A palladium(II) complex with a chelating (carboxy) phosphanoalkyl ligand

Article abstract of DOI:10.1016/j.inoche.2003.12.028

rac-[SP-4-2]-{2-[(dimethylamino-κN)methyl]phenyl-κC ¹}{[2-(diphenylphosphanyl-κP)ferrocenyl](methoxycarbonyl) methyl-κC}palladium(II) (1) was synthesized by deprotonation of [SP-4-4]-chloro{2-[(dimethylamino-κN)methyl]phenyl-κC ¹}{rac-methyl 2-(diphenylphosphanyl)ferrocenylacetate-κP} palladium(II) with t-BuOK. Complex 1 was characterized by spectral methods and its reactivity studied. The structure of 1 was determined by X-ray crystallography and discussed in relation to other complexes with phosphanoalkyl ligands derived from phosphanoacetic esters.

Full text of DOI:10.1016/j.inoche.2003.12.028

Inorganic Chemistry Communications 7 (2004) 426–430
www.elsevier.com/locate/inoche
A palladium(II) complex with a chelating
(carboxy) phosphanoalkyl ligand
ꢀ
Petr Stepnicka
ꢀ
ꢀ
Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, Prague 2 12840, Czech Republic
Received 13 November 2003; accepted 3 December 2003
Published online: 4 February 2004
Abstract
rac-[SP-4-2]-{2-[(dimethylamino-jN)methyl]phenyl-jC1}{[2-(diphenylphosphanyl-jP)ferrocenyl](methoxycarbonyl)methyl-jC}
palladium(II) (1) was synthesized by deprotonation of [SP-4-4]-chloro{2-[(dimethylamino-jN)methyl]phenyl-jC1}{rac-methyl 2-
(diphenylphosphanyl)ferrocenylacetate-jP}palladium(II) with t-BuOK. Complex 1 was characterized by spectral methods and its
reactivity studied. The structure of 1 was determined by X-ray crystallography and discussed in relation to other complexes with
phosphanoalkyl ligands derived from phosphanoacetic esters.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Palladium; Phosphinoester ligands; Alkyl complexes; Ferrocene; X-ray crystallography
Indroduction
there is a direct relation between these novel organo-
metallic ligands and the respective (diphenylphosp-
hano)acetic acid derivatives, we have turned, in view of
the above results, to study the reactivity of C-deproto-
nated ferrocene phosphanoester.
Phosphanoalkyl ligands obtained from phosphano-
carboxylic ligands often shown interesting coordination
behaviour. It has been shown that anions resulting from
a deprotonation of phosphanoacetic esters ([R12PCH
CO2R2]ꢀ) can coordinate as chelating enolate (A [1], B
[2]) or phosphanomethanide(1)) (C, [2,3]) ligands.
These two modes are mutually intercovertible [2] and
can even coexist in one molecule (D) [4]. Besides, the
anion [Ph2PCHCO2Et]ꢀ is capable of acting as a l-
1jP:2jC1 bridge between two palladium(II) atoms
bearing additional ortho-metallated ligands, the respec-
tive bridged dinuclear complex being accessible from A-
type compounds [1,5]. Complexes A–D react willingly
with polar molecules, affording various insertion and
addition products (Chart 1).
Ph Ph
P
Ru
Cl
i-Pr P
2
Pd
O
N
O
OMe
OMe
A
B
We have recently reported about the synthesis of rac-
[2-(diphenylphosphano)ferrocenyl]acetic acid and coor-
dination chemistry of this acid and its methyl ester in a
series of palladium(II) complexes with ortho-metallated
N,N-dimethylbenzylamine as an auxiliary ligand [6]. As
Ru
Ru
C
H
Cl
H
O
i-Pr P
2
P
C
CO Me
2
CO Me
2
MeO
i-Pr
C
D
ꢀ
E-mail address: stepnic@mail.natur.cuni.cz (P. Stepnicka).
ꢀ
ꢀ
Chart 1.
