Chiral "P-N-P" ligands, (C20H12O 2)PN(R)PY2 [R = CHMe2, Y = C6H 5, OC6H5, OC6H4-4-Me, OC6H4-4-OMe or OC6H4-4- tBu] and their allyl palladium complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.09.082

Chiral "P-N-P" ligands, (C₂₀H₁₂O ₂)PN(R)PY₂ [R = CHMe₂, Y = C₆H ₅ (1), OC₆H₅ (2), OC₆H ₄-4-Me (3), OC₆H₄-4-OMe (4) or OC ₆H₄-4-^tBu (5)] bearing the axially chiral 1,1′-binaphthyl-2,2′-dioxy moiety have been synthesised. Palladium allyl chemistry of two of these chiral ligands (1 and 2) has been investigated. The structures of isomeric η³-allyl palladium complexes, [Pd(η³-1,3-R′₂-C₃H ₃){κ²-(racemic)-(C₂₀H₁₂O ₂)PN(CHMe₂)PY₂}](PF₆)(R′ = Me or Ph; Y = C₆H₅ or OC₆H₅) have been elucidated by high field two-dimensional NMR spectroscopy. The solid state structure of [Pd(η³-1,3-Ph₂-C₃H ₃){κ²-(racemic)-(C₂₀H₁₂O ₂)PN(CHMe₂)PPh₂}](PF₆) has been determined by X-ray crystallography. Preliminary investigations show that the diphosphazanes, 1 and 2 function as efficient auxiliary ligands for catalytic allylic alkylation but give rise to only moderate levels of enantiomeric excess.

Full text of DOI:10.1016/j.jorganchem.2004.09.082

Journal of Organometallic Chemistry 690 (2005) 742–750
www.elsevier.com/locate/jorganchem
Chiral ‘‘P–N–P’’ ligands, (C20H12O2)PN(R)PY2 [R = CHMe2,
Y = C6H5, OC6H5, OC6H4-4-Me, OC6H4-4-OMe or OC6H4-4-tBu]
and their allyl palladium complexes q
a
Swadhin K. Mandal , G.A. Nagana Gowda , Setharampattu S. Krishnamurthy
b
a,
*
,
c
Thomas Stey , Dietmar Stalke
c
a
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
b
Sophisticated Instruments Facility, Indian Institute of Science, Bangalore 560012, India
c
Institut fu¨r Anorganische Chemie, Universita¨t Wu¨rzburg, Am Hubland, 97074 Wu¨rzburg, Germany
Received 26 May 2004; accepted 6 September 2004
Available online 10 December 2004
Abstract
Chiral ‘‘P–N–P’’ ligands, (C20H12O2)PN(R)PY2 [R = CHMe2, Y = C6H5 (1), OC6H5 (2), OC6H4-4-Me (3), OC6H4-4-OMe (4) or
OC6H4-4-tBu (5)] bearing the axially chiral 1,10-binaphthyl-2,20-dioxy moiety have been synthesised. Palladium allyl chemistry of
two of these chiral ligands (1 and 2) has been investigated. The structures of isomeric g3-allyl palladium complexes,
½Pdðg3-1; 3-R02-C3H3Þfj2-ðracemicÞ-ðC20H12O2ÞPNðCHMe2ÞPY2gꢀðPF6Þ (R0 = Me or Ph; Y = C6H5 or OC6H5) have been elucidated
by high field two-dimensional NMR spectroscopy. The solid state structure of [Pd(g3-1,3-Ph2-C3H3){j2-(racemic)-
(C20H12O2)PN(CHMe2)PPh2}](PF6) has been determined by X-ray crystallography. Preliminary investigations show that the
diphosphazanes, 1 and 2 function as efficient auxiliary ligands for catalytic allylic alkylation but give rise to only moderate levels
of enantiomeric excess.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Chiral ‘‘P–N–P’’ ligands; g3-allyl palladium complexes; NMR spectroscopy; X-ray crystal structure; allylic alkylation
1. Introduction
phosphorus centres as well as at the substituents at-
tached to the nitrogen or to the two phosphorus atoms.
There are only a few reports on chiral diphosphazanes
and their transition metal complexes [2a,3–6]. As a part
of our ongoing investigations on the organometallic
chemistry of diphosphazane ligands, we had reported
the synthesis and dynamic behaviour of allyl palladium
complexes of a range of diphosphazane and diphosphaz-
ane monosulfide ligands [7]. The chemistry of g3-allyl
palladium(II) complexes is a topic of considerable
importance in view of the various dynamic processes ob-
served in these systems and also their potential applica-
tions in asymmetric synthesis [8,9]. Herein, we report the
design and synthesis of several chiral diphosphazane lig-
ands based on the ‘‘P–N–P’’ backbone bearing C2-sym-
metric [1,10-binaphthyl]-2,20-dioxy moiety and the
There is considerable interest in the design and syn-
thesis of new trivalent chiral phosphorus ligands in view
of their applications in enantioselective catalysis, which
has developed in recent years as a topic of fundamental
importance [1]. Diphosphazanes constitute a class of
versatile short-bite bidentate phosphorus-donor ligands
based on the ‘‘P–N–P’’ framework that have engendered
a varied and extensive transition metal organometallic
chemistry [2]. An attractive feature of diphosphazane
ligands is that ‘‘chirality’’ can be incorporated at the
q
Organometallic chemistry of diphosphazanes – Part 21; for part
20, see [6d].
