Preparation and X-ray analysis of novel carbonyltungsten(0) complexes of diphosphinidenecyclobutenes

Article abstract of DOI:10.1039/a706963d

A sterically protected diphosphinidenecyclobutene 5 bearing a bulky 2,4,6-triisopropylphenyl group is prepared and allowed to react with W(CO)₅(thf) to give a doubly tungsten-coordinated complex 8, with chelate- and π-type coordination; the str

Full text of DOI:10.1039/a706963d

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Preparation and X-ray analysis of novel carbonyltungsten(0) complexes of
diphosphinidenecyclobutenes
Masaaki Yoshifuji,* Yoshito Ichikawa, Naoki Yamada and Kozo Toyota
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-77, Japan
A sterically protected diphosphinidenecyclobutene 5 bearing
a bulky 2,4,6-triisopropylphenyl group is prepared and
allowed to react with W(CO)5(thf) to give a doubly tungsten-
coordinated complex 8, with chelate- and p-type coordina-
tion; the structure of the complex is confirmed by X-ray
analysis.
The structure of 8 was confirmed by the X-ray analysis§ to
reveal a novel coordination type. Fig. 1 depicts an ORTEP
drawing of the molecular structure for the bis-tungsten complex
8. There are observed two WCO moieties, one is tetracarbonyl
with chelate type coordination, the other is tricarbonyl with
p-coordination. The two phosphorus atoms coordinate doubly
on both W(CO)4 and W(CO)3 adopting sp3 type configuration.
The exocyclic PNC bonds are bent strongly from the ring plane
[interplanar angle between the plane P(1)P(2)C(3)C(4) and the
plane C(1)–C(4) 32.3°] to adopt a good interaction with the 6p
system to coordinate on W(CO)3, thus exhibiting a sharp
contrast to the regular group 6 metal tetracarbonyl or palladium
complexes of diphosphinidenecyclobutenes, where the system
is planar with all sp2 type configuration as exemplified in W,11
Mo,12 and Pd complexes.13
Sterically protected phosphorus-containing multiple bonded
compounds with bulky substituents are currently of interest. We
have been interested in cumulated and conjugated systems1,2
involving phosphorus atom(s) in low coordination states, as
well as diphosphenes3 and phosphaethenes.4 Recently, Appel
et al.,5 Ma¨rkl et al.6 and ourselves7–9 have reported the
preparation and isolation of diphosphinidenecyclobutenes
(1a–c, Scheme 1) utilizing 2,4,6-tri-tert-butylphenyl as a
protecting group (Ar), as well as their E/Z isomerization about
the PNC bonds.7,10 We have also reported on their transition
metal complexes, where metals are Cr, Mo, W,8,11,12 Pt and
Pd.13 We now report a new type of tungsten carbonyl complex
ligated with diphosphinidenecyclobutenes carrying the
2,4,6-triisopropylphenyl group14 (Tip) as well as the Ar
group.
The PNC bond lengths of 8 [av. 1.763(10) Å] are elongated
upon coordination compared to those of (E,E)-1a [1.677(6) Å]12
and (E,E)-1b [1.690(8) Å].5 The bond length C(1)–C(2) of 8
[1.47(1) Å] is fairly elongated compared to the values of
1.400(9) Å and 1.380(9) Å for (E,E)-1a and (E,E)-1b,
respectively. Thus, the interaction between the W(CO)3 group
and the ligand is apparently strong, since little change in bond
lengths has been observed upon coordination with the che-
late.8,11–13
Furthermore, in the case of compound (E,E)-1c, carrying the
two Ar groups and no substituents on the cyclobutene ring, a
doubly coordinated complex 9 was formed under similar
conditions using W(CO)4(MeCN)2 (Scheme 3).16 Complex 9
seems to have been formed via 10 as an intermediate, since 10
reacted with W(CO)4(MeCN)2 to give 9.¶ It appeared to require
less hindered environment than 1a or 1b to obtain double
coordination products such as 8 or 9.
ArP
R
1a R = SiMe3
1b R = Ph
1c R = H
ArP
R
Scheme 1 Ar = C6H2But3-2,4,6
According to a slightly modified procedure employed for the
preparation of 1b, (2-phenylethynyl)(2,4,6-triisopropyl-
phenyl)phosphinous halides 3 were prepared by the reaction of
2-phenylethynylphosphinous dichloride 215 with 2,4,6-tri-
isopropylphenylmagnesium bromide in thf at 278 °C. Then 3
was allowed to react with ButLi at 278 °C or with Zn powder
at room temp. to give diphosphane 4 as a diastereomeric mixture
(d,l:meso = ca. 1:1) and the mixture was refluxed in thf to
Although Rau and Behrens reported on the formation and the
6
structural analysis of (h -dimethylenecyclobutene)tricar-
Tip
i, ii
iii
PhC CH
PhC CPCl2
PhC C P
give
(E,Z)-1,2-diphenyl-3,4-bis(2,4,6-triisopropylphenyl-
X
2
phosphinidene)cyclobutene 5.† It should be noted that only a
trace amount of (E,E)-5 was observed by 31P NMR spectro-
scopy.
