Iridium carbonyl cluster complexes with bidentate phosphine ligands; The X-ray crystal structure of [Ir4(CO)8(dppa)2]·3(THF)

Article abstract of DOI:10.1016/S0022-328X(00)00140-6

Reactions of [Ir₄(CO)₁₂] with 1,1-bis(diphenylphosphino)ethene, Ph₂PC(=CH₂)PPh₂ (dppen) and 1,1-bis(diphenylphosphino)amine, Ph₂PN(H)PPh₂(dppa) gave [Ir₄(CO)_12-n<

Full text of DOI:10.1016/S0022-328X(00)00140-6

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Journal of Organometallic Chemistry 602 (2000) 137–143
Iridium carbonyl cluster complexes with bidentate phosphine
ligands; the X-ray crystal structure of [Ir4(CO)8(dppa)2]·3(THF)
Nagwa Nawar *
Department of Chemistry, Faculty of Science, Mansoura Uni6ersity, PO Box 79, Mansoura 35516, Egypt
Received 26 January 2000; received in revised form 20 February 2000
Abstract
Reactions of [Ir4(CO)12] with 1,1-bis(diphenylphosphino)ethene, Ph2PC(ꢀCH2)PPh2 (dppen) and 1,1-bis(diphenylphos-
phino)amine, Ph2PN(H)PPh2(dppa) gave [Ir4(CO)12−n(L)n−2)] (L=dppen or dppa and n=2 or 4) depending upon the reaction
conditions. The structures of the cluster complexes are discussed on the basis of IR, 31P-NMR spectroscopic data and FAB mass
spectra. The structure of the disubstituted species [Ir4(CO)8(dppa)2]·3(THF) (THF=tetrahydrofuran, C4H8O) has been deter-
mined by X-ray crystallography. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Iridium; Carbonyl; Cluster complexes; bis(Diphenylphosphino)ethene complexes; bis(Diphenylphosphino)amine complexes
1. Introduction
2. Results and discussion
In last two decades there has been a great deal of
interest in the preparation and properties of transition
metal cluster carbonyl complexes stabilized with multi-
dentate ligands [1–10]. It has been shown that the
presence of bridging or capping ligands can increase the
stability of the metal atom framework [5] and thus
provide useful compounds for the study of catalysis by
cluster complexes [11–15]. Compared with the vast
body of data accumulated on diphosphines in which the
phosphorus nuclei are linked by a carbon atom or
chain [8], less has appeared on ligands where the back-
bone of the molecule comprises a heteroatom or group
[16]. In this respect, diphosphines, where the phospho-
rus nuclei are connected by nitrogen atom, have re-
ceived little coverage. The only example existing in the
literature of a cluster complex stabilized by bis(-
diphenylphosphino)amine, Ph2PN(H)PPh2(dppa), is the
silver halide cluster complex [16,17]. In this respect
dppa has received our attention because dppen and
dppa have shared features in the formation and stabi-
lization of cluster complexes. The X-ray crystal struc-
ture of the disubstituted species [Ir4(CO)8(dppa)2]·
3(THF) was determined.
Our attention has been centered on substitution reac-
tions involving loss of carbon monoxide from the te-
tranuclear metal carbonyl cluster [Ir4(CO)12] by the
bidentate phosphine ligands dppen and dppa. In spite
of the cluster carbonyl, [Ir4(CO)12] is generally consid-
ered to be rather unreactive and has an all-terminal CO
ligand structure, we find that [Ir4(CO)12] reacts with
equimolar amounts of dppen or dppa to give
[Ir4(CO)8(dppen)2] or [Ir4(CO)8(dppa)2] in good yield.
