Addition reactions of a phosphorus triamide to nitrosoarenes and acylpyridines

Article abstract of DOI:10.1080/10426507.2020.1804188

Tricoordinate phosphorus compounds react with a wide variety of double bonds through addition reactions. The dipolar and cyclic products formed are important intermediates in organophosphorus chemistry. We investigated the reactivity between phosphorus triamide 1 and nitrosoarenes and 2-acylpyridines. For sterically congested substrates, the formation of σ⁵,λ⁵-phosphorus products is observed. DFT calculations indicate this product is formed through a concerted [4 + 1] mechanism. For less sterically congested substrates, products are observed arising from cleavage of the N = O or C = O bond with formation of a terminal P = O bond and aryl nitrene or carbene migration into a P–N bond of the phosphorus triamide core. DFT calculations are consistent with an initial [2 + 1] addition to phosphorus followed by formal carbene/nitrene migration in these cases.

Full text of DOI:10.1080/10426507.2020.1804188

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: https://www.tandfonline.com/loi/gpss20
Addition reactions of a phosphorus triamide to
nitrosoarenes and acylpyridines
Colet te Grotenhuis, Jared T. Mattos & Alexander T. Radosevich
To cite this article: Colet te Grotenhuis, Jared T. Mattos & Alexander T. Radosevich (2020)
Addition reactions of a phosphorus triamide to nitrosoarenes and acylpyridines, Phosphorus, Sulfur,
and Silicon and the Related Elements, 195:11, 940-946, DOI: 10.1080/10426507.2020.1804188
To link to this article: https://doi.org/10.1080/10426507.2020.1804188
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
020, VOL. 195, NO. 11, 940–946
2
https://doi.org/10.1080/10426507.2020.1804188
Addition reactions of a phosphorus triamide to nitrosoarenes and acylpyridines
#
#
Colet te Grotenhuis , Jared T. Mattos , and Alexander T. Radosevich
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
ABSTRACT
ARTICLE HISTORY
Tricoordinate phosphorus compounds react with a wide variety of double bonds through addition
reactions. The dipolar and cyclic products formed are important intermediates in organophos-
phorus chemistry. We investigated the reactivity between phosphorus triamide 1 and nitrosoar-
enes and 2-acylpyridines. For sterically congested substrates, the formation of r ,k -phosphorus
products is observed. DFT calculations indicate this product is formed through a concerted [4 þ 1]
mechanism. For less sterically congested substrates, products are observed arising from cleavage
of the N ¼ O or C ¼ O bond with formation of a terminal P ¼ O bond and aryl nitrene or carbene
migration into a P–N bond of the phosphorus triamide core. DFT calculations are consistent with
ta hn es ien ict ai as le s [. 2 þ 1] addition to phosphorus followed by formal carbene/nitrene migration in
Received 30 March 2020
Accepted 9 June 2020
5
5
KEYWORDS
Acylpyridine; addition
reaction; DFT calculations;
nitrosoarene; phosphorus
GRAPHICAL ABSTRACT
[
17–22]
Introduction
III and oxaphosphirane [2 þ 1] adducts IV.
Similarly,
oxazaphosphiranes V have been suggested to arise from
Tricoordinate phosphorus compounds are known to
undergo a number of addition reactions with unsaturated
5
5
[
2 þ 1] addition of phosphines to nitrosoarenes. r ,k
[
1–3]
Dioxophospholenes with 1-to-1 stoichiometry are formed
organic substrates.
undergo conjugate addition to give dipolar intermediates I
Scheme 1), which are key intermediates in numerous
organophosphorus-mediated and -catalyzed transforma-
For instance, polarized alkenes
via formal [4 þ 1] addition to 1,2-dicarbonyl com-
[
23,24]
pounds.
The synthetic importance of these intermedi-
(
ates are underscored by the numerous reports in which the
addition of phosphine to carbonyl or nitroso substrates leads
to net deoxygenation with transfer of a carbene or nitrene
equivalent, respectively.
We have recently been investigating the reactivity of
Compound 1 and
related species have been shown to undergo a number of
addition reactions with polarized single bonds (O–H, N–H,
[
4–14]
tions.
