Transition metal chemistry of phosphorus based ligands. Ruthenium(II) chemistry of bis(phosphino)amines, X2PN(R)PX2 (R=H or Ph, X=Ph; R=Ph, X2=O2C6H4)

Article abstract of DOI:10.1016/S0022-328X(98)00464-1

Reactions of CpRuCl(PPh₃)₂ with bis(phosphino)amines, X₂PN(R)PX₂ (1 R=H, X=Ph; 2 R=X=Ph; 3 R=Ph, X₂=O₂C₆H₄) give neutral or cationic mononuclear complexes depending on the reaction conditions. Reaction of 1 with CpRuCl(PPh₃)₂ gives one neutral complex, [CpRu(Cl)(η²-Ph₂PN(H)PPh₂)] (4) and two cationic complexes, [CpRu(η²-Ph₂PN(H)PPh₂)(η¹-Ph ₂PN(H)PPh₂)]Cl (5) and [CpRu(PPh₃)(η²-Ph₂PN(H)PPh₂)]Cl (6), whereas the reaction of 2 with CpRuCl(PPh₃)₂ leads only to the isolation of cationic complex, [CpRu(PPh₃)(η²-Ph₂PN(Ph)PPh₂)]Cl (7). The catechol derivative 3, in a similar reaction, affords an interesting mononuclear complex [CpRu(PPh₃){η¹-(C₆H₄O₂)PN(Ph)P(O₂H₄C₆)}₂]Cl (8) containing two monodentate bis(phosphino)amine ligands. The structural elucidation of the complexes was carried out by elemental analyses, IR and NMR spectroscopic data.

Full text of DOI:10.1016/S0022-328X(98)00464-1

Journal of Organometallic Chemistry 560 (1998) 131–136
Transition metal chemistry of phosphorus based ligands.
Ruthenium(II) chemistry of bis(phosphino)amines, X2PN(R)PX2
(R=H or Ph, X=Ph; R=Ph, X2=O2C6H4)
Maravanji S. Balakrishna *, Krishna Ramaswamy, Rita M. Abhyankar
Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400 076, India
Received 26 November 1997
Abstract
Reactions of CpRuCl(PPh3)2 with bis(phosphino)amines, X2PN(R)PX2 (1 R=H, X=Ph; 2 R=X=Ph; 3 R=Ph, X2=
O2C6H4) give neutral or cationic mononuclear complexes depending on the reaction conditions. Reaction of 1 with CpRu-
Cl(PPh3)2
gives
one
neutral
complex,
[CpRu(Cl)(p2-Ph2PN(H)PPh2)]
(4)
and
two
cationic
complexes,
[CpRu(p2-Ph2PN(H)PPh2)(p1-Ph2PN(H)PPh2)]Cl (5) and [CpRu(PPh3)(p2-Ph2PN(H)PPh2)]Cl (6), whereas the reaction of 2 with
CpRuCl(PPh3)2 leads only to the isolation of cationic complex, [CpRu(PPh3)(p2-Ph2PN(Ph)PPh2)]Cl (7). The catechol derivative
3, in a similar reaction, affords an interesting mononuclear complex [CpRu(PPh3){p1-(C6H4O2)PN(Ph)P(O2H4C6)}2]Cl (8)
containing two monodentate bis(phosphino)amine ligands. The structural elucidation of the complexes was carried out by
elemental analyses, IR and NMR spectroscopic data. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Bis(phosphino)amines; Mononuclear; Ruthenium(II) complexes; Cationic; Monodentate; Bidentate
1. Introduction
appropriate ligand system it is possible to fine tune the
electronic and steric properties of the donor centers to
bind the metals in desired oxidation state with a specific
coordination number so that a catalyst may be gener-
ated for a specific organic transformation. In this con-
text bis(phosphino)amines play a major role because of
easy and high yield synthetic methodologies and flexi-
bility in their reactivity toward transition metals in their
various oxidation states [24–26]. As a part of our
interest in this area [26–32], the above considerations
prompted us to study the chemistry of bis(phos-
phino)amines, X2PN(R)PX2 (1 R=H, X=Ph; 2 R=
X=Ph; 3 R=Ph, X2=O2C6H4) with the versatile
ruthenium(II) complex such as CpRuCl(PPh3)2. Of con-
cern in the present study was to show the versatility of
the bis(phosphino)amine ligands in exhibiting different
coordination behavior when the donor–acceptor prop-
erties are altered by incorporating different substituents
at both the phosphorus centers and at the bridging
nitrogen atom.
