2-(Diphenylphosphino)-pyridine as an ambidentate ligand in homo- and hetero-binuclear complexes of copper, silver, and gold

Article abstract of DOI:10.1515/znb-1997-0210

The reaction of 2-diphenylphosphino-pyridine (1) with AgBF₄ in an equimolar ratio affords the cyclic, dinuclear complex 2 with mixed P,N-coordination of the metal atoms. With two equivalents of 1 the 2:1 complexes 4a,b are formed which have the metal atoms solely P-coordinated. The previously reported gold complex (3), an analogue of 2, or [Au(tht)₂]ClO₄ (tht = tetrahydrothiophen) also give the 2:1 complexes (5a,b) when treated with an excess of ligand 1. Addition of AgClO₄ to a solution of 5a in acetone, or treatment of 4a with [Au(tht)₂]ClO₄ in dichloromethane, give the same mixed-metal complex 6, where the Au atoms are exclusively P-coordinated, while the Ag atoms are coordinated by the two pyridine nitrogen atoms. In the crystal there are also weak interactions of the perchlorate counterions with the silver atom. Addition of [Cu(MeCN)₄]BF₄ to compound 5b gives the Cu/Au-complex with P,P-coordinated gold and N,N-bonded copper centers. All products were characterized by standard analytical and spectroscopic techniques; the crystal structure of complex 6 was determined in a single crystal X-ray diffraction study.

Full text of DOI:10.1515/znb-1997-0210

2-(Diphenylphosphino)-pyridine as an Ambidentate Ligand in Homo- and
Hetero-binuclear Complexes of Copper, Silver, and Gold
M. Elena Olmos, Annette Schier, Hubert Schmidbaur*
Anorganisch-chemisches Institut der Technischen Universität München,
Lichtenbergstrasse 4, D-85748 Garching, Germany
Z. Naturforsch. 52 b,203-208 (1997); received December 12, 1996
Copper(I), Silver(I), Gold(I) Coordination, 2-(Diphenylphosphino)-pyridine, 1-Pyridyl-diphe-
nylphosphine, Ambidentate Ligand
The reaction of 2-diphenylphosphino-pyridine (1) with AgBF4 in an equimolar ratio affords
the cyclic, dinuclear complex 2 with mixed P,N-coordination of the metal atoms. With two
equivalents of 1 the 2:1 complexes 4a,b are formed which have the metal atoms solely P-
coordinated. The previously reported gold complex (3),an analogue of 2,or [Au(tht)2]C104 (tht
= tetrahydrothiophen) also give the 2:1 complexes (5a,b)when treated with an excess of ligand
1. Addition of AgClCU to a solution of 5a in acetone, or treatment of 4a with [Au(tht)2]C104 in
dichloromethane, give the same mixed-metal complex 6, where the Au atoms are exclusively
P-coordinated, while the Ag atoms are coordinated by the two pyridine nitrogen atoms. In the
crystal there are also weak interactions of the perchlorate counterions with the silver atom.
Addition of [Cu(MeCN)4]BF4 to compound 5b gives the Cu/Au-complex with P,P-coordinated
gold and N,N-bonded copper centers. All products were characterized by standard analytical
and spectroscopic techniques; the crystal structure of complex 6 was determined in a single
crystal X-ray diffraction study.
complexes of Cu(I) and Ag(I) salts with the same
ligand were also successful [6 -9 ], but no mixed-
metal systems have been considered to-date. In the
work presented in this report we have therefore be-
come engaged in the synthesis and stereochemistry
of Cu/Au and Ag/Au compounds containing lig-
and 1 , which were expected to show interesting iso-
merism depending either on the donor preferences
of these metals for N or P donor sites, or on ef-
fects of metal-metal bonding. It should be noted
that the metal-metal bonding referred to here is of
the non-classical type between seemingly closed-
shell atoms, which is now recognized to contribute
significantly to the overall stability of compounds
of this type [10].
