New mono- and di-nuclear complexes of PdII, PtII and NiII of PNNP ligands with a 2,2′-biaryl bridging unit

Article abstract of DOI:10.1039/a704170e

The Schiff bases 2,2′-bis{N-[(2-diphenylphosphino)phenyl]formimidoyl}biphenyl (L¹) and 2,2′-bis{[(2-diphenylphosphino)benzylidene]amino}biphenyl (L²) were synthesized from the appropriate amine and aldehyde. Their co-ordination behaviour towards Pd^II, Pt^II and Ni^II has been studied. Dinuclear complexes were formed when treating L¹ with 2 equivalents of [PdCl(Me)(cod)] (cod = cycloocta-1,5-diene) and Pd(O₂CMe)₂. In the case of the reaction of L¹ with Pd(O₂CMe)₂ an unexpected double cyclopalladated complex was formed. However, treatment of L¹ with 2 equivalents of [PtCl₂(MeCN)₂] resulted in hydrolysis of the ligand and a mononuclear complex of (2-diphenylphosphino)benzenamine was obtained. The structure of [Pd₂L¹Cl₂Me₂] 1 has been established by an X-ray diffraction study. The dihedral angle between the biphenyl rings is 49.2(8)° and the intramolecular Pd ... Pd distance is 7.165(3) A. The biphenyl bridging moiety shows a remarkable bending of 169.2(8)°. Treatment of 1 with carbon monoxide resulted in a double CO insertion, yielding the bis(acetyl)palladium compound [Pd₂L¹Cl₂-{C(O)Me}₂] 2. The structure of [Pd₂L¹(O₂CMe)₂]·4CH ₂Cl₂ 3 was also determined by X-ray diffraction. The dihedral angle between the biphenyl rings is 75.9(14)° while the intramolecular Pd ... Pd distance is 8.655(2) A. The reaction of L² with 2 equivalents of anhydrous [PdCl₂(MeCN)₂] or NiCl₂ afforded mononuclear complexes. The crystal and molecular structure of [PdL²]Cl₂·3.5CH₂Cl₂ was determined. The compound has an approximately square-planar P₂N₂ geometry.

Full text of DOI:10.1039/a704170e

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New mono- and di-nuclear complexes of PdII, PtII and NiII of PNNP
ligands with a 2,2Ј-biaryl bridging unit
Alette G. J. Ligtenbarg,a Esther K. van den Beuken,a Auke Meetsma,a Nora Veldman,b
Wilberth J. J. Smeets,b Anthony L. Spekb and Ben L. Feringa*,a
a Department of Organic and Molecular Inorganic Chemistry, Groningen Center for Catalysis and
Synthesis, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
b Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research,
University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands
The Schiff bases 2,2Ј-bis{N-[(2-diphenylphosphino)phenyl]formimidoyl}biphenyl (L1) and 2,2Ј-bis{[(2-diphenyl-
phosphino)benzylidene]amino}biphenyl (L2) were synthesized from the appropriate amine and aldehyde. Their
co-ordination behaviour towards PdII, PtII and NiII has been studied. Dinuclear complexes were formed when
treating L1 with 2 equivalents of [PdCl(Me)(cod)] (cod = cycloocta-1,5-diene) and Pd(O2CMe)2. In the case of the
reaction of L1 with Pd(O2CMe)2 an unexpected double cyclopalladated complex was formed. However, treatment
of L1 with 2 equivalents of [PtCl2(MeCN)2] resulted in hydrolysis of the ligand and a mononuclear complex of
(2-diphenylphosphino)benzenamine was obtained. The structure of [Pd2L1Cl2Me2] 1 has been established by an
X-ray diffraction study. The dihedral angle between the biphenyl rings is 49.2(8)Њ and the intramolecular Pd ؒ ؒ ؒ Pd
distance is 7.165(3) Å. The biphenyl bridging moiety shows a remarkable bending of 169.2(8)Њ. Treatment of 1 with
carbon monoxide resulted in a double CO insertion, yielding the bis(acetyl)palladium compound [Pd2L1Cl2-
{C(O)Me}2] 2. The structure of [Pd2L1(O2CMe)2]ؒ4CH2Cl2 3 was also determined by X-ray diffraction. The
dihedral angle between the biphenyl rings is 75.9(14)Њ while the intramolecular Pd ؒ ؒ ؒ Pd distance is 8.655(2) Å.
The reaction of L2 with 2 equivalents of anhydrous [PdCl2(MeCN)2] or NiCl2 afforded mononuclear complexes.
The crystal and molecular structure of [PdL2]Cl2ؒ3.5CH2Cl2 was determined. The compound has an
approximately square-planar P2N2 geometry.
The chemistry of dinuclear transition-metal complexes has
b
attracted considerable interest in recent years.1 In particular
N
N
dinuclear models of metalloproteins2 have received great atten-
tion3 and a variety of new homo-4 and hetero-dinuclear5 com-
plexes has been synthesized. In the design of these types of
compounds the choice of the ligand system is of prime import-
ance.6 When the two metal centres are incorporated in close
proximity the complexes have the potential of catalysing reac-
tions either more efficiently, or with different chemo-, regio- or
stereo-selectivity than those of corresponding mononuclear
ones, due to co-operation of the two metals in the transition
state of the catalytic reaction.7 An excellent example of a
dinuclear catalyst which exhibits higher regioselectivity and
reactivity than those of the related mononuclear system by
bimetallic co-operation is the dirhodium system reported by
Stanley and co-workers8 for the hydroformylation of α-olefins.
In our group oxygen activation on dinuclear copper complexes
contain a meta-arene-bridged ligand system was investigated.9
Recently dinuclear rhodium phosphite complexes based on a
tetranaphthol skeleton were studied as catalysts in hydro-
formylation reactions.10 In the systems studied so far ligands are
often either highly flexible or rigid; in the second case the two
metal centres are in a fixed orientation towards each other. It
was envisaged that when the distance between the two metal ions
is flexible this might result in optimum co-operation of the
metal centres in the transition state of a catalytic reaction. A
building block for this approach is a biphenyl unit, which can
act as a bridging moiety between two ligating groups. Réglier et
al.11 have reported a dinuclear complex of a bis(pyridyl)-
substituted biphenyl ligand which acts as a functional mimic of
tyrosinase, a copper-containing monooxygenase. However, in
most cases where a biaryl backbone is used, mononuclear com-
plexes are obtained e.g. with NiII, CuII, CoII, ZnII and PdII.12,13
In the approach described here a biphenyl ligand system is
developed consisting of two fairly rigid arms connected to
P
P
a
b
the backbone which has flexibility at point a. Owing to the
bulky 2,2Ј substituents, however, hindered rotation is expected
around the biaryl bond (atropisomerism), which might result
in stereoisomers of these ligands or complexes. As donor sets
phosphorus and imino-nitrogen atoms were chosen, and the
co-ordination behaviour of these ligands with metals of Group
VIII, e.g. PdII, PtII and NiII, was studied. The co-ordination
geometry of the metals will largely be determined by the angle
between the two phenyl rings in the biphenyl moiety (a) and by
rotation around the single bonds connecting the side-arms to
this unit (b).
Results
Synthesis of 2,2Ј-bis{N-[(2-diphenylphosphino)phenyl]-
formimidoyl}biphenyl (L1)
The tetradentate diimine ligand 2,2Ј-bis{N-[(2-diphenyl-
phosphino)phenyl]formimidoyl}biphenyl (L1) was synthesized
by the Schiff-base formation of 2 equivalents of biphenyl-2,2Ј-
dicarbaldehyde with (2-diphenylphosphino)benzenamine14
(Scheme 1). The synthesis of biphenyl-2,2Ј-dicarbaldehyde by
phenanthrene ozonolysis is a known literature procedure15 but
the yields are often low. Therefore we developed a more con-
venient route towards this compound starting from diphenic
acid ([1,1Ј-biphenyl]-2,2Ј-dicarboxylic acid).16 In a first step the
dimethyl ester I was formed in 80% yield. Subsequently reduc-
tion with lithium aluminium hydride gave the corresponding
J. Chem. Soc., Dalton Trans., 1998, Pages 263–270
263

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OH
OH
(ii)
(i)
CO2H
CO2H
CO2Me
CO2Me
PPh2
Me
N
(i)
Pd
1 + 2[PdCl(Me)(cod)]
Me
Cl
N
L
Cl
Pd
Ph2P
I
II
1
(iii), (iv)
PPh2
N
N
(v)
CHO
CHO
O
PPh2
N
(ii)
Pd
MeC
Cl
N
1
+ 2CO
Cl
CMe
O
PPh2
Pd
Ph2P
L1
III
2
Ph2
P
Scheme 1 (i) MeOH, H2SO4, reflux, 16 h, yield 80%; (ii) LiAlH4,
tetrahydrofuran (thf), reflux, 17 h, 90%; (iii) ClCOCOCl, dimethyl
sulfoxide (dmso), Ϫ60 ЊC, 45 min; (iv) NEt3, 90%; (v) (2-diphenyl-
phosphino)benzenamine, toluene-p-sulfonic acid, benzene, molecular
sieves (4 Å), Dean–Stark, reflux, 24 h, 65%
MeCO2
Pd
N
(iii)
L1 + 2Pd(O2CMe)2
N
P
Pd
O2CMe
(i)
(ii)
CO2H
CO2H
NH2
NH2
N
N
PPh2
PPh2
Ph2
3
2+
Ph2
P
H2
N
(iv)
2 Cl–
L1 + 2[PtCl2(MeCN)2]
Pt
L2
N
P
Scheme 2 (i) NaN3, H2SO4, 30–40 ЊC, 95 min, yield 65%; (ii) 2-
(diphenylphosphino)benzaldehyde, toluene-p-sulfonic acid, benzene,
Dean–Stark, reflux, 4 h, 92%
H2
Ph2
4
Scheme 3 (i) thf, room temperature (r.t.), 16 h, yield 65%; (ii) CDCl3,
r.t., 15 min; (iii) CH2Cl2, r.t.; (iv) CH2Cl2, r.t., 1 h
diol II in 90% yield. Next, a mild Swern oxidation was per-
formed, affording the dialdehyde III in high yield (90%). The
synthesis of L1 was carried out under a nitrogen atmosphere in
dry benzene. The reaction was followed by 31P NMR spectro-
scopy, which revealed that imine formation was rather slow and
was complete after 24 h. Besides a Dean–Stark trap, addition of
molecular sieves was necessary in order to remove all the water
produced during the reaction and to drive it to completion.
Even small amounts of water in the reaction mixture caused
oxidation of the product. The compound L1 was purified
by crystallisation from a dichloromethane–pentane solvent
mixture. It showed in the 31P NMR spectrum an absorption
at δ Ϫ14.9 and is air-stable in the solid state. Furthermore,
Ϫ15.2 in the 31P NMR spectrum. The product was also charac-
terised as for L1.
Compound L2 was air-stable in the solid state as well as in
solution. The Schiff-base reaction yielding it was much faster
than the imine formation affording L1 as only 4 h for complete
conversion for L2 and 24 h for L1 were required. In addition, a
larger overall yield for L2 compared to L1 (60 and 45%, respect-
ively) was found.
Palladium and platinum complexes based on L1
Ligand L1 was allowed to react with 2 equivalents of
[PdCl(Me)(cod)]19 (cod = cycloocta-1,5-diene) in tetrahydro-
furan for 16 h at room temperature yielding a precipitate, which
was crystallised from dichloromethane–pentane as pale yellow
crystals in 65% yield. The cod group of the starting material
was replaced by L1, giving rise to dinuclear complex 1 (Scheme
3). The 31P NMR spectrum shows a singlet at δ 35.4 (CDCl3),
which indicates that the two phosphorus atoms are identical.
Compared with the free biphenyl (δ Ϫ14.9, CDCl3) a strong
downfield shift is observed. The 1H NMR spectrum of 1
revealed that the methyl groups on the metal ions are equivalent
giving a sharp doublet at δ 0.86 due to phosphorus proton
coupling [J(P᎐H) = 2.93 Hz]. The magnitude of this coupling
indicates a cis relationship20 between two groups having a large
trans influence,21 i.e. the phosphorus atom and the methyl
group. The crystal structure of [Pd2L1Cl2Me2] 1 was established
by an X-ray diffraction study (Fig. 1). Selected bond lengths,
angles and torsion angles are listed in Table 1.
1
the ligand was characterised by H NMR spectroscopy, ele-
mental analysis and mass spectrometry (see Experimental
section).
Synthesis of 2,2Ј-bis{[2-(diphenylphosphino)benzylidene]amino}-
biphenyl (L2)
A related tetradentate Schiff-base ligand (L2) with phosphorus
and imino-nitrogen donor sets was also synthesized. In L2 the
imino nitrogen atom is attached to the biphenyl moiety, instead
of the imino carbon atom in L1. We expected this ligand to be
more stable towards oxidation and more easily synthesized.
Furthermore, upon co-ordination of the phosphorus and
nitrogen atoms to a metal ion, a six-membered chelate ring will
be formed instead of a five-membered ring in the case of L1.
