Synthesis and oxidation of Cp*IrIII compounds: Functionalization of a Cp* methyl group

Article abstract of DOI:10.1039/b820839e

[Cp*IrCl₂]₂ (1) and new Cp*Ir ^III(L-L)X complexes (L-L = N-O or C-N chelating ligands; X = Cl, I, Me) have been prepared and their reactivity with two-electron chemical oxidants explored. Reaction of 1 with PhI(OAc)₂ in wet solvents yields a new chloro-bridged dimer in which each of the Cp* ligands has been singly acetoxylated to form [Cp^OAcIr^IIICl₂] ₂ (2) (Cp^OAc = η⁵-C₅Me ₄CH₂OAc). Complex 2 and related carboxy- and alkoxy-functionalized Cp^OR complexes can also be prepared from 1 plus (PhIO)_n and ROH. [Cp^OAcIr^IIICl ₂]₂ (2) and the methoxy analogue [Cp^OMeIr ^IIICl₂]₂ (3) have been structurally characterized. Treatment of [Cp*IrCl₂]₂ (1) with 2-phenylpyridine yields Cp*Ir^III(ppy)Cl (4Cl) (ppy = cyclometallated 2-phenylpyridyl) which is readily converted to its iodide and methyl analogues Cp*Ir^III(ppy)I (4I) and Cp*Ir ^III(ppy)Me (4Me). Cp*Ir^III complexes were also prepared with N-O chelating ligands derived from anthranilic acid (2-aminobenzoic acid) and α-aminoisobutyric acid (H₂NCMe ₂COOH), ligands chosen to be relatively oxidation resistant. These complexes and 1 were reacted with potential two-electron oxidants including PhI(OAc)₂, hexachlorocyclohexadienone (C₆Cl₆O), N-fluoro-2,4,6-trimethylpyridinium (Me₃pyF⁺), [Me ₃O]BF₄ and MeOTf (OTf = triflate, CF₃SO ₃). Iridium(V) complexes were not observed or implicated in these reactions, despite the similarity of the potential products to known Cp*Ir^V species. The carbon electrophiles [Me ₃O]BF₄ and MeOTf appear to react preferentially at the N-O ligands, to give methyl esters in some cases. Overall, the results indicate that Cp* is not inert under oxidizing conditions and is therefore not a good supporting ligand for oxidizing organometallic complexes. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b820839e

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and oxidation of Cp*IrIII compounds: functionalization
of a Cp* methyl group†
Lisa S. Park-Gehrke,a John Freudenthal,b Werner Kaminsky,b Antonio G. DiPasqualec and James M. Mayer*a
Received 21st November 2008, Accepted 17th December 2008
First published as an Advance Article on the web 29th January 2009
DOI: 10.1039/b820839e
[Cp*IrCl2]2 (1) and new Cp*IrIII(L–L)X complexes (L–L = N–O or C–N chelating ligands; X = Cl, I,
Me) have been prepared and their reactivity with two-electron chemical oxidants explored. Reaction of
1 with PhI(OAc)2 in wet solvents yields a new chloro-bridged dimer in which each of the Cp* ligands
5
has been singly acetoxylated to form [CpOAcIrIIICl2]2 (2) (CpOAc = h -C5Me4CH2OAc). Complex 2 and
related carboxy- and alkoxy-functionalized CpOR complexes can also be prepared from 1 plus (PhIO)n
and ROH. [CpOAcIrIIICl2]2 (2) and the methoxy analogue [CpOMeIrIIICl2]2 (3) have been structurally
characterized. Treatment of [Cp*IrCl2]2 (1) with 2-phenylpyridine yields Cp*IrIII(ppy)Cl (4Cl)
(ppy = cyclometallated 2-phenylpyridyl) which is readily converted to its iodide and methyl analogues
Cp*IrIII(ppy)I (4I) and Cp*IrIII(ppy)Me (4Me). Cp*IrIII complexes were also prepared with N–O
chelating ligands derived from anthranilic acid (2-aminobenzoic acid) and a-aminoisobutyric acid
(H2NCMe2COOH), ligands chosen to be relatively oxidation resistant. These complexes and 1 were
reacted with potential two-electron oxidants including PhI(OAc)2, hexachlorocyclohexadienone
(C6Cl6O), N-fluoro-2,4,6-trimethylpyridinium (Me3pyF+), [Me3O]BF4 and MeOTf (OTf = triflate,
CF3SO3). Iridium(V) complexes were not observed or implicated in these reactions, despite the
similarity of the potential products to known Cp*IrV species. The carbon electrophiles [Me3O]BF4 and
MeOTf appear to react preferentially at the N–O ligands, to give methyl esters in some cases. Overall,
the results indicate that Cp* is not inert under oxidizing conditions and is therefore not a good
supporting ligand for oxidizing organometallic complexes.
The known isolated organometallic IrV complexes, while reac-
Introduction
tive and often not very stable, do not appear to be strong oxidants.
Oxidation reactions and oxidizing compounds have histori-
In contrast, high oxidation state iridium systems with non-
cally been among the least developed areas of organometallic
organometallic ligands are very strongly oxidizing. For example,
chemistry. Recent years have seen advances in organometal-
hexachloroiridate(IV), IrIVCl62-, has E◦ = 0.67 V vs. SHE in
lic ruthenium(IV),1 palladium(IV),2 and platinum(IV)3 chem-
MeCN12 and IrV is not accessible with chloride ligation. This
istry and some mildly oxidizing species have been prepared.
dichotomy arises because replacement of a Cl ligand for an alkyl
Iridium(V) compounds have the potential to be stronger ox-
or aryl group typically shifts the redox potential down by ca.
idants, but this oxidation state remains mostly unexplored.
0.3 V per ligand, based on related Re and Os complexes.13 Thus,
The relatively few known IrV compounds predominantly have
variation in the ligands should have a substantial effect on the
cyclopentadienyl, hydrocarbyl and hydride ligands, including
redox character and reactivity of IrV complexes. Another strategy
Cp*IrMe4,4 Cp*IrMe3X and Cp*IrMe3(L)+ (X- = Cl-, OTf-
for stabilizing high oxidation states is the use of ligands that
can be deprotonated upon oxidation, as in aquo/hydroxo/oxo
and amine/amide/imido complexes of ruthenium and osmium.14
[CF3SO3 ], L = PR3, etc.),5 [CpIrH3(PMe3)]+,6 (mes)3Ir(O),7
-
Cp0IrH3SiEt3,8 (iPrBDI)IrH4,9 and others10 [Cp = C5H5, Cp* =
C5Me5, Cp0 = (2-methoxyethyl)cyclopentadienyl), mes = 2,4,6-
The osmium aniline/anilide complexes TpOsCl2(NHxPh) are a
i
trimethylphenyl, PrBDI = ArNC(Me)CH(Me)CNAr, Ar = 2,6-
iPr2C6H3]. The IrIII/IrV redox couple has also been implicated in a
number of catalytic reactions.11
particularly dramatic example, as the OsIII/OsIV redox potential
shifts from +0.48 to -1.05 V (vs. Cp2Fe+/0 in MeCN) upon
deprotonation.15
aDepartment of Chemistry, Campus Box 351700, University of Washington,
Seattle, WA 98195, US. E-mail: mayer@chem.washington.edu; Fax: 1 206
685 8665; Tel: 1 206 543 2083
The studies reported herein are part of a program to use
these approaches to develop the chemistry of the IrIII/IrV redox
couple and, more generally, to develop the chemistry of oxidizing
organometallic compounds. We describe the reactivity of new
and known IrIII complexes with two-electron chemical oxidants
such as those in Chart 1. These reagents are all formally sources
of electrophiles X+ (Cl+, OAc+, F+, or Me+) which could add
to an IrIII centre to form [IrV–X]+ complexes. While this work
was in progress, Periana et al. reported related reactions of IrIII
compounds with strong oxidants.16 Our studies have used the
bUniversity of Washington X-ray Crystallographic Facility, Seattle, WA
98195, US
c20A Lewis Hall, X-ray Crystallographic Facility, College of Chemistry,
University of California, Berkeley, CA 94720, US. E-mail: adipasqu@
berkeley.edu; Tel: 1 510 642 7336
† Electronic supplementary information (ESI) available: Crystallographic
data for complex 4Cl. CCDC reference number 710446–710452. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b820839e
1972 | Dalton Trans., 2009, 1972–1983
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five and six coordinate Cp*IrIII complexes.21 The Cp* ligand
was chosen for this study because it has been widely used as a
supporting ligand, both in IrV compounds and reactions that have
implicated IrV intermediates.4–6,10b,e,f,11b,c,h,i We find, however, that
under oxidizing conditions the Cp* ligand is not an inert bystander
but can be oxidized.
