Coordination modes of cis-P,P′-diphenyl-1,4-diphospha-cyclohexane to metal ions of Groups 9 and 10

Article abstract of DOI:10.1016/S0020-1693(02)01211-2

Complexes of a tertiary diphosphine with cyclic core, cis-P,P′-diphenyl-1,4-diphospha-cyclohexane (dpdpc), with metal ions of Groups 9 and 10 have been prepared and characterised. In neutral M(0) or M(II) (M=Pt, Pd) complexes the diphosphine acts as a bridge affording polynuclear products. Instead, in cationic mononuclear Pt(II) and Pd(II) species a clear preference for chelation of dpdpc is observed. Also the cation [Ni(dpdpc)₂Cl]⁺ contains the two dpdpc moieties as chelates. The molecular and crystal structure of [Ni(dpdpc)₂Cl]₂(NiCl₄) discloses a significantly small bite angle of the chelate and interaction of near phenyl rings pertaining to opposite dpdpc moieties. Coordination of dpdpc to cobalt prompts its oxidation to the corresponding P,P′-dioxide.

Full text of DOI:10.1016/S0020-1693(02)01211-2

Inorganica Chimica Acta 343 (2003) 209ꢂ216
/
www.elsevier.com/locate/ica
Coordination modes of cis-P,P?-diphenyl-1,4-diphospha-cyclohexane
to metal ions of Groups 9 and 10
Maria Elena Cucciolito a, Vincenzo De Felice b, Ida Orabona a, Achille Panunzi a,*,
Francesco Ruffo a
a
`
Dipartimento di Chimica, Universita di Napoli ‘Federico II’, Complesso Universitario di Monte S. Angelo, via Cintia, I-80126 Napoli, Italy
b
` `
Facolta di Scienze MM.FF.NN., Universita del Molise, via Mazzini 8, I-86170 Isernia, Italy
Received 28 April 2002; accepted 3 July 2002
Abstract
Complexes of a tertiary diphosphine with cyclic core, cis-P,P?-diphenyl-1,4-diphospha-cyclohexane (dpdpc), with metal ions of
Groups 9 and 10 have been prepared and characterised. In neutral M(0) or M(II) (MꢀPt, Pd) complexes the diphosphine acts as a
/
bridge affording polynuclear products. Instead, in cationic mononuclear Pt(II) and Pd(II) species a clear preference for chelation of
dpdpc is observed. Also the cation [Ni(dpdpc)2Cl]ꢁ contains the two dpdpc moieties as chelates. The molecular and crystal structure
of [Ni(dpdpc)2Cl]2(NiCl4) discloses a significantly small bite angle of the chelate and interaction of near phenyl rings pertaining to
opposite dpdpc moieties. Coordination of dpdpc to cobalt prompts its oxidation to the corresponding P,P?-dioxide.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Diphosphine; Crystal structures; Nickel; Palladium; Platinum; Cobalt
1. Introduction
of the N,N?-chelates [2], is hardly attainable by use of
the single chain vicinal diphosphines.
Vicinal diphosphines are a class of ligands, which
hardly can be matched in the field of organometallic
homogeneous catalysis for their ability to sturdily bind
the metal centre [1]. It is to note that, although the use of
For the sake of comparison we remind that nitrogen
analogous of the above cited ligands, such as N,N?-
diphenylpiperazine [3] and N,N?-dimethylpiperazine [4],
can act as chelates towards d8 ions, the latter being
responsible of relevant in plane hindrance.
diphosphines with a single chain skeleton ÈPÃ
/
CÃ
/
CÃ
/
In this work we have examined the coordination
behaviour of P,P?-diphenyl-1,4-diphospha-cyclohexane.
The preparation of this compound as the mixture of cis
and trans stereoisomers was described many years ago
[5], while more recently the stereoselective synthesis of
the cis isomer (henceforth ‘dpdpc’) was attained [6]. We
have investigated the behaviour of the cis form since this
stereoisomer is in principle suitable not only to act as a
bridge by binding two metal centers (Fig. 1(a)), but also
to chelate one metal atom (Fig. 1(b)). In chelate dpdpc
the steric hindrance of the two phenyl groups can be
conformationally modulated and it is not likely to cause
a forceful constraint, undesired in this initial part of the
study.
PÇ is accordingly quite extended, it appears that no
substantial investigation has dealt with the double chain
cyclic compounds having a Ã
/
P(Ã
/
CÃ
/
CÃ
/
)2PÃ
/
skeleton.
Yet the use in coordination chemistry of the latter
compounds as ligands could possibly present some
innovative features. For instance, diphosphines with
cyclic core, particularly the P,P?-disubstituted 1,4-
diphospha-cyclohexanes, in case act as chelates, can be
suited to afford a fairly rigid steric hindrance towards
the adjacent ligands within the plane, where the metal
and the two phosphorus atoms sit. This feature, which
proved to be a source of quite relevant effects in the case
Here results on the coordination mode(s) of dpdpc in
the environment of platinum(0 or II), palladium(0 or II),
nickel(II) and cobalt(II) are reported. These ions are
* Corresponding author. Tel.: ꢁ
090
E-mail address: panunzi@chemistry.unina.it (A. Panunzi).
