Rh and Ir β-Diiminate Complexes of Boranes, Silanes, Germanes, and Stannanes

Article abstract of DOI:10.1021/acs.organomet.7b00469

Reported here are several new adducts of the type (^RBDI)M(HE)₂ where ^RBDI is the β-diiminate ligand [2,6-R₂C₆H₃N? - ?CMe]₂CH (R = Me, Et, MeO; M = Rh, Ir; HE = HSiEt₃, HGeEt₃, HSnⁿBu₃, HBPin). DFT calculations are used to analyze the bonding in these and related Cp? complexes, in particular with respect to the degree of oxidative addition (OA) of the H-E bonds: this increases in the order H₂ < HBPin < HSiEt₃ a‰ HGeEt₃ a‰ HSnⁿBu₃, it proceeds further for Ir than for Rh, and Cp? promotes OA to a larger degree in comparison to the BDI ligand. The first metal-HE dissociation energy is rather sensitive to steric effects and increases in the order CH₄ a‰ H₂ a‰ HBPin a‰ HSiMe₃ a‰ HGeMe₃ < HSnMe₃, with Ir uniformly binding HE more strongly than Rh by about 10 kcal/mol. M-HE dissociation is the first step of the intramolecular ligand functionalization first reported for (^MeBDI)Rh(HSiEt₃)₂. Such functionalization was not observed for any of the new complexes reported here. On the basis of the idea that stannane dissociation might be prohibitive, we obtained evidence that it is possible to effect such functionalization via generation of a stannane within the coordination sphere of the metal: treatment of (^MeBDI)Rh(COE)(N₂) with SnMe₄ and H₂ produced a mixture of (^MeBDI)Rh(HSnMe₃)₂ and its functionalized derivative (^MeBDIa§SnHMe₂)Rh(HSnMe₃) via Sn-C cleavage.

Full text of DOI:10.1021/acs.organomet.7b00469

Article
Cite This: Organometallics XXXX, XXX, XXX-XXX pubs.acs.org/Organometallics
Rh and Ir β‑Diiminate Complexes of Boranes, Silanes, Germanes, and
Stannanes
Nan Zhang,† Rebecca S. Sherbo,†,∥ Gurmeet Singh Bindra,†,⊥ Di Zhu,†,‡ and Peter H. M. Budzelaar*,†,§
†Department of Chemistry, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada
‡State Key Laboratory of Heavy Oil Processing, College of Science, China University of Petroleum, Beijing 102249, People’s Republic
of China
§Department of Chemical Sciences, Federico II University of Naples, Via Cintia, Complesso di Monte S. Angelo, 80126 Napoli, Italy
S
* Supporting Information
ABSTRACT: Reported here are several new adducts of the
type (RBDI)M(HE)2 where RBDI is the β-diiminate ligand
[2,6-R2C6H3NCMe]2CH (R = Me, Et, MeO; M = Rh, Ir;
HE = HSiEt3, HGeEt3, HSnnBu3, HBPin). DFT calculations
are used to analyze the bonding in these and related Cp*
complexes, in particular with respect to the degree of oxidative
addition (OA) of the H−E bonds: this increases in the order
H2 < HBPin < HSiEt3 ≈ HGeEt3 ≈ HSnnBu3, it proceeds
further for Ir than for Rh, and Cp* promotes OA to a larger
degree in comparison to the BDI ligand. The first metal−HE
dissociation energy is rather sensitive to steric effects and increases in the order CH4 ≪ H2 ≈ HBPin ≈ HSiMe3 ≈ HGeMe3 <
HSnMe3, with Ir uniformly binding HE more strongly than Rh by about 10 kcal/mol. M−HE dissociation is the first step of the
intramolecular ligand functionalization first reported for (MeBDI)Rh(HSiEt3)2. Such functionalization was not observed for any of
the new complexes reported here. On the basis of the idea that stannane dissociation might be prohibitive, we obtained evidence
that it is possible to effect such functionalization via generation of a stannane within the coordination sphere of the metal:
treatment of (MeBDI)Rh(COE)(N2) with SnMe4 and H2 produced a mixture of (MeBDI)Rh(HSnMe3)2 and its functionalized
derivative (MeBDI∧SnHMe2)Rh(HSnMe3) via Sn−C cleavage.
Chart 1. Extreme Interpretations of Cp*M(HE)2 and
(BDI)M(HE)2 structures
INTRODUCTION
■
Oxidative addition of C−H and X−H bonds ranks among the
most important elementary steps in organometallic catalysis.
The reaction requires a coordinatively unsaturated metal center
in a low oxidation state. Since coordinative unsaturation is often
associated with high reactivity, well-characterized examples of
X−H addition often involve bulky ligands that shield the metal
center from various unwanted side reactions.
Cp*Rh and Cp*Ir fragments (often generated in situ) are
very effective in activating even unreactive C−H bonds.1−4 The
Cp* ligand stabilizes high oxidation states, and examples of
formally MV complexes (Chart 1, structural type B) such as
Cp*IrH45 and Cp*RhH2(SiEt3)26 have been reported. There is
always some ambiguity about the “actual” oxidation state7 of
the metal atom in such complexes, since they can also be
viewed as MI σ complexes (Chart 1, structural type A) or
perhaps some intermediate structure. Presumably the locations
of the hydrogen atoms could distinguish between these
alternatives, but the problems associated with accurately
locating H atom positions near heavy atoms in X-ray structure
determinations mean that uncertainty remains.
computational (DFT) methods. As early as 1984, Fernandez et
al. reported the synthesis of Cp*Rh(HSiEt3)2 and its full
characterization (including neutron diffraction),6 leading to
identification as a dihydride (RhV) species. Values for JRhH (37
Hz) and JSiH (8 Hz) were reported. The structure of the
isomorphous Ir analogue was reported shortly thereafter8−10
(no JSiH value reported). A few years later Duckett and co-
workers generated CpRh(HSiEt3)2 and concluded, in part on
Because of this ambiguity, bonding in Cp*M(HE)2
complexes (M = Rh, Ir; HE = silane, germane, stannane,
borane) has been studied by several groups, using both
experimental (NMR, X-ray and neutron diffraction, IR) and
Received: June 20, 2017
© XXXX American Chemical Society
A
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the basis of a sizable JRhH value of 38 Hz and a small JSiH value
of 7 Hz, that a dihydride structure was more plausible than the
σ-silane alternative.11 They then prepared several CpRhH-
(SiR3)3 complexes and described these as containing RhV but
also having some η2-silane character, on the basis of
substantially larger Si−H coupling constants (>20 Hz).12
This JSiH criterion (20−70 Hz indicating residual interactions13)
) has been cited frequently, but recently Scherer et al. argued
that interpretation of these coupling constants may not always
be straightforward since near the oxidative-addition range of the
reaction trajectory the observed J value is the sum of a negative
They concluded that the dominant description is that of an
oxidative-addition product, but with significant residual H−Z
interactions. For the more electropositive Zn and Mg
fragments, the negative charge on Rh becomes significant and
a dihydridorhodate limiting structure contributes.
The β-diiminate (BDI) ligand (Chart 2) has proven to be
very effective in stabilizing low-coordinate metal environments
R
Chart 2. The Basic BDI Ligand and Other Specific Ligand
Variations Mentioned in the Text
1JSiH and a positive JSiH contribution that nearly cancel.14
2
Vyboishchikov and Nikonov performed a careful DFT analysis
of the above CpRh bis(silyl) and tris(silyl) complexes15 and
concluded that there are weak residual Si−H interactions,
implying that a description as RhV is not completely correct
(though presumably better than RhI or RhIII alternatives). They
also emphasized that the energy surface for stretching or
compressing the Si−H “bonds” is extremely flat so that a
particular observed geometry does not tell the whole story. In
an experimental study on related Cp*Rh(PMe3)(silane)+
complexes, Taw et al. noted formation of σ-silane derivatives16
in cases where the analogous Ir complex tends toward full
oxidative addition,17 and this seems to be a rather general
feature.
In any case, it seems to be generally accepted that
Cp*M(HSiR3)2/CpM(HSiR3)2 complexes are best regarded
as having MV (with some residual Si−H interaction) but the
situation is somewhat less clear for analogous complexes of
boranes, germanes, and stannanes. Cook et al. have reported
the formation of Cp*Rh(HBPin)(HSiEt3) and concluded on
the basis of an X-ray structure and DFT studies18 that the
bonding is more ambiguous than in Cp*Rh(HSiEt3)2, featuring
one relatively short B−H contact (X-ray, 1.745 Å; DFT, 1.970
Å). The somewhat broadened hydride signal (12 Hz, narrowing
to 8 Hz on 11B decoupling; JRhH = 42 Hz) was also taken as
evidence for some degree of B−H interaction. Nevertheless, the
structure is probably closer to an RhV(H)(boryl) complex than
to a RhIII(σ-borane) species. Soon after, the group of Hartwig
also reported the synthesis and characterization of Cp*Rh-
(HBPin)2 and Cp*RhH(BPin)3 and concluded that these have
some σ-borane character, on the basis of X-ray structures and of
broadened hydride signals (40 and 32 Hz)19 (in contrast, the
hydride signal of Cp*Ir(HBPin)2 is sharp1). DFT studies
confirmed the presence of short B−H contacts but also
revealed that these contacts can be stretched or compressed
with very low energetic cost: the calculated free energy barrier
for switching B−H contacts is only 0.8 kcal/mol.
and in allowing isolation and characterization of species that
with other ligands would be reactive intermediates.23 We24 and
others25 have noted that there are certain parallels between the
chemistry of Cp* and BDI ligands, in particular in combination
with the group 9 metals Rh and Ir. In a mini-review,26 we
concluded that there are significant similarities but that Cp* is
decidedly a more strongly donating ligand.
