Tebbe-like and Phosphonioalkylidene and -alkylidyne Complexes of Scandium

Article abstract of DOI:10.1021/jacs.0c02742

The bonding between scandium and carbon in a series of alkylidene- and alkylidyne-like moieties is compared. The Tebbe analogue complex (PNP)Sc(μ2-CHSiMe3)(μ2-CH3)[Al(CH3)(CH2SiMe3)] (2) (PNP- = N[2-PiPr2-4-methylphenyl]2) could be formed by adding AlMe3 to (PNP)Sc(CH2SiMe3)2 (1). The fluxional behavior of 2 is studied by a combination of 2D 13C-1H HMQC, HMBC, and other heteronuclear NMR spectroscopic experiments. The phosphonioalkylidene complex (PNP)Sc(CHPPh3)(CH3) (3) could be prepared from 2 by treatment with 2 equiv of the ylide H2CPPh3 or by methane elimination from (PNP)Sc(CH3)2 and 1 equiv of H2CPPh3. The reactivity of the alkylidene in 2 was further explored with N3Ad, which gave insertion at the Sc-C bond, yielding (PNP)Sc(CH3)[η2-N3AdCHSiMe3Al(CH3)(CH2SiMe3)] (4), while DMAP provided C-H activation across the alkylidene with loss of the Al-C bond to form (PNP)Sc(η2-NC5H3NMe2)(CH2SiMe3) (5). Utilizing the same approach that yielded 2, methane elimination in 3 could further be promoted with Al(CH3)3 to furnish the first example of a scandium phosphonioalkylidyne complex, (PNP)Sc(μ2-CPh3)(μ2-CH3)Al(CH3)2 (6). Experimental and theoretical studies were combined to compare the bonding in 2, 3, and 6, in order to understand the legitimacy of Sc-C multiple bond character.

Full text of DOI:10.1021/jacs.0c02742

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Article
Tebbe-Like and Phosphonio-Alkylidene
and -Alkylidyne Complexes of Scandium
Pavel Zatsepin, Eunji Lee, Jun Gu, Michael R. Gau, Patrick Carroll, Mu-Hyun Baik, and Daniel J. Mindiola
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c02742 • Publication Date (Web): 21 Apr 2020
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Page 1 of 11
Journal of the American Chemical Society
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Tebbe-Like and Phosphonio-Alkylidene and -Alkylidyne Complexes of
Scandium
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‡
‖
‡
‡
‡
‖
Pavel Zatsepin, Eunji Lee, Jun Gu, Michael R. Gau, Patrick J. Carroll, Mu-Hyun Baik, * Daniel J.
Mindiola *
‡
‡Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
‖Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST) and the Center for Catalytic
Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea.
Supporting Information Placeholder
ABSTRACT: The bonding between scandium and carbon in a
series of alkylidene and alkylidyne-like moieties is compared.
2 3 2
The Tebbe-analogue complex (PNP)Sc(μ -CHSiMe )(μ -
–
i
CH
methylphenyl]
(PNP)Sc(CH SiMe
3
)[Al(CH
3
)(CH
2
2
SiMe
3
)]
(2)
(PNP
=
N[2-PPr
2
-4-
to
), could be formed by adding AlMe
3
2
3
)
2
(1). The fluxional behavior of 2 is studied
by a combination of 2D C- H HMQC, HMBC and other het-
eronuclear NMR spectroscopic experiments. The phosphonio-
1
3
1
alkylidene complex (PNP)Sc(CHPPh
pared from 2 by treatment with 2 equiv of the ylide H
by methane elimination from (PNP)Sc(CH and one equiv of
CPPh . The reactivity of the alkylidene in 2 was further ex-
plored with N Ad, which gave insertion at the Sc–C bond yield-
ing (PNP)Sc(CH
while DMAP provided C–H activation across the alkylidene with
3
)(CH
3
) (3) could be pre-
2
CPPh or
3
3 2
)
Figure 1. Bonding modes of alkylidenes or nucleophilic
carbenes to the Sc(III) ion.
H
2
3
3
2
3
)[η -N
3
AdCHSiMe
3
Al(CH
3
)(CH
2
SiMe
3
)] (4)
Al-center may bind to the highly nucleophilic carbon, signifi-
4
a-f
cantly diminishing the RE-C bond order (Figure 1c). Interest-
ingly, the only crystallographically characterized example of a
RE alkylidene that involves bridging strictly between two cen-
2
loss
NC
of
NMe
the
)(CH
Al–C
bond
to
form
(PNP)Sc(η -
5
H
3
2
2
SiMe ) (5). Utilizing the same approach that
3
yielded 2, methane elimination in 3 could further be promoted
with Al(CH to furnish the first example of a scandium phos-
phonio-alkylidyne (PNP)Sc(μ -CPh )(μ -CH )Al(CH (6). Ex-
perimental and theoretical studies were combined to compare
the bonding in 2, 3 and 6, in order to understand the legitimacy
of Sc–C multiple bond character.
ters of different metals,
is Cp’(py)Sc(μ
2
-CHSiMe
3 2
)(μ -
t
5
3
)
3
N Bu)IrCp* (Cp’ = C Me SiMe ) (Figure 1d). More recently, the
5 4 3
2
3
2
3
3
)
2
first examples of terminally bound RE-alkylidene structures
have been obtained by delocalizing the excess charge within
the metal-carbon-heteroatom multiple bonds, where the het-
2
+
eroatom in question can be a phosphonium, PPh
3
(Figure
6
1
e). These systems avoid chelation of other heteroatom frag-
3
e
2
ments such as phosphino groups (PPh , Figure 1f) which
sometimes compromise the reactive nature of the Sc–C multi-
+
3d
Introduction
2
ple bonds as in the case of [P(S)Ph ] (Figure 1g). Similar
strategies have enabled isolation of rare and otherwise highly
The nature of the metal-carbon multiple bonds involving
rare-earth (RE) ions is an ongoing topic of debate. The empty
orbitals of these metals are highly contracted f-orbitals and/or
very high-energy d-orbitals; characteristics precluding for-
mation of strong, covalent bonds with carbon-centered orbitals.
In other words, the metal is commonly a hard Lewis acid,
whereas the carbon-containing ligand is a soft Lewis base.
reactive titanium alkylidyne structures supported by either sta-
t
bilization with trimethylaluminium, (PNP)Ti(μ
2
-C Bu)(μ
2
-
3 2
)AlMe
,7 or with a phosphonium substituent in the form of
a
CH
2
PNP)Ti≡CPPh Me(OTf). Hence, we sought to extend this
7
b
(
methodology to the synthesis of complexes containing scan-
dium–carbon multiple bonds, utilizing the same pincer ligand.
We report an AlMe
structure of the iconic Tebbe reagent Cp
CH )Al(CH )
2 3 2
3
stabilized alkylidene that closely mirrors the
Ti(μ -Cl)(μ
(Figure 1h). We also explored the reactivity of
the new reagent and compared its structure and bonding to that
While terminally bound RE alkylidenes can be generated in the
1a,b
2
2
2
-
gas phase via reaction with methane,
there is a dearth of
8
examples of RE systems featuring a legitimate π-bond between
the two atoms in the condensed phase. Because the alkylidene
2
+
2
a-f
of the covalently linked PPh
nally, we showcase the utility of Al(CH )
3
(phosphoniomethylidene). Fi-
by integrating the two
moieties tend to bridge and/or oligomerize (Figure 1),
one
3 3
strategy for stabilizing mononuclear systems is the use of
metallacycles or rings, but this approach often diminishes the
groups and disclose the first example of a phosphonio-alkyli-
dyne complex of scandium (Figure 1i).
3a-e
reactivity at the M=C bond in question.
An abstraction/elimi-
nation approach using trialkylaluminum reagents has also been
employed targeting such structures; however, more than one
Experimental Section
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 11
General Procedures. All operations were performed in an M.
Braun glove box or using standard Schlenk techniques under a
nitrogen atmosphere unless otherwise stated. Anhydrous hy-
drocarbon solvents were purchased from Fisher Scientific. All
anhydrous hydrocarbon solvents (pentane, hexanes, toluene,
benzene) were purified and dried by passage through two col-
umns of activated alumina and Q-5 drying agent in a two-col-
umn solvent system. All bulk solvents were kept over sodium
Si(CH
3
)
3
); 29Si INEPT NMR (79 MHz, benzene-d
6
, 300 K) δ –
31
1
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4.66; P{ H} NMR (162 MHz, benzene-d
Δν1/2 = 52 Hz). Analysis calc’d: C: 63.03, H: 9.65, N: 2.16;
Found: C: 52.89, H: 9.14, N: 1.10.
