Synthesis of Bi-and trinuclear bis(alkynyl) complexes [PtM (M = Rh, Ir), PtRh2] starting from [cis-Pt(C6F5)2(C≡CR)2] 2-

Article abstract of DOI:10.1021/om990314z

The course of the reactions of Q₂[cis-Pt(C₆F₅)₂(C≡CR) ₂] (Q = PPh₃Me, R = Ph 1a; Q = NBu₄, R = ^tBu 1b, SiMe₃ 1c) with [M(μ-Cl)(COD)]₂ (M = Rh, Ir

Full text of DOI:10.1021/om990314z

4344
Organometallics 1999, 18, 4344-4353
Syn th esis of Bi- a n d Tr in u clea r Bis(a lk yn yl) Com p lexes
[P tM (M ) Rh , Ir ), P tRh 2] Sta r tin g fr om
[cis-P t(C6F 5)2(CtCR)2]2-
Irene Ara,† J esu´s R. Berenguer,‡ Eduardo Eguiza´bal,‡ J uan Fornie´s,*,†
Elena Lalinde,*,‡ and Francisco Mart´ınez†
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-Consejo Superior de Investigaciones Cientı´ficas, 50009 Zaragoza,
Spain, and Departamento de Quı´mica, Universidad de La Rioja, 26001 Logron˜o, Spain
Received April 29, 1999
The course of the reactions of Q2[cis-Pt(C6F5)2(CtCR)2] (Q ) PPh3Me, R ) Ph 1a ; Q )
t
NBu4, R ) Bu 1b, SiMe3 1c) with [M(µ-Cl)(COD)]2 (M ) Rh, Ir) is strongly influenced by
the metal and the substituents, as well as the stoichiometry. Thus, whereas treatment of
1a with either 0.5 or 1 equiv of [Rh(µ-Cl)(COD)]2 gives the chelating-type binuclear highly
polar compound (PPh3Me)[cis-Pt(C6F5)2(µ-1κCR:η2-CtCPh)2Rh(COD)], 2a , analogous reactions
using 1b as the precursor afford only the trinuclear complex (NBu4)[{cis-Pt(C6F5)2(µ-1κCR:
η2-CtCtBu)2}{Rh2(µ-Cl)(COD)2}], 4b. On the other hand, related bi- and trinuclear SiMe3
derivatives (NBu4)[cis-Pt(C6F5)2(µ-1κCR:η2-CtCSiMe3)2Rh(COD)], 2c, and (NBu4)[{cis-Pt-
(C6F5)2(µ-1κCR:η2-CtCSiMe3)2}{Rh2(µ-Cl)(COD)2}], 4c, are easily obtained by treating 1c with
the binuclear rhodium substrate in the adequate molar ratio [1:0.5 for 2c; 1:1 for 4c]. Complex
2b and, alternatively, 2a ,c derivatives can be produced by reacting 1 with the cationic
solvento species [Rh(COD)(Et2O)x]+ (prepared in situ). The molecular structures of 2a and
4b have been confirmed by X-ray diffraction. By contrast, whereas the reactions of 1a ,b
with [Ir(µ-Cl)(COD)]2 lead to the formation of undefined products, the heterobinuclear σ,π
double-alkynyl-bridged complex (NBu4)[cis-Pt(C6F5)2(µ-1κCR:η2-CtCSiMe3)(µ-η2:2κCR-Ct
CSiMe3)Ir(COD)], 3c, (X-ray) is isolated from reaction of 1c with the dimer iridium complex
regardless of the molar ratio used (1:0.5 or 1:1).
In tr od u ction
ally, in the resulting complexes, the LnM(CtCR)2
compound used as the starting material acts as a
chelating ligand toward the second metal center, form-
ing planar (tweezer-like) or hinged (V-shaped) M2C4
central cores (B, Scheme 1).2c,4,7 However, monoalkynyl
transfer processes yielding type C symmetrical or
The chemistry of metal alkynyl complexes is an
intensely researched area, particularly due to the
versatile reactivity of the unsaturated fragment and its
wide variety of modes of interaction with transition
metals.1-3 In this area, homo and hetero double-alkynyl-
bridged complexes4-7 have gained particular signifi-
cance as frozen structures at various points on the
reaction paths for either C-C bond coupling alkynide
processes6a,8 or C-C bond cleavage on butadiynes6b-f,7a,9
mediated by metal centers (Scheme 1).10,11
Binuclear M(µ-CtCR)2M′ compounds have been pre-
pared through the activation and cleavage of the central
C-C single bond of R-CtC-CtC-R with “Cp2M” (M
) Ti, Zr) fragments,6b-f,7a,9 but the most widely used
route is based on the addition of a second metal
fragment “LnM′” to a M-σ-bis(alkynyl) compound. Usu-
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† Universidad de Zaragoza-Consejo Superior de Investigaciones
Cient´ıficas.
‡ Universidad de La Rioja.
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10.1021/om990314z CCC: $18.00 © 1999 American Chemical Society
Publication on Web 09/23/1999

Bi- and Trinuclear Bis(alkynyl) Complexes
Organometallics, Vol. 18, No. 21, 1999 4345
Sch em e 1
unsymmetrical σ/π bridging systems (Scheme 1) have
also been reported.6g-i,k,q,12 We have recently reported
a new family of bis(µ-CtCR) binuclear [(PEt3)Cp*M(µ-
CtCR)2M′(C6F5)2] d6(Rh, Ir)-d8(Pt, Pd) complexes.11,13
The Ir-Pt complexes (chelating type, V-shape) were
prepared by an unprecedented double intramolecular
alkynyl migration from Pt to Ir, whereas the analogous
Rh derivatives (σ/π) were formed through a unique
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alkynyl migration, either from Pt to Rh or from Rh to
Pt. A double alkynyl migration has also been recently
suggested by Choukroun et al.14 to explain the formation
of the coupled product [Cp2V(µ-η2:η4-butadiyne)MCp′2]
(Cp′ ) Cp, M ) Ti, Zr; Cp′ ) C5H4SiMe3, M ) Zr) (E,
Scheme 1) starting from [Cp2M(CtCPh)2] and vana-
docene and could also be related to the oxidatively
induced coupling of CtCR moieties to free butadiynes
(eq 1), only observed with very electrophilic MLn frag-
ments15 (Ni(II) or Pd(II) vs Ni(0) or Pd(0); AuCl3py vs
AuR or AgPF6).
LmM′(CtCR)2 + MLn f LmM′Ln + M(0) +
RCtC-CtCR (1)
The driving force of these alkynyl transfer processes
is still an open question.6g-i,k,12,16 With this in mind, we
have studied the reactivity of alkynyl platinum com-
plexes toward low-valence substrates of Rh or Ir(I), and
the synthesis and characterization of several new bi-
and trinuclear bis(alkynyl)-bridged [PtM, M ) Rh, Ir;
PtRh2] complexes are reported.
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Resu lts a n d Discu ssion
P r epar ation of Com plexes. We have recently shown
that treatment of the allyl chloride-bridged dimer [Pd-
(µ-Cl)(η3-C3H5)]2 with the anionic platinum complexes
Q2[cis-Pt(C6F5)2(CtCR)2] 1 (Q ) PPh3Me, R ) Ph; Q )
t
NBu4, R ) Bu, SiMe3) provides an excellent route to
the heterobinuclear double-alkynyl V-shaped anionic
derivatives [{cis-Pt(C6F5)2(µ-CtCR)2}{Pd(η3-C3H5}]- 17
(B, Scheme 1). In these reactions the chloride ligands
are easily displaced as NBu4Cl or PPh3MeCl. These
results led us to investigate the reactivity of 1 toward
the chloride-bridged dimers [M(µ-Cl)(COD)]2 (M ) Rh,
Ir) as a reasonable route to the desired alkynyl bridging
Pt-M (M ) Rh, Ir) compounds. These reactions display
a surprising dependence on the nature of M, the alkynyl
organic substituent R, and the proportions of the
reagents as summarized in Scheme 2. The expected
(14) Danjoy, C.; Zhao, J .; Donnadieu, B.; Legros, J .-P.; Valade, L.;
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Soc., Chem. Commun. 1995, 1227.

4346 Organometallics, Vol. 18, No. 21, 1999
Ara et al.
Sch em e 2
to afford the analogous trinuclear 4c. In these 4b,c
complexes, as has been shown by an X-ray diffraction
study on 4b, the bis(alkynyl)platinate precursor acts as
a bidentate bridging ligand replacing one chloride group
in the rhodium chloride-bridged dimer. Attempts to
obtain the phenyl derivative 4a using the appropiate
platinum-rhodium molar ratio were unsuccessful, and
instead, after workup, an orange solid which is identi-
fied (IR and NMR spectroscopy) as a mixture of the
dimer 2a and unreacted [Rh(µ-Cl)(COD)]2 (2.5:1) is
obtained. No other product can be detected by NMR
techniques. The formulation given in Scheme 2 for
complexes 2 and 4 is based on spectroscopic data (IR,
1H, 19F, 13C NMR) and confirmed by X-ray diffraction
studies of complexes 2a and 4b, respectively. All com-
plexes have been additionally characterized by elemen-
tal analyses, mass spectrometry (FAB), and conductivity
measurements (see Experimental Section).
As it is shown in the formulas that appear in Scheme
2, no alkynylation processes have been observed in the
formation of complexes 2 and 4. The platinum centers
retain the σ-coordination to the alkynyl fragments while
the rhodium centers are stabilized through η2-alkyne
interactions, indicating that, as expected for a third-
row metal, the platinum center shows a greater prefer-
ence for the σ-electron density than the Rh center does.
