Synthesis and reactions of nickel(0) η2-cyclohexyne complexes and X-ray crystal structure of Ni(η2-C6H8)(C6H 11)2PCH2CH2P(C6H 11)2

Article abstract of DOI:10.1021/om9504516

Reduction of 1,2-dibromocyclohexene with 1% sodium amalgam in the presence of Ni(η²-C₂H₄)L₂ gives cyclohexyne nickel(O) complexes Ni(η₂-C₆H₈)L₂ [L₂ = 2PPh₃ (1), dcpe (2), 2PEt₃ (3); dcpe = 1,2-bis(dicyclohexylphosphino)ethane, Cy₂PCH₂CH₂PCy₂], which are structurally similar to, but less stable than, the corresponding platinum(O) compounds. The crystal structure of 2 has been determined. The molecule contains a nickel atom bound to η²-cyclohexyne [Ni-C(1) = 1.875(4) A?, Ni-C(2) = 1.867(4) A?] and to dcpe [Ni-P(1) = 2.139-(1) A?, Ni-P(2) = 2.138(1) A?]. The geometry is close to trigonal planar if the midpoint of the coordinated triple bond is regarded as occupying one coordination site, and the C=C distance [1.272(5) A?] is slightly less than that in Pt(η²-C₆H₈)(PPh₃)₂ [1.297(8) A?]. Complex 2 reacts with methyl iodide and with CO₂ to give insertion products containing nickel(II), NiI(2-MeC₆H₈)(dcpe) (7) and Ni{C₆H₈C(O)O}(dcpe)(9), respectively. Dimethyl acetylenedicarboxylate inserts into the Ni-C σ-bond of 9 to give a seven-membered nickelacycle Ni{C(CO₂-Me)=C(CO₂Me)C₆H ₈C(O)C-(dcpe) (10).

Full text of DOI:10.1021/om9504516

68
Organometallics 1996, 15, 68-74
Syn th esis a n d Rea ction s of Nick el(0) η2-Cycloh exyn e
Com p lexes a n d X-r a y Cr ysta l Str u ctu r e of
Ni(η2-C6H8)((C6H11)2P CH2CH2P (C6H11)2)
Martin A. Bennett,* J ulian A. J ohnson, and Anthony C. Willis
Research School of Chemistry, The Australian National University,
Canberra, ACT 0200, Australia
Received J une 13, 1995X
Reduction of 1,2-dibromocyclohexene with 1% sodium amalgam in the presence of Ni(η2-
C2H4)L2 gives cyclohexyne nickel(0) complexes Ni(η2-C6H8)L2 [L2 ) 2PPh3 (1), dcpe (2), 2PEt3
(3); dcpe ) 1,2-bis(dicyclohexylphosphino)ethane, Cy2PCH2CH2PCy2], which are structurally
similar to, but less stable than, the corresponding platinum(0) compounds. The crystal
structure of 2 has been determined. The molecule contains a nickel atom bound to
η2-cyclohexyne [Ni-C(1) ) 1.875(4) Å, Ni-C(2) ) 1.867(4) Å] and to dcpe [Ni-P(1) ) 2.139-
(1) Å, Ni-P(2) ) 2.138(1) Å]. The geometry is close to trigonal planar if the midpoint of the
coordinated triple bond is regarded as occupying one coordination site, and the CdC distance
[1.272(5) Å] is slightly less than that in Pt(η2-C6H8)(PPh3)2 [1.297(8) Å]. Complex 2 reacts
with methyl iodide and with CO2 to give insertion products containing nickel(II), NiI(2-
MeC6H8)(dcpe) (7) and Ni{C6H8C(O)O}(dcpe)(9), respectively. Dimethyl acetylenedicarboxy-
late inserts into the Ni-C σ-bond of 9 to give a seven-membered nickelacycle Ni{C(CO2-
Me)dC(CO2Me)C6H8C(O)O}(dcpe) (10).
In tr od u ction
Resu lts
The cyclohexyne nickel(0) complexes Ni(η2-C6H8)L2
[L2 ) 2PPh3 (1), dcpe (2)] can be isolated as yellow, air-
sensitive solids in ca. 60% yield from the reduction of
1,2-dibromocyclohexene with 1% sodium amalgam in
the presence of Ni(η2-C2H4)L2 (eq 1); this procedure is
similar to that used for the preparation of Pt(η2-C6H8)-
(PPh3)2.2,4
Small cyclic alkynes such as cycloheptyne (C7H10) and
cyclohexyne (C6H8) exist only transiently in the free
state, but can be stabilized in the form of transition
metal complexes of platinum(0), palladium(0), and zir-
conium(II), such as M(η2-C7H10)L2 (M ) Pt, Pd; L2
)
2PPh3, dppe),1-4 M(η2-C6H8)L2 (M ) Pt, L2 ) 2PPh3,2-4
2P-t-BuPh2,5 2P-t-Bu2Ph,5 2PMe3,5 dppe,2,4 dppp,6 dmpe;5
M ) Pd, L2 ) 2PPh3, dppe4), and Zr(η5-C5H5)2(η2-C6H8)-
(PMe3).7 Because complexes of nickel(0) are usually
structurally similar to their palladium(0) and platinum-
(0) counterparts, but are often more air-sensitive and
catalytically more active,8,9 we were interested to de-
termine whether cycloalkyne complexes of nickel(0)
corresponding to the palladium(0) and platinum(0)
complexes and to the η2-benzyne nickel(0) complexes
Ni(η2-C6H4)L2 (2L ) 2PEt3, dcpe)10,11 could be made.
The results of the investigation are described in this
paper.
The triethylphosphine complex Ni(η2-C6H8)(PEt3)2 (3)
was isolated similarly as a yellow oil that could not be
crystallized, even from pentane at -78 °C. The IR
spectrum of 1 shows a strong band at 1735 cm-1, which
is assigned to ν(CtC) modified by coordination. It is
ca. 14 cm-1 higher frequency than the corresponding
absorption in Pt(η2-C6H8)(PPh3)2,2,4 in accord with the
trend observed for Ni(0) and Pt(0) complexes of acyclic
acetylenes.12,13 The ν(CtC) bands in the spectra of 2
and 3 are ca. 20 cm-1 lower frequency than those in 1,
probably due to increased back-bonding into the cyclo-
hexyne π*-orbitals induced by the more electron-donat-
ing alkylphosphines.6,13,14 The 31P{1H} NMR spectra of
X Abstract published in Advance ACS Abstracts, October 15, 1995.
(1) Abbreviations: dppe, 1,2-bis(diphenylphosphino)ethane, Ph2-
PCH2CH2PPh2; dppp, 1,3-bis(diphenylphosphino)propane, Ph2PCH2-
CH2CH2PPh2; dppb, 1,4-bis(diphenylphosphino)butane, Ph2PCH2CH2-
CH2CH2PPh2; dmpe, 1,2-bis(dimethylphosphino)ethane, Me2PCH2CH2-
PMe2; dcpe, 1,2-bis(dicyclohexylphosphino)ethane, Cy2PCH2CH2PCy2.
(2) Bennett, M. A.; Robertson, G. B.; Whimp, P. O.; Yoshida, T. J .
Am. Chem. Soc. 1971, 93, 3797.
(3) Robertson, G. B.; Whimp, P. O. J . Am. Chem. Soc. 1975, 97, 1051.
(4) Bennett, M. A.; Yoshida, T. J . Am. Chem. Soc. 1978, 100, 1750.
(5) Bennett, M. A.; Fick, H.-G.; Warnock, G. F. Aust. J . Chem. 1992,
45, 135.
(6) Bennett, M. A.; Rokicki, A. Aust. J . Chem. 1985, 38, 1307.
(7) Buchwald, S. L.; Lum, R. T.; Dewan, J . C. J . Am. Chem. Soc.
1986, 108, 7441.
