Supersilylated Tetraphosphene DeriWatiWes
the formation of isolable phosphanylcyclotriphosphane and
benzophenone. C
6 6
D was dried over molecular sieves and stored
9
19,22
under dry nitrogen. Li(thf)
3
[Si-t-Bu
2
[1] were prepared according to published procedures. All other
3
], Na[Si-t-Bu
3
],
and
cyclotetraphosphane derivatives (e.g., 9 (R ) R′ ) t-Bu
2
Sn);
14
Na
6
(R ) I, R′ ) I); Schemes 3 and 5), and on the other hand,
starting materials were purchased from commercial sources and
used without further purification. NMR spectra were recorded on
a Bruker AM 250, a Bruker DPX 250, a Bruker Avance 300, and
decomposition of the protonated disupersilylated cis- and
trans-tetraphosphene (R ) H, R′ ) H) occurs in the
formation of t-Bu
3
SiPH
2
. In addition, the reactivity of Na
2
[1]
2
9
a Bruker Avance 400 spectrometer. The Si NMR spectra were
recorded using the INEPT pulse sequence with empirically opti-
mized parameters for polarization transfer from the tert-butyl
substituents. Elemental analyses were performed at the microana-
lytical laboratories of the Universit a¨ t Frankfurt. Mass spectrometry
was performed with a Fisons VG Platform II, a Varian CH7, and
a Kratos MS 80 RFA instrument. UV-vis absorption spectroscopy
wascarriedoutinTHFusingaVarianCary50scanspectrophotometer.
toward the Lewis acids BH
3
and AlMe has been studied by
3
heteronucleus NMR spectroscopy and mass spectrometry.
High-level quantum chemical calculations reveal that the
2
-
acyclic cis and trans dianions of [HPPPPH]
and
2
-
[H SiPPPPSiH ] , 10 and 11, as well as 14 and 15,
3 3
respectively, are thermodynamically favored over the cyclic
phosphanylcyclotriphosphane or tetracyclophosphane iso-
mers. However, upon sodium coordination in Na (H Si) P ,
2 3 2 4
the preference for cis configuration increases significantly.
In contrast to the corresponding dianions, the neutral cyclic
4 4 2 3 2 4
isomers of H P and H (H Si) P , 24, 25, 28, and 29, are in
turn significantly more stable than the isomers 22, 23, 26,
and 27 with their acyclic tetraphosphene units. It is interesting
to note that the MOs of the silylated tetraphosphene dianions
[
2 2 2
Na(18-crown-6)(thf) ] [1]. To a solution of Na [1] (2.0 mmol)
in 20 mL of THF was added 18-crown-6 (0.54 g, 2.1 mmol) in
one portion. The purple solution was stirred overnight. Slow
evaporation of the solvent yielded the product as crystalline dark
1
violet plates (0.58 g, 53%). H NMR (THF-d
8
, internal TMS): δ
13
1
1
.08 (br, t-Bu). C{ H} NMR (THF-d
8
, internal TMS): δ 25.2 (br,
31
1
37
CMe
3
1
), 32.2 (br, CMe
3
). P{ H} NMR: (see Figures 2 and 3).
, external TMS): (see Figure 5). UV-vis:
λmax ) 494 nm, 561 nm.
Li [1]. A solution of Li(thf) [Si-t-Bu ] (3.30 mmol) in 6.5 mL
29
Si{ H} NMR (THF-d
8
1
4 and 15, which are comparable with those of the ion-
2-
separated supersilylated tetraphosphenediide [1] calculated
at the HF/6-311G(d)//B3LYP/6-31G(d) level, show a highest
occupied antibonding π * MO (HOMO). Therefore, the
supersilylated tetraphosphene dianion shows promise as a
non-innocent ligand for potentially redox-active transition-
metal complexes.
2
3
3
4
of THF was added dropwise to a cooled solution of P (1.50 mmol)
in 15 mL of THF. The reaction solution was warmed up to room
temperature. Slow evaporation of the solvent yielded the tetraphos-
phenediide Li
2
[1] as crystalline purple blocks (57%). Several
1
attempts to determine the structure failed. H NMR (THF-d
internal TMS): δ 1.06 (br, 54H, t-Bu). C{ H} NMR (THF-d
8
,
,
1
3
1
8
3
1
1
internal TMS): δ 25.0 (br, CMe
3
), 32.1 (br, CMe
3
). P{ H} NMR:
Experimental Section
37 29
1
(
see Figure 2).
