New bisphosphomide ligands, 1,3-phenylenebis((diphenylphosphino)methanone) and (2-bromo-1,3-phenylene)bis((diphenylphosphino)methanone): Synthesis, coordination behavior, DFT calculations and catalytic studies

Article abstract of DOI:10.1039/c3dt51046h

The bisphosphomide, 1,3-{Ph₂PC(O)}₂C ₆H₄ (1), was prepared by the reaction of isophthaloyl chloride with diphenylphosphine in the presence of triethylamine. The corresponding bromo-derivative, 2-Br-1,3-{Ph₂PC(O)}₂C ₆H₃ (2), was obtained by the reaction of 2-bromoisophthaloyl chloride with diphenylphosphine. The reaction of 1 with elemental sulfur or selenium yielded the bis(chalcogenides), 1,3-{Ph ₂P(S)C(O)}₂C₆H₄ (3) and {1,3-Ph ₂P(Se)C(O)}₂C₆H₄ (4). The reaction between 1 and [Ru(η⁶-p-cymene)Cl₂]₂ and [Pd(η³-C₃H₅)Cl]₂ in 1:1 stoichiometry yielded the corresponding binuclear complexes, [Ru ₂(η⁶-p-cymene)₂Cl₄{1,3-{Ph ₂PC(O)}₂(C₆H₄)}] (5) and [Pd ₂(η³-C₃H₅)₂Cl ₂{1,3-{Ph₂PC(O)}₂(C₆H₄)}] (6). The reaction of 1 with AgClO₄ followed by the addition of [Pd(COD)Cl₂] at room temperature resulted in the formation of a pincer complex [PdCl{2,6-{Ph₂PC(O)}₂(C₆H ₃)}] (9), via transmetallation. Pincer complex formation through C-H activation requires drastic conditions and yields are generally moderate. The oxidative addition reaction between 2 and [Ni(COD)₂] gave a pincer complex [NiBr{2,6-{Ph₂PC(O)}₂(C₆H ₃)}] (8), whereas the 2:1 reaction of 2 with [Pd₂(dba) ₃] yielded the palladium analogue [PdBr{2,6-{Ph₂PC(O)} ₂(C₆H₃)}] (9) in quantitative yield. The reaction between 1 and CuX in a 1:1 molar ratio produced binuclear complexes, [Cu₂(μ-X)₂{1,3-{Ph₂PC(O)}₂(C ₆H₄)}₂] (10, X = Cl; 11, X = Br; 12, X = I), whereas the reaction between 1 and [Cu(NCCH₃)₄]BF ₄ led to the isolation of a spirocyclic complex, [Cu(CH ₃CN)₂{1,3-{Ph₂PC(O)}₂(C ₆H₄)}]BF₄ (13). The silver complexes [Ag ₂(μ-ClO₄)₂{1,3-{Ph₂PC(O)} ₂(C₆H₄)}₂] (14), [Ag ₂(μ-OTf)₂{1,3-{Ph₂PC(O)}₂(C ₆H₄)}₂] (15) and [Ag₂X ₂{1,3-{Ph₂PC(O)}₂(C₆H₄)}] (16, X = ClO₄; 17, X = OTf) were obtained by treating 1 with AgClO₄ or AgOTf in 1:1 or 1:2 molar ratios. The reactions of 1 with [AuCl(SMe₂)] in 1:1 and 1:2 molar ratios afforded mono- and binuclear complexes, [AuCl{1,3-{Ph₂PC(O)}₂(C₆H ₄)}₂] (18) and [Au₂Cl₂{1,3-{Ph ₂PC(O)}₂(C₆H₄)}AuCl] (19), in good yield. The structures of complexes 5, 7-10, 12 and 14a were confirmed by single-crystal X-ray diffraction studies. DFT calculations were performed in order to gain additional insights into the structure and bonding of the pincer complexes. An additional analysis of the orbital interactions in the case of palladium complex 9 is also included. The in situ generated rhodium complex of bisphosphomide 1 showed moderate to good selectivity in the hydroformylation of hex-1-ene and styrene derivatives.

Full text of DOI:10.1039/c3dt51046h

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New bisphosphomide ligands, 1,3-phenylenebis-
((diphenylphosphino)methanone) and (2-bromo-1,3-
phenylene)bis((diphenylphosphino)methanone):
synthesis, coordination behavior, DFT calculations
and catalytic studies†
Cite this: DOI: 10.1039/c3dt51046h
Pawan Kumar,a Mujahuddin M. Siddiqui,a Yerrnaidu Reddi,a Joel T. Mague,b
Raghavan B. Sunoj*a and Maravanji S. Balakrishna*a
The bisphosphomide, 1,3-{Ph2PC(O)}2C6H4 (1), was prepared by the reaction of isophthaloyl chloride with
diphenylphosphine in the presence of triethylamine. The corresponding bromo-derivative, 2-Br-1,3-
{Ph2PC(O)}2C6H3 (2), was obtained by the reaction of 2-bromoisophthaloyl chloride with diphenylphos-
phine. The reaction of 1 with elemental sulfur or selenium yielded the bis(chalcogenides), 1,3-{Ph2P(S)-
C(O)}2C6H4 (3) and {1,3-Ph2P(Se)C(O)}2C6H4 (4). The reaction between 1 and [Ru(η6-p-cymene)Cl2]2 and
[Pd(η3-C3H5)Cl]2 in 1 : 1 stoichiometry yielded the corresponding binuclear complexes, [Ru2(η6-p-cyme-
ne)2Cl4{1,3-{Ph2PC(O)}2(C6H4)}] (5) and [Pd2(η3-C3H5)2Cl2{1,3-{Ph2PC(O)}2(C6H4)}] (6). The reaction of 1
with AgClO4 followed by the addition of [Pd(COD)Cl2] at room temperature resulted in the formation of
a pincer complex [PdCl{2,6-{Ph2PC(O)}2(C6H3)}] (9), via transmetallation. Pincer complex formation
through C–H activation requires drastic conditions and yields are generally moderate. The oxidative
addition reaction between 2 and [Ni(COD)2] gave a pincer complex [NiBr{2,6-{Ph2PC(O)}2(C6H3)}] (8),
whereas the 2 : 1 reaction of 2 with [Pd2(dba)3] yielded the palladium analogue [PdBr{2,6-{Ph2PC(O)}2-
(C6H3)}] (9) in quantitative yield. The reaction between 1 and CuX in a 1 : 1 molar ratio produced
binuclear complexes, [Cu2(µ-X)2{1,3-{Ph2PC(O)}2(C6H4)}2] (10, X = Cl; 11, X = Br; 12, X = I), whereas the
reaction between 1 and [Cu(NCCH3)4]BF4 led to the isolation of a spirocyclic complex, [Cu(CH3CN)2{1,3-
{Ph2PC(O)}2(C6H4)}]BF4 (13). The silver complexes [Ag2(µ-ClO4)2{1,3-{Ph2PC(O)}2(C6H4)}2] (14), [Ag2(µ-
OTf )2{1,3-{Ph2PC(O)}2(C6H4)}2] (15) and [Ag2X2{1,3-{Ph2PC(O)}2(C6H4)}] (16, X = ClO4; 17, X = OTf) were
obtained by treating 1 with AgClO4 or AgOTf in 1 : 1 or 1 : 2 molar ratios. The reactions of 1 with [AuCl-
(SMe2)] in 1 : 1 and 1 : 2 molar ratios afforded mono- and binuclear complexes, [AuCl{1,3-{Ph2PC(O)}2-
(C6H4)}2] (18) and [Au2Cl2{1,3-{Ph2PC(O)}2(C6H4)}AuCl] (19), in good yield. The structures of com-
plexes 5, 7–10, 12 and 14a were confirmed by single-crystal X-ray diffraction studies. DFT calculations
were performed in order to gain additional insights into the structure and bonding of the pincer com-
plexes. An additional analysis of the orbital interactions in the case of palladium complex 9 is also
included. The in situ generated rhodium complex of bisphosphomide 1 showed moderate to good
selectivity in the hydroformylation of hex-1-ene and styrene derivatives.
Received 22nd April 2013,
Accepted 4th June 2013
DOI: 10.1039/c3dt51046h
www.rsc.org/dalton
Introduction
aPhosphorus Laboratory, Department of Chemistry, Indian Institute of Technology
Bombay, Powai, Mumbai 400 076, India.
