Phosphorus and olefin substituent effects on the insertion chemistry of nickel(II) hydride complexes containing amido diphosphine ligands

Article abstract of DOI:10.1021/om701294a

A series of nickel(II) hydride complexes supported by amido diphosphine ligands, including symmetrical [N(o-C₆H₄PR ₂)₂]^- ([R-PNP]^-; R = Ph, ⁱPr, Cy) and unsymmetrical [N(o-C

Full text of DOI:10.1021/om701294a

3082
Organometallics 2008, 27, 3082–3093
Phosphorus and Olefin Substituent Effects on the Insertion
Chemistry of Nickel(II) Hydride Complexes Containing Amido
Diphosphine Ligands
Lan-Chang Liang,* Pin-Shu Chien, and Pei-Ying Lee
Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen UniVersity,
Kaohsiung 80424, Taiwan
ReceiVed December 28, 2007
A series of nickel(II) hydride complexes supported by amido diphosphine ligands, including symmetrical
[N(o-C6H4PR2)2]- ([R-PNP]-; R ) Ph, iPr, Cy) and unsymmetrical [N(o-C6H4PPh2)(o-C6H4PiPr2)]- ([Ph-
PNP-iPr]-), have been prepared for the investigation of olefin insertion chemistry. The unsymmetrical
ligand precursor H[Ph-PNP-iPr] (1d) that features different substituents (phenyl and isopropyl) at the
two phosphorus donors was prepared in 53% yield as colorless crystals. Treatment of Ni(COD)2 (COD
) cycloocta-1,5-diene) with H[R-PNP] (R ) Ph (1a), iPr (1b), Cy (1c)) or 1d produced the corresponding
four-coordinate nickel hydride complexes 2a-d. Attempts to isolate 2a led instead to the cyclooct-4-
en-1-yl complex [Ph-PNP]Ni(η1-C8H13) (3a) as a consequence of COD insertion into the Ni-H bond of
2a. The reactions of 2a,d with ethylene, 1-hexene, and norbornene, respectively, generated cleanly the
corresponding ethyl (4a,d), n-hexyl (5a,d), and 2-norbornyl (6a,d) complexes. The quantitative formation
of 5a,d is indicative of exclusive 1,2-insertion of 1-hexene. In contrast, styrene inserts into the Ni-H
bond of 2d in an exclusively 2,1-manner to afford [Ph-PNP-iPr]NiCH(Me)Ph (7d) quantitatively. The
selective 2,1-insertion products [Ph-PNP]NiCH(Me)CO2Me (8a), [iPr-PNP]NiCH(Me)CO2Me (8b), [Cy-
PNP]NiCH(Me)CO2Me (8c), and [Ph-PNP-iPr]NiCH(Me)CO2Me (8d) were also isolated from the reactions
of methyl acrylate with the corresponding nickel hydride complexes 2a-d. The effects of the phosphorus
and olefin substituents on the reactivity and regioselectivity of the olefin insertion reactions are discussed.
In addition to solution NMR spectroscopic data for all new compounds, X-ray structures of 1d, 2b-d,
3a, and 5d-7d are reported.
Isomerization of a propagating alkyl chain in catalytic olefin
polymerization is often composed of metal-mediated ꢀ-elimina-
tion followed by olefin reinsertion.36–43 The effective control
Introduction
Olefin insertion and ꢀ-hydrogen elimination are mutually
microscopic reverse; the former represents a valuable C-H or
C-C bond forming method for higher alkyl homologue
preparation, whereas the latter epitomizes perhaps the most
common decomposition pathway for metal alkyl complexes to
produce metal hydride derivatives.1,2 Both processes are par-
ticularly relevant to transition-metal-catalyzed olefin polymer-
ization, in that olefin insertion into a metal-hydrogen bond is
an essential (re)initiation step while ꢀ-hydrogen elimination from
a metal alkyl species is a major termination process.3–35
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* To whom correspondence should be addressed. E-mail: lcliang@
mail.nsysu.edu.tw.
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10.1021/om701294a CCC: $40.75
2008 American Chemical Society
Publication on Web 05/29/2008

Insertion Chemistry of Ni(II) Hydride Complexes
Organometallics, Vol. 27, No. 13, 2008 3083
of exclusive 1,2- or 2,1-regioselectivity of R-olefin insertion is
crucial for the production of transient propagating species with
a virtually identical metal-based core structure and thus the
resultingpoly-R-olefinswithwell-definedmicrostructures.4,6,36,44–52
It has been shown that the regiospecificity of olefin insertion
has a dramatic impact on polymer molecular weights,53 indicat-
ing that the reactivity and stability of propagating species derived
from 1,2-olefin insertion are different from those of 2,1
-insertion.54 Such regiospecificity also plays an important role
in transition-metal-catalyzed olefin hydroformylation.55,56
alkyl complexes of [N(o-C6H4PR2)2]- ([R-PNP]-; R ) Ph, iPr,
Cy) have been demonstrated to be markedly stable even at
elevated temperatures.65,66 Of particular note is the stability of
those containing ꢀ-hydrogen atoms. For instance, [Ph-PNP]NiEt,
[iPr-PNP]Ni(n-Bu), and [Cy-PNP]Ni(n-Bu) do not decompose
at all after prolonged heating at 80 °C. Though not uncommon
in early-transition-metal chemistry, ꢀ-hydrogen-containing alkyl
complexes of late transition metals that resist ꢀ-elimination at
high temperatures are extremely rare. Understanding the decisive
factors that control ꢀ-hydrogen elimination and olefin insertion
is of current interest.67–71 We thus became interested in
examining its microscopic reverse to better understand the
inherent nature of this unusual property. To this end, we have
set out to prepare a series of nickel hydride complexes supported
by these amido diphosphine ligands and study their insertion
chemistry with a number of olefins. The interesting unsym-
metrical amido diphosphine ligand [N(o-C6H4PPh2)(o-
C6H4PiPr2)]- ([Ph-PNP-iPr]-), which carries different hydro-
carbon substituents at the two phosphorus donors, was designed
and employed in this study. The electronic and steric properties
of this unsymmetrically substituted ligand are anticipated to lie
somewhere in between those of the symmetrical [Ph-PNP]- and
[iPr-PNP]-, as are those of the corresponding metal derivatives.
In this contribution, we describe the reactivity of nickel hydride
complexes containing [R-PNP]- (R ) Ph, iPr, Cy) or [Ph-PNP-
iPr]- with olefins featuring divergent electronic and steric
characteristics. The effects of the substituents at the phosphorus
donors in these tridentate amido diphosphine ligands and those
at olefinic substrates on insertion reactivity and regioselectivity
are discussed.
We are currently exploring reaction chemistry with amido
phosphine complexes.57–64 In particular, a series of nickel(II)
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Results and Discussion
Following the synthetic protocol established for the sym-
metrically substituted H[R-PNP] (R ) Ph (1a), Pr (1b), Cy
i
(1c)),65,72 the unsymmetrical H[Ph-PNP-iPr] (1d) was prepared
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3084 Organometallics, Vol. 27, No. 13, 2008
Liang et al.
Scheme 1
and 31P NMR spectroscopy, elemental analysis, and X-ray
crystallography. The amino proton is observed as a characteristic
doublet of doublets resonance at 7.99 ppm in the H NMR
(56 ppm)74 and 2c (47 ppm).74 The 31P{1H} NMR spectrum of
2d displays two doublet resonances at 31 ppm for PPh2 and 59
ppm for PiPr2, values that are very similar to those of
1
spectrum. 31P{1H} NMR spectroscopy reveals two signals at
-16.66 and -14.79 ppm for the diphenyl- and the diisopropyl-
substituted phosphorus atom, respectively. Interestingly, these
31P chemical shifts are comparable to those found for sym-
metrically substituted 1a (-18.62 ppm)65,66 and 1b (-13.31
ppm),65 respectively. Figure 1 depicts the X-ray structure of
1d. Crystallographic data are summarized in Table 1.
symmetrically substituted 2a,b,74 respectively. The large JPP
2
value of 244 Hz found for 2d is indicative of a trans orientation
for the two phosphorus donors, suggesting that the tridentate
[Ph-PNP-iPr]- ligand adopts a meridional coordination mode.
The 13C{1H} NMR spectra of 2b,c exhibit virtual triplet
resonances for the o-phenylene carbon atoms,74 indicating a
square-planar geometry for these molecules. On the basis of
the solution NMR studies, the structure of 2a is likely analogous
to those of 2b-d.
The oxidative addition reactions of Ni(COD)2 (COD )
cycloocta-1,5-diene) with 1a-d in benzene at room temperature
produced cleanly the corresponding nickel(II) hydride complexes
2a-d (Scheme 2). Nickel hydride complexes supported by a
tolyl-derived amido diphosphine ligand have also been prepared
similarly.73 Though it was generated quantitatively, as evidenced
Single crystals of 2b-d suitable for X-ray diffraction analysis
were grown from a concentrated diethyl ether solution at -35
°C. As depicted in Figures 2–4, the amido diphosphine ligands
all adopt a meridional coordination mode in these nickel hydride
species, consistent with the solution structures determined by
multinuclear NMR spectroscopy. Selected bond distances and
angles are summarized in Tables 2 and 3, respectively. The core
structures of 2b-d closely resemble each other, although each
has different substituents at the phosphorus donors. In particular,
the two Ni-P lengths in 2d are virtually identical, in spite of
bearing different substituents at the two phosphorus donors.
