to those in 5 (2.1425(17) Å and 2.6309(12) Å, respectively)
provides further supportive evidence.
Selenation of 5 from the WR ligand with concomitant bond
forming and breaking followed by intramolecular bond rearrange-
ments with dimerization, decarbonylation and oxygen abstraction
has led to the formation of 6 (route vii). It was not possible for us to
conclude experimentally the source of oxygen in 6 as all manipu-
lations were performed in the absence of water and oxygen.
The ease of fragmentation of the P–Se heterocyclic ligand which
leads to ring opening in WR resembles well with its P–S analogue,
LR. Indeed, both ligands behaved showed similar patterns of reac-
tivity which yielded some structurally identical products with 1
[23].
Fig. 1. Molecular structure of CpCr(CO)2(SeP(H)Ph) (4). Thermal ellipsoids are
shown at the 50% probability level.
3.3. Molecular structures of 4, 5 and 6
The molecular structures of 4, 5 and 6 are shown in Figs. 1–3.
Selected bond lengths and angles are listed in Tables 3–5,
respectively.
The structure of CpCr(CO)2(SeP(H)Ph) (4) possesses a four-
legged piano-stool configuration at Cr. 4 contains a Cp moiety at
the apical position while bonded to two CO groups and a g2
-
arylselenaphosphetane ligand. The complex is isostructural to
CpCr(CO)2(SP(H)Ar) (Ar = C6H4OMe) obtained from the reaction of
1 with LR [23] and [MoCp{j
2-OP(OC6H4OH)R⁄}(CO)2] (R⁄ = 2,4,6-
r
C6H2 Bu3) from p-benzoquinone oxidation of [MoCp(CO)2
{P(O)R⁄}]ꢁ to [43].
The Cr–P bond is indicated as a single bond with bond distance
0
Fig. 2. Molecular structure of trans-[CpCr(CO)2(SePPh)]2 (5). Thermal ellipsoids are
of 2.2643(15) ÅA which is similar with some of the reported com-
shown at the 50% probability level.
0
plexes such as CpCr(CO)2(SP(H)Ar) (2.2607(8) ÅA) [23];
CpCr(CO)2(SPR2) (R = Me, 2.2704(6) ÅA; Et, 2.2738 (18) ÅA) [44]. The
Cr–Se bond distance of 2.6389(9) Å possessed a single Cr–Se bond
0
0
which is longer than those observed in the (
[CpCr(CO)2]2Se2 (2.277 Å) [35] or Cp4Cr4(CO)8(P2Se2) (2.566(2) and
l-g
2-Se2) complexes of

R.C.S. Wong, M.L. Ooi / Inorganica Chimica Acta 366 (2011) 350–356
355
Table 5
Bond lengths (Å) and angles (°) for 6.
Bond lengths
Cr(1)–O(1)#1
Cr(1)–Se(1)
Cr(1)–Se(2)
Cr(1)–Cr(1)#1
Se(1)–P(1)
1.954(2)
2.4957(6)
2.5089(6)
Se(1)–Se(1)#1
Se(2)–P(1)
Se(2)–Se(2)#1
5.3724(7)
2.1842(8)
5.3978(7)
1.514(2)
1.804(3)
1.954(2)
5.0598(10) P(1)–O(1)
2.1785(8)
3.4112(4)
4.1669(5)
P(1)–C(6)
O(1)–Cr(1)#1
Se(1)–Se(2)
Se(1)–Se(2)#1
Bond angles
O(1)#1–Cr(1)–C(1)
O(1)#1–Cr(1)–C(5)
O(1)#1–Cr(1)–C(2)
O(1)#1–Cr(1)–C(3)
O(1)#1–Cr(1)–C(4)
O(1)#1–Cr(1)–Se(1)
O(1)#1–Cr(1)–Se(2)
146.64(18) P(1)–Se(1)–Se(1)#1
110.24(18) Cr(1)–Se(1)–Se(1)#1
48.13(2)
58.308(12)
50.859(8)
139.9(2)
103.8(2)
90.22(15)
97.00(7)
97.53(7)
Se(2)–Se(1)–Se(1)#1
Se(2)#1–Se(1)–Se(1)#1 39.416(6)
P(1)–Se(2)–Cr(1)
P(1)–Se(2)–Se(1)
Cr(1)–Se(2)–Se(1)
P(1)–Se(2)–Se(2)#1
81.66(3)
38.50(2)
46.868(14)
47.90(2)
O(1)#1–Cr(1)–Cr(1)#1 45.70(6)
Se(1)–Cr(1)–Se(2)
Se(1)–Cr(1)–Cr(1)#1
Se(2)–Cr(1)–Cr(1)#1
P(1)–Se(1)–Cr(1)
85.941(19) Cr(1)–Se(2)–Se(2)#1
64.617(14) Se(1)–Se(2)–Se(2)#1
64.771(14) O(1)–P(1)–C(6)
57.992(13)
50.530(8)
104.41(14)
114.98(10)
110.03(10)
114.43(10)
110.22(11)
102.87(3)
158.80(14)
82.08(2)
38.62(2)
77.23(2)
O(1)–P(1)–Se(1)
C(6)–P(1)–Se(1)
O(1)–P(1)–Se(2)
P(1)–Se(1)–Se(2)
P(1)–Se(1)–Se(2)#1
Cr(1)–Se(1)–Se(2)
Cr(1)–Se(1)–Se(2)#1
Se(2)–Se(1)–Se(2)#1
47.191(14) C(6)–P(1)–Se(2)
83.049(14) Se(1)–P(1)–Se(2)
90.275(10) P(1)–O(1)–Cr(1)#1
Fig. 3. Molecular structure of [CpCr(Se2P(O)Ph)]2 (6). Thermal ellipsoids are shown
at the 50% probability level.