The recent interest in the chemistry of pincer ligands is pri-
marily due to their rigid chelating ability which provides excep-
tional thermal stability1 to the metal complexes. In addition,
phosphorus based pincer ligands confer excellent electronic
and steric tuning options around the metal center which
makes them ideal candidates not only for homogeneous
E-mail: krishna@chem.iitb.ac.in, msb_krishna@iitb.ac.in, sunoj@chem.iitb.ac.in
bDepartment of Chemistry, Tulane University, New Orleans, Louisiana 70118, USA
†Electronic supplementary information (ESI) available. CCDC 934905–934911.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt51046h
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catalysis but also in material applications.2 The phosphorus
based pincer ligands known in the literature are mainly of
three types: PCP3, PNP4 and POP5 with each one having either
–CH2–, –O– or –N′– (N′ = N(R) or NH) links or any of the two
Results and discussion
Synthesis of 1,3-{Ph2PC(O)}2(C6H4) (1),
1-Br-2,6-{Ph2PC(O)}2C6H3 (2) and chalcogen derivatives
combinations6 with phosphorus having alkyl, aryl, alkoxy, Nucleophilic substitution at carbonyl groups is the only feas-
aryloxy or amino substituents. Pincer complexes are known to ible method for the synthesis of phosphomides where the
promote a variety of organic transformations, such as Aldol choice of nucleophile mostly decides the rate as well as the
and Michael addition reactions,7 C–C8 and C–X (X = halogen) reaction economy.19 The bis(phosphomide), 1,3-{Ph2PC(O)}2-
bond formation,9 oxidative addition of C–O and C–F bonds,10 C6H4 (1), was synthesized in quantitative yield by the reac-
polymerization of olefins,11 alkane metathesis,12 alkane de- tion of isophthaloyl chloride with diphenylphosphine in the
hydrogenation13 as well as CO2 14 and N2 15 activation. Further, presence of triethylamine (Scheme 1). Bis(phosphomide) 1 is a
pincer complexes with PCCCP, PCNCP and PN(H)CN(H)P moisture sensitive and low melting yellow-orange solid soluble
frameworks can also come across interesting reaction in most of the organic solvents. The 31P{1H} NMR spectrum of
sequences involving reversible dearomatization which makes 1 consists of a single resonance at 12.3 ppm. The IR spectrum
them an even more versatile catalytic system in organic syn- of 1 shows νCO at 1649 cm−1
.
thesis,16 in particular the direct synthesis of amides from alco-
hols and amines.17
The oxidation of bromo-m-xylene with KMnO4 gave 2-bromo-
isophthalic acid, which on further treatment with SOCl2
Surprisingly, monophosphine or bis(phosphine) ligands resulted in the formation of 2-bromoisophthaloyl chloride in
based on carbonyl links also called phosphomides are less moderate yield.21 The 2-bromoisophthaloyl chloride was
extensive and their coordination chemistry is scant. This may reacted with diphenylphosphine in the presence of triethyl-
be due to the extreme sensitivity of P–CO bonds towards moist- amine to obtain the bromo-functionalized bis(phosphomide),
ure.18 A few known monophosphomide ligands along with 1-Br-2,6-{Ph2PC(O)}2C6H3 (2), as a yellow solid in quantitative
compound IV, the only known bis(phosphomide), are given in yield (Scheme 2). The 31P{1H} NMR spectrum of 2 shows a
Chart 1.19
The molybdenum,19e rhodium19g and iron19f complexes of
single resonance at 21.1 ppm.
The reaction of 1 with elemental sulfur or selenium in a
ligands of the type I, III and IV are the only reported transition 1 : 2 molar ratio in diethyl ether afforded the corresponding
metal complexes with single crystal X-ray structure available bis(chalcogenide) derivatives, 1,3-{Ph2P(S)C(O)}2C6H4 (3) and
only in the case of the rhodium complex [Cp*Rh(Ph2PC(O)- 1,3-{Ph2P(Se)C(O)}2C6H4 (4). The 31P{1H} NMR spectrum of 3
CH3)Cl2].19g In view of this we sought to design pincer capable shows a single resonance at 38.1 ppm, whereas the selenide
bis(phosphomide) ligands and wanted to explore their cataly- derivative 4 shows a major singlet at 31.1 ppm with character-
1
tic applications, in particular hydroformylation reactions, as to istic selenium satellites. The JPSe coupling of 746 Hz is com-
the best of our knowledge, the utility of pincer complexes in parable with the same reported for analogous compounds in
1
hydroformylation reactions is not known. As a continuation of the literature.22 Usually the magnitude of JPSe increases with
our interest in designing new inexpensive ligands20 and study- an increase in electron withdrawing ability of the phosphorus
ing their transition metal chemistry and catalytic applications, substituents and vice versa. The electron withdrawing groups
we report on two new bis(phosphomide) ligands and their leave slightly less ‘p’ and more ‘s’ character in the lone pair
transition metal chemistry. The DFT calculations and the which is eventually utilized in making PvSe bonds, as is
utility of rhodium(I) complex in hydroformylation reactions are
also described.
Scheme 1
Chart 1
Scheme 2
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1
reflected in the magnitude of the phosphorus–selenium coup- In the H NMR spectrum of 7, disappearance of the signal due
ling constant.
to the ipso-proton around 8.50 ppm confirms the Pd–C bond
formation through the elimination of HClO4. The structure of 7
has been confirmed by single crystal X-ray analysis.
Synthesis of Ru and Pd complexes
Another convenient method for the synthesis of pincer
complexes is the oxidative addition of bromo- or iodo deriva-
tive to low-valent metal precursors. Thus the reaction between
bromo-functionalized bis(phosphomide) 2 and [Ni(COD)2] in
THF yielded the pincer complex, [NiBr{2,6-{Ph2PC(O)}2(C6H3)}]
(8), while a similar reaction between 2 and [Pd2(dba)3] gave
[PdBr{2,6-{Ph2PC(O)}2(C6H3)}] (9) in good yield (Scheme 5).
The 31P{1H} NMR spectra of complexes 8 and 9 show single
resonances at 49.6 and 52.2 ppm, respectively.
The reaction of bis(phosphomide) 1 with one equiv. of [Ru(η6-
p-cymene)Cl2]2 in dichloromethane afforded
a binuclear
complex, [Ru2(η6-p-cymene)2Cl4{1,3-{Ph2PC(O)}2(C6H4)}] (5).
The 1 : 1 reaction between 1 and [Pd(η3-C3H5)Cl]2 resulted in
the formation of a binuclear complex, [Pd2(η3-C3H5)2Cl2{1,3-
{Ph2PC(O)}2(C6H4)}] (6), in 89% yield (Scheme 3). The 31P{1H}
NMR spectra of 5 and 6 consist of single resonances at 30.7
and 28.7 ppm, respectively.
Synthesis of Ni and Pd pincer complexes
Synthesis of group 11 metal complexes
Attempts to synthesize pincer complexes of platinum metals
containing bis(phosphomide) (1) through C–H activation
using well established methods even under drastic conditions
have been unsuccessful. The coordination preferences of a
pincer ligand is decisive in the formation of a pincer complex
via C–H activation.23 For pincer complex formation, the ligand
has to optimize itself for suitable positioning of the donor
arms. In addition, the reaction is believed to be electrophilic
in nature and thus the higher electron density in the ring
favors C–H activation.24 In the case of PCP, POCOP and
PNCNP types of pincer ligands the aromatic ring is electron
rich because of the positive hyperconjugative or mesomeric
effect of substituents which facilitates the C–H bond activation.
In the case of bisphosphomide 1 the electron withdrawing car-
bonyl groups decrease the electron density at the ipso position
which probably deters it to undergo C–H activation. However,
the reaction of 1 with AgClO4 followed by transmetallation with
[Pd(COD)Cl2] in dichloromethane at room temperature yielded
the desired pincer complex [PdCl{2,6-{Ph2PC(O)}2(C6H3)}] (7) in
moderate yield as shown in Scheme 4. The 31P{1H} NMR spec-
trum of complex 7 consists of a single resonance at 49.3 ppm.
Bis(phosphomide) 1, on treatment with cuprous halides (CuX,
X = Cl, Br, I), yielded the binuclear complexes [Cu2(µ-X)2{1,3-
{Ph2PC(O)}2(C6H4)}2] (10, X = Cl; 11, X = Br; 12, X = I) contain-
ing rhombic Cu2X2 units as shown in Scheme 6. All the com-
plexes were highly soluble in most of the organic solvents. The
31P{1H} NMR spectra of complexes 10–12 show single reson-
ances at 4.0, 1.9 and 1.3 ppm, respectively. Treatment of 1
with [Cu(NCCH3)4]BF4 in a 1 : 1 ratio afforded the tetrahedral
cationic complex, [Cu(NCCH3)2{1,3-{Ph2PC(O)}2(C6H4)}]BF4
(13). The 31P{1H} NMR spectrum of complex 13 shows a single
resonance at 10.5 ppm. The reaction of 1 with AgClO4 in a
Scheme 5
Scheme 3
Scheme 6 (i) CuX, CH3CN/CH2Cl2, (ii) [Cu(CH3CN4]BF4, CH2Cl2, (iii) AgX, THF,
Scheme 4
(iv) 2AgX, THF, (v) [AuCl(SMe2)], CH2Cl2, and (vi) 2[AuCl(SMe2)], CH2Cl2.
