A dearomatized anionic PNP pincer rhodium complex: C-H and H-H bond activation by metal-ligand cooperation and inhibition by dinitrogen

Article abstract of DOI:10.1021/om200104b

The anionic dearomatized complex [(PNP*)Rh^ICl]K (2; PNP = 2,6-bis((di-tert-butylphosphino)methyl)pyridine, PNP* = deprotonated PNP) was prepared by reaction of the aromatic (PNP)Rh^ICl complex 1 with KN(SiMe₃)₂ in dry benzene. Spectroscopic characterization and DFT calculations confirm a nonaromatic square-planar structure of complex 2. Under an atmosphere of dry argon, 2 undergoes facile C-H activation of benzene by cooperation between the metal center and the pincer ligand, with aromatization of the ligand, to form the complex (PNP)Rh^I(C ₆H₅) (3a). This reaction is inhibited by dinitrogen, which reacts with 2 to form the complex (PNP*)Rh^I(N₂) (4), indicating higher stabilization of the 14-electron (PNP*)Rh ^I species 5 by dinitrogen as compared with chloride. Similarly, treatment of 2 with CO results in KCl liberation to form the dearomatized (PNP*)Rh^ICO (8). In a protic environment, the dearomatized complex 2 is quickly reprotonated to regenerate the aromatic starting complex 1. Upon treatment with MeI, 2 undergoes oxidative addition to form the nonaromatic (PNP*)Rh^III(CH₃)Cl (10), while the dearomatized ligand remains intact. Complex 2 undergoes facile activation of H₂ to form the monohydride (PNP)Rh^I(H) (11a) and with D₂ to form (PNP)Rh^I(D) (11b) with benzylic-D incorporation, via metal-ligand cooperation by aromatization of the ligand. The reactivity of 2 with H₂ is significantly higher than that of 4.

Full text of DOI:10.1021/om200104b

ARTICLE
pubs.acs.org/Organometallics
A Dearomatized Anionic PNP Pincer Rhodium Complex:
CÀH and HÀH Bond Activation by MetalÀLigand Cooperation and
Inhibition by Dinitrogen
Leonid Schwartsburd,† Mark A. Iron,‡ Leonid Konstantinovski,‡ Eyal Ben-Ari,† and David Milstein*,†
†Department of Organic Chemistry and ‡Department of Chemical Research Support, The Weizmann Institute of Science,
Rehovot 76100, Israel
S Supporting Information
b
ABSTRACT:
The anionic dearomatized complex [(PNP*)RhICl]K (2; PNP = 2,6-bis((di-tert-butylphosphino)methyl)pyridine, PNP* =
deprotonated PNP) was prepared by reaction of the aromatic (PNP)RhICl complex 1 with KN(SiMe3)2 in dry benzene.
Spectroscopic characterization and DFT calculations confirm a nonaromatic square-planar structure of complex 2. Under an
atmosphere of dry argon, 2 undergoes facile CÀH activation of benzene by cooperation between the metal center and the pincer
ligand, with aromatization of the ligand, to form the complex (PNP)RhI(C6H5) (3a). This reaction is inhibited by dinitrogen, which
reacts with 2 to form the complex (PNP*)RhI(N2) (4), indicating higher stabilization of the 14-electron (PNP*)RhI species 5 by
dinitrogen as compared with chloride. Similarly, treatment of 2 with CO results in KCl liberation to form the dearomatized
(PNP*)RhICO (8). In a protic environment, the dearomatized complex 2 is quickly reprotonated to regenerate the aromatic starting
complex 1. Upon treatment with MeI, 2 undergoes oxidative addition to form the nonaromatic (PNP*)RhIII(CH3)Cl (10), while
the dearomatized ligand remains intact. Complex 2 undergoes facile activation of H2 to form the monohydride (PNP)RhI(H) (11a)
and with D2 to form (PNP)RhI(D) (11b) with benzylic-D incorporation, via metalÀligand cooperation by aromatization of the
ligand. The reactivity of 2 with H2 is significantly higher than that of 4.
’ INTRODUCTION
analogue of this complex was shown to be effective in the direct
hydrogenation of amides to form amines and alcohols.4i The
dearomatized (PNP*)RuII(H)(CO) analogue (PNP = 2,6-bis-
((di-tert-butylphosphino)methyl)pyridine; PNP* = deprotonated
PNP) is effective in the NÀH bond activation of amines and
ammonia,6a the coupling of alcohols and amines to form imines and
H2,6b and the dehydrogenation of secondary alcohols to ketones.6c
Further, the complex (iPrPNP)FeII(H)(CO)(Br) (iPrPNP = 2,6-
bis((diisopropylphosphino)methyl)pyridine), also believed to op-
erate by metalÀligand cooperation, was very recently reported
to be highly efficient in the hydrogenation of ketones at room
temperature and mild pressure.6d Long-range metalÀligand co-
operation involving dearomatization of the central acridine ring was
recently reported for an acridine-based (PNP)RuII(H)Cl(CO)
complex,6e which catalyzes the dehydrogenative coupling of alco-
hols to form acetals6f and the selective coupling of primary alcohols
with ammonia togive primaryamines.6g MetalÀligandcooperation
MetalÀligand cooperation plays an important role in homo-
geneous catalysis by metal complexes,1À3 such as in the hydro-
genation of polar bonds by ruthenium amido complexes.1b,c
Recently, we discovered a new mode of metalÀligand coopera-
tion involving reversible dearomatization of pyridine- and acri-
dine-based pincer complexes.3À9
MetalÀligand cooperation via reversible dearomatization can
play a key role in the catalytic OÀH bond activation of alcohols,3
exemplified by the direct coupling of alcohols to form esters with
the liberation of H2,4a,b the hydrogenation of esters to alcohols
under mild pressure,4c the dehydrogenative coupling of alcohols
with amines to produce amides4d and polyamides,4e,f the dehydro-
genative amidation of esters with amines,4g and the acylation of
alcohols with esters.4h These reactions are catalyzed by the
dearomatized (PNN*)RuII(H)(CO) complex (PNN = 2-((di-
tert-butylphosphino)methyl)-6-(diethylaminomethyl)pyridine;
PNN* = deprotonated PNN).4 Furthermore, this powerful com-
plex promotes splitting of water to H2 and O2 in consecutive heat-
and light-induced steps.5 Very recently, a bipyridine-based PNN
Received: February 3, 2011
Published: April 22, 2011
r
2011 American Chemical Society
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Scheme 1
by aromatizationÀdearomatization is involved in the very effective
catalytic hydrogenation of CO2 by a PNP-iridium complex.7
Recent reports from our group describe CÀHactivationprocesses
that involve metalÀligand cooperation by reversible dearomatization
of the ligand with no change in the formal oxidation state of the
metal.8 The dearomatized (PNP*)IrI(COE) complex activates
CÀH bonds in benzene and acetone to yield the aromatic
(PNP)IrI(C6H5)8a and (PNP)IrI(CH2COCH3)8b complexes,
respectively (COE = cyclooctene). Our studies indicate that the
dearomatized oxidative addition intermediates (PNP*)IrIII(H)(R)
(R = C6H5, CH2COCH3) are involved.8a,b Indeed, the nonaromatic
(PNP*)IrIII(H)(C6H5) was prepared independently by deprotona-
tion of the cationic [(PNP)IrIII(H)(C6H5)]BF4 complex8c at
À78 °C. When the complex is warmed to room temperature, proton
transfer to the side “arm” occurs, with aromatization and concomitant
reduction of the metal center, to give the (PNP)IrI(C6H5) complex.8a
The (PNP)IrI(R) complexes react with H2 to exclusively form
the trans-dihydride (PNP)IrIII(H)2(R) complexes, and with D2
the trans hydrido-deuteride (PNP)IrIII(H)(D)(R) complexes are
formed, with one deuterium atom incorporated into a benzylic
position.8a,b Computational studies corroborate an unobserved
equilibrium between the aromatic (PNP)IrI(R) complex and the
nonaromatic (PNP*)IrIII(H)(R) complex, which is the species
that activates H2.8b,9
In this paper, we report the preparation and reactivity of an
electron-rich, anionic dearomatized [(PNP*)RhICl]K complex.
