cis,cis,cis-1,5,9-cyclododecatriene-metal complexes

Article abstract of DOI:10.1021/om7004172

The ligand properties of cis,cis,cis-1,5,9-cyclododecatriene (c,c,c-cdt) have been explored. For the known (c,c,c-cdt)Ni (1b) and (c,c,c-cdt)(AgNO ₃)₃ (5) complexes and the new [(c,c,c-cdt)Cu(MeOH)]BF ₄ (6b), [(c.c,c-cdt)Cu][Al{OC(CF₃)₃} ₄] (6d), and (^tBu₂PC₂H ₄P^tBu₂)Ni(η²-c,c,c-cdt) (7b) complexes, the molecular structures have been determined. The c,c,c-cdt ligand in 5 and 7b retains the C₂ symmetrical helical conformation of the free c,c,c-cdt, whereas in lb and 6b,d, it assumes a C₃ symmetrical ratchet conformation. The coordination geometry of the metal in 6b is tetrahedral, and it is trigonal pyramidal in lb and 6d. Details of the synthesis and chemical and spectroscopic properties of the complexes are reported.

Full text of DOI:10.1021/om7004172

4872
Organometallics 2007, 26, 4872-4880
Articles
cis,cis,cis-1,5,9-Cyclododecatriene-Metal Complexes
Eleonora S. Chernyshova, Richard Goddard, and Klaus-Richard Po¨rschke*
Max-Planck-Institut fu¨r Kohlenforschung, D-45466 Mu¨lheim an der Ruhr, Germany
ReceiVed April 30, 2007
The ligand properties of cis,cis,cis-1,5,9-cyclododecatriene (c,c,c-cdt) have been explored. For the known
(c,c,c-cdt)Ni (1b) and (c,c,c-cdt)(AgNO3)3 (5) complexes and the new [(c,c,c-cdt)Cu(MeOH)]BF4 (6b),
[(c,c,c-cdt)Cu][Al{OC(CF3)3}4] (6d), and (tBu2PC2H4PtBu2)Ni(η2-c,c,c-cdt) (7b) complexes, the molecular
structures have been determined. The c,c,c-cdt ligand in 5 and 7b retains the C2 symmetrical helical
conformation of the free c,c,c-cdt, whereas in 1b and 6b,d, it assumes a C3 symmetrical ratchet
conformation. The coordination geometry of the metal in 6b is tetrahedral, and it is trigonal pyramidal
in 1b and 6d. Details of the synthesis and chemical and spectroscopic properties of the complexes are
reported.
(3c)7d soon also became available, mainly by displacement of
the t,t,t-cdt ligand in 1a with the respective alkene. Notwith-
standing intrinsic properties of the alkenes, such as the cyclo-
trienes bearing 2-fold substituted CdC bonds in contrast to the
parent ethene, and that trans-cyclooctene and norbornene are
strained alkenes, the driving force for the t,t,t-cdt-alkene
displacement reactions of 1a appears to result from the out-of-
plane twist of the CdC bonds in 1a and the associated poor
backbonding from Ni(0), making 1a less stable than the other
trigonal planar complexes 1b and 3a-c, which, due to an in-
plane arrangement of the CdC bonds, have enhanced back-
bonding, as anticipated both on the basis of experimental
evidence7 and on the basis of MO calculations.8
Complexes 1a, 2, and 3c are frequently used as a source of
“naked nickel”,1b but little is known about the properties of 1b.
Whereas 1a forms a series of tetrahedral adducts (t,t,t-cdt)NiL
with a broad range of ligands such as L ) PR3, P(OR)3, CO,
HAlR3-, and Me-,1c,9 for the isomeric 1b, only a single adduct
(c,c,c-cdt)Ni{P(OC6H4-2-C6H5)3} (4)6 with a sterically much
encumbered phosphite has been briefly mentioned. Beyond it,
the only other metal complexes of c,c,c-cdt that are known so
far are (c,c,c-cdt)(AgNO3)3 (5)10a and (c,c,c-cdt)CuOTf (6a).10b
The reason for the scarcity of the c,c,c-cdt complexes may lie
in the laborious synthesis6a,10 of the ligand. We were intrigued
to learn more about the structure of 1b and the ligand properties
of c,c,c-cdt11 and have therefore studied some c,c,c-cdt-metal
complexes in detail.
Introduction
Wilke’s discovery of trigonal planar Ni(t,t,t-cdt) (1a; t,t,t-
cdt ) trans,trans,trans-1,5,9-cyclododecatriene) and tetrahedral
Ni(cod)2 (2; cod ) cis,cis-1,5-cyclooctadiene) in 1960 laid the
foundation for the then quite spectacular and even today still
fascinating class of homoleptic transition metal(0)-alkene
complexes.1 These complexes have to be seen in a historic
context with other milestones of organometallic chemistry, such
as ferrocene,2 the Ziegler catalysts,3 bis(benzene)chromium,4 and
bis(π-allyl)nickel,5 all of which were discovered within a single
decade. A series of derivatives of 1a such as the isomeric Ni-
(c,c,c-cdt) (1b; c,c,c-cdt ) cis,cis,cis-1,5,9-cyclododecatriene),6
tris(trans-cyclooctene)nickel(0) (3a),6a tris(norbornene)nickel-
(0) (3b),7a and, above all, the parent tris(ethene)nickel(0)
* Corresponding author. E-mail: poerschke@mpi-muelheim.mpg.de;
fax: 011492083062980.
(1) (a) Wilke, G. Angew. Chem. 1960, 72, 581. (b) Wilke, G. Angew.
Chem. 1963, 75, 10. (c) Bogdanovic´, B.; Kro¨ner, M.; Wilke, G. Liebigs
Ann. Chem. 1966, 699, 1.
(2) (a) Kealy, T. J.; Pauson, P. L. Nature 1951, 168, 1039. (b) Miller, S.
A.; Tebboth, J. A.; Tremaine, J. F. J. Chem. Soc. 1952, 632. (c) Wilkinson,
G.; Rosenblum, M.; Whiting, M. C.; Woodward, R. B. J. Am. Chem. Soc.
1952, 74, 2125. (d) Fischer, E. O.; Pfab, W. Z. Naturforsch., B: Chem.
Sci. 1952, 7, 377.
(3) Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem. 1955,
67, 426.
(4) (a) Fischer, E. O.; Hafner, W. Z. Naturforsch., B: Chem. Sci. 1955,
10, 665. (b) Fischer, E. O.; Hafner, W. Z. Anorg. Allg. Chem. 1956, 286,
146. (c) Fischer, E. O.; Fritz, H.-P. Angew. Chem. 1961, 73, 353.
(5) (a) Wilke, G.; Bogdanovic´, B. Angew. Chem. 1961, 73, 756. (b)
Wilke, G. Angew. Chem. 1966, 78, 157; Angew. Chem., Int. Ed. 1966, 5,
151.
(8) (a) Ro¨sch, N.; Hoffmann, R. Inorg. Chem. 1974, 13, 2656. (b) Pitzer,
R. M.; Schaefer, H. F., III. J. Am. Chem. Soc. 1979, 101, 7176. (c) Schaefer,
H. F., III. J. Mol. Struct. 1981, 76, 117.
(6) (a) Jonas, K. Ph.D. Thesis, Universita¨t Bochum, 1968. (b) Jonas,
K.; Heimbach, P.; Wilke, G. Angew. Chem. 1968, 80, 1033; Angew. Chem.,
Int. Ed. 1968, 7, 949. (c) Hoffmann, E. G.; Jolly, P. W.; Ku¨sters, A.; Mynott,
R.; Wilke, G. Z. Naturforsch., B: Chem. Sci. 1976, 31, 1712. (d) Jolly, P.
W.; Mynott, R. AdV. Organomet. Chem. 1981, 19, 257.
(7) (a) Wilke, G.; Yamamoto, A.; Kru¨ger, K.; Tsay, Y.-H. Unpublished
results; cited in ref 7b,c. (b) Fischer, K.; Jonas, K.; Misbach, P.; Stabba,
R.; Wilke, G. Angew. Chem. 1973, 85, 1002; Angew. Chem., Int. Ed. 1973,
12, 943. (c) Fischer, K.; Jonas, K.; Mollbach, A.; Wilke, G. Z. Naturforsch.,
B: Chem. Sci. 1984, 39, 1011. (d) Fischer, K.; Jonas, K.; Wilke, G. Angew.
