Bulky 4-phosphacyclohexanones: Diastereoselective complexations, orthometallations and unprecedented [3.1.1]metallabicycles

Article abstract of DOI:10.1039/b607490a

The 4-phosphacyclohexanones, 2,2,6, 6-tetramethyl-1-phenyl-4-phosphorinanone (L_a), 1,2,6-triphenyl-4-phosphorinanone (^PhL_b), 1-cyclohexyl-2,6-diphenyl-4-phosphorinanone (^CyL_b) and 1-tert-butyl-2,6-dip

Full text of DOI:10.1039/b607490a

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www.rsc.org/dalton | Dalton Transactions
Bulky 4-phosphacyclohexanones: diastereoselective complexations,
orthometallations and unprecedented [3.1.1]metallabicycles
Ruth Doherty, Mairi F. Haddow, Zoe¨ A. Harrison, A. Guy Orpen,* Paul G. Pringle,* Alex Turner and
Richard L. Wingad
Received 26th May 2006, Accepted 27th June 2006
First published as an Advance Article on the web 26th July 2006
DOI: 10.1039/b607490a
The 4-phosphacyclohexanones, 2,2,6,6-tetramethyl-1-phenyl-4-phosphorinanone (La),
1,2,6-triphenyl-4-phosphorinanone (PhLb), 1-cyclohexyl-2,6-diphenyl-4-phosphorinanone (CyLb) and
1-tert-butyl-2,6-diphenyl-4-phosphorinanone (BuLb) have been made by modifications of literature
methods. Phosphines RLb are each formed as mixtures of meso- and rac-diastereoisomers. Isomerically
pure rac-PhLb, rac-CyLb and meso-BuLb can be isolated by recrystallisation from MeCN. Heating mixtures
of isomers of RLb with TsOH leads to isomerisations to give predominantly the meso-RLb. The complex
trans-[PdCl2(La)2] (1) is readily made from [PdCl2(NCPh)2] but the analogous platinum complex 2 has
not been detected and instead, cyclometallation at the 3-position (a to the ketone) in the phosphacycle
occurs to give trans-[PtCl(La)(La–3H)] (3) (where La–3H = La deprotonated at the 3-position) featuring
a [3.1.1]metallabicycle as confirmed by X-ray crystallography. The analogous palladabicycle 4 has been
detected upon treatment of 1 with Et3N in refluxing toluene. The type of complex formed by RLb
depends on which diastereoisomer (meso or rac) is involved. rac-PhLb (a mixture of R,R- and
S,S-enantiomers, labelled a and b) forms trans-[MCl2(rac-PhLb)2], M = Pd (5) or Pt (6), as mixtures of
diastereoisomers (aa/bb and ab forms). The structure of aa-6 has been determined by X-ray
crystallography. Ligand competition experiments monitored by 31P NMR showed that Pd(II) and Pt(II)
have a significant preference to bind rac-PhLb over meso-PhLb. meso-BuLb reacts with [PtCl2(NCBut)2]
under ambient conditions to give the binuclear complex [Pt2Cl2(meso-BuLb-2ꢀH)2] (7) where
orthometallation has occurred on one of the exocyclic phenyl substituents as confirmed by X-ray
crystallography. rac-BuLb reacts with [PtCl2(NCBut)2] to give a mononuclear cyclometallated species
assigned the structure trans-[PtCl(rac-BuLb-2ꢀH)(BuLb)] (8) on the basis of its 31P NMR spectrum.
rac-CyLb reacts with [PtCl2(NCBut)2] in refluxing toluene to give trans-[PtCl2(rac-CyLb)2] (9) and the
crystal structure of ab-9 has been determined.
coordination chemistry and catalytic activity; indeed bulky 4-
phosphorinanones have been claimed as ligands for Pd-catalysed
Introduction
alkene carbonylation4 and, while this work was in progress,
the application of related phosphorinanes in Pd-catalysed C–C
coupling reactions has been reported.5 There is the potential to
vary the 2,6-substituents on the ring enabling manipulation of the
ligand stereoelectronic effects. Finally, the carbonyl group should
allow further elaboration of the ligand at a site remote from the
donor atom.
The reaction of primary phosphines with dienones to give bulky 4-
phosphacyclohexanones (4-phosphorinanones) was first reported1
by Welcher and Day in 1962 (Scheme 1).
In this paper the coordination chemistry of the 4-phospho-
rinanones shown in Scheme 2 with palladium(II) and platinum(II)
is reported including the observation of cyclometallation at
different sites on the ligand and a clear ligand diastereomeric
preference in complexation.
Scheme 1
To date, the work reported on 4-phosphorinanones has primar-
ily concerned ring conformational analysis2,3 and their coordina-
tion chemistry remains unexplored.
4-Phosphorinanones are of interest as bulky ligands for several
reasons. The six-membered ring constrains the 2,6-substituents to
be in close proximity to the metal which may lead to unusual
Results and discussion
Ligand synthesis
The ligands La and RLb (R = Ph, Cy and But) were made by
modifications of the literature routes1 as shown in Scheme 2
and the products were fully characterised (see Experimental
section). In our hands, the solventless reaction of PhPH2 with
School of Chemistry, University of Bristol, Bristol, UK BS8 1TS. E-mail:
paul.pringle@bristol.ac.uk; Fax: +44 (0)117 925 1295; Tel: +44 (0)117
928 7645
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Scheme 3
The ratio of diastereoisomers of RLb formed depends on R and
the conditions used. When the syntheses were carried out in MeCN
in the presence of TsOH catalyst, the approximate meso : rac ratios
were 1 : 3 for PhLb, 4 : 1 for CyLb, and >100 : 1 for BuLb. These data
appear to correlate with the bulk of the R substituent but when
the syntheses were carried out solventless and in the absence of
catalyst, the ratios were 1 : 7 for PhLb, 1 : 4 for CyLb, and 1 : 1 for
BuLb.
Further insight into the relative stabilities of meso- and rac-
RLb was obtained from the observation that, when mixtures of
diastereoisomers were refluxed in MeCN in the presence of TsOH
catalyst, the proportion of meso- and rac-isomers changed over
a period of days in favour of the meso-RLb, e.g. an initially 1 : 7
mixture of meso : rac-PhLb became a 3 : 1 mixture after 7 days.
The rac-RLb to meso-RLb isomerisations show that the Michael
addition is reversible and that meso-RLb is the thermodynamically
more stable isomer. It also suggests that rac-RLb only forms
when the reaction is under kinetic control. The stereochemical
outcome of the reaction is determined at the cyclisation step
(see Scheme 4). Assuming the pseudo-chair conformations for
the transition states7 shown in Scheme 4, it can be understood
why the initial proportions of meso and rac isomers differ from the
thermodynamic ratios.
Scheme 2
dibenzylideneacetone (i.e. the literature route1 to PhLb) gave several
unidentified products in addition to PhLb but, by employing MeCN
as solvent and an acid catalyst, only isomers of PhLb were observed.