The PNP ligand and the metal of the dearomatized complex
act jointly in the activation of a benzene CÀH bond. This
reaction is inhibited by dinitrogen coordination to form the
(PNP*)RhI(N2) complex or by reprotonation of the benzylic
position in the ligand by adventitious water to regenerate the
(PNP)RhICl starting complex. The dearomatized complex is also
capable of HÀH bond activation by metalÀligand cooperation
via reversible dearomatization of the ligand.
’ RESULTS AND DISCUSSION
Reaction of (PNP)RhICl (1) with Benzene in the Presence
of a Base To Form (PNP)RhI(C6H5) (3a). Formation of the
Dearomatized [(PNP*)RhICl]K (2). Treatment of our previously
reported complex (PNP)RhICl 111 with an equimolar amount of
KN(SiMe3)2 in dry benzene under an atmosphere of dry argon
for 12 h at room temperature results in quantitative formation of
the known (PNP)RhI(C6H5) complex 3a12 with concomitant
formation of KCl and HN(SiMe3)2 (Scheme 1). Interestingly,
after addition of KN(SiMe3)2 to the benzene solution of 1 an
orange precipitate is formed. Subsequently, full consumption of
the precipitate results in a homogeneous dark brown solution of
3a (by 31P{1H} NMR analysis).
In one experiment, the orange precipitate was separated from
the benzene solution at an early stage of the reaction (after 3 h).
The 31P{1H} NMR spectrum of the precipitate redissolved in dry
THF revealed formation of the dearomatized anionic complex 2
(Scheme 1), while the 31P{1H} NMR spectrum of the benzene
solution revealed full consumption of complex 1 and formation
of some 3a. Further reaction of the separated 2 with dry benzene
under an atmosphere of dry argon gave a quantitative amount of
3a (Scheme 1). In fact, complex 2 is a separable reaction
intermediate in the reaction of 1 with benzene in the presence
of base. Note that, in the absence of KN(SiMe3)2, no transfor-
mation of 1 in benzene is observed, even upon prolonged heating
at 80 °C.
The (PNP*)IrIII(H)(C6H5) complex can be trapped by treat-
ing the (PNP)IrI(C6H5) complex with CO, forming the nonaro-
matic (PNP*)IrIII(CO)(H)(C6H5) complex.8a Treatment of the
complex (PNP)IrI(CH2COCH3) with CO results in elimination
of acetone to form the dearomatized (PNP*)IrICO complex,
involving proton migration from the ligand “arm” to the acetonyl
moiety with concomitant dearomatization.8b The PNP ligand and
the metal center also act jointly in benzene CÀH activation by
(PNP)IrI(CH2COCH3), resulting in substitution of the acetonyl
group by a phenyl group.8b
Following the metalÀligand cooperation studies with pyridine-
based pincer iridium complexes, we decided to examine
the potential of rhodium-based systems. Preparation of the
nonaromatic (PNP*)RhI(N2) complex has been recently
reported.10
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ARTICLE
Figure 1. DFT optimized structures of 1, anionic 2, and 4.
Dry samples of 2 are relatively stable at À35 °C under an
atmosphere of dry argon (up to 2 weeks). Complex 2 was
characterized by 31P{1H}, 1H, and 13C{1H} NMR spectroscopy
and by elemental analysis. The 31P{1H} NMR spectrum of 2
displays a characteristic AB pattern of doublets at 57.6 ppm
(JPÀP = 345 Hz, JRhÀP = 151 Hz) and 49.2 ppm (JPÀP = 345 Hz,
JRhÀP = 147 Hz), indicating nonequivalent phosphorus atoms.
The high RhÀP coupling constants indicate that 2 is formally a
RhI complex (cf. 1, JRhÀP = 145 Hz). A one-proton doublet at
Table 1. Selected Bond Lengths (Å) for DFT Optimized
Structures of 1, Anionic 2, and 4
bond
1
anionic 2
4
N(1)ÀRh
RhÀCl
2.028
2.466
2.286
2.061
2.527
2.256
2.308
1.511
1.401
1.863
1.774
2.091
RhÀP(1)
RhÀP(2)
C(1)ÀC(2)
C(3)ÀC(4)
C(2)ÀP(1)
C(4)ÀP(2)
2.318
2.345
1.509
1.396
1.853
1.767
1.506
1.865
1
3.31 ppm (JPÀH = 3.2 Hz) in the H NMR spectrum and a
doublet at 63.84 ppm (JPÀC = 46.4 Hz) in the 13C{1H} NMR
spectrum, assigned to the PyÀCHÀP group, indicate the for-
mation of a dearomatized PNP* system. Signals at 6.00, 5.67, and
1
5.11 ppm in the H NMR spectrum are attributed to three
different protons of the dearomatized pyridine backbone.
A number of anionic transition-metal complexes lacking
strong π-acceptor ligands capable of lowering the electron
density at the metal center (such as CO, olefins, and electron-
withdrawing phosphines) have been reported to date.13 Among
them are the recently reported dearomatized anionic complexes
[(PNN*)PtII(Cl)(R)]Li (R = CH3, C6H5), with a decoordinated
hemilabile amine arm,13a and the anionic doubly deprotonated
complexes [(PNP**)MII(X)]Y (PNP** = doubly deprotonated
PNP; M = Pd, Pt; X = Cl, Me; Y = Li, K).13b
configuration. The corresponding bond lengths in the optimized
structure of the neutral dearomatized (PNP*)RhI(N2) complex 4
(Figure 1) are very similar to those in the anionic 2 (Table 1).
