Lewis base adducts derived from transfer hydrogenation catalysts: Scope and selectivity

Article abstract of DOI:10.1021/om700996m

The coordination tendencies of the unsaturated 16e Lewis acid [Cp*Ir(TsDPEN)]⁺ ([1H]⁺), where TsDPEN is H ₂NCHPhCHPhNTs^-, are surveyed, together with parallel studies on analogous complexes such TsDACH (TsDACH =

Full text of DOI:10.1021/om700996m

1542
Organometallics 2008, 27, 1542–1549
Lewis Base Adducts Derived from Transfer Hydrogenation
Catalysts: Scope and Selectivity
Zachariah M. Heiden, Bradford J. Gorecki, and Thomas B. Rauchfuss*
School of Chemical Sciences, UniVersity of Illinois, Urbana, Illinois 61801
ReceiVed October 5, 2007
The coordination tendencies of the unsaturated 16e Lewis acid [Cp*Ir(TsDPEN)]+ ([1H]+), where
TsDPEN is H2NCHPhCHPhNTs-, are surveyed, together with parallel studies on analogous complexes
such TsDACH (TsDACH ) H2NC6H10NTs-) and Tsen (Tsen ) H2NC2H4NTs-) derivatives as well as
Rh analogues. Crystallographic analyses of the adducts of [Cp*IrL(TsDPEN)]+, where L ) NCMe, NH3,
PPh3, and CO, and [Cp*Ir(CO)(R,R-TsDACH)]+ are described. In the TsDPEN system, the Lewis base
adducts contain an absolute configuration that is opposite that for the TsDPEN ligand and feature equatorial
phenyl groups. In the case of [Cp*Ir(CO)(R,R-TsDACH)]+, both R and S metal centers cocrystallize.
Isomerization of the R to the S metal center was first order in [Cp*(R-Ir)(CO)(R,R-TsDACH)]+ with
minimal solvent effects. The pKa of the amine of the Lewis base adducts correlated linearly with the pKa
of the free ligand in MeCN and the pKa of the amine (H2NCHPhCHPhNTs) of the Lewis base adduct in
MeCN. Amines with pKa < 16 (MeCN scale), in the absence of additional hydrogen bonding to the
TsDPEN ligand set, do not to bind to [1H]+, whereas bulky bases with pKa > 20 deprotonated the
iridium amine.
Lewis acids derived from the amine-hydrides and bis-amides.7
Introduction
Specifically, [Cp*Ir(TsDPEN)]+, [1H]+ (where TsDPEN is
H2NCHPhCHPhNTs-), proved to be a versatile Lewis acid that
Catalysis by chiral Lewis acids is a highly active area that
originated with Koga and co-workers, who in 1979 described
the use of menthoxyaluminum chloride to induce asymmetric
Diels–Alder reactions.1 Of the many subsequent developments
in chiral catalysis,2 one of the most striking is the asymmetric
transfer hydrogenation using metal-amine hydride catalysts.3–5
The key feature of most transfer hydrogenation catalysts is the
presence of a protic N-H functionality adjacent to a hydridic
M-H subunit, i.e., L4Hδ-M-NHδ+R2. These two hydrogen atoms
transfer to polar unsaturated substrates avoiding direct coordina-
tion of the substrate to the metal. This hydrogen transfer converts
the catalyst into a 16e amido entity L4M-NR2, which can add
H2 to re-form the 18e amino hydride. In addition to the studies
by Ikariya and Noyori, Morris, Casey, and their co-workers have
examined several mechanistic features of the Noyori-Ikariya
catalysts.4,6
is not poisoned by either water or related oxygenic ligands8,9
and has been recently shown to serve as a hydrogenation
catalyst.10 Noyori et al. also recently described a related
complex, [(p-cymene)Ru(OTf)(TsDPEN)], which is also an
excellent hydrogenation catalyst.11 In this paper, we describe
the binding of neutral Lewis bases by [1H]+ including guidelines
for predicting which bases will bind and their relative affinity.
A future report will describe the addition of anions to this same
Lewis acid.12
Results
The “Naked” Cation [1H]+. For this work, the principal
starting metal complex was the 16e Ir(III) amido-amine, which
(6) (a) Abdur-Rashid, K.; Clapham, S. E.; Hadzovic, A.; Harvey, J. N.;
Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2002, 124, 15104–15118.
(b) Guo, R.; Chen, X.; Elpelt, C.; Song, D.; Morris, R. H. Org. Lett. 2005,
7, 1757–1759. (c) Abbel, R.; Abdur-Rashid, K.; Faatz, M.; Hadzovic, A.;
Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2005, 127, 1870–1882. (d)
Clapham, S. E.; Guo, R.; Zimmer-De Iuliis, M.; Rasool, N.; Lough, A.;
Morris, R. H. Organometallics 2006, 25, 5477–5486. (e) Koike, T.; Ikariya,
T. AdV. Synth. Catal 2004, 346, 37–41. (f) Koike, T.; Ikariya, T.
Organometallics 2005, 24, 724–730. (g) Koike, T.; Ikariya, T. J. Organomet.
Chem. 2007, 692, 408–419.
Within the realm of transfer hydrogenation catalysis, an
opportunity was defined by our recent synthesis of a family of
* Corresponding author. E-mail: rauchfuz@uiuc.edu.
(1) Hashimoto, S.; Komeshima, N.; Koga, K. J. Chem. Soc., Chem.
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improving enantiomeric purities via the tandem use of mirror-image catalysts
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Catalysis, Malhotra, S. V., Ed.; ACS Symposium Series 880; American
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T.-P.; Chua, G.-L Chem. Commun. 2006, 2739–2749.
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Chem. Soc. ReV 2006, 35, 237–248. (b) Clapham, S. E.; Hadzovic, A.;
Morris, R. H Coord. Chem. ReV. 2004, 248, 2201–2237. (c) Blacker, A. J.;
Mellor, B. J. Preparation of chiral arylalkanols by transfer hydrogenation
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10.1021/om700996m CCC: $40.75
2008 American Chemical Society
Publication on Web 03/13/2008

Lewis Base Adducts
Organometallics, Vol. 27, No. 7, 2008 1543
Scheme 1. Synthetic Routes to [1H]+
was generated by protonation of the bis-amide Cp*Ir(TsDPEN–H)
evolution.15 This conversion is rapid with both HBF4 · Et2O and
H(OEt2)2BArF . A summary to the synthetic routes for the
(1) with H(OEt2)2BArF (where BArF - ) B(C6H5-3,5-
4
4
4
preparation of [1H]+ is presented in Scheme 1.
