Synthesis, structure, and reactivity of (tBu2PC2H4PtBu 2)Ni(CH3)2 and {(tBu2PC2H4PtBu 2)Ni}2(μ-H)2

Article abstract of DOI:10.1021/om980705y

Oxidative addition of CH₃I to (d^tbpe)Ni(C₂H₄) (d^tbpe = ^tBu₂PC₂H₄P^tBu ₂) affords (d^tbpe)-Ni(I)CH₃ (1). The reaction of (d^tbpe)NiCl₂ or 1 with the stoichiometric quantity of (tmeda)-Mg(CH₃)₂ yields (d^tbpe)Ni(CH₃)₂ (2). (d^tbpe)Ni(I)CD₃ (1-d₃) and (d^tbpe)Ni(CD₃)₂ (2-d₆) have been prepared analogously. Thermolysis of 2 in benzene affords {(d^tbpe)Ni}₂(μ-η²:η ²-C₆H₆) (4). The reaction of either 2 or 4 with hydrogen (H₂, HD, D₂) gives {(d^tbpe)Ni}₂(μ-H)₂ (3) and the isotopomers {(d^tbpe)Ni}₂(μ-H)(μ-D) (3-d) and {(d^tbpe)Ni}₂(μ-D)₂ (3-d₂). According to the NMR spectra, the structure of 3 is dynamic in solution. The crystal structures of 2 and 3 have been determined by X-ray crystallography. Solution thermolysis of 2 or reduction of (d^tbpe)NiCl₂ with Mg* in the presence of alkanes probably involves σ-complex-type intermediates [(d^tbpe)Ni(η²-R′H)] (R′ = e.g. C₂H₅, A). While the nonisolated [(d^tbpe)Ni⁰] σ-complexes A are exceedingly reactive intermediates, isolated 3 and 4 represent easy to handle starting complexes for [(d^tbpe)Ni⁰] reactions. Partial protolysis of 2 with CF₃SO₃H affords (d^tbpe)Ni(CH₃)(OSO₂CF₃) (5). Complex 5 reacts slowly with 2 equiv of ethene to give equimolar amounts of [(d^tbpe)Ni(C₂H₅)]⁺(OSO ₂CF₃^-) (6) and propene. The reaction is thought to be initiated by an insertion of ethene into the Ni-CH₃ bond of 5 to form the intermediate [(d^tbpe)Ni(C₃H₇)(OSO₂CF ₃)] (G), followed by elimination of propene to give the hydride intermediate [(d^tbpe)Ni(H)(OSO₂CF₃)] (H), which on insertion of ethene into the Ni-H bond affords 6.

Full text of DOI:10.1021/om980705y

10
Organometallics 1999, 18, 10-20
Articles
Syn th esis, Str u ctu r e, a n d Rea ctivity of
(tBu 2P C2H4P tBu 2)Ni(CH3)2 a n d
†
{(tBu 2P C2H4P tBu 2)Ni}2(µ-H)2
Ingrid Bach, Richard Goddard, Carsten Kopiske, Klaus Seevogel, and
Klaus-Richard Po¨rschke*
Max-Planck-Institut fu¨r Kohlenforschung, D-45466 Mu¨lheim an der Ruhr, Germany
Received August 18, 1998
t
Oxidative addition of CH3I to (dtbpe)Ni(C2H4) (dtbpe ) Bu2PC2H4PtBu2) affords (dtbpe)-
Ni(I)CH3 (1). The reaction of (dtbpe)NiCl2 or 1 with the stoichiometric quantity of (tmeda)-
Mg(CH3)2 yields (dtbpe)Ni(CH3)2 (2). (dtbpe)Ni(I)CD3 (1-d3) and (dtbpe)Ni(CD3)2 (2-d6) have
been prepared analogously. Thermolysis of 2 in benzene affords {(dtbpe)Ni}2(µ-η2:η2-C6H6)
(4). The reaction of either 2 or 4 with hydrogen (H2, HD, D2) gives {(dtbpe)Ni}2(µ-H)2 (3) and
the isotopomers {(dtbpe)Ni}2(µ-H)(µ-D) (3-d) and {(dtbpe)Ni}2(µ-D)2 (3-d2). According to the
NMR spectra, the structure of 3 is dynamic in solution. The crystal structures of 2 and 3
have been determined by X-ray crystallography. Solution thermolysis of 2 or reduction of
(dtbpe)NiCl2 with Mg* in the presence of alkanes probably involves σ-complex-type
intermediates [(dtbpe)Ni(η2-R′H)] (R′ ) e.g. C2H5, A). While the nonisolated [(dtbpe)Ni0]
σ-complexes A are exceedingly reactive intermediates, isolated 3 and 4 represent easy to
handle starting complexes for [(dtbpe)Ni0] reactions. Partial protolysis of 2 with CF3SO3H
affords (dtbpe)Ni(CH3)(OSO2CF3) (5). Complex 5 reacts slowly with 2 equiv of ethene to give
equimolar amounts of [(dtbpe)Ni(C2H5)]+(OSO2CF3-) (6) and propene. The reaction is thought
to be initiated by an insertion of ethene into the Ni-CH3 bond of 5 to form the intermediate
[(dtbpe)Ni(C3H7)(OSO2CF3)] (G), followed by elimination of propene to give the hydride
intermediate [(dtbpe)Ni(H)(OSO2CF3)] (H), which on insertion of ethene into the Ni-H bond
affords 6.
In tr od u ction
on the Ni0 metal center. Hence, whereas the somewhat
i
smaller Pr2PC2H4PiPr2 ligand allows the formation of
Increasing the size of ligands attached to metal
tetrahedral (T-4) and trigonal-planar (TP-3) Ni0-alkene
complexes,6 (dtbpe)Ni0-alkene complexes are exclu-
sively TP-3.3-5 Thus, for polyene ligands such as buta-
diene, 1,5-cyclooctadiene,3 and cyclooctatetraene5 only
one CdC bond is coordinated to the [(dtbpe)Ni0] frag-
ment. Interestingly, Spencer et al. have reported that
protolysis of (dtbpe)Ni(C2H4) by HBF4 affords [(dtbpe)-
Ni(C2H5)]+(BF4-) in which the C2H5 substituent is
â-agostic.7
As part of our studies into the reactivity of the [(d-
tbpe)Ni0] complexes, we were interested in investigating
the properties of (dtbpe)NiII,I-alkyl and -hydride com-
plexes. In particular, we wished to establish whether
they could be used to generate [(dtbpe)Ni0] moieties
directly in situ. Here we report the synthesis, structure,
and properties of the title compounds, (tBu2PC2H4P-
tBu2)Ni(CH3)2 and {(tBu2PC2H4PtBu2)Ni}2(µ-H)2.8
centers can have a marked influence on reactivity. For
example, Brookhart et al. have recently shown that
cationic NiII- and PdII-methyl complexes containing
bulky diimine ligands represent highly active catalysts
for the polymerization of ethene and R-olefins.1 For some
time we have been interested in Ni0 and Pd0 complexes
in which the metal center is ligated by the bidentate
phosphane tBu2PC2H4PtBu2 (dtbpe).2-5 The combination
of an exceedingly bulky phosphane ligand and the
relatively small size of Ni confers interesting properties
† Abbreviations: bipy, 2,2′-bipyridine; dtbpe, Bu2PC2H4PtBu2, bis-
t
(di-tert-butylphosphino)ethane; OTf, OSO2CF3, trifluoromethane-
sulfonate; tmeda, N,N,N′,N′-tetramethyl-1,2-ethanediamine.
(1) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414.
(2) Krause, J .; Bonrath, W.; Po¨rschke, K.-R. Organometallics 1992,
11, 1158.
(3) Po¨rschke, K.-R.; Pluta, C.; Proft, B.; Lutz, F.; Kru¨ger, C. Z.
Naturforsch., B: Anorg. Chem., Org. Chem. 1993, 48, 608.
(4) Bach, I.; Po¨rschke, K.-R.; Goddard, R.; Kopiske, C.; Kru¨ger, C.;
Rufinska, A.; Seevogel, K. Organometallics 1996, 15, 4959.
(5) Bach, I.; Po¨rschke, K.-R.; Proft, B.; Goddard, R.; Kopiske, C.;
Kru¨ger, C.; Rufinska, A.; Seevogel, K. J . Am. Chem. Soc. 1997, 119,
3773.
(6) Po¨rschke, K.-R. Angew. Chem. 1987, 99, 1321; Angew. Chem.,
Int. Ed. Engl. 1987, 26, 1288 and unpublished results.
(7) Conroy-Lewis, F. M.; Mole, L.; Redhouse, A. D.; Litster, S. A.;
Spencer, J . L. J . Chem. Soc., Chem. Commun. 1991, 1601.
(8) Bach, I. Dissertation, Universita¨t Du¨sseldorf, 1996.
10.1021/om980705y CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/11/1998

Sterically Encumbered Ni Phosphane Complexes
Organometallics, Vol. 18, No. 1, 1999 11
Resu lts
Attempts to synthesize (dtbpe)Ni(H)CH3 by reacting
1 with hydridic reagents such as LiAlHiBu3 or NaBHEt3
in diethyl ether or THF resulted in the formation of the
dinuclear NiI-hydride 3 as the main product. It seems
likely that (dtbpe)Ni(H)CH3 is formed as an intermedi-
ate but that it decomposes into 3, similar to the solution
thermolysis of 2 (see below). Thus, whereas trans-L2-
Ni(H)CH3 complexes have been known for a long time,14
complexes of the type cis-L2Ni(H)CH3 remain elusive.
When the red suspension of (dtbpe)NiCl2 in diethyl
ether is stirred with 1 equiv of (tmeda)Mg(CH3)2 at -30
°C, a yellow-orange solution is formed from which, after
(C4H8O2)2MgCl2 is precipitated with dioxane, yellow
cubes of 2 (69%) crystallize at -78 °C. Similarly, (d-
tbpe)NiCl2 reacts with (tmeda)Mg(CD3)2 to give (dtbpe)-
Ni(CD3)2 (2-d6). Complex 2 can also be obtained from
the reaction of 1 with the stoichiometric amount of
(tmeda)Mg(CH3)2 (eq 2). Surprisingly, no reaction occurs
(t Bu 2P C2H 4P t Bu 2)Ni(I)Me (1) a n d (t Bu 2P C2H 4-
P tBu 2)NiMe2 (2). (dtbpe)NiI2 and (dtbpe)NiCl2 were
prepared as possible starting materials for the syntheses
of 1 and 2. When NiCl2 suspended in methanol is stirred
with dtbpe, large red needles of (dtbpe)NiCl2 crystallize
at -78 °C. Treating yellow (dtbpe)Ni(C2H4)3 with 1,2-
diiodoethane in THF results in evolution of ethene and
precipitation of blue microcrystals of (dtbpe)NiI2 (0 °C).
