Chelates formed by a constrained bis(diphenylphosphino)xylene; The crystal structures of [FeCl2(anphos)] and [RhCl(CO)(anphos-monoxide)]

Article abstract of DOI:10.1016/j.jorganchem.2004.06.022

The indan derived diphosphine, cis -1,3-(diphenylphosphino)indan (anphos) is synthesised by the addition of Ph₂P (BH₃)Li to cis-1,3-dibromoindan followed by deprotection with diethylamine. Anphos readily forms the bicyclic chelates [RhCl(CO)(anphos)], [PtCl₂(anphos)], [PtCl(Me)(anphos)] and [FeCl₂(anphos)]. The crystal structures of [FeCl₂ (anphos)] and the monoxide complex, [RhCl(CO)(anphosO)] have been determined. Reaction of the diphosphine with [Rh(acac)(CO)₂] under moderate hydroformylation conditions catalysed the formation of 1-heptanal and branched aldehydes from 1-hexene in a ratio of 1.5:1.

Full text of DOI:10.1016/j.jorganchem.2004.06.022

Journal of Organometallic Chemistry 689 (2004) 2963–2968
www.elsevier.com/locate/jorganchem
Chelates formed by a constrained bis(diphenylphosphino)xylene;
the crystal structures of [FeCl2(anphos)] and
[RhCl(CO)(anphos-monoxide)]
Lee J. Higham ,1, Ann J. Middleton, Katie Heslop, Paul G. Pringle ,
*
*
Angharad Barber, A. Guy Orpen
School of Chemistry, University of Bristol, Cantocks Close, Bristol, BS8 1TS, UK
Received 15 June 2004; accepted 17 June 2004
Available online 3 August 2004
Abstract
The indan derived diphosphine, cis-1,3-(diphenylphosphino)indan (anphos) is synthesised by the addition of Ph2P(BH3)Li to cis-
1,3-dibromoindan followed by deprotection with diethylamine. Anphos readily forms the bicyclic chelates [RhCl(CO)(anphos)],
[PtCl2(anphos)], [PtCl(Me)(anphos)] and [FeCl2(anphos)]. The crystal structures of [FeCl2(anphos)] and the monoxide complex,
[RhCl(CO)(anphosO)] have been determined. Reaction of the diphosphine with [Rh(acac)(CO)2] under moderate hydroformylation
conditions catalysed the formation of 1-heptanal and branched aldehydes from 1-hexene in a ratio of 1.5:1.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Diphosphine; Hydroformylation; Synthesis and characterisation
1. Introduction
Here we report the indan-derived diphosphine, an-
phos (1), which has a rigidified xylenyl backbone, and
show that it readily forms chelates with square planar
or tetrahedral metal centres.
The bite angle and flexibility of diphosphines are im-
portant parameters when considering their potential for
application in homogeneous catalysis [1]. Ortho-xylenyl
diphosphines have a flexible C4 backbone and these di-
phosphines have found several applications in catalysis:
a,a-bis(diphenylphosphino)xylene (dppx) [2] with a cal-
culated ligand-preferred bite angle of 90ꢁ has been
reported as a ligand for Pt–Sn catalysed hydroformyla-
tion [3] and rhodium-catalysed CO2 hydrogenation [4].
1,2-Bis(di-tert-butylphosphino)xylene (dbpx) has been
shown to be an excellent ligand for Pd-catalysed pro-
pene methoxycarbonylation, a reaction of potential
commercial value [5].
2. Results and discussion
The anphos ligand was synthesised according to
Scheme 1. The dibromo precursor 2 was made by the
reaction of N-bromosuccinimide with indan [6]. Treat-
ment of 2 with LiPPh2 did not give anphos and the only
detected product was Ph2PH. However, Ph2PBH3Li
reacted with 2 to give the borane-protected diphosphine
2Æ(BH3)2 which upon treatment with diethylamine
yielded anphos (1). Our attempts to make cis-1,3-(di-
tert-butylphosphino)indan under similar conditions by
reaction of 2 with But2PLi or Bu2t PLi Á BH3 were
unsuccessful.
*
Corresponding authors.
E-mail address: lee.higham@ucd.ie (L.J. Higham).
1
Present address: Chemistry, University College Dublin, Belfield,
Dublin, Ireland. Tel.: +35317162316; fax: +35317162308.
