8628 J. Am. Chem. Soc., Vol. 119, No. 37, 1997
Leoni et al.
Table 2. Crystallographic and Experimental Data for the X-ray
cage.12 In complex 4, the carbon atom is bonded to four metal
centers and still binds the two sulfur atoms. In this way the
CS2 molecule retains its identity and, as shown above and
despite the hexacoordination, can be easily removed from the
coordination pocket.
Diffraction Study of (4)‚CH2Cl2
formula
fw
crystal dimens, mm
data colln T, °C
cryst syst
space group
a, Å
C54H68Cl2 I2P4Pd4S2
1655.48
0.30 × 0.20 × 0.20
23
orthorombic
Pna21
21.221(8)
Experimental Section
General Procedures. All preparations were performed under a
nitrogen atmosphere using standard Schlenk techniques. Solvents were
refluxed under nitrogen several hours over suitable drying agents and
freshly distilled under nitrogen prior to use. Deuterated solvents were
used without further purification but were deoxygenated by freeze-
pump-thaw cycles and stored under nitrogen on molecular sieves.
[Pd2(µ-PtBu2)(PPh3)3]BF4, (1)BF4,5 and [Pd2(µ-PtBu2)(µ,η2:η2-CS2)-
(PPh3)2]BF4, (2)BF4,5 were prepared by the previously reported
procedures. CS2 (Aldrich), 13CS2 (Cambridge Isotope Labs), PPh3
(Aldrich), and Me4NI (Aldrich) were used as purchased.
IR spectra (Nujol mulls, KBr) were recorded on a Perkin-Elmer FT-
IR 1725X spectrophotometer. NMR spectra were recorded on a Varian
Gemini 200 BB instrument; frequencies are referenced to the residual
signal of the deuterated solvent (1H, 13C) or to external 85% H3PO4
(31P, the shifts downfield from the reference being considered as
positive).
b, Å
17.916(2)
16.526(2)
6283(1)
c, Å
V, Å3
Z
4
F (calcd), g cm-3
radiation
1.750
Mo KR (graphite monochromated
λ ) 0.710 69 Å)
23.681
1.206-0.849
2.5 < θ < 27.0
6453
µ, cm-1
transmission coeff
θ range, deg
no. of obsd reflns (no)
(|Fo| > 3.0σ(|F|))
Ra
0.034
0.046
2.177
a
Rw
GOF
2
a R ) ∑(|Fo - (1/k)Fc|)/∑|Fo|; Rw ) [∑w(Fo - (1/k)Fc)2/∑w|Fo| ]1/2
,
Preparation of [Pd2(µ-PtBu2)(µ-I)(PPh3)2] (3). A red solution of
(1)BF4 (297 mg, 0.241 mmol) in acetone (10 mL) turned immediately
deep green upon the addition of Me4NI (58 mg, 0.289 mmol). The
mixture was stirred for 15 min at room temperature, and the solvent
was evaporated. The residue was dissolved in toluene (20 mL) and
filtered. A green microcrystalline solid precipitated out by the addition
of n-hexane (20 mL), and the suspension was kept 12 h at -20 °C and
filtered; the solid was washed twice with n-hexane (5 mL) and Vacuum
dried (229 mg, 94.1%). Elemental Anal. Calcd for C44H48IP3Pd2: C,
52.4; H, 4.80. Found: C, 52.1; H, 4.75. IR (Nujol, KBr): 3040 (ν)CH),
1572, 1494 (νCdC) cm-1. NMR (C6D6, 293 K): 31P{1H} δ (ppm) 443.5
(t, 2JPP ) 85 Hz, µ-P), 34.3 (d, 2JPP ) 85 Hz, PPh3); 1H δ (ppm) 7.96
2
2
where w ) [σ2(Fo)]-1, σ(Fo) ) [σ2(Fo ) + f 4(Fo )]1/2/2Fo, and f ) 0.03.
mixtures. IR and NMR spectra of the sample were undistinguishable
from those described above for the sample obtained with method a).
By the same procedure of method b, starting from 13CS2, we prepared
the labeled Pd4(µ-PtBu2)2(µ4-13CS2)(PPh3) 2I2, (4*). NMR (CDCl3, 293
K): 31P{1H} δ (ppm) 403.2 (br d, 2JPP ) 36 Hz, µ-P), 23.8 (dd, 2JPP
)
36 Hz, 2JPC ) 14 Hz, PPh3); 13C{1H} δ (ppm) 134.5 (d, 2JCP ) 12 Hz,
C
ortho), 133.1 (d, 1JCP ) 42 Hz, Cipso), 130.5 (br s, Cpara), 128.7 (d, 3JCP
) 7 Hz, Cmeta), 117.1 (br t, JCP ) 14 Hz, CS2), 42.9 (br s, CMe3), 33.0
(br s, CH3), 31.7 (br s, CH3).
3
(m, 12 H), 7.02 (m, 18 H), 1.03 (d, JPH ) 13 Hz, 18H, CH3).
Molecular Orbital Calculations. The molecular orbital calculations
are of the extended Hu¨ckel type.13 A modified Wolfsberg-Helmholtz
formula is employed for the calculation of Hij matrix elements.14 The
atomic parameters (wave functions, valence state ionization energies)
used for C and H are standard ones; those for S15 and P16 have been
taken from earlier work. For Pd the following set of atomic parameters
from an earlier SCC calculation of [Pd2(PH3)2(µ-allyl)(µ-Cp)] (ref 6a)
was used: Pd 5s, ú ) 2.190, Hii ) -7.680 eV; Pd 5p, ú ) 2.152, Hii
) -4.050 eV; Pd 4d, ú1 ) 5.983, c1 ) 0.5535, ú2 ) 2.613, c2 ) 0.6701,
Hii ) -12.51 eV. The following geometric parameters were used in
our MO calculations for 5 and the corresponding fragments [(PH3)2-
Pd2(µ-PH2)]+ in the symmetric model [Pd4(µ-PH2)2(µ4-CS2)(PH3)4]2+
of 4: C2V symmetry; distances Pd-Pd ) 2.650 Å, Pd-P ) 2.300 Å,
Pd-µP ) 2.260 Å, P-H ) 1.420 Å; Pd-µP-Pd ) 71.79°, Pd-P-H
) 109.45°, Pd-µP-H ) 116.94°, H-µP-H ) 112.0°; free CS2: C-S
) 1.610 Å; CS2 in [Pd4(µ-PH2)2(µ4-CS2)(PH3)4]2+: C-S ) 1.716 Å,
S-C-S ) 135.0°. The related parameters in our partially optimized
model [Pd4(µ-PH2)2(µ4-CS2)(PH3)4]2+ are Pd-C ) 2.174 Å, Pd-S )
2.032 Å, and Pd-Pd-P ) 152°. Note that due to well-known inability
of the extended Hu¨ckel method to accurately calculate bond distances
no attempts were made to optimize the geometry of the model [Pd4-
(µ-PH2)2(µ4-CS2)(PH3)4]2+ any further.
Molecular weight: 1039 (by cryoscopy in C6H6).
Preparation of Pd4(µ-PtBu2)2(µ4-CS2)(PPh3)2I2 (4). Method a:
An acetone (5 mL) solution of Me4NI (56 mg, 0.278 mmol) was
dropped into a yellow solution of (2)BF4 (261 mg, 0.250 mmol) in
acetone (5 mL). The color of the solution turned deep green in a few
minutes. The 31P{1H} NMR spectrum of a small sample of the solution
exhibited the resonances described above, due to complex 3, and of
uncoordinated PPh3 as the only P-containing species in solution.
Leaving the solution at room temperature, a gradual variation of its
color to red was observed, with the precipitation of a red solid. After
6 h, the solvent was evaporated and the residue dissolved in toluene
(10 mL). A white solid was filtered off, and the red solution was
concentrated to ca. one-half of the starting volume. By adding n-hexane
(10 mL) to the filtrate, a red solid precipitated out and was filtered,
washed twice with n-hexane (3 mL), and Vacuum dried (160 mg, 81.5%
yield). Elemental Anal. Calcd for C53H66I2P4Pd4S2: C, 40.6; H, 4.24.
Found: C, 40.4; H, 4.21. IR (Nujol, KBr): 3040 (νdCH), 1494, 1456
(νCdC), 1098 (νCS) cm-1. NMR (CDCl3, 293 K): 31P{1H} δ (ppm)
403.2 (d, 2JPP ) 36 Hz, µ-P), 23.8 (d, 2JPP ) 36 Hz, PPh3); 1H δ (ppm)
3
7.8 (m, 12 H), 7.45 (m, 18H), 1.17 (d, JPH ) 18 Hz, CH3), 1.13 (d,
3JPH ) 14 Hz, CH3); 13C{1H} δ (ppm) 134.4 (d, 2JCP ) 12 Hz, Cortho),
2
3
133.5 (d, JCP ) 42 Hz, Cipso), 130.4 (s, Cpara), 128.7 (d, JCP ) 7 Hz,
meta), 117.1 (s, CS2), 42.9 (br s, CMe3), 33.0 (br s, CH3), 31.7 (br s,
CH3).
Method b: CS2 (10 µL, 0.166 mmol) was added to a deep green
Crystallography. A suitable crystal was mounted, on a glass fiber,
on a CAD4 diffractometer and was used for the space group determi-
nation and for the data collection. Unit cell dimensions were obtained
by least-squares fit of the 2θ values of 25 high-order reflections (9.78
e θ e 18.18°). Selected crystallographic and other relevant data are
listed in Table 2 and Table S1 of the Supporting Information.
Data were measured with variable scan speed to ensure constant
statistical precision on the collected intensities. Three standard
C
toluene (5 mL) solution of complex 3 (124 mg, 0.123 mmol). The
color of the solution turned red in a few minutes, and a red solid started
to precipitate. The suspension was stirred for 2 h at room temperature
and was kept, after the addition of Et2O (5 mL), for 12 h at -20 °C.
The solid was filtered, washed twice with n-hexane (3 mL), and Vacuum
dried (65 mg, 67.3% yield). Single crystals for the crystal structure
determination were obtained by recrystallization from CH2Cl2/Et2O
(13) Hoffmann, R. J. Chem. Phys. 1963, 39, 1379.
(14) Ammeter, J. H.; Bu¨rgi, H. B.; Tibeault, J. C.; Hoffmann, R. J. Am.
Chem. Soc. 1978, 100, 3886.
(12) (a) Bradley, J. S. AdV. Organomet. Chem. 1983, 22, 1. (b)
Scherbaum, F.; Grohmann, A.; Huber, G.; Kru¨ger, Schmidbaur, H. Angew.
Chem., Int. Ed. Engl. 1988, 27, 1544.
(15) Pinhas, A. R.; Hoffmann, R. Inorg. Chem. 1979, 18, 654.
(16) Hofmann, P.; Ha¨mmerle, M.; Unfried, G. New. J. Chem. 1991, 15,
769.
Leoni, Piero