Crystals of ligand La were obtained from diethyl ether.
From previous conformational analysis work on six-membered
phosphacycles,2,6 an axial Ph–P was expected in La and the
structure of La in the solid state (see Fig. 1 and Table 1) confirms
this assignment.
Fig. 1 Crystal structure of La (50% thermal ellipsoids). Hydrogen atoms
removed for clarity.
◦
˚
Table 1 Selected bond distances (A) and angles ( ) for La
Scheme 4
P1–C10
P1–C5
P1–C1
1.8359(15)
1.8880(14)
1.8875(14)
C10–P1–C5
C10–P1–C1
C5–P1–C1
103.23(6)
104.88(6)
104.19(6)
The compound rac-CyLb was air-sensitive and crystals of its
oxide suitable for X-ray crystallography were obtained from
hot acetonitrile; the crystal structure (see Fig. 2 and Table 2)
reveals a twist-boat conformation of the phosphorinanone. This
conformation is well known for trans-1,3-tert-butylcyclohexanes8
as occupation of pseudo-axial sites by bulky substituents (which
would be inevitable in a chair conformation) is avoided.
Crystals of meso-BuLb were grown from acetonitrile solution and
its structure in the solid state determined by single crystal X-ray
methods. The phosphacycle adopts a near-perfect mirror symmet-
rical chair conformation with the phenyl and But substituents in
pseudo-equatorial sites (see Fig. 3, Table 3).
The reaction of RPH2 (R = Ph, Cy and But) with dibenzyli-
deneacetone gave two products in each case, as evidenced by the
two singlets observed in their 31P NMR spectra. Theoretically, the
three diastereoisomers shown in Scheme 3 are possible for RLb:
two meso isomers (A and B) and a rac isomer (a mixture of a- and
b-enantiomers). However, steric hindrance would militate against
the formation of meso-B, with the bulky adjacent substituents cis
to one another and therefore the two observed products are most
likely to be the meso-A and rac diastereoisomers.
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Table 4 Relative energies of isomers and conformers of PhLb calculated
by DFT
Isomer
Conformation
Relative E/kJ mol−1
meso-A
eq-chair
ax-chair
twist
eq-chair
ax-chair
twist
eq-chair
ax-chair
twist
0.0
40.5
30.1
38.5
23.5
16.9
11.1
13.2
16.9
meso-B
rac
they each contain 2,6-diaxial Ph substituents; these conformers
were therefore not considered further.
Fig. 2 Crystal structure of the oxide of rac-CyLb (50% thermal ellipsoids).
Hydrogen atoms removed for clarity.
From the data in Table 4 we note the following: (1) The stability
of the most energetically favoured conformers is in the sequence
meso-A > rac > meso-B, supporting the assignment of the two
isomers observed as meso-A and rac. (2) The conformational
preferences are: (i) for the meso-A isomer, the eq-chair conformer,
in which all phenyls are equatorial, has the lowest energy; (ii) for
the rac isomer, the eq-chair, ax-chair and twist conformers are of
similar energies; (iii) for the meso-B isomer, the twist conformer
has the lowest energy, although the optimised geometry is better
described as a twist-boat because the PC5 ring is distorted from
C2 symmetry (see below).
◦
˚
Table 2 Selected bond distances (A) and angles ( ) for the oxide of
rac-CyLb
P1–O1
P1–C18
P1–C5
P1–C1
1.485(5)
1.817(5)
1.830(4)
1.842(5)
O1–P1–C1
C18–P1–C1
C5–P1–C1
113.5(2)
104.6(2)
101.3(2)
Finally we note that these computed energies are enthalpies
(not free energies) for isolated molecules rather than the solvated
species observed in the NMR experiments, and so can only be a
guide to the equilibrium behaviour of these species.
Fig. 3 Crystal structure of meso-BuLb (50% thermal ellipsoids). Hydrogen
atoms removed for clarity.
◦
Table 3 Selected bond distances (A) and angles ( ) for meso-BuLb
˚
Palladium(II) and platinum(II) complexes of La
P1–C5
P1–C1
P1–C18
1.883(3)
1.884(3)
1.889(3)
C5–P1–C1
C5–P1–C18
C1–P1–C18
96.14(13)
102.86(13)
104.82(13)
The reaction of [PdCl2(NCPh)2] with 2 equivalents of La in toluene
at room temperature resulted in the formation of the yellow
trans-[PdCl2(La)2] (1), which has been fully characterised (see
Experimental section). The IR spectrum of 1 had a m(CO) band at
1706 cm−1 which is similar to the m(CO) of 1701 cm−1 in La itself.
From the structures of meso-BuLb and the oxide of rac-CyLb, it
would appear that the 2,6-phenyl substituents in phosphacycles
RLb promote a chair conformation in the meso-A isomers and
a twist conformation in the rac isomers, although the reported2
crystal structure of the sulfide of rac-PhLb has a chair conformation,
with equatorial Ph–P and one axial Ph–C.
Conformational analysis of PhLb
In order to probe the conformational properties of these ligands,
DFT calculations were carried out on the chair and twist con-
formers of the rac, meso-A and meso-B isomers of PhLb as shown
in Scheme 5 (with Ph–P in either equatorial or axial positions). It
was immediately clear that the energies of the chair conformer with
P–Ph axial (ax-chair) for meso-A and the eq-chair conformer for
meso-B are very high (see Table 4). This is understandable because
(1)
Crystals of 1 were grown by slow evaporation of a CDCl3
solution and the X-ray crystal structure determined. The structure
of trans-[PdCl2(La)2] (1) in the crystal has exact inversion symmetry
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Scheme 5
◦
˚
When La was reacted with [PtCl2(cod)] in a 2 : 1 ratio in
Table 5 Selected bond distances (A) and angles ( ) for complex 1
dichloromethane at room temperature, the expected product was
trans-[PtCl2(La)2] (2) but it was clear from the 31P NMR spectrum
that 2 had not been formed. The spectrum showed an AX pattern
with dA 38.2 ppm, 1J(PtPA) 2948 Hz and dX −13.0 ppm, 1J(PtPX)
2225 Hz and J(PAPX) 407 Hz consistent with the formation of a
trans complex in which cyclometallation has occurred on one of
the coordinated phosphines. The data for the highly shielded PX are
consistent with it being in a 4-membered ring.9 The ligand PhPBut2
(an acyclic analogue of La) forms the complexes [MCl2(PhPBut2)2]
(M = Pd or Pt) which undergo cyclometallation on the methyl
group of the t-butyl substituent9 or on the P-phenyl group10 to give
the 4-membered metallacycles shown in Scheme 6. Therefore it
was considered likely that the cycloplatination of La had occurred
either at one of the exocyclic methyl groups or at an ortho position
of the P-phenyl group but the crystal structure showed otherwise:
metallation had taken place at the activated 3-position (the carbon
a to the ketone) to give 3.
