Synthesis of molybdenum imido alkylidene complexes that contain 3,3′-dialkyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2, 2′-diolates (alkyl = t-Bu, adamantyl). Catalysts for enantioselective olefin metathesis reactions

Article abstract of DOI:10.1021/om000336h

Two 3,3′-dialkyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl- 2,2′-diols (where alkyl = t-Bu, adamantyl) were prepared in two steps and resolved as the menthol phosphate derivative. Addition of the dipotassium salt of each biphenolate to various Mo(N-Aryl)(CHR) (

Full text of DOI:10.1021/om000336h

3700
Organometallics 2000, 19, 3700-3715
Syn th esis of Molybd en u m Im id o Alk ylid en e Com p lexes
Th a t Con ta in
3,3′-Dia lk yl-5,5′,6,6′-tetr a m eth yl-1,1′-bip h en yl-2,2′-d iola tes
(Alk yl ) t-Bu , Ad a m a n tyl). Ca ta lysts for En a n tioselective
Olefin Meta th esis Rea ction s
J ohn B. Alexander,† Richard R. Schrock,*,† William M. Davis,† Kai C. Hultzsch,†
Amir H. Hoveyda,‡ and J effrey H. Houser‡
Departments of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, and Merkert Chemistry Center,
Boston College, Chestnut Hill, Massachusetts 02167
Received April 20, 2000
Two 3,3′-dialkyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diols (where alkyl ) t-Bu, ada-
mantyl) were prepared in two steps and resolved as the menthol phosphate derivative.
Addition of the dipotassium salt of each biphenolate to various Mo(N-Aryl)(CHR)(OTf)2-
(DME) complexes produced racemic and enantiopure compounds of the type Mo(N-aryl)-
(CHR)(biphenolate). X-ray crystallographic studies of syn-Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)-
[(S)-Biphen] and syn-Mo(N-2-CF3C6H4)(CHCMe3)[(S)-Biad](pyridine) proved the absolute
stereochemistry of the biphenolate ligands. Neophylidene and neopentylidene complexes were
found to have predominantly the syn conformation in solution. The [syn]/[anti] equilibrium
constant for Mo(N-Aryl)(CHR)[Biphen] complexes increased in magnitude with decreasing
size of the arylimido ligand, and decreased upon reducing the steric bulk of the alkylidene
substituent. The rates of exchange of syn and anti isomers, as determined by single-parameter
line shape analysis and by spin saturation transfer, were found to be on the order of ∼1 s-1
at 22 °C.
In tr od u ction
found that when the diolate was a racemic biphenolate
or binaphtholate, the tacticity of the resulting poly-
(norbornene) or poly(norbornadiene) could be controlled
to a significant degree, as could the configuration about
the carbon-carbon double bond. Therefore, we began
to explore the possibility of preparing a stable, enan-
tiomerically pure initiator for an asymmetric metathesis
reaction. We prepared a catalyst that contained an
enantiomerically pure 3,3′-dimethylphenylsilyl-substi-
tuted binaphtholate ligand, but preliminary evidence
suggested that the catalyst slowly decomposed during
the course of a ROMP metathesis reaction. In an effort
to prevent decomposition, we turned to the synthesis
of ligands in which the substituent in the 3- and
3′-positions is carbon-based and relatively bulky.
One of the potentially resolvable biphenols that we
examined in our ROMP studies was 3,3′,5,5′-tetra-tert-
butyl-6,6′-dimethyl-1,1′-biphenyl-2,2′-diol,12 which can
be prepared readily on a large scale in 50% yield by
oxidative coupling of 2,4-di-tert-butyl-5-methylphenol.10
However, we were unable to resolve this relatively
soluble species. Therefore, we turned to ligands derived
from readily available and inexpensive (and less soluble)
Metal-catalyzed olefin metathesis,1 and most recently
molybdenum- and ruthenium-catalyzed ring-closing
metathesis,2-7 has emerged as a powerful method in
organic synthesis. Although only a cis versus trans
stereochemistry can be established at a carbon-carbon
double bond in a metathesis reaction, there are many
circumstances in which an enantiomerically pure cata-
lyst might be employed in order to establish chirality
at a remote carbon center as a consequence of a meta-
thesis reaction in a kinetic resolution or desymmetri-
zation mode. We became interested in that possibility
as a consequence of exploring ring-opening metathesis
polymerization (ROMP) of norbornenes and disubsti-
tuted norbornadienes catalyzed by molybdenum com-
plexes of the type Mo(N-aryl)(CHR)(diolate).8-11 We
† Massachusetts Institute of Technology.
‡ Boston College.
(1) Ivin, K. J .; Mol, J . C. Olefin Metathesis and Metathesis Polym-
erization; Academic Press: San Diego, 1997.
(2) Schmalz, H.-G. Angew. Chem., Int. Ed. Engl. 1995, 34, 1833.
(3) Schuster, M.; Blechert, S. Angew. Chem., Int. Ed. Engl. 1997,
36, 2037.
(4) Armstrong, S. K. J . Chem. Soc., Perkin Trans. 1998, 371.
(5) Grubbs, R. H.; Miller, S. J .; Fu, G. C. Acc. Chem. Res. 1995, 28,
446.
(6) Schrock, R. R. Tetrahedron 1999, 55, 8141.
(7) Schrock, R. R. In Topics in Organometallic Chemistry: Alkene
Metathesis in Organic Synthesis; Fu¨rstner, A., Ed.; Springer: Berlin,
1998; Vol. 1, p 1.
(9) O’Dell, R.; McConville, D. H.; Hofmeister, G. E.; Schrock, R. R.
J . Am. Chem. Soc. 1994, 116, 3414.
(10) Totland, K. M.; Boyd, T. J .; Lavoie, G. G.; Davis, W. M.; Schrock,
R. R. Macromolecules 1996, 29, 6114.
(11) Schrock, R. R.; Lee, J .-K.; O’Dell, R.; Oskam, J . H. Macromol-
ecules 1995, 28, 5933.
(12) Albert, H. E. J . Am. Chem. Soc. 1954, 76, 4983.
(8) McConville, D. H.; Wolf, J . R.; Schrock, R. R. J . Am. Chem. Soc.
1993, 115, 4413.
10.1021/om000336h CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/08/2000

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3701
3,4-dimethylphenol, namely 3,3′-di-tert-butyl-5,5′,6,6′-
tetramethyl-1,1′-biphenyl-2,2′-diol (H2[Biphen]) and 3,3′-
bis(1-adamantyl)-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-
diol ([H2[Biad]). The results of these efforts are reported
here. In the last two years enantiomerically pure
complexes of the type Mo(CHR)(NAr)(Biphen) have been
employed in a variety of relatively successful asym-
metric metathesis reactions,13-17 and one version, Mo-
(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(Biphen), is available com-
mercially from Strem Chemicals, Inc. in both enantio-
merically pure forms. All indications at this stage
suggest that the nature of the imido group is also an
important determinant of activity and that a variety of
catalysts eventually should be available for testing in
order to achieve the optimum combination of catalyst
and substrate.
romethane solution of excess PCl3 followed by vacuum
distillation to separate MenOPCl2 from PCl3. Addition
of a mixture of H2[Biphen] and triethylamine to a
dichloromethane solution of MenOPCl2 followed by
treatment with 30% hydrogen peroxide afforded a
diastereomeric mixture of phosphates, BiphenP(O)-
(OMen) (eq 3). The (S)-BiphenP(O)(OMen) diastereomer
Resu lts
Syn th esis a n d Resolu tion of H2[Bip h en ] a n d H2-
[Bia d ]. Racemic 3,3′-di-tert-butyl-5,5′,6,6′-tetramethyl-
1,1′-biphenyl-2,2′-diol12 (H2[Biphen]) can be prepared
from 3,4-dimethylphenol in two steps. Treatment of 3,4-
dimethylphenol at 65 °C under 2 atm of isobutene in
the presence of a catalytic amount of sulfuric acid18
followed by oxidative coupling with potassium dichro-
mate gave H2[Biphen] in 50% overall yield (eq 1). 3,3′-
Bis(1-adamantyl)-5,5′,6,6′-tetramethyl-1,1′-biphenyl-
2,2′-diol ([H2[Biad]) was prepared in a similar fashion
in ∼70% overall yield from 2-(1-adamantyl)-4,5-dimeth-
ylphenol19,20 in ∼50% yield overall (eq 2).
was selectively crystallized from refluxing acetic acid.
Two crops were collected, and the combined precipitate
was recrystallized from refluxing acetic acid to give (S)-
BiphenP(O)(OMen) in >99% de (eq 4). The acetic acid
was removed by vacuum distillation from the fraction
enriched in (R)-BiphenP(O)(OMen), and the residue was
recrystallized from refluxing methanol. Diastereomeri-
cally pure (R)-BiphenP(O)(OMen) was obtained after
two crystallizations (eq 5). The phosphate that remained
in the methanol solution was approximately racemic.
Treatment of (S)-BiphenP(O)(OMen) with excess Red-
Al in toluene produced enantiomerically pure (S)-H2-
[Biphen]. (R)-H2[Biphen] was obtained similarly by
reduction of (R)-BiphenP(O)(OMen). Approximately 20
g each of (S)-H2[Biphen] and (R)-H2[Biphen] typically
can be obtained from 100 g of racemic H2[Biphen]. The
approximately 60 g of racemic H2[Biphen] is then
recycled through the resolution process. The absolute
configuration of (S)-H2[Biphen] was established via an
X-ray structure of a molybdenum compound to be
discussed later. This method of resolving H2[Biphen] is
more convenient than that published in the preliminary
communication on this subject.13
(-)-Menthoxy dichlorophosphite10,21 (MenOPCl2) was
prepared by addition of (-)-menthol to a dichlo-
(13) Alexander, J . B.; La, D. S.; Cefalo, D. R.; Hoveyda, A. H.;
Schrock, R. R. J . Am. Chem. Soc. 1998, 120, 4041.
(17) Zhu, S. S.; Cefalo, D. R.; La, D. S.; J amieson, J . Y.; Davis, W.
M.; Hoveyda, A. H.; Schrock, R. R. J . Am. Chem. Soc. 1999, 121, 8251.
(18) Stevens, D. R. J . Org. Chem. 1955, 20, 1232.
(19) Aigami, K.; Inamoto, Y.; Takaishi, N.; Hattori, K.; Takatsuki,
A.; Tamura, G. J . Med. Chem. 1975, 18, 713.
(20) Voevodskaya, M. V.; Khardina, I. A.; Radchienko, S. S.;
Khudyakov, I. V. J . Appl. Chem. USSR 1985, 1459.
(21) Brunel, J .-M.; Buono, G. J . Org. Chem. 1993, 58, 7313.
(14) La, D. S.; Alexander, J . B.; Cefalo, D. R.; Graf, D. D.; Hoveyda,
A. H.; Schrock, R. R. J . Am. Chem. Soc. 1998, 120, 9720.
(15) La, D. S.; Ford, J . G.; Sattely, E. S.; Bonitatebus, P. J .; Schrock,
R. R.; Hoveyda, A. H. J . Am. Chem. Soc. 1999, 121, 11604.
(16) Weatherhead, G. S.; Ford, J . G.; Alexanian, E. J .; Schrock, R.
R.; Hoveyda, A. H. J . Am. Chem. Soc. 2000, 122, 1828.

3702 Organometallics, Vol. 19, No. 18, 2000
Alexander et al.
Ta ble 1. Rea ction Deta ils, Yield s (fr om th e Cor r esp on d in g Bis(tr ifla tes)), a n d NMR Da ta for Bip h en a n d
Bia d Com p lexesa
complex
cryst solvent
yield (%)
δ(syn)
J CH(syn)
δ(anti)
J CH(anti)
Keq
17
Mo(NArPr2)(CHCMe2Ph)[Biphen]
Mo(NArPr2)(CHCMe2Ph)[(S)-Biphen]
Mo(NArPr2)(CHEt)[Biphen]b
ether
ether
72
78
10.98
123
12.77
146
10.68
10.64
11.04
12.15
13.37
12.94
3.1
2.0
110
Mo(NArPr2)(CHMe)[Biphen]b
Mo(NArEt2)(CHCMe2Ph)[Biphen]
Mo(NArEt2)(CHCMe2Ph)[(S)-Biphen]
Mo(NArMe2)(CHCMe2Ph)[Biphen]
Mo(NArMe2)(CHCMe2Ph)[(S)-Biphen]
Mo(NArCF3)(CHCMe2Ph)[Biphen]c
Mo(NArCF3)(CHCMe3)[Biphen] c
Mo(NArCF3)(CHCMe3)[(S)-Biphen]c
Mo(NArCF3)[CHC6H4(OMe)][Biphen]d
Mo(NArCF3)[CHC6H4(OMe)][(S)-Biphen]d
Mo(NArBu2Me)(CHCMe3)[(S)-Biphen]
Mo(NArPr2)(CHCMe2Ph)[Biad]
ether
ether/i-Pr2O
ether
ether
x
pentane
x
ether
60
27
77
30
96
38
95
74
12
36
54
34
30
35
44
41
43
121
121
11.01
13.03
244
10.91
10.61
124
120
large
large
12.85
151
small
ether
pentane
pentane
pentane
pentane
ether
i-Pr2O
pentane
pentane
10.63
10.94
126
120
12.86
12.88
51
12
Mo(NArPr2)(CHCMe2Ph)[(S)-Biad]
Mo(NArEt2)(CHCMe2Ph)[(S)-Biad]
Mo(NArMe2)(CHCMe2Ph)[Biad]
Mo(NArMe2)(CHCMe2Ph)[(S)-Biad]
Mo(NArCF3)(CHCMe3)[Biad]c
11.03
11.04
121
122
12.91
100
large
10.64
120
large
Mo(NArCF3)(CHCMe3)[(S)-Biad]c
a
The reaction solvent was THF, unless otherwise noted. NMR data were obtained on ∼15 mg of complex in C6D6 at 20 °C, unless
otherwise noted. In the crystallization solvent category “x” means that the complex could not be crystallized and was isolated by simply
removing the solvent in vacuo. Keq was measured at ∼22 °C. These species were prepared on an NMR scale in toluene-d8; see text. c The
b
d
reaction solvent was toluene. The reaction solvent was diethyl ether.
The phosphate resolution developed for H2[Biphen]
also allows (S)-H2[Biad] to be isolated in moderate yield,
but so far (R)-H2[Biad] has not been isolated in pure
form. Deprotonation of H2[Biad] with excess benzylpo-
tassium followed by addition of MenOPCl2 generates the
diastereomeric mixture of phosphites (31P NMR reso-
nances at 143.6 and 138.8 ppm). Oxidation of BiadP-
(OMen) with 30% hydrogen peroxide yielded a mixture
of diastereomeric phosphates with 31P NMR resonances
at -3.29 and -5.57 ppm in benzene. (S)-BiadP(O)-
(OMen) (31P NMR δ -3.29 ppm, 98% de) could be ob-
tained by Soxhlet extraction of BiadP(O)(OMen) with
refluxing acetone. The phosphate remaining in the ace-
tone was enriched in (R)-BiadP(O)(OMen) (∼90% de),
but we were not able to increase the diastereomeric
excess of (R)-BiadP(O)(OMen) above 90%. Reduction of
(S)-BiadP(O)(OMen) with Red-Al yielded (S)-H2[Biad],
the absolute configuration of which was established in
an X-ray study of a molybdenum compound to be
described later.
Syn th esis of Molybden u m Im ido Alkyliden e Com -
p lexes. A list of all compounds prepared here can be
found in Table 1. Mo(NArPr2)(CHEt)[Biphen] and Mo-
(NArPr2)(CHMe)[Biphen] were prepared and observed
in situ as part of an NMR study to be described later.
The most facile synthesis of precursors to molybde-
num imido alkylidene complexes that contain a given
arylimido group consists of the series of steps shown in
eq 6. The only difference between this sequence and that
molybdate instead of ammonium dimolybdate in the
first step. The advantage is that significantly less
trimethylchlorosilane is required (8 vs 17 equiv). Known
species were prepared that contain N-2,6-i-Pr2C6H3
(NArPr2), N-2,6-Me2C6H3 (NArMe2), or N-2-CF3C6H4
(NArCF3) imido groups. The only new imido ligands
reported here are N-2,6-Et2C6H3 (NArEt2) and N-2,4-t-
Bu2-6-MeC6H3 (NArBu2Me). The synthesis of Mo-
(NArEt2)(CHCMe2Ph)(OTf)2(DME) (DME
) 1,2-di-
methoxyethane) was carried out without difficulty in a
manner analogous to that published for related species.
However, the reaction of 2,4-di-tert-butyl-6-methyl-
aniline with sodium molybdate, triethylamine, and
chlorotrimethylsilane generated what we propose to be
[HNEt3][Mo(NArBu2Me)2Cl3] in 35% isolated yield,
although it could not be purified by recrystallization.
The lutidinium salt [lutidineH][Mo(NArBu2Me)2Cl3]
was prepared in a 81% crystallized yield in a similar
manner and was analyzed successfully. Presumably the
increased steric bulk of the arylimido ligand pre-
vents DME coordination to give Mo(NArBu2Me)2Cl2-
(DME), but there is still sufficient room to bind one
chloride to yield [Mo(NArBu2Me)2Cl3]-. Addition of 3
equiv of neopentylmagnesium chloride to [HBase][Mo-
(NArBu2Me)Cl3] (Base ) NEt3, 2,6-lutidine) in diethyl
ether generated Mo(NArBu2Me)2(CH2-t-Bu)2 as a vis-
cous red oil which crystallized upon cooling. The 1H
NMR spectrum of Mo(NArBu2Me)2(CH2-t-Bu)2 at
room temperature did not reveal resolved methylene
protons. However, at -40 °C in toluene-d8 the diaste-
reotopic methylene protons Ha and Hb could be re-
solved as an AB pattern at 3.10 and 1.54 ppm with
J HH ) 14 Hz. These data suggest that the molecule
has C2 symmetry as a consequence of a preferred
Na2MoO4
9
(a)8 Mo(NAr)2Cl2(DME)
9
(b)8
Mo(NAr)2(CH2R)2
9
(c)8
Mo(NAr)(CHR)(OTf)2(DME) (6)
(22) Fox, H. H.; Yap, K. B.; Robbins, J .; Cai, S.; Schrock, R. R. Inorg.
Chem. 1992, 31, 2287.
(23) Oskam, J . H.; Fox, H. H.; Yap, K. B.; McConville, D. H.; O’Dell,
R.; Lichtenstein, B. J .; Schrock, R. R. J . Organomet. Chem. 1993, 459,
185.
(24) Schrock, R. R.; Murdzek, J . S.; Bazan, G. C.; Robbins, J .;
DiMare, M.; O’Regan, M. J . Am. Chem. Soc. 1990, 112, 3875.
Legend: (a) 2 ArNH2, 4 NEt3, 10 TMSCl, DME,
60-65 °C, 4-12 h; (b) 2 RCH2MgCl, ether,
12-24 h; (c) 3 HOTf, DME, -25 °C, 4-16 h
which has been published22-24 is the use of sodium

