Isolation, structural and spectroscopic investigations of complexes with tridentate [O,P,O] and [O,O,O] donor ligands

Article abstract of DOI:10.1039/b005693f

A phosphorus-containing potentially tridentate ligand bis(3,5-di-fer/-butyl-2-hydroxyphenyl)phenylphosphine H2L, 1, was prepared. 1 reacts directly in solution with aerial oxygen or hydrogen peroxide to form bis(3,5-di-/e/7butyl-2-hydroxyphenyl)phenylphos

Full text of DOI:10.1039/b005693f

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Isolation, structural and spectroscopic investigations of complexes
with tridentate [O,P,O] and [O,O,O] donor ligands
Rolf Siefert, Thomas Weyhermüller and Phalguni Chaudhuri*
Max-Planck-Institut für Strahlenchemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr,
Germany. E-mail: Chaudh@mpi-muelheim.mpg.de
Received 14th July 2000, Accepted 16th October 2000
First published as an Advance Article on the web 28th November 2000
A phosphorus-containing potentially tridentate ligand bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine
H2L, 1, was prepared. 1 reacts directly in solution with aerial oxygen or hydrogen peroxide to form bis(3,5-di-tert-
butyl-2-hydroxyphenyl)phenylphosphine oxide H2LO, 2. It yields complexes [NiII(HL)2] 3, [CoIII(OH2)(HL)(L)] 4,
[RhIIICl(H2L)(L)] 5, and [RhIII(HL)(L)(H2O)] 6 characterized by various physical techniques, including IR,
MS, UV-vis, 1H and 31P-{1H} NMR and electrochemical methods. The crystal structures of 3, 4 and 5 show
tridentate [O,P,O] and bidentate [O,P,OH] coordination of deprotonated 1 and the coordination geometry of
the metal centre. The structure of 2 reveals strong hydrogen bonding between the phenolic hydroxyl groups and
the O᎐P group in the solid state. That the ligand 2 produces a weak ligand field providing tridentate [O,O,O]
᎐
coordination sites has been evidenced by the structure and paramagnetism of [CoII2(LO)2(C2H5OH)3] 7.
Introduction
The current explosive development in the coordination
chemistry of phenol-containing ligands1 is mainly due to the
discovery of the widespread occurrence of tyrosine radicals
in metalloproteins involved in oxygen-dependent enzymatic
radical catalysis.2 Amongst the catalytically essential redox-
active amino acids, tyrosine-based radical enzymes are the best
᎐
ions. The ligands H2LP and H2LP᎐O are abbreviated as H2L and
characterized.
As part of an effort directed toward the development of
biologically inspired homogeneous catalysts3–5 for the aerial
oxidation of organic substrates like alcohols, amines, etc., we
are investigating the synthesis and reactivity of phenolate
complexes of the late transition metals, together with their one-
electron oxidized phenoxyl-radical complexes. Such phenoxyl-
radical complexes are rather rare. This is partly due to the fact
that the metal–phenolate bond to a late-transition metal ion
should be relatively weak. For the early transition metal ions
the metal–phenolate bonding is strengthened by π donation
from the lone pair of electrons on oxygen into an empty d
orbital on the metal, but for the late transition metal ions such
empty low-lying orbitals are not always available.
H2LO in the paper, respectively. In forthcoming papers we will
describe the catalytic properties of these complexes.
Results and discussion
One of the major advantages of homogeneous catalysis is the
possibility of fine tuning the catalyst by varying the ancillary
ligands. In this way, chemo-, regio-, and stereo-selectivity can
be directed toward the desired products. One way to achieve this
is by changing donor atoms in ligands, e.g. nitrogen, oxygen,
phosphorus, sulfur, etc.; and a more subtle way is to change
the substituents on the ligands, thereby influencing the
catalytic centre electronically and/or sterically. An additional
advantage of the ligands with heterodonor sets is that the
hardness/softness of the ligand can be adjusted so as to
accommodate variations in the hardness/softness property of
the metal ions.
Synthesis and characterization of the ligands
Unsubstituted bis(o-hydroxyphenyl)phenylphosphine contain-
∩ ∩
ing the donor atoms O
P O has been prepared for the first
time in 50% yield from ortho-bromophenol via reaction with
n-butyllithium followed by dichlorophenylphosphine.6 The
same ligand was described as an intermediate in the synthesis of
macrocyclic monophospha-crown ether ligands starting from
anisole; ortho-lithiated anisole was treated with dichloro-
phenylphosphine to afford the bis adduct of methyl phenyl
ether, which was subsequently demethylated with 48% HBr to
yield 62% of the desired phosphine.7 A third method in which
the methoxymethyl group was used to protect the phenolic
OH for the synthesis of unsubstituted bis(o-hydroxyphenyl)-
phenylphosphine with a yield of 67% is also known.8 On
the basis of our experience in reactions with 2,4-di-tert-
butylphenol, we realized that the first methodology, starting
from ortho-bromophenol, can be extended to the preparation
of sterically demanding phenolic derivatives with ortho- and
Since tridentate ligands which comprise three donor groups
like [O,X,O] where X = N or S have been found to form
complexes with copper() which are active catalysts for aerial
oxidation of alcohols and for oxidative C–C coupling reactions,
we have extended our study of the type of ligands H2LS 3 and
᎐
O
H2LN 4 and prepared the new ligands H2LP and H2LP᎐ to
investigate their coordination behaviours with transition metal
4656
J. Chem. Soc., Dalton Trans., 2000, 4656–4663
This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b005693f

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᎐
Fig. 1 An ORTEP12 diagram of the ligand H2LP᎐O 2.
Table 1 Selected bond lengths (Å) and angles (Њ) for H2LO, 2
P(1)–O(3)
P(1)–C(1)
P(1)–C(29)
P(1)–C(15)
1.514(2)
1.805(2)
1.807(2)
1.801(2)
C(16)–O(2)
C(2)–O(1)
1.364(3)
1.360(3)
O(3)–P(1)–C(29)
O(3)–P(1)–C(1)
O(3)–P(1)–C(15)
C(1)–P(1)–C(29)
C(29)–P(1)–C(15)
C(1)–P(1)–C(15)
110.27(11)
110.42(10)
110.32(10)
109.46(11)
109.60(11)
106.70(11)
P(1)–C(1)–C(2)
P(1)–C(1)–C(6)
P(1)–C(29)–C(34)
P(1)–C(29)–C(30)
P(1)–C(15)–C(16)
P(1)–C(15)–C(20)
120.5(2)
119.7(2)
124.6(2)
115.9(2)
119.1(2)
120.2(2)
of single crystals of 2, H2LO, performed at 100 K, reveals
strong hydrogen bonding between the phenolic hydroxyl groups
and the O᎐P group in the solid state (O2 ؒ ؒ ؒ O3 2.645 and
᎐
O3 ؒ ؒ ؒ O1 2.638 Å). The bond lengths and angles (Table 1) seem
reasonable and do not warrant special discussion.
Scheme 1
para-tert-butyl substituents. So we adapted a method using 2-
bromo-4,6-di-tert-butylphenol to our preparation of the ligand
H2LP, 1 (Scheme 1). A very similar method has been used by us
Molecular structure of compound 3, trans-(P,P)-[Ni(HL)2].
A single-crystal structure analysis of green complex 3 confirms
the trans configuration for the nickel() complex. An ORTEP
drawing of the molecule is displayed in Fig. 2, with selected
bond distances and angles provided in Table 2.
