Diastereoselective Hydride Addition to [Tp′W(CO)(PhCCMe)(NH=CRR′)][BAr′4]: Effects of Equilibrium and Kinetic Acidity

Article abstract of DOI:10.1021/om0344022

A series of alkyl and aryl amido, imine, azavinylidene, and amine complexes containing the [Tp′W(CO)(PhCCMe)]⁺ fragment have been synthesized. Reaction of Na[HBEt₃] with an E/Z mixture of [Tp′W(CO)(PhCCMe)(NH=CMeEt)] [BAr′₄] results in hydride addition at the imine carbon to form the amido complex with high diastereoselectivity. This high diastereoselectivity reflects differentiation between methyl and ethyl groups on the substrate imine carbon. A competing reaction forms an azavinylidene complex as a minor product via deprotonation of the coordinated imine ligand in the reagent. The ratio of amido to azavinylidene products tracks the E to Z isomer ratio and suggests that different reaction pathways characterize these two isomers. Relative _pK_a's of the various imine and amine complexes have been measured in THF, and kinetic acidity measurements of related imine complexes have been used to help understand these results.

Full text of DOI:10.1021/om0344022

1378
Organometallics 2004, 23, 1378-1389
Dia ster eoselective Hyd r id e Ad d ition to
[Tp ′W(CO)(P h CCMe)(NHdCRR′)][BAr ′4]: Effects of
Equ ilibr iu m a n d Kin etic Acid ity
Neil J . Vogeley, Peter S. White, and J oseph L. Templeton*
W. R. Kenan Laboratory, Department of Chemistry, University of North Carolina,
Chapel Hill, North Carolina 27599-3290
Received December 23, 2003
A series of alkyl and aryl amido, imine, azavinylidene, and amine complexes containing
the [Tp′W(CO)(PhCCMe)]+ fragment have been synthesized. Reaction of Na[HBEt3] with
an E/Z mixture of [Tp′W(CO)(PhCCMe)(NHdCMeEt)][BAr′4] results in hydride addition at
the imine carbon to form the amido complex with high diastereoselectivity. This high
diastereoselectivity reflects differentiation between methyl and ethyl groups on the substrate
imine carbon. A competing reaction forms an azavinylidene complex as a minor product via
deprotonation of the coordinated imine ligand in the reagent. The ratio of amido to
azavinylidene products tracks the E to Z isomer ratio and suggests that different reaction
pathways characterize these two isomers. Relative pKa’s of the various imine and amine
complexes have been measured in THF, and kinetic acidity measurements of related imine
complexes have been used to help understand these results.
In tr od u ction
Stereoselective reduction of an unsaturated bond
usually requires that one isomer (E/ Z) of the reagent
predominates and that reduction occurs at only one face
of the substrate. Examples where the E/ Z ratio has no
impact on the stereoselectivity of the reaction are rare.1,2
Many reactions that involve stereoselection rely on
steric differences between large and small groups to
differentiate two stereofaces of the substrate. Few
reactions successfully discriminate between methyl and
ethyl groups.3-6
Many methods for stereoselectively converting imines
to amines have been developed.7-11 Examples of sto-
ichiometric, diastereoselective nucleophile addition to
coordinated imine complexes have been reported. Gla-
dysz has effectively utilized electrophilic CpRe(NO)-
(PPh3)(imine)+ complexes to add nucleophiles diastere-
oselectively to coordinated imines (eq 1).12-20 The
F igu r e 1. Tp′ ) hydrido tris(3,5-dimethylpyrazolyl)borate.
enantiomers of this rhenium system have been resolved,
so a single amine enantiomer can be synthesized.14
Restriction of reagent E/ Z imine isomers via chelation
in Boncella’s orthometalated N-phenylbenzaldimine
complex allows nucleophiles to add to form a 98:2
diastereomer ratio of amido products (eq 2).21 Imines
bound to the arene in chiral (η6-arene)Cr(CO)3 com-
plexes also undergo stereoselective nucleophilic addition
at the imine carbon.22,23
Acetonitrile coordinated to [Tp′W(CO)(PhCCMe)]+ can
be reduced by sequential hydride and proton additions
to give an ethylamine complex [Tp′ ) hydrido tris(3,5-
dimethylpyrazolyl)borate, see Figure 1],24 and stepwise
* To whom correspondence should be addressed. E-mail: joetemp@
unc.edu.
(1) Burk, M. J .; Feaster, J . E.; Nugent, W. A.; Harlow, R. L. J . Am.
Chem. Soc. 1993, 115, 10125-10138.
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Int. Ed. 1998, 37, 1103-1107.
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Soc. 1997, 119, 10859-10860.
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M.; Gladysz, J . A. Chem. Eur. J . 1995, 1, 294-303.
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A. M.; Gladysz, J . A. Organometallics 1993, 12, 4523-4534.
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Chem. 2001, 925-933.
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Gladysz, J . A. J . Am. Chem. Soc. 1993, 115, 11863-11873.
(17) Stark, G. A.; Arif, A. M.; Gladysz, J . A. Organometallics 1994,
13, 4523-4530.
(18) Stark, G. A.; Gladysz, J . A. Inorg. Chem. 1996, 35, 5509-5513.
(19) Stark, G. A.; Gladysz, J . A. Inorg. Chim. Acta 1998, 269, 167-
180.
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C. J . Am. Chem. Soc. 1997, 119, 7893-7894.
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Am. Chem. Soc. 1999, 121, 686-699.
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Soc. 1993, 115, 4415-4416.
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(8) Denmark, S. E.; Nicaise, O. J .-C. Chem. Commun. 1996, 999-
1004.
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1895-1946.
(10) J ames, B. R. Catal. Today 1997, 37, 209-221.
(11) Kobayashi, S.; Ishitani, H. Chem. Rev. 1999, 99, 1069-1094.
(12) J ohnson, T. J .; Arif, A. M.; Gladysz, J . A. Organometallics 1994,
13, 3182-3193.
(20) Cantrell, W. R., J r.; Richter-Addo, G. B.; Gladysz, J . A. J .
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10.1021/om0344022 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 02/21/2004

Diastereoselective Hydride Addition
Organometallics, Vol. 23, No. 6, 2004 1379
route allows the isolation of a variety of alkyl and aryl
amido complexes.
oxidation of coordinated benzylamine to benzonitrile has
also been described (Scheme 1).25 Addition of CN- to
the imine carbon in [Tp′W(CO)(PhCCMe)(NHdCHMe)]-
[BF4], which exists as the E isomer, occurs diastereo-
selectively.24 Enantiomers of the Tp′W(CO)(PhCCMe)+
fragment are available since derivative complexes have
been resolved by fractional crystallization.26
Hydride addition to [Tp′W(CO)(PhCCMe)(NHd
CMeEt)][BAr′4] (3a ) (BAr′4 ) tetrakis[3,5-bis(trifluo-
romethyl)phenyl]borate) occurs with high diastereose-
lectivity to yield an amido complex through E/ Z isomer
reactivity differences.27 Effective differentiation between
methyl and ethyl groups on the prochiral imine carbon
is a distinguishing feature of this system. Here we
report both kinetic and thermodynamic acidity studies
as well as structural and mechanistic details for the
reactions of the E and Z isomers of complex 3a .
Syn t h esis of Im in e Com p lexes [Tp ′W(CO)(P h -
CCMe)(NHdCR R ′)][BAr ′4] (3a -c,e). Oxidation of
electron-rich amido complexes 2a -c,e (R/R′ ) Me/Et,
2a ; Me/Me, 2b; Et/Et, 2c; Me/p-C6H4OMe, 2e) by I2 in
the presence of NEt3 in CH2Cl2 yields the imine com-
plexes [Tp′W(CO)(PhCCMe)(NHdCRR′)][I] via net hy-
dride removal. Anion exchange is effected by cannula
transferring a diethyl ether solution of Na[BAr′4] into
the reaction mixture (eq 4).
Resu lts a n d Discu ssion
Since oxidation of amido complexes 2d ,f (R/R′ ) Me/
Ph, 2d ; Me/p-C6H4Br, 2f) by I2 in the presence of base
led to the isolation of azavinylidene complexes 4d ,f (see
below), imine complexes 3d ,f were synthesized by
protonation of the azavinylidene complexes 4d ,f by
H[BAr′4] (eq 5).
The sythesis of amido, imine, azavinylidene, and
amine complexes has previously been reported. Com-
plexes 2-5a , 2-4b, 2-4c, and 2-5d have been de-
scribed.27,28 Complexes 5b,c and 2-5e,f are reported
here for the first time.
Syn th esis of Am id o Com p lexes Tp ′W(CO)(P h C-
CMe)(NH CH R R′) (2a -f). Heating [Tp′W(CO)2(PhC-
CMe)][OTf] (1) in THF at reflux for 1 h leads to the loss
of one CO ligand and coordination of the triflate coun-
terion. Addition of a primary amine, NH2CHRR′, and
continued heating for 1 to 2 days, depending on the
amine, displaces the coordinated triflate and forms
neutral amido complexes 2a -f (eq 3).28 This synthetic
Sch em e 1

