Reaction of carbodiphosphorane Ph3P=C=PPh3 with Ni(CO)4. Experimental and theoretical study of the structures and properties of (CO)3NiC(PPh3)2 and (CO)2NiC(PPh3)2

Article abstract of DOI:10.1021/om9804632

The carbodiphosphorane Ph₃P=C=PPh₃ (1) readily reacts with Ni(CO)₄ in toluene to give the substitution product (CO)₃NiC(PPh₃)₂ (2). If the reaction is carried out in THF solution, additionally red crystals of the dicarbonyl complex (CO)₂NiC(PPh₃)₂ (3) are formed. 2 smoothly converts into 3 when dissolved in THF. The compounds have been characterized by single-crystal X-ray diffraction. Quantum chemical calculations at the DFT level of theory (B3LYP) are given for the geometries of model compounds 1a-3a with PH₃ ligands instead of PPh₃, which are in good agreement with the experimental results for 1-3. The metal-ligand bond energies are also predicted at B3LYP. The calculated Ni-C(PH₃)₂ bond energy of 3a (D₀ = 33.7 kcal/mol) is nearly the sum of the Ni-C(PH₃)₂ (D₀ = 20.9 kcal/mol) and first Ni-CO bond energy of 2a (D₀ = 16.3 kcal/mol). The analysis of the metal-ligand bonding using the CDA method shows that there is mainly ligand → metal donation and much less metal → ligand back-donation between Ni and C(PH₃)₂ in 2a. Donation and back-donation become stronger and back-donation becomes more important in 3a than in 2a.

Full text of DOI:10.1021/om9804632

Organometallics 1999, 18, 619-626
619
Rea ction of Ca r bod ip h osp h or a n e P h 3P dCdP P h 3 w ith
Ni(CO)4. Exp er im en ta l a n d Th eor etica l Stu d y of th e
Str u ctu r es a n d P r op er ties of (CO)3NiC(P P h 3)2 a n d
(CO)2NiC(P P h 3)2
Wolfgang Petz,* Frank Weller, J amal Uddin, and Gernot Frenking*
Fachbereich Chemie der Universita¨t Marburg, Hans-Meerweinstrasse,
35032 Marburg, Germany
Received J une 5, 1998
The carbodiphosphorane Ph3PdCdPPh3 (1) readily reacts with Ni(CO)4 in toluene to give
the substitution product (CO)3NiC(PPh3)2 (2). If the reaction is carried out in THF solution,
additionally red crystals of the dicarbonyl complex (CO)2NiC(PPh3)2 (3) are formed. 2
smoothly converts into 3 when dissolved in THF. The compounds have been characterized
by single-crystal X-ray diffraction. Quantum chemical calculations at the DFT level of theory
(B3LYP) are given for the geometries of model compounds 1a -3a with PH3 ligands instead
of PPh3, which are in good agreement with the experimental results for 1-3. The metal-
ligand bond energies are also predicted at B3LYP. The calculated Ni-C(PH3)2 bond energy
of 3a (D0 ) 33.7 kcal/mol) is nearly the sum of the Ni-C(PH3)2 (D0 ) 20.9 kcal/mol) and
first Ni-CO bond energy of 2a (D0 ) 16.3 kcal/mol). The analysis of the metal-ligand bonding
using the CDA method shows that there is mainly ligand f metal donation and much less
metal f ligand back-donation between Ni and C(PH3)2 in 2a . Donation and back-donation
become stronger and back-donation becomes more important in 3a than in 2a .
In tr od u ction
istry has been reviewed by Bestmann.6 More than 20
years ago Kaska and co-workers described the prepara-
tion of the carbonyl derivatives (CO)3NiC(PPh3)2 and
Carbodiphosphoranes, R3PdCdPR3, are of consider-
able interest because of their versatile physical and
chemical properties. These double ylides are known with
linear1 or bent2-4 structures, depending on the nature
of the group R. However, the structures are not rigid
and the energy differences between linear and bent
forms are probably very small. Similar behavior is
reported for the isoelectronic cation [Ph3PdNdPPh3]+
with P-N-P angles ranging between 135° and 180° as
the anion is changed.5 The crystal structure of Ph3Pd
CdPPh3 (1) shows two types of molecules in the unit
cell differing in the P-C-P angles by about 14°.2 Also
structural differences between triboluminescent and
nontriboluminescent crystals of 1 exist.3
7
(CO)5WC(PPh3)2,8 which are the first and only com-
pounds with 1 coordinated to zerovalent transition
metals; however, no structural details were reported.
Later, complexes of 1 with higher valent transition
metals were presented such as ClMC(PPh3)2 (M ) Ag,
Cu), (η5-C5Me5)CuC(PPh3)2,9 and the ionic species
[O3ReC(PPh3)2]-,10 which have also been studied by
X-ray structure analysis.
The chemistry of 1 toward transition metal carbonyl
compounds is apparently governed by two main routes
as depicted in Scheme 1. In pathway A a CO group is
replaced, while the Wittig-type pathway B generates
heteroallene-like compounds initiated by a nucleophilic
attack of 1 at a carbonyl carbon atom.7,8
In the course of our studies concerning the reactions
of Fe(CO)5 and (CO)4FeCS with ylides and various hard
and soft nucleophilic species we have also tested the
reactivity of 1. In the case of Fe(CO)5, even under
various reaction conditions, we have not been able to
isolate the related (CO)4FeC(PPh3)2 complex; instead we
observed the formation of the Wittig products (CO)4Fed
The bent structure of 1 suggests nucleophilic proper-
ties, and the application as ligand for transition metals
has been studied by various groups; the organic chem-
* To whom correspondence should be addressed. E-mail: petz@
mailer.uni-marburg.de and frenking@chemie.uni-marburg.de.
(1) Appel, R.; Baumeister, U.; Knoch, F. Chem. Ber. 1983, 116 (6),
2275.
(2) Vincent, A. T.; Wheatley, P. J . J . Chem. Soc., Dalton Trans. 1972,
617.
(3) Hardy, G. E.; Zink, J . I.; Kaska, W. C.; Baldwin, J . C. J . Am.
Chem. Soc. 1978, 100, 8001.
(4) Ebsworth, E. A. V.; Fraser, T. E.; Rankin, D. W. H.; Gasser, O.;
Schmidbaur, H. Chem. Ber. 1977, 110, 3508.