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.06.022

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L.J. Higham et al. / Journal of Organometallic Chemistry 689 (2004) 2963–2968
Br
PPh2.BH3
PPh2
2 Ph2P(BH3)Li
excess Et2NH
Br
PPh2.BH3
PPh2
2
1
Scheme 1. Synthesis of anphos.
Ph2
P
Cl
Ph2
P
Cl
Pt
Fe
Cl
Ph2P
PPh2
Cl
4
3
[PtCl2(cod)]
FeCl2
Ph2
P
Me
Cl
Pt
PPh2
Ph2P
[PtClMe(cod)]
PPh2
5
1
0.5 [Rh2Cl2(CO)4]
Ph2
Ph2
CO
P
[O]
O
P
Rh
Cl
Ph2
P
Rh
Cl
CO
Ph2P
7
6
Scheme 2. Anphos coordination chemistry.
A summary of the coordination chemistry investi-
gated with anphos is shown in Scheme 2.
118.22(3)ꢁ and 93.18(3)ꢁ, respectively. The bond angles
in complexes of the type [FeCl2P2] (where P2 is a diphos-
phine or two monophosphines) span a range of values:
[FeCl2(iPr2PCH2CH2PiPr2)] [7] for example, has a Cl–
Fe–Cl bond angle of 118.0(4)ꢁ and a P–Fe–P value of
83.7(3)ꢁ, whereas for [FeCl2(tBu2PMe)2] the correspond-
ing angles are 110.97(3)ꢁ and 106.375(26)ꢁ [8]. Complex-
es of the type [FeCl2(PR3)2] and [FeCl2(diphos)] have
been shown to insert diazoalkanes into the Fe–P bonds
[9] and catalyse the reaction of propargyl sulphides with
trimethylsilyldiazomethane to give homoallenylsilanes
[10].
Treatment of anhydrous FeCl2 with anphos in
CH2Cl2 gave 3 which has been fully characterised (see
Section 4). Crystals of the same product 3 were obtained
when anphos reacted with [Fe(CO)3(bda)] in CDCl3
over several days. The crystal structure of 3 was deter-
mined and is shown in Fig. 1 (selected bond lengths
and angles are given in Table 1).
It can be seen from the data that [FeCl2(anphos)] (3)
adopts a strongly distorted tetrahedral structure, with
bond angles for Cl(1)–Fe–Cl(2) and P(1)–Fe–P(2) of

L.J. Higham et al. / Journal of Organometallic Chemistry 689 (2004) 2963–2968
2965
Fig. 1. The crystal structure of 3.
Fig. 2. The crystal structure of 7.
Table 1
Selected bond lengths and angles for [FeCl2(anphos)] (3)
with a larger bite angle. The constraints of the indan
backbone decisively favour the formation of the chelate
6 rather than a binuclear [Rh2Cl2(CO)2(l-diphos)2]
species.
It was found that CH2Cl2 solutions of 6 slowly depos-
ited red-brown crystals suitable for X-ray crystallogra-
phy. The crystal structure revealed that the
coordinated anphos had been mono-oxidised to give a
P,O-chelate 7 (Fig. 2).
From Table 2 the degree of distortion in the interior
angles of the five-membered indan ring in 7 can be
clearly seen, the angles ranging from 103.6(8)ꢁ to
111.3(9)ꢁ (102.3(2)ꢁ to 110.9(2)ꢁ for 3). The remaining
bond lengths and angles are broadly as expected. Coor-
dination at rhodium is square planar with the phosphine
oxide function of the oxidised anphos ligand trans to
carbonyl and the remaining phosphine trans to the chlo-
ride ligand, in accord with the concept of anti-symbiosis.
