α-Zincated phosphorus ylides

Article abstract of DOI:10.1039/a704248e

1,3-Dizincata-2,4-diphosphoniacyclobutane rearranges into a zincataphosphoniaindane which reacts with benzaldehyde to give 1,3-diphenylallene.

Full text of DOI:10.1039/a704248e

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a-Zincated phosphorus ylides
Matthias Steiner,a Hansjo¨rg Gru¨tzmacher,*a Hans Prtizkowb and Laszlo Zsolnaib
a ETH-Zu¨rich, Laboratorium fu¨r Anorganische Chemie, Universita¨tsstrasse 6, CH-8092 Zu¨rich, Switzerland
b Anorganisch Chemisches Institut der Universita¨t, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany
1,3-Dizincata-2,4-diphosphoniacyclobutane rearranges into
a zincataphosphoniaindane which reacts with benzaldehyde
to give 1,3-diphenylallene.
While 5a is thermally unstable, 5b could be recrystallised
from n-hexane and its structure determined by an X-ray
analysis.‡ All bonds [av. Zn–N 1.956(3) Å, Zn–C 2.077(4) Å]
to the slightly pyramidalised zinc centre (0.138 Å above the
N(1)N(2)C(1) plane] are ca. 0.1 Å longer than comparable Zn–
N (av. 1.857 Å) and Zn–C (av. 1.952 Å) bonds in other
tricoordinated zinc compounds.5 The P(1)–C(1) distance
[1.738(3) Å] is slightly longer than corresponding distances in
a lithium phosphorus ylide complex6 (P–C 1.702 Å) or
uncomplexed ylides themselves (i.e. 3a: 1.693 Å).7 Keeping
solutions of 5a at room temp. or adding pyridine causes loss of
1 equiv. of HN(SiMe3)2 and leads almost quantitatively to
zincatacyclobutane 6 which precipitates as colourless crystals
from the reaction mixture. Compound 6 can be recrystallised
from THF–n-hexane (1:6 v/v). X-Ray analysis of 6‡ reveals a
four-membered planar centrosymmetric Zn2C2 heterocycle in
which the Ph3PCH units adopt bridging positions between the
tricoordinated zinc centres. The Zn–N [1.931(3) Å] and Zn–C
distances [2.068(4) Å] being again longer than in other low
coordinated zinc compounds compare well with the ones in 5b.
The Zn–C–Zn angles [84.5(1)°] are smaller than the C–Zn–C
angles [95.5(1)°]. In order to extrude 1 more equiv. of
By reacting phosphorus ylides (R = aryl) with mercury
bis(trimethylsilyamide) we found a simple synthesis of a-mer-
curated phosphorus ylides, Ph3PNCR[HgN(SiMe3)2], which
react in a Wittig type alkenation reaction with aldehydes to give
vinylmercury compounds.1 We explored the possibility of
synthesising comparable organozinc compounds in a similar
way. These reagents seemed promising to us since they contain
two oxophilic sites (P and low coordinated Zn) for the attack of
a carbonyl oxygen centre. Like titanacycles 12 or allenic
diazophosphorus ylides 23 they may serve as synthons for
carbon atoms (Scheme 1). In the course of the studies, we
observed an unprecedented cyclometallation reaction4 invol-
ving, presumably, a low coordinated zinc centre.
