Facile synthesis and ambident coordination of cyclohexylbis-(2-pyridyl)phosphane: Novel dinuclear complexes of Cu+1, Ag+1, and Co+2 ions

Article abstract of DOI:10.1002/1099-0682(200109)2001:10<2661::AID-EJIC2661>3.0.CO;2-8

The title compound cyclohexylbis(2-pyridyl)phosphane (1) was synthesized by a Pd⁰-catalyzed cross-coupling reaction from 2-bromopyridine and cyclohexylphosphane in 98% yield. Compound 1 formed colorless crystals that were moderately air-stable.

Full text of DOI:10.1002/1099-0682(200109)2001:10<2661::AID-EJIC2661>3.0.CO;2-8

FULL PAPER
Facile Synthesis and Ambident Coordination of Cyclohexylbis-
(2-pyridyl)phosphane: Novel Dinuclear Complexes of Cu؉1, Ag؉1, and Co؉2 Ions
Matthias Driess,*[a] Felix Franke,[a] and Klaus Merz[a]
Keywords: Phosphanes / Cross-coupling / Copper / Silver / N ligands
The title compound cyclohexylbis(2-pyridyl)phosphane (1)
was synthesized by a Pd0-catalyzed cross-coupling reaction
from 2-bromopyridine and cyclohexylphosphane in 98%
yield. Compound 1 formed colorless crystals that were mod-
erately air-stable. It reacted, in CH3CN, with CuOTf (OTf =
OSO2CF3), AgBF4, and Co(BF4)2 to form the complexes
[Cu2{CyP(2-Py)2}2(NCCH3)2](OTf)2 (2), [Ag2{CyP(2-Py)2}2-
(NCCH3)2](BF4)2 (3), and [Co2{CyP(2-Py)2}2(NCCH3)2](BF4)4
amples of dimeric dinuclear pyridylphosphane complexes
showing the P,N,NЈ coordination. Reactions of 1 with other
salts containing Cu+1 and Co+2 centers and coordinating an-
ions resulted in different coordination modes. Thus, CuI re-
acted with 1 to form the complex [Cu2{CyP(2-Py)2}2I2] (5)
with both coordinated P and N donor centers and a terminal
iodide. In contrast, the reaction of 1 with CoCl2 afforded the
mononuclear complex [Co{CyP(2-Py)2}Cl2}] (6) in which only
(4), respectively. In these complexes, the pyridylphosphane the pyridyl N atoms and the chlorine ligands were coordin-
ligands coordinate to two metal centers in a head-to-tail fash- ated to the metal center. X-ray analyses of the compounds 1,
ion involving both the P and the N atoms simultaneously. The 2, 3, 5, and 6 are reported.
compounds represent the first structurally characterized ex-
Introduction
In contrast to the extensive use of diphenyl-2-pyridylpho-
sphane[4] and its derivatives,[5] and the numerous complexes
described with tris(2-pyridyl)phosphane,[6] the knowledge
of bis-2-pyridylphosphanes is scarce.[7,8] Only recently,
Agϩ1 and Auϩ1 complexes of 1,2-bis(dipyridylphosphanyl)-
ethane have been shown to provide a promising approach
in cancer research for their potent and selective antitumor
activity.[9]
Since 2-pyridylphosphanes can act as monodentate (P-
coordinated), bidentate (P,N- or N,NЈ-chelating or P,N-
bridging), or tridentate (P,N,NЈ-chelating or N,NЈ,NЈЈЈ-che-
lating) ligands with both hard (N) and soft (P) donor cen-
ters, they have been a topic of interest in the last 30 ye-
ars.[1,2] Scheme 1 shows the various possible coordination
modes for pyridylphosphanes AϪH. All displayed modes
have been described, except the coordination mode H.
Usually, the synthesis of 2-pyridylphosphanes is achieved
by the reaction of the 2-lithium pyridine with the appropri-
ate chlorophosphane at very low temperatures (less than
Ϫ90 °C). In searching for a convenient and more selective
way of synthesizing pyridylphosphanes with varying alkyl
substituents we have found that the reaction of cyclohexyl-
phosphane with 2-bromopyridine in acetonitrile in a Pd0-
catalysed cross-coupling reaction[10] furnished cyclohexyl(2-
pyridyl)phosphane (1) in 98% yield. This reaction type,
which resembles the Stille coupling reaction,[11] has been
extended to phosphanes without silyl or stannyl groups by
Stelzer et al., and tolerates a number of functional groups
that limit the versatility of the lithium pyridyl method.[12]
Reactions of cyclohexylbis(2-pyridyl)phosphane (1) in ace-
tonitrile with different Cuϩ1, Agϩ1, and Coϩ2 salts con-
taining weakly coordinating anions (CF3OSO2Ϫ, BF4Ϫ) fur-
nished the dinuclear complexes 2, 3, and 4, respectively. In
these complexes, the pyridylphosphane ligands coordinate
in a head-to-tail bridging mode involving both the P and
the N donor centers. To the best of our knowledge, these
are the first structurally characterized complexes of (2-pyri-
dyl)phosphanes that represent the coordination mode H
(Scheme 1). CuI with the stronger coordinating iodide an-
ion reacted with 1 to form the isostructural complex 5,
while CoCl2 lead to the mononuclear complex 6, which rep-
resents the coordination mode E, involving only the pyridyl
Scheme 1. Some possible coordination modes AϪH for pyridylpho-
sphanes toward metal centers
Apart from the interesting structural features, pyridyl-
phosphane metal complexes have been shown to act as
good catalysts for reactions like the carbonylation of al-
kynes to form methacrylate,[3] showing surprisingly high
turnover rates combined with an excellent product selectiv-
ity.
