Preparation and properties of 1,2-bis[(2,4,6-tri-t-butylphenyl) phosphinidene]cyclobuta[l]phenanthrene

Article abstract of DOI:10.1246/cl.2004.1570

Sterically protected 1,2-bis[(2,4,6-tri-t-butylphenyl)phosphinidene] cyclobuta[l]phenanthrene (4) and its group(6) and group(10) transition metal complexes were prepared. X-ray crystallographic analysis of 4 revealed a planar structure of the diphosphinidenecyclobuta[l]phenanthrene moiety. Copyright

Full text of DOI:10.1246/cl.2004.1570

1570
Chemistry Letters Vol.33, No.12 (2004)
Preparation and Properties of 1,2-Bis[(2,4,6-tri-t-
butylphenyl)phosphinidene]cyclobuta[l]phenanthrene
Akitake Nakamura, Subaru Kawasaki, Kozo Toyota, and Masaaki Yoshifujiꢀ
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578
(Received September 16, 2004; CL-041090)
Sterically protected 1,2-bis[(2,4,6-tri-t-butylphenyl)phos-
phinidene]cyclobuta[l]phenanthrene (4) and its group(6) and
group(10) transition metal complexes were prepared. X-ray
crystallographic analysis of 4 revealed a planar structure of the
diphosphinidenecyclobuta[l]phenanthrene moiety.
lows. Bis-olefination of 56 with a CBr4/PPh3 derived ylide7 pro-
vided 6. Treatment of 6 with n-BuLi followed by MesꢀPHCl8
gave 7. Compound 7 was then treated with n-BuLi (2 molar
ratio) and 1,2-dibromoethane (1 molar ratio) in a dilute THF
solution to give 4 [(E,E)-form] in 10% yield.9
The structure of (E,E)-4 was unambiguously determined by
X-ray crystallography.10 Figure 1 shows a molecular structure of
(E,E)-4, which has a C2 symmetry. The cyclobutaphenanthrene
moiety was almost planar [deviation of atoms C(1)–C(8) and
Sterically protected 3,4-diphosphinidenecyclobutenes (1:
abbreviated to DPCB),1 bearing an extremely bulky 2,4,6-tri-t-
butylphenyl group (abbreviated as Mesꢀ)2 are unique ligands
of interest,3 because of their relatively rigid framework contain-
ing phosphorus–carbon ꢀ-bonds,4 whose low-lying ꢀꢀ orbital3d
plays an important role in catalytic activity of their transition
metal complexes.3b–e
DPCB derivatives containing phenyl groups at the 1,2-posi-
tions, such as 1b, 1c have been reported.1a,3c X-ray crystallo-
graphic data from (E,E)-1b suggest that the aromatic rings at
the 1,2-positions are not co-planar, at least in the crystalline
state.1a Extension of the ꢀ-system of the DPCB moiety with a
planar aromatic skeleton is of interest, because the extended
ꢀ-conjugation may affect the frontier orbitals, which in turn
affect electronic states and catalytic activity.3d
ꢀ
ꢀ
ꢀ
C(1) –C(8) from planarity was within 0.03(1) A]. Table 1 lists
selected bond lengths of (E,E)-4 as well as those of the related
compounds (E,E)-1b,1a 2,5a and parent phenanthrene (8).11 The
P(1)–C(1), P(1)–C(9), and C(1)–C(1)ꢀ bond lengths of 4 are
slightly shorter than those of 1b, while C(1)–C(2) is longer in
4 than in 1b. The bond lengths in the phenanthrene moiety of
4 are in general very similar to those of 2 and 8. The C(1)–
C(1)ꢀ bond length for 2, however, is apparently longer than that
for 4: this may be due to the electrostatic repulsion between the
two carbonyl groups. The difference between the bond lengths of
4 and 1b mentioned above suggests that the phenanthrene system
co-planar to the –P=C–C=P– moiety affect the P=C ꢀ-bond.