(5) (a) Handy, L. P.; Ruff, J . K.; Dahl, L. F. J . Am. Chem. Soc. 1970,
92, 7312. (b) Handy, L. P.; Ruff, J . K.; Dahl, L. F. J . Am. Chem. Soc.
1970, 92, 7312. (c) Ruff, J . K.; White, R. P.; Dahl, L. F. J . Am. Chem.
Soc. 1971, 93, 2159. (d) Smith, M. B.; Bau, R. J . Am. Chem. Soc. 1973,
95, 2388. (e) Goldfield, S. A.; Raymond, K. N. Inorg. Chem. 1974, 13,
770. (f) Chin, H. B.; Smith, M. B.; Wilson, R. D.; Bau, R. J . Am. Chem.
Soc. 1974, 96, 5285. (g) Wilson, R. D.; Bau, R. J . Am. Chem. Soc. 1974,
96, 7601.
(6) For the chemistry of 1 see: (a) Bestmann, H. J . Angew. Chem.
1977, 89, 361; Angew. Chem., Int. Ed. Engl. 1977, 16, 349. See also
recent reviews concerning similar ylides and phosphinocarbenes: (b)
Kaska, W. C.; Starzewski, K. A. O. Ylides and Imines of Phosphorus;
J ohnson, W. A., Ed.; J ohn Wiley & Sons: New York, 1993. (c) Bertrand,
G. Coord. Chem. Rev. 1994, 137, 323.
(7) Kaska, W. C.; Mitchell, D. K.; Reichelderfer, R. F.; Korte, W. D.
J . Am. Chem. Soc. 1974, 96, 2847.
(8) Kaska, W. C.; Mitchell D. K.; Reichelderfer, R. F. J . Organomet.
Chem. 1973, 47, 391.
(9) Zybill, C.; Mu¨ller, G. Organometallics 1987, 6, 2489.
10.1021/om9804632 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 01/20/1999

620 Organometallics, Vol. 18, No. 4, 1999
Petz et al.
Sch em e 1
Sch em e 2
CdCdPPh3 and Fe3(CO)9(µ3-η2-CtCPPh3), following
pathway B;11 the thiocarbonyl derivative gives a yellow
adduct at low temperature which rapidly decomposes
on warming to room temperature producing only tarry
materials. The different behavior of 1 toward iron and
nickel carbonyls prompted us to look again at the
reaction with Ni(CO)4. We report here about new results
concerning this old reaction including spectroscopic
information and present the first X-ray structure analy-
ses of nickel carbodiphosphorane complexes. We also
present the results of quantum chemical investigations
using gradient-corrected density functional theory
(B3LYP) of the structures and bonding situation of 1-3
with PH3 ligands instead of PPh3. The metal-ligand
bond energies of Ni(CO)n (n ) 1-4) have been calculated
for comparison at B3LYP and using coupled-cluster
theory12 at the CCSD(T) level.13 The analysis of the
bonding situation was carried out with the help of the
product (CO)3NidCdCdPPh3 according to pathway B
could not be detected. Although coordination number 3
and formation of 16 valence electron compounds is very
common in Ni(0) chemistry, to our knowledge, 3 is the
first complex in which the (CO)2Ni fragment is bonded
to only one further donor ligand, generating a three-
coordinate electron-deficient nickel atom.17
The relatively weak bond of 1 to the Ni atom is
documented by reacting the compounds with better π
acceptor ligands such as phosphines. Thus, a mixture
of 2 and 3 in THF solution reacts even at -78 °C with
PPh3, liberating quantitatively the carbodiphosphorane
to give a mixture of (CO)3NiPPh3 and (CO)2Ni(PPh3)2;
both compounds were identified by their characteristic
IR and 31P NMR data.
NBO method14 and the CDA partitioning scheme.15
A
short outline of the CDA method is given in the
Theoretical methods section. More details about the
method and a discussion of the application and results
can be found in the literature.16
2, 3 + PPh3 f (CO)nNi(PPh3)m + 1
(1)
The spectroscopic data for 2 and 3 are consistent with
the structures proposed. The IR spectrum of 2 exhibits
the typical pattern of a Ni(CO)3 group with local C3v
symmetry. A sharp band at 2032 cm-1 and a broad band
at 1933 cm-1 correspond to the symmetrical (A1) and
antisymmetrical (E) ν(CO) vibrations, respectively. Two
sharp and intense vibrations at 1976 cm-1 (A1) and 1895
cm-1 (B1) in the spectrum of 3 are typical for a Ni(CO)2
group. However, the center of the bands is shifted to
lower frequencies relative to that of related (CO)2Ni-
(PR3)2 compounds,17 but comparable with the shift found
in a (CO)2Ni(carbene)2 compound.18 This indicates that
the presence of 1 at the Ni atom induces a strong back-
donation of negative charge into the CO π* orbitals
comparable to the action of two nucleophilic carbene
ligands of the Arduengo type.18
To get more insight into the properties of the com-
pounds for further chemical reactions, the molecular
structures of 2 and 3 have been determined by single-
crystal X-ray diffraction studies. Suitable crystals were
grown from toluene and THF solutions, respectively, by
layering with pentane. ORTEP views of the molecules
are presented in Figures 1 and 2. A special view of the
core of 3 is shown in Figure 3. Selected bond distances
and angles are collected in Tables 1 and 2.
Resu lts a n d Discu ssion
In contrast to the literature report7 the reaction of 1
with Ni(CO)4 produces not only one single product. In
toluene as solvent one CO group is replaced to produce
exclusively (CO)3NiC(PPh3)2 (2) as large yellow-orange
crystals in good yields in agreement with the results of
Kaska. However, if the reaction is carried out in THF
under the same reaction conditions, deep red crystals
are additionally formed along with 2. To our surprise,
the red compound differs from 2 only by loss of one CO
group, and the X-ray analysis confirms the monomeric
formula (CO)2NiC(PPh3)2 (3) in which the Ni atom
attains coordination number 3 with 16 instead of 18
valence electrons (Scheme 2).
2 can be transformed into 3 by dissolving in THF. In
contrast to the results with Fe(CO)5, the related Wittig
(10) Sundermeyer, J .; Weber, K.; Peters, K.; von Schnering, H. G.