6
, 300 K) δ –1.41 (br,
Synthesis
CH )[Al(CH
(PNP)Sc(CH
while stirring vigorously, 219 μL of a 2 M hexanes solution of
Al(CH (438 μmol) was added. This was allowed to stir for 1
of
SiMe
SiMe were dissolved in ~7 mL of pentane, then
(PNP)Sc(μ
)] (2). 284 mg (438 μmol) of
2 3 2
-CHSiMe )(μ -
3
3
)(CH
2
2
3
3 2
)
8 6
and 4 Å molecular sieves. Toluene-d and benzene-d (Cam-
bridge Isotope Laboratories) were dried and degassed over a
potassium mirror prior to use. Celite and 4 Å molecular sieves
3 3
)
h, then the solution was filtered through glass fibre, concen-
trated to saturation (~0.5 – 1 mL volume; solution appears vis-
cous as it is evaporating) and placed into a –35 °C freezer. Yel-
low crystals were obtained over time. After sitting for 2 days,
267 mg (379 μmol, 86.7%) could be collected following de-
cantation of the mother liquor and rinsing the crystals with ~0.5
mL of –35 °C pentane and drying under vacuum. H NMR (500
MHz, benzene-d
1H, PNP aryl), 6.87 (br, 1H, PNP aryl), 6.81 (br, 2H, PNP aryl),
6.71 (br, PNP aryl), 2.26 (br, 1H, Pr CH(CH
9
2 3
were activated under vacuum overnight at 200 °C. H CPPh ,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
0
10
(
PNP)ScCl
to previous reports. [H
Sigma-Aldrich, 99 atom % C) and PPh
deprotonated under identical conditions using the unlabeled de-
rivative [H CPPh ][I]. All other chemicals were purchased from
commercial sources and degassed before being used. H, C,
2
,
and (PNP)Sc(CH
3
)
2
were prepared according
13
13
3
3 3
CPPh ][I] was prepared from CH I
13
(
3
in THF and then
1
3
3
1
13
6
, 300 K): δ 7.37 (br, 1H, PNP aryl), 7.03 (d br,
3
1
29
P, Si, HSQC, HMBC and COSY NMR spectral data were
recorded on Bruker AVII and AVIII 500 MHz, DRX 500 MHz or
AV-III 400 MHz spectrometers. H, and C NMR chemical
shifts are reported referenced to the internal residual proton,
i
3 2
) ), 2.17 (s, 3H,
1
13
i
PNP tolyl CH ), 2.08 (s, 3H, PNP tolyl CH ), 1.97 (br, 2H, Pr
3
3
i
i
CH(CH
CH(CH
CH(CH
CH(CH
3
3
3
3
)
)
)
)
2
2
2
2
3 2
), 1.57 (br, 1H, Pr CH(CH ) ), 1.45 (d br, 3H, Pr
i
i
deuterium or carbon resonances of toluene-d
8
(δ = 2.08 or
3 2
), 1.32 (d br, 3H, Pr CH(CH ) ), 1.19 (d br, 3H, Pr
), 1.08 (d br, 3H, Pr CH(CH
3
1
i
i
20.43) or benzene-d
shifts are reported with respect to external H
NMR chemical shifts are reported with respect to external
Si(CH (δ = 0.0).
6
(δ = 7.15 or 128.06). P NMR chemical
3
)
2
), 0.93 (br, 3H, Pr
), 0.80 (d br, 4H: 3H Pr CH(CH + 1H Sc-CH-
), 0.48 (s, 9H, Si(CH ),
); C NMR
, 300 K) δ 161.49 (d br, Ar), 155.10 (d br,
Ar), 137.25 (Sc-CH(Si(CH ), 133.72 (Ar), 133.59 (Ar), 132.95
2
9
i
3
PO
4
(δ = 0.0). Si
3 2
)
i
Si(CH
0.07 (s. 9H, Si(CH
101 MHz, benzene-d
3
)
3
), 0.67 (br, 6H, Pr CH(CH
3
)
2
3 3
)
1
3
3
)
4
3
)
3
), −0.38 (br, 2H, -CH (Si(CH )
2 3 3
(
6
Statement on elemental analyses (EA): Each of the compounds
that could be purified without significant impurities were submit-
ted for EA to Midwest Microlab, each returning extremely low
carbon values despite the request to use a combustion aid, and
possibly attributable to formation of carbides. In the interest of
transparency, those results are listed here. Comprehensive
NMR spectral data of each compound are presented in the Sup-
porting Information, in lieu of EA, and as proof of the bulk purity
of material constitutions which match those of corresponding
single crystal X-ray diffraction structures being presented.
3 3
)
(Ar), 132.31 (Ar), 131.78 (Ar), 125.91 (Ar), 125.44 (Ar), 118.83
(d br, Ar), 114.51 (Ar), 114.31 (d br, overlapping with neighbor-
ing signal, Ar), 24.71 (br, 2C, Pr CH(CH
i
3
)
2
), 21.03 (PNP tolyl
i
i
CH
3
), 20.81 (Pr CH(CH
3
i
)
2
), 20.75 (PNP tolyl CH
3
), 20.55 (Pr
i
CH(CH
CH(CH
CH(CH
3
3
3
)
)
)
2
2
2
), 19.95 (2C, Pr CH(CH
3
)
2
i
), 19.11 (m br, 3C, Pr
i
i
, Pr CH(CH
), 4.90 (Si(CH
, 300 K) δ -15.08 (a second, weak signal
3
)
2
), 18.38(2C, Pr CH(CH
3
)
2
), 16.54 (Pr
29
3
)
3
), 3.56 (Si(CH
3
)
3
); Si INEPT NMR
(79 MHz, benzene-d
6
1
29
is revealed at 0.97 using an H- Si HMBC experiment; see SI);
Synthesis of (PNP)Sc(CH
were suspended 300 mg (551 μmol) of (PNP)ScCl
mixture was cooled to –35 °C. In a separate vessel, 104 mg
1.10 mmol) of LiCH (SiMe ) was dissolved in toluene and
cooled to –35 °C. The cold solution of LiCH (SiMe ) was added
dropwise to the suspension of (PNP)ScCl while stirring vigor-
2
SiMe
3
)
2
(1). In 10 mL of toluene
31
1
P{ H} NMR (162 MHz, benzene-d
29 Hz, PNP) , −1.21 (br, Δν1/2 = 92 Hz, PNP). Analysis calc’d:
C: 61.42, H: 9.59, N: 1.99; Found: C: 59.25, H: 9.67, N: 1.70.
6
, 300 K) δ 7.10 (br Δν1/2 =
2
, then this
1
(
2
3
2
3
Synthesis of (PNP)Sc(CHPPh
84 mg (366 μmol) of (PNP)Sc(CH
cooled to –35 °C. In a separate vessel, 101 mg (366 μmol)
CPPh were dissolved into 8 mL of toluene and cooled to –
5 °C. Once both mixtures were cold, the H CPPh solution
was added dropwise to the (PNP)Sc(CH solution while vigor-
3
)(CH
3
) (3). In 8 mL of toluene
2
1
3 2
)
were dissolved and
ously. After allowing to stir for 1.5 h, while coming to ambient
temperature, the toluene was evacuated leaving a cloudy oil, to
which 1 mL of pentane was added, stirred and evacuated again.
The product was extracted with pentane (~10 mL) and filtered
through Celite, then concentrated to a volume of ~2 mL (the
solution appears very viscous as it is evaporating) then placed
into a –35 °C freezer overnight. Yellow crystals grow from which
the mother liquor can be decanted, and then the crystals were
rinsed with ~0.5 mL of –35 °C pentane and dried under vacuum.
H
2
3
3
2
3
3 2
)
ously stirring. This mixture was stirred for two hours, being al-
lowed to come to ambient temperature, then concentrated un-
der vacuum to a volume of ~4 mL and filtered through Celite,
after which ~4 mL of pentane was added. This new solution was
concentrated to a total volume of ~3 mL and placed into a –35
1
This yielded 319 mg (492 μmol, 89.3%) of the product. H NMR
°
C freezer. After sitting in the freezer overnight, yellow crystals,
3
4
(
=
500 MHz, benzene-d
4.2 Hz; 2 H, PNP aryl), 6.88 (dd, JHH = 8.4 Hz, JHH = 1.8 Hz;
2H, PNP aryl), 6.83 (d br, 2H, PNP aryl), 2.14 (s, 6H, PNP tolyl
6
, 300 K): δ 7.06 (dd, JHH = 8.4 Hz, JHP
with a slightly orange tint, grew and were separated from the
mother liquor, rinsed with ~0.5 mL of –35 °C toluene and ~0.5
mL of –35 °C pentane and dried under vacuum. This first crop
of crystals yields 156 mg (204 μmol, 55.9 %); the decanted so-
lution and rinses could be combined and concentrated further
3
4
i
CH
3 3 2
), 2.10 (m, 4H, Pr CH(CH ) ), 1.22 (multiple overlapping
i
3
3
resonances, 18H, Pr CH(CH ) ), 0.85 (dd, JHH = 6.7 Hz, JPH
3 2
i
2
=
9.3 Hz, 6H, Pr CH(CH
3
)
2
), 0.49 (d, JHH = 11.3 Hz, 2H, -CHH-
), 0.41 (d, JHH = 11.3 Hz, 2H, -CHH-SiMe ), 0.35 (s, 13H,
, 300 K) δ 159.75 (t,
PC = 10.9 Hz; Ar), 133.17 (Ar), 133.03 (Ar), 128.00 (overlaps
with solvent, Ar), 120.11 (t, JPC = 3.3 Hz, Ar), 116.59 (dd, JPC
