Iminophosphines: Synthesis, formation of 2,3-dihydro-1 H-benzo[1,3]azaphosphol-3-ium salts and N-(pyridin-2-yl)-2-diphenylphosphinoylaniline, coordination chemistry and applications in platinum group catalyzed Suzuki coupling reactions and hydrosilylations

Article abstract of DOI:10.1016/S0022-328X(02)01203-2

The aprotic and protic bi- and multidentate iminophosphines 2-Ph₂PC₆H₄N=CR¹R² (R¹ = H, R² = Ph = 2a; R¹ = Me R² = Ph = 2b; R¹ = H, R² = 2-thienyl = 2c; R¹ = H, R² = C₆H₄-2-PPh₂ = 2d; R¹ = H, R² = C₆H₄-2-OH = 2e, R¹ + H,R² = C₆H₄-2-OH-3Bu′ = 2f: R¹ = H, R² = CH₂C(O)Me = 2g) have been prepared by the acid catalyzed condensation of 2-(diphenylphosphino)aniline with the corresponding aldehyde-ketone. Iminophosphine 2d can be reduced with sodium cyanoborohydride to give the corresponding amino-diphosphine has been characterized by single-crystal X-ray crystallography, as its palladium dichloride derivative. The attempted condensation of 2-(diphenylphosphino)aniline with pyridine-2-carboxaldehyde to give the corresponding pyridine-functionalized iminophosphine resulted in an unusual transformation involving the diastereoselective addition of two equivalents of aldehyde to give 1,2-dipyridin-2-yl-2-(o-diphenylphosphinoyl) phenylamino-ethanol, which has been characterized by a single-crystal X-ray structure determination. The bidentate iminosphosphine 2-Ph₂PC₆H₄N=C(H)Ph reacts with [(cycloocta-1,5-diene)PdCIX] X = Cl. Me) to give [Pd 2- Ph₂PC₆H₄N-C(H)Ph|CIX] and the imino-diphosphine 2-Ph₂PC₆H₄N=C(H)C₆H₄-PPh₂ reacts with [(cycloocta-1,5-diene)PdClMe] to give [Pd|2-Ph₂PC₆H₄N=C(H)C₆H₄-PPh₂}ClMe] and each has been characterized by single-crystal X-ray crystallography. The monobasic iminophosphine 2-Ph₂PC₆H₄N=C(Me)CH₂C(O)Me reacts with [Ni(PPh₃)₂Cl₂] in the presence of NaH to give the phosphino-ketoiminate complex [Ni{2-Ph₂PC₆H₄N=C(Me)CHC(O)Me}Cl], which has been structurally characterized. Mixtures of iminophosphines 2a-h and a palladium source catalyze the Suzuki cross coupling of 4-bromoacetophenone with phenyl boronic acid. The efficiency of these catalysts show a marked dependence on the palladium source, catalysts formed from [Pd₂(OAc)₆ giving consistently higher conversions than those formed from [Pd₂(dba)₃] and [PdCl₂(MeCN)₂]. Catalysts formed from neutral bi- and terdentate iminophosphines 2a-d gave significantly higher conversions than those formed from their monobasic counterparts 2e-f. Notably, under our conditions the conversions obtained with 2a-c compare favorably with those palladium. In addition, mixtures of [Ir(COD)Cl]₂ and 2a-h are active for the hydrosilytation of acetophenone; in this case catalysts formed from monobasic iminophosphines 2e-f giving the highest conversions.

Full text of DOI:10.1016/S0022-328X(02)01203-2

Journal of Organometallic Chemistry 650 (2002) 231–248
www.elsevier.com/locate/jorganchem
Iminophosphines: synthesis, formation of
2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium salts and
N-(pyridin-2-yl)-2-diphenylphosphinoylaniline, coordination
chemistry and applications in platinum group catalyzed Suzuki
coupling reactions and hydrosilylations
Simon Doherty a,*, Julian G. Knight b, Tom H. Scanlan b, Mark R.J. Elsegood b,1,
William Clegg b
a School of Chemistry, Da6id Keir Building, The Queen’s Uni6ersity of Belfast, Stranmillis Road, Belfast BT9 5AG, UK
b Department of Chemistry, Bedson Building, The Uni6ersity of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK
Received 6 December 2001; accepted 11 January 2002
Abstract
The aprotic and protic bi- and multidentate iminophosphines 2-Ph2PC6H4NꢀCR1R2 (R1=H, R2=Ph=2a; R1=Me R2=
Ph=2b; R1=H, R2=2-thienyl=2c; R1=H, R2=C6H4-2-PPh2=2d; R1=H, R2=C6H4-2-OH=2e, R1=H, R2=C6H4-2-OH-
3-But=2f; R1=H, R2=CH2C(O)Me=2g) have been prepared by the acid catalyzed condensation of
2-(diphenylphosphino)aniline with the corresponding aldehyde–ketone. Iminophosphine 2d can be reduced with sodium
cyanoborohydride to give the corresponding amino-diphosphine 2-Ph2PC6H4N(H)CH2C6H4-2-PPh2 (2h). In the presence of a
stoichiometric quantity of acid, 2-(diphenylphosphino)aniline reacts in an unexpected manner with benzaldehyde, salicylaldehyde,
or acetophenone to give the corresponding 2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium salts and with pyridine-2-carboxalde-
hyde to give N-(pyridin-2-ylmethyl)-2-diphenylphosphinoylaniline, the latter of which has been characterized by single-crystal
X-ray crystallography, as its palladium dichloride derivative. The attempted condensation of 2-(diphenylphosphino)aniline with
pyridine-2-carboxaldehyde to give the corresponding pyridine-functionalized iminophosphine resulted in an unusual transforma-
tion involving the diastereoselective addition of two equivalents of aldehyde to give 1,2-dipyridin-2-yl-2-(o-diphenylphosphi-
noyl)phenylamino-ethanol, which has been characterized by a single-crystal X-ray structure determination. The bidentate
iminophosphine 2-Ph2PC6H4NꢀC(H)Ph reacts with [(cycloocta-1,5-diene)PdClX] X=Cl, Me) to give [Pd{2-
Ph2PC6H4NꢀC(H)Ph}ClX] and the imino-diphosphine 2-Ph2PC6H4NꢀC(H)C6H4-PPh2 reacts with [(cycloocta-1,5-diene)PdClMe]
to give [Pd{2-Ph2PC6H4NꢀC(H)C6H4ꢁPPh2}ClMe] and each has been characterized by single-crystal X-ray crystallography. The
monobasic iminophosphine 2-Ph2PC6H4NꢀC(Me)CH2C(O)Me reacts with [Ni(PPh3)2Cl2] in the presence of NaH to give the
phosphino–ketoiminate complex [Ni{2-Ph2PC6H4NꢀC(Me)CHC(O)Me}Cl], which has been structurally characterized. Mixtures
of iminophosphines 2a–h and a palladium source catalyze the Suzuki cross coupling of 4-bromoacetophenone with phenyl
boronic acid. The efficiency of these catalysts show a marked dependence on the palladium source, catalysts formed from
[Pd2(OAc)6] giving consistently higher conversions than those formed from [Pd2(dba)3] and [PdCl2(MeCN)2]. Catalysts formed
from neutral bi- and terdentate iminophosphines 2a–d gave significantly higher conversions than those formed from their
monobasic counterparts 2e–f. Notably, under our conditions the conversions obtained with 2a–c compare favorably with those
of the standards; catalysts formed from tris(2-tolyl)phosphine and tris(2,4-di-tert-butylphenyl)phosphite and a source of
palladium. In addition, mixtures of [Ir(COD)Cl]2 and 2a–h are active for the hydrosilylation of acetophenone; in this case
catalysts formed from monobasic iminophosphines 2e–f giving the highest conversions. © 2002 Elsevier Science B.V. All rights
reserved.
Keywords: Iminophosphines; Multidentate; Template synthesis; Platinum group catalysis; Suzuki coupling reactions; Hydrosilylation
* Corresponding author. Tel.: +44-28-90274475; fax: +44-28-90665297.
E-mail address: s.doherty@qub.ac.uk (S. Doherty).
1 Present address: Chemistry Department, Loughborough University, Loughborough, LE11 3TU, UK.
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(02)01203-2

