Synthesis and characterization of mono- and bimetallic complexes with phosphine-salicylaldimine ligands. The X-ray crystal structure of trans-PdCl2{Ph2P(CH2)3 N=CHC6H4-o-OH}2

Article abstract of DOI:10.1016/S0020-1693(01)00298-5

Complexes of the type M{Ph₂P(CH₂)_nN=CHC₆ H₄-o-OH}₂ (n = 3, 4 and M = cis- and trans-PdCl₂, cis-PtCl₂, cis,cis,trans-RuCl₂(CO)₂) have been synthesized by the reactions of the ligands with the appropriate metal precursors. All of the complexes are obtained in high yields, and, in all of the complexes, the ligands are coordinated solely through the phosphorus. Attempts to form bimetallic complexes by reaction of these complexes with either nickel acetate or diethylzinc give incomplete reactions and mixtures of products. A bimetallic Pd(II)-Ni(II) complex has been obtained by the reaction of {Ph₂P(CH₂)₄N=CHC₆H₄- o-O}₂Ni and Pd(cod)Cl₂. Crystals of this complex are yellow-brown but yield a green powder when ground. NMR spectra of the complex suggest that it is monomeric in solution. The X-ray crystal structure of trans-PdCl₂{Ph₂P(CH₂)₃ N=CHC₆H₄-o-OH}₂ has been determined. The coordination geometry of the Pd is a nearly perfect, trans square plane containing two phosphines and two chlorides. The Pd-Cl bonds are nearly parallel to the P-CH₂ bond, and the salicylaldimine groups lie on opposite sides of the plane formed by Pd, P and Cl.

Full text of DOI:10.1016/S0020-1693(01)00298-5

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Inorganica Chimica Acta 314 (2001) 133–138
Synthesis and characterization of mono- and bimetallic complexes
with phosphine–salicylaldimine ligands. The X-ray crystal
structure of trans-PdCl2{Ph2P(CH2)3NꢀCHC6H4-o-OH}2
Gary M. Gray *, Joe M. George, Minjane Jan
Department of Chemistry, The Uni6ersity of Alabama at Birmingham, CHEM 201, 1530 3rd A6enue South, Birmingham, AL 35294-1240, USA
Received 28 April 2000; accepted 15 December 2000
Abstract
Complexes of the type M{Ph2P(CH2)nNꢀCHC6H4-o-OH}2 (n=3, 4 and M=cis- and trans-PdCl2, cis-PtCl2, cis,cis,trans-
RuCl2(CO)2) have been synthesized by the reactions of the ligands with the appropriate metal precursors. All of the complexes
are obtained in high yields, and, in all of the complexes, the ligands are coordinated solely through the phosphorus. Attempts to
form bimetallic complexes by reaction of these complexes with either nickel acetate or diethylzinc give incomplete reactions and
mixtures of products. A bimetallic Pd(II)–Ni(II) complex has been obtained by the reaction of {Ph2P(CH2)4NꢀCHC6H4-o-O}2Ni
and Pd(cod)Cl2. Crystals of this complex are yellow–brown but yield a green powder when ground. NMR spectra of the complex
suggest that it is monomeric in solution. The X-ray crystal structure of trans-PdCl2{Ph2P(CH2)3NꢀCHC6H4-o-OH}2 has been
determined. The coordination geometry of the Pd is a nearly perfect, trans square plane containing two phosphines and two
chlorides. The Pd–Cl bonds are nearly parallel to the P–CH2 bond, and the salicylaldimine groups lie on opposite sides of the
plane formed by Pd, P and Cl. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Binuclear PdꢁNi complexes; Monometallic complexes; Bimetallic complexes; Phosphine–salicylaldimine ligands; X-ray crystal struc-
tures
1. Introduction
The reactions used to prepare group VI complexes with
X=NH ligands cannot be used to prepare related
Pt-group metal complexes because chlorodiphenylphos-
phine complexes of these metals analogous to the
M(CO)6−n(Ph2PCl)n (n=1, 2) are not available [3]. It
should be possible to prepare Pt-group metal complexes
with the X=(CH2)n ligands because the ligands are first
synthesized and then coordinated to the metal centers.