*
Corresponding author. Fax: +91 80 23600683.
E-mail address: sskrish@ipc.iisc.ernet.in (S.S. Krishnamurthy).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.09.082

S.K. Mandal et al. / Journal of Organometallic Chemistry 690 (2005) 742–750
743
reactivity of some of these chiral diphosphazane ligands
with g3-allyl palladium dimers. The results of high-field
two-dimensional NMR studies on the resulting g3-allyl
palladium complexes of chiral diphosphazanes are re-
ported. Preliminary experiments have been carried out
to probe the utility of some of these ligands in palladium
catalysed alkylation reactions. A part of this work has
been reported in a Conference Proceedings [6a].
stirred for 6 h. The precipitate of Me2CHNH2 Æ HCl
was filtered off and the solvent removed under reduced
pressure to obtain a pale yellow viscous oil. This oil
was dissolved in 30 cm3 of toluene and PCl3 (1.0 cm3,
0.012 mol) in 20 cm3 toluene was added drop-wise to
it at 0 ꢁC in the presence of Et3N (2.1 cm3, 0.015 mol).
The reaction mixture was warmed to 25 ꢁC and stirred
for 12 h. The precipitate of Et3N Æ HCl was filtered off
and solvent was evaporated to dryness under reduced
pressure to obtain (C20H12O2)PN(CHMe2)PCl2 as a yel-
low viscous oil [31P{1H} NMR (81.0 MHz, toluene):
2. Experimental
2
157.3 (d, J(P,P) = 12.0 Hz); 169.4 (d)]. A solution of
2.1. Materials and general procedures
this oil in 30 cm3 toluene was added drop-wise to a mix-
ture of phenol (1.880 g, 0.02 mol) and Et3N (4.2 cm3,
0.03 mol) in 30 cm3 toluene at 0 ꢁC. The reaction mix-
ture was stirred for 12 h at 25 ꢁC; the resulting
Et3N Æ HCl was removed by filtration and the filtrate
was evaporated to dryness to give a light yellow foamy
solid. This solid was loaded over a silica gel column
and chromatographed (ꢂ400 cm3 of a 1:1 mixture
(v/v) benzene/hexane (b.p. 40–60 ꢁC) was used as eluant)
to obtain the title compound 2 as a colourless solid after
evaporation of the eluant. Yield: 52%. Anal. Calc. for
C35H29P2NO4: C, 71.3; H, 4.9; N, 2.4. Found: C, 70.8;
H, 5.0; N, 2.0%. M.p.122–123 ꢁC. The NMR data for
(racemic)-(C20H12O2)PN(CHMe2)P(OC6H5)2 are given
here. 1H NMR (200 MHz, CDCl3): 4.32 (m, CH–
CHMe2); 1.61 (d, 3J(H,H) = 6.8 Hz, CH3–CHMe2);
1.45 (d, 3J(H,H) = 6.8 Hz, CH3–CHMe2). 31P{1H}
NMR (81.0 MHz, toluene): 156.4 (d, 2J(P,P) = 56.3
All reactions and manipulations were carried out un-
der an atmosphere of dry nitrogen using standard Sch-
lenk and vacuum-line techniques. The solvents were
purified by standard procedures [10] and distilled under
nitrogen prior to use. The synthesis of (racemic)-1,10-
binapthyl-2,20-diol [11] and its resolution [12] were
carried out as described in the literature. The chloro-
bridged allyl palladium dimers, [Pd(g3-1,3-Me2-
C3H3)(l-Cl)]2 [13] and [Pd(g3-1,3-Ph2-C3H3)(l-Cl)]2
[14] were prepared according to the literature proce-
dures. The NMR spectra were recorded at 25 ꢁC using
Bruker AMX-400 MHz and Bruker ACF-200 MHz
spectrometers. Chemical shifts downfield from the refer-
ence standard were assigned positive values. Optical
rotations were measured on a Jasco DIP-370 digital
polarimeter. Elemental analyses were carried out using
a Perkin–Elmer 2400 CHN analyser.
Hz); 136.2 (d). [a]D25 = ꢁ274.0ꢁ (c = 1.0, CH2Cl2) for
25
(R)-(C20H12O2) PN(CHMe2)P(OC6H5)2 and [a]D =
+231.0ꢁ (c = 1.0, CH2Cl2) for (S)-(C20H12O2)PN-
(CHMe2)P(OC6H5)2.
2.2. (Racemic, R or S)-(C20H12O2)PN(CHMe2)PPh2
(1)
The ligand, racemic-(C20H12O2)PN(CHMe2)PPh2 (1)
was prepared by a slight modification of the procedure
previously described [15]. The phosphoro chloridite (race-
mic)-(C20H12O2)PCl was prepared [16] by the reaction of
PCl3 with (racemic)-1,10-binaphthyl-2,20-diol in toluene
at ꢁ78 ꢁC in the presence of Et3N and was treated with
Ph2PNH(CHMe2) in toluene to obtain racemic –
(C20H12O2)PN(CHMe2)PPh2 (1) (yield 50%). In the same
way, (R or S)-(C20H12O2)PN(CHMe2)PPh2 was prepared
by starting from (R or S)-(C20H12O2)PCl. 31P{1H} NMR
2.4. (Racemic)-(C20H12O2)PN(CHMe2)P(OC6H4-4-Me)2
(3)
The ligand was prepared following the same procedure
as described for 2 using 4-methyl phenol (1.842 g, 0.02
mol). The title compound could not be isolated in a pure
form owing to its high sensitivity to air and moisture. 1H
NMR (200 MHz, CDCl3): 4.28 (m, CH–CHMe2); 2.34,
3
2.23 (s, CH3-OC6H4-4-Me); 1.57, 1.46 (d, J(H,H) = 6.4
Hz, CH3–CHMe2). 31P{1H} NMR (81.0 MHz, toluene):
158.4 (d, 2J(P,P) = 56.6 Hz); 137.2 (d).