(CF3)2)4-) or HBF4 · Et2O. In a typical experiment, addition of
HBF4 · Et2O to a mixed CH2Cl2-ether solution of 1 resulted in
immediate precipitation of the pale rust-colored salt [1H]BF4.
The reaction tolerates excess acid. Protonation in the presence
of a ligand, given that the Lewis base was not protonated by
the acid, gave Lewis base adducts. The related diaminocyclo-
hexane (TsDACH) derivative, [2H]+, was prepared by anion
metathesis of 2H(Cl) and NaPF6. We were unable to prepare
pure samples of the related ethylenediamine (Tsen) derivative,
[3H]+. Pure products of Lewis base adducts were obtained when
anion metathesis was conducted in the presence of a ligand.13
Lewis Base Adducts of [1H]+. Addition of Lewis bases to
[1H]+ was found to strongly affect the conformation of the
diamine backbone. In both [1H]+ and 1, the phenyl groups are
diaxial with respect to the IrN2C2 ring. In contrast, the phenyl
groups are diequatorial in all Lewis base adducts reported herein
as well as elsewhere, including the hydride 1H(H) and chloride
1H(Cl).16 Diequatorial phenyl groups are also observed in related
Ru and Rh TsDPEN systems.17,18 C-Substituted ethylenediamine
ligands in octahedral complexes typically adopt conformations
that project the substituents equatorially,19 whereas axial
orientation of these same substituents is favored for square-
planar complexes.
The 1H NMR pattern for the TsDPEN backbone is diagnostic
of five- vs six-coordination at iridium (where Cp* is considered
tridentate). When the phenyl groups are equatorial, the coupling
constants for CHPh-CHPh are 8–13 Hz, characteristic of three-
bond coupling between diaxial vicinal protons.20 The multiplets
are well resolved because of these relatively large coupling
constants. In contrast, the corresponding three-bond coupling
constants for mutually equatorial protons are ca. 2–5 Hz and
are often poorly resolved (Figure 1).
An alternative route to the cations entails oxidation of the
amino-hydride complexes 1H(H), 2H(H), and 3H(H).7,14 Oxida-
tion with either Cp2FePF6 or Ph3CPF6 is less attractive because
it produced side products of [Cp*2Ir2H3]PF6 and, in the case of
TsDPEN, a cyclometalated derivative.7 The formation of
[Cp*2Ir2(µ-H)3]PF6 was found to increase with the basicity
of the ligand set (TsDACH > Tsen > TsDPEN). Finally,
protonation of 1H(H) also gave [1H]+ concomitant with H2
(15) (a) Kubas, G. Metal Dihydrogen and σ-Bond Complexes; Kluwer
Academic/Plenum: New York, 2001; (b) Papish, E. T.; Magee, M. P.;
Norton, J. R. In Recent AdVances in Hydride Chemistry; Peruzzini, M.,
Poli, R., Eds.; Elsevier: New York, 2001; pp 39–74. (c) Ayllon, J. A.; Sayers,
S. F.; Sabo-Etienne, S.; Donnadieu, B.; Chaudret, B.; Clot, E. Organome-
tallics 1999, 18, 3981–3990. (d) Gründemann, S.; Ulrich, S.; Limbach, H.-
H.; Golubev, N. S.; Denisov, G. S.; Epstein, L. M.; Sabo-Etienne, S.;
Chaudret, B. Inorg. Chem. 1999, 38, 2550–2551. (e) Lenero, K. A.;
Kranenburg, M.; Guari, Y.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.;
Sabo-Etienne, S.; Chaudret, B. Inorg. Chem. 2003, 42, 2859–2866. (f)
Matthes, J.; Gründemann, S.; Toner, A.; Guari, Y.; Donnadieu, B.; Spandl,
J.; Sabo-Etienne, S.; Clot, E.; Limbach, H.-H.; Chaudret, B. Organometallics
2004, 23, 1424–1433. (g) Toner, A.; Matthes, J.; Gründemann, S.; Limbach,
H.-H.; Chaudret, B.; Clot, E.; Sabo-Etienne, S. Proc. Natl. Acad. Sci. U.S.A.
2007, 104, 6945–6950.
(13) Anion metathesis in the presence of a Lewis base was the preferred
method for isolation of the Lewis base adducts of the TsDACH and Tsen
ligand sets due to more straightforward preparation. Dehydrohalogenation
of the TsDACH and Tsen amino-chlorides proved to be less straightforward
and more difficult than with the TsDPEN ligand set.
(14) (a) Smith, K.-T.; Tilset, M.; Kuhlman, R.; Caulton, K. G. J. Am.
Chem. Soc. 1995, 117, 9473–9480. (b) Pedersen, A.; Tilset, M. Organo-
metallics 1994, 13, 4887–94. (c) Pedersen, A.; Tilset, M. Organometallics
1993, 12, 3064–3068. (d) Smith, K. T.; Tilset, M. J. Organomet. Chem.
1992, 431, 55–64. (e) Ryan, O. B.; Tilset, M.; Parker, V. D. Organometallics
1991, 10, 298–304. (f) Pleune, B.; Morales, D.; Meunier-Prest, R.; Richard,
P.; Collange, E.; Fettinger, J. C.; Poli, R. J. Am. Chem. Soc. 1999, 121,
2209–2225.
(16) Mashima, K.; Abe, T.; Tani, K. Chem. Lett. 1998, 1201–1202.
(17) (a) Haack, K.-J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R.
Angew. Chem., Int. Ed. 1997, 36, 285–288. (b) Mao, J.; Baker, D. C. Org.
Lett. 1999, 1, 841–843.
(18) Fujii, A.; Hashiguchi, S.; Uematsu, N.; Ikariya, T.; Noyori, R. J. Am.
Chem. Soc. 1996, 118, 2521–2522.
(19) von Zelewsky, A. Stereochemistry of Coordination Compounds;
Wiley: Chichester, 1996.
(20) (a) Pouzard, G.; Rajzmann, M.; Bodot, H.; Pujol, L. Org. Magn.
Reson. 1973, 5, 209–214. (b) Sudmeier, J. L.; Blackmer, G. L. Inorg. Chem.
1971, 10, 2010–2018. (c) Tormena, C. F.; Vilcachagua, J. D.; Karcher, V.;
Rittner, R.; Contreras, R. H. Magn. Reson. Chem. 2007, 45, 590–594.

1544 Organometallics, Vol. 27, No. 7, 2008
Heiden et al.