Chem. 1973, 85, 620; Angew. Chem., Int. Ed. 1973, 12, 565.
(9) Wilke, G. Angew. Chem. 1988, 100, 189; Angew. Chem., Int. Ed.
1988, 27, 185 and references therein.
(10) (a) Untch, K. G.; Martin, D. J. J. Am. Chem. Soc. 1965, 87, 3518.
(b) Salomon, R. G.; Kochi, J. K. J. Am. Chem. Soc. 1973, 95, 1889. (c)
Trauer, H.; Haufe, G. Z. Chem. 1988, 28, 290.
(11) For reports on physical properties of c,c,c-cdt (registry no. 4736-
48-5), see: (a) (conformational analysis) Anet, F. A. L.; Rawdah, T. N. J.
Org. Chem. 1980, 45, 5243. (b) (exclusion of tris-homoconjugation)
McEwen, A. B.; Schleyer, P. v. R. J. Org. Chem. 1986, 51, 4357. (c) (vicinal
olefinic 1H-1H coupling constant) Radeglia, R.; Poleschner, H.; Haufe, G.
Magn. Res. Chem. 1993, 31, 1054.
10.1021/om7004172 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/30/2007

cis,cis,cis-1,5,9-Cyclododecatriene-Metal Complexes
Organometallics, Vol. 26, No. 20, 2007 4873
most solvents, including MeOH, H2O, THF, and MeCN,
consistent with a durable catenate structure, although it modestly
dissolves in CH2Cl2. Compound 5 is thermally stable to about
160 °C (DSC) and thus less stable than either A or AgNO3 itself
(mp 212 °C).15 In the ESI mass spectrum (CH2Cl2), a series of
intense ions is observed of which only [(C12H18)Ag]+ (m/e 269)
and [(C12H18)2Ag2(NO3)]+ (m/e 600) allowed ready assignment.
Among the numerous structurally known AgNO3-alkene
complexes,17 there are examples in which one or several AgNO3
entities are bound to a single cyclopolyene ligand,16 one AgNO3
is coordinated by two cyclopolyene ligands,18 AgNO3 and the
cyclopolyene are both in bridging modes,19 and one central Ag+
is coordinated to all CdC bonds of the cyclopolyene ligand.20
The molecular structure of 5 is shown in Figure 2a, and details
of the crystal structure analysis are given in Table 2. Bearing
in mind the conclusion from previous structural investigations
that ring conformations of cyclopolyenes are generally not
significantly altered by AgNO3 coordination,21 it is not unex-
pected that the conformation of the c,c,c-cdt ligand in 5
corresponds to the helical conformation of the free c,c,c-cdt,
with the obvious distinction that all three CdC bonds of the
c,c,c-cdt ligand are coordinated by individual Ag+ centers. Apart
from the Ag coordination, the c,c,c-cdt ligand has a conforma-
tional C2 symmetry with the 2-fold axis running through the
midpoints of the double bond C1-C2 and the single bond C7-
C8. The CdC bonds C5-C6 and C9-C10 each have the cis-
bonded C2H4 substituents in syn alignment, and Ag2 and Ag3
coordinate at the opposite face of the respective CdC bond with
retention of the conformational C2 symmetry. The C2H4
substituents at C1-C2 have anti orientation, and the inherent
C2 symmetry is broken by the coordination of Ag1. Conse-
quently, the full (c,c,c-cdt)Ag3 core has only C1 symmetry.
The mean Ag-C coordination bond length in 5 is 2.39(6) Å
(A: 2.379 and 2.411 Å), and the mean distances for the CdC,
dCHsCH2, and CH2-CH2 bonds are 1.364(5), 1.508(3), and
1.549(7) Å, respectively. The torsional angles of the CH2-CH2
bonds are almost identical (170(2)°) and correspond to a near
single-trans conformation.
Figure 1. Schematic representation of the helical conformation
of c,c,c-cdt and its enantiomerization.
Results and Discussion
(c,c,c-cdt)(AgNO3)3 (5). We begin with a discussion of the
structure of free c,c,c-cdt and its AgNO3 complex, 5. For
uncoordinated c,c,c-cdt, the most prominent supposable con-
formations are associated with C2 (denoted helix), Cs (saddle),
C3 (ratchet),12 D3 (propeller), C3V (crown),13 and C3h (plate)
symmetry with increasing energy along this series. Untch and
Martin10a first suggested the helix conformation as the ground
state conformation of the free c,c,c-cdt, and this has since been
confirmed by Anet and Rawdah by a combination of low-
temperature NMR and empirical force field calculations.11a In
the helix conformation, all three C2H4 units of c,c,c-cdt adopt
a single-trans conformation, with two cis-CdC bonds having
the C2H4 substituents in a syn alignment and the third in an
anti alignment (Figure 1). Enantiomerization14 of this chiral
conformation occurs by a 180° CH2-CH2 bond rotation of one
of the two C2H4 substituents (a or b) at the anti aligned cis-
CdC bond, through which the original C2 axis passes. Thereby,
the former anti and syn alignments of the C2H4 substituents at
the corresponding cis-CdC bonds interchange, causing a
migration of the C2 axis of symmetry. By repetition, all three
CH2-CH2 bonds equally participate in the process.11a Because
of dynamic D3h symmetry, in the ambient temperature solution
NMR spectra, only one signal each is observed for the sCHd
and -CH2- groups, including equivalence of the geminal allyl
protons (Table 1).
Complex 5, which was originally obtained during the
synthesis process of c,c,c-cdt, 10a contains strictly three entities
of AgNO3; this is also the case in the presence of an excess of
c,c,c-cdt, where only 5 is isolated. It is closely related to the by
Untch and Martin also prepared (c,c,c-1,4,7-cyclononatriene)-
(AgNO3)3 (A; mp 248 °C dec),15 which was structurally
characterized by others.16c We obtained large colorless cubes
of 5 by cooling a water-THF solution of AgNO3 and c,c,c-cdt
to 5 °C. After isolation, the complex was almost insoluble in
The crystal structure of 5 including the AgNO3 framework
is shown in Figure 2b. Whereas in the crystals of (C9H12)-
(AgNO3)3 (A) 16c and C60(AgNO3)522 silver nitrate forms a 3-D
network with the cyclononatriene and buckminsterfullerene
molecules occupying channels, in the crystal of 5, the silver
nitrate network is only 2-D with sheets of AgNO3 separated by
c,c,c-cdt ligands. Clearly, the AgNO3 framework is important
for the formation of the solid. So far, we have not been able to
isolate Ag-η2-c,c,c-cdt complexes with only one or two
circumferentially coordinated AgNO3 entities or [(η2,η2,η2-c,c,c-
cdt)Ag]NO3 (5a) with a central Ag+ cation.
(12) The ratchet conformation has been denoted by Untch and Martin
as “symmetrical s-trans” (see their IId)10a and by Anet and Rawdah as
“crown-I”.11a According to the latter authors, the “crown-I” conformation
undergoes enantiomerization via interconversion with a C1 symmetrical
“crown-II” conformation (likewise having an energy minimun and thus
invoking a further transition state), and they discount the C3V symmetrical
conformation, which Untch and Martin originally termed crown, due to its
high energy. To avoid confusion, we refer to the C3 symmetrical “crown-
I” conformation with the term “ratchet” since the conformation has a sense
of rotation and to the C3V symmetrical as “crown”.
(13) According to DFT calculations, the C3V symmetrical crown con-
formation represents neither a minimum nor a regular transition state on
the potential surface since it comprises three imaginary frequencies. At the
B3LYP/6-31G* level, the C3V symmetrical crown lies about 6 kcal mol-1
above the C3 symmetrical ratchet minimum (4 kcal mol-1 including zero-
point and enthalpic corrections); Bu¨hl, M., personal communication.
(14) Enantiomerization is defined as the reversible interconversion of
one enantiomer into the other.
If the conformation of the c,c,c-cdt ligand of 5 in solution
1
were the same as that in the solid, rather complicated H and
13C NMR spectra would be expected due to the inequivalent
CdC bonds, even if the complex underwent a dynamic process
similar to that depicted in Figure 1. This is not the case, and
the 1H NMR spectrum of a solution of 5 in CD2Cl2 shows one
(17) Currently, there are 32 examples in the Cambridge Structural
Database (CSD), version 5.28, updated November 2006.