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1 : 1 molar ratio followed by crystallization from dichloro-
methane/hexane resulted in the formation of a binuclear
complex, [Ag2(µ-ClO4)2{1,3-{Ph2PC(O)}2(C6H4)}2] (14), which
was contaminated with a trace (∼4%) amount of [Ag2(µ-Cl)(µ-
ClO4){1,3-{Ph2PC(O)}2(C6H4)}2] (14a) which gave single crystals
suitable for X-ray diffraction study. The presence of a bridging
chloride ion is due to the presence of a trace amount of AgCl
found in AgClO4. However, attempts to grow crystals of 14 suit-
able for single crystal X-ray diffraction studies have been
unsuccessful. A similar reaction between bis(phosphomide) 1
and AgOTf in a 1 : 1 molar ratio yielded the complex [Ag2(µ-
OTf)2{1,3-{Ph2PC(O)}2(C6H4)}2] (15) in good yield.
The bis(phosphomide) 1 on treatment with 2 equiv. of AgX
Fig. 2 Molecular structure of the complex [PdCl{2,6-{Ph2PC(O)}2(C6H3)}] (7). All
(X = ClO4, OTf) produced binuclear complexes, [Ag2X2{1,3- hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at a
50% probability level.
{Ph2PC(O)}2(C6H4)}] (16, X = ClO4; 17, X = OTf), in good yield.
Complexes 16 and 17 are colorless solids which are highly
light-sensitive in solution but moderately stable in the solid
state. The 31P{1H} NMR spectra of complexes 14–17 show
broad resonances at 15.8, 14.8, 19.7 and 18.8 ppm, respect-
ively. The unresolved broad resonances are due to the presence
of two isotopes of silver (109Ag (48%) and 107Ag (52%)) almost
in equal proportions. However, in the case of silver complex
17, the 31P{1H} NMR spectrum recorded at −40 °C showed two
doublets centered at 18.8 ppm with 1J
and 1J
coup-
107AgP
109AgP
lings of 730.5 and 641.4 Hz, respectively. The 1 : 1 reaction
between and [AuCl(SMe2)] in dichloromethane gave
1
[AuCl{1,3-{Ph2PC(O)}2(C6H4)}] (18) while a similar reaction of
1 with two equivalents of AuCl(SMe2) afforded a binuclear
complex [Au2Cl2{1,3-{Ph2PC(O)}2(C6H4)}] (19) with ligand 1
exhibiting the bridged bidentate mode of coordination. The
31P{1H} NMR spectra of complexes 18 and 19 exhibit single reso-
nances at 22.2 and 31.4 ppm, respectively.
Fig. 3 Molecular structure of [NiBr{2,6-{Ph2PC(O)}2(C6H3)}] (8). All hydrogen
atoms have been omitted for clarity. Thermal ellipsoids are drawn at a 50%
probability level.
Molecular structures of complexes 5, 7–10, 12, and 14a
Perspective views of the molecular structures of complexes 5,
7–10, 12 and 14a with atom numbering schemes are shown in
Fig. 1–7. Selected bond distances and bond angles are listed in
Fig. 4 Molecular structure of [PdBr{2,6-{Ph2PC(O)}2(C6H3)}] (9). All hydrogen
atoms have been omitted for clarity. Thermal ellipsoids are drawn at a 50%
probability level.
Tables 1 and 3 and crystallographic data and the details of the
structure determinations are given in Table 4.
In the molecular structure of 5 the ligand coordinates to
the ruthenium centers in a bridging fashion. The ruthenium
atoms adopt pseudo octahedral geometries with the p-cymene
coordinating in a typical η6 fashion. The C23–P1–Ru1 and
Fig. 1 Molecular structure of [Ru2(η6-p-cymene)2Cl4{1,3-{Ph2PC(O)}2(C6H4)}]
(5). All hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
drawn at a 50% probability level.
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C30–P2–Ru2 bond angles (Table 1) are significantly different, a
feature which is likely to be due to packing considerations.
The Cl1–Ru1–Cl2 and Cl3–Ru2–Cl4 bond angles are slightly
different but compare well with the reported range of Cl–Ru–
Cl bond angles (86.27–89.77°) for analogous ruthenium
p-cymene complexes.25 The P1–C23 and P2–C30 bond lengths
are equal within experimental error as are the Ru1–P1 and
Ru2–P2 bond distances (Table 1). There appears to be a weak
C–H⋯π interaction between C34 and H34 and the phenyl ring
based on C11 at 1 − x, 1 − y, −z (H34⋯ring centroid = 2.83 Å,
C34–H34⋯ring centroid = 153°).
In the molecular structures of nickel and palladium com-
plexes 8, 7 and 9, the ligand binds to the metal in a typical
terdentate fashion. Bond distances and bond angles of some
related nickel and palladium pincer complexes along with
those of complexes 7–9 are given in Table 2. Notably, com-
plexes 7–9 show larger P–Ni–P (172.80(3)°) and P–Pd–P
(169.15(3) and 168.56(2)°) bond angles than the corres-
ponding complexes of PCP and POCOP ligands. This may be
due to the longer P–C(O) bond distances in complexes 7–9 as
compared to the relatively shorter P–C and P–O bond dis-
tances in the corresponding PCP and POCOP pincer com-
plexes. The Ni–C14 and Pd–C19 bond lengths (Table 1)
compare well with the reported range of 1.87–1.90 Å for
nickel and 1.99–2.03 Å for palladium complexes.26,27 The two
five-membered chelate rings are coplanar. The P1–C13–C15
and P2–C20–C19 bond angles for 8 and the P1–C13–C14 and
P2–C20–C18 bond angles for 9 (Table 1) are considerably
different from the P–C–C bond angles in PCP type pincer
complexes but are close to the P–O–C bond angles found in
POCOP type pincer complexes (Table 2). On the other hand,
the M–P–C bond angles in 7–9 are within the range observed
in similar pincer complexes (Table 2). Complex 8 shows two
weak C–H⋯O and one C–H⋯π interactions but 9 shows only
the latter.
Fig. 5 Molecular structure of [Cu2(µ-Cl)2{1,3-{Ph2PC(O)}2(C6H4)}2] (10). All
hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at a
50% probability level.
Fig. 6 Molecular structure of [Cu2(µ-I)2{1,3-{Ph2PC(O)}2(C6H4)}2] (12). All
hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at a
50% probability level.
The molecular structures of copper complexes, 10 and 12,
show binuclear units in which the metals are coordinated by
two phosphorus atoms and two halide ions in a distorted tetra-
hedral arrangement. The bis(phosphomides) act as bridging
ligands coordinating to two different copper centers. The
copper atoms are also linked by the halides so that the core of
the complex is a rhomboid with Cu–Cu and X–X diagonals. As
is evident from Fig. 4 and 5, the Cu2X2 core is almost perpen-
dicular to the plane formed by the four coordinating phos-
phorus atoms. The P–C(O) bond distances for complexes 10
and 12 are in the range 1.8803(38) to 1.9054(61) Å while the
Cu–P bond distances in 10 are slightly shorter than those in 12
(Table 3). The Cu⋯Cu distances are 3.1684(8) and 3.2361(8) Å,
respectively, for 10 and 12 while the bond angles Cl1–Cu1–Cl2
and Cl1–Cu2–Cl2 are 96.35(3)° and 96.14(3)° for complex 10
and for complex 12 the bond angles I1–Cu1–I2 and I1–Cu2–I2
are 105.165(20)° and 105.376(20)°. Similar to complexes 10
and 12 the molecular structure of 14a also shows the presence
of two bridging ligands and a discrete core of two tetrahedrally
coordinated silver(I) centers with bridging perchlorate and
chloride ions. The PCP ligand, 1,3-C6H4(CH2PPh2)2, is also
Fig. 7 Molecular structure of [Ag2(µ-ClO4)(µ-Cl){1,3-{Ph2PC(O)}2(C6H4)}2] (14a).
All hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn
at a 50% probability level.
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Table 1 Selected bond distances (Å) and bond angles (°) for 5 and 7–9a
Compound 5
Bond length (Å)
Ru1–P1
Compound 7
Bond length (Å)
Pd1–C19
Pd1–P1
Compound 8
Bond length (Å)
Ni1–C14
Ni1–P1
Compound 9
Bond length (Å)
Pd1–C19
Pd1–P2
2.3505(13)
(2.387)
2.3554(13)
(2.389)
2.030(3)
(2.049)
2.2651(9)
(2.328)
1.923(2)
(1.946)
2.1611(6)
(2.222)
2.039(2)
(2.057)
2.2744(10)
(2.327)
Ru2–P2
Ru1–Cl1
Ru1–Cl2
Ru2–Cl3
Ru2–Cl4
P1–C23
2.4207(14)
(2.441)
2.4012(12)
(2.434)
2.4131(13)
(2.447)
2.4057(16)
(2.414)
Pd1–P2
2.2763(9)
(2.328)
2.3590(10)
(2.416)
1.881(4)
(1.90)
1.881(4)
(1.90)
Ni1–P2
2.1704(6)
(2.222)
2.3315(4)
(2.378)
1.882(2)
(1.898)
1.876(2)
(1.898)
Pd1–P1
2.2826(10)
(2.327)
2.4828(10)
(2.528)
1.889(2)
(1.903)
1.888(2)
(1.903)
Pd1–Cl1
Ni1–Br1
Pd1–Br1
P1–C13
P1–C13
P1–C13
P2–C20
P2–C20
P2–C20
1.892(4)
(1.909)
C13–O1
1.216(4)
(1.220)
O1–C13
1.212(3)
(1.218)
O1–C13
1.212(3)
(1.219)
P2–C30
1.881(5)
(1.962)
C20–O2
1.205(5)
(1.220)
O2–C20
1.212(3)
(1.218)
O2–C20
1.211(3)
(1.219)
O1–C23
1.206(5)
(1.227)
O2–C30
1.227(6)
(1.211)
Bond angle (°)
P1–Ru1–Cl2
P1–Ru1–Cl1
P2–Ru2–Cl3
P2–Ru2–Cl4
O1–C23–P1
O2–C30–P2
C23–P1–Ru1
C30–P2–Ru2
C24–C23–P1
C28–C30–P2
Bond angle (°)
P1–Pd1–P2
Bond angle (°)
P1–Ni1–P2
Bond angle (°)
P2–Pd1–P1
90.03(5)
(89.97)
86.12(4)
(87.74)
96.40(4)
(84.49)
83.79(4)
(86.79)
117.9(3)
(115.60)
119.1(3)
(111.85)
111.26(14)
(107.10)
107.22(15)
(116.01)
121.5(3)
(123.47)
121.6(3)
(127.51)
169.15(3)
(168.74)
177.42(10)
(180.00)
111.0(2)
(111.89)
111.1(2)
(111.89)
102.45(11)
(101.33)
102.29(12)
(101.33)
172.80(3)
(172.73)
175.11(7)
(179.97)
109.10(15)
(109.89)
109.66(16)
(109.89)
103.11(8)
(101.52)
102.52(8)
(101.52)
168.56(2)
(168.57)
177.22(6)
(179.96)
111.00(15)
(111.92)
111.01(16)
(111.92)
102.39(8)
(101.33)
102.10(7)
(101.33)
C19–Pd1–Cl1
C14–C13–P1
C18–C20–P2
C13–P1–Pd1
C20–P2–Pd1
C14–Ni1–Br1
C15–C13–P1
C19–C20–P2
C13–P1–Ni1
C20–P2–Ni1
C19–Pd1–Br1
C18–C20–P2
C14–C13–P1
C13–P1–Pd1
C20–P2–Pd1
a The optimized geometrical parameters obtained at the B3LYP/6-31G**, SDD level of theory are provided in parentheses below the
corresponding values obtained from X-ray crystallographic analyses.
reported to form a similar type of Ag(I) complexes.28 The catalyzed hydroformylation of alkenes.19g The hydroformyla-
average P–C(O) bond distance in 14a is comparable to those in tion of hex-1-ene was studied as a test reaction for evaluating
10 and 12 while the Ag–P bond distances range from 2.4246(15) the catalytic utility of 1. The reactions were performed at 60 °C
to 2.4533(13) Å (Table 3). The perchlorate ion coordinates in with a 2 : 1 ratio of ligand 1 and [Rh(acac)(CO)2], and the
an asymmetric bridged monodentate fashion to both silver formation of the products was determined by gas chromato-
atoms with Ag1–O5 and Ag2–O5 bond lengths of 2.707(5) and graphy. Initially, the reaction was studied at different syngas
2.529(4) Å, respectively. All the three complexes show weak (CO/H2) pressures in the range of 10–30 bar (Table 5, entries
C–H⋯O interactions.
1–3) where 30 bar was found to provide the maximum conver-
sion and selectivity of the desired product. Surprisingly, with a
decrease in catalyst loading the regioselectivity towards the
linear aldehyde was increased and a l : b ratio of 2.3 was
achieved (Table 5, entry 5).
Hydroformylation of alkenes
The utility of bisphosphomides in homogeneous catalysis is
not known. However, the catalytic activity of a few monophos-
phomides ligands have been investigated in the rhodium
Further the catalytic activity of the bisphosphomide 1 was
investigated in the hydroformylation of styrene. Styrene has a
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Table 2 Selected bond lengths (Å) and bond angles (°) for nickel and palladium pincer complexes with ligands of the type R2PYCYPR2 (Y = C(O), CH2, O; R = Ph, Cy,
tBu)
No.
1
Metal
Ni
X
Y
R
M–C
M–X
P–M
P–Y
P–M–P
172.80
165.3
M–P–Y
P–Y–C
Br
Br
Br
Br
Cl
I
C(O)
CH2
CH2
O
Ph
Ph
Cy
Ph
Ph
Ph
Ph
Ph
Ph
tBu
Ph
Cy
1.923
1.920
1.909
1.874
1.879
1.890
2.039
2.030
2.027
2.022
1.998
2.012
2.3315
2.3290
2.360
2.1611
2.1704
2.177
2.173
2.168
1.882
1.876
1.814
1.821
1.824
1.817
1.649
1.648
1.6462
1.6441
1.6486
1.6488
1.889
1.888
1.881
1.881
1.833
1.826
1.843
1.818
1.815
1.824
1.826
1.824
103.11
102.52
102.9
102.5
103.6
109.10a
109.66
103.126a
104.0
2
Ni
3
Ni
167.6
108.326b
105.6
2.185
105.0
4
Ni
2.3002
2.1880
2.4976
2.4828
2.3590
2.495
2.1544
2.1550
2.1556
2.1582
2.1553
2.1601
2.2826
2.2744
2.2651
2.2763
2.292
2.287
2.318
2.325
2.228
2.294
2.226
2.294
164.39
164.16
164.20
168.56
169.15
162.5
106.15
106.54
106.46
105.94
106.67
106.42
102.10
102.17
102.45
102.29
101.8
101.6
101.6
101.6
101.04
101.3
111.5126c
111.26
111.4326d
111.74
111.5026e
111.67
111.00a
111.01
109.10a
109.66
105.126a
106.2
5
Ni
O
6
Ni
O
7
Pd
Pd
Pd
Pd
Pd
Pd
Br
Cl
Br
Br
Cl
Cl
C(O)
C(O)
CH2
CH2
CH2
CH2
8
9
10
11
12
2.5534
2.367
166.88
162.0
110.127a
110.1
105.727b
105.4
2.427
165.5
102.6
104.1
111.227c
108.6
a This work.
preference for the formation of branched aldehyde, due to the complexes. The geometric comparisons for compounds 5,
formation of a stable η3-benzylic-rhodium complex.29a,b At 30 7–10, 12 and 14a, as provided in Tables 1 and 3, indicate that
bar pressure, the hydroformylation of styrene showed 96% the agreement between the computed geometric parameters
conversion with good regioselectivity towards the branched and those obtained using the X-ray crystallographic methods
aldehyde (Table 6, entry 1). Encouraged by the high activity is generally good.31 An additional analysis of the orbital inter-
and selectivity, a series of substituted styrenes were then actions responsible for the bonding pattern for a representa-
hydroformylated to investigate the viability of the process. A tive pincer complex [PdBr{2,6-{Ph2PC(O)}2(C6H3)}] (9) was
slight increase in the regioselectivity towards the branched carried out using the Natural Bonding Orbital (NBO) method
aldehyde was observed with electron withdrawing substituents using the optimized geometries at the B3LYP/6-31G**, SDD
on the phenyl ring.29c It was found that the electron-donating level of theory. The atomic orbital contributions to the impor-
substituents on styrene gave higher conversion than those with tant molecular orbitals were examined using the AOMix pro-
electron-withdrawing substituents (Table 6, entries 2–5).30 Allyl cedure. The key results are summarized in the following
anisole formed three structural aldehydes due to the isomeri- sections.