However, this route is complicated by the fact that the
P-donor ligand/salicylaldiminato ligands can chelate to
Pt-group metals centers [4–7]. This is particularly true
for ligands that contain relatively short spacers between
the P-donor and salicylaldiminato groups.
In this paper, we report the synthesis of several
Pt-group metal complexes containing P-coordinated
Ph2P(CH2)nNꢀCHC6H4-o-OH (n=3, 4) ligands. The
X-ray crystal structure of one of these complexes, trans-
PdCl2[Ph2P(CH2)3NꢀCHC6H4-o-OH] has been deter-
mined and is discussed. We also describe our attempts
Phosphine complexes containing two different metal
centers are of interest because they can exhibit unusual
catalytic activities and selectivities [1,2]. We have earlier
reported that ligands containing both a P-donor group
and a salicylaldiminato N/O-donor group can be used
to prepare the bi- and trinuclear heterometallic com-
plexes in Fig. 1 [3–5]. Unfortunately, none of these
complexes are useful as catalysts due to the inertness of
the Group VIB metal centers.
Complexes of the types shown in Fig. 1 in which a
Ru(II), Rh(I), Pd(II) or Pt(II) center replaces the group
VI metal center could exhibit interesting catalytic prop-
erties, however, no such complexes have been reported.
* Corresponding author. Tel.: +1-205-9344747; fax: +1-205-
9342543.
E-mail address: gmgray@uab.edu (G.M. Gray).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00298-5

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G.M. Gray et al. / Inorganica Chimica Acta 314 (2001) 133–138
to prepare bimetallic complexes containing a Pt-group
metal center and either Ni2+ and Zn2+ and compare
our results with those obtained previously with the
methane solution with diethyl ether yielded pure
PdCl2[Ph2P(CH2)4NꢀCHC6H4-o-OH]2·0.5H2O (m.p.
188–194°C). Anal. Found: C, 60.82; H, 5.56; N, 2.91.
C46H49Cl2N2O2.5P2Pd Calc.: C, 60.77; H, 5.43; N,
3.08%. 31P NMR (chloroform-d1): l 28.52 (minor cis
isomer, s), 16.89 (major trans isomer, s). 13C NMR of
major trans isomer (chloroform-d1): l 164.89 (CꢀN, s);
161.25 (C–OH, s); 133.63 (ortho P-phenyl, aq,
related
Group
VI
metal
complexes,
cis-
M(CO)4[Ph2P(CH2)nNꢀCHC6H4-o-OH]2 (M=Cr, Mo;
n=3–5) [4] and M(CO)5[Ph2P(CH2)4NꢀCH–C6H4-o-
OH] (M=Cr, W) [5].
2
ꢀ J(PC)+4J(PC)ꢀ=11 Hz); 130.45 (para P-phenyl, s);
1
2. Experimental
129.99 (ipso P-phenyl, aq, ꢀ J(PC)+3J(PC)ꢀ=46 Hz);
3
128.26 (meta P-phenyl, aq, ꢀ J(PC)+5J(PC)ꢀ=9 Hz);
All reactions were carried out under dry N2. The
Ph2P(CH2)nNꢀCHC6H4-o-OH, (n=4, 1) and (n=3, 2)
[5], trans-[Ph2P(CH2)4NꢀCHC6H4-o-O]2Ni (3) [5],
Pd(PhCN)2Cl2 [8], M(cod)Cl2 (M=Pd, Pt) [9], and
RuCl2(CO)3THF [10] precursors were synthesized by
literature methods. All other reagents and solvents were
reagent grade and were used as received.