Pd1–Cl1
Pd1–P1
P1–C10
P1–C1
2.3060(6)
2.3751(6)
1.831(2)
1.882(2)
P1–C5
1.893(2)
101.76(10)
112.27(10)
104.69(10)
C10–P1–C1
C10–P1–C5
C1–P1–C5
(see Fig. 4 and Table 5) with the palladium(II) centre having the
expected trans square planar configuration. The ligands show
a twist conformation with the PC5 rings having approximate
C2 symmetry. The metal and phenyl groups therefore are in
approximately isoclinal sites. The ligand orientation is such that
one methyl group attached to C1 (C6, see Fig. 4) is above the metal
coordination plane resulting in a pair of short Pd · · · H contacts
˚
(2.72 A).
Scheme 6
Crystals of 3 were grown by slow evaporation of its CDCl3
solution and the X-ray crystal structure determined (see Fig. 5,
Table 6). The crystal structure shows that 3 contains a [3.1.1]met-
allaphosphabicycle. The platinum atom is in a distorted square
planar environment, since the 4-membered ring constrains the
P(2)–Pt(1)–C(17) angle to 66◦. The metallated carbon C(17) is
trans to Cl(1) and the two phosphorus atoms are trans to each other
(P(1)–Pt(1)–P(2) 163.23(3)◦). The phosphacyclohexane ligand at
Fig. 4 Crystal structure of complex 1 (50% thermal ellipsoids). All
hydrogens have been omitted for clarity. The symmetry operation invoked
for the atoms with ‘A’ letters is (2 − x, −y, 1 − z).
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˚
˚
similar (C–O in P(1) ligand 1.218(4) A, in P(2) ligand 1.221(4) A;
˚
PtC–C(O) in the P(2) ligand is 1.486(5) A while the two C–C(O)
˚
˚
in P(1) ligand are 1.499(5) A and 1.500(5) A).
Thus La undergoes cycloplatination readily but not cyclopalla-
dation (see above). However, upon refluxing a mixture of 1 and
NEt3 in toluene for 20 h, several products were formed but the
major one (ca. 70%) had very similar 31P parameters to 3 (dA
41.1 ppm, dX −12.7 ppm, J(PAPX) 423 Hz) and is therefore assigned
the analogous structure 4.
Palladium(II) and platinum(II) complexes of RLb
When a 1 : 2 meso : rac mixture of isomers of PhLb (2 equiv.) was
added to [PdCl2(NCPh)2] in CH2Cl2, the 31P NMR spectrum of the
resulting solution showed no free ligand remained, consistent with
complexation of both meso- and rac-PhLb to give several species (see
Experimental section). Addition of further 1 : 2 meso : rac-PhLb led
to a great simplification of the spectrum: a singlet for meso-PhLb
and two singlets assigned to the aa/bb- and ab-diastereoisomers
of 5 (see Scheme 7). Thus palladium(II) has a significant preference
for complexing with rac-PhLb over meso-PhLb.
Fig. 5 Crystal structure of complex 3 (50% thermal ellipsoids). All
hydrogens have been omitted for clarity.
◦
˚
Table 6 Selected bond distances (A) and angles ( ) for complex 3
Pt1–C17
Pt1–P2
Pt1–P1
Pt1–Cl1
P1–C10
P1–C1
P1–C5
P2–C25
P2–C16
P2–C20
C17–Pt1–P2
C17–Pt1–P1
P2–Pt1–P1
P2–Pt1–Cl1
2.107(3)
2.2773(10)
2.3251(9)
2.3799(10)
1.822(3)
1.881(3)
1.887(3)
1.813(3)
1.841(3)
1.846(3)
66.20(10)
97.03(10)
163.23(3)
100.80(4)
C10–P1–C1
C10–P1–C5
C1–P1–C5
105.67(15)
108.04(15)
104.62(15)
114.48(16)
109.34(16)
106.44(16)
87.05(12)
89.5(2)
C25–P2–C16
C25–P2–C20
C16–P2–C20
C16–P2–Pt1
C17–C16–P2
C16–C17–Pt1
C17–Pt1–P2–C16
Pt1–P2–C16–C17
P2–C16–C17–Pt1
P2–Pt1–C17–C16
Even greater isomer-selective complexation was observed when
an excess of rac/meso-PhLb was added to [PtCl2(NCBut)2] in
toluene and the mixture refluxed for 16 h. The 31P NMR spectrum
of the resulting solution showed unreacted meso-PhLb to be present
and the yellow solid product had two Pt-containing species in the
101.4(2)
24.34(14)
−30.76(17)
34.29(17)
−29.85(17)
1
1
ratio of ca. 1 : 10 (d 16.3, J(PtP) 2700 Hz and d 20.7, J(PtP)
2770 Hz) assigned to the diastereoisomers of trans-[PtCl2(rac-
PhLb)2], ab-6 and aa/bb-6. This reaction is so selective that we
have used it as a way of separating rac-PhLb and meso-PhLb
by decomplexing rac-PhLb from 6 with KCN (see Experimental
section).
P(1) adopts a near-perfect mirror symmetric chair conformation
with the phenyl substituent almost eclipsing the Pt–C bond.
It is likely that the selective formation of this unprecedented
cyclometallated product (presumably via 2) under such mild
conditions is associated with the activation of the CH by the
a-carbonyl group. The IR spectrum of 3 had m(CO) bands at
1705 and 1654 cm−1 with the lower frequency band assigned
to the CO adjacent to the metallated carbon. The ca. 50 cm−1
lowering is consistent with delocalisation of the d− charge on
The preference of platinum(II) and palladium(II) to complex
rac-PhLb over meso-PhLb is consistent with access to the P lone pair
in meso-PhLb being inhibited by the cis-2,6-phenyl substituents.
Further insight into this diastereoisomer preference was gained
from a DFT study. Geometry optimisations were carried out for
the complexes formed by chair and twist conformations for meso
(A and B) and rac isomers of PhLb bound to a [PtCl3]− fragment
(with Pt at the lone pair site). Their energies are given in Table 7.
Chair and twist conformers did not interconvert during geometry
optimisation indicating that they are robust local minima but for
meso-A and meso-B, the twist conformers distorted to twist-boat
conformations upon optimisation.
=
to the C O through partial enolate character in the Pt–C–C(O)
moiety. However, the crystallographically determined CO bond
lengths do not reflect this effect and do not differ significantly.
