C-H activation with iridium(III) and rhodium(III) alkyl complexes containing a 2,2-cipyridyl ligand

Article abstract of DOI:10.1002/ejic.201000041

Heating [Rh(dtbpy)(K₂-C,C′-CH₂CMe ₂C₆H₄)(CH₂CMe₂Ph)] (1; dtbpy = 4,4′-di-tert-butyl-2,2′-bipyridyl) in p-xylene at 110°C resulted in the formation of the 2-tert-butylphenyl complex. [Rh(dtbpy) (K ₂- C,C′ -CH₂CMe₂C₆H ₄) (C₆H₄ tBu-2)] (3). Treatment of complex 1 with diethyl phosphite gave the phosphito-bridged dimer [Rh(dtbpy) (K ₂-C, C-CH₂CMe₂C₆H ₄)[P(O)(OEt)₂)]₂ (4). Refluxing [Ir(dtbpy)(K₂-C,C′-CH₂CMe₂C ₆H₄)(C₆.H₄tBu-2)J (2) with 2-phenylpyridine (ppyH) and 4-(2-pyridyl)benzaldehyde in toluene followed by col-umn chromatography afforded [Ir(dtbpy)(CH₂CMe₂Ph) Cl(k₂N,C-ppy)J (5) and the carbonyl complex [Ir(dtbpy)(CH ₂CMe₂Ph)(CO)(R)] (6) [R = 4-(2-pyridyl)phenyl], respectively. Anion metathesis of [M(dtbpy)(CH₂CMe ₂Ph)(H₂O)(OTs)₂] with NaBAr^F ₄ [Ar^F = 3,5-(CF₃)₂C₆ H₃] afforded cationic [M(dtbpy)(CH₂CMe₂Ph) (H₂O)(μ-OTs)]₂[BAr^F₄] ₂ [M = Rh (7), Ir (8)] that are capable of catalyzing H/D exchange of tetrahydrofuran by using D₂O as the deuterium, source. The crystal structures of complexes 4-7 were determined.

Full text of DOI:10.1002/ejic.201000041

FULL PAPER
DOI: 10.1002/ejic.201000041
C–H Activation with Iridium(III) and Rhodium(III) Alkyl Complexes
Containing a 2,2Ј-Bipyridyl Ligand
Xiao-Yi Yi,[a] Ka-Wang Chan,[a] Enrique Kwang Huang,[a] Yiu-Keung Sau,[a]
Ian D. Williams,[a] and Wa-Hung Leung*[a]
Keywords: Iridium / Rhodium / N ligands / C–H activation
Heating [Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)(CH2CMe2Ph)]
(1; dtbpy = 4,4Ј-di-tert-butyl-2,2Ј-bipyridyl) in p-xylene at
110 °C resulted in the formation of the 2-tert-butylphenyl
umn chromatography afforded [Ir(dtbpy)(CH2CMe2Ph)Cl(κ2-
N,C-ppy)] (5) and the carbonyl complex [Ir(dtbpy)(CH2-
CMe2Ph)(CO)(R)] (6) [R = 4-(2-pyridyl)phenyl], respectively.
Anion metathesis of [M(dtbpy)(CH2CMe2Ph)(H2O)(OTs)2]
complex
[Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)(C6H4tBu-2)]
(3). Treatment of complex 1 with diethyl phosphite gave the
phosphito-bridged dimer [Rh(dtbpy)(κ2-C,CЈ-CH2CMe2-
C6H4){P(O)(OEt)2}]2 (4). Refluxing [Ir(dtbpy)(κ2-C,CЈ-CH2-
CMe2C6H4)(C6H4tBu-2)] (2) with 2-phenylpyridine (ppyH)
and 4-(2-pyridyl)benzaldehyde in toluene followed by col-
with NaBArF [ArF
=
3,5-(CF3)2C6H3] afforded cationic
4
[M(dtbpy)(CH2CMe2Ph)(H2O)(µ-OTs)]2[BArF
]
[M = Rh (7),
4 2
Ir (8)] that are capable of catalyzing H/D exchange of tetra-
hydrofuran by using D2O as the deuterium source. The crys-
tal structures of complexes 4–7 were determined.
interesting organometallic chemistry and thus are poten-
tially useful in C–H activation. Recently, Periana and co-
workers reported that cyclometalated Ir complexes with
Introduction
Organoiridium complexes stabilized by 2,2Ј-bipyridyl
(bpy) are of interest due to their applications as catalysts
for borylation of arenes with borane and diborane rea-
gents.[1] It is believed that the mechanism of Ir(bpy)-cata-
lyzed borylation involves oxidative addition of the arene C–
H bond with IrIII boryl species.[2] Therefore, to develop new
Ir-based catalysts for C–H activation and functionalization,
knowledge of the organometallic chemistry of Ir(bpy) alkyl
complexes is essential.
∧ ∧
N N C ligands can mediate C–H activation and H/D ex-
change reactions.[6] This prompted us to explore the reactiv-
ity of Ir and Rh dtbpy alkyl complexes in C–H activation.