/
39-081-674 458; fax: ꢁ39-081-674
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 2 1 1 - 2

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M.E. Cucciolito et al. / Inorganica Chimica Acta 343 (2003) 209ꢂ216
/
2.2. [PtClMe(m-dpdpc)]3
A solution of dpdpc (30 mg, 0.11 mmol) in 1 ml of
CHCl3 was added to
a
stirred solution of
[PtClMe(Me2S)2] (40 mg, 0.11 mmol) in CHCl3 (1.5
ml). After 4 h the white microcrystalline precipitate was
recovered by filtration. The solid was washed with Et2O
(4 ml) and dried in vacuo. Yield: 85%. Anal. Calc. for
Fig. 1. Formula of cis-P,P?-diphenyl-1,4-diphospha-cyclohexane in
the chair conformation (a) and in the boat conformation (b).
known to be particularly suitable to bind open-chain
vicinal diphosphines. The molecular and crystal struc-
ture of [Ni(dpdpc)2Cl]2(NiCl4) and the molecular struc-
ture of a cobalt(II) complex containing the P,P?-dioxide
of cis-P,P?-diphenyl-1,4-diphospha-cyclohexane are
also reported.
C17H21ClP2Pt: C, 39.44; H, 4.09. Found: C, 39.58; H,
1
4.11%. H NMR (CDCl3) d: 7.8ꢂ
/
7.3 (m, 10H); 3.6ꢂ
/
3.3
2
(br, 4H); 2.7ꢂ
/
2.3 (br, 4H); 0.28 (t, 3H, JPtÃH
ꢀ
/
83 Hz,
3JPÃH
2588 Hz).
ꢀ
/
6.5 Hz); 31P NMR (CDCl3) d: 8.0 (1JPtÃP
ꢀ
/
2.3. [PtMe(PPh3)(dpdpc)]BF4
To a stirred solution of triphenylphosphine (26 mg,
0.10 mmol) in CHCl3 (2 ml) was added at r.t. solid
AgBF4 (20 mg, 0.10 mmol) and a few drops of
nitromethane to obtain complete dissolution. After 5
min the solution was added to a mixture of [PtClMe(m-
dpdpc)]3 (51 mg, 0.033 mmol) and 5 ml of CHCl3, and
stirring was continued 24 h at r.t. The solvent was
removed in vacuo and the residue was extracted with
2. Experimental
All reactions were carried out under a nitrogen
atmosphere by using Schlenk techniques. Solvents
were dried before use with standard procedures. 1H
NMR spectra were recorded at 298 K with a Gemini
300-MHz spectrometer. CDCl3 and CD3NO2 were used
as solvents, and CHCl3 (dꢀ
/
7.26 ppm) and CHD2NO2
4.33 ppm) as internal standards. 31P NMR spectra
3ꢃ2 ml portions of CHCl3. The solution was passed on
/
(dꢀ
/
a small Celite bed and concentrated to a small volume.
Addition of Et2O prompted the precipitation of the
white product. The yield was approximately 80%. Anal.
Calc. for C35H36BF4P3Pt: C, 50.56; H, 4.36. Found: C,
were recorded on an AM 400-MHz Bruker model. The
following abbreviations were used for describing NMR
multiplicities: no attribute, singlet; d, doublet; t, triplet;
q, quartet; dd, double doublet; m, multiplet; br, broad.
Conductivity measurements were performed on a Crison
Conductimeter model microCM 2200. The complexes
[PtCl2(SMe2)2] [7], [PtCl2(1,5-COD)] [8], [PtClMe-
(SMe2)2] [9], [PtCl2(PPh3)2] [10], [Pt(norbornene)3] [11],
[PdClMe(1,5-COD)] [12] and [PdCl2(1,5-COD)] [13]
were obtained by known methods. Particular care was
employed in excluding moisture or air in the synthesis of
dpdpc, which was obtained as previously reported [14]
from the commercially available 1,2-bis(phenylphosphi-
no)ethane (Aldrich).
50.27; H, 4.26%. 1H NMR (CDCl3) d: 7.8ꢂ
/
7.2 (m, 25H);
66 Hz); 31P
2
2.9ꢂ
/
2.5 (br, 8H); 0.32 (app q, 3H, JPtÃH
ꢀ
/
1
NMR resonances (CDCl3) d: 48.0 (dd, JPtÃP
ꢀ
/
2550
69 Hz); 39.4 (d,
2915 Hz). Conduc-
2
2
Hz, JPÃP(trans)ꢀ
/
393 Hz; JPÃP(cis)ꢀ
/
1JPtÃP
ꢀ
/
1398 Hz); 29.0 (d, JPtÃP
ꢀ
/
1
tivity in nitromethane at 298 K: 81.2 S molꢄ1 cmꢄ1
.