(18) Kuribayashi, S.; Yasuoka, N.; Mitsui, T.; Takahashi, H.; Yamaguchi,
M. Bull. Chem. Soc. Jpn. 1964, 37, 1242.
(19) (a) Coggon, P.; McPhail, A. T.; Sim, G. A. J. Chem. Soc. B 1970,
1024. (b) Mak, T. C. W. J. Organomet. Chem. 1983, 246, 331.
(20) Faure, R.; Loiseleur, H.; Haufe, G.; Trauer, H. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1985, 41, 1593.
(15) Untch, K. G.; Martin, D. J. J. Org. Chem. 1964, 29, 1903.
(16) (a) Mathews, F. S.; Lipscomb, W. N. J. Phys. Chem. 1959, 63, 845.
(b) Hartsuck, J. A.; Paul, I. C. Chem. Ind. (London) 1964, 977. (c) McPhail,
A. T.; Sim, G. A. J. Chem. Soc. B 1966, 112. (d) Jackson, R. B.; Streib,
W. E. J. Am. Chem. Soc. 1967, 89, 2539.
(21) Ganis, P.; Dunitz, J. D. HelV. Chim. Acta 1967, 50, 2379.
(22) Olmstead, M. M.; Maitra, K.; Balch, A. L. Angew. Chem. 1999,
111, 243; Angew. Chem., Int. Ed. 1999, 38, 231.

4874 Organometallics, Vol. 26, No. 20, 2007
ChernyshoVa et al.
Ag(I). While we would expect a C3 symmetrical ground state
structure for 5a, it undergoes enantiomerization to result in a
dynamic C3V symmetrical structure in solution. This process is
described next for complexes 6a-d in more detail.
(c,c,c-cdt)CuOTf (6a), [(c,c,c-cdt)Cu(MeOH)]BF4 (6b),
(c,c,c-cdt)CuBF4 (6c), and [(c,c,c-cdt)Cu][Al{OC(CF3)3}4]
(6d). In connection with this work, we became interested in
Kochi and Salomon’s Cu(I) complex 6a, which in its ionic form
is isoelectronic with the Ni(0) complex 1b. While the original
synthesis was hampered by the fact that the complex tends to
oil out of a benzene-pentane mixture, requiring repeated
recrystallizations,10b we found that the 1,5-hexadiene ligand in
(C6H10)CuOTf23 is readily displaced by 1 equiv of c,c,c-cdt.
Colorless cubes of pure 6a crystallize at ambient temperature
from a concentrated CH2Cl2-diethyl ether solution (eq 1).
Kochi and Salomon have already noted the extraordinary
thermal stability of solid 6a.10b As determined by DSC, the
melting point of 6a is 170 °C (lit. mp 160 °C),10b and
decomposition occurs only at 240 °C. DSC revealed also the
occurrence of four reversible endothermic events at -56, -24,
0, and 8 °C, indicative of increasing disorder. In the EI mass
spectrum (170 °C), the molecular ion (m/e ) 374, 5%) is
observed, which fragments by elimination of the OTf ligand to
give [(c,c,c-cdt)Cu]+ (m/e ) 225, 42%) as a further prominent
ion. The latter is also the base ion in the ESIpos spectrum.
According to NMR, a possible exchange of the c,c,c-cdt ligand
in 6a with free c,c,c-cdt or ethene is slow in solution (CD2Cl2)
at ambient temperature. The high stability of 6a can be attributed
to the macrocyclic effect;24 that is, c,c,c-cdt is ideally suited
for coordination to a central Cu+. On the basis of the single
CdC stretching band in the IR spectrum (ν(CdC) ) 1585
cm-1), Kochi and Salomon have already concluded that all three
CdC bonds in 6a are symmetrically coordinated at the Cu(I)
center. This leaves open the question as to whether 6a has an
essentially ionic structure with a possibly trigonal planar
coordinated Cu center10b or whether the complex has a
tetrahedral Cu center with tight binding of the OTf ligand, as
is suggested by the EI mass spectrum. Also, the exact
conformation of the c,c,c-cdt ligand is unknown. Unfortunately,
a single crystal grown at ambient temperature and investigated
by X-ray analysis revealed a disordered molecule. At a lower
temperatures, the crystals become opaque.
Figure 2. (a) Molecular structure of (c,c,c-cdt)(AgNO3)3 (5) (nitrate
ions are omitted for clarity, atomic displacement ellipsoids are
shown at the 50% probability level). Selected bond lengths (Å)
and torsional angles (deg): C1-C2 ) 1.360(2), C2-C3 ) 1.512-
(2), C3-C4 ) 1.545(2), C4-C5 ) 1.509(2), C5-C6 ) 1.369(2),
C6-C7 ) 1.508(2), C7-C8 ) 1.557(2), C8-C9 ) 1.506(3), C9-
C10 ) 1.364(2), C10-C11 ) 1.511(2), C11-C12 ) 1.544(2),
C12-C1 ) 1.504(2), Ag1-C1 ) 2.379(2), Ag1-C2 ) 2.479(2),
Ag2-C5 ) 2.339(2), Ag2-C6 ) 2.377(2), Ag3-C9 ) 2.442(2),
Ag3-C10 ) 2.327(2); C2-C3-C4-C5 ) 169(1), C6-C7-C8-
C9 ) 167(1), C10-C11-C12-C1 ) 7(1). (b) Crystal structure
of (c,c,c-cdt)(AgNO3)3 (5), including nitrate ions, showing the
layered structure. Ag, yellow; O, red; N, blue; and C, gray.
We therefore synthesized the BF4 derivative by reacting CuI
with AgBF4 and c,c,c-cdt. At the first attempt, the complex
crystallized as the MeOH solvate 6b due to the presence of
adventitious MeOH in the CH2Cl2-diethyl ether solvent
mixture. Compound 6b is conveniently prepared by the deliber-
ate addition of 1 equiv of MeOH (eq 2a). It is worth noting
signal for the olefinic protons (δ(H) 6.07) and two resonances
for the geminal allylic protons (δ(H) 2.70 and 2.39), while in
the 13C NMR spectrum, just two single resonances are found
(Table 1). Clearly, the structure of 5 in solution is highly
symmetric, with all six sCHd and six CHaHb groups each
equivalent, but with inequivalent geminal allylic protons. We
denote the structure in solution as 5a. From a comparison of
the NMR data of 5a with those of the (c,c,c-cdt)Cu complexes
6a-d, we conclude that 5 upon dissolution eliminates two
AgNO3 molecules to form mononuclear 5a comprising a central
(23) Nickel, T.; Po¨rschke, K.-R.; Goddard, R.; Kru¨ger, C. Inorg. Chem.
1992, 31, 4428.
(24) (a) Cabbiness, D. K.; Margerum, D. W. J. Am. Chem. Soc. 1969,
91, 6540. (b) Hinz, F. P.; Margerum, D. W. J. Am. Chem. Soc. 1974, 96,
4993. (c) Hinz, F. P.; Margerum, D. W. Inorg. Chem. 1974, 13, 2941. (d)
Izatt, R. M.; Bradshaw, J. S.; Nielsen, S. A.; Lamb, J. D.; Christensen, J.
J. Chem. ReV. 1985, 85, 271. (e) Hancock, R. D.; Martell, A. E. Comments
Inorg. Chem. 1988, 6, 237. (f) Haack, K.-J.; Goddard, R.; Po¨rschke, K.-R.
J. Am. Chem. Soc. 1997, 119, 7992.

cis,cis,cis-1,5,9-Cyclododecatriene-Metal Complexes
Organometallics, Vol. 26, No. 20, 2007 4875
Figure 3. Molecular structure of 6b in the crystal (BF4 anion is
omitted, atomic displacement ellipsoids are shown at the 50%
probability level).
mirror the C3 symmetry of the ligand. Thus, whereas two protons
at dCHsCH2 of the more tightly bound C1, C5, and C9 are
anti to one another (CdCsCsC torsion angle -136(1)°, mean),
those at dCHsCH2 of the more loosely bound C2, C6, and
C10 are eclipsed (CdCsCsC torsion angle 79(2)°, mean). The
CH2-CH2 bonds are all gauche with a mean C-C-C-C
torsion angle of 38(2)°. The C3 symmetry of the cation is
necessarily broken by the methanol ligand, although O1 only
deviates from the 3-fold axis of the c,c,c-cdt ligand by an angle
of 12(1)° at the metal. The Cu1-O1 bond at 2.149(1) Å is
normal, as is the Cu1-O1-C13 angle at 125.3(1)°. The cations
are arranged in the crystal in layers of enantiomers.
that the positive Cu+ center prefers to coordinate the neutral
methanol rather than the negatively charged BF4 anion, so
MeOH appears to be the stronger donor ligand. The MeOH
ligand is nonvolatile when drying the compound under vacuum
at ambient temperature for 1 h.