1380 Organometallics, Vol. 23, No. 6, 2004
Vogeley et al.
E and Z isomers of imine complex 3a (R/R′ ) Me/Et)
exist in a 75:25 ratio as determined by 1H NMR
spectroscopy; these isomers do not interconvert at 100
°C on the NMR time scale in C6D5Br, indicating a ∆Gq
of >18 kcal/mol.28 NMR spectra for the two isomers were
assigned by a combination of COSY and NOESY tech-
niques. In contrast, only the E isomer is observed for
complexes 3d -f (R/R′ ) Me/Ph, 3d ; Me/p-C6H4OMe, 3e;
Me/p-C6H4Br, 3f).
Recrystallization of imine complex 3a by slow diffu-
sion of hexanes into a CH2Cl2 solution of the imine
yields a 75:25 E/Z ratio of isomers. Addition of THF to
the CH2Cl2/hexanes solvent system provides a method
of enriching the solid in the E isomer. Slow diffusion of
hexanes into a solution of the imine complex in 3:2:1
hexanes/CH2Cl2/THF allows for a range of E/ Z ratios
from 80:20 to 93:7 to be obtained in 91% yield. Isomer-
ization of the imine ligand may be promoted by THF
since deprotonation at nitrogen to form azavinylidene
complex 4a followed by reprotonation of the opposite
nitrogen face will interconvert E and Z isomers (vide
infra).
Syn th esis of Aza vin ylid en e Com p lexes Tp ′W-
(CO)(P h CCMe)(dNdCRR′) (4a -f). For imine com-
plexes 3a -c,e (R/R′ ) Me/Et, 3a ; Me/Me, 3b; Et/Et, 3c;
Me/p-C6H4OMe, 3e) that were isolated cleanly from the
amido oxidation reaction above, the corresponding aza-
vinylidene complexes 4a-c,e were synthesized by simple
deprotonation of the imine complex by using KH as the
base.
Oxidation of electron-poor amido complexes 2d ,f (R/
R′ ) Me/Ph, 2d ; Me/p-C6H4Br, 2f) with I2 and 1 equiv
of NEt3 led to the formation of a mixture of imine and
azavinylidene complexes.28 Rather than isolate the
imine complexes, excess NEt3 was added to deprotonate
the imine ligand, and neutral azavinylidene complexes
4d ,f (eq 6) were isolated.
Va r ia ble-Tem p er a tu r e NMR Stu d ies. Perhaps
surprisingly, both the E and Z isomers of imine complex
3a show broad signals for the imine alkyl groups cis to
tungsten, whether CH3 or CH2CH3. The E isomer has
a broad methyl singlet at 2.05 ppm, and the Z isomer
has a broad methyl triplet at 1.06 ppm. Since the E and
Z isomers do not interconvert on the NMR time scale,
some other more facile dynamic process must be occur-
ring within each isomer independently to account for
the broad signals. Hindered rotation around the W-N
imine bond can account for this observation; each imine
isomer apparently has one W-N conformation with the
NH pointed between the pyrazole rings and another
conformation with the NH pointed between the CO and
alkyne ligands (Scheme 2, see NOESY data below). The
broad signals for the methyl group of the E isomer and
the ethyl group of the Z isomer reflect large chemical
shift differences for that group in the two conformers
due to anisotropic diamagnetic shielding by the pyrazole
rings. The minor conformation would shift the alkyl
methyl groups upfield when they lie between the pyra-
zole rings. Interconversion of these two conformers is
rapid at room temperature, but since coalescence de-
pends on the chemical shift differential, each of the
signals can sharpen into one signal at different tem-
peratures, and the result is selective broadening of a
few signals. Signals for the minor conformations could
not be identified even at low temperature since the
majority of the sample exists in the conformation with
the NH’s directed toward the pyrazole rings of Tp′. The
methyl singlet at 2.05 ppm for the E isomer broadens
from 260 to 315 K and begins to sharpen again above
315 K at 1.90 ppm. This indicates that the minor
rotamer’s methyl signal lies upfield from 1.90 ppm, as
expected. The ∆Gq for W-N rotation from the major
rotamer to the minor rotamer for the E isomer was
calculated from line broadening of the methyl singlet
at 2.05 ppm and determined to be 15 kcal/mol at 296
K.
NOESY of [Tp ′W(CO)(P h CCMe)(NHdCMeEt)]-
[BAr ′4] (3a ). In the original report describing [Tp′W-
(CO)(PhCCMe)(NHdCMeEt)][BAr′4] (3a ), an observed
4J HH coupling of 1 Hz in one CH3 signal of the minor
species led to its incorrect assignment as being trans to
the NH proton in the E isomer.28 Using NOESY cor-
relations between the NH proton and the methyl and
ethyl groups of the imine ligand, the E isomer has now
been assigned as the major species. Intuitively, the E
isomer should be favored on the basis of steric factors.
In both isomers, the NH protons, which appear at 8.92
ppm, show strong NOE correlations to Tp′ methyl
groups at 1.21 and 2.47 ppm, indicating that these imine
protons lie between two pyrazole rings. The X-ray
structure of the imine complex also reveals the NH
proton situated between two pyrazole rings.28 The NH
proton also correlates to the methyl triplet of the major
isomer at 0.92 ppm and the 1 Hz methyl doublet of the
minor isomer at 2.22 ppm. Other NOE correlations are
schematically depicted in Figure 2. This system shows
Syn th esis of Am in e Com p lexes [Tp ′W(CO)(P h -
CCMe)(NH2CHRR′)][BAr ′4] (5a -f). Amine complexes
were synthesized by protonation of the corresponding
amido complexes 2a -f by H[BAr′4] in CH2Cl2 (eq 7).
(22) Solladie´-Cavallo, A.; Suffert, J .; Haesslein, J .-L. Angew. Chem.,
Int. Ed. Engl. 1980, 19, 1005-1006.
(23) David, D. M.; Kane-Maguire, L. A. P.; Pyne, S. G. J . Chem.
Soc., Dalton Trans. 1994, 289-295.
(24) Feng, S. G.; Templeton, J . L. Organometallics 1992, 11, 1295-
1303.
(25) Gunnoe, T. B.; White, P. S.; Templeton, J . L. J . Am. Chem. Soc.
1996, 118, 6916-6923.
(26) Caldarelli, J . L.; White, P. S.; Templeton, J . L. J . Am. Chem.
Soc. 1992, 114, 10097-10103.
(27) Vogeley, N. J .; White, P. S.; Templeton, J . L. J . Am. Chem. Soc.
2003, 125, 12422-12423.
(28) Francisco, L. W.; White, P. S.; Templeton, J . L. Organometallics
1996, 15, 5127-5136.

Diastereoselective Hydride Addition
Organometallics, Vol. 23, No. 6, 2004 1381
Sch em e 2
75:25 ratio. The azavinylidene plane is oriented per-
pendicular to the W-CO axis so it can donate its lone
pair into the empty dπ orbital on tungsten; this places
the ethyl group proximal to the alkyne ligand in one
rotamer (p r ox-4a ) and distal to the alkyne in the other
(d is-4a ).31 In the NOESY spectrum, the major rotamer
displayed a correlation between the methyl triplet of the
azavinylidene ethyl group at 0.67 ppm and the alkyne
methyl singlet at 3.07 ppm. This suggests that p r ox-
4a is the major rotamer and d is-4a is the minor rotamer
(Figure 3). Note that the orientation of the ethyl group
proximal to the alkyne methyl in the major azavi-
nylidene isomer is opposite the orientation in the imine
major isomer.
Isom er iza tion of E a n d Z [Tp ′W(CO)(P h CCMe)-
(NHdCMeEt)][BAr ′4] (3a ). Imine complex 3a that had
been enriched in the E isomer by careful recrystalliza-
tion was isomerized to a 75:25 E/Z distribution of
isomers immediately in CD2Cl2 upon addition of 5 mol
% NEt3. The 75:25 E/ Z ratio is the thermodynamic
1
ratio. A H NMR spectrum of 90:10 E/ Z ratio imine
complex showed isomerization to a 60:40 E/ Z ratio upon
dissolution in THF-d8.
Hyd r id e Ad d ition to [Tp ′W(CO)(P h CCMe)(NHd
CMeEt)][BAr ′4] (3a ). In an NMR tube, Na[HBEt3] was
added to an 80:20 mixture of E/Z imine isomers of
F igu r e 2. NOE correlations (dashed arrows) in the E and
Z isomers of imine complex 3a . The three Tp′ methyl
groups that are directed toward the three ancillary ligands
1
are depicted as black circles. H NMR chemical shifts are
given in ppm.
the value of the Tp′ methyl groups as NOE reporter sites
for determining the orientation of ancillary ligands.29,30
NOESY of Tp ′W(CO)(P h CCMe)(dNdCMeEt) (4a ).
Azavinylidene complex 4a exists as two rotamers in a
F igu r e 3. Major and minor W-N rotamers as determined
by NOESY for azavinylidene complex 4a .
(29) Frohnapfel, D. S.; White, P. S.; Templeton, J . L.; Ru¨egger, H.;
Pregosin, P. S. Organometallics 1997, 16, 3737-3750.

1382 Organometallics, Vol. 23, No. 6, 2004
Vogeley et al.
Ta ble 1. Dia ster eoselectivity a n d Am id o to Aza vin ylid en e Ra tios for Differ en t E/Z Ra tios of th e Sta r tin g
Im in e Rea gen t
amido complex 2a
azavinylidene complex 4a
imine
complex 3a
E/Z
2a -SS/RR
2a -SR/RS
p r ox-4a
d is-4a
3a -E
3a -Z
maj. diast.
min. diast.
maj. rot.
min. rot.
maj. products:min. productsa
add.:depr.b
add.:depr.c
80:20
80:20
83:17
93:7
70
71
71
78
5
6
4
3
13
12
17
13
12
11
7
83:17
83:17
88:11
91:8
5:1
6:1
4:1
6:1
0.4:1
0.5:1
0.6:1
0.6:1
5
a
b
2a -SS/RR, p r ox-4a :2a -SR/RS, d is-4a . 2a -SS/RR:p r ox-4a . c 2a -SR/RS:d is-4a .
1
complex 3a in CD2Cl2. H NMR spectroscopy showed
an unexpected 93:7 diastereomer ratio (SS/ RR:SR/ RS,
vide infra) of amido complex 2a (eq 8). This ratio is
surprisingly high in view of the low E/ Z ratio of the
coordinated imine reagent. Azavinylidene complex 4a
was also observed as a product from deprotonation of
imine complex 3a (76:24 addition to deprotonation,
Table 1).
tonation for the Z isomer is approximately 0.5:1 (2a -
SR/RS:d is-4a ), so deprotonation is favored by a ∆∆Gq
of about 0.5 kcal/mol.
The orientation of the azavinylidene rotamers has
been determined by NOESY. Assignment of the azavi-
nylidene products formed in the reaction reveals that
the major azavinylidene rotamer, p r ox-4a , described
above results from deprotonation of the E isomer of
imine complex 3a . Structural similarity between the
minor W-N rotamer of 3a -E and the major azavi-
nylidene rotamer, p r ox-4a , suggests that deprotonation
of the imine complex occurs from the minor W-N
rotamer (eq 9). Deprotonation of the minor W-N
rotamer of 3a -Z would form the other azavinylidene
rotamer, d is-4a . Molecular models suggest that the NH
proton would be more accessible in the minor rotamer,
where it is not in the cleft between two pyrazole rings.
The effect of the E/ Z ratio on diastereoselectivity was
probed from the nonequilibrium ratio of E/ Z imine
complex isomers (93:7 E/ Z). Na[HBEt3] was added to
a solution of 93:7 E/Z isomer mixture of imine complex
3a in an NMR tube. Slightly higher diastereoselectivity
was observed, 96:4, but less azavinylidene complex was
formed from deprotonation (81:18 addition to deproto-
nation, Table 1).
The two rotamers of the azavinylidene complex do not
interconvert on the time scale of these experiments. It
appears that formation of the azavinylidene ligand via
deprotonation of the imine ligand occurs diastereose-
lectively. That is, ratios of products suggest that depro-
tonation of the E isomer of imine complex 3a leads to a
single rotamer of azavinylidene complex 4a ; the Z
isomer of imine complex 3a leads to the other. The ratio
of the sum of the major diastereomer (2a -SS/RR) plus
the major rotamer (p r ox-4a ) to the sum of the minor
diastereomer (2a -SR/RS) plus the minor rotamer (d is-
4a ) is approximately equal to the E/ Z ratio of the
starting imine complex regardless of the starting E/ Z
ratio (Table 1). This suggests that the E isomer can add
hydride to form 2a -SS/RR or be deprotonated to form
p r ox-4a . Since both hydride addition and imine depro-
tonation form distinct products from each imine isomer,
the ratio of addition to deprotonation for the E isomer
can be calculated to be about 5:1 (2a -SS/RR:p r ox-4a ),
so addition of hydride is favored by a ∆∆Gq of roughly
1 kcal/mol. In contrast, the ratio of addition to depro-
The symmetrical imine complex 3b (R/R′ ) Me/Me)
reacts with hydride to lead to an 80:20 ratio of addition
to deprotonation, while addition of hydride to imine
complex 3c (R/R′ ) Et/Et) displays a 30:70 ratio of
addition to deprotonation. The barrier to deprotonation
as well as the barrier for hydride addition to the imine
carbon are affected by the imine substituents. Diethyl
substitution at the imine carbon sufficiently slows down
hydride addition so that deprotonation dominates de-
spite 3c’s low kinetic acidity (see below). Even though
all of these reactions occur in a matter of seconds, the
reaction of hydride with 3c is noticeably slower than
with 3b.
(30) Pregosin, P. S.; Macchioni, A.; Templeton, J . L.; White, P. S.;
Feng, S. G. Magn. Reson. Chem. 1994, 32, 415-421.
(31) Feng, S. G.; White, P. S.; Templeton, J . L. Organometallics
1993, 12, 2131-2139.
Rela tive p Ka Mea su r em en ts. Proton transfer be-
tween acids and bases in organic solvents is important
for understanding reaction pathways. Work in this area

