Synthesis and coordination of 7-diphenylphosphinoazaindole (dppai)

Article abstract of DOI:10.1016/j.inoche.2004.08.007

Index entry: 7-diphenylphosphinoazaindole has been synthesised and coordinated as a P,N bidentate ligand. 7-diphenylphosphinoazaindole has been synthesised and coordinated as a P,N bidentate ligand. Reaction of dppai with [PtCl₂(cod)], [PtClMe(cod)] and [PtClPh(cod)] in dichloromethane gives [PtCl₂(dppai-P,N)], [PtClMe(dppai-P,N)] and [PtClPh(dppai-P,N)] respectively.

Full text of DOI:10.1016/j.inoche.2004.08.007

Inorganic Chemistry Communications 7 (2004) 1106–1108
www.elsevier.com/locate/inoche
Synthesis and coordination of 7-diphenylphosphinoazaindole (dppai)
Heather L. Milton, Matthew V. Wheatley, Alexandra M.Z. Slawin,
*
J. Derek Woollins
School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9NB, UK
Received 17 June 2004; accepted 7 August 2004
Available online 11 September 2004
Abstract
7-diphenylphosphinoazaindole has been synthesised and coordinated as a P,N bidentate ligand. Reaction of dppai with
[PtCl2(cod)], [PtClMe(cod)] and [PtClPh(cod)] in dichloromethane gives [PtCl2(dppai-P,N)], [PtClMe(dppai-P,N)] and
[PtClPh(dppai-P,N)] respectively.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Ligands; Phosphines; Crystal structure
1) proceeds straightforwardly (Eq. (1)) to give 1 in
36% yield.
N
NH
N
N
PPh2
PPh2
Ph2P-Cl, Et3N
DMAP, thf
dppap
dppai
N
N
H
N
N
ð1Þ
PPh2
1
Hemilabile ligands continue to illicit great interest.
The chemistry of dppap has been thoroughly explored
by Aucott et al. [1], furthermore we have studied a
range of phosphines obtained by P–N bond forma-
tions [2–7]. Here we report on the chemistry of an
analogue of dppap which has the rotational freedom
about the amine functionality removed by addition
of a second ring thus providing a stabilising influence.
The synthesis of 7-diphenylphosphinoazaindole (dppai,
This colourless solid is moderately air stable, it will
completely degrade when exposed to air for a few
days, it is however very soluble in all common labora-
tory solvents. The 31P NMR (CDCl3) displays a sin-
glet at d(P) 33.2 ppm, which is similar to dppap
(26.4 ppm). The pyC[6] proton is observed at d(H)
8.4 ppm as a double doublet, (JH–H 5 and 2 Hz).
The m(P–N) vibration is observed at 983 cmꢀ1 and
the m(C–N) in the pyridyl ring is at 1589 cmꢀ1
.
Reaction of dppai with [PtCl2(cod)] in dichloro-
methane gives [PtCl2(dppai-P,N)], 2 with d(P) 55
ppm, and JPt–P of 4160 Hz. This NMR data is consist-
ent with a phosphorus trans- to a chloride but is signif-
icantly larger coupling constant than the average value
1
*
Corresponding author. Tel.: +441334463869; fax: +441334463384.
E-mail addresses: jdw3@st-andrews.ac.uk, jdw3@st-and.ac.uk (J.D.
Woollins).
1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2004.08.007

