Rhodium Dithiocarbamate Compounds as Metalloligands: A Controlled Way for the Construction of Binuclear Complexes

Full text of DOI:10.1021/ic971053t

824
Inorg. Chem. 1998, 37, 824-829
Rhodium Dithiocarbamate Compounds as
Metalloligands: A Controlled Way for the
Construction of Binuclear Complexes
Anabel Elduque,† Cristina Finestra,† Jose´ A. Lo´pez,†
Fernando J. Lahoz,† Francisco Mercha´n,‡
Luis A. Oro,*,† and M. Teresa Pinillos§
Figure 1. Schematic representations of the different dithiocarbamate
coordinations in [Rh2{S2CNMe2}5]+ (A) and [Ru2{S2CNEt2}5]+ (B).
Departamento de Qu´ımica Inorga´nica and Departamento de
Qu´ımica Orga´nica, Instituto de Ciencia de Materiales de
Arago´n, Universidad de Zaragoza-Consejo Superior de
Investigaciones Cient´ıficas, 50009 Zaragoza, Spain, and
Departamento de Qu´ımica Inorga´nica,
Universidad de La Rioja, 26001 Logron˜o, Spain
Figure 2. Resonance structures for dithiocarbamate anions.
ReceiVed August 20, 1997
It is worth keeping in mind that each of the two sulfur atoms
of a metal-coordinated chelate dithiocarbamate ligand maintains
an additional coordination capability due to the availability of,
at least, one pair of potentially bonding electrons. This
potentiality has been contemporarily exploited in the coordina-
tion chemistry of thiolato and pyridine-2-thiolato complexes
allowing the tailored synthesis of homo- and heteronuclear
rhodium aggregates.7
We report in this paper the synthesis of mononuclear
N-methyl,N-phenyl-dithiocarbamate rhodium complexes and
their capacity to act as metalloligands in the controlled construc-
tion of binuclear dithiocarbamate-bridged species. The struc-
tural parameters of the dithiocarbamate ligand are compared
before and after binucleation from the X-ray structures of two
complexes.
Introduction
Metal dithiocarbamates are the subject of current research
activity due to their potential applications and their interesting
coordination behavior.1 There are some examples of dithio-
carbamate binuclear compounds, but most complexes are
mononuclear in solution, although in some cases crystallize in
polymeric forms.2 The early preparation of mononuclear
rhodium(I and III) dithiocarbamates was reported by Cotton and
McCleverty,3 while an interesting example of a binuclear
complex is the cation [RhIII2{S2CN(Me)2}5]+, in which the two
rhodium atoms achieve an octahedral environment as a conse-
quence of the additional coordination of two bridging sulfur
atoms from two different dithiocarbamate groups (Figure 1A).4
Meanwhile, in the related [RuIII2{S2CN(Et)2}5]+ cation, one of
the dithiocarbamate groups acts as an exo-bridging ligand across
the Ru-Ru bond (Figure 1B).5 Thus, although transition metal
complexes containing dithiocarbamate groups as bridging or,
most frequently, as chelating ligands are well-known,6 the
chemical behavior of dithiocarbamate metal complexes as
metalloligands remains essentially unexplored. Only very
recently, the neutral rhodium and iridium(III) tris(dithiocar-
bamate) complexes have been described as metalloligands
toward the silver cation Ag+, forming cationic complexes of
the type [Ag{M(S2CNR2)3}2]BF4 (M ) Rh, Ir).1g
Results and Discussion
The mononuclear complexes [Rh{S2CN(Me)(Ph)}(diolefin)]
(diolefin ) 1,5-cyclooctadiene (COD), 1, and norbornadiene
(NBD), 2) could be easily prepared by reaction of the binuclear
rhodium(I) complexes [Rh2(µ-Cl)2(diolefin)2] (diolefin ) COD,
NBD) and HNEt3{S2CN(Me)(Ph)} in a 1:2 molar ratio.
Compounds 1 and 2 have been isolated as yellow or orange
1
microcrystalline solids. The H NMR spectrum of complex 1
shows for the cyclooctadiene ligands four broad signals at δ
4.59 and 4.26 ppm and at δ 2.21 and 1.61 ppm, integrating by
2:2:4:4, respectively. The 13C NMR spectrum exhibits two
doublets (δ 81.91, 80.60 ppm, JRhC 11 Hz) and two singlets (δ
31.21, 30.02 ppm) corresponding to the olefinic and aliphatic
carbon atoms, respectively, of the cyclooctadiene ligand. At δ
212.91 ppm a singlet from the tertiary carbon of the dithiocar-
bamate ligand also appears. These data indicate that the
dithiocarbamate ligand is chelating the rhodium center with a
significant contribution of the resonance form III (Figure 2), in
such a way that the mononuclear molecule presents inequiva-
lence of the olefinic and also of the aliphatic cyclooctadiene
atoms, adopting a Cs symmetry. Additionally, the presence in
the IR spectrum of a medium band at 1590 cm-1, corresponding
† Departamento de Qu´ımica Inorga´nica, Universidad de Zaragoza.
‡ Departamento de Qu´ımica Orga´nica, Universidad de Zaragoza.
§ Departamento de Qu´ımica Inorga´nica, Universidad de La Rioja.
(1) (a) Coucouvanis, D. Prog. Inorg. Chem. 1979, 26, 301. (b) Bond, A.
