C-H Bond Activations by Monoanionic, PNP-Supported Scandium Dialkyl Complexes

Article abstract of DOI:10.1021/acs.organomet.5b00213

A series of scandium dialkyl complexes, (PNP)ScR₂ (R = neopentyl, trimethylsilylmethyl), supported by the monoanionic, chelating PNP ligand (2,5-bis(dialkylphosphinomethyl)pyrrolide; alkyl = cyclohexyl, tert-butyl) was synthesized, and the reactivities of these complexes toward simple hydrocarbons was investigated. The scandium-carbon bonds undergo σ-bond metathesis reactions with hydrogen, and these complexes are catalysts for the hydrogenation of alkenes. Reactions with primary amines led to formation of amido complexes that undergo cyclometalation via σ-bond metathesis, without involvement of an imido complex intermediate. A variety of carbon-hydrogen bonds are also activated, including sp-, sp²-, and sp³-C-H bonds (intramolecularly in the latter case).

Full text of DOI:10.1021/acs.organomet.5b00213

Article
pubs.acs.org/Organometallics
C−H Bond Activations by Monoanionic, PNP-Supported Scandium
Dialkyl Complexes
Daniel S. Levine,† T. Don Tilley,* and Richard A. Andersen*,†,‡
,‡
,†,‡
†
Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, United States
‡
Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
*
S Supporting Information
ABSTRACT: A series of scandium dialkyl complexes, (PNP)ScR2
R = neopentyl, trimethylsilylmethyl), supported by the mono-
(
anionic, chelating PNP ligand (2,5-bis(dialkylphosphinomethyl)-
pyrrolide; alkyl = cyclohexyl, tert-butyl) was synthesized, and the
reactivities of these complexes toward simple hydrocarbons was
investigated. The scandium−carbon bonds undergo σ-bond meta-
thesis reactions with hydrogen, and these complexes are catalysts for
the hydrogenation of alkenes. Reactions with primary amines led to
formation of amido complexes that undergo cyclometalation via σ-
bond metathesis, without involvement of an imido complex
intermediate. A variety of carbon−hydrogen bonds are also
2
3
activated, including sp-, sp -, and sp -C−H bonds (intramolecularly
in the latter case).
INTRODUCTION
and strongly donating character. Thus, for this work, a PNP
ligand set was designed to possess these same properties, which
are readily tuned by straightforward synthetic modifications.
Contemporaneous with this study, these same ligands were
■
For the past 30 years, there has been a concerted effort by
synthetic chemists to cleave the C−H bonds of unactivated
hydrocarbons in a selective, catalytic manner.
1
−4
The direct
16
synthesized and explored with late transition metal systems.
functionalization of C−H bonds could lead to new ways to
Polarizable ligands may be key to producing active complexes
produce organic substances, such as polymers, pharmaceuticals,
0
5
−7
for σ-bond metathesis with d metal centers. Computational
and fuels.
One mechanism for C−H activation, mainly
0
8−10
studies indicate that the σ-bond metathesis transition state may
be described as a proton transfer between carbanion- or
hydride-like groups that are stabilized by the electropositive
associated with d metals, is a σ-bond metathesis process.
11,12
Notable advances in this area, by the groups of Watson
and
1
3
Bercaw, demonstrated aliphatic C−H bond activation
17
metal center (see Scheme 1). Ligands with polarizable donor
(
including methane) by permethylscandocene and permethyl-
lanthanocene (Ln = Y, Lu) alkyl complexes. While a number of
related systems have been discovered, few have been
incorporated into a catalytic cycle. Previous work in this
laboratory demonstrated the catalytic hydromethylation of
Scheme 1. σ-Bond Metathesis Reaction
1
4b
14c
alkenes, dehydrocoupling of silanes, and dehydrogenative
14d
+
silation of methane with Cp* ScCH or [CpCp*HfMe] as
2
3
the catalyst. However, these catalytic reactions suffer from long
14
reaction times and low turnover numbers.
The rapid and efficient functionalization of unactivated
substrates such as methane remains one of the great challenges
in chemistry, and the transformations described above indicate
that d complexes offer a potentially viable pathway to achieve
this goal. Notably, productive methane conversion by σ-bond
groups increase the polarizability of the metal center, and this
may stabilize the charge buildup in the transition state and
lower the activation energy for the proton transfer reaction.
Experimental support for the proposition that increasing metal
polarizability promotes σ-bond metathesis may be found by
0
metathesis is exclusively associated with the ancillary Cp* (Cp*
5
=
η -C Me ) ligand set or modifications thereof. Additionally,
5
5
noting the increase in the rate of reactions of Cp* MMe (M =
2
considerable work has focused on various strategies for
development of “non-Cp-based” ligand sets that might promote
15
Special Issue: Gregory Hillhouse Issue
Received: March 13, 2015
comparable or greater σ-bond-metathesis activity. Properties
of the Cp* ligand thought to be relevant to σ-bond metathesis
0
reactivity at a d metal center are its steric bulk, polarizability,
©
XXXX American Chemical Society
A
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Sc, Y, Lu) with methane, in the order Y > Lu > Sc, which
Article
18
Scheme 2. Synthesis of PNP-Supported Scandium
Complexes 1a,b and 2a−c
1
8,19
parallels the polarizability of the free metal atoms.
However, a broader experimental study and theoretical
underpinnings for the role of polarizability in σ-bond
metathesis reactivity are currently lacking. Further studies of
monomeric complexes supported by polarizable ligands are
therefore needed.
Due to their electropositive nature and high Lewis acidity,
the early transition and f-block metals are mainly associated
with ligands possessing nonpolarizable donor atoms (e.g., N,
O). Relatively few complexes of these metals feature softer
donor atoms such as phosphorus, but notable exceptions
20
involve PNP and P2N2 donor sets developed by Fryzuk and
3,21a,b
21c
the PNP ligand employed by Mindiola
and Hou
(
Figure 1). The σ-bond metathesis chemistry of these
Figure 1. Examples of PNP-supported early transition metal or
lanthanide complexes.
complexes has not been extensively explored. In this context,
the results reported here target investigations of scandium alkyl
complexes supported by ligands possessing polarizable donors
(phosphines) and an anionic, anchoring pyrrolide group.
RESULTS AND DISCUSSION
Synthesis of Monanionic, Phosphine-Based Ligands.
The ligands 2,5-bis(dicyclohexylphosphinomethyl)pyrrole
■
Figure 2. Crystal structure of (PNP-Cy)ScNp (2b), with a square
2
(
PNP-CyH) and 2,5-bis(di-tert-butylphosphinomethyl)pyrrole
pyramidal geometry. Hydrogen atoms have been omitted for clarity.
Thermal ellipsoids are set at the 50% probability level. Carbon atoms
are shown in gray, phosphorus in orange, nitrogen in blue, and
scandium in yellow.
t
(
PNP- BuH) were prepared by an adaptation of the method
22
described by Kumar and co-workers. Two equivalents of
t
HPCy2 or HP Bu was added to 2,5-bis(dimethylamino)-
2
pyrrole, and the reaction mixture was heated to 140 °C. The
compound PNP-CyH was readily crystallized in 76% yield from
pentane over 3 days. Subsequent deprotonation with LiN-
2
0,21
bonds.