[a]
Lehrstuhl für Anorganische Chemie I, Molekül- und
Koordinationschemie, Ruhr-Universität Bochum,
44780 Bochum, Germany
E-mail: matthias.driess@ac1.ruhr-uni-bochum.de
Eur. J. Inorg. Chem. 2001, 2661Ϫ2668
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/1010Ϫ2661 $ 17.50ϩ.50/0
2661

M. Driess, F. Franke, K. Merz
FULL PAPER
N atoms and the two chlorine atoms as donor centers to- to the values observed for tris(2-pyridyl)phosphane (δ ϭ
ward the Co atom.
Ϫ1.3), phenylbis(2-pyridyl)phosphane (δ ϭ Ϫ2.9), and di-
phenyl(2-pyridyl)phosphane (δ ϭ Ϫ1.9).[13]
Results and Discussion
Crystal Structure of 1
Crystals of 1 suitable for an X-ray diffraction analysis
were obtained from solutions in hexane. A view of its mo-
lecular structure is shown in Figure 1 and the crystallo-
graphic details are given in the Experim. Section.
Synthesis of Cyclohexylbis(2-pyridyl)phosphane (1)
If cyclohexylphosphane is allowed to react with two
molar equivalents 2-bromopyridine and triethylamine in the
presence of catalytic amounts of tetrakis(triphenylphos-
phane)palladium(0) in acetonitrile for 24 hours, the desired
cyclohexylbis(2-pyridyl)phosphane (1) is formed in 98%
yield. The reaction can easily be monitored by 31P-NMR
spectroscopy, and proceeds stepwise via cyclohexyl-2-pyrid-
ylphosphane as the initial product. The latter can be identi-
1
fied by its diagnostic 31P NMR signal (δ ϭ Ϫ26.8, JPH
ϭ
212.6 Hz).
Figure 1. Molecular structure of cyclohexylbis(2-pyridyl)phos-
˚
phane 1. Selected distances [A] and angles [°]: P1ϪC11 1.847(4),
P1ϪC6 1.851(4), P1ϪC1 1.854(5), C11ϪPϪC6 101.6(1),
C11ϪPϪC1 101.4(1), C6ϪPϪC1 97.6(1)
˚
The PϪC distance of 1.847(4) A in 1 is similar to those
˚
˚
in tris(2-pyridyl)phosphane (1.83 A and 1.82 A). As ex-
pected, the P atom has a pyramidal coordination, with the
sum of bond angles at phosphorus of 300.6°. The latter
value is only slightly smaller than that in tris(2-pyridyl)pho-
sphane (305.6°).
While the C11ϪPϪC6 and the C11ϪPϪC1 angles
[101.6(1) and 101.4(1)°] are practically identical to the cor-
responding angles in tris(2-pyridyl)phosphane, the
C6ϪP1ϪC1 angle of 97.6(1)° is notably smaller. The N cen-
ters are directed away from the lone pair at the P atom. A
similar orientation is also found for two pyridyl groups in
tris(2-pyridyl)phosphane, while the third pyridyl substituent
in the latter compound is rotated away from the other
two.[14]
This type of Pd-catalyzed cross-coupling reaction has
been described previously by Stelzer et al.,[10] and resembles
the Stille coupling reaction.[11] The synthesis of 1 is the first
example in which a primary aliphatic phosphane and 2-bro-
mopyridine have been successfully coupled. The mechanism
of the reaction involves the oxidative addition of 2-bromop-
yridine to the palladium catalyst, followed by the substitu-
tion of one triphenylphosphane ligand by cyclohexylphos-
phane or cyclohexyl-2-pyridylphosphane, respectively. Fi-
nally, the product is formed through a PϪC bond formation
in a reductive-elimination step (Scheme 2).[12]
Coordination Reactions of 1 with Cu؉1, Ag؉1, and Co؉2
Salts
Treatment of acetonitrile solutions of Cu(O3SCF3),
AgBF4, and Co(BF4)2 with 1 at room temperature affords
the dinuclear complexes 2, 3, and 4, respectively. All three
complexes form colorless (2, 3) or pink (4) crystals from
acetonitrile solution and are practically insoluble in other
common solvents.