M.; Martin, R. L. Coord. Chem. ReV. 1984, 54, 23. (c) Heras, J. V.;
Pinilla, E.; Ovejero, P. J. Organomet. Chem. 1984, 269, 277. (d) Cano,
M.; Campo, J. A.; Pe´rez-Garc´ıa, V.; Gutierrez-Puebla, E. J. Orga-
nomet. Chem. 1990, 396, 49. (e) Bardaj´ı, M.; Laguna, A.; Laguna,
M.; Mercha´n, F. Inorg. Chim. Acta 1994, 215, 215. (f) Price, D. J.;
Wali, M. A.; Bruce, D. W. Polyhedron 1997, 16, 315. (g) Bond, A.
M.; Colton, R.; Gatehouse, B. M.; Mah, Y. A. Inorg. Chim. Acta 1997,
260, 61.
(2) Bond, A. M.; Colton, R.; Mah, Y. A.; Traeger J. C. Inorg. Chem.
1994, 33, 2548 and references therein. Exarchos, G.; Robinson, S. D.
Polyhedron 1997, 16, 1573.
(3) Cotton, F. A.; McCleverty, J. A. Inorg. Chem. 1964, 3, 1398.
(4) Hendrickson, A. R.; Martin, R. L.; Taylor, D. Aust. J. Chem. 1976,
29, 269.
(7) Ciriano, M. A.; Pe´rez-Torrente, J.; Viguri, F.; Lahoz, F. J.; Oro, L.
A.; Tiripicchio, A.; Tiripicchio-Camellini, M. J. Chem. Soc., Dalton
Trans. 1990, 1493. Ciriano, M. A.; Pe´rez-Torrente, J.; Oro, L. A.;
Tiripicchio, A.; Tiripicchio-Camellini, M. J. Chem. Soc., Dalton Trans.
1991, 255. Ciriano, M. A.; Pe´rez-Torrente, J.; Lahoz, F. J.; Oro, L.
A. J. Chem. Soc., Dalton Trans. 1992, 1831.
(5) Mattson, B. M.; Heiman, J. R.; Pignolet, L. H. Inorg. Chem. 1976,
15, 564.
(6) Wilkinson, G., Guillard, R. D., McCleverty, J. A., Eds. ComprehensiVe
Coordination Chemistry; Pergamon: Oxford, U.K., 1987; Vol. 2, p
585.
S0020-1669(97)01053-7 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/31/1998

Notes
Inorganic Chemistry, Vol. 37, No. 4, 1998 825
Table 1. Selected Bond Distances (Å) and Angles (deg) for 3a
Rh‚‚‚Rh′
Rh-S(1)
Rh-S(2)
Rh-C(9)
Rh-C(10)
3.2528(7)
2.3629(14)
2.3727(14)
1.868(5)
S(1)-C(1)
S(2)-C(1)
N-C(1)
1.715(4)
1.718(5)
1.317(6)
1.469(6)
1.450(5)
N-C(2)
1.883(6)
N-C(3)
S(1)-Rh-S(2)
74.35(4)
96.28(16)
170.47(15)
170.61(16)
97.26(15)
92.0(2)
S(1)-C(1)-S(2)
S(1)-C(1)-N
S(2)-C(1)-N
C(1)-N-C(2)
C(1)-N-C(3)
C(2)-N-C(3)
Rh-C(9)-O(1)
Rh-C(10)-O(2)
113.0(3)
122.6(3)
124.4(3)
122.1(4)
121.5(4)
116.3(4)
178.8(4)
177.4(5)
S(1)-Rh-C(9)
S(1)-Rh-C(10)
S(2)-Rh-C(9)
S(2)-Rh-C(10)
C(9)-Rh-C(10)
Rh-S(1)-C(1)
Rh-S(2)-C(1)
86.50(17)
86.12(15)
Figure 3. Molecular structure of 3 together with the atomic numbering
scheme used. The relative disposition of three contiguous stacked
molecules is also shown.
a Primed atoms are is related to the unprimed ones by the following
1
symmetry transformation: 1/2 + x, /2 - y, z.
Scheme 1
to the ν(CdN) stretching frequency, supports the existence of
a partially multiple C-N bond.3,5,6 The spectroscopic data
obtained for compound 2 also suggest a Cs symmetry for this
molecule.
Bubbling carbon monoxide through dichloromethane solutions
of complexes 1 or 2 leads to the displacement of the coordinated
diolefins causing an instantaneous change of color from yellow
(1) or orange (2) to dark yellow, and after addition of diethyl
ether, precipitation of dark green microcrystals formulated as
[Rh{S2CN(Me)(Ph)}(CO)2] (3) took place.
The spectroscopic data measured for 3 again suggest the
coordination of the dithiocarbamate as chelate. The planarity
of the dithiocarbamate ligand together with the feeble steric
demand of the carbonyl groups and the square-planar coordina-
tion of the metal center confer the metal coordination sphere of
this molecule a reasonable planarity suitable for the formation
of stacked arrangements with potential intermetallic interac-
tions.8-11 This proposal is supported by the complex solid-
state IR spectrum exhibited by 3 and also by the dark color of
the isolated solid.12
the most probable for this compound although other molecular
arrangements could not be excluded.
Preparation of Binuclear Species. An effective synthetical
way to prepare species of higher nuclearity consists of the
incorporation of metal fragments into metalloligands.7,16 In this
context we have explored the ability of the previously described
mononuclear rhodium(I) dithiocarbamate complexes to coor-
dinate an additional metal fragment giving rise to binuclear
species. These mononuclear complexes are expected to behave
as metalloligands due to the potentiality of the sulfur atoms of
the dithiocarbamate group to act as η2-bridging centers.