2
(81.0 MHz, toluene): 28.5 (d, J(P,P) = 25.8 Hz); 148.3
(d). [a]D25 = ꢁ161.5ꢁ (c = 1.0, CH2Cl2) for (R)-
(C20H12O2)PN(CHMe2)PPh2
and
[a]D25 = +166.0ꢁ
(c = 1.0, CH2Cl2) for (S)-(C20H12O2) PN(CHMe2)PPh2.
2.5. (Racemic)-(C20H12O2)PN(CHMe2)P(OC6H4-4-OMe)2
(4)
2.3. (Racemic, R or S)-(C20H12O2)PN(CHMe2)P-
(OC6H5)2 (2)
The ligand was prepared following the same procedure
as described for 2 using 4-methoxy phenol (2.482 g, 0.02
mol). Yield: 54%. Anal. Calc. for C37H33P2NO6: C,
68.4; H, 5.1; N, 2.2. Found: C, 68.7; H, 5.1; N, 2.1%.
M.p. 121–122 ꢁC. H NMR (200 MHz, CDCl3): 4.23
(m, CH–CHMe2); 3.80, 3.71 (s, CH3-OC6H4-4-OMe);
A solution of (racemic, R or S)-(C20H12O2)PCl (0.01
mol) in 30 cm3 toluene was added drop-wise at 0 ꢁC to a
30 cm3 toluene solution of Me2CHNH2 (2.6 cm3, 0.03
mol). The reaction mixture was warmed to 25 ꢁC and
1

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S.K. Mandal et al. / Journal of Organometallic Chemistry 690 (2005) 742–750
1.56, 1.44 (d, 3J(H,H) = 6.9 Hz, CH3–CHMe2). 31P{1H}
NMR (81.0 MHz, toluene): 155.7 (d, 2J(P,P) = 64.5
Hz); 138.3 (d).
2.8. [Pd(g3-1,3-Ph2-C3H3){j2-(racemic)-(C20H12O2)-
PN(CHMe2)PPh2}](PF6) (7)
The title complex was prepared by the same procedure
as that for 6. Crystals suitable for X-ray crystallography
were grown from toluene/hexane (5:1 v/v) mixture. Yield:
78%. Anal. Calc. for C50H42F6P3O2NPd: C, 60.0; H, 4.2;
N, 1.4. Found: C, 60.6; H, 3.9; N, 1.2%. M.p. 193–195 ꢁC
dec. Major isomer 7a: 1H NMR (400 MHz, CDCl3): 6.41
2.6. (Racemic, R or S)-(C20H12O2)PN(CHMe2)P-
(OC6H4-4-tBu)2 (5)
The ligand was prepared following the same procedure
as described for 2 using 4-tert-butyl phenol (3.020 g, 0.02
mol). Yield: 55%. Anal. Calc. for C43H45P2NO4: C, 73.6;
H, 6.4; N, 2.0. Found: C, 73.5; H, 6.4; N, 1.8%. M.p.124–
125 ꢁC. The NMR data for (racemic)-(C20H12O2)PN(CH-
Me2)P(OC6H4-4-tBu)2 are presented here. 1H NMR (200
MHz, CDCl3): 4.28 (m, CH–CHMe2); 1.59 (d,
3J(H,H) = 7.0 Hz, CH3–CHMe2); 1.43 (d, 3J(H,H) = 6.8
Hz, CH3–CHMe2); 1.35 (s, CH3–tBu); 1.24 (s, CH3–tBu).
31P{1H} NMR (81.0 MHz, toluene): 155.9 (d,
2J(P,P) = 63.7 Hz); 136.4 (d). [a]D25 = ꢁ162.0ꢁ (c = 1.0,
CH2Cl2) for (R)-(C20H12O2)PN(CHMe2)P(OC6H4-
4-tBu)2 and [a]D25 = +146.0ꢁ (c = 1.0, CH2Cl2) for (S)-
(C20H12O2)PN(CHMe2)P(OC6H4-4-tBu)2.
(m, Hc); 5.85 (m, Ha); 5.75 (m, ðm; H0 Þ. 13C NMR (100.6
a
MHz, CDCl3): 114.9 (dd, 2J(P,C) = 17.4 and 9.7 Hz, cen-
tral allyl carbon); 93.2 (dd, 2J(P,C)trans = 28.3 Hz,
2J(P,C)cis = 16.5 Hz, terminal allyl carbon); 89.2 (dd,
2J(P,C)trans = 43.1 Hz, 2J(P,C)cis = 8.1 Hz, terminal allyl
carbon). 31P{1H} NMR (162.0 MHz, CDCl3): 57.9 (d,
2J(P,P) = 115.3 Hz); 110.7 (d). Minor isomer 7b: 1H
NMR (400 MHz, CDCl3): 6.95 (m, Hc); 5.59 (m, Ha);
5.17 ðm; H0aÞ. 13C NMR (100.6 MHz, CDCl3): 113.5
2
(dd, J(P,C) = 16.7 and 9.2 Hz, central allyl carbon);
96.0 (dd, 2J(P,C)trans = 27.5 Hz, 2J(P,C)cis = 17.1 Hz, ter-
minal allyl carbon); 86.8 (dd, 2J(P,C)trans = 43.2 Hz,
2J(P,C)cis = 8.0 Hz, terminal allyl carbon). 31P{1H}
NMR (162.0 MHz, CDCl3): 56.8 (d, 2J(P,P) = 122.1
Hz); 109.8 (d).
