1,1′-Bis(phosphoranylidenamino)ferrocene palladium(II) complexes: An unusual case of dative Fe → Pd bonding

Article abstract of DOI:10.1016/j.jorganchem.2006.01.012

Subtle differences in the electron-richness of nitrogen atoms in 1,1′-bis(phosphoranylidenamino)ferrocenes can change the coordination geometry of their palladium(II) complexes from cis to trans. Trans complexation results in concomitant formation of a relatively short dative Fe-Pd bond of 2.67 ?.

Full text of DOI:10.1016/j.jorganchem.2006.01.012

Journal of Organometallic Chemistry 691 (2006) 2044–2047
www.elsevier.com/locate/jorganchem
Note
1,10-Bis(phosphoranylidenamino)ferrocene palladium(II) complexes:
An unusual case of dative Fe ! Pd bonding
a,
a
a
b
Costa Metallinos *, Deanna Tremblay , Fred B. Barrett , Nicholas J. Taylor
a
Department of Chemistry, Brock University, St. Catharines, Ont., Canada L2S 3A1
Department of Chemistry, University of Waterloo, Waterloo, Ont., Canada N2L 3G1
b
Received 21 November 2005; received in revised form 9 January 2006; accepted 9 January 2006
Available online 20 February 2006
Abstract
Subtle differences in the electron-richness of nitrogen atoms in 1,10-bis(phosphoranylidenamino)ferrocenes can change the coordina-
tion geometry of their palladium(II) complexes from cis to trans. Trans complexation results in concomitant formation of a relatively
˚
short dative Fe–Pd bond of 2.67 A.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Ferrocene; Iminophosphorane; Palladium; Complex; Dative bond
1. Introduction
knowledge, only three such compounds have been reported
[9,10], one of which is the potentially bidentate ligand 3a,
R = Ph [11]. The coordination chemistry of type II ferroce-
nyl bisiminophosphoranes has not been explored [12].
In recent years there has been a surge of interest in the
preparation of homobidentate transition metal complexes
of bisiminophosphoranes [1,2] as alternatives to more com-
monly used sp2-hybridized nitrogen donor ligands such as
bis-imines and bis-oxazolines [3]. Among the two basic
structural types of iminophosphoranes, the coordination
chemistry of those of exemplified by type I (Fig. 1) have
been studied more extensively than ligands of type II.
The study of type II iminophosphoranes received a boost
with the report by Reetz [4] that the chiral binaphthyl-
derived bisiminophosphorane (1) can be used as a ligand
for asymmetric cyclopropanation. Although ferrocenyl
bisiminophosphoranes of type I (2) [5–7], and ferrocenes
bearing pendant [8] iminophosphorane moieties are
known, there are few examples of ferrocenyl iminophos-
phoranes of type II (3) (1,10-bis(phosphoranylidena-
mino)ferrocenes) in which the nitrogen atoms are directly
attached to the cyclopentadienyl rings. To the best of our
2. Results and discussion
As part of an investigation into the potential of type II
ferrocenyl bisiminophosphoranes as ligands for palladium,
two homobidentate compounds were prepared by the Stau-
dinger [13] reaction of triphenylphosphine and tricy-
clohexylphosphine with 1,10-diazidoferrocene [14] (4) to
provide 3a and 3b as brick-red solids (Scheme 1). Imino-
phosphoranes 3a and 3b were readily coordinated to Pd(II)
by treatment with dichlorobis(acetonitrile)palladium(II) in
toluene to give the corresponding complexes 5a and 5b
which were characterized spectroscopically (see Section
3). Notably, a slight downfield shift was observed in the
31P NMR spectra for both 5a and 5b (d 35.0 and 45.2,
respectively) compared to the free iminophosphoranes
3a,b (d 27.2 and 39.8, respectively).
Initially, the cis coordination geometry was assigned to
both 5a and 5b based on the reported crystal structure of
bisiminoferrocene palladium(II) complex (6) [15], which
*
Corresponding author. Tel.: +1 905 688 5550x3848; fax: +1 905 682
9020.
E-mail address: metallic@brocku.ca (C. Metallinos).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.01.012