The 31P NMR spectrum of 7 (CDCl3) gives the follow-
˚
Bond lengths (A)
Angles (ꢁ)
Fe(1)–Cl(2)
Fe(1)–Cl(1)
Fe(1)–P(2)
2.2292(7)
2.2297(7)
2.4390(8)
2.4627(8)
1.546(4)
1.548(4)
1.512(3)
1.391(3)
1.392(4)
1.390(4)
1.373(4)
1.383(4)
1.385(3)
1.518(3)
Cl(2)–Fe(1)–Cl(1)
Cl(2)–Fe(1)–P(2)
Cl(1)–Fe(1)–P(2)
Cl(2)–Fe(1)–P(1)
Cl(1)–Fe(1)–P(1)
P(2)–Fe(1)–P(1)
118.22(3)
114.80(3)
103.77(3)
113.15(3)
110.64(3)
93.18(3)
105.7(2)
102.3(2)
120.6(2)
128.6(2)
110.9(2)
120.4(2)
128.9(3)
110.7(2)
102.4(2)
Fe(1)–P(1)
C(13)–C(21)
C(13)–C(14)
C(14)–C(15)
C(15)–C(16)
C(15)–C(20)
C(16)–C(17)
C(17)–C(18)
C(18)–C(19)
C(19)–C(20)
C(20)–C(21)
C(21)–C(13)–C(14)
C(15)–C(14)–C(13)
C(16)–C(15)–C(20)
C(16)–C(15)–C(14)
C(20)–C(15)–C(14)
C(19)–C(20)–C(15)
C(19)–C(20)–C(21)
C(15)–C(20)–C(21)
C(20)–C(21)–C(13)
Addition of 1 equivalent of anphos to [PtCl2(cod)]
gave 4 as a white solid. The 31P{1H} NMR spectrum
of the product is a singlet at d À3.5 ppm with
1JPtP =3484 Hz, consistent with the cis-PtCl2 geometry.
Similarly, addition of 1 equivalent of anphos to
[PtClMe(cod)] gave 5. The 31P{1H} NMR spectrum
showed two doublets at d 4.6 and 12.7 ppm (1JPP 20
Hz) with 1JPtP 1704 and 4344 Hz, respectively and there-
fore the signal at 4.6 is assigned to the P trans to methyl.
The product of the reaction of anphos with
[RhCl(CO)2]2 was assigned the chelate structure 6 on
the basis of 31P NMR, IR and mass spectrometric data
(see Section 4). The 31P{1H} NMR spectrum showed
two doublets of doublets at d 7.7 (JRh–P =120.0 Hz)
2
3
ing data; P(1) 54.4 ppm, JRh–P =6.0 Hz, JP–P =2.8
1
3
Hz; P(2) 53.1 ppm, JRh–P =179.1 Hz, JP–P =2.8 Hz.
The anphos ligand (1) was tested for the rhodium-
catalysed hydroformylation of 1-hexene. Under the
Table 2
Selected bond lengths and angles for [RhCl(CO)(anphos-O)] (7)
˚
Bond lengths (A)
Angles (ꢁ)
Rh(1)–C(34)
Rh(1)–O(2)
Rh(1)–P(2)
Rh(1)–Cl(1)
P(1)–O(2)
1.800(13)
2.076(6)
2.232(3)
2.387(3)
1.517(7)
1.563(13)
1.518(13)
1.369(13)
1.412(14)
1.370(14)
1.140(12)
O(1)–C(34)–Rh(1)
P(1)–O(2)–Rh(1)
O(2)–Rh(1)–P(2)
C(34)–Rh(1)–Cl(1)
C(1)–C(7)–P(1)
C(3)–C(2)–C(1)
C(21)–C(3)–C(2)
C(2)–C(1)–C(7)
C(3)–C(21)–C(7)
C(1)–C(7)–C(21)
178.5(11)
136.1(4)
96.50(19)
89.8(4)
111.4 (7)
105.4(8)
109.4(9)
104.8(8)
111.3(9)
103.6(8)
2
and 32.8 ppm (1JRh–P =168.4 Hz) with JP–P of 47.0
C(1)–C(7)
C(2)–C(3)
C(3)–C(4)
C(3)–C(21)
C(8)–C(21)
C(34)–O(1)
Hz. The 31P NMR and IR (mCO 2003 cmÀ1) data for 6
are similar to those for the five-membered chelate
[RhCl(CO)(dppe)] [11] and differ from the bridged binu-
clear complexes trans-[Rh2Cl2(CO)2(l-dppp)2] and
trans-[Rh2Cl2(CO)2(l-dppb)2] formed by diphosphines

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L.J. Higham et al. / Journal of Organometallic Chemistry 689 (2004) 2963–2968
reaction conditions employed (7.5 bar H2/CO, 36 ꢁC, 16
h) the conversion to aldehydes was 91% with a n:iso ra-
tio of 1.5:1. These results are similar to those for dppx
which we tested under the same conditions and observed
a conversion of 73% and a n:iso ratio of 2.4:1. Anphos
and dppx react with the precatalyst [Rh(acac)(CO)2] in
C6D6 to give species which have similar 31P NMR pa-
rameters (1JRh–P =186 and 189 Hz, respectively).
at reflux for 2 h resulting in a suspension in a pale peach
solution. The solution was filtered, and the solid washed
with carbon tetrachloride. The filtrates were combined
and the solvent was removed in vacuo to give a pale or-
ange oil. Hexane (5 cm3) was added to this and the mix-
ture was cooled to À5 ꢁC, producing a pale yellow
crystalline solid. This solid was recrystallised from ace-
tone to give pale yellow crystals. Yield=1.7 g, 6.0 mmol,
14%. 1H NMR data: 2.94 (dt, 1H, J=16.2, 2.8 Hz), 3.27
(dt, 1H, J=16.2, 6.8 Hz), 5.50 (dd, 2H, J=6.8, 2.8 Hz),
7.3–7.5 (m, 4H) ppm.