We recently reported the formation of (MeBDI)Rh(HSiEt3)2
(1) and its further rearrangement to the complex
(MeBDI∧SiHEt2)Rh(HSiEt3) (1′) involving Si−C cleavage
and ligand functionalization (Scheme 1).27 Extension to an
Scheme 1. Intramolecular Ligand Functionalization of
(MeBDI)Rh(HSiEt3)2 (1) to 1′
intermolecular, catalytic version would be of obvious interest.
Transition-metal-catalyzed silylation and subsequent function-
alization of even unactivated C−H bonds has become a useful
tool in organic transformations, mainly due to work by the
group of Hartwig, using Rh and Ir catalysis.28,29 The field is
dominated by arene C−H activation, but a recent report
demonstrates that also unactivated C(sp3)−H bonds can be
selectively functionalized.30
The functionalization of 1 was proposed to start with
dissociation of one HE (silane/germane) unit from the
complex, followed by a cascade of bond-breaking and -forming
steps. In view of this, the ease of HE dissociation from
(BDI)Rh(HE)2 is expected to be important. In the present
paper, we report several new (RBDI)M(HE)2 complexes (HE =
HSiEt3, HGeEt3, HSnnBu3, HBPin). Structure and bonding in
Cp*M(HE)2 and (RBDI)M(HE)2 are analyzed and compared
on the basis of crystal structures and DFT calculations, focusing
on the position of various LM(HE)2 complexes between the
extremes of pure σ complex and full oxidative addition (Chart
1). Trends in HE dissociation energies are explored as a
function of metal, ligand, and substrate variation. While no
Very few Cp*M stannane complexes have been reported.
The X-ray structure of Cp*IrH3SnPh3 shows a four-legged
piano-stool geometry (shortest Sn−H contact 2.42 Å);20 the
1H NMR spectrum showed separate trans and cis hydride
signals at low temperature, which coalesced on warming to a
single resonance with average JSnH value of 28 Hz
(Cp*IrH3SnMe3 behaved similarly). Both the reported piano-
stool geometry and the relatively small JSnH value indicate a
mostly IrV structure; for comparison, (C5H4Me)Mn-
(CO)2(HSnPh3) has been assigned a σ-stannane structure on
the basis of the short Sn−H distance of 2.16 Å (X-ray) and a
large JSnH value of 270 Hz.21
Recently, the group of Crimmin reported on the synthesis,
characterization, and DFT studies of Cp*Rh(HSiEt3)(HZ)
complexes where Z = (MeBDI)AlH, (MeBDI)Zn, (MeBDI)Mg.22
B
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rearrangement analogous to that in Scheme 1 was observed
starting with isolated stannane complexes, we report evidence
that a stannane-functionalized BDI ligand can be generated by
treating (MeBDI)Rh(COE)(N2) with SnMe4 and H2, presum-
ably via formation of HSnMe3 within the coordination sphere
of the metal.
dominant decomposition product is in most cases free
(RBDI)H; for Ir complexes, a black precipitate of metallic Ir
was frequently observed. We have not been able to identify any
Rh- or Ir-containing decomposition products, although for 8
high-field triplets (∼−20 ppm in 1H NMR) are highly
suggestive of formation of dinuclear hydrides similar to
complexes reported by the group of Tilley.32
NMR Spectroscopic Characterization. Bis(HE) com-
plexes 1-11 show effective C2v symmetry in solution, with two
equivalent E groups and two equivalent hydrides. The mixed
complexes 12 and 13 appear Cs symmetric, with a single
hydride (2H) signal but inequivalent “top” and “bottom” sides
of the BDI ligand. The most characteristic and informative
signals are the hydride resonances, which are found between
−13.6 and −15.6 ppm for Rh or around −16.5 ppm for Ir. All
Rh complexes show well-defined Rh−H coupling constants
with magnitudes that seem to depend mostly on the nature of
E, decreasing in the order BPin (∼25 Hz) > SiEt3 (∼21 Hz) >
GeEt3 (15 Hz) > SnnBu3 (∼12 Hz); these are a bit smaller than
those observed for the corresponding Cp* complexes (vide
supra).
RESULTS AND DISCUSSION
■
New Complexes. In the present work we systematically
examine the complexation of (RBDI)M fragments (R = Me, Et,
MeO; M = Rh, Ir) with HE compounds HSiEt3, HGeEt3,
HSnnBu3, and HBPin. The complexes studied are given in
Chart 3. The synthesis and X-ray structures of 1 and 1′ have
Chart 3. (RBDI)M(HE)2 Complexes Studied Experimentally
The observation of clear Rh couplings on sharp (except for 8
and 12) hydride resonances rules out dissociation of HE on the
NMR time scale, although the synthesis of 13 via
comproportionation proves that HE dissociation does happen
at a longer time scale. This is similar to the behavior of
(PyPyr)Rh(HSiRPh2)2 (R = Ph, tBu), where silane dissociation
is slow on the NMR time scale and rate-limiting for silane
exchange with HSiEt3.32
For Rh-silane complexes 2, 3, and 12, JSiH values could be
determined from 29Si satellites as being 9, 10, and 8 Hz,
respectively; for Ir silane complexes 9−11 no 29Si satellites
could be resolved, indicating |JSiH| < 3 Hz.33 These small JSiH
values firmly place the silane complexes in the “mostly classical”
category. However, in view of work by Scherer et al.14 the
smaller JSiH observed for Ir than for Rh complexes does not
necessarily mean that oxidative addition has progressed further
for Ir than for Rh.
HBPin complexes 8 and 12 show some broadening of the
hydride signals (33 and 14 Hz, respectively) likely due to
residual coupling to B, which suggests a degree of direct B−H
interaction (cf. 40 Hz for Cp*Rh(HBPin)219). 119Sn/117Sn
satellites were observed for the hydride signals of 6, 7, and 12
(22, 23, and 24 Hz, respectively). These couplings are much
smaller than direct 1JSnH couplings,34 indicating structures close
to the oxidative-addition extreme.
X-ray Structure Determinations. The structures of
complexes 2, 3, 5, and 7−13 have been determined by X-ray
diffraction. In all cases, hydrogens were located and refined at
expected hydride positions but the usual caveat about H atoms
near heavy atoms applies. Stick drawings of representative
examples (5, 7, 10, and 13) emphasizing the metal
coordination environment are shown in Figure 1; thermal
ellipsoid plots for all structures, showing the adopted
numbering schemes and important bond lengths and angles,
are included in the Supporting Information.
The molecular shapes can be described as a roughly
tetrahedral N2E2M environment with hydrides each capping a
NE2 face, similar to the case for Rh and Ir complexes
(PyPyr)M(HSiRPh2)2.32 An alternative, which we prefer
because it facilitates comparison with Cp* complexes, is to
look at the BDI ligand as occupying a single position at the
bisector of the NMN angle: this leads to a description as a four-
been reported in earlier work.27 Several related complexes were
mentioned in that communication, including 2−5, but these
1
were only characterized by H NMR spectroscopy. Since then,
Meier et al.31 reported the formation of (F-BDI)Rh(HSiMe3)2
from (F-BDI)Rh(CO)(NCMe) and excess HSiMe3; the
complex was not structurally characterized, but DFT studies
produced a structure roughly similar to complex 1. Relevant in
this context is also the structure of (iPrBDI)IrH4 reported in
2004.25
Complexes 3, 5, and 7 were prepared by generating
(
MeOBDI)Rh(COE) in situ and reacting it with a stoichiometric
amount (5) or excess (3, 7) of HE. Attempts to prepare 6 in a
similar manner always resulted in mixtures of the desired
product, the free ligand (MeBDI)H, and unidentified impurities.
For the synthesis of 8, which is not very stable, it proved
beneficial to use isolated (MeBDI)Rh(COE). The three Ir
complexes 9−11 were obtained by reacting [Ir(COE)2Cl]2 first
with an excess of HSiEt3 and then with 1 equiv of (RBDI)Li.
Efforts to prepare (EtBDI)Rh(HSnnBu3)2 failed, as did
attempted syntheses of HBPin complexes other than 8 or Ir
complexes with HE other than HSiEt3. In all of these reactions
we observed the formation of (RBDI)H but could not identify
any organometallic products. Two examples of mixed HE/HE′
complexes were isolated: complex 12 was obtained by
sequentially adding 2.2 equiv of HSiEt3 and 1 equiv of
HSnnBu3 to a solution of (MeBDI)Rh(COE), while complex 13
was easily obtained via comproportionation of 1 and 8. All
compounds are air-sensitive and most decompose slowly in
solution (8 within 1 day); they are stable in the solid state,
under inert atmosphere, at −35 °C. None of the new
complexes show clean rearrangement to a ligand-functionalized
complex analogous to the transformation of 1 to 1′. The
C
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deformations away from this idealized geometry. The first one
(“T”) has the axis of the piano stool tilted out of the NMN
plane, so that one E group ends up in a roughly apical position
(relative to the BDI plane) while the second E group occupies
an equatorial position (Figure 2). The resulting structure has
Figure 2. Schematic representation of T type deformation from
idealized C2v structures of (BDI)M(HE)2, quantified by angle Δϕ = |
ϕ1 − ϕ2|.
approximate Cs symmetry, with the mirror plane passing
through the metal and the two E heteroatoms. The structures
of 10 (Figure 1) and one of the two independent molecules of
13 (Figure 1, 13A) illustrate this deformation; it can be
quantified as the difference Δϕ between the two QME angles,
where Q is the midpoint of the BDI N−N vector (0° = no
deformation).
The second deformation (“R”) is a rotation of the piano
stool E2H2M unit around its axis, relative to the BDI ligand
(Figure 3), as clearly seen in the structure of 5 (Figure 1). In
terms of heavy atoms only, this can be quantified as the angle χ
between the NMN and EME planes (90° = no deformation).
Figure 3. Schematic representation of R type deformation from
idealized C2v structures of (BDI)M(HE)2, quantified by angle χ
between NMN and EME planes.