The synthesis and structural chemistry of ruthenium
complexes containing tertiary mono- and bis(phos-
phine)s have attracted considerable interest in recent
years [1–8]. Besides their potential use in classical cata-
lytic processes such as hydrogenation, isomerization,
decarbonylation, etc. [9–13], processes such as reduc-
tive elimination and oxidative addition for making and
breaking C–H bonds [14–21], formation and cleavage
of N–H and O–H bonds [22] were also observed in
monomeric complexes that are stabilized by one or
more tertiary mono- or bis(phosphine)s. The thermal
and mechanistic aspects [23] along with the synthesis of
new bis(phosphine) complexes are also interesting in
view of their assistance in understanding the catalytic
processes that take place at metal sites. By choosing an
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00464-1

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M.S. Balakrishna et al. / Journal of Organometallic Chemistry 560 (1998) 131–136
2. Experimental section
product 5 was obtained by crystallizing in a 1:3 mixture
of dichloromethane and n-hexane.
All experimental manipulations were performed un-
der an atmosphere of dry nitrogen. Solvents were dried
and distilled prior to use. Ph2PN(Ph)PPh2 [33],
Ph2PN(H)PPh2 [34], (C6H4O2)PN(Ph)P(O2H4C6) [32]
and CpRuCl(PPh3)2 [35] were prepared according to
published procedures or with minor modifications
Complex 5: Orange crystalline material, m.p. 167°C
(decomposes). Anal. Found: C 65.28, H 4.78, N 2.67%.
Calc. for C53H47N2P4RuCl: C 65.46, H 4.83, N 2.88%.
IR (nujol) wmax:3312 m, 3065 s, 2930s, 1600vs, 1235 vs,
1110m, 1015m, 975m, 810sh, 795 m, 680 m cm−1
.
1H-NMR (CDCl3): l phenyl, 7.26 (m, 40H), l Cp, 4.40
(s, 5H). 31P{1H}-NMR (CDCl3): l (Pr) 60.6 (d), l (Pc)
92.1 (td), l (Pu) 31.2(d), JPrPc=40.4 Hz, JPcPu=18.8
Hz.
1
thereof. H- and 31P-NMR spectra were recorded on a
VXR 300S spectrometer operating at the appropriate
frequencies using TMS and 85% H3PO4 as internal and
external references, respectively. CDCl3 was used as
both solvent and internal lock. Positive shifts lie
downfield in all cases. IR spectra were recorded on
FTIR Nicolet Impact 400 spectrometer in nujol mull or
KBr disk. Microanalyses were carried out in the De-
partment of Chemistry, IIT, Powai.
2.3. Preparation of [CpRu(PPh3)(p2-Ph2PN(H)PPh2)]Cl
(6)
A solution of Ph2PN(H)PPh2 (0.026 g, 0.068 mmol)
in toluene (8 ml) was added dropwise to a solution of
CpRuCl(PPh3)2 (0.050 g, 0.068 mmol), also in toluene
(10 ml) and the reaction mixture was heated to reflux
for 3 h. A clear solution was obtained. The solution
was cooled to r.t. and 3 ml of n-hexane was added. An
orange/yellow-colored crystalline product was precipi-
tated, which was isolated by filtration and then dried
under vacuum.
2.1. Preparation of [CpRu(Cl)(p2-Ph2PN(H)PPh2)] (4)
A solution of Ph2PN(H)PPh2 (0.026 g, 0.068 mmol)
in toluene (8 ml) was added dropwise to a solution of
CpRuCl(PPh3)2 (0.050 g, 0.068 mmol), also in toluene
(8 ml) and the reaction mixture was stirred at 80°C for
6 h. A clear solution was obtained. The solution was
cooled to room temperature (r.t.) and 3 ml of n-hexane
was added. An orange-colored crystalline product was
precipitated which was isolated by filtration and then
dried under vacuum.
When the above reaction was carried out in methanol
under refluxing conditions the same product 6 was
formed.