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S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
1. Introduction
(2S)-N[(1-diphenylphosphino-3-methyl-2-butyl)]-N,N-
dimethylformamidine [10].
Iminophosphines are an interesting class of ligand
due to the combination of the weak p-accepting nature
of the imine and the strong s-donor properties of the
phosphine [1]. Recently, there have been a number of
noteworthy reports of the use of these ligands in palla-
dium-mediated catalysis. Shirakawa has shown that
palladium complexes of iminophosphine form remark-
ably active catalysts for the cross coupling of organos-
tannanes with aryl halides [2], the addition of
alkynylstannanes to alkynes leading to the regio- and
stereoselective formation of conjugated (stannyl)enynes
[3] and the carbostannylation of arynes [4]. The steric
bulk of the imino phosphine was found to influence
both the regioselectivity and rate of alkyne alkynylstan-
nation, those with bulky imino substituents affording
higher yields and regioselectivities. Feringa, reasoning
that the strongly coordinating soft P-donor and weakly
coordinating hard nitrogen donor of imino phosphines
could be used to tune the reactivity of palladium com-
plexes in alkene coupling reactions, found that the high
temperature oligomerization of ethene in polar solvents
gave higher alkenes (C6ꢁC16) with an oligomer selectiv-
ity that was determined by the nature of the ligand
substituents [5]. The iminophosphine complex [Pd{o-
(diphenylphosphino)-N-benzaldimime}Me(MeCN)]-
[BF4] catalyses the copolymerization of COꢁethylene
and COꢁnorbornylene and several intermediates of se-
quential CO and ethylene insertion have been isolated
and characterized including [Pd{o-(diphenylphos-
phino)-N-benzaldimime}{CH2CH2C(O)CH2CH2C(O)-
CH3}][BF4] [6a]. A novel route to a family of bulky
One of the most attractive features of iminophosphi-
nes is their ease of synthesis, which involves either
condensation of 2-(diphenylphosphino)benzaldehyde
with an appropriate amine or condensation of 2-
(diphenylphosphino)aniline with an aldehyde or ketone
to give (A) and (B), respectively. In principle this
methodology is extremely versatile and could be used to
generate an extensive library of new bi- and multiden-
tate ligands, since a wide range of amines and alde-
hydes of varying steric bulk and with additional donor
groups are either commercially available or can be
readily synthesized. The increasing number of reports
of the use of iminophosphines in palladium-catalyzed
reactions has prompted us to describe the preliminary
results of our own study involving the synthesis of
iminophosphines, their coordination chemistry and ap-
plications in platinum group catalyzed Suzuki coupling
reactions and the hydrosilylation of ketones.
2. Experimental
2.1. General procedures
iminophosphine
ligands
[Ph2PCH2C(Ph)ꢁN(2,6-
Me2C6H3)] has recently been developed by Green and
co-workers and shown to form active catalysts for
CO–ethylene copolymerization [6b]. Turnover numbers
as high as 106 have been achieved using palladium (II)
complexes of neutral bidentate iminophosphines to cat-
alyze the Heck reaction between iodobenzene with
methyl acrylate, in the presence of N-methylpyrrolidi-
none [7]. Palladium complexes of iminophosphines have
also been shown to catalyze the alkoxycarbonylation of
terminal alkynes, albeit with much lower rates and
regioselectivity than their pyridyldiphenylphosphine
counterparts [8]. Five and six-coordinate ruthenium
All manipulations involving air sensitive materials
were carried out in an inert atmosphere glove box or
using standard Schlenk line techniques under an atmo-
sphere of nitrogen or argon in oven-dried glassware.
Diethyl ether and hexane were distilled from potas-
sium–sodium alloy, THF from potassium, CH2Cl2
from CaH2 and MeOH from magnesium. Unless other-
wise stated commercially purchased materials were pur-
chased and used without further purification.
Deuteriochloroform was pre-dried with CaH2 and vac-
,
uum transferred and stored over 4 A molecular
sieves.1H- and 31P{1H}- and 13C{1H}-NMR spectra
were recorded on a JEOL LAMBDA 500 or Bruker AC
200, AMX 300 and DRX 500 machines. GC analyses
were conducted on a Varian CP3800 connected to a
Varian C8400 auto sampler. Response factors were
determined by injection of samples containing known
quantities of authentic sample. The palladium com-
plexes [(cycloocta-1,5-diene)PdCl2] [11a,11b] and [(cy-
complexes
containing
the
iminophosphine
2-
Ph2PC6H4CHꢀNtBu are active for the transfer hydro-
genation of alkyl–aryl and dialkyl ketones in
propan-2-ol [9]. Surprisingly, the iminophosphine com-
plexes are more efficient than those based on the corre-
sponding
amino-phosphine
derivatives,
2-Ph2P-
C6H4CH2NHtBu. Excellent levels of asymmetric induc-
tion (95%) have been obtained in the palladium-cata-
lyzed enantioselective allylic alkylation of 1,3-diphenyl-
2-propenyl acetate using the chiral iminophosphine
cloocta-1,5-diene)PdClMe]
[11c],
2-(diphenylphos-
phino)aniline [12] and its nickel nitrate complex were
prepared according to literature methods.

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
233
2.2. Synthesis
2.2.5. Synthesis of [2-PPh2C6H4NꢀC(H)C6H4OH] (2e)
Iminophosphine 2e was isolated as a pale yellow
solid in 61% yield. 31P{1H}-NMR (121.5 MHz, CDCl3,
1
2.2.1. Synthesis of [2-Ph2PC6H4NꢀC(H)C6H5] (2a)
A methanol solution (ca. 30 ml) of 2-(diphenylphos-
phino)aniline (0.5 g, 1.8 mmol), formic acid (one drop)
and benzaldehyde (1.8 mmol, 0.18 ml) was stirred for
18 h after which time the solvent was removed under
vacuum. The residue was dissolved in CH2Cl2, washed
with water, separated, dried with Na2SO4, and filtered.
The solvent was removed under reduced pressure to
give iminophosphine 2a as a colorless solid in 66% yield
(0.44 g). 31P{1H} (202.0 MHz, CDCl3, l): −13.0 (s).
1H-NMR (500.1 MHz, CDCl3, l): 8.06 (s, 1H, NꢀCH),
7.14 (m, 19H, C6H5 and C6H4). 13C{1H}-NMR (33.9
MHz, CDCl3, l): 160.0 (s, NꢀC, 140–122 (m, C6H5 and
C5H4N). m/z (EI): 365 [M+]. Anal. Calc. for
C25H20NP: N, 3.83; C, 82.26; H, 7.18. Found: N, 4.11;
C, 82.55; H, 7.48%.
l) −13.9 (s). H-NMR (500.1 MHz, CDCl3, l): 12.41
(s, 1H, OH), 8.32 (s, 1H, HCꢀN), 7.28–6.95 (m, 18H,
C6H5 and C6H4). 13C{1H}-NMR (33.9 MHz, CDCl3, l)
160.0 (s, NꢀC) 143–129 (m, C6H5). m/z (EI): 381 [M+].
Anal. Calc. for C25H20NOP: N, 3.67; C, 78.7; H, 5.29.
Found: N, 3.71; C, 78.48; H, 5.48%.
2.2.6. Synthesis of [2-PPh2C6H4NꢀC(H)C6H4(But)OH]
(2f)
Iminophosphine 2f was isolated as a pale yellow solid
in 83% yield. 31P{1H}-NMR (121.5 MHz, CDCl3, l):
1
−12.6 (s). H-NMR (500.1 MHz, CDCl3, l): 12.9 (s,
1H, OH), 8.31 (s, 1H, NꢀCH), 7.11–6.9 (m, 17H, C6H5
and C6H4), 1.34 (s, 9H, CMe3). 13C{1H}-NMR (33.9
MHz, CDCl3, l): 163.0 (s, CꢀN), 141–132 (m, C6H5),
34.9 (s, CCH3), 29.3 (s, CH3). m/z (EI): 437 [M+].
Anal. Calc. for C29H29NOP: N, 3.19; C, 79.42; H, 6.66.
Found: N, 2.92; C, 79.58; H, 6.36%.
Iminophosphines 2b–h were prepared according to
the procedure described above for 2a.
2.2.2. Synthesis of [2-Ph2PC6H4NꢀC(Me)C6H5] (2b)
Iminophosphine 2b was isolated as a colorless solid
in 77% yield. 31P{1H}-NMR (121.5 MHz, CDCl3, l):
2.2.7. Synthesis of
[2-PPh2C6H4NꢀC(Me)CH2C(O)CH3] (2g)
Iminophosphine 2g was isolated as a pale yellow
solid in 56% yield. 31P{1H}-NMR (121.5 MHz, CDCl3,
l): −14.5 (s). 1H-NMR (500.1 MHz, CDCl3, l): 7.25–
6.89 (m, 14H, C6H5 and C6H4), 4.93 (s, 2H, CH2), 1.94
(s, 3H, CH3), 1.54 (s, 3H, CH3). 13C{1H}-NMR (33.9
MHz, CDCl3, l): 196.0 (CꢀO), 160.0 (s, CꢀN), 141–
131 (m, C6H5), 97.5 (s, CH2), 29.1 (s, CH3), 19.5 (s,
CH3). m/z (EI): 359 [M+]. Anal. Calc. for C23H22NOP:
N, 3.90; C, 76.86; H, 6.17. Found: N, 4.14; C, 77.14; H,
6.44%.
1
−14.1 (s). H-NMR (500.1 MHz, CDCl3, l): 7.19 (m,
22H, C6H5 and C6H4), 3.41 (s, 3H, CH3). 13C{1H}-
NMR (33.9 MHz, CDCl3, l): 160.0 (NꢀC), 142–128
(m, C6H5), 17.5 (CH3). m/z (EI): 379 [M+].
2.2.3. Synthesis of [2-PPh2C6H4NꢀC(H)C3H3S] (2c)
Iminophosphine 2c was isolated as a colorless solid in
67% yield. 31P{1H}-NMR (121.5 MHz, CDCl3, l):
1
−13.0 (s). H-NMR (500.1 MHz, CDCl3, l): 8.15 (d,
J=1.0 Hz, 1H, NꢀCꢁH), 7.71 (dd, J=1.0, 4.1 Hz, 1H,
C3H3S), 7.24–6.98 (m, 15H, C6H5, C6H4 and C3H3S),
6.94 (dd, J=4.1 Hz, J=7.1 Hz, 1H, C3H3S). 13C{1H}-
NMR (33.9 MHz, CDCl3, l): 154.0 (s, NꢀC), 153.0
(SCꢀCH), 152.1 (s, CꢁH), 143.3 (s, CꢁH), 137.2 (s,
CꢁH), 141–131 (m, C6H5). m/z (EI): 359 [M+]. Anal.
Calc. for C22H18NPS: N, 3.90; C, 73.61; H, 5.05.
Found: N, 4.09; C, 73.67; H, 5.22%.
2.2.8. Reduction of [2-PPh2C6H4NꢀC(H)C6H4PPh2]
(2d)
To a THF solution (ca. 10 ml) of [2-PPh2C6-
H4NꢀC(H)C6H4PPh2] (0.40 g, 0.73 mmol) was added
NaCNBH3 (0.046 g, 0.73 mmol) portion wise over 5
min and the resulting mixture allowed to stir overnight.
The solvent was removed under reduced pressure and
the resulting oily residue was extracted into CH2Cl2.
The organic phase was washed with water (2×10 ml)
separated, dried over Na2SO4, filtered and the solvent
2.2.4. Synthesis of [2-PPh2C6H4NꢀC(H)C6H4PPh2]
(2d)
1
removed to afford 2i in 80% yield (0.32 g). H-NMR
(500.1 MHz, CDCl3, l): 4.30 (s, br, 2H), 5.22 (s, br,
1H, NꢁH), 7.0 (m, 28H, C6H5). 13C{1H}-NMR (125.65
MHz, CDCl3, l): 141–130 (m, C6H5), 45.9 (3JPC=26.7
Hz, CH2).
Iminophosphine 2d was isolated as a pale yellow
solid in 56% yield. 31P{H}-NMR (121.5 MHz, CDCl3,
l): −13.1 (s), −13.7 (s). 1H-NMR (500.1 MHz,
CDCl3, l): 8.82 (d, J=5.5 Hz, 1H, NꢀCH), 7.21–6.82
(m, 29H, C6H5 and C6H4). 13C{1H}-NMR (33.9 MHz,
CDCl3, l): 155.0 (s, NꢀC), 143–132 (m, C6H5), 115.1
2.2.9. Synthesis of the 2-phenyl-2,3-dihydro-1H-benzo-
[1,3]azaphosphol-3-ium salt (3a)
3
(d, JPC=13.3 Hz). m/z (EI): 549 [M+]. Anal. Calc. for
C37H29NP2: N, 2.55; C, 80.85; H, 5.32. Found: N, 2.79;
C, 81.17; H, 5.43%.
Concentrated sulfuric acid (1 ml) was added drop-
wise to a rapidly stirred solution of 2-(diphenylphos-