Symmetry transformations used to generate equivalent atoms: #1 ꢁx, ꢁy, ꢁz.
Trans-[CpCr(CO)2(SePPh)]2 (5) consists of a similar framework
with its sulfur analogue, trans-[CpCr(CO)2(SPPhOMe)]2 [23]. The
dimer is bridged by a P–P bond (2.212(3) Å) with both CpCr(CO)2
moieties and bridged [–SePAr]2 ligand in a trans orientation which
is comparable to that of trans-[CpCr(CO)2(SPPhOMe)]2 (2.219(2) Å)
[23]. The C(6)–P(1)–P(1)#1 angle (104.5(2)°) is more than 90° indi-
cates that the phenyl ring was experiencing steric repulsion from
the CpCr(CO)2 moiety. The P–Se (2.1425(17) Å) and Cr–Se bond
Table 3
Bond lengths (Å) and angles (°) for CpCr(CO)2(SeP(H)Ph) (4).
Bond lengths
Cr(1)–C(7)
Cr(1)–C(6)
Cr(1)–P(1)
Cr(1)–Se(1)
1.837(5)
1.837(5)
2.2643(15)
2.6389(9)
Se(1)–P(1)
P(1)–C(8)
O(1)–C(6)
O(2)–C(7)
2.1487(14)
1.802(5)
1.150(6)
1.147(6)
Bond angles
C(7)–Cr(1)–C(6)
C(7)–Cr(1)–P(1)
C(6)–Cr(1)–P(1)
C(7)–Cr(1)–Se(1)
C(6)–Cr(1)–Se(1)
P(1)–Cr(1)–Se(1)
81.0(2)
P(1)–Se(1)–Cr(1)
Se(1)–P(1)–Cr(1)
O(1)–C(6)–Cr(1)
O(2)–C(7)–Cr(1)
C(9)–C(8)–P(1)
55.31(4)
73.40(5)
177.2(5)
178.9(4)
119.9(4)
(2.6309(12) Å) distances of
5
are longer than the P–S
83.68(16)
112.14(16)
118.84(15)
81.36(16)
51.29(4)
(2.0003(15) Å) and Cr–S bonds (2.4962(15) Å) found in trans-
[CpCr(CO)2(SPPhOMe)]2 which is possibly due to the larger atomic
radii of Se as compared to S.
6 is isostructural with [CpCr(S2P(O)PhOMe]2 isolated from the
reaction of 1 with Lawesson’s reagent [23]. The molecule com-
prises of two CpCr and two [SeP(O)Ar] moieties attached to an
eight-membered ring center. The almost equivalent Cr(1)–Se(1)
and Cr(1)–Se(2) bond lengths (2.4957(6) and 2.5089(6) Å, respec-
tively) are significantly longer than the Cr–S bond distance
(2.3862(10) and 2.3951(10) Å) of the sulfur analogue. Such obser-
vation is likely due to the lower electronegativity of Se as com-
pared to S, resulting in lower electron density at the metal centre
Table 4
Bond lengths (Å) and angles (°) for 5.
