One-step synthesis of alkenyl ketone complexes from CP*RhCl2(PPh3), alkyne and H2O in the presence of KPF6

Article abstract of DOI:10.1039/b108953f

The reaction of Cp*RhCl₂(PPh₃) 1 with 1-alkyne and H₂O in the presence of KPF₆ afforded the alkenyl ketone complex [Cp*Rh(PPh₃)(CPh=CHCOCH₂R)](PF₆) [R = p-tolyl (3a), R = Ph (3b)

Full text of DOI:10.1039/b108953f

One-step synthesis of alkenyl ketone complexes from Cp*RhCl2(PPh3),
alkyne and H2O in the presence of KPF6
Kenichi Ogata,a Katsuaki Kuge,b Kazuyuki Tatsumib and Yasuhiro Yamamoto*a
a Department of Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510,
Japan. E-mail: yamamoto@chem.sci.toho-u.ac.jp; Fax: (+81)47-475-1855
b Research Center for Materials Science and Department of Chemistry, Graduate School of Science, Nagoya
University, Furo-cho, Chikusa-ku, Nagoya 454-8602, Japan
Received (in Cambridge, UK) 2nd October 2001, Accepted 21st November 2001
First published as an Advance Article on the web 9th January 2002
The reaction of Cp*RhCl2(PPh3) 1 with 1-alkyne and H2O in
the presence of KPF6 afforded the alkenyl ketone complex
[Cp*Rh(PPh3)(CPhNCHCOCH2R)](PF6) [R = p-tolyl (3a),
R = Ph (3b)], whereas Cp*IrCl2(PPh3) 2 or [(h6-C6Me6)-
RuCl2(PPh3)
(CO)(PPh3)](PF6)
(CO)(PPh3)](PF6).
gave
the
5a
corresponding
[Cp*IrCl-
and
[(h6-C6Me6)RuCl-
In metal-assisted organic syntheses the five-membered un-
saturated g-lactones are biologically important synthetic tar-
gets.1 For example, the a,b-butenolide ring is present in a large
number of biologically important natural products and certain
butenolides exhibit antitumor, antifugal, and antibacterial
activities. Carmona et al. have reported that dimeric butenolides
were generated by sequential insertion of phenylacetylene and
carbon monoxide into nickel–acyl bonds, in which alkenyl
ketone complexes are precursors of butenolides.2 The alkenyl
ketone complexes have been usually generated by two or more
steps: (1) an initial synthesis of acyl complexes and subsequent
insertion of alkynes into metal–acyl bonds,3 and (2) an initial
preparation of the metal carbonyl complexes and the photo-
induced or thermal reactions of them with acetylenes.2,4
Scheme 1 Reactions of [Cp*MCl2(L))] (M = Ir, Rh; L = PPh3, PPh2Me)
or [(p-cymene)RuCl2(PPh3)] with 1-alkyne and H2O in the presence of
KPF6. The PF6 anion was omitted for clarity.
During our research on the reactions of pentamethylcyclo-
pentadienyl rhodium(III) and iridium(III) complexes with 1-al-
kynes, we found that treatment of Cp*RhCl2(PPh3) 1 (Cp* =
C5Me5) with 1-alkyne and water in the presence of KPF6 led to
the direct formation of alkenyl ketone complexes, whereas a
similar reaction of Cp*IrCl2(PPh3) 2 cleaves a C–C triple bond
of the alkyne to give [Cp*IrCl(PPh3)(CO)](PF6) and saturated
hydrocarbon with one less carbon atom. In this article we report
the novel one-step synthesis of alkenyl ketone complexes