The yields are about 80%. While (dtbpe)NiCl2 is stable
to 282 °C, solid (dtbpe)NiI2 decomposes at 90 °C. In the
EI mass spectrum of (dtbpe)NiCl2 the molecular ion is
observed, whereas for (dtbpe)NiI2 the largest ion ob-
served is [(dtbpe)NiI]+. Both complexes are almost
insoluble in pentane and diethyl ether, but (dtbpe)NiI2
dissolves in THF. Paramagnetism (NMR) indicates the
presence of T-4 NiII centers.9
As far as we can ascertain, 1 cannot been synthesized
from (dtbpe)NiI2 by partially substituting iodide for
methyl. Instead, the reaction of (dtbpe)Ni(C2H4) with
CH3I (neat, 1 h) yields large brown crystals of 1 (77%;
eq 1). In a similar reaction using CD3I, partially
between (tmeda)Ni(CH3)2 and dtbpe, although the tmeda
ligand can be displaced by Me2PC2H4PMe2 (-30 °C) to
give (Me2PC2H4PMe2)Ni(CH3)2.15 Complex 2, which is
best stored at -30 °C, melts at 124 °C with decomposi-
tion. Slow decomposition at 110 °C affords elimination
of a mixture of ethane (55%), methane (23%), and ethene
(16%). The 31P NMR spectrum of the residue indicates
the formation of several species, among which (dtbpe)-
Ni(C2H4)3,7 has been identified.
deuterated (dtbpe)Ni(I)CD3 (1-d3) has also been pre-
pared.
Solid 1 (mp 223 °C) is thermally surprisingly stable.10
In the EI mass spectrum the molecular ion (m/e 518;
15%) is observed, which fragments by successive cleav-
age of methyl ([(dtbpe)NiI]+, base ion) and iodine to
produce [(dtbpe)Ni]+, corresponding to a formal CH3I
elimination from [1]+. Complex 1 dissolves well in THF.
However, at ambient temperature the solutions decom-
pose over the course of several days with elimination of
ethane (NMR). Decomposition is presumably initiated
by a metathesis reaction of 1 to give (dtbpe)NiI2 and 2,
which then eliminates ethane (see below). In the IR
spectrum of 1 a CH-stretching mode (3026 cm-1), a CH3-
sym-deformation mode (1126 cm-1), and a CH3-rocking
band (752 cm-1) can be assigned by comparison with
In the EI mass spectrum (110 °C) of 2 the molecular
ion (m/e 406, 2%) is observed, which fragments by a
stepwise loss of methyl groups to afford the ions [(d-
tbpe)NiCH3]+ (8%) and [(dtbpe)Ni]+ (74%). Complex 2
dissolves well in diethyl ether and THF. The solutions
slowly decompose above 0 °C and are only stable below
-20 °C for long periods. In the NMR spectra (-30 °C)
2 displays, besides the signals of the dtbpe ligand, for
the NiCH3 groups multiplets at δH -0.08 (AA′XX′; A,
1
1-d3.11 In the H and 31P NMR spectra the dtbpe ligand
of 1 shows signals for inequivalent CH2PtBu2 parts; the
1
A′ ) 31P; X, X′ ) H) and δC 1.8 (AA′X; X ) 13C).
2
coupling J (PP) ) 3 Hz is smaller than expected for a
five-membered (R2PC2H4PR2)Ni ring.12,13b The signal for
Cr ysta l Str u ctu r e of 2. The molecular structure of
2 has been determined by single-crystal X-ray structure
analysis (Figure 1). The molecule is characterized by a
square-planar (SP-4) NiII center coordinated to a chelat-
ing dtbpe ligand and two methyl groups in cis positions.
Conformational folding of the ethylene bridge between
the two P atoms confers approximate C2 symmetry on
the molecule. The C2 symmetry extends as far as the
methyl groups, which do not lie exactly in the P1,P2,Ni
plane but are arranged such that one methyl group is
displaced above and the other below the plane (dihedral
the NiCH3 protons occurs at δH 0.55.
(9) Schro¨der, M. In Encyclopedia of Inorganic Chemistry; Wiley:
Chichester, U.K., 1994; Vol. 5, p 2392.
10a
(10) The complexes trans-(Me3P)2Ni(I)CH3 and trans-(iPr3P)2Ni-
10b
(I)CH3
melt below 100 °C with decomposition: (a) Klein, H.-F.;
Karsch, H. H. Chem. Ber. 1972, 105, 2628. Klein, H.-F.; Karsch, H.
H.; Buchner, W. Chem. Ber. 1974, 107, 537. Klein, H.-F.; Karsch, H.
H. Chem. Ber. 1976, 109, 2524. (b) Green, M. L. H.; Smith, M. J . J .
Chem. Soc. A 1971, 639.
(11) For the IR characterization of [CH3NiH] and [CD3NiD], which
are reported to be formed by the reaction of Ni atoms with methane
(11-14 K), see: Chang, S.-C.; Hauge, R. H.; Billups, W. E.; Margrave,
J . L.; Kafafi, Z. H. Inorg. Chem. 1988, 27, 205.
(12) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(14) For trans-{(c-C6H11)3P}2Ni(H)CH3, see: J onas, K.; Wilke, G.
Angew. Chem. 1969, 81, 534; Angew. Chem., Int. Ed. Engl. 1969, 8,
519.
(15) Kaschube, W.; Po¨rschke, K.-R.; Wilke, G. J . Organomet. Chem.
1988, 355, 525.
(13) (a) Hackett, M.; Ibers, J . A.; J ernakoff, P.; Whitesides, G. M.
J . Am. Chem. Soc. 1986, 108, 8094. (b) Hackett, M.; Ibers, J . A.;
Whitesides, G. M. J . Am. Chem. Soc. 1988, 110, 1436. (c) Hackett, M.;
Whitesides, G. M. J . Am. Chem. Soc. 1988, 110, 1449.

12 Organometallics, Vol. 18, No. 1, 1999
Bach et al.
Sch em e 1
F igu r e 1. Molecular structure of 2. Selected bond dis-
tances (Å) and angles (deg): Ni-C1 ) 1.977(5), Ni-C2 )
1.965(5), Ni-P1 ) 2.213(1), Ni-P2 ) 2.209(1); P1-Ni-
P2 ) 90.44(4), C1-Ni-C2 ) 83.7(2).
pling of the methyl groups in 2, which generates the
intermediate Ni0-σ-ethane complex [(dtbpe)Ni(η2-H-
C2H5)] (A). If neither a suitable π-ligand nor H2 is
present, intermediate A presumably undergoes an
oxidative addition of the ethane C-H bond to Ni0 to
form a further intermediate, [(dtbpe)Ni(H)C2H5] (B),19
from which, by â-H elimination and formation of ethene,
a third intermediate, [(dtbpe)NiH2] (C), results. We
tentatively assign a weak 31P NMR singlet at δP 72.4
to this intermediate (or its structural isomer F ; cf.
Schemes 2 and 3). A subsequent reaction of intermedi-
ate A with the generated ethene would produce (dtbpe)-
Ni(C2H4) and 1 equiv of C2H6, whereas a combination
of intermediates A and C would be expected to afford
the dinuclear hydride complex 3 and 1 equiv more of
C2H6.
angle P1,P2,Ni/C1,C2,Ni 9°). Several short intramo-
lecular distances indicate this is a result of steric
interactions with the dtbpe methyl groups. The C-Ni-C
angle (83.7°) is also smaller than expected for SP-4
coordination even though the P1-Ni-P2 angle is 90.4°,
and this can be attributed to the same cause. The Ni-C
bond distance at 1.97(1) Å (mean) is nevertheless
normal and lies within the expected range for C trans
16
to P. In the isoelectronic (bipy)Ni(CH3)2 the N-Ni-N
angle of 81.4(1)° is accompanied by a C-Ni-C angle of
86.6(2)° and a shorter Ni-C distance of 1.923(4) Å
associated with C trans to N.17,18
Solu tion Th er m olysis of 2. When a yellow solution
of 2 in THF-d8 is maintained at 20 °C for a few days,
the color changes to dark red. In the 31P NMR spectrum
(2: δP 78.5) new signals are observed for (dtbpe)Ni(C2H4)
(δP 92.7) and 3 (δP 94.6) with relative intensities 1:2.
After about 1 week the singlet from 2 completely
disappears. In the 1H NMR spectrum, in addition to the
overlapping signals of various dtbpe ligands, the signal
of the ethene ligand in (dtbpe)Ni(C2H4) (δH 1.84), a very
narrow signal of ethane (δH 0.85), and a high-field
quintet for the hydride ligand in 3 (δH -10.6) of
approximate relative intensities 4:12:2 are observed.
According to these observations, complex 2 decomposes
in solution (20 °C) to yield equimolar amounts of (d-
tbpe)Ni(C2H4) and dinuclear 3, concomitant with the
elimination of 2 equiv of C2H6 (Scheme 1). The hydride
in 3 arises from NiCH3, since no deuterium has been
abstracted from the solvent (cf. 3-d2, see below). Meth-
ane is apparently only formed to a small extent.
Similar results are obtained in the solution thermoly-
sis of 2-d6 in THF-d8. In addition to the 31P singlet of
(dtbpe)Ni(C2D4) (δP 92.8) and the quintet of 3-d2 (δP 94.6;
see below), a further, now quite intense, signal is
observed at δP 72.6, which we attribute to [(dtbpe)NiD2]
(C-d2 or F -d2).20
When the thermolysis of 2 (20 °C) is carried out in
the presence of ethene, equimolar amounts of (dtbpe)-
Ni(C2H4) and ethane, but no NiI-hydride 3, is formed.
