Allylic Amination of Unactivated Olefins by Nitroarenes, Catalyzed by Ruthenium Complexes. A Reaction Involving an Intermolecular C-H Functionalization

Article abstract of DOI:10.1021/om980843n

A reaction is reported, resulting in the allylic amination of an unactivated olefin, cyclohexene, by a nitroarene, catalyzed by Ru₃(CO)₁₂Ar-BIAN (Ar-BIAN = bis(arylimino)-acenaphthene), under CO pressure. The reaction involves an int

Full text of DOI:10.1021/om980843n

928
Organometallics 1999, 18, 928-942
Allylic Am in a tion of Un a ctiva ted Olefin s by Nitr oa r en es,
Ca ta lyzed by Ru th en iu m Com p lexes. A Rea ction
In volvin g a n In ter m olecu la r C-H F u n ction a liza tion
Fabio Ragaini, Sergio Cenini,* Stefano Tollari, Giovanni Tummolillo, and
Raffaella Beltrami
Dipartimento di Chimica Inorganica, Metallorganica e Analitica and CNR Center, V. G.
Venezian 21, I-20133 Milano, Italy
Received October 9, 1998
A reaction is reported, resulting in the allylic amination of an unactivated olefin,
cyclohexene, by a nitroarene, catalyzed by Ru3(CO)12/Ar-BIAN (Ar-BIAN ) bis(arylimino)-
acenaphthene), under CO pressure. The reaction involves an intermolecular catalytic C-H
functionalization by a transition metal complex. Best results (selectivity up to 81.9%, with
a substrate/Ru3(CO)12 ratio ) 50) are obtained by using nitroarenes bearing electron-
withdrawing substituents and Ph-BIAN as a ligand. Other olefins can also be employed in
place of cyclohexene. The reaction mechanism has been investigated. The reaction is first
order in nitroarene and olefin, which is used as solvent in most cases, but the rate equation
also contains an olefin-independent term. A rate acceleration by small amounts of toluene
in the solvent mixture is due to a faster formation of Ru(CO)3(Ar-BIAN) from Ru3(CO)12
and Ar-BIAN in its presence. This last complex is in equilibrium with the active species
Ru(Ar-BIAN)(CO)2(cyclohexene), and its direct reaction with the nitroarene accounts for the
olefin-independent term in the rate law. The reaction of Ru(CO)3(Ar-BIAN) with nitroarenes
gives Ru(CO)2(Ar-BIAN)(η2-ArNO), which has been isolated in one case, but this complex is
not an intermediate in the synthesis of allylamines. Coupling between a coordinated
nitrosoarene and a coordinated olefin appears to be responsible for the C-N bond formation.
In tr od u ction
synthesis of these intermediates usually requires the
availability of a prefunctionalized starting material,
such as an allyl acetate. A few methods have been
reported in the literature, which afford an allylic amine
by a C-H activation reaction.6-14 Stoichiometric reac-
tions have been performed employing sulfur or selenium
Transition metal-mediated intermolecular activation
and functionalization of C-H bonds is a topic of high
current interest. However, with the partial exception
of oxidation reactions, few practical reactions have been
developed using this approach, and the large majority
of them are only stoichiometric in the metal component
or show at best a very limited catalytic efficiency.1 From
another perspective, the functionalization of a simple
olefin by an external amine is also a topic that has
attracted much interest. However, the direct intermo-
lecular addition of an amine to an unactivated olefin,
either metal-mediated or not, has met with only a
limited success.2 Good results have only been obtained
by using much more reactive nitrogen compounds, such
as PhIdNTs (aziridines are usually obtained in this
case).3 As far as allylic amines are considered as
products,4 most reported synthetic procedures proceed
via a palladium or nickel4,5 allyl complex. However, the
(4) J ohannsen, M.; J ørgensen, K. A. Chem. Rev. 1998, 98, 1689, and
references therein.
(5) (a) Frost, C. G.; Howarth, J .; Williams, J . M. J . Tetrahedron:
Asymmetry 1992, 3, 1089, and references therein. (b) Consiglio, G.;
Waymouth, R. M. Chem. Rev. 1989, 89, 257, and references therein.
(c) Bricout, H.; Carpentier, J .-F.; Monrtreux, A. Tetrahedron 1998,
1073, and references therein.
(6) (a) Sharpless, K. B.; Hori, T. J . Org. Chem. 1976, 41, 176. (b)
Sharpless, K. B.; Hori, T.; Truesdale, L. K.; Dietrich, C. O. J . Am.
Chem. Soc. 1976, 98, 269. (c) Kresze, G.; Braxmeier, H.; Mu¨nsterer,
H. Org. Synth. 1987, 65, 159. (d) Katz, T. J .; Shi. S. J . Org. Chem.
1994, 59, 8297. (e) Bruncko, M.; Khuong, T.-A. V.; Sharpless, K. B.
Angew. Chem., Int. Ed. Engl. 1996, 35, 454. (f) Tsushima, S.; Yamada,
Y.; Onami, T.; Oshima, K.; Chaney, M. O.; J ones, N. D.; Swartzen-
druber, J . K. Bull. Chem. Soc. J pn. 1989, 62, 1167.
(7) (a) Liebeskind, L. S.; Sharpless, K. B.; Wilson, R. D.; Ibers, J . A.
J . Am. Chem. Soc. 1978, 100, 7061. (b) Møller, E. R.; J ørgensen, K. A.
J . Am. Chem. Soc. 1993, 115, 11814.
(8) (a) Mahy, J . P.; Bedi, G.; Battioni, P.; Mansuy, D. Tetrahedron
Lett. 1988, 29, 1927. (b) Na¨geli, I.; Baud, C.; Bernardinelli, G.; J acquier,
Y.; Moran, M.; Mu¨ller, P. Helv. Chim. Acta 1997, 80, 1087.
(9) Srivastava, R. S.; Ma, Y.; Pankayatselvan, R.; Dinges, W.;
Nicholas, K. M. J . Chem. Soc., Chem. Commun. 1992, 853.
(10) Srivastava, R. S.; Nicholas, K. M. J . Org. Chem. 1994, 59, 5365.
(11) J ohannsen, M.; J ørgensen, K. A. J . Org. Chem. 1994, 59, 214.
(12) J ohannsen, M.; J ørgensen, K. A. J . Org. Chem. 1995, 60, 5979.
(13) Srivastava, R. S.; Nicholas, K. M. Tetrahedron Lett. 1994, 35,
8739.
* Corresponding author. Fax: (39)-02-2362748. E-mail: scenini@
csmtbo.mi.cnr.it.
(1) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154, and references therein.
(2) Reviews: (a) Mu¨ller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675.
(b) Roundhill, D. M. Chem. Rev. 1992, 92, 1. (c) Roundhill, D. M. Catal.
Today 1997, 37, 155. (d) Brunet, J .-J . Gazz. Chim. Ital. 1997, 127, 111.
(3) For some recent examples see: (a) Evans, D. A.; Faul, M. M.;
Bilodeau, M. T. J . Am. Chem. Soc. 1994, 116, 2742. (b) Pe´rez, P. J .;
Brookhart, M.; Templeton, J . L. Organometallics 1993, 12, 261. (c)
O’Connor, K. J .; Wey, S.-J .; Burrows, C. J . Tetrahedron. Lett. 1992,
33, 1001.
(14) (a) Srivastava, R. S.; Khan, M. A.; Nicholas, K. M. J . Am. Chem.
Soc. 1996, 118, 3311. (b) Srivastava, R. S.; Nicholas, K. M. J . Am.
Chem. Soc. 1997, 119, 3302.
10.1021/om980843n CCC: $18.00 © 1999 American Chemical Society
Publication on Web 02/06/1999

Allylic Amination of Unactivated Olefins
Organometallics, Vol. 18, No. 5, 1999 929
Ta ble 1. Syn th esis of Allyla m in es 1 fr om
Com m er cia l Cycloh exen e a n d Differ en t
Nitr oa r en esa
chloride complex of the ligand is formed, from which the
ligand is liberated by boiling the solid in an aqueous
solution of sodium carbonate.
entry
no.
allylamine aniline
select. %b select. %b
nitroarene
ligand
1c 4-MeOC6H4NO2 Tol-BIAN
26.3 (1e)
55.0 (1d )
58.9 (1c)
63.8 (1b)
71.1(1a )
22.4 (1a )
77.4 (1a )
15.1
27.4
22.8
26.3
20.7
34.4
23.4
30.5
29.1
25.5
42.7
2
3
4
5
6
7
8
9
4-MeC6H4NO2 Tol-BIAN
PhNO2
4-FC6H4NO2
Tol-BIAN
Tol-BIAN
3,4-Cl2C6H3NO2 Tol-BIAN
3,4-Cl2C6H3NO2 TMPhen
3,4-Cl2C6H3NO2 Ph-BIAN
3,4-Cl2C6H3NO2 4-MeOC6H4-BIAN 61.8 (1a )
3,4-Cl2C6H3NO2 4-ClC6H4-BIAN
57.7 (1a )
74.3 (1a )
26.2 (1a )
10d 3,4-Cl2C6H3NO2 Tol-BIAN
11e 3,4-Cl2C6H3NO2 DPPE
We performed the first step of the synthesis as
previously reported, but we used a different procedure
to free the ligand from the zinc salt. The zinc complex
is suspended in CH2Cl2 (in which it is moderately
soluble), and an aqueous solution of potassium (or
sodium) oxalate is added. Simple shaking of the biphasic
solution in a separating funnel for a few minutes causes
the precipitation of zinc oxalate (which remains as a
suspension in the aqueous phase) and complete solubi-
lization of the ligand in the CH2Cl2 layer. Usual workup
of the organic layer affords the analytically pure ligand
in almost quantitative yields (from the zinc complex)
and without the need for a recrystallization.
Ca ta lytic Resu lts. The reduction of aromatic nitro
compounds, Ar′NO2, by CO catalyzed by Ru3(CO)12 in
the presence of Ar-BIAN, in commercial cyclohexene as
solvent and at 160 °C and 40 bar, gives the correspond-
ing allylamine derivatives as the main products (eq 1,
Table 1):
a
Experimental conditions: Ru3(CO)12 ) 0.01 mmol, ligand )
0.03 mmol, ArNO2 ) 0.5 mmol, T ) 160 °C, PCO ) 40 bar, t ) 6 h,
b
in commercial cyclohexene (10 mL). Conversion ) 100%. Calcu-
lated with respect to the converted nitroarene; GC analysis.
c Conversion ) 78.3%. 3,4-Cl2C6H3NO2 ) 1 mmol, conversion )
d
86.0%. e Ru(CO)3(DPPE) (0.03 mmol) was used as catalyst, without
any added ligand; conversion ) 51.6%.
imino compounds (RNdXdNR; X ) S, Se)6 or molyb-
denum oxaziridines.7 A few catalytic processes have also
been reported employing PhIdNTs,8 PhNHOH,9-14 or
peroxycarbamates15 as the nitrogen-containing com-
pound, but the turnover numbers are quite low and the
aminating reagents are not readily available.16 An
interesting approach has also more recently been re-
ported,17 which employs an amine in the presence of an
oxidant as the aminating agent, thus avoiding the
preliminary synthesis of the hydroxylamine, but the
turnover numbers are still low, although selectivities
are high in some cases.
In this paper, we report on a new synthetic way to
produce allylic amines, employing a simple unactivated
olefin, cyclohexene, and an aromatic nitro compound as
the aminating reagent, under reducing conditions (CO
pressure). Although the method requires the use of a
high-pressure apparatus, the reagents are bulk, cheap
commercial products that do not need to be purified
(although a higher selectivity can be achieved by purify-
ing the olefin), the experimental operations are easy,
the selectivity is high (up to 81.9%), and the turnover
numbers are higher than those reported for most C-H
activation reactions. Only one precedent exists for an
analogous reaction also examined in our laboratories,18
but only trace amounts of allylic amine were obtained
in that case, the main products being ureas and
anilines.19,20 A preliminary communication on part of
the results reported here has been published.21
Byproducts of the reaction are the anilines corre-
sponding to the nitro compounds. With a substrate/
catalyst ratio of 50, only in the case of Ar ) 4-MeOC6H4
is a complete conversion not achieved (entry 1). More-
(19) More than 20 years ago, in a review dedicated to the reactions
of nitroarenes catalyzed by Rh6(CO)16/pyridine, Iqbal included in a table
on the different reactions effected an entry on the reaction between a
nitro compound and an olefin to yield an aziridine. However, in the
text, the section dealing with the reactions of acetylenes begins clearly
stating that “olefins failed to undergo any reaction”: Iqbal, A. F. M.
CHEMTECH 1974, 566.
Resu lts
(20) Intramolecular reactions of a nitro group and an olefin under
CO pressure have already been reported by us and others to afford
several types of heterocycles. However, in this case, the attack occurs
at an olefin, rather than allylic carbon. For some examples see: (a)
Cenini, S.; Ragaini, F. Catalytic Reductive Carbonylation of Organic
Nitro Compounds; Kluwer Academic Publishers: Dordrecht, 1997;
Chapter 5, and references therein. (b) Crotti, C.; Cenini, S.; Rindone,
B.; Tollari, S. J . Chem. Soc., Chem. Commun. 1986, 784. (c) Crotti, C.;
Cenini, S.; Todeschini, R.; Tollari, S. J . Chem. Soc., Faraday Trans.
1991, 87, 2811. (d) Akazone, M.; Kondo, T.; Watanabe, Y. Chem. Lett.
1992, 769. (e) Tollari, S.; Cenini, S.; Crotti, C.; Giannella, E. J . Mol.
Catal. 1994, 87, 203. (f) Tollari, S.; Cenini, S.; Ragaini, F.; Cassar, L.
J . Chem. Soc., Chem. Commun. 1994, 1741. (g) Annunziata, R.; Cenini,
S.; Palmisano, G.; Tollari, S. Synth. Commun. 1996, 26, 495.
(21) Cenini, S.; Ragaini, F.; Tollari, S.; Paone, D. J . Am. Chem. Soc.
1996, 118, 11964.
Syn th esis of th e Liga n d s. A synthesis of the Ar-
BIAN22 ligands employed in this study has already been
reported.23,24 The most general procedure requires the
reaction of acenaphthenequinone with an aromatic
amine in the presence of dry zinc chloride. A zinc
(15) Kohmura, Y.; Kawasaki, K.; Katsuki, T. Synlett 1997, 1456.
(16) Photochemical activation of azides may also result in C-H
functionalization. For a recent reference see: Clauss, K.-U.; Buck, K.;
Abraham, W. Tetrahedron 1995, 51, 7181.
(17) Srivastava, R. S.; Nicholas, K. M. Chem. Commun. 1996, 2335.
(18) (a) Bassoli, A.; Rindone, B.; Cenini, S. J . Mol. Catal. 1991, 66,
163. (b) Bassoli, A.; Rindone, B.; Tollari, S.; Cenini, S.; Crotti, C. J .
Mol. Catal. 1990, 60, 155.