᎐
for preparation of H2LP᎐O, 2, by using dichlorophenylphosphine
oxide instead of dichlorophenylphosphine.
Ligand 2 can also be prepared by treating 1 with H2O2 and
purified by thin layer chromatography in very good yield (95%).
Ligand 2 without the tert-butyl groups, i.e. bis(o-hydroxy-
phenyl)phenylphosphine oxide, prepared in a completely differ-
ent way, has been reported.9 The ligands 1 and 2 are soluble in a
range of organic solvents and stable to hydrolysis and aerial
oxidation in the solid state, but 1 in solution is susceptible to
aerial oxidation to 2.
The geometry about the Ni atom is distorted square planar,
consisting of a trans arrangement defined by P(1), P(2) and the
phenoxide oxygen atoms O(2) and O(4). The deviation of the
geometry around the Ni(1) from square planar is evident from
the acute angles defined by the five-membered metallacycle
Ni(1)P(1)C(21)C(22)O(2) for which P(1)–Ni(1)–O(2) 86.5(1)Њ
and Ni(1)P(2)C(61)C(62)O(4) for which P(2)–Ni(1)–O(4)
87.0(1)Њ. Ring strain in 3 is also evidenced by angles of O(4)–
Ni(1)–O(2) 172.4(1)Њ and P(2)–Ni(1)–P(1) 161.1(1)Њ. Hydrogen
atoms attached to the phenol oxygens O(1) and O(3) have been
detected in the Fourier difference map and strong hydrogen
bonds can be envisaged between phenoxide oxygens O(4), O(2)
and phenol oxygens O(1), O(3), respectively, with the contacts
O(1) ؒ ؒ ؒ O(4) 2.781 Å and O(3) ؒ ؒ ؒ O(2) 2.715 Å. The Ni–P
bond lengths av. 2.183(1) Å and av. Ni–O(phenoxide) 1.862(2) Å
are consistent with other values found in the literature.11,13,14
Axial interactions involving the nickel centre and pendant
phenol groups are longer than the sum of the covalent radii15
of the two atoms (Ni(1) ؒ ؒ ؒ O(1) 3.374 and Ni(1) ؒ ؒ ؒ O(3)
3.480 Å), which is in accord with the diamagnetism of 3 both
in solution and the solid state.
1
1 and 2 were fully characterized by 31P, H, 13C NMR, mass
and IR spectroscopy and microanalysis together with their
melting point determinations. X-Ray structural data for 2 were
also obtained and are reported here. The IR bands due to
ν(OH), ν(C–H of t-Bu), ν(C᎐C), ν(P–Ph), ν(P᎐O) are readily
᎐
᎐
identified for free 1 and 2. ν(OH) of 1, which occurs as a strong
peak at around 3400 cmϪ1, serves as a useful indication that
complexation has occurred. There is a distinct bathochromic
shift typical for phenolates on coordination to transition metal
centres. For both ligands 1 and 2 the mass spectrometric parent
ion peaks at m/z = 518 for 1 and 534 for 2 were observed,
consistent with the elemental analysis. In the 31P-{1H} NMR
spectrum in CDCl3 a singlet at δ Ϫ49.9 for 1 was observed,
which is in the region expected for a trivalent phosphine.10,11
A singlet at δ ϩ52.6 was present in the spectrum of 2. Thus
there is a downfield shift of 102.5 ppm in the values of the 31P
chemical shift on oxidizing PIII in 1 to PV in 2.
Molecular structure of [Co(OH2)(HL)(L)]ؒ1.25THF 4.
Single crystals of brown fac-cis(P,P)-[Co(OH2)(HL)(L)] 4 were
obtained from tetrahydrofuran solution by slow evaporation.
The ORTEP diagram of 4 is shown in Fig. 3, while selected
bond distances and angles are summarized in Table 3.
Single crystal X-ray diffraction studies
Molecular structure of compound 2. Fig. 1 displays the
structure of compound 2 in the solid state. The X-ray analysis
The overall geometry around the cobalt atom Co(1) is best
described as a distorted facial octahedron with two cis phos-
J. Chem. Soc., Dalton Trans., 2000, 4656–4663
4657

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Fig. 2 Molecular structure of [NiII(HL)2] 3.
Fig.
3
Structure of the brown crystals of [CoIII(OH2)(HL)(L)]ؒ
1.25 THF 4. The THF molecules have been omitted for clarity.
Table 2 Selected bond distances (Å) and angles (Њ) for [Ni(HL)2], 3
Table 3 Selected bond lengths (Å) and angles (Њ) for [Co(OH2)(HL)-
(L)]ؒ1.25THF, 4
Ni(1)–O(4)
Ni(1)–O(2)
1.859(2)
1.866(2)
Ni(1)–P(1)
Ni(1)–P(2)
2.186(1)
2.180(1)
Co(1)–O(1)
Co(1)–O(4)
Co(1)–O(3)
Co(1)–O(10)
Co(1)–P(2)
Co(1)–P(1)
P(1)–C(2)
1.898(2)
1.922(2)
1.955(2)
2.049(3)
2.1416(10)
2.1849(11)
1.789(4)
1.819(3)
P(1)–C(15)
O(1)–C(1)
O(2)–C(16)
P(2)–C(49)
P(2)–C(35)
P(2)–C(63)
O(3)–C(36)
O(4)–C(50)
1.830(4)
1.332(4)
1.378(4)
1.783(3)
1.786(3)
1.801(3)
1.329(4)
1.346(4)
C(55)–P(2)–Ni(1)
C(61)–P(2)–Ni(1)
C(41)–P(2)–Ni(1)
C(55)–P(2)–C(61)
C(55)–P(2)–C(41)
C(61)–P(2)–C(41)
117.6(1)
99.4(1)
112.0(1)
110.8(2)
108.0(2)
108.5(2)
C(15)–P(1)–C(15)
C(1)–P(1)–Ni(1)
C(21)–P(1)–Ni(1)
C(15)–P(1)–C(1)
C(21)–P(1)–C(1)
C(21)–P(1)–C(15)
124.2(1)
109.1(1)
99.0(1)
105.7(2)
107.9(2)
110.1(2)
P(1)–C(29)
O(4)–Ni(1)–O(2)
O(2)–Ni(1)–P(2)
O(2)–Ni(1)–P(1)
172.4(1)
94.3(1)
86.5(1)
O(4)–Ni(1)–P(2)
O(4)–Ni(1)–P(1)
P(2)–Ni(1)–P(1)
87.0(1)
94.7(1)
161.1(1)
O(1)–Co(1)–O(4)
O(1)–Co(1)–O(3)
O(4)–Co(1)–O(3)
O(1)–Co(1)–O(10)
O(4)–Co(1)–O(10)
O(3)–Co(1)–O(10)
O(1)–Co(1)–P(2)
O(4)–Co(1)–P(2)
O(3)–Co(1)–P(2)
O(10)–Co(1)–P(2)
O(1)–Co(1)–P(1)
178.30(10)
87.91(11)
91.32(10)
93.82(11)
84.57(11)
81.83(10)
93.79(8)
87.60(7)
82.07(7)
161.90(9)
86.08(8)
O(4)–Co(1)–P(1)
O(3)–Co(1)–P(1)
O(10)–Co(1)–P(1)
P(2)–Co(1)–P(1)
C(2)–P(1)–C(29)
C(2)–P(1)–C(15)
C(29)–P(1)–C(15)
C(2)–P(1)–Co(1)
C(29)–P(1)–Co(1)
C(15)–P(1)–Co(1)
94.63(7)
173.56(8)
96.26(8)
100.62(4)
108.9(2)
108.2(2)
103.5(2)
99.49(12)
121.80(11)
114.35(12)
∩ ∩
O]2Ϫ
P ,
phine ligands 1. The doubly deprotonated ligand, [O
is bound in a facial manner, the meridional mode being steri-
cally unavailable. The second phosphine ligand is present in the
monoprotonated form [HO
∩ ∩
P
O]Ϫ. It coordinates in a biden-
tate fashion with a dangling phenolic OH group, O(2), such that
its P(1) donor is cis to the P(2) in [OPO]2Ϫ. The sixth coordin-
ation site is occupied by a water molecule, presumably derived
from moisture present in trace amounts in the solvent. A hydro-
gen bond is present between the dangling non-coordinated O(2)
and the cobalt-bound phenolate O(4) with the O(2) ؒ ؒ ؒ O(4)
distance of 2.650 Å. The Co(1) atom is 0.137 Å out of the
equatorial plane formed by the donors O(4), P(2), O(1) and
O(10). All the phenyl rings attached to the P atoms are found to
be planar, indicating that upon coordination the aromaticity of
the phenyl rings is retained.
The cobalt–water bond, Co(1)–O(10) at 2.049(3) Å, is in the
range of comparable bond lengths reported16,17 and signifi-
cantly longer than the Co–O(phenolate) bond lengths, average
1.925(2) Å. The Co(1)–P(1) bond length at 2.185(1) Å is some-
what longer than the Co(1)–P(2) bond at 2.142(1) Å, indicating
that the double-phenolato anchored P donor in tridentate
[OPO]2Ϫ is bound to the cobalt centre significantly more closely
than the single-phenolato anchored P atom in bidentate
[HOPO]Ϫ and these bond distances belong to the lower range of
CoIII–P bond lengths known.17 The strengthening of the Co–P
bond with increased anchoring can be explained by the syn-
ergistic electronic effect (σ ϩ π) as well as reduced steric
effects18 due to reorientation and bonding of the anchoring
arms. The orientation of the o-oxyphenyl rings is coplanar or
perpendicular to the equatorial plane, possibly locating the P
atom in a position that favours transferring π donation from the
metal to the o-oxyphenyl rings. Thus, the steric repulsion
decreases and the π back bonding and σ bonding increases in
the order of [HOPO]Ϫ, [OPO]2Ϫ, resulting in Co–P distances
that decrease in the same order.
86.08(8), P(2)–Co(1)–O(3) 82.07(7) and P(2)–Co(1)–O(4)
87.60(7)Њ. While the P(1)–Co(1)–O(3) angle is 173.56(8)Њ, the
corresponding P(2)–Co(1)–O(10) angle at 161.90(9)Њ deviates
remarkably from linearity.
Although all the C–O bond lengths except one found in com-
plex 4 are unremarkable (average 1.336(4) Å), the C–O bond
length in the dangling phenol group is significantly longer,
C(16)–O(2) 1.378(4) Å. The Co–O and Co–P bond lengths are
in accord with those of a low-spin d6 cobalt() complex.17,19,20
Molecular structure of [RhCl(H2L)(L)]ؒH2O 5. Orange crys-
tals of 5, fac-cis-(P,P)-[RhCl(H2L)(L)]ؒH2O were easily grown
to suitable size from a pentane solution. The crystal structure of
5 (Fig. 4, Table 4) shows that two phosphine ligands H2LP are
coordinated to Rh(1) via two phenolate, O(1) and O(2), two
phosphorus P(1) and P(2) and one phenol O(4) groups, so that
one of the ligands acts as a tridentate chelate and the second
with a dangling phenolic OH group, O(3), is present in the
protonated phenol form O(4); thus the second ligand coordin-
ates in a bidentate fashion via one phosphorus P(2) and one
phenol oxygen O(4). The sixth coordination site of the RhIII is
occupied by an axial chloride ion, Cl(1). The overall geometry
around the rhodium atom is thus best described as a highly
distorted facial octahedron with cis position of the phosphorus
atoms, P(1) and P(2). The bond lengths and angles seem
reasonable17,21 and do not warrant any special discussion.
The distortion from octahedral geometry is mainly caused by
the acute bite angles between the phenolate O atom and the P
atom of the [OPO]2Ϫ and [HOPO]Ϫ ligands: P(1)–Co(1)–O(1)
Molecular structure of [Co2(LO)2(C2H5OH)3]ؒ2C2H5OH 7. A
solid mixture of deep blue and colourless crystals was obtained
after recrystallization. A blue crystal of complex 7 was used
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J. Chem. Soc., Dalton Trans., 2000, 4656–4663

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Fig. 5 A perspective view of the neutral complex [CoII2(LO)2(C2H5-
OH)3]ؒ2C2H5OH 7. Ethanol solvent of crystallization is not shown.
Fig.
4
An ORTEP representation of [RhIIICl(H2L)(L)]ؒH2O 5.
Hydrogen bonding involving the water of crystallization is also shown.
Table 5 Selected bond lengths (Å) and angles (Њ) for [CoII2(LO)2-
(C2H5OH)3]ؒ2C2H5OH, 7
Table 4 Selected bond lengths (Å) and angles (Њ) for [RhCl(H2L)-
(L)]ؒH2O, 5
Co(1)–O(2)
Co(1)–O(80)
Co(1)–O(1)
Co(2)–O(6)
Co(2)–O(70)
Co(2)–O(4)
P(1)–O(1)
P(1)–C(15)
P(2)–O(4)
P(2)–C(49)
O(2)–C(2)
1.969(3)
2.109(3)
2.178(3)
1.977(3)
2.101(3)
2.146(3)
1.536(3)
1.792(5)
1.533(3)
1.782(4)
1.337(5)
1.347(5)
Co(1)–O(5)
Co(1)–O(4)
Co(1)–O(9)
Co(2)–O(3)
Co(2)–O(1)
Co(2)–O(9)
P(1)–C(1)
P(1)–C(29)
P(2)–C(35)
P(2)–C(63)
O(3)–C(16)
O(6)–C(50)
2.023(3)
2.115(3)
2.332(3)
2.015(3)
2.120(3)
2.369(3)
1.780(4)
1.803(4)
1.780(4)
1.795(5)
1.344(5)
1.328(5)
Rh(1)–O(2)
Rh(1)–O(1)
Rh(1)–P(1)
Rh(1)–O(4)
Rh(1)–P(2)
Rh(1)–Cl(1)
P(1)–C(15)
P(1)–C(2)
2.0108(14)
2.0540(13)
2.1814(6)
2.2506(14)
2.2893(6)
2.3733(6)
1.788(2)
P(1)–C(29)
P(2)–C(49)
P(2)–C(63)
P(2)–C(35)
O(1)–C(1)
O(2)–C(16)
O(3)–C(36)
O(4)–C(50)
1.816(2)
1.816(2)
1.820(2)
1.832(2)
1.320(2)
1.336(2)
1.390(2)
1.412(2)
1.804(2)
O(2)–Rh(1)–O(1)
O(2)–Rh(1)–P(1)
O(1)–Rh(1)–P(1)
O(2)–Rh(1)–O(4)
O(1)–Rh(1)–O(4)
P(1)–Rh(1)–O(4)
O(2)–Rh(1)–P(2)
O(1)–Rh(1)–P(2)
P(1)–Rh(1)–P(2)
O(4)–Rh(1)–P(2)
O(2)–Rh(1)–Cl(1)
O(1)–Rh(1)–Cl(1)
P(1)–Rh(1)–Cl(1)
O(4)–Rh(1)–Cl(1)
P(2)–Rh(1)–Cl(1)
87.27(5)
85.88(4)
83.47(4)
86.69(6)
94.12(5)
172.29(4)
86.74(4)
170.20(4)
103.82(2)
77.80(4)
174.29(4)
87.03(4)
93.42(2)
93.76(4)
98.92(2)
C(15)–P(1)–C(2)