Complexes 1a,b react readily with alkyllithium
reagents to afford monomeric dialkyl complexes (PNP-
Cy)Sc(CH SiMe ) (2a), (PNP-Cy)ScNp (2b, Figure 2; Np
= −CH CMe ), and (PNP- Bu)ScNp (2c, Figure 4). Complex
2b was also prepared more directly by addition of the
(
SiMe3)2 afforded (PNP-Cy)Li (78% isolated yield). All
2
3 2
2
t
t
attempts to isolate pure PNP- BuH by crystallization or
sublimation were unsuccessful. However, after deprotonation
2
3
2
t
23
with LiN(SiMe ) , pure (PNP- Bu)Li was readily isolated by
protonated ligand (PNP-Cy)H to ScNp (THF) . The
3
2
3
2
washing the resulting solid with pentane in 48% yield over two
steps. This material was protonated with dimethylamine
hydrochloride in THF to afford (PNP- Bu)H after trituration
with pentane to remove LiCl. The protonated ligand is a waxy
solid in pure form, possibly accounting for the difficulty in
crystallization.
cyclohexyl derivatives 2a and 2b crystallize in the same space
group with very similar metrical parameters. Notably, two
crystallographically independent molecules are present in the
unit cell, one of which adopts a distorted trigonal bipyramidal
structure with the phosphine groups occupying the axial
positions, while the other exhibits a square pyramidal
coordination geometry with one alkyl group in the apical
position (Figure 2). The tert-butyl complex 2c crystallizes with
the metal center in a distorted trigonal bipyramidal environ-
ment (Figure 3). Comparison of the Sc−P bond lengths (see
Table 1) in 2b and 2c appears to reflect a higher steric demand
t
Synthesis of Scandium Alkyl Complexes. Salt meta-
thesis reactions of ScCl (THF) with the (PNP-R)Li reagents
3
3
t
yielded [(PNP-Cy)ScCl ] (1a) and (PNP- Bu)ScCl (1b) in
2
2
2
82% and 45% isolated yields, respectively. These complexes
were structurally characterized by X-ray crystallography (see
Figure 3). Complex 1a crystallizes as the chloride-bridged
dimer, while 1b forms a monomeric, distorted square pyramid
with one chloride occupying the apical position. Both structures
feature Sc−P bond lengths of ∼2.76 Å (see Table 1). This bond
length is within the range of those reported for Sc−P
t
for PNP- Bu as compared to PNP-Cy.
Reactions of Scandium Alkyl Complexes with Hydro-
gen. Initial reactivity studies with the dineopentyl complexes
involved examination of their interactions with hydrogen.
Addition of hydrogen (1 atm) to a benzene-d solution of 2b or
6
B
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Table 1. Selected Bond Lengths (Å) for (PNP-R′)ScX
a
Compounds
Sc−X (X = Cl,
compound
Sc−N
Sc(1):
.150(3)
Sc(2):
.133(3)
Sc−P
Sc(1):
2.753(12)
R)
[
(PNP-Cy)ScCl ] (1a)
Sc(1):
2
2
2
2.3661(11) (t)
2.7540(12) 2.5222(11) (μ)
Sc(2): 2.5695(11) (μ)
.7228(13) Sc(2):
.7288(13) 2.3632(12) (t)
2
2
2
2
2
.5606(11) (μ)
.5851(11) (μ)
t
(
PNP- Bu)ScCl (1b)
Sc(1):
.145(2)
Sc(2)
.135(2)
Sc(1):
Sc(1):
2
2
2.7198(9)
2.7557(9)
Sc(2):
2.3717(10)
2.3287(11)
Sc(2):
2
2
2
.7948(9)
.7400(9)
2.3658(9)
2.3373(10)
TBP:
(
(
(
PNP-Cy)Sc(CH SiMe )
TBP:
.141(3)
SP:
TBP:
2
3 2
(2a)
2
2.7927(7)
SP:
2.216(3)
SP:
2
.1780(18)
2.7876(7)
2.202(2) (ax)
2.242(2) (eq)
TBP:
2
.7587(7)
PNP-Cy)ScNp , (2b)
TBP:
TBP:
2
2
.174(3)
2.8291(7)
SP:
2.223(3)
SP:
SP:
2
.188(2)
2.7955(8)
2.202(3) (ax)
2.256(3) (eq)
2.187(3) (ax)
2.240(3) (eq)
2
.7773(8)
2.8667(7)
.8887(7)
t
PNP- Bu)ScNp (2c)
2.1783(19)
2
2
Figure 3. Crystal structure of (a) 1a and (b) 1b. Hydrogen atoms have
been omitted for clarity. Thermal ellipsoids are set at the 50%
probability level. Chlorine is shown in green.
a
TBP = trigonal bipyramidal, SP = square pyramidal, t = terminal, μ =
bridging, ax = axial, eq = equatorial.
2
c led to the release of 2 equiv of neopentane, as observed by
1
H NMR spectroscopy, and apparent decomposition of the
resulting scandium complex to a mixture of unidentified species
after 1 h. In both cases, the expected initial product of this
reaction is the scandium dihydride complex [(PNP-R)ScH ] ,
2
x
but this species is too reactive to isolate or directly observe.
Consistent with this postulate, addition of D to 2b or 2c
2
afforded 2 equiv of neopentane-d after 1 h and decomposition
1
1
of the scandium-containing product as determined by H NMR
spectroscopy. The H NMR spectrum did not reveal
2
incorporation of deuterium into any well-defined product
other than neopentane-d . However, in the presence of 10
1
equiv of 1-hexene, treatment of 2b with H2 resulted in
formation of the new dialkyl complex (PNP-Cy)Sc(n-hexyl)2
t
Figure 4. Crystal structure of (PNP- Bu)ScNp (2c). Hydrogen atoms
(
2d, Scheme 3), presumably by insertion of the alkene into the
Sc−H bonds of putative [(PNP-Cy)ScH ] . This suggests that
2
have been omitted for clarity. Thermal ellipsoids are set at the 50%
2
x
probability level.
the unobserved dihydride complex is stable enough to engage
in reactions with suitable trapping reagents, such as unsaturated
hydrocarbons.
Scheme 3. Addition of Hydrogen and 1-Hexene to 2b
These results led us to suspect that complexes 2a−c might be
effective hydrogenation catalysts. Indeed, treatment of a sample
of 1-octene and 5 mol % of 2b or 2c with hydrogen in C D led
6
6
1
to the formation of octane (>99% yield by H NMR
spectroscopy and GC/MS) over the course of 12 h. The
di(octyl) complexes analogous to 2b were observed during
catalysis by 1H NMR spectroscopy, suggesting that these
species are resting states in the catalysis. These data suggest that
olefin hydrogenation in these complexes proceeds by a
C
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Article
mechanism analogous to that found by Marks and co-workers
24
with lanthanocene catalysts.
Reactions of Scandium Alkyl Complexes with Amines.
Complex 2c reacted cleanly with 1 equiv of 2,6-diphenyl-p-
t
toluidine in benzene-d to afford the complex (PNP- Bu)Sc-
6
(
NHAr)Np (3) (Ar = 4-methyl-2,6-diphenylbenzene) with loss
1
of neopentane as determined by H NMR spectroscopy. On
heating to 60 °C, 3 underwent cyclometalation of one of the
phenyl groups of the amido ligand to form 4 (Scheme 4). The
Scheme 4. Possible Mechanisms for Formation of 3
Figure 5. Crystal structure of 5. Hydrogen atoms have been omitted
for clarity. Thermal ellipsoids are set at the 50% probability level.
that the DMAP-induced pathway also proceeds by direct
activation of the phenyl groups with no intermediacy of a
scandium imido complex.
Reactions of Scandium Alkyl Complexes with
Alkynes. Complexes 2b,c were found to cleanly engage in
certain intermolecular C−H activation reactions. Thus, treat-
cyclometalated product 4 was isolated in 83% yield and
characterized by X-ray crystallography (see Supporting
Information). To determine whether this cyclometalation
proceeded via σ-bond metathesis or by formation of a transient
ment of 2c with isopropylacetylene (10 equiv) in benzene-d
6
cleanly afforded 2 equiv of neopentane and the bis(acetylide)
t
scandium imido complex (Scheme 4), 2,6-diphenyl-p-tolui-
complex (PNP- Bu)Sc(CCCHMe
2 2
) (6b) after 1.5 h, as
t
1
dene-d was added to 2c to afford (PNP- Bu)Sc(NDAr)Np
determined by H NMR spectroscopy. No evidence for
polymerization of the alkyne was observed by H NMR
2
1
2
1
with loss of neopentane-d by H and H NMR spectroscopy.
