Alkoxide attack on coordinated olefin can be reversible

Article abstract of DOI:10.1021/om950905z

Alkoxide (MeO^-, EtO^-, ⁱPrO^-) attack occurs at the coordinated olefin of Ir(Tripod)(COD) (Tripod = MeC(CH₂PPh₂)₃, COD = 1,5-cyclooctadiene) in CH₂Cl₂ to give Ir(Tripod)(2-alkoxycyclooct-5-en-1-yl), primarily as the exo isomer. These products slowly eliminate alcohol to give Ir(Tripod)((1,2-η²)-6-σ-cycloocta-1,4-dienyl), which is the only product detected when the alkoxide is ^tBuO^-. Addition of excess methanol to exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl) abstracts MeO^- (i.e., heterolytic O-C bond cleavage), and thus a hydrogen-bonding solvent reverses the nucleophilic attack on coordinated olefin. Alkoxide (MeO^-, ⁱPrO^-, ^tBuO^- and 2-BuO^-) addition occurs at an olefinic carbon of Rh(Tripod)(NBD)⁺ (NBD = norbornadiene) to give Rh(Tripod)(2-alkoxynorborn-4-en-1-yl). The crystal structure of the exo/ methoxy example has been determined. While this product cannot unimolecularly eliminate alcohol, attempts to protonate the norbornyl ether in the presence or absence of added NBD were not successful. Here again, acid abstracts RO^- from the ligand ether.

Full text of DOI:10.1021/om950905z

1856
Organometallics 1996, 15, 1856-1864
Alk oxid e Atta ck on Coor d in a ted Olefin Ca n Be
Rever sible
Bryan E. Hauger, J ohn C. Huffman, and Kenneth G. Caulton*
Department of Chemistry and Molecular Structure Center, Indiana University,
Bloomington, Indiana 47405-4001
Received November 24, 1995X
i
Alkoxide (MeO-, EtO-, PrO-) attack occurs at the coordinated olefin of Ir(Tripod)(COD)
(Tripod ) MeC(CH2PPh2)3, COD ) 1,5-cyclooctadiene) in CH2Cl2 to give Ir(Tripod)(2-
alkoxycyclooct-5-en-1-yl), primarily as the exo isomer. These products slowly eliminate
alcohol to give Ir(Tripod)((1,2-η2)-6-σ-cycloocta-1,4-dienyl), which is the only product detected
t
when the alkoxide is BuO-. Addition of excess methanol to exo-Ir(Tripod)(2-methoxycyclooct-
5-en-1-yl) abstracts MeO- (i.e., heterolytic O-C bond cleavage), and thus a hydrogen-bonding
solvent reverses the nucleophilic attack on coordinated olefin. Alkoxide (MeO-, iPrO-, tBuO-
and 2-BuO-) addition occurs at an olefinic carbon of Rh(Tripod)(NBD)+ (NBD ) norborna-
diene) to give Rh(Tripod)(2-alkoxynorborn-4-en-1-yl). The crystal structure of the exo/
methoxy example has been determined. While this product cannot unimolecularly eliminate
alcohol, attempts to protonate the norbornyl ether in the presence or absence of added NBD
were not successful. Here again, acid abstracts RO- from the ligand ether.
In tr od u ction
sequence (eq 2). For late transition elements and an
Attack by an oxygen nucleophile at a coordinated
olefin is a central step in Wacker oxidation (ethylene to
acetaldehyde).1 It is also anticipated to be the crucial
activation step in transition-metal-catalyzed olefin hy-
dration or ether formation (eq 1). This latter reaction
(2)
18-electron count, step 2a may be especially favored,
since it eliminates a 4-electron destabilization.7 How-
ever, our earlier studies with later transition metals (Ir,
Rh) have shown8 that an alkoxide ligand, in the pres-
ence of a hydride ligand, is readily eliminated as alcohol.
This indicates that it might be more productive to study
a hydride-free complex for the purpose of alcohol addi-
tion to an olefin.
CH2dCH2 + ROH [M]8 H3CsCH2OR
(1)
R ) H, alkyl
has seen at most modest progress,2 particularly in the
most recent period of development of organometallic
chemistry. The utility of nucleophilic attack on an η4-
bound diene complex in organic synthesis is widely
recognized3 and generally occurs anti to the metal.
However, this reaction remains relatively unexplored
for systems containing metals other than platinum4 and
palladium.5 In 1976, attack of methoxide on η4-COD
(COD ) 1,5-cyclooctadiene) at iridium was reported to
yield the crystallographically characterized Ir(1,10-
phenanthroline)(η2-fumaronitrile)(8-methoxycycloocta-
4-enyl).6
We report here some observations which relate to
fundamental aspects of reaction 1, both in stoichiometric
and in catalytic modes. These should serve to define
features which must receive fuller consideration in
future development of olefin hydration, as well as in the
related amination chemistry.9
Exp er im en ta l Section
An alternative mechanism, for eq 1, to exo attack on
coordinated olefin involves a migration/elimination
Gen er a l Con sid er a tion s. All manipulations were carried
out under an inert atmosphere (N2 or argon) using standard
Schlenk techniques. Solid transfers were accomplished in a
Vacuum Atmospheres Corp. glovebox. THF and pentane were
distilled under nitrogen from potassium/benzophenone. CH2-
Cl2 was dried over CaH2 and distilled before use. Toluene was
distilled under nitrogen from sodium. C6D6 and d8-THF were
dried over sodium metal, vacuum-distilled, and stored in a
X Abstract published in Advance ACS Abstracts, March 15, 1996.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; p 412.
(2) J ensen, C. M.; Trogler, W. C. Science 1986, 233, 1069. Ram-
prasad, D.; Yue, H. J .; Marsella, J . A. Inorg. Chem. 1988, 27, 3151.
Woerpel, K. A.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 7888.
(3) See ref 1, Chapter 17.
(4) (a) Chatt, J .; Vallario, L. M.; Venanzi, L. M. J . Chem. Soc. 1957,
2496. (b) Mulliez, E.; Soulie, J .; Chottard, C.; Sanchez, C.; Guilhem J .
Chem. Res. 1982, 440. (c) Giordano, F.; Vitagliano, A. Inorg. Chem.
1981, 20, 633. (d) Goel, A. B.; Goel, S.; VanDerveer, D. G. Inorg. Chim.
Acta 1981, 54, L169. (e) Rakowsky, M. H.; Woolcock, J . C.; Rettig, M.
F.; Wing, R. M. Organometallics 1988, 7, 2149.
(5) Wipke, W. T.; Goeke, G. L. J . Am. Chem. Soc. 1974, 96, 4244.
(6) Bresciani-Pahor, N.; Calligaris, M.; Nardin, G.; Delise, P. J .
Chem. Soc., Dalton Trans. 1976, 762.
(7) Caulton, K. G. New J . Chem. 1994, 18, 25.
(8) Hauger, B. E.; Caulton, K. G. J . Organomet. Chem. 1993, 450,
253. J ohnson, T. J .; Huffman, J . C.; Caulton, K. G. J . Am. Chem. Soc.
1992, 114, 2725. J ohnson, T. J .; Coan, P. S.; Caulton, K. G. Inorg.
Chem. 1993, 32, 4594.
(9) Roundhill, D. M. Chem. Rev. 1992, 92, 1. Gagne, M. R.; Stern,
C. L.; Marks, T. J . J . Am. Chem. Soc. 1992, 114, 275. Casalnuovo, A.
L.; Calabrese, J . C.; Milstein, D. J . Am. Chem. Soc. 1988, 110, 6738.
0276-7333/96/2315-1856$12.00/0 © 1996 American Chemical Society

Alkoxide Attack on Coordinated Olefin
Organometallics, Vol. 15, No. 7, 1996 1857
Ta ble 1. Qu a n tita tion of th e Effect of Ad d ition of
Meth a n ol to
glovebox prior to use. CD2Cl2 was dried over CaH2, vacuum-
distilled, and stored in a glovebox prior to use.
exo-Ir (Tr ip od )(2-m eth oxycyclooct-5-en -1-yl) To
Tripod (MeC(CH2PPh2)3) was purchased from Strem Chemi-
cal Co. and used without further purification. Norbornadiene
(NBD) was purchased from Aldrich Chemical Co. and vacuum-
distilled before use. KOMe and (S)-(+)-2-butanol were pur-
chased from Aldrich Chemical Co. and used without further
purification. Other alkali-metal alkoxides were prepared by
reaction between the alkali-metal hydride and alcohol in THF.
[Ir(Tripod)(COD)]Cl,10 [Rh(NBD)Cl]2,11 and [H(Et2O)2][(3,5-
(CF3)2-C6H3)4B]12 were prepared by the literature methods.
31P (146 MHz) NMR spectra were obtained on a Nicolet NT-
360 instrument. 1H (300 MHz) and 13C{1H} (75 MHz) NMR
spectra were obtained on a Varian XL300 spectrometer. 2D
1H-1H NOESY spectra were obtained on a Varian VXR400
spectrometer.