arising from two molecules of 1-alkyne and water.
The reaction consists of initial formation of a vinylidene
complex and subsequent addition of H2O to produce a
hydroxybenzyl carbene (Scheme 2). This process was con-
firmed by the facts that an incorporation of a deuterium atom
into the benzylic group occurred in the presence of D2O to give
[Cp*Rh(PPh3)(CPhNCHCOCDHPh)](PF6) and the reaction of
[Cp*RhCl(PPh3){NCNCHPh}](PF6) with phenylacetylene in
the presence of H2O gave 3b. The next process proceeds with
the insertion of another 1-alkyne into the Rh–acyl intermediate
derived from the elimination of HCl, followed by an intra-
molecular coordination of the acyl oxygen to the Rh. The acyl
intermediate was assumed from the fact that formation of an
acyl as the product of the protonation of alkynyl complexes has
been found in several instances and takes place by the reaction
When 1 was treated with a mixture of tolylacetylene and H2O
in the presence of KPF6 in CH2Cl2 and acetone at rt, orange
crystals formulated as [Cp*Rh(PPh3)(C(p-tolyl)NCHCOCH2(p-
tolyl)](PF6) 3a (p-tolyl = 4-MeC6H4) from elementary analysis
and FAB mass spectrometry were generated (Scheme 1).† The
IR spectrum showed the presence of a PF6 anion at ca. 840
cm21. The 1H NMR spectra showed a doublet at d 1.20 due to
Cp* protons, two singlets at d 1.57 and 2.34 due to p-methyl
protons, and an AB system with a center at d 3.2 due to
methylene protons. The 31P{1H} NMR spectrum showed a
doublet at d 38.0 and a septet at d 2143.7. X-Ray analysis
revealed that the rhodium atom was connected by triphenyl-
phosphine, and the carbon and oxygen atoms of the alkenyl
ketone moiety (Fig. 1).‡ The O(1)–Rh–C(11) bite angle is
80.4(4)°. The Rh–C(11) and Rh–O(1) bond lengths are 2.01(1)
and 2.102(8) Å, respectively. The C(11)–C(19) and C(20)–O(1)
bond lengths are 1.42(2) and 1.26(1) Å, respectively, compared
with those found for the C–C and C–O double bond lengths.
Complex 3b, [Cp*Rh(PPh3)(CPhNCHCOCH2Ph)](PF6) having
a similar structure was obtained in the reaction with phenyl-
acetylene.† Diphenylphosphine complex Cp*RhCl2(PPh2Me)
also gave [Cp*Rh(PPh2Me)(CPhNCHCOCH2Ph)](PF6) 4b.†
Fig. 1 Molecular structure of complex cation of [Cp*Rh(PPh3){C(p-
tolyl)NCHCOCH2(p-tolyl)}](PF6) 3a. Selected bond lengths (Å) and angles
(°): Rh–P(1) 2.339(3), Rh–O(1) 2.102(8), Rh–C(11) 2.01(1), O(1)–C(20)
1.26(1), C(11)–C(19) 1.42(2); P(1)–Rh–O(1) 86.4(2), P(1)–Rh–C(11)
93.5(4), O(1)–Rh–C(11) 80.4(5), Rh–C(11)–C(19) 110.7(8), C(11)–C(19)–
C(20) 116(1), O(1)–C(20)–C(19) 119(1).
6
When 2 or (h -C6Me6)RuCl2(PPh3) were treated under
6
similar conditions, [Cp*IrCl(CO)(PPh3)](PF6) 5a or (h -
C6Me6)RuCl(CO)(PPh3)](PF6), and toluene were generated.
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CHEM. COMMUN., 2002, 128–129
This journal is © The Royal Society of Chemistry 2002

