Synthesis and molecular structure of the first tetranuclear copper(I) silylphosphido cluster [Cu(CyPSiMe2PHCy)]4

Article abstract of DOI:10.1039/a803394c

The reaction of N,N-diethylamino(cyclohexylphosphino)dimethylsilane 1 with the benzene solvate of copper(I) trifluoromethylsulfonate furnishes the title complex 2, which has been structurally characterized by X-ray diffraction; the same product results on

Full text of DOI:10.1039/a803394c

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Synthesis and molecular structure of the first tetranuclear copper(
I)
silylphosphido cluster [Cu(CyPSiMe2PHCy)]4
Markus Faulhaber, Matthias Driess*† and Klaus Merz
Lehrstuhl für Anorganische Chemie I, Ruhr-Universität, Universitätsstr. 150, D-44801 Bochum, Germany
The reaction of N,N-diethylamino(cyclohexylphosphino)di-
methylsilane 1 with the benzene solvate of copper( )
I
trifluoromethylsulfonate furnishes the title complex 2, which
has been structurally characterized by X-ray diffraction; the
same product results on conversion of bis(cyclohexylphos-
phino)dimethylsilane 3 with copper( ) trifluoromethylsulfo-
I
nate in the presence of lithium diisopropylamide as an
auxilliary base.
Scheme 1
Secondary phosphido anions [RRP]2 are of considerable
interest as ligands in the coordination chemistry of transition
metals and clusters thereof.1 Such complexes are also attractive
as soft nucleophilic transphosphination reagents for selective
synthesis of functionalized phosphane ligands. This has re-
transphosphination–silylation reactions were observed, leading
to a CuI silylphosphidophosphane aggregate. Hence the N,N-
diethylamino(cyclohexylphosphino)dimethylsilane
1
reacts
with the benzene solvate of [CuOTf] in toluene to give 2 in the
form of dark red crystals in 75% yield (Scheme 1).
Compound 1 (colourless liquid, bp0.01Torr = 85 °C) is readily
accessible via a procedure analogous to that for the synthesis of
N,N-diethylamino(methylphosphino)dimethylsilane.5 The reac-
tion mechanism for the formation of 2 is unknown, but we
suggest the stepwise process as outlined in Scheme 2.
cently been shown for oligomeric copper(
I
) phosphido com-
plexes.2 Hitherto knowledge of the structural chemistry and the
structure–reactivity relationship of copper phosphido aggre-
gates has been relatively scarce and a silylphosphido cluster has
not been described. A convenient method for the preparation of
phosphido bridged transition metal complexes and clusters is
the electrophilic cleavage of Si–P bonds in silylphosphanes
through the corresponding metal halides and alkoxides.3
However, we recently reported on the template synthesis of the
first hexaphosphahexasilacyclododecane by the reaction of a
Apparently, the first step is the electrophilic cleavage of the
Si–P bond in 1 to give the corresponding copper phosphide as
intermediate and the corresponding silyl(amino)triflate. The
copper phosphide intermediate could then co-ordinate another
molecule of 1 and subsequent replacement of the NEt2 group
leads to the PSiP chelate moiety in the co-ordination sphere of
the CuI centre. Compound 2 (Fig. 2) is also accessible starting
from bis(cyclohexylphosphino)dimethylsilane 3 and [CuOTf]
in the presence of LDA (lithium diisopropylamide) as base in
70% yield. Compound 3 was prepared through phosphination of
dimethyldichlorosilane with LiAl(PHCy)4 (Cy = cyclohexyl).5
The composition of 2 was confirmed by elemental analysis. As
expected, the 1H NMR spectrum of 2 shows two signals at d 0.3
and 0.4 for the diastereomeric methyl groups of the SiMe2
moiety. The cyclohexyl groups exhibit unresolved multiplets
between d 0.7 and 2.9, and the signal of the chemically
equivalent P–H protons is observed as a doublet at d 3.7 (1JPH
= 267 Hz). The 31P NMR spectrum of 2 shows multiplets at d
2100 and 272, which are relatively broad due to the
quadrupole moment of the 63/65Cu nuclei (I = 3/2) . The P–H
stretching vibration is observed in the IR spectrum at 2290
triphosphatrisilacyclohexane with copper(
I
) or silver( ) tri-
I
fluoromethylsulfonate, where the building up of new Si–P
bonds instead of cleavage was observed.4 In order to extend this
building up method for the preparation of acyclic silylphos-
phane and 2phosphido chelate ligands, we are exploring the
reactivity of Si-functionalized silylphosphanes toward coin
metal(I) complexes.
Here we report on two preparation routes to the first
tetranuclear copper( ) silyl phosphido complex 2 (Fig. 1),
I
containing the [CyPHSiMe2CyP]2 ligand, and we describe its
molecular structure which was elucidated by single-crystal
X-ray diffraction.
While it was anticipated that the P–H bond in a secondary
silylphosphane of the type R3Si–PH–R would be metalated by
copper(
I) trifluoromethylsulfonate ([CuOTf]), surprisingly,
cm21
.
Fig. 1 Chelated cluster 2
Scheme 2
Chem. Commun., 1998
1887

