Monomeric rhodium(II) complexes supported by a diarylamido/bis(phosphine) PNP pincer ligand and their reactivity toward dihydrogen

Article abstract of DOI:10.1021/om300760j

A rhodium(II) complex of a diarylamido/bis(phosphine) PNP pincer ligand, (PNP)Rh(OTf) (2, where OTf = O₃SCF₃ and PNP = [κ³-P,N,P-(4-Me-2-(ⁱPr₂P)-C ₆H₃)₂N]), has been prepared by oxidation of the rhodium(I) precursor (PNP)Rh(H₂CCHBu^t) (1) with AgOTf. A series of related rhodium(II) complexes of the general formula (PNP)Rh(X) (where X = OAc (3), OSiPh₃ (4), OC₆H₄F (5), Cl (6)) was synthesized via simple anion metathesis reactions starting from 2. In addition, complexes 3 and 6 could be prepared by hydrogen atom abstraction from (PNP)Rh(H)(OAc) (7) or (PNP)Rh(H)(Cl) (8) with TEMPO ((2,2,6,6- tetramethylpiperidin-1-yl)oxyl). Solid-state X-ray structures of compounds 2-6 revealed an approximately square-planar environment about Rh. Analysis of the structural features of 2-6, EPR spectroscopic data, and DFT computational studies are most consistent with a +2 oxidation state for rhodium. Reactions of 2, 3, 5, and 6 with H₂ were explored. The reaction of 2 with H ₂ gave the new complex (PN(H)P)Rh(H)₂(OTf) (9), and the reaction of 3 with H₂ produced (PNP)Rh(H)(OAc) (7), whereas the reaction of 5 with H₂ gave the known (PNP)Rh(H₂) (10), all with complete consumption of the starting rhodium(II) complexes. In contrast, the reaction of 6 with H₂ produced a mixture of (PNP)Rh(H)(Cl) (8) and (PN(H)P)Rh(H)₂(Cl) (11) in apparent equilibrium with 6 and H ₂. (PNP)Rh(H₂) (10) was identified as an elongated dihydrogen complex.

Full text of DOI:10.1021/om300760j

Article
pubs.acs.org/Organometallics
Monomeric Rhodium(II) Complexes Supported by a Diarylamido/
Bis(phosphine) PNP Pincer Ligand and Their Reactivity Toward
Dihydrogen
Dan A. Smith,† David E. Herbert,† Justin R. Walensky,‡ and Oleg V. Ozerov*,†
†Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, Texas 77842, United States
‡Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
S
* Supporting Information
ABSTRACT: A rhodium(II) complex of a diarylamido/
bis(phosphine) PNP pincer ligand, (PNP)Rh(OTf) (2,
where OTf = O3SCF3 and PNP = [κ3-P,N,P-(4-Me-2-
(iPr2P)-C6H3)2N]), has been prepared by oxidation of the
rhodium(I) precursor (PNP)Rh(H2CCHBut) (1) with
AgOTf. A series of related rhodium(II) complexes of the
general formula (PNP)Rh(X) (where X = OAc (3), OSiPh3
(4), OC6H4F (5), Cl (6)) was synthesized via simple anion
metathesis reactions starting from 2. In addition, complexes 3
and 6 could be prepared by hydrogen atom abstraction from
(PNP)Rh(H)(OAc) (7) or (PNP)Rh(H)(Cl) (8) with
TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl). Solid-state
X-ray structures of compounds 2−6 revealed an approximately square-planar environment about Rh. Analysis of the structural
features of 2−6, EPR spectroscopic data, and DFT computational studies are most consistent with a +2 oxidation state for
rhodium. Reactions of 2, 3, 5, and 6 with H2 were explored. The reaction of 2 with H2 gave the new complex
(PN(H)P)Rh(H)2(OTf) (9), and the reaction of 3 with H2 produced (PNP)Rh(H)(OAc) (7), whereas the reaction of 5 with
H2 gave the known (PNP)Rh(H2) (10), all with complete consumption of the starting rhodium(II) complexes. In contrast, the
reaction of 6 with H2 produced a mixture of (PNP)Rh(H)(Cl) (8) and (PN(H)P)Rh(H)2(Cl) (11) in apparent equilibrium
with 6 and H2. (PNP)Rh(H2) (10) was identified as an elongated dihydrogen complex.
under mild conditions at a (TMP)RhII porphyrin complex
(where TMP = tetramesitylporphyrinato dianion), which exists
INTRODUCTION
■
In recent years there has been a growing interest in the
in equilibrium with its dimeric form [(TMP)Rh]2.17,18
Furthermore, using tetratolylporphyrin (TTP) as a scaffold
for rhodium(II), Chan et al. reported ring opening of
cyclooctane, giving rise to a (TPP)Rh(n-octyl) complex in
high yields.2 The application of the fac-coordinating ligand
N,N-bis(2-pyridylmethyl)amine (DPA) to rhodium and iridium
by de Bruin et al. has led to the exploration of the reactivity of
(DPA)MII(COD) and other related metalloradicals.19,20
Pincer ligands21 are particularly well-suited for supporting
square-planar complexes, a geometry expected for low-spin
RhII. Few examples of pincer supported RhII complexes,
however, are known. The groups of Tilley and Bergman have
demonstrated that bis(oxazoline) pincer ligated RhII complexes
are capable of olefin cyclopropanation with ethyl diazoace-
tate,22,23 and Milstein and co-workers have reported sterically
congested Rh(II) complexes of the 2,6-bis((di-tert-
butylphosphino)methyl)pyridine ligand.24
chemistry of metalloradical complexes,1 with their potential to
homolytically cleave challenging bonds making them candidates
for a wide range of processes, including CC activation,2−4 olefin
oxidation,5 and hydrogen atom transfer.6 For rhodium, isolated
monomeric open-shell species of the +2 oxidation state are
uncommon relative to +1 and +3 oxidation states, in part due
to the well-established RhI/RhIII oxidative addition chemistry.7,8
RhII complexes are most often encountered as bimetallic
species with a metal−metal bond supported by a set of bridging
ligands, with chiral dirhodium tetracarboxylates notably
successful for asymmetric metal carbenoid mediated catalysis.9
Monomeric RhII complexes without chelating ligands are very
rare, with their synthesis and isolation hindered by
disproportionation reactions.7,8,10−12 Instead, access to mono-
meric RhII often depends on a sterically cumbersome
environment at the metal center to disfavor dimerization. To
date, the exploration of RhII species has primarily focused on
porphyrin-ligated complexes that have been shown to be
capable of supporting a variety of X−H activations at Rh(II)
(where X = Si, C, H, O).13−16 Wayland et al. demonstrated that
methane and the alkyl C−H bonds of toluene can be split
Received: August 7, 2012
© XXXX American Chemical Society
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Scheme 1. Syntheses of Complexes 2−8
The diarylamido-based PNP ligand class25−27 has proven to
be a very useful supporting ligand for metals across the periodic
table, in various oxidation states, including a number of species
with unusual structure or reactivity.28−36 We have previously
reported on the chemistry of PNP complexes of Rh in the
context of RhI/RhIII reactivity.37−46 It was envisaged that both
the steric bulk and conformational rigidity of this PNP pincer
would also allow for well-defined, square-planar RhII species.
The synthesis of one of these compounds has been previously
communicated.43 PNP complexes of cobalt, the lighter
congener of rhodium, in oxidation state +2 have been reported
by Mindiola et al.47 Herein, an exploration of a series of
(PNP)RhII(X) complexes is presented, alongside computa-
tional studies to further the understanding of the nature of
these species. Additionally, we report on the reactivity of
(PNP)RhII(X) complexes with dihydrogen.
