Cyclometalated complexes with triphosphine ligands: A novel route for promoting pentacoordination in palladium(II)

Article abstract of DOI:10.1021/om9906363

The palladium(II) compound [Pd{3,4-(MeO)₂C₆H₂C(H)=NCy}{(Ph ₂PCH₂CH₂)₂PPh-P,P,P}]-[PF ₆] was synthesized and characterized by elemental analysis (C, H, N) and by ¹H and ³¹P{¹H} NMR spectroscopy in CDCl₃ and ³¹P{¹H} solid-state NMR spectroscopy. The molecular structure was determined by X-ray crystallography, showing it to be the first pentacoordinated cyclometalated palladium(II) complex.

Full text of DOI:10.1021/om9906363

5484
Organometallics 1999, 18, 5484-5487
Cyclom eta la ted Com p lexes w ith Tr ip h osp h in e Liga n d s:
A Novel Rou te for P r om otin g P en ta coor d in a tion in
P a lla d iu m (II)
J ose´ M. Vila,* Ma Teresa Pereira, and J uan M. Ortigueira
Departamento de Quı´mica Inorga´nica, Universidad de Santiago de Compostela,
15706 Santiago de Compostela, Spain
J esu´s J . Ferna´ndez, Alberto Ferna´ndez, and Margarita Lo´pez-Torres
Departamento de Quı´mica Fundamental e Industrial, Universidad de La Corun˜a,
15071 La Corun˜a, Spain
Harry Adams
Department of Chemistry, The University of Sheffield, Sheffield S3 7HF, U.K.
Received August 9, 1999
The palladium(II) compound [Pd{3,4-(MeO)2C6H2C(H)dNCy}{(Ph2PCH2CH2)2PPh-P,P,P}]-
1
[PF6] was synthesized and characterized by elemental analysis (C, H, N) and by H and
31P{1H} NMR spectroscopy in CDCl3 and 31P{1H} solid-state NMR spectroscopy. The
molecular structure was determined by X-ray crystallography, showing it to be the first
pentacoordinated cyclometalated palladium(II) complex.
In tr od u ction
of stable complexes in many metals with different
oxidation states and coordination numbers and the
stereoselective occupation of centers of the cooordination
polyhedron.4 In the past few years, there has been a
growing interest in the synthesis of transition metal
complexes containing polydentate phosphine ligands,
mainly due to their applications as homogeneous and
heterogeneous catalysts.5 Here, we wish to present the
results of the reaction between bis(2-diphenylphosphi-
noethyl)phenylphosphine (triphos) and the cyclometa-
lated palladium(II) dimer complex 1.6
The stereochemistry of divalent palladium is charac-
terized by the square-planar arrangement in the major-
ity of its coordination and organometallic compounds.
Coordination number six has been reported for a few
unusual complexes whose structures have been inves-
tigated, generally showing two weaker interactions on
the metal atom.1 Five-coordinate Pd(II) complexes have
been more extensively investigated, probably due to the
interest in clarifying the kinetic properties for substitu-
tion and exchange reactions for palladium complexes
in solution and in biological systems.2 When we reacted
cyclometalated halide-bridged palladium(II) dimer com-
plexes with tertiary mono- and diphosphines, we ob-
tained only four-coordinate compounds with a square-
planar environment for the palladium atom,3 and as
part of our studies on reactions of the mentioned halide-
bridged complexes with phosphines we are currently
interested in reactions with tri- and tetradentate phos-
phines, a strategy that we reasoned would modify the
geometry and coordination number at the metal center.
In addition, polyphosphine ligands offer a number of
special characteristics, among which are the formation
Reu slts a n d Discu ssion
The reaction of 1 with 2 equiv of (Ph2PCH2CH2)2PPh
and ammonium hexafluorophosphate in acetone at room
temperature for 6 h afforded complex 2 (Figure 1) as a
yellow solid in 91% yield.
