Stabilization of tetrafluorobutatriene by complex formation

Article abstract of DOI:10.1002/anie.200701081

Now tamed: For decades preparative research on 1,1,4,4- tetrafluorobutatriene was not pursued because of the explosive nature of the compound. Two new transition-metal complexes containing a tetrafluorobutatriene ligand (see picture; green F/Cl, gray C, red O, purple P, orange Ir/Rh) have been prepared from the free triene, and both complexes are air-stable. (Figure Presented)

Full text of DOI:10.1002/anie.200701081

Communications
DOI: 10.1002/anie.200701081
Cumulene Complexes
Stabilization of Tetrafluorobutatriene by Complex Formation**
Floris A. Akkerman and Dieter Lentz*
Dedicated to Professor Neil Bartlett on the occasion of his 75th birthday
1,1,4,4-Tetrafluorobutatriene (1) was first synthesized by
of a sec-perfluorobutyl ligand using 6 equiv of sodium
naphthalide (Scheme 2). Like other iridium complexes of
reactive unsaturated compounds, 4 is reported to be relatively
stable.
Martin and Sharkey in 1959 and was characterized by IR
[1]
and 19F NMRspectroscopy. Later, Raman and PE spectro-
scopic data were added.[2] The compound is very unstable: it
polymerizes even at À858C and is reported to explode
violently on warming to À58C or contact with air. These
properties precluded further investigations, limiting the
known chemistry of 1 to a few derivatives, which were also
prepared by Martin and Sharkey by addition of bromine and
chlorine and by oxidation.[1]
After development of a more efficient synthesis of 1,1,4,4-
tetrafluorobutatriene, we were able to determine its crystal
structure and charge density by high-resolution X-ray dif-
fraction.[3] Handling the triene is quite challenging. Once
prepared, it can be transferred only by condensation at
reduced pressure and must be stored at À1968C. These
precautions have so far prevented explosions as well as
polymerization of the substance. Since compound 1 decom-
poses even in absolute solvents within a few hours, further
reactions or characterization involving solutions must be
conducted immediately after its preparation.
Scheme 2. Synthesis of [IrCp*(PMe3)(C4F4)] (Hughes et al.[4]).
Single crystals suitable for X-ray analysis of 2 and 3 were
prepared by crystallization from dichloromethane
(Figure 1).[6] Both compounds crystallize as dichloromethane
The reaction of Vaskaꢀs complex ([Ir(CO)(PPh3)2Cl])[5] in
anhydrous toluene with 3–5 equiv of 1 yielded 2, the first
transition-metal complex prepared directly from the free
cumulene. The rhodium analogue also reacted with 1, yielding
the 2,3-h2-triene complex 3 (Scheme 1).
Figure 1. Molecular structure of 3·2CH2Cl2.[6] Solvent molecules and
hydrogen atoms omitted for clarity, selected bond lengths [Š]: Rh1-Cl1
2.491(10), Rh1-P1/P2 2.361(5)/2.373(6), Rh1-C1O 1.911(8).
Scheme 1. Syntheses of tetrafluorobutatriene complexes 2 and 3.
In 1994 Hughes et al. reported the preparation of [IrCp*-
(PMe3)(C4F4)] (4; Cp* = C5Me5), the first coordination com-
pound of 1.[4] The cumulene ligand in this complex was
prepared in the coordination sphere of iridium by reduction
solvates containing one (2) or two (3) solvent molecules. The
chloroform solvate of the iridium compound 2 contains three
solvent molecules, one of which is strongly disordered. The
molecular structures of the complexes are very similar. Both
of them possess a distorted trigonal-bipyramidal coordination
sphere, with the triphenylphosphine ligands occupying the
axial positions. Coordination to the metal centers greatly
elongates the central double bond of the triene ligand. The C-
C-C bond angles are markedly smaller than 1808 (Figure 2,
Table 1). The terminal double bonds are strikingly short
compared to those in 1. The bonds between the carbon atoms
(C3B) bound trans to the chloro ligand and the metal are
[*] Dipl.-Chem. F. A. Akkerman, Prof. Dr. D. Lentz
Institut für Chemie und Biochemie
Anorganische und Analytische Chemie
Freie Universität Berlin
Fabeckstrasse 34/36, 14195 Berlin (Germany)
Fax: (+49)30-838-52-424
E-mail: lentz@chemie.fu-berlin.de
[**] This work was supported by Deutsche Forschungsgemeinschaft. We
are grateful to Solvay Fluor und Derivate for the donation of starting
materials.