Chart 1
Results
1. Oxidation of [Cp*IrCl2]2 to [CpORIrCl2]2
Cp* ligand that appears in many of the known IrV complexes.
We have also used cyclometallated 2-phenylpyridine (ppyH) and
chelating amide ligands (Chart 2), to explore how different types of
ligands influence the reactivity of IrIII in an oxidizing environment.
Cyclometallated 2-arylpyridine ligands are strong donors and
their iridium complexes are of much current interest due to their
photophysical properties.17 Complexes of this ligand are also
involved in palladium oxidation catalysis.18 The N-O chelating
ligands that have been used, derivatives of anthranilic acid
(o-H2NC6H4CO2H, anthrH-NH2) and N-tosyl-o-aminoisobutyric
acid (TsNHCMe2CO2H, TAIBAH2), should be fairly oxidation
resistant due to the absence of C–H bonds a to the nitrogen
donor.19 Anthranilic acid is an unusual b-amino acid that can
coordinate as the singly, doubly, or triply deprotonated ligand.20
TAIBAH2 is related to a-amino acid ligands that make interesting
As part of our survey of oxidation reactions of Cp*IrIII complexes,
the well-known [Cp*IrCl2]2 dimer (1)22 was reacted with the
hypervalent iodine reagent PhI(OAc)2 in wet MeCN (eqn (1)).
PhI(OAc)2 is being increasingly used in organometallic oxidations,
for instance in the palladium reactions developed by Sanford
et al.23 Over a day at room temperature, or during 2 hours at
50 ◦C, reactions of 1 and PhI(OAc)2 convert to one main product,
1
2, and a few side products, according to H NMR spectra. The
single crystal X-ray structure of 2 (Fig. 1, Table 1) shows an iridium
chloro-bridged dimer very similar to 1,24 except that one methyl
group on each Cp* ligand has been oxidized to a CH2OAc group:
5
[(h -C5Me4CH2OAc)IrCl2]2 ([CpOAcIrCl2]2, 2). The metrical data
for this structure are discussed below.
The 1H NMR spectrum of 2 in CD3CN shows a char-
acteristic four signals with constant relative integrations of
6:6:3:2, consistent with the solid state structure: two pairs
of Cp*-CH3 groups (each 6H, d1.73, 1.66 ppm), the OAc
group (3H, d2.01 ppm), and the acetoxylated CH2 downfield at
d4.67 ppm. This 1H NMR spectrum is similar to that reported by
Maitlis and co-workers for the related CpOAc-ruthenium complex
[(C5Me4CH2OAc)Ru(CO)2Cl].25 ESI mass spectra of 2 show a pri-
mary peak at 421.1 m/z, which corresponds to CpOAcIrCl+.
Chart 2
(1)
Fig. 1 ORTEPs of 2·PhI and 3·PhI (PhI and hydrogen atoms omitted for clarity) with thermal ellipsoids drawn at the 50% probability level.
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5
Table 1 Selected bond distances (A) for comparison of [CpOAc IrCl2]2 (2) and [CpOMeIrCl2]2 (3) with [Cp*IrCl2]2 (1) and other h -C5Me4CH2R)IrIII
˚
complexes
b
[Cp*IrCl2]2 (1)a
[CpOAc IrCl2]2 (2)
[CpOMeIrCl2]2 (3)
[CpPPh3IrCl(PPh3)2]+
CpCO2HIrMe(CO)Clc
Ir–C1
Ir–C2
Ir–C3
Ir–C4
2.121(12)
2.118(16)
2.121(11)
2.155(12)
2.145(14)
2.132(16)
2.120(13)
2.123(13)
2.134(14)
2.127(13)
2.140(12)
2.129(8)
2.117(13)
2.138(12)
2.150(12)
2.095(12)
2.021(18)
2.112(8)
2.226(10)
2.278(10)
2.289(10)
2.258(10)
2.245(10)
2.259(25)
1.479(15)
1.495(11)
2.291(15)
2.277(15)
2.225(17)
2.260(20)
2.191(17)
2.249(40)
1.539(54)
1.526(26)
Ir–C5
Avg Ir–C
C–Cfunc
Avg C–C
1.468(19)
1.499(9)
1.485(18)
1.543(67)
1.531(15)
a Ref. 24. b Ref. 26. c Ref. 27.
The maximum conversion of 1 to 2 in reaction 1 is about 60%
by NMR and a number of minor products are also formed. Yellow
reaction mixtures rapidly turn a dark brown colour which lightens
to a golden hue upon heating or if left standing for hours. Heating
also causes some decomposition of the PhI(OAc)2, both in the
presence and absence of iridium complexes. Even with the addition
of 8 equivalents of PhI(OAc)2, some 1 remains; addition of further
aliquots of oxidant leads to reaction with both 1 and 2. The further
reaction between 2 and PhI(OAc)2 appears to lead to oxidation of
additional Cp*-Me groups, as far as we can tell from the complex
1H NMR spectra that result.
very slow—not complete after a month at 22 ◦C—perhaps due
to poor solubility of the isolated iodosylbenzene polymer in
acetonitrile.
Complex 1 also reacts with iodosylbenzene-dibenzoate and
-di-p-toluate, PhI(O2CPh)2 and PhI(O2CTol)2, in wet MeCN. The
primary products appear to be aryl analogues of 2, [CpO2CPhIrCl2]2
and [CpO2CTolIrCl2]2, although the modest yields and inseparable
side products have precluded their isolation. [CpO2CPhIrCl2]2 and
[CpO2CTolIrCl2]2 are also formed from 1 + (PhIO)n + ArCO2H
◦
at 50 C (Scheme 1). The CpO2CAr iridium dimers are identified
1
by the characteristic 6:6:2 signal pattern in the H NMR and
The balanced reaction to form 2 from 1 and PhI(OAc)2 (eqn (1))
gives two equiv of acetic acid, which is quantitatively observed by
1H NMR. While water is not stoichiometrically needed, under
anhydrous conditions there is virtually no reaction between 1 and
PhI(OAc)2.
Complex 2 is formed well in wet (undried) bench-top MeCN, or
in MeCN to which significant water has been added. This suggests
that a hydrolysis product of PhI(OAc)2, a hydroxyl derivative or a
(PhIO)n oligomer (eqn (2)), is the actual reactive oxidant.28
the correct integral ratio with the carboxylate groups. Their
ESI mass spectra show prominent peaks for the respective
CpO2CArIrCl+ fragment, at m/z 483.1 for [CpO2CPhIrCl2]2 and m/z
497.1 for [CpO2CTolIrCl2]2. The PhI(O2CAr)2 reactions are much
slower than those with PhI(OAc)2, requiring 7 days at 50 ◦C
in MeCN, apparently due to poor solubility of the iodine
reagents.