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S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
phino)aniline (0.5 g, 1.8 mmol) in methanol (30 ml).
Benzaldehyde (0.19 g, 1.8 mmol) was added and the
reaction mixture was allowed to stand overnight. The
resulting precipitate was filtered and washed with a
little methanol to give 3b in 70% isolated yield (0.58 g)
as colorless crystals, after crystallization by slow diffu-
sion of hexane into a CH2Cl2 solution at room temper-
ature (r.t.). 31P{1H}-NMR (121.4 MHz, CDCl3, l):
m/z (EI): 384 [M+]. Anal. Calc. for C23H21N2OP: N,
7.29; C, 75.07; H, 5.51. Found: N, 7.03; C, 74.83; H,
5.18%.
2.2.13. Preparation of
[PdCl2{PPh2(O)C6H4N(H)CH2-2-C5H4N}] (5)
A solution of [(cycloocta-1,5-diene)PdCl2] (0.1 g, 0.35
mmol) in CH2Cl2 (8–10 ml) was treated with a CH2Cl2
solution of 4 (0.13 g, 0.35 mmol) and stirred vigorously
overnight. The reaction mixture was filtered, the solvent
removed and the residue washed with n-hexane and
dried under vacuum to give 5 as a yellow solid (0.14 g,
70%). Crystallization by slow diffusion of a CH2Cl2
solution layered with n-hexane gave X-ray quality crys-
tals of 5. 31P{1H}-NMR (121.4 MHz, CDCl3, l): 40.73
1
37.7 (s). H-NMR (200.1 MHz, CDCl3, l); 7.4–6.9 (m,
19H, C6H5 and C6H4). 6.28 (d, 2JPH=10.3 Hz,
NCHC6H5). m/z (EI): 365 [M+]. Anal. Calc. for
C25H22NPSO4: N, 3.02; C, 64.8; H, 4.79. Found: N,
2.82; C, 65.3; H, 5.08%.
2.2.10. Synthesis of the 2-phenyl-2-methyl-2,3-
dihydro-1H-benzo[1,3]azaphosphol-3-ium salt (3b)
Rapid stirring of a methanol solution (ca. 40 ml) of 1
(0.5 g, 1.8 mmol), concentrated H2SO4 (ca. 1 ml) and
salicylaldehyde (0.2 g, 1.87 mmol) gave 3b in 58%
isolated yield (0.49 g) as colorless crystals, after crystal-
lization by slow diffusion of hexane into the reaction
mixture. 31P{1H}-NMR (121.4 MHz, CDCl3, l): 41.5
1
(s). H-NMR (500.1 MHz, CDCl3, l): 10.7 (m br, 1H,
NH), 7.5 (m, 18H, C6H5 and C5H4N), 4.57 (AB quar-
2
tet, JHH=16.5 Hz, 1H, CHaHb), 4.49 (AB quartet,
2JHH=16.5 Hz, 1H, CHaHb). Anal. Calc. for
C24H21N2PPdCl2O: N, 4.98; C, 51.3; H, 3.77. Found:
N, 4.86; C, 50.91; H, 3.45%.
1
(s). H-NMR (500.1 MHz, CDCl3, l): 8.2 (s br, 1H,
2.2.14. Reaction of 2-(diphenylphosphino)aniline with
pyridine-2-carboxaldehyde in toluene
3
NH), 7.3 (m, 14H, C6H5 and C6H4), 1.73 (d, JPꢁH
=
16.7 Hz, 3H, CH3), 13C{1H}-NMR (CDCl3, 125.65
MHz, l): 141–129 (m, C6H5 and C6H4), 68.8 (d,
A toluene solution (ca. 30 ml) of 1 (0.5 g, 1.8 mmol)
and pyridine-2-carboxaldehyde (0.19 g, 1.8 mmol) was
stirred rapidly for 30 min and then allowed to stand
overnight, during which time colorless crystals of 6
formed in 36% yield (0.32 g). The reaction mixture was
filtered, the crystals washed with n-hexane and dried
under vacuum. 31P{1H}-NMR (121.4 MHz, CDCl3, l):
35.8 (s). 1H-NMR (500.1 MHz, CDCl3, l): 4.9 (dd,
J=8.2, 2.4 Hz, ArH, 2-pyH, 1H), 5.11 (d, J=2.2 Hz,
1H, ArH, 2-pyH), 6.35 (m, 2H, ArH, 2-PyH), 6.68
(ddd, J=1.6, 7.7, 14.4 Hz, 1H, ArH, 2-PyH), 6.92
(ddd, J=1.0, 4.9, 7.4 Hz, 1H, ArH, 2-PyH), 7.05 (m,
2H, ArH, 2-PyH), 7.17 (d, J=8 Hz, 1H, ArH, 2-PyH),
7.1–7.6 (m, 15H, ArH, 2-PyH), 7.83 (d, J=8.3 Hz,
1H, ArH, 2-PyH), 8.23 (d, J=4.6 Hz, 1H, ArH, 2-
PyH) 8.45 (m, 1H, ArH, 2-PyH). 13C{1H}-NMR (33.9
MHz, CDCl3, l): 150–120 (m, C6H5), 62.9 (s, CH),
75.1 (s, CH). Anal. Calc. for C30H26N3PO2: N, 8.54; C,
5.33; H, 5.06. Found: N, 8.34; C, 73.2; H, 5.39%.
1JPC=55.9 Hz, CC6H5CH3), 25.5 (d, JPC=131.3 Hz,
2
CH3). Anal. Calc. for C26H24NPSO4: N, 2.93; C, 65.4;
H, 5.06. Found: N, 2.77; C, 65.31; H, 4.9%.
2.2.11. Synthesis of the 2-phenol-2-methyl-2,3-
dihydro-1H-benzo[1,3]azaphosphol-3-ium salt (3c)
Azaphosphol-3-ium salt 3c was prepared according
to the procedure described above for 3a and isolated as
colorless crystals in 65% yield. 31P{1H}-NMR (121.4
MHz, CDCl3, l): 38.88 (s). 1H-NMR (500.1 MHz,
CDCl3, l): 10.9 (s, 1H, OH), 9.8 (s, 1H, NH), 7.7–6.8
(m, 18H, C6H5 and C6H4), 1.1 (m, 1H, CH). Anal.
Calc. for C25H22NPSO5: N, 2.92; C, 62.6; H, 4.63.
Found: N, 2.95; C, 62.3; H, 4.43%.
2.2.12. Preparation of
[Ph2P(O)}C6H4N(H)CH2-2-C5H4N] (4)
Pyridine-2-carboxaldehyde (0.19 g, 1.8 mmol) was
added to
a stirred solution of 2-(diphenylphos-
phino)aniline (0.5 g, 1.8 mmol) and formic acid (ca.
three drops) in methanol (10 ml). The mixture was
allowed to stir overnight and the solvent removed un-
der reduced pressure. Purification of the crude material
by column chromatography (CH2Cl2:MeOH, 20:1) gave
phosphine oxide 4 as a foam in 48% yield (0.33 g).
2.2.15. Preparation of
[Ni(PPh2C6H4NꢀC(H)-2-C5H4N)2[NO3]2 (7)
A solution of [Ni(2-Ph2PC6H4NH2)2][NO3]2 (0.5 g,
0.7 mmol) in CH2Cl2 (ca. 30 ml) was treated with
pyridine-2-carboxaldehyde (0.15 g, 0.7 mmol). The re-
action mixture was left to stir overnight to give a
deep purple solution, which was filtered and layered
with Et2O to give deep purple crystals of 7 in 43% yield
(0.27 g). Anal. Calc. for C48H38N4NiO6P2·5CH2Cl2: N,
6.27; C, 47.48; H, 3.61. Found: N, 6.44; C, 47.79; H,
3.77%.
1
31P{1H}-NMR (121.4 MHz, CDCl3, l): 37.4. H-NMR
(500 MHz, CDCl3, l): 8.45 (dd, J=0.9, 4.9 Hz, 1H),
7.61 (m, 12H), 7.03 (dd, J=5.0, 6.7 Hz, 1H), 6.94 (d,
J=7.9 Hz, 2H), 6.73 (ddd, J=1.5, 7.7, 14.7 Hz, 1H),
6.48 (dd, J=4.6, 7.5 Hz, 2H), 4.44 (d, 2H, J=5.9 Hz),