1
This complex (3-d ) was heated to 60 °C, at which point clean
spectroscopy, although some insoluble material is observed
when very large (>20 equiv) amounts of isopropylacetylene are
used. The insolubility of this material and its low yield (<10%)
have prevented its characterization. The reaction of isopropy-
1
cyclometalation occurred with loss of neopentane-d ; less than
0
1
% neopentane-d1 was observed. Since only unlabeled
neopentane was evolved in the latter reaction, α-abstraction
of the N−D bond by the neopentyl group does not occur, and
cyclometalation likely proceeds via an intramolecular σ-bond
metathesis pathway. Addition of deuterium (1 atm) to the
lacetylene (3 equiv, Scheme 5) in benzene-d with 2b was much
6
Scheme 5. Addition of Isopropylacetylene to 2b
cyclometalated complex in benzene-d resulted in deuterium
6
incorporation into all of the ortho positions of the amido ligand
phenyl substituents after 5 h at 60 °C, indicating that this C−H
activation is reversible. Cyclometalation of 3 could also be
induced at 22 °C by addition of 2 equiv of DMAP to form
complex 5 (eq 1). Crystallographic analysis of 5 reveals two
faster (<10 min), affording the bis(acetylide) complex (PNP-
Cy)Sc(CCCHMe ) (6a), which was isolated in 67% yield as
2
2
a slightly yellow solid by recrystallization from pentane as a
bridging acetylene complex (Figure 6).
Reactions of Scandium Alkyl Complexes with
Benzene. The mild conditions for formation of the
bis(acetylide) complex suggested that 2b,c might engage in
more challenging C−H activations (i.e., involving less acidic
aryl or alkyl C−H bonds) at higher temperatures. Heating 2b
coordinated DMAP molecules, while one of the phosphine
to 100 °C in benzene affords (PNP-Cy)ScPh (7) and
2
group arms is completely dissociated from the metal center
neopentane after 12 h in approximately 10% yield, as
1
1
(
Figure 5). The H NMR spectrum at room temperature
determined by H NMR spectroscopy. The identity of 7 was
indicates the presence of two inequivalent phosphine groups.
However, on heating to 45 °C, the molecule is dynamic on the
NMR time-scale, as both phosphine arms are equivalent.
Treatment of 3c-d1 with DMAP afforded 5 with loss of
neopentane-d (<1% neopentane-d was observed), indicating
confirmed by an independent synthesis from 1a and phenyl-
lithium. Additionally, heating 2c to 100 °C in benzene-d for 36
6
h led to formation of (PNP-Cy)ScPh -d in approximately
2
10
1
10% yield, as determined by H NMR spectroscopy. Notably,
this appears to be the first example of a non-cyclopentadienyl-
0
1
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Scheme 6. Possible Mechanisms for Isobutylene Formation
a
from 2c-d4
Figure 6. Crystal structure of (PNP-Cy)Sc(CCCHMe ) (6a).
2
2
Hydrogen atoms and cyclohexyl groups have been omitted for clarity.
Thermal ellipsoids are set at the 50% probability level.
a
supported scandium complex that undergoes an intermolecular
Pathway (a) is an E2-like mechanism, while pathway (b) is a β-
2
methyl elimination. Each proposal gives a different pattern for
deuterium incorporation.
σ-bond metathesis reaction with an sp -hybridized C−H bond.
Complex 2b reacts less readily with toluene-d and requires
8
heating to 120 °C for elimination of neopentane-d to be
1
1
observed by H NMR spectroscopy, at which point many
complexes of scandium or the lanthanides. These results
suggest that the key to generation of reactive centers for σ-bond
metathesis may be to employ strongly donating, highly
polarizable ligands. This strategy is being investigated.
scandium-containing products were observed. No reaction was
observed between 2b and tetramethylsilane or methane in
toluene-d at 100 °C.
8
Reaction of Scandium Alkyl Complexes with Intra-
3
3
molecular sp Bonds. Intramolecular activation of the sp
EXPERIMENTAL SECTION
General Procedures. Unless otherwise noted, all experiments
were conducted with dry, oxygen-free solvents using standard Schlenk
techniques or in a N2 atmosphere glovebox. Deuterated solvents,
■
carbon−hydrogen bonds of the PNP ligands was observed for
both 2b and 2c. After heating 2b to 100 °C in toluene-d for 5
8
days, trace amounts (∼0.1 equiv) of cyclohexene were
liberated. Similarly, heating 2c to 60 °C in benzene-d liberated
6
deuterium, and methane-d were purchased from Cambridge Isotope
4
∼2 equiv of neopentane and ∼1 equiv of isobutylene over 24 h
Laboratories, Inc. Benzene-d was dried by vacuum distillation from
6
and led to decomposition of the complex. The isobutylene is
likely formed by C−H activation and elimination from the tert-
butyl groups of the phosphine ligand in a manner analogous to
an E2 reaction. To obtain more evidence for this mechanistic
Na/K alloy. Toluene-d was dried by refluxing over molten sodium
8
metal followed by vacuum distillation. Unless otherwise noted,
reagents were obtained from commercial suppliers and used as
received. Pyrrole was obtained from Aldrich, dried over CaH , and
2
t
distilled. 2,5-Bis(dimethylaminomethyl)pyrrole, ScCl (THF) , and
3
3
proposal, labeled complex (PNP- Bu)Sc(CD CMe ) (2c-d )
2
3 2
4
25−27
LiCD CMe were prepared according to literature procedures.
2
3
was prepared and heated to 60 °C for 24 h. The isobutylene
Analytical Methods. Solution NMR spectroscopy was performed
produced in this reaction (∼1 equiv) was observed to contain
using Bruker AV-300, AVB-400, AVQ-400, AV-500, or AV-600 MHz
1
2
no deuterium (as probed by H and H NMR spectroscopy),
consistent with activation of the tert-butyl groups and
inconsistent with, for example, β-methyl elimination of the
neopentyl groups, which would result in deuterium incorpo-
ration into the vinyl position of the isobutylene (Scheme 6). In
the case of both complexes, this activation−elimination of the
phosphine substituent is concurrent with decomposition of the
metal complex into a complex mixture and illustrates a major
weak point for these ligands. No reaction was observed
1
13
1
31
1
spectrometers at room temperature. H, C{ H}, and P{ H} NMR
spectra were calibrated internally to either the resonance for the
solvent or residual proteo solvent relative to tetramethylsilane.
Elemental analyses were carried out by the College of Chemistry
Microanalytical Laboratory at the University of California, Berkeley.
Melting points were determined on a Mel-Temp II melting point
apparatus.
X-ray Crystallography Details. X-ray diffraction data for crystals
t
t
of ScNp (THF) , (PNP- Bu)ScCl , (PNP- Bu)ScNp , (PNP-Cy)-
3
2
2
2
t
ScCl , (PNP-Cy)Sc(CH SiMe ) , (PNP-Cy)ScNp , (PNP- Bu)-
2
2
3
2
2
between 2b and tetramethylsilane or methane in toluene-d at
t
8
ScNHAr, (PNP- Bu)ScNHAr(DMAP) , and (PNP-Cy)Sc(C
2
100 °C.
CCHMe ) were collected using a Bruker AXS modified four-circle
2
2
diffractometer coupled CCD detector with Mo Kα (λ = 0.710 73 Å)
radiation monochromated by a system of QUAZAR multilayer
mirrors. Crystals were kept at 100(2) K throughout collection. Data
collection, refinement, and reduction were performed with Bruker
APEX2 software (v. 2013.4). Structures were solved by direct methods
using SHELXS-97. All structures were refined with SHELXL-97 with
SUMMARY AND CONCLUSIONS
■
A series of novel monoanionic PNP-supported scandium
complexes have been prepared and characterized, and their
reactivity with C−H bonds has been examined. In addition to
well-known hydrogen, amine, and sp C−H bond activation,
2
refinement of F against all reflections by full-matrix least-squares. In
2
reactivity with intermolecular sp bonds was also observed. To
all models, non-hydrogen atoms were refined anisotropically, and
hydrogen atoms were included at their geometrically calculated
positions and refined using a riding model. The 3D molecular
the best of our knowledge, this type of C−H bond activation
has not previously been observed for non-Cp-supported
E
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structure figures were visualized with ORTEP 3.2, rendered with POV-
Ray 3.6. Crystal data and complete details are available in the
Supporting Information.