H.L. Milton et al. / Inorganic Chemistry Communications 7 (2004) 1106–1108
1107
1
seen in dppap (3576 Hz) for the equivalent reaction.
ton would show a considerable shift. The proton is
found at d(H) 9.4 ppm as a doublet (2JH–H = 6 Hz)
with platinum satellites giving a JPt–H = 43 Hz, this
1
The H NMR is also enlightening with respect to the
pyC[6] proton, as we predict that on chelation this pro-
3
is confirmation that 2 is a chelate complex. The m(C–
N) stretch in 2 is found at 1648 cmꢀ1, this is a consid-
erable shift from the value for the free ligand and
provides further support for our proposed structure.
Furthermore, there are two m(M–Cl) stretches observed
in the spectrum at 339 and 318 cmꢀ1, the presence of
two peaks again indicates two chlorides bound cis to
the metal centre.
1
7-diphenylphosphinoazaindole (dppai) (1): Chlorodiphenylphos-
phine (3.80 cm3, 21.1 mmol) was added to a solution of 1H-indole
(2.5 g, 21.1 mmol), triethylamine (3.10 ml, 22.2 mmol) and DMAP
(259 mg, 2.1 mmol) in THF (100 cm3) and refluxed overnight. The
reaction mixture was filtered to remove a white solid (Et3NHCl) and
washed with THF (50 cm3). The solvent was removed in vacuo leaving
a pale yellow solid. This solid was recrystallised by cooling a
concentrated diethyl ether solution in a fridge overnight (yield: 2.3 g,
36%). mmax/cmꢀ1: 1589, 1405, 983. 31P NMR (109.3 MHz, CDCl3), d
33.2. 1H NMR (270 MHz, CDCl3), 8.4 (1H, dd, J = 5 Hz, 2 Hz,
aromatic), 7.9 (1H, dt, J = 8 Hz, 1 Hz, aromatic), 7.4–7.3 (10H, m,
aromatic), 7.1 (1H, dd, J = 8 Hz, 5 Hz, aromatic), 7.0 (1H, dd, J = 4
Hz, 2Hz, aromatic), 6.5 (1H, dd, J = 4 Hz, 1 Hz, aromatic).
dppai
N
Cl
Cl
Cl
Cl
M
M
[PtCl2(dppai-P,N)] (2): Dppai (81 mg, 0.268 mmol) and
[PtCl2(cod)] (100 mg, 0.268 mmol) were weighed into a schlenk type
flask and DCM (5 cm3) added. The solution was stirred for 10 min and
the majority of the solvent removed in vacuo. A white solid was
isolated after addition of Et2O then filtered and washed with further
ether (yield: 56 mg, 37%). C19H15N2PCl2Pt requires: C, 40.1; H, 2.66;
N, 4.93. Found: C, 40.7; H, 2.68; N, 4.86%. mmax/cmꢀ1: 1648, 1438,
1107, 996. 31P NMR (109.3 MHz, CDCl3), d 55.4 (JP–Pt = 4160 Hz). 1H
NMR (270 MHZ, CDCl3), 9.4 (1H, m, JP–H = 6 Hz, JPt–H = 43 Hz,
pyC[6]H), 8.1 (2H, m, aromatic), 7.8 (3H, m, aromatic), 7.5 (5H, m,
aromatic), 7.2 (4H, m, aromatic).
dcm
N
P
Ph2
M = Pt (2) or Pd (3)
The X-ray structure of 2 is shown (Fig. 1) confirms
the square planar geometry and chelation of the lig-
and. Using Pd(COD)Cl2 we formed [PdCl2(dppai-
P,N)] (3), d(P) 81 ppm which is structurally very
similar to 2.
When dppai was reacted with [PtClMe(cod)] and
[PtClPh(cod)] the expected bidentate complex was
formed, giving [PtClMe(dppai-P,N)] (4) and [PtClPh
(dppai-P,N)] (5), respectively. The 31P NMR in both
cases showed peaks consistent with the earlier platinum
[PdCl2(dppai-P,N)] (3): As 2. Dppai (106 mg, 0.35 mmol), and
[PdCl2(cod)] (100 mg, 0.35 mmol) gave a yellow solid (yield: 133 mg,
79%). C19H15N2PCl2Pd requires: C, 47.5; H, 3.15; N, 5.84. Found: C,
47.0; H, 2.63; N, 5.95%. mmax/cmꢀ1: 1438, 1104, 994, 344, 312. 31P
1
NMR (109.3 MHz, CDCl3), d 80.5. H NMR (270 MHz, CDCl3), 9.2
(1H, dd, JP–H = 6 Hz, pyC[6]H), 8.1 (1H, m, aromatic), 7.8 (4H, m,
aromatic), 7.7–7.6 (2H, m, aromatic), 7.6–7.5 (4H, m, aromatic), 7.3
(1H, dd, aromatic), 7.2 (1H, m, aromatic), 7.0 (1H, m, aromatic).
Compounds 4 and 5 were prepared by similar procedures.
Crystal data: Single crystal X-ray diffraction studies on crystals were
performed using a Bruker SMART diffractometer with graphite-
˚
monochromated Mo-Ka radiation (k = 0.71073 A). The structure was
solved by direct methods, the non-hydrogen atoms were refined with
anisotropic displacement parameters; hydrogen atoms were fixed.
Structural refinements were by the full-matrix least-squares method on
F2 using SHELXTL [8].
˚
2 C19H15N2PCl2Pt, M = 568.29, orthorhombic, a = 9.0694(15) A,
3
˚
˚
˚
b = 15.250(3) A, c = 26.813(5) A, b = 92.036(3)°. U = 3708.3(11) A ,
T = 125 K, space group Pbca Z = 8, l(Mo-Ka) = 7.946 mmꢀ1. Of
14,950 measured data, 2658 were unique, to give R1[I > 2r(I)] =
0.0241, wR 0.0448.
˚
3 C19H15N2PCl2Pd, M = 479.60, monoclinic, a = 9.8511(10) A,
˚
˚
b = 15.5407(16) A, c = 12.3756(12) A, b = 111.174(2)°. U = 1766.7ꢀ(31)
3
˚
A , T = 125 K, space group P2(1)/c, Z = 4, l(Mo-Ka) = 1.477 mm
.
Of 7581 measured data, 2527 were unique to give R1[I > 2r(I)] =
0.0228, wR 0.0574.
˚
20H18N2PClPt, M = 547.87, triclinic, a = 9.584(3) A,
4
C
˚
˚
b = 10.289(3) A, c = 10.965(4) A, a = 88.925(5), b = 77.471(5),
3
˚
ꢀ
c = 62.072(4)°. U = 928.3(5) A , T = 125 K, space group P1, Z = 2,
l(Mo-Ka) = 7.792 mmꢀ1. Of 4703 measured data, 2632 were unique to
give R1[I > 2r(I)] = 0.0395, wR 0.1027. Crystallographic Data for the
structural analyses has been deposited with the Cambridge Crystallo-
graphic data centre, CCDC No. 240298–240300. Copies of this
information may be obtained free of charge from The Director
CCDC, 12 Union Road, Cambridge, CB2 1EZ UK (fax: +44 1223 336
033 or E-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk.
Fig. 1. Crystal structure of [PtCl2(dppai-P,N)] (2), [PdCl2(dppai-P,N)]
(3) has a similar structure and is not illustrated. Selected bond lengths
˚
(A) and angles (°): P(1)–M(1) 2.1998(11), Pt(1)–Cl(1) 2.3381(11),
Pt(1)–Cl(2) 2.3068(11), P(1)–N(2) 1.716(3), N(2)–C(10) 1.373(5), N(9)–
C(10) 1.326(5), P(1)–M(1)–Cl(1) 176.70(4), P(1)–M(1)–Cl(2) 91.04(4),
M(1)–N(9) 85.93(10), M(1)–P(1)–N(2) 99.73(12).