With this idea in mind, we have studied the reactivity of the
mononuclear compounds [Rh{S2CN(Me)(Ph)}L2] (L2 ) COD
(1), (CO)2 (3)) toward the cationic solvate rhodium(I) species
[Rh(COD)(acetone)n]+. These reactions give rise to binuclear
complexes of formula [Rh2{µ-S2CN(Me)(Ph)}(COD)L2]BF4 (L2
) COD (5), (CO)2 (6)) (Scheme 2). Their formulation as
binuclear complexes is consistent with their mass spectrometry
measurements and has been definitively confirmed for com-
pound 5 by X-ray diffraction.
The formation of a columnar stacking with intermetallic
interactions for complex 3 has been definitively determined by
an X-ray diffraction study (Figure 3). The molecules are
forming almost linear metal chains (Rh‚‚‚Rh‚‚‚Rh angle of
179.47(1)°) with equal Rh‚‚‚Rh distances of 3.2528(7) Å (Table
1). This distance is similar to those reported in other stacked
rhodium(I) square-planar complexes such as [Rh(C2O4)(CO)2]-,
3.243(1) Å,10 and [Rh(acac)(CO)2], 3.253 and 3.271 Å.11 Along
the stacking direction each planar molecule is rotated by 131.4-
(1)°, in such a way that one carbonyl group is situated bisecting
both dithiocarbamate groups of the neighboring molecules. This
disposition probably is adopted to minimize the interligand
repulsion with respect to an eclipsed disposition as it has been
suggested for related d8 stacked complexes.8
Interestingly, when carbon monoxide is bubbled through a
diethyl ether suspension of [Rh{S2CN(Me)(Ph)}(NBD)] (2), a
dimerization process occurs with formation of the compound
formulated as [Rh2{µ-S2CN(Me)(Ph)}2(CO)2(NBD)] (4) (Scheme
1). The expected square-planar coordination for the metal
centers in rhodium(I) complexes led us to assume a µ-η1(S),η1-
(S′) coordination mode13-15 for the dithiocarbamate ligands as
The cationic complex in 5 is formed by two “Rh(COD)”
fragments linked through the dithiocarbamate anion acting as a
bridging η,2η2(S,S′) ligand. Each metal is in a square-planar
(12) Bonati, F.; Oro, L. A.; Pinillos, M. T.; Apreda, M. C.; Foces-Foces,
C.; Cano, F. H. J. Organomet. Chem. 1989, 369, 253.
(13) Bardaj´ı, M.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Laguna, M.
Organometallics 1994, 13, 3415.
(14) Lei, X.; Huang, Z.; Liu, Q.; Hong, M.; Liu, H. Inorg. Chem. 1989,
28, 4302.
(15) Heinrich, D. D.; Wang, J.; Fackler, J. P. Acta Crystallogr., C 1990,
46, 1444.
(16) Elduque, A.; Navarro, N.; Oro, L. A.; Pinillos, M. T. Anal. Qu´ım.
Int. Ed. 1996, 92, 349. Tejel, C.; Villarroya, B. E.; Ciriano, M. A.;
Oro, L. A.; Lanfranchi, M.; Tiripicchio A.; Tiripicchio-Camellini, M.
Inorg. Chem. 1996, 35, 1782.
(8) Alvarez, S.; Aullo´n, G. Chem. Eur. J. 1997, 3, 655.
(9) Miller, J. S.; Epstein, A. J. Prog. Inorg. Chem. 1976, 20, 1.
(10) Real, J.; Bayo´n, J. C.; Lahoz, F. J.; Lo´pez, J. A. J. Chem. Soc., Chem.
Commun. 1989, 1889.
(11) Bailey, N. A.; Coates, E.; Robertson, G. B.; Bonati, F.; Ugo, R. J.
Chem. Soc., Chem. Commun. 1967, 1041. Huq, S.; Skapski, A. C.
Cryst. Mol. Struct. 1974, 4, 411.

826 Inorganic Chemistry, Vol. 37, No. 4, 1998
Notes
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 5
Rh(1)‚‚‚Rh(2)
Rh(1)-S(1)
Rh(1)-S(2)
Rh(1)-C(9)
Rh(1)-C(10)
Rh(1)-C(13)
Rh(1)-C(14)
S(1)-C(1)
2.8948(10)
2.3679(18)
2.3686(18)
2.158(8)
2.150(7)
2.171(7)
2.145(7)
1.741(7)
1.397(13)
1.381(11)
1.314(8)
1.452(9)
Rh(2)-S(1)
Rh(2)-S(2)
Rh(2)-C(17)
Rh(2)-C(18)
Rh(2)-C(21)
Rh(2)-C(22)
S(2)-C(1)
C(17)-C(18)
C(21)-C(22)
N-C(2)
2.387(2)
2.4050(19)
2.135(7)
2.141(8)
2.144(7)
2.146(7)
1.756(7)
1.382(12)
1.367(10)
1.478(9)
C(9)-C(10)
C(13)-C(14)
N-C(1)
N-C(3)
S(1)-Rh(1)-S(2)
73.93(6) S(1)-Rh(2)-S(2)
72.92(6)
S(1)-Rh(1)-M(1)a 170.9(3)
S(1)-Rh(2)-M(3)a 173.3(3)
S(1)-Rh(1)-M(2)a
S(2)-Rh(1)-M(1)a
99.4(3)
98.8(3)
S(1)-Rh(2)-M(4)a
98.3(3)
S(2)-Rh(2)-M(3)a 100.9(3)
S(2)-Rh(1)-M(2)a 171.3(3)
S(2)-Rh(2)-M(4)a 168.7(3)
Figure 4. Molecular drawing of the binuclear cationic complex of 5
showing the labeling scheme.