Since the substitution of more than two carbonyl lig-
ands is kinetically favored in this reaction [18], the
derivative [Ir4(CO)10(dppa)] or [Ir4(CO)10(dppa)] cannot
be prepared by this route. Instead, we used the method
of Stuntz and Shapley [19], which leads to [Ir4(CO)11L]
and [Ir4(CO)10L2] (L=monodentate tertiary phosphine)
derivatives. Thus, the reaction of [Ir(CO)2Cl(p-tolu-
idine)] with dppen or dppa ligands in the presence of
zinc metal and under CO pressure gives a mixture of
[Ir4(CO)10(dppen)] (1) and [Ir4(CO)8(dppen)2] (2) or
[Ir4(CO)10(dppa)] (3) and [Ir4(CO)8(dppa)2] (4). The
mono- and disubstituted cluster complexes can be sepa-
rated by a florisil column chromatography. The IR
spectra of these iridium derivatives are very similar to
the analogous [Ir4(CO)10(dppm)] and [Ir4(CO)8(dppm)2]
complexes (Table 1) [20] in which its dppm ligand
* Fax: +20-50-346781/353584.
E-mail address: sinfac@mum.mans.eun.eg (N. Nawar)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 0 ) 0 0 1 4 0 - 6

138
N. Nawar / Journal of Organometallic Chemistry 602 (2000) 137–143
adopts a bridging mode. Further support is provided by
the fact that the IR spectrum of [Ir4(CO)10(diars)] (di-
ars=1,2-bis(dimethylarsino)benzene) (w(CO): 2071 m,
2038 s, 2026 w, 2001 m, 1996 w, 1847 vw, br, 1805 w,
br) [21], in which the diars ligand is coordinated in a
chelating mode to one iridium atom, is quite different
from the dppen or dppa derivatives reported here or
dppm [20]. However, the chemical shifts observed in the
31P-NMR
spectra
of
[Ir4(CO)10(dppen)]
(1),
[Ir4(CO)8(dppen)2] (2), [Ir4(CO)10(dppa)] (3) and
[Ir4(CO)8(dppa)2] (4) (Table 1) suggest that in all com-
plexes the phosphorus atoms are involved in a five-
membered rings and therefore that the dppen or dppa
ligands are coordinated in a chelating mode to two
iridium atoms. Also, the IR stretching frequencies of
1825 and 1778 cm−1 indicated the presence of bridging
carbonyls
in
the
[Ir4(CO)10(dppen)]
(1)
or
[Ir4(CO)10(dppa)] (3). Further support for this conclu-
sion is provided by the 31P-NMR spectra of
[Ir4(CO)10(dppen)] (1) or [Ir4(CO)10(dppa)] (3) (Table 1).
The chemical shifts observed in the 31P-NMR spectra of
1 and 3 (Table 1) suggest that in both complexes the
phosphorus atoms are involved in a five-membered ring
and therefore the dppen and dppa ligands are coordi-
nated in a bridging mode. Since only a singlet reso-
nance at −17.0 ppm for 1 or −18.1 ppm for 3 were
observed on the 31P-NMR spectrum, the two phospho-
rus atoms in [Ir4(CO)10(dppen)] or [Ir4(CO)10(dppa)] are
equivalent and coordinated to two iridium atoms in
basal plane of the tetrahedron. This suggests that the
iridium complexes are structurally quite similar to that
reported with dppm derivatives [22] and adopts a bridg-
ing coordination mode in the diaxial sites of the basal
plane of iridium metals framework.
Analysis
by
FAB
mass
spectroscopy
of
[Ir4(CO)10(dppen)] (1) or [Ir4(CO)10(dppa)] (3) gave a
parent ion at the desired positions: m/z 1445 for 1 or
m/z 1435 for 3. The fragmentation of 1 or 3 occurs
mainly via initial loss of a carbonyl group. The stepwise
losses of ten carbonyl groups are observed. Unfortu-
nately, we have not succeeded in isolating good single
crystal for 1 or 3.
[Ir4(CO)8(dppen)2] (2) and [Ir4(CO)8(dppa)2] (4) were
characterized by microanalysis, IR and 31P-NMR spec-
troscopic data (Table 1). The IR stretching frequencies,
1780, 1765 and 1830 cm−1 are due to bridging carbonyl
ligands, the rest being due to five terminal carbonyls.
