Reactions of cobaloxime η1-allyl complexes with electron deficient alkenes

Article abstract of DOI:10.1016/S0022-328X(02)01596-6

The preparation of several new η¹-allyl (dimethylglyoxime)₂ cobalt complexes (7-12) containing varied axial pyridine ligands is reported. These complexes are synthesized via three different methods: (1) in situ generation and allylat

Full text of DOI:10.1016/S0022-328X(02)01596-6

Journal of Organometallic Chemistry 656 (2002) 217ꢀ227
/
www.elsevier.com/locate/jorganchem
Reactions of cobaloxime h1-allyl complexes with electron deficient
alkenes
Dean R. Lantero, Mark E. Welker *
Department of Chemistry, Wake Forest University, P.O. Box 7486, Winston-Salem, NC 27109, USA
Received 1 April 2002; received in revised form 20 May 2002; accepted 20 May 2002
Abstract
The preparation of several new h1-allyl (dimethylglyoxime)2 cobalt complexes (7ꢀ
reported. These complexes are synthesized via three different methods: (1) in situ generation and allylation of [L(dmg)2Co]2 dimers
(where Lꢁvarious pyridines); (2) generation and allylation of L(dmg)2Co anions; and (3) an apparent 1,4-hydrocobaltation of 1,3-
dienes. Tetracyanoethylene addition to cobaloxime allyl complexes (5ꢀ12) yielded cyclized complexes (17ꢀ23) and insertion
products (24ꢀ27). Yields of the cyclized and uncyclized complexes are influenced by the electronics of the axial pyridine ligand with
the more electron withdrawing pyridine ligands favoring the formation of more cyclized product. Treatment of cobaloxime allyl
complexes (8ꢀ10) with benzoquinone yielded rearranged cobaloxime allyl complexes (30 and 31) along with para-allyloxysub-
stituted phenols (32ꢀ34). The substituted phenols presumably arise from a Michael addition of the allyl fragment onto
/12) containing varied axial pyridine ligands is
/
/
/
/
/
/
benzoquinone followed by a retro Claisen reaction. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Cobaloxime h1-allyl complexes; Electron deficient alkenes; Pyridine ligands
1. Introduction
3ꢂ2 cycloaddition products [2b]. Branchaud [3] and
/
Pattenden [4] then subsequently showed that the h2-
alkene cobaloxime complexes, proposed as intermedi-
Cobaloxime h1-allyl complexes (such as 1)
(Cobaloximeꢁ
/
pyridine(dimethylglyoxime)2Co)
were
ates in the allyl complexꢀ
/
SO2 reactions and the allyl
first prepared in the early 1970s [1] and their reactions
with tetracyanoethylene (TCNE) and sulfur dioxide
were reported shortly thereafter [2]. The reactions of
allyl cobaloximes with TCNE were reported to give ‘a
complexꢀTCNE cycloadditions, were unusual in struc-
/
ture and reactivity compared to many other alkenyl
complexes. The cobaloxime alkenyl complexes contain
alkenes which are invariably unsymmetrically bound
and nucleophiles add to these cationic alkene complexes
at the most substituted carbon. Most recently, Brown et
al. have studied the thermal decomposition of allyl
cobaloximes and find that the allyl and dimethyl
glyoxime fragments react to produce pyridines [5]. We
variety of products of different colors’ from which 3ꢂ2
/
cycloaddition products could, in most cases, only be
isolated in moderate yields. A two step cycloaddition
mechanism involving a cationic cobaloxime alkene
complex (3) as an intermediate was proposed based on
the observation that the trans cinnamyl complex led to
trans disubstituted cyclopentyl products [2a]. Conver-
sely, reactions of cobaloxime allyls with SO2 were
reported to give only SO2 insertion products and no
have had some success modulating DielsꢀAlder cy-
/
cloaddition chemistry of cobaloxime dienyl complexes
by changing the axial ligand trans to the dienyl
component [6]. Here, we report a systematic study of
the reactions of cobaloxime allyls with alkenyl electro-
philes where the electron donating abilities of the ligands
axial to the allyl fragment and the constitution of the
allyl fragment have been systematically varied.
* Corresponding author. Tel.: ꢂ
7584321
E-mail address: welker@wfu.edu (M.E. Welker).
/
1-336-7585325/6139; fax: ꢂ1-336-
/
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 5 9 6 - 6

218
D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ227
/
2. Experimental
mg, 4.48 mmol in H2O (1 ml)) was added causing the
cobalt complex to dissolve and turning the reaction deep
orange. After degassing, the solution was cooled to
0 8C. A NaBH4 solution (90 mg, 2.38 mmol in H2O (1
ml)) was then added turning the solution to deep blue. A
MeOH solution (5 ml) of 4-bromo-2-methyl-2-butene
(583 mg, 3.92 mmol) was added dropwise over 5 min.
The reaction vessel was wrapped in Al foil and allowed
to warm to room temperature (r.t.). After 3 h, a deep
orange solid had precipitated from the red orange
solution. Water (20 ml cooled to 0 8C) was added and
the resulting slurry was further cooled in an ice H2O
bath and filtered. The collected orange solid was rinsed
with ice H2O and vacuum dried yielding 7 (295 mg, 0.68
2.1. General
All reactions were performed under an atmosphere of
N2 or Ar unless specified otherwise. Chloro(pyridi-
ne)bis(dimethyglyoxime)cobalt(III) was synthesized ac-
cording to the literature [7]. Chloro(4-dimethylamino-
pyridine)bis(dimethylglyoxime)cobalt(III) and chloro-
(4-tbutylpyridine)bis(dimethylglyoxime)cobalt(III) were
synthesized via a procedure analogous to [7] using the
appropriate pyridine ligand. (Pyridine)cobaloxime(2-
butene) (6) (obtained in a 25:75 ratio of cis ꢀtrans
/
isomers) and (pyridine)cobaloxime(allyl) (5) were pre-
pared according to the literature method [8]. Com-
pounds 17 and 18 had been characterized previously
[2b]. TCNE (Aldrich) and benzoquinone (Fisher) were
sublimed prior to use. Allyl bromide, 4-dimethylamino-
pyridine (DMAP), isoprene, 2-bromopropene, pyridine,
4-bromo-2-methyl-2-butene, potassium tert-butoxide
(1.0 M in THF), sodium borohydride, sodium borodeu-
teride and AcOH-d1 were purchased from Aldrich and
used without further purification. Crotyl bromide was
purchased from Fluka and used without further pur-
ification. Dimethylglyoxime (dmg) was purchased from
Fisher Scientific and recrystallized from 95% EtOH
prior to use. Cobalt chloride hexahydrate (Strem) was
used as received.
mmol, 52%). M.p: 146ꢀ
(CDCl3): d 8.53 (d, Jꢁ4.9 Hz, 2H), 7.66 (t, Jꢁ
Hz, 1H), 7.26 (m, 2H), 4.98 (t, Jꢁ9.4 Hz, 1H), 2.41 (d,
9.4 Hz, 2H), 2.08 (s, 12H), 1.22 (s, 3H), 1.12 (s, 3H).
/
148 8C (dec). 1H-NMR
7.6
/
/
/
Jꢁ
/
13C-NMR (CDCl3): d 150.0, 149.0, 137.2, 131.4, 130.5,
125.1, 27.3, 18.2, 11.8. Anal. Calc. for C18H28CoN5O4:
C, 49.44; H, 6.41; N, 16.02. Found: C, 49.30; H, 6.45; N,
15.86%.
