An unprecedented type of insertion of an alkyne into a metal - carbon bond

Article abstract of DOI:10.1021/om990851j

Treatment of the (allenylidene)iridium complex trans-[IrCl(=C=C=CPh₂)(PiPr₃)₂] (1) with KOH leads to trans-[Ir(OH)(=C=C=CPh₂)(PiPr₃)₂](2), which reacts with Br?nsted acids such as HF and ph

Full text of DOI:10.1021/om990851j

5
426
Organometallics 1999, 18, 5426-5428
An Un p r eced en ted Typ e of In ser tion of a n Alk yn e in to a
Meta l-Ca r bon Bon d
Kerstin Ilg and Helmut Werner*
Institut f u¨ r Anorganische Chemie der Universit a¨ t W u¨ rzburg, Am Hubland,
D-97074 W u¨ rzburg, Germany
Received October 22, 1999
Sch em e 1a
Summary: Treatment of the (allenylidene)iridium com-
plex trans-[IrCl(dCdCdCPh2)(PiPr3)2] (1) with KOH
leads to trans-[Ir(OH)(dCdCdCPh2)(PiPr3)2] (2), which
reacts with Brønsted acids such as HF and phenol to
give trans-[IrF(dCdCdCPh2)(PiPr3)2] (3) and trans-[Ir-
(OPh)(dCdCdCPh2)(PiPr3)2] (4). Moreover, an unusual
reaction of 2 with excess alkynes RCtCH (R ) Ph, CO2-
Me) takes place to afford trans-[Ir(CtCR)2{(E)-CHd
CRCHdCdCPh2}(PiPr3)2] (5, 6). Compounds 3 and 5
were characterized by X-ray structure analysis.
In a continuation of our studies to prepare highly
reactive rhodium-allenylidenes of the general composi-
1
tion trans-[Rh(X)(dCdCdCRR′)(PiPr3)2], we recently
reported that the hydroxo derivatives (X ) OH) react
with acetic acid and phenol at room temperature to give
a
3
L ) PiPr .
7
adduct NEt3‚3HF) and phenol to afford the substitution
products 3 and 4 in, respectively, 88% and 82% yields.8
the corresponding acetato (X ) MeCO2) and phenolato
,9
2
(
X ) OPh) metal compounds in excellent yield. More-
over, these square-planar (allenylidene)rhodium(I) com-
plexes undergo in the presence of CO a migratory
insertion of the CdCdCRR′ unit into the Rh-O bond
to generate γ-functionalized alkynyl ligands.2 Follow-
ing this work, we have now prepared the hydroxoirid-
ium(I) compound 2, which seems to be an even more
promising starting material than the rhodium counter-
part for carrying out substitution and insertion reac-
tions.
(
6) Selected spectroscopic data for 2-5, with the 1H and 13C NMR
data for the aryl groups omitted, are as follows (abbreviations: vt )
3
5
1
3
1
virtual triplet; N ) J (PH) + J (PH) or J (PC) + J (PC)). 2: H NMR
(400 MHz, C
dvt, N ) 13.5, J (HH) ) 7.3 Hz, 36 H, PCHCH
MHz, C
12.7 Hz, IrdCdCdC), 22.6 (vt, N ) 24.4 Hz, PCHCH
PCHCH
,3
6
D
6
) δ 4.25 (br s, 1 H, IrOH), 2.80 (m, 6 H, PCHCH
3
), 1.31
3
13
1
(
3
); C{ H} NMR (100.6
3
2
6
D
6
) δ 252.8 (t, J (PC) ) 3.1 Hz, IrdCdCdC), 202.7 (t, J (PC)
), 20.0 (s,
3
), resonance of IrdCdCdC not observed; P NMR (162.0
)
3
31
-1
MHz, C
6
D
6
) δ 23.5 (s); IR (C
6
H
6
) ν(OH) 3643, ν(CdCdC) 1857 cm . 3:
), 1.33 (dvt, N )
); C{ H} NMR (100.6 MHz,
) δ 273.9 (m, IrdCdCdC), 205.8 (m, IrdCdCdC), 127.3 (m, Ird
CdCdC), 23.1 (vt, N ) 25.4 Hz, PCHCH ), 20.1 (s, PCHCH ); 19F NMR
1
H NMR (400 MHz, C ) δ 2.81 (m, 6 H, PCHCH
6
D
6
3
3
13
1
1
3.5, J (HH) ) 7.0 Hz, 36 H, PCHCH
3
6 6
C D
4
Treatment of the chloro derivative 1 in acetone with
3
3
2
31
(
188.0 MHz, C
6 6
D ) δ -145.3 (t, J (PF) ) 20.0 Hz); P NMR (162.0
an excess of KOH results in a clean and nearly quan-
2
MHz, C ) δ 26.2 (d, J (PF) ) 20.3 Hz); IR (CH
6
D
6
2
Cl
2
) ν(CdCdC) 1872
), 1.25
3
dvt, N ) 13.2, J (HH) ) 7.0 Hz, 36 H, PCHCH ); C{ H} NMR (100.6
3
5
-1
1
titative formation of the hydroxo complex 2 (Scheme 1).
