Facile synthesis and molecular structure of [Ni(PPh2NHPh)4]

Article abstract of DOI:10.1002/1521-3749(200007)626:7<1591::AID-ZAAC1591>3.0.CO;2-D

NiCl₂ · 6 H₂O readily reacts with PPh₂NHPh in the presence of zinc dust to yield the homoleptic nickel(0) tetrakis-phosphine complex [Ni(PPh₂NHPh)₄] (1). 1 crystallises triclinic P1 (no. 2), with a= 1

Full text of DOI:10.1002/1521-3749(200007)626:7<1591::AID-ZAAC1591>3.0.CO;2-D

Facile Synthesis and Molecular Structure of [Ni(PPh2NHPh)4]
Olaf KuÈhl, Peter C. Junk1), and Evamarie Hey-Hawkins*
Leipzig, Institut fuÈr Anorganische Chemie der UniversitaÈt Leipzig
Received March 13th, 2000.
Professor Ulrich MuÈller on the Occasion of his 60th Birthday
Abstract. NiCl2 ´ 6 H2O readily reacts with PPh2NHPh in the
presence of zinc dust to yield the homoleptic nickel(0) tetra-
kis-phosphine complex [Ni(PPh2NHPh)4] (1). 1 crystallises
triclinic P1 (no. 2), with a = 14.656(1), b = 17.124(2), c =
distorted tetrahedral fashion by four phosphorus atoms, re-
sembling a compressed tetrahedron along one of the non-
crystallographic S4 axes.
Ê
17.424(1) A, a = 95.998(1), b = 111.845(1), c = 111.402(1)°,
3
Ê
V = 3630.04(5) A , Z = 2, R values [I > 2r(I)]: R1 = 0.0554,
Keywords: Nickel(0) tetrakisphosphine complex; Phosphi-
noamine ligand; Molecular structure
all data: wR2 = 0.1720. The nickel atom is coordinated in a
Einfache Synthese und MolekuÈlstruktur von [Ni(PPh2NHPh)4]
3
Ê
InhaltsuÈbersicht. NiCl2 ´ 6 H2O reagiert rasch mit PPh2NHPh
in Gegenwart von Zinkstaub unter Bildung des
homoleptischen Nickel(0)-tetrakis-phosphan Komplexes
[Ni(PPh2NHPh)4] (1). 1 kristallisiert triklin in der Raum-
gruppe P1 (Nr. 2) mit den Gitterkonstanten a = 14,656(1),
c = 111,402(1)°, V = 3630,04(5) A , Z = 2, R-Werte [I > 2r(I)]:
R1 = 0,0554, alle Daten: wR2 = 0,1720. Das Nickelatom ist
verzerrt tetraedrisch durch vier Phosphoratome koordiniert.
Das MolekuÈl bildet einen entlang einer der nicht-kristallo-
graphischen S4-Achsen gestauchten Tetraeder.
Ê
b = 17,124(2), c = 17,424(1) A, a = 95,998(1), b = 111,845(1),
Nickel complexes are active catalysts for a wide vari-
ety of reactions, and many of them are employed in
technical processes with an annual production of more
than a million tons [1]. In these complexes, nickel has
either the oxidation state +II (e. g., SHOP process [2]
and Wilke catalyst [1]), or zero (e. g., Reppe process
[3], hydrocyanation [4]). Reppe initially used
[Ni(CO)4] as a catalyst and later introduced phos-
phines to block coordination sites in the active cata-
lyst. In the hydrocyanation process, complexes of the
general formula [NiL4] are employed as catalysts,
where L is a tertiary phosphine or phosphite. The ac-
tive catalyst is thought to be [NiL3], generated by dis-
sociation of [NiL4] [4]. Tolman showed that the equili-
brium is shifted towards [NiL3] when the steric bulk
of the phosphine or phosphite is increased [4 a, 5].