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
235
2.2.16. Synthesis of [Pd{Ph2PC6H4NꢀC(H)C6H5}Cl2]
(8a)
A solution of [(cycloocta-1,5-diene)PdCl2] (0.15 g,
2.2.19. Preparation of
[Pd{Ph2PC6H4NꢀC(H)C6H4Ph2]Me]Cl (9b)
A sample of 9a (0.30 g, 0.33 mmol) and [PPN][Cl]
(0.20 g, 35 mmol) was dissolved in CH2Cl2 (ca. 15 ml)
and the resulting solution stirred for 3 h after which
time the solvent was removed and the resulting pale
yellow solid was washed with petrol and dried under
vacuum. Crystallization from a CH2Cl2 solution layered
with n-hexane at r.t. gave X-ray quality crystals of 9b.
31P{1H}-NMR (121.5 MHz, CDCl3, l): 38.4 (AB quar-
tet, 2Jpp=392.1 Hz), 31.4 (AB quartet, 2Jpp=392.1
0.52 mmol) in CH2Cl2 (ca. 10 ml) was treated with a
CH2Cl2 solution of 2a (0.19 g, 0.52 mmol) and stirred
vigorously overnight. The reaction mixture was filtered,
the solvent removed and the residue washed with n-hex-
ane and dried under vacuum to give 8a as a yellow solid
(0.22 g, 78%). Crystallization by slow diffusion of a
CH2Cl2 solution layered with hexane at r.t. gave X-ray
quality crystals of 8a. 31P{1H}-NMR (36.4 MHz,
1
1
CDCl3, l): 35.6 (s). H-NMR (500.1 MHz, CDCl3, l):
Hz). H-NMR (200 MHz, CDCl3, l): 8.71 (dd, J=5.1,
8.66 (s, 1H, HꢁCꢀN), 7.2–6.9 (m, 19H, C6H5 and
C6H4), 13C{1H}-NMR (33.9 MHz, CDCl3, l): 164.4
(NꢀCꢁH), 140–129 (m, C6H5). Anal. Calc. for
C25H20Cl2NPPd: N, 2.58; C, 55.36; H, 3.71. Found: N,
2.76; C, 55.65; H, 3.99%.
8.0 Hz, 1H, NꢀCH), 7.3–6.8 (m, 28H, C6H5 and C6H4),
0.53 (t, 3JPH=6.1 Hz, 3H, PdCH3). Anal. Calc. for
C38H32ClNP2Pd: N, 1.98; C, 64.63; H, 4.57. Found: N,
2.22; C, 64.97; H, 4.83%.
2.2.20. Reaction of [NiCl2(PPh3)2] and
[{PPh2(C6H4)}NꢀC(Me)CH2C(O)CH3] (10)
2.2.17. Synthesis of
Addition of sodium hydride (0.004 mg, 0.17 mmol)
to a CH2Cl2 solution (ca. 20 ml) of iminophosphine 2g
(0.06 g, 0.17 mmol) and [NiCl2(PPh3)2] (0.17 mmol, 0.1
g) resulted in an immediate color change from deep
green to intense amber. After stirring over night the
solvent was removed and the residue was washed with
a small amount of THF and then crystallized from
THF–hexane to give 10 as an orange crystalline solid
in 44% yield (0.038 g). 31P{1H}-NMR (121.5 MHz,
[Pd{Ph2PC6H4NꢀC(H)C6H5}ClMe] (8b)
A solution of [(cycloocta-1,5-diene)PdClMe] (0.1 g,
0.38 mmol) in CH2Cl2 (ca. 10 ml) was treated with a
CH2Cl2 solution of 2a (0.14 g, 0.38 mmol) and stirred
vigorously overnight. The reaction mixture was filtered,
the solvent removed and the residue washed with n-hex-
ane and dried under vacuum to give 8b as a yellow solid
(0.19 g, 70%). Crystallization by slow diffusion of a
CH2Cl2 solution layered with Et2O gave X-ray quality
crystals of 8b. 31P{1H}-NMR (36.4 MHz, CDCl3, l):
1
CDCl3, l): 22.7(s). H-NMR (200.1 MHz, CDCl3, l):
7.20–6.9 (m, 14H, C6H5 and C6H4), 5.23 (s, 1H, meth-
ane CH). 2.10 (s, 3H, CH3) 1.90 (s, 3H, CH3). m/z (EI):
451 [M+]. Anal. Calc. for C23H22ClNNiOP: N, 3.09; C,
66.90; H, 4.89. Found: N, 2.92; C, 66.64; H, 4.43%.
1
36.1 (s). H-NMR (500.1 MHz, CDCl3, l): 8.59 (s, 1H,
HꢁCꢀN), 7.45–6.80 (m, 19H, C6H5 and C6H4), 1.49 (d,
3JPH=7.5 Hz, 3H, CH3). 13C{1H}-NMR (33.9 MHz,
CDCl3, l): 164.0 (NꢀCꢁH), 141–130 (m, C6H5), 3.69
(d, 2JPC=22.3 Hz, 3H, CH3). Anal. Calc. for
C25H20Cl2NPPd: N, 2.58; C, 46.45; H, 3.72. Found: N,
2.77; C, 46.78; H, 4.07%.
2.3. Catalysis
2.3.1. General procedure for the Suzuki coupling of
aryl bromides
2.2.18. Preparation of
A test tube was charged with phenyl boronic acid
(0.122 g, 1 mmol), K2CO3 (0.19 g, 1.3 mmol), 4-bro-
moacetophenone (1 mmol), [Pd3(OAc)6] (0.1 mmol) and
dioxane (2 ml). The reaction mixture was stirred at
70 °C for 2 h after which time it was cooled, diluted
and a sample removed and diluted with toluene and
filtered through celite before being analyzed by gas
chromatography. GC conditions: CP-sil5 10 m×0.53
mm capillary, temperature ramp from 130 to 230 °C,
[Pd{Ph2PC6H4NꢀC(H)C6H4PPh2}Me][SnMe3Cl2 (9a)
A solution of [(cycloocta-1,5-diene)PdClMe] (0.1 g,
0.38 mmol) in CH2Cl2 (ca. 10 ml) was treated with a
CH2Cl2 solution of 2d (0.20 g, 0.38 mmol) and stirred
vigorously overnight. The reaction mixture was filtered,
the solvent removed and the residue washed with n-hex-
ane and dried under vacuum to give 9a as a yellow solid
in 64% yield. 31P{1H}-NMR (121.5 MHz, CDCl3, l):
2
38.4 (AB quartet, JPP=392.1 Hz), 31.4 (AB quartet,
ramp rate 8 °C min−1
.
2Jpp=392.1 Hz). 1H-NMR (500.1 MHz CDCl3, l):
8.47 (dd, J=4.2, 7.0 Hz, 1H, NꢀCH), 7.5–6.9 (m, 28H,
2.3.2. General procedure for the hydrosilylation of
acetophenone
3
C6H5 and C6H4), 0.69 (s, 9H, SnMe3), 0.53 (t, JPH
=
6.1 Hz, 3H, PdꢁCH3). 13C{1H}-NMR (125.65 MHz,
CDCl3, l): 142.0 (d, 2JPꢁC=9.0 Hz), 140–130 (m,
C6H5), 5.68 (s, CH3), −1.85 (CH3). Anal. Calc. for
A test tube was charged with acetophenone (120 ml, 1
mmol), Ph2SiH2 (220 ml, 1.2 mmol), the respective
ligand (1 ml of a 10 mM solution), [Ir(COD)Cl]2 (0.5 ml
of 20 mM solution) and THF (2 ml). Separate test
tubes were charged with the same reactants and the
C42.5H45NP2PdCl5Sn: N, 1.35; C, 49.40; H, 4.38.
Found: N, 1.23; C, 49.12; H, 4.13%.

236
S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
control ligands. Catalytic runs were performed both in
air and under argon. The reaction mixture was stirred
for 18 h at ambient temperature and MeOH–2 M HCl
(1:1, 0.5 ml) was added and the solution left to stand
for 2 h after which time a sample (0.5 ml) of the
reaction mixture was removed for analysis by GC.
2.4. Crystal structure determinations of 3b, 3c, 5, 6, 7,
8a, 8b, 9b and 10
All measurements were made on a Bruker AXS
SMART IK CCD area-detector diffractometer using
graphite-monochromated Mo–Ka radiation (u=
Scheme 1. (a) HCO2H cat. or H2SO4 cat., MeOH, rt, 18 h; (b) H2SO4
(ca. five equivalents), MeOH, rt, 18 h; (c) H2SO4 (ca. five equiva-
lents), MeOH, rt, 18 h.
,
0.71073 A), except for 9b, for which the very small
crystal size required the use of synchrotron radiation
,
(Daresbury SRS station 9.8; u=0.6890 A). Cell
parameters were refined from all strong reflections in
each data set. Intensities were corrected semi-empiri-
cally for absorption, based on symmetry-equivalent and
repeated reflections. The structures were solved and
refined by standard methods, with most H atoms con-
strained [13a]. Crystal data and other information are
given in Table 1. Disorder was resolved and refined for
one solvent molecule in 7, and some of the more highly
disordered solvent molecules in this structure were
treated by the PLATON SQUEEZE procedure [13b].
There is also two-fold disorder of orientation for the
ligand in 9b, equivalent to exchange of the central N
and C atoms of the imido linkage.
bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-
diimine}] is almost inactive for the transfer hydrogena-
tion of acetophenone whereas its amino-phosphine
counterpart
[RuCl2{N,N%-(S,S)-bis[o-(diphenylphos-
phino)benzyl]cyclohexane-1,2-diamine}] gives high con-
versions [16]. The ligands are soluble in a range of
organic solvents and stable to hydrolysis and aerial
oxidation in the solid state over several weeks. Each of
the iminophosphines 2a–g and amino-diphosphine 2h
has been characterized using conventional spectroscopic
and analytical methods.
3. Results and discussion
3.1. Acid mediated reactions of
2-(diphenylphosphino)aniline with aromatic carbonyl
compounds: synthesis of iminophosphines and formation
of 2,3-dihydro-1H-benzo[1, 3]azaphosphol-3-ium salts
and N-(pyridin-2-yl)-2-diphenylphosphinoylaniline
Iminophosphines 2a–d were prepared by the acid
catalyzed condensation of 2-(diphenylphosphino)aniline
(1) with the appropriate aldehyde–ketone [14]. Thus,
2-(diphenylphosphino)aniline reacted with benzalde-
hyde, acetophenone, 2-thiophene carboxaldehyde and
2-(diphenylphosphino)benzaldehyde in methanol in the
presence of a catalytic quantity of either formic or
sulfuric acid to give the corresponding iminophosphines
2a–d, shown in Chart 1. Similarly, 2-(diphenylphos-
phino)aniline reacted with salicylaldeyhde, 3-tert-butyl-
2-salicylaldehyde and 2,4-pentanedione under similar
conditions to give the corresponding monobasic terden-
tate iminophosphines, 2e–g. Reduction of iminophos-
phine, 2d, using sodium cyanoborohydride [15] gave the
corresponding amino-diphosphine, 2h, in near quantita-
tive yield. Interestingly, Noyori has recently reported
that the iminophosphine complex [RuCl2{N,N%-(S,S)-
During our attempts to optimize the conditions re-
quired for the condensation we found that, in the
presence of excess H2SO4 in methanol, the condensa-
tion between 2-(diphenylphosphino)aniline and ben-
zaldehyde, acetophenone or salicylaldehyde gave rise to
the corresponding benzoazaphospholium salts, 3a–c,
rather than the desired iminophosphines (Scheme 1,
pathway b). The first evidence for this unexpected
1
transformation was the absence of a low-field H-NMR
signal associated with the imine NꢁH. The 31P{1H}-
NMR spectrum of 3a contains a singlet at l 37.7 ppm,
shifted to low-field of that for the corresponding