Two broad peaks at −19.5 and −42.5 ppm for 2 and
0.3 and −12.4 ppm for 4 were observed in the 31P-
Table 1
Infrared and 31P-NMR data
a
Complex
w(CO) (cm−1
)
31P-NMR b
[Ir4(CO)10(dppm)]
[Ir4(CO)8(dppm)2]
2071 s, 2041 m, 2012 s, 1985m (sh), 1860 w, 1826 m, 1790 m. −52.3 (s) (at 25 and −95°C)
2007 s, 1974 s(br), 1957 s, 1832 vw, 1783 m, 1762 m. −49.4 (br, s) (at 25°C); −23.5 (P1) (d, J(P1–P4) 42);
−44.85 (P2) (dd, J(P2–P3) 48), J(P2–P4) 101); −49.8
(P3) (d, J(P3–P2) 48), −61.5 (P4) (dd, J(P4–P1); 42,
J(P4–P2) 101) (at −95°C).
dppen
−3.4 (s)
[Ir4(CO)10(dppen)] (1) 2070 vs, 2040 s, 2011 vs, 1980 w, 1860 vw, 1825 m, 1778 m.
[Ir4(CO)8(dppen)2] (2) 2009 s, 1975 vs(br), 1950 w, 1830 w, 1780 m, 1765 w.
−18.1 (s) (at 25 and −95°C)
−19.5 (br, s), −42.5(br, s) (at 25°C); 8.9 (P1) (d,
J(P1–P4) 93); −37.7 (P2) (br, t, J(P2–P3) 97), J(P2–
P4) 94); −45.8 (P3) (d, J(P3–P2) 97); −49.8 (P4) (br,
t, J(P4–P1) 93, J(P4–P2) 94) (at −95°C).
43.8 (s)
dppa
[Ir4(CO)10(dppa)] (3) 2070 s, 2041 m, 2012 vs, 1980 m, 1860 w, 1825 m, 1778 m.
[Ir4(CO)8(dppa)2] (4) 2008 s, 1975 s(br), 1957 s, 1835 w, 1780 m, 1765 m.
−17.1 (s) (at 25 and −95°C)
0.3 (br, s), −12.4 (br, s) (at 25°C)
a CH2Cl2 solvent.
b Chemical shifts with respect to H3PO4 as external references; CH2Cl2 used as solvent; all coupling constants given in Hz; br, broad; s, singlet;
d, doublet; dd, doublet of doublets; t, triplet.

N. Nawar / Journal of Organometallic Chemistry 602 (2000) 137–143
139
Fig. 1. The 31P-NMR spectra of cluster complexes [Ir4(CO)8(dppen)2] (2) at −95°C and [Ir4(CO)8(dppa)2] (4) at 25°C.
with coupling constants J(P1P4) 93 and J(P3P2) 97 Hz,
respectively. A resonance at −37.7 and −49.8 ppm
(a shift of −34.3 or −46.4 ppm from free dppen
ligand (−3.4 ppm)), due to the phosphorus atoms
coordinated to the iridium metal framework, consists of
a broadened triplet, which results from phosphorus–
phosphorus coupling with coupling constants J(P4P1)
93, J(P3P2) 97 and J(P2P4) 94 Hz. The two resonances
at −45.8 and −49.8 ppm appear at lower field than
that of the diaxial phosphorus P1 and P2 from dppen
coordinated to the iridium metal framework. The
present results are in agreement with those previously
reported [6,7,18]. The FAB mass spectra of
[Ir4(CO)8(dppen)2] (2) or [Ir4(CO)8(dppa)2]·3(THF) (4)
show a parent ion at m/z 1786 or m/z 1763 as expected,
respectively. The stepwise loss of eight carbonyl groups
is also observed. The mass spectrum of the cluster
complex 4 did not give a molecular ion peak at the
desired position of m/z 1980. There is a difference of
217 amu, indicating the loss of three THF molecules.
This result supported by the X-ray crystallographic
determination of the cluster iridium complex 4.