We recently showed that [Zr(NPhPPh2)4] catalyses
the polymerisation of propylene to elastomeric poly-
propylene [6] and are now investigating phosphino-
amides and -amines as potential mono- and bidentate
ligands in other transition metal complexes. We now
report a facile synthetic route to [Ni(PPh2NHPh)4] (1)
from NiCl2 ´ 6 H2O and PPh2NHPh in the presence of
zinc dust.
Synthesis and Spectroscopic Properties
of [Ni(PPh2NHPh)4] (1)
Tetrakis-phosphine complexes of nickel(0) are usually
synthesised either from labile nickel(0) complexes [7],
such as [Ni(COD)2] (COD = cyclooctadiene) [8, 9,
10, 11, 12], [Ni(CO)2(COD)] [13 b], [Ni(CO)2L2]
(L = phosphine), or by reduction of an appropriate
nickel(II) complex, such as NiCl2 or [NiX2L2] (X = Cl,
Br, L = phosphine) [4 b, 13, 14] with for example zinc
dust or NaBH4 [15] in the presence of phosphine. As
[NiCl2L2] (L = phosphine) can be prepared by displa-
cement of water from the readily available NiCl2 ´
6 H2O by the corresponding phosphine [13 b], we as-
sumed that this synthetic approach could also be em-
ployed in the preparation of nickel(0) phosphine com-
plexes. Indeed, NiCl2 ´ 6 H2O readily reacts with
PPh2NHPh [16] in THF in the presence of zinc dust
* Prof. Dr. E. Hey-Hawkins,
Institut fuÈr Anorganische Chemie,
der UniversitaÈt Leipzig,
Johannisallee 29,
D-04103 Leipzig,
Germany
1)
permanent address:
Department of Chemistry
James Cook University
Townsville, Qld, 4811
Australia
E-Mail: hey@rz.uni-leipzig.de
Z. Anorg. Allg. Chem. 2000, 626, 1591±1594 Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0044±2313/00/6261591±1594 $ 17.50+.50/0 1591

O. KuÈhl, P. C. Junk, E. Hey-Hawkins
(one-pot reaction) to yield the homoleptic nickel(0)
tetrakis-phosphinoamine complex [Ni(PPh2NHPh)4]
(1) in 84% yield (eq. 1), which is, like other compar-
able complexes [8 e, 13 a], yellow. When 1 is stirred in
THF over a prolonged period, decomposition occurs.
We were as yet unable to fully characterise the pro-
ducts which are formed.
distorted tetrahedral fashion by four phosphorus atoms
[Ni±P 2.175(1)±2.183(1) A] (Fig. 1, Table 1), resembling
Ê
a compressed tetrahedron along one of the S4 axes,
with four of the six P±Ni±P bond angles being smaller
by 2.3±4.7° than expected for a perfect tetrahedron
[P(3)±Ni(1)±P(4) 106.06(4), P(3)±Ni(1)±P(1) 104.89(4),
P(4)±Ni(1)±P(2) 105.08(4), and P(1)±Ni(1)±P(2)
107.25(4)°], while two are larger by 7.3±7.6°
[P(4)±Ni(1)±P(1) 116.89(4), P(3)±Ni(1)±P(2) 117.21(4)°].
The phosphorus atoms are coordinated in a distorted
tetrahedral fashion by two phenyl rings, the nickel
atom, and a nitrogen atom with small N±P±C [99.5(2)±
NiCl2 ´ 6 H2O + 4 PPh2NHPh + Zn
® [Ni(PPh2NHPh)4] (1) + ZnCl2 + 6 H2O
(1)
Only a small number of transition metal [17, 18] and
lanthanide complexes [19] with phosphinoamido li-
gands are known; the anionic ligand can be terminal,
chelating or bridging. Fenske et al. observed N±P bond
cleavage in the reaction between [NiCl2(PPh3)2]
and PPh2NHPh in the presence of zinc dust in di-
methoxyethane (DME), in which [Ni2(l-PPh2)-
(l-NPhPPh2)(PPh2NHPh)3] is formed in 10% yield
besides [ZnCl2(NHPh2)2] [17]. When [NiCl2(PPh3)2] is
treated with LiNPhPPh2 in DME or THF, N±P cleav-
age and N±P bond formation is observed with forma-
tion of [{Ni(l-PPh2)(g2-N,N'±NPhPPh2NPh)}2] (in
DME, 15%) and [{Ni(g2-N,N'±NPhPPh2NPh)2] (in
THF, 40%) [17].
