Palladium(II) Arenethiolates with Chelating Diamines: Formation of N-H?S Hydrogen Bonds with Protonated N,N,N',N'-Tetramethylethylenediamine

Full text of DOI:10.1021/ic950701a

534
Inorg. Chem. 1996, 35, 534-536
Notes
Table 1. Crystallographic Data for 2
Palladium(II) Arenethiolates with Chelating
Diamines: Formation of N-H‚‚‚S Hydrogen
Bonds with Protonated
formula
space group
cryst system
Z
C24F20PdS4‚C6H18N2
C2/c (No. 15)
monoclinic
4
9.9905(6)
N,N,N′,N′-Tetramethylethylenediamine
a, Å
b, Å
c, Å
18.8645(11)
19.2540(14)
90.399(5)
3628.6(4)
1.869
8.5
0.71073 (graphite monochromator)
298
0.047
0.046
Gerardus M. Kapteijn,† David M. Grove,†
Wilberth J. J. Smeets,‡ Huub Kooijman,‡
Anthony L. Spek,‡,§ and Gerard van Koten*,†
â, deg
V, Å3
D
µ
calcd, g cm-3
calcd, cm-1
Department of Metal-Mediated Synthesis, Debye Institute,
and Crystal and Structural Chemistry, Bijvoet Center for
Biomolecular Research, Utrecht University, Padualaan 8,
3584 CH Utrecht, The Netherlands
radiation (Mo KR), Å
T, K
RF
RwF
a
b
b
a RF ) ∑||Fo| - |Fc||/∑|Fo|. RwF ) [∑[w(Fo - Fc)2]/∑[w(Fo)2]]1/2
.
ReceiVed June 7, 1995
enediamine) were prepared according to the literature.5 1H NMR
(300.13 MHz) spectra were recorded on a Bruker AC 300 spectrometer
at ambient temperature in CD3CN obtained from ISOTEC Inc. Infrared
spectra (KBr disks) were recorded on a Perkin-Elmer 283 spectrometer.
Elemental analyses were carried out by Dornis and Kolbe, Mikroana-
lytisches Laboratorium, Mu¨lheim a.d. Ruhr, Germany.
Introduction
Recently, the formation of N-H‚‚‚S hydrogen bonds has
attracted attention in transition metal arenethiolate chemistry.1
Several model complexes, e.g. [FeII(SAr)4]2- 2a
,
[FeIII(Cys-
have been
[Pd(SC6F5)2(Et2NCH2CH2NEt2)] (1). To a stirred solution of [Pd-
(OC6H5)2(teeda)] (0.20 g, 0.43 mmol) in CH2Cl2 (10 mL) was added
pentafluorothiophenol (0.70 g, 3.5 mmol). The pure product was
obtained by diffusion of pentane into this solution. The resulting
needle-shaped deep-red crystals were washed with pentane (2 × 5 mL)
and dried in Vacuo. Yield: 0.28 g (95%). Mp: 166 °C dec. 1H NMR
S)4]-,2b [MoVO(SAr)4]-,3a and [NiII(SAr)4]2- 3b
,
studied in order to establish the influence of such bonds on M-S
coordination. Understanding the nature of N-H‚‚‚S bonds in
inorganic complexes is also important for biochemists to gain
insights into the function of enzymes on a molecular level.4
Here, we report the reaction of bidentate N-donor-ligated bis-
(aryloxo)palladium(II) complexes with an aromatic thiol; de-
pending upon the alkyl substitution in the tetraalkylethylene-
diamine ligand used, either a neutral bis(arenethiolato)-
palladium(II) diamine species or a tetrakis(arenethiolato)-
palladium(II) diprotonated diamine species is formed. The latter
complex is the first example of a hydrogen-bonded “bridging”
[Me2(H)NCH2CH2N(H)Me2]2+ ligand, and this paper describes
the influence of N-H‚‚‚S hydrogen bonding on the square-
planar coordination geometry of the Pd(SC6F5)4 dianion.
2
3
(CD3CN): δ 3.20 (dq, 4H, CHaHbMe, Ja,b ) 13 Hz, Ja,Me ) 7 Hz),
2
3
3.01 (dq, 4H, CHaHbMe, Ja,b ) 13 Hz, Jb,Me ) 7 Hz), 2.86 (s, 4H,
N(CH2)2N), 1.40 (t, 12H, CH3). Anal. Calcd for C22H24F10N2S2Pd:
C, 39.03; H, 3.57; N, 4.14. Found: C, 38.74; H, 3.75; N, 4.08.
