Reactions of group 4 metallocene complexes with mono- and diphenylacetonitrile: Formation of unusual four- and six-membered metallacycles

Article abstract of DOI:10.1002/chem.201204211

Reactions of Group 4 metallocene alkyne complexes [Cp'₂M(η ²-Me₃SiC₂SiMe₃)] (1: M=Zr, Cp'=Cp=η⁵-pentamethylcyclopentadienyl; 2 a: M=Ti, Cp'=Cp*, and 2 b: M=Ti, Cp'₂=rac-(ebthi)=rac-1,2-ethylene-1,1'- bis(η⁵-tetrahydroindenyl)) with diphenylacetonitrile (Ph ₂CHCN) and of the seven-membered zirconacyclocumulene 3 with phenylacetonitrile (PhCH₂CN) were investigated. Different compounds were obtained depending on the metal, the cyclopentadienyl ligand and the reaction temperature. In the first step, Ph₂CHCN coordinated to 1 to form [Cp*₂Zr(η²-Me₃SiC ₂SiMe₃)(NCCHPh₂)] (4). Higher temperatures led to elimination of the alkyne, coordination of a second Ph₂CHCN and transformation of the nitriles to a keteniminate and an imine ligand in [Cp*₂Zr(NC₂Ph₂)(NCHCHPh₂)] (5). The conversion of 4 to 5 was monitored by using ¹H NMR spectroscopy. The analogue titanocene complex 2 a eliminated the alkyne first, which led directly to [Cp*₂Ti(NC₂Ph ₂)₂] (6) with two keteniminate ligands. In contrast, the reaction of 2 b with diphenylacetonitrile involved a formal coupling of the nitriles to obtain the unusual four-membered titanacycle 7. An unexpected six-membered fused zirconaheterocycle (8) resulted from the reaction of 3 with PhCH₂CN. The molecular structures of complexes 4, 5, 6, 7 and 8 were determined by X-ray crystallography. Metal made modes: [Cp'M₂] complexes with different metals and Cp' ligands react differently with Ph ₂CHCN (see scheme). M=Zr gives keteniminate and imine ligands as [Cp*₂Zr(NC₂Ph₂)(NCHCHPh₂)], M=Ti forms two keteniminates as [Cp*₂Ti(NC₂Ph ₂)₂]. If Cp'₂=rac-(ebthi)=rac-1,2-ethylene-1, 1'-bis(η⁵-tetrahydroindenyl) and M=Ti, an unusual four-membered titanacycle is formed. [Cp₂Zr(η²-Me ₃SiC₄SiMe₃)] reacts with PhCH₂CN to give an unexpected six-membered fused zirconaheterocycle. Copyright

Full text of DOI:10.1002/chem.201204211

DOI: 10.1002/chem.201204211
Reactions of Group 4 Metallocene Complexes with Mono- and
Diphenylacetonitrile: Formation of Unusual Four- and Six-Membered
Metallacycles
ACHTUNGTRENNUNG
Lisanne Becker,[a] Vladimir V. Burlakov,[a, b] Perdita Arndt,[a] Anke Spannenberg,[a]
Wolfgang Baumann,[a] Haijun Jiao,[a] and Uwe Rosenthal*[a]
Abstract: Reactions of Group 4 metal-
locene alkyne complexes [Cp’2M(h2-
Me3SiC2SiMe3)] (1: M=Zr, Cp’=
Cp*=h5-pentamethylcyclopentadienyl;
2a: M=Ti, Cp’=Cp*, and 2b: M=Ti,
Cp’2 =rac-(ebthi)=rac-1,2-ethylene-
1,1’-bis(h5-tetrahydroindenyl)) with di-
phenylacetonitrile (Ph2CHCN) and of
the seven-membered zirconacyclocu-
the first step, Ph2CHCN coordinated to
The analogue titanocene complex 2a
eliminated the alkyne first, which led
directly to [Cp*2TiACHTGUNTERNNU(G NC2Ph2)2] (6) with
1 to form [Cp*2Zr(h2-Me3SiC2SiMe3)-
(NCCHPh2)] (4). Higher temperatures
led to elimination of the alkyne, coor-
dination of a second Ph2CHCN and
transformation of the nitriles to a ke-
two keteniminate ligands. In contrast,
the reaction of 2b with diphenylaceto-
nitrile involved a formal coupling of
the nitriles to obtain the unusual four-
membered titanacycle 7. An unexpect-
ed six-membered fused zirconahetero-
cycle (8) resulted from the reaction of
3 with PhCH2CN. The molecular struc-
tures of complexes 4, 5, 6, 7 and 8 were
determined by X-ray crystallography.
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
The conversion of 4 to 5 was moni-
mulene
3
with phenylacetonitrile
tored by using 1H NMR spectroscopy.
(PhCH2CN) were investigated. Differ-
ent compounds were obtained depend-
ing on the metal, the cyclopentadienyl
ligand and the reaction temperature. In
Keywords: metallacycles
· N li-
gands · titanium · zirconium
Introduction
During the last decades, low-membered metallacycles of
Group 4 metallocenes have attracted great interest because
of their stability and reactivity. In particular, the three- and
five-membered all-carbon metallacycles, metallacyclopro-
penes, 1-metallacyclopent-3-ynes (metallacyclopentynes), 1-
metallacyclopenta-2,3,4-trienes (metallacyclocumulenes) and
1-metallacyclopenta-2,3-dienes (metallacycloallenes) were
synthesised to study their reaction behaviour.[1] The ana-
logue all-carbon four-membered metallacyclobuta-2,3-diene
of Group 4 metallocenes (A, Scheme 1) has not been suc-
cessfully prepared to date, but theoretical studies have pre-
dicted its existence.[2] In most cases, the stabilisation of
strained ring systems has been realised by incorporating het-
eroatoms.[1b,3] Therefore, we were interested in the synthesis
Scheme 1. Different four-membered metallacycles.
