124
Yu.S. Varshavsky et al. / Journal of Organometallic Chemistry 761 (2014) 123e126
X-ray structure data
Table 1
ꢀ
ꢁ
Selected bond lengths (A) and angles ( ) for the complex [Rh(Oxq)(CO)(DMSO)] (I)
with estimated standard deviations in parentheses.
Crystal of I suitable for X-ray structure determination was taken
directly from 1st fraction obtained as described above. The mo-
lecular structure of the complex is shown in Fig. 1. The selected
bond lengths and angles are listed in Table 1. The molecule of I
occupy a special position on the mirror plane and, consequently,
possesses a strictly planar geometry excepting for the two methyl
groups.
The major result obtained is the evidence of the expected DMSO
coordination in I through sulfur atom (DMSO-S). All values of the
bond lengths and angles lie within the intervals typical for square-
ꢀ
ꢁ
Bond lengths, A
Bond angles ( )
Rh(1)eC(1)
Rh(1)eN(1)
Rh(1)eO(1)
Rh(1)eS(1)
C(1)eO(2)
S(1)eC(9)
1.782(8)
2.059(6)
2.022(6)
2.2115(19)
1.168(10)
1.783(9)
C(1) Rh(1) N(1)
N(1) Rh(1) O(1)
C(1) Rh(1) S(1)
O(1) Rh(1)S(1)
N(1) Rh(1) S(1)
C(1) Rh(1) O(1)
O(2) C(1) Rh(1)
94.7(3)
81.7(2)
92.5(2)
91.15(15)
172.9(2)
176.4(3)
176.3(6)
planar rhodium(I) complexes, in particular for (DMSO-S) complexes
IR and NMR parameters of carbonyl ligand
The IR spectrum of I contains an intense carbonyl group
ꢀ
[8e11]. The value of the SeO bond length, 1.474(6) A, is common
with complexes containing (DMSO-S) ligand [6,8e11]. Central atom
bonds to the oxyquinolinato donor atoms, N and O, in I differ
markedly in their lengths from the corresponding values for
ammonia analog (2.024(3) and 2.058(2), respectively [1]). Notice
that the length of oxyquinolinato N to Rh bond increases in the
ꢀ1
stretching band, its position being solvent-dependent: 2000 cm
ꢀ
1
1
in CHCl , 1988e1990 cm in CH Cl , THF, and acetone. Carbonyl
3 2 2
13
carbon resonance in C{ H} spectrum of I in THF solution appears
1
as a doublet at 189.38 ppm with J(CRh) 74.6 Hz. The carbonyl
order of trans-ligands L ¼ NH
3 3
< DMSO < P(OR) : 2.024(3) [1];
.059(6) (this work); 2.097(2) for R ¼ Ph [12] and 2.091(3) for
group spectral parameters pinpoint the place of S-coordinated
DMSO within the series of ligands considered in Ref. [1] and cited
above. In line with generally accepted notion articulated as early as
in 1960s [18], DMSO-S belongs to the right part of that series, i.e. to
2
R ¼ 2,6-dimethyl Ph [13]). As to the CeO bond length in I, its ESD
value is rather high which does not allow for including this bond
length in the further discussion on the n(CO) e r(CO) interrelation,
which we touched briefly in Ref. [1].
the category of ligands with pronounced
series of [Rh(Oxq)(CO)(L)] complexes it is close to P(OPh)
cifically with regard to (CO) value) and C 14 (specifically with
p
-acceptor ability. In the
3
(spe-
n
8
H
IR and NMR parameters of DMSO ligand
13
regard to
d C value).
A strong, broad absorption band at 1108e1112 cmꢀ1 in the IR
spectra of I in CHCl , CH Cl , and THF solutions should be assigned
to the SeO stretching vibration. This frequency value is consider-
NMR parameters of oxyquinolinato ligand
3
2
2
13
1
C{ H} and 1H NMR spectra of 8-oxyquinoline and 8-
ꢀ
1
ably higher than n(SO) of free DMSO (1055 cm [6,14]) and is
oxyquinolinato complexes were studied widely within the last
four decades. Our data presented below provide additional infor-
indicative of the S-coordination of DMSO ligand [6,7,14,15]. In the
1
3
1
C{ H} spectrum of I (THF solution), the signal from two equivalent
13
1
e
2
mation concerning spinespin coupling of C and H nuclei of Oxq
methyl carbons appears as a doublet at 46.69 ppm, J(CRh) ¼ 2.1 Hz.
103
ligand to
Rh nucleus, and thus may stimulate further discussion
The position of this signal is typical for DMSO-S in rhodium com-
1
on the bonding situation within the system of three condensed
coplanar cycles (chelatoaromatic system [19]): two six-membered
plexes [16,17]. In the methyl region, H NMR spectrum of I (THF
solution) exhibits one doublet at 3.29 ppm with intensity (6H)
equal to the total intensity of six oxyquinolinato proton resonances.
The position of this signal is typical for DMSO-S [6,16,17]. Its doublet
e
aromatic rings of Oxq ligand and a five-membered metal chelate
ring, Rh-OCCN. The data obtained are presented in Tables 2e4 (the
numbering of carbon atom positions is shown in Fig. 1; the
hydrogen atoms are numbered in the same order). Assignments of
103
3
splitting is apparently caused by coupling to Rh nucleus, J(HRh)
.7 Hz (confirmed by experiments at various operating
frequencies).
0
1
13
the H and C resonances suggested in Tables 2 and 3 are based on
the published data [20e28] and supported by our heteronuclear 2D
correlation experiment on complex I. Regarding the assignment of
resonances H5 and H7, we presumed that in the spectrum of
complex I the H7 resonance is shifted upfield in relation to H5, as
this is commonly observed in the spectra of 8-hydroxyquinolines
and their complexes [20e28].
Examination of Table 2 data shows that all the 13C chemical
e
shifts of Oxq anion are more or less sensitive to the protonation
effect (see the gray line for the molecule HOxq). One of these values
changes dramatically (w15 ppm decrease), namely that for C8
carbon which is directly bound to the phenolato oxygen atom. By
contrast, coordination to the rhodium metallocenter affects fore-
most C2, C4, and C7 carbons, chemical shifts of which increase
e
more than by 4 ppm on passing from free Oxq anion to the
dicarbonyl rhodium complex. The difference between protonation
and coordination effects demonstrates that electron acceptor po-
þ
tency of H cation is directed predominantly toward oxygen atom
e
of Oxq anion, whereas influence of rhodium metallocenter is
rather delocalized. An important point is that all three, C2, C4, and
C7, chemical shifts show the smallest increase for L ¼ NH
3
and the
greatest increase for L ¼ CO, while the DMSO complex, I, occupies
Fig. 1. The structure of [Rh(Oxq)(CO)(DMSO)] (50% probability ellipsoids).
an intermediate position. Evidently these values of the chemical
Varshavsky