A ligand exchange of acetonitrile by other solvent molec-
ules, as has been found in similar complexes,[15,16] could
therefore not be achieved. The 31P-NMR spectra show sing-
let signals at δ ϭ 0.2 for 2 and at δ ϭ 23.6 for 3, thus
confirming the coordination of the phosphorus atom by a
downfield shift with respect to the value for the ‘‘free’’ li-
gand 1. These values compare well with those in similar
Scheme 2. Proposed mechanism for the Pd0-catalyzed synthesis of
1 based on previous results, starting from CyPH2, 2-bromopyridine,
and a Base. RЈ ϭ H, L ϭ PPh3, solv ϭ solvent
Compound 1 forms colorless, fairly air-stable crystals Cu and Ag complexes with bridging pyridylphosphanes, as
that are soluble in most organic solvents. The 31P NMR observed in [Cu2(µ-Ph2P-Py)3CH3CN]2ϩ (δ ϭ 5.45)[15] and
spectrum of 1 in C6D6 shows a singlet at δ ϭ Ϫ3.2, similar [Ag2(Ph2PϪPy)2]2ϩ (δ ϭ 25.7), respectively.[17]
2662
Eur. J. Inorg. Chem. 2001, 2661Ϫ2668

Facile Synthesis and Ambident Coordination of Cyclohexyl-bis(2-pyridyl)phosphane
FULL PAPER
In order to investigate the influence of the anion on the
coordination mode, and also to overcome the poor solubil-
ity properties of the ion pairs 2, 3, and 4, CuI was allowed
to react with 1 in THF at 50 °C. Yellow crystals of 5 precip-
itated as the desired product from the reaction mixture.
Compound 5 turned out to be well soluble in THF, CH2Cl2,
CHCl3, and acetone. Its 31P-NMR spectrum reveals a sing-
let at δ ϭ 1.5, very similar to that chemical shift observed
for 2. The crystal structure, which is described below, in-
deed shows that 5 is isostructural with the cation in 2, ex-
cept that the terminal acetonitrile ligands were replaced by
iodine ions.
coordination mode H, according to Scheme 1. In addition,
both metal centers bear an acetonitrile ligand to achieve a
distorted tetrahedral coordination sphere. Espinet et al.
have merely described several dipyridylphosphane Mo0
complexes for one of which the P,N,NЈ-coordination mode
F was postulated, but crystallographic evidence could not
be achieved.[18]
In contrast, the reaction of CoCl2 with 1 yielded the com-
plex 6 in good yields, which implies a different coordination
mode of the dipyridylphosphane 1, involving only the pyri-
dyl N donor atoms and the Cl ligands as donor centers. As
expected for a Coϩ2 complex, 6 is paramagnetic and unlike
the other complexes, which are rather sensitive to air and
water, is indefinitely resistant in air and moisture. It is sol-
uble in most organic solvents and reacts with two equiv. of
AgBF4 in acetonitrile giving the separated ion pair 4 and
AgCl.
Figure 2. Molecular structure of the dication in 2. For the sake of
˚
clarity, the H atoms have been omitted. Selected distances [A] and
Crystal Structures of 2, 3, and 4
angles [°]: Cu2···Cu1 3.225(2), CuϪN(Py, average) 2.077(3), CuϪN
(acetonitrile, average) 2.093(3), Cu1ϪP2 2.202(1), Cu2ϪP1
2.186(1); N2ϪCu1ϪN1 94.2(1), N2ϪCu1ϪP2 123.7(1),
N1ϪCu1ϪP2 126.2(1), N3ϪCu2ϪN4 90.7(1), N3ϪCu2ϪP1
125.2(1), N4ϪCu2ϪP1 127.9(1), Cu2ϪN5ϪC33 171.0(4),
Cu1ϪN6ϪC35 171.5(4)
The molecular structures of 2 and 3 are shown in Fig-
ure 2 and 3, while experimental details of the X-ray analyses
are described in the Experim. Section and in Table 2. In all
three complexes, the metal centers are held together in close
proximity by the two bridging ligands that coordinate in a
In 2, the copper centers are surrounded, in a distorted
head-to-tail fashion and resemble the dimeric form of the tetrahedral geometry, by one phosphorus and three nitro-
Eur. J. Inorg. Chem. 2001, 2661Ϫ2668
2663

M. Driess, F. Franke, K. Merz
FULL PAPER
[17]
˚
gen donors. The Cu centers lie about 48 pm outside of the Ph2P-Py)2](ClO4)2 (3.07 A),
P,N,NЈ-plane. The N(Py)ϪCuϪN(Py) bond angles of A),
[Ag2(Ph2P-Py)3]Cl2 (3.08
[22]
˚
and [Ag2(µ-L)2(CH3CN)2](ClO4)2 [L
90.7(1) and 94.2(1)°, respectively, are considerably smaller phenylphosphanyl)-6-(pyrazol-1-yl)pyridine] (2.96 A).