cm . 4: H NMR (400 MHz, C
6
D
6
) δ 2.60 (m, 6 H, PCHCH
3
3
13
1
(
The presence of the hydroxo ligand is indicated both by
2
MHz, C
6
D
6
) δ 255.7 (t, J (PC) ) 3.6 Hz, IrdCdCdC)], 203.6 (t, J (PC)
J (PC) ) 3.1 Hz, IrdCdCdC), 23.8
(vt, N ) 25.8 Hz, PCHCH ), 20.2 (s, PCHCH ); 31P NMR (162.0 MHz,
the strong absorption at 3643 cm-1 in the IR and by
4
) 13.7 Hz, IrdCdCdC), 131.8 (t,
1
the broadened singlet at δ 4.25 in the H NMR spec-
3
3
) ν(CdCdC) 1868 cm . 5: 1H NMR (400
-1
C
6
D
6
) δ 23.3 Hz (s); IR (C
MHz, C ) δ 9.36 (s, 1 H, HCdCdCPh
.27 (m, 6 H, PCHCH ), 1.32 (dvt, N ) 13.2, J (HH) ) 6.6 Hz, 18 H,
PCHCH ), 1.27 (dvt, N ) 13.2, J (HH) ) 7.0 Hz, 18 H, PCHCH
6 6
H
6
trum.
6
D
6
2
), 7.93 (br s, 1 H, IrCHdC),
3
3
3
Like the hydroxorhodium derivatives trans-[Rh(OH)-
3
13
1
3
3
); C-
6 6
H} NMR (100.6 MHz, C D ) δ 211.6 (s, CdCdC), 177.3 (t, J (PC) )
2
(
dCdCdCRR′)(PiPr3)2], compound 2 reacts with equimo-
1
3
{
3
lar amounts of Brønsted acids such as HF (used as the
4.0 Hz, IrCHdC), 119.3 (t, J (PC) ) 12.2 Hz, IrCtC), 115.3 (t, J (PC)
2
)
4.1 Hz, IrCtC), 111.4 (s, HCdCdC), 104.5 (t, J (PC) ) 8.1 Hz,
IrCHdC), 100.9 (s, CHdCdC), 24.6 (vt, N ) 26.4 Hz, PCHCH ), 20.4
) δ 13.0 (s); IR
) ν(CtC) 2076 and 2078 cm . 6: H NMR (400 MHz, C ) δ
9.40 (s, 1 H, HCdCdCPh ), 8.63 (br s, 1 H, IrCHdC), 3.41 (s, 6 H,
CO CH ), 3.33 (s, 3 H, CO CH ), 3.11 (m, 6 H, PCHCH ), 1.13 (dvt, N
) 14.0, J (HH) ) 7.0 Hz, 36 H, PCHCH ); C{ H} NMR (100.6 MHz,
) δ 211.4 (s, CdCdC), 162.8 and 154.5 (both s, CO CH ), 126.4 (t,
J (PC) ) 3.5 Hz, IrCtC), 123.5 (t, J (PC) ) 7.1 Hz, IrCHdC), 94.2 (s,
CHdCdC), 111.4 (s, HCdCdC), 51.4 and 51.3 (both s, CO CH ), 25.1
(vt, N ) 27.3 Hz, PCHCH ), 19.9 (s, PCHCH ), resonances of IrCHdC
and IrCtC not observed; P NMR (162.0 MHz, C ) δ 16.9 (s); IR
3
3
1
(
(
1) Werner, H. Chem. Commun. 1997, 903-910.
and 20.2 (both s, PCHCH
(C
3 6 6
); P NMR (162.0 MHz, C D
1 1
-
2) Werner, H.; Wiedemann, R.; Laubender, M.; Wolf, J .; Wind-
6
H
6
6 6
D
m u¨ ller, B. Chem. Commun. 1996, 1413-1414.
3) Laubender, M. Ph.D. Thesis, Universit a¨ t W u¨ rzburg, Germany,
998.