The C–C(O) lengths in the two phosphine ligands in 3 are also
Scheme 7
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◦
Table 7 Relative energy and expected distribution of conformers for
[PtCl3(PhLb)]−
˚
Table 8 Selected bond distances (A) and angles ( ) for complex aa-6
Pt1–Cl1
Pt1–P2
Pt1–P1
Pt1–Cl2
P1–C18
P1–C5
2.2990(12)
2.3078(12)
2.3114(11)
2.3245(12)
1.815(5)
1.863(4)
1.870(4)
P2–C28
P2–C24
1.861(4)
1.874(4)
107.5(2)
102.2(2)
101.87(19)
107.7(2)
Isomer
meso-A
meso-B
rac
Conformation
Relative E/kJ mol−1
C18–P1–C5
C18–P1–C1
C5–P1–C1
C41–P2–C28
C41–P2–C24
C28–P2–C24
eq-chair
twist
ax-chair
twist
eq-chair
ax-chair
twist
0.0
34.7
4.4
4.6
8.0
33.3
3.2
P1–C1
P2–C41
102.92(19)
101.87(19)
1.829(4)
of the two enantiomers. Each molecule of 6 in the crystal has
approximate C2 symmetry with the platinum coordination trans
and square planar as expected. The individual ligands adopt twist
conformations with the phenyl groups in the 2- and 6-positions
in pseudo-equatorial sites and the metal and 1-phenyl group
isoclinal. The orientation of the phosphine ligands, as regards
rotation about the Pt–P bonds, leaves both the P-phenyl groups
close to the same chloride ligand (Cl(1)) and one of the C-phenyl
groups on each ligand shielding the axial sites on the platinum
centre.
From the data in Table 7 we can make the following observa-
tions: (1) Twist and eq-chair conformers of complexed rac-PhLb
will be populated at room temperature but the ax-chair conformer
(which is accessible in the free ligand) is highly unfavourable. This
is presumably due to a steric clash of the metal fragment with
the adjacent axial C–Ph substituent; the crystal structure of 6
described below does indeed contain twist conformations of rac-
PhLb. (2) The preferred conformation (eq-chair) for complexed
meso-A remains as in the uncoordinated ligand. (3) For complexed
meso-B (not observed experimentally) the ax-chair and twist
conformations will have approximately equal energy.
Upon treatment of [PtCl2(NCBut)2] with 1 equivalent of meso-
BuLb in refluxing toluene, a precipitate of the binuclear cyclometal-
lated complex 7 forms whose structure was assigned on the basis
of NMR spectroscopy and X-ray crystallography (see below). The
31P NMR spectrum of 7 showed a singlet at high frequency (d
From the data in Tables 4 and 7, DH for the reaction shown in
eqn (2) is −7.9 kJ mol−1. This is in qualitative agreement with the
experimental observation of the greater coordinating strength of
rac-PhLb than meso-PhLb.
1
64.9) and a large J(PtP) of 4846 Hz, consistent with the five-
membered metallacycle 7 containing l-Cl ligands. Crystals of
[Pt2(l-Cl)2(meso-BuLb-2ꢀH)2] (7) as a toluene solvate were grown
by slow evaporation of a CH2Cl2/toluene solution and the X-ray
crystal structure determined (see Fig. 7, Table 9). The molecular
structure has exact Ci symmetry with the metal atoms in square
planar coordination and the entire central Pt2(l-Cl)2(PCCC)2 unit
close to planar.
[PtCl3(meso-PhLb]− + rac-PhLb → [PtCl3(rac-PhLb]− + meso-PhLb (2)
Notably the data in Tables 4 and 7 indicate that the meso-B
isomer would displace rac-PhLb from its [PtCl3L]− complex (DE
−4.6 kJ mol−1), though testing this hypothesis experimentally is
precluded because the meso-B form of PhLb was not observed under
the conditions we used for the synthesis of PhLb.
Crystals of aa/bb-trans-[PtCl2(rac-PhLb)2] (aa/bb-6) were grown
by slow evaporation of a CDCl3 solution and the X-ray crystal
structure determined (see Fig. 6, Table 8). The structure shown is of
the aa-enantiomer although the crystal contains a racemic mixture
Fig. 7 Crystal structure of complex 7 (50% thermal ellipsoids). All
hydrogens have been omitted for clarity. The symmetry operation invoked
for the atoms with ‘A’ letters is (1 − x, 2 − y, 1 − z).
When a 1 : 1 mixture of meso : rac-BuLb was reacted with
[PtCl2(NCBut)2] in refluxing toluene, binuclear 7 precipitates
from solution as expected and in the filtrate, a single complex
was identified by its characteristic AX pattern in the 31P NMR
Fig. 6 Crystal structure of complex aa-6 (50% thermal ellipsoids). All
hydrogens have been omitted for clarity.
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◦
◦
˚
˚
Table 10 Selected bond distances (A) and angles ( ) for complex ab-9
Table 9 Selected bond distances (A) and angles ( ) for complex 7
Pt1–C7
Pt1–P1
Pt1–Cl1A
Pt1–Cl1
P1–C1
P1–C18
P1–C5
C1–C6
C7–C6
2.017(6)
2.1914(18)
2.3937(17)
2.4315(16)
1.848(6)
1.858(6)
1.862(7)
1.511(9)
1.417(9)
84.0(2)
C1–P1–C18
C1–P1–C5
C18–P1–C5
C1–P1–Pt1
C6–C1–P1
C6–C7–Pt1
105.4(3)
101.8(3)
109.1(3)
106.6(2)
107.5(4)
121.7(5)
119.5(5)
8.5(5)
3.9(5)
1.2(8)
−6.6(7)
Pt1–Cl1
Pt1–P1
P1–C18
P1–C5
2.3169(13)
2.3322(13)
1.847(5)
P1–C1
1.881(5)
104.9(2)
110.1(2)
99.4(2)
C18–P1–C5
C18–P1–C1
C5–P1–C1
1.873(6)
C7–C6–C1
its toluene solution and the X-ray crystal structure determined (see
Fig. 8, Table 10). Molecules of ab-9 have exact inversion symmetry
(confirming the geometric and diastereoisomer assignment). As
in all the complexes reported in this paper, one P–C bond of
the PC5 moiety (here P1–C5) is perpendicular to the metal
Pt1–P1–C1–C6
P1–Pt1–C7–C6
Pt1–C7–C6–C1
P1–C1–C6–C7
C7–Pt1–P1
C7–Pt1–Cl1A
P1–Pt1–Cl1
95.8(2)
99.90(6)
1
spectrum. The data for this species (dA 60.0, J(PtPA) 2994 Hz,
dX 35.5, 1J(PtPX) 2900 Hz, 2J (PAPX) 396 Hz) are consistent with
structure 8a (see Scheme 8) which features a cyclometallated rac-
BuLb. Cyclometallated rac-BuLb rather than meso-BuLb is suggested
because isolated 7: (i) does not react with an excess of pure meso-
BuLb and (ii) reacts with meso/rac-BuLb to give a different, bridge-
cleaved product according to its 31P NMR data (d 64.1, 1J(PtPA)
1
2
3063 Hz, d 33.6, J(PtPA) 3016 Hz, J(PAPX) 426 Hz) assigned
structure 8b. The observation of complexes 7 and 8a establishes
that both meso- and rac-BuLb undergo orthometallation.