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
237

238
S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
Table 2
,
Selected bond distances (A) and angles (°) for 3b and 3c
3b
3c
Bond lengths
P(1)ꢁC(14)
P(1)ꢁC(1)
P(1)ꢁC(15)
P(1)ꢁC(21)
C(1)ꢁN(1)
N(1)ꢁC(9)
C(9)ꢁC(14)
1.7669(17)
1.8941(17)
1.7915(17)
1.7885(17)
1.458(2)
P(1)ꢁC(1)
P(1)ꢁC(7)
P(1)ꢁC(14)
P(1)ꢁC(20)
C(7)ꢁN(1)
N(1)ꢁC(6)
C(1)ꢁC(6)
1.767(2)
1.865(2)
1.796(2)
1.789(2)
1.455(2)
1.372(3)
1.404(3)
1.367(2)
1.407(2)
Bond angles
C(1)ꢁP(1)ꢁC(14)
C(1)ꢁP(1)ꢁC(15)
C(1)ꢁP(1)ꢁC(21)
C(14)ꢁP(1)ꢁC(15) 111.64(8)
C(14)ꢁP(1)ꢁC(21) 110.81(8)
C(15)ꢁP(1)ꢁC(21) 112.45(8)
943.77(8)
110.29(8)
116.51(8)
C(1)ꢁP(1)ꢁC(7)
C(1)ꢁP(1)ꢁC(14)
C(1)ꢁP(1)ꢁC(20)
C(7)ꢁP(1)ꢁC(14)
C(7)ꢁP(1)ꢁC(20)
C(14)ꢁP(1)ꢁC(20) 110.57(9)
C(6)ꢁN(1)ꢁC(7) 116.64(17)
93.87(10)
112.31(10)
111.84(10)
112.61(10)
114.74(10)
Fig. 1. Molecular structure of one of the two independent molecules
of the 2-phenyl-2-methyl-2,3-dihydro-1H-benzo[1,3]azaphosphol-3-
ium salt (3b).
C(1)ꢁN(1)ꢁC(9)
116.95(14)
not centrosymmetric, as it involves two symmetry-inde-
pendent anions. Relevant distances are N(1)···O(8)
2.822, N(2)···O(3) 2.853, O(2)···O(6) 2.581,O(4)···O(5)
,
2.542 A, with angles of 168, 169, 171, and 169° at the
respective hydrogen atoms. In the absence of the alco-
hol group, further hydrogen bonding interactions are
not possible, and only discrete groups of two anions
with two cations are formed rather than chains.
It is likely that the imines 2a–c are intermediates in
the formation of the phospholium salts since treatment
of the salicylaldehyde-derived iminophosphine, 2c, with
excess sulfuric acid in methanol gave rise to the salt 3c
Fig. 2. Molecular structure of the 2-phenol-2-methyl-2,3-dihydro-1H-
benzo[1,3]azaphosphol-3-ium salt (3c).
(pathway
c).
The
formation
of
neutral
iminophosphine, which in the case of 2a appears at l
−13.0 ppm. The identity of the salicylaldehyde- and
acetophenone-derived salts 3b and 3c has been confi-
rmed by single-crystal X-ray structure determinations.
Perspective views of the molecular structures of 3b and
3c, together with their atomic numbering schemes, are
shown in Figs. 1 and 2, respectively, and a selection of
bond lengths and angles for both molecules is listed in
Table 2. The structure of 3c reveals that individual ions
are linked through intermolecular H-bonding interac-
tions: between the azaphospholium NꢁH and the oxy-
gen atom of one hydrogen sulfate [N(1)···O(4%)=2.974
[1,3]azaphospholidines by condensation of b-amino sec-
ondary phosphines with aldehydes and ketones is well
known [17], as is formation of a stable five-membered
thiazole ring via the condensation of 2-(diphenylphos-
phino)benzaldehyde with 2-aminobenzenethiol [18]. Al-
though 2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium
salts have been synthesized by P-alkylation of the corre-
sponding azaphospholines [19], we are not aware of any
reports of direct preparation from an amino-containing
tertiary phosphine and a carbonyl compound.
In our attempts to synthesize the potentially triden-
tate pyridyl-functionalized iminophosphine 2i, 2-
(diphenylphosphino)aniline (1) was reacted with
pyridine-2-carboxyaldehyde in the presence of formic
acid. Surprisingly, this reaction did not produce the
desired iminophosphine but instead gave the amino-
phosphine oxide 4 (Scheme 2). The 31P{1H}-NMR
spectrum of 4 contains a single resonance at l 37.4
ppm, the down-field shift relative to that expected for
an iminophosphine clearly indicating formation of
phosphine oxide. The identity of 4 was unequivocally
confirmed by a single-crystal X-ray crystal structure
determination of its palladium dichloride derivative, 5,
,
A and an NꢁH···O angle of 164°] and the alcohol group
of the benzo ring and the oxygen atom of another
,
hydrogen sulfate [O(1)···O(3%)=2.638
O(1)···H···O(3%) angle of 162°], together with double
A
and an
hydrogen bonds between pairs of HSO−4 ions across
,
inversion centers [O(5)ꢁO(2%)=2.618
A
and an
O···H···O angle of 170°]. These hydrogen-bonding inter-
actions propagate through the crystal to form linear 1D
arrays along the c-axis. Similar NꢁH···O(anion) and
(anion)OꢁH···O (anion) hydrogen bonds are found in
the structure of 3b, but the resulting anion pairing is

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
239
4.49 ppm (J=16.5 Hz) that corresponds to the
diastereotopic methylene protons and a high-field mul-
tiplet at l 10.7 ppm, which belongs to the NꢁH proton.
A perspective view of the molecular structure of 5 is
shown in Fig. 3 and a selection of relevant bond lengths
and angles is listed in Table 3. The X-ray structure of a
dichloromethane solvate clearly shows that 5 coordi-
nates in a bidentate manner as an N2-donor forming a
puckered five-membered chelate ring. The coordination
sphere at Pd(1) is close to square planar, the largest
deviation of Cl(1), Cl(2), N(1) and N(2) from their
prepared by slow addition of a dichloromethane solu-
tion of 4 into a dichloromethane solution of [(cyclocta-
1
1,5-diene)PdCl2], at room temperature. The H-NMR
spectrum of 5 contains an AB multiplet at l 4.57 and
,
mean plane being 0.100 A. The difference between the
palladium–chlorine bond lengths Pd(1)ꢁCl(1)
,
,
[2.3028(7) A)] and Pd(1)ꢁCl(2) [(2.2894(6) A] of 0.0134
,
A reflects the stronger trans influence of the pyridyl
group compared with the secondary amine. As a result,
Scheme 2.
,
Pd(1)ꢁN(1) [2.032(2) A] is significantly shorter than
,
Pd(1)ꢁN(2) [2.0557(18) A], both of which are in the
range previously reported for pyridyl-amine complexes
of palladium. The natural bite angle of 81.98(8)° for
N(1)ꢁPd(1)ꢁN(2) is smaller than the ideal value of 90°
and is similar to that of 80.82(9)° reported for the
related pyridyl-amine complex [PdLCl2] (where L=
trans,trans-1-methyl-2-pyridin-2-yl-pyrrolidine-3,4-di-
carboxylic acid dimethyl ester) [20]. While the
Cl(1)ꢁPd(1)ꢁCl(2) angle is close to 90° [91.48(2)°] the
remaining cis angles N(2)ꢁPd(1)ꢁCl(1) [93.29(6)°] and
N(1)ꢁPd(1)ꢁCl(2) [93.63(6)°] are both greater than 90°.
Although the mechanism of alkaline hydrolysis of
phosphonium salts is well understood [21,22], hydroly-
sis under acidic conditions has received much less atten-
tion. Uchida has reported the observation of ligand
coupling products on acid treatment of phosphonium
salts containing at least two 2-pyridyl groups on phos-
phorus [23]. The CꢁP bond of aryl phosphonic acids
and esters possessing electron donating groups in ortho
or para positions is known to be susceptible to acid
cleavage [24]. A mechanism leading to the unexpected
phosphine oxide product is proposed in Scheme 3.
Formation of the azaphospholium species I from the
imine 2i may be followed by nucleophilic attack at
phosphorus by water (liberated from the aldehyde dur-
ing imine formation) to give the P(V) intermediate II,
which is protonated at the pyridine nitrogen. Cleavage
of the benzylic CꢁP bond concomitant with formation
of the PꢀO is assisted by the electron withdrawing effect
of the protonated pyridine, which acts as an electron
sink. The resulting 2-alkylidene-1,2-dihydropyridine III
tautomerises to give the product 4. Interestingly, Vrieze
has prepared a hemilabile ligand that contains phos-
phine, imine and pyridyl donor groups, N-(2-
(diphenylphosphino)benzylidene)(2-(2-pyridyl)ethyl)
amine, by the condensation of 2-(diphenylphos-
phino)benzaldehyde with 2-(2-aminoethyl)pyridine [25].
This iminophosphine is stable with respect to the corre-
Fig. 3. Molecular structure of [Pd{2-Ph2P(O)C6H4NHCH2Ph}-
Cl2·CH2Cl2 (5). The CH2Cl2 molecule of crystallization has been
omitted.
Table 3
,
Selected bond distances (A) and angles (°) for 5
Bond lengths
Pd(1)ꢁN(1)
Pd(1)ꢁN(2)
Pd(1)ꢁCl(1)
Pd(1)ꢁCl(2)
N(1)ꢁC(5)
N(2)ꢁC(6)
P(1)ꢁO(1)
2.032(2)
2.0557(28)
2.3028(7)
2.2894(6)
1.356(3)
1.497(3)
1.4975(19)
Bond angles
N(1)ꢁPd(1)ꢁN(2)
Cl(1)ꢁPd(1)ꢁCl(2)
N(1)ꢁPd(1)ꢁCl(2)
N(2)ꢁPd(1)ꢁCl(1)
N(1)ꢁPd(1)ꢁCl(1)
N(2)ꢁPd(1)ꢁCl(2)
C(6)ꢁN(2)ꢁC(7)
Pd(1)ꢁN(2)ꢁC(7)
C(1)ꢁN(1)ꢁC(5)
Pd(1)ꢁN(2)ꢁC(6)
Pd(1)ꢁN(1)ꢁC(5)
Pd(1)ꢁN(1)ꢁC(1)
81.98(8)
91.48(2)
93.63(36)
93.29(6)
172.06(6)
174.24(6)
112.36(17)
116.57(14)
119.0(2)
108.09(13)
114.18(15)
125.67(17)