4902
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Angew. Chem. Int. Ed. 2007, 46, 4902 –4904

Angewandte
Chemie
explained by a large coupling constant between the phospho-
rus atoms in trans coordination. It has been observed in many
trans bisphosphine complexes.[8] The 19F NMRspectra show
large coupling constants between F1 and F3 (32 Hz in 2, 34 Hz
in 3), which can be explained only by through-space
coupling.[9] In 4, such a coupling is also observed.[4] The
19F NMRspectrum of 2 in [D8]toluene does not change
significantly in the temperature range À60 to + 1208C. This
leads to the conclusion that there is no propeller rotation of
the triene ligand at these temperatures. Compounds 2 and 3
are stable against air and water in solution and in crystalline
form.
Experimental Section
2: Vaskaꢀs complex ([Ir(CO)(PPh3)2Cl]; 83 mg, 0.107 mmol) was put
into a dried Schlenk flask equipped with a magnetic stirrer bar.
Anhydrous toluene (8 mL) and triene 1 (0.5 mmol) were condensed
into the evacuated flask cooled with liquid nitrogen. On warming to
room temperature, the yellow starting material dissolved completely,
and within 10 min the color of the solution had changed from yellow
to almost colorless. Stirring was continued at room temperature for an
additional 4 h. The solution darkened slightly during this time, and a
colorless precipitate formed. The solvent was removed in high
vacuum, and the residue was dissolved in dichloromethane together
with the precipitate. The resulting solution was filtered using a 5-mm
syringe filter, and the threefold volume of hexane was added. Slow
cooling to À358C yielded colorless needles and plates of [Ir(CO)-
(C4F4)(PPh3)2Cl]·CH2Cl2 after seven days; solvent evaporated from
the crystals under high vacuum and 70 mg of the dried substance was
obtained (0.077 mmol, 72%).
Figure 2. Structure of the butatriene ligand in 2 and 3. Other ligands
and solvent molecules omitted; bond lengths and angles in Table 1.
Table 1: Bond lengths [Š] and angles [8] in the butatriene ligands of
2·CH2Cl2, 3·2CH2Cl2,[6] and 4,[4] and in 1.[3]
Distance
2[6]
3[6]
4[4]
1[3]
C1B-C2B
C3B-C4B
C2B-C3B
C1B-F1
C4B-F3
C1B-F2
C4B-F4
C2B-M[a]
C3B-M[a]
F1-F3
1.275(12)
1.297(12)
1.412(12)
1.352(10)
1.336(10)
1.323(11)
1.329(11)
2.112(9)
2.072(8)
3.199(5)
1.298(9)
1.287(9)
1.390(9)
1.358(8)
1.353(7)
1.326(9)
1.324(8)
2.072(7)
2.034(8)
3.246(10)
1.279(4)
1.283(4)
1.418(5)
1.352(4)
1.346(3)
1.348(4)
1.343(4)
2.039(3)
2.042(3)
3.356(3)
1.3162(3)
1.3162(3)[b]
1.2679(5)
1.3198(3)
1.3198(3)[b]
1.3222(3)
1.3222(3)[b]
–
Elemental analysis: (IrP2F4OC41H30) C 54.95 (calcd 54.46), H 3.01
(calcd 3.34); m.p. 239–2418C (decomp.); 1H NMR(399.65 MHz,
218C, [D2]dichloromethane, TMS): d = 7.67–7.62 (m, 12H; meta-
PPh3), 7.49–7.39 ppm (m, 18H; ortho/para-PPh3); 13C{1H,19F} NMR
(100.40 MHz, 208C, [D2]dichloromethane, TMS): d = 176.30 (t, 2J-
–
–
[3]
Angle
2[6]
3[6]
4[4]
C4F4
C1B,2B,3B
C2B,3B,4B
F1,C1B,F2
F3,C4B,F4
139.0(9)
142.0(9)
106.6(8)
108.2(8)
137.5(6)
145.4(5)
107.7(6)
108.3(5)
142.3(3)
140.4(3)
106.9(3)
106.6(3)
122.3(1)[b]
122.3(1)[b]
109.7(1)
=
(C,P) = 9.1 Hz; CO), 148.50 (s; 2 CF2), 134.69 (ortho-PPh3), 131.83
= = =
(para-PPh3), 129.09 (ipso-PPh3), 128.43 (meta-PPh3), 66.66 ( C C ),
19F NMR(376.00 MHz,
20
8C,
= = =
59.06 ppm
( C C );
109.7(1)[b]
[D2]dichloromethane, CFCl3): d = À68.03 (d[a]
,
2J(gem-F,F) =
[a]
2
=
=
65.2 Hz, 1F; CF2), À81.48 (d , J(gem-F,F) = 74.1 Hz, 1F; CF2),
[a] M=Ir (2, 4), M=Rh (3); in 2 and 3 C1B and C2B are cis relative to the
chloro ligand, C3B and C4B are cis relative to the carbonyl ligand, the
environment of the triene ligand in 4 is symmetric. [b] Generated by
symmetry operations.