RhIII−H bond falls within the 55−60 kcal/mol range,18,49,50 and
therefore, TEMPO did appear to be an appropriate hydrogen
atom abstractor (the BDE for TEMPO-H is 69.6 kcal/mol).51
(PNP)Rh(H)(κ2-OAc) (7) was synthesized in high yield by the
addition of an excess of acetic acid to 1. For complex 7, the
1
hydride resonance of −23.77 ppm in the H NMR spectra is
downfield of the −29.91 ppm value for (PNP)Rh(H)(Cl)
(8),37 in accordance with the now filled coordination site trans
to the hydride. The 31P NMR spectroscopic resonances are
similar for complexes 7 (52.7 ppm (JRhP = 107 Hz)) and 8
(50.6 ppm (JRhP = 105 Hz)), though the chromophores of each
are notably different, with the former exhibiting a red coloration
and the latter an intense green. Upon addition of an equimolar
amount of TEMPO to 7 or 8, consumption of the rhodium
1
hydride complex was noted in the H NMR spectra with
concurrent generation of broad resonances identifiable as the
desired Rh(II) species. The conversion of 7 to 3 is
accompanied by a distinctive color change from red to dark
green. The greater solubility of TEMPO-H in nonpolar solvents
allowed the isolation of the organometallic complexes in
reasonable yields by recrystallization. This synthesis of 6 from 8
has been previously communicated.43
RESULTS AND DISCUSSION
■
Synthesis and Characterization. Addition of the one-
electron oxidant AgOTf to the previously reported41,45 Rh(I)
precursor (PNP)Rh(H2CCHtBu) (1) in toluene successfully
led to the corresponding rhodium(II) triflate complex (PNP)-
Rh(OTf) (2), which was isolated in 75% yield (Scheme 1). The
reaction was observed to be near-instantaneous, with a color
change from orange to dark green and concomitant deposition
of metallic silver clearly visible. 1H NMR spectroscopic analysis
of complex 2 revealed a set of broadened peaks, suggesting a
paramagnetic species. Not all the expected proton resonances
could be accounted for, presumably due to the extent of
paramagnetic broadening. Analysis of the 19F NMR spectrum of
2 revealed a resonance at −73.4 ppm, with this value likely
influenced by the paramagnetic environment. No resonances
were observed by 31P NMR spectroscopy.
The isolation of 2−6 as green, semicrystalline materials
allowed for their characterization with combustion analysis,
confirming the proposed formulations of the bulk samples.
Measurements of the magnetic moment in solution by the
Evans method gave values in the range 1.9−2.1 μB,
representative of complexes with a single unpaired electron
and in accordance with reported monomeric Rh(II) com-
pounds.11,24 In recent years, many ligands have been found to
display noninnocent behavior toward metal centers under
certain circumstances.52 The PNP pincer is no exception, with
Mindiola et al. demonstrating that the oxidation of [(PNP)-
Ni(Cl)] to [(PNP)Ni(Cl)][OTf] occurs at the ligand with the
metal remaining in the +2 oxidation state.53 To this end it was
of interest to interrogate a (PNP)RhIIX compound by electron
paramagnetic resonance (EPR) spectroscopy. Collection of the
EPR spectrum of complex 2 at ambient temperature in toluene
(Figure 1) gave a broad unresolved signal with a g value of 2.19,
corresponding well to other reported Rh(II) g values.54,55 At
lower temperatures the signal was not found to sharpen and
remains broad.
Attempts to extend this synthetic pathway to the use of
AgOAc for the synthesis of the corresponding (PNP)RhII
acetate complex led to a mixture of species. Instead, the
synthesis of (PNP)Rh(OAc) (3), (PNP)Rh(OSiPh3) (4), and
(PNP)Rh(OC6H5F) (5) was possible by salt metathesis of 2 in
toluene with KOAc, NaOSiPh3, and NaOC6H5F, respectively
(Scheme 1). Reaction of 3 with Me3SiCl in C6D6 rapidly gave
1
(PNP)RhCl (6), as detected by H NMR spectroscopy, with
Me3SiOAc as the byproduct.
X-ray Structural Studies. Fortunately, single crystals
suitable for a set of X-ray diffraction studies could be grown
for compounds 2−6, allowing their structural elucidation
(Figure 2 and Table 1). Complexes 2−6 were found to be
Another facile route to complexes 3 and 6 was envisaged via
hydrogen atom abstraction from the corresponding RhIII
hydride complexes, similarly to the precedent in the work of
Chan et al.48 The bond dissociation energy (BDE) of a typical
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Interestingly, the Rh−NPNP distances in five-coordinate,
approximately square pyramidal RhIII complexes fall into the
same 2.02−2.06 Å range, as well: (PNP)Rh(Me)(Cl), 2.059(4)
Å;37 (PNP)Rh(Ph)(Br), 2.048(5) Å;39 (PNP)Rh(Me2SiCl)-
(Cl), 2.027(2) Å.42 The octahedral RhIII complex (PNP)Rh-
(Ph)(κ2-O2CNEt2)46 possesses a similar Rh−N bond distance
of 2.044(2) Å. On the other hand, the Rh−N distances in the
five RhII complexes (2−6) reported here all fall within a narrow
1.93−1.97 Å range (Table 1).
Moreover, the X-ray molecular structure of (PNP)RhCl (6)
allows a direct comparison with the analogous palladium
complex (PNP)PdCl previously reported.26 A shortening of the
metal−nitrogen distance is noted upon moving from palladium
(2.0258(19) Å) to rhodium (1.968(2) Å), in contrast to the
expected contraction of bond length for a transition metal of a
later group. A similar contrast is evident in comparing the
metal−nitrogen distance in (PNP)Rh(OAc) (3; 1.968(3) Å)
with that of the closely analogous (FPNP)Pd(OAc) (2.015(5)
Å).56
The lone pair of the amido group of PNP is potentially
capable of a π-interaction with a metal orbital. In square-planar
RhI or PdII (d8) complexes, and in square-pyramidal or
octahedral RhIII (d6) complexes, the matching d orbitals of the
metal are doubly filled, leading to a four-electron two-center
pπ−dπ repulsion or, at least, a lack of π-bonding. However, in a
square-planar RhII complex (d7), a half-filled dπ orbital provides
for a three-electron, two-center π-interaction, which may be
thought of as a half-order π-bond.
Figure 1. X-band EPR spectrum of complex 2 obtained at 293 K in
toluene.
monomeric, with the PNP ligand binding in a meridional
fashion to give an approximately square planar geometry at the
four-coordinate rhodium center, as expected for low-spin RhII.8
The geometries of the corresponding (PNP)Rh fragments in
these five compounds were found to be very similar to each
other. The slightly shorter Rh−N distance in 2 in comparison
to those in 3−6 can be read as the manifestation of the weaker
trans-influence character of the triflate trans to N. Likewise, the
spread of Rh−O distances in 2−5 appears to reflect the relative
basicity of the oxygenous ligands: the shortest Rh−O distance
was recorded for the strongest O-donor (triphenylsiloxide in
4), and the longest Rh−O distance was recorded for the
weakest O-donor (triflate in 2).
The most notable structural feature of the series is the
contraction of the Rh−N bond relative to the PNP compounds
of RhI and RhIII that have been previously characterized. In the
RhI compounds (PNP)Rh(H2CCHtBu) (1) and (PNP)Rh-
(−NN−)Rh(PNP),41 the Rh−NPNP distances were found to
be 2.062(4) and 2.0358(12)/2.0444(12) Å, respectively.