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3703
orientation of the aryl groups:
These included Mo(NArPr2)(CHCMe2Ph)[Biad], Mo-
(NArMe2)(CHCMe2Ph)[Biad], and Mo(N-Aryl)(CHCMe2-
Ph)[(S)-Biad] (N-Aryl ) NArPr2, NArEt2, NArMe2).
Toluene was employed as the reaction solvent in order
to prepare solvent-free Mo(NArCF3)(CHCMe3)[Biad]
and Mo(NArCF3)(CHCMe3)[(S)-Biad].
One of the problems with the isolation of enantio-
merically pure Biphen or Biad complexes is their
generally higher solubility relative to their racemic
analogues, which are often already relatively soluble.
As can be seen in Table 1, isolated yields of enantio-
merically pure complexes in general are lower than
those of the racemic complexes, even though crude
yields, according to proton NMR, are often relatively
high. Complexes that contain the NArBu2Me ligand
were especially soluble. In fact, spectroscopically pure
Mo(NArBu2Me)(CHCMe3)[(S)-Biphen] was prepared on
three occasions, but in only one case could it be iso-
lated from pentane by crystallization. Crystals of Mo-
(NArCF3)(CHCMe2Ph)[Biphen] can be obtained from
pentane, but Mo(NArCF3)(CHCMe3)[(S)-Biphen] so far
has not yet been purified by crystallization.
One confusing aspect of the synthesis of Mo(NArCF3)
complexes has come to light that has yet to be com-
pletely elucidated. On the basis of the presence of a
downfield resonance in the 13C NMR spectrum that is
not split by a proton, it is proposed that variable
amounts of (e.g.) Mo(NHArCF3)(CCMe3)[(S)-Biphen] are
formed under some conditions. (See the NMR section
for a more detailed discussion.) Although trialkoxoal-
kylidyne complexes of Mo and W25 are not known to
react readily with olefins, contamination of the imido
alkylidene complex by the amido alkylidyne complex in
principle could lead to spurious and irreproducible
enantioselectivities.
At 60 °C a broad singlet was observed for the neopentyl
methylene resonances as a consequence of relatively
rapid rotation of the aryl rings about the Cipso-N bond.
A slight excess of potassium hydride or a stoichio-
metric quantity of benzylpotassium was employed to
doubly deprotonate H2[Biphen] in THF. We believe that
benzylpotassium yields more reproducible results than
does potassium hydride. Then either a solution of Mo-
(N-Aryl)(CHR)(OTf)2(DME) is added to a THF solution
of BiphenK2 or vice versa. The latter procedure appears
to produce purer products. The desired complex gener-
ally was separated from KOTf by extraction into ben-
zene or pentane. Isolated yields of recrystallized prod-
ucts generally were in the 40-50% range, although in
several cases the yield was much higher. Yields also
tended to be higher in larger scale syntheses, especially
of the more soluble species. Not all yields were opti-
mized. In all formulas of compounds discussed here the
ligand should be assumed to be racemic if no specific
enantiomer is noted.
X-r a y Cr ysta llogr a p h ic Stu d ies of Mo(NAr P r 2)-
(CHCMe2P h )[(S)-Bip h en ] a n d Mo(NAr CF 3)(CH-
CMe3)[(S)-Biad](pyr idin e). X-ray crystallographic stud-
ies were carried out on single crystals of Mo(NArPr2)-
(CHCMe2Ph)[(S)-Biphen] (1) and Mo(NArCF3)(CHCMe3)-
[(S)-Biad](py) (2). The latter was prepared straightfor-
wardly by addition of pyridine to Mo(NArCF3)(CHCMe3)-
[(S)-Biad]; crystals of Mo(NArCF3)(CHCMe3)[(S)-Biad]
suitable for an X-ray study could not be obtained.
Crystallographic data, collection parameters, and re-
finement parameters for both complexes are given in
Table 2, while selected bond lengths, angles, and
dihedral angles are given in Table 3. The S configura-
tions of the Biphen and Biad ligands were established
during the solution process using the usual criteria.
The molecular structure of syn-Mo(NArPr2)(CHCMe2-
Ph)[(S)-Biphen] along with the atom-labeling scheme
is shown in Figure 1. (The syn isomer of Mo(NArPr2)-
(CHCMe2Ph)[(S)-Biphen] is the major isomer in solu-
tion; see below.) This structure is related to that of
several other molybdenum and tungsten imido alkyli-
dene bis(alkoxide) and biphenolate complexes.9,10,26 The
(S)-Biphen bite angle O(1)-Mo-O(2) (127.0°) and di-
hedral angle between the two aryl rings of the Biphen
backbone (C(31)/C(32)/C(42)/C(41) ) 102.2°) are es-
sentially identical with the corresponding values in syn-
Complexes in which the arylimido group contained
only one o-CF3 substituent could not be prepared in good
yield using potassium hydride for deprotonation of H2-
[Biphen]; the benzene extract of the reaction mixture
contained significant amounts of H2[Biphen] in addition
to the desired product. However, a pure product was
obtained when H2[Biphen] was deprotonated with 2
equiv of benzylpotassium. Base-free Mo(NArCF3)-
(CHCMe3)[Biphen] could be prepared in 38% yield
when toluene was employed, but Mo(NArCF3)(CHCMe3)-
[(S)-Biphen] could not be crystallized. (If THF is em-
ployed as the reaction solvent and diethyl ether as the
solvent of crystallization, THF and diethyl ether are
found in the sample, most likely as a consequence of
their binding to the sterically more accessible metal; see
later.) Addition of a slight excess of 2-methoxystyrene
to Mo(NArCF3)(CHCMe2Ph)[Biphen] generated a ben-
zylidene complex, Mo(NArCF3)(CH-o-MeOC6H4)[Biphen],
which precipitated from the reaction mixture in 74%
yield. At first glance formation of this type of complex
would appear to be a good approach to less soluble
and more crystalline pseudo-six-coordinate alkylidene
complexes. Unfortunately, if too much stilbene is gener-
ated via homometathesis of the styrene, the desired
product is difficult to separate from the stilbene by
crystallization.
Racemic and optically pure complexes that contain
the Biad ligand were prepared by methods analogous
to those employed to prepare the Biphen complexes.
(25) Murdzek, J . S.; Schrock, R. R. High Oxidation State Alkylidyne
Complexes; VCH: New York, 1988.
(26) Feldman, J .; Schrock, R. R. Prog. Inorg. Chem. 1991, 39, 1.

3704 Organometallics, Vol. 19, No. 18, 2000
Alexander et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta , Collection
P a r a m eter s, a n d Refin em en t P a r a m eter s for
Mo(NAr P r 2)(CHCMe2P h )[(S)-Bip h en ] (1) a n d
Mo(NAr CF 3)(CHCMe3)[(S)-Bia d ](p y) (2)a
1
2
empirical formula
fw
C
46H61MoNO2
C53H63F3MoN2O2
912.99
755.90
cryst dimens (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.20 × 0.20 × 0.20 0.15 × 0.15 × 0.30
monoclinic
P21
orthorhombic
P212121
12.948(3)
28.452(6)
30.376(6)
90
10.7064(3)
13.5262(5)
14.8726(5)
90
R (deg)
â (deg)
103.8060(10)
90
90
90
γ (deg)
V (Å3), Z
2091.58(12), 2
1.200
11191(4), 8
1.084
D
calcd (Mg/m3)
θ range (deg)
1.41-23.24
1.34-20.00
scan type
ω
ω
temp (K)
173(2)
170(2)
no. of rflns collected
no. of indep rflns
8659
5360
(Rint ) 0.0547)
452
33 558
10 427
(Rint ) 0.1033)
543
F igu r e 1. ORTEP drawing of the structure of syn-Mo(N-
2,6-i-Pr2C6H3)(CHCMe2Ph)[(S)-Biphen] (1).
no. of params
R1 (I > 2σ(I), all data)
0.0587, 0.0634
0.1119, 0.1312
0.2789, 0.2991
1.199
wR2 (I > 2σ(I), all data) 0.1445, 0.1555
GOF
1.191
a
Data were collected on a Siemens SMART/CCD diffractometer
using Mo KR (0.710 73 Å) radiation, and the structure was solved
using a full-matrix least-squares refinement on F2. No absorption
correction was applied.
Ta ble 3. Selected In ter a tom ic Dista n ces (Å)
a n d An gles (d eg) for th e Non -Hyd r ogen Atom s in
1 a n d 2
2A and 2B
1
2A
2B
Bond Lengths
1.999(5) Mo-O(1)
2.006(5) Mo-O(2)
1.885(10) Mo-C(40)
1.738(6) Mo-N(1)
1.407(9) Mo-N(2)
1.489(13) C(40)-C(41)
1.385(9) O(1)-C(16)
1.366(9) O(2)-C(22)
Mo-O(1)
Mo-O(2)
Mo-C(1)
Mo-N
N-C(11)
C(1)-C(2)
O(1)-C(31)
O(2)-C(41)
2.020(11) 2.022(10)
1.986(10) 1.962(13)
1.90(2)
1.70(2)
1.87(2)
1.73(2)
2.276(12) 2.270(13)
1.51(2)
1.35(2)
1.36(2)
1.49(3)
1.36(2)
1.35(2)
Bond Angles
N-Mo-O(1)
N-Mo-O(2)
N-Mo-C(1)
O(1)-Mo-O(2) 127.0(2) O(1)-Mo-O(2)
O(1)-Mo-C(1) 96.9(3)
110.2(2) N(1)-Mo-O(1)
101.2(6) 101.5(6)
136.7(7) 133.7(6)
107.9(3) N(1)-Mo-O(2)
105.2(3) N(1)-Mo-C(40) 107.1(8) 113.3(9)
88.8(4) 90.3(5)
Mo-N(1)-C(38) 167.3(14) 148.2(12)
O(2)-Mo-C(1) 107.0(3) Mo-C(40)-C(41) 148.0(13) 148(2)
Mo-N-C(11) 169.0(6) N(2)-Mo-O(1) 165.1(4) 167.0(5)
Mo-C(1)-C(2) 143.8(7) O(1)-Mo-C(40) 95.3(6)
F igu r e 2. ORTEP drawing of the structure of syn-Mo(N-
2-CF3C6H4)(CHCMe3)[(S)-Biad](pyridine) (2A).
91.0(7)
83.4(6)
77.9(5)
98.2(7)
Mo-O(1)-C(31) 97.1(4)
Mo-O(2)-C(41) 96.8(4)
N(1)-Mo-N(2)
N(2)-Mo-O(2)
N(2)-Mo-C(40) 95.3(6)
85.6(6)
77.4(4)
group points toward the alkylidene (2B). The major
difference between the two molecules is that the imido
group is considerably more bent in 2B, as a consequence
of steric repulsion between the trifluoromethyl group
and the alkylidene ligand. We will discuss only 2A here.
The pyridine is found to have added to the C(40A)/
N(1A)/O(2A) face to give one of the two possible dia-
stereomers of the syn isomer; the resulting N(2A)-
Mo(1)-O(1A) angle is 165.1(4)°. This species is analogous
to the mirror image of the diastereomer of syn-Mo-
(NArPr2)(CHCMe2Ph)[(R)-BINO(TRIP)2](py) (where (R)-
BINO(TRIP)2 is the dianion of (R)-3,3′-bis(2,4,6-triiso-
propylphenyl)-2,2′-dihydroxy-1,1′-dinaphthyl).17 The Biad
“bite angle” (O(1A)-Mo-O(2A) ) 88.8(4)°), ModCR-Câ
angle (Mo(1)-C(40A)-C(41A) ) 148.0(13)°), ModN-C
Dihedral Angles
C(31)/C(32)/
C(42)/C(41)
102.2
C(16A)/C(15A)/
C(17A)/C(22A)
72.3
Mo(NArMe2)(CHCMe2Ph)[t-Bu4Me2Biphen] ([t-Bu4Me2-
Biphen] ) 6,6′-dimethyl-3,3′,5,5′-tetra-tert-butyl-1,1′-
biphenyl-2,2′-diolate; 123.5 and 102.5°, respectively).10
Other distances and angles in syn-Mo(NArPr2)(CHCMe2-
Ph)[(S)-Biphen] are virtually identical with what they
are in syn-Mo(NArMe2)(CHCMe2Ph)[t-Bu4Me2Biphen].
Yellow blocks of Mo(NArCF3)(CHCMe3)[(S)-Biad](py)
(Figure 2) were grown from a mixture of ether and
pyridine. The unit cell contains two independent mol-
ecules, one in which the CF3 group points away from
the alkylidene (2A; Figure 2), and one in which the CF3

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3705
Ta ble 4. 1H NMR Lin e Wid th s, Equ ilibr iu m
Con sta n ts, a n d Ra te Con sta n ts ka s a n d ksa , for syn
a n d a n ti Isom er s of Mo(NAr )(CHCMe2P h )[Bip h en ]
in Tolu en e-d 8 betw een -10.9 a n d 68.2 °C
temp (°C)
ωsyn (Hz)
ωanti (Hz)
kas (s-1
)
ksa (s-1
)
Keq
68.2
59.4
50.2
40.7
31.7
20.7
10.5
-0.3
-10.9
7.639
4.103
2.610
1.870
1.548
1.172
1.365
1.615
1.338
46.529
32.298
13.034
9.243
5.108
3.060
2.389
2.314
1.974
145.18
100.47
39.95
28.04
15.05
8.61
6.50
6.27
5.20
12.52
8.21
3.08
2.02
0.95
0.50
0.32
0.26
0.18
11.6
12.2
13.0
13.9
15.9
17.0
20.3
24.2
29.5
The proton NMR spectrum of Mo(NArPr2)(CHCMe2-
Ph)[Biphen] in the alkylidene region is temperature
dependent (Figure 3). At room temperature resonances
for the two alkylidene isomer are sharp. The 13C
satellites on the HR resonance for the syn isomer can
be seen clearly up to ∼70 °C, and the syn HR resonance
(more than the anti) shifts slightly upfield at higher
temperatures. The 13C satellites cannot be seen for the
anti HR resonance as a consequence of its relatively low
intensity. The anti HR resonance begins to broaden by
40 °C, and by 80 °C it has almost disappeared into the
baseline, without shifting significantly. This behavior
is fully reversible, independent of concentration, and
fully consistent with interconversion of syn and anti
isomers at a rate of the order of the NMR time scale.
The rates of interconversion for several complexes were
measured and are discussed later. The syn and anti
alkylidene resonances do not change appreciably when
the sample is cooled below 20 °C.
The variable-temperature proton NMR spectrum of
Mo(NArPr2)(CHCMe2Ph)[Biphen] in THF-d8 is shown
in Figure 4. At -80 °C four alkylidene resonances are
observed at 13.97, 13.92, 12.81, and 12.39 ppm in a ratio
of 54.9:11.8:4.5:1. We assign the resonances at 13.97 and
13.92 ppm to the two diastereomeric THF adducts of
the anti isomer and the relatively weak resonances at
12.81 and 12.39 ppm to the two diastereomeric THF
adducts of the syn isomer. Note that each set is 1-2
ppm downfield of the anti and syn resonances for the
“base-free” species in toluene-d8 (Figure 3). The two
diastereomers of the syn THF adduct begin to intercon-
vert rapidly on the NMR time scale at ca. -50 °C as a
consequence of THF dissociating rapidly from each syn
THF adduct. At higher temperatures the average syn
resonance moves upfield toward the resonance for the
“base-free” syn alkylidene resonance near 11 ppm as the
equilibrium between syn THF adducts and base-free syn
species shifts toward the base-free species. Also, the
equilibrium between anti and syn alkylidene isomers
shifts toward the syn isomer between -40 and 40 °C.
At 20 °C the syn alkylidene is largely base-free, accord-
ing to the position of the syn alkylidene resonance near
11 ppm. In contrast, the anti THF adducts equilibrate
less readily (-40 to -30 °C), but the average does not
shift appreciably toward the position of the “base-free”
anti resonance near 13 ppm in toluene-d8. According to
these data we can say that the anti alkylidene complex
binds THF much more strongly than the syn alkylidene
complex and that the ratio of the anti THF adduct and
1
F igu r e 3. Variable-temperature H NMR spectra of Mo-
(NArPr2)(CHCMe2Ph)(Biphen) in toluene-d8.
angle (Mo(1)-N(1A)-C(38A) ) 167.3(14)°), and dihedral
angle between the aryl rings (C(16A)/C(15A)/C(17A)/
C(22A) ) 72.3°) are all similar to the corresponding
angles in syn-Mo(NArPr2)(CHCMe2Ph)[(R)-BINO(TRIP)2]-
(py) (86.5(3), 149.5(10), 158.6(8), and 60.0°, respectively).
An X-ray structure of a third adduct of this type, anti-
Mo(NArMe2)(CHCMe2Ph)[BINO(Ph)2](THF),10 reveals
similar analogous angles, except for the ModCR-Câ
angle of 128.1(6)°, which is characteristically smaller26
as a consequence of the anti conformation of the alkyli-
dene ligand. A smaller ligand “bite angle” and smaller
dihedral angle between the aryl rings in five-coordinate
adducts versus four-coordinate syn-Mo(NArPr2)(CHCMe2-
Ph)[(S)-Biphen] and syn-Mo(NArMe2)(CHCMe2Ph)[t-
Bu4Me2Biphen]10 are a direct consequence of the man-
ner in which the biaryloxide ligand is bound (axial/
equatorial) in pseudo-trigonal-bipyramidal adducts. The
arylimido ring is approximately coplanar with C(40A)
and C(41A) of the neopentylidene ligand, and the CF3
group points away from the syn neopentylidene ligand.
The arylimido ligand in Mo(NArCF3)(CHCMe3)[(S)-
Biad](py) is approximately linear, despite the monosub-
stituted nature of the aryl ring. Like other arylimido
rings in related adducts, the aryl ring lies approximately
in the equatorial plane of the trigonal bipyramid.
P r oton NMR Stu d ies. The 1H NMR spectrum of Mo-
(NArPr2)(CHCMe2Ph)[Biphen] in toluene-d8, which is
typical for a solvent-free complex in this study, revealed
alkylidene HR resonances for the two possible isomers
(Table 1; Figure 3). The sharp HR resonance at 10.98
ppm (at 22 °C) can be ascribed to the syn isomer on the
basis of the J CH value of 123 Hz. (In this work coupling
constants typically were determined in a high signal-
to-noise (∼1000 transients) spectrum by observing the
13C satellites (1.1% total area); in several cases they
were confirmed in a proton-coupled 13C NMR spectrum.)
A second (weak) resonance at 12.77 ppm (in C6D6) could
be ascribed to HR for the anti isomer on the basis of a
J CH value of 146 Hz. At 20.7 °C (in toluene-d8) the ratio
of these resonances ([syn]/[anti] ) Keq) was found to be
17.0. The value for Keq varied from 29.5 at -10.9 °C to
11.6 at 68.2 °C (Table 4). A plot of ln Keq versus 1/T
gave values of ∆H° ) - 2.0(0.3) kcal/mol and ∆S° )
-1.0(0.7) eu, with ∆G°298 ) -1.7(0.3) kcal/mol. Other
species reported here behaved similarly, as did Mo-
(NArPr2)(CHCMe2Ph)(DIPP)2 (DIPP ) O-2,6-i-Pr2C6H3),
a compound that has been studied previously.27
(27) Schrock, R. R.; Crowe, W. E.; Bazan, G. C.; DiMare, M.;
O’Regan, M. B.; Schofield, M. H. Organometallics 1991, 10, 1832.

3706 Organometallics, Vol. 19, No. 18, 2000
Alexander et al.
a smaller substituent on the alkylidene allows a larger
amount of the anti isomer to be formed. Similar experi-
ments involving cis-2-butene and Mo(NArPr2)(CHCMe2-
Ph)[Biphen] are consistent with this proposal, Keq for
syn-Mo(NArPr2)(CHMe)[Biphen] and anti-Mo(NArPr2)-
(CHMe)[Biphen] being 2.0 (Table 1). The equilibrium
constant (K ) [Mo(CHMe)][PhMe2CHdCHMe]/[Mo-
(CHCMe2Ph)][MeCHdCHMe]) was measured in this
case and found to be 9.1 × 10-4 at 20 °C.
Decreasing the size of the substituents in the ortho
positions of the disubstituted imido ligand led to forma-
tion of more syn isomer, i.e, Keq ) 110 for Mo(NArEt2)-
(CHCMe2Ph)[Biphen] and 244 for Mo(NArMe2)(CHCMe2-
Ph)[Biphen] (Table 1). The Keq value for Mo(NArBu2-
Me)(CHCMe2Ph)[Biphen] was 51, which suggests that
the steric influence of the NArBu2Me group is roughly
between that of the NArPr2 and NArEt2 groups. (One
might expect some “weighted average” steric influence
in view of the presence of a methyl group in one ortho
position and a tert-butyl group in the other, depending
on the percentage of different rotamers that result from
restricted rotation about the N-Cipso bond.) The value
of Keq for Mo(NArCF3)(CHCMe2Ph)[Biphen] could not
be measured readily, although it was clear that the
magnitude was large (>300). Apparently the NArCF3
group is operationally the smallest of the imido groups,
at least as measured in terms of the syn/anti equilibri-
um. Only the anti isomer is observed in the case of Mo-
(NArCF3)[CHC6H4(OMe)][Biphen] (HR at 12.85 ppm,
J CH ) 151 Hz), as expected as a consequence of
coordination of the o-methoxy group to the metal. The
ability of donors to stabilize the anti isomer has been
known for some time in the literature.29
1
F igu r e 4. Variable-temperature H NMR spectra of Mo-
(NArPr2)(CHCMe2Ph)[Biphen] in THF-d8.
NMR spectra of the Biad complexes that contain the
NArPr2 and NArEt2 imido groups are similar to those
for the Biphen complexes, and the values for Keq are
roughly the same. However, essentially only the syn HR
resonance is observable in the spectrum of Mo(NArCF3)-
(CHCMe2Ph)[Biad] and Mo(NArMe2)(CHCMe3)[Biad].
Relatively facile interconversion of syn and anti
isomers of molybdenum imido alkylidene complexes
has been reported in the literature for two aryloxide
complexes, Mo(NArPr2)(CHCMe2Ph)(DIPP)2 and Mo-
(NArPr2)(CHCMe2Ph)(O-2-t-BuC6H4)2.27 The reported
activation parameters for their interconversion, deter-
mined by line shape analysis, are listed in Table 5. A
redetermination of the overall rate constant for inter-
conversion of isomers of Mo(NArPr2)(CHCMe2Ph)-
(DIPP)2 at -42 °C using line shape analysis gave k )
3.81 × 10-4 s-1, which is faster than the literature
the syn, largely base-free, species near room tempera-
ture is approximately 3:1. Note that at the highest
temperature in Figure 4, the interconversion of anti and
syn isomers is still relatively slow on the NMR time
scale. (It is believed that only base-free syn and anti
isomers can interconvert readily and that their inter-
conversion therefore is retarded in the presence of a
base that can bind to the metal.26) The behavior of Mo-
(NArPr2)(CHCMe2Ph)[Biphen] in THF-d8 is relevant to
asymmetric metathesis of substrates that contain an
ether functionality,13-17 although the details are still
obscure at this stage.
Addition of trans-3-hexene to Mo(NArPr2)(CHCMe2-
Ph)[Biphen] at 22 °C generated a mixture of syn- and
anti-Mo(NArPr2)(CHCMe2Ph)[Biphen], syn- and anti-
Mo(NArPr2)(CHEt)[Biphen], cis- and trans-PhMe2CCHd
CHEt, and cis- and trans-3-hexene. Approximately a 20-
fold excess of trans-3-hexene was required in order to
generate a mixture that contained ∼5% Mo(NArPr2)-
(CHEt)[Biphen]. It was not possible to isolate Mo-
(NArPr2)(CHEt)[Biphen], because its concentration was
too low to allow it to be crystallized selectively from the
mixture, and because removal of the volatile compo-
nents of such a mixture resulted in re-formation of
exclusively syn- and anti-Mo(NArPr2)(CHCMe2Ph)-
[Biphen] through the back-reaction of syn- and anti-Mo-
(NArPr2)(CHEt)[Biphen] with PhMe2CCHdCHEt. How-
ever, it is interesting to note that the ratio of syn-Mo-
(NArPr2)(CHEt)[Biphen] to anti-Mo(NArPr2)(CHEt)-
[Biphen] is 3.1 at 22 °C (Table 1), which suggests that
value (k ) 1.35 × 10-4 s-1 27,28
by a factor of ∼3. The
)
rate constant at -42 °C was determined using spin
saturation transfer and found to be 2.61 × 10-5 s-1
which is slower than the literature value by a factor
of ∼4. (The discrepancy between line shape analysis
and the spin saturation transfer experiments, in part,
may be due to the assumption that T1 was the same for
both isomers; see Experimental Section for a further
discussion.)
,
The activation parameters for interconversion of syn
and anti isomers of Mo(NArPr2)(CHCMe2Ph)[Biphen]
(28) Oskam, J . H.; Schrock, R. R. J . Am. Chem. Soc. 1993, 115,
11831.
(29) Fox, H. H.; Lee, J .-K.; Park, L. Y.; Schrock, R. R. Organome-
tallics 1993, 12, 759.

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3707
Ta ble 5. Activa tion P a r a m eter s by Lin e Sh a p e An a lysis (lsa ) a n d Sp in Sa tu r a tion Tr a n sfer (sst)
b
complexa
technique
∆Gq
∆Hq b
∆Sq c
298
Mo(NArPr2)(CHCMe2Ph)[Biphen]
Mo(NArPr2)(CHCMe2Ph)[Biphen]
Mo(NArPr2)(CHCMe2Ph)[Biad]
Mo(NArPr2)(CHCMe2Ph)(DIPP)2
Mo(NArPr2)(CHCMe2Ph)(DIPP)2
lsa
sst
sst
lsa
sst
lsa
lsa
16.0(2.3)
16.2(1.6)
16.7(3.6)
17.2(1.5)
17.6(1.4)
17.5(1)
12.5(1.2)
15.1(0.8)
14.4(1.8)
16.2(0.8)
20.1(0.7)
17.8(1.0)
22.8(2.1)
-11.6(3.7)
-4.0(2.8)
-7.4(6.2)
-3.4(2.4)
8.3(2.3)
d
Mo(NArPr2)(CHCMe2Ph)(DIPP)2
Mo(NArPr2)(CHCMe2Ph)(O-2-t-BuC6H4)2
1.0(2.7)
15(6)
d
18.3(1)
a
b
d
Amount of complex ∼15 mg in toluene-d8. Units in kcal/mol. c Units in eu. Values from ref 27.
were determined by both line shape analysis (lsa) and
spin saturation transfer (sst) (Table 5). (In lsa experi-
ments only rate constants that were obtained at room
temperature or above yielded a linear Eyring plot.) The
values from the two methods largely agree and are
similar to those found for Mo(NArPr2)(CHCMe2Ph)-
(DIPP)2. The activation parameters for interconversion
of syn and anti isomers of Mo(NArPr2)(CHCMe2Ph)-
[Biad] were found to be consistent with the other
values shown in Table 5. The most important conclusion
to be drawn from these data is that relatively rapid
interconversion of isomers does not appear to depend
on whether the aryloxide in question is bidentate or
monodentate. It is also important to note that the rates
of interconversion for aryloxide species near room
temperature are 4-5 orders of magnitude faster than
the rate of conversion of the syn isomer of Mo-
(NArPr2)(CHCMe2Ph)[OCMe(CF3)2]2 to the anti isomer
(where Keq is ∼2500) and approximately the same as
the estimated rate of conversion of the syn isomer of
Mo(NArPr2)(CHCMe2Ph)[OCMe3]2 to the anti isomer.28
If the stoichiometry is carefully controlled, the syn-
thesis of Mo(NArCF3) complexes yields samples that
are essentially pure syn, according to proton NMR
studies, the notable exception being Mo(NArCF3)-
(CH-o-MeOC6H4)[Biphen]. It also can be shown readily
that syn complexes which contain the N-2-CF3C6H4
ligand bind THF more readily than syn complexes which
contain N-2,6-R2C6H3 ligands, presumably as a conse-
quence of the overall less crowded coordination sphere.
However, occasionally samples that contain a resonance
near 11.7 ppm are produced. For example, the sample
shown in Figure 5 contains about 5% of this “impurity.”
These spectra at first glance appear to be characteristic
of mixtures of syn and anti isomers. However, the
resonance near 11.7 ppm broadens and shifts upfield
upon raising the temperature, unlike a typical base-free
anti resonance. Furthermore, the 11.7 ppm resonance
varies in intensity from sample to sample. Finally, a
singlet resonance is observed at 315.7 ppm in the carbon
NMR spectrum in an amount that correlates with the
intensity of the 11.7 ppm resonance in the proton NMR,
a region that is characteristic of alkylidyne R-carbon
atoms in high-oxidation-state Mo and W complexes.25
Therefore, we propose that the resonance near 11.7 ppm
is actually the NH proton in Mo(NHArCF3)(CCMe2Ph)-
[Biphen], which is formed as an impurity during the
synthesis of Mo(NArCF3)(CHCMe2Ph)[Biphen]. How-
ever, once Mo(NHArCF3)(CCMe2Ph)[Biphen] and Mo-
(NArCF3)(CHCMe2Ph)[Biphen] are formed, they cannot
be interconverted cleanly in a base-catalyzed (NEt3 or
K2Biphen) reaction. Other compounds discussed here
did not contain significant amounts of an analogous
amido alkylidyne complex, although small amounts of
impurities that have one or more resonances in the
F igu r e 5. Variable-temperature 1H NMR spectra of
Mo(NArCF3)(CHCMe2Ph)[Biphen] in toluene-d8.
alkylidene region of the proton NMR spectrum are often
observed in crude samples. A possible mechanism of
forming the amido alkylidyne complex is presented in
the Discussion.
Discu ssion
In general, complexes of the type Mo(NR)(CHR′)-
(OR′′)2 cannot be isolated unless R is a (bulky) substi-
tuted aryl group, R′ is CMe3 or CMe2Ph, and R′′ is a
bulky group such as CMe3, CMe(CF3)2, a 2,6-disubsti-
tuted aryl group, etc. The presence of four bulky groups
discourages bimolecular decomposition of an alkylidene
complex of this type.26 Complexes that contain a smaller
R′ group, e.g., an ethylidene complex, can be observed
in solution but cannot be isolated. This type of alky-

