of 72
S
1
CO Coupling Chemistry of a Terminal Mo Carbide: Sequential
Addition of Proton, Hydride, and CO Releases Ethenone
Joshua A. Buss,
Gwendolyn A. Bailey,
Julius Oppenheim,
David G. VanderVelde, William A. Goddard III, and
Theodor Agapie
Division of Chemistry
and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd.
MC 127
-
72, Pasadena, CA, USA
Supporting Information
Contents
Experimental Details
S3
General Considerations
S
3
Carbide
CO Coupling from Carbide
1
S3
In situ generation of carbide
1
S
3
Figure S1
Partial
13
C{
1
H} (126 MHz, THF,
-
50 °C) and
31
P{
1
H} (202 MHz, THF,
-
50 °C) NMR
spectra showing clean deprotonation of methylidyne
4
with benzyl potassium.
S
4
Addition of CO to Carbide
1
to form Metallaketene Complex
2
S
4
Figure S2
1
H
NMR Spectrum (400 MHz, C
6
D
6
, 23 °C) of
2
.
S
5
Figure S3
31
P{
1
H}
NMR Spectrum (162 MHz, C
6
D
6
, 23 °C) of
2
.
S
5
Figure S4
13
C{
1
H}
NMR Spectrum (101 MHz, C
6
D
6
, 23 °C) of
2
.
S
6
Figure S5
31
P{
1
H}
NMR spectrum (202 MHz, THF, 23 °C) of
2
-
13
C
.
S
6
Figure S6
13
C{
1
H}
NMR spectrum (126 MHz, THF,
23 °C) of
2
-
13
C
.
S
6
Preparation of a mixture predominantly
of carbide
isomer
3
S
7
Figure S7
1
H
NMR Spectrum (400 MHz, C
6
D
6
, 23 °C) of
3
-
13
C
.
S
8
Figure S8
31
P{
1
H}
NMR spectrum (162 MHz, C
6
D
6
, 23 °C) of
3
-
13
C
.
S8
Figure S9
13
C{
1
H}
NMR spectrum (101 MHz, C
6
D
6
, 23 °C) of
3
-
13
C
.
S8
Sequential Addition of Proton, Hydride, and CO to Carbide
1
S9
Synthesis of Methylidyne
4
S
9
Figure S
10
1
H
NMR
Spectrum (300 MHz, C
6
D
6
, 23 °C) of
4
.
S
9
Figure S
11
13
C{
1
H}
NMR Spectrum (101 MHz, C
6
D
6
, 23 °C) of
4
.
S
10
Figure S
12
31
P
{
1
H}
NMR Spectrum (121 MHz, C
6
D
6
, 23 °C) of
4
.
S
10
Figure S1
3
1
H
NMR Spectrum (300 MHz, C
6
D
6
, 23 °C) of
4
-
13
C
.
S
11
Figure S1
4
31
P
{
1
H}
NMR Spectrum (121 MHz, C
6
D
6
, 23 °C) of
4
-
13
C
.
S
11
Figure S1
5
13
C
{
1
H}
NMR Spectrum (126 MHz, C
7
D
8
,
-
78 °C) of
4
-
13
C
.
S
1
2
Addition of NaBEt
3
H to
4
In Situ Formation of
5
and Synthesis of
6
S
1
2
Figure S1
6
1
H
NMR Spectrum
(500 MHz, C
7
D
8
,
-
80 °C) of
5
-
13
C
.
S
1
3
Figure S1
7
13
C{
1
H}
NMR Spectrum (126 MHz, C
7
D
8
,
-
80 °C) of
5
-
13
C
.
S
1
3
Figure S1
8
31
P{
1
H}
NMR spectrum (202 MHz, C
7
D
8
,
-
80 °C) of
5
-
13
C
.
S
1
3
Figure S1
9
Variable temperature
13
C{
1
H} (126 MHz, THF,
-
50 °C) spectra of methylidene complex
7
-
13
C
. Upon warming, clean conversion to
6
-
13
C
is observed.
S
1
5
Figure S
20
1
H
NMR spectrum (600 MHz, C
6
D
6
, 23 °C) of
6
-
13
C
.