Significantly, the reaction of the dearomatized complex 2
(formed in situ or purified) with dry C6D6 under an atmosphere
of dry argon yields the aromatic complex 3b, with incorporation
1
of deuterium into the benzylic position (Scheme 1). The H
NMR spectrum indicates incorporation of one deuterium atom
into the benzylic position (27% deuterium incorporation by
2
integration). The H{1H} NMR spectrum of the 3b has a
The DFT-optimizedstructures (Figure 1) illustrate a symmetry
distortion in the square-planar geometry on going from 111b to the
anionic 2. Selected bond lengths are given in Table 1. The lengths
of the C(1)ÀC(2) and C(2)ÀP(1) bonds, which involve the
unaffected benzylic position C(2), are almost the same for 1 and
the anionic 2. In the optimized structure of the anionic 2, the bond
length of C(3)ÀC(4) is shorter than C(1)ÀC(2) by 0.110 Å,
while the bond length of C(4)ÀP(2) is shorter than C(2)ÀP(1)
to a lesser extent (0.089 Å), indicating that the dearomatized form
contributes dominantly to the structure of the anionic 2, with a
significant stabilizing participation of the aromatic phosphorylide
benzylic-D signal at 2.80 ppm and three phenyl-D signals at
8.13, 7.24, and 6.98 ppm. This indicates involvement of the
ligand arm in the CÀH bond activation process. The reaction of
2 with benzene (Scheme 2) most likely involves formation of the
dearomatized 14-electron RhI species 514 with concomitant
liberation of KCl, benzene precoordination to give 6, and
intramolecular benzene CÀH bond activation, resulting in the
RhIII intermediate 7 followed by proton migration to the side arm
and aromatization to yield the RhI phenyl complex 3a. The
overall process involves no overall change in the formal metal
oxidation state (Scheme 2).
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ARTICLE
Scheme 2
Scheme 3
Scheme 4
Dinitrogen was found to inhibit the CÀH bond activation
process by formation of the known dinitrogen complex 410
(Scheme 1). Treatment of 1 with an equimolar amount of
KN(SiMe3)2 in dry benzene under an atmosphere of dry nitrogen
(rather than dry argon) for 12 h at room temperature results in
formation of the dearomatized complex (PNP*)RhI(N2) (4; 91%)
and only a small amount of the complex (PNP)RhI(C6H5) (3a;
9%) (Scheme 1). After addition of KN(SiMe3)2 to the benzene
solution of 1, complex 2 was formed as a precipitate (Scheme 1).
Subsequently, 2 reacted with dinitrogen to give 4 and to a smaller
extent with benzene to give 3a (Scheme 1). The reaction of 2 with
dinitrogen probably involves the intermediacy of the dearomatized
14-electron RhI species 5 with liberation of KCl (Scheme 2).
Attempting to perform the reverse reaction by treatment of 4 with
excess tetrabutylammonium chloride as a soluble chloride source in
dry THF at room temperature under dry argon was unsuccessful.
The observation that N2 is more tightly bound to complex 4 than
chloride to 2 might be a result of the anionic nature of 2 and the
steric hindrance imposed by the t-Bu groups.15
Formation of 3a from 4 at room temperature can be excluded
(Scheme 1), since under these conditions 4 is stable in benzene.
Only with prolonged heating can reactivity of 4 with benzene be
observed. Heating a benzene solution of 4 at 80 °C under an
atmosphere of dry nitrogen for 12 h results in the formation of 3a
in 40% purity accompanied by decomposition byproducts (by
31P{1H} NMR analysis). Apparently, N2 coordination to the metal
center in 4 inhibits formation of the reactive intermediate 5, which
is essential for the CÀH bond activation process (Scheme 2).
Traces of N2 have been shown to inhibit dehydrogenation
reactions of hydrocarbons catalyzed by the (PCP)Ir(H)2 complex
by formation of [(PCP)Ir]2(N2) and (PCP)Ir(N2) complexes
(PCP = 2,6-bis((di-tert-butylphosphino)methyl)benzene).16
Reaction of [(PNP*)RhICl]K (2) with CO. Formation of the
Nonaromatic Complex (PNP*)RhI(CO) (8). In analogy to the
reaction with dinitrogen, treatment of complex 2 with a slight
excess of CO in dry THF at room temperature under dry argon
Scheme 5
results in formation of the nonaromatic (PNP*)RhI(CO) com-
plex 8 with concomitant liberation of KCl (Scheme 3). A color
change from orange to pink is observed during the reaction.
Complex 8 can also be prepared by deprotonation of the cationic
complex [(PNP)RhI(CO)]BF4 (9)17 with an equimolar amount
of KN(SiMe3)2 in dry THF (Scheme 3).
Complex 8 was characterized by 31P{1H}, H, and 13C{1H}
1
NMR spectroscopy. The 31P{1H} NMR spectrum of 8 displays a
characteristic AB pattern of doublets at 77.0 ppm (JPÀP = 244 Hz,
JRhÀP = 125 Hz) and 74.2 ppm (JPÀP = 244 Hz, JRhÀP = 125 Hz),
1
indicating nonequivalent phosphorus atoms. In the H NMR
spectrum a one-proton doublet at 3.65 ppm (JPÀH = 4.4 Hz)
corresponds to the PyÀCHÀP group and signals at 6.42, 6.36,
and 5.37 ppm correspond to the three different protons of the
dearomatized pyridine backbone. The carbonyl carbon gives rise
to a doublet of apparent triplets centered at 199.21 ppm (JRhÀC
=
66.1 Hz, JPÀC = 12.6 Hz) in the 13C{1H} NMR spectrum. The IR
spectrum of 8 shows a sharp band at νCO 1946 cmÀ1, indicating a
significantly higher degree of back-bonding to CO than in the
aromatic cationic complex 9 (νCO 1982 cmÀ1), as expected.
Protonation of [(PNP*)RhICl]K (2) To Regenerate the Aro-
matic Complex (PNP)RhICl (1). The dearomatized complex 2 is
quickly protonated to regenerate the initial aromatic complex 1
(Scheme 4). Thus, treatment of 2 with an equivalent amount of
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Scheme 6
water (or excess) in THF results in formation of 1, along with an
immediate color change from orange to red. Reaction of 2 with
an equivalent amount of D2O in THF yields complex 1a, with in-
corporation of deuterium into the benzylic position (by 2H{1H}
NMR analysis) (Scheme 4).
cooperation between the metal and the ligand and no overall
change in the formal metal oxidation state.
Complex 11a was characterized by 31P{1H}, 1H, and 13C{1H}
NMR spectroscopy. The 31P{1H} NMR spectrum of 11a exhibits
a doublet at 83.2 ppm (JRhÀP = 165.9 Hz), arising from the two
equivalent phosphorus atoms. The high RhÀP coupling constant
indicates formation of a RhI complex. The benzylic protons give
rise to one virtual triplet at 2.92 ppm (JPÀH = 3.0 Hz) in the
1H NMR spectrum, implying rearomatization of the PNP ligand.