132.00, 131.21, 118.77, 118.34, 116.94 (other salicy-
laldiminato aromatic carbons, all s); 58.60 (N–CH2, s);
3
31.90 (N–CH2–CH2, aq, ꢀ J(PC)+5J(PC)ꢀ=14 Hz);
1
24.94 (P–CH2, aq, ꢀ J(PC)+3J(PC)ꢀ=30 Hz); 21.71
(P–CH2–CH2, s). IR (dichloromethane): 1635, 1585
cm−1 (CꢀN, C–O stretches).
Both 31P and 13C nuclear magnetic resonance spectra
of approximately 0.1 M chloroform-d1 solutions of the
complexes were run on a Nicolet 300MHz, wide-bore,
FT NMR spectrometer. The 13C NMR spectra were
referenced to internal TMS, and the 31P NMR spectra
were referenced to external 40% phosphoric acid with
downfield considered positive. IR spectra of
dichlormethane solutions of the complexes in the 1700–
1500 cm−1 region were run on a Perkin–Elmer 283B
infrared spectrometer.
2.2. PdCl2[Ph2P(CH2)3NꢀCHC6H4-o-OH]2 (5)
Using the procedure for the synthesis of 4, 1.39 g
(4.00 mmol) of Ph2P(CH2)3NꢀCHC6H4-o-OH (2) and
0.71 g (2.0 mmol) of Pd(PhCN)2Cl2 yielded 1.68 g
(96%) of crude product. This material was identified by
comparison of its 31P and 13C NMR spectra with those
of 4. 31P NMR (chloroform-d1): l 29.27 (minor cis
isomer, s), 17.30 (major trans isomer, s). 13C NMR of
major trans isomer (chloroform-d1): l 165.37 (C=N,
s); 161.16 (C–OH, s); 133.71 (ortho P-phenyl, aq,
2
2.1. PdCl2[Ph2P(CH2)4NꢀCHC6H4-o-OH]2 (4)
ꢀ J(PC)+4J(PC)ꢀ=7 Hz); 130.64 (para P-phenyl, s);
1
129.88 (ipso P-phenyl, aq, ꢀ J(PC)+3J(PC)ꢀ=47 Hz);
3
A solution of 0.54 g (1.4 mmol) of Ph2P(CH2)4-
NꢀCHC6H4-o-OH (1) and 0.25 g (0.7 mmol) of
Pd(PhCN)2Cl2 in 25 ml of dichloro-methane was stirred
at ambient temperature for 2 h. The solution was then
evaporated to dryness, and the residue was washed with
diethyl ether to yield 0.59 g (95%) of the crude product.
Precipitation of the crude product from a dichloro-
128.43 (meta P-phenyl, aq, ꢀ J(PC)+5J(PC)ꢀ=7 Hz);
132.21, 131.31, 118.75, 118.54, 116.99 (other salicyl-
aldiminato aromatic carbons, all s); 60.20 (N–CH2, aq,
3
ꢀ J(PC)+5J(PC)ꢀ=16 Hz); 25.85 (N–CH2–CH2, s);
1
23.14 (P–CH2, aq, ꢀ J(PC)+3J(PC)ꢀ=30 Hz). IR
(dichloromethane): 1635, 1584 cm−1 (CꢀN, C–O
stretches).
Fig. 1. Bi- and trinuclear complexes with phosphorus-donor/salicylaldiminato ligands.

G.M. Gray et al. / Inorganica Chimica Acta 314 (2001) 133–138
135
2.3. cis-PtCl2[Ph2P(CH2)4NꢀCHC6H4-o-OH]2 (6)
(3) in 50 ml of dichloromethane was stirred at ambient
temperature for 4 days. The solution was then evapo-
rated to dryness to yield 0.41 g (100%) of the crude
product. Recrystallization of this material by diffusion
of diethyl ether into a THF solution of the crude
A solution of 1.5 g (4.1 mmol) of Ph2P(CH2)4-
NꢀCHC6H4-o-OH (1) and 0.78 g (2.0 mmol) of Pt(-
cod)Cl2 in 25 ml of dichloromethane was stirred at
ambient temperature for 2 h. The solution was then
evaporated to dryness, and the residue was washed with
diethyl ether to yield 1.9 g (96%) of crude product.