Inspection of the C−N bonds of the ligand scaffold of 2
reveals a slight elongation (1.418(2) Å) relative to those of
Rh(I) (e.g.: (PNP)Rh(H2CCHtBu), 1.394(6) and 1.403(5)
Å; (PNP)Rh(N2)Rh(PNP), 1.3952(18), 1.3899(18),
1.3930(18), and 1.3953(18) Å).41 The other RhII complexes
Figure 2. POV-Ray rendition57 of the ORTEPs58 of complexes 2−6 (ellipsoids set to 50% probability) showing selected atom labeling. The
following were omitted for clarity: (a) hydrogen atoms in all structures; (b) one of the two disordered triflate positions in 2.
C
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Table 1. Selected Bond Distances (Å) and Angles (deg) in the Solid State Structures of Complexes 2−6
2
3
4
5
6
Rh1−P1
Rh1−P2
Rh1−N1
Rh1−X
P1−Rh1−P2
N1−Rh1−X
X
2.3085(7)
2.3228(6)
1.9324(14)
2.1073(13)
165.778(16)
175.39(6)
O(Tf)
2.2941(13)
2.2834(14)
1.968(3)
2.298(8)
2.309(9)
1.961(6)
2.002(5)
166.52(7)
177.33(13)
O(SiPh3)
2.2962(14)
2.2920(13)
1.959(2)
2.2905(9)
2.2905(9)
1.968(2)
2.3230(13)
164.60(3)
180
2.065(3)
2.023(2)
168.55(3)
171.43(11)
O(Ac)
166.73(3)
177.31(10)
O(C6H4F-p)
Cl
Figure 3. Spin density plots of 2 (left), 5 (center), and 6 (right).
3−6 show similarly elongated C−N distances, while the C−N
distances in the aforementioned structures of RhIII and PdII
complexes are shorter, at ca. 1.39−1.40 Å (where resolution of
the determination and lack of disorder allow such compar-
isons). Thus, the elongation of the C−N bonds in the RhII
complexes is slight but very consistent. It can be interpreted as
indicative of the greater π-donation from N to Rh resulting in a
lesser π-interaction between the aryl rings and the amide lone
pair.
Scheme 2
Computational Studies. To further explore the electronic
structure, a computational study was undertaken with
complexes 2, 5, and 6. Optimization (Rh and P, B3LYP/
Stuttgart; H, C, N, F, and O, B3LYP/6-31G(d′)) gave bond
lengths and angles in good agreement with those of the X-ray
molecular structure. The calculated spin density plots are
shown in Figure 3. The spin densities at Rh were calculated to
be 0.65, 0.70, and 0.72 in 2, 5, and 6, respectively. This
supports the Rh(II) formulation, although with a significant
contribution from the ligand, and fits the conclusion of a two-
center, three-electron Rh−N π-bond we arrived at on the basis
of the crystallographic metrics. The lack of resolved hyperfine
coupling in the EPR spectrum of 2 can be attributed to the
significant delocalization of the free electron over the PNP
ligand.
Reactions with H2. Vlugt and co-workers have recently
reported the activation of H2 by a tripodal tetraphosphine-
supported RhII complex.59 The complex [(PP3)Rh(Cl)][PF6]
(where PP3 = tris(N-diphenylphosphino-3-methylindolyl)-
phosphine) was found to undergo reaction with molecular
hydrogen at 5 bar over a period of 12 h. The authors proposed
a mechanism involving an outer sphere redox process to Rh(I)
followed by protonation to give the resultant [(PP3)Rh(Cl)-
(H)][PF6].
hydrogen gas gave rise to a color change from dark green to
light red with the consumption of starting material apparent by
NMR spectroscopy in 15 min, with concurrent formation of 7.
This corresponds to net addition of a hydrogen atom to 3, and
the favorability of this reaction makes sense on the basis of
BDE arguments. If the Rh−H BDE in 7 is indeed on the order
of 55−60 kcal/mol,18,49,50 formation of two such bonds should
be enough to compensate for the cleavage of the H−H bond
(104 kcal/mol), particularly since it is additionally favored by
coordination of the second acetate oxygen.
The reaction of 5 with H2 yielded (PNP)Rh(H2) (10), which
can be viewed as the consequence of hydrogenolysis of the
putative intermediate (PNP)Rh(H)(OAr), by analogy with the
formation of 7. It is not surprising that the Rh−OAr bond is
favorably hydrogenolyzed but the Rh−OAc bond is not. The
It was of interest therefore to explore the potential of
complexes 2−6 for splitting molecular hydrogen (Scheme 2).
Exposure of a solution of complex 3 to an atmosphere of
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latter should be a stronger Rh−O bond, and the binding of the
acetate is additionally strengthened by the κ2 coordination.
Yet another outcome was observed for 2, where complete
reaction, even with a large excess of molecular hydrogen at 1
atm, only occurred over a period of 24 h to yield a light yellow
although both are broadened with no well-defined coupling.
Additionally, a broad proton resonance was observed at 8.31
ppm, tentatively assigned to the NH proton. These data are
consistent with an octahedral environment about the rhodium
center, now in the oxidation state +3, with two hydrides in a cis
arrangement; one trans to NH, another trans to Cl. We cannot
reliably establish whether chloride is located syn or anti with
respect to the N−H bond, but precedent exists for the syn-H−
N−M−Cl orientation resulting in a weak H···Cl hydrogen-
bonding interaction in a closely related pincer system.66
Compound 11 exhibits a doublet resonance at 67.2 ppm with
a JRhP coupling constant of 114 Hz in its 31P{1H} NMR
spectrum, comparable to those of 9 (65.1 ppm, d, 114 Hz). The
hydride chemical shifts in 11 compare well to those of the
reported complexes Rh(H)2(Cl)(PPh3)(Py)2, (−17.2 and
−18.0 ppm) and Rh(H)2(Cl)(PPh3)2(Py) (−16.8 and −17.8
ppm), which possess hydrides trans to Cl and a nitrogen donor,
analogously to 11.67,68 Compound 11 can be viewed as the
product of heterolytic addition of H2 across the N−Rh bond in
8, whereas 8 can be viewed as analogous to 7 in being formed
by net hydrogen atom addition to 6. As chloride is more
donating than a triflate, addition of H2 to 8 to give 11 would be
expected to be less favorable than addition of H2 to 2 to give 9.
This reactivity toward molecular hydrogen for complexes 2−
6 is in stark contrast to the observed stability of rhodium(II)
pincer complexes reported by Milstein and co-workers.24 This
is likely a consequence of the amido lone pair in our series that
can participate in the heterolytic splitting, whereas in the
examples presented by Milstein et al., the nitrogen atom of the
pincer exists within a metal-bound pyridine ring and without an
active lone pair of electrons.
1
solution. Analysis of the solution by H NMR spectroscopy
revealed the single species 9, possessing a multiplet resonance
at −19.76 ppm and a singlet resonance at 9.51 ppm with an
integration ratio of 2:1, the latter signal indicative of
protonation at the amide functionality of the PNP pincer.60
The signal at −19.76 ppm possesses a T1 value of 541 ms at 25
°C and evolves into two signals (each of 1H intensity) at −16.2
and −23.2 ppm upon cooling to −63 °C. This is most
consistent with the ground-state dihydride structure (PN(H)-
P)Rh(H)2(OTf) with a kinetically facile degenerate exchange
mechanism of the two hydride positions. In the related Pd(II)
complex [(PN(H)P)PdH]+, we previously determined that
hydrogen bonding with the triflate anion shifts the resonance of
an NH proton to around 9 ppm, as opposed to chemical shifts
of around 7 ppm observed with weakly interacting anions, such
as [B(C6H3(CF3)2)4]− and [HCB11H11]−.61 It seems reason-
able to expect the triflate in 9 to be hydrogen bonded to the
1
NH proton. At the same time, the low-temperature H NMR
chemical shifts of the hydride signals of 9 are most consistent
with one hydride (−16.2 ppm) trans to the NH and the other
(−23.2 ppm) trans to a weak but present donor (such as
triflate). A hydride trans to an empty site in a RhIII square-
pyramidal complex is expected to resonate at around −30
ppm.37 These observations can be reconciled by the ground-
state structure, in which the triflate is bound to Rh and
hydrogen bonded to the NH proton, as depicted in Scheme 2.