The relevant quantities are given in Table 1. Inspection
shows that the more hindered MeBDI and EtBDI complexes
mostly show a T type deformation (1, 2, 9, 10, 12: Δϕ = 13−
19°, χ = 86−90°), whereas with the less bulky MeOBDI ligand
the R type deformation is more prevalent (3, 5, 8, 11: Δϕ < 3°,
χ = 67−75°). The calculated geometry reported for (F-
31
BDI)Rh(HSiMe3)2 also fits in the latter category. The
somewhat atypical stannane complex 7 shows both types of
deformation (Δϕ = 16°, χ = 75°). Interestingly, in mixed
borane/silane complex 13 one of the two independent
molecules shows a pure T type deformation (Δϕ = 13°, χ =
90°), while the other shows less of the T type but instead a
significant R deformation (Δϕ = 8°, χ = 71°), suggesting that
both deformations are comparatively easy. The fact that
solution NMR spectra suggest higher symmetry (C2v for 1-
11, Cs for 12 and 13) proves that both distortions are easily
reversible (Figure 4).
It seems likely that the preference of the bulky E groups for
“up” and “down” positions is mainly steric. The ligand aryl
“arms” strongly limit space within the plane of the (BDI)M
fragment. In complex (iPrBDI)IrH4,25 containing the smallest
possible E groups, rotation of the piano stool bottom has
proceeded over ∼45°, all the way toward the alternative C2v
geometry:
Figure 1. X-ray structures of 5, 7, 10, and 13 (for full labeling schemes
see the Supporting Information). All hydrogens except hydrides are
omitted for clarity. For each structure, two projections are shown that
emphasize T and R deformations: the left view looks up the piano
stool (N−N vector horizontal), and the right view is along the N−N
vector. 13A,B are the two independent molecules in the unit cell of 13;
for 5, only one of three independent molecules is shown.
legged piano stool. In either picture, the idealized geometry has
the C2v symmetry suggested by the solution NMR data. The
structures actually observed exhibit two types of significant
D
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over a range of 95−112°; for complexes with the same HE
substrate the E−M−E angle is 5−10° smaller for (BDI)M-
(HE)2 than for Cp*M(HE)2. The trend in H−M−H angles is
less clear but this may be due to the large uncertainty in H
atom positions. In any case, the E−M−E and H−M−H angles
agree much better with the piano-stool interpretation than with
a strongly distorted octahedral coordination (where an E−M−
E angle closer to 180° would be expected).
Structure and Bonding: DFT Results. Cp*M(HE)2 and
(BDI)M(HE)2 complexes were studied by DFT: geometry
optimization with Turbomole, def-TZVP basis, DFT-D3
dispersion corrections, and enthalpy and entropy corrections
to free energies. For both Rh and Ir, a range of HE substrates
was investigated in combination with the ligands Cp* and
MeBDI. For the “benchmark” substrate HSiMe3, a set of 10
ligands was studied. Dissociation free energies of the first and
second HE substrate from the metal are collected in Tables 3
(substrate variation) and 4 (ligand variation).
Table 1. T and R Type Deformations of (BDI)M(HE)2
Complexes
a
T: Δϕ
R: χ
(deg)
complex
ligand
M
E
(deg)
127
2
MeBDI
EtBDI
Rh
Rh
Rh
Rh
Rh
Rh
Ir
Si
Si
Si
17.0
13.5
0.0
88.9
89.5
71.2
69.5
75.1
67.0
87.8
86.7
88.7
89.3
75.3
90.0
71.1
89.8
3
MeOBDI
MeOBDI
MeOBDI
MeBDI
MeBDI
EtBDI
5
Ge
Sn
B
0.0
7
15.9
2.4
8
9
Si
13.9
19.2
18.2
18.4
0.0
b
10
Ir
Si
11
12
13
MeOBDI
MeBDI
MeBDI
Ir
Si
Rh
Rh
Sn/Si
Si/B
14.9
7.9
c
−13.4
ΔG1
LM(HE)2 ⎯⎯⎯→ LM(HE) + HE
32
32
(PyPyr)Rh(SiPh3)2
(PyPyr)
22.9
22.8
87.2
84.7
ΔG2
LM(HE) ⎯⎯⎯→ LM + HE
32
t
Rh(SiPh2 Bu)2
(PyPyr)Rh(SiPh3)2
17.8
89.1
For most substrates, only a single local minimum was found
for H−E coordination/oxidative addition. H−C bonds behave
atypically, yielding usually separate local minima for σ-complex
and oxidative addition product. In the following we focus on
bonds other than H−C.
a
For the meaning of angles Δϕ and χ see the text and Figures 2 and 3.
b
c
Three independent molecules in unit cell. Two independent
molecules in unit cell.
HE Dissociation Energies. Table 3 summarizes the
variation in M−HE dissociation free energy as a function of
the substrate HE. The calculated ΔG1 value of 30.7 kcal/mol
for Cp*Rh(HSiMe3)2 agrees fairly well with the 28.1 kcal/mol
reported for dissociation of HSiEt3 from Cp*Rh(HSiEt3)2.22
The first HE dissociation energy varies fairly consistently in the
order H2 < HBPin ≈ HSiMe3 ≈ HGeMe3 < HSnMe3. Binding
to Ir is stronger than to Rh by about 10 kcal/mol, and Cp*M
fragments have higher dissociation energies than (MeBDI)M
fragments by 10−15 kcal/mol. The second HE dissociation
energy is larger than the first by 5−25 kcal/mol but shows
roughly similar trends. Oxidative addition of H−C bonds is
much less favorable than of the other H−E bonds, and
dissociation (elimination) of the first H−C bond is consistently
exergonic.
A more fine grained comparison is presented in Table 4,
where binding of HSiMe3 is collected for variously substituted
ligands. For both ΔG1 and ΔG2, the trend is MeBDI ≈ EtBDI >
Me,iPrBDI > iPrBDI ≈ Me,tBuBDI, reflecting increasing steric bulk
of the ligands. Reducing the electron-donating power of the
BDI ligand by introducing CF3 groups at the imine positions
decreases ΔG1 and ΔG2 (relative to MeBDI) by a few kcal/
mol.35 In contrast, strongly increased binding is observed with
MeOBDI and BDI-F. Since electronic effects should work in the
opposite direction, steric factors probably play a role here; this
would be consistent with the observed/calculated structural
deformations mentioned earlier. The strong HE binding to
unsubstituted versions of (PyPyr)M fragments is also likely due
to steric factors.
Figure 4. Reversibility of T and R deformations leading to effective C2v
symmetry.
Using the same type of analysis, complexes (PyPyr)M-
32
(HSiR3)2 (included in Table 1) are found to exhibit clear T
type deformations (Δϕ = 18−23°). Also in that case, the
observation of equivalent E groups implies easy reversibility.
A description as piano-stool complexes allows easy
comparison of the M(HE)2 fragments between Cp* and BDI
complexes. Relevant data are collected in Table 2. The
Cp*M(HE)2 complexes reported to date have more or less
regular four-legged piano-stool geometries, with E−M−E
angles in the range of 100−110° and H−M−H angles
(where determined) somewhat smaller (80−100°). (PyPyr)Ir-
32
(HSiPh3)2 has a somewhat larger SiMSi angle of 116.10(4)°,
presumably because there is little hindrance above and below
the N2Ir plane and/or because HSiPh3 requires more space
than HSiEt3.
Degree of Oxidative Addition. The set of complexes
studied here displays a near-continuous variation between the
extremes of simple σ-complex formation (Chart 1A, formally
MI) and full oxidative addition (Chart 1B, formally MV). HE
bonding was analyzed for MeBDI and Cp* ligands in
combination with Rh and Ir, on the basis of bond distances
19
Like Cp*Rh(HBPin)2 and Cp*Rh(HBPin)(HSiEt3),18
HBPin complexes 8 and 13 show one short B−H contact per
boron atom, while complexes of silanes, germanes, and
stannanes do not have comparably short E−H contacts (after
correction for differences in atomic radii). E−M−E angles vary
E
DOI: 10.1021/acs.organomet.7b00469
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Article
a
Table 2. Piano-Stool Geometries (Å and deg) for Cp*M(HE)2 and (BDI)M(HE)2 Type Complexes
d
compound
ref
M−E
2.379(2)
M−H
E−H
∠HMH
∠EME
b
Cp*Rh(HSiEt3)2
6
1.581(2)
1.49(3)
1.58(3)
2.212(2)
166(3)
94.84(18)
88(2)
107.90(8)
104.9(1)
102.6(2)
Cp*Rh(HBPin)2
Cp*Rh(HBPin)(HSiEt3)
19
18
2.071(3)
2.038(5) (B)
2.368(2) (Si)
2.390(1)
1.74(4)
2.27(4)
2.272(2)
92(5)
b
Cp*Ir(HSiEt3)2
8
1.594(2)
1.66(2)
99.50(16)
84(2)
109.49(6)
116.10(4)
(PyPyr)Ir(HSiPh3)2
32
2.333(1)
2.26(3)
(
(
(
iPrBDI)IrH4
25
27
27
c
1.47(2)
1.51(2)
1.50(2)
1.38(3)
1.50(3)
1.57(3)
1.47(4)
1.53(2)
1.4(1)
96(2)
96(2)
92(1)
94(2)
93(3)
99(2)
92(3)
94(1)
98(5)
101(1)
103(3)
98(2)
MeBDI)Rh(HSiEt3)2 (1)
MeBDI∧SiHEt2)Rh(HSiEt3) (1′)
2.3511(6)
2.3435(6)
2.352(2)
2.19(2)
1.96(2)
2.1(2)
101.54(2)
111.98(3)
99.68(3)
105.46(6)
104.31(3)
104.89(2)
96.0(1)
(EtBDI)Rh(HSiEt3)2 (2)
(
(
(
(
(
MeOBDI)Rh(HSiEt3)2 (3)
MeOBDI)Rh(HGeEt3)2 5
MeOBDI)Rh(HSnnBu3)2 (7)
MeBDI)Rh(HBPin)2 (8)
MeBDI)Ir(HSiEt3)2 (9)
c
2.353(1)
1.99(3)
2.13(3)
2.27(4)
1.49(2)
2.1(1)
c
2.4308(7)
2.563(1)
c
c
2.061(2)
c
2.359(2)
101.35(7)
102.23(2)
106.84(5)
97.31(3)
(EtBDI)Ir(HSiEt3)2 (10)
c
2.3601(4)
2.357(1)
1.32(1)
1.47(4)
1.57(3)
2.14(1)
2.17(4)
2.06(3)
2.54(3)
1.72(2)
2.11(2)
(
(
MeOBDI)Ir(HSiEt3)2 (11)
MeBDI)Rh(HSiEt3)(HSnnBu3) (12)
c
c
2.356(1) (Si)
2.6005(8) (Sn)
2.035(2) (B)
2.361(2) (Si)
(
MeBDI)Rh(HSiEt3)(HBPin) (13)
c
1.48(2)
96(1)
96.3(1)
a
b
Corresponding bond lengths/angles are averaged; see Table S4 in the Supporting Information for all individual bond lengths/angles. Combined
c
d
X-ray + neutron diffraction structure determination. This work. Average over each E of its shortest E−H contact.
