Synthesis and reactions of novel dipalladium(II) complexes of the type [{Pd[PPh2CH=C(R)-N-N=C(R)CHPPh2]}2] (R = But or Ph). Crystal structure of the tert-butyl complex containing two Pd-C bonds and five fused chelate rings

Article abstract of DOI:10.1039/a700153c

Treatment of the neutral chloropalladium(III) complexes [PdCl{PPh₂CH=C(R)-N-N=C(R)CH₂PPh₂}] (R = Bu^t 1a or Ph 1b) with two equivalents of Li[N(SiMe₃)₂] gave the novel dipalladium(II) complexes [{Pd[PPh₂CH=C(R)-N-N=C(R)CHPPh₂]}₂] (R = Bu^t 2a or Ph 2b) containing two palladium-carbon bonds, five fused chelate rings and enamine type (C=C-N) moieties. Treatment of the chloroplatinum(II) complex [PtCl{PPh₂CH=C(Bu^t)-N-N=C(Bu^t)CH ₂PPh₂}] 1c with an excess of KOBu^t in dimethyl sulfoxide (dmso) gave what was probably the species [Pt{PPh₂CH=C(Bu^t)-N-N=C(Bu^t)CHPPh ₂}(dmso)] 3 containing both a coordinated and an unco-ordinated phosphine. The dipalladium(II) complex 2a or 2b underwent electrophilic attack at the enamine carbon with acids (HX) to give salts of type [{Pd[PPh₂CH₂C(R)=N-N=C(R)CHPPh₂]} ₂]X₂ 4 (R = Bu^t or Ph; X = trifluoroacetate, chloride or picrate); these, when treated with sodium methoxide, deprotonated at the methylene carbon to give the neutral complex 2a or 2b. Treatment of 2a with less than 2 equivalents of trifluoroacetic acid gave the monoprotonated complex [Pd{PPh₂CH=C(Bu^t)N-N=C(Bu^t)CHPPh ₂}-{PPh₂CH₂C(Bu^t)=N-N=C(Bu ^t)CHPPh₂}][O₂CCF₃]5a, mixed with 2a and 4a. Complex 2a with Br₂ or MeI underwent attack at the enamine carbon C=C-N to give the corresponding bromo or methyl derivatives [{Pd[PPh₂CH(R)CBu^t=N-N=C(Bu^t)CHPPh ₂]}₂]X₂ (R = Br, X = Br 6a; R = Me, X = I 6b) respectively. When the methyl-substituted salt was treated with KOBu^t it gave the neutral dipalladium(II) complex [{PdCl[PPh₂C(Me)= C(Bu^t)-N-N=C(Bu^t)CHPPh₂]}₂]7. The crystal structure of 2a was determined.

Full text of DOI:10.1039/a700153c

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Synthesis and reactions of novel dipalladium(II) complexes of the
type [{Pd[PPh CH᎐C(R)᎐N᎐N᎐C(R)CHPPh ]} ] (R ؍ But or Ph).
᎐
᎐
2
2
2
Crystal structure of the tert-butyl complex containing two Pd᎐C
bonds and five fused chelate rings
Uchenna U. Ike, Bernard L. Shaw* and Mark Thornton-Pett
School of Chemistry, University of Leeds, Leeds, UK LS2 9JT
Treatment of the neutral chloropalladium() complexes [PdCl{PPh CH᎐C(R)᎐N᎐N᎐C(R)CH PPh }]
᎐
᎐
2
2
2
(R = But 1a or Ph 1b) with two equivalents of Li[N(SiMe3)2] gave the novel dipalladium() complexes
[{Pd[PPh CH᎐C(R)᎐N᎐N᎐C(R)CHPPh ]} ] (R = But 2a or Ph 2b) containing two palladium–carbon bonds,
᎐
᎐
2
2
2
five fused chelate rings and enamine type (C᎐C᎐N) moieties. Treatment of the chloroplatinum() complex
᎐
[PtCl{PPh CH᎐C(But)᎐N᎐N᎐C(But)CH PPh }] 1c with an excess of KOBut in dimethyl sulfoxide (dmso) gave
᎐
᎐
2
2
2
what was probably the species [Pt{PPh CH᎐C(But)᎐N᎐N᎐C(But)CHPPh }(dmso)] 3 containing both a co-
᎐
᎐
2
2
ordinated and an unco-ordinated phosphine. The dipalladium() complex 2a or 2b underwent electrophilic attack
at the enamine carbon with acids (HX) to give salts of type [{Pd[PPh CH C(R)᎐N᎐N᎐C(R)CHPPh ]} ]X 4
᎐
᎐
2
2
2
2
2
(R = But or Ph; X = trifluoroacetate, chloride or picrate); these, when treated with sodium methoxide,
deprotonated at the methylene carbon to give the neutral complex 2a or 2b. Treatment of 2a with less than 2
equivalents of trifluoroacetic acid gave the monoprotonated complex [Pd{PPh CH᎐C(But)N᎐N᎐C(But)CHPPh }-
᎐
᎐
2
2
{PPh CH C(But)᎐N᎐N᎐C(But)CHPPh }][O CCF ] 5a, mixed with 2a and 4a. Complex 2a with Br or MeI
᎐
᎐
2
2
2
2
3
2
underwent attack at the enamine carbon C᎐C᎐N to give the corresponding bromo or methyl derivatives
᎐
[{Pd[PPh CH(R)CBut᎐N᎐N᎐C(But)CHPPh ]} ]X (R = Br, X = Br 6a; R = Me, X = I 6b) respectively. When the
᎐
᎐
2
2
2
2
methyl-substituted salt was treated with KOBut it gave the neutral dipalladium() complex [{PdCl[PPh C(Me)᎐
᎐
2
C(But)᎐N᎐N᎐C(But)CHPPh ]} ] 7. The crystal structure of 2a was determined.
᎐
2
2
In previous work, we have shown that the azine diphosphine
[PdX2(dppm)] or [PtX2(dppm)] (X = Cl or I; dppm = Ph2P-
CH2PPh2) to give complexes of type [MR2(dppm)] (M = Pd or
Pt, R = alkyl or aryl). However, bulky bases such as lithium
bis(trimethylsilyl)amide Li[N(SiMe3)2] removed a proton from
the methylene of the dppm. Thus treatment of a suspension of
[PtI2(dppm)] with 1 mol equivalent of Li[N(SiMe3)2] in tetra-
hydrofuran, followed by methyl iodide, gave [PtI2{Ph2PCH-
(Me)PPh2}].6,7
PPh CH C(But)᎐N᎐N᎐C(But)CH PPh I can react in the Z,E
᎐
᎐
2
2
2
2
configuration and then act as a terdentate P,N,PЈ ligand with
fused five- and six-membered rings, in square-planar, octa-
hedral or seven-co-ordinate complexes.1–3 Thus with Group 6
metal carbonyls we prepared complexes of the type fac-
[M(CO) {PPh CH C(But)᎐N᎐N᎐C(But)CH PPh }] (M = Mo,
᎐
᎐
3
2
2
2
2
W or Cr). A recent publication 4 from this laboratory has
described completely specific alkylations of the ligand back-
bone of the molybdenum or tungsten complexes. The proton on
the carbon atom α to phosphorus in the metal carbonyl azine
diphosphine complexes fac-[M(CO) {PPh CH C(But)᎐N᎐N᎐
In the present work we describe how treatment of palladium
complexes of type [PdCl{PPh CH᎐C(R)᎐N᎐N᎐C(R)CH -
᎐
᎐
2
2
PPh2}] (R = But or Ph) with Li[N(SiMe3)2] gives the novel dipal-
ladium complexes [{Pd[PPh CH᎐C(R)᎐N᎐N᎐C(R)CHPPh ]} ]
᎐
᎐
᎐
᎐
3
2
2
2
2
2
C(But)CH2PPh2}] is activated and the carbon could be depro-
tonated by n-butyllithium. The complexes were first deproto-
nated in the five-membered ring chelate and treatment of the
resultant carbanions with electrophiles such as an alkyl halide
(RX) gave derivatives fac-[M(CO) {PPh CH(R)C(But)᎐N᎐N᎐
containing five fused chelate rings and two palladium–carbon
bonds. Some chemistry of these dipalladium complexes is
described, in particular electrophilic attack on the ligand back-
bones. The behaviour of an analogous platinum complex when
treated with Li[N(SiMe3)2] was also investigated.
