Synthesis and Characterization of the First Mononuclear Ni(II) Phosphorane Imino Complex

Full text of DOI:10.1021/ja9738440

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

2974 J. Am. Chem. Soc., Vol. 120, No. 12, 1998
Communications to the Editor
Scheme 1
Figure 1. ORTEP drawing of the cation [NiCl(PMe3)(PNdPMe3)]+ of
3; the PF6- anion is omitted for clarity. Thermal ellipsoids are drawn at
the 50% probability level. Selected bond lengths (pm) and angles (deg):
Ni-Cl 221.7(2), Ni-P(1) 215.9(2), Ni-P(2) 219.2(2), Ni-N(1) 201.1(7),
N(1)-Ni-P(3) 158.9(7); Cl-Ni-P(1) 176.0(1), P(2)-Ni-N(1) 177.6(2),
Cl-Ni-N(1) 93.4(2), N(1)-Ni-P(1) 83.1(2), P(1)-Ni-P(2) 97.5(1),
P(2)-Ni-Cl 86.2(1), Ni-N(1)-P(3) 123.9(4), Ni-N(1)-C(6) 113.8(5),
P(3)-N(1)-C(6) 121.2(5).
Complex 322 was structurally characterized by X-ray diffraction,
and Figure 1 shows the cation present in 3.
In this complex, the metal atom is located in a distorted square-
planar coordination sphere consisting of the P,N-donor atoms of
the bidentate ligand, the P(2) atom from PMe3, and the chloride
ion. The trans angles in the Ni coordination sphere are 176.0(1)
and 177.6(2)° while the cis angles range from 83.1(2) to 97.5-
(1)°. The four donor atoms deviate alternatively from the mean
coordination plane by (4 pm, the dihedral angle between this
plane and the C(1)-(6) plane being 149.1°. The conformation
of the five-membered chelate ring is envelope (Cs). The nitrogen
atom is in an essentially trigonal-planar environment (Ni-N(1)-
P(3) 123.9(4), Ni-N(1)-C(6) 113.8(5), and P(3)-N(1)-C(6)
121.2(5)°), and its hybridization does not affect the Ni-N
distances which are 201.1(7) pm in 3 and 198.1(5) pm in [NiCl-
(PMe3)(PNHMe)]PF6 (PNHMe ) (o-diphenylphosphino)-N-meth-
ylaniline),23 which contains an sp3-hybridized N-atom. The P-N
bond distance of 158.9(7) pm in 3 is similar to the values observed
in several closely related phosphorane imino complexes, and it
is indicative of π interaction between P and N.16,17
Although nitrene pathways have been postulated for the
formation of phosphorane imines,13-20 the nucleophilic amido
pathway appears to be more plausible in the system we have
investigated since (a) [HPMe3]+ is detected by 31P NMR in the
reaction mixture during the formation of 3 and (b) the concomitant
addition of equimolar amounts of [HPMe3]+ 21 and 2,4-lutidine
produces 3 in almost quantitative yield, upon starting from 1.
Indeed, under these experimental conditions, the lutidine (pKa)
6.99) is expected to selectively deprotonate the coordinated PNH2
ligand to give 2*, while the trimethylphosphonium cation (pKa)
8.65) provides the electrophilic fragment for the metal-assisted
formation of the final phosphorane imine ligand (Scheme 1B).
Acknowledgment. This work was partially supported by CNR
Progetto Strategico, Tecnologie Chimiche Innovative.
(13) Basolo, F. J. Ind. Chem. Soc. 1977, 54, 6-10.
(14) Poznyak, A. L.; Pavlovski, V. I. Angew. Chem., Int. Ed. Engl. 1988,
27, 789-796.
Supporting Information Available: Summary of data collection and
refinement and tables of crystal data, bond distances and angles, final
fractional coordinates, thermal parameters, and other spectroscopic data
of complexes 1 and 3 (11 pages, print/PDF). See any current masthead
page for ordering information and Web access instructions.
(15) Sleiman, H. F.; Mercer, S.; McElwee White, L. J. Am. Chem. Soc.
1989, 111, 8007-8009.
(16) Fourquet, J. L.; Leblanc, M.; Saravanamuthu, A.; Bruce, M. R. M.;
Bruce, A. E. Inorg. Chem. 1991, 30, 3241-3243.
(17) Saravanamuthu, A.; Ho, D. M.; Kerr, M. E.; Fitzgerald, C.; Bruce,
M. R. M.; Bruce, A. E. Inorg. Chem. 1993, 32, 2202-2206.
(18) Staudinger, H.; Meyer, J. HelV. Chim. Acta 1919, 2, 635-638.
(19) Refosco, F.; Tisato, F.; Moresco, A.; Bandoli, G. J. Chem. Soc., Dalton
Trans. 1995, 3475-3482.
(20) Chatt, J.; Rove, G. J. J. Chem. Soc. 1962, 4019-4023.
(21) [HPMe3]+ was generated in situ by bubbling anhydrous HCl into an
anhydrous Et2O solution containing PMe3 originating from the AgI‚PMe3
adduct.
JA9738440
(22) Crystal data for 3: C24H32ClF6NNiP4, Mw ) 666.5, red cuboid,
monoclinic, space group P21/n, a ) 14.464(4), b ) 12.007(4), and c ) 18.518-
(5) Å, â ) 110.17(2)°, Z ) 4, R(F) ) 0.063, GOF ) 1.19.
(23) L. Crociani, et al., unpublished results.
(24) Cooper, M. K.; Downes, J. M.; Duckworth, P. A.; Kerby, M. C.;
Powell, R. J.; Soucek, M. D. Inorg. Synth. 1989, 25, 129-133.