3 (X = Cl/Br)
iv
Tip
P
In the 1H NMR spectrum of 5 in [2H8]toluene, there appeared
six types of isopropyl peaks at 295 K. At higher temperatures,
only two sets due to the ortho-isopropyl groups became
coalesced, but the other two sets due to the other ortho-
isopropyl groups remained magnetically non-equivalent. The
remainder of the isopropyl groups assigned to the para-
isopropyl groups remained unchanged even at 375 K. The fact
suggests that one of the Tip groups, probably (E)-Tip, taking the
steric congestion into account, starts to rotate at 323 K, while
(Z)-Tip appears not to rotate even at 375 K.
Tip
Tip
Ph
PhC
PhC
C
C
P
P
v
Tip
P
Ph
4
(E,Z)-5
vi
Tip
Tip
P
Tip
P
W(CO)3
Ph
Ph
Ph
P
(OC)4W
+ (OC)4W
Ph
+
We are now able to obtain a novel class of tungsten complex
by the reaction of the diphosphinidenecyclobutene 5 with
W(CO)5(thf)16 in refluxing thf.‡ The reaction gave 8 together
with 6 and 7 (Scheme 2).† The 31P NMR chemical shift of 8
appeared at dP 57, indicating that the phosphorus atom is
strongly shielded compared with the value in the free ligand of
either dP 164 for (E,E)-5 or dP 169 and 183 for (E,Z)-5.
Ph
P
Tip
P
P
Ph
Tip
Tip
W(CO)5
6
7
8
Scheme 2 Tip = C6H2Pri3-2,4,6. Reagents and conditions: i, NEt3; ii, PCl3;
iii, (Tip)MgBr; iv, ButLi or Zn; v, reflux in thf; vi, W(CO)5(thf), reflux in
thf.
Chem. Commun., 1998
27

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380 (3.94), 456 (3.66), 505 (sh, 3.54), 598 nm (3.30); MS (FAB): m/z 1166
(M+), 1138 (M+ 2 CO), 968 (M+ 2 7CO 2 2). 10: orange powder, mp
198–199.5 °C (decomp.); 1H NMR (200 MHz, CDCl3): d 1.34 (18 H, s,
p-But), 1.63 (36 H, s, o-But), 6.45 (2 H, dd, 3JPH
=
4JPH 3.6 Hz, PNC–CH);
31P{1H} NMR (81 MHz, CDCl3): d 154.1 (satellite d, 1JPW 250.1 Hz); UV–
VIS (n-hexane): lmax(log e) 242 (4.79), 319 (4.12), 413 (4.09), 482 nm
(3.45); MS (FAB): m/z 898 (M+), 870 (M+ 2 CO).
‡ Preparative procedure: 8: under argon, a solution of phenylethynyl-
phosphonous dichloride 2 (356 mg, 1.8 mmol)15 in thf (10 ml) was cooled
at 278 °C and was allowed to react with triisopropylphenylmagnesium
bromide (1.8 mmol) and the mixture was warmed to room temp. to give
phenylethynylphosphinous chloride 3 (X = Cl, dP 40) together with the
bromide 3 (X = Br, dP 22) (chloride:bromide = 1:0.8). The mixture of the
halides 3 (X = Cl, Br) was allowed to react with Zn (261 mg, 4.0 mmol) in
thf (7 ml) at room temp. for 3 h to give the corresponding diphosphane 4 as
a diastereomeric mixture (dP 266, 265); d,l:meso = ca. 1:1. It was then
refluxed in thf for 24 h to give (E,Z)-5. The ligand (E,Z)-5 was allowed to
react with W(CO)5(thf) (1.7 mmol) in refluxing thf for 9 h. 8 (62 mg, 0.051
mmol)† was isolated in 6% yield based on 2, together with 6 [dP 114
(satellite d, 1JPW 265 Hz) and 186, AB, 4JPP 8 Hz] and 7 [dP 139, 1JPW 251
Hz].
