Carbodiimide metathesis catalyzed by vanadium oxo and imido complexes via imido transfer

Article abstract of DOI:10.1016/S0022-328X(99)00142-4

Vanadium oxo and imido complexes: V(NC₆H₄Me)(O^tBu)₃ (1), V(NC₆H₄Me)Cl₃ (2), V(O)(O^tBu)₃ (3), V(O)(O^tPr)₃ (4), V(O)(acac)₂ (

Full text of DOI:10.1016/S0022-328X(99)00142-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 584 (1999) 200–205
Carbodiimide metathesis catalyzed by vanadium oxo and imido
complexes via imido transfer
K.R. Birdwhistell *, J. Lanza, J. Pasos
Department of Chemistry, Loyola Uni6ersity, New Orleans, LA 70118, USA
Received 18 June 1998
Abstract
Vanadium oxo and imido complexes: V(NC6H4Me)(OtBu)3 (1), V(NC6H4Me)Cl3 (2), V(O)(OtBu)3 (3), V(O)(OiPr)3 (4),
V(O)(acac)2 (5), are catalysts for the metathesis of symmetrical carbodiimides (RNCNR, where R=cyclohexyl, isopropyl, and
p-tolyl). At 138°C in p-xylene using 5 mol% of complexes 1–5, the above carbodiimides are metathesized to the asymmetrical
carbodiimides: N-cyclohexyl,N%-p-tolylcarbodiimide (6), N-isopropyl,N%-p-tolylcarbodiimide (7), N-cyclohexyl,N%-isopropylcar-
bodiimide (8). An equilibrium mixture of carbodiimides is reached within minutes to hours depending on the catalyst employed.
Yields obtained from gas chromatography range from 32 to 70%. Complex 2 is the most efficient catalyst with a turnover
frequency greater than 100 h−1. The oxo complexes (3–5) appear to be precatalysts. A mechanism is proposed for initiation with
oxo complexes and a subsequent catalytic cycle involving imido complexes. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Vanadium imido; Vanadium oxo; Carbodiimide metathesis; Unsymmetrical carbodiimide; Catalysis; Imido transfer
1. Introduction
and W(CO)5(CNiPr) [5]. Both catalytic and stoichio-
metric imine metathesis has been observed using imido
complexes [6]. Sita has developed a stoichiometric
metathesis to unsymmetrical carbodiimides mediated by
Group 14 amide complexes [7].
Reactions involving imido complexes and imido
transfer are of great current interest due to the use of
these complexes as catalysts in alkene metathesis and
their proposed intermediacy in catalytic ammoxidation
of arenes and alkenes [1]. We reported that several high
valent vanadium oxo and imido complexes are catalysts
for the condensation of phenyl isocyanate to N,N%-
diphenylcarbodiimide (Eq. (1)) [2]. Imido transfer ap-
pears to be a key step in this catalytic process.
Condensation of phenyl isocyanates (Eq. (1)) and
metathesis of carbodiimides (Eq. (2)) are both examples
of heterocumulene metatheses. The similarities in these
reactions led us to investigate the use of vanadium oxo
and imido complexes as carbodiimide metathesis cata-
lysts. We now report the use of the following vanadium
complexes: V(NC6H4Me)(OtBu)3 (1), V(NC6H4Me)Cl3
(2), V(O)(OtBu)3 (3), V(O)(OiPr)3 (4), V(O)(acac)2 (5) as
precatalysts or catalysts for the metathesis of N,N%-di-
alkylcarbodiimides and N,N%-diarylcarbodiimides (Eq.
(3)).
2PhNCO[V(E)OR ]
X
3 PhNCNPh+CO2
(1)
where E=O, NR.
Weiss proposes an imido transfer in the catalytic
metathesis of carbodiimides by W(NPh)Cl4 (Eq. (2)) [3].
R−NꢀCꢀN−R+R%−NꢀCꢀN−R% _` 4
R−NꢀCꢀN−R+R%−NꢀCꢀN−R%[_V c`at.]
PhNWCl
2R−NꢀCꢀN-R%
(3)
2R−NꢀCꢀN-R%
(2)
Imido transfer in Eq. (2) purportedly occurs via a
diazametallacyclobutane intermediate. Carbodiimide
metathesis has also been catalyzed by Cr(II)/SiO2 [4]
2. Results and discussion
We studied the use of complexes 1–5 as catalysts or
precatalysts for the metathesis of N,N%-dialkyl- and
N,N%-diarylcarbodimiides (Eq. (4)).
* Corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00142-4

K.R. Birdwhistell et al. / Journal of Organometallic Chemistry 584 (1999) 200–205
201
where E=NR, O; X=OR, Cl, acac.
R–NꢀCꢀN–R
DTC
DiPC
R
R–NꢀCꢀN–R%
CTC, 6
iPTC, 7
R
R%
p-C6H4Me
iPr
C6H11
iPr
p-C6H4Me
p-C6H4Me
iPr
DCC
C6H11
CiPC, 8
C6H11
The above metatheses were performed in p-xylene at
138°C with millimolar concentrations of reagents and
catalyst. Typically 3–7 mol% of catalyst is used.
Product concentrations are monitored by GC as a
function of time using the internal standard method.
Reactions are followed until equilibrium is established
as indicated by little change in concentration over
several hours. A typical reaction profile for a metathesis
is shown in Fig. 1.
Equilibrium in these metatheses results in an approx-
imate 2:1 mixture of products and reagents. The equi-
librium nature of these reactions was confirmed by the
metathesis of one of the products (CiPC) using
V(O)(OiPr)3 to make DCC and DiPC under the same
reaction conditions as the standard metathesis (Eq. (5)).
Fig. 1. Reaction profile of the metathesis of DiPC and DTC catalyzed
by V(O)(OtBu)3, 3.
R−NꢀCꢀN−R+R%−NꢀCꢀN−R%[V_(E`)Xn]
2R−NꢀCꢀN-R%
(4)
(5)
Table 1
i
Results from the catalytic metathesis of N,N%-diaryl and N,N%-dialkylcarbodiimides (RNCNR where R=C6H11, Pr, p-C6H4Me with vanadium
oxo and imido complexes (Eq. (4))
Catalyst
Metathesis products
C6H11NCNiPr, 8
C6H11NCNC6H4Me, 6
iPrNCNC6H4Me, 7
Cat. (mol%) % Yielda TOFb (h−1
)
Cat. (mol%) % Yielda TOFb (h−1
)
Cat. (mol%) % Yielda TOFb (h−1
)
V(NPhMe)(OtBu)3, 1f
5
4
5
7
5
32
0.5
40c
2
2
3
4
5
4
5
70
3
60c
2
4
4
3
5
6
5
4
61
8
60c
2
4
3
V(NPhMe)Cl3,
2
63d
44d
61d
69d
65d
60d
60d
50d
0
50d
41d
41d
49d
V(O)(OtBu)3,
3
V(O)(OiPr)3, 4
V(O)(acac)2
Control
5
6
0e
a Yields were determined by gas chromatography. Percent yield based on 100% conversion of limiting carbodiimide. These yields represent
10–20 catalyst turnovers.
b The turnover frequency (TOF) was determined by finding the maximum in the following ratio: {[D[Prod]/Dt]/[Cat.]}. TOF was determined
from a plot of mmol of product versus time constructed from GC data.
c These values represent a lower limit to TOF due to limitations of the sampling procedure.
d Average of two runs.
e After 9 h at 138° C
f Complex 1 has one run for each reaction due to the difficulty using this catalyst.