The rate of the thermolysis of 2 is apparently unaffected
by the amount of ethene added. These results support
the view that for the reactions shown in Scheme 1
oxidative coupling of the methyl groups in 2 is rate-
determining and that intermediate A is long-lived with
respect to the subsequent reaction A f B; i.e., displace-
ment reactions of the presumed σ-ethane ligand are
faster than a C-H oxidative addition. This mechanism
explains also the thermolysis of 2 in benzene, which
produces mononuclear (dtbpe)Ni(η2-C6H6) in solution,
from which dinuclear {(dtbpe)Ni}2(µ-η2:η2-C6H6) (4) is
isolated.4
The mechanism of the solution thermolysis of 2,
therefore, is suggested to occur through oxidative cou-
(16) Wilke, G.; Herrmann, G. Angew. Chem. 1966, 78, 591; Angew.
Chem., Int. Ed. Engl. 1966, 5, 581.
(19) As pointed out by a reviewer, 2 may alternatively undergo an
R-elimination of H to generate a nickel methyl methylene hydride
intermediate, which then forms B by migration of the methyl group
to the methylene carbon. However, for such a mechanism one would
also expect the formation of methane, but the amount is negligible in
solution.
(17) Tucci, G. C.; Holm, R. H. J . Am. Chem. Soc. 1995, 117, 6489.
(18) For other structurally characterized (bipy)NiR2 complexes,
see: (a) Binger, P.; Doyle, M. J .; McMeeking, J .; Kru¨ger, C.; Tsay, Y.-
H. J . Organomet. Chem. 1977, 135, 405. (b) Binger, P.; Doyle, M. J .;
Kru¨ger, C.; Tsay, Y.-H. Z. Naturforsch., B: Anorg. Chem., Org. Chem.
1979, 34, 1289.
(20) Experiments are in progress which are aimed at the synthesis
and isolation of intermediates C (C-d2) and F (F -d2), respectively.

Sterically Encumbered Ni Phosphane Complexes
Organometallics, Vol. 18, No. 1, 1999 13
The chemistry of C-H activation reactions and metal-
σ-alkane complexes is now well-established.21 A prece-
dent for the chemistry shown in Scheme 1 is provided
THF and the problem of avoiding cocrystallization of
the (THF)4MgCl2 present.26
An improved synthesis of 3 is provided by stirring an
ethereal solution of the (dtbpe)Ni0-benzene complex 4
with hydrogen gas between -60 and 20 °C (eq 3b). The
red color of the solution intensifies immediately, and
microcrystalline 3 precipitates in 80% yield. Larger
crystals of 3 can be obtained by exposing a THF solution
of 4 to hydrogen without stirring (20 °C). The reaction
of 4 with D2 affords the NiI-deuteride {(dtbpe)Ni}2(µ-
D)2 (3-d2). Similarly, the reaction of 4 with HD at -40
°C yields the pure mixed NiI-hydride-deuteride {(d-
tbpe)Ni}2(µ-H)(µ-D) (3-d). When this reaction is carried
out at 20 °C, however, 3-d is still the main product, but
the isotopomers 3 and 3-d2 are also formed due to a
subsequent H/D exchange reaction of 3-d with HD.
t
by thermolysis of (R2PC2H4PR2)Pt(H)(CH2 Bu) (R )
c-C6H11), which is reported to result in formation of the
[(R2PC2H4PR2)Pt0] moiety.13,22 In the presence of CH4
or c-C6H12 additional (R2PC2H4PR2)Pt(H)(R′) complexes
(R′ ) CH3, c-C6H11) were obtained. Moreover, it has been
reported that reduction of (Ph2PC2H4PPh2)PtCl2 with
Na/Hg in THF affords the [(Ph2PC2H4PPh2)Pt0] frag-
ment, which reacts with the solvent to yield (Ph2PC2H4-
PPh2)PtH2.22a,23 It has also been suggested that the
related species [(iPr2PC2H4PiPr2)Ni0] is formed upon
reduction of (iPr2PC2H4PiPr2)NiCl2 with activated mag-
nesium (Mg*).22a,24
{(tBu 2P C2H4P tBu 2)Ni}2(µ-H)2 (3). As we have seen,
thermolysis of 2 in an inert solvent leads to partial
formation of the dinuclear NiI-hydride 3 (Scheme 1).
Since the yield is relatively small, we were interested
in obtaining a more efficient synthesis of 3. When the
red suspension of (dtbpe)NiCl2 in THF is stirred with
Mg*25a under H2 gas between -40 and 20 °C,25b an
intensively colored dark red solution is obtained. When
the temperature is lowered to -78 °C, dark crystals of
3, exhibiting a green metallic sheen, precipitate (eq 3a).
Solid 3 is thermally very stable and melts at 218 °C
without decomposition. In the EI mass spectrum (175
°C) the molecular ion appears at m/e 754 (61%). Deg-
radation of the Ni2(µ-H)2 moiety is accompanied by
cleavage and partial fragmentation of the dtbpe ligands,
but [(dtbpe)NiH]+ (377, 5%) and [(dtbpe)Ni]+ (376, 4%)
are also detected. An analogous mass spectrum (160 °C)
is obtained for 3-d2 (M+: m/e 756, 9%). On the whole,
the results indicate that the Ni2(µ-H)2 moiety is remark-
ably stable. In the IR spectra of 3 and 3-d2 the Ni-H
(1280 cm-1) and Ni-D (920 cm-1) absorption bands27
are broad and weak, and the maxima were located by
numerical subtraction of one spectrum from the other.
1
In the H NMR spectrum (300 MHz, 27 °C) of 3, the
dtbpe ligand gives rise to single signals for the PCH2
and PtBu2 protons with poorly resolved J (PH) couplings.
For the hydridic H atoms a sharp A4X2 quintet (A )
31P, X ) 1H) is observed at δH -10.6 (J (PH) ) 21.6 Hz).
The 31P{1H} NMR spectrum displays a sharp singlet (δP
94.6). According to the spectra the four CH2PtBu2
subunits of 3 are equivalent on the NMR time scale.
The spectra are essentially unchanged at -80 °C.
In the 1H NMR spectrum (27 °C) of 3-d, the Ni2(µ-
H)(µ-D) moiety also gives rise to a quintet at δH -10.6
(J (PH) ) 22 Hz), the lines of which are furthermore
3-fold split28 due to coupling to deuterium. The signal
lies at slightly lower field (0.02 ppm) relative to that of
nondeuterated 3, which is best discernible when a
solution contains both species. The small coupling
2J (HD) ≈ 1.5 Hz corresponds to a geminal dihydride;
i.e., no direct H‚‚‚D interaction is present.29 In the 31P-
{1H} NMR spectrum (27 °C) of 3-d an apparent singlet
is observed at δP 95.6, which is at 1 ppm lower field than
for 3.
Although the formation of 3 utilizing this route is almost
quantitative (NMR), the resulting isolated yield remains
only about 50% because of the high solubility of 3 in
(21) (a) Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983,
250, 395. (b) Bergmann, R. G. Science 1984, 223, 902. (c) Crabtree, R.
H. Chem. Rev. 1985, 85, 245. (d) Green, M. L. H.; O’Hare, D. Pure
Appl. Chem. 1985, 57, 1897. (e) Halpern, J . Inorg. Chim. Acta 1985,
100, 41. (f) Yamamoto, A. Organotransition Metal Chemistry; Wiley-
Interscience: New York, 1986; p 229. (g) Ryabov, A. D. Chem. Rev.
1990, 90, 403. (h) Crabtree, R. H. Angew. Chem. 1993, 105, 828; Angew.
Chem., Int. Ed. Engl. 1993, 32, 789. (i) Crabtree, R. H. Chem. Rev.
1995, 95, 987.
(22) (a) No intermediates of the type [(R2PC2H4PR2)M0] (M ) Ni,
i
Pt; R ) C6H5, Pr, c-C6H11) have yet been isolated or spectroscopically
characterized. In light of the present knowledge on the properties of
bent [L2M0] fragments and on metal-σ-alkane complexes21 it appears
most likely that monomeric [(R2PC2H4PR2)M0] species in solution are
in fact the σ-alkane complexes [(R2PC2H4PR2)M0(σ-R′H)] (M ) Ni, Pt).
For the Ni2(µ-D)2 complex 3-d2 the 31P NMR signal
(27 °C) is at δP 94.6 and therefore comes at the same
(b) Upon generation of [{R2P(CH2)nPR2}Pd0] (n ) 1, 2; R ) iPr, c-C6H11
)
the chelate ring opens to afford the dinuclear complexes Pd2{µ-R2P-
(CH2)nPR2}2 with formally linear L-Pd0-L geometries: Pan, Y.;
Mague, J . T.; Fink, M. J . J . Am. Chem. Soc. 1993, 115, 3842. Do¨hring,
A.; Goddard, R.; Hopp, G.; J olly, P. W.; Kokel, N.; Kru¨ger, C. Inorg.
Chim. Acta 1994, 222, 179. (c) In [{tBu2P(CH2)3PtBu2}Pt0]2 each
bidentate phosphane chelates a TP-3 Pt0 center with a relatively large
P1-Pt-P2 angle of 102.6°. The L2Pt0 moieties are coordinated to each
other via an unsupported d10-d10 Pt0-Pt0 bond (2.76 Å).61
(23) Otsuka, S. J . Organomet. Chem. 1980, 200, 191.
(26) Partial formation of 3 is also observed (NMR) when (dtbpe)-
NiCl2 is reduced by Mg* in the absence of molecular hydrogen. Here
the hydridic H atoms of 3 presumably result from the reaction of the
generated [(dtbpe)Ni0] fragment with the solvent, i.e., either by attack
of a THF C-H bond or, more likely, by protonation from inevitable
amounts of moisture. A corresponding reactivity has been reported for
the postulated [(tBu2PC3H6PtBu2)Pt0], giving rise to (tBu2PC3H6PtBu2)-
PtH2.23
(24) Scott, F.; Kru¨ger, C.; Betz, P. J . Organomet. Chem. 1990, 387,
113.
(27) For a terminal Ni-H group an intense IR stretching band is
expected between 1950 and 1800 cm-1
.
(25) (a) Bartmann, E.; Bogdanovic, B.; J anke, N.; Liao, S.; Schlichte,
K.; Spliethoff, B.; Treber, J .; Westeppe, U.; Wilczok, U. Chem. Ber.
1990, 123, 1517. (b) The activity of Mg* varies from batch to batch.
The low-temperature reduction of (dtbpe)NiCl2 is feasible with the most
active Mg*.