In contrast to the behavior observed in relation to the
rhodium species, we were able to obtain only a mixed-
metal binuclear species stabilized by a double alkynyl-
bridging system by the reaction of 1c and the dimeric
iridium complex [Ir(µ-Cl)(COD)2]. As shown in Scheme
2, the Ir-Pt complex (NBu4)[cis-Pt(C6F5)2(µ-CtCSiMe3)2-
Ir(COD)], 3c, is readily obtained as a deep yellow
microcrystalline solid by reacting 1c with the chloride-
dimer iridium complex in acetone, regardless of the Pt/
Ir ratio used (1:0.5 31% yield; 1:1 65% yield). Complex
3c is also generated in very good yield, as is observed
by NMR spectroscopy (19F), by mixing equimolar amounts
of 1c and the solvento [Ir(COD)S2](ClO4) species in
acetone. However, due to the presence of NBu4ClO4 in
the reaction mixture, 3c can be isolated as a pure
compound only in extremely low yield (15%). All at-
tempts to prepare any other alkynyl-bridged Pt(II)-Ir-
(I) dimer (or trimer) using 1a and 1b as the reagents
for the Ir derivatives have been unsuccessful. The
reaction mixtures of 1a ,b with either [Ir(µ-Cl)(COD)]2
or [Ir(COD)S2]+ evolve giving a complex mixture of
products from which we were not able to isolate any
pure compound. Interestingly, NMR examination of the
initial reaction mixture of 1a and [Ir(µ-Cl)(COD)]2 (1:
0.5 or 1:1 molar ratio) reveals the presence of the doubly
alkynyl bridged diplatinum complex (PPh3Me)2[Pt(µ-Ct
CPh)(C6F5)2]2,6i suggesting that, in this case, after initial
alkynyl transfer from Pt to Ir, the resulting fragments
probably disproportionate, producing the diplatinum
and presumably the dimer [Ir(µ-CtCPh)(COD)]2. By
usual workup (see Experimental Section) an orange
solid was obtained and identified (NMR) as a mixture
of products, with the known dimer (PPh3Me)2[Pt(µ-Ct
CPh)(C6F5)2]2 as the major component.
heterobinuclear platinum-rhodium complexes Q[cis-Pt-
(C6F5)2(µ-CtCR)2Rh(COD)] (Q ) PPh3Me, R ) Ph 2a ;
Q ) NBu4, R ) SiMe3 2c) can be isolated, as orange
solids, in good (81%, 2a ) or moderate (42%, 2c) yield by
the reaction of [Rh(µ-Cl)(COD)]2 with 2 equiv of 1a and
1c, respectively (Rh/Pt, 1:1 ratio). As expected, both
complexes can also be obtained directly by the reaction
of 1a and 1c with the solvento species [Rh(COD)S2]-
(ClO4) in diethyl ether. The analogous tert-butylalkynyl
derivative 2b can only be synthesized (64% yield)
starting from [Rh(COD)S2]+ (S ) diethyl ether) and the
corresponding tert-butylalkynyl platinum precursor 1b.
Attempts to synthesize 2b by the reaction of [Rh(µ-Cl)-
(COD)]2 with 2 molar equiv of 1b lead to the trinuclear
anionic complex (NBu4)[{cis-Pt(C6F5)2(µ-CtCtBu)2}{Rh2-
(µ-Cl)(COD)2}], 4b, instead. This is isolated in low yield
(56% based on Rh) as a microcrystalline orange solid.
If the reaction is carried out in a 1:1 molar ratio,
complex 4b is generated in higher yield (67%). The
reaction of [Rh(µ-Cl)(COD)]2 with 1 equiv of 1c also
results in the displacement of one of the chloride ligands
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For complex 3c, the formulation given with a type C
σ/π double-alkynyl bridging system (Scheme 1) coincides
with its spectroscopic data (IR, NMR) and has been
confirmed by a single-crystal X-ray diffraction study.
(17) (a) Berenguer. J . R.; Fornie´s, J .; Lalinde, E.; Mart´ınez, F. J .
Organomet. Chem. 1994, 470, C15. (b) Ibid. Organometallics 1996, 15,
4537.

Bi- and Trinuclear Bis(alkynyl) Complexes
Organometallics, Vol. 18, No. 21, 1999 4347
cyclobutadiene18a,20 complexes has precluded the isola-
tion of derivatives with a rhodium atom η2-bonded to
two alkyne ligands. We have recently reported two
similar complexes,21 but this structure represents the
first crystallographically characterized example of this
structural situation.
The platinum and rhodium atoms exhibit conven-
tional square-planar environments, and each organo-
metallic core shows the expected structural fea-
tures.4,11,13,16a,17a,21,22 The rhodium atom is located out
of the 3-metalla-1,4-diyne plane (V-shape). We have
previously observed this structural feature when using
square-planar d8 metal moieties as chelating frag-
ments.6i,7e,11,13,16a,17,21 The dihedral angle formed by the
best least-squares planes around the Pt and Rh atoms
[96.86(1)°] is notably smaller than those found for other
related complexes [121.54(6)-148.3(4)°],6i,7e,13,16a allow-
ing the metal centers to be in a closer position. Finally,
the π-interactions between the acetylene fragments and
the Rh atom are rather unsymmetrical [Rh-CR 2.29(2)
Å, 2.29(3) Å; Rh-Câ 2.53(3) Å, 2.49(2) Å]. This type of
asymmetry (Rh-CR < Rh-Câ bond distances), although
not as marked, has been previously found in the penta-
nuclear species [{Pt(CtCtBu)4}{Rh2(µ-X)(COD)2}2] (X )
OH, Cl), [P tRh 4X2], previously reported21 and in related
complexes containing η2-Rh-acetylide interactions.23
The structure of the dimetallic anion of 3c is shown
in Figure 2 together with the atom-numbering scheme.
Selected bond distances and angles are displayed in
Table 1. As can be seen, the anion is formed by two or-
ganometallic “(COD)Ir” and “Pt(C6F5)” moieties [Ir‚‚‚Pt
) 3.639(1) Å] with the metal centers connected by two
alkynyl groups. Each alkynyl ligand is σ-bonded to one
metal atom (Pt/Ir) and leans over the other metal center
(Ir/Pt). All structural data are in good agreement with
F igu r e 1. Molecular structure of the anion complex 2a ,
showing the atom-numbering scheme.
This well-studied bridging system has been found to
stabilize both early (d1-d1),6a-c,e-g,k-o,q middle(d6-d6),6p
and late (d8-d8)6h-j transition metal homobinuclear
molecules, but the number of heterodimetallic systems
is rather scarce.6b,d,11,12 As far as we know, the only
related metal complexes (Pt, Rh, or Ir) previously
reported are the dimers [(COD)M(CtCSiMe3)]2 [M )
Ir (X-ray), Rh],6j and we have also shown that anionic
{[Pt(CtCR)(C6F5)2]2}2-6i and neutral [Pt(CtCR)(C6F5)-
6h
(PPh3)]2 binuclear complexes display a similar struc-
tural disposition. Complex 3c represents the first het-
erobimetallic d8-d8 compound characterized by an X-ray
diffraction study that also possesses a σ/π doubly
alkynyl bridging system. The formation of 3c implies
the migration of one σ-CtCSiMe3 group from Pt to Ir.
However, the migration of the second alkynyl ligand,
previously observed in the reaction between [cis-Pt-
(C6F5)2(CtCR)2]2- and [Cp*Ir(PEt3)(acetone)2]2+ 11
, is not
observed with the “Ir(COD)+” fragment.
Str u ctu r a l In vestiga tion s. The structures of com-
plexes 2a , 3c, and 4b have been established by an X-ray
crystal study. The drawing of complex anion [cis-Pt-
(C6F5)2(µ-CtCPh)2Rh(COD)]-, 2a , is presented in Fig-
ure 1, and selected bond distances and angles are given
in Table 1. The type of structure with a chelating doubly
alkynyl bridging system (B, Scheme 1) is not new, but,
to the best of our knowledge, this is the first example
involving these metal centers [Pt(II) and Rh(I)]. We have
recently described the Pt(II)-Rh(III) binuclear zwitter-
ionic neutral complex [(PEt3)Cp*Rh+(µ-CtCSiMe3)2Pt--
(C6F5)2], but it contains a σ/π bis(alkynyl) system (C,
Scheme 1).11 In 2a both alkynyl groups are σ-bonded to
the platinum atom [Pt(1)-C(13) 2.02(2) Å, Pt(1)-C(21)
2.04(3) Å] and η2-bonded to the rhodium center, result-
ing in a very polar anion (formally zwitterionic). It has
to be mentioned that the final arrangement around the
rhodium atom is actually new. Athough there is a large
number of examples of η2-acetylene-rhodium bonds,18
the easy activation of the alkynes coordinated to rhod-
ium centers to give metallacyclopentadiene19 and
the structures of the previously reported homobimetal-
6i
lic species {[Pt(CtCPh)(C6F5)2]2}2-, [P t2]2-
,
and [Ir-
(CtCSiMe3)(COD)]2, [Ir 2],6j which display a similar
geometric arrangement of the alkynyl ligands. In par-
ticular, the central organometallic framework IrPtC4
adopts a puckered conformation, the dihedral angle
between the planes Pt(1)Ir(1)C(18)C(19) and Pt(1)Ir-
(1)C(1)C(2) being 21.5(3)°. It is worth noting that the
influence of the metal centers in the bonding parameters
of the Ir(µ-alkynide)2Pt unit is quite insignificant. Thus,
both the M-C σ-bonds [1.987(8), 2.005(8) Å] and the
equivalent complexed η2-bond lengths [2.339(8), 2.233-
(20) (a) Mu¨ller, E.; Thomas, R.; Zountsas, G. Liebigs. Ann. Chem.