202
K.R. Birdwhistell et al. / Journal of Organometallic Chemistry 584 (1999) 200–205
2.3. Catalytic metathesis
Eqs. (6) and (7) display proposed initiation steps and
Scheme 1 shows the catalytic cycle for the metathesis of
carbodiimides using oxo and imido complexes. Scheme
1 is essentially the mechanism proposed by Weiss [3]
using tungsten imido complexes. Imido 12 reacts with
another carbodiimide (R%NꢀCꢀNR%) to form one asym-
metrical carbodiimide (R%NꢀCꢀNR) and imido 14. The
cycle is completed by the reaction of RNꢀCꢀNR and 14
to form another asymmetrical carbodiimide (R%NCNR)
and reform 12. The diazametallacycles 13 and 15 repre-
sent possible transition states.
Scheme 1. Proposed catalytic cycle for metathesis with imido com-
plexes.
V(O)X3+R−NꢀCꢀN−R X RNCO+V(NR)X3 (6)
10
12
V(O)X3+RNCO X CO2(g)+V(NR)X3
(7)
The results for all metatheses are summarized in Table
1. The time required to reach equilibrium for the
metatheses in Table 1 varied from 20 min to several
hours depending on catalyst and carbodiimides
employed.
10
12
Eqs. (6) and (7) are proposed initiation pathways for
the metal oxo complexes. Oxo 10 reacts with RNꢀCꢀNR
to form one equivalent of imido 12 and RNCO (Eq. (6)).
A possible intermediate is the oxometallacyle formed by
addition of the carbodiimide CꢀN bond across the VꢀO
bond with the nitrogen ligating the vanadium. Related
oxometallacycles of this type formed by addition of an
isocyanate CꢀN bond across the MꢀO bond have been
isolated for Mo, Re, and Ir [8]. Another pathway for
formation of imido 12 is reaction of the isocyanate
formed in Eq. (6) with oxo 10 (Eq. (7)). Reaction of
isocyanates with metal oxo complexes is a common
synthetic route to metal imido complexes [9]. Moreover
oxos 3–5 catalyze the condensation of PhNCO to
PhNCNPh via an imido intermediate (Eq. (1)) [2].
Several experiments support these proposed initiation
pathways.
2.1. Yields
The yields were determined by GC using 1,2,3,4-te-
tramethylbenzene as an internal standard. Table 1 shows
a large amount of variability in the yield of the various
carbodiimides depending on which catalyst was used.
Some of the yield variability can be attributed to side
reactions which decompose the asymmetrical carbodi-
imides to unknown products. The reported yields are
not optimized.
2.2. Catalyst efficiency
The initiation step of the metathesis using oxo 5
combined with DCC and DiPC in refluxing p-xylene is
observed as a blue–yellow color change over 2 h fol-
lowed by initial product formation (CiPC). An IR
experiment with oxo 5 further substantiates the oxo
initiation paths of Eqs. (6) and (7). The same color
change is observed upon heating a mixture of oxo 5 and
a three fold excess of DiPC in p-xylene. An infrared
spectrum following the color change shows the intense
NCN absorption for DiPC and a weak absorption at
2255 cm−1 attributed to the NCO absorption of iso-
propyl isocyanate [10]. The 2255 cm−1 absorption dis-
appears upon continued heating, consistent with Eqs. (6)
and (7). A complementary experiment heating oxo 5 and
a three fold excess of DCC in p-xylene resulted in
immediate formation of cyclohexyl isocyanate (CyNCO)
as observed by GC. The CyNCO was quantified by
using an internal standard. The CyNCO concentration
increased for 5 h where it maximized at 17 mol% of oxo
5. Wholly consistent with the reactions in Eqs. (6) and
(7), the continued heating of the reaction mixture results
in the disappearance of the CyNCO.
