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ꢀ
A. Skarzynska et al. / Journal of Organometallic Chemistry 743 (2013) 179e186
184
In addition to symmetrical ligands, also unsymmetrical ones
2-hexene
aldehydes
l/b
were synthesised to determine the preferences in their coordi-
nation modes. It was established that rhodium complexes
80
60
40
20
0
8
7
6
5
4
3
2
1
0
exclusively exhibit
fashion, and
k
2-P,E (E ¼ N, O) bidentate coordination
7
k
1-P coordination fashion for the tetraoxaspir-
ophosporane ligand, postulated in the literature, was not
observed. Some of the complexes appeared to be effective cata-
lysts for the isomerisation of 1-hexene, producing 2-hexene in
high yield. However, in the presence of a modifying ligand
P(OPh)3, the same complexes turn out to be regioselective cata-
lysts for 1-hexene hydroformylation. The introduction of tri-
phenylphosphite to the system suppressed the isomerisation of
1-hexene and caused an increase in the amount of aldehydes. It
was observed that even small changes in ligand structure affect
the activity and regioselectivity of the catalytic system, but it is
difficult in our opinion to find the systematic correlation between
catalytic properties and electronic properties of H-spi-
rophosphorane ligands.
5,3
5,2
4,3
3,7
66
50
2,2
42
39
29
22
16
14
14
3
13
1
1
2
3
4
5
6
Complexes
Fig. 6. Results of hydroformylation of 1-hexene catalysed by rhodium complexes 1e6
modified with triphenylphosphite P(OPh)3, P/[Rh] ¼ 6; the left axis describes yield (%)
of the products, right axis describes the linear-to-branched-aldehydes ratio (l/b).
possibility that rhodium complexes incorporating H-spi-
rophosphorane ligands along with the triphenylphosphite ligand can
participate in catalytic cycle. The stability of these complexes under
hydroformylation reaction conditions may have a pronounced effect
on the course of the catalytic process. This tentative conclusion was
drawn based on the observation that when complex [RhCl(CO)
{P(OCMe2CMe2O)OCMe2CMe2OH}] 3 reacted with an equimolar
amountofP(OPh)3, newspecies wereformed within1.5h. Apart from
uncoordinatedL3, a new phosphorus species at 9.4 ppm andcomplex
[Rh(CO)Cl{P(OPh)3}2] [20a,29] were detected in 31P{1H} NMR spec-
trum. Moreover, the downfield range of the spectrum also consists of
two doublets, at 121.4 and 128.08 ppm, with J(RheP) equal to 208.0
and 199.5 Hz, pertinent to two magnetically non-equivalent phos-
phorus atoms, probably belonging to coordinated P(OPh)3 and L3
ligands. Quite different observations were made when the more
active complexes 5 and 1 reacted with P(OPh)3. The complexes
appeared to be more labile and the substitution reaction in both cases
immediately led to the decomposition of coordinated spi-
rophosphorane ligands and the formation of the new phosphorus
species at 12.1 ppm (5) and 1.3 ppm (1) respectively. Considering the
electronicproperties ofthecoordinatedspirophosphoraneligands, in
our opinion it is hard to find a correlation between this factor and the
catalytic activity of the complexes, though complex 3 incorporating
supposedly the most basic ligand HP(OCMe2CMe2O)2 L3 exhibits the
lowest catalytic activity.
Our subsequent efforts were directed towards determining the
active form of catalyst present in a system without triphenylphos-
phite. Therefore, a deuterated toluene solution of the catalyst 5 was
heated (353 K) under 1 MPa of CO/H2 (1:1) for 4 h and analysed by
means of 31P{1H} NMR spectroscopy. The presence of a doublet at
135.3 ppm and a singlet at 13.10 ppm observed for the post-reaction
mixture, attributed to catalyst 5 and the spirophosphorane ligand
decomposition product respectively, apart from high yields of iso-
merisation products, i.e. 2-hexene obtained in the hydroformylation
reaction, may suggest that some amounts of the rhodium carbonyl
complexes Rh6(CO)16, Rh4(CO)12 are also formed during the catalytic
process [30]. The presence of rhodium carbonyl complexes known to
produce 2-hexene with 70e90% yield [31], was additionally evi-
denced by the IR spectrum of the post-reaction solution.