Orange/red crystals, yield 87% (0.049 g), m.p. 201–
203°C. Anal. Found: C 65.78, H 4.81, N 1.51%. Calc.
for C47H41NP3ClRu: C 66.47, H 4.83, N 1.65%. IR
(KBr) wmax: 3122s, 3055m, 2910m, 2822s, 1198sh,
Orange/red crystals, yield 78% (0.031 g), m.p. 179–
181°C. Anal. Found: C 61.48, H 4.81, N 2.10%. Calc.
for C29H26NP2Cl·0.5C6H5CH3 [36]: C 61.49, H 4.73, N
2.21%. IR (KBr) [37] wmax: 3115m, 3054m, 2934sh,
1
1170sh, 1048m, 812s, 805sh cm−1. H-NMR (CDCl3):
l Phenyl region, 7.28 (m, 35H), l Cp, 4.42 (s, 5H).
1
2853s, 1238m, 1103sh, 1030s, 802sh, 695sh cm−1. H-
31P{1H}-NMR (CDCl3): l (Pr) 58.0 (d), l (PPh3) 49.1
2
NMR (CDCl3) [38]: l Phenyl region, 7.44 (m, 20H), l
(t), JPP=36.6 Hz.
Cp, 4.42 (s, 5H). 31P{1H}-NMR (CDCl3): l 72.6 (s).
2.4. Preparation of
2.2. Reaction of Ph2PN(H)PPh2 with CpRuCl(PPh3)2
in 2:1 molar ratio
[CpRu(PPh3)(p2-Ph2PN(Ph)PPh2)]Cl (7)
A solution of Ph2PN(Ph)PPh2 (0.032 g, 0.068 mmol)
in toluene (8 ml) was added dropwise to a solution of
CpRuCl(PPh3)2 (0.05 g, 0.068 mmol), also in toluene (8
ml) and the reaction mixture was stirred at r.t. for 6 h.
During that period a yellow crystalline product was
separated from the reaction mixture. The solution was
cooled to r.t. and the product was isolated by filtration
and dried under vacuum.
A solution of Ph2PN(H)PPh2 (0.054 g, 0.14 mmol) in
toluene (8 ml) was added dropwise to a solution of
CpRuCl(PPh3)2 (0.050 g, 0.068 mmol) also in toluene(8
ml) and the reaction mixture was heated to 80°C for 8
h. A clear solution was obtained at the end of the
reaction to which 3 ml of n-hexane was added. An
orange-colored crystalline product obtained was found
to be a mixture of three products 4, 5 and 6 identified
by 31P-NMR spectrum. The relative yields calculated
from 31P-NMR spectrum for 4, 5 and 6 were 20, 65 and
15%, respectively.
When the reaction was carried out using two equiva-
lents of ligand 1 with one equivalent of CpRuCl(PPh3)2
the yields of 5 and 6 were 90 and 10%, respectively, and
there was no evidence for the formation of 4, evidence
by 31P-NMR spectroscopy. The analytically-pure
The above reaction was carried out in 1:2 and 1:3
molar ratios at 80–100°C in toluene to give the same
product in almost quantitative yield.
Light yellow crystals, yield 95% (0.061 g), m.p. 223–
225°C. Anal. Found: C 68.98, H 4.91, N 1.42%. Calc.
for C53H45NP3ClRu: C 68.83, H 4.87, N 1.51%. IR
(KBr) wmax: 3054m, 2927sh, 2853s, 1968w, 1633sh,
1699sh, 1486sh, 1224m, 1090sh, 1020s, 930sh, 889sh
cm−1 1H-NMR (CDCl3): l Phenyl region, 7.32 (m,
.

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 560 (1998) 131–136
133
Fig. 1. 31P{1H}-NMR spectrum of reaction mixture containing compounds 4, 5 and 6.
40H), l Cp, 4.41 (s, 5H); 31P{1H}-NMR (CDCl3): l
(Pr) 79.0 (d), l (PPh3) 45.0 (t), JPP=33.26 Hz.
reduced pressure to afford a yellow residue. The residue
was extracted with 12 ml of n-hexane to remove free
PPh3. The remaining residue was dissolved in 3 ml of
dichloromethane and diluted with 1 ml of n-hexane and
cooled to 0°C to give pale yellow crystals of [(p5-
C5H5)Ru(p2-Ph2PN(Ph)PPh2)(CO)]Cl (9).
2
2.5. Preparation of
[CpRu(PPh3){p1-(C6H4O2)PN(Ph)P(O2H4C6)}2]Cl (8)
A solution of (C6H4O2)PN(Ph)P(O2H4C6) (0.025 g,
0.067 mmol) in toluene (8 ml) was added dropwise to a
solution of CpRuCl(PPh3)2 (0.050 g, 0.068 mmol) in the
same solvent (10 ml) and the reaction mixture was
heated to 80°C for 6 h. During that period a yellow
crystalline product was separated. The solution was
cooled to r.t. and the precipitate was isolated by filtra-
tion and dried under vacuum.