S
1
6
Figure S
21
(a)
1
H and (b)
1
H{
13
C} NMR spectra
(600 MHz, C
6
D
6
, 23 °C) of
6
-
13
C
showing resolution
of the two PC
H
2
doublets of triplets into triplets on
13
C decoupling.
S
1
6
Figure S
22
13
C{
1
H}
NMR spectrum (101 MHz, C
6
D
6
, 23 °C) of
6
-
13
C
.
S
1
7
Figure S
23
31
P{
1
H}
NMR spectrum (126 MHz, C
6
D
6
, 23 °C) of
6
-
13
C
.
S
1
7
Figure S
24
Partial
1
H/
1
H COSY NMR spectrum (400 MHz, C
6
D
6
, 23 °C) of
6
-
13
C
.
S
1
8
Figure S2
5
Partial
1
H/
13
C HSQC NMR spectrum (400/101 MHz, C
6
D
6
, 23 °C) of
6
-
13
C
.
S
1
9
Figure S2
6
Partial
1
H/
13
C HMBC
NMR spectrum (400/101 MHz, C
6
D
6
, 23 °C) of
6
-
13
C
.
S1
9
Figure S2
7
1
H
NMR spectrum (400 MHz, C
6
D
6
, 23 °C) of
6
.
S
20
Figure S2
8
31
P{
1
H}
NMR spectrum (126 MHz, C
6
D
6
, 23 °C) of
6
.
S
20
CO
-
Promoted Ethenone Formation from
5
-
13
C
S
21
S
2
Figure S2
9
1
H (500 MHz),
13
C{
1
H} (126 MHz), and
31
P{
1
H} (202 MHz) NMR spectra (all C
7
D
8
,
-
78 °C) following the sequential addition of NaBEt
3
H (A) and
13
CO (B) to
4
.
S
2
2
Figure S
30
Partial
13
C{
1
H} NMR spectra (101 MHz, C
7
D
8
, 23 °C) of
EtOAc
-
13
C
2
,
8
, without (A)
and with (B) selective
13
C decoupling.
S
2
3
Hydride Addition to Silylcarbyne
9
S
2
3
Addition of NaBEt
3
H to
9
In Situ Formation of
10
&
11
S
2
3
Figure S
31
Variable temperature partial
1
H (500 MHz, C
7
D
8
) and
31
P{
1
H} (202 MHz, C
7
D
8
)
NMR spectra monitoring the addition of NaBEt
3
H to silylalkylidyne
9
.
S
2
4
Figure S
32
.
Variable temperature partial
13
C{
1
H} (126 MHz, C
7
D
8
) NMR
spectra following the reaction
of NaBEt
3
H with silylalkylidyne
9
.
S
2
5
Figure S3
3
Partial
1
H/
13
C HSQCAD
,
HMB
C
spectra (500/126 MHz, C
7
D
8
,
-
30 °C)
of
silylcarbene
10
.
S
2
5
Figure S3
4
Partial low
-
temperature
13
C (
126
MHz, C
7
D
8
) and
13
C{
1
H} (
126
MHz, C
7
D
8
) spectra of
silylcarbene
1
0
.
S
2
6
Figure S3
5
11
B NMR
s
pectrum (160 MHz, C
7
D
8
,
-
30 °C) following addition of NaBEt
3
H to
9
at
-
30 °C.
S
2
6
Figure S3
6
31
P{
1
H} NMR spectra
showing
the i
ndependent
synthesis of
trimethylsilylketene
complex
1
1
via
addition of authentic trimethylsilylketene to N
2
adduct
1
2
.
S
2
7
Crystallization of Trimethylsilylketene Complex
11
S
2
7
Thermochemical Studies
S
2
8
Synthesis of NaBHPh
3
S
2
8
Figure S3
7
1
H
NMR spectrum (400 MHz, C
6
D
6
, 23 °C) of NaBHPh
3
.
S
2
8
Figure S3
8
11
B
NMR spectrum (128 MHz, C
6
D
6
, 23 °C) of NaBHPh
3
.
S2
8
Independent Synthesis and Characterization of Methylidyne
4’•X
(X = Cl, BAr
F
4
)
S
2
9
Figure S3
9
1
H
NMR spectrum (400 MHz, C
6
D
6
, 23 °C) of
4’•Cl
.
S
2
9
Figure S
40
13
C{
1
H} NMR spectrum (MHz, C
6
D
6
, 23 °C) of
4’•Cl
.
