Bis(diphenylphosphino)methane and related ligands as hydrogen bond donors

Article abstract of DOI:10.1039/a803905d

A search of the Cambridge Structural Database reveals that the methylene group of coordinated bis(diphenylphosphino)methane and related ligands can act as a hydrogen bond donor, with H...O distances as short as 2.20 A; analogous C-H...Cl^- interactions are a feature of the packing of dppmSe complexes of silver(I) and gold(I).

Full text of DOI:10.1039/a803905d

Bis(diphenylphosphino)methane and related ligands as hydrogen bond donors†
Peter G. Jones and Birte Ahrens
Institut für Anorganische und Analytische Chemie, Technical University of Braunschweig, Postfach 3329, 38023
Braunschweig, Germany. E-mail: jones@xray36.anchem.nat.tu-bs.de
Received (in Basel, Switzerland) 26th May 1998, Accepted 15th September 1998
A search of the Cambridge Structural Database reveals that
the methylene group of coordinated bis(diphenylphos-
phino)methane and related ligands can act as a hydrogen
bond donor, with H···O distances as short as 2.20 Å;
analogous C–H···Cl2 interactions are a feature of the
packing of dppmSe complexes of silver(i) and gold(i).
there are presumably many more with somewhat longer H···O
distances.
Although this initial search was restricted to oxygen
acceptors, it is clear that other electronegative elements should
accept hydrogen bonds from dppm. In view of our interest in
coinage metal complexes with selenium ligands,8 we therefore
determined structures of the type [(dppmSe)2M]+Cl2 (1a, M =
Ag, dichloromethane solvate; 1b, M = Ag, ethanol solvate; 2a,
M = Au, chloroform solvate; 2b, M = Au, ethanol solvate).‡§
These are the first complexes involving P2Se2 coordination at
silver(i) and gold(i). The coordination at the metal atoms is
distorted tetrahedral; angular distortions arise from the re-
stricted bite of the ligands, but the gold complexes additionally
display a major difference in Au–Se bond lengths (0.16 Å in 2b
and 0.30 Å in 2a; values are given in Figs. 1 and 2). The
structure of a two-coordinate gold(i) complex of the same
ligand has been reported by Schmidbaur, et al.9 and by chance
belongs to the set of 23 compounds discussed above; it displays
two C–H···Oacetone hydrogen bonds.
Secondary bonding interactions have been the focus of
increased interest for several years. The classical hydrogen
bond is a well known structural phenomenon; the C–H···O
hydrogen bond, at first a controversial postulate, is now
accepted as an important factor in determining the nature and
stability of solid-state structures.1 It has been recognised that
more acidic C–H groups are likely to provide stronger (shorter)
hydrogen bonds, although the inverse correlation between
length and strength may not be totally reliable.1
It is normal practice in X-ray structure determination to check
newly determined structures for possible hydrogen bonds, and
indeed this process can now be performed automatically for
classical hydrogen bonds.2 The search for C–H···X interactions
is less well integrated into common program systems; corre-
spondingly, it may be assumed that many such interactions fail
to be reported. In this Institute, such searches have only recently
become routine;3 we use a default cutoff of 2.6 Å for the H···O
distance, although appreciably longer interactions (up to 3 Å)
have often been considered genuine hydrogen bonds.
In a recent study of six-membered heterocycles involving the
P–CH2–P unit, we observed some strikingly short inter-
molecular C–H···O interactions (H···O 2.25, C···O 3.24 Å)
involving the methylene group between the phosphorus atoms.4
This prompted us to re-inspect some of our older structures
involving organic phosphorus heterocycles, and we discovered
two cases where we had overlooked short intermolecular
contacts between the H atoms of a P–CH2–P unit and keto
oxygens (H···O 2.38, 2.29 Å).5
Another molecule involving the P–CH2–P group is the
common ligand bis(diphenylphosphino)methane (dppm),
Ph2PCH2PPh2. The methylene hydrogens of dppm are known to
be acidic, particularly in metal complexes; the deprotonated
form of the ligand contains an additional donor, the methanide
group.6 It thus seemed likely that dppm complexes might
display C–H···O hydrogen bonds.
Fig. 1 The structure of 1a in the crystal. Hydrogen atoms of the phenyl
groups are omitted for clarity, radii are arbitrary. Dashed lines represent H
bonds. Selected bond lengths (Å) and angles (°): Ag–Se1 2.7086(12), Ag–
Se2 2.7749(13), Ag–P2 2.453(3), Ag–P4 2.439(2); bite angles P2–Ag–Se1
92.49(6), P4–Ag–Se2 91.40(6); H···Cl2···H 164. The structures of 1b
(isostructural) and 2b (equivalent packing) are similar to 1a: 1b Ag–Se1
2.7179(10), Ag–Se2 2.7643(10), Ag–P2 2.454(2), Ag–P4 2.440(2); P2–
Ag–Se1 92.69(5), P4–Ag–Se2 91.64(5); H···Cl2···H 159. 2b Au–Se1
2.9459(12), Au–Se2 2.7891(12), Au–P2 2.306(3), Au–P4 2.319(2); P2–
Au–Se1 89.64(7), P4–Au–Se2 91.61(7); H···Cl2···H 160.
A search of the Cambridge Structural Database7 (Oct. 1997
version) was conducted for the fragment P–CH2–P with an
intermolecular H···O contact of < 2.5 Å to any O–C bond. The
search was restricted to error-free, ordered structures. Apart
from the two structures previously mentioned, a total of 23
structures (all of them complexes or clusters involving dppm or
related ligands) with 28 C–H···O substructures were found. The
geometry was in all cases acceptably linear (one C–H···O angle
of 133°, all others > 143°). The shortest H···O contact was 2.20
Å.
The hydrogen bonds can be classified as follows: M–
COterminal···H, 10 cases; M–CObridging···H, 2; Osolvent···H, 8;
Oanion···H, 3; ligand CNO···H, 5. In no case were the C–H···O
hydrogen bonds mentioned in the original publication; in
several cases it was explicitly stated that no unusual inter-
molecular contacts were observed. It should be noted that these
relatively few examples represent the shortest such interactions;
Fig. 2 The structure of 2a in the crystal. Hydrogen atoms of the phenyl
groups are omitted for clarity, radii are arbitrary. Dashed lines represent H
bonds. Selected bond lengths (Å) and angles (°): Au–Se1 3.0571(10), Au–
Se2 2.7535(9), Au–P1 2.298(2), Au–P3 2.329(2); P1–Au–Se1 83.46(5),
P3–Au–Se2 92.65(5), H···Cl2···H 112.
Chem. Commun., 1998, 2307–2308
2307