2.4. [Pt(PPh3)2(dpdpc)](BF4)2
Solid AgBF4 (49 mg, 0.25 mmol) was added at r.t. to a
stirred solution of [PtCl2(PPh3)2] (100 mg, 0.127 mmol)
in phenyl cyanide (2 ml). After 24 h the mixture is
filtered and the solvent was removed in vacuo. The
white residue was dissolved in 6 ml of CHCl3 and a
solution of dpdpc (34 mg, 0.125 mmol) in the same
solvent (0.5 ml) was added at r.t. After 48 h stirring the
solvent was removed in vacuo and the white residue was
dissolved in a minimum amount of CH2Cl2/nitro-
methane (9:1). Hexane was added to achieve crystal-
lization of the product in 70% yield. Anal. Calc. for
2.1. Attempt to prepare [Pt(dpdpc)(dmf)]
Solid [Pt(norbornene)3] (96 mg, 0.20 mmol) was
added at room temperature (r.t.) to a solution of dmf
(28 mg, 0.20 mmol) in Et2O (5 ml). After 10 min of
stirring the resulting solution was added to a solution of
dpdpc (54 mg, 0.20 mmol) in 2.5 ml of Et2O. The yellow
product was collected by filtration after approximately
24 h, washed with Et2O and dried in vacuo. The yield
was approximately 95%. The molecular weight, as
determined by osmometric measurements, was 1980
C52H48B2F8P4Pt: C, 53.59; H, 4.15. Found: C, 53.25; H,
1
4.24%. H NMR (CDCl3) d: 7.7ꢂ
/
7.4 (br, 32H); 7.2ꢂ
/7.0
(m, 4H); 6.9ꢂ
/
6.7 (m, 4H); 3.4ꢂ
/
3.2 (br, 4H); 2.8ꢂ2.5 (br,
/
4H); 31P NMR resonances (CDCl3) d: 50.3 (d, JPtÃP
ꢀ
/
1
2
1
2684 Hz, JPÃP
Conductivity in nitromethane at 298 K: 175.6 S molꢄ1
cmꢄ1
ꢀ
/
278 Hz); 15.5 (d, JPtÃP
ꢀ/2710 Hz).
uma. 1H NMR (CDCl3): 7.6ꢂ
(br, 16H).
/
7.0 (br, 10H); 3.6ꢂ1.6
/
.

M.E. Cucciolito et al. / Inorganica Chimica Acta 343 (2003) 209ꢂ
/
216
211
2.5. [Pt(dpdpc)2](BF4)2
CHCl3, and stirring was continued 24 h at r.t. The
solvent was removed in vacuo and the residue extracted
To a solution of [PtCl2(Me2S)2] (30 mg, 0.077 mmol)
in methylene chloride (2 ml) a solution of dpdpc (42 mg,
0.15 mmol) in 1 ml of the same solvent and AgBF4 (30
mg, 0.15 mmol) dissolved in a few drops of nitro-
methane were added at r.t. After 48 h of stirring a
precipitate was filtered off, and the solvent was removed
in vacuo to give an oily residue. This crude product was
dissolved in a minimum amount of a CHCl3/nitro-
methane mixture (9:1) and Et2O was added to achieve
crystallisation of the product in 75% yield. Anal. Calc.
for C32H36B2F8P4Pt: C, 42.09; H, 3.97. Found: C, 42.30;
with 3ꢃ2 ml portions of CHCl3. The solution was
/
passed on a small Celite bed and concentrated to a small
volume. Addition of Et2O prompted the precipitation of
the white product in 80% yield. Anal. Calc. for
C19H24BF4NP2Pd: C, 43.76; H, 4.64. Found: C, 43.52;
1
H, 4.51%. H NMR (CD3NO2/CDCl3 1:5) d: 7.55 (br,
4H); 7.45 (br, 6H); 2.75 (br, 8H); 2.13 (3H); 0.80 (3H,
3JPÃH
ꢀ
6 Hz); 31P NMR (CD3NO2/CDCl3 1:5) d: 6.6.
/
Conductivity in nitromethane at 298 K: 79 S molꢄ1
cmꢄ1
.
1
H, 4.02%. H NMR (CD3NO2) d: 7.25 (m, 4H); 7.15
(br, 8H); 6.98 (m, 8H); 3.10 (app d, 8H); 2.4 (br, 8H); 31
2.9. [PdMe(PPh3)(dpdpc)](BF4)
P
2410 Hz). Conduc-
NMR (CD3NO2) d: 48.8 (1JPtÃP
ꢀ
/
A solution of AgBF4 (19 mg, 0.10 mmol) in 1 ml of
nitromethane was added to a stirred mixture of
[PdClMe(m-dpdpc)]3 (42 mg, 0.033 mmol) and triphe-
nylphosphine (26 mg, 0.10 mmol) in 4 ml of CH2Cl2,
and stirring was continued 1 h at r.t. The mixture was
passed on a small Celite bed and concentrated to a small
volume (1 ml). Addition of Et2O prompted the pre-
cipitation of the white product in 70% yield. Anal. Calc.
tivity in nitromethane at 298 K: 164 S molꢄ1 cmꢄ1
.
2.6. [Pt(dpdpc)(1,5-COD)](BF4)2
A solution of [PtCl2(1,5-COD)] (56 mg, 0.15 mmol) in
2 ml of CH2Cl2 was added at r.t. to a stirred solution of
dpdpc (41 mg, 0.15 mmol) in the same solvent (2 ml).
After 3 h stirring a solution of AgBF4 (60 mg, 0.30
mmol) in a few drops of nitromethane was added to the
resulting suspension. After 18 h the white precipitate
was removed by filtration and the solvent was elimi-
nated in vacuo to afford an oily residue. This crude
product was dissolved in a minimum amount of CHCl3/
nitromethane (9:1) and Et2O was added to crystallise the
product as a white solid in 75% yield. Anal. Calc. for
for C35H36BF4P3Pd: C, 56.60; H, 4.88. Found: C, 56.80;
1
H, 5.01%. H NMR (CDCl3) d: 7.60ꢂ/7.20 (br, 20H);
7.15 (t, 1H); 6.95 (t, 2H); 6.70 (t, 2H); 2.7 (br, 8H); 0.25
3
(t, 3H, JPÃH
ꢀ
6 Hz); 31P NMR (CDCl3) d: 47.2 (d,
/
2JPÃP
ꢀ369 Hz); 34.1 (d); 30.3. Conductivity in nitro-
/
methane at 298 K: 85 S molꢄ1 cmꢄ1
.