Synthesis of 2,5-Bis(dicyclohexylphosphinomethyl)pyrrole (PNP-
CyH). A Schlenk flask was charged with 2,5-bis(dimethylamino-
methyl)pyrrole (1.80 g, 9.93 mmol). Dicyclohexylphosphine (1.23 mL,
MHz, C D ): δ 6.03 (s, 2H, pyr-CH), 3.17 (d, J = 4.6 Hz, 4H,
6
6
−CH PCy ), 2.04 (d, J = 12.8 Hz, 4H, −Cy), 1.90 (d, J = 10.9 Hz, 8H,
2
2
−Cy), 1.69 (br s, 8H, −Cy), 1.56 (d, J = 10.4 Hz, 4H, −Cy), 1.48 (t, J
13
1
= 11.8 Hz, 8H, −Cy), 1.25−1.02 (m, 12H, −Cy). C{ H} NMR
(
2
150.90 MHz, C D ): δ 135.48, 106.07, 33.75, 29.39, 27.86, 27.56,
6 6
6.42. 31P{ H} NMR (161.98 MHz, C D ): δ 9.63. Anal. Calcd for
1
6 6
6
1
.62 mmol) was added, and the reaction mixture was stirred for 22 h at
50 °C. The reaction mixture was allowed to cool to 22 °C, and
C H Cl NP Sc: C, 59.80; H, 8.36; N, 2.32. Found: C, 60.08; H, 8.53;
30
50
2
2
N, 2.09.
toluene (3 mL) was added to dissolve the resulting amorphous solid.
The volatile components were removed in vacuo, and the resulting
foam was dissolved in pentane (10 mL) and stored at −35 °C for 3 d
Synthesis of (2,5-Bis(di-tert-butylphosphinomethyl)pyrrolyl)-
scandium dichloride (1b), (PNP-tBu)ScCl . ScCl (THF) (539 mg,
2
3
3
t
1.47 mmol) and (PNP- Bu)Li (571 mg, 1.47 mmol) were combined as
solids and suspended in toluene (15 mL). The reaction mixture
became pink and homogeneous in about 30 s and was stirred for 12 h,
at which point the reaction mixture had become turbid. All solvent was
removed by vacuum, and fresh toluene (2 mL) was added. The
mixture was filtered to remove lithium chloride. Pentane (4 mL) was
added to the toluene solution, and the mixture was stored at −35 °C
for 48 h to afford slightly orange blocks, which were collected and
to afford a colorless solid (3.0 g, 62% yield), which was isolated by
1
filtration. H NMR (400.13 MHz, C D ): δ 8.22 (br s, 1H, NH), 6.09
6
6
(
2
d, J = 2.7 Hz, 2H, pyr-CH), 2.67 (s, 4H, −CH PCy ), 1.91−1.46 (m,
2
2
13 1
8H, −Cy), 1.35−1.17 (m, 16H, −Cy). C{ H} NMR (150.90 MHz,
C D ): δ 134.48 (d, J = 12.1 Hz), 107.05 (d, J = 4.8 Hz), 33.94 (d, J =
6
6
1
1
5.1 Hz), 30.33 (d, J = 13.5 Hz), 29.39 (d, J = 8.8 Hz), 27.77 (d, J =
0.6 Hz), 27.67 (d, J = 7.8 Hz), 26.93, 21.38 (d, J = 19.6 Hz). 31P{ H}
1
NMR (161.98 MHz, C D ): δ −8.06. Anal. Calcd for C H NP : C,
1
6
6
30 51
2
dried under vacuum (330 mg, 45% yield). H NMR (500.23 MHz,
7
3.88; H, 10.54; N, 2.87. Found: C, 74.02; H, 10.57; N, 2.83.
Synthesis of Lithium 2,5-Bis(dicyclohexylphosphinomethyl)-
pyrrolide, (PNP-Cy)Li. A solution of lithium bis(trimethylsilylamide)
380 mg, 2.25 mmol) in THF (5 mL) was added to a solution of 2,5-
bis(dicyclohexylphosphinomethyl)pyrrole (1.00 g, 2.05 mmol) in THF
5 mL). The solution was stirred for 4.5 h and remained homogeneous
C D ): δ 6.12 (s, 2H, pyr-CH), 2.99 (d, J = 6.2 Hz, 4H,
6
6
−
CH P(C(CH ) ) ), 1.13 (d, J = 12.7 Hz, 36H, −P(C(CH ) ) ).
2
3
3
2
3 3 2
13
1
C{ H} NMR (100.61 MHz, C D ): δ 136.83, 107.01 (t, J = 4.2 Hz),
6
6
(
3
3.09 (t, J = 2.4 Hz), 29.38 (t, J = 2.8 Hz), 21.04 (t, J = 4.3 Hz).
3
1
1
P{ H} NMR (161.98 MHz, C D ): δ 33.94 (br). Anal. Calcd for
6
6
(
C H Cl NP Sc: C, 53.02; H, 8.49; N, 2.81. Found: C, 53.31; H, 8.69;
22
42
2
2
throughout the course of the reaction. THF was removed in vacuo, and
the resulting white powder was washed with pentane (3 × 2 mL) to
afford analytically pure product (792 mg, 78% yield). The product is
N, 2.70. Mp: 175−179 °C.
Synthesis of ScNp (THF) . Neopentyllithium (318.6 mg, 4.08
3
2
1
mmol) was dissolved in pentane (8 mL) and added dropwise to a
stirred suspension of ScCl (THF) (500 mg, 4.08 mmol) in pentane
insoluble in pentane but is slightly soluble in aromatic solvents. H
3
2
NMR (400.13 MHz, C D ): δ 6.39 (s, 2H, pyr-CH), 3.43 (s, 4H,
6
6
(8 mL). The reaction mixture became cloudy and produced a fine
−
CH PCy ), 2.07−1.51 (m, 32H, −Cy), 1.60−1.21 (m, 12H, −Cy).
2
2
1
3
1
white precipitate. After stirring for 4 h, the reaction mixture was
filtered through a fritted funnel, and the filtrate was concentrated to 10
mL. The concentrated filtrate was cooled at −35 °C for 10 h to afford
the product as large, colorless, single-crystal needles (270 mg, 49%
C{ H} NMR (150.90 MHz, C D ): δ 136.03, 108.52, 33.08 (br),
6
6
31
1
3
0.25 (br), 29.80 (br), 27.74 (br), 26.85, 25.33 (br). P{ H} NMR
1
(
161.98 MHz, C D ): δ −10.18 (hept, J = 24.0 Hz). Anal. Calcd for
3
6
6
LiP
C H NP Li: C, 73.00; H, 10.21; N, 2.84. Found: C, 72.65; H, 10.09;
0
50
2
yield). A second crop was obtained by concentrating the mother liquor
N, 2.72.
Synthesis of Lithium 2,5-Bis(di-tert-phosphinomethyl)pyrrolide,
1
(
131 mg, 24% yield, total combined: 401 mg, 73% yield). H NMR
t
(500 MHz, C D ): δ 3.80−3.75 (m, 8H, O(CH CH ) ), 1.33 (s, 27H,
(
PNP- Bu)Li. A Schlenk flask was charged with 2,5-bis(dimethylamino-
6
6
2
2 2
J
0
= 121.6 Hz, −CH C(CH ) ), 1.25−1.22 (m, 8H, O(CH CH ) ),
methyl)pyrrole (1.20 g, 6.62 mmol). Di-tert-butylphosphine (2.50 mL,
CH
2
3
3
2
2 2
1
1
3
.62 (s, 6H, J = 99.6 Hz, −CH C(CH ) ). C NMR (151 MHz,
6
1
1
3.2 mmol) was added, and the reaction mixture was stirred for 22 h at
50 °C. The reaction mixture was cooled to 22 °C to afford a dark
CH
2
3 3
C D ): δ 71.44 (−CH C(CH ) ), 70.55 (O(CH CH ) ), 36.07
(
The assignments and coupling constants were determined by H− C
HSQC and H− C HMBC experiments (see Supporting Informa-
tion).
