Fluorinated heterobutadienes/trimethylphosphine: A reactivity study

Article abstract of DOI:10.1080/10426500212312

The reactions of fluorinated heterobutadienes F₂C=X-C(R)=Y (X = N, CH; Y = O, N-Mes; R = Ph, t-Bu), A-D, with the PMe₃ were studied. In any case, a different reaction pathway was observed, depending on the specific nature of A-D. The

Full text of DOI:10.1080/10426500212312

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Phosphorus, Sulfur, and Silicon and the Related
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Fluorinated Heterobutadienes/Trimethylphosphine: A
Reactivity Study
Hans H. Karsch a & Andreas W. Leithe a
a Anorganisch-chemisches Institut , Technische Universität München , Lichtenbergstraße 4,
Garching, D-85747, Germany
Published online: 27 Oct 2010.
To cite this article: Hans H. Karsch & Andreas W. Leithe (2002) Fluorinated Heterobutadienes/Trimethylphosphine: A
Reactivity Study, Phosphorus, Sulfur, and Silicon and the Related Elements, 177:6-7, 1907-1911, DOI: 10.1080/10426500212312
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:1907–1911
C
Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
DOI: 10.1080/10426500290093838
FLUORINATED
HETEROBUTADIENES/TRIMETHYLPHOSPHINE:
A REACTIVITY STUDY
Hans H. Karsch and Andreas W. Leithe
Anorganisch-chemisches Institut, Technische Universita¨t
Mu¨nchen, Lichtenbergstraße 4, D-85747 Garching, Germany
(Received July 29, 2001; accepted December 25, 2001)
The reactions of fluorinated heterobutadienes F2C X C(R) Y (X = N,
CH; Y = O, N-Mes; R = Ph, t-Bu), A–D, with the PMe3 were stud-
ied. In any case, a different reaction pathway was observed, depend-
ing on the specific nature of A–D. These reactions lead to some novel
organophosphorus species, including P-ylides and 5-azaphosphinines.
5-phospholenes, as observed with phosphites, for example, were not
observed, but with phosphinidine (P Ph), the heterobutadienes B and
C form 3-oxazaphospholenes. Therein the complex (Me3P)3Ni[cyclo-
P(Ph)OC(Ph)NC(CF3)2] was obtained and structurally characterized.
Keywords: Fluororganics; heterobutadienes; phosphines; phos-
phinidenes; phospholenes; ylides
INTRODUCTION
Fluorinated heterobutadienes are valuable synthons in organic synthe-
sis, in particular for pharmaceuticals, due to their high electrophilicity.
To further exploit their synthetic potential, the heterobutadienes A–D
(Figure 1) were introduced into organometallic systems with the aim of
an “umpolung” of the heterobutadiene skeleton. Indeed, various metal
complexes could be obtained with A–D as ligands (Ni, Ti, Zr, Fe, Rh1). In
some cases, trimethylphosphine complexes of these metals were used.
Since reactions of phosphites and phosphines with the heterobuta-
dienes were known,2 it was not surprising that reaction products with
PMe3 were observed in these cases. These reactions apparently took
a different course as in the known cases, however. In particular, no
Address correspondence to H. H. Karsch, Anorganisch-chemisches Institut, Technis-
che Universita¨t Mu¨nchen, Lichtenbergstraße 4, D-85747 Garching, Germany. E-mail:
Hans.H.Karsch@lrz.tum.de
1907