C. Metallinos et al. / Journal of Organometallic Chemistry 691 (2006) 2044–2047
2045
Fig. 1. Structural types of iminophosphoranes.
Scheme 1. Preparation of type II 1,10-bis(phosphoranylidenamino)ferrocene palladium(II) complexes.
was also prepared by reaction of the free ligand with
(MeCN)2PdCl2. However, complexes 5a and 5b showed
significant differences in the number and position of signals
dium(II) complex (9) has been reported to have cp. ring
resonances at d 4.90 and 3.00, although its structure has
not been confirmed by X-ray analysis [21].
1
arising from the cyclopentadienyl (cp.) rings in their H
To verify whether complex 5a did indeed possess a
dative Fe–Pd bond, crystals were grown from CH2Cl2/
MeOH. Subjection of 5a to X-ray analysis revealed what
had been suspected, that the Pd center was cationic and
nearly square planar (bond angles: N1–Pd–N2 =
162.07(14)ꢁ; Fe1–Pd1–Cl1 = 177.15(3)ꢁ) with the nitrogen
atoms in a pseudo-trans coordination geometry. The trans
geometry brings the iron atom in close proximity to palla-
dium, resulting in the formation of a dative bond (Fig. 3).
To the best of our knowledge, 5a is the first example of a
bidentate ferrocene with dative Fe–Pd bonding in which
the coordinating heteroatoms are nitrogen. Interestingly,
and 13C NMR spectra. Whereas 5b exhibited four cp. ring
1
proton signals, consistent with the H NMR data reported
1
for the cis-coordinated bisimine 6 [15], the H NMR spec-
trum of 5a showed only two cp. ring signals at d 5.46 and
3.02, a difference of 2.44 ppm. Similar differences were
observed in the 13C NMR spectra, where 5a displayed three
cp. ring signals, versus five for 5b. A two-dimensional
1H–13C correlation experiment (HSQC) verified the coher-
ence of two 13C signals for 5a at 79.2 and 69.3 ppm with the
1
signals at 5.46 and 3.02 ppm, respectively, in the H NMR
spectrum.
The observation of only two cp. 1H NMR signals with a
large chemical shift difference for 5a was a strong indication
of trans coordination and the possible presence of a dative
Fe–Pd bond. Although uncommon [16], several ferrocenyl
palladium complexes with dative Fe–Pd bonds, especially
those derived from bidentate phosphorus [17] or sulfur
[18] donors, have been characterized crystallographically.
It is typical in these complexes to observe a large difference
in chemical shift of approximately 2 ppm or more for the
cp. protons. For example, the 1,10-diphosphinoferrocene-
palladium(II) iodide (7) (Fig. 2) has resonances at d 6.08
and 4.10 [19]. Similarly, 1,10-dithiolatoferrocenepalla-
dium(II) complex (8) has resonances at d 5.16 and 2.86
[20]. A third example, the 1,10-ferrocenedioxalatopalla-
Fig. 3. ORTEPꢂ plot of 5a. Thermal ellipsoids are shown at 50%
Fig. 2.
probability.

