E.P. Shestakova et al. / Journal of Organometallic Chemistry 696 (2011) 3214e3222
3221
possible to propose a tentative assignment of
for the inequivalent methyl and trifluoromethyl substituents in the
complexes with symmetric -diketonate ligands, cis-[Rh(A-
d
1H and
d
19F values
added to the solid and white precipitate was filtered off. The
solution was concentrated to give a red-orange solid (0.263 g).
Yellow crystals of 1 as CH3CN 1:1 solvate could be obtained by
dissolving the red-orange solid in acetonitrile (2 ml), adding
toluene (7 ml) and layering the solution with 8 ml of petroleum
(b.p. range 70ꢀ100 ꢁC). Yield: 0.12 g (40%). Anal. Calc. for
C70H63BF3N2O2P2Rh: C, 70.24; H, 5.31. Found: C, 70.31; H, 5.31%.
b
cac)(PPh3)2(CH3)I] (5), trans-[Rh(Acac)(PPh3)2(CH3)I] [12], and
trans-[Rh(HFA)(PPh3)2(CH3)I] (HFA is hexafluorocetylacetonate)
[12]. According to this criterion, in the 1H spectra of the (Peq Pax
)
isomer of 5 and of trans-[Rh(Acac)(PPh3)2(CH3)I] chemical shifts
1.93 and 1.49 ppm, respectively (Table 2), correspond to the CH3
substituent trans to CH3(eRh) ligand; in the 19F spectrum of trans-
[Rh(HFA)(PPh3)2(CH3)I] chemical shift ꢀ71.9 ppm (Table 3) corre-
sponds to the CF3 substituent trans to CH3(eRh) ligand.
For every (Peq Pax) isomer of the complexes under discussion
there are two well separated 31P resonances with distinct coupling
constants, 1J(PRh), (Table 1). We attempted to assign these reso-
nances specifically to Pax and Peq nuclei. Our consideration is based
on a noticeable difference in the sensitivity of the 1J(PRh) values,
presented in Table 1, toward specific changes in the ligand
surrounding of the metallocenter. We tentatively ascribe to equa-
torial phosphines the signals which 1J(PRh) values are more sensi-
4.1.2. Preparation of cis-[Rh(TFA)(PPh3)2(CH3)(NH3)][BPh4] (2)
Methyl iodide (0.1 ml, 1.6 mmol) was added to a suspension of
[Rh(TFA)(PPh3)2] (0.208 g, 0.27 mmol) in acetonitrile (15 ml)
at ꢀ20 ꢁC with stirring. The reaction mixture was allowed to warm
to þ10 ꢁC. After 1 h the starting complex was entirely dissolved,
and the yellow-orange solution was formed. The solution thus
obtained was mixed with NaBPh4 (0.5 g, 1.46 mmol) in acetonitrile
(10 ml). The resulting reaction mixture was stirred for 10 min,
filtered, and volatiles were removed in vacuo. Methylene chloride
(15 ml) was added to the oily residue, and the white precipitate was
filtered off. The volume of filtrate was reduced to about 5 ml, and
a steam of gaseous NH3 was passed through the solution for 5 min
at room temperature. Then, the solvent was removed in vacuo and
the oily residue was recrystallized from methylene chloride/diethyl
ether to form pale-yellow bright crystals of solvate 2$(C2H5)2O.
Yield: 0.16 g (50%). Anal. Calc. for C70H70BF3NO3P2Rh: C, 69.72; H,
5.85. Found: C, 69.36; H, 5.85%.
tive to the nature of
26.7; 23.1; 25.8 ppm for L ¼ MeCN, NH3, Py, I, respectively, in the
-diket ¼ Acac series and 24.7; 27.5; 24.4; 26.2 ppm for the same
b-diketonate ligand. These are signals at 23.6;
b
sequence ofligands Lin the
b
-diket¼ TFA series (major isomers). The
remaining signals in these spectra which 1J(PRh) values are more
sensitive to variation in the axial ligands, we assign to axial
phosphines.
It is interesting to note that cations with the (Peq Pax) structure of
complexes under discussion have very close values of constants
4.1.3. Preparation of cis-[Rh(TFA)(PPh3)2(CH3)Py][BPh4] (3)
Methyl iodide (0.1 ml, 1.6 mmol) was added to a suspension of
[Rh(TFA)(PPh3)2] (0.190 g, 0.24 mmol) in acetonitrile (15 ml)
at ꢀ20 ꢁC with stirring. The reaction mixture was allowed to warm
to þ10 ꢁC. After 1 h the starting complex was entirely dissolved and
the yellow-orange solution was formed. The solution thus obtained
was mixed with NaBPh4 (0.44 g, 1.3 mmol) in acetonitrile (12 ml).