Give Ir (Tr ip od )(η4-COD)+
log([Ir(Tripod)(η4-COD)+]2/
[exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl)])
log[MeOH]
-0.74
-0.44
-0.27
-0.15
-0.05
-0.02
0.09
-5.40
-4.94
-4.34
-3.53
-3.05
-2.59
-2.28
31P{1H} NMR was integrated. This procedure was repeated
with further incremental additions of MeOH. The results
show a continuous increase in the concentration of Ir(Tripod)-
(COD)+ and a corresponding decrease in the concentration of
exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl). The ratios result-
ing from the integration of spectra of these solutions are
reported in Table 1.
Syn th esis a n d Ch a r a cter iza tion of exo-Ir (Tr ip od )(2-
m eth oxycyclooct-5-en -1-yl). [Ir(Tripod)(η4-COD)]Cl (305 mg
0.317 mmol) was weighed into a flask with 307 mg (4.39 mmol)
of KOMe. Approximately 15 mL of CH2Cl2 was added to give
an orange solution, which was stirred for 75 min. The CH2-
Cl2 was then removed in vacuo to yield a tan solid. Toluene
(35 mL) was added to give a yellow solution with a white
precipitate. The solution was filtered, yielding a clear yellow
solution. The toluene was then removed in vacuo to yield a
tan solid. The tan solid was extracted with 30 mL of pentane,
which was then removed in vacuo. A tan solid (186 mg, 0.198
mmol, 62% yield) was isolated. The compound decomposes to
Ir(Tripod)((1,2-η2)-6-σ-cycloocta-1,4-dienyl) quite slowly (weeks)
in benzene (see below for spectral data). The following 1H
NMR assignments are based on decoupling and T1 measure-
ments and enable assignment of mutual coupling between 9
of the 12 resonances of protons attached directly to the C8 ring.
These are designated A, B, C, F, G, I, J , K, and L. Chemical
shifts for signals D, E, and M lie under other resonances.
Syn th esis a n d Ch a r a cter iza tion of exo-Ir (Tr ip od )(2-
eth oxycyclooct-5-en -1-yl). [Ir(Tripod)(η4-COD)]Cl (210 mg,
0.219 mmol) and 30 mg (0.357 mmol) of KOEt were weighed
into a flask. Approximately 25 mL of CH2Cl2 was added, and
the solution was stirred for 1 h. The CH2Cl2 was then removed
in vacuo. Toluene (40 mL) was added to the resulting solid.
The resulting solution was filtered, and the toluene was
removed in vacuo to yield 135 mg (0.141 mmol, 65% yield) of
yellow powder which was a 9:1 mixture of exo-Ir(Tripod)(2-
ethoxycyclooct-5-en-1-yl) and Ir(Tripod)((1,2-η2)-6-σ-cycloocta-
1,4-dienyl) (spectra below). 31P{1H} NMR (CD2Cl2, 25 °C):
-24.5 (app t, 2J PP′ ) 18 Hz, 2J PP′′ ) 18 Hz), -25.0 (dd, 2J P′P′′
)
2
2
2
46 Hz, J PP′ ) 18 Hz), -30.0 (dd, J P′P′′ ) 46 Hz, J PP′′ ) 18
Hz).
2
2
31P{1H} NMR (CH2Cl2, 25 °C): -24.9 (dd, J PP′) 46 Hz, J PP′′
Syn th esis a n d Ch a r a cter iza tion of exo-Ir (Tr ip od )(2-
isop r op oxycyclooct-5-en -1-yl). [Ir(Tripod)(η4-COD)]Cl (200
mg, 0.208 mmol) and 40 mg (0.487 mmol, 2.3 equiv) of NaOi-
Pr were weighed into a flask. Approximately 20 mL of CH2-
Cl2 was added, and the solution was stirred for 15 min. The
CH2Cl2 was then removed in vacuo. Toluene (10 mL) was
added to the resulting solid and was then removed in vacuo.
Toluene (20 mL) was added to the resulting solid. The
resulting solution was filtered and the toluene was removed
in vacuo to yield 68 mg (0.069 mmol, 33% crude yield) of a 9:1
mixture of exo-Ir(Tripod)(2-isopropoxycyclooct-5-en-1-yl) and
Ir(Tripod)((1,2-η2)-6-σ-cycloocta-1,4-dienyl) (see spectra below).
Spectral data for the former compound: 31P{1H} NMR (C6D6,
25 °C): -24.6 (app t, 2J PP′′ ) 20 Hz, 2J PP′ ) 17 Hz), -26.8 (dd,
2
2
) 18 Hz), -25.5 (app t, J PP′′ ) 18 Hz, J P′P′′ ) 18 Hz), -31.5
(dd, J PP′ ) 46 Hz, J P′P′′ ) 18 Hz). 13C{1H} NMR (CD2Cl2, 25
2
2
°C): 134-125 (m, phenyl region), 88.1 (br s, CHOCH3), 54.0
2
2
(s, CHOCH3), 47.2 (dd, vinyl carbon, J PC ) 36 Hz, J PC ) 6
Hz), 40.5 (dd, C8 ring CH2, J PC ) 5 Hz, J PC ) 5 Hz), 40.2 (app
3
q, CH3C(CH2PPh2)3, J PC ) 10 Hz), 39.2 (d, C8 ring CH2, J PC
) 16 Hz), 37.2 (dd, CH2PPh2, 1J PC ) 17 Hz, 3J PC ) 7 Hz), 36.6
1
3
(dd, CH2PPh2, J PC ) 22 Hz, J P′C ) 5 Hz), 35.4 (dt, CH2PPh2,
1J PC ) 24 Hz, 3J PC ) 4 Hz, 3J PC ) 4 Hz), 33.1 (app q, CH3C(CH2-
PPh2)3, 2J PC ) 4 Hz), 31.1 (dd, vinyl carbon, 2J PC ) 35 Hz, 2J PC
) 8 Hz), 30.6 (s, C8 ring CH2), 29.7 (s, C8 ring CH2), 21.6 (dt,
Ir-C, J PC ) 68 Hz, J PC ) 4 Hz). 1H NMR (CD2Cl2, 25 °C):
2
2
3
3
7.8-6.6 (m, phenyl region), 3.64 (dd, A, J AJ ) 13 Hz, J AF
)
2
2 Hz, T1 ) 541 ms, 1H), 3.25 (ddd, B, J PB ) 20 Hz, J BC ) 15
2
2
2
2J PP′′ ) 47 Hz, J PP′ ) 17 Hz), -29.4 (dd, J P′P′′ ) 47 Hz, J PP′′
) 20 Hz). 1H NMR (C6D6, 25 °C): 8.1-6.0 (phenyl region),
4.10 (m, COD, 1H), 3.80 (m, COD, 1H), 3.3-1.8 (alkyl region),
Hz, 2J BJ ) 7 Hz, T1 ) 314 ms, 1H), 2.79 (ddd, C, 2J BC ) 15 Hz,
2J CF ) 7Hz, J CJ ) 6 Hz, T1 ) 260 ms, 1H), 2.70-2.56 (m,
2
CH2PPh2), 2.60 (s, OCH3), 2.35-2.09 (m, CH2PPh2), 2.17 (d,
3
2.93 (app septet, OCH(CH3)2, J HH ) 6 Hz), 1.05 (br s,
3
L, J LK ) 8 Hz), 2.07 (dd, K, J PK ) 15 Hz, J LK ) 8 Hz, T1
)
3
CH3C(CH2PPh2)3), 1.00 (d, OCH(CH3)2, J HH ) 6 Hz), 0.93 (d,
2
2
314 ms, 1H), 1.81 (ddd, F, J J F ) 13 Hz, J CF ) 7 Hz, J AF ) 2
OCH(CH3)2,3J HH ) 6 Hz).
3
3
Hz, T1 ) 319 ms, 1H), 1.66 (ddd, G, J PG ) 12 Hz, J PG ) 12
Syn th esis a n d Ch a r a cter iza tion of Ir (Tr ip od )((1,2-η2)-
6-σ-cycloocta -1,4-d ien yl). [Ir(Tripod)(η4-COD)]Cl (100 mg,
0.104 mmol) and 100 mg (0.891 mmol) of KOtBu were weighed
into separate flasks. Approximately 10 mL of CH2Cl2 was used
to dissolve both solids. The solution containing [Ir(Tripod)-
(η4-COD)]Cl was added to the KOtBu solution. The mixture
was stirred for 75 min. At this time the solvent was removed
in vacuo. The resulting solid was extracted into 35 mL of
toluene and filtered. The toluene was then removed in vacuo.
The resulting solid was washed with 5 mL of hexanes and
dried in vacuo, yielding 48 mg (0.052 mmol, 50% yield) of a
light yellow solid. 31P{1H} NMR (CD2Cl2, 25 °C): -17.0 (dd,
3
3
Hz, J GI ) 6 Hz, T1 ) 498 ms, 1H), 1.56 (dddd, J , J AJ ) 13
2
2
2
Hz, J J F ) 13 Hz, J J B ) 7 Hz, J CJ ) 6 Hz, T1 ) 253 ms, 1H),
4
4
4
1.43 (ddd, CH3C(CH2PPh2)3, J PH ) 3 Hz, J PH ) 3Hz, J PH
)
3 Hz, 3H), 1.31 (dddd, I, 2J IE ) 6 Hz, 3J GI ) 6 Hz, 2J ID ) 6 Hz,
4J IP ) 6 Hz, T1 ) 258 ms, 1H).
