Synthesis and coordination of 2-diphenylphosphinopicolinamide

Article abstract of DOI:10.1016/j.poly.2004.10.004

The new ligand 2-diphenylphosphinopicolinamide behaves as a monodentate P or bidentate P, O; P, N donor. The synthesis and coordination of 2-diphenylphosphinopicolinamide (dpppa 1) is reported. Coordination complexes with Pd, Pt, Ru, Rh, Ir and Au are described. The ligand behaves as a monodentate P donor in complexes such as [PtCl₂(dpppa-P ₂)], [PdCl(allyl)(dpppa-P)], [RuCl₂(p-Cymene)(dpppa-P)], cis-[PtCl₂(dpppa-P)(PR₃)] and [AuCl(dpppa-P)]. Bidentate P, O coordination was accomplished by reaction of BuLi with [RuCl ₂(p-Cymene)(dpppa-P)], to give [RuCl(p-Cymene)(dpppa-P,O). P,N donor behaviour was achieved by reaction of a monodentate complex with a halide abstractor [AgBF₄] generating [RuCl(p-Cymene)(dpppa-P,N)][ClO ₄] and[RhCl(η⁵-C₅Me₅)(dpppa-P,N) ][BF₄]. The X-ray structures of dpppa, dpppaO, dpppaS, four monodentate complexes and [RuCl(p-Cymene)(dpppa-P,O) are reported. All of the structures contain intramolecular N-H?N hydrogen bonding.

Full text of DOI:10.1016/j.poly.2004.10.004

Polyhedron 23 (2004) 3211–3220
www.elsevier.com/locate/poly
Synthesis and coordination of 2-diphenylphosphinopicolinamide
*
Heather L. Milton, Matthew V. Wheatley, Alexandra M.Z. Slawin, J.Derek Woollins
School of Chemistry, University of St Andrews, St Andrews, Fife KY16 9NB, UK
Received 17 August 2004; accepted 21 October 2004
Available online 13 November 2004
Abstract
The synthesis and coordination of 2-diphenylphosphinopicolinamide (dpppa 1) is reported. Coordination complexes with Pd, Pt,
Ru, Rh, Ir and Au are described. The ligand behaves as a monodentate P donor in complexes such as [PtCl2(dpppa-P2)], [PdCl(al-
lyl)(dpppa-P)], [RuCl2(p-Cymene)(dpppa-P)], cis-[PtCl2(dpppa-P)(PR3)] and [AuCl(dpppa-P)]. Bidentate P, O coordination was
accomplished by reaction of BuLi with [RuCl2(p-Cymene)(dpppa-P)], to give [RuCl(p-Cymene)(dpppa-P,O). P,N donor behaviour
was achieved by reaction of a monodentate complex with a halide abstractor [AgBF4] generating [RuCl(p-Cymene)(dpppa-
P,N)][ClO4] and[RhCl(g5-C5Me5)(dpppa-P,N)][BF4]. The X-ray structures of dpppa, dpppaO, dpppaS, four monodentate com-
plexes and [RuCl(p-Cymene)(dpppa-P,O) are reported. All of the structures contain intramolecular N–Hꢀ ꢀ ꢀN hydrogen bonding.
Ó 2004 Published by Elsevier Ltd.
Keywords: 2-Diphenylphosphinopicolinamide (dpppa 1); Coordination chemistry; Monodentate donors; Bidentate donors
1. Introduction
Here, we will describe our investigations into an
amalgamation of two of these aspects of coordination
chemistry; aminopyridylphosphines and phosphino-eno-
lates in the synthesis and coordination of 2-diphenyl-
phosphinopicolinamide (dpppa 1). We report a range
of coordination modes incorporating both the pyridyl-
phosphine and phosphino-enolate character of dpppa.
The ligand, its derivatives and the complexes generated
have been principally characterised by multi-element
NMR spectroscopy and X-ray crystallography.
There is widespread interest in hemilabile phospho-
rus–nitrogen ligands, which has focused on the presence
of both ÔhardÕ (nitrogen) and soft (phosphorus) donor
atoms on one ligand. One aspect of the hemilabile nat-
ure of these ligands is based around the presence of
spacer atoms between the phosphorus nitrogen donor
atom which can influence electronic properties as well
as flexibility. For example in pyridine based systems,
N–H (A) [1–3], CH2–CH2 (B) [4–7], NH–NH (C) [8–
10] have been used as spacer atoms/groups (see Fig. 1).
There has also been considerable interest in phospho-
rus–oxygen ligands, with oxygen acting as the ÔhardÕ do-
nor atom. There are numerous examples where oxygen
has been incorporated into a ligand, examples include
etherphosphines (D) [11], 1,3-dioxolane derivatives (E)
[12], aldehyde functionlised phosphines (F) [13–15] and
furylphosphines (G) [16] systems (see Fig. 2).
2. Results and discussion
The synthesis of dpppa is straightforward
O
O
Ph2PCl, Et3N
reflux, THF
PPh2
NH2
N
H
N
N
Et N.HCl
+
3
*
Corresponding author. Tel.: +441 3344 63869; fax: +441 3344
dpppa 1
63384.
ð1Þ
E-mail address: jdw3@st-andrews.ac.uk (J.D. Woollins).
0277-5387/$ - see front matter Ó 2004 Published by Elsevier Ltd.
doi:10.1016/j.poly.2004.10.004

3212
H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
H
H
N
N
PPh2
PPh2
PPh2
N
H
N
N
N
(a)
(b)
(c)
Fig. 1. Pyridylphosphines.
PPh2
O
O
Ph2P
O
H
(d)
(f)
Fig. 3. The crystal structure of dpppa (1).
O
PPh2
O
O
with an intramolecular hydrogen bond between the
amide proton and the pyridyl nitrogen, generating an
effective five-membered ring that is almost planar
Ph2P
PPh2
(e)
(g)
˚
[N(2)–N(5) 2.67 A] The phosphorus–nitrogen bond
Fig. 2. Phosphorus–oxygen ligands.
˚
length of 1.702(3) A is well within acceptable boundaries
previously established in aminophosphine chemistry.
Dpppa was recrystallised from boiling methanol to
give a colourless crystalline solid in a tolerable yield
(55%) and is relatively air stable; however exposure to
air for prolonged periods resulted in degradation. It is
readily soluble in chlorinated solvents, acetone, thf,
somewhat less so in toluene, methanol and diethyl ether.