For certain a,b-unsaturated carbonyl compounds,
the intermediate phosphonium enolate can undergo a ring
[
19,25–27]
5
5
closing to give persistent cyclic r ,k -phosphoranes II
through a stepwise, formal [4 þ 1] addition. The synthetic
[
28–30]
[
15,16]
bicyclic phosphorus triamide 1.
utility of these intermediates has been demonstrated.
Related addition chemistry of tricoordinate phosphorus
compounds is known for heteroalkene substrates, such as
carbonyl (C ¼ O) and nitroso (N ¼ O) compounds. The add- and B–H).
[
31–33]
In order to probe the reactivity of 1 with
ition of tricoordinate phosphines to simple carbonyl com- respect to a selected number of polar unsaturated substrates,
pounds is known to lead to a diversity of adducts with 1:1 we report here the addition of 1 to nitrosoarenes and acyl-
stoichiometry, including zwitterionic phosphonium alkoxides pyridines. We find evidence for a partitioning of the
CONTACT Alexander T. Radosevich
Authors contributed equally.
Supplemental data for this article is available online at https://doi.org/10.1080/10426507.2020.1804188. The Supplemental Materials are available online.
radosevich@mit.edu
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.
#
Crystallographic data for compounds 4 and 6 has been deposited at the Cambridge Crystallographic Data Center (CCDC numbers 1993347 and CCDC 1993348).
Copies of the information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1 EZ, UK (Fax: þ 44-1223-336033; email:
deposit@ccdc.cam.ac.uk or www.ccdc.cam.ac.uk).
ß 2020 Taylor & Francis Group, LLC

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
941
Scheme 1. Phosphorus adducts formed with various unsaturated compounds.
reaction pathway along [2 þ 1] and [4 þ 1] addition modes
as a function of the steric demand of the electro-
philic substrate.
Results and discussion
31
The reaction of 1 ( P NMR d 160 ppm) with 2,4,6-tri-tert-
butylnitrosobenzene (2) in acetonitrile resulted in the con-
sumption of the starting materials and deposition of a yel-
31
low precipitate. When redissolved in benzene, a P NMR
spectrum of the precipitate shows a single peak whose
chemical shift (d ꢀ 19 ppm) suggests a pentacoordinate
Scheme 2. (a) Reactivity of phosphorus triamide 1 with 2,4,6-tri-tert-butylnitro-
sobenzene. (b) Crystal structure of 4 indicating the dearomatization of the aryl
[
28,34,35]
1
phosphorus environment.
By H NMR spectroscopy, ring thermal ellipsoids rendered at 50% probability level. Tert-butyl methyls
and C–H hydrogen atoms excluded for clarity. Selected bond lengths (Å) and
both the N-methyl groups of the triamide ligand as well as
ꢁ
angles ( ) of P–O(1) 1.72(1), P–C(15) 1.89(9), O(1)–N(4) 1.42(4), N(4)–C(20)
the tert-butyl groups of the nitroso fragment are found to 1.29(3), C(19)–C(20) 1.47(7), C(18)–C(19) 1.34(2), C(17)–C(18) 1.46(4),
31
13
C(17)–C(16) 1.34(6), O(1–P(1)–N(4) 110.8(7), O(1)–P(1)–C(15) 86.4(2),
C(21)–C(15)–P(1) 115.2(2).
be inequivalent. Both the P and C NMR spectrum pro-
vide evidence for coupling between phosphorus and an
ortho carbon atom of the nitrosoarene fragment with a mag-
1
be more stable than 3 with an energy difference of 14.2 kcal/
mol, in accord with the experimental observation.
Interestingly, an opposite thermochemical outcome is pre-
dicted if parent nitrosobenzene (i.e., devoid of 2,4,6-tri-tert-
butyl substituents) is employed in the calculation (at the
M06-2X/6-311þþG(2d,2p) level of theory). As depicted in
nitude ( J
¼ 154 Hz) indicative of a direct bonding inter-
C–P
action and is not consistent with the previously expected
oxazaphosphirane (3).
