The co-ordination chemistry of 2-(diphenyIphosphinoamino)pyridine 1

Article abstract of DOI:10.1039/b003294h

2-(Diphenylphosphinoamino)pyridine, dppap [Ph₂PNHpy], and over 40 illustrative examples of its complexes have been prepared. Monodentate, bidentate and bridging co-ordination of the neutral (and bidentate deprotonated ligand) has been demonstrated in a range of palladium, platinum and gold complexes. Ten demonstrative examples have been characterised by single crystal X-ray diffraction. Ph₂PNHpy exists as hydrogen-bonded dimer pairs; cis[PtCl(Ph₂PNHpy-P,Ar){Ph₂PNHpy-P}]Cl packs in hydrogen-bonded infinite chains; cis-[PtCPh₂PNpy-.P.A₂] and cis-[Pd(Ph₂PNpy-P,N)₂] are isomorphous. The structures of cis-[Pd(Ph₂PNHpy-P,N)₂][BF₄]₂, [AuCl(Ph₂PNHpy-.P)], [Pt(C₈H₁₂OMe)(Ph₂PNpy-P,N)]-H₂O illustrating hydrogen-bonding, cis-[PtCl(Ph₂PNHpy-P,N)(PMe₃)]Cl, cis[PtCl(Ph₂PNpy-P,N(PMe₃)] and cis-[PtCl(Ph₂PNHpy-P,N)(P(OPh)₃)]Cl are also reported. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b003294h

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The co-ordination chemistry of 2-(diphenylphosphinoamino)pyridine†
Stephen M. Aucott, Alexandra M. Z. Slawin and J. Derek Woollins*
Department of Chemistry, University of St Andrews, St Andrews, Fife, UK KY16 9ST.
E-mail: j.d.woollins@st-andrews.ac.uk
Received 25th April 2000, Accepted 21st June 2000
Published on the Web 12th July 2000
2-(Diphenylphosphinoamino)pyridine, dppap [Ph2PNHpy], and over 40 illustrative examples of its complexes have
been prepared. Monodentate, bidentate and bridging co-ordination of the neutral (and bidentate deprotonated
ligand) has been demonstrated in a range of palladium, platinum and gold complexes. Ten demonstrative examples
have been characterised by single crystal X-ray diffraction. Ph2PNHpy exists as hydrogen-bonded dimer pairs; cis-
[PtCl(Ph2PNHpy-P,N){Ph2PNHpy-P}]Cl packs in hydrogen-bonded infinite chains; cis-[Pt(Ph2PNpy-P,N)2] and
cis-[Pd(Ph2PNpy-P,N)2] are isomorphous. The structures of cis-[Pd(Ph2PNHpy-P,N)2][BF4]2, [AuCl(Ph2PNHpy-P)],
[Pt(C8H12OMe)(Ph2PNpy-P,N)]ؒH2O illustrating hydrogen-bonding, cis-[PtCl(Ph2PNHpy-P,N)(PMe3)]Cl, cis-
[PtCl(Ph2PNpy-P,N)(PMe3)] and cis-[PtCl(Ph2PNHpy-P,N)(P(OPh)3)]Cl are also reported.
The co-ordination chemistry of pyridylphosphine ligands has
extensively been studied1–3 but most research has been focused
upon the chemistry of 2-(diphenylphosphino)pyridine A;
much of the interest is due to the willingness of 2-(diphenyl-
phosphino)pyridine to act as a bidentate ligand containing both
hard (nitrogen) and soft (phosphorus) donor atoms. Simple
Ph2Ppy chelate complexes are unstable because of ring strain
and, as such, uncommon compared to complexes containing
monodentate P bound or bidentate P, N bridging Ph2Ppy
ligands. This rigid short-bite ligand has been used to assemble
homo- and hetero-binuclear complexes possessing metal–
metal bonds which themselves have unusual reactivities.
Numerous other ligand systems which utilise the same donor
set as Ph2Ppy but which contain organic spacer groups between
the phosphorus and pyridyl nitrogen donor sites are known
and include Ph2PCH(R)py (where R = H,4–6 CH2OEt,7,8 or
PPh29–13 B) and Ph2PCH2CH2py14–22 C (Fig. 1).
Fig. 1 Examples of phosphinopyridines.
Surprisingly, considering the comparative ease of phos-
phorus–nitrogen bond forming reactions compared to those
in which phosphorus-carbon bonds are formed, relatively few
examples of pyridylphosphines in which the donor atoms are
separated by amino groups are known, examples include D,23
E,23,24 F,23 G,25,26 and H27 (Fig. 2). In addition the 4-methyl
and 6-methyl substituted pyridyl analogues of D have been
reported.28 We have resynthesized D 2-(diphenylphosphino-
amino)pyridine (dppap) 1 as we were interested to see what
differences the secondary amine spacer group between the
phosphorus and nitrogen donor sites would have on the co-
ordination chemistry of 1 and whether the added flexibility
would favour simple chelation over bridging or monodentate
P bound co-ordination modes compared to that of 2-(diphenyl-
phosphino)pyridine. During our investigation we have studied
the reactions of dppap with [AuCl(tht)] (tht = tetrahydro-
thiophene) and a number of complexes of PtII and PdII
and have observed three, possibly four, distinct modes of
co-ordination. The products from these reactions have been
characterised principally by multi-element NMR spectroscopy
and X-ray crystallography.
Fig. 2 Examples of phosphinoaminopyridines.
Experimental
General
Unless otherwise stated, operations were carried out under an
oxygen-free nitrogen atmosphere using predried solvents and
standard Schlenk techniques. The complexes [AuCl(tht)],29
[MCl2(cod)] (M = Pt or Pd; X = Cl, Br, or I; cod = cycloocta-
1,5-diene),30,31 [PtMeX(cod)] (M = Cl or Me),32 [{Pt(µ-OMe)-
(C8H12OMe)}2]33 and [{PtCl(µ-Cl)(PMe2Ph)}2]34 were prepared
using literature procedures. Complexes of the type cis-
[MCl2(PR3)2] (M = Pt or Pd) were prepared by the addition of
stoichiometric quantities of the appropriate free phosphine
or phosphite to [MCl2(cod)] (M = Pd or Pt). Chlorodiphenyl-
phosphine (Strem) was distilled prior to use. 2-Aminopyridine
(99% purity), Et3N (99% purity), 2,6-dimethylpyridine (99%
purity), Ag[BF4] (98% purity), Ag[ClO4] (99.9% purity), tBuOK
(95% purity) and HBF4ؒOEt2 (85% in diethyl ether) were
purchased from Aldrich; H2O2 (Fisher, 30 wt.% in water) and
reagent grade KBr and NaI (Fisons) were all used without
further purification. Infrared spectra were recorded as KBr
pellets in the range 4000–220 cmϪ1 on a Perkin-Elmer System
2000 Fourier-transform spectrmeter, 1H NMR spectra (250
MHz) on a Bruker AC250 FT spectrometer with δ referenced to
† Electronic supplementary information (ESI) available: FAB MS and
IR data for the ligands and complexes. See http://www.rsc.org/suppdata/
dt/b0/b003294h/
DOI: 10.1039/b003294h
J. Chem. Soc., Dalton Trans., 2000, 2559–2575
This journal is © The Royal Society of Chemistry 2000
2559

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external SiMe4 and 31P-{1H} NMR spectra (36.2 or 101.3 MHz)
either on a JEOL FX90Q or Bruker AC250 spectrometer
with δ referenced to external H3PO4. Microanalyses were per-
formed by the Loughborough University service and fast
atom bombardment (FAB) mass spectra by the Swansea
Mass Spectrometer service. All compounds gave satisfactory
positive-ion FAB mass spectra, details of which are included
in the supplementary information. We are grateful to Johnson
Matthey PLC for the loan of precious metal salts.
the stirred suspension was added Ph2PNHpy 1 (0.143 g,
0.514 mmol) as a solid in one go. The mixture was heated until
complete solution was achieved and on cooling to room tem-
perature a white solid was deposited. The product was collected
by suction filtration, washed with diethyl ether (3 × 20 cm3)
and dried in vacuo. Yield 0.21 g, 96%. Found (Calc. for
C34H30Cl2N4P2Pt): C 48.75 (49.65), H 3.32 (3.68), N 6.83
(6.81)%. 1H NMR (CDCl3): δ 11.26 (br m, 1 H, NH), 8.24 (br d,
2 H, py C[6]H), 7.70 (br d, 4 H, aromatics), 7.49 (m, 13 H,
aromatics and NH), 7.30 (m, 8 H, aromatics) and 6.93 (m, 2 H,
aromatics). Selected IR data (KBr): 2708 ν(N–H), 1615, 1596
Preparations
ν(py C᎐N) and 905 cmϪ1 ν(P–N).
᎐
Ph2PNHpy 1. Neat chlorodiphenylphosphine (13.5 cm3,
16.6 g, 75.2 mmol) was added dropwise over 15 min to a
solution of 2-aminopyridine (7.07 g, 75.2 mmol) and Et3N
(10.8 cm3, 7.84 g, 77.48 mmol) in thf (250 cm3) at 0 ЊC. The
mixture was slowly warmed to room temperature and stirred
for 24 h after which time it was filtered to remove precipitated
triethylamine hydrochloride. The precipitate was washed with
thf (2 × 50 cm3). The washings and the filtrate were combined
and taken to dryness under reduced pressure leaving a pale
yellow oil which on cooling spontaneously crystallised. The
material was removed from the flask and washed with MeOH
(100 cm3) then diethyl ether (2 × 75 cm3) and dried in vacuo.
Yield 16.3 g, 78%. Found (Calc. for C17H15N2P): C 72.99
cis-[PtX(Ph2PNHpy-P,N){Ph2PNHpy-P}]X (X ؍ Br 6 or
I 7). A suspension of cis-[PtCl(Ph2PNHpy-P,N){Ph2PNHpy-
P}]Cl 5 (0.040 g, 0.049 mmol) and KBr or NaI (0.60 mmol) was
heated to reflux in acetone (10 cm3) for 2 h. After cooling to
room temperature the solvent was removed in vacuo and the
residue extracted with CH2Cl2 (3 × 10 cm3). The extracts were
combined and filtered through a small plug of Celite. The
filtrate was evaporated to ca. 8 cm3 and diethyl ether (25 cm3)
added to precipitate the product. The bromide and the iodide
were isolated as cream and pale yellow solids respectively. 6:
yield 0.033 g, 75%. Found (Calc. for C34H30Br2N4P2Pt): C 45.48
(44.88), H 3.47 (3.33), N 6.75 (6.16)%. Selected IR data (KBr):
1
(73.37), H 5.44 (5.43), N 9.97 (10.07)%. H NMR (CDCl3):
3052 ν(N–H), 1618, 1586 ν(py C᎐N) and 902 cmϪ1 ν(P–N). 7:
᎐
δ 7.97 (d, 1 H, py C[6]H), 7.45 (m, 3 H, aromatics) 7.34 (m, 8 H,
yield 0.038 g, 78%. Found (Calc. for C34H30I2N4P2Pt): C 40.28
(40.62), H 3.13 (3.01), N 5.82 (5.57)%. Selected IR data (KBr):
aromatics), 7.04 (br d, 1 H, aromatic), 6.66 (m, 1 H, aromatic)
2
and 5.71 (d, 1 H, J(31P–1H) 8.4 Hz, NH). Selected IR data
3052 ν(N–H), 1616, 1587 ν(py C᎐N) and 899 cmϪ1 ν(P–N).
᎐
(KBr): 3121 ν(N–H), 1601 ν(py C᎐N) and 920 cmϪ1 ν(P–N).
᎐
cis-[PdCl(Ph2PNHpy-P,N){Ph2PNHpy-P}]Cl 8. This was
prepared in the same way as the platinum complex 5 using
[PdCl2(cod)] (0.085 g, 0.298 mmol) and Ph2PNHpy 1 (0.168 g,
0.604 mmol) to give a pale yellow product. Yield 0.22 g, 98%.
Found (Calc. for C34H30Cl2N4P2Pd): C 54.95 (55.64), H
Ph2P(O)NHpy 2. Aqueous H2O2 (30% w/w, 2.0 cm3, 17.64
mmol) was added dropwise over 5 min to a solution of Ph2-
PNHpy 1 (2.5 g, 8.50 mmol) in thf (20 cm3) and the mixture
stirred for 30 min and then taken to dryness. The crude product
was dissolved in hot CH2Cl2 (100 cm3), dried over anhydrous
MgSO4 and filtered while hot. The filtrate was concentrated
to ca. 20 cm3 and stored at Ϫ4 ЊC for 2 h during which time a
white crystalline solid was deposited. The colourless crystals
2 were collected by suction filtration, washed with CH2Cl2
(10 cm3) and dried in vacuo. Yield 2.13 g, 81%. Found (Calc. for
C17H15N2OP): C 69.31 (69.38), H 5.10 (5.14), N 9.51 (9.52)%.
1H NMR (CDCl3): δ 7.89 (m, 5 H, aromatics and NH), 7.45
(m, 8 H, aromatics), 7.00 (br d, 1 H, aromatic) and 6.74 (m,
1 H, aromatic). Selected IR data (KBr): 3201 ν(N–H), 1599
ν(py C᎐N), 1196 ν(P᎐O) and 950 cmϪ1 ν(P–N).
1
3.53 (4.12), N 6.86 (7.63)%. H NMR (CDCl3): δ 8.12 (br m,
2 H, py C[6]H), 7.46 (br m, 18 H, aromatics and NH), 7.21
(m, 10 H, aromatics) and 6.79 (m, 2 H, aromatics). Selected IR
data (KBr): 2709 ν(N–H), 1611, 1597 ν(py C᎐N) and 907 cmϪ1
᎐
ν(P–N).
cis-[PdX(Ph2PNHpy-P,N){Ph2PNHpy-P}]X (X ؍ Br 9 or
I 10). These compounds were prepared in the same way as
their platinum analogues 5 and 6 using cis-[PdCl(Ph2PNHpy-
P,N){Ph2PNHpy-P}]Cl 8 (0.040 g, 0.055 mmol) and KBr or
NaI (0.70 mmol). The bromide and the iodide were isolated as
pale yellow and yellow solids respectively. 9: yield 0.033 g, 73%.
Found (Calc. for C34H30Br2N4P2Pd): C 49.02 (49.63), H 3.32
(3.67), N 6.83 (6.81)%. Selected IR data (KBr): 3052 ν(N–H),
᎐
᎐
Ph2P(E)NHpy (E ؍ S 3 or Se 4). These compounds were
prepared by the same general procedure. Ph2PNHpy 1 (1.00 g,
3.59 mmol) and a stoichiometric quantity of the appropriate
chalcogen were heated to reflux in toluene (20 cm3) for 20–30
min. The reaction mixture was taken to dryness and the residue
taken up in CH2Cl2 then filtered through a Celite plug. The
filtrate was again taken to dryness and the pale yellow solid
recrystallised from the minimum of hot toluene and stored at
Ϫ4 ЊC to give 3 and 4 as colourless crystalline solids. 3: yield
0.97 g, 87%. Found (Calc. for C17H15N2PS): C 65.32 (65.97), H
4.80 (4.87), N 8.97 (9.03)%. 1H NMR (CDCl3): δ 8.03 (m, 4 H,
aromatics), 7.85 (d, 1 H, 2J(31P–1H) 5.1 Hz, NH), 7.45 (m, 8 H,
aromatics), 6.93 (br d, 1 H, aromatic) and 6.71 (m, 1 H,
1617, 1594 ν(py C᎐N) and 905 cmϪ1 ν(P–N). 10: yield 0.036 g,
᎐
72%. Found (Calc. for C34H30I2N4P2Pt): C 45.22 (44.54), H 3.55
(3.30), N 6.23 (6.11)%. Selected IR data (KBr): 3079 ν(N–H),
1619, 1589 ν(py C᎐N) and 905 cmϪ1 ν(P–N).