The elemental analyses are consistent with the em-
pirical formula [C49H53NO2P3Pd][PF6] (2), which indi-
cates a mononuclear structure and suggests that the
chlorine ligands are absent. This was confirmed by the
IR spectrum, which revealed the absence of bands due
to Pd-Cl bonds. The 31P{1H} spectrum shows a triplet
(δ ) 85.3, 1P) and a doublet (δ ) 42.6, 2P). This suggests
two mutually trans phosphorus atoms, with the third
(1) (a) Wiedhardt, K.; Ku¨ppers, H. J .; Raabe, E.; Kru¨ger, C. Angew.
Chem., Int. Ed. Engl. 1986, 25, 1101-1103. (b) Byers, P. K.; Canty, A.
J .; Skelton, B. W.; Traill, P. R.; Watson, A. A.; White, A. H. Organo-
metallics 1992, 11, 3085-3088.
(2) Wilkins, R. G. Kinetics and Mechanism of Reactions of Transition
Metals, 2nd ed.; VCH: Weinheim, 1991; Chapter 4.
(3) (a) Vila, J . M.; Gayoso, M.; Lo´pez Torres, M.; Ferna´ndez, J . J .;
Ferna´ndez, A.; Ortigueira, J . M.; Bailey, N. A.; Adams. H. J . Orga-
nomet. Chem. 1996, 511, 129-138. (b) Vila, J . M.; Gayoso, M.; Pereira,
M. T.; Ortigueira, J . M.; Lo´pez Torres, M.; Castin˜eiras, A.; Sua´rez, A.;
Ferna´ndez, J . J .; Ferna´ndez, A. J . Organomet. Chem., 1997, 547, 297-
307. (c) Vila, J . M.; Pereira, M. T.; Ortigueira, J . M.; Lo´pez Torres, M.;
Castin˜eiras, A.; Lata, D.; Ferna´ndez, J . J .; Ferna´ndez, A. J . Organomet.
Chem. 1998, 556, 31-39.
(4) (a) Levason, W. In The Chemistry of Organo Phosphorus
Compounds; Hartley, F. R., Ed.; J ohn Wiley and Sons: New York,
1990; pp 617-624. (b) Mayer, H. A.; Kaska, W. C. Chem. Rev. 1994,
94, 1239. (c) Cotton, F. A.; Hong, B. Prog. Inorg. Chem., 1992, 40, 179.
(5) (a) Bianchini, C.; Graziani, M.; Kaspar, J .; Meli, A.; Vizza, F.
Organometallics 1994, 13, 1165-1173. (b) Bianchini, C.; Marchi, A.;
Marvelli, L.; Peruzzini, M.; Romerosa, A.; Rossi, R.; Vacca, A. Orga-
nometallics 1995, 14, 3203-3215. (c) Seebach, D.; Sommerfeld, T. L.;
J iang, Q.; Venanzi, L. M. Helv. Chim. Acta 1994, 77, 1313-1330.
(6) Vila, J . M.; Gayoso, M.; Ferna´ndez, A.; Bailey, N. A.; H. Adams,
H. J . Organomet. Chem. 1993, 448, 233-239.
10.1021/om9906363 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/03/1999

Cyclometalated Complexes
Organometallics, Vol. 18, No. 26, 1999 5485
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 2
identification code
empirical formula
fw
hard12
50H54Cl3F6NO2P4Pd
1151.57
C
temperature
wavelength
cryst syst
293(2) K
0.71073 Å
triclinic
space group
unit cell dimens
P1h
F igu r e 1. C49H53NO2P3Pd cation.