Whereas in 6b the Cu is tetrahedrally coordinated by the c,c,c-
cdt and MeOH ligands, in the Al{OC(CF3)3}4 salt 6d, the Cu
cation is only bonded to the c,c,c-cdt ligand, and the structure
is truly ionic with a large cation-anion separation (Figure 4).
The (c,c,c-cdt)Cu cation in 6d is partially disordered by the
inverted molecule in the X-ray analysis. Since the disorder was
only light, it was modeled by a second Cu atom (Cu2) 2.103 Å
away from Cu1, such that the combined occupancy of Cu1 and
Cu2 was 1. The refined occupancy of Cu2 is 0.2058(1). A
second crystal showed a similar effect, so some disorder of the
(c,c,c-cdt)Cu cation (ca. 20%) appears to take place on crystal-
lization, which is not surprising in view of the symmetrical
nature of the cation.
Repeating the reaction in the absence of MeOH afforded the
actual BF4 adduct 6c as a colorless solid, but its structure has
not been determined (eq 2b). Similarly, CuI was reacted with
c,c,c-cdt and [Ag(CH2Cl2)][Al{OC(CF3)3}4]25a to afford equally
well-formed colorless crystals of the ionic 6d (eq 2c).
-
Al{OC(CF3)3}4 has a reputation as ranking among the “least
coordinating anions”.25 While 6b appears to be stable to 230
°C, 6d shows no tendency to melt or decompose up to 320 °C.
We have successfully performed X-ray single crystal structure
determinations of 6b,d, details of which are given in Table 2.
Structural data are shown in Table 3. Crystals of 6b (Figure 3)
are made up of discrete Cu(I) complex cations and BF4 anions.
The Cu(I) center is coordinated in a tetrahedral fashion to the
three CdC bonds of the c,c,c-cdt ligand and the oxygen atom
of the methanol ligand, and the Cu atom lies 0.656(1) Å out of
the olefinic plane defined by the midpoints of the three CdC
bonds. The c,c,c-cdt ligand adopts an almost exact C3 sym-
metrical (ratchet) conformation (root-mean-square deviation of
0.037 Å), with three short Cu1-C distances to C1, C5, and C9
(2.194(4) Å, mean) and three longer distances to C2, C6, and
C10 (2.25(1) Å, mean). The olefinic bonds are twisted by 6(1)°
out of the mean plane through the midpoints of the bonds so
the CdC carbon atoms are approximately coplanar (root-mean-
square deviation of 0.078 Å). Within the C12 ring, the olefinic
CdC bonds are shortest (1.359 Å, mean) as expected and only
slightly lengthened as compared to an uncoordinated CdC bond
(1.32 Å), and the CH2-CH2 bonds are longest (1.538 Å, mean).
Interestingly, the dCHsCH2 bonds are shorter to the tighter
coordinated C1, C5, and C9 (1.506 Å, mean) than those to the
more loosely coordinated C2, C6, and C10 (1.529 Å, mean).
The difference is also reflected in the torsion angles, which all
The (c,c,c-cdt)Cu cation in the major component of 6d is C3
symmetric within the error margin of the analysis. The
conformation of the c,c,c-cdt ligand is very similar to that in
6b (root-mean-square deviation of 0.053 Å) with each CdC
bond asymmetrically coordinated at Cu1 (Table 3). The Cu atom
is displaced 0.47(8) Å out of the mean plane of the three olefinic
bonds away from the C2H4 groups. The ligand does not appear
to be flexible enough to accommodate an ideally trigonally
planar coordinated metal atom, and the coordination geometry
of the Cu atom is therefore perforce distorted toward trigonal
pyramidal.
The crystal structures of 6b and 6d make a convenient starting
point for a discussion of the solution 1H and 13C NMR spectra
of 6a-d. Assuming that the structure of 6a-d in solution is
the same as in the solid state, one would expect for the c,c,c-
cdt ligand in the rigid ratchet conformation six 1H and four 13
C
1
resonances. However, down to -80 °C, the H NMR spectra
of 6a-d in CD2Cl2 (Table 1) show only three equally intense
and sharply resolved 1H NMR multiplets for the c,c,c-cdt ligand,
namely, one for the olefinic protons (6a: δ(H) 6.10) and two
for the inequivalent geminal protons at the methylene groups
(6a: δ(H) 2.74 and 2.46), and in the 13C NMR spectra there
(25) (a) Krossing, I. Chem.sEur. J. 2001, 7, 490. (b) Krossing, I.; Raabe,
I. Angew. Chem. 2004, 116, 2116; Angew. Chem., Int. Ed. 2004, 43, 2066.
(c) Krossing, I.; Reisinger, A. Coord. Chem. ReV. 2006, 250, 2721.

4876 Organometallics, Vol. 26, No. 20, 2007
Table 1. 1H and 13C NMR Data of c,c,c-cdt and c,c,c-cdt Ligands in 1b, 5a, 6a-d, and 7b and the Reference Complex 4a
δ(H) δ(C)
ChernyshoVa et al.
dCHs
-CH2-
2.18
2.70, 2.39
2.74, 2.46
2.75, 2.52
2.74, 2.52
2.83, 2.65
2.40deg
dCHs
-CH2-
c,c,c-cdtb,c
5.58
6.07
6.10
6.12
6.14
6.16
4.80
130.8
129.4
125.0
124.7
124.7
126.5
89.3
28.4
27.0
27.4
27.7
27.7
27.8
29.2
29.9
[(c,c,c-cdt)Ag]NO3 (5a)b
(c,c,c-cdt)CuOTf (6a)b
[(c,c,c-cdt)Cu(MeOH)]BF4 (6b)b
(c,c,c-cdt)CuBF4 (6c)b
[(c,c,c-cdt)Cu][Al{OC(CF3)3}4] (6d)b
(c,c,c-cdt)Ni (1b)c
(c,c,c-cdt)NiL (4)6d
99.5
(dtbpe)Ni(η2-c,c,c-cdt) (7b)c,e
5.60, 5.56 (uncoord.)
2.73 (coord.)
2.40, 1.79 (R)
2.74, 2.09 (â)
2.17, 2.08 (γ)
132.5, 129.8 (uncoord.)
55.2 (“t”, coord.)
33.8 (“t”), 33.5, 29.6
a Temperature: 25 °C. deg ) degenerate. b Solvent: CD2Cl2. c Solvent: THF-d8. d L ) P(OC6H4-2-C6H5)3. Solvent: toluene-d8. Temperature: -20 °C.
t
e dtbpe: δ(H) 1.67deg (PCHaHb), 1.21deg (PtBua Bub). δ(C) 35.2, 35.1 (each “t”, PCMe3), 31.4, 30.5 (each “t”, PCMe3), 24.1 (“t”, PC2H4P). δ(P) 83.9.
are only two equally intense signals for the olefinic and allylic
C atoms, so all olefinic protons and carbon atoms and all
methylene groups are equivalent on the time average. The
solution NMR spectra of 6a-d reveal the dynamic nature of
the c,c,c-cdt ligand in the chiral ratchet conformation, which
results in rapid enantiomerization. While the coordination
chemical shifts are small, in agreement with the expected weak
backbonding from Cu(I), there are distinct chemical shift
differences in the c,c,c-cdt signals of 6a-d, suggesting that
6a-c remain undissociated in CD2Cl2 solution with respect to
the OTf, MeOH, and BF4 coordination. Consistent with a stable
MeOH coordination in 6b and consequently slow proton
exchange, the MeOH 13C signal (δ(C) 51.5) differs from that
of free MeOH (δ(C) 50.7), and the MeOH ligand gives rise to
Thus, our studies on the Ag(I) and Cu(I) complexes are in
agreement with the results from Anet’s conformational analysis
a 1H doublet (δ(H) 3.44, 3J(HH) ) 5.3 Hz) and a quartet (δ(H)
2.10), unlike free MeOH (δ(H) 3.41, 1.50) for which the
couplings are unresolved. The addition of some free MeOH
causes the MeOH ligand multiplets to collapse.