1
Figure 1. 500 MHz H NMR spectra of the amine region of (A)
complex 1 (axial phenyl groups), (B) [1H]BArF (axial phenyl
4
groups), (C) 1H(Cl) (equatorial phenyl groups), (D) 1H(H) (equato-
rial phenyl groups), (E) [1H(NH3)]BF4 (equatorial phenyl groups),
and (F) [1H(CO)]BF4 (equatorial phenyl groups) in CD2Cl2. The
peak observed at δ 5.32 is attributed to residual solvent (CDHCl2).
-
Figure 3. Molecular structure of [1H(NH3)]BF4. The BF4 coun-
teranion is removed for clarity. The thermal ellipsoids are shown
at 50% probability and are omitted on the Cp* ring, phenyl, and
tosyl groups for clarity.
[1H(NH3)]BF4. The ammonia derivative [1H(NH3)]+ was
prepared by treatment of 1 with an ammonium salt or by reaction
of NH3 with [1H(NCMe)]+. In contrast to the behavior of
[1H(NCMe)]BF4, samples of [1H(NH3)]BF4 showed no ten-
dency to dissociate ammonia under vacuum. Crystallographic
analysis reveals a weak hydrogen bond between NH3 and an
oxygen atom of the tosyl group (Figure 3). Intermolecular
-
bonding between the BF4 counteranion and NH3 is also
observed.
The Ir-NH3 bond distance of 2.157(3) Å is unexceptional.24,25
In [Cp*Ir(PMe3)(Ph)(NH3)]OTf, NH3 is slightly stronger bound
than in [Cp*Ir(PMe3)(CF(CF3)2)(NH3)]BF4 with Ir-NH3 dis-
tances of 2.135 and 2.171 Å, respectively. The 1H NMR signals
for [1H(NH3)]+ occur as a broad singlet at δ 3.85, as seen in
related complexes (Figure 1).24,25
Figure 2. Molecular structure of the cation in [1H(NCMe)]PF6.
Thermal ellipsoids are shown at 50% probability and are omitted
on the Cp* ring, phenyl, and tosyl groups for clarity.
[1H(PR3)]BF4. Despite their large size, triaryl phosphines
PAr3 (Ar ) Ph, p-FC6H4, p-MeOC6H4) were found to react
immediately with [1(NCMe)]BF4 to afford stable, well-behaved
adducts. These phosphines were also found to displace NH3 from
[1H(NH3)]BF4. The equilibrium constants from the displacement
of ammonia were used to verify the pKa’s of the phosphine
adducts (see below). 1H NMR spectroscopy indicated that
the phenyl groups on the TsDPEN ligand are equatorial in these
adducts. 1H and 31P NMR spectra, however, revealed the
presence of 5, 8, and 10% of a second diastereomer for the
p-FC6H4, Ph, and p-MeOC6H4 derivatives of PAr3, respectively
(Figure 4). The amount of the second diastereomer was greatest
for the least basic phosphine, P(p-FC6H4)3 (pKa ) 7.60 vs 8.56
and 10.86 for P(p-FC6H4)3, PPh3, and P(p-MeOC6H4)3 in MeCN,
respectively).26 The temperature dependence of the equilibrium
ratios of the major to minor PPh3 adduct was measured over a
35 °C range. The results, ∆H ) 3.80 kJ/mol and ∆S ) 37.9
J/mol · K, indicate that the difference is mainly entropic,
indicating that the equilibrium is influenced by steric effects
involving the phenyl groups (eq 1).
[1H(NCMe)]X (X ) BF4, PF6). The MeCN adduct [1H-
(NCMe)]+ formed when any of the above methodssprotonation
of 1H(H), oxidation of 1H(H), or protonation of 1swas
conducted in an MeCN solution. The weakness of this adduct
is indicated by the finding that crystalline samples lost MeCN,
as signaled by the appearance of a red coloration characteristic
of [1H]+ (and loss of crystallinity of crystalline samples by
collapse of the crystal lattice). Loss of MeCN is fully reversible:
the red solids became yellow upon re-exposure to vapors of
acetonitrile (or other donor ligands, see below).
Crystallographic analysis of [1(NCMe)]PF6 revealed the
expected distorted octahedral geometry (Figure 2). The Ir-NCMe
bond distance of 2.053(2) Å is similar to previously reported
Cp*Ir(NCMe) complexes.21–23 The catalytically active [Cp*Ir-
(NCMe)2(carbene)]2+ complexes reported by Yamaguchi and
co-workers exhibit slightly longer Ir-NCMe bonds at 2.088
and 2.060 Å,23 whereas the substitutionally inert complex
[Cp*(PMe3)Ir(NCMe)(SiPh3)][BArF ] has a shorter Ir-NCMe
4
distance of 2.042 Å.21 Apparently the Ir-NCMe bond distance
in [1H(NCMe)]+ is on the borderline between labile and inert
adducts.
Keq
+
)
(
)
Cp*Ir PPh TsDPEN minor y z
[
(
]
3
+
)
(21) Klei, S. R.; Tilley, T. D.; Bergman, R. G. Organometallics 2002,
21, 4648–4661.
(
Cp*Ir PPh TsDPEN
]
(1)
major
[
(
)
3
(22) Herberich, G. E.; Ganter, B. Inorg. Chem. Commun. 2001, 4, 100–
103.
A crystallographic study of [1H(PPh3)]BF4 revealed the
expected distorted octahedral complex (Figure 5). The Ir-PPh3
distance was found to be 2.334(5) Å, which is similar to other
reported Cp*Ir(PPh3) complexes.27,28 Interestingly, the other
(23) (a) Hanasaka, F.; Fujita, K.-i.; Yamaguchi, R. Organometallics
2004, 23, 1490–1492. (b) Hanasaka, F.; Fujita, K.-i.; Yamaguchi, R.
Organometallics 2005, 24, 3422–3433.

Lewis Base Adducts
Organometallics, Vol. 27, No. 7, 2008 1545
Figure 4. Coordination of the Lewis base could result in a chiral metal center by coordination of the ligand to the prochiral metal center.
The major isomer was found to contain a metal center with inverse chirality to the diamine backbone.
-
Figure 5. Molecular structure of [1(PPh3)]BF4. The BF4 coun-
-
teranion is omitted for clarity. The thermal ellipsoids are shown at
50% probability and are omitted on the Cp* ring, phenyl, and tosyl
groups for clarity.
Figure 6. Molecular structure of [1H(CO)]BF4. The BF4 coun-
teranion is omitted for clarity. The thermal ellipsoids are shown at
50% probability and are omitted on the Cp* ring, phenyl, and tosyl
groups for clarity.