Table 1 Hydrogen bond geometry in compounds 1a,b, 2a,b
Bis[(diphenylphosphino)(diphenylphosphineselenido)methane]gold(i)
chloride 2 was obtained from the reaction of dppmSe with a suspension of
(tht)AuCl (tht = tetrahydrothiophene) in 2:1 molar ratio in toluene,
Compound, H bond
H···Cl2/Å
C···Cl2/Å
C–H···Cl2/°
followed by precipitation with diethyl ether (yield 66%). Crystals were
grown by diffusion of diethyl ether into a solution of 2 in chloroform (2a)
or ethanol (2b).
1a, C–Hdppm···Cl2
1a, C–Hdppm···Cl2
1a, C–Hsolv···Cl2
1b, C–Hdppm···Cl2
1b, C–Hdppm···Cl2
2a, C–Hdppm···Cl2
2a, C–Hdppm···Cl2
2a, C–Hsolv···Cl2
2b, C–Hdppm···Cl2
2b, C–Hdppm···Cl2
2b, O–Hsolv···Cl2
2.87
2.61
2.58
2.82
2.75
2.64
2.57
2.70
2.68
2.61
3.839(9)
3.556(9)
3.467(14)
3.779(6)
3.705(7)
3.576(7)
3.535(7)
3.554(12)
3.616(9)
3.567(10)
3.042(10)
168
160
149
164
163
157
166
144
157
163
Satisfactory elemental analyses and consistent NMR spectra (1H, 13C,
31P, 77Se) were obtained.
§ X-Ray structure determinations: data were measured at 2100 °C on a
Siemens P4 diffractometer using Mo-Ka radiation. Absorption corrections
using psi-scans (2b: SHELXA2). Structures were refined on F2 using all
reflections (program SHELXL-932). Hydrogen atoms were included using
a
riding model; C–H bond lengths (and H···X contacts) are thus
systematically shortened with respect to the true values.
Crystal data: 1a, 1·3CH2Cl2: C53H50AgCl7P4Se2,
M = 1324.75,
monoclinic, C2/c, a = 38.984(7), b = 14.010(2), c = 21.952(4) Å, b =
101.534(12)°, V = 11747(4) Å3, Z = 8, m = 2.0 mm21, 10 989 reflections,
10 260 unique, wR2 0.201, R1 0.066.
1b, 1·3.5EtOH: C57H65AgClO3.5P4Se2, M = 1231.21, monoclinic, C2/c,
a = 39.315(7), b = 14.026(2), c = 22.214(3) Å, b = 100.538(10)°, V =
12 043(3) Å3, Z = 8, m = 1.7 mm21, 21 045 reflections, 10 577 unique,
wR2 0.101, R1 0.051.
2a, 2·2CHCl3: C52H46AuCl7P4Se2, M = 1397.80, monoclinic, P21/c, a =
12.917(2), b = 22.285(3), c = 19.050(3) Å, b = 99.850(10)°, V =
5403.0(13) Å3, Z = 4, m = 4.6 mm21, 14 225 reflections, 9509 unique, wR2
0.108, R1 0.046.
2b, 2·EtOH: C52H50AuClOP4Se2, M = 1205.14, orthorhombic, Pna21, a
= 22.425(3), b = 13.713(2), c = 16.035(2) Å, V = 4930.9(11) Å3, Z = 4,
m = 4.7 mm21, 11 215 unique reflections, wR2 0.104, R1 0.048. CCDC
182/987.
All four structures 1a,b, 2a,b display C–H···Cl hydrogen
bonds (Table 1), which play a central role in determining the
crystal packing. In each structure, the ions are connected into
chains (Figs. 1 and 2) by hydrogen bonds C–Hdppm···Cl2,
whereby the chloride accepts two hydrogen bonds. Addition-
ally, there is a C–Hsolv···Cl2 contact from a solvent molecule in
1a and 2a, an O···Cl contact involving the ethanol of 2b, and a
similar contact in 1b, in which however the ethanol is poorly
resolved.
A second database search,7 this time for C–H···Cl contacts,
also proved fruitful; a total of 28 hydrogen bonds in 21
structures were found with H···Cl < 2.8 Å and C–H···Cl >
130°. These contacts can be classified as: 14 C–Hdppm···Clcoord
;
1 G. R. Desiraju, Acc. Chem. Res., 1996, 29, 441; T. Steiner, Chem.