These results are likely ascribable to the small size of the hydride
ligand. The Ni-N distance of 1.920(3) Å found in 2b is slightly
shorter than that of [iPr-PNP]NiMe (1.945(3) Å)65 but slightly
longer than that of [iPr-PNP]NiCl (1.903(2) Å),65 indicating the
trans influence order of Cl < H < Me for these formally anionic
ligands. Interestingly, the P-Ni-P angle of 175.05(4)° in 2b
is notably wider than those of [iPr-PNP]NiCl (168.81(2)°)65 and
[iPr-PNP]NiMe (166.68(5)°),65 consistent with the steric repul-
sion arising from the relatively larger chloride and methyl
ligands in the latter complexes. The Ni-P distances in 2b
(2.1373 Å average) are thus slightly shorter than those of [iPr-
PNP]NiCl (2.18985 Å average)65 and [iPr-PNP]NiMe (2.1677
Å average).65 Similar phenomena are also found for 2c and [Cy-
PNP]NiMe.65 Though 2a was not crystallographically character-
ized, its core structure is presumably similar to those of 2b-d
on the basis of little deviation observed for the X-ray structures
of 2b-d.
1
by the H and 31P{1H} NMR spectra, complex 2a was not
isolable under the conditions employed. This compound,
however, can be prepared in situ and used directly for
subsequent reactions (vide infra). In contrast, complexes 2b-d
were all isolated as crystalline solids. Complexes 2a-c display
solution C2V symmetry on the NMR time scale, while 2d is Cs-
symmetric. The nickel-bound hydride ligand in 2a-c appears
as a characteristic triplet resonance at ca. -18 ppm with a 2JHP
1
value of ca. 63 Hz in the H NMR spectra, whereas that in 2d
exhibits a doublet of doublets resonance at -18 ppm with a
i
PPh2
2
2JHP
value of 58 Hz and a JHPP Pr2 value of 68 Hz. The
2
two distinct JHP coupling constants for the hydride ligand in
2d were determined by selective undecoupling of NiH in the
31P{1H} NMR spectra, which revealed two doublet of doublets
resonances for the two chemically inequivalent phosphorus
donors. The phosphorus atoms in 2a appear as a singlet
resonance in the 31P{1H} NMR spectrum at 33 ppm, a value
that is significantly shifted upfield as compared to those of 2b
Though 2a could be generated quantitatively from the reaction
of Ni(COD)2 with 1a, attempts to isolate 2a from the reaction
mixture led instead to the cyclooct-4-en-1-yl complex [Ph-
PNP]Ni(η1-C8H13) (3a) in 83% yield as a consequence of COD
insertion into the reactive Ni-H bond. Prolonged stirring of
the reaction mixture containing the in situ prepared 2a and
liberated COD gave quantitative formation of 3a, as evidenced
1
by H and 31P{1H} NMR spectra. In contrast, no reaction was
observed for 2b-d, even in the presence of an excess amount
of COD at 25-80 °C. Such a discrepancy in reactivity between
2a and 2b-d with respect to the COD insertion highlights
(73) Ozerov, O. V.; Guo, C. Y.; Fan, L.; Foxman, B. M. Organometallics
2004, 23, 5573–5580.
Figure 1. Molecular structure of H[Ph-PNP-iPr] (1d) with thermal
ellipsoids drawn at the 35% probability level.
(74) Liang, L.-C.; Chien, P.-S.; Huang, Y.-L. J. Am. Chem. Soc. 2006,
128, 15562–15563.

Insertion Chemistry of Ni(II) Hydride Complexes
Organometallics, Vol. 27, No. 13, 2008 3085

3086 Organometallics, Vol. 27, No. 13, 2008
Liang et al.
Scheme 2
particularly the phosphorus substituent effect on the electro-
philicity and steric accessibility of the divalent nickel center in
these molecules. With the phenyl-substituted phosphorus donors,
the nickel center in 2a is more electrophilic and sterically more
accessible than those in 2b-d, leading to facile COD coordina-
tion to the former and thus the subsequent insertion reaction to
produce 3a. It should be noted that phosphine dissociation from
the nickel center is rather unlikely in view of the markedly
thermal stability of nickel alkyl complexes of [Ph-PNP]-,65,66
particularly for those containing ꢀ-hydrogen atoms. Association
of COD from the axial faces of square-planar 2a is thus more
possible.4,42,75,76 For 2b-d, the eight-membered COD ring is
perhaps too bulky to access the nickel center in these sterically
more demanding molecules. Complex 3a was fully characterized
by 1H, 13C, and 31P NMR spectroscopy, elemental analysis, and
Figure 4. Molecular structure of [Ph-PNP-iPr]NiH (2d) with thermal
ellipsoids drawn at the 35% probability level.
Table 2. Selected Bond Distances (Å) for 2b-d, 3a, and 5d-7d
compd
Ni-N Ni-Xa
Ni-P
[iPr-PNP]NiH (2b)
[Cy-PNP]NiH (2c)b
[Ph-PNP-iPr]NiH (2)
1.920(3)
1.918(4)
1.924(2)
2.137(1), 2.138(1)
2.140(1), 2.139(1)
2.1214(7), 2.1235(8)
[Ph-PNP]Ni(5-cyclooctenyl) (3) 1.965(3) 1.973(3) 2.136(1), 2.195(1)
[Ph-PNP-iPr]Ni(n-hexyl) (5d)b
1.961(6) 1.979(7) 2.154(2), 2.198(2)
[Ph-PNP-iPr]Ni(2-norbornyl) (6d) 1.975(2) 1.974(3) 2.1942(8), 2.2006(8)
[Ph-PNP-iPr]NiCH(Me)Ph (7d) 1.949(7) 1.997(9) 2.188(3), 2.196(3)
a X represents
a
hydrogen or an R-carbon atom. b The data
summarized represent one of the two independent molecules found in
the asymmetric unit cell.
X-ray crystallography. Similar to previously reported nickel
alkyl complexes of [Ph-PNP]-,65,66 3a displays solution C2V
symmetry on the NMR time scale. The phosphorus donors are
observed as a singlet resonance at 24.27 ppm in the 31P{1H}
NMR spectrum. The cyclooct-4-en-1-yl ligand exhibits a
1
characteristic signal at 5.33 ppm for olefinic protons in the H
NMR spectrum, consistent with this unsaturated cyclohydro-
carbon being bound to nickel in an η1 rather than an η3
fashion.77 The o-phenylene carbon atoms are observed as virtual
triplet resonances in the 13C{1H} NMR spectrum, consistent
with a square-planar geometry for this molecule.
Orange crystals of 3a suitable for X-ray diffraction analysis
were grown from a concentrated diethyl ether solution at -35
°C. The solid-state structure of 3a is depicted in Figure 5.
Unexpectedly, the coordination geometry deviates severely from
the ideal square plane by 0.4085 Å. In sharp contrast to those
foundforsquare-planargroup10complexesof[Ph-PNP]-,65,66,78,79
the dihedral angle of 31.0° between the two N-Ni-P planes
in 3a is notably large and the P(1)-Ni(1)-P(2) angle of
147.37(4)° and the N(1)-Ni(1)-C(37) angle of 163.1(1)° are
relatively small. The nickel center is displaced from the mean
coordination plane by 0.1220 Å. Both ꢀ-methylene groups are
tilted toward P(2), leading to Ni(1)-P(2) (2.195(1) Å) being
longer than Ni(1)-P(1) (2.136(1) Å) and the N(1)-Ni(1)-P(2)
angle(82.76(9)°)beingsharperthanN(1)-Ni(1)-P(1)(86.78(9)°).
The deviation of the core structure of 3a from the ideally square
Figure 2. Molecular structure of [iPr-PNP]NiH (2b) with thermal
ellipsoids drawn at the 35% probability level.
(75) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414–6415.
(76) Killian, C. M.; Johnson, L. K.; Brookhart, M. Organometallics 1997,
16, 2005–2007.
(77) Thompson, M. R.; Day, V. W.; Tau, K. D.; Muetterties, E. L. Inorg.
Chem. 1981, 20, 1237–1241.
(78) Liang, L.-C.; Lin, J.-M.; Lee, W.-Y. Chem. Commun. 2005, 2462–
2464.
Figure 3. Molecular structure of [Cy-PNP]NiH (2c) with thermal
ellipsoids drawn at the 35% probability level.
(79) Huang, M.-H.; Liang, L.-C. Organometallics 2004, 23, 2813–2816.