The same reaction between 1 and 2 in a standing solu-
tion of acetonitrile at room temperature deposits large dif-
fraction-quality crystals overnight. Refinement of the X-ray
diffraction data provides a model describing oximinophos-
pholene 4 (Scheme 2), in which the nitrosoarene has added
0
Figure 1, the [2 þ 1] adduct 3 is favored over the [4 þ 1]
0
adduct 4 by 9.3 kcal/mol. A further survey of the energy
landscape suggests that a stepwise pathway for the formation
5
5
in 1,4-fashion to give a r ,k -phosphorus product. The bond
0
╪
of 3 (DG ¼ 22.4 kcal/mol via TS1) is favored over a direct
distance between the nitroso nitrogen and ipso carbon
╪
[
2 þ 1] cycloaddition (DG
¼ 32.6 kcal/mol via TS3),
(
N –C ) bond has shortened to 1.29(3) Å, approaching that
4 20
whereas a concerted [4 þ 1] pathway resides at lower energy
[
36]
╪
of a double bond (typically 1.28 Å).
Conversely, the
(
DG ¼ þ23.6 kcal/mol via TS6) relative to a stepwise for-
0
╪
nitroso N–O bond distance is elongated (N –O ¼ 1.42(4)
4
1
mation of 4 (DG ¼ 26.4 kcal/mol via TS4).
Å) as expected for a single bond order. The formation of
The major hypothesis emerging from the DFT studies is
that steric effects might dictate the [2 þ 1] vs. [4 þ 1] parti-
tioning of reactions involving 1 and substituted nitrosoben-
the new P–C bond in
4
(P –C ¼ 1.89(9) Å, the average P–C bond is 1.85 Å),
1
15
coincides with the breaking of the aromaticity of the nitro- zenes. Consistent with the forgoing prediction, when 1 is
soarene; the C–C bonds of the former aryl ring show alter- treated with the less sterically hindered 2,4,6-trimethylnitro-
nating bond lengths between C16 through C20.
[
36]
sobenzene (5) (Scheme 3), an oximinophosphole analogous
3
1
The preference for the [4 þ 1] adduct 4 over the [2 þ 1] to 4 is not formed. Rather a single species (6) with a
P
adduct 3 is supported by DFT calculations. At the M06-2X/ NMR shift of d þ 18 ppm is produced. Five distinct peaks in
1
6
-311 þ G(d,p) level of theory, compound 4 is predicted to the H NMR spectrum corresponding to the methyl groups

9
42
C. TE GROTENHUIS ET AL.
0
0
Figure 1. DFT calculations on formation of oxazaphosphirane 3 and oximinophosphole 4 using Gaussian 09 M06-2X /6-311þþG(2d,2p).
X-ray diffraction data from a single crystalline sample of
, prepared from acetonitrile and dichloromethane by slow
6
evaporation, coincides with the spectral observations and
indicates a structure as depicted in Scheme 3. In effect, com-
pound 6 represents a formal migration of the mesityl nitrene
into a P–N bond of the phosphorus triamide core with the
formation of a terminal P ¼ O bond (Scheme 3).
On the basis of prior literature which supports the forma-
tion of nitrene or nitrenoid reactive intermediates by deoxy-
[
26,37–39]
genation of nitro- and nitrosoarenes,
we infer that
compound 6 is formed via initial access to an oxazaphos-
phirane compound, similar to 3, followed by subsequent
arylnitrene migration. Indeed, the relative Gibbs free ener-
gies computed by DFT support this hypothesis; the Gibbs
free energy of 6 is 31.8 kcal/mol lower than that of the cor-
responding oxazaphosphirane.
A related [4 þ 1] vs. [2 þ 1] dichotomy is observed in
addition reaction of 1 with 2-acylpyridines. Treatment of 1
ꢁ
with bis(2-pyridyl) ketone 7 at 80 C in benzene results in
formation of a deep red solid. Dissolution in benzene and
1
analysis by H NMR spectroscopy reveals the presence of
new signals appearing at intermediate chemical shift (ca. d
31
5
.77 ppm and 4.82 ppm). A P NMR spectrum shows a sin-
gle septet at d ꢀ 50 ppm. Based on these observations and by
[
40]
Scheme 3. (a) Product of 1 with 2,4,6-trimethylnitrosobenzene upon nitrenoid analogy with 4, the structure is postulated to be that of 8.
migration. (b) Crystal structure of 6 displaying different surroundings for all
Computations support 8 as being thermodynamically down-
gen atoms excluded for clarity. Selected bond lengths (Å) and angles ( ) of hill by 7.2 kcal/mol via concerted [4 þ 1] addition analogous
methyl groups. Thermal ellipsoids rendered at 50% probability level. C–H hydro-
ꢁ
P–O(1) 1.47(0), P(1)–N(1) 1.67(2), P(1)–N(2) 1.68(3), P(1)–N(4) 1.65(0), N(3)–N(4)
to the formation of 4 (Scheme 4).