Introduction
2-Diphenylphosphino-pyridine( 1-pyridyl-diphe-
nylphosphine, 1 ) is an ambidentate ligand system
widely employed in the coordination chemistry of
Transition Metals. The 1,3-stereochemistry of the
two donor centers (N,P) in compound 1 is not suit-
able for metal chelation, which would lead to highly
strained four-membered rings, but is rather in favour
of metal bridging in homo- or heteropolynuclear
systems (M,M; M,M') with our without metal-metal
bonding (M-M; M-M') [1-4].
The coinage (group 11) metals in their low oxy-
dation state +1 have a strong affinity for phosphine
and pyridine donor centers and can be expected to
form a wide variety of strong complexes with ligand
1 , in which the metal atoms are held in close prox-
imity thus allowing direct metal-metal interactions.
This concept was used in the synthesis of a dinu-
clear dicationic 1:1 complex of ligand 1 with Au+
BF4- , where one of the shortest Au-Au contacts
between the two d 10 metal centers has been observed
[5]. Preparative and structural studies of analogous
Results and Discussion
The reaction of silver tetrafluoroborate with lig-
and 1 (pyPh2P) in a molar ratio 1:1 in acetone
in the dark gives high yields of a binuclear com-
plex {[(pyPh2P)2Ag2]2+ (BF4~)2}, 2 , as a colour-
less microcrystalline solid (Scheme 1). The product
has been identified by microanalysis, mass spec-
trometry and NMR spectroscopy (Exp. Part). The
31P NMR spectrum is proof for a structure with
* Reprint requests to Prof. Dr. H. Schmidbaur.
K
0939-5075/97/0200-0203 $ 06.00
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204
M. E. Olmos et al. ■2-(Diphenylphosphino)-pyridine
2+
Phz
Ph2
P— Au— P
[BF4']2
AgCKX,
PPh—2 Au—PPhj
2+
PPhjpy, 1
[BF4’]2
1/2
r
NN -A u — P
Phj
C /n \ j
X = C104 (5aX BF4 (5b)
Scheme 1
equivalent phosphorus atoms, and therefore a so-
Treatment of the dinuclear 1:1 complex of gold(I)
called "head-to-tail" structure 2 is proposed for this (3) with two equivalents of ligand 1 gives the 1:2
compound in solution. This result is in agreement complex 5b, and the perchlorate 5a is accessible
with the data available for the gold(I) analogue (3, from [Au(tht)2]+ C I O 4 - , (tht = tetrahydrothiophen)
Scheme 1), the structure of which was confirmed and the ligand (Scheme 1). The analytical and spec-
by an X-ray structure analysis [5]. The structure is troscopic data are indicative of a structure closely
related to that of the silver salts (above), although in
the absence of diagnostic P,Au spin-spin coupling
there is no direct evidence for this structure.
somewhat fluxional in CDCI3 solution at ambient
temperature as suggested by significant line broad-
ening, but at -60°C (6 20.4 ppm) the sharp lines of
a well-resolved AA'XX'/YY'/XY spin system are
observed (A: 31P; X: 109Ag; Y: 107Ag).
Compounds 4a and 5a were used as the pre-
cursors for the synthesis of a mixed-metal cluster
(Ag/Au: 6): Treatment of the gold complex 5a with
AgC104 in acetone, or of the silver complex 4a
with [Au(tht)2]+ CIO4- in dichloromethane, lead to
identical colourless crystalline products, as readily
demonstrated through standard analytical and spec-
troscopic fingerprint techniques (Exp. Part). These
results suggest a non-centrosymmetrical "head-to-
head" structure in solution (CDCI3), with the gold
atom coordinated only to the P-donor sites, and the
silver atoms exclusively engaged in bonding to the
N-donor ends.