3708 Organometallics, Vol. 19, No. 18, 2000
Alexander et al.
lidene complex is a 14-electron species if donation of an
electron pair from the imido ligand is included and
donation of π electron density from the oxygen atoms
is ignored. Five-coordinate, 16-electron adducts are
comparatively stable toward bimolecular decomposition,
but the base must be lost to generate the 14-electron
four-coordinate species in order for the alkylidene to
react with an olefin. The complexes prepared here fall
into the category of sterically hindered Mo(NR)(CHR′)-
(OR′′)2 species as a consequence of tert-butyl or ada-
mantyl groups being present in the 3- and 3′-positions
of the biphenolate ligand. Bulky groups in the 3- and
3′-positions are highly desirable in order to transmit
chiral information efficiently to an incoming olefin,
which is believed to bind to the metal first on a CNO
face of the pseudo tetrahedron, and also in order to
discourage coordination of a base such as THF, which
would behave as a competitive inhibitor in reactions
involving olefins. Several of the Biphen complexes
reported here in fact are highly efficient for enantiose-
lective ring-closing, ring-opening/ring-closing, and ring-
opening/cross-metathesis reactions.13-17 A comparison
of the rates and efficiencies of enantiomerically pure
Biphen and Biad complexes for asymmetric metathesis
of a variety of substrates will be presented in due course
elsewhere.
One of the important issues in reactions involving Mo-
(NR)(CHR′)(OR′′)2 complexes is the relative reactivity
of syn and anti isomers and their rate of interconversion.
We have found that syn and anti isomers interconvert
readily in biphenolate complexes, as they do in mono-
dentate phenoxide complexes. We believe this is a more
desirable circumstance than one in which syn to anti
conversion is slow: e.g., in Mo(NArPr2)(CHCMe2Ph)-
[OCMe(CF3)2]2 (∼10-5 s-1 at room temperature).30 The
relative reactivities of syn and anti isomers of course
depend on the nature of the imido ligand and the
substrate in question. However, if syn and anti isomers
interconvert readily, as found here, then the relative
reactivities become difficult to determine experimen-
tally. Although it was estimated that the relatively
inaccessible anti form of Mo(NArPr2)(CHCMe2Ph)-
[OCMe(CF3)2]2 was several orders of magnitude more
reactive than the syn form toward one specific substrate
(2,3-bis(trifluoromethyl)norbornadiene), we cannot as-
sume that to be the case in biphenolate complexes, even
though evidence suggests that the anti isomer in general
binds a base more strongly than the syn isomer.
Therefore, at this stage we are uncertain whether the
difference in reactivities of syn and anti isomers of the
Biphen and Biad complexes is large or not.
It is worth pointing out some differences between the
biphenolate complexes reported here and a complex (A)
that contains a chiral chelating alkoxide which forms a
pseudo-nine-membered ring with the molybdenum (NAr
) N-2,6-i-Pr2C6H3).31-33 This complex appears to be
much less successful in enantioselective ring-closing
metathesis reactions than the complexes reported here.
Perhaps the most obvious difference is the large,
relatively nonrigid nature of the diolate ring and the
relatively remote chiral centers δ with respect to the
metal center. This particular chiral ligand perhaps was
chosen in order to mimic the high metathesis activity
of Mo(NArPr2)(CHCMe2Ph)[OCMe(CF3)2]2. Although
the rate of interconversion of syn and anti isomers in A
was not determined, it seems likely to be as slow, as it
is in Mo(NArPr2)(CHCMe2Ph)[OCMe(CF3)2]2 itself. If
the more reactive anti isomer is also more enantiose-
lective, then enantioselectivity would suffer if it could
not be accessed readily.
One of the characteristics of the compounds reported
here that contain a 2,6-disubstituted arylimido ligand
is that they bind THF more weakly than imido neo-
phylidene analogues that contain the dianion of 3,3′-
bis(2,4,6-triisopropylphenyl)-2,2′-dihydroxy-1,1′-dinaph-
thyl17 ([BINOTrip2]2-). In both systems, however, THF
binds more strongly to the anti isomer than to the syn
isomer, according to NMR studies. Dissociation of THF
from the anti isomer is relatively fast at 60 °C in
[BINOTrip2]2- species. Recent results concerning imido
neophylidene initiators that contain the dianion of
3,3′,6,6′-tetra-tert-butyl-2,2′-dihydroxy-1,1′-dinaphthyl
suggest that they too will not readily bind THF.34
Therefore, it is the tert-butyl groups in particular in
either biphenolate or binaphtholate ligands that lead
to somewhat weaker binding of THF, probably largely
for steric reasons. A stronger base such as pyridine will
bind even to a Biad complex, as reported here, and
complexes that contain the smaller N-o-CF3C6H4 ligand
will also bind THF more strongly than complexes that
contain N-2,6-R2C6H3 ligands.
One of the potential complications of synthesis of
imido alkylidene complexes of the type reported here,
especially complexes that contain imido ligands that are
not substituted in the 2- and 6-positions, is formation
of an amido alkylidyne complex. It is interesting to note
that the first imido alkylidene complexes were prepared
from neopentylidyne amido complexes by a base-
catalyzed migration of a proton from the amido ligand
to the alkylidyne carbon.26 Proton transfer does not take
place readily once alkoxides have been attached to the
The situation becomes even more complex when one
considers that even weakly basic functionalities within
a substrate involved in a metathesis reaction (e.g.,
ethers) could bind to the metal and inhibit reaction of
an olefin with one of the two isomers present. Perhaps
a more interesting possibility is that a donor and an
olefin that are present in the substrate could both bind
to the 14-electron alkylidene complex (if π donation from
the alkoxide to the metal is not a consideration) and
thereby accelerate the reaction between an alkylidene
ligand and an incoming substrate. Attempts to answer
some of these intriguing questions are in the offing.
(31) Fujimura, O.; Grubbs, R. H. J . Org. Chem. 1998, 63, 824.
(32) Fujimura, O.; de la Mata, F. J .; Grubbs, R. H. Organometallics
1996, 15, 1865.
(33) Fujimura, O.; Grubbs, R. H. J . Am. Chem. Soc. 1996, 118, 2499.
(34) Zhu, S. S. Unpublished results.
(30) Oskam, J . H.; Schrock, R. R. J . Am. Chem. Soc. 1992, 114, 7588.

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3709
35% dispersion in mineral oil; it was washed repeatedly with
pentane and dried in vacuo. Isopropyl ether (Aldrich) was
distilled from sodium and stored over 4 Å molecular sieves
for 1 day prior to use. H2[Biphen]12 and 2-tert-butyl-4,5-
dimethylphenol18 were prepared by modified literature proce-
dures (see below). 2-(1-Adamantyl)-4,5-dimethylphenol was
prepared by the literature procedure.20 All other reagents were
used as received from Lancaster Synthesis, Inc., or Aldrich
Chemical Co., Inc. C6D6 and toluene-d8 (Cambridge Isotope
Laboratories) were degassed with dinitrogen and dried over 4
Å molecular sieves for approximately 1 day prior to use.
Elemental analyses were performed in our laboratories on a
Perkin-Elmer 2400 CHN analyzer or by H. Kolbe Mikroana-
lytisches Laboratorium (Mu¨hlheim an der Ruhr, Germany).
3,3′-Di-ter t-bu tyl-5,5′,6,6′-tetr am eth yl-1,1′-biph en yl-2,2′-
d iol (H2[Bip h en ]). (This method is a variation of that
reported in the literature.12) Potassium dichromate (54 g, 0.184
mol) in sulfuric acid (100 mL) and water (300 mL) was slowly
added over a period of 10 min to an acetic acid (550 mL)
solution of 3,4-dimethyl-2-tert-butylphenol (137 g, 0.544 mol)
at 60 °C. The color changed from orange to green, and a tan
precipitate formed. The reaction mixture was then heated for
1 h at 60 °C, and cooled to room temperature. The reaction
mixture was filtered, and the brown solid was washed with
water (2 × 250 mL) and methanol (3 × 200 mL). The off-white
solid was dried in vacuo to give H2[Biphen] (54.4 g, 50%): 1H
NMR (CDCl3) δ 7.12 (s, 2, Ar), 4.79 (s, 2, OH), 2.24 (s, 6, Me),
1.80 (s, 6, Me), 1.38 (s, 18, t-Bu); 13C{1H} NMR δ 151.24,
134.60, 134.13, 127.73, 128.79, 121.64, 35.15, 30.19. 20.46,
16.35.
(Men th oxy)P Cl2 (Men OP Cl2).10 A solution of (-)-menthol
(78 g, 0.50 mol) in CH2Cl2 (50 mL) was added dropwise to
a solution of phosphorus trichloride (137.5 g, 1.0 mol) in
CH2Cl2 (50 mL) over 30 min. The mixture was stirred at room
temperature for 1 h under a nitrogen atmosphere before
removing the volatile components by vacuum transfer (room
temperature, 100 mTorr). Purification by short-path vacuum
distillation yielded MenOPCl2 (bp 62 °C/150 mTorr): 31P{1H}
NMR (THF) δ 177.4.
Bip h en P (OMen ). Triethylamine (30 mg, 0.3 mmol) and H2-
[Biphen] (35 mg, 0.1 mmol) were dissolved in THF (3 mL).
MenOPCl2 (26 mg, 0.1 mmol) was added, and the reaction
mixture stood at room temperature for 18 h. The precipitate
was removed by filtration and dissolved in THF for NMR
examination: 31P{1H} NMR (THF) δ 143.7 ((R)-BiphenP-
(OMen)), 138.0 ((S)-BiphenP(OMen)).
metal, but only in dihalide or bis(triflate) complexes
where it is arguably more acidic. At the present time
we propose that the amido alkylidyne impurity that
forms in N-2-CF3C6H4 complexes is formed at an early
stage in the synthesis before the triflates are completely
substituted by the biphenolate and that it is a phenolate
base that moves the proton. We hope to gather more
information about proton transfer reactions of this type
in future studies and determine whether amido alkyli-
dyne complexes are, in fact, relatively inert toward
olefins, as brief observations of related amido alkylidyne
complexes in the past have suggested.
Many of the enantiomerically pure catalysts described
here cannot be prepared readily in a high yield, in part
because of low yields upon crystallization. The yields
of enantiomerically pure Biad complexes reported here,
for example, currently are unacceptable. However,
another disadvantage in the long run is that the ligand
must be resolved. Therefore, it would be useful if more
efficient methods of resolving Biphen and (especially)
Biad ligands could be found. In the meantime, in general
we will continue to search for new diolate/imido ligand
combinations that will allow enantiomerically pure
catalysts to be isolated relatively easily. The long-term
goal will be to prepare and compare a number of
catalysts for efficient enantioselectivity, which on the
basis of ongoing studies we already know can vary
dramatically with the substrate. Ultimately we hope to
test a variety of catalysts, substrates, and reaction types
using high throughput screening techniques. Efforts
aimed in these directions are currently under way.
Exp er im en ta l Section
Gen er a l P r oced u r es. Unless otherwise noted, all experi-
ments were performed in the absence of oxygen and moisture
in a dinitrogen-filled glovebox or using standard Schlenk
procedures. Diethyl ether, THF, and pentane were degassed
with dinitrogen and passed through two 1 gal columns of
activated alumina.35 Toluene and benzene were distilled from
sodium benzophenone ketyl. Methylene chloride was distilled
from calcium hydride. NMR spectra were acquired at 75.4 or
1
125.8 MHz for 13C and 300 or 500 MHz for H. 1H NMR spectra
R esolu t ion of (R)- a n d (S)-H 2[Bip h en ] via Bip h en P -
(O)(OMen ). A solution of (-)-menthol (44 g, 282 mmol) in
CH2Cl2 (100 mL) was added to a 0 °C solution of phosphorus
trichloride (1.5 equiv, 58 g, 423 mmol) in CH2Cl2 (200 mL) over
a period of 30 min. The ice bath was removed, and after 1 h at
room temperature, the volatile components were removed in
vacuo. The oil was redissolved in CH2Cl2 (250 mL), and a CH2-
Cl2 (400 mL) solution of triethylamine (3 equiv, 118 mL, 847
mmol) and H2[Biphen] (100 g, 282 mmol) was added over 30
min. After 2 h the reaction mixture was filtered and hydrogen
peroxide (30%, 200 mL) was added slowly with stirring
(Caution! extremely vigorous reaction). The biphasic mixture
was stirred rapidly for 2 h, and the layers were allowed to
separate. The organic phase was washed with water and brine
(200 mL) and dried over MgSO4. The drying agent was
removed by filtration, and the solution was concentrated by
rotary evaporation to give a white solid, which was dried in
vacuo to afford BiphenP(O)(OMen) (124 g, 85%): 31P{1H} NMR
δ -3.37 ((S)-BiphenP(O)(OMen)), -4.89 ((R)-BiphenP(O)-
(OMen)).
were referenced using residual protons in the deuterated
solvents (7.16 ppm for C6D5H, 2.09 ppm for toluene-d8 (CD2H)).
13C{1H} NMR spectra were referenced assuming δ 128.4 ppm
in C6D6. All NMR spectra were taken at room temperature in
C6D6 unless otherwise noted. Temperatures during variable-
temperature NMR studies were calibrated with external
ethylene glycol (T > 20 °C) or methanol (T < 20 °C) and the
tempcal macro in the Varian software. Benzylpotassium,36
2-methoxystyrene,37 2,4-di-tert-butyl-6-methylaniline,38 t-BuCH2-
MgCl,39 PhMe2CCH2MgCl,39 and known molybdenum bis(tri-
flates)22-24,40,41 were prepared according to literature proce-
dures. Potassium hydride was purchased from Aldrich as a
(35) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518.
(36) Lochmann, L.; Trekoval, J . J . Organomet. Chem. 1987, 326, 1.
(37) Hayashi, T.; Matsumoto, Y.; Ito, Y. Tetrahedron: Asymmetry
1991, 2, 601.
(38) Geuze, J .; Ruinard, C.; Soeterbroek, J .; Verkade, P. E.; Wepster,
B. M. Recl. Trav. Chim. Pays-Bas 1956, 75, 301.
(39) Schrock, R. R.; Sancho, J .; Pederson, S. F. In Inorganic
Syntheses; Kaesz, H. D., Ed.; Wiley: New York, 1989; Vol. 26, pp
44-51.
The diastereomeric mixture of phosphates was dissolved in
a minimum amount of refluxing acetic acid (∼450 mL). After
16 h white crystals were collected by filtration and washed
with cold acetic acid (2 × 50 mL). The solid was then dried in
vacuo to give (S)-BiphenP(O)(OMen) (42 g, 97-99% de). This
(40) Fox, H. H. Ph.D. Thesis, Massachusetts Institute of Technology,
1993.
(41) Oskam, J . H. Ph.D. Thesis, Massachusetts Institute of Technol-
ogy, 1993.