[Pd(SC6F5)4][Me2(H)NCH2CH2N(H)Me2] (2). To a stirred solution
of [Pd(OC6H5)2(tmeda)] (0.20 g, 0.49 mmol) or a solution of [Pd-
(OC6F5)2(tmeda)] (0.29 g, 0.49 mmol) in CH2Cl2 (10 mL) was added
pentafluorothiophenol (0.80 g, 4.0 mmol). After 1 min the dark red
solution was filtered. The pure product was obtained by diffusion of
pentane into this solution. The resulting block-shaped red crystals
(suitable for X-ray diffraction) were washed with pentane (3 × 10 mL)
and dried in Vacuo. Yield: 0.49 g (97%). Mp: 185 °C dec. 1H NMR
(CD3CN): δ 2.84 (s, 4H, NCH2), 2.72 (s, 12H, NCH3), 2.69 (br s, 2H,
NH). IR(KBr): νN-H 3250 cm-1. UV-vis (CD3CN): abs. (ꢀ (L mol-1
cm-1)): 24 300 (4100, d-d), 37 500 (49 200, MLCT), 49 500 (34 200,
MLCT) cm-1. Anal. Calcd for C30H18F20N2S4Pd: C, 35.29; H, 1.78;
N, 2.74. Found: C, 35.02; H, 2.07; N, 3.19.
Experimental Section
General Considerations. Pentafluorothiophenol was purchased
from Aldrich Chemical Co. and used as received. The complexes [Pd-
(OC6X5)2(tmeda)] (tmeda ) N,N,N′,N′-tetramethylethylenediamine; X
) H, F) and [Pd(OC6H5)2(teeda)] (teeda ) N,N,N′,N′-tetraethylethyl-
Crystal Structure Determination of 2. A dark red block-shaped
crystal was glued to the tip of a glass fiber and transferred to an Enraf-
Nonius CAD4-Turbo diffractometer with rotating anode. Lattice
parameters were determined by least-squares treatment, using the setting
angles (SET4) of 25 reflections in the range 10.0° < θ < 13.7°. The
unit cell parameters were checked for the presence of higher lattice
symmetry.6 Crystal data and details on data collection and refinement
are given in Table 1. Data were collected at ambient temperature in
ω/2θ mode with scan angle ∆ω ) 0.63 + 0.35 tan θ. Intensity data
of 4667 reflections were collected in the range 1.06° < θ < 27.50°, of
which 4159 are independent. A total of 2222 reflections with intensities
above 2.5σ(I) were used in the structure analysis. Data were corrected
for Lorentz-polarization effects and for a linear decay of 3% of the
three periodically measured reference reflections (2h25h, 225, 4h42) during
11 h of X-ray exposure time. The structure was solved by automated
* To whom correspondence should be addressed.
† Debye Institute.
‡ Bijvoet Center for Biomolecular Research.
§ Address correspondence regarding the crystallography to this author.
(1) (a) Okamura, T.-A.; Ueyama, A.; Ainscough, E. W.; Brodie, A. M.;
Waters, J. M. J. Chem. Soc., Chem. Commun. 1993, 1658. (b) Huang,
J.; Dewan, J. C.; Walters, M. A. Inorg. Chim. Acta 1995, 228, 199.
(c) Huang, J.; Ostrander, R. L.; Rheingold, A. L.; Walters, M. A. Inorg.
Chem. 1995, 34, 1090.
(2) (a) Ueyama, N.; Okamura, T.-A.; Nakamura, A. J. Chem. Soc., Chem.
Commun. 1992, 1019. (b) Maelia, L. E.; Millar, M.; Koch, S. A. Inorg.
Chem. 1992, 31, 4594.
(3) (a) Ueyama, N.; Okamura, T.-A.; Nakamura, A. J. Am. Chem. Soc.
1992, 114, 8129. (b) Huang, Y.-H.; Moura, I.; Moura, J. J. G.; LeGall,
J.; Park, J.-B.; Adams, M. W. W.; Johnson, M. K. Inorg. Chem. 1993,
32, 406.
(4) (a) Ueyama, N.; Sun, W.-Y.; Nakamura, A. Inorg. Chem. 1992, 31,
4053. (b) Huang, J.; Walters, M. A. Inorg. Biochem. 1993, 51, 24.
(c) Huang, J.; Ostrander, R. L.; Rheingold, A. L.; Leung, Y.; Walters,
M. A. J. Am. Chem. Soc. 1994, 116, 6769.
(5) (a) Kapteijn, G. M.; Grove, D. M.; Smeets, W. J. J.; Spek, A. L.; van
Koten, G. Inorg. Chim. Acta 1993, 207, 131. (b) Hunter, C. A.; Lu,
X.-J.; Kapteijn, G. M.; van Koten, G. J. Chem. Soc., Faraday Trans.
1995, 91, 2009.
(6) Spek, A. L. J. Appl. Crystallogr. 1988, 21, 578.
0020-1669/96/1335-0534$12.00/0 © 1996 American Chemical Society

Notes
Inorganic Chemistry, Vol. 35, No. 2, 1996 535
Table 2. Final Coordinates and Equivalent Isotropic Thermal
Parameters of the Non-Hydrogen Atoms for 2
atom
x
y
z
Ueq,a Å2
1
1
Pd(1)
S(1)
S(2)
F(1)
F(2)
F(3)
F(4)
F(5)
F(6)
/
0.37648(4)
/
0.0367(2)
0.0449(5)
0.0574(6)
0.101(2)
0.124(2)
0.100(2)
2
4
0.28190(14) 0.36327(8)
0.56562(15) 0.38069(11) 0.36665(8)
0.29010(8)
0.1689(5)
-0.0003(5)
-0.0870(4)
-0.0093(5)
0.1580(4)
0.4990(5)
0.3219(6)
0.1947(5)
0.2424(4)
0.4043(4)
0.1714(5)
0.1259(7)
0.0397(7)
-0.0043(6)
0.0354(7)
0.1226(6)
0.4573(6)
0.4357(7)
0.3470(8)
0.2820(7)
0.3052(7)
0.3896(6)
0.6221(7)
0.6014(9)
0.7295(8)
0.4921(8)
0.2472(2)
0.2602(3)
0.3884(3)
0.5060(2)
0.1997(3)
0.0923(3)
0.0516(2)
0.1232(2)
0.0924(19)
0.0758(16)
0.49347(19) 0.2308(2)
0.5292(2)
0.6191(2)
0.5865(3)
0.4601(2)
0.3660(2)
0.3695(3)
0.3121(4)
0.3176(4)
0.3829(5)
0.4410(4)
0.4336(3)
0.4428(3)
0.5093(4)
0.5569(4)
0.5402(4)
0.4772(4)
0.4290(3)
0.2018(3)
0.2093(4)
0.1481(4)
0.1861(3)
0.31977(19) 0.0922(19)
F(7)
F(8)
F(9)
0.3756(2)
0.4925(3)
0.5544(2)
0.118(2)
0.103(2)
0.0865(17)
Figure 1. Formation of arenethiolate palladium complexes 1 and 2.
F(10)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
N(1)
C(13)
C(14)
C(15)
0.49667(19) 0.0726(16)
0.2187(3)
0.1818(4)
0.1260(4)
0.1064(3)
0.1413(4)
0.1969(3)
0.4045(3)
0.3772(3)
0.4058(4)
0.4650(4)
0.4948(3))
0.4653(3)
0.1766(3)
0.0999(4)
0.1910(4)
0.2108(3)
0.0430(19)
0.060(3)
0.072(3)
0.065(3)
0.063(3)
0.046(2)
0.0440(19)
0.055(3)
0.062(3)
0.061(3)
0.055(3)
0.048(2)
0.067(2)
0.086(3)
0.079(3)
0.064(3)
1
a Ueq ) /3 of the trace of the orthogonalized U tensor.
Patterson methods and subsequent difference Fourier techniques
(DIRDIF-92).7 Refinement on F was carried out by full-matrix least-
squares techniques (SHELX76).8 Hydrogen atoms were included in
the refinement on calculated positions (C-H ) 0.98 Å) riding on their
carrier atoms, except for the amine hydrogen which was located on a
difference Fourier map and subsequently included in the refinement.
All non-hydrogen atoms were refined with anisotropic thermal param-
eters; the hydrogen atoms were refined with isotropic thermal param-
eters of 0.076(7) Å2. Weights were introduced in the final refinement
cycles. Convergence was reached at R ) 0.047, Rw ) 0.046, w )
1/[σ2(F) + 0.000337F2], S ) 3.28, for 262 parameters. A final
difference Fourier map showed no residual density outside -0.43 and
0.48 e Å3. Positional parameters are listed in Table 2.
Figure 2. Thermal motion ellipsoid plot (ORTEP, 50% probability)
of the molecular structure of [Pd(SC6F5)4][Me2(H)NCH2CH2N(H)Me2]
(2) together with the adopted numbering scheme. Hydrogen atoms
except those of the N-H‚‚‚S units are omitted for clarity.