ϭ
2-(di-
[23]
˚
than those of the PϪCuϪN(Py) angles, which vary between
Surprisingly, the Ag···Ag distance in 3 is smaller than the
123.7(1) and 127.9(1)°, respectively. Such a difference has Cu···Cu distance in 2, and the same is true for the homolog-
also been observed in the [Cu2(µ-dppy)3(CH3CN)]2ϩ ion ous complexes [Ag2(µ-L)2(CH3CN)2](ClO4)2 and [Cu2(µ-
[dppy ϭ diphenyl(2-pyridyl)phosphane],[15] in which one Cu L)2(CH3CN)2](ClO4)2 [L ϭ 2-(diphenylphosphanyl)-6-(pyr-
center is also coordinated in a distorted tetrahedral ar- azol-1-yl)pyridine].[23,24] This observation may indicate at-
rangement. However, the differences between the tractive interactions between the Ag centers due to a larger
N(Py)ϪCuϪN(Py)- and the PϪCuϪN(Py) angles, respect- contribution of relativistic effects. However, in the case of
ively, are less significant in the latter complex, due to bridging ligands, it is difficult to distinguish between ligand-
stronger geometric constraints in the ligand backbone in induced effects (strain) and true ‘‘metallophilic’’ d10-d10 dis-
2 than in dppy in [Cu2(µ-dppy)3(CH3CN)]2ϩ. The Cu···Cu persion-type interactions.[25] It is also noteworthy that one
˚
distance of 3.225(2) A is larger than the respective distance of the acetonitrile molecules is coordinated to the Ag center
in [Cu2(µ-dppy)3(CH3CN)]2ϩ (2.72 A), in which one Cu with an AgϪNϪC angle of 125.9(7)°, while the other
˚
center is tetrahedral and the other trigonal-planar coordin- AgϪNϪC moiety adopts an angle of 158.9(5)°. A similar
ated.[19]
It
is,
however,
shorter
than
in small CuϪNϪC bond angle of 129.2° has also been ob-
[Cu2(dppy)2(CH3CN)2]2ϩ (3.58 A) with both Cu atoms be- served in the case of the Cu(ϩ1) complex [Cu(acac)-
ing trigonal coordinated.[19] The value is also considerably (phen)(CH3CN)](ClO4) (acac ϭ acetylacetonate; phen ϭ
shorter than in [Cu2(µ-Ph2PCH2PPh2)2(CH3CN)4]2ϩ (3.75 1,10-phenanthroline),[26] but 3 represents the first Agϩ1 ace-
˚
[20]
˚
A),
in which both Cu centers are surrounded by four tonitrile complexes with an AgϪNϪC angle Ͻ 140°
donor atoms. The close proximity between the Cu atoms in (Table 1).
compared with that in [Cu2(µ-
2
Ph2PCH2PPh2)2(CH3CN)4]2ϩ probably reflects the higher
ring strain induced by the relatively rigid threefold coor-
dination within the ligand backbone rather than suggesting
attractive intermetallic interactions. According to Figure 3,
the dinuclear Ag complex 3 adopts the same core structure
as 2. However, the tetrahedral coordination geometry
around the Ag centers is even more distorted than that in
2 with PϪAgϪN(Py) angles varying between 126.6(1) and
135.2(1)°, while the N(Py)ϪAgϪN(Py) angles are 86.7(2)
and 87.4(2)°, respectively.
Table 1. Comparison of AgϪN bond length and the AgϪNϪC
angle in different Ag(ϩ1)-acetonitrile complexes
AgNC[a]
AgϪN[b]
compound
ref.
[30]
[31]
[32]
[33]
[34]
[23]
174.5
156.2
178.8
165.3
162.0
146.1
2.08
2.11
2.14
2.25
2.27
2.27
[Ag{CF(CF3)2}(NCCH3)]
[Ag3L1(NCCH3)3][c]
[Rh6C(CO)15{Ag(NCCH3)2}2]
[Ag(NCCH3)4]ϩ
[Ag2L2(NCCH3)2](BF4)2
[d]
[Ag{NCCH3)2-
[e]
{µ4-3,6-(Ph2P)2Pyr}]n
[35]
[23]
162.7
152.5
158.9
156.0
2.28
2.28
2.37
2.41
[AgL3(NCCH3)2] (SbF5)[f]
[AgL3(NCCH3)2] (SbF5)[f]
3, this work
[23]
[36]
[Ag{µ2-2-(Ph2P)-6-(Pyz)Py}2-
(NCCH3)]2(ClO4)2
[g]
140.7
2.42
2.47
[{µ2-2,6-(Ph2P)2Py}-
Ag(NCCH3)2]
3, this work
125.9
[a]
[b]
AgϪNϪC angle at the coordinated CH3CN (°). Ϫ
Bond
length (A). Ϫ L1 ϭ µ3-6,13,20-trimethoxycalix(3)pyridine. Ϫ
L2 ϭ µ2-1,11-(1,2)Ph-3,6,9,13,16,19-hexathiacycloicosaphane. Ϫ
[c]
[d]
˚
[e]
Pyr ϭ pyridazine. Ϫ [f] L3 ϭ µ2-3,7-di-tert-butyl-2,8-dioxa-5-aza-1-
[g]
phosphabicyclo(3.3.0)octa-2,4,6-triene. Ϫ Pyz ϭ pyrazole
It has been proposed that the MϪNϪC angle of the ace-
tonitrile
ligand
corresponds
well
with
the
Figure 3. Molecular structure of the dication in 3. For the sake of
˚
MϪN(acetonitrile) distance in such a way that longer
MϪN bonds imply a smaller MϪNϪC angle, thereby re-
presenting a rather early stage of acetonitrile coordina-
tion.[15] This trend is supported by the respective data of
CH3CNϪAgϩ1 complexes that are summarized in Table 1.
