Di-, tri-, and tetranuclear cyclobutenylidene complexes

Article abstract of DOI:10.1002/(sici)1099-0682(199809)1998:9<1225::aid-ejic1225>3.0.co;2-b

Pentacarbonyl(dimethylvinylidene)chromium, [(CO)₅Cr=C= CMe₂] (1), reacts with the butadiynyl complexes [Cp(CO)₂FeC≡CC≡CR] [2; R = SiMe₃ (a), nBu (b), Ph (c)] and [Cp(CO)(PPh₃)FeC≡CC≡CSiMe₃] (3a) by regiospecific cycloaddition of the C^α≡C^β bond of the butadiynyl complexes to the C=C bond of 1 to form the 1,3-heterobinuclear cyclobutenylidene complexes 4a-c and 5a with an alkynyl substituent at C-2 of the bridging ring. Desilylation of the 2-C≡CSiMe₃ substituent in 4a and 5a with tetrabutylammonium fluoride affords the 2-C≡CH-substituted complexes 6 and 7. Complex 4a reacts with HNMe₂ and HN(CH₂)₅ by substitution of NR₂ for the 3-Fe(CO)₂Cp fragment to form the corresponding 3-aminocyclobutenylidene complexes 10 and 11. Sequential reactions of 4a with [nBu₄N]F and nBu₃SnNEt₂ give the trinuclear 2-C≡CSnnBu₃-substituted complex 12. Coupling of 12 with C₆H₄I₂-P yields the 2-C≡CC₆H₄I-p-substituted complex 13. Coupling of 7 with C₆H₄I₂-P yields a mixture of the mono-coupling product 14 and the tetranuclear C≡C-C₆H₄-C≡C-bridged bis(cyclobutenylidene) complex 15. Coupling of 7 with trans-[(Et₃P)₂MCl₂] in the presence of CuI/[Pd(PPh₃)₄] gives the trinuclear 2-C≡C-M(PEt₃)₂X-substituted complexes 16 (M = Pd, X = I) and 17 (M = Pt, X = Cl). The spectroscopic data as well as the results of the X-ray-structural analysis of 5a indicate strong electronic communication between the metal centers. In the solid state, 5a exhibits a butterfly conformation.

Full text of DOI:10.1002/(sici)1099-0682(199809)1998:9<1225::aid-ejic1225>3.0.co;2-b

FULL PAPER
Di-, Tri-, and Tetranuclear Cyclobutenylidene ComplexesȠ
´ ´
Frederic Leroux, Rüdiger Stumpf, and Helmut Fischer*
Fakultät für Chemie, Universität Konstanz, Fach M727,
D-78457 Konstanz, Germany
Fax: (internat.) ϩ 49(0)7531/88-2783
E-mail: hfischer@dg6.chemie.uni-konstanz.de
Received April 24, 1998
Keywords: Vinylidene complexes / Cyclobutenylidene complexes / Bridging ligands / Cycloadditions / Cross-coupling
Pentacarbonyl(dimethylvinylidene)chromium, [(CO)5Cr=C=
CMe2] (1), reacts with the butadiynyl complexes
[Cp(CO)2FeCϵCCϵCR] [2; R = SiMe3 (a), nBu (b), Ph (c)]
and [Cp(CO)(PPh3)FeCϵCCϵCSiMe3] (3a) by regiospecific
cycloaddition of the CαϵCβ bond of the butadiynyl
reactions of 4a with [nBu4N]F and nBu3SnNEt2 give the
trinuclear 2-CϵCSnnBu3-substituted complex 12. Coupling
of 12 with C6H4I2-p yields the 2-CϵCC6H4I-p-substituted
complex 13. Coupling of 7 with C6H4I2-p yields a mixture
of the mono-coupling product 14 and the tetranuclear CϵC–
C6H4–CϵC-bridged bis(cyclobutenylidene) complex 15.
complexes to the C=C bond of
1 to form the 1,3-
heterobinuclear cyclobutenylidene complexes 4a–c and 5a Coupling of 7 with trans-[(Et3P)2MCl2] in the presence of
with an alkynyl substituent at C-2 of the bridging ring.
Desilylation of the 2-CϵCSiMe3 substituent in 4a and 5a with
tetrabutylammonium fluoride affords the 2-CϵCH-
CuI/[Pd(PPh3)4] gives the trinuclear 2-CϵC–M(PEt3)2X-
substituted complexes 16 (M = Pd, X = I) and 17 (M = Pt, X =
Cl). The spectroscopic data as well as the results of the X-
substituted complexes 6 and 7. Complex 4a reacts with ray-structural analysis of 5a indicate strong electronic
HNMe2 and HN(CH2)5 by substitution of NR2 for the 3-
Fe(CO)2Cp fragment to form the corresponding 3-
aminocyclobutenylidene complexes 10 and 11. Sequential
communication between the metal centers. In the solid state,
5a exhibits a “butterfly” conformation.
Introduction
Scheme 1
Electronic communication between the metal centers in
bi- and polynuclear transition-metal complexes containing
unsaturated carbon bridges should lead to unusual physical
and chemical properties[1]. For example, carbon-bridged
bimetallic π-conjugated complexes of the type
[LnMCmMЈ(LЈ)nЈ] have been proposed as a new class of one-
dimensional molecular wires[2]. Rigid-rod polymers like
[LnMCϵCXCϵC]m (X ϭ aryl) can exhibit both liquid-crys-
talline[3] and nonlinear optical properties[4] similar to cer-
tain metal acetylides[5]. Binuclear complexes with different
LnM end groups at a conjugated π system should exhibit
second-order nonlinear optical (NLO) properties.
kynyl complexes to the CαϭCβ bond of allenylidene(penta-
carbonyl)chromium and -tungsten complexes[6b]
. The
properties of these 1,3-heterobinuclear complexes are
strongly influenced by the substituents at both non-metal-
bonded ring atoms.
Related to linear Cn bridges are rigid cyclic bridges with
Transition-metal
butadiynyl
complexes,
a delocalized π system. We recently reported on the syn- [LnMCαϵCβCγϵCδR], are related to alkynyl complexes
theses of 1,3-heterobinuclear complexes with a cyclic C4R3 [LnMCϵCR]. In alkynyl complexes the HOMO is mainly
bridging ligand (cyclobutenylidene complexes)[6]. By varia- localized at the terminal C atom. Therefore, electrophiles
tion of the substituents at the bridging ligand a fine-tuning add to this carbon atom. Spectroscopic investigations of bu-
of the magnetic, electronic, and spectroscopic properties of tadiynyl complexes indicate a strong communication be-
such binuclear complexes should be possible. Until now, tween the metal center and the butadiynyl ligand[7][8]. In
1,3-heterobinuclear cyclobutenylidene complexes with alkyl contrast to alkynyl complexes, two pathways are conceiv-
and aryl substituents as well as with functional groups at able for the reactions of butadiynyl with vinylidene com-
the bridging ligand, and with various metal-ligand frag- plexes as electrophiles depending on whether initial electro-
ments in 1- and 3-position of the ring have been prepared philic attack of the vinylidene Cα atom in [LnMϭCαϭ
by reaction of suitable vinylidene complexes of chromium CβR1 ] is directed towards the Cβ or the Cδ atom of the
2
and tungsten, [(CO)5MϭCϭCR1 ], with alkynyl complexes, butadiynyl ligand. Attack at the Cβ atom and subsequent
2
[LnMЈ-CϵCR2] (Scheme 1)[6a]
.
ring closure would lead to 1,3-heterobinuclear cyclobutenyl-
Cyclobutenylidene complexes with an exocyclic CϭC idene complexes with an alkynyl functionality at C-2 of the
bond were accessible by a regiospecific cycloaddition of al- ring (A; Scheme 2). Such complexes should constitute inter-
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234
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F. Leroux, R. Stumpf, H. Fischer
FULL PAPER
esting starting compounds for further derivatization by viously published procedure[7a] by reaction of [Cp(CO)2FeI]
coupling reactions. An attack at the butadiynyl Cδ atom with Li[(CϵC)2SiMe3], obtained by monodesilylation of
followed by ring closure would lead to complexes of type B 1,4-bis(trimethylsilyl)-1,3-butadiyne
with
MeLiиLiBr
(Scheme 2) thus extending the conjugated system between (Scheme 4)[10]. The corresponding phenyl- and n-butyl-sub-
the metal centers in cyclobutenylidene complexes.
Scheme 2
stituted butadiynyl complexes [2b (R ϭ nBu) and 2c (R ϭ
Ph)] were accessible by coupling of [Cp(CO)2FeI] with
nBu3SnϪCϵCCϵCϪR (R ϭ nBu, Ph) in THF with CuI/
[Pd(PPh3)4] as the catalyst (Scheme 4).
Scheme 4
In this paper we report on the syntheses of the first 1,3-
heterobinuclear cyclobutenylidene complexes with an alky-
nyl substituent at the bridging ring and on coupling reac-
tions of these complexes leading to new di-, tri-, and tetra-
metallic systems.