El
El
Mes*
P
R1
R1
R2
R2
P
2: El = O; 3: El = S
5: R2 = CHO
Mes*
(E,E)-1a: R1 = H
(E,E)-1b: R1 = Ph
6: R2 = CH CBr2
7: R2 = C
Figure 1. Molecular structure of (E,E)-4, showing the atomic
labeling scheme with thermal ellipsoids (50% probability).
(E,E)-1c: R1 = p-MeOC6H4
CP(H)Mes*
UV–vis spectra of compounds 1a,1c 1b,1a and 4 are shown
in Figure 2. The absorption of 4 at 260–300 seems to be due
to phenanthrene ring system. Preliminary calculation (HF/3-
21G) of a model (p-t-Bu was replaced by H) of (E,E)-4 indicated
that HOMO is ꢀ-orbital (rather than n orbital) containing P=C
and phenanthrene ꢀ-system, and energy gap between LUMO
and LUMO+1 is smaller than that of the corresponding 1,2-
diphenyl derivative. The absorption of 4 at 340–400 nm appears
to correspond to the ꢀ ! ꢀꢀ transitions.
(E,E)-4: m = none
9Cr: m = Cr(CO)4
9Mo: m = Mo(CO)4
9W: m = W(CO)4
9Pd: m = PdCl2
9Pt: m = PtCl2
Mes*
P
m
P
Mes*
Mes* = 2,4,6-t-Bu3C6H2
Extension of the ꢀ-system by incorporation of a planar
fused-ring aromatic system such as phenanthrene is thus of inter-
est. We report here the preparation and properties of diphosphi-
nidenecyclobuta[l]phenanthrene 4 as well as its transition metal
complexes. It should be noted here that cyclobuta[l]phenan-
threne derivatives such as 2 or 3 have rarely been studied,5 in
contrast to the abundant research on phenanthrene derivatives.
Compound 4 was prepared by an ordinary method1b as fol-
31P NMR spectrum of (E,E)-4 [ꢁP (CDCl3) 173.8] shows a
shift to a lower field, compared with that for (E,E)-1b [ꢁP
(CDCl3) 169.7]. Although chemical shift of the ꢂ-carbon (C1
in Figure 1) of (E,E)-4 is similar to that of (E,E)-1b in 13C NMR
spectrum, the ꢃ-carbon (C2) shifts to a higher field in (E,E)-4
[(E,E)-4: ꢁ(C1) 177.8, ꢁ(C2) 149.6; (E,E)-1b1a: ꢁ(C1) 176.3,
ꢁ(C2) 155.3].
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.12 (2004)
1571
ꢀ
Table 1. Selected bond lengths (A) for compounds (E,E)-1b,
(E,E)-4, 2, and 8
S. Nagase, Bull. Chem. Soc. Jpn., 65, 2297 (1992). d) N.
Yamada, K. Abe, K. Toyota, and M. Yoshifuji, Org. Lett., 4,
569 (2002).
(E,E)-4
(E,E)-1ba
2b
8c
2
3
a) M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu, and T.
Higuchi, J. Am. Chem. Soc., 103, 4587 (1981); 104, 6167
(1982). b) M. Yoshifuji, J. Organomet. Chem., 611, 210 (2000).
a) K. Toyota, K. Tashiro, and M. Yoshifuji, Chem. Lett., 1991,
2079. b) K. Toyota, K. Masaki, T. Abe, and M. Yoshifuji, Chem.
Lett., 1995, 221. c) T. Minami, H. Okamoto, S. Ikeda, R.
Tanaka, F. Ozawa, and M. Yoshifuji, Angew. Chem., Int. Ed.,
40, 4501 (2001). d) F. Ozawa, S. Kawagishi, T. Ishiyama,
and M. Yoshifuji, Organometallics, 23, 1325 (2004). e) M.
Yoshifuji, J. Synth. Org. Chem. Jpn., 61, 1116 (2003) and
references cited therein.