CH2N(H)Me2] (2) is obtained (see Figure 1). Complex 2 has
been isolated in high yield as a red, thermally stable, crystalline
solid. A solid state IR spectrum of 2 shows a broad band at
ca. 3250 cm-1, which is characteristic of the presence of
Results and Discussion
1
N-H‚‚‚S hydrogen bonding,1,2a and H NMR solution data
Reaction of the bis(aryloxy)palladium complex [Pd(OC6H5)2-
(teeda)] (teeda is the tetraethyl-substituted diamine ligand Et2-
NCH2CH2NEt2) with an excess of pentafluorothiophenol affords
the neutral bis(arenethiolate) complex [Pd(SC6F5)2(teeda)] (1).
1H NMR spectra of 1 show the NCH2CH3 protons of the diamine
ligand to be diastereotopic; i.e. the nitrogen atom has a stable
prochiral ligand array, and this means that the diamine N-donor
atoms are chelate cis-coordinated to the palladium center.
Formation of 1 is not unexpected since in previous studies we
have shown that reaction of HOC6F5 with [Pd(OC6H5)2(tmeda)]
leads to replacement of phenoxide ligands by OC6F5 groups to
form the corresponding neutral complex [Pd(OC6F5)2(tmeda)].5
However, when the bis(aryloxy)palladium complexes [Pd-
(OC6X5)2(tmeda)] (X ) H or F) containing a tetramethyl
substituted diamine ligand are reacted with HSC6F5, an unex-
pected tetrakis(arenethiolate) complex [Pd(SC6F5)4][Me2(H)NCH2-
(CD3CN) are consistent with the proposed stoichiometry. To
further characterize the N-H‚‚‚S interaction, the molecular
structure of 2 was determined by a single crystal X-ray
diffraction study (see Figure 2). This complex is found to have
a square-planar-coordinated palladium(II) center that is S-bonded
to four anionic SC6F5 groups to form a [Pd(SC6F5)4]2- dianion.
This dianion binds in a unique way to a dicationic doubly
protonated tmeda ligand, which bridges over the metal atom
by forming two N-H‚‚‚S hydrogen bonds with trans-positioned
sulfur atoms.
The most intriguing aspects of the structure of 2 lie in the
geometry and positioning of the two N-H‚‚‚SC6F5 units. In
each unit the amine hydrogen atom, which was located on a
difference Fourier map, is clearly involved in an interaction with
S (N‚‚‚S ) 3.256(6) Å), but its distances from both Pd (H‚‚‚Pd
) 3.11 Å) and the closest F atom of the C6F5 ring (H‚‚‚F(1)) )
2.72(3) Å) are not considered significant for inclusion in the
bonding description of this complex. In 2 the Pd-SH-C angle
(SH ) hydrogen-bonded sulfur atom) of 108.5(2)° compares
well with the angle of 109.0(3)° for Pt-S-C in [Pt(SC6F5)2-
(7) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garc´ıa-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF
program system. Technical report of the Crystallography Laboratory,
University of Nijmegen: The Netherlands, 1992.
(8) Sheldrick, G. M. SHELX76. Program for crystal structure determi-
nation. University of Cambridge, Cambridge, 1976.

536 Inorganic Chemistry, Vol. 35, No. 2, 1996
Notes
(PBu3)2],9 whereas the Pd-S-C angle of the C6F5 ligand in 2
that is not involved in hydrogen bonding is slightly smaller at
104.6(2)°. The arenethiolate ligands participating in hydrogen
bonding have the C6F5 ring almost orthogonal (93.2(2)°) to the
Pd-SH-C plane, representing an out-of-plane conformation for
this ring. This preference of the SH-C6F5 ring in 2 for the
out-of-plane conformation is unexpected, since the in-plane
conformation is usually found in transition metal arenethiolate
chemistry.10 In contrast, the Pd-S-C plane and the C6F5 ring
in the non-hydrogen-bonded SC6F5 anion make an angle of
50.6°, creating a situation in-between the in- and out-of-plane
conformations. The latter orientation of the C6F5 ring could
be a result of steric interactions with the methyl groups of the
protonated tmeda ligand.