1
.43(1), N(4)–C(15) 1.44(3), O(1)–P(1)–N(1) 114.0(9), O(1)–P(1)–N(2) 121.0(9),
By contrast, reaction of 1 with 2-pyridinecarboxaldehyde
(9) for two hours at 80 C resulted in the formation of a sin-
O(1)–P(1)–N(4) 110.4(4), N(1)–P(1)–N(4) 114.6(7), P(1)–N(4)–C(15) 122.6(1),
N(3)–N(4)–C(15) 114.9(4).
ꢁ
gle product exhibiting an apparent multiplet (d þ 32 ppm) in
31
(
d 2.90, 2.46, 2.38, 2.09, and 2.01 ppm) indicate a low-sym- the P NMR spectrum. A phosphorus-coupled doublet is
13
metry structure with respect to both the phosphorus tria- observed in the C NMR spectrum at d 72.4 ppm with
1
1
mide core as well as the mesityl moiety.
JP–C¼119 Hz coupling constant. Using
H
NMR

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
943
0
Scheme 4. (Top) [4 þ 1] addition of 1 with 2,2 -bispyridylketone results in oximinophospholene 8. (Bottom) Formation of 11 via treating 1 with 2-pyridinecarboxal-
dehyde 9. DFT calculations using Gaussian 09 M06-2X /6-311þþG(2d,2p).
spectroscopy, a doublet integrating to one proton can be believe this ring expansion to proceed through [2 þ 1] cyclo-
found at d 5.35 ppm with a coupling constant J ¼ 22 Hz addition followed by formal nitrene and carbene migrations.
2
whose magnitude is consistent with two-bond J
spin–s- The compounds described in this work provide insight into
P–H
pin coupling. Moreover, two distinct methyl groups can be the diverging reactivity of important intermediates in
3
found at d 2.80 ppm ( J ¼8.9 Hz) and d 2.0 ppm organophosphorus transformations.
P–H
4
(
JP–H¼2.1 Hz), indicating the triamide ligand that is no lon-
ger symmetrically bound to the phosphorus. Taken together,
these spectral data are consistent with the assignment of the
Experimental section
reaction product as 11 (Scheme 4), in which aldehyde General information
deoxygenation by phosphorus triamide 1 leads to carbene
Phosphorus triamide 1 was prepared according to literature
migration into one of the distal P–N bonds and formation
of a terminal P ¼ O. As was suggested for 6, the formation
of 11 presumably arises via an unobserved [2 þ 1] adduct,
ground state energies by DFT deem this feasible as well.
Indeed, the formation of carbene and carbenoid reactive
equivalents by P(III) mediated carbonyl deoxygenation is
[
44]
procedures.
All other reagents were purchased from com-
mercial vendors and used without further purification unless
otherwise indicated. Manipulations conducted under an
inert atmosphere (N ) are noted accordingly in the following
2
1
13
31
procedures. H, C and P NMR spectra were collected
with either Bruker AVANCE-400 or AVANCE Neo-500
[
2,23,24,41–43]
extensively supported in the literature.
1
spectrometers and processed using MestReNova. H NMR
chemical shifts are given in ppm with respect to the solvent
residual peak (CDCl , d 7.26 ppm; C D d 7.16 ppm).
Conclusions
3
6 6
13
1
Cf Hg NMR chemical shifts are given in ppm with respect
3
1
In this article, we show that phosphorus triamide 1 reacts
with 2,4,6-tri-tert-butylnitrosobenzene and bis(2-pyridyl)
ketone to form a r ,k -phosphole. Crystallography data con-
to the solvent (CDCl d 77.16 ppm, C D d 128.06 ppm).