Ad d ition of MeOH to exo-Ir (Tr ip od )(2-m eth oxycy-
clooct-5-en -1-yl). exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl)
(17.2 mg, 0.0183 mmol) was weighed into an NMR tube. C6D6
(500 µL) was added via a 500 µL syringe. 2.3 µL of MeOH
was added through the septum via a 5.0 µL syringe, and the
2
2
2
2J PP′ ) 44 Hz, J PP′′ ) 15 Hz), -27.2 (dd, J PP′′ ) 15 Hz, J P′P′′
(10) Frazier, J . F.; Merola, J . S. Polyhedron 1992, 11, 2917.
(11) Abel, E. W.; Bennett, M. A.; Wilkinson, G. J . Chem. Soc. 1959,
3178.
(12) Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992,
11, 3920.
) 15 Hz), -42.2 (dd, J PP′ ) 44 Hz, J P′P′′ ) 15 Hz). 1H NMR
(CD2Cl2, 25 °C): 7.9-6.2 (phenyl and vinyl H), 3.7-3.6 (br m,
alkyl region), 3.5-3.4 (br m, alkyl region), 2.9-2.8 (br m, alkyl
2
2

1858 Organometallics, Vol. 15, No. 7, 1996
Hauger et al.
Ta ble 2. Qu a n tita tion of th e Effect of Ad d ition of
Meth a n ol to
region), 2.7-2.6 (br m, alkyl region), 2.2-2.0 (br m, alkyl
region), 2.0-1.9 (br m, alkyl region), 1.7-1.5 (br m, alkyl
region), 1.37 (br s, alkyl region), 1.10 (br s, alkyl region).
Syn th esis a n d Ch a r a cter iza tion of [Rh (Tr ip od )(η4-
NBD)]Cl. [Rh(η4-NBD)Cl]2 (296 mg, 0.64 mmol) was placed
in a Schlenk flask and dissolved in 30 mL of toluene to give
an orange solution. Tripod (804 mg, 1.29 mmol) was placed
in a Schlenk flask and dissolved in 10 mL of toluene. The
solution of [Rh(η4-NBD)Cl]2 was added dropwise to the solution
of Tripod. A large amount of precipitate was observed after
several minutes of stirring. The mixture was stirred for 6 h
and then the volatiles were removed in vacuo. A 1.046 g (1.22
mmol, 95% yield) amount of yellow solid was isolated. 31P{1H}
NMR (CD2Cl2, 25 °C): 10.1 (d, 1J RhP ) 114 Hz). 1H NMR (CD2-
Cl2, 25 °C): 7.4-7.0 (phenyl region), 3.89 (s, NBD, 2H), 3.59
(s, NBD vinyl, 4H), 2.43 (br s, CH2PPh2, 6H), 1.63 (br s,
CH3C(CH2PPh2)3, 3H), 1.45 (s, NBD, 2H). Anal. Calcd (found)
for C48H47ClP3Rh: %H, 5.54 (5.50).
Syn t h esis a n d Ch a r a ct er iza t ion of R h (Tr ip od )(2-
Meth oxyn or bor n -4-en -1-yl). [Rh(Tripod)(η4-NBD)]Cl (200
mg, 0.233 mmol) and 100 mg (1.43 mmol) of KOMe were
weighed into a Schlenk flask. THF (15 mL) was added, and
the resulting solution was stirred for 12 h. The solution was
then filtered to yield a clear orange solution. The THF was
removed in vacuo. Pentane (10 mL) was then added and
removed in vacuo to yield 170 mg (0.200 mmol, 85%) of yellow
Rh(Tripod)(2-methoxynorborn-4-en-1-yl); the exo:endo ratio
was 7:1 (31P NMR). Exo isomer: 31P{1H} NMR (d8-THF, 25
exo-Rh (Tr ip od )(2-m eth oxyn or bor n -4-en -1-yl) To
Give Rh (Tr ip od )(η4-NBD)+
log([Rh(Tripod)(η4-NBD)+]2/
[exo-Rh(Tripod)(2-methoxynorborn-4-en-1-yl)])
log[MeOH]
-0.14
-0.02
0.07
0.14
0.21
0.26
0.31
0.35
0.39
-4.16
-4.00
-3.74
-3.19
-2.86
-2.30
-1.84
-1.19
0.13
2
3.11 (br m, NBD, 1H), 2.73 (d, NBD, J H
) 8 Hz, 1H), 2.59
H
a
b
2
2
(dd, CH2PPh2, J HH ) 15 Hz, J PH ) 8 Hz, 1H), 2.28 (dd, CH2-
2
2
2
PPh2, J HH ) 16 Hz, J PH ) 8 Hz, 1H), 2.23 (d, NBD, J H
)
H
a
b
8 Hz, 1H), 2.10-1.94 (m, CH2PPh2, 3H), 1.80 (dd, CH2PPh2,
2J HH ) 15 Hz, J PH ) 7 Hz, 1H), 1.30 (br m, NBD), 1.14 (br s,
2
CH3C[CH2PPh2]3, 3H) 1.04 (d, OCH(CH3)2, 3J HcHd ) 6 Hz, 3H),
3
0.84 (d, OCH(CH3)2, J H H ) 6 Hz, 3H). Anal. Calcd (found)
c
e
for C51H54OP3Rh: H 6.19 (6.15).
Syn th esis a n d Ch a r a cter iza tion of exo-Rh (Tr ip od )(2-
ter t-bu toxyn or bor n -4-en -1-yl). [Rh(Tripod)(η4-NBD)]Cl (200
mg, 0.233 mmol) and 58 mg (0.52 mmol, 2.25 equiv) of KOtBu
were weighed into a Schlenk flask. The addition of 20 mL of
THF produced a homogeneous orange solution. After 2 h of
stirring, the THF was removed in vacuo. The resulting solid
was extracted with 30 mL of toluene. The resulting orange
solution was filtered and pumped to dryness. Benzene (10 mL)
was then added to give an orange solution, which was pumped
to dryness. The resulting oily solid was extracted with 5 mL
of pentane to give a light yellow powder and a faintly colored
solution. The pentane was removed in vacuo, giving 203 mg
(0.227 mmol, 97% yield) of product. 31P{1H} NMR (C6D6, 25
1
2
2
°C): 10.5 (ddd, J RhP ) 138 Hz, J PP′ ) 32 Hz, J PP′′ ) 35 Hz),
1
2
2
7.0 (ddd, J RhP′ ) 84 Hz, J P′P′′ ) 27 Hz, J PP′ ) 32 Hz), 3.2
1
(ddd, J RhP′′ ) 125 Hz, J PP′′ ) 35 Hz, J P′P′′ ) 27 Hz); 1H NMR
2
2
(d8-THF, 25 °C) 8.0-6.6 (phenyl region), 3.63 (br m, NBD),
3.55 (br m, NBD) 3.05 (br m, NBD), 2.75 (dd, CH2PPh2, J HH
2
2
) 15 Hz, J PH ) 7 Hz), 2.54 (br m, NBD), 2.49 (s, OCH3), 2.44
(dd, CH2PPh2, 2J HH ) 15 Hz, 2J PH ) 7 Hz), 2.17 (dd, CH2PPh2,
2J HH ) 15 Hz, 2J PH ) 7 Hz), 2.09 (dd, CH2PPh2, 2J HH ) 15 Hz,
2J PH ) 7 Hz), 1.93 (dd, CH2PPh2, J HH ) 15 Hz, J PH ) 7 Hz),
2
2
1
2
2
1.90 (d, NBD, 2J H
) 8 Hz), 1.54 (d, NBD, 2J H
) 8 Hz),
°C): 10.8 (ddd, J RhP ) 138 Hz, J PP′ ) 32 Hz, J PP′′ ) 35 Hz),
H
H
a
b
a
b
1
2
2
7.5 (ddd, J RhP′ ) 84 Hz, J PP′ ) 32 Hz, J P′P′′ ) 27 Hz), 0.2
1.47 (br m, CH3C[CH2PPh2]3), 0.85 (br m, NBD). Anal. Calcd
(found) for C49H50OP3Rh: P, 10.92 (11.14); C, 69.18 (68.87);
H, 5.92 (6.13). Endo isomer: 31P{1H} NMR (d8-THF, 25 °C):
(ddd, J RhP′′ ) 125 Hz, J PP′′ ) 35 Hz, J P′P′′ ) 27 Hz). 13C{1H}
NMR (C6D6, 25 °C): 29.9 (s, OC[CH3]3). 1H NMR (C6D6, 25
°C): 8.0-6.6 (phenyl region), 4.42 (br m, NBD, 1H), 4.25 (br
m, NBD, 1H), 3.93 (br m, NBD, 1H), 3.60 (br m, NBD, 1H),
3.09 (br m, NBD, 1H), 2.83 (d, NBD, 2J H b ) 7.5 Hz, 1H), 2.55
1
2
2
1
2
2
12.4 (ddd, J RhP ) 137 Hz, J PP′ ) 31 Hz, J PP′′ ) 39 Hz), 5.4
1
2
2
(ddd, J RhP′ ) 82 Hz, J PP′ ) 31 Hz, J P′P′′ ) 26 Hz), 1.3 (ddd,
1J RhP′′ ) 131 Hz, 2J PP′′ ) 39 Hz, 2J P′P′′ ) 26 Hz). The exo isomer
can be obtained pure by fractional crystallization (Et2O/
toluene).