of four-membered heterometallacycles of Group 4 metallo-
cenes. The reactions of [Cp2M(L)(h2-Me3SiC2SiMe3)] (M=
Ti, no L; M =Zr, L=pyridine; Cp=h5-cyclopentadienyl)
with the sulfur diimide Me3SiN=S=NSiMe3 gave the four-
membered metallacycles [Cp2M(k2-N,N-Me3SiNSNSiMe3)]
(M=Ti, Zr; B).[4] Additionally, the reaction of [Cp2Ti(h2-
Me3SiC2SiMe3)] with the carbodiimide CyN=C=NCy (DCC)
formed a dimetallic complex, with coordination of the metal
fragments to the two nitrogen atoms and to the central
carbon atom of the substrate (D).[5]
[a] L. Becker, Dr. V. V. Burlakov, Dr. P. Arndt, Dr. A. Spannenberg,
Dr. W. Baumann, Dr. H. Jiao, Prof. Dr. U. Rosenthal
Leibniz-Institut fꢀr Katalyse e.V. an der Universitꢁt Rostock
Albert-Einstein-Straße 29a, 18059 Rostock (Germany)
Fax : (+49)381-1281-51176
E-mail: uwe.rosenthal@catalysis.de
[b] Dr. V. V. Burlakov
A. N. Nesmeyanov Institute of Organoelement Compounds
Russian Academy of Sciences
Vavilov St. 28, 119991, Moscow (Russia)
In the reaction of [Cp2Zr(py)(h2-Me3SiC2SiMe3)] (py=
pyridine) with the same carbodiimide, the five-membered
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201204211.
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FULL PAPER
heterometallacycloallene complex [Cp2Zr(Me3SiC=C=C{N-
(SiMe3)(Cy)}N(Cy))] was obtained.[6] In a very recent study
ACHTUNGTRENNUNG
of the coordination chemistry of the bis(diphenylphosphi-
no)amide ligand [Ph2P-N-PPh2] in Group 4 metallocenes,
the highly strained four-membered heterometallacycles
[Cp2M(k2-P,P-Ph2PNPPh2)] (M=Ti, Zr; F) were formed.[7]
Due to these results, we were interested in the reactions
of Group 4 metallocenes with nitriles. These substrates are
known for insertion reactions in Group 4 organometallic
chemistry.[8] In the presence of an acidic a-proton, a depro-
tonation of the nitrile and the formation of keteniminate
species can take place.[9] Notably, the total deprotonation of
monophenylacetonitrile (PhCH2CN) or the complexation of
diphenylacetonitrile (Ph2CHCN) can occur to give as yet un-
known four-membered metallacycles that contain only one
nitrogen atom, for example, [Cp’2M(k2-N,C-N=CHCPh2)]
(G) or [Cp’2M(k2-N,C-N=C=CPh)] (H). Xi and co-workers
investigated the reactions of diphenylacetonitrile with zir-
Scheme 2. Reaction of complex 1 with Ph2CHCN.
ACHTUNGTRENNUNGconACHTUNGTRENNUNGocene complexes to obtain five-membered heterometal-
lacycles by alkyne nitrile coupling. This involved deprotona-
tion of a second nitrile and its conversion to a keteniminate
ligand due to the need to stabilise the formed azazirconacy-
clopentadiene intermediate.[10] Other examples of isolated
products of alkyne nitrile coupling at Group 4 metallocene
complexes are also stabilised by, for example, transfer of H,
but they are few in number.[11]
Herein, we describe reactions of different alkyne com-
plexes [Cp’2M(h2-Me3SiC2SiMe3)] 1 (M=Zr, Cp’=Cp*=h5-
pentamethylcyclopentadienyl); 2a (M=Ti, Cp’=Cp*) and
2b (M=Ti, Cp’2 =rac-(ebthi)=rac-1,2-ethylene-1,1’-bis(h5-
tetrahydroindenyl)) with diphenylacetonitrile and of the
seven-membered zirconacyclocumulene 3 with PhCH2CN.
Unfortunately, we could not obtain the predicted and very
attractive four-membered metallacycles [Cp’2M(k2-N,C-N=
CHCPh2)] (G) and [Cp’2M(k2-N,C-N=C=CPh)] (H).
Figure 1. Molecular structure of 4 with thermal ellipsoids set at the 30%
probability level. All hydrogen atoms (except H10) have been omitted
À
for clarity. Selected bond lengths [ꢃ] and angles [8]: Zr1 N1 2.309(1),
À
À
À
C1 C2 1.312(2), N1 C9 1.147(2), C9 C10 1.479(2); N1-C9-C10 175.0(2).
Results and Discussion
Treatment of a solution of [Cp*2Zr(h2-Me3SiC2SiMe3)] (1)[12]
in toluene with one equivalent of diphenylacetonitrile at
ambient temperature led to complex 4, which could be iso-
lated as yellow crystals in 77% yield (Scheme 2).
À
1.312(2) ꢃ) of the alkyne. The C N bond lengths in 4 and in
À
the uncomplexed diphenylacetonitrile are the same (4: N1
[9b]
À
C9 1.147(2) ꢃ, Ph2CHCN: N1 C9 1.147(2) ꢃ). The struc-
tural motif is also known for a zirconacyclopropene com-
plex, stabilised by N C tBu, (C Calkyne 1.322(8) ꢃ, C N
In addition to the signals of the Cp* ligand, 1H and
13C NMR spectra of 4 revealed characteristic resonances of
ꢀ À
À
À
13
the alkyne (1H: d=0.49 ppm, C: d=232.7 ppm (C C)) and
1.150(9) ꢃ).[8b]
ꢀ
the coordinated nitrile (1H: d=5.02 ppm (CH), 13C: d=
The reaction of 1 with two equivalents of Ph2CHCN at
858C gives, after elimination of the alkyne and a hydrogen
transfer, red crystals of complex 5 (yield 85%) with a ke
ACHTUNGTRENiNUGN minate and an imine ligand (Scheme 2). The diphenylaceto-
nitrile acts as a protonation agent due to its acidic a-proton
and also as a proton acceptor. The resonances of the two
different protons of the imine ligand appear in the H NMR
spectra at d=4.70 (CHPh2) and 9.12 ppm (CH=N). The
strong shift of the second signal is caused by the neighbour-
ing nitrogen. The signal of the Cp* ligand is shifted upfield
(d=1.65 ppm) in comparison with the corresponding com-
ꢀ
117.8 ppm (C N)). These values are in the same range as
those observed for the corresponding zirconocene com-
ACHTUNGTRENNUNGten-
[12]
plexes (1: 13C: d=260.5 (C C),
[Cp2Zr(py)(h2-
ꢀ
Me3SiC2SiMe3)]: C: d=220.5 ppm (C C)[13]). The typical
13
ꢀ
À
IR resonance of the C N triple bond is shifted from 2240 to
2214 cmÀ1. This slight change reveals the coordination as an
h1-ligand. The molecular structure of 4 (Figure 1) consists of
a zirconocene with a coordinated alkyne and nitrile. In com-
1
À
parison with starting complex 1, it shows a very similar C
À
À
Calkyne bond length (1: C1 C2 1.320(3), 4: C1 C2
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4231