930 Organometallics, Vol. 18, No. 5, 1999
Ragaini et al.
Ta ble 2. Effect of th e BIAN/Ru Ra tio on th e
Syn th esis of 1a fr om P u r ified Cycloh exen e a n d
a
3,4-Cl2C6H3NO2
ligand/Ru nitroarene allylamine
mol ratio
aniline
run
ligand
conv. %b
select. %c select. %c
1
2
3
4
5
6
7
8
9
Ph-BIAN
Ph-BIAN
Ph-BIAN
Ph-BIAN
Ph-BIAN
Tol-BIAN
Tol-BIAN
Tol-BIAN
Tol-BIAN
1
30.0
33.0
31.0
29.8
30.9
32.2
37.1
38.5
49.1
72.0
71.0
70.9
64.4
65.0
66.6
65.2
57.7
40.8
12.7
12.8
13.0
12.9
12.2
7.1
9.8
6.1
5.0
1.25
1.5
2
3
1
1.5
2
3
a
Experimental conditions: Ru3(CO)12 ) 0.01 mmol, ArNO2
)
1.0 mmol, T ) 160 °C, PCO ) 40 bar, t ) 1.5 h, in purified
b
cyclohexene (9 mL) + toluene (1 mL). Calculated with respect
to the initial nitroarene. c Calculated with respect to the converted
nitroarene.
formed, but moisture in the undried solvent plays a
negligible role. The hydrogen-transfer reduction of ni-
troarenes by cyclohexene has long been known to be
catalyzed by heterogeneous palladium catalysts,26 but,
to the best of our knowledge, this is the first time that
this reaction is found to be catalyzed by a homogeneous
complex. The higher selectivity obtained with the puri-
fied substrate also indicates that, although the com-
mercial olefin is a suitable substrate, it contains some
impurities which lower the selectivity, affording uni-
dentified, high-boiling products.
We also examined the effect of changing the substitu-
ent at the para position on the aryl rings of the ligand.
In all cases, the conversion was complete, but the
selectivity in allylamine followed the order R ) H > Me
> OMe > Cl (Table 1, entries 5, 7-9). An influence on
the basicity of the ligand is evident, but there is no
correlation with the Hammet σ constants. Use of 3,4,7,8-
tetramethyl-1,10-phenanthroline (TMPhen) as ligand in
place of Ar-BIAN gave much poorer results (entry 6).
Phosphines are even less efficient as ligands, even when
the preformed complex (see later) Ru(CO)3(DPPE) (DPPE
) 1,2-bis(diphenylphosphino)ethane) was employed (en-
try 11). Use of other catalytic systems such as Pd(2,4,6-
trimethylbenzoate)2/TMPhen27 or Rh4(CO)12/Bipy27 also
afforded much poorer yields.
At this point we started an optimization study on the
reaction conditions. Cyclohexene purified over sodium
was used for these and all of the following reactions,
and 10% toluene was also added to the solvent mixture
as the presence of a small amount of this solvent has
been found to increase the rate of the reaction (see
later). The use of purified cyclohexene led to much
higher reaction rates with respect to the ones obtained
in the commercial solvent, and the reaction time had
to be reduced to 1.5 h and the catalytic ratio ArNO2/Ru
increased to 100 in order to avoid complete conversion
of the substrate. We initially examined the effect of
changing the ligand/Ru ratio with the two best ligands
found in the screening study, Ph-BIAN and Tol-BIAN.
As it is evident from the results reported in Table 2, in
F igu r e 1. Effect of the substituent on the catalytic
intermolecular amination of cyclohexene: (9) selectivity
percent in allylamine; (+) selectivity percent in R-aniline.
The last point corresponds to 3,4-Cl2C6H3NO2, and the sum
of the Hammet σp and σm values for a chloro substituent
was used. The best straight line passing through the last
four points in the selectivity in the allylamine series has
the equation Select. % ) 21.0σ + 58.9, with R2 ) 0.970.
over, in this case the reaction shows a poor selectivity.
In the other cases, a complete conversion is also ac-
companied by a much better selectivity. The selectivity
increases with an increase in the electron-withdrawing
power of the substituent on the nitroarene (Table 1,
entries 1-5, Figure 1). A linear relationship exists
between the selectivity in allylamine and the Hammet
σ constant for all of the nitroarenes employed (the last
point in Figure 1 corresponds to 3,4-Cl2C6H3NO2 and
the sum of the Hammet σp and σm values for a chloro
substituent was used) except for 4-MeOC6H4NO2 (select.
% ) 21.0σ + 58.9, with R2 ) 0.970).
The amount of aniline formed during the reaction is
quite insensitive to the nature of the substituents. Its
formation may be attributed to the presence of moisture
in the solvent and in the CO gas.25 However, when we
employed cyclohexene purified by distillation over so-
dium under the conditions of entry 5 in Table 1, the
selectivity in aniline was slightly changed, although the
selectivity in allylic amine increased to 81.9% (with a
mass balance of 98.4%). Moreover, we could evidence
(by GC-MS) the formation of benzene and cyclohexa-
diene in the volatile fraction after the end of the reaction
The same two products were not present in the starting
solvent, and their formation indicates that the substrate
itself is responsible for at least part of the aniline
(22) Note that in previous papers we used the name DIAN-R for
these ligands. However, since other groups are using the general name
Ar-BIAN for this class of ligands and this last terminology is of more
general application, we have decided to adhere to this convention in
order to avoid the use of different names in the literature for the same
compound.
(23) van Asselt, R.; Elsevier: C. J .; Smeets, W. J . J .; Spek, A. L.;
Benedix, R. Recl. Trav. Pays-Bas 1994, 113, 88.
(24) Matei, I.; Lixandru, T. Bul. Ist. Politeh. Iasi 1967, 13, 245;
Chem. Abstr. 1969, 70, 3623m.
(25) (a) The Ru3(CO)12/Tol-BIAN system is one of the best catalysts
for the reduction of nitrobenzene to aniline by CO/H2O. (b) Ragaini,
F.; Cenini, S.; Tollari, S. J . Mol. Catal. 1993, 85, L1.
(26) (a) Brieger, G.; Nestrick, T. J . Chem. Rev. 1974, 74, 567. (b)
J ackman, L. M. Adv. Org. Chem. 1960, 2, 329. (c) Braude, E. A.;
Linstead, R. P.; Wooldridge, K. R. H. J . Chem. Soc. 1954, 3586. (d)
Entwistle, I. D.; J ohnstone, R. A. W.; Povall, T. J . J . Chem. Soc., Perkin
Trans. 1 1975, 1300.
(27) Cenini, S.; Ragaini, F.; Pizzotti, M.; Porta, F.; Mestroni, G.;
Alessio, E. J . Mol. Catal. 1991, 64, 179.