1972, 758, 16. (b) Cash, G. G.; Helling, J . F.; Mathew, M.; Palenick,
G. J . J . Organomet. Chem. 1973, 50, 277. (c) Nixon, J . F.; Kooti, M. J .
Organomet. Chem. 1976, 104, 231. (d) King, R. B.; Ackermann, M. N.
J . Organomet. Chem. 1974, 67, 431. (e) Winter, W. Angew. Chem., Int.
Ed. Engl. 1975, 14, 170. (f) Rausch, M. D.; Gardner, S. A.; Tokas, E.
F.; Bernal, I.; Reisner, G. M.; Clearfield, A. J . Chem. Soc., Chem.
Commun. 1978, 187. (g) Moreto, J .; Maruya, K.; Bailey, P. M.; Maitlis,
P. M. J . Chem. Soc., Dalton Trans. 1982, 1341. (h) Borrini, A.; Diversi,
P.; Ingrosso, G.; Lucherini, A.; Serra, G. J . Mol. Catal. 1985, 30, 181.
(21) Ara, I.; Berenguer, J . R.; Fornie´s, J .; Lalinde, E. Organometal-
lics 1997, 16, 3921.
(18) (a) Comprehensive Organometallic Chemistry; Wilkinson, G.,
Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press Ltd.: Oxford, U.K.,
1982; Vol. 5. (b) Comprehensive Organometallic Chemistry II; Atwood,
J . D., Vol. Ed.; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.;
Elsevier: Oxford, U.K., 1995; Vol. 8.
(19) (a) Mague, J . T.; Wilkinson, G. Inorg. Chem. 1968, 7, 542. (b)
Mu¨ller, E. Synthesis 1974, 761. (c) Winter, W. Angew. Chem., Int. Ed.
Engl. 1976, 15, 241. (d) Sa´nchez-Delgado, R. A.; Wilkinson, G. J . Chem.
Soc., Dalton Trans. 1977, 804. (e) Su¨nkel, K. Chem. Ber. 1991, 124,
2449. (f) Bianchini, C.; Masi, D.; Meli, A.; Peruzzini, M.; Vacca, A.;
Laschi, F.; Zanello, P. Organometallics 1991, 10, 636.
(22) (a) Selent, A.; Ramm, M. J . Organomet. Chem. 1995, 485, 35.
(b) Tejel, C.; Villoro, J . M.; Ciriano, M. A.; Lo´pez, J . A.; Eguiza´bal, E.;
Lahoz, F. J .; Bakhmutov, V. I.; Oro, L. A. Organometallics 1996, 15,
2967.
(23) Hutton, A. T.; Langrick, C. R.; McEvan, D. M.; Pringle, P. G.;
Shaw, B. L. J . Chem. Soc., Dalton Trans. 1985, 2121. (b) Cowie M.;
Loeb, S. Organometallics 1985, 4, 852. (c) Esteruelas, M. A.; Lahuerta,
O.; Modrego, J .; Nu¨rnberg, O.; Oro, L. A.; Rodr´ıguez, L.; Sola E.;
Werner, H. Organometallics 1993, 12, 266. (d) Antwi-Nsiah, H. F.; Oke
O.; Cowie, M. Organometallics 1996, 15, 506. (e) George, D. S. A.;
McDonald, R.; Cowie, M. Organometallics 1998, 17, 2553.

4348 Organometallics, Vol. 18, No. 21, 1999
Ara et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles (d eg) for Com p lexes 2a , 3c, a n d 4b
Complex 2a
Pt(1)-C(13)
2.02(2)
2.13(3)
2.13(3)
2.29(2)
1.24(4)
1.43(4)
Pt(1)-C(21)
2.04(3)
2.12(3)
2.14(3)
2.49(2)
1.18(4)
2.889(3)
Pt(1)-C(7)
2.08(3)
Pt(1)-C(1)
Rh(1)-C(33)
Rh(1)-C(29)
Rh(1)-C(22)
C(21)-C(22)
Pt(1)-Rh(1)
Rh(1)-C(30)
Rh(1)-C(21)
Rh(1)-C(14)
C(29)-C(30)
2.12(3)
2.29(3)
2.53(3)
1.44(5)
Rh(1)-C(34)
Rh(1)-C(13)
C(13)-C(14)
C(33)-C(34)
C(13)-Pt(1)-C(21)
C(21)-Pt(1)-C(1)
80.6(10)
93.2(10)
85.69(2)
86.98(2)
164(2)
C(13)-Pt(1)-C(7)
C(7)-Pt(1)-C(1)
94.6(11)
91.9(11)
97.26(2)
91.08(2)
173(3)
C(13,14)-Rh(1)-C(21,22)
C(29,30)-Rh(1)-C(33,34)
C(14)-C(13)-Pt(1)
C(21,22)-Rh(1)-C(29,30)
C(33,34)-Rh(1)-C(13,14)
C(13)-C(14)-C(15)
C(22)-C(21)-Pt(1)
168(3)
C(21)-C(22)-C(23)
167(3)
Complex 3c
Pt(1)-C(1)
Pt(1)-C(18)
Ir(1)-C(2)
Ir(1)-C(26)
C(1)-C(2)
1.987(8)
Pt(1)-C(6)
Pt(1)-C(19)
Ir(1)-C(18)
Ir(1)-C(27)
C(18)-C(19)
2.016(9)
2.233(9)
2.005(8)
2.117(9)
1.244(12)
Pt(1)-C(12)
2.054(8)
2.308(8)
2.199(9)
2.199(10)
3.639(1)
2.339(8)
2.186(9)
2.123(10)
1.273(12)
Ir(1)-C(1)
Ir(1)-C(23)
Ir(1)-C(30)
Pt(1)‚‚‚Ir(1)
C(1)-Pt(1)-C(6)
90.4(3)
103.4(2)
105.3(1)
88.2(2)
174.6(7)
173.3(7)
C(6)-Pt(1)-C(12)
C(1)-Pt(1)-C(18,19)
C(1,2)-Ir(1)-C(18)
87.1(3)
79.1(2)
80.2(2)
86.3(1)
136.9(7)
145.0(8)
C(12)-Pt(1)-C(18,19)
C(1,2)-Ir(1)-C(23,30)
C(18)-Ir(1)-C(26,27)
Pt(1)-C(1)-C(2)
C(26,27)-Ir(1)-C(23,30)
Si(1)-C(2)-C(1)
Ir(1)-C(18)-C(19)
Si(2)-C(19)-C(18)
Complex 4b
Pt(1)-C(13)
1.995(14)
2.076(13)
2.14(2)
2.421(4)
2.12(2)
2.266(12)
1.21(2)
1.44(2)
Pt(1)-C(19)
Rh(1)-C(26)
Rh(1)-C(29)
Rh(1)-C(14)
Rh(2)-C(38)
Rh(2)-Cl(1)
C(19)-C(20)
C(33)-C(34)
Pt(1)‚‚‚Rh(2)
2.01(2)
2.11(2)
2.15(2)
2.500(14)
2.15(2)
2.420(4)
1.21(2)
1.45(3)
3.206(1)
Pt(1)-C(1)
2.072(13)
2.14(2)
2.238(13)
2.11(2)
2.16(2)
2.547(14)
1.43(3)
Pt(1)-C(7)
Rh(1)-C(30)
Rh(1)-C(13)
Rh(2)-C(33)
Rh(2)-C(37)
Rh(2)-C(20)
C(25)-C(26)
C(37)-C(38)
Rh(1)‚‚‚Rh(2)
Rh(1)-C(25)
Rh(1)-Cl(1)
Rh(2)-C(34)
Rh(2)-C(19)
C(13)-C(14)
C(29)-C(30)
Pt(1)‚‚‚Rh(1)
1.44(3)
3.670(1)
3.238(1)
C(13)-Pt(1)-C(19)
C(19)-Pt(1)-C(7)
98.1(5)
85.2(5)
88.3(2)
88.1(2)
95.0(1)
98.60(14)
169(2)
C(13)-Pt(1)-C(1)
C(1)-Pt(1)-C(7)
85.9(5)
91.0(5)
87.4(2)
89.7(2)
96.8(1)
Cl(1)-Rh(1)-C(13,14)
Cl(1)-Rh(1)-C(25,26)
Cl(1)-Rh(2)-C(19,20)
Cl(1)-Rh(2)-C(33,34)
C(19,20)-Rh(1)-C(37,38)
C(14)-C(13)-Pt(1)
C(13,14)-Rh(1)-C(29,30)
Rh(2)-Cl(1)-Rh(1)
C(13)-C(14)-C(15)
C(19)-C(20)-C(21)
172.2(12)
171.2(12)
C(20)-C(19)-Pt(1)
169(2)
Ch a r t 1
structural situation of the alkynyl ligands. In accordance
with this structural fact, the M-CRtCâ fragments
remain almost linear [174.6(7)°, 173.3(7)°] and the CRt
Câ-Si units deviate significantly from linearity [136.9-
(7)°, 145.0(8)°], suggesting, as has been previously
pointed out,6d,g,h a considerable vinylidene contribution
to the bonding mode of the bridging alkynyl ligands
(Chart 1). The opposite asymmetry (M-CR < M-Câ) or
more symmetrical η2-metal acetylenic bonding interac-
tions have usually been observed in complexes with
chelating-type structural arrangements (M in-plane,
tweezer-like and outside-plane, V-shaped),2c,4,7 although
we have also found some exceptions.4,7d
F igu r e 2. View of the molecular structure of the anion
complex 3c, showing the atom-numbering scheme.
(9) Å for Pt(1) and 2.308(8), 2.186(9) Å for Ir(1)] are
comparable within experimental error. The η2-metal
acetylenic linkages are asymmetric, the M-Câ bonds ca.