a ) 11.569(3) Å, R ) 96.030(7)°
b ) 12.105(4) Å, â ) 106.59(2)°
c ) 20.001(5) Å, γ ) 92.44(4)°
2661.8(13) Å3
phosphorus nearly trans to the metalated carbon. The
31P resonance of the central phosphorus nucleus appears
at higher frequency due to the smaller trans influence
of the carbon atom.7 Interaction of the metal to the Cd
N nitrogen atom is shown by the shift of the ν(CdN)
stretching vibration to lower wavenumbers8 and by the
volume
Z
density (calcd)
abs coeff
F(000)
cryst size
θ range for data collection
index ranges
2
1.437 Mg/m3
0.679 mm-1
1176
0.7 × 0.4 × 0.25 mm
1
upfield shift to the HCdN proton resonance in the H
1.84-22.50°
NMR spectrum;9 the spectroscopic evidence points to a
square-pyramidal geometry in solution, with the nitro-
gen atom at the apical position; low-temperature NMR
(213 K) did not show any significant changes. The
proton in the ortho position to the Pd-C bond appears
as a doublet by coupling to one 31P atom. The value of
the conductivity data (135 Ω-1 cm2 mol-1 in dry aceto-
nitrile) shows the compound to be a 1:1 electrolyte.10
The 31P solid-state NMR spectrum exhibits a different
pattern with respect to the solution spectrum: a singlet
(δ ) 75.1, 1P) and a doublet of doublets (δ ) 44.6, 2P)
were observed. We thought this could be consistent with
a trigonal-bipiramidal geometry for the palladium atom,
with the resonances assigned to the phosphorus nucleus
at the apical position, trans to the phenyl carbon atom,
and to the other two phosphorus nuclei in the equatorial
-1 e h e 11, -12 e k e 12,
-21 e l e 21
no. of reflns collected
no. of indep reflns
abs corr
max. and min. transmn
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole
8324
6829 (Rint ) 0.0182)
semiempirical
0.678 and 0.457
full-matrix least-squares on F2
6829/0/594
1.050
R1 ) 0.538, wR2 ) 0.1471
R1 ) 0.0637, wR2 ) 0.1545
0.807 and -0.657 e Å-3
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 2
Bond Distances
Pd(1)-C(6)
Pd(1)-P(3)
Pd(1)-N(1)
C(5)-C(11)
2.072(5)
2.306(2)
2.359(4)
1.461(7)
Pd(1)-P(1)
Pd(1)-P(2)
N(1)-C(5)
C(6)-C(11)
2.293(2)
2.321(2)
1.269(7)
1.407(7)
2
plane, respectively. The J (PP) value in solution is 27
2
Hz, while in the solid state J (P1P2) is 300 Hz. So, not
Bond Angles
only the appearance of the spectrum changes from a
triplet and a doublet (in solution) to a singlet and a
doublet of doublets (in the solid) but also the coupling
constant undergoes a remarkably large variation. This
we think is due to the structural changes mentioned
above. We reasoned that if no changes took place, both
spectra should be fairly alike, so we looked at the PF6
signals (for which no changes are to be expected) and
we observed that there are five lines in each spectrum
(the two outermost lines are not observed) centered at
-143 ppm in both spectra, and with the same J (PP)
value in solution and in the solid, i.e., 710 Hz.