11.7, 8.8 Hz, Ar), 55.05 (br, -CH Si(CH ), 24.09 (t, JPC = 2.7
), 20.81 (PNP tolyl CH ), 20.29 (t, JPC = 3.3 Hz,
and recrystallized to yield 64 mg more product for a total yield
of 220 mg (288 μmol, 78.8%). H NMR (500 MHz, benzene-d
2
SiMe
Si(CH
J
3
3
1
6
,
1
3
3
)
3
); C NMR (101 MHz, benzene-d
6
3
3
2
00 K): δ 7.72 (m, 6H, o-H Ph-PPh -CH-Sc), 7.36 (dd, JHH =
4
3
8
J
PPh
.6 Hz, JHP = 4.4 Hz; 1H, PNP aryl), 7.19 (dd, JHH = 8.6 Hz,
=
4
HP = 4.7 Hz; 1H, PNP aryl), 7.08–7.05 (m, 9H, m,p-H Ph-
-CH-Sc), 6.98–6.96 (m, 2H, PNP aryl, two different posi-
2
3 3
)
2
i
Hz, Pr CH(CH
3
)
2
3
tions on same ring overlapping), 6.92 – 6.90 (m, 2H, PNP aryl,
two different positions on same ring overlapping), 3.42 (d, JHP
i
i
Pr CH(CH
PC = 6.3, 5.1 Hz, Pr CH(CH
CH(CH ), 16.25 (t, JPC = 2.8 Hz, Pr CH(CH
3
)
2
), 19.92 (t, JPC = 3.6 Hz, Pr CH(CH
3
)
2
), 19.77 (dd,
2
i
i
J
3 2
) ), 19.06 (t, JPC = 5.9 Hz, Pr
=
14.1 Hz, 1H, Sc-CH-PPh
3
), 2.21 (s, 3H, PNP tolyl CH
3
), 2.20–
i
3
)
2
3
)
2
), 4.48 (-CH
2
-
i
2
.15 (m, 1H, Pr CH(CH ) , overlapping with tolyl peaks), 2.18
3 2
ACS Paragon Plus Environment

Page 3 of 11
Journal of the American Chemical Society
i
i
), 19.65 (d, 3JCP = 13.7 Hz; Pr
i
(
s, 3H, PNP tolyl CH
3
), 2.10 (m, 1H, Pr CH(CH
3
)
2
, overlapping
19.71 (m, 2C, Pr CH(CH
3
)
2
i
i
1
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
with residual toluene signal), 2.00–1.92 (m, 2H, Pr CH(CH
3
3
)
2
),
CH(CH
3
)
2
i
), 19.45–19.28 (2C, Pr CH(CH
13.3 Hz; Pr CH(CH
3
)
2
), 19.22 (d, JCP
=
),
i
3
3
i
1
=
.29–1.13 (m, 18H, Pr CH(CH
3
)
2
), 0.97 (dd, JHH = 6.9 Hz, JHP
), 0.95 (dd, JHH = 7.0 Hz, JHP = 4.3
), 0.23 (t, JHP = 1.9 Hz, 3H, Sc-CH
3
)
2
), 18.58 (d, JCP = 10.6 Hz; Pr CH(CH
3
)
2
i
3
3
3
i
3.7 Hz; 3H, Pr CH(CH
3
)
2
16.51 ( JCP = 5.6 Hz; Pr CH(CH
2.53 (Al(CH (Si(CH ))), 0.44 (Ad-NNN-CH(Si(CH
4.54 (Al-CH ); Si INEPT NMR (79 MHz, benzene-d
0.06 (Al(CH (Si(CH ))), –1.82 (Ad-NNN-CH(Si(CH
P{ H} NMR (162 MHz, benzene-d , 300 K) δ 3.43 (br, Δν1/2
3
)
2
), 3.40 (Al(CH
2
(Si(CH
)[Al]), –
, 300 K) δ
)[Al]);
3 3
) ))),
i
3
13
Hz; 3H, Pr CH(CH
NMR (101 MHz, benzene-d
3
)
2
3
);
C
2
3
)
3
3 3
)
6
2
29
6
, 300 K) δ 161.90 (d, JCP = 21.7
Hz; PNP Ar), 160.19 (dd, JCP = 21.4 Hz, JCP = 2.3 Hz; PNP
Ar), 137.56 (d, JCP = 78.8 Hz; ipso-C Ph-PPh
3
2
4
2
3
)
3
3 3
)
1
31
1
2
-CH-Sc), 133.39
6
=
(d, JCP = 1.85 Hz; PNP Ar), 133.27 (d, JCP = 1.3 Hz; PNP Ar),
132.78 (d, JCP = 1.5 Hz; PNP Ar), 132.74 (d, JCP = 1.3 Hz; PNP
110 Hz, PNP), 0.07 (br, Δν1/2 = 84 Hz, PNP).
2
2
Ar), 132.66 (d, JCP = 9.4 Hz; o-C Ph-PPh
2
-CH-Sc), 129.79 (d,
-CH-Sc), 128.13 (m-C Ph-PPh -CH-
Sc), 127.63 (d, JCP = 3.3 Hz; PNP Ar), 125.30 (d, JCP = 3.5 Hz;
Synthesis of (PNP)Sc(η -NC
5
H
3
NMe
2
)(CH
2
SiMe
3
)
(5).
3
J
CP = 2.7 Hz; p-C Ph-PPh
2
2
[NOTE: These procedures were carried out with glovebox lights
turned off as the product is slightly light sensitive.] (PNP)Sc(μ
CHSiMe )(μ -CH )[Al(CH )(CH SiMe )] (120 mg, 170 μmol)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
-
3
1
PNP Ar), 121.85 (d, JCP = 6.2 Hz; PNP Ar), 119.51 (d, JCP
8.3 Hz; PNP Ar), 117.88 (d, JCP = 7.0 Hz; PNP Ar), 116.88 (d,
CP = 18.6 Hz; PNP Ar), 73.99 (br, Sc-CH-PPh
), 24.20 (2C overlapping, Pr CH(CH
), 20.78 (PNP tolyl CH ), 20.28 (d,
), 20.15 (d, JCP = 6.0 Hz; Pr CH(CH ), 20.05 (d,
3 2
CP = 8.6 Hz; Pr CH(CH ) ), 19.83 (d, JCP = 7.2 Hz; Pr
), 19.33 (d obscured by neighbouring signal, Pr
), 19.27 (2C overlapping, Pr CH(CH
= 4.5 Hz; Pr CH(CH
16.27 (d, JCP = 5.6 Hz; Pr CH(CH
=
3
2
3
3
2
3
3
1
J
was dissolved in 7 mL of pentane stirred vigorously as a 3 mL
solution of DMAP (41.6 mg, 341 μmol) in toluene was added.
The resulting mixture was allowed to stir for 2 h at ambient tem-
perature. The mixture was then filtered through glass fiber and
the solvent was removed in vacuo. The product was then ex-
tracted with ~ 6 mL of 50/50 pentane/toluene, filtered through
Celite, concentrated to saturation and placed into the –35 °C
freezer. Pale yellow microcrystalline solids form in a yellow
green solution. The final product was obtained following de-
cantation of the supernatant, rinsing with –35 °C toluene and
drying under vacuum. This produced 86 mg of a product that
was ~95% pure – multiple attempts to separate another
1
3
), 33.85 (br, Sc-
i
CH
CH
3
3 2
) ), 20.96 (PNP tolyl
3
i
3
3
J
CP = 7.4 Hz; Pr
3
i
CH(CH
3
)
2
3 2
)
3
i
3
i
J
i
CH(CH
CH(CH
3
)
)
2
i
2
3
2
i
3
)
2
), 19.14 (d, JCP
3
i
3
)
2
), 17.04 (d, JCP = 4.2 Hz; Pr CH(CH
3
)
2
),
3
i
); 31P{ H} NMR (162 MHz,
1
3 2
)
benzene-d , 300 K) δ 5.10 (-CH-PPh
6
3
), 2.94 (br, Δν1/2 = 80 Hz,
PNP), 2.04 (br, Δν1/2 = 69 Hz, PNP). Analysis calc’d: C: 72.33,
H: 7.79, N: 1.83; Found: C: 62.81, H: 7.61, N: 1.16.
“(PNP)Sc”-containing compound were attempted but were un-
1
successful. H NMR (500 MHz, benzene-d
6
, 300 K): δ 8.29 (d,
)[η2-
3
J
HH = 6.1 H; 1H, o-to Sc-N in NC
7.14 (m overlapping with solvent peak, 1H), 7.00 (d, JHH = 2.3
Hz; 1H, o-to Sc-C in NC NMe ), 6.99–6.97 (m, 2H, PNP aryl),
6.94 (d, JHH = 8.5 Hz; 1H PNP aryl), 6.83 (d, JHH = 8.3 Hz; 1H
PNP aryl), 6.13 (dd, JHH = 6.2 Hz, JHH = 2.7 Hz; 1H, m-to Sc-
N in NC NMe ), 2.27 (s, 6H, N(CH ), 2.21 (s, 3H, PNP tolyl
CH ), 2.17 (s, 3H, PNP tolyl CH ), 2.05 (m, 1H, Pr CH(CH
the other methine peaks overlap with tolyl, dimethylamino, and
H NMe ), 7.20 (m, PNP aryl),
5 3 2
Synthesis
AdCHSiMe
CHSiMe )(μ -CH
and N
of
(PNP)Sc(CH
(4). (PNP)Sc(μ
)] (189 mg, 268 μmol)
3
4
N
3
3
Al(CH
3
)(CH
2
SiMe
3
)]
SiMe
2
-
3
2
3
)[Al(CH
3
)(CH
2
3
5
H
3
2
3
3
3
Ad (47 mg, 265 μmol) were placed into a vial with a stir
3
4
bar and dissolved in 7 mL of pentane and 3 mL of toluene and
allowed to stir for 1 h. The solution was concentrated to a vol-
ume of ~2 mL and filtered through glass fiber, then placed in
the –35 °C freezer for recrystallization. Pale yellow microcrys-
talline product deposits itself on the bottom of the vial, which is
washed with –35 °C pentane/toluene (50/50) and dried under
vacuum, giving 94 mg of product (107 μmol, 39.8%, ~85% pu-
rity). This product, despite multiple recrystallizations could not
be made totally pure, consistently containing another
5
H
3
2
3 2
)
i
3
3
3 2
) ,
3
3
residual solvent signals), 1.41 (dd, JHP = 14.7 Hz, JHH = 7.1
Hz; 3H, Pr CH(CH
1.04 (m, 9H, Pr CH(CH
i
i
3
)
2
), 1.35–1.26 (m, 9H, Pr CH(CH
3
3
)
2
), 1.14–
i
3
3
)
2
), 0.98 (dd, JHP = 8.7 Hz, JHH = 7.5
i
2
Hz; 3H, Pr CH(CH
3
)
2
), 0.41 (s, 9H, Si(CH
3
)
3
), 0.83 (d, JHH
), 0.23 (d, JHH = 11.6 Hz , 1H,
); C NMR (101 MHz, benzene-d , 300 K) δ
), 162.43 (d, JCP = 20.4 Hz, PNP
CP = 20.43 Hz, PNP Ar), 152.39 (ipso-to
NMe ), 143.93 (o-to Sc-N in NC NMe ),
132.86 (PNP Ar), 132.71 (PNP Ar), 132.33 (PNP Ar), 132.19
=
2
11.6 Hz, 1H, Sc-CHH-Si(CH )
3 3
1
3
“(PNP)Sc”-containing compound; it is not clear whether this is
Sc-CHH-Si(CH
3
)
3
6
2
an isomer of 4 or a different complex, however many peaks ap-
pear to resemble 4 suggesting that it may be a diastereomer.