A singlet is observed in the 31P spectra of dpppa (in
O
O
O
O
E
PPh2
PPh2
PPh2
Se or S
H2O2
N
H
N
H
N
H
N
N
Reflux
Toluene
N
1
2
E = S (3) or Se (4)
ð2Þ
The oxide, sulfide and selenide of dpppa were also
synthesised as seen in Eq. (2). The expected downfield
shift is found in the 31P NMR spectra of all three com-
pounds (Table 2), the JP–Se is 788 Hz which is typical
for a phosphorus–selenium double bond.
In 2, the P–N bond is somewhat shorter than in
dpppa (Table 1 and Fig. 4), the C(4)–C(3)–N(2)–P(1)
backbone is essentially planar [mean deviation of
0.0391 A] and as in 1 there is an H-bonded five-mem-
bered ring linking N(5) and H(2) [N(2)–N(5) is 2.653
1
CDCl3) at d(P) 22.0 ppm. The H NMR clearly shows
the presence of an amide proton at d(H) 8.65 ppm, as
a doublet JP–H = 4 Hz. The IR spectra shows a weak
1
2
m(N–H) band at 3297 cmꢁ1, and bands attributable to
m(pyCN) and m(P–N) at 1452 and 996 cmꢁ1 respectively.
The expected m(C@O) signature is visible at 1691 cmꢁ1
.
Satisfactory microanalysis was also obtained. The crys-
tal structure of dpppa (Table 1 and Fig. 3) reveals that
the P(1)–N(2)–C(3)–O(3) backbone is essentially planar
˚
˚
A, N(2)–H(2)ꢀ ꢀ ꢀN(5) 109°]. It has been shown that the
oxides and sulfides of phosphorus(III) ligands can dis-
play different solid state motifs [17]. We found that the
sulfide 3 crystallises in a dimer arrangement rather than
favouring the internal bonding seen in the oxide. The
backbone of the molecule remains mostly planar, with
Table 1
˚
Selected bond lengths (A) and angles (°) for dpppa, dppaO and dppaS
Dpppa 1
DpppaO 2
DpppaS 3
Bond lengths
P–O/S
˚
the N(2) and N(5) distance [2.65 A] indicating that the
N(2)–H(2)ꢀ ꢀ ꢀN(5) hydrogen bond interaction is retained
1.478(2)
1.683(2)
1.370(4)
1.506(4)
1.217(3)
2.65(5)
1.9475(9)
1.699(2)
1.378(3)
!.502(5)
1.219(3)
2.65
P(1)–N(2)
N(2)–C(3)
C(3)–C(4)
C(3)–O(3)
N(2)ꢀ ꢀ ꢀN(5)
1.702(3)
1.355(5)
1.500(6)
1.221(5)
2.67(5)
(Table 1 and Fig. 5).
We formed a number of monodentate complexes,
thus dpppa reacts with [PtCl2(cod)] in dichloromethane
to give cis-[PtCl2(dpppa-P2)] (5) as a white crystalline
solid in good yield [80%] which is in marked contrast
to 2-(diphenylphosphino)aminopyridine (dppap) which
is reported to give [PtX(Ph2PNHpy-P,N)(Ph2 PNHpy-
P)][Cl] (X = Cl or Me) [1–3]. The 31P NMR (CDCl3)
of 5 is a singlet at d(P) 31.2 ppm [1JPt–P = 3984 Hz],
Bond angles
C(3)–N(2)–P(1)
N(2)–C(3)–C(4)
O(3)–C(3)–N(2)
O(3)–C(3)–C(4)
N(2)–H(2)ꢀ ꢀ ꢀN(5)
126.1(3)
116.2(4)
122.1(4)
121.7(4)
129(3)
124.09(19)
114.4(2)
123.1(3)
122.6(3)
109(3)
125.33(18)
114.1(2)
123.4(2)
122.6(2)
111(2)

H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
3213
Table 2
Spectroscopic data for Ph2P(E)C(O)NHpy
Compound
d(1H)
d(31P)
IR (cmꢁ1
)
NH
Aromatics
P
P@E
C@O
NH
CN(py)
1
2
3
4
a
8.7
9.4
9.3
9.3
8.5–7.2
8.5–7.3
8.6–7.4
8.6–7.1
22.0
22.1
54.4
48.7a
N/A
1215
837
1691
1694
1689
1698
3297
3302
3268
3288
1452
1451
1447
1391
Obscured
1JP–Se = 788 Hz.
IR spectrum (320 and 302 cmꢁ1), further evidence of a
cis-conformation for 5. In contrast, reaction of
[PdCl2(cod)] with dpppa gives [PdCl2(dpppa-P)2] (6),
which is insoluble and displays only one Pd–Cl stretch
(310 cmꢁ1), suggesting a trans-arrangement, the other
expected IR peaks are observed clearly, m(N–H) at
3232, m(C@O) at 1694, m(P–N) at 997 cmꢁ1. This trans-
arrangement is consistent with previous examples of
pyridylaminophosphines found in the literature [1–3].
A series of palladium complexes were synthesised
bearing only one dpppa monodentate bound via the
phosphorus (Fig. 6). Complexes [PdCl(allyl)(dpppa-P)]
(7), [PdCl(C10H6NO)(dpppa-P)] (8), [PdCl(C9H12N)-
(dpppa-P)] (9), [PdCl(C12H12N)(dpppa-P)] (10), were
all synthesised via bridge cleavage reactions of the
respective dimer starting materials. Complex 7 is a yel-
low solid which shows the expected singlet at d(P) 54.5
Fig. 4. The crystal structure of dpppaO (2).
1
ppm. The amide proton is shifted downfield in the H
NMR spectra (CDCl3), to d(H) 10.7 ppm, this mirrors
the shift of the amide proton in 5, and also in common
2
with 5 the JP–H coupling constant is enlarged, stretch-
ing to 22 Hz. The IR spectrum shows the m(N–H) stretch
has shifted to a much greater extent than seen in 5, this
could be due to much stronger hydrogen bonding inter-
action being present in 7, and once again the m(C@O) is
relatively unmoved in comparison with the free ligand
being found at 1686 cmꢁ1. In the solid state (Table 3
and Fig. 7), complex 7 has a hydrogen-bonds between
˚
H(2)–N(5) and H(2)–Cl(1) [N(2)–Cl(1) 3.204 A and
˚
N(2)–N(5) 2.67(8) A]. The interaction with Cl(1) causes
the five-membered ring to distort with a N(5)–C(4)–
C(3)–N(2) torsion angle of ꢁ15.08°.