᎐
cis-[Pt(Ph2PNpy-P,N)2] 11.
A
stirred solution of
cis-[PtCl(Ph2PNHpy-P,N){Ph2PNHpy-P}]Cl 5 (0.130 g, 0.158
mmol) in MeOH (2 cm3) was treated with solid tBuOK (0.037 g,
0.330 mmol) causing the immediate precipitation of a yellow
solid. After stirring for 10 min the product was filtered off,
washed with MeOH (2 × 2 cm3) and diethyl ether (2 × 1 cm3)
and dried in vacuo. Yield 0.096 g, 81%. Found (Calc. for
C34H28N4P2Pt): C 53.75 (54.48), H 3.45 (3.76), N 7.20 (7.47)%.
1H NMR (CDCl3): δ 7.78 (m, 2 H, py C[6]H), 7.30 (m, 14 H,
aromatics), 7.07 (m, 8 H, aromatics), 6.98 (br d, 2 H, aromatics)
and 6.26 (m, 2 H, aromatics). Selected IR data (KBr): 1609,
aromatic). Selected IR data (KBr): 1599 ν(py C᎐N), 941 ν(P–N)
᎐
and 642 cmϪ1 ν(P᎐S). 4: yield 1.07 g, 83%. Found (Calc.
᎐
for C17H15N2PSe): C 56.73 (57.16), H 4.20 (4.23), N 7.57
(7.84)%.1H NMR (CDCl3): δ 8.04 (m, 4 H, aromatics), 7.84
(d, 1 H, 2J(31P–1H) 5.3 Hz, NH), 7.45 (m, 8 H, aromatics), 6.92
(br d, 1 H, aromatic) and 6.73 (m, 1 H, aromatic). Selected IR
data (KBr): 1598 ν(py C᎐N), 941 ν(P–N) and 550 cmϪ1 ν(P᎐Se).
ν(py C᎐N) and 936 cmϪ1 ν(P–N).
᎐
᎐
᎐
cis-[Pd(Ph2PNpy-P,N)2] 12. This was prepared in the same
way as the platinum complex 11 using 8 (0.120 g, 0.164 mmol)
and BuOK (0.038 g, 0.339 mmol) to give a bright yellow
cis-[PtCl(Ph2PNHpy-P,N){Ph2PNHpy-P}]Cl 5. [PtCl2(cod)]
(0.095 g, 0.254 mmol) was suspended in MeCN (5 cm3). To
t
2560
J. Chem. Soc., Dalton Trans., 2000, 2559–2575

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product. Yield 0.082 g, 76%. Found (Calc. for C34H28N4P2Pd):
C 60.97 (61.78), H 4.17 (4.27), N 8.20 (8.48)%. 1H NMR
(CDCl3): δ 7.77 (m, 2 H, py C[6]H), 7.31 (m, 14 H, aromatics),
7.10 (m, 8 H, aromatics), 6.90 (br d, 2 H, aromatics) and 6.31
39.99 (39.98), H 2.80 (2.96), N 5.08 (5.49)%. 1H NMR (CDCl3):
δ 8.01 (m, 1 H, py C[6]H), 7.76 (m, 3 H, aromatics), 7.48 (m,
9 H, aromatics and NH), 6.89 (m, 1 H, aromatic) and 6.83 (m,
1 H, aromatic). Selected IR data (KBr): 3373 ν(N–H), 1593
(m, 2 H, aromatics). Selected IR data (KBr): 1604, ν(py C᎐N)
ν(py C᎐N) and 909 cmϪ1 ν(P–N).
᎐
᎐
and 942 cmϪ1 ν(P–N).
[{Au(ꢀ-Ph2PNHpy-P,N)}2][ClO4]2 (HT) 18. To a stirred solu-
tion of complex 17 (0.125 g, 0.245 mmol) in CH2Cl2 (20 cm3)
was added Ag[ClO4] (0.051 g, 0.247 mmol) in nitromethane
(10 cm3) and the mixture stirred in the dark for 5 h. The preci-
pitated AgCl was filtered off through a small Celite plug, the
solution concentrated by evaporation under reduced pressure
to ca. 4–5 cm3 and diethyl ether (25 cm3) added. The white
product was collected by suction filtration, washed with diethyl
ether (10 cm3) and dried in vacuo. Yield 0.103 g, 71%. Found
(Calc. for C17H15AuClN2O4P): C 34.89 (35.52), H 2.45 (2.63),
N 4.40 (4.87)%. 1H NMR (CDCl3): δ 8.10 (m, 2 H, py C[6]H),
7.91–7.16 (m, 24 H, aromatics and NH), 7.05 (br d, 2 H,
aromatic) and 6.86 (m, 2 H, aromatic). Selected IR data (KBr):
3204 ν(N–H), 1611 ν(py C᎐N), 1102, 623 ν(ClO ) and 924 cmϪ1
cis-[Pt(Ph2PNHpy-P,N)2][BF4]2 13. To a stirred solution of
complex 5 (0.127 g, 0.154 mmol) in CH2Cl2 (20 cm3) was
added solid Ag[BF4] (0.061 g, 0.313 mmol). After stirring
for approximately 16 h the precipitated AgCl was filtered
off through a small Celite plug, the solution concentrated by
evaporation under reduced pressure to ca. 2–3 cm3 and diethyl
ether (30 cm3) added. The cream product was collected by
suction filtration, washed with diethyl ether (10 cm3) and dried
in vacuo. Yield 0.116 g, 81%. Found (Calc. for C34H30B2F8-
1
N4P2Pt: C 44.72 (44.14), H 3.46 (3.27), N 7.01 (6.06)%. H
NMR (d6-dmso): δ 8.20 (m, 2 H, NH), 7.99 (m, 2 H, py C[6]H),
7.48 (m, 22 H, aromatics), 7.24 (m, 2 H, aromatics) and 7.14
(br d, 2 H, aromatics). Selected IR data (KBr): 3235 ν(N–H),
᎐
4
1615 ν(py C᎐N) and 900 cmϪ1 ν(P–N).
ν(P–N).
᎐
cis-[Pd(Ph2PNHpy-P,N)2][BF4]2 14. This was prepared in the
same way as the platinum complex 13 using 8 (0.122 g, 0.166
mmol) and Ag[BF4] (0.066 g, 0.339 mmol) to give a cream
product. Yield 0.110 g, 79%. Found (Calc. for C34H30B2F8-
[Pt(C8H12OMe)(Ph2PNpy-P,N)]ؒH2O 19. To a stirred sus-
pension of [{Pt(µ-OMe)(C8H12OMe)}2] (0.150 g, 0.205 mmol)
in MeOH (3 cm3) were added in quick succession the solids
t
Ph2PNHpy 1 (0.114 g, 0.410 mmol) and BuOK (0.046 g,
1
N4P2Pd): C 49.63 (48.81), H 4.16 (3.61), N 8.20 (8.48)%. H
0.410 mmol) resulting in a pale yellow solution that was stirred
for 30 min. Distilled water (ca. 12 drops) was added dropwise
to the mixture causing a fine pale yellow precipitate to be
deposited which was collected by suction filtration, washed with
distilled water (2 × 2 cm3) and dried in vacuo. Yield 0.231 g,
92%. Found (Calc. for C26H31N2O2PPt): C 49.37 (49.60), H
5.09 (4.96), N 4.07 (4.45)%. 1H NMR (CDCl3): δ 7.73 (m, 1 H,
py C[6]H), 7.53 (m, 3 H, aromatics) 7.34 (m, 8 H, aromatics),
7.19 ( m, 1 H, aromatic), 6.98 (br d, 1 H, aromatic) and expected
NMR (d6-dmso): δ 8.17 (m, 2 H, NH), 7.97 (m, 2 H, py C[6]H),
7.45 (m, 22 H, aromatics), 7.22 (m, 2 H, aromatics) and 7.11
(br d, 2 H, aromatics). Selected IR data (KBr): 3236 ν(N–H),
1615 ν(py C᎐N) and 900 cmϪ1 ν(P–N).
᎐
cis-[PtMe(Ph2PNHpy-P,N){Ph2PNHpy-P}]Cl 15. To
a
stirred CH2Cl2 (2 cm3) solution of [PtClMe(cod)] (0.102 g,
0.288 mmol) was added Ph2PNHpy 1 (0.162 g, 0.582 mmol) as a
solid in one go. The mixture was stirred for 20 min, filtered
through Celite and diethyl ether (40 cm3) added. The white solid
was collected by suction filtration, washed with diethyl ether
(3 × 10 cm3) and dried in vacuo. Yield 0.219 g, 95%. Found
(Calc. for C35H33ClN4P2Pt): C 52.49 (52.41), H 4.21 (4.15),
N 6.40 (6.98)%. 1H NMR (CDCl3): δ 11.49 (m, 1 H, NH), 8.35
(m, 1 H, py C[6]H), 7.97 (br d, 1 H, py C[6]H), 7.84 (br m, 1 H,
NH), 7.45 (m, 22 H, aromatics), 6.69 (m, 2 H, aromatics), 6.19
(m, 2 H, aromatics) and 0.64 (dd, 3 H, 3J(31P–1H) 4, 2J(195Pt–1H)
51 Hz, PtMe). Selected IR data (KBr): 2706 ν(N–H), 1614, 1592
C H OMe resonances. Selected IR data (KBr): 1607 ν(py C᎐N)
᎐
8
12
and 941 cmϪ1 ν(P–N).
cis-[PtCl(Ph2PNHpy-P,N)(PMe3)]Cl 20. A typical synthesis
was performed as follows. Solid Ph2PNHpy 1 (0.074 g, 0.266
mmol) was added to a stirred suspension of cis-[PtCl2(PMe3)2]
(0.110 g, 0.263 mmol) in CH2Cl2 (3 cm3) giving a clear solution.
The mixture was stirred for 10 min and diethyl ether (20 cm3)
slowly added causing a white crystalline solid to be deposited.
The crude product 20 was collected by suction filtration,
recrystallised from CH2Cl2–diethyl ether and dried in vacuo.
Yield 0.150 g, 92%. Found (Calc. for C20H24Cl2N2P2Pt): C
38.87 (38.72), H 3.75 (3.90), N 4.22 (4.52)%. 1H NMR (CDCl3):
δ 11.71 (m, 1 H, NH), 9.14 (m, 1 H, py C[6]H), 8.03 (m, 4 H,
aromatics), 7.65 (m, 8 H aromatics), 6.92 (m, 1 H, aromatic)
ν(py C᎐N) and 907 cmϪ1 ν(P–N).
᎐
cis-[PtMe(Ph2PNpy-P,N){Ph2POMe-P}] 16. A stirred solu-
tion of complex 15 (0.112 g, 0.140 mmol) in MeOH (1 cm3)
t
was treated with solid BuOK (0.040 g, 0.352 mmol) and the
3
2
and 1.50 (d, 9 H, J(195Pt–1H) 34.3, J(31P–1H) 11.7 Hz, PMe).
resultant yellow solution stirred for 90 min. Dropwise addition
of distilled water (3 cm3) to the stirred reaction mixture gave 16
as a pale yellow solid which was collected by suction filtration
and dried over phosphorus pentaoxide in vacuo. Yield 0.077 g,
78%. Found (Calc. for C31H30N2OP2Pt): C 52.57 (52.92), H 3.75
Selected IR data (KBr): 2642 ν(N–H), 1616 ν(py C᎐N) and
᎐
911 cmϪ1 ν(P–N).
cis-[PtCl(Ph2PNpy-P,N)(PMe3)] 21. A typical deprotonation
1
t
(4.30), N 3.61 (3.98)%. H NMR (CDCl3): δ 8.14 (m, 1 H, py
was performed as follows. Solid BuOK (0.018 g, 0.160 mmol)
C[6]H), 7.68 (m, 3 H, aromatics), 7.26 (m, 16 H, aromatics),
6.89 (m, 2 H, aromatics), 6.28 (m, 2 H, aromatics), 3.00 (d, 3 H,
3J(31P–1H) 8 Hz, OMe) and 0.25 (dd, 3 H, 3J(31P–1H) 4, 2J(195Pt–
was added to a stirred solution of complex 20 (0.100 g,
0.161 mmol) in MeOH (1 cm3) causing a pale yellow solid to
be deposited. Distilled water (3–5 drops) was added to com-
plete the precipitation. The product was collected by suction
filtration, washed with distilled water (2 × 1 cm3) and ice cold
MeOH (2 × 1 cm3) and dried over phosphorus pentaoxide
in vacuo. Yield 0.082 g, 87%. Found (Calc. for C20H23ClN2P2Pt):
C 40.83 (41.14), H 3.37 (3.97), N 4.34 (4.80)%. 1H NMR
(CDCl3): δ 8.90 (m, 1 H, py C[6]H), 7.86 (m, 3 H, aromatics),
7.46 (m, 6 H aromatics), 7.29 (m, 2 H, aromatic), 6.99 (m, 1 H,
aromatic), 6.33 (m, 1 H, aromatic) and 1.42 (d, 9 H, 3J(195Pt–1H)
33.7, 2J(31P–1H) 11.1 Hz, PMe). Selected IR data (KBr):
1H) 55 Hz, PtMe). Selected IR data (KBr): 1613 ν(py C᎐N),
᎐
1020 ν(P–OMe) and 937 cmϪ1 ν(P–N).
[AuCl{Ph2PNHpy-P}] 17. Ph2PNHpy 1 (0.094 g, 0.338
mmol) was added as a solid to a stirred CH2Cl2 (3 cm3) solution
of [AuCl(tht)] (0.108 g, 0.337 mmol). After stirring for 20 min
the solution was filtered through a small Celite plug and diethyl
ether (30 cm3) added. The white solid was collected by suction
filtration, washed with diethyl ether (5 × 10 cm3) and dried in
vacuo. Yield 0.155 g, 90%. Found (Calc. for C17H15AuClN2P): C
1608 ν(py C᎐N) and 940 cmϪ1 ν(P–N).
᎐
J. Chem. Soc., Dalton Trans., 2000, 2559–2575
2561

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cis-[PtCl(Ph2PNHpy-P,N)(PEt3)]Cl 22. As for complex 20
using Ph2PNHpy 1 (0.064 g, 0.234 mmol) and cis-[PtCl2(PEt3)2]
(0.117 g, 0.233 mmol) to give a white crystalline product. Yield
0.133 g, 86%. Found (Calc. for C23H30Cl2N2P2Pt): C 41.74
(41.70), H 4.27 (4.56), N 3.66 (4.23)%. 1H NMR (CDCl3):
δ 11.82 (m, 1 H, NH), 9.20 (m, 1 H, py C[6]H), 8.02 (m, 3 H,
aromatics), 7.61 (m, 8 H, aromatics), 7.30 (m, 1 H, aromatic),
cis-[PtCl(Ph2PNpy-P,N)(PMe2Ph)] 27. As for complex 21
using 26 (0.123 g, 0.180 mmol) and tBuOK (0.020 g,
0.178 mmol) to give a pale yellow powder. Yield 0.098 g, 84%.
Found (Calc. for C25H25ClN2P2Pt): C 46.34 (46.48), H 4.21
(3.90), N 3.84 (4.34)%. δ 8.94 (m, 1 H, py C[6]H), 7.72 (m, 3 H,
aromatics), 7.35 (m, 12 H, aromatics), 6.93 (m, 1 H, aromatic),
6.29 (m, 2 H, aromatics) and 1.68 (d, 6 H, 3J(195Pt–1H)
2
2
6.90 (m, 1 H, aromatic), 1.82 (dq, 6 H, J(31P–1H) 10.0 Hz,
35.1, J(31P–1H) 10.7 Hz, PMe). Selected IR data (KBr): 1612
PCH2) and 0.97 (dt, 9 H, Me). Selected IR data (KBr): 2664
ν(py C᎐N) and 941 cmϪ1 ν(P–N).