212.75 (Sc-C in NC H NMe
5 3 2
2
Ar), 160.20 (d,
N(CH in NC
J
1
H NMR (500 MHz, benzene-d
6
4
, 300 K): δ 7.13 (m, 2H, PNP
3
)
2
5
H
3
2
5
H
3
2
3
Aryl), 6.94 (dd, JHH = 8.5 Hz, JHH = 2.1 Hz; 1H, PNP Aryl),
3
4
3
6
.90–6.84 (m, 2H, PNP Ar), 6.75 (dd, JHP = 5.5 Hz, JHH = 2.0
Hz; 1H, PNP Ar), 2.93 (s, 1H, Ad-NNN-CH(Si(CH )[Al]), 2.25
br, 6H, CH adamantyl 2,9,8 positions), 2.17 (s, 3H, PNP tolyl
CH ), 2.15 (s, 3H, PNP tolyl CH ), 2.09 (br, 3H, CH, adamantyl
,5,7 positions), 1.96–1.84 (m, 4H, Pr CH(CH
CH , adamantyl 4,6,10 position), 1.62 (br, 3H, CH
4,6,10 position), 1.30–0.80 (m, 24H, Pr CH(CH
Sc-CH ), 0.37 (s, 9H, Al(CH (Si(CH ))), 0.05 (br, 9H, Ad-NNN-
CH(Si(CH )[Al]), –0.06 (s, 3H, Al-CH
Hz, Al(CHH(Si(CH ))), –0.64 (d,
(PNP Ar), 127.08 (PNP Ar), 125.60 (PNP Ar), 121.09 (d, JCP =
1
3
)
3
6.0 Hz; PNP Ar), 120.04 (d, JCP = 20.0 Hz; PNP Ar), 118.78 (d,
3
1
(
2
J
CP = 6.8 Hz; PNP Ar), 117.96 (d, JCP = 19.4 Hz; PNP Ar),
110.88 (o-to Sc-N in NC NMe ), 107.19 (m-to Sc-N in
NC NMe ), 40.66 (Sc-CH -Si(CH ), 38.48 (N(CH ), 24.47
(2C overlapping, Pr CH(CH ), 20.96 (PNP tolyl CH ), 20.85
), 20.14
), 19.90
3
3
5
H
2
3
2
i
3
3
)
2
), 1.73 (br, 3H,
, adamantyl
), 0.45 (s, 3H,
5
H
3
2
3
)
3
3 3
)
3
i
2
2
3
)
2
i
1
i
3
)
2
(PNP tolyl CH
3
), 20.30 (d, JCP = 9.5 Hz; Pr CH(CH
3
)
2
3
i
i
3
2
3
)
3
(d, JCP = 5.9 Hz; Pr CH(CH
3
)
2
), 19.99 (Pr CH(CH
), 19.51 (d, JCP = 6.1 Hz;
), 19.27 (d, JCP = 11.9 Hz; Pr CH(CH
3
)
2
2
i
i
3
3
)
3
3
), –0.53 (d, JHH = 12.2
(Pr CH(CH
3
)
2
), 19.82 (Pr CH(CH
3
)
2
2
i
3
i
3
1
)
3
3
J
HH
=
12.2 Hz,
Pr CH(CH
3
)
2
3
)
2
), 18.95
1
3
i
3
i
Al(CHH(Si(CH
3
)
3
2
))); C{ H} NMR (126 MHz, benzene-d , 300
6
3 2
(d, JCP = 11.6 Hz; Pr CH(CH ) ), 17.36 (d, JCP = 2.8 Hz; Pr
2
3
i
K) δ 160.49 (d, JCP = 21.0 Hz; PNP Ar), 159.4 (d, JCP = 19.7
CH(CH
3
)
2
), 16.62 (d,
J
CP = 4.8 Hz; Pr CH(CH
); Si INEPT NMR (79 MHz, benzene-d , 300 K) δ
, 300 K) δ 0.98 (br
Δν1/2 = 67 Hz, PNP), −1.58 (br, Δν1/2 = 73 Hz, PNP).
3 2
) ), 4.90
29
Hz; PNP Ar), 133.32 (2C, PNP Ar), 133.10 (PNP Ar), 132.34
(Si(CH
3
)
3
6
3
3
31
1
(PNP Ar), 127.25 (d, JCP = 4.2 Hz; PNP Ar), 126.56 (d, JCP
=
−3.49; P{ H} NMR (162 MHz, benzene-d
6
3
3
J
.8 Hz; PNP Ar), 121.65 (d, JCP = 6.1 Hz; PNP Ar), 118.30 (d,
CP = 7.1 Hz; PNP Ar), 117.14 (d, JCP = 23.3 Hz; PNP Ar),
16.53 (d, JCP = 21.3 Hz; PNP Ar), 58.01 (N-Cquaternary Ad 1
3
1
1
1
Synthesis
(PNP)Sc(CHPPh
5 mL toluene and cooled to –35 °C. Once cooled, a hexanes
solution of 2 M Al(CH (76 μ, 157 μmol) was added and the
of
(PNP)Sc(μ
2
-CPh
3
)(μ
2
-CH
3
)Al(CH
3
)
2
(6).
position), 56.30 (Ad-NNN-CH(Si(CH
,9,8 positions), 40.48 (Sc-CH ), 36.67 (Ad CH
tions), 30.32 (Ad CH, 3,5,7 positions), 24.53 (d, JPC = 6.6 Hz;
3
)
3
)[Al]), 43.75 (Ad CH
2
3
)(CH ) (120 mg, 157 μmol) was dissolved in
3
2
3
2
2
4,6,10 posi-
3 3
)
i
2
i
Pr CH(CH
J
3
)
2
), 24.18 (d, JPC = 5.7 Hz; Pr CH(CH
3
)
2
), 21.08 (d,
), 20.79 (PNP Ar tolyl CH ), 20.73
3 3 2
PNP Ar tolyl CH ), 20.00 ( JCP = 12.7 Hz; Pr CH(CH ) ), 19.83–
solution was stirred vigorously for 1 hr, then concentrated by
vacuum to a volume of ~0.5 mL and filtered through glass fibre.
An equal volume of pentane was added to the solution, and it
3
i
CP = 10.8 Hz; Pr CH(CH
3
1
)
2
3
i
(
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 11
was concentrated to apparent saturation, and then filtered once
more. Crystals in P2 /n space group could be obtained by plac-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
ing an open vial containing the concentrated solution into a jar
and allowing for crystallization by evaporation at ambient tem-
perature gave large yellow crystals after 1 day, from which the
mother liquor was decanted and the solids rinsed with –35 °C
toluene, and –35 °C pentane then dried under vacuum (53 mg,
6
5 μmol, 41.1%). A similar procedure wherein the concentrated
solution was placed into a freezer (–35 °C) gave crystals in C2/c
space group after about one week, but with inferior yields (and
with widely varying degrees of purity) the best sample showing
1
a 24 % yield. H NMR (500 MHz, benzene-d
6
, 300 K): δ 7.68
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
3
4
(
ddd, JHP = 11.6 Hz, JHH = 7.7 Hz, JHH = 1.8 Hz; 6H, o-H Ph-
3
4
PPh
2
-CH-Sc), 7.40 (dd, JHH = 7.4 Hz, JHP = 3.8 Hz; 1H, PNP
-CH-Sc + 2H PNP
Scheme 1. Synthesis of the scandium bis-alkyl complex 1
aryl), 7.07–7.00 (m, 11H: 9H m,p-H Ph-PPh
2
3
3
along with the Tebbe-like complex 2, and phosphonio-alkyli-
dene complex 3. Two synthetic entries for complex 3 are
shown in addition to the fluxional behavior of 2 in solution.
aryl), 6.93 (d, JHP = 5.0 Hz; 1H, PNP aryl), 6.82 (d, JHH = 8.6
3
Hz; 1H, PNP aryl), 6.77 (d, JHP = 5.7 Hz; 1H, PNP aryl), 2.24
(
s, 3H, PNP tolyl CH
residual toluene peak), 2.15–2.00 (m, 3H, Pr CH(CH
these is under the benzylic position signal from toluene and
3
), 2.11 (s, 3H, PNP tolyl CH
3
, under the
i
3 2
)
, one of
solution even when stored at low temperature, with loss of pro-
pylene (Figure S20) akin to what was reported for similar com-
i
3
3 2
PNP), 1.69 (m, 1H, Pr CH(CH ) ), 1.49 (dd, JHP = 16.0 Hz,
1
1a
11b
plexes of Ce, and Sc, but the resulting products could not
3
i
i
J
HH = 6.9 Hz; 3H, Pr CH(CH ),
3
)
2
), 1.21 (m, 6H, Pr CH(CH
3
)
2
be characterized.