sation reaction. Thus, under mild conditions, higher selecti-
vity, good regioselectivity and moderate turnover numbers
were obtained in the hydroformylation of styrenes. The
rhodium complex generated in situ during the hydroformyla-
tion reaction has the composition, [Rh(acac)(η2-bisphospho-
mide)] (no C–H activation was observed to form a pincer
complex). The 31P{1H} NMR spectrum of the complex shows a
1
doublet at 62.8 ppm with a JRhP coupling of 149 Hz. In the
The AOMix analysis, as summarized in Table 7, reveals that the
absence of ligand, the conversions were in the range of
HOMO and LUMO are primarily located on the pincer ligand
30–40% and 20–30%, for styrene derivatives and hex-1-ene,
(PCP) fragment. In particular, LUMO exhibits an exclusive con-
tribution by the pincer backbone while a small contribution
respectively.
from palladium is evident in the HOMO. The orbital inter-
actions responsible for strong stabilizing interaction between
Density functional theory studies
We have performed density functional theory studies using the the phosphorus and palladium are noticeable with a more
B3LYP/6-31G**, SDD level of theory in order to gain additional than 80% contribution from phosphorus to such orbitals. For
insights into the structure and bonding of the pincer instance, HOMO − 35 has an overwhelming contribution from
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Table 3 Selected bond distances (Å) and bond angles (°) for complexes 10, 12 and 14a
Compound 10
Bond length (Å)
P2–Cu2
Compound 12
Bond length (Å)
P3–Cu1
Compound 14a
Bond length (Å)
Ag1–P1
2.2616(12)
(2.332)
2.2871(14)
(2.370)
2.4506(14)
(2.519)
P3–Cu2
2.2579(11)
(2.333)
P1–Cu1
2.2882(14)
(2.356)
Ag2–P2
2.4368(13)
(2.519)
P1–Cu1
2.2584(11)
(2.327)
P4–Cu2
2.2891(16)
(2.351)
Ag1–P3
2.4533(13)
(2.517)
P4–Cu1
2.2594(12)
(2.357)
P2–Cu2
2.2794(14)
(2.357)
Ag2–P4
2.4246(15)
(2.519)
Cu1–Cl1
Cu1–Cl2
Cu2–Cl1
Cu2–Cl2
C20–O2
2.3908(11)
(2.437)
2.3522(11)
(2.428)
2.3931(11)
(2.482)
2.3578(11)
(2.489)
Cu1–I1
2.6750(7)
(2.881)
2.6613(7)
(2.754)
2.6852(7)
(2.761)
2.6435(7)
(2.894)
Ag1–Cl1
Ag2–Cl1
Ag1–O5
2.5868(13)
(2.664)
2.5189(13)
(2.617)
2.707(5)
(2.564)
2.529(4)
(2.538)
Cu1–I2
Cu2–I1
Cu2–I2
Ag2–O5
1.2054(54)
(1.218)
C45–O3
1.207(6)
(1.215)
Bond angle (°)
C20–P2–Cu2
C45–P3–Cu2
C13–P1–Cu1
C52–P4–Cu1
P2–Cu2–Cl1
P1–Cu1–Cl1
Bond angle (°)
C45–P3–Cu1
C52–P4–Cu2
C13–P1–Cu1
C20–P2–Cu2
P3–Cu1–I1
Bond angle (°)
P1–Ag1–P3
116.18(15)
(111.43)
123.67(14)
(124.18)
122.39(14)
(126.97)
116.82(15)
(121.65)
111.44(4)
(109.85)
108.35(4)
(118.76)
122.03(16)
(124.28)
120.35(18)
(122.52)
120.75(18)
(126.07)
122.22(15)
(111.85)
106.21(4)
(93.90)
112.58(4)
(111.99)
129.12(5)
(132.61)
121.15(5)
(123.58)
82.44(9)
(88.52)
87.48(12)
(90.09)
94.81(4)
(88.68)
P4–Ag2–P2
Cl1–Ag1–O5
Cl1–Ag2–O5
Ag2–Cl1–Ag1
Ag2–O5–Ag1
C20–P2–Ag2
C13–P1–Ag1
C14–C13–P1
P4–Cu2–I1
91.70(16)
(92.69)
116.49(16)
(128.40)
121.81(16)
(120.81)
118.1(3)
(119.08)
the phosphorus orbital. The relative contributions to the mole- towards HOMO and LUMO from both metal and donor atoms.
cular orbitals are pictorially represented using orbital contour This information about the overall electron density present at
diagrams in Fig. 8.
the metal center can eventually assist in understanding their
catalytic behavior in various organic transformations. Further
work in this direction is in progress.
Conclusions
The transition metal chemistry of bis(phosphomide) ligands is
described. The transmetallation reaction afforded palladium(II)
pincer complex under mild conditions. The nickel and pal-
Experimental
General procedures
ladium pincer complexes were also obtained via oxidative All manipulations were performed using standard vacuum-line
addition of bromo-functionalized bis(phosphomide) ligand to and Schlenk techniques under a nitrogen atmosphere unless
nickel(0) and palladium(0) metal reagents. Although both the otherwise stated. All of the solvents were purified by conven-
ligands are sensitive to moisture, the metal complexes are tional procedures32 and distilled prior to use. The compounds
moderately stable but on prolonged exposure they decompose; CuCl,33 CuBr,33 [Cu(CH3CN)4]BF4,34 [AuCl(SMe2)],35 [Ru(η6-p-
37
a palladium complex, being more sensitive, readily gives palla- cymene)Cl2]2,36 [Pd(η3-C3H5)Cl]2 and [Pd2dba3]38 were pre-
dium black. The in situ generated rhodium(I) complex contain- pared according to the published procedures. The metal pre-
ing bis(phosphomide) ligand catalyses the hydroformylation cursors CuI, AgOTf, AgClO4 and [Ni(COD)2] were purchased from
of styrenes and hex-1-ene with moderate selectivity. The DFT Aldrich Chemicals and used as received. Other chemicals were
calculations have hinted at the overall electron contributions obtained from commercial sources and purified prior to use.
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Table 5 Hydroformylation of hex-1-ene with bisphosphomide 1
Entry
Ligand
CO/H2(Bar)
Conversion
l : b
TON
1
2
3
4
5
1
1
1
1
1
10
20
31
66
81
68
52
1.5
1.4
1.5
1.4
2.3
620
1080
1776
3400
5200
30
30a
30b
Time = 4 h, temp. = 60 °C, solvent = toluene. S/C = 2000, isomerised
alkenes were not detected. a S/C = 5000. b S/C = 10 000.
Table 6 Hydroformylation of styrene and its derivatives
Entry
Substrate
Conversion
b : l
% b
TON
1
2
3
4
5
6
Styrene
96
98.5
99
66
77.6
92.6
2.2
2.9
2.2
2.7
2.6
1.58
69
74
68
73
72
46
1920
1970
1980
1320
1553
1852
4-tert-Butylstyrene
4-Methyl styrene
4-Cl-styrene
4-Br-styrene
4-Allyl anisolea
Time = 4 h, temp. = 60 °C, P = 30 bar (1 : 1, CO : H2), solvent = toluene,
S/C = 2000. a Isomerised aldehyde = 24%.
Table 7 Compositiona and energies of important Kohn–Sham orbitals of palla-
dium pincer complex 9 obtained using the wave function generated at the
B3LYP/6-31G**, SDD level of theory
Orbital
Energy (eV)
Orbital character
LUMO + 2
LUMO
HOMO
HOMO − 1
HOMO − 2
HOMO − 18
HOMO − 35
HOMO − 36
HOMO − 38
−2.072
−2.600
−3.164
−6.498
−6.874
−9.500
−11.42
−11.55
−11.63
12.67% Pd dz2, 87.32% PCP
100% PCP
11.56% Pd dyz, 88.44% P Px
2.72% Pd dxz, 97.28% PCP
0.51% Pd dyz, 99.49% PCP
0.11% Pd dxz, 99.9% C Py
11.76% Pd dx2−y2, 88.24% P Px
1.30% Pd dz2, 98.69% P Py
2.7% Pd S, 97.30% C Pz
a PCP pincer and Pd–Br are considered as two interacting partners in
AOMix analysis. The contributions listed as coming from palladium
are inclusive of those of bromine.