Allylic Amination of Unactivated Olefins
Organometallics, Vol. 18, No. 5, 1999 931
Ta ble 3. Effect of th e Tem p er a tu r e on th e
Syn th esis of 1a fr om P u r ified Cycloh exen e a n d
3,4-Cl2C6H3NO2, Ca ta lyzed by Ru 3(CO)12 a n d
P h -BIANa
Ta ble 5. Syn th esis of Allyla m in es Der ived fr om
3,4-Cl2C6H3NO2 a n d Oth er Olefin sa
nitroarene
conv. %b
allylamine
select. %c
run
olefin
nitroarene
conv. %b
allylamine
select. %c
aniline
1
2
3
cyclooctene
cyclopentene
R-methylstyrene
81.2
98.9
94.5
57.2 (1f)
37.7 (1g)
51.8 (1j)
run
T/°C
select. %c
1
2
3
4
155
160
165
170
29.6
33.0
34.4
41.0
55.5
71.0
62.9
59.8
10.5
12.8
8.2
a
Experimental conditions: Ru3(CO)12 ) 0.01 mmol, Ph-BIAN
) 0.0375 mmol, ArNO2 ) 1.0 mmol, T ) 160 °C, PCO ) 40 bar, t
) 6 h (unoptimized conditions). The purified olefin was used as
solvent (10 mL). b Calculated with respect to the initial nitroarene.
c Calculated with respect to the converted nitroarene.
17.6
a
Experimental conditions: Ru3(CO)12 ) 0.01 mmol, Ph-BIAN
) 0.0375 mmol, ArNO2 ) 1.0 mmol, PCO ) 40 bar, t ) 1.5 h, in
b
purified cyclohexene (9 mL) + toluene (1 mL). Calculated with
respect to the initial nitroarene. c Calculated with respect to the
converted nitroarene.
dihydrophenanthrene), analogous to the BIAN ligands
mostly employed in this study, was also tested under
the conditions of entry 2 in Table 2. A higher conversion
(45.2%) was obtained with respect to the use of Ph-
BIAN, but with a lower selectivity (48.8% in allylamine
and 28.3% in 3,4-dichloroaniline); thus its use was not
investigated further.
Ta ble 4. Effect of P r essu r e on th e Syn th esis of 1a
fr om P u r ified Cycloh exen e a n d 3,4-Cl2C6H3NO2,
Ca ta lyzed by Ru 3(CO)12 a n d P h -BIANa
nitroarene
conv. %b
allylamine
select. %c
aniline
run
PCO/bar
select. %c
After all of the catalytic reactions, the only products
that could be observed by CG and GC-MS were the
allylamine and the aniline. Only during some of the
optimization experiments, was a very small peak ob-
served in the gaschromatogram, which showed in the
mass spectrum a parent peak at the same mass as the
allylamine, but with a different fragmentation pathway.
This peak (which typically corresponds to 2-3% that of
the allylamine) can be attributed to an isomer of the
allylamine, but the available data are not sufficient to
indicate if this is the vinyl or the omoallylic isomer and
the very small amount of this substance prevented
isolation and full characterization. This compound is
likely formed by an isomerization of the initially formed
allylamine, as the present catalytic system has been
shown to be able to isomerize olefins easily (see later).
It should be noted that we cannot completely exclude
that this byproduct is the aziridine formally derived
from cyclohexene and a 3,4-dichlorophenylnitrene, which
would show the same parent peak in the mass spectrum
as for the allylamine, although we have obtained no
evidence for the formation of such products in our
reactions. Any other nitroarene-derived byproduct ap-
pears to be polymeric and was not investigated. A very
small amount of a product showing in the GC-MS
spectrum a peak with a mass corresponding to a dimer
of cyclohexene was also observed in some cases.
The reaction is not limited to cyclohexene as sub-
strate, and cyclopentene, cyclooctene, and R-methylsty-
rene also afford moderate to good yields of the desired
adduct (Table 5). However, 1-hexene gave only poor
yields of a mixture of isomeric adducts, accompanied by
isomerization of the unreacted olefin to a mixture of 1-,
2-, and 3-hexene, and allyl alcohol reacted as an alcohol,
to afford the carbamate 3,4-Cl2C6H3NHCOOCH2CHd
CH2, as it is common in this kind of system.
The rate of the isomerization reaction of the starting
olefin is much higher than that of the amination
reaction, and this fact prevented us from assessing the
regiochemistry of the amination reaction in more detail.
Kin etic Stu d ies. The results above-reported for the
Ru3(CO)12/Ar-BIAN catalytic system suggest that the
reaction rate depends on the nitroarene concentration.
The reaction conducted on 3,4-Cl2C6H3NO2 and cyclo-
hexene under the usual catalytic conditions was also
followed by using a high-pressure IR cell. Plotting the
1
2
3
4
20
30
40
50
31.7
30.3
31.3
34.2
65.2
78.4
78.9
68.8
18.3
16.0
18.0
12.7
a
Experimental conditions: Ru3(CO)12 ) 0.03 mmol, Ph-BIAN
) 0.1125 mmol, ArNO2 ) 3.0 mmol, T ) 160 °C, t ) 1.5 h, in
b
purified cyclohexene (9 mL) + toluene (1 mL). Calculated with
respect to the initial nitroarene. c Calculated with respect to the
converted nitroarene.
the case of Ph-BIAN, an increase of the ligand/Ru molar
ratio from 1 to 3 leads to only very small variations in
the nitroarene conversion, with differences close to the
experimental error. However, the selectivity in allyl-
amine decreases when the amount of ligand is in-
creased. In the case of Tol-BIAN, an analogous decrease
in selectivity is observed in the same series, but this
time the conversion regularly increases with an increase
in the ligand amount, indicating that even a very small
variation in the ligand structure can markedly alter the
reaction. The reactions conducted with Ph-BIAN gave
better selectivities, but lower conversions with respect
to reactions conducted with Tol-BIAN at the same
ligand/Ru ratio. The reason for this behavior has been
investigated and will be discussed later in this paper.
An increase in the reaction temperature from 150 to
170 °C led to a regular increase in the conversion, but
the selectivity was highest at 160 °C (Table 3). A
variation in the CO pressure in the range 20-50 bar
had a negligible effect on conversion and a moderate
effect on selectivity (Table 4). A pressure between 30
and 40 bar gives the best results. Note that the
selectivities reported in Tables 2-4 are generally infe-
rior to the highest selectivity (81.9%) obtained in neat
cyclohexene and at a 50:1 catalytic ratio for 6 h, but a
higher catalytic ratio and a shorter reaction time were
necessary to better discriminate the effect of the differ-
ent variables.
At least part of the decrease in selectivity at higher
catalytic ratios is due to the accumulation of the
byproduct aniline. Indeed, by adding a molar amount
of 3,4-dichloroaniline equal to that of nitroarene to a
reaction run under the conditions of entry 5 in Table 1
but for 2 h (using dry cyclohexene), the conversion and
selectivity dropped from 95.5% to 64.6% and from 76.8%
to 51.0%, respectively.
Another ligand, Ph-BIP (9,10-bis(phenylimino)-9,10-

932 Organometallics, Vol. 18, No. 5, 1999
Ragaini et al.
F igu r e 2. 3,4-Cl2C6H3NO2 conversion percent as a func-
tion of the volume percent of cyclohexene in the solvent
mixture, the remaining being toluene. Experimental condi-
tions: 3,4-Cl2C6H3NO2 ) 1 mmol, Ru3(CO)12 ) 0.01 mmol,
Tol-BIAN ) 0.045 mmol, T ) 160 °C, PCO ) 40 bar, for 1
h, in cyclohexene/toluene (total volume 10 mL).
F igu r e 4. Selectivity in allylamine 1a as a function of the
volume percent of cyclohexene in the solvent for the
reactions described in Figure 2.
alkyl diazabutadiene derivative, iPrNdC(Me)-C-
(Me)dNiPr (iPr-DAB), to give a mononuclear complex
(eq 2):28
Ru3(CO)12 + 3 iPr-DAB n-hexane, reflux8
N2
3 Ru(CO)3(iPr-DAB) + 3 CO (2)
When an analogous reaction was performed in Deca-
line or toluene at 110 °C, using 2,6-iPr2C6H3-BIAN
ligand instead of R-DAB and in a 3:1 molar ratio with
respect to Ru3(CO)12, the analogous complex Ru(CO)3-
(2,6-iPr2C6H3-BIAN) (2a ) could be isolated in analyti-
cally pure form and was characterized by spectroscopic
means. In particular, the IR spectrum of 2a (in Decaline)
showed three bands in the carbonyl region at 2044 (s),
1978 (m), and 1972 (m) cm-1, to be compared with the
ones at 2040 (s) and 1967 (s) reported for Ru(CO)3(iPr-
DAB) in n-hexane.28 The splitting of the lower frequency
band in the carbonyl region of 2a is clearly due to the
more rigid structure of Ar-BIAN with respect to iPr-
DAB. The use of 2,6-iPr2C6H3-BIAN as a model ligand
is justified by the fact that it could also be employed in
catalytic reactions, although both conversion and selec-
tivity were lower than those obtained with Ph-BIAN or
Tol-BIAN. In the case of Ph-BIAN and Tol-BIAN, the
same kind of complex was clearly formed (2b and 2c,
F igu r e 3. Plot of the function ln([ArNO2]0/[ArNO2]f) as a
function of the volume percent of cyclohexene in the solvent
for the reaction described in Figure 2. [ArNO2]0 ) concen-
tration of 3,4-Cl2C6H3NO2 at the beginning of the reaction;
[ArNO2]f ) concentration of 3,4-Cl2C6H3NO2 at the end of
the reaction.
ln(absorbance) for the νas NO2 at 1540 cm-1 versus time
gave a straight line (R2 ) 0.996), clearly indicating a
first-order dependence of the reaction rate on the
nitroarene concentration.
The rate was also found to be a function of the olefin
concentration. Use of mixtures of cyclohexene and
toluene (both purified over sodium) as solvents led to
the observation that the reaction rate linearly increases
as the olefin concentration is increased from 5% of the
total volume to 75%, but then decreases when only the
olefin is used as solvent, indicating a positive effect of
the presence of a small amount of toluene, which will
be discussed in more detail later in this paper. The data
collected (see Figures 2 and 3) show that the rate follows
the equation -d[3,4-Cl2C6H3NO2]/dt )[3,4-Cl2C6H3NO2]-
(k[cyclohexene] + c), with k ) 0.186 L h-1 mol-1, c )
0.331 L h-1, and R2 ) 0.9994 (at 160 °C and under 40
bar CO). This equation indicates the rate is also first
order in olefin, but the nonzero intercept in Figure 3
indicates that there is a contribution from an olefin-
independent reaction (see also later).
1
respectively), on the basis of the IR and H NMR data,
but the complexes could not be isolated in an analyti-
cally pure form due to their very high reactivity and
solubility. For these last two ligands, the reaction is
much faster and is complete in a few minutes in
refluxing n-hexane or in toluene at 60 °C, but a 6:1 ratio
BIAN/Ru3(CO)12 had to be used (analogously to what
was reported for the iPr-DAB reaction) in order to avoid
formation of polynuclear complexes. Apparently, the
larger steric hindrance of 2,6-iPr2C6H3-BIAN completely
inhibits the dimerization reactions and even the sensi-
tivity to dioxygen of the product is somewhat reduced.
Interestingly, we found that the reaction between Ru3-
(28) Kraakman, M. J . A.; Vrieze, K.; Kooijman, H.; Spek, A. L.
Organometallics 1992, 11, 3760.
(29) Solutions of 2b and 2c are not stable, and upon long standing
at room temperature under dinitrogen, a yellow precipitate is formed,
showing in the IR spectrum (in toluene) two main bands at 2036 and
1974 (for 2c) cm-1. In the FAB+ mass spectrum of this material, a
peak was observed attributable to a complex with the stoichiometry
Ru2(CO)4(Tol-BIAN)2, but the elemental analysis was not consistent
with this attribution and, moreover, was not constant from one
preparation to another. Thus this material appears to be a mixture
and was not investigated further. Several different di- and trinuclear
ruthenium carbonyl complexes containing the iPr-DAB ligand have
already been characterized.30
The selectivity in allylamine is also a function of the
olefin concentration, but there is no linear relationship
between the two (Figure 4).
F or m a tion of Or ga n om eta llic In ter m ed ia tes. To
gain more information on the identity of the catalytically
active species, we have investigated the reactivity of
Ru3(CO)12 with several BIAN ligands. It is known that
Ru3(CO)12 reacts in refluxing n-hexane with a nonrigid