Table 3. First and Second HE Dissociation Free Energies (kcal/mol) from (MeBDI)M(HE)2 and Cp*M(HE)2
(
MeBDI)Rh
(
MeBDI)Ir
Cp*Rh
Cp*Ir
HE
ΔG1
ΔG2
ΔG1
ΔG2
ΔG1
ΔG2
ΔG1
ΔG2
a
a
H2
13.0
15.4
26.9
28.7
28.6
30.3
−2.1
22.2
30.1
26.6
29.3
39.5
−8.0
28.3
39.6
44.6
43.7
42.8
12.2
17.9
26.8
26.9
32.4
34.4
37.7
41.5
14.6
26.9
35.1
38.9
39.8
47.0
−3.7
52.1
56.6
58.5
61.5
63.8
41.3
HBPin
17.2
15.8
19.6
28.2
HSiMe3
HGeMe3
HSnMe3
HMe
30.7
32.7
40.3
b
N/A
−10.0
a
b
These are dihydrogen complexes. Bis-HMe adduct not a local minimum.
Table 4. First and Second HSiMe3 Dissociation Free
Energies (kcal/mol) of (BDI)M(HSiMe3)2 and
Cp*M(HSiMe3)2
M−H WBIs are ∼0.6 while H−E bond indexes are on the order
of 0.1, in good agreement with the values of 0.12−0.21
reported by the Crimmin group for these residual inter-
actions.22 The only exceptions are the HBPin complexes, for
which Hartwig et al. already reported short B−H distances and
significant B−H interactions.19 We obtain a WBI of 0.35 for the
short B−H contacts, with an M−H WBI of 0.44, suggesting a
position close to the middle of the oxidative-addition scale; the
experimental H atom positions18,19 also agree with this picture.
The Ir analogue, however, is predicted to be much closer to full
oxidative addition, with an H−E WBI of only 0.17 and an M−
H WBI of 0.55.
The WBI data indicate a systematic shift toward less
complete oxidative addition on moving from Cp* to MeBDI
complexes: H−E WBIs become larger and M−E and M−H
WBIs become smaller. The trend of less complete addition for
Rh is retained. The most extreme case is (MeBDI)Rh(H2)2,
which is predicted to be a bis(dihydrogen) complex, while both
Cp*RhH4 and (MeBDI)IrH4 are still true tetrahydrides.
(MeBDI)Rh(HBPin)2 is closer to the σ-complex side of the
scale, while (MeBDI)Ir(HBPin)2 is closer to the oxidative-
Rh
Ir
ligand
MeBDI
EtBDI
ΔG1
ΔG2
ΔG1
ΔG2
15.8
15.0
8.5
28.7
30.3
24.2
27.3
23.7
33.7
35.1
25.2
36.5
34.4
26.6
26.5
19.7
24.9
15.7
33.3
32.8
23.9
38.3
38.9
44.6
45.7
40.0
42.8
40.2
50.9
52.9
40.7
53.2
58.5
iPrBDI
Me,iPrBDI
Me,tBuBDI
MeOBDI
F-BDI
13.2
4.2
23.1
22.3
12.4
27.1
30.7
MeBDI-CF3
a
PyPyr
Cp*
a
See ref 32. Calculations were done for a model ligand without Ph
substituents.
(M−E, M−H, and H−E) as well as the corresponding Wiberg
bond indexes (WBIs, Table 5). The Cp* systems are nearly all
best described as MV with mostly complete oxidative addition;
F
DOI: 10.1021/acs.organomet.7b00469
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Article
a
Table 5. Wiberg Bond Indexes for M(HE)2 Cores and Derived OA Values (Eq 1)
Cp*Rh
Cp*Ir
b
b
HE
M−E
M−H
H−E
OA
M−E
M−H
H−E
OA
H2
0.64
0.58
0.52
0.52
0.49
0.68
0.64
0.44
0.57
0.58
0.61
0.61
0.09
0.35
0.12
0.12
0.11
0.10
82
57
74
74
76
79
0.66
0.66
0.58
0.57
0.54
0.69
0.66
0.55
0.60
0.60
0.64
0.65
0.08
0.17
0.10
0.10
0.09
0.08
84
72
77
77
79
83
HBPin
HSiMe3
HGeMe3
HSnMe3
HMe
(
MeBDI)Rh
(
MeBDI)Ir
b
b
HE
M−E
M−H
H−E
OA
M−E
M−H
H−E
OA
H2
0.35
0.54
0.50
0.48
0.46
c
0.35
0.36
0.51
0.51
0.56
0.56
0.47
0.20
0.24
0.17
35
46
66
65
70
0.64
0.70
0.60
0.58
0.53
0.75
0.64
0.51
0.59
0.60
0.63
0.64
0.18
0.25
0.12
0.12
0.12
0.15
75
66
76
76
77
79
HBPin
HSiMe3
HGeMe3
HSnMe3
HMe
(PyPyr)Rh
(PyPyr)Ir
b
b
HE
M−E
M−H
H−E
OA
67
M−E
M−H
H−E
OA
77
HSiMe3
0.50
0.55
0.24
0.61
0.62
0.12
a
b
c
Averaged over C2 symmetry. Largest of H−E and H−E′ values. HMe adduct is not a local minimum.
addition side. As a rough indication of the degree of oxidative
addition we suggest the use of a quantity OA defined by eq 1:
⎛
⎞
WH−E + WH−E′(complex)
OA = 1 −
× 100%
⎜
⎟
⎠
WH−E(free)
⎝
(1)
which is based on the loss of net H−E bonding due to
coordination and oxidative addition; Table 5 includes the
resulting OA values.36 Crabtree et al. have mapped out a path
for oxidative addition of a C−H bond to a metal center on the
basis of relevant X-ray structures.37 Their conclusion was that
the reaction path is highly curved, starting with approach of the
hydrogen atom to the metal center and only involving side-on
interaction at a later stage. This is likely to apply to other E−H
bonds as well;38,39 thus, the OA value we proposed probably
does not represent a linear scale. However, it at least allows us
to put complexes with different supporting ligands and HE
substrates on a common scale. Figure 5 shows calculated core
geometries and individual WBIs for the four HBPin complexes,
which show one of the largest ranges of OA values.
In summary, we conclude that Cp*M(HE)2 and (BDI)M-
(HE)2 complexes show strong analogies. Oxidative addition
progresses further for Cp* than for BDI and more for Ir than
for Rh. With HBPin oxidative addition does not progress as far
as with H−Si, H−Ge, and H−Sn bonds. Sterics play an
important role, as noted earlier by the Tilley group.32
Figure 5. Optimized M(HBPin)2 core geometries for (MeBDI)M-
(HBPin)2 and Cp*M(HBPin)2 complexes: C2-averaged bond lengths
(Å) and Wiberg bond indexes (in blue and italics). Distances marked
with asterisks show significant deviations from C2 symmetry: (*) 1.51/
1.60 Å; (**) 1.89/1.98 Å.
A Stannane-Functionalized Ligand? The path previously
proposed for the rearrangement of 1 to 1′,27 on the basis of
DFT calculations, involves initial dissociation of HSiEt3,
cleaving of one Si−C bond, benzylic ligand C−H activation,
elimination of ethane, formation of a new Si−C bond, and
recapture of previously dissociated HSiEt3.
As mentioned above, we never observed a similar rearrange-
ment of HSnnBu3 complexes. This might be due to the high
dissociation energy of stannanes from (RBDI)M(HSnR3)2
(Table 3). Attempts using substoichiometric amounts of
HSnnBu3 to avoid formation of the bis(stannane) adduct
resulted in incomplete conversion and messy reaction mixtures.
One way to avoid this problem might be to start with organotin
compounds not containing any Sn−H bonds. We observed that
(MeBDI)Rh(COE)(N2) reacts with SnMe4, but the reaction is
not very clean and produces a mixture of as yet unidentified
compounds. However, if the reaction is carried out in the
presence of H2 (with Rh:Sn ≈ 1:4), NMR indicates formation
of a mixture of two complexes (14 and 14′) and free ligand in
the approximate ratio 1:1.2:0.8. So far we have been unable to
separate these, and characterization is thus mostly based on
NMR.40 Both contain two hydrogens bound to Rh. In
compound 14, the hydrogens are equivalent at all temperatures
G
DOI: 10.1021/acs.organomet.7b00469
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studied, and they show equal coupling to the two tin atoms.