Insertion Chemistry of Ni(II) Hydride Complexes
Organometallics, Vol. 27, No. 13, 2008 3087
Table 3. Selected Bond Angles (deg) for 2b-d, 3a, and 5d-7d
compd
N-Ni-P
P-Ni-P
P-Ni-Xa
N-Ni-Xa
Pr-PNP]NiH (2b)
87.44(8), 87.65(9)
87.2(1), 87.9(1)
88.41(7), 88.09(7)
86.78(9), 82.76(9)
84.1(2), 83.5(2)
83.90(7), 83.13(7)
82.3(2), 85.1(2)
175.05(4)
172.78(6)
174.15(3)
147.37(4)
165.65(9)
165.08(3)
162.8(1)
[Cy-PNP]NiH (2c)b
[Ph-PNP-Pr]NiH (2d)
[Ph-PNP]Ni(5-cyclooctenyl) (3a)
[Ph-PNP-Pr]Ni(n-hexyl) (5d)b
[Ph-PNP-Pr]Ni(2-norbornyl) (6d)
[Ph-PNP-Pr]NiCH(Me)Ph (7d)
95.4(1), 103.5(1)
93.8(2), 98.9(2)
100.17(9), 92.84(9)
99.1(3), 94.6(3)
163.1(1)
176.7(3)
176.7(1)
174.6(4)
a X represents a hydrogen or an R-carbon atom. b The data summarized represent one of the two independent molecules found in the asymmetric unit
cell.
center induced by the phosphorus substituents in 2a-d likely
plays an important role in differentiating the insertion reactivity
of these olefins, particularly for those with small sizes such as
ethylene. Collectively, the reactivity of 2d clearly lies in between
those of 2a and 2b. Consistent with the insertion reactivity,
complexes 4-6 are all thermally stable, even at elevated
temperatures.
With their unsymmetrically substituted amido diphosphine
ligands, complexes 4d-6d display lower solution symmetry
than 4a-6a on the NMR time scale. Unlike the data for the
C2V-symmetric 4a and 5a, the solution NMR spectroscopic data
of 4d and 5d are consistent with Cs symmetry for these
1
molecules. For instance, the H NMR spectrum of 4d reveals
one signal at 2.16 ppm for the isopropylmethine moieties and
two doublet of doublets resonances at 1.29 and 1.08 ppm for
the isopropylmethyl groups. The NiCH2 moiety in 4d is
observed as two signals at 1.42 and 0.96 ppm, indicating a
diastereotopic nature for these R-hydrogen atoms. The chemical
nonequivalence of these R-hydrogen atoms is ascribable to the
lack of symmetry with respect to the internal rotation involving
the R-methylene group.81 Figure 6 depicts a Newman projection
of [Ph-PNP-iPr]NiCH2R (R ) Me (4d), n-pentyl (5d)), which
features the most stable rotamer of these compounds from a
steric viewpoint. Rapid rotation of the alkyl ligand in 4d and
5d about the Ni-C bonds should be responsible for the observed
solution symmetry.82 With the stereoactive 2-norbornyl group
in 6a,d, the symmetry of these molecules is lower than that of
the corresponding 2-5, as evidenced by their NMR spectro-
scopic data. Reminiscent of what has been observed for 2d,
the phosphorus donors in 4d-6d are observed as two doublet
resonances with 2JPP values of ca. 270 Hz in the 31P{1H} NMR
spectra, consistent with a trans orientation for the two phos-
phorus donors in these molecules. The regiospecificity of
1-hexene insertion to produce n-hexyl complexes 5a and 5d is
exclusive, as evidenced by the DEPT 13C NMR spectra of these
molecules. These results indicate selective 1,2- rather than 2,1-
insertion of 1-hexene into the Ni-H bond of 2a and 2d.
Single crystals of 5d and 6d suitable for X-ray diffraction
analysis were grown by slow evaporation of a concentrated
benzene solution at room temperature. Figures 7 and 8 depict
the molecular structures of these compounds. The coordination
geometry of 5d and 6d is best described as square planar. The
bond distances and angles are all similar to those of nickel(II)
hydrocarbyl complexes of symmetrically substituted [R-PNP]-
(R ) Ph, iPr, Cy),65 except for 3a (vide supra). Consistent with
the solution NMR data, 5d is an n-hexyl derivative. In 6d, the
[Ph-PNP-iPr]Ni fragment occupies one of the exo rather than
endo positions in the 2-norbornyl ligand, consistent with what
is anticipated from a steric viewpoint. The norbornyl ligand is
oriented such that the one-carbon bridge is tilted toward the
Figure 5. Molecular structure of [Ph-PNP]Ni(η1-C8H13) (3a) with
thermal ellipsoids drawn at the 35% probability level.
planar geometry is thus ascribable to significant steric congestion
arising from the cyclooct-4-en-1-yl ligand and the phosphorus-
bound phenyl groups. This phenomenon is somewhat consistent
with the result that no reaction was found for COD with 2b-d,
as the amido diphosphine ligands in the latter molecules are
sterically more demanding than that in 2a. The C(41)-C(42)
distance of 1.304(7) Å in 3a is characteristic of a CdC double-
bond length. The small torsion angle of 2.41° found for
C-C(41)-C(42)-C is consistent with C(41) and C(42) atoms
having sp2 hybridization. It is interesting to note that 3a is
resistant to ꢀ-hydrogen elimination, in spite of its severely
distorted square planar geometry. On the basis of microscopic
reverse between ꢀ-elimination and olefin insertion, the highly
reactive 2a must be much higher in energy than ꢀ-hydrogen-
containing alkyl complexes such as 3a. This result is apparently
phenomenal, as nickel hydride species are usually thermally
more stable than their alkyl counterparts that bear ꢀ-hydrogen
atoms.
The in situ prepared 2a also reacts with other olefins such as
ethylene, 1-hexene, and norbornene to generate [Ph-PNP]NiEt
(4a), [Ph-PNP]Ni(n-hexyl) (5a), and [Ph-PNP]Ni(2-norbornyl)
(6a), respectively (Scheme 3). In general, these reactions proceed
at room temperature cleanly to produce quantitatively the olefin
insertion products. Similar reactions were also found for 2d,
from which [Ph-PNP-iPr]NiEt (4d), [Ph-PNP-iPr]Ni(n-hexyl)
(5d), and [Ph-PNP-iPr]Ni(2-norbornyl) (6d) were isolated upon
treating with appropriate olefins. In contrast, no reaction was
found for 2b,c under similar conditions or even at elevated
temperatures. The lack of ethylene insertion reactivity was also
found for a palladium hydride complex supported by a similar
amido phosphine ligand.80 The electrophilicity of the nickel
(81) Waugh, J. S.; Cotton, F. A. J. Phys. Chem. 1961, 65, 562–563.
(82) Liang, L.-C.; Huang, M.-H.; Hung, C.-H. Inorg. Chem. 2004, 43,
2166–2174.
(80) Fafard, C. M.; Ozerov, O. V. Inorg. Chim. Acta 2007, 360, 286–
292.

3088 Organometallics, Vol. 27, No. 13, 2008
Liang et al.
Scheme 3
Scheme 4
phosphorus donor that contains phenyl instead of isopropyl
substituents, so as to minimize the intramolecular steric repul-
sion. Unlike that of 3a, the core structure of 6d deviates only
negligibly by 0.0728 Å from the ideal square plane, although
both molecules contain a secondary cycloalkyl ligand and the
Ni-C distances are virtually identical (Table 2). It is likely that
the steric repulsion arising from the ꢀ-CH2 moieties in 3a is
significantly larger than that in 6d, as evidenced by the
Ni-CR-Cꢀ bond angles of 94.7(2) and 119.4(3)° for the former,
whereas they are 111.2(2) and 123.6(2)° for the latter.
Figure 6. Newman projection of [Ph-PNP-iPr]NiCH2R (R ) Me
(4d), n-pentyl (5d)) along the Ni-CR bond.
In contrast to the selective 1,2-insertion found for 1-hexene,
styrene inserts into the Ni-H bond of 2d in an exclusively 2,1-
manner to afford [Ph-PNP-iPr]NiCH(Me)Ph (7d) (Scheme 4).
Such regiospecificity of styrene insertion is reminiscent of what
has been reported for [(η5-C5H4-CMe3)2ZrH2]2,67 [Y(η5:η1-
C5Me4CH2SiMe2NCMe3)(THF)(µ-H)]2,83 and [Y(L)(µ-H)]2 (L
) (C5Me4CH2SiMe2NCH2CH2NMe2)2- 18
but is in contrast
)
with that of Cp*2ZrH2 (Cp* ) η5-C5Me5),67 Cp*{(η5-C5H3-
1,3-(CMe3)2}ZrH2,67 and {(η5-C5H3-1,3-(CMe3)2}2ZrH2 (ex-
clusively 1,2-insertion).67 The DEPT 13C NMR spectrum shows
the characteristic R-methine and ꢀ-methyl groups. No methylene
signal was observed. Consistently, the R-proton appears in the
1H NMR spectra at 3.30 ppm with an intensity corresponding
to one hydrogen atom. As a result, the solution symmetry of
7d is C1. Similar to the case for other complexes derived from
[Ph-PNP-iPr]-, the phosphorus donors in 7d are observed as
two doublet resonances in the 31P{1H} NMR spectrum. A
similar reaction involving the in situ prepared 2a led to a mixture
of 3a and the presumed styrene insertion product (7a; δP 23.4
ppm). Attempts to selectively isolate 7a, however, were not
successful. The identity of its regiospecificity was thus inde-
terminate. No reaction was found for 2b,c under similar or
forcing conditions (80 °C).
Figure 7. Molecular structure of [Ph-PNP-iPr]Ni(n-hexyl) (5d) with
thermal ellipsoids drawn at the 35% probability level.
Red crystals of 7d suitable for X-ray diffraction analysis were
grown from a concentrated diethyl ether solution at -35 °C.