This assignment is consistent with the apparent Cs symmetry
observed in the 1H NMR spectra of 9, where four environments
are clearly evident for the methyl groups of the isopropyl
moieties. Compound 9 can be regarded as arising from the
putative intermediate (PNP)Rh(H)(OTf) via addition of H2
across the metal−amido bond. The greater unsaturation of
(PNP)Rh(H)(OTf) in comparison to 7 is the likely cause of
the favorability of the heterolytic addition of H2. The exchange
process may well involve intermediate dissociation of triflate
(or at least cleavage of the O−Rh bond) and conversion to a
RhI dihydrogen complex. Analogous cationic RhI dihydrogen
complexes with pyridine/bis(phosphine) PN*P pincer ligands
have been reported.62 Neutral (PCP)Rh(H2) complexes have
also been characterized as having dihydrogen ligands.63
Faced with the preponderance of pincer-supported RhI
dihydrogen complexes, we also decided to examine the nature
of (PNP)Rh(H2) (10). Treatment of 2 with excess CaH2 and
D2O generated (PNP)Rh(HD) (10-d) in situ, for which a JHD
value of 18.3 Hz was measured. Low-temperature NMR
experiments yielded a minimal value of 39 ms for T1 relaxation,
measured at −48 °C. On the basis of relationships between H−
H distances and T1,min values or JH‑D coupling established in the
literature,64 these data indicate a “stretched” or “elongated”
dihydrogen complex,65 with a predicted H−H distance of 1.13
Å.
CONCLUSION
■
Rhodium(II) complexes of the PNP pincer have been prepared
and demonstrated to be stable and monomeric. These
compounds are readily accessible in good yields by oxidation,
hydrogen atom abstraction, or salt metathesis. Exploration of
the nature of a few of the studied complexes by DFT
calculations reveal that the spin density is manifested most
greatly at Rh, but with significant delocalization into the ligand.
(PNP)RhIIX compounds readily reacted with H2, and the
nature of the products of these reactions depended heavily on
the identity of X.
EXPERIMENTAL SECTION
■
General Considerations. Unless specified otherwise, all manip-
ulations were performed under an argon atmosphere using standard
Schlenk line or glovebox techniques. Toluene, diethyl ether, C6D6,
THF, and pentane were dried over and distilled from NaK/Ph2CO/
18-crown-6 and stored over molecular sieves in an Ar-filled glovebox.
Fluorobenzene and CDCl3 were dried with and then distilled from
CaH2 and stored over molecular sieves in an Ar-filled glovebox. The
following compounds were prepared according to literature
procedures: (PNP)Rh(H2CCHtBu) (1)45 and (PNP)Rh(H)(Cl)
(8).37 NaOSiPh3 and KOC6H4F were synthesized by reaction of the
corresponding silanol and alcohol with NaHMDS (HMDS =
hexamethyldisilazide) and KOtBu, respectively. All other chemicals
were purchased from either Aldrich or Acros and used as received
unless otherwise noted. NMR spectra were recorded on a Varian Inova
300, Varian Mercury 300, or Varian NMRS 500 spectrometer. For 1H
and 13C{1H} NMR spectra, the residual solvent peak was used as an
internal reference. 31P NMR spectra were referenced externally using
85% H3PO4 at 0 ppm. 19F NMR spectra were referenced externally
using neat trifluoroacetic acid at −78.5 ppm. Chemical shifts are
Reacting 6 with H2 (ca. 1 atm) produced a mixture of
compounds we have identified as 8 and (PN(H)P)Rh(H)2Cl
(11), with some unreacted 6 and H2 remaining. Addition of
extra H2 and heating did not result in complete conversion to
11. The structure of 11 was tentatively established on the basis
of the solution NMR data. Two distinct hydride environments
of equal intensity at −16.68 and −18.33 ppm were observed,
E
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reported in ppm and coupling constants in Hz. The conventional
inversion−recovery method was used to determine the variable-
temperature longitudinal relaxation time T1 (16−20 variable delays
were used with the waiting time 5 times longer than the expected
relaxation time). NMR spectroscopic measurements for both (PNP)-
RhH2 and (PN(H)P)Rh(H)2(OTf) (9) were conducted on a Bruker
AV 500 MHz NMR spectrometer. EPR spectra were recorded on an
X-band Bruker EMS spectrometer with an Oxford ESR900 liquid He
cryostat.
with vigorous stirring. After 16 h the volatile components were
removed in vacuo, pentane was added, and the resultant green solution
was filtered through Celite. Concentration and cooling to −30 °C gave
rise to a green crystalline material that was isolated by filtration and
1
washed with cold pentane (3 × 1 mL) (28 mg, 53%). H NMR (300
MHz, C6D6): δ 43.47 36.45 (3H, br, overlapping), 17.79 (2H, br),
3.57 (24H, br), −16.39 (1H, br). 19F NMR (282 MHz, C6D6): δ
−105.17. Anal. Calcd: C, 59.82; H, 6.90. Found: C, 59.85; H, 6.95. μeff
(Evans NMR method) = 2.0 μB.
Computational Details. All B3LYP69 (Becke-3 exchange70 and
Lee−Yang−Parr correlation71 functional) calculations were performed
using the Gaussian 09 suite of software.72 Full geometry optimizations
were performed, and stationary points were characterized via analytical
frequency calculations using the Pople double-ζ quality basis set (6-
31G(d′))73,74 for the C, H, and N atoms, which contains a polarization
(d) function on the C, N, and O atoms. The Stuttgart/Dresden
(SDD) triple-ζ quality basis set (SDD) with an effective core potential
(ECP)75 for the Rh and P atoms was employed with an additional d
basis function of 0.387 added for P.
Synthesis of (PNP)RhCl (6). An alternative synthesis via hydrogen
atom abstraction from 8 by TEMPO was reported elsewhere.43 To a
solution of (PNP)Rh(OAc) (30 mg, 0.052 mmol) in benzene-d6 (0.8
mL) was added Me3SiCl (9.9 μL, 0.78 mmol). After 15 min the
volatile components were removed in vacuo to give a green residue
which could be recrystallized as a green crystalline solid from pentane.
1H NMR (300 MHz, C6D6): δ 46.26 39.39 (2H, br, overlapping), 8.06
(overlaps with protio solvent), 3.51 (24H, br). Anal. Calcd: C, 55.08;
H, 7.11. Found: C, 54.97; H, 7.03. μeff (Evans NMR method) = 1.9 μB.
Synthesis of (PNP)Rh(H)(OAc) (7). To a solution of 1 (180 mg,
0.29 mmol) in toluene (20 mL) was added an excess of acetic acid (50
μL, 0.88 mmol), and the mixture was heated to 85 °C for 16 h.
Removal of the volatile components in vacuo gave rise to a red residue.
