J. Am. Chem. Soc. 1998, 120, 2973-2974
2973
planar compounds of the type [NiCl(PR3)(PNHMe)]+ (R3
Ph2Me, PhMe2, and Me3).
)
Synthesis and Characterization of the First
Mononuclear NiII Phosphorane Imino Complex
On the other hand, when equimolar amounts of [NiCl2(PMe3)2]
and PNH2 were reacted in the presence of KPF6, molecular
hydrogen was evolved,8 and complexes 39 (21% yield), cis-
[Ni(PNH)2] (5),10 and cis-[Ni(PNH2)2]2+ (6)10 were formed. 31P
NMR control spectra of the reaction mixture, performed after 20
min, indicated that the solution also contained 2 (two broad signals
centered at 40.2 and -4.9 ppm),11 a small amount of 3, and
[HPMe3]+. The signals arising from 2 disappear with time, as
those for 3 and 5 concomitantly increase. Free PNdPMe3 12 can
be recovered from complex 3, by treatment with sodium cyanide
in a H2O/C6H6 mixture.
On the basis of these findings, one can propose the reaction
pathways shown in Scheme 1. Here the NiII ion makes the N-H
bonds of the coordinated phosphino amine in 2 sufficiently acidic
to be deprotonated by the free PMe3 present in solution with
formation of [HPMe3]+ and the amido complex 2*. The latter
reacts further through two competitive routes. The first one, A,
produces the cationic bis-substituted phosphino amino derivative
6 through the intermediates binuclear 4 and uncharged 5. The
second one, B, consists of the nucleophilic attack of the activated
amido nitrogen of 2* at the trimethylphosphonium cation giving
3*. This step is followed by the intramolecular redox reaction
which affords molecular hydrogen and the ylide-type fragment.
The phosphorane imine ligand remains coordinated to the NiII
ion as a neutral chelating agent.
Laura Crociani, Francesco Tisato,* Fiorenzo Refosco,
Giuliano Bandoli, Benedetto Corain, and Luigi M. Venanzi
ICTIMA-C.N.R., C.so Stati Uniti 4, 35020 PadoVa, Italy
Dipartimento di Scienze Farmaceutiche
Via Marzolo 5, 35131 PadoVa, Italy
Dipartimento di Chimica Ingegneria
Chimica e Materiali, Via Vetoio Coppito Due
67010 L’Aquila, Italy
Centro Studio Stabilita` ReattiVita`
Composti di Coordinazione
CNR, Via Marzolo 1, 35131 PadoVa, Italy
ETH Zentrum Laboratorium fu¨r Anorganische
Chemie UniVersita¨strasse 6
CH-8092 Zu¨rich, Switzerland
ReceiVed NoVember 10, 1997
A recent contribution by Klein et al. describes the first examples
of NiII phosphorane imido complexes.1 These diamagnetic
clusters, prepared by photochemical activation of the [NiCl(N3)-
(PMe3)2] azido precursor contain the trimethylphosphorane imido
ligand as a triply bridging group. The authors suggest that their
formation involves a nitrene intermediate which traps PMe3 from
the reaction mixture giving the phosphorane imido moiety,
Me3PdN-. Further examples of tetrametallic paramagnetic NiII
phosphorane imido clusters of the type [NiX(NPEt3)]4 (X ) Cl,
Br) have been reported by Dehnicke et al.2
(8) To confirm the evolution of H2, a gentle stream of N2 was bubbled
through the reaction mixture and the volatile products were collected by a
cannula in an aqueous solution containing Na2PdCl4. A black powder (metallic
Pd) accumulated in the aqueous solution according to the reduction PdII
Pd° operated by H2.
f
(9) Synthesis of [NiCl(PMe3)(PNdPMe3)]PF6 (3): (a) From [NiCl2(PMe3)2].
To a mixture of [NiCl2(PMe3)2] (0.115 g, 0.40 mmol) and KPF6 (0.110 g,
0.59 mmol) in CH2Cl2 (10 mL) was added solid PNH2 (0.114 g, 0.41 mmol).
After 3 h of stirring at room temperature, a whitish precipitate (excess of
KPF6 and KCl) was filtered off. The filtrate was concentrated to 5 mL and
treated with Et2O (15 mL), which afforded initially an oil and, after vigorous
stirring, gave a brown solid. This solid was collected by filtration and washed
with water (3 mL), Et2O (2 × 5 mL), and MeOH (0.5 mL). The resulting red
compound was recrystallized from a CH2Cl2/MeOH/C6H6 mixture (3/1/3) and
dried under vacuum (0.057 g, 21.5%). Crystals suitable for X-ray analysis
We report here the synthesis and characterization of the
unprecedented mononuclear NiII N-arylphosphino-substituted
phosphorane imino complex [NiCl(PMe3)(PNdPMe3)]PF6 (3) and
of the corresponding free ligand (o-diphenylphosphino)-N-(trim-
ethylphosphoranyl)phenylimine (PNdPMe3). Complex 3 is
formed when (o-diphenylphosphino)aniline (PNH2) is present in
the coordination sphere of the NiII phosphino amino starting
compounds, as in [NiCl2(PMe3)(PNH2)] (1)3 or [NiCl(PMe3)-
(PNH2)]PF6 (2).4 Evidence is also provided that the presence of
[HPMe3]+ in solution and the evolution of molecular hydrogen
play key roles in the formation of 3.