At room temperature, only one signal is observed
in the 31P NMR spectrum of 1 at 16.6 ppm, which is
shifted to high field by 12 ppm relative to the phosphi-
noamine PPh2NHPh (28.6 ppm). Apparently, no disso-
ciation occurs at room temperature as was observed
for other nickel(0) tetrakis-phosphine complexes with
bulky phosphine ligands, such as [Ni(PPh3)4] [4, 5].
The difference in chemical shift between the free
phosphine ligand and the corresponding Ni(0)
complex is smaller in the case of 1 than for
[Ni{(PMe2CH2)2ZrCp2}2] (d31Pcomplex±d31Pligand = 41.9)
[8 a] and [Ni(PH2Mes)4] (Mes = 2,4,6-Me3C6H2,
d31Pcomplex±d31Pligand = 66.5) [8 b].
In the IR spectrum of 1, the typical bands for the
PPh2 and NPh group are observed, as well as a strong
absorption band for the N±H (3383 cm±1) vibration
(cf. free ligand, m(N±H): 3295 cm±1). The m(P±N) band
cannot be unambiguously assigned. For related amino-
phosphines, values of 840±740 cm±1 were given for
m(P±N) [20] (assumption: P±N single bond), and for
1,2-(PPh2NH)2C6H4 two strong P±N bands are ob-
served at 904 and 738 cm±1 [21]. In related Ni and Pd
complexes, this vibration occurs at 1262±1271 cm±1
(assumption: P±N double bond) [17].
Fig. 1 Molecular structure of [Ni(PPh2NHPh)4] (1). Hydro-
gen atoms (other than N±H) have been omitted for clarity.
Ê
Table 1 Selected bond lengths/A and angles/° for 1
Ni(1)±P(1)
Ni(1)±P(3)
P(1)±N(1)
P(3)±N(3)
P(1)±C(1)
P(2)±C(25)
P(3)±C(43)
P(4)±C(61)
N(1)±C(13)
N(3)±C(49)
2.180(1)
2.175(1)
1.707(3)
1.700(4)
1.850(4)
1.848(4)
1.846(4)
1.849(4)
1.412(5)
1.418(5)
Ni(1)±P(2)
Ni(1)±P(4)
P(2)±N(2)
P(4)±N(4)
P(1)±C(7)
P(2)±C(19)
P(3)±C(37)
P(4)±C(55)
N(2)±C(31)
N(4)±C(67)
2.183(1)
2.179(1)
1.703(3)
1.702(3)
1.848(4)
1.849(4)
1.853(4)
1.851(4)
1.406(5)
1.412(5)
P(3)±Ni(1)±P(4)
P(4)±Ni(1)±P(1)
P(4)±Ni(1)±P(2)
N(1)±P(1)±C(7)
N(2)±P(2)±C(25)
N(3)±P(3)±C(43)
N(4)±P(4)±C(61)
C(7)±P(1)±C(1)
C(43)±P(3)±C(37)
N(1)±P(1)±Ni(1)
N(3)±P(3)±Ni(1)
C(1)±P(1)±Ni(1)
C(25)±P(2)±Ni(1)
C(43)±P(3)±Ni(1)
C(61)±P(4)±Ni(1)
C(13)±N(1)±P(1)
C(49)±N(3)±P(3)
106.06(4)
116.89(4)
105.08(4)
103.8(2)
104.1(2)