Table 1. IR Data (νCO) for [(C5Me4R)Ir(CO)(amido-amine)]BF4
(R ) H, Me, Et) Adducts
by Ingrosso and co-workers27 exhibits two of the Cp* methyls
nearly eclipsing the Ir-C/N bonds, which is also observed in
[1H(PPh3)]+.
compound
νCO (cm-1, CH2Cl2 soln)
[Cp*Ir(CO)(Tsen)]BF4
2059
2059
2064
2071
2072
[Cp*Ir(CO)(TsDACH)]BF4
[Cp*Ir(CO)(TsDPEN)]BF4
[(C5Me4H)Ir(CO)(TsDPEN)]BF4
[(C5Me4Et)Ir(CO)(TsDPEN)]BF4
Addition of PMe3 to [1H]BF4 resulted in immediate formation
of [1H(PMe3)]BF4, which was found to exist as only a single
isomer in solution, unlike the previously described PAr3 adducts.
We were unable to deprotonate [1H(PMe3)]BF4 with 1,1,3,3-
tetramethylguanidine, indicating that this highly basic phosphine
depresses the acidity of the amine protons. In contrast,
[2H(PMe3)]BF4 formed two diastereomers in a 3:1 equilibrium
ratio. In the case of [2H(PPh3)]BF4, the ratio of diastereomers
was 2:1.
ligands are more distant from the metal center than seen in
related adducts, including the Ir-N (+0.01 Å) and the Cp*
centroid-Ir distances (+0.05 Å). The crowded environment
about Ir is accentuated by the large cone angle of PPh3 (145°).29
In related Cp*IrIII(PPh3) adducts, the Ir-PPh3 bond distances
range from 2.223 to 2.300 Å, with [1H(PPh3)]+ exhibiting an
Ir-PPh3 distance 0.03 Å longer than previously observed.27,28
For example, a Cp*Ir(PPh3)-based metallacyclopentane prepared
We also found that the related Rh phosphine complexes could
be synthesized from the amino-chlorides in the presence of PPh3
1
and NaBF4. For these adducts, J(Rh-P) coupling constants
on the order of 143–145 Hz were observed in the 31P NMR
(24) Rais, D.; Bergman, R. G. Chem.-Eur. J. 2004, 10, 3970–3978.
(25) Hughes, R. P.; Smith, J. M.; Incarvito, C. D.; Lam, K.-C.; Rhatigan,
B.; Rheingold, A. L. Organometallics 2002, 21, 2136–2144.
(28) (a) Diversi, P.; Ingrosso, G.; Lucherini, A.; Porzio, W.; Zocchi,
M. Inorg. Chem. 1980, 19, 3590–3597. (b) Dinger, M. B.; Henderson, W.;
Oliver, A. G.; Rickard, C. E. F. Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1999, C55, 1778–1780. (c) Yang, K.; Don, M. J.; Sharma, D. K.;
Bott, S. G.; Richmond, M. G. J. Organomet. Chem. 1995, 495, 61–69. (d)
Le Bras, J.; Amouri, H.; Vaissermann, J. J. Organomet. Chem. 1997, 548,
305–307.
(26) (a) Angelici, R. J. Acc. Chem. Res. 1995, 28, 51–60. (b) Augustin-
Nowacka, D.; Chmurzynski, L. Anal. Chim. Acta 1999, 381, 215–220.
(27) Bertani, R.; Diversi, P.; Ingrosso, G.; Lucherini, A.; Marchetti, F.;
Adovasio, V.; Nardelli, M. J. Chem. Soc., Dalton Trans. 1988, 2983–2994.

1546 Organometallics, Vol. 27, No. 7, 2008
Heiden et al.
-
Figure 7. Molecular structure of the cocrystallized diastereomers of [2H(CO)]BF4 ((left) S-Ir isomer, (right) R-Ir isomer). The BF4
counteranion is omitted for clarity. The thermal ellipsoids are shown at 50% probability and are omitted on the Cp* ring and tosyl ring for
clarity.
Table 2. Selected Bond Distances (Å) and Related Structural Features of Lewis Base (L) Adducts
1
[1H]BArF (ref 7) [1H(CO)]BF4 (S)-[2H(CO)]BF4, (R)-[2H(CO)]BF4 [1H(PPh3)]BF4 [1H(NH3)]BF4 [1H(NCMe)]PF6
4
Ir-Cp*(centroid)
Ir-N(1)Ts
Ir-N(2)Hx (x ) 1, 2) 1.901(5)
Ir-L
phenyl group
orientation
1.794(6)
2.058(5)
1.782(6)
1.984(4)
2.096(5)
1.847(3)
2.124(2)
2.123(2)
1.898(3)
equatorial
1.836(8), 1.846(8)
2.142(6), 2.130(6)
2.117(8), 2.124(7)
1.910(8), 1.872(9)
1.924(7)
2.162(13)
2.141(14)
2.334(5)
equatorial
1.785(3)
2.157(2)
2.133(2)
2.157(3)
equatorial
1.743(8)
2.146(2)
2.110(2)
2.053(2)
equatorial
axial
axial
spectra. Similar equilibrium isomer ratios, as seen in the Ir-
based PPh3 adducts, were observed in the Rh-based PPh3
complexes. No PPh3 adducts were observed in the (p-
cymene)Ru(TsDPEN) systems, which is attributed to the greater
bulk of the arene ring, which is about 0.2 Å closer to the metal
than the Cp* ring in the Rh- and Ir-based systems.30 In
agreement with these observations, reported Ru(arene)-PPh3
complexes contain planar or small ancillary ligands (such as
halides) with cone angles < 100°.29,31
Addition of 0.5 equiv of dppe (1,2-bis(diphenylphosphino)et-
hane) or dmpe (1,2-bis(dimethylphosphino)ethane) to [1H]+ af-
forded salts of the corresponding dimetallic adducts, {[1H]2-
(diphosphine)}2+. Crystallographic characterization was not achieved
due to the tendency of the crystals to desolvate. 1H and 31P NMR
indicate that these diiridium complexes exist as single diastereomers
(the precursor complexes were racemic), arising from the exclusive
formation in either homochiral or racemic adducts. The nature of
the dppe adduct was indicated by the treatment of [S,S-1H]+ with
0.5 equiv of dppe, which gave the same compound that arises from
the racemic mixture of iridium complexes, indicating the formation
of the homochiral adduct (eq 2). The formation of {[Cp*(R-Ir)(S,S-
TsDPEN)]2(dppe)}2+ and {[Cp*(R-Ir)(S,S-TsDPEN)](dppe)][Cp*(S-
Ir)(S,S-TsDPEN)]}2+ would be the only possibilities. The formation
from a pale yellow to a virtually colorless solution. The
corresponding derivatives [2(CO)]BF4 and [3(CO)]BF4 were
prepared by treatment of solutions of 2H(Cl) and 3H(Cl) with
an atmosphere of CO in the presence of NaBF4. IR data for
these CO adducts are shown in Table 1. The related rhodium
derivatives appeared to be unstable, consistent with the de-
creased π-basicity of the Rh compounds. Crystallography
showed that in [1(CO)]BF4 (Figure 6) the Ir-CO distance is
1.898(3) Å, with a relatively short C-O distance of 1.132 Å,
consistent with the high frequency for νCO. At 169.9°, the
Ir-C-O bond is bent; a similar phenomenon was observed in
the MeCN adduct, in which the Ir-N-CCH3 angle was found
to be 172.3(2)°. The value of νCO for [1H(CO)]BF4, 2064 cm-1
is high relative to previously reported Cp*IrIII(CO) complexes,
which ranged from 1953 to 2050 cm-1 32
,
.