1908
H. H. Karsch and A. W. Leithe
FIGURE 1
5-phospholenes were formed. We therefore investigated systematically
the reactions of compounds A–D with PMe3 and, in addition, with in
situ generated phosphinidene P Ph.
RESULTS
Every individual heterobutadiene A–D reacted in an individual man-
ner, and thus four different types of products were obtained, as depicted
in Scheme 1. The vinyl ketone A most likely is attacked at the central
1
C2 atom, yielding crystalline, orange 1A [ P{ H} = 5.94 s; F = 13.47 d
(9.9 Hz); H: CH(CF3)2 = 4.64 dsept (9.9/28.6 Hz)]. The other three
reactions of PMe3 with heterobutadienes B–D, proceed via a common
initial step, i.e., the phosphine attacks the heterobutadiene at the CF3-
substituted carbon atom. In the case of B and C, the respective inter-
1
mediates can be identified by NMR spectroscopy: B: P{ H} = 2.06 s;
1
1
F = 11.61 s; C{ H}: C(CF3)2 = 74.1 dsept (52.0/26.1 Hz); C: P{ H} =
1
21.30 s; F = 11.87 s; C{ H}: PMe3 = 18.5 d (91.4 Hz), C(CH3)3 =
27.6 s, C(CH3)3 = 65.8 Hz, C(CF3)3 = 72.60 dsept (56.6/26.5 Hz), CF3 =
124.20 dqq (7/3/287 Hz), CO = 181.6 d (9.5 Hz). Most likely via a cyclic
intermedite or transition state (i.e., a phosphorane), Me3PO is elimi-
nated in the cases of B and C, and the residual nitril ylide adds an-
1
other molecule of PMe3 to give red crystals of 2B [ P{ H} = 8.41 s, br;
1
F = 19.50 dq (3.4/8.1 Hz), 22.29 dq (2.1/8.1 Hz); C{ H}: C(CF3)2 =
131.66 qq (1.2/3.3 Hz)] in the respective case. In the case of C, an
1
analogous species 2C [ P{ H} = 12.9 s,br] can be identified spectro-
scopically as an intermediate, but above 0 C reacts further under a
double HF elimination and cyclization to yield a yellow solid of the 1,3-
1
5-azaphosphinine 3C [ P{ H} = 5.58 dq (48.8/1.5 Hz); F: CF3
=
12.49 dd (19.8/1.5 Hz), CF = 109.9 ddq (9.1/48.8/19.8 Hz); H:
1
CH = 4.08 dd (14.3/9.1 Hz); C{ H}: CH = 65.10 dd (7.2/96.0 Hz),
C-tBu = 179.39 d (39.0 Hz), CF = 123.63 dd (2JCP = 125.7/1JCF
=
258.4 Hz)]. Besides the signals of 3C, the signals of Me3PO and F2PMe3
1
[ P{ H} = 15.60 t (543 Hz); F = 72.12 ddec (543/12.2 Hz)] are

Fluorinated Heterobutadienes/Trimethylphosphine
1909
SCHEME 1 Reactions of Heterobutadienes A–D with PMe3.
detected in the toluene extract from the solid obtained, whereas
the pentane extract is essentially free of these impurities. An acid-
1
base adduct of PMe3 with HF was tentatively assigned [ P{ H} =
1.20] but is obviously too volatile to survive the work-up and/or re-
acts further to F2PMe3. In contrast to 2C, which with excess PMe3