M(1)-Rh(1)-M(2)a
Rh(1)-S(1)-Rh(2)
Rh(1)-S(1)-C(1)
Rh(2)-S(1)-C(1)
S(1)-C(1)-S(2)
S(1)-C(1)-N
87.3(4)
M(3)-Rh(2)-M(4)a
87.5(4)
74.66(5)
86.2(2)
75.00(6) Rh(2)-S(2)-Rh(1)
86.6(2)
68.8(2)
109.1(4)
125.8(5)
125.1(5)
Rh(1)-S(2)-C(1)
Rh(2)-S(2)-C(1)
C(1)-N-C(2)
Scheme 2
68.1(2)
119.8(6)
120.9(6)
118.6(6)
C(1)-N-C(3)
S(2)-C(1)-N
C(2)-N-C(3)
a M(1), M(2), M(3), and M(4) represent the midpoints of the olefinic
bonds C(9)-C(10), C(13)-C(14), C(17)-C(18), and C(21)-C(22),
respectively.
This conformation also causes a relatively short Rh(2)-C(1)
distance (2.389(7) Å) which led us to think about the possibility
of a µ-η3(S,C,S′) coordination mode of the dithiocarbamate
ligand, similar to that previously observed for the related
S2CPR3 ligands.20
The distances Rh(1)-S (2.3679 and 2.3686(18) Å) are equal
to those observed for compound 3 (2.3629 and 2.3727(14) Å)
and are very similar to those previously described for the
binuclear rhodium(III) complex [Rh2(µ-dppe)(S2CNEt2)2(C5-
Me5)2]2+, 2.3493 and 2.3638(18) Å, where the dithiocarbamate
anions are coordinated as chelates.21 However, the Rh(2)-S
distances are slightly longer (2.387(2) and 2.4050(19) Å),
probably originated by the perpendicular coordination of the
dithiocarbamate ligand.
The S-C bond lengths are also correlated with the coordina-
tion mode of the sulfur atoms. Thus, the distances presented
by the mononuclear compound 3 are slightly shorter (1.715(4)
and 1.718(5) Å) than those observed in the binuclear complex
5 (1.741(7) and 1.756(7) Å). Probably, the multiple S-C bond
contribution present in the mononuclear compound 3 (Figure
2, forms I and II) has to decrease, or even disappear, in the
binuclear compound 5, due to the coordination of the S atoms
to the second metal center through the same p-orbitals previously
involved in 3 in the dithiocarbamate S-C(N)-S π-bonding
system.
environment, coordinated to a cyclooctadiene ligand and to both
sulfur atoms of the dithiocarbamate bridging group (Figure 4).
Although examples of an η1(S),η1(S′)13,14,17 and also of an η1-
(S),η2(S,S′)13,18 coordination modes of the dithiocarbamate
groups in transition metal complexes have been described,
complex 5 is the first dithiocarbamate compound crystallo-
graphically characterized exhibiting a µ-η,2η2(S,S′) coordination.
In this complex both sulfur atoms are bonded to both metal
centers furnishing formally eight electrons to the binuclear entity.
The most intriguing feature of this molecular structure is the
asymmetrical coordination of the bridging ligand, showing the
C(sp2) plane of the dithiocarbamate ligand nearly coplanar with
the coordination plane of Rh(1) (dihedral angle 160.4(3)°) but
almost perpendicular to that of the second rhodium atom (101.2-
(3)°). This structural disposition brings about the intermetallic
distance to be very short (2.8948(10) Å; see Table 2), in the
range described for short intermetallic bonding interactions that,
in some cases, have been confirmed by theoretical calculations.19
Expecting that some insight about the possible interaction
between the tertiary carbon of the dithiocarbamate ligand and
1
one rhodium center could be obtained, we performed H and
13C{1H} NMR spectra measurements of complex 5, decreasing
the temperature to -60 °C. No changes in the spectra were
observed from room temperature to -60 °C. All the 13C{1H}
NMR spectra of complex 5 show the signal of the central carbon
(17) Bino, A.; Cotton, F. A.; Dori, Z.; Sekutowski, J. C. Inorg. Chem.
1978, 17, 2946. Iwasaki, H. Acta Crystallogr. 1973, B29, 2115.
(18) Goel, A. B.; Goel, S.; VanDerveer, D.; Brinkley, C. G. Inorg. Chim.
Acta 1982, 64, L173. Pignolet, L. H.; Wheeler, S. H. Inorg. Chem.
1980, 19, 935. Ileperuma, O. A.; Felthaur, R. D. Inorg. Chem. 1975,
14, 3042. Landgrafe, C.; Sheldrick, W. S. J. Chem. Soc., Dalton Trans.
1994, 1885.
(19) Masdeu, A. M.; Ruiz, A.; Castillo´n, S.; Claver, C.; Hitchcock, P. B.;
Chaloner, P. A.; Bo´, C.; Poblet, J. P.; Sarasa, P. J. Chem. Soc., Dalton
Trans 1993, 2689.
(20) Galindo, A.; Gutierrez-Puebla, E.; Monge, A.; Pastor, A.; Pizzano,
A.; Ruiz, C.; Sa´nchez, L.; Carmona, E. Inorg. Chem. 1993, 32, 5569.
Miguel, D.; Pe´rez- Mart´ınez, J. A.; Riera, V. Organometallics 1993,
12, 1394. Lo´pez, E. M.; Miguel, D.; Pe´rez-Mart´ınez, J. A.; Riera, V.;
Garc´ıa-Granda, S. J. Organomet. Chem. 1995, 492, 23.
(21) Blake, A. J.; Fotheringham, J. D.; Stephenson, T. A.; Hambling, S.
G.; Sawyer, L. Acta Crystallogr. 1991, C47, 648.