3710 Organometallics, Vol. 19, No. 18, 2000
Alexander et al.
material was recrystallized from refluxing acetic acid to afford
(S)-BiphenP(O)(OMen) (37.8 g, >99% de, corresponding to 61%
of the S diastereomer).
The liquor from the first crystallization was concentrated
in vacuo to give a solid enriched with (R)-BiphenP(O)(OMen).
This solid was recrystallized from refluxing MeOH (300 mL).
When the solution was cooled to 0 °C, white crystals formed
(32 g, ∼98% de). This solid was recrystallized a second time
from refluxing MeOH to give (R)-BiphenP(O)(OMen) in two
crops (26.8 g, >99% de, 43% R diastereomer).
The reaction mixture was stirred for 10 min, and water (0.2
mL) was added dropwise. The volatile components were
removed by rotary evaporation to yield a pale yellow solid. The
crude phosphite was dissolved in CH2Cl2 (13 mL), and hydro-
gen peroxide (30%, 2.0 mL, 17.6 mmol) was added. The bi-
phasic mixture was stirred vigorously for 1 h. The layers were
separated, and the aqueous layer was extracted with CH2Cl2
(1 × 5 mL). The combined organic layers were rinsed with
water (1 × 20 mL) and brine (1 × 20 mL). The organic layer
was dried with magnesium sulfate. The mixture was filtered,
and the solvent was removed from the filtrate under reduced
pressure to produce an orange-yellow solid. The crude material
was purified by silica gel column chromatography (4:1 pentane/
diethyl ether, Rf ) 0.44): 1H NMR (CDCl3) δ 4.37, 4.26; 31P
NMR (C6H6) δ -3.29, -5.57; 31P NMR (CDCl3) δ -4.97, -6.30.
P r ep a r a tion of Dia ster eom er ica lly P u r e P h osp h a te.
The crude mixture of (()-BiadP(O)(OMen) diastereomers (1.37
g, 1.93 mmol) was placed in a Soxhlet extraction apparatus
under an argon atmosphere. Acetone (20 mL) was added, and
the reaction mixture was heated to reflux. After 18 h all the
material had disappeared from the thimble. The reaction
mixture was cooled to room temperature, and the white
precipitate was collected by filtration. The product was dias-
The MeOH solution was concentrated to give approximately
racemic BiphenP(O)(OMen), which was reused in subsequent
resolution processes.
Resolved (S)-BiphenP(O)(OMen) (37.83 g, 70.3 mmol) was
dissolved in toluene (500 mL) in a 2 L round-bottom Schlenk
flask equipped with an addition funnel. Red-Al (53 mL, 65 wt
% in toluene) was introduced into the addition funnel by
cannula and then added dropwise at 0 °C to the phosphate
solution. The reaction mixture was stirred at room tempera-
ture for 16 h and then carefully quenched with water (75 mL)
and bleach (75 mL). The slurry was filtered through Celite,
and the pad was washed with toluene (250 mL). The layers
were allowed to separate. The toluene layer was washed with
bleach and brine (200 mL each) and then dried over MgSO4.
The drying agent was removed by filtration, and the toluene
was removed by vacuum distillation at 0 °C to give a white
solid. The menthol was removed by repeated trituration with
MeOH (50 mL/wash) until the minty odor disappeared. The
resolved (S)-H2[Biphen] was collected by filtration and dried
in vacuo; yield 17.5 g (70%, >99% ee). The optical purity of
(S)-H2[Biphen] was tested by 31P NMR of the (S)-BiphenP-
(OMen) derivative. The reduction of (R)-BiphenP(O)(OMen) to
(R)-H2[Biphen] followed an identical procedure.
tereomerically pure (S)-BiadP(O)(OMen), as determined by 31
P
NMR (CDCl3) -4.97 (0.41 g, 30% over three steps). The
remaining acetone solution was then concentrated to give
enriched (R)-BiadP(O)(OMen) (mp 239-242 °C; [R]20D ) -52.5°
(c ) 1.34, CH2Cl2)): 1H NMR (CDCl3) δ 7.18 (s, 1), 7.16 (s, 1),
4.37 (dq, J ) 6.6, 2.7 Hz, 1 H), 2.32-2.24 (m, 3), 2.28 (s, 3),
2.26 (s, 3), 2.19 (s, 9), 2.22-2.06 (m, 12), 1.95-1.90 (m, 1),
1.84-1.74 (m, 17), 1.70-1.60 (m, 2), 1.37-1.28 (m, 2), 1.07-
0.92 (m, 2), 0.88 (d, 3, J ) 4.3 Hz), 0.85 (d, 3, J ) 4.3 Hz), 0.82
(d, J ) 2.1 Hz, 3); IR (neat) 2904, 2848, 1451, 1293, 1218, 998
cm-1. Anal. Calcd for C46H63O4P: C, 77.71; H, 8.93; P, 4.36.
Found. C, 77.46; H, 8.80; P, 4.15.
2-(1-Adam an tyl)-4,5-dim eth ylph en ol. This compound was
1
prepared by a literature procedure:19,20,42 mp 135-138 °C; H
(S)-3,3′-Bis(1-a d a m a n t yl)-5,5′,6,6′-t et r a m et h yl-1,1′-b i-
p h en yl-2,2′-d iol ((S)-H2[Bia d ]). Diastereomerically pure (S)-
BiadP(O)(OMen) (2.50 g, 3.52 mmol) was dissolved in toluene
(4 mL) at -23 °C under an argon atmosphere. Red-Al (4.20
mL, 14.0 mmol, 65 wt % in toluene) was added dropwise via
syringe. The reaction mixture was warmed to ambient tem-
perature while it was stirred over a period of 1.5 h. Water (50
mL) and bleach (50 mL) were added slowly, and the reaction
mixture was stirred for 30 min. The mixture was filtered
through Celite, and the solid was rinsed with toluene (100 mL).
The layers were separated, and the organic layer was rinsed
with H2O (1 × 100 mL) and brine (1 × 100 mL). The organic
layer was dried with magnesium sulfate, and the mixture was
filtered. The solvent was removed from the filtrate to give a
white solid. The material was rinsed with hexanes (3 × 20
mL) in order to remove any residual menthol. Optically pure
NMR (CDCl3) δ 6.96 (s, 1), 6.47 (s, 1), 4.50 (s, 1), 2.19 (s, 3),
2.17 (s, 3), 2.10 (s, 6), 2.05 (br s, 3), 1.78 (s, 6).
3,3′-Bis(1-adam an tyl)-5,5′,6,6′-tetr am eth yl-1,1′-biph en yl-
2,2′-d iol (H2[Bia d ]). A solution of potassium dichromate (6.50
g, 22.1 mmol) in sulfuric acid (12 mL) and water (48 mL) was
added dropwise over 30 min to an acetic acid (64 mL) slurry
of 2-(1-adamantyl)-4,5-dimethylphenol (16.0 g, 63.0 mmol) at
65 °C. The reaction mixture was stirred for 2 h at 65 °C. The
green suspension was then cooled to room temperature and
filtered. The precipitate was washed with water (250 mL) and
triturated with methanol (3 × 150 mL). The resulting white
solid was dried in vacuo to afford the title compound (()-
BiadH2 (11.1 g, 70% yield, mp >300 °C): 1H NMR (CDCl3) δ
7.07 (s, 2), 4.80 (s, 2), 2.25 (s, 6), 2.13 (br s, 12), 2.06 (br s, 6),
1.82 (s, 6), 1.76 (br s, 12); 13C NMR (CDCl3) δ 150.6, 134.0,
133.8, 128.7, 128.3, 121.1, 40.7, 37.4, 36.9, 29.4, 20.4, 16.3; IR
(neat) 2911, 2886, 2848, 1602, 1451, 1174, 1111 cm-1. Anal.
Calcd for C36H46O2: C, 84.66; H, 9.08. Found. C, 84.78; H, 9.18.
Bia d P (OMen ). To a slurry of H2[Biad] (25 mg, 0.049 mmol)
in THF (1 mL) was added potassium hydride (5 mg, 0.12
mmol). Upon addition of MenOPCl2 (13 mg, 0.051 mmol) in
THF (0.5 mL) to the blue solution, the reaction mixture became
yellow and a white precipitate formed. The mixture was
filtered through a Kimwipe plug into an NMR tube for
examination: 31P{1H} NMR (THF) δ 143.6 ((R)-BiadP(OMen)),
138.8 ((S)-BiadP(OMen)).
(S)-BiadH2 was dried in vacuo (1.46 g, 81%). [R]20 ) -32.1°
D
(c ) 3.3, THF). Spectral data were identical with data for the
racemic compound.
Mo(N-2,6-Et2C6H3)2Cl2(DME). Sodium molybdate (5 g,
24.3 mmol) was suspended in DME (200 mL). Triethylamine
(4 equiv, 9.8 g, 97.2 mmol) and 2,6-diethylaniline (2 equiv, 7.24
g, 48.6 mmol) were added sequentially with rapid stirring over
5 min. Chlorotrimethylsilane (8 equiv, 21 g, 194 mmol) was
then introduced. The reaction vessel was sealed and heated
to 60 °C for 5 h. The solution became brick red, and copious
amounts of salt precipitated. The suspension was filtered
through Celite, and the pad was washed with dimethoxyethane
until only a pale orange color persisted in the pad. The volume
was reduced to ∼75 mL in vacuo, and the solution was stored
overnight at -25 °C. Analytically pure dark red blocks were
recovered from the DME solution (3.71 g). A second crop (1.6
g) was collected from diethyl ether (30 mL); total yield 5.3 g
(40%): 1H NMR δ 6.90 (d, 4, J HH ) 7.2 Hz, m-Ar), 6.81 (t, 2,
J HH ) 7.2 Hz, p-Ar), 3.40 (s, 6, OCH3), 3.23 (q, 8, J HH ) 7.8
Hz, CH2CH3), 3.32 (s, 4, OCH2), 1.27 (t, 12, J HH ) 7.8 Hz,
P r ep a r a tion of Ra cem ic P h osp h a tes. (()-3,3′-Bis(1-
adamantyl)-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diol ((()-H2-
[Biad]; 1.00 g, 1.96 mmol) was suspended in THF (16 mL) at
ambient temperature under an argon atmosphere. Benzylpo-
tassium in THF (2 M) was added dropwise until an orange
color persisted. The orange solution was stirred, and MenOPCl2
(0.51 g, 1.98 mmol) in THF (1.0 mL) was added over 5 min.
(42) J ardina, I. A.; Radchienko, S. S. Zh. Vses. Khim. O-va. im D.I.
Mendeleeva 1981, 5, 113.

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3711
CH2CH3); 13C{1H} δ 155.74, 140.79, 127.46, 126.52, 71.29,
63.06, 25.19, 16.57. Anal. Calcd for C24H36Cl2MoN2O2: C,
52.28; H, 6.58; N, 5.08. Found: C, 52.21; H, 6.61; N, 5.08.
[HNEt3][Mo(N-2,4-t-Bu -6-MeC6H2)2Cl3]. A 1 L pear shaped
Schlenk flask was charged with sodium molybdate (10.3 g, 50
mmol), triethylamine (20.2 g, 200 mmol), 2,4-di-tert-butyl-6-
methylaniline (21.9 g, 100 mmol) and DME (400 mL). The
reaction vessel was sparged with nitrogen and chlorotrimeth-
ylsilane (54.2 g, 500 mmol) was added. A ground glass stopper
was firmly attached with copper wire, and the sealed system
was heated to 65 °C for 12 h. The brick red solution was then
filtered through Celite, and the precipitate was washed with
DME until the pad was colorless. The red solution was
concentrated in vacuo to give an oily residue. The red oil was
taken up in diethyl ether (100 mL), and red needles precipi-
tated (13 g, 35%): 1H NMR δ 8.30 (br s, 1, HNEt3), 7.46 (d, 2,
J HH ) 1.8 Hz, Ar), 7.12 (d, 2, J HH ) 1.8 Hz, Ar), 3.06 (s, 6,
Me), 2.65 (d q, 6, CH2Me), 1.92 (s, 18, t-Bu), 1.20 (s, 18, t-Bu),
0.83 (t, 9, CH2Me); 13C{1H} NMR δ 155.04, 150.21, 144.80,
141.73, 127.21, 120.88, 46.89, 37.31, 35.38, 32.85, 31.91, 21.35,
9.08.
[H-2,6-lu tid in e][Mo(N-2,4-t-Bu -6-MeC6H2)2Cl3]. A 1 L
pear-shaped Schlenk flask was charged with sodium molyb-
date (11.29 g, 54.8 mmol), 2,6-lutidine (35.2 g, 329 mmol), 2,4-
di-tert-butyl-6-methylaniline hydrochloride (28 g, 109.6 mmol),
and DME (400 mL). The reaction vessel was sparged with
nitrogen, and chlorotrimethylsilane (59.4 g, 550 mmol) was
added. A ground-glass stopper was firmly attached with copper
wire, and the sealed system was heated to 65 °C for 14 h. The
brick red solution was then filtered through Celite, and the
precipitate was washed with ether until the pad was colorless.
The red solution was concentrated in vacuo to a foam which
was crushed to a powder, slurried in ether (400 mL), and cooled
to -25 °C overnight. The bright red solid was collected by
filtration, washed with pentane (100 mL), and dried in vacuo;
yield 33.3 g (81%): 1H NMR δ 14.55 (br s, 1, Hlut), 7.48 (d, 2,
J HH ) 2.1 Hz, Ar), 7.13 (d, 2, J HH ) 2.7 Hz, Ar), 6.86 (t, 1, J HH
) 8.1 Hz, p-lut), 6.30 (d, 2, J HH ) 7.8 Hz, m-lut), 3.08 (s, 6,
Me), 2.46 (s, 6, Me), 1.934 (s, 18, t-Bu), 1.22 (s, 18, t-Bu); 13C-
{1H} NMR δ 155.11, 153.07, 150.30, 145.29, 144.84, 141.79,
127.23, 124.97, 120.90, 37.18, 35.22, 32.68, 31.73, 21.20, 20.15.
Anal. Calcd for C37H56Cl3MoN3: C, 59.64; H, 7.57; N, 5.64.
Found: C, 59.78; H, 7.69; N, 5.61.
Mo(N-2,6-Et2C6H3)2(CH2CMe2P h )2. Mo(N-2,6-Et2C6H3)2-
Cl2(DME) (5.02 g, 9.11 mmol) was dissolved in ether (100 mL),
and the solution was cooled to -25 °C. Neophylmagnesium
chloride (18.9 mL, 0.99 M in ether, 18.68 mmol) was added
over a period of 5 min with rapid stirring. The solution color
turned from red to orange, and a precipitate formed. The
reaction mixture was stirred at room temperature for 2 h and
filtered through Celite, and the pad was washed with ether
until it was pale yellow. The red solution was concentrated to
10 mL. Orange blocks formed on standing at room temperature
for 1 h. The solution was then cooled to -25 °C for 3 h. The
supernatant was decanted, and the crystals of Mo(N-2,6-
Et2C6H3)2(CH2CMe2Ph)2 were dried in vacuo; yield 4.47 g
(75%): 1H NMR δ 7.41 (d, 4, m-Ar), 7.18 (t, 2, J HH ) 2 Hz,
p-Ph), 7.05 (t, 2, p-Ar), 6.95-6.85 (m, 8, o-,m-Ph), 2.66 (q, 8,
CH2CH3), 1.81 (s, 4, MoCH2R), 1.46 (s, 12, C(CH3)2Ph), 1.07
(t, 12, CH2CH3); 13C{1H} NMR δ 155.25, 151.15, 138.42, 128.99,
126.93, 126.62, 126.05, 125.83, 78.90, 40.35, 32.72, 25.26,
14.92. Anal. Calcd for C40H52MoN2: C, 73.15; H, 7.98; N, 4.27.
Found C, 73.29; H, 8.38; N, 4.24.
ether (50 mL) at -25 °C. Orange crystals were collected by
filtration (8.00 g, 68%): 1H NMR δ 7.46 (br d, 2, NAr), 7.01
(br d, 2, NAr), 2.16 (s, 6, Me), 1.82 (s, 18, t-Bu), 1.24 (s, 18,
1
t-Bu), 1.19 (s, 18, t-Bu); H NMR (C7D8, -40 °C) δ 7.44 (br s,
2, Ar), 6.96 (br s, 2, Ar), 3.10 (br d, 2, J HH ) 14.4 Hz, CHaHbt-
Bu), 2.07 (s, 6, Me), 1.79 (s, 18, t-Bu), 1.54 (br d, 2, J HH ) 13.5
Hz, CHaHb-t-Bu), 1.21 (s, 18, t-Bu), 1.14 (s, 18, t-Bu); 13C{1H}
NMR δ 154.46, 147.50, 140.28, 136.59, 126.47, 121.49, 84.96,
36.78, 35.22, 34.78, 34.22, 31.97, 31.35, 22.36. Anal. Calcd for
C
40H68MoN2: C, 71.39; H, 10.19; N, 4.16. Found: C, 71.46; H,
10.28; N, 4.07.
Mo(N-2-CF3C6H4)2(CH2CMe3)2. Neopentylmagnesium chlo-
ride (52 mL, 2.27 M in ether, 117.7 mmol) was added over 30
min to a cooled ether (500 mL) solution of Mo(N-2-CF3C6H4)2-
Cl2(DME) (33.68 g, 58.6 mmol). The reaction mixture was
stirred at room temperature for 12 h and was then filtered
through Celite. The pad was washed with ether until colorless.
The clear red solution was then concentrated in vacuo to an
oil. On standing overnight at -25 °C, the oil crystallized as
red blocks (29 g, 89%): 1H NMR δ 7.31 (d, 2, Ar), 7.18 (d, 2,
Ar), 6.79 (t, 2, Ar), 6.55 (t, 2, Ar), 2.33 (s, 4, CH2-t-Bu), 1.16 (s,
18, t-Bu); 13C{1H} NMR δ 153.96, 132.85, 128.42, 126.42 (q,
J CF ) 5.7 Hz), 125.15, 124.93 (q, J CF ) 294.4 Hz), 121.15 (q,
J CF ) 29.0 Hz), 86.49, 35.90, 33.52. Anal. Calcd for C24H30F6-
MoN2: C, 51.80; H, 5.43; N, 5.03. Found: C, 51.65; H, 5.53;
N, 4.92.
Mo(N-2,6-Et2C6H3)(CHCMe2P h )(OTf)2(DME). Triflic acid
(2.925 g, 19.5 mmol) was dissolved in cold (-25 °C) DME (10
mL) and then added to a precooled DME (50 mL) solution of
Mo(N-2,6-Et2C6H3)2(CH2CMe2Ph)2 (4.264 g, 6.5 mmol). The
solution was stirred at room temperature for 18 h. The volatile
components were removed in vacuo, and the yellow residue
was extracted with cold toluene (∼175 mL). The mixture was
then filtered through Celite. The toluene was removed from
the filtrate in vacuo, and the solid was washed with ether (50
mL) to yield a pale yellow powder (1.5 g) which was pure by
1H NMR. The ether filtrate was then concentrated to 7 mL to
give additional yellow powder (700 mg, total yield 44%): 1H
NMR δ 14.28 (s, 1, Mo(CHR)), 7.62 (d, 2, J HH ) 8.4 Hz, o-Ph),
6.98 (t, 1, J HH ) 7.6 Hz, p-Ph), 6.80-6.66 (m, 5, Ar), 3.83 (s, 3,
OCH3), 3.24 (br t, 2, J HH ) 5.1 Hz, OCH2), 2.95-2.67 (m, 4,
diastereotopic CH2CH3), 2.82 (br t, 2, J HH ) 5.1 Hz, OCH2),
2.67 (s, 3, OCH3), 1.77 (s, 6, CMe2Ph), 1.22 (t, 6, CH2CH3); 13C-
{1H} NMR δ 327.99, 153.05, 148.54, 146.88, 129.94, 128.50,
127.37, 126.84, 125.84, 120.33, 73.24, 70.18, 65.83, 61.74,
58.84, 30.69, 25.21, 13.89. Anal. Calcd for C26H35F6MoNO8S2:
C, 40.90; H, 4.62; N, 1.83. Found: C, 40.95; H, 4.55; N, 1.77.
Mo(N-2,4-t-Bu -6-MeC6H2)(CHCMe3)(OTf)2(DME). Triflic
acid (5.25 g, 35 mmol) was dissolved in cold (-25 °C) DME
(10 mL) and then added to a cold (-25 °C) suspension of Mo-
(N-2,4-t-Bu-6-MeC6H2)2(CH2-t-Bu)2 (7.84 g, 11.67 mmol) in
DME (125 mL). The reaction mixture was stirred for 16 h at
room temperature and then concentrated in vacuo to a light
brown solid. The product was extracted with benzene (100 mL),
and the extract was filtered through Celite. The pad was
washed with additional benzene until colorless. The filtrate
was concentrated in vacuo to a tan foam. Ether (30 mL) was
added. A yellow powder was collected by filtration, washed
with ether until the solid was bright yellow, and dried in vacuo
(5.4 g, 60%): 1H NMR δ 14.16 (s, 1, CH-t-Bu), 7.38 (d, 1, J )
1.8 Hz, Ar), 7.06 (d, 1, J ) 1.8 Hz, Ar), 3.97 (s, 3, OCH3), 3.60
(br t, 1, OCH2), 2.98 (br t, 2, OCH2), 1.74 (br s, 7, overlapped
ArMe, OCH3, and one OCH2), 1.60 (s, 9, t-Bu), 1.43 (s, 9, t-Bu),
1.14 (s, 9, t-Bu); 13C{1H} NMR δ 329.06, 153.19, 153.14, 150.66,
145.29, 127.20, 121.95, 72.98, 70.67, 66.69, 61.83, 53.84, 37.07,
35.60, 31.47, 30.92, 22.93. Anal. Calcd for C26H43F6MoNO8S2:
C, 40.47; H, 5.62; N, 1.82. Found: C, 40.68; H, 5.75; N, 1.76.
Mo(N-2-CF3C6H4)(CHCMe3)(OTf)2(DME). Triflic acid (15.9
g, 105.9 mmol) was dissolved in cold DME (50 mL) and added
to a cold (-25 °C) solution of Mo(N-2-CF3C6H4)2(CH2CMe3)2
(19.63 g, 35.3 mmol) in DME (200 mL). The reaction mixture
Mo(N-2,4-t-Bu -6-MeC6H2)2(CH2CMe3)2. A slurry of [HNEt3]-
[Mo(N-2,4-t-Bu-6-MeC6H2)2Cl3] (13 g, 17.58 mmol) in ether
(250 mL) was cooled to -25 °C. Neopentylmagnesium chloride
(24 mL, 2.27 M in ether, 54.5 mmol) was added over 5 min,
and the reaction mixture was stirred at room temperature for
16 h. The suspension was filtered and the precipitate washed
with ether until the pad was colorless. The red solution was
concentrated in vacuo, and the residue was crystallized from