᎐
ν(N–H), 1615 ν(py C᎐N) and 912 cmϪ1 ν(P–N).
᎐
cis-[PtCl(Ph2PNHpy-P,N)(PPh2H)]Cl 28. As for complex
20 using Ph2PNHpy 1 (0.045 g, 0.162 mmol) and cis-
[PtCl2(PPh2H)2] (0.102 g, 0.160 mmol) to give a fine white
powder. Yield 0.111 g, 95%. Found (Calc. for C29H26Cl2N2-
P2Pt): C 46.85 (47.68), H 3.63 (3.59), N 3.70 (3.83)%. 1H NMR
(CDCl3): δ 12.51 (m, 1 H, NH), 9.17 (m, 1 H, py C[6]H), 7.97
(d, 1 H, aromatic), 7.83 (m, 3 H, aromatics), 7.73 (m, 1 H,
aromatic), 7.48 (m, 16 H, aromatics), 7.28 (m, 1 H, aromatic),
7.04 (m, 1 H, aromatic), 6.98 (m, 1 H, aromatic), 6.79 (m, 1 H,
cis-[PtCl(Ph2PNpy-P,N)(PEt3)] 23. As for complex 21 using
t
22 (0.125 g, 0.187 mmol) and BuOK (0.021 g, 0.187 mmol).
The reaction mixture was diluted with distilled water (20 cm3)
and then extracted with CH2Cl2 (2 × 10 cm3). The extracts were
combined and dried over anhydrous MgSO4, the drying agent
filtered off and the filtrate evaporated under reduced pressure
to ca. 1–2 cm3. Hexane (30 cm3) was added with stirring to
give a pale yellow powder. Yield 0.109 g, 92%. Found (Calc.
for C23H29ClN2P2Pt): C 43.75 (44.13), H 4.32 (4.67), N 3.98
2
1
aromatic) and 5.22 (d, 1 H, J(195Pt–1H) 90.2, J(31P–1H) 395
1
Hz, PH).
(4.48)%. H NMR (CDCl3): δ 8.94 (m, 1 H, py C[6]H), 7.85
(m, 3 H, aromatics), 7.44 (m, 6 H, aromatics), 7.25 (m, 2 H,
aromatic), 6.92 (m, 1 H, aromatic), 6.28 (m, 1 H, aromatic),
cis-[PtCl(Ph2PNHpy-P,N)(PPh3)]Cl 29. As for complex 20
using Ph2PNHpy 1 (0.059 g, 0.212 mmol) and cis-[PtCl2(PPh3)2]
(0.167 g, 0.211 mmol) to give a white crystalline product. Yield
0.158 g, 93%. Found (Calc. for C35H30Cl2N2P2Pt): C 51.38
(52.12), H 3.85 (3.75), N 3.22 (3.47)%. 1H NMR (CDCl3):
δ 12.03 (m, 1 H, NH), 9.32 (m, 1 H, py C[6]H), 7.93 (d,
1 H, aromatic), 7.72–7.21 (m, 26 H, aromatics) and 6.89
(m, 1 H, aromatic). Selected IR data (KBr): 2578 ν(N–H), 1617
2
1.75 (dq, 6 H, J(31P–1H) 10.1 Hz, PCH2) and 0.89 (dt, 9 H,
Me). Selected IR data (KBr): 1612 ν(py C᎐N) and 943 cmϪ1
᎐
ν(P–N).
cis-[PtCl(Ph2PNHpy-P,N)(PnBu3)]Cl 24. [PtCl2(cod)] (0.105
g, 0.281 mmol) and PnBu3 (0.14 cm3, 0.114 g, 0.563 mmol) were
stirred in CH2Cl2 (5 cm3) for 10 min. Ph2PNHpy 1 (0.079 g,
0.284 mmol) was added as a solid in one go, giving a pale yellow
solution which was stirred for 10 min. Diethyl ether (50 cm3)
was added to give a fine white powder. Recrystallisation from
CH2Cl2–diethyl ether gave complex 24 as a fine white powder.
Yield 0.182 g, 87%. Found (Calc. for C29H42Cl2N2P2Pt): C 47.00
(46.65), H 5.52 (5.67), N 3.11 (3.75)%. 1H NMR (CDCl3):
δ 11.73 (m, 1 H, NH), 9.20 (1 H, m, py C[6]H), 7.98 (m, 3 H,
aromatics), 7.64 (m, 8 H, aromatics), 7.31 (m, 1 H, aromatic),
6.90 (m, 1 H, aromatic) and 1.77–0.73 (m, 27 H, PnBu). Selected
ν(py C᎐N) and 912 cmϪ1 ν(P–N).
᎐
cis-[PtCl(Ph2PNpy-P,N)(PPh3)] 30. As for complex 21 using
t
29 (0.173 g, 0.214 mmol) and BuOK (0.024 g, 0.214 mmol)
to give a pale yellow powder. Yield 0.143 g, 87%. Found (Calc.
for C35H29ClN2P2Pt): C 53.93 (54.59), H 3.32 (3.80), N 3.54
1
(3.64)%. H NMR (CDCl3): δ 9.16 (m, 1 H, py C[6]H), 7.45–
7.16 (m, 26 H, aromatics), 6.98 (d, 1 H, aromatic) and 6.30 (m,
1 H, aromatic). Selected IR data (KBr): 1612 ν(py C᎐N) and
᎐
937 cmϪ1 ν(P–N).
IR data (KBr): 2599 ν(N–H), 1612 ν(py C᎐N) and 913 cmϪ1
᎐
ν(P–N).
cis-[PtBr(Ph2PNHpy-P,N)(PPh3)]Br 31. As for complex 20
using Ph2PNHpy 1 (0.063 g, 0.226 mmol) and cis-[PtBr2(PPh3)2]
(0.197 g, 0.224 mmol) in methanol (10 cm3) to give a white
crystalline product. Yield 0.179 g, 89%. Found (Calc. for
C35H30Br2N2P2Pt): C 47.05 (46.94), H 3.63 (3.38), N 2.91
cis-[PtCl(Ph2PNpy-P,N)(PnBu3)] 25. As for complex 21 using
24 (0.130 g, 0.174 mmol) and BuOK (0.020 g, 0.178 mmol)
t
the resulting pale yellow solution was diluted with distilled
water (30 cm3) and extracted with CH2Cl2 (2 × 15 cm3). The
extracts were combined and dried over anhydrous MgSO4. The
drying agent was filtered off and the filtrate concentrated by
evaporation under reduced pressure to ca. 2–3 cm3. Addition of
hexane (40 cm3) followed by slow evaporation over 3 days gave
25 as pale yellow crystals. Yield 0.110 g, 89%. Found (Calc. for
C29H41ClN2P2Pt): C 49.65 (49.05), H 5.39 (5.82), N 3.61
(3.13)%. Selected IR data (KBr): 2699 ν(N–H), 1616 ν(py C᎐N)
᎐
and 911 cmϪ1 ν(P–N).
cis-[PtI(Ph2PNHpy-P,N)(PPh3)]I 32. As for complex 20
using Ph2PNHpy 1 (0.059 g, 0.212 mmol) and [PtI2(PPh3)2]
(0.205 g, 0.211 mmol) to give a pale yellow crystalline product.
Yield 0.190 g, 91%. Found (Calc. for C35H30I2N2P2Pt): C 41.53
(42.49), H 3.16 (3.06), N 2.10 (2.83)%. Selected IR data (KBr):
1
(3.94)%. H NMR (CDCl3): δ 8.93 (m, 1 H, py C[6]H), 7.82
(m, 3 H, aromatics), 7.44 (m, 6 H, aromatics), 7.24 (m, 2 H,
aromatic), 6.89 (m, 1 H, aromatic), 6.26 (m, 1 H, aromatic)
and 1.84–0.72 (m, 27 H, PnBu). Selected IR data (KBr): 1612
2701 ν(N–H), 1615 ν(py C᎐N) and 912 cmϪ1 ν(P–N).
᎐
ν(py C᎐N) and 943 cmϪ1 ν(P–N).
cis-[PtMe(Ph2PNHpy-P,N)(PPh3)]Cl 33. As for complex 20
using Ph2PNHpy 1 (0.050 g, 0.180 mmol) and cis-[PtClMe-
(PPh3)2] (0.137 g, 0.178 mmol) to give a fine white powder.
Yield 0.123 g, 88%. Found (Calc. for C36H33Cl2N2P2Pt): C 54.56
(55.00), H 4.20 (4.23), N 3.44 (3.56)%. 1H NMR (CDCl3):
δ 11.45 (m, 1 H, NH), 8.46 (m, 1 H, py C[6]H), 8.08 (d,
1 H, aromatic), 7.62 (m, 1 H, aromatic), 7.46–7.21 (m, 25 H,
᎐
cis-[PtCl(Ph2PNHpy-P,N)(PMe2Ph)]Cl 26. As for com-
plex 20 using Ph2PNHpy 1 (0.071 g, 0.255 mmol) and
cis-[PtCl2(PMe2Ph)2] (0.138 g, 0.254 mmol) to give a white
crystalline product. Yield 0.163 g, 94%. Found (Calc. for
C25H26Cl2N2P2Pt): C 43.71 (44.00), H 3.55 (3.84), N 3.91
(4.10)%. 1H NMR (CDCl3): δ 12.20 (m, 1 H, NH), 9.17 (m, 1 H,
py C[6]H), 7.87 (m, 3 H, aromatics), 7.65 (m, 1 H, aromatic),
7.40 (m, 12 H, aromatics), 6.87 (m, 2 H, aromatics) and 1.77
2
aromatics), 6.79 (m, 1 H, aromatic) and 0.62 (dd, J(195Pt–1H)
49.8 Hz, PtMe). Selected IR data (KBr): 2666 ν(N–H), 1616
ν(py C᎐N) and 908 cmϪ1 ν(P–N).
᎐
3
2
(d, 6 H, J(195Pt–1H) 35.1, J(31P–1H) 11.3 Hz, PMe). Selected
IR data (KBr): 2570 ν(N–H), 1616 ν(py C᎐N) and 916 cmϪ1
cis-[PtCl(Ph2PNHpy-P,N)(P(OMe)3)]Cl 34. As for complex
20 using Ph2PNHpy 1 (0.085 g, 0.305 mmol) and cis-
᎐
ν(P–N).
2562
J. Chem. Soc., Dalton Trans., 2000, 2559–2575

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[PtCl2(P(OMe)3)2] (0.137 g, 0.303 mmol) to give a fine white
powder. Yield 0.196 g, 97%. Found (Calc. for C20H24Cl2N2-
O3P2Pt): C 36.68 (35.94), H 3.49 (3.62), N 4.35 (4.19)%.
aromatic). Selected IR data (KBr): 1614 ν(py C᎐N) and 932
᎐
cmϪ1 ν(P–N).
Selected IR data (KBr): 2642 ν(N–H), 1618 ν(py C᎐N) and 914
᎐
cis-[PdCl(Ph2PNHpy-P,N)(PMe2Ph)]Cl 41. As for complex
20 using Ph2PNHpy 1 (0.102 g, 0.367 mmol) and cis-[PdCl2-
(PMe2Ph)2] (0.165 g, 0.364 mmol) to give a cream crystalline
product. Yield 0.192 g, 89%. Found (Calc. for C25H26-
Cl2N2P2Pd): C 50.28 (50.57), H 4.29 (4.41), N 4.03 (4.72)%.
1H NMR (CDCl3): δ 11.91 (m, 1 H, NH), 8.99 (m, 1 H, py
C[6]H), 7.87–7.77 (m, 5 H, aromatics), 7.62 (m, 2 H, aromatics),
7.49 (m, 4 H, aromatics), 7.28–7.23 (m, 6 H, aromatics), 6.88
(m, 1 H, aromatic) and 1.79 (d, 6 H, 2J(31P–1H) 11.6 Hz, PMe).
cmϪ1 ν(P–N).
cis-[PtCl(Ph2PNpy-P,N)(P(OMe)3)] 35. As for complex 21
using 34 (0.136 g, 0.203 mmol) and tBuOK (0.023 g,
0.205 mmol) to give a pale yellow powder. Yield 0.113 g, 88%.
Found (Calc. for C20H23ClN2O3P2Pt): C 38.13 (38.02), H 3.42
1
(3.67), N 4.14 (4.43)%. H NMR (CDCl3): δ 8.87 (m, 1 H, py
C[6]H), 7.84 (m, 3 H, aromatics), 7.50 (m, 6 H, aromatics), 7.40
(m, 2 H, aromatics), 7.07 (d, 1 H, aromatic), 6.34 (m, 1 H,
aromatic) and 3.98 (d, 9 H, 3J(31P–1H) 8.2 Hz, POMe). Selected
Selected IR data (KBr): 2619 ν(N–H), 1614 ν(py C᎐N) and
᎐
915 cmϪ1 ν(P–N).
IR data (KBr): 1615 ν(py C᎐N) and 944 cmϪ1 ν(P–N).
᎐
cis-[PdCl(Ph2PNpy-P,N)(PMe2Ph)] 42. As for complex 21
using 41 (0.149 g, 0.251 mmol) and BuOK (0.028 g, 0.250
t
cis-[PtCl(Ph2PNHpy-P,N)(P(OEt)3)]Cl 36. As for complex
20 using Ph2PNHpy 1 (0.071 g, 0.255 mmol) and cis-
[PtCl2(P(OEt)3)2] (0.152 g, 0.254 mmol) to give a fine white
powder. Yield 0.143 g, 79%. Found (Calc. for C23H30Cl2-
mmol) to give a bright yellow crystalline product. Yield 0.123 g,
88%. Found (Calc. for C25H25ClN2P2Pd): C 53.65 (53.89), H
4.29 (4.52), N 4.75 (5.03)%. 1H NMR (CDCl3): δ 8.76 (m, 1 H,
py C[6]H), 6.69 (m, 4 H, aromatics), 7.48 (m, 2 H, aromatics),
7.40–7.18 (m, 10 H, aromatics), 6.87 (br d, 1 H, aromatic), 6.32
(m, 1 H, aromatic) and 1.63 (d, 6 H, 2J(31P–1H) 10.7 Hz, PMe).
1
N2O3P2Pt): C 38.60 (38.89), H 4.14 (4.26), N 3.76 (3.94)%. H
NMR (CDCl3): δ 12.25 (m, 1 H, NH), 9.08 (m, 1 H, py C[6]H),
7.91 (m, 3 H, aromatics) 7.72 (m, 1 H, aromatic), 7.52 (m, 8 H,
aromatics), 7.30 (m, 1 H, aromatic), 6.92 (m, 1 H, aromatic),
4.06 (dq, 6 H, 3J(31P–1H) 8.8 Hz, POCH2) and 1.19 (t, 9 H, Me).
Selected IR data (KBr): 2616 ν(N–H), 1607 ν(py C᎐N) and 949
᎐
cmϪ1 ν(P–N).
Selected IR data (KBr): 2590 ν(N–H), 1618 ν(py C᎐N) and 913
᎐
cmϪ1 ν(P–N).
cis-[PdCl(Ph2PNHpy-P,N)(PPh3)]Cl 43. As for complex 20
using Ph2PNHpy 1 (0.065 g, 0.234 mmol) and cis-[PdCl2-
(PPh3)2] (0.162 g, 0.231 mmol) to give a cream crystalline
product. Yield 0.159 g, 96%. Found (Calc. for C35H30Cl2-
cis-[PtCl(Ph2PNpy-P,N)(P(OEt)3)] 37. As for complex 21
t
using 36 (0.164 g, 0.243 mmol) and BuOK (0.027 g, 0.241
mmol) to give a pale yellow powder. Yield 0.139 g, 90%. Found
(Calc. for C23H29ClN2O3P2Pt): C 40.68 (40.99), H 4.15 (4.34),
N 4.13 (4.16)%. 1H NMR (CDCl3): δ 8.83 (m, 1 H, py C[6]H),
7.79 (m, 3 H, aromatics), 7.43 (m, 6 H, aromatics), 7.38 (m, 2 H,
aromatics), 7.02 (d, 1 H, aromatic), 6.31 (m, 1 H, aromatic),
4.04 (dq, 6 H, 3J(31P–1H) 8.4 Hz, POCH2) and 1.07 (t, 9 H, Me).