Bond lengths
Cr(1)–C(13)
Cr(1)–C(12)
Cr(1)–P(1)
Cr(1)–Se(1)
Cr(1)–Cr(1)#1
1.833(7)
1.854(7)
2.2700(18)
2.6309(12)
6.1018(19)
Se(1)–P(1)
P(1)–C(6)
P(1)–P(1)#1
O(1)–C(12)
O(2)–C(13)
2.1425(17)
1.823(6)
2.212(3)
1.140(8)
1.148(8)
hence reducing its
p back bonding effect.
Bond angles
Acknowledgments
C(13)–Cr(1)–P(1)
C(12)–Cr(1)–P(1)
C(13)–Cr(1)–Se(1)
C(12)–Cr(1)–Se(1)
P(1)–Cr(1)–Se(1)
C(13)–Cr(1)–Cr(1)#1
C(12)–Cr(1)–Cr(1)#1
P(1)–Cr(1)–Cr(1)#1
Se(1)–Cr(1)–Cr(1)#1
86.7(2)
P(1)–Se(1)–Cr(1)
C(6)–P(1)–Se(1)
C(6)–P(1)–P(1)#1
Se(1)–P(1)–P(1)#1
C(6)–P(1)–Cr(1)
Se(1)–P(1)–Cr(1)
P(1)#1–P(1)–Cr(1)
O(1)–C(12)–Cr(1)
O(2)–C(13)–Cr(1)
55.66(5)
114.2(2)
104.5(2)
108.70(11)
124.6(2)
73.14(6)
125.74(11)
178.4(7)
177.2(6)
110.7(2)
124.4(2)
82.3(2)
51.20(5)
73.60(19)
97.4(2)
We would like to thank the University of Malaya (RG024/09AFR
and FP052/2008C) for financial support is gratefully acknowledged.
We also thank Ms. G.K. Tan (CMMAC, National University of Singa-
pore) for crystallographic data collection.
17.11(4)
56.34(2)
Appendix A. Supplementary material
Symmetry transformations used to generate equivalent atoms: #1 ꢁx + 1, ꢁy + 1,
ꢁz.
CCDC 735485, 735486 and 735487 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.11.034.
2.575(2) Å) [17]. However, both the C@O bonds (1.361(4) and
0
1.420(5) ÅA) for CpCr(CO)2(SP(H)Ar) are longer than those in 4
(1.150(6) and 1.147(6) Å). The hydrogen atom bonded to phospho-
rus was confirmed by 31P proton coupled NMR (d, J = 387.6 Hz).

356
R.C.S. Wong, M.L. Ooi / Inorganica Chimica Acta 366 (2011) 350–356
[22] M. Di Vaira, I. de los Rios, F. Mani, M. Peruzzini, P. Stoppioni, Inorg. Chem.
References
Commun. 5 (2002) 879.
[23] Z. Weng, W.K. Leong, J.J. Vittal, L.Y. Goh, Organometallics 22 (2003) 1645.
[24] H. Alper, F.W.B. Einstein, J.F. Petrignani, A.C. Willis, Organometallics 2 (1983)
1422.
[25] R.C.S. Wong, M.L. Ooi, S.W. Ng, N.F. Thomas, Inorg. Chim. Acta 363 (2010)
2307.
[1] C.A. McAullffe (Ed.), Transition Metal Complexes of Phosphorus, Antimony,
Macmillian, London, 1973.
[2] L. Vaska, Acc. Chem. Res. 1 (1968) 335.
[3] L.Y. Goh, W. Chen, R.C.S. Wong, W.-H. Yip, T.C.W. Mak, Organometallics 10
(1991) 875 (and references therein).
[4] I. Bernal, H. Brunner, W. Meier, H. Pfisterer, J. Wachter, M.L. Ziegler, Angew.
Chem., Int. Ed. Engl. 23 (1984) 438.
[5] M. Di Vaira, M. Peruzzini, P. Stoppioni, J. Chem. Soc., Chem. Commun. (1983)
903.
[6] M. Di Vaira, M. Peruzzini, P. Stoppioni, Inorg. Chim. Acta 132 (1987) 37.
[7] H. Brunner, H. Kauermann, B. Nuber, J. Wachter, M.L. Ziegler, Angew. Chem.,
Int. Ed. Engl. 25 (1986) 557.
[8] L.Y. Goh, W. Chen, R.C.S. Wong, Angew. Chem., Int. Ed. Engl. 32 (1993) 1728.
[9] L.Y. Goh, W. Chen, R.C.S. Wong, K. Karaghiosoff, Organometallics 14 (1995)
3886.
[10] M. Di Vaira, M. Peruzzini, P. Stoppioni, Inorg. Chem. 22 (1983) 2196.