1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.12.028

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P. Stꢀepniꢀcka / Inorganic Chemistry Communications 7 (2004) 426–430
427
Of the two general approaches, i.e., pre-formation of
a phosphanomethanide anion followed by the reaction
with a transition metal compound [1,5] or a deproto-
nation of an already coordinated ligand [2–4], the latter
one was chosen. Thus, a reaction of complex 4 with
excess potassium tert-butoxide in tetrahydrofuran fol-
lowed by crystallization from dichloromethane–hexane
afforded bis-chelate compound 1 (see Scheme 1) as a
rusty-orange, crystalline solid, which is well soluble in
THF and halogenated solvents. The same compound
was obtained using sodium hydride as the base or when
complex 4 was formed in situ by reacting stoichiometric
amounts of the precursors 2 and 3 [6].
of the unchanged starting material whereas a reactions
with iodine or HBF4 (both ca. 1 equiv.) gave only in-
tractable mixtures.
The molecular structure of 1 was determined by
single-crystal X-ray diffraction and is shown on Fig. 1.
The selected geometric data are given in Table 1. The
coordination sphere around palladium is almost per-
fectly planar [the maximum deviation from the least-
NMR spectra of 1 show characteristic signals due to
the palladium-bonded methine group [dH 3.26 (s), dC
41.28 (d, JPC ¼ 4 Hz)] and phosphorus coupling patterns
C27
C33
C32
C26
N
3
(4JPH [1,6,7] and JPC [6]) typical for a trans-P,N ar-
C25
rangement. 31P NMR spectrum displays a singulet at
dP þ 41:5, significantly downfield compared to the par-
ent complex 4 (dP 28.0, [6]). Another characteristic fea-
ture of 1 is a strong mC@O band in IR spectra at 1652
cmꢀ1, shifted by ca. 80 cmꢀ1 to lower energies from the
position observed for 3 and 4 [6]. The shift corresponds
well to the trends in the series [Ru(g6-1,3,5-Me3C6H3)
RuCl2(i-Pr2PCH2CO2Me-jP)] (mC@O 1719 cmꢀ1), B
(mC@O=C@C 1524 cmꢀ1) and C (mC@O 1661 cmꢀ1) [2b].
Compared to the related compounds mentioned
above, complex 1 is chemically very robust. It remains
unchanged when stored in air for several weeks. The
complex does not react with CO2 but slowly decomposes
to metallic palladium when exposed to CO (in CH2Cl2
at room temperature and 1 atm). Attempted insertion
reactions with internal alkynes [MeO2CCBCCO2Me (1
or 3 equiv.), PhCBCPh (1 equiv.) or EtCBCEt (3
equiv.); in CH2Cl2 at 50 °C for 20 h] lead to a recovery
C34
Pd
C14
C19
O2
C13
O1
C12
P
C20
C11
C2
C1
Fe
C7
C6
Fig. 1. A perspective view of the molecular structure of 1 showing the
atom labelling scheme. Thermal motion ellipsoids are drawn at the
30% probability level.
PPh
2
Cl
N
CO Me
2
Pd
Pd
+
Fe
N
Cl
2
3
Ph
MeO C
2
Ph
Cl
Ph
Ph
P
P
Pd
Pd
KOt-Bu
N
Fe
N
Fe
CO Me
2
- t-BuOH, - KCl
1
4
Scheme 1.

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428
P. Stꢀepniꢀcka / Inorganic Chemistry Communications 7 (2004) 426–430
Table 1
a
ꢁ
The selected geometric data for 1 (in A and °)
Pd–P
Pd–N
2.2318(6)
2.167(2)
2.208(2)
2.054(2)
P–Pd–C(11)
P–Pd–C(26)
N–Pd–C(11)
N–Pd–C(26)
86.11(6)
96.27(6)
96.66(7)
81.06(7)
PdC(11)
Pd–C(26)
P–C(2)
P–C(13)
P–C(19)
1.794(2)
1.825(2)
1.825(2)
1.223(3)
1.367(3)
1.436(3)
1.503(3)
1.456(3)
C–P–Cb
101.82(9)–108.99(9)
114.1(2)
126.8(2)
C(1)–C(11)–C(12)
C(11)–C(12)–O(1)
C(11)–C(12)–O(2)
O(1)–C(11)–O(2)
C(12)–O(2)–C(25)
Pd–C(11)–C(12)
C(12)–O(1)
C(12)–O(2)
O(2)–C(25)
C(1)–C(11)
C(11)–C(12)
113.1(2)
120.1(2)
115.4(2)
102.5(1)
Fe–Cg1
Fe–Cg2
1.6464(9)
1.655(1)
Cg1–Fe–Cg2
177.90(5)
a Plane definitions: Cp1: C(1–5); Cp2: C(6–10); Ar: C(26–31); Ph1: C(13–18); Ph2: C(19–24). Cg1 and Cg2 are the centroids of the cyclopentadienyl
rings Cp1 and Cp2, respectively.