0.1 Å (0.10 for Pt and 0.122 for Ir) being shorter than
the corresponding M-CR distances. This asymmetry has
been previously found in related complexes,6 and it
would now seem to be characteristic of this particular
The Ir-(olefin) distances fall within the range of
2.117(9)-2.199(10) Å, with the two metal-carbon dis-

Bi- and Trinuclear Bis(alkynyl) Complexes
Organometallics, Vol. 18, No. 21, 1999 4349
(2)°] are similar to those found in [P tRh 4X2]21 and in
2a . The π-complexed Rh atoms are located in a pseudo-
trans arrangement with respect to the platinum coor-
dination plane, resulting in rather long Pt-Rh(1,2)
[3.238(1) and 3.206(1) Å] and Rh(1)-Rh(2) [3.670(1) Å]
separations, which exclude any significant metal-metal
bonding interaction.
Sp ectr oscop ic Stu d ies (IR, NMR). In accordance
with previous observations,11 the ν(CtC) for the bi-
nuclear platinum rhodium compounds 2 (1940-2044
cm-1) and, particularly, the ∆ν(CtC) shift in relation
to the precursors 1 (∼60 cm-1) are in keeping with a
chelating-type arrangement. In contrast, the formation
of complex 3c is accompanied by a considerably larger
shift of the ν(CtC) to lower frequencies (1868, 1823
cm-1, ∆ν(CtC)average 173 cm-1), clearly reflecting stron-
ger η2-M-alkyne interactions with this type of arrange-
ment of both alkynyl ligands.
F igu r e 3. Molecular structure of the anion complex 4b,
showing the atom-numbering scheme.
Complex 3c, like many other examples that have this
σ/π structural formulation,6a-i,q,11,12,16a is dynamic and
undergoes an intramolecular exchange of both alkynyl
groups within the dimetallic framework that is rapid
on the NMR time scale at room temperature. Thus, at
16 °C it shows only one proton and carbon olefinic
resonances due to the COD ligands, only one type of
C6F5 ligand (AA′MXX′ system), and only one set of Ct
CSiMe3 signals (1H, 13C, and 19F NMR), evidencing an
apparent overall C2v symmetry. Lowering the temper-
ature produces a broadening of CHd and SiMe3 reso-
nances in the proton spectra and of the o-F signals
(broadening of p-F and m-F is also observed) in the 19F
NMR spectra, which eventually split in each case into
two separate signals (1:1 ratio) at low temperature (-50
°C). Using the coalescence temperatures for the olefinic
protons (253 K), SiMe3 (230 K), and o-F (253 K), a
similar Gibbs activation barrier26 is obtained (∆G#
10.84, 11.86, and 11.13 kcal‚mol-1, respectively), sug-
gesting that all these signals are involved in the same
dynamic process. However, the low-temperature NMR
patterns indicate that only the intramolecular Ct
CSiMe3 migration between the metal centers is frozen
at low temperature (-50 °C). For a rigid puckered dimer
one should expect to observe four proton and carbon
olefinic resonances for the chelating COD ligand and
four different fluorine signals (endo and exo of each C6F5
group) in the o-F region. Therefore, the reduced number
of observable HCd (1H δ 4.89, 3.55; 13C δ 62.3, 58.1)
and o-F signals (-114.21, 3J Pt-o-F ) 373 Hz, 2 o-F trans
tances trans to the CtC triple bond shorter than
those trans to the sp CR carbon donor, thus revealing
not only the asymmetric arrangement of the µ-Ct
CSiMe3 ligands but also the stronger trans influence of
the σ-donor CR carbon atom. Similar observations have
previously been made on the basis of 195Pt-31P coupling
constants.6h
For complex 4b the unit cell contains 1.5 independent
anions. The half anion sits on a crystallographic sym-
metry element. Both anions are essentially similar;
therefore, the discussion will be limited to only one. The
molecular structure of the trinuclear anion of 4b is
presented in Figure 3. This type of structure features a
different behavior of the anionic substrates [cis-Pt-
(C6F5)2(CtCR)2]2-. In this case, the bis(alkynyl) frag-
ment acts as a bridging diyne ligand (η2:η2) to two nearly
identical “Rh(COD)” units. The structure is similar to
the pentanuclear species [P tRh 4X2],21 in which the
tetraalkynylplatinate(II) anion acts as a tetradentate
bridging ligand between two related cationic dirhodium
“Rh2(µ-X)(COD)2” units. The anion contains two pseudo-
square-planar Rh(I) units sharing a common bridged
chlorine atom [Rh(1,2)-Cl(1) 2.421(4), 2.420(4) Å; Rh-
(1)-Cl-Rh(2) 98.60(14)°]. The two chelating diolefin
ligands (COD) are not identical, but all the rhodium-
carbon separations are very similar [2.11(2)-2.16(2)
Å], in agreement with the values indicated in the
literature.21,24,25 Both rhodium centers complete their
coordination, being η2-bonded to a 3-platinadiyne
bridging building block “cis-(C6F5)2Pt(CtCtBu)2”. In
this fragment the coordination around Pt(1), including
bond lengths and angles, is similar to those found in
other heteropolynuclear bis(alkynyl)platinum com-
pounds.4,7d,17,21 As for 2a , the most remarkable feature
is that the η2-interactions to the Rh atom show asym-
metry opposite that found in 3c: the Rh-CR distances
[2.238(13), 2.266(12) Å] are considerably shorter than
the corresponding Rh-Câ [2.500(14), 2.547(14) Å]. The
parameters of the acetylenic fragments [CtC 1.21(2) Å;
Pt-CRtCâ 172.2(12)°, 171.2(12)°; CRtCâ-C(tBu) 169-
3
to σ-CtC; -116.26, J Pt-o-F ) 520 Hz, 2 o-F trans to
η2-CtC) clearly indicates that a very fast inversion of
the central dimetallacycle is taking place, even at 223
K, to account for the apparent time-averaged plane of
symmetry.
Fluxional behavior for binuclear chelating platinum
rhodium compounds 2a -2c is also evident. At ambient
temperature their proton and fluorine NMR spectra
correspond to species for which the central Pt(CtC)2Rh
framework is, on the NMR time scale, an average plane
(see Experimental Section for data). The observed
apparent overall C2v symmetry is consistently ex-
plained6i,7d,11,17 by means of a fast exchange of the “Rh-
(24) (a) Ibers, J . A.; Snyder, R. G. Acta Crystallogr. 1962, 15, 923.
(b) Ridder, D. J . A.; Imhoff, P. Acta Cristallogr. 1994, C50, 1569.
(25) (a) Feiken, N.; Pregosin, P.; Trabesinger, G. Organometallics
1998, 17, 4510. (b) Polborn, K.; Severin, K. Eur. J . Inorg. Chem. 1998,
1187.
(26) Gu¨nther, H. NMR Spectroscopy; Wiley: New York, 1980;
p 241.

4350 Organometallics, Vol. 18, No. 21, 1999
Ara et al.
[{cis-Pt(C6F5)2(µ-CtCR)2}{Rh2(µ-Cl)(COD)2}]-
(COD)” unit below and above the 3-platina-1,4-diyne
fragments “(C6F5)2Pt(CtCR)2”, as is shown in eq 2.
f
4b,c
[cis-Pt(C6F5)2(µ-CtCR)2Rh(COD)}]-
+
2b,c
1/2[Rh(µ-Cl)(COD)]2 (3)
Spectroscopic data for 4b and 4c are easily extracted
from these mixtures. Only a single olefinic resonance
1
was seen at 16 °C for both complexes in the H NMR
spectra, and the 19F NMR spectra at the same temper-
ature exhibit a typical AA′MXX′ system, consistent with
the existence of mirror planes on the three metal centers
and, in the case of the rhodium atoms, with an ad-
ditional time-averaged plane which equilibrates both
halves (trans to Cl and trans to acetylenic unit) of the
COD ligands. This latter equilibration could be related
to the equilibrium shown in eq 3, which presumably
requires the involvement of three-coordinated rhodium
species resulting from cleavage of either rhodium-
chloride and/or rhodium-η2-alkyne linkages. However,
the 1H phase-sensitive NOESY spectra at room tem-
perature of 4b in CDCl3 and 4c in acetone-d6 do not
show cross negative peaks correlating the olefinic
signals of 4 with those in 2 and [Rh2], thus suggesting
that the intermolecular exchange between these species
is very slow on the NMR time scale. In fact, coalescence
of the three olefinic signals is not reached up to the
maximum temperature registered (∼50 °C). For 4c, the
ortho-fluorine signal (δ -114.69, acetone-d6) broadens
as the temperature is lowered, coalesces at ca. -73 °C,
and finally splits into two very broad humps at -80 °C
As has been previously suggested,6i the formal inver-
sion of the central PtC4Rh core could occur through
intermediate species (or transition state) with one or
both CtCR symmetrically bridging the two metal
centers. According to this proposal, the process should
be more favorable for the phenylethynyl derivative 2a ,
as the positive charge developed at the â-position should
be stabilized by conjugation with the π-electron density
of the phenyl group. This is further supported by the
fact that for complex 2a both the 19F and proton NMR
spectra did not change significantly over the observed
temperature range (16 to -50 °C in CDCl3 or 16 to
-90 °C in acetone-d6), indicating that the dynamic
process has a very low energetic barrier. In contrast,
for complexes 2b and 2c upon cooling at low tempera-
ture (below -50 °C in acetone-d6) usual line broad-
ening takes place and the signals due to olefinic pro-
tons for complex 2c and to o-F for both complexes fin-
ally split into two different resonances at -80 °C (δ
1
(δ -112.7, -117.0). However, in the H NMR spectrum
the broad singlet olefinic signal at δ 4.55 attributed to
4c does not change within the observed range (-80 to
50 °C), indicating that it is still dynamic on the NMR
time scale. For 4b the o-F resonance broadens by
lowering the temperature, but does not split. The
coalescence was very near to the lower accessible
temperature limit (ca. -80 °C). In contrast, its proton
spectrum displays a marked dependence on the tem-
perature. Thus, the broad olefinic signal of 4b (δ 4.62)
-114.11, -114.63 o-F; ∆G198 ≈ 9.15 kcal‚mol-1; 2b. δ
#
#
coalesces at ca. -30 °C (∆G243 ) 11.1 kcal‚mol-1) and
#
4.79, 4.60 olefinic protons; ∆G213 ≈ 10.27 kcal‚mol-1
splits at -50 °C into two broad proton resonances (δ
4.91 and 4.20). These signals belong to protons of
different CdC bonds (trans to Cl δ 4.20 and trans to
and δ -114.21, -114.73 o-F; ∆G200 ) 9.25 kcal‚mol-1
2c).