However, the [AgL3(NCCH3)2] cation [L3 ϭ µ2-3,7-di-tert-
clarity, the H atoms have been omitted. Selected distances [A] and
angles [°]: Ag1···Ag2 2.932(4), AgϪN(Py, average) 2.397(5),
Ag1ϪN6 2.466(7), Ag2ϪN5 2.373(6), Ag1ϪP2 2.390(1), Ag2ϪP1
2.383(2); N2ϪAg1ϪN1 86.7(2), N1ϪAg1ϪP2 129.5(1),
N2ϪAg1ϪP2 134.6(1), N3ϪAg2ϪN4 87.4(2), N3ϪAg2ϪP1
135.2(1), N4ϪAg2ϪP1 126.6(1), Ag1ϪN6ϪC35 125.9(7),
Ag2ϪN5ϪC33 158.9(5)
˚
The Ag···Ag distance of 2.932(4) A is shorter than that butyl-2,8-dioxa-5-aza-1-phosphabicyclo(3.3.0)octa-2,4,6-
in other complexes with bridging pyridylphosphanes like triene] is an exception, revealing two different AgϪNϪC
[21]
[Ag2(η1-Ph2P-Py)(µ- angles (∆ ϭ 10°), and at the same time, equidistant AgϪN
Eur. J. Inorg. Chem. 2001, 2661Ϫ2668
˚
[Ag2(Ph2P-Py)2](NO3)2 (3.14 A),
2664

Facile Synthesis and Ambident Coordination of Cyclohexyl-bis(2-pyridyl)phosphane
[32]
FULL PAPER
˚
bonds (2.28 A).
Quantitative correlation of the Agϩ1 BuLi, and lithium phenylacetylide, did not lead to any isol-
complexes seems very difficult because a clear distinction able product.
between electronic effects, steric influences, and possible
packing effects cannot be made. Nonetheless, the relatively
small AgϪNϪC angle of 125.6(1) at one Ag center and the
˚
much shorter Ag···Ag distance in 3 [2.932(4) A] are consist-
ent
with
the
presence
of
metallophilic
Ag(donor)ϪAg(acceptor) interactions. This is because its
Cu-homologue 2 is apparently different, possessing a much
˚
longer M···M distance of 3.225(2) A and both acetonitrile
ligands are inconspicuously coordinated to the Cuϩ1 cen-
ters [averaged CuϪNϪC angle 171.2(4)°].
The paramagnetic dicobalt complex 4 shows basically the
same core-structure as 2 and 3. According to a preliminary
X-ray structure analysis of moderate crystals of 4, which
crystallizes in the monoclinic space group P21/c [R1 ϭ
0.1319, wR2 (all data) ϭ 0.3397], the Co···Co distance of
Figure 4. Molecular structure of 5. For the sake of clarity, the H
˚
atoms have been omitted. Selected distances [A] and angles [°]:
˚
2.976(5) A is larger than that in other dinuclear complexes
Cu1···Cu2 3.333(3), Cu1ϪI1 2.7201(8), Cu2ϪI2 2.6978(8),
CuϪN(Py, average) 2.052(4), Cu1ϪP2 2.189(2), Cu2ϪP1 2.218(2);
N2ϪCu1ϪN1 100.8(2), N2ϪCu1ϪP2 114.6(1), N1ϪCu1ϪP2
122.5(1), N3ϪCu2ϪN4 93.9(2), N3ϪCu2ϪP1 116.6(1),
N4ϪCu2ϪP1 127.5(1)
like [CoICo0(µ-Ph2PPy)2(µ-CO)(CO)Cl][27,34] and [Co02(µ-
Ph2PPy)(η2-µ-HCϵCSiMe3)].[28,35] The latter complexes
imply CoϪCo bonds due to short intermetallic distances
and electron deficiency. In the acetylene complex, the ob-
served diamagnetism, shown by a 31P-NMR spectrum, pro-
vides further proof of an antiferromagnetic coupling of the
unpaired electrons at the Co centers. This is, however, not
the case in 4, which is reluctant to undergo direct- or li-
gand-induced coupling of the d7-Co centers even at 15 K.
This was proven by temperature-dependent magnetic sus-
ceptibility measurements and fitting of the observed data
with the calculated values. The effective magnetic moment
of ηeff ϭ 5.5 B.M. at room temperature seems relatively
large in comparison to mononuclear tetrahedral Coϩ2 com-
plexes that show ηeff values in the range between 4.3 and
5.2 B.M. However, larger values can be expected due to the
different nature of the ligands and their ligand fields.[36,37]
In line with that, simulations of the magnetic moment of
high-spin Coϩ2 ions in a tetrahedral ligand field revealed
the ηeff value of 4.82 B.M., which can be increased using
appropriate ligands. The results suggest that spin-spin coup-
ling between the Coϩ2 ions in 4 is negligible.