NMR spectrum at room temperature (r.t.). These are
because fluxionality is observed in [Ir4(CO)8(dppen)2]
(2) or [Ir4(CO)8(dppa)2] (4). When the 31P-NMR spec-
trum was run at a lower temperature (−95°C) two
sharp doublets and two broadened triplets, which
should be doublet of doublet, were observed. The spec-
trum can be represented as shown in Fig. 1. The
31P-NMR spectroscopic data for complexes 2 or 4
(Table 1) suggest that each two phosphorus atoms in
the same bidentate ligand are in similar chemical envi-
ronments. This leads us to suggest that one of the
bidentate phosphine ligand (P1 and P2) is coordinated
at the diaxial sites and is bridged the Ir(1)ꢁIr(2). The
second bidentate phosphine ligand (P3 and P4) would
lead to a 31P-NMR chemical shift difference. It occu-
pies the radial site of the Ir(3) and the unique apical
Ir(4) atom. It was found that when apical substitution
occurs, basal phosphines rearrange to one radial and
two axial groups [1,18]. Therefore, the AA%XX% system
that arises from complexes 2 gives a spectrum (Fig. 1)
that allows phosphorus–phosphorus coupling to be
obtained directly. The spectrum of the cluster complex
2 shows that all the phosphorus atoms are coordinated.
It displays four sets of resonances. At 8.9 and −45.8
ppm, there are two doublets corresponding to the two
phosphorus atoms P1 and P3 bound to Ir1 and Ir4,
which result from phosphorus–phosphorus coupling
The X-ray crystal structure of the disubstituted spe-
cies [Ir4(CO)8(dppa)2]·3(THF) (4) was determined. A
perspective view of one molecule drawn to illustrate the
mutual disposition of the bridging ligands is shown in
Fig. 2. A listing of the selected bond distances and

140
N. Nawar / Journal of Organometallic Chemistry 602 (2000) 137–143
angles is given in Table 2. The molecule consists of a
tetrahedral core of iridium atoms, with the two dppa
ligands coordinated in a bridging mode such that one
carbonyl group on each Ir atom has been replaced by a
phosphine. The geometry of this skeleton is better
illustrated in Fig. 3, where phenyl groups have been
removed and the stereochemistry of the remaining
atoms emphasized. It is clear that the cluster iridium
complex has the usual tetrahedral arrangement of irid-
ium atoms. Three carbonyl groups are bridged to basal
iridium atoms, which have two bridged dppa ligands.
One dppa ligand was found to be bridged Ir(1) and
Ir(2) and the other dppa ligand bridged Ir(3) and Ir(4)
atoms. Relevant differences have been detected in bond
distances between iridium atoms having bridged- or
linearly-bonded carbonyl groups (e.g. Ir(1)ꢁC(106)
sites in the basal plane of the Ir4 tetrahedron, whereas
in [Ir4(CO)9(PPh2Me)3], which adopts the carbonyl-
bridging C36 structure, the phosphine ligands occupy
one basal-axial and two basal-equatorial sites [25]. The
average PꢁN bond distances of P(1)ꢁN(1) 1.707(9);
P(2)ꢁN(1) 1.680(9); P(3)ꢁN(2) 1.703(9) and P(4)ꢁN(2)
1.674(8) are normal PꢁN bond distances [26]. One of
the most notable features for the cluster complex 4 is
the twisted configuration of one dppa ligand. The phos-
phorus atoms P(3) and P(4) are tilted away from the
plane of Ir(2)ꢁIr(3)ꢁIr(4) triangle, forcing P(3) below
and P(4) above the plane of the metal triangle. This
favored conformation of the five-membered ring con-
tributes to the tilting of the axial carbonyl ligands away
from the precise positions.
,
2.171(12) and Ir(1)ꢁC(101) 1.877(14) A). The IrꢁIr
3. Experimental
,
bond lengths range from 2.6845(9) to 2.7498(8) A,
typical values for phosphine substituted tetrahedral
iridium carbonyl clusters [4,23], and slightly longer than
the average determined in the parent [Ir4(CO)12] cluster
All reactions and manipulations of the new com-
pounds were performed under a nitrogen or argon
atmosphere, unless otherwise stated, using dry, de-
gassed solvents and standard Schlenk-line techniques.
IR spectra were recorded as dichloromethane (CH2Cl2)
solutions in 0.5 mm NaCl solution cells. The 31P{1H}-
NMR spectra were obtained on JEOL FX-60 or Bruker
WM250 instruments. The chemical shifts are relative to
85% H3PO4. Microanalyses were carried out in the
Department of Chemistry, Liverpool University, UK.
FAB mass spectra were recorded on a VG 7070E
spectrometer. The compounds Ph2PC(ꢀCH2)PPh2 [27],
Ph2PN(H)PPh2 [28] and [Ir4(CO)12] [29] were prepared
according to published procedures.
,
(2.693) A [24]. It may be significant that the shortest
IrꢁIr bond, Ir(1)ꢁIr(2), is between the Ir atoms that are
bridged by both the carbonyl group and the dppa
ligand. This feature was also observed in the analogous
iridium complex [Ir4(CO)8(dppm)2]. Also, there is slight
asymmetry (only possibly significant) in the bridging
carbonyl groups (Ir(1)ꢁC(104) 2.054(11), Ir(2)ꢁC(104)
2.143(13);
Ir(1)ꢁC(106)
2.171(12),
Ir(3)ꢁC(106)
2.066(12); Ir(2)ꢁC(105) 2.040(13), Ir(3)ꢁC(105) 2.172
,
(12) A). It may be significant that the bidentate phos-
phine ligand dppa is constrained to coordinate at axial
Fig. 2. Perspective drawing of [Ir4(CO8(dppa)2]·3(THF) (4) with ellipsoids drawn at the 40% probability level.

N. Nawar / Journal of Organometallic Chemistry 602 (2000) 137–143
Table 2 (Continued)
141
Table 2
,
Selected bond distances (A) and angles (°) for [Ir4(CO8(dppa)2]·
3(THF) (4)
C(108)ꢁIr(4)ꢁC(107) 101.1(5)
O(105)ꢁC(105)ꢁIr(3) 135.8(9)
Ir(2)ꢁC(105)ꢁIr(3) 81.5(5)
C(108)ꢁIr(4)ꢁP(3)
C(107)ꢁIr(4)ꢁP(3)
C(108)ꢁIr(4)ꢁIr(1)
C(107)ꢁIr(4)ꢁIr(1)
P(3)ꢁIr(4)ꢁIr(1)
96.8(4)
102.6(4)
91.6(4)
102.2(3)
151.76(8)
101.1(3)
Bond distances
O(106)ꢁC(106)ꢁIr(3) 143.6(10)
O(106)ꢁC(106)ꢁIr(1) 135.9(10)
Ir(1)ꢁC(101)
Ir(1)ꢁC(104)
Ir(1)ꢁC(106)
Ir(1)ꢁP(1)
Ir(1)ꢁIr(2)
Ir(1)ꢁIr(4)
1.877(14)
2.054(11)
2.171(12)
2.271(3)
2.6845(9)
2.7110(8)
C(101)ꢁO(101)
C(102)ꢁO(102)
C(103)ꢁO(103)
C(104)ꢁO(104)
C(105)ꢁO(105)
C(106)ꢁO(106)
1.132(14)
1.119(13)
1.153(14)
1.148(14)
1.162(14)
1.133(13)
1.128(14)
1.128(14)
1.707(9)
Ir(3)ꢁC(106)ꢁIr(1)
80.4(4)
O(107)ꢁC(107)ꢁIr(4) 179.0(11)
O(108)ꢁC(108)ꢁIr(4) 174.8(12)
C(108)ꢁIr(4)ꢁIr(3)
Ir(1)ꢁIr(4)
2.7366(10) C(107)ꢁO(107)
3.1. Preparation of [Ir4(CO)10(dppen)] (1) or
[Ir4(CO)10(dppa)] (3)
Ir(2)ꢁC(102)
Ir(2)ꢁC(105)
Ir(2)ꢁC(104)
Ir(2)ꢁP(2)
Ir(2)ꢁIr(4)
Ir(2)ꢁIr(3)
Ir(3)ꢁC(103)
Ir(3)ꢁC(106)
Ir(3)ꢁC(105)
Ir(3)ꢁP(4)
1.875(11)
2.040(13)
2.143(13)
2.300(3)
C(108)ꢁO(108)
P(1)ꢁN(1)
P(1)ꢁC(11A)
P(1)ꢁC(11b)
1.801(11)
1.855(12)
1.680(9)
[Ir(CO)2Cl(p-toluidine)] (1.063 g, 2.72 mmol), dppen
(0.2702 g, 0.68 mmol), or dppa (0.2627 g, 0.68 mmol),
acid-washed mossy zinc (9.0 g), 2-methoxyethanol (150
cm3), and water (6 cm3) were placed in a 500 cm3
heavy-walled glass pressure vessel. The mixture was
saturated with CO and then pressurized to 4 atm with
CO. The reaction vessel was heated to 90°C for 45 min,
with stirring, and then cooled, vented, and the solution
filtered under nitrogen. The filtrate was reduced in
volume and chromatography on Florisil using a 5:1
petroleum ether–dichloromethane eluant. Two bands
were collected, a yellow band of [Ir4(CO)10(dppen)] or
[Ir4(CO)10(dppa)], followed by an orange band of
[Ir4(CO)8(dppen)2] or [Ir4(CO)8(dppa)2]. The yellow
product was recrystallised from THF–hexane to give
yellow crystals of [Ir4(CO)10(dppen)] (1) (66 mg, 6.7%).