Diastereoselective Hydride Addition
Organometallics, Vol. 23, No. 6, 2004 1383
Ta ble 2. Rela tive p Ka ’s for Im in e a n d Am in e
reflects limited proton transfer to NEt3, while a negative
∆pKa reflects a strongly acidic imine or amine complex.
Com p lexes
standardized
∆pKa
(NEt3)
∆pKa
scale
R/R′
(4-MeOpy) [HNEt3]+ ≡ 0
Me/Me imine (3b)
Me/Et imine (3a )
Me/Me amine (5b)
Me/Et amine (5a )
Et/Et imine (3c)
Et/Et amine (5c)
Me/p-C6H4OMe amine (5e) -0.13(7)
Me/Ph amine (5d )
Me/p-C6H4Br amine (5f)
1.58(4)
0.88(6)
0.63(4)
0.38(13)
0.23(5)
-0.02(2)
1.58(4)
0.88(6)
0.63(4)
0.38(13)
0.23(5)
-0.02(2)
-0.13(7)
-0.71(14)
-1.41(14)
-1.78(10)
-2.42(10)
-3.59(11)
-0.71(14)
-1.41(14)
Me/p-C6H4OMe imine (3e) -1.78(4)
Me/Ph imine (3d )
Me/p-C6H4Br imine (3f)
1.29(9)
0.65(2)
-0.52(4)
has often used DMSO32 or acetonitrile solvents;33 less
studied are relative pKa’s in THF.34-37 Measurements
in THF are complicated by its low dielectric constant,
which prevents dissociation of ion pairs. Measured acid/
base values in THF have been termed pKip to reflect
ion pair phenomenon (eq 10a).37 This equation describes
the reaction between a neutral acid and a neutral base.
The reaction of a cationic acid and a neutral base shown
in eq 10b more closely describes our cationic imine and
amine complexes.36
Kip
Kdiss
A-H+ + B y z BH+A- y z BH+ + A- (10a)
Kdiss
HB1+A- + B2 y
z
1/Kdiss
HB1+ + A- + B2 y
\
Kz B1 + A- + HB2+ y
B1 + HB2+A- (10b)
z
Relative pKa’s were measured in THF by monitoring
the intense CO stretch of cationic and neutral complexes
in the IR spectrum. Each imine or amine complex was
dissolved in THF, and base, either triethylamine or
4-methoxypyridine, was added. The ratio of the two CO
absorbances was measured for either the imine/azavi-
nylidene (eq 11) or the amine/amido (eq 12) pairs. From
this ratio and the relative molar absorptivities, the
equilibrium constant, Keq (eq 13), was obtained and can
be used to calculate a ∆pKa for the acidic imine or amine
complexes relative to [HNEt3]+, selected as the standard
acid. The relative pKa’s for complexes 3a -c,e and 5a -f
were measured using NEt3. The acidities of complexes
3d -f were measured using 4-methoxypyridine. The two
scales were linked by matching measurements with both
bases for complex 3e, and [HNEt3]+/NEt3 was defined
as the standard with a pKa of 0. Table 2 shows the
∆pKa’s for the tungsten imine and amine complexes
reported here, where the equilibrium constant for reac-
The acidity of imine and amine complexes increases
in the same order, (least acidic) Me/Me < Me/Et < Et/
Et < Me/p-C6H4OMe < Me/Ph < Me/p-C6H4Br (most
acidic), but the imine pKa’s span a range of about 5
orders of magnitude, while the amine complexes span
only about 2 orders of magnitude. For the aliphatic
imines the diethyl derivative (3c, ∆pKa ) 0.23) is more
than an order of magnitude more acidic than the
dimethyl analogue (3b, ∆pKa ) 1.58), a result that is
difficult to reconcile with electronic properties. The
larger imine complex 3c (R/R′ ) Et/Et) is more acidic
than the smaller dialkyl analogues, probably due to a
relief of steric strain in the tungsten complex upon
deprotonation to form the linear azavinylidene complex.
Separate pKa values for the E and Z isomers of 3a
could not be obtained due to rapid isomerization of the
imine double bond in the presence of base. Relative pKa
measurements of related imine complexes were used to
probe factors influencing the acidity of these isomers.
[Tp′W(CO)(PhCCMe)(NHdCMe2)][BAr′4] (3b) with two
methyl groups, and of course a methyl group cis to
tungsten, is less acidic than the methyl/ethyl imine
complex 3a (R/R′ ) Me/Et). The dimethyl imine complex
3b may approximate the E isomer of complex 3a in acid/
base behavior because they both have a methyl group
cis to tungsten. Correspondingly, the diethyl imine
tion 11 would be 10-∆pK for B ) NEt3. A positive ∆pKa
a
(32) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456-463.
(33) Kaljurand, I.; Rodima, T.; Leito, I.; Koppel, I. A.; Schwesinger,
R. J . Org. Chem. 2000, 65, 6202-6208.
(34) Abdur-Rashid, K.; Fong, T. P.; Greaves, B.; Gusev, D. G.;
Hinman, J . G.; Landau, S. E.; Lough, A. J .; Morris, R. H. J . Am. Chem.
Soc. 2000, 122, 9155-9171.
(35) Fraser, R. R.; Bresse, M.; Chuaqui-Offermanns, N.; Houk, K.
N.; Rondan, N. G. Can. J . Chem. 1983, 61, 2729-2734.
(36) Rodima, T.; Kaljurand, I.; Pihl, A.; Ma¨emets, V.; Leito, I.;
Koppel, I. A. J . Org. Chem. 2002, 67, 1873-1881.
(37) Streitwieser, A.; Kim, Y. J . J . Am. Chem. Soc. 2000, 122,
11783-11786.

1384 Organometallics, Vol. 23, No. 6, 2004
Vogeley et al.
Ta ble 3. P r oton Tr a n sfer Ra te Con sta n ts (in
M-1s-1
)
R/R′
k1 (k-1
)
k2
k-2
Me/Me (3b) 4600 ( 2000 (39 ( 10) × 104
(20 ( 4) × 104
Et/Et (3c)
470 ( 300
(1.8 ( 0.2) × 104 (0.61 ( 0.1) × 104
complex [Tp′W(CO)(PhCCMe)(NHdCEt2)][BAr′4] (3c) is
more acidic than methyl/ethyl imine complex 3a . This
complex, with an ethyl group cis to tungsten, may
approximate the acidity of the Z isomer of imine
complex 3a . Note that the relative pKa of imine complex
3a reflects an average of the pKa’s of both the E and Z
isomers.
All of the aromatic imine complexes are more acidic
than the aliphatic complexes. Substitution at the para
position reveals a clear electronic influence on their
acidity. The electron-withdrawing bromo-substituted
imine complex 3f is the most acidic, while the electron-
donating methoxy-substituted imine complex 3e is the
least acidic of the three aromatic imine complexes. The
aromatic amine complexes follow a similar trend, al-
though the variation in acidity is less pronounced.
Deprotonation of an amine complex to form an amido
complex leads to little relief of steric strain, and since
there is no conjugation between the phenyl group and
the nitrogen in the amine/amido pairs, electronic influ-
ences are muted in the amine/amido acid/base pairs.38-40
Kin etic Acid ity Mea su r em en ts. The difference in
reactivity between the E and Z isomers of imine complex
3a in the presence of Na[HBEt3] is surely a kinetic
phenomenon. Direct assessment of the kinetic acidity
of each of these E/ Z isomers proved to be elusive since
fast isomerization of the E and Z isomers in the presence
of base makes it difficult to separate their reactivity.
Kinetic acidity measurements of the symmetrically
substituted imine complexes 3b and 3c were used to
probe germane features of these complexes.
Self-exchange proton transfer rates were measured
between imine complexes and the corresponding aza-
vinylidene complexes using 1H NMR line shape analysis
(eq 14).41,42 The proton transfer rate between each imine
complex and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene)
was also measured (eq 15). The self-exchange rate was
too slow to contribute to the observed proton transfer
rate with DBU, so k1 (due to self-exchange) was ignored
in the calculation of k2 (due to DBU). Rate constants
for eqs 14 and 15 are shown in Table 3.
an ethyl group cis to the imine proton, which would
impede deprotonation and thus allow hydride addition
to dominate. This difference in E/ Z reactivity coupled
with high facial selectivity for hydride addition to the
E isomer can explain the observed diastereoselectivity.
Kin etic ver su s Th er m od yn a m ic Acid ity. The
kinetic acidities for imine complexes 3b and 3c are
juxtaposed with the equilibrium acidity data. In other
words, complex 3b has a lower equilibrium acidity but
a higher kinetic acidity than complex 3c. This is
contrary to the Brønsted catalysis law, which states that
equilibrium acidity should be proportional to kinetic
acidity.43 There are, however, numerous examples of
systems with a negative Brønsted coefficient.44-47
In this system, the negative Brønsted coefficient
results from the alkyl substituents on the imine carbon.
The thermodynamic acidity is governed by the substitu-
ent cis to tungsten, with larger substituents resulting
in a more acidic imine proton through release of steric
strain upon deprotonation. Kinetic acidity is controlled
by the substituent trans to tungsten, with larger groups
blocking access to the imine proton and decreasing the
rate of proton transfer. This results in a need for
different model complexes to estimate the thermody-
namic and kinetic acidities of the E and Z isomers of
complex 3a (Table 4). Note that the E isomer is expected
to have both a lower thermodynamic and kinetic acidity
than the Z isomer due to unsymmetrical substitution
at the imine carbon.
The proton transfer rate constant (k2) for imine
complex 3c, with an ethyl group cis to the imine proton,
is 20 times slower than for imine complex 3b, with a
methyl group cis to the imine proton. The difference in
rates can be attributed to steric crowding of the imine
proton by the ethyl group. This result provides a
plausible explanation for the reactivity observed for the
E and Z isomers of imine complex 3a . The Z isomer has
a methyl group cis to the imine proton and would be
susceptible to rapid deprotonation. The E isomer has
Mech a n ism for Dia ster eoselectivity. To probe
why hydride addition occurs with such high diastereo-
(38) Another possibility is that the acidity of the bulky complexes
is due to steric hindrance inhibiting effective solvation.
(39) Brown, H. C.; Kanner, B. J . Am. Chem. Soc. 1966, 88, 986-
992.
(40) Condon, F. E. J . Am. Chem. Soc. 1965, 87, 4494-4496.
(41) Edidin, R. T.; Sullivan, J . M.; Norton, J . R. J . Am. Chem. Soc.
1987, 109, 3945-3953.
(42) J ordan, R. F.; Norton, J . R. J . Am. Chem. Soc. 1982, 104, 1255-
1263.
(43) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in
Organic Chemistry, 3rd ed.; Harper & Row: New York, 1987.
(44) March, J . Advanced Organic Chemistry: Reactions, Mecha-
nisms, and Structure, 4th ed.; J ohn Wiley & Sons: New York, 1992.
(45) Kresge, A. J . Can. J . Chem. 1974, 52, 1897-1903.
(46) Bordwell, F. G.; Bartmess, J . E.; Hautala, J . A. J . Org. Chem.
1978, 43, 3107-3113.
(47) Bernasconi, C. F.; Sun, W.; Garcia-R´ıo, L.; Yan, K.; Kittredge,
K. J . Am. Chem. Soc. 1997, 119, 5583-5590.