Ligand L2 was synthesized by a Schiff-base reaction of 2,2Ј-
diaminobiphenyl17 and 2-(diphenylphosphino)benzaldehyde
(Scheme 2).18 After 4 h reflux in benzene under Dean–Stark
conditions with a catalytic amount of toluene-p-sulfonic acid
L2 was obtained in 92% yield. It showed an absorption at δ
The notion that the ligand has imposed C2 symmetry on the
palladium complex was confirmed by the X-ray diffraction
analysis showing a two-fold axis dividing the C(25)᎐C(25a)
264
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Table 1 Selected bond distances (Å) and angles (Њ) and torsion angles
(Њ) of complex 1 with estimated standard deviations (e.s.d.s) in paren-
theses
Table 2 Selected bond distances (Å) and angles (Њ) and torsion angles
(Њ) of complex 3 with e.s.d.s in parentheses
Pd(1)᎐N(1)
Pd(1)᎐O(1)
Pd(1)᎐P(1)
2.000(7)
2.051(7)
2.319(2)
Pd(1)᎐C(21)
C(25)᎐C(25a)
Pd(1) ؒ ؒ ؒ Pd(1a)
1.978(10)
1.508(14)
8.655(2)
Pd᎐N
Pd᎐Cl
Pd᎐P
2.237(4)
2.3625(15)
2.1963(16)
Pd᎐C(26)
C(25)᎐C(25a)
Pd(1) ؒ ؒ ؒ Pd(1a)
2.020(6)
1.486(6)
7.165(3)
P(1)᎐Pd(1)᎐O(1)
P(1)᎐Pd(1)᎐N(1)
O(1)᎐Pd(1)᎐C(21)
N(1)᎐Pd(1)᎐C(21)
100.0(2)
84.5(2)
93.4(2)
82.0(3)
O(1)᎐Pd(1)᎐N(1)
172.7(3)
166.6(3)
122.5(8)
119.8(9)
Cl᎐Pd᎐N
P᎐Pd᎐N
P᎐Pd᎐C(26)
Cl᎐Pd᎐C(26)
98.57(11)
79.70(11)
92.0(2)
Cl᎐Pd᎐P
N᎐Pd᎐C(26)
C(20)᎐C(25)᎐C(25a) 126.0(4)
C(24)᎐C(25)᎐C(25a) 116.5(4)
178.21(5)
169.6(2)
P(1)᎐Pd(1)᎐C(21)
C(20)᎐C(25)᎐C(25a)
C(24)᎐C(25)᎐C(25a)
89.8(2)
C(20)᎐C(25)᎐C(25a)᎐C(20a) 75.9(14)
C(20)᎐C(25)᎐C(25a)᎐C(20a) 49.2(8)
isocyanate resulted in the formation of some palladium(0) and a
complex reaction mixture, according to NMR spectroscopy,
which was not further identified.
Reaction of 2 equivalents of Pd(O2CMe)2 with L1 was
carried out in dichloromethane at room temperature under a
nitrogen atmosphere for 1.5 h. Subsequently, the solvent was
removed in vacuo and the resulting dark yellow-brown oil was
crystallised from dichloromethane–pentane. Dark red crystals
of the cyclopalladated complex 3 were obtained after a few
weeks and its structure confirmed by X-ray crystallography
(Fig. 2). The 31P NMR spectrum shows a singlet at δ 44.9
(CDCl3), which indicates that the two phosphorus atoms are
identical.
The complex has C2 symmetry with a two-fold axis dividing
the C(25)᎐C(25a) bond. The two phenyl rings of the biphenyl
moiety are twisted with respect to each other with a dihedral
angle of 75.9(14)Њ for C(20)᎐C(25)᎐C(25a)᎐C(20a). Atoms
C(22), C(25) and C(25a), C(22a) show a nearly linear arrange-
ment. For example the angle between C(22), C(25) and C(25a)
is 179.1(9)Њ. The distances between palladium and the co-
ordinated donor atoms in complex 3 are in the normal range,
Pd᎐N and Pd᎐P are 2.000(7) and 2.319(2) Å, respectively and
Pd᎐O and Pd᎐C are respectively 2.051(7) and 1.978(10) Å.26
The intramolecular metal–metal distance is 8.655(2) Å. The
metal adopts a distorted square-planar co-ordination geom-
etry: the angles P(1)᎐Pd(1)᎐N(1) [84.5(2)Њ] and N(1)᎐Pd(1)᎐
C(21) [82.0(3)Њ] are significantly less than the ideal 90Њ. The
angles P(1)᎐Pd(1)᎐O(1) and O(1)᎐Pd(1)᎐C(21) are respectively
100.0(2) and 93.4(3)Њ. Selected bond lengths and angles are
listed in Table 2.
Fig. 1 An ORTEP22 plot of complex 1 (50% probability level)
bond. The metals adopt
a distorted square-planar co-
ordination geometry. The P᎐Pd᎐N angle of 79.70(11)Њ is signifi-
cantly smaller than the ideal 90Њ angle, whereas the Cl᎐Pd᎐N
angle of 98.57(11)Њ is significantly larger than 90Њ. The distances
between palladium and the donor atoms are within the normal
range;20b,23,24a Pd᎐N and Pd᎐P distances are 2.237(4) and
2.1963(16) Å, respectively whereas Pd᎐Cl and Pd᎐CH3 are
2.3625(15) and 2.020(6) Å, respectively. The Pd ؒ ؒ ؒ Pd distance
is 7.165(3) Å and the metal ions are directed to the outside
(anti-folding, see Scheme 5, structure A). The two phenyl rings
of the biphenyl are twisted with respect to each other resulting
in a dihedral angle of 49.2(8)Њ for C(20)᎐C(25)᎐C(25a)᎐C(20a).
A remarkable feature of the biphenyl moiety is the significant
non-linearity as shown by the orientation of the atoms C(22),
C(25), C(25a) and C(22a). The angle C(22)᎐C(25)᎐C(22a) is
169.2(8)Њ instead of the ideal 180Њ. The carbon atoms of the
phenyl ring of C(20) to C(25) deviate 0.022 Å from the mean
plane. Carbon atom C(22a) is 0.366(6) Å and C(25a) 0.123(5) Å
out of that plane.
From 31P and 1H NMR studies it can be concluded that
cyclometallation of L1 with Pd(O2CMe)2 in dichloromethane is
a very slow process. Initially, upon addition of Pd(O2CMe)2, a
mixture of products is formed. These products eventually
rearrange to give the more stable cyclopalladated compound
together with acetic acid. The formation of [Pd2(O2CMe)2L1] is
irreversible.
The binding of L1 to PtII was briefly examined by treating a
solution of L1 in dichloromethane with 2 equivalents of bis-
(acetonitrile)platinum() chloride. After 1 h at room temper-
ature 31P NMR spectroscopy showed the presence of various
compounds. After 1 night this composition had not changed.