b The range of C(2)–P–C(13,19), C(13)–P–C(19) angles.
squares plane defined by palladium and the four
ꢁ
ligating atoms is 0.049(2) A for N] with a trans-P–N
group, which is disposed above the coordination plane.
This supports the formulation of 1 as a compound with
simple phosphane-modified alkyl ligand, related to C-
type complexes.
In summary, complex 1 represents a new entry among
complexes with functionalized organyl ligands. Notably,
its is available in a stereodefined form since racemic 4 (or
3) gives (S,Rp)/(R,Sp)-1 as the only diastereoisomer
detected by NMR spectra. Further studies on the
reactivity of 1 and the carboxy(phosphanoferrocenyl)
methanide anion are currently underway.
geometry. The Pd-donor distances compare well to
similar, structurally characterized compounds [SP-4-2]-
{2-[(dimethylamino)methyl]phenyl-j2C1,N}[{1,1,2,2-tet-
racyano-3-ethoxycarbonyl-4-(diphenylphosphanyl)but-
1-yl-j2C1,P}]palladium(II) [8] and [SP-4-2]-{(R)-2-[1-
(dimethylamino)ethyl]phenyl-j2C1,N}(3-diphenylphos-
phanyl-2-diphenylphosphonia-1-methoxycarbonylprop-
1-yl-j2C1,P3)palladium(II) perchlorate [9] (in square
brackets for the latter compound): Pd–P 2.221(2)
[2.245], Pd–N 2.159(7) [2.150], Pd–C(aryl) 2.027(9)
ꢁ
[1.970] and Pd–C(alkyl) 2.211(8) [2.171] A.
The palladium atom in 1 is a part of two five-
membered metallacycles with similar chelate bite an-
gles: P–Pd–C11 86.11(6) and N–Pd–C26 81.06(7)°. The
ring of the (aminomethyl)phenyl ligand is twisted with
a conformation between an envelope and a half-chair,
having the aryl ring rotated from the coordination
plane by as much as 18.57(8)° along the C26–C29 axis.
The other ring involving the phosphinoferrocenyl li-
gand is planar due to the rigidity of the conjugated
ferrocene unit [the maximum displacement from the
Experimental
Materials and methods
The syntheses were carried under argon atmosphere
with an exclusion of the direct day light. Tetrahydrofuran
was dried over potassium and freshly distilled from po-
tassium-benzophenone ketyl under argon. Dichlorome-
thane was dried over potassium carbonate. Hexane for
crystallizations was used without purifica- tion. Di-l-
chlorobis{2-(dimethylaminomethyl-jN)phenyl-jC1}dipal-
ladium(II) (2) [10], rac-methyl [2-(diphenylphosphanyl)
ferrocenyl]acetate (3) and [SP-4-4]-chl oro{2-[(dimethyla-
mino-jN)methyl]phenyl-jC1}{rac-methyl [2-(diphenyl-
phosphanyl)ferrocenyl]acetate-jP}palladium(II) (4) [6]
were prepared as described previously.
ꢁ
ring plane is 0.053(2) A for C11] and nearly coincides
with the coordination plane (dihedral angle 4.32(6)°). A
comparison with the structure of 4 [6] indicates that the
deprotonation/coordination of P-bonded ester does not
alter the ligand structure in any significant way (cf.
relative bond length changes vs. 4: Pd–P )2%, Pd–N
+0.7%, Pd–C26 +2%, C1–C11 +0.7%, C11–C12 )3%,
C12–O1 +1%, C12–O2 +2%, O2–C25 )1%). The
phosphanoalkyl ligand is bonded without a torsion at
the ferrocene unit (cf. s(C11–C1–C2–P) of only 0.2(3)°)
and any significant contribution of a resonance enol
form as indicated by tetrahedral arrangement around
C11 and unchanged geometry of the methoxycarbonyl
NMR spectra were recorded on a Varian UNITY
Inova 400 spectrometer (1H, 399.95; 13C, 100.58; 31P,
161.90 MHz) at 298 K. Chemical shifts (d/ppm) are gi-
ven relative to an internal tetramethylsilane (1H and
13C) or an external 85% aqueous H3PO4 (31P). IR
spectra were recorded on an FT IR Nicolet Magna 650
instrument in the range of 400–4000 cmꢀ1
.