P(1)–C(1)
P(1)–C(9)
C(1)–C(2)
C(2)–C(3)
C(1)–C(1)ꢀ
C(2)–C(2)ꢀ
1.669(2)
1.841(1)
1.488(2)
1.430(2)
1.515(6)
1.380(2)
1.690(8)
1.861(6)
1.467(10)
—
1.535(8)
1.380(9)
—
—
1.489d
1.423d
1.580
1.362
—
—
—
1.422d
—
1.338
aData taken from Ref. 1a. bData taken from Ref. 5a. cData taken from
Ref. 11. dTaking approximate C2v symmetry of the molecule into ac-
count, the corresponding two bond lengths are averaged.
4
5
‘‘Multiple Bonds and Low Coordination in Phosphorus
Chemistry,’’ ed. by M. Regitz and O. J. Scherer, Georg Thieme
Verlag, Stuttgart (1990).
a) P. R. Buckland, N. P. Hacker, and J. F. W. McOmie, J. Chem.
Soc., Perkin Trans. 1, 1983, 1443. b) N. P. Hacker, F. W.
McOmie, J. Meunier-Piret, and M. Van Meerssche, J. Chem.
Soc., Perkin. Trans. 1, 1982, 19, and references cited therein.
a) F. Weygand, G. Eberhardt, H. Linden, F. Schafer, and I.
Eigen, Angew. Chem., 65, 525 (1953). b) W. J. Schmitt, E. J.
Moriconi, and W. F. O’Connor, J. Am. Chem. Soc., 77, 5640
(1955).
6
7
8
E. J. Corey and P. L. Fuchs, Tetrahedron Lett., 1972, 3769.
a) G. Markl and P. Kreitmeier, Angew. Chem., Int. Ed. Engl., 27,
¨
1360 (1988). b) A. H. Cowley, J. E. Kilduff, N. C. Norman, M.
Pakulski, J. L. Atwood, and W. E. Hunter, J. Am. Chem. Soc.,
105, 4845 (1983).
9
(E,E)-4: Yellow solid, mp >275 ꢁC (decomp.); 1H NMR (400
MHz, CDCl3) ꢁ ¼ 1:53 (18H, p-t-Bu), 1.59 (36H, o-t-Bu), 5.64
3
3
Figure 2. UV–vis spectra of (E,E)-1a, (E,E)-1b, and (E,E)-4 in
CH2Cl2.
(2H, d, JHH ¼ 8:0 Hz, arom.), 7.00 (2H, t, JHH ¼ 7:6 Hz,
3
arom.), 7.43 (2H, t, JHH ¼ 7:4 Hz, arom.), 7.65 (4H, m-Mesꢀ),
3
and 8.47 (2H, d, JHH ¼ 8:4 Hz, arom.); 13C{1H} NMR (100
We then prepared several transition metal complexes of 4 as
follows. Reaction of (E,E)-4 with [group(6) transition metal]-
[(bicyclo[2.2.1]hepta-2,5-diene)tetracarbonyl] gave the corre-
sponding chelate tetracarbonylmetal complexes 9Cr,Mo,W.12
When (E,E)-4 was treated with (RCN)2MCl2 [(M = Pd, R =
Me) or (M = Pt, R = Ph)], chelate complexes 9Pd,Pt were
MHz, CDCl3) ꢁ ¼ 32:1 (p-CMe3), 33.6 (o-CMe3), 35.7
(p-CMe3), 38.9 (p-CMe3), 122.5 (m-Mesꢀ), 123.6, 125.7,
127.3, 127.5, 127.9, 132.3, 136.6 (pseudo t, JPC ¼ 18:1 Hz,
ipso-Mesꢀ), 149.6 (pseudo t, JPC ¼ 4:0 Hz, P=C–C), 151.2,
1
3
156.5, and 177.8 (dd, JPC ¼ 16:5 Hz and JPC ¼ 7:0 Hz,
P=C); 31P{1H} NMR (162 MHz, CDCl3) ꢁ ¼ 173:8; IR (KBr)
2960, 2908, 2870, 1593, 1473, 1396, 1362, 1238, 1209, and
758 cmꢂ1; UV–vis (hexane) 278 (log " 4.40), 290 (sh, 4.35),
and 338 nm (4.55). Found: m=z 753.4711. Calcd. for C52H67P2,
MHþ, 753.4713.