The five-coordinate structural geometry of 2, which
crystallizes as yellow prisms from chloroform, has been
definitively ascertained by an X-ray structure analysis
(Experimental Details and Tables 1 and 2). A view of
the molecular structure is shown in Figure 2. In the case
of palladium(II) cyclometalated compounds the presence
of five-coordinate species has been suggested assuming
weak Pd‚‚‚N interactions on the basis of Pd-N bond
distances in the range 2.710(6)-2.805(5) Å;11 a value
of 2.576(4) Å has been recently given.12 To the best of
our knowledge, the Pd-N bond length reported here for
2, 2.359(4) Å, is thus far the shortest distance known
C(6)-Pd(1)-P(1)
P(1)-Pd(1)-P(3)
94.5(2)
83.69(6)
C(6)-Pd(1)-P(3)
C(6)-Pd(1)-P(2)
P(3)-Pd(1)-P(2)
P(1)-Pd(1)-N(1)
174.24(14)
92.41(14)
85.55(6)
116.07(11)
103.61(11)
118.8(5)
P(1)-Pd(1)-P(2) 140.28(6)
C(6)-Pd(1)-N(1)
77.3(2)
P(3)-Pd(1)-N(1) 108.41(11) P(2)-Pd(1)-N(1)
C(5)-N(1)-Pd(1) 109.5(3)
N(1)-C(5)-C(11) 120.0(5)
C(6)-C(11)-C(5)
C(11)-C(6)-Pd(1) 114.4(4)
for these types of compounds and very close to the Pd-N
bond length of 2.23(2) Å in an authentic trigonal-
bipyramidal Pd(II) complex.13 The molecular structure
of 2 consists of discrete [Pd(C-N)(triphos)]+ cations and
-
PF6 anions. The palladium(II) atom is bonded to five
atoms: three phosphorus atoms from a tridentate bis-
(2-diphenylphosphinoethyl)phenylphosphine, one nitro-
gen atom, and the adjacent ortho carbon of a N-(3,4-
dimethoxybenzylidene)cyclohexylamine ligand in a
distorted trigonal-bipyramidal coordination. The equa-
torial plane is formed by palladium, nitrogen, and the
terminal phosphorus atoms of the phosphine ligand
(maximum deviation from the Pd(1)-N(1)-P(1)-P(2)
mean plane is 0.074 Å for P(1)). Carbon, C(6), and
central phosphorus, P(3), complete the coordination
sphere at the apical positions. The P(1)-Pd(1)-P(2)
(11) Granell, J .; Sales, J .; Vilarrasa, J .; Declercq, P. G.; Germain,
G.; Miravitlles, C.; Solans, X. J . Chem. Soc., Dalton Trans. 1983, 2441-
2446. Granell, J .; Sainz, D.; Sales, J .; Solans, X.; Font-Altaba, M. J .
Chem. Soc., Dalton Trans. 1986, 1785-1790. Butler, I. R.; Kalaji, M.;
Nehrlich, L.; Hurthouse, M.; Karaulov, A. I.; Malik, K. M. A. J . Chem.
Soc., Chem. Commun. 1995, 459-460.
(12) Vicente, J .; Arcas, A.; Bautista, D.; J ones, P. G. Organometallics
1997, 16, 2127-2138.
(13) Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Moneti, S.; Orlandini,
A.; Scapacci, G. J . Chem. Soc., Dalton Trans. 1989, 211-216.
(7) Pregosin, P. S.; Kuntz, R. W. In 31P and 13C NMR of Transition
Metal Phosphine Complexes; Diehl, P., Fluck, E., Kosfeld, R., Eds.;
Springer: Berlin, 1979; p 52.
(8) Onoue, M.; Moritani, I. J . Organomet. Chem. 1972, 43, 431-
436.
(9) Ustynyuk, Y.; Chertov, V. A.; Barinov, J . V. J . Organomet. Chem.
1971, 29, C53-C54.
(10) Geary, W. J . Coord. Chem. Rev. 1971, 7, 81-122.

5486 Organometallics, Vol. 18, No. 26, 1999
Vila et al.
ligand. This together with recent results obtained by
us portrays a new and systematic route to produce five-
coordinate cyclometalated palladium(II) complexes. Our
efforts are now focused on the preparation of similar
complexes with other polyphosphine ligands and metals.