101.3(2)
103.5(2)
102.3(2)
101.2(2)
112.3(1)
110.6(1)
121.3(1)
117.2(1)
119.6(1)
117.1(1)
131.5(3)
134.5(3)
P(3)±Ni(1)±P(1)
P(3)±Ni(1)±P(2)
P(1)±Ni(1)±P(2)
N(1)±P(1)±C(1)
N(2)±P(2)±C(19)
N(3)±P(3)±C(37)
N(4)±P(4)±C(55)
C(25)±P(2)±C(19)
C(61)±P(4)±C(55)
N(2)±P(2)±Ni(1)
N(4)±P(4)±Ni(1)
C(7)±P(1)±Ni(1)
C(19)±P(2)±Ni(1)
C(37)±P(3)±Ni(1)
C(55)±P(4)±Ni(1)
C(31)±N(2)±P(2)
C(67)±N(4)±P(4)
104.89(4)
117.21(4)
107.25(4)
99.5(2)
101.2(2)
104.3(2)
100.7(2)
101.2(2)
102.7(2)
111.7(1)
111.9(1)
115.2(1)
119.3(1)
117.6(1)
118.7(1)
134.4(3)
132.5(3)
Molecular Structure of [Ni(PPh2NHPh)4] (1)
Yellow crystals of 1 ´ 2 Et2O were obtained from a satu-
rated diethyl ether solution at room temperature. The
compound crystallises in the triclinic space group P1
(no. 2) with two molecules of 1 and four non-coordi-
nating ether molecules in the unit cell. As expected for
Ni(0) complexes, the nickel atom is coordinated in a
1592
Z. Anorg. Allg. Chem. 2000, 626, 1591±1594

Facile Synthesis and Molecular Structure of [Ni(PPh2NHPh)4]
The amino groups are planar with large C±N±P bond
angles [131.5(3)±134.5(3)°].
When the centres of all twelve phenyl rings in 1 are
viewed (Fig. 3), one observes that these centres form a
section of a cubic close-packed structure with Ni as
the central atom.
Even though a large number of homoleptic tetrahe-
dral Ni(0) phosphine complexes [NiL4] is known, only
a few crystal structures have been reported, e. g., those
Ê
of [Ni(PEt3)4] (Ni±P 2.210(1)-2.215(1) A; P±Ni±P
from 102.4±111.6(1)°] [13 a], [Ni(PH2Mes)4] (Ni±P
Ê
2.140(8)±2.158(7) A] [8 b], [Ni(PF2R)4] (R = 2-thienyl;
Ê
Ni±P 2.093(3) A] [23], [NiL4] (L = azaphosphole deri-
1
Ê
vative, Ni±P 2.146(1), 2.143(1) A [24]; L = g -phospha-
benzene, Ni±P 2.1274(5) A [11]; L = 3,4-di-t.-butyl-5-
Fig. 2 Cuboid arrangement of the centres of the eight phe-
nyl rings of the PPh2 groups in 1. Numbering scheme of the
centres of the phenyl rings X(1 a): C1±C6, X(1 b): C7±C12,
X(2 a): C19±C24, X(2 b): C25±C30, X(3 a): C37±C42, X(3 b):
C43±C48, X(4 a): C55±C60, X(4 b): C61±C66. X±X±X angles:
83.3±95.3°.