᎐
᎐
3
2
C(But)CH2PPh2}] (M = Mo or W), exclusively. When treated
with a second mole of base the methylene in the six-membered
chelate ring of this complex was deprotonated and the carbon
alkylated. The alkylations in both five- and six-membered rings
were stereospecific; thus dimethylation of the complex with the
A configuration at the metal gave exclusively the R,R configur-
ations on the two substituted carbons and the complex with the
C configuration at the metal gave the S,S configurations at the
carbons. We had earlier shown that in terdentate complexes of
type [MCl{PPh CH C(But)᎐N᎐N᎐C(But)CH PPh }]X (M = Pd
Results and Discussion
The various complexes and their transformations are shown
in Schemes 1–3. Treatment of a solution of the chloropal-
ladium() complex 1a 3 in tetrahydrofuran with 2 equivalents of
Li[N(SiMe3)2] gave an intensely red solution, from which the
complex 2a was isolated as red prisms, in 80% yield. Complex
2a was stable in tetrahydrofuran solution in air at ambient tem-
peratures for several days, after which it started to decompose.
Preparative details, mass spectral and elemental analytical data
are in the Experimental section; phosphorus-31 NMR, infra-
red, proton and carbon-13 NMR data are in Tables 2–4. The
product 2a was characterised by elemental analysis (C, H and
N) and the mass spectrum (FAB) showed a group of peaks at
m/z 1332–1345 for the molecular ion with the maximum of
1338 as expected for the formula C72H80N4P4Pd2 and suggests a
dinuclear complex. The 31P-{1H} NMR spectrum (Fig. 1) of 2a
᎐
᎐
2
2
2
2
or Pt; X = Cl, picrate or formate) the CH2 hydrogens underwent
H/D exchange with acid catalysts, i.e. they were activated and
that on treatment with a base such as triethylamine the five-
membered ring chelate in the cationic complex rapidly loses
a proton to give a neutral complex of type [MCl{PPh2-
CH᎐C(But)᎐N᎐N᎐C(But)CH PPh }] (M = Pd or Pt).3
᎐
᎐
2
2
It has been shown 5 that alkyl- or aryl-lithium, LiR, reagents
or Grignard reagents, MgRX, react with complexes such as
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620
2613

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Fig. 2 An ORTEP 13 diagram of the crystal structure of the dipal-
ladium() complex 2a showing the five fused chelate rings and two
palladium–carbon bonds
Scheme 1 (i) [PdCl2(NCPh)2] or [PtCl2(cod)] (cod = cycloocta-1,5-
diene), NEt3; (ii) for 1a or 1b, thf, 2 equivalents Li[N(SiMe3)2]; (iii) for
1c, dmso, KOBut
Fig. 1 The 31P-{1H} NMR spectrum (101.25 MHz) of complex 2a in
deuteriochloroform showing the ‘deceptively simple’ triplets of the
AAЈXXЈ spin system with N = |J(PF PS) ϩ J(PF PSЈ)| = 46 Hz
shows two ‘virtual’8–10 or ‘deceptively simple’8 1:2:1 triplets, at
δ 31.5 and 12.4. The four-spin system, which gives rise to this
spectrum, is of the AAЈXXЈ type in which the various coupling
constants are of magnitude and relative signs so as to give
the observed spectrum. Any ‘outer’ peaks are of such very low
intensity that they are unobserved, hence the use of the expres-
sions ‘deceptively simple’ or ‘virtual’, see refs. 8–12 for a discus-
sion of the phenomenon with some examples of how it has
been used for studying tertiary phosphine–metal complexes,
especially before 31P-{1H} NMR spectroscopy became more
readily available. It is likely that the weak peaks are overlapped
and obscured by the strong peaks in the spectra shown in Figs.
1, 4 and 5 and with the spectra of related compounds discussed
in this paper. The structure was determined by a single-
crystal X-ray diffraction study which showed the complex to
have a binuclear diphosphine-bridged structure 2a (see Fig. 2).
Selected bond lengths and bond angles are in Table 1. The
deprotonated azine diphosphine ligand is co-ordinated in a ter-
dentate manner to one palladium, through one nitrogen, one
phosphorus and the carbon α to the second phosphorus atom;
the second phosphorus acts as a bridge to the other palladium
atom. This arrangement gives five fused chelate rings, with the
central, six-membered ring, puckered as seen in Fig. 3. There
is thus a ‘pocket’ in the molecule with the six-membered
ring involving the sequence of atoms Pd᎐C᎐P᎐Pd᎐C᎐P, at the
bottom of the pocket. The hydrogen atoms of the two CHPd
groups are on the outside of the pocket. The Pd ؒ ؒ ؒ Pd distance
is long [3.1598(10) Å, see Table 1] and is indicative of little,
if any, bonding interaction between the palladiums. In 2a we
have labelled the two chemically equivalent phosphorus atoms
Fig. 3 View of the crystal structure of the dipalladium() complex 2a
showing the puckering of the central six-membered chelate ring which
forms a ‘pocket’ in the centre of the molecule. For clarity the phenyl
rings have been omitted
in the central six-membered ring, PS and PSЈ and the two
chemically equivalent phosphorus atoms in a five-membered
ring, PF and PF Ј.
The NMR data for complex 2a and of related species shown
in Schemes 1–3 were assigned on the basis of 31P-{1H}, 1H, 1H-
{31P} and 13C-{1H} NMR spectroscopy [including attached pro-
ton tests (APTs)], some two-dimensional correlation spec-
troscopy, e.g. 13C᎐1H, 31P᎐1H and 31P᎐31P COSY spectra, and
also by arguments based on the chemistry. For 2a the resonance
at δP 31.5 is assigned to PF and that at 12.4 to PS (these
assignments are especially based on the results obtained by the
1
protonation and methylation experiments on 2a). In the H-
{31P} NMR spectrum of 2a there are singlets at δ 0.31 and
1.45, each of relative intensity 18 due to the two kinds of tert-
butyl groups (two of each kind), and singlets at δ 4.21 and 4.65,
each of relative intensity two, due to the two different kinds of
CH protons. That at δ 4.21, assigned to CHPF , became a doub-
1
let in the H NMR spectrum and a 31P᎐1H COSY spectrum
established that this proton was coupled to PS and not to PF ; this
result may at first sight seem surprising but there are many
examples of two-bond (geminal couplings) being very small, or
zero, for example in systems such as C᎐CH ; presumably
᎐
2
because positive and negative contributions to the J value cancel
2614
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620

View Article Online
one another out. The resonance at δ 4.65, assigned to CHPd,
was a double doublet in the 1H NMR spectrum and the 31P᎐1H
COSY spectrum established that the hydrogen was coupled to
both PF and PS. A 13C-{1H} NMR spectrum, and 13C᎐1H and
31P᎐1H COSY spectra, established that the resonance at δC 77.2
(Table 4) was due to CHPF and that at δC 54.3 due to CHPd.
Other proton and carbon-13 data are in Tables 3 and 4.