Organometallics 1994, 13, 2560.
(11) Petz, W.; Weller, F. Z. Naturforsch. 1996, 51b, 1598.
(12) (a) Cizek, J . J . Chem. Phys. 1966, 45, 4256. (b) Cizek, J . Adv.
Chem. Phys. 1966, 14, 35.
(13) (a) Pople, J . A.; Krishnan, R.; Schlegel, H. B.; Binkley, J . S.
Int. J . Quantum Chem. 1978, 14, 545. (b) Bartlett, R. J .; Purvis, G. D.
Ibid. 1978, 14, 561. (c) Purvis, G. D.; Bartlett, R. J . J . Chem. Phys.
1982, 76, 1910. (d) Purvis, G. D.; Bartlett, R. J . Ibid. 1987, 86, 7041.
(14) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899.
The geometry of 2 at the Ni atom is that of a nearly
ideal tetrahedron, with angles ranging between 105°
and 113°, consistent with a 18-electron configuration.
(15) Dapprich, S.; Frenking, G. J . Phys. Chem. 1995, 99, 9352.
(16) (a) Frenking, G.; Pidun, U. J . Chem. Soc., Dalton Trans. 1997,
1653. (b) Pidun, U.; Frenking, G. J . Organomet. Chem. 1996, 525, 269.
(c) Pidun, U.; Frenking, G. Organometallics 1995, 14, 5325. (d) Ehlers,
A. W.; Dapprich, S.; Vyboishchikov, S. F.; Frenking, G. Organometallics
1996, 15, 105. (e) Dapprich, S.; Frenking, G. Organometallics 1996,
15, 4547. (f) Frenking, G.; Dapprich, S.; Ko¨hler, K. F.; Koch, W.; Collins,
J . R. Mol. Phys. 1996, 89, 1245.
(17) (a) Gmelin Handbuch der Anorganischen Chemie; Springer-
Verlag: Berlin, 1975; Nickel-Organische Verbindungen Teil 1. (b)
Gmelin Handbook of Inorganic and Organometallic Chemistry; Springer-
Verlag: Berlin, 1996; Organonickel Compounds Suppl. Vol. 3.
(18) Two ν(CO) vibrations are observed at 1946 and 1873 cm-1
:
O¨ fele, K.; Herrmann, W. A.; Mihalios, D.; Elison, M.; Herdtweck, E.;
Scherer, W.; Mink, J . J . Organomet. Chem. 1993, 459, 177.

Reaction of Ph3PdCdPPh3 with Ni(CO)4
Organometallics, Vol. 18, No. 4, 1999 621
Ta ble 1. Exp er im en ta l Da ta for th e X-r a y
Diffr a ction Stu d ies of Com p lexes 2 a n d 3
2
3
formula
mw
C
40H30NiO3P
C39H30NiO2P
651.28
679.29
crystal system
space group
a (pm)
b (pm)
c (pm)
monoclinic
P2(1)/c
1635.3(3)
1133.94(14)
1903.7(3)
90
109.978(11)
90
3317.7(8)
4
triclinic
P1h
1100.89(17)
1241.3(3)
1318.5(3)
89.771(18)
78.547(11)
68.087(11)
1633.4(5)
2
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
dcalcd (g/cm3)
abs coeff (mm3)
F(000)
1.360
0.719
1408
1.324
0.725
676
crystal size (mm)
temp (K)
θ range for data
collection (deg)
index range
0.18 × 0.23 × 0.41
0.15 × 0.27 × 0.37
293(2)
293(2)
2.13-24.99
1.77-24.00
-1 e h e 19, -1 e k
e 13, -1 e l e 18
6786/5558
-12 e h e 0, -14 e k
e 13, -15 e l e 14
5381/5079
F igu r e 1. Molecular structure of (CO)3NiC(PPh3)2 (2).
no. of reflns
Hydrogen atoms are omitted for clarity.
collected/unique
completeness to
2θ ) 24.99
[R(int) ) 0.0289]
90.2%
[R(int) ) 0.0677]
98.9%
refinement method
full-matrix
full-matrix
least-squares on F2
least-squares on F2
5079/0/331
no. of data/restraints/ 5558/0/349
params
goodness-of-fit on F2 1.013
1.021
final R indices
R1 ) 0.0432,
R1 ) 0.0378,
wR2 ) 0.0882
R1 ) 0.0481,
wR2 ) 0.0928
0.386 and -0.309
[I < 2σ(I)]
wR2 ) 0.0974
R1 ) 0.0658,
R indices (all data)
wR2 ) 0.1079
0.360 and -0.367
largest diff peak
and hole (e Å-3
)
a
Sheldrick, G. M. SHELXTL-Plus, Release 4.0 for R3 Crystal-
lographic Research Systems; Siemens Analytical X-ray Instru-
ments Inc.: Madison, WI, 1989. b Spek, A. L. Platon-89; University
of Utrecht, 1989. c Keller, E. Schakal-86, A FORTRAN Program
for the Graphical Presentation of Molecular and Crystallographic
d
Models; Freiburg, 1989. Sheldrick, G. M. SHELXL-93; Univer-
sita¨t Go¨ttingen, 1993. e International Tables 1974.
Ta ble 2. Selected Dista n ces a n d An gles in
(CO)3NiC(P P h 3)2 (2) a n d (CO)2NiC(P P h 3)2 (3)
2
3
F igu r e 2. Molecular structure of (CO)2NiC(PPh3)2 (3).
Hydrogen atoms are omitted for clarity.
Distances (pm)
Ni(1)-C(3)
Ni(1)-C(2)
Ni(1)-C(4)
Ni(1)-C(1)
P(1)-C(1)
178.2(4)
Ni(1)-C(3)
Ni(1)-C(2)
174.0(3)
175.2(3)
178.6(4)
179.2(4)
211.0(3)
168.1(3)
Ni(1)-C(1)
P(1)-C(1)
199.0(3)
167.7(3)
P(1)-C(121)
P(1)-C(131)
P(1)-C(111)
P(2)-C(1)
P(2)-C(231)
P(1)-C(221)
P(1)-C(211)
C(2)-O(2)
C(3)-O(3)
C(4)-O(4)
183.42(16) P(1)-C(121)
183.90(16) P(1)-C(131)
184.41(15) P(1)-C(111)
183.82(14)
184.11(15)
184.40(13)
167.6(3)
183.37(14)
183.47(14)
184.83(14)
114.4(4)
167.4(3)
P(2)-C(1)
183.11(16) P(2)-C(231)
183.28(16) P(1)-C(221)
185.47(16) P(1)-C(211)
114.0(4)
113.0(4)
113.5(4)
C(2)-O(2)
C(3)-O(3)
F igu r e 3. View down the C(1)-Ni axis in 3.