As depicted in Figure 9, 7d is a four-coordinate species
containing an R-methylbenzyl ligand, consistent with the result
derived from the solution NMR studies. The coordination
geometry, and bond distances and angles for the core structure
of 7d are all similar to those of 5d and 6d. Consistent with the
steric standpoint, both methyl and phenyl substituents at the
R-carbon atom in 7d are tilted toward the phosphorus donor
bearing phenyl rather than isopropyl groups.
Though 2b,c do not react with electronically neutral olefins
(vide supra), treatment of these nickel hydride complexes with
electronically activated olefins such as methyl acrylate afforded
quantitatively the corresponding insertion products [iPr-
PNP]NiCH(Me)CO2Me (8b) and [Cy-PNP]NiCH(Me)CO2Me
Figure 8. Molecular structure of [Ph-PNP-iPr]Ni(2-norbornyl) (6d)
with thermal ellipsoids drawn at the 35% probability level.
(83) Trifonov, A. A.; Spaniol, T. P.; Okuda, J. Organometallics 2001,
20, 4869–4874.

Insertion Chemistry of Ni(II) Hydride Complexes
Organometallics, Vol. 27, No. 13, 2008 3089
Figure 10. Proposed four-membered cyclic transition states which
contain electron-releasing (left) or electron-withdrawing (right)
substituents.
these donors. These results are consistent with a hindered
rotation of the nickel-bound, asymmetric -CH(Me)CO2Me
group about the Ni-C bond. Similar phenomena were also
found for 8a,c. Consistent with the insertion reactivity, 8a-d
are all thermally stable and resistant to ꢀ-elimination even at
elevated temperatures (80 °C, 3 days).
Figure 9. Molecular structure of [Ph-PNP-iPr]NiCH(Me)Ph (7d)
with thermal ellipsoids drawn at the 35% probability level.
Scheme 5
It is interesting to note that 2a is most reactive toward olefin
insertion among the nickel hydride species investigated. The
reaction times in all cases are short, as compared to those of
the corresponding reactions involving 2b-d. The electronic and
steric properties of 2a derived from the phenyl-substituted amido
diphosphine ligand are thus comparatively superior in this
regard. The reactivity of 2b,c with methyl acrylate is in sharp
contrast to that with electronically neutral olefins (vide supra).
The regioselectivity of methyl acrylate (in reactions with 2a,d)
and styrene (in a reaction with 2d) also is in contrast with that
of 1-hexene (in reactions with 2a,d) under similar conditions.
These results highlight the olefin substituent effect. The reactiv-
ity discrepancy between methyl acrylate and electronically
neutral olefins such as ethylene with respect to 2b,c underscores
the significance of the enhanced back-π-acceptor nature of the
former, which encourages coordination to the nickel center. The
divergent regioselectivities of 1-hexene versus styrene and
methyl acrylate insertion, however, suggest two different cyclic
transition states in these reactions, where the electropositive
charge of the coordinated olefins is likely localized at the
ꢀ-carbon atom for the former, whereas it is at the R-carbon for
the latter (Figure 10). This hypothesis is consistent with the
anticipated electron-releasing character of an n-butyl group and
electron-withdrawing nature of a phenyl or ester substituent. In
accord with these results, Cundari and Holland also reported
that the relative ratio of R-methylbenzyl to isomeric phenylethyl
complexes in a ꢀ-diketiminate iron(II) system decreases as the
electron-releasing ability of the para substituents increases.68
The distinct regiospecificities of 1-hexene versus styrene and
methyl acrylate insertion described herein are reminiscent of
what has been found for early-transition-metal chemistry such
as [Y(η5:η1-C5Me4SiMe2NCMe3)(THF)(µ-H)]285 with 1-hexene
and styrene. The divergent insertion regiospecificities are also
relevant to those of polymer microstructures derived from
copolymerization of R-olefins with styrene or acrylates. For
instance, Proto and co-workers have shown that the microstruc-
ture of propylene-styrene multiblock copolymer prepared by
a bis-phenolate titanium catalyst is composed of 2,1-styrene units
and 1,2-propylene building blocks.49
(8c) (Scheme 5). A similar reaction employing 2d produced
[Ph-PNP-iPr]NiCH(Me)CO2Me (8d) cleanly. Reminiscent of
that with styrene, the reaction of the in situ prepared 2a with
methyl acrylate gave
a
mixture of 3a and [Ph-
PNP]NiCH(Me)CO2Me (8a). Recrystallization of the reaction
mixture from a diethyl ether solution at -35 °C, however,
selectively afforded 8a as a red crystalline solid in 71% yield.
Similar to that of 7d, the DEPT 13C NMR spectra of 8a-d
reveal a characteristic methine rather than methylene signal for
the nickel-bound carbon atom in these molecules (2JCP ) ca.
18 Hz), indicating an exclusive 2,1-insertion product for these
reactions. The R-proton is observed in the 1H NMR spectra of
8a-d at ca. 2.4 ppm with intensity corresponding to one
hydrogen atom. Complexes 8a-d are thus chiral and the two
phosphorus donors in these molecules are chemically inequiva-
lent. Notably, two isopropylmethine signals are observed for
8b (Figure S1, Supporting Information). This result is intriguing,
particularly for compounds derived from symmetrically substi-
tuted [R-PNP]-. It is interesting to note that the generation of
a chiral center at the R-carbon atom by olefin insertion is
relevant to stereoregular polymerization via a chain-end control
mechanism.84 The 31P{1H} NMR spectrum of 8b at room
temperature reveals two broad singlet resonances with equal
intensity at 33.4 ppm (∆V1/2 ) 638 Hz) and 31.4 ppm (∆V1/2
)
657 Hz). A variable-temperature 31P{1H}NMR study of 8b (in
toluene-d8) indicated that the two broad signals coalesce at 310
K and become sharper to give a singlet resonance at tempera-
tures higher than 330 K. When the temperature is lowered to
280 K, the two broad signals resolve to give two doublet
2
Conclusions
resonances with a JPP value of 253 Hz, a value that is
comparable to those of unsymmetrically substituted [Ph-PNP-
In summary, we have demonstrated that the reactivity and
regioselectivity of olefin insertion into a Ni-H bond can be
effectively manipulated by the electronic and steric properties
of substituents at the olefinic substrates and the phosphorus
iPr]- derivatives such as 4d (2JPP ) 271 Hz), 5d (2JPP ) 273
Hz), 6d (2JPP ) 258 Hz), 7d (2JPP ) 259 Hz), and 8d (2JPP
)
268 Hz). The large coupling constant found between the two
phosphorus atoms in 8b is indicative of a trans orientation for
(85) Hultzsch, K. C.; Voth, P.; Beckerle, K.; Spaniol, T. P.; Okuda, J.
Organometallics 2000, 19, 228–243.
(84) Coates, G. W. Chem. ReV. 2000, 100, 1223–1252.

3090 Organometallics, Vol. 27, No. 13, 2008
Liang et al.
and evaporated to dryness under reduced pressure. The resulting
solid residue was dissolved in diethyl ether (15 mL), and deionized
water (10 mL) was added at room temperature. The solution was
then dried over MgSO4, filtered, and evaporated to dryness under
reduced pressure. The oily residue thus obtained was dissolved in
a mixture of diethyl ether (5 mL) and pentane (1 mL). The solution
was cooled to -35 °C to afford the product as a pale yellow solid,
which was isolated and dried in vacuo. Crystals suitable for X-ray
diffraction analysis were grown from a concentrated diethyl ether
solution at -35 °C: yield 390 mg (53%). 1H NMR (C6D6, 500
MHz): δ 7.99 (dd, 1, JHP ) 10.5 and 3.5, NH), 7.56 (m, 5, Ar),
7.39 (dd, 1, Ar), 7.28 (m, 5, Ar), 7.14 (m, 6, Ar), 6.87 (dt, 2, Ar),
1.95 (m, 2, CHMe2), 1.10 (dd, 6, CHMe2), 0.95 (dd, 6, CHMe2).
31P{1H} NMR (C6D6, 202.3 MHz): δ -14.79 (br s, PiPr2), -16.66
(d, JPP ) 9.10, PPh2). 13C{1H} NMR (C6D6, 125.5 MHz): δ 149.96
donors of the amido diphosphine ligands. With various substit-
uents at the phosphorus donors, the electronic and steric
characteristics of the derived nickel(II) hydride complexes are
finely tunable. The unsymmetrically substituted 2d is unique,
as it exhibits reactivity resembling that of 2a and/or 2b,
depending on the olefinic substrates employed. Among the
nickel hydride complexes investigated, 2a is the most reactive
due to its higher electrophilic and sterically more accessible
nickel center. Remarkably, exclusive 1,2-insertion products were
generated from reactions with 1-hexene, whereas selective 2,1-
insertion occurs for reactions involving styrene and methyl
acrylate. The creation of a chiral center at the nickel-bound
hydrocarbyl ligand by 2,1-insertion is intriguing, particularly
for those derived from symmetrically substituted amido diphos-
phine ligands. Consistent with the insertion reactivity described
herein, the hydrocarbyl complexes containing ꢀ-hydrogen atoms
are all thermally stable and resistant to ꢀ-elimination, even at
elevated temperatures. These results suggest that the hydride
species 2a-d are higher in energy than their corresponding
olefin insertion products on the basis of the microscopic reverse
between ꢀ-elimination and olefin insertion.
(d, JCP ) 19.20, C), 147.20 (d, JCP ) 19.20, C), 137.13 (d, JCP
)
10.4, C), 134.99 (s, CH), 134.85 (d, JCP ) 20.08, CH), 133.95 (s,
CH), 130.29 (d, JCP ) 16.44, CH), 129.31 (d, JCP ) 6.40, CH),
129.24 (s, CH), 129.13 (d, JCP ) 10.92, C), 128.68 (s, CH), 122.77
(s, CH), 122.60 (d, JCP ) 15.56, C), 120.46 (s, CH), 119.33 (s,
CH), 117.04 (d, JCP ) 2.76, CH), 23.71 (d, JCP ) 10.92, CHMe2),
20.63 (d, JCP ) 19.20, CHMe2), 19.38 (d, JCP ) 9.16, CHMe2).
Anal. Calcd for C30H33NP2: C, 76.74; H, 7.08; N, 2.98. Found: C,
77.03; H, 7.23; N, 3.03.
Experimental Section
In Situ Synthesis of [Ph-PNP]NiH (2a). A solid mixture of
H[Ph-PNP] (10 mg, 0.019 mmol) and Ni(COD)2 (5 mg, 0.019
mmol) was dissolved in C6D6 (0.6 mL) at room temperature. The
reaction solution was transferred to an NMR tube, and the 1H and
31P{1H} NMR spectra were taken in 10 min. The spectroscopic
data indicate quantitative formation of [Ph-PNP]NiH along with 2
equiv of liberated COD. 1H NMR (C6D6, 200 MHz): δ 7.88 (d, 2,
Ar), 7.69 (m, 8, Ar), 7.25 (m, 4, Ar), 6.97 (m, 12, Ar), 6.48 (t, 2,
General Procedures. Unless otherwise specified, all experiments
were performed under nitrogen using standard Schlenk or glovebox
techniques. All solvents were reagent grade or better and purified
by standard methods. The NMR spectra were recorded on Varian
instruments. Chemical shifts (δ) are listed as parts per million
downfield from tetramethylsilane. Coupling constants (J) and peak
1
widths at half-height (∆V1/2) are listed in hertz. H and 13C NMR
spectra are referenced using the residual solvent peaks at δ 7.16
and 128.39, respectively, for C6D6. The assignment of the carbon
atoms for all new compounds is based on DEPT 13C NMR
spectroscopy. 31P NMR spectra are referenced externally using 85%
H3PO4 at δ 0. Routine coupling constants are not listed. All NMR
spectra were recorded at room temperature in specified solvents
unless otherwise noted. Elemental analysis was performed on a
Heraeus CHN-O Rapid analyzer.
2
Ar), -18.31 (t, JHP ) 62, NiH). 31P{1H} NMR (C6D6, 80.95
MHz): δ 32.65. Liberated COD molecules present in the reaction
1
aliquot: H NMR (C6D6, 200 MHz) δ 5.58 (s, 8, CHdCHCH2),
2.23 (s, 16, CHdCHCH2).
Synthesis of [Ph-PNP-iPr]NiH (2d). Benzene (6 mL) was added
to a solid mixture of [Ph-PNP-iPr]NiH (60 mg, 0.128 mmol) and
Ni(COD)2 (35 mg, 0.128 mmol) at room temperature. The red
reaction solution was stirred at room temperature for 10 min and
evaporated to dryness under reduced pressure. The oily residue was
washed with pentane (1 mL × 2) to remove liberated COD and
dried in vacuo, affording the product as a dark red solid: yield 60
mg (89%). Crystals suitable for X-ray diffraction analysis were
Materials. The compounds H[Ph-PNP] (1a)65,66 and [R-PNP-
i
]NiH (R ) Pr (2b), Cy (2c))74 were prepared according to the
procedures reported previously. All other chemicals were obtained
from commercial vendors and used as received.
X-ray Crystallography. Crystals of 2b,c suitable for X-ray
diffraction analysis were grown from a concentrated diethyl ether
solution at -35 °C. Table 1 summarizes the crystallographic data
for all structurally characterized compounds. Data were collected
on a Bruker-Nonius Kappa CCD diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.7107 Å). Structures were
solved by direct methods and refined by full matrix least-squares
procedures against F2 using the maXus or WinGX crystallographic
software package. All full-weight non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were placed in calculated positions.
Synthesis of H[Ph-PNP-iPr] (1d). n-BuLi (1.94 mL, 1.6 M in
hexane solution, 311 mmol, 2 equiv) was added dropwise to a
diethyl ether solution (50 mL) of bis(2-bromophenyl)amine (508
mg, 155 mmol) at -35 °C. The reaction solution was stirred at
room temperature for 3 h and cooled to -35 °C again. To this was
added dropwise a cold diethyl ether solution (2 mL) of chlorodi-
isopropylphosphine (237 mg, 155 mmol) at -35 °C. The reaction
mixture was stirred at room temperature overnight and cooled to
-35 °C before addition of n-BuLi (0.97 mL, 1.6 M in hexane, 155
mmol) dropwise. The solution was stirred at room temperature for
3 h and cooled to -35 °C again, and a cold (-35 °C) diethyl ether
solution (2 mL) of chlorodiphenylphosphine (324 mg, 155 mmol)
was added dropwise. The reaction solution was subsequently stirred
at room temperature overnight, filtered through a pad of Celite,
1
grown from a concentrated diethyl ether solution at -35 °C. H
NMR (C6D6, 500 MHz): δ 7.92 (dd, 1, Ar), 7.88 (dd, 1, Ar), 7.79
(m, 4, Ar), 7.26 (td, 1, Ar), 7.06 (m, 4, Ar), 7.00 (m, 5, Ar), 6.56
(t, 1, Ar), 6.48 (t, 1, Ar), 2.01 (m, 2, CHMe2), 1.21 (dd, 6, CHMe2),
i
PPh2
0.93 (dd, 6, CHMe2), -18.22 (dd, 1, JHPP Pr2 ) 68, JHP
) 58,
NiH). 31P{1H} NMR (C6D6, 202.3 MHz): δ 58.97 (d, JPP ) 243.78,
PiPr2), 31.27 (d, JPP ) 243.78, PPh2). 13C{1H} NMR (C6D6, 125.5
MHz): δ 163.55 (dd, JCP ) 21.59, JCP ) 4.14, C), 162.92 (dd, JCP
) 25.60, JCP ) 3.26, C), 135.20 (s, CH), 134.20 (d, JCP ) 12.30,
CH), 134.17 (d, JCP ) 44.80, C), 133.03 (s, CH), 132.15 (d, JCP
48.95, CH), 130.34 (d, JCP ) 1.88, CH), 129.11 (d, JCP ) 10.17,
CH), 128.68 (s, CH), 125.56 (d, JCP ) 42.55, C), 123.21 (d, JCP
)
)
34.76, C), 116.79 (d, JCP ) 6.40, CH), 116.40 (d, JCP ) 6.02, CH),
116.27 (d, JCP ) 10.04, CH), 115.68 (d, JCP ) 11.42, CH), 24.01
(d, JCP ) 25.98, CHMe2), 19.90 (d, JCP ) 6.02, CHMe2), 18.65 (s,
CHMe2). Anal. Calcd for C30H33NNiP2: C, 68.21; H, 6.30; N, 2.65.
Found: C, 68.06; H, 6.38; N, 2.65.
Synthesis of [Ph-PNP]Ni(η1-C8H13) (3a). A solid mixture of
H[Ph-PNP] (50 mg, 0.093 mmol) and Ni(COD)2 (25 mg, 0.093
mmol) was dissolved in benzene (1 mL) at room temperature. The
reaction solution was stirred at room temperature for 1 min and
evaporated to dryness under reduced pressure. The solid thus
obtained was washed with pentane (1 mL) and dried in vacuo to

Insertion Chemistry of Ni(II) Hydride Complexes
Organometallics, Vol. 27, No. 13, 2008 3091
give the product as a yellowish orange powder (52 mg, 83%).
Orange crystals suitable for X-ray diffraction analysis were grown
from a concentrated diethyl ether solution at -35 °C. H NMR
Synthesis of [Ph-PNP-iPr]Ni(n-hexyl) (5d). Neat 1-hexene (64
mg, 0.757 mmol, 4 equiv) was added to a solution of [Ph-PNP-
iPr]NiH (100 mg, 0.189 mmol) in benzene (2 mL) at room
temperature. The red reaction solution was stirred at room tem-
perature for 45 h and evaporated to dryness under reduced pressure,
affording the product as a red solid: yield 100 mg (86%). Crystals
suitable for X-ray diffraction analysis were grown by slow
evaporation of a concentrated benzene solution at room temperature.
1H NMR (C6D6, 500 MHz): δ 7.80 (m, 4, Ar), 7.72 (dd, 1, Ar),
7.62 (dd, 1, Ar), 7.20 (t, 1, Ar), 7.06 (br s, 6, Ar), 7.00 (m, 2, Ar),
6.95 (t, 1, Ar), 6.51 (t, 1, Ar), 6.43 (t, 1, Ar), 2.22 (m, 2, CHMe2),
1.33 (dd, 6, CHMe2), 1.19 (m, 4, Ni(CH2)5Me), 1.13 (m, 10, CHMe2
and Ni(CH2)5Me), 0.85 (m, 5, Ni(CH2)5Me and Ni(CH2)5Me).