1
N2P2Pd): C 58.64 (58.56), H 4.04 (4.21), N 4.15 (3.90)%. H
NMR (CDCl3): δ 11.25 (m, 1 H, NH), 8.90 (m, 1 H, py C[6]H),
7.95 (m, 1 H, aromatic), 7.75–7.22 (m, 20 H, aromatics), 6.90–
6.81 (m, 6 H, aromatics) and 6.66 (m, 1 H, aromatic). Selected
IR data (KBr): 2659 ν(N–H), 1612 ν(py C᎐N) and 913 cmϪ1
᎐
ν(P–N).
Selected IR data (KBr): 1614 ν(py C᎐N) and 947 cmϪ1 ν(P–N).
᎐
cis-[PdCl(Ph2PNpy-P,N)(PPh3)] 44. As for complex 21 using
43 (0.160 g, 0.223 mmol) and BuOK (0.025 g, 0.223 mmol)
cis-[PtCl(Ph2PNHpy-P,N)(P(OnBu)3)]Cl 38. As for complex
24 using [PtCl2(cod)] (0.093 g, 0.249 mmol), (0.14 cm3, 0.130 g,
0.519 mmol) and Ph2PNHpy 1 (0.070 g, 0.252 mmol) to give 38
as a fine white powder. Yield 0.164 g, 83%. Found (Calc. for
C29H42Cl2N2O3P2Pt): C 43.75 (43.84), H 5.35 (5.33), N 3.62
(3.53)%. 1H NMR (CDCl3): δ 10.66 (m, 1 H, NH), 9.15 (m, 1 H,
py C[6]H), 7.82 (m, 3 H, aromatics), 7.48 (m, 2 H, aromatics),
7.26 (m, 6 H, aromatics), 6.82 (m, 2 H, aromatics), 3.62 (m,
6 H, POCH2), 1.23 (m, 6 H, CH2), 1.06 (m, 6 H, CH2) and
0.74 (t, 9 H, Me). Selected IR data (KBr): 2637 ν(N–H), 1619
t
to give a bright yellow product. Yield 0.143 g, 94%. Found
(Calc. for C35H29ClN2P2Pd): C 60.99 (61.69), H 4.19 (4.29), N
4.02 (4.11)%. 1H NMR (CDCl3): δ 8.70 (m, 1 H, py C[6]H) and
7.97–6.59 (m, 28 H, aromatics). Selected IR data (KBr): 1604
ν(py C᎐N) and 944 cmϪ1 ν(P–N).
᎐
cis-[PdCl(Ph2PNHpy-P,N)(P(OMe)3)]Cl 45. As for complex
20 using Ph2PNHpy 1 (0.063 g, 0.226 mmol) and cis-[PdCl2-
(P(OMe)3)2] (0.131 g, 0.308 mmol) to give a fine cream powder.
Yield 0.170 g, 95%. Found (Calc. for C20H24Cl2N2O3P2Pd): C
42.01 (41.44), H 4.16 (4.17), N 5.16 (4.83)%. Selected IR data
ν(py C᎐N) and 912 cmϪ1 ν(P–N).
᎐
cis-[PtCl(Ph2PNHpy-P,N)(P(OPh)3)]Cl 39. As for complex
20 using Ph2PNHpy 1 (0.054 g, 0.194 mmol) and cis-[PtCl2-
(P(OPh)3)2] (0.171 g, 0.193 mmol) to give a fine white powder.
Yield 0.160 g, 97%. Found (Calc. for C35H30Cl2N2O3P2Pt): C
48.98 (49.19), H 3.41 (3.54), N 2.94 (3.28)%. 1H NMR (CDCl3):
δ 12.52 (m, 1 H, NH), 9.08 (m, 1 H, py C[6]H), 8.02 (br d, 1 H,
aromatic), 7.77 (m, 4 H, aromatics), 7.60 (m, 2 H, aromatics),
7.41 (m, 6 H, aromatics), 7.27–7.21 (m, 8 H, aromatics), 6.91 (br
d, 1 H, aromatic) and 6.86–6.81 (m, 6 H, aromatics). Selected
(KBr): 2688 ν(N–H), 1614 ν(py C᎐N) and 914 cmϪ1 ν(P–N).
᎐
cis-[PdCl(Ph2PNHpy-P,N)(P(OEt)3)]Cl 46. As for complex
24 using [PdCl2(cod)] (0.095 g, 0.333 mmol), P(OEt)3 (0.12 cm3,
0.116 g, 0.698 mmol) and Ph2PNHpy 1 (0.093 g, 0.334 mmol)
to give 46 as a cream powder. Yield 0.199 g, 96%. Found (Calc.
for C23H30Cl2N2O3P2Pd): C 44.67 (44.43), H 4.65 (4.86), N 4.48
1
(4.51)%. H NMR (CDCl3): δ 11.88 (br s, 1 H, NH), 8.88 (m,
IR data (KBr): 2616 ν(N–H), 1619 ν(py C᎐N) and 916 cmϪ1
1 H, py C[6]H), 7.96–7.80 (m, 4 H, aromatics), 7.70–7.26 (m,
8 H, aromatics), 6.89 (m, 1 H, aromatic), 4.12 (dq, 6 H, 3J(31P–
1H) 9.0 Hz, POCH2) and 1.12 (t, 9 H, Me). Selected IR data
᎐
ν(P–N).
(KBr): 2587 ν(N–H), 1614 ν(py C᎐N) and 914 cmϪ1 ν(P–N).
cis-[PtCl(Ph2PNpy-P,N)(P(OPh)3)] 40. As for complex 21
᎐
t
using 39 (0.173 g, 0.202 mmol) and BuOK (0.023 g, 0.205
mmol) to give a pale yellow powder. Yield 0.141 g, 85%. Found
(Calc. for C35H29ClN2O3P2Pt): C 50.62 (51.39), H 3.37 (3.57),
N 2.73 (3.42)%. 1H NMR (CDCl3): δ 8.81 (m, 1 H, py C[6]H),
7.62 (m, 4 H, aromatics), 7.46 (m, 2 H, aromatics), 7.28 (m,
6 H, aromatics), 7.20–7.16 (m, 8 H, aromatics), 6.96 (br d, 1 H,
aromatic), 6.89–6.84 (m, 6 H, aromatics) and 6.26 (m, 1 H,
cis-[PdCl(Ph2PNHpy-P,N)(P(OnBu)3)]Cl 47. As for complex
24 using [PdCl2(cod)] (0.101 g, 0.354 mmol), 90% pure
P(OnBu)3 (0.22 cm3, 0.199 g, 0.715 mmol) and Ph2PNHpy 1
(0.099 g, 0.356 mmol) to give 46 as a cream powder. Yield 0.205
g, 82%. Found (Calc. for C29H42Cl2N2O3P2Pd): C 48.75 (49.34),
H 5.35 (6.00), N 4.62 (3.97)%. 1H NMR (CDCl3): δ 10.22 (br s,
J. Chem. Soc., Dalton Trans., 2000, 2559–2575
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1 H, NH), 8.89 (m, 1 H, py C[6]H), 7.81 (m, 3 H, aromatic),
7.51–7.14 (m, 9 H, aromatics), 6.75 (m, 1 H, aromatic), 3.54 (m,
6 H, POCH2), 1.22–0.95 (m, 12 H, CH2CH2) and 0.72 (t, 9 H,
Me). Selected IR data (KBr): 2684 ν(N–H), 1615 ν(py C᎐N)
᎐
and 910 cmϪ1 ν(P–N).
cis-[PdCl(Ph2PNHpy-P,N)(P(OPh)3)]Cl 48. As for complex
20 using Ph2PNHpy 1 (0.057 g, 0.205 mmol) and cis-[PdCl2-
(P(OPh)3)2] (0.163 g, 0.204 mmol) to give a cream crystalline
product. Yield 0.144 g, 92%. Found (Calc. for C35H30Cl2N2-
O3P2Pd): C 54.65 (54.88), H 3.82 (3.95), N 3.45 (3.66)%.
1H NMR (CDCl3): δ 11.25 (br s, 1 H, NH), 8.90 (m, 1 H,
py C[6]H), 7.95 (m, 3 H, aromatic), 7.75–6.22 (m, 18 H,
aromatics), 6.90–6.81 (m, 6 H, aromatics) and 6.66 (m, 1 H,
aromatic). Selected IR data (KBr): 2664 ν(N–H), 1614
ν(py C᎐N) and 915 cmϪ1 ν(P–N).
᎐
Fig. 3 Crystal structure of Ph2PNHpy 1 showing the hydrogen-
bonded dimer pairs.
cis-[PdCl(Ph2PNpy-P,N)(P(OPh)3)] 49. To a CH2Cl2 (30
cm3) solution of complex 48 (0.134 g, 0.175 mmol) was added
dropwise a CH2Cl2 (DCM) (10 cm3) solution of Et3N (0.018 g
0.179 mmol) and the reaction mixture stirred for 1 h. Distilled
water (20 cm3) was added and the DCM layer separated and
retained. The water layer was extracted with 10 cm3 of DCM.
The extracts were combined and dried over anhydrous MgSO4.
The drying agent was removed by filtration and the filtrate
concentrated under reduced pressure to ca. 1–2 cm3. Diethyl
ether (40 cm3) was slowly added to give a bright yellow powder.
Yield 0.115 g, 90%. Found (Calc. for C35H29ClN2O3P2Pd): C
56.97 (57.62), H 3.91 (4.01), N 3.64 (3.84)%. 1H NMR (CDCl3):
δ 8.70 (m, 1 H, py C[6]H), 7.93 (m, 3 H, aromatics), 7.65 (m, 24
H, aromatics) and 6.34 (m, 1 H, aromatic). Selected IR data
(1)
readily soluble in chlorinated solvents, acetone, thf and toluene
but less soluble in MeOH, diethyl and light petroleum. dppap
exhibits a single 31P-{1H} NMR resonance (in CDCl3) at δ(P)
1
26.4. The H NMR spectrum in the same solvent shows the
pyridyl C[6] proton as a multiplet at δ(H) 7.97 and the amine
proton appears as a broad doublet at δ(H) 5.7 [2J(31P–1H) = 8
Hz]. In the IR spectrum we observe a very weak ν(N–H) band,
due to intermolecular hydrogen bonding, at 3121 cmϪ1 and two
(KBr): 1610 ν(py C᎐N) and 930 cmϪ1 ν(P–N).
strong bands at 1601 and 920 cmϪ1 assigned to ν(py C᎐N) of the
᎐
᎐
pyridine ring and ν(P–N) respectively. Microanalytical data
were satisfactory and the positive-ion FAB mass spectrum gave
the expected parent ion and fragmentation patterns. Crystals of
Ph2PNHpy suitable for X-ray crystallography were obtained by
slow evaporation of a concentrated CDCl3 solution (Fig. 3,
Table 2). The molecular structure reveals that the P(1)–N(2)–
C(2)–N(2) backbone is essentially planar with a mean deviation
of 0.03 Å. In addition, the crystal structure also shows that
in the solid state the molecule exists as hydrogen bonded
dimers. The NH proton of one molecule is hydrogen bonded
to the pyridyl nitrogen of a second and the pyridyl nitrogen
of the second interacts with the NH proton of the first,
leading to a head to tail type arrangement of molecules. The
H(2N) ؒ ؒ ؒ N(1A) distance is 2.04 Å with an intermolecular
X-Ray crystallography
Details of the structure determination are given in Table 1.
X-Ray diffraction measurements were made at room temper-
ature with graphite-monochromated Mo-Kα X-radiation
(λ = 0.71073 Å) using a Siemens SMART diffractometer (17,
19, 20, 21 39) or with Cu-Kα radiation and a Rigaku AFC7S
serial diffractometer (1, 5, 11, 12, 14). For the SMART data,
intensity data were collected using 0.3 or 0.15Њ width ω steps
accumulating area detector frames spanning a hemisphere of
reciprocal space for all structures (data integrated using the
SAINT program) and for the Rigaku AFC7S data collections
by ω scans over a single quadrant of reciprocal space. All
data were corrected for Lorentz, polarisation and long-term
intensity fluctuations. Absorption effects were corrected on the
basis of multiple equivalent reflections or by semi-empirical
methods. Structures were solved by direct methods and refined
by full-matrix least squares against F (TEXSAN35) or F2
(SHELXTL36) for all data with I > 3σ(I).
N(1A) ؒ ؒ ؒ N(2) separation of 2.289(4)
H(2N) ؒ ؒ ؒ N(1A) angle of 160Њ.
Å and an N(2)–
Curiously, the oxide of dppap was not previously reported
alongside the thio and seleno analogues. We have found that
Ph2P(O)NHpy 2 can easily be prepared by the addition of a
small excess of aqueous H2O2 to a thf solution of the phos-
phorus() species. Ph2P(S)NHpy 3 was prepared according to
the literature method28 by refluxing the ligand with a stoichio-
metric quantity of sulfur in toluene. The seleno derivative
Ph2P(Se)NHpy 4 was also prepared in the same manner using
selenium metal although the published procedure requires the
use of the highly toxic potassium selenocyanate. Although
compounds 2-4 display a number of very similar spectroscopic
properties, the strong ν(N–H) band observed in the spectrum
of the oxide was not apparent in the spectra of either the thio
or seleno analogue. Selected analytical data for Ph2P(E)NHpy
(where E = O 2, S 3 or Se 4) are detailed in Table 3.
CCDC reference number 186/2050.
See http://www.rsc.org/suppdata/dt/b0/b003294h/ for crystal-
lographic files in .cif format.
Results and discussion
Synthesis and chalcogen derivatives of dppap
The first reported synthesis of 2-(diphenylphosphinoamino)-
pyridine,23 1, and its subsequent use in the preparation of a
number of metal complexes was published in 1967 followed by
the chalcogen derivatives Ph2P(E)NHpy, E = S 2 and Se 3, in
1970.28 The original synthesis of dppap involved slow dropwise
addition of Ph2PCl in diethyl ether to 2-aminopyridine and
Et3N in the same solvent. Our synthesis is essentially the same
(eqn. 1): the dropwise addition of neat Ph2PCl to a thf solution
of 2-aminopyridine, containing a small excess of Et3N as base.