3712 Organometallics, Vol. 19, No. 18, 2000
Alexander et al.
was stirred at room temperature for 16 h and concentrated in
vacuo to yield a brown solid. Toluene (50 mL) was added, and
the solution was concentrated again in vacuo to remove
residual DME. The brown residue was extracted with toluene
(250 mL) and benzene (200 mL), and the extracts were filtered
through Celite. The filtrate was concentrated in vacuo. The
resulting brown solid was triturated with ether to give a yel-
low powder that was collected by filtration (16.3 g, 65%): 1H
NMR (4:1 mixture of isomers) major δ 14.02 (s, 1, CH-t-Bu),
8.38 (d, 1, Ar), 7.04 (d, 1, Ar), 6.82 (t, 1, Ar), 6.52 (t, 1, Ar),
3.65 (br s, 3, OCH3), 3.22 (br s, 2, OCH2), 2.82 (br s, 5, OCH3
and OCH2), 1.44 (s, 9, t-Bu), minor δ 15.03 (s, 1, CH-t-Bu),
8.38 (d, 1, Ar), 7.04 (d, 1, Ar), 6.82 (t, 1, Ar), 6.52 (t, 1, Ar),
3.59 (s, 3, OCH3), 3.42 (br t, 1, OCH2), 3.15 (s, 4, OCH3 and
one OCH2), 2.64 (br t, 1, OCH2), 1.21 (s, 9, t-Bu); 13C{1H} NMR
δ 329.53, 151.78, 133.88, 133.54, 133.48, 133.41, 129.85,
129.54, 126.45, 126.22, 124.99, 124.48, 124.25, 122.82, 122.29,
121.72, 119.20, 116.67, 78.16, 77.58, 74.23, 70.56, 70.33, 65.40,
62.17, 61.44, 54.42, 53.92, 31.27, 30.91. Anal. Calcd for
C18H24F9MoNO8S2: C, 30.30; H, 3.39; N, 1.96. Found: C, 30.36;
H, 3.37; N, 2.00.
extracted with benzene (10 mL), and the suspension was
filtered through Celite. The benzene was removed from the
filtrate in vacuo, and the residue was crystallized from ether
(5 mL). Red crystals of the product formed upon standing the
solution in an open vial for 1 h at room temperature (550 mg).
Reducing the volume of the liquor afforded additional pre-
cipitate (180 mg); yield 730 mg combined (60%): 1H NMR
syn δ 11.04 (s, 1, J CH ) 121 Hz, CHR), 7.45 (s, 1, Biphen),
7.39 (br s, 2, o-Ph), 7.36 (s, 1, Biphen), 7.16 (t, 2, J HH ) 6.7
Hz, m-Ph), 7.00 (t, 1, J HH ) 6.7 Hz, p-Ph), 6.83 (br s, 3, Ar),
2.80 (q, 4, J HH ) 7.4 Hz, CH2CH3), 2.14 (s, 3, Biphen), 2.03 (s,
3, Biphen), 1.78 (s, 3, Biphen), 1.76 (s, 3, Biphen), 1.68 (s, 3,
C(CH3)(MePh), 1.60 (s, 9, Biphen), 1.54 (s, 9, Biphen), 1.20 (s,
3, C(CH3)(MePh), 1.06 (t, 6, J HH ) 7.4 Hz, CH2CH3); anti δ
12.94 (s, 1, CHR); 13C{1H} NMR δ 277.51, 155.62, 155.00,
153.74, 151.17, 142.55, 140.25, 138.48, 136.62, 135.70, 132.12,
131.11, 130.95, 130.74, 130.61, 129.80, 128.56, 127.83, 127.35,
126.29, 126.00, 53.82, 36.02, 35.73, 32.69, 30.79, 30.47, 25.67,
20.85, 20.73, 17.30, 16.77, 14.62. Anal. Calcd for C44H57
-
MoNO2: C, 72.61; H, 7.89; N, 1.92. Found: C, 72.50; H, 7.80;
N, 2.13.
Mo(N-2,6-Et2C6H3)(CHCMe2P h )[(S)-Bip h en ]. Potassium
hydride (3.1 equiv, 250 mg, 6.2 mmol) was added in portions
to a stirred THF (30 mL) solution of (S)-H2[Biphen] (708 mg,
2 mmol). After 12 h, solid Mo(N-2,6-Et2C6H3)(CHCMe2Ph)-
(OTf)2(DME) (1 equiv, 1.526 g, 2 mmol) was added. The
solution was stirred for 4 h, and the volatile components were
then removed in vacuo. The solid was extracted with benzene
(20 mL) and the suspension was filtered through Celite. The
benzene was then removed in vacuo and the residue dissolved
in ether/isopropyl ether (1:1, 4 mL). The solution was cooled
to -30 °C. Two crops of the dark orange product were collected
by filtration; yield 390 mg (27%).
Mo(N-2,6-i-P r 2C6H3)(CHCMe2P h )[Biph en ]. Potassium hy-
dride (440 mg, 11 mmol) was added in portions to a stirred
THF (40 mL) solution of H2[Biphen] (1.77 g, 5 mmol). After 3
h, solid Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) (3.96 g,
5 mmol) was added. The red solution was stirred for 2 h and
then concentrated in vacuo. The residue was extracted with
benzene (10 mL). The suspension was filtered through Celite,
and the pad was washed with benzene until colorless. The
benzene was removed in vacuo, and the residue was taken up
in diethyl ether (18 mL) and transferred to a 20 mL vial. When
the vial stood for 12 h uncapped in a well-purged glovebox,
the volume decreased to ∼5 mL. The red solution was decanted
and the red blocks were washed with cold ether and dried in
vacuo (2.71 g, 72%): 1H NMR syn δ 10.98 (s, 1, J CH ) 123 Hz,
MoCH), 7.42 (m, 3, Biphen and o-Ph), 7.16 (m, 3, Biphen and
m-Ph), 7.05 (br t, J HH ) 7.6 Hz, 1, p-Ph), 6.92 (s, 3, Ar), 3.70
(sept, J HH ) 7.0 Hz, 2, CHMe2), 2.13 (s, 3, Biphen), 2.05 (s, 3,
Biphen), 1.85 (s, 3, Biphen), 1.74 (s, 3, Biphen), 1.66 (s, 3,
C(CH3)(MePh)), 1.59 (s, 9, t-Bu), 1.54 (s, 9, t-Bu), 1.14 (d, J HH
) 7.0 Hz, 6, CH(CH3)(Me), 1.13 (s, 3, C(CH3)(MePh), 0.90 (d,
J HH ) 7.0 Hz, 6, CH(CH3)(Me)), anti δ 12.77 (s, J CH ) 146 Hz,
1, MoCH); 13C{1H} NMR δ 277.1 (d, J CH ) 123 Hz, CHR),
155.4, 154.5, 154.3, 151.3, 146.8, 140.0, 138.0, 136.5, 135.7,
132.0, 131.1, 130.9, 130.7, 130.6, 129.6, 128.7, 127.9, 127.3,
126.3, 123.8 (aryl), 53.7 (CMe2Ph), 36.0, 35.7 (CMe3), 33.2, 33.0
(C(CH3)(MePh), 30.9, 30.4 (C(CH3)3), 29.2 (CHMe2), 24.6 (CH-
Mo(N-2,6-Me2C6H3)(CHCMe2P h )[Bip h en ]. Potassium hy-
dride (240 mg, 6 mmol) was added to a THF (50 mL) solution
of H2[Biphen] (708 mg, 2 mmol). After 18 h, solid Mo(N-2,6-
Me2C6H3)(CHCMe2Ph)(OTf)2(DME) (1.446 g, 2 mmol) was
added. After 3 h the solvents were removed in vacuo and the
residue was extracted with benzene (40 mL). The suspension
was filtered through Celite, and the benzene was removed from
the filtrate in vacuo. The residue was triturated with ether
(10 mL) and the resulting orange powder was collected by
filtration, washed with ether (5 mL), and dried in vacuo: yield
1.06 g (77%); 1H NMR syn δ 11.01 (s, 1, J CH ) 121 Hz, CHR),
7.39 (s, 1, Biphen), 7.25 (d, 2, o-Ph), 7.11 (s, 1, Biphen), 7.05
(t, 2, m-Ph), 6.88 (t, 1, p-Ph), 6.63 (s, 3, Ar), 2.22 (s, 6, ArCH3),
2.10 (s, 3, Biphen), 1.97 (s, 3, Biphen), 1.72 (s, 3, Biphen), 1.61
(s, 3, Biphen), 1.56 (s, 3, C(CH3)(MePh), 1.53 (s, 9, t-Bu), 1.50
(s, 9, t-Bu), 1.20 (s, 3, C(CH3)(MePh); anti δ 13.03 (s, 1, CHR);
13C{1H} NMR δ 278.94 (d, J CH ) 121 Hz), 155.97, 155.10,
154.18, 150.94, 140.16, 138.28, 137.16, 136.82, 135.65, 132.10,
131.04, 130.91, 130.82, 130.47, 130.05, 128.51, 128.31, 127.38,
127.25, 54.16, 36.00, 35.76, 32.83, 31.93, 30.92, 30.56, 20.84,
20.73, 19.80, 17.34, 16.82. Anal. Calcd for C42H53MoNO2: C,
72.08; H, 7.63; N, 2.00. Found C, 72.21; H, 7.58; N, 1.94.
Mo(N-2,6-Me2C6H3)(CHCMe2P h )[(S)-Bip h en ]. Potassium
hydride (3 equiv, 360 mg, 9 mmol) was added in portions to a
stirred solution of (S)-H2[Biphen] (1.062 g, 3 mmol) in THF
(100 mL). After 18 h, solid Mo(N-2,6-Me2C6H3)(CHCMe2Ph)-
(OTf)2(DME) (0.94 equiv, 2.235 g, 2.83 mmol) was added. After
3 h, the solvents were removed in vacuo and the residue was
extracted with benzene. The suspension was filtered through
Celite, and the benzene was removed from the filtrate in vacuo.
The residue was dissolved in ether (6 mL). Red crystals formed
at room temperature over 1 h and were collected by filtration;
yield 600 mg (30%).
(CH3)2), 20.8, 20.7, 17.2, 16.7 (aryl-CH3). Anal. Calcd for C46H61
-
MoNO2: C, 73.09; H, 8.13; N, 1.85. Found: C, 72.98; H, 8.44;
N, 1.66.
Mo(N-2,6-i-P r 2C6H 3)(CH CMe2P h )[(S)-Bip h en ]. Potas-
sium hydride (1.2 g, 30 mmol) was added in portions to a THF
(100 mL) solution of (S)-H2[Biphen] (3.54 g, 10 mmol). After
the solution was stirred for 18 h at room temperature, solid
Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OTf)2(DME) (0.99 equiv, 7.83
g, 9.9 mmol) was added to the reaction mixture. The solution
was stirred for 3 h, and the solvent was removed in vacuo.
The red solid was extracted with benzene (30 mL). The
suspension was filtered through Celite, and the pad was
washed with benzene until colorless. The benzene was removed
from the filtrate in vacuo, and the residue was dissolved in
ether (30 mL). The volume was reduced to ∼10 mL in vacuo
and allowed to stand at 20 °C for 2 h. Mo(N-2,6-i-Pr2C6H3)-
(CHCMe2Ph)[(S)-Biphen] was collected as red microcrystals
in four crops and dried in vacuo; yield 5.81 g (78%).
Mo(N-2,6-Et2C6H3)(CHCMe2P h )[Bip h en ]. Potassium hy-
dride (3 equiv, 190 mg, 4.8 mmol) was added in portions to a
stirred THF (10 mL) solution of H2[Biphen] (561 mg, 1.58
mmol). After 18 h solid Mo(N-2,6-Et2C6H3)(CHCMe2Ph)(OTf)2-
(DME) (1.21 g, 1.6 mmol) was added. After 3 h, the solution
was concentrated to dryness in vacuo. The red solid was
Mo(N-2-CF 3C6H4)(CHCMe2P h )[Bip h en ]. Solid benzylpo-
tassium (2 equiv, 260 mg, 2.0 mmol) was added in portions to
a solution of H2[Biphen] (355 mg, 1.0 mmol) in toluene (15
mL). After 2 h, solid Mo(N-2-CF3C6H4)(CHCMe2Ph)(OTf)2-
(DME) (780 mg, 1.0 mmol) was added to the reaction mixture