(28) Multiplicity 2nI + 1: for 3-d, I ) 1, n ) 1; for 3-d2, I ) 1, n )
2.
(29) (a) Kubas, G. J . Acc. Chem. Res. 1988, 21, 120. (b) J essop, P.
G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155. (c) Heinekey, D.
M.; Oldham, W. J ., J r. Chem. Rev. 1993, 93, 913.

14 Organometallics, Vol. 18, No. 1, 1999
Bach et al.
F igu r e 3. Discussed geometries of the (P2Ni)2(µ-H)2 core
of 3 and derivatives: (a) calculated “square-planar dimer”
D2h ground state; (b) energetically forbidden “tetrahedral
dimer” D2h state; (c) suggested C2v transition state for the
structural dynamics.
Since the substituents at P are more bulky in the case
of 3, the distortions from θ ) 0° would appear to be the
result of minimization of steric strain.32 A direct com-
parison of 3 with 3a ,b is, however, complicated by the
fact that the P(CH2)nPNi chelate complexes have dif-
ferent ring sizes, resulting in different bite angles of the
P ligands at Ni (P1-Ni-P2 for 3 (n ) 2) is 93.4(1)° and
for 3a ,b (n ) 3) is 103°) and in a change of not only the
steric but also the electronic situation. Indeed, the Ni-
Ni bond length of 2.433(1) Å in 3, although typical for a
NiI-NiI bond, is slightly shorter than that found in 3a ,b
(2.44 Å), whereas an elongation might have been
expected from steric arguments.
F igu r e 2. Molecular structure of 3. Selected bond dis-
tances (Å) and angles (deg): Ni-Ni* ) 2.433(1), Ni-P1 )
2.165(1), Ni-P2 ) 2.158(1), Ni-H1 ) 1.58(4), H1‚‚‚H1* )
2.02(7); P1-Ni-P2 ) 93.42(4), H1-Ni-H1* ) 79(2), Ni-
H-Ni* ) 101(3).
field as that for 3 (sharp singlet), but it occurs as a
quintet due to coupling to two equivalent deuterium
nuclei (J (PD) ) 3.4 Hz).28 The isotopomers 3, 3-d, and
3-d2 are thus clearly distinguishable from each other
1
on the basis of their H and 31P NMR spectra.
The Ni-P bond length in 3 (2.161(5) Å, mean) is
longer than that for 3a (2.13 Å, mean) and 3b (2.14 Å,
mean) but significantly less than that for the (dtbpe)-
NiII complex 2 (2.211(3) Å, mean). The H atoms are
symmetrically bound to both Ni centers (Ni-H 1.58(4)
Å, mean), as is also the case for 3a ,b (within the limits
of the experimental error). The large H1‚‚‚H1* distance
in the Ni(µ-H)2Ni moiety (2.02(7) Å) precludes direct
bonding between the H atoms.
The NMR spectra of 3 are indicative of a structural
dynamic process and will be discussed following a
description of the molecular structure in the crystal.
Molecu la r Str u ctu r e of 3. The molecular structure
of 3 has been determined by a single-crystal X-ray
structure analysis, which confirms the dimeric nature
of the molecule. Two [(tBu2PC2H4PtBu2)NiI] moieties are
bridged by two H atoms, forming a central planar Ni-
(µ-H)2Ni four-membered ring (Figure 2). The structure
of 3 is closely related to those of {(R2PC3H6PR2)NiI}2-
(µ-H)2 (R ) c-C6H11 (3a ),30 iPr (3b)31a),31b and it is
convenient to compare it with them. Extended Hu¨ckel
calculations on the sterically unhindered (P2Ni)2(µ-H)2
moiety predict a completely square-planar dimeric D2h
ground-state structure (Figure 3a).30c
In 3 and 3a ,b the Ni centers are, however, not square
planar, but the molecules are twisted about the Ni-Ni
axis such that the two NiP2 planes lie on either side of
the Ni(µ-H)2Ni ring with the result that the (P2Ni)2(µ-
H)2 core adopts D2 symmetry. If we define the angle θ
as the dihedral angle between the planes through the
two NiP2 units, then we find that θ is 80° for 3 while it
is 63° for 3a and 75° for 3b. In 3 the planes P1,P2,Ni
and P1*,P2*,Ni* are thus almost perpendicular to one
another. It follows that θ/2, i.e., the distortion from the
square-planar coordination at the Ni centers (P,P,Ni/
Ni,H,H), is a large 40°.
Str u ctu r a l Dyn a m ics of 3. The NMR spectra of 3
indicate the equivalence of the four CH2PtBu2 moieties
and, within these, the equivalence of the PCHaHb and
PtBua Bub protons. If the structure of 3 in solution were
t
the same as that in the crystal (D2 symmetry) and static
with regard to the (P2Ni)2(µ-H)2 core, one should observe
1
separate H NMR signals for the PCHaHb and PtBua-
tBub protons, which is not the case. Other possible rigid
solution structures of 3 include the calculated “square-
planar dimer” D2h ground state (Figure 3a),30c but the
(P2Ni)2(µ-H)2 hydrogen atoms are expected to give rise
to an A2A′2XX′ multiplet due to different couplings to
cis- and trans-positioned 31P nuclei, which is at variance
with the observed A4X2 multiplet. The spectra fit a
“tetrahedral dimer” D2h structure (Figure 3b), but this
arrangement is unlikely on the basis of the MO calcula-
tions, which predict a very high energy for this
geometry.30c A rapid reversible dissociation of 3 into the
monomer [(dtbpe)NiIH] can be ruled out because of the
extraordinary thermal stability of the complex and the
A4X2 coupling of the hydride resonance.
(30) (a) J onas, K.; Wilke, G. Angew. Chem. 1970, 82, 295; Angew.
Chem., Int. Ed. Engl. 1970, 9, 312. J onas, K. J . Organomet. Chem.
1974, 78, 273. (b) Kru¨ger, C. Angew. Chem. 1972, 84, 412; Angew.
Chem., Int. Ed. Engl. 1972, 11, 387. (c) Barnett, B. L.; Kru¨ger, C.; Tsay,
Y.-H.; Summerville, R. H.; Hoffmann, R. Chem. Ber. 1977, 110, 3900.
Summerville, R. H.; Hoffmann, R. J . Am. Chem. Soc. 1976, 98, 7240.
(31) (a) Fryzuk, M. D.; Clentsmith, G. K. B.; Leznoff, D. B.; Rettig,
S. J .; Geib, S. J . Inorg. Chim. Acta 1997, 265, 169. (b) Further
derivative: {(iPr2PC2H4PiPr2)Ni}2(µ-H)2 (3c): Vicic, D. A.; J ones, W.
D. J . Am. Chem. Soc. 1997, 119, 10855.
1
Thus, the H NMR spectrum of 3 in solution (-80 to
27 °C) is best explained by a dynamic structure, repre-
(32) The extreme steric congestion in 3 can also be deduced from
the fact that neither Ni(dtbpe)2 nor {(dtbpe)Ni}2(µ-dtbpe) nor Ni2(µ-d-
tbpe)2 is formed.3

Sterically Encumbered Ni Phosphane Complexes
Organometallics, Vol. 18, No. 1, 1999 15
Sch em e 2
Sch em e 3
displays, besides the singlet of residual 3 (δP 94.6), as
the main signal the quintet of 3-d2 (δP 94.6) and
furthermore the singlet of 3-d (δP 95.6). In the corre-
1
sented by a rotation of the Ni2(µ-H)2 and P,P,Ni planes
relative to each other. How could this rotation proceed?
With the solid-state D2 structure of the (P2Ni)2(µ-H)2
core as a starting point, a libration through the square-
planar dimer D2h structure will not give rise to the A4X2
quintet, and a libration through the tetrahedral dimer
D2h state is probably energetically forbidden. In addi-
tion, these transformations would imply a significant
reorientation of the phosphorus atoms, which seems
unlikely in view of the bulk of the phosphorus ligands
and the ease with which the dynamics occur (-80 °C).
We therefore think that the spectra are best described
by a motion whereby both P,P,Ni planes take up an
approximately perpendicular arrangement (resulting
from a distortion of the ground-state planar D2h struc-
ture by strain imposed by the phosphorus ligands) and
this is maintained in the course of the dynamic process,
while the central Ni2(µ-H)2 plane rotates in steps of 90°
(eq 4).
sponding H NMR spectrum the hydride quintets of 3
and 3-d (δH -10.6) are observed. Thus, the bridging
hydride substituents of the (P2Ni)2(µ-H)2 moiety are
exchanged by D2 predominantly as a H2 unit (H2/D2
exchange), but slow H/D scrambling also occurs. The
mechanisms of the H2/D2 exchange and H/D scrambling
reactions33 are apparently related to one another. Since
H2 dissociation from 3 is unlikely and does not explain
the formation of 3-d, it is suggested that 3 associatively
reacts with D2 to give the dinuclear tetrahydride/
deuteride intermediate {(dtbpe)Ni}2(µ-H2D2) (D), for-
mally a dimer of the NiII-dihydride C (Scheme 2). For
D a principal structure may be envisaged in which the
original H atoms have gained close contact while the
incoming D2 is not yet fully split. Intermediate D is
related to a series of ionic complexes [(L2M)2H3]+ (M )
Ni, Pt)34a and [(L2Pt)2(µ-H)2]2+ 34b (L2 ) bidentate phos-
phane) by formal hydride addition to the latter. The
formation of D explains both the preferred H2/D2
exchange 3 f 3-d2 and the H/D scrambling 3 f 3-d
upon addition of D2 (respectively H/D scrambling 3-d
f 3 + 3-d2 with HD).
Complex 3 reacts with alkenes or alkynes by displace-
ment of the H2 moiety to afford the corresponding (d-
tbpe)Ni0-alkene and -alkyne complexes; a similar
reactivity has been noted previously for 3a 30a and
related complexes.35 For example, when ethene is added
to an ethereal solution of 3 at 20 °C, the color changes
from red to yellow within 20 min and (dtbpe)Ni(C2H4)3
is isolated. When ethyne is added to a THF-d8 solution
of 3 at -60 °C, the color lightens in about the same time,
After a rotation of 45°, the complex passes through a
2v transition state, in which one Ni center has attained
SP-4 coordination geometry and the other T-4 geometry.