(8) J olly, P. W.; Wilke, G. The Organic Chemistry of Nickel;
Academic: New York and London, 1974; Vol. 1 (1975, Vol. 2).
(9) J olly, P. W. In Comprehensive Organometallic Chemistry; Wilkin-
son, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, 1982;
Vol. 6, pp 1-231; Vol. 8, pp 613-797.
(10) Bennett, M. A.; Hambley, T. W.; Roberts, N. K.; Robertson, G.
B. Organometallics 1985, 4, 1992.
(11) Bennett, M. A.; Wenger, E. Organometallics 1995, 14, 1267.
(12) Greaves, E. O.; Lock, C. J . L.; Maitlis, P. M. Can. J . Chem. 1968,
46, 3879.
(13) Rosenthal, U. Z. Anorg. Allgem. Chem. 1981, 482, 179.
(14) Rosenthal, U.; Schulz, W. J . Organomet. Chem. 1987, 321, 103.
0276-7333/96/2315-0068$12.00/0 © 1996 American Chemical Society

Reactions of Nickel(0) η2-Cyclohexyne Complexes
Organometallics, Vol. 15, No. 1, 1996 69
1-3 each show a singlet and in the 13C NMR spectra
there is a characteristic five-line AA′X pattern at δ ca.
140 due to the coordinated carbon atoms, the separation
of the outer lines, J (PC) + J (P′C), being ca. 80 Hz.
Similar patterns have been observed in the 13C NMR
spectra of benzyne nickel(0) complexes,10,11 cycloalkyne
platinum(0) complexes,5 and alkyne complexes M(η2-
RC2R)(PR′3)2 (M ) Ni, Pt);15,16 they confirm that rotation
of the coordinated cyclohexyne is slow on the NMR time
scale. The EI mass spectrum of 2 shows a parent ion
at m/z 560, but parent ions were not observed for 1 and
3. The analytical and spectroscopic data thus strongly
support the formulation as cyclohexyne nickel(0) com-
plexes, and this has been confirmed in the case of 2 by
X-ray structural analysis (see the following).
Sch em e 1. P ossible Rou tes to Cycloh exyn e
Nick el(0) Com p lexes
Complexes 1 and 3 were also formed from 1,2-
dibromocyclohexene and 1% Na/Hg in the presence of
Ni(COD)2 and 2 equiv of PPh3 or PEt3, but in the case
of PPh3 some Ni(PPh3)3 was also formed, as shown by
31P NMR spectroscopy.17,18 A similar reaction with
PMe3 (2 equiv), dppe (1 equiv), or depe (1 equiv) gave,
5 (δP 60.2). Under similar conditions, reaction of 1 with
dcpe gave an approximately 1:1 mixture of 2 and Ni-
(dcpe)2 (δP 43.5).24
In the complete absence of air, solutions of 1-3 in
benzene are stable for 2 weeks before appreciable
decomposition occurs. In the case of 1, formation of a
black deposit is accompanied in the 31P{1H} NMR
spectrum by the growth of a singlet at δ 24.0, probably
due to Ni(PPh3)3, as well as other broad, ill-defined
peaks. Complex 2 slowly gives two species character-
ized by 31P NMR singlets at δ 55 and 60 that have not
been investigated further.
21
respectively, Ni(PMe3)4,19 Ni(dppe)2,20 and Ni(depe)2
as the only products identifiable by 31P NMR spectros-
copy. Under the same conditions, dmpe (1 equiv)
afforded an oil, which was shown by 31P NMR spectros-
copy to contain two products in ca. 3:1 ratio. The main
product was Ni(dmpe)2 (δP 18.0);19,22 the minor product
(δP 24.5) may be Ni(η2-C6H8)(dmpe), because the IR
spectrum of the oil contained a weak band at 1715 cm-1
assignable to ν(CtC) modified by coordination. The two
species could not, however, be separated by fractional
crystallization.
Reduction of 1,2-dibromocyclohexene with 1% Na/Hg
in the presence of Ni(η2-C2H4)(PCy3)2 gave, after 24 h,
an oil whose IR spectrum showed a band of medium
intensity at 1720 cm-1, indicative of the presence of Ni-
(η2-C6H8)(PCy3)2 (4). The 31P{1H} NMR spectrum of the
oil showed four main singlets at δ 9, 37, 45, and 49, the
first two being due to unchanged PCy3 and Ni(η2-C2H4)-
(PCy3)2, respectively, and the third due to Ni(PCy3)3.23
After 36 h the peak at δ 49, presumed to be due to 4,
had disappeared, and only those due to PCy3 and Ni-
(PCy3)3 remained.
Attempts to prepare nickel(0) cyclohexyne complexes
containing ditertiary phosphines by displacement of
PPh3 from 1 were only partly successful, in contrast to
the behavior of the corresponding platinum(0) system.6
The IR spectrum of the yellow solid isolated from the
reaction of 1 with dppe in benzene at room temperature
showed a strong band at 1720 cm-1 due to Ni(η2-C6H8)-
(dppe) (5), but the 31P NMR spectrum showed the
presence of Ni(dppe)2 (δP 43.0) (ca. 20%) in addition to
The reaction described by eq 1 could proceed by two
routes, as summarized in Scheme 1. First, cyclohexyne,
generated transiently from 1,2-dibromocyclohexene and
1% Na/Hg,27-29 could react with the zero-valent metal
complex. This idea was behind the original synthesis
of Pt(η2-C6H8)(PPh3)22,4 and has also been suggested for
the corresponding formation of the 4-homoadamantyne
complex Pt(η2-C11H14)(PPh3)2 from 4,5-dibromo-4-ho-
moadamantene.30 In the second possible pathway, 1,2-
dibromocyclohexene could undergo oxidative addition to
the nickel(0) complex to give a (2-bromocyclohexenyl)-
nickel(II) bromide, NiBr(2-BrC6H8)L2, which could be
reduced to Ni(η2-C6H8)L2 by 1% Na/Hg. The synthesis
of the closely related benzyne complex Ni(η2-C6H4)(dcpe)
by alkali metal reduction of NiBr(2-BrC6H4)(dcpe)10
provides a close analogy. In contrast, (2-bromocycloalk-
enyl)platinum(II) complexes PtBr(CnH2n-4Br)L2 (n ) 5,
6) are not reduced by 1% Na/Hg to the corresponding
cycloalkyne platinum(0) complexes. In the case of n )
5, however, it has been shown that the cyclopentyne
complex Pt(η2-C5H6)(PPh3)2 is formed by 1% Na/Hg
reduction of the π-complex of 1,2-dibromocyclopentene,
(15) Po¨rschke, K. R.; Mynott, R.; Angermund, K.; Kru¨ger, C. Z.
Naturforsch. B 1985, 40, 199.
(16) Boag, N. M.; Green, M.; Grove, D. M.; Howard, J . A. K.; Spencer,
J . L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1980, 2170.
(17) Tolman, C. A.; Seidel, W. C.; Gerlach, D. H. J . Am. Chem. Soc.
1972, 94, 2669.
(24) This compound has been made as bright yellow crystals by the
reduction of Ni(acac)2 with Et2AlOEt in toluene/ether in the presence
of dcpe (2 equiv).25 It is clearly different from the purple product
isolated from the reaction of nickelocene with dcpe in refluxing toluene,
which has been formulated as a three-coordinate species, Ni(dcpe-PP′)-
(dcpe-P).26
(18) Mynott, R.; Mollbach, A.; Wilke, G. J . Organomet. Chem. 1980,
199, 107.
(19) Tolman, C. A.; Seidel, W. C.; Gosser, L. W. J . Am. Chem. Soc.
1974, 96, 53.
(20) Fisher, K. J .; Alyea, E. C. Polyhedron 1989, 8, 13.
(21) A sample of Ni(depe)2 prepared in situ by the addition of depe
(2 equiv) to Ni(COD)2 in C6D6 showed a 31P{1H} NMR singlet at δP
44.7.