The reaction of the same components in the ra-
tio 1 :2 , or treatment of complex 2 with two mole
equivalents of ligand 1 , afford the 1:2 complex salt
4b, which is also available as the perchlorate 4a
(Scheme 1). The two products, colourless air-stable
salts, are also readily identified through their ana-
lytical and spectroscopic data. The 31P NMR spec-
tra are identical and obviously independent of the
nature of the anion. The 31P signals (6 10.8 ppm)
show P,Ag coupling at -60 °C, but there is again
line broadening at +20°C. The large coupling con-
stants 7(Ag,P) leave no doubt that the metal atoms
are exclusively P-bonded (4, Scheme 1).
The solid state structure of compound 6 has been
determined by a single crystal X-ray diffraction
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205
M. E. Olmos et al. ■2-(Diphenylphosphino)-pyridine
Table I. Crystal data, data collection, and structure refine-
ment for compound 6 x CH2CI2.
Crystal data
Formula
Mr
C35H3oAgAuCl4N208P2
1115.19
Crystal system
Space group
a (A)
b(A)
c (A)
monoclinic
P2,/n [No. 14]
10.537(1)
23.989(1)
15.530(1)
95.69(1)
ß o ,
3906.2(5)
1.896
V(A)
Pcalc (g e m ‘ )
4
Z
F(000)(e)
H (Mo Kq) (cm-1)
2168
46.61
Data collection
Diffractometer
Radiation
Enraf Nonius CAD4
Mo Kq, 0.71073 Ä
-68
T(°C)
Scan mode
hkl Range
u>-0
-13—+ 1 3 /0 ^ + 3 0 /
0^+ 19
3-27
8769
8459
8440
2 a l
psi-scans
0.575/0.999
Fig. 1. Molecular structure of compound 6 with atom
numbering (ORTEP plot with 50% probability ellip-
soids, H atoms omitted for clarity). Selected bond lengths
(Ä) and angles (°); Au-Pl 2.296(2), Au-P2 2.297(2),
Au...Ag 2.820(1), Ag-Nl 2.289(8), Ag-N2 2.310(9), Ag-
0 12.52(2), Ag-05 2.47(2); P1-Au-P2 171.77(7), N 1-Ag-
N2 142.3(3).
0-Range for data collection (°)
Measured refl.
Unique refl.
Observed refl.
I >
Absorption correction
T min/T
max
Refinement
Refined parameters
H atoms (found/calcd.)
444
Ph2PjQ
-O
N
P it P
N
N '
Ph2P
0/28, solvent H atoms
neglected
0.0563
'PPb2
I
I
I
I
NT
M
M
NT
M
y
/?l[al
Ph2P^ -N
ph2P\
ph2P, .N
wR2[h]
GOOF
0.1469
1.091
<0.001
X )
X )
Scheme 2
X J
(shift/error)max o_
Pfin(max/min) (eA-3)
+4.15/-1.46[cl
[a| R1= £ llF 0WFcll/£lF0l;
silver-perchlorate interactions, the N-Ag-N moiety
deviates strongly from linearity [142.3(3) A], while
the linear P-Au-P arrangement within the eight-
membered metalla-heterocycle remains almost un-
affected [171.77(7)°]. This structure is of consid-
erabe interest because 1) it demonstrates the strong
preference of Au(I) for P-coordination, clearly over-
ruling any similar preference of the Ag(I) competi-
tor; thus, out of three possible isomers (Scheme 2)
only one is experimentally observed; 2 ) it shows the
residual acceptor properties of two-coordinate sil-
ver(I), which leads to weak, but obvious perchlorate
contacts, overruling such tendencies, if any, of two-
coordinate gold(I); 3) the short transannular Au-Ag
[bl wR2 = {[y;vr(Fo2-Fc2)2]/E[w(F^)2]}
w = l/2o-(F0) + (ap) + bp; p = (F0 +
a = 0.0720; b = 35.31.