C
This transition state implies a formal disproportionation
of the NiI (µ-H)2 group into T-4 Ni0 and SP-4 NiIIH2
1
and the H and 31P NMR spectra display the signals of
2
moieties held together by hydride bridges (Figure 3c).33
Hence, the structural dynamics are mechanistically
closely related to the suggested formation of 3 from
intermediates A [Ni0] and C [NiII] (Scheme 1).
(dtbpe)Ni(C2H2)3 but no signals for C2H4, (dtbpe)Ni-
(C2H4), or C2H6. Thus, in these reactions ethene and
ethyne cleanly displace H2 without hydrogenation or
formation of NiC2H5 or NiCHdCH2 groups. As for the
H2/D2 exchange reaction, we suggest for the mechanism
of these H2 displacement reactions (Scheme 3) that
dinuclear 3 reacts associatively with the substrates.
Coordination of the π-ligand to one Ni center in di-
Rea ctivity of 3. We have already mentioned that the
mixed NiI-hydride-deuteride 3-d undergoes (slow) H/D
scrambling with additional HD to give 3 and 3-d2 (20
°C). Similarly, when a solution of 3 in THF-d8 is stirred
under D2 at 20 °C for 30 min, the 31P NMR spectrum
(34) (a) Tenorio, M. J .; Puerta, M. C.; Valerga, P. J . Chem. Soc.,
Dalton Trans. 1996, 1305 and literature cited therein. (b) Mole, L.;
Spencer, J . L.; Litster, S. A.; Redhouse, A. D.; Carr, N.; Orpen, A. G.
J . Chem. Soc., Dalton Trans. 1996, 2315.
(33) For (dtbpe)Pt(H)-Pt(H)(dtbpe),64 which is stoichiometrically
analogous to 3 but structurally quite different (see Discussion),
different mechanisms are suggested for the structural dynamics and
the H/D scrambling process encountered there.
(35) Bennett, B. L.; Roddick, D. M. Inorg. Chem. 1996, 35, 4703.

16 Organometallics, Vol. 18, No. 1, 1999
Bach et al.
Sch em e 4
nuclear 3 initiates the disproportionation NiI(µ-H)2NiI
f [NiIIH2/Ni0] (E). While the Ni0-π-ligand complex is
formed directly, coupling of the H substituents in the
resulting C presumably affords the Ni0-σ-H2 interme-
diate F , from which H2 is displaced by further substrate.
The reaction is closely related to both the H2/D2 ex-
change reaction (Scheme 2) and the structural dynamics
of 3 via the C2v symmetrical transition state. Upon
addition of an excess of PMe3 to 3 (THF-d8, 20 °C) all
ligands are displaced to form Ni(PMe3)4 (δP -21.0). In
conclusion, although 3 is spectroscopically and structur-
ally best regarded as a NiI complex, chemically it acts
as a Ni0 source.
While 3 reacts with ethene and ethyne by displacing
H2 from the [(dtbpe)Ni0] fragment, it can, on the other
hand, be synthesized from the Ni0-benzene complex 4
by displacing benzene with H2 (eq 3b). In turn, the Ni0-
σ-complex A, generated by thermolysis of 2, is a likely
common intermediate in the synthesis reactions of 4,4
the NiI-hydride 3, and (dtbpe)Ni(C2H4) (Scheme 1). We
have no indication that a hot ligand-free [(dtbpe)Ni0]
fragment has a reasonable lifetime as a strongly bent
L2Ni0 complex in solution. Instead, we rather assume
that it forms σ-R′H complexes with either the solvent
(THF, benzene), ethane (when generated from 2), or
other potential substrates containing C-H bonds.22
Thus, complexes [(dtbpe)Ni0(η2-R′H)] such as A which
may be generated by various routes (thermolysis of 2;
reduction of (dtbpe)NiCl2 with Mg* in THF) can be
considered to be the most reactive nonisolated [(dtbpe)-
Ni0] species and serve to synthesize all isolable deriva-
tives. Nevertheless, the benzene complex 4 is the most
reactive isolated [(dtbpe)Ni0] complex and provides the
best starting material for the synthesis of further
complexes. The NiI-hydride 3 is less reactive than 4
but markedly more reactive than (dtbpe)Ni(C2H4), for
which a low reactivity has already been stated.3 When
the various [(dtbpe)Ni0] sources are arranged according
to the relative reactivities, a cascade of displacement
reactions may be carried out, as depicted in Figure 4.
(d t b p e)Ni(CH 3)(OSO2CF 3) (5) a n d [(d t b p e)Ni-
(C2H5)]+(OSO2CF 3)- (6). When the ethereal solution
of 2 is reacted with 1 mol equiv of CF3SO3H at -30 to
20 °C, ocher microcrystals of 5 precipitate in 75% yield
(route a). Further synthetic routes to 5, which, however,
have not been optimized, are (b) oxidative addition of
MeOTf to 2 via a NiIV intermediate, (c) oxidative
addition of MeOTf to the Ni0-benzene complex 4, and
Figu r e 4. Relative reactivity of various [(dtbpe)Ni0] sources.
(d) halide substitution in 1 with AgOTf. As for 1, solid
5 (mp 180 °C) is rather stable. Both complexes are
almost insoluble in pentane and only sparingly soluble
in diethyl ether but dissolve well in THF. A very slow
solution decomposition of 5 with evolution of ethane (20
°C) is explained by a metathesis reaction to afford (d-
tbpe)Ni(OTf)2 and 2, which decomposes as described.
The NMR and EI-MS data of 5 are unexceptional. Since
-
5 does not contain additional Et2O, the anion CF3SO3
is most likely coordinated to the SP-4 NiII center.
In contrast to 1, complex 5 in THF solution reacts
slowly at 20 °C with 2 equiv of ethene to give equimolar
amounts of 6 and propene36 (Scheme 4). As monitored
by H and 31P NMR, the reaction is complete after 3
1
days. The H and 31P NMR data of 6 (THF-d8, 27 °C)
1
agree with those reported for [(dtbpe)Ni(C2H5)]+(BF4)-
(6a ) (CD2Cl2),7 which features an agostic â-proton
interaction of the ethyl substituent with the SP-4 NiII
center (X-ray). In the 1H NMR spectrum 6 displays
(besides the dtbpe signals) a characteristic multiplet at
δH -1.13 for the NiC2H5 methyl protons, while the
signal of the NiCH2 protons is obscured by dtbpe signals.
The high-field shift of the (coalesced) â-proton signal is
due to the agostic Ni-H interaction of one of the three
protons.7 In the 31P NMR spectrum complex 6 exhibits
a pair of doublets at δP 102.0 and 96.6 with 2J (PP) )
13.4 Hz. We assume that the structure of 6 (which has
not been isolated so far) is ionic, as for 6a .
As far as the mechanism of the formation of 6 and
propene is concerned, we suggest that complex 5 reacts
(36) 1H NMR of propene (THF-d8): δH 5.79 (dCH-), 4.98 (dCHZH),
4.89 (dCHHE), 1.70 (CH3).

Sterically Encumbered Ni Phosphane Complexes
Organometallics, Vol. 18, No. 1, 1999 17
with ethene by insertion into the Ni-CH3 bond (rate-
determining step) to form the intermediate [(dtbpe)Ni-
(C3H7)(OSO2CF3)] (G), which is structurally related to
6 and 6a . Intermediate G, as a result of â-H activation,
eliminates propene to give the NiII-hydride intermedi-
ate [(dtbpe)Ni(H)(OSO2CF3)] (H), which rapidly inserts
ethene into the Ni-H bond to yield 6 (Scheme 4).37
The ring-opening step is presumably supported by steric
repulsion between the PtBu2 groups and the rest of the
complex. It apparently proceeds more readily at the
SP-4 NiII than at the TP-3 Ni0 center, and consequently,
reduction to Ni0 supports the reverse ring closure. The
proposed primary product from the C-C coupling step
is the intermediate [(dtbpe)Ni0(σ-H-C2H5)] (A). The
σ-ethane ligand in A may be displaced by suitable
substrates (C2H4, H2, C6H6), or otherwise, A undergoes
a C-H activation reaction (Scheme 1). The supposed
C-H activation step results from the strong dπ donor
capability of bent 14e L2M0 (M ) Ni, Pd, Pt) complex
fragments.23 Correspondingly, reduction of (dtbpe)NiCl2
with Mg*/THF (-40 °C) likely generates the initial
intermediate [(dtbpe)Ni0(σ-R′H)] (R′H ) C4H8O), from
which the further products arise (eq 6).
Discu ssion
The [(dtbpe)Ni] fragment displays interesting features
due to the combination of an exceedingly bulky chelating
ligand and the smallest metal center of the homologous
series Ni, Pd, Pt. One consequence is that typical (d-
tbpe)Ni0-alkene complexes (alkene: e.g. ethene, 1,5-
hexadiene, trans,trans,trans-1,5,9-cyclododecatriene) have
unexpectedly low kinetic reactivities. For example, when
it is dissolved in undiluted butadiene or cyclooctatet-
raene, (dtbpe)Ni(η2-C12H18) is inert (20 °C, 24 h) and (d-
tbpe)Ni(C2H4) reacts only very slowly to give (dtbpe)Ni-
(η2-C4H6)3 and (dtbpe)Ni(η2-C8H8),3,5 respectively. The
low reactivity is in sharp contrast to the otherwise facile
displacement of alkene ligands from Ni0 centers. It
follows that complexes such as (dtbpe)Ni(C2H4) are not
suited for the ready generation of [(dtbpe)Ni0] as a
reactive intermediate for reactions with, e.g., H2, N2,
or CH4.
In addition to 2 there are numerous trans- and cis-
L2Ni(CH3)2 complexes that are known, e.g., trans-
(Me3P)2NiMe2,10a {(Ph-2-C6H4O)3P}2NiMe2,16 (bipy)-
NiMe2,16,39a (ArNdCHCHdNAr)NiMe2 (Ar ) 2,6-iPr2C6-
H3),40 (tmeda)NiMe2,15 and (Me2PC2H4PMe2)NiMe2.15
Early detailed studies on the parameters that determine
reductive elimination reactions have been carried out
for (bipy)NiR2 (R ) Me, Et, Pr, nBu)39a and {Ph2P(CH2)n-
PPh2}NiMe2.39b
B. The profound interest in Ni-hydride complexes
arises from the function of Ni as a heterogeneous41 or
possibly homogeneous42 hydrogenation catalyst,43 the
likely occurrence of Ni-hydride intermediates in cata-
lytic reactions,44 and also the function of NiFe hydro-
genase.45 For NiII, a variety of neutral 16e [trans-
(Cy3P)2Ni(H)X]14,46-49 and 18e [(Ph3P)3Ni(H)Br]50 com-
Two aspects concerning the properties of the title
complexes are particularly noteworthy.
