Tunable hemilabile ligands for adaptive transition metal complexes

Article abstract of DOI:10.1021/om100804k

A new family of monoanionic hemilabile ligands L1H-L3H with a PNN donor set has been developed, based on Pd-catalyzed C-N bond formation and straightforward phosphorylation. For these structurally related compounds with a hybrid set of donor atoms, the coordination chemistry with both Rh and Ir has been studied. The anticipated hemilabile character of the dimethylamino group was assessed by NMR and IR competition experiments, using isopropyl isocyanide as exogenous substrate. Supporting DFT calculations were used to quantify the electronic differences between the various members of the ligand family. In effect, we have constructed a modular ligand class that exhibits tunable hemilability.

Full text of DOI:10.1021/om100804k

Organometallics 2011, 30, 499–510 499
DOI: 10.1021/om100804k
Tunable Hemilabile Ligands for Adaptive Transition Metal Complexes
Ronald Lindner,† Bart van den Bosch,† Martin Lutz,‡ Joost N. H. Reek,† and
Jarl Ivar van der Vlugt*,†
†van ’t Hoff Institute for Molecular Sciences, Supramolecular and Homogeneous Catalysis Group, University
of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands, and ‡Department for Crystal and
Structural Chemistry, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands
Received August 18, 2010
A new family of monoanionic hemilabile ligands L1H-L3H with a PNN donor set has been
developed, based on Pd-catalyzed C-N bond formation and straightforward phosphorylation. For
these structurally related compounds with a hybrid set of donor atoms, the coordination chemistry
with both Rh and Ir has been studied. The anticipated hemilabile character of the dimethylamino
group was assessed by NMR and IR competition experiments, using isopropyl isocyanide as
exogenous substrate. Supporting DFT calculations were used to quantify the electronic differences
between the various members of the ligand family. In effect, we have constructed a modular ligand
class that exhibits tunable hemilability.
Introduction
Hemilabile coordination is a frequently observed design
principle in natural systems, wherein the coordination geo-
metry around and hence the activity displayed by the active
metal center are manipulated by controlled access to an open
coordination site through a reversible but weak bonding
interaction of specific donor groups.1-3 This in turn allows
for selective transformation and efficient catalytic turnover.
Figure 1. Generalized description of adaptive coordination
behavior of a hemilabile ligand (left) and schematic representa-
In contrast with the elegant use of these principles in Nature,
man-made ligand analogues present in the first coordination
tion of a tridentate pincer-ligand scaffold with different types
sphere of transition metals are generally not poised to display
of donor groups.
flexible coordination during productive turnover. Typically,
ligands employed in “traditional” homogeneous catalysis
lead to stable, isolable, and well-defined metal complexes.
However, it is precisely this lack of lability that can impede
certain activation and/or propagation pathways, and it might
therefore prove beneficial to have systems (ligand-metal
combinations) that can structurally adapt to changes at inter-
mediate stages of a catalytic cycle and/or accommodate differ-
ent geometric or electronic requirements (Figure 1).
*Corresponding author. E-mail: j.i.vandervlugt@uva.nl.
The term “hemilabile ligand” was first introduced in
synthetic chemistry in 1979 by Jeffrey and Rauchfuss,4 and
several reviews have highlighted the versatile coordination
chemistry with various types of scaffolds.5,6 However, the
targeted and tunable (catalytic) application of ligands that
adapt to exogenous ligands or alternative external stimuli
remains relatively unexplored.7,8 Recently, Milstein et al.
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r
2011 American Chemical Society
Published on Web 01/12/2011
pubs.acs.org/Organometallics

500 Organometallics, Vol. 30, No. 3, 2011
Scheme 1. Examples of Non-C2-symmetric, Potentially Hemilabile PNN Ligands
Lindner et al.
reported elegant applications of Ru complexes with hybrid,
formally neutral PNN0 pincer system A,9 while our own
group reported chemistry with Cu, Ni, and Pd.10 Besides
the implied hemilabile character of this ligand system under
catalytic conditions, which is suggested to be beneficial for
the reaction rate and chemoselectivity, the lutidine core also
enables a formal charge-switch from neutral to monoanionic
by dearomatization of the heterocyclic framework. Chelat-
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to display strong tridentate coordination to (late) transition
metals. Within this class of rigid ligands, mixed donor sets
ECE0 have been studied to some extent, although the sym-
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their synthetic simplicity. Particularly noteworthy are con-
Lately, especially pincer systems with a non-carbon pivot
atom have drawn significant attention, and various classes of
monoanionic tridentate scaffolds are now available that
have revitalized traditional pincer chemistry with new ap-
proaches, methodologies, and modes of reactivity.14-19
Notably, very few of these examples bearing a non-
carbon pivot deal with non-C2-symmetric frameworks
(Scheme 1).20,21 Peters and co-workers recently described Pt
complexes with a potentially tridentate asymmetric, all-nitro-
gen donor ligand B, showing that square-planar coordination
of the Pt center prevailed, thereby leaving a dimethylamine
side-group uncoordinated and rotated out of the Pt(NN)
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(22) Coordination of the dimethylamino group in ligand B was not
observed to date. B should therefore as yet not be regarded as a
potentially hemilabile ligand.

Article
Organometallics, Vol. 30, No. 3, 2011 501
Scheme 2. Synthetic Methodologies for the Preparation of
Compounds L1H and L2Ha
Figure 2. Concept of novel PNN-based tunable hemilabile
ligands.
plane.16a,22 Furthermore, mixed (or hybrid) donor sets have
hardly been investigated to date with EXE0 ligands (X ¼ C).
Gusev prepared ligand C and described its (Noyori-type)
cooperative behavior in Ir-catalyzed transfer hydrogena-
tion.23 Surprisingly, to the best of our knowledge, no
(pincer) ligand classes exist in which the hemilabile character
is selectively changed and tuned to alter the coordination
behavior selectively from tri- to bidentate, a tool that is
considered very relevant from a conceptual point of view.
Such control over the ligand denticity is crucial to fully
understand the impact of this property on catalytic reactions.
Furthermore, novel modes of adaptive complexes could also
lead to new or tunable reactivity.
We therefore sought a modular approach to a family of
hemilabile ligands, amenable to both steric and electronic
modification and tunable variation in the side-group func-
tionalities without impeding the intrinsic coordinating prop-
erties of the core atom.24 With these conceptual prerequisites
in mind, we set out to design a family of PNN ligands with a
variable backbone (Figure 2). We herein report on the
synthesis of these ligands with tunable hemilabile character
and general trends in their coordination chemistry to Rh and
Ir. Notably, we also determined the degree of hemilability by
means of competition experiments between various closely
related members of this class, combined with various DFT
calculations, to establish the first selection rules and hemil-
ability scale for these novel systems.
a [Pd] is formed in situ by reaction of equimolar Pd2(dba)3 and dppf.
Scheme 3. Synthetic Methodologies for the Preparation of
Compound L3H
ligands, for which these selectivity issues have not been
observed to this extent.15 However, targeted double lithiation
and subsequent phosphorylation provided the phosphine-
phosphinamine species in good yield.25 This was directly
converted by selective hydrolysis of the P-N bond, using
concentrated aqueous HCl in MeOH, to obtain the desired
PNN0 ligand L1H (Scheme 2).
Notably, the archetypical, symmetric pincer ligands, when
coordinated to a given metal center, give rise to tridentate
coordination with two five-membered chelate rings (a 5,50-
system). To probe the effect of different geometries on the
potentially tunable hemilabile character of the overall ligand
structure, we also prepared a backbone that leads to a 5,60-
complex upon coordination. Such asymmetry in coordina-
tion geometry, by means of differing chelate ring size, is
rarely explored to probe or tune the labilization of a parti-
cular donor functionality.26 Therefore, we devised a syn-
thetic approach to vary the amine side arm, which led to
ligand L2H. We sought extension of our dedicated, novel
hybrid ligand family by preparing the semialiphatic analogue
L3H of the diarylamide backbones (Scheme 3).27 Liang
previously reported the preparation of this species after
Results and Discussion
Ligand Synthesis. To introduce an inherent linkage asym-
metry in our target ligand framework, we devised a three-step
synthetic route, starting from commercially available precur-
sors. To prepare the diarylamine backbones, we opted for
Buchwald-Hartwig-type Pd-catalyzed amination chemistry.
Coupling the appropriate aryl iodide reagent with the desired
ortho-substituted aniline in the presence of Pd2(dba)3/dppf as
catalyst yielded the corresponding disubstituted amines in
good yields. However, introduction of the phosphorus frag-
ment proved to be less straightforward then initially assumed.
Phosphorylation of ortho-bromodiarylamine using 2
equiv of n-BuLi and 1 equiv of ClPPh2 and subsequent
aqueous workup unexpectedly led to mixtures of mono-
and diphosphorus compounds. Hence, it appears that the
character of the secondary amine is slightly different from the
diarylamine precursors used to prepare the known PNP
(25) Some bidentate phosphine-phosphinamines have been reported
in the literature; see: (a) Aucott, S. M.; Slawin, A. M. Z.; Woollins, J. D.
J. Organomet. Chem. 1999, 582, 83. (b) Xavier, K. O.; Smolensky, E.;
Kapon, M.; Aucott, S. M.; Woollins, J. D.; Eisen, M. S. Eur. J. Inorg. Chem.
2004, 4795, and references therein. (c) For related bidentate aminophosphine
ligands, see: Zijp, E. J.; van der Vlugt, J. I.; Tooke, D. M.; Spek, A. L.; Vogt.,
D. Dalton Trans. 2005, 512.
(26) Tridentate0 diphosphinoazines, featuring a PNP donor set,
ꢁ
coordinate in a 5,6 -chelate fashion: (a) Posta, M.; Cermak, J.; Vojtı
ꢁ
ꢀ
ꢁ
sek,
´
ꢀ
ꢁ ꢀ
´
P.; Sykora, J.; Cısarova, I. Inorg. Chim. Acta 2009, 362, 208, and
references therein. Also a PNN ligand based on lutidine has been reported:
(b) Poverenov, E.; Leitus, G.; Shimon, L. J .W.; Milstein, D. Organometallics
2005, 24, 5937. (c) Schaub, T.; Radius, U.; Diskin-Posner, Y.; Leitus, G.;
Shimon, L. J. W.; Milstein, D. Organometallics 2008, 27, 1892. For related
5,60-PCN ligands see: (d) Poverenov, E.; Gandelman, M.; Shimon, L. J .W.;
Rozenberg, H.; Ben-David, Y.; Milstein, D. Chem.;Eur. J. 2004, 10, 4673.
(e) Poverenov, E.; Gandelman, M.; Shimon, L. J .W.; Rozenberg, H.;
Ben-David, Y.; Milstein, D. Organometallics 2005, 24, 1082.
(23) Choualeb, A.; Lough, A. J.; Gusev, D. G. Organometallics 2007,
26, 5224.
(24) Alternative approaches to introduce “masked” vacant coordina-
tion sites: (a) Allgeier, A. M.; Mirkin, C. A. Angew. Chem., Int. Ed. 1998,
37, 894. (b) Gianneschi, N. C.; Masar, M. S., III; Mirkin, C. A. Acc. Chem.
Res. 2005, 38, 825.
(27) In principle, the same general synthetic protocol could also be
used to install other functionalities besides dialkylamines or allow for
different substitution patterns.