(AB system, J = 16.0 Hz, CH2, 2H), 6.73 (s, CH, 1H), ca. 6.9–7.8 (c, ArH,
25H). 31P{1H}NMR (CDCl3) d 38.0 (d, JRh–P = 152 Hz), 2143.7 (sep.
JRh–P = 710 Hz, PF). FAB MS (m/z of cation part (M)): found: 721 (M+ 2
1).
3a (reddish brown, 42.9%): IR (Nujol) 1599, 1537 (CNO and CNC), 835
cm21 (PF6). UV (CH2Cl2) lmas ≈ 298 nm. dH (CDCl3) 1.20 (d, JP–H = 2.6
Hz, Cp*, 15H), 1.57 (s, p-Me 3H), 2.34 (s, p-Me, 3H), 3.11 and 3.29 (AB
type system, J = 16.5 Hz, 2H), 6.67 (s, CH, 1H), ca. 6.9–7.8 (c, ArH, 23H).
31P{1H}NMR (CDCl3) d 38.0 (d, JRh–P = 151 Hz), 2143.7 (sep. JP–F
712 Hz, PF). FAB MS (m.z of cation part, M) found 749 (M+ 2 1).
=
4b (yellow, 61.5%): IR (Nujol) 1545 (CNO and CNC), 839 cm21 (PF6).
UV (CH2Cl2) lmax ≈ 268(sh), 400(sh) nm. dH (CDCl3) 1.25 (d, JP–H = 2.7
Hz, Cp*, 15H), 2.07 (d, JP–H = 9.2 Hz, Me 3H), 3.61 and 3.72 (AB type
system, J = 15.5 Hz, 2H), 6.65 (d, JP–H = 2.2 Hz, 1H), ca. 6.8–7.9 (c, ArH,
20H). 31P{1H}NMR (CDCl3) d 17.9 (d, JRh–P = 148 Hz), 2143.7 (sep. JP–F
=
712 Hz, PF). Anal. Found:
C 58.47, H 5.44%. Calcd. for
C39H41OF6P2Rh: C 58.22, H 5.14%.
‡ Crystal data for 3a: M = monoclinic, space group Pn (No. 7), Z = 2, a
= 11.363(8), b = 9.32(1), c = 20.289(7) Å, b = 103.06(4)°, U = 2093(2)
Å3. The structure was solved by Patterson methods and refined by full-
matrix least-squares techniques for all unique reflections (3676) to R =
0.121 and Rw = 0.180 [w = 1/s2(Fo2)] and R1 = 0.060 (for 3285
reflections (I
> 2.0s(I))), GOF = 2.34. CCDC 163783. See http://
Scheme 2 Possible pathway for the formation of alkenyl ketone complexes.
The PF6 anion was omitted for clarity.
www.rsc.org/suppdata/cc/b1/b108953f/ for crystallographic files in .cif
format.
of a highly reactive vinylidene intermediate with traces of
water.5 Formation of the acyl complex of ruthenium has been
reported by Bianchini et al.6 In the iridium complex the C–C
bond cleavage from the hydroxycarbene complex occurred to
form the carbonyl complex and toluene. It was confirmed by the
following separate experiment that the oxygen atom of the
carbonyl ligand was generated from water; the reaction of
Cp*Ir(MDMPP-P,O)Cl2 with 18OH2 in the presence of KPF6
1 M. Ryang, Y. Sawa, S. N. Somasundaram, S. Murai and S. Tsutumi, J.
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gave [Cp*Ir(MDMPP-P,O)(C18O)](PF6) (MDMPP-P,O
=
PPh2(C6H3-2-MeO-6-O)).7 The metal-assisted cleavage of the
C–C triple bond with formation of the carbonyl complex and the
saturated hydrocarbon with one less carbon atom has been
known in ruthenium, platinum or iridium complexes.6,8
The present reactions provide a convenient one-pot synthesis
of alkenyl ketone complexes from metal halide bearing
pentamethylcyclopentadienyl group, alkynes and water. We are
currently investigating application of the reaction to the
synthesis of lactone and vinylketone using a catalytic amount of
a rhodium complex.
We thank Professor Shigetoshi Takahashi and Dr Fumie
Takei for measurements of FAB mass spectroscopy. This work
was partially supported by a Grant-in Aid for Scientific
Research from the Ministry of Education, Science, Sports, and
Culture of Japan.
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7 K. Sugawara and Y. Yamamoto, unpublished results.
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Notes and references
† Satisfactory analytical data were obtained for new complexes: Prepara-
tion of 3b: A solution of 1 (97.6 mg, 0.171 mmol), phenylacetylene (0.2 mL,
18 mmol) and H2O (1.5 mL, 83 mmol) in CH2Cl2 (10 mL) and acetone (15
mL) was stirred at rt. After 24 h, the solvent was removed, and the residue
was extracted with CH2Cl2. The CH2Cl2 was concentrated, and diethyl ether
was added to give reddish brown crystals of 3b (80.0 mg, 54.6%). IR
(Nujol): 1588, 1547 (CNO and CNC), 839 cm21 (PF6); UV (CH2Cl2): lmax
≈ 302 nm. dH (CDCl3): 1.19 (d, JPH = 2.7 Hz, Cp*, 15H), 3.16 and 3.32
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