2.10. [Pd(dpdpc)2](BF4)2
C24H30B2F8P2Pt: C, 38.48; H, 4.04. Found: C, 38.55; H,
1
3.99%. H NMR (CD3NO2) d: 7.9ꢂ
/
7.7 (m, 10H); 5.81
50 Hz); 3.7 (br, 4H); 2.9ꢂ2.5 (br, 12H);
3000 Hz). Con-
To a stirred solution of [PdCl2(1,5-COD)] (29 mg,
0.10 mmol) in methylene chloride (5 ml) a solution of
dpdpc (54 mg, 0.20 mmol) in the same solvent (1 ml) and
a solution of AgBF4 (39 mg, 0.20 mmol) in nitro-
methane (1 ml) were added at r.t. After 24 h of stirring
the mixture was filtered, and approximately half of the
solvent was removed in vacuo. After dropwise addition
of approximately 3 ml of Et2O, the white precipitate was
recovered by filtration, washed with Et2O and dried in
vacuo. Yield: 80%. Anal. Calc. for C32H36B2F8P4Pd: C,
2
(t, 4H, JPtÃH
ꢀ
/
/
31P NMR (CD3NO2) d: 51.7 (1JPtÃP
ꢀ
/
ductivity in nitromethane at 298 K: 178 S molꢄ1 cmꢄ1
.
2.7. [PdMeCl(dpdpc)]3
A solution of [PdMeCl(1,5-COD)] (40 mg, 0.15 mmol)
in 1 ml of methylene chloride was added at r.t. to a
stirred solution of dpdpc (41 mg, 0.15 mmol) in 2 ml of
the same solvent. After 3 h stirring Et2O (3 ml) was
added dropwise in order to increase the amount of the
white precipitate. The solid was recovered by filtration,
washed with Et2O and dried in vacuo in 85% yield.
Anal. Calc. for C17H21ClP2Pd: C, 47.58; H, 4.93. Found:
1
46.61; H, 4.40. Found: C, 46.73; H, 4.48%. H NMR
(CD3NO2) d: 7.25 (m, 2H); 7.15 (m, 4H); 7.0 (m, 4H);
3.15 (d, 4H); 2.35 (br, 4H); 31P NMR (CD3NO2) d: 57.4.
Conductivity in nitromethane at 298 K: 170 S molꢄ1
cmꢄ1
.
1
C, 47.65; H, 5.02%. H NMR (CDCl3) d: 7.7 (m, 4H);
7.4 (m, 6H); 3.4 (br, 4H); 2.45 (br, 4H); 0.10 (t, 3H,
2.11. [Pd(py)2(dpdpc)](BF4)2
3JPÃH
ꢀ
6 Hz); 31P NMR (CDCl3) d: 8.8.
/
To a stirred solution of [PdCl2(1,5-COD)] (29 mg,
0.10 mmol) in methylene chloride (5 ml) were added a
solution of dpdpc (27 mg, 0.10 mmol) in the same
solvent (1 ml), pyridine (20 mg, 0.25 mmol), and a
solution of AgBF4 (39 mg, 0.20 mmol) in nitromethane
(1 ml) at r.t. After 24 h of stirring, the mixture was
2.8. [PdMe(MeCN)(m-dpdpc)]3(BF4)3
A solution of AgBF4 (20 mg, 0.10 mmol) in methyl
cyanide (1 ml) was added at r.t. to a mixture of
[PdClMe(m-dpdpc)]3 (42 mg, 0.033 mmol) and 5 ml of

212
M.E. Cucciolito et al. / Inorganica Chimica Acta 343 (2003) 209ꢂ216
/
filtered, and approximately half of the solvent was
removed in vacuo. After dropwise addition of approxi-
mately 3 ml of Et2O, the white precipitate was recovered
by filtration, washed with Et2O and dried in vacuo.
Yield: 70%. Anal. Calc. for C26H28B2F8N2P2Pd: C,
Table 1
Crystallographic parameters for chloronickel(dpdpc)2 tetrachloronick-
elate
Formula weight
Temperature (K)
System
C64H72Cl6Ni3P8
29591
triclinic
¯
43.95; H, 3.97; N, 3.94. Found: C, 44.09; H, 3.89; N,
1
Space group
Crystal color
Crystal shape
Corrections
#2 P1/
3.79%. H NMR (CDCl3) d: 8.81 (d, 4H), 7.6ꢂ
/7.4 (m,
blue
needles
8H); 7.3 (m, 4H); 7.18 (d, 4H); 3.78 (app t, 4H); 2.37
(app t, 4H). 31P NMR (CDCl3) d: 66.8. Conductivity in
Lorentz-polarization
linear decay (from 0.988 to 1.000 on
nitromethane at 298 K: 168 S molꢄ1 cmꢄ1
.