The platinum(II) coordination chemistry of PhLb and BuLb differs
in that a complex of the type trans-[PtCl2(RLb)2] was observed
only with PhLb and cyclometallation was only observed with BuLb,
indicating that the But substituent promotes the C–H activation.
In view of these differences, it was of interest to investigate ligands
of intermediate bulk, such as meso/rac-CyLb.
The reaction of
2
equivalents of pure rac-CyLb with
[PtCl2(NCBut)2] in refluxing toluene gave two similar species in ca.
1 : 1 ratio (d 17.3, 1J(PtPA) 2591 Hz and d 15.0, 1J(PtPA) 2535 Hz)
assigned to the diastereoisomers of trans-[PtCl2(rac-CyLb)2], aa/bb-
9 and ab-9. In this reaction rac-CyLb is behaving in a similar fashion
to rac-PhLb. Crystals of ab-9 were grown from slow evaporation of
Fig. 8 Crystal structure of complex ab-9 (50% thermal ellipsoids). All
hydrogens have been omitted for clarity. The symmetry operation invoked
for the atoms with ‘A’ letters is (1/2 − x, 3/2 − y, 2 − z).
Scheme 8
4316 | Dalton Trans., 2006, 4310–4320
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coordination plane. The ring has a twist conformation with the
metal and cyclohexyl groups isoclinal.
were made by literature methods. All other starting materials were
purchased from Aldrich or Strem.
The reaction of
a
mixture of meso/rac-CyLb with
[PtCl2(NCBut)2] in refluxing toluene gave the expected aa/bb-9
and ab-9 along with a third species whose characteristic AX
Preparation of 2,2,6,6-tetramethyl-1-phenyl-4-phosphorinanone
(La)
1
1
pattern (dA 51.8, J(PtPA) 2892 Hz, dX 29.4, J(PtPX) 2938 Hz,
J(PAPX) 403 Hz) indicated that meso-CyLb had cyclometallated
to give a complex tentatively assigned the structure 10, i.e. an
analogue of 8b.
A 250 cm3, 2-necked, round-bottomed flask was charged with
phorone (2,6-dimethyl-2,5-heptadien-4-one) (7.82 g, 57.0 mmol).
Phenylphosphine (5.00 cm3, 5.00 g, 45.4 mmol) was added to the
flask and the mixture was refluxed at 120 ◦C for 21 h. Upon cooling
the flask, a yellow waxy solid was obtained. This was triturated
with pentane (2 × 30 cm3) to give a white solid (6.53 g, 58%).
1
31P{ H} NMR (CDCl3): d = 17.1 (s). 1H NMR (CDCl3): d = 7.36–
2
7.19 (5H, m, ArH), 2.90 (2H, d, J(HH) 13 Hz, CH2), 2.32 (2H,
dd, 2J(HH) 13 Hz 3J(PH) 5 Hz, CH2), 1.32 (6H, d, 3J(PH) 8 Hz,
CH3), 0.93 (6H, d, 3J(PH) 11 Hz, CH3). 13C NMR (CDCl3): d =
211.4 (s, CO), 135.8 (d, 2J(PC) 23 Hz), 129.7 (s), 128.4 (d, 3J(PC)
9 Hz), 53.1 (d, 3J(PC) 2 Hz, CH2), 35.2 (d, 1J(PC) 18 Hz, C(CH3)2),
2
2
31.1 (d, J(PC) 31 Hz, CH3), 30.0 (d, J(PC) 11 Hz, CH3). m/z
(EI) 248 (M+). Elemental analysis (calc) C: 72.60 (71.98), H: 8.50
(8.42%). IR (CH2Cl2): mCO 1701.2 cm−1.
The studies with meso- and rac-CyLb support the conclusion
that the meso-isomer is more susceptible than the rac-isomer to
cyclometallation and that a bulky P–R substituent promotes this
reaction.
Preparation of 1,2,6-triphenyl-4-phosphorinanone (PhLb)
In a 100 cm3, 2-necked, round-bottomed flask, dibenzylideneace-
tone (3.19 g, 13.6 mmol) was dissolved in acetonitrile (20 cm3) and
phenylphosphine (1.50 g, 13.6 mmol) was added to the solution.
para-Toluenesulfonic acid (0.50 g, 1.36 mmol) was added to the
flask and the yellow solution refluxed at 105 ◦C for 48 h. A
creamy-white solid which precipitated from the orange solution
was washed with diethyl ether and crystallised from a saturated
acetonitrile solution to give the product as a white solid (1.97 g,
42%). The product was a 1 : 3 meso : rac mixture of isomers.
Conclusion
The palladium(II) and platinum(II) coordination chemistry of the
bulky phosphorinanones PhLa, PhLb, BuLb and CyLb has revealed that
the combination of the six-membered phosphacycle, the ketone
function and the exocyclic phenyl groups gives these ligands
unusual properties. For example, cyclometallation of PhLa occurs at
the activated carbon adjacent to the carbonyl to form a remarkable
bicyclic complex whereas cyclometallation of BuLb occurs on the
exocyclic phenyl substituent. Unexpectedly, there is such a degree
of discrimination in favour of complexation of the less stable rac-
PhLb over the meso-PhLb that this has been exploited in a method
for the separation of the isomers. DFT calculations suggest that
the source of the greater ligating power of rac-RLb can be traced
to ring conformational effects: the twist conformation which
is accessible in the free rac-RLb becomes favoured upon metal
binding because the R and metal groups occupy synclinal sites
and thereby minimise steric clashing. In other words, rac-RLb is
better preorganised for complexation than meso-RLb.
1
1
31P{ H} NMR (CDCl3): d = −2.2 (s, meso), −5.6 (s, rac). H
NMR (CDCl3): d = 7.40–7.00 (13H, m, Ar), 6.82–6.68 (2H, m,
Ar), 3.90–3.65 (2H, m, CH), 3.20–2.80 (4H, m, CH2). m/z (EI) 344
(M+). Elemental analysis (calc) C: 79.55 (80.21) H: 6.57 (6.15%).