Exp er im en ta l Deta ils
Solvents were purified by standard methods.17 Chemicals
were reagent grade. Palladium(II) acetate was purchased from
Alfa Products. The phosphine bis(2-diphenylphosphinoethyl)-
phenylphosphine (triphos) was purchased from Aldrich-Che-
mie. Microanalyses were carried out at the Servicio de Ana´lisis
Elemental at the University of Santiago using a Carlo Erba
elemental analyzer, model 1108. NMR spectra were obtained
as CDCl3 or DMSO-d6 solutions and referenced to SiMe4 (1H,
13C) or 85% H3PO4 (31P{1H}) and were recorded on Bruker
WM250 and AMX-300 spectrometers. All chemical shifts were
reported downfield from standards. Coumpound [Pd{3,4-
(MeO)2C6H2C(H)dNCy}(µ-Cl)]2 (1) has been synthesized by us
before.6
F igu r e 2. Structure of the cation for compound 2 showing
the atom-numbering scheme. Hydrogen atoms were omit-
ted for clarity.
Syn th esis of Com p ou n d 2. To a suspension of the chloro-
bridged dimer complex [Pd{3,4-(MeO)2C6H2C(H)dNCy}(µ-Cl)]2
(1) (120.0 mg, 0.154 mmol) in acetone (10 cm3) was added (Ph2-
PCH2CH2)2PPh (105.0 mg, 0.308 mmol). The mixture was
stirred at room temperature for 1 h, then NH4PF6 (0.051 mg,
0.312 mmol) was added, and the resulting solid was filtered
off and dried in vacuo. Recrystallization from dichloromethane/
hexane gave the final compound as a pale yellow solid. Yield:
95%. Anal. (%) Found: C 57.08, H 5.21, N 1.42. Calcd for
C49H53F6NO2P4Pd: C 57.01, H 5.18, N 1.36. IR: ν(CdN) )
angle between terminal phosphorus atoms is enlarged,
140°, so that the polyhedron may be viewed as distorted
toward square-based pyramidal, although the P(3)-Pd-
(1)-C(6) angle remains at 174°. The cation has very
approximate mirror symmetry through the unique
phosphorus, the palladium, and the mean plane of the
tridentate ligand. The donor atoms of the chelating
Schiff base ligand occupy cis sites with a somewhat
reduced bond angle (C(6)-Pd(1)-N(1) 77.3(2)°) conse-
quent upon chelation. The sum of angles on palladium
in the equatorial plane is 359.96°. The Pd(1)-C(6) bond
length, 2.072(5) Å, is longer than those found in related
complexes where partial multiple-bond character of the
Pd-C bond was assumed,14 supporting a phosphine
ligand in the trans position. The Pd-P bond lengths
[Pd(1)-P(1), 2.293(2) Å; Pd(1)-P(2), 2.321(2) Å; Pd(1)-
P(3), 2.306(2) Å] suggest that a slightly partial double
bond between the palladium and phosphorus atoms may
exist.15 The shortest Pd‚‚‚F contact with the PF6 coun-
terion is 6.0237(0.0094) Å, and the shortest Pd‚‚‚Cl
contact with the solvent is 6.9895(0.0054) Å.16
1603 cm-1; ΛM ) 135 Ω-1 cm2 mol-1 31P NMR (CDCl3): δ )
.
85.3 (t, 1P), δ ) 42.6 (d, 2P). 31P NMR (solid): δ ) 75.1 (s,
1P), δ ) 44.6 (dd, 2P). 1H NMR (CDCl3): δ ) 8.45 (s, 1H, HCd
N), δ ) 6.17 (d, 1H, H4, 3J (H4,H5) ) 7.50 Hz), δ ) 5.50 (t,
1H, H5 4J (P,H5) ) 7.50 Hz).