Results and Discussion
Thermal decarbonylation of 2a by refluxing in toluene in
the presence of PPh3 yielded the monocarbonyl-butadiynyl
complex [Cp(CO)(PPh3)FeCϵCCϵCSiMe3] (3a)[7a] albeit
in rather low yield (about 30%). Significantly higher yields
were achieved by oxidative decarbonylation of 2a with tri-
methylamine N-oxide in the presence of PPh3 at room tem-
perature. By this procedure, complex 3a was obtained in
63% yield (Scheme 5). The lower yield in the former route
is presumably due to competition between formation and
decomposition of 3a at the temperature of boiling toluene.
The vinylidene complex [(CO)5CrϭCϭCMe2] (1)[6a] was
chosen as the starting compound. Complex 1 was generated
by the reaction sequence shown in Scheme 3.
Scheme 3
Scheme 5
Reduction of Cr(CO)6 with potassium-graphite (C8K)
laminate in tetrahydrofuran at 0°C followed by reaction
with isobutyryl chloride afforded pentacarbonyl(isobutyryl)
chromate by a method described by M. F. Semmelhack et
When solutions of the vinylidene complex 1 and the buta-
al.[9]. Treatment of the chromate with trifluoroacetic anhy- diynyl complexes 2a؊c or 3a in CH2Cl2 were combined at
dride/DBU finally gave the vinylidene complex 1. Com- Ϫ60°C and then warmed to room temperature, the color of
pound 1 is thermally very labile. Therefore, 1 was not iso- the solutions changed within about 30 minutes from green
lated and its solutions were immediately employed in the to red. Chromatographic workup of the reaction mixtures
subsequent reactions with butadiynyl complexes.
The dicarbonyl-butadiynyl complex
afforded the novel 2-alkynyl-substituted 1,3-heterobinuclear
[Cp(CO)2- cyclobutenylidene complexes 4a؊c and 5a (Scheme 6) in
FeCϵCCϵCSiMe3] (2a) was prepared in analogy to a pre- 45Ϫ65% yield. Alternatively, complex 5a was also formed
1226
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234

Di-, Tri-, and Tetranuclear Cyclobutenylidene Complexes
FULL PAPER
when 4a was oxidatively decarbonylated with trimethyl- plex 9 by a formal substitution of “O” for [Cp(CO)2Fe]ϩ
amine N-oxide in the presence of PPh3.
(Scheme 8)[11]. In contrast, 2-alkyl-substituted 1,3-hetero-
binuclear cyclobutenylidene complexes are inert towards
amines.
Scheme 6
Scheme 8
The dicarbonyl complex 4a reacted rapidly at room tem-
perature in THF with aqueous dimethylamine or with pi-
peridine by substitution of NR2 for the 3-dicarbonyl(cyclo-
pentadienyl)iron fragment to form the 3-aminocyclobuteny-
lidene complexes 10 and 11 (Scheme 9).
The
addition
of
the
butadiynyl
complexes
[LnMϪCαϵCβϪCγϵCδϪR] to the vinylidene ligand in 1 is
highly regioselective. In each case, only the product of
cycloaddition of the CαϵCβ bond of the butadiynyl ligand
to the CϭC bond of the vinylidene ligand was obtained
(complex type A; Scheme 2). The formation of isomers de-
rived from cycloaddition of the CγϵCδ bond to the CϭC
bond of the vinylidene ligand (complex type B; Scheme 2)
was not detected. Likewise, 1,2-dimetallated cyclobutenylid-
enes, derived from the inverse regiochemistry of the cyclo-
addition of either the CαϵCβ or the CγϵCδ bond of the
butadiynyl ligand to the CϭC bond of the vinylidene li-
gand, were not observed.
3-Alkoxy-substituted cyclobutenylidene complexes of
chromium analogously react with secondary amines HNR2
by displacement of OR by NR2 to form 3-aminocyclobut-
enylidene complexes[12]. These substitution reactions are
reminiscent of the aminolysis of alkoxycarbene com-
plexes[13] and emphasize the close relationship of these
cyclobutenylidene complexes with π-donor-substituted car-
bene complexes. Thus, cyclobutenylidene complexes can be
regarded as a novel type of vinylogous heteroatom-stabil-
ized carbene complexes. However, the ready displacement
of the substituent in 3-position of the cyclobutenylidene
complex by amines excludes the use of primary and second-
ary amines as solvents in coupling reactions with 4a and
6. Therefore, palladium-catalyzed CϪC coupling reactions
require the use of the corresponding C-stannylated com-
Desilylation of 4a and 5a with tetrabutylammonium fluo-
ride (TBAF) in THF afforded the 2-ethynylcyclobutenylid-
ene complexes 6 and 7 after chromatographic workup in
67% and 57% yield, respectively (Scheme 7). The highest
yields were obtained when 0.4 equivalents of TBAF was
used instead of the stoichiometric amount. Similar obser-
vations have been reported for the desilylation of other
pound (Stille coupling)[14]
.
compounds with TBAF[7a]
Scheme 7
.
The heterotrinuclear tributyltin-substituted compound 12
was obtained as a red oil by transformation of 4a with
[nBu4N]F in THF into 6 and subsequent reaction of 6 with
nBu3SnNEt2 in toluene[15] (Scheme 9). The palladium-cata-
lyzed coupling of 12 with half an equivalent of 1,4-diiodo-
benzene in the presence of CuI[16] afforded only the mono-
coupling product 13 (Scheme 9). The formation of a tetra-
nuclear complex by coupling of two molecules of 12 with
one molecule of 1,4-diiodobenzene was not observed.
In contrast to 4a, the triphenylphosphane-substituted
cyclobutenylidene complex 5a did not react with amines to
The complexes 4a, 5a, 6, and 7 should constitute con- give 3-aminocyclobutenylidene complexes but was inert
venient starting compounds for the synthesis of tri- and towards amines presumably due to the better back-bonding
tetranuclear complexes by coupling reactions. In coupling properties of Cp(CO)(PPh3)Fe compared to Cp(CO)2Fe
reactions, often amines are employed as the solvent. There- and thus the reduced electrophilicity of 3-C in 5a. There-
fore, we investigated the reactivity of these 2-alkynyl-substi- fore, coupling reactions of 3-Cp(CO)(PPh3)Fe-substituted
tuted cyclobutenylidene complexes towards amines with the cyclobutenylidene complexes in amines as the solvent
example of 4a and 5a. In earlier experiments it was ob- should be possible.
served that a cationic 1,3-homobinuclear cyclobutenylidene
This was confirmed by the reaction of 7 with half an
complex 8 reacts with aqueous Et3N yielding the iron com- equivalent of 1,4-diiodobenzene in HNEt2 and [Pd(PPh3)4]/
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234
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F. Leroux, R. Stumpf, H. Fischer
FULL PAPER
Scheme 9
by iodide from CuI. Presumably, the substitution took place
in the trinuclear complex initially formed from 7 and trans-
[(PEt3)2PdCl2]. The displacement of ClϪ for XϪ in trans-
[(PEt3)2Pd(CϵCR)Cl] complexes in the presence of NaX
(X ϭ Br, I) has been observed several times[17]. Although a
threefold excess of 7 over trans-[(PEt3)2PdCl2] was used, the
formation of a pentanuclear complex by coupling of trans-
[(PEt3)2PdCl2] with two molecules of 7 was not detected.
The trimetallic trans-chloroplatinum complex 17 was ob-
tained by initial C-stannylation of 7 with nBu3SnNEt2 in
toluene followed by [Pd(PPh3)4]/CuI-catalyzed coupling of
the product with trans-[(PEt3)2PtCl2] in THF. A halide ex-
change was not observed in these reactions. Presumably,
free iodide was trapped as nBu3SnI (Scheme 11). A penta-
nuclear complex was likewise not detected.
Scheme 11
CuI as the catalyst. The mono-coupling product 14 as well
as the tetranuclear complex 15 were formed within several
hours (Scheme 10) and, after chromatographic workup, ob-
tained in 35% (14) and 10% (15) yield. Complex 15 was
isolated in form of a single diastereomer (meso or R/S).
Scheme 10
When 11 was stannylated in situ and the resulting deriva-
tive then coupled with iodobenzene under Stille conditions
complex 5c was obtained (see Scheme 6).
Spectroscopic Investigations and Molecular Structure of 5a
All new compounds were stable at room temperature and
fully characterized by spectroscopic means and by elemen-
tal analyses.
The ν˜(CO) absorptions of the pentacarbonyl chromium
moiety in 4Ϫ7 and 10؊17 are at rather low wave numbers
indicating considerable transfer of electron density from
C4R3ϪFeCO(L)Cp to (CO)5Cr. The ν˜(CO) spectra are
similar to those of aminocarbene complexes (e. g.