Instrumentation
The NMR spectra were recorded at the following frequencies:
400 MHz (1H), 100 MHz (13C), 162 MHz (31P) using either a
Varian VXR 400 or a Bruker AV 400 spectrometer. 13C and 31P
NMR spectra were acquired using broad band decoupling. The
spectra were recorded in CDCl3 solutions with CDCl3 as an
1
internal lock; chemical shifts of H and 13C NMR spectra are
reported in ppm downfield from TMS, used as an internal
standard. The chemical shifts of 31P{1H} NMR spectra are
referred to 85% H3PO4 as an external standard. The microana-
lyses were performed using a Carlo Erba Model 1112 elemental
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yellow-orange solid. Yield: 94% (4.60 g). Mp: 99–101 °C. Anal.
Calcd for C32H24O2P2: C, 76.49; H, 4.81. Found: C, 76.42; H,
1
4.78. FT IR (KBr disc) cm−1: νCO: 1649 s. H NMR (400 MHz,
4
3
CDCl3): δ 8.58 (t, 1H, Ar, JHH = 1.8 Hz), 7.99 (d, 2H, Ar, JHH
=
7.7 Hz), 7.44–7.29 (m, 21H, Ar). 31P{1H} NMR (162 MHz,
CDCl3): δ 12.3 (s).
Synthesis of 2-Br-1,3-{Ph2PC(O)}2C6H3 (2)
To a solution of diphenylphosphine (0.66 g, 3.547 mmol) in
diethyl ether (20 mL) at 0 °C was added a solution of 2-bromo-
isophthaloyl chloride (0.50 g, 1.773 mmol) in the same solvent
(10 mL) in the presence of Et3N (0.358 g, 0.49 mL,
3.547 mmol). The color of the solution immediately turned
yellow. The reaction mixture was stirred for 3 h at room temp-
erature. The amine hydrochloride was removed by filtration
and the solvent was removed under reduced pressure to give a
yellow solid. The solid was dissolved in 5 mL of CH2Cl2 and
saturated with 6 mL of hexane and stored at −20 °C to give an
analytically pure 2 as a yellow solid. Yield: 95% (0.979 g). Mp:
112–114 °C. Anal. Calcd for C32H23BrO2P2: C, 66.11; H, 3.99.
Found: C, 66.19; H, 3.83. FT IR (KBr disc) cm−1: νCO: 1649 s.
1H NMR (400 MHz, CDCl3):
δ 7.42–7.59 (m, 8H, Ar),
3
7.37–7.29 (m, 14H, Ar), 7.09 (t, 1H, Ar, JHH = 7.6 Hz). 31P{1H}
NMR (162 MHz, CDCl3): δ 21.1 (s).
Synthesis of 1,3-{Ph2P(S)C(O)}2(C6H4) (3)
A mixture of 1 (0.1 g, 0.198 mmol) and elemental sulfur
(0.013 g, 0.417 mmol) in diethyl ether (12 mL) was stirred vigo-
rously for 3 h at room temperature. The bis(sulfide) derivative
precipitated out as a yellow solid which was filtered off and
washed with 10 mL of diethyl ether. The solid was dissolved in
THF followed by filtration to remove unreacted sulfur. The
yellow filtrate obtained was dried under reduced pressure to
yield 3 as a yellow solid. Yield: 60% (0.067 g). Mp: 124–126 °C.
Anal. Calcd for C32H24O2P2S2: C, 67.83; H, 4.27; S, 11.32.
Found: C, 67.49; H, 4.23; S, 10.86. FT IR (KBr disc) cm−1: νCO
:
1
1656 s. H NMR (400 MHz, CDCl3): δ 8.51 (s, 1H, Ar), 8.10 (d,
3
2H, Ar, JHH = 6.1 Hz), 7.93–7.68 (m, 12H, Ar), 7.65–7.36 (m,
Fig. 8 Selected set of Kohn–Sham orbital contours for key orbitals of Pd-pincer
complex 9.
9H, Ar). 31P{1H} NMR (162 MHz, CDCl3): δ 38.1 (s).
Synthesis of 1,3-{Ph2P(Se)C(O)}2(C6H4) (4)
Compound 4 was synthesized by a procedure similar to that of
3 using selenium (0.033 g, 0.417 mmol) and 1 (0.1 g,
0.198 mmol). Yield: 67% (0.087 g). Mp: 196–197 °C (dec). Anal.
Calcd for C32H24O2P2Se2: C, 58.20; H, 3.66. Found: C, 58.16; H,
analyzer. Mass spectra were recorded using a Waters Q-Tof
micro (YA-105). The melting points were observed in capillary
tubes and are uncorrected.
1
3.68. FT IR (KBr disc) cm−1: νCO: 1653 s. H NMR (400 MHz,
3
CDCl3): δ 8.89 (s, 1H, Ar), 8.39 (d, 2H, Ar, JHH = 6.1 Hz),
Synthesis of 1,3-{Ph2PC(O)}2(C6H4) (1)
7.85–7.76 (m, 12H, Ar), 7.58–7.46 (m, 9H, Ar). 31P{1H} NMR
A solution of isophthaloyl chloride (2.0 g, 9.85 mmol) in (162 MHz, CDCl3): δ 31.1 (s), 1JPSe = 746 Hz.
15 mL diethyl ether was added dropwise over 10 minutes to a
solution of diphenylphosphine (3.6 g, 19.7 mmol) in diethyl
Synthesis of [Ru2(η6-p-cymene)2Cl4{1,3-{Ph2PC(O)}2(C6H4)}] (5)
ether (40 mL) at 0 °C in the presence of Et3N (1.9 g, 2.7 mL, A solution of 1 (0.040 g, 0.079 mmol) in CH2Cl2 (3 mL) was
19.7 mmol). The color of the solution immediately turned added dropwise to the solution of [Ru(η6-p-cymene)Cl2]2
yellow. The reaction mixture was stirred for 3 h at room temp- (0.024 g, 0.039 mmol) also in CH2Cl2 (4 mL) during which
erature and the amine hydrochloride was removed by filtration. time the color of the solution turned from orange to brown.
The solvent was removed under reduced pressure to give 1 as a The reaction was allowed to stir for 3 h after which the
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solution was concentrated to 5 mL and saturated with 2 mL of Ar), 7.86 (d, 2H, Ar, 3JHH = 7.4 Hz), 7.54–7.43 (m, 12H, Ar), 7.38
petroleum ether to afford brown crystals of 5. Yield: 91% (m, 1H, Ar). 31P{1H} NMR (162 MHz, CDCl3): δ 49.6 (s).
(0.080 g). Mp: 219–210 °C. Anal. Calcd for C52H52Ru2Cl4O2P2:
Synthesis of [PdBr{2,6-{Ph2PC(O)}2(C6H3)}] (9)
cm−1: νCO: 1699 s. 1H NMR (400 MHz, CDCl3): δ 8.24 (s, 1H, Compound 9 was synthesized by a procedure similar to that of
C, 56.02; H, 4.70. Found: C, 56.12; H, 4.53. FT IR (KBr disc)
3
Ar), 7.84–7.79 (m, 8H, Ar), 7.71(d, 2H, Ar, JHH = 7.9 Hz), 8 using [Pd2(dba)3] (0.053 g, 0.051 mmol) and 2 (0.060 g,
3
7.31–7.25 (m, 12H, Ar), 6.88 (t, 1H, Ar, JHH = 7.9 Hz), 5.36 (d, 0.103 mmol). Yield: 95% (0.068 g). Mp: 253–254 °C (dec). Anal.
4H, Cym, 3JHH = 5.8 Hz), 5.26 (d, 4H, Cym, JHH = 5.8 Hz), 2.60 Calcd for C32H23BrPdO2P2: C, 55.88; H, 3.37. Found: C, 55.51;
3
(m, 2H, CH), 1.69 (s, 6H, CH3), 0.97 (d, 12H, CH3, JHH = 7.0 H, 3.48. FT IR (KBr disc) cm−1: νCO: 1653 s. 1H NMR (400 MHz,
3
Hz). 31P{1H} NMR (162 MHz, CDCl3): δ 30.7.
CDCl3): δ 8.02–7.97 (m, 10H, Ar), 7.54–7.41 (m, 13H, Ar). 31P
{1H} NMR (162 MHz, CDCl3): δ 52.2 (s).