Ê
aza-2,8-dioxa-1-phosphabicyclo-[3.3.0]octa-2,4,6-triene,
Ê
Ni±P 2.093 A) [12], and the heterobimetallic complex
6
Ê
[Ni({PMe2(g -C6H5)}2Cr)2] [Ni±P 2.146(1), 2.151(1) A]
[10]. These complexes also exhibit distorted NiP4
tetrahedra, as observed for 1. Several bis-chelate
complexes of Ni(0), such as [NiL' ] with L' =
2
Ê
Ê
Ph2PCH2CH2PPh2 [Ni±P 2.152(3)±2.177(3) A] [9],
L' = Ph2PC7H10PPh2 [Ni±P 2.187(2)±2.210(3) A] [25],
L' = Me2PCH2P(Me)CH2PMe2
[Ni±P
2.136(1),
Ê
2.140(1) A]
[26],
L' = 2,2'-biphosphinine
[Ni±P
Ê
2.141(1) A] [14] and L' = Cy2PCH2PCy2 [Ni±P
Ê
2.193(2)±2.218(2) A] [27] and the heterobimetallic
complex with L' = (PMe2CH2)2ZrCp2 [Ni±P 2.156(3)±
Ê
2.186(4) A] [8 a], have also been structurally charac-
terised. The Ni±P bond lengths in all these complexes
and 1 are in the same range.
The structural data of the coordinated PPh2NHPh
Ê
ligands [P±N 1.700(4) to 1.707(3) A] are only slightly
different from those of the free ligand [P±N
Ê
1.696(3) A] [19]. The P±N bond lengths lie between
Ê
those expected for a P±N single (1.80 A) and P±N
Ê
Fig. 3 Depiction of the centres of the twelve phenyl rings
in [Ni(PPh2NHPh)4] (1), resembling a cubic closest packing.
Numbering scheme of the centres of the phenyl rings as in
Fig. 2 and additionally: X(1 n): C13±C18, X(2 n): C31±C36,
X(3 n): C49±C54, X(4 n): C67±C72.
double bond (1.60 A).
Experimental
All experiments were carried out under purified dry argon.
Solvents were used as purchased. NMR spectra: Avance
DRX 400 (Bruker), standards: 1H NMR (400 MHz): trace
amounts of protonated solvent, C6D6, 31P NMR (162 MHz):
external 85% H3PO4. The IR spectra were recorded on KBr
mulls on a Perkin-Elmer FT-IR spectrometer System 2000 in
the range 350±4000 cm±1. The mass spectrum was recorded
with a Vacuum Generators Ltd. VG ZAB HSQ, England
(FAB). The melting point was determined in a sealed capil-
lary under argon and is uncorrected. NiCl2 ´ 6 H2O is com-
mercially available; PPh2NHPh [16] was prepared by the lit-
erature procedure.
104.3(2)°] and C±P±C [101.2(2)±102.7(2)°] and large
N±P±Ni [110.6(1)±112.3(1)°] and C±P±Ni bond angles
[115.2(1)±121.3(1)°]. The distortion of both the
NiP4 and PNC2Ni tetrahedra are due to steric interac-
tion of the phenyl substituents on the phosphorus
atoms. The cone angle of the PPh2NHPh ligand is 160°
[calculated from structural data, sum of angles o-H(P-
phenyl)±P±Ni ´ 2 and o-H(N-phenyl)±P±Ni], which is
larger than that of PPh3 (145°), similar to that of PPr3i
(160°), and smaller than that of PBut3 (182°) [22].
The centres of the phenyl rings of the four PPh2
groups form a distorted cuboid (Fig. 2). The phenyl
rings on each P atom are oriented at 57.1 to 69.9° to
each other, and those at P(1) and P(4) are also at an
angle of 63.8 to 71.0° to those on P(2) and P(3) (Fig. 1).
[Ni(PPh2NHPh)4] (1). 0.31 g (1.32 mmol) NiCl2 ´ 6 H2O and
1.47 g (5.28 mmol) PPh2NHPh were stirred in 50 ml THF.
After 5 min., 0.09 g (1.38 mmol) zinc dust was added, and
the suspension stirred 12 h. The solvent was removed in va-
cuo, the residue dissolved in toluene and ZnCl2 filtered off.