;
#
1
Interestingly, dissolution of crystals of the trinuclear
complexes 4b and 4c occurs with partial dissociation
according to eq 3, to yield an equilibrium mixture of
compounds 4b,c with the related 2b,c and the corre-
sponding rhodium dimer [Rh(µ-Cl)(COD)]2, [Rh2]. Simi-
lar final ratios 4/2/[Rh2] are observed by monitoring
equimolar mixtures of 1b,c and the rhodium chloride
dimer [Rh2], suggesting that 4b and 4c formed in situ
rapidly equilibrate with the thermodynamically more
stable dimers 2b and 2c, respectively. In each case, the
final ratio of the three complexes 4/2/[Rh2], which is
obtained by the integration of the olefinic signals of 1,5-
COD in the three species, strongly depends on the
solvent (see Experimental Section). However, in the
range observed (-80 to 50 °C), the temperature has
very little influence on the extent of the dissociation in
both species. We note that this equilibration process
requires only small changes in the central bridging
framework.
acetylenic δ 4.91) since a correlation H-COSY spectrum
at -50 °C confirms that they are not coupled. At the
same temperature, its 13C NMR also displays, in addi-
tion to alkynyl carbon signals (CR/Câ 81.1/105.2), only
two olefinic (δ 75.9, 74.9) and two aliphatic carbon
resonances (δ 30.0, 29.9). This suggests the existence
of a fast intramolecular process, presumably a rapid ring
inversion of the central six-membered Pt(acetylenic)-
Rh2Cl, which equilibrates the endo and exo CHd units
in the diolefin. This process cannot be frozen even at
-80 °C. Below -50 °C, the olefinic proton signals
broaden again, but only the high-frequency signal (trans
to acetylenic fragment) disappears into the baseline at
-80 °C.
Exp er im en ta l Section
General methods and instrumentation have been described
previously.21 All coupling constants are given in hertz. 1H-

Bi- and Trinuclear Bis(alkynyl) Complexes
Organometallics, Vol. 18, No. 21, 1999 4351
1
COSY and H phase-sensitive NOESY spectra were recorded
(m br, CH2<, COD, 4H); 1.74 (m, CH2< (COD) and -CH2-
(NBu4), 12H); 1.32 (m, -CH2-, NBu4, 8H); 1.18 (s, C(CH3)3,
18H); 0.89 (s br, -CH3, NBu4, 12H). 19F NMR (acetone-d6, δ):
following literature methods.27 Q2[cis-Pt(C6F5)2(CtCR)2] (Q )
PPh3Me, R ) Ph;28 Q ) NBu4, R ) tBu,28SiMe317a), [Rh(µ-Cl)-
(COD)]2,29 [Ir(µ-Cl)(COD)]2.30 and AgClO4 were prepared by
at 16 °C, -114.44 (dm, J Pt-o-F ) 400.9, 4 o-F); -167.82 (m, 4
31
3
published methods.
m-F); -168.40 (t, 2 p-F). The signal due to the o-F of the
#
P r ep a r a tion of Q[{cis-P t(C6F 5)2(µ-1KCr:η2-CtCR)2}Rh -
C6F5 groups coalesces at ca. -75 °C (∆G198 ≈ 9.15 kcal‚
mol-1), splitting into two broad signals at -80 °C: -114.11 (2
o-F), -114.63 (2 o-F) (v br, platinum satellites are observed
but are not well resolved); -166.29 (m, 4 m-F, 2 p-F). 13C NMR
t
(COD)] (Q ) P P h 3Me, R ) P h 2a ; Q ) NBu 4, R ) Bu 2b,
SiMe3 2c). A yellow solution of [Rh(µ-Cl)(COD)]2 (0.0476 g,
0.096 mmol) in Et2O (40 mL) was treated with AgClO4 (0.040
g, 0.190 mmol), and the mixture was stirred for 1 h at room
temperature and then filtered through Kieselgurh. To the
resulting yellow solution, which probably contains [Rh(COD)-
(Et2O)2](ClO4), was added (PPh3Me)2[cis-Pt(C6F5)2(CtCPh)2]
(0.240 g, 0.190 mmol), and a white suspension (PPh3MeClO4)
in a deep orange solution immediately formed. After stirring
for 30 min, the suspension was filtered through Kieselgurh
and the filtrate evaporated to dryness. Treatment of the
resulting oily residue with 5 mL of cold hexane afforded 2a
(orange, 70% yield).
1
2
(CDCl3, δ): at -50 °C, 147.5 (dd, J C-F ) 220, J C-F ) 24),
135.7 (dm, 1J C-F ≈ 250), 134.8 (dm, 1J C-F ≈ 244) (C6F5); 109.1
2
t
1
(s, J Pt-C ≈ 240, Câ, CRtCâ Bu); 95.0 (s br, J Pt-C ≈ 825 Hz,
t
CR, CRtCâ Bu); 75.7, 73.8 (br, CHd, COD); 58.1 (s, N-CH2-
(CH2)2-CH3); 32.5 (s, C(CH3)3); 31.0 (br, CH2<, COD); 30.5 (s,
CMe3); 23.2, 19.3 (s, N-CH2-(CH2)2-CH3); 13.5 (s, N-(CH2)3-
CH3).
Da ta for 2c. Anal. Calcd for C46F10H66NPtRhSi2: C, 46.93;
H, 5.65; N, 1.19. Found: C, 46.72; H, 6.01; N, 1.43. ΛM: 115.2
Ω-1‚cm2‚mol-1. MS FAB(-): m/z ) 934 [M] 100; 836 [M - C2-
SiMe3 - 1] 4; 626 [Pt(C6F5)2(C2SiMe3)] 16; 362 [Pt(C6F5)] 12.
IR (cm-1): ν(CtC) 1965 (vs), 1940 (vs); ν(C6F5)x-sensitive 786 (vs),
Complexes 2b and 2c (orange solids) were obtained similarly
starting from (NBu4)2[cis-Pt(C6F5)2(CtCR)2] (R ) Bu, 0.250
g, 0.21 mmol 2b; R ) SiMe3, 0.300 g, 0.25 mmol 2c) and [Rh-
(COD)(Et2O)2](ClO4) (2b 0.23 mmol, 64% yield; 2c 0.27 mmol,
88% yield).
t
1
777 (vs). H NMR (acetone-d6, δ): at 16 °C, 4.78 (s br, CHd,
COD, 4H); 3.46 (m, N-CH2-, NBu4, 8H); 2.56 (br, CH2<, COD,
4H); 1.85 (m, CH2< (COD) and -CH2- (NBu4), 12H); 1.44 (m,
-CH2-, NBu4, 8H); 0.98 (t, -CH3, NBu4, 12H); 0.18 (s, SiMe3,
18H). The signal due to the olefinic protons of the COD
Da ta for 2a . Anal. Calcd for C55F10H40PPtRh: C, 54.15; H,
3.30. Found: C, 53.96; H, 3.17. ΛM: 84.5 Ω-1‚cm2‚mol-1. MS
FAB(-): m/z ) 942 [M] 100; 835 [M - COD + 1] 15; 774 [M
- C6F5 - 1] 9; 733 [Pt(C6F5)2(C2Ph)2 + 2] 15; 630 [Pt(C6F5)2(C2-
Ph)] 27; 529 [Pt(C6F5)2] 32; 510 [Pt(C6F5)(C6F4)] 57; 362 [Pt-
(C6F5)] 43. IR (cm-1): ν(CtC) 2024(m br); ν(C6F5)x-sensitive 798
#
coalesces at ca. -60 °C (∆G213 ≈ 10.27 kcal‚mol-1), splitting
into two broad singlets at lower temperature [e.g., at -80 °C,
4.79 (2H), 4.60 (2H) (s br, CHd, COD); 3.41 (m br, N-CH2-,
NBu4, 8H); 2.50 (4H), 1.96 (4H) (m br, CH2<, COD); 1.74 (8H),
1.31 (8H) (m br, -CH2-, NBu4); 0.89 (m, -CH3, NBu4, 12H);
0.13 (s, SiMe3, 18H)]. 19F NMR (acetone-d6, δ): at 16 °C,
-114.51 (dm, 3J Pt-o-F ) 386, 4 o-F); -167.42 (m, 4 m-F, 2 p-F)].
The signal due to the o-F of the C6F5 groups coalesces at ca.