240
S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
Scheme 3.
sponding phosphine oxide since the cyclization to give
an azaphospholium salt cannot occur.
In an attempt to prevent formation of phosphine
1,2-H migration affords the stabilized zwitterionic inter-
mediate IV. Alternatively, I may be formed by protona-
tion using the water produced in the imine formation
and then subsequent deprotonation by the resulting
hydroxide ion would give rise to IV. Intermediate IV
readily undergoes addition to the carbonyl carbon of
oxide
4
the condensation of 2-(diphenylphos-
phino)aniline with pyridine-2-carboxaldehyde was con-
ducted in toluene, in the absence of acid. The
condensation of 2-(diphenylphosphino)aniline with pyr-
idine-2-carboxaldehyde in the absence of acid did not
give the desired pyridyl iminophosphine, 2i, but instead
resulted in addition of two equivalents of aldehyde to
give a diastereoisomeric mixture of 1,2-dipyridin-2-yl-2-
(o-diphenylphosphinoyl)phenylamino-ethanol (6). For-
tunately, X-ray quality crystals of one of the
diastereoisomers of 6 slowly deposited from the reac-
tion mixture upon prolonged standing at room temper-
1
ature. The H-NMR spectrum of this product clearly
did not correspond to either 4 or the desired pyridyl
iminophosphine and a single-crystal X-ray structure
determination was undertaken in order to unequivo-
cally establish its formulation. A perspective view of the
molecular structure of 6, together with the atomic
numbering scheme, is shown in Fig. 4 and a selection of
relevant bond lengths and angles is listed in Table 4.
Molecules of 6 are linked to give centrosymmetric
dimers in the crystal structure, through hydrogen bonds
between the hydroxy group of one molecule and the
Fig. 4. Molecular structure of the 1,2-dipyridin-2-yl-2-(o-
diphenylphosphinoyl)phenylamino-ethanol (6).
Table 4
,
Selected bond distances (A) and angles (°) for 6
Bond lengths
N(1)ꢁC(1)
N(1)ꢁC(13)
C(1)ꢁC(2)
C(2)ꢁO(1)
P(1)ꢁO(2)
,
phosphine oxide of the other [O(1)···O(2%) 2.646 A, with
1.455(2)
1.368(2)
1.529(2)
1.418(2)
1.4964(12)
an angle of 178° at H]. The amido hydrogen atom is
not involved in hydrogen bonding (Eq. (1)).
Bond angles
C(1)ꢁN(1)ꢁC(13)
C(1)ꢁC(2)ꢁC(3)
C(1)ꢁC(2)ꢁO(1)
C(3)ꢁC(2)ꢁO(1)
O(2)ꢁP(1)ꢁC(25)
O(2)ꢁP(1)ꢁC(19)
O(2)ꢁP(1)ꢁC(18)
C(18)ꢁP(1)ꢁC(25)
C(18)ꢁP(1)ꢁC(19)
C(19)ꢁP(1)ꢁC(25)
123.12(14)
110.48(14)
106.46(13)
114.38(15)
112.89(8)
110.89(7)
112.24(7)
105.97(8)
109.68(7)
104.80(8)
(1)
A mechanism accounting for the formation of 6 is
proposed in Scheme 4. In the absence of an acid, the
azaphospholium species I does not form and instead

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
241
Scheme 4.
another molecule of pyridine-2-carboxaldehyde, in
much the same manner that one aldehyde molecule
adds to the carbonyl carbon atom of another in the
cyanide mediated benzoin condensation i.e. the electron
withdrawing power of the pyridyl group facilitates loss
of the proton in much the same manner as the CN−
increases the acidity of the aldehyde CꢁH [26].
respectively, within the ligand are significantly less than
the ideal value of 90°. The small natural bite angle of
the iminophosphine manifests itself in an expansion of
the cis angles between the ligands, namely,
P(1)ꢁNi(1)ꢁN(3) [100.55(9)°] and P(2)ꢁNi(1)ꢁN(1)
[97.75(10)°], which are substantially greater than the
ideal value of 90°. The angle formed by the two imine
nitrogen atoms is N(1)ꢁNi(1)ꢁN(3) is 177.48(13)° while
the two remaining trans angles P(1)ꢁNi(1)ꢁN(2)
[157.53(10)°] and P(2)ꢁNi(1)ꢁN(4) [158.21(10)°] are con-
siderably smaller, the compression presumably resulting
from the less than 90° bite angles associated with the
five-membered chelate rings. The sum of the angles at
N(3) [359.9°] and N(1) [359.9°] together with the short
Since template reactions involving condensation be-
tween a carbonyl compound and a metal coordinated
primary amine have been used extensively for the
stereospecific synthesis of complex macrocyclic ligands
[27], it seemed reasonable to believe that this strategy
could be used to prepare pyridyl iminophosphine 2i.
Indeed, we have successfully prepared the target
iminophosphine via a template reaction involving con-
densation of the 2-(diphenylphosphino)aniline complex
[Ni(2-PPh2C6H4NH2)2][NO3]2 with pyridine-2-carbox-
aldehyde, according to Eq. (2). Addition of pyridine-2-
carboxaldehyde to a dichloromethane solution of
[Ni(2-PPh2C6H4NH2)2][NO3]2 resulted in the rapid ap-
pearance of a deep purple coloration. After stirring
overnight, X-ray quality crystals of 7 were obtained by
slow diffusion of diethyl ether into the reaction mixture,
at room temperature. The molecular structure of 7 is
shown in Fig. 5, a selection of bond lengths and angles
is listed in Table 4 and crystal data is provided in Table
1. The structure is based on a distorted octahedron and
the two iminophosphines adopt a meridional configura-
tion with the two phosphorus donors and the two
pyridyl nitrogen donors cis and the two imino N-
donors trans. The coordinated iminophosphine forms a
five-membered ring by P,N chelation and another by
N,N chelation. The distortion from octahedral geome-
try is clearly evident from the NꢁNi(1)ꢁP and
NꢁNi(1)ꢁN angles. The P(1)ꢁNi(1)ꢁN(1) and
P(2)ꢁNi(1)ꢁN(3) angles of 81.91(10) and 81.19(10)°,
N(3)ꢁC(31) and N(1)ꢁC(7) bond distances of 1.274(5)
2
,
and 1.276(5) A, respectively, are consistent with sp -hy-
bridization and characteristic of a coordinated imine.
The CꢁN bond lengths of coordinated iminophosphines
,
can range from 1.25 to 1.442 A.
Fig. 5. Molecular structure of [Ni{2-Ph2PC6H4NꢀC(H)C5H4-
N}2][NO3]2·5CH2Cl2 (7). Hydrogen atoms and the CH2Cl2 molecules
of crystallization have been omitted. Key atoms are labeled.
respectively,
and
the
N(1)ꢁNi(1)ꢁN(2)
and
N(3)ꢁNi(1)ꢁN(4) angles of 78.98(13) and 79.28(13)°,

242
S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
(2)
3.2. Iminophosphine coordination chemistry
Fig. 6. Molecular structure of [Pd{2-PPh2C6H4NꢀC(H)Ph}-
Cl2]·0.5CH2Cl2 (8a). The solvent molecule has been omitted.
Dropwise addition of a dichloromethane solution of
iminophosphine 2a into a dichloromethane solution of
[(cycloocta-1,5-diene)PdClX] (X=Cl, Me) resulted in
near quantitative formation of [Pd{2-Ph2PC6H4-
NꢀC(H)Ph}ClX] (X=Cl, 8a; X=Me, 8b). The
31P{1H}-NMR spectrum of 8a contains a singlet at l
35.6 ppm and that of 8b a singlet at l 36.1 ppm, the
latter being consistent with the formation of a single
coordination isomer, most likely that with the methyl
trans to the imino-nitrogen atom. A high-field doublet
1
at l 1.49 ppm (JPH=7.5 Hz) in the H-NMR spectrum
of 8b corresponds to the palladium-bound methyl and a
broad singlet at l 8.59 ppm belongs to the imine NꢁH.
The magnitude of this coupling is consistent with a cis
arrangement of methyl and phosphorus in the coordi-
nation sphere of palladium [28], as would be expected
for two groups exhibiting a large trans influence [29].
Both compounds are air stable for prolonged periods,
in the solid state and in solution, and dissolve readily in
polar solvents. Single-crystal X-ray structure determina-
tions of 8a and 8b have been undertaken to obtain
precise details of the structures and to compare with
that of [Pd{2-Ph2PC6H4NꢀC(H)Ph}PhI], which has re-
cently appeared in the literature. The molecular struc-
tures of 8a and 8b are shown in Figs. 6 and 7,
respectively, and a selection of bond lengths and angles
for both compounds is listed in Tables 5 and 6. Since
the structures of both compounds are based on palla-
dium complexes of iminophosphines and are clearly
related they will be discussed in parallel. In both cases
the coordination sphere around Pd(1) is close to square
planar, as indicated by the dihedral angles of 12.1 and
15.9°, for 8a and 8b, respectively, between the planes
containing P(1)Pd(1)N(1) and Cl(1)Pd(1)X. The natural
bite angles of 82.10(6)° (8a) and 80.65(8)° (8b) are
similar to those reported for related complexes includ-
ing [Pd{2-Ph2PC6H4NꢀC(H)Ph}PhI] [80.3(2)°] and
[Pd2(2.2%-bis{N-[(2-diphenylphosphino)phenyl] formimi-
doyl}biphenyl)Cl2Me2] [79.70(11)°] [7,30] and signifi-
cantly smaller than the ideal value of 90°. The PdꢁCl
Fig. 7. Molecular structure of [Pd{2-PPh2C6H4NꢀC(H)Ph}ClMe]
(8b).
Table 5
,
Selected bond distances (A) and angles (°) for 7
Bond lengths
Ni(1)ꢁN(1)
Ni(1)ꢁN(2)
Ni(1)ꢁN(3)
Ni(1)ꢁN(4)
Ni(1)ꢁP(1)
Ni(1)ꢁP(2)
N(1)ꢁC(7)
N(3)ꢁC(31)
2.045(3)
2.117(3)
2.056(3)
2.079(3)
2.3795(11)
2.4090(12)
1.276(5)
1.274(5)
Bond angles
P(1)ꢁNi(1)ꢁN(2)
P(2)ꢁNi(1)ꢁN(4)
N(1)ꢁNi(1)ꢁN(3)
P(1)ꢁNi(1)ꢁN(1)
P(1)ꢁNi(1)ꢁN(4)
P(1)ꢁNi(1)ꢁN(3)
P(2)ꢁNi(1)ꢁN(3)
P(2)ꢁNi(1)ꢁN(1)
P(2)ꢁNi(1)ꢁN(2)
P(2)ꢁNi(1)ꢁP(1)
N(2)ꢁNi(1)ꢁN(3)
N(1)ꢁNi(1)ꢁN(4)
N(3)ꢁNi(1)ꢁN(4)
N(2)ꢁNi(1)ꢁN(4)
N(1)ꢁNi(1)ꢁN(2)
157.53(10)
158.21(10)
177.48(13)
81.91(10)
89.70(9)
100.55(9)
81.19(10)
97.75(10)
90.90(9)
103.35(4)
98.72(13)
101.36(13)
79.28(13)
82.62(13)
78.98(13)
,
bond trans to phosphorus [2.3866(6) A] in 8a is signifi-
,
cantly longer than that trans to nitrogen [2.2859(6) A]
and reflects the stronger trans influence of the
diphenylphosphino group compared with an imine. The
molecular structure of 8b clearly shows that the methyl