Preparation of 1-cyclohexyl-2,6-diphenyl-4-phosphorinanone (CyLb)
Preparation of 4 : 1 meso : rac-CyLb. In a 100 cm3, 2-
necked, round-bottomed flask, dibenzylideneacetone (2.343 g,
10.2 mmol) was dissolved in acetonitrile (20 cm3) and cyclo-
hexylphosphine (1.162 g, 10.0 mmol) was added to the solution.
para-Toluenesulfonic acid (0.475 g, 2.5 mmol) was added to the
flask and the yellow solution refluxed for 144 h. A creamy-white
solid which precipitated from the orange solution was washed with
diethyl ether and crystallised from a saturated acetonitrile solution
to give the product as a white solid (1.330 g, 38%). The product
Experimental
Unless otherwise stated, all work was carried out under a dry nitro-
gen atmosphere, using standard Schlenk line techniques. Dry N2-
saturated solvents were collected from a Grubbs system11 in flame
and vacuum dried glassware. 1H, 13C and 31P NMR spectra were
recorded at 400, 100, and 121 MHz respectively at +23 ◦C. Mass
spectra were recorded on a VG Analytical Autospec (EI) or VG
Analytical Quattro (ESI). Elemental analyses were carried out
by the Microanalytical Laboratory of the School of Chemistry,
University of Bristol. IR spectra were recorded on a Perkin
Elmer 1600 Series Spectrometer in dichloromethane. [PtCl2(1,5-
cod),12 [PdCl2(NCPh)]13 and [PtCl2(NCBut)2]14 starting materials
1
was a 4 : 1 meso : rac mixture of isomers. 31P{ H} NMR (toluene):
1
d = 6.2 (s, meso), 0.9 (s, rac). H NMR (CDCl3): d = 7.39–7.13
(10H, m, Ar), 3.67–3.46 (2H, m, CH), 3.20–2.93 (2 H, m, CH2),
2.92–2.75 (2 H, m, CH2), 1.78–1.31 (11H, m, Cy–H). 13C NMR
(CDCl3): d = 208.2 (s, CO), 126.8–141.7 (12 C, m, Ar), 49.5 (d,
2J(PC) 13 Hz, CH2), 40.1 (d, 1J(PC) 15 Hz, CH), 32.4 (d, 1J(PC)
19 Hz, CH(Cy)), 28.9 (d, 3J(PC) 8 Hz, CH2), 27.5 (d, 2J(PC) 9 Hz,
CH2), 26.1 (s, CH2). m/z (EI) 350 (M+). HRMS (EI): Calculated
for C23H27OP: 350.1800. Found 350.1802.
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Preparation of 1 : 4 meso : rac-CyLb. A 100 cm3, 2-necked,
round-bottomed flask was charged with dibenzylideneacetone
(4.713 g, 20.5 mmol). Cyclohexylphosphine (2.323 g, 20.0 mmol)
was added to the flask and the mixture was refluxed at 120 ◦C for
36 h. When the mixture cooled to ambient temperature, a yellow
oil was observed which was triturated with acetonitrile (2 × 3 cm3)
to give the product as a creamy-white solid (2.651 g, 38%). The
product was a 1 : 4 meso : rac mixture of isomers. From this mixture
the white solid obtained redissolved in CH2Cl2. Crystalline 3 was
obtained by slow diffusion of hexane into this CH2Cl2 solution
1
(0.130 g, 32%). 31P{ H} NMR (CDCl3): d = 38.2 (d, 2J(PP) 407 Hz,
1J(PtP) 2948 Hz), −13.0 ppm (d, 2J(PP) 407 Hz, 1J(PtP) 2225 Hz).
1H NMR (CDCl3): d = 8.10–7.36 (10H, m, Ar), 4.08 (1H, dd,
3
2
J(HH) 3 Hz, J(PC) 17 Hz, CH), 3.79 (1H, dd, J(HH) 7 Hz,
3J(PC) 20 Hz, CH), 2.83 (1H, dd, J(HH) 8 Hz, J(PC) 27 Hz,
CH), 2.33 (1H, dd, 2J(HH) 11 Hz, 3J(PC) 19 Hz, CH), 2.22 (1H,
dd, 2J(HH) 12 Hz, 3J(PC) 30 Hz, CH), 2.19 (1H, d, 3J(PC) 20 Hz,
CH), 2.07–1.96 (1H, m, PtCH), 1.84 (3H, d, 3J(PC) 16 Hz, CH3),
1.65 (3H, d, 3J(PC) 18 Hz, CH3), 1.54 (3H, d, 3J(PC) 18 Hz, CH3),
1.38 (3H, d, 3J(PC) 9 Hz, CH3), 1.20 (3H, d, 3J(PC) 13 Hz, CH3),
2
3
1
pure rac-CyLb was recrystallised from acetonitrile. 31P{ H} NMR
(CDCl3): d = 0.9 (s, rac).
Preparation of 1-tert-butyl-2,6-diphenyl-4-phosphorinanone (BuLb)
1.10 (3H, d, J(PC) 12 Hz, CH3). 13C NMR (CDCl3): d = 209.4
3
Preparation of pure meso-BuLb. In a 100 cm3, 2-necked, round-
bottomed flask dibenzylideneacetone (2.34 g, 10.0 mmol) was
dissolved in acetonitrile (20 cm3) and tert-butylphosphine (0.82 g,
9.07 mmol) was added to the solution. para-Toluenesulfonic acid
(0.50 g, 2.60 mmol) was added to the flask and the yellow solution
refluxed at 105 ◦C for 72 h. On cooling the mixture, a lemon
solid precipitated from the dark orange solution. The solid was
filtered off and washed with cold acetonitrile (10 cm3) to give a
3
3
(d, J(PC) 4.6 Hz, CO), 203.5 (d, J(PC) 14 Hz, CO), 135.8 (d,
1J(PC) 22 Hz, ipso-C), 135.1 (dd, J(PC) 8 Hz, J(PC) 3 Hz),
2
4
2
2
2
133.4 (d, J(PC) 8 Hz), 132.0 (d, J(PC) 2 Hz), 130.0 (d, J(PC)
2 Hz), 128.9 (d, J(PC) 10 Hz), 127.9 (d, J(PC) 9 Hz), 124.5
2
2
2
4
(dd, J(PC) 36 Hz, J(PC) 11 Hz, ipso-C), 56.4 (s, CH2), 55.4 (s,
CH2), 53.2 (d, 2J(PC) 2 Hz, CH2), 43.6 (d, 1J(PC) 30 Hz, C(CH3)),
1
3
1
40.0 (dd, J(PC) 19 Hz, J(PC) 4 Hz, C(CH3)), 38.5 (dd, J(PC)
19 Hz, J(PC) 2 Hz, C(CH3)), 37.3 (d, J(PC) 29 Hz, C(CH3)),
32.5 (s, CH3), 32.4 (d, J(PC) 3 Hz, CH3), 31.6 (d, J(PC) 7 Hz,
CH3), 30.6 (d, J(PC) 5 Hz, CH3), 28.9–28.7 (m, CH3), 26.7 (t,
3
1
1
yellow solid (1.56 g, 53%). 31P{ H} NMR (CDCl3): d = 17.9 (s).
2
2
1H NMR (CDCl3): d = 7.45–7.10 (10H, m, Ar), 3.33–3.14 (2H, m,
CH), 2.92 (2H, td, J(HH) 14 Hz, J(HH) 7 Hz, CH2), 2.79–2.57
(2H, m, CH2), 0.64 (9H, d, 2J(PC) 11 Hz, CH3). 13C NMR (CDCl3):
d = 208.3 (s, CO), 143.7 (d, 2J(PC) 9 Hz, ipso-C), 128.9 (s), 128.3
(d, 3J(PC) 9 Hz), 126.8 (s), 50.2 (d, 2J(PC) 11 Hz, CH2), 40.8 (d,
1J(PC) 20 Hz, CHPh), 30.6 (d, 1J(PC) 20 Hz, C(CH3)3), 28.4 (d,
2J(PC) 11 Hz, CH3). m/z (EI) 324 (M+). Elemental analysis (calc)
C: 77.92 (77.75) H: 8.21 (7.77%).
