Group 9 half-sandwich complexes containing the unique P,P′-diphenyl-1,4-diphospha-cyclohexane ligand: Synthesis, X-ray structure analyses and spectroscopic studies

Article abstract of DOI:10.1016/j.jorganchem.2009.06.023

We wish to report the synthesis and characterization of Group 9 metal complexes with the novel P,P′-diphenyl-1,4-diphospha-cyclohexane (dpdpc) ligand. The complexes are readily prepared by direct ligand substitution reactions from the dichloro-bridged bin

Full text of DOI:10.1016/j.jorganchem.2009.06.023

Journal of Organometallic Chemistry 694 (2009) 3506–3510
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Group 9 half-sandwich complexes containing the unique P,P0-diphenyl-
1,4-diphospha-cyclohexane ligand: Synthesis, X-ray structure analyses
and spectroscopic studies
Joshua E. Sussman a, Tara S. Morey a, Susie M. Miller b, Monte L. Helm a,
*
a Chemistry Department, Fort Lewis College, 1000 Rim Drive, Durango, CO 81301, USA
b Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA
a r t i c l e i n f o
a b s t r a c t
We wish to report the synthesis and characterization of Group 9 metal complexes with the novel P,P0-
Article history:
Received 17 March 2009
Received in revised form 17 June 2009
Accepted 19 June 2009
diphenyl-1,4-diphospha-cyclohexane (dpdpc) ligand. The complexes are readily prepared by direct
ligand substitution reactions from the dichloro-bridged binuclear complexes, [{g
5-Cp*M(Cl)2}2]. The
complexes include: [g l-dpdpc) (1), [g l-dpdpc) (2), and [g
5-Cp*Rh(Cl)2]2( 5-Cp*Ir(Cl)2]2( 5-Cp*Rh(Cl)-
Available online 24 June 2009
(dpdpc)]PF6 (3). The structures for all three complexes are supported by 1H, 13C{1H}, and 31P{1H} NMR
spectroscopy as well as elemental analysis. The molecular structures of 1 and 3 have also been estab-
lished by single-crystal X-ray analysis.
Keywords:
P,P0-diphenyl-1,4-diphospha-cyclohexane
Rhodium complexes
Ó 2009 Elsevier B.V. All rights reserved.
Iridium complexes
Mixed sandwich complexes
Phosphine ligands
Pentamethylcyclopentadienide complexes
1. Introduction
parts. One cyclic bidentate phosphine ligand that shows potential
for interesting metal coordination behavior is P,P0-diphenyl-1,4-
Over the years, phosphine ligands have played an essential
role in the development of metal-mediated catalysis [1–6]. The
ability to form a wide variety of sterically and electronically
unique phosphine ligands has lead to a pleathora of information
about how to influence catalytic cycles. For example, the role of
the P–M–P bite angle in migratory insertion of ethylene and
carbon monoxide in palladium complexes has been well docu-
mented [7]. Additionally, a recent review documents the influ-
diphospha-cyclohexane (dpdpc) [9]. Synthesis of the dpdpc ligand
results in formation of both cis- and trans-isomers as shown in
Fig. 1. Previous work conducted by Panunzi et al. on the metal
coordination properties of this ligand demonstrate its versatility
towards binding M(II) centers (M = Co, Ni, Pd and Pt) [10]. Further-
more, previous work from our laboratories have resulted in the for-
mation and structural characterization of [M(dpdpc)2]Cl2, (M = Pd,
Pt) complexes [11,12]. Interestingly, these complexes show an
average 73° P–M–P bite angle, much smaller then that for typical
acyclic bidentate phosphines.
The interesting coordination properties of the dpdpc ligand
have lead us to focus our attention on further understanding the
steric and electronic coordination properties of this compound. A
study completed by De Fraldi and Roviello indicated Group 10 me-
tal coordination of the dpdpc ligand can be influenced by the
charge of the metal center [13]. Their research indicated cationic
Group 10 metal centers preferred chelation by the dpdpc ligand,
where neutral metal centers preferred binucleation through a
bridging dpdpc ligand. The unique and varying coordination modes
of the dpdpc ligand has lead us to focus our attention on extending
the metal coordination of the dpdpc ligand to Group 9 metal cen-
ters [14,15].
ence of phosphine ligand bite angle in
a variety of metal
catalyzed carbon–carbon bond formation reactions [8]. The abil-
ity to synthesize phosphine ligands with unique electronic and
steric properties continues to be an important piece in catalytic
development.
Although there exists a large body of knowledge in the litera-
ture on bidentate phosphine ligands with a single bridging carbon
chain (i.e. R2P–C–C–PR2), very little research has been done on cyc-
lic bidentate phosphines with two connecting carbon chains (i.e.
RP(–C–C–)2PR). Such compounds are of particular interest due to
the fact that the phosphorus atoms are held in a rigid steric posi-
tion that could lead to distorted metal coordination geometries
and different reaction chemistry than seen in their acyclic counter-
In this work we have synthesized three new coordination com-
pounds of the dpdpc ligand with Rh(III) and Ir(III) metal centers
* Corresponding author. Tel.: +1 970 247 7635; fax: +1 970 247 7567.
E-mail address: helm_m@fortlewis.edu (M.L. Helm).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.06.023

J.E. Sussman et al. / Journal of Organometallic Chemistry 694 (2009) 3506–3510
3507
mer (2a) 1H NMR (CDCl3): d, 7.33–7.56 (m, C6H5, 10H); 3.55 and
2.55 (m, –CH2–, 8H); 1.32 (m, –CH3, 30H). 13C{1H} NMR (CDCl3):
d, 133.1, 131.5, 130.8, 128.8 (m, C6H5, 12C); 92.2 (s, Cp*, 10C);
19.3 (m, –CH2–, 4C); 8.67 (s, –CH3, 10C). 31P{1H} NMR (CDCl3): d,
ꢀ19.6 (s, 2P). trans-isomer (2b) 31P{1H} NMR (CDCl3): d, ꢀ15.3 (s,
2P).
a
b
P
P
Ph
Ph
Ph
P
P
Ph
2.2.3. Synthesis of [Cp*Rh(Cl)(dpdpc)][PF6] (3)
A mixture of [Cp*RhCl2]2 (0.151 g, 0.25 mmol) and dpdpc
(0.322 g, 1.18 mmol) in 50 mL of degassed ethanol was refluxed
under N2 for 3 h after which the solution had turned bright red/or-
ange. Solvent was removed via vacuum and 8.5 mL of degassed
ethanol followed by a solution of ammonium hexafluorophosphate
(170 mg in 8.5 mL water) was added. A red precipitate formed, was
filtered and dried under vacuum leaving 48 mg (28% yield). Anal.
Calc. for C26H33ClF6P3Rh: C, 45.20; H, 4.81. Found: C, 45.28; H,
4.93%. 1H NMR (CDCl3): d, 7.75–7.58 (C6H5, m, 10H); 2.96, 2.58
and 2.32 (CH2, m, 8H); 1.44 (Cp*–CH3, s, 15H). 13C{1H} NMR
(CDCl3): d, 133.2, 131.3, 129.8, and 124.2 (m, C6H5, 6C); 103.2 (m,
Cp*, 5C); 25.2 and 21.3 (m, –CH2–, 4C); 9.01 (s, –CH3, 5C). 31P{1H}
cis-isomer
trans-isomer
Fig. 1. Structure of the (a) cis-dpdpc and (b) trans-dpdpc ligand.
and the
g
5-pentamethylcyclopentadienide (Cp*) ligand. The data
reported herein indicate the Rh(III) monomeric cationic complex
of dpdpc is formed through a bridged dimeric intermediate. X-
ray crystal structures of the dimeric [Cp*Rh(Cl)2]2(l-dpdpc) and
monomeric [Cp*Rh(Cl)(dpdpc)][PF6] will be reported.
1
NMR (CDCl3): d, 67.0 (d, JRh–P = 125.7 Hz, 2P); ꢀ143.7 (sept., PF6,
2. Experimental
1JP–F = 715.3 Hz, 1P).
2.1. General remarks
2.3. Single crystal X-ray structure analyses
Standard procedures for the manipulation of air-sensitive
materials were employed. Unless stated otherwise, all manipula-
tions were carried out at ambient temperature under an atmo-
sphere of dry argon or nitrogen gas using standard Schlenk,
syringe and high-vacuum line techniques. All solvents were dried
and distilled prior to use. The ruthenium, [Cp*RhCl2]2, and iridium,
[Cp*IrCl2]2, starting compounds (Sigma–Aldrich) were purchased
and used as received. Elemental analyses of the complexes were
performed by Huffman Laboratories in Goldon, CO USA. The
NMR spectra were recorded on a JEOL ESX-400 MHz instrument
and referenced using external standards. Infrared spectra were
recorded on a Thermo Nicolet Avatar 360 FT-IR spectrophotome-
ter. The dpdpc ligand was made according to literature procedure
[9].
X-ray quality crystals of the complexes 1b and 3 were grown by
slow evaporation of THF from a solution of the compounds. X-ray
intensity data were collected on a standard SMART 1K CCD diffrac-
tometer using graphite-monochromated Mo
Ka radiation,
k = 0.71073 Å. Absorption and other corrections were applied using
SADABS [16]. In all cases the space group was determined by obser-
vation of systematic absences and intensity statistics. Structures
were solved by direct methods using SHELXTL and refined by
full-matrix least squares on F2 [17]. Crystallographic details are
summarized in Table 1.
Table 1
Crystallographic and structure refinement parameters for 1 and 3.
2.2. Preparation of complexes 1–3
[Cp*Rh(Cl)2]2
(dpdpc) (1)
[Cp*Rh(Cl)(dpdpc)]
[PF6] (3)
2.2.1. Synthesis of [Cp*Rh(Cl)2]2(l-dpdpc) (1)
Chemical formula
Formula weight
Crystal system
Space Group
Crystal color and shape
Crystal size (mm3)
a (Å)
C18H24Cl2PRh
445.15
Triclinic
C30H41ClF6OP3Rh
762.90
Monoclinic
P2(1)
A mixture of [Cp*RhCl2]2 (0.151 g, 0.25 mmol) and dpdpc ligand
(0.068 g, 0.25 mmol) in 25 mL of degassed ethanol was refluxed
under N2 for 2 h, after which an orange precipitate formed. The
dark orange solid was filtered and dried under vacuum, leaving
100 mg (45% yield). Anal. Calc. for C36H48Cl4P2Rh2: C, 48.56; H,
5.43. Found: C, 48.20; H, 5.68%. cis-Isomer (1a) 1H NMR (CDCl3):
d, 7.67–7.29 (m, C6H5, 10H); 3.69 and 2.37 (m, –CH2–, 8H); 1.38
(m, –CH3, 30H). 13C{1H} NMR (CDCl3): d, 132.7, 131.1, 130.4 and
128.5 (m, C6H5, 12C); 98.6 (m, Cp*, 5C); 19.3 (m, CH2, 4C); 9.01
ꢀ
P1
Orange hexagonal plate Orange rod
0.20 ꢁ 0.12 ꢁ 0.05
8.7058(6)
13.6352(10)
16.4117(12)
71.103(4)
86.161(4)
85.464(4)
1835.6(2)
4
0.60 ꢁ 0.08 ꢁ 0.07
10.2073(5)
8.5765(5)
18.8761(10)
90
b (Å)
c (Å)
a
(°)
b (°)
99.420(3)
90
1630.19(15)
2
1.554
0.811
c
(°)
V (Å3)
(s, –CH3, 10C). 31P{1H} NMR (CDCl3): d, 14.1 (d, JRh–P = 138.7 Hz,
1
2P). trans-isomer (1b) 31P{1H} NMR (CDCl3): d, 18.0 (d, JRh–P
=
1
Z
Dcalc (Mg/m3)
1.611
1.303
138.7 Hz, 2P).
l
(mmꢀ1
)
Scan range (°)
Reflections collected
Independent reflections
Rint
1.58 < h < 33.35
67 364
14 122
2.02 < h < 33.36
20 635
11 031
2.2.2. Synthesis of [Cp*Ir(Cl)2]2(
A solution of dpdpc (0.038 g, 0.125 mmol) in 3.75 mL CH2Cl2
was added dropwise to solution of [Cp*IrCl2]2 (0.100 g,
0.125 mmol) in 3.15 mL CH2Cl2 that was cooled to 0 °C. The mix-
ture was then stirred overnight. The next morning the volume
was reduced by half, approximately 3 mL of ethanol was added,
followed by removal of solvents until an orange precipitate formed.
The orange solid was filtered, washed with ethanol and dried with
ether giving 69 mg of product (52% yield). Anal. Calc. for
C36H48Cl4P2Rh: C, 40.45; H, 4.53. Found: C, 40.11; H, 4.55%. cis-Iso-
l-dpdpc) (2)
0.0408
0.0357
a
Final R indices [I > 2
r
(I)]a
R1 = 0.0315,
wR2 = 0.0789
R1 = 0.0446,
wR2 = 0.0885
0.824
R1 = 0.0396,
wR2 = 0.0892
R1 = 0.0497,
wR2 = 0.0943
0.965
R indices (all data)a
Goodness-of-fit (GOF) on F2
Maximum, minimum
D
q
1.209, ꢀ1.150
1.271, ꢀ0.641
(e Åꢀ3
)
h
i
1=2
P
P
P
P
2
2
a
R1
¼
jjFoj ꢀ jFcjj= jFoj. wR2
¼
wðjFoj ꢀ jFcjÞ = wðFoÞ
.

3508
J.E. Sussman et al. / Journal of Organometallic Chemistry 694 (2009) 3506–3510
assignment of their P-31 NMR peaks. The compounds are readily
a
*Cp
Cl
b
identified through their distinct 31P{1H} NMR spectra, that consist
of a major peak for the trans-isomer and minor peak for the cis-iso-
mer in approximately 9:1 ratio, as determined by P-31 NMR inte-
gration. Although P-31 NMR of the reactions mixtures shows
quantitative formation of the products, the compounds are isolated
in 40–50% yields as pure orange solids as characterized by their ele-
mental analysis.‘ The isolated products are non-hydroscopic, air-
stable solids, soluble in THF, acetonitrile and chlorinated solvents.
Compounds 1a and 2a are fully characterized through 1H, 13C
and 31P NMR, and elemental analysis. Attempts to isolate the
trans-isomers (1b, 2b) were unsuccessful, so their characterization
relies only on P-31 NMR and elemental analysis of the bulk sample.
The P-31 NMR spectra of all compounds show the expected down-
field chemical shift from the free dpdpc ligand upon metal coordi-
nation (44 ppm average). Further evidence of metal coordination in
compounds 1a and 1b is illustrated through the observation of
Cl
*Cp
Cl
M
Cl
M
P
P
Cl
Ph
Ph
Cl
Ph
M
P
P
Cp*
M
Cp*
Ph
Cl
Cl
cis-isomer
trans-isomer
M = Rh, Ir
Fig. 2. Structure of the (a) cis- and (b) trans-isomers of 1 and 2.
J1
coupling of 137.8 Hz. Interestingly, there is no difference in
Rh–P
the Rh–P coupling between the cis- and trans-isomers. The proton
and carbon-13 NMR spectra of 1a and 2a show the correct number
of peaks, splittings and intensities associated with the Cp*-ring and
carbon backbone of the dpdpc ligand. The proton NMR of the
dpdpc –CH2– carbon backbone appears as a pair of two distinct
multiplets of approximate AA0BB0 splitting pattern. The magnetic
inequivalency of these methylene protons are attributed to them
being in fixed axial or equatorial positions (on the NMR time scale).
There are no noteworthy differences between the proton and car-
bon-13 NMR spectra between the Rh(III) and Ir(III) complexes.
The reaction of the dimeric chloro-bridged metal complex
3. Results and discussion
3.1. Syntheses and NMR spectroscopy
The reaction of the dimeric chloro-bridged metal complexes,
[Cp*M( -Cl)Cl]2 (M = Rh, Ir), with a stoichiometric amount of the
dpdpc ligand results in formation of the dimeric diphosphine-
l
bridged complexes of general type [Cp*M(Cl)2]2(
as shown in Eq. (1).
l
-dpdpc) (1, 2)
½CpꢂMð
l
-ClÞClꢃ2 þ dpdpc ! ½CpꢂMðClÞ2ꢃ2ð
-dpdpcÞ
l
[Cp*Rh(l-Cl)Cl]2 with an excess of the dpdpc ligand, and subse-
M ¼ Rhð1Þ; Irð2Þ
ð1Þ
quent reaction with NH4PF6, results in formation of the mono-
meric diphosphine complex [Cp*Rh(Cl)(dpdpc)][PF6] (3), as
shown in Eq. (2). The formation of 3 in the reaction mixture
can be monitored through appearance of a distinct singlet with
Rh-coupled satellites in the P-31 NMR. The isolated orange solid
is non-hydroscopic, air-stable, and soluble in THF, acetonitrile
and chlorinated solvents.
The synthesis of compounds 1 and 2 result in formation of two dis-
tinct isomers arising from the configuration of the 6-membered ring
of the phosphorus ligand, the major (cis) isomer and minor (trans)
isomer (a and b, respectively, Fig. 2). The configuration of the 6-
membered ring of the phosphorus ligand can be inferred from the
ratio of products, as the starting dpdpc ligand occurs in approxi-
mately the same 9:1 cis/trans ratio in the P-31 NMR. Further,
through serendipitous crystallization, the minor trans-isomer of
the Rh dimer (1b) was crystallized, which allowed for absolute
½CpꢂRhð
-ClÞClꢃ2 þ dpdpc ðexcessÞ þ NH4PF6
l
! ½CpꢂRhðdpdpcÞðClÞꢃ½PF6ꢃð3Þ þ NH4Cl
ð2Þ
*Cp
Cl
Cl
M
M
Cl
PhP
PPh
+
Cl
Cp*
M= Rh, Ir
*Cp
Cl
M
P
Cl
+
Cl
Cp*
Ph
Rh
Rh: CH3CN
reflux 2h, NH4PF6
-
Ph
PF6
PhP
PPh
P
Cl
M
Cl
Cp*
Scheme 1. Overall reaction summary.

J.E. Sussman et al. / Journal of Organometallic Chemistry 694 (2009) 3506–3510
3509
Compound 3 is fully characterized through 1H, 13C and 31P NMR,
elemental analysis and X-ray crystallography. The P-31 NMR of 3
shows an expected downfield chemical shift from the free dpdpc
1
ligand of 94 ppm and JRh–P coupling of 125.7 Hz. The downfield
chemical shift in 3 is approximately 50 ppm greater then the
downfield chemical shift observed in 1 and 2. The increase in the
downfield chemical shift may be due to the phosphorus ligand’s
ability to function as a stronger sigma-donor to the rhodium with
the loss of one additional chlorine, or the formation of a 5-mem-
bered chelate ring to one metal center. The P-31 NMR also shows
the expected peaks for the 19F coupled PF6ꢀ anion in the correct ra-
tio. The proton and carbon-13 NMR spectra of 3 show the correct
number of peaks, splittings and intensities associated with the
Cp*-ring and carbon backbone of the dpdpc ligand. As observed
in the dimeric-bridged compounds, proton NMR of the dpdpc
–CH2– carbon backbone appears as a pair of two distinct multiplets
of approximate AA’BB’ splitting pattern.
In an attempt to understand the reaction progress for formation
of the monomeric Rh-dpdpc complex (3), direct conversion of the
dimeric-Rh complex 1 to monomeric 3 was explored. Refluxing 1
in acetonitrile results in the disappearance of the P-31 NMR peaks
at 14.1 and 18.0 ppm (due to 1a/b) and appearance of a peak at
67.0 ppm due to 3. After 2 h of reflux time, conversion of 1–3 ap-
pears complete as analyzed by P-31 NMR. This data indicates that
di-metallic bridged complex 1 can function as an intermediate in
formation of 3, as shown in Scheme 1. Conversion of 1 from 3 re-
quires the loss of one metal center and, as a result, formation of
a secondary metallic product is expected. Because this product
does not contain phosphorus, its appearance is not observed in
the P-31 NMR and no attempts were made to isolate it. Interest-
ingly, we were unable to convert the di-metallic iridium complex
(2) to the analogous monometallic complex, even with extended
reflux times.
Fig. 3. Thermal ellipsoid perspective (50% probability) of 1b.
tallographic summary is given in Table 1, selected bond lengths
and angles in Table 2. Both structures show facial coordination of
the
g
5-Cp* ligand in addition to 3-anciliary ligands, resulting in a
six-coordinate distorted octahedral geometry around the Rh(III)
center.
Compound 1b clearly shows the dpdpc ligand functioning in a
bridging fashion between two Rh(III) metal centers. The bond an-
gles between the Rh(III) metal center, the two chlorine ligands
and phosphorus atom in the dpdpc ligand are all near the expected
90° values. The structure also shows the six-membered ring of the
dpdpc ligand in the chair-type confirmation with coordination to
3.2. X-ray structural data
The structures of trans-[Cp*Rh(Cl)2]2(l-dpdpc) (1b) and
[Cp*Rh(Cl)(dpdpc)][PF6] (3) were determined by single-crystal X-
ray diffraction, as illustrated in Figs. 3 and 4, respectively. A crys-
ꢀ
Fig. 4. Thermal ellipsoid perspective (50% probability) of cation of 3 (PF6 anion omitted for clarity).

3510
J.E. Sussman et al. / Journal of Organometallic Chemistry 694 (2009) 3506–3510
Table 2
dinate in both mono- and bridging fashions to metal centers. The
dimeric rhodium complex can be converted into the monomeric
complex, but conversion of the iridium complex was unsuccessful
in our hands. As shown by the X-ray crystal structure for the
monomeric rhodium complex, dpdpc produces a very acute bite
angle between P–Rh–P of 71.6°. These results are worthy of further
investigations which are ongoing in our laboratories.
Selected bond distances (Å) and angles (°) for trans-[
g
5-Cp*Rh(Cl)2]2(
l
-dpdpc) (1b)
and [
g
5-Cp*Rh(Cl)(dpdpc)][PF6] (3).
Distances (Å)
1b
3
Angles (°)
1b
3
Rh1–Cl1
Rh1–Cl2
2.4033(6) 2.4026(8) Around Rh1
2.4200(6)
–
Cl1–Rh1–
Cl2
92.21(2)
–
Rh1–P1
Rh1–P2
2.2940(5) 2.2818(6) Cl2–Rh1–P1
85.49(2)
90.43(2)
–
–
–
–
2.2802(8) Cl1–Rh1–P1
P2–Rh1–Cl1
92.14(3)
92.69(3)
71.60(3)
5. Supplementary material
P1–C11
P1–C12
P1–C13
1.826(2)
1.823(2)
1.819(2)
1.831(3)
1.837(3)
1.794(3)
P1–Rh1–P2
CCDC 716707 and 716708 contain the supplementary crystallo-
graphic data for compounds 2 and 1a, respectively. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Around P1
Rh1–P1–C11 111.49(7)
Rh1–P1–C12 112.83(7)
Rh1–P1–C13 114.62(7)
C11–P1–C12 103.51(9)
C11–P1–C13 108.55(10) 108.86(15)
C12–P1–C13 105.06(10) 110.33(15)
106.80(10)
105.68(10)
122.83(9)
99.89(16)
Cp–M distances
Rh1–C1
Rh1–C2
Rh1–C3
Rh1–C4
2.141(2)
2.168(2)
2.162(2)
2.236(2)
2.231(2)
2.241(3)
2.226(3)
2.225(3)
2.169(3)
2.244(3)
Acknowledgements
Rh1–C5
We would like to acknowledge the Donors of the American
Chemical Society Petroleum Research Fund and Fort Lewis College
for support of this research.
two metal centers in a trans-position. Until now the only structural
reports containing the dpdpc ligand have been with the ligand in
the boat-type confirmation bound to a metal in a bidentate fashion.
Compound 3 shows the dpdpc ligand bound in a bidentate fash-
ion to the Rh metal center. The bond angles around the metal cen-
ter in 3 are more distorted then observed in 1b, with the most clear
example being the acute 71.60° P–Rh–P bite angle. This acute bite
angle observed when the dpdpc ligand binds in a bidentate way to
a metal center has been reported in other dpdpc metal complexes.
To the author’s knowledge, complex 3 displays the smallest P–M–P
bite angle of any 2-carbon bridged diphosphine (i.e. P–C–C–P)
ligand to date. In addition to the acute bite angle, compound 3
displays shorter Rh–P bond distances that observed in 1b. This is
in agreement with the P-31 NMR data that shows the phosphorus
atoms in 3 function as stronger sigma-donors to the Rh(III) center
then observed in 1b. These crystals structures support the idea that
the dpdpc ligand is capable of functioning both as a strongly
bound, bidentate chelating ligand as well as a bridging diphos-
phine ligand.
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Herein, we reported the synthesis of
a new series of
RP(–C–C–)2PR diphosphine complexes with rhodium(III) and irid-
ium(III) metal centers. In this work we demonstrated the versatile
coordination properties of the dpdpc ligand, which is able to coor-