A. As has been shown here and in the concurrent
report on 4,4 an access to highly reactive [(dtbpe)Ni0]
complexes is provided both by solution thermolysis of 2
and by Mg* reduction of (dtbpe)NiCl2. Thermolysis of 2
in solution (0 °C) proceeds under conditions markedly
milder than those in the solid state and leads mainly
to the elimination of ethane with only negligible amounts
of methane. In agreement with the mechanism sug-
gested for elimination reactions from SP-4 MII centers
(M ) Pd, Pt),38 it seems likely that also for M ) Ni the
C-C coupling step to form ethane is initiated by
lowering the coordination number from 4 to 3 by a
reversible ring-opening of the (dtbpe)Ni chelate complex
(eq 5),13b a process which, for obvious reasons, proceeds
(39) (a) Yamamoto, T.; Yamamoto, A.; Ikeda, S. J . Am. Chem. Soc.
1971, 93, 3350. (b) Kohara, T.; Yamamoto, T.; Yamamoto, A. J .
Organomet. Chem. 1980, 192, 265.
(40) Svoboda, M.; tom Dieck, H. J . Organomet. Chem. 1980, 191,
321.
(41) For the chemisorption of H2 on a Ni surface, see: (a) Bock, H.;
Wolf, H. P. Angew. Chem. 1985, 97, 411; Angew. Chem., Int. Ed. Engl.
1985, 24, 418 and literature cited therein. (b) Maartensson, A. S.;
Nyberg, C.; Andersson, S. Phys. Rev. Lett. 1986, 57, 2045; Chem. Abstr.
1986, 105, 214327x.
(42) Homoleptic Ni0-alkene complexes such as Ni(C8H12
) (20 °C),
2
Ni(C12H18) (-40 °C), and Ni(C2H4)3 (-40 °C) (“naked nickel”) react with
hydrogen by hydrogenation of the alkene ligand and precipitation of
metallic Ni. Excess alkene and even benzene as a solvent is (in part)
also hydrogenated. Most likely the precipitated Ni, not the dissolved
complexes, acts like a highly reactive Raney nickel catalyst as the
hydrogenation catalyst: (a) Bogdanovic, B.; Kro¨ner, M.; Wilke, G.
J ustus Liebigs Ann. Chem. 1966, 699, 1. (b) Po¨rschke, K.-R. Habili-
tationsschrift, Universita¨t Du¨sseldorf, 1988; p 19.
(43) J ames, B. R. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford,
U.K., 1982; Vol. 8, p 285.
more readily for the dissolved complex than for the solid.
(44) (a) J olly, P. W.; Wilke, G. The Organic Chemistry of Nickel;
Academic Press: New York, 1975; Vol. 2. (b) J olly, P. W. In Compre-
hensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel,
E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 8, p 613 ff.
(45) Roberts, L. M.; Lindahl, P. A. J . Am. Chem. Soc. 1995, 117,
2565.
(46) Green, M. L. H.; Saito, T. J . Chem. Soc. D 1969, 208. Green,
M. L. H.; Saito, T.; Tanfield, P. J . J . Chem. Soc. A 1971, 152.
(47) Imoto, H.; Moriyama, H.; Saito, T.; Sasaki, Y. J . Organomet.
Chem. 1976, 120, 453.
(37) For a recent theoretical treatment of the basic intermediates
and insertion steps, see: Fan, L.; Krzywicki, A.; Somogyvari, A.;
Ziegler, T. Inorg. Chem. 1994, 33, 5287; 1996, 35, 4003.
(38) (a) Gillie, A.; Stille, J . K. J . Am. Chem. Soc. 1980, 102, 4933.
Moravskiy, A.; Stille, J . K. J . Am. Chem. Soc. 1981, 103, 4182. (b)
Tatsumi, K.; Hoffmann, R.; Yamamoto, A.; Stille, J . K. Bull. Chem.
Soc. J pn. 1981, 54, 1857. (c) Ozawa, F.; Ito, T.; Nakamura, Y.;
Yamamoto, A. Bull. Chem. Soc. J pn. 1981, 54, 1868. (d) Ozawa, F.;
Kurihara, K.; Yamamoto, T.; Yamamoto, A. Bull. Chem. Soc. J pn. 1985,
58, 399. (e) Stille, J . K. In The Chemistry of the Metal-Carbon Bond;
Hartley, F. R., Patai, S., Eds.; Wiley: New York, 1985; Vol. 2, p 625.
(48) Nesmeyanov, A. N.; Isaeva, L. S.; Morozova, L. N. Inorg. Chim.
Acta 1979, 33, L173.

18 Organometallics, Vol. 18, No. 1, 1999
Bach et al.
plexes and also ionic 18e [L4NiH]+X- 51-53 complexes
have been described, whereas initial reports on “NiH2”54a
have been questioned.54b In seminal studies J onas and
Wilke have shown that {R2P(CH2)nPR2}NiIICl2 and
{R2P(CH2)nPR2}NiICl (R ) c-C6H11, n ) 2-4) react with
NaHBMe3 and {R2P(CH2)nPR2}Ni0-arene with H2 to
afford the formal NiI-hydrides [{R2P(CH2)nPR2}NiI]2-
(µ-H)2 (cf. 3a ).30,31 Isolable NiI-hydrides are so far
confined to those stabilized by bidentate phosphane
ligands, whereas the corresponding complexes with
monodentate ligands are labile. Thus, for a solution of
Ni(PEt3)3 pressurized with H2 (10 bar; -63 °C) two high-
field 1H NMR signals have been observed, which are
attributed to {(Et3P)2NiI}2(µ-H)2 (δH -11.9, quintet; 3d )
and (Et3P)3NiH2 (δH -13.3, quartet; (Et3P)3Ni0(η2-H2)
or trans-(Et3P)3NiIIH2) in slow equilibrium (eq 7).52b,55
Similarly, photolysis of Ni(CO)4 in an H2/Ar matrix
(<4.4 K) is reported to produce labile (CO)3Ni(η2-H2).56
(tBu2PCH2-o-C6H4CH2PtBu2)PtH2,60 {RR′P(CH2)nPRR′}-
PtH2 (R, R′ ) tBu, Men, Ph; n ) 2, 3),61 and {R2P(CH2)n-
62
PR2}PtH2 (n ) 2-4; R ) c-C6H11
)
are readily acces-
sible.63 Although the coordination of the hydride in these
complexes is static on the 1H NMR time scale (the
hydride substituents couple with cis and trans P at-
oms),60,61 they undergo a (slow) H2/D2 exchange, indica-
tive of a PtIIH2 h Pt0(η2-H2) equilibrium.61,62 Purging a
solution of (dtbpe)PtH2 with N2 (90 °C) affords H2
61
64
elimination and formation of {(dtbpe)PtIH}2 as the Pt
analogue to 3. Structurally the Pt complex is a dimer
of SP-4 (dtbpe)PtIH moieties with terminal hydride
substituents and is connected by an unsupported Pt-
Pt bond (2.61 Å). In solution (1H NMR), the 31P nuclei
equilibrate via a L2Pt(µ-H)2PtL2 transition state. Upon
addition of H2 (20 °C) mononuclear (dtbpe)PtH2 is
recovered. Thus, there is the further equilibrium 2L2-
PtIIH2 h {L2PtIH}2 + H2.64,65 Both types of complexes
react with electron-poor alkenes61 and alkynes62 with
elimination of H2 to yield the corresponding Pt0
complexes.65a
On the basis of the properties of 3 and the results
cited above the following general characteristics of the
system L2M0/H2 (M ) Ni, Pd, Pt; L2 ) 2 PR3, R2P(CH2)n-
PR2) can be established.
(a) In the dinuclear {L2MIH}2 complexes short MI-
MI bonds are encountered for M ) Ni, Pt, while the PdI-
PdI bond is long. The hydride bridges are symmetrical
and strong for L2Ni(µ-H)2NiL2 but unsymmetrical and
weaker for L2Pd(µ-H)2PdL2 (semibridging hydride),
whereas the hydride is terminally bound in L2Pt(H)-
Pt(H)L2.
It is evident that complex 3 is closely related to 3a -
d . A further relationship is found in Pd and Pt ana-
logues which have been synthesized in recent times.57
Regarding palladium, {iPr2P(CH2)3PiPr2}PdI2 has been
reacted with KHBEt3 to afford [{iPr2P(CH2)3PiPr2}PdI]2-
(µ-H)2.58 This complex displays a nearly planar P4Pd2H2
core (θ ) 24°). Interestingly, the PdI-PdI bond is
relatively long (2.82 Å) and the hydride ligands are
semibridging the PdI centers (Pd1-H1 1.67 Å; Pd2-
H1 2.11 Å). Similar to what is observed for 3 and 3a ,
H2 is displaced by ethene without the latter becoming
hydrogenated. No stable mononuclear complexes cis-Ln-
(b) The di- and mononuclear complexes form the
equilibrium
{L2MIH}2 + H2 h 2L2MIIH2
This equilibrium is shifted to the side of the mono-
nuclear complexes in the series Ni < Pd < Pt and with
an increasing bulk of the L2 ligand. Thus, for the
combination Pt/dtbpe the preferred complex is mono-
nuclear (dtbpe)PtH2, whereas for Ni the equilibrium is
still on the side of dinuclear 3, despite the bulk of the
dtbpe ligand. However, it follows from the above that
the mononuclear Ni derivative L2NiIIH2 (cf. C; Schemes
1-3) should possibly be accessible for dtbpe (in contrast
to the situation for smaller bidentate phosphanes) by
t
Pd(H2) are known,59 but trans-L2PdIIH2 (L2 ) Bu2P-
(CH2)3-p-C6H4(CH2)3PtBu2) has been synthesized.23
Regarding platinum, cis-L2PtII-dihydrides such as
(49) Kalies, W.; Witt, B.; Gaube, W. Z. Chem. 1980, 20, 310.