502 Organometallics, Vol. 30, No. 3, 2011
Lindner et al.
Scheme 4. Preparation of Metal Complexes X1-X5
Figure 3. ORTEP plot (50% probability thermal ellipsoids) of
complex X4, [Ir(κ3-P,N,N0-L3)(COE)]. Selected bond lengths
(A) and angles (deg): Ir-P 2.2010(4); Ir-N1 2.002(1); Ir-N2
2.212(1); Ir-C1 2.109(2); Ir-C2 2.156(2); P-Ir-N1 82.25(4);
N1-Ir-N2 79.13(6), P-Ir-N2 161.34(4); P-Ir-C1 105.58(5);
P-Ir-C2 98.66(5); N1-Ir-C1 154.05(7); N1-Ir-C2 166.15(6);
N1-Ir-{C1-C2}mid 172.83(6); N2-Ir-{C1-C2}mid 95.85(5).
Torsion angles (deg): Ir-N1-C9-C10 -18.5(2); Ir-N1-C11-
reaction of intermediate A with KPPh2 in refluxing dioxane
for seven days.28 With our improved microwave-assisted
methodology, this reaction only took six hours to reach full
conversion to obtain L3H. Overall yields for the synthesis of
compounds L1H-L3H, which feature subtle but significant
backbone modifications and represent the first members of a
new class of hemilabile ligands, were in the range 30-70%.
Rh(I) and Ir(I) Alkene Complexes of PNN Pincer Ligands.
In order to get a first approximation of the complexation
characteristics of these new ligands, we investigated their
coordination with RhI and IrI. However, using common
precursors of group 8 metals, e.g., chloro-bridged RhI and IrI
dimer species, we failed to obtain PNN pincer-based com-
plexes. More successful was the use of hydroxy- or methoxy-
bridged RhI and IrI dimers, wherein the internal base is
sufficiently reactive to ensure formation of the desired
[M(PNN0)(COE)] complexes in high yields. For example,
reaction of 1 equiv of the readily accessible dimer [{Rh(μ-OH)-
(COE)2}2]29 or [{Ir(μ-OMe)(COD)}2]30 with 2 equiv of the
appropriate ligand in diethyl ether at -80 °C led to smooth
formation of the desired well-defined MI(cycloalkene) species
C
12 15.1(2).
in moderate to good yields (Scheme 4). Strikingly, all com-
pounds X1-X5 were found to be very air- and moisture-
sensitive, the Ir derivatives even more so than the Rh analogues.
The 31P chemical shifts and Rh-P coupling constants are in the
expected ranges.31
The coordination mode of the hemilabile side arm of the
pincer ligand was determined by the chemical (in)equivalency of
the olefinic protons. When the meridinal κ3-coordination mode
of the ligand prevails, the complexes exhibit mirror symmetry in
the coordination plane of the central metal atom, resulting in
one signal for the olefinic protons of the COE fragment in
X1-X4. For species X5, the olefinic protons were detected as
two broad signals at room temperature. To determine the
barrier for rotation around the Namido-Calkyl bond in complex
X5, we performed variable-temperature NMR experiments.
According to the coalescence temperature (approximately
10 °C, with a ν0 value of 60.5 Hz), the corresponding energy
barrier for rotation is calculated to be around 58 kJ/mol.32,33
X-ray Crystallographic Analysis. The molecular structure
for species X4, depicted in Figure 3, could be determined via
X-ray crystallography. Relevant bond lengths for the com-
plex [Ir(κ3-P,N,N0-L3)(COE)] include Ir-N1 (2.002(1) A)
and Ir-N2 (2.112(1) A). The small difference between the
Ir-amide and Ir-amine bond is in accord with previous
reports by Peters and Hu on related complexes.16 The
(28) Lee, W.-Y.; Liang, L.-C. Dalton Trans. 2005, 1952.
(29) (a) Werner, H.; Bosch, M.; Schneider, M. E.; Hahn, C.; Kukla,
€
€
F.; Manger, M.; Windmuller, B.; Weberndorfer, B.; Laubender, M. J.
Chem. Soc., Dalton Trans. 1998, 3549. (b) Vicente, J.; Gil-Rubio, J.;
Bautista, D.; Sironi, A.; Masciocchi, N. Inorg. Chem. 2004, 43, 5665.
(30) Wanninger-Weiss, C.; Wagenknecht, H.-A. Eur. J. Org. Chem.
2008, 64.
(31) The 31P NMR chemical shifts are in the range δ 56.5 (X1) to 63.0
ppm (X2) for Rh and δ 15.2 (X4) to 28.6 ppm (X5) for Ir. For the Rh
complexes, characteristic coupling constants JRhP in the range of ∼200
Hz were observed. Recent work from our laboratories involving other
Rh-phosphine complexes: (a) Chikkali, S. H.; Bellini, R.; Berthon-
Gelloz, G.; van der Vlugt, J. I.; de Bruin, B.; Reek, J. N. H. Chem.
Commun. 2010, 49, 1244. (b) 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. (c) Wassenaar, J.; Siegler, M. A.; Spek, A. L.; de Bruin, B.; Reek,
J. N. H.; van der Vlugt, J. I. Inorg. Chem. 2010, 49, 6495.
(32) The signal of the methylene protons NCH2CH2NEt2 close to the
amido group was used to determine the coalescence temperature.
(33) Johnson, E. S. In Advances in Magnetic Resonance, Vol. 1;
Waugh, J. S., Ed.; Academic Press: New York, 1956; pp 64-68.
Preliminary NMR investigations with ligand L1H or L2H in combination
with [{M(m-OMe)(COD)}2] (M = Rh or Ir) also indicate the presence of four
inequivalent olefinic protons in the 1H NMR spectra, indicating κ2-P,N-
coordination with a dangling dimethylamino arm.

Article
Organometallics, Vol. 30, No. 3, 2011 503
Scheme 5. Hemilabile Behavior of the Diaryl PNN Backbone in
Complex [Rh(L1)(COE)] with CNiPr
Scheme 6. Formation of Square-Planar MI Species X00 Is
Favored over Five-Coordinated Analogues Y, As Determined
by DFT Calculations
Figure 4. Sequential NMR spectra (in toluene-d8 at -45 °C) for
the stoichiometric reaction of compound X1 (top) with 1.2 equiv
(middle) and 2 equiv of CNiPr (bottom).
geometry around the IrI center is distorted square planar, as
suggested by the rather acute angles P-Ir-N1 (82.25(4)°)
and P-Ir-N2 (161.34(4)°) and the N1-Ir-C1 angle of
154.05(6)°. Surprisingly, there are only very few examples
of Ir complexes featuring a PN-N donor set.22,34 The C1dC2
bond of the cyclooctene ligand in X4 is lengthened slightly
due to back-bonding induced by the strongly π-donating trans-
amide,35-37 compared to other Ir(COE) complexes.38-40
Substitution Reactions of [RhI(L)(cycloalkene)] Complexes.
We investigated the reactivity of complex X1 using the strongly
coordinating isopropyl isocyanide CNiPr. This approach al-
lows for the facile addition of near-stoichiometric amounts of
exogenous ligand. The addition of one equivalent of isopropyl
isocyanide (CNiPr) resulted in clean substitution of the cy-
cloalkene ligand and formation of mono(isocyanide) complex
[Rh(L1)(CNiPr)] (X6). We observed similar behavior for
[Rh(L2)(COE)] and [Rh(L3)(COE)] (X2 and X3, respectively),
leading to the clean formation of [Rh(L2)(CNiPr)] (X8) and
[Rh(L3)(CNiPr)] (X10). The bonding situation in the
(mono)isocyanide complexes can be examined by an analysis
of various geometric parameters. Most commonly the CtN
bond length is used as a measure for the back-donation in
isocyanide complexes. Alternatively, the CtN-C bond angle
in the isocyanide ligand should decrease with increased M-C
back-donation. We therefore performed DFT calculations for
all (mono)isocyanide complexes relevant to the current study.
An inspection of these values leads to the following order for
the CtN bond lengths and CtN-C angles: [Rh(L1)(CNiPr)]
1.205 A/152.5°; [Rh(L2)(CNiPr)] 1.208 A/150.1°; [Rh(L3)-
(CNiPr)] 1.211 A/146.7°. The trend in lengthening of the
CtN bond as well as the significant change of the CtN-C
angle in the same order indicates an increasingly π-accepting
Figure 5. Structure of different conformers of [Rh(L1)(CNiPr)]
(XC6) and calculated harmonic CtN vibration frequencies.
H atoms of the pincer ligands are omitted for clarity.
isocyanide ligand due to the increase in the π-donating char-
acter of the amide in the trans position.41 Similar observations
were made for the corresponding Ir complexes.
Addition of a second equivalent of CNiPr to complex X6
resulted in splitting of the hemilabile Ir-N(Me2) bond of the
pincer ligand with formation of [Rh(L1)(CNiPr)2] (X7)
(Scheme 5). To exclude the possibility of five-coordinated
RhI complexes with overall formula [Rh(κ3-P,N,N0-L)(CNiPr)2]
(see Scheme 6), we performed comparative DFT calculations on
the conversion of complexes X0 (with ligands L1-L3) to the
corresponding four- and five-coordinated bis(isocyanide) analo-
gues X00 and Y.
(34) Casalnuovo, A. L.; Calabrese, J. C.; Milstein, D. Inorg. Chem.
1987, 26, 971.
(35) For an X-ray structure of the related [Ir(PNP)(COE)] complex,
see: Calimano, E.; Tilley, T. D. J. Am. Chem. Soc. 2009, 131, 11161.
(36) Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am.
Chem. Soc. 2006, 128, 15390.
(37) Friedrich, A.; Ghosh, R.; Kolb, R.; Herdtweck, E.; Schneider, S.
Organometallics 2009, 28, 708.
(38) Iimura, M.; Evans, D. R.; Flood, T. C. Organometallics 2003, 22,
5370.
These investigations revealed that for each case no stable
isomer Y exists (i.e., no minimum could be located on either
respective potential energy surface). Also the 31P NMR
spectroscopic data for complex Z [Rh(L4)(CNiPr)2], based
(39) Budzelaar, P. H. M.; Moonen, N. N. P.; de Gelder, R.; Smits,
J. M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2000, 753.
(40) Bernskoetter, W. H.; Lobkovsky, E.; Chirik, P. J. Chem. Com-
mun. 2004, 764.
(41) It could also be related to the different substitution pattern on the
amino side-group, although this appears less intuitive due to the mutual
cis-arrangement rather than the direct trans-influence exerted by the
amide donor.