Allylic Amination of Unactivated Olefins
Organometallics, Vol. 18, No. 5, 1999 933
Sch em e 1
cyclohexene under catalytic conditions (160 °C, 40 bar
CO), only the aniline 4-Cl,2-CF3C6H3NH2 was obtained
as a product, despite the fact that the corresponding
allylamine was clearly observed as the dominant prod-
uct when a normal catalytic reaction was run employing
4-Cl,2-CF3C6H3NO2 as the aminating agent. This fact
is consistent with the data on the selectivity upon
varying the olefin concentration, which will be discussed
later.
Id en tifica tion of th e Or ga n ic In ter m ed ia tes.
Metal-catalyzed nitroarene carbonylation in the pres-
ence of alcohols is known to produce carbamates.32
Anilines have been shown to be intermediates in these
reactions in several cases,33-36 most notably when the
reaction was catalyzed by Ru(CO)3(DPPE) or Ru3-
(CO)12.33,36 To ascertain if the aniline is only a byproduct
or an intermediate of the reaction reported here, one
experiment was carried out by using 3,4-Cl2C6H3NO2
as substrate, but also adding unsubstituted aniline to
the reaction mixture. Only the adduct containing the
substituted aryl ring and no adduct derived from aniline
was detected among the products. Thus aniline is clearly
not an intermediate in the reaction leading to the
allylamine, although the aforementioned lower selectiv-
ity when the aniline is also added indicates that it may
be an intermediate in the synthesis of one or more of
the polymeric byproducts.
Other possible organic intermediates are nitrosoare-
nes. Allylic amination of olefins by hydroxylamines
catalyzed by molybdenum complexes10 and by iron
phthalocyanine complexes12 has been found to proceed
through the formation of free nitrosoarene, which then
reacts with the olefin in an “off metal” reaction called
“ene reaction”37,38 to afford a hydroxylamine. This is in
turn reduced by the metal complex to the allylic amine.
However, in the case of the iron salts-catalyzed reaction,
an active role of free nitrosoarenes was excluded.14 As
a test for the involvement of free nitrosoarenes in
reactions of this kind, the authors of these works have
performed their catalytic reactions in the presence of a
diene as the olefin. Indeed dienes react with free
nitrosoarenes to yield the hetero Diels-Alder adduct (eq
3)37,39 instead of the hydroxylamine, and the absence of
this product is strong evidence against the formation
of the free nitrosoarene.
(CO)12 and all BIAN ligands is inhibited by just one
atmosphere of CO, and even the easy synthesis of 2b
and 2c is not complete after several hours in refluxing
n-hexane in its presence. As later discussed in more
detail, this fact is relevant to the formation of the
catalytically active species under catalytic conditions,
where a much higher CO pressure is applied.29
Complexes 2 react instantaneously with nitroarenes
at room temperature. The reaction is fast even with a
deactivated nitroarene such as 3,4-(MeO)2C6H3NO2,
contrary to what has been reported for Ru(CO)3-
(DPPE),31 indicating that the BIAN-containing com-
plexes are much more reactive than the diphosphine-
containing one. In the cases of 2b and 2c, complete
decomposition of the starting material, accompanied by
the disappearance of any IR absorption band in the
region of the carbonyl ligands, was always observed
under any condition. However, in the case of the more
hindered 2a , an isolable complex (3) could be obtained
when working with 4-Cl,2-CF3C6H3NO2. This last ni-
troarene has been previously used by Skoog and Glad-
felter in a reaction with Ru(CO)3(DPPE) and allowed
for the isolation of an otherwise unstable nitrosoarene
complex.31 The formation of a complex 4, which appears
to be analogous to 3 on the basis of the similarity in
the IR spectrum, was also observed when 2a was
reacted with 3,4-Cl2C6H3NO2, but this complex decom-
posed in solution and could not be isolated.
The mass spectrum and elemental analysis of complex
3 indicates it is the nitrosoarene complex Ru(CO)2(2,6-
iPr2C6H3-BIAN)(η2-ONC6H3-4-Cl,2-CF3). This complex
showed in its IR spectrum two bands at 2012 and 1946
cm-1 (in toluene), indicating cis coordination of the two
1
CO groups. In the H NMR spectrum, four signals for
the isopropyl C-H were observed, indicating complete
inequivalence of the isopropyl groups. In the 19F NMR
of 3, only one signal was observed for the CF3 group of
the nitrosoarene, indicating that only one of the two
possible isomers, the nitroso oxygen trans to CO or to a
BIAN nitrogen, has been formed. Based on the similar-
ity of our compound to the analogous DPPE complex
for which the X-ray structure has been reported,31 we
propose structure 3A for the present complex, although
structure 3B is also consistent with the available data
and cannot be completely excluded (Scheme 1).
No allylic amine was formed during reaction 3, even
when the nitrosobenzene was added (by means of an
high-pressure reservoir) to a solution of the olefin
preheated to 160 °C and under 40 bar CO, but in the
absence of the metal.
Complex 3 did not react with cyclohexene at temper-
atures up to 50 °C. When it was reacted in neat
(32) Cenini, S.; Ragaini, F. Catalytic Reductive Carbonylation of
Organic Nitro Compounds; Kluwer Academic Publishers: Dordrecht,
1997; Chapter 3, and references therein.
(33) Gargulak, J . D.; Berry, A..J .; Noirot, M. D.; Gladfelter, W. L.
J . Am. Chem. Soc. 1992, 114, 8933.
(34) Ragaini, F.; Cenini, S.; Demartin, F. Organometallics 1994, 13,
1178.
(35) Ragaini, F.; Cenini, S. J . Mol. Catal. (A) 1996, 109, 1.
(36) Ragaini, F.; Ghitti, A.; Cenini, S. Submitted.
(30) (a) Mul, W. P.; Elsevier: C. J .; Fru¨hauf, H.-W.; Vrieze, K., Pein,
I.; Zoutberg, M. C.; Stam, C. H. Inorg. Chem. 1990, 29, 2336. (b) Polm,
L. H.; Elsevier: C. J .; van Koten, G.; Ernsting, J . M.; Stufkens, D. J .;
Vrieze, K.; Andre´a, R. R.; Stam, C. H. Organometallics 1987, 6, 1096.
(31) (a) Skoog, S. J .; Gladfelter, W. L. J . Am. Chem. Soc. 1997, 119,
11049. (b) Skoog, S. J .; Campbell, J . P.; Gladfelter, W. L. Organome-
tallics 1994, 13, 4137.

934 Organometallics, Vol. 18, No. 5, 1999
Ragaini et al.
Experiments conducted in other groups generally
gave either only the hetero Diels-Alder adduct or only
the allylic amine, thus allowing for a clear differentia-
tion. However, in our case, reaction of nitrobenzene with
2,3-dimethylbutadiene under typical catalytic conditions
gave a mixture of the hetero Diels-Alder adduct 5 and
allylamine 6 in an approximately 3:1 molar ratio (by
GC) (eq 4), together with small amounts of aniline.
The formation of the pyrrole from the hetero Diels-
Alder adduct is not completely unprecedented, and the
same reaction has been reported to be catalyzed by [Rh-
(COD)Cl]2 under CO pressure, although use of Co2(CO)8
afforded a CO inserted product.40,41 Thus it is clear that
6 must derive from an independent pathway.
Although we have not investigated this reaction in
more detail up to now, it is worth noting that by
conducting reaction 3 for a prolonged time, good yields
of the pyrrole may be obtained directly from the ni-
troarene and the diolefin, thus representing a new
versatile synthesis of N-arylpyrroles.
High -P r essu r e IR Stu d ies. To get more information
on the real catalytic system, a series of high-pressure
IR spectra were recorded. The cluster Ru3(CO)12 is
known to be in equilibrium under CO pressure and in
inert solvents with Ru(CO)5, and under conditions
similar to ours, the equilibrium is almost completely
shifted on the side of the mononuclear complex.42 In our
experiments we found the following.
(a) In the absence of Ar-BIAN, Ru3(CO)12 very slowly
converts into Ru(CO)5 up to an equilibrium position
shifted on the side of this last product (at 160 °C and
45-50 bar CO) both in n-hexane and cyclohexene. Even
in this second case, no bands in the carbonyl region were
observed apart from those attributable to the two
aforementioned compounds. In particular no bands were
observed that may be attributable to Ru(CO)4-
(cyclohexene). This last compound has never been
reported in the literature, but the analogous complexes
with other olefins43 are known and their IR bands
should fall close to the ones expected for Ru(CO)4-
(cyclohexene), in a region that is at least in part free
from the absorptions of both Ru3(CO)12 and Ru(CO)5.44
(b) In n-hexane, Ru3(CO)12 reacts with Ar-BIAN to
give, as the only primary product, Ru(CO)3(Ar-BIAN).
This last complex, in turn, partly transforms on a longer
time scale into Ru(CO)5, until an equilibrium is reached.
It is interesting to note that the equilibrium between
Ru(CO)3(Ar-BIAN) and Ru(CO)5 is more shifted on the
side of the Ar-BIAN complex for Ar ) Ph than for Ar )
Tol under all conditions. In particular, at a 2:1 Ar-BIAN/
Ru ratio (at 160 °C and 45 bar CO), the equilibrium is
almost completely shifted on the side of the Ar-BIAN
complex in the case Ar ) Ph, but appreciable amounts
of Ru(CO)5 are still present for Ar ) Tol (Figure 5).
The 5/6 ratio was insensitive to the olefin amount (0.5,
1, or 2 mL, the complement to 10 mL being toluene),
indicating that the competition between the two pro-
cesses is not influenced by the olefin concentration. On
the other hand, the reaction rate increased along the
series (nitrobenzene conversion 42, 60, and 65%), analo-
gously to what is observed in the case of cyclohexene
(vide supra), indicating that the two processes leading
to 5 and 6 share a common rate-determining step. If
3,4-dichloronitrobenzene was used in place of nitroben-
zene, the corresponding two products were obtained,
although in this case the products were not isolated and
characterization is only based on the GC-MS analysis
and the analogy with the previous reactions. When this
last reaction was repeated in the presence of unsubsti-
tuted aniline, only the hetero Diels-Alder adduct
derived from the nitroarene was detected, indicating
that the presence of a conjugated diolefin does not allow
for a reaction of the aniline not available in the other
cases. The 5/6 ratio was influenced neither by a lower
reaction temperature (80 °C) nor by a change in the CO
pressure from 20 to 50 bar.
To be sure that 6 does not derive from a following
reaction of 5, the stability of this last product was
investigated. Compound 5 is stable under the reaction
conditions but in the absence of metal, both in toluene
and in cyclohexene. However, in cyclohexene and in the
presence of the catalytic system, partial transformation
to yield the pyrrole was observed upon prolonging the
reaction time, but no allylic amine (derived either from
the diene or from cyclohexene) was observed (eq 5):
(37) Zuman, P.; Shah, B. Chem. Rev. 1994, 94, 1621.
(38) (a) Knight, G. T. J . Chem. Soc., Chem. Commun. 1970, 1016.
(b) Banks, R. E.; Haszeldine, R. N.; Miller, P. J . Tetrahedron Lett. 1970,
4417. (c) D. Mulvey, W. A. Waters J . Chem. Soc., Perkin. Trans. 2 1978,
1959.
(39) Boger, D. L.; Weinreb, S. N. Hetero Diels-Alder Methodology
in Organic Synthesis; Academic Press: New York, 1987.
(40) (a) Okuro, K.; Dang, T. D.; Khumtaveeporn, K.; Alper, H.
Tetrahedron Lett. 1996, 37, 2713. (b) The formation of the pyrrole is
probably a more general phenomenon at even higher temperature, even
in the absence of the metal, as some 7 is always formed during the
gas chromatographic analysis of 5 and, in the EI mass spectrum of 5,
the peak at highest mass observable corresponds to 7.
(41) (a) Analogous reactions have been reported even for more
complex systems.41b (b) Streith, J .; Defoin, A. Synlett 1996, 189.
(42) (a) Bor, G. Pure Appl. Chem. 1986, 58, 543. (b) Koelliker, R.;
Bor, G. J . Organomet. Chem. 1991, 417, 439.
(43) (a) Leadbeater, N. E. J . Chem. Soc., Dalton Trans. 1995, 2923.
(b) Grevels, F.-W.; Reuvers, J . G. A.; Takats, J . J . Am. Chem. Soc. 1981,
103, 4069.
(44) In our first communication on this subject,21 we said that a
strong band at 1992 cm-1 was observed in cyclohexene. However, this
band was later shown to be the result of the use of commercial
cyclohexene in that experiment. When purified cyclohexene was
employed (as in all spectra reported in this paper) this band was no
longer observed.