Diastereoisomerization of [Cp*(R-Ir)(CO)(R,R-TsDACH)]-
BF4. The adduct [Cp*Ir(CO)(R,R-TsDACH)]+, [2H(CO)]BF4,
crystallized as a pair of diastereomers (Figure 7) that differ in
terms of the relative configuration at Ir. Structurally the two
isomers differ only subtly (Table 2). The CO is bound more
tightly in the R-Ir isomer with Ir-C and C-O distances being,
respectively, 0.038 Å shorter and 0.063 Å longer than for the
major isomer. The fact that the CO is bound more tightly in
the less stable isomer compound is intriguing. Comparisons of
the diastereomers of [2H(CO)]BF4 with the other adducts are
shown in Tables 2 and S4.
of
{[Cp*(R-Ir)(S,S-TsDPEN)](dppe)][Cp*(S-Ir)(S,S-
TsDPEN)]}2+is unlikely because of the rapid isomerization
observed in [Cp*Ir(PPh3)(TsDPEN)]+ (see above).
In CD3CN, CD3OD, and CD2Cl2 solutions, the 1:1 mixture
of the two diastereomers equilibrated to a ratio of 8:1 for S-Ir:
R-Ir over the course of hours at room temperature (see
Experimental Section, Figure 10). The rate of the isomerization
of [Cp*(R-Ir)(CO)(R,R-TsDACH)]BF4 was found to be first
order in the complex. Rates were measured over a 20 °C range,
allowing us to determine ∆Hq ) 82.0 ( 0.4 kJ/mol and ∆S q
) -34.3 ( 0.2 J/mol K for the isomerization (Ea ) 84.31 kJ/
mol). The rate was found to be virtually unaffected by the
solvent (See Supporting Information, Table S3). The rate of
deuteration of the amine protons of both isomers of
[2H(CO)]BF4 were found to occur in seconds, thus indicating
that proton exchange by deprotonation may aid in ligand loss
[
(
)]
4 Cp*Ir rac-TsDPEN BF4 + 2 dppe f
[
(
)(
)]
(
)
Cp* R-Ir S, S-TsDPEN dppe BF
+
{
}
(
(
)
)
2
4 2
[
{
(
)(
)
]
Cp* S-Ir R, R-TsDPEN dppe BF (2)
}
(
)
4 2
2
[1H(CO)]BF4. Treatment of MeCN solutions of [1H-
(NCMe)]BF4 with CO resulted in an immediate color change
(29) Tolman, C. A. Chem. ReV. 1977, 77, 313–48.
(30) Hashiguchi, S.; Fujii, A.; Haack, K.-J.; Matsumura, K.; Ikariya,
T.; Noyori, R. Angew. Chem., Int. Ed. 1997, 36, 288–290.
(31) (a) Brunner, H.; Oeschey, R.; Nuber, B. Angew. Chem., Int. Ed.
Engl. 1994, 33, 866–869. (b) Gül, N.; Nelson, J. H. Organometallics 1999,
18, 709–725. (c) Dinger, M. B.; Henderson, W.; Nicholson, B. K. J.
Organomet. Chem. 1998, 556, 75–88.

Lewis Base Adducts
Organometallics, Vol. 27, No. 7, 2008 1547
basis of this correlation, Lewis bases with pKa’s (MeCN) >
26.7 would deprotonate [1H]+. The fact that N-heterocyclic
carbenes have pKa’s > 26 (MeCN)36 suggests that carbene
adducts would not form. In accord with this prediction,
1-methylimidazole was found to bind through nitrogen, as
opposed to through the carbon, as indicated by 13C NMR
analysis.37
Amines less basic than NH3 (pKa ) 16.46), such as aniline
(pKa ) 10.56),38 were found not to bind in the absence of a
contribution from hydrogen bonding.12 Amines more basic than
pyrrolidine (pKa ) 19.58) were found to act as bases instead of
ligands. Nonbulky amines with pKa’s intermediate between NH3
and pyrrolidine such as DMAP (pKa ) 17.95)35 were found to
bind. Water, diethyl ether, and THF were found not to bind,
consistent with their low basicities.34
Substituents on the C5R5 ring affected the acidity of the amine
in the expected ways. For the complexes [(C5Me4R)Ir-
(NCMe)(TsDPENH)]+, the pKa was lowered by 1 when R )
Me was changed to R ) H. Changing R to Et increased the
pKa of the amine by 0.33 pKa units.
Figure 8. Ladder diagram showing the pKa’s (MeCN soln.) of the
adducts [Cp*Ir(L)(TsDPEN)]+ and some calibrating bases.
and reassociation upon reprotonation. The deuteration of the
amine protons of [1H(CO)]BF4 was found to occur over the
course of 400 s, at least 5 times slower than [2H(CO)]BF4.
Consistent with this proposed mechanism, the isomerization was
found to be slowed by about 20% in the presence of a CO
atmosphere (∼1 atm) (see Supporting Information, Table S3).
Influence of Coligands on the pKa of the TsDPEN
Amine. We have briefly communicated the finding that depro-
tonation of the adducts [1H(L)]+ gives 1 concomitant with
liberation of L.7 Deprotonation at the amine in TsDPEN is well
behaved; deprotonation of Cp* to give a fulvene-type derivative9,33
was not observed. We have now determined the pKa’s for these
adducts, and the results are presented in the form of a ladder
diagram (Figure 8) that also includes the standard bases
employed in this analysis. A linear correlation between the pKa
of the free base and the Lewis base adduct was observed (Figure
9). In an illustrative observation, the complex [1H(NH3)]+ was
found to be only partially deprotonated by 1,1,3,3-tetrameth-
ylguanidine (TMG), indicating pKa ) 24.9. Using both TMG
and PhTMG,34,35 the PPh3 adduct was found to be slightly more
acidic, with a pKa ) 23.8. As mentioned above, [1H(PPh3)]+
exists as both a minor and a major diastereomer. Since
diastereoisomerization of the phosphine complexes requires
several seconds, we could estimate that the minor diastereomer
was 1.3 pKa units less than the major isomer (through equilib-
rium measurements). We were unable to determine the pKa of
[1H(CO)]+ because the CO ligand was highly reactive toward
bases. The NCMe adduct was found to not fit the trend, which
is attributed to its lability. The linear correlation observed in
Figure 9 predicts that the pKa of the amine in the Lewis base
adducts is 0.173 × (free base pKa in MeCN) + 22.1. On the
Conclusions
As shown in this work, [1H]+ is a versatile Lewis acid that
can be generated in several ways and binds a variety of ligands,
especially those that are both Lewis basic and π-acidic.
Protonation of 1 causes the Ir-NHx bond to elongate by about
0.2 Å and the Ir-NTs bond to decrease by about 0.1 Å,
indicative that protonation redirects π-bonding from one nitrogen
to the other (Table 2).7 Upon binding of Lewis bases to [1H]+,
the Ir-NTs bond lengthens (Table 2) and the acidity of the
amine decreases by ∼103.
The chirality of the Lewis base adducts has been found to
primarily result in an R metal center in the presence of an S,S-
amido-amine and an S metal center in the presence of an R,R-
amido-amine. Noyori and Ikariya et al. have previously observed
ca. 1% of the minor diastereomer (S-metal center) of (p-
cymene)RuH(S,S-TsDPEN).30 The observed diastereoselectivity
of Lewis base adducts of [1H]+ is consistent with the diaste-
reoselectivity of Cp*IrH(TsDPEN)-catalyzed transfer hydro-
genations.5,17,39 Underscoring the coupling of stereoselectivity
to intramolecular hydrogen bonding, ligands lacking the ability
to hydrogen-bond (e.g., tertiary phosphines, CO) were found
to bind with only modest stereoselectivity.
We propose that the diastereoisomerization proceeds via
deprotonation of the amine. Deprotonation of the TsDPEN
ligand precedes and probably causes dissociation of the Lewis
base. Whereas deprotonation of [Cp*Ir(PMe3)(Ph)(NH3)]+ af-
fords the amido derivative,24 deprotonation of [1H(NH3)]+ gave
ammonia and 1. Xiao and co-workers have proposed a “swing”
mechanism for diastereoisomerization, whereby the tosylated
amide reversibly protonates and then dissociates. Such a
mechanism would be promoted by acids,40 whereas our reactions
are not. If the opening of the chelate ring were occurring, we
would expect to observe chelation by dppe, which has been
(32) (a) Lei, X.; Bandyopadhyay, A. K.; Shang, M.; Fehlner, T. P.
Organometallics 1999, 18, 2294–2296. (b) Alaimo, P. J.; Arndtsen, B. A.;
Bergman, R. G. J. Am. Chem. Soc. 1997, 119, 5269–5270. (c) Wang, J.-
Q.; Weng, L.; Jin, G.-X. J. Organomet. Chem. 2005, 690, 249–252. (d)
Simpson, R. D.; Marshall, W. J. Organometallics 1997, 16, 3719–3722.
(e) Einstein, F. W. B.; Glavina, P. G.; Pomeroy, R. K.; Rushman, P.; Willis,
A. C. J. Organomet. Chem. 1986, 317, 255–265. (f) Einstein, F. W. B.;
Pomeroy, R. K.; Rushman, P.; Willis, A. C. Organometallics 1985, 4, 250–
255. (g) Hughes, R. P.; Laritchev, R. B.; Williamson, A.; Incarvito, C. D.;
Zakharov, L. N.; Rheingold, A. L. Organometallics 2002, 21, 4873–4885.
(33) Kreindlin, A. Z.; Rybinskaya, M. A. Russ. Chem. ReV. 2004, 73,
417–432.
(36) Magill, A. M.; Cavell, K. J.; Yates, B. F. J. Am. Chem. Soc. 2004,
126, 8717–8724.
(37) Ruiz, J.; Perandones, B. F. J. Am. Chem. Soc. 2007, 129, 9298–
9299.
(38) Coetzee, J. F.; Padmanabhan, G. R. J. Am. Chem. Soc. 1965, 87,
5005–5010.
(39) (a) Hamada, T.; Torii, T.; Izawa, K.; Noyori, R.; Ikariya, T Org.
Lett. 2002, 4, 4373–4376. (b) Mashima, K.; Abe, T.; Tani, K. Chem. Lett.
1998, 1199–1200.
(34) Izutsu, K., Acid-Base Dissociation Constants in Dipolar Aprotic
SolVents; Blackwell Scientific Publications: Oxford, 1990; Vol. 35.
(35) Kaljurand, I.; Kütt, A.; Sooväli, L.; Rodima, T.; Mäemets, V.; Leito,
I.; Koppel, I. A. J. Org. Chem. 2005, 70, 1019–1028.
(40) Wu, X.; Li, X.; King, F.; Xiao, J. Angew. Chem., Int. Ed. 2005,
44, 3407–3411.

1548 Organometallics, Vol. 27, No. 7, 2008
Heiden et al.
Figure 9. Graph of the pKa of various ligands and the amine of the TsDPEN ligand. Compounds designated in bold were found to bind,
those in italics did not bind, and underlining designates Lewis bases that acted as Bronsted bases.
previously observed.41 The rate of proton exchange of the amine
(s, 1H, H2NCHPhCHPhNTs), 4.64 (s, 1H, H2NCHPhCHPhNTs),
6.92–7.43 (m, 14H). 1H NMR (500 MHz, CD2Cl2): δ 1.86 (s, 15H,
Cp*), 2.30 (s, 3H, SO2C6H4-4-CH3), 4.36 (d, 1H, 4 Hz, HHNCH-
PhCHPhNTs), 4.68 (s, 1H, 12 Hz, HHNCHPhCHPhNTs), 4.84 (s,
1H, HHNCHPhCHPhNTs), 5.90 (br d, 1H, 13 Hz, HHNCHPh-
CHPhNTs), 6.89–7.36 (14H). 13C NMR (125 MHz, CD2Cl2): δ
10.40, 21.47, 67.86, 76.01, 91.71, 126.6, 126.7, 127.6, 128.5, 128.6,
129.0, 129.1, 129.6, 135.3, 136.6, 139.4, 143.5, 143.7. 13C NMR
(125 MHz, CD3CN): δ 9.26 (t, 14.3 Hz), 9.58, 9.78, 21.19, 71.01,
75.32, 90.16, 127.50, 128.3, 128.5, 129.0, 129.2, 129.4, 129.5, 129.8,
130.0, 139.3, 141.3, 141.9. Anal. Calcd for C31H36IrN2O2SBF4 ·
0.5CH2Cl2: C, 46.02; H, 4.54; N, 3.41. Found: C, 45.68; H, 4.43; N,
3.50.