S
30
Figure S
41
31
P{
1
H} NMR spectrum (400 MHz, C
6
D
6
, 23 °C) of
4’•Cl
.
S
30
Figure S
42
Partial
1
H/
13
C HMQC spectrum (MHz, C
6
D
6
, 23 °C) of
4’•Cl
.
S
30
Protonation of Carbide
1
with [PhAr
2
PMe]Cl (Ar = 2,4,6
-
trimethoxyphenyl)
S
31
Figure S4
3
31
P{
1
H}
NMR spectra (162 MHz, C
6
D
6
, 23 °C) showing protonation of carbide
1
with
[PhAr
2
PMe]Cl (Ar = 2,4,6
-
trimethoxyphenyl).
S
31
Reaction of
Methylidyne
4
with NaBHPh
3
: variable temperature NMR study
S
31
Figure S4
4
Variable
-
temperature
31
P{
1
H
}
NMR spectra (
162
MHz, C
6
D
6
) showing low
-
temperature
.
conversion of methylidyne
4
to methylidene
5
on addition of NaBHPh
3
.
S
32
Computational Details
S3
3
General Considerations
S3
3
Proposed Reaction Mechanism
S3
3
Figure S4
5
Potential Energy Landscape of C
C Bond Formation
S3
3
Figure S4
6
Select Molecular Orbitals Near th
e Minimum Energy Crossing Point
S3
5
Figure S4
7
Ketene
Dihedral Angle as a Function of C
C Distance
S
3
6
Additional Considerations
S
3
6
Figure S4
8
trans
-
and
cis
-
Alkylidene Isomers Con
sidered in DFT Calculations
S
3
6
Figure S4
9
Optimized Structures of the “Endo” and “Exo” SiMe
3
/CO Isomers of
2
S
3
7
Figure S
50
Parent Methylidene and Silylalkyli
dene Insertions into Mo
P Bonds
S
3
7
Cartesian Coordinates of Molecules
S
3
8
Crystallographic Information
S
6
8
Refinement Details
S
6
8
Table S
1
Crystal and Refinement Data for Complexes
2
,
4
,
4’
,
6
,
and
11
S
6
8
Figure S
51
Structural Drawing of
2
S
6
9
Figure S
52
Structural Drawing of
4
S
6
9
Figure S5
3
Structural Drawing of
4’
S
70
Figure S5
4
Structural Drawing of
6
S
70
Figure S
5
5
Structural Drawing of
11
S
71
References
S
7
2
S
3
EXPERIMENTAL DETAILS
General Considerations
Note
.
Below,
we distinguish
the
13
C
-
labelled
compounds
from the
ir
non
-
labelled
derivatives
by adding the
modifier “
-
13
C
” after the compound number
. In the
main article, this modifier
is omitted
for clari
t
y, as mainly
the
13
C
-
labelled compounds are discussed.
Unless otherwise specified, all operations were carried out in an MBraun drybox
under a nitrogen atmosphere
or using standard Schlenk and high vacuum line techniques. Solvents for air
-
and moisture
-
sensitive reactions
were dried over sodium benzophenone ketyl, or by the method of Grubbs.
1
C
6
D
6
was purchased from
Cambridge
Isotope Laboratories and vacuum transferred from sodium benzophenone ketyl. Solvents, once
dried and degassed, were vacuum transferred directly prior to use or stored under inert atmosphere over 4 Å
molecular sieves. Molybdenum complexes
9
2
and
12
;
3
trimethylsilyl
ketene
;
4
anhydrous
tetrabutylammonium
fluoride (TBAF)
in MeCN
;
5
benzyl po
tassium
;
6
and PhAr
2
PMeCl (Ar
= 2,4,6
-
trimethoxyphenyl)
7
were
prepared and purified according to literature procedures. [Et
3
NH][Cl] was
prepared by condensing HCl gas
(freeze
-
pump
-
thawed three times and condensed from
-
78 to
-
196 °C) onto a frozen pentane solution of dry
N
Et
3
. The solids that formed upon warming
to room temperature (with stirring)
were collected via vacuum
filtration and u
sed without further purification.
P2Et•HCl was prepared by addition of 1.0 M HCl in anhydrous
Et
2
O (1.1 equiv) to P2Et in THF, followed by concentrating in vacuo to dryness.