U. Rosenthal et al.
plexes (d=1.76[12] (1) and 1.75 ppm (4)). Furthermore, com-
plex 5 was characterised by IR spectroscopy. The strong in-
frared band at 2048 cmÀ1 was assigned to the N=C=C
stretching mode, as observed for lithium[9b] and barium kete-
niminate complexes.[9c] In contrast to 4, this is a shift of
nearly 200 cmÀ1 in comparison to diphenylacetonitrile
In regard to a possible formation pathway, we considered
complex 4 to be an intermediate of the reaction from 1 to 5.
This was corroborated by heating the solution of 4 in
1
[D8]toluene to 858C. The H NMR spectra of the solution
were recorded before heating and after 19 h at 858C. After
heating, the signals of complex 4 (d=0.32 (SiMe3), 1.69
(C5Me5), 4.86 ppm (CHnitrile)) disappeared. This implies that
two molecules of 4 were converted into one molecule of 5
(d=1.59 (C5Me5), 4.56 (CbH), 9.03 ppm (CaH)), one mole-
cule of 1 (d=0.11 (SiMe3), 1.71 ppm (C5Me5)) and one free
Me3SiC2SiMe3 molecule (d=0.09 ppm (SiMe3)).
(2240 cmÀ1 (N C)). This illustrates the conversion of the
ꢀ
À
triple bond to a C N double bond.
Complex 5 was characterised by using X-ray diffraction
(Figure 2), which revealed it as a zirconocene with a keten-
ACHTUNGTRENNUNGimACHTUNGTRENNUNGinate and an imine ligand. The bonding situation of the
À
À
keteniminate unit (N2 C15 1.170(3), C15 C16 1.366(4) ꢃ)
corresponds to that of the already described [Cp2Zr(C-
The reaction of the analogous titanocene alkyne complex
[Cp*2Ti(h2-Me3SiC2SiMe3)] (2a)[20] with diphenylacetonitrile
in toluene was completed after 4 d at 808C and gave the bis-
keteniminate complex 6 (Scheme 3). Its molecular ion peak
in the mass spectrum can be found at m/z 702. The IR reso-
nances of the N=C=C bonds are located at 2060 and
À
(SiMe3)=C(Me)C
(CHPh2)=NH)
(N=C=CPh2)] complex (N
Scheme 3. Reaction of titanocene complexes 2a and 2b with Ph2CHCN.
2025 cmÀ1 and are thus in the same region as for complex 5.
Figure 2. Molecular structure of 5 with thermal ellipsoids set at the 30%
probability level. All hydrogen atoms (except H1 and H2) and the
second molecule of the asymmetric unit have been omitted for clarity. Se-
lected bond lengths [ꢃ] and angles [8], corresponding values of the
second molecule in the asymmetric unit are given in square brackets:
A decisive characterisation of complex 6 by NMR spec
ACHTUNGTRENNUNGtros-
AHCTUNGTREGcNNUN opy was not possible due to the formation of mixtures in
solution. The molecular structure of 6 was confirmed by
using X-ray analysis and is depicted in Figure 3. It shows
À
À
À
À
Zr1 N1 2.036(2) [Zr2 N3 2.026(2)], Zr1 N2 2.177(2) [Zr2 N4 2.184(2)],
À
À
two keteniminate units (N1 C1 1.179(3), C1 C2 1.360(3) ꢃ)
bonded to titanocene. The bond lengths and angles of these
ligands are comparable to those of the keteniminate moiety
in complex 5 and to similar complexes of zirconium,[10] irid-
À
À
À
À
N1 C1 1.232(3) [N3 C49 1.243(3)], N2 C15 1.170(3) [N4 C63 1.169(3)],
À
À
À
À
C1 C2 1.521(4) [C49 C50 1.526(3)], C15 C16 1.366(4) [C63 C64
1.367(4)]; N1-C1-C2 125.5(3) [N3-C49-C50 123.1(3)], N2-C15-C16
176.7(3) [N4-C63-C64 178.9(3)], Zr1-N1-C1 164.6(2) [Zr2-N3-C49
171.6(2)].
AHCTUNGTRENNUNG
ium,[9a] indium,[9b] gallium,[9b] lithium,[9b,d] barium,[9c] magne-
sium[9c,g] and strontium.[9c]
[10]
À
C 1.159(5), C C 1.386(6) ꢃ).