of [2H(CO)]+ is at least 1000 times faster than the rate of
diastereoisomerization and at least 5 times faster than the proton
exchange of [1H(CO)]+. In other words, adducts of the
deprotonated complexes, i.e., [1(CO)], have a significant
lifetime. Buckingham and Clark have detected the related
conjugate base of cobalt(III) amines.42
Experimental Section
Materials and Methods. Tosyl chloride (Aldrich) was purified
by recrystallization from diethyl ether. (()-DPEN (TCI America)
was used as received. The monotosylated stilbenediamine, R,R-
TsDACH, and Tsen were prepared according to Noyori et al.43
H(OEt2)2BArF4 was prepared from NaBArF4 according to Brookhart,
except that 1.0 M HCl in ether was used in place of aqueous HCl.44
Cp2FePF6 was purchased from Aldrich and recrystallized by
extraction into acetone followed by precipitation by ethanol, as
reported by Geiger,45 before use. All other reagents were obtained
commercially or prepared or purified by standard methods.46
Cp*Ir(TsDPEN-H) (1) and Cp*IrH(TsDPEN) (1H(H)) were pre-
pared as previously described.9 Complexes [1(CO)]BF4, [1(NH3)]BF4,
[1H]BArF , [1(NCMe)]X (where X ) BArF -, BF4-, and PF6-), and
Note: minimal CH2Cl2 is used to dissolve 1, and the mixture is
diluted with Et2O. Using only CH2Cl2 results in diminished yields
of [1H]BF4 and a less pure product. The reaction tolerates excess
acid.
{[Cp*Ir(TsDPEN)]2(dppe)}(BF4)2 ({[1H]2(dppe)}(BF4)2). A
solution of 35 mg (88 µmol) of dppe in 10 mL of CH2Cl2 was added
to a solution of 0.135 g (173 µmol) of [1H]BF4 in CH2Cl2. The
resulting yellow solution was allowed to stir for 30 min before
removing solvent under reduced pressure. The resulting bright yellow
solid was recrystallized from CH2Cl2 by the addition of Et2O. Yield:
0.136 g (88%). 1H NMR (500 MHz, CD3CN): δ 1.42 (d, 30H, 3 Hz,
Cp*), 2.22 (s, 6H, SO2C6H4-4-CH3), 2.50 (s, 4H, Ph2PCH2CH2PPh2),
3.40 (br t, 2H, 12 Hz, H2NCHPhCHPhNTs), 3.85 (d, 2H, 11 Hz,
H2NCHPhCHPhNTs), 5.01 (br s, 2H, HHNCHPhCHPhNTs), 6.47 (br
s, 2H, HHNCHPhCHPhNTs), 6.34–8.77 (48H). 31P NMR (203 MHz,
CD3CN): δ 3.52. ESI-MS: m/z 891.6 ([Cp*Ir(TsDPEN)]2(dppe)2+).
Anal. Calcd for C88H96B2F8Ir2N2O4P2S2: C, 53.98; H, 4.94; N, 2.86.
Found: C, 53.15; H, 4.73; N, 2.91.
4
4
[1(PPh3)]BF4 were prepared as previously described.7
[Cp*Ir(TsDPEN)]BF4 ([1H]BF4). A solution of 0.63 g (0.91
mmol) of Cp*Ir(TsDPEN-H) in 2 mL of CH2Cl2 and 30 mL of
Et2O was treated with 13 mL of a 0.07 M (0.91 mmol) HBF4 · Et2O
in Et2O solution, resulting in an immediate color change from dark
purple to orange, followed by immediate precipitation. The resulting
orange precipitate was collected and washed with diethyl ether.
The collected solid was recrystallized from addition of 50 mL of
diethyl ether into a 1 mL CH2Cl2 solution and allowed to stir for
an hour before filtration. Yield: 0.66 g (92%). 1H NMR (500 MHz,
CD3OD): δ 1.95 (s, 15H, Cp*), 2.30 (s, 3H, SO2C6H4-4-CH3), 4.25
Isomerization of [Cp*Ir(PPh3)(TsDPEN)]BF4 as a Function
of Temperature. The sample was allowed to equilibrate for 15
min at each temperature (-20, -10, 0, 10, 20, 30, 40, 50) before
spectra were recorded (see supporting Figure S1 for van’t Hoff
plot).
[Cp*Ir(CO)(R,R-TsDACH)]BF4 ([2H(CO)]BF4). Dissolution
of 0.16 g (0.253 mmol) of Cp*IrCl(R,R-TsDACH) and 0.029 g
(0.259 mmol) of NaBF4 in 20 mL of MeOH gave a red solution.
Purging the solution with CO resulted in an immediate color change
to colorless. The solution was filtered and the solvent was removed
under reduced pressure, resulting in a pale yellow solid. Yield: 0.147
g (82%). Slow diffusion of ether into a MeCN solution resulted in
pale yellow crystals suitable for X-ray crystallography. IR (CH2Cl2):
(41) Glueck, D. S.; Bergman, R. G. Organometallics 1990, 9, 2862–
2863.
(42) Clark, C. R.; Buckingham, D. A. Inorg. Chim. Acta 1997, 254,
339–343.
(43) Ikariya, T.; Hashiguchi, S.; Murata, K.; Noyori, R. Org. Syn. 2005,
82, 10–17.
(44) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920–3922.
(45) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877–910.
(46) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: New York, 1988.

Lewis Base Adducts
Organometallics, Vol. 27, No. 7, 2008 1549
procedure was scaled up to allow for pKa analysis of [1H(L)]+ (see
Supporting Information).