Commun., 1997, 727; T. Steiner and G. R. Desiraju, Chem. Commun.,
1998, 891.
2 SHELXL-97, a program for refining crystal structures. G. M. Sheldrick,
Univ. of Göttingen, Germany, 1997. The earlier version SHELXL-93
was used to refine the structures 1a,b, 2a,b.
3 See, for example: D. Henschel, O. Moers, A. Blaschette and P. G. Jones,
Acta Crystallogr., Sect. C, 1997, 53, 1877.
4 P. G. Jones and A. Weinkauf, Acta Crystallogr., Sect. C, 1998, 54, in
press.
12 C–Hdppm···Cl2, 2 C–Hdppm···Cl(other anions). Only one of these
contacts was mentioned explicitly as an interaction with dppm
in the original publications;10 it should however be stressed that
it was until recently not usual to look for hydrogen bonds
involving C–H units. As an example of an unrecognised
hydrogen bond, we can again cite our own work; the structure of
[(dppm)2Au3Cl2]+[(C6F5)3AuCl]211 involves a contact C–
Hdppm···Clanion with H···Cl 2.70 Å, C–H···Cl 139°.
It may be concluded that coordinated dppm is capable of
acting as a C–H···X hydrogen bond donor; in such cases it
presumably exerts a significant influence on structure and
stability, although to the best of our knowledge this possibility
has not previously been discussed in detail. An obvious
corollary is that structures of complexes of dppm and related
ligands should be routinely screened for such hydrogen
bonds.
5 I. V. Shevchenko, A. Fischer, P. G. Jones and R. Schmutzler, Chem.
Ber., 1992, 125, 1325; 1247.
6 R. Usón, A. Laguna, M. Laguna, B. R. Manzano, P. G. Jones and G. M.
Sheldrick, J. Chem. Soc., Dalton Trans., 1984, 839.
7 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 31.
REFCODES: C–H···O: CERREW, DAMMOT, DISMEX, FELCUU,
GIJDAE, JARDEL, JARTOL, JITYUG, JITZAN, KAXYAJ,
KIGROH, PAKFEM, PAKFOW, SEJBEO, SINBOG, TETKUY,
TIVQUK, TUMLUI, VIVLUH, VUFPAN, ZASCUR, ZOWZOA,
ZUXQOY. C–H···Cl: CACPOL, CEYNOJ, DILNIV, DOJKOC,
DPMCPD, HEBXUH, JAGNEK, JUMLUY, KIFPUK, KOPRUC,
KUKNAF, TAZZID, TUFKEK, TUFKIO, TUPNIB, VOBHID,
VUFPAN, YASTAN, YAYSUM, ZUGTOK, ZURGUO.
8 P. G. Jones and C. Thöne, Acta Crystallogr., Sect. C, 1992, 48, 2114,
and references therein.
We thank the Fonds der Chemischen Industrie (Frankfurt) for
financial support and Dr C. Tho¨ne for helpful discussions.
Notes and references
† Dedicated to Professor Armand Blaschette on the occasion of his 65th
birthday.
9 H. Schmidbaur, J. Ebner von Eschenbach, O. Kumberger and G. Müller,
Chem. Ber., 1990, 123, 2261.
‡
Bis[(diphenylphosphino)(diphenylphosphineselenido)methane]silver(i)
chloride 1 was obtained from dppmSe and AgCl in 2:1 molar ratio in
acetone; after filtration, the product was precipitated in 67% yield with light
petroleum. Crystals were grown by diffusion of light petroleum into a
solution of 1 in dichloromethane (1a) or by diffusion of diethyl ether into a
solution of 1 in ethanol (1b).
10 B. R. Sutherland and M. Cowie, Organometallics, 1985, 4, 1637.
11 R. Usón, A. Laguna, M. Laguna, E. Fernández, M. D. Villacampa, P. G.
Jones and G. M. Sheldrick, J. Chem. Soc., Dalton Trans., 1983, 1679.
Communication 8/03905D
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Chem Commun., 1998