2
(
2
3
3
2
3
3
13
1
1
3
(
4) Werner, H.; Lass, R. W.; Gevert, O.; Wolf, J . Organometallics
C
6
D
6
2
3
3
2
1
997, 16, 4077-4088.
(5) The preparation of 2 is as follows. A solution of 1 (70 mg, 0.09
2
3
mmol) in 20 mL of acetone was treated with KOH (34 mg, 0.60 mmol),
and the mixture was stirred at room temperature for 2 h. The solvent
was removed in vacuo, the residue was suspended in 50 mL of pentane,
and the solution was filtered. The filtrate was concentrated to 3 mL
in vacuo and stored at -78 °C in order to complete crystallization.
The orange solid was separated from the mother liquor, washed with
small quantities of pentane, and dried: yield 54 mg (84%); mp 104 °C
3
3
3
1
6
D
6
) ν(CtC) 2084 cm- , ν(OCO)as 1686 cm , ν(OCO)
(7) (a) Triethylamine tris(hydrogen fluoride) is a new, versatile
fluorinating agent which has recently been used for the first time in
1
-1
1431 cm
-1
.
(C
6
H
6
s
7
b,c
the chemistry of late transition metals.
(b) Fraser, S. L.; Antipin,
M. Y.; Khroustalyov, V. N.; Grushin, V. V. J . Am. Chem. Soc. 1997,
119, 4769-4770. (c) Pilon, M. C.; Grushin, V. V. Organometallics 1998,
17, 1774-1781.
dec. Anal. Calcd for C33
H, 7.57.
2
H53IrOP : C, 55.05; H, 7.42. Found: C, 55.53;
1
0.1021/om990851j CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/02/1999

Communications
Organometallics, Vol. 18, No. 26, 1999 5427
Sch em e 2a
a
3
L ) PiPr .
violet or red and, after chromatographic workup and
recrystallization from pentane, gave 5 and 6 as crystal-
line, slightly air-sensitive solids in 85-90% yield.11 The
elemental analyses as well as the NMR spectra of both
complexes indicated that not only a substitution of the
OH for the CtCR unit but also the generation of a C5
ligand had taken place. This proposal was confirmed by
an X-ray crystal structure analysis of 5 (Figure 2).12 The
coordination sphere around the iridium center is square
pyramidal, with two trans-disposed alkynyls and two
trans-disposed phosphines in the basal plane and the
σ-bonded CHdCPhCHdCdCPh2 unit in the apical
position. In contrast to the reaction of trans-[RhCl(d
CdCdCPh )(PiPr ) ] with phenylacetylene, which af-
F igu r e 1. Molecular diagram of compound 3. Selected
bond lengths (Å) and angles (deg): Ir-F ) 2.015(10), Ir-
P1 ) 2.317(4), Ir-P2 ) 2.326(4), Ir-C1 ) 1.85(2), C1-C2
)
)
1.22(2), C2-C3 ) 1.37(2); F-Ir-P1 ) 88.5(3), F-Ir-P2
89.0(3), F-Ir-C1 ) 179.3(6), P1-Ir-P2 ) 177.51(16),
P1-Ir-C1 ) 91.0(5), P2-Ir-C1 ) 91.5(5), Ir-C1-C2 )
1
77.1(17), C1-C2-C3 ) 173(2).
Typical spectroscopic features of 3 and 4 (both are red,
only moderately air-sensitive solids) are their respective
low-field signals at δ 273.9 or 255.7 (â-C) and 205.8 or
2
3 2
fords via coupling of the allenylidene with the alkyne
and one phosphine a complex containing a highly
1
3
2
03.6 (R-C) in the C NMR as well as the single
13
unsaturated Wittig-type ylide as a π-bonded ligand,
3
1
6
resonance at δ 26.2 or 23.3 in the P NMR spectra.
upon treatment of 2 with HCtCPh presumably a
substitution (of OH by C2Ph), an oxidative addition (of
HCtCPh to iridium(I)), and an insertion of an alkyne
molecule into an iridium-allenyl linkage occurs. The
bond lengths Ir-C1, Ir-C40, and Ir-C50 differ only
slightly, while the distances C3-C4 and C4-C5 are
The X-ray crystal structure analysis of 3 (Figure 1)
reveals an almost perfect square-planar coordination
sphere around the iridium center with the two phos-
phines in a trans disposition.10 The C1-C2-C3 chain
is nearly linear, with the ipso-carbon atoms of the
phenyl rings lying in the same plane as Ir, P1, P2, F,
C1, C2, and C3.