I)
reflection averaging (agreement on
2.12. [CoCl2(dpdpc-P,P?-dioxide)]2
Iꢀ3.2%)
empirical absorption (from 1.536 to
A solution of CoCl2×
/
6H2O (30 mg, 0.13 mmol) in
isopropanol was added dropwise to a stirred solution of
0.671 on I)
10.878 (1)
17.794 (1)
20.294 (1)
106.36 (1)
105.58 (2)
107.82 (1)
3306.8
˚
a (A)
˚
b (A)
dpdpc (34 mg, 0.13 mmol) in 2.5 ml of the same solvent.
A
˚
c (A)
brown microcrystalline precipitate immediately
a (8)
b (8)
g (8)
formed, while the solution turned to a turquoise-green
color. The precipitate was recovered by filtration,
washed with isopropanol and dried in vacuo. Attempt
to recrystallise the brown compound from MeOH by
addition of Et2O resulted in the attainment of azure
crystals, which were used for an X-ray analysis (see
text). Anal. Calc. for C32H36Cl4Co2O4P4: C, 44.27; H,
4.18. Found: C, 44.35; H, 4.27%.
3
˚
V (A )
Z
2
1.48
Dcalc (g cmꢄ3
Radiation
)
˚
Cu Ka (1.54184 A)
54.4
1528
m (cmꢄ1
F(000)
Crystal dimensions (mm)
)
0.25ꢃ0.01ꢃ0.01
77.4
7082 total, 7048 unique
Maximum 2u (8)
Reflections measured
Number unobserved data
Reflections included
Parameters refined
2.13. {[NiCl(dpdpc)2]}2[NiCl4]
3274
3774 with Fo2ꢀ3.0s(Fo
410
)
2
A solution of NiCl2×/6H2O (24 mg, 0.10 mmol) in
EtOH (1 ml) was added dropwise to a stirred solution of
dpdpc (27 mg, 0.10 mmol) in 1 ml of methylene chloride.
Unweighted agreement factor
Weighted agreement factor
Factor including unobserved
data
0.059
0.068
0.198
After 1 h standing at r.t. addition of Et2O gave a redꢂ
/
brown microcrystalline precipitate, which was recovered
by filtration, washed with Et2O and dried in vacuo.
Recrystallization from CHCl3 by addition of Et2O
resulted in the attainment of dark-red crystals (yield:
Esd of observed of unit weight 1.35
Convergence, largest shift
Refinement
0.01s
full-matrix least-squares
Minimization function
Least-squares weights
High peak in final difference
a w(jFojꢄjFcj)2
4Fo2/s2(Fo
)
2
1
75%). H NMR (CDCl3) d: 7.4 (br, 4H); 7.25 (t, 2H);
0.48 (9)
7.16 (t, 4H); 3.24 (d, 4H); 2.02 (d, 4H); 31P NMR
(CDCl3) d: 62.2. Anal. Calc. for C64H72Cl6Ni3P8: C,
52.01; H, 4.91. Found: C, 52.29; H, 4.89%.
ꢄ3
˚
map (e A
)
Low peak in final difference
0.39 (9)
ꢄ3
˚
map (e A
)
2.14. Crystal structure determination of
{[NiCl(dpdpc)2]}2(NiCl4)
analysis of the data was applied. Relative transmission
coefficients ranged from 148.966 to 65.106 with an
average value of 101.572. The structure was solved by
routine application of the Patterson and Fourier tech-
niques and refined by full-matrix least-square procedure
Details of the structure analysis are listed in Table 1.
The compound was recrystallised from CH2Cl2/Et2O.
X-ray data were collected at r.t. on an EnrafꢂNonius
CAD4-F automatic diffractometer using Mo Ka gra-
phite-monochromated radiation and operating in the v/
u scan mode. The unit cell parameters were obtained by
a least-squares fitting of the setting values of 25
/
minimizing the quantity a w(jFojꢄ
/
jFcj)2 with wꢄ1ꢀ
/
[s2(Fo)ꢁ(0.02Fo)2ꢁ
/
/
1] where s is derived from counting
statistics. All non-hydrogen, but carbon atoms, were
refined anisotropically. The H atoms were placed in
calculated positions and included but not refined in last
refinement cycles with isotropic thermal parameters
reflections in u range 1485
/
u ]128. Three monitoring
/
reflections, measured every 500, showed an intensity
decay of about 2.37% and a linear correction was
applied. In addition to the corrections for Lp factors,
an empirical absorption correction based on Fourier
equal those of the carrier atoms. The final Fourier
ꢄ3
˚
difference map showed no peaks greater than 0.5 e A
.

M.E. Cucciolito et al. / Inorganica Chimica Acta 343 (2003) 209ꢂ
/
216
213
[PtClMe(m-dpdpc)]3 ꢁ3AgBF4 ꢁ3PPh3
ꢀ3[PtMe(PPh3)(dpdpc)]BF4 ꢁ3AgCl
All calculations were performed by using the Enrafꢂ
Nonius SDP set of programs [15].