Cr ysta l d a ta for 2: C49H53F6NO2P4Pd‚CHCI3, yellow oblong
crystals, Mr ) 1151.57, crystal dimensions 0.7 × 0.4 × 0.25
mm3, a ) 11.569(3) Å, b ) 12.105(4) Å, c ) 20.001 (5) Å, R )
96.030(7)°, â ) 106.59(2)°, γ ) 92.44(4)°. V ) 2661.8(13) Å3,
Fcalc ) 1.437 g/cm3, µ ) 0.679 mm-1, Z ) 2, triclinic, space group
P1h (no. 2). Crystal structure determination: Three-dimen-
sional, room-temperature X-ray data were collected in the
range 4°< 2θ < 45° on a Siemens P4 diffractometer by the
omega scan method using graphite-monochromated Mo KR
radiation (λ ) 0.7107 Å). Of the 8324 reflections measured,
all of which were corrected for Lorentz and polarization effects,
and for absorption by analysis of 10 psi scans (max./min.
transmision 0.678, 0.457), 6829 independent reflections ex-
ceeded the significance level |F|/σ(|F|) > 4.0. The structure was
solved by direct methods (SHELXS-86) and refined (SHELXS-
Con clu sion s
We have shown that five-coordinate cyclometalated
palladium(II) compounds may be synthesized with
ligands such as tridentate phosphines that control the
geometry and coordination number at the metal center.
This is the first example of a “true” five-coordinate
example of its kind, by formation of three five-membered
rings at palladium: two comprising the triphos ligand
and the palladacycle from the C,N-bonded organic
(16) To ascertain that the 3-MeO group is not a steric trap that
prevents the imine function from being anywhere else but in the
proximity of the palladium atom, thus forcing the complex to be five-
coordinate, we have synthesized a related complex with no substituents
at the 3 or 5 positions, [Pd{4-(CHO)C6H3C(H)dNCy}{(Ph2PCH2CH2)2-
PPhP,P,P}][PF6], and the results are similar to the ones reported here.
Thus, the IR and 1H NMR data show there is interaction of the
palladium atom with the CdN nitrogen atom; in the 31P{1H} NMR
spectrum in CDCl3 a triplet and a doublet were observed, as for
complex 2. The molecular structure of this compound was determined
by X-ray crystallography; the Pd-N distance of 2.438 Å is, with the
exception of compound 2, the shortest distance so far reported for these
compounds (see text), pointing toward a close-to-pentacoordinated
complex, as well.
(14) Selbin, J .; Abboud, K.; Watkins, S. F.; Gutierrez, M. A.;
Fronczek, F. R. J . Organomet. Chem. 1983, 241, 259-268.
(15) (a) Albert, J .; Granell, J .; Sales, J .; Solans, X.; Font-Altaba, M.
Organometallics 1986, 5, 2567. (b) Housecroft, C. E.; Shaykh, B. A.
M.; Rheingold, A. L.; Haggerty, B. S. Acta Crystallogr. Sect. C 1990,
46, 1549. (c) DuBois, B. L.; Miedaner, A.; Haltiwanger, R. C. J . Am.
Chem. Soc. 1991, 119, 8753.
(17) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. P. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon: Oxford, 1983.

Cyclometalated Complexes
Organometallics, Vol. 18, No. 26, 1999 5487
93) by full matrix blocked least squares on F2 with allowance
for the thermal anisotropy of all non-hydrogen atoms. Hydro-
gen atoms were included in calculated positions and refined
in riding mode. Refinement converged at a final R ) 0.0538,Rw
) 0.1471 (for 594 refined parameters). Max./min. residual
electron density are 0.807/-0.657 e Å-3. Crystallogrphic data
(excluding structure factors) for the structure reported in this
paper have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication no.
112251. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
U.K.(fax: (+44)1223-336-033;e-mail: deposit@ccdc.cam.ac.uk).
Ack n ow led gm en t. This work was supported by the
Xunta de Galicia, Spain (XUGA20913B96).
Su p p or tin g In for m a tion Ava ila ble: Atomic coordinates
and equivalent isotropic displacement parameters, bond lengths
and angles, anisotropic displacement parameters, hydrogen
coordinates, and isotropic displacement parameters. This
material is available free of charge via the Internet at http://
pubs.acs.org. Crystallographic data (excluding structure fac-
tors) for the structure have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
no. 112251.
OM9906363