C(15)–P(1)–C(29)
C(2)–P(1)–C(29)
C(15)–P(1)–Rh(1)
C(2)–P(1)–Rh(1)
C(29)–P(1)–Rh(1)
C(49)–P(2)–C(63)
C(49)–P(2)–C(35)
C(63)–P(2)–C(35)
C(49)–P(2)–Rh(1)
C(63)–P(2)–Rh(1)
C(35)–P(2)–Rh(1)
C(1)–O(1)–Rh(1)
C(16)–O(2)–Rh(1)
C(50)–O(4)–Rh(1)
111.20(9)
111.87(10)
108.40(10)
100.21(7)
101.20(7)
123.25(7)
106.00(9)
102.20(10)
109.85(9)
98.70(7)
120.09(7)
116.90(6)
117.72(13)
117.36(13)
112.69(11)
O(5)–C(36)
O(2)–Co(1)–O(5)
O(5)–Co(1)–O(80)
O(5)–Co(1)–O(4)
O(2)–Co(1)–O(1)
O(80)–Co(1)–O(1)
O(2)–Co(1)–O(9)
O(80)–Co(1)–O(9)
O(1)–Co(1)–O(9)
O(6)–Co(2)–O(70)
O(6)–Co(2)–O(1)
O(70)–Co(2)–O(1)
O(3)–Co(2)–O(4)
O(1)–Co(2)–O(4)
O(3)–Co(2)–O(9)
O(1)–Co(2)–O(9)
P(1)–O(1)–Co(2)
Co(2)–O(1)–Co(1)
C(16)–O(3)–Co(2)
P(2)–O(4)–Co(2)
C(36)–O(5)–Co(1)
111.07(12)
90.41(12)
89.70(11)
86.73(12)
93.90(11)
85.73(12)
172.90(11)
79.14(10)
95.50(13)
156.84(12)
96.54(12)
161.18(11)
72.17(11)
95.75(12)
79.45(10)
120.3(2)
O(2)–Co(1)–O(80)
O(2)–Co(1)–O(4)
O(80)–Co(1)–O(4)
O(5)–Co(1)–O(1)
O(4)–Co(1)–O(1)
O(5)–Co(1)–O(9)
O(4)–Co(1)–O(9)
O(6)–Co(2)–O(3)
O(3)–Co(2)–O(70)
O(3)–Co(2)–O(1)
O(6)–Co(2)–O(4)
O(70)–Co(2)–O(4)
O(6)–Co(2)–O(9)
O(70)–Co(2)–O(9)
O(4)–Co(2)–O(9)
P(1)–O(1)–Co(1)
C(2)–O(2)–Co(1)
P(2)–O(4)–Co(1)
Co(1)–O(4)–Co(2)
C(50)–O(6)–Co(2)
95.37(13)
155.56(12)
97.28(13)
161.23(11)
71.64(11)
95.76(11)
79.27(11)
109.70(12)
93.04(13)
89.34(11)
87.61(11)
92.52(12)
85.44(11)
170.28(12)
77.84(11)
120.6(2)
for the diffraction study. As 7 was not obtained in pure form
even after several recrystallizations, spectroscopic studies
could not be performed. Hence only the structure is discussed
in brief here. To the best of our knowledge there are no reports
91.56(10)
121.1(2)
119.6(2)
125.8(3)
119.1(2)
92.61(11)
124.1(3)
᎐
involving only the ligand H2LP᎐
.
O
120.1(3)
The molecular geometry and the atomic labelling scheme are
shown in Fig. 5. The structure shows that a (µ-ethanol)bis(µ-
phosphoryl)dicobalt() complex has indeed been formed in
such a way that a confacial-bioctahedral geometry containing
to the bridging oxygen atom O(9) of an ethanol molecule. The
largest deviation from idealized 90Њ interbond angles is 21.1Њ,
which is obtained for O(2)–Co(1)–O(5). Distortion of the
cobalt centres from octahedral geometry is evident from the
deviation from linearity for the O(2)–Co(1)–O(4) and O(6)–
᎐
CoII as central atom is present in the lattice. Ligand 2, H2LP᎐O, is
coordinated to cobalt via two phenolate and one P᎐O group so
᎐
that it acts as a tridentate chelate via all three oxygen atoms.
Three oxygen atoms (two from the phosphoryl ligands O(1) and
O(4) and one from an ethanol molecule O(9)) form the bridging
Co(2)–O(1) angles, av. 156.2Њ, involving the P᎐O and phenoxide
᎐
groups. The P(1)–O(1) and P(2)–O(4) bond lengths (1.53 Å) are
᎐
slightly longer than that in free H2LP᎐O, 2 (1.51 Å) (Table 1). The
atoms between two cobalt centres Co(1) and Co(2). Two phen-
᎐
olate oxygens O(2) and O(3) belonging to the ligand (LP᎐
)
O
2Ϫ
bond lengths are consistent with a d7 high-spin electron con-
figuration of the cobalt() centres22 and accordingly 7 exhibits
paramagnetism, detected by its 1H NMR spectrum.
containing the phosphorus atom P(1) are bonded to two differ-
ent cobalt centres, to Co(1) and Co(2), respectively. The
᎐
coordination of the second (LP᎐
)
ligand is similar. Each of
O
2Ϫ
the cobalt centres is additionally bonded to an ethanol mol-
ecule. Thus the cobalt coordination geometry is distorted
octahedral with six oxygen atoms. The bond lengths and angles
Spectroscopic and electrochemical characterization of complexes
Selected IR data for complexes 3–6 are given in the Experi-
mental section. The peaks which convey most information are
those due to ν(OH) which occur as broad peaks in the region
3143–3250 cmϪ1. For free 1 there is a strong sharp peak at 3387
cmϪ1 present before complexation. There are strong peaks in
the region 2960–2760 cmϪ1 due to the t-butyl groups together
᎐
involving the ligand LP᎐O seem reasonable, e.g. the average Co–
O–Co angle is 92.1Њ. Selected bond distances and angles are
listed in Table 5. The Co(1) ؒ ؒ ؒ Co(2) separation is 3.081 Å. The
Co–O bond lengths can clearly be divided into two groups of
ca. 2.0–2.15 and ca. 2.3 Å, the latter interestingly belonging
J. Chem. Soc., Dalton Trans., 2000, 4656–4663
4659

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with the other ν(C–H) and ν(C᎐C) and ν(C–O) vibrations found
᎐
in the normal range for these types of linkages.23
The optical spectra for complexes 3–6 have been measured in
the range 200–1000 nm in dry hexane to avoid any hydrolysis.
They are dominated by charge transfer bands, as judged by the
high absorption coefficients of the bands.24 The bands at 646
nm (ε = 520 MϪ1 cmϪ1) for 3, 594(sh) for 4 and 405(640) for 5
are ascribed to the d–d transitions of the metal.