/
(1)
Relevant NMR features for the structure assignment
are the following ones: (i) one doublet in the 31P NMR
2
spectrum at 39.4 ppm (1JPtÃP
Hz), diagnostic [18] of a phosphorus atom trans to Me;
ꢀ
/
1398 Hz, JPÃP(cis)ꢀ
/
69
3. Results and discussion
(ii) two more signals at 48.0 ppm (double doublet,
2
3.1. Platinum complexes
2
1JPtÃP
ꢀ
/
2550 Hz, JPÃP(trans)ꢀ
/
393 Hz; JPÃP(cis)ꢀ69
/
2
Hz) and at 29.0 ppm (1JPtÃP
ꢀ
/
2915 Hz, JPÃP(trans)ꢀ
/
Attempts to isolate monomeric Pt(0) complexes of
chelate dpdpc of the more common type known for
single chain diphosphines [16], i.e. [Pt(P,P?-chelate)(ol)]
393 Hz). It is noteworthy the large low-field shift of the
31P signal observed on comparing this spectrum and that
pertaining to the parent compound. Conductivity mea-
surements [19] and elemental analyses support the above
structure.
(olꢀ electron-poor olefin) failed. In fact, the reaction of
/
Pt(norbornene)3 with dpdpc in presence of dimethylfu-
marate (‘dmf’) or fumarodinitrile (‘fdn’) gave poorly
soluble products with scarcely significant broad 1H
NMR spectra. The only fairly reliable molecular weight
determination pointed to the formula [Pt3(dpdpc)3-
(dmf)3].
Also mononuclear cationic dipositive complexes of
general formula [PtL2(dpdpc)](BF4)2, (L2ꢀ
/
dpdpc or
PPh3) could be isolated. The first one
1,5-COD or 2×
/
was prepared according to Eq. (2).
[PtCl2(Me2S)2]ꢁ2AgBF4 ꢁ2dpdpc
ꢀ[Pt(dpdpc)2](BF4)2 ꢁ2AgClꢁ2Me2S
Also the nature of the products obtained from
PtCl2L2 (Lꢀ
/
Me2S or L2ꢀ1,5-COD) and dpdpc could
/
(2)
not be satisfactorily understood, due to their very poor
solubility.
A fairly poor solubility was displayed also by the
white microcrystalline air stable solid obtained by
The presence of only one signal at 48.8 ppm (1JPtÃP
ꢀ
/
2410 Hz) in the 31P NMR support the above formula,
which is in keeping with conductivity measurements and
elemental analyses.
reacting [PtClMeL2] (Lꢀ
/
Me2S or L2ꢀ1,5-COD) with
/
The 1,5-COD derivative has been obtained according
to Eq. (3).
the diphosphine. Although also in this case neither
single crystal suitable for X-ray analysis nor a reliable
molecular weight determination could be obtained, at
least the NMR spectra at room temperature gave useful
information. Only one signal is observed in the 31P
[PtCl2(1; 5-COD)]ꢁdpdpcꢁ2AgBF4
ꢀ[Pt(dpdpc)(1; 5-COD)](BF4)2 ꢁ2AgCl
(3)
1
The H NMR spectrum of the product discloses the
NMR spectrum, at 8.0 ppm (1JPÃPt
ꢀ2588 Hz), which
/
presence of the diolefin through the signal of olefin
2
discloses the equivalence of the two phosphorous atoms.
Thus, the compound should not be a mononuclear one.
protons (d 5.81, JPtÃH
ꢀ
/
50 Hz). The single signal at
3000 Hz)
is in agreement with the equivalence of the two
51.7 ppm in the 31P NMR spectrum (1JPÃPt
ꢀ
/
1
In the H NMR spectrum the PtÃ
/
Me signal is a triplet
6.5 Hz) and has satellites
due to coupling with 195Pt (2JPtÃH
83 Hz). The former
coupling is in keeping with a cis MeÃPtÃP arrangement.
centred at 0.28 ppm (3JPÃH
ꢀ
/
phosphorus atoms.
ꢀ
/
The triphenyl phoshine dipositive cation could be
obtained by preparing in situ [Pt(PPh3)2(PhCN)2](BF4)2,
and by exchanging the two phenylcyanide ligands with
dpdpc (Eqs. (4) and (5)).
/
/
Measurement of low temperature spectra was not
permitted by the low solubility.
As for the molecular complexity of the product, we
note: (i) the compound is not an electrolyte, thus ruling
out an A-frame dimer of the type invoked for the related
bisdiphenylphosphinomethane derivative [17,18]; (ii) the
FAB mass spectrum only allows to rule out a mono-
meric structure. On consideration of the molecular
complexity of the above reported dmf derivative we
[PtCl2(PPh3)2]ꢁ2AgBF4 ꢁ2PhCN
ꢀ[Pt(PPh3)2(PhCN)2](BF4)2 ꢁ2AgCl
[Pt(PPh3)2(PhCN)2](BF4)2 ꢁdpdpc
(4)
ꢀ[Pt(PPh3)2(dpdpc)](BF4)2 ꢁ2PhCN
(5)
The doublet at 15.5 ppm (2JPÃP(trans)ꢀ
/278 Hz) can
tentatively assume
a
trinuclear cyclic structure
be attributed to the equivalent phosphorous atoms of
the two triphenylphosphines, while the donor atoms of
dpdpc resonate at 50.3 ppm.
[PtMeCl(m-dpdpc)]3 [17,18]. Similarly, we will indicate
as [PtCl2(m-dpdpc)]3 the above mentioned dichloro
derivative.
A simple mononuclear dpdpc complex of formula
[PtMe(PPh3)(dpdpc)]BF4 could be isolated by reaction
of the putative neutral trinuclear species with silver
tetrafluoroborate in presence of triphenylphosphine,
according to Eq. (1).