Diastereoselective Hydride Addition
Organometallics, Vol. 23, No. 6, 2004 1385
Ta ble 4. Com p a r ison of Mod el Com p lexes Used for Kin etic a n d Th er m od yn a m ic Acid ity
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Tp ′W(CO)(P h CCMe)(NH2CHMeEt)][BAr ′4]
(5a )
Ta ble 6. Cr ysta llogr a p h ic Da ta Collection
P a r a m eter s for 5a
formula
mol wt
cryst syst
space group
a, Å
WC61H53B2F24N7O
1561.55
triclinic
P1h
12.3978(5)
15.9301(7)
17.9054(7)
90.020(1)
75.844(1)
72.9054(7)
3261.47(23)
2
W1-N3
N3-C4
W1-C10
W1-C9
W1-N21
W1-N31
W1-N41
2.204(4)
1.494(8)
2.005(5)
2.025(5)
2.219(4)
2.149(4)
2.233(4)
W1-N3-C4
N3-C4-C5
N3-C4-C6
C4-C5-C6
C1-W1-N41
N3-W1-N31
125.5(4)
113.8(7)
111.6(7)
113.2(9)
166.51(19)
158.75(15)
b, Å
c, Å
R, deg
â, deg
γ, deg
selectivity, identification of the amido diastereomer
formed upon hydride addition was pursued. Hydride
reduction of imine complex 3a on a preparatory scale
yields amido complex 2a . Chromatography on alumina
protonates the amido complex to form amine complex
5a , [Tp′W(CO)(PhCCMe)(NH2CHMeEt)][BAr′4]. Neither
stereocenter (W or C) is involved in protonation at
nitrogen. Recrystallization using CH2Cl2 and hexanes
resulted in X-ray quality crystals of one diastereomer
of amine complex 5a , and an X-ray structure revealed
that the SS enantiomer was obtained. An ORTEP of
[Tp′W(CO)(PhCCMe)(NH2CHMeEt)][BAr′4] (5a) is shown
in Figure 4. Selected bond distances and angles are
shown in Table 5, and crystallographic data collection
parameters are shown in Table 6. Chirality at tungsten
was assigned by treating Tp′ as an η3 ligand and using
V, Å3
Z
calcd density, g/mL
F(000)
1.590
1552.28
0.25 × 0.25 × 0.20
-100
Mo KR, 0.71073
5-56
1.89
cryst dimens, mm
temp, °C
radiation (λ,Å)
2θ range, deg
µ, mm-1
scan mode
total no. of rflns
total no. of unique rflns
Rmerge
ω
27 407
11 477
0.030
(I > 2.5σ(I))
RF, %
10103
0.042
Rw, %
0.051
GoF
2.0406
max ∆/σ
0.004
-1.210 to 1.170
residual density, e/Å3
the Baird/Sloan modification of the Cahn-Ingold-
Prelog priority rules.48,49 1H NMR spectroscopy of the
single crystal actually used in the X-ray data collection
and analysis confirmed it to be the major diastereomer.
In order for hydride addition to form the SS/ RR pair
of enantiomers from the E isomer of the imine ligand,
hydride must attack along the tungsten-alkyne axis in
the major W-N conformation with the NH between the
pyrazole rings. The preference for this direction of attack
may result from a steric interaction between the imine
methyl and alkyne methyl groups. This interaction
would cause the W-N bond to rotate such that one face
of the imine ligand is blocked by a Tp′ methyl group.
Figure 5 shows the orientation of the imine ligand and
the direction of hydride addition required for formation
of the diastereomer that predominates. For the minor
(48) Sloan, T. E. Top. Stereochem. 1981, 12, 1-36.
(49) Stanley, K.; Baird, M. C. J . Am. Chem. Soc. 1975, 97, 6598-
9599.
F igu r e 4. ORTEP of (SS)-[Tp′W(CO)(PhCCMe)(NH2-
CHMeEt)][BAr′4] (5a ).