(50) Nesmeyanov, A. N.; Isaeva, L. S.; Lorens, L. N. J . Organomet.
Chem. 1977, 129, 421.
(51) Drinkard, W. C.; Eaton, D. R.; J esson, J . P.; Lindsey, R. V., J r.
Inorg. Chem. 1970, 9, 392.
(52) (a) Schunn, R. A. Inorg. Chem. 1970, 9, 394. (b) Schunn, R. A.
Inorg. Chem. 1976, 15, 208.
(60) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Chem. Commun.
1976, 365.
(61) Yoshida, T.; Yamagata, T.; Tulip, T. H.; Ibers, J . A.; Otsuka, S.
J . Am. Chem. Soc. 1978, 100, 2063.
(53) Tolman, C. A. Inorg. Chem. 1972, 11, 3128.
(54) (a) Schlenk, W.; Weichselfelder, T. Chem. Ber. 1923, 56, 2230.
Weichselfelder, T. Liebigs Ann. Chem. 1926, 447, 64; Chem. Ber. 1929,
62, 769. (b) Sarry, B. Naturwissenschaften 1954, 41, 115; Z. Allg. Anorg.
Chem. 1955, 280, 65, 78.
(55) For the reaction of Ni(PEt3)4 with H2 at 1 atm, see: Cundy, C.
S. J . Organomet. Chem. 1974, 69, 305.
(62) Clark, H. C.; Hampden-Smith, M. J . J . Am. Chem. Soc. 1986,
108, 3829.
(63) In addition, sterically unhindered complexes cis-/ trans-(R3P)2-
PtH2 (R ) Me, Et) are known: (a) Paonessa, R. S.; Trogler, W. C. J .
Am. Chem. Soc. 1982, 104, 1138. (b) Paonessa, R. S.; Prignano, A. L.;
Trogler, W. C. Organometallics 1985, 4, 647. (c) Packett, D. L.; J ensen,
C. M.; Cowan, R. L.; Strouse, C. E.; Trogler, W. C. Inorg. Chem. 1985,
24, 3578.
(56) Sweany, R. L.; Polito, M. A.; Moroz, A. Organometallics 1989,
8, 2305.
(57) For related d8 complexes {(R2PC2H4PR2)RhI}2(µ-H)2, see: Fryzuk,
M. D.; J ones, T.; Einstein, F. W. B. Organometallics 1984, 3, 185.
Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J . Organometallics 1996, 15,
2871 and references therein.
(64) Schwartz, D. J .; Andersen, R. A. J . Am. Chem. Soc. 1995, 117,
4014.
(65) Of the known dinuclear PtI complexes {(R2PC2H4PR2)PtIH}2
only the derivatives with R ) Ph65a and iPr can be isolated in the
presence of excess H2. In contrast, the derivatives with R ) c-C6H11
(58) Fryzuk, M. D.; Lloyd, B. R.; Clentsmith, G. K. B.; Rettig, S. J .
J . Am. Chem. Soc. 1991, 113, 4332; 1994, 116, 3804.
(59) Condensation of Pd atoms into Kr/H2 and Xe/H2 matrixes (12
K) gives rise to Pd(η1-H2) and Pd(η2-H2) species: Ozin, G. A.; Garcia-
Prieto, J . J . Am. Chem. Soc. 1986, 108, 3099.
t
and Bu are converted into (R2PC2H4PR2)PtIIH2.64 For a discussion of
the peculiarities of the synthesis of {(R2PC2H4PR2)PtIH}2 (R
)
c-C6H11),62 see: (a) Carmichael, D.; Hitchcock, P. B.; Nixon, J . F.;
Pidcock, A. J . Chem. Soc., Chem. Commun. 1988, 1554.

Sterically Encumbered Ni Phosphane Complexes
Organometallics, Vol. 18, No. 1, 1999 19
°C for 1 h, whereupon the color of the mixture changed from
yellow to red-brown. After diethyl ether was added (30 mL)
and the solvent was discarded, large brown crystals remained,
which were washed with pentane and dried under vacuum (20
°C): yield 800 mg (77%); mp 223 °C. EI-MS (140 °C): m/e (%)
518 (15) M+, 503 (100) [(dtbpe)NiI]+, 376 (74) [(dtbpe)Ni]+. IR
(KBr, 20 °C): 3026 (ν(CH3)), 1126 (δs(CH3)), 752 (Fr(CH3)) cm-1
(NiCH3). 1H NMR (400 MHz, 27 °C): δ 1.91, 1.71 (each m, 2H,
PCH2 and P′CH2), 1.48, 1.44 (each d, 18H, PtBu2 and P′tBu2),
0.55 (m, 3H, NiCH3). 31P NMR (81 MHz, 27 °C): δ 86.3, 72.7
(2J (PP) ) 3.0 Hz). Anal. Calcd for C19H43INiP2 (519.1): C,
43.96; H, 8.35; Ni, 11.31; P, 11.93; I, 24.45. Found: C, 43.91;
H, 8.31; Ni, 11.36; P, 11.98; I, 24.34.
(tBu 2P C2H4P tBu 2)Ni(I)CD3 (1-d 3). The synthesis was car-
ried out as for 1, but by using CD3I. IR (KBr): 2255/2204, 2096/
2038 (ν(CD3)), 866 (δs(CD3)) cm-1 (NiCD3). 1H NMR (dtbpe
part): as for 1. 31P NMR (81 MHz, 27 °C): δ 86.5, 72.8 (2J (PP)
) 3.4 Hz).
(tBu 2P C2H4P tBu 2)Ni(CH3)2 (2). (a) (dtbpe)NiCl2 (896 mg,
2.00 mmol) suspended in diethyl ether (30 mL) was reacted
with (tmeda)Mg(CH3)2 (436 mg, 2.10 mmol) at -30 °C until a
clear solution had formed. After addition of dioxane (0.35 mL,
4.2 mmol) colorless (C4H8O2)2MgCl2 precipitated, which was
separated by filtration and washed with ether. Yellow cubes
crystallized from the orange yellow filtrate at -78 °C and were
freed from the mother liquor, washed with cold pentane, and
dried under vacuum at -30 °C: yield 566 mg (69%).
increasing the concentration of H2. Corresponding ex-
periments are in progress.66
(c) From the above it is to be expected that for the
series of dinuclear Ni complexes [{R2P(CH2)nPR2}NiI]2-
i
t
(µ-H)2 (R ) e.g. Me, Et, c-C6H11 (3a ), Pr (3b), Bu (3)),
concomitant with an increasing distortion θ from the
calculated ground-state D2h symmetry, (i) a lowering of
the energy barrier of the structural dynamics according
to eq 4, (ii) a lowering of the energy barrier for H2/D2
exchange reactions (Scheme 2), and (iii) a more facile
generation of the formal [L2Ni0] fragments (e.g. Scheme
3) take place. While this hypothesis still has to be tested
for the smaller homologues of the given series, it
explains the ready generation of the formal [(dtbpe)Ni0]
fragment in solution, as shown in Figure 4.
Exp er im en ta l Section
All reactions and manipulations were performed using
Schlenk-type techniques under an inert atmosphere of argon.
Solvents were dried by distillation from NaAl(C2H5)4. dtbpe,3
(dtbpe)Ni(C2H4),3 {(dtbpe)Ni}2(µ-η2:η2-C6H6) (4),4 and (tmeda)-
67
Mg(CH3)2 and (tmeda)Mg(CD3)2 were prepared as reported.
Microanalyses were performed by the Mikroanalytisches Labor
Kolbe, Mu¨lheim, Germany. 1H NMR spectra (δ relative to
internal TMS) were measured at 200, 300, and 400 MHz, 13C
NMR spectra (δ relative to internal TMS) at 50.3, 75.5, and
100.6 MHz, and 31P NMR spectra (δ relative to external 85%
aqueous H3PO4) at 81 and 162 MHz on Bruker AM-200, WM-
300, and AMX-400 instruments. The solvent for solution NMR
was THF-d8. EI mass spectra (the data refer to 58Ni) were
recorded at 70 eV on a Finnigan MAT 8200 and IR spectra on
a Nicolet 7199 FT-IR instrument.
(b) A suspension of (dtbpe)Ni(I)CH3 (1; 519 mg, 1.00 mmol)
and (tmeda)Mg(CH3)2 (102 mg, 0.50 mmol) in diethyl ether
was stirred at -30 °C until all 1 was dissolved. The precipitate
of MgI2 was filtered off, and yellow crystals were obtained from
the remaining solution at -30 °C. The mother liquor was
discarded, and the product was washed with cold pentane and
dried under high vacuum at -30 °C: yield 155 mg (40%); mp
124 °C dec. EI-MS (110 °C): m/e (%) 406 (2) M+, 391 (8) [(d-
tbpe)NiCH3]+, 376 (74) [(dtbpe)Ni]+. IR (KBr, 20 °C): 1116 (δs-
(CH3)), 735 (Fr(CH3)) cm-1 (NiCH3); all CH stretching bands
are obscured by phosphane vibrations. 1H NMR (400 MHz, -30
(tBu 2P C2H4P tBu 2)NiCl2. A suspension/solution of NiCl2
(259 mg, 2.00 mmol) and dtbpe (637 mg, 2.00 mmol) in
methanol (40 mL) was stirred at 40 °C for 10 h. Large red
needles crystallized from the resulting deep red solution at
-78 °C. The product was separated from the mother liquor,
washed with cold pentane, and dried under vacuum (20 °C):
yield 700 mg (78%); dec pt 282 °C. The complex is paramag-
netic; hence, no NMR signals were observed. EI-MS (210 °C):
m/e (%) 446 (7) M+, 354 (4) [(tBu2PC2H4PtBu)NiCl]+, 261 (88)
[tBu2PC2H4PtBu]+. Anal. Calcd for C18H40Cl2NiP2 (448.1): C,
48.25; H, 9.00; Cl, 15.83; Ni, 13.10; P, 13.83. Found: C, 48.10;
H, 9.28; Cl, 15.81; Ni, 13.11; P, 13.76.