Notes
Inorganic Chemistry, Vol. 37, No. 4, 1998 827
of the S2CNR2 ligand as a singlet at 178.89 ppm excluding any
rhodium-carbon bonding interaction. This signal appears at a
δ value similar to that of compound 1 which exhibits a chelating
S,S′ coordination mode for the dithiocarbamate ligand, and it
is far from the higher field resonance detected in related
complexes showing an η3(S,C,S′) coordination.20 The cyclo-
octadiene carbon resonances appear as four doublets (JRhC 11
Hz) for the olefinic carbon atoms and as four singlets for the
aliphatic carbon atoms, according with a Cs symmetry for
compound 5. In addition, the 1H NMR spectrum of 5, and those
obtained for 6 (1H and 13C), also agree with this proposal.
In consequence, it seems reasonable to propose that in
solution, in the NMR time scale, the dithiocarbamate ligand in
5 and 6 is symmetrically bonding to the two metal centers. This
can be due to a rapid oscillation, even at -60 °C, of the
dithiocarbamate CNR2 moiety at both sides of the ideal plane
defined by the two S atoms and the middle point of the Rh-
Rh vector, as it has been observed in binuclear alkynyl
complexes.22 Another possibility to explain this behavior could
consider a static symmetrical bridging coordination as the most
stable situation for this type of bonding mode, despite the
observed asymmetric solid-state structure.
Taking into account the above results, it seems that the Rh-
(2)-C(1) distance obtained in the solid state, although relatively
short, is not representative of an η3(S,C,S′) coordination mode.
At this point, two interrelated questions arise: If there is not
interaction between the central carbon and the rhodium atom
Rh(2), why is the solid-state structure asymmetrical, and what
type of movementsif existentsis responsible for the Cs
symmetry observed in solution?
We have performed some theoretical calculations with a
simplified model [Rh2{µ-S2CN(Me)2}(CO)4]+, built up with the
bond lengths and angles deduced from both X-ray determina-
tions. Using the extended Hu¨ckel approach,23 the Walsh
diagram for the oscillation movement of the dithiocarbamate
ligand around the S-S axis has been evaluated, and we have
found the symmetrical bridging situation to be the most stable.
Without modifying the bridging ligand geometry or that of both
“Rh(CO)2” units, we have calculated the energy of the different
conformations obtained by rotating any of the three fragments
around the S-S axis and, in consequence, varying the dihedral
angles between the dithiocarbamate ligand and each Rh(CO)2
groups (R and â) (Figure 5). The calculation performed
evidences a particular flat potential energy well indicating a
relative conformational freedom for the hypothetical movement
analyzed. The shape of this potential energy well (Figure 5)
shows any conformational motion of L (CNMePh) varying R,
and consequently â, along the line a (R + â ) 250°, 105 e R,
â e 145°) to be nearly isoenergetical; however any conforma-
tional change perpendicular to line a (that is, implying a
modification of the dihedral angle between the two metal
coordination planes and consequently the intermetallic separa-
tion) results energetically unfavorable. If the oscillation of L
around the S-S axis is not energetically demanding under the
limits described above, this movement should be taking place
in solution even at low temperature and would confer the
molecule an apparently static Cs symmetry. In the solid state
the packing forces could presumably bring the conformation
of the molecule slightly out of the potential energy well to the
Figure 5. Potential energy map calculated from the model [Rh2{µ-
S2CN(Me)2}(CO)4]+ for conformers differing in the relative dihedral
angles (R and â) between the dithiocarbamate CNMe2 moiety and the
two metal coordination planes. S represents the position of the solid-
state structure. Isoenergetic contours are drawn at 0.1 eV intervals.
asymmetric disposition determined. In fact, the conformation
found in the solid state (R ) 160.4(3), â ) 101.2(3)°) is only
ca. 8 kJ mol-1 higher in energy than the minimun calculated R
) â ≈ 125°.
Another dynamical alternative to generate the solution Cs
symmetry observed for 5 and 6 could imply the rotation of the
phenyl and methyl groups around the CN bond of the dithio-
carbamate ligand. We have also evaluated the Walsh diagrams
for this rotation using the same model and approach and starting
from both conformations: the symmetrical (proposed to exist
in solution) and the asymmetrical (found in the solid state). The
energy activation barrier calculated for this rotation is in both
cases approximately 42-63 kJ mol-1; most probably, this barrier
is high enough to avoid the movement to take place at room
temperature and, consequently, to be observed in the NMR
experiments.
In conclusion, the present paper has shown the ability of
mononuclear rhodium dithiocarbamate compounds to act as
metalloligands, allowing the construction of binuclear complexes
in a controlled way. In addition, the X-ray studies have revealed
a novel bridging η2,η2(S,S′) coordination mode for the dithio-
carbamate ligand and a columnar stacking of the mononuclear
complex [Rh{S2CN(Me)(Ph)}(CO)2] assembled with clear
Rh‚‚‚Rh intermolecular interactions.
Experimental Section
All reactions were carried out under nitrogen using standard Schlenk
techniques and were monitored by solution IR spectroscopy (carbonyl
stretching region). [Rh2(µ-Cl)2(COD)2]24 and [Rh2(µ-Cl)2(NBD)2]25
were prepared according to literature methods. Solvents were purified
according to standard procedures and distilled under nitrogen prior to
use. All other reagents were purchased and used without further
purification. Solution and Nujol mull infrared spectra were recorded
on a Nicolet Magna 550 spectrometer. NMR spectra were recorded
on a Varian UNITY, a Varian Gemini 2000, or a Bruker ARX 300
MHz spectrometer. 1H and 13C chemical shifts were measured relative
to partially deuterated solvent peaks but are reported in ppm relative
(22) Esteruelas, M. A.; Lahuerta, O.; Modrego, J.; Nurnberg, O.; Oro, L.