Complexes 8, 9 and 10 are similar and display the ex-
pected spectroscopic properties.
Complexes of ruthenium, rhodium and iridium were
synthesised to further investigate the coordination of
dpppa. [RuCl2(p-Cymene)(dpppa-P)] (11) was generated
by reaction of [RuCl(l-Cl)(p-Cymene)]2 with dpppa and
isolated as a red solid. The rhodium and iridium
complexes were synthesised by reaction with [MCl-
(l-Cl)(g5-C5Me5)]2 (where M = Rh or Ir), and dpppa,
to give complexes of the type [MCl2(g5-C5 Me5)(dpp-
pa-P)] (where M = Rh (12) or Ir (13)). Crystals of 12
and 13 proved to be isomorphous; here we will only con-
sider 13 (Table 3 and Fig. 8). On inspection of the ligand
Fig. 5. Crystal structure of dpppaS (3).
whilst in the 1H NMR it displays some significant
changes from the free ligand. The amine proton is
2
shifted to d(H) 10.7 ppm, and JP–H at 15 Hz is signifi-
cantly increased Two Pt–Cl stretches are visible in the

3214
H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
O
O
N
Ph2
N
PN
N
Ph
P2
N
H
Pd
Cl
H
Pd
Cl
7
9
dcm
dcm
1/2 [{Pd(µ-Cl)(η3-C3H5)}2]
1/2 [{Pd(µ-Cl)(C9H12N)}2]
O
PPh2
N
H
N
1/2 [{Pd(µ-Cl)(C12H12N)}2]
1/2 [{Pd(µ-Cl)(C10H6NO)}2]
dcm
dcm
O
O
Ph
P2
Ph2
N
N
H
P
N
Pd
N
N
Cl
Pd
H
Cl
N
O
8
10
Fig. 6. Reaction of dpppa with palladium dimers.
Table 3
˚
Selected bond lengths (A) and angles (°) for monodentate complexes of dpppa:
[PdCl(allyl)(dpppa-P)] (7), [IrCl2(g5-C5Me5)(dpppa-P)] (13), [PtCl2(dpppa-
P)(PEt3)] (15) and [AuCl(dpppa-P)] (17)
7
13
15
17
Bond lengths
P(1)–M(1)
M(1)–Cl(1)
M(1)–Cl(2)
P(1)–N(2)
N(2)–C(3)
C(3)–C(4)
O(3)–C(3)
N(2)ꢀ ꢀ ꢀCl
2.2786(8)
2.3800(8)
2.287(2)
2.4126(19)
2.4034(18)
1.699(7)
1.379(10)
1.494(11)
1.233(9)
3.403(6)
2.71(1)
2.2389(14)
2.3446(14)
2.3554(13)
1.693(4)
1.377(7)
1.507(8)
1.211(6)
3.011(5)
2.64(7)
2.2168(18)
2.2993(17)
1.703(3)
1.366(4)
1.512(4)
1.216(4)
3.204(7)
2.67(8)
1.694(5)
1.395(8)
1.495(9)
1.215(8)
N(2)ꢀ ꢀ ꢀN(5)
2.64(7)
Bond angles
P(1)–M(1)–Cl(1)
P(1)–M(1)–Cl(2)
Cl(1)–M(1)–Cl(2)
C(3)–N(2)–P(1)
O(3)–C(3)–N(2)
O(3)–C(3)–C(4)
N(2)–C(3)–C(4)
96.52(3)
88.49(7)
87.72(7)
87.57(7)
129.0(5)
123.3(7)
122.1(7)
114.6(6)
175.94(5)
91.05(5)
177.82(6)
130.3(2)
124.5(3)
121.4(3)
114.1(3)
126.6(4)
124.3(5)
122.6(5)
113.1(5)
125.6(4)
124.1(6)
122.6(6)
113.3(6)
Fig. 7. Crystal structure of [PdCl(allyl)(dpppa-P)] (7).
ino)hydrazinopyridine displays a similar deviation [18].
Also as seen with the 2-(diphenylphosphino)hydrazino-
pyridine example there are two types of hydrogen bond-
ing displayed, the first is between the amine proton and
backbone, we observe a modest shift out of plane, with
the mean deviation of C(3)–N(2)–P(1)–Ir(1) being
˚
0.1160A, this is the highest deviation seen so far with
monodentate dpppa complexes but is not unexpected
the analogous complex formed with 2-(diphenylphosph-
˚
one of the chlorides [N(2)ꢀ ꢀ ꢀCl(2) 3.403 A]. The second
type of hydrogen bonding observed in the complex is of

H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
3215
described above. Two different hydrogen bonding motifs
are again observed within the complex [N(2)–Cl(2)
˚
3.011, N(2)–N(5) 2.64(7) A]
Cl
Cl
PR3
Pt
PPh2
N
R3P
Cl
Cl Cl
Pt Pt
Dpppa
dcm
O
H
ð3Þ
PR3
Cl
N
PR3 = Me2PhP (14) or Et3 (15)
Reaction of dpppa with [RhCl(cod)]2 in dichloro-
methane gave [RhCl(cod)(dpppa-P)] (16) as a yellow so-
1
lid in average yield (63%), (P) 58.3 JRh–P = 162 Hz.
Cl
Rh
Cl
Cl
PPh2
HN
Rh
Rh
O
O
PPh2
N
Fig. 8. Crystal structure of [IrCl2(g5-C5Me5)(dpppa-P)] (13).
H
N
N
a similar motif to that found in the free ligand, oxide
˚
and sulfide [N(2)–N(5) 2.71(1) A].
16
Dpppa reacts with [{PtCl(l-Cl)(PR3)}2](PR3@
PMe2Ph or PEt3), to give complexes of the type cis-
[PtCl2(dpppa-P)(PR3)](PR3@PMe2Ph (14) or PEt3
(15)). Monodentate binding was the only observed mode
of coordination in both instances. The 31P NMR shows
ð4Þ
When dpppa was reacted with [AuCl(tht)] in dichlo-
romethane the anticipated monodentate [AuCl(dpppa-
P)] (17) complex was generated as a colourless solid,
d(P) 53.5 ppm, On inspection of the crystal data (Table
3 and Fig. 10), we see the now familiar hydrogen-bond-
1
the expected AM spectra and the large JPt–P coupling
2
constants and the small JP–P couplings are consistent
˚
with a cis-arrangement of phosphorus around the plati-
num centre.