The ligand skeleton has effective C2v symmetry, and we believe
the most reasonable assignment for this complex is (MeBDI)-
Rh(HSnMe3)2. Complex 14′ shows two strongly broadened
hydride signals at room temperature which on cooling sharpen
to reveal coupling patterns (Figure 6). On heating the broad
Scheme 2. Calculated Profile for Proposed Mechanism for
Hydride Exchange in 14′: Free Energies (298 K, 1 bar) in
kcal/mol
exchange in CpRhH(silyl)3.15 Our calculated activation
parameters (ΔH⧧ = 17.2 kcal mol−1, ΔS⧧ = 2.8 cal mol−1
K−1) agree very well with those obtained from an Eyring plot
(ΔH⧧ = 18 1 kcal mol−1, ΔS⧧ = 10
3 cal mol−1 K−1),
confirming the intramolecular nature of the process. Calculated
energies and geometries along the exchange path are shown in
Figure S52 in the Supporting Information.
Figure 6. Hydride region of 500 MHz 1H NMR spectra of a mixture of
14 and 14′ in THF-d8.
1
signals broaden even further, while all other H signals remain
Dihydrogen complexes are often characterized by short
T1(min) values,42,43 typically <160 ms at 500 MHz. We
performed temperature-dependent T1 determinations for the
hydride signals of the 14/14′ mixture (for details see the
Supporting Information). All three signals show a slow, smooth
decrease in T1 with temperature (+50 → −50 °C) to
asymptotic values between 700 and 1100 ms, well within the
criterion of >300 ms accepted for regular dihydrides. The
negligible contribution from a dihydrogen complex structure
agrees with the energy profile in Scheme 2, according to which
the expected time fraction spent as a H2 complex is ∼4 × 10−7
at 298 K.
Formation of complexes 14 and 14′ can be rationalized by
assuming the same types of steps invoked earlier for ligand
functionalization, complemented by Sn−C and H−H oxidative
addition. A possible sequence of steps is shown in Scheme 3.
SnMe4 first adds to “(MeBDI)Rh”. Addition of H2 and
elimination of methane lead to (MeBDI)Rh(H)(SnMe3).
From here, a second series of SnMe4 oxidative addition,
methane elimination, and H2 addition produces 14. Alter-
natively, (MeBDI)Rh(H)(SnMe3) could first undergo intra-
molecular ligand functionalization analogous to the 1 → 1′
transformation, followed by the same steps of SnMe4 oxidative
addition, methane elimination, and H2 addition to finally
produce 14′. In agreement with this competition between intra-
and intermolecular reactivity, experiments using a larger excess
of SnMe4 (Rh:Sn ≈ 1:8) produced less 14′ (14:14′:free ligand
≈ 1:0.3:0.4), whereas the use of less SnMe4 led to extensive
decomposition.
sharp. Both hydrides of 14′ couple to Rh, to each other, and to
two tin atoms. The H−H and Rh−H couplings are comparable
to those reported previously for the ligand-functionalized
HSiEt3 complex 1′ (which was not fluxional). The ligand
skeleton does not appear to have any symmetry, and one of the
expected aryl methyl groups is missing, while a tin-bound CH2
group has been formed. Even though a full assignment of all
signals of this compound in the product mixture (see the
Experimental Section and Figures S37 and S38 in the
Supporting Information) is tentative at this point, it seems
plausible that complex 14′ is the ligand-functionalized version
of 14. In support of this, ESI-MS of the mixture in THF (see
Figures S44−S47 in the Supporting Information) shows peaks
corresponding to the ions (M + H)+ expected for 14, 14′, and
free ligand, with the expected isotope patterns, and HR-MS
measurements confirm the proposed compositions of these
ions.
The core geometries of 14 and 14′ could be expected to be
rather similar (cf. the similar cores of 1 and 1′27), except that
any dynamic T or R type deformation in 14 would be frozen
out by the BDI−Sn connection in 14′. The observed JSnH of 41
1
Hz for 14 represents C2v-averaged values. Assuming that JSnH
and 2JSnH have opposite signs,34 the corresponding C2v-averaged
J
SnH value for 14′ is 79 Hz,41 i.e. significantly larger than for 14,
suggesting that the ligand-functionalized complex 14′ has
somewhat higher σ-stannane character, although the calculated
structure and WBI indicate that the dominant description is still
that of a dihydride (see also Figure S48 in the Supporting
Information).
Limits of Steric Hindrance. Steric hindrance appears to be
a key factor in controlling reactivity with HE substrates. To
explore the limits of steric hindrance, we tested the reaction of
(MeBDI)Rh(COE) with 2 equiv of the bulky PPh3 ligand.
Molecular models indicate that two PPh3 ligands would
definitely not fit at Rh in a (RBDI)Rh fragment. The reaction
of (MeBDI)Rh(COE) with PPh3 in THF initially produces a
Calculations indicate the observed fluxionality can be
explained by a dihydride−dihydrogen equilibrium as shown
in Scheme 2. In the rate-limiting step, the hydride closest to the
functionalized ligand arm moves between the tin atoms to the
other hydride, forming the H2 complex; this step bears some
similarity to the H migration path identified by DFT for silyl
H
DOI: 10.1021/acs.organomet.7b00469
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Article
report evidence that it is possible to partially circumvent this
issue and generate a stannane-functionalized BDI ligand by
avoiding the use of free tin hydrides, but forming HSnMe3
within the Rh coordination sphere from SnMe4 and H2.
Scheme 3. Possible Pathways for the Reaction of
a
“(MeBDI)Rh” with SnMe4 and H2 To Give 14 and 14′
EXPERIMENTAL SECTION
■
Syntheses. All syntheses (with the exception of the free MeBDI and
EtBDI ligands) were performed under an inert atmosphere (argon)
with Schlenk techniques or in a nitrogen-filled drybox. Solvents were
distilled from Na/benzophenone. 2,6-Diethylaniline, acetylacetone,
and n-butyllithium (1.6 M in hexanes) were purchased from Sigma-
Aldrich and used as received. [Rh(COE)2Cl]2 was purchased from
Strem Chemicals. [Ir(COE)2Cl]2 was prepared according to a
literature procedure;62 (RBDI)H and (RBDI)Li(THF) (R = MeO,
Me, Et) were prepared according to the literature.63 Syntheses of
complexes 1, 1′, and 3−5 have been reported before.27
Elemental analyses was done by Guelph Chemical laboratories Ltd.
Due to the “oily” nature of the complexes studied, even repeated
crystallization did not always yield a material with perfect analysis. As
a
1
additional evidence of purity, H and 13C NMR spectra of all new
The ligand functionalization sequence labeled A would follow the
same path as the 1 → 1′ transformation.
complexes are provided in the Supporting Information.
ESI-MS spectra were recorded at the Mass Spectrometry Facility of
brownish suspended solid which we have not yet been able to
characterize. Over time (days) this solid converts to a final
product (still suspended) that according to 31P NMR (in
benzene-d6) contains two inequivalent PPh3 ligands bound to
Rh(I). A crystal structure determination showed that the ligand
had tautomerized, forming an allyl moiety η3-bound to Rh (15;
see Scheme 4 and Figure S14 in the Supporting Information).
the University of Alberta (Edmonton, AB, Canada).
All NMR spectra were recorded on Bruker Avance 300 MHz and
Bruker Avance III 500 MHz spectrometers. Spectra were run with
CDCl3, C6D6, C6D5CD3, C4D8O, or C6D12 as indicated and calibrated
with the corresponding reference peaks (1H, δ 7.26, 7.16, 2.08, 3.58,
and 1.72 and 1.44 ppm; 13C, δ 77.16, 128.06, 20.43, 67.21, and 25.31
and 27.58 ppm).64 All chemical shifts are in ppm, and all J couplings
and line widths (fwhm) are in Hz. VT-NMR spectra were simulated
using gNMR.65 The numbering used for the BDI ligand is:
R
Scheme 4. Reaction of (MeBDI)Rh(COE)with PPh3
Synthesis of (EtBDI)Rh(HSiEt3)2 (2). A solution of (EtBDI)Li-
(THF) (100 mg, 0.23 mmol) in THF was added to a solution/
suspension of [Rh(COE)2Cl]2 (81 mg, 0.12 mmol) in THF. All solids
dissolved, producing a dark brown solution. All solvents were
evaporated in vacuo, and the solid was extracted with hexane in a
nitrogen-filled drybox. After removal of solids by centrifugation,
HSiEt3 (79 mg, 0.68 mmol) was added to the hexane solution, which
was stirred for 5 min. Solvents were removed in vacuo, and the residue
A fair number of complexes of C-deprotonated BDI ligands
have been reported,44−61 but to the best of our knowledge this
is the first example where a single metal atom prefers to bind to
the carbon backbone of such a ligand rather than to its nitrogen
atoms. This rearrangement may be an indication of the nature
of decomposition pathways occurring in reactions of (RBDI)-
Rh(COE) with bulky HE substrates or other ligands.
i
was crystallized from Pr2O (+25 to −35 °C), producing a dark green
crystalline solid. The mother liquor was removed, and the solid was
washed with cold hexane and dried, leaving 0.066 g (42%) of 2.
1H NMR (THF-d8, 300 MHz): δ 7.15−7.00 (6H, m, m, p), 5.22
(1H, s, 3), 2.7−2.9 (4H, m, ArCH2), 2.4−2.6 (4H, m, ArCH2), 1.70
(6H, s, 1), 1.24 (12H, t, J 7.6, ArCH2CH3), 0.70 (30H, br s, SiEt),
−14.82 (2H, d, JRh 20.7, JSi 9, RhH). 13C NMR (THF-d8, 75 MHz): δ
160.8, 156.0 (2, i), 136.2 (o), 125.7 (m), 125.3 (p), 99.3 (JRh 1.1, 3),
25.5 (ArCH2), 22.9 (1), 13.4 (ArCH2CH3), 13.0, 9.3 (SiEt). Anal.
Calcd for C37H65N2RhSi2 (697.02): C, 63.76; H, 9.40; N, 4.02. Found:
C, 63.53; H, 9.48; N, 3.87.