Treatment of II with [PdCl2(NCPh)2], followed by triethyl-
amine, gave complex 1b as a purple solid; see Experimental
section for details and Tables 2 and 3 for characterising spectro-
scopic data. Similar treatment of the chloropalladium() com-
plex 1b with 2 equivalents of Li[N(SiMe3)2] gave the corres-
ponding dinuclear palladium() complex 2b as an orange solid,
in 85% yield. This was characterised in a similar fashion to 2a.
We have also made the azine diphosphine II by condensing
The infrared (KBr disc) spectrum showed a ν(C᎐N) absorption
᎐
the known keto phosphine Ph PCH C(᎐O)Ph 14 with hydrazine.
band at 1485 cmϪ1. The 31P-{1H} NMR spectrum was an
AAЈXXЈ pattern with two sets of ‘deceptively simple’ triplets at
δ 20.3 and 17.3 with N = |JAX ϩ JAXЈ| = 34 Hz. Proton NMR
᎐
2
2
Table 1 Selected bond lengths (Å) and angles (Њ) for compound 2a
with estimated standard deviations (e.s.d.s) in parentheses
Pd᎐N(4)
2.018(5)
2.282(2)
3.1598(10)
1.839(6)
1.374(7)
1.383(6)
1.527(8)
Pd᎐C(7)
Pd᎐P(1)
2.102(6)
2.298(2)
1.779(6)
1.355(8)
1.545(8)
1.282(7)
1.541(7)
Table 2 31P-{1H} NMR a and infrared b data
Pd᎐P(2*)
Pd ؒ ؒ ؒ Pd*
P(2)᎐C(7)
C(3)᎐N(4)
N(4)᎐N(5)
C(6)᎐C(7)
P(1)᎐C(2)
C(2)᎐C(3)
C(3)᎐C(31)
N(5)᎐C(6)
C(6)᎐C(61)
Compound
δ(PA)
δ(PB)
J or N
ν(C᎐N)
᎐
1b
2a
2b
3
4a
4b
4c
4d
4e
6a
6b
6c
7
49.4
31.5
20.3
23.3
51.4
37.0
55.1
50.5
36.6
53.8
49.9
52.4
56.6
31.3
12.4
17.3
Ϫ11.4
14.8
22.7
17.2
12.6
22.8
16.9
20.6
18.4
13.9
453
46
34
d
54
42
56
54
43
54
50
52
40
1615m c
1490m
1485m
—
1485m
1490w
1495w
1490m
1490m
1485w
1495m
1495m
1490m
N(4)᎐Pd᎐C(7)
C(7)᎐Pd᎐P(2*)
C(7)᎐Pd᎐P(1)
N(4)᎐Pd᎐Pd*
P(2*)᎐Pd᎐Pd*
C(2)᎐P(1)᎐Pd
C(3)᎐C(2)᎐P(1)
C(2)᎐C(3)᎐C(31)
C(3)᎐N(4)᎐N(5)
N(5)᎐N(4)᎐Pd
N(5)᎐N(6)᎐C(7)
C(7)᎐C(6)᎐C(61)
C(6)᎐C(7)᎐Pd
79.7(2)
91.6(2)
162.4(2)
120.29(14)
65.58(4)
98.8(2)
118.6(4)
122.4(5)
118.9(5)
116.7(3)
121.0(5)
122.3(5)
105.1(4)
N(4)᎐Pd᎐P(2*)
N(4)᎐Pd᎐P(1)
P(2)᎐Pd᎐P(1)
C(7)᎐Pd᎐Pd*
P(1)᎐Pd᎐Pd*
C(7)᎐P(2)᎐Pd*
C(2)᎐C(3)᎐N(4)
N(4)᎐C(3)᎐C(31)
C(3)᎐N(4)᎐Pd
C(6)᎐N(5)᎐N(4)
N(5)᎐C(6)᎐C(61)
C(6)᎐C(7)᎐P(2)
P(2)᎐C(7)᎐Pd
167.68(14)
82.83(14)
105.29(6)
78.5(2)
112.96(4)
112.1(2)
117.5(5)
120.2(5)
122.1(4)
114.4(5)
116.6(5)
120.5(4)
100.7(3)
a
Recorded at 101.25 MHz, chemical shifts are in ppm relative to 85%
H3PO4, solvent CDCl3, J values are in Hz; for the monopalladium
complexes, J = J(PP); for the dipalladium complexes, N = J(PF PS) ϩ
J(PF PSЈ). b As KBr disc, m = medium, s = strong, w = weak. c ν(Pd᎐Cl)
* Atoms marked with an asterisk are related to their unmarked equiva-
lents by the operator ³ Ϫ x, ¹ Ϫ y, z.
(Nujol mull between Polythene plates) 330w cmϪ1 d No observable
.
3J(PP) coupling; 1J(PtPA) 2118, 1J(PtPB) 112 Hz.
¯
²
¯
²
Table 3 Proton NMR data a
Compound
δ(But)
δ(CH2P/᎐CHP/CHPd/CH)
᎐
1b
2a
2b
4a
—
3.33 [2 H, dd, 2J(PH) 10.8, 4J(PH) 3.9, CH2P]
4.65 [2 H, dd, 2J(PH) 6.4, J(PH) 1.6, ᎐CHP]
᎐
0.31 (18 H, s, 2But)
1.45 (18 H, s, 2But)
—
4.21 [2 H, d, J(PH) 4.1, 2᎐CHPd]
᎐
4.65 [2 H, dd, J(PH) 8.0 and 3.4, 2CHPd]
3.73 [2 H, d, 2J(PH) 6.5, 2CHP]
5.97 (2 H, m, 2CHP)
0.50 (18 H, s, 2But)
1.16 (18 H, s, 2But)
3.48 [2 H, dd, 2J(PH) 14, 2J(HH) 15.8, 2CH2P]
4.46 [2 H, dd, 2J(PH) 5.5, 2J(HH) 15.8, 2CH2P]
7.03 (2 H, t,b 2CHPd)
4b
4c
—
3.59 [2 H, dd, 2J(PH) 13.3, 2J(HH) 17.0, 2CH2P]
4.20 [2 H, dd, 2J(PH) 6.2, 2J(HH) 17.0, 2CH2P]
6.75 (2 H, m, 2CHPd)
0.56 (18 H, s, 2But)
1.14 (18 H, s, 2But)
3.29 [2 H, m, 2J(HH) 16.6, 2CH2P]
3.61 [2 H, m, 2J(HH) 16.6, 2CH2P]
6.24 (2 H, t,b 2CHPd)
4d
4ec
0.59 (18 H, s, 2But)
1.17 (18 H, s, 2But)
3.24 [2 H, dd, 2J(PH) 14.4, 2J(HH) 16.2, 2CH2P]
3.49 [2 H, dd, 2J(PH) 5.1, 2J(HH) 16.2, 2CH2P]
5.81 (2 H, t,b 2CHPd)
—
3.71 [2 H, dd, 2J(PH) 13.1, 2J(HH) 17.2, 2CH2P]
4.11 [2 H, dd, 2J(PH) 6.3, 2J(HH) 17.2, 2CH2P]
6.75 (2 H, m, 2CHPd)
6a
0.64 (18 H, s, 2But)
1.30 (18 H, s, 2But)
0.68 (18 H, s, 2But)
1.20 (18 H, s, 2But)
0.57 (18 H, s, 2But)
1.20 (18 H, s, 2But)
0.29 (18 H, s, 2But)
1.53 (18 H, s, 2But)
3.77 [2 H, d, 2J(PH) 11.2, 2CHBr]
5.28 [2 H, d, 2J(PH) 9.2, 2CHPd]
4.08 [2 H, m, 3J(HH) 6.6, 2CHMe]
6.26 (2 H, m, 2CHPd)
6bd,e
6cd, f
7g
3.99 [2 H, m, 3J(HH) 6.5, 2CHMe]
6.49 (2 H, m, 2CHPd)
4.04 [2 H, dd, J(PH) 8.5, 7.2, 2CHPd]
a
Recorded at 250.13 MHz, chemical shifts (δ) are in ppm relative to SiMe4, J values are in Hz, solvent CDCl3 unless otherwise stated. In all cases, 1H
and 1H-{31P} NMR spectra were measured: multiplicities refer to 1H NMR spectra; the CHPd and ᎐CHP resonances in the 1H-{31P} spectra were in
᎐
all cases singlets. b Probably a ‘deceptively simple’ 1:2:1 triplet with the outer doublet peaks 17 (4a), 16 (4c) and 14.8 Hz (4d) apart; these resonances
were singlets in the 1H-{31P} NMR spectra. c In CD2Cl2. d Recorded at 400.13 MHz. e δ(Me) 1.61 [6 H, dd, J(HH) 6.6, J(PH) 16.1 Hz, 2CHMe].
3
3
f δ(Me) 1.89 [6 H, dd, 3J(HH) 6.5, 3J(PH) 15.4 Hz, 2CHMe]. g δ(Me) 1.82 [6 H, d, 3J(PH) 10.7 Hz, 2᎐CMe].
᎐
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620
2615

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Table 4 13C-{1H} NMR data a
Compound
δC
I
2a
29.2 [1 C, d, 1J(PC) 21.3, CH2P], 161.1 [1 C, d, 2J(PC) 8.2, C᎐N]
᎐
30.7 (6 C, s, 2CMe3), 31.2 (6 C, s, 2CMe3), 35.8 [2 C, d, J(PC) 4.1, 2CMe3], 37.6 [2 C, d, J(PC) 13.7, 2CMe3], 54.3 (2 C, dt,b
3
3
2CHPd), 77.2 [2 C, d, J(PC) 53.0, 2CHPF , 153.4 (2 C, m, 2CN), 182.3 [2 C, d, J(PC) 17.9, 2CN]
3
3
4a c
4c
28.6 (6 C, s, 2CMe3), 30.1 (6 C, s, 2CMe3), 38.4 [2 C, d, J(PC) 3.6, 2CMe3], 40.2 [2 C, d, J(PC) 1.6, 2CMe3], 43.8 [2 C, dd,
J(PC) 23.8 and ≈2, 2CH2P], 57.3 (2 C, see text, 2CHPd), 185 (4 C, m, 4CN)
3
3
28.6 (6 C, s, 2CMe3), 30.1 (6 C, s, 2CMe3), 38.5 [2 C, d, J(PC) 3.9, 2CMe3], 40.2 [2 C, d, J(PC) 1.8, 2CMe3], 44.6 [2 C, d,
1J(PC) 23.3, 2CH2P], 57.4 (2 C, m, 2CHPd), 185 (4 C, m, 4CN)
4d
28.7 (6 C, s, 2CMe3), 30.1 (6 C, s, 2CMe3), 38.3 [2 C, d, 3J(PC) 3.2, 2CMe3], 40.4 (2 C, m, 2CMe3), 44.1 [2 C, d, 1J(PC) 23.8, 2CH2P],
57.3 [2 C, dd, 1J(PC) 10.0, 2J(PC) 72.7, 2CHPd], 184.4 (2 C, m, 2CN), 185.5 (2 C, m, 2CN)
6a
30.0 (6 C, s, 2CMe3), 30.7 (6 C, s, 2CMe3), 35.3 [2 C, d, 3J(PC) 3.0, 2CMe3], 37.1 [2 C, d, 3J(PC) 14.4, 2CMe3], 54.1 (2 C, m, 2CHBr),
76.2 (2 C, m, 2CHPd), 181.8 [2 C, d, 2J(PC) 16.7, 2CN], 185.5 (2 C, m, 2CN)
6bc
21.5 [2 C, d, 2J(PC) 6.3, 2CHMe], 28.6 (6 C, s, 2CMe3), 30.8 (6 C, s, 2CMe3), 39.5 (2 C, s, 2CMe3), 40.0 (2 C, s, 2CMe3),
51.3 [2 C, d, 1J(PC) 23.4, 2CHMe], 60.2 (2 C, m, 2CHPd), 186.5 (2 C, m, 2CN), 190.0 (2 C, m, 2CN)
a
Recorded at 62.9 MHz, unless shown otherwise, chemical shifts (δ) in ppm relative to SiMe4, J values are in Hz, solvent CDCl3 unless otherwise
stated. An attached proton test was applied to the carbon resonances to establish whether the carbons were CH3, CH2, CH or CN and for complexes
2a and 4a 13C᎐1H COSY experiments were conducted to establish connectivities. b The doublet spacing was 80.8 Hz and the separation of the peaks
of the 1:2:1 triplets was 14.4 Hz; this pattern was probably a doublet of deceptively simple 1:2:1 triplets, i.e. with N = |1J(PSC) ϩ 2J(PSЈC)| = 28.8
Hz. c Recorded at 100.6 MHz in CD2Cl2.
data are in Table 3 but the complex was rather insoluble and a
carbon-13 NMR spectrum was not recorded.
with N = |JAX ϩ JAXЈ| = 54 Hz, as shown in Fig. 4. The proton-
ation was reversible, and on addition of a solution of sodium
methoxide the deep red neutral species 2a was reformed (NMR
evidence). The diprotonated complex was isolated as the tri-
fluoroacetate 4a as yellow microcrystals, by evaporation and
addition of diethyl ether to the residue but the product con-
tained solvent of crystallisation (chloroform). Similarly the
phenyl analogue 2b reacted with trifluoroacetic acid to give the
diprotonated derivative 4b. Treatment of 2a with hydrochloric
acid gave the cationic dichloride 4c and treatment of 2a or 2b
with picric acid gave the corresponding dipicrate salts 4d and
4e, respectively. Further details are in the Experimental section
with elemental analytical and mass spectral data, and NMR
data in Tables 2–4.
We suggest that the novel and stable dipalladium() com-
plexes of type 2 are formed by deprotonation of a complex of
type 1 with 1 equivalent of Li[N(SiMe3)2] to give a carbanion
which loses a chloride ion and rearranges to give a species con-
taining an unco-ordinated PPh2 group. This PPh2 group then
rapidly attacks the palladium of another molecule of the same
species in an intermolecular reaction to give the five fused-
chelate-ring product of type 2; see Scheme 2.
We attempted to synthesize the analogous diplatinum()
complex by treating the neutral platinum complex 1c3 with 2
equivalents of Li[N(SiMe3)2] in tetrahydrofuran. On adding the
base there was an immediate change from orange to dark brown
but, after 3 d, no substantial amount of a single product could
be observed by 31P-{1H} NMR spectroscopy. However, treat-
ment of 1c with an excess of potassium tert-butoxide in dry
dimethyl sulfoxide (dmso) gave a dark solution whose 31P-{1H}
NMR spectrum showed two phosphorus singlets, each with
We studied complex 4a in some detail by NMR spec-
troscopy. The 31P-{1H} data are in Table 1. The 1H-{31P} NMR
spectrum of 4a showed two tert-butyl resonances at δ 0.50 and
1.16, an AB pattern due to the non-equivalent methylene pro-
3
tons at δ 3.48 and 4.46, J(HH) = 15.8 Hz, and a singlet at δ
1
1
satellites, one at δ 23.3, J(PtP) = 2118 Hz, and the other at δ
7.03 due to the PCH᎐ protons. In the H NMR spectrum the
᎐
3
Ϫ11.4, J(PtP) = 112 Hz. The resonance at δ 23.3, indicates a
methylene hydrogens were further coupled to one phosphorus
giving an ABX pattern; for δH 3.48, J(PH) = 14.0 Hz and for
δH 4.46, J(PH) = 5.5 Hz. A selective decoupling experiment
established that the methylene hydrogens were coupled to the
phosphorus directly bonded to platinum and trans to carbon,
whilst the small value of J(PtP) = 112 Hz for the resonance at
δ Ϫ11.4 and the negative chemical shift is indicative of phos-
phorus not directly bonded to platinum. We tentatively suggest
structure 3 for this complex. There was no observable coupling
between the two phosphorus atoms. After 2 d there was no
noticeable change in the 31P-{1H} NMR spectrum. The product
did not react with either carbon monoxide or triphenylphos-
phine as evidenced by a 31P-{1H} NMR study. Attempts to iso-
late 3 gave an orange product whose 31P-{1H} NMR spectrum
showed an AB pattern at δ 49.9 and 26.0 [2J(PP) = 394,
1J(PtPA) = 2886 at 1J(PtPB) = 2773 Hz]. However, this de-
composed on attempted purification.
phosphorus, δ 51.4, i.e. P . The ᎐CHPd protons were coupled
᎐
P
F
to both PF and PS and gave an apparent triplet (a deceptively
simple 1:2:1 triplet). Carbon-13, APT and heteronuclear
COSY experiments established that the protons of the tert-
butyls absorbing at δ 0.50 were attached to the carbons absorb-
ing at δ 28.6 and those absorbing at δ 1.16 were attached to the
carbons absorbing at δ 30.1. The methylene carbons absorbed
at δ 43.8 as a doublet of doublets with J(PC) = 23.8 Hz and ≈2
Hz; such a chemical shift (δ ca. 44) is typical of a methylene
carbon in a five-membered chelate ring.1–4 The PCH᎐ carbons
᎐
The dinuclear palladium() complexes 2a and 2b contain
absorbed at δ 57.3 as a second-order quartet with a doublet
separation of N 73.5 Hz and two equally intense outer peaks
95.3 Hz apart.
The protonations of complexes 2a and 2b were reversible. In
the presence of sodium methoxide 4a–4e were deprotonated
readily at the methylene carbon to give the neutral dipal-
ladium() complexes 2a or 2b, as indicated by the discharge of
the yellow colour to red (or orange) and subsequently con-
firmed by NMR studies. Although 4a, 4c and 4d contain the
same dipalladium dications the chemical shifts of the CH2P and
enamine type (C᎐C᎐N), i.e. ene–hydrazone, moieties. Enamines
᎐
react with electrophiles in what is a very useful and selective
synthetic method in organic chemistry,15–19 and we have
reported that platinum complexes of type 1 react with a proton
or with methyl iodide or bromine with electrophilic attack at an
ene–hydrazone carbon (C᎐C᎐N᎐N) on the ligand backbone.3
᎐
We have since studied electrophilic substitution reactions on the
backbone of palladium complexes of type 1.20 We have now
investigated the action of electrophiles on complexes 2a and 2b.
Treatment of a deuteriochloroform solution of 2a with 2 mol of
trifluoroacetic acid (one per Pd atom) at ca. 20 ЊC gave an
immediate reaction, with a change from deep red to yellow. The
31P-{1H} NMR spectrum of the resultant solution was of the
AAЈXXЈ type with the two chemical shifts at δ 51.4 and 14.8
the ᎐CHPd protons differ a lot between the three species, e.g.
᎐
for the CH2P protons δ 3.48 and 4.46 (4a), 3.29 and 3.61 (4c)
and 3.24 and 3.49 (4d), and for the PdCH proton δ 7.03 (4a),
6.24 (4c) and 5.81 (4d), i.e. ion-pair interaction has a consider-
able effect on chemical shifts.
2616
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620

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Fig. 4 The 31P-{1H} NMR spectrum (101.25 MHz) of complex 4a,
formed in situ by treating a deuteriochloroform solution of 2a with 2
mol equivalents of CF3CO2H. The spectrum is of the AAЈXXЈ type and
deceptively simple. The doublet of separations N = |J(PF PS) ϩ J(PF PSЈ)|
are shown
at δ 5.62 and 5.66 due to the CHPd proton. We could also
identify the two tert-butyl resonances of 2a (δ 0.31 and 1.45)
and the two tert-butyl resonances of 4a (δ 0.50 and 1.16) in the
mixture and also see four equally intense tert-butyl resonances
of the monoprotonated species 5a (δ 0.72, 0.96, 1.00 and 1.03),
i.e. although PS and PSЈ have virtually the same chemical shift
the hydrogens of the four tert-butyl groups do not. Treatment
of 2a with 0.5 mol equivalent of trifluoroacetic acid, i.e. 0.25
mol of acid per Pd atom, gave a 31P-{1H} NMR spectrum cor-
responding to a mixture of 2a, 4a and 5a but with peaks d and
dЈ of very low intensity, s and sЈ of high intensity and m, mЈ and
mЉ of medium intensity. From the spectrum shown in Fig. 5 and
from the chemical shifts given above, a phosphorus of type PS
absorbs within the range δ 10.2–17, a phosphorus PF adjacent
to a CH absorbs at δ 28.6–31.7 and a phosphorus PF adjacent to
a CH2, i.e. adjacent to a protonated carbon, absorbs at δ 50–
53.6. We also studied the action of increasing proportions of
2,4,6-trinitrophenol (picric acid) on 2a in chloroform and
observed the intermediate monoprotonated species 5b. On ad-
ding 1 mol equivalent of picric acid to 2b in chloroform the 31P-
{1H} NMR spectrum showed the almost exclusive formation of
5b, with second-order patterns very similar to the ones marked
mЉ, mЈ and m in Fig. 5, at δ 11.1, 28.8 and 49.9 in the intensity
ratios 2:1:1; very little of 2a and 4d were present in the solution.
Treatment of complex 2a with 2 mol equivalents of bromine
in carbon tetrachloride at ca. 20 ЊC gave the brominated salt 6a.
The 31P-{1H} NMR spectrum of 6a showed an AAЈXXЈ pat-
tern, at δ 53.8 and 16.9 with N = |JAX ϩ JAXЈ| = 54 Hz. In the 1H
2
NMR spectrum the doublet at δ 3.77, J(PH) = 11.2 Hz, is
Scheme 2 A possible mechanism for the formation of a dinuclear
palladium() complex of type 2; thf = tetrahydrofuran
assigned to CHBr. Bromination also resulted in a shift of the
CHPd hydrogen to the higher value of δ 5.28 as a doublet,
2J(PH) = 9.2 Hz. Electrophilic attack at the enamine type car-
We have also investigated the action of less than 2 mol of an
acid on complex 2a in attempts to identify the formation of a
monoprotonated species. Treatment of a deuteriochloroform
solution of 2a with 1 mol equivalent of trifluoroacetic acid (i.e.
0.5 mol equivalent per palladium atom) gave a dark green solu-
tion which soon faded to a pale green-yellow, exhibiting the 31P-
{1H} NMR spectrum shown in Fig. 5. The green species was
presumably due to an unstable intermediate, present in small
amount. The peaks marked n and nЈ in Fig. 5 are due to the
starting complex 2a, d and dЈ to the diprotonated species 4a and
the other three peaks, m, mЈ and mЉ, with relative intensities in
the ratio 1:1:2, are assigned to the monoprotonated species 5a.
bon, C᎐C᎐N, by Br would generate a chiral centre at carbon.
᎐
One might therefore expect to get R and S isomers at both
enamine carbons and therefore produce dibrominated products
with chemically inequivalent bromines. However, a careful
study of the reaction mixture by 31P-{1H} NMR spectroscopy
showed only one product. Examination of the crystal structure
of 2a, particularly the view shown in Fig. 3, suggests that attack
on the enamine carbon would be much more likely to occur
exterior to the ‘pocket’, i.e. the racemic mixture (RR ϩ SS)
would preferentially be formed. Since we could detect only one
product we suggest that no attack on C᎐CH from the side with-
᎐
A
31P᎐31P COSY experiment established that the phosphorus
in the pocket occurred.
atoms causing m, mЈ and mЉ were coupled together giving a
deceptively simple spectral pattern. Thus PS and PSЈ must reson-
ate with virtually the same chemical shifts. In the 1H NMR spec-
tra of this protonated mixture we could identify the patterns
due to 2a and 4a and the methylene hydrogens, CH2P, of 5a as
resonating at δ ≈3.4 and 3.13, J(HH) = 15.2 Hz, and two singlets
When a solution of complex 2a in chloroform was treated
with an excess of methyl iodide at ca. 20 ЊC it slowly turned
green and finally yellow. After putting the reaction mixture
aside for 5 d at ca. 20 ЊC the dimethylated palladium() salt 6b
was isolated as a yellow solid, in 79% yield. Complex 6b was
also obtained nearly quantitatively (92%) by heating the neutral
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620
2617

View Article Online
Scheme 3 (i) At least 2 mol equivalents of CF3CO2H, HCl or 2,4,6-(O2N)3C6H2OH; (ii) NaOMe; (iii) 1 equivalent of CF3CO2H; (iv) Br2–CCl4 or
MeI, with NH4PF6 added for 6c; (v) KOBut
NMR spectrum of 6c confirmed the replacement of ClϪ with
Ϫ
.
PF6
The dimethylated complex 6b was resistant to deprotonation
by sodium methoxide. However, treatment with an excess of
potassium tert-butoxide in dry dimethyl sulfoxide gave the neu-
tral dimethyldipalladium() complex 7 as a brown solid, in 88%
yield. The 31P-{1H} NMR spectrum of this neutral complex
showed two triplets at δ 56.6 and 13.9 with |JAX ϩ JAXЈ| = 40 Hz.
In the 1H NMR spectrum, the methyl ᎐CMe hydrogens gave a
᎐
3
doublet at δ 1.82, J(PH) = 10.7 Hz whilst the CHPd hydrogen
gave a doublet of doublets at δ 4.04, J(PH) = 8.5 and 7.2 Hz
and a singlet in the 1H-{31P} NMR spectrum.
We attempted to prepare salts from complex 2a using elec-
trophiles more bulky than methyl iodide, such as allyl bromide,
benzyl bromide, p-toluenediazonium hexafluorophosphate or
dimethyl acetylenedicarboxylate. These attempts all failed.
Products showing AAЈXXЈ patterns were observed by 31P-{1H}
NMR spectroscopy but these could not be isolated due to their
extreme solubility in most organic solvents. For example the
31P-{1H} NMR spectrum of the dark solution obtained from
the prolonged treatment (at ca. 20 ЊC for 3 weeks) of a solution
of 2a in chloroform with an excess of p-toluenediazonium
hexafluorophosphate showed triplets at δ 48.1 and 12.8,
N = |JAX ϩ JAXЈ| = 42 Hz.
Fig. 5 The 31P-{1H} NMR spectrum (101.25 MHz) of the mixture of
complexes 2a, 4a and 5a, formed by treating 2a with 1 mol equivalent of
CF3CO2H. The resonances are identified as follows: n and nЈ for the
neutral complex 2a, m, mЈ and mЉ for the monoprotonated complex 5a
and d and dЈ for the diprotonated complex 4a; the linkages were estab-
lished by a 31P᎐31P COSY experiment. The chemical shifts of the phos-
phorus atoms of 5a with the separation of the outer peaks of the three
‘deceptively simple’ patterns are as follows: m, δ 49.9(t), separation 42.5
Hz; mЈ δ 28.6(t), separation 49.5 Hz; mЉ, δ ≈10.9(q), separation 46 Hz
dipalladium() complex 2a with methyl iodide in chloroform at
ca. 61 ЊC for 11 h, i.e. as with the bromination (above) only the
racemic and none of the meso isomer was formed. The 31P-{1H}
NMR spectrum of 6b showed an AAЈXXЈ pattern with triplets
Experimental
1
at δ 49.9 and 20.6, N = |JAX ϩ JAXЈ| = 50 Hz. In the H NMR
All the reactions were carried out in a dry atmosphere of nitro-
gen or argon using degassed solvents. Tetrahydrofuran and
benzene were distilled from sodium and benzophenone under
argon immediately before use. The chloropalladium() and
chloroplatinum() complexes 1a and 1c were prepared accord-
ing to our published procedure.3 Infrared spectra were recorded
on a Perkin-Elmer model 257 grating spectrometer (4000–600
cmϪ1), NMR spectra using a JEOL FX-90Q (operating fre-
spectrum the doublet of doublets resonance at δ 1.61,
3
3J(PH) = 16.1 Hz and J(HH) = 6.6 Hz, was assigned to the
3
methyl CHMe hydrogens, the multiplet at δ 4.08, J(HH) = 6.6
Hz, to the methine CHMe hydrogen and the multiplet at δ 6.26
to the CHPd hydrogen. The 13C-{1H} NMR spectrum showed a
doublet at δ 51.3, 1J(PC) = 23.4 Hz, for the CHMe carbon and a
multiplet at δ 60.2 for the CHPd carbon. The corresponding
PF6Ϫ salt 6c was prepared by the addition of ammonium hexa-
fluorophosphate to a solution of 6b in methanol. The 31P-{1H}
1
quencies for H and 31P were 89.5 and 36.2 MHz, respectively),
1
a JEOL FX-100 (operating frequencies for H and 31P of 99.5
2618
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620

View Article Online
MHz and 40.25 MHz, respectively), a Bruker ARX-250 (oper-
reduced pressure after which addition of diethyl ether to the
1
ating frequencies for H, 31P and 13C of 250.13, 101.25 and 62.9
residue gave the protonated complex 5a as a yellow solid.
Yield 0.10 g, 80% [Found: (i) C, 53.15; H, 4.6; N, 2.9. (ii) C,
53.25; H, 4.75; N, 3.2. C76H82F6N4O4P4Pd2ؒ1.5CHCl3 requires
C, 53.3; H, 4.8; N, 3.2%]. Mass spectrum (FAB): m/z 1338
(M Ϫ 2CF3CO2H).
MHz, respectively) or a Bruker AM-400 spectrometer (operat-
1
ing frequencies for H, 31P and 13C of 400.13, 161.9 and 100.6
MHz, respectively). Proton and 13C shifts are relative to tetra-
methylsilane and 31P shifts to 85% phosphoric acid. Fast atom
bombardment (FAB) mass spectra were recorded using a VG
Autospec instrument with 8 kV acceleration. For the metal
complexes m/z values are quoted for 106Pd.
The following four compounds were prepared in a similar
manner to that described for 4a: [{Pd[PPh CH C(Ph)᎐N᎐
᎐
2
2
N᎐C(Ph)CHPPh ]} ][O CCF ] 4b, by addition of CF CO H to
᎐
2
2
2
3
2
3
2
2b, yield 76%, sample for microanalysis recrystallised from
chloroform–methanol (Found: C, 57.55; H, 3.5; N, 2.95.
C84H66F6N4O4P4Pd2ؒCHCl3 requires C, 57.8; H, 3.8; N, 3.15%),
mass spectrum (FAB): m/z 1418 (M Ϫ 2CF3CO2H); [{Pd[PPh2-
CH C(But)᎐N᎐N᎐C(But)CHPPh ]} ]Cl 4c, by the addition of
Preparations
Z,Z-PPh CH C(Ph)᎐N᎐N᎐C(Ph)CH PPh II. A solution
᎐
᎐
2
2
2
2
containing the keto phosphine Ph PCH C(᎐O)Ph 9 with (19.3 g,
᎐
2
2
᎐
᎐
2
2
2
2
63.3 mmol) and hydrazine monohydrate (1.5 cm3, 31.7 mmol)
and acetic acid (3.0 cm3) in ethanol (150 cm3) was heated at ca.
78 ЊC for 22 h. The resultant solution was concentrated to low
volume under reduced pressure and the product was isolated as
yellow needles. Yield (14.2 g, 74%) (Found: C, 79.3; H, 5.75; N,
4.5. C40H34N2P2 requires C, 79.45; H, 5.65; N, 4.65%). Electron-
impact (EI) mass spectrum: m/z: 604 (M).
concentrated HCl (0.05 cm3) to 2a (60 mg) in chloroform (2
cm3), yield 59 mg (93%) (Found: C, 61.1; H, 5.8; Cl, 5.25; N, 3.9.
C72H82Cl2N4P4Pd2 requires C, 61.3; H, 5.85; Cl, 5.05; N, 3.95%),
mass spectrum (FAB): m/z 1338 [(M Ϫ 2) Ϫ 2Cl]; [{Pd[PPh2-
CH C(But)᎐N᎐N᎐C(But)CHPPh ]} ][OC H (NO ) ] 4d, as
᎐
᎐
2
2
2
6
2
2 3 2
yellow microcrystals by the addition of 2 equivalents of picric
acid to 2a in chloroform solution and evaporation of the result-
ant solution to low volume and addition of hexane, yield 90%,
sample for analysis recrystallised from dichloromethane–
hexane (Found: C, 55.25; H, 4.5; N, 7.9. C84H86N10O14P4-
Pd2ؒ0.5CH2Cl2 requires C, 55.1; H, 4.75; N, 7.6%), mass
spectrum (FAB): m/z 1568 [M Ϫ (NO2)3C6H2O] and 1338
[PdCl{PPh CH᎐C(Ph)᎐N᎐N᎐C(Ph)CH PPh }] 1b. A solu-
᎐
᎐
2
2
2
tion containing [PdCl2(NCPh)2] (0.60 g, 0.26 mmol) and the
azine diphosphine II (0.16 g, 0.26 mmol) in chloroform (5
cm3) was heated at ca. 61 ЊC for 3 h. An excess of triethyl-
amine (0.3 cm3) was then added and the resultant purple solu-
tion was concentrated to low volume under reduced pressure.
Addition of methanol to the residue gave the required product
1b as a purple solid. Yield 0.84 g, 72% (Found: C, 64.6; H,
4.65; Cl, 4.65; N, 3.8. C40H33ClN2P2Pd requires C, 64.45; H,
4.45; Cl, 4.75; N, 3.75%). Mass spectrum (FAB): m/z 745
(M ϩ 1).
[(M Ϫ 2) Ϫ 2(NO2)3C6H2O]; and [{Pd[PPh CH C(Ph)᎐N᎐
᎐
2
2
N᎐C(Ph)CHPPh ]} ][OC H (NO ) ] 4e, by the addition of pic-
᎐
2
2
6
2
2 3 2
ric acid to 2b, yield 90%, sample for analysis recrystallised from
dichloromethane–diethyl ether (Found: C, 57.5; H, 3.7; N, 6.95.
C92H70N10O14P4Pd2ؒ0.5CH2Cl2 requires C, 57.4; H, 3.7; N,
7.2%), mass spectrum (FAB): m/z 1418 [(M Ϫ 2) Ϫ 2(NO2)3-
C6H2O].
[{Pd[PPh CH᎐C(But)᎐N᎐N᎐C(But)CHPPh ]} ] 2a. A solu-
[{Pd[PPh CH(Br)C(But)᎐N᎐N᎐C(But)CHPPh ]} ]Br
2
6a.
᎐
᎐
2
2
2
᎐
᎐
2
2
2
tion of lithium bis(trimethylsilyl)amide Li[N(SiMe3)2] (0.1 mol
dmϪ3 in thf, 0.45 cm3, 0.45 mmol) was added to a solution of
complex 1a (0.16 g, 0.22 mmol) in tetrahydrofuran (5 cm3).
After 15 min the solution was concentrated to low volume (ca. 1
cm3) under reduced pressure after which addition of methanol
gave complex 2a as red crystals. Yield 0.12 g, 80%. A sample
was recrystallised from dichloromethane–methanol for analysis
(Found: C, 62.0; H, 6.0; N, 3.8. C72H80N4P4Pd2ؒ2CH2Cl2
requires C, 61.6; H, 5.8; N, 3.9%). Mass spectrum (FAB): m/z
1338 (M).
Solutions of complex 2a (0.24 g, 0.18 mmol) in chloroform (4
cm3) and bromine (0.36 mmol) in tetrachloromethane (0.46
cm3) were stirred together at ca. 20 ЊC for 30 min. The result-
ant yellow solution was evaporated to dryness under reduced
pressure when addition of diethyl ether to the residue gave
complex 6a as a yellow solid. Yield 0.28 g, 94% (Found: C,
51.55; H, 4.8; N, 3.15. C72H80Br4N4P4Pd2ؒ0.25CHCl3 requires
C, 51.45; H, 4.8; N, 3.35%). Mass spectrum (FAB): m/z 1578
(M Ϫ Br), 1498 (M Ϫ 2Br), 1418 (M Ϫ 3Br) and 1338
(M Ϫ 4Br).
[{Pd[PPh CH᎐C(Ph)᎐N᎐N᎐C(Ph)CHPPh ]} ] 2b. A solu-
᎐
᎐
[{Pd[PPh CH(Me)C(But)᎐N᎐N᎐C(But)CHPPh ]} ]I 6b. (i)
2
2
2
᎐
᎐
2
2
2
2
tion of Li[N(SiMe3)2] (0.1 mol dmϪ3 in thf, 1.90 cm3, 1.90
mmol) was added to a solution of complex 1b (0.70 g, 0.095
mmol) in tetrahydrofuran (10 cm3). After 15 min the resultant
solution was concentrated to low volume (ca. 1 cm3) under
reduced pressure; addition of methanol then gave complex 2b
as an orange solid. Yield 0.57 g, 85% [Found: (i) C, 64.95; H,
3.75; N, 3.05. (ii) C, 65.25; H, 4.05; N, 3.25. C80H64N4P4Pd2
requires C, 67.75; H, 4.55; N, 3.95%]. Mass spectrum (FAB):
m/z 1418 (M).
A solution containing an excess of methyl iodide (0.1 cm3) and
complex 2a (0.40 g, 0.30 mmol) in chloroform (10 cm3) was
heated at ca. 61 ЊC for 11 h. The resultant yellow solution was
evaporated to dryness under reduced pressure and the residue
recrystallised from dichloromethane–hexane to give complex 6b
as yellow microcrystals. Yield 0.45 g, 92% (Found: C, 52.65; H,
4.9; N, 3.3. C74H84I2N4P4Pd2ؒCH2Cl2 requires C, 52.8; H, 5.2; N,
3.3%). Mass spectrum (FAB): m/z 1494 (M ϩ 1 Ϫ I) and 1367
(M ϩ 1 Ϫ 2I).
(ii) A solution of complex 2a (0.40 g, 0.30 mmol) and an
excess of methyl iodide (0.1 cm3) was stirred in chloroform
(5 cm3) at ca. 20 ЊC for 5 d. The product was isolated as above.
Yield 0.38 g, 79%.
[Pt{PPh CH᎐C(But)᎐N᎐N᎐C(But)CHPPh }(dmso)] 3. An
᎐
᎐
2
2
excess of KOBut (ca. 0.06 g, 0.50 mmol) was added to a solution
of complex 1c (0.10 g, 0.13 mmol) in dry dimethyl sulfoxide
(3 cm3). The NMR spectrum was recorded, see Discussion.
Attempts to isolate the complex by removing the solvent under
reduced pressure and trituration of the residue with n-hexane
gave an orange solid which decomposed on attempted re-
crystallisation.