of the free c,c,c-cdt, which concluded that not only the helical
but also the ratchet conformation (crown-I)12 is relatively low
in energy, and hence, the c,c,c-cdt can take up one of these
conformations in the corresponding Ag(I) and Cu(I) complexes
(the likewise low-energy saddle conformation has so far not
been encountered in c,c,c-cdt-metal complexes). While for
M-η2-c,c,c-cdt coordination the helical conformation is pre-
ferred as in 5, the ratchet conformation of the c,c,c-cdt ligand
suits both a tetrahedral (6b) and a distorted trigonal coordination
geometry (6d) of the central metal. In the ratchet conformation,
all three CdC bonds are almost in-plane, which appears
favorable for backbonding in the case of the trigonal planar
coordination mode, but each individual CdC bond is unsym-
metrically coordinated, thereby counteracting an optimal back-
bonding. The hypothetical C3V symmetrical crown conformation
is not a viable conformation13 for the free c,c,c-cdt or when it
is ligated to a metal due to the considerable Pitzer strain.
(c,c,c-cdt)Ni (1b). The insight gained with the Ag(I) and Cu-
(I) complexes will help us to discuss the conformational aspects
of the Ni(0)-c,c,c-cdt complexes 1b and 7b. Complex 1b is
obtained by reaction of a pentane or diethyl ether solution of
1a (not 2) with 1 equiv of c,c,c-cdt at 20 °C. The red color of
1a fades within a few minutes, and a yellow-brown solution
is formed from which the pale yellow, similarly trigonal 1b
crystallizes at -40 °C in high yield (eq 3a).6a,b Although 1b is
thermodynamically more stable, it is even more sensitive to
oxygen than 1a. Furthermore, complex 1b is only stable in
solution at ambient temperature for a short period, preventing
an extensive solution investigation (e.g., by 61Ni NMR).26 Below
(26) (a) Benn, R.; Rufinska, A. Angew. Chem., Int. Ed. 1986, 25, 861.
(b) Benn, R.; Rufinska, A. Magn. Reson. Chem. 1988, 26, 895. (c) Behringer,
K. D.; Blu¨mel, J. Magn. Reson. Chem. 1995, 33, 729.
Figure 4. Molecular structure of 6d in the crystal (atomic
displacement ellipsoids shown at the 50% probability level).

cis,cis,cis-1,5,9-Cyclododecatriene-Metal Complexes
Organometallics, Vol. 26, No. 20, 2007 4877
Table 2. Crystal Data for (c,c,c-cdt)Ni (1b), (c,c,c-cdt)(AgNO3)3 (5), [(c,c,c-cdt)Cu(MeOH)]BF4 (6b),
[(c,c,c-cdt)Cu]Al{OC(CF3)3}4 (6d), and (tBu2PC2H4PtBu2)Ni(η2-c,c,c-cdt) (7b)
1b
5
6b
6d
7b
empirical formula
color
C12H18Ni
yellow
220.97
100
C12H18Ag3N3O9
colorless
671.90
C13H22BCuF4O
colorless
344.66
C28H18AlCuF36O4
colorless
1192.94
C30H58NiP2
orange-brown
539.41
fw (g mol-1
temp (K)
)
100
100
100
100
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.71073
0.71073
0.71073
0.71073
0.71073
triclinic
rhombohedral
R3hm (No. 166)
7.7327(5)
7.7327(5)
7.7327(5)
115.346(1)
115.346(1)
115.346(1)
250.42(3)
1
250.4
1.465
1.885
118
0.34 × 0.03 × 0.03
4.40-31.44
-11 e h e 11
-11 e k e 11
-11 e l e 11
5594
monoclinic
P21/c (No. 14)
7.1207(1)
12.9571(2)
19.3026(2)
90.0
100.200(1)
90.0
1752.78(4)
4
438.2
2.546
3.373
1296
0.20 × 0.17 × 0.05
3.14-33.11
-10 e h e 10
-19 e k e 19
-29 e l e 29
52502
monoclinic
Cc (No. 9)
9.7840(5)
10.9423(6)
13.7195(7)
90.0
95.568(2)
90.0
1461.87(13)
4
365.5
1.566
1.529
712
0.14 × 0.10 × 0.06
2.98-31.55
-14 e h e 14
-16 e k e 16
-20 e l e 20
18575
monoclinic
P21/c (No. 14)
13.6998(5)
14.6452(5)
19.7498(7)
90.0
99.439(2)
90.0
3908.9(2)
4
977.2
2.027
0.791
2336
0.09 × 0.07 × 0.02
2.97-27.48
-17 e h e 17
-19 e k e 18
-25 e l e 25
43009
P1h (No. 2)
12.8797(2)
13.9842(2)
18.4902(3)
72.7950(8)
75.4380(8)
81.7670(8)
3070.55(8)
4
767.6
1.167
0.752
1184
0.18 × 0.16 × 0.16
2.96-31.53
-18 e h e 18
-20 e k e 19
-27 e l e 27
79638
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
V/Z (Å3)
calcd density (Mg m-3
)
abs coeff (mm-1
F(000) (e)
)
cryst size (mm3)
θ range for data collection (deg)
index ranges
no. of reflns collected
no. of ind reflns
no. of reflns with I > 2σ(I)
completeness (%)
abs correction
318 (Rint ) 0.0529)
300
6641 (Rint ) 0.0343)
6380
99.7 (θ ) 33.11°)
Gaussian
4810 (Rint ) 0.0376)
4248
8944 (Rint ) 0.0905)
5720
20428 (Rint ) 0.0378)
17696
99.7 (θ ) 31.44°)
semiempirical from
equivalents
1.0/0.91
99.8 (θ ) 31.55°)
semiempirical from
equivalents
0.75/0.43
F2
99.9 (θ ) 27.48°)
semiempirical from
equivalents
1.00/0.95
F2
99.8 (θ ) 31.53°)
semiempirical from
equivalents
1.00/0.97
F2
max/min transmission
full-matrix least-squares
no. of data/restraints/params
GOF on F2
0.85/0.56
F2
6641/0/244
1.100
F2
318/0/22
1.161
4810/2/197
1.059
8944/0/659
1.018
20428/0/591
1.038
final R indices (I > 2σ(I))
R1
0.0565
0.1419
0.0233
0.0556
0.0272
0.0595
0.0588
0.1229
0.0358
0.0803
wR2
R indices (all data)
R1
wR2
0.0598
0.1436
0.0244
0.0562
0.0347
0.0620
0.1085
0.1453
0.0448
0.0842
abs structure param
0.017(7)
0.247/-0.352
largest diff peak/hole (e Å-3
)
0.315/-0.281
0.972/-1.059
0.927/-0.407
0.931/-0.466
Table 3. Selected Bond Lengths (Å), Angles (deg), and
Torsion Angles (deg) for [(c,c,c-cdt)Cu(MeOH)]BF4 (6b) and
[(c,c,c-cdt)Cu][Al{OC(CF3)3}4] (6d)
The spectra are in accord with rapid enantiomerization of 1b
in solution at the given temperatures assuming the ratchet
conformation for the c,c,c-cdt ligand and thus a C3 symmetrical
chiral ground state structure. A previous 13C NMR study6c,d has
shown that while the coordination chemical shift for the c,c,c-
cdt ligand in 1b of ∆δ(C) ) -41.5 is larger than for the t,t,t-
cdt ligand in 1a (∆δ(C) ) -25.0), it is substantially smaller
than for the ethene ligands in 3c (∆δ(C) ) -65.5), suggesting
that backbonding from Ni(0) to the c,c,c-cdt ligand in 1bs
although larger than for the t,t,t-cdt ligand in 1asis clearly
weaker than the optimal backbonding of the ethene ligands in
the D3h symmetrical 3c.8 This result seems to agree with the
anticipated ratchet conformation of the c,c,c-cdt ligand with an
asymmetric Nisη2-CdC coordination, in which backdonation
from the trigonal planar Ni(0) to the in-plane CdC bonds is
hampered.