The aromaticity of the ligand backbone is further indicated by the
1H and 13C{1H} NMR spectra. The hydride gives rise to an
apparent quartet centered at À12.82 ppm integrating to 1H.
It should be noted that no reaction was observed for the aromatic
complex 1 with excess H2 in dry THF at room temperature.
Reversible H2 addition to the complex 1 is in accord with theoretical
calculations, which predict that a rigid square-planar geometry should
disfavor oxidative addition and favor reductive elimination of H2.21
Reaction of [(PNP*)RhICl]K (2) with CH3I. Exclusive For-
mation of the Nonaromatic Complex (PNP*)RhIII(CH3)Cl
(10). The addition of methyl iodide (in excess) as an electrophilic
reagent to a solution of 2 in THF under an atmosphere of dry
argon leads to the immediate and exclusive formation of the
nonaromatic (PNP*)RhIII(CH3)Cl complex 10 (Scheme 5).
This reaction is accompanied by a color change from orange to
dark green. Thus, in complex 2 electrophilic addition is favored at
the metal center over the benzylic position. Electrophilic addition
of methyl triflate to the deprotonated benzylic position of a
dearomatized (PNP*)CuI complex has been reported.18
Complex 10 was characterized by 31P{1H}, 1H, and 13C{1H}
NMR spectroscopy, mass spectroscopy, and elemental analysis.
The 31P{1H} NMR spectrum of 10 displays a characteristic AB
pattern of doublets at 53.3 ppm (JPÀP = 390 Hz, JRhÀP = 101 Hz)
and 44.7 ppm (JPÀP = 390 Hz, JRhÀP = 105 Hz), indicating
nonequivalent phosphorus atoms. The low RhÀP coupling
constants (compared to those of the RhI complexes 1À4)
indicate that 10 is a RhIII complex. A one-proton doublet at
’ SUMMARY
Reaction of the aromatic pincer complex (PNP)RhICl (1) with
base in benzene under an atmosphere of dry argon results in the
formation of the dearomatized anionic [(PNP*)RhICl]K complex
2, which undergoes facile CÀH activation of benzene by coopera-
tion between the metal center and the pincer ligand, with aroma-
tization of the ligand, to form the complex (PNP)RhI(C6H5) (3a).
Nitrogen gas inhibits this process by reaction with 2 to form the
dearomatized complex (PNP*)RhI(N2) (4) with concomitant
liberation of KCl. This is probably a result of a more favorable
coordination of dinitrogen to the 14-electron (PNP*)RhI species 5
as compared with chloride. Similarly, treatment of 2 with CO
results in KCl liberation to form the dearomatized (PNP*)RhICO
(8). In a protic environment, the benzylic position of the dear-
omatized complex 2 is quickly reprotonated to regenerate the initial
aromatic complex 1. Reaction of 2 with MeI as an electrophilic
reagent occurs exclusively at the metal center (rather than at the
arm), yielding the nonaromatic (PNP*)RhIII(CH3)Cl (10). Com-
plex 2 reacts with H2 by cooperation between the metal center and
the pincer ligand to form the complex (PNP)RhI(H) (11a) and
with D2 to form (PNP)RhI(D) (11b) with benzylic-D incorpora-
tion, with aromatization of the ligand and no change in the formal
oxidation state of the metal. The reactivity of the anionic chloride
complex 2 with H2 is significantly higher than that of the dinitrogen
complex 4. Further experimental and theoretical investigations on
metalÀligand cooperation via aromatizationÀdearomatization,
and its implications on catalytic design, are in progress.
1
3.55 ppm (JPÀH = 5.9 Hz) in the H NMR spectrum and a
doublet at 63.09 ppm (JPÀC = 52.7 Hz) in the 13C{1H} NMR
spectrum, assigned to the PyÀCHÀP group, indicate conserva-
tion of the dearomatized PNP* system. A doublet of apparent
triplets centered at 3.77 ppm (JRhÀC = 28.2 Hz, JPÀC = 4.5 Hz) in
the 13C{1H} NMR spectrum and a doublet of apparent triplets
centered at 2.19 ppm (JRhÀH = 2.9 Hz, JPÀH = 4.8 Hz) in the
1H NMR spectrum are assigned to the methyl ligand coordinated
in the apical position, as found in related systems.19
Reaction of [(PNP*)RhICl]K (2) vs (PNP*)RhI(N2) (4) with H2.
Formation of the Aromatic Complex (PNP)RhIH (11a). The
nonaromatic complex 2 is capable of HÀH bond activation via
metalÀligand cooperation by aromatization of the ligand. Treat-
ment of 2 with excess H2 in dry THF under an atmosphere of dry
argon at room temperature for 16 h results in formation of the
aromatic RhI-H complex 11a with concomitant liberation of KCl
(Scheme 6).20 Significantly, in order to prepare the complex 11a
from the nonaromatic dinitrogen complex 4 under an atmo-
sphere of dry nitrogen at room temperature (Scheme 6), hydro-
gen pressure is required for 96 h. Thus, the reactivity of complex
2 is significantly higher than that of complex 4.
The reaction of 2 with excess D2 in dry THF under an
atmosphere of dry argon yields the aromatic RhI-D complex
11b, with incorporation of deuterium into the benzylic position
’ EXPERIMENTAL SECTION
2
(Scheme 6). The H{1H} NMR spectrum of the 11b in THF
has a Rh-D signal at À13.51 ppm and a benzylic-D signal at
3.16 ppm. This indicates involvement of the ligand arm in the
HÀH bond activation process. The overall process involves
General Procedures. All experiments (if not mentioned
otherwise) with metal complexes and the phosphine ligand were carried
out under an atmosphere of purified argon in an MBRAUN Unilab
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glovebox or using standard Schlenk techniques. All glassware was
rigorously dried. All solvents were reagent grade or better. All non-
deuterated solvents and some deuterated solvents (C6D6 for reactions
and THF-d8) were refluxed over sodium/benzophenone ketyl and
distilled under an argon atmosphere. Additional deuterated solvents
were used as received. All the solvents were degassed with argon and
kept in the glovebox over 4 Å molecular sieves. Commercially available
reagents were used as received. The complex (PNP)RhICl (1) was
prepared according to the literature procedure.11a
Reaction of [(PNP*)RhICl]K (2) with Benzene. Formation of
(PNP)RhI(C6H5) (3a). Solid 2 (22.0 mg, 0.039 mmol) was stirred in
benzene (3 mL) under an argon atmosphere until a clear homogeneous
dark brown solution was formed (for 9 h). The 31P{1H} NMR spectrum
of the solution revealed formation of 3a, which was present in >90%
purity. The reaction solution was evaporated, leaving a dark brown
residue. The residue was extracted with pentane, leaving an off-white
KCl remainder. The pentane solution was filtered through a cotton pad
and evaporated to dryness, giving 20.2 mg (90% yield) of 3a as a dark
brown solid. The spectroscopic properties of 3a were as reported in the
literature.12
Analysis. The NMR spectra were recorded at 400 MHz (1H), 100 MHz
(13C), and 162 MHz (31P) using a Bruker Avance-400 NMR spectro-
meter and at 500 MHz (1H), 126 MHz (13C), and 202 MHz (31P)
using a Bruker Avance-500 NMR spectrometer. All spectra were
Reaction of (PNP)RhICl (1) with C6D6 in the Presence of
KN(SiMe3)2. Formation of (PNP)RhI(C6D5) (3b). A C6D6 solution
(1 mL) of KN(SiMe3)2 (5.8 mg, 0.029 mmol) was added to a stirred
dark red C6D6 solution (0.5 mL) of 1 (14.0 mg, 0.026 mmol) under an
argon atmosphere. After the addition, 2 was formed and gradually
consumed during 12 h, resulting in a homogeneous dark brown solution.