115.1(3)
The sum of the angles at C(1) amounts to 360°, indicat-
ing planarity. The dative bond from the ligand to Ni
yields a bond separation of 211.0 pm, which is the
longest one found for a Ni-C bond length. To our
knowledge, only two crystal structure studies of com-
pounds are available in which the (CO)3Ni fragment is
bond to a carbon donor ligand. These are the ylide
complex (CO)3NiCH(Me)dPCy3, with a Ni-C bond
length of 209.6 pm,19 and the Arduengo type carbene
Angles (deg)
C(3)-Ni(1)-C(2) 113.23(16) C(3)-Ni(1)-C(2) 118.02(14)
C(3)-Ni(1)-C(4) 107.71(17)
C(2)-Ni(1)-C(4) 104.95(16)
C(3)-Ni(1)-C(1) 110.43(15) C(3)-Ni(1)-C(1) 120.96(12)
C(2)-Ni(1)-C(1) 112.59(14) C(2)-Ni(1)-C(1) 120.90(12)
C(4)-Ni(1)-C(1) 107.52(14)
124.58(19) P(1)-C(1)-P(2)
P(1)-C(1)-Ni(1) 120.25(17) P(1)-C(1)-Ni(1) 112.81(13)
P(2)-C(1)-Ni(1) 115.16(16) P(2)-C(1)-Ni(1) 115.06(13)
P(1)-C(1)-P(2)
132.13(16)
complex (CO)3NiCN(R)CHdCHNR (R ) CHMePh), in
(19) Barnett, B. L.; Kru¨ger, C. J . Cryst. Mol. Struct. 1972, 2, 271.
which a separation of 198.6 pm was measured.20

622 Organometallics, Vol. 18, No. 4, 1999
Petz et al.
Ta ble 3. Com p a r ison of Rela ted Bon d in g
P a r a m eter s of 1-3 a n d th e Ylid e Com p lex
(CO)3NiCH(Me)dP Cy3 (4)
found in the IR spectrum. On the other hand, the
P-C(ylide) bond distances in 2 and 3 are nearly equal
but are shorter (167 pm) than those in the anion
[O3ReC(PPh3)2]-, where a strong Re-C double bond is
suggested, causing an elongation of the P-C(ylide) bond
distances to 177 pm.10
In both compounds a perfectly planar donor center is
operative, with the angles at the donating carbon atom
summing up to 360°. A nearly parallel arrangement of
two phenyl rings is found in the free ligand as well as
in the versatile complexes.
Ni-C(P) P-C(ylide) Ni-C(O)
P-C-P
(deg)
complex
(pm)
(pm)
(pm)
ref
1
163.3 (I),
130.1 (I),
2a
3b
162.9 (II)
143.8 (II)
1
2
3
4
161.0
167.3
167.6
174.5
134.4
124.6
132.1
211.0
199.0
209.6
178.7
174.6
175
this work
this work
19
a
b
Triboluminescent crystals, molecules I and II. Nontribolu-
minescent crystals.
A comparison of the chemistry of 1 toward various
transition metal carbonyl compounds reveals some
interesting questions. Why does the carbodiphosphorane
react so differently with Fe(CO)5 and Ni(CO)4?
The results show that the carbodiphosphorane mol-
ecule can be considered first as a “hard” Lewis base,
which preferently attacks an electrophilic carbonyl
carbon atom. In the bent structure the carbon p orbital
is not empty as in the related carbene ligands, which
makes 1 not very attractive for low-valent transition
metal fragments. In Ni(CO)4 the carbonyl carbon atoms
are probably less electrophilic than in Fe(CO)5, because
more d electrons form back-bonds to fewer CO mol-
ecules. On the other hand the first carbonyl dissociation
energy is less for Ni(CO)4 (calc 29.9, expt 25 kcal/mol)
than for Fe(CO)5 (calc 45.7,23 expt 42 kcal/mol), which
is probably the most important reason for preferring CO
substitution over nucleophilic attack at the carbon atom
in the nickel complex.23,24
The short P-C bonds and the very long Ni-C bond
lead to the conclusion that the carbodiphosphorane
ligand in 2 acts as a pure σ donor with P-C double
bonds, while a carbene-like Ni-C double bond plays no
significant role.
The loss of one CO group in going from 2 to 3 induces
a variety of interesting changes in bond parameters, as
depicted in Table 3. The most dramatic change is the
shortening of the Ni-C separation by 12 pm, indicating
an appreciable increase in bond order. Additionally the
P-C-P bond angle opens from 124° in 2 to 132° in 3.
The Ni atom of 3 lies in a trigonal planar environment
with approximately 120° angles at the Ni center (Σ )
359.9(1)°). As in 2 the donating carbon atom C(1) is
exactly sp2 hybridized (Σ ) 360.0(1)°) with angles
varying between 115° and 132°. The C-Ni-C plane
forms a dihedral angle with the plane spanned by the
P-C-P atoms of only 9.3°. Nearly 10 atoms including
the ipso carbon atoms of two phenyl groups are located
approximatly in one plane. The relatively short Ni-C
distance and the nearly planar ligand arrangement
forms an “ethene”-like molecule core; a view down the
carbodiphosphorane C-Ni bond is shown in Figure 3.
The small deviation by 9° from ideal planarity is
probably due to packing effects and not electronic in
nature.
Calculations on the model system 3a , which are
described in detail below, show that loss of one CO group
on going from 2 to 3 increases the σ donor properties of
the ligand and also the π back-donation from metal d
orbitals to all the ligands; the compound however
remains a 16-electron species. An alternative function
of the carbodiphosphorane as a four-electron donor as
in highly oxidized systems10 can be excluded.