Crystal Structure of 6
The CoCl2 complex 6 affords dark-blue crystals that
could be recrystallized in most organic solvents. According
to its X-ray diffraction analysis, the ligand 1 adopts a differ-
ent coordination mode in the mononuclear complex than
in the dimeric acetonitrile complex 4, which is also apparent
from their different color. Crystallographic details for 6 are
summarized in Table 2 and Figure 5 shows a model of its
crystal structure. In 6, both N donor atoms of the ligand
coordinate to the Coϩ2 center, affording a distorted tetra-
hedral N2Cl2 coordination geometry around the Co atom,
while the P atom is only a spectator, bridging center. The
ligand and the metal form a six-membered CoN2C2P ring
that prefers the thermodynamically favorable chair con-
formation. As expected, the structure is similar to that of
[Co(N,NЈ-PhPPy2)Cl2].[38] The CoϪN distances are ident-
ical with those in other Co(ϩ2) dipyridyl complexes like
Crystal Structure of 5
Crystals of 5 suitable for an X-ray diffraction analysis
were obtained by recrystallization in CH2Cl2. Its structure
is shown in Figure 4. As expected, the structure of 5 is
identical with that of 2, but in place of the terminal aceto-
nitrile ligands, iodine ions are coordinated to the Cu centers
of 5. This can be explained by the superior coordinating
ability of the iodine ions compared to the triflate anion.
˚
˚
The Cu···Cu distance of 3.333(3) A is ca. 0.1 A longer than
that in 2, and the tetrahedral coordination geometry of the
Cu centers is notably distorted. The two N(Py)ϪCuϪN(Py)
angles of 93.9(2) and 100.8(2)° are considerably different
from the corresponding values in 2 [90.7(1) and 94.2(1)°].
Several attempts to exchange the iodine atoms at copper by
Figure 5. Molecular structure of 6. For the sake of clarity, the H
˚
atoms have been omitted. Selected distances [A] and angles [°]:
CoϪCl1 2.213(1), CoϪCl2 2.222(1), CoϪN1 2.034(3), CoϪN2
2.028(3); Cl1ϪCoϪCl2 113.34(5), N1ϪCoϪN2 99.5(1),
organo substituents, through reaction of 5 with MeLi, N1ϪCoϪCl1 115.18(8), N2ϪCoϪCl1 116.32(8)
Eur. J. Inorg. Chem. 2001, 2661Ϫ2668
2665

M. Driess, F. Franke, K. Merz
FULL PAPER
[Co(4-vinylpyridine)2Cl2][29,39] and [Co(4-methyl pyrid-
ine)2Cl2], respectively.[40] The tetrahedral coordination geo-
metry at the Co(ϩ2) center is somewhat more distorted
than in the latter because of the phosphane linkage between
the pyridyl rings in the meta positions. The NϪCoϪN
angle of 99.5° in 6, especially, shows a considerable devi-
ation from the ideal tetrahedral angle. An even smaller
NϪCoϪN angle of 94.8° is observed in [Co(N,NЈ-
PhPPy2)Cl2].[38]
Synthesis of {Cu2[CyP(2-Py)2]2(NCCH3)2}(OTf)2 (2): A solution of
0.33 g (0.7 mmol) of (CuOTf)2·C6H6 in 10 mL of acetonitrile was
allowed to react with 0.35 g (1.3 mmol) of 1 in 5 mL of acetonitrile
at room temperature. After stirring the mixture overnight, a white
precipitate formed that was recrystallized in acetonitrile to afford
slightly yellowish crystals in 79% yield (1.0 g). Ϫ 31P NMR: δ ϭ
0.2 (s); elemental analysis calcd. (%): calcd. C 43.55, H 4.23, N
8.02; found (%) C 43.05, H 4.18, N 7.90.
Synthesis of {Ag2[CyP(2-Py)2]2(NCCH3)2}(BF4)2 (3): To 0.20 g (1.0
mmol) of AgBF4 in 10 mL of acetonitrile a solution of 0.30 g
(1.0 mmol) of 1 in 5 mL of acetonitrile was added at room temper-
ature. After stirring the mixture overnight, a white precipitate was
formed that was recrystallized in acetonitrile to form colorless crys-
tals in 85% yield (0.86 g). Ϫ 31P NMR: δ ϭ 0.2 (s); elemental ana-
lysis calcd. (%): calcd. C 42.72, H 4.38, N 8.30; found (%) C 43.21,
H 4.35, N 8.35.
Conclusion
We reported here on an economical and at the same time
facile synthesis of (cyclohexyl)bis(2-pyridyl)phosphane (1).