1
formed.12 Although the JWP of 9W is similar to that of (E,E)-
1
1b W(CO)4 complex ( JWP ¼ 257 Hz), the 1JPtP of 9Pt is appa-
.
rently smaller than that of (E,E)-1b PtCl2 complex (1JPtP
4499:2 Hz). The reason for this small JPtP value in 9Pt is not
clear at this time. The structure-JPtP relationship is still unclear
¼
.
1
10 C52H66P2, Mr ¼ 753:04. monoclinic, space group C2 (#5), a ¼
ꢁ
ꢀ
14:948ð5Þ, b ¼ 10:385ð3Þ, c ¼ 15:264ð6Þ A, ꢃ ¼ 106:963ð2Þ ,
V ¼ 2266:3ð14Þ A , Z ¼ 2, ꢄ ¼ 1:103 gcmꢂ3, ꢅ ¼ 1:29 cmꢂ1
;
ꢀ 3
.
in other known DPCB PtCl2 complexes.
R1 [I > 2ꢆðIÞ] = 0.034, R = 0.036 (all data), wR2 (all data) =
0.076. 5171 Unique reflections with 2ꢇ ꢃ 55:0ꢁ were recorded
(Mo Kꢂ radiation, graphite monochrometer) at ꢂ100 ꢁC. Crys-
tallographic data have been deposited at the Cambridge Crystal-
lographic Data Centre (No. CCDC 241967).
In summary, we have prepared diphosphinidenecyclo-
buta[l]phenanthrene derivative for the first time. A planar struc-
ture was confirmed by X-ray crystallography. Electronic pertur-
bation was shown by UV–vis and NMR spectroscopies. Further
studies on the properties of 4 and 9 are now in progress.
11 V. Petricek, I. Cisarova, L. Hummel, J. Kroupa, and B. Brezina,
Acta Crystallogr., Sect. B, 46, 830 (1990).
12 9Cr: Brown solid, mp 165–168 ꢁC (decomp.); 31P NMR (162
MHz, CDCl3) ꢁ ¼ 193:1; UV–vis (CH2Cl2) 247 (log " 4.85),
339 (4.46), and 456 nm (4.29). 9Mo: Brown solid, mp >
160 ꢁC (decomp.); 31P NMR ꢁ ¼ 176:3; UV–vis (CH2Cl2) 245
(log " 4.92), 334 (4.50), and 436 nm (4.42). 9W: Brown solid,
mp 222–226 ꢁC (decomp.); 31P NMR ꢁ ¼ 154:4 (satellite d,
1JWP ¼ 256:4 Hz); UV–vis (CH2Cl2) 244 (log " 4.95), 334
(4.52), 437 (4.52), and 530 nm (3.88). 9Pd: Brown solid, mp
This work was supported by Grant-in-Aid for Scientific Re-
search from the Ministry of Education, Culture, Sports, Science
and Technology (Nos. 13304049, 14044012, 15036206, and
16033207). We thank Dr. Chizuko Kabuto (Instrumental Analy-
sis Center for Chemistry, Tohoku Univ.) for crystallographic
analysis.
ꢁ
231–234 C (decomp.); 31P NMR ꢁ ¼ 149:5; UV–vis (CH2Cl2)
References and Notes
1
a) R. Appel, V. Winkhaus, and F. Knoch, Chem. Ber., 120,
243 (1987). b) M. Yoshifuji, K. Toyota, M. Murayama, H.
Yoshimura, A. Okamoto, K. Hirotsu, and S. Nagase, Chem.
Lett., 1990, 2195. c) K. Toyota, K. Tashiro, M. Yoshifuji, and
249 (log " 4.73) and 359 nm (4.63). 9Pt: Orange solid, mp >
1
300 ꢁC (decomp.); 31P NMR ꢁ ¼ 125:7 (satellite d, JPtP
¼
4441:4 Hz); UV–vis (CH2Cl2) 250 (log " 4.62), 261 (4.60), 274
(4.61), and 365 nm (4.67).
Published on the web (Advance View) November 13, 2004; DOI 10.1246/cl.2004.1570