Attempts to isolate either a mono- or a di-nuclear complex
of L1 failed. The only complex that was isolated according
Complexes containing a metal–carbon σ bond can undergo
insertion reactions with e.g. carbon monoxide24 and iso-
cyanides.25 Treatment of a solution of 1 with carbon monoxide
in CDCl3 at room temperature for 15 min resulted smoothly
and nearly quantitatively in double CO insertion leading to
the formation of the dinuclear acetylpalladium compound
[Pd2L1Cl2{C(O)Me}2] 2 which was characterised by IR and
NMR spectroscopy. The CO stretching vibration at 1697 cmϪ1
1
to H, 13C NMR spectroscopy and elemental analysis was the
platinum complex 4 of (2-diphenylphosphino)benzenamine
IV. Obviously, the complexes formed initially are highly water
sensitive. During work-up by filtering the solution in the pres-
ence of air the ligand was hydrolysed, followed by complexation
of Pt to form 4.
1
indicates inserted carbon monoxide.24a In the H NMR spec-
trum the methyl absorption is shifted to δ 2.25 compared with
δ 0.86 in 1 and the coupling pattern has disappeared. The
13C NMR spectrum shows an additional carbonyl absorption at
δ 210.8 and an acetyl methyl signal at δ 10.93 whereas the
methyl resonance in 1 was located at δ Ϫ1.42. The 31P resonance
has shifted upfield to δ 14.29. Reaction of 1 with tert-butyl
Palladium and nickel complexes based on L2
To study the co-ordination behaviour of L2, 2 equivalents of
[PdCl2(MeCN)2] were added to a solution of L2 in dichloro-
methane at room temperature. Remarkably, in this case no
J. Chem. Soc., Dalton Trans., 1998, Pages 263–270
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Fig. 2 An ORTEP plot of complex 3 (50% probability level)
2+
(i)
L2
+
[PdCl2(MeCN)2]
2Cl–
N
N
Pd
P
P
Ph2 Ph2
5
2+
(ii), (iii)
L2
+ NiCl2
–
N
N
2BF4
Ni
P
P
Ph2 Ph2
6
Scheme 4 (i) CH2Cl2, r.t., 1.5 h, yield 66%; (ii) absolute EtOH, reflux,
3 h; (iii) CH2Cl2, 4 NaBF4, r.t., 2 h, 53%
Fig. 3 An ORTEP plot of one of the two independent molecules in
the crystals of complex 5 (50% probability level)
Table 3 Selected bond distances (Å) and angles (Њ) and torsion angles
(Њ) of complex 5* with e.s.d.s in parentheses
(dichloromethane). In both structures the chlorides are non-
co-ordinating. The palladium ion adopts a slightly distorted
square-planar geometry. The twist in the biphenyl moiety is
51.4(11)Њ for C(241)᎐C(251)᎐C(261)᎐C(271) and 51.5(11)Њ for
the corresponding carbon atoms in the second structure. The
distances between palladium and the donor atoms are within
the normal range.23 The distances between Pd(1) and P(1) and
P(2) are 2.243(2) and 2.262(2) Å, respectively. The Pd᎐N dis-
tances are 2.086(6) Å for Pd(1)᎐N(1) and 2.164(6) Å for
Pd(1)᎐N(2). Also in this compound the atoms C(221)᎐C(251)᎐
C(261)᎐C(291) show a non-linear arrangement, but the bending
in the biaryl unit is significantly less than in complex 1 (see
above). The angle between C(251), C(261) and C(291) is
175.5(6)Њ and for the corresponding atoms in the second struc-
ture 175.2(6)Њ. For a related mononuclear rhodium() complex
of an asymmetric 6,6Ј-dimethyl-2,2Ј-bis{[2-diphenylphos-
phino)benzylidene]amino}biphenyl ligand27 no bend in the
biphenyl moiety was reported, whereas the dihedral angle
between the rings was larger (69Њ).
Pd(1)᎐N(1)
Pd(1)᎐N(2)
Pd(1)᎐P(1)
2.086(6)
2.164(6)
2.243(2)
Pd(1)᎐P(2)
Pd(1) ؒ ؒ ؒ Cl(1)
C(251)᎐C(261)
2.262(2)
2.8025(19)
1.470(11)
P(1)᎐Pd(1)᎐N(2)
P(1)᎐Pd(1)᎐P(2)
N(1)᎐Pd(1)᎐N(2) 90.0(2)
P(2)᎐Pd(1)᎐N(1) 88.29(17)
85.08(18)
96.56(8)
P(1)᎐Pd(1)᎐N(1)
P(2)᎐Pd(1)᎐N(2)
C(201)᎐C(251)᎐C(261) 122.6(7)
C(241)᎐C(251)᎐C(261) 119.5(7)
175.08(17)
161.98(16)
C(241)᎐C(251)᎐C(261)᎐C(271) 51.4(11)
* Values for only one crystallographically independent molecule are
given. The dimensions of the second are very similar.
formation of a dinuclear species was observed. According to
31P NMR spectroscopy, mononuclear complex 5 (Scheme 4)
was formed quantitatively, giving rise to a 31P NMR absorption
at δ 31.1 (free biphenyl δ Ϫ15.2). Crystallisation from
dichloromethane–pentane afforded orange crystals suitable for
X-ray analysis. The crystal structure of 5 is shown in Fig. 3.
Selected bond lengths, angles and torsion angles are listed in
Table 3.
Upon reaction of L2 with anhydrous nickel() chloride mono-
nuclear complex 6 was formed which was characterised by 31P
and 1H NMR spectroscopy, elemental analysis and mass
spectrometry (see Experimental section). The complex shows
an absorption in the 31P NMR spectrum at δ 31.3.
Complex 5 exists in two forms in the unit cell which slightly
differ from one another, together with seven solvent molecules
266
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200 spectrometer (at 80.95 MHz) with triphenyl phosphate as
M
M
an external reference (δ Ϫ18). High-resolution mass spectra
were obtained on an AEI MS-902 spectrometer by electron
impact (EI), electron spray (ES) mass spectra on a NERMAG
mass spectrometer. Infrared spectra were recorded on a Perkin-
Elmer 841 spectrometer. Elemental analyses were performed in
the Microanalytical Department of our laboratory.
N
N
N
N
N
N
P
P
P
P
P
P
M
M
M
All manipulations were carried out under an atmosphere
of dry dinitrogen except for the synthesis of compound I.