(22) Tolman, C. A. J . Am. Chem. Soc. 1970, 92, 2956.
(23) J olly, P. W.; J onas, K.; Kru¨ger, C.; Tsay, Y.-H. J . Organomet.
Chem. 1971, 33, 109.
(25) Bu¨ch, H. M. Ph.D. Thesis, University of Kaiserslautern, 1982,
p 210.
(26) Connor, J . A.; Riley, P. I. Inorg. Chim. Acta 1968, 15, 217.
(27) Faworsky, A.; Bushowsky, M. J ustus Liebigs Ann. Chem. 1912,
390, 122.
(28) Wittig, G.; Mayer, U. Chem. Ber. 1963, 96, 329, 342. (b) Wittig,
G.; Weinlich, J . Chem. Ber. 1965, 98, 471.
(29) (a) Wittig, G.; Krebs, A. Chem. Ber. 1961, 94, 3260. (b) Wittig,
G.; Pohlke, R. Chem. Ber. 1961, 94, 3276.
(30) Komatsu, K.; Kamo, H.; Tsuji, R.; Masuda, H.; Takeuchi, K. J .
Chem. Soc., Chem. Commun. 1991, 71.

70 Organometallics, Vol. 15, No. 1, 1996
Bennett et al.
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) in Ni(η2-C6H8)(d cp e) (2)
Ni-P(1)
2.139(1)
1.875(4)
1.860(4)
1.856(4)
1.854(4)
1.272(5)
1.504(6)
Ni-P(2)
2.138(1)
1.867(4)
1.863(4)
1.852(4)
1.865(7)
1.875(7)
1.481(6)
Ni-C(1)
Ni-C(2)
P(1)-C(11)
P(1)-C(111)
P(1)-C(121)
C(1)-C(2)
C(1)-C(6)
P(2)-C(21)
P(2)-C(211)
P(2)-C(221A)
P(2)-C(221B)
C(2)-C(3)
P(1)-Ni-P(2)
P(1)-Ni-C(1)
P(1)-Ni-C(2)
Ni-P(1)-C(11)
Ni-P(1)-C(111)
Ni-P(1)-C(121)
91.33(4) C(1)-Ni-C(2)
152.6(1) P(2)-Ni-C(2)
112.8(1) P(2)-Ni-C(1)
108.5(1) Ni-P(2)-C(21)
118.2(1) Ni-P(2)-C(211)
117.4(1) Ni-P(2)-C(221A)
Ni-P(2)-C(221B)
39.7(2)
155.6(1)
116.1(1)
106.9(1)
120.1(1)
123.4(2)
112.0(2)
100.9(2)
C(11)-P(1)-C(111) 103.4(2) C(21)-P(2)-C(211)
C(11)-P(1)-C(121) 103.8(2) C(21)-P(2)-C(221A) 107.2(2)
F igu r e 1.
Molecular structure of Ni(η2-C6H8)-
C(21)-P(2)-C(221B)
99.5(3)
(Cy2PCH2CH2PCy2) (2) with atom labeling and 50% prob-
C(111)-P(1)-C(121) 103.9(2) C(211)-P(2)-C(221A) 95.7(2)
C(211)-P(2)-C(221B) 114.2(3)
ability ellipsoids.
Ni-C(1)-C(2)
Ni-C(1)-C(6)
C(2)-C(1)-C(6)
69.8(2) Ni-C(2)-C(1)
164.7(3) Ni-C(2)-C(3)
125.5(4) C(1)-C(2)-C(3)
70.5(2)
161.1(3)
128.4(4)
Pt(η2-C5H6Br2)(PPh3)2.31 Moreover, the formation of the
cycloheptyne complex Pt(η2-C7H10)(PPh3)2 from 1-bro-
mocycloheptene, LiN-i-Pr2, and Pt(PPh3)3 appears to
proceed by elimination of HBr from an intermediate
π-complex Pt(η2-C7H11Br)(PPh3)2, rather than via free
cycloheptyne.32
In an attempt to find out which pathway is operative
in the reaction described by eq 1, we studied the reaction
of an excess of 1,2-dibromocyclohexene with Ni(η-C2H4)-
(dcpe) in the absence of 1% Na/Hg. The main product,
formed over the course of 24 h, was NiBr2(dcpe), as
shown by 31P NMR spectroscopy, but a small amount
Ta ble 2. Cr ysta llogr a p h ic Da ta for
Ni(η2-C6H8)(d cp e) (2)a
chem formula
fw
cryst system
space group
a (Å)
C32H56NiP2
561.44
monoclinic
P21/n
10.006(1)
17.772(1)
17.721(1)
90.27(1)
3151.2(4)
4
b (Å)
c (Å)
â (deg)
V (Å3)
Z
of a product having an AB quartet (δP 61.4, 64.9; J AB
)
D
calc (g cm-3
)
1.183
19.9
20(1)
11.4 Hz) was also present; it may be NiBr(2-BrC6H8)-
(dcpe) (6). The second product was formed in a much
higher proportion by the addition of 1,2-dibromocyclo-
hexene to 2, but attempts to isolate it in a pure state
failed, and over 48 h it decomposed to NiBr2(dcpe).
Reduction of impure 6 with 1% Na/Hg gave 2 as the
main product, identified in situ by comparison of its 31P-
{1H} NMR and IR spectra with those of an authentic
sample. These results indicate that 6 is a plausible
intermediate in the synthesis of 2, but do not rule out
the possible involvement of free cyclohexyne.
µ[Cu KR] (cm-1
T (°C)
)
cryst dimens (mm)
X radiation
λ (Å)
data range, deg in 2θ
no. unique data
no. data refined
no. variables
no. restraints
R
0.34 × 0.14 × 0.17
Cu KR
1.5418
4-128
5241
3932 [I > 3σ(I)]
308
42
0.048
0.056
1.70
Rw
GOF
Str u ctu r e of Ni(η2-C6H8)(d cp e) (2). The molecular
structure with atom labeling is shown in Figure 1;
selected bond lengths and bond angles are summarized
in Table 1, and details of the data collection are given
in Table 2. The molecule consists of a central nickel
atom symmetrically coordinated by η2-cyclohexyne [r(Ni-
C1) 1.875(4) Å, r(Ni-C2) ) 1.867(4) Å] and the diter-
tiary phosphine [r(Ni-P1) ) 2.139(1) Å, r(Ni-P2) )
2.138(1) Å] in an arrangement that is close to trigonal
planar, on the assumption that the midpoint of the
coordinated triple bond occupies one coordination site.
This coordination geometry is typical of M(η2-alkyne)-
L2 complexes of the d10 metals.33 The dihedral angle
between the Ni-P1-P2 and Ni-C1-C2 planes is 3.8°.
The M-C and M-P distances in 2 are ca. 0.15 Å shorter
than those in Pt(η2-C6H8)(PPh3)2,3 but are similar to
those in Ni(η2-C6H4)(dcpe) [Ni-P 2.203(4) Å, 2.170(4)
Å; Ni-C 1.951(12) Å, 1.988(12) Å].10 The Ni-C and
F(000)
1224
R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) {∑w(|Fo| - |Fc|)2/∑(wFo)2}1/2; GOF
a
) {∑w(|Fo| - |Fc|)2/(no. ref - no. var)}1/2
.