6b
6d
Cu1-C1
2.197(2)
2.250(2)
2.189(2)
2.237(2)
2.197(2)
2.261(2)
1.361(2)
1.359(3)
1.356(3)
2.149(2)
125.3(1)
36(1)
2.178(4)
2.191(4)
2.174(4)
2.200(4)
2.218(4)
2.194(5)
1.376(6)
1.354(6)
1.352(6)
Cu1-C2
Cu1-C5
Cu1-C6
Cu1-C9
Cu1-C10
C1-C2
C5-C6
C9-C10
Cu1-O1
Cu1-O1-C13
C2-C3-C4-C5
37(3)
32(3)
33(3)
7(1)
C6-C7-C8-C9
38(1)
40(1)
6(1)
C10-C11-C12-C1
mean twist of the CdC bonds out of the olefinic
plane (deg)
Complex 1b reacts with ethene at 0 °C to afford 3c (eq 3c)
in accord with restricted backbonding, just as is the case for 1a
(eq 3b). Thus, although 1a,b bear cyclopolyene ligands (t,t,t-
cdt and c,c,c-cdt) in which the chelate and macrocyclic effects
might be assumed to play a stabilizing role, the stabilization of
the Ni(0) complexes by these effects is not sufficient to retard
the reactions with ethene to give 3c. In this respect, there is a
sharp contrast between stability and reactivity of the t,t,t-/c,c,c-
cdt complexes of Ni(0) (1a,b) and those of Cu(I) (6a-d).
displacement of Cu1 from the olefinic plane (Å)
0.656(1)
0.47(8)
-40 °C, the solubility of 1b in typical solvents is poor. In the
1
ambient temperature H NMR spectrum (THF-d8), one signal
each, with considerable line-broadening, is observed for the
olefinic protons (δ(H) 4.80) and the allylic protons (δ(H) 2.40),
so that the latter appears degenerate. As for 5a and 6a-d, there
are just two 13C signals (Table 1). The spectra are unchanged
at -30 °C.

4878 Organometallics, Vol. 26, No. 20, 2007
ChernyshoVa et al.
unfortunately not possible to say with certainty whether the
molecules crystallize as monomers or weakly bound dimers
(Figure 5b). Arguments that support the presence of a dimer in
the crystal are that (a) the (c,c,c-cdt)Ni units pack vertically
above one another, (b) weak d10-d10 transition metal interactions
are not unknown,27 (c) weak Ni‚‚‚Ni interactions have been
discussed in connection with the crystal structures of a series
of complexes containing Ni(II) bound to macromolecules,28 and
(d) the Ni atoms lie 0.4(1) Å above the mean plane of the
midpoints of the three olefinic bonds, although as we have seen
in the case of the (c,c,c-cdt)Cu cation of 6d, the conformation
of the c,c,c-cdt ligand does not allow the metal to lie exactly in
the olefinic plane.
The only previously known adduct of 1b is 4 with the
sterically much encumbered P(OC6H4-2-C6H5)3 ligand (eq
3f).6a,b Complex 4 separates from solution as a microcrystalline
powder, so far unsuitable for a crystallographic structure
determination. All attempts to synthesize further adducts of 1b
with monodentate ligands have failed. Thus, whereas (t,t,t-cdt)-
Ni(PMe3) is a stable compound,29a 1b can be recovered
unchanged from a pentane solution containing 1 equiv of the
sterically small and strongly donating PMe3 (-20 °C). Similarly,
1b resists forming adducts with alkyl phosphites or the very
strongly electron donating carbenes C{N(tBu)CH}2 and C{N-
(C6H3-2,6-iPr2)CH}2. In contrast, whereas 1a forms with the
strongly accepting CO the isolable (t,t,t-cdt)Ni(CO) below -20
°C,1c,29b 1b reacts with 4 equiv of CO already at -60 °C by
displacement of the c,c,c-cdt to yield Ni(CO)4 (eq 3d). This
reaction is related to the aforementioned displacement reaction
with ethene to give 3c (eq 3c).
These experimental findings can be rationalized as follows:
as is evident from the 13C NMR data, backbonding from Ni(0)
to the c,c,c-cdt ligand is already inherently imperfect for 1b
because of the anticipated asymmetric coordination of the
conformationally restricted CdC bonds and the out-of-plane
position of the Ni atom. An even poorer backbonding is expected
for a tetrahedral Ni(0)-alkene complex.30 In a hypothetical
tetrahedral (c,c,c-cdt)NiL species with a strongly electron
donating L, the charge imposed by L on the Ni atom could not
be properly transferred further onto the accepting orbitals of
the structurally constrained c,c,c-cdt ligand, and consequently,
the Ni atom simply resists to coordinate L.
Thus, a stable tetrahedral (c,c,c-cdt)NiL complex such as 4
can only be realized for a predominantly electron accepting
ligand L, requiring only mediocre backbonding of Ni(0) to the
c,c,c-cdt ligand, similar to the electronic situation in the likewise
tetrahedral Cu(I) derivatives 6a-c. Such accepting ligands L
are furnished by, for example, CO, CNMe, C2H4, and aryl
phosphites. However, for the smaller L the c,c,c-cdt ligand can
be readily displaced by further L to give products NiLn such as
3c (eq 3c) and Ni(CO)4 (eq 3d), via a non-isolatable (c,c,c-
cdt)NiL intermediate. Only for a bulky acceptor ligand such as
P(OC6H4-2-Ph)3, for which the c,c,c-cdt displacement is ham-
pered, can the reaction halt at the stage of the 1:1 adduct (4).
Figure 5. (a) Crystal structure of 1b, viewed along the crystal-
lographic a-axis, showing the arrangement of disordered (c,c,c-
cdt)Ni moieties in the unit cell. As a result of the disorder, it is not
possible to distinguish between a CH2-CH2 and a CHdCH group
bound to Ni. (b) View of molecules of 1b, showing the possible
weak interaction between two (c,c,c-cdt)Ni moieties. Selected
distances (Å) and angles (deg): Ni-C1 ) 2.298(12), Ni-C2 )
2.119(6), C1-C2 ) 1.440(12), C1-C2* ) 1.484(10), Ni‚‚‚Ni )
3.048(3), C1-C2-C1* ) 115.4(6), C2-C1-C2* ) 119.6(6).
Because of the significance of 1b as a pendant to the isomeric
1a, we considered it worthwhile to determine its crystal structure
by X-ray crystallography (Table 2). The molecules crystallize
in the trigonal space group R3hm, with one (c,c,c-cdt)Ni moiety
in the unit cell. Figure 5a shows the packing of the molecules
in the unit cell. The molecules are close-packed and positionally
disordered, as was observed to a smaller extent for the (c,c,c-
cdt)Cu cation in the crystal structure of 6d. Despite the disorder,
the structure of 1b refines to a satisfactory R-index of 0.0565
(5594 measured data, 318 independent observations, Rav
)
(27) (a) Dedieu, A.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100, 2074.
(b) Merz, K. M., Jr.; Hoffmann, R. Inorg. Chem. 1988, 27, 2120.
(28) For Ni‚‚‚Ni distances around 3 Å, see: (a) 2.788 Å: Peng, S.-M.;
Goedken, V. L. J. Am. Chem. Soc. 1976, 98, 8500. (b) 2.800 Å: Herebian,
D.; Bothe, E.; Neese, F.; Weyhermu¨ller, T.; Wieghardt, K. J. Am. Chem.
Soc. 2003, 125, 9116. (c) 3.358 Å: Stephens, F. S.; Vagg, R. S. Inorg.
Chim. Acta 1980, 43, 77.
(29) (a) Po¨rschke, K.-R.; Wilke, G.; Mynott, R. Chem. Ber. 1985, 118,
298 and references therein. (b) Po¨rschke, K.-R.; Wilke, G. Chem. Ber. 1984,
117, 56.
0.0529, and data/parameter ratio >14). In 1b, each (c,c,c-cdt)-
Ni unit occupies two positions with equal occupancy, and they
are stacked vertically above one another, with a Ni‚‚‚Ni distance
of 3.048(3) Å between the closest units. The disorder (see
comment in the CIF) precludes a detailed discussion of the
structure, apart from confirming the existence of the (c,c,c-cdt)-
Ni moiety and revealing its general structure.