NaH (purchased as 60%
dispersion in mineral oil; Sigma Aldrich) was purified by ri
nsing with
copious
pentane and then drying in
vacuo.
A
ll other chemicals were utilized as received.
T
rimethylsilyl chloride (dried over CaH
2
and distilled
prior to use) w
as
purchased from Alfa Aesar.
Sodium triethylborohydride (
NaBEt
3
H,
1.0 M in
PhMe)
,
triphenylborane,
sodium tetraphenylborate,
phosphazene base P2Et, anhydrous HCl (1.0 M solution in Et
2
O),
HCl (gas, ≥99%)
,
and CO
( ≥99%)
were purchased from Sigma
Aldrich.
N
Et
3
(dried
over CaH
2
and distilled
prior to use) was purchased from Oakwood Chemicals.
13
CO gas was purchased from Monsanto Research
;
and
butane
was
purchased from Matheson.
1
H,
13
C{
1
H}, and
31
P{
1
H} NMR spectra were recorded
on Varian
300 MHz,
400 MHz
,
Varian INOVA
-
500
, or Va
rian
600 MHz
spectrometers with
chemical
shifts reported in
parts per million (ppm).
1
H and
13
C{
1
H} NMR spectra are referenced to residual solvent peaks.
8
31
P{
1
H}
chemical shifts are referenced to an external
sample of
85% H
3
PO
4
(0
ppm).
Multiplicities are abbreviated as
follows: s = singlet, d = doublet,
t = triplet, dd = doublet of doublets, dt = doublet of
triplets, td = triplet of
doublets, m = multiplet, br = broad, and app = apparent.
Infrared
(IR)
spectra
were collected
on a
Bruker
Alpha II FTIR spectromet
er equipped with an ATR sampling accessory.
Elemental analysis was performed
using a
PerkinElmer 2400 Series II CHN Elemental Analyzer.
Carbide
CO Coupling from Carbide 1
In Situ Generation of
Carbide
1
For synthesis of methylidyne
4
, see below.
A J. Young NMR tube was charged with solid
4
(25 mg. 0.039 mmol)
and solid BnK (5.1 mg, 0.039 mmol). The tube was sealed and appended to a high vacuum manifold. The tube was
thoroughly evacuated and THF (
ca.
0.5 mL) was admitted via vacuum transfer by cooling the reaction tube to
-
78
°C with a dry i
ce/acetone slurry. The tube was sealed and carefully mixed, ensuring that the reaction solution
remained cold. The orange solids dissolved, providing a deep red homogeneous solution.
P
P
i
Pr
i
Pr
i
Pr
i
Pr
Mo
C
Cl
H
C
O
4
P
P
i
Pr
i
Pr
i
Pr
i
Pr
C
C
O
Mo
1
BnK, THF
-5
0
°
C
,
-K
C
l
S
4
The J. Young tube was carefully transferred to an NMR probe pre
-
cooled t
o
-
50 °C. Multinuclear NMR
spectroscopy showed complete conversion of
4
to previously characterized carbide complex
1
(Fig. S1).
2
Figure S1
Partial
13
C{
1
H}
(126 MHz, THF,
-
50 °C
; left
)
and
31
P{
1
H}
(202 MHz, THF,
-
50 °C
; right
)
NMR spectra
demonstrating the clean deprotonation of methylidyne
4
with benzyl potassium.
Addition of CO to Carbide
1
to form
Metallaketene Complex
2
A deep red THF
solution of
1
(0.047 mmol
in 600
L THF) in a J. Young tube, prepared as above,
was degassed
via three freeze pump thaw cycles (thawing to
-
78 °C). The headspace was backfilled
with CO gas (1 atm) at
-
78
°C, and then warmed to RT, resulting
in a darkening of the reaction mixture to
brown
.
After 2 h
at RT
, volatiles
were removed in vacuo. The resulting brown residue was triturated with hexanes (3x5 mL), and then washed with
hexamethyldisiloxane (HMDSO
;
5x5 mL). The remaining solids was extracted
with benzene (5 mL), and the
benzene extracts lyophilized to provide
2
as a red
-
brown, free
-
flowing solid (5 mg,
17
%).
