Intramolecular Hydroamination Catalyzed by Cationic Rhodium and Iridium Complexes with Bidentate Nitrogen-Donor Ligands

Article abstract of DOI:10.1021/om0343871

Cationic rhodium(I) and iridium(I) complexes of the general formula [M(N-N)(CO)₂]⁺⁺-[X]^-, incorporating the bidentate heterocyclic nitrogen donor ligands (N-N) bis(1-methylimidazol-2- yl)methane (bim) and bis(l-pyrazolyl)methane (bpm), are efficient catalysts for hydroamination. The cyclization of an aliphatic aminoalkyne to the corresponding fivemembered imine heterocycle was achieved in good yield with excellent regioselectivity using both rhodium and iridium catalysts. The nature of the counterion to the cationic catalysts has a significant effect on the rate of the hydroamination reaction and interionic contacts between the metal complexes and their counterions in solution were clearly visible by NMR spectroscopy using the nuclear Overhauser effect, indicating a strong anion/cation interaction in solution. The nature of the coligands also had a significant effect on the efficiency of the metal complexes as catalysts, and complexes containing phosphine coligands were less effective catalysts compared to those complexes containing CO coligands. The X-ray crystal structure of the new iridium(I) complex [Ir(bim)(CO)₂]⁺[BPh₄]^- (2) is reported, as well as the synthesis and characterization of the Rh complex [Rh(bpm)(CO)₂]⁺[BPh₄]^- (3).

Full text of DOI:10.1021/om0343871

1714
Organometallics 2004, 23, 1714-1721
In tr a m olecu la r Hyd r oa m in a tion Ca ta lyzed by Ca tion ic
Rh od iu m a n d Ir id iu m Com p lexes w ith Bid en ta te
Nitr ogen -Don or Liga n d s
Suzanne Burling,† Leslie D. Field,*,† Barbara A. Messerle,*,‡ and Peter Turner†
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia, and School of
Chemistry, University of New South Wales, Sydney, NSW 2052, Australia
Received December 18, 2003
Cationic rhodium(I) and iridium(I) complexes of the general formula [M(N-N)(CO)2]+-
[X]-, incorporating the bidentate heterocyclic nitrogen donor ligands (N-N) bis(1-meth-
ylimidazol-2-yl)methane (bim) and bis(1-pyrazolyl)methane (bpm), are efficient catalysts for
hydroamination. The cyclization of an aliphatic aminoalkyne to the corresponding five-
membered imine heterocycle was achieved in good yield with excellent regioselectivity using
both rhodium and iridium catalysts. The nature of the counterion to the cationic catalysts
has a significant effect on the rate of the hydroamination reaction and interionic contacts
between the metal complexes and their counterions in solution were clearly visible by NMR
spectroscopy using the nuclear Overhauser effect, indicating a strong anion/cation interaction
in solution. The nature of the coligands also had a significant effect on the efficiency of the
metal complexes as catalysts, and complexes containing phosphine coligands were less
effective catalysts compared to those complexes containing CO coligands. The X-ray crystal
structure of the new iridium(I) complex [Ir(bim)(CO)2]+[BPh4]- (2) is reported, as well as
the synthesis and characterization of the Rh complex [Rh(bpm)(CO)2]+[BPh4]- (3).
In tr od u ction
challenge, and recently significant developments in
active group 4 metal complexes, including alkylti-
tanocenes and titanium amido complexes, have been
made, in particular with titanium complexes with labile
nitrogen donor ligands.7 Titanium complexes are, how-
ever, extremely oxophilic, and this reduces their func-
tional group tolerance. While the lanthanide catalysts
are very efficient catalysts for intermolecular hydroami-
nation, their sensitivity to oxygen and moisture have
limited their general use in many applications.2 The
late-transition-metal catalysts for hydroamination gen-
erally have greater functional group tolerance and lower
oxygen and moisture sensitivity. There are now several
reports of catalytic systems of intermolecular hydroami-
nation using rhodium8 and iridium9 complexes.
The hydroamination reaction involves the addition of
N-H bonds across carbon-carbon double and triple
bonds and offers an atom-efficient pathway to produce
new primary, secondary, and tertiary amines as well
as imines and enamines.1,2 The syntheses of amines,
enamines, and imines are key reactions in organic
chemistry and in the production of chemicals on an
industrial scale.3 While the hydroamination reaction is
thermodynamically reasonable, there is a high activa-
tion barrier under normal conditions, necessitating the
use of a catalyst.1-3 A number of catalysts which effect
hydroamination have been developed,2,4 and examples
of catalysts which have been successful for intramo-
lecular hydroamination reactions include both late-
transition-metal1,5 and lanthanide complexes.6 The area
of intermolecular hydroamination has provided a greater
We recently reported the successful application of the
cationic rhodium(I) bis(1-methylimidazol-2-yl)methane
† University of Sydney.
(6) Li, Y.; Marks, T. J . J . Am. Chem. Soc. 1996, 118, 9295.
Arredondo, V. M.; McDonald, F. E.; Marks, T. J . J . Am. Chem. Soc.
1998, 120, 4871. Giardello, M. A.; Conticello, V. P.; Brard, L.; Gagne,
M. R.; Marks, T. J . J . Am. Chem. Soc. 1994, 116, 10241. Gagne, M. R.;
Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1992, 114, 275. Gagne,
M. R.; Brard, L.; Conticello, V. P.; Giardello, M. A.; Stern, C. L.; Marks,
T. J . Organometallics 1992, 11, 2003. Arredondo, V. M.; McDonald, F.
E.; Marks, T. J . Organometallics 1999, 18, 1949. Ryu, J .-S.; McDonald,
F. E.; Marks, T. J . Org. Lett. 2001, 3, 3091. Douglass, M. R.;
Ogasawara, M.; Hong, S.; Metz, M. V.; Marks, T. J . Organometallics
2002, 21, 283. Kim, Y. K.; Livinghouse, T.; Horino, Y. J . Am. Chem.
Soc. 2003, 125, 9560.
(7) Haak, E.; Bytschkov, I.; Doye, S. Angew. Chem., Int. Ed. 1999,
38, 3389. Haak, E.; Siebeneicher, H.; Doye, S. Org. Lett. 2000, 2, 1935.
Pohlki, F.; Doye, S. Angew. Chem., Int. Ed. 2001, 40, 2305. Cao, C.;
Ciszewski, J . T.; Odom, A. L. Organometallics 2001, 20, 5011. Bytsch-
kov, I.; Doye, S. Tetrahedron Lett. 2002, 43, 3715. Tillack, A.; Castro,
I. G.; Hartung, C. G.; Beller, M. Angew. Chem., Int. Ed. 2002, 41, 2541.
Ackermann, L.; Bergman, R. G. Org. Lett. 2002, 4(9), 1475. Bytschkov,
I.; Doye, S. Eur. J . Org. Chem. 2003, 935. Shi, Y.; Hall, C.; Ciszewski,
J . T.; Cao, C.; Odom, A. L. Chem. Commun. 2003, 586.