Previously, we reported the syntheses of Ir and Rh alkyl
complexes stabilized by 4,4Ј-di-tert-butyl-2,2Ј-bipyridyl
(dtbpy).[3,4] We found that the alkylation of [Rh(dtbpy)-
Cl3(dmf)] (dmf
Me2CCH2PhMgCl afforded the neophyl complex
[Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)(CH2CMe2Ph)] (1),
=
N,N-dimethylformamide)
with
whereas that with [Ir(dtbpy)Cl3(dmf)] yielded the 2-tert-
butylphenyl complex [Ir(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)-
(C6H4tBu-2)] (2; structures of complexes 1 and 2 are shown
Schemes 1 and 2, respectively). It seems likely that intramo-
lecular C–H activation of an unisolated IrIII neophyl inter-
mediate that is isostructural with complex 1 is involved in
the formation of complex 2. Reaction of complexes 1 and
2 with disulfides in refluxing toluene gave RhIII and IrIII
bis(thiolate) complexes.[5] These results suggest that elec-
tron-rich MIII(dtbpy) (M = Ir, Rh) alkyl complexes exhibit
Scheme 1. Syntheses of complexes 3 and 4.
Cationic late transition-metal diimine alkyl complexes
have attracted much attention due to their catalytic activity
in organic transformations. In particular, the C–H acti-
∧
vation and functionalization with cationic [Pt(N N)-
[a] Department of Chemistry, The Hong Kong University of
Science and Technology,
R(solv)]+ complexes has been studied extensively.[7,8]
Bergman and co-workers demonstrated that the activity of
[Cp*Ir(PMe3)Me(OTf)] (Cp* = η5-C5Me5) in C–H acti-
Clear Water Bay, Kowloon, Hong Kong, P. R. China
Fax: +852-2358-1594
E-mail: chleung@ust.hk
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X.-Y. Yi, K.-W. Chan, E. K. Huang, Y.-K. Sau, I. D. Williams, W.-H. Leung
FULL PAPER
2-tert-butylphenyl ligands are scrambling rapidly around
Rh on the NMR timescale. A similar result was found for
Ir analogue 2.[4]
Reaction of Complex 1 with Diethyl Phosphite
Reactivity of complex 1 toward main group hydride com-
pounds was examined. No reaction was found when com-
plex 1 was treated with boranes such as pinBH (pin = pin-
acolate) and Et3SiH. However, complex 1 reacted readily
with diethyl phosphite to give the phosphito-bridged dimer
[Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4){P(O)(OEt)2}]2
(4).
The 31P{1H} NMR spectrum showed two doublets of dou-
blets at δ = 100.99 and 120.63 ppm due to the bridged phos-
phite ligands.
The structure of complex 4 (Figure 1) consists of two
symmetry-related {Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)}+
fragments bridged by two µ-phosphito P,O ligands. Dinu-
clear complexes containing µ-phosphito P,O ligands, for ex-
ample, [{(tBu4Ph2O2)P=O}Rh(CO)(MeCN)]2,[11,12] are well
documented. The geometry around Rh in complex 4 is
pseudo-octahedral with the P=O group opposite to the
methylene group of the rhodacycle. The Rh–C(trans to N)
and Rh–C(trans to O) distances are 2.000(2) and
2.047(2) Å, respectively. The Rh–O distance is
2.2142(15) Å, which is longer than that in [{(tBu4Ph2O2)-
P=O}Rh(CO)(MeCN)]2 (2.071 Å). The Rh–P distance of
2.2057(6) Å is comparable to that in [{(tBu4Ph2O2)-
P=O}Rh(CO)(MeCN)]2 (2.207 Å).[12] The Rh···Rh separa-
tion is 3.933 Å, indicating the absence of a direct Rh–Rh
bond.
Scheme 2. Syntheses of complexes 5 and 6.
vation is greatly enhanced by replacing the weakly coordi-
nating triflate (OTf–) ligand with noncoordinating BArF
4
[ArF = 3,5-(CF3)2C6H3], demonstrating the significance of a
vacant coordination site in the IrIII-based C–H activation.[9]
These findings led us to explore the C–H activation chemis-
try of cationic Ir and Rh complexes [MIII(dtbpy)R]+ (M =
Ir, Rh) complexes containing noncoordinating BArF –. In
4
this paper, we report the intramolecular C–H activation of
complex 1 to give a 2-tert-butylphenyl complex. The cyclo-
metalation of 2-phenylpyridine and decarbonylation of 4-
(2-pyridyl)benzaldehyde with complex 2 will be described.
The synthesis and characterization of cationic Ir and Rh
dtbpy alkyl complexes and their catalytic activity in H/D
exchange of tetrahydrofuran will be reported.
Results and Discussion
Intramolecular C–H Activation of Complex 1
Heating complex 1 in p-xylene at 110 °C for 48 h resulted
1
in the formation of orange species 3 (Scheme 1). H NMR
spectroscopy indicated that the conversion of complex 1
into 3 was a clean process that did not involve any detect-
able intermediate(s). A preliminary X-ray diffraction study
confirmed that complex 3 is a RhIII 2-tert-butylphenyl com-
plex that is isostructural with complex 2, featuring an agos-
tic interaction between Rh and a methyl C–H bond of the
2-tert-butylphenyl ligand.[10] The conversion of complex 1
to 3 presumably involves intramolecular C–H activation of
the neophyl ligand and subsequent C–H bond elimination.