Pale yellow crystals, yield 75% (0.041 g), m.p. 218°C
(decomposes). Anal. Found: C 62.31, H 4.18, N 1.98%.
Calc. for C36H30NOP2RuCl: C 62.56, H 4.34, N 2.02%.
IR (nujol) w(CO): 1957 cm−1; other bands, wmax: 2921s,
2858m, 1641m, 1597m, 1458s, 1375s, 1360sh, 1104m,
1
930m, 742s, 693s cm−1. H-NMR (CDCl3): l phenyl
region, 7.34 (m, 15H), l Cp, 4.42 (s, 5H). 31P{1H}-
NMR (CDCl3): l 48.0 (s).
Pale yellow crystals, yield 56% (0.045 g), m.p. 171–
173°C. Anal. Found: C 61.54, H 4.30, N 2.21%. Calc.
for C59H46N2O8P5ClRu·C6H5CH3: C 61.21, H 4.2, N
2.16%. IR (KBr) wmax: 3066vs, 3029s, 1600s, 1478vs,
3. Results and discussion
1228s, 942sh, 1096w, 1008sh, 824m, 729s, 526m cm−1
.
The reaction between (p5-C5H5)RuCl(PPh3)2 and
bis(phosphino)amines is profoundly affected by the
steric and electronic properties of two donor phospho-
rus atoms as well as the substituents on the bridging
nitrogen center.
1H-NMR (CDCl3): l Phenyl region, 7.32 (m, 41H), l
Cp, 4.40 (s, 5H). 31P{1H}-NMR (CDCl3): l (PPh3) 53.6
(t), l (Pc) 169.6 (dd), l (Pu) 141.7 (d), l (Pu%) 140.5 (d),
2
2JPPc=54.4 Hz, JPcPu=2JPc%Pu%=55 Hz.
The yield of 8 was improved to 85% when the
stochiometry of the reactants i.e. the metal to the ligand
was increased to 1:2 molar ratio.
Reaction
of
(p5-C5H5)RuCl(PPh3)2
with
Ph2PN(H)PPh2 (1) in toluene solution in a ratio of 1:1
at 70°C for 6 h gives an orange/red solution. The
solution was concentrated and cooled to 0°C. The
orange/red crystals of the neutral complex 4 formed
from this solution were separated and dried in vacuo.
The yield was 78%. The 31P-NMR spectrum of com-
pound 4 shows a singlet at 72.6 ppm indicating that
both the PPh3 ligands are replaced by Ph2PN(H)PPh2
which is acting as a bidenate chelating ligand. The
reaction of (p5-C5H5)RuCl(PPh3)2 with two equivalents
of Ph2PN(H)PPh2 yielded an orange/yellow product.
The 31P-NMR spectrum of the product (Fig. 1) indi-
cated that it is a mixture of three products, 4, 5 and 6
2.6. Preparation of
[(p5-Cp5H5)Ru(p2-Ph2PN(Ph)PPh2)(CO)]Cl (9)
A solution of Ph2PN(Ph)PPh2 (0.037 g, 0.070 mmol)
in toluene (8 ml) was added dropwise to a solution of
CpRuCl(PPh3)2 (0.051 g, 0.070 mmol), also in toluene
(8 ml) while CO gas was bubbled through the solution.
After the completion of the addition the reaction mix-
ture was heated to 100°C for 4 h. A clear yellow
solution was obtained. Solvent was removed under

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M.S. Balakrishna et al. / Journal of Organometallic Chemistry 560 (1998) 131–136
Scheme 1. Reaction pathway indicating the structures 4–9 and the conditions necessary for the reactions to occur.