In 15 (Table 3 and Fig. 9), the C(3)–N(2)–P(1)–Pt(1)
ing pattern [N(2)ꢀ ꢀ ꢀN(5) 2.64 A, N(2)–H(2)–N(5) 114°].
Chelation of dpppa was achieved by reaction of a
chloride containing monodentate complex with BuLi
backbone is essentially planar, with a mean deviation of
˚
0.0334 A, which is consistent with the other structures
Ru
Cl
Cl
BuLi
PPh2
N
Ru
Cl
O
PPh2
O
H
N
N
N
11
18
ð5Þ
As can be seen this generates a five-membered ÔtrueÕ
heterocycle, with the oxygen binding to the metal centre.
The 31P NMR shows a downfield shift in the complex, to
d(P) 101.5 ppm, indicating chelation. As expected the
amide proton disappears from the 1H spectrum, and
the pyC[6]H shift and coupling constant is relatively un-
changed. The IR spectrum also confirms the loss of the
amide proton, and shows a m(C–O) stretch at 1351 cmꢁ1
,
confirming C–O is present and not C@O. Acceptable
microanalytical data was obtained. The five-membered
Fig. 9. Crystal structure of [PtCl2(dpppa-P)(PEt3)] (15).

3216
H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
Table 4
˚
Selected bond lengths (A) and angles (°) for P, O bidentate [RuCl(p-
Cymene)(dpppa-P,O)] (18)
Bond lengths
P(1)–Ru(1)
P(1)–N(2)
C(3)–O(3)
C(4)–C(9)
Ru(1)–Cl(1)
2.2812(19)
1.715(6)
1.276(9)
Ru(1)–O(3)
N(2)–C(3)
C(3)–C(4)
C(4)–N(5)
2.097(5)
1.380(10)
1.465(10)
1.315(9)
1.423(10)
2.3910(18)
Bond angles
P(1)–Ru(1)–O(3)
O(3)–Ru(1)–Cl(1)
Ru(1)–P(1)–N(2)
N(2)–C(3)–O(3)
N(2)–C(3)–C(4)
C(3)-C(4)–C(9)
C(9)–C(4)–N(5)
80.28(14)
81.53(14)
101.2(2)
120.6(6)
117.5(7)
119.2(7)
123.8(7)
P(1)–Ru(1)–Cl(1)
86.32(6)
P(1)–N(2)–C(3)
C(3)–O(3)–Ru(1)
O(3)–C(3)–C(4)
C(3)–C(4)–N(5)
116.3(5)
120.0(5)
121.9(7)
117.0(7)
value at d(H) 8.6 ppm in both cases [2JP–H of 5 and 4 Hz,
respectively].
Fig. 10. Crystal structure of [AuCl(dpppa-P)] (17).
ring that is formed is essentially planar (Fig. 11 and Ta-
ble 4), the Ru–O and Ru–P bond lengths within the ring
are normal whilst the angles are typical for a five mem-
bered ring.
Ru
H
AgClO4
Cl
Cl
PPh2
N
Ru
O
ClO4
Cl
N
PPh2
dcm
O
N
H
N
A second mode of chelation [via the pyridyl nitrogen]
is possible for dpppa. This was facilitated by reaction of
the appropriate monodentate complex with a halide abs-
tractor [AgBF4 or AgClO4] generating the cationic spe-
cies [RuCl(p-Cymene)(dpppa-P,N)][ClO4] (19) and
[RhCl(g5-C5Me5)(dpppa-P,N)][BF4] (20) in good yield
(93% and 74%, respectively). The 31P NMR shows the
downfield shift generated by chelate ring formation with
d(P) 98.1 and 85.2 ppm for 19 and 20, respectively, also
the amine proton is shifted back toward the free ligand
19
11
ð6Þ
3. Experimental
3.1. General conditions
All manipulations were carried out in an atmosphere
of nitrogen, unless stated otherwise. All solvents were
either freshly distilled from an appropriate drying agent
(thf, Et2O from sodium, CH2Cl2 from calcium hydride)
1
or obtained as anhydrous grade from Aldrich. H and
31P NMR spectra were recorded using a Jeol Delta FT
(270 MHz) spectrometer. IR spectra were recorded as
KBr discs (prepared in air) on a Perkin–Elmer 2000
FTIR/Raman spectrometer. All significant peaks (>800
cmꢁ1) are quoted to serve as a fingerprint. Silver salts,
2-picolinamide (Aldrich Chemical Co.) and BuLi (2.5
M, Lancaster) were purchased and used as received. Tri-
ethylamine and chlorodiphenylphosphine were distilled
prior to use. Dimethylaminopyridine (DMAP) was sub-
limed before use. The various metal starting materials
were made by the appropriate literature methods;
[AuCl(tht)] [19], [MCl2(cod)] (M = Pt or Pd;
cod = cycloocta-1,5-diene) [20,21], [PdCl(L–L)]2 dimers
[22], [{PtCl(l-Cl)(PMe2 Ph)}2] [23], [{MCl(l-Cl)-
(Cp*)}2] (M = Rh or Ir) [24], [{Rh(l-Cl)(cod)}2] [25],
Fig. 11. Crystal structure of [RuCl(p-Cymene)(dpppa-P,O)] (18).

H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
3217
½fRuClðl-ClÞðg6p-MeC6H4i PrÞg2ꢂ [26], [{PdCl(l-Cl)-
(g3-C3H5)}2] [27].
This solid was recrystallised by cooling a concentrated
toluene solution at 4 °C overnight (yield: 105 mg,
48%). Anal. Calc. for C18H15N2OPSe: C, 56.1; H, 3.92;
3.1.1. 2-Diphenylphosphinopicolinamide (1)
N, 7.27. Found: C, 56.4; H, 3.77; N, 7.05%. mmax/
Chlorodiphenylphosphine (3.7 cm3, 20 mmol) was
added to a solution of 2-picolinamide (2.5 g, 20 mmol),
triethylamine (3.0 cm3, 21 mmol) and DMAP (240 mg,
2.0 mmol) in thf (100 cm3) and refluxed overnight. The
reaction mixture was filtered to remove a white solid
(Et3NHCl) and washed with thf (50 cm3). The solvent
was removed in vacuo leaving a pale yellow solid. This
solid was recrystallised by cooling a concentrated meth-
anol solution at 4 °C overnight (yield: 3.38 g, 55%).