The turnover frequency (TOF) for each catalyst was
determined by finding the slope maximum in the plot of
mmols of product versus time. We report maximum
turnover frequency in Table 1 because the oxo com-
plexes 3–5 have variable initiation periods before prop-
agation proceeds smoothly. Except for imido 2, all
catalysts showed similar turnover frequencies. Imido 2
was by far the most efficient catalyst. Using a lower
catalyst concentration (0.4 mol% of imido 2) than the
standard metathesis conditions with DCC and DiPC as
reagents, the TOF of imido 2 was 90 h−1
.
The catalytic lifetime of imido 2 was also investigated.
A mixture of DCC and DiPC with 0.4 mol% imido 2 was
metathesized to CiPC within 30 min in p-xylene at
138°C. After establishing equilibrium, another aliquot of
DCC and DiPC was added. Equilibrium was reestab-
lished within 20 min after addition, producing over 100
catalyst turnovers without loss of catalytic activity. The
yields reported in Table 1 represent 10–20 catalyst
turnovers.

K.R. Birdwhistell et al. / Journal of Organometallic Chemistry 584 (1999) 200–205
203
In Scheme 1, the carbodiimides are metathesized by
imido exchange or imido transfer via a diazametalla-
cycle. The metathesis of DCC and DiPC with
tolylimido 2 provides supporting evidence for the
imido transfer step in Scheme 1. In the initial 20 min
of the metathesis, GC evidence shows carbodiimides 6
and 7 are formed (Eq.(8)). These carbodiimides (6
and 7) are produced by transfer of the tolyl imido
group of imido 2 to DCC and DiPC, respectively
(Eq.(8))
tetramethylbenzene, mercuric oxide, V(O)(OiPr)3, and
V(O)(acac)2 were used as obtained from commercial
suppliers. V(NC6H4Me)(OtBu)3 [11], V(NC6H4Me)Cl3
[11], and V(O)(OtBu)3 [12] were prepared by literature
methods. The asymmetrical carbodiimides (N-cyclo-
hexyl,N%-isopropylcarbodiimide
(CiPC),
N-iso-
propyl,N%-p-tolylcarbodiimide (iPTC), N-cyclohexyl,
N%-p-tolylcarbodiimdide (CTC)) used for GC refer-
ences were prepared according to a modified literature
method [13]. All syntheses were done under dry nitro-
gen with dry solvents. The solvents were distilled
from potassium or sodium under dry nitrogen. Ace-
,
tone was dried over activated 4 A mole sieves.
4.1.1. Equipment
(8)
The GC analyses were performed on a Hewlett–
Packard 5890 chromatograph fitted with a 12 m×0.2
mm×0.33 mm HP-1 capillary column and a flame
ionization detector. The infrared spectra were ob-
tained on a Mattson Cygnus 100 series FTIR or a
Perkin–Elmer model 1430 spectrometer. The high-res-
olution mass spectra were obtained on a Kratos Con-
Quantitative GC results indicate greater than 50%
of the tolyl group of imido 2 is found in carbodi-
imides 6 and 7.
3. Conclusions
1
cept H Spectrometer in positive ion mode at 30°C at
70 eV. The elemental analysis was done by Desert
Analytics of Tucson, AZ. The 1H-NMR were
recorded on an IBM AMX 200 MHz or a General
Electric QE 400 MHz spectrometer. The 13C-NMR
were recorded on a General Electric QE 400 MHz
spectrometer.
The above data show that complexes 1–5 catalyze
the metathesis of both N,N%-dialkyl- and N,N%-diaryl-
carbodiimides to equilibrium mixtures. The oxo com-
plexes 3–5 are precatalysts which are converted to
imido complexes by the reactions indicated in Eqs. (6)
and (7). The turnover frequency (TOF) data indicate
imido 2 is by far the most active metathesis catalyst.
It is not clear whether the rate difference between
imido 2 and catalysts (1, 3–5) is purely a conse-
quence of steric factors or results from some elec-
tronic contribution. Interestingly, while imido 2 is the
most efficient carbodiimide metathesis catalyst, 2 is
the only one of the complexes 1–5 which shows no
catalytic activity for isocyanate condensation (Eq.