[11] M. Di Vaira, M. Peruzzini, P. Stoppioni, J. Organomet. Chem. 258 (1983) 373.
[12] R. Jefferson, H.F. Klein, J.F. Nixon, J. Chem. Soc., Chem. Commun. (1969) 536.
[13] A.W. Cordes, R.D. Joyner, R.D. Shores, E.D. Hill, Inorg. Chem. 13 (1974) 132.
[14] H. Brunner, U. Klement, W. Meier, J. Wachter, J. Organomet. Chem. 335 (1987)
339.
[15] L.Y. Goh, W. Chen, R.C.S. Wong, Phosphorus Sulphur Silicon 93–94 (1994) 209.
[16] L.Y. Goh, W. Chen, R.C.S. Wong, Z.Y. Zhou, H.K. Fun, Mendeleev Commun.
(1995) 60.
[17] L.Y. Goh, W. Chen, R.C.S. Wong, Organometallics 18 (1999) 306.
[18] M. Di Vaira, B.E. mann, M. Peruzzini, P. Stoppioni, Inorg. Chem. 27 (1988) 3725.
[19] P. Stoppioni, M. Di Vaira, M. Peruzzini, S. Moneti, L. Sacconi, Phosphorus Sulfur
Relat. Elem. 18 (1983) 295.
[20] M. Di Vaira, I. de los Rios, F. Mani, M. Peruzzini, P. Stoppioni, Eur. J. Inorg.
Chem. 2 (2004) 293.
[21] I. de los Rios, F. Mani, M. Peruzzini, P. Stoppioni, J. Organomet. Chem. 689
(2004) 164.
[26] A.C. Cano, R.A. Toscano, S. Bernes, O.G. Mellado, C. Alvarez-Toledano, H. Rudler,
J. Organomet. Chem. 496 (1995) 153.
[27] I.P. Parkin, M.J. Pilkington, A.M. Slawin, D.J. Williams, Polyhedron 7 (1990) 987.
[28] W. Kuchen, B. Knop, Angew. Chem., Int. Ed. Engl. 3 (1964) 507.
[29] W. Kuchen, B. Knop, Angew. Chem., Int. Ed. Engl. 4 (1965) 245.
[30] M.J. Pilkington, A.M.Z. Slawin, D.J. Williams, J.D. Woollins, Polyhedron 10
(1991) 2641.
[31] R.P. Davies, M.G. Martinelli, Inorg. Chem. 41 (2002) 348.
[32] R.P. Davies, M.G. Martinelli, A.E.H. Wheatley, A.J.P. White, D.J. Williams, Eur. J.
Inorg. Chem. 43 (2004) 4802.
[33] R. Birdwhistell, P. Hackett, A.R. Manning, J. Organomet. Chem. 157 (1978) 239.
[34] L.Y. Goh, W. Chen, S. Ekk, J. Chem. Soc., Chem. Commun. (1985) 462.
[35] L.Y. Goh, W. Chen, S. Ekk, Organometallics 7 (1988) 2020.
[36] G.M. Sheldrick, SADABS, Bruker Nonius Area Detector Scaling and Absorption
Correction – V2.05, University of Gottingen, Germany, 1999.
[37] G.M. Sheldrick, SHELXS97 and SHELXL97, University of Göttingen, 1997.
[38] N.A. Cooley, P.T.F. MacConnachie, M.C. Baird, Polyhedron 7 (1988) 1965 (and
refs. therein).
[39] P. Hackett, P.O. O’Neill, A.R. Manning, J. Chem. Soc., Dalton Trans. (1974) 1625.
[40] R.D. Adams, D.E. Collins, F.A. Cotton, J. Am. Chem. Soc. 96 (1974) 749.
[41] L.Y. Goh, Y.Y. Lim, M.S. Tay, T.C.W. Mak, Z.Y. Zhou, J. Chem. Soc., Chem.
Commun. (1992) 1239.
[42] M.J. Pilkington, A.M.Z. Slawin, D.J. Williams, P.T. Wood, J.D. Woollins,
Heteroatom Chem. 1 (5) (1990) 351.
[43] M. Alonso, M.A. Alvarez, M.E. Garcıa, M.A. Ruiz, H. Hamidov, J.C. Jeffery, J. Am.
Chem. Soc. 127 (2005) 15012.
[44] L.Y. Goh, Z. Weng, W.K. Leong, J.J. Vittal, I. Haiduc, Organometallics 21 (2002)
5287.