6
2
3
3
2
2 2
−CH C(CH ) ), 34.89 (−CH C(CH ) ), 25.25 (O(CH CH ) ).
brown, viscous oil consisting principally of (2,5-bis(di-tert-butyl)-
phosphinomethyl)pyrrole. H NMR (400.13 MHz, C D ): δ 8.55 (br
2
3
3
2
3
3
2
2 2
1 13
1
6
6
1
13
s, 1H, NH), 6.01 (d, J = 2.7 Hz, 2H, pyr-CH), 2.71 (s, 4H,
CH P(C(CH ) ) ), 1.03 (d, J = 10.8 Hz, 36H, −P(C(CH ) ) ).
−
2
3
3
2
3 3 2
1
3
1
C{ H} NMR (100.61 MHz, C D ): δ 128.86 (d, J = 12.2 Hz),
Synthesis of (2,5-Bis(dicyclohexylphosphinomethyl)pyrrolyl)bis-
6
6
(
(trimethylsilyl)methyl)scandium (2a), (PNP-Cy)Sc(CH SiMe ) .
1
2
06.93 (d, J = 5.6 Hz), 31.40 (d, J = 22.8 Hz), 29.78 (d, J = 13.1 Hz),
2 3 2
0.73 (d, J = 23.6 Hz). 31P{1H} NMR (161.98 MHz, C D ): δ 22.28.
Method 1. (Trimethylsilyl)methyllithium (15.6 mg, 0.166 mmol) in
6
6
pentane (3 mL) was added dropwise over 20 min to a stirred solution
The oil was dissolved in THF (4 mL). To this solution was added
lithium bis(trimethylsilylamide) (1.17 g, 7.00 mmol) in THF (5 mL).
The reaction mixture was stirred for 12 h, at which point the THF was
removed in vacuo. The resulting peach-colored solid was collected on a
fritted funnel and washed with pentane (5 × 2.5 mL) to afford a white
of (PNP-Cy)ScCl (50.0 mg, 0.083 mmol) in pentane (2 mL). The
2
reaction mixture was stirred for 14 h and then filtered to remove
lithium chloride. The filtrate was then stored at −35 °C for 9 days to
afford colorless crystals (11.0 mg, 20% yield).
Method 2. A solution of (PNP-Cy)H (100 mg, 0.205 mmol) in
pentane (3 mL) was added to a solution of Sc(CH SiMe ) (THF)
2
powder (883 mg, 34.3% yield over two steps). Caution: the material
1
was highly pyrophoric. H NMR (400.13 MHz, DMSO-d ): δ 5.38 (s,
2
3
3
6
(92.4 mg, 0.205 mmol) in pentane (5 mL), and the reaction mixture
2
3
1
1
H, pyr-CH), 2.72 (s, 4H, −CH P(C(CH ) ) ), 1.03 (d, J = 9.9 Hz,
2
3 3 2
13 1
was then stirred for 1 h. The volatile materials were removed to afford
the desired product in high purity (129.5 mg, 89% yield).
6H, −P(C(CH ) ) ). C{ H} NMR (100.61 MHz, DMSO-d ): δ
3
3
2
6
33.71, 102.83 (d, J = 6.7 Hz), 30.83 (d, J = 23.6 Hz), 29.87 (d, J =
1
1
2.6 Hz), 24.05 (d, J = 19.2 Hz). 31P{ H} NMR (161.98 MHz,
1
H NMR (600.13 MHz, C D ): δ 6.20 (s, 2H, pyr-CH, J = 163.3
6 6 CH
2
1
Hz), 3.04 (d, J = 3.8 Hz, 4H, −CH PCy , J = 131.4 Hz), 1.92−
DMSO-d ): δ 22.80. Anal. Calcd for C H LiNP : C, 67.85; H, 10.87;
HP
2
2
CH
6
22 42
2
1
−
.85 (m, 4H, −Cy), 1.82−1.71 (m, 8H, −Cy), 1.70−1.58 (m, 8H,
Cy), 1.57−1.49 (m, 4H, −Cy), 1.38−1.27 (m, 8H, −Cy), 1.16−1.01
N, 3.60. Found: C, 67.56; H, 11.01; N, 3.74.
Synthesis of (2,5-Bis(dicyclohexylphosphinomethyl)pyrrolyl)-
1
scandium Dichloride (1a), (PNP-Cy)ScCl . ScCl (THF) (309 mg,
(m, 12H, −Cy), 0.62 (s, 4H, −CH
2
SiMe
) , JCH = 117.1 Hz). C{ H} NMR (150.90
3 3
3
, JCH = 100.3 Hz), 0.41 (s,
2
3
3
1
13
1
0
.841 mmol) and (PNP-Cy)Li (415 mg, 0.841 mmol) were combined
18H, −CH
MHz, C
55.45 (br, −CH
26.38, 24.50, 21.75 (d, JCP = 5.6 Hz, −CH
2
SiC(CH
): δ 134.30 (t, JCP = 4.5 Hz, pyr-C), 106.46 (pyr-CH),
SiMe ), 33.54, 30.04, 28.98, 27.52 (q, J = 4.4 Hz),
2
as solids and suspended in toluene (15 mL). The reaction mixture
became yellow and homogeneous in about 30 s and was stirred for 5 h,
at which point the reaction mixture was turbid. All solvent was
removed under vacuum, and toluene (2 mL) was added. The mixture
was filtered to remove lithium chloride. Solvent was removed in vacuo
D
6 6
2
3
1
PCy
), 4.41 (−CH Si-
2
2
2
31
1
(CH ) ). P{ H} NMR (161.98 MHz, C D ): δ 0.84. Anal. Calcd for
3
3
6
6
C H NP ScSi : C, 64.64; H, 10.28; N, 1.98. Found: C, 64.27; H,
38
72
2
2
1
to afford a yellow powder (413 mg, 82% yield). H NMR (600.13
10.02; N, 1.86. Mp: 97−100 °C.
F
DOI: 10.1021/acs.organomet.5b00213
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Synthesis of (2,5-Bis(dicyclohexylphosphinomethyl)pyrrolyl)di-
Hydrogenation of 1-Octene by Scandium Alkyl Complexes. A
sample of 2b or 2c (13.5 or 11.4 mg, 0.020 mmol) and 1-octene (11.2
(
neopentyl)scandium (2b), (PNP-Cy)ScNp . Method 1. Neopentyl-
2
lithium (3.0 mg, 0.04 mmol) in toluene (3 mL) was added dropwise
mg, 0.10 mmol) were dissolved in benzene-d (0.6 mL) in a 5 mm
6
over 20 min to a stirred solution of (PNP-Cy)ScCl (12.2 mg, 0.020
NMR tube with a Teflon screw cap. The tube was degassed to remove
nitrogen, cooled to 77 K, and placed under vacuum. The tube was
opened to hydrogen or deuterium at 1 atm for 2 min and then sealed.
The sealed tube was allowed to warm to room temperature to attain a
hydrogen (or deuterium) pressure of approximately 3.9 atm due to gas
2
mmol) in toluene (2 mL). The reaction mixture was stirred for 1 h and
filtered to remove lithium chloride. The toluene was removed under
vacuum, and pentane (2 mL) was then added to dissolve the resulting
foam. This solution was then stored at −35 °C for 9 d to afford
colorless crystals (6.0 mg, 45% yield).
1
expansion. After 12 h, analysis by H NMR spectroscopy and GC/MS
Method 2. A solution of (PNP-Cy)H (171.0 mg, 0.351 mmol) in
pentane (3 mL) was added to a solution of ScNp (THF) (141.2 mg,
showed complete conversion of 1-octene and >99% yield of n-octane.
Synthesis of Cyclometalated Scandium Complex 4. A sample of
2,6-diphenyltoluidine (43.9 mg, 0.169 mmol) in pentane (2 mL) was
added to 2c (96.4 mg, 0.169 mmol) in pentane (8 mL), and this
solution was stirred for 1 h. The concentration must be at least this
low to prevent formation of the bis(anilide) complex. The volatile
3
2
0
.351 mmol) in pentane (5 mL), and the resulting reaction mixture
was stirred for 1 h. The volatile materials were removed to afford
analytically pure product (222 mg, 94% yield).