Found: C, 29.65; H, 1.48. Ir4C36H22O10P2. Calc.: C,
29.92; H, 1.53%. m/z=1445 (mass spectrometry) as
required for [Ir4(CO)10(Ph2PC(ꢀCH2)PPh2)]; and
[Ir4(CO)10(dppa)] (3) (80 mg, 8.2%) Found: C, 28.32; H,
1.45; N, 0.88. Ir4C34H21O10P2N. Calc.: C, 28.47; H,
1.48; N, 0.98%. m/z=1435 (mass spectrometry) as
2.7323(11) P(2)ꢁN(1)
2.7498(8)
1.858(11)
2.066(12)
2.172(12)
2.252(3)
P(2)ꢁC(21b)
P(2)ꢁC(21A)
P(3)ꢁN(2)
P(3)ꢁC(31A)
P(3)ꢁC(31B)
1.836(13)
1.836(12)
1.703(9)
1.833(11)
1.837(13)
1.674(8)
Ir(4)ꢁIr(4)
2.7175(11) P(4)ꢁN(2)
Ir(4)ꢁC(108)
Ir(4)ꢁC(107)
Ir(4)ꢁP(3)
1.886(13)
1.902(12)
2.289(3)
P(4)ꢁC(41A)
P(4)ꢁC(41B)
1338(13)
1.842(12)
Bond angles
C(101)ꢁIr(1)ꢁC(104) 101.8(5)
C(101)ꢁIr(1)ꢁC(106) 94.3(5)
C(104)ꢁIr(1)ꢁC(106) 159.0(5)
C(101)ꢁIr(1)ꢁP(1)
C(104)ꢁIr(1)ꢁP(1)
C(106)ꢁIr(1)ꢁP(1)
C(101)ꢁIr(1)ꢁIr(2)
C(104)ꢁIr(1)ꢁIr(2)
C(106)ꢁIr(1)ꢁIr(2)
P(1)ꢁIr(1)ꢁIr(2)
C(101)ꢁIr(1)ꢁIr(4)
C(104)ꢁIr(1)ꢁIr(4)
C(106)ꢁIr(1)ꢁIr(4)
P(1)ꢁIr(1)ꢁIr(4)
C(102)ꢁIr(2)ꢁP(2)
C(105)ꢁIr(2)ꢁP(2)
C(104)ꢁIr(2)ꢁP(2)
C(102)ꢁIr(2)ꢁIr(1)
C(105)ꢁIr(2)ꢁIr(1)
C(104)ꢁIr(2)ꢁIr(1)
P(2)ꢁIr(2)ꢁIr(1)
C(102)ꢁIr(2)ꢁIr(4)
C(105)ꢁIr(2)ꢁIr(4)
C(104)ꢁIr(2)ꢁIr(4)
P(2)ꢁIr(2)ꢁIr(4)
100.6(4)
104.6(3)
86.1(3)
141.6(4)
111.8(3)
48.8(3)
93.68(7)
102.5(4)
84.5(3)
99.2(4)
92.4(3)
98.3(3)
150.7(3)
51.7(4)
109.1(3)
94.75(8)
107.2(4)
80.5(3)
72.6(3)
153.57(7)
60.06(2)
143.5(4)
51.4(3)
108.8(3)
106.92(7)
60.46(3)
59.43(3)
96.7(5)
Ir(1)ꢁIr(2)ꢁIr(4)
81.9(3)
C(102)ꢁIr(2)ꢁIr(3)
C(105)ꢁIr(2)ꢁIr(3)
C(104)ꢁIr(2)ꢁIr(3)
P(2)ꢁIr(2)ꢁIr(3)
Ir(1)ꢁIr(2)ꢁIr(3)
Ir(4)ꢁIr(2)ꢁIr(3)
C(103)ꢁIr(3)ꢁC(106)
C(103)ꢁIr(3)ꢁC(105)
C(106)ꢁIr(3)ꢁC(105) 157.2(5)
C(103)ꢁIr(3)ꢁP(4)