P
3
6 6
NMR chemical shifts are given in ppm with respect to 85%
5
5
H PO (d 0.0 ppm) as an external standard. Multiplicities
3
4
firms the loss of aromaticity in the arene ring while DFT are described as s, singlet; br s, broad singlet; d, doublet; t,
calculations indicate these reactions to proceed through a triplet; q, quartet; dd, doublet of doublets; td, triplet of dou-
concerted [4 þ 1] cycloaddition. In contrast, when either blets; m, multiplet. Coupling constants are reported in Hertz
2
,4,6-trimethylnitrosobenzene or 2-pyridine carboxaldehyde (Hz). High-resolution ESI mass spectra were obtained at the
is treated with 1 a deoxygenative process occurs in which MIT department of chemistry instrumentation facility on an
the substrate inserts into the phosphorus triamide core. We Agilent 6545 QTOF/Agilent 1260 LC system.

9
44
C. TE GROTENHUIS ET AL.
[
45]
ꢁ
2
,4,6-Tri-tert-butylnitrosobenzene (2).
At 0 C, m-chlor- (dd, J ¼ 7.6, 1.6 Hz, 1H), 6.91 (tt, J ¼ 7.7, 1.2 Hz, 2H),
operbenzoic acid (3.9 g, 2.0 equiv) in diethyl ether (25 mL) 6.88 ꢀ 6.79 (m, 3H), 6.75 ꢀ 6.66 (m, 3H), 6.47 (dt, J ¼ 7.7,
was added to 2,4,6-tert-butylaniline (3.0 g, 1.0 equiv) in 1.1 Hz, 1H), 2.91 (d, J ¼ 8.9 Hz, 3H), 2.47 (d, J ¼ 1.4 Hz, 3H),
13
diethyl ether (10 mL) and stirred overnight. The bright green 2.40 (s, 3H), 2.10 (s, 3H), 2.02 (s, 3H). C NMR (101 MHz,
solution was then treated with saturated sodium bicarbonate benzene-d ) d 151.15 (d, J ¼ 3.0 Hz), 140.17, 138.33 (d,
6
solution (5.0 mL) and the biphasic mixture was transferred J ¼ 13.7 Hz), 137.39, 137.17, 136.29 (d, J ¼ 16.0 Hz), 134.65
to a separatory funnel and partitioned. The organic phase (d, J ¼ 4.3 Hz), 134.61 (d, J ¼ 16.7 Hz), 130.94, 129.19, 128.67
was washed with water, dried over Na SO4 and filtered (d, J ¼ 4.4 Hz), 127.09, 125.56, 122.52, 122.17, 119.74, 111.07
2
through a plug of silica gel. The filtrate was then concen- (d, J ¼ 8.1 Hz), 108.67 (d, J ¼ 9.3 Hz), 43.36, 29.23 (d,
3
1
trated to yield 2 as a bright green solid (1.7 g) in 52% yield. J ¼ 4.5 Hz), 20.93, 20.43, 19.43. P NMR (162 MHz, C D ) d
6
6
1
H NMR (400 MHz, benzene-d ) d 7.43 (s, 2H), 1.22 (s, 18.30. HRMS (EI) calcd for Chemical Formula:
6
þ
1
8H), 1.21 (s, 9H).
,4,6-Trimethylnitrosobenzene (5).
fC H N OPg , 405.1839; found, 405.1838.
23
26 4
[
45]
ꢁ
2
At 0 C, m-chloro-
Adduct 8. In a glovebox, a vial charged with a solution of
perbenzoic acid (17 g, 2.0 equiv) in diethyl ether (50 mL) compound 1 (100 mg, 0.39 mmol) in benzene (2.0 mL) was
was added to 2,4,6-trimethylaniline (5.2 mL, 1.0 equiv) in treated with bis(2-pyridyl)ketone (41 mg, 0.39 mmol). The
diethyl ether (50 mL) and stirred overnight. During the add- mixture was then heated to reflux for 2 h, at which time the
31
ition, the brown solution first turned green and then became reaction was judged complete by P NMR spectroscopy.
a brown suspension with white precipitate. The reaction Removal of solvent in vacuo gave 8 as a dark red glass in
1
mixture was treated with saturated sodium bicarbonate solu- quantitative yield. H NMR (500 MHz, benzene-d ) d
6
tion (5.0 mL) and the biphasic mixture was transferred to a 8.53 ꢀ 8.47 (m, 1H), 8.23 (ddt, J ¼ 9.6, 2.7, 1.3 Hz, 1H),
separatory funnel and partitioned. The aqueous layer was 7.37 ꢀ 7.32 (m, 3H), 7.27 (td, J ¼ 7.7, 1.9 Hz, 1H), 6.99 (ddd,
extracted twice with diethyl ether. The combined organic J ¼ 8.7, 7.2, 2.2 Hz, 1H), 6.96 ꢀ 6.91 (m, 4H), 6.82 ꢀ 6.77 (m,
layers were concentrated to yield an orange/brown solid, 1H), 6.52 (ddd, J ¼ 7.4, 4.8, 1.2 Hz, 1H), 6.46 (dt, J ¼ 7.4,
which was purified by silica gel chromatography (2/1 ! 1/1 1.6 Hz, 2H), 5.77 (dd, J ¼ 9.6, 5.8 Hz, 1H), 4.82 (dddd,
3
1
hexane/CH Cl ). Product 5 eluted as a green band on the J ¼ 7.4, 5.6, 4.2, 1.3 Hz, 1H), 3.00 (d, J ¼ 10.1 Hz, 6H).
P
2
2
13
silica gel column, yielding an orange/white solid upon col- NMR (203 MHz, benzene-d )
d
ꢀ48.29.
C
NMR
6
1
lection and concentration (1.6 g, 11 mmol, 29%). H NMR (126 MHz, benzene-d ) d 149.42, 135.63, 134.39, 134.23,
6
(
1
CDCl ) d 6.99 (s, 2H), 2.62 (s, 2H), 2.41 (s, 4H), 2.34 (s, 132.40 (d, J ¼ 4.4 Hz), 132.30, 128.22, 127.98, 126.44, 125.23
3
H), 2.33 (s, 2H).
(d, J ¼ 10.4 Hz), 121.64, 120.21 (d, J ¼ 7.0 Hz), 119.67,
Adduct 4. In a glovebox, compound 1 (50 mg, 0.20 mmol) 116.97, 115.15, 111.53 (d, J ¼ 9.1 Hz), 109.76 (d, J ¼ 11.8 Hz),
was dissolved in acetonitrile (2.0 mL). 2,4,6-Tri-tert-butylni- 105.72 (d, J ¼ 7.8 Hz), 33.47. MS (ESI) calcd for Chemical
trosobenzene (30 mg, 0.20 mmol) was added and the result- Formula: fC H N O Pggþ, 637.3; found, 637.3.
39
48 3 3
ant mixture was aged overnight at ambient temperature,
Adduct 11. In a glovebox, a vial was charged with com-
during which time yellow crystals of adduct 4 developed pound 1 (30 mg, 0.12 mmol) and pyridine-2-carboxaldehyde
1
and were collected by filtration (17 mg, 21% yield). H NMR (13 mg, 0.12 mmol). The solids were then dissolved in ben-
(
7
500 MHz, benzene-d ) d 7.36 (dd, J ¼ 7.5, 1.5 Hz, 1H), zene (3.0 mL) and heated to reflux for 2 h. The solution was
6
.31 ꢀ 7.28 (m, 1H), 6.97 (tt, J ¼ 7.6, 1.4 Hz, 1H), 6.93 (td, then concentrated and product 11 was isolated in quantita-
1
J ¼ 7.6, 1.6 Hz, 1H), 6.84 ꢀ 6.80 (m, 2H), 6.59 (dt, J ¼ 7.5, tive yield. H NMR (500 MHz, benzene-d ) d 8.39 (d,
6
1
5
.4 Hz, 1H), 6.32 ꢀ 6.25 (m, 1H), 6.07 (t, J ¼ 1.6 Hz, 1H), J ¼ 4.7 Hz, 1H), 7.27 (dd, J ¼ 7.6, 1.6 Hz, 1H), 7.03 (td,
.84 (dd, J ¼ 9.5, 1.7 Hz, 1H), 3.43 (d, J ¼ 7.1 Hz, 3H), 2.96 J ¼ 8.0, 1.6 Hz, 1H), 6.99 (ddt, J ¼ 8.2, 2.0, 1.1 Hz, 1H), 6.92
(
d, J ¼ 9.1 Hz, 3H), 1.45 (s, 9H), 0.84 (s, 9H), 0.79 (s, 9H).