The 1H NMR spectrum of complex 3 is similar to that of 2,
except that the methylene protons in the metallacycle (Ha)
appeared as two doublets of doublets at δ = 2.56 and
2.62 ppm (2JRh,H = 9.4 Hz) instead of two doublets. Only a
singlet at δ = 0.98 ppm was observed for the tert-butyl pro-
Figure 1.
Molecular
structure
of
[Rh(dtbpy)(κ2-C,CЈ-
CH2CMe2C6H4){P(O)(OEt)2}]2 (4). Hydrogen atoms are omitted
for clarity. The ellipsoids are drawn at 30% probability level. Sym-
metry operator: A = –x + 1, –y + 1, –z + 1. Selected bond lengths
[Å]: Rh1–C4 2.000(2), Rh1–C1 2.047(2), Rh1–N1 2.1543(18), Rh1–
N2 2.171(2), Rh1–P1 2.2057(6), Rh1–O3A 2.2142(15).
Reaction of Complex 2 with 2-Arylpyridines
No reaction was found when complex 2 was heated at
tons at 25 °C, indicating that the three methyl groups in the reflux in arene solvents such as benzene, toluene, and p-
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C–H Activation with IrIII/RhIII Alkyl Complexes
xylene. We next turned our attention to the C–H activation to isolation of the carbonyl complex [Ir(dtbpy)(κ2-C,CЈ-
of 2-arylpyridines. Treatment of complex 2 with 2-phenyl- CH2CMe2Ph)(CO)(R)] (6), where R = 4-(2-pyridyl)phenyl
pyridine (ppyH) in refluxing toluene followed by column (Scheme 2). Therefore, the decarbonylation of the formyl
chromatography on silica (CH2Cl2) afforded [Ir(dtbpy)- group with complex 2 is favored over phenyl C–H acti-
(CH2CMe2Ph)Cl(κ2-N,C-ppy)] (5; Scheme 2). It seems vation. It may be noted that for the reaction of IrCl3 with 4-
likely that the reaction between complex 2 and ppyH in- (2-pyridyl)benzaldehyde, the cyclometalated product [Ir(κ2-
volved C–H activation of ppyH and the formation of an N,C-ppy-CHO)2Cl]2 was isolated.[14] The IR spectrum of
unisolated IrIII κ2-N,C-ppy bis(neophyl) intermediate. Col- complex 6 displayed the νCO band at 1986 cm–1, which is
umn chromatography on silica resulted in protonolysis of typical for IrIII carbonyl complexes.
one Ir–neophyl bond of this intermediate. The resulting cat-
The asymmetric unit of complex 6 in the solid state con-
ionic mononeophyl species reacted with chloride (presum- sists of a pair of enantiomers, the structures of which are
ably derived from CH2Cl2) to afford chloride product 5. shown in Figure 3. The geometry around Ir in each enanti-
Complex 5 was not isolated if the initial product was not omer is pseudo-octahedral with the carbonyl and the phenyl
purified by silica column chromatography.
ring of the iridacycle opposite to dtbpy. The three Ir–C
The molecular structure of complex 5 is shown in Fig- bonds adopt a mer arrangement possibly because the trans
ure 2. The geometry around Ir is pseudo-octahedral with arrangement between the trans-directing alkyl and π-ac-
the neophyl and the pyridyl ring of the ppy ligand opposite cepting carbonyl ligands is not favored. By contrast, a fac
to dtbpy. The ligand atom (N42) opposite to N22 of dtbpy arrangement was found for the three Ir–C bonds in
is assigned as a nitrogen instead of carbon because the Ir– [Ir(dtbpy)(C8H9)3(xylNC)] (C8H9 = 2,5-dimethylphenyl; xyl
N22 bond [2.061(4) Å] is shorter than the Ir–N11 bond = 2,6-dimethylphenyl).[3] As expected, the two transoid Ir–
[2.125(4) Å]. By comparison, the Ir–N(dtbpy) distance C bonds [av. 2.147(7) Å] are longer than the Ir–C(trans to
(trans to phenyl) in complex 2 is 2.142(3) Å, whereas the N) bond [av. 2.059(7) Å] due to the trans influence of the
Ir–N(dtbpy) distance (trans to Cl) in [Ir(dtbpy)- alkyl/phenyl ligand. The average Ir–CO distances [av.
(CH2CMe2Ph)Cl2]2 is 2.029(4) Å.[4] Consistent with this as- 1.806(8) Å] are shorter than that of [IrMe(CO)(PPh3)2-
signment, the Ir–Cl distance in complex 5 is rather long (mnt)] [1.859(5) Å].[15]
{2.4961(14) Å cf. 2.383 Å for [Ir(dtbpy)(CH2CMe2Ph)-
Cl2]2} due to the trans influence of the opposite phenyl
ring.[4] The Ir–C(ppy) [2.011(5) Å] and Ir–N(ppy)
[2.038(5) Å] distances are similar to those in [Ir(di-n-non-
ylbpy)(κ2-N,C-ppy)2][PF6] (di-n-nonylbpy
=
4,4Ј-di-n-
nonyl-2,2Ј-bipyridyl) [av. 2.015(7) and 2.057(6) Å, respec-
tively].[13]
Figure 3.