C(106)ꢁIr(3)ꢁP(4)
C(105)ꢁIr(3)ꢁP(4)
C(107)ꢁIr(4)ꢁIr(3)
P(3)ꢁIr(4)ꢁIr(3)
Ir(1)ꢁIr(4)ꢁIr(3)
C(108)ꢁIr(4)ꢁIr(2)
C(107)ꢁIr(4)ꢁIr(2)
P(3)ꢁIr(4)ꢁIr(2)
Ir(1)ꢁIr(4)ꢁIr(2)
Ir(3)ꢁIr(4)ꢁIr(2)
153.52(8)
60.85(3)
139.5(4)
112.2(4)
48.1(3)
100.62(8)
60.95(2)
59.85(3)
98.8(5)
Ir(2)ꢁIr(1)ꢁIr(4)
required
for
[Ir4(CO)10(Ph2PN(H)PPh2)];
C(101)ꢁIr(1)ꢁIr(3)
C(104)ꢁIr(1)ꢁIr(3)
C(106)ꢁIr(1)ꢁIr(3)
P(1)ꢁIr(1)ꢁIr(3)
Ir(2)ꢁIr(1)ꢁIr(3)
Ir(4)ꢁIr(1)ꢁIr(3)
C(102)ꢁIr(2)ꢁC(105)
C(102)ꢁIr(2)ꢁC(104)
C(105)ꢁIr(2)ꢁC(104) 159.2(5)
C(103)ꢁIr(3)ꢁIr(4)
C(106)ꢁIr(3)ꢁIr(4)
C(105)ꢁIr(3)ꢁIr(4)
P(4)ꢁIr(3)ꢁIr(4)
C(103)ꢁIr(3)ꢁIr(1)
C(106)ꢁIr(3)ꢁIr(1)
C(105)ꢁIr(3)ꢁIr(1)
P(4)ꢁIr(3)ꢁIr(1)
[Ir4(CO)8(dppen)2] (2) (0.14 g, 14%). Found: C, 41.12;
H, 2.55. Ir4C60H52O8P4. Calc.: C, 41.48; H, 2.86%.
m/z=1183 (mass spectrometry) as required for
[Ir4(CO)8(Ph2PC(ꢀCH2)PPh2)2]; or [Ir4(CO)8(dppa)2] (4)
(0.129 g, 14.8%). Found: C, 41.11; H, 3.45; N, 1.35.
Ir4C68H66O11P4N2. Calc.: C, 41.25; H, 3.36; N, 1.41%.
m/z=1980 (mass spectrometry) as required for
[Ir4(CO)8(Ph2PN(H) PPh2)2]·3(C4H8O).
96.1(4)
96.6(4)
101.00)
96.2(4)
152.1(4)
91.33(8)
60.55(3)
150.0(3)
92.1(4)
96.6(5)
176.3(4)
83.6(3)
82.5(3)
3.2. Preparation of [Ir4(CO)8(dppen)2] (2) or
[Ir4(CO)8(dppa)2] (4)
87.03(7)
117.7(4)
51.5(3)
105.8(3)
136.11(8)
59.61(3)
116.6(3)
110.0(3)
47.2(3)
106.50(8)
59.10(2)
60.60(2)
[Ir4(CO)12] (0.282 g, 0.28 mmol) and dppen (0.224 g,
0.56 mmol) or dppa (0.218 g, 0.56 mmol) in toluene (30
cm3) were heated under reflux for 3 h. The resulting
orange–red solution was filtered and evaporated to
dryness under reduced pressure to give an orange solid.