The N2-C15-C16 angle
Changing the cyclopentadienyl ligand from Cp* to rac-
(ebthi) provokes a different kind of reaction. Whereas the
nitriles were deprotonated and converted to keteniminate
species in the reaction with 2a, a coupling occurred when
(176.7(3)8) confirms the almost linear nature. In contrast,
À
the second ligand in 5 is an imine species (N1 C1 1.232(3),
À
C1 C2 1.521(4) ꢃ; N1-C1-C2 125.5(3), C1-C2-C3 114.2(2),
C1-C2-C9 109.7(2), Zr1-N1-C1 164.6(2)8), which is compara-
(ebthi))(h2-Me3SiC2SiMe3] (2b)[21] was applied. This
[TiACTHNGUTRENNU(G rac-ACHTGNUTRENNUNG
ble with the molecular structure of the known zirconocene
was accompanied by a formal reduction of the metal from
TiIV to TiIII, and the unusual paramagnetic four-membered
titanaheterocycle 7 is formed (Scheme 3). It is supposed that
the origin of the additional hydrogen atom is either the sol-
vent or a deprotonation of Ph2CHCN.
complex [Cp2ClZr
170.5(5)8). A titanocene complex with such an imine ligand
(N=CHPh)][14] (N C 1.259(7) ꢃ; Zr-N-C
À
[15]
À
À
was also described (N C 1.258(6), C C 1.487(6) ꢃ). Sev-
eral examples with similar imine ligands are known in the
literature for elements such as niobium,[16] aluminium,[17]
iron[18] and samarium.[19]
Complex 7 was characterised by using mass spectrometry;
its molecular ion peak can be found at m/z 699. The typical
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Unusual Four- and Six-Membered Metallacycles
FULL PAPER
Figure 3. Molecular structure of 6 with thermal ellipsoids set at the 30%
probability level. All hydrogen atoms and the second molecule of the
asymmetric unit have been omitted for clarity. Selected bond lengths [ꢃ]
and angles [8], corresponding values of the second molecule in the asym-
Figure 4. Molecular structure of 7 with thermal ellipsoids set at the 30%
probability level. All hydrogen atoms (except H1, H2 and H15) and the
solvent molecule (n-hexane) have been omitted for clarity. Selected bond
À
À
metric unit are given in square brackets: Ti1 N1 1.996(2) [Ti2 N2
À
À
À
À
2.002(2)], N1 C1 1.179(3) [N2 C25 1.177(3)], C1 C2 1.360(3) [C25 C26
1.359(3)]; N1-C1-C2 175.6(3) [N2-C25-C26 176.5(2)].
À
À
À
lengths [ꢃ] and angles [8]: Ti1 N1 2.148(1), Ti1 N2 2.254(1), N1 C1
À
À
À
1.311(1), N2 C1 1.345(1), N2 C15 1.388(1), C1 C2 1.533(2); C1-N1-Ti1
96.32(7), C1-N2-Ti1 90.56(6), N1-Ti1-N2 60.27(3), N1-C1-N2 112.74(10),
N1-C1-C2 124.42(10), N2-C1-C2 122.83(9).
À
IR resonances of the C N bonds at 1489, 1502 and
1592 cmÀ1 are comparable to those of analogue four-mem-
bered metallacycles of other metals.[22,23] The molecular
structure of 7 is depicted in Figure 4. Similar complexes with
metals such as samarium,[22] molybdenum,[23] yttrium[24] or
aluminium[25] were obtained in reactions of metal complexes
of the appropriate elements with carbodiimides. Analogue
four-membered paramagnetic titanaheterocycles were pre-
sumed to be intermediates in the reactions of [Cp2Ti(h2-
Me3SiC2SiMe3)] with carbodiimides. These need to be stabi-
lised by complexation, dimerisation or substitution of the
carbon atom in the ring system.[26] Compound 7 is compara-
ble to the complexes of titanium and zirconium with guani-
dinate ligands, which consist of substituents at the ring
carbon atom as well.[27] The coupling product of two nitriles
with an yttrium complex was published very recently.[28]
The difference between complex 7 and the known struc-
tures, except the yttrium complex,[28] is the substitution of
the nitrogen atoms. N1 carries a hydrogen atom, whereas an
organic residue is found at N2. Therefore, the bond lengths
angles of N1-C1-C2 (124.42(10)8), N2-C1-C2 (122.83(9)8)
and N1-C1-N2 (112.74(10)8) illustrate the sp2 hybridisation
of carbon atom C1.
Additionally, coupling of two nitriles is observed in the re-
action of seven-membered zirconacyclocumulene 3[29] with
two equivalents of phenylacetonitrile. It is presumed that
one butadiyne molecule is eliminated and a five-membered
zirconacyclocumulene is formed as an intermediate in the
first step of the reaction. Consequently, four- and five-mem-
bered cycles are obtained by coupling of one nitrile with the
diyne in addition to insertion of PhCH2CN. The coupling of
the nitriles leads to a six-membered zirconaheterocycle 8
(Scheme 4), in contrast to complex 7. Similar reactions of
the alkyne complexes [Cp2M(h2-Me3SiC2SiMe3)] (M=Ti,
Zr) with phenylacetonitrile and with diphenylacetonitrile
produced complex mixtures that have not been separated
yet.
À
À
and angles in the ring system differ (Ti1 N1 2.148(1), Ti1
À
N2 2.254(1), N1 C1 1.311(1),
À
N2 C1 1.345(1) ꢃ; C1-N1-Ti1
96.32(7), C1-N2-Ti1 90.56(6)8).
This structural feature can also
be found in the yttrium com-
pound
NC(Ph)=CHPh)ACHTUNGTRENNUNG
N1 2.371(3), Y1 N2 2.430(3),
[CpY
ACHTUNGTRENNUNG(N(H)CAHTUNGTRENNCUGN (Ph)-
(TpMe )] (Y1
2
À
À
À
À
N1 C1
1.312(5),
N2 C1
1.332(5) ꢃ; C1-N1-Y1 96.4(2),
C1-N2-Y1 93.2(2)8).[28] The ti-
ACHTUNGTRENNUNGtanACHTUNGTRENNUNGaACHTUNGTRENNUNGcycle reveals two relatively
À
À
short N C bonds (see N1 C1,
À
N2 C1 above), which indicates
À
a
partial N C double-bond
character.[5] Additionally, the Scheme 4. Reaction of seven-membered zirconacyclocumulene 3 with PhCH2CN.
Chem. Eur. J. 2013, 19, 4230 – 4237
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4233

U. Rosenthal et al.
À
The assumed reaction steps to form 8 from 3 are accom-
panied by shifts of the acidic a-protons of one of the nitriles.