Allylic Amination of Unactivated Olefins
Organometallics, Vol. 18, No. 5, 1999 935
F igu r e 6. High-pressure IR spectrum of the solution
during a catalytic reaction in cyclohexene 20 min after
reaching the final temperature. Molar ratio Ph-BIAN/Ru
) 2, at 160 °C and PCO ) 45 bar. × ) Ru(CO)3(Ar-BIAN).
F igu r e 5. High-pressure IR spectra of solutions of Ru3-
(CO)12 and Ar-BIAN in n-hexane (molar ratio Ar-BIAN/
Ru ) 2) after 1 h 30 min at 160 °C and PCO ) 45 bar. (a)
Ar ) Ph, (b) Ar ) Tol, × ) Ru(CO)3(Ar-BIAN), + ) Ru-
(CO)5.
(c) In cyclohexene and in the presence of Ar-BIAN,
the same species are observed as in n-hexane. The
equilibrium is still almost completely shifted on the side
of Ru(CO)3(Ar-BIAN) in the case of Ar ) Ph (under the
same conditions of the spectra in Figure 5, except for
the solvent), but it is now markedly shifted on the side
of Ru(CO)5 for Ar ) Tol.
(d) In an attempt to observe a complex containing a
coordinated olefin, we examined a reaction between Ru3-
(CO)12 and Ph-BIAN in the presence of 2,3-dimethylb-
utadiene (and n-hexane as a cosolvent), in the hope that
the higher coordinating power of the diolefin allowed
for the observation of a product of substitution of CO.
The reaction initially proceeded in the usual way,
generating Ru(CO)3(Ph-BIAN). Only at 160 °C is a
following reactions observed, which is not complete even
after several hours at this temperature. However,
spectra subtraction clearly evidenced the disappearance
of the bands of Ru(CO)3(Ph-BIAN) and the appearance
of three new bands, which grow at the same time at
2062, 1999, and 1987 cm-1. These bands are inconsis-
tent with the formation of a complex in which one or
two COs have been substituted by the olefin, but are
identical with those reported in the literature for Ru-
(CO)3(η4-2,3-dimethylbutadiene).45 Thus it is clear that,
on a longer time scale, Ar-BIAN can be substituted by
a diolefin.
(e) During a typical catalytic reaction, conducted with
a 2:1 Ph-BIAN/Ru ratio, the species largely predominant
at 160 °C is Ru(CO)3(Ph-BIAN) (Figure 6).
(f) The reaction between Ru3(CO)12 and Ar-BIAN to
yield Ru(CO)3(Ar-BIAN) is not fast under CO pressure
both in n-hexane and in cyclohexene even at high
temperature, in accord with the inhibiting effect of just
one atmosphere of CO noted previously. However, the
addition of toluene (10 vol %) to cyclohexene notably
F igu r e 7. High-pressure IR spectra of solutions of Ru3-
(CO)12 and Tol-BIAN (molar ratio Tol-BIAN/Ru ) 2) after
5 min at 120 °C and PCO ) 43 bar: (a) in neat cyclohexene,
(b) in cyclohexene + toluene 9:1, × ) Ru(CO)3(Ar-BIAN),
O ) Ru3(CO)12.
increases its rate, as evidenced by the comparison of
spectra run after the same time in parallel reactions
(Figure 7).
The effect is only a kinetic and not a thermodynamic
one. Indeed, once equilibrium is reached, the amount
of Ru(CO)3(Tol-BIAN) with respect to Ru(CO)5 and Ru3-
(CO)12 is essentially the same both in neat cyclohexene
and in cyclohexene/toluene.
Discu ssion
In this paper we have reported a new reaction
affording allylic amines from nitroarenes and unacti-
(45) Gambino, O.; Valle, M.; Aime, S.; Vaglio, G. A. Inorg. Chim.
Acta 1974, 8, 71.

936 Organometallics, Vol. 18, No. 5, 1999
Ragaini et al.
vated olefins. Although the range of substrates screened
is still limited, the very large number of nitroarenes and
olefins commercially available at a low price renders this
methodology appealing. The optimization study, which
was performed by using cyclohexene and 3,4-dichloro-
nitrobenzene as substrates, has given the somewhat
unexpected result that the conditions we had initially
selected based on our experience in other carbonylation
reactions of nitroarenes were indeed very close to the
optimal ones. Despite the fact that this result did not
allow us to further increase the selectivity of the
reaction with respect to the early results, a large
amount of data has been collected that allow us now to
trace a clearer picture of the reaction mechanism. As
the synthetic aspects of the reaction do not need to be
analyzed in any more detail, the present discussion will
mostly focus on the mechanistic aspects of the reaction.
The cluster Ru3(CO)12 was already known to react
with diazabutadiene to afford mononuclear complexes
(eq 2), and all Ar-BIAN ligands behave in this same
way. No cluster species containing the Ar-BIAN ligand
was obtained or observed by high-pressure IR under
conditions similar to the ones used in catalysis. The use
of high-pressure IR spectroscopy also allowed us to
understand the different effect of changing the ligand
concentration for Ph-BIAN and Tol-BIAN. As it is
evident from the results reported in Table 2, in the case
of Ph-BIAN, an increase in the ligand/Ru molar ratio
from 1 to 3 leads to only very small variations in the
nitroarene conversion, whereas in the case of Tol-BIAN,
the conversion regularly increased with an increase in
the ligand amount. What we found is that under CO
pressure an equilibrium is set between Ru(CO)3(Ar-
BIAN) and Ru(CO)5 (eq 6), and this equilibrium is more
shifted on the side of the Ar-BIAN complex for Ar ) Ph
than for Ar ) Tol.
a palladium(0) complex more strongly than those bear-
ing electron-releasing groups.
It should be noted that this effect of the ligand
concentrations on the rate of the catalytic reactions
clearly indicates that the active species must contain a
coordinated Ar-BIAN, and the effect of the ligand is not
just to accelerate the breaking of the cluster to ulti-
mately afford Ru(CO)5.48 Why an increase in the ligand
amount lowers selectivity is not clear at this stage.
However, it can be excluded that this effect is due to
the formation of more substituted species such as Ru-
(CO)(Ar-BIAN)2, as their formation should considerably
alter the kinetics of the reaction, and moreover no
spectroscopic evidence for the formation of any such
species has been obtained under any conditions.
The formation of Ru(CO)3(Ar-BIAN) as the only
primary product of the reaction between Ru3(CO)12 and
Ar-BIAN and its only subsequent equilibration with Ru-
(CO)5 is worth more comment. Chelating ligands have
long been known to induce fragmentation of Ru3(CO)12
to mononuclear species containing the ligand,49 but, to
the best of our knowledge, this is the first time that this
process is shown to be kinetically controlled and not
thermodynamically driven. In other words, at least in
this case, formation of the substituted mononuclear
compound does not proceed because this product is more
stable than both Ru3(CO)12 and Ru(CO)5, but simply
because the reaction of a basic ligand with the cluster
is faster than that of CO. Once formed, the Ru(CO)3-
(L-L) complex may even be unstable with respect to
the conversion to Ru(CO)5. This has implications even
for other catalytic carbonylation systems in which a
complex of the type Ru(CO)3(L-L) is the active species.
Indeed, there are surely experimental conditions under
which the catalytic system will deactivate with time not
because of the formation of aggregated species, as it is
most often proposed in these cases, but because of the
conversion of the active species into Ru(CO)5. Retro-
spectively, this was surely the case in some of the
reactions reported in this paper. A reinvestigation of
several ruthenium-based carbonylation catalytic sys-
tems with an eye to this problem would probably lead
to an improvement of the catalysts’ performances.
Ru(CO)3(Ph-BIAN) + 2 CO h Ru(CO)5 + Ar-BIAN
(6)
Thus it appears that a 1.25:1 ratio Ph-BIAN/Ru
(under the concentration, temperature, and pressure
conditions employed) is sufficient to keep almost all the
ruthenium in the form of Ru(CO)3(Ph-BIAN), and any
further increase in the ligand amount is not influential
with respect to the equilibrium in eq 6. On the other
hand, a complete shift to the left of the same equilibrium
is not reached for Ar ) Tol even for a 3:1 Tol-BIAN/Ru
ratio under the same conditions, thus explaining the
continuous rate increase with the increase in Tol-BIAN
amount. The weaker coordinating ability of Tol-BIAN
with respect to Ph-BIAN toward Ru(CO)3 is not com-
pletely unexpected, given the thermodynamic preference
of this fragment for CO and its low oxidation state.
Indeed the Tol-BIAN ligand is more electron-donating
than Ph-BIAN, as also evidenced by the position of the
IR bands in the Ru(CO)3(Ar-BIAN) complexes and by
the position of the NMR signals and the oxidation
potentials of the complexes PdCl2(Ar-BIAN).46 Very
recently, it was shown47 that arylphosphines bearing
electron-withdrawing groups on the aryl rings bind to
The first-order dependence of the reaction rate upon
the nitroarene concentration indicates that the initial
activation of the nitroarene is the rate-determining step
of the catalytic cycle, and the fact that the only substrate
for which a complete conversion was not achieved is the
one with a para-methoxy group, that is the one with
the most electron-releasing group among those tested,
suggests that, analogously to all other investigated
Ru,31,50 Rh,34 Fe,51 and Ni52 systems, this activation is
an electron transfer from the complex to the nitroarene.
(48) We have recently shown36 that in the Ru3(CO)12/[Et4N][Cl]
catalytic system for the carbonylation of nitroarenes to carbamates
one role of chloride is just to accelerate the conversion of Ru3(CO)12
into the catalytically active Ru(CO)5 and the halide does not bind to
any intermediate in the effective catalytic cycle.
(49) Sanchez-Delgado, R. A.; Bradley, J . S.; Wilkinson, G. J . Chem.
Soc., Dalton Trans. 1974, 399.
(50) (a) Sherlock, S. J .; Boyd, D. C.; Moasser, B.; Gladfelter, W. L.
Inorg. Chem. 1991, 30, 3626. (b) Kunin, A. G.; Noirot, M. D.; Gladfelter,
W. L. J . Am. Chem. Soc. 1989, 111, 2739.
(46) van Asselt, R.; Elsevier: C. J .; C. J . Amatore, C. J .; J utand, A.
Organometallics 1997, 16, 317.
(47) Amatore, C.; J utand, A.; Meyer, G. Inorg. Chim. Acta 1998, 273,
76.
(51) (a) Ragaini, F.; Song, J .-S.; Ramage, D. L.; Geoffroy, G. L.;
Rheingold, A. L. Organometallics 1995, 14, 387. (b) Belousov, Yu. A.;
Kolosova, T. A. Polyhedron 1987, 6, 1959.
(52) Berman, R. S.; Kochi, J . K. Inorg. Chem. 1980, 19, 248.

Allylic Amination of Unactivated Olefins
Organometallics, Vol. 18, No. 5, 1999 937
Sch em e 2
data. Moreover, the fact that the equilibrium in Scheme
2 should be almost completely shifted to the left is also
in agreement with the IR spectra recorded under
pressure, in which no cyclohexene complex could be
detected. Despite intense effort, we have not yet suc-
ceeded in isolating or univocally characterizing an olefin
complex of the type Ru(CO)2(olefin)(Ar-BIAN).53 How-
ever, the related complex Ru(CO)2(iPr-DAB)(η2-dimeth-
ylfumarate) is known,54 and related iron complexes have
also been reported.55
When a diene was employed as the olefin, a very slow
conversion of the initially formed Ru(CO)3(Ph-BIAN) to
Ru(CO)3(η4-2,3-dimethylbutadiene) was observed. This
conversion is much slower than the actual catalytic
reactions, and the diene complex is unlikely to play any
relevant role in it. Moreover, at least in the case of
monoolefins, a large amount of evidence indicates that
the Ar-BIAN ligand is bound to the metal during the
reaction. However, the fact that such a displacement is
observed suggests that even with monoolefins the active
species may be of the kind Ru(CO)3(olefin)(η1-Ar-BIAN)
rather than Ru(CO)2(olefin)(η2-Ar-BIAN), as previously
suggested. A palladium complex having a p-MeOC6H4-
BIAN ligand coordinated in a monodentate fashion has
been structurally characterized.56 The data available at
the moment do not allow distinguishing between these
two possibilities. In the following we will continue to
refer to the active species as having a chelating Ar-BIAN
ligand, but the aforementioned ambiguity must be
always kept in consideration.
As evident from the data in Figures 2 and 3, the rate
of the catalytic reactions is first order in olefin concen-
tration at least up to a 75% fraction of cyclohexene in
toluene, but the rate decreases if the neat olefin is used
as solvent. The same effect has been observed in other
series of reactions (not reported) and is thus a general
phenomenon, at least with cyclohexene. This accelerat-
ing effect of a small amount of toluene and its leveling
off at higher concentrations has intrigued us for some
time. Toluene had been selected as a diluting solvent
for cyclohexene based on the similarity in polarity
between the two. Toluene has a lower dipole moment
with respect to that of cyclohexene (0.36 versus 0.55 D,
in the gas phase),57 but a higher dielectric constant
(2.379 versus 2.220).57 However, it turned out that the
addition of toluene to a cyclohexene solution of Ru3-
(CO)12 and the ligand accelerates the formation of Ru-
(CO)3(Tol-BIAN), a transformation that would otherwise
take a time not negligible with respect to the total
reaction time. It appears that 25% toluene in the solvent
is sufficient to render this induction time short enough
The electron-transfer nature of the rate-determining
step explains why a higher conversion is generally
observed when Tol-BIAN is used in place of Ph-BIAN,
despite the fact that more “active species” should be
present at the equilibrium in the latter case.
The reaction rate has been found to be first order in
olefin concentration, but with an olefin-independent
term. As it is very unlikely that the rate-determining
step is a single act involving a ruthenium complex, the
olefin, and the nitroarene and since the interaction of
the complex with the nitroarene is surely irreversible,
the best explanation for the observed rate is that a fast
preequilibrium exists between Ru(CO)3(Ar-BIAN) and
an olefin-containing complex and the latter reacts with
the nitroarene at a faster rate (Scheme 2).
The direct reaction of Ru(CO)3(Ar-BIAN) with the
nitroarene would account for the olefin-independent
term in the rate. As cyclohexene should be a poorer
electron acceptor with respect to CO, the olefin complex
should be more reactive toward nitroarenes, and the
relatively large difference in reactivity shown by the Tol-
BIAN and Ph-BIAN complexes supports the idea that
even small differences in the donating/accepting power
of the ligands can profoundly alter the rate of this
reaction.
A process such as the one depicted in Scheme 2 should
in general follow a rate equation of the type
-d[ArNO2]/dt ) [ArNO2](k1[Ru(CO)3(Ar-BIAN)] +
k2[Ru(CO)2(olefin)(Ar-BIAN)]) (7)
If we consider a fast preequilibrium with a constant
K (assuming that the amount of free olefin and CO in
solution are not altered by the position of the equilib-
rium), define [Ru-BIANtot] ) [Ru(CO)3(Ar-BIAN)] + [Ru-
(CO)2(olefin)(Ar-BIAN)] and consider its amount con-
stant (that is, we assume that the equilibrium between
Ru(CO)3(Ar-BIAN) and Ru(CO)5 is not significantly
altered by the formation of some olefin complex, which
is acceptable in view of the discussion below), we can
write
[Ru(CO)2(olefin)(Ar-BIAN)] )
(K′ [Ru-BIANtot][olefin])/(1 + K′[olefin]) (8)
(53) By performing the reaction between Ru3(CO)12 and Ph-BIAN
in R-methylstyrene at 160 °C and under 5 bar CO and 10 bar N2, a
complex was obtained showing in the IR spectrum two bands at 2037
and 1973 cm-1, consistent with a species of the aforementioned type.
However, this complex proved to be extremely sensitive, and we could
not fully characterize it. Use of olefins such as dimethylfumarate or
maleic anhydride, successfully employed in the case of reactions of Ru-
(CO)3(iPr-DAB)54 and related iron complexes,55 in stoichiometric
reactions gave complete decomposition of the complex, with loss of all
carbonyl absorptions in the IR spectrum.
(54) van Wijnkoop, M.; de Lange, P. P. M.; Fru¨hauf, H.-W.; Vrieze,
K.; Smeets, W. J . J .; Spek, A. Organometallics 1995, 14, 4781.
(55) Fru¨hauf, H.-W.; Pein, I.; Seils, F. Organometallics 1987, 6, 1613.
(56) Groen, J . H.; Elsevier: C. J .; Vrieze, K.; Smeets, W. J . J .; Spek,
A. L. Organometallics 1996, 15, 3445.
where K′ ) K/[CO]. By substitution of eq 8 in eq 7 a
kinetic low is obtained that is not in general first order
in olefin concentration. However, in case the equilibrium
in Scheme 2 were almost completely shifted to the left
(K′ , 1), then [Ru(CO)3(Ar-BIAN)] = [Ru-BIANtot] and
eq 7 reduces to
-d[ArNO2]/dt ) [ArNO2](k1 +
k2K′[olefin])[Ru-BIANtot] (9)
(57) Handbook of Chemistry and Physics, 48th ed.; Weast, R. C.,
Ed.; CRC Press: Cleveland, 1967-1968.
which is in perfect agreement with the observed kinetic

938 Organometallics, Vol. 18, No. 5, 1999
Ragaini et al.
aspect, is that the intercept at - 4.5 implies that the
olefin-independent pathway should have a 4.5% selec-
tivity in allylamine. Within the frame of the experimen-
tal errors in the determination of the selectivities (which
are sensitive to the error in the determination of both
the allylamine and the remaining nitroarene amounts),
this number cannot be considered to be precise, but the
true value must however be low (actually, it may even
be lower than 4.5%). This implies that the reaction
starting from Ru(CO)3(Ar-BIAN) in Scheme 2 either
does not produce the allylamine at all or does it with
only very low yields. This is consistent with the failure
to obtain any allylic amine from the reactions of isolated
complex 3, despite the fact that the corresponding allylic
amine had been obtained in normal catalytic reactions.
Thus complex 3 should not be considered as an inter-
mediate in the synthesis of the allylic amines, but only
in the synthesis of the byproducts of the reaction.
Interestingly, this also means that even Ru(CO)3(Ar-
BIAN) complexes are not a part of the catalytic cycle
for the desired product, but only a reservoir for Ru(CO)2-
(olefin)(Ar-BIAN) and a source of byproducts. In this
context, the lower selectivity obtained with Tol-BIAN
with respect to Ph-BIAN can be easily explained as the
stronger electron-donating power of the tolyl ligand
increasing the reactivity of the tricarbonyl complex,
rendering the competition between it and the corre-
sponding olefin complex less selective toward the latter.
As the first act of the reaction is the rate-determining
step, the following steps can only be investigated by
competition experiments. The most important point is
the extent of reduction of the aminating agent at the
stage of the coupling with the olefin. Basically, three
possibilities exist. The aminating reagent may be an
aniline, a nitrosoarene, or an imido (nitrene) fragment.
Moreover, in the case of the nitrosoarene, coupling may
occur either while the nitrosoarene is coordinated to the
metal or while it is free in solution. Precedents exist
for all of these possibilities.58-60
F igu r e 8. Selectivity in allylamine 1a as a function of the
relative contribution of the process starting from the olefin
complex Ru(CO)2(Tol-BIAN)(cyclohexene) with respect to
the total reaction (defined as X ) {ln([ArNO2]0/[ArNO2]f)
- 0.331}/{ln([ArNO2]0/[ArNO2]f)}; for the other amounts see
the caption to Figure 3) for the reactions described in
Figure 2. The straight line passing through the data has
the equation Selectivity ) 76.7X - 4.57(R2 ) 0.977).
that the relative differences in it at higher concentra-
tions become negligible. Although we cannot completely
exclude that other small effects on the rate of the
reaction are operating (for example a small linear
acceleration or retardation of the initial electron transfer
may be obscured by the stronger effect of the olefin
concentration), all these effects should operate in a
proportional way at all concentrations and could not
explain the discontinuity observed in the rate law. The
higher rate of formation of Ru(CO)3(Ar-BIAN) species
in more polar solvents is also evident in the synthesis
of 2a conducted under dinitrogen. In this case, the
reaction was about 5 times slower in Decaline than in
toluene.
As the equilibrium in Scheme 2 is almost completely
shifted to the left, the concentration of Ru(CO)3(Tol-
BIAN) can be considered to be constant at different
olefin concentrations, and thus even the contribution
of the olefin independent term in the rate equation can
be considered as constant. This means that the relative
contribution of the olefin-dependent process (called X)
with respect to the total can be obtained from the
equation
One experiment conducted with 3,4-dichloronitroben-
zene in the presence of unsubstituted aniline afforded
only the allylamine derived from the nitroarene, thus
clearly indicating that the aniline is not involved in the
formation of the allylamine. However, the lower selec-
tivity observed in the presence of added aniline indicates
that this compound must be involved in the synthesis
of some byproduct.
X ) {ln([ArNO2]0/[ArNO2]f) -
0.331}/ln([ArNO2]0/[ArNO2]f) (10)
where [ArNO2]0 and [ArNO2]f are the nitroarene con-
centrations at the beginning and at the end of the
reaction and 0.331 is the intercept in the rate law.
Although the selectivity of the amination reaction and
the percentage of olefin in the solvent are not linearly
correlated, a good linear correlation exists between the
selectivity and the X value calculated in eq 10 (Figure
8).
The linearity of this correlation gives us two impor-
tant pieces of information. The first is that the selectiv-
ity in allylamine for the process starting from the olefin
complex is not (or very little) altered by the olefin
concentration in solution. In other terms, once the olefin
is coordinated to the metal and the resulting complex
reacts with the nitroarene, the remaining olefin plays
no role. This excludes any process in which a reversible
decoordination of the olefin may occur after the reaction
with the nitroarene. The second, and more important
The identification of the role of nitrosoarene inter-
mediates is less straightforward. The formation of both
the allylamine and the hetero Diels-Alder adduct when
the reaction is run in the presence of a diene indicates
that some coupling must occur at the stage of the
nitrosobenzene. Several possibilities are shown in
Schemes 3-5.
The easiest explanation is that an initially formed
nitrosoarene complex dissociates the organic group and
this reacts either with the free diene, to afford the hetero
Diels-Alder adduct, or with an olefin complex molecule,
(58) (a) Meyer, K. E.; Walsh, P. J .; Bergman, R. G. J . Am. Chem.
Soc. 1995, 117, 974. (b) Wigley, D. E. Prog. Inorg. Chem. 1994, 42,
239.
(59) Crotti, C.; Cenini, S.; Bassoli, A.; Rindone, B.; Demartin, F. J .
Mol. Catal. 1991, 70, 175.
(60) (a) Song, J .-S.; Han, S.-H.; Nguyen, S. T.; Geoffroy, G. L.;
Rheingold, A. L. Organometallics 1990, 9, 2386. (b) Pizzotti, M.; Cenini,
S.; Crotti, C.; Demartin, F. J . Organomet. Chem. 1989, 375, 123.