À91.21 (ddtd, 2J(gem-F,F) = 65.2 Hz, 5J(F,F[b]) = 32.1 Hz, 4J(F,P) =
4.0 Hz, 5J(F,F) = 3.5 Hz, 1F; CF2), À96.90 ppm (dddt, 2J(gem-F-
=
F) = 74.1 Hz, 5J(F,F[b]) = 32.1 Hz, 5J(F,F) = 7.0 Hz, 4J(F,P) = 2.1 Hz,
1F; CF2); 31P{1H} NMR(161.70 MHz, 21 8C, [D2]dichloromethanÀe1,
=
ꢀ
70% H3PO4): d = 0.49 (m; PPh3); IR(CHCl ): n˜ = (C O) 2018 cm
3
(s); IR(CH 2Cl2): n˜(C O) 2015 cmÀ1 (s); IR(KBr): n˜ = 3057 (w), 2012
ꢀ
about 0.04 Š shorter than those trans to the carbonyl ligand
(C2B).
(vs), 1960 (w), 1870 (vw), 1820 (s), 1700 (vs), 1588 (vw), 1573 (w), 1482
(m), 1435 (s), 1383 (w), 1332 (vw), 1315 (w), 1289 (vw), 1265 (vw),
1237 (m), 1204 (m), 1189 (m), 1159 (w), 1096 (s), 1074 (w), 1028 (w),
999 (w), 974 (m), 849 (vw), 815 (m), 743 (m), 723 (w), 710 (m), 694 (s),
618 (vw), 605 (vw), 581 (w), 559 (vw), 536 (w), 520 (vs), 506 (m), 456
(vw), 424 cmÀ1 (vw); Raman (crystals): 3172 (w), 3146 (w), 3060 (vs),
3006 (w), 2957 (w), 2006 (s), 1821 (m), 1586 (m), 1573 (w), 1482 (vw),
1436 (w), 1188 (w), 1159 (w), 1097 (m), 1074 (w), 1028 (m), 1000 (vs),
722 (vw), 710 (w), 688 (w), 616 (m), 604 (w), 558 (w), 537 (m), 517 (w),
472 (w), 455 (vw), 435 (vw), 424 (vw), 382 (vw), 304 (w), 276 (s), 258
(m), 230 (m), 203 (m), 161 cmÀ1 (s); MS (70 eV): m/z (%) = 904 (0.1)
[M+], 876 (10) [M+ÀCO], 780 (2) [M+ÀC4F4], 752 (4) [MÀCO,
ÀC4F4], 716 (2) [Ir(PPh3)2+], 637 (3), 387 (6), 365 (4), 336 (2), 262
(100), [PPh3+], 183 (33) [PPh2+], 108 (13) [PPh+].
The trans effects of these two equatorial ligands on the
triene ligand can also be seen in the 19F and 13C NMRspectra.
The two groups of NMRsignals could not be assigned to one
particular half of the triene ligand as the chemical shifts could
not be predicted quantitatively. The fluorine atoms could be
assigned to the corresponding carbon atoms using two-
dimensional NMRspectroscopy. All atoms of the triene
ligands in 2 and 3 are chemically inequivalent. In 2, the two
13C NMRsignals of the terminal CF groups share the same
2
chemical shift. In 3, the corresponding signals are only d =
0.21 ppm apart. The 13C NMRsignals of the phenyl rings
exhibit pseudo-triplet splitting due to coupling with the
phosphorus atom bound to those rings. This effect can be
3: In a similar procedure as for 2, [Rh(PPh3)2(CO)Cl] (60 mg,
0.085 mmol) was reacted with 1 (0.26 mmol, volumetric). Crystals of 3
(25 mg, 0.032 mmol; 38% yield) were obtained by recrystallization
Angew. Chem. Int. Ed. 2007, 46, 4902 –4904
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www.angewandte.org 4903

Communications
from dichloromethane/hexane 1:2 (yellow needles of 3·2CH2Cl2) and
evaporation of the solvent in high vacuum.
