Rhodium(I) and iridium(I) complexes with bidentate phosphine-pyrazolyl ligands: Highly efficient catalysts for the hydroamination reaction

Article abstract of DOI:10.1021/om070057v

A range of rhodium(I) and iridium(I) complexes containing bidentate phosphine-pyrazolyl ligands of general formulas [M(R₂PyP)(COD)] BPh₄ (R = Me, iPr, Ph, M = Ir, 3b-3d and M = Rh, 4b-4d), [Ir(R ₂PyP)(CO)₂]BPh₄ (R = Me, iPr, 5b,5c), and [M(R₂PyP)(CO)Cl] (R = Me, iPr, Ph, M = Ir, 6b-6d and M = Rh, 7b-7d) were successfully synthesized. A number of these complexes and their analogues with unsubstituted ligands are extremely active as catalysts for the intramolecular hydroamination of alkynes. The air-stable cationic iridium complexes containing 1,5-cyclooctadiene, COD, as co-ligands, [Ir(R ₂PyP)(COD)]BPh₄ (R = H, Me, iPr, and Ph, 3a-3d), are efficient as catalysts for the cyclization of 4-pentyn-1-amine (8) to 2-methyl-1-pyrroline (9) with the turnover rate at 50% conversion (N _t) of up to 3100 h^-1, at 60 °C. The cationic iridium complexes containing carbonyl co-ligands, [Ir(R₂PyP)(CO) ₂]-BPh₄ (R = H, Me, iPr, 5a-5c), are moderately effective in catalyzing this reaction, and the neutral complexes [M(R₂PyP)(CO) Cl] (M = Ir, 6a Ir, 7a) are ineffective. Generally, an increase in steric bulk of the substituent R near the nitrogen donor leads to an improvement in catalytic performance of the resulting metal complexes.

Full text of DOI:10.1021/om070057v

2058
Organometallics 2007, 26, 2058-2069
Rhodium(I) and Iridium(I) Complexes with Bidentate
Phosphine-Pyrazolyl Ligands: Highly Efficient Catalysts for the
Hydroamination Reaction
Leslie D. Field,† Barbara A. Messerle,*,† Khuong Q. Vuong,† Peter Turner,‡ and Tim Failes‡
School of Chemistry, UniVersity of New South Wales, Kensington, Sydney, NSW 2052, Australia, and
Crystal Structure Analysis Facility, School of Chemistry, UniVersity of Sydney, Camperdown,
Sydney, NSW 2006, Australia
ReceiVed January 18, 2007
A range of rhodium(I) and iridium(I) complexes containing bidentate phosphine-pyrazolyl ligands of
general formulas [M(R2PyP)(COD)]BPh4 (R ) Me, iPr, Ph, M ) Ir, 3b-3d and M ) Rh, 4b-4d),
[Ir(R2PyP)(CO)2]BPh4 (R ) Me, iPr, 5b,5c), and [M(R2PyP)(CO)Cl] (R ) Me, iPr, Ph, M ) Ir, 6b-6d
and M ) Rh, 7b-7d) were successfully synthesized. A number of these complexes and their analogues
with unsubstituted ligands are extremely active as catalysts for the intramolecular hydroamination of
alkynes. The air-stable cationic iridium complexes containing 1,5-cyclooctadiene, COD, as co-ligands,
[Ir(R2PyP)(COD)]BPh4 (R ) H, Me, iPr, and Ph, 3a-3d), are efficient as catalysts for the cyclization of
4-pentyn-1-amine (8) to 2-methyl-1-pyrroline (9) with the turnover rate at 50% conversion (Nt) of up to
3100 h-1, at 60 °C. The cationic iridium complexes containing carbonyl co-ligands, [Ir(R2PyP)(CO)2]-
BPh4 (R ) H, Me, iPr, 5a-5c), are moderately effective in catalyzing this reaction, and the neutral
complexes [M(R2PyP)(CO)Cl] (M ) Ir, 6a Ir, 7a) are ineffective. Generally, an increase in steric bulk
of the substituent R near the nitrogen donor leads to an improvement in catalytic performance of the
resulting metal complexes.
hydroboration.3-5,11 The chemistry of metal complexes with
bidentate ligands with mixed pyrazolyl-phosphine metal donors
has been, however, underexplored.12-18 Examples of the ap-
plication of pyrazolyl-phosphine donor ligands in homogeneous
catalysis include palladium-catalyzed hydration of terminal
alkynes,19 hydrosilylation of norbornene,20 allylic amination,14,21
Suzuki reactions,22 nickel-promoted polymerization,23 and rhod-
ium-catalyzed hydroboration.15,24
The hydroamination reaction of C-C double and triple bonds
has been of great interest academically and in industry due to
the central importance of amines and imines in organic
chemistry.25-28 Lanthanide29,30 and both early31,32and late transi-
tion metal33-38 complexes have been found to catalyze the
Introduction
Complexes containing hemilabile ligands have been used
successfully in a range of catalytic reactions, primarily due to
the ability of hemilabile ligands to liberate vacant coordination
sites as well as to stabilize reactive transition metal centers
during a catalytic cycle.1 A large number of metal complexes
containing potentially hemilabile hybrid bidentate P-N donor
ligands have been reported.1-3 These studies have mainly
focused on cases where the nitrogen donors are the sp2-N atom
from pyridines4,5 or oxazolines6,7 and the P-donors are phos-
phines. Many late transition metal complexes (e.g., Ru, Rh, Pd,
Ir) with mixed donor sp2-N-P ligands are efficient catalysts
for a range of organic transformations including allylic substitu-
tions,2,3,5 hydrogenation,3,6,8-10 transfer hydrogenation,4,10 and
(11) Carroll, A. M.; O’Sullivan, T. P.; Guiry, P. J. AdV. Synth. Catal.
2005, 347, 609-631.
(12) Grotjahn, D. B.; Combs, D.; Van, S.; Aguirre, G.; Ortega, F. Inorg.
Chem. 2000, 39, 2080-2086.
* Corresponding author. E-mail: b.messerle@unsw.edu.au. Fax: (+612)
93856141.
(13) Tanaka, S.; Dubs, C.; Inagaki, A.; Akita, M. Organometallics 2005,
24, 163-184.
† University of New South Wales.
‡ University of Sydney.
(14) Togni, A.; Burckhardt, U.; Gramlich, V.; Pregosin, P. S.; Salzmann,
R. J. Am. Chem. Soc. 1996, 118, 1031-1037.
(1) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48, 233-350.
(2) Gavrilov, K. N.; Polosukhin, A. I. Russ. Chem. ReV. 2000, 69, 721-
743.
(15) Schnyder, A.; Togni, A.; Wiesli, U. Organometallics 1997, 16, 255-
260.
(16) Caiazzo, A.; Dalili, S.; Yudin, A. K. Org. Lett. 2002, 4, 2597-
2600.
(3) Guiry, P. J.; Saunders, C. P. AdV. Synth. Catal. 2004, 346, 497-
537.
(17) Esquius, G.; Pons, J.; Ya´n˜ez, R.; Ros, J.; Mathieu, R.; Donnadieu,
B.; Lugan, N. Eur. J. Inorg. Chem. 2002, 2999-3006.
(18) Esquius, G.; Pons, J.; Ya´n˜ez, R.; Ros, J.; Mathieu, R.; Lugan, N.;
Donnadieu, B. J. Organomet. Chem. 2003, 667, 126-134.
(19) Grotjahn, D. B. U.S. Pat. Appl. Publ. (San Diego State University
Foundation), US2002115860, 2002.
(20) Pioda, G.; Togni, A. Tetrahedron: Asymmetry 1998, 9, 3903-3910.
(21) Burckhardt, U.; Baumann, M.; Trabesinger, G.; Gramlich, V.; Togni,
A. Organometallics 1997, 16, 5252-5259.
(22) Mukherjee, A.; Sarkar, A. Tetrahedron Lett. 2004, 45, 9525-9528.
(23) Mukherjee, A.; Subramanyam, U.; Puranik, V. G.; Mohandas, T.
P.; Sarkar, A. Eur. J. Inorg. Chem. 2005, 1254-1263.
(24) Schnyder, A.; Hintermann, L.; Togni, A. Angew. Chem., Int. Ed.
Engl. 1995, 34, 931-933.
(4) Espinet, P.; Soulantica, K. Coord. Chem. ReV. 1999, 195, 499-556.
(5) Chelucci, G.; Orru`, G.; Pinna, G. A. Tetrahedron 2003, 59, 9471-
9515.
(6) Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336-345.
(7) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680-
699.
(8) McIntyre, S.; Ho¨rmann, E.; Menges, F.; Smidt, S. P.; Pfaltz, A. AdV.
Synth. Catal. 2005, 347, 282-288.
(9) Pfaltz, A.; Blankenstein, J.; Hilgraf, R.; Ho¨rmann, E.; McIntyre, S.;
Menges, F.; Schonleber, M.; Smidt, S. P.; Wu¨stenberg, B.; Zimmermann,
N. AdV. Synth. Catal. 2003, 345, 33-43.
(10) Blaser, H. U.; Malan, C.; Pugin, B.; Spindler, F.; Steiner, H.; Studer,
M. AdV. Synth. Catal. 2003, 345, 103-151.
10.1021/om070057v CCC: $37.00 © 2007 American Chemical Society
Publication on Web 03/14/2007

Rhodium(I) and Iridium(I) Complexes
Organometallics, Vol. 26, No. 8, 2007 2059
Chart 1
hydroamination reactions of alkynes and alkenes. Organome-
tallic complexes with late transition metals offer the advantage
of being much less oxophilic when compared with lanthanide
and early transition metal complexes. Hydroamination catalysts
based on late transition metals are generally the most functional
group tolerant catalysts and do not normally require stringent
anaerobic conditions during the catalytic process.25-27
The intramolecular reaction leading to nitrogen-containing
heterocyclic products is a significant target since these hetero-
cycles are present in many biologically active compounds. The
intramolecular hydroamination of alkynes is more facile than
the equivalent reaction with allenes or alkenes and has been
achieved by a range of catalytic systems.25,27 Among the late
transition metal catalysts used for the intramolecular hydroami-
nation of alkynes, palladium is now the most widely used metal,
particularly in the construction of the aromatic indole nu-
cleus.27,39-41 The intramolecular hydroamination of aliphatic
amino-alkynes using palladium complexes as catalysts presents
different challenges and is less extensively studied.34,40-43 The
use of other late transition metal complexes as catalysts for the
intramolecular hydroamination of alkynes has received increased
attention recently with the focus mainly on second- and third-
row metals of groups VIII, X, and XI.35,37,42 A few examples
of using platinum,44 silver,45 and gold46 complexes as catalysts
for the intramolecular hydroamination of alkynes have also been
reported.
Scheme 1
on hydroamination, we have reported that rhodium and iridium
complexes containing bidentate bis-pyrazolyl, bis-imidazolyl,
bis-N-heterocyclic carbene (NHC), or mixed phosphine-NHC
donor ligands48-52 are effective catalysts for the intramolecular
hydroamination of aliphatic and aromatic alkynes, and the
efficiency of the catalyst changes significantly even with a small
change in the ligand donor set.49,53,54 We have also previously
reported the synthesis of rhodium and iridium complexes
containing the unsubstituted bidentate phosphine-pyrazolyl
donor ligand 1-[(2-diphenylphosphinoethyl)]pyrazole, PyP, and
their applications as catalysts for the hydrothiolation55 and
double-hydroalkoxylation56 of alkynes.54 In this paper, we report
the synthesis of a range of rhodium and iridum complexes
containing modified phosphine-pyrazolyl donor ligands with
systematic variations of substituents on the 3 and 5 positions
of the pyrazolyl ring (Chart 1). The efficiency of metal
complexes containing the R2PyP (R ) H, Me, iPr, and Ph;
2a-2d) ligands as catalysts for the cyclization of 4-pentyn-1-
amine (8) to 2-methyl-1-pyrroline (9) is explored, and some
extremely efficient catalysts are identified.
Rhodium and iridium complexes have not been extensively
studied for the intramolecular hydroamination of alkynes, and
the development of highly efficient group IX catalysts for
hydroamination remains an important goal.27,35,47 In our work
(25) Brunet, J. J.; Neibecker, D. In Catalytic Heterofunctionalization;
Togni, A., Gru¨tzmacher, H., Eds.; Wiley-VCH: Weinheim, 2001; pp 91-
141, and references therein.
(26) Mu¨ller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675-703, and
references therein.
(27) Alonso, F.; Beletskaya, I. P.; Yus, M. Chem. ReV. 2004, 104, 3079-
3159, and references therein.
(28) Hultzsch, K. C. AdV. Synth. Catal. 2005, 347, 367-391, and
references therein.
(29) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673-686, and
references therein.
(30) Molander, G. A.; Romero, J. A. C. Chem. ReV. 2002, 102, 2161-
2185.
(31) Pohlki, F.; Doye, S. Chem. Soc. ReV. 2003, 32, 104-114, and
references therein.
(32) Odom, A. L. Dalton Trans. 2005, 225-233, and references therein.
(33) Hartwig, J. F. Pure Appl. Chem. 2004, 76, 507-516.
(34) Lutete, L. M.; Kadota, I.; Yamamoto, Y. J. Am. Chem. Soc. 2004,
126, 1622-1623.
(35) Mu¨ller, T. E.; Pleier, A.-K. J. Chem. Soc., Dalton Trans. 1999, 583-
587.
Results and Discussion
Synthesis of Phosphine-Pyrazolyl Ligands. The bidentate
phosphine-pyrazolyl ligands R2PyP (Me, 2b; iPr, 2c; Ph, 2d)
were synthesized using a two-step sequence (Scheme 1)
analogous to that used in the synthesis of 1-[(2-diphenylphos-
phinoethyl)]pyrazole, PyP, 2a.55 The first step involved the
(36) Hartung, C. G.; Tillack, A.; Trauthwein, H.; Beller, M. J. Org. Chem.
2001, 66, 6339-6343.
(37) Kondo, T.; Okada, T.; Suzuki, T.; Mitsudo, T. J. Organomet. Chem.
2001, 622, 149-154.
(38) Brunet, J. J.; Cadena, M.; Chu, N. C.; Diallo, O.; Jacob, K.; Mothes,
E. Organometallics 2004, 23, 1264-1268.
(39) Wolfe, J. P.; Thomas, J. S. Curr. Org. Chem. 2005, 9, 625-655.
(40) Cacchi, S.; Fabrizi, G. Chem. ReV. 2005, 105, 2873-2920.
(41) Nakamura, I.; Yamamoto, Y. Chem. ReV. 2004, 104, 2127-2198,
and references therein.
(48) Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner, P. Organo-
metallics 2005, 24, 4241-4250.
(49) Burling, S.; Field, L. D.; Messerle, B. A.; Turner, P. Organometallics
2004, 23, 1714-1721.
(42) Mu¨ller, T. E.; Grosche, M.; Herdtweck, E.; Pleier, A. K.; Walter,
E.; Yan, Y.-K. Organometallics 2000, 19, 170-183.
(43) Richmond, M. K.; Scott, S. L.; Alper, H. J. Am. Chem. Soc. 2001,
123, 10521-10525.
(44) Krogstad, D. A.; Owens, S. B.; Halfen, J. A.; Young, V. G., Jr.
Inorg. Chem. Commun. 2005, 8, 65-69.
(50) Burling, S.; Field, L. D.; Li, H. L.; Messerle, B. A.; Shasha, A.
Aust. J. Chem. 2004, 57, 677-680.
(51) Burling, S.; Field, L. D.; Li, H. L.; Messerle, B. A.; Turner, P. Eur.
J. Inorg. Chem. 2003, 3179-3184.
(52) Burling, S.; Field, L. D.; Messerle, B. A. Organometallics 2000,
19, 87-90.
(45) van Esseveldt, B. C. J.; Vervoort, P. W. H.; van Delft, F. L.; Rutjes,
F. P. J. T. J. Org. Chem. 2005, 70, 1791-1795.
(46) Hoffmann-Ro¨der, A.; Krause, N. Org. Biomol. Chem. 2005, 3, 387-
391.
(47) Penzien, J.; Su, R. Q.; Mu¨ller, T. E. J. Mol. Catal. A: Chem. 2002,
182, 489-498.
(53) Burling, S. Ph.D. Thesis, University of Sydney, 2001.
(54) Vuong, K. Q. Ph.D. Thesis, University of New South Wales, 2006.
(55) Burling, S.; Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner, P.
Dalton Trans. 2003, 4181-4191.
(56) Messerle, B. A.; Vuong, K. Q. Pure Appl. Chem. 2006, 78, 385-
390.

2060 Organometallics, Vol. 26, No. 8, 2007
Field et al.
Scheme 2
formation of the bromo intermediates (1a-1d) in a biphasic
reaction between the appropriate pyrazole, sodium hydroxide,
and 1,2-dibromoethane (1,2-DBE) with tetrabutylammonium
bromide (TBAB) as the phase transfer catalyst.57 As the steric
bulk of the R groups increased, higher temperatures were
required for the reaction to proceed. Small quantities of bis-
(pyrazolyl)ethane ((3,5-R2PyCH2)2, where R ) H, Me, and iPr)
were also formed.57 The yield of the bis(pyrazolyl)ethane
increased for R ) H < Me < iPr, but none of the bis(pyrazolyl)-
ethane byproduct was observed in the reaction of 3,5-diphen-
ylpyrazole.
In step 2 of Scheme 1, nucleophilic substitution of the
bromide with the diphenylphosphide afforded the final product
R2PyP as an oxygen-sensitive viscous oil (R ) Me, 2b; iPr,
2c) or waxy solid (R ) H, 2a; Ph, 2d) in approximately 80%
yield. The 31P{1H} NMR (C6D6) spectra of the final products
show a singlet in the region -20 to -22 ppm, which is typical
for alkyldiarylphosphines.58
Figure 1. ORTEP depiction of the cationic fragment of [Ir(Me2-
PyP)(COD)]BPh4 (3b) at 20% thermal ellipsoids for the non-
hydrogen atoms. Selected bond lengths (Å) and angles (deg): Ir(1)-
P(1) ) 2.2882(6); Ir(1)-N(1) ) 2.1045(16); Ir(1)-C(1) )
2.2072(2); Ir(1)-C(2) ) 2.33(2); Ir(1)-C(5) ) 2.132(7); Ir(1)-
C(6) ) 2.140(2); C(1)-C(2) ) 1.379(3); C(5)-C(6) ) 1.408(3);
P(1)-Ir(1)-N(1) ) 84.31(5); P(1)-Ir(1)-C(5) ) 93.73(7); P(1)-
Ir(1)-C(6) ) 95.99(6); N(1)-Ir(1)-C(1) ) 91.43(7); N(1)-Ir-
(1)-C(2) ) 96.69(8); C(1)-Ir(1)-C(6) ) 81.05(8); C(2)-Ir(1)-
C(5) ) 80.62(10); C(1)-Ir(1)-C(5) ) 96.92(9); C(2)-Ir(1)-C(6)
) 87.92(9).
Synthesis of Cationic Iridium and Rhodium Complexes
with R2PyP and 1,5-Cyclooctadiene as Co-ligands, [M(R2PyP)-
(COD)]BPh4 (M ) Rh, Ir). Cationic metal complexes of the
general formula [M(R2PyP)(COD)]BPh4 (R ) H, Me, iPr, Ph,
M ) Ir, 3a-3d and M ) Rh, 4a-4d) were synthesized by the
addition of a methanol solution of the ligand to a methanol
suspension/solution of the [M(µ-Cl)(COD)]2 (M ) Rh, Ir) metal
precursor at room temperature (Scheme 2). Sodium tetraphen-
ylborate was added to precipitate the metal complex. While other
solvents, e.g., tetrahydrofuran, could also be used in the synthesis
of these metal complexes,55 methanol is more convenient due
to the lower solubility of the product and the ease with which
the sodium chloride byproduct can be washed away. All of the
metal complexes were isolated in good to excellent yields. The
color of all of the rhodium complexes is bright yellow, and the
color of all of the iridium analogues is bright orange. The metal
complexes 3a-4d are all reasonably air stable, so that samples
in the solid state can be handled in air with no apparent
decomposition.
We have previously reported the solid-state structures of
[M(PyP)(COD)]BPh4 (M ) Ir, 3a; Rh, 4a).55 Single crystals of
[Ir(Me2PyP)(COD)]BPh4 (3b), suitable for X-ray crystallogra-
phy, were obtained by vapor diffusion of n-hexane to a THF
solution of the complex. The solid-state structure of 3b as
determined by X-ray crystallography is shown in Figure 1 and
is similar to the structure of 3a and 4a.55
The coordination around the iridium center of 3b is square
planar. In the solid-state structures of 3a and 4a the bite angles
of 89.47(6)° and 88.86(4)° respectively for P(1)-M(1)-N(1)
(M ) Ir, Rh)55 are close to the ideal angle of 90° expected for
square planar complexes, which implies a very low level of
ring strain upon chelation of the PyP (2a) ligand. The rather
acute bite angle of 84.31(5)° for [Ir(Me2PyP)(COD)]BPh4 (3b)
is very similar to the value of 82.68(5)° reported by Esquius et
al.17 for the analogous rhodium complex [Rh(Me2PyP)(COD)]-
BF4. The deviation from the ideal value of 90° is probably due
to steric effects imposed by the CH3 group interacting with the
COD ligand in 3b and [Rh(Me2PyP)(COD)]BF4.
All of the six-membered metallacycles defined by M(1),
Na(1), N(2), C(12), C(13), and P(1) in 3a, 4a,55 and 3b adopt
pseudoboat conformations. Similar pseudoboat conformations
have also been observed in the reported X-ray structures of
related complexes.17,62 All of the M-N, M-P, and M-C bond
distances (M ) Ir, Rh, Table 2) are within the range reported
in the literature for similar complexes.17,59,61-63
Synthesis of Cationic Iridium Complexes with R2PyP
Ligands and Carbonyls as Co-ligands, [Ir(R2PyP)(CO)2]-
BPh4. The cationic iridium(I) complexes [Ir(R2PyP)(CO)2]BPh4
Multinuclear (1H, 13C, and 31P) and two-dimensional (COSY,
NOESY, 1H-13C HMQC, and, in some cases, 1H-13C HMBC)
NMR spectroscopy was used to establish the solution structures
of the metal complexes 3a-4d. In many cases, the complexes
are fluxional at room temperature and it was necessary to obtain
the NMR spectra at low temperature to slow the chemical
1
exchange. The chemical shifts and JRh-P coupling constants
are similar to those reported for other similar rhodium15,17 and
iridium59-61complexes with bidentate P-N ligands where six-
membered metallacycles are formed upon chelation.
(57) Lo´pez, P.; Seipelt, C. G.; Merkling, P.; Sturz, L.; AÄ lvarez, J.; Do¨lle,
A.; Zeidler, M. D.; Cerda´n, S.; Ballesteros, P. Bioorg. Med. Chem. 1999,
7, 517-527.
(58) Davies, J. A.; Mierzwiak, J. G.; Syed, R. J. Coord. Chem. 1988,
17, 25-43.
(59) Hou, D. R.; Reibenspies, J.; Colacot, T. J.; Burgess, K. Chem. Eur.
J. 2001, 7, 5391-5400.
(60) Lightfoot, A.; Schnider, P.; Pfaltz, A. Angew. Chem., Int. Ed. 1998,
37, 2897-2899.
(62) Anderson, M. P.; Casalnuovo, A. L.; Johnson, B. J.; Mattson, B.
M.; Mueting, A. M.; Pignolet, L. H. Inorg. Chem. 1988, 27, 1649-1658.
(63) Yang, H.; Lugan, N.; Mathieu, R. Organometallics 1997, 16, 2089-
2095.
(61) Menges, F.; Neuburger, M.; Pfaltz, A. Org. Lett. 2002, 4, 4713-
4716.