2.7. [Pd(g3-1,3-Me2-C3H3){j2-(racemic)-(C20H12O2)-
PN(CHMe2)PPh2}](PF6) (6)
A mixture of 0.042 g (0.99 · 10ꢁ4 mol) of [Pd(g3-1,3-
Me2-C3H3)(l-Cl)]2, 0.033 g (2.02 · 10ꢁ4 mol) of NH4PF6
and 0.115 g (2.06 · 10ꢁ4 mol) of (racemic)-(C20H12O2)
PN(CHMe2)PPh2 was dissolved in 20 cm3 of acetone.
The solution was stirred for 1 h at 25 ꢁC and the white
precipitate formed during the reaction was filtered off.
The resulting filtrate was concentrated under reduced
pressure to 10 cm3 and the solution was layered by add-
ing 10 cm3 of hexane (b.p. 40–60 ꢁC) to yield colourless
crystals. Yield: 90%. Anal. Calc. for C40H38F6P3O2NPd:
C, 53.4; H, 4.3; N, 1.6. Found: C, 55.2; H, 4.5; N, 1.5%.
2.9. [Pd(g3-1,3-Ph2-C3H3){j2-(racemic)-(C20H12O2)-
PN(CHMe2)P(OC6H5)2}](PF6) (8)
The title complex was prepared by the same proce-
dure described above for 6. Yield: 65%. Anal. Calc.
for C50H42F6P3O4NPd: C, 58.1; H, 4.1; N, 1.4. Found:
C, 58.0; H, 4.4; N, 1.2%. M.p. 170–172 ꢁC dec. Major
1
isomer 8a: H NMR (400 MHz, CDCl3): 6.24 (m, Hc);
5.52 ðm; Ha and H0 Þ. 13C NMR (100.6 MHz, CDCl3):
a
114.7 (t, J(P,C) = 15.4 Hz, central allyl carbon); 96.4
2
2
2
(dd, J(P,C)trans = 38.2 Hz, J(P,C)cis = 11.8 Hz, termi-
nal allyl carbon); 89.9 (dd, 2J(P,C)trans = 36.0 Hz,
2J(P,C)cis = 14.4 Hz, terminal allyl carbon). 31P{1H}
NMR (162.0 MHz, CDCl3): 110.8 (d, 2J(P,P) = 58.5
1
M.p. 165–167 ꢁC dec. Major isomer 6a: H NMR (400
MHz, CDCl3): 5.26 (t, 3J(H,H) = 11.8 Hz, Hc); 4.50
ðm; Ha and H0aÞ; 1.64 (m, CH3-allyl); 0.83 (m, CH3-al-
lyl). 13C NMR (100.6 MHz, CDCl3): 120.6 (br.d,
2J(P,C) = 12.5 Hz, central allyl carbon); 89.8 (dd,
1
Hz); 115.5 (d). Minor isomer 8b: H NMR (400 MHz,
CDCl3): 6.62 (m, Hc); 5.50 ðm; H0 Þ; 4.88 (m, Ha). 13C
a
2
2J(P,C)trans = 29.3 Hz, J(P,C)cis = 16.7 Hz, terminal al-
NMR (100.6 MHz, CDCl3): 113.0 (t, 2J(P,C) = 14.3
Hz, central allyl carbon); 95.6 (dd, 2J(P,C)trans = 32.9
Hz, 2J(P,C)cis = 14.4 Hz, terminal allyl carbon); 90.6
lyl carbon); 85.9 (dd, 2J(P,C)trans = 47.3 Hz,
2J(P,C)cis = 8.4 Hz, terminal allyl carbon); 18.7 (br.s,
CH3-allyl); 18.5 (br.s, CH3-allyl). 31P{1H} NMR (162.0
2
2
(dd, J(P,C)trans = 39.8 Hz, J(P,C)cis = 13.8 Hz, termi-
nal allyl carbon). 31P{1H} NMR (162.0 MHz, CDCl3):
2
MHz, CDCl3): 59.0 (d, J(P,P) = 64.6 Hz); 113.4 (d).
1
Minor isomer 6b: H NMR (400 MHz, CDCl3): 5.93 (t,
2
110.5 (d, J(P,P) = 66.9 Hz); 114.9 (d).
3J(H,H) = 12.0 Hz, Hc); 4.10 (m, Ha); 3.94 ðm; H0 Þ;
a
1.75 (m, CH3-allyl); 1.30 (m, CH3-allyl). 13C NMR
(100.6 MHz, CDCl3): 121.8 (br.d, 2J(P,C) = 14.0 Hz,
central allyl carbon); 92.2 (dd, 2J(P,C)trans = 29.1 Hz,
2J(P,C)cis = 17.0 Hz, terminal allyl carbon); 84.1 (dd,
2J(P,C)trans = 46.5 Hz, 2J(P,C)cis = 8.2 Hz, terminal allyl
carbon); 19.1 (br.s, CH3-allyl); 18.8 (br.s, CH3-allyl).