Precipitation of this material from dichloromethane
with diethyl ether yielded pure cis-PtCl2[Ph2P(CH2)4-
NꢀCHC6H4-o-OH]2·0.5H2O (m.p. 180–181°C). Anal.
mixture
yielded
analytically
pure
trans-
PdCl2[Ph2P(CH2)4NꢀCHC6H4-o-O]2Ni·THF
(m.p.
195–196°C). Anal. Found: C, 58.32; H, 5.17; N, 2.92.
C50H54Cl2N2NiO3P2Pd; Calc.: C, 58.30; H, 5.24; N,
2.72%. 31P NMR (chloroform-d1): l 16.72 (s). 13C
NMR (chloroform-d1): l 163.40 (CꢀN, s); 162.54 (C–
2
Found: C, 55.16; H, 5.03; N, 2.70. C46H49Cl2N2O2.5
-
OH, s); 133.66 (ortho P–phenyl, aq, ꢀ J(PC)+
P2Pt; Calc.: C, 55.36; H, 4.95; N, 2.81%. 31P NMR
4J(PC)ꢀ=10 Hz); 133.40 (ortho P-phenyl, bs); 130.50
1
1
(chloroform-d1): l 8.22 (s and d, ꢀ J(PtP)ꢀ=3655 Hz).
(para P-phenyl, s); 130.25 (ipso P-phenyl, aq, ꢀ J(PC)+
13C NMR (chloroform-d1): l 165.05 (CꢀN, s), 161.24
3J(PC)ꢀ=46 Hz); 129.81 (para P-phenyl, s); 129.45 (ipso
2
1
(C–OH, s); 133.29 (ortho P-phenyl, aq, ꢀ J(PC)+
P-phenyl, aq, ꢀ J(PC)+3J(PC)ꢀ=47 Hz); 128.48 (meta
4J(PC)ꢀ=9 Hz); 130.96 (para P-phenyl, s); 129.13 (ipso
P-phenyl, aq, ꢀ J(PC)+5J(PC)ꢀ=10 Hz); 127.78 (meta
3
1
3
P-phenyl, aq, ꢀ J(PC)+3J(PC)ꢀ=64 Hz); 128.25 (meta
P-phenyl, aq, ꢀ J(PC)+5J(PC)ꢀ=9 Hz); 132.33, 128.66,
3
P-phenyl, aq, ꢀ J(PC)+5J(PC)ꢀ=10 Hz); 132.09,
121.53, 120.77, 114.95 (other salicylaldiminato aromatic
131.34, 118.71, 118.46, 116.88 (other salicylaldiminato
carbons, all s); 58.78 (N–CH2, s); 35.81 (N–CH2–CH2,
1
aromatic carbons, all s); 58.35 (N–CH2, s); 31.58 (N–
bs); 25.22 (P–CH2, aq, ꢀ J(PC)+3J(PC)ꢀ=25 Hz);
1
3
CH2–CH2, s); 30.01 (P–CH2, aq, ꢀ J(PC)+ J(PC)ꢀ=
46 Hz); 22.64 (P–CH2–CH2, s). IR (dichloromethane):
1635, 1555 cm−1 (CꢀN, C–O stretches).
22.73 (P–CH2–CH2, s). IR (dichloromethane): 1617,
1545 cm−1 (CꢀN, C–O stretches).