These protons show resonances in the H NMR spectra at
the zirconacyclocumulene. As a result, a new C4 C5 bond
(1.507(3) ꢃ) is created. Such insertion reactions have al-
ready been established in zirconium-mediated multi-compo-
nent reactions of butadiynes with nitriles[8] or carbamoyl cy-
anides.[30] The subsequent coupling of N1 and C2 leads to
the formation of the five-membered cycle in 8. In this ring
1
d=5.10 and 6.99 ppm. The first signal is assigned to the
proton at the nitrogen atom and the second proton is locat-
ed at the former cumulene in the five-membered cycle. Fur-
1
À
thermore, the H NMR spectra shows two different signals
system, the C3 C4 bond (1.368(3) ꢃ) corresponds to a
for the SiMe3 groups (d=À0.09, 0.43 ppm) and the reso-
double bond. Due to the planarity of the six-membered zir-
conacycle, it could be considered as an aromatic system;
theoretical calculations should lead to a better understand-
ing.
Due to the interaction of the metal centre and the unsatu-
rated carbon atoms on the metallacycle, metallacyclopro-
penes,[31] 1-metallacyclopent-3-ynes and 1-metallacyclopen-
ta-2,3,4-trienes[32] have been characterised as aromatic on
nance of the Cp at d=5.72 ppm.
Single crystals of 8 for X-ray analysis were obtained from
a solution in C6D6. The molecular structure, depicted in
Figure 5, shows three different cycles. The four-membered
À
the basis of their geometric, (equalised C C lengths), ener-
getic (extra stabilisation energy) and magnetic (negative nu-
cleus-independent chemical shifts (NICS) and downfield
chemical shifts[33]) properties. The aromatic stabilisation is
the governing factor for the stability of these low-membered
metallacycles. To understand the possible aromatic nature of
complex 8, we calculated the NICS values for the four-
(Zr1-N1-C2-C1), five- (N1-C2-C3-C4-C5) and six- (Zr1-N2-
C7-C6-C5-N1) membered rings at 1 ꢃ over the ring centres.
As given in the Supporting Information, the computed
structural parameters are in very good agreement with the
data from X-ray analysis. The NICS(1) value is d=
À0.89 ppm for the six-membered ring, d=À4.97 ppm for the
five-membered ring and d=À1.39 ppm for the four-mem-
bered ring. The small NICS difference for six- and five-
membered rings (d=À4.97 vs. À1.39 ppm) is in agreement
Figure 5. Molecular structure of 8 with thermal ellipsoids set at the 30%
probability level. All hydrogen atoms (except H2 and H3) have been
1
with the difference in the observed H NMR signals of H-
À
omitted for clarity. Selected bond lengths [ꢃ] and angles [8]: Zr1 N1
C3 (d=6.99 ppm) and H-N2 (d=5.10 ppm). However, these
rather small NICS values reveal the non-aromatic character
of complex 8.
À
À
À
À
2.162(2), Zr1 N2 2.282(2), C1 C2 1.360(3), N1 C2 1.392(3), N1 C5
À
À
À
À
1.327(3), N2 C7 1.331(3), C3 C4 1.368(3), C4 C5 1.507(3), C5 C6
À
1.412(3), C6 C7 1.412(3); C2-C1-Zr1 89.76(15), C2-N1-Zr1 98.71(14),
C5-N1-Zr1 149.27(17), C7-N2-Zr1 138.59(17), C5-C6-C7 119.0(2), C5-C6-
C15 122.5(2), C7-C6-C15 118.6(2).
Conclusion
À
metallacycle was formed by a formal N C coupling of one
Herein, we present a detailed experimental study of the re-
action of phenylated nitriles with Group 4 metallocene
alkyne complexes and a zirconacyclocumulene. Different
compounds were obtained depending on the metal, the cy-
clopentadienyl ligand and the reaction temperature. The re-
actions of pentamethylcyclopentadienyl-substituted com-
plexes 1 and 2a with diphenylacetonitrile led to the forma-
tion of 4, 5 and 6, which contain the nitrile coordinated as
an h1-ligand, as either a keteniminate or an imine ligand.
Replacement of the Cp ligand with rac-(ebthi) in 2b result-
ed in a coupling of two nitriles and the four-membered met-
allacycle 7 is obtained. This ring system is stabilised by the
substitution of the ring carbon atom. Another coupling of
two nitriles was observed in the reaction of 3 with phenyl-
À
nitrile and the diyne. The bond lengths of C1 C2
À
(1.360(3) ꢃ) and C2 N1 (1.392(3) ꢃ) correspond to
double bond and to a single bond, respectively. The Zr N
bond (Zr1 N1 2.162(2) ꢃ) is also assigned to a single bond.
In contrast, the bond between Zr and N2 is somewhat
a
À
À
À
longer (Zr1 N2 2.282(2) ꢃ), which is caused by the differ-
ent substitution of the nitrogen atoms.
À
The N C bond lengths of the planar six-membered zir-
acycle, which is formed by coupling of the nitriles, are
equal (N1 C5 1.327(3), N2 C7 1.331(3) ꢃ). The same was
observed for the C C linkages (C5 C6 1.412(3), C6 C7
1.412(3) ꢃ). This fact implies two possible resonance forms
of 8 (Scheme 4). The angles of C5-C6-C7 (119.0(2)8), C5-
C6-C15 (122.5(2)8) and C7-C6-C15 (118.6(2)8) highlight the
proposed sp2 hybridisation of the carbon atom C6.
con
U
À
À
À
À
À
AHCTUNGTREGaNNNU cetonitrile to form 8. This was accompanied by the forma-
tion of a four-membered metallacycle by coupling of the bu-
tadiyne and the nitrile. These results clearly show the differ-
ent functions of nitriles in organometallic chemistry. Nitriles
It is presumed that the first step in the formation of com-
plex 8 is an insertion of one nitrile into the M C bond of
À
4234
www.chemeurj.org
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 4230 – 4237

Unusual Four- and Six-Membered Metallacycles
FULL PAPER
150(2) K; space group P2/c; Z=4; 74831 reflections measured, 8396 in-
can behave as a coordination agent in complex 4. Due to
the acidic a-proton, nitriles act as protonation agents and
also as proton acceptors, which promote the formation of
compounds 5–8. It is supposed that this behaviour influences
the coupling reactions that lead to 7 and 8. Studies on the
reaction behaviour of the established complexes and of the
reactions with differently substituted nitriles are still on-
going and will be published in due course.
dependent reflections (Rint =0.0584), final
R values (I>2s(I)): R1 =
0.0504, wR2 =0.1188, final R values (all data): R1 =0.0757, wR2 =0.1318,
447 parameters.