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3713
and the resulting red solution was stirred for 1 h. The volatile
components were removed in vacuo and the residue extracted
with pentane (15 mL). The suspension was passed through
Celite, and the pentane was removed in vacuo, affording Mo-
(NArCF3)(CHCMe2Ph)[Biphen] as a red powder: yield 708 mg
1, J HH ) 7.5 Hz, Ar), 6.61 (br t, 1, J HH ) 7.5 Hz, Ar), 6.51 (br
t, 1, J HH ) 7.5 Hz, Ar), 6.42 (br d, 1, J HH ) 8.5 Hz, Ar), 3.26 (s,
3, OCH3), 2.20 (s, 6, 2 Me), 1.91 (s, 3, Me), 1.65 (s, 3, Me), 1.48
(s, 9, t-Bu), 1.39 (s, 9, t-Bu); 13C NMR δ 255.66, 161.57, 158.96,
154.05, 152.90, 139.36, 137.53, 136.64, 136.26, 135.53, 132.56,
131.12, 130.91, 130.56, 130.38, 130.11, 129.70, 126.34, 126.30
(q, J CF ) 5.3 Hz), 123.99 (q, J CF ) 274.5 Hz), 123.37 (q, J CF )
29.4 Hz), 122.46, 120.70, 109.96, 107.72, 104.54, 58.78, 35.90,
35.84, 30.54, 30.49, 20.97, 20.86, 17.27, 17.03. Anal. Calcd for
1
(96%); H NMR δ 10.91 (s, 1, J CH ) 123 Hz, syn CHR), 7.44
(m, 3, Biphen and o-Ph), 7.19 (d, 1, J HH ) 7.6 Hz, p-Ph), 7.15
(s, 1, Biphen), 7.12 (d, 1, J HH ) 7.9 Hz, 3-C6H4CF3), 7.00 (m,
2, m-Ph), 6.80 (d, 1, J HH ) 7.2 Hz, 6-C6H4CF3), 6.76 (“t”, 1,
J HH ) 7.7 Hz, 5-C6H4CF3), 6.47 (“t”, 1, J HH ) 7.4 Hz, 4-C6H4-
CF3), 2.10 (s, 3, Biphen), 2.01 (s, 3, Biphen), 1.70 (s, 6, Biphen
and CMeMePh), 1.69 (s, 3, Biphen), 1.64 (s, 9, t-Bu), 1.54 (s,
9, t-Bu), 1.16 (s, 3, CMeMePh); 13C{1H} NMR δ 279.27, 153.79,
153.41, 152.84, 151.53, 139.36, 139.19, 135.89, 135.56, 131.60,
131.57, 131.14, 130.86, 130.47, 130.29, 129.76, 129.48, 128.42,
127.13, 125.64 (q, J CF ) 30.0 Hz), 125.64 (q, J CF ) 274 Hz),
126.05, 126.00, 125.64 (q, J CF ) 5.1 Hz), 54.77, 35.78, 35.37,
32.61, 31.63, 30.29, 30.14, 20.48, 20.37, 16.87, 16.51. Anal.
Calcd for C41H48F3MoNO2: C, 66.47; H, 6.54; N, 1.89. Found:
C, 66.55; H, 6.65; N, 2.01.
C
39H44F3MoNO3: C, 64.37; H, 6.09; N, 1.92. Found: C, 64.25;
H, 6.15; N, 1.74.
Mo(N-2-CF 3C6H 4)(CH -2-MeOC6H 4)[(S)-Bip h en ]. Ben-
zylpotassium (520 mg, 4 mmol) was added in portions to a
stirred THF (40 mL) solution of (S)-H2[Biphen] (708 mg, 2
mmol). After 20 min, solid Mo(N-2-CF3C6H3)(CHCMe2Ph)-
(OTf)2(DME) (1.550 g, 2 mmol) was added, and the red solution
was stirred for an additional 1 h. The volatile components were
removed in vacuo, and the solid was extracted with benzene
(20 mL). The suspension was filtered through Celite. 2-Meth-
oxystyrene (326 mg, 2.4 mmol) was added, and the solution
was stirred for 15 min. The volatile components were removed
in vacuo, and the dark red residue was dissolved in ether (15
mL). The mixture was filtered through Celite, and the filtrate
was concentrated to 5 mL in vacuo and stored at -25 °C
overnight. Colorless plates of a mixture of cis- and trans-2,2′-
dimethoxystilbene43 were collected by filtration (60 mg). The
mother liquor was then concentrated to 3 mL. A brick red
powder precipitated after 2 h at room temperature. The
product was collected by filtration, washed with pentane, and
dried in vacuo; yield 174 mg (12%).
Mo(N-2,4-t-Bu 2-6-MeC6H2)(CHCMe3)[(S)-Bip h en ]. Ben-
zylpotassium (286 mg, 2.2 mmol) was added in portions to a
stirred THF (25 mL) solution of (S)-H2[Biphen] (354 mg, 1
mmol) until a pale orange color persisted. After 10 min, solid
Mo(N-2,4-t-Bu-6-MePh)(CHCMe3)(OTf)2(DME) (772 mg, 1 mmol)
was added. After 30 min, the volatile components were
removed in vacuo. The residue was dissolved in benzene (30
mL), and the suspension was filtered through Celite. The
benzene was removed from the filtrate in vacuo, and the red
residue was dissolved in pentane (2 mL). When the solution
was transferred to a vial with a pipet, small orange crystals
formed. The crystals were collected by filtration, washed with
cold pentane (1 mL), and dried in vacuo; yield 266 mg (36%).
The crystallization conditions could not be reproduced, and the
source of the inconsistencies could not be identified: 1H NMR
syn δ 10.63 (s, 1, J CH ) 126 Hz, CHR), 7.48 (s, 1, Biphen),
7.32 (d, 1, J HH ) 1.8 Hz, Ar), 7.22 (d, 1, J HH ) 1.8 Hz, Ar),
7.16 (s, 1, Biphen), 2.95 (s, 3, ArCH3), 2.18 (s, 3, Biphen), 2.00
(s, 3, Biphen), 1.81 (s, 3, Biphen), 1.60 (s, 3, Biphen), 1.64 (s,
9, t-Bu), 1.55 (s, 9, t-Bu), 1.53 (s, 9, t-Bu), 1.18 (s, 9, t-Bu),
1.13 (s, 9, t-Bu); anti δ 12.86 (s, 1, CHR); 13C{1H} NMR δ
278.64, 156.02, 154.37, 149.76, 146.28, 139.97, 137.81, 137.62,
136.65, 135.47, 131.85, 130.65, 130.58, 130.55, 130.24, 125.89,
131.40, 119.77, 113.87, 48.43, 36.61, 36.14, 35.91, 35.43, 32.04,
31.82, 31.23, 31.01, 30.83, 22.00, 21.04, 20.95, 17.67, 16.96.
Anal. Calcd for C44H65MoNO2: C, 71.81; H, 8.90; N, 1.90.
Found: C, 71.83; H, 8.16; N, 1.84.
If several equivalents of THF is added to the pentane
solution of Mo(N-2-CF3C6H4)(CHCMe2Ph)[Biphen], then the
isolated product contains 1 equiv of THF bound to the metal.
Mo(N-2-CF 3C6H4)(CHCMe3)[Bip h en ]. Solid benzylpotas-
sium (2.0 equiv, 260 mg, 2.0 mmol) was added in portions to
a toluene (20 mL) solution of H2[Biphen] (354 mg, 1.0 mmol)
at room temperature. After 5 h, the reaction mixture was
cooled to -25 °C and solid Mo(N-2-CF3C6H4)(CHCMe3)(OTf)2-
(DME) (714 mg, 1 mmol) was added. After 45 min the solvents
were removed in vacuo and the residue was extracted with
pentane (40 mL). The suspension was filtered through Celite,
and the filtrate volume was reduced to 4 mL. The solution was
cooled to -25 °C overnight. The red precipitate of Mo(NArCF3)-
(CHCMe3)[Biphen] was collected by filtration, washed with
cold pentane (1 mL), and dried in vacuo: yield 260 mg (38%);
1H NMR syn δ 10.61 (s, 1, CH-t-Bu), 7.59 (d, 1, J HH ) 8.1 Hz,
Ar), 7.48 (s, 1, Biphen), 7.16 (s, 1, Biphen), 7.12 (d, 1, J HH
)
6.9 Hz, Ar), 6.91 (t, 1, J HH ) 7.5 Hz, Ar), 6.52 (t, 1, J HH ) 7.5
Hz, Ar), 2.15 (s, 3, Biphen), 2.01 (s, 3, Biphen), 1.73 (s, 3,
Biphen), 1.67 (s, 9, t-Bu), 1.64 (s, 3, Biphen), 1.59 (s, 9, t-Bu),
1.14 (s, 9, t-Bu); 13C{1H} NMR δ 281.18, 154.60, 154.22, 153.47,
139.69, 139.23, 136.22, 135.79, 132.15, 131.92, 131.30, 131.11,
130.77, 130.67, 130.18, 130.12, 126.80 (q, J CF ) 30.3 Hz),
126.63, 126.48 (q, J CF ) 5.2 Hz), 124.64 (q, J CF ) 274 Hz),
49.09, 36.16, 35.84, 32.59, 30.80, 30.54, 20.89, 20.77, 17.30,
16.89. Anal. Calcd for C36H46F3MoNO2: C, 63.80; H, 6.84; N,
2.07. Found: C, 63.84; H, 6.80; N, 2.22.
Mo(N-2-CF 3C6H4)(CHCMe3)[(S)-Bip h en ]. Benzylpotas-
sium (325 mg, 2.50 mmol) was added to a toluene (40 mL)
solution of (S)-H2[Biphen] (442 mg, 1.25 mmol). After 1 h, the
reaction mixture was cooled to -25 °C and solid Mo(N-2-
CF3C6H3)(CHCMe3)(OTf)2(DME) (892 mg, 1.25 mmol) was
added. After an additional 1 h at room temperature the volatile
components were removed in vacuo and the red solid was
dissolved in pentane. The mixture was filtered through Celite,
and the pentane was removed from the filtrate in vacuo. The
resulting foam was crushed to give spectroscopically pure Mo-
(N-2-CF3C6H3)(CHCMe3)[(S)-Biphen] as a red powder; yield
804 mg (95%). Recrystallization conditions for Mo(N-2-CF3C6H3)-
(CHCMe3)[(S)-Biphen] were not perfected.
Mo(N-2,6-i-P r 2C6H3)(CHCMe2P h )[Bia d ]. Benzylpotassi-
um (269 mg, 2.07 mmol) was added in portions to a THF (30
mL) solution of H2[Biad] (510 mg, 1 mmol) until a pale orange
color persisted. After 10 min solid Mo(NArPr2)(CHCMe2Ph)-
(OTf)2(DME) (791 mg, 1 mmol) was added. After 1 h, the
volatile components were removed in vacuo, and the residue
was taken up in benzene (15 mL). The suspension was filtered
through Celite, and the benzene was removed from the filtrate
in vacuo. The resulting orange powder was triturated with
pentane (15 mL), and orange Mo(N-2,6-i-Pr2C6H3)(CHCMe2-
Ph)[Biad] was collected by filtration, washed with cold pen-
tane, and dried in vacuo; yield 495 mg (54%): 1H NMR syn δ
Mo(N-2-CF 3C6H4)(CH-2-MeOC6H4)[Bip h en ]. A toluene (2
mL) solution of 2-methoxystyrene (241 mg, 1.8 mmol) was
added in one portion to a toluene (6 mL) solution of Mo(N-2-
CF3C6H4)(CHCMe2Ph)[Biphen](THF) (1.217 g, 1.5 mmol), and
the reaction mixture was stirred for 10 min. The solvents were
removed in vacuo, and the residue was triturated with ether
(5 mL) and collected by filtration. The red powder was washed
1
with ether and dried in vacuo: yield 800 mg (74%); H NMR
anti δ 12.85 (s, 1, J CH ) 151 Hz, CHAr), 7.29 (d, 1, J HH ) 7.5
Hz, Ar), 7.28 (s, 1, Biphen), 7.20 (s, 1, Biphen), 7.11 (br d, 1,
J HH ) 8.0 Hz, Ar), 6.93 (br t, 1, J HH ) 7.5 Hz, Ar), 6.88 (br t,
(43) Pascal, P.; Normand, L. Bull. Soc. Chim. Fr. 1911, 9, 1059.