During our studies of the reactivity of chelating phosphino
amines with [NiCl2(PMe3)2], it was found that the bidentate
phosphino amine (o-diphenylphosphino)-N-methylaniline (PN-
HMe) gave first a stable five-coordinated intermediate,5,6 which,
in the presence of KPF6, produced the expected cationic5,7 square-
1
were grown by slow evaporation of acetone solutions. H NMR (200 MHz,
2
2
CD2Cl2): δ 1.14 (d, J(HP) ) 12 Hz, 9 H; P[CH3]3), 1.88 (d, J(HP) ) 13
Hz, 9 H; NdP[CH3]3), 6.50-7.90 (m, 19 H; aromatic). 31P{1H} NMR (200
MHz, CD2Cl2): δ -144.3 (septet, J(PF) ) 713 Hz, 1P; PF6), -12.6 (dd,
2J[P(2)P(1)] ) 108 Hz, 3J(P(2)P(3)) ) 5 Hz, 1P; P(2)[CH3]3), 37.9 (d,
2J[P(1)P(2)] ) 108 Hz, 1P; P(1)NdP(3)[CH3]3), 41.8 (d, 3J[P(3)P(2)] ) 5
Hz, 1P, P(1)N)P(3)[CH3]3). (b) From complex 1. To a solution of 1 (0.143
g, 0.3 mmol) in CH2Cl2 (10 mL) was added an excess of KPF6 (0.074 g, 0.4
mmol) under stirring at room temperature. After 3 h, the inorganic salts were
filtered off and the filtrate was concentrated to 5 mL and treated with Et2O
(20 mL) to give an oil and, finally, a brown powder as above. This solid was
redissolved in EtOH (5 mL), and after the solution was allowed to stand in a
closed test tube for 3 days, crystals of complex 3 (yield 9%) were obtained.
This yield can be improved by addition of 1 equiv of both [HPMe3]+ and
2,4-lutidine to the starting reaction mixture containing complex 1 and excess
KPF6. After the reaction was completed as above, an additional equimolar
amount of [PPh4]Cl was added as internal standard and an aliquot of the
mixture was subjected to 31P NMR. Relative integration yield a NiII complex
3/tetraphenylphosphonium cation ratio of 85/100.
(1) Klein, H. F.; Haller, S.; Ko¨nig, H.; Dartiguenave, M.; Dartiguenave,
Y.; Menu, M. J. J. Am. Chem. Soc. 1991, 113, 4673-4675.
(2) Mai, H.-J.; Kang, H.-C.; Wocadlo, S.; Massa, W.; Dehnicke, K. Z.
Anorg. Allg. Chem. 1995, 621, 1963-1968.
24
(3) Synthesis of [NiCl2(PMe3)(PNH2)] (1): Solid PNH2 (0.315 g, 1.14
mmol) was added to a blood red solution of [NiCl2(PMe3)2] (0.319 g, 1.12
mmol) in CH2Cl2 (15 mL). The solution immediately turned red-violet. After
1 h of stirring under N2 at room temperature, the reaction mixture was
concentrated to 5 mL and treated with n-hexane (25 mL) to give a blue
precipitate. The solid was filtered off, washed with n-hexane (2 × 5 mL),
C6H6 (1 mL) and Et2O (5 mL), and dried under vacuum (0.471 g, 87.0%). 1H
NMR (200 MHz, CDCl3): δ 1.29 (s, 9 H; P[CH3]3), 2.53 (bs, 2 H; NH2),
7.97-7.10 (m, 14 H; aromatic).
(10) Cooper, M. K.; Downes, J. M.; Duckworth, P. A.; Tiekink, E. R. T.
J. Chem. Soc., Dalton Trans. 1989, 1067-1073.
(11) Related square-planar complexes [NiCl(PMe2Ph)(PNMe2)]+ and [NiCl-
(PMePh2)(PNMe2)]+ (see also ref 6) show, analogously, a two broad singlet
31P NMR pattern with values falling at δ ) 38.6, -5.7 ppm and 37.3, -6.4
ppm, respectively.
(4) Compound 2: This species is not sufficiently stable to be characterized
in the solid state. 31P NMR spectra of the crude material show, inter alia, two
broad singlets (centered at δ ) 40.2 and - 4.9 ppm) and the septet of the PF6
anion.
(12) Synthesis of [Ph2P(o-C6H4)NPMe3] (abbreviated PNdPMe3): To an
orange-red suspension of 3 (0.300 g, 0.45 mmol) in benzene (50 mL) was
added a 10% sodium cyanide solution (50 mL) with stirring. After 1 h, the
color was discharged, and the organic phase was separated. The aqueous phase
was treated twice with Et2O (2 × 15 mL). The combined organic portions
were dried over Na2SO4 and reduced in volume to a crude pale yellow oil.
The ligand was then purified by alumina column chromatography (2.5 × 10
cm) eluted with benzene. 1H NMR (200 MHz, CDCl3): δ 1.28 (d, 2J(HP) )
13 Hz, 9H; P[CH3]3), 7.40-6.40 (m, 14 H; aromatic). 31P{1H} NMR (200
MHz, CDCl3): δ -15.6 (s, PNdP(CH3)3), 6.2 (s, PNdP(CH3)3).
(5) Crociani, L.; Refosco, F.; Tisato, F.; Gatto, S.; Corain, B. Inorg. Chim.
Acta 1996, 249, 131-133.
(6) Crociani, L.; Refosco, F.; Tisato, F.; Dolmella, A.; Gatto, S. Bandoli,
G. Z. Kristallogr. 1997, 212, 745-751.
(7) Bonnet, M. C.; Dahan, F.; Ecke, A.; Keim, W.; Schulz, R. P.;
Tkachenko, I. J. Chem. Soc., Chem. Commun. 1994, 615-616.
S0002-7863(97)03844-4 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/17/1998