The subsequent addition and removal of toluene and then pentane in
vacuo gave a red powder (149 mg, 86%). 1H NMR (300 MHz, C6D6):
δ 7.55 (2H, dt, J = 8.6, J = 2.0, ArH), 6.85 (2H, s, ArH), 6.60 (2H, d, J
= 8.0, ArH), 2.41 (2H, m, CH), 2.19−2.05 (8H, m, CH and ArCH3),
1.79 (3H, s, COCH3), 1.30 (6H, dd, J = 15.8, J = 7.7, CHCH3), 1.24−
1.10 (12H, m, CHCH3), 1.05 (6H, dd, J = 15.1, J = 7.4, CHCH3),
−23.77 (1H, dt, J = 30.5, J = 11.4, RhH). 13C{1H} NMR (300 MHz,
C6D6): δ 181.4 (s, CO), 162.3 (vt, J = 10.6, CN), 131.5 (s, CAr), 131.4
(s, CAr), 124.8 (s, CAr), 120.6 (vt, J = 3.0, CAr), 117.0 (vt, J = 5.6, CAr),
24.9 (vt, J = 12.3, PCH), 24.7 (vt, J = 11.6, PCH), 23.3 (s, COCH3),
20.5 (s, ArCH3), 18.7 (s, CHCH3), 18.5 (s, CHCH3), 18.3 (s,
CHCH3), 17.6 (s, CHCH3). 31P{1H} NMR (300 MHz, C6D6): δ 52.3
(d, JRhP = 107). Anal. Calcd: C, 56.85; H, 7.50. Found: C, 56.92; H,
7.41.
Synthesis of (PNP)Rh(OTf) (2). To a solution of (PNP)Rh-
(H2CCHtBu) (1; 1000 mg, 1.62 mmol) in toluene (8 mL) was
added AgOTf (422 mg, 1.64 mmol), and a color change from orange
to dark green was observed immediately. Removal of the volatile
components in vacuo gave a residue which could be recrystallized as a
green solid from pentane (824 mg, 75%). Single crystals suitable for an
X-ray diffraction study were grown by cooling a saturated pentane
1
solution. H NMR (300 MHz, C6D6): δ 11.10 (2H, ν1/2 = 900), 3.92
(∼20H, ν1/2 = 470). 19F NMR (282 MHz, C6D6): δ −73.4 (s). Anal.
Calcd: C, 47.62; H, 5.92. Found: C, 47.72; H, 6.12. μeff (Evans NMR
method) = 2.1 μB.
Synthesis of (PNP)Rh(OAc) (3). Method 1. To a solution of 2 (50
mg, 0.073 mmol) in toluene (5 mL) was added KOAc (8 mg, 0.08
mmol), and the mixture was stirred. After 16 h the volatile
components were removed in vacuo, pentane was added, and the
resultant solution was filtered through Celite. Concentration and
cooling (−30 °C) gave rise to a green crystalline material that was
isolated by filtration and washed with cold pentane (3 × 1 mL) (22
mg, 53%).
Synthesis of (PN(H)P)Rh(H)2(OTf) (9). Exposure of a degassed
solution of 2 (22.8 mg, 0.033 mmol) in benzene-d6 (0.8 mL) in a 100
mL Teflon-stoppered flask to 1 bar of H2 gave rise to a light yellow
solution after 24 h. Transfer of the solution to a Young NMR tube
Method 2. To a solution of (PNP)Rh(H)(OAc) (7; 200 mg, 0.35
mmol) in toluene (10 mL) was added TEMPO (55 mg, 0.35 mmol),
and a color change from red to dark green was observed within 15
min. Removal of the volatile components in vacuo gave a green residue
which could be recrystallized as a green crystalline solid from pentane
(116 mg, 58%). Single crystals suitable for an X-ray diffraction study
1
gave the following data. H NMR (300 MHz, C6D6): δ 9.51 (1H, s,
NH), 7.12−7.05 (4H, m, ArH), 6.75 (2H, d, J = 8.2, ArH), 2.87−2.71
(2H, m, H), 2.13−1.96 (8H, m, CH + ArCH3), 1.50 (6H, app quartet
(dvt), J = 8, CHCH3), 1.31 (6H, app quartet (dvt), J = 8, CHCH3),
1.16 (6H, app quartet (dvt), J = 8, CHCH3), 0.62 (6H, app quartet
(dvt), J = 8, CHCH3), −19.62 to −19.90 (2H, m, RhH2). 13C{1H}
NMR (75 MHz, CD2Cl2): δ 148.6 (vt, J = 8.8, CN), 137.3 (s, CAr),
135.1 (vt, J = 14.2, CAr), 134.8 (s, CAr), 131.4 (s, CAr), 125.0 (s, CAr),
27.8 (vt, J = 10.3, CH(CH3)2), 24.5 (vt, J = 11.4, CH(CH3)2), 21.1 (vt,
J = 8.0, CH3), 20.7 (s, CH3), 20.0 (s, CH3), 19.8 (s, CH3), 18.9 (s,
CH3). 31P NMR (121 MHz, C6D6): δ 65.1 (d, J = 114). 19F NMR
(282 MHz, C6D6): δ −77.9 (s). For complex 9, a T1 value of 541 ms
was recorded at 298 K in toluene-d8. As the sample was cooled, the
single hydride signal broadened and split into two resonances (see the
Supporting Information for a figure). At 210 K these were at −16.2
and −23.1 ppm with half-heights of 180 Hz.
1
were grown by cooling a saturated pentane solution. H NMR (300
MHz, C6D6): δ 40.08 (2H, br), 37.43 (2H, br), 10.16−14.72 (6H, m,
br), 5.43 (24H, br). MS (ESI+): m/z 590 (M+). Anal. Calcd: C, 56.95;
H, 7.34. Found: C, 56.93; H, 7.39. μeff (Evans NMR method) = 2.0 μB.
Attempted Synthesis of (PNP)Rh(OAc) (3). To a solution of 1
(30 mg, 0.049 mmol) in toluene (8 mL) was added AgOAc (8 mg,
0.049 mmol), and a color change from orange to brown was observed
over 15 min. Removal of the volatile components in vacuo and
dissolution in C6D6 of the residue allowed the observation by NMR
spectroscopy of predominantly starting material 1, 3, and a complex
exhibiting a resonance by 31P NMR spectroscopy at 66.8 (d, J = 134
Hz).
Synthesis of (PNP)Rh(OSiPh3) (4). To a Young NMR tube
containing a solution of 2 (60 mg, 0.088 mmol) in toluene (10 mL)
was added NaOSiPh3 (25 mg, 0.089 mmol), and the mixture was
sonicated for 16 h. Removal of the volatile components in vacuo gave a
green residue. Addition of CH2Cl2 (8 mL) and filtration through
Celite gave a green solution. Concentrating (∼2 mL), layering with
pentane, and cooling to −30 °C gave rise to a green crystalline
material that was isolated by filtration and washed with cold pentane
Addition of H2 to (PNP)Rh(OAc) (3). To a Young NMR tube
containing a degassed solution of 3 (20 mg, 0.035 mmol) in C6D6 (0.6
mL) was added 1 bar of H2. A color change from green to red was
observed over a period of 15 min. Near-quantitative (95%) formation
of (PNP)Rh(H)(OAc) (7) was noted by 1H and 31P NMR
spectroscopy.
