Full Paper
less explored. In fact, there are only two reports on the synthe-
sis and reactivities of phosphane(sulfane)carbon(0) (PSCs) as
To prevent hydrolytic degradation of the iSPC, we synthe-
sized derivatives 2 and 3, which contained electron-donating
substituents at the para position of the phenyl group on the
phosphorus center (Scheme 2). The corresponding cationic
salts (2·H and 3·H) were obtained by the reaction of 4 with tri-
arylphosphonium salts in the presence of LDA (3 equiv) in
moderate to good yields (64 and 80%, respectively). Com-
pounds 2 and 3 were prepared in nearly quantitative yield by
[
11]
mixed P,S-bisylides by Baceiredo et al. (Figure 1, E, F). They
used F as an unsymmetrical atomic carbon source to create
quaternary carbon centers; however, so far research into the
nature of PSCs is limited to a monometalated copper(I) com-
[11]
plex or monocationic salts. Further studies on the carbone
character of PSCs, such as in diaurated complexes or dicationic
salts, have never been reported, although the predicted elec-
deprotonation of cationic salts 2·H and 3·H with NaNH in THF
2
[1d,11a]
tron-donating ability of E is similar to that of A.
or by passing through a column of the ion-exchange resin.
Upon exposure to air, compound 2 is more stable than 1. In
fact, the decomposition half-life at room temperature in the
solid state of 2 under air is approximately 24 h, whereas 1 com-
pletely decomposes under the same conditions. Derivative 3 is
stable in air (less than three months) and thermally stable
(m.p. 120–1218C, decomposed over 1358C). To the best of our
knowledge, compound 3 is the first air, moisture, and thermal-
ly stable phosphorus- and sulfur-stabilized carbone.
PSCs are thermally unstable, even if they are stabilized by
a directly induced diamino substituent on the phosphorus
center (E: decomposes at room temperature; F: m.p. 30–328C),
whereas other heteroatom-stabilized carbones are thermally
stable (m.p. A: 208–2108C; B: 163–1648C; C:110–111 8C; D: 95–
[
7a,10–12]
9
68C).
For catalytic applications, heat- and moisture-
[13]
stable carbones are required. We reason that to obtain ther-
mally stable phosphorus- and sulfur-stabilized carbones, imino-
sulfane and triarylphosphane compounds should be used as li-
gands. The iminosulfane ligand of B binds more strongly to
the carbon center than the sulfane ligand through n–s* inter-
13
In the C NMR spectra, the central carbon atom of 1–3 ap-
1
pears as a doublet (1: d=23.1 ppm, J(P,C)=62 Hz; 2: d=
1
1
23.0 ppm, J(P,C)=58 Hz; 3: d=23.6 ppm, J(P,C)=68 Hz; see
Table S1 in the Supporting Information), which is shifted to
a lower field compared with the cationic salts (1·H: d=
[
10b]
actions.
Furthermore, the electronic properties at the phos-
phorus center of the triarylphosphine ligand of A can be easily
tuned by choosing appropriate substituents. Herein, we report
the synthesis of this new type of iminosulfane(phosphane)car-
1
1
18.4 ppm, J(P,C)=114 Hz; 2·H: d=19.4 ppm, J(P,C)=114 Hz;
1
3·H: d=19.7 ppm, J(P,C)=112 Hz), and is intermediate be-
tween BPC (d=12.3 ppm) and BiSC (d=39.9 ppm). In the
!
[8]
[15]
bon(0) (iSPCs; Ar P!C SPh (NMe); Ar=Ph(1), 4-MeOC H (2),
3
2
6
4
31
4
-(Me N)C H (3)). Among these iSPC derivatives, compound 3
P NMR spectra, the signals of 1–3 (1: d=À2.64 ppm; 2: d=
2
6
4
is heat and moisture stable and provides the first experimental
proof of the carbone character. The synthesis of silver(I) com-
plexes and their function as carbone transfer reagents are also
described.
À3.51 ppm; 3: d=À1.39 ppm) are shifted to a higher field
than those of cationic salts (1·H: d=15.9 ppm; 2·H: d=
13.4 ppm; 3·H: d=12.7 ppm) and are comparable to that of
[
8]
BPC (d=À2.14 ppm).
Results and Discussion
Abstraction of a proton from the
corresponding protonated salts
is the general method for pre-
paring carbones; thus, protonat-
ed salt 1·H appears to be a po-
tential precursor for desired iSPC
1
. Cationic salt 1·H was obtained
in 30% yield by the reaction of
Scheme 1. Synthesis and hydrolysis reaction of 1. Reagents and conditions: a) nBuLi, THF, 08C to RT, 0.5 h; b) THF,
iminosulfonium salt 4 with tri-
phenylphosphonium methylide 17 h, then H
À788C, 17 h, then H O (30%); c) nBuLi, THF, 08C to RT, 0.5 h, then tBuLi (2 equiv), À788C, 5 h; d) 4, THF, À788C,
2
2
O (50%); e) NaNH
10 ion-exchange resin (OH form), MeOH, RT; 6 (96%), 7 (92%).
2
, THF, À788C to RT, 0.5 h (97%); f) RT, air, 24 h; 6 (95%), 7 (91%); g) Amberlite IRA-
À
4
(
Scheme 1). Alternatively, the re-
action of 4 with a-lithioylide 5
afforded protonated salt 1·H in
[14]
5
0% yield (Scheme 1). Compound 1 is cleanly generated by
deprotonation of 1·H with NaNH in THF; it is stable under an
2
inert atmosphere in the solid state (m.p. 65–668C, decom-
posed over 1208C) and in C D , but is rapidly hydrolyzed to
6
6
phosphine oxide 6 and sulfimide 7 under air in the solid state
(
Scheme 1). In addition, passing 1·H through an ion-exchange
À
Scheme 2. Synthesis of 2 and 3. Reagents and conditions: a) lithium diiso-
propylamide (LDA; 3 equiv), 4, THF, À788C, 2 h, À108C, 0.5 h, À788C, 18 h,
resin column (IRA-410, OH form) afforded the hydrolyzed
products. We assume that 1 is hydrolyzed by attack at the cat-
ionic phosphorus center by H O or OH .
2
then H O; 2·H (64%), 3·H (80%); b) Amberlite IRA-410 ion-exchange resin
À
À
2
2
(OH form), MeOH, RT; 2 (95%), 3 (97%); c) NaNH , THF, RT, 0.5 h; 2 (97%), 3
(96%).
Chem. Eur. J. 2015, 21, 15405 – 15411
15406
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim