Dicoordinate copper(I) silanechalcogenolates

Article abstract of DOI:10.1021/ic061579q

The copper silanechalcogenolates ^tBu₃PCuESiPh ₃ (1, E = O; 2, E = S; 3, E = Se) were prepared from the reaction of [^tBu₃PCu(CH₃CN)₃]BF₄ with [Ph₃SiELi(THF)<

Full text of DOI:10.1021/ic061579q

Inorg. Chem. 2006, 45, 8844−8846
Dicoordinate Copper(I) Silanechalcogenolates
Iliana Medina, Heiko Jacobsen, Joel T. Mague, and Mark J. Fink*
Department of Chemistry, Tulane UniVersity, New Orleans, Louisiana 70118
Received August 21, 2006
t
Scheme 1
The copper silanechalcogenolates Bu3PCuESiPh3 (1, E
E
) O; 2,
) S; 3, E )
Se) were prepared from the reaction of [tBu3PCu-
(CH3CN)3]BF4 with [Ph3SiELi(THF)2]2 in acetonitrile. The compounds
were obtained as colorless, crystalline, but thermally labile solids.
X-ray crystallography shows that complexes 1−3 are monomeric
in the solid state with no Cu‚‚‚Cu interactions. The Cu atoms have
either a linear or a near-linear coordination geometry in all three
complexes. Interestingly, the O atom in complex 1 is also linear,
which is in contrast to the highly bent S (2) and Se analogues (3).
Density functional theory calculations suggest that both the linear
systems in which the Cu atom is coordinatively saturated
by phosphine ligands and the chalcogen is sterically pro-
tected. For instance, the solid-state structures of the copper
n
chalcogenide complexes (R3P)3CuESiMe3 (R ) Et, Pr; E
) S, Se, Te) show discrete monomeric units with a
coordination number of 4 about the Cu atom.7 These
thermally labile complexes are prone to the removal of the
silyl group via acetoxydesilylation or thermolysis, resulting
in the formation of clusters with extensive chalcogen bridge
bonding.8
geometry of 1 and an associated extremely short Cu
−O distance
[1.769(4) Å] are not the result of delocalization but are the result
π
of a fine balance of electrostatic interaction and Pauli repulsion.
CuI complexes with the group 16 elements are of great
interest as models for metalloprotein active sites,1 as
catalysts,2 and for use as photovoltaic materials.3,4 Because
of the ability of the group 16 atom to adopt either terminal
or bridge bonding modes, complexes of the type LnCuX (L
) monodentate phosphine; X ) O, S, Se) display a rich
coordination chemistry. Bridge bonding allows for the
formation of Cu-based oligomers, cluster compounds, and
polymers.5 However, monomeric CuI complexes are rela-
tively rare and generally exist either as loose bimolecular
aggregates with short Cu‚‚‚Cu or Cu‚‚‚X contacts or as
structures with a cyclic Cu2X2 core.6 Nonetheless, discrete
monomeric copper(I) chalcogenides may be isolated in
We now report the first series of monomeric dicoordinate
copper(I) silanolates and silanechalcogenolate complexes, t-
Bu3PCuESiPh3 (E ) O, S, Se). The sterically demanding
tBu3P ligand in conjunction with the bulky silyl chalcogenide
ligand both promotes coordinative unsaturation at the Cu
center and also prevents association with other molecules.
The empty orbitals on the Cu atom are, therefore, potentially
available for novel π-bonding interactions with the lone pairs
of the chalcogen atoms.
t
The compounds Bu3PCuESiPh3 (1, E ) O; 2, E ) S; 3,
E ) Se) have been synthesized in moderate to high yields
from the reaction of [tBu3PCu(CH3CN)3]BF4 with [Ph3SiELi-
(THF)2]2 (E ) O, S, Se) in acetonitrile (Scheme 1).
Compounds 1-3 were isolated as colorless crystalline, air-
sensitive solids that decompose before melting (∼100 °C),
generating black powders. The thermal stability of 1 and 2
is significantly greater than that observed for 3. Whereas
compounds 1 and 2 can be handled briefly at room
temperature, compound 3 slowly decomposes in solution
even at 0 °C.9 All compounds gave satisfactory analytical
* To whom correspondence should be addressed. E-mail:
fink@mailhost.tcs.tulane.edu.