The Cp* functionalization is not limited to carboxylate groups:
heating [Cp*IrCl2]2 (1) and (PhIO)n at 50 ◦C in methanol
yields the related methoxy-functionalized dimer, [CpOMeIrCl2]2 (3;
1
(2)
Scheme 1). The H NMR spectrum of 3 in dry CD2Cl2 exhibits
the now-familiar 6:6:3:2 pattern: Cp-Me groups at d1.58, 1.61;
a methoxy group at d3.36; and the methoxylated methylene
group at 4.07 ppm. The ESI/MS spectrum of 3 shows the
characteristic fragment for [CpOMeIrCl]+, 393.2 m/z. Complex 3
has also been characterized by an X-ray crystal structure (Fig. 1
above). The reaction of 1 plus PhIO in ethanol proceeds similarly
Monitoring reaction 1 over time by 1H NMR shows that
PhI(OAc)2 is consumed faster than 2 appears, implicating an
intermediate iodine species. In support of this, 2 is also formed
from 1 plus independently prepared iodosylbenzene [(PhIO)n] and
excess AcOH in wet MeCN (Scheme 1). This reaction is, however,
Scheme 1
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1
to [CpOEtIrCl2]2, based on H NMR and ESI-mass spectra. In
2. Cp*Ir(ppy)X (4X) complexes
the formation of 3 via Scheme 1, addition of (PhIO)n to an orange
suspension of 1 in MeOH forms a forest green solution, which then
changes to the orange-brown of 3 over a day at room temperature
(or rapidly upon heating). 1H NMR spectra of the green solutions
shows signals in the Cp*-region for as yet unidentified species,
including a material (“A”) that is seen in many of the oxidations
of 1. As the green solution turns orange, most of the Cp* signals
decay leaving primarily 3, A, PhI and 1. The formation of multiple
products means that these reactions, while somewhat general,
are not (as yet) attractive synthetic routes to functionalized Cp*
compounds.
Complexes 1–3 have similar Ir–C and Ir–Cl bond lengths
(Table 1), suggesting that the acetoxy and methoxy groups do
not have a significant electronic effect on the metal centre. The
C–C bonds between the Cp*-ring and the CH2OAc or CH2OMe
carbon, on both sides of both molecules, are at most only
slightly shorter than the Cp*–Me bond lengths. For Ir(1) in
A. Synthesis and characterization. The chemistry of cy-
clometallated 2-phenylpyridine complexes Cp*Ir(ppy)X (4X) has
been explored because these compounds should be more electron
rich than the dichloride derivative [Cp*IrCl2]2 (1). Addition of
2-phenylpyridine (ppyH) to methanol solutions of 1 forms orange
solid Cp*Ir(ppy)Cl (4Cl) in good yield (Scheme 2). While this work
was in progress, 4Cl was described by Djukic et al., who prepared
it from 1, ppyH and NaOAc in CH2Cl2, and isolated it by air-free
column chromatography at 0 ◦C.31 The synthesis of 4Cl described
here (see Experimental section) appears to be simpler, with easier
isolation and comparable product yields.
˚
2, for instance, the C1–C6 bond of 1.468(19) A is within 2s
˚
of the 1.499(9) A average of the (Cp)C–Me bonds. Thus there
appears to be little contribution from a fulvene resonance form
5
+
-
29
=
[h -(MeC)4C CH2 OR ].
Reacting 1 with (PhIO)n in wet CD3CN in the absence of any acid
or alcohol gives a new species (in addition to A). This compound
has a similar 6:6:2 pattern of NMR resonances in CD3CN except
that the methylene signal is a doublet (d4.13 ppm, 3JHH = 5.5 Hz),
in addition to the two Cp*–Me singlets (d1.71 and 1.65 ppm). A
triplet integrating to 1 H is also observed at d3.42 ppm (3JHH
=
5.5 Hz). These data indicate that a Cp*-methyl group has been
oxidized to CH2OH, with the CH2 signal split into a doublet by
the OH and the OH signal likewise split into a triplet by the CH2.
The splitting disappears when an excess of a proton source (e.g.,
AcOH) is added to the reaction solution and is not visible when the
reaction is carried out in the presence of D2O. While it is unusual
to observe coupling to an OH group, Maitlis and co-workers
have reported similar 3-bond CH–OH couplings for hydroxylated
Cp* ligands bound to ruthenium.25,30 ESI mass spectra of the
1 + (PhIO)n + H2O/CD3CN reaction solution show major peak
clusters for Cp*IrCl+ and for (C5Me4CHO)IrCl+; it is not evident
why a CpOHIrCl+ ion analogous to other [CpORIrCl2]2 complexes is
not observed. ESI/MS of [Cp*IrCl2]2 + (PhI16O)n + H218O reaction
mixtures show the formation of (C5Me4CH18O)IrCl+.
Scheme 2
Addition of excess MeI to 4Cl in methanol proceeds by Cl-for-
I exchange, yielding rust-coloured Cp*Ir(ppy)I (4I; Scheme 1).
When the reaction is conducted in CD3OD, CH3Cl is observed
1
by H NMR at d3.01 ppm (confirmed by comparison with an
authentic sample). Treatment of 4Cl with AgOTf, AgPF6 or AgBF4
-
in MeCN yields [Cp*Ir(ppy)NCMe]X (4MeCN; X- = OTf-, PF6 ,
or BF4 ) (Scheme 2), which were characterized by 1H NMR. The
-
Complex 1 reacts readily with PhICl2 or PhI(TFA)2 (TFA =
trifluoroacetate, O2CCF3) but by 1H NMR no [CpClIrCl2]2 is
formed and there is at most a trace of [CpTFAIrCl2]2. Heating 1
with a slight excess of◦benzoyl peroxide [PhC(O)O]2 and PhCO2H
in wet CD3CN at 75 C gives a small amount of [CpO2CPhIrCl2]2,
suggesting that functionalization of the Cp*–Me group could
proceed by a radical pathway.
Attempts to elucidate the mechanism of oxidation of 1 by
PhI(OR)2 or (PhIO)n + ROH have been complicated by the
moderate yields and side products that are observed by 1H
NMR. These materials may include dimers with singly or other-
wise non-symmetrically functionalized Cp* ligands, or monomeric
analogues. One significant product, called A above, is initially
present in roughly 20–30% yield in all reactions. It has the
characteristic 6:6:2 1H NMR signals (d1.65, 1.72, and 4.26 ppm)
and could possibly be an alkoxide analogue, [(OCH2Me4)IrCl]n,
but attempts to isolate it have not been successful.
red methyl derivative Cp*Ir(ppy)Me (4Me) is prepared by reaction
of MeLi with 4Cl in THF (Scheme 2).
1H NMR spectra of 4Cl, 4I, 4MeCN, and 4Me in CD2Cl2 all
show a single Cp* resonance (d1.66 for 4Cl) and eight sometimes
overlapping ppy signals (d7.04–8.68 for 4Cl). The assignments for
1
4Cl were confirmed by H 2D NMR (COSY).32 Complex 4Me
also has an IrMe signal at d-0.33 ppm, while 4MeCN has an
IrCH3CN signal at d2.30 ppm. ESI mass spectra of 4Cl, 4I and
4Me show ion clusters at M+ and prominent Cp*Ir(ppy)+ peaks
(M+ - X). ESI mass spectra of 4MeCN variants show primarily the
(M+ - X) peak.
The X-ray crystal structures of 4Cl and 4I† are very similar, both
containing isolated molecules with “three-legged piano stool”
geometries (Fig. 2). As expected, the Ir–I bond of 2.691(5) in 4I is
˚
almost 0.3 A longer than the 2.401(3) Ir–Cl bond in 4Cl. Selected
bond lengths and angles for 4I are listed in Table 2; Table 3 gives
the data collection parameters (the data for 4Cl are given in the
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Fig. 2 ORTEPS of Cp*Ir(ppy)Cl (4Cl) and Cp*Ir(ppy)I (4I) with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms have been
omitted for clarity.
carbene (NHC) complex Cp*IrIII(C–NHC)Cl, where C–NHC =
Table 2 Selected bond distances (A) and angles (◦) for
˚
cyclometallated 1-benzyl-3-methylimidazolylidene.33e To test for
possible catalytic 2-phenylpyridine deuteration, solutions of ppyH
in CD3OD were heated with 5–20 mol% 4Cl for 1.5 days.1H NMR
spectra indicated deuteration of 4Cl, but the signals for free ppyH
remained unchanged.