Rhodium(I) and Iridium(I) Complexes
Organometallics, Vol. 26, No. 8, 2007 2061
Table 1. Infrared Carbonyl Stretching Frequencies,a 13C{1H} NMR (13CO Resonances), and 31P{1H} NMRb Chemical Shift
Data for Neutral [M(R2PyP)(CO)Cl] (M ) Rh, Ir) Complexes
iridium complex
ν(CO) (cm-1
)
13C (CO) ppm (2JP-C Hz)
31P ppm
[Ir(PyP)(CO)Cl] (6a)c
[Ir(Me2PyP)(CO)Cl] (6b)
[Ir(iPr2PyP)(CO)Cl] (6c)
[Ir(Ph2PyP)(CO)Cl] (6d)
1983
1968
1974
1949
174.4 (d, 13.8)
1175.8 (d, 12.6)
175.3 (d, 12.3)d
n/a
10.4
13.5
13.8
14.8
rhodium complex
ν(CO (cm-1
)
13C (CO) ppm (1JRh-C, 2JP-C Hz)
31P ppm (1JRh-P Hz)
[Rh(PyP)(CO)Cl] (7a)c
[Rh(Me2PyP)(CO)Cl] (7b)
[Rh(iPr2PyP)(CO)Cl] (7c)
[Rh(Ph2PyP)(CO)Cl] (7d)
1995
1980
1986
1980
188.7 (dd, 71.2, 18.2)
189.7 (dd, 72.7, 16.1)
189.7 (dd, 72.1, 17.0)
188.4 (dd, 73.3, 6.9)e
38.7 (165.5)
41.9 (163.8)
42.0 (163.8)
42.1 (164.5)e
b
c
a IR spectra were acquired using KBr disks. Spectra were acquired in CD2Cl2. Complexes 6a and 7a have been reported previously55 and were included
d
e
here for completeness. Spectra were acquired at 240 K. Spectra were acquired in CDCl3.
Table 2. Selected Bond Lengths and Anglesa of the Inner Coordination Spheres of [Ir(PyP)(CO)Cl] (6a), [Ir(Me2PyP)(CO)Cl]
(6b), [Ir(iPr2PyP)(CO)Cl] (6c), [Rh(PyP)(CO)Cl] (7a), [Rh(Me2PyP)(CO)Cl] (7b), and [Rh(iPr2PyP)(CO)Cl]BPh4 (7c)
atoms (M ) Rh, Ir)
6ab
6b
6c
7ab
7b
7c
M(1)-P(1)
2.2161(7)
2.119(2)
1.811(3)
2.3890(7)
1.146(3)
93.21(5)
88.28(5)
89.72(8)
88.88(8)
175.40(10)
178.14(2)
2.2120(17)
2.110(4)
1.806(6)
2.4005(17)
1.163(7)
86.77(13)
88.99(13)
92.48(19)
91.92(19)
178.1(2)
2.2206(7)
2.1018(19)
1.808(2)
2.3947(7)
1.159(3)
87.56(5)
90.90(6)
91.29(7)
90.56(7)
2.2150(7)
2.1233(18)
1.798(3)
2.3931(7)
1.146(3)
92.93(5)
89.76(5)
88.86(8)
88.58(8)
174.93(10)
176.96(2)
2.2206(5)
2.1138(14)
1.8079(18)
2.4030(5)
1.143(2)
81.83(4)
91.25(4)
93.98(6)
93.55(6)
2.2256(7)
2.1185(16)
1.816(2)
2.4154(7)
1.146(2)
87.52(5)
93.12(5)
89.68(6)
90.14(6)
M(1)-N(1)
M(1)-C(1)
M(1)-Cl(1)
C(1)-O(1)
P(1)-M(1)-N(1)
N(1)-M(1)-Cl(1)
Cl(1)-M(1)-C(1)
C(1)-M(1)-P(1)
N(1)-M(1)-C(1)
Cl(1)-M(1)-P(1)
176.20(8)
174.234(17)
175.35(7)
172.927(16)
175.06(7)
173.825(16)
172.07(6)
b
a Estimated standard deviations in the least significant figures are given in parentheses. The solid-state structures of 7a and 6a were reported previously55
and were included here for comparison.
Scheme 3
Figure 2. NMR spectra of [Ir(PyP)(13CO)2]BPh4 (5a′) in CD2Cl2.
(a) Carbonyl region of the 13C{1H} (125 MHz) spectra at 298 K
(R ) H, 5a; Me, 5b; iPr, 5c) were synthesized by the
displacement of COD from [Ir(R2PyP)(COD)]BPh4 (R ) H,
Me, iPr; 3a-3c) in methanol/n-hexane suspensions under an
atmosphere of carbon monoxide (Scheme 3) in the same manner
as used in the synthesis of [Ir(PyP)(CO)2]BPh4 (5a).55 Analogous
reactions with the iridium complex [Ir(Ph2PyP)(COD)]BPh4 (3d)
and rhodium complexes [Rh(R2PyP)(COD)]BPh4 (R ) H, 4a;
R ) Me, 4b) were not successful.
(bottom) and 215 K (top); (b) 31P{1H} (202 MHz) spectra at 298
K (bottom) and 215 K (top).
and a sharp resonance was observed in the 31P{1H} spectrum
at 11.4 ppm (dd, 2J13CO-P ) 104.2 Hz and 2J13CO-P ) 11.2 Hz)
(Figure 2). These observations indicate that at room temperature
the two carbonyl groups exchange with each other, possibly
via a solvent-stabilized five-coordinate transition state, and the
exchange is significantly slowed at 215 K. A similar exchange
process was observed for an analogous rhodium complex,
[Rh(PC)(13CO)2]BPh4, where PC ) 3-[2-(diphenylphosphino)-
ethyl]-1-methylimidazol-2-ylidene.48
Synthesis of Neutral Rhodium and Iridium Complexes
with R2PyP Ligands and Carbonyl and Chloride as Co-
ligands [M(R2PyP)(CO)Cl]. Neutral complexes of iridium
(6a-6d) and rhodium (7a-7d) were synthesized by slow
addition of a solution of the appropriate ligand to a solution of
[M(µ-Cl)(CO)2]2 (M ) Rh or Ir, Scheme 4). All of the
complexes were isolated as reasonably air-stable, pale yellow
solids.
Complexes 5a-5c were isolated as mildly air-sensitive bright
yellow solids. The IR spectra of 5a-5c show two strong
absorption bands of near equivalent intensity for the metal-bound
carbonyls, consistent with the presence of two CO groups bound
in a cis fashion to the metal center. Complexes 5a-5c, while
only mildly air sensitive, are unstable in solution at room
temperature, particularly, in coordinating solvents such as THF
or acetone. At room temperature, the 13C{1H} NMR (125 MHz,
CD2Cl2) spectrum of the 13CO-labeled complex [Ir(PyP)(13CO)2]-
BPh4 (5a′) contains two very broad resonances at 177.2 and
171.3 ppm due to the two 13CO groups, while resonances due
to other 13C nuclei in the complex are sharp, and the 31P{1H}
NMR (202 MHz, CD2Cl2) spectrum shows a broad resonance
that is devoid of any coupling to the two labeled carbonyls. At
The stereochemistry around all the metal centers of these
complexes has CO cis to P, i.e., trans to the N donor. The
assignment of this stereochemistry is based on the ν(CO)
2
215 K, relatively well-resolved resonances at 177.6 (d, JP-C
2
2
) 104.2 Hz,13CO (trans to P)) and 170.6 (d, JP-C ) 11.2
stretching frequencies in the IR spectra and the small JP-C
Hz,13CO (cis to P)) ppm were observed in the 13C{1H} spectrum,
values (<20 Hz) observed for all complexes (Table 1). The

2062 Organometallics, Vol. 26, No. 8, 2007
Field et al.
Scheme 4
Chart 2
ν(CO) values are in agreement with values reported in the
literature for analogous complexes whose stereochemistry had
been confirmed by X-ray crystallography.15,62 The CO 13C
chemical shifts of these complexes, 2JP-CO and 1JRh-CO (Table
2), are all in agreement with previously reported similar
complexes with the same stereochemistry.15,62 The observed
stereochemistry can be rationalized as being due to the place-
ment of the strongly π-accepting carbonyl ligand trans to the σ
donor N. The mixing of the orbitals involved in the binding of
these mutually trans ligands will best stabilize both the M-CO
and the M-N bonds.64
All of the metal complexes 6a-7d were characterized by
NMR spectroscopy. The NMR spectra of 6b-6d and 7b-7d
indicate that the molecules are fluxional at room temperature
due to ring flip of the six-membered metallacycle formed upon
chelation of the bidentate P-N ligand. Low-temperature NMR
was in these cases essential to undertake the full spectroscopic
characterization of the complexes (Figure 3).
Formation of Highly Symmetrical Dinuclear Neutral
Complexes. In the synthesis of neutral complexes 6a-7d, it
was essential that the ligand solution be added slowly for the
clean formation of the monomeric complex. If the rate of ligand
addition was not properly controlled, a mixture of two species,
the monomer as well as a possibly dimeric compound, was
formed (Chart 2, 7c′, 7d′, 7c′′, 7d′′). The formation of the second
species occurred more readily in the case of the rhodium
complexes than the iridium complexes and also occurred more
readily in the cases where the substituents on the pyrazole ring
were larger (R2PyP, R ) iPr, Ph). Changing the reaction solvent
from methanol to acetonitrile favored the formation of the
desired monomeric species. This was manifested most clearly
in the successful synthesis, in acetonitrile solvent, of the
monomeric complex [Rh(iPr2PyP)(CO)Cl] (7c), whose solid-
state structure was determined (see Figure 5).
The NMR, IR, and ESI-MS spectra and elemental analysis
do not confidently allow the unambiguous assignment of the
second species formed to either the neutral complexes 7c′ and
7d′ or the cationic complexes 7c′′ and 7d′′ (Chart 2). Because
of the very similar spectroscopic data obtained for the dimer in
comparison with the monomer, the most likely dimer formed
was 7c′ and 7d′. The low solubility of the dimer complexes in
methanol suggests that they are unlikely to be of the form of
the cationic complexes 7c′′ and 7d′′.
Solid-State Structures of [M(Me2PyP)(CO)Cl] (M ) Ir,
6b; Rh, 7b) and [M(iPr2PyP)(CO)Cl] (M ) Ir, 6c; Rh, 7c).
Crystals of [M(Me2PyP)(CO)Cl] (M ) Rh, 6b; Ir, 7b) and
[M(iPr2PyP)(CO)Cl] (M ) Rh, 6c; Ir, 7c) suitable for X-ray
analysis were obtained by layering a concentrated dichlo-
romethane (dcm) or dcm-d2 solution of the complexes with
diethyl ether, n-pentane, or n-hexane. The ORTEP diagrams
containing the atom-numbering schemes are shown in Figures
4 (6b and 7b) and 5 (6c and 7c), with selected bond lengths
and bond angles presented in Table 2.
The solid-state structures unequivocally confirm the mono-
meric nature of these metal complexes, and similar monomeric
structures could be assigned to the equivalent complexes
reported here on the basis of the similarity in spectroscopic data.
The solid-state structures of 6a,55 6b, 6c and 7a,55 7b, 7c are
all similar, with the coordination spheres around the metal
centers being slightly distorted square planar. The phosphorus
and the CO ligands are positioned cis on the metal center, as
was also observed for the solution structure using NMR.
All of the six-membered metallacycles defined by P(1)-
C(6)-C(5)-N(2)-N(1)-M(1) adopt a similar highly distorted
boat conformation in comparison to the conformation adopted
in the equivalent cationic metal complexes with a COD co-
ligand, 3a, 4a,55 and 3b. The P(1)-M(1)-N(1) (M ) Rh and
Ir) angles varied from 81.8° to 93.2° (Table 2) and decreased
with the placement of substituents on the pyrazolyl ring of the
ligand. These bite angles are similar to values reported in the
literature for similar metal complexes.15,62 All of the remaining
cis angles are close to the ideal orthogonal angles and fall within
the range 88.3-94.0°. These cis angles increase with the
increasing steric bulk of the pyrazolyl-C3/C5 substituents. The
trans P-M-Cl and N-M-C angles ranging from 172° to 178°
(Table 2) deviate more from the ideal value of 180° for square
planar geometry as the size of the pyrazolyl-C3/C5 substituents
increases. All the M-P, M-N, M-Cl, and M-C bond lengths
(M ) Ir, Rh) are within the reported values for similar
Figure 3. 1H NMR spectra (500 MHz, CD2Cl2) of [Ir(iPr2PyP)-
(CO)Cl] (6c) at (a) 298 K and (b) 240 K (* denotes the residual
solvent resonance).
(64) Roundhill, D. M.; Bechtold, R. A.; Roundhill, S. G. N. Inorg. Chem.
1980, 19, 284-289.

Rhodium(I) and Iridium(I) Complexes
Organometallics, Vol. 26, No. 8, 2007 2063
Figure 5. ORTEP depictions with atom-numbering schemes of
(a) [Ir(iPr2PyP)(CO)Cl] (6c) and (b) [Rh(iPr2PyP)(CO)Cl] (7c) at
50% thermal ellipsoids for the non-hydrogen atoms.
Scheme 5
Figure 4. ORTEP depictions with atom-numbering schemes of
(a) [Ir(Me2PyP)(CO)Cl] (6b) and (b) [Rh(Me2PyP)(CO)Cl] (7b)
at 50% thermal ellipsoids for the non-hydrogen atoms.
complexes.15,62 The M-P bond lengths were observed to be
shorter than those found in the equivalent cationic complexes
with the COD co-ligand.
the intramolecular catalyzed hydroamination reaction37,42,49,65,66
and provides a good basis for comparison of catalyst efficiency.
Catalyzed Cyclization Using Iridium Cationic Complexes
with Bidentate Phosphine-Pyrazolyl Ligands and COD as
Co-ligands, [Ir(R2PyP)(COD)]BPh4 (3a-3d). The cationic
iridium complexes [Ir(R2PyP)(COD)]BPh4 (3a-3d) were ex-
tremely efficient catalysts for the cyclization of 4-pentyn-1-
amine (8) to 2-methyl-1-pyrroline (9). Using a catalyst loading
of 1.2-1.5 mol % in CDCl3 at 60 °C, the cyclization of 8 to 9
was complete within minutes. The calculated turnover rates at
50% conversions (Nt) range from 1200 to 3100 h-1 (Table 3).
A similar Nt value was also observed when the cyclization using
[Ir(PyP)(COD)]BPh4 (3a) was conducted in THF-d8. These
turnover rates are significantly higher than any of the rates
reported to date for late transition metal complexes in promoting
the cyclization of 4-pentyn-1-amine (8).37,42,66-68
The M-N bond lengths in the solid-state structures of the
neutral complexes [M(R2PyP)(CO)Cl] (M ) Ir, R ) Me, 6b
and R ) iPr, 6c; M ) Rh, R ) Me, 7b and R ) iPr, 7c) were
slightly shorter than the M-N bond lengths in the solid-state
structure of the complexes containing the unsubstituted phos-
phine-pyrazolyl ligand, [M(PyP)(CO)Cl] (M ) Ir, 6a and M
) Rh, 7a) (see Table 2). This was attributed to the stronger
donor ability of the methyl- and isopropyl-substituted pyrazolyl
donors resulting from the electron-donating properties of the
methyl and isopropyl groups.
Catalytic Intramolecular Hydroamination. A range of the
iridium and rhodium cationic, [M(R2PyP)(COD)]BPh4 and
[M(R2PyP)(CO2)]BPh4, and neutral, [M(R2PyP)(CO)Cl], com-
plexes described above were examined as catalysts for intramo-
lecular hydroamination, by studying the cyclization of 4-pentyn-
1-amine (8) to 2-methyl-1-pyrroline (9) (Scheme 5). 4-Pentyn-
1-amine has been widely used as a substrate for studying
(65) Panda, T. K.; Zulys, A.; Gainer, M. T.; Roesky, P. W. Organome-
tallics 2005, 24, 2197-2202.
(66) Li, Y.-W.; Marks, T. J. J. Am. Chem. Soc. 1996, 118, 9295-9306.

2064 Organometallics, Vol. 26, No. 8, 2007
Field et al.
Table 3. Catalytic Efficiency of Cationic Iridium Complexes
[Ir(R2PyP)(COD)]BPh4 (R ) H, 3a; Me, 3b; iPr, 3c; and Ph,
3d) for the Cyclization of 4-Pentyn-1-amine (8) to
2-Methyl-1-pyrroline (9)a
time (h) at
>98% conv
b
complex
mol %
Nt (h-1
)
[Ir(PyP)(COD)]BPh4 (3a)c
[Ir(PyP)(COD)]BPh4 (3a)
[Ir(PyP)(COD)]BPh4 (3b)
[Ir(Me2PyP)(COD)]BPh4 (3c)
[Ir(Ph2PyP)(COD)]BPh4 (3d)
[Ir(PyP)(COD)]BPh4 (3a)d
1.4
1.4
1.2
1.4
1.5
1.5
1800
1200
2250
3100
1800
400
0.50
1.50
0.25
0.17
0.20
1.00
b
a Reactions were performed in CDCl3 at 60 °C. Nt (at 50% conversion)
are estimated from time course profiles (see Supporting Information).
d
c Reactions were performed in THF-d8 at 60 °C. Reaction was performed
in CDCl3 at room temperature.
The Nt values for cyclization promoted by [Ir(R2PyP)(COD)]-
BPh4 (3a-3d) vary with the substituents on the pyrazolyl donor
following the trend iPr > Me > Ph > H; that is, an increase in
the steric bulk of R correlates with an increase in catalytic
activity of the resulting metal complexes. This observation
suggests that the catalyst efficiency is specifically dependent
on crowding at the metal center.
At an early stage of the cyclization of 4-pentyn-1-amine (8)
to 2-methyl-1-pyrroline (9) catalyzed by [Ir(R2PyP)(COD)]BPh4
(R ) H, 3a; Me, 3b), the dissociation of the COD co-ligand
was observed. Resonances due to free COD were observed in
1
the H NMR spectra, and ESI-MS performed on the reaction
mixtures on completion of the catalytic reactions showed the
presence of ions corresponding to the iridium catalyst with
product molecules bound to [Ir(R2PyP)(2-methyl-1-pyrroline)n]+
(n ) 1-3, R ) H and Me), further confirming the dissocia-
tion of the COD co-ligand. This suggests that the loss of COD
may be necessary to form the catalytically active species and
also that the product could become involved in the catalytic
cycle.
Figure 6. Reaction profile of the [Ir(Me2PyP)(COD)]BPh4 (3b)
([) (1.2 mol % in CDCl3 at 60 °C) catalyzed cyclization of
4-pentyn-1-amine to 2-methyl-1-pyrroline with the addition of a
second (at 100% conversion) and third (at 198% conversion) aliquot
of the amine.
Catalyst Lifetime. The lifetime of the highly active catalyst
[Ir(PyP)(COD)]BPh4 (3a) in promoting the cyclization of
4-pentyn-1-amine to 2-methyl-1-pyrroline (at 1.4 mol %, in
THF-d8 at 60 °C) was investigated by the addition of a second
aliquot of substrate after the complete conversion of the first
aliquot of substrate to product, as observed by 1H NMR
spectroscopy, and the catalyst 3a remained highly active in
promoting the transformation of 8 to 9. Where the turnover rate,
first to the second addition of substrate was only approximately
2-fold. The turnover rate for the third substrate aliquot was found
to be 20-fold lower than the rate observed for the second aliquot
of substrate. The result here illustrates that the catalyst 3b has
a reasonably long lifetime at low catalyst loading (1.2 mol %),
even though the catalytic efficiency decreases slowly through
either deactivation of the catalyst or product inhibition of the
cyclization reaction.
In short, air-stable metal complexes [Ir(R2PyP)(COD)]BPh4
(R ) H, Me, iPr, Ph; 3a-3d) were demonstrated to be extremely
efficient as catalysts for the intramolecular hydroamination of
alkynes using 4-pentyn-1-amine (8) as the model substrate.
These catalysts were also demonstrated to have long lifetimes
with near quantitative conversion achieved for three consecutive
additions of substrate. The catalyst [Ir(PyP)(COD)]BPh4 (3a)
is highly reactive even at room temperature.
Catalyzed Cyclization Using Cationic Rhodium Complex
[Rh(PyP)(COD)]BPh4 (4a). The efficiency of rhodium complex
[Rh(PyP)(COD)]BPh4 (4a) in promoting the intramolecular
hydroamination of 4-pentyn-1-amine (8) was also investigated.
In contrast with the high activity shown for the iridium analogue
3a, the turnover rate observed using rhodium complex 4a for
the cyclization of 8 was only 3 h-1. The reaction was incomplete
even after 3 days at 60 °C.
Nt, for first aliquot of substrate was approximately 1800 h-1
,
the Nt for the second aliquot was, however, about 6-fold less at
300 h-1. The rate of cyclization for the second addition of
substrate also slowed significantly after reaching about 80%
conversion (180% total conversion), and complete conversion
was reached only after approximately 600 min. The observed
decrease in turnover rate with time is attributed to product
inhibition, as has been established using closely related com-
plexes as catalysts for the transformation of the same sub-
strate.49,53 The product, 2-methylpyrroline, competitively inhibits
the reaction, and as its concentration builds up in the reaction
mixture, the catalyst efficiency decreases.
In a similar fashion, a second and third aliquot of substrate
were added into the [Ir(Me2PyP)(COD)]BPh4 (3b)-promoted
cyclization of 8 (Figure 6). The reaction profile and the turnover
rates, Nt, clearly show that the rates decrease with subsequent
additions of aliquots of substrate. The decrease in Nt from the
(67) McGrane, P. L.; Livinghouse, T. J. Am. Chem. Soc. 1993, 115,
11485-11489.
(68) Bu¨rgstein, M. R.; Berberich, H.; Roesky, P. W. Chem.-Eur. J. 2001,
7, 3078-3085.

Rhodium(I) and Iridium(I) Complexes
Organometallics, Vol. 26, No. 8, 2007 2065
Table 4. Catalytic Efficiency of [Ir(R2PyP)(CO)2]BPh4 (R )
H, 5a; Me, 5b; and iPr, 5c) and [Ir(bpm)(CO)2]BPh4 for the
Catalyzed Cyclization of 4-Pentyn-1-amine to
2-Methyl-1-pyrrolinea
conversion after 14.0 h) as the solvent. The neutral rhodium
complex [Rh(PyP)(CO)Cl] (7a) was also found to be ineffective
in catalyzing the cyclization of 8 (1.5 mol %, CDCl3, 60 °C,
72% conversion after 45 h).
time (h) at
>98% conv
In comparing the efficiency of all three iridium complexes
with the phosphine-pyrazolyl bidentate ligand PyP (2a) and
different co-ligands [Ir(PyP)(COD)]BPh4 (3a), [Ir(PyP)(CO)2]-
BPh4 (5a), and [Ir(PyP)(CO)Cl] (6a) as catalysts for the
cyclization of 4-pentyn-1-amine (8), it was found that (i) the
cationic complex [Ir(PyP)(COD)]BPh4 (3a) with a COD co-
ligand was extremely efficient in catalyzing the cyclization of
8; (ii) the cationic complex [Ir(PyP)(CO)2]BPh4 (5a) with
carbonyls as co-ligands is much less efficient when compared
with 3a but is still able to promote the complete conversion of
8 to 2-methyl-1-pyrroline (9) with reasonable efficiency; and
(iii) the neutral complex [Ir(PyP)(CO)Cl] (6a) is not an effective
catalyst for promoting this transformation.
catalyst
mol %
Nt (h-1
)
[Ir(PyP)(CO)2]BPh4 (5a)
1.3
1.5
1.5
1.5
11
35
26
50
38.0
11.0
10.5
2.2
[Ir(Me2PyP)(CO)2]BPh4 (5b)
[Ir(iPr2PyP)(CO)2]BPh4 (5c)
b
[Ir(bpm)(CO)2]BPh4
b
a Reactions were performed in CDCl3 at 60 °C. The reaction was
performed in THF-d8 by Burling, S.49
Catalyzed Cyclization Using Cationic Iridium Complexes
with Bidentate Phosphine-Pyrazolyl Ligands and Carbonyls
as Co-ligands. The efficiency of a series of iridium complexes
[Ir(R2PyP)(CO)2]BPh4 (R ) H, 5a; Me, 5b; iPr, 5c) as catalysts
for the catalyzed cyclization of 4-pentyn-1-amine (8) to 2-meth-
yl-1-pyrroline (9) was also investigated (Table 4). Complete
conversions of substrate to product were achieved in all cases.
The complexes 5a-5c are however much less efficient when
compared with the catalytic activity of the analogous complexes
having COD as co-ligands, [Ir(R2PyP)(COD)]BPh4 (3a-3d)
(Table 4).
Conclusions
This paper reports the synthesis of a series of bidentate
phosphine-pyrazolyl donor ligands and some cationic and
neutral complexes [M(R2PyP)(COD)]BPh4 (M ) Ir and Rh, R
) Me, iPr, and Ph, 3a-4d), [Ir(R2PyP)(CO)2]BPh4 (R ) Me,
iPr, and Ph; 5a-5c), and [M(R2PyP)(CO)Cl] (M ) Ir and Rh,
R ) Me, iPr, and Ph 6a-7d). The solid-state structures of
complexes [Ir(Me2PyP)(COD)]BPh4 (3b), [M(Me2PyP)(CO)-
Cl] (M ) Ir, 6b; Rh, 7b), and [M(iPr2PyP)(CO)Cl] (M ) Ir,
6c; Rh, 7c) were determined by single-crystal diffraction
analysis. In all of these structures the coordination around the
metal center is square planar, as expected for four-coordinate
Rh(I) and Ir(I) complexes. In all cases, the metallacycles formed
upon chelation of bidentate phosphine-pyrazolyl donor ligands
adopt distorted boat conformations.
The cationic iridium complexes with phosphine-pyrazolyl
donor ligands and a COD co-ligand [Ir(R2PyP)(COD)]BPh4
(3a-3d) are very efficient in promoting the cyclization of 8 to
9 under mild conditions and are among the most efficient
catalysts reported in the literature to date for the same
transformation. These complexes also have long catalytic
lifetimes and are effective even at ambient temperature. The
high efficiency of [Ir(R2PyP)(COD)]BPh4 (3a-3d) is undoubt-
edly the result of a balance of both electronic and steric factors
brought about from the choice of the metal, ligand, co-ligand,
counterion, and substrate. The scope of applications of these
complexes as general catalysts for hydroamination and mecha-
nistic studies of the hydroamination reaction using these catalysts
are underway in our laboratory.
The effect of the systematic modification of the pyrazolyl
donor of the phosphine-pyrazolyl donor ligands on the catalytic
efficiency for the hydroamination of 4-pentyn-1-amine of the
resulting metal complexes has been demonstrated. Placing
sterically demanding substituents (R) on the pyrazolyl ring of
bidentate phosphine-pyrazolyl ligands in complexes [Ir(R2PyP)-
(COD)]BPh4 (3a-3d) varied the relative catalyst efficiency
following the trend iPr > Me > Ph > H. An increase in the
steric bulk of R correlates directly with an increase in catalytic
activity of the resulting metal complexes. The cationic iridium
complexes with COD as the co-ligand, [Ir(R2PyP)(COD)]BPh4,
were much more efficient than the corresponding complexes
with CO co-ligands.
The presence of bulky R substituents on the pyrazolyl ring
of the bidentate ligands R2PyP (R ) 2a; R ) Me, 2b; R ) iPr,
2c) significantly alters the catalytic reactivity of the resulting
metal complexes [Ir(R2PyP)(CO)2]BPh4 (5a-5c) for the cy-
clization of 4-pentyn-1-amine (8). As the substituent on the
pyrazolyl ring of the phosphine-pyrazolyl ligands R2PyP of
[Ir(R2PyP)(CO)2]BPh4 changes from R ) H to R ) Me, the
turnover rate (Nt) increased by a factor of more than 3, and the
time taken to reach complete conversion (tc) decreased in a
corresponding fashion. Further increases in the size of R to iPr
led to a drop in conversion rate. The conversion rates are all
low and there is no clear correlation of catalyst activity to the
nature of the substituents. The IR stretching frequencies of the
metal-bound carbonyls of these complexes also do not show
any clear correlation to the variation in catalytic efficiency.
The analogous complex containing the bidentate nitrogen
donor ligand [Ir(bpm)(CO)2]BPh4 (where bpm ) bis(1-pyra-
zolyl)methane), in THF-d8 solvent, was reported by Field,
Messerle, and co-workers49 to be more efficient than the
complexes 5a-5c (in catalyzing the cyclization of 4-pentyn-
1-amine (8) (Table 4)). The complex [Ir(bpm)(COD)]BPh4 (in
THF-d8), with COD as co-ligand, was ineffective for the
cyclization of 4-pentyn-1-amine (8) (1.5 mol %, 92% after 24.0
h).69 This contrasts with the analogous complexes with bidentate
phosphine-pyrazolyl ligands [Ir(R2PyP)(COD)]BPh4 (3a-3d),
which were extremely efficient for this transformation (Table
3 above) and much more efficient than the analogous complexes
with CO co-ligands. There is a clear difference between the
bidentate COD and a pair of carbonyls in the catalytic activity
of the complexes, and this identifies the importance of these
co-ligands in the catalytic activity of the metal complexes.
Catalyzed Cyclization Using Neutral Iridium Complexes
with Bidentate Phosphine-Pyrazolyl Ligands. The neutral
complex [Ir(PyP)(CO)Cl] (6a) was a very inefficient catalyst
for the cyclization of 4-pentyn-1-amine (8), and complete
conversion of 8 to 2-methyl-1-pyrroline (9) was not achieved
using either CDCl3 (1.5 mol % catalyst, 60 °C, 50% conversion
after 63 h) or THF-d8 (1.7 mol % catalyst, 60 °C, 18%
The neutral complexes [Ir(PyP)(CO)Cl] (6a) and [Rh(PyP)-
(CO)Cl] (7a) are catalytically active, but are poor catalysts for
the conversion of 8 to 9 when compared with the cationic
analogues [Ir(PyP)(CO)2]BPh4 (5a) and [Ir(PyP)(COD)]BPh4
(69) Burling, S.; Field, L. D.; Messerle, B. A.; Wren, S. L. In IC03-
Conference of the Inorganic DiVision of the Royal Australian Chemical
Institute; The University of Melbourne: Australia, 2003; p P154.