3. Conclusion
The constrained bite angle in anphos has the effect of
making its coordination chemistry resemble dppe in its
propensity to chelate. In terms of hydroformylation cat-
alytic activity and selectivity however, anphos performs
similarly to its unconstrained analogue dppx. These re-
sults further confirm the complexity of the factors at
work in hydroformylation catalysis.
4.3. Synthesis of 1,3-bis(diphenylphosphino)indan (an-
phos) (1)
Diphenylphosphine (1.25 cm3, 7.20 mmol) in THF
(15 cm3) was cooled to 0 ꢁC and then BH3 ÆTHF (7.20
cm3, 7.20 mmol, 1M solution in THF) was added slowly
(over 10 min) to the stirred solution. The resulting solu-
tion of PPh2HÆBH3 was cooled to À78 ꢁC and then nBu-
Li (4.50 cm3, 7.20 mmol, 1.6 M solution in hexanes) was
added dropwise over 10 min. The solution was then al-
lowed to warm to room temperature. This was then add-
ed by syringe to a stirred, cooled (0 ꢁC) solution of 2
(1.00 g, 3.60 mmol) in THF (10 cm3). The ice-bath
was removed and the reaction stirred for 3 h. An excess
of diethylamine (30 cm3) was added and the reaction
mixture was stirred for 48 h. The volatiles were removed
to give a white powder, which was extracted into pen-
tane (40 cm3). Filtration from the salt by-products fol-
lowed by removal of the pentane in vacuo gave a
white powder that was washed with 2·40 cm3 of meth-
anol. The product was dried at 50 ꢁC for 5 h.
Yield=0.40 g, 22.8%. NMR (CD2Cl2): dH 7.16–7.59
(m, 20H, ArH), 6.82 (m, 2H, ArH), 6.37 (m, 2H,
ArH), 3.96 (m, 2H, CH), 2.38 (m, 1H, CH2), 1.99 (m,
1H, CH2) ppm; dC 34.6 (t, CH2), 41.8 (m, CH), 125.0-
134.3 (m, CH, aromatic C) 137.7 (m, quaternary C),
144.3 (m, quaternary C) ppm; dP À7.4 (s) ppm; IR (sol-
id, cmÀ1): m(aryl-H) 3068 (w), 746 (s), 737 (s), m(C‚C)
1598 (m), m(C–H) 1478 (m), m(aryl-P) 1431 (m); EI mass
spectrum: m/z 486 (M+), 502 (M+ +O), 518 (M+ +2O).
Elemental composition found by accurate mass meas-
urement was within 1.6 ppm.
4. Experimental
4.1. General methods
All operations were carried out under a N2 atmos-
phere using standard Schlenk line techniques. Dichloro-
methane, diethyl ether, hexane, and tetrahydrofuran
were dried and purged with nitrogen using the Grubbs
system [12]. Anhydrous n-pentane was purchased from
Aldrich. Carbon tetrachloride and acetone were dried
˚
over 4 A molecular sieves. Diethylamine was distilled
from potassium hydroxide. Indan, N-bromosuccinimide
and [Rh2Cl2(CO)2] were purchased from Aldrich.
[PtCl2(1,5-cyclooctadiene)] [13] and [PtCl(Me)(1,5-cy-
clooctadiene)] [14] were prepared according to the liter-
ature procedures. [Fe(CO)3(benzylideneacetone)] was a
gift from BP chemicals but it can be prepared by the
method of Brookhart and Nelson [15]. Anhydrous FeCl2
was supplied by Fluka.