3
°C): δ 1.69 (m, J (PH) ) 10 Hz, 4H, PCH2), 1.32 (d, J (PH) )
11 Hz, 36H, CCH3), -0.08 (m, 6H, NiCH3). 13C NMR (100.6
MHz, 27 °C): δ 36.1 (4C, CCH3), 31.2 (12C, CCH3), 23.8 (2C,
PCH2), 1.80 (2C, AA′X spin system, 2J (PC) ) 71 Hz, 2J (P′C) )
2
-17.6 Hz, J (PP) ) 17.6 Hz, NiCH3). 31P NMR (81 MHz, -30
°C): δ 78.5. Anal. Calcd for C20H46NiP2 (407.2): C, 58.99; H,
11.39; Ni, 14.41; P, 15.21. Found: C, 58.91; H, 11.42; Ni, 14.48;
P, 15.20.
(tBu 2P C2H4P tBu 2)NiI2. 1,2-Diiodoethane (311 mg, 1.1 mmol)
was added at 20 °C to a yellow solution of (dtbpe)Ni(C2H4) (405
mg, 1.00 mmol) in THF (50 mL). The color of the solution
changed to dark green, and a dark blue microcrystalline
precipitate formed. After completion of the crystallization at
0 °C the product was isolated by filtration, washed with
pentane, and dried under vacuum (20 °C): yield 430 mg (78%);
mp 90 °C dec. The complex is paramagnetic. EI-MS (150 °C):
m/e (%) 503 (48) [(dtbpe)NiI]+, 447 (21) [(tBu2PC2H4P(H)tBu)-
NiI]+, 391 (27) [(tBu(H)PC2H4P(H)tBu)NiI]+, 335 (39) [(tBu(H)-
PC2H4PH2)NiI]+, 279 (12) [(H2PC2H4PH2)NiI]+. Anal. Calcd for
(tBu 2P C2H4P tBu 2)Ni(CD3)2 (2-d 6). The synthesis was car-
ried out as for 2, route a, but by using (tmeda)Mg(CD3)2. IR
(KBr): 2213/2183, 2083/2048 (ν(CD3)), 863sh, (δs(CD3)) cm-1
(NiCD3). 1H NMR (dtbpe part): as for 2. 31P NMR (81 MHz,
27 °C): δ 79.6.
{(tBu 2P C2H4P tBu 2)Ni}2(µ-H)2 (3). (a) The red solution of
4 (833 mg, 1.00 mmol) in diethyl ether (20 mL) was kept under
hydrogen without stirring for 1 h (20 °C). Thereafter the color
intensified to dark red and dark green crystals separated. After
completion of the crystallization at -78 °C the mother liquor
was removed by means of a capillary and the product was
washed with cold pentane and dried under vacuum at 20 °C:
yield 620 mg (82%).
(b) Stirring a red suspension of (dtbpe)NiCl2 (448 mg, 1.00
mmol) and Mg* (50 mg, excess) in THF (40 mL) under H2 gas
for several hours at 20 °C afforded a deep red solution. When
the solution was cooled to -78 °C, dark green crystals
precipitated, which were isolated as described: yield 200 mg
(53%); mp 218 °C. IR (KBr): ∼1280vw cm-1 (broad, ν(NiH)).
EI-MS (175 °C): m/e (%) 754 (61) M+, 377 (5) [(dtbpe)NiH]+,
376 (4) [(dtbpe)Ni]+, 261 (100) [tBu2PC2H4PtBu]+. 1H NMR (300
MHz, 27 °C): δ 1.67 (m, 8H, PCH2), 1.28 (m, 72H, CCH3),
-10.6 (quint, 2H, 2J (PH) ) 22 Hz, Ni(µ-H)2Ni). 31P NMR (121
MHz, 27 °C): δ 94.6. Anal. Calcd for C36H82Ni2P4 (756.3): C,
C
18H40I2NiP2 (631.0): C, 34.26; H, 6.39; I, 40.23; Ni, 9.30; P,
9.82. Found: C, 34.19; H, 6.45; I, 40.16; Ni, 9.36; P, 9.78.
(tBu 2P C2H4P tBu 2)Ni(I)CH3 (1). (dtbpe)Ni(C2H4) (810 mg,
2.00 mmol) was reacted with neat methyl iodide (3 mL) at 20
(66) The 31P NMR spectrum of a THF-d8 solution of 3 saturated with
H2 shows a weak singlet at δP 108 in addition to the singlet of 3 (δP
94.6). The extremely low field location of the new signal is indicative
of oxidation of the Ni center, and thus the signal is tentatively
attributed to either [(dtbpe)NiIIH2] (C) or [(dtbpe)NiIVH4]. The formation
of the latter would also explain (together with the process described
in Scheme 2) the slow H/D scrambling that is observed in the H2/D2
exchange reaction of 3.
(67) (a) Coates, G. E.; Heslop, J . A. J . Chem. Soc. A 1966, 26. (b)
Kaschube, W.; Po¨rschke, K.-R.; Angermund, K.; Kru¨ger, C.; Wilke, G.
Chem. Ber. 1988, 121, 1921.

20 Organometallics, Vol. 18, No. 1, 1999
Bach et al.
57.17; H, 10.93; Ni, 15.52; P, 16.38. Found: C, 57.28; H, 10.67;
Ni, 15.58; P, 16.35.
[No. 61], Enraf-Nonius CAD4 diffractometer, λ ) 0.710 69 Å,
ω-2θ scan, 10 116 reflections, 5174 independent, 3568 ob-
served (I > 2σ(I)), [(sin θ)/λ]max ) 0.65 Å-1, no absorption
correction, direct methods (SHELXS-97),68a least-squares re-
{(tBu 2P C2H4P tBu 2)Ni}2(µ-H)(µ-D) (3-d ). The reaction was
carried out as for 3, route a, but by using HD and stirring the
mixture at -40 °C. For NMR data, see text. C36H81DNi2P4
(757.3).
finement on Fo (SHELXL-97),68b H riding, 210 refined param-
2
eters, R1 ) 0.061 (obsd data), wR2 ) 0.157 (Chebyshev-
weights), final shift/error 0.001, residual electron density +1.56
{(tBu 2P C2H4P tBu 2)Ni}2(µ-D)2 (3-d 2). Synthesis was as for
3, route a, but by using D2 instead of H2. IR (KBr): ∼920vw
cm-1 (broad, ν(NiD)). EI-MS (160 °C): m/e (%) 756 (9) M+, 376
(2) [(dtbpe)Ni]+, 261 (79) [tBu2PC2H4PtBu]+. 1H NMR spectrum
(dtbpe part): as for 3. For 31P NMR spectrum, see text.
e Å-3
.
Cr ysta l Da ta for 3: C36H82Ni2P4, Mr ) 756.3, black crystal,
size 0.39 × 0.39 × 0.39 mm, a ) 11.5188(3) Å, b ) 16.4946(6)
Å, c ) 22.9190(8) Å, V ) 4354.6(2) Å3, T ) 293 K, Z ) 4, Dcalcd
) 1.15 g cm-3, µ ) 2.60 mm-1, orthorhombic, space group Pbcn
[No. 60], Enraf-Nonius CAD4 diffractometer, λ ) 1.541 78 Å,
ω-2θ scan, 4494 reflections, 3615 observed (I > 2σ(I)), [(sin
θ)/λ]max ) 0.63 Å-1, ψ-scan absorption correction, direct
C
36H80D2Ni2P4 (758.3).
(d tbp e)Ni(CH3)(OSO2CF 3) (5). CF3SO3H (0.09 mL, 1.0
mmol) was slowly added to a stirred yellow solution of 2 (407
mg, 1.00 mmol) in diethyl ether (30 mL) at -30 °C. When the
mixture was warmed to 20 °C, the color darkened to ocher and
a microcrystalline precipitate formed. After completion of the
crystallization at -78 °C, the product was freed of the mother
liquor by means of a capillary, washed with cold pentane, and
dried under vacuum at 20 °C: yield 405 mg (75%); mp 180 °C
dec. EI-MS (140 °C): m/e (%) 540 (7) M+, 525 (62) [(dtbpe)Ni-
(OTf)]+, 469 (35) [(tBu(H)PC2H4PtBu2)Ni(OTf)]+, 413 (27)
[(tBu(H)PC2H4P(H)tBu)Ni(OTf)]+, 357 (22) [(H2PC2H4P(H)tBu)-
methods (SHELXS-97),68a least-squares refinement on Fo
2
(SHELXL-97),68b H atom isotropic, remaining H atoms riding,
Me groups disordered (50:50) isotropic, 182 refined parameters,
R1 ) 0.059 (obsd data), wR2 ) 0.159 (Chebyshev weights),
final shift/error 0.001, residual electron density +0.413 e Å-3
.
Ack n ow led gm en t . We wish to thank the Volks-
wagen-Stiftung and the Fonds der Chemischen Indus-
trie for financial support.
1
Ni(OTf)]+. H NMR (300 MHz, 27 °C): δ 1.97, 1.58 (each m,
2H, PCH2 and P′CH2), 1.46, 1.42 (each d, 18H, PtBu2 and P′-
tBu2); 0.22 (dd, 3H, NiCH3). 13C NMR (75.5 MHz, 27 °C): δ
38.6, 35.7 (each d, 2C, CCH3), 31.6, 31.0 (each d, 6C, CCH3),
27.8, 26.6 (each m, 1C, PCH2 and P′CH2); 19.1 (m, 1C, NiCH3);
CF3 not detected. 31P NMR (81 MHz, 27 °C): δ 79.5, 71.2
(2J (PP) ) 12 Hz). Anal. Calcd for C20H43F3NiO3P2S (541.3): C,
44.38; H, 8.01; Ni, 10.84; P, 11.45; F, 10.53; O, 8.87; S, 5.92.
Found: C, 44.48; H, 8.12; Ni, 10.06; P, 11.42; F, 10.04.
Cr ysta l Da ta for 2: C20H46NiP2, Mr ) 407.2, yellow crystal,
size 0.46 × 0.60 × 0.88 mm, a ) 13.702(2) Å, b ) 14.661(2) Å,
Su p p or tin g In for m a tion Ava ila ble: Tables of data col-
lection information, anisotropic displacement parameters,
hydrogen atom coordinates, and bond lengths and angles for
2 and 3 (9 pages). Ordering information is given on any current
masthead page.
OM980705Y
c ) 22.648(3) Å, V ) 4550(1) Å3, T ) 100 K, Z ) 8, Dcalcd
)
(68) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(b) Sheldrick, G. M. Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997.
1.19 g cm-3, µ ) 0.99 mm-1, orthorhombic, space group Pbca