A.; Rodr´ıguez, L.; Sola, E.; Werner, H. Organometallics 1993, 12,
266 and references therein.
(23) Hoffmann, R. J. Chem. Phys. 1963, 39, 1397. Hoffmann, R.;
Lipscomb, W. N. Ibid. 1962, 36, 2179; 1962, 37, 2872.
(24) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1979, 19, 218.
(25) Abel, E. W.; Bermeti, M. A.; Wilkinson, G. J. Chem. Soc. 1958,
3178.

828 Inorganic Chemistry, Vol. 37, No. 4, 1998
Notes
Table 3. Crystallographic Data for [Rh{S2CN(Me)(Ph)}(CO)2] (3)
to Me4Si. 31P{1H} NMR spectra were measured relative to H3PO4
(85%). Elemental analyses were carried out with a Perkin-Elmer 240B
microanalyzer. Fast atom bombardment (FAB) mass spectra were
recorded on a AUTOSPEC V6 spectrometer.
and [Rh2{µ-S2CN(Me)(Ph)}(COD)2]BF4 (5)
3
5
chem formula
fw
temp, K
space group
a, Å
b, Å
c, Å
C10H8NO2RhS2
341.20
C24H32BF4NRh2S2
691.26
Preparation of HNEt3{S2CN(Me)(Ph)}. A mixture of NEt3 (10
g, 0.130 mmol) and HNMePh (10 g, 0.093 mmol) in diethyl ether (15
mL) was added dropwise into a CS2 (30 g) solution leading to the
formation of a yellow precipitate. The solid was isolated by filtration,
washed with cold diethyl ether, and vacuum-dried (12 g, 34%). Anal.
Calcd for C14H24N2S2: C, 59,31; H, 8.17; N, 9.88; S, 22.61. Found:
C, 59,33; H, 8.55; N, 9.86; S, 21.62. IR (cm-1, Nujol mulls): 1590
[υ(CN)]. 1H NMR (CDCl3): δ 7.26 (m, 5H, Ph), 3.79 (s, 3H, Me),
3.19 (q, 6H, N(CH2CH3)3, JHH 7.4), 1.32 (t, 9H, N(CH2CH3)3, JHH 7.4).
Preparation of [Rh{S2CN(Me)(Ph)}(COD)] (1). A solution of
HNEt3{S2NC(Me)(Ph)} (460 mg, 1.62 mmol) in dichloromethane (10
mL) was added to a solution of [Rh2(µ-Cl)2(COD)2] (400 mg, 0.81
mmol) in acetone (15 mL). The initial orange solution transformed
immediately to a yellow suspension which was stirred for 30 min.
Evaporation of the solvents to dryness and addition of methanol (15
mL) allowed the complete precipitation of a yellow solid which was
filtered out, washed with cold methanol, and vacuum-dried (575 mg,
90%). Anal. Calcd for C16H20NRhS2: C, 48.85; H, 5.12; N, 3.56; S,
16.30. Found: C, 48.86; H, 5.19; N, 3.65; S, 16.16. FAB (m/z): 393
(calcd for C16H20NRhS2: 393.367). IR (cm-1, Nujol mulls): 1590
[υ(CN)]. 1H NMR (CDCl3): δ 6.95 (m, 5H, Ph), 4.59 (s, 2H, CH),
COD), 4.26 (s, 2H, CHd, COD), 3.08 (s, 3H, Me), 2.21 (s, 4H, CH2,
COD), 1.61 (s, 4H, CH2, COD). 13C NMR (CDCl3): δ 212.91 (s,
NCS2), 142.21 (s, Ph), 129,45 (s, Ph), 128.60 (s, Ph), 126.32 (s, Ph),
81.91 (d, CHd, COD, JRhC 11), 80.60 (d, CH), COD, JRhC 11), 40.70
(s, Me), 31.21 (s, CH2, COD), 30.02 (s, CH2, COD).
233.0(2)
Pna21 (No. 33)
6.5055(12)
17.153(4)
10.8222(13)
90
1207.7(4)
4
1.877
1.742
0.0241
0.0532
1.035
283.0(2)
P21/c (No. 14)
13.086(2)
14.048(3)
14.533(4)
105.933(18)
2569.0(10)
4
1.787
1.490
0.0462
0.1227
â, deg
V, Å3
Z
F
calcd, g cm-3
µ(Mo KR), mm-1
R(F) [F2 > 2σ(F2)]a
wR(F2) (all data)b
S (all data)c
0.996
a R(F) ) Σ(|Fo| - |Fc|)/Σ|Fo|, for 1733 and 3205 observed
2
2
reflections. b wR(F2) ) (Σ[w(Fo2 - Fc2)2]/Σ[w(Fo )2])1/2 c S ) [Σ[w(Fo
.
- Fc2)2]/(n - p)]1/2; n ) number of reflections, p ) number of
parameters.
[Rh2{µ-S2CN(Me)(Ph)}(COD)2]BF4 (5). Addition of a solution of
[Rh(COD)(acetone)n]+ (0.40 mmol) (prepared by reaction of AgBF4
(77.87 mg, 0.4 mmol) and [Rh2(µ-Cl)2(COD)2] (98.61 mg, 0.20 mmol)
in acetone (10 mL)) to a solution of [Rh{S2CN(Me)(Ph)}(COD)] (157
mg, 0.40 mmol) also in acetone (10 mL) caused immediately the
formation of an orange solution which was stirred for 15 min.
Evaporation of the solvent to ca. 1 mL and addition of diethyl ether (5
mL) allowed the precipitation of a red-orange solid, which was filtered
out, washed with diethyl ether, and vacuum-dried (202 mg, 73%). Anal.