Synthesis of [Pd2(η3-C3H5)2Cl2{1,3-{Ph2PC(O)}2(C6H4)}] (6)
Synthesis of [Cu2(µ-Cl)2{1,3-{Ph2PC(O)}2(C6H4)}2] (10)
To a solution of [Pd(η3-C3H5)Cl]2 (0.018 g, 0.049 mmol) in
CH2Cl2 (3 mL) was added a solution of 1 (0.050 g, 0.099 mmol)
in the same solvent (4 mL) and the mixture was stirred for 2 h.
The yellow colored solution obtained was concentrated to
3 mL and saturated with 1 mL of petroleum ether to yield 6 as
a microcrystalline solid. Yield: 89% (0.078 g). Mp: 176–178 °C
(dec). Anal. Calcd for C38H32Pd2Cl2O2P2: C, 52.68; H, 3.72.
Found: C, 52.52; H, 3.61. FT IR (KBr disc) cm−1: νCO: 1657 s.
1H NMR (400 MHz, CDCl3): δ 8.66 (s, 1H, Ar), 8.14 (d, 2H,
A solution of 1 (0.06 g, 0.119 mmol) in dichloromethane
(6 mL) was added dropwise to a solution of CuCl (0.011 g,
0.119 mmol) in CH3CN (4 mL). The reaction mixture was
stirred for 3 h to give an orange-yellow solution. The solution
was concentrated to 4 mL and stored at −20 °C to yield orange-
yellow crystals of 10. Yield: 80% (0.065 g). Mp: 228–230 °C
(dec). Anal. Calcd for C72H60Cl2Cu2N4O4P4: C, 63.25; H, 4.42.
Found: C, 63.43; H, 3.31. FT IR (KBr disc) cm−1: νCO: 1662 s.
1H NMR (400 MHz, CDCl3): δ 10.13 (s, 1H, Ar), 7.27 (d, 2H,
3
Ar, JHH = 8.0 Hz), 7.69–7.64 (m, 8H, Ar), 7.48–7.38 (m, Ar,
3
3
Ar, JHH = 7.6 Hz), 7.26–7.16 (m, 12H, Ar), 7.10–7.07 (m, 9H,
12H), 7.27 (t, 1H, Ar, JHH = 8.0 Hz), 5.58–5.43 (m, 2H, allyl),
Ar). 31P{1H} NMR (162 MHz, CDCl3): δ 4.0 (s).
4.19 (br, s, 4H, allyl), 3.05 (br, s, 4H, allyl). 31P{1H} NMR
(162 MHz, CDCl3): δ 28.7.
Synthesis of [Cu2(µ-Br)2{1,3-(Ph2PC(O))2(C6H4)}2] (11)
Compound 11 was synthesized by a procedure similar to that
of 10 using CuBr (0.011 g, 0.079 mmol) and 1 (0.040 g,
0.079 mmol). Yield: 82% (0.041 g). Mp: 269–270 °C. Anal.
Calcd for C64H48Br2Cu2O4P4: C, 59.50; H, 3.75. Found: C,
Synthesis of [PdCl{2,6-{Ph2PC(O)}2(C6H3)}] (7)
A solution of 1 (0.050 g, 0.099 mmol) in 5 mL of CH2Cl2 was
added dropwise to
a suspension of AgClO4 (0.021 g,
0.099 mmol) in CH2Cl2 (4 mL) and the reaction mixture was
allowed to stir for 30 minutes to give a light yellow solution. To
this solution was added the solution of [Pd(COD)Cl2] (0.028 g,
0.099 mmol) in 4 mL of CH2Cl2. The reaction mixture was
stirred for 6 h and the silver chloride was removed by filtration
59.44; H, 3.86. FT IR (KBr disc) cm−1: νCO: 1660 s. 1H NMR
3
(400 MHz, CDCl3): δ 10.22 (s, 1H, Ar), 7.24 (d, 2H, Ar, JHH
=
8.0 Hz), 7.20–7.16 (m, 12H, Ar), 7.09–7.05 (m, 9H, Ar). 31P{1H}
NMR (162 MHz, CDCl3): δ 1.9 (s).
to give a clear yellow solution. The solution was concentrated Synthesis of [Cu2(µ-I)2{1,3-(Ph2PC(O))2(C6H4)}2] (12)
to 3 mL and saturated with 5 mL of petroleum ether to get ana-
Compound 12 was synthesized by a procedure similar to that
lytically pure 7 as a yellow solid. Yield: 62.5% (0.040 g). Mp:
of 10 using CuI (0.015 g, 0.079 mmol) and 1 (0.040 g,
238–239 °C (dec). Anal. Calcd for C32H23ClO2P2Pd·CH2Cl2: C,
0.079 mmol). Yield: 86% (0.047 g). Mp: 240–241 °C (dec). Anal.
54.42; H, 3.46. Found: C, 54.66; H, 3.48. FT IR (KBr disc) cm−1
:
Calcd for C64H48I2Cu2O4P4: C, 55.47; H, 3.49. Found: C, 54.68;
νCO, 1659 s. 1H NMR (400 MHz, CDCl3): δ 8.12–7.98 (m, 6H,
Ar), 7.86–7.80 (m, 4H, Ar), 7.57–7.31(m, 12H, Ar), 7.01 (m, 1H,
Ar). 31P{1H} NMR (162 MHz, CDCl3): δ 49.3(s).
H, 3.24. FT IR (KBr disc) cm−1: νCO: 1654 s. 1H NMR (400 MHz,
3
CDCl3): δ 10.28 (s, 1H, Ar), 7.25 (d, 2H, Ar, JHH = 7.6 Hz),
7.21–7.14 (m, 12H, Ar), 7.10–7.06 (m, 9H, Ar). 31P{1H} NMR
(162 MHz, CDCl3): δ 1.3 (s).
Synthesis of [NiBr{2,6-{Ph2PC(O)}2(C6H3)}] (8)
Synthesis of [Cu(CH3CN)2{1,3-(Ph2PC(O))2(C6H4)}]BF4 (13)
The bis(phosphomide) 2 (0.06 g, 0.103 mmol) and [Ni(COD)2]
(0.028 g, 0.103 mmol) were placed in a round bottom flask and To a solution of 1 (0.050 g, 0.099 mmol) in dichloromethane
THF (7 mL) was added. The resulting solution was allowed to (5 mL) was added dropwise a solution of [Cu(CH3CN)4]BF4
stir for 4 h during which the solution turned deep brown in (0.031 g, 0.099 mmol) in the same solvent (5 mL) and the reac-
color. The solvent was removed under reduced pressure and tion mixture was stirred for 3 h. The yellow solution obtained
the brown residue obtained was washed with petroleum ether was concentrated under reduced pressure to a small bulk and
dissolved in CH2Cl2 (6 mL) and saturated with 3 mL of pet- kept at −20 °C to give 13 as a yellow crystalline solid. Yield:
roleum ether to produce orange crystals of 8. Yield: 96% 74% (0.053 g). Mp: 219–220 °C (dec). Anal. Calcd for
(0.064 g). Mp: 214–115 °C. Anal. Calcd for C32H23BrNiO2P2: C, C36H30BCuF4N2O2P2: C, 58.83; H, 4.11; N, 3.81. Found: C,
1
60.05; H, 3.62. Found: C, 59.98; H, 3.60. FT IR (KBr disc) cm−1
:
58.26; H, 4.14; N, 3.62. FT IR (KBr disc) cm−1: νCO: 1658 s. H
νCO: 1686 s. 1H NMR (400 MHz, CDCl3): δ 7.97–7.92 (m, 8H, NMR (400 MHz, CDCl3): δ 7.91 (s, br, 1H, Ar), 7.57 (s, br, 2H,
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Ar), 7.47–7.43 (m, 4H, Ar), 7.39–7.27 (m, 16H, Ar), 7.00 (s, br, Synthesis of [Ag2(CF3SO3)2{1,3-(Ph2PC(O))2(C6H4)}] (17)
1H, Ar). 31P{1H} NMR (162 MHz, CDCl3): δ 10.5 (s).