‡ University of New South Wales.
(1) See for example: Mu¨ller, T. E.; Beller, M. Chem. Rev. 1998, 98,
675.
(2) Pohlki, F.; Doye, S. Chem. Soc. Rev. 2003, 32, 104.
(3) Taube, R. In Applied Homogeneous Catalysis with Organome-
tallic Compounds;), 1st ed.; Cornils, B., Herrmann, W. A., Eds.;
VCH: Weinheim, Germany, 1996; Vol. 1, p 507.
(4) Nobis, M.; Driessen-Ho¨lscher, B. Angew. Chem., Int. Ed. 2001,
40, 3983.
(5) Hegedus, L. S.; McKearin, J . M. J . Am. Chem. Soc. 1982, 104,
2444. Tamaru, Y.; Hojo, M.; Higashimura, H.; Yoshida, Z. J . Am. Chem.
Soc. 1988, 110, 3994. McGrane, P. L.; Livinghouse, T. J . Am. Chem.
Soc. 1993, 115, 11485. Mu¨ller, T. E. Tetrahedron Lett. 1998, 39, 5961.
Mu¨ller, T. E.; Pleier, A.-K. J . Chem. Soc., Dalton Trans. 1999, 583.
Kadota, I.; Shibuya, A.; Lutete, L. M.; Yamamoto, Y. J . Org. Chem.
1999, 64, 4570. Mu¨ller, T. E.; Grosche, M.; Herdtweck, E.; Pleier, A.-
K.; Walter, E.; Yan, Y.-K. Organometallics 2000, 19, 170. Kondo, T.;
Okada, T.; Suzuki, T.; Mitsudo, T. J . Organomet. Chem. 2001, 622,
149. Shimada, T.; Yamamoto, Y. J . Am. Chem. Soc. 2002, 124, 12670.
Togni, A.; Fadini, L. Chem. Commun. 2003, 30.
10.1021/om0343871 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 03/11/2004

Hydroamination Catalyzed by Rh and Ir Complexes
Organometallics, Vol. 23, No. 8, 2004 1715
complex (1a ) to the intramolecular hydroamination of
alkynes.10 This demonstrated that cationic, coordina-
tively unsaturated complexes of group 9 metals with
bidentate nitrogen donors are potentially active cata-
lysts for the hydroamination reaction. A number of
charged transition-metal complexes catalyze the in-
tramolecular hydroamination of aminoalkynes,11 while
a recently developed dicationic palladium complex has
been shown to catalyze an intermolecular hydroamina-
tion reaction.12 There is increasing evidence that, for a
charged transition-metal catalyst, the activity, lifetime,
stability, and product selectivity of the reaction are sig-
ionic Rh(I) and Ir(I) complexes [Rh(bim)(CO)2]+[X]- (1:
a , X)BPh4;b, X)PF6;c, X)BF4), [Rh(bim)(PPh3)2]+[B-
Ph4]-(1d),[Ir(bim)(CO)2]+[BPh4]-(2),[Rh(bpm)(CO)2]+[B-
Ph4]- (3), and [Ir(bpm)(CO)2]+[BPh4]- (4) with the
bidentate nitrogen donor ligands bis(1-methylimidazol-
2-yl)methane (bim) and bis(1-pyrazolyl)methane (bpm).
nificantly influenced by the nature of the counterion.13-18
-
Smaller, more tightly binding anions such as PF6
,
BF4-, and ClO4 are, in some cases, less favored as
counterions for many homogeneous catalysts,13 whereas
tetraphenylborate has been commonly utilized as a
counterion, due to its size, its inertness, and its tendency
to more readily form stable crystalline compounds.
-
In solution, there is a strong interaction between the
cationic complex and the counterion, and both the
nature of the counterion and the coligands have a
significant effect on the catalytic efficiency. We also
report the synthesis and characterization of the new
cationic rhodium(I) complex [Rh(bpm)(CO)2]+[BPh4]- (3)
and present the crystallographic characterization of the
recently reported iridium(I) complex [Ir(bim)(CO)2]+[B-
Ph4]- (2).19
-
However, although BPh4 is usually considered as an
unreactive or “innocent” counterion, it is known to act
as a phenylating agent toward organic molecules and
also to participate in π-interactions with metal centers.14
The anion effect has received the most attention in
studies of homogeneous olefin polymerization cataly-
sis,15 and some of the most extensively used anions of
recent interest in olefin polymerization chemistry are
the perfluorophenylborates and aluminates, including
the tetrakis(3,5-bis(trifluoromethyl)phenyl)borate an-
ion.16 These polyfluorinated anions have properties such
as low nucleophilicity, chemical inertness, improved
solubility, and weaker coordinating strength,17 all of
which can enhance catalyst efficiency.
Resu lts a n d Discu ssion
Syn th esis of Meta l Com p lexes. The nitrogen donor
ligands bim and bpm, used in the synthesis of complexes
1-4, were prepared by previously reported methods.10,20
The cationic dicarbonyl complexes of rhodium and
iridium [Rh(bim)(CO)2]+[BPh4]- (1a ), [Ir(bim)(CO)2]+[B-
Ph4]-(2),[Rh(bpm)(CO)2]+[BPh4]-(3),and[Ir(bpm)(CO)2]+[B-
Ph4]- (4) were prepared in good yield by addition of the
bidentate ligand to the appropriate metal precursor in
methanol. The complexes were precipitated as air-stable
crystalline solids with tetraphenylborate counterions.
The synthesis of [Rh(bim)(CO)2]+[BPh4]- (1a ) has
been reported previously,10,21 and the synthesis of the
rhodium(I) bis(1-pyrazolyl)methane complex 3 followed
an analogous route. Two equivalents of the bpm ligand
in methanol was added to [Rh(CO)2Cl]2 in methanol
under nitrogen, and [Rh(bpm)(CO)2]+[BPh4]- (3) was
precipitated by addition of NaBPh4 as a fine yellow
crystalline solid. In air, the complex is stable indefi-
nitely; however, it decomposes rapidly in solution. The
synthesis of the rhodium complexes 1b,c again followed
a similar route, with the addition of methanol solution
of the bim ligand to a solution of [Rh(CO)2Cl]2 in
methanol under nitrogen, followed by addition of an
excess of the appropriate counterion and isolation of the
resulting precipitates. The synthesis of 1d has been
reported elsewhere.22 The synthesis of [Rh(bpm*)(CO)2]+-
[BF4]- (bpm* ) bis(3,5-dimethylpyrazolyl)methane) has
also been reported recently.23
In this paper, we report the results of intramolecular
hydroamination reactions of aminoalkynes to form
nitrogen-containing heterocycles catalyzed by the cat-
(8) Brunet, J .-J .; Neibecker, D.; Philippot, K. Tetrahedron Lett. 1993,
34, 3877. Brunet, J .-J .; Commenges, G.; Neibecker, D.; Philippot, K.