Calcd for C24H32NBF4Rh2S2: C, 41.70; H, 4.66; N, 2.02; S, 9.27.
Found: C, 41.60; H, 4.71; N, 1.89; S, 9.20. FAB (m/z): 604 (calcd
for C24H32NRh2S2 +: 604.456). 1H NMR (CDCl3): δ 6.83 (m, 5H,
Ph), 4.97 (s, 2H, CHd, COD), 4.84 (s, 2H, CHd, COD), 4.73 (s, 2H,
CHd, COD), 4.69 (s, 2H, CHd, COD), 3.71 (s, 3H, Me), 2.46 (m,
8H, CH2, COD), 2.10 (m, 8H, CH2, COD). 13C NMR (CDCl3): δ
178.89 (s, NCS2), 141.61 (s, Ph), 130.82 (s, Ph), 130.35 (s, Ph), 124.42
(s, Ph), 85.47 (d, CHd, COD, JRhC 11), 84.90 (d, CHd, COD, JRhC
11), 84.62 (d, CHd, COD, JRhC 11), 83.98 (d, CHd, COD, JRhC 11),
45.75 (s, Me), 31.59 (s, CH2, COD), 31.39 (s, CH2, COD), 30.76 (s,
CH2, COD), 29.18 (s, CH2, COD).
[Rh2{µ-S2CN(Me)(Ph)}(COD)(CO)2]BF4 (6). A solution of [Rh-
(COD) (acetone)n]+ (0.44 mmol) (prepared by reaction of AgBF4 (85.65
mg, 0.44 mmol) and [Rh2(µ-Cl)2(COD)2] (108.47 mg, 0.22 mmol) in
acetone (10 mL)) was added dropwise to a solution of [Rh{S2CN(Me)-
(Ph)}(CO)2] (150.13 mg, 0.44 mmol) also in acetone (10 mL). After
10 min of stirring the solution became darker. Evaporation of the
solvent and addition of diethyl ether led a dark blue solid, which was
filtered out, washed with diethyl ether, and vacuum-dried (104 mg,
75%). Anal. Calcd for C18H20NBF4O2Rh2S2: C, 33.82; H, 3.15; N,
2.19; S, 10.03. Found: C, 34.00; H, 2.69; N, 2.23; S, 9.77. FAB
(m/z): 552 (calcd for C18H20NO2Rh2S2+: 552.294). IR (cm-1, CH2-
Cl2): 2004 and 2068 [υ(CO)]. 1H NMR (CDCl3): δ 7.39 (m, 5H,
Ph), 4.99 (s, 1H, CHd, COD), 4.84 (s, 1H, CHd, COD), 4.74 (s, 1H,
CHd, COD), 4.63 (s, 1H, CHd, COD), 3.72 (s, 3H, Me), 2.57 (m,
4H, CH2, COD), 2.13 (m, 4H, CH2, COD).
Preparation of [Rh{S2CN(Me)(Ph)}(NBD)] (2). Complex 2 was
prepared by the same method described for complex 1 starting from
HNEt3{S2NC(Me)(Ph)} (370 mg, 1.30 mmol) and [Rh2(µ-Cl)2(NBD)2]
(300 mg, 0.65 mmol). The complex was isolated as an orange solid
(382 mg, 78%). Anal. Calcd for C15H16NRhS2: C, 47.74; H, 4.27;
N, 3.71; S, 16.99. Found: C, 47.57; H, 3.94; N, 4.21; S, 16.40. FAB
(m/z): 377 (calcd for C15H16NRhS2: 377.325). IR (cm-1, Nujol
mulls): 1590 [υ(CN)]. 1H NMR (CDCl3): δ 7.00 (m, 5H, Ph), 3.88
(m, 4H, CHd, NBD), 3.40 (b, 2H, CH, NBD), 3.13 (s, 3H, Me), 1.68
(m, 2H, CH2, NBD).
Preparation of [Rh{S2CN(Me)(Ph)}(CO)2] (3). Method 1. Car-
bon monoxide was bubbled through a solution of [Rh{S2CN(Me)(Ph)}-
(COD)] (500 mg, 1.46 mmol) in dichloromethane (20 mL), during 30
min, to give first a dark yellow solution and finally a dark green
suspension. Concentration of the solvent to ca. 1 mL and addition of
diethyl ether (4 mL) allowed the complete precipitation of a dark green
solid, which was separated by filtration, washed with cold diethyl ether,
and vacuum-dried (310 mg, 71%). Anal. Calcd for C10H8NO2RhS2:
C, 35.20; H, 2.36; N, 4.10, S, 18.79. Found: C, 35.90; H, 2.82; N,
3.94; S, 18.67. FAB (m/z): 341 (calcd for C10H8NO2RhS2: 341.204).
IR (cm-1, Nujol mulls): 1989, 1995, 2043 and 2054 [υ(CO)]. IR (cm-1
,
CH2Cl2): 1990 and 2050 [υ(CO)]. 1H NMR (CDCl3): δ 7.37 (m, 5H,
Ph), 3.66 (s, 3H, Me).
Method 2. Through a solution of [Rh{S2CN(Me)(Ph)}(NBD)] (300
mg, 0.79 mmol) in dichloromethane (20 mL), carbon monoxide was
bubbled during 45 min. The initial yellow solution transformed to a
dark yellow solution and finally to a green suspension. Evaporation
of the solvent and addition of diethyl ether (5 mL) gave a dark green
solid, which was filtered and vacuum-dried (151 mg, 56%).