The ligand was isolated after work-up as an air and moisture
tolerant colourless crystalline solid in good yield (78%). It is
Mixed dppap co-ordination mode complexes
dppap reacts with [MCl2(cod)] (M = Pt or Pd) in warm aceto-
nitrile to give the cationic species cis-[MCl(Ph2PNHpy-P,N)-
{Ph2PNHpy-P}]Cl (M = Pt 5 or Pd 8) in excellent yield, 96 and
98% respectively (Scheme 1). No evidence was found for either
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Table 2 Selected bond lengths (Å) and angles (Њ) for Ph2PNHpy 1
P(1)–N(2)
C(2)–N(1)
1.705(3)
1.329(4)
N(2)–C(2)
C(2)–C(3)
1.374(5)
1.415(5)
C(7)–P(1)–N(2)
P(1)–N(2)–C(2)
N(2)–C(2)–N(1)
103.9(2)
124.4(2)
115.7(3)
C(13)–P(1)–N(2)
C(7)–P(1)–C(13)
N(2)–C(2)–C(3)
99.6(2)
101.5(2)
122.9(4)
Scheme 1 (i) Ph2PNHpy, MeCN; (ii) KBr or NaI, acetone; (iii)
tBuOK, MeOH; (iv) Ag[BF4], CH2Cl2; (v) HBF4ؒOEt2, CH2Cl2.
trans bis(ligand)- or mono(bidentate ligand)-palladium() or
-platinum() complexes. By comparison, the Ph2Ppy equiv-
alents of 5 and 8 cis-[MCl(Ph2Ppy-P,N){Ph2Ppy-P}]ϩ (where
M = Pt37 or Pd38) were prepared by the addition of one
equivalent of halide abstractor to the appropriate cis-[MCl2-
{Ph2Ppy-P}2] complex in solution. The 31P-{1H} NMR
spectrum (in CDCl3) of 5 shows a broad singlet at δ(P)
1
51.4 with platinum satellites. The large J(195Pt–31P) coupling
constant of 3576 Hz is indicative of a cis arrangement of
phosphines around a platinum() centre. Complete assignment
of the 1H NMR spectra (in CDCl3) of 5 and 8 is difficult due to
the fluxional nature (see below) of these molecules in solution.
The expected downfield shifted pyridyl C[6] proton normally
observed for complexes containing co-ordinated pyridine
groups12,39 is evident in the 1H NMR spectra at δ(H) 8.24
for 5 and 8.12 for 8 and appears as a multiplet. The spectrum
of 5 also displays a very broad resonance at δ(H) 11.2 with
an integration which roughly equates to one proton. A D2O
exchange experiment was performed to determine whether this
resonance was attributable to the pyridyl C[6] proton(s) or
those of the amino groups and it was found to be due to the
acidic amine protons. The anticipated high-frequency NH
resonance was not apparent in the 1H NMR spectrum of
the palladium complex 8. The line broadening of the amine
resonance is most likely due to fluxionality within the molecule;
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Table 3 Selected spectroscopic data for Ph2P(E)NHpy, E = O, S or Se
δ(1H)
IR(cmϪ1
)
Compound
NH
Aromatics
δ(31P)
P᎐E
᎐
PN
NH
CN(py)
a
2
3
4
—
7.9–6.7
8.1–6.7
8.1–6.7
16.8
51.6
47.4b
1196
642
550
950
941
941
3201
—
—
1599
1599
1598
7.8(d)b
7.8(d)b
a Amine proton resonance obscured by aromatic resonances. b 2J(31P–1H) 5 Hz. c 1J(31P–77Se) 783 Hz.
Table
4
Selected bond lengths (Å) and angles (Њ) for cis-
[PtCl(Ph2PNHpy-P,N){Ph2PNHpy-P}Cl 5
Pt(1)–P(1)
P(1)–N(2)
N(2)–C(2)
C(2)–N(1)
N(1)–Pt(1)
2.219(2)
1.689(7)
1.360(1)
1.350(1)
2.109(2)
Pt(1)–P(21)
P(21)–N(22)
N(22)–C(22)
C(22)–N(21)
Pt(1)–Cl(1)
2.252(2)
1.686(6)
1.380(1)
1.330(1)
2.345(2)
P(1)–Pt(1)–P(21)
P(1)–Pt(1)–Cl(1)
P(1)–Pt(1)–N(1)
P(1)–N(2)–C(2)
N(2)–C(2)–N(1)
99.18(8)
172.79(7)
82.9(2)
120.2(6)
118.0(7)
N(1)–Pt(1)–Cl(1)
P(21)–Pt(1)–N(1)
P(21)–Pt(1)–Cl(1)
P(21)–N(22)–C(22)
92.0(2)
176.5(2)
86.20(8)
123.7(6)
N(22)–C(22)–N(21) 117.1(7)
of the monodentate P bound ligand is very similar to that
observed for the “free” ligand [124.4(2)Њ] and is marginally
reduced upon chelation [120.2(6)Њ]. A small reduction in the
P–N bond length [dppap P–N length, 1.705(3) Å] is displayed
upon co-ordination to the platinum centre but no significant
difference is observed between monodentate [1.686(6) Å] and
bidentate [1.689(7) Å] ligand co-ordination modes. Although
chelation causes no obvious change in P–N bond length the
N(2)–C(2) and C(2)–N(1) bonds of the bidentate ligand are
contracted and elongated by approximately 0.02 Å respectively.
The Pt(1) and unbound pyridyl nitrogen N(21) ؒ ؒ ؒ Pt distance
of 3.06 Å does not rule out the proposed fluxional behaviour of
the molecule. The structure also confirms the cationic nature of
5 and reveals that the chloride counter ion Cl(2) is involved in
hydrogen-bonding interactions with two NH protons and acts
as a bridge between adjacent molecules. The first is with an NH
proton of a monodentate P bound ligand [H(22) ؒ ؒ ؒ Cl(2) 2.34,
Cl(2) ؒ ؒ ؒ N(22) 3.223(7) Å, N(22)–H(22) ؒ ؒ ؒ Cl(2) 160.6Њ]. The
second interaction is with an NH proton of a chelating ligand
on an adjacent molecule [H(2A) ؒ ؒ ؒ Cl(2) 2.16, Cl(2) ؒ ؒ ؒ N(2A)
3.111(7) Å, N(2A)–H(2A) ؒ ؒ ؒ Cl(2) 169.1Њ] a consequence
of which is the chain like packing of molecules in the crystal
lattice. The solid state hydrogen bonding also explains the
absence of free ν(N–H) bands corroborating the IR spectral
assignment.
Fig. 4 Crystalstructureofcis-[PtCl(Ph2PNHpy-P,N){Ph2PNHpy-P}]-
Cl 5 showing the hydrogen-bonded infinite chains.
also hydrogen bonding to the counter ion may contribute to
this effect. The expected free ν(N–H) in the IR spectra were
not observed but the presence of strong broad bands at 2708
5 and 2709 cmϪ1 8 are characteristic of strong hydrogen-
bonding interactions between the amine protons and the
chloride counter ions, causing a significant reduction in the
NH stretching frequency. Also contained within the IR
spectrum are two bands [1615 and 1596 5, 1611 and 1597 cmϪ1
8] both of which correspond to pyridine ring ν(C=N)
vibrations. The first band has significantly been shifted (to
higher wavenumber by 11–14 cmϪ1);7,12,39 the second is
Clearly the 31P-{1H} NMR data for complex 5 contradict the
solid state structure which should (if this species persists in
solution) give an AX type spectrum. The broad phosphorus
resonance is indicative of an intramolecular fluxional process
(eqn. 2) which means that δ(P) is intermediate between values
comparable with that of the “free” ligand value (1601 cmϪ1
)
accounting for the chelating and ‘dangling’ ligands respectively.
The positive-ion FAB mass spectra gave two clusters of peaks
at m/z 750/1 and 786/7 for 5 and 698 and 663 for 8 which
correspond to [M Ϫ Cl]ϩ and [M Ϫ 2Cl]2ϩ and micro analytical
data were in good agreement with calculated values. The crystal
structure of cis-[PtCl(Ph2PNHpy-P,N){Ph2PNHpy-P}]Cl 5
(Fig. 4, Table 4) shows that the molecule is square planar at
platinum [maximum deviations from Pt(1)–Cl(1)–P(21)–N(1)–
P(1) mean plane 0.2 Å below for Cl(1) and 0.14 Å above for
P(21)] with distortions from idealised square-planar geometry
at the metal due to the bulk of the phosphine groups and to
the bite angle of the chelating ligand [P(21)–Pt(1)–P(1)
99.18(8), P(1)–Pt(1)–N(1) 82.9(2)Њ]. The five-membered Pt(1)–
P(1)–N(2)–C(2)–N(1) ring is planar with a mean deviation
of only 0.03 Å. The P(21)–N(22)–C(22) bond angle [123.7(6)Њ]
(2)
observed for monodentate P bound and bidentate P–N
bound structures. This type of behaviour has been observed in
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Table 5 Selected bond lengths (Å) and angles (Њ) for complexes 11
and 12
a number of platinum() systems containing ligands having
both phosphorus and nitrogen donor sites.13,40 Habtemariam
and Sadler41 found that in solution (D2O, pH 8.6) cis-[PtCl-
(Ph2P(CH2)2NMe2-P,N){Ph2P(CH2)2NMe2-P}]Cl (ring opened
form) was in equilibrium with cis-[Pt{Ph2P(CH2)2NMe2-
P,N}2]Cl2 (ring closed form). Their 31P and 195Pt NMR studies
gave spectra with very broad peaks, which they suggested was
due to a possible exchange reaction between the two species.
Balch and co-workers42 observed, by variable temperature
31P-{1H} NMR, a rapid exchange between cis-[PtI2{Ph2Ppy-
P}2] and the chelated form cis-[PtI{Ph2Ppy-P}(Ph2Ppy-P,N)]I
in dichloromethane. Their work showed that ionic dissociation
is favoured at low temperatures. A variable temperature
31P-{1H} NMR study of cis-[PtCl(Ph2PNHpy-P,N){Ph2-
PNHpy-P}]Cl 5 in CD2Cl2 down to 183 K did not reveal
any spectral changes. The bromo and iodo derivatives cis-
[MX(Ph2PNHpy-P,N){Ph2PNHpy-P}]X (M = Pt, X = Br 6 or
I 7; M = Pd, X = Br 9 or I 10) can be prepared by metathesis
with an excess of the appropriate halide ion in refluxing acetone
(Scheme 1). The complexes display IR and mass spectral data
comparable to those of their chloro analogues; the 31P-{1H}
NMR δ values (in dmso/C6D6) are closer to those observed for
the dicationic species 13 and 14 suggesting that in solution the
bis-chelate dicationic form is favoured.
11
12
M–P(1)
M–P(2)
2.243(2)
2.234(1)
1.640(5)
1.644(5)
1.322(7)
1.333(7)
1.390(7)
1.380(7)
2.112(4)
2.112(4)
2.247(1)
2.244(1)
1.638(3)
1.645(3)
1.331(5)
1.341(5)
1.381(4)
1.374(5)
2.119(3)
2.118(3)
P(1)–N(2)
P(2)–N(22)
N(2)–C(2)
N(22)–C(22)
C(2)–N(1)
C(22)–N(21)
N(1)–M
N(21)–M
P(1)–M–P(2)
105.68(5)
97.7(1)
169.1(1)
172.8(1)
79.0(1)
104.62(4)
98.9(1)
N(1)–M–N(21)
P(1)–M–N(21)
P(2)–M–N(1)
P(1)–M–N(1)
P(2)–M–N(21)
M–P(1)–N(2)
M–P(2)–N(22)
P(1)–N(2)–C(2)
P(2)–N(22)–C(22)
N(2)–C(2)–N(1)
N(22)–C(22)–N(21)
168.99(9)
173.13(9)
78.89(8)
78.80(9)
103.5(1)
104.7(1)
114.7(3)
114.5(3)
121.1(4)
121.3(3)
78.7(1)
104.5(2)
105.5(2)
113.8(4)
114.0(4)
122.2(5)
121.6(5)
Neutral bis-bidentate complexes of dppap
The first, and to the best of our knowledge only reported
example of a complex containing the [Ph2PNpy]Ϫ ligand is
trans-[Ni(Ph2PNpy-P,N)2]43 prepared in 20% yield by the
addition of phenyllithium to a thf solution of dppap followed
by [NiBr2(thf)2]. We have found that deprotonation is possible
under much milder conditions. Treatment of the dichloro
t
species 5 and 8 with two equivalents of BuOK in methanol
leads to (Scheme 1) deprotonation of the dppap ligands giving
neutral species cis-[M(Ph2PNpy-P,N)2] (M = Pt 11 or Pd 12).
Both the palladium and the platinum complexes display sharp
single 31P-{1H} NMR resonances that occur at significantly
higher frequencies than those of their starting materials, [δ(P)
63.0 11 and 84.5 12 , cf. 51.4 5 and 71.4 8] since deprotonation
results in the formation of stable, non-fluxional bis-chelate
complexes (the chelate-ring effect).44 Furthermore, the 1J(195Pt–
31P) coupling constant of 11 (3334 Hz) is considerably smaller
Fig. 5 Crystal structure of cis-[Pt(Ph2PNpy-P,N)2] 11; cis-[Pd(Ph2-
PNpy-P,N)2] 12 is isomorphous and is not illustrated.
1
than that of 5 (3576 Hz). The H NMR spectra of 11 and 12
confirm the absence of any amine protons and the pyridyl C[6]
protons are observed as multiplets at δ(H) 7.77 and are sig-
nificantly shifted downfield from the remaining aromatic
resonances. The IR spectra also lend evidence to support the
proposed structure including the absence of any ν(N–H) bands
ically equivalent M–P–N–C–N rings, which, upon crystallo-
graphic examination, are found to contain subtle geometrical
differences. The five-membered rings in the platinum com-
plex 11 are slightly distorted from planar with P(1) lying
0.17 Å below the Pt(1)–P(1)–N(2)–C(2)–N(1) mean plane and
P(2) lying 0.14 Å above the Pt(1)–P(2)–N(22)–C(22)–N(21)
mean plane. The angle between these planes is 14Њ. The
five-membered, PdPCN2 rings of complex 12 exhibit similar
deviations from planarity. The pyridyl nitrogens N(1) and
N(21) lie 0.34 Å above and 0.28 Å below the Pd(1)–P(1)–N(2)–
C(2)–N(1) and Pd(1)–P(2)–N(22)–C(22)–N(21) mean planes
respectively and are inclined by ca. 12Њ to their respective five-
membered rings. The P–N bond lengths are not significantly
different, P(1)–N(2) and P(2)–N(22) [1.640(5), 1.644(5) Å for 11
and 1.638(3), 1.645(3) Å for 12] but shorter than those observed
for 5 [1.686(6) and 1.689(7) Å] and much shorter than in
free dppap [1.705(3) Å]. A significantly larger contraction of
the N(2)–C(2), N(22)–C(22) [1.332(7), 1.333(7) Å for 11 and
1.331(5), 1.341(5) Å for 12] and elongation of the C(2)–N(1),
C(22)–N(21) [1.390(7), 1.380(7) Å for 11 and 1.381(4), 1.374(5)
Å for 12] bonds is observed compared to those of the neutral
chelating ligand in 5 [N(2)–C(2) 1.360(1) and C(2)–N(1)
1.350(1) Å]. The P–N–C bond angles [114.0(4) and 113.8(4)Њ for
11, 114.7(3) and 114.5(3)Њ for 12] are considerably smaller than
those of either the “free” ligand 1 [124.4(2)Њ] or the chelating
and only one pyridyl ν(C᎐N) band occurring at slightly higher
᎐
wavenumber [1609 11 and 1604 cmϪ1 12] than for the “free”
ligand [1601 cmϪ1 1]. Deprotonation of the amino group causes
an increase in P–N bond order and shifts the ν(PN) to higher
frequency compared to that of free dppap. This phenomenon
has been observed in a number of related ligand systems con-
taining PNP,45,46 PNP(E) (E = O,47–51 S or Se52), and (E)PNP(E)
(E = O,53–57 S58–64 or Se64–67) backbones, where electron delocal-
isation upon deprotonation occurs over the three four or five
atom backbone. Lengthening of the P᎐E and shortening of the
᎐
P–N bonds is the net result. This effect is much less pronounced
with P–N–py systems and only small changes in bond angles
and lengths occur in the P–N–C–N backbone as a consequence
of deprotonation (see below). In the platinum complex 11
deprotonation is accompanied by an increase in ν(PN) from 920
to 936 cmϪ1 and in the palladium complex 12 to 942 cmϪ1
.