J . Organomet. Chem. 1994, 469, 221. Beller, M.; Trauthwein, H.;
Eichberger, M.; Breindl, C.; Herwig, J .; Mu¨ller, T. E.; Thiel, O. R. Chem.
Eur. J . 1999, 5, 1306. Tillack, A.; Hartung, C. G.; Trauthwein, H.;
Beller, M. J . Org. Chem. 2001, 66, 6339.
(9) Casalnuovo, A. L.; Calabrese, J . C.; Milstein, D. J . Am. Chem.
Soc. 1988, 110, 6738. Dorta, R.; Egli, P.; Zurcher, F.; Togni, A. J . Am.
Chem. Soc. 1997, 119, 10857.
(10) Burling, S.; Field, L. D.; Messerle, B. A. Organometallics 2000,
19, 87.
(11) Mu¨ller, T. E.; Grosche, M.; Herdtweck, E.; Pleier, A.-K.; Walter,
E.; Yan, Y.-K. Organometallics 2000, 19, 170.
(12) Li, K.; Hii, K. K. Chem. Commun. 2003, 1132. Li, K.; Hii, K.
K.; Horton, P. N.; Hursthouse, M. B. J . Organomet. Chem. 2003, 665,
250.
(13) Strauss, S. H. Chem. Rev. 1993, 93, 927.
(14) Aresta, M.; Quaranta, E.; Tommasi, I. New J . Chem. 1996, 21,
595. Schrock, R. R.; Osborn, J . A. Inorg. Chem. 1970, 9, 2339.
(15) Yang, X.; Stern, C.; Marks, T. J . J . Am. Chem. Soc. 1994, 116,
10015. Liting, L.; Stern, C. L.; Marks, T. J . Organometallics 2000, 19,
3332. Chen, Y.-X.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J . J .
Am. Chem. Soc. 1998, 120, 6287. Chen, Y.-X.; Stern, C. L.; Yang, S.;
Marks, T. J . J . Am. Chem. Soc. 1996, 118, 12451. Chen, Y.-X.; Stern,
C. L.; Marks, T. J . J . Am. Chem. Soc. 1997, 119, 2582. J ia, L.; Yang,
X.; Stern, C. L.; Marks, T. J . Organometallics 1997, 16, 842.
(16) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267. Mecking, S.; J ohnson, L. J .; Wang, L.; Brookhart, M.
J . Am. Chem. Soc. 1998, 120, 888. Chen, E. Y.-X.; Marks, T. J . Chem.
Rev. 2000, 100, 1391.
(19) Burling, S.; Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner,
P. Dalton 2003, 4181.
(17) Reed, C. A. Acc. Chem. Res. 1998, 31, 133.
(18) Macchioni, A.; Bellachioma, G.; Cardaci, G.; Travaglia, M.;
Zuccaccia, C.; Milani, B.; Corso, G.; Zangrando, E.; Mestroni, G.;
Carfagna, C.; Formica, M. Organometallics 1999, 18, 3061. LaPointe,
R. E.; Roof, G. R.; Abboud, K. A.; Klosin, J . J . Am. Chem. Soc. 2000,
122, 9560. Piers, W. E. Chem. Eur. J . 1998, 4, 13. Beswick, C. L.;
Marks, T. J . Organometallics 1999, 18, 2410. Boche, G. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 731.
(20) J ulia, S.; Sala, P.; Mazo, J . d.; Sancho, M.; Ochoa, C.; Elguero,
J .; Fayet, J .-P.; Vertut, M.-C. J . Heterocycl. Chem. 1982, 19, 1141.
(21) Elgafi, S.; Field, L. D.; Messerle, B. A.; Turner, P.; Hambley,
T. W. J . Organomet. Chem. 1999, 588, 69.
(22) Elgafi, S. Ph.D. Thesis, University of Sydney, 1996.
(23) Teuma, E.; Loy, M.; Le Berre, C.; Etienne, M.; Daran, J .-C.;
Kalck., P.; Organometallics 2003, 22, 5261.

1716 Organometallics, Vol. 23, No. 8, 2004
Burling et al.
Ta ble 1. Selected Geom etr y fr om th e Cr ysta l
Str u ctu r e of [Ir (bim )(CO)2]+[BP h 4]- (2)
Bond Distances (Å)
Ir(1a)-N(1a)
Ir(1a)-N(2a)
Ir(1b)-N(1b)
Ir(1b)-N(2b)
2.079(6)
2.067(6)
2.077(6)
2.075(5)
Ir(1a)-C(1a)
Ir(1a)-C(2a)
Ir(1b)-C(1b)
Ir(1b)-C(2b)
1.823(8)
1.836(8)
1.846(8)
1.843(8)
Bond Angles (deg)
N(1a)-Ir(1a)-N(2a) 86.8(2) N(2a)-Ir(1a)-C(1a) 90.0(3)
N(1b)-Ir(1b)-N(2b) 87.3(2) N(2b)-Ir(1b)-C(1b) 92.3(3)
N(1a)-Ir(1a)-C(2a)
92.8(3) C(1a)-Ir(1a)-C(2a)
90.6(3)
Ta ble 2. Cr ysta llogr a p h ic Da ta for th e Str u ctu r e
Deter m in a tion of [Ir (bim )(CO)2]+[BP h 4]- (2)
formula
formula wt
C36.5H35BIrN4O2.50
772.70
cryst syst
monoclinic
color, habit
red, prism
space group
a
b
c
â
V
Z
Dcalcd
P21/c (No. 14)
22.140(3) Å
11.3650(14) Å
28.0281(10) Å
111.781(7)°
6548.9(12) Å3
8
1.567 g cm-3
135.00°
2θmax
hkl range
0-26, 0-13, -33 to +31
12 066
no. of rflns measd (N)
no. of unique rflns (N0)
λ(Cu KR)
11 744 (Rmerge ) 0.0515)
1.541 78 Å
µ(Cu KR)
8.209 mm-1
0.795, 1.000
0.0401
T(ψ scans)min,max
R1(F)a
wR2(F2)a
0.1228
residual extrema
-1.674, 1.226 e Å-3
R1 ) ∑||Fo| - |Fc||/∑|Fo| for Fo > 2σ(Fo); wR2 ) (∑w(Fo2 - Fc2)2/
a
∑(wFc2)2)1/2. For all reflections w ) 1/(σ2(Fo2) + (0.0508P)2
+
2
1.8264P), where P ) (Fo + 2Fc2)/3.