,/2;
Fc)/3;
[c| for the residual electron density see Experimental Part.
study (Table I, Fig. 1). 6 crystallizes together with
one molecule of solvent CH2CI2 in the monoclinic
space group P2]/n without any crystallographically
imposed molecular symmetry. The lattice is com-
posed of dinuclear mixed metal dications associated
with two perchlorate anions. The gold atom is P,P-
coordinated, whereas the silver atom is bound to
the nitrogen atoms of the pyridine rings and car-
ries the two perchlorate counterions. Due to the
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206
M. E. Olmos et al. • 2-(Diphenylphosphino)-pyridine
contact is suggesting attractive forces between the
two metals, reminiscent of such interactions in the
homonuclear complex [5].
C34H28AgClN204P2 (733.88):
Calcd. C 55.65, H 3.85, N 3.82%,
Found C 54.81, H 3.96, N 3.57%.
[Ag(PPhipy)2 ]BF^ (4b): Method 1: A solution of 2
(0.1 mmol, 0.091 g) in 20 ml of acetone was treated with
ligand 1 (0.2 mmol, 0.053 g) and the solution was stirred
for lh in the dark. The solvent was then removed in a
vacuum. Addition of diethylether gave complex 4b as a
white solid, yield 0.128 g (89%).
Method 2: To a solution of silver tetrafluoroborate (0.2
mmol, 0.039 g) in 20 ml of acetone was added ligand
1 (0.4 mmol, 0.106 g). After lh of stirring in the dark
the solvent was evaporated and 15 ml of diethylether was
added to precipitate complex 4b as a white solid, yield
0.133 g (92%). - 1H NMR: 6 =6.97 (m, py, 2H), 7.05-7.41
(m, Ph, 20H + py, 2H), 7.66 (m, py, 2H), 9.10 (m, py, 2H).
- 3IP{'H} NMR (22°C): 6 = 12.0 (m); -60°C: 6 = 10.8
(dd, ‘y(l09AgP) = 374.9, 'A 107AgP) = 324.8 Hz). -
The reaction of complex 5b with [Cu(MeCN)4]+
BF4- also gives a mixed metal complex (Cu/Au:
7), but the pale-yellow product could not be crys-
tallized. All analytical and spectroscopic data are
consistent with a structure related to that of com-
pound 6 in solution, but details of the solid state
structure regarding e.g. cation/anion packing can-
not be predicted.
Experimental
General: All experiments were carried out at room
temperature without special precautions against mois-
ture, except for complex 7. The complexes of silver
must be protected against daylight. Warning: Perchlorate
salts may be explosive. 2-(Diphenylphosphino)pyridine
was purchased from Aldrich. [Au2(PPh2py)2][BF4b[5],
[Au(tht)2]C104[l 1] and [Cu(NCMe)4]BF4[12] were pre-
pared following the literature procedures. MS: Varian
MAT 311A spectrometer; NMR: JEOL GX 400 spec-
trometer, CDCb or (CD ^CO (7) as solvents with TMS
as internal standard for ’H, and H3PO4 (85%) as external
standard for31P{1H}.
C34H28AgBF4N2P2 (721.23):
Calcd. C 56.62, H3.91, N 3.88%,
Found C 55.79, H 4.08, N 3.69%.
[Au(PPh2pyh]Cl0 4 (5a): To a solution of ligand 1 (0.4
mmol, 0.106 g) in dichloromethane (20 ml) was added
[Au(tht)2]C104 (0.2 mmol, 0.095 g). After lh of stirring
at room temperature the solution was concentrated in a
vacuum. Addition of diethylether lead to the precipitation
of 4 as a white solid. Yield 0.145 g (88%). - 'H NMR:
6 = 7.52-7.65 (m, Ph, 20H + py, 4 H), 7.96 (m, py, 2H),
8.85 (d, py, 2H). - 31P{'H} NMR: 6 = 44.4 (s). - MS
(FAB): m/z (%) = 723.3 (100) [M-C104]+, 460.4 (50.86)
[AuPPh2py+]. -
[Ag2(PPh2py)2][BF4]2 (2): To a solution of silver
tetrafluoroborate (0.4 mmol, 0.078 g) in acetone (20 ml)
was added ligand 1 (0.4 mmol, 0.106 g). After lh of stir-
ring in the dark the solution was concentrated in a vacuum.