i
1.01 (s, 3H, Sc-CH -Al), 0.99 (m, 6H, Pr CH(CH ) ), 0.89–0.80
(m, 6H, Pr CH(CH ) ), 0.77 (dd, JHP = 8.0 Hz, JHH = 8.0 Hz;
3 2
3
3 2
i
3
3
The solid-state structure determined by X-ray crystallog-
raphy is shown in Figure 2 (top). Despite the lack of a formal
i
3
H , Pr CH(CH
3
)
2
), –0.09 (s, 3H, Al-CH
3
), –0.31 (s, 3H, Al-CH
3
);
=
1
3
2
multiple bond between Sc and C27, the Sc−CHSiMe distance
C NMR (101 MHz, benzene-d , 300 K) δ 161.80 (d, JCP
1.3 Hz; PNP Ar), 158.31 (d, JCP = 18.1 Hz; PNP Ar), 138.09
6
3
2
is surprisingly short at 2.0845(14) Å compared to what is found
in the bridging CH group (2.3641(14) Å) or the Sc−CH dis-
3 2
tance in the methylidene complex (PNP)Sc(μ -CH )(μ -
3 2 2
2
1
(
d, JCP = 79.9 Hz; ; ipso-C Ph-PPh
2
-CH-Sc), 133.25 (3C, PNP
Ar signals coincide), 133.03 (d, JCP = 9.6 Hz; o-C Ph-PPh -CH-
CP = 15.2 Hz, Sc-
)), 129.40 (d, JCP = 2.7 Hz; p-C Ph-PPh -CH-
Sc), 129.34 (PNP Ar), 127.91 (m-C Ph-PPh -CH-Sc), 125.08
PNP Ar), 123.71 (PNP Ar), 119.26 (d, JCP = 20.0 Hz; PNP Ar),
2
2
1
3 2 3 2 2
CH ) [Al(CH ) ] (2.3167(17) Å) that is stabilized by two Lewis
Sc), 132.83 (PNP Ar), 132.45 (d,
C(AlMe
J
3
b
4
acids. The solid-state structure of 2 also reveals what tanta-
3
)(PPh
3
2
2
1
(
3
1
1
16.18 (d, JCP = 6.4 Hz; PNP Ar), 115.59 (d, JCP = 21.3 Hz;
i
PNP Ar), 24.92 (Sc-CH
3
-Al), 24.15 (2C, overlapping, Pr
), 20.60 (PNP tolyl CH ), 20.50
), 20.02
), 19.25 (d,
overlap-
), –1.27 (Al-
); P{ H} NMR (162 MHz, benzene-d , 300
K) δ 6.75 (br d, Δν1/2 = 54 Hz, JPP = 13 Hz; PNP), –1.31 (br,
CH(CH ), 21.00 (PNP tolyl CH
3
)
2
3
3
3
i
i
3 2 3 2
(d, JCP = 6.6 Hz; Pr CH(CH ) ), 20.15 (Pr CH(CH )
i
3
i
3 2 3 2
(Pr CH(CH ) ), 19.67 (d, JCP = 6.1 Hz; Pr CH(CH )
3
i
i
J
3 2 3 2
CP = 7.3 Hz; Pr CH(CH ) ), 18.82 (3C, Pr CH(CH )
i
i
3 2 3 2
ping), 16.98 (Pr CH(CH ) ), 15.93 (Pr CH(CH )
3
1
1
CH
3
), –1.85 (Al-CH
3
6
2
2
3 3
Δν1/2 = 52 Hz, JPP = 13 Hz; PNP), –21.53 (-C(AlMe )(PPh ).
Analysis calc’d: C: 70.32, H: 7.87, N: 1.71; Found (Attempt 1):
C: 59.71, H: 8.00, N: 0.96; (Attempt 2): C: 62.94, H: 8.16, N:
1.34.
Results and Discussion
Isolation and Characterization of a Tebbe-Analogue of
Scandium. Our investigation began with a re-examination of
the μ
2
-bridging methylene fragment that closely resembles the
-CH )(μ
-4-methylphenyl] ), M =
-trispyrazolylborate, M =
We hypothesized that a com-
plex formed by a single equivalent of AlR binding to the bridg-
Tebbe reagent as an intermediate en route to LM(μ
2
2
2
-
−
i
CH
3
)
2
(AlMe
2
)
2
that we (L = N[2-PPr
2
2
−
t
Sc) and Anwander (L = 3,5- Bu,CH
3
4
b,c
La) reported some time ago.
3
ing carbon should be accessible with sterically demanding alkyl
groups. For this reason, we first prepared the bis-alkyl complex
(PNP)Sc(CH
2
SiMe
3
)
2
(1) in 89% yield from the transmetallation
of (PNP)ScCl
2
with two equivalents of LiCH
2
SiMe in toluene
3
over 1.5 hours. Complex 1 was fully characterized by multinu-
clear NMR spectroscopy in addition to single crystal X-ray dif-
Figure 2. Top: Solid-state structures of the Tebbe-analogue
. Solvent and hydrogens with the exception of α-hydrogen,
have been omitted for clarity. Bottom: HMBC NMR spectrum
fraction studies. Adding a single equivalent of AlMe
3
as a 2 M
2
solution in hexanes to a pentane solution of 1 readily resulted
in
CH
the
)[Al(CH
formation
)(CH SiMe )] (2), isolable in 87% yield, along with
(Scheme 1). While this complex was easily
prepared at ambient temperature, it gradually decomposed in
of
2 3 2
(PNP)Sc(μ -CHSiMe )(μ -
13
1
of 2 displaying the cross peak in the C{ H} trace at 137 ppm
3
3
2
3
1
to the Si(CH
trum.
3 3
) hydrogens at 0.07 ppm in the H NMR spec-
the liberation of CH
4
ACS Paragon Plus Environment

Page 5 of 11
Journal of the American Chemical Society
lizingly implies an α-H agostic interaction between the alkyli-
dene hydrogen and the Sc(III) ion, with a Sc–H distance of
.25(2) Å and acute Sc–C–H angle of 87.3(13)° where the H
Sc=C multiple bond character for the former in accord with what
was previously argued in (nacnac)Sc(CHPPh )(X). The for-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
2
atom was located and refined isotropically. Complex 2 shows a
1
H NMR spectrum where all resonances are extremely broad-
ened, especially with respect to any protons that are bound to
a carbon attached to the Al center, to the extent where cross-
peaks are not observable in the HSQC spectrum at room tem-
perature. One notable feature in complex 2 is the presence of
1
two inequivalent SiMe
3
groups at 0.07 and 0.48 ppm in the H
NMR spectrum, although only the one incorporated into the al-
2
9
kylidene is visible in the Si INEPT spectrum at –15.08 ppm at
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
room temperature. The second weak signal can be found by
1
29
H- Si HMBC spectrum (Figure S11). What is most intriguing
13
1
in the C{ H} NMR spectrum of 2 is a broad signal at 137 ppm
with cross-peaks to a Si(CH ) moiety’s H resonances in the
3 3
1
HMBC and a proton that corresponds to the α-H (Figure 2, bot-
tom) in the HMQC spectrum; this highly downfield chemical
shift is consistent with the presence of a bridging alkylidene
species analogous to d depicted in Figure 1. While the two me-
thyl groups and (trimethylsilyl)methyl group bound to Al are in
rapid exchange in solution at ambient temperature, they resolve
2
9
into three distinct species discernable in Si INEPT NMR ex-
1
31
1
periment, with overlapping resonances in H and P{ H} spec-
tra at 199 K; ostensibly two are diastereomers where a different
methyl group bridges between Sc and Al, and a minor isomer
wherein the (trimethylsilyl)methyl moiety bridges. Complex 2 is
a close analogue of the Tebbe complex, and hence we explored
some of its reactivity.
Figure 3. Conceptual MO-diagram that compares the fron-
tier orbitals of a typical Sc-alkylidene 2* (a) to those of 2
(b). Contour plots of relevant orbitals of 2 are shown in (c).
mation of 3 from 2 and the phosphorus ylide H
that the Al−CHSiMe interaction is more stable than the
Sc−CHSiMe bonding, however the alkylidene group CHSiMe
2 3
CPPh suggests
3
Reactivity of Complex 2. Although compound 2 could be cat-
egorized as a Tebbe-like reagent structurally, the ionicity and
3
3
can depart with either the Sc or Al ion depending on the sub-
strate used.
the basicity in Sc(μ
notably different compared to the Tebbe reagent, Cp
Cl)(μ -CH )Al(CH . For example, compound 2 does not ex-
trude the Lewis acidic protecting group Al(CH (CH SiMe
when treated with a Lewis base such as H CPPh . Instead, the
alkylidene moiety deprotonates the ylide to give the phos-
phonio-alkylidene methyl complex (PNP)Sc(CHPPh )(CH ) (3)
along with what we propose to be the Lewis acid-base adduct
Me SiCH (CH )Al(CH PPh ) (Scheme 1, Figure S34). Com-
pound could also be independently synthesized via
PNP)Sc(CH with one equivalent of H CPPh (Scheme 1).
2
-CHSiMe
3
)(μ
2
-CH
3
)[Al(CH
3
)(CH
2
SiMe
3
) is
2
2
Ti(μ -
2
2
3 2
)
3
)
2
2
3
)
Electronic Structure. In order to better understand the elec-
tronic structure of 2, DFT calculations were carried out and the
frontier orbitals were analyzed. The most salient features are
summarized in Figure 3. The alkylidene moiety in a typical
Sc(III)-alkylidene of the Schrock-type is best pictured as a dian-
2
3
3
3
(
3
2
)
2
3
2
3
3
(
3
)
2
2
3
Complex 3 is relatively stable in the solid state, but decomposes
gradually in solution to a mixture of products which we have
6
been unable to identify. In accord with Chen’s studies, complex
3
is characterized by a relatively far downfield CHPPh
3
reso-
13
1
nance in C NMR spectrum, 73.97 ppm, ( JPC = 22.5 Hz ob-
served in P{ H} spectrum by using C–enriched sample,
(PNP)Sc( CHPPh
3
1
1
13
1
3
13
1
3 3
)(CH ) (3- C)), whereas the H NMR spec-
2
trum reveals a doublet centered at 3.42 ppm ( JHP = 14.1 Hz;
1
13
J
CH = 108.9 Hz in 3- C) corresponding to the α-H for the phos-
31
1
phonioalkylidene. The P{ H} spectrum displays two inequiva-
lent, but broad resonances for the (PNP) ligand at 2.94 and
Figure 4. Contour plots of most representative molecular or-
bitals which show Schrock-carbene character of 3.
−
2.04 ppm, and a sharper signal at 5.10 ppm for the phosphoni-
omethylidene, with an integration under the three resonances
in a 1:1:1 ratio. However, the most definitive proof of 3 pos-
sessing a terminal phosphonio-alkylidene unit stems from the
solid-state structure depicted in Figure 3. Metrical parameters
ionic ligand capable of donating four electrons, of which two are
2
in a sp -hybridized σ-orbital and two are in a p-orbital that can
engage a dyz orbital to afford a π-bond, as illustrated in Figure
1
2a-d
3a.