1108
H.L. Milton et al. / Inorganic Chemistry Communications 7 (2004) 1106–1108
The X-ray structure of 4 (Fig. 1) shows similar fea-
tures to 2 and 3 though the P–N bond is slightly longer
˚
in this example, being 1.730(6) A [cf. 1.719(2) and
˚
1.716(4) A] whilst 4 has a Pt–N bond length of
˚
˚
2.145(7) A compared to 2.039(3) A for 2 reflecting the
change of trans ligands (see Fig. 2).
References
[1] S.M. Aucott, A.M.Z. Slawin, J.D. Woollins, J. Chem. Soc., Dalton
Trans. (2000) 2559.
[2] S.M. Aucott, M.L. Clarke, A.M.Z. Slawin, J.D. Woollins, JCS
Dalton (2001) 972;
S.M. Aucott, A.M.Z. Slawin, J.D. Woollins, J . Organomet. Chem.
582 (1999) 83.
Fig. 2. Crystal Structure of [PtClMe(dppai-P,N)] (4), selected bond
˚
[3] M.R.i. Zubiri, A.M.Z. Slawin, M. Wainwright, J.D. Woollins,
Polyhedron 21 (2002) 1729.
lengths (A) and angles (°) P(1)–Pt(1) 2.168(2), Pt(1)–Cl(1) 2.349(2),
Pt(1)–N(9) 2.145(7), P(1)–N(2) 1.730(6), Pt(1)–C(30) 2.042(8), N(2)–
C(10) 1.369(10), N(9)–C(10) 1.333(11), P(1)–Pt(1)–Cl(1) 177.37(6),
P(1)–Pt(1)–C(30) 93.7(3), P(1)–Pt(1)–N(9) 85.35(19), Pt(1)–P(1)–N(2)
101.1(2).
[4] M.R.i. Zubiri, M.L. Clarke, D.F. Foster, D.J. Cole-Hamilton,
A.M.Z. Slawin, J.D. Woollins, JCS Dalton (2001) 969.
[5] M.L. Clarke, A.M.Z. Slawin, M.V. Wheatley, J.D. Woollins, J.
Chem. Soc., Dalton Trans. (2001) 3421.
[6] A.M.Z. Slawin, M. Wainwright, J.D. Woollins, New J. Chem. 24
(2000) 69.
examples with resonances observed at d(P) 60.9 ppm,
[7] A.M.Z. Slawin, M. Wainwright, J.D. Woollins, JCS Dalton (2002)
513.
[8] SHELXTL, Bruker AXS Madison, 2001.
1
and 58.5 ppm for 4 and 5, respectively, with JPt–P
5070 Hz for 4 and 4960 Hz for 5.
=