31P{1H} NMR (C6D6, 202.3 MHz): δ 34.56 (d, JPP ) 273.12, PiPr2),
27.38 (d, JPP ) 273.12, PPh2). 13C{1H} NMR (C6D6, 125.5 MHz):
δ 163.20 (dd, JCP ) 20.08, JCP ) 3.64, C), 162.91 (dd, JCP ) 24.72,
JCP ) 3.64, C), 134.27 (s, CH), 134.11 (d, JCP ) 10.92, CH), 132.92
1
(C6D6, 500 MHz): δ 7.99 (m, 4, Ar), 7.72 (m, 4, Ar), 7.66 (dt, 2,
Ar), 7.24 (m, 2, Ar), 7.07 (m, 12, Ar), 6.94 (t, 2, Ar), 6.45 (t, 2,
Ar), 5.33 (m, 2, HCdCH), 2.36 (d, 1, cyclooctenyl), 2.00 (m, 1,
cyclooctenyl), 1.82 (m, 1, cyclooctenyl), 1.67 (m, 3, cyclooctenyl),
1.53 (m, 1, cyclooctenyl), 1.28 (m, 2, cyclooctenyl), 0.99 (m, 1,
cyclooctenyl), 0.85 (m, 1, cyclooctenyl). 31P{1H} NMR (C6D6,
202.31 MHz): δ 24.27. 13C{1H} NMR (C6D6, 125.5 MHz): δ
162.25 (t, JCP ) 13.2, C), 134.61 (t, JCP ) 6.7, CH), 134.08 (t, JCP
) 5.7, CH), 133.81 (t, JCP ) 6.54, C), 133.76 (s, CH), 133.70 (t,
JCP ) 5.7, C), 132.01 (s, CH), 130.80 (s, CH), 130.60 (s, CH),
130.13 (s, CH), 129.75 (s, CH), 129.16 (t, JCP ) 4.8, CH), 128.96
(t, JCP ) 4.7, CH), 116.85 (s, CH), 116.33 (s, CH), 39.38 (t, JCP
)
5.7, CH2), 33.48 (t, JCP ) 3.8, CH2), 30.33 (s, CH2), 28.88 (s, CH2),
2
25.40 (s, CH2), 20.82 (t, JCP ) 14.2, NiCH). Anal. Calcd for
(dd, JCP ) 39.78, JCP ) 1.88, C), 132.48 (s, CH), 132.31 (d, JCP
)
C44H41NNiP2: C, 75.02; H, 5.87; N, 1.99. Found: C, 74.65; H, 5.53;
N, 1.62.
1.38, CH), 131.55 (d, JCP ) 1.38, CH), 130.39 (d, JCP ) 1.88,
CH), 129.06 (d, JCP ) 9.16, CH), 125.95 (d, JCP ) 45.31, C), 121.88
Synthesis of [Ph-PNP]NiEt (4a). A benzene solution (1 mL)
of [Ph-PNP]NiH was prepared in situ from H[Ph-PNP] (10 mg,
0.019 mmol) and Ni(COD)2 (5 mg, 0.019 mmol) as described
above. The solution was transferred to a reaction vessel and
degassed with three freeze-pump-thaw cycles. Ethylene (1 atm)
was introduced. The reaction solution was stirred at room temper-
ature for 1 day and evaporated to dryness under reduced pressure
to afford the product as a red solid: yield 10 mg (83%). The NMR
spectroscopic data are all identical with those obtained from the
reaction of [Ph-PNP]NiCl with EtMgCl, as reported previously.66
Synthesis of [Ph-PNP-iPr]NiEt (4d). A reaction vessel was
charged with a solution of [Ph-PNP-iPr]NiH (20 mg, 0.038 mmol)
in benzene (2 mL). The solution was degassed with three
freeze-pump-thaw cycles, and ethylene (1 atm) was introduced.
The reaction solution was stirred at room temperature for 3 days.
The resulting yellow solution was evaporated to dryness under
reduced pressure to afford the product as a yellowish brown solid:
yield 20 mg (95%). 1H NMR (C6D6, 500 MHz): δ 7.80 (m, 4, Ar),
7.74 (dd, 1, J ) 5.0 and 8.5, Ar), 7.65 (dd, 1, J ) 4.0 and 8.5, Ar),
7.18 (dt, 1, Ar), 7.05 (m, 7, Ar), 6.99 (dt, 1, Ar), 6.95 (dt, 1, Ar),
6.51 (t, 1, J ) 7.5, Ar), 6.42 (t, 1, J ) 7.5, Ar), 2.16 (m, 2, CHMe2),
1.42 (m, 1, NiCHACHBMe), 1.29 (dd, 6, J ) 7.0 and 15.5, CHMe2),
1.08 (dd, 6, J ) 7.0 and 15.5, CHMe2), 0.96 (m, 1, NiCHACHBMe),
0.92 (m, 3, NiCH2Me). 31P{1H} NMR (C6D6, 202.3 MHz): δ 34.68
(d, JPP ) 271.30, PiPr2), 27.18 (d, JPP ) 271.30, PPh2). 13C{1H}
NMR (C6D6, 125.5 MHz): δ 163.24 (dd, JCP ) 20.08 and 4.02,
C), 162.91 (dd, JCP ) 23.85 and 3.64, C), 134.34 (s, CH), 134.09
(d, JCP ) 11.42, CH), 132.91 (dd, JCP ) 39.78 and 1.76, C), 132.49
(s, CH), 132.29 (d, JCP ) 1.38, CH), 131.54 (d, JCP ) 1.88, CH),
130.38 (d, JCP ) 1.88, CH), 129.11 (d, JCP ) 9.66, CH), 125.88
(d, JCP ) 37.02, C), 116.58 (d, JCP ) 9.16, CH), 116.46 (d, JCP
)
6.90, CH), 116.15 (d, JCP ) 5.52, CH), 115.67 (d, JCP ) 10.54,
CH), 35.41 (s, CH2), 32.36 (s, CH2), 31.69 (s, CH2), 24.10 (d, JCP
) 20.08, CHMe2), 23.53 (s, CH2), 19.25 (s, CHMe2), 18.13 (s,
CHMe2), 14.83 (s, CH3), 0.17 (vt, JCP ) 20.58, NiCH2). Anal. Calcd
for C36H45NNiP2: C, 70.61; H, 7.41; N, 2.29. Found: C, 70.22; H,
7.26; N, 2.24.
Synthesis of [Ph-PNP]Ni(2-norbornyl) (6a). To a solid mixture
of H[Ph-PNP] (100 mg, 0.19 mmol) and Ni(COD)2 (51 mg, 0.19
mmol) was added a toluene solution of norbornene (245 mg, 50
wt %, 1.3 mmol, 6.8 equiv) and benzene (3 mL) at room
temperature. The reaction solution was stirred at room temperature
for 14 h and evaporated to dryness under reduced pressure. The
solid thus obtained was washed with pentane (2 mL × 2) and dried
in vacuo to give the product as a brownish red powder: yield 118
mg (92%). Layering diethyl ether on a concentrated THF solution
at room temperature afforded a red microcrystalline solid. 1H NMR
(C6D6, 500 MHz): δ 7.92 (m, 8, Ar), 7.53 (dt, 2, Ar), 7.14 (m, 2,
Ar), 7.06 (m, 12, Ar), 6.88 (t, 2, Ar), 6.40 (t, 2, Ar), 2.01 (br s, 1,
norbornyl), 1.80 (t, 1, norbornyl), 1.62 (m, 1, norbornyl), 1.50
(quintet, 1, norbornyl), 1.23 (m, 1, norbornyl), 1.03 (m, 2,
norbornyl), 0.90 (m, 2, norbornyl), 0.68 (t, 1, norbornyl), 0.62 (d,
1, norbornyl). 31P{1H} NMR (C6D6, 202.3 MHz): δ 25.32. 13C{1H}
NMR (C6D6, 125.5 MHz): δ 161.94 (t, JCP ) 13.1, C), 134.62 (t,
JCP ) 6.0, CH), 134.53 (t, JCP ) 6.0, CH), 133.77 (s, CH), 133.39
(t, JCP ) 20.1, C), 133.16 (t, JCP ) 20.1, C), 132.11 (s, CH), 130.43
(s, CH), 129.04 (t, JCP ) 4.8, CH), 126.76 (t, JCP ) 23.5, C), 116.87
(t, JCP ) 3.0, CH), 116.40 (t, JCP ) 4.4, CH), 45.79 (t, JCP ) 6.0,
CH), 42.22 (t, JCP ) 4.8, CH2), 38.72 (s, CH), 38.58 (s, CH2), 34.70
(s, CH2), 30.21 (s, CH2), 25.00 (t, 2JCP ) 16.6, NiCH). Anal. Calcd
for (C43H39NNiP2)3(THF)2: C, 74.26; H, 6.05; N, 1.90. Found: C,
73.94; H, 5.73; N, 1.90.