(1) Winge, D. R.; Dameron, C. T.; George, G. N.; Pickering, I. J.; Dance,
I. G. Bioinorg. Chem. Copper 1993, 110.
(2) (a) Grigg, R.; Cooper, D. M.; Holloway, S.; McDonald, S.; Millington,
E.; Sarker, M. A. B. Tetrahedron 2005, 81, 8677. (b) Percec, V.;
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(9) Because of their thermal instability, all compounds should be stored
at -25 °C.
8844 Inorganic Chemistry, Vol. 45, No. 22, 2006
10.1021/ic061579q CCC: $33.50
© 2006 American Chemical Society
Published on Web 09/30/2006

COMMUNICATION
Figure 1. Molecular structure of 1 with atomic numbering (ORTEP, 50%
probability ellipsoids; H atoms are omitted for clarity). Selected bond lengths
(Å) and angles (deg) for 1: O-Cu, 1.769(4); Cu-P, 2.1496(17); O-Si,
1.578(4); Cu-O-Si, 180.00(1); O-Cu-P, 180.00(1).
Figure 2. Molecular structure of 2 with atomic numbering (ORTEP, 50%
probability ellipsoids; H atoms are omitted for clarity). Selected bond lengths
(Å) and angles (deg) for 2: S-Cu, 2.1578(11); Cu-P, 2.2016(10); S-Si,
2.0916(14); Cu-S-Si, 97.63(5); P-Cu-S, 174.12(4).
and spectroscopic data.10 Interestingly, the 31P{1H} NMR
spectra of all three complexes show a single broadened
resonance due to quadrupolar interactions with the multiple
1
I > /2 Cu isotopes in a low-coordinate environment.11
X-ray-quality crystals of complexes 1-3 were grown from
benzene/pentane (1:3) mixtures at low temperatures. The
X-ray structures of 1-3 reveal that these compounds are
monomeric in the solid state and possess a linear coordination
environment about the Cu atom. The isolation of coordina-
tively unsaturated CuI complexes is a likely result of the
combined steric demand of both the phosphine and the
chalcogenide moieties.
The copper siloxide (1) crystallizes in the P3h point group;
the linear P-Cu-O-Si skeleton lies exactly on a crystal-
lographic 3-fold rotation axis (Figure 1). Two monomeric
units of 1 pack in a head-to-tail fashion in the unit cell.
Although there are some nonbonding interactions between
the peripheral phenyl and isopropyl groups, there are no
apparent d10-d10 Cu‚‚‚Cu interactions (shortest contact, 8.077
Å).12 This contrasts with an analogous linear gold siloxide
system, Ph3PAuOSiPh3, which exists as head-to-tail mono-
mers in the unit cell but with a Au‚‚‚Au interaction distance
of 3.376(2) Å.13 The observed Cu-O bond distance of 1.769-
(4) Å in 1 is significantly shorter than the Cu-O distances
reported for related compounds (hfac)Cu(PMe3) [1.990(8)
and 2.034(7) Å], (dmp)Cu(PMe3) [1.941(5) and 2.030(5) Å],
and (dmb)Cu(PMe3) [1.985(2) Å] (where hfac ) hexafluo-
roacetylacetonate, dmp ) dipivaloylmethanate, and dmb )
dibenzoylmethanate).14
Figure 3. Molecular structure of 3 with atomic numbering (ORTEP, 50%
probability ellipsoids; H atoms are omitted for clarity). Selected bond lengths
(Å) and angles (deg) for 3: Se-Cu, 2.2650(6); Se-Si, 2.2326(10); Cu-P,
2.2014(10); Cu-Se-Si, 95.27(3); Se-Cu-P, 173.28(3).
The molecular geometries of the S (2) and Se (3) analogues
are shown in Figures 2 and 3, respectively. These isomorphic
structures of 2 and 3 show a linear geometry at the Cu atom
similar to the siloxide 1; however, they strikingly differ from
the linear siloxide structure by the nearly orthogonal angle
at the chalcogen atom [97.63(5)° for 2 and 95.27(3)° for 3].
Complex 3 is one of the few examples of a terminally bonded
copper(I) selenolate complex.
The length of the Cu-S bond in 2 [2.1578(11) Å] is in
the normal range for homoleptic copper thiolates: [Cu-
15
(SSiMe2But)]4 [2.1666(4) Å], [Cu(SSiPhtBu2)]4 [2.1597-
17
(7) Å],16 and [Cu(SSiPh3)]4 [2.1633(5) Å]. However, the
Cu-S bond of 2 is significantly shorter than that reported
for (Et3P)3CuSSiMe3 [2.4022(5) Å] and (nPr3P)3CuSSiMe3
[2.3970(10) Å]. Complex 3 also shows a shorter Cu-Se bond
length when compared with the Cu-Se bond lengths in the
analogous complexes (Et3P)3CuSeSiMe3 [2.5124(6) Å] and
(nPr3P)3CuSeSiMe3 [2.5160(4) Å].7 The shorter Cu-chal-
cogen bond lengths in 2 and 3 may be attributed to a
combination of diminished sterics at the Cu atom (dicoor-
(10) Compound Characterization. 1. 1H NMR (δ, C6D6): 0.98 (d, 27H,
3JH-P ) 13 Hz), 7.32 (m, 9H), 8.16 (m, 6H). 13C NMR (δ, C6D6):
142.5 (o-Ph), 135.6 (m-Ph), 128.4 (p-Ph), 36.2 (d, C(CH3)3), 31.6 (d,
C(CH3)3). 31P NMR (δ, C6D6): 72.17. 29Si NMR (δ, C6D6): -24.29.
Elem anal. Calcd: C, 66.57; H, 7.82. Found: C, 66.65; H, 7.25. Mp:
1
3
126 °C (dec). 2. H NMR (δ, C6D6): 0.90 (d, 27H, JH-P ) 13 Hz),
7.20 (m, 9H), 8.12 (m, 6H). 13C NMR (δ, C6D6): 141.6 (o-Ph), 135.9
(m-Ph), 128.4 (p-Ph), 36.3 (d, C(CH3)3), 31.7 (d, C(CH3)3). 31P NMR
(δ, C6D6): 62.4. Elem anal. Calcd: C, 64.65; H, 7.59. Found: C,
64.53; H, 7.07. Mp: >100 °C (dec). 3. 1H NMR (δ, C6D6): 0.93 (d,
3
27H, JH-P ) 13 Hz), 7.25 (m, 9H), 7.75 (m, 6H). 13C NMR (δ,
C6D6): 140.9 (o-Ph), 136.2 (m-Ph), 128.6 (p-Ph), 36.5 (d, C(CH3)3),
31.8 (d, C(CH3)3). 31P NMR (δ, C6D6): 61.2. Mp: >100 °C (dec).
(11) Verkade, J. G.; Mosbo, J. E. In Phosphorus-13 NMR Spectroscopy in
Stereochemical Analysis; Verkade, J. G., Quinn, L., Eds.; VCH
Publishers: Deefield, FL, 1987; p 441.
(12) Pyyko¨, P. Chem. ReV. 1997, 97, 597.
(13) Bauer, A.; Schneider, W.; Angermeier, K.; Schier, A.; Schmidbauer,
H. Inorg. Chem. Acta 1996, 251, 249.
(14) Shin, H. K.; Chi, K. M.; Farkas, J.; Hampden-Smith, M. J.; Kodas, T.
T.; Duesler, E. N. Inorg. Chem. 1992, 31, 424.
(15) Komuro, T.; Matsuo, T.; Kawaguchi, H.; Tatsumi, K. Dalton Trans.
2004, 1618.
(16) Ku¨ckmann, T. I.; Hermsen, M.; Bolte, M.; Wagner, M.; Lerner, H.-
W. Inorg. Chem. 2005, 44, 3449.
(17) Komuro, T.; Kawaguchi, H.; Tatsumi, K. Inorg. Chem. 2002, 41, 5083.