Recrystallization from THF–hexane gave orange crys-
tals of [Ir4(CO)8(dppen)2] (2) (0.35 g, 34.7%) or
[Ir4(CO)8(dppa)2] (4) (0.45 g, 45%).
Ir(4)ꢁIr(3)ꢁIr(1)
C(103)ꢁIr(3)ꢁIr(2)
C(106)ꢁIr(3)ꢁIr(2)
C(105)ꢁIr(3)ꢁIr(2)
P(4)ꢁIr(3)ꢁIr(2)
Ir(4)ꢁIr(3)ꢁIr(2)
Ir(1)ꢁIr(3)ꢁIr(2)
O(101)ꢁC(101)ꢁIr(1) 177.4(12)
O(102)ꢁC(102)ꢁIr(2) 175.3(12)
O(103)ꢁC(103)ꢁIr(3) 176.2(11)
O(104)ꢁC(104)ꢁIr(1) 142.2(10)
O(104)ꢁC(104)ꢁIr(2) 138.3(9)
Ir(1)ꢁC(104)ꢁIr(2)
O(105)ꢁC(105)ꢁIr(2) 142.7(9)
130.19(7)
59.96(3)
58.59(3)
79.5(4)

142
N. Nawar / Journal of Organometallic Chemistry 602 (2000) 137–143
3.3. X-ray crystallography procedures
(−100°C) on an Enraf–Nonius CAD-4S diffractome-
ter equipped with graphite monochromator and Mo–
,
3.3.1. General information
Ka (u=0.71073 A) radiation. Reflections (250) in the
Orange crystals of the cluster complex [Ir4(CO)8-
(dppa)2]·3(THF) suitable for X-ray diffraction studies
were obtained. The basic crystallographic procedures
used have been fully described elsewhere [30,31]. Data
sets were collected, corrected for Lorentz, polarization,
absorption effects, and merged. The positions of the Ir
and P atoms were given by a Patterson superposition
method. The remainder of the atoms were found in
subsequent sets of least-squares refinement cycles, fol-
lowed by difference Fourier maps using the SHELX-93
structure refinement program [32]. All calculations were
performed on a DEC 3000-800 AXP workstation. A
listing of the selected bond distances and angles for
[Ir4(CO)8(dppa)2]·3(THF) is presented in Table 2. It was
found that two fully occupied sites containing THF
molecules were located, as were two other approxi-
mately half-occupied sites. Hydrogen atoms were added
to the model in calculated positions for the phenyl
groups of the metal cluster complex. In the final refine-
ment cycles, all the non-hydrogen atoms of the metal
complex were given anisotopic displacement para-
meters, as were the atoms on the two fully occupied
THF sites.
range 9.0–20.1 q were centered to refine the reduced
parameters corresponding to the triclinic crystal system.
A total of 8979 data were collected using an ꢀ scan
technique. Full refinement of 797 parameters led to
residuals of R=0.052 (for 8971 reflections with I\
2|(I)) and R=0.062 (for all 8979 data).
3.3.3. Crystal data
C68H66Ir4N2O11P4, M=1979.91, triclinic, space
group P1, a=12.452(3), b=16.181(3), c=17.806(4) A,
(
,
3
,
i=89.01(3)°, V=3545.4(12) A , Z=2, Dcalc=1.855 g
cm−3, v=7.63 mm−1, T= −60°C, R=0.052 (for
8971 reflections with I\2|(I)) and Rint=0.000 (for all
8979 data).
4. Supplementary material
Crystallographic data for the structure analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 139261 for the compound
[Ir4(CO8(dppa)2]·3(THF). Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44-1223-336033 or e-mail: deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
3.3.2. Crystal structure analysis of
[Ir4(CO)8(dppa)2]·3(THF) (4)
Orange
crystals
of
the
cluster
complex
[Ir4(CO)8(dppa)2]·3(THF) were grown from a THF–
hexane solution. The crystals were sensitive to solvent
loss and thus a suitable crystal of dimensions of 0.40×
0.25×0.18 mm was attached to the tip of a quartz fiber
with a small amount of grease and immediately
transferred into a low-temperature stream of nitrogen
Acknowledgements
We thank Dr Lee M. Daniels (Laboratory for Molec-
ular Structure and Bonding, Texas A&M University)
for the diffraction data collection.
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