Cp*Ir(ppy)I (4I), Cp*Ir(H2NC6H4CO2)Cl·MeOH (6·MeOH) and
Cp*Ir(TsNC6H4CO2)(MeCN)·H2O (7·H2O)
4I
6·MeOH
7·H2O
Ir(1)–C(1)
Ir(1)–C(2)
Ir(1)–C(3)
Ir(1)–C(4)
Ir(1)–C(5)
Ir(1)–I(1)
2.167(7)
2.164(8)
2.260(8)
2.256(6)
2.168(7)
2.691(5)
2.122(7)
2.170(8)
2.150(8)
2.146(7)
2.152(7)
2.130(6)
2.153(6)
2.150(6)
2.143(6)
2.148(6)
Ir(1)–Cl(1)
Ir(1)–N(1)
Ir(1)–C(11)
Ir(1)–O(1)
2.3875(16)
2.133(5)
2.082(7)
2.053(7)
2.115(5)
(3)
2.136(5)
2.083(4)
2.062(5)
82.92(17)
89.02(18)d
80.05(17)f
Ir(1)–N(2)
N(1)–Ir(1)–O(1)
N(1)–Ir(1)—X
I(1)–Ir(1)–C(11)
77.7(3)a
89.17(15)b
110.5(3)
77.8(2)
82.60(17)c
83.91(15)e
a N(1)–Ir(1)–C(11). b N(1)–Ir(1)–I(1). c N(1)–Ir(1)–Cl(1). d N(1)–Ir(1)–
N(2). e Cl(1)–Ir(1)–O(1). f N(2)–Ir(1)–O(1).
B. Oxidations of Cp*IrIII(ppy)X (4X). Compounds 4X were
treated with the two-electron chemical oxidants shown above
in Chart 1. In a typical experiment, the oxidant was added to
Cp*IrIII(ppy)L in ‘dry’ CD3CN in a J. Young NMR tube at ambient
temperatures, except for reactions between Me3pyF+ and 4Cl or
4I, which were heated at 100◦C because no reactivity was seen at
room temperature. All reactions were monitored by 1H NMR.
Heating a solution of 4Me and PhI(OAc)2 for an hour at 45 ◦C
supporting information†). The metrical data for 4Cl and 4I are
similar to related IrIII complexes, in the 2.15–2.23 A Ir–C(Cp*)
˚
bond lengths5,33 and in the Ir–C and Ir–N bond lengths to the ppy
moiety.34
◦
Heating 4Cl (but not 4I) in CD3OD over two hours at 120 C
1
results in exchange of one hydrogen on the ppy ligand for
gives a single new iridium species. Its H NMR spectrum shows
1
deuterium. H NMR spectra show the gradual disappearance of
signals for phenylpyridyl and Ir-Me ligands, a 3:3:3:3 pattern in
the Cp* region, a –OAc signal at d1.92 integrating to 3 hydrogens,
and a quasi-quartet centred at d4.65 integrating to 2 hydrogens.
These data suggest that a Cp*-methyl functionalized product
has been formed, CpOAcIr(ppy)Me (5) (eqn (4)), similar to the
formation of 2. The ESI/MS of 5 shows peaks at m/z = 554 and
540 which correspond to [CpOAcIr(ppy)Me–H]+ and CpOAcIr(ppy)+,
consistent with this formulation. In contrast to 2 and 3, the iridium
centre of 5 is chiral and therefore the four CpOAc methyl groups are
inequivalent, accounting for the 3:3:3:3 pattern. In addition, the
methylene hydrogens are diastereotopic, so the apparent quartet
at d4.65 is actually an AB pattern.
one ppy resonance and the conversion of one triplet resonance
2
to a doublet signal. The H NMR spectrum of the exchanged
compound shows a single, sharp signal at d7.72. Based on
assignments of the 1H NMR spectrum of 4Cl by COSY and
NOESY experiments, the exchanged hydrogen is H4 of the ppy
1
phenyl ring (eqn (3)). No other changes occur in the H NMR
spectrum, and ESI/MS analysis in CD3OD shows a [M-d1]-Cl
peak for 4Cl-d1 (483 m/z), confirming that 4Cl is unchanged
except for exchange of one D for H. This ortho-H/D exchange
in CD3OD is very similar to the exchange recently reported
by Peris and co-workers for the cyclometallated N-heterocyclic
1976 | Dalton Trans., 2009, 1972–1983
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Table 3 Crystal data and structure refinement for [CpOAc IrCl2]2·PhI (2·PhI) and [CpOMeIrCl2]2 (3·PhI), Cp*Ir(ppy)I (4I), Cp*Ir(H2NC6H4CO2)Cl
(6·MeOH), Cp*Ir(TsNC6H4CO2)(MeCN)·H2O (7·H2O)
2·PhI
3·PhI
4I
6·MeOH
7·H2O
Empirical formula
Formula weight
Temperature (K)
C30H39Cl4IIr2O4
1116.76
130(2)
C28H39Cl4IIr2O2
1060.73
130(2)
C21H23IIrN
608.50
130(2)
C18H25ClIrNO3
531.04
130(2)
C26H31IrN2O5S
675.79
143(2)
˚
Wavelength (A)
0.71073
0.71073
0.71073
0.71073
0.71073
Crystal description/colour
Crystal system
Space group
Cut block/yellow
Triclinic
P-1
Cut block/orange
Triclinic
P-1
Prism/yellow
Monoclinic
P21/c
Needle/yellow
Orthorhombic
P212121
Plate/yellow
Triclinic
P-1
Unit cell dimensions
˚
a (A)
8.8660(4)
8.7721(5)
13.6754(10)
14.3727(9)
105.435(4)
100.301(3)
99.207(3)
1595.41(18)
2
2.208
9.659
996
0.20 ¥ 0.10 ¥ 0.10
468
2.42 to 25.47
-10 ≤ h ≤ 10
-16 ≤ k ≤ 16
-17 ≤ l ≤ 17
10263
13.7010(4)
9.0000(3)
15.8690(5)
90
99.9800(15)
90
1927.18(10)
4
2.097
8.532
1144
0.35 ¥ 0.32 ¥ 0.15
1320
7.18200(10)
15.0380(3)
16.8710(4)
90
90
90
1822.12(6)
4
1.936
7.490
1032
0.59 ¥ 0.10 ¥ 0.07
1294
2.41 to 28.36
-9 ≤ h ≤ 9
-19 ≤ k ≤ 19
-21 ≤ l ≤ 21
6923
8.686(3)
8.726(3)
˚
b (A)
13.3300(5)
16.1160(7)
112.939(2)
94.7220(19)
98.9320(17)
1711.27(12)
2
2.167
9.016
1052
0.30 ¥ 0.30 ¥ 0.10
52
2.35 to 25.56
-10 ≤ h ≤ 10
-15 ≤ k ≤ 16
-19 ≤ l ≤ 19
11070
˚
c (A)
19.065(6)
76.821(4)
87.514(4)
63.397(3)
1255.1(7)
2
1.788
5.442
688
0.08 ¥ 0.04 ¥ 0.02
1294
3.05 to 27.02
-11 ≤ h ≤ 10
-10 ≤ k ≤ 10
-22 ≤ l ≤ 23
11426
a (◦)
b (◦)
g (◦)
V (A )
Z
3
˚
Calculated density (g cm-3)
Abs coeff (mm-1)
F(000)
Crystal size (mm)
Reflections for indexing
q range for data coll. (deg)
Index ranges
2.61 to 28.33
-18 ≤ h ≤ 18
-11 ≤ k ≤ 11
-21 ≤ l ≤ 21
8271
Reflns collected
Unique reflns
4517 Rint = 0.081
4343 Rint = 0.047
4877 Rint = 0.042
6230 Rint = 0.129
5708 Rint = 0.087
Completeness to q = 25.00
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R indices (all data)
98.9%
97.3%
98.2%
99.9%
98.7%
Full-matrix least-squares on F2
6230/30/380
S = 0.979
R1 = 0.058
wR2 = 0.127
5708/0/346
S = 0.926
4517/0/222
S = 1.004
4343/0/224
S = 1.049
4877/0/329
S = 1.058
R1 = 0.053
wR2 = 0.112
R1 = 0.058
wR2 = 0.155
R1 = 0.037
wR2 = 0.098
R1 = 0.038
wR2 = 0.076
independently synthesized material. With 4Cl + MeOTf, a signal
at d3.01 indicates that CH3Cl is formed (eqn (5)). Monitoring
reaction 4 from -40 ◦C to 25 ◦C in an NMR probe showed no
chemical change until the spectrometer was at room temperature,
and then only product formation was observed with no evidence
of an intermediate species.