2.6. X-ray crystal structure of
2.4. cis,cis,trans-RuCl2(CO)2-
[Ph2P(CH2)4NꢀCHC6H4-o-OH]2 (7)
trans-PdCl2[Ph2P(CH2)3NꢀCHC6H4-o-OH] (5)
A yellow, plate-like crystal of trans-PdCl2[Ph2P-
(CH2)3NꢀCHC6H4-o-OH] (5) was obtained by cooling
a dichloromethane/hexanes solution of the complex to
−5°C. The crystal was mounted on a glass fiber with
epoxy cement, and the cell constants were obtained
from least-squares refinement of 25 reflections with
255q535°. All measurements were taken on an En-
raf–Nonius CAD4 diffractometer at 23°C using
graphite-monochromated Cu Ka radiation (u=1.5418
A solution of 0.91 g (3.2 mmol) of Ph2P(CH2)4-
NꢀCHC6H4-o-OH, 1, and 0.40 g (1.6 mmol) of
RuCl2(CO)3THF in 100 ml of dichloromethane was
stirred at ambient temperature for 4 days. The solution
was then evaporated to dryness to yield 1.2 g (94%) of
the crude product. Trituration of this material with a
1:1 mixture of diethyl ether and hexanes yielded analyt-
ically
pure
cis,cis,trans-RuCl2(CO)2[Ph2P(CH2)4-
,
NꢀCHC6H4-o-OH]2. Anal. Found: C, 60.83; H, 5.40; N,
3.08. C48H48N2O4P2Cl2Ru Calc.: C, 60.63; H, 5.05; N,
2.95%. 31P NMR (chloroform-d1): l 19.09 (s). 13C
A). Data were collected by ꢀ–2q scans, and an empiri-
cal absorption correction was applied.
The structure was solved by heavy-atom methods
and refined by a full-matrix least squares procedure
that minimized w(ꢀFoꢀ−ꢀFcꢀ)2 where w=1/|2(Fo) using
the MOLEN package of programs from Enraf–Nonius.
The hydrogen atoms bonded to carbons were placed in
2
NMR (chloroform-d1): l 192.46 (CO, t, ꢀ J(PC)=10
Hz); 164.95 (CꢀN, s); 161.18 (C–OH, s); 133.72 (ortho
2
P–phenyl, aq, ꢀ J(PC)+4J(PC)ꢀ=10 Hz); 130.63 (para
1
P-phenyl, s); 130.06 (ipso P-phenyl, aq, ꢀ J(PC)+
3
3J(PC)ꢀ=66 Hz); 128.48 (meta P-phenyl, aq, ꢀ J(PC)+
calculated positions (C–H=0.96 A, Uiso(H)=1.3×
,
5J(PC)ꢀ=9 Hz); 131.97, 131.25, 118.61, 118.30, 116.80
Uiso(C)) and were ridden on the carbons. The hydrogen
on the salicylaldimine oxygen was located in a differ-
ence Fourier map, and its positional parameters were
refined. The data was weighed using a non-Poisson
scheme. A secondary extinction correction was applied
to the data [11], and the extinction coefficients were
refined. In the last stage of the refinement for the
structure, no parameter varied by more than 0.01 of its
standard deviation, and the final difference Fourier
map had no interpretable peaks. Heavy atom scattering
factors were taken from the compilations of Cromer
and Weber [12], and those for hydrogen were taken
(other salicylaldiminato aromatic carbons, all s); 58.02
3
(N–CH2, s); 31.10 (N–CH2–CH2, aq, ꢀ J(PC)+
1
5J(PC)ꢀ=13 Hz); 30.01 (P–CH2, aq, ꢀ J(PC)+
3J(PC)ꢀ=27 Hz); 20.09 (P–CH2–CH2, s). IR
(dichloromethane solution): 2058, 1996 (carbonyl
stretches), 1636, 1553 cm−1 (CꢀN, C–O stretches).
2.5. trans-PdCl2[Ph2P(CH2)4NꢀCHC6H4-o-O]2Ni (8)
A solution of 0.11 g (0.38 mmol) of Pd(cod)Cl2 and
0.30 g (0.38 mmol) of [Ph2P(CH2)4NꢀCHC6H4-o-O]2Ni

136
G.M. Gray et al. / Inorganica Chimica Acta 314 (2001) 133–138
Table 1
and palladium. Data for the X-ray structure analysis
are given in Table 1. Values of selected bond lengths
are given in Table 2, and values of selected bond angles
are given in Table 3. Tables of atomic positional
parameters, thermal parameters, torsion angles and
least squares planes are available as supplementary
material. An ORTEP [15] drawing of the structure is
given in Fig. 2.