Ni-P distances in 2 are also comparable with those
observed in bis(tertiary phosphine)nickel(0) complexes
of acyclic alkynes, Ni(RC2R)L2 (2L ) 2PPh3,34 R ) H,
SiMe3,35 CO2Me;36 2L ) dmpe, R ) Ph15). The C1-C2
bond distance of 1.272(5) Å in 2 falls within the range
1.25-1.30 Å found in Ni(η2-RC2R)L2 complexes and is
slightly less than that in Pt(η2-C6H8)(PPh3)2 [1.297(8)
Å].3 The mean deformation from 180° of the internal
CtCsC angle, 53.1°, is similar to those in Pt(η2-C6H8)-
3
(PPh3)2 and in Zr(η5-C5H5)2(η2-C6H8)(PMe3).7
R ea ct ion s of t h e Cycloh exyn e Nick el Com -
p lexes. In general, the products of reaction of complex
2 (Scheme 2) are more stable and retain the C6H8
(34) Po¨rschke, K. R.; Tsay, Y.-H.; Kru¨ger, C. Angew. Chem., Int. Ed.
Engl. 1985, 24, 323.
(35) Rosenthal, U.; Schulz, W.; Go¨rls, H. Z. Anorg. Allgem. Chem.
1987, 550, 169.
(31) Bennett, M. A.; Warnock, G. F. Unpublished work, cited in
Bennett, M. A.; Schwemlein, H. P. Angew. Chem., Int. Ed. Engl. 1989,
28, 1296.
(32) Lu, Z.; Abboud, K. A.; J ones, W. M. Organometallics 1993, 12,
1471.
(33) Ittel, S. D.; Ibers, J . A. Adv. Organomet. Chem. 1976, 14, 33.
(36) Rosenthal, U.; Oehme, G.; Go¨rls, H.; Burlakov, V. V.; Polyakov,
A. V.; Yanovskii, A. I.; Struchkov, Yu. T. J . Organomet. Chem. 1990,
389, 251.

Reactions of Nickel(0) η2-Cyclohexyne Complexes
Organometallics, Vol. 15, No. 1, 1996 71
Sch em e 2. Oxid a tive Ad d ition a n d In ser tion
{C6H8C(O)O}(dcpe) (9) in high yield as a yellow, air-
stable solid; a similar product is formed from Ni(η2-
C6H4)(dcpe) and CO2.12 Compound 9 shows a parent
ion peak in its EI mass spectrum, together with a
fragment due to Ni(dcpe). The IR spectrum contains a
strong ν(CdO) band at 1620 cm-1 due to the carboxylate
group and a weak band at 1555 cm-1 due to ν(CdC).
The ester carbon atom appears in the 13C{1H} NMR
spectrum at δ 185.0, the carbon atom σ-bonded to nickel
occurs as a 31P-coupled doublet of doublets at δ 166.2,
and a singlet at δ 128.6 can be assigned to the remaining
vinyl carbon atom. The 31P{1H} NMR spectrum shows
an AB quartet (2J PP ) 34 Hz) arising from cis-
phosphorus atoms. A solution of complex 9 in benzene
reacted with CO at room temperature and pressure and
with 3-hexyne at 80 °C to give, respectively, Ni(CO)2-
(dcpe) and Ni(η2-EtC2Et)(dcpe); the fate of the organic
fragment has not been investigated.
Rea ction s of Ni(η2-C6H8)(d cp e) (2)
Dimethyl acetylenedicarboxylate inserted into the
Ni-C σ-bond of 9 to give the seven-membered metal-
fragment more readily than those of complexes 1 and
3, containing monodentate tertiary phosphines.
Complex 2 reacted immediately with an equimolar
amount of methyl iodide to give the (2-methylcyclohex-
enyl)iodonickel(II) complex NiI(2-MeC6H8)(dcpe) (7),
which was isolated as an orange, air-stable powder in
64% yield. A small amount of NiI2(dcpe) was also
formed, as shown by the presence of a singlet at δ 95.2
in the 31P{1H} NMR spectrum. Compound 6 is easily
soluble in benzene and THF, but is unstable in chlori-
nated solvents, even in an inert atmosphere. The
structure follows from the NMR data: the 31P{1H} NMR
lacycle Ni{C(CO2Me)dC(CO2Me)C6H8C(O)O}(dcpe) (10),
which was isolated in 57% yield as an amber solid. It
is air-stable in the solid state and stable in solution in
the absence of air. The structural assignment rests on
spectroscopic data. The 13C{1H} NMR spectrum shows
three singlets at δ 173.6, 175.0, and 186.0 due to the
carbonyl carbon atoms and a pair of doublets of dou-
blets, arising from 31P coupling, at δ 163.5 and 175.1,
assignable to the C(CO2Me) groups. The olefinic carbon
atoms of the cyclohexene ring appear as singlets at δ
133.5 and 135.8. The inequivalent methoxyl groups give
rise to a pair of methyl singlets at δ 3.50 and 4.70 in
the 1H NMR spectrum and at δ 51.4 and 52.7 in the
13C NMR spectrum. There is an AB quartet in the 31P-
{1H} NMR spectrum (2J PP ) 34 Hz) indicative of cis-
inequivalent phosphorus atoms. Complex 10 was re-
covered unchanged after heating in the solid state for 4
h at 102 °C; there was no evidence for thermal elimina-
tion of CO2. The compound did decompose in refluxing
xylene to give a yellow solid, which was shown by 31P
NMR spectroscopy to contain Ni(CO)2(dcpe) in addition
to other unidentified products.
2
spectrum shows an AB quartet (δ 57.7, 60.4; J PP ) 9
Hz), and the 1H NMR spectrum shows a singlet at δ
2.4, due to the methyl group, in addition to broad,
overlapping multiplets in the region δ 1.0-3.0 due to
the methylene protons of the 2-methylcyclohexenyl and
dcpe ligands.
Complex 3 reacted with methyl iodide to give an oil
whose 1H NMR spectrum showed a singlet at δ 2.4,
suggestive of the presence of the 2-methylcyclohexenyl
complex NiI(2-MeC6H8)(PEt3)2 (8). The 31P{1H} NMR
spectrum, however, showed three singlets at δ 9.4, 10.8,
and 12.4 in a ratio of about 1:10:6. The first and last
are probably due to NiI2(PEt3)2 and trans-NiI(Me)-
(PEt3)2, respectively, as shown by comparison with
authentic samples. Attempts to obtain a pure sample
of 8 by fractional crystallization at low temperatures
were unsuccessful. The reactions of 2 and 6 with methyl
iodide are generally similar to those of Pt(η2-C6H8)L2
(L2 ) 2PPh3, dppe), although there was no evidence for
an intermediate product of oxidative addition to nickel
corresponding to PtI(Me)(η2-C6H8)(PPh3)2, which is the
first detectable species formed from Pt(η2-C6H8)(PPh3)2
and methyl iodide.37
Complex 2 reacted readily with bromine or iodine to
form NiX2(dcpe) (X ) Br, I) and, presumably, the 1,2-
dihalocyclohexene. In contrast to the behavior of Pt-
(η2-C6H8)L2, there was no evidence for the expected
intermediates NiX(2-XC6H8)(dcpe) [X ) Br(6), I], prob-
ably because their Ni-C σ-bonds are rapidly cleaved by
halogens.
The sulfur analogue of 10, Ni{C6H8C(S)S}(dcpe) (11),
is probably formed by reaction of 2 with CS2 in benzene
at room temperature, but it could not be separated from
by products, including Ni(η2-CS2)(dcpe). The IR spec-
trum of 11 shows several bands in the ν(CdS) region
(1100-1200 cm-1), and the 31P{1H} NMR spectrum
shows an AB quartet (2J PP ) 21 Hz).
Although complexes 1 and 3 readily react with both
CO2 and CS2, we were unable to isolate insertion
products analogous to 9 and 11. The main product from
1 and CO2 showed a sharp singlet at δ 24.5, apparently
due to Ni(PPh3)3. There was no evidence for the
formation of oligomers of cyclohexyne27,28 and, when the
reaction was carried out in the presence of tetraphe-
nylcyclopentadienone or 2,5-diphenyl-3,4-isobenzofuran,
the appropriate Diels-Alder adducts of cyclohexyne29
were not formed. Other reactions in which cyclohexyne
was apparently displaced from the coordination sphere
were those of 1 with CS2, 1 and 2 with acetylenes, and
1-3 with ethylene to give, respectively, [Ni(η2-CS2)-
(PPh3)]n, [Ni(η2-RC2R)L2] (R ) Et, CO2Me; L2 ) 2PPh3,
dcpe), and [Ni(η2-C2H4)L2] (L2 ) 2PPh3, 2PEt3, dcpe).