Microanalytical and mass spectral data were satisfactory for
both complexes. The molecular structures of the platinum
complex 11 and its palladium analogue 12 (Fig. 5, Table 5)
display cis geometry with respect to the phosphorus atoms and
are square planar at metal. Each complex consists of two chem-
J. Chem. Soc., Dalton Trans., 2000, 2559–2575
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Table 6 Selected bond lengths (Å) and angles (Њ) for cis-[Pd(Ph2-
PNHpy-P,N)2][BF4]2 14
ligand of complex 5 [120.2(6)Њ]. This contraction in bond angle
upon deprotonation is also observed in related systems con-
taining other P–N–P fragments in their backbones.45–67
Pd(1)–P(1)
P(1)–N(2)
N(2)–C(2)
2.234(2)
1.677(7)
1.39(1)
C(2)–N(1)
N(1)–Pd(1)
1.33(1)
2.084(9)
Dicationic bis-bidentate complexes of dppap
We have also found (Scheme 1) that chloride abstraction from
cis-[MCl(Ph2PNHpy-P,N){Ph2PNHpy-P}]Cl (M = Pt 5 or Pd
8) with Ag[BF4] in dichloromethane affords the dicationic
species cis-[M(Ph2PNHpy-P,N)2][BF4]2 (M = Pt 13 or Pd 14).
In addition, complexes 13 and 14 were easily prepared by
treatment of cis-[M(Ph2PNpy-P,N)2] (M = Pt 11 or Pd 12) with
a small excess of HBF4ؒOEt2 in dichloromethane. Compounds
13 and 14 were isolated as cream solids in good yield (81
and 79% respectively) and display the expected spectral and
analytical properties. The platinum complex displayed a
sharp single resonance with platinum satellites in the 31P-{1H}
NMR spectrum (in d6-dmso) [δ(P) 64.1, 1J(195Pt–31P) 3475 Hz].
Similarly, the palladium complex gave a sharp singlet at δ(P)
P(1)–Pd(1)–P(1A)
P(1)–Pd(1)–N(1A)
P(1)–Pd(1)–N(1)
N(2)–C(2)–N(1)
101.9(1)
167.6(2)
81.2(2)
N(1)–Pd(1)–N(1A)
P(1)–N(2)–C(2)
C(2)–N(1)–Pd(1)
98.3(5)
119.1(6)
119.8(7)
114.2(8)
1
88.0. The H NMR spectra (in d6-dmso) of the two complexes
clearly showed the NH proton resonances as multiplets at δ(H)
8.20 (13) and 8.17 (14) and the pyridyl C[6] proton resonances
as multiplets at δ(H) 7.99 (13) and 7.97 (14). The IR spectra
displayed broad ν(N–H) bands at 3235 cmϪ1. This shift to
higher wavenumber, compared to that of cis-[PtCl(Ph2PNHpy-
P,N){Ph2PNHpy-P}]Cl 5 [ν(N–H) 2666 cmϪ1], is because of
the much weaker hydrogen bonding between the amine protons
and the [BF4]Ϫ anions. Additional bands for both 13 and 14 at
ca. 900 cmϪ1 [ν(P–N)], and single bands at higher wavenumber
Fig. 6 Crystal structure of cis-[Pd(Ph2PNHpy-P,N)2][BF4]2 14.
70% of the isolated material. The positive-ion FAB mass
spectrum gave parent ion peaks which coincide with the pro-
posed species observed in the 31P-{1H} NMR spectrum.
Slow dropwise addition of a CH2Cl2 solution of 1 to a solu-
tion of [PtMe2(cod)] in the same solvent gave by 31P-{1H}
NMR [PtMe2(Ph2PNHpy-P,N)] exclusively. All attempts to
isolate this material from the reaction mixture failed due
to its extremely high solubility in all common solvents. The
preparation of [PtMe2{Ph2PNHpy-P}2] as a pure solid was
abandoned due to constant contamination with unchanged
ligand and the mono(bidentate ligand) species. By com-
parison, the addition of two equivalents of solid Ph2PNHpy 1
to a dichloromethane solution of [PtClMe(cod)] gave a single
product, characterised as cis-[PtMe(Ph2PNHpy-P,N){Ph2-
PNHpy-P}]Cl 15, in 95% yield. The Ph2Ppy equivalent of 15
cis-[PtMe(Ph2Ppy-P,N){Ph2Ppy-P}][BF4] was prepared by the
addition of a halide abstractor to cis-[PtClMe{Ph2Ppy-P}2]
in solution and the product has crystallographically been
characterised.68 There is good 31P-{1H} NMR evidence for the
structural assignment of 15. The complex displays a well
resolved AX type 31P-{1H} NMR spectrum, with a low fre-
quency resonance at δ(P) 38.4 [1J(195Pt-31PA) 3948 Hz] assigned
to monodentate P bound ligand trans to pyridyl nitrogen of the
chelating ligand. The observed large trans P–Pt–N(py) coupling
constant [3948 Hz] is much greater than that observed for
than that of free dppap, at 1615 cmϪ1 [ν(py C᎐N)], indicative
᎐
of protonated ligand and pyridyl co-ordination respectively,
were in evidence. Microanalytical data were satisfactory and
the positive ion FAB mass spectra gave, for both complexes,
the expected [M Ϫ 2BF4]2ϩ parent ion with appropriate isotope
distribution and fragmentation patterns. The structure of
cis-[Pd(Ph2PNHpy-P,N)2][BF4]2 14 (Fig. 6, Table 6) reveals it to
be a four-co-ordinate species with cis geometry and is square
planar at palladium. In addition the molecule possesses crystal-
lographic twofold symmetry, the palladium atom is located on
the twofold axis. The small bite angle of the ligand causes con-
siderable distortions from idealised square planar geometry.
The trans P–Pd–N [167.6(2)Њ] axes are less than 180Њ and the
cis P–Pd–P [101.9(1)Њ] and N–Pd–N [98.3(5)Њ] angles exceed
90Њ. The five-membered rings of 14 are slightly puckered with
the amine nitrogen N(1) lying 0.2 Å above the Pd(1)–P(1)–
N(2)–C(2)–N(1) mean plane. The angle between the planes
defined by the two rings is 21Њ. The P(1)–N(2)–C(2) angle is
119.1(6)Њ whilst the P(1)–N(2), N(2)–C(2) and C(2)–N(1)
distances are 1.677(7), 1.39(1) and 1.33(1) Å respectively.
The P(1)–N(2)–C(2) angle and the P(1)–N(2) distance are as
expected for protonated chelating ligands, however a small
increase (the converse of previously discussed examples) in the
N(2)–C(2) distance is exhibited. In addition, the elongation of
the C(2)–N(1) bond (also evident in previous examples) does
not occur. The crystal structure also shows that the NH protons
are hydrogen bonded to the [BF4]Ϫ counter ions [H(2) ؒ ؒ ؒ F(3)
2.24, F(3) ؒ ؒ ؒ N(2) 2.95(1), N(2)–H(2) ؒ ؒ ؒ F(3) 163.0Њ].
69
cis-[Pt(PPh3)2(py)2][ClO4]2 [3276 Hz] but is in fairly good
agreement with that of cis-[PtMe(Ph2Ppy-P,N){Ph2Ppy-P}]-
[BF4]68 [4226 Hz]. The high frequency resonance occurs at
δ(P) 84.2 [1J(195Pt–31PX) 2019 Hz] assigned to the PN chelating
ligand and displays a typical trans P–Pt–Me coupling constant.
The small 2J(31PA–31PX) coupling constant of 11 Hz is indicative
of a mutual cis arrangement of phosphines around the metal.
Reactions of dppap with [PtMeX(cod)] (where X ؍ Me or Cl)
1
Further evidence is provided by the H NMR spectrum (in
Reaction of two equivalents of complex 1 with [PtMe2(cod)]
gives a mixture of products. 31P-{1H} NMR shows three singlet
resonances; δ(P) 26.4 corresponding to unchanged ligand,
δ(P) 54.3 [1J(195Pt–31P) 2090 Hz] to [PtMe2{Ph2PNHpy-P}2] and
δ(P) 70.7 [1J(195Pt–31P) 2178 Hz] to [PtMe2(Ph2PNHpy-P,N)].
The observed difference in chemical shift of these two com-
plexes is also evident in cf. 5 and 13 where increased δ(P) values
were obtained upon chelation (the chelate ring effect).44 The
relative intensities of the signals indicates that the expected
complex [PtMe2{Ph2PNHpy-P}2] constitutes approximately
CDCl3) which shows a broad peak at δ(H) 11.5 and a multiplet
at δ(H) 8.3 assigned respectively to the amine and the pyridyl
C[6] protons of the chelating ligand. Two broad doublets
δ(H) 7.8 and 8.0 have been tentatively assigned to the amine
and pyridyl C[6] protons respectively of the ‘dangling’ P bound
ligand. The methyl group resonance appears as a double
2
doublet at δ(H) 0.64 [3J(31P–1H) 4, J(195Pt–1H) 51 Hz]. The
IR spectrum of 15 is very similar to those of 5 and 8 with
respect to the absence of the expected free ν(N–H) band. The
lack of which, considering the structural similarities of 5 and
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J. Chem. Soc., Dalton Trans., 2000, 2559–2575

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Table 7 Selected bond lengths (Å) and angles (Њ) for [AuCl-
15, is almost certainly due to the same type of solid state
hydrogen bonding observed in the crystal structure of 5. This
assumption is supported by the broad ν(N–H) band at 2706
cmϪ1 which, as discussed earlier, is characteristic of strongly
hydrogen-bonded NH protons. Also, there are two bands at
(Ph2PNHpy-P)] 17
Cl(1)–Au(1)
P(1)–N(2)
C(2)–N(1)
2.2813(12)
1.687(4)
1.336(6)
Au(1)–P(1)
N(2)–C(2)
2.2187(11)
1.399(7)
1614 and 1592 cmϪ1 assigned as the ν(C᎐N) of the pyridine
᎐
ring, indicative of two dppap co-ordination modes, bidentate
PN and ‘dangling’ P bound. The absence of a ν(Pt–Cl) stretch
is also consistent with the proposed structure. Microanalytical
data were in good agreement with calculated values and the
positive ion FAB mass spectrum showed a peak at m/z 766
which corresponds to [PtMe(Ph2PNHpy)2]ϩ. No attempt to
synthesize mono(bidentate ligand) complexes from [PtClMe-
(cod)] was made. Reaction of 15 with 2.5 molar equivalents of
tBuOK in methanol leads to Ph2P–N bond cleavage of one of
the dppap ligands and deprotonation of the other to give, in
78% yield, the unexpected platinum() species cis-[PtMe(Ph2-
PNpy-P,N){Ph2POMe-P}] 16 (eqn. 3). The AX 31P-{1H} NMR
Cl(1)–Au(1)–P(1)
P(1)–N(2)–C(2)
177.14(5)
121.7(3)
Au(1)–P(1)–N(2)
N(2)–C(2)–N(1)
114.3(2)
116.0(4)
(3)
Fig. 7 Crystal structure of [AuCl{Ph2PNHpy-P}] 17 showing the
hydrogen-bonded infinite chains.
bis(diphenylphosphino)methylamine,
Ph2PN(Me)PPh2],
yielding [Pt{Ph2PN(Me)PPh2}(Ph2PNHMe)(Ph2POMe)]2ϩ. In
addition to the above examples of ring opening reactions,
recent publications from our group have demonstrated that
methanolysis of Ph2P–N bonds in complexes bearing
monodentate phosphines can be induced by prolonged reflux
in methanol49 or via the reaction of four equivalents of
Ph2PNHP(O)Ph2 with the cyclometallated dimer [{Pd(µ-Cl)-
(C6H4CH2NMe2-o-C,N)}2] in methanol at ambient temperature
yielding [PdCl{Ph2PNP(O)Ph2-P,O)(Ph2POMe)].48
spectrum (in CDCl3) of 16 shows a high-frequency resonance
at δ(P) 100.6 [1J(195Pt–31P) 4447 Hz], which we have assigned
as the co-ordinated Ph2POMe. Although comparison of the
previously mentioned Ph2POMe δ(P) and J values found for
16 to those observed for cis-[PtCl2(Ph2POMe)2], δ(P) 85.6
[1J(195Pt–31P) 4175 Hz],70 is not entirely valid it highlights the
high frequency resonances and the large J values associated
with platinum() methyl diphenylphosphinite complexes. The
lower frequency resonance occurs at δ(P) 90.0 [1J(195Pt–31P)
1950 Hz], and is assigned to the deprotonated chelating ligand.
The small coupling constant [1950 Hz] is similar to that of
complex 15 [2019 Hz], establishing that the chelating ligand
trans P–Pt–Me geometry of 15 persists in 16. Additional evi-
dence in support of the proposed retention of cis geometry
Gold complexes of dppap
The reaction of dppap with [AuCl(tht)] proceeds by the dis-
placement of tht to give the anticipated product [AuCl-
{Ph2PNHpy-P}] 17 in excellent yield (90%). The complex
exhibits the expected spectroscopic and analytical properties.
It showed a single sharp resonance in the 31P-{1H} NMR
spectrum (in CDCl3) at δ(P) 55.4 and the 1H NMR spectrum in
the same solvent showed the pyridyl C[6] proton as a multiplet
at δ(H) 8.01 and that the amine proton was obscured by the
aromatic resonances. From the IR spectrum we can identify a
strong ν(N–H) band at 3373 cmϪ1; in contrast to previously
discussed complexes where strong hydrogen-bonding inter-
actions have broadened and shifted this band to a much lower
frequency. We can also identify ν(P–N) at 909 cmϪ1 and ν(py
2
is the small J(31PA–31PX) coupling constant of 8 Hz, a value
1
consistent with a cis configuration of ligands. The H NMR
spectrum of 16 supports the proposed structural assignment.
The absence of amine proton resonances and the presence of
the anticipated pyridyl C[6] proton multiplet at δ(H) 8.1 are in
accord with the structure, but, most significant, is the doublet
resonance of the P–OMe methyl group that integrates to three
protons at δ(H) 3.0 [3J(31P–1H) 8 Hz] . The three methyl protons
in common with complex 15 occur as a double doublet at δ(H)
0.25 [3J(31P–1H) 4, 2J(195Pt–1H) 55 Hz]. Supporting IR data
include only one pyridyl ν(CN) band [1613 cmϪ1] in contrast to
two [1614 and 1592 cmϪ1] observed for complex 15 and the
ν(PN) band [937 cmϪ1] at higher energy than those of 15 [907
cmϪ1], which is indicative of deprotonation. Microanalytical
data were satisfactory and the positive-ion FAB mass spectrum
gave the expected parent ion for [PtMe(Ph2PNpy)(Ph2POMe)]ϩ
at m/z = 704 and isotope distribution patterns.
C᎐N) at 1593 cmϪ1 which is at lower wavenumber than the
᎐
“free” ligand vibration (1601 cmϪ1) which suggests that there is
little, if any, interaction between the pyridyl nitrogen and the
gold atom. Suitable crystals of 17 were grown by slow diffusion
of diethyl ether into a dichloromethane solution.
The crystal structure (Fig. 7, Table 7) confirmed the absence
of any interaction between the gold and pyridyl nitrogen atoms;
the Au(1) ؒ ؒ ؒ N(1) distance is 3.23 Å. The Cl(1)–Au(1)–P(1)
angle at 177.14(5)Њ is unremarkable and the P(1)–N(2)–C(2)
angle of 121.7(3)Њ is as expected for a monodentate P bound
ligand. The P(1)–N(2) and C(2)–N(1) distances of 1.687(4) and
1.336(6) Å are as anticipated. A long distance intermolecular
hydrogen-bonding interaction between the NH proton H(2N)
and the pyridyl nitrogen N(1A) of adjacent molecules is evi-
dent. The H(2N) ؒ ؒ ؒ N(1A) distance of 2.06 Å and the N(2)–
H(2N) ؒ ؒ ؒ N(1A) angle of 139Њ may be compared with those in
1 [H(2N) ؒ ؒ ؒ N(1A) 2.04 Å] and [N(2)–H(2N) ؒ ؒ ؒ N(1A) 160Њ].
