The preparation and complexation of 5,10-bis(diphenylphosphino)phenazine

Article abstract of DOI:10.1016/j.inoche.2003.10.019

Reaction of 5,10-dihydrophenazine with two equivalents of Ph ₂PCl, in the presence of n-BuLi at -78°C in thf gives Ph ₂PN(C₆H₄)(C₆H₄)NPPh ₂ (1) which can be oxidised with selenium to Ph₂P(Se) N(C₆H₄)(C₆ H₄)NP(Se)Ph₂ (2) or coordinated with Pt(II) in cis-[PtCl₂{Ph₂PN(C ₆H₄)(C₆H₄)NPPh₂}] (3) The structure of 3 reveals a severely distorted (non-planar) phenazine backbone.

Full text of DOI:10.1016/j.inoche.2003.10.019

Inorganic Chemistry Communications 7 (2004) 201–203
www.elsevier.com/locate/inoche
The preparation and complexation
of 5,10-bis(diphenylphosphino)phenazine
Mireia Rodriguez i Zubiri, Heather L. Milton, David J. Cole-Hamilton,
*
Alexandra M.Z. Slawin, J. Derek Woollins
School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK
Received 2 October 2003; accepted 11 October 2003
Published online: 11 December 2003
Abstract
Reaction of 5,10-dihydrophenazine with two equivalents of Ph2PCl, in the presence of n-BuLi at )78 °C in thf gives
Ph2PN(C6H4)(C6H4)NPPh2 (1) 1 which can be oxidised with selenium to Ph2P(Se)N(C6H4)(C6 H4)NP(Se)Ph2 (2) 2 or coordinated
3
with Pt(II) in cis-[PtCl2{Ph2PN(C6H4)(C6H4)NPPh2}] (3) The structure of 3 reveals a severely distorted (non-planar) phenazine
backbone.
Ó 2003 Published by Elsevier B.V.
Keywords: X-ray crystallography; Synthesis; Structure
Phosphine ligands have many important applications
in organometallic chemistry and catalysis [1–4]. We have
recently demonstrated that phosphines derived from two
N-bound pyrrolidine groups and one alkyl or aryl group
are amongst the strongest r-donor ligands, and sur-
prisingly are even more electron rich than tris(N-pyr-
rolidinyl)phosphine [5]. We have also examined the
ability of P–N containing phosphines to function as
catalysts [6] and recently studied structural facets in-
cluding cone angle effects [7]. We have now extended our
studies to investigate the properties of the new phos-
phine formed from 5,10-dihydrophenazine – in part to
establish if it possible to distort the phenazine backbone
sufficiently to obtain bidentate coordination – and since
* Corresponding author. Tel.: +441334463869; fax: +441334463384.
E-mail addresses: jdw3@st-andrews.ac.uk, jdw3@st-and.ac.uk (J.D. Woollins).
1
Ph2PN(C6H4)(C6H4)NPPh2 (1). To a )78 °C thf (40 ml) solution of 5,10-dihydrophenazine (1.053 g, 5.78 mmol) was added dropwise a hexane