The geometry is essentially square planar about the
iridium center, with the coordinating ligands comprising
two carbonyl ligands and one bis(1-methylimidazol-2-
yl)methane ligand, which provides two nitrogen donor
atoms. There is a slight deviation from the ideal square-
planar geometry, resulting from the small restraint
placed on the heterocyclic donors by the flexible meth-
ylene bridge of the bidentate ligand. This is evident by
the placement of C(6a) 1.05(1) Å out of the least-squares
plane defined by C(1a)-C(2a)-N(1a)-N(2a).
The two iridium complexes in the asymmetric unit
have a stacking interaction (Figure 1c), similar to that
reported for the analogous rhodium complex.21 The
tendency for stacking in the solid state has been
attributed to an interaction between the imidazole
residues of the two independent complexes rather than
by association with the phenyl rings of the tetraphen-
ylborate counterion, which are situated far from the
iridium metal center. The close contact between the two
complexes is supported by the interatomic distance of
3.49(1) Å between N(1b) and the imidazole ring of
complex A containing N(2a)-C(7a)-N(3a)-C(8a)-
C(9a).
F igu r e 1. ORTEP25 depictions and crystal structure
numbering of the cationic fragment of [Ir(bim)(CO)2]+[BPh4]-
(2): (a) illustration of the four-coordinate square-planar
geometry; (b) projection through the C6A-Ir1A axis; (c)
stacking of the two independent complexes in the asym-
metric unit. Displacement ellipsoids are shown at the 25%
level.
The syntheses of the iridium(I) bim (2) and iridium-
(I) bpm (4) complexes have been reported previously.19,24
The synthesis of 2 involved adding 2 equiv of the bim
ligand to the iridium precursor [Ir(COD)Cl]2 and NaB-
Ph4 and then placing the mixture under an atmosphere
of carbon monoxide. [Ir(bim)(CO)2]+[BPh4]- (2) was
isolated as a fine yellow crystalline solid, which recrys-
tallized from acetone as large red prisms suitable for
X-ray diffraction analysis.
The asymmetric unit of 2 contained two crystallo-
graphically independent complex molecules and their
counterions. ORTEP25 depictions of the complexes are
shown in Figure 1, and selected bond lengths and angles
for the inner coordination sphere are listed in Table 1.
Complex 2 is isomorphous and isostructural with the
analogous rhodium complex 1a , published previously.21
In t er ion ic Con t a ct s in Solu t ion . Intermolecular
proton-proton or proton-fluorine NOESY cross-peaks
due to interactions between protons of the bim and bpm
ligands and protons and fluorine atoms of the anion
were observed in the NOESY (or HOESY) NMR spectra
for the complexes [Rh(bim)(CO)2]+[X]- (1: a , X ) BPh4;
(24) Field, L. D.; Messerle, B. A.; Soler, L. P.; Rehr, M.; Hambley,
T. W. Organometallics 2003, 22, 2387-2395.
(25) J ohnson, C. K. ORTEPII; Report ORNL-5138; Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.

Hydroamination Catalyzed by Rh and Ir Complexes
Organometallics, Vol. 23, No. 8, 2004 1717
F igu r e 3. Section of the 19F{1H} HOESY NMR spectrum
of [Rh(bim)(CO)2]+[PF6]- (1b) in acetone-d6, demonstrating
the intermolecular HOE interactions between the rhodium
cation and the hexafluorophosphate anion. The fluorine
signal appears as a doublet, due to coupling to the central
phosphorus atom.
F igu r e 2. Interionic NOESY contacts observed for
[Ir(bim)(CO)2]+[BPh4]- (2): cross-peak region of the 1H
NOESY NMR spectrum of [Ir(bim)(CO)2]+[BPh4]- (2) in
tetrahydrofuran-d8 at 300 K, indicating the interionic
contacts between the ortho, meta, and para protons of
pyrazolyl)methane ligand.26,27 In particular, interionic
contacts have been previously identified for the analo-
gous iridium complex [Ir(bpm)(CO)2]+[BPh4]- (4), where
interactions were observed between H3 and H4 of the
pyrazole ring and the meta and para protons of tet-
raphenylborate,27 and the bridging methylene group
also produced interionic contacts with the anion.
Using HOESY (the heteronuclear analogue of the
NOESY experiment), interionic contacts were also
detected for [Rh(bim)(CO)2]+[PF6]- (1b) in acetone-d6
solution. In 19F/1H HOESY NMR experiments, HOE
interactions between the protons of N-Me and the
methylene bridge of the bis(1-methylimidazol-2-yl)-
methane ligand and the fluorines of the hexafluoro-
phosphate anion were evident (Figure 3), with no
interactions between protons H4 and H5 of the imida-
zole ring and the fluorines of the PF6- counterion. This
again shows that the main interaction with the coun-
terion is not close to the metal center but, rather, away
from the metal center near the remote edge of the
coordinated bim ligand of the complex. The interaction
predominantly at this part of the molecule could, in part,
be due to a hydrogen bonding interaction between the
relatively acidic methylene protons on the coordinated
bim ligand and the counterion. Macchioni and co-
-
BPh4 and the N-CH3 and CH2 protons of the ligand.
b,X)PF6),[Ir(bim)(CO)2]+[BPh4]-(2),[Rh(bpm)(CO)2]+[BPh4]-
(3), and [Ir(bpm)(CO)2]+[BPh4]- (4) in solution.
For the complexes [Rh(bim)(CO)2]+[BPh4]- (1a )
and [Ir(bim)(CO)2]+[BPh4]- (2), strong proton-proton
NOESY cross-peaks were observed between protons of
the bidentate nitrogen donor ligand and the protons of
the tetraphenylborate counterion (Figure 2). Clear,
strong NOE interactions were evident between the ortho
-
and para hydrogen atoms of the BPh4 anion and the
N-Me and bridging methylene group of the bis(1-
methylimidazol-2-yl)methane ligand in complexes 1 and
2 (see Figure 2). No intermolecular contacts were
observed between the imidazole protons H4 and H5 and
the counterions. The region of the NOESY spectrum of
[Ir(bim)(CO)2]+[BPh4]- (2) shown in Figure 2 illustrates
the relative strengths of the interionic interactions. Only
one set of phenyl resonances is observed for BPh4-, and
this indicates that there is rapid internal motion in the
anion. However, the interaction between the anion and
cation is sufficiently long-lived to permit the buildup of
strong NOE interactions. This is a dynamic system, and
it is difficult to quantify the NOE interactions; however,
the strongest interactions between the cationic complex
and the counterion are at the edge of the metal complex
at the periphery of the ligand structure, away from the
metal center.