Addition of H2 to (PNP)Rh(Cl) (6). To a Young NMR tube
containing a degassed solution of 6 (16 mg, 0.032 mmol) in C6D6 (0.6
mL) was added 1 bar of H,2 and the solution was heated to 70 °C for
48 h. In addition to 6, two other species were observed, including the
previously characterized37 (PNP)Rh(H)(Cl) (8). The third com-
pound was assigned as (PN(H)P)Rh(H)2(Cl) (11). Additional H2 gas
or further heating did not affect the ratio of these compounds. Select
1
(3 × 1 mL) (50 mg, 70%). H NMR (300 MHz, C6D6): δ 40.65
(overlaps), 34.78 (overlaps), 5.25 (overlaps), 3.13 (overlaps). Anal.
Calcd: C, 65.50; H, 6.87. Found: C, 65.44; H, 6.79. μeff (Evans NMR
method) = 2.0 μB.
Synthesis of (PNP)Rh(OC6H4F) (5). To a toluene solution (5 mL)
of 2 (50 mg, 0.073 mmol) was added NaOC6H4F (12 mg, 0.80 mmol)
1
NMR data for 11 are as follows. H NMR (300 MHz, C6D6): δ 8.31
F
dx.doi.org/10.1021/om300760j | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(br, NH, overlapping with other resonances), −16.68 (1H, br, Rh−H),
−18.33 (1H, br, Rh−H). 31P NMR (121 MHz, C6D6): δ 67.2 (d, JRhP
= 114).
Addition of H2 to (PNP)Rh(OC6H4F) (5). To a Young NMR tube
containing a degassed solution of 5 (28 mg, 0.44 mmol) in C6D6 (0.6
mL) was added 1 bar of H2 gas. After 16 h at 80 °C additional H2 gas
was added and the reaction mixture was heated for a further 16 h.
Complete conversion to HOC6H4F and the previously reported40
(PNP)Rh(H2) (10) was observed by 1H, 19F, and 31P NMR
spectroscopy.
restraints, R1 = 0.0588 (I > 2σ) and wR2 = 0.1461 (all data), GOF =
0.916, residual electron density 0.913/−0.959 e Å−3.
Crystal structure data for 5: C32H44FNOP2Rh, 642.55 g/mol,
orthorhombic, space group Pna21; a = 26.147(15) Å, b = 14.062(8) Å,
c = 8.548(5) Å, α = β = γ = 90°, V = 3143(3) Å3; Z = 4, ρcalcd =1.358 g
cm−3; crystal dimensions 0.18 × 0.09 × 0.08 mm; diffractometer
Bruker APEXII CCD; Mo Kα radiation, 110(2) K, 2θmax = 54.96°;
32371 reflections, 7102 independent (Rint = 0.0616), direct methods;
absorption coefficient μ = 0.676 mm−1, absorption correction
2
multiscan (SADABS); refinement (against Fo ) with SHELXTL
V6.1, 353 parameters, 1 restraints, R1 = 0.0332 (I > 2σ) and wR2 =
0.0693 (all data), GOF = 1.020, residual electron density 0.503/−
0.417 e Å−3.
Observation of (PNP)Rh(HD) (10-d) and T1,min for (PNP)Rh-
(H2) (10). To a C6D6 solution (1 mL) containing ca. 5 mg of
(PNP)Rh(OTf) (2) was added an excess of CaH2 (ca. 5 mg) followed
by slow careful addition of D2O (ca. 0.1 mL). After 24 h the solution
Crystal structure data for 6: C26H40ClNP2Rh, 566.91 g/mol,
monoclinic, space group P2/c; a = 11.506(4) Å, b = 9.706(4) Å, c =
18.323(5) Å, α = γ = 90°, β = 127.603(14)°, V = 1621.2(10) Å3; Z = 2,
ρcalcd = 1.161 g cm−3; crystal dimensions 0.20 × 0.12 × 0.09 mm;
diffractometer Bruker APEXII CCD; Mo Kα radiation, 150(2) K,
2θmax = 55.56°; 18473 reflections, 3813 independent (Rint = 0.0700),
direct methods; absorption coefficient μ = 0.719 mm−1, absorption
1
was observed to be yellow and by H and 31P NMR spectroscopy a
mixture of (PNP)Rh(H)(D) (major product) and (PNP)RhH2
(minor product) was apparent. Collection of a 1H{31P} NMR
spectrum allowed the JHD coupling to be measured from the simplified
splitting pattern. 1H{31P} NMR (500 MHz, C6D6): δ −13.76 (m, JRhH
= 20.0 Hz, JHD = 18.3 Hz, Rh(H)(D)). For (PNP)RhH2 (10) a T1,min
value of approximately 39 ms was found at −48 °C (toluene-d8).
X-ray Crystallography Details. In each case of 2−6, multifaceted
crystals of suitable size and quality were selected from representative
samples of the same habit using an optical microscope and mounted
onto a nylon loop. Low-temperature X-ray data were obtained on a
Bruker APEXII CCD-based diffractometer (Mo sealed X-ray tube,
λ(Mo Kα) = 0.71073 Å). All diffractometer manipulations, including
data collection, integration, and scaling, were carried out using the
Bruker APEXII software.76 Absorption corrections were applied using
SADABS.77 Space groups were determined on the basis of systematic
absences and intensity statistics, and structures were solved by direct
methods and refined by full-matrix least squares on F2. The structures
were solved in the space groups noted in each case using XS78
(incorporated in SHELXTL), and PLATON79 was used to check for
missed symmetry. Except where noted, all non-hydrogen atoms were
refined with anisotropic thermal parameters.
2
correction multiscan (SADABS); refinement (against Fo ) with
SHELXTL V6.1, 147 parameters, 0 restraints, R1 = 0.0316 (I > 2σ)
and wR2 = 0.0805 (all data), GOF = 1.064, residual electron density
0.454/−0.415 e Å−3. The “squeeze” protocol incorporated in
PLATON was used to account for the disordered benzene solvent
molecule found in the crystal lattice (verified by 1H NMR) that could
not be satisfactorily modeled.
ASSOCIATED CONTENT
* Supporting Information
CIF files giving crystallographic data, DFT coordinate files, and
■
S
1
a figure showing variable-temperature H NMR spectra of 9.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail for O.V.O.: ozerov@chem.tamu.edu.
■
Crystal structure data for 2: C27H40F3NO3P2RhS, 680.52 g/mol,
monoclinic, space group P21/c; a = 17.845(5) Å, b = 10.692(3) Å, c =
18.267(6) Å, α = γ = 90°, β = 118.197(3)°, V = 3071.7(16) Å3; Z = 4,
ρcalcd =1.472 g cm−3; crystal dimensions 0.30 × 0.15 × 0.14 mm;
diffractometer Bruker APEXII CCD; Mo Kα radiation, 110(2) K,
2θmax = 55.18°; 31780 reflections, 7092 independent (Rint = 0.0313),
direct methods; absorption coefficient μ = 0.775 mm−1, absorption
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
2
■
correction multiscan (SADABS); refinement (against Fo ) with
We are thankful for the support of this work by the U.S.
National Science Foundation through the “Powering the
Planet” Center for Chemical Innovation grant (CHE-
0802907), the Welch Foundation (Grant A-1717), and the
Dreyfus Foundation (Camille Dreyfus Teacher-Scholar Award
to O.V.O.). J.R.W. expresses gratitude to the Nuclear Forensics
Education Award Program for support. We thank Dr. Sylvain
Gatard for a preliminary synthesis of compound 7 and Prof.
Michael B. Hall for valuable discussions pertaining to the DFT
studies.
SHELXTL V6.1, 417 parameters, 0 restraints, R1 = 0.0236 (I > 2σ)
and wR2 = 0.0623 (all data), GOF = 1.036, residual electron density
0.478/−0.461 e Å−3. The triflate moiety was found to be disordered
over two positions with 65%:35% occupancy and was modeled and
refined accordingly.