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
243
The terdentate iminophosphine 2d was reacted with
[(cyclocta-1,5-diene)PdClMe] in dichloromethane. After
stirring overnight the cationic palladium complex
[Pd{2-PPh2C6H4NꢀC(H)C6H4PPh2}Me]+ (9a) was iso-
lated as its [SnMe3Cl2]−, salt by crystallization from a
dichloromethane solution layered with hexane. The
31P{1H}-NMR spectrum of 9a contains two signals
which appear as an AB quartet at l 38.4 and 31.4
(JPP=392.1 Hz), as expected for terdentate coordina-
group occupies the site trans the imine nitrogen
[N(1)ꢁPd(1)ꢁC(1)=173.96(14)°]. The difference of
0.133 A between the Pd(1)ꢁN(1) bond lengths in 8a
,
,
[Pd(1)ꢁN(1)=2.053(2) A] and 8b [Pd(1)ꢁN(1)=
,
2.196(3) A] reflects the much greater trans influence of
methyl compared with chloride. Not surprisingly, the
,
PdꢁP bond lengths in 8a [Pd(1)ꢁP(1)=2.2104(6) A] and
8b [Pd(1)ꢁP(1)=2.2004(10) A] are similar as a result of
,
both being trans to chloride. The PdꢁCl bond trans to
2
tion of 2d, and the magnitude of JPP is consistent with
,
phosphorus in 8a [Pd(1)ꢁCl(2)=2.3866(6) A] is similar
a trans arrangement of diphenylphosphino groups [33].
The presence of two high-field signals, a triplet at l 0.53
(JPH=6.1 Hz) and a singlet at l 0.69 ppm, the latter
flanked by satellite peaks, provided the first indication
that the palladium complex was not formed as its
chloride salt. Moreover, the 1:3 intensity of these high-
field signals strongly suggests that the counterion is in
fact [SnMe3Cl2]−, which is most likely formed by ab-
straction of chloride from [Pd{2-PPh2C6H4Nꢀ
C(H)C6H4PPh2}Me][Cl] by SnMe3Cl, which is present
in the reaction mixture as a byproduct formed during
the preparation of [(cyclocta-1,5-diene)PdMeCl] via se-
lective methylation of [(cyclocta-1,5-diene)PdCl2] with
tetramethyltin [12]. Treatment of a dichloromethane
in length to the comparable bond in 8b [Pd(1)ꢁCl(1)=
,
2.3834(9) A], both of which are within the range ex-
pected for palladium complexes of iminophosphines
including
[2.3734(11) A], [Pd{2-(diphenylphosphino)-benzylidene-
[Pd{2-PPh2C6H4C(H)ꢀNC6H3Pri2}MeCl]
,
,
S(−)-a-methylbenzylamine}ClX] [X=Cl, 2.370(2) A;
X=Me, 2.371(3) A] and [Pd2(L H)Cl2Me2] [2.3837(9)
A] (L H=1,3-bis[(2-(diphenylphosphino)benzylidene)-
1
,
1
,
amino]-propan-2-ol) [5,31,32].
Table 6
,
Selected bond distances (A) and angles (°) for 8a and 8b
8a
8b
solution
of
[Pd{2-PPh2C6H4NꢀC(H)C6H4PPh2}-
Bond lengths
Pd(1)ꢁP(1)
Pd(1)ꢁN(1)
Pd(1)ꢁCl(1)
Pd(1)ꢁCl(2)
N(1)ꢁC(7)
Me][SnMe3Cl2] with a slight excess of [PPN][Cl] re-
sulted in clean and quantitative anion exchange to give
[Pd(2-PPh2C6H4NꢀC(H)C6H4PPh2)Me][Cl] (9b). This
formulation is supported by elemental analysis, as well
2.2104(6)
2.063(2)
2.2859(6)
2.3866(6)
1.297(3)
Pd(1)ꢁP(1)
Pd(1)ꢁN(1)
Pd(1)ꢁCl(1)
Pd(1)ꢁC(1)
N(1)ꢁC(8)
2.2004(10)
2.196(3)
2.3834(9)
2.028(3)
1.281(4)
1
as H-NMR spectroscopy, which shows the disappear-
ance of the high-field singlet associated with the
[SnMe3Cl2] anion. A single-crystal X-ray structure de-
termination of 9b has been undertaken to provide
precise details on the mode of coordination of 2d. A
perspective view of the molecular structure is shown in
Fig. 8 and a selection of bond lengths and angles is
listed in Table 7, while crystal data is provided in Table
1. The molecular structure clearly reveals that 2d coor-
dinates in a terdentate manner, forming a five-mem-
bered ring by chelating P(2)N(1) and a six-membered
ring by chelating P(2)N(1). There is two fold disorder
of orientation of the ligand, equivalent to exchange of
N(1) and C(8); both disorder components have essen-
tially the same geometry, and only one is presented
here. The coordination sphere around palladium is
close to square-planar, as indicated by a root-mean
Bond angles
P(1)ꢁPd(1)ꢁN(1)
Cl(1)ꢁPd(1)ꢁCl(2) 91.68(2)
P(1)ꢁPd(1)ꢁCl(1) 90.89(2)
N(1)ꢁPd(1)ꢁCl(2) 95.95(6)
N(1)ꢁPd(1)ꢁCl(1) 172.01(6)
P(1)ꢁPd(1)ꢁCl(2) 168.32(2)
C(6)ꢁN(1)ꢁC(7)
Pd(1)ꢁN(1)ꢁC(6) 113.15(15)
Pd(1)ꢁN(1)ꢁC(7) 129.57(18)
82.10(6)
P(1)ꢁPd(1)ꢁN(1)
Cl(1)ꢁPd(1)ꢁC(1)
P(1)ꢁPd(1)ꢁC(1)
N(1)ꢁPd(1)ꢁCl(1)
N(1)ꢁPd(1)ꢁC(1)
P(1)ꢁPd(1)ꢁCl(1)
C(7)ꢁN(1)ꢁC(8)
Pd(1)ꢁN(1)ꢁC(7)
Pd(1)ꢁN(1)ꢁC(8)
80.65(8)
89.92(12)
93.82(12)
96.06(8)
173.96(14)
163.98(3)
118.3(3)
108.7(2)
132.8(2)
117.1(2)
,
square deviation of the coordinating atoms of 0.100 A
from their mean plane. The PdꢁP bond lengths
,
,
[Pd(1)ꢁP(1)=2.2648(14) A, Pd(1)ꢁP(2)=2.2742(14) A]
are in the range expected for palladium complexes with
a trans arrangement of diphenylphosphino groups such
as [Pd{1,8-bis(diphenylphosphino)-3,6-dioxaoctane}Cl2]
[34] and [Pd{1,11-bis(diphenylphosphinomethyl)benzo-
[c]phenanthrene}Cl2] [35]. The Pd(1)ꢁN(1) bond length
Fig. 8. Molecular structure of [Pd{2-PPh2C6H4NꢀC(H)C6H4-2-
PPh2}CH3][Cl]·2CH2Cl2 (9b). Solvent molecule, chloride anion and
disorder are omitted.
,
,
of 2.136(9) A is similar to that of 2.063(2) A in [Pd{2-
PPh2C6H4NꢀC(H)Ph}Cl2] and 2.020(3) A in [Pd{2-
,

244
S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
Table 7
phino–ketoiminate complex [Ni{2-Ph2PC6H4NꢀC-
(Me)CHC(O)Me}Cl] (10), according to Eq. (3). The
31P{1H}-NMR spectrum of 10 contains a sharp singlet
at l 22.7 ppm, in the region characteristic of a coordi-
,
Selected bond distances (A) and angles (°) for 9b
Bond lengths
Pd(1)ꢁP(1)
Pd(1)ꢁP(2)
Pd(1)ꢁN(1)
Pd(1)ꢁC(1)
N(1)ꢁC(8)
2.2648(14)
2.2742(14)
2.136(9)
2.052(6)
1.264(16)
1
nated diphenylphosphino group. In the H-NMR spec-
trum two singlets at l 1.84 and 1.94 ppm, each of
intensity 3H, correspond to the two methyl substituents
of the ketoiminate fragment and a singlet at l 4.94
ppm, intensity 1H, belongs to the methine proton. The
formulation shown in Eq. (3) is also supported by
elemental analysis and EIMS, where the parent molecu-
lar ion gives rise to the most abundant peak in the mass
spectrum.
Bond angles
P(1)ꢁPd(1)ꢁP(2)
P(1)ꢁPd(1)ꢁN(1)
P(2)ꢁPd(1)ꢁN(1)
C(1)ꢁPd(1)ꢁP(1)
C(1)ꢁPd(1)ꢁP(2)
N(1)ꢁPd(1)ꢁC(1)
C(8)ꢁN(1)ꢁC(9)
Pd(1)ꢁN(1)ꢁC(8)
Pd(1)ꢁN(1)ꢁC(9)
173.63(6)
94.4(3)
80.1(3)
93.24(17)
92.62(17)
169.2(3)
113.7(8)
127.8(8)
118.4(6)
(3)
Since platinum group complexes of terdentate ligands
containing three different donor groups are relatively
rare [37] a single-crystal X-ray structure determination
of 10 was undertaken to confirm the mode of binding
and to provide precise structural details of the metal’s
coordination environment. A perspective view of one of
the two independent molecules is shown in Fig. 9 and a
selection of relevant bond lengths and angles is listed in
Table 8 and crystal data is provided in Table 1. The
molecular structure reveals that 10 coordinates in a
terdentate manner, as a monobasic ligand, and forms a
distorted square-planar complex, as evidenced by the
dihedral angle of 9.5° between the planes containing
Ni(1)O(1)N(1) and Ni(1)P(1)Cl(1) (6.5° for the second
Fig. 9. Molecular structure of one of the two independent molecules
of [Ni{2-PPh2C6H4NC(Me)C(H)C(Me)O}Cl] (10).
PPh2C6H4NꢁC(H)C6H4-4-Cl-2-O}Cl2]. The P(1)Pd(1)-
N(1) bite angle of 94.4(3)° is significantly larger than
that of 80.1(3)° for P(2)Pd(1)N(1) and is similar to
those previously reported for related compounds in-
cluding [Pd2(L1)(OAc)2][BF4] [95.36(17)°] and [Pd2(L1)-
Me2][BF4] [94.47(11)° and 93.78(11)°] (L1H=1,3-bis[(2-
(diphenylphosphino)benzylidene)amino]-propan-2-ol)
,
molecule). The NiꢁCl bond length of 2.171(2) A is
similar to those reported for related nickel complexes
such as [Ni{2-PPh2C5H4NꢀC(H)C6H4-2-O}Cl] [2.187(1)
,
,
A], [Ni{2-PPh2C6H4C(H)ꢀNC6H4-2-O}Cl] [2.148(3) A]
and [Ni{Ph2PC6H4NC(H)C6H3-5-Br-2-O}Cl] [2.1857(8)
,
A], reported earlier by Parr and coworkers [38]. The
Ni···O(1) six-membered chelate ring is somewhat dis-
and
[Pd{N-(2-(diphenylphosphino)benzylidene)(2-(2-
,
torted from planar, Ni(1) being displaced by 0.475 A
pyridyl)ethyl)amine}Me][CF3SO3] [91.87(13)°]. While
PꢁPdꢁN bite angles in palladium complexes of
iminophosphines that form six-membered chelate rings
are generally larger than those that form five-membered
rings, the latter appear to be extremely flexible and
cover a broad range (84–95°). The trans angles
P(1)Pd(1)P(2) 173.63(6)° and N(1)Pd(1)C(1) 169.2(3)°
are slightly less than 180°, such distortions being com-
mon in platinum group complexes of P2N ligands coor-
dinated in a terdentate manner [36].
from the plane containing the remaining five atoms
,
(0.587 A for the second molecule). The ketoiminate
nitrogen atom N(1) is close to planar (sum of angles=
,
359.7°) and the N(1)ꢁC(3) bond distance of 1.335(9) A
is comparable to the CꢁN distances of 1.311(3) and
,
1.321(5) A in the iminophosphine complex [Ni{2-
PPh2C6H4NꢀC(H)C6H4O}Cl] [38] and the ketoiminate
complex [Zr{CH3C(NPh)CH(O)CH3}2Cl2] [39], respec-
tively. The bond length pattern within the six-mem-
bered ring system suggests significant delocalization of
bonding electron density as evidenced by a difference of
Addition of NaH to a dichloromethane solution con-
taining [NiCl2(PPh3)2] and 2-Ph2PC6H4NꢀC(Me)-
CH2C(O)Me resulted in a dramatic color change from
green to deep amber with the formation of the phos-
,
,
only 0.026 A in the C(1)ꢁC(2) [1.389(12) A] and
,
C(2)ꢁC(3) [1.415(11) A] bond lengths, which is signifi-