(
dd, J ¼ 7.6, 1.7 Hz, 1H), 6.86 (d, J ¼ 7.7 Hz, 1H), 6.81 (qt,
1
3
C NMR (126 MHz, benzene-d ) d 165.95 (d, J ¼ 10.3 Hz),
6
J ¼ 8.0, 7.5, 1.1 Hz, 2H), 6.68 (t, J ¼ 7.8 Hz, 1H), 6.60 ꢀ 6.53
1
44.13 (d, J ¼ 14.5 Hz), 141.71 (d, J ¼ 11.4 Hz), 139.26 (d,
(
1
m, 1H), 6.53 (dd, J ¼ 8.0, 1.4 Hz, 1H), 6.34 (d, J ¼ 7.7 Hz,
J ¼ 15.6 Hz), 136.18 (d, J ¼ 7.3 Hz), 135.53 (d, J ¼ 10.0 Hz),
H), 5.35 (dthept, J ¼ 22.0, 7.8, 1.0 Hz, 1H), 2.80 (d,
13
1
1
34.26 (d, J ¼ 18.8 Hz), 124.16 (d, J ¼ 5.7 Hz), 121.32, 120.57,
20.20, 120.14, 118.95, 112.53 (d, J ¼ 7.8 Hz), 110.76 (d,
J ¼ 8.9 Hz, 3H), 2.30 (d, J ¼ 2.1 Hz, 3H).
C NMR
(
1
126 MHz, benzene-d ) d 156.65 (d, J ¼ 3.3 Hz), 148.86,
6
J ¼ 7.2 Hz), 109.91 (d, J ¼ 10.7 Hz), 108.97 (d, J ¼ 9.6 Hz),
44.55 (d, J ¼ 3.8 Hz), 136.86 (d, J ¼ 11.7 Hz), 135.78, 134.39
5
9.45 (d, J ¼ 154.8 Hz), 39.88, 36.21, 35.17, 34.19, 33.11 (d,
(
(
d, J ¼ 13.0 Hz), 128.64 (d, J ¼ 4.6 Hz), 128.22, 127.65, 122.39
J ¼ 2.9 Hz), 29.93, 28.59 (d, J ¼ 1.9 Hz), 26.32 (d, J ¼ 6.1 Hz).
d, J ¼ 2.3 Hz), 122.15, 121.41, 120.61, 119.69, 116.85, 109.40
3
1
P NMR (203 MHz, benzene-d ) d ꢀ19.61 (dt, J ¼ 16.9,
6
(d, J ¼ 6.3 Hz), 107.87 (d, J ¼ 7.8 Hz), 72.44 (d, J ¼ 119.3 Hz),
31
7
.9 Hz). HRMS (EI) calcd for Chemical Formula:
3
9.08 (d, J ¼ 12.9 Hz), 26.79 (d, J ¼ 4.8 Hz).
P NMR
þ
fC H N O Pg , 531.3247; found, 531.3244.
3
2
43 4 3
(162 MHz, C D ) d 31.95. HRMS (EI) calcd for Chemical
Formula: fC H N OPg , 363.1369; found, 363.1365.
6
6
þ
Adduct 6. In a glovebox, a vial was charged with com-
pound 1 (100 mg, 0.39 mmol) and 2-nitrosomesitylene
20
20 4
(
58 mg, 0.39 mmol). The solids were then dissolved in ben-
Acknowledgment
zene (3.0 mL) and heated to reflux for 2 h. The solution was
then concentrated and product 6 was isolated without fur-
We thank Dr. Peter Muller (MIT) for assistance with crystallographic
1
ther purification. H NMR (400 MHz, benzene-d ) d 7.26 data collection and structure elucidation of compound 6.
6

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
945
Funding
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Funding for synthetic chemistry was provided by NSF (CHE-1900060).
This work was supported by The Netherlands Organization for
Scientific Research (Rubicon Postdoctoral Fellowship 019.181EN.020 to
CtG). ChemMatCARS Sector 15 is principally supported by the
Divisions of Chemistry (CHE) and Materials Research (DMR),
National Science Foundation, under grant number NSF/CHE1346572.
Use of the PILATUS3 X CdTe 1M detector is supported by the
National Science Foundation under the grant number NSF/DMR-
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