[(CO)5CrϭC(NHMe)Me])[18] and 3-amino-substituted
cyclobutenylidene complexes[19] as well as to those of the
previously described 1,3-heterobinuclear[6] cyclobutenylid-
ene complexes. The positions of the absorptions are
The [Pd(PPh3)4]/CuI-catalyzed reaction of 7 with trans- strongly influenced by the donor capacity of the substituent
[(PEt3)2PdCl2] in HNEt2 afforded the mono-coupling prod- in 3-position and shift in the series Fe(CO)2Cp, NR2,
uct 16 in 23% yield (Scheme 11). In addition to the coupling Fe(CO)(PPh3)Cp towards smaller wave numbers. In con-
of both complexes, Pd-coordinated chloride was replaced trast, the influence of the substituent in 2-position (alkyl,
1228
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234

Di-, Tri-, and Tetranuclear Cyclobutenylidene Complexes
FULL PAPER
CϵCϪR) is only small. With increasing donor capacity of plexes[19], (cyclobut-1-en-3-one)iron complexes[21a][21c], free
R the ν˜(CϵC) absorption shifts towards smaller wave num- cyclobut-1-en-3-ones[23], and 1,3-homobinuclear cyclobut-
bers [R ϭ SiMe3: ν˜(CϵC) ϭ 2141 cmϪ1 (5a); R ϭ trans- enylidene complexes[24] is nearly planar. As a consequence
(PEt3)2PdI: ν˜(CϵC) ϭ 2092 cmϪ1 (16)].
of the puckering, the transannular distance C(6)ϪC(8) in
5a is small (1.986 A) and the distance is well below the
sum of the van der Waals radii. Therefore, direct electronic
exchange cannot be excluded.
˚
The 13C resonances of both the chromium- (1-C) and the
iron-bound (3-C) ring carbon atoms appear at low field.
The 1-C resonance is in the range usually observed for al-
koxycarbene complexes (δ ϭ 290Ϫ320)[20]. The resonance
of the 3-C atom is in the region characteristic for alkenyli-
ron complexes[21]. Increasing the ability of the alkynyl
group CϵCϪR at 2-C to donate electron density {R ϭ Ph
(4c) Ǟ SiMe3 (5a) Ǟ trans-[(PEt3)2PdI] (16)} leads to an
upfield shift of the 1-C and 3-C resonances and to a down-
field shift of the 2-C resonance. These results are consistent
with earlier observations with 1,3-heterobinuclear cyclobut-
Figure 1. Molecular structure of complex 5a in the crystal (hydro-
gen atoms are omitted for clarity)[a]
enylidene complexes[6]
.
In general, the UV/Vis spectra of these cyclobutenylidene
complexes are solvent-dependent. The UV/Vis absorption
at lowest energy is shifted to shorter wavelength when a
nonpolar solvent like pentane is replaced by a more polar
one (DMF). However, whereas the solvent dependence of
the 3-aminocyclobutenylidene complexes 10 and 11 is pro-
nounced [∆ν˜ ϭ 1930 (10), 1820 cmϪ1 (11)] that of the 3-
Fe(CO)LCp-substituted complexes 5a, 7, 14, and 15 is
rather small [∆ν˜ ϭ 80Ϫ300 cmϪ1].
[a]
˚
Selected bond lengths [A], bond angles, and torsion angles [°]:
Cr(1)ϪC(6) 2.054(4), C(6)ϪC(9) 1.401(4), C(8)ϪC(9) 1.410(5),
C(9)ϪC(10) 1.428(4), C(10)ϪC(11) 1.199(5), C(8)ϪFe(1) 1.910(4);
C(6)ϪC(9)ϪC(8)
89.9(3),
C(7)ϪC(6)ϪC(9)
91.3(3),
C(7)ϪC(8)ϪC(9) 91.0(3); C(7)ϪC(6)ϪC(9)ϪC(8) 22.7(2).
The structure of the complex 5a was additionally estab-
lished by an X-ray-structural analysis (Table 1, Figure 1).
Conclusion
Our results demonstrate that an alkynyl functionality is
readily introduced into the 2-position of 1,3-heterobinuclear
cyclobutenylidene complexes by [2ϩ2] cycloaddition of
butadiynyl complexes to vinylidene complexes. These cyclo-
butenylidene complexes offer an easy access to a wide range
of di-, tri-, and tetranuclear cyclobutenylidene complexes by
derivatization of the alkynyl group and coupling reactions.
In addition, the substituents in 4- and 3-position can be
modified by use of other vinylidene complexes and by varia-
tion of the starting butadiynyl complexes.
By substitution of amines for the Fe(CO)2Cp fragment in
5a a large variety of amines such as chiral amines can be
introduced into the 3-position which is crucial for the non-
linear optical properties of these compounds. Thus, the syn-
thesis of butadiynes RϪCϵCCϵCϪNR2[25], which are
rather difficult to prepare, can be avoided.
˚
The C(6)ϪC(9) [1.401(4) A] and the C(8)ϪC(9) distance
˚
[1.410(5) A] are almost equal in length indicating that the
resonance structures C and D (Scheme 12) contribute to
almost the same extent to the overall bonding description.
The distances are in between the characteristic bond lengths
2
2
[22]
˚
of a C(sp )ϪC(sp ) single bond (1.46 A)
and a C(sp2)ϭ
C(sp ) double bond (1.32 A)[22]. The Cr(1)ϪC(6) distance
2
˚
˚
[2.054(4) A] is typical for heteroatom-stabilized carbene
complexes[13]
.
Scheme 12
The nonplanarity of the cyclobutenylidene ring in 5a de-
creases the symmetry of the molecule. Thus, taking into ac-
The FeϪC(8) distance is comparable to that in cyclobut- count the chirality of the iron center the existence of two
1-en-3-one complexes[21a][21c]. The FeϪC(36) axis in 5a is diastereomers might be expected. However, only one isomer
almost coplanar with the plane formed by the atoms C(7), of 5a could be isolated and the NMR spectra of 5a exhibit
C(8), C(9) [torsion angle C(9)ϪC(8)ϪFe(1)ϪC(36) ϭ only one set of signals. Obviously, in solution a rapid inver-
170.9°]. This conformation allows for maximal FeǞC(8) sion of the four-membered ring occurs. For the analogous
backdonation.
The most striking feature is the nonplanarity of the Cp(PEt3)Ni fragment at 3-C this dynamic process is still
bridging ligand in 5a. The puckering angle [angle between fast even at Ϫ80°C[6a]
the planes formed by the atoms C(7), C(6), C(9) and C(7), The geometry of the complexes 7 and 15 is similarly flex-
compound with an nBu substituent at 2-C and a
.
C(8), C(9)] is 148.2°. A similar puckering has been observed ible. However, for the diastereoselective coupling of 7 to 15
with other 1,3-heterobinuclear cyclobutenylidene com- a second effect has to be considered. Probably due to the
plexes[6], however, usually the four-membered ring in 3-ami- steric demand of the bulky PPh3 substituent, only one iso-
no- and 3-ethoxy-substituted cyclobutenylidene com- mer of 15 (meso or R/S) was formed. A similar selectivity
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234
1229

F. Leroux, R. Stumpf, H. Fischer
FULL PAPER
pounds. Therefore, a satisfactory elemental analysis could not be
obtained.
has been reported by Gladysz et al. for the formation of
comparable cyclobutenylidene complexes[24a]
.
Carbonyl(η5-cyclopentadienyl)(trimethylsilyl-1,3-diynyl)(tri-
phenylphosphane)iron (3a): A THF solution (50 ml) of 3.0 g (10.0
mmol) of 2a, 0.8 g (10.0 mmol) of Me3NO, and 4.0 g (15.0 mmol)
of PPh3 was stirred at room temp. The reaction was monitored by
IR spectroscopy. After ca. 2 h, the solvent was removed in vacuo,
the residue dissolved in 30 ml of CH2Cl2 and transferred to a col-
umn packed with silica gel. Gradient elution at 0°C with a mixture
of pentane/CH2Cl2 (ratio slowly decreasing from 1:0 to 3:7) yielded
the product as an orange band. After evaporation of the solvent in
vacuo, the product was obtained as an orange oil. Yield: 3.4 g
(63%, based on 2a). The product was identified by comparison
with literature data.[7a]
Support of this work by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie is gratefully acknowledged.
We also thank B. Weibert for collecting the data set for the X-ray-
structural analysis.
Experimental Section
General: All operations were performed under either nitrogen or
argon by using standard Schlenk techniques. Solvents were dried
by refluxing over CaH2 (CH2Cl2) or sodium/benzophenone ketyl
(pentane, Et2O, THF) and were freshly distilled prior to use. Silica
gel (Fa. J. T. Baker; silica gel for flash chromatography) and alum-
ina (Fa. Fluka) used for chromatography were nitrogen-saturated.