(4)
The reaction of Cp*Ir(ppy)Cl (4Cl) with PhI(OAc)2 gives a
complex mixture of products, but 4Cl + C6Cl6O in methylene
chloride may give a Cp*-oxidized material similar to 2, 3, and 5.
C6Cl6O (Chart 1) is a valuable Cl+ donor in organic reactions,
with pentachlorophenoxide as the leaving group,35 but to our
knowledge it has not been used in transition metal chemistry.
A major product of this reaction exhibits a 6:6:2 pattern in the 1H
NMR, with the 2H signal at d4.30 ppm, which is characteristic of
the CpOR compounds. A new set of ppy signals is also observed.
This product unfortunately could not be isolated cleanly, away
from the [Cp*Ir(ppy)MeCN]+ and other products formed. ESI-
MS analysis of this solution showed a peak at 516 m/z (4Cl-
H+), which likely corresponds to the functionalized Cp* fragment
(5)
The reaction of 4Me with MeOTf is very slow unless water is
present. In wet MeCN, this reaction gives 4MeCN and CH4 (eqn
(6)). When CD3OTf is used, only CH4 is formed (d0.20 ), while 4Me
and CH3OTf in MeCN/D2O gives CH3D (d0.18, 3JHD = 1.8 Hz).
These results suggest that the methane results from protonation
of 4Me. Consistent with this conclusion, additions of the protic
acids NH4OTf or HOTf to 4Me also yield methane and 4MeCN.
Me3pyF+ (which has been used by Sanford et al.36) reacts with 4Me
in wet CD3CN to also give CH4 and 4MeCN but it is not reactive
with 4Cl or 4I.
5
ion (h -C5Me4CH2Cl)Ir(ppy)+, although the fulvene derivative
(C5Me4CH2)Ir(ppy)Cl+ cannot be ruled out.
Reactions of the Me+ donors MeOTf and [Me3O]BF4 with
4Cl in acetonitrile yield [Cp*Ir(ppy)NCMe]X (4MeCN, X-
=
-
OTf- or BF4 ), by comparison of the 1H NMR signals with
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(6)
(7)
(8)
3. IrIII complexes with N–O chelates
Three Cp*IrIII complexes with N–O chelating ligands have been
synthesized to test reactivity with the oxidants in Chart 1:
Cp*Ir(H2NC6H4CO2)Cl (6), Cp*Ir(TsNC6H4CO2)(MeCN) (7),
and Cp*Ir(TAIBA) (8). Grotjahn et al. has prepared related
Cp*IrIII(N–O) compounds from [Cp*IrCl2]2 (1), an amino
acid, and K2CO3 in N2-sparged MeCN.21d,e These pseudo-five-
coordinate Cp*Ir(N–O) complexes contain a doubly deprotonated
(N,O) ligand.
To facilitate deprotonation of the amino group and in-
hibit amide bridging, complexes of tosylated amino acid
ligands have been explored. Using N-tosyl anthranilic acid
and Grotjahn’s synthetic method mentioned above,21 yellow
Cp*Ir(TsNC6H4CO2)(MeCN) (7) was isolated in 67% yield (eqn
(9)). The yellow colour indicates a pseudo-six-coordinate species,
since five-coordinate Cp*Ir(N–O) compounds are typically red.21e
Complex 7 has been characterized by elemental analysis, ESI/MS
(M+ - MeCN = 618.1 m/z), 1H NMR, and X-ray crystallography
(Fig. 3, right). The NMR resonances for 7 are broad in CD2Cl2
but sharp in CD3CN, where the Cp* and aryl peaks are evident;
surprisingly, the signal for the MeCN is not visible (either as
free MeCN or coordinated to Ir). Anthranilate and its derivatives
thus do not appear to form pseudo five-coordinate Cp*Ir(N-O)
complexes as readily as alkylamine-carboxylate ligands.
With anthranilic acid, H2NC6H4CO2H, we find that Grotjahn’s
synthetic procedure yields a mixture of products. A few crystals of
one of these products were isolated and structurally characterized
to reveal an asymmetric dimer with a bridging amido ligand
(eqn (7); ESI†). In an alternative approach, 1 was stirred with
anthranilic acid and NaOH or NaOMe in methanol, yielding
Cp*Ir(H2NC6H4CO2)Cl (6) as a yellow precipitate (eqn (8)) in 31%
1
yield. H NMR spectra of 6 in CD2Cl2 show resonances for one
Cp* and one coordinated anthranilate ligand (the NH2 signal was
not observed). Despite the limited stability of 6 in solution, single
crystals were grown by slow evaporation of a benzene solution,
and the crystal structure shows six-coordinate “piano-stool” 6
(Fig. 3). The anthranilate ligand is mono-deprotonated, with
carboxylate group and aniline donors to the iridium. Surprisingly,
the anthranilate ring is nearly parallel to the plane of the Cp* ring.
In other amino-acid Cp*IrIII(N–O)Cl complexes, the plane of the
ligand contains the metal centre and intersects the plane of the
Cp* ring.37
(9)
Fig. 3 ORTEPs of the iridium complexes in Cp*Ir(H2NC6H4CO2)Cl·MeOH (6·MeOH) (left) and Cp*Ir(TsNC6H4CO2)(MeCN)·H2O (7·H2O) (right)
with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms and solvent molecules have been omitted for clarity.
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Reaction of 1 with N-p-toluenesulfonyl-o-aminoisobutyric
acid (TsNHCMe2CO2H) and K2CO3 forms Cp*Ir(TAIBA) (8)
(TAIBA = N(Ts)CMe2CO2) in good yield (eqn (10)). In this
case, the red colour of 8 indicates a pseudo-five coordinate
complex.21e 1H NMR spectra of 8 in CD3CN show a Cp* resonance
(d1.52 ppm), methyl and aryl resonances for the tosyl group, and
a singlet at d1.29 ppm integrating to six protons (vs. Cp* =
15) for the equivalent TAIBA methyl groups. The equivalence
of the two methyl groups also indicates a five-coordinate Cs
structure, since these would be inequivalent in a (non-fluxional)
three-legged piano-stool complex. Addition of PPh3 to a red
acetonitrile solution of 8 causes a colour change to yellow and
the 1H NMR spectrum of the product shows inequivalent TAIBA
methyl groups, both indicating phosphine binding to unsaturated
8 to make a six-coordinate chiral-at-metal adduct.
functionalization have involved initial deprotonation to give a
fulvene which is then susceptible to attack.40 Nucleophile-induced
hydride transfer to Ir has been suggested in the formation of
5
(h -C5Me4CH2PPh3)Ir(PPh3)2H.26 We are aware of just a few other
examples of activation of a Cp* methyl group under oxidative
conditions.41
The active oxidant in the [Cp*IrCl2]2 (1) ligand oxidation
appears to be a hydrolysis product of PhI(OAc)2 since water is
required. However, isolated (PhIO)n is much less reactive, perhaps
because of its low solubility. The Cp* oxidation by (PhIO)n in wet
MeCN or in ROH forms a C5Me4CH2OR ligand, where the OR
group is derived from the carboxylic acid, alcohol, or water present
in the solution. This suggests that an intermediate functionalized
derivative is generated, which then reacts with ROH to give
[(C5Me4CH2OR)IrCl2]2 ([CpORIrCl2]2: 2, 3). Although [CpORIrCl2]2
are readily formed, the stronger oxidant PhICl2 does not appear to
convert 1 to [CpClIrCl2]2. An open coordination site at Ir does not
appear to be required since 4Me is readily functionalized. More
detailed mechanistic studies, however, have been stymied by the
complexity of the reactions.
(10)
Functionalized Cp* derivatives have been isolated starting from
1, and observed starting from 4Me. The apparent formation of
CpClIr(ppy)Cl from 4Cl and the “Cl+” donor C6Cl6O is another
example of this oxidative reactivity. There are also hints of similar
chemistry in a number of the other reactions explored here,
from observations of 6:6:2 patterns with downfield methylene
signals in the 1H NMR spectra of reaction mixtures. These
observations indicate that Cp* is not a good supporting ligand for
oxidations of IrIII to IrV, and more generally for use in oxidation
chemistry.