1386 Organometallics, Vol. 23, No. 6, 2004
Vogeley et al.
Na[BAr′4], and H(OEt2)2[BAr′4] were synthesized according to
literature procedures.51
NMR spectra were obtained using a Bruker AMX300,
DRX400, AMX400, or Avance 500 spectrometer. 2D spectra
were recorded on the Bruker AMX400 or Avance 500 spec-
trometer. NMR spectra of single X-ray crystals were obtained
on a Bruker Avance 500 spectrometer using a 3 mm probe.
Rep r esen ta tive [BAr ′4]- NMR Da ta . 1H NMR data for
the [BAr′4]- counterion are reported separately for simplicity.
1H NMR (CD2Cl2, δ): 7.72 (br, 8H, o-Ar′), 7.56 (br, 4H, p-Ar′).
13C{1H} NMR (CD2Cl2, δ): 162.2 (q, 1J BC ) 50 Hz, ipso of Ar′),
F igu r e 5. Newman-type projection along the imine-
tungsten axis of imine complex 3a showing the direction
of hydride addition to give the SS diastereomer.
2
4
135.2 (br, o-Ar′), 129.3 (q of q, J CF ) 31 Hz, J CF ) 3 Hz,
1
3
m-Ar′), 125.0 (q, J CF ) 272 Hz, CF3), 117.9 (septet, J CF ) 4
Hz, p-Ar′).
W-N conformation of the E isomer, the imine carbon
would be embedded in Tp′ shrubbery.
Tp ′W(CO)(P h CCMe)(NHCHMe2) (2b). [Tp′W(CO)2(PhC-
CMe)][OTf] (1.98 g, 2.5 mmol) was dissolved in THF to form a
green solution, which was heated at reflux for 1 h. After 1 h
the solution had turned blue, and 4.5 mL (53 mmol) of
isopropylamine was added. The solution temperature was
maintained at 40 °C overnight. The solvent was then removed
by rotary evaporation, and the orange oil was purified on an
alumina column with CH2Cl2 as the eluent. The lone orange
band was collected, and the solvent was removed by rotary
evaporation. The residual orange oil was dissolved in pentane
and sonicated to give an orange powder (1.33 g, 76% yield).
The product was recrystallized from a concentrated hexanes
Con clu sion
Hydride addition to an N-protio imine complex (3a )
occurs with high diastereoselectivity to form a primary
amido complex (2a ). The reaction of imine complex 3a
with hydride is under kinetic control. The E isomer
undergoes mostly hydride addition to give amido com-
plex 2a -SS/RR, while the Z isomer is mostly deproto-
nated to form azavinylidene complex d is-4a . This
difference in reactivity leads to effective differentiation
between methyl and ethyl groups despite the low E/ Z
ratio in the reagent imine complex.
The kinetic acidities of the E and Z isomers can be
explained using imine complexes 3b,c as models. Alkyl
substituents cis to the imine proton affect the kinetic
acidity. An ethyl group blocks access to the proton and
decreases the rate of proton transfer. If the substituent
cis to the imine proton is a methyl group, proton transfer
becomes more rapid. These data suggest that the Z
isomer of complex 3a is more kinetically acidic than the
E isomer.
The equilibrium acidity of the alkyl imine complexes
(3a -c) appears to be dominated by a steric interaction
due to the substituent cis to the tungsten complex. Relief
of this unfavorable steric interaction upon deprotonation
suggests that the Z isomer of 3a would have a greater
acidity. For the aryl imine complexes (3d -f), the acidity
is dominated by the electronic influence of the aryl ring.
Electron-donating substituents decrease the acidity,
while electron-withdrawing groups increase the acidity.
Both electronic and steric factors are less pronounced
in the acidity of the amine complexes (5a -f).
solution. IR (KBr): νCO ) 1856 cm-1 1H NMR (CD2Cl2, δ):
.
7.03, 6.30 (m, 5H, Ph), 5.86, 5.82, 5.57 (s, 3H, Tp′-CH), 4.46 (d
3
of septets, J HH ) 7 Hz, 10 Hz, 1H, NHCHMe2), 3.19 (s, 3H,
MeCtCPh), 2.76, 2.54, 2.39, 2.35, 1.60, 1.59 (s, 18H, Tp′-CH3),
0.96, 0.62 (d, 3J HH ) 7 Hz, 6H, NHCHMe2). 13C{1H} NMR (CD2-
Cl2, δ): 237.9 (CO), 169.6 (MeCtCPh), 166.6 (MeCtCPh),
153.4, 151.5, 150.6, 144.50, 144.46, 144.41 (Tp′-CMe), 137.9
(ipso Ph), 128.4, 128.1 (o,m Ph), 126.3 (p Ph), 108.4, 107.1,
106.3 (Tp′-CH), 64.1 (NHCHMe2), 27.5, 26.0 (NHCH(CH3)2),
18.4 (MeCtCPh), 15.7, 15.6, 14.8, 12.94, 12.92, 12.8 (Tp′-CH3).
Anal. Calcd for C28H38N7OBW‚C3H7: C, 51.26; H, 6.24; N,
13.50. Found: C, 51.23; H, 6.29; N, 13.25.
Tp ′W(CO)(P h CCMe)(NHCHE t2) (2c). [Tp′W(CO)2(PhC-
CMe)][OTf] (1.86 g, 2.3 mmol) was dissolved in THF to form a
green solution, which was heated at reflux for 1 h. 3-Amino-
pentane (NH2CHEt2) (0.8 mL, 6.9 mmol) was added, and the
reaction was heated at reflux for 2 days. The solvent was
removed by rotary evaporation. The residual oil was then
purified on an alumina column with CH2Cl2 as the eluent. The
orange band was collected, and the solvent was removed. The
remaining orange oil was dissolved in hexanes and sonicated
to produce an orange powder (1.38 g, 83% yield). IR (KBr):
νCO ) 1856 cm-1. 1H NMR (CD2Cl2, δ): 7.03, 6.27 (m, 5H, Ph),
5.85, 5.82, 5.56 (s, 3H, Tp′-CH), 4.11 (m, 1H, NH2CHEt2), 3.13
(s, 3H, MeCtCPh), 2.80, 2.54, 2.38, 2.35 (s, 12H, Tp′-CH3),
1.60 (s, 6H, Tp′-CH3), 1.19 (m, 3H, CH2CH3, CHHCH3), 1.00
(m, 1H, CHHCH3), 0.77 (t, 3J HH ) 8 Hz, 3H, CH2CH3), 0.57 (t,
3J HH ) 8 Hz, 3H, CH2CH3). 13C{1H} NMR (CD2Cl2, δ): 237.9
(CO), 169.2 (MeCtCPh), 166.1 (MeCtCPh), 153.4, 151.4,
150.5, 144.5, 144.29, 144.26 (Tp′-CMe), 138.0 (ipso Ph), 128.3,
128.1 (o,m Ph), 126.2 (p Ph), 108.4, 107.2, 106.2 (Tp′-CH), 73.7
(NH2CHEt2), 30.5, 29.7 (CH2CH3), 18.1 (MeCtCPh), 16.1, 15.7,
14.6, 13.0, 12.9, 12.8 (Tp′-CH3), 10.4, 9.8 (CH2CH3). Anal. Calcd
for C30H42N7OBW: C, 50.65; H, 5.95; N, 13.78. Found: C,
50.79; H, 6.06; N, 13.78.
Exp er im en ta l Section
Gen er a l P r oced u r es. Reactions were carried out under a
nitrogen atmosphere using Schlenk techniques. Methylene
chloride, diethyl ether, pentane, and hexanes were purified
by passage through a column of activated alumina. Tetrahy-
drofuran was distilled under nitrogen from sodium and ben-
zophenone. CD2Cl2, DBU, NEt3, and 4-methoxypyridine were
distilled from CaH2 and degassed by several freeze, pump,
thaw cycles. [Tp′W(CO)2(PhCCMe)][OTf] (1),26,50 Tp′W(CO)-
(PhCCMe)(NHCHMeEt) (2a ), [Tp′W(CO)(PhCCMe)(NHdCMe-
Et)][BAr′4] (3a), Tp′W(CO)(PhCCMe)(dNdCMeEt) (4a), [Tp′W-
(CO)(PhCCMe)(NHdCMePh)][BAr′4] (3d), [Tp′W(CO)(PhCCMe)-
(NH2CHMeEt)][BAr′4] (5a ),28 Tp′W(CO)(PhCCMe)(NHCHMe-
Ph) (2d ), [Tp′W(CO)(PhCCMe)(NH2CHMePh)][BAr′4] (5d ),26
Tp′W(CO)(P h CCMe)(NHCHMe(p-C6H4OMe)) (2e). Tp′W-
(CO)2(PhCCMe)[OTf] (1.88 g, 2.3 mmol) was dissolved in THF
to form a green solution, which was heated at reflux for 1 h.
4-Methoxy-R-methylbenzylamine [NH2CHMe(p-C6H4OMe)] (0.10
g, 6.6 mmol) was added, and the reaction was heated at reflux
overnight. By IR spectroscopy, the reaction was still incomplete
so more amine was added (0.37 g), and the reaction was heated
(50) Feng, S. G.; Philipp, C. C.; Gamble, A. S.; White, P. S.;
Templeton, J . L. Organometallics 1991, 10, 3504-3512.
(51) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.