Since the (c,c,c-cdt)Ni units can either pack with all the Ni
atoms orientated in the same direction or alternating, it is
(30) Po¨rschke, K.-R.; Mynott, R. Z. Naturforsch., B: Chem. Sci. 1984,
39, 1565.

cis,cis,cis-1,5,9-Cyclododecatriene-Metal Complexes
Organometallics, Vol. 26, No. 20, 2007 4879
(tBu2PC2H4PtBu2)Ni(η2-c,c,c-cdt) (7b). While an adduct of
1b with a monodentate phosphane appears to be inaccessible,
we have reacted 1b with the sterically encumbered bidentate
t
phosphane Bu2PC2H4PtBu2 (dtbpe) to afford yellow-brown
cubes of adduct 7b (eq 3g). In the course of this reaction, the
Ni atom in 1b moves from its central position within the ring
to an outside position. It can be shown on a model that in this
process the Ni atom can maintain a continued binding to one
CdC bond of the c,c,c-cdt ligand while the cycloalkene
undergoes eversion. Complex 7b (mp 185 °C dec) is thermally
rather stable. In the EI mass spectrum (140 °C), the molecular
ion (m/e ) 538, 10%) is observed, which fragments by
elimination of the cycloalkene to give [(dtbpe)Ni]+ as the base
ion. The η2-c,c,c-cdt ligand in 7b is readily displaced by ethene
to afford the known (dtbpe)Ni(C2H4).31
Complex 7b is isomeric to the previously studied (dtbpe)Ni-
(η2-t,t,t-cdt) (7a), which is practically inert and resists a
displacement reaction of the η2-t,t,t-cdt ligand by ethene or even
butadiene and cyclooctatetraene at ambient temperature.31 The
low reactivity of 7a can be rationalized in terms of its C2
symmetrical structure, which, by virtue of the four tBu substit-
uents of the dtbpe ligand assuming a gear-like orientation relative
to the trans substituents of the coordinated CdC bond, results
in a shielding of the Ni atom by the two ligands.
Figure 6. Molecular structure of (tBu2PC2H4PtBu2)Ni(η2-c,c,c-cdt)
(7b) (molecule 1, atomic displacement ellipsoids are shown at the
50% probability level). Selected bond distances (Å), a bond angle
(deg), interplanar angle (deg), and dihedral angles (deg): Ni1-P1
) 2.1855(4), Ni1-P2 ) 2.1876(3), Ni1-C1 ) 1.977(1), Ni1-C2
) 1.986(1), C1-C2 ) 1.429(2), C2-C3 ) 1.516(2), C3-C4 )
1.552(2), C4-C5 ) 1.507(2), C5-C6 ) 1.299(3), C6-C7A )
1.529(3), C7A-C8A ) 1.536(3), C8A-C9 ) 1.543(3), C9-C10
) 1.316(2), C10-C11 ) 1.503(2), C11-C12 ) 1.548(2), C12-
C1 ) 1.519(2); P1-Ni1-P2 ) 93.23(1); P1,P2,Ni1/Ni1,C1,C2 )
7(1); C2-C3-C4-C5 ) 189(1), C6-C7A-C8A-C9 ) 192(1),
C10-C11-C12-C1 ) 170(1).
The ambient temperature NMR spectra of 7b are in agreement
with the presence of a η2-c,c,c-cdt ligand and effective Cs
symmetry of the complex in solution, resulting from the time
average of the different conformations of the η2-c,c,c-cdt ligand.
Thus, the latter displays nine 1H and six 13C signals (Table 1):
besides two low-field signals for the inequivalent sCHdgroups
of the uncoordinated CdC bonds (δ(H) 5.60, 5.56; δ(C) 132.5,
129.8), there is an upfield signal for the coordinated CdC bond
(δ(H) 2.73; δ(C) 55.2), with the latter 13C signal representing a
virtual triplet due to two 31P couplings. The geminal CHaHb
protons, which are inequivalent because of their endo and exo
positions in the ring, are quite different for the methylene groups
R and â to the coordinated CdC bond (δ(H)R 2.40, 1.79;
δ(H)â 2.74, 2.09) and less so for the distant γ methylene group
(δ(H)γ 2.17, 2.08). While the R and γ methylene groups give
rise to 13C singlets (δ(C)R 33.5; δ(C)γ 29.6), the â methylene
groups produce a virtual triplet (δ(C)â 33.8, Σ4J(PP) ) 10 Hz).
This pattern of signal splittings seems unusual but is charac-
teristic for a series of substituted bis(phosphane)Ni-alkene
complexes. The signal assignment has been verified by C,H-
and H,H-COSY NMR. The total of five dtbpe 13C signals (the
of the plane defined by the phosphorus atoms and the midpoint
D1 of the coordinated CdC bond toward the ring. Whereas the
C atoms of the CdC bond lie approximately parallel to the P‚
‚‚P vector (1 and 4°) in 7b, this is not the case for the isomeric
complex 7a where the comparable angles are 27 and 19°. The
puckering in the (PC2H4P)Ni chelate ring is slightly larger for
7b (P-C-C-P ) 42 and 37°) than for 7a (P-C-C-P ) 29
and 30°). While the Ni-P bond distances in 7b (2.186 Å, mean)
are very similar to those in the isomeric 7a, the Ni-C1/C2
coordination bonds at 1.977(1) and 1.986(1) Å are slightly
shorter (7a, 2.007 Å, mean), and the coordinated bond C1-C2
at 1.429(2) Å is somewhat longer (7a, 1.398(4) Å). Within the
η2-c,c,c-cdt ligand, we see typical bond lengths for dCHsCH2
(1.52 Å, mean), CH2-CH2 (1.55 Å, mean), and uncoordinated
CdC (1.31 Å, mean).
PCHaHb and PtBua Bub protons are degenerate) indicates in-
t
t
equivalent Bu substitutents at the phosphorus atoms, thereby
ruling out rotation of the coordinated CdC bond about the bond
axis to Ni. The 31P resonance is a singlet. The spectra are
practically unchanged at -80 °C. It will be shown at the end
that the effective Cs symmetry of 7b in solution is due to
enantiomerization of a chiral structure, which is rapid even at
-80 °C.
Data on the X-ray structure analysis of 7b are given in Table
2, and the molecular structure is shown in Figure 6. The complex
crystallizes with two independent molecules 1 and 2 in the
asymmetric unit, which differ mainly in the orientation of one
tBu group and the conformation of the η2-c,c,c-cdt ligand at
the distal CH2-CH2 bond, where there is slight (ca. 20%)
disorder. The complex is chiral in the solid state.
The conformation of the η2-c,c,c-cdt ligand in 7b corresponds
to the helical conformation of the uncoordinated c,c,c-cdt, which
has emerged as the most stable,10a,11a and the same conformation
is also present in the 3-fold AgNO3 coordinated 5 (Figure 2a).
Although in principle the (dtbpe)Ni moiety can coordinate to
the c,c,c-cdt ligand in this conformation in three different modes,
the only isomer that is observed is the one in which Ni is bound
to the opposite face (exo) of one of the two CdC bonds with
the two C2H4 substituents in syn alignment, and so minimizing
steric effects.
While the free c,c,c-cdt in its helical conformation has C2
symmetry, with the C2 axis passing through the midpoint of
the cis-CdC bond bearing the two anti aligned C2H4 substituents
and the midpoint of the opposite CH2-CH2 bond, coordination
of the (dtbpe)Ni moiety at one of the cis-CdC bonds off the
original C2 axis lowers the symmetry to C1 in 7b. Enantiomer-
In both molecules, the geometry at the Ni atom is ap-
proximately trigonal planar with the Ni atom lying 0.1 Å out
(31) Po¨rschke, K.-R.; Pluta, C.; Proft, B.; Lutz, F.; Kru¨ger, C. Z.
Naturforsch., B: Chem. Sci. 1993, 48, 608.

4880 Organometallics, Vol. 26, No. 20, 2007
ChernyshoVa et al.
Ni(c,c,c-cdt) (1b).6a,b To a red solution of 1a (932 mg, 4.00
mmol) in 20 mL of diethyl ether was added c,c,c-cdt (0.73 mL,
4.0 mmol) at -40 °C. On keeping the solution at room temperature
for 30 min, the solution turned yellow. Slow cooling of the solution
to -25 °C afforded colorless needles, which were separated from
the mother liquor, washed twice with cold ether, and dried under
vacuum (20 °C): yield 780 mg (88%); dec 65 °C. EI-MS (65 °C):
m/e (%) 220 ([M]+, 28). C12H18Ni (221.0).