P(2)
C(3)
C(1)
C(2)
C(4)
W(1)
W(2)
P(1)
C(26)
C(28A)
§ Crystal data for 8: recrystallised from ethanol–benzene. C53H56O7P2W2,
C(27A)
M
= 1234.67, monoclinic, space group P21/n, a = 10.241(3),
Fig. 1 The molecular structure of bis-tungsten complex 8 showing the
atomic labelling scheme; only atoms with dominant occupancy factors are
displayed. Important bond lengths (Å) and angles (°): W(1)–P(1) 2.493(3),
W(1)–P(2) 2.490(3), W(2)–P(1) 2.679(3), W(2)–P(2) 2.664(3), W(2)–C(1)
2.35(1), W(2)–C(2) 2.321(10), W(2)–C(3) 2.24(1), W(2)–C(4) 2.18(1),
P(1)–C(3) 1.788(10), P(2)–C(4) 1.737(9), C(1)–C(2) 1.47(1), C(1)–C(4)
1.49(1), C(2)–C(3) 1.47(1), C(3)–C(4) 1.47(1); P(1)–W(1)–P(2) 73.22(9),
P(1)–W(2)–P(2) 67.60(8), C(2)–C(1)–C(4) 90.0(8), C(1)–C(2)–C(3)
90.2(8), C(2)–C(3)–C(4) 90.4(8), C(1)–C(4)–C(3) 89.2(8).
b = 25.462(4), c = 20.219(3) Å, b = 92.61(2)°, U = 5266(1) Å3, Z = 4,
T = 223 K, Dc = 1.557 g cm23; 9529 reflections with 2q @ 50.0° were
recorded on a four-circle diffractometer using graphite-monochromated
Mo-Ka radiation. Of these, 6693 with I > 3s(I) were judged as observed.
The structure was solved using SIR92.19 The non-hydrogen atoms, except
for C(27) and C(28), were refined anisotropically. Atoms C(27) and C(28)
were disordered and refined isotropically (occupancy factor for the
dominant: 0.55). Hydrogen atoms except for those on C(26)–C(28) were
included, but their positions were not refined. R = 0.054, Rw = 0.064.
CCDC 182/653.
Ar
P
¶ Preparative procedure: 9 (E,E)-1c (86 mg, 0.14 mmol) was allowed to
react with 0.43 mmol of W(CO)4(MeCN)2 in refluxing thf (30 ml) for 1.5
h to give 90 mg of 9 in 54% yield.† 10: a mixture of diphos-
phinidenecyclobutene (E,E)-1c (31 mg, 0.051 mmol) and W(CO)4-
(MeCN)2 (40 mg, 0.11 mmol) was dissolved in thf (20 ml) and the solution
was stirred at room temp. for 21 h to give 10 (20 mg, 43% yield).†
Ar
P
W(CO)3
H
H
H
i
(OC)4W
1c
+
(OC)4W
H
P
P
Ar
9
Ar
1 M. Yoshifuji, K. Toyota and N. Inamoto, J. Chem. Soc., Chem.
Commun., 1984, 689; M. Yoshifuji, K. Toyota, K. Shibayama and
N. Inamoto, Tetrahedron Lett., 1984, 25, 1809; M. Yoshifuji, K. Toyota,
H. Yoshimura, K. Hirotsu and A. Okamoto, J. Chem. Soc., Chem.
Commun., 1991, 124; M. Yoshifuji, K. Toyota and H. Yoshimura,
Chem. Lett., 1991, 491.
2 S. Ito, K. Toyota and M.Yoshifuji, Chem. Lett., 1995, 747.
3 M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu and T. Higuchi, J. Am.
Chem. Soc., 1981, 103, 4587; 1982, 104, 6167.
4 M. Yoshifuji, K. Toyota, I. Matsuda, T. Niitsu, N. Inamoto, K. Hirotsu
and T. Higuchi, Tetrahedron, 1988, 44, 1363.
5 R. Appel, V. Winkhaus and F. Knoch, Chem. Ber., 1987, 120, 243.
6 G. Ma¨rkl, P. Kreitmeier, H. No¨th and K. Polborn, Angew. Chem., Int.
Ed. Engl., 1990, 29, 927; G. Ma¨rkl and R. Hennig, Liebigs Ann., 1996,
2059.
10
Scheme 3 Ar = C6H2But3-2,4,6. Reagents and conditions: i, W(CO)4-
(MeCN)2, thf, in the dark.
bonylchromium(0)17 and (h -diisopropylidenecyclobutene)tri-
6
carbonylchromium(0),18 this is the first example in the di-
phosphinidenecyclobutene–tungsten carbonyl system, where
the ligand is doubly coordinated to tungsten.
This work was supported in part by the Grants-in-Aid for
Scientific Research (Nos. 08454193 and 09239101) from the
Ministry of Education, Science, Sports and Culture, Japanese
Government.