Molecular
structures
of
[Ir(dtbpy)(κ2-C,CЈ-
CH2CMe2Ph)(CO)(R)] (6). Hydrogen atoms, one enantiomer, and
cocrystallized solvent are omitted for clarity. The ellipsoids are
drawn at 30% probability level. Selected bond lengths [Å]: Ir1A–
C1A 1.820(8), Ir1A–C21A 2.056(6), Ir1A–N1A 2.077(5), Ir1A–
N12A 2.110(5), Ir1A–C33A 2.151(7), Ir1A–C28A 2.151(6), Ir1B–
C(1B) 1.789(8), Ir1B–C21B 2.061(6), Ir1B–N1B 2.122(5), Ir1B–
N12B 2.111(5), Ir1B–C33B 2.144(7), Ir1B–C28B 2.143(7).
Figure 2. Molecular structure of [Ir(dtbpy)(CH2CMe2Ph)Cl(κ2-
N,C-ppy)] (5). Hydrogen atoms are omitted for clarity. The ellip-
soids are drawn at 30% probability level. Selected bond lengths
[Å]: Ir1–C1 2.086(6), Ir1–C31 2.011(5), Ir1–N42 2.038(5), Ir1–N11
2.125(4), Ir1–N22 2.061(4), Ir1–Cl1 2.4961(14).
Cationic Rh and Ir Alkyl Complexes
Protonation of complex 2 with p-toluenesulfonic acid af-
To compare the reactivity of phenyl and formyl C–H forded the ditosylate complex analyzed as [Ir(dtbpy)-
bonds in the oxidative addition with IrIII, the reaction of (CH2CMe2Ph)(OTs)2]. A preliminary X-ray diffraction
complex 2 with 4-(2-pyridyl)benzaldehyde was studied. study confirmed that this tosylate compound is a mono-
Treatment of complex 2 with 4-(2-pyridyl)benzaldehyde in meric aqua complex containing one aqua and two η1-tosyl-
refluxing toluene followed by column chromatography led ate ligands.[16] Similarly, the Rh analogue [Rh(dtbpy)-
Eur. J. Inorg. Chem. 2010, 2369–2375
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X.-Y. Yi, K.-W. Chan, E. K. Huang, Y.-K. Sau, I. D. Williams, W.-H. Leung
FULL PAPER
(CH2CMe2Ph)(OTs)2(H2O)] was prepared by protonation Catalytic H/D Exchange of thf
of complex 1 with p-toluenesulfonic acid in CH2Cl2. In an
The catalytic activity of Ir and Rh dtbpy alkyl complexes
attempt to increase the reactivity of the Ir and Rh dtbpy
alkyl complexes, the tosylate ligands in [M(dtbpy)-
(CH2CMe2Ph)(OTs)2(H2O)] were exchanged with nonco-
ordinating [BArF4]–, where ArF = 3,5-(CF3)2C6H3. Treat-
ment of [M(dtbpy)(CH2CMe2Ph)(OTs)2(H2O)] with NaB-
in H/D exchange of organic substrates was examined. Of
particular interest is H/D exchange with the use of D2O as
the deuterium source.[17] The H/D exchange of thf with
D2O in the presence of catalytic amounts of Ir and Rh alkyl
1
complexes was studied by H NMR spectroscopy, and the
ArF in CH2Cl2 afforded dimeric [M(dtbpy)(CH2CMe2Ph)-
4
results are summarized in Table 1. Cationic alkyl complexes
7 and 8 were found to be active catalysts for the H/D ex-
change of thf. For example, heating thf in D2O in the pres-
ence of complex 8 (5 mol-%) at 135 °C resulted in 59% deu-
terium incorporation into thf. A slightly lower deuteration
level (52%) was found for Rh analogue 7. For comparison,
under the same conditions, a total deuteration level of 61%
was obtained with the use of [Cp*Ir(PMe3)Cl2] as the cata-
lyst. When the catalyst loading was reduced to 1 mol-%, the
deuteration level was decreased to 38 and 31% for com-
plexes 7 and 8, respectively. No/little selectivity for either
the α- or β-position of thf was found for the M(dtbpy)-
catalyzed H/D exchange (α/β ca. 1). A similar result was
found for [TpMe2IrH4] [TpMe2 = hydridotris(3,5-dimeth-
ylpyrazolyl)borate].[18] This is in contrast with the IrCp*
system that exhibits a preference for the α position.[17] Com-
plexes 1 and 2 containing three metal–carbon bonds and
[M(dtbpy)(CH2CMe2Ph)(H2O)(OTs)2] are inactive in the
H/D exchange, indicating the presence of a vacant coordi-
nation site on the metal center is critical for C–H activation.
(H2O)(µ-OTs)]2[BArF4]2 [M = Rh (7), Ir (8)] containing two
µ-tosylate O,OЈ ligands (Scheme 3). Complexes 7 and 8 are
highly hygroscopic solids. They exhibit rather broad 1H
NMR signals. The diastereotopic methylene protons of
complex 7 appeared as two doublets at δ = 3.40 and
1
3.44 ppm in the H NMR spectrum, presumably because
the Rh–H coupling is too small to be resolved.
Scheme 3. Syntheses of complexes 7 and 8.
The solid-state structure of complex 7 is shown in Fig-
ure 4. The geometry around Rh is pseudo-octahedral with
the aqua and the bridged tosylate ligand opposite to dtbpy.