H
a
(dd, CH2PPh2, 2J HH ) 15 Hz, 2J PH ) 8 Hz, 1H), 2.25 (dd, NBD,
2J H ) 7.5 Hz, 1H), 2.17 (dd, CH2PPh2, 2J HH ) 15 Hz, 2J PH
)
H
a
b
2
8 Hz), 2.13-2.02 (m, CH2PPh2) 1.82 (dd, CH2PPh2, J HH ) 15
Hz, 2J PH ) 7 Hz, 1H), 1.27 (br m, NBD), 1.12 (br s, CH3C[CH2-
PPh2]3), 1.05 (s, OC[CH3]3, 9H).
Rea ction of exo-Rh (Tr ip od )(2-m eth oxyn or bor n -4-en -
1-yl) w ith CD2Cl2. Upon standing in CD2Cl2 for 24 h a
solution of exo-Rh(Tripod)(2-methoxynorborn-4-en-1-yl) cleanly
converts to Rh(Tripod)(η4-NBD)+, as observed by 31P{1H} NMR
spectroscopy. 1H NMR spectroscopy shows a singlet at 3.38
ppm which cannot be assigned to either Rh(Tripod)(η4-NBD)+
or exo-Rh(Tripod)(2-methoxynorborn-4-en-1-yl). The signal is
assigned to the methoxy protons of CH3OCD2Cl.
Syn th esis a n d Ch a r a cter iza tion of exo-Rh (Tr ip od )(2-
isopr opoxyn or bor n -4-en -1-yl). [Rh(Tripod)(η4-NBD)]Cl (200
mg, 0.233 mmol) and 90 mg (1.1 mmol) of NaOiPr were
weighed into a Schlenk flask. The addition of 15 mL of THF
produced a homogeneous orange solution. After 1 h of stirring,
the THF was removed in vacuo. The resulting solid was
extracted with 30 mL of toluene and pumped to dryness. The
solid was extracted with 30 mL of toluene again. The resulting
orange solution was filtered and pumped to dryness. The solid
was covered with 7 mL of pentane and pumped to dryness. A
140 mg (0.159 mmol, 68% yield) amount of fine yellow powder
was isolated. 31P{1H} NMR (C6D6, 25 °C): 10.8 (d app t, 1J RhP
Rea ction of [Rh (Tr ip od )(η4-NBD)]Cl w ith (S)-(+)-2-
Bu toxid e. [Rh(Tripod)(η4-NBD)]Cl was reacted with a C6D6
solution of sodium (S)-(+)-2-butoxide. 31P{1H} NMR shows
complete conversion of [Rh(Tripod)(η4-NBD)]Cl to a 1:1 mixture
of diastereomeric products. 31P{1H} NMR in C6D6: 11.8 (d app
1
2
2
t, J RhP ) 137 Hz, J PP′ ) 33 Hz, J PP′′ ) 33 Hz), 10.7 (d app t,
1J RhP ) 137 Hz, 2J PP′ ) 35 Hz, 2J PP′′ ) 35 Hz), 8.3-7.3 (m), 2.6
(d app t, J RhP ) 126 Hz, J PP′ ) 37 Hz, J PP′′ ) 37 Hz), 1.2 (d
app t, J RhP ) 126 Hz, J PP′ ) 37 Hz, J PP′′ ) 37 Hz).
1
2
2
1
2
2
Rea ctivity Stu d ies. (a ) exo-Rh (Tr ip od )(2-m eth oxyn or -
bor n -4-en -1-yl) + MeOH. exo-Rh(Tripod)(2-methoxynorborn-
4-en-1-yl) (22 mg, 0.0258 mmol) was weighed into an NMR
tube with 500 µL of d8-THF. MeOH (5 µL) was added through
the septum via a 10.0 µL syringe, and the 31P{1H} NMR was
integrated. This procedure was repeated with incremental 5
µL additions of MeOH. The results generally show an increase
in the concentration of Rh(Tripod)(η4-NBD)+ and a correspond-
ing decrease in the concentration of exo-Rh(Tripod)(2-meth-
oxynorborn-4-en-1-yl). Relevant concentration data resulting
from the integrations are reported in Table 2.
2
2
1
) 137 Hz, J PP′ ) 35 Hz, J PP′′ ) 35 Hz), 7.8 (d app t, J RhP′
)
2
2
1
85 Hz, J PP′ ) 27 Hz, J P′P′′ ) 27 Hz), 1.9 (ddd, J RhP′′ ) 125
Hz, J PP′′ ) 35 Hz, J P′P′′ ) 27 Hz). 1H NMR (C6D6, 25 °C):
8.0-6.6 (phenyl region), 4.33 (br m, NBD, 1H), 4.18 (br m,
NBD, 1H), 4.02 (br m, NBD, 1H), 3.62 (br m, NBD, 1H), 3.38
2
2
(b) exo-Rh (Tr ip od )(2-isop r op oxyn or bor n -4-en -1-yl) +
iP r OH + NBD. (1) In d8-Tolu en e. exo-Rh(Tripod)(2-isopro-
poxynorborn-4-en-1-yl) (19.9 mg, 0.023 mmol) was placed in
3
3
(app septet, OCH(CH3)2, J HcHd ) 6 Hz, J HcHe ) 6 Hz, 1H),

Alkoxide Attack on Coordinated Olefin
Organometallics, Vol. 15, No. 7, 1996 1859
Ta ble 3. Cr ysta llogr a p h ic Da ta for
exo-Rh (Tr ip od )(2-m eth oxyn or bor n -4-en -1-yl)
an NMR tube with 500 µL of d8-toluene, 100 µL (0.927 mmol,
40.3 equiv) of NBD, and 100 µL (1.306 mmol, 56.8 equiv) of
iPrOH. An inhomogeneous yellow solution results. The tube
was freeze/pump/thaw-degassed three times and sealed with
a flame. After 20 min the 31P{1H} NMR showed no conversion
to Rh(Tripod)(NBD)+ but only unchanged exo-Rh(Tripod)(2-
isopropoxynorborn-4-en-1-yl).
formula
color
C49H50P3ORh
orange
cryst dimens (mm)
space group
0.10 × 0.08 × 0.12
Pbca
cell dimensions (at -171 °C; 72 rflns)
a (Å)
b (Å)
c (Å)
10.096(3)
20.694(7)
38.502(15)
8
(2) in d8-THF . exo-Rh(Tripod)(2-isopropoxynorborn-4-en-
1-yl) (18.2 mg, 0.021 mmol) was placed in an NMR tube with
500 µL of d8-THF, 100 µL (0.927 mmol, 44.1 equiv) of NBD,
Z (molecules/cell)
i
and 100 µL (1.306 mmol, 62.2 equiv) of PrOH. An inhomo-
V (Å3)
8044.50
1.405
geneous yellow solution resulted. The tube was freeze/pump/
thaw-degassed three times and sealed with a flame. After 20
min the 31P{1H} NMR showed no conversion to Rh(Tripod)-
(η4-NBD)+; only unchanged exo-Rh(Tripod)(2-isopropoxynor-
born-4-en-1-yl) was observed.
(c) exo-Rh (Tr ip od )(2-ter t-bu toxyn or bor n -4-en -1-yl) +
tBu OH + NBD. exo-Rh(Tripod)(2-tert-butoxynorborn-4-en-
1-yl) (15 mg, 0.017 mmol) was placed in an NMR tube with
approximately 600 µL of C6D6, 40 mg (0.540 mmol, 31.8 equiv)
of HOtBu, and 40 µL (0.371 mmol, 21.8 equiv) of NBD. The
tube was freeze/pump/thaw-degassed and sealed with a flame.
31P{1H} NMR showed no conversion to Rh(Tripod)(η4-NBD)+;
only unchanged exo-Rh(Tripod)(2-tert-butoxynorborn-4-en-1-
yl) was evident. The tube was heated to 80 °C. After 4 days
no catalytic reactivity was observed (by 1H NMR). The
temperature was increased to 110 °C. After 9 days no catalytic
reactivity was observed.
calcd density
wavelength (Å)
mol wt
0.710 69a
850.76
5.7
linear abs coeff (cm-1
)
no. of unique intensities
no. with F > 0.0
no. with F > 2.33σ(F)
R for averaging
5248
4253
2386
0.089
final residuals
R(F)b
0.0760
0.0631
1.33
Rw(F)c
goodness of fit for the last cycle
max ∆/σ for last cycle
0.05
a
b
Graphite monochromator. R ) ∑||Fo| - |Fc||/∑|Fo|. c Rw
)
2
(∑w(|Fo| - |Fc|)2/∑w|Fo| )1/2 where w ) 1/σ2(|Fo|).