Flash chromatography was performed at a nitrogen pressure of 1.4
bar. The complexes 1[6a], 2a[7a], 3a[7a], [Cp(CO)2FeI][26], and
Pentacarbonyl{3-dicarbonyl(η5-cyclopentadienyl)ferrio]-4,4-
dimethyl-2-(trimethylsilylethynyl)cyclobut-2-en-1-ylidene}chromium
(4a): At Ϫ60°C, a solution of 1.49 g (5.0 mmol) of 2a in 50 ml of
CH2Cl2 was added to a solution of 1[6a]. The reaction mixture was
allowed to slowly warm up to room temp. Then, 50 ml of pentane
was added. The resulting suspension was filtered through a 2-cm
layer of alumina and the alumina was eluted with CH2Cl2. The
solvent was removed in vacuo and the residue was chromatog-
raphed at Ϫ30°C on silica gel. Elution with pentane/CH2Cl2 (ratio
decreasing from 1:0 to 4:1) gave a red solution. The solvent was
removed in vacuo and the residue recrystallized from 20 ml of pen-
tane/CH2Cl2 (3:1). Red crystals of 4a. Yield: 1.79 g (65%, based
on [Cr(CO)6]), m.p. 84°C. Ϫ IR (CH2Cl2): ν˜(CO) ϭ 2053 cmϪ1 s,
2034 s, 1990 s, 1939 vs; ν˜(CϵC) ϭ 2148 cmϪ1 vw. Ϫ UV/Vis (pen-
tane): λmax (lg ε) ϭ 494 nm (4.212); (DMF): λmax (lg ε) ϭ 492 nm
[Pd(PPh3)4][26] as well as RϪCϵCϪCϵCϪSnnBu3 (R ϭ nBu,
[28]
Ph)[27] and nBu3SnNEt2
were prepared according to literature
procedures. Ϫ NMR: Bruker AC 250 (1H and 13C) and Jeol JNX
400 (1H, 13C, and 31P); chemical shifts are reported relative to in-
ternal TMS (1H and 13C) or external H3PO4 (31P). Unless men-
tioned otherwise, NMR spectra were recorded in CDCl3 at room
temperature. Ϫ IR: Biorad FTS 60. Ϫ MS: Finnigan MAT 312,
modified either for EI or FAB (NBOH or NBOE used as solvent
for FAB). Ϫ UV/Vis: Hewlett-Packard diode-array spectrophoto-
meter 8452A. Ϫ Elemental analyses: Heraeus CHN-O-RAPID.
Dicarbonyl(η5-cyclopentadienyl)(octa-1,3-diynyl)iron (2b): 9.9 g
(25.0 mmol) of nBu3SnϪCϵCϪCϵCϪnBu, 0.3 g (2.0 mmol) of
CuI, and 2.5 g (2.0 mmol) of [Pd(PPh3)4] were added to a solution
of 6.1 g (20.0 mmol) of [Cp(CO)2FeI] in 150 ml of THF. The reac-
tion mixture was stirred at room temp. for about 1 h. The solvent
was evaporated in vacuo and the residue was chromatographed at
Ϫ20°C first two times with pentane/CH2Cl2 (ratio decreasing from
1:0 to 4:1) on alumina and then two times with pentane/CH2Cl2
(ratio decreasing from 1:0 to 3:2) on silica gel. The solvent was
evaporated in vacuo. The residue was recrystallized from 40 ml of
pentane/CH2Cl2 (3:2) to give 2b as a yellow powder. Yield: 2.3 g
(32%, based on [Cp(CO)2FeI]), m.p. 45°C. Ϫ IR (CH2Cl2):
1
(4.178). Ϫ H NMR (250 MHz): δ ϭ 0.25 (s, 9 H, SiMe3), 1.33 (s,
6 H, CH3), 5.25 (s, 5 H, C5H5). Ϫ 13C NMR (CD2Cl2, 250 MHz):
δ ϭ Ϫ0.4 (SiMe3), 26.4 (CH3), 74.3 (4-C), 87.1 (C5H5), 100.2, 104.4
(CϵC), 180.6 (2-C), 211.9 (FeϪCO), 217.9 (cis-CO), 229.2 (trans-
CO), 251.5 (3-C), 313.3 (1-C). Ϫ C23H20CrFeO7Si (544.3): calcd.
C 50.75, H 3.70; found C 50.52, H 3.88.
Pentacarbonyl{3-dicarbonyl(η5-cyclopentadienyl)ferrio]-4,4-
dimethyl-2-(hexa-1-ynyl)cyclobut-2-en-1-ylidene}chromium
(4b):
The synthesis of 4b from 1 and 1.4 g (5.0 mmol) of 2b in 50 ml of
CH2Cl2 at Ϫ60°C and the purification of the product with pentane/
CH2Cl2 (ratio decreasing from 1:0 to 2:1) were carried out anal-
ogously to that of 4a. Red oil. Yield: 1.19 g (45%, based on
[Cr(CO)6]). Ϫ IR (CH2Cl2): ν˜(CO) ϭ 2051 cmϪ1 m, 2031 s, 1981
vs, 1935 vs; ν˜(CϵC) ϭ 2142 cmϪ1 vw. Ϫ UV/Vis (solvent): λmax (lg
ε) ϭ (pentane) 490 nm (4.116), (DMF) 486 nm (4.161). Ϫ 1H NMR
1
ν(CO) ϭ 2040 cmϪ1 vs, 1997 vs; ν(CϵC) ϭ 2203 cmϪ1 vw. Ϫ H
˜
˜
3
NMR (250 MHz): δ ϭ 0.88 (t, JHH ϭ 7.0 Hz, 3 H, CH3),
1.32Ϫ1.51 (m, 4 H, CH2), 2.24 (t, JHH ϭ 6.7 Hz, 2 H, CH2), 5.06
3
(s, 5 H, C5H5). Ϫ 13C NMR (250 MHz): δ ϭ 13.5 (CH3), 18.7,
21.9, 30.9 (CH2), 67.1, 67.9, 83.8 (CϵC), 85.2 (C5H5), 97.4 (CϵC),
211.4 (CO). Ϫ C15H14FeO2 и CH2Cl2 (367.0): calcd. C 52.36, H
4.39; found C 51.86, H 3.97.
3
(CD2Cl2, 250 MHz): δ ϭ 0.86 (t, JHH ϭ 7.1 Hz, 3 H, CH3), 1.27
3
(s, 6 H, CH3), 1.39Ϫ1.54 (m, 4 H, CH2), 2.41 (t, JHH ϭ 6.9 Hz, 2
Dicarbonyl(η5-cyclopentadienyl)(phenylbuta-1,3-diynyl)iron (2c):
The synthesis of 2c from 6.1 g (20.0 mmol) of [Cp(CO)2FeI], 10.4
g (25.0 mmol) of nBu3SnϪCϵCϪCϵCϪPh, 0.3 g (2.0 mmol) of
CuI, and 2.5 g (2.0 mmol) of [Pd(PPh3)4] in 150 ml of THF and the
purification of the product by chromatography first with pentane/
CH2Cl2 (ratio decreasing from 1:0 to 3:1) on alumina and then
with pentane/CH2Cl2 (ratio slowly decreasing from 1:0 to 1:1) on
silica gel] were carried out similarly to that of 2b. Recrystallization
from 40 ml of pentane/CH2Cl2 (1:1) gave 2c. Yellow powder. Yield:
H, CH2), 5.14 (s, 5 H, C5H5). Ϫ 13C NMR (CD2Cl2, 250 MHz):
δ ϭ 13.8 (CH3), 19.8, 22.5 (CH2), 26.8 (CH3), 30.9 (CH2), 74.3
(4-C), 75.9 (CϵC), 86.9 (C5H5), 100.6 (CϵC), 182.7 (2-C), 212.1
(FeϪCO), 218.3 (cis-CO), 228.9 (trans-CO), 245.3 (3-C), 304.8 (1-
C). Ϫ C24H20CrFeO7 (528.0): calcd. C 54.55, H 3.82; found C
54.29, H 4.11. Ϫ MS (FAB); m/z (%): 528 (22) [Mϩ], 500 (14), 472
(38), 444 (10), 416 (100), 388 (50), 360 (10), 332 (12) [Mϩ Ϫ n CO;
n ϭ 1Ϫ7].
2.7 g (45%, based on [Cp(CO)2FeI]), m.p. 91°C. Ϫ IR (CH2Cl2):
Pentacarbonyl{3-dicarbonyl(η5-cyclopentadienyl)ferrio]-4,4-
ν˜(CO) ϭ 2042 cmϪ1 vs, 1994 vs; ν˜(CϵC) ϭ 2184 cmϪ1 m. Ϫ H dimethyl-2-(phenylethynyl)cyclobut-2-en-1-ylidene}chromium (4c):
NMR (250 MHz): δ ϭ 5.06 (s, 5 H, C5H5), 7.24, 7.39 (m, br., 5 H, The synthesis of 4c from 1 and 1.5 g (5.0 mmol) of 2c and the
C6H4). Ϫ 13C NMR (250 MHz): δ ϭ 64.8, 77.3 (CϵC), 85.4 purification of the product were carried out analogously to 4b.