2046
C. Metallinos et al. / Journal of Organometallic Chemistry 691 (2006) 2044–2047
unlike in previous cases where the length of the Fe–Pd
bond has ranged from approximately 2.8–3.0 A [22], the
solution of triphenylphosphine (155 mg, 0.594 mmol, 1.98
equiv) in CH2Cl2 (2 mL), transferred by cannula over
10 min, resulting in a color change from orange to cherry
red. The flask was removed from the ice bath, wrapped
in foil and left to stir behind a blast shield for 24 h. The
reaction mixture was concentrated in vacuo to give a dark
brown oil. The oil was taken up in a minimum quantity of
CH2Cl2, and hexane was added to induce precipitation of
the product. The product was isolated by suction filtration,
washed with cold hexane and recrystallized from CH2Cl2/
hexane to give 3a (110 mg, 50%) as a red powder; m.p.
>230 ꢁC (CH2Cl2/hexane); IR (KBr) mmax 3426, 3046,
˚
length of the Fe–Pd bond in 5a is significantly shorter at
˚
2.67 A. This value is at the long end of the range for what
is usually observed in clusters containing Fe–Pd single
˚
bonds (2.6–2.7 A) [18,23]. The shortness of the Fe–Pd bond
in 5a is presumably a result of the smaller atomic radius of
nitrogen compared to phosphorus or sulfur.
The difference in coordination geometry of 5a versus 5b
may be tentatively attributed to the relative electron rich-
ness of nitrogen in the two ligands. In complex 5a, the pres-
ence of three phenyl rings on each phosphorus atom may
curtail electron donation to the nitrogen atoms through
resonance, thus leaving the Pd(II) center electronically
unsaturated and favoring the formation of a dative bond
with iron. The same delocalization of phosphorus electrons
is not possible in the case of 5b where there is resonance
only with nitrogen, making the nitrogen atoms stronger
electron donors, enough to satisfy the electronic require-
ments of Pd(II). This subtle difference in the electronic
environment of nitrogen in type II ferrocenyl iminophos-
phorane complexes as a potential determinant of coordina-
tion geometry warrants further study.
2999, 1470, 1433 cmꢀ1 31P NMR (243 MHz, CD2Cl2) d
;
27.2; EIMS [m/z (%)] 736 (M+, 1.3), 277 (HNPPh3þ, 100);
Anal. calcd for C46H38FeN2P2: C, 75.01; H, 5.20; N,
3.80; found C, 74.03; H, 4.81; N, 3.89%.
3.3. 1,10-Bis(tricyclohexylphosphoranylidenamino)ferrocene
(3b)
An oven-dried 50 mL round-bottomed flask containing
a solution of 1,10-diazidoferrocene (4) [14] (100 mg,
0.37 mmol) in dry CH2Cl2 (10 mL) under argon was cooled
to 0 ꢁC in subdued light. The resulting solution was treated
3. Experimental
with a solution of tricyclohexylphosphine (207 mg,
0.74 mmol) in CH2Cl2 (2 mL), transferred by cannula over
10 min, resulting in a color change from orange to cherry
red. The flask was removed from the ice bath, wrapped
in foil and left to stir behind a blast shield for 12 h. The
dark brown reaction mixture was concentrated in vacuo
to give a dark brown oil. The oil was taken up in a mini-
mum quantity of CH2Cl2 and cold hexane (ꢀ30 ꢁC) was
added to induce precipitation of the product. The product
was isolated by suction filtration and washed with cold hex-
ane to give 3b (113 mg, 39%) as an orange powder; m.p.
92–94 ꢁC (CH2Cl2/hexane); IR (KBr) mmax 2929, 2852,
3.1. General
All reagents were purchased from Aldrich, Fisher Scien-
tific or Strem and used as received unless otherwise indi-
cated. Dichloromethane was distilled over CaH2 under an
atmosphere of nitrogen. Toluene was distilled over sodium
under a nitrogen atmosphere. All reactions were performed
under argon in flame- or oven-dried glassware using syr-
inge-septum cap techniques or Schlenk conditions unless
otherwise indicated. NMR spectra were obtained on a Bru-
ker Aspect 200, Avance 300 or Avance 600 instrument and
are referenced to TMS or to the residual proton signal of
1447, 1113 cmꢀ1 31P NMR (121.5 MHz, CD2Cl2) d 39.8;
;
1H NMR (300 MHz, CD2Cl2) d 4.48 (t, 4H, J = 1.9 Hz),
4.05 (t, 4H, J = 1.9 Hz), 2.36–2.26 (m, 6H), 2.01–1.97 (m,
12H), 1.87 (m, 12H), 1.76 (m, 6H), 1.58–1.54 (m, 12H),
1.34–1.28 (m, 18H); 13C NMR (75.5 MHz, CD2Cl2) d
1
the deuterated solvent for H spectra, and to the carbon
multiplet of the deuterated solvent for 13C spectra accord-
ing to values given in Spectrometric Identification of
Organic Compounds, sixth ed., p. 200,240. FTIR spectra
were recorded on an ATI Mattson Research Series spec-
trometer. Low and high-resolution mass spectral data were
obtained on a Kratos Concept 1S Double Focusing spec-
trometer. Elemental analyses were performed by Canadian
Microanalytical Service, Delta, BC, Canada. Melting
points were determined on a Kofler hot-stage apparatus
and are uncorrected.
108.2, 67.2, 61.6, 32.9 (d, 1J
13C–31P
EIMS [m/z (%)] 772(M+, 4), 280(6), 214(100); HRMS
¼ 51:2 Hz), 26.7 (d,
13C–31P
2J
¼ 10:6 Hz), 26.3 (d, 3J
¼ 4:4 Hz), 25.7;
13C–31P
(EI) calcd for C46H74FeN2P2: 772.4677; found 772.4619.
3.4. [1,10-Bis(triphenylphosphoranylidenamino)ferrocene
Pd(II)Cl]Cl Æ H2O (5a)
An oven-dried 25 mL round-bottomed flask containing
iminophosphorane 3a (100 mg, 0.136 mmol), Pd(MeCN)2-
Cl2 (35.3 mg, 0.136 mmol) and PhMe (4 mL) under an
atmosphere of argon was stirred at ambient temperature
for 18 h. The solvent was removed in vacuo to give 5a
(102 mg, 82%) as a light orange-brown powder; m.p.
>230 ꢁC (CH2Cl2/hexanes); IR (KBr) mmax 3049, 1459,
3.2. 1,10-Bis(triphenylphosphoranylidenamino)ferrocene
(3a) [11]
An oven-dried 25 mL round-bottomed flask containing
a
solution of 1,10-diazidoferrocene (4) [14] (80 mg,
0.298 mmol) in dry CH2Cl2 (4 mL) was cooled to 0 ꢁC in
subdued light. The resulting solution was treated with a
1435 cmꢀ1 31P NMR (243 MHz, CD2Cl2) d 35.0; 1H
;