We have also calculated the structure of the experimen-
involving the CHPh
Sc−CHPPh distance of 2.121(2) Å from that reported by Chen
)(X)
CH, Ar = 2,6-
3
moiety in 3 show a slightly longer
tally elusive, hypothetical Sc-alkylidene 2* without the Al Lewis-
acid stabilizer, which serves as a reference. The frontier orbitals
drawn schematically in Figure 3a can readily be located in 2*
and are shown in the supporting information (Figure S59). The
Mayer bond order of Sc–C27 is calculated to be 1.69 in 2*,
which is the reference value for a Sc=C double bond expected
in the unmasked alkylidene without the Lewis-acid. In compari-
son, a notably lower bond order of 1.13 is found in 2, indicating
3
and co-workers involving the complex (nacnac)Sc(CHPPh
3
−
−
(X = CH
3
, OTf, and I; nacnac = [ArNC(CH
3
)]
2
i
Pr
.670(2) Å, and an obtuse Sc−C−P angle of 145.42(14)°. The
longer distance is not surprising given the higher coordination
number at the Sc(III) ion in 3. The Sc−CHPPh distance is
shorter than the Sc−CH distance of 2.232(3) Å implying a
2 6 3
C H ) (see Table 1), but with a comparable C−P distance of
1
3
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 11
that the double bond and alkylidene character is understanda-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
bly lowered, but not completely erased when the Lewis-acid is
added. The C27–Al interaction is mainly electrostatic in nature
with a bond order of 0.59. Despite careful inspection, we were
unable to find any MO that promotes a covalent interaction be-
tween these two atoms. Instead, the positive electrostatic po-
tential of the Al-center lowers the fragment orbital energies of
the alkylidene and changes the orientation of the silyl and hy-
drogen groups, as indicated in Figure 3b. As a result, the alkyli-
dene becomes a weaker Lewis-base and the two donor inter-
actions are structurally distorted, as the contour plots of the two
important frontier orbitals show in Figure 3c as well as concep-
tualized illustration in Figure 3b. Nonetheless, the σ and π-bond
origins of the two bonding orbitals can easily be recognized.
This electronic structure is in good agreement with the down-
field-shifted NMR spectral signal observed for C27.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
Scheme 3. Reactivity of 3 with AlMe to form either zwit-
terion C or D followed by methane extrusion to produce 6.
Divergent Reactivity of 2. We also probed the reactivity of the
Figure 5. Solid-state structures of the Sc based products 3 (left), 4 (center) and 5 (right) resulting from addition of H
Ad and DMAP, respectively to 2. Solvent, disorder and hydrogens with the exception of α-hydrogen have been omitted for
clarity.
2 3
CPPh ,
N
3
Compound 3 offers an interesting alternative way of stabiliz-
alkylidene ligand in 2 with the azide N
Monitoring the addition of N Ad to 2 by NMR spectroscopy in
benzene-d showed two major products in roughly a 1:1 ratio
3
Ad (Ad = 1-adamantyl).
ing the excess charge of the alkylidene functionality, as ex-
plained above. Our DFT-calculations reveal that the excess
charge of the alkylidene remains mainly centered on the carbon
in the phosphonio-alkylidene. As the contour plots shown in Fig-
ure 4 illustrate, the HOMO is a lone pair orbital centered on the
alkylidene carbon with minimal interactions to the neighboring
Sc or P atoms. Consequently, the Mayer bond order of the Sc–
C bond is 1.02, which is mostly attributed to the σ-donor orbital
HOMO–6, also shown in Figure 4. Thus, the phosphonio func-
tionality again exerts only an electrostatic interaction, leading to
the preservation of the Schrock-carbene character.
3
6
(Figure S40), but upon work-up by recrystallization, these can
be obtained in a ~4:1 ratio. Single crystal X-ray diffraction stud-
ies (Figure 5, center) reveal that insertion of the azide into the
Sc−CHSiMe
3
bond occurs, accompanied by the complete
transfer of the bridging methyl group from the Al to the Sc center
2
to
form
AdCHSiMe
the
Al(CH )(CH
complex
3
(PNP)Sc(CH )[η -
N
3
3
3
2
SiMe )] (4) (Scheme 2) as the pre-
3
dominant product. This reactivity renders the alkylidene moiety
in 2 more like a AlMe substituted alkyl rather than a Lewis acid
2
stabilized alkylidene, and hence follows the established pattern
of reactivity of insertion to RE/early transition metal/actinide
13a-e
metal–carbon bonds with organic azides.
The other major
product observed in the in situ NMR monitoring experiment
could not be separated as effectively, but given the similar res-
onances as those of 4, such species may simply be a diastere-
omer. It is also notable that the trimethylsilyl group formerly be-
longing to the bridging alkylidene appears to be in a hindered
1
environment giving rise to broadening of the H NMR spectral
29
signal of its methyl groups as well as a weaker signal in the Si
1
INEPT spectrum; the H resonances belonging to the adaman-
tyl group are also quite broad (Figure S31). Complex 4 is also
thermally robust in solution, not undergoing any noticeable
transformation following heating at 60 °C overnight, or for
weeks at room temperature.
Conversely, the divergent reactivity of 2 can be demon-
strated when this species is treated with two equivalents of
DMAP. In such a case, DMAP likely deprotects the alkylidene,
and is subsequently coordinated by a second DMAP to form
Scheme 2. Synthesis of the scandium phosphonio-alkylidene
complex 1 along with its independent synthesis from the
Tebbe-like complex 3, which synthesis is also shown.
3
transient [(PNP)Sc=CHSiMe (DMAP)] (B), whic deprotonates
ACS Paragon Plus Environment

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Journal of the American Chemical Society
the ortho-CH of the pyridine to form (PNP)Sc(η2-
NC NMe )(CH SiMe ) (5) along with the Lewis acid-base ad-
duct (Me SiCH )(H C) Al(DMAP) in accordance with Scheme
. However, we concede it may also be possible that DMAP
coordinates to the Sc center first, and is then deprotonated, and
(PNP)Sc≡CPPh
ing the -bond into the PPh
or one of its other resonance forms delocaliz-
3
2+
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
5
H
3
2
2
3
3
motif. The latter two fragment
3
2
3
2
combine via an incomplete Al−C bond addition across the Sc−C
2
multiple bonds to form the adduct 6. However, an alternative
mechanism is possible wherein Al(CH
of the phosphoniomethylidene group generating (PNP)Sc((μ
CHPPh )(Al(CH ))(CH ) (D), and then promoting methane
elimination.
3 3
) is bound by the carbon
2
the resulting [(PNP)Sc(η -NC
5
H
3
NMe
2
)][Al(CH
3
)
2
(CH
2
SiMe
3
)
2
]
2
-
subsequently converts to 5. It is worth noting that addition of
only one equivalent of DMAP to 2produces roughly half as
much of 5 with the rest of 2 remaining. Interestingly, bases such
as 1,4-diazabicyclo[2.2.2]octane and trimethylphosphine do not
react with 2, suggesting steric congestion precludes coordina-
tion of nucleophiles of even a modest steric profile. Multinuclear
NMR spectroscopic studies are consistent with the formation of
3
3
)
3
3
The structural assignment of complex 6 was substantiated
by X-ray crystallography across three independent molecules
belonging to two separate space groups P2
7) with an average Sc–C(alkylidyne) distance of 2.036 Å, the
1
/n and C2/c (Figure
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
13
1
5
, including a broad resonance in the C{ H} spectrum at 212.8
ppm corresponding to the Sc-bound carbon of the pyridyl moi-
ety (Figure S44). A solid-state structure, shown in Figure 5
(right), reaffirmed the formation of a Sc−pyridyl and alkyl moie-
ties in 5 (Sc−Cpyridyl, 2.219(3) Å; Sc−Npyridyl, 2.148(2) Å;
Sc−Calkyl, 2.265(3) Å). As a result, the alkylidene unit of complex
2
shows differing reactivity and implies it is highly ionic with both
scandium alkylidene character or alternatively, as an alane sub-
stituted alkyl. Such a small disparity in the electronegativity dif-
ference between Al and Sc (~0.2) might impart the dual nature
1
4
3
in the Sc(CHSiMe )Al motif in 2.
A Scandium Phosphonio-Alkylidyne Complex. Having suc-
ceeded in synthesizing complex 2, we reasoned that α-H elim-
ination might be possible at the phosphoniomethylidene in 3,
t
mirroring our previous observation that (PNP)Ti=CH Bu(R) (R =
CH
would readily eliminate RH when treated with AlMe
Tebbe-alkylidyne analogue (PNP)Ti(μ
Accordingly, treatment of 3 with Al(CH
solution in hexane) in a benzene or toluene solution resulted in
3
or Ph) complexes are quite resistant to α-H abstraction, but
3
to form the
t
2
-C Bu)(μ
2
-
7
a
CH
3
)Al(CH
3
)
2
.
3 3
)
(2 M
1
immediate extrusion of CH
4
( H NMR: 0.16 ppm) and formation
1
31
of several new products based on a combination of H and
P
NMR spectral data. Most notably, workup of the mixture and
subsequent isolation of one such new product, in yields ranging
o
from 24-41%, and which is unstable in solution at 25 C for ex-
tended periods, revealed spectral features consistent with a
Sc=C bond and in accord with the formulation (PNP)Sc(μ
CPPh )(μ -CH )Al(CH (6) (Scheme 3). For instance, a highly
downfield shifted resonance at 132.4 ppm with a coupling con-
2
-
3
2
3
3 2
)
1
31
stant of JPC = 15.2 Hz (15.4 Hz in the P NMR spectrum) was
13
13
observed in the C NMR spectrum with the aid of a C-en-
riched sample, (PNP)Sc(μ
and as shown in Figure 6. Strikingly, this C chemical shift is
8.5 ppm further downfield than that of 3, while the JPC cou-
1
3
13
2 3 2 3 3 2
- CPPh )(μ -CH )Al(CH ) (6- C)
1
3
1
13
13
1
Figure 6. Top: H- C HMBC spectrum of 6- C. Bottom:
5
31
1
13
1
P{ H} spectrum of 6- C with an inset including superim-
pling constant is 7.1 Hz smaller. It should be noted that this JPC
posed spectrum of unlabeled 6.
coupling constant is markedly smaller than that found in termi-
7b
2 3
nal phosphonioalkylidyne (PNP)Ti≡CPPh CH (OTf), 32.5 Hz.
shortest Sc–C distance recorded to date, slightly shorter than
Chen’s recent (nacnac)Sc(CHPPh
solid-state structure, both the alkylidyne carbon (CPPh
The phosphonio-alkylidene α-H resonance originally presents
6
3
1
3
)(I) (see Table 1). In the
in 3 was absent. Akin to 3, the P NMR spectrum indicates an
asymmetrical complex with two very broadened signals, which
in this case were resolvable as doublets. Two inequivalent
phosphorus atoms of the PNP ligand appear at 6.75 and 1.30
ppm and a highly shielded singlet resonance at −21.53 ppm
3
) and a
Table 1. Selected Sc–C bond distances in the alkylidene units
of recently reported complexes including 2, 3, and 6.