504 Organometallics, Vol. 30, No. 3, 2011
Scheme 7. 31P NMR Competition Experiment Involving Complexes X1 and X3
Lindner et al.
on bidentate ligand L4,42,43 which showed a doublet at δ 47.2
ppm (1JRhP = 138.7 Hz), provide further strong indications
that the assignment for X7 is valid. Thus, the reaction of
mono(isocyanide) complex [Rh(L1)(CNiPr)] (X6) with an
additional equivalent of isocyanide leads to rupture of the
hemilabile Rh-N(Me2) bond, as observed by NMR spec-
troscopy and supported by DFT calculations. The corre-
sponding 31P NMR spectra after reaction of the analogous
Rh complex X1 with 1.2 and 2 equiv of CNiPr are depicted in
Figure 4. The chemical shifts and the coupling constants for
the three relevant species are clearly distinguishable, which
enables in situ monitoring of substitution reactions (vide
infra). In all experiments with more than one equivalent of
added CNiPr, low-temperature NMR spectra were recorded
as broad signals were observed at ambient temperature. This
indicates a rapid equilibrium between the mono- and bis-
(isocyanide) complex (X6/X7) and a small amount of un-
coordinated CNiPr at room temperature, which severely
hampered the isolation of bis(isocyanide) complexes. The
complexes proved very air-sensitive, both in solution and as
solid materials. As a result, attempts to fully characterize
these compounds or to obtain solid-state information via
X-ray crystallography failed. We observed similar adaptive
behavior in NMR experiments with either monoisocyanide
complex X8 or X10, which resulted in the corresponding
bis(isocyanide) complex [Rh(L2)(CNiPr)2] (X9) or [Rh(L3)-
(CNiPr)2] (X11). Thus, our PNN ligands act as a bidentate
PN- ligand rather than a tridentate PN-N ligand in the
presence of strong coligands such as isocyanides.
To further substantiate the formation of a bis(isocyanide)
species, we monitored the substitution reaction of [Rh(L1)-
(COE)] (X1) with CNiPr by in situ IR spectroscopy in C6D6.
DFT calculations on the relevant mono- and bis(isocyanide)
species suggested an effect of decreasing bond order of the
linear C-tNþR fragment into a bent CdNR isomer, due to
π-back-bonding, on the IR signature of the isocyanide
ligand. For the mono(isocyanide) complexes [Rh(L1)-
(CNiPr)] the DFT calculations (Figure 5) indicate that the
precise conformation of the resulting nonlinear CNiPr ligand
has a significant influence on the vibration frequency, leading
to multiple bands in the νCN (trans-N) region of the IR
spectrum of [Rh(L1)(CNiPr)] (X6), which was experimentally
verified. For the bis(isocyanide) complex [Rh(L1)(CNiPr)2] the
DFT calculations suggest a significantly higher bond order of
the isocyanide ligand trans to the P atom upon introduction of
the second equivalent of isocyanide. For complex X7, we
observed a strong band at νCN 2161 cm-1. Similar observations
were made for complexes with L2 and L3. Comparison with
data obtained for complex Z, [Rh(L4)(CNiPr)2], and literature
values44 strongly suggest the formation of four-coordinate
ꢂ
(42) Eggenstein, M.; Thomas, A.; Theuerkauf, J.; Francio, G.; Leitner,
W. Adv. Synth. Catal. 2009, 351, 725.
(43) Notably, complex Z is the first example of a [Rh(PN)(L0)2]
complex with a monoanionic phosphine-amide PN coordination sphere.
For related work on amido-phosphinoalkenyl ligands, see: (a) Sasa-
mori, T.; Matsumoto, T.; Tokitoh, N. Polyhedron 2010, 29, 425. Rare
dinuclear examples: (b) Schenk, T. G.; Downes, J. M.; Milne, C. R. C.;
Mackenzie, P. B.; Boucher, H.; Whelan, J.; Bosnich, B. Inorg. Chem. 1985,
24, 2334. (c) Dubs, C.; Yamamoto, T.; Inagaki, A.; Akita, M. Organome-
tallics 2006, 25, 1359.
(44) Northcutt, T. O.; Lachicotte, R. J.; Jones, W. D. Organometallics
1998, 17, 5148.

Article
Organometallics, Vol. 30, No. 3, 2011 505
Figure 6. Sequential 31P NMR spectra for a mixture of com-
plexes X1 and X3 with 1 equiv (top), 2 equiv (middle). and
3 equiv of CNiPr, relative to total [Rh].
bis(isocyanide) species and PN rather than PNN coordination
in all cases.
NMR Competition Experiments. We further examined the
hemilabile behavior in a direct competition experiment using
Rh complexes [Rh(L1)(COE)] (X1) and [Rh(L3)(COE)] (X3)
(Scheme 7 and Figure 6). In situ monitoring of a 1:1 reaction
mixture of both complexes with 1 equiv of CNiPr (relative to
total molar concentration of Rh complexes) by NMR spec-
troscopy at room temperature revealed that the first equiva-
lent of CNiPr substitutes either cycloalkene ligand without
specific preference or selectivity and that no side-arm
substitution occurs. Thus, a mixture of unreacted X1 and
X3 together with the intermediate species [Rh(L1)(CNiPr)]
(X6) and [Rh(L3)(CNiPr)] (X10) was present in solution, as
well as free 1,5-cyclooctene. Subsequent addition of 2 equiv
of CNiPr led to the selective formation of bis(isocyanide)
species X7, concomitant with freshly generated X6 (from X1)
and an increased concentration of X10.
In order to probe the existence and degree of tunable
hemilability among the different members of this novel
ligand class, we also performed an NMR competition ex-
periment with the [Rh(L)(COE)] complexes of L2H vs L3H
(X2 and X3). In this case, only minor preference for either
scaffold to undergo rupture of the Rh-NMe2 bond was
observed, as both complexes [Rh(L2)(CNiPr)2] (X9) and
[Rh(L3)(CNiPr)2] (X11) could be identified with 31P NMR
spectroscopy. Note that the interconversion between mono-
and bis(isocyanide) complex is fast on the NMR time scale,
as shown by coalescence effects at temperatures above -45 °C.
Furthermore, it was proven that the relative concentration of
these complexes is constant for more than 24 h, which indicates
that the reaction reaches equilibrium and the observed com-
plexes are the thermodynamic products.
Determination of Tunable Hemilabile Character. As for-
mation of the bidentate bis(isocyanide) complexes [Rh(L)-
(CNiPr)2], via the corresponding monoisocyanide complexes
[Rh(L)(CNiPr)] featuring tridentate coordination of L, was
proven to be very fast, any kinetic hindrance for coordina-
tion of the second equivalent of CNiPr is considered to be
small and was therefore neglected in this investigation. On
the other hand, the thermodynamic balance between both
coordination modes was found to be only slightly exergonic
and seems to be a decisive factor for the stability of the
bidentate coordination mode and the hemilabile coordina-
tion behavior. The various equilibrium constants were ex-
tracted from the NMR spectroscopic competition experi-
Figure 7. Relative scale of hemilability within the novel family
of PNN ligands, expressed as ΔΔG values, as determined from
the NMR competition experiments.
ments, and these were used to calculate the free energy
differences, ΔΔG. This reflects the driving force for “sub-
stitution” of the amine side-arm of the pincer ligand for the
more strongly coordinating isocyanide ligand in square-
planar [MI(L)(CNiPr)] complexes, which relates to the
hemilability of the pincer side-arm or more specifically the
thermodynamic stability of the chelating Rh-N bond.
To substantiate these experimental findings, we calculated
the formation of these rhodium and iridium bis(isocyanide)
complexes, starting from the corresponding [MI(L)(COE)]
(M = Rh, Ir; L = L1, L2, L3) complexes, at the DFT level of
theory (BP86/TZVP). The concept of bond strength has been
shown to be quite successful for a rationalization of reaction
energies. The particular reaction ([MI(L)(CNiPr)] þ CNiPr
f [MI(L)(CNiPr)2]) can be broken down into two different
processes: (1) cleavage of the M-N bond of the pincer side-
arm and (2) M-C bond formation of the new isocyanide
ligand. The first contribution is expected to differ signifi-
cantly between the observed ligands and contains the differ-
ences of the electronic properties as well as ring-strain effects,
whereas the second contribution is expected to be quite
similar for all expected pincer ligands (similar phosphorus
donor in the trans position) and is effected mainly by the
(difficult to rationalize) steric interaction between the “new”
isocyanide ligand and the other ligands. The advantage of
this formal partition is that the first contribution is indepen-
dent of the nature of the new ligand, and therefore this
dissociation energy is a much more general description of the
hemilability of these pincer ligands than the overall reaction
([MI(L)(CNiPr)] þ CNiPr f [MI(L)(CNiPr)2]). Note also
that such a formalistic breakdown makes no statement about
the mechanism of the overall reaction, which could be either
associative or dissociative.45
The energies of the corresponding calculated structures
are displayed in Figure 8. Obviously, the complete reaction is
strongly exergonic for both the Rh and the Ir complexes
(ΔRG = -30.4 - -42.1 kcal/mol). Furthermore, it can be