Most remarkably, the hydroxo compound 2 is also
highly reactive toward phenylacetylene and methyl
propiolate (Scheme 2). Stirring a solution of 2 in benzene
with a 10-fold excess of the alkyne for 30 min at room
temperature led to a change of color from orange to
comparable to those of the substituted allenylrhodium
1
complex
(
trans-[Rh{η -C(CHdCH2)dCdCPh2}(CO)-
13
PiPr3)2]. With regard to the formation of 5 and 6, the
most noteworthy feature is that despite the strength of
4
the Ir-C double bond in 1 and the analogous com-
pounds 2-4, a coupling of the alkyne with the C3 unit
takes place under exceedingly mild conditions. It is
conceivable that the insertion reaction is preceded by
the generation of the iridium-hydride intermediate
[IrH(CtCR)2(dCdCdCPh2)(PiPr3)2], which rearranges
(8) The preparation of 3 is as follows. A solution of 2 (69 mg, 0.10
mmol) in 10 mL of benzene was treated with NEt ‚3HF (5.2 µL, 0.10
3
mmol). An instant change of color from orange to red occurred. The
solvent was removed in vacuo, the residue was extracted with 50 mL
of pentane, and the extract was brought to dryness in vacuo. The oily
residue was dissolved in 3 mL of acetone, and the solution was stored
at -78 °C. After 24 h red crystals precipitated, which were separated
from the mother liquor, washed twice with 1 mL of pentane, and
(11) The preparation of 5 is as follows. A solution of 2 (55 mg, 0.08
mmol) in 10 mL of benzene was treated with phenylacetylene (81 µL,
0.80 mmol), and the mixture was stirred at room temperature for 30
min. A change of color from orange to violet occurred. After concentra-
dried: yield 61 mg (88%); mp 89 °C dec. Anal. Calcd for C33
C, 54.90; H, 7.26. Found: C, 55.09; H, 7.11.
2
H53FIrP :
2 3
tion to 1 mL in vacuo, the solution was chromatographed on Al O
(
9) The preparation of 4 is as follows. A solution of 2 (57 mg, 0.08
(neutral, activity grade V, height of column 5 cm). With pentane a violet
phase was eluted and brought to dryness in vacuo. The oily residue
was recrystallized from pentane at -78 °C: yield 70 mg (87%); mp 53
mmol) in 10 mL of benzene was treated with phenol (7.5 mg, 0.08
mmol). An instant change of color from orange to red occurred. After
the mixture was stirred at room temperature for 5 min, the solvent
was removed in vacuo. The residue was extracted with 25 mL of
acetone, and the extract was concentrated to 2 mL in vacuo. The
solution was stored at -78 °C for 20 h, which led to the precipitation
of red crystals. They were separated from the mother liquor, washed
twice with small quantities of pentane (0 °C), and dried: yield 49 mg
2
°C dec. Anal. Calcd for C57H63IrP : C, 67.90; H, 6.90. Found: C, 68.01;
H, 7.04. Compound 6 was prepared analogously, using 2 (57 mg, 0.08
mmol) and methyl propiolate (50 µL, 0.80 mmol) as starting materi-
als: red microcrystalline solid; yield 71 mg (89%); mp 62 °C dec. Anal.
6 2
Calcd for C45H63IrO P : C, 56.65; H, 6.66. Found: C, 56.95; H, 6.51.
(12) Crystal data for 5: crystals from diethyl ether; crystal size
0.21 × 0.18 × 0.16 mm; triclinic, space group P 1h (No. 2), Z ) 2; a )
13.600(4) Å, b ) 13.634(4) Å, c ) 14.994(4) Å, R ) 83.29(2)°, â ) 66.63-
(
82%); mp 86 °C dec. Anal. Calcd for C39
Found: C, 58.63; H, 7.45.
2
H57IrOP : C, 58.84; H, 7.22.
3
-3
(
10) Crystal data for 3: crystals from acetone; crystal size 0.19 ×
.14 × 0.11 mm; monoclinic, space group P2 /n (No. 14), Z ) 4; a )
.6057(13) Å, b ) 34.735 (3) Å, c ) 10.8869(15) Å, â ) 95.737(15)°, V
(3)°, γ ) 87.23(2)°, V ) 2537.8(13) Å , dcalcd ) 1.319 g cm ; 2θ(max) )
44.92° (Mo KR, λ ) 0.710 73 Å, graphite monochromator, ω/θ scan, Zr
filter with factor 15.4, T ) 193(2) K; 6946 reflections scanned, 6598
unique, 5794 observed (I > 2σ(I)), Lorentz-polarization and empirical
absorption corrections (ψ scans, minimum transmission 84.03%); direct
methods (SHELXS-97), 598 parameters, reflex/parameter ratio 11.03;
R1 ) 0.0370, wR2 ) 0.0718; residual electron density +0.620/-1.097
0
8
)
0
1
1
3
-3
3237.7(7) Å , dcalcd ) 1.481 g cm ; 2θ(max) ) 46.50° (Mo KR, λ )
.710 73 Å, graphite monochromator, ω/θ scan, Zr filter with factor
5.4, T ) 173(2) K; 5131 reflections scanned, 4604 unique, 2743
observed (I > 2σ(I)), Lorentz-polarization and empirical absorption
-3
corrections (ψ scans, minimum transmission 90.00%); direct methods
e Å
.