EI and FAB mass spectra were recorded on a Micro-
mass MD800 and an Autospectrometer. Infrared spec-
tra were recorded on a Perkin–Elmer Spectrum 1
Spectrometer as KBr disks or as powder samples using
a universal ATR sampling accessory. The NMR spectra
were recorded on JEOL ecp300 and 400 spectrometers
1
(d relative to SiMe4 for H and 13C spectra and 85%
4.4. Synthesis of [FeCl2(anphos)] (3)
H3PO4 for 31P spectra) at 23 ꢁC in CDCl3 unless other-
wise stated. CDCl3, CD2Cl2 and C6D6 were purged with
4.4.1. From anhydrous FeCl2
˚
nitrogen and dried over 4 A molecular sieves.
Anphos (1.50 g, 3.10 mmol) and anhydrous FeCl2
(0.39 g, 3.10 mmol) were combined in a flask. The addi-
tion of dichloromethane (20 cm3) yielded a suspension,
which was stirred for 1 week. No solution 31P NMR sig-
nal was observed. The solution was filtered off and
cooled to 0 ꢁC. The resultant white precipitate was fil-
tered, washed with 5 cm3 of dichloromethane and dried
4.2. Synthesis of cis-1,3-dibromoindan (2)
Indan (5.0 g, 42.3 mmol) was dissolved in CCl4 (70
cm3) and N-bromosuccinimide (18.8 g, 105.8 mmol)
was added as a solid. The reaction mixture was heated

L.J. Higham et al. / Journal of Organometallic Chemistry 689 (2004) 2963–2968
2967
in vacuo at 45 ꢁC for 4 h. Yield=1.54 g, 81.0%. IR (sol-
4.6. Synthesis of [PtClMe(anphos)] (5)
id, cmÀ1): m(aryl-H) 3051 (w), 749 (s), 743 (s), m(C‚C)
1590 (w), m(C–H) 1484 (m), m(aryl-P) 1435 (s). FAB
mass spectrum: m/z 612 (M+). Elemental Anal.
C33H28P2FeCl2 requires: C, 64.63; H, 4.60. Found C,
64.45; H, 4.80%. Recrystallisation from CDCl3 yielded
green crystals (0.68 g, 35.8%).
A dichloromethane (20 cm3) solution of anphos (0.14
g, 0.28 mmol) was added to [PtClMe(1,5-cyclooctadi-
ene)] (0.10 g, 0.28 mmol). The pale yellow solution
was stirred for 1 h, during which time a white precipitate
appeared. The solid was filtered, washed with 2·5 cm3
portions of cold chloroform and filtered again. The
white product was dried in vacuo. Yield=0.15 g,
73.6%. 31P NMR: 4.6 (d, JP–P =20 Hz, JPt–P =1704
Hz), 12.7 (d, JP–P =20 Hz, JPt–P =4344 Hz) ppm. FAB
mass spectrum: m/z 717 (M+ ÀCH3), 696 (M+ ÀCl).
4.4.2. From [Fe(CO)3(benzylideneacetone)]
Anphos (0.05 g, 0.10 mmol) was dissolved in CDCl3
(0.7 cm3), solid [Fe(bda)(CO)3] (0.03 g, 0.10 mmol)
was added and the mixture transferred to an NMR tube.
No immediate colour change was apparent and only un-
coordinated anphos was detected by 31P NMR. The
tube was wrapped in aluminium foil and after 16 h the
solution had become yellow and no anphos signal was
detected by 31P NMR. Over a period of weeks green
crystals deposited which were suitable for X-ray
cystallography.
4.7. Synthesis of cis-[RhCl(CO)(anphos)] (6)
To a solution of anphos (0.14 g, 0.29 mmol) in dichlo-
romethane (20 cm3) was added [RhCl(CO)2]2(0.06 g,
0.14 mmol). Evolution of CO ensued and the resultant
yellow/brown solution was stirred for 1 h at room tem-
perature. Removal of the solvent afforded a deep orange
solid that was washed with 2·10 cm3 portions of diethyl
ether and dried in vacuo. Yield=0.12 g, 66.2%. 31P
NMR: 7.7 (dd, JRh–P =120.0 Hz, JP–P =47.0 Hz), 32.8
(dd, JRh–P =168.4 Hz, JP–P =47.0 Hz) ppm. IR (KBr,
cmÀ1) 2003 s m(CO). FAB mass spectrum: m/z 624
(M+ ÀCO), 617 (M+ ÀCl), 589 (M+ ÀCO, Cl).
4.5. Synthesis of [PtCl2(anphos)] (4)
To a solution of [PtCl2(1,5-cyclooctadiene)] (0.10 g,
0.26 mmol) in dichloromethane (20 cm3) was added
anphos (0.14 g, 0.28 mmol). The resulting solution was
stirred for 1 h at room temperature, followed by
removal of the solvent in vacuo to afford a white solid.