3.2. Palladium complexes of dpdpc
A close similarity is observed on comparing the above
results concerning platinum with the behaviour of dpdpc

214
M.E. Cucciolito et al. / Inorganica Chimica Acta 343 (2003) 209ꢂ216
/
in palladium environments. Attempts to obtain a simple
mononuclear organometallic derivative [20] of the type
[Pd(dpdpc)(ol)] from Pd(dba)2 and an electron poor
olefin failed. The products were possibly polynuclear
species similar to the proposed platinum species.
In the 31P spectrum of the former complex the 4 equiv.
phosphorous atoms resonate at 57.4 ppm, while in the
spectrum of the latter one a singlet is observed at 66.8
ppm. Both conductivity measurements and elemental
analyses support the proposed structures.
The product from [PdCl2(1,5-COD)] and dpdpc was
poorly soluble and also its structure, possibly poly-
nuclear, could not be unambiguously determined.
Also in this case, the fairly soluble Pd(II) chloro/
3.3. Nickel complex of dpdpc
Given the ability of nickel(II) to give complexes with
vicinal diphosphines, we attempted the preparation of a
1
methyl derivative displayed well resolved H and 31P
NMR spectra. The former exhibits a triplet at 0.10 ppm
(3JPÃH
dpdpc derivative by reacting the ligand with NiCl2×
6H2O in ethanol/methylene chloride. The reaction can
be described by Eq. (10).
/
ꢀ6.0 Hz). In the latter one only one signal is
/
observed at 8.8 ppm, pointing to the equivalence of the
two P atoms. Thus, a mononuclear species should be
ruled out. Unfortunately, the solubility was not suffi-
cient for a molecular weight determination in solution.
By analogy with the corresponding platinum complex
we will denote this product as [PdClMe(m-dpdpc)]3.
Again, a cationic complex could be obtained by
reaction of the putative neutral trinuclear species with
silver tetrafluoroborate in presence of MeCN (Eq. (6)).
3NiCl2 ×6H2Oꢁ4dpdpc
ꢀf[NiCl(dpdpc)2]g2(NiCl4)ꢁ18H2O
(10)
The chelated phosphorous atoms of the brick colored
product resonate at 62.2 ppm in the 31P NMR spectrum.
Crystals suited for X-ray analyses were grown from
chloroform/diethyl ether (see before).
[PdClMe(m-dpdpc)]3 ꢁ3AgBF4 ꢁ3MeCN
3.4. Cobalt complex of the dpdpc-P,P?-dioxide
ꢀ[PdMe(MeCN)(m-dpdpc)]3(BF4)3 ꢁ3AgCl
(6)
The attempt to react CoCl2×
afforded a brown microcrystalline material, which
appeared very sensitive to air and turned to a blueꢂ
/
6H2O with dpdpc
The following NMR data are in keeping with the
1
structure assigned to the complex: (i) a triplet in the H
/
NMR spectrum, centred at 0.80 ppm, (3JPÃH
ꢀ6 Hz);
/
green microcrystalline stable compound also in presence
of traces of oxygen. In spite of several crystallisation
attempts, the last product could be obtained only as very
small single crystals, on which an X-ray analysis was
attempted. Although the molecular structure resolution
was unsatisfactory, the general stereogeometry was
unequivocally determined and is shown in Fig. 3. The
compound is a binuclear derivative with two bridging
cis-chair dpdpc-P,P?-dioxide moieties. Unfortunately,
the standard errors of the structure model are quite high
and not useful for a comparative discussion.
(ii) only one signal in the 31P NMR spectrum at 6.6
ppm. On consideration that lowering the temperature at
243 K does not affect significantly the proton spectrum
and of the minor shift of the 31P resonance with respect
to the starting complex it appears that the polynuclear
structure is retained in the cation.
Also for palladium a simple mononuclear complex of
formula [PdMe(PPh3)(dpdpc)]BF4 could be prepared
according to Eq. (7).
[PdClMe(m-dpdpc)]3 ꢁ3AgBF4 ꢁ3PPh3
ꢀ3[PdMe(PPh3)(dpdpc)]BF4 ꢁ3AgCl
(7)
3.5. Molecular structure of chloronickel(dpdpc)2
tetrachloronickelate
Three phosphorous signals are present in the 31P
spectrum. The singlet at d 30.3 is attributable to the
phosphorus atom of dpdpc trans to Me, while the
doublets at 34.1 and 47.2 ppm (2JPÃP(trans)ꢀ
369 Hz)
pertain to the mutually trans phosphorous nuclei. Also
in this case the large low field shift of the signals of
dpdpc is in support for its chelation to the metal centre
with formation of a mononuclear compound.
The molecular structure of the complex, together with
the atom-labelling scheme, is shown in Fig. 2. Selected
bond distances and angles are listed in Table 2. In the
cation, displaying typical [21] square planar pyramidal
geometry, the nickel atom is coordinated to four
phosphorus atoms of two chelate dpdpc molecules and
/
The
mononuclear
dipositive
complexes
to one apical chlorine atom. The NiÃ
/
Cl distance is
[Pd(dpdpc)2](BF4)2 and [Pd(py)2(dpdpc)](BF4)2 were
obtained according to Eqs. (8) and (9).
˚
approximately 0.3 A longer that the sum of atomic radii.