The Rh–C distance [2.050(5) Å] is similar to the Rh–C(neo-
phyl) distance in complex 1.[3] The Rh–OTs bond opposite
to carbon [2.379(3) Å] is obviously longer than that oppo-
site to nitrogen [2.108(3) Å] due to the trans influence of
the neophyl ligand. The long Rh···Rh separation (5.321 Å)
indicates the absence of a Rh–Rh bond.
Table 1. Catalytic H/D exchange of tetrahydrofuran with D2O.[a]
% Dincorp.
Catalyst
α
β
Total
1
0
0
0
0
0
0
0
0
0
2
Rh(dtbpy)(CH2CMe2Ph)(H2O)(OTs)2
Ir(dtbpy)(CH2CMe2Ph)(H2O)(OTs)2
4
4
4
7
51
30
57
38
53
32
60
37
52
31
59
38
7[b]
8
8[b]
[a] Experimental conditions: thf (0.12 mmol), D2O (0.5 mL), cata-
lyst (0.006 mmol), 135 °C, 40 h. [b] 1 mol-% of catalyst used.
Conclusions
In summary, we found that heating complex 1 in p-xylene
resulted in intramolecular C–H activation of the neophyl
ligand and formation of 2-tert-butylphenyl complex 3.
Complex 1 reacted readily with diethyl phosphite to afford
a phosphito-bridged dimer. Reaction of complex 2 with 2-
phenylpyridine resulted in cyclometalation of 2-phenylpyr-
idine, whereas that with 4-(2-pyridyl)benzaldehyde led to
decarbonylation of the formyl group. Cationic Ir and Rh
alkyl complexes 7 and 8 containing the noncoordinating
Figure 4. Molecular structure of [Rh(dtbpy)(CH2CMe2Ph)-
(H2O)(µ-OTs)]2[BArF4]2 (7). Hydrogen atoms are omitted for clar-
ity. The ellipsoids are drawn at 30% probability level. Symmetry
operator: A = –x + 1, –y + 1, –z + 1. Selected bond lengths [Å]:
Rh1–C1 2.050(5), Rh1–N21 2.006(4), Rh1–N32 1.976(4), Rh1–O1
2.080(3), Rh1–O11 2.108(3), Rh1A–O13 2.379(3).
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C–H Activation with IrIII/RhIII Alkyl Complexes
8.56–8.59 (m, 2 H, H5), 10.01 (d, J = 5.9 Hz, 4 H, H6) ppm. 31P
counteranion BArF – are capable of catalyzing H/D ex-
change of thf with the use of D2O as the deuterium
source.
4
1
{1H} NMR (162 MHz, C6D6, 25 °C): δ = 100.99 (dd, JRh,P
=
=
2
1
2
205 Hz, JRh,P = 52.0 Hz), 120.63 (dd, JRh,P = 123 Hz, JRh,P
52.0 Hz) ppm. C64H92N4O6P2Rh2 (1281.2): C 60.00, H 7.24, N
4.37; found C 60.32, H 7.50, N 4.19.
[Ir(dtbpy)(CH2CMe2Ph)Cl(κ2-N,C-ppy)] (5): To a solution of com-
plex 2 (100 mg, 0.138 mmol) in toluene (10 mL) was added 2-phen-
ylpyridine (18 µL, 0.138 mmol), and the mixture was heated at re-
flux for 24 h. The volatiles were removed in vacuo, and the residue
was purified by silica gel column chromatography (CH2Cl2).
Recrystallization (CH2Cl2/hexane) afforded brown crystals suitable
for X-ray diffraction. Yield: 45 mg (42%). 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 1.09 [s, 3 H, -C8(Me)2-], 1.22 [s, 3 H, -C8-
(Me)2-], 1.25 (s, 9 H, tBu), 1.49 (s, 9 H, tBu), 2.37 (d, J = 11.7 Hz,
1 H, H7), 2.81 (d, J = 11.7 Hz, 1 H, H7), 6.30 (dd, J = 7.5 Hz,
1.1 Hz, 1 H, H18), 6.65–6.81 (m, 7 H, H13, H16, H17, H19, H20, and
H21), 7.02 (d, J = 1.2 Hz, 2 H, H14), 7.05 (dd, J = 6.9, 1.2 Hz, 1
H, H5), 7.17 (dd, J = 7.6, 1.2 Hz, 1 H, H22), 7.33 (d, J = 7.6 Hz, 1
H, H15), 7.50 (dt, J = 7.6, 1.5 Hz, 1 H, H12), 7.60 (dd, J = 6.2,
2.1 Hz, 1 H, H5), 7.87 (s, 1 H, H3), 7.99 (d, J = 2.1 Hz, 1 H, H3),
9.40 (d, J = 6.2 Hz, 1 H, H6), 9.67 (dd, J = 5.6, 0.9 Hz, 1 H, H6)
ppm. C39H45ClIrN3 (783.5): C 59.79, H 5.79, N 5.36; found C
59.69, H 5.86, N 5.13.
Experimental Section
General Remarks: All manipulations were carried out under an at-
mosphere of nitrogen by standard Schlenk techniques. Solvents
were purified, distilled, and degassed prior to use. NMR spectra
were recorded with a Varian Mercury 300 spectrometer operating
at 300, 121.5, and 282.3 MHz for 1H, 31P, and 19F, respectively.