Treatment of 17 in dichloromethane with solid Ag[ClO4]
gave after work-up a white powder which we have characterised
as [{Au(µ-Ph2PNHpy-P,N)}2][ClO4]2 (HT) 18 (HT = head to
Although the synthesis of complex 16, via methanolysis
of a Ph2P–N bond, is rather unusual, a number of similar Ph2-
P–N bond cleavage reactions have been observed. Krishna-
murthy and co-workers71 recently reported the facile P–N
bond cleavage in unsymmetrical diphosphazene complexes
of palladium() giving products of the type [PdCl2{PhP(NHiPr)-
R}(Ph2POMe)] (where R = OC6H4Br-4 or OC6H3Me2-3,5).
Browning and Farrar72 reported
a
similar reaction in
the dicationic platinum(II) complex [Pt(dppma)2]2ϩ [dppma =
J. Chem. Soc., Dalton Trans., 2000, 2559–2575
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Table 8 Selected bond lengths (Å) and angles (Њ) for [Pt(C8H12OMe)-
(Ph2PNpy-P,N)]ؒH2O 19
(4)
Pt(1)–P(1)
2.2233(11)
Pt(1)–N(1)
P(1)–N(2)
N(2)–C(2)
C(2)–N(1)
2.132(3)
1.647(3)
1.354(5)
1.380(5)
Pt(1)–C(23)
Pt(1)–C(19)
Pt(1)–C(20)
2.064(4)
2.261(4)
2.290(5)
P(1)–Pt(1)–N(1)
P(1)–Pt(1)–C(23)
P(1)–Pt(1)–C(19)
P(1)–Pt(1)–C(20)
N(1)–Pt(1)–C(23)
N(1)–Pt(1)–C(19)
79.77(9)
96.43(13)
155.68(14)
169.13(14)
176.2(2)
N(1)–Pt(1)–C(20)
C(23)–Pt(1)–C(19)
C(23)–Pt(1)–C(20)
Pt(1)–P(1)–N(2)
P(1)–N(2)–C(2)
N(2)–C(2)–N(1)
103.6(2)
87.8(2)
80.2(2)
106.97(13)
115.3(3)
121.4(4)
95.4(2)
tail), eqn. (4). The complex displays a sharp single resonance
in the 31P-{1H} NMR (in CH2Cl2–C6D6) at δ(P) 62.7, a shift
to higher frequency of 7 ppm relative to the starting material
16. The 1H NMR was particularly uninformative but the
IR spectrum showed a higher energy pyridyl ν(C᎐N) band at
᎐
1611 cmϪ1 compared to 1592 cmϪ1 for 15 which is indicative of
co-ordinating behaviour. The positive-ion FAB mass spectrum
gave evidence for the formation of the bimetallic species
showing a peak at m/z 951 which corresponds to [{Au(µ-Ph2-
PNHpy-P,N)}2]2ϩ. Attempts to grow crystals of 18 from
MeOH–Et2O and CH2Cl2–Et2O solvent systems resulted in
complete decomposition and isolation of crystalline Au[ClO4].
Bridge cleavage reactions of dppap
The rapid sequential addition of two equivalents of Ph2PNHpy
t
1 followed by BuOK to a suspension of [{Pt(µ-OMe)(C8H12-
OMe)}2] in methanol resulted in methoxy bridge cleavage of the
platinum() dimer, eqn. (5). Obtaining the product (which was
Fig. 8 Crystal structure of [Pt(C8H12OMe)(Ph2PNpy-P,N)]ؒH2O 19
illustrating the hydrogen-bonding.
role in dimer formation. The pseudo-eight membered ring
is symmetric and displays two distinct pairs of hydrogen
bonds [H(30A) ؒ ؒ ؒ N(2) 2.14, N(2) ؒ ؒ ؒ O(30) 3.11 Å,
O(30)–H(30A) ؒ ؒ ؒ N(2) 167Њ and H(30B) ؒ ؒ ؒ N(2A) 2.01,
N(2A) ؒ ؒ ؒ O(30) 2.95 Å, O(30)–H(30b) ؒ ؒ ؒ N(2A) 162Њ]. The
six-membered O2H4 ring is inclined by ca 76Њ to the co-
ordination plane.
(5)
The synthesis of the mixed ligand complex cis-[PtMe-
(Ph2PNpy-P,N){Ph2POMe-P}] 16, discussed above, represents
a rather unusual reaction. A more established route to com-
plexes of the type [MCl2(PR3)(PRЈ3)] is via a redistribution
reaction and a number of mixed phosphine ligand complexes
of platinum() and palladium() have previously been
reported.73,74 We found that chloride bridge cleavage of the
platinum() dimer [{PtCl(µ-Cl)(PMe2Ph)}2] with dppap in
dichloromethane affords the unsymmetrical cationic complex
cis-[PtCl{Ph2PNHpy-P,N}(PMe2Ph)]Cl 26; eqn. (6). The 31P-
first isolated as a pale yellow oil) as a solid proved troublesome.
Precipitation (of a pale yellow solid) was finally achieved by
dropwise addition of distilled water to a methanol solution of
19. Examination of this material by 31P-{1H} NMR (in CDCl3)
showed that a single phosphorus-containing product had been
isolated, characterised as [Pt(C8H12OMe)(Ph2PNpy-P,N)] 19.
The 31P-{1H} NMR displays a single resonance at δ(P) 63.2
which is very similar to δ(P) 63.0 observed for cis-[Pt(Ph2PNpy-
1
P,N)2] 11. The large J(195Pt–31P) of 4087 Hz enabled us to
establish which isomer had been synthesized, i.e. phosphorus
trans to the olefin portion of C8H12OMe, as P trans to Pt–C
bonds have typical 1J(195Pt–31P) values of 2000 Hz. The 1H
NMR spectrum gave the expected C8H12OMe resonances and
also confirmed that the ligand was deprotonated. Assignment
of the IR spectrum was difficult but we were able to identify
(6)
ν(py C᎐N) at 1607 cmϪ1 and ν(P–N) at 941 cmϪ1 which are
᎐
consistent with deprotonated chelating ligand behaviour and
also very close to those found for complex 11 [ν(py C᎐N) 1609,
᎐
ν(P–N) 936 cmϪ1]. Micro analytical data were satisfactory and
the positive-ion FAB mass spectrum gave the expected parent
ion peak. The crystal structure of 19 (Fig. 8, Table 8) shows that
the complex is approximately square planar at platinum with
the predicted phosphorus trans to olefin geometry. The five-
membered Pt(1)–P(1)–N(2)–C(2)–N(1) ring is planar with a
mean deviation of only 0.01 Å. The bond lengths and angles of
the ring are very similar to those observed in the PtPCN2 rings
of cis-[Pt(Ph2PNpy-P,N)2] 11, most notably the contracted
P(1)–N(2)–C(2) angle [115.3(3)Њ] and the reduced P(1)–N(2)
distance [1.647(3) Å]. The crystal structure clearly established
the presence of water molecules in the lattice and their bridging
{1H} NMR spectrum (in CDCl3) of 26 is an AX type with
platinum satellites, and reveals a small phosphorus–phosphorus
coupling constant indicative of a structure with a mutual
cis arrangement of phosphine ligands. The chemical shift of the
P–N ligand, δ(P) 62.2, and the sharp spectral lines suggest
bidentate co-ordination behaviour with no fluxionality. This is
2570
J. Chem. Soc., Dalton Trans., 2000, 2559–2575

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substantiated upon examination of the 1H NMR spectrum
which shows the amine proton as a broad multiplet at
δ(H) 12.22 and the pyridyl C[6] proton as a multiplet at
δ(H) 9.17 both significantly shifted to higher frequency than
those observed for the “free” ligand [δ(H) 7.97 C[6]H and 5.71
NH 1], which are also consistent with chelating behaviour.
The cationic nature of the complex is exemplified by the very
broad ν(N–H) band at 2570 cmϪ1 in the IR spectrum, which is
characteristic of strong hydrogen bonding, in this case with the
chloride counter ion.
Cationic mixed ligand complexes of PtII and PdII
We also found that complex 26 was the sole product formed
upon reaction of dppap with cis-[PtCl2(PMe2Ph)2] in dichloro-
methane (eqn. 6) confirmed by 31P-{1H} NMR. The crude
product was precipitated by the addition of diethyl ether to the
reaction mixture but recrystallisation from dichloromethane–
diethyl ether was necessary to remove residual PMe2Ph,
evidenced by its characteristic odours and line broadening
in the 31P-{1H} NMR spectrum. The reaction proceeds rapidly
by substitution of PMe2Ph and halide, presumably as a con-
sequence of the chelate ring effect. This substitution reaction
was generally applied in the synthesis of a range of unsym-
metrical cationic mixed ligand platinum and palladium com-
plexes of the type cis-[MXЈ(Ph2PNHpy-P,N)(PR3)]X (M = Pt,
X’ = X = Cl, PR3 = PMe3 20, PEt3 22, PnBu3 24, PMe2Ph 26,
PPh2H 28 or PPh3 29; XЈ = X = Br 31 or I 32, PR3 = PPh3);
XЈ = Me, X = Cl, Pr3 = PPh3; 33, XЈ = X = Cl, PR3 = P(OMe)3
34, P(OEt)3 36, P(OnBu)3 38 or P(OPh)3 39; M = Pd,
XЈ = X = Cl, PR3 = PMe2Ph 41, PPh3 43, P(OMe)3 45, P(OEt)3
46, P(OnBu)3) 47 or P(OPh)3 48). Of the complexes listed
above the majority were synthesized using solutions of solid
[MCl2(PR3)2] (M = Pt or Pd) type materials. The formation and
isolation in good to excellent yield (82–96%) of complexes 24,
38, 46 and 47 by addition of dppap to quickly prepared dichloro-
methane solutions of [MCl2(cod)] (M = Pt or Pd) and the
appropriate phosphorus ligand clearly demonstrates that
precursor isolation and purification is not necessary. All of
the complexes displayed similar spectroscopic properties to
those described for compound 26, i.e. AX type 31P-{1H} NMR
spectra with small 2J(31PA–31PX) coupling constants. High
frequency pyridyl C[6]H and amine proton resonances as well
as broad ν(NH) bands were in evidence in the 1H NMR and IR
spectra respectively. As well as the characterising data described
above the 1H NMR spectrum of cis-[PtCl(Ph2PNHpy-P,N)-
(PPh2H)]Cl 28 displays a doublet at δ(H) 5.22 with platinum
satellites [1J(195Pt–1H) 90 Hz] due to the PPh2H proton as well
Fig. 9 Crystal structure of cis-[PtCl(Ph2PNHpy-P,N)(PMe3)]Cl 20.
Fig. 10 Crystal structure of cis-[PtCl(Ph2PNHpy-P,N)(P(OPh)3)]Cl
39.
[1J(195Pt–31P) 2013 Hz], assigned to the chelating PN ligand with
the phosphorus donor atom as suggested by the magnitude of
the coupling constant lying trans to the Pt–C bond. The lower
frequency resonance at δ(P) 16.7 [1J(195Pt–31PA) 3948 Hz]
displays a large platinum–phosphorus coupling constant that
is identical to the value observed for complex 15 [1J(195Pt–31PA)
3948 Hz] which has the same cis R3P–Pt–N(py) geometry.
The 1H NMR (CDCl3) spectrum of 33 shows the methyl
protons as a double doublet with platinum satellites at δ(H)
0.62 [2J(195Pt–1H) 50 Hz]. The platinum complexes 36, 38 and
39, which have co-ordinated triethyl, tributyl and triphenyl
phosphite groups respectively, all display the characteristically
large coupling constants expected for these ligands. Most of the
products were isolated as analytically pure crystalline solids
after one or two recrystallisations from dichloromethane–
diethyl ether. The one exception was cis-[PtCl{Ph2PNHpy-
P,N}(PMe3)]Cl 20, which was stirred overnight in a thf–
dichloromethane mixture with elemental sulfur which effected
oxidation of the residual PMe3 allowing its removal from
the complex. The crystal structures of 20 and 39 (Figs. 9 and
10 and Table 9) show the anticipated cis geometry of phos-
phorus atoms and reveal square-planar geometry at platinum
[maximum deviations from Pt(1)–P(1)–P(2)–Cl(1)–N(1) mean
plane 0.4 Pt(1) and 0.01 Å Pt(1) for 20 and 39 respectively]. A
small difference is observed in the planarity of the Pt(1)–P(1)–
N(2)–C(2)–N(1) five-membered rings. The ring of 20 is near
planar with a mean deviation of only 0.05 Å, whilst that of 39
is slightly more distorted with maximum deviations of 0.09 Å
above and below the mean plane for P(1) and N(2) respectively.
The P(2) and Cl(1) substituents of both complexes lie sig-
nificantly below the previously specified mean ring plane by
0.28 P(2) and 0.16 Å Cl(1) for 20 and 0.26 P(2) and 0.24 Å Cl(1)
for 39. Interestingly, in these cases the pyridyl plane is only
1
a J(31P–1H) of 395 Hz in the non-decoupled 31P NMR. Also
the IR spectrum contains a band at 2319 cmϪ1 which is charac-
teristic of ν(P-H). The chloro 29, bromo 31 and iodo 32
analogues of cis-[PtX(Ph2PNHpy-P,N)(PPh3)]X were prepared
in an identical manner from the relevant [PtX2(PPh3)2] (X = Cl,
Br or I) starting material. However, we also found that 31 and
32 could be prepared from the chloro analogue 29 by metathesis
with a large excess of the appropriate halide ion in refluxing
acetone, a procedure which should be applicable, but was not
extended to other chloro-complexes. Poorly resolved 31P-{1H}
NMR spectra were obtained for complexes 31 and 32 when
run in CDCl3 due to rapid halide exchange with the solvent.
The CDCl3 solutions of 31 and 32 were left to stand for 1 week
and then re-examined by 31P-{1H} NMR had undergone 100%
conversion into the corresponding chloro-complexes. Positive
ion FAB mass spectral and micro analytical data were consist-
ent with the proposed structural assignments of 31 and 32. The
addition of a stoichiometric quantity of dppap to a dichloro-
methane solution of cis-[PtClMe(PPh3)2] gave the anticipated
product cis-[PtMe(Ph2PNHpy-P,N)(PPh3)]Cl 33, in 88% yield.
The expected AX type 31P-{1H} NMR spectrum in CDCl3 is
displayed, and shows a high-frequency resonance at δ(P) 82.3
J. Chem. Soc., Dalton Trans., 2000, 2559–2575
2571

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Table 9 Selected bond lengths (Å) and angles (Њ) for complexes 20
and 39
20
30
Pt(1)–P(1)
Pt(1)–P(2)
Pt(1)–N(1)
Pt(1)–Cl(1)
P(1)–N(2)
N(2)–C(2)
C(2)–N(1)
2.216(2)
2.258(3)
2.129(7)
2.358(2)
1.681(7)
1.376(10)
1.337(9)
2.2338(13)
2.2113(12)
2.117(4)
2.3459(14)
1.681(4)
1.374(6)
1.353(6)
P(1)–Pt(1)–P(2)
N(1)–Pt(1)–Cl(1)
P(1)–Pt(1)–N(1)
P(2)–Pt(1)–Cl(1)
P(1)–Pt(1)–Cl(1)
P(2)–Pt(1)–N(1)
Pt(1)–P(1)–N(2)
P(1)–N(2)–C(2)
N(2)–C(2)–N(1)
C(2)–N(1)–Pt(1)
97.27(8)
91.9(2)
82.6(2)
88.29(9)
174.44(8)
176.9(2)
101.3(2)
119.8(5)
118.5(7)
116.8(5)
96.03(5)
92.77(11)
82.50(11)
88.69(5)
175.27(5)
178.14(12)
100.7(2)
120.1(3)
118.0(4)
117.0(3)
Fig. 11 Crystal structure of cis-[PtCl(Ph2PNpy-P,N)(PMe3)] 21.