In 2 the N-H‚‚‚S hydrogen bonds of 3.256(6) Å are much
shorter than those in neutral organic compounds (∼3.40 Å) but
do fall in the range encountered in inorganic model complexes
with amides (3.24-3.50 Å).1 The angle of approach of the
N-H‚‚‚S hydrogen bonds to the normal of the plane containing
the Pd-S-C atoms (i.e. angle of electrophilic approach) is
12.7°. This angle is similar to those reported for electrophiles
in close proximity to divalent organic sulfur; the most prevalent
angle (relative to the normal of the M-S-C plane) on S has
been found to be 21 ((9)°.11 The relatively small angle in 2 is
due to the fact that the two N-H‚‚‚S hydrogen bonds in this
complex originate from the same ligand, which is positioned
as a [Me2(H)NCH2CH2N(H)Me2]2+ bridge over the [Pd(SAr)4]2-
dianion. Larger angles of approach would elongate the N-H‚‚‚S
hydrogen bonds and destabilize the structure. The two N-H
vectors (N-H ) 0.89(6) Å) point toward the S atoms ( N-
H‚‚‚S ) 163(5)°) and force the tmeda unit into a specific
orientation (NCCN dihedral angle ω ) 155.5(3)°) over the metal
center. Bridging units over metal centers and N-H‚‚‚S interac-
tions like those in 2 have also been reported for the Cys-X-
Y-Cys unit (X, Y ) amino acids) in rubredoxin, and they have
been shown to be an important factor in the shift of the redox
potential of metalloproteins.4 According to the “frontier orbital”
model,12 the HOMO in the N-H‚‚‚S unit is essentially a sulfur
lone pair which has substantial p-orbital character and which
extends nearly perpendicular to the Pd-S-C plane. The other
sulfur lone pair can be considered to belong to an orbital with
predominantly sp2 character that lies in the Pd-S-C plane. This
description indicates a sulfur valence orbital hybridization
intermediate between {sp3} and {sp2 + p}.1a,2b In 2 the non-
hydrogen-bonded sulfur atom, S(2), affords a Pd-S bond length
of 2.3367(16) Å, which is slightly longer than the hydrogen-
bonded Pd-S(1) bond length of 2.3301(14) Å. This small
difference in bond length is consistent with the N-H‚‚‚S
hydrogen bond utilizing a sulfur orbital which has nearly pure
p character and which is orthogonal to, and therefore has little
influence on, the Pd-S σ-orbital.
In 2 one can expect some weakening of the Pd-S bond
through the interaction of the sulfur π-orbitals (occupied by lone
pair electrons) with occupied orbitals on the palladium center
that results in the formation of molecular orbitals with anti-
bonding character. However, this is more than counterbalanced
by the stabilizing factors mentioned above. Namely, stabiliza-
tion of the Pd-SH interaction is provided by involvement of
SH p-orbitals in N-H‚‚‚S hydrogen bonding with conjugation
with the aryl ring π-electrons (out-of-plane), whereas stabiliza-
tion of the Pd-S interaction is afforded by conjugation of S
p-electrons with those of the aryl ring (partly in-plane).
In conclusion, a subtle variation in the nature of the N-donor
dialkyl substituents (Me or Et) in tetraalkylethylenediamines
leads to a different reactivity of the corresponding palladium
bis(aryloxide) complex with HSC6F5 to afford either di- or tetra-
substituted products. The unexpected situation in 2 where a
diprotonated tmeda functions as a bridging ligand, through
formation of N-H‚‚‚S hydrogen bonds, reveals a new aspect
of tmeda chemistry in the field of N-H‚‚‚X interactions in metal
amine species. In particular, N-H‚‚‚X interactions are believed
to be important in a number of metal-complex-catalyzed
processes,13 and in a related context we have investigated the
occurrence of N-H‚‚‚Pt and N-H‚‚‚Br interactions in orga-
nometallic species.14
Acknowledgment. Shell Research B.V. is gratefully thanked
(G.M.K.) for financial support. The investigations were sup-
ported in part (A.L.S.) by the Netherlands Foundation for
Scientific Research (SON) with financial aid from the Nether-
lands Organization for Scientific Research (NWO).
Supporting Information Available: For 2, further details of the
structure determination, including listings of data collection parameters,
atomic coordinates, bond lengths and angles, and thermal parameters
(9 pages). Ordering information is given on any current masthead page.
(9) Fenn, R. H.; Segrott, G. R. J. Chem. Soc. A 1970, 2781.
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Soc. 1978, 100, 1932. (b) Coucouvanis, D.; Swenson, D.; Baenziger,
N. C.; Murphy, C.; Holah, D. G.; Sfarnas, N.; Simopoulos, A.;
Kostikas, A. J. Am. Chem. Soc. 1981, 103, 3350.
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1977, 99, 4860.
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