CONCLUSIONS
■
A combined experimental and computational study has
revealed strong similarities between Cp*M and (BDI)M
fragments (M = Rh, Ir) in their interaction with H−E
compounds (silanes, germanes, stannanes, boranes) to give
LM(HE)2 complexes. There appears to be for these
compounds a near-continuous scale from mostly σ-complex
type to full oxidative addition. In general, BDI complexes
feature less complete oxidative addition of the H−E bonds to
the metal, and Rh complexes show a lower degree of oxidative
addition than Ir complexes. Cp*Ir shows the strongest bonds to
substrates, while (BDI)Rh shows the weakest bonds. Substrate
binding is rather sensitive to steric effects in both substrate and
BDI ligand. The general trend is H2 < HBPin < silanes ≈
germanes < stannanes.
Synthesis of (MeOBDI)Rh(HSiEt3)2 (3). A solution of (MeOBDI)-
Li(THF) (50 mg, 0.16 mmol) in 0.4 mL of THF was added to a
solution/suspension of [Rh(COE)2Cl]2 (49.2 mg, 0.08 mmol) in THF
(0.5 mL). The mixture was stirred at room temperature for 10 min.
HSiEt3 (37.2 mg, 0.32 mmol) was added, and stirring was continued
for 5 min. Solvents were removed in vacuo, and the residue was
extracted with diethyl ether. Cooling to −35 °C produced a yellow
crystalline solid. The mother liquor was removed, and the solid was
washed with cold hexane and dried, leaving 0.035 g (45%) of 3.
1H NMR (THF-d8, 500 MHz): δ 6.99 (2H, t, J 8.5, p), 6.57 (4H, d,
J 8.5, m), 5.02 (1H, s, 3), 3.75 (12H, s, OMe), 1.65 (6H, s, 1), 0.63−
0.78 (15H, m, Et), −14.67 (2H, d, JRh 21.0, JSi 10, RhH). 13C NMR
The large dissociation energy of stannanes may be a factor
limiting ligand functionalization with this class of substrates. We
I
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(THF-d8, 125 MHz): δ 161.4 (2), 153.6 (o), 138.0 (i), 124.8 (p),
104.2 (m), 98.6 (JRh 1.6, 3), 55.1 (OMe), 23.2 (1), 11.7, 9.3 (Et). Anal.
Calcd for C33H57N2O4RhSi2 (704.90): C, 56.23; H, 8.15; N, 3.97.
Found: C, 55.66; H, 8.17; N, 3.97.
(44%) of 8. The compound decomposes in solution at room
temperature in about 1 day.
1H NMR (cyclohexane-d12, 500 MHz): δ 6.94 (4H, d, J 7.4, m), 6.84
(2H, t, J 7.4, p), 5.15 (1H, s, 3), 2.37 (12H, s, o-Me), 1.72 (6H, s, 1),
1.06 (24H, s, BPin Me), −13.36 (2H, br d (fwhm 33), JRh 25, RhH).
13C NMR (cyclohexane-d12, 125 MHz): δ 160.9, 158.8 (2 and i), 133.4
(o), 129.3 (m), 125.7 (p), 99.5 (JRh 2.5, 3), 84.5 (OC), 26.0 (BPin
Me), 23.9 (1), 21.3 (o-Me). 11B NMR (cyclohexane-d12): δ 33.8. Anal.
Calcd for C33H51B2N2O4Rh (664.30): C, 59.67; H, 7.74; N, 4.22.
Found: C, 59.52; H, 7.77; N, 3.94.
Synthesis of (MeOBDI)Rh(HGeEt3)2 (5). In a N2-filled drybox,
[Rh(COE)2Cl]2 (0.0625 g, 0.174 mmol) was weighed into a small vial
and dissolved in dry THF (3 mL) to form an orange solution.
(
MeOBDI)Li(THF) (0.0780 g, 0.174 mmol) was weighed into another
vial and dissolved in dry THF (3 mL). These two solutions were
combined to form a red solution. This solution was transferred into a
25 mL Schlenk tube, and HGeEt3 (59 μL, 0.348 mmol, 2.0 equiv) was
added. Evolution of gas (N2) was observed. After the mixture was
stirred for 15 min at room temperature, all solvents were evaporated
and the brown solid residue was extracted with 5 mL of Et2O. After
centrifugation, the red solution was layered with 5 mL of hexane and
cooled to −35 °C overnight, producing a crystalline solid. The mother
liquor was pipetted off, and the solids were washed with cold pentane
and dried, leaving 0.052 g (40%) of 5.
Synthesis of (MeBDI)Ir(HSiEt3)2 (9). A solution of (MeBDI)Li-
(THF) (75 mg, 0.24 mmol) in 2 mL of THF was added to a stirred
solution of [Ir(COE)2Cl]2 (84 mg, 0.120 mmol) and excess HSiEt3
(167 mg, 1.44 mmol) in 0.5 mL of diethyl ether. All solvents were
evaporated in vacuo, and the solid was extracted with pentane in a
nitrogen-filled drybox. Solids were removed by centrifugation, and the
pentane solution was cooled to −35 °C. After 3 days, a single large
yellow crystal had formed. The mother liquor was removed, and the
solid was washed with cold hexane and dried, leaving 0.031 g (22%) of
9.
1H NMR (THF-d8, 500 MHz): δ 6.99 (2H, t, J 8.4, p), 6.58 (4H, d,
J 8.4, m), 5.04 (1H, s, 3), 3.75 (12H, s, OMe), 1.67 (6H, s, 1), 0.77−
0.88 (15H, m, Et), −15.02 (2H, d, JRh 14.5, RhH). 13C NMR (THF-d8,
125 MHz): δ 161.0 (2), 153.5 (o), 138.8 (i), 124.6 (p), 104.3 (m),
98.6 (JRh 1.6, 3), 55.2 (OMe), 23.1 (1), 13.3, 10.3 (Et). Anal. Calcd for
C33H57Ge2N2O4Rh (794.00): C, 49.92; H, 7.24; N, 3.53. Found: C,
50.18; H, 7.11; N, 3.68.
1H NMR (THF-d8, 300 MHz): δ 7.06 (4H, d, J 7.3, m), 6.91 (2H, t,
J 7.4, p), 5.54 (1H, s, 3), 2.21 (12H, s, o-Me), 1.74 (6H, s, 1), 0.5−0.8
(30H, m, SiEt), −16.33 (2H, s, JSi not resolved, IrH). 13C NMR (THF-
d8, 75 MHz): δ 160.2, 157.7 (2, i), 131.0 (o), 129.0 (m), 125.6 (p),
102.6 (3), 22.7 (1), 19.9 (o-Me), 13.1, 9.5 (SiEt). Anal. Calcd for
C33H57N2Si2Ir (730.21): C, 54.28; H, 7.87; N, 3.84. Found: C, 54.05;
H, 7.64; N, 3.96.
Attempted Synthesis of (MeBDI)Rh(HSnnBu3)2 (6). A solution
of (MeBDI)Li(THF) (50 mg, 0.16 mmol) in 0.4 mL of THF was added
to a stirred suspension of [Rh(COE)2Cl]2 (49.2 mg, 0.08 mmol) in
THF. After 10 min, HSnnBu3 (140 mg, 0.48 mmol) was added and the
mixture was stirred for another 5 min. After evaporation of the solvent,
1H NMR showed the presence of product 6 and free ligand in an
approximately 4:1 ratio as well as some remaining COE. Purification
attempts failed due to the high and similar solubilities of the various
SnnBu3 compounds. The same reaction executed with a very large
excess of HSnnBu3 produced a mixture containing 6 and free ligand in
a 1:1.2 ratio. Again, attempts at purification failed. 1H NMR spectra for
both reactions are included in the Supporting Information.
1H NMR (benzene-d6, 300 MHz), tentative assignments: δ 6.9−7.1
(m, m, p), 5.23 (1H, s, 3), 2.33 (12H, s, o-Me), −15.03 (2H, d, JRh 11,
JSn 22, RhH).
Synthesis of (EtBDI)Ir(HSiEt3)2 (10). A solution of (EtBDI)Li-
(THF) (75 mg, 0.170 mmol) in 2 mL of THF was added to a stirred
solution of [Ir(COE)2Cl]2 (60 mg, 0.085 mmol) and excess HSiEt3
(60 mg, 0.51 mmol) in 0.4 mL of benzene. All solvents were
i
evaporated in vacuo, and the solid was extracted with Pr2O in a
i
nitrogen-filled drybox. After centrifugation, the Pr2O solution was
cooled to −35 °C, forming a yellow crystalline solid. The mother
liquor was removed, and the solid was washed with cold hexane and
dried, leaving 0.044 g (33%) of 10.
1H NMR (THF-d8, 300 MHz): δ 7.0−7.2 (6H, m, m, p), 5.48 (1H,
s, 3), 2.7−2.9, 2.4−2.6 (4H each, m, ArCH2), 1.76 (6H, s, 1), 1.24
(12H, t, J 7.5, ArCH2CH3), 0.6−0.7 (30H, m, SiEt), −16.48 (2H, s, JSi
not resolved, IrH). 13C NMR (THF-d8, 75 MHz): δ 160.4, 156.5 (2, i),
135.9 (o), 126.0 (p), 125.6 (m), 102.7 (3), 25.2 (ArCH2), 22.9 (1),
13.2 (ArCH2CH3), 13.0, 9.5 (SiEt). Anal. Calcd for C37H65N2Si2Ir
(786.32): C, 56.52; H, 8.33; N, 3.56. Found: C, 56.23; H, 8.09; N,
3.69.