1910
H. H. Karsch and A. W. Leithe
obviously acting as a base, gives 3C spontaneously, 2B gives the cor-
responding 3B only in traces under the same conditions. On heat-
ing a solution of 2B with excess PMe3 (toluene/80 C) or by ad-
dition of a more powerful base than PMe3 (i.e., DABCO or pyri-
1
dine in THF), 3B may be isolated as a yellow solid [ P{ H} =
4.75 d (51.9 Hz); F: CF3 = 12.74 d (20.1 Hz), CF = 106.7 ddq
(20.1/51.9/9.1 Hz); H: PMe2 = 0.76 d (13.5 Hz), CH = 4.49 dd
(13.5/9.1 Hz)].
In the case of the 1,3-Diaza-1,3-butadiene D, the assumed cyclic phos-
phorane intermediate obviously undergoes a rapid degradation reac-
tion, where the PMe3 removes two fluorines from a CF3 group under
formation of F2PMe3. The remaining imidazole ring 4D [ F: CF3
=
16.64 d (12.2 Hz), CF = 63.54 q (12.2 Hz)] is known and was also ob-
tained on thermal decomposition of the cyclic reactions products from
D with SnCl2, with GeCl2 or with SiCl2.3
Unlike phosphines, in situ generated phosphinidene P Ph (from B or
C and Li2PPh via LiF abstraction) reacts with B and C under formation
1
of cyclic phospholenes 5B [ P{ H} = 111.4 qq (27/2 Hz); F = 6.74 dq
1
(2/9.5 Hz) and 14.40 dq (27/9.5 Hz)] and 5C [ P{ H} = 110.1 q (29 Hz);
F = 5.93 dq (29/9.5 Hz) and 13.90 q (9.5 Hz); C: C(CF3)2 = 88.6 dsept
(48/24 Hz)] (Scheme 2).
SCHEME 2
1
Red crystals of the oxazaphospholene nickel complex 6B [ P{ H}:
PMe3 = 19.40 dq (43.1/5.0 Hz), PPh = 125.79 qq (43.1/19 Hz); F =
10.27 dqq (19/5.0/10 Hz) and 15.68 q (10 Hz)] are isolated from the
reaction of 5B with (Me3P)2Ni(COD). An X-ray structure determina-
tion of the crystals (P21/C; a = 31.552(6), b = 11.754(2), c = 27.345(6)
˚
A; Z 12) confirmed the presence of the phospholene ring as a ligand to a
tetrahedrally coordinated nickel(0) centre with three additional PMe3
ligands (Figure 2). The structural parameters of the 12 molecules in the
unit cell differ to some extent, however, and large standard deviations
result in some uncertainty for the mean values for distances and angles
(Table I).

Fluorinated Heterobutadienes/Trimethylphosphine
1911
˚
TABLE I Some Mean Distances [A] and Angles [ ] of 6B
P(1) O(1):
O(1) C(1):
C(1) N(1):
N(1) C(2):
C(2) P(1):
Ni(1) P(1):
Ni(1) P(2,3,4):
1.72(3)
1.38(8)
1.28(2)
1.45(2)
1.98(7)
2.04(2)
2.18(3)
P(1) O(1) C(1):
O(1) C(1) C(11):
N(1) C(1) C(11):
O(1) C(1) N(1):
C(1) N(1) C(2):
O(1) P(1) C(2):
C(2) P(1) C(5):
114(2)
115(2)
125(3)
120(3)
111(3)
85(1)
98(3)
P(1) C(2) N(1):
C(3) C(2) C(4):
P(1) C(2) C(3):
P(1) C(2) C(4):
N(1) C(2) C(3):
N(1) C(2) C(4):
106(2)
110(3)
115(2)
109(4)
109(2)
107(2)
O(1) P(1) C(5):
97(1)
134(2)
117(1)
115(1)
Ø 106.3
Ø 112.3
Ni(1) P(1) C(2):
Ni(1) P(1) C(5):
Ni(1) P(1) O(1):
P(2-4) Ni(1) P0(2-4):
P(2-4) Ni(1) P(1):
FIGURE 2 Molecular Structure of 6B.
REFERENCES
[1] H. H. Karsch, A. W. Leithe, M. Reisky, and E. Witt, Organometallics, 18, 90 (1999);
A. W. Leithe, Dissertation, TU Mu¨nchen (2000).
[2] K. Burger, S. Tremmel, G. Trost, R. Simmerl, and D. Hu¨bl, Z. Naturforsch., 38b, 76
(1983).
[3] K. Burger, K. Geith, and N. Sewald, J. Fluorine Chem., 46, 105 (1990); H. H. Karsch,
F. Bienlein, M. Heckel, O. Steigelmann, K. Burger, J. Cyremer, Z. Naturforsch., 50b,
289 (1995).