Allylic Amination of Unactivated Olefins
Organometallics, Vol. 18, No. 5, 1999 939
Sch em e 3
Sch em e 5
Sch em e 4
tion. However, it is unlikely that two such different
processes such as dissociation of the nitrosoarene and
its coupling with a coordinated ligands showed the same
dependency on the temperature from 80 to 160 °C, as
experimentally observed. Moreover, the predominance
of the hetero Diels-Alder adduct over the allylamine
would imply that, during reactions involving cyclohex-
ene, where even the “off metal” process should yield the
allylamine, most of the reaction would occur from the
free nitrosoarene. This is difficult to reconcile with the
fact that nitrosoarene complexes such as 3 do not afford
allylamine.
to afford the allylamine. However, this mechanism is
inconsistent with the independence of the 5/6 ratio from
the olefin concentration and (in the case L ) CO) even
with the rate enhancement at higher olefin concentra-
tions.
The process in Scheme 5 is consistent with all the
experimental facts. In it both 5 and 6 derive from the
reactions of a metal-bound nitrosoarene and the reac-
tions pass from a common intermediate. This can then
either reductively eliminate 5 or insert CO in the
metal-oxygen bond (the oxygen atom of the hydroxy-
laminato ligand is formally negatively charged and
should be nucleophilic) with subsequent elimination of
CO2. Rearrangement of the obtained complex would
yield 6. The scheme would be little altered if the olefin
were initially coordinated with both double bonds and/
or the Ar-BIAN were coordinated in a monodentate
fashion. In the case of cyclohexene, the initially formed
Several related mechanisms can be imagined, in
which the hetero Diels-Alder adduct derives from an
“off metal” reaction of a nitrosoarene irreversibly dis-
sociated from the metal, while the allylic amine derives
from a reaction of a coordinated nitrosoarene (Scheme
4). In this last case, coupling with the olefin may precede
or follow deoxygenation by CO. In this last eventuality,
an imido complex would be the real aminating agent.
It should be noted that coupling between a monoolefin
and a nitrosoarene in the coordination sphere of a metal
has several precedents in platinum chemistry.61 An
example has also been reported of a coupling between
a butadiene coordinated to a zirconium or hafnium
complex and tBuNO.62 This scenario cannot be com-
pletely dismissed and, in case L is the butadiene, is also
consistent with the rate dependence, but selectivity
independence, of the reaction on the olefin concentra-
(61) (a) Mansuy, D.; Dreˆme, M.; Chottard, J .-C.; Girault, J .-P.;
Guilhem, J . J . Am. Chem. Soc. 1980, 102, 844. (b) Bellon, P. L.; Cenini,
S.; Demartin, F.; Pizzotti, M.; Porta, F. J . Chem. Soc., Chem. Commun.
1982, 265. (c) Cenini, S.; Porta, F.; Pizzotti, M.; La Monica, G. J . Chem.
Soc., Dalton Trans. 1984, 355. (d) Cenini, S.; Porta, F.; Pizzotti, M.;
Crotti, C. J . Chem. Soc., Dalton Trans. 1985, 163. (e) Pizzotti, M.;
Porta, F.; Cenini, S.; Demartin, F.; Masciocchi, N. J . Organomet. Chem.
1987, 330, 265.
(62) Erker, G.; Humphrey, M. G. J . Organomet. Chem. 1989, 378,
163.

940 Organometallics, Vol. 18, No. 5, 1999
Ragaini et al.
Sch em e 6
are good for several substrates, and the mechanism has
been understood at least in its basic features. At the
moment, the main limit of the system lies in its decrease
in selectivity when higher catalytic ratios are employed,
apparently due to the negative effect of the aniline
byproduct. The catalytic system, on the other hand,
appears to still be active after the end of the reactions
even at the highest catalytic ratio employed. This fact
is very promising and indicates that this reaction may
be rendered more efficient if a way is found to further
decrease the amount of aniline formed or to avoid its
negative interaction with the catalytic system.
If we compare the present catalytic system with the
ones employing phenylhydroxylamine9-14 or an aniline
in the presence of an oxidant,17 we found that they are
partly complementary in their synthetic scope. Our
system works the best with nitroarenes containing an
electron-withdrawing group, but acceptable yields are
obtained even in other cases. The use of hydroxylamines
has been up to now limited to phenylhydroxylamine,
and for the aniline-oxidant system, the only example
we are aware of in which a different aniline was used
involved p-chloroaniline and gave a very low turnover
number (2.4 in 24 h), although the selectivity was high.
More interestingly, our system gives good yields with
respect to the nitroarene, but requires the use of a very
large excess of olefin. On the other hand, systems
employing hydroxylamine generally give good yields
with respect to the olefin, but several byproducts derived
from the aminating agent are observed, so that yields
are usually quoted with respect to the olefin. Thus this
last synthetic procedure may be preferable when the
olefin is a complex molecule and the aminating fragment
is simple, while our reaction may be better when the
reverse is true. A more in-depth comparison will only
be possible when data on more aminating fragments (for
the hydroxylamine reaction) and more olefins (for the
nitroarene reaction) are available.
coupling product would be unlikely to reductively elimi-
nate an azaoxacyclobutane and would evolve toward the
allylamine.
The reaction pathway for cyclohexene, as determined
by the discussed data, is reported in Scheme 6. Note
that in this case the final step may even proceed by a
metal-mediated hydrogen shift, that is, a â-hydrogen
elimination followed by reductive elimination of the
allylamine.
The formation of an intermediate nitrosoarene com-
plex having also coordinated both an olefin and CO may
explain why nitroarenes bearing electron-withdrawing
groups not only give higher rates but also afford higher
selectivities in allylamine. Indeed, in the coupling with
the olefin, the nitrosoarene acts as an electrophile, and
these kinds of couplings are known to be accelerated
by electron-withdrawing groups on the aromatic ring.63
Alternatively the nitrosoarene may attack the coordi-
nated CO, a reaction that has been observed for the
related Ru(CO)2(DPPE)(η2-ArNO) complexes31,64 and is
the only one occurring when no olefin is present. This
reaction will eventually lead to byproducts, but in this
case the nitrosoarene acts a nucleophile and the reaction
is retarded by the same groups on the arene that
accelerate the reactions with olefins.
Not e Ad d ed in P r oof: After acceptance of this
paper, a related article on the allylic amination of olefins
by nitroarenes, catalyzed by iron complexes, has been
published: Srivastava, R. S.; Nicholas, K. M. Chem.
Commun. 1998, 2705.
Exp er im en ta l Section
Gen er a l P r oced u r e. Unless otherwise specified, all reac-
tions and manipulations were performed under a N2 atmo-
sphere using standard Schlenk apparatus, cannula techniques,
and magnetic stirring. Solvents were dried and distilled by
standard procedures and stored under dinitrogen. Olefins were
purified by distillation over sodium and stored under dinitro-
gen in the dark before use. Nitrobenzene was purified by
shaking with 10% H2SO4, washing with water, and drying with
Na2SO4, followed by distillation under dinitrogen and storage
under an inert atmosphere. Other organic reagents were used
Con clu sion s
65
as received. Ru3(CO)12 and Ru(CO)3(DPPE)49 were synthe-
In this paper we have reported a new catalytic system
for the synthesis of allylamines from nitroarenes and
unactivated olefins working under CO pressure and
involving a formal C-H bond activation. Selectivities
sized by methods reported in the literature or slight modifica-
tions thereof. All other compounds, except for those mentioned
below, were commercial products and were used as received.
Gas chromatographic analyses were performed on a Perkin-
Elmer 8420 capillary gas chromatograph equipped with a PS
(63) (a) Hamer, J .; Ahmad, M.; Holliday, R. E. J . Org. Chem. 1963,
28, 3034. (b) Kresze, G.; Firl, J .; Zimmer, H.; Wollnik, U. Tetrahedron
1974, 20, 1605.
(65) Eady, C. R.; J ackson, P. F.; J ohnson, B. F. G.; Lewis, J .;
Malatesta, M. C.; McPartlin, M.; Nelson, W. J . J . Chem. Soc., Dalton
Trans. 1980, 383.
(64) Note 30 in ref 34.