Diastereoselective Hydride Addition
Organometallics, Vol. 23, No. 6, 2004 1387
at reflux for 4 h. The solvent was then removed by rotary
evaporation, and the orange oil was purified on an alumina
column with CH2Cl2 as the eluent. The orange band was
collected, and the solvent was removed by rotary evaporation.
Dissolution of the residual oil in hexanes and removal of
solvent gave an orange powder (0.95 g, 52% yield). Crystals
were obtained by slow diffusion of methanol into a CH2Cl2
solution of the amido complex. IR (KBr): νCO ) 1850 cm-1. 1H
NMR (CD2Cl2, δ): 7.1-6.7, 6.18 (6.33) (m, 9H, Ar-H), 5.90,
5.85, 5.55 (5.82, 5.74, 5.59) (s, 3H, Tp′-CH), 5.49 (5.41) (m, 1H,
CH), 3.82 (3.72) (s, 3H, OCH3), 2.86 (3.26) (s, 3H, MeCtCPh),
2.55, 2.39, 2.36 (x2), 1.72, 1.49 (2.55, 2.53, 2.39, 2.31, 1.66, 1.63)
190.4 (NHdCMe2), 153.1, 152.1, 151.1, 147.6, 147.4, 146.3 (Tp′-
CMe), 135.5 (ipso Ph), 130.7 (p Ph), 129.3, 129.0 (o,m Ph),
109.0, 108.5, 107.9 (Tp′-CH), 31.1, 27.1 (NHdCMe2), 23.1
(PhCtCMe), 16.0, 15.3, 13.7, 12.9, 12.7, 12.6 (Tp′-CH3). Anal.
Calcd for C60H49N7OF24B2W: C, 46.63; H, 3.20; N, 6.34.
Found: C, 46.50; H, 3.33; N, 7.03.
[Tp ′W(CO)(P h CCMe)(NHdCEt2)][BAr ′4] (3c). Tp′W(CO)-
(PhCCMe)(NHCHEt2) (2c) (0.55 g, 0.77 mmol) was dissolved
in CH2Cl2. Iodine (0.20 g, 0.77 mmol) and NEt3 (0.11 mL, 0.77
mmol) were added, and the solution was allowed to stir for 2
h. A solution of Na[BAr′4] (0.68 g, 0.77 mmol) in Et2O was
prepared and cannula transferred into the reaction vessel. A
white precipitate formed. The solution was cannula filtered,
and the solvent was removed by rotary evaporation. The
residual blue oil was purified on an alumina column using 1:1
CH2Cl2/hexanes as the eluent. The solvent was gradually
changed to pure CH2Cl2. The blue band was collected, the
solvent was removed, and the blue oil was recrystallized from
CH2Cl2/hexanes (0.62 g, 51% yield). IR (KBr): νCO ) 1920, 1927
3
(s, 18H, Tp′-CH3), 1.20 (0.92) (d, J HH ) 7 Hz, 3H, CHCH3).
13C{1H} NMR (CD2Cl2, δ): 237.7, 237.2 (CO), 171.2, 170.4,
169.9, 167.1 (MeCtCPh), 153.7, 153.3, 151.5, 151.2, 150.7,
150.6, 144.6, 144.5, 144.4 (×2), 142.5, 141.9 (Tp′-CMe), 158.4,
158.3, 138.2, 137.9, 126.3, 126.2 (ipso Ar), 128.4, 128.2, 128.1,
128.08, 127.6, 126.7, 113.8, 113.6 (o,m,p Ar), 108.5, 108.4,
107.4, 107.0, 106.3, 106.2 (Tp′-CH), 72.1, 70.8 (NHCHMeAr),
55.7, 55.5 (OCH3), 30.1, 28.7 (NHCHMeAr), 18.5, 17.2 (MeCt
CPh), 16.0, 15.7 (×2), 15.6, 15.0, 14.8, 13.0, 12.93, 12.91, 12.86,
12.80 (×2) (Tp′-CH3). Anal. Calcd for C34H42N7O2BW: C, 52.67;
H, 5.46; N, 12.64. Found: C, 52.39; H, 5.38; N, 12.66.
1
cm-1. H NMR (CD2Cl2, δ): 8.84 (br, 1H, NH), 7.31, 6.70 (m,
5H, Ph), 6.02, 5.95, 5.79 (s, 3H, Tp′-CH), 3.80 (s, 3H, PhCt
CCH3), 2.58, 2.52, 2.42, 2.40, 1.40, 1.19 (s, 18H, Tp′-CH3), 2.55
(m, 1H, CHHCH3), 2.45 (m, 2H, CHHCH3, CHHCH3), 2.15 (m,
3
1H, CHHCH3), 1.03 (br t, J HH ) 8 Hz, 3H, CH2CH3), 0.87 (t,
Tp ′W(CO)(P h CCMe)(NHCHMe(p-C6H4Br )) (2f). [Tp′W-
(CO)2(PhCCMe)][OTf] (1.88 g, 2.3 mmol) was dissolved in THF
to form a green solution that was heated at reflux for 1 h.
4-Bromo-R-methylbenzylamine [NH2CHMe(p-C6H4Br)] (1.6
mL, 11.2 mmol) was added to the reaction, and it was heated
at reflux overnight. The solvent was then removed by rotary
evaporation, and the orange oil was purified on an alumina
column with CH2Cl2 as the eluent. The orange band was
collected, and the solvent was removed to give an orange oil.
The oil was dissolved in hexanes and sonicated to give an
3J HH ) 8 Hz, 3H, CH2CH3). 13C{1H} NMR (CD2Cl2, 260 K, δ):
228.8 (CO), 216.3 (PhCtCMe), 213.2 (PhCtCMe), 196.6 (NHd
CEt2), 152.9, 152.2, 151.3, 147.63, 147.57, 146.4 (Tp′-CMe),
135.6 (ipso Ph), 130.8 (p Ph), 129.2, 129.1 (o,m Ph), 109.1,
108.6, 108.0 (Tp′-CH), 33.0, 32.4 (CH2CH3), 23.1 (PhCtCCH3),
16.1, 15.4, 13.9, 12.9, 12.8, 12.7 (Tp′-CH3), 10.0, 9.1 (CH2CH3).
Anal. Calcd for C62H53N7OF24B2W: C, 47.32; H, 3.39; N, 6.23.
Found: C, 47.35; H, 3.37; N, 6.36.
[Tp ′W(CO)(P h CCMe)(NH dCMe(p -C6H 4OMe))][BAr ′4]
(3e). Tp′W(CO)(PhCCMe)(NHCHMe(C6H4OMe)) (2e) (0.46 g,
0.59 mmol) was dissolved in CH2Cl2. Iodine (0.15 g, 0.60 mmol)
and NEt3 (82 µL, 0.59 mmol) were added, and the reaction
was allowed to stir for 2 h. The solvent was then removed by
rotary evaporation to give a green oil, which was purified on
an alumina column with 1:1 CH2Cl2/hexanes as the eluent.
The solvent was gradually changed to pure CH2Cl2. The green
band was collected and recrystallized from CH2Cl2/hexanes
(0.51 g, 53% yield). IR (KBr): νCO ) 1918 cm-1. 1H NMR (CD2-
Cl2, 271 K, δ): 9.16 (s, 1H, NH), 7.28 (m, 5H, C6H4OMe, Ph),
6.88 (d, 2H, C6H4OMe), 6.71 (m, 2H, Ph), 5.99, 5.92, 5.80 (s,
3H, Tp′-CH), 3.86 (s, 3H, PhCtCCH3), 3.78 (s, 3H, OCH3),
2.57, 2.51, 2.41, 2.39, 1.42, 1.13 (s, 18H, Tp′-CH3), 2.45 (NHd
CMeAr). 13C NMR (CD2Cl2, 271 K, δ): 229.2 (CO), 215.4 (PhCt
CMe), 212.9 (PhCtCMe), 182.3 (NHdCMeAr), 153.2, 152.3,
151.4, 147.63, 147.55, 146.4 (Tp′-CMe), 164.4, 135.7, 130.7,
126.9 (ipso, p C6H4OMe, Ph), 129.4, 129.1, 128.9, 115.1 (o,m
C6H4OMe, Ph), 109.2, 108.7, 108.1 (Tp′-CH), 56.0 (OCH3), 24.6
(NHdCMeAr), 23.2 (PhCtCCH3), 16.1, 15.3, 13.7, 13.0, 12.8,
12.7 (Tp′-CH3). Anal. Calcd for C66H53N7O2B2F24W: C, 48.41;
H, 3.26; N, 5.99. Found: C, 48.54; H, 3.25; N, 6.04.
orange powder (1.63 g, 83% yield). IR (KBr): νCO ) 1854 cm-1
.
1H NMR (CD2Cl2, δ): 7.40, 6.83 (7.32) (d, 4H, C6H4Br), 7.04,
6.19 (6.33) (m, 5H, Ph), 5.91, 5.86, 5.55 (5.83, 5.75, 5.59) (s,
3
3H, Tp′-CH), 5.51 (dq, J HH ) 7 Hz, 8 Hz, 1H, NHCHMeAr)
3
(5.43) (dq, J HH ) 7 Hz, 10 Hz, 1H, NHCHMeAr), 2.85 (3.27)
(s, 3H, MeCtCPh), 2.55, 2.39, 2.37, 2.36, 1.72, 1.49 (2.54, 2.48,
3
2.40, 2.32, 1.65, 1.62) (s, 18H, Tp′-CH3), 1.21 (0.92) (d, J HH
)
7 Hz, 3H, NHCHMeAr). 13C{1H} NMR (CD2Cl2, δ): 236.9
(237.5) (CO), 172.1 (171.2) (MeCtCPh), 170.3 (167.8) (MeCt
CPh), 153.7 (153.2) (ipso C6H4Br), 151.5, 150.8, 148.9, 144.64,
144.56, 144.5 (151.2, 150.7, 149.3, 144.5) (Tp′-CMe), 138.0
(137.8) (ipso Ph), 131.2, 128.8, 128.20, 128.16 (131.5, 128.4,
128.14, 127.7) (o,m Ph, C6H4Br), 126.3 (126.4) (p Ph), 119.4
(119.7) (ipso C6H4Br), 108.5, 107.4, 106.4 (108.4, 107.0, 106.3)
(Tp′-CH), 70.8 (72.3) (NHCHMeAr), 28.5 (26.1) (NHCHMeAr),
17.2 (18.6) (MeCtCPh), 15.68, 15.65, 15.0, 13.0, 12.9, 12.8
(16.0, 15.6, 14.7, 12.85) (Tp′-CH3). Anal. Calcd for C33H39N7-
OBrBW‚C3H7: C, 49.85; H, 5.35; N, 11.30. Found: C, 49.98;
H, 5.24; N, 11.24.
[Tp ′W(CO)(P h CCMe)(NH dCMe2)][BAr ′4] (3b ). Tp′W-
(CO)(PhCCMe)(NHCHMe2) (2b) (0.77 g, 1.1 mmol) was dis-
solved in CH2Cl2. Iodine (0.28 g, 1.1 mmol) and NEt3 (0.15 mL,
1.1 mmol) were added, and the solution was allowed to stir
for 2 h. A solution of Na[BAr′4] (0.98 g, 1.1 mmol) in Et2O was
prepared and cannula transferred into the reaction vessel. A
white precipitate formed. The solution was cannula filtered
away from the solid, and the solvent was removed from the
filtrate by rotary evaporation. The residual blue oil was
purified on an alumina column using 1:1 CH2Cl2/hexanes. The
solvent mixture for elution was gradually changed to pure CH2-
Cl2. The blue band was collected, solvent was removed, and
the blue oil was recrystallized from CH2Cl2/hexanes (1.02 g,
[Tp ′W(CO)(P h CCMe)(NHdCMe(p-C6H4Br ))][BAr ′4] (3f).
Tp′W(CO)(PhCCMe)(dNdCMe(C6H4Br)) (4f) (0.11 g, 0.13
mmol) was dissolved in CH2Cl2 to give an orange solution. In
the drybox, H[BAr′4] (0.13 g, 0.13 mmol) was weighed into
another flask. The H[BAr′4] was put on the Schlenk line, cooled
to 0 °C, and dissolved in CH2Cl2. The H[BAr′4] solution was
then cannula transferred to the azavinylidene complex solu-
tion, which turned blue. The solvent was removed in vacuo,
and the blue oil was recrystallized using CH2Cl2/hexanes (0.18
1
g, 77% yield). IR (KBr): νCO ) 1918 cm-1. H NMR (CD2Cl2,
253 K, δ): 9.38 (s, 1H, NH), 7.57, 7.11 (d, 4H, C6H4Br), 7.28,
6.73 (m, 5H, Ph), 6.01, 5.91, 5.79 (s, 3H, Tp′-CH), 3.88 (s, 3H,
PhCtCCH3), 2.57, 2.50, 2.41, 2.40, 1.39, 1.10 (s, 1:1:1:2:1:1,
21H, Tp′-CH3, NHdCMeAr). 13C NMR (CD2Cl2, 253 K, δ):
228.0 (CO), 216.0 (PhCtCMe), 213.8 (PhCtCMe), 182.5 (NHd
CMeAr), 152.9, 152.1, 151.2, 147.60, 147.56, 146.4 (Tp′-CMe),
135.4, 133.8, 130.8, 128.9 (ipso, p C6H4Br, Ph), 133.0, 129.3,
1
60% yield). IR (KBr): νCO ) 1924 cm-1. H NMR (CD2Cl2, δ):
8.99 (br, 1H, NH), 7.31, 6.71 (m, 5H, Ph), 6.01, 5.95, 5.79 (s,
3H, Tp′-CH), 3.81 (s, 3H, PhCtCCH3), 2.58, 2.51, 2.44, 2.42,
3
1.39, 1.24 (s, 18H, Tp′-CH3), 2.25 (d, J HH ) 2 Hz, 3H, NHd
CMeCH3), 2.09 (br, 3H, NHdCH3Me). 13C{1H} NMR (CD2Cl2,
263K, δ): 229.1 (CO), 215.8 (PhCtCMe), 212.9 (PhCtCMe),