(26) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Reichenbach, G.;
Terenzi, S. Organometallics 1996, 15, 4349. Macchioni, A.; Bella-
chioma, G.; Cardaci, G.; Gramlich, V.; Ruegger, H.; Terenzi, S.;
Venanzi, L. Organometallics 1997, 16, 2139. Macchioni, A.; Bella-
chioma, G.; Cardaci, G.; Cruciani, G.; Foresti, E.; Sabatino, P.;
Zuccaccia, C. Organometallics 1998, 17, 5549. Zuccaccia, C.; Bella-
chioma, G.; Cardaci, G.; Macchioni, A. Organometallics 1999, 18, 1.
(27) Soler, L. P. Ph.D. Thesis, University of Sydney, 1999.
Intermolecular contacts have been previously re-
ported for metal complexes coordinating the bis(1-

1718 Organometallics, Vol. 23, No. 8, 2004
Burling et al.
Ta ble 3. Rela tive Efficien cy of Ca ta lysts for th e
Cycliza tion of 4-P en tyn -1-a m in e to
2-Meth yl-1-p yr r olin e (th f-d 8, 1.5 m ol % Ca ta lyst)a
time (h)
50%
98%
b
complex
[Rh(bim)(CO)2]+[BPh4]- (1a ) 17
[Ir(bim)(CO)2]+[BPh4]- (2)
[Rh(bpm)(CO)2]+[BPh4]- (3) 20
Nt conversn conversnc temp
2.0
14
60 °C
reflux
60 °C
reflux
60 °C
reflux
60 °C
reflux
4.5 (75)
24 (92)
4.5
12 (90)
4
5
6.3
1.7
[Ir(bpm)(CO)2]+[BPh4]- (4)
50
0.70
2.2
0.5
a
b
Conditions: in thf-d8; 1.5 mol % catalyst. Turnover number
) (mol of product produced)/((mol of catalyst used) h), typically
calculated at time of 50% conversion. c Values in parentheses are
the conversions (%) at the time indicated.
Sch em e 1
workers used 19F/1H HOESY NMR spectroscopy to study
the interaction of the tetrafluoroborate anion with
platinum complexes coordinating N,N-diimine ligands,
[Pt(Me)(η2-olefin)(N,N)]+[BF4]-.28 In that work, the
counterion was reported to prefer the diimine side of
the complex, rather than the less hindered olefin side,
and this was attributed to the expected delocalization
of the positive charge on the bidentate ligand.
Ca ta lysis: In tr a m olecu la r Hyd r oa m in a tion . The
catalytic activity of [Rh(bim)(CO)2]+[BPh4]- (1a ) for the
intramolecular hydroamination of aminoalkynes to
produce nitrogen-containing heterocycles, including in-
doles, has already been reported.10 Rhodium(I) and
iridium(I) complexes with bim and bpm as ligands,
[Rh(bim)(CO)2]+[BPh4]- (1a ), [Ir(bim)(CO)2]+[BPh4]- (2),
[Rh(bpm)(CO)2]+[BPh4]- (3), and [Ir(bpm)(CO)2]+[BPh4]-
(4), were tested as catalysts for a standard intramo-
lecular hydroamination using the substrate 4-pentyn-
1-amine to form 2-methyl-1-pyrroline (Scheme 1, Table
3).
F igu r e 4. Reaction profiles of the [Rh(bim)(CO)2]+[BPh4]-
(1a ) and [Ir(bim)(CO)2]+[BPh4]- (2) catalyzed cyclization
of 4-pentyn-1-amine with the batchwise addition of aliquots
of substrate (5 mol % catalyst, tetrahydrofuran-d8, 60 °C,
second and third aliquots of substrate added at times T2
and T3, respectively).
of the initial substrate loading. These experiments
clearly demonstrated that the iridium complexes were
significantly more robust under the reaction conditions
and continued to act as effective catalysts over several
cycles, while the performances of the rhodium analogues
were reduced on addition of new substrate (Figure 4).
In the first instance, 4-pentyn-1-amine was treated
with 1.5 mol % of each complex in thf-d8 at 60 °C and
the reactions were monitored regularly by 1H NMR
spectroscopy. The reaction was regioselective for the
five-membered ring in all four experiments, producing
2-methyl-1-pyrroline as the sole product of reaction. The
complexes with bis(pyrazolyl)methane ligands produced
superior conversion rates and turnover numbers. The
iridium(I) analogue 4, in particular, reached full conver-
sion in just over 2 h (Table 3). Significant improvement
in the turnover rates was found at the somewhat higher
reflux temperature (67 °C), with the iridium analogue
4 achieving full conversion in only 30 min and the
rhodium analogue 3 reaching complete conversion in
only 4 h.
Effects of Coliga n d s a n d Cou n ter ion s. The role
of the CO ligands in the catalyzed reaction was inves-
tigated through the synthesis of a derivative of 1a ,
where the CO ligands were substituted by PPh3 to form
[Rh(bim)(PPh3)2]+[BPh4]- (1d ). The PPh3 ligand has a
more significant steric impact than CO, and the relative
strengths of the metal-CO and metal-phosphine bonds
as well as the relative labilities of the carbonyl and
triphenylphosphine ligands may also influence the
efficiency of the catalysis. The cyclization of 4-pentyn-
1-amine with 1d was significantly slower than with 1a
under identical conditions (Table 4). The coligands do
have a significant impact on the reaction rate. This
indicates either that the nature of the coligand affects
the relative stability of reactive intermediates in the
reaction pathway or that the initial coligand dissociation
has a significant impact on the reaction rate.
The four complexes tested were further differentiated
by the catalyst lifetime. For each of the catalysts
studied, several reaction cycles were followed, where
additional batches of substrate were added consecutively
to the reaction mixture following complete conversion
The efficiency of hexafluorophosphate and tetrafluo-
roborate analogues [Rh(bim)(CO)2]+[PF6]- (1b) and
[Rh(bim)(CO)2]+[BF4]- (1c) as catalysts was investi-
gated to assess the potential influence of the counterion
on the catalytic activity of the charged transition-metal
(28) Zuccaccia, C.; Macchioni, A.; Orabona, I.; Ruffo, F. Organome-
tallics 1999, 18, 4367.

Hydroamination Catalyzed by Rh and Ir Complexes
Organometallics, Vol. 23, No. 8, 2004 1719
Ta ble 4. Yield of 2-Meth yl-1-p yr r olin e Obta in ed
fr om th e Rh od iu m (I)-Ca ta lyzed Cycliza tion of
4-P en tyn -1-a m in e in Tetr a h yd r ofu r a n -d 8 a t 60 °C
w ith a Va r ia tion of Coliga n d a n d Cou n ter ion
a
complex
conversn (%) time (h) Nt
[Rh(bim)(CO)2]+[BPh4]- (1a )d
[Rh(bim)(CO)2]+[PF6]- (1b)e
[Rh(bim)(CO)2]+[BF4]- (1c)d
100b
59
14
24
12
24
24
17
2c
1c
18b
23
[Rh(bim)(PPh3)2]+[BPh4]- (1d )f
63
2c
a
Turnover number ) (mol of product produced)/((mol of cata-
b
lyst) h), typically calculated at time of 50% conversion. Heating
in the spectrometer magnet with spectra recorded every 10 min
using an automated time course program. c Turnover calculated
d
at 18% conversion. Catalyst loading 1.5 mol %. e Catalyst loading
1.7 mol %. f Catalyst loading 1.4 mol %.
Ta ble 5. Yield of 2-Meth yl-1-p yr r olin e fr om th e
Rh od iu m - a n d Ir id iu m -Ca ta lyzed Cycliza tion of
4-P en tyn -1-a m in e w ith Ca ta lysts 1a a n d 2-4 in th e
P r esen ce of Excess 2-Meth yl-1-p yr r olin e in
Tetr a h yd r ofu r a n -d 8 a t 60 °Ca
amt of cat. time yield of 2-methyl-
complex
(mol %)
(h)
1-pyrroline (%)
[Rh(bim)(CO)2]+[BPh4]- (1a )
[Ir(bim)(CO)2]+[BPh4]- (2)
[Rh(bpm)(CO)2]+[BPh4]- (3)
[Ir(bpm)(CO)2]+[BPh4]- (4)
1.6
2
1.5
1.5
15
15
15
5
36
84
87
98
a
One equivalent of 2-methyl-1-pyrroline was added to a solution
containing 1 equiv of 4-pentyn-1-amine.
complex (Table 4).29 The introduction of either the
hexafluorophosphate or tetrafluoroborate counterion
resulted in a decrease in catalyst activity compared to
that of the complex with the tetraphenylborate coun-
terion (Table 4). With [Rh(bim)(CO)2]+[PF6]- (1b) as a
catalyst, the rate of reaction decreased by approximately
40%. An even greater influence was evident for the
reaction of 4-pentyn-1-amine with [Rh(bim)(CO)2]+[BF4]-
(1c), where only 23% conversion to the cyclized product
was achieved after 24 h. The reduced activity with the
smaller, more coordinating anions indicates that the
nature of the counterion is important in determining
the catalyst performance for this reaction.
Rea ction Kin etics a n d P r od u ct In h ibition . The
pyrroline product of the cyclization reaction contains a
nitrogen atom that could itself behave as a donor,
competing with the substrate for binding sites at the
metal center. The impact of the product buildup on the
reaction rate was examined by performing cyclization
of the substrate 4-pentyn-1-amine in the presence of the
reaction product 2-methyl-1-pyrroline using complexes
1a and 2-4 as catalysts.
F igu r e 5. 2D EXSY spectrum (400 MHz, tetrahydrofuran-
d8, 210 K) of [Ir(bpm)(CO)2]+[BPh4]- (4) in exchange with
free bpm ligand (the cross-peaks due to exchange are
marked with dashed squares).
particularly pronounced for the rhodium catalyst
[Rh(bim)(CO)2]+[BPh4]- (1a ). When using 1a as a
catalyst, 100% conversion was achieved after 14 h in
the absence of any additional product and only 36%
conversion was obtained after 15 h in the presence of
excess 2-methyl-1-pyrroline.
Liga n d La bilit y. N-donor ligands are, in general,
more labile than those containing the more strongly
binding phosphine or carbene donors. In solution, the
bidentate N-donor ligands coordinated to the metal
center underwent rapid exchange with added free ligand
and 2D EXSY and variable-temperature NMR experi-
ments were used to study the exchange. Qualitative
data gave an indication of the relative rates of exchange
of bim and bpm with the rhodium and iridium catalysts
in solution. Typically, 1 equiv of the bidentate ligand
was added to the complex in acetone-d6 or tetrahydro-
furan-d8 in an NMR tube under nitrogen. The reactions
occurred immediately at room temperature, and no
heating was required to initiate the ligand exchange.
For [Ir(bpm)(CO)2]+[BPh4]- (4) in the presence of
excess free bpm ligand, the 1H NMR spectrum exhibited
very broad ligand resonances at room temperature
indicative of rapid exchange between 4 and free bpm
ligand. In addition to the usual NOESY-type cross-peaks
between protons in the BPh4- counterion, the strongest
peaks in the 2D EXSY spectrum (acquired at 210 K;
Figure 5) are the series of cross-peaks arising from
Approximately 1 equiv of 2-methyl-1-pyrroline was
added to a solution containing 1 equiv of 4-pentyn-1-
amine and the catalyst (∼1.5 mol %) in tetrahydrofuran-
d8. Reactions were performed at 60 °C and monitored
1
by H NMR spectroscopy (Table 5).
Comparison of the conversions presented in Table 5,
obtained in the presence of excess product (2-methyl-
1-pyrroline), with those in Table 3, which present the
catalyzed cyclization under a standard set of conditions,
demonstrates a significant inhibitory effect of the
product on the catalytic activity. The inhibition is
(29) Analogous complexes synthesized using tetrakis(3,5-bis(tri-
fluoromethyl)phenyl)borate as the counterion were not sufficiently
stable to permit characterization.

1720 Organometallics, Vol. 23, No. 8, 2004
Burling et al.
tained from Aldrich or J ohnson Matthey and was used without
further purification. Iridium(III) trichloride hydrate was ob-
tained from Strem and used without further purification.
Tetracarbonyldichlorodirhodium, [Rh2(CO)4Cl2], was syn-
thesized by the procedure described by McCleverty and
Wilkinson.30 [Ir2(COD)2Cl2] was prepared by the method of
Herde.31 The ligands bim10 and bpm20 were prepared by
literature methods. Complexes 110,21 and 424 were also prepared
by following literature methods.
4-Pentyn-1-amine was synthesized from 5-bromo-1-pentyne
by reaction with liquid ammonia. Tetrahydrofuran and hexane
were dried over sodium wire and distilled under nitrogen
immediately prior to use from sodium benzophenone-ketyl.
Methanol was distilled from magnesium turnings under
nitrogen. Acetone was distilled from CaSO4 under nitrogen.
Deuterated solvents for NMR purposes were obtained from
Merck and Cambridge Isotopes. Chloroform-d was used as
supplied. Tetrahydrofuran-d8 was dried over sodium/ben-
zophenone and vacuum-distilled immediately prior to use.
Acetone-d6 was dried over molecular sieves and vacuum-
distilled immediately prior to use.
exchange between the uncoordinated bpm ligand and
the ligand bound to iridium. Similar ligand exchange
was observed between [Ir(bim)(CO)2]+[BPh4]- (2) and
added free bim ligand. [Rh(bim)(CO)2]+[BPh4]- (1a ) and
[Rh(bpm)(CO)2]+[BPh4]- (3) also showed exchange with
the corresponding free ligand. The rate of exchange was
slowest for [Rh(bim)(CO)2]+[BPh4]- (1a ), with the 1H
NMR resonances for the free and coordinated ligand
independently observed at room temperature.
In competitive ligand binding studies with rhodium
complexes, there was no exchange between the ligands
upon addition of approximately 1 equiv of bpm to
[Rh(bim)(CO)2]+[BPh4]- (1a ). Conversely, the addition
of bim to [Rh(bpm)(CO)2]+[BPh4]- (3) resulted in com-
plete displacement of the bpm ligand with bim, sug-
gesting that the bidentate imidazole ligand binds more
strongly to the rhodium center.
Con clu sion s
1H and 13C NMR spectra were recorded on a Bruker DRX400
spectrometer at 400.13 and 100.62 MHz, respectively. 1H and
13C NMR chemical shifts (δ) were referenced to internal solvent
resonances. All spectra were recorded at 300 K for character-
ization purposes unless otherwise stated and at 333 K for
NMR-monitored catalytic reactions. Infrared spectra were
recorded on a Perkin-Elmer 1600 Series FTIR spectrometer,
the samples being recorded as KBr disks. Melting points were
determined using a Gallenkamp apparatus and are uncor-
rected. Elemental analyses were carried out at the Campbell
Microanalytical Laboratory, University of Otago, Otago, New
Zealand.
Syn th esis of (Bis(1-m eth ylim id a zol-2-yl)m eth a n e)d i-
ca r bon ylir id iu m (I) Tetr a p h en ylbor a te (2). Solutions of
bis(1-methylimidazol-2-yl)methane (252 mg, 1.43 mmol) in
methanol (5 mL) and sodium tetraphenylborate (548 mg, 1.6
mmol) in methanol (5 mL) were added to a solution of
[Ir(COD)Cl]2 (457 mg, 0.68 mmol) in methanol (20 mL) and
hexane (5 mL) at room temperature. The reaction mixture was
stirred for 2 h, degassed, and placed under an atmosphere of
carbon monoxide gas for 3 days, during which time a pale
yellow solid formed. The solid was isolated by filtration and
washed with hexane and methanol. Recrystallization from
acetone produced orange crystals of (bis(1-methylimidazol-2-
yl)methane)dicarbonyliridium(I) tetraphenylborate (2; 895 mg,
89%). Mp: 190-193 °C dec.
This paper explores characteristics of the cationic Ir-
(I) and Rh(I) complexes which catalyze intramolecular
hydroamination of aminoalkynes. In terms of chemical
robustness, the iridium complexes examined demon-
strated much greater lifetimes than their rhodium
analogues. The ligands were found to be labile, with the
bis(pyrazolyl)methane ligand more labile than the bis-
(1-methylimidazol-2-yl)methane ligand. The complexes
with the more labile bis(pyrazolyl)methane ligands
produced superior conversion rates and turnover num-
bers. The most active catalyst of those studied was the
Ir complex [Ir(bpm)(CO)2]+[BPh4]- (4).
The nature of the counterion associated with the
cationic catalysts does have a significant effect on the
rate of the hydroamination reaction, and this indicates
a strong anion/cation interaction in solution. The fact
that these interionic interactions are clearly visible by
NOE spectroscopy indicates that there is a long-lived
association between the cations and anions (ion pairing)
in the reaction mixture. This ion pairing could influence
the formation of the active catalytic species and affect
both access of the substrate to the reactive metal center
as well as the charge distribution and electronic proper-
ties at the metal center.
Syn t h esis of (Bis(1-p yr a zolyl)m et h a n e)d ica r b on yl-
r h od iu m (I) Tetr a p h en ylbor a te (3). A solution of bis(1-
pyrazolyl)methane (76 mg, 0.51 mmol) in methanol (5 mL) was
added to a solution of [Rh(CO)2Cl]2 (100 mg, 0.26 mmol) in
methanol (20 mL) at room temperature. The reaction mixture
was stirred for 1 h, and an excess of sodium tetraphenylborate
(150 mg) in methanol (5 mL) was added. The yellow solid that
precipitated was filtered immediately, as the solution began
to discolor, and washed with methanol. Recrystallization from
acetone produced fine yellow crystals of (bis(1-pyrazolyl)-
methane)dicarbonylrhodium(I) tetraphenylborate (3; 228 mg,
71%). Mp: 151-152 °C dec. 1H NMR (400 MHz, tetrahydro-
furan-d8): δ 7.88 (d, 2H, H5), 7.36 (m, 10H, H3 and o-H), 6.86
(t, 8H, m-H), 6.73 (t, 4H, p-H), 6.36 (t, 2H, H4), 5.25 (br(s),
2H, CH2) ppm. 13C{1H} NMR (100 MHz, tetrahydrofuran-d8):
Among the limited set of counterions examined, there
is a trend toward increased reactivity with the bulkier,
less coordinating anions. This trend suggests that
catalytic activity may well be improved by further
reducing the coordinating ability of the anions in
solution. On the other hand, the stabilizing effect of
suitable anions undoubtedly influences the chemical
stability of the catalyst and, in practical terms, in-
creased reactivity may have to be balanced against the
convenience of handling a relatively stable catalyst
system.
Exp er im en ta l Section
1
δ 183.4 (d, J Rh-CO ) 70 Hz, Rh-CO), 165.7-164.3 (m, B-C),
All manipulations of metal complexes and air-sensitive
reagents were carried out using standard Schlenk, high-
vacuum, and glovebox techniques. Air-sensitive NMR samples
were prepared in a nitrogen-filled glovebox with the solvent
being vacuum-transferred into an NMR tube fitted with a
concentric Teflon valve.
147.2 (C5), 137.1 (o-C), 135.7 (C3), 126.2 (m-C), 122.3 (p-C),
109.0 (C4), 63.2 (CH2) ppm. IR (KBr): ν 2093 (Rh-CO), 2032
(Rh-CO) cm-1. Anal. Found: C, 63.5; H, 4.7; N, 9.1. Calcd for
C
33H28BN4O2Rh: C, 63.3; H, 4.5; N, 8.9.
(30) McCleverty, J . A.; Wilkinson, G. Inorg. Synth. 1991, 28, 84.
(31) Herde, J . L.; Lambert, J . C.; Senoff, C. V. Inorg. Synth. 1974,
15, 18.
