Russian Chemical Bulletin, International Edition, Vol. 51, No. 6, pp. 1077—1078, June, 2002
1077
PCP pincer ligands based on metallocenes. Crystal structure
of the rhodium complex cisꢀRhCl2(CO)[{2,5ꢀ(Pri2PCH2)2C5H2}Fe(C5H5)]
a
a
a
a
A. A. Koridze,a,b A. M. Sheloumov, S. A. Kuklin, V. Yu. Lagunova, I. I. Petukhova,
ꢀ
F. M. Dolgushin,a M. G. Ezernitskaya,a P. V. Petrovskii,a A. A. Macharashvili,b and R. V. Chediab
aA. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: koridze@ineos.ac.ru
bI. Javakhishvili Tbilisi State University, Chemical Department,
1 av. Chavchavadze, 380028 Tbilisi, Georgia.
Fax: (995 32) 22 5107
The
anionic
pincer
tridentate
ligands
reduction with LiAlH4 (ether, 22°C, 2 h) produced diol
{1,3ꢀ(HOCH2)2C5H3}Fe(C5H5) (3). The ruthenocene
analog {1,3ꢀ(HOCH2)2C5H3}Ru(C5H5) (4) was syntheꢀ
sized analogously starting from [(C5H5)Ru(MeCN)3]PF6
and fulvene 2.
Heating of diols 3 and 4 with secondary phosphines
HPR2 (R = Pri or But) in acetic acid at 80 °C afforded
the corresponding diphosphine derivatives of metallocenes
{1,3ꢀ(R2PCH2)2C5H3}M(C5H5) (M = Fe, R = Pri, 5a;
M = Fe, R = But (5b); M = Ru, R = Pri (6a); M = Ru,
R = But (6b)).
[2,6ꢀ(R2PCH2)2C6H3]– find wide use in the organomeꢀ
tallic synthesis and catalysis.1—3 Recently, it has been
demonstrated4 that the rhodium and iridium hydride comꢀ
plexes with such ligands, viz., MH2{2,6ꢀ(R2PCH2)2C6H3}
(M = Rh or Ir; R = Pri or But), catalyze dehydrogenaꢀ
tion of alkanes to form H2 and olefins.
We believed that the PCP pincer ligands based on
ferrocene could possess electronic and steric features,
which distinguish them from their benzene analogs and
are attractive from the viewpoint of their use in catalysis.
It is known that the ferrocenyl group has a stronger elecꢀ
tronꢀdonating ability than the phenyl group, which can
be favorable for the oxidative addition of the C—H bonds
of alkanes to the activation center, viz., rhodium or iriꢀ
dium. The sandwich nature of the metallocenyl unit can
help in tuning the steric environment about the rhodium
or iridium atoms. This property can prevent isomerizaꢀ
tion of αꢀolefins (which are initially generated by dehyꢀ
drogenation of alkanes) into less desirable internal oleꢀ
fins. Finally, the iron atom in ferrocene can rapidly and
reversibly enter into redox reactions thus providing the
electronic effect on the nearby catalytic center.
The reaction of complex 1 with 6,6ꢀbis(dimethylꢀ
amino)ꢀ3ꢀ(ethoxycarbonyl)fulvene yielded {1ꢀ(EtOOC)ꢀ
3ꢀ(Me2NCO)C5H3}Fe(C5H5). Reduction of the latter
with LiAlH4 in THF gave rise to 3ꢀdimethylaminomethylꢀ
1ꢀ(hydroxymethyl)ferrocene. Heating of this amino alꢀ
cohol with HPPh2 in AcOH afforded aminophosphine
{1ꢀ(Ph2PCH2)ꢀ3ꢀ(Me2NCH2)C5H3}Fe(C5H5} (7).
Compounds 5a,b, 6a,b, and 7 were obtained in ∼40%
1
total yields. These compounds were characterized by H
and 31P NMR spectroscopy and mass spectrometry.
31P NMR (CDCl3), δ: 10.91 (5a); 23.18 (5b); 9.61 (6a);
36.83 (6b); –15.53 (7).
Due to the geometric characteristics, the P donor
atoms in 1,3ꢀbis(dialkylphosphinomethyl)metallocenes
are more remote from each other than those in the corꢀ
responding benzene derivatives. Hence, the possibility
of the formation of pincer complexes based on metalloꢀ
cenes was not evident. One would expect that the formaꢀ
tion of these complexes will be accompanied by a deꢀ
crease in the bond angles at the C(1) and C(3) atoms
compared to the standard value (126°).
We synthesized 1,3ꢀdisubstituted metallocenes accordꢀ
ing to a procedure based on the use of the approꢀ
priately substituted fulvenes.5 Thus, the reaction of
[(C5H5)Fe(1,4ꢀMe2C6H4)]PF6 (1) with 6ꢀdimethylꢀ
aminoꢀ3ꢀ(ethoxycarbonyl)fulvene (2) gave rise to
3ꢀethoxycarbonylꢀ1ꢀformylferrocene whose subsequent
We obtained unambiguous evidence for the formaꢀ
tion of the PCP complex based on ferrocene. The complex
cisꢀcarbonyl[2,5ꢀbis(diisopropylphosphinomethyl)ferꢀ
rocenꢀ1ꢀyl]dichlororhodium(III), cisꢀRhCl2(CO)[{2,5ꢀ
(Pri2PCH2)2C5H2}Fe(C5H5)] (8), was synthesized by the
reaction of diphosphine 5a with [Rh(COE)2Cl]2 (COE
is cyclooctene) in 2ꢀmethoxyethanol (120 °C, 1 h, nonꢀ
optimized yield was 25%) (Scheme 1). The 31P NMR
spectrum (CDCl3) of complex 8 shows a doublet at δ 62.61
1
(JRh,P = 82.8 Hz). The H NMR spectroscopic data are
indicative of orthoꢀmetallation of the cyclopentadienyl
ring. Thus, this ring gives only a singlet at δ 4.15 (2 H)
without evidence for splitting. In addition, the methylꢀ
ene protons of the CH2PPri2 groups are pairwise nonꢀ
equivalent and are observed as a doublet of virtual tripꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 988—990, June, 2002.
1066ꢀ5285/02/5106ꢀ1077 $27.00 © 2002 Plenum Publishing Corporation
Koridze