Ta ble 4. Selected Bon d Len gth s (Å) of
exo-Rh (Tr ip od )(2-m eth oxyn or bor n -4-en -1-yl)
(d) exo-Rh (Tr ipod)(2-isopr opoxyn or bor n -4-en -1-yl) an d
Acid s. (1) H(OEt2)2{B[C6H3(m-CF3)2]4}. exo-Rh(Tripod)(2-
isopropoxynorborn-4-en-1-yl) (26.2 mg, 0.0298 mmol) was
weighed into an NMR tube. C6D6 (0.5 mL) was added to make
a suspension of the compound. Solid H(OEt2)2{B[C6H3(m-
CF3)2]4} (31.2 mg, 0.0308 mmol, 1.03 equiv) was added to the
tube. The solution rapidly became homogeneous, and a
reddish oil was formed. 31P{1H} NMR shows complete conver-
sion to Rh(Tripod)(η4-NBD)+ as the sole metal-containing
product.
Rh(1)-P(14)
Rh(1)-P(28)
Rh(1)-P(42)
Rh(1)-C(2)
Rh(1)-C(3)
Rh(1)-C(8)
O(9)-C(7)
2.286(5)
2.325(5)
2.327(5)
2.187(17)
2.092(17)
2.149(16)
1.484(19)
1.436(21)
C(2)-C(3)
C(2)-C(6)
C(3)-C(4)
C(4)-C(5)
C(4)-C(8)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
1.460(23)
1.513(22)
1.557(23)
1.537(24)
1.573(22)
1.531(23)
1.483(22)
1.523(23)
O(9)-C(10)
Ta ble 5. Selected Bon d An gles (d eg) of
exo-Rh (Tr ip od )(2-m eth oxyn or bor n -4-en -1-yl)
(2) HCl. exo-Rh(Tripod)(2-isopropoxynorborn-4-en-1-yl) (15.2
mg, 0.0173 mmol) was weighed into an NMR tube. C6D6 (0.5
mL) was added to make a suspension of the compound. A 17
µL (0.0170 mmol, 0.98 equiv) amount of 1.0 M HCl in C6H6
(Aldrich) was added via syringe. Immediate precipitation of
an orange solid was observed. 31P{1H} NMR of the solution
shows production of Rh(Tripod)(η4-NBD)+ as the sole metal-
containing product, both in the (saturated) solution and as the
orange solid.
Str u ctu r e Deter m in a tion of exo-Rh (Tr ip od )(2-m eth -
oxyn or bor n -4-en -1-yl). Crystals suitable for an X-ray dif-
fraction study were obtained in the following manner. A light
yellow saturated solution of exo-Rh(Tripod)(2-methoxynorborn-
4-en-1-yl) in toluene was filtered through Celite. A few
milliliters of the resulting solution was cannula-transferred
into a glass tube contained in a larger vessel. Approximately
20 mL of Et2O was placed in the outer chamber of the larger
vessel, and the outer flask was sealed. Vapor diffusion of the
Et2O into the toluene produced a yellow powder at the bottom
of the tube after 5 days. Over the course of 2 weeks, yellow
crystalline material formed on the side of the tube. The
mother liquor and Et2O solution were removed. The solid was
dried under vacuum.
P(14)- Rh(1)- P(28)
P(14)-Rh(1)-P(42)
P(14)-Rh(1)-C(2)
P(14)-Rh(1)-C(3)
P(14)-Rh(1)-C(8)
P(28)-Rh(1)-P(42)
P(28)-Rh(1)-C(2)
P(28)-Rh(1)-C(3)
P(28)-Rh(1)-C(8)
P(42)-Rh(1)-C(2)
P(42)-Rh(1)-C(3)
P(42)-Rh(1)-C(8)
C(2)-Rh(1)-C(8)
C(7)-O(9)-C(10)
Rh(1)-C(2)-C(6)
Rh(1)-C(3)-C(4)
93.03(16) C(2)-C(3)-C(4)
87.91(17) C(3)-C(4)-C(5)
100.4(14)
100.0(14)
97.5(13)
105.6(14)
92.1(13)
103.4(13)
107.1(14)
101.2(13)
108.9(13)
112.4(13)
99.8(13)
39.8(6)
156.8(4)
117.3(5)
97.6(5)
C(3)-C(4)-C(8)
C(5)-C(4)-C(8)
C(4)-C(5)-C(6)
87.36(17) C(2)-C(6)-C(5)
109.3(4)
148.9(5)
103.4(4)
99.0(4)
100.1(5)
167.6(4)
71.7(6)
113.8(13)
113.0(11)
97.7(10)
C(2)-C(6)-C(7)
C(5)-C(6)-C(7)
O(9)-C(7)-C(6)
O(9)-C(7)-C(8)
C(6)-C(7)-C(8)
C(2)-Rh(1)-C(3)
C(3)-Rh(1)-C(8)
Rh(1)-C(2)-C(3)
Rh(1)-C(3)-C(2)
C(3)-C(2)-C(6)
67.4(6)
66.6(9)
73.6(10)
106.9(14)
unique space group Pbca. Subsequent solution and refinement
of the structure confirmed this to be the proper space group.
Data were collected (6° < 2θ < 45°, Table 3) using a standard
moving crystal-moving detector technique with fixed back-
ground counts at each extreme of the scan. Data were
corrected for Lorentz and polarization terms and equivalent
data averaged. Because of the small size of the crystal, only
2386 of the 5284 unique data were considered observed on the
basis of the 2.33σ criteria. In spite of the weak data the
structure was readily solved by direct methods (MULTAN78)
and Fourier techniques. Because of the limited data, only the
metal atom was allowed to vary anisotropically. A difference
Fourier showed half of the hydrogen atoms, and all hydrogen
atoms were placed in fixed idealized positions for the final
cycles of refinement. A final difference Fourier was essentially
featureless, the largest peaks lying in the vicinity of the metal
atom. The results of the study are shown in Tables 4 and 5
and Figure 1.
Standard inert-atmosphere handling techniques were used
throughout the crystallographic investigation.13 A small well-
formed crystal was affixed to the end of a glass fiber using
silicone grease and was then transferred to the goniostat,
where it was cooled to -171 °C for characterization and data
collection. A systematic search of a limited hemisphere of
reciprocal space located a set of data with orthorhombic
symmetry and systematic absences corresponding to the
(13) Huffman, J . C.; Lewis, L. N.; Caulton, K. G. Inorg. Chem. 1980,
19, 2755.

1860 Organometallics, Vol. 15, No. 7, 1996
Hauger et al.
1
The H NMR spectrum of the product shows multi-
plets for the diastereotopic methylene protons (CH2-
PPh2) of the phosphine. The methyl group of the
phosphine is observed as a sharper resonance. Several
COD-derived multiplets of intensity 1 are observed
between 3.7 and 1.3 ppm. The singlet for the methoxy
group is clearly observed in the 1H NMR spectra at 2.60
ppm.
Multiple homonuclear decoupling experiments and T1
1
measurements permit the H NMR spectrum of the C8
ring of Ir(Tripod)(2-methoxycyclooct-5-en-1-yl) complex
to be assigned. The crucial resonances for structure
determination are found at 3.64 ppm and 2.07 ppm. The
3
resonance at 3.64 is a doublet of doublets with J HH
couplings of 13 and 2 Hz. This resonance is character-
ized by a long T1 of 541 ms, indicating the absence of
an accompanying geminal proton (T1 values for protons
with accompanying geminal protons are found between
250 and 320 ms in this complex). By the T1 value and
by its chemical shift, this resonance (HA) is on the
carbon to which methoxide has been added:
F igu r e 1. ORTEP drawing of the structure of exo-Rh-
(Tripod)(2-methoxynorborn-4-en-1-yl). Open spheres rep-
resent hydrogen atoms.
Resu lts
Rea ctivity of Ir (Tr ip od )(η4-COD)+ Ca tion w ith
Oxygen Nu cleop h iles. This is the desired first step
in the overall addition of ROH to an olefin. Stirring a
CH2Cl2 solution of [Ir(Tripod)(COD)]Cl with KOMe for
1 h results in a slight darkening of the solution to
orange. Removal of CH2Cl2 followed by extraction into
toluene (in which the compound is only slightly soluble)
and filtering yields the product of nucleophilic attack
on an olefinic carbon, Ir(Tripod)(2-methoxycyclooct-5-
en-1-yl) (1 in eq 3). The reactivity of [Ir(Tripod)(COD)]-
The resonance at 2.07 ppm is a doublet (15 Hz) of
doublets (8 Hz). Homonuclear decoupling at 2.07 ppm
affects the multiplicity of the 2.17 ppm signal but not
that at 3.64 ppm. Reinforcing this result, the resonance
at 2.07 ppm is only altered by homonuclear decoupling
at 2.17 ppm (i.e., to HL), whereupon it is becomes a 15
Hz doublet. This demonstrates that the 15 Hz coupling
observed at 2.07 ppm is actually coupling to one
phosphorus. This definitively establishes the 2.07 ppm
resonance as belonging to the proton (HK) on the carbon
σ-bonded to Ir. The lack of observed coupling of J (HK-
HA) means this value is less than 2 Hz. The expected
dihedral angles for exo-14 and endo-Ir(Tripod)(2-meth-
oxycyclooct-5-en-1-yl)15 products are 58 and 120°. Un-
fortunately, the Karplus relationship shows that the
geminal H/H coupling will be <2 Hz for both of these
angles, leaving no decisive spectroscopic basis for dis-
tinguishing exo from endo stereochemistry of the ob-
tained product.