3714 Organometallics, Vol. 19, No. 18, 2000
Alexander et al.
10.94 (s, 1, J CH ) 120 Hz, CHR), 7.47 (d, 2, J HH ) 7.5 Hz, o-Ph),
7.34 (s, 1, Biad), 7.25 (t, 2, J HH ) 8 Hz, m-Ph), 7.11 (s, 1, Biad),
7.06 (t, 1, J HH ) 7.5 Hz, p-Ph), 6.91 (s, 3, m,p-Ar), 3.65 (sept,
2, J HH ) 7.0 Hz, CHMe2), 2.37 (AB q, 6, Ad-CH2), 2.28 (AB q,
6, Ad-CH2), 2.21 (s, 3, Biad), 2.14 (br d, 6, Ad-CH), 2.13 (s, 3,
Biad), 1.90 (s, 3, CH(CH3)(MePh)), 2.1-1.82 (m, 12, Ad), 1.78
(s, 3, Biad), 1.74 (s, 3, Biad), 1.16 (d, 6, J HH ) 7.0 Hz, CH-
(CH3)(Me)), 1.15 (s, 3, C(CH3)(Me)Ph)), 0.94 (d, 6, J HH ) 7.0
mg (33%); 1H NMR δ 11.04 (s, 1, J CH ) 122 Hz, CHR), 7.37 (s,
1, Biad), 7.31 (d, 2, o-Ph), 7.13 (t, 2, m-Ph), 7.10 (s, 1, Biad),
6.98 (t, 1, p-Ph), 6.69 (s, 3, Ar), 2.34 (br AB pattern, 12 H,
Ad-CH2), 2.31 (s, 6, Ar(CH3)2), 2.22 (s, 3, Biad), 2.14 (br s, 6,
Ad-CH), 2.08 (s, 3, Biad), 1.86 (br AB pattern, 12, Ad-CH2),
1.80 (s, 3, Biad), 1.71 (s, 3, Biad), 1.65 (s, 3, C(CH3)(MePh)),
1.24 (s, 3, C(CH3)(MePh)); 13C{1H} NMR δ 278.09, 125.89,
154.98, 154.13, 151.11, 140.26, 138.55, 137.27, 136.43, 135.34,
132.16, 131.14, 131.04, 130.90, 130.42, 129.64, 128.50, 128.27,
127.42, 127.20, 126.28, 54.21, 41.67, 41.56, 38.33, 38.15,
38.10, 37.99, 32.94, 32.26, 30.10, 21.10, 20.96, 19.92, 17.43,
17.01.
Hz, CH(CH3)(Me)), anti δ 12.88 (s, 1, CHR), 7.75 (d, 2, J HH
)
7.5 Hz, o-Ph), 7.29 (t, 2, J HH ) 8.0 Hz, m-Ph), 7.12 (s, 1, Biad),
3.48 (sept, 2, CHMe2), 1.42 (d, 6, CH(CH3)(Me)), 1.03 (d, 6, CH-
(CH3)(Me)); 13C{1H} NMR δ 274.88, 155.61, 154.41, 154.23,
151.48, 146.48, 139.78, 138.68, 135.97, 135.70, 131.80, 131.12,
130.97, 130.45, 130.43, 128.70, 127.77, 127.30, 126.60, 126.36,
123.64, 53.61, 41.64, 41.51, 38.30, 38.12, 37.97, 37.90, 37.82,
33.42, 33.26, 29.97, 29.93, 29.27, 24.55, 25.52, 23.09, 20.97,
20.76, 17.00, 16.66, 14.65. Anal. Calcd for C58H73MoNO2: C,
76.37; H, 8.07; N, 1.54. Found: C, 76.45; H, 8.14; N, 1.47.
Mo(N-2,6-i-P r 2C6H3)(CHCMe2P h )[(S)-Bia d ]. Solid ben-
zylpotassium (2.04 equiv, 53 mg, 0.41 mmol) was added in
portions to a solution of (S)-H2[Biad] (102 mg, 0.2 mmol) in
THF (6 mL). After 10 min, Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)-
(OTf)2(DME) (158 mg, 0.2 mmol) in THF (2 mL) was added.
After 1 h, the volatile components were removed in vacuo. The
residue was dissolved in toluene (2 mL), and the solution was
concentrated again in vacuo in order to remove residual THF.
The solid was then extracted with pentane (10 mL). The
suspension was filtered through Celite, and the filtrate’s
volume was reduced to ∼1 mL. A golden precipitate formed
when the solution stood for 1 h at room temperature, which
was collected by filtration and dried in vacuo; yield 62 mg
(34%).
Mo(N-2,6-Et2C6H3)(CHCMe2P h )[(S)-Bia d ]. Benzylpotas-
sium (2.08 equiv, 146 mg, 1.12 mmol) was added in portions
to a stirred solution of (S)-H2[Biad] (275 mg, 0.54 mmol) in
THF (30 mL). After 30 min solid Mo(N-2,6-Et2C6H3)(CHCMe2-
Ph)(OTf)2(DME) (412 mg, 0.54 mmol) was added. After 1 h,
the volatile components were removed in vacuo and the residue
was dissolved in pentane (5 mL). The red slurry was filtered
through Celite. Orange microcrystals formed in the filtrate.
Two crops were collected by filtration and dried in vacuo: yield
145 mg (30%); 1H NMR syn δ 11.03 (s, 1, J CH ) 121 Hz, CHR),
7.37 (d, 2, J HH ) 7.0 Hz, o-Ph), 7.37 (s, 1, Biad), 7.19 (t, 2, J HH
) 8.0 Hz, m-Ph), 7.08 (s, 1, Biad), 7.02 (t, 1, J HH ) 7.5 Hz,
p-Ph), 6.86-6.79 (m, 3, m, p-Ar), 2.93 (ABX3 sextet, 2, CHaHb-
Me), 2.74 (ABX3 sextet, 2, CHaHbMe), 2.37 (AB q, 6, Ad-CH2),
2.28 (AB q, 6, Ad-CH2), 2.21 (s, 3, Biad), 2.16 (br s, 3, Ad-CH),
2.11 (br s, 3, Ad-CH), 2.10 (s, 3, Biad), 1.93-1.80 (2 overlapping
AB q, 12, 2 Ad-CH2), 1.97 (s, 3, Me), 1.769 (s, 3, Biad), 1.73 (s,
3, C(CH3)(MePh)), 1.20 (s, 3, C(CH3)(MePh)), 1.01 (t, 6, J )
7.5 Hz, CHaHbCH3); anti δ 12.91 (s, 1, CHR), 3.35 (ABX3 m, 4,
CHaHbMe), 0.95 (t, 6, CH2CH3); 13C{1H} NMR 276.84, 155.76,
155.13, 153.82, 151.27, 142.37, 140.21, 138.70, 136.32, 135.49,
132.11, 131.19, 131.00, 130.80, 130.52, 129.37, 128.68, 127.76,
127.40, 126.27, 125.69, 53.77, 41.56, 41.49, 38.25, 38.02, 37.96,
37.85, 32.94, 32.92, 30.01, 29.98, 25.60, 20.95, 20.79, 17.95,
16.79, 14.30. Anal. Calcd for C56H69MoNO2: C, 76.08; H, 7.87;
N, 1.58. Found: C, 75.92; H, 7.96; N, 1.51.
Mo(N-2,6-Me2C6H3)(CHCMe2P h )[(S)-Bia d ]. Benzylpotas-
sium (146 mg, 1.12 mmol) was added in portions to a stirred
solution of (S)-H2[Biad] (255 mg, 0.5 mmol) in THF (30 mL).
After 30 min, solid Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OTf)2-
(DME) (368 mg, 0.5 mmol) was added. After 1 h, the volatile
components were removed in vacuo and benzene (10 mL) was
added to the residue. The slurry was filtered through Celite,
and the solvents were removed from the filtrate in vacuo. The
residue was dissolved in isopropyl ether (4 mL). An orange-
red precipitate formed on standing at room temperature. The
orange-red powder was collected by filtration, washed with cold
isopropyl ether, and dried in vacuo; yield 190 mg (44%).
Mo(N-2-CF 3C6H4)(CHCMe3)[Bia d ]. Benzylpotassium (52
mg, 0.4 mmol) was added in portions to a solution of H2[Biad]
(102 mg, 0.2 mmol) in toluene (6 mL). After 2 h solid Mo(N-
2-CF3C6H4)(CHCMe3)(OTf)2(DME) (142 mg, 0.2 mmol) was
added. After an additional 45 min, all solvents were removed
in vacuo. The dark red residue was extracted with pentane (5
mL), and the suspension was filtered through Celite. The
filtrate was concentrated to 2 mL, at which point red micro-
crystals began to form. The solution was stored at -25 °C
overnight. The red-orange microcrystals were collected by
decanting the liquor and drying in vacuo: yield 68 mg (41%);
1H NMR δ 10.64 (s, 1, J CH ) 120, CH-t-Bu), 7.62 (d, 1, J HH
7.8 Hz, Ar), 7.42 (s, 1, Biad), 7.11 (d, 1, J HH ) 7.5 Hz, Ar),
7.06 (s, 1, Biad), 6.92 (t, 1, J HH ) 7.8 Hz, Ar), 6.53 (t, 1, J HH
)
)
7.8 Hz, Ar), 2.45 (br q, 6, Ad-CH2), 2.31 (br s, 6, Ad-CH2), 2.22
(s, 3, Biad), 2.17 (br q, 6, Ad-CH), 2.06 (s, 3, Biad), 2.02-1.82
(multiple signals, 12, Ad), 1.76 (s, 3, Biad), 1.68 (s, 3, Biad),
1.16 (s, 9, t-Bu); 13C{1H} NMR δ 281.75, 154.53, 154.34, 153.68,
139.86, 139.47, 136.02, 135.49, 132.09, 131.98, 131.48, 131.18,
130.96, 130.62, 130.47, 130.26, 126.93 (q, J CF ) 29.5 Hz),
126.74, 126.52 (q, J CF ) 5.1 Hz), 124.23 (q, J CF ) 272.8 Hz),
46.10, 41.59, 38.47, 38.05, 37.92, 32.70, 30.05, 30.02, 23.10,
21.01, 20.86, 17.32, 16.95, 14.66. Anal. Calcd for C48H58F3-
MoNO2: C, 69.13; H, 7.01; N, 1.68. Found: C, 68.95; H, 6.91;
N, 1.70.
Mo(N-2-CF 3C6H4)(CHCMe3)[(S)-Bia d ]. Solid benzylpo-
tassium (130 mg, 1.0 mmol) was added in portions to a stirred
solution of (S)-H2[Biad] (254 mg, 0.5 mmol) in toluene (40 mL).
After 1 h solid Mo(N-2-CF3C6H4)(CHCMe3)(OTf)2(DME) (356
mg, 0.5 mmol) was added. After 1.5 h, the solvents were
removed in vacuo and the residue was dissolved in pentane
(75 mL). The suspension was filtered through Celite, and the
volume of the filtrate was reduced to approximately 5 mL. Red-
orange microcrystals formed and were collected by decanting
the solution. A second crop of red-orange powder was collected
by filtration and dried in vacuo; yield 180 mg (43%).
Mo(N-2,6-Me2C6H3)(CHCMe2P h )[Bia d ]. Benzylpotassium
(286 mg, 2.2 mmol) was added in portions to a solution of H2-
[Biad] (510 mg, 1 mmol) in THF (25 mL). After 1 h, solid Mo-
(N-2,6-Me2C6H3)(CHCMe2Ph)(OTf)2(DME) (735 mg, 1 mmol)
was added and the resulting dark red solution was stirred for
75 min. The reaction mixture was then concentrated in vacuo
to yield a red film. The product was extracted into benzene
(10 mL), and the suspension was filtered through Celite. The
benzene was removed from the filtrate in vacuo, and the
residue was dissolved in ether (4 mL). Orange crystals began
to form at room temperature. After 20 min, the solution was
cooled to -25 °C to promote additional crystallization. Two
crops were collected by filtration and dried in vacuo: yield 297
Ob ser va t ion of Mo(NAr P r 2)(CH Me)[Bip h en ]. cis-2-
Butene (∼20 mg) was added to a toluene-d8 (0.7 mL) solution
of Mo(NArPr2)(CHCMe2Ph)[Biphen] (25 mg, 0.033 mmol). The
orange solution was transferred to an NMR tube with a 14/20
standard taper joint, and a vacuum adapter was attached. The
solution was degassed with two freeze-pump-thaw cycles and
1
then sealed under an active vacuum. After 18 h, the H NMR
spectrum revealed a mixture of Mo(NArPr2)(CHCMe2Ph)-
[Biphen] (rel 16), Mo(NArPr2)(CHMe)[Biphen] (1.0), and cis-/
trans-2-butene (rel 68): δ 13.37 (q, 1, J HH ) 8.5 Hz, anti
CHMe), 10.64 (q, 1, J HH ) 6.5, syn CHMe); Ksyn/anti ) 2.0.

Catalysts for Olefin Metathesis Reactions
Organometallics, Vol. 19, No. 18, 2000 3715
Obser va tion of Mo(NAr P r 2)(CHEt)[Bip h en ]. A sealed
NMR sample was prepared as described immediately above
that contained [Biphen](NArPr2)Mo(CHCMe2Ph) (38 mg, 0.05
mmol), hexamethylbenzene (1-2 mg), toluene-d8 (0.7 mL), and
conversion of syn and anti isomers studied here. The resonance
for one isomer was selectively inverted and spectra were
recorded, varying the delay time, t (in s), between inversion
and data acquisition. The equilibrium concentrations of atro-
pisomers a and b were a∞ and b∞, and the integration areas
for a and b at delay time, t, were at and bt. The relaxation
time (R1 ) T1) for the nuclei under investigation was obtained
using eq 8. The rate constant ka b was obtained by inserting
the value for R1 into eq 9. The derivation of these equations
assumed that the relaxation times (R1) for a and b were the
same.
1
3-hexene (42 mg, 0.5 mmol). After 2 days a H NMR spectrum
showed that it contained a mixture of Mo(NArPr2)(CHCMe2-
Ph)[Biphen] and Mo(NArPr2)(CHEt)[Biphen] in a 17.4:1 ratio
and that Ksyn/anti ) 3.1: δ 12.15 (dd, 1, J HH ) 11.9, 7.0 Hz, anti
CHEt), 10.68 (dd, 1, J HH ) 6.8, 6.4 Hz, syn CHEt).
Activa tion P a r a m eter s by Sp in -Sa tu r a tion Tr a n sfer .
T1 measurements were obtained for syn and anti isomers of
Mo(NArPr2)(CHCMe2Ph)[Biphen] at -10 °C, where the rate
of isomer interconversion is ∼0.02 s-1. At this temperature
T1(syn) ) 1.00 s and T1(anti) ) 0.72 s. It was assumed in
calculations below that R1(syn) ) R1(anti).
Applying eqs 8 and 9 to alkylidene rotation generated eqs
10 and 11, substituting anti for a and syn for b. A T1
ln{(anti∞ + syn∞) - (antit + synt)} ) -R1t + C (10)
Rotational exchange between syn and anti isomers broaden
NMR resonances to a degree that depends on the relative
chemical shifts, the rate constants for exchange (kas and ksa),
the transverse relaxation times (T2), and the populations of
the different sites.44 The line broadening of the anti resonance
(ωanti) is a function of the transverse relaxation time, i.e., ωanti
) (π[T2(anti)])-1. The observed relaxation time (T2(obs))-1 is a
sum of the natural line broadening (T2(nat))-1, broadening due
to the spectrometer (T2(spect))-1, and broadening due to
exchange (T2(exch)-1) (eq 7).
anti
anti∞
syn∞
ln antit -
∞synt ) -R1 - kas 1 +
t + C (11)
(
)
(
)
]
[
syn∞
measurement was attempted at room temperature for [Biphen]-
(NArPr2)Mo(CHCMe2Ph), which yielded T1(syn) ) 1.2 s and
T1(anti) ) 1 s. The delay time was varied (t ) 0, 0.05, 0.1, ...,
0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 12 s), and the integrated areas for
synt and antit were collected. The values for t ) 12 s were
assigned to be syn∞ and anti∞, as both isomers had sufficient
time to completely relax to the ground state (t ≈ 10T1). A linear
regression of eqs 10 and 11 gave kas for [Biphen](NArPr2)Mo-
(CHCMe2Ph). A plot of ln(k/T) versus 1/T afforded the activa-
tion parameters, ∆Hq and ∆Sq, for the total rate of isomer
exchange.
1
1
1
1
)
+
+
(7)
T2(obs) T2(nat) T2(spect) T2(exch)
The sum of the natural and instrument line broadening was
set as (T2)-1 ≈ 1 s-1. This approximation could lead to some
systematic error in the calculation of the activation param-
eters. To minimize this error, data for temperatures where ωanti
< 5 Hz were excluded from the calculation of the activation
parameters. The observed line broadening was then expressed
Ack n ow led gm en t. This work was supported by the
National Science Foundation (Grant No. CHE-9700736
to R.R.S. and CHE-9905806 to A.H.H.). K.C.H. thanks
the Alexander von Humboldt Foundation for a Feodor
Lynen Research Fellowship. We thank A. Casado for
experimental assistance and helpful discussions.
as ωanti ) (1 + kas)/π and the rate constant expressed as kas
[πωanti - 1] s-1
Equations 8 and 945,46 were employed in this study. The
)
.
Su p p or tin g In for m a tion Ava ila ble: Labeled ORTEP
drawings, crystallographic data, atomic coordinates, bond
lengths and angles, and anisotropic displacement parameters
for 1 and 2. This material is available free of charge via the
Internet at http://pubs.acs.org.
ln{(a∞ + b∞) - (at + bt)} ) -R1t + C
(8)
(9)
a
a∞
b∞
ln at - ∞bt ) -R1 - ka b 1 +
t + C
(
)
(
)
]
[
b∞
OM000336H
study of the interconversion of syn (isomer a ) and anti (isomer
46
b) forms of cis-Pd(THT)2(C6BrF4)2 is analogous to the inter-
(45) Green, M. L. H.; Sella, A.; Wong, L.-L. Organometallics 1992,
11, 2650.
(44) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:
New York, 1982.
(46) Albe´niz, A. C.; Casado, A. L.; Espinet, P. Inorg. Chem. 1999,
38, 2510.