The formation of its new complexes 2Ϫ5 proves the exist-
ence of the missing P,N,NЈ-coordination mode H for dipyri-
dylphosphanes. Apparently, this coordination mode sup-
ports the formation of dinuclear complexes. The metals in
2Ϫ5 are in close proximity, which in general permits inter-
metallic interactions influenced by the terminal ligands at
the metal center. The formation of the mononuclear Co
complex 6 illustrates the directing influence of the hardness
of the anion and its coordination ability on the coordina-
tion properties of the metal toward the chelate ligand 1.
Further investigations to synthesize related water-soluble
dinuclear complexes and to probe their use in metal-assisted
organic synthesis are in progress.
Synthesis of {Co2[CyP(2-Py)2]2(NCCH3)2}(BF4)4 (4): A blue solu-
tion of 0.26 g (1.0 mmol) of CoCl2 in 20 mL of CH3CN was added
to 0.40 g (2.0 mmol) of AgBF4 at room temperature, from which
the color of the solution turned pink and AgCl precipitated. The
latter was filtered off and the clear filtrate allowed to react with
0.30 g (1.0 mmol) of 1 in 10 mL of CH3CN at room temperature.
After stirring the pink solution for 12 h, the reaction mixture was
reduced to 2 mL in vacuo and stored at Ϫ25 °C. The product pre-
cipitated in the form of pink crystals in 58% yield (0.34 g, 0.58
mmol). Elemental analysis of the mono-solvate with CH3CN,
calcd. (%): calcd. C 39.77, H 3.95, N 7.74; found (%): C 39.36, H
4.19, N 7.51.
Synthesis of {Cu2[CyP(2-Py)2]2I2} (5): CuI (0.70 g, 3.7 mmol) was
dissolved in 120 mL of THF at 50 °C and a solution of 0.99 g (3.7
mmol) of 1 in 30 mL of THF was added with vigorous stirring.
The reaction mixture turned yellow and standing of the solution at
room temperature yielded, after 3 d, 1.75 g (1.64 mmol, 89%) of
the product in the form of yellow crystals. Ϫ 31P NMR (CDCl3):
δ ϭ 1.5 (s, w1/2 ϭ 22.8 Hz). Ϫ 1H NMR (CDCl3): δ ϭ 1.2Ϫ2.2
[m, 20 H, CH(CH2)5], 3.1 [m, 2 H, CH(CH2)5], 7.5 (m, 4 H, Py),
7.8 (m, 8 H, Py), 9.1 (m, 4 H, Py); elemental analysis (solvate with
two molecules THF) calcd. (%): calcd. C 45.08, H 5.12, N 5.26;
found (%) C 44.14, H 5.10, N 5.36.
Experimental Section
All reactions and manipulations were carried out under an atmo-
sphere of dry argon using standard Schlenk techniques unless
otherwise stated. Solvents and reagents were dried by standard
methods and distilled prior to use. Ϫ The 31P- and 1H-NMR spec-
tra were measured on a Bruker Avance 250 spectrometer at
250 MHz (1H) and 101.3 MHz (31P), respectively. Chemical shifts
are given in ppm relative to respective standards. External stand-
1
ards for H NMR: SiMe4; 31P NMR: H3PO4 (85% aq. solution).
Synthesis of {Co[CyP(2-Py2]Cl2] (6): CoCl2 (0.13 g, 1.0 mmol) was
dissolved in 20 mL of CH3CN at room temperature. To this deep-
blue mixture a solution of 1 (0.27 g, 1.0 mmol) in 10 mL of CH3CN
was added, and the reaction mixture was stirred for 12 hours. Solv-
ent was removed in vacuo to leave 5 mL of a dark-blue solution
from which 6 crystallized in the form of dark-blue crystals. Yield:
0.37 g (0.93 mmol, 93%). Ϫ MS (EI, 70 eV): m/z (%) ϭ 399 ([M]ϩ,
0.5), 364 ([M Ϫ Cl]ϩ, 3), 327 ([M Ϫ 2Cl]ϩ, 10), 270 ([CyPpy2]ϩ,
80), 193 ([CyPpy2-C6H4N]ϩ, 82), 187 ([CyPpy2-C6H11]ϩ, 100), 109
([CyPpy2 -C6H11-C6H4N], 78); elemental analysis calcd. (%): calcd.
C 48.03, H 4.79, N 7.00; found (%): calcd. C 47.80, H 5.22, N 6.99.
Ϫ Elemental analyses were performed on an Elementar VarioEL
microanalyser.