Data collection and structure solution and refinement parameters for
trans-PdCl2[Ph2P(CH2)3NꢀCHC6H4-o-OH]2 (5)
Formula
C44H44Cl2N2O2P2
Pd
872.11
MW (Da)
Space group
P21/n
,
a (A)
9.960(1)
9.2662(8)
22.188(2)
100.251(9)
2015(1)
2
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
3. Results and discussion
Dcalc (g cm−3
)
1.437
Crystal dimensions (mm)
hmax, hmin
kmax, kmin
0.13×0.34×0.49
12, −12
11, 0
3.1. Syntheses of mono- and bimetallic complexes
Platinum-group metal complexes with phosphorus-
coordinated Ph2P(CH2)nNꢀCHC6H4-o-OH (n=4, 1;
and n=3, 2), ligands were prepared by the reactions of
the appropriate metal precursors with the free ligands
as shown in Eqs. (1)–(3). These reactions were run at
ambient temperatures and gave high yields of the de-
sired products. This is in contrast to the reaction of
Rh(acac)(CO)2 with 1, which gives exclusively the
chelated product, Rh(CO)(Ph2P(CH2)nNꢀCHC6H4-o-
O), under similar conditions [4]. This difference is most
likely due to the fact that the acetylacetonate (acac)
ligand in Rh(acac)(CO)2 is sufficiently basic to be pro-
tonated by the salicylaldimine and allow coordination
of the salicylaldiminato group to occur. The chloride
ligands in the Pd(II), Pt(II) and Ru(II) precursors used
in this study will not do this.
lmax, lmin
27, 0
Cu Ka (1.54184)
22
6.1209
0.1–74
,
u (A)
Temperature (°C)
Absorption coefficient (mm−1
q limits (°)
)
Decay correction
Absorption correction
Tmax, Tmin
Reflections measured
Scan width (°)
Reflections with I\n|I (no)
No. of variables (nv)
Function minimized
Weighing scheme
none
analytical
0.5346, 0.1752
4256
1.3
3595 (n=3)
242
w(ꢀFoꢀ−ꢀFcꢀ)2
non-Poisson a
0.05
Instrumental uncertainty factor (p)
Secondary extinction correction type
Minimized extinction coefficient
R (%) b
Zachariesen
7.5×10−7
3.52
5.24
1.38
Rw (%) c
GOF d
−3
,
Max., min. residual electron density (e A
Max. shift/error
)
0.615, −0.674
0.01
Pd(PhCN)2Cl2+2Ph2P(CH2)nNꢀCHC6H4-o-OH“
cis-PdCl2[Ph2P(CH2)nN=CHC6H4-o-OH]2
a w=(2Fo)2/ꢀ|(I)2+(pFo2)2ꢀ.
b R=ꢁꢀꢀFoꢀ−ꢀFcꢀꢀ/ꢁꢀFoꢀ).
+trans-PdCl2[Ph2P(CH2)=N(CHC2H4-o-OH]2
(1)
(2)
c Rw=(ꢁwꢀꢀFoꢀ−ꢀFcꢀꢀ /ꢁwꢀFoꢀ )
.
2
2 0.5
d GOF=[ꢁw(ꢀꢀFoꢀ−ꢀFcꢀꢀ)2/(no−nv)]0.5
.