1388 Organometallics, Vol. 23, No. 6, 2004
Vogeley et al.
129.0, 127.8 (o,m C6H4Br, Ph), 109.0, 108.7, 108.0 (Tp′-CH),
24.9 (NHdCMeAr), 23.4 (PhCtCCH3), 16.1, 15.3, 13.7, 12.9,
12.8, 12.6 (Tp′-CH3). Anal. Calcd for C65H50N7OB2BrF24W: C,
46.29; H, 2.99; N, 5.81. Found: C, 46.30; H, 3.03; N, 5.73.
Tp ′W(CO)(P h CCMe)(dNdCMe2) (4b). KH (1 g, 30 w/w
in mineral oil) was washed three times with 10 mL of pentane
and dried in vacuo. A THF solution of imine complex 3b (0.14
g, 0.09 mmol) was cannula transferred into the flask contain-
ing the dry KH. After a few minutes, the blue solution turned
orange. The solution was cannula filtered, and the solvent was
removed in vacuo. The residual orange oil was dissolved in
pentane. This solution was then cannula filtered away from
the insoluble salts. The solvent was concentrated in vacuo, and
complex 3f to azavinylidene complex 4f. Four more equivalents
of NEt3 were added to fully deprotonate the imine complex.
The solvent was then removed by rotary evaporation, and the
residual oil was purified on an alumina column with 1:1 CH2-
Cl2/hexanes. The orange band was collected, and the solvent
was removed to give an orange oil. A powder was obtained by
sonication of the product in hexanes (0.19 g, 64% yield). Two
1
isomers are observed in the H NMR in a 7:1 ratio. IR (KBr):
νCO ) 1883 cm-1. 1H NMR (CD2Cl2, δ): 7.36, 6.77 (d, 4H, C6H4-
Br), 7.06, 6.47 (m, 5H, Ph), 5.96, 5.65, 5.64 (Tp′-CH), 3.27 (3.19)
(s, 3H, PhCtCCH3), 2.74, 2.50, 2.42, 2.41, 1.67, 1.17 (2.52, 2.44,
2.43, 2.32, 1.61, 1.46) (s, 18H, Tp′-CH3), 1.98 (s, 3H, dNdCCH3-
Ar). 13C{1H} NMR (CD2Cl2, δ): 229.9 (CO), 158.5 (PhCtCMe),
157.1 (PhCtCMe), 152.8, 152.5, 151.0, 144.9, 144.3, 144.0 (Tp′-
CMe), 150.1 (dNdCMeAr), 139.2, 137.6 (ipso C6H4Br, Ph),
130.8, 128.6, 128.3, 127.1 (o,m C6H4Br, Ph), 126.5 (p Ph), 119.9
(ipso C6H4Br) (131.5, 130.7, 128.6, 128.4, 126.9) (minor Ar),
107.3, 107.0, 106.8 (107.2, 106.6) (Tp′-CH), 18.0 (PhCtCCH3),
16.8, 15.9, 14.6, 13.0, 12.9, 12.85 (Tp′-CH3), 16.3 (dNdCCH3-
Ar). Anal. Calcd for C33H37N7OBrBW‚C3H7: C, 49.97; H, 5.12;
N, 11.33. Found: C, 49.58; H, 5.04; N, 11.37.
crystals began to grow (0.050 g, 78% yield). IR (KBr): νCO
)
1868 cm-1 1H NMR (CD2Cl2, δ): 7.06, 6.41 (m, 5H, Ph), 5.89,
.
5.71, 5.60 (s, 3H, Tp′-CH), 3.11 (s, 3H, PhCtCCH3), 2.70, 2.51,
2.40, 2.38, 1.60, 1.49 (s, 18H, Tp′-CH3), 1.62, 1.57 (s, 6H, d
NdCMe2). 13C{1H} NMR (CD2Cl2, δ): 234.0 (CO), 159.0, 158.0,
152.1 (dNdCMe2, PhCtCMe), 152.5, 152.3, 150.7, 144.6,
144.1, 143.8 (Tp′-CMe), 138.0 (ipso Ph), 128.6, 128.2 (o,m Ph),
126.2 (p Ph), 107.2, 106.8, 106.5 (Tp′-CH), 22.0, 21.1 (dNd
CMe2), 17.8 (PhCtCCH3), 16.7, 15.8, 14.6, 12.94, 12.90, 12.8
(Tp′-CH3). Satisfactory elemental analysis was not obtained.
Tp ′W(CO)(P h CCMe)(dNdCEt2) (4c). KH (1 g, 30 w/w in
mineral oil) was washed three times with 10 mL of pentane
and dried in vacuo. A THF solution of imine complex 3c (0.19
g, 0.12 mmol) was cannula transferred into the flask contain-
ing the dry KH. After a few minutes, the blue solution turned
yellow. The solution was cannula filtered, and the solvent was
removed in vacuo. The residual orange oil was dissolved in
pentane. This solution was then cannula filtered away from
the insoluble salts. The solvent was removed in vacuo. Crystals
were grown in a concentrated pentane solution (0.065 g, 75%
yield). IR (KBr): νCO ) 1868 cm-1. 1H NMR (CD2Cl2, δ): 7.06,
6.43 (m, 5H, Ph), 5.88, 5.70, 5.60 (s, 3H, Tp′-CH), 3.07 (s, 3H,
PhCtCCH3), 2.68, 2.50, 2.40, 2.38, 1.60, 1.50 (s, 18H, Tp′-CH3),
2.24, 2.08 (dq, 2H, 3J HH ) 8 Hz, 2J HH ) 17 Hz, CH2CH3), 1.90,
[Tp ′W(CO)(P h CCMe)(NH2CHMe2)][BAr ′4] (5b). Tp′W-
(CO)(PhCCMe)(NHCHMe2) (2b) (0.17 g, 0.25 mmol) was
dissolved in CH2Cl2 to give an orange solution. In the drybox,
H[BAr′4] (0.23 g, 0.25 mmol) was weighed into another flask.
The H[BAr′4] was put on the Schlenk line, cooled to 0 °C, and
dissolved in CH2Cl2. The H[BAr′4] solution was then cannula
transferred to the amido complex solution, which turned blue.
The solvent was removed in vacuo, and the blue oil was
recrystallized using CH2Cl2/hexanes (0.27 g, 72% yield). IR
1
(KBr): νCO ) 1930 cm-1. H NMR (CD2Cl2, δ): 7.37, 6.77 (m,
5H, MeCtCPh), 6.13, 6.05, 5.83 (s, 3H, Tp′-CH), 3.83 (s, 3H,
MeCtCPh), 2.79, 2.60, 2.54, 2.45, 1.55, 1.36 (s, 18H, Tp′-CH3),
3
2
3.45 (dd, J HH ) 5 Hz, J HH ) 13 Hz, 2H, NH2), 2.86 (d of
3
septets, J HH ) 5 Hz, 6 Hz, 1H, NH2CHMe2), 1.45, 0.89 (d,
3J HH ) 7 Hz, 6H, NH2CH(CH3)2). 13C NMR (CD2Cl2, δ): 230.3
(CO), 216.8 (PhCtCMe), 214.5 (PhCtCMe), 152.8, 151.4,
151.3, 148.4, 148.2, 147.0 (Tp′-CMe), 136.1 (ipso PhCtCMe),
131.2 (p-PhCtCMe), 129.5, 129.4 (o,m-PhCtCMe), 109.7,
109.6, 108.3 (Tp′-CH), 55.1 (NH2CHMe2), 24.7, 23.8 (NH2-
CHMe2), 23.3 (PhCtCMe), 16.1, 16.0, 14.2, 13.0, 12.9, 12.8
(Tp′-CH3). Anal. Calcd for C60H51N7OB2F24W: C, 46.57; H, 3.32;
N, 6.34. Found: C, 46.82; H, 3.40; N, 6.37.
3
2
1.77 (dq, 2H, J HH ) 8 Hz, J HH ) 14 Hz, CH2CH3), 0.67, 0.43
(t, 6H, 3J HH ) 8 Hz, CH2CH3). 13C{1H} NMR (CD2Cl2, δ): 234.6
(CO), 160.5, 158.8, 158.3 (dNd CEt2, PhCtCMe), 152.5, 152.1,
150.5, 144.4, 144.0, 143.6 (Tp′-CMe), 138.3 (ipso Ph), 128.5,
128.2 (o,m Ph), 126.1 (p Ph), 107.2, 106.7, 106.5 (Tp′-CH), 28.2,
27.1 (CH2CH3), 17.6 (PhCtCCH3), 16.8, 15.9, 14.2, 13.0, 12.91,
12.86 (Tp′-CH3), 11.6, 10.3 (CH2CH3). Satisfactory elemental
analysis was not obtained.
[Tp ′W(CO)(P h CCMe)(NH2CH E t 2)][BAr ′4] (5c). Tp′W-
(CO)(PhCCMe)(NHCHEt2) (2c) (0.15 g, 0.20 mmol) was dis-
solved in CH2Cl2 to give an orange solution. In the drybox,
H[BAr′4] (0.19 g, 0.20 mmol) was weighed into another flask.
The H[BAr′4] was put on the Schlenk line, cooled to 0 °C, and
dissolved in CH2Cl2. The H[BAr′4] solution was then cannula
transferred to the amido complex solution, which turned blue.
The solvent was removed in vacuo, and the blue oil was
recrystallized using CH2Cl2/hexanes (0.23 g, 75% yield). IR
Tp ′W(CO)(P h CCMe)(dNdCMe(p-C6H4OMe)) (4e). KH
(1 g, 30 w/w in mineral oil) was washed three times with 10
mL of pentane and dried in vacuo. A THF solution of imine
complex 3e (0.19 g, 0.11 mmol) was cannula transferred to
the dry KH. After a few minutes, the green solution had turned
orange. The solution was cannula filtered, and solvent was
removed in vacuo. The orange oil was dissolved in pentane.
This solution was then cannula filtered away from the
insoluble salts. The solvent was removed in vacuo to give an
1
(KBr): νCO ) 1937 cm-1. H NMR (CD2Cl2, δ): 7.33, 6.72 (m,
5H, MeCtCPh), 6.09, 6.00, 5.77 (s, 3H, Tp′-CH), 3.77 (s, 3H,
MeCtCPh), 2.74, 2.57, 2.50, 2.42, 1.49, 1.32 (s, 18H, Tp′-CH3),
orange powder (0.074 g, 87% yield). IR (KBr): νCO ) 1881 cm-1
.
3
2
1H NMR (CD2Cl2, δ): 7.04, 6.45 (m, 5H, Ph), 6.81 (m, 4H, C6H4-
OMe), 5.95, 5.64 (m, 1:2H, Tp′-CH), 3.78 (3.69) (s, 3H, OMe),
3.26 (3.16) (s, 3H, PhCtCCH3), 2.74, 2.50, 2.41, 2.40, 1.96,
1.67, 1.18 (2.54, 2.44, 2.43, 1.61, 1.47) (s, 21H, Tp′-CH3, dNd
CCH3Ar). 13C{1H} NMR (CD2Cl2, δ): 242.4 (CO), 158.7, 158.5,
157.2 (dNdCMeAr, PhCtCMe), 152.7, 152.5, 150.8, 144.8,
144.1, 143.8 (Tp′-CMe), 137.8, 132.5 (ipso Ph), 128.5, 128.2,
126.8, 126.3 (o,m Ph), 124.7 (ipso Ph), 113.3 (p Ph), 107.2,
106.9, 106.7 (Tp′-CH), 55.5 (OCH3), 18.0 (PhCtCCH3), 16.8,
16.7, 15.9, 14.6, 12.95, 12.9, 12.8 (Tp′-CH3, dNdCCH3Ar).
Satisfactory elemental analysis was not obtained.
3.33 (dd, J HH ) 7 Hz, J HH ) 13 Hz, 1H, NHH), 2.76 (m, 1H,
NHH), 2.67 (m, 1H, NH2CHEt2), 1.87 (ddq, 3J HH ) 4.5 Hz, 3J HH
2
) 8 Hz, J HH ) 15 Hz, 1H, NH2CH(CHHCH3)Et), 1.69 (d of
3
2
quintets, J HH ) 7 Hz, J HH ) 15 Hz, 1H, NH2CH(CHHCH3)-
Et), 1.03 (dq, 3J HH ) 6 Hz, 8 Hz, 2H, NH2CHEt(CH2CH3)), 0.89,
0.81 (t, 3J HH ) 8 Hz, 6H, CH2CH3). 13C NMR (CD2Cl2, δ): 230.1
(CO), 216.7 (PhCtCMe), 214.5 (PhCtCMe), 153.0, 151.5,
151.4, 148.4, 148.2, 147.0 (Tp′-CMe), 136.0 (ipso PhCtCMe),
131.2 (p-PhCtCMe), 129.4 (o,m-PhCtCMe), 109.73, 109.67,
108.3 (Tp′-CH), 64.0 (NH2CHEt2), 26.6, 25.4 (CH2CH3), 23.3
(PhCtCMe), 16.2, 16.0, 14.4, 12.98, 12.97, 12.8 (Tp′-CH3), 8.6,
8.5 (CH2CH3). Anal. Calcd for C62H55N7OB2F24W: C, 47.26; H,
3.52; N, 6.22. Found: C, 47.04; H, 3.40; N, 6.23.
Tp ′W(CO)(P h CCMe)(dNdCMe(p -C6H 4Br )) (4f). Tp′W-
(CO)(PhCCMe)(NHCHMe(p-C6H4Br)) (2f) (0.30 g, 0.36 mmol)
was dissolved in CH2Cl2. Iodine (0.092 g, 0.36 mmol) and NEt3
(50 µL, 0.36 mmol) were added, and the reaction was stirred
for 3 h. The IR spectrum then showed a 2:1 ratio of imine
[Tp ′W(CO)(P h CCMe)(NH 2CHMe(p-C6H4OMe))][BAr ′4]
(5e). Tp′W(CO)(PhCCMe)(NHCHMe(p-C6H4OMe)) (2e) (0.1959
g, 0.25 mmol) was dissolved in CH2Cl2 to give an orange