Anal. Calc. for C18H15N2OP: C, 70.6; H, 4.9; N, 9.1.
Found: C, 70.29; H, 4.58; N, 8.95%. mmax/cmꢁ1: 3297,
cmꢁ1: 3288, 1698, 1391, 998.31P NMR (CDCl3) d 47.8,
1JP–Se = 788 Hz. 1H NMR (CDCl3), d 9.3 (1H, d,
J = 13 Hz, N–H), 8.6 (1H, d, J = 1 Hz, pyC[6]H), 8.2–
7.7 (6H, m, aromatic), 7.5–7.3 (7H, m, aromatic).
3.1.5. [PtCl2(dpppa-P)2] (5)
Dpppa (50 mg, 0.16 mmol) and [PtCl2(cod)] (30 mg,
0.08 mmol) were weighed into a schlenk type flask and
CH2Cl2 (5 cm3) added. The solution was stirred for 10
min and the majority of the solvent removed in vacuo.
A white solid was precipitated after addition of Et2O
(20 cm3) then isolated by filtration and washed with fur-
ther ether (10 cm3) (yield: 57 mg, 80%). Anal. Calc. for
C36H30N4O2P2Cl2Pt(CH2Cl2)0.5: C, 47.6; H, 3.39; N,
1691, 1452, 1412, 996. 31P NMR d 22.0 ppm H NMR
1
(CDCl3), 8.65 (1H, d, J = 4 Hz, N–H), 8.54 (1H, d,
J = 5 Hz, pyC[6]H), 8.26 (1H, d, J = 8 Hz, pyC[3]H),
7.85 (1H, t, J = 8 Hz, pyC[5]H), 7.6–7.2 (11H, m,
aromatic).
6.08. Found: C, 47.5; H, 3.20; N, 5.81%. mmax/cmꢁ1
:
3251, 1692, 1446, 1391, 998, 320, 302. 31P NMR
1
(CDCl3) d 31.2 ppm, JPt–P = 3984 Hz. 1H NMR
(CDCl3), 10.7 (2H, d, J = 15 Hz, N–H), 8.5 ((2H, d,
J = 4 Hz), pyC[6]H), 7.7–7.2 (26H, m, aromatic).
3.1.2. 2-Diphenylphosphinopicolinamide oxide (2)
Aqueous H2O2 (30% w/w, 0.0071 cm3, 0.065 mol) was
added dropwise over 5 min to a solution of dpppa (200
mg, 0.065 mol) in thf (10 cm3) and the mixture stirred
for 30 min and then reduced to dryness. The residue
was dissolved in CH2Cl2, and filtered while hot and sub-
sequently dried over MgSO4. The filtrate was stored at
ꢁ4 °C during which time a crystalline solid was depos-
ited and filtered and dried. Yield: 85 mg, 41%. Anal.
Calc. for C18H15N2O2P: C, 67.1; H, 4.69; N, 8.69.
Found: C, 66.7; H, 4.26; N, 8.41%. mmax/cmꢁ1: 3302,
3.1.6. [PdCl2(dpppa-P)2] (6)
Dpppa (258 mg, 0.86 mmol) and [PdCl2(cod)] (120
mg, 0.43 mmol) were weighed into a schlenk type flask
and CH2Cl2 (10 cm3) added. The solution was stirred
for 10 min. This resulted in precipitation of the desired
product, which was filtered and washed with ether (10
cm3). Yield: 307 mg, 92%. Anal. Calc. for
C36H30N4O2P2Cl2Pd: C, 54.6; H, 3.83; N, 7.09. Found:
C, 53.9; H, 3.64; N, 6.85%. mmax/cmꢁ1: 3232, 1694,
1446, 1392, 997, 310.
1694, 1451, 1403, 1215, 998. 31P NMR d 22.1 ppm. H
NMR (CDCl3), d 9.46 (1H, d, J = 9 Hz, N–H), 8.58
(1H, d, J = 4 Hz, pyC[6]H), 8.1–7.7 (6H, m, aromatic),
7.5–7.2 (7H, m, aromatic).
1
3.1.7. [PdCl(allyl)(dpppa-P)] (7)
Reaction followed as for 5. Dpppa (84 mg, 0.27
mmol) and [{Pd(l-Cl)(g3-C3H5)}2] (50 mg, 0.13 mmol)
gave a pale yellow solid, (yield: 117 mg, 87%). Anal.
Calc. for C21H20N2OPClPd: C, 51.5; H, 4.12; N, 5,72.
Found: C, 51.8; H, 3.93; N, 5.61%. mmax/cmꢁ1: 3193,
1686, 1446, 1396, 1103, 998. 31P NMR (CDCl3) d 54.5
3.1.3. 2-Diphenylphosphinopicolinamide sulfide (3)
Sulfur (105 mg, 3.3 mmol) was added to a solution of
2-diphenylphosphinopicolinamde (1 g, 3.3 mmol) in tol-
uene (100 cm3) and refluxed overnight. The solvent was
removed in vacuo leaving an off-white solid. This solid
was recrystallised by cooling a concentrated toluene
solution at 4 °C overnight (yield: 900 mg, 82%). Anal.
Calc. for C18H15N2OPS: C, 63.9; H, 4.47; N, 8.28.
Found: C, 63.6; H, 4.22; N, 8.26%. mmax/cmꢁ1: 3268,
1689, 1387, 997. 31P NMR d 54.4 ppm. 1H NMR
(CDCl3), d 9.3 (1H, d, J = 11 Hz, N–H), 8.6 (1H, d,
J = 1 Hz, pyC[6]H), 8.1–7.8 (6H, m, aromatic), 7.6–7.4
(7H, m, aromatic).
1
ppm. H NMR (CDCl3), 10.5 (1H, d, J = 22 Hz, N–
H), 8.7 (1H, d, J = 4 Hz, pyC[6]H), 7.8–7.4 (12H, m,
aromatic), 5.5 (1H, m, allyl), 4.7 (1H, t, J = 7 Hz, allyl),
3.7 (1H, t, J = 13 Hz, allyl), 3.3 (1H, d, J = 7 Hz, allyl),
2.6 (1H, d, J = 13 Hz, allyl).