(d, JCP ) 45.68, C), 121.87 (d, JCP ) 37.15, C), 116.65 (d, JCP
)
9.16, CH), 116.48 (d, JCP ) 6.40, CH), 116.18 (d, JCP ) 6.02,
CH), 115.66 (d, JCP ) 10.04, CH), 24.02 (dd, JCP ) 19.58 and
1.76, CHMe2), 19.25 (d, JCP ) 5.02, CHMe2), 18.10 (d, JCP ) 0.88,
CHMe2), 15.78 (t, JCP ) 2.39, NiCH2Me), -8.51 (vt, JCP ) 20.58,
NiCH2Me). Anal. Calcd for C32H37NNiP2: C, 69.09; H, 6.70; N,
2.52. Found: C, 68.92; H, 6.57; N, 2.50.
Synthesis of [Ph-PNP]Ni(n-hexyl) (5a). To a solid mixture of
H[Ph-PNP] (10 mg, 0.019 mmol) and Ni(COD)2 (5 mg, 0.019
mmol) was added 1-hexene (25 mg, 0.297 mmol, 16 equiv)
followed by benzene (1 mL) at room temperature. The reaction
solution was transferred to an NMR tube, and the reaction was
monitored by 31P{1H} NMR spectroscopy, which showed quantita-
tive formation of [Ph-PNP]Ni(n-hexyl) in 1 day. The NMR
spectroscopic data are all identical with those obtained from the
reaction of [Ph-PNP]NiCl with n-hexylmagnesium chloride, as
reported previously.65
Synthesis of [Ph-PNP-iPr]Ni(2-norbornyl) (6d). Neat nor-
bornene (36 mg, 0.379 mmol, 2 equiv) was added to a solution of
[Ph-PNP-iPr]NiH (100 mg, 0.189 mmol) in benzene (4 mL) at room
temperature. The red reaction solution was stirred at room tem-
perature for 23 h and evaporated to dryness under reduced pressure,
affording the product as a red solid: yield 80 mg (68%). Red crystals
suitable for X-ray diffraction analysis were grown by slow
evaporation of a concentrated benzene solution at room temperature.
1H NMR (C6D6, 500 MHz): δ 8.16 (t, 2, Ar), 7.62 (t, 2, Ar), 7.55
(dd, 1, Ar), 7.42 (dd, 1, Ar), 7.13 (t, 1, Ar), 7.03 (m, 7, Ar), 6.96
(t, 1, Ar), 6.83 (t, 1, Ar), 6.42 (q, 2, Ar), 2.23 (m, 1, CHMe2), 1.98
(br s, 1, norbornyl), 1.82 (m, 1, CHMe2), 1.54 (m, 1, norbornyl),
1.47 (dd, 3, CHMe2), 1.42 (m, 1, norbornyl), 1.38 (dt, 1, norbornyl),
1.30 (dd, 3, CHMe2), 1.27 (dd, 3, CHMe2), 1.21 (m, 1, norbornyl),
1.91 (m, 2, norbornyl), 1.03 (dd, 3, CHMe2), 0.91 (m, 3, norbornyl),

3092 Organometallics, Vol. 27, No. 13, 2008
Liang et al.
(d, J ) 4.52, CH), 125.98 (t, JCP ) 24.22, C), 117.65 (t, JCP
0.56 (d, 1, norbornyl). 31P{1H} NMR (C6D6, 202.3 MHz): δ 29.62
(d, JPP ) 257.54, PiPr2), 25.76 (d, JPP ) 257.54, PPh2). 13C{1H}
NMR (C6D6, 125.5 MHz): δ 163.27 (dd, JCP ) 4.14 and 18.70,
C), 162.28 (dd, JCP ) 3.64 and 21.46, C), 134.99 (d, JCP ) 11.92,
CH), 134.66 (d, JCP ) 10.04, CH), 134.49 (d, JCP ) 4.14, C), 133.82
(d, JCP ) 2.26, C), 133.76 (s, CH), 133.55 (d, JCP ) 2.26, C), 132.07
(s, CH), 131.90 (d, JCP ) 1.38, CH), 131.57 (d, JCP ) 1.88, CH),
130.62 (d, JCP ) 1.88, CH), 129.96 (d, JCP ) 1.76, CH), 129.03
(d, JCP ) 9.16, CH), 128.93 (s, CH), 120.65 (d, JCP ) 38.40, C),
116.72 (d, JCP ) 6.40, CH), 116.54 (d, JCP ) 8.66, CH), 116.09
)
3.26, CH), 116.85 (t, JCP ) 4.52, CH), 50.12 (s, OCH3), 15.93 (s,
NiCH(CH3)), 9.61 (t, JCP ) 16.06, NiCH). Anal. Calcd for
(C40H35NNiO2P2)(OEt2)0.5 (confirmed by integration of 1H NMR):
C, 70.10; H, 5.61; N, 1.95. Found: C, 70.40; H, 5.90; N, 1.79.
Synthesis of [iPr-PNP]NiCH(Me)CO2Me (8b). Benzene (1 mL)
was added to a mixture of solid [iPr-PNP]NiH (50 mg, 0.10 mmol)
and methyl acrylate (87 mg, 0.86 mmol, 8.6 equiv) at room
temperature. The reaction solution was stirred at room temperature
for 2 h to give a red solution, which was evaporated to dryness
under reduced pressure, triturated with pentane (2 mL × 2), and
dried in vacuo to afford the product as a red solid: yield 58 mg
(95%). 1H NMR (C6D6, 500 MHz): δ 7.55 (d, 2, Ar), 7.02 (br s, 2,
Ar), 6.92 (t, 2, Ar), 6.45 (t, 2, Ar), 3.49 (s, 3, OMe), 2.47 (br s, 2,
(d, JCP ) 8.28, CH), 115.62 (d, JCP ) 5.52, CH), 46.63 (dd, JCP
)
2.26 and 12.80, norbornyl CH), 42.25 (d, JCP ) 3.26, norbornyl
CH2), 38.51 (s, norbornyl CH2), 38.06 (s, norbornyl CH2), 35.17
(s, norbornyl CH2), 30.44 (s, norbornyl CH2), 25.21 (dd, JCP
)
3
3
2.76 and 15.06, NiCH), 23.13 (dd, JCP ) 1.88 and 20.58, CHMe2),
20.22 (d, JCP ) 5.90, CHMe2), 18.46 (d, JCP ) 3.64, CHMe2), 18.53
(d, JCP ) 3.26, CHMe2), 17.24 (dd, JCP ) 2.76, CHMe2), 15.94
(vt, JCP ) 18.70, CHMe2). Anal. Calcd for C37H43NNiP2: C, 71.40;
H, 6.96; N, 2.25. Found: C, 71.03; H, 7.00; N, 1.88.
CHMe2), 2.41 (qt, 1, JHP ) 13, JHH ) 7, NiCH), 2.22 (br s, 2,
CHMe2), 1.42 (br s, 12, CHMe2), 1.33 (d, 3, JHP ) 7, NiCH(CH3)),
1.16 (dd, 6, CHMe2), 1.10 (dd, 6, CHMe2). 31P{1H} NMR (C6D6,
202.3 MHz): δ 33.36 (br s, ∆V1/2 ) 638 Hz), 31.42 (br s, ∆V1/2
)
657 Hz). 13C{1H} NMR (C6D6, 125.7 MHz): δ 184.18 (CdO),
163.78 (m, C), 132.53 (m, CH), 131.51 (s, CH), 121.51 (m, C),
116.72 (s, CH), 116.32 (t, JCP ) 2.77, CH), 50.11 (s, OMe), 24.19
Synthesis of [Ph-PNP-iPr]NiCH(Me)Ph (7d). Neat styrene (24
mg, 0.23 mmol) was added to a solution of [Ph-PNP-iPr]NiH (100
mg, 0.189 mmol) in benzene (2 mL) at room temperature. The
reaction solution was stirred at room temperature for 18 h and
evaporated to dryness under reduced pressure. Diethyl ether (10
mL) was added. The solution was filtered through a pad of Celite,
concentrated under reduced pressure, and cooled to -35 °C to afford
the product as a red crystalline solid: yield 107 mg (90%). 1H NMR
(C6D6, 500 MHz): δ 7.70 (m, 2, Ar), 7.54 (dd, 1, Ar), 7.45 (dd, 1,
Ar), 7.20 (m, 2, Ar), 7.05 (m, 6, Ar), 6.94 (m, 9, Ar), 6.46 (t, 1,
Ar), 6.33 (t, 1, J ) 7, Ar), 3.30 (m, 1, NiCH(Me)Ph), 2.32 (m, 1,
CHMe2), 2.08 (m, 1, CHMe2), 1.39 (d, 3, NiCH(Me)Ph), 1.37 (dd,
3, CHMe2), 1.27 (dd, 3, CHMe2), 1.17 (dd, 3, CHMe2), 1.10 (dd,
(m, CHMe2), 23.89 (br s, CHMe2), 19.76 (br s, CH3), 19.51 (br s,
2
CH3), 17.95 (m, CH3), 17.88 (s, NiCH(CH3)), -0.11 (t, JCP
)
18.35, NiCH). IR (Nujol): 1697 cm-1 (CdO). Anal. Calcd for
C28H43NNiO2P2: C, 61.56; H, 7.93; N, 2.56. Found: C, 62.75; H,
8.08; N, 2.30. Multiple attempts to obtain satisfactory analysis data
were not successful.