Mass spectrometry in the EI and ESI-positive mode
unambiguously demonstrates the nuclearity of all the com-
plexes examined and also provides identification of the metal
centres, and, in general, the compositions are consistent with
the elemental analyses. It seems that 3–6 are not fragile and can
withstand the conditions of EIMS ionization. In the EI mass
spectrum of 3 the parent ion peak is observed centred around
m/z 1092 with the expected isotope distribution pattern as
is confirmed by its simulation. A relatively weaker peak at m/z
517 with an abundance of ≈30% corresponding to the mono-
deprotonated parent ligand C34H46PO2 is also observed. Inter-
estingly, the EIMS for the cobalt-containing 4 is very similar
to that for 3 with the molecule ion peak centred also around
m/z 1092 (100%), but with a different isotope pattern, as
expected, confirming the Co:ligand ratio of 1:2, which is
consistent with the elemental analysis.
Mass spectrometry in ESI-positive mode in CH3OH has
proved to be a very useful tool for characterization of the
rhodium complex 5. The two intense peaks centred around m/z
1173 (28%) and 1137 (100%) correspond to the molecular ion
peak and the same ion that has lost one chlorine atom. Thus,
that 5 contains two ligands and a chlorine atom coordinated to
a rhodium atom is without doubt.
Fig. 6 Cyclic voltammograms of complex 4 in CH2Cl2 at different
scan rates (50–400 mV sϪ1).
a glassy carbon working electrode at different scan rates. All
redox potentials in the following are referenced in volts versus
ferrocenium–ferrocene. Two irreversible oxidation waves are
detected in the potential range ϩ1.5 to 0.0 V at E1ox = ϩ0.860 V
and E2ox = ϩ1.20 V for the ligand 1 in the presence of t-BuOK.
These are assignable to phenoxyl radical formation from the
phenolate ligand.
Two irreversible electron-transfer waves are detected in the
potential range ϩ1.5 to 0.0 V at E1ox = ϩ0.386 V and
E2ox = 0.878 V for complex 3. Both oxidative processes can
tentatively be assigned to the phenolate ligand rather than
metal-centred electron-transfer waves. This assignment is
supported by comparison with the CV of 4. Two consecutive
quasi-reversible steps of oxidation at E11/2 = ϩ0.250 V and
E21/2 = ϩ0.800 V are detected for 4, as depicted in Fig. 6. Thus
the following redox scheme, involving oxidation of the ligand
(phenolate/phenoxyl) in 4, is proposed:
The mass spectrum in EI mode for complex 6 exhibits only a
few peaks and the highest peak with an abundance of 100%
is in conformity with [RhL2H]ϩ, C68H91O4P2Rhϩ, thus confirm-
ing the formulation as a molecule with a coordinated water
molecule, which is necessary to make rhodium six-coordinated.
No chlorine atom was observed in the mass spectrometry.
Hence 6 is the rhodium analogue of 4 and possesses a similar
structure, as elucidated by X-ray diffraction.
E2
1/2
III
CoIII(OH2)(HL)(L)
Co (OH2)(HL)(L )
ؒ
The chemical shifts in the 1H NMR spectra of the complexes
are given in the Experimental section. Owing to the overlapping
of multiplets particularly in the aromatic hydrogen region
(δ 5.0–8.5) full assignments were not attempted; nevertheless
the spectra were still useful in verifying the similarities amongst
3–6. On the other hand, 31P-{1H} NMR spectroscopy played a
crucial role in both identifying and determining the purity of
E1
1/2
III
ؒ
ؒ
Co (OH2)(HL )(L )
The cyclic voltammetric behaviour of 5 shows one reversible
one-electron oxidation at ϩ0.36 V vs. Fcϩ–Fc, tentatively
assigned to the phenolate–phenoxyl radical couple. An irrevers-
ible oxidation at ϩ1.02 V is also attributable to the ligand
oxidation.
the complexes (absence of the P᎐O group).
᎐
The 31P-{1H} NMR spectra of complex 3 in the temperature
range 223–323 K show two singlets, suggesting the presence
of two isomers in solution. The isomerism is consistent with
the two possible orientations syn and anti of the phenyl rings
attached to the phosphorus atoms P(1) and P(2). Thus the solid
state structure of 3 containing two equivalent phosphorus
atoms as determined by X-ray diffraction differs from its solu-
tion structure. Upon coordination of 1 to the Ni an increase in
chemical shift is observed from that of δ Ϫ49.9 for the “free”
ligand to δ ϩ10.2 and ϩ6.9, as is generally seen for most phos-
phines due to the resulting deshielding effect.25 For 4 and 6
singlets with consistent and noticeable shifts to lower fields on
complexation to δ 56.6 and 60.9, respectively, are observed.
This behaviour is comparable to that seen previously.13 For 5
four sharp doublets showing couplings to both phosphorus and
Interestingly, the CV of complex 6, which is the rhodium
analogue of 4, is similar to that of 4 and exhibits two con-
secutive quasi-reversible one-electron oxidation transfer
waves detectable at E11/2 = ϩ0.279 V and E21/2 = ϩ0.836 V vs.
Fcϩ–Fc which are assigned to phenolate/phenoxyl radical
complexes.
Experimental
Reactions were carried out in dried apparatus under a dry, inert
atmosphere of argon. All chemicals were of reagent grade used
as received. Solvents were dried prior to use when necessary
with appropriate reagents.
Infrared spectra were recorded as KBr pellets in the range
4000–400 cmϪ1 on a Perkin-Elmer 1720X FT-IR spectrometer.
Cyclic voltammograms, square-wave voltammograms, and
coulometric experiments were performed on EG & G equip-
ment (potentiostat/galvanostat model 273A). Potentials were
referenced vs. the Ag–AgNO3 electrode, and ferrocene was
added as internal standard. Mass spectra were obtained with
either a Finnigan MAT 8200 (electron ionization, EIMS) or a
MAT 95 (electrospray ESI-MS and FAB-MS) instrument,
NMR spectra on a Bruker DRX 400 instrument. All 1H
1
rhodium atoms, with J(PRh) couplings in the range 124–126
Hz and 2J(PP) 20 Hz are observed. These findings are consistent
with two non-equivalent phosphorus donors being cis to one
another.8 Thus the solid state cis(P,P) structure of 5, as revealed
by X-ray diffraction, also prevails in solution.
Cyclic voltammetry (CV)26 of complexes 3–6 was performed
at ambient temperature in CH2Cl2 containing 0.1 M tetrabutyl-
ammonium hexafluorophosphate as supporting electrolyte at
4660
J. Chem. Soc., Dalton Trans., 2000, 4656–4663

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chemical shifts are reported in ppm relative to tetramethylsilane
and 31P-{1H} (162 MHz) chemical shifts relative to external
orthophosphoric acid (85%).
138.2, 132.7, 131.9, 129.3, 128.6, 126.0, 110.2, 109.2, 35.4, 34.2,
31.3 and 29.5. IR (KBr disk) (cmϪ1): 3097m (br) (νO-H), 2962–
2871s (νC-H), 1590m (sh) (νC C), 1437, 1429s (νP-Ph) and 1249s
᎐
᎐
(νP O).27
᎐
᎐
Preparations
Method B. A solution of H2L 1 (50 mg; 0.096 mmol) in
diethyl ether was treated with a solution of H2O2–ether (1:10).
Preparative TLC (hexane–ethyl acetate 30:1 eluent) was used to
obtain 49 mg (95%) of the desired product.
2-Bromo-4,6-di-tert-butylphenol. To a solution of 461 g (2.2
mol) of 2,4-di-tert-butylphenol in 900 cm3 of CCl4 at room
temperature was added very slowly dropwise 122 cm3 of Br2
dissolved in 200 cm3 of CCl4. The resulting homogeneous faint
yellow solution was stirred for 24 h at 80 ЊC then extracted
first with 10% NaHSO4 (2 × 200 cm3) then with water (4 × 400
cm3) and the organic phase dried over anhydrous MgSO4. The
dry CCl4 layer was concentrated in vacuo and cooled overnight
at 4 ЊC to yield 380 g of the product (60%), mp 57–58 ЊC. IR
(KBr disk) (cmϪ1): 3509 sharp (strong, νO-H), 2997–2865s (sh)
[NiII(HL)2], 3. To degassed absolute ethanol (10 cm3)
anhydrous NiCl2 (32.4 mg; 0.25 mmol) was added and the
mixture stirred at room temperature for 12 h until a clear solu-
tion was obtained. On addition of H2L (259 mg; 0.5 mmol)
a brown solid formed, which was removed by filtration and
washed several times with ethanol. Recrystallization of this
material from diethyl ether on cooling produced yellow-green
single crystals of [Ni(HL)2]. Yield: 120 mg (44%). Calc. for
C68H92NiO4P2: C, 74.65; H, 8.48; P, 5.66. Found: C, 74.8; H, 8.4;
P, 5.8%. EIMS: m/z = 1092 [Mϩ]. 31P NMR (CDCl3): δ 10.2 (s,
2P) and 6.9 (s, 2P). 1H NMR (CDCl3): δ 9.12 (s, 2H, OH), 8.74
(s, 2H, OH), 7.79–6.69 (m, 18H), 1.22 (s, 36H, t-Bu), 1.17 (s,
36H, t-Bu), 1.14 (s, 36H, t-Bu) and 0.91 (s, 36H, t-Bu). IR (KBr
disk) (cmϪ1): 3180br (νOH). UV-vis in hexane: λmax/nm (ε/MϪ1
cmϪ1) 646 (520), 457 (4570), 429 (6090) and 304 (25950). Cyclic
voltammetry (CH2Cl2): E11/2 = 386, E21/2 = 878 mV.
(t-butyl, νC-H). EIMS: m/z = 284 (Mϩ, 21) and 271 (100%). H
NMR (CDCl3): δ 7.34–7.24 (m, 2H), 5.65 (s, 1H), 1.42 (s, 9H)
and 1.29 (s, 9H). 13C NMR (CDCl3): δ 148.0, 143.7, 136.7,
126.3, 123.7, 111.9, 35.8, 35.6, 31.7, 31.5, 29.7 and 29.4.
1
Bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine, H2L
1. To a solution of 2-bromo-4,6-di-tert-butylphenol (4.2 g,
14.7 mmol) in absolute diethyl ether (25 cm3) at Ϫ60 ЊC
was added dropwise within half an hour a 1.6 M solution of
n-butyllithium (18.4 cm3, 29.4 mmol) in hexane. The resulting
pale yellow solution was stirred for 8 h, during which time it
warmed to room temperature. After it was cooled again to
Ϫ50 ЊC, PhPCl2 (1 cm3, 7.37 mmol) dissolved in 10 cm3 of ether
was added dropwise (90 min). The reaction mixture was stirred
overnight at 10 ЊC and for 2 h at room temperature and then the
suspension of LiCl was removed by filtration under argon. The
solution was extracted as fast as possible with a vigorously
oxygen-free 0.1 M solution of NaH2PO4 (2 × 20 cm3) followed
by water. The Et2O phase was dried over anhydrous sodium
sulfate (2 h) and then concentrated to a white solid. Crystalliz-
ation by cooling from acetonitrile yielded analytically pure col-
ourless crystals of H2L. Yield: 1.53 g (40%). mp 111–112 ЊC
(518.71 g molϪ1). Calc. (found) for C34H47O2P: C, 78.73 (78.6);
[CoIII(OH2)(HL)(L)]ؒ1.25THF, 4. Anhydrous CoCl2 (50.1
mg; 0.386 mmol) was dissolved in degassed dry THF (15 cm3).
Addition of solid H2L (200 mg; 0.386 mmol) yielded a blue
reaction mixture, which with NEt3 (150 µL; 1.08 mmol)
changed to deep green. The resulting solution was stirred in the
presence of air for 7 days and on concentration yielded a micro-
crystalline solid, which was collected by filtration and washed
with cold ethanol. Recrystallization from THF at room temper-
ature gave 115 mg (25%) of X-ray quality brown crystals. Calc.
for C68H93CoO5P2ؒ1.25 THF: C, 73.0; H, 8.60; Co, 4.90. Found:
C, 73.4; H, 8.4; Co, 5.0%. EIMS: m/z = 1092 [Mϩ]. 31P NMR
(CDCl3): δ 56.6 (s, 2P). 1H NMR (CDCl3): δ 7.48–6.78 (m, 18H),
4.22 (s, 1H, OH), 1.59 (s, 18H, t-Bu), 1.16 (s, 18H, t-Bu), 1.11 (s,
18H, t-Bu) and 1.02 (s, 18H, t-Bu). IR (KBr disk) (cmϪ1):
3190br (νOH). UV-vis in hexane: λmax/nm (ε/MϪ1 cmϪ1) 594 (sh)
and 446 (1100). Cyclic voltammetry (CH2Cl2, glassy carbon
electrode, room temp.): E11/2 = 250 (rev.), E21/2 = 800 mV (rev.).
H, 9.13 (9.1); P, 5.97 (6.0)%. EIMS: m/z = 518 [Mϩ, 100%]; 31
P
NMR (CDCl3), δ Ϫ49.9 (s, 1P). 1H NMR (CDCl3): δ 7.36–7.24
(m, 7H), 6.90 (dd, 3J(HH) = 6.6, 4J(HH) = 2.5, 2H), 6.28 (s,
J 8.4 Hz, 2H, OH), 1.42 (s, 9H, t-Bu) and 1.16 (s, 9H, t-Bu). 13
C
NMR (CDCl3): δ 155.7, 155.4, 142.7, 135.7, 132.9, 132.6, 128.9,
128.6, 126.4, 118.3, 35.1, 34.4, 31.4 and 29.7. IR (KBr disk)
(cmϪ1): 3492w, 3387s (νOH), 2961, 2908, 2780s (νC-H), 1578m
[RhIIICl(H2L)(L)]ؒH2O, 5. To a suspension of RhCl3ؒnH2O
containing 37.9% Rh (68 mg; 0.25 mmol) in dry THF (10 cm3)
was added dropwise a solution of H2L (259 mg; 0.5 mmol) in
THF (5 cm3). The resulting red solution was concentrated on a
rotary evaporator (to ≈1 cm3), after which methanol (10 cm3)
was added. The solvent was removed again in vacuo and the
orange solid filtered off. The solid dissolved in CH2Cl2 was
purified by preparative TLC using CH2Cl2–hexane (1:2) as
eluent. X-Ray quality orange crystals were obtained by cooling
from a pentane solution. Yield: 197 mg (66%). Calc. for
C68H94ClO5P2Rh: C, 68.53; H, 7.95; Cl, 3.0; P, 5.19. Found: C,
70.89; H, 7.80; Cl, 2.5; P, 5.5%. ESI-MS: m/z = 1173 [Mϩ]. 31P
NMR (CDCl3): δ 72.7 (dd, 1J(PRh) = 126, 2J(PP) = 20, 1P) and
32.0 (dd, 1J(PRh) = 124, 2J(PP) = 20 Hz, 1P). 1H NMR
(CDCl3): δ 7.53–6.44 (m, 18H), 5.56 (s, 2H, OH), 4.16 (s, 2H,
2H2O), 1.63 (s, 9H, t-Bu), 1.42 (s, 9H, t-Bu), 1.15 (s, 9H, t-Bu),
1.15 (s, 18H, t-Bu), 1.10 (s, 9H, t-Bu), 0.98 (s, 9H, t-Bu) and
0.97 (s, 9H, t-Bu). IR (KBr disk) (cmϪ1): 3250 (br, OH). UV-vis
in hexane: λmax/nm (ε/MϪ1 cmϪ1) 405 (640). Cyclic voltammetry
(CH2Cl2, glassy carbon electrode, room temp.): E11/2 = 360
(rev.), E2 ≈ 1020 mV (irrev.).
(νC C), 1438s (νP-Ph). Cyclic voltammogram (glassy carbon, room
᎐
᎐
temp., CH2Cl2): E1ox ≈ 860 mV (irrev.).
Bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine(V)
oxide, H2LO 2. Method A. 100 cm3 of n-butyllithium (159
mmol) (1.6 M n-hexane solution) were added dropwise to a
solution of 2-bromo-4,6-di-tert-butylphenol (22.7 g, 79.5
mmol) in 200 cm3 of diethyl ether and stirred overnight at room
temperature. The resulting yellow solution cooled at 0 ЊC was
treated dropwise with dichlorophenylphosphine oxide (5.5 cm3)
dissolved in 50 cm3 of diethyl ether. The reaction mixture was
stirred overnight at room temperature and then the suspension
of lithium halide was removed by filtration. The ether phase
was washed once with 30 cm3 of 1 M NaH2PO4 and 200 cm3 of
water, followed by 200 cm3 of 1 M NaH2PO4. The organic layer
was dried over magnesium sulfate and then the solvent was
distilled off under low pressure to yield 10 g (48%) of a white
solid; X-ray quality crystals were obtained from a solution in
ether–pentane by evaporation. mp 194–196 ЊC. Calc. (found)
for C34H47O3P: C, 76.4 (76.6); H, 8.9 (8.8); P, 5.8 (5.7)%. EIMS:
m/z 534 [Mϩ, 100] and 519 ([H2LO Ϫ O]ϩ, 28%). 31P NMR
1
(CDCl3): δ ϩ52.6 (s, 1P). H NMR (CDCl3): δ 10.62 (s, 2H,
[RhIII(HL)(L)]ؒH2O, 6. A solution of [RhCl(H2L)(L)]ؒH2O
(150 mg; 0.126 mmol) in CH2Cl2–pentane (1:1) was stirred for
7 d at 20 ЊC. Using preparative thick layer chromatography
OH), 7.61–7.44 (m, 7H) and 6.85 (dd, 3J(HH) = 14.2,
4J(HH) = 2.4 Hz, 2H). 13C NMR (CDCl3): δ 160.5, 140.6,
J. Chem. Soc., Dalton Trans., 2000, 4656–4663
4661

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Table 6 Crystallographic data and structure refinement for complexes 2, 3, 4, 5 and 7
2
3
4
5
7
Empirical formula
C34H47O3P
C68H92NiO4P2
C68H93CoO5P2ؒ
1.25THF
1201.42
C68H92ClO4P2Rhؒ
H2O
1191.73
C74H108Co2O9P2ؒ
3C2H5OH
1422.5
Formula weight
T/K
534.69
100(2)
1094.07
100(2)
100(2)
100(2)
100(2)
Crystal system
Space group
a/Å; α/Њ
Monoclinic
P21/n
10.153(1)
21.418(3); 97.80(2)
14.176(2)
3054.1(7); 4
0.122
Triclinic
P1
13.432(1); 89.99(2)
15.174(2); 79.00(2)
17.048(2); 72.07(2)
3238.8(6); 2
0.393
Monoclinic
P21/c
14.428(2)
17.910(3); 95.61(2)
27.350(5)
7033(2); 4
0.338
Monoclinic
P21/n
13.4953(9)
19.8157(12); 92.23(2)
24.397(2)
6519.3(8); 4
0.398
Triclinic
P1
15.036(2); 99.19(2)
16.294(3); 102.99(2)
18.969(3); 108.59(2)
4155.3(12); 2
0.490
¯
¯
b/Å; β/Њ
c/Å; γ/Њ
V/Å3; Z
µ/mmϪ1
Reflections collected
No. unique data [I >2σ(I)]
Data/restraints/parameters
Final R1, wR2 [I > 2σ(I)]
(all data)
10765
24941
10960/6917
10960/0/675
0.0589, 0.119
0.1152, 0.141
36148
39050
33548
14060/9657
14060/2/847
0.0691, 0.164
0.1266, 0.198
4630/3658
4630/0/349
0.0478, 0.11
0.0648, 0.125
12335/7002
12335/33/764
0.0663, 0.16
0.1306, 0.190
14756/10344
14756/1/704
0.0378, 0.081
0.0679, 0.089
with an eluent of CH2Cl2–hexane (1:2) a yellow complex with
a yield of 134 mg was isolated. Square-form yellow crystals,
which became dull very quickly, were obtained by crystalliz-
ation from pentane. Calc. for C68H93O5P2Rh: C, 70.69; H, 8.11;
P, 5.36. Found: C, 70.8; H, 8.1; P, 5.1%. ESI-MS: m/z = 1137
References
1 For example: J. A. Halfen, B. A. Jazdzewski, S. Mahapatra, L. M.
Berreau, E. C. Wilkinson, L. Que, Jr. and W. B. Tolman, J. Am.
Chem. Soc., 1997, 119, 8217; Y. Wang and T. D. P. Stack, J. Am.
Chem. Soc., 1996, 118, 13097; D. Zurita, I. Gautier-Luneau,
S. Menage, J. L. Pierre and E. Saint-Aman, J. Biol. Inorg. Chem.,
1997, 2, 46; E. Bill, J. Müller, T. Weyhermüller and K. Wieghardt,
Inorg. Chem., 1999, 38, 5795 and references therein; M. A. Halcrow,
L. M. Lindy Chia, X. Liu, E. J. L. McInnes, L. J. Yellowlees, F. E.
Mabbs, I. J. Scowen, M. McPartlin and J. E. Davies, J. Chem. Soc.,
Dalton Trans., 1999, 1753; S. Itoh, S. Takayama, R. Arakawa,
A. Furuta, M. Komatsu, A. Ishida, S. Takamuku and S. Fukuzumi,
Inorg. Chem., 1997, 36, 1407; K. Yamato, T. Inada, M. Doe,
A. Ichimura, T. Takui, Y. Kojima, T. Kikunaga, S. Nakamura,
N. Yanagihara, T. Onaka and S. Yano, Bull. Chem. Soc. Jpn., 2000,
73, 903; Y. Shimazaki, S. Huth, A. Odani and O. Yamauchi, Angew.
Chem., Int. Ed., 2000, 112, 1666.
2 Chem. Rev., 1996, 96; Metal Ions in Biological Systems, eds. H.
Sigel and A. Sigel, Marcel–Dekker, New York, 1994, vol. 30;
G. T. Babcock, M. Espe, C. Hoganson, N. Lydakis-Simantiris,
J. McCracken, W. Shi, S. Styring, C. Tommas and K. Warncke, Acta
Chem. Scand., 1997, 51, 533; M. M. Fontecave and J. L. Pierre, Bull.