(3)
Cl with KOEt and NaOiPr is slightly more complex.
Stirring a CH2Cl2 solution of [Ir(Tripod)(η4-COD)]Cl
with either KOEt or NaOiPr for 1 h results in a slight
darkening of the solution to orange. Removal of CH2-
Cl2 followed by extraction into toluene and filtering
yields the two compounds (1 and 2) shown in eq 3, which
have been identified by their spectroscopic signatures
The reactions of Ir(Tripod)(η4-COD)+ with ethoxide
or isopropoxide each yield two products with AMX
patterns in 31P{1H} NMR spectra. On the basis of the
1
similarity of the 31P{1H} and H NMR spectra to those
for exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl), the ma-
jor products of reaction of Ir(Tripod)(η4-COD)+ with
ethoxide or isopropoxide are assigned as exo-Ir(Tripod)-
(2-ethoxycyclooct-5-en-1-yl) and exo-Ir(Tripod)(2-isopro-
poxycyclooct-5-en-1-yl), respectively. The spectral pa-
rameters in the minor (10%) AMX pattern in the
t
(see below). With BuO- (K+ salt) as nucleophile, only
deprotonation of COD (to give product 2) is observed.
Sp ectr oscop ic Ch a r a cter iza tion of Ir (Tr ip od )(η4-
COD)+-Der ived P r od u cts. In the course of the reac-
tion of Ir(Tripod)(η4-COD)+ with methoxide, the single
31P{1H} NMR resonance of the fluxional cationic com-
plex is replaced by an AMX pattern indicating a product
of low symmetry. On the basis of the following spec-
troscopic data, we assign the AMX pattern to exo-Ir-
(Tripod)(2-methoxycyclooct-5-en-1-yl) (exo-1).
(14) For exo-(2-hydroxycyclooct-5-en-1-yl)(cyclopentadienyl)palladi-
um(II): Villa, A. C.; Manfredotti, A. G.; Guastini, C. Cryst. Struct.
Commun. 1973, 2, 181.
(15) For endo-(2-(pentafluorophenyl)cycloocta-5-en-1-yl)(hexafluoro-
acetylacetonato)palladium(II): Albe´niz, A. C.; Espinet, P.; J eannin, Y.;
Philoche-Levisalles, M.; Mann, B. E. J . Am. Chem. Soc. 1990, 112,
6594.

Alkoxide Attack on Coordinated Olefin
Organometallics, Vol. 15, No. 7, 1996 1861
Sch em e 1
F igu r e 2. 31P{1H} NMR spectra showing the addition of
methanol to exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl) in
C6D6. The number of equivalents of methanol added is
shown on the right. The arrow shows the singlet of
Ir(Tripod)(COD)+.
reaction of [Ir(Tripod)(η4-COD)]+ with isopropoxide are
identical with those of the minor product (10%) in the
reaction of [Ir(Tripod)(η4-COD)]+ with ethoxide, indicat-
ing that the alkoxy groups are no longer present. This
product is assigned as Ir(Tripod)((1,2-η2)-6-σ-cycloocta-
1,4-dienyl) (2), which corresponds to the Ir(Triphos)((1,2-
η2)-6-σ-cycloocta-1,4-dienyl) product crystallographically
characterized by Gull et al.16 Observing the 31P{1H}
NMR of exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl) over
the course of several days shows conversion (by loss of
MeOH) to this same species, Ir(Tripod)((1,2-η2)-6-σ-
cycloocta-1,4-dienyl). This compound has been inde-
pendently synthesized by reacting Ir(Tripod)(η4-COD)+
with tert-butoxide, where it is the sole product after only
75 min.
with increasing MeOH concentration. This concentra-
tion dependence is consistent with equilibrium 4. The
exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl) +
nMeOH h Ir(Tripod)(COD)+ + (MeOH)nOMe- (4)
[Ir(Tripod)(COD)+]2
)
[exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl)]
Keq[MeOH]n (5)
Mech a n ism of Alcoh ol E lim in a t ion . Gull et al.
proposed16 that two mechanisms effect deprotonation
of IrL3(COD)+ (L3 ) PhP(C2H4PPh2)2) using KOH,
NaOMe, NaOAr, NEt3, pyridine, or Proton Sponge in
THF. After 12 h at 25 °C, the L3Ir(C8H11) product was
isolated and fully characterized. With NaOMe and
NaOAr, 31P NMR evidence was offered for intermediates
in which RO- had added to a ring carbon. These
“cannot be isolated” but did convert, without added base,
to the product. The authors concluded that direct
deprotonation occurs (path a) for the “strong bases” (B′)
KOH, NEt3, pyridine, and Proton Sponge, while the
“weak bases” (B) NaOMe and NaOAr proceed through
the necessary intermediate Q (path b) by a syn 1,2-
elimination of alcohol (see Scheme 1). Our observations
further substantiate their proposed mechanism of al-
cohol formation in a related system. However, this
alcohol elimination reaction is clearly counterproductive
for our desired conversion of olefin to ether (eq 1).
variable n is included to recognize that an alkoxide
anion is capable of hydrogen bonding to more than one
alcohol.17,18 Rearranging the standard equilibrium
equation and presuming that the concentration of cation
and anion on the right side of the equilibrium are equal
leads to eq 5. Plotting log([Ir(Tripod)(COD)+]2/[exo-Ir-
(Tripod)(2-methoxycyclooct-5-en-1-yl)]) against log[MeOH]
should result in a slope of n. Figure 3 shows the result
of plotting the data for MeOH concentrations in the
range 0.18-1.23 M. The slope of the line is found to be
4.0 ( 0.5 (i.e., n ) 4). Even at these high methanol
concentrations, Ir-C(sp3) bond protonolysis does not
occur. The n value shows that methoxide removal is
significantly stabilized by hydrogen bonding, which
renders MeO- a much less nucleophilic species. The
reaction could in fact begin by hydrogen bonding to the
ether oxygen of 1. Support for such hydrogen bonding
is evident in Figure 2 in the change in the 31P chemical
shifts of 1 as the concentration of added methanol
increases. Such hydrogen bonding thus makes the ether
RO- a better leaving group.
Rea ctivity of exo-Ir (Tr ip od )(2-m eth oxycyclooct-
5-en -1-yl) w ith MeOH. In order to protonate the Ir-C
σ bond (and thus move along the hoped-for catalytic
cycle), MeOH was added to exo-Ir(Tripod)(2-methoxy-
cyclooct-5-en-1-yl). This resulted in the production of
Ir(Tripod)(η4-COD)+, as demonstrated by the production
of a singlet in 31P{1H} NMR spectra (Figure 2) of such
solutions at the chemical shift for Ir(Tripod)(η4-COD)+.
The reaction is not stoichiometric in MeOH but is an
equilibrium process. Integration of the 31P{1H} NMR
spectra over a variety of MeOH concentrations shows
that the concentration of Ir(Tripod)(η4-COD)+ increases
Rh od iu m a s th e “Activa tin g” Meta l. The net
protonation of ether oxygen for the iridium/COD com-
plex by added alcohol is clearly counterproductive for
our goal of olefin addition with ROH. We therefore
chose to study alkoxide attack on η4-diolefin complexes
by utilizing the commercially available [Rh(η4-NBD)-
Cl]2 and tridentate phosphine ligand Tripod (Tripod )
1,1,1-Tris((diphenylphosphino)methyl)ethane, NBD )
(17) Caulton, K. G.; Chisholm, M. H.; Drake, S. R.; Folting, K.;
Huffman, J . C.; Streib, W. E. Inorg. Chem. 1993, 32, 1970. Kellersohn,
T.; Beckenkamp, K.; Lutz, H. D.; J ansen, E. Acta Crystallogr. 1991,
C47, 483.
(16) Gull, A. M.; Fanwick, P. E.; Kubiak, C. P. Organometallics 1993,
12, 2121.
(18) Kunert, M.; Zahn, G.; Sieler, J . Z. Anorg. Allg. Chem. 1995,
621, 1597.

1862 Organometallics, Vol. 15, No. 7, 1996
Hauger et al.
in THF and toluene. An X-ray crystallographic study
of the triflate salt shows that the molecular geometry
is intermediate between trigonal bipyramidal and square
pyramidal, making the three phosphorus atoms in-
equivalent.7 However, the cation exhibits a single 31P-
{1H} NMR doublet, indicating rapid exchange between
inequivalent sites at room temperature common for five-
1
coordinate molecules. The J RhP coupling constant is
1
114 Hz.20 Fluxionality is also observed in the H NMR
spectrum at room temperature, which shows only three
NBD proton chemical shift environments and only two
phosphine alkyl chemical shift environments.