Crystal data for 7: C51H54N2Ti; Mr =742.86; triclinic; a=12.0263(3), b=
12.5669(3), c=15.3150(3) ꢃ; a=70.552(1), b=69.230(1), g=89.308(1)8;
3
¯
V=2025.90(8) ꢃ ; T=150(2) K; space group P1; Z=2; 98562 reflections
measured, 10466 independent reflections (Rint =0.0387), final R values
(I>2s(I)): R1 =0.0334, wR2 =0.0836, final
0.0417, wR2 =0.0892, 492 parameters.
R values (all data): R1 =
Crystal data for 8: C36H42N2Si2Zr; Mr =650.12; monoclinic; a=
15.3032(4), b=10.3810(3), c=20.4205(6) ꢃ; b=92.446(2)8; V=
3241.10(16) ꢃ3; T=150(2) K; space group P21/n; Z=4; 81921 reflections
measured, 7450 independent reflections (Rint =0.0523), final R values (I>
2s(I)): R1 =0.0375, wR2 =0.0883, final R values (all data): R1 =0.0501,
wR2 =0.0951, 340 parameters.
Experimental Section
General information: All manipulations were carried out under an
oxygen- and moisture-free argon atmosphere by using standard Schlenk
and dry-box techniques. Non-halogenated solvents were dried over
sodium/benzophenone and freshly distilled prior to use. Diphenylacetoni-
trile is commercially available and was dried in vacuum prior to use. Met-
allocene complexes 1,[12] 2,[20] 2b[21] and 3[29] were synthesised as described
previously in the literature. NMR spectra were recorded by using Bruker
AV300 and AV400 spectrometers. 1H and 13C chemical shifts were refer-
enced to the solvent signals of [D6]benzene (dH =7.16 ppm, dC =
128.0 ppm) and [D8]toluene (dH =2.03 ppm, dC =20.4 ppm). 29Si chemical
shifts are given relative to SiMe4, 15N chemical shifts are relative to nitro-
methane (X=10.136767 MHz). Detailed NMR data of 4, 5 and 8 are
given in Supporting Information. IR spectra were recorded by using a
Nicolet 6700 FT-IR spectrometer equipped with a smart endurance atte-
nuated total reflection (ATR) device and a Bruker Alpha FT-IR spec-
trometer. MS data were recorded by using a Finnigan MAT 95-XP instru-
ment (Thermo-Electron). Elemental analyses were recorded by using a
Leco Tru Spec elemental analyser. Melting points were recorded by using
an E/Z-Melt instrument (Stanford Research Systems). Melting points are
uncorrected and were measured in sealed capillaries.
CCDC-907143 (4), CCDC-907146 (5), CCDC-907144 (6), CCDC-907145
(7) and CCDC-907147 (8) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Preparation of complex 4: A solution of Ph2CHCN (0.193 g, 1.00 mmol)
in toluene (10 mL) was added with stirring to a solution of 1 (0.530 g,
1.00 mmol) in toluene (5 mL). The orange solution was stirred 4 h at
room temperature. The solvent was removed under vacuum and the resi-
due washed with cold n-hexane. The resulting yellow crystals were dried
under vacuum (yield: 0.556 g, 0.77 mmol, 77%). M.p: 1128C (decomp.)
under Ar; 1H NMR (300 MHz, [D6]benzene, 297 K): d=0.49 (s, 18H,
SiMe3), 1.77 (s, 30H, C5Me5), 5.02 (s, 1H, CHnitrile), 6.98 (m, 2H, CHPh),
7.04 (m, 4H, CHPh), 7.17 ppm (m, 4H, CHPh); 13C NMR (75 MHz,
[D6]benzene, 297 K): d=4.8 (SiMe3), 12.3 (C5Me5), 44.9 (CHnitrile), 113.9
ꢀ
(C5Me5), 117.8 (C N), 128.5, 128.7, 129.3 (CH-Ph), 135.5 (i-C-Ph),
232.7 ppm (CꢀC); IR (ATR): n˜ =2894 (w), 2214 (vw), 1491 (w), 1239
(m), 825 (vs), 738(s), 696 (vs), 650 (m), 624 (m), 542 (m), 459 cmÀ1 (m);
MS (CI): m/z (%): 532 (12) [M-NCCHPh2]+, 360 (100) [Cp*2Zr]+, 194
(30) [Ph2CHCN+H]+; elemental analysis calcd (%) for C42H59NSi2Zr: C
69.55, H 8.20, N 1.93; found: C 69.64, H 8.07, N 1.83.
Computational details: Structure optimisation (8) has been carried out at
the BP86[34] density functional level of theory with the TZVP basis set[35]
for C, H, N, Si and the LANL2DZ basis set with the effective core poten-
tials of Hay and Wadt for Zr[36] by using Gaussian 09 program package.[37]
The optimized geometries are characterised as energy minima at the po-
tential-energy surface from frequency calculations at the same level of
theory (BP86/TZVP), that is, the energy minimum structure has only real
frequencies, whereas transition-state structures have only one imaginary
frequency. To judge the extent of cyclic delocalisation of electrons in
complex 8, nucleus-independent chemical shifts (NICS) were calculated
at the geometrical centre point of the ring. This gives an insight into the
possible interaction between the Zr centre and the unsaturated carbon
atoms in the metallacycle (see the Supporting Information).