A shorter Ni-C bond as in 3 is found in the 16-
electron diolefin carbene complex (CH2dCH2)2NidC(Ph)-
NMeBu-t with 188.9 pm;21 the shortest Ni-C bond with
183.0 pm was reported by Arduengo et al. to be opera-
tive in the linear biscarbene complex R2CdNidCR2
containing the 1,3-dimesitylimidazol-2-ylidene ligand
R2C.22
Th eor etica l Stu d ies
We optimized the geometries of the model compounds
C(PH3)2 (1a ), (CO)3NiC(PH3)2 (2a ), and (CO)2NiC(PH3)2
(3a ) at the B3LYP/II level of theory. The Ni-CO and
Ni-C(PH3)2 bond energies were also calculated at
B3LYP/II. We present also for comparison calculated
results of Ni(CO)n (n ) 1-4) at B3LYP/II and CCSD-
(T)/II using B3LYP/II optimized geometries.
The excellent agreement of the calculated geometries
of the model compounds 1a -3a shown in Figure 4 with
the experimentally derived structures of 1-3 given in
Table 3 justifies the use of PH3 for PPh3 in the model
compounds. 1a has a bent structure with a calculated
P-C-P bond angle of 138.1°. The experimentally
reported P-C-P angle for 1 is 130.1-143.8°.2,3 The
P-C-P bond angle becomes more acute in 2a (124.6°)
and slightly less acute in 3a (126.6°). This is in agree-
ment with the trend of the experimental values for 2
and 3, although the opening of the bond angle from 2
to 3 (124° to 132°) is larger than it is calculated for 2a
and 3a . The Ni-C(PH3)2 and Ni-CO bond lengths in
3a (Ni-C(PH3)2 197.7 pm; Ni-CO 176.8 pm) are
significantly shorter than in 2a (Ni-C(PH3)2 209.0 pm;
Ni-CO 181.0 pm), which confers with the experimental
values for 2 and 3. The C-PH3 bond lengths in the
complexes 2a (167.0 pm) and 3a (166.8 pm) are nearly
the same. They are slightly longer than in free 1a (163.1
The change of geometry at Ni on going from 2 to 3 is
also accompanied by a shortening of the Ni-C bond
distances to the carbonyl groups by about 4.5 pm,
indicating an increase in Ni f CO π back-donation
being in line with the low-frequency ν(CO) vibration
(20) Herrmann, W. A.; Goossen, L. J .; Artus, G. R. L.; Ko¨cher, C.
Organometallics 1997, 16, 2472.
(21) Gabor, B.; Kru¨ger, C.; Marczinke, B.; Mynott, R.; Wilke, G.
Angew. Chem. 1991, 103, 1711; Angew. Chem., Int. Ed. Engl. 1991,
30, 1666.
(23) (a) Li, J .; Schreckenbach, J .; Ziegler, T. J . Am. Chem. Soc. 1995,
117, 486. (b) Ziegler, T.; Tschinke, V.; Ursenbach, C. J . Am. Chem.
Soc. 1987, 109, 4825, and literature therein. See also: Angelici, R. J .
Acc. Chem. Res. 1972, 5, 335.
(22) Arduengo, A. J ., III; Gamper, S. F.; Calabrese, J . C.; Davidson,
F. J . Am. Chem. Soc. 1994, 116, 4391.
(24) Delley, B.; Wrinn, M.; Lu¨thi, H. P. J . Chem. Phys. 1994, 100,
5785.

Reaction of Ph3PdCdPPh3 with Ni(CO)4
Organometallics, Vol. 18, No. 4, 1999 623
basis sets, may be estimated by comparing the theoreti-
cal bond energies for Ni(CO)n at B3LYP/II and CCSD-
(T)/II with experimental values25,26 and with a previous
theoretical study at the CCSD(T) level using larger all-
electron basis sets than in our work.27 Table 4 shows
that the CCSD(T)/II values are in good agreement with
the experimental values, except for Ni(CO)2, where the
theoretical bond energy is too low. However, CCSD(T)
calculations with a larger basis set27 and CASPT2
calculations28 give similar bond energies for Ni(CO)2,
as predicted at CCSD(T)/II. It seems possible that the
experimental value for the bond energy of Ni(CO)2 is
too high. The B3LYP/II bond energies are similar to the
CCSD(T)/II values, with the exception of Ni(CO). It has
been shown that DFT methods have problems with
transition metal monocarbonyls.29
Generally, the CCSD(T) calculations with the moder-
ate basis set II are in good agreement with experimental
results, which is due to a fortuitous error cancellation
of BSSE effects and insufficient description of the
bonding region. This seems to be a general effect of this
level of theory. Previous calculations have shown that
the first dissociation energies of transition metal
carbonyls predicted at CCSD(T)/II are in very good
agreement ((3 kcal/mol) with experimental results.31,32
Partial cancellation of BSSE effects and basis set incom-
pletion error has also been noticed for DFT calcula-
tions.49
Table 5 shows the calculated C-O stretching frequen-
cies of Ni(CO)n 2a and 3a together with the experimen-
tal values for the nickel carbonyls 2 and 3. Please note
that the calculated values refer to harmonic frequencies,
(25) Stevens, A. E.; Feigerle, C. S.; Lineberger, W. C. J . Am. Chem.
Soc. 1982, 104, 5026.
(26) Sunderlin, L. S.; Squires, R. R. Private communication, cited
in ref 27.
(27) Blomberg, M. R. A.; Siegbahn, P. E. M.; Lee, T. J .; Rendell, A.
P.; Rice, J . E. J . Chem. Phys. 1991, 95, 5898.
(28) Persson, B. J .; Roos, B. O.; Pierloot, K. J . Chem. Phys. 1994,
101, 6810.
(29) For example, the metal-CO bond energies of the monocarbonyls
F igu r e 4. Calculated structures of the model compounds
1a -3a at B3LYP/II. Bond lengths in angstroms, angles in
degree.
Cu(CO)+ and Ag(CO)+ are predicted at BP86 and B3LYP to be lower
+
than the first bond dissociation energies of the dicarbonyls Cu(CO)2
and Ag(CO)2+, respectively. This is in disagreement with experimental
evidence and with the results of MP2 and CCSD(T) calculations: J onas,
V.; Lupinetti, A. J .; Frenking, G.; Strauss, S. H.; Thiel, W. J . Phys.