Complex 2 reacted readily with CO2 at room temper-
ature and pressure to form the insertion product Ni-
(37) Appleton, T. G.; Bennett, M. A.; Singh, A.; Yoshida, T. J .
Organomet. Chem. 1978, 154, 369.

72 Organometallics, Vol. 15, No. 1, 1996
Bennett et al.
separated from the excess amalgam by centrifugation and was
evaporated to dryness in vacuo to give a brown oil. The yellow
solid that formed upon addition of ether was isolated by
filtration, washed with hexane (10 mL), and dried in vacuo to
give 1 (1.06 g, 56%). 1H NMR (CD2Cl2): δ 1.71, 2.65 (each br
s, CH2), 6.9-7.6 (m, C6H5). 13C{1H} NMR (CD2Cl2): δ 27.3,
27.5 (each s, CH2), 128.8, 131.6, 134.1 (each s, CH), 132.5 (t,
In the first two cases, the nickel-containing products
were identified by comparison of their 31P{1H} NMR
spectra with those of the complexes resulting from the
displacement of ethylene from Ni(η2-C2H4)L2 by the
appropriate ligand; the fate of the C6H8 moiety has not
been determined.
1
CHP, J PC ) 10 Hz), 138.1 (five line m, CtC, separation
between outer lines ) 65 Hz). 31P{1H} NMR (CD2Cl2): δ 43.1
(s). IR (KBr, cm-1) 1735 [s, ν(CtC)]. Anal. Calcd for C42H38P2-
Ni: C, 76.0; H, 5.8; Ni, 8.9. Found: C, 76.5, 74.2; H, 6.0, 6.1;
Ni, 8.5.
Discu ssion
Cyclohexyne nickel(0) complexes Ni(η2-C6H8)L2 1-3
can be made similarly to their platinum(0) analogues,
but the coordinated C6H8 fragment seems to be more
readily lost. This behavior is in apparent contrast to
the trend in stability of the η2-ethylene complexes of the
d10 metals: the equilibrium constants governing eq 2
increase in the order Ni > Pt > Pd.17 Although 2
Ni(η2-C6H8)(d cp e) (2). This was prepared similarly to 1
from Ni(C2H4)(dcpe) (4.86 g, 9.55 mmol), 1,2-dibromocyclohex-
ene (5.04g, 20.8 mmol), and 1% sodium amalgam [from sodium
(2.3 g) and mercury (228 g)] in THF (70 mL). The yellow oil
that was obtained after centrifugation and removal of solvent
crystallized upon addition of ether at -30 °C. Recrystallization
from ether at -30 °C gave 2 (3.25 g, 61%) as a yellow,
crystalline solid (mp 140-145 °C (dec). 1H NMR (CD2Cl2): δ
1.4-2.7 (m, CH, CH2). 13C{1H} NMR (CD2Cl2): δ 22.8 (t,
M(PPh3)3 + C2H4 h M(η2-C2H4)(PPh3)2 + PPh3 (2)
undergoes stoichiometric insertion with CO2 and CS2,
other π-acceptors induce rapid displacement of C6H8
from 1-3, although not as free cyclohexyne. The
π-acceptors may undergo double insertion into the Ni-
C6H8 bond to give unstable nickelacycles that rapidly
eliminate the organic moiety, leaving NiL2. This type
of pathway has been established in the reactions of
alkynes with η2-benzyne and (2,3-η)-naphthalyne nickel-
1
CH2P, J PC ) 40 Hz), 26.7, 28.1, 29.5 (each s, CH2), 30.6 (t,
2
1
CH2, J PC ) 16 Hz), 35.5 (t, CHP, J PC ) 21 Hz), 139.7 (five-
line m, CtC, separation between outer lines ) 97 Hz). 31P{1H}
NMR (CD2Cl2) δ 79.1 (s). IR (KBr, cm-1): 1710 [s, ν(CtC)].
EI mass spectrum: m/z 560 (parent ion). Anal. Calcd for
C
32H56P2Ni: C, 68.5; H, 10.1; P, 11.0. Found: C, 68.1; H, 10.5;
P, 11.0.
Ni(η2-C6H8)(P Et3)2 (3). This was made similarly to 1 from
11
(0) complexes, Ni(η2-C6H4)L2 and Ni(η2-C10H6)L2.38
Ni(C2H4)(PEt3)2 (0.34 g, 1.04 mmol), 1.2-dibromocyclohexene
(0.62 g, 2.60 mmol), and 1% sodium amalgam [Na (0.25 g),
Hg (24.7 g)] in THF (20 mL). Complex 3 was obtained as a
yellow oil (0.25 g, 64%) that could not be crystallized from
pentane at -78 °C. 1H NMR (C6D6): δ 1.0 (t, CH3), 1.2-2.2
(m, CH2). 13C{1H} NMR (C6D6): δ 9.0 (s, CH3), 20.7 (t, CH2P,
1J PC ) 23 Hz), 27.6, 28.5 (each m, CH2), 139.7 (five-line m,
CtC, separation between outer lines ) 72 Hz). 31P{1H} NMR
(C6D6): δ 30.4 (s). IR (neat oil, cm-1): 1715 [s, ν(CtC)].
Exp er im en ta l Section
All reactions were performed under nitrogen or argon with
the use of standard Schlenk techniques. NMR spectra were
recorded on J eol FX-200 (1H, 200 MHz), Varian XL-200 (1H,
200 HMz; 13C, 50.3 MHz; 31P, 80.98 MHz) and J eol FX-60 (31P,
24.21 MHz) spectrometers. The 1H and 13C NMR chemical
shifts are reported as δ-values relative to Me4Si; 31P NMR
chemical shifts are reported relative to external 85% H3PO4,
values of high frequency being positive. Infrared spectra were
measured as KBr disks or as neat oils on KBr plates in the
range 4000-250 cm-1 on a Perkin-Elmer 683 instrument.
Mass spectra (EI) were recorded at 70 eV on a VG Micromass
7070 spectrometer. Melting points were measured in sealed
tubes under nitrogen and are uncorrected. Elemental analyses
were performed in-house.
Sta r tin g Ma ter ia ls. The compounds 1,2-dibromocyclohex-
ene,27 PMe3,39 Me2PCH2CH2PMe2(dmpe),40 Et2PCH2CH2PEt2-
(depe),40 Cy2PCH2CH2PCy2(dcpe),40 Ni(COD)2,41 and Ni(C2H4)-
L2 (2L ) 2PPh3,42-44 2PEt3,42 2PCy3,45 and dcpe10) were
prepared by the appropriate literature methods. All other
compounds were obtained from commercial suppliers.
P r ep a r a tion s. Ni(η2-C6H8)(P P h 3)2 (1). A solution con-
taining Ni(C2H4)(PPh3)2 (1.72 g, 2.82 mmol) and 1,2-dibro-
mocyclohexene (2.15 g, 8.96 mmol) in THF (30 mL) was added
to 1% sodium amalgam that had been freshly prepared from
sodium (0.59 g) and mercury (58.5 g), and the mixture was
stirred for 15 h. The resulting yellow-brown solution was
Attem p ted P r ep a r a tion of Ni(η2-C6H8)(P Cy3)2 (4).