(1)). Both of these catalytic reactions are heterocumu-
lene metatheses which appear to involve imido trans-
fer. In a continuing effort to understand imido
transfer in these systems we are attempting to deter-
mine what factors effectively shut off imido transfer
from V(NC6H4Me)Cl3 (2) to aryl isocyanates, but al-
low 2 to be an efficient imido transfer agent for car-
bodiimide metatheses.
4.2. Representati6e metathesis reaction
4.2.1. Metathesis of DTC and DiPC catalyzed by
i
V(O)(OtBu)3, 3 to prepare PTC, 7
A
100 ml Schlenk flask is charged with
V(O)(OtBu)3 (0.063 g, 0.22 mmol), DiPC (0.349 g,
1.55 mmol), DTC (0.449 g, 1.94 mmol), 1,2,3,4-te-
tramethylbenzene (TMB, internal standard) (0.068 g,
0.51 mmol), and 30 ml of p-xylene resulting in a light
yellow mixture. The initial concentrations of reagents
are as follows: [V(O)(OtBu)3]=0.0074 M, [DiPC]=
0.052 M, [DTC]=0.065 M. The mixture is heated to
reflux under nitrogen. The reaction mixture is periodi-
cally sampled by removing a 1–2 ml aliquot of the
reaction mixture via cannula and transferring it to a
sealed test tube containing an equivalent amount of
dry (0°C) THF. These samples are analyzed immedi-
ately upon cooling by gas chromatography. An initial
sample is taken upon reaching reflux temperature and
other samples are taken at least every hour for a
minimum of 5 h. Reaction is allowed to continue
overnight and a final sample is taken after 25 h. Fi-
nal reaction mixture is spiked with (independently
4. Experimental
4.1. General
The reagents N,N%-di-p-tolylcarbodiimide (DTC),
N,N%-di-isopropylcarbodiimide (DiPC), N,N%-dicyclo-
hexylcarbodiimide (DCC), isopropylamine, p-tolyl iso-
thiocyanate, cyclohexyl iso-thiocyanate, 1,2,3,4-
i
prepared, see below) PTC, 7 to confirm GC assign-
i
ment. The yield of PTC determined by GC using the
internal standard method is 58%.

204
K.R. Birdwhistell et al. / Journal of Organometallic Chemistry 584 (1999) 200–205
4.3. Preparation of N-cyclohexyl-N%-p-tolylcarbodi-
imide, (C6H11NCNC6H4Me) (CTC) 6
J(1H–1H)=6 Hz, NCH(CH3)2, 6H) IR (neat, w, cm−1
)
3020 w, 2970 m, 2920 w, 2120 vs(NCN), 1605 m, 1505
s, 812 m, 610 m; 13C-NMR (100 MHz)(CDCl3) l: 137.7
(s, ipso Ph or NCN) 136.9 (s, ipso Ph or NCN) 134.0 (s,
ipso Ph or NCN), 129.7 (s, CH of Ph), 122.9 (s, CH of
Ph), 49.95 (s, NCH(CH3)2), 24.66 (s, NCH(CH3)2),
20.69 (s, PhCH3); Anal. Calc. for C11H14N2: C, 75.82;
H, 8.10; N, 16.08; Found: C, 75.38; H, 8.04; N, 15.57;
GC/MS (70 eV) m/z (% relative intensity): 174 (56)
[M+], 132 (100) [M–C3H6+], 131 (64) [M–C3H7+];
HRMS Calc. for C11H14N2: 174.115698; Found:
174.1157(0.06 ppm deviation).
A Schlenk flask is charged with cyclohexyl isothio-
cyanate (6.89 g, 48.8 mmol) and 40 ml of THF. To this
solution a solution of p-toluidine (6.04 g, 56.4 mmol) in
40 ml of THF, at 0°C, is added dropwise over 10 min.