C. Metallinos et al. / Journal of Organometallic Chemistry 691 (2006) 2044–2047
2047
NMR (300 MHz, CD2Cl2) d 7.79 (dd, 12 H, J = 12.9,
Appendix A. Supplementary data
7.8 Hz), 7.69 (t, 6H, J = 7.2 Hz), 7.56–7.52 (m, 12 H),
5.46 (s, 4H), 3.02 (s, 4H); 13C NMR (150.9 MHz, CD2Cl2)
d 133.6 (d, J = 10.6 Hz), 133.5, 128.9 (d, J = 12.1 Hz),
Crystallographic data for 5a have been deposited with
the Cambridge Crystallographic Data Centre (CCDC
No. 277349). Copies of this data may be obtained free of
charge from the Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: +44 1223 336 033; email:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.jorganchem.2006.01.012.
1
125.9 (d, J
¼ 102:6 Hz), 96.1 (d, J = 4.5 Hz), 79.2,
13C–31P
69.3 (d, J = 6 Hz); FABMS [m/z (%)] 877 (M+ꢀ Cl,
27.5), 736 (M+ꢀPdCl2, 70.9), 340 (100), 262 (30); Anal.
calcd for C46H38Cl2FeN2P2Pd: C, 59.28; H, 4.33; N, 3.01;
found C, 59.77; H, 3.83; N, 2.90%.
35
3.5. 1,10-Bis(tricyclohexylphosphoranylidenamino)ferrocene
Pd(II)Cl2 (5b)
References
An oven-dried 25 mL round-bottomed flask containing
iminophosphorane 3b (50.0 mg, 0.065 mmol), Pd(MeCN)2-
Cl2 (16.8 mg, 0.065 mmol) and PhMe (3 mL) under an
atmosphere of argon was stirred at ambient tempera-
ture for 18 h. The solvent was removed in vacuo to give
5b (51.6 mg, 84%) as an orange-brown powder; m.p.
>190 ꢁC (decomp.) (hexanes/CH2Cl2); 31P NMR (81
MHz, CD2Cl2) d 45.2; 1H NMR (300 MHz, CD2Cl2) d
5.92 (s, 2H), 4.49 (s, 2H), 4.30 (s, 2H), 3.97 (s, 2H), 2.41–
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3
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¼ 10:9 Hz), 25.9 (d, J
¼
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´
´
´
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3.6. Crystallography
X-ray analysis of 5a was performed on a dark red plate
fragment (0.32 · 0.21 · 0.07 mm) which was obtained by
recrystallization
from
CH2Cl2/MeOH:
C46H40Cl2-
FeN2OP2Pd, M = 931.94, orthorhombic, Pca21, a =
˚
˚
˚
19.0488(15) A, b = 11.8259(9) A, c = 35.916(3) A, V =
3
3
˚
8090.7(11) A , Z = 8; Dc = 1.530 g/cm , F(000) = 3808,
T = 180(1) K. Data were collected on a Bruker APEX
CCD system with graphite monochromated Mo Ka radia-
˚
tion (k = 0.71073 A); 19302 data were collected. The struc-
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Hartwig, Organometallics 22 (2003) 2775;
ture was solved by Direct Methods (SHELXTL) and refined
by full-matrix least squares on F2 resulting in final R, Rw
and GOF (for 16210 data with F > 2r(F)) of 0.0384,
0.0708 and 1.481, respectively. N.B: Each asymmetric unit
contains two molecules and some phenyl rings are disor-
dered over two positions.
P.W.N.M. van Leeuwen, M.A. Zuideveld, B.H.G. Swennenhuis, Z.
Freixa, P.C.J. Kamer, K. Goubitz, J. Fraanje, M. Lutz, A.L. Spek,
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[18] For the first crystallographically verified example of Fe–Pd dative
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M. Cowie, R.S. Dickson, Organometallics 2 (1983) 472.
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Tamura, M. Sato, Organometallics 6 (1987) 526.
Acknowledgements
We thank NSERC Canada for support of our research
program, and Mr. Tim Jones and Mr. Razvan Simionescu
for assistance with NMR and MS determinations. D.T.
thanks NSERC for an Undergraduate Student Research
Award (2004). F.B. thanks Career Services at Brock Uni-
versity for an Experience Works award, which made his
contribution possible.
[21] S. Akabori, T. Kumagai, T. Shirahige, S. Sato, K. Kawazoe, C.
Tamura, M. Sato, Organometallics 6 (1987) 2105.
˚
[22] Fe–Pd bond lengths of up to 3.228 A have been reported. See: M.
Sato, H. Asano, S. Akabori, J. Organomet. Chem. 452 (1993) 105.
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