cis-4 (n=4), cis-5 (n=3)
trans-5 (n=3)
trans-4 (n=4),
from the International Tables for X-ray Crystallogra-
phy, vol. IV [13]. Corrections for anomalous dispersion
were taken from the compilations of Cromer and
Lieberman [14] and applied to chlorine, phosphorus
Pt(cod)Cl2+2Ph2P(CH2)4NꢀCHC6H4-o-OH“
cis-PtCl2[Ph2P(CH2)46N=CHC6H4-o-OH]2
Table 2
,
Selected bond lengths (A) for trans-PdCl2[Ph2P(CH2)3NꢀCHC6H4-o-OH]2 (5)
Atom 1
Atom 2
Distance
Atom 1
Atom 2
Distance
Pd
Pd
P
P
P
O1
N1
N1
C13
Cl
P
C1
C7
C13
C18
C15
C16
C14
2.2949(8)
2.3354(6)
1.820(3)
1.820(3)
1.828(3)
1.329(4)
1.452(6)
1.258(4)
1.523(5)
C14
C16
C17
C17
C18
C19
C20
C21
C15
C17
C18
C22
C19
C20
C21
C22
1.516(5)
1.460(5)
1.402(5)
1.374(5)
1.387(6)
1.360(6)
1.369(7)
1.372(8)

G.M. Gray et al. / Inorganica Chimica Acta 314 (2001) 133–138
137
Table 3
Selected bond angles (°) for trans-PdCl2[Ph2P(CH2)3NꢀCHC6H4-o-OH]2 (5)
Atom 1
Atom 2
Atom 3
Angle
Atom 1
Atom 2
Atom 3
Angle
Cl
Pd
P
P
P
N1
C13
P
C1
C7
C13
C16
C14
89.32(2)
108.81(8)
118.64(9)
116.9(1)
118.3(3)
113.9(2)
C13
N1
N1
C16
O1
C14
C15
C16
C17
C18
C15
C14
C17
C18
C17
110.2(3)
112.7(3)
123.0(3)
121.6(3)
121.8(3)
Pd
Pd
Pd
C15
P
fac-Ru(CO)3Cl2(THF)+2Ph2P(CH2)4Nꢀ
CHC6H4-o-OH“
its molecular weight to be obtained by either cryoscopy
or vapor phase osmometry. However, the facts that the
complex did crystallize and that it exhibited a sharp
and symmetric 31P NMR resonance suggest that it is
monomeric. This suggestion is further supported by the
fact that the phenyl rings of the phosphine groups are
inequivalent. The constrained and helical orientation of
the ligands in bimetallic complexes of the type shown in
Fig. 1 could result in inequivalent phenyls. The ligand
orientation in an oligomeric complex would be less
constrained should not result in inequivalent phenyls.
Both the fact that 8 is diamagnetic and its d–d transi-
tion at 623 nm (dichloromethane solution) are consis-
tent with a square planar coordination geometry for the
Ni [3c].
In contrast to the clean reaction of 3 and Pd(cod)Cl2
to yield 8, the reaction of 3 and Pt(cod)Cl2 gave a
mixture of products including cis-PtCl2[Ph2P-
(CH2)4NꢀCHC6H4-o-OH]2 (6). Complex 3 used in this
reaction did not contain any free ligand, and thus 6
must be formed by decomplexation of the Ni2+ after
coordination of the phosphines of 3 to the platinum.
This suggests that bimetallic complexes with cis-coordi-
nated phosphines are more strained and less stable than
those with trans-coordinated phosphines. This conclu-
sion is consistent with the fact that the closely related
cis,cis,trans-RuCl2(CO)2[Ph2P(CH2)4N=
CHC6H4-o-OH]2 7
(3)
The reactions shown in Eqs. (1)–(3) yield complexes
with a variety of coordination geometries. The palla-
dium, 4 and 5, and platinum, 6, complexes are square
planar. Both the cis and trans isomers of 4 and 5 are
formed as indicated by 31P NMR resonances at approx-
imately 28 ppm for the cis isomers and at approxi-
mately 17 ppm for the trans isomers. The cis:trans ratio
is approximately 7:93 for 4 based on the integration of
these resonances. In contrast, only the cis isomer of 6 is
1
observed as indicated by the large ꢀ J(PtP)ꢀ of 3655 Hz.