2.2.1.2. Method 1. Cobalt (II) chloride hexahydrate
(2.380 g, 10.00 mmol) was dissolved in a two-neck
round bottom flask containing degassed MeOH (50 ml).
DMG (2.320 g, 20.00 mmol) was added turning the
solution pink. Sodium hydroxide (NaOH) (0.800 g in
H2O (5 ml)) was added followed by pyridine (0.790 g,
10.00 mmol). The deep orange solution was stirred at r.t.
for 1 h. Another NaOH solution (0.800 g in H2O (5 ml))
was added followed immediately by 4-bromo-2-methyl-
2-butene (1.490 g, 10.00 mmol). The mixture was again
stirred at r.t. for 1 h after which H2O (40 ml) was added.
1H-NMR spectra were recorded on a Bruker Avance
300 DPX or Bruker Avance 500 DRX operating at
300.1 and 500.1 MHz, respectively, and 13C-NMR
spectra were recorded on a Bruker Avance 300 DPX
operating at 75.5 MHz or Bruker Avance 500 DRX
1
operating at 125.5 MHz. H-NMR spectra were refer-
enced to the residual proton solvent signal and 13C-
The solution was then cooled in a iceꢀH2O bath for 1 h
/
NMR spectra were referenced to the 13C-NMR reso-
prompting an orange solid to precipitate from solution.
The solid was collected by filtration and washed with
small quantities of cold H2O until the filtrates were
colorless. The collected solid was vacuum dried over-
night yielding 7 (1.632 g, 3.70 mmol, 37%).
2
nance of the deuterated solvent. H-NMR spectra were
recorded on a Bruker Avance 500 DRX operating at
76.8 MHz and referenced to the residual deuterium
signal of the protonated solvent. Elemental analyses
were performed by Atlantic Microlab, Inc., Norcross,
GA. High resolution mass spectra (HRMS) were
obtained at the mass spectrometry facility at Duke
University, Durham, NC. M.p.s were determined on a
Mel-Temp apparatus and are reported uncorrected.
2.2.2. 4-Dimethylaminopyridine(allyl)bis-
(dimethylglyoxime)cobalt(III) (8)
Cobalt(II) chloride hexahydrate (476 mg, 2.00 mmol)
was dissolved in degassed MeOH (20 ml). DMG (464
mg, 4.00 mmol) was then added turning the solution
pink. NaOH (160 mg), dissolved in H2O (1 ml), was
added turning the solution orange and then 4-dimethy-
laminopyridine (DMAP) (246 mg, 2.02 mmol) was
added as a solid immediately thereafter. The reaction
2.2. Experimental procedures for the preparation of
cobaloxime allyl complexes
2.2.1. Pyridine(3-methyl-2-
butene)bis(dimethylglyoxime)cobalt(III) (7)
was stirred for 1 h at r.t. during which time dark rustꢀ
/
orange microcrystals were deposited. A NaOH solution
(160 mg in H2O (1 ml)) was then added followed
immediately by allyl bromide (242 mg, 2.00 mmol).
The reaction was stirred at r.t. covered in Al foil for
another 1.5 h. The volatiles were removed by rotary
2.2.1.1. Method 2. This compound was synthesized in a
fashion similar to that found in the literature [8]. A
slurry of Cl(C5H5N)(dmg)2Co (526 mg, 1.31 mmol) in
MeOH (20 ml) was degassed. A NaOH solution (180

D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ
/
227
219
1
evaporation and H2O (20 ml) was added to the orange
solid. The reaction was vacuum filtered and the collected
orange solid was washed with H2O until the filtrates
were colorless. The orange solid was dried on a vacuum
Hz, 3H). H-NMR (minor isomer) (CDCl3): d 8.07 (d,
Jꢁ6.3 Hz, 2H), 6.27 (d, Jꢁ6.9 Hz, 2H), 5.54 (m, 1H),
5.26 (m, 1H), 2.93 (s, 6H), 2.28 (d, Jꢁ9.6 Hz, 2H), 2.10
(s, 12H), 1.12 (dd, Jꢁ
7.0, 1.2 Hz, 3H). 13C-NMR
/
/
/
/
pump yielding 8 (444 mg, 0.98 mmol, 49%). M.p: 187ꢀ
/
(combined isomeric mixture) (CDCl3): d 154.2, 149.1,
149.0, 148.6, 148.4, 137.9, 137.0, 121.5, 120.8, 107.5,
39.0, 19.0, 13.0, 12.0, 11.9. Anal. Calc. for
C19H31CoN6O4: C, 48.94; H, 6.65; N, 18.03. Found:
C, 48.77; H, 6.63; N, 18.18%.
1
190 8C (dec). H-NMR (CDCl3): d 8.01 (d, Jꢁ
2H), 6.38 (d, Jꢁ7.1 Hz, 2H), 5.65 (m, 1H), 4.87 (dd,
Jꢁ9.8 Hz, 2.8 Hz, 1H), 4.80 (dd, Jꢁ16.8, 2.5 Hz, 1H),
2.95 (s, 6H), 2.17 (d, Jꢁ
8.8 Hz, 2H), 2.13 (s, 12H). 13C-
/
7.1 Hz,
/
/
/
/
ꢃ
NMR (C6D6): d 154.2, 149.6, 148.4, 146.2, 109.8, 107.6,
37.9, 12.1. *Prolonged exposure to chlorinated solvent
resulted in gradual decomposition. Anal. Calc. for
C18H29CoN6O4: C, 47.80; H, 6.42; N, 18.59. Found:
C, 47.06; H, 6.18; N, 18.83%.
2.2.4. 4-Dimethylaminopyridine(3-methyl-2-
butene)bis(dimethylglyoxime)cobalt(III) (10)
Chloro(DMAP)bis(dmg)cobalt (III) (1.458 g, 3.27
mmol) was dissolved in a basic EtOH solution (450
mg NaOH dissolved in 95% EtOH (50 ml)) and
degassed. The reaction mixture was cooled in an
2.2.3. 4-Dimethylaminopyridine(E and Z-2-
butene)bis(dimethylglyoxime)cobalt(III) (9)
ethylene glycolꢀdry ice bath after which NaBH4 (225
/
This compound was synthesized in a similar fashion
as that found in the literature [8]. To a degassed MeOH
solution (50 ml) of cobalt(II) chloride hexahydrate
(2.380 g, 10.00 mmol) was added dmg (2.320 g, 20.00
mmol). NaOH (0.800 g in H2O (5 ml)) was added
turning the pink solution to orange, then DMAP was
added (1.230 g, 10.00 mmol). The mixture was stirred
mg, 5.91 mmol) was added. After 1 h, AcOH was added
dropwise until the pH 7 at which point the color had
turned to a deep blueꢀgreen. Isoprene (444 mg, 6.53
/
mmol) was added and the solution was allowed to warm
to 25 8C. After 2 h, a rust orange solid appeared and
after 4 h, the reaction was poured into ice H2O (60 ml)
and filtered. The deep orange solid was washed several
times with 5 ml quantities of H2O and vacuum dried
for 30 min at r.t. during which time dark rustꢀorange
/
microcrystals were deposited. Crotyl bromide (1.350 g,
10.00 mmol) was added followed by NaOH (800 mg in
H2O (5 ml)). The solution was stirred at r.t. for another
1.5 h while covered with Al foil. An orange solid
precipitated from solution. Water (50 ml) was added
and the solution was stirred for an additional 20 min
then vacuum filtered. The collected solid was washed
with H2O until the filtrates were colorless. The orange
solid was vacuum dried overnight yielding 9 (2.104 g,
4.50 mmol, 45%). Two isomers were synthesized in a
71:29 ratio based on 1H-NMR spectral integration. M.p.