2
J(PC) 4 Hz, CH3), 26.4 (t, J(PC) 3 Hz, CH3). The cyclometallated
carbon has not been identified. m/z (EI) 726 (M+), 689 (M+ − Cl).
IR (CH2Cl2): mCO 1704.5 cm−1, 1654.3 cm−1.
Preparation of trans-[PdCl2(rac-PhLb)2] (5)
A 1 : 2 mixture of meso : rac-PhLb (0.10 g, 0.30 mmol) was dissolved
in toluene (10 cm3), [PdCl2(NCPh)2] (0.06 g, 0.15 mmol) was added
and the solution was refluxed at 120 ◦C for 6 h during which
time a pale yellow solid precipitated from the solution. The solid
was filtered off and washed with toluene to give the product as a
Preparation of 1 : 1 meso : rac-BuLb. A 50 cm3, 2-necked, round-
bottomed flask was charged with dibenzylideneacetone (2.34 g,
10.0 mmol). tert-Butylphosphine (0.82 g, 9.07 mmol) was added
to the flask and the mixture was heated at 120 ◦C for 72 h. Upon
cooling the flask, an off-white, glassy solid was obtained. This was
triturated with pentane (2 × 30 cm3) to give an off-white solid
1
pale yellow powder (0.06 g, 69% based on rac-isomer). 31P{ H}
NMR (CDCl3): d = 28.4 (s) which indicates that only one of the
diastereoisomers had precipitated tentatively assigned to aa/bb-5
by analogy with the platinum species aa/bb–6. 1H NMR (CDCl3):
1
(2.79 g, 95%). 31P{ H} NMR (CDCl3): d = 17.9 (s, meso), 17.0 (s,
2
2
rac).
d = 7.24–6.82 (30, m, Ar), 5.20 (2H, dd, J(PC) 17 Hz, J(HH)
2 Hz, CH), 4.20 (2H, dd, 2J(PC) 18 Hz 2J(HH) 3 Hz, CH), 4.10–
3.99 (2H, m, CH2), 3.19–2.99 (4H, m, CH2), 2.84–2.68 (2H, m,
CH2). m/z (EI) 865 (M+).
Preparation of trans-[PdCl2(La)2] (1)
Ligand La (0.27 g, 1.08 mmol) was dissolved in toluene (4 cm3)
and [PdCl2(NCPh)2] (0.20 g, 0.52 mmol) was added. A yellow
suspension formed rapidly. The solvent was removed in vacuo to
Reaction of meso : rac-PhLb with [PdCl2(NCPh)2]
1
give a yellow solid (1) (0.34 g, 97%). 31P{ H} NMR (CDCl3): d =
A 1 : 2 mixture of meso : rac-PhLb (0.028 g, 0.08 mmol) was
dissolved in CH2Cl2 in an NMR tube at room temperature and
[PdCl2(NCPh)2] (15 mg, 0.04 mmol) was added. The 31P NMR
spectrum of the resulting solution changed with time. The initial
spectra showed the presence of 2 species in addition to aa/bb-5:
42.2 (s). 1H NMR (CDCl3): d = 7.97–7.89 (4H, m, Ar), 7.48–7.38
(6H, m, Ar), 3.40 (4H, dt, 2J(HH) 15 Hz, J(PC) 5 Hz, CH2), 2.44
2
(4H, dt, J(HH) 15 Hz, J(PC) 9 Hz, CH2), 1.86 (12H, t, J(PC)
9 Hz, CH3), 1.24 (12 H, t, J(PC) 6 Hz, CH3). 13C NMR (CDCl3):
d = 135.1 (s), 130.3 (s), 127.5 (s), 55.3 (s, CH2), 38.3 (t, J(PC)
8 Hz, P–C), 31.7 (t, J(PC) 10 Hz, CH3), 29.4 (s, CH3). m/z (ESI)
638 (M+ − Cl). IR (CH2Cl2): mCO 1705.9 cm−1. Elemental analysis
(calc) C: 54.02 (53.50) H: 6.22 (6.30%).
2
an AB pattern (dA 28.7, dB 21.7, JAB 434 Hz) assigned to trans-
[PdCl2(rac-PhLb)(meso-PhLb)] and a singlet (d 22.4) assigned to ab-5
or trans-[PdCl2(meso-PhLb)2]. The proportions of products changed
over 3 days and the final spectrum showed the presence of mainly
aa/bb-5.
Preparation of trans-[PtCl2(La–3H)(La)] (3)
Preparation of trans-[PtCl2(rac-PhLb)2] (6)
Ligand La (0.280 g, 1.13 mmol) was dissolved in CH2Cl2 (4 cm3),
[PtCl2(cod)] (0.184 g, 0.48 mmol) was added and the mixture
refluxed for 4 d. The solvent was then removed in vacuo and
A 1 : 2 mixture of meso : rac-PhLb (0.34 g, 0.97 mmol) was dissolved
in toluene (10 cm3), [PtCl2(NCBut)2] (0.21 g, 0.49 mmol) was added
4318 | Dalton Trans., 2006, 4310–4320
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◦
and the solution was refluxed at 118 C for 16 h. A yellow solid
precipitated from the solution which was filtered off and washed
1
with toluene (0.13 g, 43% based on rac-isomer). 31P{ H} NMR
(CDCl3): d = 21.27 (s, 1J(PtP) 2770 Hz, aa/bb-6), 16.20 (s, 1J(PtP)
1
2700 Hz, ab-6). H NMR (CDCl3): d = 7.42–6.79 (30, m, Ar),
5.80–5.46 (2H, m, CH), 4.67–4.33 (2H, m, CH), 4.12–3.85 (2H,
m, CH2), 3.34–2.98 (4H, m, CH2), 2.92–2.69 (2H, m, CH2). m/z
(FAB) 978 (M+ + Na).
Separation of rac- and meso-PhLb by selective complexation
[PtCl2(rac-PhLb)2] (6) (0.10 g, 0.11 mmol) was suspended in a
mixture of CH2Cl2 (5 cm3) and acetone (5 cm3). Aqueous KCN
solution (3.21 cm3, 0.5 M, 1.60 mmol) was added and the mixture
then vigorously stirred overnight to produce an emulsion. All
the solvents were removed in vacuo and to the resulting solid
dichloromethane (25 cm3) and water (10 cm3) were added. The
dichloromethane layer was syringed off and the aqueous layer was
washed with dichloromethane (2 × 5 cm3). The combined organic
layers were dried over MgSO4, filtered and the solvent was removed
1
in vacuo to give rac-PhLb as a white solid (0.015 g, 40%). 31P{ H}
NMR (CDCl3): d = −5.6 (s).