Dichloromethane, pentane and hexane were distilled from
phosphorus pentaoxide, methanol from magnesium, benzene
from sodium wire and tetrahydrofuran from sodium–
benzophenone. Dimethyl sulfoxide was dried by stirring over
barium oxide during 18 h before use. (2-Diphenylphosphino)-
A
B
C
Scheme 5 Representation of the geometries of mono- and di-nuclear
complexes based on PNNP ligands
Discussion
From these results it can be concluded that L1 is an excellent
dinucleating ligand for palladium. When [PdCl(Me)(cod)] is
added to L1 a geometry is adopted in which the ligating groups
at each phenyl ring point to the ‘inside’ and the two metal
centres are directed to the ‘outside’ as illustrated in Scheme 5,
structure A. Probably steric interactions between the two side-
arms disfavour the formation of a syn-folded geometry as indi-
cated in structure B, although it must be emphasised that in
solution rotation around the single bonds connecting the side-
arms to the backbone is still possible. In geometry B the two
metals are in closer proximity, yielding a complex in which they
might be able to co-operate in a catalytic reaction. However, in
the double cyclometallated complex 3 (Fig. 2), despite the biaryl
rotation, the formation of a syn-folded geometry is not possible
because the palladium ions are directly attached to the biphenyl
backbone via C(21)᎐Pd(1) [C(21a)᎐Pd(1a)] aryl–metal bonds.
In the case of L2 only mononuclear complexes were formed
with the general structure as shown in Scheme 5, C. In spite of
the possibility of adopting a conformation able to accom-
modate two metal ions simultaneously, by rotation around the
single bond in the biphenyl backbone, only mononuclear com-
plexes are formed. Apparently, these are very stable. Once a
metal ion is complexed between the four donor atoms in the
ligand, the binding of a second metal ion is disfavoured.
benzenamine,14
2,2Ј-diaminobiphenyl,17
2-(diphenylphos-
phino)benzaldehyde18 and [PdCl(Me)(cod)]19 were synthesized
using literature procedures. Diphenic acid, 2-bromo-
benzaldehyde and chlorodiphenylphosphine obtained from
Aldrich were used without further purification.
Preparations
Biphenyl-2,2Ј-dicarboxylic acid dimethyl ester I. To biphenyl-
2,2Ј-dicarboxylic acid (25.0 g, 103 mmol) in methanol (250 cm3)
was added sulfuric acid (4 cm3) and the solution was heated
under reflux for 16 h. The resulting dark brown reaction mix-
ture was poured into a water–ice mixture (300 cm3) and sub-
sequently ethyl acetate (300 cm3) was added. Evaporation of
most of the methanol yielded a two-phase system. The dark
green aqueous layer was extracted with ethyl acetate (2 × 75
cm3) and the combined organic layers were subsequently
washed with saturated sodium hydrogencarbonate solution
(2 × 75 cm3), water (1 × 75 cm3) and brine (1 × 50 cm3). Drying
(MgSO4) and evaporation of the solvent yielded a pale brown
solid which was crystallised from ethyl acetate (10 cm3). Yield:
1
22.6 g as white crystals (80%). M.p. 76.7–77.7 ЊC; H NMR
(CDCl3) δ 8.05–8.00 (m, 2 H), 7.60–7.40 (m, 4 H), 7.24–7.20 (m,
2 H) and 3.63 (s, 6 H); 13C NMR (CDCl3) δ 167.4 (C), 143.3 (C),
131.4 (CH), 130.2 (CH), 129.8 (CH), 129.3 (C), 127.2 (CH) and
51.8 (CH3).
Conclusion
Two new ligand systems, L1 and L2, were developed containing
a PNNP donor-atom sequence and a biphenyl backbone. We
have shown that L1 can readily accommodate two palladium
ions. Furthermore, a mild double cyclometallation reaction
was observed with Pd(O2CMe)2 although the process is rather
slow. In contrast, L2 only affords mononuclear complexes of
palladium and nickel. Notably, the crystal structures of [Pd2-
L1Cl2Me2] 1 and [Pd2L2]Cl2 5 obtained by X-ray analyses
showed that the biphenyl moiety is twisted to approximately the
same degree (about 50Њ) for both complexes. However, the twist
in the biphenyl moiety of [Pd2L1(O2CMe)2] 3 is much larger
(75.9Њ). Another remarkable feature of these compounds is the
significant non-linearity in the biphenyl entity leading to sig-
nificant biphenyl bending. Finally with complex 1 a successful
double-insertion reaction was performed with carbon mon-
oxide yielding [Pd2L1Cl2{C(O)Me}2] 2.
2,2Ј-Di(hydroxymethyl)biphenyl II. Dimethyl ester I (7.0 g,
25.9 mmol) in thf (100 cm3) was added slowly to a sus-
pension of LiAlH4 (2.0 g, 0.21 mol) in thf (150 cm3) at 0 ЊC. The
reaction mixture was refluxed for 17 h. After cooling to 0 ЊC,
aqueous 1.4  KOH (20 cm3) was added carefully. After reflux-
ing for 1 h, filtering, drying (MgSO4) and evaporation of the
solvent, II was obtained in 94% yield as a white solid which was
recrystallised from ethyl acetate (10 cm3). Yield: 5.0 g as white
1
needles (90%). M.p. 112.4–113.5 ЊC; H NMR (CDCl3) δ 7.36
(m, 6 H), 7.13 (dd, J = 0.9, J = 3.6 Hz, 2 H), 4.27 (s, 4 H) and
3.66 (s, OH, 2 H); 13C NMR (CDCl3) δ 140.0 (C), 138.6 (C),
129.61 (CH), 129.55 (CH), 128.0 (CH), 127.6 (CH) and 62.7
(CH2).
Biphenyl-2,2Ј-dicarbaldehyde III. A solution of oxalyl chlor-
ide (2.75 cm3, 0.032 mol, 2.7 equivalents) in dichloromethane
(50 cm3) was cooled to Ϫ60 ЊC and a mixture of dmso (3 cm3,
0.042 mol, 3.5 equivalents) and dichloromethane (10 cm3) was
added carefully. After stirring for 5 min, II (2.6 g, 0.012 mol) in
dmso (1 cm3) and dichloromethane (50 cm3) was added in less
than 5 min. The resulting white solution was stirred for 45 min
at Ϫ60 ЊC. Next a large excess of triethylamine (10 cm3, 0.072
mol, 6.0 equivalents) was added carefully. The mixture was
allowed to warm to room temperature and subsequently
washed with 5% HCl solution (30 cm3), aqueous NaHCO3
(saturated, 30 cm3) and brine (30 cm3). Drying (MgSO4) and
evaporation of the solvent gave dialdehyde III as a pale yellow
oil that solidified upon standing. Yield: 2.3 g as a yellow solid
(90%). M.p. 63.2–64.3 ЊC (lit.,15 62.5–63.5 ЊC); 1H NMR
Experimental
Melting points (uncorrected) were determined on a Mettler FP-
2 apparatus equipped with a FP-21 microscope and are un-
corrected. Proton NMR spectra were recorded on a Varian
Gemini-200 (at 200 MHz), on a VXR-300 (at 300 MHz) or on a
Unity 500 spectrometer (at 500 MHz). Chemical shifts are
reported in δ units (ppm) relative to the solvent and converted
into the SiMe4 scale (δ 0) using δ (CHCl3) 7.26. Carbon-13
NMR spectra were recorded on a Varian Gemini-200 (at 50.3
MHz), on a VXR-300 (at 75.4 MHz) or on a Unity 500 spec-
trometer (at 125 MHz), 31P NMR spectra on a Varian Gemini-
J. Chem. Soc., Dalton Trans., 1998, Pages 263–270
267

View Online
(CDCl3) δ 9.80 (s, CHO, 2 H), 8.02 (d, J = 4, 2 H), 7.70–7.57 (m,
4 H) and 7.33 (d, J = 3 Hz, 2 H); 13C NMR (CDCl3) δ 191.0
(CH), 141.2 (C), 134.5 (C), 133.4 (CH), 131.7 (CH), 128.8 (CH)
and 128.5 (CH).