[{Pd[PPh CH(Me)C(But)᎐N᎐N᎐C(But)CHPPh ]} ][PF ]
6 2
᎐
᎐
2
2
2
6c. A mixture of ammonium hexafluorophosphate (15 mg, 0.09
mmol) in methanol (1 cm3) and complex 6b (0.10 mg, 0.06
mmol) in methanol (3 cm3) was set aside at ca. 20 ЊC for 1 h. The
required product 6c was obtained as a yellow solid which was
filtered off and recrystallised from chloroform–methanol. Yield
0.10 g, 95% (Found: C, 52.3; H, 4.9; N, 3.25. C74H86F12N4P6-
Pd2ؒ0.5CHCl3 requires C, 52.1; H, 5.1; N, 3.25%). Mass spec-
trum (FAB): m/z 1513 (M Ϫ PF6) and 1368 (M ϩ 2 Ϫ 2PF6).
[{Pd[PPh CH C(But)᎐N᎐N᎐C(But)CHPPh ]} ][O CCF ]
3 2
᎐
᎐
2
2
2
2
2
4a. An excess of CF3CO2H (0.05 cm3) was added to a solution
of complex 2a (0.10 g, 0.074 mmol) in chloroform (3 cm3). The
resultant yellow solution was evaporated to dryness under
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620
2619

View Article Online
were applied to the phenyl rings so that they remained flat with
overall C2v symmetry. All hydrogen atoms were constrained to
idealised positions with a riding model including free rotation
of methyl groups.
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/530.
Table 5 Crystallographic data for compound 2a
Empirical formula
(C36H40N2P2Pd)2ؒ2CH2Cl2
T/K
200
λ/Å
Crystal system
Space group
0.710 73
Orthorhombic
Pccn
a/Å
b/Å
13.839(2)
20.696(4)
25.069(5)
7180(2)
c/Å
U/Å3
Z
4
Dc/Mg mϪ3
1.395
0.783
Acknowledgements
µ/mmϪ1
We thank Dr. K. S. D. Perera for help and valuable discussion,
Dr. J. D. Vessey for some of the NMR spectra, Dr. B. Ackers
for help with the preparation of compound II, the EPSRC for
support, and the Commonwealth Scholarship Commission
(UK) for a scholarship (to U. U. I.).
F(000)
Crystal size/mm
θmin, θmax/Њ
3104
0.19 × 0.15 × 0.12
2.0, 25.0
0–16; Ϫ5 to 24; Ϫ29 to 29
6616
6326
3226
0.0377, 6.8967
6326, 203, 403
1.017
0.0499
0.1126
hkl Ranges
Reflections collected
Independent reflections, p
Reflections with Fo2 > 2σFo
2
Weighting scheme parameters a, ba
Data, restraints, parameters (n)
Goodness of fit on F 2, S b
R1c
References
1 S. D. Perera, B. L. Shaw and M. Thornton-Pett, J. Chem. Soc.,
Dalton Trans., 1992, 1469.
2 S. D. Perera, B. L. Shaw and M. Thornton-Pett, J. Chem. Soc.,
Dalton Trans., 1993, 3653.
3 S. D. Perera, B. L. Shaw and M. Thornton-Pett, J. Chem. Soc.,
Dalton Trans., 1994, 3311.
4 U. U. Ike, S. D. Perera, B. L. Shaw and M. Thornton-Pett, J. Chem.
Soc., Dalton Trans., 1995, 2057.
5 S. Al-Jibori, Ph.D. Dissertation, University of Leeds, 1984.
6 S. Al-Jibori and B. L. Shaw, Inorg. Chim. Acta, 1982, 65, L123.
7 S. Al-Jibori and B. L. Shaw, Inorg. Chim. Acta, 1983, 74, 235.
8 H. Günther, NMR Spectroscopy, an Introduction, Wiley, Chichester,
New York, Brisbane, Toronto, 1980, pp. 39, 146 and 168.
9 J. W. Akitt, NMR and Chemistry, an Introduction to the Fourier
Transform-multinuclear Era, 2nd edn., Chapman and Hall, London,
New York, 1983, pp. 56, 145 and 212.
wR2d
Largest difference map peak and
0.998, Ϫ0.620
hole/e ÅϪ3
a
2
w = 1/[σ2(Fo2) ϩ aP2 ϩ bP], where P = (Fo2 ϩ 2Fc )/3. b S = {Σw(Fo2 Ϫ
¹
Fc )2/(n Ϫ p)}². c R1 = (Σ Fo| Ϫ |Fc )/Σ|Fo|. d wR2 = {Σw(Fo2 Ϫ Fc )2/
2
2
¹
Σ(Fo2)2}².
[{Pd[PPh C(Me)᎐C(But)᎐N᎐N᎐C(But)CHPPh ]} ] 7. A mix-
᎐
᎐
2
2
2
ture of an excess of KOBut (0.2 g) and complex 6b (0.40 g, 0.25
mmol) in dry dimethyl sulfoxide (2 cm3) was set aside at ca.
20 ЊC for 1 h. The solvent was removed under reduced pressure
and addition of methanol (ca. 5 cm3) to the residue gave 7 as a
brown solid, which was filtered off, washed with methanol and
dried in vacuo. Yield 0.30 g, 88% (Found: C, 61.45; H, 6.15; N,
3.6. C74H84N4P4Pd2ؒ2dmso requires C, 61.5; H, 6.35; N, 3.6%).
Mass spectrum (FAB): m/z 1367 (M ϩ 1).
10 R. K. Harris, Can. J. Chem., 1964, 42, 2275.
11 J. M. Jenkins and B. L. Shaw, Proc. Chem. Soc., 1963, 279.
12 A. Bright, B. E. Mann, C. Masters, B. L. Shaw, R. M. Slade and
R. E. Stainbank, J. Chem. Soc. A, 1971, 1826 and refs. therein.
13 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
14 S.-E. Bouaoud, P. Braunstein, D. Grandjean, D. Matt and D. Nobel,
Inorg. Chem., 1986, 25, 3765.
Crystallography
15 J. March, Advanced Organic Chemistry, 4th edn., Wiley, New York,
1992, p. 601.
16 J. K. Whitesell, in Comprehensive Organic Synthesis, ed. B. M. Trost,
Pergamon, Oxford, 1991, vol. 6, p. 703.
17 J. K. Whitesell and M. A. Whitesell, Synthesis, 1983, 517.
18 Enamines: Synthesis, Structure and Reactions, ed. A. G. Cook,
Marcel Dekker, New York, 1969.
19 G. Stork, A. Brizzolara, H. Landesman, J. Szmuszkovicz and
R. Terrell, J. Am. Chem. Soc., 1963, 85, 207.
20 B. L. Shaw and E. A. Staley, unpublished work.
21 G. M. Sheldrick, SHELXS 86, Acta Crystallogr., Sect. A, 1990, 46,
467.
22 G. M. Sheldrick, SHELXL 93, Program for refinement of crystal
structures, University of Göttingen, 1993.
All crystallographic measurements were made on a Stoe
STADI4 diffractometer operating in the ω–θ scan mode using
graphite monochromated Mo-Kα radiation (λ = 0.710 73 Å).
Crystal data are given in Table 5 together with refinement
details. Cell dimensions were refined from the values of 40
selected reflections (together with their Friedel opposites)
measured at ±2θ in order to minimise systematic errors.
The structure was solved by heavy-atom methods using
SHELXS 8621 and developed by full-matrix least-squares
refinement (on F 2) using SHELXL 93.22 The dimer possesses
crystallographic C2 symmetry and there is also a CH2Cl2 solvate
molecule in the asymmetric part of the unit cell. All non-
hydrogen atoms (including those of the solvate molecule) were
refined with anisotropic displacement parameters. Restraints
Received 7th January 1997; Paper 7/00153C
2620
J. Chem. Soc., Dalton Trans., 1997, Pages 2613–2620