Soc. Chim. Fr., 1996, 133, 653; D. P. Goldberg and S. J. Lippard,
Adv. Chem. Ser., 1995, 246, 59; J. Stubbe and W. A. van der Donk,
Chem. Rev., 1998, 98, 705.
1
1
[Mϩ]. 31P NMR (CDCl3): δ 60.9 (dd, J(PRh) = 132 Hz). H
NMR (CDCl3): δ 7.33–6.76 (m, 18H), 5.76 (s, 1H, OH), 1.56 (s,
9H, t-Bu), 1.19 (s, 9H, t-Bu), 1.14 (s, 9H, t-Bu) and 1.10 (s, 9H,
t-Bu). IR (KBr disk) (cmϪ1): 3143br (OH). UV-vis in hexane:
λmax/nm (ε/MϪ1 cmϪ1) 386 (2540) and 327 (11600). Cyclic
voltammetry (CH2Cl2, glassy carbon electrode): E11/2 = 279
(rev.), E2 = 836 mV (quasi-reversible).
[CoII (LO)2(C2H5OH)3]ؒ2C2H5OH, 7. To a degassed sus-
2
pension of the ligand H2LO 2 (536 mg; 1 mmol) in ethanol
(30 cm3) containing Et3N (3 cm3), solid Co(OAc)2ؒ4H2O (249
mg; 1 mmol) was added. The resulting suspension was heated to
reflux under argon for 3 h to yield a deep blue clear solution,
which was kept overnight in a refrigerator. A mixture of the
ligand and a blue solid was obtained as the microcrystalline
solid product which was recrystallized from ethanol–pentane as
0.14 g of a mixture of white ligand and blue crystals of complex
7 suitable for X-ray analysis. Several attempts to obtain a pure
sample proved unsuccessful. Yield: 200 mg.
3 P. Chaudhuri, M. Hess, U. Flörke and K. Wieghardt, Angew. Chem.,
Int. Ed., 1998, 110, 2217.
4 P. Chaudhuri, M. Hess, T. Weyhermüller and K. Wieghardt, Angew.
Chem., Int. Ed., 1999, 38, 1095.
5 P. Chaudhuri, M. Hess, J. Müller, K. Hildenbrand, E. Bill, T.
Weyhermüller and K. Wieghardt, J. Am. Chem. Soc., 1999, 121, 9599.
6 A. Tzschach and E. Nietschmann, Z. Chem., 1980, 20, 341.
7 A. van Zon, G. J. Torny and J. H. G. Frijns, Recl. Trav. Chim. Pays-
Bas, 1983, 102, 326.
8 H. Luo, I. Setyawati, S. J. Rettig and C. Orvig, Inorg. Chem., 1995,
34, 2287.
X-Ray crystallography
The crystallographic data of H2LP᎐O 2, [NiII(HL)2] 3, [CoIII-
᎐
(OH2)(HL)(L)]ؒ1.25THF 4, [RhIIICl(H2L)(L)]ؒH2O
5 and
[CoII2(LO)2(C2H5OH)3]ؒ2C2H5OH 7 are summarized in Table 6.
Graphite monochromated Mo-Kα X-radiation (λ = 0.71073 Å)
was used throughout. X-Ray diffraction data were collected on
a Siemens SMART diffractometer and corrected for Lorentz
and polarization effects. The structures were solved by direct
methods and subsequent Fourier-difference techniques, and
refined anisotropically by full-matrix least squares on F2 with
the program SHELXTL PLUS.28 Hydrogen atoms attached
to carbon were placed at calculated positions with isotropic
thermal parameters. Those bound to oxygen were located from
the difference map.
9 R. S. Tanke, E. M. Holt and R. H. Crabtree, Inorg. Chem., 1991, 30,
1714.
10 M. Hesse, H. Meier and B. Zeeh, Spektroskopische Methoden in
der Organischen Chemie, Georg Thieme Verlag, Stuttgart, 1995.
11 J. Heinicke, M. He, A. Dal, H.-F. Klein, O. Hetche, W. Keim,
U. Flörke and H.-J. Haupt, Eur. J. Inorg. Chem., 2000, 431; P.
Bhattacharya, M. L. Loza, J. Parr and A. M. Z. Slawin, J. Chem.
Soc., Dalton Trans., 1999, 2917.
12 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
13 J. Parr and A. M. Z. Slawin, Inorg. Chim. Acta, 2000, 303, 116.
14 J. Heinicke, M. Koesling, R. Brüll, W. Keim and H. Pritzkow,
Eur. J. Inorg. Chem., 2000, 299.
CCDC reference number 186/2239.
See http://www.rsc.org/suppdata/dt/b0/b005693f/ for crystal-
lographic files in .cif format.
15 F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry,
5th edn., John Wiley & Sons, New York, 1988.
16 S. Alvarez and C. Lopez, Inorg. Chim. Acta, 1982, 64, L99.
17 Comprehensive Coordination Chemistry, eds. G. Wilkinson, R. D.
Gillard and J. A. McCleverty, Pergamon Press, Oxford, 1987, vol. 4.
18 W. Levason, in The Chemistry of Organophosphorus Compounds, ed.
F. R. Hartley, Wiley-Interscience, Chichester, 1990, vol. 1, ch. 15.
19 L. Sacconi and F. Mani, Transition Met. Chem. (N. Y.), 1982, 8, 179
and references cited therein.
Acknowledgements
We thank Degussa-Hüls (Hanau, Germany) for a postdoctoral
fellowship (to R. S.), the Fonds der Chemischen Industrie and
the Max-Planck-Society for support. Skilful technical assist-
ance of André de Bache is also thankfully acknowledged.
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20 K. Heinze, G. Huttner and O. Walter, Eur. J. Inorg. Chem., 1999,
593.
21 F. H. Allen, G. Chang, K. K. Cheung, T. F. Lai, L. M. Lee and
A. Pidcock, Chem. Commun., 1970, 1297; A. C. Skapski and F. A.
Stephens, J. Chem. Soc., Dalton Trans., 1973, 1789.
J. Am. Chem. Soc., 1988, 110, 1827; C. L. Simpson, S. R. Boone and
C. G. Pierpont, Inorg. Chem., 1989, 28, 4379.
24 A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier,
Amsterdam, 1984.
25 R. V. Parish, NMR, NQR, EPR and Mössbauer Spectroscopy in
Inorganic Chemistry, 1st edn., Ellis Horwood, New York, 1990.
26 A. Sokolowski, H. Leutbecher, T. Weyhermüller, R. Schnepf, E.
Bothe, E. Bill, P. Hildebrandt and K. Wieghardt, J. Biol. Inorg.
Chem., 1997, 2, 444.
27 W. Kläui and K. Dehnicke, Chem. Ber., 1978, 111, 451.
28 G. M. Sheldrick, SHELXTL PLUS, program package (PC version),
Siemens Analytical X-ray Instruments Inc., Madison, WI, 1990.
22 F. A. Cotton and R. H. Soderberg, J. Am. Chem. Soc., 1963, 85,
2402.
23 A. Y. Girgis and A. L. Balch, Inorg. Chem., 1975, 14, 2724;
A. Ozarowski, B. R. McGarvey, A. El-Hadad, Z. Tian, D. G. Tuck,
D. J. Krovich and G. C. DeFotis, Inorg. Chem., 1993, 32, 841;
S. Bruni, A. Caneschi, F. Cariati, C. Delfs, A. Dei and D. Gatteschi,
J. Am. Chem. Soc., 1994, 116, 1388; S. K. Larsen and C. G. Pierpont,
J. Chem. Soc., Dalton Trans., 2000, 4656–4663
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