Inorganic Chemistry, Vol. 45, No. 22, 2006 8845

COMMUNICATION
dinate vs tetracoordinate) and an increase in the nominal “s”
character at the Cu (“sp” vs “sp3”).
potential at a significantly bent Cu-O-Si bond. Thus, the
equilibrium bond angle θ(Cu-O-Si) found for H3PCuOSiH3
is 135° but requires only 3 kJ/mol to deform to a linear
geometry. In the case of 1, it is likely that crystal packing
forces would be sufficient to stabilize the observed linear
geometry. In contrast, DFT calculations indicate predomi-
nately covalent interactions for H3PCuSSiH3 and H3-
PCuSeSiH3 with nearly orthogonal bond angles (97.1° and
93.1°, respectively) and a large difference in energy between
the bent ground state and the linear transition state (67 and
85 kJ/mol, respectively).23
The chemistry of low-coordinate copper(I) silanechalco-
genolates is currently being investigated. These coordina-
tively unsaturated complexes may serve as building blocks
to heterobimetallic complexes or as chemical vapor deposi-
tion precursors to CuE (E ) O, S, Se).
Trends in the Cu-E-Si bond angles for complexes 1-3
closely parallel those for the Si-E-Si bond angles of (Ph3-
Si)2E. Thus, for (Ph3Si)2E, θ(Si-E-Si) varies in the series
E ) O (180°),18 S [111.94(8)°],19 Se [110.51(2)°].20 In
addition, the unique bonding in the Cu-O-Si fragment of
1 is manifested not only by its linear geometry but also in
some extremely short Cu-O and Si-O bond distances. To
our knowledge, the Cu-O bond distance of 1.769(4) Å in 1
is the shortest known for a CuI-O bond.21 The very short
Si-O bond distance of 1.578(4) Å is also notable. In contrast,
Cu-E and Si-E (E ) S and Se) bond distances found for
2 and 3, respectively, are more in the expected range.
Traditionally, the siloxane linkage is believed to have
considerable multiple-bond character because of dative π
bonding from the O lone pairs to low-lying acceptor orbitals
on the Si, thus giving rise to shorter than expected Si-O
bonds and near-linear geometries about the O atom. How-
ever, density functional theory (DFT) calculations on H3-
PCuOSiH3 suggest that almost no π bonding occurs between
the O and Cu atoms and that the primary interaction is
electrostatic in nature.22 The combined effects of ionic
bonding and Pauli repulsion result in a very flexible bending
Acknowledgment. Financial support from NASA (Grant
NCC3-946) through the Tulane Institute for Macromolecular
Engineering and Science, NASA (Grant NCC3-97) through
the Ohio Aerospace Institute, and the Louisiana Board of
Regents (LaSPACE Grant C164092) is gratefully acknowl-
edged. We thank Prof. L. Cavallo for providing access to
the MoLNaC Computing Facilities at Dipartimento di
Chimica, Universita` di Salerno, Salerno, Italy.
Supporting Information Available: Synthetic procedures and
crystallographic data (CIF) for compounds 1-3. This material is
available free of charge via the Internet at http://pubs.acs.org.
(18) Glidewell, C.; Liles, D. C. Acta Crystallogr., Sect. B 1978, B34 (1),
124.
IC061579Q
(19) Wojnowski, W.; Peters, K.; Peters, E. M.; Von Schnering, H. G. Z.
Anorg. Allg. Chem. 1985, 525, 121.
(20) Medina, I.; Mague, J. T.; Donahue, J. P.; Fink, M. J. Acta Crystallogr.,
Sect. E 2005, E61, o2687.
(21) A very short Cu-O bond is also found for the dicoordinate cuprate
(o-xylyl-O)2Cu-, 1.798(8) Å. Fiaschi, P.; Floriani, C.; Pasquali, M.;
Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1986, 25, 462.
(22) Ionic bonding has also been proposed as an alternative model for
siloxane bonds. Apeloig, Y. Theoretic Aspects of Organosilicon
Compounds. In The Chemistry of Organic Silicon Compounds; Patai,
S., Rappaport, Z., Eds.; Wiley: Chichester, U.K., 1989; Vol. 1, Chapter
2, p 57.
(23) Details of the calculations will be published in a full paper.
8846 Inorganic Chemistry, Vol. 45, No. 22, 2006