as shown in Scheme 1. A singlet at 72.6 ppm was
assigned to the compound 4. Compound 6 exhibits a
doublet at 58.0 ppm for chelating Ph2PN(H)PPh2 and a
sphino)amine ligand under different reaction condi-
tions. The 31P-NMR spectrum of the compound 7 is
similar to that of compound 4. The triplet at 45 ppm is
assigned to PPh3 whereas the resonance due to the
chelating ligand appears as a doublet at 79.0 ppm with
a two bond P–P coupling of 33.3 Hz. When the above
reaction was carried out while CO gas was bubbled
through the solution, a carbonylated product 9 was
formed in quantitative yield. The IR spectrum of 9
shows a w(CO) at 1957 cm−1 indicating the presence of
a carbonyl group on the ruthenium center. Further
evidence for the carbonylation and the subsequent elim-
ination of PPh3 group came from 31P-NMR data. The
31P-NMR spectrum of the complex 9 shows a singlet at
48.0 ppm indicating the presence of only the chelating
Ph2PN(Ph)PPh2. The complex 9 can also be prepared
by bubbling the CO gas through a solution of 4 in
toluene at 50°C.
2
triplet at 49.1 ppm for PPh3 with a JPP value of 36.6
Hz. Compound 5, with two Ph2PN(H)PPh2 ligands,
shows three sets of 31P-NMR resonances with relative
intensities of 1:2:1, which is consistent with this struc-
tural formulation. The doublet at 60.6 ppm was as-
signed to the chelating Ph2PN(H)PPh2 which is coupled
to the metal bound phosphorus of the monodentate
2
ligand with a JPP value of 40.4 Hz. The relatively low
field shift of coordinated phosphorus atom of the
monodentate Ph2PN(H)PPh2 when compared to that of
chelating Ph2PN(H)PPh2 is a direct consequence of
chelate-ring contribution [39]. The resonance due to
coordinated phosphorus center appears at 92.1 ppm as
a triplet of doublets. The uncoordinated phosphorus
2
center appears at 31.2 ppm as a doublet with a JPP
value of 18.8 Hz. The compounds 4 and 5 were pre-
pared in their pure form separately using different
reaction conditions.
The
reaction
of
catechol
(3)
derivative
with
(C6H4O2)PN(Ph)P(O2H4C6)
(p5-
C5H5)RuCl(PPh3)2 in equimolar quantities afforded a
rather interesting cationic compound 8 containing one
triphenylphosphine and two monodentate bis(phos-
phino)amine ligands. The 31P-NMR spectrum (Fig. 2) is
The reaction of Ph2PN(Ph)PPh2 (2) with [(p5-
C5H5)RuCl(PPh3)2] afforded only the chelated cationic
complex 7, even in the presence of an excess of bis(pho-

M.S. Balakrishna et al. / Journal of Organometallic Chemistry 560 (1998) 131–136
135
Fig. 2. 31P{1H}-NMR spectrum of compound 8.
quite consistent with the structure. The phosphorus
resonance due to the triphenylphosphine appears at
53.6 ppm as a triplet. The resonance at l 69.6 arises
from coupling to the triphenylphosphine center and one
uncoordinated phosphorus center is assigned to two
coordinated phosphorus centers of monodenate ligands.
For the catecholato monodentate ligands the two coor-
dinated phosphorus centers are effectively magnetically
equivalent (same l value and coupling to PPh3) even
though the two uncoordinated atoms are inequivalent
(differing l values but identical coupling to the bound
P atom), presumably due to folding and conformation
effects. The two uncoordinated phosphorus centers ap-
pear as two doublets having very similar chemical shift
values (l 141.2 and l 140.5) close to that of free ligand
3 (l 130.9). The uncoordinated phosphorus centers do
not show any long range coupling with triphenylphos-
phine.
These observations are similar to those made for the
related bis(dimethylphosphino)methane complexes [7].
However, unlike dppm/Ru(II) chemistry [1,2], the
product formation in our work is not affected by the
polarity of the solvents. For the dppm complexes, the
cationic species only resulted when polar solvents were
used and neutral complexes were formed when aro-
matic hydrocarbons were employed.
the bridging nitrogen atom. This once again demon-
strates the versatility of bis(phosphino)amine ligands.
The steric and electronic influence of substituents on
phosphorus centers will directly control the donor and
acceptor ability of these class of ligands that in turn
dictates their coordination modes. Many of these com-
plexes containing monodentate bis(phosphino)amines
could act as metalloligands toward transition metal, to
form a series of homo- and/or heterobimetallic com-
plexes. Further work in this direction and in possible
utilization of these complexes for catalytic purposes is
in progress.
Acknowledgements
We are grateful to the Department of Atomic Energy
(DAE) for generous support. We also thank Dr C.V.
Sathyanarayana of the Regional Sophisticated Instru-
mentation Center (RSIC) for recording NMR spectra.
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