Preparation of complex 5: To a stirred solution of 1 (0.530 g, 1.00 mmol)
in toluene (5 mL) was added
a solution of Ph2CHCN (0.385 g,
2.00 mmol) in toluene (10 mL). The solution was stirred for 2 h at room
temperature and subsequently for 4 h at 858C; the colour of the solution
turned deep red. All volatiles were removed under vacuum and the resi-
due was dissolved in n-hexane. After filtration, the solution was allowed
to stand at room temperature. Red crystals of 5 formed within 3 d (yield:
0.633 g, 0.85 mmol 85%). M.p: 1658C (decomp.) under Ar; 1H NMR
(300 MHz, [D6]benzene, 297 K): d=1.65 (s, 30H, C5Me5), 4.70 (d, 3J=
7.3 Hz, 1H, CbH), 7.02 (m, 8H, CHPh), 7.39 (m, 8H, CHPh), 7.80 (m, 4H,
CHPh), 9.12 ppm (d, 3J=7.3 Hz, 1H, CaH); 13C NMR (75 MHz,
[D6]benzene, 297 K): d=11.3 (C5Me5), 55.9 (N=C=CPh2), 62.7 (N=
CHCHPh2), 118.4 (C5Me5), 141.9, 142.4 (i-CPh), 160.4 (N=C=CPh2), 165.0
(N=CHCHPh2), 121.2, 125.9, 127.0, 128.6, 128.8, 129.1 ppm (CHPh); IR
(ATR): n˜ =2902 (w), 2048 (s), 1675 (w), 1588 (m), 1486 (m), 693 cmÀ1
(vs); MS (EI): m/z (%): 746 (73) [M]+, 554 (69) [M-NC2Ph2]+, 552 (18)
[M-NCHCHPh2]+.
Crystallographic data: Diffraction data for 4, 5, 6, 7 and 8 were collected
by using a Bruker Kappa APEX II Duo diffractometer with graphite-
monochromated MoKa radiation. The structures were solved by using
direct methods and refined by full-matrix least-squares procedures on F2
with the SHELXTL software package.[38] Diamond was used for graphi-
cal representations.[39]
1H NMR investigation of the conversion of complex 4 to 5: Complex 4
was dissolved in [D8]toluene in
(300 MHz, [D8]toluene, 297 K): d=0.32 (SiMe3), 1.69 (C5Me5), 4.86 ppm
(CHnitrile). Subsequently it was warmed to 858C for 19 h, 1H NMR
(300 MHz, [D8]toluene, 297 K): d=0.11 (SiMe3 freealkyne), 1.71 (C5Me5, 1),
1.59 (C5Me5, 5), 9.04 ppm (CaH, 5). For the spectra, see the Supporting
Information.
Crystal data for 4: C42H59NSi2Zr; Mr =725.30; monoclinic; a=14.4529(2),
b=16.2004(2), c=17.1335(3) ꢃ; b=96.943(1)8; V=3982.27(10) ꢃ3; T=
150(2) K; space group P21/c; Z=4; 99901 reflections measured, 8782 in-
a
Young tube. Initially, 1H NMR
dependent reflections (Rint =0.0362), final
R values (I>2s(I)): R1 =
0.0271, wR2 =0.0656, final R values (all data): R1 =0.0353, wR2 =0.0709,
431 parameters.
Crystal data for 5: C48H52N2Zr; Mr =748.14; triclinic; a=14.9276(3), b=
17.4124(4), c=18.0249(5) ꢃ; a=65.159(1), b=68.119(1), g=89.989(1)8;
V=3876.74(16) ꢃ ; T=150(2) K; space group P1; Z=4; 72384 reflec-
tions measured, 18482 independent reflections (Rint =0.0512), final R
values (I>2s(I)): R1 =0.0418, wR2 =0.0973, final R values (all data): R1 =
0.0720, wR2 =0.1075, 903 parameters.
Preparation of complex 6: Ph2CHCN (0.387 g, 2.00 mmol) was dissolved
in toluene (10 mL) and subsequently added with stirring to a solution of
complex 2a (0.490 g, 1.00 mmol) in toluene (5 mL). The solution was stir-
red at 808C for 4 days and the colour turned from green to brown. All
volatiles were removed from the brown solution under vacuum, followed
by addition of n-hexane to the oily residue. The solution was filtered,
concentrated and allowed to stand at room temperature. Brown crystals
3
¯
Crystal data for 6: C48H50N2Ti; Mr =702.80; monoclinic; a=17.9736(4),
b=11.3581(2), c=19.2637(4) ꢃ; b=95.665(1)8; V=3913.40(14) ꢃ3; T=
Chem. Eur. J. 2013, 19, 4230 – 4237
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4235

U. Rosenthal et al.
started to form within 30 min. The crystals were separated from the
mother liquor by decanting, washed with cold n-hexane and dried under
vacuum to give complex 6 (yield: 0.177 g, 0.252 mmol, 25%). M.p: 219–
2218C (decomp.) under Ar; IR (ATR): n˜ =2921 (w), 2845 (w), 1502 (s),
1489 (s), 1259 (m), 761 (m), 698 (vs), 644 (s), 554 (m), 468 cmÀ1 (m); MS
(EI): m/z (%): 702 (8) [M]+, 510 (2) [M-NC2Ph2]+, 318 (4) [Cp*2Ti]+,
388 (6) [2ꢄNCCHPh2]+, 312 (39) [ebthi-Ti]+; elemental analysis calcd
(%) for C48H50N2Ti: C 82.03, H 7.17, N 3.99; found: C 82.11, H 7.11, N
3.99.
10816; f) J. Ugolotti, G. Kehr, R. Frçhlich, S. Grimme, G. Erker, J.
Am. Chem. Soc. 2009, 131, 1996–2007; g) N. Suzuki, T. Shimura, Y.
Sakaguchi, Y. Masuyama, Pure Appl. Chem. 2011, 83, 1781–1788.
[2] S. Roy, E. D. Jemmis, A. Schulz, T. Beweries, U. Rosenthal, Angew.
Chem. 2012, 124, 5442–5446; Angew. Chem. Int. Ed. 2012, 51, 5347–
5350.
[3] M. Lamac, A. Spannenberg, H. Jiao, S. Hansen, W. Baumann, P.
Arndt, U. Rosenthal, Angew. Chem. 2010, 122, 2999–3002; Angew.
Chem. Int. Ed. 2010, 49, 2937–2940.
[4] K. Kaleta, M. Ruhmann, O. Theilmann, S. Roy, T. Beweries, P.