1
(C5H5), 96.2, 97.3 (CϵC), 123.6, 127.5, 128.1, 132.4 (C6H5), 211.1
(CO). Ϫ MS (EI, 70 eV); m/z (%): 302 (38) [Mϩ], 274 (23), 246 tals of 4c. Yield: 1.65 g (60%, based on [Cr(CO)6]), m.p. 84°C. Ϫ
(100) [Mϩ Ϫ n CO; n ϭ 1, 2]. Ϫ Although the product was chroma- IR (CH2Cl2): ν˜(CO) ϭ 2052 cmϪ1 m, 2033 m, 1989 m, 1937 vs;
tographed several times, it still contained small amounts of tin com- ν˜(CϵC) ϭ 2146 cmϪ1 vw. Ϫ UV/Vis (pentane): λmax (lg ε) ϭ 494
Recrystallization from 20 ml of pentane/CH2Cl2 (3:1) gave red crys-
1230
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234

Di-, Tri-, and Tetranuclear Cyclobutenylidene Complexes
FULL PAPER
nm (4.062); (DMF): λmax (lg ε) ϭ 492 nm (4.183). Ϫ 1H NMR
(s). Ϫ C43H31CrFeO6P и 1/2 CH2Cl2 (824.6): calcd. C 63.35, H 3.91;
(CD2Cl2, 250 MHz): δ ϭ 1.40 (s, 6 H, CH3), 5.29 (s, 5 H, C5H5), found C 63.51, H 4.40. Ϫ MS (FAB); m/z (%): 782 (16) [Mϩ], 754
7.38Ϫ7.56 (m, 5 H, C6H5). Ϫ 13C NMR (CD2Cl2, 250 MHz): δ ϭ (2), 698 (2), 670 (16), 642 (30), 614 (46) [Mϩ Ϫ n CO; n ϭ 1, 3Ϫ6].
26.6 (CH3), 74.8 (4-C), 84.8 (CϵC), 87.0 (C5H5), 98.0 (CϵC),
Pentacarbonyl{3-dicarbonyl(η5-cyclopentadienyl)ferrio]-4,4-
123.3, 128.9, 131.5, 132.3 (C6H5), 180.7 (2-C), 211.9 (FeϪCO),
dimethyl-2-(ethynyl)cyclobut-2-en-1-ylidene}chromium (6): At
Ϫ90°C, 0.4 equiv. of tetrabutylammonium fluoride (1  solution
in THF) was added to a solution of 4a (5.4 g, 10.0 mmol) in 100
ml of THF. The mixture was warmed to room temp. and stirred
for ca. 3 h at room temp. The progress of the reaction was moni-
tored by thin-layer chromatography. The solvent was removed in
vacuo and the residue dissolved in 30 ml of CH2Cl2. Chromatogra-
phy at Ϫ40°C with pentane/CH2Cl2 (ratio decreasing from 1:0 to
1:1) and recrystallization from 20 ml of pentane/CH2Cl2 (1:1) af-
forded red crystals of 6. Yield: 3.16 g (67%, based on 4a), m.p.
68°C. Ϫ IR (CH2Cl2): ν˜(CO) ϭ 2054 cmϪ1 s, 2033 s, 1990 m, 1938
vs; ν˜(CϵC) ϭ 2139 cmϪ1 vw, br. Ϫ UV/Vis (pentane): λmax (lg ε) ϭ
492 nm (4.206); (DMF): λmax (lg ε) ϭ 486 nm (4.238). Ϫ 1H NMR
(CD2Cl2, 250 MHz): δ ϭ 1.35 (s, 6 H, CH3), 3.68 (s, 1 H, CϵCH),
5.25 (s, 5 H, C5H5). Ϫ 13C NMR (CD2Cl2, 250 MHz): δ ϭ 26.3
(CH3), 74.2 (4-C), 79.0, 86.3 (CϵC), 87.0 (C5H5), 179.5 (2-C),
211.8 (FeϪCO), 217.8 (cis-CO), 229.1 (trans-CO), 253.7 (3-C),
315.1 (1-C). Ϫ C20H12CrFeO7 (472.2): calcd. C 50.88, H 2.52;
found C 50.80, H 2.61.
218.1 (cis-CO), 229.0 (trans-CO), 250.6 (3-C), 311.5 (1-C). Ϫ
C26H16CrFeO7 (548.3): calcd. C 56.96, H 2.94; found C 57.12, H
3.06. Ϫ MS (FAB); m/z (%): 548 (38) [Mϩ], 520 (22), 492 (40), 464
(10), 436 (100), 408 (52), 380 (10), 352 (30) [Mϩ Ϫ n CO; n ϭ 1Ϫ7].
Pentacarbonyl{3-[carbonyl(η5-cyclopentadienyl)(triphenyl-
phosphane)ferrio]-4,4-dimethyl-2-(trimethylsilylethynyl)cyclo-
but-2-en-1-ylidene}chromium (5a): The synthesis of 5a from 1 and
2.7 g (5.0 mmol) of 3a in 50 ml of CH2Cl2 at Ϫ60°C, the purifi-
cation, and the chromatography of the product were carried out
analogously to that of 4a. The red fraction was eluted with pentane/
CH2Cl2 (ratio decreasing from 1:0 to 1:1). Recrystallization from
20 ml of pentane/CH2Cl2 (3:1) gave red crystals of 5a. Yield: 2.53
g (65%, based on [Cr(CO)6]), m.p. 152°C. Ϫ IR (CH2Cl2): ν˜(CO) ϭ
2043 cmϪ1 m, 1950 sh, 1927 vs; ν˜(CϵC) ϭ 2141 cmϪ1 vw. Ϫ UV/
Vis (pentane): λmax (lg ε) ϭ 520 nm (4.246); (DMF): λmax (lg ε) ϭ
512 nm (3.889). Ϫ 1H NMR (CD2Cl2, 250 MHz): δ ϭ 0.26 (s, 9
3
H, SiMe3), 0.49 (s, 3 H, CH3), 1.25 (s, 3 H, CH3), 4.82 (d, JPH
ϭ
1.5 Hz, 5 H, C5H5), 7.41Ϫ7.56 (m, 15 H, Ph). Ϫ 13C NMR
(CD2Cl2, 250 MHz): δ ϭ Ϫ0.1 (SiMe3), 25.8, 27.9 (CH3), 76.2 (4-
C), 87.2 (C5H5), 102.9, 104.1 (CϵC), 128.9, 129.0, 130.8, 130.9,
Pen t ac ar b ony l{ 3 -[ ca rb o ny l ( η5 -cycl op en ta di enyl )-
(triphenylphosphane)ferrio]-4,4-dimethyl-2-(ethynyl)-
cyclobut-2-en-1-ylidene}chromium (7): The synthesis of 7 by reac-
tion of 5a (7.8 g, 10.0 mmol) with 0.4 equiv of tetrabutylammonium
fluoride and the purification were performed analogously to 6. Red
crystals of 7. Yield: 4.24 g (57%, based on 5a), m.p. 72°C. Ϫ IR
2
133.7, 133.9, 135.2, 135.9 (C6H5), 183.2 (2-C), 218.4 (d, JPC ϭ 30
2
Hz, FeϪCO), 219.1 (cis-CO), 228.6 (trans-CO), 276.5 (d, JPC
ϭ
19 Hz, 3-C), 288.5 (1-C). Ϫ C40H35CrFeO6PSi (778.6): calcd. C
61.69, H 4.53; found C 61.91, H 4.63.
Decarbonylation of 4a with Me3NO in the Presence of PPh3: A
solution of 1.6 g (3.0 mmol) of 4a, 0.3 g (3.0 mmol) of Me3NO,
and 1.6 g (6.0 mmol) of PPh3 in 30 ml of THF was stirred at room
temp. The progress of the reaction was monitored by IR spec-
troscopy. After about 1 h, the solvent was removed in vacuo, the
residue dissolved in 15 ml of CH2Cl2, and the solution transferred
to a chromatography column packed with silica gel. Gradient elu-
tion at Ϫ20°C with pentane/CH2Cl2 (ratio slowly decreasing from
1:0 to 1:1) yielded 1.71 g (72%, based on 4a) of 5a.
(CH Cl ): ν(CO) ϭ 2043 cmϪ1 s, 1950 sh, 1927 vs, 1888 sh;
˜
2
2
ν(CϵC) ϭ 2143 cmϪ1 vw, br. Ϫ UV/Vis (pentane): λmax (lg ε) ϭ
˜
518 nm (4.030); (DMF): λmax (lg ε) ϭ 512 nm (4.166). Ϫ 1H NMR
(CD2Cl2, 250 MHz): δ ϭ 0.62 (s, 3 H, CH3), 1.24 (s, 3 H, CH3),
3
3.58 (s, 1 H, CϵC-H), 4.80 (d, JPH ϭ 1.5 Hz, 5 H, C5H5),
7.39Ϫ7.54 (m, 15 H, Ph). Ϫ 13C NMR (CD2Cl2, 250 MHz): δ ϭ
25.9, 27.4 (CH3), 76.3 (4-C), 81.3, 86.1 (CϵC), 86.9 (C5H5), 128.4,
128.6, 129.0, 129.7, 130.9, 133.2, 133.7, 133.9, 135.1, 135.8 (C6H5),
181.8 (2-C), 218.1 (d, 2JPC ϭ 29 Hz, FeϪCO), 219.0 (cis-CO), 228.4
(trans-CO), 280.7 (d, 2JPC ϭ 17 Hz, 3-C), 289.9 (1-C). Ϫ 31P NMR:
δ ϭ 68.8 (s). Ϫ C37H27CrFeO6P и 1/2 C5H12 (742.5): calcd. C 63.98,
H 4.35; found C 63.95, H, 4.51. Ϫ MS (FAB); m/z (%): 706 (8)
[Mϩ], 594 (15), 566 (20), 538 (35) [Mϩ Ϫ n CO; n ϭ 4, 5, 6], 263
(100) [HPPh3ϩ].