3.1.8. [PdCl(C10H6NO)(dpppa-P)] (8)
Dpppa (205 mg, 0.66 mmol) and [Pd(l-Cl)-
(C10H6NO)]2 (200 mg, 0.33 mmol) were weighed into a
schlenk type flask and CH2Cl2 (10 cm3) added. The solu-
tion was stirred for 10 min. This resulted in precipitation
of the desired product, which was filtered and washed
with ether (10 cm3) (yield: 371 mg, 95%). Anal. Calc.
for C28H21N3O2PClPd: C, 55.6; H, 3.50; N, 6.95.
3.1.4. 2-Diphenylphosphinopicolinamide selenide (4)
Selenium (52 mg, 0.65 mmol) was added to a solution
of 2-diphenylphosphinopicolinamde (200 mg, 0.65
mmol) in toluene (5 cm3) and refluxed overnight. The
solvent was removed in vacuo leaving an off-white solid.

3218
H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
Found: C, 55.7; H, 3.18; N, 6.04%. mmax/cmꢁ1: 3231,
1673, 1446, 1394, 996, 322. FAB MS: m/z 568
([M ꢁ Cl]+).
aromatic), 7.9 (1H, d, aromatic), 7.7 (1H, m, aromatic),
7.5 (7H, m, aromatic), 7.3 (1H, m, aromatic), 1.4 (15H,
d, J = 12 Hz, Cp*–H).
3.1.9. [PdCl(C9H12N)(dpppa-P)] (9)
3.1.13. [IrCl2(g5-C5Me5)(dpppa-P)] (13)
Dpppa (223 mg, 0.72 mmol) and [Pd(l-Cl)(C9H12N)]2
(200 mg, 0.36 mmol) gave a yellow solid, (yield: 136 mg,
64%). Anal. Calc. for C27H25N3OPClPd(CH2Cl2)0.5: C,
52.9; H, 4.51; N, 6.73. Found: C, 54.3; H, 4.46; N,
6.07%. mmax/cmꢁ1: 3187, 1683, 1449, 1391, 997. 31P
Prepared as for 5. Dpppa (77 mg, 0.25 mmol) and
[{IrCl(l-Cl)(g5-C5Me5)}2] (100 mg, 0.13 mmol) gave a
yellow/orange solid, (yield: 162 mg, 91%). Anal. Calc.
for C28H30N2OPCl2Ir: C, 47.6; H, 4.29; N, 3.98. Found:
C, 47.1; H, 4.27; N, 3.83%. mmax/cmꢁ1: 3288, 1678, 1450,
1
1
NMR (CDCl3) d 63.3 ppm. H NMR (CDCl3) d 10.9
1412, 997. 31P NMR (CDCl3) d 32.7 ppm. H NMR
(1H, d, J = 19 Hz, N–H), 8.6 (1H, d, J = 4 Hz,
pyC[6]H), 8.1 (1H, m, aromatic), 8.0 (1H, m, aromatic),
7.8 (1H, m, aromatic), 7.4 (8H, m, aromatic) 7.0, (1H,
m, aromatic), 6.8 (1H, m, aromatic), 6.4 (1H, m, aro-
matic), 3.4 (2H, d J = 3 Hz, CH2) 2.8 (6H, d, J = 3
Hz, NMe–H). FAB MS: m/z 546 ([M ꢁ Cl]+).
(CDCl3) d 10.2 (1H, d, J = 17 Hz, N–H), 8.6 (1H, d,
J = 4 Hz, pyC[6]H), 8.1–7.7 (6H, m, aromatic), 7.4
(6H, m, aromatic), 1.4 (15H, d, J = 2 Hz, Cp*–H).
3.1.14. [PtCl2(Me2PhP)(dpppa-P)] (14)
Prepared as for 5. Dpppa (76 mg, 0.25 mmol) and
[{PtCl(l-Cl)(PMe2Ph)}2] (100 mg, 0.12 mmol) gave a
white solid, (yield: 114 mg, 65%). Anal. Calc. for
C26H26N2OP2Cl2Pt: C, 44.0; H, 3.69; N, 3.95. Found:
C, 43.77; H, 3.61; N, 3.82%. mmax/cmꢁ1: 1686, 1447,
1384, 1107. 31P NMR (CDCl3) d 30.9 (1JPt–P = 3930),
ꢁ14.5 (1JPt–P = 3500), 2JP–P = 19 Hz. 1H NMR (CDCl3)
d 11.1 (1H, d, J = 15 Hz, N–H), 8.6 (1H, d, J = 4 Hz,
pyC[6]H), 8.0–7.7 (6H, m, aromatic), 7.5–7.0 (12H, m,
aromatic), 1.6–1.5 (6H, d, J = 11 Hz, Me–H).
3.1.10. [PdCl(C12H12N)(dpppa-P)] (10)
Reaction followed as for 5. Dpppa (197 mg, 0.64
mmol) and [Pd(l-Cl)(C12H12N)]2 (200 mg, 0.32 mmol)
gave a yellow/green solid, (yield: 176 mg, 44%). Anal.
Calc. for C30H27N3OPClPd: C, 58.2; H, 3.40; N, 6.80.
Found: C, 58.09; H, 2.92; N, 6.62%. mmax/cmꢁ1: 3203,
1678, 1446, 1388, 997. 31P NMR (CDCl3) d 64.3 ppm.
1H NMR (CDCl3) 11.3 (1H, d, J = 18 Hz, N–H), 8.7
(1H, d, J = 5 Hz, pyC[6]H), 8.2 (4H, m, aromatic), 8.0
(1H, d, aromatic), 7.8 (1H, d, aromatic), 7.6 (1H, d, aro-
matic), 7.5–7.4 (10H, m, aromatic), 6.7 (1H, m, aro-
matic), 6.5 (1H, m, aromatic), 3.5 (6H, d, J = 3 Hz,
NMe–H).