When a toluene solution of ylides 3a,b is added to zinc amide
4 at room temp. in toluene the expected adducts1 5a,b are
formed. They can be isolated as colourless precipitates after
short reaction times (10 min) by concentrating the volume of the
reaction mixture to 20% and adding n-hexane.†
P(NMe2)3
C
Y
X
X
Y
Ti
Ti
C
(Pri2N)2P
C N2
P(NMe2)3
1
Cl
2
PhCH
O
S8
PhHC
C
+
CHPh
S
C S
H
CH2PR3
Zn
R3P
C
Zn[N(SiMe3)2]2
(Me3Si)2N
N(SiMe3)2
H
5a R = Ph
b R = NMe2
4
3a, b
–HN(SiMe3)2
H
N(SiMe3)2
C
Zn
py
N(SiMe3)2
Ph2P
Zn
py
PPh3
H
C
Ph3P
1/2
C
H
H
Zn
N(SiMe3)2
i, ii
6
A
PhCH
O
60 °C
py
py
–pyH+
PhHC
C
CHPh
8
H
H
–
H
C
iii
C
py
N(SiMe3)2
py
Ph2P
Zn
Ph2P
Zn
pyH+
–py
N(SiMe3)2
B
7
Scheme 1 Reagents and conditions: i, 60 °C, 24 h, no py, 7%; ii, 60 °C, 16 h, py, 12%; iii, 60 °C, 16 h, 31%
Chem. Commun., 1998
285

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HN(SiMe3)2 we warmed 6 to 60 °C in presence of pyridine. A
clean reaction was evidenced by one new 31P resonance at d
34.8 (6: d 25.9). The new product 7 was purified by
recrystallization from toluene–n-hexane and completely cha-
racterised including an X-ray analysis. In order to explain the
formation of zincataphosphoniaindane 7, we assume that
pyridine cleaves the four-membered Zn2C2 heterocycle 6 to
envelope conformation [angle between P(1)C(1)Zn and the
ZnC(3)C(2)P plane = 30°].
The Zn–C(3) (aryl) bond length [2.049(3) Å] is normal while
the Zn–C(1) (alkyl) bond [2.138(4) Å] is long. The Zn–
N(SiMe3)2 bond [1.982(3) Å] is 0.1 Å shorter than the Zn–Npy
bond. Owing to electrostatic interactions between the negatively
charged carbon center C(1) (being bonded to the electropositive
1
5
4
give intermediate A which corresponds to an h -arene complex
Zn centre) and the highly positively charged l ,s -phosphorus
centre, the P–C(1) (sp3) bond [1.732(4) Å] is significantly
shorter than the P–C(2) (sp2) bond [1.803(3) Å].
to an electrophilic metal centre. Precedence for such a Zn–arene
interaction is found in ZnPh2 which forms a trapezoid dimer in
the solid state with two ipso-carbon centres of the phenyl
substituents adopting an unsymmetrical bridging binding mode
(Zn–C 2.01, 2.40 Å).8 Being an intramolecular organometallic
s-complex, A possesses a ortho-hydrogen centre which be-
comes sufficiently acidic to be abstracted by pyridine to give
intermediate B. Reprotonation at the C(1) centre yields the
thermodynamically more stable product 7. Unfortunately, we
could not isolate compound B by deprotonation of 7 with a
strong base like NaN(SiMe3)2. Earlier work showed that 1a may
be lithiated by BunLi either at the CH2 group or at the ortho-
position of one of the phenyl groups attached to the phosphorus
centre.9 Our results confirm that the first product may be
obtained under kinetic control while the second one is
thermodynamically more stable.
Footnotes and References
* E-mail: gruetz@inorg.chem.ethz.ch
† Selected 1H (200 MHz), 13C (50.232 MHz), 29Si (17.75 MHz) and 31P
(36.19 MHz) NMR data for 5a,b (C6D6), 6 ([2H8]THF) and 7 (C6D6): 5a:
Mp 187–189 °C. 1H NMR: d 0.37 (s, 36 H, SiMe3), 1.30 (d, 2 H, 2JHP 16.8
Hz, CH2), 6.95–7.16 (m, 9 H, m, p-H, PPh3), 7.54–7.80 (m, 6 H, o-H, PPH3).