1
3
(
splitting into a doublet with the C-labelled sample). This third
resonance is even further upfield than free triphenylphosphine,
reminiscent of what is observed for terminal phosphonioalkyli-
Complex
Sc–C (Å)
2.089(3)
2.105(2)
2.060(3)
2.044(5)
Ref.
3e
6
1
5a-c
(nacnac)Sc(C(SiMe )PPh )(thf)
dyne species (Figure 6).
Unlike 2, the Al(CH
3
)
3
unit is fixed
3
2
firmly such that the methyl groups do not exchange at room
temperature on the NMR timescale, similar to what was ob-
(nacnac)Sc(CHPPh )(CH )
3 3
(nacnac)Sc(CHPPh )(OTf)
6
t
7a
3
served for the related (PNP)Ti(μ
propose complex 6 to form via methyl abstraction by Al(CH
to give putative [(PNP)Sc(CHPPh )][Al(CH ] (C), in which the
] deprotonates the phosphonioal-
kylidene α-H to liberate CH by forming Al(CH and
2
-C Bu)(μ
2
-CH
3
)Al(CH
3
)
2
.
We
(
nacnac)Sc(CHPPh )(I)
6
3
)
3
3
3
3
)
4
2
3
6
2
.0845(14)
2.121(2)
2.036(5)
This work
This work
This work
−
3 4
strong anionic base [Al(CH )
4
3 3
)
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Journal of the American Chemical Society
Page 8 of 11
methyl bridge the Sc3+ and Al3+ centers. The C–PPh
bond dis-
the σ-bond, which is the major contributor to the alkylidyne bind-
3
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
ing. The two π-orbitals, HOMO–2 and HOMO–1, are mostly iso-
lated and interact only very weakly with the metal center, which
is the result of the positive electrostatic potential exerted upon
the alkylidyne carbon by the Al- and phosphonio groups.
Conclusion
In summary, the successful stabilization of rare unsaturated
Sc–C bonds with a single trialkyl aluminum unit has provided
new insight into the nature of multiple bonds between carbon
and RE metals. The Lewis acid stabilized alkylidene (2), the ter-
minal phosphonio–alkylidene (3) and the Lewis acid stabilized
phosphonio–alkylidyne (6) complexes of scandium have been
prepared, and spectroscopically and structurally analyzed. Both
experimental and theoretical studies validate the multiple bond
characters of Sc–C in the 2, 3 and 6. The Sc–alkylidene or Al–
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
alkylidene bond of 2 breaks when it reacts with N Ad and DMAP
respectively showing the divergent reactivity of 2. Both the
phosphino and Al-based Lewis acids stabilize the alkylidene
and alkylidyne moieties through electrostatic interactions only,
resulting in a significant localization of the charge on the car-
bon, which becomes a much weaker Lewis base. We are cur-
rently probing the reactivity of 6 with various Lewis bases.
Figure 7. Top: Solid-state structure of complex 6 showing
thermal ellipsoids at the 50% probability level. Only α-H
are shown for clarity.
tance (average 1.668 Å in the P2
lower R ) does not differ significantly from that of 3, and the Sc–
C–P angle of 149.54° (averaged from P2 /n structure) suggest-
1
/n structure which has the
1
1
ing that the nature of the C–P bond in the solid state structures
1
in both complexes are similar, in spite of the different JCP cou-
ASSOCIATED CONTENT
pling constants observed by NMR spectroscopy.
Supporting Information
For a true alkylidyne, it is expected that all three p-orbitals of
the carbon are utilized to give one σ- and two π-bonds. To
gauge the impact of the Al fragment, we also calculated the
The Supporting Information is available free of charge on the
ACS Publications website.
structure and electronics of 6*, a hypothetical, Al(CH
3
)
3
-free al-
NMR, XRD and computational data (PDF)
X-ray crystallographic data for complex 1 (CIF)
X-ray crystallographic data for complex 2 (CIF)
X-ray crystallographic data for complex 3 (CIF)
X-ray crystallographic data for complex 4 (CIF)
X-ray crystallographic data for complex 5 (CIF)
X-ray crystallographic data for complex 6 (CIF)
kylidyne containing a simpler ScCPPh fragment. We found that
3
the Sc–C bond is expectedly short at 1.903 Å and the bond or-
der is calculated to be 1.88, indicating that the two π-bonds are
weak, but contribute notably to the bonding. As seen for 2, the
addition of the Al-based Lewis acid is anticipated to lead to a
significant weakening of the triple bond character and localiza-
tion of the charge on the alkylidyne carbon. Our calculations
show that the bond order in 6 is only 1.31, which is higher than
what was found in 2 and 3, but remarkably low for a bond that
is formally a triple bond. Figure 8 shows the three frontier orbit-
als that are responsible for the triple bond in 6. HOMO–16 is
AUTHOR INFORMATION
Corresponding Author
mindiola@sas.upenn.edu; mbaik2805@kaist.ac.kr
ORCID
Daniel J. Mindiola:
Mu-Hyun Baik:
Pavel Zatsepin:
Eunji Lee:
Jun Gu:
Michael R. Gau:
Patrick J. Carroll:
0000-0001-8205-7868
0000-0002-8832-8187
0000-0001-7196-8009
0000-0002-8925-2954
0000-0003-2701-4421
0000-0002-4790-6980
0000-0002-8142-7211
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
For funding, we thank the University of Pennsylvania and the
National Science Foundation (CHE-0848248 and CHE-
1
152123 to D.J.M.). The authors also acknowledge the NIH
supplements award 3R01GM118510-03S1 and
3R01GM087605-06S1 and financial supports of Vagelos Insti-
tute for Energy Sciences and Technology for the purchase of
NMR instrument NEO600. This research was also supported in
part by the Institute for Basic Science (IBS-R010-D1) in Korea.
Figure 8. The three orbitals that are responsible for the tri-
ple bond character of 6. All hydrogens and isopropyl groups
on PNP ligand are omitted for clarity. [Sc] represents
the(PNP)Sc fragment. Isodensity value = 0.05 a.u.
REFERENCES
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Journal of the American Chemical Society
(
(
1) (a) Sunderlin, L. S.; Armentrout, P. B. Periodic Trends in
(7) (a) Bailey, B. C.; Fout. A. R.; Fan, H.; Tomaszewski, J.; Huff-
+
+
+
+
1
2
3
4
5
6
7
8
9
Chemical Reactivity of Sc , Y , La , and Lu with Methane and
Ethane. J. Am. Chem. Soc. 1989, 111 (11), 3845–3855. (b) Cho, H.
man, J. C.; Mindiola, D. J. An Alkylidyne Analogue of Tebbe’s
Reagent: Trapping Reactions of a Titanium Neopentylidyne by
Incomplete and Complete 1,2-Additions. Angew. Chem. Int.
Ed. 2007, 46 (43), 8246–8249. (b) Kamitani, M.; Pinter, B.;
Searles, K.; Crestani, M. G.; Hickey, A.; Manor, B. C.; Carroll,
P. J.; Mindiola, D. J. Phosphinoalkylidene and -alkylidyne
Complexes of Titanium: Intermolecular C–H Bond Activation
and Dehydrogenation Reactions. J. Am. Chem. Soc. 2015, 137
(37), 11872–11875.
-
3
G.; Andrews, L. Methane Activation by Laser-Ablated Group
Metal Atoms: Infrared Spectra and Structures of the CH -MH
Complxes. Organometallics 2007, 26 (3), 633–
3
and CH
2
-MH
2
643.
2) (a) Zhang, W. -X.; Wang. Z.; Nishiura, M.; Xi, Z.; Hou, Z.
Ln (CH Cubane-Type Rare-Earth Methylidene Complexes
Consisting of “(C Me SiMe )LnCH ” Units (Ln = Tm, Lu). J.
4
)
2 4
5
4
3
2
Am. Chem. Soc. 2011, 115 (15), 5712–5715. (b) Hong, J.; Zhang, L.;
Wang, K.; Zhang, Y.; Weng, L.; Zhou, X. Methylidene Rare‐
Earth‐Metal Complex Mediated Transformations of C=N, N=N
and N–H Bonds: New Routes to Imido Rare‐Earth‐Metal Clus-
ters. Chem. Eur. J. 2013, 19 (24), 7865–7873. (c) Li, S.; Wang,
M.; Liu, B.; Li, L.; Cheng, J.; Wu, C.; Liu, D.; Liu, J.; Cui, D.
Lutetium‐Methanediide‐Alkyl Complexes: Synthesis and
Chemistry. Chem. Eur. J. 2014, 20 (47), 15493–15498. (d) Zhou,
J.; Li, T.; Maron, L.; Leng, X.; Chen. Y. A Scandium Complex
Bearing Both Methylidene and Phosphinidene Ligands: Syn-
thesis, Structure, and Reactivity. Organometallics 2015, 34 (2),
(8) (a) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. Olefin homolo-
gation with titanium methylene compounds. J. Am. Chem.