3.1.15. [PtCl2(Et3P)(dpppa-P)] (15)
A solution of [{PtCl(l-Cl)(PEt3)}2] (50 mg, 0.07
mmol), in CH2Cl2 (10 cm3) was added dropwise to a
solution of dpppa (40 mg, 0.13 mmol) in CH2Cl2 (10
cm3). The solution was stirred for 10 min and the major-
ity of the solvent removed in vacuo. A white solid was
precipitated after addition of Et2O then isolated by fil-
tration and washed with further ether (10 cm3) (yield:
55 mg, 66%). Anal. Calc. for C24H30N2OP2Cl2Pt: C,
41.9; H, 4.38; N, 4.06. Found: C, 42.8; H, 3.60; N,
4.15%. mmax/cmꢁ1: 3162, 1687, 1446, 1385, 998, 310.
31P NMR (CDCl3) d 30.0 (1JPt–P = 4010), 7.6 (1JPt–
3.1.11. [RuCl2(p-Cymene)(dpppa-P)] (11)
Prepared as for 5. Dpppa (200 mg, 0.66 mmol) and
[{RuCl(l-Cl)(p-Cymene)}2] (200 mg, 0.33 mmol) gave
a red solid, (yield: 324 mg, 84%). Anal. Calc. for-
C28H29N2OPCl2Ru: C, 54.9; H, 4.77; N, 4.57. Found:
C, 55.8; H, 4.82; N, 4.07%. mmax/cmꢁ1: 3261, 1684,
1449, 1406, 997, 292. 31P NMR (CDCl3) d 59.3 ppm..
1H NMR (CDCl3) d 9.6 (1H, d, J = 18 Hz, N–H), 8.6
(1H, d, J = 7 Hz, pyC[6]H), 8.0 (6H, m, aromatic), 7.8
(1H, m, aromatic), 7.6 (1H, m, aromatic) 7.4 (4H, m,
aromatic), 7.2 (1H, m, aromatic), 5.3 (2H, m, aromatic
[p-Cymene]), 5.2 (2H, m, aromatic [p-Cymene]), 2.6
(1H, m, Pri-H), 1.8 (3H, m, Me–H), 0.8 (6H, d, J = 7
Hz, Pri–Me).
2
P = 3360), JP-P = 19 Hz. 1H NMR (CDCl3) d 11.4
(1H, d, J = 16 Hz, N–H), 8.7 (1H, d, J = 1 Hz,
pyC[6]H), 8.2 (2H, m, aromatic), 7.9–7.7 (5H, m, aro-
matic), 7.5–7.3 (3H, m, aromatic), 7.1 (1H, m, aro-
matic), 1.5 (6H, m, –CH2–), 0.9 (9H, m, Me–H).
3.1.16. [RhCl(cod)(dpppa-P)] (16)
Dpppa (125 mg, 0.41 mmol), and [{Rh(l-Cl)(cod)}2]
(100 mg, 0.20 mmol) were weighed into a schlenk type
flask and toluene (5 cm3) added. The solution was stir-
red for 10 min and the majority of the solvent removed
in vacuo. A yellow solid was precipitated after addition
of n-hexane (20 cm3) then isolated by filtration and
washed with further hexane (10 cm3) (yield: 142 mg,
63%). Anal. Calc. for C26H27N2OPClRh: C, 56.5; H,
4.92; N, 5.07. Found: C, 56.05; H, 4.76; N, 4.90%.
3.1.12. [RhCl2(g5-C5Me5)(dpppa-P)] (12)
Prepared as for 5. Dpppa (198 mg, 0.65 mmol) and
[{RhCl(l-Cl)(g5-C5Me5)}2] (200 mg, 0.32 mmol) gave
a orange solid, (yield: 363 mg, 91%). Anal. Calc. for
C28H30N2OPCl2 Rh: C, 54.6; H, 4.91; N, 4.55. Found:
C, 54.0; H, 4.65; N, 4.40%. mmax/cmꢁ1: 3298, 1678,
1449, 1410, 997, 282. 31P NMR (CDCl3) d 62.8 ppm,
1
JRhP 150 Hz. H NMR (CDCl3) d 9.9 (1H, d, J = 18
Hz, N–H), 8.6 (1H, d, J = 5 Hz, pyC[6]H), 8.1 (4H, m,
m
max/cmꢁ1 : 3194, 1698, 1448, 1407, 997. 31P NMR

H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
3219
1
(CDCl3) d 58.3 (1JRh–P = 162 Hz). H NMR (270 MHz,
CDCl3) d 10.4 (1H, d, J = 21Hz, N–H), 8.6 (1H, d,
J = 2Hz, pyC[6]H), 8.0–7.8 (6H, m, aromatic), 7.6–7.2
(6H, m, aromatic), 2.3 (4H, br.s, cod), 2.0 (8H, br.s,
cod).
3.1.17. [AuCl(dpppa-P)] (17)
Prepared as for 5, Dpppa (67 mg, 0.021 mmol) and
[AuCl(tht)] (70 mg, 0.021 mmol) reacted in CH2Cl2
gave a white solid, (yield: 78 mg, 70%). Anal. Calc.
for C15H15N2OPClAu: C, 40.0; H, 2.80; N, 5.20.
Found: C, 39.5; H, 2.75; N, 5.09%. mmax/cmꢁ1 : 3288,
1698, 1391, 998. 31P NMR (CDCl3) 53.5 ppm. 1H
NMR (CDCl3) 9.1 (1H, d, J = 13 Hz, N–H), 8.6
(1H, d, J = 1 Hz, pyC[6]H), 8.2–7.5 (13H, m,
aromatic).
3.1.18. [RuCl(p-Cymene)(dpppa-P,O)] (18)
A solution of BuLi (65 l l,. 0.16 mmol) in THF (2
cm3) was added dropwise to a solution of [RuCl2-
(p-Cymene)(dpppa-P)] (100 mg, 0.16 mmol) in THF (5
cm3) at 0 °C. The solution was stirred for 10 min and al-
lowed to reach room temperature, and filtered through a
bed of celite. The majority of the solvent removed in va-
cuo. A dull beige solid was precipitated after addition of
Et2O then isolated by filtration and washed with further
ether (10 cm3) (yield: 47 mg, 52%). Recryst from
CH2Cl2/hexane. Anal. Calc. for C28H28N2OPCl-
Ru(CH2Cl2): C, 52.7; H, 4.57; N, 4.24. Found: C,
51.9; H, 4.00; N, 4.38%. mmax/cmꢁ1: 3312, 1351, 249.