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P. Stꢀepniꢀcka / Inorganic Chemistry Communications 7 (2004) 426–430
429
Synthesis of rac-[SP-4-2]-{2-[(dimethylamino-jN)methyl]
X-ray crystallography
phenyl-j1C}{[2-(diphenylphosphanyl-jP)ferrocenyl](meth-
oxycarbonyl)methyl-jC}palladium(II) (1)
Crystallographic data for 1: C34H34FeNO2PPd
(M ¼ 681:84 g molꢀ1), orange block, 0.43 ꢂ 0.43 ꢂ 0.45
3
ꢂ
Di-l-chlorobis{2-(dimethylaminomethyl-jN)phenyl-
jC1}dipalladium(II) (2) (276 mg, 0.50 mmol) and
rac-methyl [2-(diphenylphosphanyl)ferrocenyl]acetate
(3) (443 mg, 1.0 mmol) were dissolved in THF (30 mL).
The resulting, clear orange solution was stirred for 30
min. Potassium tert-butoxide (337 mg, 3.0 mmol) was
added and the mixture was stirred for 24 h. Then, the
solvent was removed under reduced pressure and the
solid residue extracted into dichloromethane-hexane
(1:1, v/v; 50 mL in several portions). The extract was
filtered, evaporated to dryness, redissolved in dichlo-
romethane, and re-crystallized by a careful addition of
hexane and crystallization by liquid-phase diffusion over
several days at room temperature to give solvate 1 ꢁ 1/
2CH2Cl2 as a rusty orange crystalline solid (427 mg,
59%; two crops).
mm ; triclinic, space group P1 (no. 2), T ¼ 150 K,
ꢁ
ꢁ
ꢁ
a ¼ 9:5707ð2Þ A, b ¼ 10:6603ð2Þ A, c ¼ 16:1091ð3Þ A;
a ¼ 107:3043ð6Þ°, b ¼ 97:0567ð6Þ°, c ¼ 107:1371ð8Þ°,
3
V ¼ 1459:04ð5Þ A , Z ¼ 2, qcalc ¼ 1:552 g cmꢀ3, F ð000Þ ¼
ꢁ
696; 2hmax ¼ 27:5°, 23 792 total, 6665 unique, 6094
observed [I > 2rðIÞ] diffractions (Nonius KappaCCD
diffractometer); 368 parameters. Cell parameters were
determined by least-squares analysis from 6162 partial
diffractions with 1:0 6 h 6 27:5°. The intensity data were
numerically corrected for absorption (l(Mo KaÞ ¼ 1:20
mmꢀ1), transmission coefficient range: 0.704–0.790.
The structure was solved by direct methods (SIR92,
[11]) and refined by weighted full-matrix least-squares
on F2 (SHELXL97, [12]). All non hydrogen atoms were
refined with anisotropic thermal motion parameters.
The hydrogen atom at C11 was identified on a difference
ꢁ
A similar reaction but with defined complex 4 gave an
identical product. Recrystallization of crude 1 from di-
chloromethane solutions gives solvates with varying
solvent content depending on the crystallization condi-
tions. Crystals of unsolvated 1 used for X-ray diffraction
analysis were obtained by recrystallization from THF-
hexane.
density map and isotropically refined (C–H 0.96(2) A).