The 31P{1H} and 1H NMR spectra of the solution revealed formation of
complex 3b. The reaction solution was evaporated, leaving a dark brown
solid. The 2H{1H} NMR spectrum of the solid redissolved in dry C6H6
showed a signal at 2.80 ppm, indicating deuterium incorporation into the
benzylic position. The solvent was removed under reduced pressure, and
the residue was dissolved in pentane, followed by filtration through a
cotton pad. Evaporation of pentane gave 13.4 mg (89% yield) of 3b as a
dark brown solid.
1
recorded at 23 °C. H NMR and 13C{1H} NMR chemical shifts are
1
reported in parts per million downfield from tetramethylsilane. H
NMR chemical shifts were referenced to the residual hydrogen signals
of the deuterated solvents (3.58 ppm, THF-d8; 7.15 ppm, C6D6), and
the 13C NMR chemical shifts were referenced to the 13C signals of
the deuterated solvents (67.4 ppm, THF-d8; 128.0 ppm, C6D6). 31P
NMR chemical shifts are reported in ppm downfield from H3PO4 and
referenced to an external 85% solution of phosphoric acid in D2O.
Abbreviations used in the description of NMR data are as follows: b,
broad; s, singlet; d, doublet; t, triplet; m, multiplet; v, virtual; app,
apparent; Py, pyridine; Ph, phenyl. IR spectra were measured with a
Nicolet-6700 FT-IR spectrometer. Elemental analyses were performed
by the Unit of Chemical Research Support, Weizmann Institute of
Science.
31P{1H} NMR (C6D6): 59.4 (m, JRhÀP = 172 Hz). 1H NMR (C6D6):
6.97 (t, JHÀH = 7.5 Hz, 1H, Py H4), 6.45 (d, JHÀH = 7.5 Hz, 2H,
Py H3,5), 2.85 (distorted vt, JPÀH = 3.1 Hz, 3H, PyÀCH2P), 1.25 (vt,
JPÀH = 6.0 Hz, 36H, PÀt-Bu). 2H{1H} NMR (C6H6; measured with-
Reaction of (PNP)RhICl (1) with KN(SiMe3)2. Formation
of [(PNP*)RhICl]K (2). A benzene solution (2 mL) of KN(SiMe3)2
(10.2 mg, 0.051 mmol) was added to a stirred dark red benzene solution
(1 mL) of 1 (24.7 mg, 0.046 mmol) under an argon atmosphere. After 3
h a noticeable amount of orange precipitate was present in the solution.
The precipitate was separated from the solution by centrifugation,
washed with pentane, and dried under vacuum, giving 22.0 mg (85%
yield) of 2 as an orange solid. The 31P{1H} and 1H NMR spectra of the
solid redissolved in dry THF-d8 revealed formation of 2.
2
out H lock): 8.13 (bs, Ph D), 7.24 (bs, Ph D), 6.98 (bs, Ph D), 2.80
(bs, PyÀCDHP).
Reaction of [(PNP*)RhICl]K (2) with C6D6. Formation of
(PNP)RhI(C6D5) (3b). Solid 2 (10.0 mg, 0.018 mmol) was stirred in
C6D6 (1.5 mL) under an argon atmosphere until a clear homogeneous
dark brown solution was formed (for 9 h). The 31P{1H} and 1H NMR
spectra of the solution revealed formation of complex 3b. The reaction
solution was evaporated, leaving a dark brown solid. The 2H{1H} NMR
spectrum of the solid redissolved in dry C6H6 showed a signal at 2.80
ppm, indicating deuterium incorporation into the benzylic position. The
solvent was removed under reduced pressure, and the residue was
dissolved in pentane, followed by filtration through a cotton pad.
Evaporation of pentane gave 9.1 mg (87% yield) of 3b as a dark brown
solid.
31P{1H} NMR (THF-d8): 57.6 (dd (AB), 1P, JPÀP = 345 Hz, JRhÀP
=
151 Hz), 49.2 (dd (AB), 1P, JPÀP = 345 Hz, JRhÀP = 147 Hz). 1H NMR
(THF-d8): 6.00 (t, JHÀH = 7.4 Hz, 1H, Py H4), 5.67 (d, JHÀH = 8.5 Hz,
1H, Py H3), 5.11 (d, JHÀH = 6.3 Hz, 1H, Py H5), 3.31 (d, JPÀH = 3.2 Hz,
1H, PyÀCHP), 2.63 (d, JPÀH = 7.8 Hz, 2H, PyÀCH2P), 1.38 (m, 36H,
PÀt-Bu). 13C{1H} NMR (THF-d8): 174.02 (d, JPÀC = 24.4 Hz, Py C2),
162.72 (d, JPÀC = 9.0 Hz, Py C6), 127.93 (s, Py C4), 109.18 (d, JPÀC
17.8 Hz, Py C3), 95.98 (d, JPÀC = 11.2 Hz, Py C5), 63.84 (d, JPÀC
=
=
Reaction of (PNP)RhICl (1) with KN(SiMe3)2 under Nitro-
gen. Formation of (PNP*)RhI(N2) (4). Under nitrogen, a benzene
solution (1 mL) of KN(SiMe3)2 (4.1 mg, 0.021 mmol) was added to a
stirred dark red benzene solution (0.5 mL) of 1 (10.0 mg, 0.019 mmol).
After the addition, 2 was formed and gradually consumed during 12 h,
resulting in a clear homogeneous bright red solution. The 31P{1H}
NMR spectrum of the solution revealed formation of the previously
reported complex 410 (91% NMR yield) together with complex 3a
(9% NMR yield). The reaction solution was evaporated, leaving a bright
red residue. The residue was extracted with pentane, leaving an off-white
KCl remainder. The pentane solution was filtered through a cotton pad
and evaporated to dryness, yielding 9.3 mg of a bright red solid, which
contains 4 (91%) and 3a (9%). The 31P{1H} and 1H NMR analysis, IR
spectroscopy, and mass spectroscopy confirmed the formation of the
previously reported 4.10
46.4 Hz, PyÀCHP), 37.44 (d, JPÀC = 13.3 Hz, PyÀCH2P), 36.21
(m, PÀC(CH3)3), 34.76 (m, PÀC(CH3)3), 30.84 (d, JPÀC = 6.9 Hz,
PÀC(CH3)3), 30.14 (d, JPÀC = 6.6 Hz, PÀC(CH3)3). Assignment of
13C{1H} NMR signals was confirmed by 13C DEPT. Anal. Found (calcd
for C23H42ClKNP2Rh): C, 48.32 (48.30); H, 7.44 (7.40).
Reaction of (PNP)RhICl (1) with Benzene in the Presence
of KN(SiMe3)2. Formation of (PNP)RhI(C6H5) (3a). A benzene
solution (2 mL) of KN(SiMe3)2 (14.6 mg, 0.073 mmol) was added to a
stirred dark red benzene solution (1 mL) of 1 (35.5 mg, 0.067 mmol)
under an argon atmosphere. After the addition, 2 was formed as an
orange precipitate and gradually consumed during 12 h, resulting in a
homogeneous dark brown solution. The 31P{1H} NMR spectrum
revealed formation of the previously reported complex 3a,12 which
was present in >90% purity. The reaction solution was evaporated,
leaving a dark brown residue. The residue was extracted with pentane,
leaving an off-white KCl remainder. The pentane solution was filtered
through a cotton pad and evaporated to dryness, giving 36.1 mg (94%
yield) of 3a as a dark brown solid. Complex 3a was identified by its
31P{1H} and 1H NMR spectra, which were the same as those reported in
the literature.12
Reaction of [(PNP*)RhICl]K (2) with N2. Formation of
(PNP*)RhI(N2) (4). Under nitrogen, solid 2 (10.0 mg, 0.018 mmol)
was stirred in benzene (1.5 mL) for 9 h, resulting in a clear homogeneous
bright red solution. The 31P{1H} NMR spectrum of the solution
revealed formation of the previously reported complex 410 (93%
NMR yield) together with complex 3a (7% NMR yield). The reaction
2726
dx.doi.org/10.1021/om200104b |Organometallics 2011, 30, 2721–2729

Organometallics
ARTICLE
solution was evaporated, leaving a bright red residue. The residue was
extracted with pentane, leaving an off-white KCl remainder. The
pentane solution was filtered through a cotton pad and evaporated to
dryness, giving 8.9 mg of a bright red solid, which contains 4 (93%) and
3a (7%).
excess (5.0 μL, 0.080 mmol). The immediate reaction was accompanied
by a color change from orange to dark green. The 31P{1H} NMR
spectrum revealed formation of complex 10, which was present in >90%
purity. The reaction solution was evaporated, leaving a dark green
residue. The residue was extracted with pentane, leaving a white KI
remainder. The pentane solution was filtered through a (0.2 μm) Teflon
filter and evaporated to dryness, giving 9.5 mg (81% yield) of 10 as a dark
green solid.
Reaction of [(PNP*)RhICl]K (2) with CO. Formation of
(PNP*)RhI(CO) (8). In a THF solution (0.5 mL) of 2 (15.0 mg,
0.026 mmol) under an argon atmosphere, in a screw-capped NMR tube
equipped with a septum, was injected CO (1.0 mL, 0.045 mmol). The
solution changed from orange to pink. The 31P{1H} spectrum of the
solution revealed formation of 8. The solution was evaporated, leaving a
pink residue. The residue was extracted with pentane, leaving an off-
white KCl remainder. The pentane solution was filtered through a
cotton pad and evaporated to dryness, giving 12.0 mg (88% yield) of 8 as
a pink solid.
31P{1H} NMR (C6D6): 53.3 (dd (AB), 1P, JPÀP = 390 Hz, JRhÀP
=
101 Hz), 44.7 (dd (AB), 1P, JPÀP = 390 Hz, JRhÀP = 105 Hz). 1H NMR
(C6D6): 6.43 (m, 1H, Py H4), 6.36 (d, JHÀH = 8.2 Hz, 1H, Py H3), 5.48
(d, JHÀH = 6.2 Hz, 1H, Py H5), 3.55 (d, JPÀH = 5.9 Hz, 1H, PyÀCHP),
2.68 (dbd (AB), JHÀH = 16.9 Hz, JPÀH = 6.7 Hz, 1HA, PyÀCH2P), 2.53
(ddd (AB), JHÀH = 16.9 Hz, JPÀH = 10.8 Hz, JPÀH = 2.2 Hz, 1HB,
PyÀCH2P), 2.19 (d app t, JRhÀH = 2.9 Hz, JPÀH = 4.8 Hz, 3H,
Reaction of [(PNP)RhI(CO)]BF4 (9) with KN(SiMe3)2. For-
mation of (PNP*)RhI(CO) (8). A THF solution (2 mL) of KN-
(SiMe3)2 (7.2 mg, 0.036 mmol) was added to a THF solution (2 mL) of
916 (20.0 mg, 0.033 mmol). The solution was stirred for 6 h, accom-
panied by a color change from yellow to pink. The 31P{1H} spectrum of
the solution revealed formation of 8. The solution was evaporated,
leaving a pink residue. The residue was extracted with pentane, leaving a
KBF4 remainder. The pentane solution was filtered through a cotton pad
and evaporated to dryness, giving 15.9 mg (92% yield) of 8 as a
pink solid.
RhÀCH3), 1.43 (d, JPÀH = 12.2 Hz, 9H, PÀt-Bu), 1.40 (dd, JPÀH
=
12.3 Hz, JPÀH = 0.7 Hz, 9H, PÀt-Bu), 1.18 (d, JPÀH = 12.3 Hz, 9H,
PÀt-Bu), 1.09 (d, JPÀH = 11.7 Hz, 9H, PÀt-Bu). 13C{1H} NMR (C6D6):
172.86 (bd, JPÀC = 19.7 Hz, Py C2), 159.55 (m, Py C6), 131.30 (s, Py
C4), 114.14 (d, JPÀC = 17.6 Hz, Py C3), 100.60 (d, JPÀC = 11.0 Hz, Py
C5), 63.09 (d, JPÀC = 52.7 Hz, PyÀCHP), 41.69 (dd, JPÀC = 20.8 Hz,
JPÀC = 3.5 Hz, PÀC(CH3)3), 37.55 (dd, JPÀC = 18.7 Hz, JPÀC = 6.6 Hz,
PÀC(CH3)3), 35.86 (vt, JPÀC = 6.0 Hz, PÀC(CH3)3), 35.28 (dd,
JPÀC = 9.2 Hz, JPÀC = 3.7 Hz, PÀC(CH3)3), 33.41 (d, JPÀC = 16.7 Hz,
PyÀCH2P), 30.43 (bs, PÀC(CH3)3), 29.81 and 29.78 overlapping (bs,
PÀC(CH3)3), 29.19 (bs, PÀC(CH3)3), 3.77 (d app t, JRhÀC = 28.2 Hz,
JPÀC = 4.5 Hz, CH3). Assignment of 13C{1H} NMR signals was
confirmed by 13C DEPT. ES-MS: m/z 548.27 (calcd 547.93). Anal.
Found (calcd for C24H45ClNP2Rh): C, 52.57 (52.61); H, 8.13 (8.28).
Reaction of [(PNP*)RhICl]K (2) with H2. Formation of
(PNP)RhIH (11a). In a THF solution (0.5 mL) of 2 (9.5 mg, 0.017 mmol)
under an argon atmosphere, in a screw-capped NMR tube equipped with
a septum, was injected an excess of dry H2 (6.0 mL, 0.270 mmol). After
16 h at room temperature, the 31P{1H} NMR analysis of the reaction
solution revealed full consumption of 2 and formation of compound 11a,
which was present in 70% purity, together with 30% of complex 1. The
ratio was determined by integration. The reaction was accompanied by a
color change from orange to brown. The solvent was evaporated, and the
residue was extracted with cold (À35 °C) pentane (2 mL), followed by
filtration through a (0.2 μm) Teflon filter. Evaporation of pentane gave
4.1 mg (48% yield) of 11a as a brown solid.
31P{1H} NMR (C6D6): 77.0 (dd (AB), 1P, JPÀP = 244 Hz, JRhÀP
=
125 Hz), 74.2 (dd (AB), 1P, JPÀP = 244 Hz, JRhÀP = 125 Hz). 1H NMR
(C6D6): 6.42 (m, 1H, Py H4), 6.36 (d, JHÀH = 8.7 Hz, 1H, Py H3), 5.37
(d, JHÀH = 6.3 Hz, 1H, Py H5), 3.65 (d, JPÀH = 4.4 Hz, 1H, PyÀCHP),
2.73 (d, JPÀH = 8.9 Hz, 2H, PyÀCH2P), 1.46 (d, JPÀH = 12.8 Hz, 18H,
PÀt-Bu), 1.08 (d, JPÀH = 12.9 Hz, 18H, PÀt-Bu). 13C{1H} NMR
(C6D6): 199.21 (d app t, JRhÀC = 66.1 Hz, JPÀC = 12.6 Hz, CO), 172.93
(m, Py C2), 160.39 (m, Py C6), 132.33 (s, Py C4), 114.20 (d, JPÀC
18.6 Hz, Py C3), 97.44 (d, JPÀC = 11.6 Hz, Py C5), 64.28 (dd, JPÀC
=
=
49.5 Hz, JPÀC = 1.8 Hz, PyÀCHP), 36.55 (m, PÀC(CH3)3), 35.31 (d,
JPÀC = 16.3 Hz, PyÀCH2P), 34.74 (m, PÀC(CH3)3), 29.86 (d, JPÀC
=
6.0 Hz, PÀC(CH3)3), 29.13 (d, JPÀC = 5.8 Hz, PÀC(CH3)3). Assign-
ment of 13C{1H} NMR signals was confirmed by 13C DEPT. IR (thin
film): νCO 1946 cmÀ1. Anal. Found (calcd for C24H42NOP2Rh): C,
54.85 (54.86); H, 8.03 (8.06).
Reaction of [(PNP*)RhICl]K (2) with H2O. Regeneration of
1. To a stirred THF solution (1.5 mL) of 2 (10.0 mg, 0.018 mmol)
under an argon atmosphere was added an aliquot of THF containing an
equivalent amount of H2O (or excess). The immediate reaction was
accompanied by a color change from orange to red. The 31P{1H} NMR
spectrum of the solution revealed formation of complex 1, which was
present in >90% purity. The solvent was removed under reduced
pressure, and the residue was dissolved in pentane, followed by filtration
through a (0.2 μm) Teflon filter. Evaporation of pentane gave 8.3 mg
(89% yield) of 1 as a red solid. 31P{1H} and 1H NMR spectra of the solid
confirmed the formation of 1.
Reaction of [(PNP*)RhICl]K (2) with D2. Formation of
(PNP)RhID (11b). In a THF solution (0.5 mL) of 2 (15.0 mg,
0.026 mmol) under an argon atmosphere, in a screw-capped NMR tube
equipped with a septum, was injected an excess of dry D2 (5.0 mL, 0.230
mmol). The 31P{1H} NMR analysis indicated that after 16 h at room
2
temperature 2 was fully consumed. The 31P{1H} and H{1H} NMR
spectra of the reaction solution revealed formation of compound 11b,
which was present in 70% purity, together with 30% of complex 1. The
solvent was evaporated, and the residue was extracted with cold (À35 °C)
pentane (2 mL), followed by filtration through a (0.2 μm) Teflon filter.
Evaporation of pentane gave 5.3 mg (41% yield) of 11b as a brown solid.
2H{1H} NMR (THF; measured without 2H lock): 3.16 (bs,
PyÀCDHP), À13.51 (bm, RhÀD). 31P{1H} NMR (THF): 82.2 (m,
JRhÀP = 166.4 Hz). 1H NMR (C6D6): 7.06 (t, JHÀH = 7.6 Hz, 1H, Py
H4), 6.56 (d, JHÀH = 7.6 Hz, 2H, Py H3,5), 2.91 (bs, 3H, PyÀCH2P),
1.39 (vt, JPÀH = 6.3 Hz, 36H, PÀt-Bu).
Reaction of [(PNP*)RhICl]K (2) with D2O. Deuterium In-
corporation into the Benzylic Position of 1a. To a stirred THF
solution (1.5 mL) of 2 (10.0 mg, 0.018 mmol) under an argon atmo-
sphere was added an aliquot of THF containing an equivalent amount of
D2O. The immediate reaction was accompanied by a color change from
2
orange to red. Examination of the reaction solution by H{1H} NMR
Reaction of (PNP*)RhI(N2) (4) with H2. Formation of
(PNP)RhIH (11a). Complex 410 was prepared in analogy to the
literature procedure, using KOtBu (rather than MeLi) for deprotonation
of the benzylic position.
showed a signal at 3.00 ppm, indicating deuterium incorporation into the
benzylic position. The solvent was removed under reduced pressure.
1
Examination of the H NMR spectrum (in C6D6) indicated that the
benzylic protons integrated at 70% of the normal intensity.
Reaction of [(PNP*)RhICl]K (2) with CH3I. Formation of
(PNP*)RhIII(CH3)Cl (10). To a stirred THF solution (2.0 mL) of 2
(12.2 mg, 0.021 mmol) under an argon atmosphere was added CH3I in
Method a. InaTHFsolution(0.5mL) of4(9.0mg, 0.017mmol), under
an atmosphere of dry nitrogen in a screw-capped NMR tube equipped with
a septum, was injected an excess of dry H2 (6.0 mL, 0.270 mmol).
2727
dx.doi.org/10.1021/om200104b |Organometallics 2011, 30, 2721–2729

Organometallics
ARTICLE
The 31P{1H} NMR analysis revealed that after 22 h at room temperature
only 17% of 4 was converted to 11a.
’ ACKNOWLEDGMENT
This research was supported by the European Research
Council under the FP7 framework (ERC No 246837), by the
Israel Science Foundation, and by the Kimmel Center for
Molecular design. D.M. holds the Israel Matz Professorial Chair
of Organic Chemistry.
Method b. A 90 mL FischerÀPorter tube equipped with a stirring bar
was charged under nitrogen with a THF solution (4.0 mL) of 4 (19.6 mg,
0.037 mmol) and pressurized with hydrogen to 5.5 atm. The reaction
solution was stirred at room temperature. The 31P{1H} NMR analysis of
the reaction solution revealed full consumption of 4 and formation of
compound 11a after 96 h. The reaction was accompanied by a color
change from bright red to dark brown. The solvent was evaporated, and
the residue was extracted with pentane, followed by filtration through a
(0.2 μm) Teflon filter. Evaporation of pentane gave 16.7 mg (90% yield)
of 11a (at 90% purity) as a brown solid.
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31P{1H} NMR (C6D6): 83.2 (d, JRhÀP = 165.9 Hz). 1H NMR
(C6D6): 7.06 (t, JHÀH = 7.6 Hz, 1H, Py H4), 6.56 (d, JHÀH = 7.6 Hz,
2H, Py H3,5), 2.92 (vt, JPÀH = 3.0 Hz, 4H, PyÀCH2P), 1.39 (vt, JPÀH
=
6.3 Hz, 36H, PÀt-Bu), À12.82 (vq, J = 20.5 Hz, 1H, RhÀH). 1H{31P}
NMR (C6D6): À12.82 (d, JRhÀH = 19.2 Hz, 1H, RhÀH). 13C{1H}
NMR (C6D6): 162.19 (dvt, JPÀC = 7.0 Hz, JRhÀC = 1.5 Hz, Py C2,6),
129.50 (s, Py C4), 119.31 (vt, JPÀC = 4.8 Hz, Py C3,5), 38.62 (dvt,
JPÀC = 3.1 Hz, JRhÀC = 1.1 Hz, PyÀCH2P), 33.97 (dvt, JPÀC = 5.7 Hz,
JRhÀC = 2.8 Hz, PÀC(CH3)3), 29.96 (vt, JPÀC = 4.7 Hz, PÀC(CH3)3).
Assignment of 13C{1H} NMR signals was confirmed by 13C DEPT and
1
by 13CÀ H HSQC correlation. Anal. Found (calcd for C23H44NP2Rh):
C, 55.41 (55.31); H, 8.74 (8.88).
Computational Methods. All calculations were carried out using
Gaussian09, revision A.02.22 Two members of the M06 family of DFT
functionals23 were used: M06, a meta-hybrid functional containing 27%
HF exchange,24 and M06-L, its local (nonhybrid) variant.25
With these functionals, two basis setÀRECP (relativistic effective
core potential) combinations were used. The first, denoted SDD(d), is
the combination of the HuzinagaÀDunning double-ζ (D95 V) basis
set26 on lighter elements with the StuttgartÀDresden basis setÀRECP
combination27 on transition metals; extra polarization functions (i.e. the
D95(d) basis set) were added to phosphorus. The second, denoted
SDB-cc-pVDZ, combines the Dunning cc-pVDZ basis set28 on the main-
group elements and the Stuttgart-Dresden basis setÀRECP27 on the
transition metals with an added f-type polarization exponent taken as the
geometric average of the two f exponents given in the appendix of ref 29.
In order to improve the efficiency of the calculations, density-fitting
basis sets (DFBS) were employed during the calculation of the Coulomb
interaction. The automatic DFBS generation algorithm as implemented
in Gaussian09 was employed.30
Geometries were optimized using the default pruned (75,302) grid,
while the “ultrafine” (i.e., a pruned (99,590)) grid was used for evaluat-
ing the charges, especially essential for calculations with the M06 family
of functionals.31
Geometry optimizations and frequency calculations were performed
in the gas phase at the M06-L/SDD(d)/DFBS level of theory. The
charges were reevaluated at the M06/SDB-cc-pVDZ level of theory.
This combined level of theory is conventionally denoted as M06/SDB-
cc-pVDZ//M06-L/SDD(d)/DFBS.
(7) Tanaka, R.; Yamashita, M.; Nozaki, K. J. Am. Chem. Soc. 2009,
131, 14168.
’ ASSOCIATED CONTENT
(8) (a) Ben Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am.
Chem. Soc. 2006, 128, 15390. (b) Schwartsburd, L.; Iron, M. A.;
Konstantinovski, L.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J. W.;
Milstein, D. Organometallics 2010, 29, 3817. For CÀH oxidative addition
to the aromatic [(PNP)IrI(COE)]BF4 complex see: (c) Ben-Ari, E.;
Gandelman, M.; Rozenberg, H.; Shimon, L. J. W.; Milstein, D. J. Am.
Chem. Soc. 2003, 125, 4714. (d) Ben-Ari, E.; Cohen, R.; Gandelman, M.;
Shimon, L. J. W.; Martin, J. M. L.; Milstein, D. Organometallics 2006,
25, 3190.
S
Supporting Information. Tables giving Cartesian co-
b
ordinates (XYZ format) of the DFT optimized geometries and
figures giving NMR spectra of the complexes 2, 8, 10, and 11a.
This material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
(9) (a) Iron, M. A.; Ben-Ari, E.; Cohen, R.; Milstein, D. Dalton
Trans. 2009, 9433. (b) Zeng, G.; Guo, Y.; Li, S. Inorg. Chem. 2009,
48, 10257.
Corresponding Author
*E-mail: david.milstein@weizmann.ac.il. Fax: 972-8-9346569.
2728
dx.doi.org/10.1021/om200104b |Organometallics 2011, 30, 2721–2729

Organometallics
ARTICLE
(10) (a) Kloek, S. M.; Heinekey, D. M.; Goldberg, K. I. Angew.
Chem., Int. Ed. 2007, 46, 4736. (b) Kloek, S. M.; Heinekey, D. M.;
Goldberg, K. I. Organometallics 2008, 27, 1454.
(11) (a) Hermann, D.; Gandelman, M.; Rozenberg, H.; Shimon,
L. J. W.; Milstein, D. Organometallics 2002, 21, 812. The X-ray crystal
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(12) 3a has been prepared previously by reaction of (PNP)Rh(OTf)
with diphenylzinc, as described in ref 10.
(13) (a) Vuzman, D.; Poverenov, E.; Shimon, L. J. W.; Diskin-
Posner, Y.; Milstein, D. Organometallics 2008, 27, 2627. (b) Feller, M.;
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Konstantinovski, L.; Milstein, D. Inorg. Chem. 2010, 49, 1615 and
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(14) An attempt to prepare 5 in situ in dry THF by the reaction of
the cationic complex [(PNP)RhI(THF)]BF4 with an equimolar amount
of KN(SiMe3)2 at À35 °C under dry argon resulted in the formation of a
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(15) N2 was reported to bind more strongly than ethylene to the
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