4.26; N, 2.64. Calc. for C26H22ClNPPd: C, 59.90; H, 4.25; N,
2.69%).
[Pd2L1Cl2{C(O)Me}2] 2. The complex [Pd2L1Cl2Me2] (25
mg, 0.02 mmol) in CDCl3 was stirred for 15 min under 1 bar
2,2Ј-Bis{N-[(2-diphenylphosphino)phenyl]formimidoyl}-
(105 Pa) CO at r.t. According to NMR data the conversion was
biphenyl L1. To a mixture of biphenyl-2,2Јdicarbaldehyde III
(0.31 g, 1.49 mmol), (2-diphenylphosphino)benzenamine IV
(0.83 g, 2.98 mmol, 2.0 equivalents) and a catalytic amount of
toluene-p-sulfonic acid in dry benzene (40 cm3) were added
molecular sieves (4 Å). The reaction mixture was refluxed under
Dean–Stark conditions for 16 h. After 90% completion of the
reaction according to 31P NMR spectroscopy (16 h), the mix-
ture was filtered over Celite and the yellow solution refluxed for
6 h. Evaporation of the solvent yielded a pale yellow foam. Pure
L1 was obtained upon crystallisation from dichloromethane–
pentane (1:2). Yield: 0.76 g as a pale yellow powder (65%).
M.p. 183.3–185.3 ЊC; 1H NMR (CDCl3, 200 MHz) δ 8.10–8.05
(m, 2 H), 7.87 (s, 2 H), 7.41–7.32 (m, 4 H), 7.31–7.20 (m, 22 H),
7.08 (t, J = 7.5, 2 H), 7.00–6.95 (m, 2 H), 6.79 (d, J = 1.2, 1 H),
6.77 (d, J = 1.5, 1 H), 6.74 (d, J = 4.4, 1 H), 6.71 (d, J = 1.0, 2 H)
and 6.69 (d, J = 1.2 Hz, 1 H); 13C NMR (CDCl3, 50.3 MHz)
nearly quantitative. IR (CDCl3); νCO 1687 cmϪ1 31P NMR
.
(CDCl3): δ 14.3. 1H NMR (CDCl3, 200 MHz): δ 9.35 (d, J = 7.8
Hz, 2 H), 8.57 (s, 2 H), 7.76–7.42 (m, 30 H), 7.36–7.26 (m, 2 H),
7.22–7.09 (m, 2 H) and 2.25 (s, 6 H). 13C NMR (CDCl3, 75.4
2
MHz): δ 223.39 (d, C, JPC = 7.3), 167.10 (CH), 155.03 (d, C,
2JPC = 15.9), 140.83 (C), 134.37 (CH), 133.57 (d, CH,
2JPC = 13.4), 133.17 (C), 133.11 (d, C, 2JPC = 13.4), 132.60 (CH),
132.15 (CH), 131.31 (CH), 131.00 (CH), 130.39 (CH), 129.98
3
(CH), 129.66 (CH), 129.15 (d, CH, JPC = 11.0), 129.01 (C),
128.91 (d, CH, 3JPC = 9.8), 128.41 (CH), 128.36 (CH), 120.50 (d,
CH, 2JPC = 7.3) and 37.43 (d, CH3, 3JPC = 21.8 Hz); one Cq was
not resolved.
[Pd2L1(O2CMe)2] 3. To L1 (100 mg, 0.14 mmol) in CH2Cl2
(4 cm3) was added Pd(O2CMe)2 (62 mg, 0.28 mmol, 2.0 equiv-
alents) and the resulting clear dark red solution was stirred for
1.5 h at r.t. The product was precipitated as a yellow powder by
adding the solution dropwise to pentane while stirring vigor-
ously. The pentane was decanted and the powder crystallised
from dichloromethane–pentane to yield orange-red crystals
suitable for X-ray analysis. 31P NMR (CDCl3): δ 44.9. 1H NMR
(CDCl3, 200 MHz): δ 8.14–7.98 (m, 4 H), 7.90–7.76 (m, 6 H),
7.60–7.21 (m, 24 H), 7.20–7.00 (m, 4 H) and 1.92 (s, 6 H).
4
1
δ 157.9 (CH, JPC = 1.5), 154.0 (C, JPC = 17.9), 140.3 (C),
2
2
136.8 (C, JPC = 10.7), 134.4 (C), 134.0 (CH, JPC = 20.6),
1
132.6 (C, JPC = 11.4), 132.3 (CH), 130.7, 130.2 (CH), 129.7
(CH), 128.4 (CH), 128.2 (CH, 3JPC = 7.3 Hz), 128.0 (CH), 127.2
(CH), 125.8 (CH) and 117.0 (CH); 31P NMR (CDCl3, 80.95
MHz) δ Ϫ14.9. High-resolution mass spectrum: m/z 728.251
(calc. for C50H38N2P2: 728.251) (Found: C, 82.04; H, 5.47; N,
3.75; P, 8.29. Calc. for C25H19NP: C, 82.40; H, 5.26; N, 3.84; P,
8.50%).
[Pt(H2NC6H4PPh2-2)2]Cl2 4. To L1 (100 mg, 0.14 mmol) in
CH2Cl2 (1 cm3) was added [PtCl2(MeCN)2] (49 mg, 0.14 mmol,
2.0 equivalents). The resulting yellow solution was stirred for
1 h at r.t. The solution was quickly filtered in the presence of air
to remove undissolved material. Evaporation of the solvent and
crystallisation from dichloromethane–pentane yielded pale yel-
low crystals. 31P NMR (CDCl3): δ 25.8 (s), 25.8 (d, JPPt = 3334
Hz). 1H NMR (CDCl3, 200 MHz): δ 7.79 (dd, J = 3.4 Hz, 2 H),
2,2Ј-Bis{[2-(diphenylphosphino)benzylidene]amino}biphenyl
L2. A mixture of 2-(diphenylphosphino)benzaldehyde (1.01 g,
3.44 mmol), 2,2Ј-diaminobiphenyl (0.322 g, 1.72 mmol) and a
catalytic amount of toluene-p-sulfonic acid in benzene (40 cm3)
was refluxed for 4 h under Dean–Stark conditions. The solvent
was evaporated and the product crystallised from absolute
ethanol (15 cm3). Yield: 1.15 g as a pale yellow powder (92%).