solution of BuLi (4.8 ml, 2.5 mol dmꢀ3, 12.08 mmol). The mixture was stirred at )78 °C for 1 h and another 30 min at room temperature. The
reaction solution was cooled to )78 °C again and to it was added dropwise a solution of diphenylchlorophosphine (2.1 ml, 2.613 g, 11.84 mmol) in thf
(10 ml) over 40 min. Stirring was continued for another 1 h at )78 °C and overnight at room temperature. The solution was evaporated to dryness in
vacuo and dichloromethane (30 ml) was added. Lithium chloride, which precipitated, was removed by filtration under nitrogen and then the volatiles
were evaporated in vacuo to leave a yellow solid. Yield: 2.896 g, 91%; Microanalysis: Found (Calcd) C 78.5 (78.5), H 5.1 (5.1), N 4.8 (5.1)%; 31P–{H}
NMR (CDCl3): 61.0 (s) ppm; Selected IR data (KBr): m(PN) 951 cmꢀ1; FABþ MS: m/z 550 [M], 551 [M + Hþ], 573 [M + Naþ].
2
Ph2P(Se)N(C6H4)(C6H4)NP(Se)Ph2 (2). To a dry and degassed toluene (10 ml) solution of selenium (0.029 g, 0.36 mmol) was added solid
Ph2PN(C6H4)(C6H4)NPPh2 (0.100 g, 0.18 mmol). The solution was heated to reflux for ca. 2–3 h and allowed to cool to room temperature. The
solution was evaporated to dryness in vacuo and the solid was dissolved in dichloromethane (2 ml). The dichloromethane solution was filtered
through Celite and diethyl ether (20 ml) was added. The white product was collected by suction filtration and washed with diethyl ether (2 ꢁ 10 ml).
Yield: 0.112 g, 88%; Microanalysis: Found (Calcd) C 60.3 (61.0), H 3.8 (4.0), N 3.8 (4.0)%; 31P–{H}NMR (CDCl3): 58.5 (s) ppm, 1J(77Se–31P) 832
Hz; selected IR data (KBr): m(PN) 973 cmꢀ1, m(PSe) 565 cmꢀ1; FABþ MS: m/z 708 [M], 709 [M + H]þ.
3
cis-[PtCl2{Ph2PN(C6H4)(C6H4)NPPh2}] (3). To a dichloromethane (5 ml) solution of [PtCl2(cod)] (0.068 g, 0.18 mmol) was added solid
Ph2PN(C6H4)(C6H4)NPPh2 (0.100 g, 0.18 mmol) and the colourless solution stirred for ca. 2–3 h. The solution was concentrated under reduced
pressure to ca. 1 ml and diethyl ether (10 ml) added. The white product was collected by suction filtration and washed with diethyl ether (2 ꢁ 10 ml).
Yield: 0.118 g, 80%; Microanalysis: Found (Calcd) C 53.0 (53.0), H 3.4 (3.5), N 3.3 (3.4)%; 31P–{H} NMR (CDCl3): 43.3 (s) ppm, 1J(195Pt–31P)
3854.6 Hz; selected IR data (KBr): m(PN) 949 cmꢀ1, m(PtCl) 311 and 291 cmꢀ1; FABþMS: m/z 781 [M–Clꢀ], 839 [M + Naþ], 816 [M].
1387-7003/$ - see front matter Ó 2003 Published by Elsevier B.V.
doi:10.1016/j.inoche.2003.10.019

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M. Rodriguez i Zubiri et al. / Inorganic Chemistry Communications 7 (2004) 201–203
we also have an interest in the ease of distortion of
planar aromatic systems [8].
and dichloromethane and air- and moisture-stable for
short periods in the solid state but oxidises readily in
solution in air.
H
N
N
1 was oxidised to the P(V) diselenide 2 by stirring at
reflux in toluene with selenium. Alternatively, reaction of
1 with PtCl2(cod) gives cis-[PtCl2{Ph2PN(C6H4) (C6H4)
NPPh2}] (3). The 31P–{1H} NMR spectrum of 3 is a
singlet with satellites due to coupling to 195Pt (d(P) 43.3
ppm, 1J{195Pt–31P} 3855 Hz); it has the expected parent-
ion (m/z 818,816) and fragmentation patterns consistent
with the loss of one chloride [m/z 781 [M–Clꢀ]). Ele-
mental analysis data are in agreement with calculated
values and the IR spectrum shows bands due to m(P–N)
(949 cmꢀ) and m(PtCl) (311 cmꢀ1).
Na2S2O4/H2O
O2
ð1Þ
N
N
H
Phenazine
5,10-Dihydrophenazine
5,10-Dihydrophenazine (Eq. 1) was reacted with two
equivalents of Ph2PCl, in the presence of n-BuLi at
4
)78 °C, in thf to give 1 in 91% yield (Eq. 2).
PPh2
H
N
N
thf, -78oC
Ph2PCl
+
n-BuLi
The molecular structure of 3 confirms that the ligand
is bidentate and in a cis geometry and that the chloride
ligands are mutually cis. The complex contains two
seven-membered Pt–P–N–C–C–N–P rings and the metal
adopts the expected square planar geometry. The
square-planar platinum centre is distorted and the bite
angle of the ligand is larger than the ideal 90° with P(1)–
Pt(1)–P(6) 99.90(3)° whilst Cl–Pt–Cl is 90.37(3)°. The
backbone of the ligand forms an Ôumbrella-likeÕ struc-
ture about the platinum centre with the C12N2 tricyclic
ring adopting a butterfly geometry with the aryl rings
being inclined by 122° to each other and the N(2) and
N
N
H
PPh2
ð2Þ
The 31P–{1H}NMR spectrum of 1 consists of a sin-
glet at d(P) 61.0 ppm – the large downfield shift when
compared to its P–C relative [9,10] (PAnP, d(P) ¼ )21.9
ppm) reflecting the substitution of the carbon centres in
PAnP by nitrogen atoms in 1 (it should be noted that
PanP is the aromatic analogue of 1 there is no direct
carbon analogue).
ꢀ
N(5) atoms lying 0.45 and 0.50 A above the C(3)–C(4)–
PPh2
C(11)–C(16) mean plane, and C–N–C angles of ca. 109°
as appropriate for sp3 hybridised nitrogen atoms.
The P–N bond lengths in 3 are at the upper end of the
range we have observed in P–N containing phosphines
[11].
(PAnP)
PPh2
FABþ mass spectrometry confirms the proposed
identity of the ligand 1 with the expected parent-ion
peaks (m/z 550 [M], 551 [M + Hþ] and 573 [M + Naþ])
whilst its IR spectrum shows a band that can be assigned
to m(P–N) (951 cmꢀ1) and elemental analysis data are in
agreement with calculated values. 1 is soluble in both thf
We tested the usefulness of 1 for the catalytic hydro-
formylation of oct-1-ene using a batch autoclave and
similar conditions to previously [6] – it proved to be fairly
active with a similar initial rate of reactivity to the ho-
mopiperazine ligand Ph2PN(C3H6)(C2H4)NPPh2 (4)
(2:45 ꢁ 10ꢀ3 of CO uptake in 1 versus 2:98 ꢁ 10ꢀ3 mol
dmꢀ3 in the piperazine) and a rather better lin-
ear:branched ratio of the aldehyde produce (2.5:1 in 1
versus 1.7:1 in 4) which suggest that 1 may have some
potential in catalytic applications – and certainly that it is
robust enough to behave as a supporting ligand under
hydroformylation conditions. According to simple mo-
lecular modelling studies although 1 and 4 have different
natural bite angles [ca. 90° and 110°, respectively) they
have similar flexibility ranges in their bite angles and
this may be the most significant feature in relating their
similarity in catalytic behaviour. Further work is in
progress.
4
Catalytic studies (1) The ligand (0.03 mmol, 0.005 mol dmꢀ3),
[Rh(CO)2(acac)] (5.16 ꢁ 10ꢀ3 g, 0.02 mmol, 0.004 mol dmꢀ3) and
toluene (4 ml) were charged into a Schlenk tube and stirred until
complexation of the rhodium complex with the phosphine species
(total dissolution). The phosphine/rhodium ratio used was 3/2. This
solution was placed in a glass lined steel autoclave, CO/H2 added until
20 bar pressure, the autoclave was heated to 100 °C for the appropriate
reaction time and stirred magnetically.
Single crystal X-ray diffraction studies on crystals were performed
using a Bruker SMART diffractometer with graphite-monochromated
ꢀ
Mo Ka radiation (k ¼ 0:71073 A). The structure was solved by direct
methods, the non-hydrogen atoms were refined with anisotropic dis-
placement parameters; hydrogen atoms were fixed. Structural refine-
ments were by the full-matrix least-squares method on F2 using
SHELXTL [12].
(3) C36H28N2P2Cl2Pt, M ¼ 816:5, monoclinic, a ¼ 10:7076ð17Þ, b ¼
Supplementary data
ꢀ
ꢀ3
15:392ð3Þ, c ¼ 19:078ð3Þ A, b ¼ 92:036ð3Þ°. U ¼ 1138 A , T ¼ 125 K,
space group P2ð1Þ=n, Z ¼ 4, l(Mo Ka) ¼ 4.77 mmꢀ1. Of 13,327 mea-
sured data, 4479 were unique (Rint ¼ 0:0308), to give R1 ½I > 2rðIÞꢂ ¼
0:0201.
Crystallographic data for the structural analyses has
been deposited with the Cambridge Crystallographic

M. Rodriguez i Zubiri et al. / Inorganic Chemistry Communications 7 (2004) 201–203
203
http://www.ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk
(see Fig. 1).
Acknowledgements
We are grateful to Johnson Matthey for loans of
precious metals.
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ꢀ
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