Coordination of bis(azol-1-yl)methane-based bisphosphines towards RuII, RhI, PdII and PtII: synthesis, structural and catalytic studies

Article abstract of DOI:10.1039/c6dt04094b

The coordination chemistry of bisphosphine ligands assembled on the five-membered heterocyclic platform of bis(azol-1-yl)methane viz.: bis(2-diphenylphosphinoimidazol-1-yl)methane (1), bis(5-diphenylphosphinopyrazol-1-yl)methane (2) and bis(5-diphenylphosphino-1,2,4-triazol-1-yl)methane (3) with Ru^II, Rh^I, Pd^II and Pt^II is described. The bisphosphines 1-3 react with elemental selenium to give the corresponding bis-selenoyl derivatives 4-6. The reactions of 1-3 with transition metal derivatives produce complexes with different coordination modes. Bisphosphine 1 showed a preference for the κ²-P,P mode of coordination, whereas bisphosphines 2 and 3, besides the κ²-P,P mode also showed a head-to-tail κ²-P,N coordination mode resulting in the formation of binuclear complexes [Rh₂(COD)₂{(CH₂(1,2-C₃H₂N₂PPh₂)₂)-κ²P,N}][BF₄]₂ (14), [Rh₂(COD)₂{(CH₂(1,2,4-C₂HN₃PPh₂)₂)-κ²P,N}][BF₄]₂ (15), [Pd₂(η³-C₃H₅)₂{(CH₂(1,2-C₃H₂N₂PPh₂)₂)-κ²P,N}][BF₄]₂ (21) and [Pd₂(η³-C₃H₅)₂{(CH₂(1,2,4-C₂HN₃PPh₂)₂)-κ²P,N}][BF₄]₂ (22). Several of these complexes have also been structurally characterized. The in situ generated Rh^I complex of bisphosphine 1 showed moderate to good selectivity in the hydroformylation of various styrene derivatives.

Full text of DOI:10.1039/c6dt04094b

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Coordination of bis(azol-1-yl)methane-based
bisphosphines towards RuII, RhI, PdII and PtII:
Cite this: DOI: 10.1039/c6dt04094b
synthesis, structural and catalytic studies†
Sajad A. Bhat,a Madhusudan K. Pandey,a Joel T. Magueb and
Maravanji S. Balakrishna*a
The coordination chemistry of bisphosphine ligands assembled on the five-membered heterocyclic plat-
form of bis(azol-1-yl)methane viz.: bis(2-diphenylphosphinoimidazol-1-yl)methane (1), bis(5-diphenyl-
phosphinopyrazol-1-yl)methane (2) and bis(5-diphenylphosphino-1,2,4-triazol-1-yl)methane (3) with RuII, RhI,
PdII and PtII is described. The bisphosphines 1–3 react with elemental selenium to give the corresponding bis-
selenoyl derivatives 4–6. The reactions of 1–3 with transition metal derivatives produce complexes with
different coordination modes. Bisphosphine 1 showed a preference for the κ2-P,P mode of coordination,
whereas bisphosphines 2 and 3, besides the κ2-P,P mode also showed a head-to-tail κ2-P,N coordination
mode resulting in the formation of binuclear complexes [Rh2(COD)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,N}][BF4]2
(14), [Rh2(COD)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,N}][BF4]2 (15), [Pd2(η3-C3H5)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,
N}][BF4]2 (21) and [Pd2(η3-C3H5)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,N}][BF4]2 (22). Several of these complexes
have also been structurally characterized. The in situ generated RhI complex of bisphosphine 1 showed
moderate to good selectivity in the hydroformylation of various styrene derivatives.
Received 25th October 2016,
Accepted 23rd November 2016
DOI: 10.1039/c6dt04094b
www.rsc.org/dalton
sociation of at least one of the metal–ligand bonds with a
smaller kinetic barrier simply due to the difference in the
Introduction
Despite a plethora of phosphorus based ligands available,1 the Lewis acid–base compatibilities. Among phosphines and nitro-
enthusiasm to generate new ones or to carry out structural gen-heterocycle-based hybrid systems, more attention has
modifications of the existing ones is essentially due to the been devoted to the phosphine–pyridine and the phosphine–
overwhelming demand for modulating the reactivity of metal imidazole ligands and only a limited number of complexes
complexes with relevance to their applications in homo- containing phosphine–pyrazole or phosphine-1,2,3/4-triazole
geneous catalysis. Due to the readily available steric and elec- have been reported.5 The phosphine–imidazole ligands have
tronic characteristics and the ability to provide well-defined been used in the synthesis of various mono- and bi-metallic
and desired coordination environments around metal centers, complexes7 and also in several organic transformations.6 Otero
bisphosphines are the most preferred ligands in homogeneous et al. have reported the first examples of bis(azol-1-yl)methane-
catalysis and other important applications.2 A variety of based bisphosphines viz. bis(2-diphenylphosphinoimidazol-
bisphosphine ligands with varied bite angles have been syn- 1-yl)methane (bpizm) and bis(5-diphenylphosphinopyrazol-1-
thesized and their coordination chemistry has been explored.3
yl)methane (bppzm) and studied the coordination chemistry
Mixed donor ligands or phosphines containing nitrogen of a bppzm ligand with NbIII, PdII and PtII metal centres.8a,b
heterocycles as substituents are also of importance in coordi- In recent years, Chauvin and co-workers have synthesized
nation chemistry.4 The presence of a hetero donor atom gives o/m-phenylene bridged bis(imidazolylphosphines) and studied
flexible coordination modes and also facilitates the dis- their cis/trans chelating behaviour towards RhI and PdII metal
centres.9 As a continuation of our work in designing new phos-
phorus based ligands with a flexible P⋯P bite for exploring
aPhosphorus Laboratory, Department of Chemistry, Indian Institute of Technology
Bombay, Powai, Mumbai, 400076, India. E-mail: krishna@chem.iitb.ac.in,
msb_krishna@iitb.ac.in
bDepartment of Chemistry, Tulane University, New Orlens, Louisiana, 70118, USA
†Electronic supplementary information (ESI) available. CCDC 1408417, 1408420,
1511155–1511163, 1517753 and 1517754. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c6dt04094b
their organometallic chemistry and catalytic applications,10 we
decided to contribute to the so far unexplored chemistry of
bisphosphines based on bis(azol-1-yl)methane by preparing a
new member of this family, bis(5-diphenylphosphino-1,2,4-
triazol-1-yl)methane, and to investigate its transition metal
chemistry. For comparison, the coordination chemistry of
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bisphosphines such as bis(2-diphenylphosphinoimidazol-1-yl) weaker σ-donor ability compared to that of compounds 4, 5
1
methane and bis(5-diphenylphosphinopyrazol-1-yl)methane and PPh3 (1JPSe = 730 Hz).11 In the H NMR spectra of 4–6, the
4
was also undertaken.
bridging methylene protons did not show JPH coupling,
whereas the parent compounds 1–3 showed the same in the
range of 1.5–2 Hz.
Results and discussion
The structures of 1, 2 and 4–6 were confirmed by single
Bisphosphine ligands 1–3 were synthesized according to the crystal X-ray diffraction studies. The perspective views of the
reported literature procedures.8a,c The lithiated salts of bis molecular structures of 1 and 2 along with selected bond dis-
(azol-1-yl)methanes (azole, imidazole, pyrazole, 1,2,4-triazole) tances and bond angles are shown in Fig. 1. Due to the free
n
were generated by treatment with two equivalents of BuLi in rotation about the N–Csp3–N unit in both 1 and 2, the two
tetrahydrofuran at −78 °C, which on further reaction with two azole rings are not coplanar. Since the two phosphorus atoms
equivalents of chlorodiphenylphosphine resulted in the for- in 2 are in the syn conformation with respect to the bis
mation of desired bisphosphines as shown in Scheme 1. The (pyrazol-1-yl)methane bridge, the P⋯P separation (P1⋯P2,
31P{1H} NMR spectra of 1–3 showed single resonances around 4.002 Å) is shorter than that in 1 (5.476 Å, the two phosphorus
−34.5 ppm. In order to quantify the σ-donor properties of atoms are in the anti-position) and bis(2-(diphenylphosphino)
bisphosphines 1–3, selenoyl derivatives 4–6 were synthesized phenyl)ether (4.876 Å),12a but longer compared to those of the
by treating 1–3 with an excess of elemental selenium powder short bite ligands such as bis(diphenylphosphino)benzene
in toluene at 100 °C.
(3.194
Å)
and
2,3-bis(diphenylphosphino)quinoxaline
The 31P{1H} NMR spectra of compounds 4–6 showed sing- (3.166 Å).12b The intramolecular N1⋯N4 separation in 2 is
lets at 17.8, 15.7 and 17.9 ppm with 1JPSe couplings of 729, 746 3.298 Å. The P–C bond distances and C–P–C bond angles in 1
and 754 Hz, respectively. Usually the electron withdrawing and 2 compare well with those reported for analogous phos-
groups on phosphorus increase the magnitude of phos- phine ligands.9c
phorus–selenium coupling constant (1JPSe), due to the
All the three bis-selenides 4–6 have been structurally charac-
increased s-character of the phosphorus orbital involved in terized. Crystals were obtained from dichloromethane–
1
P–Se bonding and vice versa.11a The magnitude of JPSe for 6 petroleum ether mixtures. The phosphorus atoms are in a typical
suggests a slightly more s-character and hence a marginally tetrahedral environment in all the cases (Fig. 2). The P–C and
Scheme 1 Synthesis of ligands 1–3 and their selenoyl derivatives 4–6.
Fig. 1 Molecular structures of [CH2(1,3-C3H2N2PPh2)2] (1) and [CH2(1,2-C3H2N2PPh2)2] (2). Thermal ellipsoids are drawn at 50% probability level.
Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and bond angles (°): bisphosphine 1: P1–C13 1.8219(17), P2–C19 1.8206
(15), P1–C1 1.8279(17), P1–C7 1.8339(17), P2–C20 1.8335(15), P2–C26 1.8314(15), C1–P1–C7 102.55(8), C1–P1–C13 99.85(8), C7–P1–C13 100.18(8),
P1–C13–N1 127.25(13), P1–C13–N2 122.05(12). Bisphosphine 2: P1–C13 1.8212(15), P2–C19 1.8255(15), P1–C1 1.8349(16), P1–C7 1.8366(18),
P2–C20 1.8360(2), P2–C26 1.8345(14), C1–P1–C7 102.49(8).
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shown in Chart 1. Although, chelating and bridging modes are
the most preferred coordination modes for soft and low-valent
metals, with hard metals such as NbIII, examples of complexes
adopting bridging mode IV have been reported by Otero and
co-workers.8a,b Recently, we have examined the coordination
behaviour of ligands 1 and 3 with group 11 metals.8c,14 In the
case of gold(I) derivatives, besides gold atom showing linear
geometry, complexes with trigonal and tetrahedral geometries
were also isolated and structurally characterized. In this
context, we considered studying the platinum group chemistry
owing to their catalytic potential in various organic reactions.
Equimolar reactions between ligands 1–3 and [RuCl2(η6-
p-cymene)]2 in dichloromethane at room temperature
resulted in the formation of dinuclear complexes [Ru2Cl4(η6-
p-cymene)2{(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}] (7), [Ru2Cl4(η6-
p-cymene)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,P}] (8) and [Ru2Cl4(η6-
p-cymene)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,P}] (9) as brick red
solids with the bisphosphines exhibiting bridged coordination
modes as shown in Scheme 2. The 31P{1H} NMR spectra of 7–9
showed single resonances at 11.3, 15.8 and 13.7 ppm, respect-
ively. The 1H NMR spectra of complexes 7 and 9 consists of
two sets of doublets for the methyl protons of the isopropyl
groups at 0.98, 1.01 and 1.17, 1.20 ppm with a 3JHH coupling of
6.9 Hz and septets at 2.60 and 2.85 ppm for the methine
proton [CH(Me)2]. Two sets of doublets are observed for the
p-cymene ring protons of
7 and 9 in the range of
5.09–5.31 ppm and 4.89–5.59 ppm, respectively. Similar obser-
vations are reported for the analogous RuII complexes contain-
ing cymene groups due to the different orientations of the
cymene rings.15 In complex 8, two doublets at 5.81 and
4.71 ppm are observed for the p-cymene ring protons, whereas
two sets of doublets are observed at 1.41 and 1.32 ppm for the
methyl protons of the isopropyl group.
Fig. 2 Molecular structures of [CH2(1,3-C3H2N2PPh2Se)2] (4), [CH2(1,2-
C3H2N2PPh2Se)2] (5) and [CH2(1,2,4-C2HN3PPh2Se)2] (6). Thermal ellip-
soids are drawn at 50% probability level. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and bond angles (°) for
compound 4: P1–Se1 2.1043(6), P2–Se2 2.1066(7), P1–C13 1.8145(17),
P2–C19 1.8127(18). Compound 5: P1–Se1 2.1059(8), P2–Se2 2.1064(8),
P1–C13 1.803(3), P2–C19 1.802(3). Compound 6: P1–Se1 2.102(3),
P2–Se2 2.091(3), P1–C13 1.813(8), P2–C17 1.811(9).
The reactions of 1–3 with [(η5-C5H5)RuCl(PPh3)2] in 1 : 1
ratios in toluene under refluxing conditions afforded mono-
nuclear complexes [(η5-C5H5)RuCl{(CH2(1,3-C3H2N2PPh2)2)-κ2P,
P}] (10), [(η5-C5H5)RuCl{(CH2(1,2-C3H2N2PPh2)2)-κ2P,P}] (11) and
[(η5-C5H5)RuCl{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,P}] (12) as shown
in Scheme 2.
The 31P{1H} NMR spectra of complexes 10–12 showed
single resonances at 41.2, 36.7 and 42.5 ppm, respectively. The
cyclopentadienyl ring protons in the 1H NMR spectrum appear
in the range 4.10–4.32 ppm. Furthermore, the 1H NMR spectra
of complexes 10–12 showed clearly differentiated exo and endo
protons of the bridging methylene group (CH2), as they
become diastereotopic on complexation. The endo proton in
7–9 appears as a doublet at 7.13, 7.08 and 7.18 ppm, respect-
P–Se bond lengths are consistent with covalent radii predic-
tions as well as typical bond lengths for related diaryl phos-
phine selenides.13 The P–Se bond distances in 4 [2.1043(6) Å,
2.1066(7) Å], 5 [2.1059(8) Å, 2.1064(8) Å] and 6 [2.102(3) Å,
2.091(3) Å] show marginal variations. The intramolecular P⋯P
distances in 4–6 [6.472 Å, 6.320 Å, 6.866 Å] are longer than
those found in the parent bisphospine ligands 1 and 2
[4.002 Å, and 5.476 Å respectively].
2
ively, due to the geminal JHH coupling of 14.4 Hz. The exo
proton also appeared as a doublet at 5.24, 5.99 and 5.99 ppm,
respectively, with 2JHH coupling of 14.4 Hz. The cross peak ana-
lysis of the CH2 protons in the 1H–1H COSY spectrum of 12
Synthesis of RuII, RhI, PdII and PtII complexes
The exocyclic phosphine arms appended to the nitrogen reveals the possible explanation for the observed multiplicity.
heterocycles in 1–3 can move around easily due to the free The 1H–1H COSY spectrum indicates that the doublet at
rotation around the methylene bridge and therefore will influ- 5.99 ppm due to one of the CH2 protons is correlated to the
ence their ability to achieve chelating or bridging modes of doublet of another proton at 7.18 ppm. This difference in
coordination. They offer several coordination possibilities as chemical shifts between the pair of doublets arising from the
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Chart 1 Possible coordination modes for ligands 1–3.
Scheme 2 Synthesis of ruthenium(II) complexes.
–CH2– moiety in the complexed form of these ligands is par- and the conformation of the metallacycle is such that the endo
ticularly sensitive to the nature of the metal precursor, coordi- proton is in the range of (2.464–2.638 Å) from the chloride
nation number and the presence of other ligands.
atom, whereas the exo proton shows CH⋯π interaction
Crystals of complexes 10 and 12 suitable for the single (CH21A⋯C9 = 2.848 Å) with a phenyl ring of another molecule
crystal X-ray diffraction study were obtained by slow diffusion in complex 10. The P1–Ru–P2, P1–Ru–Cl and P2–Ru–Cl bond
of petroleum ether into the dichloromethane solution of the angles are in the range of 95.33(3)–96.43(3)°, 87.694(17)–
corresponding complex, whereas those of 11 were obtained by 89.12(3)° and 93.536(16)°–100.75(2), respectively. The Ru–P
slow diffusion of petroleum ether into the chloroform solu- bond distances are in the range of 2.2794(6)–2.3060(8) Å and are
tion. These complexes (10–12) have similar bond parameters comparable to the imidazole–phosphine based complex [(η5-
(Table 1). As revealed from the crystal structures of 10–12 C5H5)RuCl(PPh3)(C3N2H3PPh2)] [2.307(1) Å],16 but are shorter
(Fig. 3), ruthenium adopts three-legged piano stool geometry than those observed for [(η5-C5H5)RuCl{Ph2PC6H4OC6H4PPh2-
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Table 1 Selected bond distances and bond angles for 10, 11 and 12
10
11
12
Bond distances (Å)
Ru1–Cl1
Ru1–P1
Ru1–P2
Ru1–C1
Ru1–C2
Ru1–C3
Ru1–C4
Ru1–C5
2.4405
2.4581(8)
2.2919(8)
2.3060(8)
2.228(3)
2.223(3)
2.189(3)
2.197(3)
2.220(3)
2.4426(6)
2.2794(6)
2.2924(6)
2.215(2)
2.209(2)
2.181(2)
2.198(2)
2.218(2)
2.2859(5)
2.2962(5)
2.196(2)
2.188(2)
2.224(2)
2.222(2)
2.216(2)
Bond angles (°)
Cl1–Ru1–P1
Cl1–Ru1–P2
P1–Ru1–P2
P1–Ru1–C1
P2–Ru1–C2
P2–Ru1–C3
Cl1–Ru1–C4
P1–Ru1–C5
90.69(2)
93.54(2)
96.38(2)
92.06(6)
96.26(6)
92.32(6)
89.35(5)
105.20(6)
89.12(3)
100.43(3)
95.33(3)
140.93(10)
92.83(10)
94.02(10)
131.63(10)
104.32(10)
87.79(2)
100.75(2)
96.43(2)
142.55(7)
90.78(7)
94.21(7)
130.02(7)
105.88(7)
κ2P,P}].15 The Ru–C bond distances range from 2.181(2) Å to
2.228(3) Å, in which Ru–C bonds trans to phosphine are longer
than those trans to the chlorine atoms.
The 2 : 1 reaction between 1 and [Rh(COD)Cl]2 in the pres-
ence of two equivalents of AgBF4 in tetrahydrofuran afforded
the cationic chelate complex, [Rh(COD){CH2(1,3-C3H2N2PPh2)2}-
κ2P,P][BF4] (13), whereas similar reactions of 2 and 3 in
1 : 1 molar ratios in the presence of two equivalents of AgBF4
yielded bimetallic P,N-chelated complexes [Rh2(COD)2{(CH2(1,2-
C3H2N2PPh2)2)-κ2P,N}][BF4]2 (14) and [Rh2(COD)2{(CH2(1,2,4-
C2HN3PPh2)2)-κ2P,N}][BF4]2 (15), respectively, as shown in
Scheme 3. The 31P{1H} NMR spectra of complexes 13–15 con-
sists of doublets centred at 3.2, 3.8 and 29 ppm with 1JRhP coup-
lings of 140, 149 and 168 Hz, respectively. The molecular struc-
ture of 14 was further confirmed by a single crystal X-ray diffrac-
tion study.
Single crystals of [Rh2(COD)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,
N}][BF4]2 (14) were grown by layering a dichloromethane solu-
tion of the complex with diethyl ether. Complex 14 has crystal-
lographically-imposed 2-fold rotation symmetry with the axis
passing through the methylene bridge carbon atom (Fig. 4).
The bond parameters are given in Table 2. The rhodium(I)
atoms are in a typical square planar environment coordinated
by a bridging µ–κ2-P,N ligand and an η2-COD ligand to form
two seven-membered chelate rings. The Rh–P bond distance
[2.3265(10) Å] in 14 is longer than that in the PPh3 ligated
Fig. 3 Molecular structures of [(η5-C5H5)RuCl{(CH2(1,3-C3H2N2PPh2)2)-
κ2P,P}] (10), [(η5-C5H5)RuCl{(CH2(1,2-C3H2N2PPh2)2)-κ2P,P}] (11) and [(η5-
C5H5)RuCl{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,P}] (12). Thermal ellipsoids are
drawn at 50% probability level. Hydrogen atoms have been omitted for
clarity.
complex, [Rh(acac)(CO)(PPh3)]17 [2.2418(9) Å], but is compar- square planar geometry. This bite angle is larger than
able to those for [RhCl(PPh3)3]18 [2.322(4) Å, 2.334(4) Å, those reported for analogous six-membered chelate complexes
2.214(4) Å] and [Rh(COD)(PPh3)2]BF4 [2.3220(10) Å, 2.3618(1) of the type [Rh{3,5-Me2-C3HN2CH2CH2PPh2-κ2P,N}(COD)]BF4
Å].19 The Rh–N bond distance of 2.123(3) Å falls between the (82.68(5)°)20 and [Rh{C3H3N2CH2CH2PPh2-κ2P,N}(COD)]BF4
experimental values reported in the literature for analogous (88.86(4)°).21
complexes containing P,N-donor ligands.20,21 The coordination
The treatment of bisphosphines 1 and 3 with a stoichio-
of N2 also decreases the N1–C16–N1 bond angle from 112.29° metric amount of [M(COD)Cl2] (M = Pd, Pt) in dichloromethane
(N2–C16–N3; free ligand) to 109.2(4)°. The N2–Rh1–P1 bite at room temperature resulted in the formation of eight-mem-
angle of 90.25(9)° indicates the formation of strain free seven- bered chelate complexes [MCl2{(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}]
membered chelate ring with the rhodium atoms in an ideal (16 M = Pd, 17 M = Pt) and [MCl2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,
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Scheme 3 Synthesis of rhodium(I) complexes.
The cationic complex [Pd(η3-C3H5){(CH2(1,3-C3H2N2PPh2)2)-
κ2P,P}][OTf] (20) was prepared by the reaction of 1 with [Pd(η3-
C3H5)Cl]2 in a 2 : 1 molar ratio in the presence of AgOTf. The
analogous reactions of 2 and 3 with [Pd(η3-C3H5)Cl]2 in
1 : 1 molar ratios in the presence of two equivalents of AgBF4
in tetrahydrofuran afforded dinuclear complexes [Pd2(η3-
C3H5)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,N}][BF4]2 (21) and [Pd2(η3-
C3H5)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,N}][BF4]2 (22). The 31P{1H}
NMR spectra of 20–22 showed single resonances at 0.01, 8.8
and 11.3 ppm, respectively. The 1H NMR spectral data are con-
sistent with the structures proposed and the structure of 21
was further confirmed by a single crystal X-ray diffraction
study.
The crystals of 16–18 suitable for the X-ray diffraction study
were obtained by slow diffusion of diethyl ether into a di-
chloromethane solution of the corresponding complexes.
Selected bond distances and bond angles are listed in Table 3.
The bridging CH2 unit of the ligand is located above the mean
plane of the Cl2MP2 unit and the dihedral angle (φ) between
P1–Pd1–P2 and P1–C31–P2/P1–C15–P2 planes in 16 and 18 are
84.31° and 82.76°. The metal centres in complexes 16–18 (Fig. 5
and 6) adopt slightly distorted square planar geometries. The
P1–M1–P2 bite angles in 16 and 18 [93.69(3)°, 94.62(3)°] are
smaller than those found in analogous eight-membered chelate
complexes [PdCl2dppf] and [PdCl2{Ph2PC6H4OC6H4PPh2-κ2P,P}]
(99.07° and 100.82° respectively) but are quite close to those for
[PdCl2{P∩P}-κ2P,P] (93.22°) [P∩P = 1,2-bis(2-diphenylphosphino-
imidazol-1-yl)benzene].9c,25,26 The decrease in the bite angles of
16 and 17 compared to that of [PdCl2{Ph2PC6H4OC6H4PPh2-κ2P,
P}] may be due to the presence of a flexible CH2 bridge as it
allows the two PPh2-appended heterocyclic rings to come closer
to each other. The Cl1–M1–Cl2 bond angles in 16 and 17
Fig. 4 Molecular structure of [Rh2(COD)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,
N}][BF4]2 (14). Thermal ellipsoids are drawn at 50% probability level.
Hydrogen atoms have been omitted for clarity.
Table 2 Selected bond distances and bond angles for 14
Bond distances (Å)
Bond angles (°)
Rh1–P1
Rh1–N2
Rh1–C17
Rh1–C18
Rh1–C21
Rh1–C22
N1–N2
2.3265(10)
N2–Rh1–P1
90.25(9)
82.32(16)
81.23(16)
90.76(15)
89.75(14)
90.84(13)
93.92(12)
159.51(12)
167.47(15)
109.2(4)
2.123(3)
2.229(4)
2.202(4)
2.148(4)
2.126(4)
1.350(5)
1.359(5)
1.338(5)
C22–Rh1–C17
C21–Rh1–C18
N2–Rh1–C18
N2–Rh1–C17
C22–Rh1–P1
C21–Rh1–P1
C18–Rh1–P1
C21–Rh1–N2
N1–C16–N1
N1–C13
N2–C15
P}] (18 M = Pd, 19 M = Pt) as shown in Scheme 4. The 31P{1H} [92.31(3)° and 90.31(3)°] are larger than those observed in
NMR spectra of complexes 16–19 showed single resonances at [PdCl2(dppb-κ2P,P)] [88.21°] and [PdCl2(dppf)] [87.8°], but are
11.8, 8.1, −9.9, and −7.4 ppm, with platinum complexes 18 and comparable to the values found in [PdCl2(dppe-κ2P,P)] [94.2°]
19 showing JPtP couplings of 3454 and 3473 Hz, respectively. and [PdCl2(dppp-κ2P,P)] [90.8°].27 The average Pd–P bond dis-
1
1
The larger JPtP coupling supports the cis-orientation of phos- tances in 16 and 17 [2.2515(4) Å and 2.26348(5) Å] are slightly
phorus atoms around the platinum centre.22–26
shorter than those found in complexes [PdCl2(Xantphos-κ2P,P)]
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Scheme 4 Synthesis of palladium(II) complexes.
Table 3 Selected bond distances and bond angles for 16–18
planar. The N4–Pd1–P1 [100.88(6)°] and N2–Pd2–P2 [98.50(6)°]
bond angles are unequal in seven-membered chelate rings and
are larger than the P1–Pd2–P2 bond angles found in eight-
membered chelate complexes 16 and 17 with κ2-P,P coordi-
nation (Table 4). The Pd1–P1 [2.2927(7) Å and Pd2–P2 [2.3215
(7) Å] bond distances are unequal and are shorter than those
found in [Pd((CH3)2C3H3){Ph2PC6H4OC6H4PPh2-κ2P,P}][BF4]
[2.336(2) Å, 2.379(2) Å] and [Pd((CH3)2C3H3)(Xantphos-κ2P,
P)][BF4] [2.372(2) Å], but are comparable to those for [Pd
((CH3)2C3H3)(dppe)][BF4] [2.296(2) Å, 2.293(2) Å] and [Pd
((CH3)2C3H3)(dppf)][BF4] [2.313(6) Å, 2.33(9) Å].29 The allyl
moieties are coordinated in an asymmetric fashion to the PdII
centres as reflected from the Pd–C bond lengths. The Pd–C
bond lengths range from 2.124(8)–2.227(9) Å and the shortest
Pd–C bonds are located as expected trans to the nitrogen
donor atom.
16
17
18
Bond distances (Å)
M1–P1
M1–P2
M–Cl1
M–Cl2
2.2461(9)
2.2568(9)
2.3597(9)
2.3350(9)
2.2696(8)
2.2572(9)
2.3495(8)
2.3136(8)
2.2327(6)
2.2442(7)
2.3420(6)
2.3641(6)
Bond angles (°)
P1–M1–P2
Cl2–M1–Cl1
Cl2–M1–P1
Cl1–M1–P2
Cl2–M1–P2
Cl1–M1–P1
93.69(3)
92.31(3)
91.94(3)
84.88(3)
169.11(3)
163.57(3)
94.62(3)
90.31(3)
172.97(3)
168.30(3)
92.37(3)
82.70(3)
94.53(2)
89.67(2)
92.50(2)
85.30(2)
169.73(2)
166.13(2)
(Pd–Pavg 2.295(3) Å) and [PdCl2(dppf)] (Pd–Pavg 2.292(3) Å) indi-
cating stronger metal to ligand bonding interaction.25,26,28
Hydroformylation reactions
The Pt–P bond distances [2.2327(6) Å, 2.2442(7) Å] and the Hydroformylation of olefins to aldehydes is one of the most
P1–M1–P2 bond angle [94.53(2)°] in 18, respectively, are important transition metal catalysed C–C bond forming reac-
shorter/smaller than those for [PtCl2{(CH2(1,2-C3H2N2PPh2)2)- tions. A significant number of catalyst systems based on
κ2P,P}] [2.252(2) Å, 2.269(5) Å; 98.85(10)°].8a
various phosphorus based ligands have been examined as pre-
In complex 21, the bisphosphine 2 shows the bridging (µ-P, catalysts for olefin hydroformylation30 with rhodium com-
P) as well as chelating (κ2-P,N) modes of coordination (Fig. 7). plexes containing bisphosphines being ideal candidates for
The geometries around the PdII centres are distorted square hydroformylation reactions. The utility of bis(azol-1-yl)
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Fig. 5 Molecular structures of [PdCl2{(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}] (16) and [PdCl2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,P}] (17). Thermal ellipsoids are
drawn at 50% probability level. Hydrogen atoms have been omitted for clarity.
Table 4 Selected bond distances and bond angles for 21
Bond distances (Å)
Bond angles (°)
Pd1–P1
Pd2–P2
2.2927(7)
2.3215(7)
2.086(2)
2.148(2)
2.124(8)
2.157(5)
2.227(9)
2.191(8)
2.170(4)
2.133(8)
N4–Pd1–P1
N2–Pd1–P2
100.88(6)
98.50(6)
66.0(4)
67.3(4)
93.9(3)
99.4(3)
95.3(3)
98.6(3)
Pd2–N2
Pd1–N4
Pd1–C32
Pd1–C33
Pd1–C34
Pd2–C35
Pd2–C36
Pd2–C37
C32–Pd1–C34
C35–Pd2–C37
C32–Pd1–P1
C34–Pd1–N4
C35–Pd2–N2
C37–Pd2–P2
investigated recently in the rhodium catalysed hydroformyla-
tion of alkenes.31–33
Fig. 6 Molecular structure of [PtCl2{(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}]
(18). Thermal ellipsoids are drawn at 50% probability level. Hydrogen
atoms have been omitted for clarity.
The bisphosphines 1–3 were employed in the hydroformyla-
tion of olefins with the initial studies conducted using 1 with
[Rh(acac)(CO)2] as a catalyst for hydroformylation of styrene as
a model reaction. Since the isolated complexes 13–15 showed
only moderate conversions with b : l ratio, so as the combi-
nation of ligands 2 and 3 with [Rh(acac)(CO)2], only the combi-
nation of ligand 1 and [Rh(acac)(CO)2] was considered for
further investigation. The results are summarized in Table 8.
The conversion of styrene increases with pressure (entries 2
and 3). It is also observed that the yield of product decreases
with decrease in catalyst concentration (entries 3 and 4). From
these, the standard reaction conditions for the catalytic runs
were set at 60 °C and 40 bar of syn gas (H2/CO = 1 : 1) for 7 h.
The substrate to catalyst ratio and ligand to metal ratio were
1 : 1000 and 1 : 1. Noteworthy is the very good selectivity (84%)
for the formation of the branched aldehyde (entry 3). Under
identical reaction conditions, ligands 2 and 3 showed almost
similar reaction rates but the regioselectivity decreased com-
pared to 1 (entries 5 and 6). The optimized reaction conditions
used in case of 1 were further applied for hydroformylation of
various olefins with electron rich as well as electron deficient
substituents which showed good conversion and selectivity to
Fig. 7 Molecular structure of [Pd2(η3-C3H5)2{(CH2(1,2-C3H2N2PPh2)2)-
κ2P,N}][BF4]2 (21). Thermal ellipsoids are drawn at 50% probability level.
Hydrogen atoms have been omitted for clarity.
methane-based bisphosphines in hydroformylation is not the desired product (Table 9). Under identical conditions PPh3
known. However, the catalytic activity of imidazolium substi- showed 84% conversion with b : l ratio of 68 : 32. Bisphosphine
tuted monophosphines with a π-acceptor character has been 1 shows good catalytic efficiency.
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Table 5 Crystallographic information for compounds 1, 2, 4 and 5
1
2
4
5
Empirical formula
Fw
C31H26N4P2
516.50
C31H26N4P2 CHCl3
635.87
C31H26N4P2Se2
674.42
C31H26N4P2Se2
674.42
Cryst. system
Space group
a, Å
b, Å
c, Å
α, °
β, °
Orthorhombic
P212121(no. 19)
8.9713(7)
10.3845(8)
27.663(2)
90
117.081(2)
90
2577.2(3)
4
Triclinic
P1 (no.2)
Monoclinic
P21/n (no. 14)
13.075(3)
13.423(3)
16.698(4)
90
103.217(4)
90
2853.0(11)
4
Monoclinic
P21/c (no. 14)
17.6873(6)
9.4183(3)
18.1538(6)
90
109.520(1)
90
2850.29(16)
4
ˉ
12.323(2)
12.892(2)
12.951(2)
93.935(2)
117.423(2)
117.267(2)
1517.9(4)
2
γ, °
V, A3
Z
Dcalc, g cm−3
µ (Mo Kα), mm−1
F(000)
1.331
0.139
1080
1.391
0.437
656
1.570
2.733
1352
1.572
4.527
1352
Crystal size, mm
T (K)
2θ range, °
Total no. of reflns
No. of indep reflns
S
0.12 × 0.12 × 0.19
100
2.1–28.2
83 301
6350
1.05
0.16 × 0.18 × 0.20
100
1.9–28.4
26 708
7461
1.04
0.15 × 0.18 × 0.24
100
2.1–29.1
49 639
7417
1.03
0.04 × 0.16 × 0.2
100
2.65–72.4
48 861
43 796
1.038
R1
wR2
0.0332
0.0847
0.0323
0.0858
0.0284
0.0730
0.0352
0.0728
Table 6 Crystallographic information for compounds 6 and 10–12
6
10
11
12
Empirical formula
Fw
C29H24N6P2Se2
676.40
C36H31ClN4P2Ru
718.11
C36H31ClN4P2Ru
718.11
C35H31Cl3N6P2Ru
805.02
Cryst. system
Space group
a, Å
b, Å
c, Å
α, °
β, °
Monoclinic
P21/n (no. 14)
14.321(3)
11.432(2)
17.924(3)
90
103.979(2)
90
2847.6(9)
4
Monoclinic
P21/n (no. 14)
11.0252(13)
25.073(3)
11.0932(13)
90
90.325(2)
90
3066.5(6)
4
Triclinic
P1
Triclinic
P1
ˉ
ˉ
9.1612(3)
12.9584(5)
15.8185(3)
98.610(2)
92.840(2)
107.317(3)
1763.73(10)
2
9.4977(3)
18.3954(4)
19.9460(5)
87.8663(17)
79.437(2)
78.663(2)
3358.93(15)
4
γ, °
V, A3
Z
Dcalc, g cm−3
µ (Mo Kα), mm−1
F(000)
1.578
2.740
1352
1.556
0.737
1464
1.352
0.641
732
1.592
0.838
1632
Crystal size, mm
T (K)
2θ range, °
Total no. of reflns
No. of indep reflns
S
0.10 × 0.11 × 0.24
150
2.3–27.01
42 623
22 031
1.041
0.08 × 0.14 × 0.14
100
2.0–29.1
54 370
8058
1.05
0.27 × 0.22 × 0.14
150(2)
2.72–25.00
14 246
6160
1.055
0.29 × 0.14 × 0.08
150(2)
2.22–25.00
57 268
11 835
1.039
R1
wR2
0.1641
0.2389
0.0293
0.0773
0.0380
0.1014
0.0298
0.0651
show larger bite angles at the metal centers irrespective of the
nature of the metal and its geometry, the ligands in the
Conclusions
The coordination behaviour of bisphosphines 1–3 towards present investigation have displayed their ability to vary the
RuII, RhI, PdII and PtII has been described. Ligand 1 forms bite angles from 88 to 115° which is a promising feature in
chelate (κ2-P,P) complexes with RuII, RhI, PdII and PtII, whereas homogeneous catalysis where bite angles play a prominent
ligands 2 and 3 show both κ2-P,P or κ2-P,N modes of coordi- role. The in situ generated RhI complex of 1 catalyses the
nation. The formation of dinuclear complexes through κ2-P,N hydroformylation of styrene with moderate selectivity. Due to
coordination in 2 and 3 is due to the free rotation of phos- the rotational fluxionality of the phosphine moieties and the
phine-appended heterocyclic rings around the central methyl- ability of the ligands to show a κ2-P,N coordination mode, it is
ene carbon. Unlike typical large bite ligands which always still possible to activate the C–H bond(s) of bridging methyl-
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Table 7 Crystallographic information for compounds 14, 16–18 and 21
14
16
17
18
21
Empirical formula
Fw
Cryst. System
Space group
a, Å
b, Å
c, Å
α, °
C47H50B2F8N4P2Rh2
1112.29
Monoclinic
C2 (no. 5)
15.8580(3)
11.7581(3)
13.3446(3)
90
C31H26Cl2N4P2Pd
693.80
C29H24Cl2N6P2Pd
695.78
C31H26Cl2N4P2Pt
782.49
C37H36B2F8N4P2Pd2·CH2Cl2
1069.98
Monoclinic
P21/n (no. 14)
12.041(4)
18.039(6)
13.169(4)
90
Monoclinic
P21/n (no. 14)
9.9501(3)
24.6633(9)
11.4922(4)
90
Monoclinic
P21/c (no. 14)
12.0662(8)
18.1114(12)
13.1999(9)
90
Monoclinic
P21/n (no. 14)
11.1418(5)
31.8019(15)
11.9253(6)
90
β, °
108.8490(6)
90
2354.80(9)
2
1.569
6.912
92.438(40)
90
2857.8(16)
4
1.613
0.978
98.4310(16)
90
2789.73(16)
4
1.657
8.474
92.314(1)
90
2882.3(3)
4
1.803
5.194
102.2500(7)
90
4129.3(3)
4
1.721
1.15
γ, °
V, A3
Z
Dcalc, g cm−3
µ (Mo Kα), mm−1
F(000)
1124
1400
1400
1528
2128
Crystal size, mm
T (K)
2θ range, °
Total no. of reflns
No. of indep reflns
S
0.030 × 0.090 × 0.13
100(2)
3.5–72.18
4256
4209
1.062
0.03 × 0.13 × 0.16
100
1.7–28.5
24 568
6702
1.03
0.03 × 0.05 × 0.2
100
3.5–72.5
10 351
4324
0.988
0.14 × 0.19 × 0.23
100
1.9–29.2
50 599
7536
1.03
0.07 × 0.14 × 0.16
150(2)
2.362–29.118
10 965
9158
1.042
R1
wR2
0.0226
0.0568
0.0355
0.0959
0.0512
0.0675
0.0221
0.0523
0.0477
0.0825
Table 8 Hydroformylation of styrene using bisphosphines 1–3
Entry
Compound
P (Bar)
Time (h)
Conversion (%)
Branched : linear
75 : 25
TON
1
2
1
1
1
1
2
3
30
30
40
40
40
40
40
20
20
20
6
7
7
7
7
7
9
9
9
9
91
90
99
96
98
96
84
70
88
92
910
900
990
480
980
960
840
700
880
920
82 : 18
84 : 16
69 : 31
72 : 28
78 : 22
68 : 32
65 : 35
61 : 39
62 : 38
3a
4b
5a
6a
7
PPh3
13
14
15
8
9
10
Temp. = 60 °C, solvent = toluene. a S/C = 1000. b S/C = 2000.
Table 9 Hydroformylation of styrene and its derivatives
ene groups to form interesting pincer complexes. Further work
in this direction and also further exploration of these ligands
in other catalytic reactions are in progress.
Entry
Substrate
Conversion
Branched : linear
TON
1
2
3
4
5
Styrene
99
99
99
99
98
84 : 16
73 : 27
72 : 28
83 : 17
76 : 24
990
990
990
990
980
4-tert-Butyl styrene
3-Methyl styrene
4-Cl styrene
Experimental section
General procedures
4-Br styrene
Temp. = 60 °C, pressure = 40 bar (1 : 1/CO : H2), time = 7 h, solvent =
toluene, S/C = 1000.
All experimental manipulations were performed under an inert
atmosphere of dry nitrogen or argon, using standard Schlenk
techniques. All the solvents were purified by conventional pro-
cedures and distilled prior to use. The compounds bis(azol-1-yl)
methane (imidazole, pyrazole, 1,2,4-triazole),34 ligands 1–3,8a–c prepared according to the published procedures. Other
[Ru(η6-cymene)Cl2]2,35 [(η5-C5H5)RuCl(PPh3)2],36 [Rh(COD)Cl]2,37 reagents were obtained from commercial sources and used after
[M(COD)Cl2] (M = Pd or Pt),38 and [Pd(η3-C3H5)Cl]2,39 were purification.
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Instrumentation
(d, 2H, 3JHH = 6.1 Hz, Ph-CH), 5.13 (d, 2H, 3JHH = 6.1 Hz, Ph-CH),
5.09 (s, 2H, Ph-CH). 31P{1H} NMR (162 MHz, CDCl3): δ 11.3 (s).
Anal. Calcd for C51H54N4P2Ru2: C, 62.02; H, 5.51; N, 5.68.
Found: C, 62.12; H, 5.45; N, 5.61%.
Solution NMR spectra were recorded on a Bruker AV-400 or
AV-500 MHz spectrometer at ambient probe temperatures.
NMR shifts are given in δ with positive values downfield of
tetramethylsilane (1H) and external 85% H3PO4 (31P). The
31P NMR spectra were recorded in a proton-decoupled mode.
Positive values indicate downfield shifts. Microanalyses were
carried out using a Carlo Erba (model 1106) elemental analy-
zer. Melting points of all compounds were determined on a
Veego melting point apparatus and are uncorrected.
Synthesis of [Ru2Cl4(η6-p-cymene)2{µ-(CH2(1,2-C3H2N2PPh2)2)-
κ2P,P}] (8)
This was synthesized by a procedure similar to that of 7 using
2 (20 mg, 0.038 mmol) and [Ru(η6-p-cymene)Cl2]2 (24 mg,
0.038 mmol). Yield: 79.5% (35 mg). Mp: >280 °C. 1H NMR
(400 MHz, CDCl3): δ 6.45 (m, 2H, CH2), 6.31 (m, 2H, H4),
3
7.70 (m, 2H, H3), 7.05–7.95 (m, 20H, ArH), 1.41 (d, 6H, JHH
=
Synthesis of [CH2(1,3-C3H2N2PPh2Se)2] (4)
6.9 Hz, iPr-CH3), 1.32 (d, 6H, 3JHH = 6.9 Hz, iPr-CH3), 1.89 (s, 6H,
A mixture of 1 (30 mg, 0.058 mmol) and elemental selenium
(9.1 mg, 0.116 mmol) in toluene (15 mL) was refluxed for 12 h.
The colourless solution was filtered through a frit containing
Celite. The filtrate was reduced to 5 mL and layered with
petroleum ether to give colourless X-ray quality crystals of 4.
i
3
p-CH3), 3.18 (sep, 2H, Pr-CH), 5.811 (d, 4H, JHH = 6.1 Hz, Ph-
CH), 4.7 (4H, Ph-CH). 31P{1H} NMR (162 MHz, CDCl3): δ 15.8
(s). Anal. Calcd for C51H54N4P2Ru2·CH2Cl2: C, 58.26; H, 5.27;
N, 5.23. Found: C, 58.35; H, 5.18; N, 5.12%.
1
Yield: 64% (25 mg). Mp: 185 °C. H NMR (400 MHz, CDCl3):
Synthesis of [Ru2Cl4(η6-p-cymene)2{µ-(CH2(1,2,4-C2HN3PPh2)2)-
κ2P,P}] (9)
δ 6.98 (s, 2H, CH2), 7.17 (s, 2H, H4), 7.44–7.51 (m, 22H, H5,
ArH). 31P{1H} NMR (162 MHz, CDCl3): δ 17.8 (s, JPSe = 729
1
Hz). Anal. Calcd for C31H26N4P2Se2: C, 55.21; H, 3.89; N, 8.31. This was synthesized by a procedure similar to that of 7 using
Found: C, 55.17; H, 3.78; N, 8.38%.
3 (25 mg, 0.048 mmol) and [Ru(η6-p-cymene)Cl2]2 (29 mg,
0.048 mmol). Yield: 72.5% (39 mg). Mp: >280 °C. 1H NMR
(400 MHz, CDCl3): δ 6.09 (s, 2H, CH2), 8.12 (s, 2H, H4),
Synthesis of [CH2(1,2-C3H2N2PPh2Se)2] (5)
3
i
7.16–8.10 (m, 20H, ArH), 1.17 (d, 6H, JHH = 6.9 Hz, Pr-CH3),
This was synthesized by a procedure similar to that of 4 using
2 (40 mg, 0.077 mmol) and elemental selenium (12 mg,
0.15 mmol). Yield: 76% (52 mg). Mp: 265–268 °C. 1H NMR
3
i
1.20 (d, 6H, JHH = 6.9 Hz, Pr-CH3), 1.82 (s, 6H, p-CH3), 2.85
(sep, 2H, iPr-CH), 5.59 (d, 2H, 2JHH = 6.1 Hz, Ph-CH), 5.54 (d, 2H,
3
3JHH = 6.2 Hz, Ph-CH), 5.28 (d, 2H, JHH = 6.1 Hz, Ph-CH), 4.89
2
(400 MHz, CDCl3): δ 5.89 (s, 2H, JHH = 2 Hz, H3), 7.04 (s, 2H,
(d, 2H, 3JHH = 6.1 Hz, Ph-CH). 31P{1H} NMR (162 MHz, CDCl3):
δ 13.7 (s). Anal. Calcd for C49H52Cl4N6P2Ru2: C, 52.04; H, 4.63;
N, 7.43. Found: C, 52.15; H, 4.52; N, 7.57%.
CH2), 7.30 (t, 2H, H4), 7.42–7.77 (m, 20H, ArH). 31P{1H} NMR
1
(162 MHz, CDCl3): δ 15.7 (s, JPSe = 746.7 Hz). Anal. Calcd for
C31H26N4P2Se2: C, 55.21; H, 3.89; N, 8.31. Found: C, 55.32;
H, 3.71; N, 8.40%.
Synthesis of [(η5-C5H5)RuCl{(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}] (10)
A solution of [(η5-C5H5)RuCl(PPh3)2] (35 mg, 0.048 mmol) in
toluene (10 mL) was added slowly to a solution of 1 (25 mg,
0.048 mmol) in toluene (10 mL) at room temperature and the
mixture was heated at 100 °C for 12 h to give a clear yellow
solution. The solvent was evaporated under reduced pressure
and the residue obtained was washed with petroleum ether
several times. The residue was dissolved in CH2Cl2 and layered
with petroleum ether, which on slow evaporation gave red crys-
tals of 10. Yield: 76.5% (26 mg). Mp: 251–254 °C. 1H NMR
Synthesis of [CH2(1,2,4-C2HN3PPh2Se)2] (6)
This was synthesized by a procedure similar to that of 4 using
3 (40 mg, 0.079 mmol) and elemental selenium (12 mg,
0.16 mmol). Yield: 74% (42 mg). Mp: 234 °C. 1H NMR
(400 MHz, CDCl3): δ 7.71 (s, 2H, CH2), 7.73 (s, 2H, H3),
7.45–7.84 (m, 20H, ArH). 31P{1H} NMR (162 MHz, CDCl3):
1
δ 17.9 (s, JPSe = 754 Hz). Anal. Calcd for C29H24N6P2Se2:
C, 51.49; H, 3.58; N, 12.42. Found: C, 51.57; H, 3.47; N, 12.51%.
Synthesis of [Ru2Cl4(η6-p-cymene)2{µ-(CH2(1,3-C3H2N2PPh2)2)-
κ2P,P}] (7)
A solution of [Ru(η6-p-cymene)Cl2]2 (35 mg, 0.058 mmol) in
CH2Cl2 (10 mL) was added dropwise to a solution of 1 (30 mg,
0.058 mmol) in CH2Cl2 (10 mL) at room temperature. The red
solution obtained was stirred for 5 h. The solvent was evapor-
ated under reduced pressure and the residue was washed with
2
(400 MHz, CDCl3): δ 5.24 (d, 1H, JHH = 14.4 Hz, CH2), 7.13 (s,
2
1H, JHH = 14.4 Hz, CH2), 6.93 (s, 2H, H5), 6.98 (s, 2H, H4),
7.26–7.53 (m, 20H, ArH), 4.17 (s, 5H, C5H5). 31P{1H} NMR
(162 MHz, CDCl3): δ 41.2 (s). Anal. Calcd for C36H31ClN4P2Ru:
C, 60.21; H, 4.35; N, 7.80. Found: C, 60.28; H, 4.26; N, 7.76%.
Synthesis of [(η5-C5H5)RuCl{(CH2(1,2-C3H2N2PPh2)2)-κ2P,P}] (11)
diethyl ether to afford the analytically pure product of 7 as a This was synthesized by a procedure similar to that of 10 using
brick red solid. Yield: 78.5% (51 mg). Mp: >280 °C. 1H NMR 2 (20 mg, 0.038 mmol) and [(η5-C5H5)RuCl(PPh3)2] (28 mg,
(400 MHz, CDCl3): δ 6.87 (s, 2H, CH2), 7.15 (s, 2H, H4), 0.038 mmol). Yield: 75.2% (21 mg). Mp: 275 °C. 1H NMR
3
i
2
7.26–7.89 (m, 22H, H3, ArH), 0.98 (d, 6H, JHH = 6.9 Hz, Pr- (400 MHz, CDCl3): δ 5.99 (d, 1H, JHH = 14.4 Hz, CH2), 7.07 (s,
CH3), 1.01 (d, 6H, JHH = 6.9 Hz, Pr-CH3), 1.67 (s, 6H, p-CH3), 1H, JHH = 14.4 Hz, CH2), 5.54 (br, 2H, H4), 6.71 (s, 2H, H3),
3
i
2
2.60 (sep, 2H, Pr-CH), 5.31 (d, 2H, JHH = 6.1 Hz, Ph-CH), 5.18 7.21–7.58 (m, 20H, ArH), 4.28 (s, 5H, C5H5). 31P{1H} NMR
i
3
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(162 MHz, CDCl3): δ 36.4 (s). Anal. Calcd for C36H31ClN4P2Ru: generate yellow coloured X-ray quality crystals of 16. Yield:
1
C, 60.21; H, 4.35; N, 7.80. Found: C, 60.27; H, 4.21; N, 7.65%.
71% (32 mg). Mp: 254–256 °C. H NMR (400 MHz, DMSO-d6):
δ 5.73 (s, 2H, CH2), 8.10 (s, 2H, H5), 7.19–7.37 (m, 22H, H4,
ArH). 31P{1H} NMR (162 MHz, DMSO-d6): δ 11.8 (s). Anal.
Synthesis of [(η5-C5H5)RuCl{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,P}] (12)
This was synthesized by a procedure similar to that of 10 using Calcd for C31H26N4P2PdCl2: C, 53.66; H, 3.78; N, 8.07. Found:
3 (20 mg, 0.038 mmol) and [(η5-C5H5)RuCl(PPh3)2] (28 mg, C, 53.55; H, 3.81; N, 7.82%.
0.038 mmol). Yield: 75% (21 mg). Mp: 272–276 °C. 1H NMR
2
(400 MHz, CDCl3): δ 5.99 (d, 1H, JHH = 14.4 Hz, CH2), 7.18 (s,
Synthesis of [PdCl2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,P}] (17)
1H, 2JHH = 14.4 Hz, CH2), 6.91–7.51 (m, 20H, ArH), 7.74 (s, 2H,
H3), 4.27 (s, 5H, C5H5). 31P{1H} NMR (162 MHz, CDCl3): δ 42.3 This was synthesized by a procedure similar to that of 16 using
(s). Anal. Calcd for C34H29ClN6P2Ru: C, 56.71; H, 4.06; 3 (30 mg, 0.058 mmol) and Pd(COD)Cl2 (16 mg, 0.058 mmol).
1
N, 11.67. Found: C, 56.52; H, 3.95; N, 11.52%.
Yield: 82% (33 mg). Mp: >280 °C. H NMR (400 MHz, DMSO-
d6): δ 5.73 (s, 2H, CH2), 8.45 (s, 2H, H4), 7.26–7.47 (m, 20H,
ArH). 31P{1H} NMR (162 MHz, DMSO-d6): δ 8.0 (s). Anal. Calcd
Synthesis of [Rh(COD){(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}]BF4 (13)
To a stirred solution of [Rh(COD)Cl]2 (10 mg, 0.02 mmol) in for C29H24N6P2PdCl2: C, 50.06; H, 3.48; N, 12.08. Found:
THF (10 mL), AgBF4 (8 mg, 0.04 mmol) was added. After C, 49.95; H, 3.52; N, 11.86%.
30 minutes, the suspension obtained was filtered to remove
AgCl, and a solution of ligand 1 (20 mg, 0.04 mmol) in THF
(6 mL) was added drop-wise and the mixture was stirred for
Synthesis of [PtCl2{(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}] (18)
2 h. The yellow coloured solution was evaporated under A solution of Pt(COD)Cl2 (21 mg, 0.058 mmol) in CH2Cl2
reduced pressure and the residue was washed with petroleum (10 mL) was added dropwise to a solution of 1 (30 mg,
ether to afford the analytically pure product of 13 as a yellow 0.058 mmol) also in CH2Cl2 (10 mL). The resultant colourless
solid. Yield: 64% (31 mg). Mp: 194–198 °C. 1H NMR (400 MHz, solution was reduced to 5 mL and layered with diethyl ether to
CDCl3): δ 7.85 (s, 2H, H5), 7.22–7.56 (m, 24H, CH2, H4, ArH), form colourless X-ray quality crystals of 18. Yield: 66.6%
4.71 (br s, 4H, COD), 2.52 (br s, 4H, COD), 2.34 (br s, 4H, (30 mg). Mp: >280 °C. 1H NMR (400 MHz, DMSO-d6): δ 5.75
1
COD). 31P{1H} NMR (162 MHz, CDCl3): δ 3.2 (s, JPRh = 140.8 (s, 2H, CH2), 8.11 (s, 2H, H5), 7.19–7.37 (m, 22H, H4, ArH).
1
Hz). Anal. Calcd for C39H38N4P2RhBF4: C, 57.52; H, 4.70; 31P{1H} NMR (162 MHz, DMSO-d6): δ −9.9 (s, JPtP = 3454 Hz).
N, 6.88. Found: C, 57.42; H, 4.64; N, 6.75%.
Anal. Calcd for C31H26N4P2PtCl2: C, 47.58; H, 3.35; N, 7.16.
Found: C, 47.44; H, 3.30; N, 7.17%.
Synthesis of [Rh2(COD)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,N}](BF4)2 (14)
This was synthesized by a procedure similar to that of 13 using
2 (20 mg, 0.04 mmol) and [Rh(COD)Cl]2 (20 mg, 0.04 mmol)
Synthesis of [PtCl2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,P}] (19)
and AgBF4 (16 mg, 0.08 mmol). Yield: 65% (28 mg). Mp: This was synthesized by a procedure similar to that of 17 using
183–187 °C. 1H NMR (400 MHz, DMSO-d6): δ 7.22 (s, 2H, CH2), 3 (30 mg, 0.058 mmol) and Pt(COD)Cl2 (21 mg, 0.058 mmol).
1
6.77 (s, 2H, H4), 8.91 (s, 2H, H3), 7.26–8.22 (m, 20H, ArH), 5.65 Yield: 80% (35 mg). Mp: >280 °C. H NMR (400 MHz, DMSO-
(br s, 8H, COD), 2.14 (br s, 8H, COD), 2.01 (br s, 8H, COD). d6): δ 5.73 (s, 2H, CH2), 8.43 (s, 2H, H4), 7.26–7.47 (m, 20H,
1
31P{1H} NMR (162 MHz, DMSO-d6): δ 3.8 (d, JPRh = 148.9 Hz). ArH). 31P{1H} NMR (162 MHz, DMSO-d6): δ −7.4 (s, 1JPtP = 3473
Anal. Calcd for C47H50N4P2Rh2B2F8: C, 50.75; H, 4.53; N, 5.05. Hz). Anal. Calcd for C29H24N6P2PtCl2.CH2Cl2: 41.44; H, 3.01;
Found: C, 50.68; H, 4.42; N, 4.83%.
N, 9.66. Found: C, 41.49; H, 2.85; N, 9.53%.
Synthesis of [Rh2(COD)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,N}](BF4)2 (15)
This was synthesized by a procedure similar to that of 13 using
Synthesis of [Pd(η3-C3H5){(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}]OTf (20)
3 (20 mg, 0.038 mmol) and [Rh(COD)Cl]2 (20 mg, 0.038 mmol) A solution of [(η3-C3H5)PdCl]2 (10 mg, 0.03 mmol) in THF
and AgBF4 (15 mg, 0.077 mmol). Yield: 61% (25 mg). Mp: (10 mL) was added dropwise to a well stirred solution of AgOTf
210 °C. 1H NMR (400 MHz, DMSO-d6), δ: 8.89 (s, 2H, H3), (15 mg, 0.06 mmol) in THF (5 mL). After 15 minutes, the sus-
7.19–7.99 (m, 22H, CH2, ArH), 4.46 (br s, 8H, COD), 2.41 (br s, pension was filtered to remove AgCl and ligand 1 (30 mg,
8H, COD), 2.12 (br s, 8H, COD). 31P{1H} NMR (162 MHz, 0.06 mmol) in THF (8 mL) was added dropwise and the
1
DMSO-d6): δ 29.1 (s, JPRh = 168.4 Hz). Anal. Calcd for mixture was stirred for an additional 2 h. The solution was
C45H48N6P2Rh2B2F8: C, 48.51; H, 4.34; N, 7.54. Found: evaporated under reduced pressure and the residue washed
C, 48.43; H, 4.27; N, 7.46%.
with petroleum ether to afford the analytically pure product of
20 as a pale orange solid. Yield: 64% (30 mg), Mp: 204–208 °C.
1H NMR (400 MHz, CDCl3): δ 5.91 (s, 2H, CH2), 7.12–7.42 (m,
Synthesis of [PdCl2{(CH2(1,3-C3H2N2PPh2)2)-κ2P,P}] (16)
A solution of Pd(COD)Cl2 (12 mg, 0.058 mmol) in CH2Cl2 24H, H4, H5, ArH), 3.48 (s, 1H, allyl), 4.15 (s, 2H, allyl), 5.31 (s,
(10 mL) was added dropwise to a solution of 1 (30 mg, 2H, allyl). 31P{1H} NMR (162 MHz, CDCl3): δ 0.01 (s). Anal.
0.058 mmol) also in CH2Cl2 (10 mL). The resultant clear yellow Calcd for C35H31F3N4O3P2PdS: C, 51.70; H, 3.84; N, 6.89;
solution was reduced to 5 mL and layered with diethyl ether to S, 3.94. Found: C, 51.58; H, 3.79; N, 6.84; S, 3.87%.
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Synthesis of [Pd2(η3-C3H5)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,N}]
(BF4)2 (21)
during the data collection (SADABS).42 The structures were
solved by direct methods, and refined by full-matrix least-
squares procedures using the SHELXTL program package.43,44
Hydrogen atoms were placed in calculated positions and
included as riding contributions with isotropic displacement
parameters tied to those of the attached non-hydrogen atoms.
In complex 11, the disordered solvent molecule could not be
identified or modeled to a known solvent, so it was SQUEEZED
using PLATON.R The results indicated 128 electrons, and a
volume of 284 Å3. In 21, both allyl groups and one tetrafluoro-
borate anion are disordered over two resolved orientations.
The disorder was modelled by restraining the two components
of each disordered group to have comparable geometries.
Pertinent crystallographic data and other experimental details
are summarized in Tables 5–7. Crystallographic data for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC 1408417 (compound 1), 1408420 (com-
pound 2), and 1511158 (compound 4), 1511161 (compound 5),
1511159 (compound 6), 1511160 (compound 10), 1517753
(compound 11), 1517754 (compound 12), 1511155 (compound
14), 1511156 (compound 16), 1511157 (compound 17),
1511162 (compound 18) and 1511163 (compound 21).
This was synthesized by a procedure similar to that of 20 using
2 (30 mg, 0.06 mmol), [(η3-C3H5)PdCl]2 (22 mg, 0.06 mmol)
and AgBF4 (23 mg, 0.12 mmol). Yield: 53% (29 mg), Mp:
1
220 °C. H NMR (400 MHz, CDCl3): δ 6.84–8.12 (m, 26H, CH2,
H4, H3, ArH), 4.04 (s, 2H, allyl), 4.45 (s, 4H, allyl), 6.09 (s, 4H,
allyl). 31P{1H} NMR (162 MHz, CDCl3): δ 8.7 (s). Anal. Calcd for
C37H36N4P2Pd2B2F8·CH2Cl2: C, 42.65; H, 3.58; N, 5.24. Found:
C, 42.44; H, 3.55; N, 5.11%.
Synthesis of [Pd2(η3-C3H5)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,N}]
(BF4)2 (22)
This was synthesized by a procedure similar to that of 20 using
3 (30 mg, 0.06 mmol), [(η3-C3H5)PdCl]2 (22 mg, 0.06 mmol)
and AgBF4 (23 mg, 0.12 mmol). Yield: 54% (31 mg), Mp:
1
235–238 °C. H NMR (400 MHz, CDCl3): δ 7.26–8.51 (m, 26H,
CH2, H3, ArH), 4.15 (s, 2H, allyl), 4.43 (s, 4H, allyl), 6.09 (br s,
4H, allyl). 31P{1H} NMR (162 MHz, CDCl3): δ 11.3 (s). Anal.
Calcd for C35H34N6P2Pd2B2F8: C, 42.59; H, 3.47; N, 8.51.
Found: C, 42.42; H, 3.23; N, 8.42%.
General procedure for hydroformylation reactions
In a typical hydroformylation reaction, a high pressure reactor
of 100 mL capacity was charged with the ligand (5 μmol,
2.6 mg), [Rh(acac)(CO)2] (5 μmol, 1.4 mg) and olefin (5 mmol)
in 20 mL of toluene. The reactor was flushed with synthesis
gas (a 1 : 1 mixture of H2 and CO gas) followed by charging to
the desired pressure at room temperature. The reactor was
heated to the desired temperature with a stirring speed of 340
rpm. After completion of the reaction, the reactor was cooled
to room temperature in an ice-water bath and the remaining
synthesis gas was carefully released in a well-ventilated fume
hood. The reaction mixture was quantitatively analysed by gas
chromatography.
Acknowledgements
We are grateful to the Science & Engineering Research Board,
New Delhi, for financial support of this work through grant
no. SB/S1/IC-08/2014. We also thank the Department of
Chemistry, the Indian Institute of Technology Bombay,
Mumbai, for instrumentation facilities as well as spectral and
analytical data. J. T. Mague thanks the Louisiana Board of
Regents for the purchase of the APEX CCD diffractometer, an
NSF-MRI grant no. 1228232 for the purchase of the D8
VENTURE diffractometer and the Chemistry Department of
Tulane University for providing X-ray laboratory facilities.
Crystal structure determination of compounds 1, 2, 4–6,
10–12, 14, 16–18, and 21
Single crystal X-ray diffraction data collections were performed
at 100–150 K using a Bruker Smart APEX CCD diffractometer
with a graphite monochromated Mo-Kα radiation source for 1,
2, 4, 6, 10, 16, 18 and 21, and a Bruker D8 VENTURE PHOTON
100 CMOS with a Cu-Kα radiation source for 5, 14 and 17.
A Rigaku Saturn 724 diffractometer with a graphite monochro-
mated Mo-Kα radiation source was used for the data collection
of complexes 11 and 12. Full spheres of data were collected
using a combination of three sets of 400 frames (0.5° width in
ω) at φ = 0, 90, and 180° plus two sets of 800 frames (0.45°
width in ω) at φ = −30, and 210° under the control of the
APEX2 40 program suite. The raw data were reduced to F2
values using SAINT41 software, and global refinements of unit
cell parameters using 4256–9958 reflections chosen from the
full data sets were performed. Multiple measurements of equi-
valent reflections provided the basis for empirical absorption
corrections as well as corrections for any crystal deterioration
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