1
H NMR (C
6
D
6
,
400
MHz, 23 °C):
7.60
7.52 (overlapping m, 2H, aryl
-
H
), 7.36
7.29 (m, 1H,
aryl
-
H
), 7.12
6.99 (
m, 3H, aryl
-
H
),
6.86
6.80 (m, 1H, aryl
-
H
), 6.75
6.67 (m, 1H, aryl
-
H
)
, 4.84
4.77 (m, 2H, central arene
-
H
), 3.98
3.89 (m, 2H,
central arene
-
H
), 3.15
3.00 (m, 1H, C
H
(CH
3
)
2
), 2.83
2.68 (m, 1H, C
H
(CH
3
)
2
), 2.01
1.87 (m, 1H, C
H
(CH
3
)
2
),
1.88
1.73 (m, 1H, C
H
(CH
3
)
2
),
1.68
(dd,
J
= 15.9 Hz,
J
= 6.9 Hz,
3
H, C
H
(C
H
3
)
2
),
1.50
1.36 (m, 6H, C
H
(C
H
3
)
2
),
1.14
0.99 (m, 6H, C
H
(C
H
3
)
2
), 0.92
0.73 (m, 12H, C
H
(C
H
3
)
2
)
.
13
C{
1
H} NMR (C
6
D
6
, 126 MHz, 23 °C): 242.90
(d,
2
J
PC
=
13.1 Hz,
C
O),
150.64 (d,
J
=
26.8 Hz, aryl
-
C
), 149.78 (d,
2
J
PC
=
1.7 Hz, aryl
-
C
),
1
50.02
(d,
2
J
PC
=
33.
3
Hz, P
C
C
O),
148.63 (d,
2
J
PC
=
29.4 Hz, aryl
-
C
),
132.54 (d,
2
J
PC
=
6.0
Hz, aryl
-
C
),
131.70 (d,
2
J
PC
=
11.7 Hz, aryl
-
C
),
126.82 (d,
2
J
PC
=
4.2 Hz, aryl
-
C
), 124.64 (d,
2
J
PC
=
12.4 Hz, aryl
-
C
), 99.93 (s, central arene
-
C
), 95.60 (s,
central
arene
-
C
), 87.41 (s, central arene
-
C
), 77.73 (dd,
J
= 7.6 Hz,
J
= 5.4 Hz, central arene
-
C
)
,
74.51 (s, central arene
-
C
),
73.62 (s, central arene
-
C
), 30.84 (d,
J
=
49.8
Hz,
C
H(CH
3
)
2
)
,
29.34 (d,
J
= 52.4 Hz,
C
H(CH
3
)
2
), 27.42 (d,
J
= 20.4
Hz,
C
H(CH
3
)
2
), 24.50 (d,
J
= 10.0 Hz,
C
H(CH
3
)
2
), 21.91 (d,
J
= 9.5 Hz,
C
H(
C
H
3
)
2
), 18.82 (d,
J
= 5.6 Hz,
C
H(
C
H
3
)
2
),
18.14 (d,
J
= 5.1 Hz,
C
H(
C
H
3
)
2
), 17.77 (d,
J
= 8.0 Hz,
C
H(
C
H
3
)
2
), 17.52 (d,
J
= 1.8 Hz,
C
H(
C
H
3
)
2
), 17.08 (d,
J
=
2.1 Hz,
C
H(
C
H
3
)
2
), 16.57 (d,
J
= 1.1 Hz,
C
H(
C
H
3
)
2
), 16.24 (d,
J
= 1.1 Hz,
C
H(
C
H
3
)
2
),
-
32.
00
(d,
1
J
PC
= 11
9
Hz,
P
C
CO).
31
P{
1
H} NMR (
C
6
D
6
, 202 MHz, 23 °C):
83.45 (d,
2
J
P
P
=
4.5
Hz,
P
Mo
),
3
8.29 (d,
3
J
PP
= 4.
4
Hz
,
P
CCO).
FTIR (ATR, cm
1
): 2029 (
s, C=C=O
), 1802 (
s, C
≡O
)
.
C
O
(1
a
tm
),
T
H
F
-8
0
°
C
to
R
T
2
P
P
Mo
i
Pr
i
Pr
i
Pr
i
Pr
C
C
O
C
O
P
P
i
Pr
i
Pr
i
Pr
i
Pr
C
C
O
Mo
1