Diastereoselective Hydride Addition
Organometallics, Vol. 23, No. 6, 2004 1389
solution. In the drybox, H[BAr′4] (0.24 g, 0.25 mmol) was
weighed into another flask. The H[BAr′4] was put on the
Schlenk line, cooled to 0 °C, and dissolved in CH2Cl2. The
H[BAr′4] solution was then cannula transferred to the amido
complex solution, which turned blue. The solvent was removed
in vacuo, and the blue oil was recrystallized using CH2Cl2/
hexanes (0.31 g, 76% yield). The ratio of diastereomers was
observed to be 3.3:1 by 1H NMR. Differences for the minor
diastereomer are given in parentheses. IR (KBr): νCO ) 1920
(123.8) (ipso BrC6H4), 109.79, 109.7, 108.39 (109.84, 109.6,
108.37) (Tp′-CH), 62.3 (63.4) (NH2CHMePhBr), 24.3 (21.7)
(NH2CHMePhBr), 23.1 (23.7) (PhCtCMe), 16.2, 16.0, 14.5,
13.0, 13.0, 12.7 (16.1, 16.06, 14.7, 14.2, 12.9, 12.8) (Tp′-CH3).
Anal. Calcd for C65H52N7OBrB2F24W: C, 46.24; H, 3.10; N,
5.81. Found: C, 46.58; H, 3.33; N, 5.70.
[Tp ′W(CO)(P h CCMe)(NHdCMeE t )][BAr ′4] (3a ). Cor-
1
rected H NMR data were determined by gradient NOESY and
COSY techniques. Differences for the minor Z isomer are listed
in parentheses. The E/ Z ratio in CD2Cl2 can range from 75:
25 to 93:7 depending on the recrystallization method. The E/ Z
ratio in THF-d8 is 60:40. 1H NMR (CD2Cl2, 298 K, δ): 8.92
(br, 1H, NH), 7.31, 6.71 (m, 5H, Ph), 6.02, 5.95, 5.79 (s, 3H,
Tp′-CH), 3.82, (3.80) (s, 3H, PhCtCMe), 2.58, 2.51, 2.42, 2.42,
1.39, (1.23), 1.21 (s, 18H, Tp′-CH3), 2.47 (m, 1H, CHHCH3)
cm-1
.
1H NMR (CD2Cl2, δ): 7.35, 6.77 (6.43) (m, 5H, MeCt
3
CPh), 7.13, 6.92 (6.85) (d, J HH ) 9 Hz, 4H, C6H4OMe), 6.02,
5.97, 5.78 (6.11, 5.92, 5.77) (s, 3H, Tp′-CH), 4.37 (3.43) (m,
1H, NH2CHMePhOMe), 3.87 (3.60) (s, 3H, CH3CtCPh), 3.77
3
(3.76) (s, 3H, OCH3), 3.77 (m, 1H, NHH), 2.94 (d, J HH ) 14
Hz, 1H, NHH), 2.55, 2.50, 2.49, 2.37, 1.69, 1.35 (2.87, 2.53,
3
4
2.41, 2.12, 1.38, 1.32) (s, 18H, Tp′-CH3), 1.02 (1.74) (d, J HH
)
(2.22) (d, J HH ) 1 Hz, 3H, NHdCMeEt), 2.05 (br, 3H, NHd
7 Hz, 3H, NH2CHMePhOMe). 13C NMR (CD2Cl2, δ): 230.4
(229.8) (CO), 217.2 (216.7) (PhCtCMe), 214.4 (214.7) (PhCt
CMe), 160.8 (ipso MeOC6H4), 153.0, 151.4, 151.3, 148.29,
148.27 (Tp′-CMe), 136.0 (ipso PhCtCMe), 134.0 (ipso C6H4-
OMe), 131.3 (p-PhCtCMe), 129.5, 129.4 (o,m-PhCtCMe),
127.1, 115.3 (127.0, 115.2) (o, m PhOMe), 109.8, 109.5, 108.3
(Tp′-CH), 63.4 (62.5) (NH2CHMePhOMe), 55.7 (OMe), 23.7
(PhCtCMe), 21.8 (23.0) (NH2CHMePhOMe), 16.0, 16.11 (16.15),
14.7 (14.2), 13.0, 12.9, 12.8 (Tp′-CH3). Anal. Calcd for
CMeEt), 1.26 (m, 1H, CHHCH3), (1.06) (br, 3H, CH2CH3), 0.92
3
(t, J HH ) 7 Hz, 3H, CH2CH3). 1H NMR (THF-d8, 298 K, δ):
10.07 (10.14) (br, 1H, NH), 7.29, 6.75 (m, 5H, Ph), 6.12, 6.03,
5.85 (s, 3H, Tp′-CH), 3.86 (3.85) (s, 3H, PhCtCMe), 2.62, 2.53,
2.50, 2.45, (1.44) 1.43, (1.31) 1.30 (s, 18H, Tp′-CH3), 2.10 (2.28)
(s, 3H, NHdCMeEt), 2.11, 2.50 (m, 2H, CH2CH3), 1.04 (1.07)
3
(t, J HH ) 8 Hz, 3H, CH2CH3).
E-En r ich ed [Tp ′W(CO)(P h CCMe)(NHdCMeEt)][BAr ′4]
(3a ). Crystals of 75:25 E:Z imine complex 3a (0.163 g, 0.105
mmol) were dissolved in a mixture of 3:2:1 hexanes/CH2Cl2/
THF (1 mL) and layered with hexanes (30 mL). The crystals
that formed were enriched in the E isomer of imine complex
(0.149 g, 0.0953 mmol, 91% yield). A range of E/ Z ratios can
be obtained by this method from 80:20 to 93:7.
C
66H55N7O2B2F24W: C, 48.35; H, 3.38; N, 5.98. Found: C,
47.70; H, 3.38; N, 6.01.
[Tp′W(CO)(P h CCMe)(NH2CHMe(p-C6H4Br ))][BAr ′4] (5f).
Tp′W(CO)(PhCCMe)(NHCHMe(p-C6H4Br)) (2f) (0.21 g, 0.25
mmol) was dissolved in CH2Cl2 to give an orange solution. In
the drybox, H[BAr′4] (0.24 g, 0.25 mmol) was weighed into
another flask. The H[BAr′4] was put on the Schlenk line, cooled
to 0 °C, and dissolved in CH2Cl2. The H[BAr′4] solution was
then cannula transferred to the amido complex solution, which
turned blue. The solvent was removed in vacuo, and the blue
oil was recrystallized using CH2Cl2/hexanes (0.34 g, 80% yield).
The ratio of diastereomers was observed to be 1.6:1 by 1H
NMR. Differences for the minor diastereomer are given in
(SS)-[Tp ′W(CO)(P h CCMe)(NH2CHMeEt)][BAr ′4] (5a ).
[Tp′W(CO)(PhCCMe)(NHdCMeEt)][BAr′4] (3a ) (90:10 E/ Z,
0.11 g, 0.07 mmol) was dissolved in CH2Cl2. Li[HBEt3] (0.12
mL, 0.12 mmol) was added to the imine solution, and Tp′W-
(CO)(PhCCMe)(NHCHMeEt) (2a ) formed immediately. The
orange solution was then purified on an alumina column with
1:1 hexanes/CH2Cl2 as the eluent. A blue band of [Tp′W(CO)-
(PhCCMe)(NH2CHMeEt)][BAr′4] (5a ) was collected and re-
crystallized using CH2Cl2/hexanes. The stereochemistry was
then determined by X-ray analysis.
parentheses. IR (KBr): νCO ) 1924 cm-1
.
1H NMR (CD2Cl2,
3
δ): 7.51, 6.89 (7.57, 7.85) (d, J HH ) 9 Hz, 4H, C6H4Br), 7.35,
6.65 (6.77) (m, 5H, MeCtCPh), 6.12, 5.93, 5.78 (6.03, 5.98,
5.78) (s, 3H, Tp′-CH), 3.40 (4.41) (m, 1H, NH2CHMePhBr), 3.89
Ack n ow led gm en t. We gratefully acknowledge the
Petroleum Research Fund and the National Science
Foundation for their support.
3
(3.78) (m, 1H, NHH), (2.97) (d, J HH ) 14 Hz, 1H, NHH), 3.23
3
2
(dd, J HH ) 9 Hz, J HH ) 13 Hz, 1H, NHH), 3.61 (3.87) (s, 3H,
CH3CtCPh), 2.87, 2.54, 2.49, 2.41, 1.36, 1.32 (2.55, 2.48, 2.37,
3
1.68, 1.35) (s, 18H, Tp′-CH3), 1.76 (1.02) (d, J HH ) 7 Hz, 3H,
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails for the hydride addition reactions, E/ Z isomerization, and
thermodynamic and kinetic acidity measurements. This mate-
rial is available free of charge via the Internet at http://
pubs.acs.org.
NH2CHMePhBr). 13C NMR (CD2Cl2, δ): 230.1 (229.6) (CO),
216.9 (PhCtCMe), 214.7 (PhCtCMe), 152.7, 151.6, 151.4,
148.6, 148.4, 147.0 (152.8, 151.5, 151.2, 158.43, 148.39, 147.1)
(Tp′-CMe), 140.2 (141.1) (ipso C6H4Br), 136.0 (135.9) (ipso
PhCtCMe), 133.2, 127.4 (133.3, 127.5) (C6H4Br), 131.2 (131.4)
(p-PhCtCMe), 129.47, 129.37 (129.53) (o,m PhCtCMe), 123.7
OM0344022