Synthesis of (MeOBDI)Rh(HSnnBu3)2 (7). A solution of (MeOBDI)-
Li(THF) (75 mg, 0.199 mmol) in 0.4 mL of THF was added to stirred
suspension of [Rh(COE)2Cl]2 (62 mg, 0.099 mmol) in THF. After 10
min, HSnnBu3 (121.6 mg, 0.398 mmol) was added. After 5 min more,
the solution was evaporated to dryness. Crystallization from Et2O at
−35 °C took a long time (months) but eventually gave large orange
crystals.
Synthesis of (MeOBDI)Ir(HSiEt3)2 (11). A solution of (MeOBDI)-
Li(THF) (15 mg, 0.040 mmol) in 2 mL of THF was added to a stirred
solution of [Ir(COE)2Cl]2 (14 mg, 0.020 mmol) and excess HSiEt3
(30 mg, 0.24 mmol) in 0.4 mL of benzene. Evaporation of the solvent,
extraction, and crystallization from iPr2O gave a light yellow crystalline
solid.
1H NMR (THF-d8, 500 MHz): δ 6.98 (2H, t, J 8.4, p), 6.59 (4H, d,
J 8.4, m), 5.11 (1H, s, 3), 3.78 (12H, s, OMe), 1.67 (6H, s, 1), 1.15−
1.35 (24H, m, C−CH2-C), 0.86−0.92 (30H, m, SnCH2 and
CH2CH3), −15.34 (2H, d, JRh 12, JSn 23, RhH). 13C NMR (THF-d8,
125 MHz): δ 160.4 (2), 153.1 (o), 140.0 (i), 124.5 (p), 104.6 (m),
99.2 (br, 3), 55.6 (OMe), 30.3 (JSn 18, CH2CH3), 28.4 (JSn 70,
SnCH2CH2), 22.7 (1), 17.1 (JRh 2, SnCH2), 14.0 (CH2CH3). Anal.
Calcd for C45H81N2O4Sn2Rh (1054.46): C, 51.26; H, 7.74; N, 2.66.
Found: C, 51.48; H, 7.88; N, 2.71.
1H NMR (THF-d8, 500 MHz): δ 6.99 (2H, t, J 8.4, p), 6.60 (4H, d,
J 8.4, m), 5.33 (1H, s, 3), 3.74 (12H, s, OMe), 1.70 (6H, s, 1), 0.66
(15H, s, Et), −16.24 (2H, s, JSi not resolved, IrH). 13C NMR (THF-d8,
125 MHz): δ 161.0 (2), 153.3 (o), 138.7 (i), 125.6 (p), 103.9 (m),
101.9 (3), 55.0 (OMe), 23.3 (1), 11.9, 9.3 (Et). Anal. Calcd for
C33H57N2O4Si2Ir (794.21): C, 49.91; H, 7.23; N, 3.53. Found: C,
49.62; H, 7.22; N, 3.39.
Synthesis of (MeBDI)Rh(HBPin)2 (8). In a N2-filled drybox,
[Rh(COE)2Cl]2 (0.20 g, 0.55 mmol) was weighed into a small vial.
Synthesis of (MeBDI)Rh(HSiEt3)(HSnnBu3) (12). A mixture of
(
MeBDI)Li(THF) (0.21 g, 0.55 mmol) was weighed into a 25 mL
(
MeBDI)Rh(COE)(N2) (79 mg, 0.145 mmol) and HSiEt3 (37 mg,
Schlenk tube and dissolved in 10 mL of dry THF. The solution was
added to the [Rh(COE)2Cl]2. After all solids had dissolved, the
resulting dark brown solution was transferred back into the Schlenk
tube. Solvent was evaporated in vacuo, the dark purple solid was
extracted with hexane in a N2-filled drybox, and solids were removed
by centrifugation. A 0.25 mL portion of HBPin (1.67 mmol, 3.0 equiv)
was added. After 5 min of stirring at room temperature, the mixture
was evaporated to dryness. The residue was washed with hexane; the
remaining solid was dissolved in THF/hexane (1/3) and cooled to
−35 °C, producing a yellow crystalline solid. The mother liquor was
removed, and the solid was washed with cold hexane, leaving 0.164 g
0.32 mmol) in hexane was stirred for 10 min at room temperature.
HSnnBu3 (46 mg, 0.16 mmol) was added, and the mixture was stirred
for another 30 min. All solvents were removed in vacuo, and the
residue was extracted with Et2O at −35 °C, yielding a red crystalline
solid. The mother liquor was removed, and the solid was washed with
cold hexane and dried, leaving 0.036 g (31%) of 12.
1H NMR (THF-d8, 300 MHz): δ 7.06, 6.99 (2H each, d, J 7.2, m),
6.90 (2H, t, J 7.4, p), 5.26 (1H, s, 3), 2.41, 2.00 (6H each, s, o-Me),
1.67 (6H, s, 1), 1.10−1.55 (18H, m, CH2CH2CH2), 0.89 (9H, t, J 7.2,
Me(Bu)), 0.3−0.5 (15H, m, Et(Si)), −15.17 (2H, d, JRh 18, JSn 24, JSi 8,
RhH). 13C NMR (THF-d8, 75 MHz): δ 160.3, 157.8 (2, i), 132.0,
J
DOI: 10.1021/acs.organomet.7b00469
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
129.4 (o, o′), 129.1, 128.9 (m, m′), 124.9 (p), 99.3 (JRh 1.8, 3), 30.5,
28.0 (CH2(Bu)), 22.4 (1), 20.4 (o-Me), 19.7 (JRh 2, CH2Sn), 19.5 (o-
Me), 13.7 (Me(Bu)), 12.3 (CH2Si), 8.3 (CH3(Et)). Anal. Calcd for
C39H69N2RhSiSn (816.33): C, 57.43; H, 8.53; N, 3.43. Found: C,
56.63; H, 8.45; N, 3.16.
(1), 19.8 (o-Me), 0.1 (JRh 2, JSn 303, SnMe3); complex 14′, δ 160.4,
159.5, 156.9, 155.6 (2/i), 135.7, 131.4, 129.9 (o), 129.3, 129.0, 127.1,
126.9 (m), 126.0 (o), 124.7, 123.0 (p), 100.0 (JRh 3, 3), 23.5 (SnCH2),
22.4, 21.5 (1), 20.1, 19.0, 18.3 (o-Me), −1.8 (JRh 1, JSn 312, SnMe3),
−0.2 (JRh 2, SnMe2), −2.7 (JRh 3, SnMe2); free (MeBDI)H, δ 161.3,
144.5 (2/i), 132.5 (o), 128.3 (m), 124.9 (p), 94.4 (3), 20.2 (1), 18.4
(o-Me).
Synthesis of (MeBDI)Rh(HSiEt3)(HBPin) (13). In a N2-filled
drybox, complex 1 (0.074 g, 0.11 mmol) was weighed into a small vial
and dissolved in 5 mL of hexane. This hexane solution was placed in a
second vial containing complex 8 (0.076 g, 0.11 mmol). After all of the
solid had dissolved, the resulting clear yellow solution was transferred
into a 25 mL Schlenk tube. The reaction mixture was evaporated to
dryness, and 2 drops of Et2O and 6 drops of hexane were added. The
resulting solution was cooled to −35 °C overnight, but no solid was
obtained. All solvents were evaporated, the residue was dissolved in 3
drops of hexane, and the resulting mixture was cooled to −35 °C. After
4 h, a solid had formed. The mother liquor was pipetted off, and the
residue was washed with a small amount of cold hexane and dried,
giving 0.020 g (27%) of 13.
Synthesis of (iso-MeBDI)Rh(PPh3)2 (15). A solution of (MeBDI)-
Li(THF) (75 mg, 0.194 mmol) in THF was added to a solution/
suspension of [Rh(COE)2Cl]2 (69 mg, 0.097 mmol) in THF. After all
solids had dissolved to give a dark brown solution, the solvent was
evaporated in vacuo and the solid was extracted with hexane in a
nitrogen-filled drybox. After centrifugation, the hexane solution was
added to a solution of PPh3 (102 mg, 0.39 mmol) in hexane. After the
mixture was stirred for 6 days at room temperature, the mother liquor
was removed and the solid was washed with cold hexane and dried,
leaving 0.08 g (44%) of 15.
1H NMR (cyclohexane-d12, 500 MHz): δ 6.97 (4H, d, J 7.5, m), 6.86
(2H, t, J 7.5, p), 5.17 (1H, s, 3), 2.35 and 2.33 (6H each, s, o-Me), 1.74
(6H, s, 1), 1.03 (12H, s, BPin Me), 0.77 (m, 6H, SiCH2), 0.70 (m, 9H,
CH2CH3), −13.59 (2H, br d (fwhm 14), JRh 25.5, RhH). 13C NMR
(cyclohexane-d12, 125 MHz): δ 161.4, 159.0 (2 and i), 134.3, 131.2
(o), 129.7, 129.4 (m), 125.7 (p), 99.5 (JRh 1.6, 3), 84.7 (OC), 26.0
(BPin Me), 24.1 (1), 21.4, 21.0 (o-Me), 12.9, 10.2 (Et). 11B NMR
(cyclohexane-d12,): δ 34.7. Anal. Calcd for C33H54BN2O2RhSi
(652.60): C, 60.73; H, 8.34; N, 4.29. Found: C, 60.59; H, 8.11; N,
4.48.