Chem., submitted for publication.
pm). Again, this is in agreement with the experimental
results for 1-3.
(30) Moore, C. E. Natl. Bur. Stand. Circ. 467; U.S. GPO: Washing-
ton, D.C., 1952.
The observation that 2 and 3 are formed together
during the reaction of 1 with Ni(CO)4 suggests that the
Ni-C(PPh3)2 bond energy of 3 should be roughly the
sum of the Ni-C(PPh3)2 and first Ni-CO bond dissocia-
tion energies of 2. We calculated the Ni-C(PH3)2 and
Ni-CO bond energies of 2a and 3a at B3LYP/II and
the Ni-CO bond energies of Ni(CO)4 at B3LYP/II and
CCSD(T)/II. The results are shown in Table 4. The
calculated metal-ligand bond energies of 2a at B3LYP/
II are D0 ) 20.9 kcal/mol for Ni-C(PH3)2 and D0 ) 16.3
kcal/mol for Ni-CO. The Ni-C(PH3)2 bond energy of
3a , D0 ) 33.7 kcal/mol, is clearly higher compared with
2a , and it is indeed nearly the sum of the Ni-C(PH3)2
and Ni-CO bond energies of 2a (37.2 kcal/mol). The
theoretically predicted bond energies at B3LYP/II
indicate that the Ni-C(PH3)2 bonds in 2a and 3a are
stronger than the Ni-CO bonds in Ni(CO)4 and Ni(CO)3,
respectively.
(31) Frenking, G.; Antes, I.; Bo¨hme, M.; Dapprich, S.; Ehlers, A. W.;
J onas, V.; Neuhaus, A.; Otto, M.; Stegmann, R.; Veldkamp, A.;
Vyboishchikov, S. F. In Reviews in Computational Chemistry, Vol. 8;
Lipkowitz K. B., Boyd, D. B., Eds.; VCH: New York, 1996; pp 63-
144.
(32) (a) Ehlers, A. W.; Frenking, G. J . Am. Chem. Soc. 1994, 116,
1514. (b) Ehlers, A. W.; Frenking, G. Organometallics 1995, 14, 423.
(c) Ehlers, A. W.; Dapprich, S.; Vyboishchikov, S. F.; Frenking, G.
Organometallics 1996, 15, 105.
(33) (a) DeKock, R. L. Inorg. Chem. 1971, 10, 1205. (b) Rosen, B.
Spectroscopic Data Related to Diatomic Molecules; Pergamon Press:
Oxford, 1971.
(34) Braterman, P. S. Metal Carbonyl Spectra; Academic Press:
London, 1975.
(35) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
(36) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 299.
(37) (a) Ditchfield, R.; Hehre, W. J .; Pople, J . A. J . Chem. Phys. 1971,
54, 724. (b) Hehre, W. J .; Ditchfield, R.; Pople, J . A. J . Chem. Phys.
1972, 56, 2257. (c) Hariharan, P. C.; Pople, J . A. Mol. Phys. 1974, 27,
209. (d) Hariharan, P. C.; Pople, J . A. Theor. Chim. Acta 1973, 28,
213. (e) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163.
(38) Bergner, A.; Dolg, M.; Ku¨chle, W.; Stoll, H.; Preuss, H. Mol.
Phys. 1993, 80, 1431.
(39) Andzelm, J .; Huzinaga, S.; Klobukowski, M.; Radzio, E.; Sakai,
Y.; Tatekawi, H. Gaussian Basis Sets for Molecular Calculations;
Elsevier: Amsterdam, 1984.
The accuracy of the theoretically predicted binding
energies, which were calculated with rather modest

624 Organometallics, Vol. 18, No. 4, 1999
Petz et al.
Ta ble 4. Ca lcu la ted a n d Exp er im en ta l Bin d in g En er gies [k ca l/m ol] De a n d ZP E-Cor r ected Va lu es D0
B3LYP/II
CCSD(T)/IIa
CCSD(T)d
CASPT2e
exptb
De
D0
De
D0
D0
D0
D0
Ni(CO) f Ni + CO
27.68f
46.52
30.76
21.89
17.80
22.27
35.23
25.98f
45.02
29.06
19.96
16.28
20.93
33.73
43.49f
42.89
32.59
24.50
41.79f
41.59
30.90
22.72
34.5
42.6
34.6
29.8
40.7
39.1
27.8
27.9
35 ( 3
51 ( 4
29 ( 2
25 ( 2c
Ni(CO)2 f Ni(CO) + CO
Ni(CO)3 f Ni(CO)2 + CO
Ni(CO)4 f Ni(CO)3 + CO
2a f 3a + CO
2a f Ni(CO)3 + C(PH3)2
3a f Ni(CO)2 + C(PH3)2
a
b
d
At B3LYP/II optimized geometry, this work. Ref 26. c Ref 25. Ref 27. e Ref 28. f Calculated using the theoretical energy for the
1S(d10) state of the Ni atom and the experimental 3D f 1S excitation energy (1.74 eV).30
Ta ble 5. Ca lcu la ted a n d Exp er im en ta l CO Str etch in g F r equ en cies (in cm -1
)
B3LYP/II
experimental
e
e
ν(CO)
∆ν(CO)
ν(CO)
∆ν(CO)
sym
sym
as
sym
as
sym
as
sym
as
CO
2211
2099
2143b
1996b
Ni(CO)
Ni(CO)2
Ni(CO)3
Ni(CO)4
2a
D∞h
C2v
D3h
Td
C1
C1
-112
-147
2178
2190
2202
2133
2097
2090
2116
2136
2071
2040
-33
-21
-9
-78
-114
-121
-95
2100a
2100a
2132c
2032d
1976d
1967b
2017b
2058c
1933d
1895d
-43
-176
-126
-85
-210
-248
-43 ( 80
-11
-75
-140
-171
-111
-167
3a
a
b
d
Ref 25. Ref 33. c Ref 34. This work, compounds 2 and 3. e Frequency shift relative to free CO.