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
245
cantly smaller than the comparable difference in
,
[Ti{CH3(O)CHC(NCH2CH2O)}Cl2(THF)] (0.071 A)
,
[40]. The NiꢁO bond length of 1.877(5) A is similar to
those reported for Ni(II) complexes of related
iminophosphine
ligands
including
[Ni{2-
,
PPh2C6H4NꢀC(H)-2-C6H4-2-O}Cl] [1.863(25) A] and
,
[Ni{2-PPh2C6H4CHꢀNC6H4-2-O}Cl] [1.875(51) A], and
,
similarly, the NiꢁN bond length of 1.882(7) A is com-
,
parable to those of 1.89(2) and 1.900(7) A in the same
two compounds, respectively [38].
3.3. Catalysis
Recent reports of the use of bidentate iminophosphi-
nes in platinum group catalyzed reactions including the
palladium catalyzed Heck arylation, the copolymeriza-
tion of ethylene with carbon monoxide and the ruthe-
nium catalyzed hydrogen transfer reduction of ketones
prompted us to evaluate the efficiency of iminophosphi-
nes 2a–h in the Suzuki cross coupling reaction and the
hydrosilylation of ketones. The Suzuki reaction is a
powerful method for the formation of C(sp2)ꢁC(sp2)
bonds which offers immense potential in organic syn-
thesis [41]. Preliminary studies have been restricted to
coupling of the electronically activated substrate 4-bro-
moacetophenone with phenyl boronic acid (Eq. (4)) by
catalysts based on mixtures of 2a–i and [Pd2(OAc)6],
[Pd2(dba)3] and [Pd(MeCN)2Cl2]. The results are sum-
marized in Charts 1 and 2, the former containing
conversion using catalysts based on aprotic iminophos-
phines 2a–d and the latter contain conversions ob-
tained using monobasic terdentate phosphines 2f–g and
Chart 1. Conversion in the Suzuki coupling reaction between bro-
mobenzene and phenylboronic acid. (A) Tris(2-tolyl)phosphine. (B)
Tris(2,4-di-tert-butylphenyl)phosphite.
Table 8
,
Selected bond distances (A) and angles (°) for 10
Molecule a
Molecule b
Bond lengths
Ni(1)ꢁP(1)
Ni(1)ꢁN(1)
Ni(1)ꢁO(1)
Ni(1)ꢁCl(1)
N(1)ꢁC(3)
O(1)ꢁC(1)
C(1)ꢁC(2)
C(2)ꢁC(3)
Chart 2. Conversion in the Suzuki coupling reaction between bro-
mobenzene and phenylboronic acid. (A) Tris(2-tolyl)phosphine. (B)
Tris(2,4-di-tert-butylphenyl)phosphite.
2.142(2)
1.882(7)
1.877(5)
2.171(2)
1.335(9)
1.264(9)
1.389(12)
1.415(11)
Ni(2)ꢁP(2)
Ni(2)ꢁN(2)
Ni(2)ꢁO(2)
Ni(2)ꢁCl(2)
N(2)ꢁC(26)
O(2)ꢁC(24)
C(24)ꢁC(25)
C(25)ꢁC(26)
2.130(2)
1.892(6)
1.880(6)
2.179(2)
1.337(10)
1.279(9)
1.387(12)
1.371(12)
the amino-diphosphines 2g. Cross coupling reactions
were carried out in dioxane by combining the palla-
dium precursor, iminophosphine and substrates and
heating at 70 °C for 2 h and the extent of reaction
monitored by GC. Herrman [42] and Bedford [43] have
recently shown that palladacycles 11 and 12, formed
from tris(2-tolyl)phosphine (A) and tris(2,4-di-tert-
butylphenyl)phosphite (B), respectively, are highly ac-
tive for the Suzuki cross coupling reaction, giving TON
in excess of 106. Thus, catalyst mixtures generated from
Bond angles
P(1)ꢁNi(1)ꢁCl(1)
P(1)ꢁNi(1)ꢁN(1)
N(1)ꢁNi(1)ꢁO(1)
O(1)ꢁNi(1)ꢁCl(1)
91.54(9)
85.7(2)
95.0(3)
P(2)ꢁNi(2)ꢁCl(2)
P(2)ꢁNi(2)ꢁN(2)
N(2)ꢁNi(2)ꢁO(2)
O(2)ꢁNi(2)ꢁCl(2)
N(2)ꢁNi(2)ꢁCl(2) 174.9(2)
P(2)ꢁNi(2)ꢁO(2) 174.06(19)
C(26)ꢁN(2)ꢁC(29) 122.0(7)
Ni(2)ꢁN(2)ꢁC(26) 119.3(6)
Ni(2)ꢁN(2)ꢁC(29) 117.7(5)
Ni(2)ꢁO(2)ꢁC(24) 123.8(6)
89.23(9)
85.8(2)
93.8(3)
88.25(18)
91.02(18)
N(1)ꢁNi(1)ꢁCl(1) 175.8(2)
P(1)ꢁNi(1)ꢁO(1)
C(3)ꢁN(1)ꢁC(6)
Ni(1)ꢁN(1)ꢁC(3)
Ni(1)ꢁN(1)ꢁC(6)
Ni(1)ꢁO(1)ꢁC(1)
170.81(18)
119.5(7)
123.2(6)
117.0(5)
123.8(5)
tris(2-tolyl)phosphine
(A)
and
tris(2,4-di-tert-
butylphenyl)phosphite (B) and a variety of palladium
sources have been used as standards under our reaction
conditions.

246
S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
via interaction of boron with the oxygen donor. Fur-
(4)
ther studies are required to investigate and determine
the origin of catalyst deactivation. Encouragingly, un-
der our conditions, the efficiency of the Pd2(OAc)6/2a–
d catalyzed Suzuki couplings compare favorably with
those of the standards.
Comparison of Charts 1 and 2 reveals a clear distinc-
tion between the performance of catalysts formed from
2a to d and these based on 2f–g. Firstly, catalyst
mixtures of 2a–d are more efficient at cross coupling
than their monobasic counterparts 2f–h, which consis-
tently resulted in less than 8% conversion. In the case of
catalysts based on 2a–d there is a marked dependence
of catalyst efficiency on the metal precursor, those
formed using [Pd2(OAc)6] consistently giving higher
conversions than those formed using [Pd2(dba)3] and
[PdCl2(MeCN)2]. The efficiency of palladium catalyzed
Suzuki coupling reactions is known to depend on the
palladium source, as well as a number of other vari-
ables including additives, solvent, temperatures and
base [42]. The dependence of catalyst efficiency on the
palladium source is clearly evident in the conversions
based on the amino-diphosphine 2h, which ranged from
2% using [Pd2(dba)3] to 53% using [Pd2(OAc)6]. Incor-
poration of an additional hard protic donor such as
OH clearly deactivates the catalyst (Chart 2, entries
2f–g), which could be due to formation of an adduct
Feringa and coworkers have recently reported that
the dinuclear rhodium complex [Rh2L1(CO)2][BF4],
where L1H corresponds to 1,3-bis[(2-(diphenylphos-
phino)benzylidene)amino]propan-2-ol) is an effective
catalyst for the hydrosilylation of acetophenone [32],
the addition of one of the SiꢁH bonds of Ph2SiH2 to the
carbonyl carbon to give the corresponding silyl ether
which can be hydrolyzed to 1-phenylethanol (Eq. (5)).
Hydrosilylation reactions were carried out in a multi-
well reactor running Crabtree’s (13) and Wilkinson’s
(14) catalysts in parallel as standards and the extent of
reaction monitored by GC. As shown in Charts 3 and
4 mixtures of [Ir(COD)Cl]2 and iminophosphines 2a–h
catalyze the room temperature hydrosilylation of ace-
tophenone, with conversions reaching 74% after 18 h.
The most effective catalysts are those based on the
monobasic terdentate iminophosphines 2f–g while
those based on the amino-diphosphines 2i resulted in
poor conversions (B30%). Notably, there are only
minor differences in the extent of conversion between
reactions conducted under argon and in air.
(5)
Chart 3. Conversion in the hydrosilylation of acetophenone.
4. Conclusions
Acid catalyzed condensation of 2-(diphenylphos-
phino)aniline has been used to prepare a range of
neutral and monobasic bi- and terdentate iminophos-
phines. In the presence of a stoichiometric amount of
acid, 2-(diphenylphosphino)aniline reacts with ben-
zaldehyde, acetophenone and salicylaldehyde to give
the corresponding 2,3-dihydro-1H-benzo[1,3]azaphos-
phol-3-ium salts. The acid catalyzed reaction between
2-(diphenylphosphino)aniline and pyridine-2-carbox-
aldehyde does not give the corresponding pyridyl
iminophosphine but affords N-(pyridin-2-ylmethyl)-2-
diphenylphosphinoylaniline. In the absence of acid, 2-
(diphenylphosphino)aniline reacts with two equivalents
Chart 4. Conversion in the hydrosilylation of acetophenone.

S. Doherty et al. / Journal of Organometallic Chemistry 650 (2002) 231–248
247
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