7 M. Yoshifuji, K. Toyota, M. Murayama, H. Yoshimura, A. Okamoto,
K. Hirotsu and S. Nagase, Chem. Lett., 1990, 2195.
8 K. Toyota, K. Tashiro and M. Yoshifuji, Chem. Lett., 1991, 2079.
9 K. Toyota, K. Tashiro, M. Yoshifuji and S. Nagase, Bull. Chem. Soc.
Jpn., 1992, 65, 2297.
10 K. Toyota, K. Tashiro, T. Abe and M. Yoshifuji, Heteroatom Chem.,
1994, 5, 549.
11 M. Yoshifuji, Y. Ichikawa, K. Toyota, E. Kasashima and Y. Okamoto,
Chem. Lett., 1997, 87.
12 K. Toyota, K. Tashiro, M. Yoshifuji, I. Miyahara, A. Hayashi and
K. Hirotsu, J. Organomet. Chem., 1992, 431, C35.
13 K. Toyota, K. Masaki, T. Abe and M. Yoshifuji, Chem. Lett., 1995,
221.
14 C. N. Smit, Th. A. van der Knaap and F. Bickelhaupt, Tetrahedron Lett.,
1983, 24, 2031.
15 G. Yu. Mikhailov, I. G. Trostyanskaya, M. A. Kazankova and
I. F. Lutsenko, Zh. Obshch. Khim., 1987, 57, 2636.
Footnotes and References
* E-mail: yoshifj@mail.cc.tohoku.ac.jp
† Selected spectroscopic data (NMR spectra were recorded on either a
Bruker AC200P, a JEOL a-500, or a Bruker AM600 spectrometer): (E,Z)-5:
1H NMR (600 MHz, at 295 K, CDCl3): d 0.92 (6 H, d, J 6.8 Hz, o-CHMe),
1.00 (6 H, d, J 6.8 Hz, o-CHMe), 1.20 (6 H, d, J 6.9 Hz, p-CHMe2), 1.25 (6
H, d, J 6.9 Hz, pA-CHMe2), 1.32 (6 H, d, J 6.8 Hz, oA-CHMe), 1.39 (6 H, d,
J 6.8 Hz, oA-CHMe), 2.75 (1 H, spt, J 6.9 Hz, p-CHMe2), 2.75 (1 H, spt, J
6.9 Hz, pA-CHMe2), 3.21 (2 H, m, o-CHMe2), 3.72 (2 H, m, oA-CHMe2);
31P{1H} NMR (81 MHz, CDCl3): d 168.6, 182.8 (AB, J 17.8 Hz). 8: dark
violet crystals, mp 183 °C (decomp.); 1H NMR (600 MHz, CDCl3): d 1.18
(6 H, d, J 6.6 Hz, o-CHMe), 1.31 (6 H, d, J 6.9 Hz, p-CHMe), 1.31 (12 H,
d, J 6.9 Hz, o-, p-CHMe), 1.41 (6 H, d, J 6.7 Hz, o-CHMe), 1.43 (6 H, d, J
6.6 Hz, o-CHMe), 2.94 (2 H, spt, J 6.9 Hz, p-CHMe2), 4.35 (2 H, br s,
o-CHMe2), 4.46 (2 H, spt, J 6.7 Hz, o-CHMe2); 31P{1H} NMR (81 MHz,
1
CDCl3): d 56.7 (satellite d, JPW 226 Hz); IR (KBr): n/cm21 2033, 1994,
1979, 1923, 1913, 1878, UV–VIS (CH2Cl2): lmax(log e) 254 (sh, 4.87), 272
(sh, 4.75), 321 (4.37), 456 (4.04), 603 nm (sh, 3.51); MS (FAB): m/z 1234
(M+), 1206 (M+– CO). 9: red needles, mp 180–181 °C (decomp.); 1H NMR
(500 MHz, CDCl3): d 1.19 (18 H, s, p-But), 1.65 (18 H, s, o-But), 1.75 (18
H, s, o-But), 4.66 (2 H, m, PNC–CH); 31P{1H} NMR (81 MHz, CDCl3): d
64.6 (satellite d, 1JPW 227.6 Hz); IR (KBr): n/cm21 2033, 1994, 1942, 1900,
1865, 604 cm21; UV–VIS (n-hexane): lmax(log e) 218 (4.88), 236 (4.71),
16 W. Strohmeier and G. Scho¨nauer, Chem. Ber., 1961, 94, 1346.
17 D. Rau and U. Behrens, Angew. Chem., Int. Ed. Engl., 1991, 30, 870.
18 D. Rau and U. Behrens, J. Organomet. Chem., 1993, 454, 151.
19 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla,
G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27, 435.
Received in Cambridge, UK, 26th September 1997; 7/06963B
28
Chem. Commun., 1998