This was washed with 2·10 cm3 portions of diethyl
ether, filtered and dried in vacuo. Yield=0.07 g,
36.3%. 31P NMR: À3.5 (s, JPt–P =3484 Hz) ppm. FAB
mass spectrum: m/z 717 (M+ ÀCl), 680 (M+ À2Cl).
4.8. Catalytic Hydroformylation of 1-hexene
The diphosphine (0.019 mmol) was added to a solu-
tion of [Rh(acac)(CO)2] (5.0 mg, 0.019 mmol) in anhy-
drous C6D6 (3 cm3) and the emerald green solution
Table 3
Important crystallographic parameters for 3 and 7
Parameters
[FeCl2(anphos)] (3)
C33H28Cl2FeP2
173(2)
[RhCl(CO)anphosO] (7)
C37H31ClO2P2Rh
173(2)
Empirical formula
Temperature (K)
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/c
Unit cell dimensions
˚
a (A)
˚
9.1548(12)
16.818(2)
19.420(2)
90
10.3901(17)
14.305(2)
b (A)
˚
c (A)
22.889(4)
90
a (ꢁ)
b (ꢁ)
c (ꢁ)
100.485(2)
90
94.335(3)
90
Z
4
0.825
4
0.707
Absorption coefficient (mmÀ1
Crystal size (mm3)
Reflections collected
Independent reflections
Absorption correction
Refinement method
Goodness-of-fit on F2
Final R indices [I>2r(I)]
R indices (all data)
)
0.10·0.20·0.40
18809
0.15·0.80·0.50
13657
6721 [R(int)=0.0467]
Multiscan
Full-matrix least-squares on F2
0.944
4137 [R(int)=0.1478]
Multiscan
Full-matrix least-squares on F2
1.028
R1 =0.0397, wR2 =0.0849
R1 =0.0815, wR2 =0.0970
R1 =0.0631, wR2 =0.1378
R1 =0.1382, wR2 =0.1656

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L.J. Higham et al. / Journal of Organometallic Chemistry 689 (2004) 2963–2968
became orange. The solution was transferred under ni-
trogen to the autoclave which was then evacuated and
refilled three times with a 1:1 mixture of H2 and CO.
The reaction mixture was stirred for 1 h at 36 ꢁC and
7.5 bar of syngas. 1-Hexene (1.2 cm3, 9.6 mmol) was in-
jected into the autoclave and the reaction monitored by
syngas uptake. After 16 h the reaction was stopped and
the autoclave purged with nitrogen. The ratio of
linear:branched products was calculated by integration
of the 1H NMR signals (in C6D6) for the aldehyde
protons at d 9.22 (n) and 9.15 (i).
Data Centre, CCDC No. 241326 for 3 and 241327 for
7. Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44(1223)336033 or e-
mail: deposit@ccdc.cam.ac.uk or www.ccdc.cam.ac.uk/
conts/retrieving.html.
Acknowledgement
We thank BP Chemicals for financial support and the
Leverhulme Trust for a Research Fellowship (to P.G.P.)
and Johnson Matthey for the loan of precious metal
compounds.
4.9. Crystal structure analysis of 3 and 7
X ray diffraction experiments on 3 as a benzene sol-
vate and 7 were carried out at À100 ꢁC on a Bruker
SMART diffractometer using Mo Ka X-radiation,
˚
References
a=0.71073 A. Crystal and refinement data are given in
Table 3: absorption corrections were based on equiva-
lent reflections and structures refined against all F2o data
with hydrogen atoms riding in calculated positions. In
the case of 3 intensity data were very weak. A benzene
solvate molecule was found in the electron density differ-
ence map, disordered about a special position. Attempts
to model this disorder produced unsatisfactory results
and an improved model was obtained by applying a dif-
fuse solvent correction to the data using the Squeeze
routine in the Platon suite of software [16]. Furthermore
the value of (2 ccosa)/a is almost exactly À1/3ꢀ indicat-
ing that twofold rotational twinning about the a axis is
possible for the lattice of this crystal. A refinement was
attempted on the data with an appropriate twinning ma-
trix (1 0 0 0 À1 0 À0.3333 0 À1). This did not improve
the final residuals and gave a scale factor for the second
twin component of almost zero. These results would ap-
pear to indicate that a single crystal is present with no
contribution from a second twin component.
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5. Supplementary material
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Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic