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ensure that the nature of the catalytic site is heterogeneous,
we analyzed the filtrate at the end of the reaction and found
that the concentration of W was less than 0.1 ppm.[11] Besides,
no reaction could be observed when adding cyclooctane to
this filtrate. To analyze the higher oligomers, a suitable GC
methodology was developed allowing the detection up to
pentamers of cyclooctane.[12]
were not found for most of the other alkanes requiring ion
fragmentation interpretation. We noticed a similar ion frag-
mentation pattern for most of alkane products in the range of
C12 to C40. The comparison between their ion fragmentation
pattern with the only cycloeicosane (cC20) and cycloheneico-
sane (cC21) patterns disclosed in literature[1b,14] supports that
C20 and C21 from the mixture are macrocyclic alkanes, and
therefore strongly support that the other alkanes from C12 to
C40 belong to this same family. Secondly, we examine the cor-
relation of the logarithm of the relative retention time versus
the carbon atom numbers, known as Kovats retention index.[15]
The experimental linear correlation found (0.996) corroborates
with the assignment for macrocyclic alkanes series as major
products (see the Supporting Information, Figure S6).
The typical GC chromatogram of cyclooctane metathesis dis-
plays a distribution of peaks. The most intense ones have mo-
lecular formula CnH2n: 1) Three peaks with lower retention time
than cyclooctane (on GC) correlate with the peaks with lower
molecular weight (<C8) (on GC-MS) and 2) other peaks with
longer retention time and higher molecular weight (Figure 2).
1
In addition with H and 13C NMR spectroscopies, the distor-
tionless enhancement by polarization transfer (DEPT-135) NMR
spectroscopy of the reaction mixture displays weak signals cor-
responding to CH and CH3 groups suggesting also the pres-
ence of substituted cyclic alkanes or linear alkanes (see Fig-
ure S5, the Supporting Information). To unambiguously distin-
guish between the pure macrocyclic alkanes and the branched
ones, we compared the ion fragmentation of octylcyclooctane
and cyclohexadecane. For this purpose, octylcyclooctane was
synthetized starting from cyclooctanone (see the Supporting
Information).[16] As expected, octylcyclooctane and cyclohexa-
decane exhibit different retention times (tR: 13.35 and
13.56 min, respectively). More importantly, their ion fragmenta-
tion pattern differs significantly (Figure S7, the Supporting In-
formation). In fact, the mass spectrum of octylcyclooctane
shows a low intense molecular ion at m/z 224 and higher in-
tensity of a characteristic ion fragment corresponding to cyclo-
octane carbocation secondary fragmentation peak at m/z 111,
which represents the loss of alkyl chain (see Figures S8 and S9,
the Supporting Information, for EI spectra of cyclic and
branched cyclic alkanes). Lately, we employed a GC preparative
fraction collector to isolate two macrocyclic alkanes from our
reaction mixture, cycloheptadecane (cC17) and cycloheneico-
Figure 2. GC chromatogram of cyclooctane metathesis products catalyzed
by 1. Reaction conditions: Batch reactor, compound 1 (300 mg, 23 mmol, W
loading: 1.4 wt%), cyclooctane (2 mL, 14.88 mmol), 190 h, 1508C. Conver-
sion=70%, TON=450. The turnover number (TON) is the number of mol of
cyclooctane transformed per mole of W.
1
sane (cC21) (Figure 3). H and 13C NMR spectroscopies of these
two samples gave single resonance signals, respectively (see
Figures S10 and S11, the Supporting Information). These ex-
periments confirm unambiguously the structure of cyclooctane
metathesis products as purely cyclic compounds.
Lower cycloalkanes with a molecular weight ranging from C5
to C7 are attributed to cyclopentane, cyclohexane, and cyclo-
heptane. They result from the ring contraction of cyclooctane
(see below for the mechanism). With very few literature data
available, the compounds with chemical formula of CnH2n rang-
ing from C12 to C40 required more thought concerning their
characterizations. From the molecular formula, they could be
either macrocyclic alkanes or linear olefins as well as branched
cyclic alkanes. Firstly, proton and carbon NMR spectra of the
resulting solution at the end of the catalytic run shows the ab-
sence of olefinic protons and sp2 carbons that would corre-
spond to a double bond (see Figures S3 and S4, the Support-
ing Information). Macrocyclic alkanes from C12–C15, C24, C28, and
C30 were identified by comparison with the mass spectra of the
corresponding library references.[13] They exhibit similar frag-
mentation pattern and ion ratio. However, EI spectral libraries
Thus, overall, these results demonstrate that the major prod-
ucts of cyclooctane metathesis in the range of C12 to C40 are
pure macrocyclic alkanes. We observe a different distribution
compared with the tandem catalytic system with a wider distri-
bution of macrocyclic alkanes. Finally, traces of linear alkanes
and n-alkyl cyclohexanes compounds were also observed (GC/
GC-MS, molar fraction: less than 1% for each family; see Fig-
ure S12, the Supporting Information). Further analysis by gel-
permeation chromatography (GPC) of the crude reaction mix-
ture shows the absence of polymeric products (see Figure S13,
the Supporting Information).
A kinetic study of the cyclooctane metathesis catalyzed by
1 was carried out at 1508C. The plots of turnover numbers
(TONs) and conversion versus time are given in Figure 4. A
final conversion of 60% is reached with 340 TONs. The catalyst
Chem. Eur. J. 2014, 20, 15089 – 15094
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