Rhodium(III) cationic methyl complexes containing
dimethylformamide ligand, cis-[Rh(b-diket)(PPh
3
)
2
(CH
3
)(DMF)][BPh
4
]
(b-diket ¼ acetylacetonate or benzoylacetonate), in comparison with
their acetonitrile analogs
Elizaveta P. Shestakova
a
, Yuri S. Varshavsky
a, *
, Victor N. Khrustalev
b
, Galina L. Starova
a
,
Sergei N. Smirnov
a
a
St. Petersburg State University, Petrodvorets, Universitetskii pr., 26,198504 St. Petersburg, Russia
b
Nesmeyanov Institute of Organoelement Compounds, Vavilova Street, 28, 117813 Moscow, Russia
article info
Article history:
Received 20 June 2014
Received in revised form
23 September 2014
Accepted 25 September 2014
Available online 7 October 2014
Keywords:
Rhodium(III) methyl complexes
b-Diketonates
Dimethylformamide
Hydrogen bonding
NMR
X-ray diffraction
abstract
The rhodium(III) cationic methyl complexes, cis-[Rh(Acac)(PPh
3
)
2
(CH
3
)(DMF)][BPh
4
] (1) and cis-
[Rh(BA)(PPh
3
)
2
(CH
3
)(DMF)][BPh
4
](2) are formed upon reactions of cis-[Rh(b-diket)(PPh
3
)
2
(CH
3
)(MeCN)]
[BPh
4
](b-diket ¼ acetylacetonate, Acac, or benzoylacetonate, BA) with excess of dimethylformamide
(DMF) in CH
2
Cl
2
solution at ambient temperature. Complexes 1 and 2 were characterized by elemental
analysis,
31
P{
1
H} and
1
H NMR spectra, and single crystal X-ray crystallography. The cations of 1 and 2
have slightly distorted octahedral geometry. The “equatorial” plane contains the b-diketonate and two
PPh
3
ligands; methyl and DMF ligands occupy the axial positions. Peculiar features of complexes 1 and 2
in solid state are: (i) unusually long RheO(DMF) bond and (ii) non-symmetrical orientation of the formyl
CeH bond in relation to two oxygen atoms of the b-diketonate ligand. The signals from formyl protons in
the
1
H NMR spectra of 1 and 2 are shifted significantly upfield relatively to free DMF. The hydrogen
bonding between formyl proton and one of the b-diketonate oxygen atoms is considered. In solutions, 1
and 2 show dynamic behavior at ambient temperature and keep their solid-state geometry at 70
C.
© 2014 Elsevier B.V. All rights reserved.
Introduction
In our previous publications [1e3] we reported on synthesis and
structure of several cationic methyl rhodium(III) complexes, cis-
[Rh(b-diket)(PPh
3
)
2
(CH
3
)(L)][BPh
4
](b-diket ¼ Acac, BA, or TFA;
L ¼ MeCN, NH
3
, Py). X-ray investigation detected substantial dif-
ference between solid state geometries of MeCN complexes
(configuration a) and complexes containing stronger N-donors, Py
and NH
3
, (configuration b):
NMR study of these complexes in solution revealed one more
significant distinction between MeCN complexes and their Py and
NH
3
analogs. Pyridine and ammonia complexes retain their b
configuration in solution whereas acetonitrile complexes exhibit
dynamic behavior at ambient temperature. At 50
C dynamic * Corresponding author. Tel.: þ7 812 274 34 45; fax: þ7 812 428 69 39.
E-mail address: yurelv@gmail.com (Y.S. Varshavsky).
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
http://dx.doi.org/10.1016/j.jorganchem.2014.09.035
0022-328X/© 2014 Elsevier B.V. All rights reserved.
Journal of Organometallic Chemistry 774 (2014) 1e5