1H NMR (benzene-d6, 500 MHz): δ 10.23 (1H, s, NH), 7.7 (6H, m,
PPh3 o), 7.5 (6H, m, PPh3 o), 6.8−7.0 (m, PPh3 and Ar m,p), 3.33
(1H, d, J 5.5, 3), 2.78 (3H, s, o-Me), 2.57 (1H, dd, J 7.0, 4.0, 1), 2.42,
2.15 (3H each, s, o-Me), 1.67 (1H, ∼q, J 3.8), 1.49 (3H, s, o-Me), 0.81
(3H, s, 5). 13C NMR (benzene-d6, 125 MHz; assignments tentative): δ
176.4 (4), 150.6 (Ar i), 139.5 (d, JP 24, PPh3 i), 139.2 (d, JP 20, PPh3
i), 139.1 (Ar i), 137.7 (unresolved couplings, 2), 136.2, 135.9 (Ar o),
135.3 (d, JP 14, PPh3 o), 134.3 (d, JP 13, PPh3 o), 128.8 (Ar o?), 128.7
(PPh3 o), 127.7 (d, JP 9, PPh3 m), 127.4 (d, JP 10, PPh3 m), 125.6,
122.5 (Ar p), 56.8 (dd, J 27, 7, 3), 44.6 (ddd, J 29, 9, 3, 1), 22.2 (5),
20.5, 19.4, 19.4, 19.0 (o-Me); remaining resonances obscured by C6D6
signal. 31P NMR (benzene-d6, 121 MHz): δ 51.2 (dd, JRh 214, JP 31),
41.3 (dd, JRh 184, JP 31). Anal. Calcd for C57H56N2P2Rh (933.94): C,
73.31; H, 6.04; N, 3.00. Found: C, 72.99; H, 5.65; N, 2.70.
X-ray Structure Determinations. Crystal fragments were broken
from large pieces of crystalline aggregate and sealed in thin glass
capillaries. Each crystal in its capillary was mounted on a Bruker D8
three-circle diffractometer equipped with a rotating anode generator
(Mo Kα X-radiation), multilayer optics incident beam path, and an
APEX-II CCD detector. Data wee collected at a crystal to detector
distance of 5 cm. Only for compound 9, data were collected on a
Bruker D8 QUEST ECO diffractometer: the crystal was mounted
using a nylon loop under a cold stream of nitrogen (150 K).
Reaction of “(MeBDI)Rh” with SnMe4 and H2 Giving 14/14′. In
a nitrogen-filled drybox, a solution of (MeBDI)Li(THF) (50 mg, 0.160
mmol) in THF was added to a solution/suspension of [Rh-
(COE)2Cl]2 (49 mg, 0.08 mmol) in THF. After the mixture was
stirred for 5 min, all solvent was removed in vacuo and the solid was
extracted with 5 mL of hexane. Solids were removed by centrifugation.
Note: conditions (volume of solvent, volume of Schlenk flask, timing) are
critical for the success of the following reaction!
The hexane solution of (MeBDI)Rh(COE)(N2) was transferred into
a 100 mL Schlenk flask. Me4Sn (115 mg, 0.64 mmol) was added. The
reaction flask was transferred to a hydrogen-filled Schlenk line, and the
contents were stirred. The flask was opened and kept open for 1 min,
letting hydrogen flow through it to replace much of the nitrogen. The
flask was closed again but left connected to the hydrogen Schlenk line
for 4 min more; then the connection to the Schlenk line was closed
and the solution was stirred for 20 h at room temperature. Solvents
were removed in vacuo, leaving a dark brown residue that according to
NMR consisted of a mixture of 14, 14′, and free ligand (MeBDI)H in
the ratio 1:1.20:0.76 on the basis of 1H NMR integration. Attempts to
separate these compounds were unsuccessful. ESI-MS spectra of the
mixture were recorded in positive ion mode through flow injection
with freshly distilled THF; (M + H)+ ions were detected for all three
Semiempirical absorption corrections (SADABS66) were applied
and identical data merged. The unit-cell parameters were obtained by
least-squares refinement on observed reflections with I > 2σ(I).
Structures were solved by direct methods (SHELXS67) and refined by
full-matrix least-squares refinement (SHELXL67). Hydrogens were
placed in calculated positions and refined in riding mode, except that
metal-bound hydrides and the H(N) of complex 15 were freely
refined. For compound 13, there is a clear and severe disorder in the
Et3Si group of Si2. It was controlled using “SADI” to force its three
Si−C and C−C bond lengths to be equal. Attempts to create an
explicit disorder model failed. There may be additionally some minor
disorder in the folding of the BPin five-membered rings. However, the
(BDI)Rh cores of both independent molecules seem to be well-
behaved. More complete details of all individual determinations are
given in Table S1 in the Supporting Information.
Computational Details. All structures were fully optimized at the
TPSSh68/def-TZVP69 level using Turbomole70 in combination with an
external optimizer.71,72 Vibrational analyses showed them to be
minima (no imaginary frequencies) or transition states (exactly one
imaginary frequency, corresponding to the reaction coordinate). These
vibrational analyses were also used to calculate thermal corrections
(enthalpy and entropy) at 298 K and 1 bar; the entropy contribution
was scaled by 0.67 to account for reduced freedom in solution.73,74
Dispersion corrections were calculated using Grimme’s DFT-D3
components. HR-MS: 14, M = C27H46N2Rh120Sn2, (M + H)+
=
741.0766 (obsd), 741.0755 (calcd); 14′, M = C26H42N2Rh120Sn2, (M
+ H)+ = 725.0453 (obsd), 725.0442 (calcd). For more details see
Figures S44−S47 in the Supporting Information.
The same experiment as described above, but using double the
amount of SnMe4 (Rh:Sn = 1:8) produced more 14 but less 14′ and
free ligand (ratio 1:0.3:0.4 from integration of the 1H NMR spectrum).
Tentative NMR assignments for the reaction mixture are as follows.
1H NMR (THF-d8, 300 MHz): complex 14, δ (6.7−7.1 m, p), 5.35
(1H, s, 3), 2.20 (12H, s, o-Me), 1.74 (6H, s, 1), 0.11 (18H, s, JSn 50,
SnMe3), −14.73 (2H, d, JRh 12, JSn 41, RhH); complex 14′, δ (6.7−7.1
m, p), 5.32 (1H, s, 3), 2.39 (1H, d, J 10, SnCH2), 2.34, 2.05, 1.99 (3H
each, s, o-Me), 1.94 (1H, d, J 10, SnCH2), 1.71, 1.66 (3H each, s, 1),
0.56 (3H, s, JSn 49, SnMe2), 0.09 (3H, s, JSn 50, SnMe2), −0.14 (9H, s,
JSn 52, SnMe3), −15.1 (1H, br, RhH), −16.5 (1H, br, RhH) (hydride
signals at 263 K −15.09 (dd, 1H, JH 8, JRh 18, JSn 258 and 49, RhH),
−16.54 (dd, 1H, JH 8, JRh 14, JSn 134 and 29, RhH); free (MeBDI), δ
12.16 (1H, s, NH), (6.7−7.1 m, p), 4.92 (1H, s, 3), 2.14 (12H, s, o-
Me), 1.66 (6H, s, 1). 13C NMR (THF-d8, 75 MHz): complex 14, δ
160.3, 159.1 (2/i), 130.2 (o), 128.8 (m), 124.6 (p), 99.4 (JRh 2, 3), 22.5
K
DOI: 10.1021/acs.organomet.7b00469
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
method75 (“-zero” damping) and were combined with the TZVP
energies and thermal corrections to arrive at the final free energies.
Wiberg bond indices were calculated using Gaussian 0976 and the
TZVP basis set69 (LANL2DZ77−79 on Rh and Ir).
(7) The term “spectroscopic oxidation state” is frequently used.
However, there is no reason the oxidation states deduced from several
spectroscopic techniques would agree with each other or e.g. with X-
ray studies.
(8) Ricci, J. S.; Koetzle, T. F.; Fernandez, M. J.; Maitlis, P. M.; Green,
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00469.
J. C. J. Organomet. Chem. 1986, 299, 383−389.
(9) Fernandez, M. J.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1984,
2063−2066.
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Crystallogr., Sect. A: Found. Crystallogr. 1984, 40, C301−C301.
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Poliakoff, M.; Upmacis, R. K. Organometallics 1988, 7, 1526−1532.
(12) Duckett, S. B.; Perutz, R. N. J. Chem. Soc., Chem. Commun. 1991,
28−31.
■
S
Crystallographic and spectroscopic details and computa-
tional results (PDF)
Cartesian coordinates of optimized structures (XYZ)
(13) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151−187.
(14) Scherer, W.; Meixner, P.; Batke, K.; Barquera-Lozada, J. E.;
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Accession Codes
CCDC 1557256, 1557259−1557262, 1557266, 1557268−
1557269, 1557272−1557276, and 1557279 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*E-mail for P.H.M.B.: p.budzelaar@unina.it.
ORCID
■
(20) Gilbert, T. M.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1985, 107, 3508−3516.
Peter H. M. Budzelaar: 0000-0003-0039-4479
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Present Addresses
∥R.S.S.: Department of Chemistry, The University of British
Columbia, 2036 Main Mall, Vancouver, British ColumbiaV6H
1Z1, Canada.
(22) Ekkert, O.; White, A. J. P.; Toms, H.; Crimmin, M. R. Chem. Sci.
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(23) Budzelaar, P. H. M.; Moonen, N. N. P.; de Gelder, R.; Smits, J.
M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2000, 2000, 753−769.
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Commun. 2004, 764−765.
⊥G.S.B.: Exigence Technologies Inc., 200-135 Innovation
Drive, Winnipeg, Manitoba R3T 6A8, Canada.
Notes
The authors declare no competing financial interest.
(26) Zhu, D.; Budzelaar, P. H. M. Dalton Trans. 2013, 42, 11343−54.
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(33) The alternative possibility of fast dissociation for these Ir
complexes seems improbable, since according to the DFT results Ir
consistently binds its HE ligands more strongly than Rh.
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(35) This change also increases steric hindrance, as the larger CF3
groups result in increased C−N−C angles.
ACKNOWLEDGMENTS
■
This work was supported in part by the National Science and
Engineering Council (NSERC RGPIN-04766) and by the
Science Foundation of China University of Petroleum, Beijing
(No. 2462013YJRC019). We are grateful to Mr. M. Cooper,
Dr. F. Hawthorne, and Dr. D. Herbert for help with X-ray
diffraction measurements.
ABBREVIATIONS
■
BDI, β-diiminate; COE, cyclooctene
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