Addition of [Me3O]BF4 to Cp*Ir(TAIBA) (8) in dry CD3CN
at ambient temperatures initially gives a new Cp*Ir(N–O) prod-
uct, “[Cp*Ir(TAIBA)]-Me+,” with an ESI mass spectral signal
at M+ = 598 m/z and a new 1H NMR methyl resonance at
d3.97 ppm. This low-field chemical shift and the equivalence of
the TAIBA methyl groups indicate that “Me+” has not added to
the iridium centre. Over 2 hours, the red solution pales in colour
and the intermediate iridium complex decomposes to give the
N-p-tosylamino-isobutyrate methyl ester (TAIBAH–Me). This
ester product was identified by 1H NMR and confirmed by
independent synthesis (see Experimental section). Thus it seems
likely that the intermediate species has Me+ added to an oxygen
of the TAIBA ligand, forming Cp*Ir(TAIBA-Me), and then slow
protonation of the TAIBA nitrogen liberates the methyl ester.
The reactions of MeOTf and [Me3O]BF4 with 7 and 8 all appear
to proceed analogously, with loss of the solution colour and for-
mation of the free methyl ester (the formation of the anthranilate
esterhasnotbeenconfirmedbyindependentsynthesis). Complex 6
reacted with the Me+ donors in CD2Cl2 to form multiple products
2. Addition of electrophiles to Ir(III) complexes
An initial motivation of this study was to generate IrV complexes
by reacting IrIII compounds with electrophiles, the sources of Me+,
Cl+, F+, or AcO+ in Chart 1. While a range of reactivity has been
observed, in no case is there good evidence for an IrV product or
transient intermediate.
Electrophiles appear to react preferentially at the ligand rather
than adding to the iridium centre. For instance, NMR spectra
indicate that [Me3O]BF4 delivers Me+ to a carboxylate oxygen of
Cp*Ir(TAIBA) (8), forming the methyl ester. This is despite the
tosylamide ligand being a significant p donor21d,e and 8 having an
apparent open coordination site for Me+ addition to the iridium.
Addition to the ligand appears to be a major pathway for many of
the reactions of the amino-acid complexes 6–8 with Me+ sources.
The most favourable case for electrophile addition to the iridium
centre should be the addition of Me+ to Cp*Ir(ppy)Me (4Me).
1
by H NMR. Reactions between 7 or 8 with the “X+ donors”
C6Cl6O or [Me3pyF+] in dry CD3CN form a complex mixtures of
products; with C6Cl6O the major species are [Cp*IrCl2]2 (1) and the
protonated ligand (TsNH2C6H4CO2H or TAIBAH2). PhI(OAc)2 is
unreactive with 7 or 8 in wet CD3CN. In sum, the Cp*Ir(N–O)(X)
compounds 6–8 are in many cases susceptible to electrophilic
attack, which appears to occur preferentially at the amino-acid
ligand rather than at the iridium centre.
+
This could have formed “Cp*IrV(ppy)Me2 ”, which would have
been very similar to known Cp*IrVMe3(L)+ species, containing
a Cp* group, three hydrocarbyl ligands and one neutral donor.5
However, the only reaction between MeOTf and 4Me appears
to involve trace acid protonating the methyl ligand to give
methane. Given this result, the ready formation of MeCl from
Cp*Ir(ppy)Cl (4Cl) plus MeI, MeOTf or [Me3O]BF4 most likely
proceeds by Me+ addition directly to the chloride ligand and
not via reductive elimination from a cationic IrV–methyl chloride
complex. In general, the iridium(III) complexes appear to have
limited nucleophilicity.
Discussion
1. Oxidation of the Cp* ligand of (Cp*IrCl2)2
The functionalization of the Cp* ligand in [Cp*IrCl2]2 by hyper-
valent iodine reagents was unexpected because Cp* has been a
widely valuable supporting ligand, even for somewhat oxidizing
compounds such as Cp*ReO3,38 Cp*RuX3 (X= Cl, Br, I)39 and
Cp*IrMe3X.4,5 Most studies of Cp*-methyl group activation and
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The reactions of the 4X complexes with electrophiles do
not form functionalized 2-phenylpyridine products such as
2-(2-chlorophenyl)pyridine or 2-(o-tolyl)pyridine (by comparison
of the 1H NMR spectra of reaction solutions with literature
spectral data42). This contrasts with the facile formation of func-
tionalized ppy derivatives upon treatment of PdII(ppy) complexes
with electrophiles.43 Similarly, MeOAc was not observed from 4Me
and PhI(OAc)2, in contrast to its formation in a related reaction of
an IrIII-methyl-triflate complex with PhI(OAc)2, recently reported
by Periana et al.16 The PdII(ppy) reactions appear to proceed via
reductive elimination from PdIV(ppy) complexes, and apparently
the IrV analogues are not accessible in these reactions. Oxidation of
a Cp* methyl group is more facile than oxidation of either Ir–Me
or Ir–aryl linkages.
on Agilent 8453 and spectral data are reported in the form of
l
performed by Atlantic Microlabs, Inc. (Norcross, GA).
max nm (extinction coefficient, M-1 cm-1). Elemental analyses were
[CpOAc IrCl2]2 (2).
A
solution of [Cp*IrCl2]2 (94 mg,
0.118 mmol) and PhI(OAc)2 (281.5 mg, 1.27 mmol) in wet
acetonitrile (5 mL) was stirred overnight at 50 ◦C. Solvent and
PhI were removed by vacuum from the light brown solution and
the precipitate was washed with 3 mL H2O and 5 mL Et2O to give
55.1 mg of light brown 2 of moderate purity (51%). Attempts at
bulk recrystallization of 2 and obtaining analytically pure material
have not been successful. In one case, crystals were obtained by
slow evaporation of a CD3CN solution.1H NMR (CD3CN, 298
K): 1.67 (s, 6H); 1.73 (s, 6H); 2.01 (s, 3H), 4.67 (s, 2H). 13C NMR
(CD3CN, 298 K): 94.37, 88.04, 58.27, 20.79, 9.27, 9.01 (one signal
was too weak to see). ESI/MS: 420 (CpOAcIrCl+). UV/vis: 230
(15937), 280 (4686).
Conclusions
[CpOMeIrCl2]2 (3). A solution of [Cp*IrCl2]2 (27 mg, 34 mmol)
and PhIO (28.5 mg, 130 mmol) in MeOH (5 mL) was stirred
overnight at 50 ◦C. Four more equivalents of PhIO were added
and the solution was stirred at 50 ◦C for an additional 10 min.
The solvent and PhI were removed in vacuo and the precipitate
was washed with 2 mL H2O and 3 mL Et2O to give 12 mg of
light brown 7 of moderate purity (42%).1H NMR (CD2Cl2, 298
K): 1.57 (s, 6H); 1.61 (s, 6H); 3.37 (s, 3H), 4.06 (s, 2H). ESI/MS:
393 (CpOMeIrCl+).
Treatment of [Cp*IrCl2]2 with the hypervalent iodine reagents
PhI(O2CR)2 or (PhIO)n + RCO2H in wet MeCN result in oxidation
of a Cp*-methyl group to form [(h -C5Me4CH2OC(O)R)IrCl2]2
5
complexes. In methanol or ethanol solvent (R¢OH), the Cp*-ether
5
derivatives [(h -C5Me4CH2OR¢)IrCl2]2 are formed. These results
show that Cp* is not an inert supporting ligand in the chemistry of
strongly oxidizing metal complexes. A number of new Cp*IrIII(L-
L)X compounds, with electron-donating chelating ligands, have
been reacted with the electrophiles MeOTf, Me3O+, C6Cl6O, and
PhI(OAc)2. None of the reactions form observable IrV complexes
despite precedent for moderately stable Cp*IrMe3X compounds.
Alkylation of the amide-carboxylate complex Cp*Ir(TAIBA)
occurs at the carboxylate group and forms the free ester, rather
than adding Me+ to the open coordination site on the IrIII centre.