31P NMR (CDCl3) d 101.5. 1H NMR (270 MHz,
CDCl3) d 8.4 (1H, d, J = 8 Hz, pyC[6]H), 7.9–7.7 (3H,
m, aromatic), 7.6–7.2 (10H, m, aromatic), 6.0 (1H, d,
J = 6 Hz, p-Cy-H), 5.7 (1H, d, J = 4 Hz, p-Cy-H), 5.4
(1H, d, J = 6 Hz, p-Cy-H), 5.0 (1H, d, J = 4 Hz, p-Cy-
H), 2.5 (1H, m, C–H), 2.0 (3H, s, Me–H), 1.1 (6H, d,
J = 10 Hz, Pri-H).
3.1.19. [RuCl(p-Cymene)(dpppa-P,N)][ClO4] (19)
AgClO4 (33 mg, 0.16 mmol) was added under dark
conditions to a solution of [RuCl2(p-Cy)(dpppa-P)]
(100 mg, 0.16 mmol) in CH2Cl2 (5 cm3). The solution
was stirred overnight and filtered through a celite bed.
The majority of the solvent was removed in vacuo. An
orange solid was precipitated after addition of Et2O
then isolated by filtration and washed with further ether
(10 cm3) (yield: 87 mg, 0.15 mmol, 93%). Anal. Calc. for
C28H28N2O5PCl2Ru(CH2Cl2)0.5: C, 47.6; H, 4.21; N,
3.90. Found: C, 47.2; H, 4.00; N, 3.89%. mmax/cmꢁ1
:
1482, 1084. 31P NMR (CDCl3) d 98.1 ppm. H NMR
(CDCl3) d 8.6 (1H, d, J = 5 Hz, N–H), 8.2 (1H, d,
J = 8 Hz, pyCH), 8.0 (1H, t, J = 8 Hz, pyCH), 7.8
(2H, m, aromatic), 7.7–7.5 (10H, m, aromatic), 5.8
(2H, m, p-Cymene-H), 5.6 (2H, m, p-Cymene-H), 2.8
(1H, m, C–H), 2.1 (3H, s, Me–H), 1.3 (6H, t, J = 6
Hz, Pri-H).
1

3220
H.L. Milton et al. / Polyhedron 23 (2004) 3211–3220
3.1.20. [RhCl(g5-C5Me5)(dpppa-P,N)][BF4] (20)
AgBF4 (31 mg, 0.16 mmol) was added under dark
conditions to a solution of [RhCl2(g5-C5Me5)(dpppa-
P)] (100 mg, 0.16 mmol) in CH2Cl2 (5 cm3). The solution
was stirred overnight and filtered through a celite bed.
The majority of the solvent was removed in vacuo. An
orange solid was precipitated after addition of Et2O
then isolated by filtration and washed with further ether
(10 cm3) (yield: 70 mg, 0.12 mmol, 74%). Anal. Calc. for
C28H30N2OPClRhBF4: C, 50.4; H, 4.54; N, 4.20.
Found: C, 49.8; H, 4.25; N, 4.04%. mmax/cmꢁ1: 1684,
free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ (fax: +44 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk or at www: http://
www.ccdc.cam.ac.uk).
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1
1477, 1421. 31P NMR (CDCl3) d 85.2 ppm. H NMR
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Chem. 582 (1999) 83.
(CDCl3) d 8.6 (1H, d, J = 4 Hz, pyC[6]H), 8.3 (1H, d,
J = 8 Hz, pyC[3]H), 8.0 (1H, t, J = 8 Hz, pyC[5]H), 7.8
(2H, m, aromatic), 7.6 (8H, m, aromatic), 1.6 (15H, d,
J = 4 Hz, Cp*-H).
[4] E. Uhlig, M. Maaser, Z. Anorg. Allg. Chem. 334 (1966) 205.
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Details of the structure determination are given in Ta-
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graphite-monochromated Mo Ka X-radiation using a
Bruker SMART diffractometer or with Cu Ka radiation
and a Rigaku Mercury diffractometer. In both cases,
intensity data were collected using x// steps accumulat-
ing area detector frames spanning a hemisphere of recip-
rocal space for all structures. All data were corrected for
Lorentz, polarisation and long-term intensity fluctua-
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multiple equivalent reflections or by semi-empirical meth-
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by full-matrix least-squares against F2
(SHELXTL).
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Hydrogen atoms were assigned isotropic displacement
parameters and were constrained to idealised geometries.
Complex 7 contains some disorder; in both 7 and 18 not
all of the protons could be included in the final refine-
ment. Refinements converged to residuals given in Table
5. All calculations were made with SHELXTL [28].
[17] D.J. Birdsall, A.M.Z. Slawin, J.D. Woollins, Polyhedron 20
(2001) 125.
[18] A.M.Z. Slawin, J. Wheatley, M.V. Wheatley, J.D. Woollins,
Polyhedron 22 (2003) 1397.
[19] R. Uson, A. Laguna, M. Laguna, Inorg. Synth. 26 (1989) 85.
[20] D. Drew, J.R. Doyle, Inorg. Synth. 28 (1991) 346.
[21] J.X. McDermott, J.F. White, G.M. Whiteside, J. Am. Chem. Soc.
60 (1976) 6521.
[22] C.A. OÕMahoney, I.P. Parkin, D.J. Williams, J.D. Woollins,
Chem. Soc., Dalton Trans. (1989) 1179.
5. Supplementary material
[23] W. Baratta, P.S. Pregosin, Inorg. Chim Acta 209 (1993) 85.
[24] C. White, A. Yates, P.M. Maitlis, Inorg. Synth. 29 (1992) 228.
[25] G. Giordano, R.H. Crabtree, Inorg. Synth. 19 (1979) 218.
[26] M.A. Bennett, T.N. Huang, T.W. Matheson, A.R. Smith, Inorg.
Synth. 21 (1982) 74.
Atomic coordinates, thermal parameters and bond
lengths and angles have been deposited at the Cam-
bridge Crystallographic data centre (CCDC) Nos
238211–238218. Any request to CCDC for this material
should quote the full literature citation and the reference
number. Copies of this information may be obtained
[27] L. Porri, M.C. Gallazzi, A. Colombo, G. Allegra, Tetrahedron
Lett. 47 (1965) 4187.
[28] SHELXTL 6.10, 2002, Bruker AXS, Madison, WI, USA.