The phenyl groups are perpendicular to the pyramid
base and face each other. This arrangement should be
caused both by mutual dipolar interactions in each pair
[PdCl2(1; 5-COD)]ꢁ2AgBF4 ꢁ2dpdpc
ꢀ[Pd(dpdpc)2](BF4)2 ꢁ2AgClꢁ1; 5-COD
[PdCl2(1; 5-COD)]ꢁ2AgBF4 ꢁdpdpcꢁ2py
(8)
(9)
of rings, and by the need of minimising steric contacts
˚
P distances are in the range 2.19ꢂ2.20 A,
[22]. The NiÃ
/
/
ꢀ[Pd(py)2(dpdpc)](BF4)2 ꢁ2AgClꢁ1; 5-COD
i.e. are in keeping with normal values for similar

M.E. Cucciolito et al. / Inorganica Chimica Acta 343 (2003) 209ꢂ
/
216
215
Fig. 3. Structure of [CoCl2(dpdpc-P,P?-dioxide)]2.
complexes [23,24]. Noticeably, the bite angle PÃ
/
NiÃ
/
P is
nearly 758, which is smaller than the values commonly
exhibited by chelate open chain vicinal diphosphines in
comparable environment [23]. The angles NiÃ
/
PÃ/Cphenyl
are 1308, thus indicating that the tetrahedral geometry
around P is significantly distorted. This can be explained
on consideration that smaller values of the angles should
accompany both to a diminished distance of facing
rings, with increase of steric hindrance, and to a loss of
the their parallelism, with decrease of the dipolar
attraction. Within the dpdpc ring the CÃ
are approximately 1008, as for free trans-dpdpc [6]. As
for the anions, they lie nearly halfway (Ni1ÃNi3ꢀ
/
PÃ
/
C angles
Fig. 2. Molecular structure of {[NiCl(dpdpc)2]}2[NiCl4] as determined
through X-ray diffraction.
/
/
˚
Ni3ꢀ5.643 A) between two cations.
5.641, Ni2Ã
/
/
Table 2
˚
Selected bond distances (A) and angles (8) for chloronickel(dpdpc)2
tetrachloronickelate
4. Conclusions
Bond distances
Complexes of dpdpc with platinum, palladium, nickel
and cobalt have been prepared and characterised. The
results indicate that a cyclic diphosphine like dpdpc can
behave not only as bridge between metal centers, but
also can chelate to one metal atom, affording a tough
and enduring contribution, with uncommon stereo-
chemistry, to the coordination environment. From our
data it appears that a main feature prompting the
attainment of chelation is the presence of a positive
charge on the complex.
Ni(1)ÃCl(5)
Ni(1)ÃP(1?)
Ni(1)ÃP(1)
Ni(1)ÃP(2)
Ni(1)ÃP(2?)
Ni(1)ÃNi(3)
Ni(2)ÃCl(6)
Ni(2)ÃP(3)
Ni(2)ÃP(3?)
Ni(2)ÃP(4)
Ni(2)ÃP(4?)
Ni(2)ÃNi(3)
2.469(3)
2.207(3)
2.189(6)
2.191(3)
2.183(5)
5.640(2)
2.463(4)
2.185(5)
2.199(4)
2.201(4)
2.195(5)
5.643(2)
Bond angles
Cl(5)ÃNi(1)ÃP(1?)
Cl(5)ÃNi(1)ÃP(1)
Cl(5)ÃNi(1)ÃP(2)
Cl(5)ÃNi(1)ÃP(2?)
P(1?)ÃNi(1)ÃP(1)
P(1?)ÃNi(1)ÃP(2)
P(1?)ÃNi(1)ÃP(2?)
P(1)ÃNi(1)ÃP(2)
P(1)ÃNi(1)ÃP(2?)
P(2)ÃNi(1)ÃP(2?)
Cl(6)ÃNi(2)ÃP(3)
Cl(6)ÃNi(2)ÃP(3?)
Cl(6)ÃNi(2)ÃP(4)
Cl(6)ÃNi(2)ÃP(4?)
P(3)ÃNi(2)ÃP(3?)
P(3)ÃNi(2)ÃP(4)
P(3)ÃNi(2)ÃP(4?)
P(3?)ÃNi(2)ÃP(4)
P(3?)ÃNi(2)ÃP(4?)
P(4)ÃNi(2)ÃP(4?)
101.6(1)
97.7(2)
5. Supplementary material
101.1(1)
94.6(2)
Supplementary data have been deposited with the
Cambridge Crystallographic Centre, CCDC No.
192717. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: ꢁ44-1223-336-
033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
103.3(2)
157.2(1)
75.0(2)
75.4(2)
/
167.6(1)
101.3(2)
94.8(2)
101.3(1)
101.4(1)
97.6(1)
101.4(1)
75.0(1)
Acknowledgements
167.6(2)
157.2(1)
75.1(2)
We thank Professor Federico Giordano, Universita` di
Napoli ‘Federico II’, for helpful discussion, the MURST
(Cofinanziamento 2000ꢂ/2001) for financial support and
103.5(2)
the Centro Interdipartimentale di Metodologie Chimi-

216
M.E. Cucciolito et al. / Inorganica Chimica Acta 343 (2003) 209ꢂ216
/
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met. Chem. 598 (2000) 103.
co-Fisiche, Universita` di Napoli ‘Federico II’ for NMR
and X-ray facilities.
[15] CAD-4 Software, Version 5.0, Enrafꢂ/Nonius, Delft, The Nether-
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