yielding 10 (1.187 g, 2.47 mmol, 76%). M.p: 174ꢀ
177 8C (dec). 1H-NMR (CDCl3): d 8.02 (d, Jꢁ
6.9
Hz, 2H), 6.38 (d, Jꢁ6.8 Hz, 2H), 4.96 (t, Jꢁ9.5 Hz,
1H), 2.94 (s, 6H), 2.29 (d, Jꢁ9.4 Hz, 2H), 2.07 (s, 12H),
/
/
/
/
/
1.24 (s, 3H), 1.13 (s, 3H). 13C-NMR (CDCl3): d 154.2,
149.0, 148.4, 131.4, 129.5, 107.5, 39.0, 27.2, 18.0, 11.7.
Anal. Calc. for C20H33CoN6O4: C, 50.01; H, 6.88; N,
17.50. Found: C, 50.19; H, 6.85; N, 17.56%.
2.2.5. Deuterium labeling experiment. Preparation of
deuterated complex 10
Sodium hydroxide (308 mg, 7.67 mmol) was dissolved
in EtOD (25 ml). Chloro(DMAP)cobaloxime (1.000 g,
2.24 mmol) was added to the basic solution which was
(combined isomeric mixture): 142ꢀ
NMR (major isomer) (CDCl3): d 8.01 (d, Jꢁ
2H), 6.38 (d, Jꢁ7.0 Hz, 2H), 5.26 (m, 2H), 2.93 (s, 6H),
2.17 (d, Jꢁ7.6 Hz, 2H), 2.10 (s, 12H), 1.17 (d, Jꢁ5.6
/
145 8C (dec). 1H-
7.0 Hz,
/
/
/
/
then cooled in a dry iceꢀethylene glycol bath. Sodium
/

220
D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ227
/
borodeuteride (170 mg, 4.05 mmol), dissolved in D2O
(1.5 ml), was added to the cold reaction. The solution
was stirred for 1 h during which time the reaction turned
to a dark color. Acetic acid-d1 was added until the pH 7
and the color of the reaction turned to a deep red.
Isoprene (305 mg, 4.48 mmol) was added and the
reaction was allowed to warm to 25 8C. The reaction
was stirred for 4 h and then H2O (30 ml) was added. The
122.6, 121.9, 115.5, 19.2, 12.3, 12.1. Anal. Calc. for
C18H28CoN5O4: C, 48.22; H, 5.58; N, 18.75. Found: C,
47.59; H, 5.58; N, 18.59%.
2.2.7. 4-tButylpyridine(3-methyl-2-
butene)bis(dimethylglyoxime)cobalt(III) (12)
Chloro(4-tbutylpyridine)bis(dmg)cobalt(III) (1.502 g,
3.27 mmol) was dissolved in basic EtOH (450 mg NaOH
mixture was cooled in an iceꢀ/H2O bath for 20 min. A
in 95% EtOH (50 ml)) and cooled in an ethylene glycolꢀ
/
light orange solid was collected by filtration and washed
several times with H2O until the filtrates were colorless.
The solid was then vacuum dried overnight yielding
monodeuterated 10 (863 mg, 1.79 mmol, 80%) based on
dry ice bath. NaBH4 (225 mg, 5.91 mmol) was added
and after 1 h, AcOH was added until the pH 7 turning
the color to a deep blue. Isoprene (444 mg, 6.53 mmol)
was added and the reaction was allowed to warm to r.t.
After 4 h, a bright orange solid had precipitated. Ice
H2O (60 ml) was then added and the reaction filtered.
The orange solid was washed with 5 ml portions of ice
H2O until the filtrates were colorless and then vacuum
1
incorporation of 1 D. According to H-NMR spectral
analysis, deuterium incorporation was 71% of theore-
tical. 1H-NMR (CDCl3): d 7.99 (d, Jꢁ
/
7.0 Hz, 2H), 6.36
9.4 Hz, 1H), 2.92 (s, 6H),
9.4 Hz, 2H), 2.05 (s, 12H), isomer 1 [1.21 (s,
(d, Jꢁ
2.26 (d, Jꢁ
/
7.0 Hz, 2H), 4.94 (t, Jꢁ
/
/
dried yielding 12 (976 mg, 1.98 mmol, 61%). M.p.: 135ꢀ
/
1
CH3), 1.08 (s, CH2D)], isomer 2 [1.19 (s, CH2D), 1.11 (s,
CH3)]. Total integral for these CH3 and CH2D reso-
nances is 5H. 13C-NMR (CDCl3): d 154.1, 148.9, 148.4,
137 8C (dec). H-NMR (CDCl3): d 8.36 (d, Jꢁ
2H), 7.21 (d, Jꢁ6.6 Hz, 2H), 4.97 (t, Jꢁ9.4 Hz, 1H),
2.37 (d, Jꢁ9.4 Hz, 2H), 2.08 (s, 12H), 1.23 (s, 9H), 1.23
/
6.6 Hz,
/
/
/
131.3, 129.4, 107.4, 39.0, 27.21, 27.18, 26.9 (t, JCD
ꢁ
/
19.2
(s, 3H), 1.13 (s, 3H). 13C-NMR (CDCl3): d 161.5, 149.5,
148.8, 131.4, 130.2, 122.3, 34.8, 30.2, 27.3, 18.1, 11.8.
Anal. Calc. for C22H36CoN5O4: C, 53.56; H, 7.30; N,
14.20. Found: C, 53.50; H, 7.47; N, 14.21%.
Hz, CH2D (APT)), 25.8, 18.0, 17.7 (t, JCD
ꢁ
/
19.3 Hz,
CH2D (APT)), 11.6. 2H{1H}-NMR (CHCl3): d 1.24,
1.14. HRFABMS: m/z Calc. for C25H32CoDN6O4
[Mꢂ]: 480.1895. Found: 480.1876.
2.3. Reactions of cobaloxime allyl complexes with carbon
electrophiles
2.2.6. 4-Cyanopyridine(E and Z-2-
butene)bis(dimethylglyoxime)cobalt(III) (11)
Cobalt(II) chloride hexahydrate (952 mg, 4.00 mmol)
was dissolved in degassed MeOH (40 ml). DMG (928
mg, 8.00 mmol) was added turning the solution pink. A
NaOH solution (320 mg dissolved in H2O (2 ml)) was
added followed by 4-cyanopyridine (420 mg, 4.04
mmol). The deep orange solution was stirred at r.t. for
1 h and then another NaOH solution (320 mg dissolved
in H2O (2 ml)) was added. Crotyl bromide (540 mg, 4.00
mmol) was added and the resulting deep orange solution
was stirred at r.t. for another hour. The volume of the
reaction was cut in half by rotary evaporation and then
H2O (35 ml) was added. The resulting solution was
2.3.1. Reaction of (pyridine)cobaloxime(2-butene)
(6)ꢂtetracyanoethylene to produce (18 and 24)
/
Pyridine(2-butene)cobaloxime (6) (200 mg, 0.47
mmol) was dissolved in distilled, degassed CH2Cl2 (25
ml). The flask was covered with Al foil and then TCNE
(120 mg, 0.95 mmol) was added as a solid under a flow
of nitrogen. The mixture was stirred at r.t. for 2 h and
then the volatiles were removed by blowing air over the
solution. The dark residue was dissolved in EtOAc and
chromatographed on a silica gel column using EtOAc as
the eluent. The EtOAc from the early fraction was
removed by reduced pressure yielding (146 mg, 0.26
stirred and cooled in an iceꢀ/H2O bath for 30 min. A
mmol, 56%) of a yellowꢀorange solid 18. Removal of
/
deep orange precipitate was collected by filtration. The
micro crystals were washed with small portions (10 ml)
of H2O until the filtrates were colorless. The solid was
the EtOAc from the later fraction by reduced pressure
yielded (46 mg, 0.084 mmol, 18%) of a red solid 24.
Analytical data for 18: M.p.: 184ꢀ
NMR (CDCl3): d 8.43 (d, Jꢁ5.1 Hz, 2H), 7.74 (t, Jꢁ
7.6 Hz, 1H), 7.32 (apparent t, Jꢁ7.0 Hz, 2H), 2.57 (dd,
Jꢁ15.0 Hz, 8.5 Hz, 1H), 2.20 (s, 6H), 2.19 (s, 6H), 2.10
(m, 2H), 1.33 (d, Jꢁ
6.9 Hz, 3H), 1.33 (buried, 1H). 13C-
/
186 8C (dec). 1H-
vacuum dried overnight yielding 11 (in a E ꢀ
/Z ratio of
/
/
71:29) (540 mg, 1.20 mmol, 30%). M.p. (combined
/
1
isomeric mixture): 126ꢀ
isomer) (CDCl3): d 8.82 (d, Jꢁ
6.4 Hz, 2H), 5.44 (m, 1H), 5.27 (m, 1H), 2.42 (d, Jꢁ
/
128 8C (dec). H-NMR (major
6.4 Hz, 2H), 7.56 (d, Jꢁ
8.7
/
/
/
/
/
NMR (CDCl3): d 151.8, 151.7, 149.7, 138.3, 125.6,
112.1, 111.7, 111.3, 110.2, 51.0, 49.0, 44.3, 41.9, 19.2,
1
Hz, 2H), 2.14 (s, 12H), 1.18 (d, Jꢁ
NMR (minor isomer) (CDCl3): d 8.82 (buried, 2H), 7.56
(buried, 2H), 5.71 (m, 1H), 5.27 (m, 1H), 2.53 (d, Jꢁ9.5
6.1 Hz, 3H).
/6.5 Hz, 3H). H-
12.7. Analytical data for 24: M.p.: 124ꢀ
1H-NMR (CDCl3): d 8.22 (d, Jꢁ
5.4 Hz, 2H), 7.74 (t,
Jꢁ7.6 Hz, 1H), 7.27 (apparent t, Jꢁ6.8 Hz, 2H), 5.76
(m, 1H), 5.34 (d, Jꢁ13.1 Hz, 1H), 5.31 (d, Jꢁ6.4 Hz,
1H), 2.64 (m, 1H), 2.38 (s, 12H), 1.26 (d, Jꢁ6.7 Hz,
/
127 8C (dec).
/
/
Hz, 2H), 2.14 (buried, 12H), 1.13 (d, Jꢁ
/
/
/
13C-NMR (combined isomeric mixture) (CDCl3): d
/
/
151.4, 151.2, 149.8, 149.6, 137.5, 136.5, 126.9, 123.4,
/

D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ
/
227
221
3H). 13C-NMR (CDCl3): d 153.4, 151.0, 144.6, 139.4,
134.7, 126.0, 120.4, 119.1, 113.6, 113.2, 45.1, 15.4, 13.2.
13C-NMR (CDCl3): Anal. Calc. for C24H29CoN10O4: C,
49.66; H, 5.00; N, 24.14. Found: C, 49.76; H, 5.11; N,
24.02%.
HRFABMS: m/z Calc. for C23H27CoN9O4 [Mꢂ
/
Hꢂ]:
552.1518. Found 552.1523.
2.3.4. Reaction of (DMAP)cobaloxime(2-butene) (9)ꢂ
/
2.3.2. Reaction of (pyridine)cobaloxime(3-methyl-2-
butene) (7)ꢂtetracyanoethylene to produce (19 and 25)
tetracyanoethylene to produce (21 and 26)
/
(Pyridine)(3-methyl-2-butene) cobaloxime (7) (206
mg, 0.472 mmol) was dissolved in distilled, degassed
CH2Cl2 (25 ml). The flask was covered in Al foil and
then TCNE (120 mg, 0.946 mmol) was added as a solid.
The mixture was stirred at r.t. for 2 h and then the
volatiles were removed by blowing air over the solution.
2.3.4.1. Method A. DMAP(2-butene)bis(dmg)cobal-
t(III) (9) (110 mg, 0.24 mmol) and DMAP (29 mg,
0.24 mmol) were dissolved in distilled, degassed CH2Cl2
(5 ml) in a two-neck round bottom flask equipped with a
dropping funnel. The resulting orange solution was
cooled to ꢄ
/
20 8C in an ethylene glycolꢀdry ice bath
/
The residue was dissolved in a 4:1 CH2Cl2ꢀ
solution and then chromatographed on silica gel using
CH2Cl2ꢀacetone as the eluent. The yellow fraction
collected first yielded 19 (13 mg, 0.024 mmol, 5%),
when the volatiles were removed by rotary evaporation.
The red fraction collected second yielded 25 (103 mg,
0.11 mmol, 38%), when the volatiles were removed by
/
acetone
and covered with Al foil. Tetracyanoethylene (60 mg,
0.473 mmol) was dissolved in distilled, degassed CH2Cl2
(10 ml) and added dropwise over 5 min and once the
addition was complete, the reaction was stirred for 1 h at
/
ꢄ
/
20 8C. The color gradually turned to yellowꢀ
during the reaction time. The volatiles were removed by
rotary evaporation yielding a greenꢀyellow solid. The
solid was dissolved in 6:1 CH2Cl2ꢀacetone and chro-
/
orange
/
reduced pressure. Analytical data for 19: M.p.: 118ꢀ
120 8C (dec). 1H-NMR (CDCl3): d 8.40 (d, Jꢁ
5.0
Hz, 2H), 7.73 (t, Jꢁ6.2 Hz, 1H), 7.30 (apparent t, Jꢁ
/
/
/
matographed on silica gel using the same solvent system.
A yellow band was collected first yielding a yellow solid
21 (74 mg, 0.12 mmol, 53%) once the volatiles were
/
/
6.6 Hz, 2H), 2.95 (m, 1H), 2.30 (m, 1H), 2.19 (s, 6H),
2.18 (s, 6H), 1.45 (m, 1H), 1.42 (s, 3H), 0.99 (s, 3H). 13C-
NMR (CDCl3): d 152.24, 152.16, 149.3, 138.3, 125.6,
113.3, 113.2, 112.0, 110.2, 58.8, 55.1, 46.9, 39.1, 25.1,
18.5, 12.6, 12.5. HRFABMS: m/z Calc. for
1
removed by rotary evaporation. A H-NMR spectrum
confirmed the product to be 21 consisting of two isomers
1
in a 90:10 ratio based on H-NMR spectra integration.
A second fraction was collected yielding a red solid 26
(14 mg, 0.024 mmol, 10%) upon solvent removal.
Analytical data for 21: M.p. (combined isomeric mix-
C24H28CoN9O4 [Mꢂ]: 565.1596. Found: 565.1600%.
1
Analytical data for 25: M.p.: 104ꢀ
NMR (CDCl3): d 8.19 (d, Jꢁ
7.1 Hz, 1H), 7.27 (apparent t, Jꢁ
Jꢁ17.2 Hz, 10.7 Hz, 1H), 5.29 (d, Jꢁ
5.22 (d, Jꢁ
/
106 8C (dec). Hꢁ
/
-
/
5.4 Hz, 2H), 7.74 (t, Jꢁ
7.0 Hz, 2H), 5.86 (dd,
10.7 Hz, 1H),
/
ture): 164ꢀ
(CDCl3): d 7.88 (d, Jꢁ
Hz, 2H), 2.97 (s, 6H), 2.57 (dd, Jꢁ
2.20 (s, 6H), 2.19 (s, 6H), 2.10 (m, 2H), 1.31 (d, Jꢁ
/
167 8C (dec). 1H-NMR (major isomer)
/
/
7.1 Hz, 2H), 6.37 (d, Jꢁ
/7.1
/
/
/14.9, 8.4 Hz, 1H),
/
17.2 Hz, 1H), 2.36 (s, 12H), 1.20 (s, 6H).
/6.8
13C-NMR (CDCl3): d 153.7, 150.9, 142.0, 139.6, 139.4,
126.1, 117.7, 113.2, 47.3, 22.4, 13.2. HRFABMS: m/z
Hz, 3H), 1.23 (m, 1H). 1H-NMR (minor isomer)
(CDCl3): d 7.85 (d, Jꢁ
2.97 (buried, 6H), 2.83 (m, 1H), 2.76 (dd, Jꢁ
Hz, 1H), 2.19 (s, 6H), 2.16 (s, 6H), 2.10 (buried, 2H),
1.81 (m, 1H), 1.05 (d, Jꢁ
7.2 Hz, 3H). 13C-NMR
/
7.2 Hz, 2H), 6.37 (buried, 2H),
Calc. for C24H29CoN9O4 [Mꢂ
/
Hꢂ]: 566.1674. Found:
/
13.6, 7.1
566.1677.
/
2.3.3. Reaction of (DMAP)cobaloxime(allyl) (8)ꢂ
tetracyanoethylene to produce (20)
/
(combined isomeric mixture) (CDCl3): d 154.4, 151.1,
151.0, 148.4, 112.2, 111.9, 111.5, 110.4, 107.7, 51.1, 49.2,
44.5, 42.1, 39.0, 19.3, 12.5. Anal. Calc. for
C25H31CoN10O4: C, 50.51; H, 5.22; N, 23.57. Found:
(DMAP) cobaloxime(allyl) (8) (165 mg, 0.36 mmol)
was added to a 100 ml two-neck round bottom flask and
dissolved in distilled CH2Cl2 (25 ml). After degassing the
orange solution, the flask was covered with Al foil and
then 93 mg TCNE (0.73 mmol) was added as a solid.
The mixture was stirred at r.t. for 2 h. The volatiles were
removed from the golden solution by rotary evapora-
tion. The resulting solid was dissolved in EtOAc and
chromatographed on silica gel using EtOAc as the
eluent. A golden yellow fraction was collected that
yielded 20 (114 mg, 0.19 mmol, 54%) when the solvent
C, 50.47; H, 5.33; N, 23.56%. Analytical data for 26:
1
M.p.: 102ꢀ
Jꢁ
5.32 (d, Jꢁ
/
105 8C (dec). H-NMR (CDCl3): d 7.53 (d,
/
7.2 Hz, 2H), 6.30 (d, Jꢁ
/
7.3 Hz, 2H), 5.76 (m, 1H),
6.3, 1H), 2.97 (s,
6.8 Hz,
/
13.0 Hz, 1H), 5.29 (d, Jꢁ
/
6H), 2.61 (m, 1H), 2.35 (s, 12H), 1.24 (d, Jꢁ
/
3H). 13C-NMR (CDCl3): d 154.7, 153.0, 148.9, 141.9,
134.9, 120.2, 113.9, 113.4, 108.4, 45.2, 42.3, 39.2, 15.4,
13.0. HRFABMS: m/z Calc. for C25H32CoN10O4 [Mꢂ
/
Hꢂ]: 595.1940. Found: 595.1919.
was removed by reduced pressure. M.p.: 194ꢀ
/
196 8C
1
(dec). H-NMR (CDCl3): d 7.86 (d, Jꢁ
6.37 (d, Jꢁ
8.6 Hz, 2H), 2.18 (s, 12H), 1.97 (m, 2H), 1.69 (m, 1H).
/6.5 Hz, 2H),
2.3.4.2. Method B. (DMAP)cobaloxime(2-butene) (9)
(110 mg, 0.24 mmol) was dissolved in distilled CH2Cl2
(10 ml) and degassed. The flask was covered with Al foil
/
6.4 Hz, 2H), 2.97 (s, 6H), 2.55 (dd, Jꢁ14.6,
/

222
D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ227
/
and then TCNE was added as a solid (60 mg, 0.47
mmol). The solution was allowed to stir at r.t. for 2 h.
The volatiles were removed by blowing a stream of air
over the solution. The tacky solid was dissolved in
EtOAc and then chromatographed on silica gel using
EtOAc as the eluent. A yellow fraction was collected
first that yielded 21 (86 mg, 0.15 mmol, 61%) containing
(s, 6H), 2.17 (s, 6H), 1.40 (s, 3H), 1.35 (dd, Jꢁ13.4, 7.8
/
Hz, 1H), 0.97 (s, 3H). 13C-NMR (CDCl3): d 154.3,
151.5, 151.4, 147.8, 113.5, 113.4, 112.1, 110.4, 107.7,
59.0, 47.1, 39.4, 39.0, 25.1, 18.5, 12.44, 12.40. Anal.
Calc. for C26H33CoN10O4: C, 51.32; H, 5.43. Found: C,
51.15; H, 5.48%. Analytical data for 27: M.p.: 100ꢀ
103 8C (dec). 1H-NMR (CDCl3): d 7.49 (d, Jꢁ
7.2
Hz, 2H), 6.30 (d, Jꢁ7.2 Hz, 2H), 5.85, (dd, Jꢁ17.2,
10.7, 1H), 5.27 (d, Jꢁ 17.2
/
/
1
two isomers in a 5:1 ratio based on H-NMR spectral
/
/
data. The major isomer for this method is the also the
major isomer that is described in Method A. A second
fraction was collected yielding 26 (5 mg, 0.010 mmol,
4%) as a red solid. The NMR data for the two
compounds from Method B are identical to that listed
above for Method A.
/
10.7 Hz, 1H), 5.20 (d, Jꢁ
/
Hz, 1H), 2.95 (s, 6H), 2.33 (s, 12H), 1.20 (s, 6H). 13C-
NMR (CDCl3): d 154.7, 153.0, 148.5, 139.65, 139.58,
117.5, 113.4, 108.3, 47.4, 39.2, 22.3, 13.0. HRFABMS:
m/z Calc. for C26H34CoN10O4 [Mꢂ
/
Hꢂ]: 609.2096.
Found: 609.2095.
NMR experiments (1H, 13C attached proton test, 13C,
1H correlation, g-COSY and g-NOESY) were under-
taken to determine the stereochemical configuration of
the major isomer 21 isolated in the above reaction. The
2.3.6. Reaction of (4-cyanopyridine)cobaloxime(2-
butene) (11)ꢂtetracyanoethylene to produce (23)
/
(4-cyanopyridine)cobaloxime(2-butene) (11) (114 mg,
0.25 mmol) was added to distilled CH2Cl2 (20 ml) and
degassed. The flask was covered with Al foil and then
TCNE (65 mg, 0.51 mmol) was added. The solution was
stirred at r.t. for 2 h and then the volatiles were removed
by rotary evaporation. The residue was dissolved in
EtOAc and chromatographed on silica gel using EtOAc
as the eluent. A yellow fraction was collected yielding a
yellow solid 23 (29 mg, 0.050 mmol, 20%) when the
solvent was removed by reduced pressure. Analytical
1
13C, H correlation spectra were used to determine the
position of the proton resonances in the 1H-NMR
spectra. Two proton resonances (2.57 and 2.10 ppm)
displayed cross peaks to one carbon resonance. A 13C
APT confirmed that carbon was a secondary carbon
resonance. Another proton resonance at 2.10 ppm (two
protons based on integration of the 1H-NMR spectrum)
was coupled to the methyl resonance at d 1.31. The last
proton resonance of the ring was centered at 1.23 ppm.
NOESY data could be used to determine if the orienta-
tion of the methyl group of the cyclized ring and the
cobaloxime cluster were cis or trans to one another. A
large NOE cross peak between the methyl resonance at
1.31 ppm and the proton resonance at 1.23 ppm would
help confirm the trans geometry while the absence of a
NOE cross peak would indicate a cis geometry. NOESY
data exhibited a large cross peak between these two
resonances, therefore the trans geometry is proposed for
the major isomer.
data for 23: M.p.: 166ꢀ
(CDCl3): d 8.68 (d, Jꢁ6.6 Hz, 2H), 7.57 (d, Jꢁ
Hz, 2H), 2.55 (dd, Jꢁ15.2, 8.6 Hz, 1H), 2.22 (s, 6H),
6.9
/
169 8C (dec). 1H-NMR
6.6
/
/
/
2.20 (s, 6H), 2.03 (m, 2H), 1.40 (m, 1H), 1.33 (d, Jꢁ
/
Hz, 3H). 13C-NMR (CDCl3) d 164.0, 152.1, 152.0,
150.6, 139.3, 124.9, 112.1, 111.7, 111.3, 110.1, 53.3, 48.9,
44.3, 41.9, 19.1, 12.7. Anal. Calc. for C24H25CoN10O4:
C, 50.01; H, 4.34. Found: C, 49.30; H, 4.83%.
2.3.7. Reaction of (DMAP)cobaloxime(3-methyl-2-
butene) (10)ꢂbenzoquinone to produce (32)
/
2.3.5. Reaction of (DMAP)cobaloxime(3-methyl-2-
butene) (10)ꢂ
27)
/
tetracyanoethylene to produce (22 and
2.3.7.1. Method A. (DMAP)cobaloxime(3-methyl-2-bu-
tene) (10) (150 mg, 0.31 mmol) was dissolved in distilled
THF (20 ml) and degassed. Benzoquinone (33 mg, 0.34
mmol) was then added as a solid and the resulting
solution was heated to reflux. After 2 h, the solution was
cooled to r.t. and filtered. The collected solid was
washed with additional EtOAc until the filtrates were
colorless. The solvent was removed from the dark red
filtrate and the residue was dissolved in EtOAc and
chromatographed on silica gel. A deep red fraction was
collected and reduced to dryness by rotary evaporation
Distilled CH2Cl2 (30 ml) was used to dissolve
(DMAP)(3-methyl-2-butene)cobaloxime (10) (226 mg,
0.47 mmol) in a 100 ml two-neck round bottom flask.
The flask was covered with Al foil and then TCNE (120
mg, 0.95 mmol) was added as a solid. The mixture was
allowed to stir at r.t. for 2 h and then the volatiles were
removed by blowing air over the solution. The dark
residue was dissolved in EtOAc and chromatographed
on silica gel using EtOAc as the eluent. The solvent was
removed by reduced pressure from the yellow fraction
collected first yielding 22 (26 mg, 0.042 mmol, 9%). The
red fraction collected second yielded 27 (48 mg, 0.080
yielding 32 (19 mg, 0.107 mmol, 35%). Analytical data
1
for 32: M.p.: 34ꢀ
Jꢁ
17.6, 10.8 Hz, 1H), 5.09 (d, Jꢁ
Jꢁ
10.3 Hz, 1H), 4.88 (br, 1H), 1.36 (s, 6H). 13C-NMR
(CDCl3): d 151.3, 148.9, 144.1, 124.2, 115.3, 113.5, 79.6,
/
37 8C. H-NMR (CDCl3): d 6.83 (d,
/
8.8 Hz, 2H), 6.66 (d, Jꢁ
/
8.8 Hz, 2H), 6.07, (dd, Jꢁ
/
mmol, 17%). Analytical data for 22: M.p.: 106ꢀ
/
108 8C
6.2 Hz, 2H),
/
17.8 Hz, 1H), 5.08 (d,
1
(dec). H-NMR (CDCl3): d 7.84 (d, Jꢁ
/
/
6.36 (d, Jꢁ/6.3 Hz, 2H), 2.96 (s, 6H), 2.32 (m, 2H), 2.18

D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ
/
227
223
26.6. HRFABMS: m/z Calc. for C11H14O2 [Mꢂ]:
178.0994. Found: 178.0996.
30 (33 mg, 0.068 mmol, 15%) identical by spectroscopic
comparison to the material reported above.
2.3.9. Reaction of (DMAP)cobaloxime(2-butene) (9)ꢂ
benzoquinone to produce (33 and 34)
/
2.3.7.2. Method B. (DMAP)cobaloxime(3-methyl-2-bu-
tene) (10) (226 mg, 0.47 mmol) was dissolved in distilled
THF (20 ml) and degassed. The solution was cooled to
0 8C. Potassium tert-butoxide (0.94 ml of a 1.0 M THF
solution, 0.94 mmol) was added slowly by syringe. The
color gradually turned from orange to deep red. After 15
min, benzoquinone (56 mg, 0.52 mmol) was added and
the flask was covered with Al foil and stirred at 0 8C for
2 h. The color gradually turned to a deep green during
the course of the reaction. Water (20 ml) was added to
the solution and then saturated aq. NH4Cl (20 ml) was
added. Methylene chloride was used to extract the
solution. The combined CH2Cl2 extractions were dried
with MgSO4, filtered and evaporated to dryness. The
resulting solid was chromatographed on silica gel using
EtOAc as the eluent. A bright yellow solid (26 mg, 0.042
mmol, 9%) was collect with data consistent with the
formulation of (DMAP)cobaloxime(1,1-dimethyl-2-pro-
DMAP(2-butene)bis(dmg)cobalt(III) (9) (600 mg,
1.29 mmol) was added to a 100 ml two-neck round
bottom equipped with a reflux condenser and dissolved
in distilled CH2Cl2 (50 ml). After degassing the orange
solution, benzoquinone (274 mg, 2.54 mmol) was added
as a solid. The resulting solution was heated to a gentle
reflux for 4 h and then the volatiles were removed by
rotary evaporation. The resulting solid was slurried in
CH2Cl2ꢀ/C3H6O (19:1) and chromatographed on a silica
gel column using the same CH2Cl2ꢀ/C3H6O solution as
the eluent. A pale red fraction was collected second that
yielded a viscous red oil (18 mg, 0.11 mmol, 9%) upon
1
evaporation of the solvent. H-NMR spectra indicated
the formation of two isomers (65% for the major isomer
(33) and 35% for the minor isomer (34)) and a low
resolution GC/MS confirmed equal masses for the two
isomers. Analytical data for major isomer (33): 1H-
NMR (CDCl3): d 6.77 (m, 2H), 6.71 (m, 2H), 5.87 (m,
pene) (30). Analytical data for 30: M.p.: 178ꢀ
/
180 8C
7.0 Hz, 1H),
17.7, 10.9 Hz,
1
(dec). H-NMR (CDCl3): d 7.71 (d, Jꢁ
6.25 (d, Jꢁ7.0 Hz, 1H), 5.82, (dd, Jꢁ
1H), 4.81 (d, Jꢁ
/
1H), 5.21 (dt, Jꢁ
/
17.3, 1.0 Hz, 1H), 5.13 (d, Jꢁ
/
10.6 Hz,
/
/
1H), 4.80 (br, 1H), 4.64 (p, Jꢁ
/
6.3 Hz, 1H), 1.38 (d, Jꢁ
/
/
17.7 Hz, 1H), 4.76 (dd, Jꢁ
/
10.9, 1.0
6.4 Hz, 3H). 13C-NMR (CDCl3): d 152.0, 149.6, 139.4,
117.7, 115.9, 115.7, 75.9, 21.3. Analytical data for minor
isomer (34): 1H-NMR (CDCl3): d 6.77 (m, 2H), 6.71 (m,
2H), 5.80 (m, 1H), 5.70 (m, 1H), 4.80 (br, 1H), 4.37 (d,
Hz, 1H), 2.91 (s, 6H), 2.24 (s, 12H), 0.96 (s, 6H). 13C-
NMR (CDCl3): d 154.3, 151.1, 149.4, 145.2, 110.9,
107.6, 39.0, 24.4, 12.4. HRFABMS: m/z Calc. for
C20H33CoN6O4 [Mꢂ]: 479.1817. Found: 479.1808.
Jꢁ
/
6.1 Hz, 2H), 1.73 (dd, Jꢁ
6.4, 1.1 Hz, 3H). 13C-
/
NMR (CDCl3): d 152.8, 149.5, 130.6, 126.2, 116.0,
115.8, 69.4, 17.9. HRFABMS (combined isomeric
mixture): m/z Calc. for C10H12O2 [Mꢂ]: 164.0837.
Found: 164.0839.
2.3.8. Reaction of (DMAP)cobaloxime(3-methyl-2-
butene) (10)ꢂpotassium tert-butoxide to produce (30)
/
(DMAP)cobaloxime(3-methyl-2-butene) (10) (226
mg, 0.47 mmol) was dissolved in distilled THF (30 ml)
and degassed. The solution was cooled to 0 8C. The
flask was covered with Al foil and then potassium tert-
butoxide (0.94 ml of a 1.0 M THF solution, 0.94 mmol)
was added slowly by syringe. The temperature was
maintained at 0 8C for 6 h during which time the color
gradually turned from orange to deep red and then onto
a deep green. Water (30 ml), cooled to 0 8C, was added
to the solution and then saturated aqueous NH4Cl (30
ml) was added. Methylene chloride was used to extract
the orange solution. The combined CH2Cl2 extractions
were dried with MgSO4, filtered and evaporated to
dryness. The resulting solid was chromatographed on
silica gel using EtOAc was the eluent. A yellow band
was collected first and then the eluent was changed to
3. Results and discussion
3.1. Preparation of cobaloxime allyl complexes
Cobaloxime allyl complexes were prepared by one of
four different methods: (1) in situ generation and
allylation of [L(dmg)2Co]2 dimers; (2) generation and
allylation of L(dmg)2Co anions prepared from
L(dmg)2CoCl complexes; and (3) 1,4-hydrocobaltation
of 1,3-dienes [9].
Generation and allylation of [L(dmg)2Co]2 dimers is
simple to effect but this method suffers from the
disadvantage of producing a mole of L(dmg)2Co-halide
for every mole of L(dmg)2Co-allyl produced. When
hydrometallation of a 1,3-diene could be used (Table 1,
entries 7 and 9) yields were generally higher. This 1,4-
hydrocobaltation is also an interesting reaction from a
mechanistic standpoint. These cobaloxime reactions are
known to contain mixtures of cobaloxime anions and
hydrides in polar protic solvents [10]. To gain some
90:10 EtOAcꢀEtOH which allowed an orange band to
/
be collected. The solvent was removed by rotary
evaporation from the yellow solution, yielding a yel-
1
orange solid, and the H-NMR spectrum of this
lowꢀ
/
solid was consistent with unreacted starting material 10
(13 mg, 0.027 mmol, 6%). The volatiles of the orange
solution were removed by rotary evaporation yielding

224
D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ227
/
additional insight into this reaction, we prepared com-
plex 10 using NaBD4 as reductant in D2OꢀEtOD and
brought the pH of the solution back to 7 using
CH3CO2D and then followed this by isoprene addition.