1
(s), 790 (s). H NMR (acetone-d6, δ): at 16 °C, 7.84, 7.54, 7.29
(m, Ph, PPh3Me, C2Ph, 25H); 4.43 (s, CHd, COD, 4H); 3.22
(d, 2J P-H ) 14.0, PPh3(CH3)); 2.47 (s br, CH2<, COD, 4H); 1.84
(d, J H-H ) 7.3, CH2<, COD, 4H). A similar but slightly broader
pattern was observed at -75 °C: 7.97, 7.85, 7.57, 7.34 (m, Ph,
PPh3Me, C2Ph, 25 H); 4.34 (v br, CHd, COD, 4H); 3.32 (d,
2J P-H ) 14.4, PPh3(CH3)); 2.43 (v br, CH2<, COD, 4H); 1.82
(d, J H-H ) 7.7, CH2<, COD, 4H). 19F NMR (acetone-d6, δ): at
16 °C, -114.76 (d, 3J Pt-o-F ) 395.1, 4 o-F); -167.31 (m, 4 m-F,
2 p-F). A similar pattern was observed at -75 °C: -114.65
(s, 3J Pt-o-F ) 402.9, 4 o-F); -165.87 (m, 4 m-F, 2 p-F). 13C NMR
-73 °C (∆G200 ≈ 9.25 kcal‚mol-1) and, finally, splits in two
#
3
broad singlets at -80 °C: -114.21 (s br, J Pt-o-F ) ≈ 340, 2
o-F), -114.73 (s br, 3J Pt-o-F ) 380.6, 2 o-F); -165.55 (t, 2 p-F),
-165.90 (m, 4 m-F). 13C NMR (CDCl3, δ): at 16 °C, 148.0 (dd,
2
1J C-F ) 224, J C-F ) 25), 135.8 (dm) (C6F5); a badly resolved
signal at 134.4, which overlaps with one of the multiplets due
to the carbon of C6F5 groups, is probably due to CR: 101.7 (d,
(CDCl3, δ): at -50 °C, 147.3 (dd, J C-F ) 227, J C-F ) 25),
1J Rh-C ) 5.4, J Pt-C ≈ 240, Câ, CRtCâSiMe3); 79.0 (d, J Rh-C
)
1
2
2
1
3
135.7 (dm) (C6F5); 134.8 (s, p-C, PPh3Me); 132.4 (d, J P-C
)
12.6, CHd, COD); 58.8 (s, N-CH2-(CH2)2-CH3); 31.2 (s,
CH2<, COD); 23.8, 19.3 (s, N-CH2-(CH2)2-CH3); 13.5 (s,
N-(CH2)3-CH3); 1.9 (s, 1J C-Si ) 55.5, SiMe3). At -50 °C, 147.4
(dm, 1J C-F ) 226), 135.4 (dm) (C6F5); 101.3 (s br, 2J Pt-C ≈ 235,
Câ, CRtCâSiMe3); 78.0 (v br, CHd, COD); 58.1 (s, N-CH2-
(CH2)2-CH3); 31.0 (v br, CH2<, COD); 23.3, 19.3 (s, N-CH2-
10.7, m-C, PPh3Me); 132.1 (s, Ph,C2Ph); 129.9 (d, 2J P-C ) 12.9,
o-C, PPh3Me); 127.8, 127.0, 126.4 (s, Ph, C2Ph); 118.0 (d, 1J P-C
1
) 89, i-C, PPh3Me); 109.6 (s br, J Pt-C ) 856 Hz, CR, CRtCâ-
2
Ph); 99.4 (s, J Pt-C ) 254 Hz, Câ, CRtCâPh); 81.0 (s br, CHd,
COD); 30.8 (s br, CH2<, COD); 9.4 (d, 1J P-C ) 57, PPh3(CH3)).
Da ta for 2b. Anal. Calcd for C48F10H66NPtRh: C, 50.35; H,
5.81; N, 1.22. Found: C, 50.19; H, 6.40; N, 1.39. ΛM: 76.6
Ω-1‚cm2‚mol-1. MS FAB(-): m/z ) 902 [M] 100; 794 [M -
1
(CH2)2-CH3); 13.5 (s, N-(CH2)3-CH3); 1.6 (s, J C-Si ) 55.3,
SiMe3).
Rea ction s of Q2[cis-P t(C6F 5)2(CtCR)2] (Q ) P P h 3Me,
R ) P h ; Q ) NBu 4, R ) tBu , SiMe3) w ith [M(µ-Cl)(COD)]2
(M ) Rh , Ir ). All the reactions were carried out treating
suspensions of [M(µ-Cl)(COD)]2 (M ) Rh, Ir) in 20 mL of
acetone at -20 °C with Q2[cis-Pt(C6F5)2(CtCR)2] (Q ) PPh3-
t
t
COD] 13; 692 [Pt(C6F5)2(C2 Bu)2 + 1] 22; 611 [Pt(C6F5)2(C2 -
Bu) + 1] 20; 530 [Pt(C6F5)2 + 1] 20; 511 [Pt(C6F5)(C6F4) + 1]
47; 362 [Pt(C6F5)] 35%. IR (cm-1): ν(CtC) 2044 (m), 2017 (m);
1
ν(C6F5)x-sensitive 783 (vs), 776 (vs). H NMR (acetone-d6, δ): at
t
16 °C, 4.76 (s br, CHd, COD, 4H); 3.46 (m, N-CH2-, NBu4,
8H); 2.52 (br, CH2<, COD, 4H); 1.84 (m, CH2< (COD) and
-CH2- (NBu4), 12H); 1.43 (m, -CH2-, NBu4, 8H); 1.24 (s,
C(CH3)3, 18H); 0.98 (t, -CH3, NBu4, 12H). At -80 °C a similar
pattern is observed with the exception of the signal due to the
olefinic protons of the COD, which practically coalesces: 4.66
(v br, CHd, COD, 4H); 3.41 (s br, N-CH2-, NBu4, 8H); 2.46
Me, R ) Ph; Q ) NBu4, R ) Bu, SiMe3), varying only the
reaction time. The resulting solutions were evaporated to
dryness, and the residues thus obtained were treated with ca.
5 mL of cold EtOH.
Rea ction s of (P P h 3Me)2[cis-P t(C6F 5)2(CtCP h )2] w ith
[R h (µ-Cl)(COD)]2. Starting from 0.0766 g (0.155 mmol) of
[Rh(µ-Cl)(COD)]2 and 0.200 g (0.155 mmol) of (PPh3Me)2[cis-
Pt(C6F5)2(CtCPh)2] (molar ratio Rh/Pt 2:1), and after 15 min
of stirring, an orange solid identified (1H NMR) as a mixture
of 2a and [Rh(µ-Cl)(COD)]2 (molar ratio 2.5:1) was obtained.
(27) Braun, S.; Kalinonowski, H.-O.; Berger, S. 100 and More Basic
NMR Experiments; VCH: Weinheim, Germany, 1996.
(28) Espinet, P.; Fornie´s, J .; Mart´ınez, F.; Sote´s, M.; Lalinde, F.;
Moreno, M. T.; Ruiz, A.; Welch, A. J . J . Organomet. Chem. 1991, 403,
253.
1
Monitoring of the reaction by H and 19F NMR spectroscopies
reveals that no other product is formed.
(29) (a) Chatt, J .; Venanzi, L. M. J . Chem. Soc. 1957, 4735. (b)
Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88.
(30) Herde, J . L.; Lambert, J . C.; Senoff, C. V. Inorg. Synth. 1974,
15, 18.
An orange solid identified as 2a was also obtained when
the reaction was performed with 0.0287 g (0.058 mmol) of [Rh-
(µ-Cl)(COD)]2 and 0.150 g (0.117 mmol) of (PPh3Me)2[cis-Pt-
(C6F5)2(CtCPh)2] (molar ratio Rh/Pt 1:1, 15 min, 81% yield).
(31) Smith, G. F.; Ring, J . J . Am. Chem. Soc. 1937, 59, 1889.

4352 Organometallics, Vol. 18, No. 21, 1999
Ara et al.
Rea ction s of (NBu 4)2[cis-P t(C6F 5)2(CtCtBu )2] w ith [Rh -
(µ-Cl)(COD)]2. Starting from 0.063 g (0.128 mmol) of [Rh(µ-
Cl)(COD)]2 and 0.151 g (0.128 mmol) of (NBu4)2[cis-Pt-
(C6F5)2(CtCtBu)2] (molar ratio Rh/Pt 2:1), and after 40 min of
stirring, an orange solid identified as (NBu4)[{cis-Pt(C6F5)2(µ-
1κCR:η2-CtCtBu)2}{Rh2(µ-Cl)(COD)2}], 4b , was obtained.
Yield: 67%.
Complex 4b was also obtained using the same reaction time
and an equimolar Rh/Pt ratio: 0.063 mg (0.128 mmol) of [Rh-
(µ-Cl)(COD)]2 and 0.300 mg (0.256 mmol) of (NBu4)2[cis-Pt-
(C6F5)2(CtCtBu)2]. Yield: 56% (based on Rh).
ratio 4c/2c/[Rh(µ-Cl)(COD)] 1:4.5:2.25; in acetone-d6, K ) 3.5
× 10-2 mol1/2‚L-1/2 at 16 °C, e.g., for a [4c]initial ) 2.6 × 10-2 M,
dissociation ca. 38%, molar ratio 4c/2c/[Rh(µ-Cl)(COD)] 3.3:
2:1. 1H NMR (acetone-d6, δ): at 16 °C, 4.55 (s br, CHd, COD);
3.46 (m, N-CH2-, NBu4); 2.54 (m br, CH2<, COD); 1.83 (m,
-CH2-, NBu4); 1.74 (m, CH2<, COD); 1.44 (m, -CH2-, NBu4);
0.98 (t, -CH3, NBu4), 0.25 (s, SiMe3). At -80 °C the same
pattern is observed: 4.45 (s br, CHd, COD); 3.42 (m, N-CH2-,
NBu4); 2.46 (m br, CH2<, COD); 1.75 (m br, -CH2-, NBu4);
1.32 (m br, CH2< (COD) and -CH2- (NBu4)); 0.89 (t, -CH3,
NBu4), 0.20 (s, SiMe3). 19F NMR (acetone-d6, δ): at 16 °C,
-114.69 (dm, 3J Pt-o-F ) 384, 4 o-F); -168.04 (m, 4 m-F, 2 p-F).