1
1
H NMR (500.23 MHz, C D ): δ 6.19 (s, 2H, pyr-CH, J = 164.1
6
6
CH
2
1
materials were removed under vacuum to afford the anilido alkyl
Hz), 3.05 (d, J = 3.7 Hz, 4H, −CH PCy , J = 130.5 Hz), 2.00−
HP
2
2
CH
1
complex 3. H NMR (400.13 MHz, C D ): δ 7.50−7.44 (m, 4H),
1
.87 (m, 4H, −Cy), 1.87−1.70 (m, 9H, −Cy), 1.70−1.58 (m, 9H,
6
6
1
7.24−7.18 (m, 4H), 7.14−7.08 (m, 2H), 6.95 (s, 2H), 5.96 (s, 2H),
−
=
=
Cy), 1.58−1.50 (m, 4H, −Cy), 1.44 (s, 18H, −CH CC(CH ) , J
2
3
3
CH
1
2.84 (dd, J = 15.5, 9.5 Hz, 2H, −CH P(C(CH ) ) ), 2.54 (d, J = 15.5
122.7 Hz), 1.43−1.31 (m, 6H, −Cy), 1.14 (s, 4H, −CH CMe , J
2
3 3 2
2
3
CH
13
1
Hz, 2H, −CH P(C(CH ) ) ), 2.17 (s, 3H, ArCH ), 2.11 (s, 1H,
98.9 Hz), 1.15−1.01 (m, 12H, −Cy). C{ H} NMR (150.90 MHz,
2
3
3
2
3
−
1
NHAr), 1.15 (d, J = 12.1 Hz, 18H, −CH P(C(CH ) ) ), 1.09 (d, J =
C D ): δ 134.38 (t, J = 4.3 Hz, pyr C), 106.33 (pyr CH), 84.54 (br,
2
3 3 2
6
6
1.3 Hz, 18H, −CH P(C(CH ) ) ), 1.00 (s, 9H, −CH C(CH ) ),
−
CH C(CH ) ), 36.54, 36.31 (−CH C(CH ) ), 33.92, 31.62, 29.97,
2
3
3
2
2
3 3
2
3
3
2
3
3
31 1
1
0.82 (d, J = 2.2 Hz, 2H, −CH CMe ). P{ H} NMR (161.98 MHz,
2
3
2
9.08, 27.63 (t, JCP = 5.0 Hz), 26.44, 22.23 (d,
J
= 6.2 Hz,
CP
C D ): δ 25.26. This material began to very slowly cyclometalate in
6
6
−
CH PCy ). Note the resonance for the carbon directly attached to
2 2
1
13
the 2-position of an arm of the terphenyl at room temperature.
Heating the material to 60 °C for 1 h resulted in the clean formation of
the scandium is difficult to observe, but was confirmed by a H− C
HSQC experiment (see Supporting Information). 3 P{ H} NMR
1
1
4
with production of neopentane. This material was isolated by
(
7
161.98 MHz, C D ): δ −1.28. Anal. Calcd for C H NP Sc: C,
6
6
40 72
2
removal of all volatile materials under vacuum (96.0 mg, 83% yield).
1.29; H, 10.77; N, 2.08. Found: C, 70.92; H, 10.95; N, 2.42.
1
H NMR (500 MHz, C D ): δ 7.86 (dd, J = 6.8, 1.6 Hz, 1H), 7.83 (d, J
6
6
Synthesis of (2,5-Bis(di-tert-butylphosphinomethyl)pyrrolyl)di-
t
= 8.0 Hz, 1H, o-ArH of metalated phenyl group), 7.69 (d, J = 2.2 Hz,
H), 7.59 (dd, J = 7.9, 1.2 Hz, 2H, o-ArH of nonmetalated phenyl
group), 7.37−7.24 (m, 4H), 7.21 (br s, 1H), 7.10 (d, J = 2.2 Hz, 1H),
(
neopentyl)scandium (2c), (PNP- Bu)ScNp . Method 1. Neopentyl-
2
1
lithium (47.0 mg, 0.602 mmol) in benzene (13 mL) was added
t
dropwise over 45 min to a stirred solution of (PNP- Bu)ScCl (150.0
2
6
.22 (s, 2H, pyr-CH), 3.13 (dd, J = 16.3, 3.8 Hz, 2H, −CH PC-
2
mg, 0.301 mmol) in benzene (2 mL). The reaction solution changed
from peach-colored to yellow over the course of the addition. The
reaction mixture was allowed to stir for 8 h and filtered to remove
lithium chloride. The solvent was removed under vacuum to afford a
brown powder. The powder was dissolved in pentane (1.5 mL) and
stored at −35 °C for 24 h to afford colorless crystals (66.0 mg, 39%
yield).
(
3
CH ) ), 2.90 (dd, J = 16.2, 7.5 Hz, 2H, −CH PC(CH ) ), 2.35 (s,
3
2
2
3 2
H, ArCH ), 2.23 (s, 1H, −NHAr), 0.92 (d, J = 12.4 Hz, 18H,
3
1
3
−
CH PC(CH ) ), 0.84 (d, J = 12.2 Hz, 18H, −CH PC(CH ) ).
C
2
3
2
2
3 2
NMR (151 MHz, C D ): δ 148.14, 147.86, 143.50, 136.33 (t, J = 5.3
6
6
Hz), 133.10, 131.90, 131.46, 130.55, 130.17, 129.81, 129.26, 128.97,
28.73, 128.55, 126.67, 124.95, 123.94, 107.05 (t, J = 4.2 Hz), 35.70,
32.70, 31.63, 29.44 (dt, J = 26.4, 3.3 Hz), 21.81 (d, J = 3.9 Hz), 21.02.
1
t
Method 2. A solution of (PNP- Bu)H (95.5 mg, 0.248 mmol) in
31
P NMR (202 MHz, C D ): δ 29.00 (br s). Anal. Calcd for
6
6
pentane (3 mL) was added to a solution of ScNp (THF) (100.4 mg,
3
2
C H N P Sc: C, 71.91; H, 8.39; N, 4.09. Found: C, 72.27; H, 8.07;
41
57
2 2
0
.248 mmol) in pentane (5 mL), and the resulting reaction mixture
N, 3.76.
was stirred for 1 h. The volatile materials were removed under vacuum.
Pentane (1 mL) was added to the resulting oily material and
subsequently removed to afford pure product (96.4 mg, 68% yield).
Synthesis of 2,6-Diphenyltoluidine-N-d . 2,6-Diphenyltoluidine
2
(
(
125 mg, 0.482 mmol) was dissolved in MeCN (2 mL), and D O
2
0.6 mL) was added to this solution. The solvent was removed under
1
H NMR (400.13 MHz, C D ): δ 6.13 (s, 2H, pyr-CH), 3.10 (d, J =
6
6
vacuum to afford the product as a slightly yellow oil (125 mg, 99%
yield). The NMR spectra of the product are identical to those of 2,6-
3
.2 Hz, 4H, −CH P(C(CH ) ) ), 1.45 (s, 18H, −CH C(CH ) ), 1.26
2
3
3
2
2
3 3
(
s, 4H, −CH CMe ), 1.14 (d, J = 11.5 Hz, 36H, −CH P(C(CH ) ) ).
2
3
2
3 3 2
diphenyltoluidine except that the −NH resonance is absent from the
1
3
1
2
C{ H} NMR (100.61 MHz, C D ): δ 134.75 (t, J = 4.3 Hz, pyr-C),
1
2
2
6
6
H NMR spectrum and present in the H NMR spectrum: H NMR
1
3
06.53 (pyr-CH), 87.95 (br, −CH C(CH ) ), 36.82 (−CH C(CH ) ),
2
3
3
2
3 3
(
92 MHz, C D ) δ 3.39 (br s).
Deuterium-Labeling Study of Cyclometalation of 2,6-Diphenyl-
6 6
6.35, 33.18, 30.14 (t, J = 3.0 Hz, −CH P(C(CH ) ) ), 22.18
2
3 3 2
31
1
(
−CH P(C(CH ) ) ). P{ H} NMR (161.98 MHz, C D ): δ 25.29.