[Rh2{µ-S2CN(Me)(Ph)}2(CO)2(NBD)] (4). Carbon monoxide was
bubbled through a suspension of [Rh{S2CN(Me)(Ph)}(NBD)] (300 mg,
0.79 mmol) in diethyl ether (20 mL) during 20 min. Hexane (20 mL)
was added to the resulting dark suspension which was kept in CO
atmosphere for 2 days at 5 °C. The resulting orange-brown solid was
separated by filtration, washed with hexane, and vacuum-dried (233
mg, 44%). Anal. Calcd for C25H24N2O2Rh2S4: C, 41.79; H, 3.36; N,
3.89; S, 17.85. Found: C, 42.26; H, 2.90; N, 3.23; S, 17.70. FAB
(m/z): 718 (calcd for C25H24N2O2Rh2S4: 718.529). IR (cm-1, CH2-
Cl2): 2060 and 1995 [υ(CO)], 1590 [υ(CN)]. 1H NMR (C6D6): δ 7.30
(m, 10H, Ph), 6.05 (m, 4H, CHd, NBD), 4.23 (b, 2H, CH, NBD),
3.41 (b, 6H, Me), 1.49 (b, 2H, CH2, NBD).
X-ray Structural Analyses of Complexes [Rh{S2CN(Me)(Ph)}-
(CO)2] (3) and [Rh2{µ-S2CN(Me)(Ph)}(COD)2]BF4 (5). A summary
of crystal data and refinement parameters is reported in Table 3. Data
were collected on a Siemens-Stoe AED-2 four circle diffractometer
with graphite-monochromated Mo KR radiation (λ ) 0.710 73 Å), using
in both cases the ω/2θ scan method. A set of three standard reflections
were monitored every 60 min of measured time throughout data
collection; no important variations were observed. All data were
corrected for Lorentz and polarization effects and for absorption using
a semiempirical method (minimum and maximum transmission factors
0.599 and 0.647 for 3; 0.576 and 0.666 for 5).26 Both structures were
solved by direct methods27 and Fourier techniques and refined by full-
matrix least squares on F2 (SHELXL-97).28 Atomic scattering factors,

Notes
Inorganic Chemistry, Vol. 37, No. 4, 1998 829
corrected for anomalous dispersion, were used as implemented in the
refinement program.
from observed positions. All hydrogens were treated in the refinement
riding on the corresponding carbon atoms. The BF4 anion was found
to be disordered and was modeled on the base of three isotropic BF4
groups with complementary occupancy factors and internal distances
restricted to tetrahedral geometry. The weighting scheme used was
analogous to that of 3 (x ) 0.055 and y ) 10.9881). Final agreement
Data for 3. A dark green prismatic block (0.22 × 0.14 × 0.10
mm) was indexed to orthorhombic symmetry. Data were collected in
the range 4 e 2θ e 50° (0 e h e 7, 0 e k e 20, 0 e l e 12 +
Friedel); 2793 measured reflections, 2137 unique (Rint ) 0.0185).
Anisotropic displacement parameters were used in the last cycles of
refinement for all non-hydrogen atoms. The hydrogen atoms were
introduced in calculated positions (C-H ) 0.94 and 0.97 Å) and refined
riding on the corresponding carbon atoms. Those of the methyl group
were clearly observed disordered in two groups with identical oc-
2
factors were R(F) ) 0.0462 (3205 observed reflections, Fo2 < 2σ(Fo ))
and wR ) 0.1227 (all data) for 317 parameters. Maximum and
minimum residual peaks in the final difference map were 0.70 and
-0.88 e Å-3
.
Molecular Orbital Calculations. Calculations of the extended
Hu¨ckel type23 were carried out using a modified version of the
Wolfsberg-Helmholz formula.29 The following bond distances (Å) were
used in the model: Rh-S ) 2.368, Rh-C ) 1.874, S-C ) 1.710,
CdN ) 1.317, N-C ) 1.470, CdO ) 1.126, and C-H ) 1.08. The
calculations were made with the CACAO program,30 and the atomic
parameters used were those implemented in this program.
2
cupancy. Weighting scheme used was w ) 1/[σ2(Fo ) + (xP)2 + yP]
(P ) (Fo2 + 2Fc2)/3) with x ) 0.0231 and y ) 0.1942. Final agreement
2
factors were R(F) ) 0.0241 (1733 observed reflections, Fo2 < 2σ(Fo ))
and wR 0.0532 (all data) for 148 parameters. The largest peak in the
final difference map is 0.25 e Å-3
.
Data for 5. An orange long needle (1.50 × 0.11 × 0.07 mm) was
mounted on the top of a fiber glass, and a set of randomly searched
reflections were indexed to monoclinic symmetry. Data were collected
in the range 3 e 2θ e 50° (-15 e h e 14, 0 e k e16, 0 e l e 17);
5016 measured reflections, 4527 unique (Rint ) 0.0536). After
refinement of all non-hydrogen atoms with anisotropic displacement
parameters (excepting those of the disordered BF4 anion), the hydrogen
atoms were positionated in calculated positions. As exceptions, the
hydrogens of the olefinic carbons bonded to the metals were included
Acknowledgment. We thank the DGICYT (Projects PB94-
1186 and PB95-0318; Programa de Promocio´n General del
Conocimiento) for financial support.
Supporting Information Available: X-ray crystallographic files,
in CIF format, for complexes 3 and 5 are available on the Internet
only. Access information is given on any current masthead page.
(26) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, 24, 351.
IC971053T
(27) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1994, 27, 435.
(28) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(29) Ammeter, J. H.; Bu¨rgi, H. B.; Thibeault, J. C.; Hoffmann, R. J. Am.
Chem. Soc. 1978, 100, 3686.
(30) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 67, 399.