The signal due to the o-F coalesces at ca. -73 °C. At -80 °C,
-112.7 (v br, 2 o-F), -117.0 (v br, 2 o-F); -166.54 (m, 4 m-F,
2 p-F). In all the spectra (1H and 19F NMR) signals due to 2c
and [RhCl(COD)]2 are also observed. Due to the extent of the
Da ta for 4b. Anal. Calcd for C56ClF10H78NPtRh2: C, 48.34;
H, 5.64; N, 1.01. Found: C, 48.16; H, 5.11; N, 1.02. ΛM: 89.8
Ω-1‚cm2‚mol-1. MS FAB(-): m/z ) 1148 [M - 1] 16; 902 [2b]
t
100; 794 [2b - COD] 15; 692 [Pt(C6F5)2(C2 Bu)2 + 1] 15; 611
t
[Pt(C6F5)2(C2 Bu) + 1] 28; 565 [Rh2(COD)3Cl] 31; 510 [Pt(C6F5)-
dissociation, the assignment of the 13C NMR spectra in
(C6F4)] 90; 362 [Pt(C6F5)] 41. IR (cm-1): ν(CtC) 2033 (s);
ν(C6F5)x-sensitive 788 (s), 780 (s). This complex dissociates in
solution to give an equilibrium mixture of 2b, 4b, and [RhCl-
(COD)]2. In CDCl3, K ≈ 5.1 × 10-2 mol1/2‚L-1/2 at 16 °C (e.g.,
for a [4]initial ) 1.47 × 10-2 M, dissociation ca. 43%, molar ratio
4b/2b/[Rh(µ-Cl)(COD)] 2.7:2:1). In acetone-d6 complex 4b
dissociates to a lesser extent (K ≈ 9.2 × 10-3 mol1/2‚L-1/2 at 16
°C, e.g., for a [4b]initial ) 1.35 × 10-2 M, dissociation ca. 20%,
1
acetone-d6 is rather uncertain: at 16 °C, 148.9 (dm, J C-F
≈
211), 136.4 (dm) (C6F5); 128.1 (m), 97.8 (m) (CR or Câ, CRtCâ-
SiMe3, 2c or 4c); 79.5 (m), 78.7 (h) (CHd, COD, 2c or 4c); 59.3
1
14
(t, J C- ) 2.8, N-CH2-(CH2)2-CH3); 31.5 (s, CH2<, COD);
N
24.3 (s, N-(CH2)2-CH2-CH3); 20.3 (t, 2J C- ) 1.3, N-CH2-
14
N
CH2-CH2-CH3); 13.8 (s, N-(CH2)3-CH3); 1.8 (s, SiMe3). Two
singlets at 31.9 (CH2<, COD, 2c) and 2.0 (SiMe3, 2c) are also
observed.
1
molar ratio 4b/2b/[Rh(µ-Cl)(COD)] 8:2:1). H NMR (acetone-
Rea ction s of (NBu 4)2[cis-P t(C6F 5)2(CtCSiMe3)2] w ith
[Ir (µ-Cl)(COD)]2. The reactions between [Ir(µ-Cl)(COD)]2 and
(NBu4)2[cis-Pt(C6F5)2(CtCSiMe3)2] in a 2:1 Ir/Pt ratio (0.100
g, 0.149 mmol, [Ir(µ-Cl)(COD)]2 and 0.180 g, 0.149 mmol,
(NBu4)2[cis-Pt(C6F5)2(CtCSiMe3)2]; 10 min) or 1:1 Ir/Pt ratio
(0.056 g, 0.084 mmol, [Ir(µ-Cl)(COD)]2 and 0.200 g, 0.164 mmol,
(NBu4)2[cis-Pt(C6F5)2(CtCSiMe3)2]; 2 h) afforded a yellow solid,
which was identified as (NBu4)[cis-Pt(C6F5)2(µ-1κCR:η2-Ct
CSiMe3)(µ-2κCR:η2-CtCSiMe3)Ir(COD)], 3c. Yields (based on
Pt): 65 and 30.5%, respectively.
Complex 3c can also be obtained in a very low yield (15%)
by treatment of an equimolar amount of 1c (0.170 g, 0.140
mmol) with a solution of [Ir(COD)(acetone)](ClO4), prepared
from 0.0497 mg (0.074 mmol) of [Ir(µ-Cl)(COD)]2 and 0.0307
mg (0.148 mmol) of AgClO4 and 1 h of stirring, in 20 mL of
acetone. The resulting yellow solution, which was shown to
contain 3c by 19F NMR, was evaporated to dryness and the
residue treated with 20 mL of Et2O to give a white suspension
(NBu4ClO4) in a yellow solution. Filtration of the mixture,
evaporation to dryness, and treatment of the resulting oily
residue with cold hexane (∼10 mL) afforded 0.027 g of a yellow
solid, which was identified as complex 3a .
Da ta for 3c. Anal. Calcd for C46F10H66IrNPtSi2: C, 43.63;
H, 5.25; N, 1.10. Found: C, 43.40; H, 4.87; N, 1.07. ΛM: 71.1
Ω-1‚cm2‚mol-1. MS FAB(-): m/z ) 1024 [M] 100; 926 [M -
C2SiMe3] 35; 627 [Pt(C6F5)2(C2SiMe3) + 1] 78; 529 [Pt(C6F5)2]
48; 509 [Pt(C6F5)(C6F4) - 1] 69; 362 [Pt(C6F5)] 67. IR (cm-1):
ν(CtC) 1868 (vs), 1823 (vs); ν(C6F5)x-sensitive 796 (vs), 781 (s).
1H NMR (CDCl3, δ): at 16 °C, 4.27 (s br, CHd, COD, 4H);
3.15 (m br, N-CH2-, NBu4, 8H); 2.16 (m, CH2<, COD, 4H);
1.89 (m, CH2<, COD, 4H); 1.60 (8H), 1.40 (8H) (m, -CH2-,
NBu4); 0.96 (t, -CH3, NBu4, 12H); -0.12 (s, SiMe3, 18H). At
-50 °C, 4.89 (2H), 3.55 (2H) (s br, CHd, COD); 3.15 (br,
N-CH2-, NBu4, 8H); 2.14 (4H), 1.87 (4H) (s br, CH2<, COD);
1.58 (8H), 1.33 (8H) (s br, -CH2-, NBu4); 0.91 (s br, -CH3,
NBu4, 12H); -0.16 (9H), -0.20 (9H) (s, SiMe3, the singlets
overlapped partially). The signal due to the SiMe3 protons
d6, δ): at 16 °C, 4.62 (s br, CHd, COD); 3.46 (m, N-CH2-,
NBu4); 2.48 (m br, CH2<, COD); 1.84 (m, -CH2-, NBu4); 1.69
(d, J H-H ) 7.9, CH2<, COD); 1.44 (m, -CH2- (NBu4) and s,
C(CH3)3); 0.98 (t, -CH3, NBu4). A similar pattern was observed
at 40 °C. By lowering the temperature, the olefinic signal
broadens, coalesces at ca. -30 °C (∆G243 ) 11.1 kcal‚mol-1),
#
and splits at -50 °C: 4.91 (br, CHd, COD); 4.20 (br, CHd
protons of the COD ligand of 4b overlapped with olefinic
protons of [RhCl(COD)]2 present due to the dissociation
process); 3.42 (m, N-CH2-, NBu4); 2.42 (m br, CH2<, COD);
1.77 (m, -CH2-, NBu4), 1.66 (m br, CH2<, COD) (both of the
signals are overlapped); 1.39 (m, -CH2- (NBu4) and s,
C(CH3)3); 0.93 (t, -CH3, NBu4). At lower temperatures both
olefinic signals (δ 4.91, 4.20) broaden again, and at ca. -80
°C the lower-field signal coalesces. 19F NMR (acetone-d6, δ):
3
at 16 °C, -114.39 (dm, J Pt-o-F ) 384, 4 o-F); -168.31 (m, 4
m-F); -168.98 (t, 2 p-F). At -80 °C, -114.30 (hump, 4 o-F);
-167.05 (m, 4 m-F); -167.48 (t, 2 p-F). In all the spectra (1H
and 19F NMR) signals due to 2b and [RhCl(COD)]2 are also
observed. 13C NMR (acetone-d6, δ): at -50 °C, 147.0 (dm, 1J C-F
1
2
) 226), 134.4 (dm, J C-F ≈ 230) (C6F5); 105.2 (s, J Pt-C ≈ 270,
t
t
Câ, CRtCâ Bu); 81.1 (m, CR, CRtCâ Bu); 75.9, 74.9 (m br, CHd
, COD); 57.2 (s, N-CH2-(CH2)2-CH3); 31.5 (s, C(CH3)3); 31.0
(s, CMe3); 30.3, 29.9 (br, CH2<, COD); 22.6, 18.8 (s, N-CH2-
(CH2)2-CH3); 12.6 (s, N-(CH2)3-CH3). A small singlet at 31.7
[C(CH3)3, 2b] is also observed.
Rea ction s of (NBu 4)2[cis-P t(C6F 5)2(CtCSiMe3)2] w ith
[Rh (µ-Cl)(COD)]2. Starting from 0.075 g (0.152 mmol) of [Rh-
(µ-Cl)(COD)]2 and 0.183 g (0.152 mmol) of (NBu4)2[cis-Pt-
(C6F5)2(CtCSiMe3)2] (molar ratio Rh/Pt 2:1), and after 10 min
of stirring, an orange solid identified as (NBu4)[{cis-Pt(C6F5)2-
(µ-1κCR:η2-CtCSiMe3)2}{Rh2(µ-Cl)(COD)2}], 4c, was obtained.
Yield: 71%.
By using the same reaction time and a 1:1 Rh/Pt ratio
(0.0225 g, 0.046 mmol, [Rh(µ-Cl)(COD)]2 and 0.110 g, 0.091
mmol, (NBu4)2[cis-Pt(C6F5)2(CtCSiMe3)2]) an orange solid
which is identified as complex 2c was obtained. Yield: 42%.
Da ta for 4c. Anal. Calcd for C54ClF10H78NPtRhSi2: C,
45.56; H, 5.52; N, 0.98. Found: C, 45.31; H, 5.28; N, 0.89. ΛM:
78.1 Ω-1‚cm2‚mol-1. MS FAB(-): m/z ) 1181 [M] 13; 934 [2c]
100; 724 [Pt(C6F5)2(C2SiMe3)2 + 1] 12; 528 [Pt(C6F5)2 - 1] 24;
361 [Pt(C6F5) - 1] 30. IR (cm-1): ν(CtC) 1966 (vs), 1952 (vs);
ν(C6F5)x-sensitive 789 (vs), 778 (vs). This complex dissociates in
solution to give an equilibrium mixture of 2c, 4c, and [RhCl-
(COD)]2. In CDCl3, K ) 4.51 × 10-1 mol1/2‚L-1/2 at 16 °C, e.g.,
for a [4c]initial ) 2.46 × 10-2 M, dissociation ca. 82%, molar
coalesces between -40 and -50 °C (∆G230# ) 11.86 kcal‚mol-1
)
and the signal due to the olefinic protons of the COD coalesces
at -20 °C (∆G253 ) 10.84 kcal‚mol-1). 19F NMR (CDCl3, δ):
#
3
at 16 °C, -114.95 (d, J Pt-o-F ) 444.5, 4 o-F); -166.29 (t, 2
3
p-F); -166.76 (m, 4 m-F). At -50 °C: -114.21 (d, J Pt-o-F
)
3
373, 2 o-F trans to σ-CtC); -116.26 (d, J Pt-o-F ) 520, 2 o-F
trans to η2-CtC); -165.23 (m br, 2 p-F); -166.30 (m, 4 m-F).
The signal due to the o-F coalesces at ca. -20 °C and the
#
corresponding one to the p-F at ca. -40 °C (∆G253 ) 11.13

Bi- and Trinuclear Bis(alkynyl) Complexes
Organometallics, Vol. 18, No. 21, 1999 4353
Ta ble 2. Cr ysta llogr a p h ic Da ta a n d Str u ctu r e Refin em en t P a r a m eter s for Com p lexes 2a , 3c, a n d 4b
2a
3c
4b
empirical formula
fw
C
55H40F10PPtRh
C46H66NF10Si2PtIr
1266.48
C87.5H150.5N1.5Cl3F15Rh3Pt1.5
2216.31
1219.84
a (Å)
b (Å)
c (Å)
21.921(4)
10.765(2)
19.765(4)
90
90
90
4664.14(2)
0.71073
200
graphite monochomated
Mo KR
orthorhombic
Pna21
14.667(7)
18.946(6)
17.603(6)
90
96.23(6)
90
4862.79
0.71073
36.629(7)
22.882(5)
28.661(6)
90
127.21(3)
90
19132(7)
0.71073
R (deg)
â (deg)
γ (deg)
volume (Å3), Z
wavelength (Å)
temperature (K)
radiation
210
200
graphite monochromated
Mo KR
monoclinic
graphite monochromated
Mo KR
monoclinic
C2/ c
crystal system
space group
P21/n
cryst dimens (mm)
0.3 × 0.2 × 0.3
0.4 × 0.3 × 0.2
0.70 × 0.45 × 0.36
abs coeff (mm-1
3.462
5.73
2.848
)
transmission factors
abs corr
diffractometer
0.975, 0.809
Ψ scans
Siemens P4
4-50
4827
4495 (Rint ) 0.074)
full-matrix least-squares on F2
1.049
R1 ) 0.0681,
wR2 ) 0.1576
R1 ) 0.1050,
wR2 ) 0.1947
0.2927, 0.1418
Ψ scans
Siemens Stoe AED2
4-47
7750
7163 (Rint ) 0.028)
full matrix leasts-squares on F
1.225
1.000, 0.591
Ψ scans
Siemens P4
4-48
15430
14788 (Rint ) 0.021)
full-matrix least squares on F2
1.045
R1 ) 0.0686,
wR2 ) 0.1832
R1 ) 0.1208,
wR2 ) 0.2210
2θ range (deg)
no. of reflns collected
no. of indep reflns
refinement method
goodness-of-fit on F2 a
final R indices (I > 2σ(I))b
R1) 0.0383,
wR ) 0.0477
R indices (all data)
-
-
Goodness-of-fit ) [∑w(Fo - Fc2)2/(nobs - nparam)]1/2. w ) [σ2 (Fo) + (g1P)2 + g2P]-1; P ) [max(Fo2; 0) + 2Fc2]/3. R1 ) ∑(|Fo| - |Fc|)/
a
2
b
∑|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑w(Fc2)2]1/2
.
2
1
kcal‚mol-1). 13C NMR (CDCl3, δ): at 16 °C, 147.6 (dd, J C-F
)
belong to a NBu4 group were refined as disordered over two
positions. In the asymmetric unit of 4b there are 1.5 molecules
of the complex, the other half-molecule being generated by
symmetry since the Pt atom and the bridging Cl are located
in special positions. The half-molecule of NBu4 is disordered
over two positions, having two common carbon atoms, C(78)
and C(79). N(2) and C(99), which belong to different NBu4
units, occupy the same site at half-occupancy. Regions of
electron density located at nonbonding distances were modeled
as interstitial solvents: a molecule of CHCl3, refined at half-
occupancy with anisotropic thermal parameters, and three
carbon atoms of a molecule of cyclohexane (the other carbon
atoms being generated by a symmetry center) refined with
isotropic thermal parameters at full occupancy. That makes
one-third of each solvent molecule per formula unit. There
are some peaks of electron density higher than 1 e/A3 in
the final map in all three structures (maximum 2.02 for 2a ,
1.16 for 3c, and 1.69 for 4b). In all cases, they are located very
close to the heavy atoms or in the disordered solvent areas
and have no chemical significance. All calculations were
carried out using the programs SHELXTL-PLUS32 and
SHELXL-93.33
2
223, J C-F ) 25), 135.9 (dm) (C6F5); 124.2, 112.85 (m, tenta-
tively ascribed to CR and Câ, CRtCâSiMe3); 69.4 (v br, CHd,
COD); 58.7 (s, N-CH2-(CH2)2-CH3); 31.9 (s, CH2<, COD);
23.8, 19.6 (s, N-CH2-(CH2)2-CH3); 13.4 (s, N-(CH2)3-CH3);
1
1
1.3 (s, SiMe3, J Si-C ) 54.6). At -50 °C, 147.1 (dm, J C-F
)
226), 135.5 (dm, 1J C-F ) 240) (C6F5); 122.9, 121.7, 117.5, 108.1
(m, tentatively ascribed to two CR and two Câ, CRtCâSiMe3);
62.3 (s br, CHd, COD); 58.1 (s br, CHd (COD) and N-CH2-
(CH2)2-CH3); 32.0, 31.5 (s br, CH2<, COD, both of the signals
are overlapped); 23.4, 19.4 (s, N-CH2-(CH2)2-CH3); 13.5 (s,
N-(CH2)3-CH3); 1.2, 1.0 (s br, SiMe3).
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of Com p lexes
2a , 3c, a n d 4b. Crystals of the three respective complexes were
obtained at low temperature (-30 °C) by slow diffusion of
hexane into chloroform solutions. Suitable crystals of 2a , 3c,
or 4b were selected and fixed with epoxy on top of glass fibers
and transferred to the cold stream of the low-temperature
device of automated four-circle difractometers Siemens P4 (2a ,
4b) or Siemens STOE AED2 (3c). For complex 2a , the
enantiomorph was chosen on the basis of the Flack parameter
x ) -0.0163 with esd 0.0183 (expected values are 0 for correct
and +1 for inverted absolute structure). Crystallographic data
and structure refinement parameters are shown in Table 2.
Cell constants were calculated from 100 well-centered reflec-
tions with 2θ angles ranging from 16° to 30° (2a , 4b) or 24
reflections with 2θ angles from 24° to 29° (3c). Data were
collected at 200 K (2a , 4b) or 210 K (3c) by the ω/2θ (2a ), ω/θ
(3c), or ω (4b) methods. Three check reflections measured at
regular intervals showed no significant loss of intensity at the
end of data collection in each case. An empirical absorption
correction based on ψ scans was applied. The structures were
solved by Patterson and Fourier methods. All non-hydrogen
atoms were located in succeeding difference Fourier syntheses
and refined with anisotropic thermal parameters except four
C atoms in 2a . No hydrogen atoms were added to the models.
In complex 2a the anisotropically refined C(1), C(6), C(13), and
C(21) have large displacement parameters, and some disorder
was observed. In complex 3c the C(33) and C(34) atoms that
Ack n ow led gm en t. We wish to thank the Direccio´n
General de Ensen˜anza Superior (Spain, Project PB 95-
0003-CO2-01,02) and the Universidad de La Rioja
(Project API-99/B17) for their financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables giving posi-
tional and thermal parameters and bond distances and bond
angles for 2a , 3c, and 4b. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM990314Z
(32) SHELXTL-PLUS, Software Package for the Determination of
Crystal Structures, Release 4.0; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1990.
(33) Sheldrick, G. M. SHELXL-93, a Program for Crystal Structure
Determination; University of Go¨ttingen: Go¨ttingen, Germany, 1993.