Crystal structure data for 3: C28H43NO2P2Rh, 590.50 g/mol,
orthorhombic, space group P212121; a = 10.394(7) Å, b = 15.819(11)
Å, c = 17.659(12) Å, α = β = γ = 90°, V = 2904(3) Å3; Z = 4, ρcalcd
=1.351 g cm−3; crystal dimensions 0.21 × 0.17 × 0.06 mm;
diffractometer Bruker APEXII CCD; Mo Kα radiation, 163(2) K,
2θmax = 55.12°; 32228 reflections, 6663 independent (Rint = 0.0833),
direct methods; absorption coefficient μ = 0.722 mm−1), absorption
2
REFERENCES
correction multiscan (SADABS); refinement (against Fo ) with
■
SHELXTL V6.1, 318 parameters, 0 restraints, R1 = 0.0345 (I > 2σ)
and wR2 = 0.0795 (all data), GOF = 1.025, residual electron density
0.408/−0.596 e Å−3.
(1) (a) Takaoka, A.; Moret, M.-E.; Peters, J. C. J. Am. Chem. Soc.
2012, 134, 6695. (b) Takaoka, A.; Gerber, L. C. H.; Peters, J. C.
Angew. Chem., Int. Ed. 2010, 49, 4088.
Crystal structure data for 4: C44H55NOP2RhSi·C7H8, 898.96 g/
(2) Chan, Y. W.; Chan, K. S. J. Am. Chem. Soc. 2010, 132, 6920.
(3) Cui, X.; Xu, X.; Lu, H.; Zhu, S.; Wojtas, L.; Zhang, X. P. J. Am.
Chem. Soc. 2011, 133, 3304.
(4) Pintauer, T.; Matyjaszewski, K. Chem. Soc. Rev. 2008, 37, 1087.
(5) de Bruin, B.; Budzelaar, P. H. M.; Gal, A. W. Angew. Chem., Int.
Ed. 2004, 43, 4142.
(6) Mayer, J. M. Acc. Chem. Res. 2011, 44, 36.
(7) DeWitt, D. G. Coord. Chem. Rev. 1996, 147, 209.
(8) Pandey, K. K. Coord. Chem. Rev. 1992, 121, 1.
mol, triclinic, space group P1; a = 12.63(3) Å, b = 13.75(4) Å, c =
̅
15.86(7) Å, α = 101.55(4)°, β = 96.30(5)°, γ = 115.73(3)°, V =
2370(14) Å3; Z = 2, ρcalcd = 1.260 g cm−3; crystal dimensions 0.19 ×
0.11 × 0.06 mm; diffractometer Bruker APEXII CCD; Mo Kα
radiation, 150(2) K, 2θmax = 55.00°; 27126 reflections, 10767
independent (Rint = 0.0918), direct methods; absorption coefficient
μ = 0.489 mm−1, absorption correction multiscan (SADABS);
2
refinement (against Fo ) with SHELXTL V6.1, 525 parameters, 0
G
dx.doi.org/10.1021/om300760j | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(9) Hansen, J.; Davies, H. M. L. Coord. Chem. Rev. 2008, 252, 545.
(10) Hay-Motherwell, R. S.; Koschmieder, S. U.; Wilkinson, G.;
Hussain-Bates, B.; Hursthouse, M. B. Dalton Trans. 1991, 2821.
(11) Masters, C.; Shaw, B. L. J. Chem. Soc. A 1971, 3679.
(12) Takaoka, A.; Peters, J. C. Inorg. Chem. 2012, 51, 16.
(13) Mizutani, T.; Uesaka, T.; Ogoshi, H. Organometallics 1995, 14,
341.
(14) Cui, W.; Wayland, B. B. J. Am. Chem. Soc. 2004, 126, 8266.
(15) Li, S.; Cui, W.; Wayland, B. B. Chem. Commun. 2007, 4024.
(16) Chan, K. S.; Li, X. Z.; Lee, S. Y. Organometallics 2010, 29, 2850.
(17) Sherry, A. E.; Wayland, B. B. J. Am. Chem. Soc. 1990, 112, 1259.
(18) Wayland, B. B.; Ba, S.; Sherry, A. E. J. Am. Chem. Soc. 1991, 113,
5305.
(45) Puri, M.; Gatard, S.; Smith, D. A.; Ozerov, O. V. Organometallics
2011, 30, 2472.
(46) Zhu, Y.; Smith, D. A.; Herbert, D. E.; Gatard, S.; Ozerov, O. V.
Chem. Commun. 2012, 48, 218.
(47) Fout, A. R.; Basuli, F.; Fan, H.; Tomaszewski, J.; Huffman, J. C.;
Baik, M.-H.; Mindiola, D. J. Angew. Chem., Int. Ed. 2006, 45, 3291.
(48) (a) Chan, K. S.; Leung, Y.-B. Inorg. Chem. 1994, 33, 3187.
(b) Feng, M.; Chan, K. S. Organometallics 2002, 21, 2743. (c) Lee, S.
Y.; Cheung, C. W.; Hsu, I.-J.; Chan, K. S. Inorg. Chem. 2010, 49, 9636.
(49) Bakac, A. Dalton Trans. 2006, 1589.
(50) Zhang, X.-X.; Wayland, B. B. J. Am. Chem. Soc. 1994, 116, 7897.
(51) Mahoney, L. R.; Mendenhal, G. D.; Ingold, K. U. J. Am. Chem.
Soc. 1973, 95, 8610.
(19) Hetterscheid, D. G. H.; Klop, M.; Kichen, R. J. N. A. M.; Smits,
J. M. M.; Reijerse, E. J.; de Bruin, B. Chem. Eur. J. 2007, 13, 3386.
(20) de Bruin, B.; Peters, T. P. J.; Thewissen, S.; Blok, A. N. J.;
Wilting, J. B. M.; de Gelder, R.; Smits, J. M. M.; Gal, A. W. Angew.
Chem., Int. Ed. 2002, 41, 2135.
(52) Kaim, W. Inorg. Chem. 2011, 50, 9752. van der Vlugt, J. I.; Reek,
J. N. Angew. Chem., Int. Ed. 2009, 48, 8832.
(53) Adhikari, D.; Mossin, S.; Basuli, F.; Huffman, J. C.; Szilagyi, R.
K.; Meyer, K.; Mindiola, D. J. Inorg. Chem. 2008, 47, 3676.
(54) Dunbar, K. R.; Haefner, S. C.; Pence, L. E. J. Am. Chem. Soc.
1989, 111, 5504.
(21) The Chemistry of Pincer Compounds; Morales-Morales, D.,
Jensen, C., Eds.; Elsevier: Amsterdam, 2007.
(22) Krumper, J. R.; Gerisch, M.; Suh, J. M.; Bergman, R. G.; Tilley,
T. D. J. Org. Chem. 2003, 68, 9705.
(55) Dixon, F. M.; Farrell, J. R.; Doan, P. E.; Williamson, A.;
Weinberger, D. A.; Mirkin, C. A.; Stern, C.; Incarvito, C. D.; Liable-
Sands, L. M.; Zakharov, L. N.; Rheingold, A. L. Organometallics 2002,
21, 3091.
(23) Gerisch, M.; Krumper, J. R.; Bergman, R. G.; Tilley, T. D. J. Am.
Chem. Soc. 2001, 123, 5818.
(56) Fan, L.; Yang, L.; Guo, C.; Foxman, B. M.; Ozerov, O. V.
Organometallics 2004, 23, 4778. The FPNP ligand is only different by
the F atoms in place of the Me groups para to the N atom.