All organic starting materials were obtained from Aldrich
Chemical Co. Inc. Rhodium(III) trichloride hydrate was ob-

Hydroamination Catalyzed by Rh and Ir Complexes
Organometallics, Vol. 23, No. 8, 2004 1721
Syn th esis of (Bis(1-m eth ylim id a zol-2-yl)m eth a n e)d i-
ca r b on ylr h od iu m (I) H exa flu or op h osp h a t e, [R h (b im )-
(CO)2]+[P F 6]- (1b). A solution of bis(1-methylimidazol-2-yl)-
methane (80 mg, 0.45 mmol) in methanol (5 mL) was added
to a solution of [Rh(CO)2Cl]2 (88 mg, 0.22 mmol) in methanol
(15 mL) at room temperature. The yellow precipitate that
formed initially disappeared upon completion of ligand addi-
tion. The mixture was stirred for 30 min before adding an
excess of potassium hexafluorophosphate (400 mg) in methanol
(10 mL). The resulting precipitate was filtered and washed
with methanol. (Bis(1-methylimidazol-2-yl)methane)dicarbo-
nylrhodium(I) hexafluorophosphate (1b) was recrystallized
from acetone as a dark pink solid (191 mg, 90%). Mp: 262 °C
dec. Anal. Found: C, 27.6; H, 2.2; N, 11.4. Calcd for
C11H12F6N4O2PRh: C, 27.5; H, 2.5; N, 11.7. 1H NMR (400 MHz,
mol % of complex in approximately 0.5 mL of solvent under
nitrogen. The progress of the reaction was monitored by 1H
NMR at regular intervals. Reactions were carried out in
tetrahydrofuran-d8 at 60 °C.
The conversion of starting material to product was deter-
mined by integration of the product resonances relative to the
1
substrate peaks in the H NMR spectrum. A 100% conversion
was taken to be the time where no remaining substrate peaks
(<1%) were evident in the NMR. The turnover rate (Nt/h) was
calculated in units of (mol of product)/((mol of catalyst) h) and
was calculated at the point of 50% conversion of substrate to
product.
Cr ysta l Str u ctu r e Deter m in a tion . An approximately
prismatic fragment was cut from a large red crystal, coated
in oil, and sealed in a glass capillary. The crystal was then
mounted on a Rigaku AFC7R diffractometer employing graph-
ite-monochromated Cu KR radiation generated from a rotating
anode. Cell constants were obtained from a least-squares
refinement against 25 reflections located between 67 and 77°
2θ. Data were collected at 294(2) K with ω-2θ scans to 135°
2θ. The intensities of 3 standard reflections measured every
150 reflections did not change significantly during the data
collection. An empirical absorption correction based on azi-
muthal scans of 3 suitable reflections was applied to the data.
The data were corrected for Lorentz and polarization effects.
Processing and calculations were undertaken with TEXSAN.32
The structure was solved in the space group P21/c (No. 14) by
direct methods with SIR9733 and extended and refined with
SHELXL-97.34 Anisotropic thermal parameters were refined
for the non-hydrogen atoms of the structure model, and a
riding atom model was used for the hydrogen atoms.
3
acetone-d6): δ 7.55 (d, 2H, J H5-H4 ) 1.4 Hz, H5), 7.42 (d, 2H,
H4), 4.63 (s, 2H, CH2), 3.97 (s, 6H, N-CH3) ppm. 13C{1H} NMR
1
(100 MHz, acetone-d6): δ 185.3 (d, J Rh-CO ) 68.2 Hz, Rh-
CO), 143.9 (C2), 130.9 (C5), 124.3 (C4), 34.8 (N-CH3), 24.4
(CH2) ppm. 31P{1H} NMR (162 MHz, acetone-d6): -135 (sep,
J P-F ) 708 Hz. PF6) ppm. 19F NMR (377 MHz, acetone-d6):
-67.5 (d, J F-P ) 708 Hz, PF6) ppm. IR (KBr): ν 2084 (Rh-
CO), 2026 (Rh-CO) cm-1. MS (ES+): m/z 335 (100%, [Rh(bim)-
(CO)2]+).
Syn th esis of (Bis(1-m eth ylim id a zol-2-yl)m eth a n e)d i-
car bon ylr h odiu m (I) Tetr aflu or obor ate, [Rh (bim )(CO)2]+-
[BF 4]- (1c). A solution of bis(1-methylimidazol-2-yl)methane
(50 mg, 0.29 mmol) in methanol (5 mL) was added to a solution
of [Rh(CO)2Cl]2 (50 mg, 0.13 mmol) in methanol (10 mL) at
room temperature. The yellow precipitate that formed initially
disappeared upon completion of ligand addition. The mixture
was stirred for 1 h before an excess of sodium tetrafluoroborate
(45 mg, 0.41 mmol) in methanol (10 mL) was added. The
resulting precipitate was filtered and washed with methanol,
affording (bis(1-methylimidazol-2-yl)methane)dicarbonylrhod-
ium(I) tetrafluoroborate (1c) as a dark pink solid (78 mg, 71%).
Mp: 268 °C dec. Anal. Found: C, 31.1; H, 2.5; N, 13.1. Calcd
Ack n ow led gm en t. We gratefully acknowledge tech-
nical assistance from Dr. Warren Shaw (University of
Sydney) with the synthesis of [Rh(bpm)(CO)2]+[BPh4]-,
Sarah Wren for assistance, and financial support from
the Australian Research Council (ARC). We also wish
to acknowledge J ohnson Matthey for the generous loan
of metal precursors.
1
for C11H12BF4N4O2Rh: C, 31.3; H, 2.9; N, 13.3. H NMR (400
MHz, dimethylformamide-d7): δ 7.62 (d, 2H, 3J H5-H4 ) 1.7 Hz,
H5), 7.41 (d, 2H, H4), 4.70 (s, 2H, CH2), 3.97 (s, 6H, N-CH3)
ppm. 13C{1H} NMR (100 MHz, dimethylformamide-d7): δ 185.5
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data are available as CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
(d, J Rh-CO ) 66.6 Hz, Rh-CO), 144.0 (C2), 130.9 (C5), 124.5
(C4), 34.5 (N-CH3), 24.4 (CH2) ppm. 11B NMR (128 MHz,
dimethylformamide-d7): 1.73 (br s, BF4) ppm. 19F NMR (377
MHz, dimethylformamide-d7): -146.3 (br s, BF4) ppm. IR
(KBr): ν 2080 (Rh-CO), 2025 (Rh-CO) cm-1. MS (ES+): m/z
335 (100%, [Rh(bim)(CO)2]+).
OM0343871
(32) teXsan for Windows: Single-Crystal Structure Analysis Soft-
ware; Molecular Structure Corp., 3200 Research Forest Drive, The
Woodlands, TX 77381, 1997-1998.
(33) Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A. J .
Appl. Crystallogr. 1993, 26, 343.
(34) Sheldrick, G. M. SHELXL97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
Gen er a l P r oced u r es for Mon itor in g Ca ta lytic Rea c-
tion s. Catalytic reactions were performed on a small scale in
an NMR tube fitted with a concentric Teflon valve. Reactions
were typically performed with 0.5 mmol of substrate and 1.5