4. Experimental section
4.1. General procedure
Chemicals and deuterated solvents were purchased from Sigmae
Aldrich and Fluka and used as received. All preparations were per-
formed in an atmosphere of dry, oxygen-free nitrogen, using con-
ventional Schlenk techniques. Solvents were carefully dried and
deoxygenated by standard methods [32]. The ligand precursors 1,6-
dioxa-4,9-diaza-5
[9], 3,3,8,8-tetramethyl-1,6-dioxa-4,9-diaza-5
nonane HP(OCH2CMe2NH)2 L2 [10], 2,2,3,3,7,7,8,8-octamethyl-
1,4,6,9-tetraoxa-5
5-phosphaspiro[4.4]nonane HP(OCMe2CMe2O)2
L3 [11],
l5-2,20-(3H,30H)-spirobi[1,3,2-benzoxazaphosphole]
HP(OC6H4NH)2 L4 [7], 2,2,3,3,8,8-hexamethyl-1,4,6-trioxa-9-aza-5l5
l
5-phosphaspiro[4.4]nonane HP(OCH2CH2NH)2 L1
5-phosphaspiro[4.4]
l
l
2
-
phosphaspiro[4.4]nonane HP(OCMe2CMe2O)(OCH2CMe2NH) L5 [2],
were prepared according to the literature methods. [RhCl2{P(OCH2C-
Me2NH)OCH2CMe2NH2}] 2 and [RhCl(CO){P(OC6H4NH)OC6H4NH2}] 4
were obtained in a manner described previously [7].
IR and FIR measurements were performed in KBr or Nujol with a
Bruker 113V FTIR. 1H and 31P{1H} NMR spectra were obtained on a
Bruker AMX (300 MHz for 1H NMR) or Bruker Avance 500 MHz
spectrometer (500 MHz for 1H NMR). The chemical shifts (
d
) are
given in ppm towards TMS (1H) and H3PO4
(
31P) using deuterated
solvents as lock and reference (1H) respectively. Elemental analyses
were performed on a 2400 CHNS Vario EL III apparatus. Analytical
gas chromatographic (GC) analyses were performed on a Hewlett
Packard 8452A.
4.2. Synthesis of the ligand HP(OCMe2CMe2O)(OC6H4NH) L6
40,40,50,50-tetramethylspiro-[1,3,2-benzoxazaphosphole]-
2(3H),20 5-[1,3,2]dioxaphospholane HP (OCMe2CMe2O)(OC6H4NH)
l
L6 was obtained using the general procedure described in the
literature for ligand L5 [2]. The crude product was purified by
recrystallisation from hexane in a freezer providing crystals suit-
able for X-ray analysis.
Anal. Calc. for C12H18NO3P: C, 56.47; H, 7.11; N, 5.49; Found: C,
54.84; H, 7.13; N, 5.20%; 1H NMR (CD2Cl2)
d 1.26, 1.27, 1.29, 1.32
3. Conclusions
(12H, s’s, CH3), 5.18 (1H, d, 2J(P, H) ¼ 17.8 Hz, NH), 6.70 (4H, m,
Ph-H) 7.97 (1H, d 1J(P, H) ¼ 823.2 Hz, PH); 31P NMR (CD2Cl2)
To determine the impact of coordinated H-spirophosphoranes
on their catalytic activity, a series of rhodium(I) complexes with
ligands incorporating variety of peripheral groups were obtained.
d
ꢀ41.8 (d 1J(P, H) ¼ 823.2 Hz); IR nmax(nujol)/cmꢀ1 743vs, 949vs,
977vs, 1009m, 1145s n(CeOeP), 2374m, 2397m n(PeH), 3370s
n
(NeH).