A
solution of Ni(C2H4)(PCy3)2 (4.09 g, 6.35 mmol) and 1,2-
dibromocyclohexene (3.01 g, 12.5 mmol) in THF (30 mL) was
added to 1% sodium amalgam that had been freshly prepared
from sodium (1.45 g) and mercury (144 g), and the mixture
was stirred for 24 h. After removal of the excess amalgam by
centrifugation, the yellow-brown solution was evaporated to
dryness in vacuo to give a brown oil that solidified upon
addition of ether. The main product 4 was identified on the
basis of its spectroscopic properties. 13C{1H} NMR (C6D6): δ
21.4-35.0 (m, CH2, CH, CHP), 139.7 (five-line m, CtC,
separation between outer lines ) 80 Hz). 31P{1H} NMR
(C6D6): δ 49.1 (s). IR (neat oil, cm-1): 1720 [m, ν(CtC)]. The
31P{1H} NMR spectrum also showed peaks at δ 9.0, 37.0, 45.0,
and 49.0, the last being due to 4. Comparison with authentic
materials showed the first three of these to be due to
unchanged Cy3P, Ni(C2H4)(PCy3)2, and Ni(PCy3)3, respectively.
Attem p ted P r ep a r a tion of Ni(η2-C6H8)L2 [L ) P P h 3 (1),
P Et3 (2)] fr om Ni(COD)2. A solution of Ni(COD)2 (1.76 g,
6.41 mmol), triphenylphosphine (3.35 g, 12.8 mmol), and 1,2-
dibromocyclohexene (6.30 g, 26.6 mmol) in THF (80 mL) was
added to sodium amalgam that had been freshly prepared from
sodium (2.3 g) and mercury (225 g), and the mixture was
stirred for 16 h. Workup as described earlier gave a brown
oil that turned into a yellow-brown, air-sensitive solid. Spec-
troscopic data showed this to be a mixture of 1 and Ni(PPh3)3:
31P{1H} NMR (C6D6): δ 43.1 (s) (1), 24.3 (s) [Ni(PPh3)3]. IR
(KBr, cm-1): 1735 [s, ν(CtC)]. A similar reaction between
Ni(COD)2, PEt3, 1,2-dibromocyclohexene, and 1% Na/Hg gave
impure 2. Attempts to make Ni(η2-C6H8)L2 (L2 ) 2PMe3,
2PCy3, dmpe, depe, dcpe, and dppe) by this method failed.
(38) Bennett, M. A.; Hockless, D. C. R.; Wenger, E. Organometallics
1995, 14, 2091.
(39) Luetkens, M. L., J r.; Sattelberger, A. P.; Murray, H. H.; Basil,
J . D.; Fackler, J . P., J r. Inorg. Synth. 1989, 26, 7.
(40) Burt, R. J .; Chatt, J .; Hussain, W.; Leigh, G. J . J . Organomet.
Chem. 1979, 182, 203.
(41) Schunn, R. A. Inorg. Synth. 1972, 13, 124.
(42) (a) Wilke, G.; Herrmann, G. Angew. Chem., Int. Ed. Engl. 1962,
1, 549. (b) Herrmann, G. Ph.D. Thesis, Technische Hochschule Aachen,
1963.
(43) Ashley-Green, J .; Green, M.; Stone, F. G. A. J . Chem. Soc. A
1969, 3019.
(44) Choi, H.; Hershberger, J . W.; Pinhas, A. R.; Ho, D. M. Orga-
nometallics 1991, 10, 2930.
(45) J olly, P. W.; J onas, K. Inorg. Synth. 1974, 15, 29.
Rea ction of 1 w ith Bid en ta te P h osp h in es. A solution
containing 1 (ca. 100 mg) and dcpe (ca. 50 mg) in benzene-d6

Reactions of Nickel(0) η2-Cyclohexyne Complexes
Organometallics, Vol. 15, No. 1, 1996 73
(0.5 mL) was set aside at room temperature for 12 h. The
31P{1H} NMR spectrum of the resulting solution showed
peaks at δP 79.2 (s) and 43.5 (s) in ca. 1:1 ratio, assigned to 2
and Ni(dcpe)2, respectively. A similar reaction between 1
and dppe gave a mixture of Ni(η2-C6H8)(dppe) [31P{1H} NMR
δP 60.2 (s); IR (KBr, cm-1) 1720 [ν(CtC)] and Ni(dppe)2 (δP
43.9).
Ni{C6H8C(O)O}(dcpe) (9) (0.83 g, 81%) as a pale yellow solid.
[mp 140-142 °C (dec)]. 13C{1H} NMR (CD2Cl2): δ 23.0-26.0
2
(m, CH2, CH2P, CHP), 128.6 (s, CCNi), 166.2 (dd, J PC + 2J P′C
) 107 Hz, CCNi), 185.0 (br s, CO2). 31P{1H} NMR (CD2Cl2):
δ 66.1, 74.1 (AB q, J ) 22 Hz). IR (KBr, cm-1): 1620 [s,
ν(CdO)], 1555 [w, ν(CdC)]. MS: m/z 605 (M+), 480 [Ni(d-
cpe)+]. Anal. Calcd for C33H56OP2Ni: C, 65.5; H, 9.3; P, 10.1.
Found: C, 65.9; H, 9.5; P, 9.0.
Rea ction of 2 w ith Meth yl Iod id e. Methyl iodide (0.1
mL, 1.60 mmol) was added to 2 (0.38 g, 0.68 mmol) in benzene
(10 mL), and the mixture was stirred for 15 min. The orange
solution was evaporated in vacuo until solid began to precipi-
tate. Addition of pentane (10 mL) gave an orange solid, which
was isolated by filtration. The yield of NiI(2-MeC6H8)(dcpe)
(7) [mp 140-141 °C (dec)] was 0.30 g (64%). 1H NMR (C6D6):
δ 1.0-2.8 (m, CH2, CHP), 2.4 (s, Me). 31P{1H} NMR (C6D6):
δ 57.7, 60.4 (AB q, J ) 9 Hz). MS: m/z 607 [NiI(dcpe)]+. Anal.
Calcd for C33H59IP2Ni: C, 56.4; H, 8.5; P, 8.7. Found: C, 57.2;
H, 8.6; P, 7.8.
Rea ction of 3 w ith CO2. The 31P{1H} NMR spectrum of
a solution of 3 in THF that had been treated with CO2 for 15
min showed a singlet at δ 17.0, which may be due to an
insertion product. After 2 h, this had been replaced by peaks
46
at δ 7 (br m) and 46.0 (s) due to Ni(η2-CO2)(PEt3)2 and Et3-
PO,47 respectively, and the IR spectrum showed a band at 1620
cm-1 due to the former.
Rea ction of 1 w ith CS2. A solution of 1 (ca. 50 mg) in
C6D6 (0.5 mL) in an NMR tube was treated with CS2 (50 µL).
After 5 h, the solution was centrifuged to remove some solid.
The 31P{1H} NMR spectrum showed a peak at δ 24.8 (s)
assigned to [Ni(η2-CS2)(PPh3)]n by comparison with the spec-
trum of an authentic sample.48
Rea ction of 2 w ith CS2. To a solution of 2 (0.15 g, 0.27
mmol) in benzene (10 mL) was added CS2 (50 µL, 0.84 mmol),
and the mixture was stirred at room temperature for 12 h.
The brown solid that deposited was isolated by filtration,
washed with hexane (10 mL), and dried in vacuo. The 31P-
{1H} NMR spectrum in C6D6 showed AB quartets at δ 71.4,
75.3 (J ) 21 Hz) and at δ 58.8, 64.0 (J ) 8 Hz), which are
A similar reaction between 3 and methyl iodide gave a
mixture of trans-NiI(2-MeC6H8)(PEt3)2 (8) [1H NMR (C6D6) δ
2.4 (s, Me); 31P{1H} NMR (C6D6) δ 10.8 (s)], trans-NiI(Me)-
(PEt3)2 [31P{1H} NMR (C6D6) δ 12.4 (s)], and trans-NiI2(PEt3)2
[31P{1H} NMR (C6D6) δ 9.3 (s)].