The allyl complexes isolated (75% yield) consisted of a
however, we also isolated a significant amount (18%) of
the uncyclized isomer (24) which had not been reported
previously. The 3-methyl-2-butenyl complex (7) reacted
with TCNE to provide a small amount of the cyclized
product (19) with the uncyclized isomer (25) being the
major product in this case. If these reactions proceed
through an alkene complex like 3, then the alkene
complex from 7 plus TCNE is presumably less stable
due to methyl group steric group interactions, thereby
facilitating alkene dissociation and leading to a pre-
ponderance of the uncyclized product. In cobaloxime
/
1:1 mixture of 15ꢀ16. This result is inconsistent with a
/
concerted 1,4-hydrocobaltation of the diene (13) and is
best explained by cobaloxime anion addition to the
isoprene (14) followed by deuteration or addition of
pyr(dmg)2Co(II) to the diene to generate allyl radical
analogs of the allyl anions shown, which are then
quenched by deuterium atom abstraction.
DielsꢀAlder chemistry, we found DMAP dienyl com-
/
3.2. Reactions of cobaloxime h1-allyl complexes with
plexes to be considerably more reactive than their
pyridine complex counterparts so we looked at the
corresponding DMAP cobaloxime allyl complex reac-
tions with TCNE. The results obtained using DMAP
TCNE
The first electrophile to be investigated was TCNE
since some reactions of pyridine cobaloxime allyl com-
plexes with this substrate had been reported in the 1970s
[2]. As reported previously [2], the unsubstituted allyl
complex (5) reacted with TCNE to produce cyclized
product (17) with none of the uncyclized product (24,
allyl complexes (8ꢀ10) were almost identical to those
/
obtained for the pyridine cobaloximes. The DMAP 2-
butenyl complex (9) was found to cyclize with TCNE at
ꢄ
/
20 8C over 1 h, consistent with enhanced DielsꢀAlder
/
reactivities we had noted for DMAP cobaloximes earlier
[6]. The electron donating DMAP ligand did not,
however, significantly alter the ratios of cyclized to
uncyclized products seen. We also hypothesized that a
R1ꢁ
Z) also provided cyclized product (18) (56%, 3:1, trans ꢀ
cis) as the major product as reported previously [2]
/
R2ꢁ
/
H) seen. The 2-butenyl complex (6) (3:1, E ꢀ
/
/

D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ
/
227
225
Table 1
Cobaloxime allyl complex preparation
Entry no.
Compound
Preparation method
L
R1
R2
%Yield
a
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
5
6
1
Pyr
Pyr
H
H
19
42 3:1 E:Z
a
1
Me
Me
Me
H
H
7
2
a
Pyr
Pyr
Me
Me
H
52
37
7
1
a
8
1
DMAP
DMAP
DMAP
4-CNpyr
4-t Bupyr
49
45 3:1 E:Z
76
a
9
1
Me
Me
Me
Me
H
10
11
12
3
a
Me
H
1
30 3:1 E:Z
61
3
Me
a
The maximum possible yield of Co-allyl from this method is 50%.
more electron withdrawing pyridine ligand might lead to
stronger alkene binding and increase the amount of
cyclized products seen. We prepared the 4?-cyanopyr-
idine 2-butenyl complex (11) and also treated it with
TCNE under conditions identical to those used for the
pyridine and DMAP allyl complexes. This more electron
withdrawing ligand would be expected to slow initial
allyl attack on TCNE but accelerate the subsequent
cyclization. We isolated a reduced amount of the
cyclized product (23) and see no evidence for production
of the uncyclized complex, consistent with the hypoth-
esis stated above (Table 2).
Table 2
Reactions of cobaloxime allyl complexes with TCNE
L
R1 R2 (#), % Cyclized (#), % Uncyclized
Pyridine
H
H
H (17) 64
Me (18) 56
Not detected
(24) 18
(25) 38
Me Me (19) 5
DMAP
H
H
H
Me
(20) 54
Not detected
(26) 10
(27) 17
Me Me
4-Cyanopyridine
H
Me (23) 20
Not detected
3.3. Reaction of DMAP allyl cobaloximes with other
carbon electrophiles
complex (9) with diethylmethylenemalonate (25 8C)
also resulted in recovery of unreacted allyl complex
starting material. Heating allyl complex (8) with diethyl-
methylenemalonate just resulted in complex decomposi-
tion. Reaction of the DMAP allyl complex (10) with
benzoquinone in refluxing THF produced a new organic
Having thoroughly investigated the reactions of
cobaloxime allyls with TCNE, we proceeded to investi-
gate other electrophiles. Treatment of the DMAP allyl
complex (8) with diethylacetylenedicarboxylate in
CH2Cl2 at 25 8C resulted in recovery of unreacted allyl
complex starting material. Likewise, treatment of allyl
compound (32, R1ꢁ
/
R2ꢁMe) in moderate yield (35%).
/
The structure of this addition product was determined
to be a para alkoxy substituted phenol (32). The

226
D.R. Lantero, M.E. Welker / Journal of Organometallic Chemistry 656 (2002) 217ꢀ227
/
isolation of this unexpected compound is best rationa-
lized by a Michael addition followed by a retro Claisen
rearrangement [11]. Cobaloxime complexation to the
alkene in (29) may accelerate the proposed retro Claisen.
We suspected that the bridging glyoxime ligand OH
protons were protonating proposed intermediate (29)
thereby quenching the possibility of isolating a cobalox-
ime product. To try to avoid this proton transfer,
cobaloxime allyl (10) was first treated with KOtBu in
THF followed by benzoquinone addition. However,
rather than isolating any new addition compounds or
complexes, we instead isolated a rearranged cobaloxime
products isolated are demetallated organic addition/
rearrangement products rather than cobaloxime com-
plex addition products.
Acknowledgements
We thank the National Science Foundation (CHE-
0104083) for support of this work. Low resolution mass
spectra were obtained on instruments purchased with
the partial support of the North Carolina Biotechnology
Center (Grant #2001 IDG 1004). The Duke University
Center for Mass Spectrometry performed high resolu-
tion mass spectral analyses.
allyl complex (30, R1ꢁ
/
R2ꢁMe). Deprotonation/re-
/
combination of allyl complex (10) can be used to
account for the production of this rearranged complex
(30, R1ꢁ
with benzoquinone also resulted in the production of
addition compounds (33, R1ꢁH, R2ꢁMe) and 34,
R1ꢁMe, R2ꢁH) in a ratio of 65:35 (9% isolated yield)
as well as some recovered starting material (9) and
rearranged allyl (31, R1ꢁH, R2ꢁMe). The unexpected
alkoxy substituted phenols (33 and 34) also presumably
arise from Michael addition/retro Claisen tandem reac-
tions.
/
R2ꢁMe). Treatment of 2-butenyl complex (9)
/
References
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/
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