[2] a) F. A. Miller, W. F. Elbert, W. Pingitore, J. Mol. Struct. 1977, 40,
25; b) H. Basch, G. Bieri, E. Heilbronner, T. B. Jones, Helv. Chim.
Acta 1978, 61, 46.
[3] A. Bach, D. Lentz, P. Luger, M. Messerschmidt, C. Olesch, M.
Patzschke, Angew. Chem. 2002, 114, 311; Angew. Chem. Int. Ed.
2002, 41, 296.
Elemental analysis: (RhP2F4OC41H30) C 59.41 (calcd 60.42), H
3.48 (calcd 3.71); m.p. 218–2208C (decomp.); 1H NMR(399.65 MHz,
218C, [D2]dichloromethane, TMS): d = 7.67–7.62 (m, 12H; meta-
PPh3), 7.49–7.39 ppm (m, 18H; ortho/para-PPh3); 13C{1H, 19F} NMR
(100.40 MHz, 248C, [D2]dichlormethane, TMS): d = 190.87 (m; CO),
[4] R. P. Hughes, R. B. Laritchev, L. N. Zakharov, A. L. Rheingold, J.
Am. Chem. Soc. 2004, 126, 2308.
=
=
150.13 (s; CF2), 149.98 (s, CF2) 134.68 (ortho-PPh3), 131.27 (para-
= = =
PPh3), 130.46 (ipso-PPh3), 128.44 (meta-PPh3) 86.26 (m; C C ),
[5] J. P. Collman, J. W. Kang, J. Am. Chem. Soc. 1967, 89, 844.
[6] Crystal structure determination: (SMART-CCD, Bruker):
2·CH2Cl2: structure solution: SHELXS-97,[7] direct methods, and
least-squares refinement (SHELXL-97[7]), monoclinic, P21/n, a =
12.092(3), b = 23.019(5), c = 13.640(3) Š, b = 90.031(6)8, V=
72.45 ppm
(m;
C C );
19F NMR(376.00 MHz,
20
8C,
= = =
[D2]dichloromethane, CFCl3): d = À66.14 (d[a]
,
2J(gem-F,F) =
65.5 Hz, 1F; CF2), À79.87 (dd[a], J(gem-F,F) = 76.2 Hz, J(F,Rh) =
2
3
=
[a]
=
=
8.5 Hz, 1F; CF2), À90.61 (dd
,
2J(gem-F,F) = 65.5 Hz, 5J(F,F[b]) =
[a]
34.3 Hz, 1F; CF2), À95.93 ppm (dd
,
2J(gem-F-F) = 76.2 Hz, 5J-
3796.5(16) Š3, Z = 4, 1calcd = 1.731 gcmÀ1
, T= 173 K, 30098
(F,F[b]) = 34.3 Hz, 1F; CF2); 31P{1H} NMR(161.70 MHz, 26 8C, [D2]-
observed, 6885 independent (Rint = 0.0956) and 4706 reflections
with I > 2s(I), MoKa, l = 0.71073 Š, 2qmax = 50.108, R1 = 0.0454,
wR2 = 0.1161, 478 parameters, anisotropic thermal parameters, H
atoms isotropic. 2·3CHCl3: structure solution: SHELXS-97,[7]
direct methods, and least-squares refinement (SHELXL-97[7]),
monoclinic, P21/c, a = 14.577(5), b = 12.233(5), c = 27.982(5) Š,
b = 101.746(5)8, V= 4885(3) Š3, Z = 4, 1calcd = 1.712 gcmÀ1, T=
173 K, 39494 observed, 8632 independent (Rint = 0.1012) and
=
dichloromethane, 70% H3PO4):d = À30.91 (d[a], J(P-Rh) = 86.5 Hz;
1
À1
ꢀ
PPh3); IR(CH 2Cl2): n˜ = (C O) 2044 cm (s); IR(KBr): n˜ = 3143
(vw), 3089 (vw), 3058 (w), 3024 (vw), 3005 (vw), 2989 (vw), 2960 (vw),
2045 (vs), 2006 (m), 2000 (m), 1984 (m), 1909 (vw), 1887 (vw), 1778
(vw), 1854 (m), 1843 (s), 1745 (vw), 1703 (vs), 1587 (w), 1574 (w), 1541