All other hydrogen atoms were included in calculated
positions [C–H bond lengths: 0.96 (methyl), 0.97
ꢁ
(methylene) and 0.93 (aromatic) A] and assigned
UisoðHÞ ¼ 1:2Ueq(C) (methylene and aromatic) or 1.5
Ueq(C) (methyl). Final R indices; observed (all) diffrac-
tions: R 2.41% (2.82%), wR 5.89% (6.07)%. Extremes
on the final difference electron density map: +0.42,
ꢁꢀ3
NMR (CDCl3): dH 2.61 (d, 4JPH ¼ 1.8 Hz, 3H, NMe),
4
3.06 (s, 3H, OMe), 3.21 (d, JPH ¼ 2.9 Hz, 3H, NMe),
)0.67 e A .
2
4
3.26 (s, 1H, CHPd), 3.57 (dd, JHH ¼ 13.1, JPH ¼ 4.0
Hz, 1H, NCH2), 3.86 (s, 5H, C5H5), 3.97 (apparent dt,
J ¼ 2:6, 1.3 Hz, 1H, C5H3), 4.25 (apparent dt, J ¼ 1:1,
2.1 Hz, 1H, C5H3), 4.43 (apparent t, J approx. 2.4 Hz,
Crystallographic data excluding the structure factors
have been deposited with the Cambridge Crystallo-
graphic Data Centre [deposition No. CCDC-222593].
Copies of the data may be obtained upon request to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK;
http://www.ccdc.cam.ac.uk, e-mail: deposit@ccdc.cam.
ac.uk.
2
1H, C5H3), 4.77 (d, JHH ¼ 13.1 Hz, 1H, NCH2), 6.69–
7.92 (m, 14 H, aromatics); dC 41.28 (d, JPC ¼ 4 Hz,
3
CHPd), 48.23 (d, JPC ¼ 3 Hz, NMe), 49.52 (s, OMe),
3
52.19 (d, JPC ¼ 2 Hz, NMe), 67.40 (s, CH of C5H3),
69.38 (d, JPC ¼ 15 Hz, CH of C5H3), 70.04 (s, C5H5),
3
74.92 (d, JPC ¼ 6 Hz, CH of C5H3), 75.34 (d, JPC ¼ 2
Acknowledgements
Hz, NCH2), 86.71 (d, 1JPC ¼ 62 Hz, CP of C5H3), 102.38
2
(d, JPC ¼ 31 Hz, CCHPd of C5H3), 121.98 (s, CH of
ꢃ ꢀ
ꢃ
The author thanks Dr. Ivana Cısarova for collecting
X-ray diffraction data. This work was supported by the
Grant Agency of the Czech Republic (Grant Nos. 203/
01/P002 and 203/99/M037) and is a part of a long-term
Research plan of the Faculty of Sciences, Charles Uni-
versity. The Grant Agency of the Czech Republic also
sponsored an access to the Cambridge crystallographic
database (Grant No. 203/02/0436).
C6H4), 123.62 (s, CH of C6H4), 125.27 (d, JPC ¼ 4 Hz,
CH of C6H4), 127.80 (d, JPC ¼ 10 Hz, CH of PPh2),
128.04 (d, JPC ¼ 10 Hz, CH of PPh2), 129.57 (d, 4JPC ¼ 2
1
Hz, CHp of PPh2), 130.35 (d, JPC ¼ 54 Hz, Cipso of
4
PPh2), 130.67 (d, JPC ¼ 2 Hz, CHp of PPh2), 133.02 (d,
JPC ¼ 12 Hz, CH of PPh2), 134.75 (d, 1JPC ¼ 46 Hz, Cipso
of PPh2), 135.13 (d, JPC ¼ 12 Hz, C H of PPh2), 139.93
(d, JPC ¼ 9 Hz, CH of PPh2), 149.04 (d, JPC ¼ 1 Hz, Cipso
of C6H4), 160.38 (d, JPC ¼ 6 Hz, Cipso of C6H4), 178.39
ꢂ
(s, C@O); dP +41.5 (s). IR (Nujol) for 1 ꢁ 1/2CH2Cl2: m/
References
cmꢀ1 mC@O 1652vs, 1235s, 1207s, 1177m, 1263m, 1039s,
1026m, 923m, 844s, 824m, 803m, 748m, 739vs, 733vs,
701s, 695s, 541s, 509s, 469s. Anal. Calc. for
C34H34FeNO2PPd ꢁ CH2Cl2: C, 54.82; H, 4.73; N, 1.83.
Found: C, 55.14; H, 4.97; N, 1.75%.
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