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tetrahedron. The Cu–Cu distances in the latter are shorter (2.74
Å for the bridged and 2.95 Å for the unbridged edges of the
tetrahedron) than in 2. The Cu–Cu and Cu–P distances in 2 are
within the range observed in other phosphido bridged Cu
clusters.2,7 According to the different co-ordination modes of
the phosphino and the phosphido P centres of the ligands, the
Si–P distances are not identical: the Si(1)–P(1) distance of the
µ2-coordinating phosphido group (2.207 Å) is about 0.5 Å
1
shorter than the Si(2)–P(1) bond of the h -coordinating P atom.
The present results underline the value of silylphosphanes for
the synthesis of new oligophosphane ligands in the co-
ordination sphere of CuI centres.
Notes and References
† E-mail: driess@ibm.anch.ruhr-uni-bochum.de
‡ Crystal data for 2: C56H112Cu4P8Si8, M = 1399.7, tetragonal, space group
I41/a, a = 23.952(6), c = 12.799(4) Å, U = 7342 Å3, Z = 4, intensity data
were collected on a Siemens P4 diffractometer (Mo-Ka radiation, l =
0.71707 Å, w-scan, T = 203 K), 2qmax = 45°, 2381 measured reflections,
164 parameters, m = 1.414 mm21 R1 = 0.070 for 921 observed reflections
{I > 2s(I), wR2 = 0.206 (all reflections, wR2 = [Sw(Fo 2 Fc2)2/
2
S(wFo4)]_}. The structure was solved by direct methods and refined by full-
matrix least squares using SHELXL-93.9 All non-hydrogen atoms were
refined using anisotropic thermal parameters; hydrogen atoms were
included by use of a riding model and fixed isotropic thermal parameters.
CCDC 182/926.
Fig. 2 Molecular structure of 2. Hydrogen atoms omitted for clarity.
Selected distances (Å) and angles (°): P(1)–Si(1) 2.207(5), P(2)–Si(1)
2.263(5), P(1)–C(1) 1.882(9), Si(1)–C(7) 1.890(11), P(2)–Cu(1) 2.261(4),
P(1)–Cu(1) 2.270(3), P(1)–Cu(1”) 2.235(4), Cu(1)–Cu(1) 3.071(3), Cu(1)–
Cu(1”) 2.911(2); P(1)–Si(1)–P(2) 98.7(2), Cu(1)–P(1)–Cu(1”) 80.5(1),
Cu(1”)–Cu(1)–Cu(1”) 63.67(6).
1 A. J. Carty, S. A. McLaughlin and D. Nucciarone, in Phosphorous-31
NMR Spectroscopy in Stereochemical Analysis, ed. J. G. Verkade and
L. D. Quin, Verlag Chemie, Weinheim, 1987, p. 559.
2 A. H. Cowley, D. M. Giolando, R. A. Jones, C. M. Nunn and J. M. Power,
J. Chem. Soc., Chem. Commun., 1988, 208; C. Meyer, H. Grützmacher
and H. Pritzkow, Angew. Chem., Int. Ed. Engl., 1997, 36, 2471.
3 D. Fenske, in Clusters and Colloids—From Theory to Applications, ed.
G. Schmid, Verlag Chemie, Weinheim, 1994, p. 219; D. J. Brauer, G.
Hessler, P. C. Knüppel and O. Stelzer, Inorg. Chem., 1990, 29, 2370.
4 M. Driess, M. Faulhaber and H. Pritzkow, Angew. Chem., Int. Ed. Engl.,
1997, 36, 1892.
5 L. D. Balashova, A. B. Bruker and L. Z. Soborovskii, J. Gen. Chem.
USSR, 1966, 36, 76.
6 A. F. Wells, Z. Kristallogr., Kristallgeom., Kristallphys., Kristallchem.,
1936, 94, 447.
7 V. Schramm, Inorg. Chem., 1978, 17, 714; C. L. Raston and A. H. White,
J. Chem. Soc., Dalton Trans., 1976, 2153; J. R. Nicholson, I. L.
Abrahams, W. Clegg and C. D. Garner, Inorg. Chem., 1985, 24, 1092; M.
Driess, S. Martin, K. Merz, H. Pritzkow, V. Pintchouk, H. Grützmacher
and M. Kaupp, Angew. Chem., Int. Ed. Engl., 1997, 9, 1894.
8 S. L. Lawton, W. J. Rohrbaugh and G. T. Kokotailo, Inorg. Chem., 1972,
11, 612.
The X-ray crystallographic analysis‡ proves that 2 exists as a
discrete tetramer and its core consists of a distorted Cu4
tetrahedron. The latter is the result of the chelate property of the
(CyPSiMe2PHCy) ligand and, at the same time, of ‘metal-
lophilic’ dispersion-type interactions between the co-ordina-
tively unsaturated CuI centres. Each phosphane-like P atom is
only bonded to one Cu centre while the phosphido-like P atoms
are µ2-co-ordinated. Therefore, two of the six edges of the Cu4
tetrahedron are not bridged by phosphorus. Accordingly, each
Cu center has six neighbouring atoms, three of which are copper
and three are phosphorus. The Cu–Cu distances are different:
those for the four edges bridged by phosphorus (2.91 Å) are
about 0.16 Å shorter than for the two unbridged edges (3.07 Å)
of the Cu4 tetrahedron. Other compounds containing cluster
cores of four or more Cu atoms have also been reported. For
6
example, the tetrameric compound Cu4I4[As(C2H5)3]4 and
others with sulfur and nitrogen ligands7,8 possess a tetrahedral
core of CuI centres. A structurally related Cu4 cluster to 2 was
reported, where O,O-diisopropyldithiophosphate coordinates
9 G. M. Sheldrick, SHELXL-93, A Program for Crystal Structure
Refinement, University of Göttingen, 1990.
1
via h and µ2 sulfur centres to the Cu centres of the Cu4
Received in Basel, Switzerland, 6th May 1998; 8/03394C
1888
Chem. Commun., 1998