7.46 (m, 2 H), 7.40–7.30 (m, 14 H) and 7.26–7.11 (m, 14 H). 13
C
1
M.p. 170.8–171.2 ЊC; H NMR (CDCl3, 200 MHz) δ 8.98 (d,
NMR (CDCl3, 50.3 MHz): δ 147.30 (C), 134.12 (CH), 133.13 (t,
2
J = 5.6 Hz, 2 H), 7.86–7.79 (m, 2 H), 7.38–7.15 (m, 30 H), 6.85–
CH, JPC = 11.8), 132.16 (CH), 132.06 (CH), 103.19 (d, C,
6.78 (m, 2 H) and 6.39 (m, 2 H); 13C NMR (CDCl3, 50.3 MHz)
1JPC = 64.9), 128.95 (t, CH, JPC = 11.8), 128.34 (t, CH,
3
3
1
3
δ 158.4 (CH, JPC = 25.2), 150.6 (C), 139.4 (C, JPC = 17.2),
3JPC = 7.6), 127.01 (t, CH, JPC = 14.1) and 125.84 (d, C,
1
2
138.0 (C, JPC = 19.5), 136.2 (C, JPC = 10.7), 134.0 (CH,
1JPC = 67.1 Hz) (Found: C, 51.26; H, 4.02; N, 3.34. Calc. for
C36H32Cl2N2P2Ptؒ1.5CH2Cl2: C, 51.35; H, 3.85; N, 3.31%).
2JPC = 20.2), 133.7 (C), 132.7 (CH), 131.0 (CH), 130.4 (CH),
3
129.0 (CH), 128.7 (CH), 128.5 (CH, JPC = 7.3), 128.1 (CH),
127.4 (CH, JPC = 4.2 Hz), 124.9 (CH) and 118.2 (CH); 31P
[PdL2]Cl2 5. To L2 (100 mg, 0.14 mmol) in CH2Cl2 (2 cm3)
was added [PdCl2(MeCN)2] (35.6 mg, 0.14 mmol, 1.0 equiv-
alent) and the clear red solution was stirred for 1.5 h at r.t.
Crystallisation from dichloromethane–pentane afforded large
red crystals suitable for X-ray analysis. Filtration and drying of
the crystals in vacuo gave 82 mg of analytically pure [PdL2]Cl2
as an orange-red powder (66%). 31P NMR (CDCl3): δ 31.3. 1H
NMR (CDCl3, 500 MHz): δ 8.17 (d, J = 11.5, 2 H), 8.02 (br, 4
H), 7.76 (m, 2 H), 7.67 (t, J = 7.6, 4 H), 7.60–7.55 (m, 8 H), 7.45
(t, J = 7.6, 2 H), 7.35 (m, 2 H), 7.30 (m, 6 H), 6.94 (br, 2 H), 6.88
(m, 4 H) and 6.58 (d, J = 7.7 Hz, 2 H). 13C NMR (CDCl3, 125
MHz): δ 168.96 (CH), 148.45 (C), 138.77 (CH), 135.60 (CH),
134.80 (CH), 133.63 (t, C, 2JPC = 26.1), 133.48 (CH), 132.89 (C),
131.87 (CH), 131.68 (CH), 131.34 (C), 131.07 (CH), 129.56
2
NMR (CDCl3, 80.95) δ Ϫ15.2. High-resolution mass spectrum:
m/z 728.251 (calc. for C50H38N2P2: 728.251) (Found: C, 82.08;
H, 5.43; N, 3.82; P, 8.35. Calc. for C25H19NP: C, 82.40; H, 5.26;
N, 3.84; P, 8.50%).
[Pd2L1Cl2Me2] 1. To L1 (100 mg, 0.14 mmol) in thf (1.5 cm3)
was added [PdCl(Me)(cod) (72.7 mg, 0.28 mmol, 2.0 equiv-
alents). After stirring for 16 h at r.t., the yellow solution was
concentrated under reduced pressure until a white precipitate
was formed. Filtration and crystallisation from dichloro-
methane–pentane yielded pale yellow crystals, 95 mg (65%). 31
P
NMR (CDCl3): δ 35.4. 1H NMR (CDCl3, 200 MHz): δ 9.16 (d,
J = 5.1, 2 H), 8.86 (s, 2 H), 7.65–7.34 (m, 30 H), 7.21–7.15 (m, 2
H), 7.05–7.00 (m, 2 H) and 0.86 (d, J = 2.9 Hz, 6 H). 13C NMR
2
(CH), 129.45 (CH), 129.37 (t, C, JPC = 11.8), 129.12 (t, CH),
2
1
1
(CDCl3, 75.4 MHz): δ 167.43 (CH), 155.89 (d, C, JPC = 15.9),
126.3 (d, CH, JPC = 52.5), 124.52 (d, C, JPC = 53.6), 123.66
(CH) and 123.30 (d, CH, 1JPC = 65.5); one CH was not resolved
due to overlap. ES mass spectrum: m/z 869 (M Ϫ Cl) and 417
(M Ϫ 2Cl).
2
140.90 (C), 134.32 (s, CH), 133.56 (d, CH, JPC = 13.4), 133.40
2
(d, CH, JPC = 11.0), 133.51 (C), 132.39 (CH), 131.97 (CH),
131.32 (CH), 131.06 (CH), 131.03 (CH), 130.45 (CH), 130.14
(CH), 129.53 (d, C, 1JPC = 40.3 Hz), 129.01 (d, CH, 3JPC = 11.0),
128.85 (d, CH, 3JPC = 11.0), 128.81 (d, C, 1JPC = 37.9), 128.35 (d,
[NiL2][BF4]2 6. To a suspension of L2 (100 mg, 0.14 mmol) in
absolute EtOH (2 cm3) was added dry NiCl2 (15 mg, 0.14
mmol, 1.0 equivalent) and the resulting clear dark brown solu-
tion was warmed to reflux for 3 h. After evaporation of the
2
2
CH, JPC = 6.1), 128.07 (C), 120.51 (d, CH, JPC = 7.3 Hz) and
Ϫ1.42 (CH3). ES mass spectrum: m/z 1007 (M Ϫ Cl), 1039
(M Ϫ Cl ϩ MeOH) and 486 (M Ϫ 2Cl) (Found: C, 59.29; H,
268
J. Chem. Soc., Dalton Trans., 1998, Pages 263–270

View Online
25.4Њ respectively. Intensity data for 3 were corrected for
absorption PLATON/DIFABS.29 The structures of 3 and 5
were solved by Patterson methods (DIRDIF)28 and direct
methods (SHELXS 8630), respectively. Least-squares refine-
ment of F 2 was done with SHELXL 96.31 Hydrogen atoms were
taken into account at calculated positions riding on their carrier
atoms. Convergence was reached at wR2 = 0.1560 [5513 reflec-
tions, R1 = 0.0653 for 3793 reflections with I > 2σ(I)] and
0.1735 [18 889 reflections, R1 = 0.0673 for 11 771 reflections
with I > 2σ(I)]. The final difference map did not show any sig-
nificant residual features. Geometrical calculations and the
ORTEP illustrations were done with PLATON.29 The final
results were checked for missed symmetry with the PLATON/
MISSYM option and solvent-accessible voids with the
PLATON/SOLV option.