The resulting solution is stirred overnight at room
temperature. The THF is removed in vacuo resulting in
the white crystalline N-cyclohexyl-N%-tolylthiourea
(m.p. 94–97).
The thiourea (48 mmol) is dissolved in 80 ml of dry
acetone under nitrogen. To this mixture is added HgO
(15 g, 69 mmol) and 1 g of anhydrous calcium chloride.
This suspension is stirred overnight under nitrogen
resulting in a black solid suspended in solution. The
mixture is filtered and the solvent removed in vacuo
producing a light yellow oil. The N-cyclohexyl-N%-tolyl-
carbodiimide (CTC) is formed essentially quantitatively
as determined by GC/MS.
4.5. Preparation of N-cyclohexyl-N%-isopropylcarbodi-
imide (C6H11NCNiPr) (CiPC) 8
Compound 8 is prepared in a similar fashion to
complex 6. A solution of isopropylamine (4.2 g, 71
mmol) in THF is added dropwise at 0°C to a THF
solution of cyclohexyl isothiocyanate (6.9 g, 49.0 mmol)
over a 10 min period. The mixture is allowed to react
overnight at room temperature. The solvent is removed
in vacuo resulting in N-cyclohexyl-N%-isopropylthiourea
as a white solid (m.p. 138).
To a solution of the thiourea (48 mmol) in 80 ml of
acetone, an excess of mercuric oxide (15.0 g, 69 mmol)
and CaCl2 (1.0 g) is added. The heterogenous mixture is
stirred overnight. The mixture is filtered and more
mercuric oxide (8.0 g, 37 mmol) is added. After another
8 h the reaction appears complete by GC/MS. The
reaction mixture is filtered and the solvent removed
from the filtrate in vacuo resulting in an essentially
quantitative yield of pure N-cyclohexyl-N%-isopropyl-
carbodiimide as a yellow oil.
1H-NMR(200 MHz) (CDCl3) l: 7.03 (ABq, J(HA–
HB)=8 Hz, NPhCH3, 4H) 3.44 (tt, J(1H–1H)=9, 4
Hz, NCH(CH2)5 1H) 2.30 (s, PhCH3, 3H), 2.00 (m,
NCH(CH2)5,2H), 1.76 (m, NCH(CH2)5,2H) 1.41 (m,
NCH(CH2)5, 6H); 13C-NMR (100 MHz) (CDCl3)
138.02 (s, ipso Ph or NCN), 134.20 (s, ipso Ph or
NCN), 130.59 (s, ipso Ph or NCN), 129.95 (s, Ph
C–H), 123.14 (s, Ph C–H), 56.64 (s, CH3–Ph), 34.99
(s, C6H11), 25.38 (s, C6H11), 24.43 (s, C6H11), 20.93 (s,
C6H11); IR (neat, w, cm−1) 3010 w, 2928 s, 2850 s, 2125
vs (NCN), 1605 m, 1510 vs, 815 vs, 610 vs; HRMS.
Anal. Calc. for C14H18N2: 214.146998; Found:
214.14706 (0.29 ppm deviation); GC/MS (70 eV) m/z
(% relative intensity) 214 (29) [M+], 132 (100) [M–
C6H1+0 ], 91 (22) [M–NCNC6H1+1 ].
1H-NMR (200 MHz) (benzene-d6) l: 3.37 [sept,
J(HH)=6 Hz, 1H, NCH(CH3)2)]; 3.07(triplet of
triplets, J(1H–1H)=10, 4 Hz, 1H, NCH(CH2)5), 1.78
(m, 2H, NCH(CH2)5), 1.54 (m, 2H, NCH(CH2)5),
1.28 (m, 2H, NCH(CH2)5), 1.06(d, J(1H–1H)=6 Hz,
6H, NCH(CH3)2); 13C-NMR (100 MHz) (CDCl3) l:
139.8 (s, NCN), 55.5 (s, N–CH), 48.7 (s, N–CH),
34.7(s, CH2), 25.2(s, CH2), 24.5(s, CH2), 24.2(s,
CH(CH3)2), assignments were aided by a DEPT experi-
ment. IR (neat, w, cm−1) 2968 m, 2923 s, 2855 m, 2120
vs (NCN), 1448 m, 1360 m, 1300 m, 1205 m, 943 m,
879 m; GC/MS (70eV) m/z (% relative intensity): 166
(2.3) [M+], 151 (100) [M–CH3+]; HRMS. Anal. Calc.