Chemical shifts (δ, ppm) were reported with reference to SiMe4 (1H
and 13C), H3PO4 (31P), and C6H5CF3 (19F). Infrared spectra were
recorded with a Perkin–Elmer 16 PC FTIR spectrophotometer and
mass spectra with a Finnigan MAT TSQ-7000 spectrometer. Ele-
mental analyses were performed by Medac Ltd., Surrey, UK. The
compounds [Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)(CH2CMe2Ph)]
(1),[3] [Ir(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)(C6H4tBu-2)] (2), [Ir-
(dtbpy)(CH2CMe2Ph)(H2O)(OTs)2],[4] and NaBArF [ArF = 3,5-
4
bis(trifluoromethyl)phenyl][19] were synthesized as described else-
where. Atom labeling schemes for the metallacycles in cyclo-
metalated complexes and the ppyH and dtbpy ligands are shown
below.
[Ir(dtbpy)(κ2-C,CЈ-CH2CMe2Ph)(CO)(R)] [R = 4-(2-pyridyl)phenyl]
(6): To a solution of complex 2 (100 mg, 0.138 mmol) in toluene
(10 mL)
was
added
4-(2-pyridyl)benzaldehyde
(25 mg,
0.138 mmol). The mixture was heated at reflux for 24 h. The vola-
tiles were removed in vacuo, and the residue was purified by silica
gel column chromatography (CH2Cl2). Recrystallization (CH2Cl2/
hexane) afforded yellow crystals suitable for X-ray diffraction
analysis. Yield: 57 mg (53%). 1H NMR (300 MHz, CDCl3, 25 °C):
δ = 0.70 (d, J = 10.5 Hz, 1 H, H7), 1.16 [s, 3 H, -C8(Me)2-], 1.20
[s, 3 H, -C8(Me)2-], 1.40 (s, 9 H, tBu), 1.41 (s, 9 H, tBu), 1.74 (d, J
= 10.5 Hz, 1 H, H7), 6.84–6.95 (m, 2 H, H17 and H20), 7.02–7.07
(m, 2 H, H13 and H14), 7.28–7.31 (m, 3 H, H3 and H18), 7.38 (dd,
J = 6.0, 1.8 Hz, 1 H, H22), 7.45–7.51 (m, 3 H, H12, H19, and H23),
7.60–7.62 (m, 2 H, H11 and H16), 7.91 (d, J = 6.2 Hz, 1 H, H6),
8.01 (d, J = 1.8 Hz, 1 H, H5), 8.03 (d, J = 1.8 Hz, 1 H, H5), 8.54
(td, J = 4.7, 1.2 Hz, 1 H, H15), 8.97 (d, J = 5.9 Hz, 1 H, H6) ppm.
MS (FAB): m/z = 776.5 [M + 1]+, 621.4 [M – ppy]+, 593.1 [M –
ppy – CO]+. IR (KBr): 1986 (νCO) cm–1. C40H44IrN3O·CH2Cl2
(860.0): C 57.27, H 5.39, N 4.89; found C 57.30, H 5.61, N 4.58.
[Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4)(C6H4tBu-2)] (3): A solution
of complex 1 (50 mg, 0.079 mmol) in p-xylene (5 mL) was heated
at 110 °C for 48 h. The volatiles were removed in vacuo, and the
residue was purified by silica gel column chromatography (ethyl
acetate). Recrystallization (Et2O/hexane) afforded orange crystals.
1
Yield: 40 mg (80%). H NMR (300 MHz, CDCl3, 25 °C): δ = 0.98
(s, 9 H, C6H4CMe3), 1.26 [s, 6 H, -C8(Me)2-], 1.38 (s, 9 H, tBu),
2
2
1.44 (s, 9 H, tBu), 2.56 (dd, JRh,H = 9.4 Hz, JH,H = 2.6 Hz, 1 H,
H7), 2.62 (dd, JRh,H = 9.2 Hz, JH,H = 4.3 Hz, 1 H, H7), 5.80 (d,
J = 7.7 Hz, 1 H, H14), 6.39 (dt, J = 7.8, 2.0 Hz, 1 H, H13), 6.64–
6.68 (m, 4 H, C6H4CMe3, H11 and H12), 6.84 (dt, J = 7.4, 3.2 Hz,
1 H, C6H4CMe3), 7.07 (dd, J = 7.8 Hz, 1.4 Hz, 1 H, C6H4CMe3),
7.36–7.61 (m, 2 H, H5), 8.05 (s, 1 H, H3), 8.11 (s, 1 H, H3), 8.22
(d, J = 5.7 Hz, 1 H, H6), 9.01 (d, J = 5.8 Hz, 1 H, H6) ppm.
C38H49N2Rh·0.5Et2O (673.8): C 71.30, H 8.08, N 4.16; found C
71.64, H 8.47, N 4.08.
2
2
[Rh(dtbpy)(CH2CMe2Ph)(H2O)(OTs)2]: This complex was synthe-
sized by
a method similar to that used for Ir(dtbpy)-
(CH2CMe2Ph)(H2O)(OTs)2 by reaction of complex 1 with p-tolu-
enesulfonic acid (2 equiv.) in CH2Cl2. Recrystallization (CH2Cl2/
hexane) afforded orange crystals. Yield: 56 mg (47%). 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 1.25 [s, 3 H, -C8(Me)2-], 1.31 [s, 3
H, -C8(Me)2-], 1.43 (s, 9 H, tBu), 1.48 (s, 9 H, tBu), 1.94 (br. s, 2
H, H2O), 2.27 (s, 3 H, Me), 2.31 (s, 3 H, Me), 3.60 (d, J = 10.3 Hz,
1 H, H7), 3.97 (d, J = 10.3 Hz, 1 H, H7), 6.18 (d, J = 7.9 Hz, 1 H,
H5), 6.44–6.55 (m, 2 H, H13), 6.69 (d, J = 6.5 Hz, 2 H, H14), 6.90
(t, J = 6.9 Hz, 1 H, H12), 7.08 (d, J = 7.3 Hz, 2 H, H14 of Ts), 7.16
(d, J = 7.9 Hz, 1 H, H5), 7.41 (d, J = 4.5 Hz, 2 H, H14 of Ts), 7.47
(d, J = 4.5 Hz, 2 H, H13 of Ts), 7.70 (br. s, 2 H, H3), 7.88 (d, J =
7.6 Hz, 2 H, H13 of Ts), 8.36 (d, J = 6.2 Hz, 1 H, H6), 8.59 (d, J =
6.0 Hz, 1 H, H6) ppm. C42H53N2O7S2Rh·0.5CH2Cl2 (907.4): C
56.26, H 6.00, N 3.09; found C 55.93, H 6.07, N 3.13.
[Rh(dtbpy)(κ2-C,CЈ-CH2CMe2C6H4){P(O)(OEt)2}]2 (4): To a solu-
tion of complex 1 (50 mg, 0.079 mmol) in thf (5 mL) was added
diethyl phosphite (10.9 mg, 0.079 mmol). The mixture was stirred
at room temperature for 12 h. The volatiles were removed in vacuo,
and the residue was washed with hexane and Et2O, and then ex-
tracted with thf. Recrystallization (thf/hexane) gave yellow crystals,
which were suitable for X-ray analysis. Yield: 32 mg (65%). 1H
NMR (300 MHz, C6D6, 25 °C): δ = 0.29 [s, 12 H, -C8(Me)2-], 0.85
(s, 18 H, tBu), 1.03 (s, 18 H, tBu), 2.98–3.04 (m, 2 H, H7), 3.26–
3.34 (m, 2 H, H7), 3.71 (t, J = 7.2 Hz, 4 H, OCH2CH3), 3.89 (q, J
= 7.4 Hz, 6 H, OCH2CH3), 4.25 (t, J = 7.0 Hz, 4 H, OCH2CH3), [M(dtbpy)(CH2CMe2Ph)(H2O)(µ-OTs)]2[BArF
] [M = Rh (7), Ir
4 2
4.45 (q, J = 7.5 Hz, 6 H, OCH2CH3), 6.18 (d, J = 5.9 Hz, 2 H, (8)]: To
H6), 7.05–7.10 (m, 4 H, H13 and H14), 7.26–7.30 (m, 4 H, H11 and (0.058 mmol) in CH2Cl2 (8 mL) was added NaBArF4·3H2O
H12), 7.73 (s, 2 H, H3), 7.86 (s, 2 H, H3), 8.27–8.30 (m, 2 H, H5),
(109 mg, 0.116 mmol). The mixture was stirred at room tempera-
a solution of [M(dtbpy)(CH2CMe2Ph)(H2O)(OTs)2]
Eur. J. Inorg. Chem. 2010, 2369–2375
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2373

X.-Y. Yi, K.-W. Chan, E. K. Huang, Y.-K. Sau, I. D. Williams, W.-H. Leung
Table 2. Crystallographic data and experimental details for complexes 4–7.
FULL PAPER
Complex
4
5
[6]2·CHCl3·1/2C6H14
7·2C4H10O
Formula
C64H92N4O6P2Rh2
1281.18
173(2)
monoclinic
P21/n
C39H45ClIrN3
783.43
100(2)
monoclinic
P21/c
C84H188Cl3Ir2N6O2
1710.4
173(2)
C142H136B2F48N4O10Rh2S2
Molecular wt. [gmol–1]
3262.11
100(2)
monoclinic
P21/c
Temperature [K]
Crystal system
Space group
triclinic
¯
P1
a [Å]
b [Å]
c [Å]
α [°]
14.7962(2)
11.95460(10)
18.3317(3)
90
96.309(2)
90
3222.92(7)
2
1.32
14.5540(10)
16.2247(11)
14.9560(10)
90
97.6480(10)
90
3500.2(4)
4
1.487
12.0181(11)
13.7836(13)
25.701(2)
87.229(2)
76.717(2)
77.595(2)
4046.7(7)
2
12.4377(15)
27.256(4)
22.429(3)
90
98.857(3)
90
7512.7(16)
2
1.442
β [°]
γ [°]
V [Å3]
Z
ρcalcd. [gcm–3]
1.405
3.432
µ [mm–1]
5.007
3.921
0.363
F(000)
1344
10586
5949
0.029
0.0304
0.0687
1.051
1576
21563
5934
0.0683
0.0385
0.0615
0.999
1722
36015
13961
0.062
0.0467
0.0828
0.998
3320
38322
13033
0.0946
0.0613
0.1255
1.010
No. reflections collected
No. independent reflections
Rint
R1 [IϾ2σ(I)]
wR2 (all data)
Goodness-of-fit on F2
ture for 12 h. The volatiles were removed in vacuo, and the residue
was washed with hexane, extracted with Et2O (10 mL), and further
recrystallized (Et2O/hexane). We have not been able to obtain satis-
factory analytical data for the compounds due to their hygroscopic
nature. These compounds have, however, been well characterized
by spectroscopic methods and X-ray diffraction (compound 7).