Pe n ta c a r bo ny l{ 3- [c a r bonyl (η 5 - cycl opentadi enyl )-
(triphenylphosphane)ferrio]-4,4-dimethyl-2-(phenylethynyl)-
cyclobut-2-en-1-ylidene}chromium (5c): A solution of 1.4 g (2.0
mmol) of 7 in 5 ml of toluene was treated at room temp. with 0.5
g (2.5 mmol) of Me3SnNMe2. The reaction was followed by thin-
layer chomatography. After 30 min, the solvent was removed in
vacuo. The remaining oil was dissolved in THF (30 ml) and 0.5 g
Pentacarbonyl[3-dimethylamino-4,4-dimethyl-2-(trimethylsilyl-
(2.5 mmol) of iodobenzene, 30 mg (0.2 mmol) of CuI, and 280 mg ethynyl)cyclobut-2-en-1-ylidene]chromium (10): An aqueous solu-
(0.2 mmol) of [Pd(PPh3)4] were added. The reaction mixture was tion of HNMe2 (40%, 0.25 ml, 2.0 mmol) was added at room temp.
stirred for 30 min at 40°C. The solvent was removed in vacuo, the to a solution of 0.5 g (1.0 mmol) of 4a in 10 ml of THF. The color
residue dissolved in 15 ml of CH2Cl2 and chromatographed at of the solution changed within a few minutes from red to yellow.
Ϫ30°C with pentane/CH2Cl2 (ratio decreasing from 1:0 to 3:2) on
The solvent was removed in vacuo and the residue chromatog-
silica gel. A red band was eluted. Recrystallization from 20 ml of
raphed at Ϫ20°C on silica gel. With pentane/CH2Cl2 (ratio decreas-
pentane/CH2Cl2 (1:1) gave red crystals of 5c. Yield: 1.25 g (76%, ing from 1:0 to 1:1) a yellow band was eluted. Recrystallization
based on 7), m.p. 95°C (dec.). Ϫ IR (CH2Cl2): ν˜(CO) ϭ 2043 cmϪ1
from 5 ml of pentane/CH2Cl2 (3:1) gave yellow crystals of 10. Yield:
m, 1950 sh, 1925 vs, 1901 sh. Ϫ UV/Vis (pentane): λmax (lg ε) ϭ 0.35 g (83%, based on 4a), m.p. 113°C. Ϫ IR (CH2Cl2): ν˜(CO) ϭ
522 nm (3.891); (DMF): λmax (lg ε) ϭ 516 nm (4.122). Ϫ 1H NMR 2046 cmϪ1 m, 1971 vw, 1929 vs, 1893 sh; ν˜(CϵC) ϭ 2146 cmϪ1 w.
(250 MHz): δ ϭ 0.56 (s, 3 H, CH3), 1.27 (s, 3 H, CH3), 4.80 (d, Ϫ UV/Vis (pentane): λmax (lg ε) ϭ 450 nm (4.383); (DMF): λmax
3JPH ϭ 1.5 Hz, 5 H, C5H5), 7.28Ϫ7.57 (m, 20 H, C6H5, PPh3). Ϫ
(lg ε) ϭ 414 nm (4.290). Ϫ 1H NMR (CD2Cl2, 250 MHz): δ ϭ
13C NMR (250 MHz): δ ϭ 25.5, 27.7 (CH3), 76.0 (4-C), 86.5 0.20 (s, 9 H, SiMe3), 1.41 (s, 6 H, CH3), 3.06, 3.42 (s, 6 H, NMe2).
(C5H5), 97.5, 123.6 (CϵC), 128.2, 128.4, 128.6, 129.5, 130.5, 131.1,
Ϫ
13C NMR (CD2Cl2, 250 MHz): δ ϭ Ϫ0.4 (SiMe3), 23.8 (CH3),
132.8, 133.2, 134.1, 134.4, 134.8, 135.5 (C6H5, PPh3), 182.0 (2-C),
39.8, 49.9 (NMe2), 60.7 (4-C), 98.4, 102.0 (CϵC), 134.2 (2-C),
217.8 (d, 2JPC ϭ 29 Hz, FeϪCO), 218.7 (cis-CO), 228.1 (trans-CO), 176.1 (3-C), 219.1 (cis-CO), 227.2 (trans-CO), 307.1 (1-C). Ϫ
2
275.8 (d, JPC ϭ 17 Hz, 3-C), 291.8 (1-C). Ϫ 31P NMR: δ ϭ 68.8
C18H21CrNO5Si и 1/10 CH2Cl2 (420.0): calcd. C 51.82, H 5.08, N,
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234
1231

F. Leroux, R. Stumpf, H. Fischer
FULL PAPER
3.88; found C 51.78, H 5.09, N 3.34. Ϫ MS (EI, 70 eV); m/z (%):
411 (9) [Mϩ], 355 (4), 299 (20), 271 (100) [Mϩ Ϫ n CO; n ϭ 2, 4, 5].
Pen t ac ar b ony l { 3 -[ ca rb o ny l ( η5 -cycl op en ta di enyl )-
(triphenylphosphane)ferrio]-2-(p-iodophenyl)ethynyl-4,4-(di-
methyl)cyclobut-2-en-1-ylidene}chromium (14) and 1,4-Bis({4-
pentacarbonylchromium-2-[carbonyl(η5-cyclopentadienyl)-
(triphenylphosphane)ferrio]-3,3-(dimethyl)cyclobut-1-en-4-yli-
dene}ethynyl)benzene (15): 0.2 g (0.5 mmol) of C6H4I2-p, 20 mg
(0.1 mmol) of CuI, and 120 mg (0.1 mmol) of [Pd(PPh3)4] were
added to a solution of 0.7 g (1.0 mmol) of 7 in 30 ml of HNEt2.
The reaction mixture was stirred for 5 h at 40°C. The solvent was
removed in vacuo, the residue dissolved in 4 ml of CH2Cl2 and then
chromatographed at Ϫ20°C with pentane/CH2Cl2 (ratio decreasing
from 1:0 to 4:1) on silica gel. Two slightly different red bands were
eluted. The first band contained 14, the second one 15.
Pentacarbonyl[4,4-dimethyl-3-piperidino-2-(trimethyl-
silylethynyl)cyclobut-2-en-1-ylidene]chromium (11): The synthesis
of 11 from 0.5 g (1.0 mmol) of 4a and 1.5 equiv. of piperidine in
10 ml of THF and the purification of the product were carried out
similarly to 10. On chromatography, pentane/CH2Cl2 (ratio
decreasing from 1:0 to 7:1) was used as the eluant. Recrystallization
from 5 ml of pentane/CH2Cl2 (6:1) afforded yellow crystals of 11.
Yield: 0.18 g (40%, based on 4a), m.p. 120°C. Ϫ IR (CH2Cl2):
ν(CO) ϭ 2046 cmϪ1 m, 1970 w, 1926 vs, 1896 sh; ν(CϵC) ϭ 2145
˜
˜
cmϪ1 w. Ϫ UV/Vis (pentane): λmax (lg ε) ϭ 450 nm (4.325); (DMF):
λmax (lg ε) ϭ 416 nm (4.360). Ϫ 1H NMR (CD2Cl2, 250 MHz):
δ ϭ 0.20 (s, 9 H, SiMe3), 1.40 (s, 6 H, CH3), 1.77, 3.40, 3.94 (m,
br., 10 H, N(CH2)5). Ϫ 13C NMR (CD2Cl2, 250 MHz): δ ϭ Ϫ0.3
(SiMe3), 23.6 (CH2), 23.8 (CH3), 26.3, 26.7, 49.0, 49.9 (CH2), 60.6
(4-C), 98.5, 102.1 (CϵC), 133.3 (2-C), 173.6 (3-C), 219.2 (cis-CO),
227.1 (trans-CO), 305.3 (1-C). Ϫ C21H25CrNO5Si (451.5): calcd. C
55.86, H 5.58, N 3.10; found C 55.80, H 5.59, N 3.37. Ϫ MS (FAB);
m/z (%): 451 (45) [Mϩ], 423 (8), 395 (42), 367 (18), 339 (100), 311
(82) [Mϩ Ϫ n CO; n ϭ 1Ϫ5], 260 (50) [(C16H25NSi)ϩ].