2
3
3
2
6
6
toluidine. 2,6-Diphenyltoluidine-N-d2 (3.3 mg, 0.0126 mmol) was
Anal. Calcd for C H NP Sc: C, 67.46; H, 11.32; N, 2.46. Found: C,
32
64
2
dissolved in benzene-d (0.3 mL) and added to a solution of 2c (7.2
6
6
7.63; H, 11.57; N, 2.33.
mg, 0.0126 mmol) in benzene-d (0.5 mL) in a 5 mm NMR tube with
6
1
Reaction of Scandium Alkyl Complexes with Hydrogen or
Deuterium. A sample of 2a, 2b, or 2c (14.1, 13.5, or 11.4 mg, 0.020
a Teflon screw cap. Formation of 3-d was apparent by H NMR
2
spectroscopy, resulting in the same spectrum as 3 except for the
mmol) was dissolved in benzene-d (0.6 mL) in a 5 mm NMR tube
6
absence of the resonance at δ 2.11, which is assignable as the −NH
with a Teflon screw cap. The tube was degassed to remove nitrogen,
cooled to 77 K, and placed under vacuum. The tube was opened to
hydrogen or deuterium at 1 atm for 2 min and then sealed. The sealed
tube was allowed to warm to room temperature to attain a hydrogen
1
resonance. Neopentane-d was observed in the H NMR spectrum as a
1
1
2
1
:1:1 triplet at δ 0.89 and in the H{ H} NMR spectrum as a singlet at
δ 0.87. The volatile materials were removed from the NMR tube by
vacuum transfer, and fresh benzene-d was added. The sample was
6
(
or deuterium) pressure of approximately 3.9 atm due to gas
heated to 60 °C for 1 h, resulting in the formation of 4-d and
1
1
2
expansion. With 2a, tetramethylsilane or tetramethylsilane-d (0.040
neopentane quantitatively by H and H NMR spectroscopy.
1
1
mmol, >99% yield as determined by H NMR spectroscopy) was
Reaction of 4 with Deuterium. A sample of 4 (7.0 mg, 0.01 mmol)
produced after 12 h with hydrogen or deuterium, respectively. With 2b
was dissolved in benzene-d (0.8 mL) in a 5 mm NMR tube with a
6
or 2c, neopentane or neopentane-d (0.040 mmol, >99% yield as
Teflon screw cap. The tube was degassed to remove nitrogen, cooled
to 77 K, and placed under vacuum. Deuterium at 1 atm was admitted
into the tube for 2 min, and the tube was then sealed. The sealed tube
was allowed to warm to room temperature to attain a deuterium
1
1
determined by H NMR spectroscopy) was produced after 1 h with
hydrogen or deuterium, respectively. In all cases, the scandium-
containing product appeared to decompose to an intractable mixture.
G
DOI: 10.1021/acs.organomet.5b00213
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
pressure of approximately 3.9 atm due to gas expansion. The sample
was heated to 60 °C, at which point deuterium was observed to
scramble into all ortho positions on the terphenyl arms (the phenyl
groups), by selective loss of the resonance corresponding to these
This sample was heated to 100 °C for 5 days. Approximately 0.1 equiv
1
of cyclohexene was observed to be formed by H NMR spectroscopy.
Thermolysis of 2c. A sample of 2c (10.8 mg) was dissolved in
benzene-d (0.8 mL) in a 5 mm NMR tube with a Teflon screw cap.
6
1
ortho hydrogens in the H NMR spectrum over the course of 5 h.
This sample was heated to 60 °C for 24 h. Approximately 1 equiv of
Synthesis of Cyclometalated Scandium Bis(DMAP) Complex 5. A
solution of 4-dimethylaminopyridine (25.8 mg, 0.211 mmol) in
pentane (5 mL) was added to 3 (80 mg, 0.108 mmol) in pentane (5
mL). This led to the rapid formation (∼10 min) of the cyclometalated
complex. Concentration of the reaction mixture to 1 mL and cooling
to −35 °C resulted in 80 mg of yellow crystalline product. Single
crystals suitable for X-ray diffraction could be obtained by
isobutylene and 2 equiv of neopentane were observed to be formed by
1
H NMR spectroscopy.
Synthesis of ScNp (THF) -d . Neopentyllithium-d (at α position)
3
2
6
2
(16.3 mg, 0.20 mmol) was dissolved in pentane (3 mL) and added
dropwise to a stirred suspension of ScCl (THF) (25.0 mg, 0.068
3
2
mmol) in pentane (5 mL). The reaction mixture became cloudy and
produced a white precipitate. After stirring for 4 h, the reaction
mixture was filtered to remove LiCl. The volatile materials were
removed from the filtrate by vacuum (22.4 mg, 81% yield). The
material showed the same NMR spectra as ScNp (THF) , except for
1
recrystallization from pentane. H NMR (600 MHz, C D , 45 °C):
6
6
δ 8.25 (br s, 4H), 7.89 (d, J = 7.9 Hz, 1H), 7.71 (d, J = 7.6 Hz, 2H),
7.66 (br s, 1H), 7.49 (br s, 1H), 7.36 (t, J = 7.6 Hz, 2H), 7.31 (t, J =
7.6 Hz, 1H), 7.14−7.10 (m, 2H), 7.07−6.91 (m, 3H), 6.86 (s, 1H),
6.65 (br s, 2H), 5.85 (d, J = 6.1 Hz, 2H), 3.18 (br s, 4H,
3
2
1
the absence of the resonance at 0.62 ppm from the H NMR spectrum
2
and the appearance of a resonance in the H NMR spectrum at δ 0.62
−
CH PC(CH ) ), 2.27 (s, 3H, ArCH ), 2.15 (s, 12H, pyr-N(CH ) ),
(s).
2
3
2
3
3 2
1
.06 (d, J = 10.8 Hz, 36H, −CH PC(CH ) ); (600 MHz, C D , 20
Synthesis of (2,5-Bis(di-tert-butylphosphinomethyl)pyrrolyl)di-
(neopentyl)scandium-d
2
3
2
6
6
t
°
C) δ 7.71 (br s, 2H), 7.53 (br s, 2H), 7.40 (br s, 3H), 7.26 (br s, 2H),
4
(2c-d
4
), (PNP- Bu)ScNp
2
-d
4
. A solution of
t
7
.12 (s, 1H), 7.10−7.04 (m, 2H), 7.03−6.93 (m, 4H), 6.89 (br s, 1H),
(PNP- Bu)H (8.4 mg, 0.024 mmol) in pentane (3 mL) was added to a
solution of ScNp (THF) -d (9.5 mg, 0.024 mmol) in pentane (5
mL), and the resulting reaction mixture was stirred for 1 h. The
volatile materials were removed under vacuum. The material showed
the same NMR spectra as 2c, except for the absence of the resonance
at 1.26 ppm from the H NMR spectrum and the appearance of a
resonance in the H NMR spectrum at δ 1.26 (s).
Thermolysis of 2c-d
was dissolved in benzene-d
5
(
=
−
.95 (s, 2H), 2.83 (dd, J = 15.5, 9.3 Hz, 2H, −CH PC(CH ) ), 2.54
3
2
6
2
3 2
d, J = 15.4 Hz, 2H, −CH PC(CH ) ), 2.17 (s, 3H, ArCH ), 1.15 (d, J
2
3
2
3
11.9 Hz, 18H, −CH PC(CH ) ), 1.09 (d, J = 11.0 Hz, 18H,
2
3 2
13
CH PC(CH ) ). C NMR (151 MHz, C D , 45 °C): δ 154.59,
2
3
2
6
6
1
151.12, 145.15, 137.91, 136.19 (t, J = 5.1 Hz), 134.08, 133.19, 131.84,
131.08, 130.67, 130.50, 129.33, 129.04, 129.00, 128.55, 126.20, 126.14,
125.69, 123.29, 106.28, 38.23, 32.32 (d, J = 15.3 Hz), 30.39 (d, J =
1
0.5 Hz), 21.40, 21.09. 31P NMR (202 MHz, C D ): δ 24.00 (br s).
2
. A sample of 2c-d
(13.4 mg, 0.023 mmol)
4
4
(0.8 mL) in a 5 mm NMR tube with a
6
6
6
Anal. Calcd for C H N P Sc: C, 71.10; H, 8.35; N, 9.04. Found: C,
Teflon screw cap. This sample was heated to 60 °C for 24 h.