[Cp*Ir(1-methylimidazole)(TsDPEN)]BF4. A 12.5 µL (0.16
mmol) CH2Cl2 solution of 1-methylimidazole was added to a
solution of 98 mg (0.13 mmol) of [Cp*Ir(TsDPEN)]BF4 in 10 mL
of CH2Cl2. An immediate color change from reddish-orange to
yellow was observed. The solution was allowed to stir for 2 min
before being concentrated to ∼1 mL. The oily residue was
recrystallized from CH2Cl2 by the addition of Et2O. Yield: 84.8
1
mg (79%). H NMR (500 MHz, CD3CN): δ 1.66 (s, 15H, Cp*),
2.19 (s, 3H, SO2C6H4-4-Me), 3.71–3.88 (m, 2 H, HNCHPhCH-
PhNTs), 3.85 (s, 3H, imidazole N-CH3), 4.23 (br d, 8 Hz, 1H,
HHNCHPhCHPhNTs), 5.56 (br s, 1H, HHNCHPhCHPhNTs),
6.56–7.20 (m, 10H), 7.24 (br s, 1H, imidazole vinyl H), 7.37 (br s,
1H, imidazole vinyl H), 8.42 (br s, 1H, imidazole CH). 13C NMR
(125 MHz, CD3CN): δ 8.23, 9.33, 21.11, 35.31, 70.14, 74.86, 88.49,
123.74, 127.48, 128.11, 128.25, 128.76, 128.99, 129.26, 129.35,
130.09, 131.13, 138.43, 139.29, 140.98, 143.41. Anal. Calcd for
C34H42N4IrO2SBF4: C, 48.78; H, 4.91; N, 6.50. Found: C, 47.94;
H, 4.80; N, 6.52.
Figure 10. Isomerization of [Cp*Ir(CO)(R,R-TsDACH)]BF4 in
CD3CN solution over a 150 min time period.
ν(CO) 2059 cm-1. (R-Ir isomer (minor isomer)) 1H NMR (500
MHz, CD3CN): δ 1.98 (s, 15H, Cp*), 0.71 – 2.72 (10H, cyclo-
hexane ring protons), 2.41 (s, 3H, SO2C6H4-4-CH3), 3.80 (br, 1H,
HHNC6H10NTs), 5.46 (br, 1H, HHNC6H10NTs), 7.32 (d, 2H, 8 Hz,
SO2C6H4-4-CH3), 7.72 (d, 2H, 8 Hz, SO2C6H4-4-CH3). (S-Ir isomer
(major isomer)) 1H NMR (500 MHz, CD3CN): δ 1.93 (s, 15H,
Cp*), 0.71 – 2.70 (10H, cyclohexane ring protons), 2.41 (s, 3H,
SO2C6H4-4-CH3), 4.45 (br, 1H, HHNC6H10NTs), 5.14 (br, 1H,
HHNC6H10NTs), 7.34 (d, 2H, 8 Hz, SO2C6H4-4-CH3), 7.72 (d, 2H,
8 Hz, SO2C6H4-4-CH3). Anal. Calcd for C24H34IrN2O3SBF4: C,
40.62; H, 4.83; N, 3.95. Found: C, 40.0; H, 4.63; N, 4.24.
Isomerization of [Cp*Ir(CO)(R,R-TsDACH)]BF4 ([2H(CO)]-
BF4). A 0.8 mL CD3CN solution of 5.0 mg (6.8 µmol) of
[Cp*Ir(CO)(R,R-TsDACH)]BF4 and 1.0 mg of C6Me6 (internal
standard) was dissolved in 0.8 mL of CD3CN. Addition of the
CD3CN solution was taken as time ) 0. Between 250 and 300 s
elapsed during the time of solvent addition and start of data
collection. Data were collected in a preacquisition delay array for
115 min, where a spectrum was recorded every 30 s with a
preacquisition delay time of 10 s, acquisition time of 5 s, and a
postpulse delay time of 15 s at a temperature of 293.0 K. The sample
was spun at a rate of 20 rpm for the duration of the experiment.
Rates were determined by following the disappearance of the Cp*
signals in accordance with the signal for C6Me6 (δ 2.19). The first
165 of the 231 data points were used in the kinetic analysis,
accounting for three half-lives (Figure 10).
pKa Measurements. pKa values were determined as previously
described.7,47 The effect of homoconjugation was neglected. pKa’s
were reported to one significant figure but were measured to two
significant figures (see Supporting Information, Table S3).
Equilibrium Measurements on the Reaction [1H(NH3)]+
+
PPh3. A 0.80 mL CD3CN solution of 9.5 mg (11.9 µmol) of
[Cp*Ir(NH3)(TsDPEN)]BF4, and 1.0 mg (6.2 µmol) of C6Me6
(internal standard) was treated with 340 µL of a 0.053 M (18.0
µmol) PPh3 in CD3CN solution, resulting in a slight darkening of
the yellow color. The addition of the PPh3 solution was repeated
four times, allowing the solution to equilibrate over a 5 min time
period before data collection for each aliquot. The equilibrium ratios
were determined by integration values of the Cp* peaks (δ 1.57
and 1.77 for [1H(PPh3)]+ and [1H(NH3)]+, respectively), with
respect to the internal standard (δ 2.19).
Acknowledgment. This research was supported by the
Department of Energy.
Supporting Information Available: Preparatory methods not
described above, van’t Hoff plot for the isomerization of [1H(PPh3)]-
BF4, kinetic data for the isomerization of [2H(CO)]BF4, space-filling
models of 1, [1H]BArF , [1H(NCMe)]PF6, [1H(NH3)]BF4, [1H-
4
(PPh3)]BF4, [1H(CO)]BF4, and [2H(CO)]BF4, comparison of cyclic
voltammograms of 1H(H), 2H(H), and 3H(H), Ru, Rh, and Ir amino
chlorides, affect of Cp ring on redox potential of 1H(H), and Lewis
base adducts. CIF files giving crystallographic data for Cp*Ir(TsDPEN–
H), [Cp*Ir(NCMe)(TsDPEN]PF6, [Cp*Ir(CO)(R,R-TsDACH)]BF4,
[Cp*Ir(PPh3)(TsDPEN)]BF4, [Cp*Ir(CO)(TsDPEN)]BF4, [Cp*Ir(NH3)-
(TsDPEN)]BF4. This material is available free of charge via the Internet
at http://pubs.acs.org.
General Procedure for Ligand Binding (formation of
[1H(L)]+). A 0.80 mL CD3CN solution of 10 mg (12.8 µmol) of
[Cp*Ir(TsDPEN)]BF4 and 1.0 mg (6.2 µmol) of C6Me6 (internal
standard) was treated with three aliquots of 1–5 equiv of ligand in
1
CD3CN solution after an initial H NMR spectrum was obtained.
A color change from a pale yellow to a darker yellow color was
observed upon ligand binding.
Note: Due to the observed lability of the NCMe adduct and the
availability of a convenient pH scale in acetonitrile,34,35 ligand
binding was based on the ability to displace NCMe from [1H(NC-
Me)]+ to result in [1H(L)]+. If a ligand was found to bind, the
OM700996M
(47) Stanley, J. L.; Heiden, Z. M.; Rauchfuss, T. B.; Wilson, S. R.; De
Gioia, L.; Zampella, G. Organometallics 2008, 27, 119–125.