14: Yield: 0.18 g (38%, based on C6H4I2-p), m.p. 87°C. Ϫ IR
(CH2Cl2): ν˜(CO) ϭ 2042 cmϪ1 m, 1948 sh, 1926 vs, 1901 sh. Ϫ
UV/Vis (pentane): λmax (lg ε) ϭ 522 nm (4.213); (DMF): λmax (lg
ε) ϭ 516 nm (4.216). Ϫ 1H NMR (400 MHz): δ ϭ 0.58 (s, 3 H,
CH3), 1.25 (s, 3 H, CH3), 4.79 (s, 5 H, C5H5), 7.14Ϫ7.69 (m, 19 H,
C6H4, C6H5). Ϫ 13C NMR (400 MHz): δ ϭ 25.4, 27.8 (CH3), 86.5
(C5H5), 88.9 (4-C), 94.0, 96.5 (CϵC), 123.2, 128.1, 128.5, 128.6,
128.8, 129.2, 130.5, 132.5, 133.0, 133.3, 133.5, 133.7, 134.9, 135.4,
137.6 (C6H4, C6H5), 181.5 (2-C), 217.7 (d, 2JPC ϭ 29 Hz, FeϪCO),
Pentacarbonyl{3-dicarbonyl(η5-cyclopentadienyl)ferrio]-4,4-di-
methyl-2-(tri-n-butylstannylethynyl)cyclobut-2-en-1-ylidene}-
chromium (12): At room temp., 0.9 g (2.5 mmol) of nBu3SnNEt2
was added to a solution of 0.9 g (2.0 mmol) of 6 in 5 ml of toluene.
The progress of the reaction was monitored by thin-layer choma-
tography. After ca. 5 min, the solvent was removed in vacuo, the
residue dissolved in 10 ml of CH2Cl2, and chromatographed at
Ϫ20°C on silica gel with pentane/CH2Cl2 (ratio decreasing from
1:0 to 1:1). Complex 12 was obtained as a red oil. Yield: 1.29 g
(85%, based on 6). Ϫ IR (pentane): ν˜(CO) ϭ 2054 cmϪ1 m, 2033
s, 1990 s, 1951 vs, 1938 sh; ν˜(CϵC) ϭ 2131 cmϪ1 vw, br. Ϫ 1H
2
218.6 (cis-CO), 228.1 (trans-CO), 277.3 (d, JPC ϭ 17 Hz, 3-C),
294.2 (1-C). Ϫ 31P NMR: δ ϭ 68.5 (s). Ϫ C43H30CrFeIO6P и 1/2
C5H12 (944.1): calcd. C 57.88, H 3.84; found C 57.74, H 3.74. Ϫ
MS (FAB); m/z (%): 908 (6) [Mϩ], 796 (12), 768 (26), 740 (52)
[Mϩ Ϫ n CO; n ϭ 4, 5, 6], 478 (30) [Mϩ Ϫ 6 CO Ϫ PPh3], 383
(100) [(CpFePPh3)ϩ].
15: Yield: 0.07 g (10%, based on C6H4I2-p), m.p. 72°C. Ϫ IR
(CH2Cl2): ν˜(CO) ϭ 2043 cmϪ1 s, 1947 sh, 1925 vs; ν˜(CϵC ) ϭ 2067
cmϪ1 vw. Ϫ UV/Vis (pentane): λmax (lg ε) ϭ 522 nm (3.890);
1
(DMF): λmax (lg ε) ϭ 516 nm (4.348). Ϫ H NMR (CD2Cl2, 250
3
NMR (250 MHz): δ ϭ 0.91 (t, JHH ϭ 7.3 Hz, 9 H, CH3),
3
MHz): δ ϭ 0.61 (s, 6 H, CH3), 1.28 (s, 6 H, CH3), 4.86 (d, JPH
ϭ
1.03Ϫ1.09 (m, 6 H, CH2), 1.29Ϫ1.43 (m, 6 H, CH2), 1.34 (s, 6 H,
CH3), 1.55Ϫ1.68 (m, 6 H, CH2), 5.24 (s, 5 H, C5H5). Ϫ 13C NMR
(250 MHz): δ ϭ 11.1 (CH3), 13.6, 26.4, 27.0 (CH2), 28.9 (CH3),
73.7 (4-C), 86.4 (C5H5), 104.2, 105.0 (CϵC), 181.6 (2-C), 211.4
(FeϪCO), 217.5 (cis-CO), 228.6 (trans-CO), 243.9 (3-C), 308.1 (1-
C). ϪIt was not possible to completely remove small amounts of
tin compounds. Therefore, a satisfactory elemental analysis was
not obtained.
Pentacarbonyl{3-dicarbonyl(η5-cyclopentadienyl)ferrio]-2-(p-
iodophenylethynyl)-4,4-(dimethyl)cyclobut-2-en-1-ylidene}-
chromium (13): Compound 12 was generated in situ from 2.8 g (6.0
mmol) of 6 and 2.2 g (6.0 mmol) of nBu3SnNEt2 in 10 ml of toluene
1.2 Hz, 10 H, C5H5), 7.30Ϫ7.57 (m, 34 H, C6H4, C6H5). Ϫ 13C
NMR (CD2Cl2, 250 MHz): δ ϭ 25.9, 27.9 (CH3), 76.6 (4-C), 87.1
(C5H5), 89.7, 97.6 (CϵC), 123.7, 128.9, 129.1, 130.9, 131.4, 133.7,
2
133.8, 135.2, 135.9 (C6H4, C6H5), 182.1 (2-C), 218.3 (d, JPC ϭ 29
2
Hz, FeϪCO), 219.2 (cis-CO), 228.6 (trans-CO), 280.0 (d, JPC
ϭ
18 Hz, 3-C), 291.1 (1-C). Ϫ 31P NMR: δ ϭ 68.5 (s). Ϫ
C80H56Cr2Fe2O12P2 (1487.0): calcd. C 64.62, H 3.80; found C
64.90, H 4.52. Ϫ MS (FAB); m/z (%): 1487 (25) [Mϩ], 1402 (4),
1374 (15), 1347 (40), 1319 (88) [Mϩ Ϫ n CO; n ϭ 3Ϫ6], 944 (38),
916 (58), 888 (60) [Mϩ Ϫ HPPh3 Ϫ n CO; n ϭ 10Ϫ12].
Pentacarbonyl{3-[carbonyl(η5-cyclopentadienyl)(triphenylphos-
as described above. After changing the solvent to THF (100 ml), phane)ferrio]-2-[trans-iodobis(triethylphosphane)palladio]-
1.0 g (3.0 mmol) of C6H4I2-p, 30 mg (0.2 mmol) of CuI, and 280 ethynyl-4,4-(dimethyl)cyclobut-2-en-1-ylidene}]chromium (16): 0.4
mg (0.2 mmol) of [Pd(PPh3)4] were added. The reaction mixture g (1.0 mmol) of trans-[(PEt3)2PdCl2], 60 mg (0.3 mmol) of CuI,
was stirred for 30 min at 40°C. The solvent was removed in vacuo,
and 350 mg (0.3 mmol) of [Pd(PPh3)4] were added to a solution of
the residue dissolved in 20 ml of CH2Cl2, and chromatographed at
2.1 g (3.0 mmol) of 7 in 30 ml of HNEt2. The reaction mixture was
Ϫ30°C with pentane/CH2Cl2 (ratio decreasing from 1:0 to 2:1) on stirred for 1 d at 40°C. The solvent was removed in vacuo, the
silica gel. A red band was eluted. Recrystallization from 20 ml of residue dissolved in 15 ml of CH2Cl2, and chromatographed at
pentane/CH2Cl2 (1:1) gave red crystals of 13. Yield: 0.41 g (20%, Ϫ20°C with pentane/CH2Cl2 (ratio decreasing from 1:0 to 1:1) on
based on C6H5I2-p), m.p. 77°C. Ϫ IR (CH2Cl2): ν˜(CO) ϭ 2053 alumina. An orange band was eluted which was then chromato-
cmϪ1 m, 2033 m, 1984 m, 1937 vs; ν˜(CϵC) ϭ 2197 cmϪ1 vw. Ϫ graphed two times at Ϫ20°C with pentane/CH2Cl2 (ratio decreas-
UV/Vis (pentane): λmax (lg ε) ϭ 494 nm (3.900); (DMF): λmax (lg ing from 1:0 to 1:1) on silica gel. Recrystallization yielded 16 as an
1
ε) ϭ 492 nm (4.187). Ϫ H NMR (CD2Cl2, 400 MHz): δ ϭ 1.39 orange powder. Yield: 0.27 g (22%, based on trans-[(PEt3)2PdCl2]),
(s, 6 H, CH3), 5.28 (s, 5 H, C5H5), 7.26Ϫ7.28, 7.72Ϫ7.74 (m, 4 H, m.p. 82°C. Ϫ IR (CH2Cl2): ν˜(CO) ϭ 2042 cmϪ1 m, 1965 sh, 1942
1
C6H4I). Ϫ 13C NMR (CD2Cl2, 400 MHz): δ ϭ 26.2 (CH3), 74.6 sh, 1919 vs, 1888 sh; ν˜(CϵC) ϭ 2092 cmϪ1 vw. Ϫ H NMR (250
(4-C), 86.8 (C5H5), 94.6, 96.7 (CϵC), 122.6, 132.7, 133.5, 137.8 MHz): δ ϭ 0.84 (s, 3 H, CH3), 1.29 (s, 3 H, CH3), 0.88Ϫ1.29 (m,
(C6H4I), 179.8 (2-C), 211.5 (FeϪCO), 217.7 (cis-CO), 228.7 (trans- br., 18 H, CH2CH3), 2.00Ϫ2.30 (m, br., 12 H, CH2), 4.63 (s, 5 H,
CO), 251.6 (3-C), 313.2 (1-C). Ϫ C27H15CrFeIO7 (686.2): calcd. C C5H5), 7.21Ϫ7.56 (m, 15 H, C6H5). Ϫ 13C NMR (250 MHz): δ ϭ
47.26, H 2.20; found C 47.36, H 2.29.