Approximately 1 equiv of isobutylene and 2 equiv of neopentane-d
were observed to be formed by H NMR spectroscopy.
55
77
6 2
7
0.87; H, 8.30; N, 9.07.
Synthesis of (2,5-Bis(dicyclohexylphosphinomethyl)pyrrolyl)bis-
isopropylacetylide)scandium (6a), (PNP-Cy)Sc(CCCHMe ) . A
2
1
(
Synthesis of (2,5-Bis(dicyclohexylphosphinomethyl)pyrrolyl)di-
phenyl)scandium (7), (PNP-Cy)ScPh . Phenyllithium (16.7 mg,
2
2
(
sample of 2b (75.0 mg, 0.111 mmol) was dissolved in benzene-d6
0.6 mL) in a 5 mm NMR tube with a Teflon screw cap, and
2
0
.199 mmol) was dissolved in benzene (8 mL) and diethyl ether (2
(
mL) and added dropwise (1 drop/6 s, the slow rate was necessary to
obtain high yield) to a sample of 1a (60.0 mg, 0.0996 mmol) in
benzene (2 mL). The reaction mixture was stirred for 2 h and then
filtered through a fritted funnel. The volatiles were removed, and
pentane (1 mL) was added to dissolve the product. Removal of solvent
isopropylacetylene (22 mg, 0.222 mmol) was added. After 10 min, the
reaction mixture had converted to (PNP-Cy)Sc(CCCHMe ) and
2
2
1
neopentane (>99% yield as determined by H NMR spectroscopy).
The volatile materials were removed by vacuum transfer, and the
resulting solid was recrystallized from pentane at −35 °C over 1 d
1
1
afforded the desired product as a white foam (49.1 mg, 72% yield). H
(
50.4 mg, 67% yield). H NMR (600 MHz, C D ): δ 6.01 (s, 2H, pyr-
6
6
NMR (500 MHz, C D ): δ 8.30 (d, J = 6.8 Hz, 4H), 7.42 (t, J = 7.2
CH), 3.01 (d, J = 5.0 Hz, 4H, −CH PCy ), 2.62 (hept, J = 6.8 Hz, 2H,
6
6
2
2
Hz, 4H), 7.32 (t, J = 7.3 Hz, 2H), 6.35 (s, 2H, pyr-CH), 3.15 (d, J =
−
CCCHMe ), 2.50−2.34 (m, 4H, −Cy), 2.18−2.03 (m, 8H, −Cy),
2
4
.7 Hz, 4H, −CH PCy ), 1.71−1.26 (m, 24H, −Cy), 1.14−0.73 (m,
1
1
.89−1.76 (m, 13H, −Cy), 1.75−1.66 (m, 7H, −Cy), 1.64−1.49 (m,
2
2
13
13
20H, −Cy). C NMR (126 MHz, C D ): δ 135.44 (br), 133.90,
1
2
2H, −Cy), 1.25 (d, J = 6.8 Hz, 12H, −CCCH(CH ) ). C NMR
6
6
3
2
28.59, 127.97, 127.14, 106.76, 33.44 (m), 29.27, 28.63, 27.42 (m),
(
150.90 MHz, C D ): δ 135.64 (t, J = 3.5 Hz), 105.61 (d, J = 6.0 Hz),
6 6
7.26 (m), 26.12, 22.41 (m). 31P{ H} NMR (202 MHz, C D ): δ 1.71.
1
3
2
3.13 (t, J = 4.4 Hz), 29.85, 29.22, 28.23 (dd, J = 22.2, 9.0 Hz), 27.73−
7.24 (m), 26.92, 26.43, 24.27, 23.15 (d, J = 8.0 Hz). Note that the
6
6
resonance for the carbon directly attached to the scandium was not
ASSOCIATED CONTENT
Supporting Information
Crystallographic data and spectral characterization. The
Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00213.
■
observed. This effect is a common feature of scandium alkyl
*
S
45
compounds, owing to the large quadrupole moment of Sc (100%
2
8,29 31
abundance, I = 7/2, −0.22 barns).
P NMR (202 MHz, C D ): δ
6 6
3
.34. Anal. Calcd for C H NP Sc: C, 72.15; H, 9.69; N, 2.10. Found:
40
64
2
C, 71.92; H, 9.57; N, 2.03.
Synthesis of (2,5-Bis(di-tert-butylphosphinomethyl)pyrrolyl)bis-
t
(
isopropylacetylide)scandium (6b), (PNP- Bu)Sc(CCCHMe ) . A
2
2
sample of 2c (11.4 mg, 0.020 mmol) was dissolved in benzene-d6
AUTHOR INFORMATION
Corresponding Authors
*E-mail: tdtilley@berkeley.edu.
*E-mail: raandersen@lbl.gov.
Notes
■
(
0.6 mL) in a 5 mm NMR tube with a Teflon screw cap, and
isopropylacetylene (20 mL, 0.2 mmol) was added. After 44 h, the
t
reaction mixture had converted to (PNP- Bu)Sc(CCCHMe ) and
2
2
1
neopentane (>99% yield as determined by H NMR spectroscopy).
1
H NMR (400.13 MHz, C D ): δ 6.17 (s, 2H, pyr-CH), 3.09 (d, J =
6
6
6
.0 Hz, 4H, −CH P(C(CH ) ) ), 2.53 (hept, J = 6.8 Hz, 2H,
2
3
3
2
The authors declare no competing financial interest.
−
CCCHMe ), 1.31 (d, J = 12.3 Hz, 36H, −CH2P(C(CH ) ) ), 1.17
2
3 3 2
13 1
(
d, J = 6.8 Hz, 12H, −CCCH(CH ) ). C{ H} NMR (100.61 MHz,
2
2
ACKNOWLEDGMENTS
■
C D ): δ 136.38, 106.50, 100.27, 33.15, 29.74, 23.84, 21.45, 21.22. The
6
6
This work was supported by the Director, Office of Science,
Office of Basic Energy Sciences of the U.S. Department of
Energy, under contract no. DE-AC02-05CH11231. D.S.L.
would like to acknowledge the support of an NSF Graduate
carbon of the acetylide attached to the scandium was not observed.
3
1
1
P{ H} NMR (161.98 MHz, C D ): δ 28.51.
6
6
Thermolysis of 2b. A sample of 2b (12.2 mg) was dissolved in
toluene-d (0.8 mL) in a 5 mm NMR tube with a Teflon screw cap.
8
H
DOI: 10.1021/acs.organomet.5b00213
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Research Fellowship, as well as Micah Ziegler for help with X-
ray crystallography. We also acknowledge the National
Institutes of Health for funding of the ChexRay X-ray
crystallographic facility (College of Chemistry, University of
California, Berkeley) under grant no. S10-RR027172.
Mindiola, D. J. J. Am. Chem. Soc. 2012, 134, 20081−20096. (c) Cheng,
J.; Shima, T.; Hou, Z. Angew. Chem., Int. Ed. 2011, 50, 1857−1860.
(22) Kumar, S.; Mani, G.; Mondal, S.; Chattaraj, P. K. Inorg. Chem.
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DEDICATION
■
J. J. Am. Chem. Soc. 1985, 107, 8111−8118.
Dedicated to the memory of Greg Hillhouse, a great
organometallic chemist and friend.
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DOI: 10.1021/acs.organomet.5b00213
Organometallics XXXX, XXX, XXX−XXX