Cp*Ir(ppy)Cl (4Cl; ppy = cyclometallated 2-phenylpyridine) re-
acts with MeI or MeOTf to give MeCl. The iridium(III) complexes
appear to have limited nucleophilicity.
[CpO2CPhIrCl2]2 and [CpO2CTolIrCl2]2. A J. Young sealable NMR
tube was charged with 1 (4 mg, 5 mmol), PhI(O2CPh)2 (7 mg,
16 mmol) [or PhI(O2CTol)2 (7 mg, 15 mmol)] and 0.75 mL of
wet (non-dried, benchtop-stored) MeCN and heated for 7 d at
50 ◦C.1H NMR for [CpO2CPhIrCl2]2 (CD3CN, 298 K): 1.66 (s, 6H);
1.80 (s, 6H); 4.94 (s, 2H); 6.95 (ddd, 1H, 3JHH = 8.0 Hz); 7.43 (d,
3
3
2H, JHH = 8.0 Hz); 8.19 (d, 2H, JHH = 7.5 Hz).1H NMR for
[CpO2CTolIrCl2]2 (CD3CN, 298 K): 1.66 (s, 6H); 1.79 (s, 6H); 4.92
(s, 2H); 6.79 (d, 2H, 3JHH = 7.5 Hz); 7.25 (d, 2H, 3JHH = 7.5 Hz).
ESI/MS: (CpO2CPhIrCl+), 483; (CpO2CTolIrCl+), 497.
Experimental
General considerations
Cp*Ir(ppy)Cl (4Cl). A solution of [Cp*IrCl2]2 (236 mg,
0.456 mmol) and excess 2-phenylpyridine (0.3 mL, 2.40 mmol)
in MeOH (10 mL) was stirred overnight. The solution was
concentrated to ~2 mL by rotary evaporation and filtered. The
‘creamsicle orange’ precipitate was washed with 10 mL H2O and
2 ¥ 10 mL benzene, and remaining ppyH was sublimed off of crude
4Cl to yield 269 mg (87%).1H NMR (CD2Cl2): 1.66 (s, 15H, Cp*);
IrCl3·nH2O was used as received from Pressure Chem-
ical Company. [Cp*IrCl2]2,6 PhI(O2CPh)2,44 PhI(O2CTol)2,44
N-p-tosyl-o-aminobenzoic acid (anthrH-NHTs),45 N-p-tosyl-2-
aminoisobutyric acid (TAIBAH2),46 2-aminoisobutyrate methyl
ester,47 and N-p-tosyl-2-aminoisobutyrate methyl ester45 were
prepared by following (or in some cases, adapting) literature
procedures. All other reagents were used as received from Aldrich.
Solvents were used as received from Fisher except for THF
which was distilled and stored over Na/Ph2CO and MeCN,
which was purchased in a steel keg (Burdick and Jackson, low-
water brand) and piped directly into a glovebox. Deuterated
solvents (from Cambridge Isotope Laboratories) were either used
as received, or dried and stored under nitrogen: CD2Cl2 over
CaH2, THF-d8 over Na/Ph2CO, and CD3CN over P2O5 then
CaH2. Reactions were performed open to ambient atmosphere
unless otherwise noted. 1H NMR spectra were recorded on Bruker
AV-500 or DRX-499 spectrometers at 298 K, with chemical
shifts (in ppm) referenced to residual solvent peaks and coupling
constants reported in Hz. ESI/MS were recorded on a Bruker
Esquire LC-Ion Trap instrument. UV-Vis spectra were recorded
3
3
7.04 (t, 1H, JHH = 7.5 Hz), 7.13 (t, 1H, JHH = 7.0 Hz), 7.18 (t,
3
3
1H, JHH = 7.5 Hz), 7.69–7.72 (m, 2H, JHH = 8.0 Hz), 7.78 (d,
3
3
1H, JHH = 8.0 Hz), 7.84 (d, 1H, JHH = 8.5 Hz), 8.68 (d, 1H,
3JHH = 5.5 Hz). ESI/MS: 517 (M+), 482 (M-Cl)+. UV/vis: 240
(12500), 252 (12000), 300 (6300), 360 (2600). Anal. Calcd (found)
for C21H23NClIr: C, 48.78 (48.81); H, 4.48 (4.53); N, 2.71 (2.70).
Cp*Ir(ppy)I (4I). MeI (1.0 mL, 18 mmol) was added to a
solution of Cp*Ir(ppy)Cl (4Cl) (25.6 mg, 0.050 mmol) in 3 mL
MeOH. The solution was stirred overnight and a brick-red solid
precipitated. The solvent was removed using a rotary evaporator,
leaving 27.7 mg of product (92%).1H NMR (CD2Cl2): 1.75 (s, 15H,
Cp*); 6.98 (t, 1H, 3JHH = 7.5 Hz), 7.05 (t, 1H, 3JHH = 7.0 Hz), 7.16
(t, 1H, 3JHH = 7.0 Hz), 7.66 (t, 1H, 3JHH = 7.0 Hz), 7.67–7.71 (m,
3
3
2H, JHH = 7.5 Hz), 7.82 (d, 1H, JHH = 8.0 Hz), 8.69 (d, 1H,
1980 | Dalton Trans., 2009, 1972–1983
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3JHH = 5.5 Hz). ESI/MS: 609 (M+), 482 (M - I)+. UV/vis: 245
(61.6 mg, 4.5 mmol). The solution was stirred for 6 h, resulting in
a yellow solution with white solids. The solvent was removed by
rotary evaporation, the residue was taken up in CH2Cl2. Filtration
to remove the white solids and addition of pentanes precipitated
yellow 4 (102.5 mg, 67%).1H NMR (CD3CN, 298 K): 1.40 (s,
(9900), 295 (5100), 360 (2600).
Cp*Ir(ppy)Me (4Me). MeLi (1.6 M in Et2O, 240 mL, 3.8 ¥
10-4 mmol, 4 equiv) was added to a solution of Cp*Ir(ppy)Cl
(4Cl) (50.5 mg, 0.097 mmol) in 20 mL THF at -78 ◦C. The yellow
solution was allowed to come to room temperature, at which time
the solution colour changed to deep red. The solution was filtered
through a plug of weakly acidic Al2O3. The solvent and other
volatiles were removed from the filtrate by rotary evaporation and
then under high vacuum, yielding 30.5 mg of dark orange-red 4Me
(63%).1H NMR (CD2Cl2): -0.38 (s, 3H, IrMe); 1.73 (s, 15H, Cp*);
3
15H); 2.29 (s, 3H); 6.86 (d, 1H, JHH = 8.5 Hz); 7.13–7.17 (m,
3
3
3H); 7.48 (d, 2H, JHH = 8.5 Hz); 7.63 (d, 1H, JHH = 7.0 Hz);
7.88 (d, 1H, 3JHH = 8.5 Hz); the CH3CN signal was not observed.
Anal. Calcd (found) for 4·2H2O, C26H34IrN2O6S: C, 44.94 (44.20);
H, 4.93 (4.43); N, 4.03 (3.97).
Cp*Ir(TAIBA) (8). To a 5 mL acetonitrile solution of
[Cp*IrCl2]2 (36.7 mg, 46.1 mmol) was added 2 equiv TAIBAH2
(23.9 mg, 92.9 mmol) and 4 equiv K2CO3 (25.7 mg, 186.2 mmol).