The resulting reaction mixture was stirred for 10 min, filtered, and
volatiles were removed in vacuo. Methylene chloride (20 ml) was
added to the oily residue, and the white precipitate was filtered off.
The volume of filtrate was reduced to about 5 ml, and excess
pyridine (0.1 ml, 1.24 mmol) was added. The reaction mixture was
stirred for 10 min at room temperature. Then excess pyridine and
the solvent were removed in vacuo, and the oily residue was re-
crystallized from methylene chloride/diethyl ether to form pale-
yellow crystals of solvate 3$0.75 C2H2Cl2. Yield: 0.23 g (76%). Anal.
Calc. for C71.75H63.50BCl1.5F3NO2P2Rh: C, 68.52; H, 5.10. Found: C,
68.98; H, 5.36%.
2J(PP) (35e37 Hz) without regard to the nature of
b-diketonate and
L-ligands (Table 1). The (Peq Pax) isomers of neutral complexes 4 and
5 also have very close values of constants 2J(PP) (22e23 Hz), but
these values differ markedly from the values for (Peq Pax) isomers of
cation complexes (L ¼ NH3, Py, MeCN).
4. Experimental
4.1. Preparation of complexes
All operations were performed under a dry argon atmosphere.
The rhodium complexes [Rh(Acac)(PPh3)2], [Rh(TFA)(PPh3)2], cis-
[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] were synthesized by the
published procedures [11,23]. Gaseous NH3 was prepared by stan-
dard methods [24]. Solvents were dried and purified by known
procedures [25] and distilled under argon. Methyl iodide was used
as freshly distilled samples. Elemental analyses were performed on
a HewlettePackard 185 microanalyzer. Conductivity measure-
ments were carried out on an E 7e11 universal CRL instrument at
25 ꢁC for 10ꢀ3 M solutions in acetone.
4.1.4. Preparation of cis-[Rh(TFA)(PPh3)2(CH3)I] (4)
Methyl iodide (0.4 ml, 6.3 mmol) was added to a suspension of
[Rh(TFA)(PPh3)2] (0.17 g, 0.22 mmol) in acetonitrile (3 ml) at ꢀ20 ꢁC
with stirring. The reaction mixture was allowed to warm to 0 ꢁC.
After stirring the suspension for 30 min at 0 ꢁC a bright-yellow bulk
solid was formed. To complete the reaction, reaction mixture was
stirred for 1 h at 0 ꢁC. Then excess methyl iodide was removed in
vacuo without heating. Acetonitrile (3 ml) was added at 0 ꢁC. The
product was filtered off and washed with cold acetonitrile and cold
methanol, and dried in vacuo. Yield: 0.15 g (75%). Anal. Calc. for
C42H37F3IO2P2Rh: C, 54.68; H, 4.04. Found: C, 54.42; H, 3.91%.
4.1.1. Preparation of cis-[Rh(TFA)(PPh3)2(CH3)(CH3CN)][BPh4] (1)
Methyl iodide (0.1 ml, 1.6 mmol) was added to a suspension of
[Rh(TFA)(PPh3)2] (0.201 g, 0.26 mmol) in acetonitrile (15 ml)
at ꢀ20 ꢁC with stirring. The reaction mixture was allowed to warm
to þ10 ꢁC. After 1 h the starting complex was entirely dissolved,
then the yellow-orange solution was mixed with solution of
NaBPh4 (0.43 g, 1.26 mmol) in acetonitrile (10 ml) at þ10 ꢁC. The
resulting reaction mixture was stirred for 10 min at þ10 ꢁC, filtered,
and then volatiles were removed in vacuo without heating. Then
acetonitrile (15 ml) was added to the resulting oil, the solution was
filtered, and solvent was removed from filtrate in vacuo. Methylene
chloride (15 ml) was added to the oily residue, and the white
precipitate was filtered off. Then solvent was removed from filtrate
yielding a yellow-orange solid. This solid was dissolved in aceto-
nitrile (10 ml), a very fine light precipitate was filtered off, and
solvent was removed from filtrate. Then, chloroform (9 ml) was
4.1.5. Preparation of cis-[Rh(TFA)(PPh3)2(CD3)I]
The complex was prepared similarly to
4 starting from
[Rh(TFA)(PPh3)2] (0.10 g, 0.13 mmol) and CD3I (0.1 ml, 1.6 mmol) in
CH3CN (3 ml). Yield: 0.07 g (57%).
4.1.6. Preparation of cis-[Rh(Acac)(PPh3)2(CH3)I](5)
A mixture of complex cis-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4]
(0.25 g, 0.22 mmol), NaI (0.11 g, 0.73 mmol), and acetone (5 ml) was
Shestakova, Elizaveta P.