506 Organometallics, Vol. 30, No. 3, 2011
Lindner et al.
Figure 8. Calculated energies of (formal) intermediates for the reaction of the COE complexes [M(L)(COE)] (M = Rh, Ir; L =
L1-L3) with isopropyl isocyanide.
seen that the mono- and bis(isocyanide) complexes exhibit
almost similar stabilities for rhodium, whereas a substantial
stabilization of the bis(isocyanide) species can be observed
for iridium. The order of the spectroscopically determined
relative stability of the bis(isocyanide) complexes is accu-
rately reproduced. The differences in stability of the bis-
(isocyanide) complexes between the various ligands are mainly
attributed to differences in the dissociation of the peripheral
M-N bond.
Thus, the most labile tridentate coordination mode was
found for complexes exhibiting the bisaryl pincer ligand L1,
whereas the saturated ligand L3 and the 5,60-membered
ligand L2 lead to stronger M-N bonds. The trend in the
lability of the N side-arm might be rationalized by the
difference in the electronic environment of the N donor
(alkyl vs aryl) as well as the resonance stabilization between
the noncoordinated NR2 donor of the side-arm with the aryl
ring, which is important for complexes of L1. The chelate
ring size and conjugative effects of the central amide donor
are less important.
scaffolds via a series of optimized three-step synthetic meth-
odologies, starting from readily available materials to yield
L1H-L3H in good yields. The Rh- and Ir-cyclooctenyl
complexes of these ligands have been characterized, and a
relationship between the substitution pattern of the central
amido fragment and the degree of hemilability is deduced.
The presence of both hard and soft donor groups in the
ligand scaffold, implying different coordination strength to
either Rh or Ir metal centers, infers hemilabile behavior of
the tridentate ligand under certain conditions, as demon-
strated by NMR-based competition experiments. We have
further supported this by DFT calculations for both Rh- and
Ir-based complexes. This has led to the formulation of a scale
for the bond strength of the chelating N-M bond, charac-
terizing the hemilability for the first proponents of this new
ligand class. These novel hybrid frameworks may be applied
as adaptive ligands, as their coordination complexes contain
a “masked” vacant site that can be accessible to incoming
substrate under specific reaction conditions, thereby en-
abling productive reactivity. We foresee various interesting
applications for these adaptive, hybrid ligand systems in
catalytic reactions, especially taking advantage of the differ-
ent, tunable binding strength of the P and N side-arm donor
groups.46 Current efforts are directed to the controlled
activation of N-H bonds47 and subsequent reactivity, utiliz-
ing the hemilabile nature of our ligand scaffolds.
Conclusions
We have described the facile and straightforward synthesis
of a series of three novel hybrid, tridentate PNN ligand
(45) The mechanism is likely to be associative, given the d8-ML4
configuration. However, these investigations are beyond the scope of
this paper, and the end results in terms of absolute ΔG values are
identical. We have no indication for thermal lability of the M-Nalkyl
bond.
(46) We have noted very interesting redox chemistry with these
Rh(PNN) species. These results will be disclosed in a separate account.
(47) van der Vlugt, J. I. Chem. Soc. Rev. 2010, 39, 2302.