Si{ H} NMR (THF-d , external TMS): δ 21.8
8
(
m).
Quantum Chemical Calculations. Quantum chemical calcula-
3
4
Synthesis of the Tetraphosphenediides M [1] (M ) Rb,
2
tions were carried out by means of the Gaussian 03 program.
The thermochemical quantities for the different structures were
Cs) and Ba[1]. A flask was charged with alkali-metal or alkaline-
earth-metal halides (RbCl: 0.120 g, 1.12 mmol; CsF: 0.064 g, 0.44
3
5
36
calculated with the compound methods G3 and CBS-QB3, as
implemented in Gaussian 03. Relative energies (Erel) refer to 1 atm
in kcal/mol. We verified the minimum nature of the isomers reported
by inspection of the Hessian matrices computed as part of the G3
and CBS-QB3 compound methods (positive eigenvalues of the
diagonalized Hessian matrices for all species reported).
mmol; BaI
of an equimolar amount of a 0.1 M solution of Na
.6 mL, Cs: 2.2 mL, Ba: 1.6 mL). After 48 h at room temperature,
2
: 0.062 g, 0.16 mmol) to which was added a solution
2
[1] in THF (Rb:
5
the products were obtained in solution. Filtration and concentration
of the filtrate yielded the microcrystalline purple tetraphosphenediides.
1
Rb
2
[1]. H NMR (THF-d
8
, internal TMS): δ 1.09 (br, t-Bu).
, internal TMS): δ 25.3 (br, CMe ), 32.2
). P{ H} NMR: (see Figure 2). Si{ H} NMR (THF-
General Considerations. All experiments were carried out under
dry argon or nitrogen using standard Schlenk and glovebox
techniques. Alkane solvents were dried over sodium and freshly
distilled prior to use. Toluene and THF were distilled from sodium/
1
3
1
C{ H} NMR (THF-d
br, CMe
8
3
3
1
1
29
1
(
3
d
1
Rb
8
, external TMS): δ 25.2 (m). An element ratio of Rb to P of
:2.3 was determined by EDX spectrometry. Anal. Calcd for
[1](thf) Rb Si : C, 45.87%; H, 8.42%. Found: C,
42.13%; H, 8.02%.
(
34) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Kudin, K. N.; Burant,
J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji,
H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida,
M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,
A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03; Gaussian,
Inc.: Wallingford, CT, 2004.
2
2
C
32
H
70
O
2
P
4
2
2
1
Cs
2
[1]. H NMR (THF-d
8
, internal TMS): δ 1.08 (br, t-Bu).
1
3
1
C{ H} NMR (THF-d
8
, internal TMS): δ 25.1 (br, CMe ), 32.3
3
3
1
1
29
1
(br, CMe
d
3
). P{ H} NMR: (see Figure 2). Si{ H} NMR (THF-
+
8
, external TMS): δ 22.8 (m). (ESI ) (%) (M ) Cs
2
[1](thf)
MeSiPCsPPCsPSiMe-
] 697 (10), [Cs] 132 (100). An element ratio of Cs to P of
2
) m/z:
+
+
[M] 932 (<5), [M - Me] 917 (<5), [t-Bu
2
+
+
t-Bu
2
1
:2.4 was determined by EDX spectrometry. Anal. Calcd for
Cs [1](thf) Cs Si : C, 41.20%; H, 7.56%. Found: C,
9.84%; H, 6.85%.
2
2
C
32
H
70
O
2
P
4
2
2
3
1
Ba[1]. H NMR (THF-d
C{ H} NMR (THF-d
br, CMe
8
, internal TMS): δ 1.09 (br, t-Bu).
, internal TMS): δ 25.2 (br, CMe ), 32.4
). P{ H} NMR: δ 428.9, 19.0. Si{ H} NMR (THF-
13
1
8
3
3
1
1
29
1
(
3
(
(
35) Curtiss, L. A.; Raghavachari, K.; Redfern, P. C.; Rassolov, V.; Pople,
J. A. J. Chem. Phys. 1998, 109, 7764.
36) Montgomery, J. A.; Frisch, M. J.; Ochterski, J. W.; Petersson, G. A.
J. Chem. Phys. 1999, 110, 2822.
(37) Iterative optimization of the simulated spectrum with the software
SpinWorks 2.5.5 yields the shown coupling constants. Marat, K.
SpinWorks 2.5.5; University of Manitoba: Winnipeg, MB, 2006.
Inorganic Chemistry, Vol. 48, No. 3, 2009 1015