Preparation of trans-[Pt2(l-Cl)2(meso-BuLb-2ꢀH)2] (7)
meso-BuLb (0.11 g, 0.34 mmol) was dissolved in toluene (10 cm3),
[PtCl2(NCBut)2] (0.15 g, 0.34 mmol) was added and the yellow
solution refluxed for 72 h. The product was obtained as a mustard
solid, which precipitated from the yellow toluene solution. The
product was filtered off and washed with toluene (4 cm3) (0.17 g,
1
46%). 31P{ H} NMR (CDCl3): d = 64.90 (s, 1J(PtP) 4846 Hz). 1H
NMR (CDCl3): d = 8.04–6.86 (18 H, m, Ar), 3.86–3.67 (4H, m),
3.20–2.90 (4H, m), 2.79–2.32 (4H, m), 1.55–1.34 (18H, m, CH3).
13C NMR (CDCl3): d = 206.6 (s, CO), 149.0 (d, J(HH) 13 Hz,
Ar), 137.4 (m, Ar), 135.9 (d, J(HH) 18 Hz, Ar), 130.5 (m, Ar),
128.8–128.2 (m, Ar), 127.8 (s, Ar), 127.4 (s, Ar), 126.0 (d, J(HH)
8 Hz, Ar), 125.4 (d, J(HH) 8 Hz, Ar), 123.5 (dd, J(HH) 19 Hz,
J 4 Hz, Ar), 45.1 (s), 42.5 (dd, J(HH) 15 Hz, J(HH) 5 Hz), 39.0
(dd, J(HH) 45 Hz, J(HH) 11 Hz), 35.3–34.5 (m), 27.4(s). m/z
(FAB) 1108 (M+). Elemental analysis (calc) C: 46.6 (45.53) H:
4.95 (4.37%).
Preparation of trans-[PtCl2(rac-CyLb)2] (9)
rac-CyLb (0.104 g, 0.29 mmol) was dissolved in toluene (10 cm3),
[PtCl2(NCBut)2] (0.058 g, 0.13 mmol) was added and the yellow
solution refluxed for 24 h. The solvent was then removed in vacuo
1
to give the pale yellow solid product. 31P{ H} NMR (toluene): d =
17.3 (s, 1J(PtP) 2591 Hz), 15.0 (s, 1J(PtP) 2535 Hz). m/z (EI) 989
[M + Na]+.
Computational details
Density functional theory geometry optimisations were calculated
for isolated molecules in the gas phase using the Jaguar 6.015
suite of programmes, using the standard Becke–Perdew (BP86)
functional and the 6-31G* basis set on all atoms except platinum,
for which the standard Los Alamos ECP (LACV3P*) basis set was
employed.
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Crystal structure determinations
2 J. B. Rampal, G. D. Macdonell, J. P. Edasery, K. D. Berlin, A. Rahman,
D. van der Helm and K. M. Pietrusiewicz, J. Org. Chem., 1981, 46,
1156.
3 (a) J. B. Rampal, K. D. Berlin, J. P. Edasery, N. Satyamurthy and D.
van der Helm, J. Org. Chem., 1981, 46, 1166; (b) J. B. Rampal, N.
Satyamurthy, J. M. Bowen, N. Purdie and K. D. Berlin, J. Am. Chem.
Soc., 1981, 103, 7602.
4 (a) M. Slany, M. Scha¨fer and M. Ro¨per (BASF), Ger. Pat.,
DE10106348, 2002; (b) G. Eastham (Lucite International), World
Patent, WO024322, 2004.
5 T. Brenstrum, J. Clattenburg, J. Britten, S. Zavorine, J. Dyck,
A. J. Robertson, J. McNulty and A. Capretta, Org. Lett., 2006, 8,
103.
An X-Ray diffraction experiment on 3 was carried out at 100 K
on a Bruker SMART APEX diffractometer; experiments on meso-
BuLb, La, 1, aa-6 and 7 (as its toluene solvate) were carried out
at 173 K on a Bruker SMART diffractometer, using Mo-Ka X-
˚
radiation (k = 0.71073 A); and experiments on the oxide of rac-
CyLb and ab-9 were carried out at 100 K on a Bruker PROTEUM
˚
diffractometer using Cu-Ka X-radiation (k = 1.54178 A); all data
collections were performed using a CCD area-detector, from a
single crystal coated in paraffin oil mounted on a glass fibre.
Intensities were integrated16 from several series of exposures, each
exposure covering 0.3◦ in x. Absorption corrections were based
on equivalent reflections using SADABS V2.10,17 and structures
6 S. L. Featherman and L. D. Quin, J. Am. Chem. Soc., 1975, 97,
4349.
7 L. A. Paquette, Angew. Chem., Int. Ed. Engl., 1990, 29, 609.
8 J. Weiser, O. Golan, L. Fitjer and S. E. Biali, J. Org. Chem., 1996, 61,
8277.
9 H. Werner and H. J. Kraus, J. Organomet. Chem., 1981, 204, 415.
10 (a) A. J. Cheney, B. E. Mann, B. L. Shaw and R. M. Slade, J. Chem.
Soc. D, 1970, 1176; (b) A. J. Cheney, B. E. Mann, B. L. Shaw and R. M.
Slade, J. Chem. Soc. A, 1971, 3833.
2
were refined against all Fo data with hydrogen atoms riding in
calculated positions using SHELXTL.18 Crystal and refinement
data are given in Table 11.
For 7, the structure contains a solvent molecule of toluene
disordered over two positions for every complex molecule present.
The geometry of the toluene was constrained to an ideal geometry
and the atoms were refined isotropically. No disorder was present
in the other crystal structures and refinements proceeded smoothly
to give the structures shown.
CCDC reference numbers 609145–609151 and 611214.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b607490a
11 A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen and F. J.
Timmers, Organometallics, 1996, 15, 1518.
12 J. X. McDermott, J. F. White and G. M. Whitesides, J. Am. Chem. Soc.,
1976, 98, 6521.
13 R. Doyle, P. E. Slade and H. B. Jonassen, Inorg. Synth., 1960, 6,
218.
14 D. Fraccarollo, R. Bertani, M. Mozzon, U. Belluco and R. Michelin,
Inorg. Chim. Acta, 1992, 201, 15.
15 Jaguar 6.0, Schrodinger, LLC, Portland, Oregon, 2005.
16 SAINT integration software, Siemens Analytical X-ray Instruments
Inc., Madison, WI, 1994.
17 G. M. Sheldrick, SADABS V2.10, University of Go¨ttingen, Germany,
2003.
References
18 SHELXTL program system version 5.1, Bruker Analytical X-ray
Instruments Inc., Madison, WI, 1998.
1 R. P. Welcher and N. E. Day, J. Org. Chem., 1962, 27, 1824.
4320 | Dalton Trans., 2006, 4310–4320
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The Royal Society of Chemistry 2006
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