Article
Organometallics, Vol. 30, No. 3, 2011 507
Experimental Section
The combined organic layers were dried over MgSO4, and the
solvent was removed in vacuo, yielding the desired product as a
brown oil. Yield: 1.7 g (81%). 1H NMR (300 MHz, CDCl3): δ
6.95-7.04 (br m, 2H, ArH), 6.60-6.74 (br m, 2H, ArH), 4.63 (br
s, 1H, NH), 3.16 (dd, 2H, NCH2CH2NEt2), 2.74 (t, 2H,
CH2CH2NEt2), 2.59 (q, 4H, NCH2CH3), 1.06 ppm (t, 6H,
General Procedures. All reactions were carried out under an
atmosphere of argon using standard Schlenk techniques. With
exception of the compounds given below, all reagents were
purchased from commercial suppliers and used without further
purification. The following compounds were synthesized ac-
cording to published procedures: 2-(dimethylamino)methyl-
aniline,48 [{Rh(μ-OH)(COE)2}2],29 [{Ir(μ-OMe)(COD)}2],30
[{Ir(μ-OH)(COE)2}2],49 and 2-iodo-N,N-dimethylaniline.50 THF,
pentane, hexane, and diethyl ether were distilled from sodium
benzophenone ketyl. CH2Cl2, isopropyl alcohol, and methanol
were distilled from CaH2, and toluene was distilled from sodium
under nitrogen. NMR spectra (1H, 31P, and 13C) were measured on
a Varian INOVA 500 MHz or a Varian Mercury 300 MHz. IR
spectra (C6D6 solution) were measured on a FT-IR Vertex-70
(Bruker). Fast atom bombardment (FAB) mass spectrometry
was carried out on a JEOL JMS SX/SX 102 A four-sector mass
spectrometer, coupled to a JEOL MS-MP9021D/UPD system
program. Samples were loaded in a matrix solution (3-nitrobenzyl
alcohol) onto a stainless steel probe and bombarded with xenon
atoms with an energy of 3 keV. During the high-resolution
FAB-MS measurements a resolving power of 10 000 (10% valley
definition) was used.
NCH2CH3). 13C NMR (76 MHz, CDCl3): δ 152.1 (d, JFC
=
28.6 Hz, Ar), 137.1 (d, JFC = 11.7 Hz, Ar), 124.4 (d, JFC = 3.5 Hz,
Ar), 116.2 (d, JFC = 6.9 Hz, Ar), 114.2 (d, JFC = 18.4 Hz, Ar),
114.2 (d, JFC = 18.4 Hz, Ar), 112.2 (d, JFC = 3.6 Hz, Ar), 51.5 (s,
N(CH2)2N), 46.7 (s, NCH2CH3), 41.0 (s, N(CH2)2N), 11.8 ppm (s,
NCH2CH3); 19F NMR (282 MHz, CDCl3): δ 136.41 ppm (s).
N-(2-Bromophenyl)aniline. A modification of the procedure
from Rossi et al.51 was used for the synthesis of N-(2-bromo-
phenyl)aniline. To a mixture of aniline (745 mg, 8.0 mmol),
2-bromoiodobenzene (2.26 g, 8.0 mmol), and NaOtBu (1.53 g,
16.0 mmol) in toluene (15 mL) were added DPPF (110.8 mg,
0.20 mmol) and Pd2(dba)3 (91.6 mg, 0.10 mmol) at room
temperature. After heating at 80 °C for 12 h the reaction mixture
was evaporated to dryness, and the resulting crude product was
extracted in CH2Cl2 (50 mL) and washed with H2O (2 ꢀ 20 mL).
The organic phase was further purified by filtration over silica
(3 A) and evaporated to dryness, which gave the product as a
1
dark oil. Yield: 1.83 g (92%). H NMR (300 MHz, CDCl3): δ
Preparation of 2-(Bromophenyl)-20-(dimethylaminophenyl)-
amine. To a mixture of 2-iodo-N,N-dimethylaniline (2.47 g,
10.0 mmol), 2-bromoaniline (1.71 g, 10.0 mmol), and NaOtBu
(1.92 g, 20.0 mmol) in toluene (20 mL) were added DPPF (111
mg, 0.20 mmol) and Pd2(dba)3 (91.6 mg, 0.10 mmol) at room
temperature. After heating at 80 °C for 12 h the reaction mixture
was evaporated to dryness, and the resulting crude product
extracted in CH2Cl2 (50 mL) and washed with H2O (2 ꢀ 20 mL).
The organic phase was further purified by filtration over silica
(3 A) and evaporated to dryness, which gave the product as a
dark oil. Yield: 2.6 g (90%). 1H NMR (300 MHz, CDCl3): δ 7.56
(m, 1H, CH), 7.42 (m, 1H, CH), 7.31 (m, 1H, ArH), 7.20 (m, 1H,
ArH), 7.12 (m, 1H, ArH), 7.07 (m, 1H, ArH), 6.76 (m, 1H, ArH),
2.71 ppm (s, 6H, NCH3). 13C NMR (121 MHz, CDCl3): δ 141.3
(s, Ar), 136.7 (s, Ar), 133.4 (s, Ar), 128.4 (s, Ar), 124.0 (s, Ar),
121.7 (s, Ar), 121.2 (s, Ar), 120.0 (s, Ar), 116.9 (s, Ar), 116.4 (s,
Ar), 113.5 (s, Ar), 44.3 ppm (s, NCH3).
Preparation of 2-Bromo-N-(2-((dimethylamino)methyl)phenyl)-
aniline. To a mixture of 2-bromoiodobenzene (2.83 g, 10.0 mmol),
2-((dimethylamino)methyl)aniline (1.50 g, 10.0 mmol), and NaOt-
Bu (1.92 g, 20.0 mmol) in toluene (20 mL) were added DPPF
(111 mg, 0.20 mmol) and Pd2(dba)3 (91.6 mg, 0.10 mmol) at room
temperature. After heating at 80 °C for 12 h the reaction mixture
was evaporated to dryness, and the resulting crude product ex-
tracted in CH2Cl2 (50 mL) and washed with H2O (2 ꢀ 20 mL). The
organic phase was further purified by filtration over silica (3 A) and
evaporated to dryness, which gave the product as a dark oil. Yield:
2.69 g (88%). 1H NMR (300 MHz, CDCl3): δ 9.15 (br, 1H, NH),
7.54 (m, 1H, ArH), 7.38 (m, 2H, ArH), 7.19 (m, 3H, ArH), 6.87 (m,
1H, ArH), 6.71 (m, 1H, ArH), 3.46 (s, 4H, CH2), 2.28 ppm (s, 6H,
NCH3).
7.51 (m, 1H, ArH), 7.32 (m, 2H, ArH), 7.23 (m, 1H, ArH), 7.15
(m, 3H, ArH), 7.03 (m, 1H, ArH), 6.92 (m, 1H, ArH), 6.08 ppm
(br, 1H, NH).
Preparation of (2-Diphenylphosphinophenyl)-20-(dimethylamino-
phenyl)amine (L1H). A 2.5 M solution of BuLi in hexane (4.00 mL,
10.0 mmol) was added to a solution of (2-bromophenyl-20-di-
methylaminophenyl)amine (1.46 g, 5.00 mmol) in Et2O (20 mL)
at -80 °C. The mixture was allowed to warm to ambient tempera-
ture and stirred for 12 h. After cooling of this solution to -80 °C
ClPPh2 (1.84 mL, 10.0 mmol) was added, and the resulting reaction
mixture warmed to room temperature again. After 12 h the
suspension was evaporated to dryness, redissolved in MeOH
(50 mL), and acidified with concentrated HCl (2 mL). After stirring
for 1 h, the solution was neutralized with an excess of Na2CO3 (4.24
g, 40.0 mmol) and evaporated to dryness. The crude product was
obtained by extraction with CH2Cl2 and further purified by
chromatography over silica (3 A) with chloroform. Yield: 807
mg (41%). 1H NMR (300 MHz, CDCl3): δ 7.34 (m, 10H, ArH),
7.20-7.42 (m, 4H, ArH), 6.75-7.00 (m, 4H, ArH), 2.31 ppm (s,
6H, NCH3). 13C NMR (121 MHz, CDCl3): δ 145.8 (d, JPH = 18.5
Hz, Ar), 143.1 (s, Ar), 138.1 (s, Ar), 136.0 (d, JPH = 10.4 Hz, Ar),
134.4 (d, JPH = 20.8 Hz, Ar), 134.2 (d, JPH = 2.3 Hz, Ar), 129.9 (s,
Ar), 129.2 (s, Ar), 128.9 d, JPH = 8.1 Hz, Ar), 128.5 d (JPH = 6.9
Hz, Ar), 126.9 (d, JPH = 9.2 Hz, Ar), 124.1 (s, Ar), 121.4 (s, Ar),
120.1 (d, JPH = 32.3 Hz, Ar), 118.8 (s, Ar), 115.0 ppm (s, Ar). 31
P
NMR (121 MHz, CDCl3): δ -16.7 ppm (s). HR-MS (FAB): m/z
calcd for C26H26N2P 397.1834 [M þ H]þ; found 397.1839.
Preparation of 2-((Dimethylamino)methyl)-N-(2-(diphenylphos-
phino)phenyl)aniline (L2H). A 2.5 M solution of BuLi in hexane
(4.00 mL, 10.0 mmol) was added to a solution of 2-bromo-
N-(2-((dimethylamino)methyl)phenyl)aniline (1.53 g, 5.00 mmol)
in Et2O (20 mL) at -80 °C. The mixture was allowed to warm to
ambient temperature and stirred over 12 h. After cooling of this
solution to -80 °C ClPPh2 (1.84 mL, 10.0 mmol) was added, and
the resulting reaction mixture stirred for 12 h at room temperature
again. Thereafter the suspension was evaporated to dryness,
redissolved in MeOH (50 mL), and acidified with concentrated
HCl(2 mL). After stirring for 1 h the solution was neutralized with
an excess of Na2CO3 (4.24 g, 40.0 mmol) and evaporated to
dryness. The crude product was obtained by extraction with
CH2Cl2 and further purified by chromatography over silica
(3 A) with chloroform. Yield: 1.08 g (53%). 1H NMR (300 MHz,
CDCl3): δ 8.92 (s, 1H, NH), 7.18-7.45 (m, 14H, ArH), 7.14
N,N-Diethyl-N0-(2-fluorophenyl)-1,2-ethane. To a mixture of
1-bromo-2-fluorobenzene (1.75 g, 10.0 mmol), N,N-(diethyl-
amino)ethylamine (1.16 g, 10.0 mmol), and NaOtBu (1.92 g,
20.0 mmol) in toluene (30 mL) were added BINAP (63.0 mg,
0.10 mmol) and Pd2(dba)3 (46 mg, 0.050 mmol) at room
temperature. After heating at 80 °C for 18 h the reaction mixture
was filtered and washed with toluene (2 ꢀ 10 mL), and the
filtrate dried in vacuo. To the resulting brown oil, 15 mL of water
was added. This mixture was washed with CH2Cl2 (3 ꢀ 15 mL).
(48) Barybin, M. V.; Diaconescu, P. L.; Cummins, C. C. Inorg. Chem.
2001, 40, 2892.
(49) Ortmann, D. A.; Werner, H. Z. Anorg. Allg. Chem. 2002, 628,
1373.
(50) Yue, D.; Larock, R. C. Org. Lett. 2004, 6, 1037.
ꢀ
(51) Buden, M. E.; Vaillard, V. A.; Martin, S. E.; Rossi, R. A. J. Org.
Chem. 2009, 74, 4490.

508 Organometallics, Vol. 30, No. 3, 2011
Lindner et al.
(m, 1H, ArH), 7.03 (m, 1H, ArH), 6.83 (m, 1H, CH), 6.75 (m, 1H,
ArH), 3.31 (s, 2H, CH2), 1.90 ppm (s, 2H, NCH3). 13C NMR (126
MHz, C6D6): δ 145.6 (d, JPC = 18.2 Hz, Ar), 142.9 (s, Ar), 137.8
(s, Ar), 135.8 (d, JPC = 9.8 Hz, Ar), 134.1 (d, JPC = 19.9 Hz, Ar),
133.9 (d, JPC = 2.6 Hz, Ar), 129.6 (s, Ar), 128.9 (s, Ar), 128.6 (s,
Ar), 128.6 (s, Ar), 126.7(d, JPC = 10.1Hz, Ar), 123.8 (s,Ar), 121.2
(s, Ar), 119.8 (d, JPC = 32.0 Hz, Ar), 117.5 (s, Ar), 114.8 (s, Ar),
118.8 (s, Ar), 118.1 (s, Ar), 95.9 (d, JPC = 12.8 Hz, Ar), 65.9 (s,
CH2), 52.5 (s, CH2), 52.0(s, CH2), 43.3 (s, NCH3), 33.7 (s), 30.3 (s,
CH2), 15.5 ppm (s, CH2). 31P NMR (121 MHz, CDCl3): δ -16.3
ppm (s).
N-(2-(Diphenylphosphino)phenyl)-N0,N0-diethylethane-1,2-diamine
(L3H). A microwave vessel was charged with N,N-diethyl-N0-(2-
fluorophenyl)-1,2-ethane (410 mg, 2.0 mmol) and KPPh2 (0.5 M
inTHF, 4.0mL, 2.0mmol). After irradiation for 6 h(150 W, 3 bar,
110 °C), the solvent was removed in vacuo. CH2Cl2 (20 mL) was
added, and this mixture was washed with water (20 mL). The two
layers were separated, and the aqueous layer was extracted with
CH2Cl2 (2 ꢀ 10 mL). The combined organic layers were dried over
MgSO4, and the solvent was removed in vacuo. The product was
purified over a silica column (3 A) using acetone as eluent, yielding
L3H as a wax-like white-yellow solid. Yield: 489 mg (65%). 1H
NMR (300 MHz, CDCl3): δ 7.40 (d, 1H, ArH), 7.16 (dd, 1H,
ArH), 6.60 (d, 1H, ArH), 6.52 (dd, 1H, ArH), 5.47 (br s, 1H, NH),
3.19 (m, 2H, NHCH2CH2), 2.55 (m, 4H, NCH2CH3), 1.80 (m,
2H, CH2CH2NEt2), 1.05 ppm (t, 6H, NCH2CH3). 13C NMR (126
MHz, CDCl3): δ 149.9 (d, JPC = 17.3 Hz, Ar), 135.1 (d, JPC = 6.9
Hz, Ar), 134.3(d, JPC = 3.5 Hz, Ar), 133.5 (d, JPC = 18.5Hz, Ar),
130.6 (s, Ar) 128.7 (s, Ar), 128.4 (d, JPC = 6.9 Hz, Ar), 119.5 (d,
JPC = 6.9 Hz, Ar), 117.7 (s, Ar), 110.1 (s, Ar), 49.3 (s, N-
(CH2)2NEt2), 46.4 (s, NCH2CH3), 40.9 (s, N(CH2)2NEt2), 8.7
ppm (s, NCH2CH3). 31P NMR (121 MHz, CDCl3): δ -20.75 ppm
(s). HR-MS (FAB): m/z calcd for C27H49N2P 377.2147 [M þ H]þ;
found 377.2151.
N-(2-(Diphenylphosphino)phenyl)aniline (L4H). Modified pro-
cedure from literature:42 A 2.5 M solution of BuLi in hexane
(4.00 mL, 10.0 mmol) was added to a solution of N-(2-bromophe-
nyl)aniline (1.24 g, 5.00 mmol) in Et2O (20 mL) at -80 °C. The
mixture was allowed to warm to ambient temperature and stirred
over 12 h. After cooling of this solution to -80 °CClPPh2 (1.84mL,
10.0 mmol) was added, and the resulting reaction mixture stirred for
12 h at room temperature again. Thereafter the suspension was
evaporated to dryness, redissolved in MeOH (50 mL), and acidified
with concentrated HCl (2 mL). After stirring for 1 h the solution
was neutralized with an excess of Na2CO3 (4.24 g, 40.0 mmol) and
evaporated to dryness. The crude product was obtained by extrac-
tion with CH2Cl2 and further purified by chromatography over
silica (3 A) with pentane/Et2O (2:1). Yield: 1.18 g (67%). 1H NMR
(121 MHz, CDCl3): δ 7.16-7.45 (m, 10H, ArH), 6.80-6.98 (m,
1H, ArH), 6.22 ppm (br, 1H, NH). 31P NMR (121 MHz, CDCl3):
δ -18.9 ppm (s).
31.4 (s, CH2), 26.8 ppm (s, CH2). 31P NMR (121 MHz, C6D6): δ
56.5 ppm (d, 1JRhP = 207.8 Hz).
[Rh(L2)(COE)] (X2). A solution of L2H (42.0 mg, 0.200 mmol)
in Et2O (10 mL) was added to [{Rh(μ-OH)(COE)2}2] (68.1 mg,
0.100 mmol) at -80 °C. The reaction mixture was slowly heated to
room temperature overnight and concentrated to 3 mL. Layering
with hexane (5 mL) resulted in the precipitation of the product as a
yellow solid, which was filtered, washed with hexane (3 ꢀ 1 mL),
and dried in vacuo, 27 mg (22%). 1H NMR (500 MHz, toluene-d8):
δ8.34 (m, 2H, ArH), 7.62 (m, 2H, ArH), 6.95-7.13 (m, 10H, ArH),
6.92 (m, 1H, ArH), 6.88 (m, 1H, ArH), 6.72 (m, 1H, ArH), 6.45 (m,
1H, ArH), 3.80(d,1H, ArCH2N), 3.07 (m, 2H, COE CH2),2.32(m,
1H, ArCH2N), 2.03-2.32 (m, 2H COE CH2), 2.15 (s, 3H, NCH3),
1.76 (s, 3H, NCH3), 1.66 (m, 1H, COE CH2), 1.45 (m, 3H, COE
CH2) 1.28 (m, 3H, COE CH2), 1.15 (m, 1H, COE CH2), 0.99 (m,
1H, COE CH2), 0.40 ppm (m, 1H, COE CH2). 13C NMR (126
MHz, C6D6):δ164.7 (d, 3JRhC = 164.7 Hz, Ar), 155.0 (s, Ar), 137.2
(d, 3JRhC = 40.4 Hz, Ar), 135.5 (s, Ar), 135.4 (s, Ar), 134.8 (s, Ar),
134.7 (s, Ar), 134.3 (d, JRhC = 41.6 Hz, Ar), 132.4 (d, JRhC = 9.2
Hz, Ar), 131.7 (s, Ar), 131.2 (s, Ar), 130.6 (s, Ar), 130.0 (s, Ar), 129.8
(s, Ar), 129.7 (s, Ar), 120.6 (s, Ar), 119.7 (d, JRhC = 11.5 Hz, Ar),
117.5 (s, Ar), 117.2 (d, JRhC = 6.9 Hz, Ar), 66.9 (d, JRhC = 12.7 Hz,
COE CH), 66.0 (s, ArCH2N), 66.9 (d, JRhC = 12.7 Hz, COE CH),
50.2 (s, NCH3), 45.6 (s, NCH3), 32.7 (s, COE CH2), 32.2 (s, COE
CH2), 31.5 (s, COE CH2), 30.6 (s, COE CH2), 26.9 (s, COE CH2),
26.8 ppm (s, COE CH2). 31P NMR (122 MHz, C6D6): δ 63.0 ppm
(d, 1JRhP = 206.2 Hz).
[Rh(L3)(COE)] (X3). A solution of L3H (105 mg, 0.279 mmol) in
Et2O (15 mL) was added to [{Rh(μ-OH)(COE)2}2] (100 mg,
0.147 mmol) at -80 °C. The reaction mixture was slowly heated
to room temperature overnight, which resulted in the precipitation
of the product as an orange-brown solid, which was filtered, washed
with hexane (3 ꢀ 1 mL), and dried in vacuo. Yield: 95 mg (58%). 1H
NMR (500 MHz, C6D6): δ 8.17 (m, 4H, ArH), 7.22 (m, 1H, ArH),
7.11 (d, 1H, ArH), 7.05 (m, 6H, ArH), 6.42 (s, 1H, ArH), 6.36 (m,
1H, ArH), 3.04 (m, 2H, NCH2CH2N), 2.88 (m, 2H, NCH2CH2N),
2.42 (m, 2H, COE CH þ CH2CH3), 2.12 (m, 2H, COE CH2), 1.61
(m, 2H, COE CH2), 1.42 (m, 4H, COE CH2), 1.19 (m, 2H, COE
CH2), 0.98 (m, 2H, COE CH2), 0.91 ppm (t, 6H, CH2CH3). 13C
NMR (126 MHz, C6D6): δ 137.0 (d, JPC = 41.6 Hz, Ar), 134.7 (s,
JPC = 11.5 Hz, Ar), 132.2 (d, JPC = 38.1 Hz, Ar), 129.6 (s, Ar),
113.2 (s, Ar), 107.7 (br, Ar) 66.9 (d, JRhC = 7.2 Hz, COE CH), 56.6
(s, NCH2CH2N), 48.4 (s, NCH2CH3), 48.1 (s, COE CH2), 32.3 (s,
COE CH2), 32.0 (s, COE CH2), 27.0 (s, COE CH2), 10.0 ppm (s,
NCH2CH3).31P NMR (122 MHz, C6D6):δ57.6 ppm (JRhP= 210.8
Hz).
[Ir(L3)COE] (X4). A solution of L3H (75.2 mg, 0.200 mmol)
in Et2O (10 mL) was added to [{Ir(μ-OH)(COE)2}2] (85.9 mg,
0.100 mmol) at -80 °C. The reaction mixture was slowly heated
to room temperature overnight and concentrated to 3 mL.
Layering with hexane (5 mL) resulted in the precipitation of
the product as a yellow solid, which was filtered, washed with
hexane (3 ꢀ 1 mL) at -70 °C, and dried in vacuo. Yield: 53 mg
(39%). Single crystals were grown from Et2O/hexane. 1H NMR
(500 MHz, C6D6): δ 8.18 (m, 4H, ArH), 6.98-7.25 (m, 8H,
ArH), 6.44 (m, 2H, ArH), 3.05 (m, 2H, N(CH2)2N), 2.55 (m, 2H,
COE), 2.44 (m, 2H, N(CH2)2N), 2.40 (m, 2H, COE), 2.21 (m,
2H, COE), 2.07 (m, 2H, COE), 1.71 (m, 2H, COE), 1.48 (m, 4H,
NCH2CH3), 1.26 (m, 2H, COE), 0.91 (m, 2H, COE), 0.85 ppm
(m, 6H, NCH2CH3). 13C NMR (126 MHz, C6D6): δ 165.7 (d,
JPC = 18.0 Hz, Ar), 135.4 (d, JPC = 50.3 Hz, Ar), 134.5 (d,
JPC = 10.6 Hz, Ar), 132.2 (s, Ar), 131.9 (d, JPC = 1.9 Hz, Ar),
130.8 (d, JPC = 58.7 Hz, Ar), 129.6 (d, JPC = 1.9 Hz, Ar), 127.6 (d,
[Rh(L1)(COE)] (X1). A solution of L1H (218 mg, 0.55 mmol)
in Et2O (15 mL) was added to [{Rh(μ-OH)(COE)2}2] (187 mg,
0.28 mmol) at -80 °C. The reaction mixture was slowly heated
to room temperature overnight, which resulted in the precipita-
tion of the product as an orange-brown solid, which was filtered,
washed with hexane (3 ꢀ 1 mL), and dried in vacuo. Yield: 304
1
mg (91%). H NMR (300 MHz, C6D6): δ 8.12 (m, 4H, ArH),
7.62 (dd, 1H, ArH), 7.54 (d, 1H, ArH), 7.20 (dd, 2H, ArH), 7.03
(s, 8H, ArH), 6.58 (dd, 1H, ArH), 6.73 (d, 1H, ArH), 6.48 (dd,
2H, ArH), 3.15 (d, 2H, dCH), 2.50 (s, 6H, NCH3), 2.20 (dt, 2H,
COE CH2), 1.30-1.62 (m, 8H, COE CH2), 0.87-1.03 ppm (m,
2H, COE CH2). 13C NMR (126 MHz, C6D6): δ 159.6 (d, JPC
=
20.3 Hz, Ar), 150.8 (s, Ar), 148.3 (d, JPC = 2.7 Hz, Ar), 135.5 (d,
PC = 42.0 Hz, Ar), 134.6 (s, Ar), 134.5 (s, Ar), 132.6 (d, JPC
50.1 Hz, Ar), 132.3 (s, Ar), 131.1 (d, JPC = 1.4 Hz, Ar), 129.7 (d,
PC = 2.3 Hz, Ar), 127.3 (s, Ar), 119.1 (s, Ar), 117.0 (d, JPC
7.2 Hz, Ar), 115.9 (s, Ar), 114.1 (s, Ar), 113.5 (d, JPC = 11.5 Hz,
Ar), 70.1 (d, JPC = 13.0 Hz, Ar), 47.4 (s, NCH3), 31.8 (s, CH2),
J
PC = 10.0 Hz, Ar), 115.0 (d, JPC = 8.7 Hz, Ar), 108.2 (d, JPC
10.8 Hz, Ar), 58.3 (d, JPC = 2.6 Hz, N(CH2)2N), 49.4 (s,
N(CH2)2N), 48.8 (d, JPC = 2.0 Hz, COE CH2), 46.9 (d, JPC
=
J
=
=
J
=
1.0 Hz, NCH2CH3), 32.7 (s, COE CH2), 32.0 (d, JRhC = 3.2 Hz,
COE CH), 27.3 (s, COE CH2), 10.1 ppm (s, NCH2CH3). 31PNMR
(202 MHz, C6D6): δ 15.2 ppm (s).