Rea ction of 2 w ith Br om in e. A solution of 2 (ca. 50 mg)
in C6D6 (0.5 mL) in an NMR tube was treated with bromine
(ca. 20 µL), and the mixture was set aside for 30 min. The
only product detectable by 31P NMR spectroscopy was NiBr2-
(dcpe) [δP (C6D6) 86.9 (s)].
Rea ction of 2 w ith 1,2-Dibr om ocycloh exen e. A solution
containing 2 (1.00 g, 1.78 mmol) and 1,2-dibromocyclohexene
(1.60 g, 4.17 mmol) in THF (30 mL) was stirred for 48 h at
room temperature. Removal of solvent gave a brown oil that
could not be crystallized from ether at -78 °C. The 31P{1H}
NMR spectrum showed an AB quartet at δ 61.4, 64.9, with
2J PP ) 11.4 Hz, tentatively assigned to NiBr(2-BrC6H8)(dcpe)
(6). A small amount of NiBr2(dcpe) [δP 87.7] was also present.
The brown oil was added to 1% sodium amalgam that had been
freshly prepared from sodium (0.5 g) and mercury (49.5 g),
and the mixture was stirred for 16 h. The excess amalgam
was removed by centrifugation, and the resulting brown
solution was evaporated to dryness in vacuo. The oil was
redissolved in ether (20 mL) and, upon being cooled to -30
°C, gave yellow crystals, which were isolated by filtration and
dried in vacuo. They were identified as 2 by 31P{1H} NMR
and IR spectroscopy; the 31P{1H} NMR spectrum also showed
a singlet at δ 56.1 due to an unidentified species, which
constituted ca. 10% of the product.
assigned tentatively to Ni{C6H8C(S)S}(dcpe) and Ni(η2-CS2)-
(dcpe); there were also some unidentified peaks.
Rea ction s of Cycloh exyn e Nick el(0) Com p lexes w ith
Alk en es a n d Alk yn es. (i) A solution of 1 (0.26 g, 0.38 mmol)
in THF (20 mL) was treated with dimethyl acetylenedicar-
boxylate (71 µL, 0.58 mmol), and the mixture was stirred for
5 h. Removal of solvent in vacuo gave a brown oil, which was
identified as Ni(MeO2CC2CO2Me)(PPh3)2 by comparison with
an authentic sample49 [31P{1H} NMR (C6D6) δ 38.8 (s)]. The
complex Ni(MeO2CC2CO2Me)(dcpe) [31P{1H} NMR (C6D6) δ
74.8 (s)] was formed similarly from 2 and dimethyl acetylene-
dicarboxylate.
(ii) A solution of 1 (0.08 g, 0.12 mmol) in C6D6 (0.5 mL) was
treated with 3-hexyne (15 µL, 0.13 mmol) and heated for 4 h
at 70 °C. The 31P{1H} NMR spectrum showed a singlet at δ
39.9 assigned to Ni(EtC2Et)(PPh3)2 by comparison with the
spectrum of an authentic sample.49 The complex Ni(EtC2Et)-
(dcpe) [31P{1H} NMR (C6D6) δ 69.7 (s)] was formed similarly
from 2 and 3-hexyne at 70 °C.
(iii) A stream of ethylene was passed through a solution of
1 (0.25 g, 0.38 mmol) in THF (20 mL) for 12 h, giving a yellow
solution. The yellow solid that remained after the solvent had
been removed in vacuo was identified as Ni(C2H4)(PPh3)2 [31P-
{1H} NMR (C6D6) δ 33.6]. A small amount of Ni(PPh3)3 [δP
24.2 (s)] was also present.
(iv) A solution of 2 (0.47 g, 0.83 mmol) in benzene (15 mL)
was saturated with ethylene and left under an ethylene
atmosphere at 80 °C for 72 h. The resulting yellow solution
was evaporated to dryness in vacuo to leave a yellow solid,
which was identified as Ni(C2H4)(dcpe) [31P{1H} NMR (C6D6)
δ 62.7 (s)].
Rea ction of 1 w ith CO2. (i) Carbon dioxide was bubbled
through a solution of 1 (0.29 g, 0.35 mmol) in THF (30 mL)
for 4 h. The resulting orange-brown solution was evaporated
in vacuo to give a brown oil whose 31P{1H} NMR spectrum in
C6D6 showed only a singlet at δ 24.3 due to Ni(PPh3)3.
A
sample of the oil was chromatographed on neutral alumina
(activity III) and eluted with THF/hexane (1:1). The first,
pale yellow fraction was evaporated to dryness, and the
residue was recrystallized from hot hexane to give triph-
enylphosphine (80 mg), identified by its 31P{1H} NMR and
mass spectra. Further elution gave triphenylphosphine oxide,
identified similarly. There was no evidence for oligomers of
cyclohexyne.
Rea ction of 9 w ith Dim eth yl Acetylen ed ica r boxyla te.
A solution of 9 (0.44 g, 0.73 mmol) in THF (25 mL) was treated
with dimethyl acetylenedicarboxylate (0.20 mL, 1.63 mmol),
and the mixture was stirred for 4 h. The resulting amber
precipitate was isolated by filtration and washed twice with
(ii) Carbon dioxide was bubbled through a solution contain-
ing 1 (0.70 g, 1.05 mmol) and 2,5-diphenyl-3,4-isobenzofuran
(DPIBF) (0.45 g, 1.67 mmol) in THF (20 mL) at room temper-
ature. Workup as described earlier gave only unchanged
DPIBF, Ph3P, and Ph3PO. A similar result was obtained
by the use of tetraphenylcyclopentadienone in place of
DPIBF.
(46) Aresta, M.; Nobile, C. F. J . Chem. Soc., Dalton Trans. 1977,
708.
(47) Hays, H. R.; Peterson, D. J . in Organic Phosphorus Compounds;
Kosolapoff, G., Maier, L., Eds.; Wiley: New York, 1972; Vol. 3, p 430.
(48) Uhlig, E.; Poppitz, W. Z. Chem. 1979, 19, 191.
(49) Rosenthal, U.; Oehme, G.; Burlakov, V. V.; Petrovskii, P. V.;
Shur, V. B.; Vol’pin, M. E. J . Organomet. Chem. 1990, 391, 119.
Rea ction of 2 w ith CO2. Carbon dioxide was bubbled
through a solution of 2 (0.96 g, 1.71 mmol) in benzene (30 mL)
for 3 h. The resulting precipitate was isolated by filtration,
washed with hexane (2 × 10 mL), and dried in vacuo to give

74 Organometallics, Vol. 15, No. 1, 1996
Bennett et al.
Ta ble 3. Atom ic Coor d in a tes a n d Equ iva len t
hexane (10 mL) to give Ni{C(CO2Me)dC(CO2Me){C6H8C(O)O}-
(dcpe) (10) (0.31 g, 57%) [mp 148-150 °C (dec)]. 1H NMR (CD2-
Cl2): δ 1.2-2.6 (m, CH2, CH2P, CHP), 3.5(s, OMe), 3.7(s, OMe).