for C10H18N2: 166.146998, Found: 166.14708 (0.51 ppm
deviation).
4.4. Preparation of N-isopropyl-N%-p-tolylcarbodiimide
(p-MeC6H4NCNiPr), (iPTC) 7
Compound 7 is synthesized similarly to compound 6.
A solution of isopropylamine (2.21 g, 37 mmol) in THF
is added dropwise to a solution of p-tolyl isothio-
cyanate (4.66 g, 31.2 mmol) at 0°C over 15 min. The
mixture is stirred overnight at room temperature. The
solvent is removed in vacuo resulting in N-isopropyl-
N%-tolylthiourea as a white solid (m.p. 106–111).
To a solution of thiourea (31 mmol) in acetone an
excess of mercuric oxide (15 g, 69 mmol) and CaCl2 (1
g) is added. The heterogeneous reaction is stirred
overnight at room temperature. The black HgS is
filtered away and the solvent removed from the filtrate
in vacuo resulting in a quantitative yield of a yellow oil
of N-isopropyl-N%-p-tolylcarbodiimide.
4.6. GC calibration graphs for asymmetrical carbodi-
imides and cyclohexyl isocyanate
1H-NMR (200 MHz) (CDCl3) l: 7.03 (ABq, J(HA–
HB)=8 Hz, N–Ph–Me, 4H), 3.76 (sep, J(1H–1H)=6
Hz, NCH(CH3)2, 1H); 2.30 (s, PhCH3, 3H) 1.32 (d,
4.6.1. GC calibration cur6e for 7 (iPTC)
i
Five standard samples of PTC are made with con-
centrations ranging from 0.00520 to 0.105 M in a 50:50

K.R. Birdwhistell et al. / Journal of Organometallic Chemistry 584 (1999) 200–205
205
(V/V) mixture of tetrahydrofuran:p-xylene. Each stan-
dard contained 0.0203 M 1,2,3,4-tetramethylbenzene
References
[1] (a) W.A. Nugent, J.M. Mayer, Metal Ligand Multiple Bonds,
Wiley, New York, 1988. (b) D.E. Wigley, Progr. Inorg. Chem. 42
(1994) 239. (c) J. de With, A.D. Horton, Angew. Chem. Int. Ed.
Engl. 32 (1993) 903. (d) Y.W. Chao, P.M. Rodgers, D.E. Wigley,
S.J. Alexander, A.L. Rheingold, J. Am. Chem. Soc. 113 (1991)
6326. (e) S. Scheuer, J. Fisher, J. Kress, Organometallics 14 (1995)
2627. (f) R.R. Schrock, R.T. DePue, J. Feldman, K.B. Yap, D.C.
Yang, W.M. Davis, L. Park, M. DiMare, M. Schofield, J. Anhaus,
E. Walborsky, E. Evitt, C. Kruger, P. Betz, Organometallics 9
(1990) 2262. (g) W.A. Nugent, B.L. Haymore, Coord. Chem. Rev.
31 (1980) 123. (h) G. Busca, F. Cavani, F. Trifiro, J. Catal. 106
(1987) 471–482. (i) E.W. Harlan, R.H. Holm, J. Am. Chem. Soc.
112 (1990) 186.