Ta ble 6. Ca lcu la ted NBO Ch a r ge Distr ibu tion
while the experimental values refer to anharmonic
frequencies. The absolute values of the stretching modes
may therefore be different, but the trend of the experi-
mental and calculated wavenumbers should run paral-
lel. The data in Table 5 indicate that the calculated and
experimentally observed shifts of the C-O stretching
mode agree very nicely. The shift of the asymmetric
C-O stretching mode is always higher compared to the
symmetric mode. We want to point out that theory and
experiment indicate that the shift of the C-O frequen-
cies toward smaller wavenumbers for 3 (3a ) and even
more for 2 (2a ) with respect to free CO is much higher
compared to Ni(CO)4. The frequency shifts suggest that
the Ni f CO π back-donation in the carbodiphosphorane
complexes is stronger than in Ni(CO)4. This conclusion
is in agreement with the analysis of the metal-ligand
interactions given below.
molecule
Ni
Ca
C(PH3)2
CO
Ni(CO)
Ni(CO)2
Ni(CO)3
Ni(CO)4
2a
0.06
0.05
0.22
0.33
0.38
0.30
-0.06
-0.03
-0.07
-0.08
-0.16
-0.19
-1.62
-1.67
-1.58
0.11
0.07
0
3a
1a
a
Carbon atom of the C(PH3)2 ligand.
charge at Ni in 2a is higher than in Ni(CO)4. It is also
higher in 3a than in Ni(CO)3. Since the carbodiphos-
phorane ligand in 2a and 3a also has a small positive
partial charge, it follows that the carbonyl ligands in
2a and 3a are more negatively charged than in the
binary carbonyls. The positive charge of the C(PH3)2
groups in 2a and 3a suggests that the Ni r C(PH3)2 σ
donation might be more important than the Ni f
C(PH3)2 π back-donation. A more detailed picture about
the donor-acceptor interactions is given by the results
of the CDA method (Table 7), which has proven to be
very helpful for the analysis of donor-acceptor interac-
tions.16 The CDA results give the amount of ligand f
metal charge donation, metal f ligand back-donation,
and also the metal rf ligand repulsive polarization,
which arises from the mixing of the occupied orbitals
of the ligand and the metal fragment. This term is
negative, because electronic charge is removed from the
overlapping area of the occupied orbitals.
The data in Table 7 show that the C(PH3)2 ligand in
the complex 2a is a much stronger electron donor than
electron acceptor. The donation/back-donation (d/b) ratio
is 4.93. This may be compared with the d/b ratio of 2.11
for CO in Ni(CO)4. Carbon monoxide becomes a slightly
better acceptor in 2a , which has a d/b ratio for CO of
1.79. The carbodiphosphorane ligand and CO become
slightly better electron acceptors in the complex 3a ,
which has a d/b ratio of 3.45 for C(PH3)2 and 1.71 for
CO. The CDA results are in agreement with the conclu-
sions that have been made from the chemical behavior
Table 6 shows the calculated charge distribution of
the molecules given by the NBO method.14 The Ni atom
always carries a positive partial charge. The positive
(40) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T. A.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomberts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, I.;
Stewart, J . J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. Gaussian
94; Gaussian Inc.: Pittsburgh, PA, 1995.
(41) Stanton, J . F.; Gauss, J .; Watts, J . D.; Lauderdale, W. J .;
Bartlett, R. J . ACES II, an ab initio program system; University of
Florida: Gainesville, FL, 1991.
(42) Werner, H.-J .; Knowles, P. J . Universita¨t Stuttgart and Uni-
versity of Birmingham.
(43) Dapprich, S.; Frenking, G. CDA 2.1; Marburg, 1994. The
program is available on-line: ftp://chemie.uni-marburg.de (/pub/cda).
(44) Ramirez, F.; Desai, N. B.; Hansen, B.; McKelvie, N. J . Am.
Chem. Soc. 1961, 83, 3539.
(45) Davidson, E. R.; Kunze, K. L.; Machado, F. B. C.; Chakravorty,
S. J . Acc. Chem. Res. 1993, 26, 628.
(46) Szilagyi, R.; Frenking, G. Organometallics 1997, 16, 4807.
(47) Herrmann, W. A.; Ko¨cer, C. Angew. Chem. 1997, 109, 2257;
Angew. Chem., Int. Ed. Engl. 1997, 36, 2162.
(48) Boehme, C.; Frenking, G. Organometallics 1998, 17, 5801.
(49) Rosa, A.; Ehlers, A. W.; Baerends, E. J .; Snijders, J . G.; te Velde,
G. J . Phys. Chem. 1996, 100, 5690.

Reaction of Ph3PdCdPPh3 with Ni(CO)4
Organometallics, Vol. 18, No. 4, 1999 625
Ta ble 7. Resu lts of th e Ch a r ge Decom p osition
An a lysis of th e Com p lexes: Ca lcu la ted (B3LYP /II)
Don a tion d (A f B), Ba ck -Don a tion b (A r B),
Rep u lsive P ola r iza tion r (A T B), a n d Resid u e
Ter m ∆ betw een th e Liga n d A a n d th e F r a gm en t B
in th e Com p lex C
the Hessian matrices at the B3LYP/II level. All struc-
tures reported here are minima on the potential energy
surface (number of imaginary frequencies i ) 0) except
Ni(CO)2. The energy minimum structure of nickel
dicarbonyl at B3LYP/II has a bent geometry with a
C-Ni-C angle of 151.3°, while the linear form is a
transition state. However, CCSD(T)/II single-point en-
ergy calculations gave a lower energy for the linear form
than for the bent structure. Therefore, we used the
energy value of the linear form for the bond energy at
CCSD(T)/II.