R ea ct ivit y of R h (Tr ip od )(NBD)+ w it h Oxygen
Nu cleop h iles. A heterogeneous mixture of Rh(Tripod)-
(NBD)+ and methoxide in THF becomes homogeneous
over the course of several hours. Solubilization occurs
nearly immediately for isopropoxide and tert-butoxide.
Removal of the THF followed by extraction into toluene
and filtering yields the desired Rh(Tripod)(2-alkoxynor-
born-4-en-1-yl) complexes in good purity. Thus, the
generality of reaction A (Scheme 2) has been estab-
lished. Dramatic differences in the solubility in toluene
are apparent. The methoxy complex is only slightly
soluble while the tert-butoxy complex is quite soluble.
The solubilities of the Rh(Tripod)(2-alkoxynorborn-4-en-
1-yl) complexes in alkanes are quite low. They are all
yellow solids when dry.
Sp ectr oscop ic Ch a r a cter iza tion of Rh (Tr ip od )-
(2-a lk oxyn or bor n -4-en -1-yl) P r od u cts. Inspection of
the 31P{1H} NMR spectra of the products of the reaction
of Rh(Tripod)(η4-NBD)+ with methoxide clearly indi-
cates that the reaction is complete. The single reso-
nance of the fluxional cationic complex is replaced by
two AHMX patterns, indicating molecules of low sym-
metry containing three phosphorus atoms bound to
rhodium. One of the AHMX patterns is of low (7:1)
intensity. These observations are consistent with the
high selectivity expected for nucleophilic attack on
bound olefin. Therefore, we tentatively assigned the
larger intensity AHMX pattern to exo-Rh(Tripod)(2-
methoxynorborn-4-en-1-yl) and the smaller intensity
AHMX pattern to endo-Rh(Tripod)(2-methoxynorborn-
4-en-1-yl). It is interesting that any endo product is
observed, in that it implies initial methoxide attack at
the metal occurs in spite of the multidentate nature of
the ligands (see Scheme 3). Single phosphine dissocia-
tive (arm-off) mechanisms have been observed previ-
ously for the Tripod ligand.21
F igu r e 3. Plot of log{[M(tripod)(diene)+]2/[M(tripod)-
(methoxydienyl)]} vs log[MeOH] for M ) Ir (filled circles)
and for M ) Rh (open circles).
Sch em e 2
norbornadiene]. The desired five-coordinate cationic
complex Rh(Tripod)(η4-NBD)+ 19 should be superior to
Ir(Triphos)(η4-COD)+ in that NBD is not susceptible to
deprotonation at the allylic (bridgehead) positions (i.e.,
Bredt’s rule). Moreover, all reactions involving M-ligand
bond scission (e.g., protonolysis) would be expected to
proceed faster for rhodium than for iridium. Our goal
became to develop the cycle shown in Scheme 2.
Syn th esis a n d Ch a r a cter iza tion of Rh (Tr ip od )-
(η4-NBD)+. The reaction of a toluene solution of [Rh-
(η4-NBD)Cl]2 and the phosphine Tripod provides rapid
conversion (6 h) to the desired [Rh(Tripod)(η4-NBD)]Cl
salt in high (95%) yield; the salt precipitates from the
reaction mixture as a light yellow solid. The compound
is soluble in methylene chloride but only slightly soluble
Consistent with the expectation that the stereoselec-
tivity should be dependent upon the size of the nucleo-
phile, no second AHMX pattern is observed for the
31P{1H} NMR spectra of the products of reaction of Rh-
(Tripod)(η4-NBD)+ with isopropoxide or tert-butoxide.
Due to the similarities of the observed resonances
(chemical shift and coupling constants) with the product
assigned as exo-Rh(Tripod)(2-methoxynorborn-4-en-1-
yl), we assign the products as exo-Rh(Tripod)(2-isopro-
poxynorborn-4-en-1-yl) and exo-Rh(Tripod)(2-tert-butoxy-
norborn-4-en-1-yl), respectively. Each 31P{1H} resonance
shows coupling to rhodium, indicating that all phos-
phines are metal-bound.
(20) 1J RhP ) 104 Hz for Rh(Tripod)Cl3. See: Thaler, E. G.; Folting,
K.; Caulton, K. G. J . Am. Chem. Soc. 1990, 112, 2664.
(21) Kiss, G.; Horvath, I. T. Organometallics 1991, 10, 3798 and
references therein.
(19) Bachechi, F.; Ott, J .; Venanzi, L. M. Acta Crystallogr. 1989,
C45, 724.

Alkoxide Attack on Coordinated Olefin
Organometallics, Vol. 15, No. 7, 1996 1863
that the major isomer (by 31P{1H} NMR spectroscopy
of the crystals used for X-ray determination) of Rh-
(Tripod)(2-methoxynorborn-4-en-1-yl) indeed contains
the methoxy group in an exo position as a consequence
of methoxide attack on one double bond anti to the
rhodium (Figure 1). The geometry of the complex can
be described as distorted trigonal bipyramidal about
rhodium, with the P(42)-Rh(1)-C(8) angle of 167.6(4)°
defining the major axis. The P-Rh-P angles are all
approximately 90°, placing the Tripod ligand in the
expected facial arrangement. The two olefinic carbons
occupy the remaining equatorial site. It has been shown
earlier that there is less back-donation, in a trigonal
bipyramid, to an apical olefin than to an equatorial
olefin.24 Hence, the site of alkoxide attachment is
consistent with this being the (kinetic) product of
nucleophilic attack at the apical olefin. The P(42)-Rh-
C(8) angle is decreased from the expected 180° due to
the multidentate nature of the 2-methoxynorborn-4-en-
1-yl ligand. This factor is apparent in the cisoid C(8)-
Rh(1)-C(2) and C(8)-Rh(1)-C(3) angles of 71.7(6) and
67.4(6)°, respectively. Selected bond lengths and angles
are contained in Tables 4 and 5.
The structure of exo-Rh(Tripod)(2-methoxynorborn-
4-en-1-yl) is related to the structures of exo-Ir(PMe3)3-
(2-indenylcyclooct-5-en-1-yl)25 and exo-Ir(PMe3)3(2-ben-
zylcyclooct-5-en-1-yl)26 derived from indenyl and benzyl
attack upon Ir(PMe3)3(η4-COD)+. In these, the geometry
about the metal is distorted trigonal bipyramidal with
the phosphines in a facial configuration. Two phos-
phines and the remaining olefin occupy the equatorial
plane. The transoid phosphorus-Ir-C angles, which
define the axis, remain slightly smaller than 180°
(168.9° benzyl and 170° indenyl). However, the multi-
dentate eight-membered rings allow for slightly larger
cisoid C-Ir-C angles for both the benzyl complex
(C(6)-Ir-C(2) ) 83.7°, C(6)-Ir-C(1) ) 78.3°) and the
indenyl complex (C(1)-Ir-C(5) ) 88°, C(1)-Ir-C(4) )
78°).
Sch em e 3
The 1H NMR spectra of the products of reaction of
Rh(Tripod)(η4-NBD)+ with alkoxides also show quite
clearly that low-symmetry molecules have been synthe-
sized. Overlapping doublets of doublets are observable
for the diastereotopic methylene protons (CH2PPh2) of
the phosphine. The methyl group of the phosphine is
clearly observed as a sharper resonance. Several broad
NBD-derived resonances of intensity 1 are observed
between 4.5 and 0.8 ppm. Among these are two
doublets which, by selective homonuclear decoupling,
are coupled to each other with a coupling constant of
7-8 Hz.
In order to determine if this 7-8 Hz coupling constant
provides a definitive probe of product regiochemistry
(i.e. endo or exo) through application of the well-known
Karplus dihedral angular relationship,22 we wished to
establish which two (of eight) NBD-derived hydrogens
corresponded to these chemical shifts. Due to the small
difference in chemical shift between the doublets and
other resonances, one-dimensional techniques (e.g. NO-
EDIFF) should be expected to be problematic. There-
Rea ctivity of Rh (Tr ip od )(η4-NBD)+ w ith a Ch ir a l
Alk oxid e. The stereogenic carbons (labeled C7, C8 in
Figure 1) in exo-Rh(Tripod)(2-methoxynorborn-4-en-1-
yl) are both in the S configuration, as shown in Figure
1. The crystallographic space group (Pcba) requires that
an equal number of S,S and R, R molecules be in the
lattice, i.e., the crystals are racemic. (S)-(+)-2-Butoxide
was reacted with Rh(Tripod)(η4-NBD)+ to establish if
chirality transfer from the alkoxide is effective. The 31P-
{1H} NMR spectrum of the products of this reaction
shows the presence of two compounds, assigned as
(S,S,S)- and (R,R,S)-exo-Rh(Tripod)[2-(((S)-butoxy)nor-
born-4-en-1-yl), in a 1:1 ratio. This demonstrates that
31P{1H} NMR spectroscopy is useful in determining the
diastereoselectivity of this reaction, which unfortunately
appears to be nearly 0.
fore, a 2D H-1H NOESY experiment was undertaken.