7: Yellow crystals. Yield: 40 mg (43%). 1H NMR (300 MHz,
CD2Cl2, 25 °C): δ = 1.04 [s, 6 H, -C8(Me)2-], 1.08 [s, 6 H, -C8-
(Me)2-], 1.32 (br. s, 36 H, tBu), 1.43 (br. s, 4 H, H2O), 2.32 (s, 6 H,
p-Me), 3.40 (d, J = 6.8 Hz, 2 H, H7), 3.44 (d, J = 6.9 Hz, 2 H, H7),
6.52 (d, J = 6.7 Hz, 4 H, H14), 6.65 (t, J = 7.5 Hz, 4 H, H13), 6.90
(t, J = 7.2 Hz, 2 H, H12), 7.06–7.19 (m, 6 H, H5 and OTs), 7.56 (s,
8 H, BArF), 7.66 (br. s, 4 H, H3), 7.74 (s, 24 H, BArF), 7.98 (d, J
= 6.0 Hz, 4 H, OTs), 8.38 (br. s, 4 H, H6) ppm. 19F NMR
(282 MHz, CD2Cl2, 25 °C): δ = –63.31 (s) ppm.
= 0.71073 Å). The data was corrected for absorption by using the
program SADABS.[20] Structures were solved by direct methods
and refined by full-matrix least-squares on F2 by using the
SHELXTL software package.[21] In complex 5, the cocrystallized
CHCl3 molecule was found to be disordered, and the chlorine
atoms Cl2 and Cl3 are split into two sites of 0.6 and 0.4 occupanc-
ies. In complex 6, one ethyl group of the phosphite ligand was
found to be disordered; the carbon atom C32 is split into two sites
of 0.5 and 0.5 occupancies. The BArF – anion in 7 was found to be
4
disordered. The fluorine atoms F46, F54, F63, and F72 are split
into two sites of 0.6 and 0.4 occupancies; F52, F57, and F73 are
split into two sites of 0.5 and 0.5 occupancies; F44 is split into
three sites of 0.35, 0.35, and 0.3 occupancies; and F75 is split into
three sites of 0.35, 0.15, and 0.5 occupancies.
CCDC-760944 (for 4), -760945 (for 5), -760946 (for 6), and -760947
(for 7) contain the supplementary crystallographic data for this pa-
per. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/
data_request/cif.
8: Orange powder. Yield: 32 mg (33%). 1H NMR (300 MHz,
CD2Cl2, 25 °C): δ = 0.87 (s, 6 H, p-Me), 1.27 [s, 6 H, -C8(Me)2-],
1.28 [s, 6 H, -C8(Me)2-], 1.36 (br. s, 36 H, tBu), 1.46 (br. s, 4 H,
H2O), 2.87 (br. s, 4 H, H7), 6.40 (br. s, 4 H, H14), 6.64 (br. s, 4 H,
H13), 6.81 (br. s, 2 H, H12), 6.96–7.17 (m, 6 H, H5 and OTs), 7.25–
7.56 (m, 6 H, H3 and OTs), 7.57 (s, 8 H, BArF), 7.74 (s, 24 H,
BArF), 8.31 (br. s, 4 H, H6) ppm. 19F NMR (282 MHz, CD2Cl2,
25 °C): δ = –63.46 (s) ppm.
Acknowledgments
We thank Dr. Herman H. Y. Sung for solving the crystal structures.
Financial support from the Hong Kong Research Grants Council
(project no. 601705) is gratefully acknowledged.
Catalytic H/D Exchange of Tetrahydrofuran with D2O: This experi-
ment was performed according to a literature procedure.[17] Typi-
cally, catalyst (6 µmol), thf (10 µL), and D2O (0.5 mL) were
charged in a degassed NMR tube, which contained a sealed exter-
nal standard capillary consisting of an internal standard, hexa-
methylbenzene (10 mg), dissolved in C6D6. The NMR tube was
sealed under vacuum. The reaction mixtures were heated at 135 °C
for 40 h. The deuteration level (%D) was calculated by dividing the
loss of thf signals in the 1H NMR spectrum by the initial standard-
ized integration of thf signals.
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X-ray Crystallography: Crystallographic data and experimental de-
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were collected with a Bruker SMART APEX 1000 CCD dif-
fractometer by using graphite-monochromated Mo-Kα radiation (λ
2374
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2369–2375

C–H Activation with IrIII/RhIII Alkyl Complexes
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Received: January 18, 2010
[10] Complex 3 was characterized by X-ray crystallography. How-
ever, the structure was not solved satisfactorily due to the poor
quality of the crystal. Crystal data for complex 3: Triclinic,
¯
P1, a = 15.7513(7) Å, b = 16.1258(7) Å, c = 17.6186(9) Å, α =
82.539(4)°, β = 71.358(4)°, γ = 62.025(5)°, V = 3735.3(3) Å3, Z
Published Online: May 3, 2010
Eur. J. Inorg. Chem. 2010, 2369–2375
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2375