Table 4 Summary of crystal data for compounds 1, 3 and 5
1
3ؒ4CH2Cl2
5ؒ3.5CH2Cl2
Formula
(C26H22-
ClNPPd)2
1042.6
(C27H21NO2-
PPd)2
1397.45
C50H38Cl2N2-
P2Pd
906.1
M
Crystal system
Space group
Monoclinic
C 2/c
Trigonal
P3121
Triclinic
P1
¯
a/Å
b/Å
c/Å
α/Њ
17.789(5)
14.170(4)
19.423(7)
13.009(2)
13.009(2)
29.706(6)
15.1653(18)
19.369(2)
20.3003(17)
100.755(10)
99.828(8)
111.470(10)
5262.1(10)
1.519
β/Њ
113.02(2)
γ/Њ
U/Å3
4506(3)
1.537
4
4353.7(13)
1.599
3
Dc/g cmϪ3
Z
CCDC reference number 186/754.
See http://www.rsc.org/suppdata/dt/1998/263/ for crystallo-
graphic files in .cif format.
4
F(000)
Crystal size/mm
2104
0.19 × 0.44 ×
0.50
2106
0.40 × 0.50 ×
0.50
10.9
0.0653
0.156
2436
0.45 × 0.70 ×
0.70
9.1
0.0673
0.174
1.008
µ(Mo-Kα)/cmϪ1
10.26
Ra
0.0471
0.1298
1.083
Acknowledgements
wR2b
S
This work was supported in part (A. L. S., W. J. J. S. and N. V.)
by the Netherlands Foundation of Chemical Research (SON)
with financial aid from the Netherlands Organisation for
Scientific Research (NWO). Financial support from Shell
Research BV (E. K. van den B., B. L. F.) is gratefully
acknowledged.
0.988
¹
a R = Σ(|Fo| Ϫ |Fc|)/Σ|Fo|. b wR2 = [Σw(Fo2 Ϫ Fc2)2/Σw(Fo )2]².
2
EtOH, CH2Cl2 (2 cm3) was added. To the resulting pale brown
suspension was added NaBF4 (60 mg, 0.55 mmol, 4 equiv-
alents). After stirring for an additional 2 h at r.t., the reaction
mixture was filtered over Celite to remove the excess of NaBF4
and evaporation of the solvent gave a dark brown solid that was
crystallised from dichloromethane–pentane to afford complex 6
as dark brown crystals: 63 mg (53%). 31P NMR (CDCl3): δ 31.3.
1H NMR (CDCl3, 200 MHz): δ 8.2–8.0 (br, 2 H), 7.9–7.3 (m, 28
H), 7.3–7.0 (br, 6 H) and 7.0–6.8 (br, 2 H). ES mass spectrum:
m/z 873 (M Ϫ BF4) and 394 (M Ϫ 2BF4) (Found: C, 62.50; H,
4.28; N, 3.12. Calc. for C50H38B2F8N2NiP2: C, 62.48; H, 3.99; N,
2.91%).
References
1 M. W. Göbel, Angew. Chem., Int. Ed. Engl., 1994, 33, 1141;
P. A. Vigato, S. Tamburini and D. E. Fenton, Coord. Chem. Rev.,
1990, 106, 25; D. E. Fenton and H. Okawa, J. Chem. Soc., Dalton
Trans., 1993, 1349; A. M. Bond, M. Haga, I. S. Creece, R. Robson
and J. C. Wilson, Inorg. Chem., 1989, 28, 559.
2 K. D. Karlin, Science, 1993, 261, 701; B. L. Vallee and D. S. Auld,
Biochemistry, 1993, 32, 6493.
3 W. H. Armstrong and S. J. Lippard, J. Am. Chem. Soc., 1983, 105,
4837; P. P. Paul, Z. Tyeklár, R. R. Jacobsen and K. D. Karlin, J. Am.
Chem. Soc., 1991, 113, 5322; N. N. Murthy, M. Mahroof-Tahir and
K. D. Karlin, J. Am. Chem. Soc., 1993, 115, 10 404; T. N. Sorell,
Tetrahedron, 1989, 45, 3; Bioinorganic Catalysis, ed. J. Reedijk,
Marcel Dekker, New York, 1994.
Crystallography
X-Ray data for compound 1 were collected at 130 K on an
Enraf-Nonius CAD-4F2 diffractometer with Mo-Kα radiation
(λ = 0.710 73 Å). The orange crystal was quickly removed from
the wall of the vessel and mounted on top of a glass fibre. The
structure was solved by Patterson methods and extension of the
model was accomplished by direct methods applied to differ-
ence structure factors using the program DIRDIF.28 The pos-
itional and anisotropic thermal displacement parameters for
the non-hydrogen atoms were refined on F 2 with full-matrix
least-squares procedures minimising the Q = Σh[w(|Fo)2 Ϫ
k(Fc)2|2], where w = 1/[σ2(Fo)2 ϩ (aP)2 ϩ bP], P = [max(Fo,02) ϩ
2Fc2]/3. Reflections were stated observed if satisfying the F 2 у 0
criterion of observability. A subsequent Fourier-difference syn-
thesis resulted in the location of all hydrogen atoms, the
coordinates and isotropic thermal displacement parameters of
which were refined. Final refinement on F 2 carried out by full-
matrix least-squares techniques converged at wR(F 2) = 0.1298
for 4269 reflections with F 2 у 0 and R(F ) = 0.0471 for 3921
reflections with F у 4.0σ(F ) and 359 parameters. A final
Fourier-difference map showed residual densities between Ϫ1.14
and ϩ1.22(13) e ÅϪ3 and one peak of 3.13 e ÅϪ3 located near
(1.86 Å) the Pd atom. No other significant peaks having chem-
ical meaning were observed in the final Fourier-difference syn-
theses. Geometrical calculations were done with PLATON.29
X-Ray data for compounds 3 and 5 were collected at 150 K
on an Enraf-Nonius CAD4T diffractometer with rotating
anode and graphite monochromated Mo-Kα radiation. Orange
crystals were cut to size and covered by inert oil to avoid
deterioration due to loss of solvent. A total of 12 388 reflec-
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