Arndt, A. Villinger, E. D. Jemmis, A. Schulz, U. Rosenthal, Eur. J.
Inorg. Chem. 2012, 611–617.
[5] O. Theilmann, M. Ruhmann, A. Villinger, A. Schulz, W. W. Seidel,
K. Kaleta, T. Beweries, P. Arndt, U. Rosenthal, Angew. Chem. 2010,
122, 9469–9473; Angew. Chem. Int. Ed. 2010, 49, 9282–9285.
[6] K. Kaleta, M. Ruhmann, O. Theilmann, T. Beweries, S. Roy, P.
Arndt, A. Villinger, E. D. Jemmis, A. Schulz, U. Rosenthal, J. Am.
Chem. Soc. 2011, 133, 5463–5473.
Preparation of complex 7: To
1.00 mmol) in toluene (5 mL) was added
a
stirred solution of 2b (0.483 g,
solution of Ph2CHCN
a
(0.387 g, 2.00 mmol) in toluene (10 mL). The solution was stirred for 7 d
at 858C. The solvent was removed under vacuum and the dark residue
dissolved in n-hexane and filtered. After 1 h green crystals had formed,
which were separated by decanting, washed with cold n-hexane and dried
under vacuum to give complex 7 (0.423 g). Concentration of the mother
liquor resulted in an additional amount of 7 (0.082 g) to give the total
yield of compound
7 (0.505 g, 0.72 mmol, 72%). M.p: 124–1278C
[7] M. Haehnel, S. Hansen, A. Spannenberg, P. Arndt, T. Beweries, U.
Rosenthal, Chem. Eur. J. 2012, 18, 10546–10553.
(decomp.) under Ar; IR (ATR): n˜ =2921 (w), 2845 (w), 1592 (w), 1502
(s), 1489 (s), 1259 (m), 761 (m), 698 (vs), 644 (s), 554 (m), 468 cmÀ1 (m);
MS (EI): m/z (%): 699 (63) [M]+, 506 (3) [M-NCCHPh2]+, 388 (6) [2ꢄ
NCCHPh2]+, 312 (39) [ebthi-Ti]+; elemental analysis calcd (%) for
C48H47N2Ti: C 82.40, H 7.06, N 3.85; found: C 82.52, H 6.97, N 3.74.
[8] Selected recent examples: a) S. Zhang, W.-X. Zhang, Z. Xi, Chem.
Eur. J. 2010, 16, 8419–8426; b) S. Zhang, W.-X. Zhang, J. Zhao, Z.
Xi, J. Am. Chem. Soc. 2010, 132, 14042–14045; c) S. Zhang, J. Zhao,
W.-X. Zhang, Z. Xi, Org. Lett. 2011, 13, 1626–1629; d) S. Zhang,
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e) W.-X. Zhang, S. Zhang, Z. Xi, Acc. Chem. Res. 2011, 44, 541–
551.
[9] For examples of the deprotonation process of Ph2CHCN, see:
a) D. M. Tellers, J. C. M. Ritter, R. G. Bergman, Inorg. Chem. 1999,
38, 4810–4818; b) E. Iravani, B. Neumueller, Organometallics 2003,
22, 4129–4135; c) I. L. Fedushkin, A. G. Morozov, O. V. Rassadin,
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P. B. Hitchcock, M. F. Lappert, A. V. Protchenko, Chem. Commun.
Preparation of complex 8: Complex 3 (1.156 g, 1.89 mmol) was dissolved
in toluene (15 mL) and PhCH2CN (0.55 mL, 4.76 mmol) was added to
the obtained solution. The yellow-orange solution was warmed at 1008C
for 24 h, then the resulting red-brown solution was evaporated to dryness.
The residue was extracted with warm n-hexane (20 mL, 608C). The dark-
red solution was filtered and allowed to stand at À788C. After 1 day, the
dark red crystals were separated from the mother liquor, washed with n-
hexane and dried in vacuum to give complex 8 (yield: 0.298 g, 24.2%).
1
M.p: 233–2348C under Ar; H NMR (300/400 MHz, [D6]benzene, 297 K):
d=À0.09, 0.43 (2ꢄs, 2ꢄ9H, SiMe3), 3.33 (s, 2H, CH2), 5.10 (s, 1H,
N2H), 5.72 (s, 10H, Cp), 6.97 (m, 2H, o-CHBn), 6.99 (s, 1H, C3H), 7.06
(m, 1H, p-CHBn), 7.14 ppm (m, 2H, m-CHBn); 13C NMR (75 MHz,
[D6]benzene, 297 K): d=0.7 (1J
U
ACHTUNGTRNE(NUNG C,H)=
ˇ
ˇ ˇ
2005, 2271–2273; f) J. Honzꢅcek, J. Vinklꢆrek, M. Erben, L. Strizꢅk,
118 Hz, SiMe3), 45.4 (CH2), 103.5 (C6), 110.6 (1J
ACHTUNGTRENNUNG
ˇ
ˇ
I. Cꢅsarovꢆ, Z. Padelkovꢆ, J. Organomet. Chem. 2009, 694, 4250–
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3464–3467.
G
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
163.1 (C2), 165.1 (C7), 205.0 ppm (C1); 29Si NMR (74.5 MHz,
[D6]benzene, 297 K): d=À10.1 (2J
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A
3J
E
[D6]benzene, 297 K): d À193.2, À182.6 (1J
2962 (w), 1343 (vw), 1260 (s), 1089 (m), 1017 (s), 797 (vs), 697 cmÀ1 (w);
MS (EI): m/z (%): 648 (100) [M]+, 575 (58) [M-SiMe3]+, 220 (26)
[Cp2Zr]+; elemental analysis calcd (%) for C36H42N2Si2Zr: C 66.51, H
6.51, N 4.31; found: C 66.13, H 6.21, N 4.09.
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Acknowledgements
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We thank our staff at LIKAT for their technical and analytical support.
Financial support by the Deutsche Forschungsgemeinschaft (RO 1269/8-
1) and the Russian Foundation for Basic Research (project code 12-03-
00036-a) is acknowledged.
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Received: November 26, 2012
Published online: February 27, 2013
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