3542 Hz], a shift to higher frequency of approximately 3 ppm
1
and a significantly reduced, by 237 Hz, J(195Pt–31P) coupling
constant relative to 20. The low-frequency resonance assigned
to the co-ordinated PMe3 group of 21 at δ(P) Ϫ27.9 [1J(195Pt–
31P) 3239 Hz] is also changed relative to 20 but to a lesser extent.
A small shift of 0.6 ppm to lower frequency occurs in con-
inclined by ca. 5Њ to the MPCN2 ring plane. The bond lengths
and angles of 20 and 39 are very similar to those displayed
by the previously discussed platinum() complex 5. Another
feature of 20 and 39 common to 5 is the cationic nature of
the complexes and the hydrogen-bonding interaction between
the amine proton H(2N) and the chloride counter ion
Cl(2) [H(2N) ؒ ؒ ؒ Cl(2) 2.14, Cl(2) ؒ ؒ ؒ N(2) 3.01 Å, N(2)–
H(2N) ؒ ؒ ؒ Cl(2) 167Њ for complex 20 and H(2N) ؒ ؒ ؒ Cl(2) 2.11,
Cl(2) ؒ ؒ ؒ N(2) 3.06 Å, N(2)–H(2N) ؒ ؒ ؒ Cl(2) 161Њ for 39].
In contrast to its rapid reaction with cis-[MCl2(PR3)2]
(M = Pt or Pd) dppap is unreactive towards trans-[MCl2(PCy3)2]
(M = Pt or Pd) even after prolonged reflux in thf. Examination
of the reaction mixture after 48 h at reflux showed the presence
of only trans-[MCl2(PCy3)2] (M = Pt or Pd) and dppap. We can
only assume that the inertness of the trans complexes is due to
steric bulk of the PCy3 ligands, which is great enough to prevent
approach of the dppap molecule to the metal centre.
1
junction with an increase of 125 Hz in J(195Pt–31P) coupling
constant. The shifts in δ(P) to higher or lower frequency and
the accompanying increase/reduction in J values that occur
upon conversion of 20 into 21 represent a trend common to all
deprotonated species (see Table 11).
Not all of the cationic species described above behaved pre-
dictably under deprotonating conditions. A dichloromethane
solution of cis-[PtCl(Ph2PNHpy-P,N)(PPh2H)]Cl 28, when
treated with a stoichiometric quantity of Et3N, initially gave the
expected yellow solution but with prolonged stirring a white
solid was deposited. The extreme insolubility of this material
prevented measurement of its NMR or mass spectra, hence
only IR and microanalytical data are available. The IR
spectrum is very similar to that of the starting material 28,
and suggests that the dppap ligand is still protonated with
ν(P–N) 903 cmϪ1 and hydrogen bonded to a chloride counter
ion as evidenced by the broad ν(N–H) band at 2675 cmϪ1 which
along with the absence of a ν(P–H) band could mean that a
bimetallic phosphido bridged species has been formed. Micro-
analytical data were in close but not perfect agreement with
the above formulation. Further work and characterisation is
needed fully to understand this reaction. Several unsuccessful
attempts to synthesize cis-[PdCl(Ph2PNpy-P,N)(P(OPh)3)]
49 using tBuOK in methanol were made. Examination of reac-
tion residues by 31P-{1H} NMR (in CDCl3) showed multiple
products and the presence of a significant quantity of starting
material. Furthermore, a gradual darkening of the NMR
sample (from bright orange to black) over the course of 1 hour
was observed. The degraded NMR sample was re-examined
and showed additional peaks not observed for the fresh sample.
The impurities and the eventual blackening of the NMR
sample are thought to stem from the formation, followed by
rapid decomposition, of unstable palladium alkoxy species. The
presence of unchanged starting material in reaction residues
suggests the possibility that two molecules of base have reacted
with one molecule of starting material resulting first in
the desired deprotonation and secondly in abstraction and
replacement of the chloride ligand with [tBuO]Ϫ or [MeO]Ϫ.
Attempted deprotonation reactions of palladium P(OMe)3 45,
P(OEt)3 46 and P(OnBu)3 47 derivatives using the same method
gave similar results to those observed for the palladium P(OPh)3
48 complex. We found that the dropwise addition of a solution
of Et3N to a dilute dichloromethane solution of 48 gave after
work-up only the anticipated deprotonated product 49 as a
bright yellow powder in 90% yield. Application of the same
mild conditions to the deprotonation of complexes 46 and 47
Neutral mixed ligand complexes of PtII and PdII
Using the same synthetic approach used to generate the neutral
bis-chelate complexes 11 and 12 neutral species of the type
cis-[MCl(Ph2PNpy-P,N)(PR3)] (M = Pt, PR3 = PMe3 21, PEt3
23, PnBu3 25, PMe2Ph 27, PPh3 30, P(OMe)3 35, P(OEt)3
37 or P(OPh)3 40; M = Pd, PR3 = PMe2Ph 42 or PPh3 44) were
easily prepared by the addition of a stoichiometric quantity
of tBuOK to a methanol solution of the corresponding
protonated cationic species, eqn. (7). The neutral species
(7)
cis-[PtCl(Ph2PNpy-P,N)(PMe3)] 21 was prepared using this
method and isolated as a pale yellow solid in 87% yield. The
31P-{1H} NMR spectrum (in CDCl3) of 21 is, as expected,
an AX type with platinum satellites.
Although the spectrum is very similar to that of its precursor
cis-[PtCl(Ph2PNHpy-P,N)(PMe3)]Cl 20, comparison of the
two spectra reveals significant differences. In common with 20
[2J(31PA–31PX) = 18 Hz], the 31P-{1H} NMR spectrum of 21
reveals a small but slightly reduced 2J(PA–PX) coupling constant
of 14 Hz which is characteristic of a mutual cis arrangement of
phosphine ligands. The deprotonated [Ph2PNpy]Ϫ ligand of 21
displays a high-frequency resonance at δ(P) 65.2 [1J(195Pt–31P)
t
gave comparable results to those obtained using BuOK in
2572
J. Chem. Soc., Dalton Trans., 2000, 2559–2575

View Article Online
methanol, and complex 45, due to poor solubility, remained
unchanged. Similar reactions conducted using stoichiometric
quantities of the hindered, non-co-ordinating base 2,6-
dimethylpyridine instead of Et3N showed, by 31P-{1H} NMR
(in CDCl3), that decomposition had not occurred. Additionally,
NMR samples left to stand over 48 hours showed no obvious
sign of darkening. The 31P-{1H} NMR spectra of reaction
mixtures using 46 and 47 displayed two sets of AX type
resonances corresponding to unchanged starting material and
possibly the expected product. Curiously, the addition of
a large excess of 2,6-dimethylpyridine to NMR samples con-
taining both protonated and deprotonated species failed to
push the reaction to completion and caused only minimal
changes in solution composition. No further attempts at
synthesizing compounds of the type cis-[PdCl(Ph2PNpy-P,N)-
(P(OR)3)] were made. An example of this type of complex was
also crystallograpically characterised. The crystal structure
of 21 (Fig. 11, Table 10) shows that the cis geometry of complex
Table 10 Selected bond lengths (Å) and angles (Њ) for complex 21
Pt(1)–P(1)
Pt(1)–N(1)
P(1)–N(2)
C(2)–N(1)
2.2136(11)
2.091(4)
1.638(4)
1.377(6)
Pt(1)–P(2)
Pt(1)–Cl(1)
N(2)–C(2)
2.2537(14)
2.3811(14)
1.329(6)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–N(1)
P(1)–Pt(1)–Cl(1)
Pt(1)–P(1)–N(2)
N(2)–C(2)–N(1)
100.06(5)
79.69(11)
172.85(5)
105.80(2)
121.10(4)
N(1)–Pt(1)–Cl(1)
P(2)–Pt(1)–Cl(1)
P(2)–Pt(1)–N(1)
P(1)–N(2)–C(2)
C(2)–N(1)–Pt(1)
93.17(12)
87.06(5)
176.44(11)
115.20(3)
116.70(3)
Table 11 31P-{1H}a NMR data for complexes 1–4
Chemical shifts (ppm)
Coupling constants/Hz
Compound
δ(PA) [dppap]
δ(PX) [PX3]
1J(Pt–Pdppap
)
1J(Pt–PX)
2J(Pdppap–PX)
1 Ph2PNHpy
26.4
16.8
51.6
47.4 [783]c
51.4
62.1
62.3
71.4
83.7
83.3
63.0
84.5
64.1
88.0
38.4, 84.2
90.0
55.4
62.7
63.2
62.3
65.2
61.7
64.7
61.5
64.7
62.2
64.8
62.1
63.7
66.4
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
3576
3559
3541
—
—
—
3334
—
3475
—
3948, 2019
1950
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
4447
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
11
8
—
—
—
18
14
17
13
16
12
15
12
16
14
9
2 Ph2P(O)NHpyb
3 Ph2P(S)NHpy
4 Ph2P(Se)NHpy
5 cis-[PtCl(HL)(HL-P)]Cl
6 cis-[PtBr(HL)(HL-P)]Brd
7 cis-[PtI(HL(HL-P)]Id
8 cis-[PdCl(HL)(HL-P)]Cl
9 cis-[PdBr(HL)(HL-P)]Brd
10 cis-[PdI(HL)(HL)-P)]Id
11 cis-[Pt(L)2]
12 cis-[Pd(L)2]
e
13 cis-[Pt(HL)2][BF4]2
e
14 cis-[Pd(HL)2][BF4]2
15 cis-[PtMe(HL)(HL-P)Clf
16 cis-[PtMe(L)(Ph2POMe)]f
17 [AuCl(HL-P)]
100.6
—
—
—
Ϫ27.3
Ϫ27.9
4.3
18 [{Au(µ-HL)}2][ClO4]2 (HT)g
19 [Pt(C8H12OMe)(L)]ؒH2O
20 cis-[PtCl(HL)(PMe3)]Cl
21 cis-[PtCl(L)(PMe3)]
—
—
—
4087
3779
3542
3816
3589
3840
3603
3750
3502
3513
3754
3493
—
—
2013
—
3847
3691
3385
3691
3552
3285
—
3114
3239
3123
3246
3106
3251
3198
3337
3271
3361
3486
—
—
3948
—
5371
5382
5560
5371
6461
5955
—
22 cis-[PtCl(HL)(PEt3)]Cl
23 cis-[PtCl(L)(PEt3)]
3.3
24 cis-[PtCl(HL)(PnBu3)]Cl
25 cis-[PtCl(L)(PnBu3)]
Ϫ3.3
Ϫ4.4
Ϫ21.3
Ϫ20.2
Ϫ16.9h
6.8
26 cis-[PtCl(HL)(PMe2Ph)]Cl
27 cis-[PtCl(L)(PMe2Ph)]
28 cis-[PtCl(HL)(PPh2H)]Cl
29 cis-[PtCl(HL)(PPh3)]Cl
30 cis-[PtCl(L)(PPh3)]
31 cis-[PtBr(HL)(PPh3)]Br
32 cis-[PtI(HL)(PPh3)I
10.3
—
—
—
—
10
—
18
17
13
18
14
13
6
—
82.3
—
33 cis-[PtMe(HL)(PPh3)]Cl
34 cis-[PtCl(HL)(P{OMe}3)]Cl
35 cis-[PtCl(L)(P(OMe)3)]
36 cis-[PtCl(HL)(P(OE)t3)]Cl
37 cis-[PtCl(L)(P(OEt)3]
16.7
—
54.9
62.4
64.3
62.5
61.4
66.5
86.1
91.8
88.8
93.6
—
71.6
68.0
82.8
67.8
63.9
74.7
1.9
Ϫ0.2
29.9
29.6
38 cis-[PtCl(HL)(P(OnBu)3)]Cli
39 cis-[PtCl(HL)(P(OPh)3)]Cl
40 cis-[PtCl(L)(P(OPh)3)]
41 cis-[PdCl(HL)(PMe2Ph)]Clj
42 cis-[PdCl(L)(PMe2Ph)]j
43 cis-[PdCl(HL)(PPh3)]Clj
44 cis-[PdCl(L)(PPh3)]j
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
4
3
n.ok
—
22
44
26
20
45 cis-[PdCl(HL)(P(OMe)3)]Cl
46 cis-[PdCl(HL)(P(OEt)3)]Cl
47 cis-[PdCl(HL)(P(OnBu)3)]Cli
48 cis-[PdCl(HL)(P(OPh)3)]Clj
49 cis-[PdCl(L)(P(OPh)3)]
—
84.6
76.7
88.1
91.6
93.5
56.2
89.3
99.1
a Spectra (36.2 MHz) measured in CDCl3 unless otherwise stated. b Spectrum (36.2 MHz) measured in CDCl–dmso. c 1J(31P–77Se) coupling constant.
HL = Ph2PNHpy 1, L = [Ph2PNpy]Ϫ. Co-ordination is bidentate in most cases. Monodentate Ph2PNHpy-P ligands are denoted by HL-P. d Spectrum
(36.2 MHz) measured in dmso–C6D6. e Spectrum (36.2 MHz) measured in d6-dmso. f Spectrum (101.3 MHz) measured in CDCl3. g Spectrum (36.2
MHz) measured in CH2Cl2–C6D6. h 1J(P–H) 395 Hz. i Spectrum (36.2 MHz) measured in CDCl3–MeOH. j Spectrum (101.3 MHz) measured in
CDCl3. k Not observed.
J. Chem. Soc., Dalton Trans., 2000, 2559–2575
2573

View Article Online
24 E. Lindner, H. Rauleder and W. Hiller, Z. Naturforsch., Teil B, 1983,
20 remains unchanged upon deprotonation and reveals approxi-
mately square-planar geometry at platinum [maximum devi-
ations from Pt(1)–P(1)–P(2)–Cl(1)–N(1) mean plane 0.22 Å
below for Cl(1) and 0.35 Å below for P(2)]. The Pt(1)–P(1)–
N(2)–C(2)–N(1) five-membered ring is essentially planar with a
mean deviation of only 0.06 Å. The bond lengths and angles
of 21 are very similar to those displayed by the previously
discussed platinum() complex 11 which also contains depro-
tonated chelating dppap ligands, but are significantly different
to those of the cationic species 20. Most notable among
these differences are the contracted P(1)–N(2) [1.638(4) Å]
and N(2)–C(2) [1.329(6) Å] and the elongated C(2)–N(1)
[1.377(6) Å] bond lengths compared to those of 20 [1.681(7),
1.376(10) and 1.337(9) Å] respectively. Another salient feature
of 21 is the contraction of the P(1)–N(2)–C(2) bond angle from
119.8(5)Њ in 20 to 115.20(3)Њ. The crystal structure also high-
lights, by the absence of counter ions, the neutral nature of the
complex.
In this work we have demonstrated that the dppap ligand
exhibits a variety of co-ordination modes including mono-
dentate P bound and bidentate PN bound. We have also
shown that the co-ordinated dppap ligand can be deprotonated
and stabilised by incorporation into a metallacycle further
extending the range of complexes available. Methanolysis of
the P–N bond in dppap under basic reaction conditions leading
to a platinum-bound Ph2POMe ligand has also been observed.
Further work on the catalytic behaviour of systems containing
this ligand is in progress.
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Acknowledgements
We are grateful to the Engineering and Physical Research
Council (EPSRC) for support and to the Joint Research
Equipment Initiative (JREI) for two equipment grants.
44 P. E. Garrou, Chem. Rev., 1981, 81, 229.
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