2066 Organometallics, Vol. 26, No. 8, 2007
Field et al.
NMR spectrometer. Room-temperature means 298 K (25 °C) in
catalytic reactions. 1H NMR spectra were recorded with a relaxation
delay of 5 s, and the conversion of substrate to product was
determined by integration of the product resonances relative to the
substrate resonances in the 1H NMR spectra. Complete conversion
(>98%) was taken to be the time where no remaining substrate
resonances were evident. The turnover rate (Nt h-1) was calculated
as the number of moles of product/mole of catalyst/hour and was
calculated at the point of 50% conversion.
(3a). The rhodium complexes with COD as co-ligands [Rh-
(PyP)(COD)]BPh4 (4a) do not have the high efficiency observed
for the [Ir(R2PyP)(COD)]BPh4 (3a-3d) series in promoting the
hydroamination of 4-pentyn-1-amine.
Experimental Section
General Considerations. All manipulations of metal complexes
and air-sensitive reagents were carried out using standard Schlenk
techniques or in a nitrogen-filled drybox. All solvents were distilled
under an atmosphere of nitrogen. Diethyl ether, THF, THF-d8,
n-hexane, n-pentane, and benzene were distilled from sodium
benzophenone ketyl. Dichloromethane was distilled from calcium
hydride. Methanol was distilled from dimethoxymagnesium. CDCl3
and CD2Cl2 were dried over calcium hydride and vacuum distilled
before use. All compressed gases were obtained from British
Oxygen Company (BOC gases) and Linde Gas Pty. Ltd. Nitrogen
(>99.5%) and carbon monoxide (>99.5%) were used as supplied
without purification. Pyrazole, 3,5-dimethylpyrazole, 1,2-dibromo-
ethane (1,2-DBE), tetrabutylammonium bromide (TBAB), 1,5-
cyclooctadiene (COD), cis-cyclooctene (COE), and sodium tet-
raphenylborate were obtained from Aldrich or Lancaster and used
without further purification. Iridium(III) chloride hydrate and
rhodium(III) chloride hydrate were obtained from Precious Metals
Online, PMO P/L, and were used without further purification.
[Ir(µ-Cl)(COD)]2,70 [Rh(µ-Cl)(COD)]2,71 [Rh(µ-Cl)(CO)2]2,72
[Ir(µ-Cl)(COE)2]2,70 [Ir(bpm)(CO)2]BPh4,73 3,5-diphenylpyra-
zole,74,75 diphenylphosphine,76 and 4-pentyn-1-amine77 were pre-
pared by literature methods.
Synthesis of Ligands. Synthesis 1-(2-Bromoethyl)pyrazoles
(1b-1d). Compounds 1b and 1d were synthesized using a method
analogous to the preparation of 1-(2-bromoethyl)pyrazole (1a).55
The synthesis of 1-(2-bromoethyl)-3,5-dimethylpyrazole (1b) is
presented here, and the preparation of 1-(2-bromoethyl)-3,5-
diisopropylpyrazole (1c) and 1-(2-bromoethyl)-3,5-diphenylpyrazole
(1d) are provided in the Supporting Information.
1-(2-Bromoethyl)-3,5-dimethylpyrazole (1b). Aqueous sodium
hydroxide (30 mL, 40% (w/v), 300 mmol) was added to a mixture
of 3,5-dimethylpyrazole (9.61 g, 100 mmol), TBAB (3.22 g, 10.0
mmol), and 1,2-DBE (216 mL, 2.50 mol). After the reaction mixture
was heated for 20 h at 60 °C with vigorous stirring, it was cooled
to RT and water (60 mL) was added. The organic layer was
separated, washed with water (60 mL), dried over anhydrous
calcium chloride, and filtered, and the solvent was removed in Vacuo
to give a pale yellow liquid. The product was purified by either
vacuum distillation through a Vigreux column or by column
chromatography (ethyl acetate). Yield: 10.6 g (52%). Bp: 83-85
1
°C/2 mmHg; lit.57 46-48 °C/0.05 mmHg. H NMR (300 MHz,
3
CDCl3): δ 5.79 (s, 1H, H4), 4.31 (t, JCH2Br-CH2N ) 6.8 Hz, 2H,
1H, 31P, and 13C NMR spectra were recorded on Bruker DPX300
or DMX500 spectrometers, operating at 300 or 500 MHz, 121 MHz
(31P), and 75 or 125 MHz (13C). All spectra were recorded at 298
3
NCH2), 3.68 (t, JNCH2-CH2Br ) 6.8 Hz, 2H, CH2Br), 2.26 (s, 3H,
C5CH3), 2.21 (s, 3H, C3CH3) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ 148.5 (C3), 139.6 (C5), 105.3 (C4), 49.8 (NCH2), 30.5
(CH2Br), 13.6 (C3CH3), 11.2 (C5CH3) ppm. IR (neat, NaCl
plates): ν 3032 (w), 2954 (m), 2921 (m), 2843 (w), 1555 (s), 1462
(s), 1424 (s), 1388 (m), 1302 (s), 1261 (m), 1032 (w), 779 (m)
1
K unless otherwise specified. H NMR and 13C NMR chemical
shifts were referenced internally to residual solvent resonances. 31
P
NMR was referenced externally using H3PO4 (85% in D2O) in a
capillary. Electrospray mass spectra were recorded on a Finnigan
LQC or a Finnigan Micromass QToF mass spectrometer.
cm-1
.
Synthesis of 1-[2-(Diphenylphosphino)ethyl]pyrazoles, R2PyP
(R ) Me, iPr, and Ph; 2b-2d). Compounds 2b-2d were
synthesized using a method analogous to that used for the synthesis
of 1-[2-(diphenylphosphino)ethyl]pyrazole (2a).55 A representative
example is presented here, and the detailed syntheses of 2c and 2d
are provided in the Supporting Information.
Melting points were recorded using a Mel-Temp apparatus and
are uncorrected. IR spectra were recorded using an ATI Mattson
Genesis Series FTIR spectrometer or an Avatar370 FTIR spec-
trometer. Elemental analyses were performed by the Campbell
Microanalytical Laboratory at the University of Otago, New
Zealand. Single-crystal X-ray structure analyses were done at the
X-ray Crystallography Centre, the University of Sydney, Australia.
General Procedure for Catalytic Hydroamination. Metal
complex catalyzed intramolecular hydroamination reactions were
performed on a small scale in NMR tubes fitted with a Youngs
concentric Teflon valve. 4-Pentyn-1-amine was added to a solution
of the catalyst in deuterated solvent (CDCl3 or THF-d8, 0.6-0.7
mL) in an NMR tube at RT, and the sample was kept frozen in
liquid nitrogen until the acquisition of 1H NMR spectra was started.
The solvent was freshly vacuum-transferred into an NMR tube
containing the catalyst prior to the addition of the substrate. Most
of the reactions were performed with approximately 1.5 mol % of
catalyst loading, at 60 °C by heating the sample in an oil bath
maintained at 60 °C or by heating at 60 °C within the probe of the
3,5-Dimethyl-1-[2-(Diphenylphosphino)ethyl]pyrazole, Me2PyP
(2b). n-Butyllithium (1.4 M in hexanes, 11.0 mL, 15.0 mmol) was
added slowly to a solution of diphenylphosphine (2.61 mL, 15.0
mmol) in tetrahydrofuran (40 mL) at -70 °C, and the resulting
red solution was stirred at this temperature for a further 30 min
and then at 0 °C for 1 h. The diphenylphosphide solution was
transferred slowly to a solution of 1-(2-bromoethyl)-3,5-dimeth-
ylpyrazole (1b, 3.05 g, 15.0 mmol) in THF (40 mL) at 0 °C, and
the reaction mixture was stirred at RT under nitrogen overnight.
THF was removed in Vacuo, and benzene (70 mL) and deoxygen-
ated water (30 mL) were added. The organic layer was separated,
washed with deoxygenated water (2 × 20 mL), dried over
anhydrous magnesium sulfate, and filtered, and the solvent was
removed in Vacuo. Unreacted diphenylphosphine was removed by
vacuum distillation to afford 3,5-dimethyl-1-[2(diphenylphosphino)-
ethyl]pyrazole (2b) as a viscous, colorless oil. Yield: 3.67 g (79%);
lit.17 mp 20-22 °C. MS (EI), m/z (%): 308 (11) [M]+, 231 (100)
[M - Ph]+, 212 (73), 183 (49), 108 (36). HRMS: found 308.1443,
calcd for C19H21N2P 308.1442. 1H NMR (500 MHz, C6D6): δ
7.37-7.33 (m, 4H, o-CH of PPh2), 7.05-7.00 (m, 6H, m- and p-CH
of PPh2), 5.67 (s, 1H, H4), 3.94 (m, 2H, NCH2), 2.50 (m, 2H,
PCH2), 2.32 (s, 3H, C3CH3), 1.68 (s, 3H, C5CH3) ppm. 31P{1H}
NMR (121 MHz, C6D6): δ -21.0 ppm. 13C{1H} NMR (75 MHz,
C6D6): δ 147.6 (s, C3), 138.9 (d, 1JP-C ) 13.5 Hz, ipso-C of PPh2),
(70) Herde, J. L.; Lambert, J. C.; Senoff, C. V. Inorg. Synth. 1974, 14,
18-20.
(71) Giordano, G. C.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88-90.
(72) McCleverty, J. A.; Wilkinson, G. Inorg. Synth. 1990, 28, 84-86.
(73) Field, L. D.; Messerle, B. A.; Rehr, M.; Soler, L. P.; Hambley, T.
W. Organometallics 2003, 22, 2387-2395.
(74) Kitajima, N.; Fujisawa, K.; Fujimoto, C.; Morooka, Y.; Hashimoto,
S.; Kitagawa, T.; Toriumi, K.; Tatsumi, K.; Nakamura, A. J. Am. Chem.
Soc. 1992, 114, 1277-1291.
(75) Walworth, B. L.; Klingsberg, E. (American Cyanamid Co.). U.S.
Patent US3922161, 1975.
(76) Bianco, V. D.; Doronzo, S. Inorg. Synth. 1976, 16, 161-163.
(77) Field, L. D.; Morgan, J. Manuscript in preparation.
2
138.2 (s, C5), 133.4 (d, JP-C ) 18.9 Hz, o-C of PPh2), 129.2 (s,