13C{1H} NMR (CD2Cl2): δ 23.0-37.0 (m, CH2, CH2P, CHP),
51.3, 51.4 (each s, OMe), 133.5, 135.6 (each s, CdC), 163.6 (dd,
Istr op ic Disp la cem en t P a r a m eter sa for th e
Non -Hyd r ogen Atom s in Ni(η2-C6H8)(d cp e) (2)
x/a
y/b
z/c
Ueqa/U, Å2
Ni
0.40408(6)
0.34903(10) 0.53969(5)
0.61136(3)
0.27862(3) 0.0477(2)a
0.18662(5) 0.0513(3)a
0.26694(5) 0.0526(3)a
2
3J PC + 3J P′C ) 12 Hz, CCNi), 171.5 (dd, J PC + 2J P′C ) 106 Hz,
P(1)
P(2)
0.60997(9)
0.3640(4)
0.2571(4)
0.1173(4)
0.1254(8)
0.1175(9)
0.2393(8)
0.2230(8)
0.3717(5)
0.5039(4)
0.2635(4)
0.3334(5)
0.2557(5)
0.2301(5)
0.1600(5)
0.2386(5)
0.2458(4)
0.3087(5)
0.2222(6)
0.0818(6)
0.0188(5)
0.1020(4)
0.6159(4)
0.7065(4)
0.6270(5)
0.7048(6)
0.7487(6)
0.8263(6)
0.7482(5)
0.58151(5)
0.6789(2)
0.6570(2)
0.6776(3)
0.7143(5)
0.7487(5)
0.7710(5)
0.7454(7)
0.7341(3)
0.4993(2)
0.5827(2)
0.6547(2)
0.6954(2)
0.6438(3)
0.5730(3)
0.5313(2)
0.4559(2)
0.4131(2)
0.3466(3)
0.3716(3)
0.4104(3)
0.4778(2)
0.4968(2)
0.5481(2)
0.4898(3)
0.4586(3)
0.5207(3)
0.5792(3)
0.6106(2)
0.6480(3)
0.6498(4)
0.7279(4)
0.7301(4)
0.7842(4)
0.7862(4)
0.7727(5)
0.7707(5)
0.6927(5)
0.6915(5)
0.6406(4)
0.6338(4)
CCNi), 173.6, 175.0 (each s, CO2Me), 186.0 (s, CO2). 31P{1H}
NMR (CD2Cl2) δ 65.5, 68.4 (AB q, J ) 35 Hz). IR (KBr, cm-1):
1710 (s), 1695 (s), 1640 (s) [ν(CdO)], 1555 (w) [ν(CdC)]. MS:
m/z 702 [M - CO2]+. Anal. Calcd for C39H62O6P2Ni: C, 62.6:
H, 8.3; P, 8.3. Found: C, 62.6; H, 8.4; P, 7.8.
C(1)
C(2)
C(3)
0.3566(2)
0.3243(2)
0.3421(3)
0.4235(4)
0.3871(5)
0.4299(6)
0.4485(5)
0.4208(3)
0.1454(2)
0.1041(2)
0.0791(2)
0.0165(3)
-0.0496(2)
-0.0254(2)
0.0360(2)
0.2085(2)
0.2744(2)
0.3007(3)
0.3183(3)
0.2515(3)
0.2267(2)
0.2051(2)
0.3499(2)
0.3926(3)
0.4607(3)
0.5120(3)
0.4701(3)
0.4027(3)
0.2325(4)
0.2057(4)
0.2542(5)
0.2287(5)
0.2254(4)
0.1763(5)
0.1413(5)
0.1710(6)
0.1227(5)
0.1480(6)
0.1477(4)
0.1989(5)
0.055(1)a
0.058(1)a
0.090(2)a
0.077(2)
0.098(3)
0.079(3)
0.100(4)
0.085(2)a
0.065(1)a
0.055(1)a
0.073(2)a
0.081(2)a
0.089(2)a
0.085(2)a
0.072(2)a
0.058(1)a
0.071(2)a
0.086(2)a
0.092(2)a
0.084(2)a
0.073(2)a
0.065(1)a
0.063(1)a
0.087(2)a
0.098(2)a
0.098(2)a
0.097(2)a
0.075(2)a
0.052(2)
0.061(2)
0.057(2)
0.070(3)
0.081(3)
0.082(3)
0.084(3)
0.096(3)
0.083(3)
0.095(4)
0.075(2)
0.074(2)
C(4A)b
C(4B)b
C(5A)b
C(5B)b
C(6)
Cr ysta llogr a p h y. A cross section cut from a yellow needle
of Ni(η2-C6H8)(dcpe) (2) was mounted on a Philips PW1100/20
diffractometer that was equipped with a graphite monochro-
mator and used Cu KR radiation. Lattice parameters were
determined by least-squares analysis of the 2θ angles of 25
reflections 66 < 2θ < 76° [λ(Cu KR) ) 1.5418 Å]. Crystal-
lographic data are given in Table 2. Intensity data for
reflections h, k, (l with 3 < 2θ < 128° (0 e h e 11, 0 e k e
20, -20 e l e 20) were collected using θ-2θ scans of width
(1.0 + 0.142 tan θ)° in θ at a rate of 3° min-1 in θ, with
background counts of 5 s on each side of every scan. Three
check reflections measured every 90 min showed a 9% decrease
in intensity during data collection, and data were corrected
accordingly.50 Data were also corrected for absorption (trans-
mission range 0.639-0.784).
The structure was solved by Patterson synthesis and ∆F
synthesis (SHELXS-86).51 Disorder was evident in cyclohexyl
group C(221)-C(226) and in atoms C(4) and C(5) of the
cyclohexyne group. Each of these atoms was considered to be
disordered over two sites of occupancy of 0.5, and in subse-
quent least-squares refinement, Waser restraints52 were im-
posed on bonds and angles involving them. Anisotropic and
isotropic displacement factors were employed for full-oc-
cupancy and half-occupancy non-hydrogen atoms, respectively.
Hydrogen atoms were placed at calculated positions [r(C-H)
) 0.95 Å, tetrahedral at the carbon atoms] and were not
refined. Refinement was continued until all shift:error ratios
were less than 0.04.
C(11)
C(111)
C(112)
C(113)
C(114)
C(115)
C(116)
C(121)
C(122)
C(123)
C(124)
C(125)
C(126)
C(21)
C(211)
C(212)
C(213)
C(214)
C(215)
C(216)
C(221A)b 0.7405(7)
C(221B)b 0.7024(7)
C(222A)b 0.7066(8)
C(222B)b 0.6798(8)
C(223A)b 0.8091(9)
C(223B)b 0.7476(8)
C(224A)b 0.8439(10)
C(224B)b 0.8965(9)
C(225A)b 0.8773(9)
C(225B)b 0.9206(10)
C(226A)b 0.7662(8)
C(226B)b 0.8512(7)
Least-squares refinement was performed by the use of full-
matrix methods, the function ∑w(|Fo| - |Fc|)2, where w ) [σ2-
(F) + (0.0009)F2]-1, being minimized. Maximum and mini-
mum heights in a final difference map were 0.44 and -0.46 e
Å-3, respectively, the major features being in the vicinity of
disordered C(4) and C(5). Data reduction and refinement
computations were performed with XTAL3.053 ; atomic scat-
tering factors for neutral atoms and real and imaginary
dispersion terms were taken from ref 54 . Final parameters
for the non-hydrogen atoms are given in Table 3.
1
a
b
Ueq
)
jUijai*aj*a ia j. Occupancy, 0.5.
i
3∑∑
Su p p or tin g In for m a tion Ava ila ble: Lists of hydrogen
atom parameters, atomic displacement parameters, all bond
lengths and bond angles for non-hydrogen atoms, distances,
angles, and torsion angles involving hydrogen atoms, and
least-squares planes (23 pages). Ordering information is given
on any current masthead page.
(50) Churchill, M. R.; Kalra, K. L. Inorg. Chem. 1974, 13, 1427.
(51) Sheldrick, G. M. SHELXS-86. In Crystallographic Computing
3; Sheldrick, G. M., Kru¨ger, C., Goddard, R., Eds; Oxford University
Press: Oxford, England, 1985; pp. 175-189.
(52) (a) Waser, J . Acta Crystallogr. 1963, 16, 1091. (b) Olthof-
Hazekamp, R. “CRYLSQ” in ref 53.
OM9504516
(54) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV, pp 99-101, 149-150 (Present
distributor: Kluwer Academic Publishers, Dordrecht, The Nether-
lands).
(53) Hall, S. R., Stewart, J . M., Eds. XTAL3.0 Reference Manual;
Universities of Western Australia and Maryland, Lamb: Perth, 1990.