Synthesis of CyP(2-Py)2 (1): A solution of 1.0 g (8.6 mmol) of
cyclohexylphosphane, 2.7 g (17.2 mmol) of 2-bromopyridine, 1.8 g
(17.8 mmol) of triethylamine, and ca. 0.1 g of tetrakis(triphenyl-
phosphanyl)palladium(0) in 20 mL of acetonitrile were degassed
thoroughly in a Schlenk tube and sealed under vacuum. The reac-
tion mixture was heated under reflux for 36 h, monitoring the pro-
gress of the reaction by 31P-NMR spectroscopy. Then the solvent
was evaporated in vacuo at 25 °C and the residue was taken up
with 30 mL of hexane. The triethylammonium bromide was then
filtered off and washed with two 5 mL portions of hexane. The
filtrates were combined and the solvent removed in vacuo. Distilla-
tion gave the crude product that was recrystallized in hexane at
Ϫ20 °C and dried in vacuo to give 2.25 g (8.4 mmol, 98%) of the
colorless crystalline product. Ϫ 31P NMR: δ ϭ 3.2 (s). Ϫ 1H NMR:
δ ϭ 1.2Ϫ2.2 [m, 10 H, CH(CH2)5], 3.2 [m, 1H, CH(CH2)5], 6.7 (m,
2 H, Py), 7.1 (m, 2 H, Py), 7.5 (m, 2 H, Py), 8.6 (m, 2 H, Py). Ϫ
X-ray Structural Determinations: The intensities were measured
with a Bruker-axs-SMART diffractometer (Mo-Kα radiation, λ ϭ
˚
0.7170 A, ω scan). The structures were solved by direct methods
(SHELXS97), and refined against F2 with all measured reflections
(SHELXL97). All non-hydrogen atoms were refined anisotropically
and the hydrogen atoms were introduced in calculated positions.
Other experimental details are summarized in Table 2.
MS (EI, 70 eV): m/z (%) ϭ 270 (35) [Mϩ], 193 ([M Ϫ C6H4N]ϩ, Crystallographic data (excluding structure factors) for the struc-
80), 187 ([M Ϫ C6H11]ϩ, 100), 109 ([M Ϫ C6H11-C6H4N], 75). Ϫ tures reported in this paper have been deposited with the
HR-MS: calcd. m/z ϭ 270.1283 for C16H19N2P, found 270.1281.
Cambridge Crystallographic Data Center as supplementary
2666
Eur. J. Inorg. Chem. 2001, 2661Ϫ2668

Facile Synthesis and Ambident Coordination of Cyclohexyl-bis(2-pyridyl)phosphane
Table 2. Experimental data of the X-ray analyses
FULL PAPER
1
2
3
5
6
empirical formula
molecular mass
temperature [K]
crystal system
space group
C16H19N2P
270.30
203(2)
monoclinic
Pn
C38H44Cu2F6N6O6P2S2 C36H44Ag2B2F8N6P2 C32H38Cu2I2N4P2 C16H19Cl2CoN2P
1654.01
203(2)
1012.07
203(2)
monoclinic
P21/c
921.526
203(2)
orthorhombic
Pbca
400.13
203
monoclinic
P21/c
triclinic
¯
P1
˚
unit cell dimensions [A, °] a ϭ 8.776(2)
a ϭ 9.667(2)
b ϭ 15.321(4)
c ϭ 25.610(6)
α ϭ 81.904(5)
β ϭ 84.210(4)
γ ϭ 72.204(5)
3569.0(1)
a ϭ 11.170(4)
b ϭ 10.083(3)
c ϭ 38.18(1)
α ϭ 90
β ϭ 90.478(1)
γ ϭ 90
a ϭ 17.473(8)
b ϭ 20.397(2)
c ϭ 21.314(6)
α ϭ 90.00
β ϭ 90.00
γ ϭ 90.00
7596.8
a ϭ 8.997(4)
b ϭ 14.310(6)
c ϭ 13.967(6)
α ϭ 90.00
β ϭ 97.16(1)
γ ϭ 90.00
1784.2(1)
4
b ϭ 10.057(2)
c ϭ 9.193(2)
α ϭ 90
β ϭ 115.45(3)
γ ϭ 90
732.8(3)
2
1.225
0.3 ϫ 0.3 ϫ 0.5 0.2 ϫ 0.2 ϫ 0.1
2.68 to 25.11
3619
2090
172
3
˚
volume [A ]
4301(2)
4
Z
2
8
calcd. density [Mg/m3]
crystal size [mm]
Θ range [°]
1.539
1.536
1.756
0.2 ϫ 0.2 ϫ 0.3
1.490
0.2 ϫ 0.2 ϫ 0.3
2.10 to 25.09
20385
0.3 ϫ 0.3 ϫ 0.5
2.05 to 25.11
9210
1.61 to 25.17
18765
reflections collected
independent reflections
parameters
40105
12478
897
7552
507
4875
406
3172
275
R1[I Ͼ 2σ(I)][a]
wR2(all data)[b]
R ϭ 0.0610
wR2 ϭ 0.1680
R ϭ 0.0502
wR2 ϭ 0.1424
R ϭ 0.0552
wR2 ϭ 0.1162
R1 ϭ 0.0410
wR2 ϭ 0.1098
R1 ϭ 0.0374
wR2 ϭ 0.0843
[a]
[b]
R ϭ (Σ(|Fo| Ϫ |Fc|)/Σ|Fc|). Ϫ wR2 ϭ {Σ[w(|Fo|2 Ϫ |Fc|2)2]/Σ[w(|Fc|2)2]}1/2
.
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Eur. J. Inorg. Chem. 2001, 2661Ϫ2668