Addition of diethylether gave complex 2 as a white solid,
yield 0.163 g (89%). - 'H NMR: 6 = 7.19-7.57 (m, Ph,
20H + py, 2H), 7.68 (m, py, 2H), 7.91 (m, py, 2H), 9.22
(m, py, 2H). - 3iP{'H} NMR (22°C): 6 = 21.5 (broad);
-60°C: 6 =20.4 (AA'XX'/YYYXY, N(109Ag) = 699.8 Hz,
N(l07Ag) = 608.2 Hz. - MS (FD): m/z (%) = 829.2 (100)
[M-BF4]+. -
C34H28AUCIN2O4P2 (822.98):
Calcd. C 49.62, H 3.43, N 3.40%,
Found C 49.12, H 3.45, N 3.24%.
[Au(PPh 2py)2]BF\ (5b): To a solution of ligand 1
(0.2 mmol, 0.053 g) in 20 ml of dichloromethane was
added [Au2(PPh2py)2][BF4]2 (0.1 mmol, 0.109 g), and
the solution was stirred for lh. The solvent was then
removed in a vacuum and 15 ml of diethylether was added
to precipitate complex 5b as a white solid, yield 0.144 g
(89%). - 'H NMR: 6 = 7.52-7.65 (m, Ph, 20H + py, 4 H),
7.98 (m, py, 2H), 8.85 (d, py, 2H). - 3IP{’H} NMR: 6 =
44.3 (s). -
C34H28Ag2B2F8N2P2 (915.90):
Calcd. C 44.59, H 3.08, N 3.06%,
Found C 44.83, H 3.48, N 2.85%.
[Ag(PPh2py)2 ]ClO4 (4a): To a solution of silver per-
chlorate (0.2 mmol, 0.041 g) in 20 ml of acetone was
added ligand 1 (0.4 mmol, 0.106 g). After lh of stirring
in the dark the solution was concentrated in a vacuum.
Addition of 15 ml of diethylether lead to the precipitation
of 4a as a white solid, yield 0.123 g (84%). - 'H NMR: Ö
= 6.86 (m, py, 2H), 7.01-7.33 (m, Ph, 20H), 7.48 (m. py,
2H), 7.66 (m, py, 2H), 9.30 (m, py, 2H). - 31P{1H} NMR
(22°C): 6 = 11.4 (broad); -60°C: <5= 10.8 (dd, './(109AgP)
= 374.9, lJ(wlAgP) =324.8 Hz). - MS (FAB): m/z (%) =
633.2 (66.32) [M-C104]+, 370.2 (100) [AgPPh2py+]. -
C34H28AuBF4NoP2(810.33):
Calcd. C 50.40, H 3.48, N 3.46%,
Found C 49.72, H 3.48, N 3.30%.
[(Oj,ClO)2Ag(p-PPh2pyhAu] (6): Method 1: To a so-
lution of silver perchlorate (0.2 mmol, 0.041 g) in acetone
was added 5a (0.2 mmol, 0.165 g), and the mixture was
stirred in the dark for 1h. The solvent was evaporated and
diethylether was added to give 6 as a white solid, yield
0.175 g (85%).