Allylic Amination of Unactivated Olefins
Organometallics, Vol. 18, No. 5, 1999 941
255 column. Ri values (Ri ) response factor, relative to
naphthalene as an internal standard) were determined by the
use of solutions of known concentrations of the compounds.
GC-MS analyses were performed on a Hewlett-Packard 5890
Series II gaschromatograph, equipped with a 5971A mass
selective detector. NMR spectra were recorded on a Bruker
AC 200 FT (200 MHz) or on a Bruker AC 300 FT (300 MHz)
at room temperature. High-pressure IR spectra were recorded
by means of a custom-made high-pressure Hastelloy C reactor
equipped with IRTRAN 1 (MgF2) windows and heating and
stirring facilities, placed inside a FTS-7 Bio Rad FT-IR
spectrometer. Elemental analyses and mass spectra were
recorded in the analytical laboratories of Milan University.
Syn th esis of th e Liga n d s. Ar -BIAN. The intermediate
(Ar-BIAN)ZnCl2 complexes were prepared as reported in the
literature.23,24 Care must be taken to eliminate any residue of
the acetic acid employed as solvent in the synthesis, as this
has a strongly negative effect on the effectiveness of the
separation in the following step. Then 10 mmol of the complex
was suspended in CH2Cl2 (200 mL) in a separating funnel, and
a solution of sodium or potassium oxalate (15 mmol) in water
(20 mL) was added. After shaking for 5 min a white precipitate
of Zn(C2O4) was present, suspended in the aqueous phase. The
phases were separated, and the organic layer was washed with
water (2 × 20 mL), dried with Na2SO4, filtered, and evaporated
to dryness, affording the analytically pure ligands in almost
quantitative yields (with respect to the intermediate complex).
A larger excess of oxalate can also be used, in which case Zn-
(C2O4) is partly solubilized in the aqueous phase as [Zn-
(C2O4)2]2-, but the efficiency of the decomplexation of the Ar-
BIAN ligand is not altered. The synthesis of 2,6-iPr2C6H3-
BIAN was performed by direct reaction of acenaphthene
quinone with the amine, without passing through the forma-
tion of the zinc complex, as reported in ref 23.
mass spectra and by comparison of the 1H spectra of the
isolated compounds with those reported in the literature and,
in the case of 5, by elemental analysis. The allylamines 1a -j
were isolated from the reaction mixtures by column flash
chromatography on silica (eluant CH2Cl2/hexane). They are
all oils and were characterized by their spectroscopic features.
After the chromatographic separation, no impurity could be
detected in the GC and 1H NMR spectra of the allylamnines.
Thus the purified compounds are evaluated to be at least 98%
pure.
1a : 1H NMR (300 MHz, CDCl3, 25 °C, TMS) δ ) 1.51-2.21
(m, 6 H, -CH2-CH2-CH2-), 3.74 (m, 1 H, -CH-NH), 3.90
(s, 1 H, NH), 5.72 (dd, J ) 8.2, 2.1 Hz, 1 H, -CH2-CHdCH-
CH-), 5.86 (dd, J ) 8.2, 2.1 Hz, 1 H, -CH2-CHdCH-CH-),
6.42 (dd, J ) 9.1, 3.2 Hz, 1 H, Ar-H), 6.68 (d, J ) 3.2 Hz, 1 H,
Ar-H), 7.16 (d, J ) 9.1 Hz, 1 H, Ar-H); 13C NMR (75.47 MHz,
CDCl3, 25 °C, TMS) δ ) 19.64, 25.17, 28.71, 48.06, 112.99,
114.11, 119.35, 127.66, 130.71, 130.95, 132.88, 146.80; MS (70
eV, EI) m/z (%): 241 (35) [M+], 213 (27) [M+ - CH2CH2], 161
(63) [Cl2C6H3NH2+], 81 (100) [C6H9+]; high-resolution mass
241.0432, calcd for C12H13NCl2 241.0425.
1b: 1H NMR (300 MHz, CDCl3, 25 °C, TMS) δ ) 1.58-2.18
(m, 6 H, -CH2-CH2-CH2-), 3.15 (s, 1 H, NH), 3.91 (m, 1 H,
-CH-NH), 5.72 (dd, J ) 8.2, 2.5 Hz, 1 H, -CH2-CHdCH-
CH-), 5.92 (dd, J ) 8.2, 2.3 Hz, 1 H, -CH2-CHdCH-CH-),
6.46-6.99 (m, 4 H, Ar-H); m/z (%) 191 (61) [M+], 1633 (56)
[M+ - CH2CH2], 111 (100) [FC6H4NH2+], 81 (42) [C6H9+].
1f: 1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ ) 1.26-2.34
(m, 10 H, -CH2-CH2-CH2-CH2-CH2-), 3.75 (s, 1 H, NH),
4.17 (m, 1 H, -CH-NH), 5.26 (dd, J ) 9.1, 8.1 Hz, 1 H, -CH2-
CHdCH-CH-), 5.78 (dt, J ) 9.1, 9.3 Hz, 1 H, -CH2-CHd
CH-CH-), 6.41 (dd, J ) 8.8, 2.7 Hz, 1 H, Ar-H), 6.63 (d, J )
2.7 Hz, 1 H, Ar-H), 7.13 (d, J ) 8.8 Hz, 1 H, Ar-H); 13C NMR
(75.47 MHz, CDCl3, 25 °C, TMS) δ ) 24.41, 26.72, 27.13, 29.41,
36.60, 51.12, 112.91, 119.61, 131.22, 132.73, 134.18, 147.41;
MS (70 eV, EI) m/z (%) 269 (16) [M+], 226 (62) [M+ - C3H7],
187 (26) [M+ - C6H10], 161 (73) [Cl2C6H3NH2+], 109 (41)
[C8H13+],67 (100) [C5H7+].
1g: 1H NMR (300 MHz, CDCl3, 25 °C, TMS) δ ) 1.25-2.49
(m, 4 H, -CH2-CH2-), 3.72 (s, 1 H, NH), 4.47 (m, 1 H, -CH-
NH), 5.77 (dd, J ) 9.1, 2.2 Hz, 1 H, -CH2-CHdCH-CH-),
6.01 (dd, J ) 9.1, 2.5 Hz, 1 H, -CH2-CHdCH-CH-), 6.41
(dd, J ) 8.9, 2.9 Hz, 1 H, Ar-H), 6.62 (d, J ) 2.9 Hz, 1 H,
Ar-H), 7.12 (d, J ) 8.9 Hz, 1 H, Ar-H). m/z (%) 227 (24) [M+],
161 (100) [Cl2C6H3NH2+], 67 (71) [C5H7+].
1j: 1H NMR (300 MHz, CDCl3, 25 °C, TMS) δ ) 3.75 (s, 1
H, NH), 4.14 (t, J ) 1.8 Hz, 2 H, -CH2-), 5.31 (dd, J ) 1.8,
1.6 Hz, 1 H, dCHH), 5.51 (d, J ) 1.6 Hz, 1 H, dCHH), 6.42
(dd, J ) 9.0 Hz, 3.0 Hz, 1 H, Ar-H), 6.61 (d, J ) 3.0 Hz, 1 H,
Ar-H), 7.11 (d, J ) 9.0 Hz, 1 H, Ar-H), 7.31-7.53 (m, 5 H,
Ar-H); 13C NMR (75.47 MHz, CDCl3, 25 °C, TMS) δ ) 48.51,
113.31, 114.61, 114.72, 120.41, 126.71, 123.31, 128.82, 131.24,
139.51, 144.62, 148.0; m/z (%) 277 (20) [M+], 174 (100)
[Cl2C6H3NHCH2+], 115 (15) [C9H7+].
Syn th esis of Ru (CO)3(Ar -BIAN) (2). Ar ) 2,6-iP r 2C6H3
(2a ). To a 50 mL Schlenk flask equipped with magnetic
stirring and a reflux condenser and under a N2 atmosphere
were added Ru3(CO)12 (50.0 mg, 0.078 mmol), 2,6-iPr2C6H3-
BIAN (117.9 mg, 0.234 mmol), and toluene (10 mL). The
solution was refluxed for 4 h, during which the color changed
from orange to deep blue-violet and all IR absorptions due to
Ru3(CO)12 disappeared. The solution was evaporated to dry-
ness, and the resulting solid was resuspended in n-hexane (5
mL), collected on a filter, and dried in vacuo (128 mg, 80%
isolated yield). The reaction can also be performed in Decaline
at the same or slightly higher temperature, but the reaction
takes about 18 h to reach completion. 1H NMR (200 MHz,
CDCl3, 25 °C, TMS): δ ) 0.96 (d, 3J (H,H) ) 6.9 Hz, 12 H,
CH3), 1.32 (d, 3J (H,H) ) 6.9 Hz, 12 H, CH3), 3.29 (sept, 3J (H,H)
) 6.9 Hz, 4 H, CH); 6.16 (d, J ) 7 Hz, 2 H, Ar); 7.12 (d, J )
7.9 Hz, 2 H, Ar); 7.28-7.44 (m, 6 H, Ar); 7.55 (d, J ) 8.2 Hz,
P h -BIP . Ph-BIP was synthesized in two steps via N,N′-
diphenyldiphenylethanediimine. The second step of the reac-
tion was performed as reported in ref 66, but the synthesis of
the intermediate product was performed by condensation of
aniline with benzil in the presence of molecular sieves, as
described in ref 67.
Ca ta lytic Rea ction s. In a typical reaction, the nitroarene,
Ru3(CO)12, and the ligand (see Tables 1-5) were weighed in a
glass liner. The liner was placed inside a Schlenk tube with a
wide mouth under dinitrogen and was frozen at - 78 °C with
dry ice, evacuated, and filled with dinitrogen, after which the
solvent was added. After the solvent was also frozen, the liner
was closed with a screw cap having a glass wool-filled open
mouth, which allows for gaseous reagents exchange, and
rapidly transferred to a 200 mL stainless steel autoclave with
magnetic stirring. The autoclave was then evacuated and filled
with dinitrogen three times. CO was then charged at room
temperature at the required pressure, and the autoclave was
immersed in an oil bath preheated at the required tempera-
ture. Other experimental conditions are reported in Tables
1-5. At the end of the reaction the autoclave was cooled with
an ice bath and vented, and the products were analyzed by
gas chromatography (naphthalene as an internal standard) or
separated by column chromatography on silica.
Id en tifica tion of th e Or ga n ic P r od u cts of Ca ta lysis.
The byproduct anilines are all commercial products and were
identified by comparison of their CG and CG-MS spectra with
those of authentic samples. Compounds 1c,68 1d ,69 1e,69 5,39
and 614 are known compounds and were identified by their
(66) van Belzen, R.; Klein, R. A.; Smeets, W. J . J .; Spek, A. L.;
Benedix, R.; Elsevier: C. J . Recl. Trav. Pays-Bas 1996, 115, 275.
(67) Shimizu, M.; Kamei, M.; Fujisawa, T. Tetrahedron Lett. 1995,
36, 8607.
(68) Tsui, F. P.; Chang, Y. C.; Vogel, T. M.; Zon, G. J . Org. Chem.
1976, 41, 3381.
(69) Abdrakhmanov, I. B.; Sharafutdinov, V. M.; Tolstikov, G. A.
Izv. Akad. Nauk. SSSR, Ser. Khim. 1982, 2160.

942 Organometallics, Vol. 18, No. 5, 1999
Ragaini et al.
2 H, Ar). IR (decaline): νCO ) 2044 (s), 1978 (m), 1972 (m)
cm-1. Anal. Calcd for C39H40N2O3Ru: C 68.20, H 5.87, N 4.08.
Found: C 67.84, H 6.06, N 3.80. The compound is very air
sensitive, but is stable for several weeks in the solid state and
under dinitrogen.
completely disappeared, and the bands of 3 were the only ones
observed in the carbonyl region. The solution was evaporated
to dryness at room temperature and the red-purple solid was
resuspended in n-hexane (5 mL), collected on a filter, and dried
in vacuo to afford analytically pure 3 (169 mg, 67% isolated
yield). 1H NMR (200 MHz, CDCl3, 25 °C, TMS): δ ) 0.71-
Ar ) P h (2b). To a 50 mL Schlenk flask equipped with
magnetic stirring and a reflux condenser and under a N2
atmosphere were added Ru3(CO)12 (50.0 mg, 0.078 mmol), Ph-
BIAN (155.6 mg, 0.468 mmol), and n-hexane (10 mL). The
solution was refluxed for 30 min, during which the color
changed from orange to deep blue-violet, all IR absorptions
due to Ru3(CO)12 disappeared, and new absorptions were
present at 2049 (s), 1984 (m), and 1975 (m) cm-1. The same
outcome is observed if the reaction is performed in toluene.
The complex could not be isolated in a pure form due to its
extreme air sensitivity and to its very similar solubility
properties with respect to the free ligand. The excess ligand
could not be extracted with 0.1 N HCl, as reported for the
analogous synthesis of Ru(CO)3(iPr-DAB),29 as Ph-BIAN was
completely insoluble in this solvent. Evaporating solutions of
2b (and also of 2c) in vacuo leads to decomposition by CO loss,
as also reported for Ru(CO)3(iPr-DAB).54
3
0.85 (m, 6 H, CH3), 0.97 (d, J (H,H) ) 6.8 Hz, 3 H, CH3); 1.08
(d, 3J (H,H) ) 6.9 Hz, 3 H, CH3); 1.22-1.29 (m, 6 H, CH3); 1.38
3
3
(d, J (H,H) ) 9.6 Hz, 3 H, CH3); 1.54 (d, J (H,H) ) 6.6 Hz, 3
H, CH3); 2.94 (sept, 3J (H,H) ) 6.8 Hz, 1 H, CH); 3.27 (sept,
3J (H,H) ) 6.9 Hz, 1 H, CH); 3.60 (sept, 3J (H,H) ) 6.6 Hz, 1 H,
3
CH); 3.84 (sept, J (H,H) ) 6.6 Hz, 1 H, CH); 6.43 (d, J ) 7.2
Hz, 1 H, Ar); 6.51 (d, J ) 7.1 Hz, 1 H, Ar); 7.15-7.59 (m, 11
H, Ar); 7.99 (d, J ) 8.3 Hz, 2 H, Ar). 19F NMR (282.4 MHz,
CDCl3, 25 °C, CFCl3): δ ) -65.61 (s, CF3). IR (toluene): νCO
) 2012 (s), 1945 (m) cm-1. MS (FAB+): m/z 867 (maximum of
the multiplet) [M+], 839 [M+ - CO], 811 [M+ - 2CO], 656 [M+
- nitrosoarene]. Anal. Calcd. for C45H43ClF3N3O3Ru: C 62.27,
H 5.00, N 4.84. Found: C 61.95, H 5.18, N 5.19.
High -P r essu r e IR Sp ectr a . Ru3(CO)12 (6.39 mg, 0.01
mmol) and the Ar-BIAN ligand in the required amount (see
text) were placed in a Schlenk tube under a dinitrogen
atmosphere, and the solvent (see text, 10 mL) was added. In
several cases, especially when the solvent was hexane, the
reagents were not completely soluble. The suspension was then
vigorously stirred for 10 min, and 3 mL of the stirred
suspension was withdrawn and added to the high-pressure IR
cell while purging with dinitrogen. Stirring for prolonged
periods or heating must be avoided, as the reaction started in
these cases in the Schlenk tube. The cell was closed under
dinitrogen and then charged with CO at the required pressure
at room temperature.
Ar ) Tol (2c). The procedure is analogous to the one
employed for 2a . IR (n-hexane): νCO ) 2047 (s), 1982 (m), and
1
1974 (m) cm-1. The H NMR spectrum after a reaction run in
C6D6 at 67 °C clearly showed the presence of equimolar
amounts of coordinated (δMe ) 2.13) and free (δMe ) 2.18 ppm)
ligand, supporting the presence of one molecule of ligand per
molecule of complex. The complex could not be isolated in a
pure form due to its extreme air sensitivity and to its very
similar solubility properties with respect to the free ligand.
Syn th esis of Ru (CO)2(2,6-iP r 2C6H3-BIAN)(η2-ONC6H3-
4Cl,2-CF 3) (3). To a 50 mL Schlenk flask were added Ru(CO)3-
(2,6-iPr2C6H3-BIAN) (200 mg, 0.29 mmol) and toluene (20 mL),
and the solution was cooled at 0 °C with an ice bath. At this
temperature was added 4-Cl,2-CF3C6H3NO2 (65.8 mg, 43 µL,
0.29 mmol). The temperature was kept constant and the
solution was stirred for 3 h, after which the color of the solution
had turned to red-purple, the IR absorptions of 2a had
Ack n ow led gm en t. This work was supported by
MURST (ex 40%). We thank Dr. Emma Gallo for help
in recording and discussing NMR spectra.
OM980843N