(vw), 1483 (m), 1436 (s), 1398 (vw), 1385 (vw), 1332 (w), 1314 (w),
1289 (vw), 1261 (m), 1248 (s), 1208 (s), 1191 (m), 1178 (m), 1157 (m),
1093 (s), 1090 (s), 1071 (m), 1028 (m), 999 (w), 960 (s), 168 (vw), 852
(vw), 790 (m), 755 (m), 746 (m), 739 (m), 619 (w), 604 (w), 569 (m),
519 (vs), 506 (s), 475 (m), 451 (w), 439 (w), 429 (w), 419 cmÀ1 (w);
Raman (crystals): 3173 (vw), 3143 (vw), 3089 (w), 3061 (m), 3005
(vw), 2990 (vw), 2959 (vw), 2906 (vw), 2047 (w), 2005 (vw), 1842 (vw),
1586 (m), 1573 (w), 1437 (w), 1190 (m), 1072 (vw), 1029 (m), 1001 (vs),
751 (vw), 707 (w), 686 (w), 617 (w), 604 (w), 533 (m), 527 (m), 518 (w),
510 (w), 473 (vw), 449 (m), 441 (m), 428 (w), 416 (w), 406 (w), 384
(vw), 324 (w), 283 (w), 263 (s), 224 (m), 194 (m), 173 (m), 153 cmÀ1
(vs); MS (70 eV): m/z (%) = 786 (0.2) [M+ÀCO], 663 (1)
5333 reflections with I > 2s(I), MoKa, l = 0.71073 Š, 2qmax
=
50.088, R1 = 0.0519, wR2 = 0.1526, 556 parameters, anisotropic
thermal parameters, H atoms isotropic. 3·2CH2Cl2: structure
solution: SHELXS-97,[7] direct methods, and least-squares refine-
ment (SHELXL-97[7]), triclinic, P1, a = 10.47(4), b = 13.78(3), c =
¯
16.20(4) Š, a = 72.91(9)8, b = 73.41(14), g = 74.1(2)8, V=
2095(10) Š3, Z = 2, 1calcd = 1.561 gcmÀ1
,
T= 173 K, 18835
observed, 8431 independent (Rint = 0.0747) and 5242 reflections
with I > 2s(I), MoKa, l = 0.71073 Š, 2qmax = 52.86 8, R1 = 0.0609,
wR2 = 0.1586, 505 parameters, anisotropic thermal parameters, H-
atoms isotropic. CCDC-637685 (2·CH2Cl2), CCDC-637686
(2·3CHCl3), and CCDC-637687 (3·2CH2Cl2) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[M+ÀCOÀC4F4], 626 (0.1) [Rh(PPh3)2 ÀH], 400 (0.1) [Rh-
+
(PPh3)Cl+], 364 (0.1) [Rh(PPh3)+], 262 (100) [PPh3+], 183 (37)
[PPh2 À2H] 108 (7) [PPh+].
+
[a]: More couplings were evident but could not be assigned
unambiguously. [b]: Through-space coupling.
[7] SHELX-97 (Release 97 – 2): G. M. Sheldrick, Universität Göttin-
gen, Germany, 1998.
Received: March 12, 2007
[8] J. P. Fackler, J. A. Fetchin, J. Mayhew, W. C. Seidel, T. J. Swift, M.
Weeks, J. Am. Chem. Soc. 1969, 91, 1941.
Published online: May 18, 2007
[9] I. E. Kareev, G. Santiso Quiꢁones, I. V. Kuvychko, P. A. Khavrel,
I. N. Ioffe, I. V. Goldt, S. F. Lebedkin, K. Seppelt, S. H. Strauss,
O. V. Boltalina, J. Am. Chem. Soc. 2005, 127, 11497.
Keywords: p complexes · carbonyl complexes · cumulenes ·
fluorine · transition metals
.
[1] E. L. Martin, W. H. Sharkey, J. Am. Chem. Soc. 1959, 81, 5256.
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Angew. Chem. Int. Ed. 2007, 46, 4902 –4904