13C d 3.7 (d, 1JCP 29.1 Hz, CH2). 29Si NMR: d 6.6. 31P NMR: d 30.1. 5b:
75 °C (decomp.). 1H NMR: d 0.48 (s, 36 H, SiMe3), 1.53 (d, 2 H, 2JHP 17.0
Hz, CH2), 2.08 (d, 18 H, 3JHP 9.3 Hz, NMe2). 13C: d 2.8 (d, 1JCP 91.7 Hz,
CH2). 29Si NMR: d 27.0. 31P NMR: d 74.0. 6: Mp 94–96 °C. 1H NMR: d
20.22 (s, 18 H, SiMe3), 0.01 [A part of AAAXXA, 1 H, (JHP + JHP) 17.7 Hz,
CH], 7.35–7.53 (m, 9 H, m-, p-H, PPh3), 7.62–7.74 (m, 6 H, o-H, PPh3). 13
C
NMR: d 6.1 (d, 1JCP 27.7 Hz, Cring). 29Si NMR: d 27.3. 31P NMR: d 28.1.
7: Mp 79 °C. 1H NMR: d 0.47 (s, SiMe3, 2JHSi 6.2 Hz), 0.76 (d, 2JCP 9.5 Hz,
CH2), 6.55–6.64 (m, arom H), 6.80–740 (m, arom H). 13C NMR (75.469
When zincatacyclobutane 6 is reacted with 4 equiv. of
benzaldehyde in toluene at 60 °C, a pale yellow oil is obtained
after hydrolysis from which ca. 7% diphenylallene 8 were
isolated by column chromatography (n-pentane–Et2O 7:1 v/v).
Other products could not be identified. If the reaction is
performed in presence of pyridine, the yield of allene 8 is
augmented to 12%. Suspecting compound 7 may be involved in
the formation of allene we reacted the zincataindane 7 with 2
equiv. of benzaldehyde. Indeed, the allene was formed in 31%
yield. The mechanism of the seemingly simply Wittig alken-
ation is still not known with certainty10 and our results show that
reactions between metallated ylides and carbonyl compounds
may be even more complex.
1
2
MHz, C6D6): d 1.3 (d. JCP 47.5 Hz, CH2), 126.4 (d, JCP 13 Hz, 6A-C,
4
3
C6H4), 130.9 (d, JCP 4.0 Hz, 4A-C, C6H4), 131.5 (d, JCP 18.1 Hz, 5A-C,
1
3
C6H4), 136.1 (d, JCP 105.7 Hz, 1A-C, C6H4), 139.4 (d, JCP 21 Hz, 3A-C,
C6H4), 176.0 (d, 2JCP 45 Hz, 2A-C, C6H4). 29Si NMR: d 26.0 31P NMR: d
34.2. All compounds gave satisfactorily elemental analyses.
‡ Crystallography: All data collected using Mo-Ka radiation, refinements
by least-squares methods (full matrix) based on Fo2 values (SHELXL-93).
5b: monoclinic, P21/n, a = 16.065(12), b = 12.239(7), c = 17.191(11) Å,
b = 109.81(5)°, U = 3180(4) Å3, Z = 4, 3.0 < 2q < 50.0°, 4568
reflections, 281 parameters, R1
= 0.0357 (only observed reflections),
wR2 = 0.0604. 6: monoclinic, P21/n, a = 12.352(14), b = 15.94(16),
c = 14.999(16) Å, b = 114.37(8)°, U = 2690(5) Å3, Z = 2, 3.62 < 2q <
50.00°, 4290 reflections, 342 parameters, R1 = 0.041 (only observed
The structure of 7 is shown in Fig. 1. The five-membered
heterocycle including a tetrahedrally distorted coordinated,
chiral zinc centre (racemic mixture in the crystal) adopts an
¯
reflections), wR2 = 0.1071. 7: triclinic, P1, a = 10.139(6), b = 14.245(8),
c
= 24.464(13) Å, a = 95.67(4), b = 99.39(4), g = 96.09(4)°;
U = 3442(3) Å3, Z = 4, 4.1 < 2q < 47.00°, 10037 reflections, 719
parameters, R1 = 0.039 (only observed reflections) wR2 = 0.0961. CCDC
182/677.