31P{1H} NMR (162.0 MHz, CDCl3): 57.7 (d,
2J(P,P) = 58.1 Hz); 114.2 (d).
2.10. General procedure for palladium-catalysed allylic
alkylation
The ligand (2.5 mol%) and [Pd(g3-C3H5)(l-Cl)]2 (1
mol%) were dissolved in 4 cm3 of degassed (by three
freeze, pump and thaw cycles) CH2Cl2. A solution of
(racemic)-1,3-diphenyl-2-propenyl acetate (I) (1 · 10ꢁ3
mol), in 2 cm3 CH2Cl2, was added followed by dimethyl

S.K. Mandal et al. / Journal of Organometallic Chemistry 690 (2005) 742–750
745
malonate (2 · 10ꢁ3 mol), N,O-bis(trimethylsilyl)aceta-
least squares methods against F2
(SHELXL-97) [22].
mide (2 · 10ꢁ3 mol) and a catalytic amount (2 mol%)
of KOAc. The mixture was stirred at 25 ꢁC for 24 h
and the reaction was monitored by TLC. A saturated
aqueous solution of NH4Cl (10 cm3) was added to the
reaction mixture and the organic part was extracted with
diethyl ether (10 · 3 cm3). The ether extract was filtered
over activated celite, washed with water (3 · 10 cm3) and
dried over anhydrous Na2SO4. Solvent was removed
from the ether extract under reduced pressure and the
crude product was purified by column chromatography
over silica gel [eluant: hexane/ethyl acetate, 9:1 (v/v)].
The optical rotation was measured for the product,
PhCH@CHACHPh{CH(CO2Me)2} (II) and the enan-
tiomeric excess (ee) was calculated from the optical rota-
tion value using the literature data [17].
All non-hydrogen atoms were refined with anisotropic
displacement parameters. All hydrogen atoms were as-
signed ideal positions and refined using a riding model
with Uiso constrained to 1.2 times the Ueq value of
the parent C(sp2) atom and 1.5 times the Ueq value
of the parent C(sp3) atom, respectively. The disorder
of the hexafluorophosphate moiety was refined using
distance and similarity restraints.
3. Results and discussion
3.1. Synthesis of ligands
The optically pure unsymmetrical diphosphazane lig-
and, (R or S)-(C20H12O2)PN(CHMe2)PPh2 (1) has been
prepared following the procedure adopted previously
for the synthesis of (racemic)-(C20H12O2)PN(CHMe2)-
PPh2 [15] by the reaction of the aminophosphane,
Ph2PNH(CHMe2) with 1,10-binaphthyl-2,20phosphoro
chloridite, (R or S)-(C20H12O2)PCl in the presence of
Et3N (Scheme 1). Unsymmetrical diphosphazane lig-
ands of the general formula, (racemic)-(C20H12O2)PN
(CHMe2)PY2 [Y = OC6H5 (2), OC6H4-4-Me (3),
OC6H4-4-OMe (4) or OC6H4-4-tBu (5)] have been pre-
pared as shown in Scheme 1. The reaction of (race-
mic)-(C20H12O2)PCl with Me2CHNH2 in toluene gives
2.11. X-ray crystallography
Crystal data for 7a were collected from shock-
cooled, oil coated crystals on a BRUKER-APEX
diffractometer with
a
D8 goniometer (graphite-
˚
monochromated Mo Ka radiation, k = 0.71073A)
equipped with a low temperature device in omega-scan
mode at 173(2)K [18]. The data was integrated with
SAINT [19] and an empirical absorption correction
was applied [20]. The structure was solved by direct
methods (SHELXS-97) [21] and refined by full-matrix
CHMe2
NH
O
O
(ii)
P
P
Cl
O
O
(i)
(iii)
CHMe2
N
CHMe2
N
Cl
Cl
O
O
O
O
P
P
P
P
1
(iv)
CHMe2
N
2; Y = OC6H5
Y
Y
O
O
3; Y = OC6H4-4-Me
4; Y = OC6H4-4-OMe
5; Y = OC6H4-4-tBu
P
P
(i) Ph2PNH(CHMe2), Et3N, toluene, 12 h; (ii) Me2CHNH2, toluene, 6 h;
(iii) PCl3, Et3N, toluene, 12 h; (iv) YH, Et3N, toluene, 12 h.
Scheme 1.

746
S.K. Mandal et al. / Journal of Organometallic Chemistry 690 (2005) 742–750
the amino derivative, (racemic)-(C20H12O2)PNH-
(CHMe2) which is treated with PCl3 in the presence of
Et3N to yield (racemic)-(C20H12O2)PN(CHMe2)PCl2.
Subsequent derivatisation with various phenols gives
the unsymmetrically substituted diphosphazane ligands
2–5.
The ligands 1–5 are characterized by 1H and 31P{1H}
NMR spectra. The 31P{1H} NMR spectra display an
AX pattern; the doublet in the range 148–159 ppm is as-
signed to the –P(O2C20H12) phosphorus nucleus in these
ligands. The resonance at 28.5 ppm is assigned to the –
PPh2 phosphorus nucleus in ligand 1. The PY2 phospho-
rus in ligands 2–5 resonates as a doublet in the range
136–139 ppm.
terminal allyl carbon resonances appear as doublet of
doublets owing to coupling with the two different phos-
phorus nuclei present in the molecule. The terminal allyl
carbon resonance trans to ꢁP(O2C20H12) gives rise to a
signal at 89.8–96.4 ppm for these isomers. The other ter-
minal allyl carbon at the trans position with respect to
the ꢁPY2 (Y = C6H5 or OC6H5) group resonates at
84.1–90.6 ppm.
Three different allylic arrangements (syn/syn-, syn/
anti-, and anti/anti-) are possible for the 1,3-disubstituted
allyl complexes (6–8), depending on the orientation of the
two substituents (Me or Ph) with respect to the central al-
lyl proton Hc [7b]. In addition, diastereomers can arise
owing to different face coordination of the allyl moiety
with the palladium centre [7c]. We performed detailed
1
3.2. Reactions of 1 and 2 with chloro-bridged allyl
palladium dimers
two-dimensional NMR studies (1Hꢁ H DQF COSY,
1
1H–1H NOESY and H–1H ROESY) to ascertain the
allylic arrangement in these complexes and their struc-
tures in solution. The COSY experiment clearly shows
that the minor isomer 6b contains two anti allylic protons
at 3.94 ppm ðH0aÞ and 4.10 ppm (Ha) which are strongly
coupled (3J (H,H) = 12.0 Hz which is typical for anti cou-
pling) to the central allyl proton indicating that the two
allyl methyl groups are situated in a syn position with re-
spect to the central allyl proton Hc. For the major isomer
6a, the resonances of the allylic protons Ha and H0a over-
lap with each other at 4.50 ppm thus making their struc-
tural assignment difficult from the COSY spectrum.
The cationic g3-allyl palladium complexes 6–8 have
been prepared by the treatment of the chlorodimer,
½Pdðg3 ꢁ 1; 3 ꢁ R02 ꢁ C3H3Þðl ꢁ ClÞꢀ (R0 = Me or Ph)
2
with the appropriate diphosphazane ligand, (racemic)-
(C20H12O2)PN(CHMe2)PY2
[Y = C6H5
(1)
or
Y = OC6H5 (2)] in the presence of NH4PF6 as shown
in Scheme 2. The 31P{1H} NMR spectra of these com-
plexes reveal the presence of two diastereomers in solu-
tion; two sets of AX patterns are observed in each case.
The –PPh2 phosphorus chemical shifts (56.8–59.0 ppm)
lie very much down field as compared to that of the free
ligand (1) and the magnitude of the coordination shift
Dd [Dd = d (complex)ꢁd (free ligand)] is in the range
28.3–30.5 ppm. On the other hand, the phosphonite
phosphorus [ꢁP(OC6H5)2 or ꢁP(O2C20H12)] chemical
shifts (109.8–114.2 ppm) lie up-field as compared to
the free ligands (1 and 2); the Dd values are in the range
ꢁ25.4 to ꢁ41.5 ppm. The 13C NMR spectra of 6–8 also
indicate the presence of two diastereomers; two sets of
allyl 13C resonances are observed in each case. The cen-
tral allyl carbon resonance for the two diastereomers ap-
pears as two separate signals at 113.0–121.8 ppm. The
1
However, the H–1H NOESY spectrum unequivocally
establishes a syn/syn- arrangement of the two allyl methyl
groups in the major isomer 6a. The 1H–1H NOESY spec-
trum shows two strong cross-peaks arising from the cen-
tral allyl proton Hc to both the allyl-methyl protons in the
isomer 6a and 6b supporting their syn/syn- allylic
1
arrangements. The H–1H NOESY spectrum shows an
NOE contact between the H0a and ortho phenyl proton
on the –PPh2 group for the major isomer 6a but no such
NOE contact is observed for the minor isomer 6b. On the
basis of this observation, the two isomers are formulated
as shown in Fig. 1. The diastereomers arise because of dif-
CHMe2
+
N
O
O
Y
PF6
(i)
[Pd(η3-1,3-R’2-C3H3)(µ-Cl)]2
P
P
Y
Pd
Ha
Ha'
R'
R'
Hc
(i) (racemic)-(C20H12O2)PN(CHMe2)PY2,
6; R' = Me, Y = C6H5
7; R' = Ph, Y = C6H5
8; R' = Ph, Y = OC6H5
NH4PF6, acetone, 1 h
Scheme 2.

S.K. Mandal et al. / Journal of Organometallic Chemistry 690 (2005) 742–750
747
CHMe2
The reaction of the diphosphonite diphosphazane lig-
and, (racemic)-(C20H12O2)PN(CHMe2)P(OC6H5)2 with
the 1,3-dimethyl-allyl dimer, [Pd(g3-1,3-Me2-C3H3)(l-
Cl)]2 yields a light yellow complex which turns into a
black mass over a period of few hours. By contrast,
the reaction of the same ligand with the 1,3-diphenyl-al-
lyl dimer, [Pd(g3-1,3-Ph2-C3H3)(l-Cl)]2 gives an allyl
complex, [Pd(g3-1,3-Ph2-C3H3){j2-(racemic)-(C20H12-
O2)PN(CHMe2)P(OC6H5)2}](PF6) (8), which is stable
to air and moisture. The stability of 8 is presumably
due to mesomeric electron release from the phenyl
groups into the allyl moiety. NMR spectroscopic data
reveal that 8 exists as a mixture of two isomers (8a,
8b) in solution in the ratio 6:1 and their structures are
similar to those of 6a/6b and 7a/7b (Fig. 1).