1
The largest positive correlation for NBD-derived protons
was found to be between the two doublets, which
establishes that they are the proximate protons on
carbon 7 (see Scheme 2) of the 2-isopropoxynorborn-4-
en-1-yl ligand. The only observable coupling constants
1
in the H NMR spectra of Rh(Tripod)(2-alkoxynorborn-
4-en-yl) compounds are thus not useful for exo/endo
determination. However, 3J HH couplings for norbornane
systems are well-known. If the alkoxy group is endo,
3
then a J HH coupling of approximately 9 Hz is expected
between the hydrogens on carbons 1 and 2 (see Scheme
2).23 Since no such coupling is observed, the alkoxy
3
group must be exo, yielding a J HH value between the
Rea ctivity of exo-Rh (Tr ip od )(2-a lk oxyn or bor n -
4-en -1-yl) P r od u cts w ith Alcoh ols. The next step
needed in the catalytic cycle of Scheme 2 is protonolysis
(step B) of the Rh-C σ bond by alcohol. The addition
of MeOH to a THF solution of exo-Rh(Tripod)(2-meth-
oxynorborn-4-en-1-yl) results in the production of Rh-
(Tripod)(η4-NBD)+, as demonstrated by the production
hydrogens on carbons 1 and 2 of approximately 4 Hz
which is not resolved due to the complication of coupling
from phosphorus atoms and rhodium. This confirms our
assignment of this isomer as having the methoxy
nucleophile exo to the metal.
Str u ctu r e of exo-Rh (Tr ip od )(2-m eth oxyn or bor n -
4-en -1-yl). The X-ray crystallographic study reveals
(22) (a) Karplus, M. J . Chem. Phys. 1959, 30, 11. (b) Karplus, M. J .
Am. Chem. Soc. 1963, 85, 2870.
(23) Breitmaier, E. Structure Elucidation by NMR in Organic
Chemistry: A Practical Guide; Wiley: Chichester, U.K., 1993; p 45.
(24) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365.
(25) Merola, J . S.; Kacmarcik, R. T. Organometallics 1989, 8, 778.
(26) Frazier, J . F.; Anderson, F. E.; Clark, R.; Merola, J . S. Inorg.
Chim. Acta 1994, 222, 135.

1864 Organometallics, Vol. 15, No. 7, 1996
Hauger et al.
of a doublet in the 31P{1H} NMR spectrum. The
reaction is, however, not the desired Rh-C protonolysis
but, rather, alkoxide abstraction (the reverse of step A
in Scheme 2). The 31P{1H} NMR spectrum identifies
the product as Rh(Tripod)(η4-NBD)+. Integrations of
such 31P{1H} NMR spectra over a variety of MeOH
concentrations show that the concentration of Rh-
(Tripod)(η4-NBD)+ increases with increasing MeOH
concentration. The concentration of exo-Rh(Tripod)(2-
methoxynorborn-4-en-1-yl) decreases with increasing
MeOH concentration. This concentration dependence
is consistent with equilibrium 6. Rearranging the
by alcohol or stronger acids in these systems is doomed
to failure due to the presence of a low, but equilibrium,
concentration of free alkoxide in solution which ef-
fectively captures the added protons before they en-
counter the metal-carbon σ bond.27
Con clu sion s
The cleavage of the C-O bonds in the exo-Rh(Tripod)-
(2-methoxynorborn-4-en-1-yl) and exo-Ir(Tripod)(2-meth-
oxycyclooct-5-en-1-yl) compounds represent unproduc-
tive side reactions in the proposed catalytic cycle seen
in Scheme 2. Equilibria 1 and 4 are good examples of
Le Chaˆtelier’s principle. The addition of methanol to a
mixture containing an undetectable but kinetically
significant amount of methoxide results in the formation
of a strong hydrogen bond which shifts the equilibria
away from the desired compounds, exo-Rh(Tripod)(2-
methoxynorborn-4-en-1-yl) and exo-Ir(Tripod)(2-meth-
oxycyclooct-5-en-1-yl). The fact that these equilibria are
present also makes the use of these compounds in
stoichiometric transformations unfeasible. Alcohol for-
mation by 1,2-syn elimination further complicates mat-
ters for COD-based reactions (i.e., where allylic CH2
groups are present).
These results reveal the challenge of finding, simul-
taneously, an alcohol selective enough to cleave a
M-C(sp3) bond in preference to protonation, and O-C
bond cleavage, of an ether oxygen â to a metal. While
this would seem to require an alcohol of considerable
acidity, it is clear that its conjugate base, RO-, must
also be sufficiently nucleophilic to attack carbon of a
coordinated olefin but not directly deprotonate the
allylic hydrogen of a coordinated olefin. A further
requirement on RO- nucleophilicity is that its ether
should not undergo the vicinal alcohol elimination we
observe in the COD complex; we have accomplished that
goal here with the very special choice of norbornadiene
as olefin. While this permits a demonstration of the
concept, it lacks generality.
Rh(Tripod)(2-methoxynorborn-4-en-1-yl) +
nMeOH h Rh(Tripod)(NBD)+ + (MeOH)nOMe- (6)
[Rh(Tripod)(NBD)+]2
)
[exo-Rh(Tripod)(2-methoxynorborn-4-en-1-yl)]
Keq[MeOH]n (7)
standard equilibrium equation and presuming that the
concentration of cation and anion on the right side of
the equilibrium are equal leads to eq 7. Plotting log-
([Rh(Tripod)(NBD)+]2/[exo-Rh(Tripod)(2-methoxynorborn-
4-en-1-yl)]) against log[MeOH] should result in a slope
of n, the number of methanol molecules participating
in the reaction. Figure 3 shows the result of plotting
the data for MeOH concentrations in the range 0.72-
1.82 M. The slope of the line is found to be 4.6 ( 0.8.
Similar behavior is not observed for either exo-Rh-
(Tripod)(2-isopropoxynorborn-4-en-1-yl) or exo-Rh(Tri-
pod)(2-tert-butoxy-norborn-4-en-1-yl) upon addition of
the respective alcohols. In fact, no generation of Rh-
(Tripod)(η4-NBD)+ is observed at similar alcohol con-
centrations, apparently due to steric inhibition to attack
by these larger alcohols at the concentrations employed.
These alcohols do not react.
Rea ctivity of exo-Rh (Tr ip od )(2-isop r op oxyn or -
bor n -4-en -1-yl) w ith Acid s. We next sought to cleave
the Rh-C(sp3) bond (Scheme 2, step B) with a stronger
acid, to release the norbornyl ether from the metal.
Unfortunately, acids with both coordinating and non-
coordinating anions (see Experimental Section) convert
exo-Rh(Tripod)(2-isopropoxynorborn-4-en-1-yl) to Rh-
(Tripod)(η4-NBD)+ (by 31P{1H} NMR spectroscopy) and
2-propanol. Thus, the product involves protonolysis at
oxygen, not at the Rh-C(sp3) bond.
Having defined those features of olefin and RO- which
can frustrate catalysis in eq 1, we are now in a better
position to manipulate aspects of the LnM catalytic
center, which might promote the reaction in a general
context. Minimal back-bonding promotes attack by even
weak nucleophiles, thus, a saturated LnM(olefin) com-
plex of Zr(IV) or Pt(II or IV), or even Cu(I) or Ag(I) (e.g.,
RB(pz)3Cu(olefin)) might suffice.
Reactivity of exo-Rh (Tr ipod)(2-m eth oxyn or bor n -
4-en -1-yl) w ith CD2Cl2. Further observations affirm
that the most nucleophilic site in the ether complex is
at oxygen. Exo-Rh(Tripod)(2-methoxynorborn-4-en-1-
yl) reacts with d2-methylene chloride overnight to
produce MeOCD2Cl and re-form Rh(Tripod)(η4-NBD)+.
We propose that it is implausible that the displacement
of chloride from the halocarbon is achieved by an
ethereal oxygen atom. The slow reactivity is consistent
with a low concentration of methoxide anion in solution
which accomplishes the standard bimolecular displace-
ment of chloride from CD2Cl2 carbon. Therefore, reac-
tion A of Scheme 2 is correctly written as an equilibrium
reaction. Clearly, protonation of metal-carbon bonds
Ack n ow led gm en t. This work was supported by the
NSF. We thank J ohnson Matthey/Aesar for material
support and J ackie Davis and Dmitry Gusev for NMR
spectroscopic assistance.
Su p p or tin g In for m a tion Ava ila ble: Tables giving posi-
tional and thermal parameters for exo-Rh(Tripod)(2-methoxy-
norborn-4-en-1-yl) (2 pages). Ordering information is given
on any current masthead page.
OM950905Z
(27) For an example of a thermally induced â-OPh elimination from
â-phenoxyethyl Pt(II) compounds, see: Komiya, S.; Shindo, T. J . Chem.
Soc., Chem. Commun. 1984, 1672.