C(18)
C(19)
C(21)
1 M. Steiner, H. Pritzkow and H. Gru¨tmacher, Chem. Ber., 1994, 127,
1177; reviews on metallated phosphorus ylides: H. Schmidbaur, Angew.
Chem., 1983, 95, 980; Angew. Chem., Int. Ed. Engl., 1983, 22, 907;
W. C. Kaska, Coord. Chem. Rev., 1983, 48, 1.
C(22)
C(6)
C(17)
C(15)
C(7)
C(5)
C(20)
C(16)
2 K. A. Hughes, P. G. Dopico, M. Sabat and M. G. Finn, Angew. Chem.,
1993, 105, 603; Angew. Chem., Int. Ed. Engl., 1993, 32, 554.
3 J.-M. Sotiropoulos, A. Bacereido and G. Bertrand, J. Am. Chem. Soc.,
1987, 109, 4711.
4 For a review on cyclometallations, see: G. R. Newkome, W. E. Pukett,
V. K. Gupta and G. E. Kieffer, Chem. Rev., 1986, 86, 451.
5 Zn–N (av.) 1.857 Å, Zn–C (av.) 1.952 Å: H. Gru¨tzmacher, M. Steiner,
H. Pritzkow, L. Zsolnai, G. Huttner and A. Sebald, Chem. Ber., 1992,
125, 2199 and references therein; M. M. Olmstead, P. P. Power and
S. C. Shoner, J. Am. Chem. Soc., 1991, 113, 3379.
C(2)
C(14)
C(8)
C(4)
C(3)
C(23)
N(1)
P
C(24)
C(1)
Zn
N(2)
C(9)
C(28)
C(13)
C(25)
Si(2)
6 D. R. Armstrong, M. G. Davidson and D. Moncrieff, Angew. Chem.,
1955, 107, 514; Angew. Chem., Int. Ed. Engl., 1995, 34, 478.
7 H. Schmidbaur, J. Jeong, A. Schier, W. Graf, D. L. Wilkinson, G. Mu¨ller
and C. Kru¨ger, New J. Chem., 1989, 13, 341.
C(10)
C(12)
Si(1)
C(11)
8 P. R. Markies, G. Schat, O. S. Akkerman and F. Bickelhaupt,
Organometallics, 1990, 9, 2243.
C(27)
C(29)
C(26)
9 E. J. Corey and J. Kang, J. Am. Chem. Soc., 1982, 104, 4724; E. J. Corey,
J. Kang and K. Kyler, Tetrahedron Lett., 1985, 26, 555; B. Schaub,
T. Jenny and M. Schlosser, Tetrahedron Lett., 1984, 25, 4097;
B. Schaub and M. Schlosser, Tetrahedron Lett., 1985, 26, 1623.
10 E. Vedejs and M. J. Peterson, Top. Stereochem., 1994, 21, 1.
Fig. 1 Molecular structure of 7: hydrogen atoms have been omitted for
clarity. Selected bond lengths (Å) and angles (°): Zn–N(1) 2.174(3), Zn–
N(2) 1.982(3), Zn–C(1) 2.137(4), Zn–C(3) 2.050(3), P–C(1) 1.733(4),
P–C(2) 1.803(3), C(2)–C(3) 1.409(4); N(1)–Zn–N(2) 103.4(1), N(1)–Zn–
C(1) 101.5(1), N(1)–Zn–C(3) 102.2(1), N(2)–Zn–C(1) 122.4(1), N(2)–Zn–
C(3) 130.1(1), C(1)–Zn–C(3) 92.9(1), Zn–C(3)–C(2) 113.3(2), C(3)–C(2)–
P 114.9(2), C(1)–P–C(2) 108.3(2), P–C(1)–Zn 100.8(2).
Received in Basel, Switzerland, 17th June 1997; 7/04248E
286
Chem. Commun., 1998
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