The solution was concentrated, and the light yellow product
Z. Anorg. Allg. Chem. 2000, 626, 1591±1594
1593

O. KuÈhl, P. C. Junk, E. Hey-Hawkins
precipitated with hexane. Yield: 1.3 g (84%). M. p.: 168±
169 °C. Elemental analysis: C72H64N4NiP4: C 73.91 (74.06),
H 5.56 (5.49), N 4.83 (4.80), P 10.48 (10.63)%. 1 is only slightly
soluble in benzene or toluene. When 1 is stirred in THF or
chloroform over a prolonged period, decomposition occurs.
1H NMR (C6D6, ppm): 6.36±7.93 (m, C6H5). N±H can not
be unambiguously assigned. ± 31P{1H} NMR (C6D6, ppm):
16.6. ± MS (FAB): m/z = 1075 (12%, M+±NHPh), 893 (4%,
M+±PPh2NHPh), 720 (16%, M+±NHPh±PPh2NHPh), and
fragmentation products thereof. Below m/z ca. 650, signals
due to fragmentation of 1 are obscured by matrix signals
(3-nitrobenzaldehyde). ± IR (KBr, cm±1): 3383 s, 3266 w,
3222 w, 3051 m, 2963 m, 1599 vs, 1496 vs, 1475 vs, 1433 s,
1391 s, 1284 vs, 1262 s, 1229 s, 1182 m, 1158 m, 1093 s, 1027 s,
998 m, 921 m, 895 s, 802 s, 747 vs, 693 vs, 618 m, 594 s, 511 vs,
460 m, 430 m.
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Crystals suitable for a structure determination were ob-
tained from diethyl ether and have the composition
[Ni(PPh2NHPh)4] ´ 2 Et2O.
Crystal
data
for
[Ni(PPh2NHPh)4]
(1) ´ 2 Et2O:
C80H84N4NiO2P4, M = 1316.10, yellow crystals, triclinic,
space group P1 (no. 2), T = 218(2) K, a = 14.656(1),
Ê
b = 17.124(2), c = 17.424(1) A, a = 95.998(1), b = 111.845(1),
3
±3
Ê
c = 111.402(1)°, V = 3630.04(5) A , Z = 2, Dc = 1.204 Mg m ,
F(000) = 1392, l(Mo-Ka) = 0.404 mm±1, 22 525 reflections
collected with 1.31 < H < 27.18°; of which 13 861 were inde-
pendent; 1013 parameters, refinements converged to
R1 = 0.0554, wR2 = 0.1298 (for reflections with I > 2r(I)),
R1 = 0.1140, wR2 = 0.1720 (all data). Data [k(MoKa) =
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[13] (a) M. B. Hursthouse, K. J. Izod, M. Motevalli, P. Thorn-
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Trans. 1994, 2761.
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Acta 1997, 264, 5.
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C 1966, 1001.
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1086.
Ê
0.71073 A] were collected with a Siemens CCD (SMART).
All observed reflections were used for determination of the
unit cell parameters. The structure was solved by direct
methods (SHELXTL PLUS [28]) and subsequent difference
Fourier syntheses and refined by full-matrix least-squares on
F2 (SHELXTL PLUS [28]). Ni, P, O, N and C atoms aniso-
tropic, H atoms of 1 located and refined isotropically. H
atoms of Et2O refined in calculated positions. Empirical ab-
sorption correction with SADABS [29]. Crystallographic
data (excluding structure factors) for the structure reported
in this paper have been deposited with the Cambridge Crys-
tallographic Data Centre (1: CCDC 141841). Copies of this
information may be obtained free of charge from The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(Fax: +44-12 23-33 60 33,
e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
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[24] K. Angermund, A. Eckerle, J. Monkiewicz, C. KruÈger,
G. Wilke, Inorg. Chim. Acta 1998, 270, 273.
We gratefully acknowledge support from the Fonds der
Chemischen Industrie and the Deutscher Akademischer
Austauschdienst (P.C.J., Gastdozentur).
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