Rhodium(I) and Iridium(I) Complexes
Organometallics, Vol. 26, No. 8, 2007 2067
3
p-C of PPh2), 129.1 (d, JP-C ) 8.8 Hz, m-C of PPh2), 105.3 (s,
Yield: 0.146 g (83%). Mp: 131-133 °C (dec). ESI-MS (MeOH/
dcm), m/z (%): ES+, 532.9 (15) [M - CO + MeOH]+, 529.1 (13)
[M]+, 501.1 (17) [M - CO]+, 471.3 (100) [M - (2×CO)]+; ES-,
319.6 (100) BPh4-. ESI-MS (acetone), m/z (%): ES+, 528.5 (19)
[M]+, 471.0 (100) [M - (2×CO)]+. Anal. Found: C, 60.32; H,
4.23; N, 3.42. Calcd for C43H37BIrN2O2P: C, 60.92; H, 4.40; N,
3.30. 1H NMR (300 MHz, CD2Cl2): δ 7.80 (d, 3JH4-H3 ) 2.4 Hz,
H3), 7.67-7.46 (m, 10H, CH of PPh2), 7.35 (br m, 8H, o-CH of
2
1
C4), 46.0 (d, JP-C ) 25.0 Hz, NCH2), 30.3 (d, JP-C ) 14.9 Hz,
PCH2), 14.3 (s, C3CH3), 10.9 (s, C5CH3) ppm. IR (neat, NaCl
plates): ν 3070 (m), 3052 (m), 2977 (m), 2919 (m), 1552 (s), 1481
(s), 1461 (s), 1422 (s), 1386 (m), 1307 (w), 1026 (w), 776 (w),
740 (s), 697 (s) cm-1
.
Synthesis of Metal Complexes. Synthesis of Cationic Iridium
and Rhodium Complexes with Phosphine-Pyrazolyl Bidentate
Ligands and 1,5-Cyclooctadiene as Co-ligands, [Ir(R2PyP)-
(COD)]BPh4 (R ) H, Me, iPr, and Ph). The synthesis of the
cationic complex [Ir(PyP)(COD)]BPh4 (3a) was performed using
a modified literature method55 and is presented here. The syntheses
of [Ir(R2PyP)(COD)]BPh4 (R ) Me, iPr, and Ph, 3b-3d) and [Rh-
(R2PyP)(COD)]BPh4 (R ) H, Me, iPr, and Ph, 4a-4d) were carried
out in a similar manner and are included in the Supporting
Information.
3
BPh4), 6.98 (t, J ) 7.2 Hz, 9H, m-CH of BPh4 and H5), 6.39
(apparent t, 3JH3-H4 H5-H4
) 2.3 Hz, 1H, H4), 3.67 (m, 2H, NCH2),
,
2.24 (m, 2H, PCH2) ppm. 31P{1H} NMR (121 MHz, CD2Cl2): δ
1
11.7 ppm. H NMR (500 MHz, CD2Cl2, 200 K): δ 7.72 (s, 1H,
H3), 7.62 (m, 2H, p-CH of PPh2), 7.54 (m, 4H, o or m-CH of PPh2),
7.48 (m, 5H, m- or o-CH of PPh2 and H5), 7.32 (br s, 8H, o-CH of
BPh4), 6.90 (t, 3J ) 7.1 Hz, 8H, m-CH of BPh4), 6.78 (t, 3J ) 7.1
Hz, 4H, p-CH of BPh4), 6.30 (s, 1H, H4), 2.69 (m, 2H, NCH2),
1.79 (m, 2H, PCH2) ppm. 31P{1H} NMR (202 MHz, CD2Cl2, 200
K): δ 11.2 ppm. 13C{1H} NMR (125 MHz, CD2Cl2, 200 K): δ
[Ir(PyP)(COD)]BPh4 (3a). A solution of 2a (1.15 g, 4.10 mmol)
in methanol (40 mL) was added slowly over 20 min to a suspension
of [Ir(µ-Cl)(COD)]2 (1.38 g, 2.06 mmol) in methanol (60 mL), and
the orange-red solution obtained was stirred at RT for 45 min under
an atmosphere of nitrogen. Sodium tetraphenylborate (1.41 g, 4.11
mmol) was added, an orange precipitate formed, and the reaction
mixture was stirred for 3 h at RT. About 40% of the methanol was
removed under reduced pressure, and the solid was collected by
filtration, washed with methanol (5 × 7 mL) and n-pentane (5 ×
9 mL), and dried under vacuum. Yield: 3.53 g (96%). Mp: 185-
186 °C (dec). ESI-MS (MeOH), m/z (%): ES+, 581.2 (100) [M]+;
ES-, 319.6 (100) BPh4-. Anal. Found: C, 64.80; H, 5.40; N, 3.26.
Calcd for C49H49BIrN2P: C, 65.40; H, 5.49; N, 3.11. 1H NMR (300
MHz, CD2Cl2): δ 7.56 (d, 3JH4-H3 ) 2.3 Hz, 1H, H3), 7.54-7.40
(m, 10H, CH of PPh2), 7.39-7.33 (br m, 8H, o-CH of BPh4), 7.20
(d, 3JH4-H5 ) 2.4 Hz, 1H, H5), 7.03 (t, 3J ) 7.2 Hz, 8H, m-CH of
2
2
177.4 (d, JP-C ) 104.0 Hz, CO (trans to P)), 170.5 (d, JP-C
)
11.2 Hz, CO (cis to P)), 163.5 (q, 1JB-C ) 48.9 Hz, ipso-C of BPh4),
148.1 (s, C3), 135.8 (s, C5), 135.2 (s, o-C of BPh4), 133.1 (d, JP-C
) 11.1 Hz, o or m-C of PPh2), 132.7 (s, p-C of PPh2), 129.5 (s, m
or o-C of PPh2), 127.5 (d, 1JP-C ) 60.3 Hz, ipso-C of PPh2), 125.9
(s, m-C of BPh4), 122.0 (s, p-C of BPh4), 108.1 (s, C4), 46.9 (s,
1
NCH2), 24.6 (d, JP-C ) 33.7 Hz, PCH2) ppm. IR (KBr disk): ν
2060 (s, CO), 2024 (s, CO) cm-1. IR (dcm solution, in NaCl cell):
ν 2092 (s, CO), 2027 (s, CO) cm-1
.
[Ir(PyP)(13CO)2]BPh4 (5a′). The 13CO-enriched complex was
synthesized using the same method as that used for the synthesis
of [Ir(PyP)(CO)2]BPh4 (5a) using 13CO in place of CO. 31P{1H}
NMR (202 MHz, CD2Cl2, 298 K): δ 11.8 (br s) ppm. 13C{1H}
NMR (125 MHz, CD2Cl2, 298 K): δ 177.2 (br m, enhanced
signal,13CO), 171.3 (br m, enhanced signal,13CO) ppm. 31P{1H}
3
BPh4), 6.88 (t J ) 7.2 Hz, 4H, p-CH of BPh4), 6.32 (apparent t,
NMR (202 MHz, CD2Cl2, 215 K): δ 11.4 (dd, 2J13CO(trans to P)-P
)
3JH3-H4,H5-H4 ) 2.3 Hz, 1H, H4), 4.95 (br, 2H, CH (trans to P) of
COD), 4.29 (m, 2H, NCH2), 3.19 (br, 2H, CH (cis to P) of COD),
2.44 (m, 2H, PCH2), 2.39-2.22 (br, 4H, CHH (2H, trans to P)
and CHH (2H, cis to P) of COD), 2.17-1.93 (br, 4H, CHH (2H,
trans to P) and CHH (2H, cis to P) of COD) ppm. 31P{1H} NMR
(121 MHz, CD2Cl2): δ 10.5 ppm. 13C{1H} NMR (75 MHz, CD2-
Cl2): δ 163.9 (q, 1JB-C ) 49.4 Hz, ipso-C of BPh4), 141.6 (s, C3),
135.8 (s, o-C of BPh4), 134.7 (s, C5), 133.1 (d, JP-C ) 10.9 Hz,
o-C or m-C of PPh2), 131.4 (d, 4JP-C ) 2.2 Hz, p-C of PPh2), 129.5
2
104.2 Hz, J13CO(cis to P)-P ) 11.2 Hz) ppm. 13C{1H} NMR (125
MHz, CD2Cl2, 215 K): δ 177.6 (d, 2JP-13CO ) 104.2 Hz,13CO (trans
to P)), 170.6 (d, 2JP-13CO ) 11.2 Hz,13CO (cis to P)) ppm. IR (KBr
disc): ν 2043 (s, 13CO), 1971 (s, 13CO) cm-1
.
Synthesis of Neutral Iridium and Rhodium Complexes with
Bidentate Phosphine-Pyrazolyl Ligands and Carbonyl and
Chloride as Co-ligands, [M(R2PyP)(CO)Cl] (R ) H, Me, iPr,
and Ph, M ) Ir, 6b-6d and M ) Rh, 7b-7d). The iridium
neutral complexes 6b-6d and the rhodium neutral complexes 7b-
7d were synthesized using a method similar to that used in the
synthesis of [Ir(PyP)(CO)Cl] (6a)55 and [Rh(PyP)(CO)Cl] (7a),55
respectively. The syntheses of 6b and 7b are included here, and
the syntheses of 6c, 6d and 7c, 7d are included in the Supporting
Information.
1
(d, JP-C ) 54.3 Hz, ipso-C of PPh2), 129.1 (d, JP-C ) 10.2 Hz,
4
m-C or o-C of PPh2), 125.6 (q, JB-C ) 2.9 Hz, m-C of BPh4),
2
121.7 (s, p-C of BPh4), 108.0 (s, C4), 95.3 (d, JP-C ) 11.6 Hz,
CH (trans to P) of COD), 64.1 (s, CH (cis to P) of COD), 51.4 (d,
2JP-C ) 2.9 Hz, NCH2), 32.4 (d, JP-C ) 2.9 Hz, CH2 of COD),
3
29.4 (d, 3JP-C ) 2.2 Hz, CH2 of COD), 27.2 (d, 1JP-C ) 32.7 Hz,
PCH2) ppm. IR (KBr disk): ν 3107 (w), 3054 (w), 2983(w), 1579
(m), 1478 (w), 1434 (w), 1283 (m), 1178 (w), 1100 (w), 1075 (w),
1030 (w), 998 (w), 843 (w), 744 (m), 734 (s), 705 (s), 613 (s), 530
[Ir(Me2PyP)(CO)Cl] (6b). A suspension of [Ir(µ-Cl)(COE)2]2
(0.407 g, 0.454 mmol) in acetonitrile (45 mL) was degassed and
placed under an atmosphere of carbon monoxide. The solid
dissolved and a greenish-yellow solution of [Ir(µ-Cl)(CO)2]2 was
obtained after about 5 min. The reaction mixture was stirred for a
further 10 min. The carbon monoxide atmosphere was replaced by
an argon atmosphere, and 3,5-dimethyl-1-[2-(diphenylphosphino)-
ethyl]pyrazole (2b) (0.280 g, 0.908 mmol) in acetonitrile (10 mL)
was added dropwise over 25 min. During the addition, the solution
slowly turned pale yellow, and the reaction mixture was stirred for
a further 45 min at room temperature. The solvent was completely
removed in Vacuo. Diethyl ether (20 mL) was added, and the pale
yellow solid was collected by filtration, washed with ice cold
methanol (4 × 2 mL) and n-pentane (3 × 5 mL), and dried under
vacuum. The pale yellow solid product obtained was recrystallized
by layering a dichloromethane solution (10 mL) with n-hexane (35
mL) and allowing it to stand at 4 °C overnight to afford [Ir(Me2-
PyP)(CO)Cl] (6b) as a pale yellow, needle-like crystalline solid.
Yield: 0.426 g (83%). Mp: 226-228 °C (dec). ESI-MS (MeOH/
(w), 491 (m), 439 (w) cm-1
.
Synthesis of Cationic Iridium Complexes with Bidentate
Phosphine-Pyrazolyl Ligands and Carbonyls as Co-ligands, [Ir-
(R2PyP)(CO)2]BPh4 (R ) H, Me, iPr, and Ph). The synthesis of
[Ir(PyP)(CO)2]BPh4 (5a)55 is presented here with full characteriza-
tion data, while the syntheses of [Ir(R2PyP)(CO)2]BPh4 (R ) Me,
iPr, 5b and 5c) were carried out in a similar fashion and are included
in the Supporting Information.
[Ir(PyP)(CO)2]BPh4 (5a). n-Pentane (15 mL) (n-hexane can also
be used) and methanol (3 mL) were added to [Ir(PyP)(COD)]BPh4
(3a) (0.187 g, 0.208 mmol) under an atmosphere of nitrogen, and
the suspension was degassed via three freeze-pump-thaw cycles.
The reaction mixture was placed under an atmosphere of carbon
monoxide for 2 h, during which time the color of the solid changed
from orange to yellow. The solid product was collected by filtration,
washed with n-pentane (4 × 3 mL), and dried under vacuum.