Synthesis of [Cy-PNP]NiCH(Me)CO2Me (8c). Benzene (3 mL)
was added to a mixture of [Cy-PNP]NiH (60 mg, 0.096 mmol)
and methyl acrylate (110 mg, 1.056 mmol, 11 equiv) at room
temperature. The reaction solution was stirred at room temperature
for 24 h and evaporated to dryness under reduced pressure. The
solid residue was washed with pentane (2 mL × 2) to afford the
3, CHMe2). 31P{1H} NMR (C6D6, 202.31 MHz): δ 30.67 (d, JPP
)
259.16, PiPr2), 22.85 (d, JPP ) 259.16, PPh2). 13C{1H} NMR (C6D6,
125.5 MHz): δ 162.97 (dd, JCP ) 19.20 and 3.64, C), 162.15 (dd,
JCP ) 21.96 and 3.26, C), 155.90 (d, JCP ) 6.90, C), 134.90 (d,
JCP ) 11.04, CH), 134.04 (d, JCP ) 11.42, CH), 133.64 (s, CH),
132.24 (dd, JCP ) 35.64 and 2.26, C), 132.01 (d, CH), 131.81 (s,
CH), 131.66 (d, JCP ) 1.38, CH), 131.50 (dd, JCP ) 32.88 and
2.26, C), 130.29 (d, JCP ) 1.88, CH), 129.86 (d, JCP ) 1.88, CH),
128.79 (d, JCP ) 9.16, CH), 128.63 (d, JCP ) 12.30, CH), 128.54
(s, CH), 127.38 (d, JCP) 47.56, C), 126.91 (s, CH), 122.85 (s, CH),
121.2 (d, JCP ) 39.78, C), 117.19 (d, JCP ) 8.66, CH), 116.67 (d,
product as a red solid: yield 68 mg (96%). H NMR (C6D6, 500
1
MHz): δ 7.66 (d, 2, Ar), 7.22 (br s, 2, Ar), 6.95 (t, 2, Ar), 6.49 (t,
2, Ar), 3.56 (s, 3, OMe), 2.51 (m, 5, NiCH and Cy), 1.86 (m, 4,
Cy), 1.68 (m, 20, Cy), 1.47 (d, 3, NiCH(Me)), 1.25 (m, 12, Cy),
1.11 (m, 4, Cy). 31P{1H} NMR (C6D6, 202.3 MHz): δ 25.45 (∆V1/2
) 58.84 Hz). 13C{1H} NMR (C6D6, 125.7 MHz): δ 184.31 (s,
CdO), 164.07 (t, JCP ) 9.18, C), 132.72 (m, CH), 131.35 (m, CH),
122.06 (m, C), 116.79 (s, CH), 116.30 (s, CH), 50.42 (s, OMe),
34.53 (t, 1JCP ) 9.18, PCH), 28.72 (s, CH2), 28.12 (m, CH2), 27.80
(s, CH2), 26.96 (s, CH2), 26.78 (s, CH2), 17.55 (s, NiCH(Me)), 0.74
(t, 2JCP ) 18.35, NiCH(Me)). IR (Nujol): 1690 cm-1 (CdO). Anal.
Calcd for C40H59NNiO2P2: C, 68.00; H, 8.42; N, 1.98. Found: C,
68.07; H, 8.55; N, 1.85.
JCP ) 6.90, CH), 116.16 (d, JCP ) 6.02, CH), 115.62 (d, JCP
)
9.16, CH), 24.91 (d, JCP ) 18.20, CHMe2), 23.27 (d, JCP ) 20.58,
CHMe2), 19.80 (d, JCP ) 5.90, CH3), 19.60 (d, JCP ) 4.14, CH3),
18.95 (d, JCP ) 4.14, CH3), 18.02 (s, CH3), 17.87 (s, CH3), 7.40
(dd, JCP ) 17.82 and 13.68, NiCH). Anal. Calcd for C38H41NNiP2:
C, 72.16; H, 6.54; N, 2.22. Found: C, 72.17; H, 6.77; N, 2.03.
Synthesis of [Ph-PNP]NiCH(Me)CO2Me (8a). A benzene
solution (3 mL) of [Ph-PNP]NiH was prepared in situ from H[Ph-
PNP] (100 mg, 0.19 mmol) and Ni(COD)2 (51 mg, 0.19 mmol) as
described above. Neat methyl acrylate (245 mg, 2.85 mmol) was
added. The reaction mixture was stirred at room temperature for
15 min. All volatiles were removed in vacuo. Diethyl ether (10
mL) was added. The solution was filtered through a pad of Celite,
concentrated under reduced pressure until the volume became ca.
4 mL, and cooled to -35 °C to afford the product as a deep red
Synthesis of [Ph-PNP-iPr]NiCH(Me)CO2Me (8d). Neat methyl
acrylate (32 mg, 0.378 mmol, 2 equiv) was added to a solution of
[Ph-PNP-iPr]NiH (100 mg, 0.189 mmol) in benzene (2 mL) at room
temperature. The red reaction solution was stirred at room tem-
perature for 24 h and evaporated to dryness under reduced pressure,
affording the product as a red solid: yield 100 mg (84%). 1H NMR
(C6D6, 500 MHz): δ 8.10 (m, 2, Ar), 7.91 (m, 2, Ar), 7.58 (dd, 1,
Ar), 7.47 (dd, 1, Ar), 7.13 (m, 2, Ar), 7.06 (m, 6, Ar), 6.88 (m, 2,
Ar), 6.47 (t, 1, Ar), 6.36 (t, 1, Ar), 3.26 (s, 3, OMe), 2.42 (m, 1,
CHMe2), 2.34 (m, 1, CHMe2), 2.14 (m, 1, NiCH(Me)CO2Me), 1.43
(dd, 3, CHMe2), 1.38 (dd, 3, CHMe2), 1.28 (dd, 3, CHMe2), 1.09
(dd, 3, CHMe2), 1.07 (d, 3, NiCH(Me)CO2Me). 31P{1H} NMR
(C6D6, 202.3 MHz): δ 35.99 (d, JPP ) 268 Hz, PiPr2), 24.62 (d, JPP
) 268 Hz, PPh2). 13C{1H} NMR (C6D6, 125.5 MHz): δ 183.24
(d, JCP ) 5.90, C), 163.40 (dd, JCP ) 3.64 and 20.08, C), 162.49
1
crystalline solid: yield 90 mg (71%). H NMR (C6D6, 500 MHz):
δ 8.22 (q, 4, Ar), 7.74 (q, 4, Ar), 7.64 (d, 2, Ar), 7.17 (m, 6, Ar),
7.00 (m, 8, Ar), 6.88 (t, 2, Ar), 6.37 (t, 2, Ar), 2.94 (s, 3, OMe),
2.19 (m, 1, CHMe), 0.90 (d, 3, J ) 7, CHMe). 31P{1H} NMR
(C6D6, 202.31 MHz): δ 26.78. 13C{1H} NMR (C6D6, 125.5 MHz):
δ 183.37 (t, JCP ) 4.14, CO), 162.52 (t, JCP ) 13.30, C), 135.06
(t, J ) 6.02, CH), 134.65 (s, CH), 133.94 (t, JCP ) 5.90, CH),
132.26 (s, CH), 131.95 (t, J ) 22.84, C), 131.26 (t, J ) 20.96, C),
130.76 (s, CH), 130.46 (s, CH), 129.19 (d, J ) 5.02, CH), 129.04
(dd, JCP ) 2.76 and 22.84, C), 134.71 (dd, JCP ) 96.64, JCP
10.54, CH), 133.91 (s, CH), 133.09 (d, JCP ) 40.29, C), 132.05 (s,
CH), 131.83 (d, JCP ) 44.80, CH), 130.53 (dd, JCP ) 41.16, JCP
1.76, CH), 129.05 (d, JCP ) 10.04, CH), 128.92 (s, CH), 127.18
(d, JCP ) 47.57, C), 121.39 (d, JCP ) 39.78, C), 117.54 (d, JCP
9.16, CH), 117.15 (d, JCP ) 6.40, CH), 116.75 (d, JCP ) 5.90,
)
)
)

Insertion Chemistry of Ni(II) Hydride Complexes
Organometallics, Vol. 27, No. 13, 2008 3093
CH), 115.85 (d, JCP ) 9.54, CH), 50.18 (s, OMe), 24.41 (d, JCP
20.58, CHMe2), 24.04 (d, JCP ) 23.34, CHMe2), 19.69 (d, JCP
)
)
Shen Kuo (National Taiwan Normal University) for assis-
tance with X-ray crystallography, and the National Center
for High-performance Computing (NCHC) for computer time
and facilities.
4.64, CHMe2), 18.89 (d, JCP ) 3.26, CHMe2), 18.08 (s, CHMe2),
17.75 (s, CHMe2), 15.88 (d, JCP ) 5.52, NiCH(Me)CO2Me), 3.70
(vt, JCP
) 16.69, NiCH(Me)CO2Me). Anal. Calcd for
C34H39NNiO2P2: C, 66.48; H, 6.40; N, 2.28. Found: C, 66.59; H,
6.27; N, 2.10.
Supporting Information Available: A figure giving the 1H
NMR spectrum of 8b and CIF files giving X-ray crystallographic
data for 1d, 2b-d, 3a, and 5d-7d. This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank the National Science Council
of Taiwan for financial support (Nos. NSC 96-2628-M-110-
007-MY3 and 96-2918-I-110-011) of this work, Mr. Ting-
OM701294A