Soc. 1978, 100, 3611-3613. (b) Scott; J.; Mindiola, D. J. A Tribute
to Frederick Nye Tebbe. Lewis Acid Stabilized Alkylidynes, Al-
kylidenes, and Imides of 3d Early Transition Metals. Dalton
Trans. 2009, 8463-8472. (c) Thompson, R.; Nakamaru-Ogiso,
E.; Chen, C.-H.; Pink, M.; Mindiola, D. J. Structural Elucidation
of the Illustrous Tebbe Reagent. Organometallics 2014, 33 (1),
429-432.
(9) Zatsepin, P.; Ahn, S.; Pudasaini, B.; Gau, M. R.; Baik, M-H.;
Mindiola, D. J. Conversion of Methane to Ethylene Using an
Iridium Complex and Phosphorus Ylide as a Methylene Trans-
fer Reagent. Chem. Commun. 2019, 55 (13), 1927-1930.
(10) (a) Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J.C.; Mindiola, D.
J. Evidence for the Existence of a Terminal Imidoscandium
Compound. Intermolecular C-H Activation and Complexation
Reactions with the Transient Sc=NAr Ligand. Angew. Chem.
Int. 2008, 47 (44), 8502-8505 (b) Scott, J.; Fan, H.; Wicker, B.
F.; Fout, A. R.; Baik, M.-H.; Mindiola, D. J. Lewis Acid Stabi-
lized Methylidene and Oxoscandium Complexes. J. Am. Chem.
Soc. 2008, 130 (44), 14438-14439.
(11) (a) Zabula, A. V.; Qiao, Y.; Kosanovich, A. J.; Cheisson, T.;
Maonr, B. C.; Carroll, P. J.; Ozerov, O. V. Schelter, E. J. Struc-
ture, Electronics and Reactivity of Ce(PNP) Complexes. Chem.
Eur. J. 2017, 23 (71), 17923–17934. (b) Levine, D. S.; Tilley, T. D.;
Andersen, R. A. C−H Bond Activations by Monoanionic, PNP-
Supported Scandium Dialkyl Complexes. Organometallics
2015, 34 (19), 4647–4655.
(12) (a) Schrock, R. R. The First Isolable Transition Metal Meth-
ylene Complex and Analogs. Characterization, Mode of De-
composition, and Some Simple Reactions J. Am. Chem. Soc.
1975, 97 (22), 6577–6578. (b) Chatt, J.; Duncanson, L. A.; Ve-
nanzi, L. M. Directing effects in inorganic substitution reac-
tions. Part I. A hypothesis to explain the trans-effect J. Chem.
Soc. 1955, 4456–4460. (c) Chatt, J.; Duncanson, L. A. Olefin co-
ordination compounds. Part III. Infra-red spectra and struc-
ture: attempted preparation of acetylene complexes J. Chem.
Soc. 1953, 2939–2947. (d) Won, J.; Jung, H.; Mane, M. V.; Heo,
J.; Kwon, S.; Baik, M.-H. Schrock vs Fischer Carbenes: A Quan-
tum Chemical Perspective. Adv. Inorg. Chem. 2019, 73, 385–
443.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4
70–476. (e) Ma, W.; Yu, C.; Chi, Y.; Chen, T.; Wang, L.; Yin,
J.; Wei, B.; Xu, L.; Zhang, W. -X.; Xi, Z. Formation and ligand-
based reductive chemistry of bridged bis-alkylidene scan-
dium(III) complexes. Chem. Sci. 2017, 8, 6852–6856. (f) Levine,
D. S.; Tilley, D. T.; Andersen, R. A. Evidence for the Existence
of Group 3 Terminal Methylidene Complexes. Organometal-
lics 2017, 36 (1), 80–88.
(
3) (a) Aparna, K.; Ferguson, M.; Cavell, R. G. A Monomeric Sa-
marium Bis(Iminophosphorano) Chelate Complex with a Sm
C Bond. J. Am. Chem. Soc. 2000, 122 (4), 726–727. (b) Can-
tat, T.; Jaroschik, F.; Nief, F.; Ricard, L.; Mézailles, N.; Le Floch,
P. New mono- and bis-carbene samarium complexes: synthe-
sis, X-ray crystal structures and reactivity. Chem. Comm. 2005,
5
178–5180. (c) Liddle, S. T.; Mills, D. P; Wooles, A. J. Early
metal bis(phosphorus-stabilised)carbene chemistry. Chem.
Soc. Rev. 2011, 40, 2164–2176. (d) Wang, C.; Zhou, J.; Zhao, X.;
Maron, L.; Leng, X.; Chen, Y. Non‐Pincer‐Type Mononuclear
Scandium Alkylidene Complexes: Synthesis, Bonding, and Re-
activity. Chem. Eur. J. 2016, 22 (4), 1258–1261. (e) Mao, W.;
Xiang, L.; Lamsfus, C. A.; Maron, L.; Leng, X.; Chen, Y. Highly
Reactive Scandium Phosphinoalkylidene Complex: C−H and
H−H Bonds Activation. J. Am. Chem. Soc. 2017, 139 (3), 1081–
1084.
(4) (a) Dietrich, H. M.; Grove, H.; Törnroos, K. W.; Anwander, R.
Multiple C-H Bond Activation in Group 3 Chemistry: Synthe-
sis and Structural Characterization of an Yttrium-Aluminum-
Methine Cluster. J. Am. Chem. Soc. 2006, 128 (5), 1458–1459.
(
b) Scott, J.; Fan, H.; Wicker, B. F.; Fout, A. R.; Baik, M. -H.;
Mindiola, D. J. Lewis Acid Stabilized Methylidene and Ox-
oscandium Complexes. J. Am. Chem. Soc. 2008, 130 (44),
1
4438–14439. (c) Litlabø, R.; Zimmermann, M.; Saliu, K.; Ta-
(13) (a) Evans, W. J.; Mueller, T. J.; Ziller, J. W. Reactivity of
kats, J.; Törnroos, K. W.; Anwander, R. A Rare‐Earth Metal
Variant of the Tebbe Reagent. Angew. Chem. Int. Ed. 2008, 47
(48), 9560–9564. (d) Venugopal, A.; Kamps, I.; Bojer, D.; Ber-
ger, R. J. F; Mix, A.; Willner, A.; Neumann, B.; Stammler, H. -
G.; Mitzel, N. W. Neutral ligand induced methane elimination
from rare-earth metal tetramethylaluminates up to the six-co-
ordinate carbide state. Dalton Trans. 2009, 5755–5765. (e)
Korobkov, I.; Gambarotta, S. Unusual Reactivity of a Tm-Pyr-
rolide/Aluminate Complex with a Metallocene-Type Struc-
tural Motif. Organometallics 2009, 28 (18), 5560–5567. (f)
Huang, W.; Carver, C. T.; Diaconescu, P. L. Transmetalation
Reactions of a Scandium Complex Supported by a Ferrocene
Diamide Ligand. Inorg. Chem. 2011, 50 (3), 978–984.
(C
clopentadienyl) Complex with Two Additional Ligands,
(C Me La(NCCMe . J. Am. Chem. Soc. 2009, 131 (7), 2678–
5
Me
5
)
3
LaL
x
Complexes: Synthesis of a Tris(pentamethylcy-
5
5
)
3
)
3 2
2686. (b) Liu, B.; Cui, D. Rare-earth metal complexes stabilized
by amino-phosphineligand. Reaction with mesityl azide and
catalysis of the cycloaddition of organic azides and aromatic
alkynes. Dalton Trans. 2009, 550–556. (c) Evans, W. J.; Wa-
lensky, J. R.; Ziller, J. W.; Rheingold, A. L. Insertion of Car-
bodiimides and Organic Azides into Actinide−Carbon Bonds.
Organometallics 2009, 28 (12), 3350–3357. (d) Ren, S.; Qiu, Z.;
Xie, Z. Synthesis of Neutral Group 4 Metal–Carboryne Com-
plexes and Their Reactivity toward Unsaturated Molecules.
Organometallics 2013, 32 (15), 4292–4300. (e) Janes, T. Xu, M.;
(5) Shima, T.; Yanagi, T.; Hou, Z. Rare-earth–iridium heterobime-
tallic complexes with bridging imido and silylmethyl ligands:
synthesis, structure and reactivity. New J. Chem. 2015, 39,
Song, D. Synthesis and reactivity of Li and TaMe complexes
3
supported by N,N′ -bis(2,6-diisopropylphenyl)-o-phenylene-
diamido ligands. Dalton Trans. 2016, 45, 10672–10680.
7608–7616.
(14) Pauling, L. Chapter 3: The Partial Ionic Character of Covalent
Bonds and the Relative Electronegativity of Atoms. Nature of
(
6) Mao, W.; Xiang, L.; Maron, L.; Leng, X.; Chen. Y. Nonchelated
Phosphoniomethylidene Complexes of Scandium and Lute-
tium. J. Am. Chem. Soc. 2017, 139 (49), 17759–17762.
rd
the Chemical Bond, 3 ed.; Cornell University Press: Ithaca,
NY, 1960; p 93.
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(
15) (a) Li, X.; Schopf, M.; Stephan, J.; Harms, K.; Sundermeyer, J.
Sun, J.; Harms, K.; Sundermeyer, J. Phosphorus Ylide as a Pre-
1
2
3
4
5
6
7
8
9
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1
1
1
1
1
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6
Heavily π-Bond-Loaded Tungsten Phosphonio-Alkylidyne
Complexes via a Domino Transylidation Cascade at (Organ-
oimido)tungsten Tetrachlorides. Organometallics 2002, 21
cursor for the Formation of New High-Valent Tantalum Phos-
phonio Methylidyne Complexes. Organometallics 2007, 26
(6), 1411–1413.
(
12), 2356–2358. (b) Li, X.; Sun, H.; Harms, K.; Sundermeyer, J.
Simple Synthesis and Structure Characterization of a Stable
Niobium(V) Phosphoniomethylidyne Complex. Organometal-
lics 2005, 24 (19), 4699–4701. (c) Li, X.; Wang, A.; Wang, L.;
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