The ruthenium complex, 7, is octahedral and can have
a number of possible isomers. Only a single isomer is
obtained and appears to contain cis carbonyl and chlo-
ride ligands and trans phosphines based on the observa-
tions of a single 31P NMR resonance, a single 1:2:1
triplet 13C NMR resonance for the carbonyls and two
equally intense IR carbonyl stretching absorptions
[10a]. The coordination geometries observed for the
complexes of 1 and 2 are similar to those reported for
related complexes of less complex phosphine ligands
suggesting that the salicylaldimine group does not sig-
nificantly affect the manner in which the phosphine
group coordinates to the metals [10a].
Although the monometallic complexes, 4–7, were
readily synthesized, they could not be cleanly converted
into bimetallic complexes by reaction either with nickel
acetate or with a solution of diethylzinc in toluene.
Invariably, these reactions were incomplete and also
gave mixtures of products. Attempts to separate the
various components in these mixtures by fractional
recrystallization were unsuccessful.
The bimetallic complex, trans-PdCl2[Ph2P(CH2)4-
NꢀCHC6H4-o-O]2Ni (8) was prepared by the reaction
of [Ph2P(CH2)4NꢀCHC6H4-o-O]2Ni (3) and PdCl2(cod).
This gave a single compound that could be recrystal-
lized by slow evaporation of a THF/diethyl ether solu-
tion to give golden–brown crystals. Complex 8 was not
sufficiently soluble in common organic solvents to allow
Fig. 2. ORTEP drawing [15] of the molecular structure of trans-
PdCl2[Ph2P(CH2)3NꢀCH–C6H4-o-OH]2 (5). The thermal ellipsoids
are drawn at the 25% probability level and the hydrogen atoms are
omitted for clarity.

138
G.M. Gray et al. / Inorganica Chimica Acta 314 (2001) 133–138
Acknowledgements
cis-Mo(CO)4[Ph2P(CH2)4NꢀCHC6H4-o-O]2Ni complex
isomerizes upon standing [4].
The authors are grateful to the Petroleum Research
Fund of the American Chemical Society for support-
ing this research. M.J.J. thanks the Graduate School
of the University of Alabama at Birmingham for a
Graduate Fellowship.
3.2. X-ray crystal structure of trans-
PdCl2[Ph2P(CH2)4NꢀCHC6H4-o-OH]2 (5)
Although 5 exists in solution as a mixture of cis and
trans isomers, crystals of the pure trans isomer could
be obtained by slowly cooling a saturated dichloro-
methane/hexanes solution of 5 to −5°C. The complex
crystallizes in the P21/n space group with the Pd lo-
cated on an inversion center so that the asymmetric
unit is one half of the molecule. An ORTEP drawing of
the molecule is shown in Fig. 2.
The coordination geometry of the Pd is an almost
perfect square plane with Cl–Pd–P angles of 89.32(2)°
and Cl–Pd–Cl and P–Pd–P angles of 90.68(2)°. The
Pd–Cl and Pd–P distances of 2.2949(8) and 2.3354(6),
respectively, are well within the ranges expected for
these bonds. The Pd–Cl bonds are nearly parallel to
the P–C13 bond (the C13–P–Pd–Cl torsion angle is
168.1(1)°) and split the angle between the two P-
phenyl bonds.
The presence of the center of symmetry in the
molecule means that the two salicylaldimine groups
are located on opposite sides of the plane formed by
Pd, P and Cl and are coplanar. This orientation would
not allow chelation of both salicylaldimine groups to a
single metal dication without significant reorganization
of the structure. If this type of orientation is also
favored in solution, it could explain why the reactions
of 4 or 5 with either nickel acetate or diethylzinc are
incomplete and give mixtures of products. The route
that was successfully used to prepare trans-
PdCl2[Ph2P(CH2)4NꢀCH–C6H4-o-O]2Ni (8) avoids this
problem by first coordinating the salicyaldimine
groups to the Ni2+ to form 3 and then reacting the
free phosphine groups in this complex with Pd-
(cod)Cl2.
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