2068 Organometallics, Vol. 26, No. 8, 2007
Table 5. Crystallographic Data for 3b, 6b, 6c, 7b, and 7c
Field et al.
3b
6b
6c
7b
7c
empirical formula
C51H53BIrN2P
927.93
C21H23Cl3IrN2OP
648.95
C24H29ClIrN2OP
620.11
C20H21ClN2OPRh
474.73
C24H29ClN2OPRh
530.82
M (g mol-1
)
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/n(#14)
20.923(4)
9.3077(16)
22.399(4)
orthorhombic
P212121(#19)
11.2909(18)
19.373(3)
triclinic
P1h(#2)
monoclinic
P21/c(#14)
12.0790
10.4534(13)
16.206(2)
Triclinic
P1h(#2)
8.553(2)
12.153(3)
12.481(4)
113.091(4)
90.348(4)
91.196(4)
1193.0(6)
1.726
8.590(3)
12.219(4)
12.467(4)
113.076(7)
90.027(4)
91.807(5)
1203.1(6)
1.465
20.890(3)
R (deg)
â (deg)
γ (deg)
V (Å3)
104.074(3)
102.057(2)
4231.0(13)
1.457
4569.3(13)
1.887
20011(4)
1.576
Dc (g cm-3
)
Z
4
8
2
4
2
T (K)
150(2)
150(2)
150(2)
150(2)
150(2)
λ Mo KR (Å)
µ Mo KR (mm-1
cryst size (mm)
cryst color
0.71073
3.231
0.71073
6.280
0.071073
5.793
0.71073
1.08
0.71073
0.905
)
0.509 × 0.164 × 0.143
0.56 × 0.25 × 0.10
pale yellow
flat needle
0.257, 0.749
56.04
0.284 × 0.264 × 0.167
0.58 × 0.43 × 0.22
0.316 × 00.245 × 0.238
red
yellow
yellow
yellow
cryst habit
block
0.309, 0657
56.62
-27 26, -12 12,
-29 29
43 524
prismatic
0.226, 0.442
56.62
-11 11, -15 15,
-16, 16
12 012
prism
0.601, 0.832
56.04
-15 15, -13 13,
-21 21
18 400
block
0.766, 0.839
56.00
T (Gaussian)min,max
2θmax (deg)
hkl range
-14 14, -25 24,
-11 11, -15 15,
-27 27
-16 16
N
43 853
11 481
Nind
10 339 (Rmerge
0.0447)
8858
507
0.0209
10 728 (Rmerge
0.0788)
9465
1.028
0.0351
5604 (Rmerge
0.0403)
5450
1.245
0.0169
4623 (Rmerge
0.0275)
4106
1.064
0.0194
5481 (Rmerge
0.0251)
4892
1.046
0.0236
N
obs (I > 2σ(I))
GoF (all data)
R1a (F, I > 2σ(I))
wR2b (F2, all data)
0.0475
0.0832
0.0448
0.0542
0.00653
a R1 ) ∑||Fo| - |F||/∑|Fo| for Fo > 2σ(Fo); wR2 ) (∑w(Fo - Fo )2/∑(wFo )2)1/2 all reflections. b w ) 1/[σ2(Fo ) + (XP)2 + YP] where P ) (Fo
+
2
2
2
2
2
2Fo )/3; X ) 0.02, Y ) 0 for 3b; X ) 0.0439, Y ) 0.00 for 6b; X ) 0.02, Y ) 0.0 for 6c; X ) 0.0260, Y ) 0.8011 for 7b; X ) 0.03 and Y ) 0.3 for 7c.
dcm), m/z (%): ES+, 560.3 (67) [M - 35Cl + MeOH]+, 558.3 (49)
[M - 37Cl + MeOH]+, 528.7 (17) [M - Cl]+, 499.1 (80) [M -
CO - 35Cl]+, 497.1 (100) [MCO - 37Cl]+. Anal. Found: C, 40.26;
H, 3.88; N, 4.62. Calcd for C20H21ClIrN2OP‚0.5CH2Cl2: C, 40.60;
H, 3.66; N, 4.62. 1H NMR (500 MHz, CD2Cl2): δ 7.66 (br s, 4H,
o-CH of PPh2), 7.43-7.40 (br m, 6H, m- and p-CH of PPh2), 5.80
(s, 1H, H4), 4.84 (br, 2H, NCH2), 2.65 (br, 2H, PCH2), 2.52 (s,
3H, C3CH3), 2.21 (s, 3H, C5CH3) ppm. 31P{1H} NMR (202 MHz,
CD2Cl2): δ 13.5 ppm. 13C{1H} NMR (121 MHz, CD2Cl2): δ 175.8
2H, NCH2), 2.64 (m, 2H, PCH2), 2.45 (s, 3H, C3CH3), 2.18 (s,
3H, C5CH3) ppm. 31P{1H} NMR (202 MHz, CD2Cl2): δ 41.9
(d,1JRh-P ) 163.8 Hz) ppm. 13C{1H} NMR (125 MHz, CD2Cl2):
δ 189.7 (dd,1JRh-CO ) 72.7 Hz,2JP-CO ) 16.1 Hz, CO), 152.4 (s,
C3), 141.8 (s, C5), 134.9 (d,1JP-C ) 50.5 Hz, ipso-C of PPh2),
133.2 (d,2JP-C ) 12.2 Hz, o-C of PPh2), 131.2 (d,4JP-C ) 2.3 Hz,
3
p-C of PPh2), 129.1 (d, JP-C ) 10.7 Hz, m-C of PPh2), 107.8 (s,
C4), 47.6 (dd,2JP-C ) 2.3 Hz, 3JRh-C ) 4.6 Hz, NCH2), 30.8 (d,1JP-C
) 29.1 Hz, PCH2), 15.3 (s, C3CH3), 11.9 (s, C5CH3) ppm. IR (KBr
2
(d, JP-C ) 12.6 Hz, CO), 153.0 (s, C3), 142.1 (s, C5), 133.3 (br,
disk): ν 1980 (s, CO) cm-1
.
ipso-C and o-C of PPh2, broad resonances were observed because
of fluxionality of the metal complex at room temperature), 131.3
(d, 4JP-C ) 2.3 Hz, p-C of PPh2), 128.9 (d, 3JP-C ) 11.1 Hz, m-C
Crystal Structure Determination. Crystallographic details are
summarized in Table 5. Single-crystal X-ray diffraction data were
collected with a Bruker SMART 1000 CCD diffractometer employ-
ing graphite-monochromated Mo KR radiation generated from a
sealed tube. Data were collected at 150(2) K with ω scans to 56°
2θ, and the crystals were quenched in a cold nitrogen gas stream
from an Oxford Cryosystems cryostream. The data integration and
reduction were undertaken with SAINT and XPREP,78 and subse-
quent computations were carried out with the WinGX79 and XTAL80
graphical user interfaces. In each case a Gaussian absorption
correction78,81 was applied to the data, and there was no evidence
of crystal decay.
2
of PPh2), 108.2 (s, C4), 48.2 (d, JP-C ) 1.9 Hz, NCH2), 30.0 (d,
1JP-C ) 36.3 Hz, PCH2), 15.4 (s, C3CH3), 12.0 (s, C5CH3) ppm.
IR (KBr disk): ν 1968 (s, CO) cm-1
.
[Rh(Me2PyP)(CO)Cl] (7b). 3,5-Dimethyl-1-[2-(diphenylphos-
phino)ethyl]pyrazole (2b) (0.293 g, 0.952 mmol) in methanol (20
mL) was added dropwise over 30 min to a solution of [Rh(µ-Cl)-
(CO)2] (0.188 g, 0.483 mmol) in methanol (15 mL) under an
atmosphere of argon at room temperature. A yellow-green solution
with some undissolved yellow solid was obtained and the reaction
mixture was stirred for a further 30 min. Approximately half of
the solvent was removed under vacuum and the solid product was
collected by filtration, washed with cold methanol (4 × 2 mL),
n-hexane (3 × 3 mL) and dried in Vacuo. The crude product was
recrystallized by layering a dichloromethane (9 mL) solution of
the complex with n-hexane (35 mL) and allowing to stand at 4 °C
overnight. [Rh(Me2PyP)(CO)Cl] (7b) was collected as needle-like
pale yellow crystals by filtration and dried under vacuum. Yield:
0.402 g (89%). Mp. 216-218 °C (decomposed). ESI-MS (MeOH/
dcm), m/z (%): ES+, 912.8 (100) [2M-Cl]+, 470.1 (35) [M-Cl +
MeOH]+, 439 (100) [M-Cl]+. Anal. Found: C, 49.95; H, 4.52;
N, 5.77. Calcd for C20H21ClN2OPRh: C, 50.60; H, 4.46; N, 5.90.
1H NMR (500 MHz, CD2Cl2): δ 7.67-7.63 (m, 4H, o-CH of PPh2),
7.44-7.39 (m, 6H, m & p-CH of PPh2), 5.72 (s, 1H, H4), 4.83 (m,
The structures were solved with direct methods, using SIR9782
or SHELXS-97, and extended and refined with SHELXL-97.83 The
(78) SAINT and XPREP; Bruker Analytical X-ray Instrument Inc.:
Madison, WI, 1995.
(79) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(80) Hall, S. R., du Boulay, D. J., Olthof-Hazelkamp, R., Eds. Xtal3.6
System; University of Western Australia: Perth, Australia, 1999.
(81) Coppens, P.; Leiserowitz, L.; Rabinovich, D. Acta Crystallogr. 1965,
18, 1035-1038.
(82) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; J., S. R.
J. Appl. Crystalltogr. 1998, 32, 115-119.
(83) Sheldrick, G. M. SHELXL-97; Institu¨t fu¨r Anorganische Chemie
der Universita¨t, University of Go¨ttingen: Tammanstrasse 4, D-3400
Go¨ttingen, Germany, 1998.

Rhodium(I) and Iridium(I) Complexes
Organometallics, Vol. 26, No. 8, 2007 2069
non-hydrogen atoms were modeled with anisotropic displacement
parameters, and a riding atom model with group displacement
parameters was used for the hydrogen atoms. ORTEP84 depictions
are provided in Figures 1, 4, and 5, with displacement ellipsoids
shown at the 50% level except for complex 3b, for which the
ellipsoids are shown at 20%. Complex 6b crystallized in the non-
centrosymmetric space group P212121(#19), and the absolute
structure was determined with the Flack parameter85-88 refining to
0.000(6).
Acknowledgment. Financial support from the Australian
Resereach Council is gratefully acknowledged. K.Q.V. would
like to thank the government of Australia for an Endeavour
International Postgraduate Research Scholarship and the School
of Chemistry for a Postgraduate Teaching Fellowship. We would
like to thank Dr. Russ Pickford and Dr. Keith Fisher for
obtaining ESI-MS and Susanne L. Huth for assistance with
crystallographic work.
Supporting Information Available: Full experimental details
for the synthesis of compounds 3,5-diisopropylpyrazole, 1,2-bis-
(3,5-dimethylpyrazol-1-yl)ethane, 1,2-bis(3,5-diisopropylpyrazol-
1-yl)ethane, 2c, 2d, 3b-3d, 4a-4d, 5b, 5c, 6c, 6d, 7c, 7d, and
7c′, 7d′; time course data for the catalyzed cyclization of 8 with
complexes 3a-3d; CIF files for complexes 3b, 6b, 6c, and 7b, 7c.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(84) Johnson, C. R. ORTEP; Oak Ridge National Laboratory: Oak Ridge,
TN, 1976.
(85) Flack, H. D. Acta Crystallogr. Sect. A 1983, 39, 876-881.
(86) Bernardinelli, G.; Flack, H. D. Acta Crystallogr. Sect. A 1985, 41,
500-511.
(87) Flack, H. D.; Bernardinelli, G. Acta Crystallogr. Sect. A 1999, 55,
908-915.
(88) Flack, H. D.; Bernardinelli, G. J. Appl. Crystallogr. 2000, 33, 1143-
1148.
OM070057V