(
0
SHELXS-97), 346 parameters, reflex/parameter ratio 13.31; R1 )
(13) Wiedemann, R.; Steinert, P.; Gevert, O.; Werner, H. J . Am.
Chem. Soc. 1996, 118, 2495-2496.
.0661, wR2 ) 0.1702; residual electron density +1.173/-1.682 e Å-
.
3

5
428 Organometallics, Vol. 18, No. 26, 1999
Communications
metals with a hydroxo ligand are thermodynamically
1
4
stable, the M-OH bond is nevertheless rather labile
and can be cleaved even by weak proton sources. In this
respect, our work complements recent studies by Mil-
1
5
16
stein and Bergman, which showed that both hy-
droxo- and alkoxo-iridium(III)snot iridium(I)scom-
pounds are useful starting materials for carrying out
substitution, elimination, and insertion reactions. We
are currently attempting to elucidate the exact mech-
anism of the formation of the novel Ir-C5 moiety and
to find a route to couple the C5 unit with one of the
alkynyl ligands.
Ack n ow led gm en t. We are grateful for financial
support of this work from the Deutsche Forschungsge-
meinschaft (SFB 347) and the Fonds der Chemischen
Industrie. We also thank Dr. J ustin Wolf for helpful
advice.
F igu r e 2. Molecular diagram of complex 5. Selected bond
lengths (Å) and angles (deg): Ir-C1 ) 1.998(6), Ir-C40 )
2
2
1
.020(6), Ir-C50 ) 2.018(6), Ir-P1 ) 2.359(2), Ir-P2 )
.371(2), C1-C2 ) 1.35(1), C2-C3 ) 1.46(1), C3-C4 )
.32(1), C4-C5 ) 1.31(1); C1-Ir-C40 ) 98.0(2), C1-Ir-
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, data collection, solution and refinement details,
positional and thermal parameters, and both distances and
angles for 3 and 5. This material is available free of charge
via the Internet at http://pubs.acs.org.
C50 ) 89.5(2), C1-Ir-P1 ) 95.1(2), C1-Ir-P2 ) 96.7(2),
C40-Ir-C50 ) 172.4(3), C40-Ir-P1 ) 92.2(2), C40-Ir-
P2 ) 89.3(2), C50-Ir-P1 ) 87.7(2), C50-Ir-P2 ) 89.3-
OM990851J
(
2), P1-Ir-P2 ) 167.77(6), Ir-C1-C2 ) 135.8(5), C1-C2-
C3 ) 125.0(6), C2-C3-C4 ) 127.9(6), C3-C4-C5 )
75.1(6), Ir-C40-C41 ) 176.9(5), Ir-C50-C51 ) 177.9-
6).
(14) (a) Bryndza, H. E.; Fong, K. L.; Paciello, R. A.; Tam, W.; Bercaw,
1
(
J . E. J . Am. Chem. Soc. 1987, 109, 1444-1456. (b) Bryndza, H. E.;
Tam, W. Chem. Rev. 1988, 88, 1163-1188.
(
15) (a) Blum, O.; Milstein, D. Angew. Chem. 1995, 107, 210-212;
Angew. Chem., Int. Ed. Engl. 1995, 34, 229-231. (b) Blum, O.; Milstein,
D. J . Am. Chem. Soc. 1995, 117, 4582-4594.
(16) (a) Woerpel, K. A.; Bergman, R. G. J . Am. Chem. Soc. 1993,
to a metal-allenyl species that undergoes the C-C
coupling process.
In summary, the results reported in this paper
illustrate that although complexes of the late transition
1
15, 7888-7889. (b) Ritter, J . C. M.; Bergman, R. G. J . Am. Chem.
Soc. 1997, 119, 2580-2581. (c) Ritter, J . C. M.; Bergman, R. G. J . Am.
Chem. Soc. 1998, 120, 6826-6827.