8.4 (PEt3), 17.5 (m, PEt3), 27.1, 30.7 (CH3), 78.2 (4-C), 86.3 (C5H5),
1232
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234

Di-, Tri-, and Tetranuclear Cyclobutenylidene Complexes
FULL PAPER
Dedicated to Professor Ernst Otto Fischer on the occasion of
Ƞ
103.4 (t, 3JPC ϭ 5 Hz, CϵC), 117.5 (t, 2JPC ϭ 14 Hz, CϵC), 128.0,
128.4, 128.8, 129.4, 130.5, 130.8, 132.9, 133.2, 133.4, 133.6, 135.2,
135.9 (C6H5), 192.2 (2-C), 218.7 (d, 2JPC ϭ 32 Hz, FeϪCO), 219.7
(cis-CO), 226.3 (trans-CO), 236.2 (d, 2JPC ϭ 18 Hz, 3-C), 241.4 (1-
C). Ϫ 31P NMR: δ ϭ 72.8 (s, PPh3), 13.8 (s, PEt3). Ϫ C49H56CrFeI-
O6P3Pd и C5H12 (1246.2): calcd. C 52.09, H 5.35; found C 52.20,
H 5.06. Ϫ MS (FAB); m/z (%): 1174 (28) [Mϩ], 1062 (25), 1034
(10), 1006 (5) [Mϩ Ϫ n CO; n ϭ 4Ϫ6], 916 (10), 888 (12) [Mϩ Ϫ n
CO Ϫ PEt3; n ϭ 5, 6], 800 (10), 772 (15), 744 (15) [Mϩ Ϫ PPh3 Ϫ
n CO; n ϭ 4Ϫ6], 383 (100) [CpFePPh3ϩ].
his 80th birthday.
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M. H. Chisholm, Angew. Chem. 1991, 103,
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Pentacarbonyl{3-[carbonyl(η5-cyclopentadienyl)(tri-
phenylphosphane)ferrio]-2-[trans-chlorobis(triethylphosphane)-
platinio]ethynyl-4,4-(dimethyl)cyclobut-2-en-1-ylidene}-
chromium (17): 1.1 g (3.0 mmol) of nBu3SnNEt2 was added at room
temp. to a solution of 2.1 g (3.0 mmol) of 7 in 5 ml of toluene. The
progress of the reaction was followed by thin-layer chomatography.
After 30 min, the solvent was removed in vacuo and the remaining
oil dissolved in THF (50 ml). This solution was treated with 0.5 g
(1.0 mmol) of trans-[(PEt3)2PtCl2], 57 mg (0.3 mmol) of CuI, and
350 mg (0.3 mmol) of [Pd(PPh3)4]. The reaction mixture was stirred
for 12 h at room temp. The solvent was removed in vacuo, the
residue dissolved in 15 ml of CH2Cl2 and chromatographed at
Ϫ30°C with pentane/acetone (ratio decreasing from 1:0 to 7:3) on
silica gel. An orange fraction was eluted. Recrystallization from 20
ml of pentane/CH2Cl2 (1:1) yielded 17 as an orange powder. Yield:
0.42 g (36%, based on trans-[(PEt3)2PtCl2]), m.p. 78°C. Ϫ IR
(CH2Cl2): ν˜(CO) ϭ 2041 cmϪ1 m, 1963 sh, 1940 sh, 1918 vs , 1889
sh; ν˜(CϵC) ϭ 2096 cmϪ1 vw. Ϫ 1H NMR (CD2Cl2, 400 MHz):
δ ϭ 0.80 (s, 3 H, CH3), 1.28 (s, 3 H, CH3), 1.09Ϫ1.26 (m, br., 18
H, CH2CH3), 1.85Ϫ2.10 (m, br., 12 H, CH2), 4.62 (s, 5 H, C5H5),
7.42Ϫ7.59 (m, 15 H, C6H5). Ϫ 13C NMR (400 MHz): δ ϭ 7.9
(PEt3), 14.1Ϫ14.6 (m, PEt3), 25.5, 26.8 (CH3), 77.6 (4-C), 86.3
(C5H5), 99.9 (m, CϵC), 128.5, 128.6, 130.3, 133.5, 133.6, 135.4,
135.8 (C6H5), 193.2 (2-C), 218.9 (d, 2JPC ϭ 32 Hz, FeϪCO), 219.8
(cis-CO), 226.4 (trans-CO), 233.9 (3-C), 239.9 (1-C). Ϫ 31P NMR:
Bartik, J. A. Gladysz, Angew. Chem. 1994, 106, 2269Ϫ2272; An-
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1
ganometallics 1991, 10, 3842Ϫ3848. Ϫ
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δ ϭ 72.9 (s, PPh3), 14.1 (s and d, JPtP ϭ 2371 Hz, PEt3). Ϫ
Robinson, J. Simpson, Organometallics 1992, 11, 501Ϫ513.
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C49H56ClCrFeO6P3Pt (1172.3): calcd. C 50.20, H 4.81; found C
50.00, H 5.06. Ϫ MS (FAB); m/z (%): 1172 (2) [Mϩ], 1060 (16),
1032 (38), 1004 (38) [Mϩ Ϫ 6 CO; n ϭ 4Ϫ6], 886 (34) [Mϩ Ϫ 6
CO Ϫ PEt3], 769 (26) [Mϩ Ϫ 6 CO Ϫ 2 PEt3 ϩ H], 742 (92) [Mϩ
Ϫ 6 CO Ϫ PPh3], 624 (100) [Mϩ Ϫ 6 CO Ϫ PPh3 Ϫ PEt3].
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X-ray-Structural Analysis of 5a: C40H35CrFeO6PSi (778.6), crys-
tal size 0.3 ϫ 0.3 ϫ 0.3 mm (obtained from pentane/CH2Cl2, 3:1),
˚
¯
triclinic, P1, a ϭ 11.555(2), b ϭ 12.599(2), c ϭ 15.382(2) A, α ϭ
83.83(2), β ϭ 75.10(1), γ ϭ 63.62(1)°, V ϭ 1937.4(5) A3, Z ϭ 2,
˚
[12]
C. C. Karl, H. Fischer, unpublished results.
dcalcd. ϭ 1.335 g cmϪ3, µ(Mo-Kα) ϭ 0.760 mmϪ1, F(000) ϭ 804,
Wyckoff scan 4° < 2Θ < 54°, scan rate variable 4.00Ϫ30.00° minϪ1
in ω; ∆ω ϭ 1.40°, T ϭ 244 K, 8873 reflections collected, 8446
independent reflections, 6373 reflections with F > 4.0 σ(F); 451
refined parameters; R ϭ 0.047, Rw ϭ 0.051. Largest difference peak
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Transition Metal Carbene Complexes (Eds.: K. H. Dötz, H.
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(hole): ϩ0.45 e AϪ3 (Ϫ0.38 e AϪ3). Data were collected with a
˚
˚
[15] [15a]
C. Cauletti, C. Furlani, A. Sebald, Gazz. Chim. Ital. 1988,
crystal mounted in a glass capillary on a Siemens P4 diffractometer
[15b]
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K. Jones, M. F. Lappert, J. Organomet.
˚
(graphite monochromator, Mo-Kα radiation, λ ϭ 0.71073 A). The
Chem. 1965, 3, 295Ϫ307.
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275Ϫ282.
˚
assuming ideal geometries (dCϪH ϭ 0.96 A) and their coordinates
[19]
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H. Fischer, O. Podschadly, A. Früh, C. Troll, R. Stumpf, A.
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were refined together with the attached C atoms as “riding mod-
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eters have been deposited[29]
.
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234
1233

F. Leroux, R. Stumpf, H. Fischer
FULL PAPER
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F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G.
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Crystallographic data (excluding structure factors) for the struc-
ture reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publi-
cation no. CCDC-101439. Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK [fax: int. code ϩ 44(1223)336-033, e-mail:
deposit@ccdc.cam.ac.uk].
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[98127]
1234
Eur. J. Inorg. Chem. 1998, 1225Ϫ1234