Article
[Ir(L3)(COD)] (X5). A solution of L3H (100 mg, 0.25 mmol)
Organometallics, Vol. 30, No. 3, 2011 509
(d, JPC = 48.5 Hz, Ar), 120.3 (s, Ar), 116.0 (d, JPC = 8.1 Hz, Ar),
115.2 (s, Ar), 115.0 (s, Ar), 115.0 (d, JPC = 14 Hz, Ar), 52.5 (s,
NCH3), 47.1 (s, CH(CH3)2), 23.9 ppm (s, CH(CH3)2). 31P NMR
(121 MHz, C6D6): δ 58.1 ppm (d, 1JRhP = 177.2 Hz). IR (C6D6):
in 10 mL of Et2O was slowly added to a mixture of [{Ir(μ-
OMe)(COD)}2] (88 mg, 0.13 mmol) in 15 mL of Et2O at -80 °C.
This resulted in a color change from orange to bright red after
stirring for 30 min. This mixture was allowed to reach ambient
temperature overnight, after which the solvent was removed in
vacuo, yielding the desired product as a bright red solid. Yield:
140 mg (83%). 1H NMR (500 MHz, toluene-d8, -45 °C): δ 7.57
(dd, 2H, ArH), 7.45 (dd, 2H, ArH), 7.18 (dd, 1H, ArH), 7.01 (m,
3H, ArH), 6.88-6.83 (br m, 5H, ArH), 6.35 (dd, 1H, ArH), 5.09
(br s, 1H, COD CH), 5.01 (br s, 1H, COD CH), 4.14 (br m, 1H,
COD CH), 3.75 (br m, 1H, COD CH), 3.03 (br s, 2H,
NCH2CH2NEt2), 2.93 (br s, 2H, NCH2CH2NEt2), 2.57-2.41
(br m, 5H, COD CH2), 2.16-2.09 (br m, 3H, COE CH2),
1.74-1.66 (br m, NCH2CH3), 0.99 ppm (t, 6H, NCH2CH3).
13C NMR (126 MHz, C6D6): δ 133.7 (d, JPC = 18.0 Hz, Ar),
133.3 (d, JPC = 10.9 Hz, Ar), 130.2 (s, Ar), 119.5 (d, JPC = 55.4
Hz, Ar), 114.8 (d, JPC = 7.5 Hz, Ar), 112.0 (d, JPC = 13.2 Hz,
Ar), 55.8 (s, COD CH2), 53.8 (s, COD CH2), 52.5 (br s, COD
CH), 50.7 (s, COD CH2), 48.4 (s, NCH2CH3), 33.3 (br s, COD
CH), 31.8 (s, COD CH2), 12.8 ppm (s, NCH2CH3). 31P NMR
(122 MHz, C6D6): δ 28.6 ppm (s).
ν
CN 2038 (m), 2070 (m) cm-1
.
[Rh(L1)(CNiPr)2] (X7). CNiPr (3.8 μL, 40 μmol) was added to
a solution of X1 (12.5 mg, 20.0 μmol) in toluene-d8 (0.7 mL). The
resulting mixture was analyzed by NMR spectroscopy. 1H
NMR (500 MHz, toluene-d8, -45 °C): δ 8.08 (m, 2H, ArH),
7.95 (m, 2H, ArH), 7.63 (m, 1H, ArH), 7.28 (m, 1H, ArH),
6.97-7.18 (m, 9H, ArH), 6.90 (m, 1H, ArH), 6.67 (m, 1H, ArH),
6.45 (m, 1H, ArH), 5.71 (m, 2H, COE CH), 2.91 (s, 6H, NCH3),
2.84 (m, 2H, CH(CH3)2), 2.09 (m, 4H, COE CH2), 1.44 (m, 8H,
COE CH2), 0.56 ppm (m, 12H, CH(CH3)2). 31P NMR (121
MHz, toluene-d8, -45 °C): δ 48.2 ppm (d, 1JRhP = 137.4 Hz). IR
(C6D6): νCN 2038 (w), 2081 (m), 2161 (s) cm-1
.
[Rh(L2)(NCiPr)] (X8). CNiPr (1.9 μL, 20 μmol) was added to
a solution of X2 (12.5 mg, 20.0 μmol) in C6D6 (0.7 mL) and
analyzed by NMR spectroscopy. 1H NMR (500 MHz, C6D6): δ
7.89-8.00 (m, 3H, ArH), 7.72 (m, 1H, ArH), 7.66 (m, 1H, ArH),
7.27 (m, 1H, ArH), 6.92-7.15 (m, 10H, ArH), 6.73 (m, 1H,
2
ArH), 6.55 (m, 1H, ArH), 3.91 (d, JHH = 10.7 Hz, 1H,
[Rh(L4)(CNiPr)2] (Z). A solution of L4H (70.7 mg, 0.200
mmol) in Et2O (10 mL) was added to [{Rh(μ-OH)(COE)2}2]
(68.1 mg, 0.100 mmol) at -80 °C. The reaction mixture was
slowly heated to room temperature overnight. CNiPr (38 μL,
0.40 mmol) was added, and the solution concentrated to 1 mL.
Layering with pentane (5 mL) resulted in the precipitation of the
product as a orange solid, which was filtered, washed with
pentane (3 ꢀ 1 mL), and dried in vacuo. Yield: 71.2 mg (60%).
1H NMR (300 MHz, C6D6): δ 8.03 (m, 4H, ArH), 7.49 (m, 2H,
ArH), 7.31 (m, 1H, ArH), 7.23 (m, 2H, ArH), 7.07-7.10 (m, 6H,
ArH), 7.00 (m, 1H, ArH), 6.92 (m, 1H, ArH), 6.75 (m, 1H, ArH),
6.40 (m, 1H, ArH), 2.99 (br, 1H, CH(CH3)2), 2.91 (br, 1H,
CH(CH3)2), 0.65 (s, 6H, CH(CH3)2), 0.59 ppm (s, 6H, CH-
(CH3)2). 13C NMR (75 MHz, C6D6): δ 169.0 (d, JPC = 2.4 Hz,
ArCH2N), 2.96 (sep, 3JHH = 6.3 Hz, 1H, CH(CH3)2), 2.78 (m,
3H, NCH3), 2.50 (m, 1H, ArCH2N), 2.14 (s, 3H, NCH3), 0.68 (d,
3JHH = 6.8 Hz, 3H, CH(CH3)2), 0.66 ppm (d, 3JHH = 6.8 Hz,
3H, CH(CH3)2). 13C NMR (126 MHz, C6D6): δ 165.5 (d, JPC
=
27.7 Hz, Ar), 154.5 (s, Ar), 137.2 (dd, JRhC/2JPC = 42.7/39.0
Hz, CNiPr), 134.0 (d, JPC = 11.5 Hz, Ar), 133.1 (d, JPC = 11.5
Hz, Ar), 133.0 (s, Ar), 131.9 (s, Ar), 131.3 (d, JPC = 2.3 Hz, Ar),
129.8 (s, Ar), 129.1 (d, JPC = 20.9 Hz, Ar), 127.3 (s, Ar), 124.6
(d, JPC = 48.5 Hz, Ar), 119.6 (s, Ar), 119.3 (d, JPC = 12.7 Hz,
1
Ar), 116.5 (s, Ar), 116.4 (d, JPC = 5.8 Hz, Ar), 65.2 (d, JRhC
=
1.4 Hz, PhCH2N), 53.8 (s, NCH3), 47.6 (s, NCH3), 47.4 (s,
CH(CH3)2), 24.0 (s, CH(CH3)2), 24.0 ppm (s, CH(CH3)2). 31P
NMR (202 MHz, C6D6): δ 62.7 ppm (d, 1JRhP = 175.2 Hz). IR
(C6D6): νCN 2036 (m), 2071 (m).
[Rh(L2)(NCiPr)2] (X9). CNiPr (3.8 μL, 40 μmol) was added to
a solution of X2 (12.5 mg, 20.0 μmol) in toluene-d8 (0.7 mL). The
resulting mixture was analyzed by NMR spectroscopy. 1H
NMR (500 MHz, toluene-d8, -45 °C): δ 8.12 (m, 3H ArH),
7.96 (m, 2H ArH), 7.78 (m, 1H, ArH), 7.50 (m, 1H, ArH),
6.98-7.35 (m, 8H, ArH), 6.92 (m, 1H, ArH), 6.41 (m, 2H, ArH),
5.71 (m, 2H, CH, COE), 4.14 (d, 2JHH = 15.1 Hz, CH2), 3.75 (d,
2JHH = 15.1 Hz, 1H, CH2), 2.83 (m, 2H, CH(CH3)2), 2.29 (s,
6H, NCH3), 2.09 (m, 4H, CH2 COE), 1.45 (m, 8H, CH2 COE),
0.56 ppm (m, 12H, CH(CH3)2). 31P NMR (121 MHz, toluene-
d8, -45 °C): δ 48.5 ppm (d, 1JRhP = 137.4 Hz).
Ar), 168.6 (d, JPC = 2.4 Hz, Ar), 160.4 (s, Ar), 136.7 (d, JPC
1.8 Hz, Ar), 136.1 (d, JPC = 1.8 Hz, Ar), 136.1 (s, Ar), 134.0 (s,
Ar), 133.9 (s, Ar), 132.5 (d, JPC = 1.8 Hz, Ar), 129.5 (d, JPC
=
=
1.8 Hz, Ar) 129.4 (s, Ar), 129.2 (s, Ar), 128.2 (s, Ar), 121.8 (s, Ar),
115.0 (s, Ar), 114.4 (s, Ar), 113.8 (d, JPC = 14.0 Hz, Ar), 111.9
(d, JPC = 6.7 Hz, Ar), 47.5 (br, CH(CH3)2), 23.6 (br, CH-
(CH3)2), 22.5 ppm (br, CH(CH3)2). 31P NMR (121 MHz, C6D6):
δ 47.2 ppm (d, 1JRhP = 138.7 Hz). IR (C6D6): νCN 2040 (w), 2080
(m), 2154 (m) cm-1
.
NMR Competition Experiments. Three equivalents of CNiPr
(2.3 μL, 24 μmol or 1.2 μL, 12.8 μmol) were added subsequently
in three steps (1 equiv, 2 equiv, 3 equiv) to a solution of X1
(14.5 mg, 23.8 μmol) and X3 (13.0 mg, 22.1 μmol) or X2 (8.0 mg,
12.8 μmol) and X3 (7.5 mg, 12.7 μmol) in toluene-d8 (0.7 mL).
After each addition the solution was analyzed by NMR spec-
troscopy and compared to spectroscopic data of independently
prepared samples. NMR spectroscopically determined relative
concentrations of the different COE and CNiPr complexes were
used to calculate the relevant equilibrium constants for isocya-
nide exchange between complexes.
[Rh(L3)(CNiPr)] (X10). CNiPr (3.8 μL, 40 μmol) was added to
a solution of X3 (23.5 mg, 40.0 μmol) in C6D6 (0.7 mL) and
analyzed by NMR spectroscopy. 1H NMR (500 MHz C6D6): δ
8.04 (m, 4H, ArH), 7.30 (m, 2H, ArH), 6.96-7.18 (m, 6H, ArH),
6.53 (m, 1H, ArH), 6.48 (m, 1H, ArH), 3.23 (m, 2H, NCH2), 3.10
(sep, 3JHH = 6 Hz, 1H, CH(CH3)2), 2.72 (m, 2H, NCH2), 2.61
(m, 2H, NCH2), 2.51 (m, 2H, NCH2), 1.29 (t, 3JHH = 6.3 Hz,
6H, NCH2CH3), 0.82 ppm (d, 3JHH = 6.3 Hz, 12H, CH(CH3)2).
13C NMR (126 MHz, C6D6): δ 166.0 (d, JPC = 25.1 Hz, Ar),
[Rh(L1)(CNiPr)] (X6). CNiPr (3.8 μL, 40 μmol) was added to
a solution of X1 (24.3 mg, 40.0 μmol) in benzene (3 mL). After
5 min the reaction mixture was concentrated to 1 mL and
precipitated by layering with pentane (3 mL) at -70 °C. The
resulting yellow precipitate was filtered, washed with pentane
(3 ꢀ 1 mL) at -70 °C, redissolved in C6D6, and analyzed by
165.9 (dd, JRhC/2JPC = 62/19 Hz, CNiPr), 138.3 (dd, JPC
/
RhC = 47.8/1.9 Hz, Ar), 134.0 (s, Ar), 133.7 (d, JPC = 1.3 Hz,
1
J
Ar), 133.6 (d, JPC = 1.3 Hz, Ar), 132.4 (d, JPC = 2.0 Hz, Ar),
128.9 (d, JPC = 2.2 Hz, Ar), 120.5 (d, JPC = 48.9 Hz, Ar), 111.3
(d, JPC = 7.5 Hz, Ar), 109.1 (d, JPC = 14.1 Hz, Ar), 59.9 (s,
N(CH2)2N), 51.9 (s, NCH2CH3), 47.8 (s, N(CH2)2N), 47.1 (s,
1
NMR spectroscopy. H NMR (300 MHz, C6D6): δ 7.85-8.02
CH2(CH3)2), 24.3 (s, CH2(CH3)2) 12.5 ppm (s, NCH2CH3). 31
P
(m, 6H, ArH), 7.30 (m, 1H, ArH), 7.01-7.22 (m, 7H, ArH), 6.95
(m, 1H, ArH), 6.87 (m, 1H, ArH), 6.54 (m, 2H, ArH), 3.06 (s,
6H, NCH3), 3.01 (sep, 3JHH = 6.6 Hz, CH(CH3)2), 0.72 ppm (d,
2JHH = 6.0 Hz, CH(CH3)2). 13C NMR (126 MHz, C6D6): δ
161.6 (dd, 1JRhC/2JPC = 63/20 Hz, CNiPr), 161.1 (d, JPC = 26.6
Hz, Ar), 151.5 (s, Ar), 146.8 (s, Ar), 137.2 (d, JPC = 46.2 Hz, Ar),
133.6 (d, JPC = 12.7 Hz, Ar), 131.2 (s, Ar), 129.2 (s, Ar), 126.9
NMR (121 MHz, C6D6): δ 58.6 ppm (d, 1JRhP = 183.2 Hz). IR
(C6D6): νCN 2026 (m), 2066 (m).
[Rh(L3)(CNiPr)2] (X11). CNiPr (3.8 μL, 40 μmol) was added
to a solution of X3 (11.8 mg, 20.0 μmol) in toluene-d8 (0.7 mL).
The resulting mixture was analyzed by NMR spectroscopy. 1H
NMR (500 MHz, toluene-d8, -45 °C): δ 7.94 (m, 3H ArH), 7.38
(m, 1H ArH), 7.24 (m, 1H ArH), 6.95-7.17 (m, 8H ArH), 6.48

510 Organometallics, Vol. 30, No. 3, 2011
Lindner et al.
(m, 1H, ArH), 5.70 (m, 2H, COE CH), 4.27 (m, 2H, N(CH2)N),
2.95 (m, 2H, N(CH2)N), 2.90 (m, 1H, CH(CH3)2), 2.59 (m, 4H,
NCH2CH3), 2.09 (m, 4H, COE CH2), 1.44 (m, 8H, COE CH2),
1.04 (m, 6H, NCH2CH3), 0.80 (br, 6H, CH(CH3)2), 0.62 ppm
(m, 6H, CH(CH3)2). 31P NMR (121 MHz, toluene-d8, -45 °C):
δ 58.3 ppm (d, 1JRhP = 183.2 Hz).
DFT Geometry Optimizations. DFT calculations of com-
pounds were carried out by the Gaussian03 program package52
using the BP86 functional.53 The 6-311G(d,p)54 basis set as
implemented in Gaussian03 was employed for C, H, N, O,
and P atoms, while the relativistic pseudopotentials of the Ahlrichs
group and related basis functions of TZVPP quality55 were
employed for Rh and Ir atoms. All systems were fully optimized
without any symmetry restrictions. The resulting geometries were
characterized as equilibrium structures and transition states, re-
spectively, by the analysis of the force constants of normal vibra-
tions.
temperature of 150(2) K. Intensity integration was performed
with EvalCCD.56 SADABS57 was used for absorption correc-
tion and scaling based on multiple measured reflections
(0.49-0.75 correction range). A total of 6622 reflections were
unique (Rint = 0.021), of which 6247 were observed [I > 2σ(I)].
The structure was solved with direct methods using the program
SHELXS-97.58 The structure was also refined with SHELXL-97
against F2 of all reflections. Non-hydrogen atoms were refined
with anisotropic displacement parameters. All hydrogen atoms
were located in difference Fourier maps. The C-H hydrogen
atoms of the coordinated double bond were refined freely with
isotropic displacement parameters; all other hydrogen atoms
were refined with a riding model. A total of 335 parameters were
refined with no restraints. R1/wR2 [I > 2σ(I)]: 0.0129/0.0290.
R1/wR2 [all reflns]: 0.0152/0.0297. S = 1.028. Residual electron
density between -0.54 and 0.69 e/A3. Geometry calculations
and checking for higher symmetry was performed with the
PLATON program.59 CCDC 779570 contains the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
X-ray Crystal Structure Determination of X4. C32H42IrN2P,
fw = 677.85, orange-yellow block, 0.45 ꢀ 0.25 ꢀ 0.10 mm,
triclinic, P1 (no. 2), a = 10.50720(2) A, b = 10.6841(2) A, c =
13.3462(2) A, R = 102.812(2)°, β = 97.385(1)°, γ = 93.308(1)°,
V = 1443.06(4) A3, Z = 2, Dx = 1.560 g/cm3, μ = 4.70 mm-1
;
33 596 reflections were measured on a Nonius KappaCCD
diffractometer with rotating anode (graphite monochromator,
λ = 0.71073 A) up to a resolution of (sin θ/λ)max = 0.65 A-1 at a
Acknowledgment. This research is financially sup-
ported by The Netherlands’ Council for Scientific Re-
search-Chemical Sciences (NWO-CW), through a
VENI Innovative Research Grant (to J.I.v.d.V.), with
additional funding from the University of Amsterdam
and the EU-FP7 COST network PhoSciNet. We thank
Dr. Bas de Bruin for helpful advice with DFT calculations
and Dr. Guillaume Berthon-Gelloz for useful synthetic
tips and tricks. This paper is dedicated to Prof. Thomas B.
Rauchfuss (Univ. Illinois at Urbana-Champaign) on the
occasion of his 60th birthday.
(52) Calculations were performed using Gaussian software at the
BP86/6-311G(d,p) level: Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.;
Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.;
Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.;
Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross,
J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
zewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; M. A. Al-Laham, Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.04; Gaussian, Inc.:
Wallingford, CT, 2004.
Note Added after ASAP Publication. This paper was pub-
lished on the Web on Jan 12, 2011, with errors in Scheme 2 and
the second paragraph of the Experimental Section. The cor-
rected version was reposted on Jan 20, 2011. Additional changes
were made to Scheme 2 and reposted on Feb 7, 2011.
Supporting Information Available: Crystallographic informa-
tion file (CIF) of complex X4, [Ir(κ3-P,N,N0-L3)(COE)], further
experimental details, and DFT computational details. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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