Compound 17 was synthesized by a procedure similar to that
of 16 using AgOTf (0.030 g, 0.119 mmol) and 1 (0.030 g,
0.059 mmol). The THF solution was concentrated to a small
Synthesis of [Ag2(µ-ClO4)2{1,3-(Ph2PC(O))2(C6H4)}2] (14)
bulk (3 mL) and stored at −20 °C to give 17 as a colorless
A solution of 1 (0.040 g, 0.079 mmol) in 5 mL of THF was
solid. Yield: 81% (0.050 g). Mp: 131–132 °C (dec). Anal. Calcd
added dropwise to a solution of AgClO4 (0.016 g, 0.079 mmol)
for C34H24Ag2F6O8P2S2·0.5C4H8O: C, 41.09; H, 2.68; S, 6.09.
in THF (5 mL) and the reaction mixture was allowed to stir for
Found: C, 41.23; H, 2.57; S, 6.79. FT IR (KBr disc) cm−1: νCO
:
1 h to give a light yellow solution. The solution was dried
under reduced pressure and the residue redissolved in CH2Cl2
(4 mL) followed by saturation with 1 mL of petroleum ether to
give light yellow crystals of [Ag2(µ-Cl)(µ-ClO4){1,3-(Ph2PC-
(O))2(C6H4)}2] (14a) in very low yield (∼4%) confirmed by single
crystal X-ray study. This is due to the trace amount of AgCl con-
taminated with commercially obtained silver perchlorate. The
bulk of the product was as expected [Ag2(µ-ClO4)2{1,3-(Ph2PC-
(O))2(C6H4)}2] (14) which did not give crystals suitable for
single crystal X-ray diffraction studies. Yield: 88% (0.051 g).
Mp: 175–177 °C (dec). Anal. Calcd for (14) C64H48Ag2-
Cl2O12P4·CH2Cl2: C, 52.00; H, 3.36. Found: C, 51.93; H, 3.42.
FT IR (KBr disc) cm−1: νCO: 1660 s. 1H NMR (400 MHz, CDCl3):
δ 8.07 (s, 1H, Ar), 7.94 (d, 2H, Ar, 3JHH = 7.9 Hz), 6.96 (t, 1H, Ar,
3JHH = 7.8 Hz), 7.72–7.39 (m, 20H, Ar). 31P{1H} NMR (162 MHz,
CDCl3): δ 15.8 (2 br s, 2P).
1
1661 s. H NMR (400 MHz, CDCl3): δ 8.41 (s, 1H, Ar), 8.02 (d,
3
2H, Ar, JHH = 7.8 Hz), 7.49–7.37(m, 21H, Ar). 31P{1H} NMR
1
(162 MHz, CDCl3(−40 °C)): δ 18.8 (2d, 2P, J(109AgP) 730.5 Hz,
1J(107AgP) 641.4 Hz).
Synthesis of [AuCl{1,3-(Ph2PC(O))2(C6H4)}] (18)
A solution of 1 (0.030 g, 0.059 mmol) in 4 mL of CH2Cl2 was
added dropwise to a solution of [AuCl(SMe2)] (0.017 g,
0.059 mmol) also in CH2Cl2 (3 mL) and the reaction mixture
was stirred for 2 h to give a light yellow solution. The solution
was concentrated to a small bulk (3 mL) and saturated with
1 mL of petroleum ether to produce analytically pure 18 as a
light yellow solid. Yield: 93% (0.040 g). Mp: 187–188 °C. Anal.
Calcd for C32H24AuClO2P2·0.25CH2Cl2: C, 51.23; H, 3.27.
Found: C, 51.45; H, 3.26. FT IR (KBr disc) cm−1: νCO: 1656
1
s. H NMR (400 MHz, CDCl3): δ 8.66 (s, 1H, Ar), 8.17 (d, 2H,
Crystals of 14a were separated manually. Anal. Calcd for
(14a) C64H48Ag2Cl2O8P4·1.5CH2Cl2: C, 53.04; H, 3.46. Found: C,
53.13; H, 3.46. Since the product was obtained in a very
minute quantity, further spectroscopic studies could not be
carried out.
3
Ar, JHH = 7.9 Hz), 7.52–7.36 (m, 21H, Ar). 31P{1H} NMR
(162 MHz, CDCl3): δ 22.2.
Synthesis of [Au2Cl2{1,3-(Ph2PC(O))2(C6H4)}] (19)
To a CH2Cl2 (4 mL) solution of 1 (0.030 g, 0.059 mmol) was
added dropwise
a solution of [AuCl(SMe2)] (0.035 g,
Synthesis of [Ag2(µ-CF3SO3)2{1,3-(Ph2PC(O))2(C6H4)}2] (15)
0.119 mmol) also in CH2Cl2 (5 mL) and the reaction mixture
was stirred for 2 h to give a colorless solution. The solution
was concentrated to 5 mL and saturated with 1 mL of pet-
roleum ether to form 19 as a colorless solid. Yield: 89%
(0.050 g). Mp: 149–150 °C. Anal. Calcd for C32H24Au2Cl2O2P2:
C, 39.73; H, 2.50. Found: C, 40.06; H, 2.61. FT IR (KBr disc)
cm−1: νCO: 1656 s. 1H NMR (400 MHz, CDCl3): δ 8.77 (s, 1H,
Compound 15 was synthesized by a procedure similar to that
of 14 using AgOTf (0.015 g, 0.059 mmol) and 1 (0.030 g,
0.059 mmol). Yield: 83% (0.037 g). Mp: 179–180 °C (dec). Anal.
Calcd for C66H48Ag2O10P4F6S2: C, 52.19; H, 3.19; S, 4.22.
Found: C, 51.85; H, 3.13; S, 4.06. FT IR (KBr disc) cm−1: νCO
:
1
1660 s. H NMR (400 MHz, CDCl3): δ 8.20 (s, 1H, Ar), 8.07 (d,
3
2H, Ar, JHH = 7.6 Hz), 7.60–7.49 (m, 20H, Ar), 6.31(t, 1H, Ar,
3
Ar), 8.35 (d, 2H, Ar, JHH = 7.9 Hz), 7.67–7.45 (m, 21H, Ar).
3JHH = 7.6 Hz). 31P{1H} NMR (162 MHz, CDCl3): δ 14.8 (2 br s,
31P{1H} NMR (162 MHz, CDCl3): δ 31.4.
2P).
Procedure for catalytic hydroformylation reactions
Synthesis of [Ag2(ClO4)2{1,3-(Ph2PC(O))2(C6H4)}] (16)
In a typical hydroformylation reaction, a high pressure reactor
To a solution of AgClO4 (0.032 g, 0.158 mmol) in THF (5 mL) of 100 mL capacity was charged with ligand 1 (5 µmol,
was added a THF (4 mL) solution of 1 (0.040 g, 0.079 mmol) 2.5 mg), [Rh(acac)(CO)2] (2.5 µmol, 0.5 mL of a 5 mM solution
and the reaction mixture was stirred for 1 h to give a colorless in toluene) and olefin (5 mmol) in 20 mL of toluene, followed
solution. The solution was dried under reduced pressure and by decane (0.1 mL) as an internal standard. The reactor was
the solid dissolved in CH2Cl2 (5 mL) followed by addition of flushed with synthesis gas (1 : 1 mixture of H2 and CO gas) fol-
1 mL of petroleum ether to give an analytically pure product of lowed by charging to desired pressure at room temperature.
16 as a colorless solid. Yield: 76% (0.060 g). Mp: 140–142 °C The reactor was heated to desired temperature at a stirring
(dec). Anal. Calcd for C32H24Ag2Cl2O10P2·CH2Cl2: C, 39.55; H, speed of 350 rpm. After completion of the reaction, the reactor
2.62. Found: C, 39.64; H, 2.75. FT IR (KBr disc) cm−1: νCO: 1662 was cooled to room temperature in an ice-water bath and the
1
s. H NMR (400 MHz, CDCl3): δ 8.25 (s, 1H, Ar), 8.11 (d, 2H, remaining synthesis gas was carefully released in a well venti-
3
3
Ar, JHH = 7.8 Hz), 6.65–7.49 (m, 20H, Ar), 7.44 (t, 1H, Ar, JHH lated fume hood. The reaction mixture was quantitatively ana-
= 7.8 Hz). 31P{1H} NMR (162 MHz, CDCl3): δ 19.7 (br s).
lyzed by gas chromatography.
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Computational methods
References
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structure factors) for the structures reported in this paper have
been deposited with the Cambridge Crystallographic Data
Centre
as
supplementary
publication
no.
CCDC
934905–934911.
Acknowledgements
We are grateful to the Department of Science and Technology
(DST), New Delhi, for financial support of this work through
grant no. SR/S1/IC-17/2010. P.K. thanks CSIR, New Delhi for
research fellowships (JRF & SRF). We also thank the Depart-
ment of Chemistry Instrumentation Facilities, IIT Bombay, for
spectral and analytical data and J.T.M. thanks the Louisiana
Board of Regents for the purchase of the CCD diffractometer
and the Chemistry Department of Tulane University for
support of the X-ray laboratory.
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