CHMe2
+
+
N
N
O
O
O
O
P
PF6
P
PF6
P
Hb
R'
P
Pd
Pd
Hb
Ha
Ha'
Hc
Ha
R'
R'
R'
Ha'
Hc
6b; R' = Me
7b; R' = Ph
6a; R' = Me
7a; R' = Ph
Fig. 1. The two diastereomers of 1,3-disubstituted allyl palladium
complex, ½Pdðg3-1; 3-R20 -C3H3Þfj2-ðracemicÞ-ðC20H12O2ÞPNðCHMe2Þ
PPh2gꢀðPF6Þ [R0 = Me (6) or Ph (7)] observed in solution.
ferent allyl face coordination to the palladium centre as
we have observed in our previous studies [7c]. Similar re-
sults are obtained for the 1,3-diphenyl-allyl complex 7,
which exists as a mixture of two diastereomers in the ratio
8:1 as revealed by its 31P{1H} NMR spectrum. The
3.3. Solid state structure of [Pd(g3-1,3-Ph2-C3H3){j2-
(racemic)-(C20H12O2)PN(CHMe2)PPh2}](PF6) (7a)
1Hꢁ H COSY spectrum suggests syn/syn- allylic arrange-
1
ment in both the diastereomers of 7. The 1H–1H NOESY
spectrum of 7 (shown in Fig. 2) displays a selective cross-
peak between the anti allyl proton H0a and ortho-phenyl
proton (Hb) of the –PPh2 group for the major diastereo-
mer 7a; for the minor diastereomer 7b no such NOE con-
tact between H0a and ortho-phenyl proton of the –PPh2
group is observed. The reaction of optically pure
diphosphazane ligand, (R or S)-(C20H12O2)PN(CH-
Me2)PPh2 with the 1,3-diphenyl-allyl dimer, [Pd(g3-1,3-
Ph2-C3H3)(l-Cl)]2 also results in two isomers whose
NMR spectra are identical to the diastereomers (7a and
7b) obtained with (racemic)-(C20H12O2)PN(CHMe2)-
PPh2.
A crystallographic study has been carried out for the
complex 7a. The details of the crystal data are presented
in Table 1. The solid state structure consists of only the
major isomer 7a as shown in Fig. 3. The molecule crys-
tallises with one molecule of solvent toluene in the unit
cell. The two terminal Pd–C(allyl) bond distances trans
to –PPh2 and trans to –P(O2C20H12) are 2.220(3) and
˚
2.183(3) A, respectively, which fall within the range of
the terminal Pd–C(alllyl) bond distances observed for
other structurally characterised allyl palladium com-
plexes bearing a bidentate phosphorus ligand [23]. The
geometry around palladium is distorted square planar.
The P(1)–Pd(1)–P(2) bond angle is 70.4(1)0 which
Fig. 2. The 1H–1H NOESY (400 MHz, CDCl3) spectrum of [Pd(g3-1,3-Ph2-C3H3) {j2-(racemic)-(C20H12O2)PN(CHMe2)PPh2}](PF6) (7) displaying
selective NOE cross-peak between H0a and the ortho-phenyl proton (Hb) on the –PPh2 group in the major diastereomer 7a.

748
S.K. Mandal et al. / Journal of Organometallic Chemistry 690 (2005) 742–750
P(2); the two planes are inclined at an angle of 62.10.
The structure can be best described as shown below:
Table 1
Crystal data and structure refinement for [Pd(g3-1,3-Ph2-C3H3){j2-
(racemic)-(C20H12O2)PN(CHMe2)PPh2}](PF6) (7a)
Identification code
Empirical formula
Formula weight
Temperature (K)
7a
C50H42F6P3O2NPd + 0.59 C7H8
2.78 Å
1056.12
173(2)
0.71073
Monoclinic
P21/n
H(62)
H(1)
˚
Wavelength (A)
C(3)
C(1)
Crystal system
Space group
Unit cell dimensions
P(1)
Pd(1)
C(2)
P(2)
˚
a (A)
12.9498(11)
28.617(2)
13.0417(11)
93.3430(10)
4824.8(7)
4
˚
b (A)
˚
c (A)
b (ꢁ)
The P(1)–Pd(1)–P(2) plane is considered as the refer-
ence plane for this description. The central allyl carbon
lies below this plane and the two terminal allyl carbon
C(1) and C(3) lie above with respect to such a plane.
The phenyl groups on the –PPh2 groups are not symmet-
rically placed with respect to the coordination plane
formed by P(1)–Pd(1)–P(2). The ortho-phenyl proton
H(62) on one of these phenyl groups is close to the anti
allylic proton H(1). From X-ray data, the estimated dis-
3
˚
Volume (A )
Z
Density (calculated) (mg/m3)
Absorption coefficient (mmꢁ1
F(000)
1.454
0.550
)
2157
0.40 · 0.35 · 0.05
Crystal size (mm3)
Theta range for data collection (ꢁ) 1.42–26.44
Index ranges
ꢁ16<=h<=16,
0<=k<=35,
0<=l<=16
˚
tance between H(62) and H(1) is 2.78 A. This short dis-
tance is reflected in the NOE interaction between these
protons in the major isomer 7a.
Reflections collected
51,332
10,063 [Rint = 0.0348]
98.6%
Full-matrix least-squares on F2
10063/282/522
1.077
Independent reflections
Completeness to theta = 26.44ꢁ
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
3.4. Catalytic allylic alkylation reactions
R1 = 0.0417, wR2 = 0.1004
R1 = 0.0500, wR2 = 0.1051
1.834 and ꢁ0.646
The catalytic activity of the chiral diphosphazane lig-
ands 1 and 2 has been tested in allylic alkylation reac-
tions of the symmetrically substituted substrate,
(racemic)-1,3-diphenyl-2-propenyl acetate (I) (Scheme
3) using dimethyl malonate anion as the nucleophile.
The reaction is found to be complete within 24 h as
Largest diffꢁer3ent peak and
˚
hole (eA
)
1
shown by the H NMR spectrum of the reaction mix-
ture. The enantiomeric excess (ee) values and the config-
uration of the alkylated product are listed in Table 2.
These ‘‘P–N–P’’ ligands give rise to only moderate levels
of asymmetric induction. The ee values do not reflect the
diastereomeric ratio observed for the two isomers of the
g3-1,3-diphenyl allyl palladium complexes, 7 and 8 (8:1
and 6:1 respectively), presumably because attack trans
to the two different phosphorus atoms would lead to dif-
ferent product configurations.
Fig. 3. The molecular structure of [Pd(g3-1,3-Ph2-C3H3){j2-(racemic)-
(C20H12O2)PN(CHMe2)PPh2}] (7a) in the solid state; hexafluorophos-
phate, lattice held toluene and hydrogen atoms [except H(1), H(2),
H(3) and H(62)] are omitted for the sake of clarity.
CH(COOMe)2
Ph
OAc
Ph
COOMe
COOMe
[Pd/L*]
H2C
+
Ph
BSA, KOAc
Ph
CH2Cl2, 25 0C
II
I
L*= chiral diphosphazane ligand
deviates very much from the ideal value. The allyl plane
formed by C(1), C(2) and C(3) atoms is not coplanar
with the coordination plane formed by P(1)–Pd(1)–
BSA = N,O-bis(trimethylsilyl)acetamide
Scheme 3.

S.K. Mandal et al. / Journal of Organometallic Chemistry 690 (2005) 742–750
749
Table 2
Results of catalytic allylic alkylation reactions of a symmetrically substituted substrate (racemic)-1,3-diphenyl-2-propenyl acetate using chiral
diphosphazane ligands
Entry
Diphosphazane ligand (L*)
Enantiomeric excessa (%)
Absolute configuration
(1)
(2)
(3)
(4)
a
(R)-(C20H12O2)PN(CHMe2)PPh2
(S)-(C20H12O2)PN(CHMe2)PPh2
(R)-(C20H12O2)PN(CHMe2)P(OC6H5)2
(S)-(C20H12O2)PN(CHMe2)P(OC6H5)2
44
40
27
20
S
R
S
S
The enantiomeric excess (ee) is calculated from the optical rotation value using the literature data [17]; the values are accurate to 5%.
(b) M. Witt, H.W. Roesky, Chem. Rev. 94 (1994) 1163;
4. Conclusions
(c) P. Bhattacharyya, J.D. Woollins, Polyhedron 14 (1995) 3367.
[3] (a) N.C. Payne, D.W. Stephan, J. Organomet. Chem. 221 (1981)
203;
A facile synthetic route for chiral and unsymmetri-
cal bidentate phosphorus ligands based on the ‘‘P–N–
P’’ motif and bearing 1,10-binaphthyl-2,20-dioxy moiety
has been developed. The reactivity of some of these
ligands towards g3-allyl palladium dimers has been
investigated. The structures of g3-allyl palladium com-
plexes have been probed by two-dimensional NMR
techniques and X-ray crystal structure analysis. These
chiral phosphorus ligands and their transition metal
complexes would be potentially useful in enantioselec-
tive catalysis.
(b) R.P.K. Babu, S.S. Krishnamurthy, M. Nethaji, Tetrahedron:
Asymmetry 6 (1995) 427.
´
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`
(b) G. Calabro, D. Drommi, G. Bruno, F. Faraone, Dalton
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[6] (a) K. Raghuraman, S.K. Mandal, T.S. Venkatakrishnan, S.S.
Krishnamurthy, M. Nethaji, Proc. Indian Acad. Sci. (Chem. Sci.)
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5. Supplementary material
(c) K. Raghuraman, S.S. Krishnamurthy, M. Nethaji, J. Organ-
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Crystallographic data (excluding structure factors)
for the structure reported in this paper have been depos-
ited with the Cambridge Crystallographic Data Centre
as supplementary publication no. CCDC-230791. Cop-
ies of the data can be obtained free of charge on appli-
cation to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [fax: (internat.) +44(1223)336-033; e-mail:
deposit@ccdc.cam.ac.uk].
(d) T.S. Venkatakrishnan, M. Nethaji, S.S. Krishnamurthy, Curr.
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(c) S.K. Mandal, G.A.N. Gowda, S.S. Krishnamurthy, C. Zheng,
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Acknowledgements
(c) R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley,
New York, 1994, p. 82.
We thank the Department of Science and Technology
(DST), New Delhi, India for financial support (SKM,
GAN and SSK). Continuous financial support from
the Deutsche Forschungsgemeinschaft, Germany is
acknowledged (TS, DS).
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