(57) POV-Ray−The Persistence of Vision Raytracer, available at http://
www.povray.org/.
(24) Feller, M.; Ben-Ari, E.; Gupta, T.; Shimon, L. J. W.; Leitus, G.;
Diskin-Posner, Y.; Weiner, L.; Milstein, D. Inorg. Chem. 2007, 46,
10479.
(25) (a) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics 2003,
22, 3007. (b) Winter, A. M.; Eichele, K.; Mack, H.-G.; Potuznik, S.;
Mayer, H. A.; Kaska, W. C. J. Organomet. Chem. 2003, 682, 149.
(26) Fan, L.; Foxman, B. M.; Ozerov, O. V. Organometallics 2004, 23,
326.
(27) For reviews on the chemistry of diarylamido-based PNP
complexes, see: (a) Liang, L.-C. Coord. Chem. Rev. 2006, 250, 1152.
(b) Ozerov, O. V. In The Chemistry of Pincer Compounds; Morales-
Morales, D., Jensen, C., Eds.; Elsevier: Amsterdam, 2007; pp 287−309.
(c) Mindiola, D. J.; Bailey, B. C.; Basuli, F. Eur. J. Inorg. Chem. 2006,
3135.
(28) Fafard, C. M.; Adhikari, D.; Foxman, B. M.; Mindiola, D. J.;
Ozerov, O. V. J. Am. Chem. Soc. 2007, 129, 10318.
(29) Gerber, L. C. H.; Watson, L. A.; Parkin, S.; Weng, W.; Foxman,
B. M.; Ozerov, O. V. Organometallics 2007, 26, 4866.
(30) Fafard, C. M.; Chen, C.-H.; Foxman, B. M.; Ozerov, O. V.
Chem. Commun. 2007, 4465.
(58) ORTEP plots were created using Ortep-3 for Windows: Farugia,
L. J. Appl. Crystallogr. 1997, 30, 565.
(59) Wassenaar, J.; de Bruin, B.; Siegler, M. A.; Spek, A. L.; Reek, J.
N. H.; van der Vlugt, J. I. Chem. Commun. 2010, 46, 1232.
(60) Gregor, L. C.; Chen, C.-H.; Fafard, C. M.; Fan, L.; Guo, C.;
Foxman, B. M.; Gusev, D. G.; Ozerov, O. V. Dalton Trans. 2010, 39,
3195.
(61) Zhu, Y.; Chen, C.-H.; Fafard, C. M.; Foxman, B.; Ozerov, O. V.
Inorg. Chem. 2011, 50, 7980.
(62) (a) Chaplin, A. B.; Weller, A. S. Organometallics 2011, 30, 4466.
(b) Findlater, M.; Schultz, K. M.; Bernskoetter, W. H.; Cartwright-
Sykes, A.; Heinekey, D. M.; Brookhart, M. Inorg. Chem. 2012, 51,
4672.
(63) (a) Kaska, W. C.; Nemeh, S.; Shirazi, A.; Potuznik, S.
Organometallics 1988, 7, 13. (b) Xu, W.; Rosini, G. P.; Gupta, M.;
Jensen, C. M.; Kaska, W. C.; Krogh-Jespersen, K.; Goldman, A. S. J.
Chem. Soc., Chem. Commun. 1997, 2273.
(31) Bacciu, D.; Chen, C.-H.; Surawatanawong, P.; Foxman, B. M.;
(64) (a) Grundemann, S.; Limbach, H. H.; Buntkowsky, G.; Sabo-
Etienne, S.; Chaudret, B. J. Chem. Phys. A 1999, 103, 4752.
Ozerov, O. V. Inorg. Chem. 2010, 49, 5328.
̈
(32) Whited, M. T.; Grubbs, R. H. Acc. Chem. Res. 2009, 42, 1607.
(33) Cantat, T.; Graves, C. R.; Scott, B. L.; Kiplinger, J. L. Angew.
Chem., Int. Ed. 2009, 48, 3681.
(b) Gelabert, R.; Moreno, M.; Lluch, J. M.; Lledos
́
, A.; Pons, V.;
Heinekey, D. M. J. Am. Chem. Soc. 2004, 126, 8813.
(34) Cavaliere, V. N.; Crestani, M. G.; Pinter, B.; Pink, M.; Chen, C.-
H.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem. Soc. 2011, 133, 10700.
(35) Melnick, J. G.; Radosevich, A. T.; Villagran, D.; Nocera, D. G.
Chem. Commun. 2010, 46, 79.
(65) Kubas, G. J. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 6901.
(66) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc.
1987, 109, 2803.
(67) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J. Chem.
Soc. A 1966, 1711.
(36) Calimano, E.; Tilley, T. D. J. Am. Chem. Soc. 2009, 131, 11161.
(37) Ozerov, O. V.; Guo, C.; Papkov, V. A.; Foxman, B. M. J. Am.
Chem. Soc. 2004, 126, 4792.
(38) Weng, W.; Guo, C.; Moura, C. P.; Yang, L.; Foxman, B. M.;
Ozerov, O. V. Organometallics 2005, 24, 3487.
(68) Heaton, B. T.; Iggo, J. A.; Jacob, C.; Nadarajah, J.; Fontaine, M.
A.; Messere, R.; Noels, A. F. Dalton Trans. 1994, 2875.
(69) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J.
Phys. Chem. 1994, 98, 11623−11627.
(70) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652.
(71) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789.
(72) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
(39) Gatard, S.; C
Ozerov, O. V. J. Am. Chem. Soc. 2006, 128, 2808.
(40) Weng, W.; Guo, C.; Celenligil-Cetin, R.; Foxman, B. M.;
Ozerov, O. V. Chem. Commun. 2006, 197.
̧elenligil-Çetin, R.; Guo, C.; Foxman, B. M.;
̧
̧
(41) Gatard, S.; Guo, C.; Foxman, B. M.; Ozerov, O. V.
Organometallics 2007, 26, 6066.
(42) Gatard, S.; Chen, C.-H.; Foxman, B. M.; Ozerov, O. V.
Organometallics 2008, 27, 6257.
(43) Smith, D. A.; Ozerov, O. V. Chem. Commun. 2011, 47, 10779.
(44) Surawatanawong, P.; Ozerov, O. V. Organometallics 2011, 30,
2972.
H
dx.doi.org/10.1021/om300760j | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; , and Fox, D. J. Gaussian
09, Revision B.01; Gaussian, Inc., Wallingford, CT, 2009.
(73) (a) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257−2261. (b) McLean, A. D.; Chandler, G. S. J. Chem. Phys.
1980, 72, 5639−5648. (c) Frisch, M. J.; Pople, J. A.; Binkley, J. S. J.
Chem. Phys. 1984, 80, 3265−3269.
(74) 6-31(d′) differs from 6-31(d) and 6-31G* by the addition of a
single diffuse function which is optimized specifically for each of the
second-row (B−F) elements.
(75) Kuechle, W.; Dolg, M.; Stoll, H.; Preuss, H. J. Chem. Phys. 1994,
100, 7535−7542.
(76) APEX2, Version 2 User Manual, M86-E01078; Bruker Analytical
X-Ray Systems: Madison, WI, 2006.
(77) Sheldrick, G. M. SADABS, Program for Absorption Correction for
Data from Area Detector Frames; University of Gottingen, Gottingen,
̈
̈
Germany, 2008.
(78) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, A64, 112.
(79) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University, Utrecht, The Netherlands, 1998.
I
dx.doi.org/10.1021/om300760j | Organometallics XXXX, XXX, XXX−XXX