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207
M. E. Olmos et al. ■2-(Diphenylphosphino)-pyridine
Method 2: To a solution of 4a (0.2 mmol, 0.147 g) in effects (psi-scans). The structure was solved by Patterson
20 ml of dichloromethane was added [Au(tht)2]C104 (0.2 methods and completed by full-matrix least-squares tech-
mmol, 0.095 g). The solution was stirred for 1h in the dark
niques against F2. The oxygen atoms of the perchlorates
and the solution was then concentrated in a vacuum. The as well as the chlorine atoms of the solvent molecule were
addition of diethylether (15 ml) gave complex 6 as a white
solid. The product was crystallized from CHiCb/pentane
at room temperature, yield 0.165 g (80%). - 1H NMR: 6 =
7.29-7.60 (m, Ph, 20H + py, 4 H), 7.98 (m, py, 2H), 9.33
(m, py, 2H). - 31P{1H} NMR (22°C): 8 =47.8 (s); -60°C:
6 =47.4 (d, 2JagP = 4.4 Hz). - MS (FD): m/z (%) = 931.1
(100) [M-C104]+, 947.1 (48.73) [M-C103]+. -
strongly disordered. The latter were refined isotropically
in split positions, whereas the oxygen atoms were in-
cluded with fixed isotropic contributions (U iSO(fix) = 0 .1 5).
All remaining non-H atoms were refined with anisotropic
displacement parameters. All H-atoms except for those of
the disordered solvent molecule were placed in idealized
calculated positions and allowed to ride on their carbon
atoms with U jSO(fix) = 1.5 x Ueq(C). The solvent H atoms
were neglected. The residual electron density of about 4
eA-3 was located between the carbon atoms C226 and
C l32, with distances and angles comparable to those of
the N 1-Ag-N2 moiety. This observation together with the
relatively large U values of the Ag atom (compared to Au)
indicate another slight disorder in the molecule. Attempts
to resolve this were not made.
Details on crystal data, data collection and structure
refinement are summarized in Table 1, selected bond
lengths and angles are given in the figure caption. Fur-
ther information on the X-ray structure determination can
be obtained from Fachinformationszentrum Karlsruhe,
Gesellschaft für wissenschaftlich-technische Information
mbH, D-7514 Eggenstein-Leopoldshafen 2, on quoting
the depository number CSD-406500, the names of the
authors, and the journal citation.
Ci4H?8AgAuChNiO^Po CH2CI2 (115.19):
Calcd. C 37.70, H2.71, N2.51%,
Found C 37.75, H 2.82, N2.51%.
[ A u C u ( n - P P h ip y h ] (7): To a solution of
[Cu(NCMe)4]BF4 (0.2 mmol, 0.063 g) in dichloro-
methane (15 ml) 5b was added (0.2 mmol, 0.162 g) and
the reaction mixture was stirred for lh under nitrogen.
The solvent was evaporated in a vacuum and diethylether
was added to precipitate complex 7 as a pale-yellow solid,
yield 0.152 g (79%). - 'H NMR: 6 = 8.55-8.74 (m, Ph,
20H + py, 2 H), 8.83 (m, py, 2H), 9.20 (m, py, 2H), 10.40
(m, py, 2H). - 3IP{'H} NMR (22°C): 6 = 48.6 (broad);
-60°C: 6 = 47.4 (s). - MS (FD): m/z (%) = 873.0 (100)
[M-BF4]+. -
C34H28AuBCuF2N2P2 (960.68):
Calcd. C 42.51, H 2.94, N 2.92%,
Found C 41.14, H 3.30, N3.01%.
Acknowledgements
Crystallographic structure determination
This work was supported by Deutsche Forschungsge-
meinschaft, by Fonds der Chemischen Industrie and by
D.A.A.D. (through a fellowship to M. E. O.). The authors
are grateful to Mr. J. Riede for establishing the X-ray data
set, to Prof. Dr. F. R. Kreissl for the mass spectrometric
measurements and to Degussa AG and Heraeus GmbH
for the donation of chemicals.
A specimen of suitable quality was mounted in a glass
capillary and used for measurements of precise cell con-
stants and intensity data collection. During data collection
three standard reflections were measured periodically as
a general check of crystal and instrument stability. No
significant changes were observed. Lp correction was ap-
plied and intensity data were corrected for absorption
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