The solution was stirred for 6 hours. White solid (KCl) was filtered
from the dark red solution and then solvent was removed from
the filtrate by rotary evaporation. The red precipitate was further
3
3
6.87 (t, 1H, JHH = 7.0 Hz), 6.96 (t, 1H, JHH = 7.5 Hz), 7.04 (t,
1H, 3JHH = 7.5 Hz), 7.52–7.57 (m, 2H, 3JHH = 7.0 Hz), 7.72 (d, 1H,
3JHH = 7.5 Hz), 7.82 (d, 1H, 3JHH = 8.5 Hz), 8.49 (d, 1H, 3JHH
=
5.5 Hz). ESI/MS: 496 (M+). Anal. Calcd (found) for (4Me)·2THF,
C30H42NO2Ir: C, 56.22 (56.76); H, 6.61 (6.37); N, 2.19 (2.38) (THF
was visible in NMR spectra of this material).
dried in vacuo to give 45 mg (84%) yield. 1H NMR (CD3CN, 298
3
K): 1.29 (s, 6H); 1.63 (s, 15H); 2.39 (s, 3H); 7.31 (d, 2H, JHH
=
[Cp*Ir(ppy)NCMe]PF6 (4MeCN). AgPF6 (22.0 mg, 1.6 mmol)
was added to an orange solution of 4Cl (14.1 mg, 0.27 mmol) in
5 mL MeCN. After stirring for thirty seconds, the resulting light
yellow solution was filtered through a glass wool/celite pipette
filter. The solvent was removed from the filtrate by rotovap and
the residue was taken up in minimal CH2Cl2 and filtered again, to
ensure that no salts remained. The solvent was removed from the
filtrate and the yellow residue was stirred with 1 mL Et2O to form
a fine yellow powder, which was isolated by filtration, yielding
8.0 Hz); 7.74 (d, 2H, JHH = 8.0 Hz). ESI/MS: 584 (M + H)+.
UV/vis: 288 (6700), 395 (2200), 520 (500). Anal. Calcd (found)
for C21H28IrNO4S: C, 43.28 (42.92); H, 4.84 (4.90); N, 2.40 (2.38).
3
N-p-tosylaminoisobutyrate methyl ester.
A
solution of
aminoisobutyrate methyl ester47 (106 mg, 390 mmol) and Et3N
(0.165 mL, 1.2 mmol, 3 equiv) in 15 mL of 2:1 H2O/THF was
cooled to 0 ◦C in an ice bath and p-toluenesulfonyl chloride added
(74.4 mg, 390 mmol, 1 equiv). The solution was warmed to 20 ◦C
and stirred for 3 hrs. The solution was reduced in volume to 10 mL
by rotovap, and white solids precipitated from the remaining
solution. The solid was dissolved in CH2Cl2, treated with MgSO4
which was then filtered off, and solvent was removed to yield 21 mg
N-p-tosylaminoisobutyrate methyl ester (13%). 1H NMR (CDCl3,
298 K): 1.410 (s, 6H); 2.394 (s, 3H, Ph-CH3); 3.63 (s, 3H, O-CH3);
7.26 (d, 2H, 3JHH = 8.5 Hz); 7.73 (d, 2H, 3JHH = 8.5 Hz).
1
14.0 mg 76% 4MeCN. H NMR (CD2Cl2): 1.70 (s, 15H, Cp*);
2.30 (s, 3H, CH3CN), 7.20 (t, 1H, 3JHH = 7.0 Hz), 7.27–7.33 (m,
3
3
2H, JHH = 5.5 Hz, 6.5 Hz), 7.74–7.78 (m, 2H, JHH = 8.5 Hz,
10.0 Hz), 7.90–7.97 (m, 2H, 3JHH = 7.5 Hz), 8.49 (d, 1H, 3JHH
=
5.0 Hz).
CpOAc Ir(ppy)Me (5). PhI(OAc)2 (2.8 mg, 8.7 mmol) was added
to a 0.6 mL CD3CN solution of Cp*Ir(ppy)Me (3.7 mg, 7.5 mmol),
which was heated in a J. Young NMR tube at 45 ◦C for one hour.1H
NMR (CD3CN, 298 K): -0.29 (s, 3H, IrMe); 1.75 (s, 3H); 1.77 (s,
Crystal structure determinations for 2, 3, 4Cl, 4I, 6, and 7†.
Crystals of yellow 2·PhI and 3·PhI were grown by slow evaporation
of MeCN (2) and MeOH (3) reaction solutions. Crystals of orange
4Cl, yellow 4I, and yellow 6 were grown by slow evaporation
of benzene (4Cl), CD3OD (4I), or CH2Cl2 (6) solutions at room
temperature. Crystals of yellow 7 were grown by vapour diffusion
of Et2O into an MeCN solution. A yellow block of 6 was cut to
0.30 ¥ 0.30 ¥ 0.10 mm orange and a block of 4Cl was cut down to
0.26 ¥ 0.25 ¥ 0.24 mm. All crystals but 7 were mounted on glass
fibres with oil; 7 was mounted on a Cryoloop. The crystal-to-
detector distance was 30 mm (60 mm for 7) and exposure time was
30 sec (4Cl), 20 sec (4I, 6), 45 sec (3) or 60 sec (7, 2) per degree. The
scan width was 2.0◦ (2, 3, 4Cl), 1.9◦ (6), 1.5◦(4I), or 0.3◦ sec (7). The
final cell parameters and specific collection parameters are given
in Table 1. 4Cl and 4I crystallize in space group P21/c (No. 14), 6
crystallizes in P212121 (No. 19) and 7, 2 and 3 crystallize in P-1 (No.
2). In each case but 7, the data were integrated and scaled using hkl-
SCALEPACK; 7 was integrated by Bruker SAINT and was scaled
by SADABS software. hkl-SCALEPACK applies a multiplicative
correction factor (S) to the observed intensities (I) and has the
following form: S = exp(2B(sinq/l)2)/scale. S is calculated from
the scale and the B factor is determined for each frame and is then
applied to I to give the corrected intensity (Icorr). Solution by direct
methods (SIR92) produced a complete heavy atom phasing model
3H); 1.79 (s, 3H); 1.81 (s, 3H); 1.92 (s, 3H); 4.65 (dd, 2H, 3JHH
=
=
=
3
3
10.5, 12.5 Hz); 6.97 (t, 1H, JHH = 7.0 Hz), 6.98 (t, 1H, JHH
3
3
7.5 Hz), 7.02 (t, 1H, JHH = 7.5 Hz), 7.52–7.57 (m, 2H, JHH
7.0 Hz), 7.65 (d, 1H, 3JHH = 7.5 Hz), 7.91 (d, 1H, 3JHH = 8.0 Hz),
8.53 (d, 1H, JHH = 6.0 Hz). ESI/MS: 554 (M - H)+, 540 (M -
3
CH3COO-)+.
Cp*Ir(H2NC6H4CO2)Cl (6). [Cp*IrCl2]2 (28.6 mg, 36 mmol),
anthranilic acid (9.8 mg, 71 mmol, 2 equiv) and NaOMe (3.8 mg,
70 mmol, 2 equiv) were mixed in 2 mL of 3:1 CH2Cl2/MeOH. Al-
ternatively, NaOMe was generated in situ by addition of NaOH to
the methanol solution. The solution was stirred for five minutes
and white solids precipitated from the mixture. The solvent was
removed by rotary evaporation and CH2Cl2 was added to the
residue. Filtration of the yellow solution removed the white solids,
and then addition of pentane gave yellow 3 (11.5 mg, 31%).1H
NMR (CD3OD, 298 K): 1.34 (s, 15H); 7.21 (m, C6H4, 2H); 7.43
(t, C6H4, 1H, 3JHH = 7.5 Hz), 7.88 (d, C6H4, 1H, 3JHH = 7.5 Hz).
ESI/MS: 499 (M+).
Cp*Ir(TsNC6H4CO2)(MeCN) (7). To a 20 mL acetonitrile
solution of [Cp*IrCl2]2 (92.3 mg, 1.16 mmol) was added 2 equiv
TsNHC6H4CO2H (60.0 mg, 2.3 mmol) and 4 equiv K2CO3
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consistent with the proposed structure. All hydrogen atoms were
located using a riding model. All non-hydrogen atoms were refined
anisotropically by full-matrix least-squares. Crystals of 4Cl had a
tendency to twin, and the crystal analyzed was of somewhat poor
quality. Complex 6 co-crystallized with a molecule of MeOH,
which hydrogen-bonds to O1. The proton on N1 (complex 6)
hydrogen-bonds to a different MeOH. The Cp* moiety exhibits
considerable oscillatory motion, causing large thermal ellipsoids
of Cp*-Me.
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Note added in proof
After this paper was submitted, the crystal structure of 4Cl was
reported by Davies et al.,48 who used the same synthetic procedure
as Djukic et al.31
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