Figure 7. Schematic representation (in the notation of refs 10a
and 11a) of the conformation of the η2-c,c,c-cdt ligand in 7b and
of the complex enantiomerization. Dashed line marks the C2
symmetry axis in the uncoordinated c,c,c-cdt.
(c,c,c-cdt)(AgNO3)3 (5).10a c,c,c-cdt (0.30 mL, 1.67 mmol) was
added to a solution of AgNO3 (849 mg, 5.00 mmol) in 2 mL of
H2O and 4 mL of THF. Cooling the mixture to 5 °C for 2 days
afforded large colorless cubes: yield 704 mg (63%); mp 150 °C,
dec >160 °C. Anal. Calcd for C12H18Ag3N3O9 (671.9): C, 21.45;
H, 2.70; Ag, 48.16; N, 6.25; O, 21.43. Found: C, 21.85; H, 2.56;
Ag, 48.12; N, 6.25.
ization of 7b is formally possible by 180° CH2-CH2 bond
rotation of the C2H4 entity a at the anti aligned cis-CdC bond
and opposite to the coordinated CdC bond (and not at b
connecting to this bond), so changing the rotational direction
of the helix (Figure 7). Enantiomerization of 7b therefore
proceeds by a similar mechanism as for free c,c,c-cdt (Figure
1), with the restriction that 180° rotation occurs only at one
and not at all three CH2-CH2 bonds of the cyclotriene (i.e.,
the bond opposite to the coordinated cis-CdC bond). (If rotation
occurs at bond b, an isomer of 7b is formed.)
As the molecular structure of 7b shows, in the c,c,c-cdt ligand,
the atoms C7 and C8 that make up the CH2-CH2 bond a
opposite to the coordinated cis-CdC bond are disordered. The
disorder can be attributed to the presence of a diastereomer of
7b (with a retained puckering of the (PC2H4P)Ni chelate ring).
(c,c,c-cdt)CuOTf (6a). To a solution of (C6H10)CuOTf (295 mg,
1.00 mmol) in 5 mL of CH2Cl2 was added c,c,c-cdt (0.2 mL, 1.06
mmol). About 1-2 mL of diethyl ether was added dropwise until
a white precipitate formed. The latter was redissolved by gentle
warming. Letting the solution stand at ambient temperature and
further slow cooling to -20 °C afforded colorless cubes: yield
300 mg (80%). EI-MS (170 °C): m/e (%) 374 ([M]+, 5), 225
([C12H18Cu]+, 42). ESIpos-MS (CH2Cl2): m/e (%) 225 ([(C12H18)-
Cu]+, 100). ESIneg-MS (CH2Cl2): m/e (%) 149 ([OTf]-, 100).
C13H18CuF3O3S (374.9).
[(c,c,c-cdt)Cu(MeOH)]BF4 (6b). A suspension of CuI (286 mg,
1.50 mmol) in 4 mL of CH2Cl2 and 0.1 mL of MeOH was stirred
with c,c,c-cdt (0.27 mL, 1.50 mmol) and solid AgBF4 (292 mg,
1.50 mmol) for 30 min. The precipitated AgI was removed by
filtration, and 2 mL of diethyl ether was added. Cooling the solution
to 0 °C afforded well-formed colorless rods, which were isolated
and dried under vacuum: yield 450 mg (87%); dec 230 °C. ESIpos-
MS (CH2Cl2): m/e (%) 225 ([(C12H18)Cu]+, 100). ESIneg-MS (CH2-
Cl2): m/e (%) 87 ([BF4]-, 100). Anal. Calcd for C13H22BCuF4O
(344.7): C, 45.30; H, 6.43; B, 3.14; Cu, 18.44; F, 22.05; O, 4.64.
Found: C, 45.10; H, 5.82; Cu, 18.68; F, 22.30.
Conclusion
The principal coordination modes and conformations of c,c,c-
cdt as a ligand in d10 Ag(I), Cu(I), and Ni(0) complexes are
described. For η2-c,c,c-cdt coordination at one (7b) or several
metal centers (5), the cyclopolyene maintains a helical confor-
mation of local C2 symmetry, which was shown previously to
be the most stable for free c,c,c-cdt. For trisdentate coordination
at a single d10 center, the ligand can accommodate both trigonal
(1b, 6d) and tetrahedral (6a-c) coordination geometries of the
metal center, thereby assuming a ratchet conformation with C3
symmetry. In solution, the chiral complexes undergo enantio-
merization.
There are striking differences in the stability and reactivity
of the d10 complexes. The Cu(I) complexes 6a-d are of
exceptionally high thermal stability. They show no exchange
with ethene, and together with donors, the c,c,c-cdt ligand
imposes a tetrahedral structure on the Cu(I) center. In contrast,
the Ni(0) complex 1b is thermally much less stable; it does not
form adducts with most donors, and the c,c,c-cdt ligand is
displaced by ethene. As a trisdentate ligand at a single d10 center,
c,c,c-cdt prefers the ratchet conformation with an out-of-plane
coordination of the metal center and as such is a poor acceptor.
(c,c,c-cdt)CuBF4 (6c). Synthesis was as for 6b, but without the
addition of MeOH; colorless crystals: yield 330 mg (70%). ESIpos-
MS (CH2Cl2): m/e (%) 225 ([(C12H18)Cu]+, 100). ESIneg-MS (CH2-
Cl2): m/e (%) 87 ([BF4]-, 100). C12H18BCuF4 (312.6).
[(c,c,c-cdt)Cu][Al{OC(CF3)3}4] (6d). A suspension of CuI (190
mg, 1.00 mmol) in 15 mL of CH2Cl2 was stirred with c,c,c-cdt
(0.18 mL, 1.00 mmol) and solid [Ag(CH2Cl2)][Al{OC(CF3)3}4]
(1160 mg, 1.00 mmol) for 30 min. The precipitated AgI was
removed by filtration. Cooling the solution to 0 °C afforded
colorless rods: yield 895 mg (75%); dec 320 °C. ESIpos-MS (CH2-
Cl2): m/e (%) 225 ([(C12H18)Cu]+, 100). ESIneg-MS (CH2Cl2): m/e
(%) 967 ([AlC16F36O4]-, 100). C12H18Cu‚AlC16F36O4 (1192.9).
(tBu2PC2H4PtBu2)Ni(η2-C12H18) (7b). To a solution of 1b,
prepared in situ from 1a (700 mg, 3.00 mmol) and c,c,c-cdt (0.55
mL, 3.00 mmol) in 15 mL of diethyl ether, was added at -40 °C
a solution of tBu2PC2H4PtBu2 (955 mg, 3.00 mmol), also in 15 mL
of diethyl ether. After warming the mixture to ambient temperature,
the solution was cooled to -60 °C to afford yellow-brown cubes:
yield 1.165 g (72%); mp 185 °C dec. EI-MS (140 °C): m/e (%)
538 ([M]+, 10), 376 ([(dtbpe)Ni]+, 100). Anal. Calcd for C30H58-
NiP2 (539.4): C, 66.80; H, 10.84; Ni, 10.88; P, 11.48. Found: C,
66.62; H, 10.86; Ni, 10.87; P, 11.47.
Experimental Procedures
All manipulations were carried out under argon with Schlenk-
type glassware. Solvents were dried prior to use by distillation from
NaAlEt4. c,c,c-cdt10a (d ) 0.89 g mL-1), (t,t,t-cdt)Ni,1c (C6H10)-
CuOTf,23 and tBu2PC2H4PtBu231 were prepared as published. (t,t,t-
cdt)Ni (1a) contained 5% cocrystallized t,t,t-cdt, so the calculated
molecular weight of 233 g mol-1 was used. Microanalyses were
performed by the local Mikroanalytisches Labor Kolbe. EI mass
spectra were recorded at 70 eV and refer to 58Ni, 63Cu, and 107Ag.
1H NMR spectra were measured at 300 MHz and 13C NMR spectra
at 75.5 MHz (both relative to TMS) on Bruker AMX-300 and DPX-
300 instruments. NMR data of the products are listed in Table 1.
Supporting Information Available: CIF data for 1b, 5, 6b,
6d, and 7b. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM7004172