(TMB). For the five samples the ratio of Areai
/
PTC
AreaTMB was plotted versus ratio of mmol iPTC/
mmolTMB resulting in a linear plot. The data is fit
to the equation below by a least-squares analysis:
Area(iPTC)/Area(TMB)
i
=1.138 {mmol PTC/mmol TMB}
−0.0614 with a correlation coefficient of 0.99.
[2] K.R. Birdwhistell, T. Boucher, M. Ensminger, S. Harris, M.
Johnson, S. Toporek, Organometallics 12 (1993) 1023.
[3] I. Meisel, G. Hertel, K. Weiss, J. Mol. Cat. 36 (1986) 159.
[4] K. Weiss, K. Hoffmann, Z. Naturforsch. 42b (1987) 769.
[5] K. Weiss, P. Kindl, Angew. Chem. Int. Ed. Engl. 23 (1984) 629.
[6] (a) K.E. Meyer, P.J. Walsh, R.G. Bergman, J. Am. Chem. Soc.
116 (1994) 2669, (b) G.K. Cantrell, T.Y. Meyer, Organometallics
16, (1997) 5381. (c) G.K. Cantrell, T.Y. Meyer, J. Am. Chem. Soc.
120, (1998) 8035.
The calibration graphs for 8, 6, and cyclohexyl iso-
cyanate are prepared similarly and display correlation
coefficients of ]0.99.
4.6.2. Metathesis plots of time 6ersus mmol of product
Using response factors obtained from the calibra-
tion curves, plots of mmols of metathesis product ver-
sus time were constructed. These curves are used to
determine percent yield of product, the stability of
product under reaction conditions, and turnover fre-
quency (TOF) of the catalyst.
[7] (a) J.R. Babcock, L.R. Sita, J. Am. Chem. Soc. 120 (1998) 5585.
(b) L.R. Sita, J.R. Babcock, R. Xi, J. Am. Chem. Soc. 118 (1996)
10912.
[8] (a) P. Jernakoff, G.L. Geoffroy, A.L. Rheingold, S.J. Geib, J.
Chem. Soc. Chem. Commun. (1987) 1610. (b) U. Kusthardt, W.A.
Herrmann, M.L. Ziegler, T. Zahn, B. Nuber, J. Organomet. Chem.
311 (1986) 163. (c) D.S. Glueck, F.J. Hollander, R.G. Bergman,
J. Am. Chem. Soc. 111 (1989) 2719. (d) D.S. Glueck, J. Wu, F.J.
Hollander, R.G. Bergman, J. Am. Chem. Soc. 113 (1991) 2041.
[9] (a) I.S. Kolomnikov, Yu D. Koreshkov, T.S. Lobeeva, M.E.
Volpin, Akad. Nauk. SSSR Ser. Khim. (1971) 2065. (b) S.F.
Pederson, R.R. Schrock, J. Am. Chem. Soc. 104 (1982) 7483. (c)
A.J. Nielson, Inorg. Synth. 24 (1986) 194.
Acknowledgements
This work received partial support from a William
and Flora Hewlett Grant of Research Corporation
and the Petroleum Research Fund, administered by
the American Chemical Society. Thanks are due to
the Tulane University Chemistry Department for use
of instrumentation. Thanks to the Schlieder Founda-
tion and Keck Foundation for equipment and reno-
vation grants.
[10] C.J. Pouchert, The Aldrich Library of Infrared Spectra, 2nd,
Aldrich Chemical, New York, 1975, p. 462.
[11] D.D. Devore, J.D. Lichtenhan, F. Takusagawa, E.A. Maatta, J.
Am. Chem. Soc. 109 (1987) 7408.
[12] J. Fuchs, K.F. Jahr, Chem. Ber. 96 (1963) 2460.
[13] (a) E.T. Hessell, W.D. Jones, Organometallics 11 (1992) 1496. (b)
V.S. Hunig, H. Lehmann, G. Grimmer, Ann. Chem. 579 (1953)
77, (c) E. Schmidt, W. Striewsky, Chem. Ber. 74 (1941) 1285.
.