Inspection of the nickel-carbene interactions was
carried out using the charge-decomposition analysis
(CDA).15 In the CDA method the (canonical, natural, or
Kohn-Sham) molecular orbitals of the complex are
expressed in terms of the MOs of appropriately chosen
fragments. In the present case, the Kohn-Sham orbitals
of the B3LYP/II calculations are formed in the CDA
procedure as a linear combination of the MOs of the
C(PH3)2 or CO ligand and those of the remaining metal
fragment NiLn in the geometry of the complex. The
orbital contributions are subdivided into four parts: (i)
the mixing of the occupied MOs of the ligand and the
unoccupied MOs of the metal fragment (donation ligand
f NiLn); (ii) the mixing of the unoccupied MOs of the
ligand and the occupied MOs of the metal fragment
(back-donation LnNi f ligand); (iii) the mixing of the
occupied MOs of the ligand and the occupied MOs of
the metal fragment (repulsive polarization ligand rf
NiLn); and (iv) the residue term arising from the mixing
of unoccupied orbitals. It has been shown that the
residue term is ∼0 for closed-shell interactions, while
shared interactions have values for the residue terms
that are significantly different from zero.16a-c A more
detailed presentation of the method and the interpreta-
tion of the results is given in refs 20 and 32. The CDA
calculations have been performed using the program
CDA 2.1.43
molecule
d
b
d/b
r
∆
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
(PH3)2C-Ni(CO)3
C(PH3)2
Ni(CO)3
0.355 0.072 4.93 -0.238 -0.027
CO-Ni(CO)2C(PH3)2 0.482 0.270 1.79 -0.206 -0.009
CO-Ni(CO)3
(CO)2Ni-C(PH3)2
(PH3)2C-Ni(CO)2
0.428 0.124 3.45 -0.238 -0.017
C(PH3)2
Ni(CO)2
CO-Ni(CO)C(PH3)2 0.505 0.296 1.71 -0.207 -0.006
CO
Ni(CO)C(PH3)2
CO-Ni
CO
Ni
0.499 0.355 1.41
0.049 -0.006
CO-Ni(CO)
CO
0.487 0.217 2.24 -0.148
0.446 0.209 2.13 -0.197
0.009
0.002
Ni(CO)
CO-Ni(CO)2
CO
Ni(CO)2
CO-Ni(CO)3
CO
0.442 0.209 2.11 -0.222 -0.011
Ni(CO)3
of 2 and 3 and from the shift of the C-O stretching
frequencies from 2 to 3.
It is nothworthy that the carbodiphosphorane ligand
C(PH3)2 is essentially a pure σ donor ligand in 2a and
at the same time stronger bonded than CO in Ni(CO)4,
because M f CO π back-donation has been found as
the dominant stabilizing contribution to the metal-
carbonyl bonding.23a,45 However, recent theoretical work
has shown that CO may also be strongly bonded to a
transition metal when there is only negligible M f CO
π back-donation.46 The bonding properties of carbo-
diphosphorane in transition metal complexes may be
compared with N-donor-stabilized carbenes, which are
also essentially σ donor ligands with negligible π back-
donation.47,48
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All operations were carried out
under an argon atmosphere in dried and degassed solvents
using Schlenk techniques. The IR spectra were run on a
Nicolet spectrometer. 31P NMR spectra were recorded on a
Bruker AC 300 instrument using 85% H3PO4 (δ ) 0.00 ppm)
as the external standard. Elemental analyses were performed
by the analytical service of the Fachbereich Chemie der
Universita¨t Marburg (Germany). Ph3PdCdPPh3 was prepared
by a published method,9 improving the original procedure;44
commercially available Ni(CO)4 was used without further
purification.
P r ep a r a tion of (CO)3NiC(P P h 3)2 (2). The complex was
prepared by slightly modifying the procedure described by
Kaska.7 A solution of 1 (620 mg, 1.15 mmol) in 30 mL of
toluene was treated with excess Ni(CO)4, and the mixture was
stirred for 1 h at room temperature. A color change from yellow
to yellow-orange occurred with gas evolution. The clear solu-
tion was layered with pentane and stored for serveral days at
room temperature. Large orange crystals were separated from
the mother liquor and dried in vacuum; yield 640 mg (82%),
mp 124-126 °C dec Anal. Calcd for C40H30NiO3P2: C 70.72,
H 4.45. Found: C 70.90, H 4.52. IR (Nujol, cm-1): ν(CO) 2032,
1933. 31P NMR (400 MHz, THF): 9.92 ppm.
Th eor etica l Meth od s
The geometry optimizations and frequency calcula-
tions have been carried out at the DFT level using the
three-parameter fit of the exchange-correlation poten-
tial suggested by Becke (B3LYP)35 with our standard
basis set II,31 which has an effective core potential
(ECP)36 with a (441/2111/41) valence basis set for Ni
and 6-31G(d) all-electron basis sets for the first- and
second-row atoms.37 An ECP with a (31/31/1) valence
basis set has been used for phosphorus.38 The exponent
for the d-type polarization functions is ú(P) ) 0.55.39
Single-point energy calculations at B3LYP/II optimized
structures have been performed using coupled-cluster
theory12 with singles and doubles and noniterative
estimation of triple excitations CCSD(T).13 The DFT
calculations were performed with Gaussian 94.40 For the
CCSD(T) calculations the programs ACES II,41 Gauss-
ian 94,40 and Molpro42 have been employed. The nature
of the stationary points was investigated by calculating
P r ep a r a tion of (CO)2NiC(P P h 3)2 (3). (a) From 1 and Ni-
(CO)4: The analogous procedure as described for 2 but in THF

626 Organometallics, Vol. 18, No. 4, 1999
Petz et al.
as solvent gives a mixture of a few large crystals of 2 and deep
red crystals of 3 which can be separated mechanically. (b) From
2: Orange crystals of 2 (520 mg, 0.77 mmol) were dissolved
in about 30 mL of THF, and the mixture was stirred for 24 h.
The red solution was layered with pentane and stored for 3
days. Dark red crystals separated on the wall of the vessel
and were collected and dried in a vacuum, mp 136-139 °C
dec. Anal. Calcd for C39H30NiO2P2: C 71.92, H 4.64. Found:
C 71.98, H 5.01. IR (Nujol, cm-1): ν(CO) 1976, 1895. 31P NMR
(400 MHz, THF): 19.20 ppm.
Rea ction of 2 w ith P P h 3. A THF solution of 2 (680 mg,
1.18 mmol) was cooled to -78 °C. To the dark orange solution
was added with stirring a slight exces of PPh3 (360 mg 1.34
mmol). The solution immediatly turned pale red and was pale
yellow at room temperature. After filtration the solvent was
removed in vacuo to give a yellow oily material. The IR
spectrum of the oil showed three ν(CO) bands at 2068, 1998,
and 1939 cm-1, due to a mixture of (CO)2Ni(PPh3)2 and (CO)3-
Ni(PPh3)2. The 31P NMR showed signals at 33.5, 31.9, and -3.9
ppm according to a mixture of (CO)2Ni(PPh3)2, (CO)3Ni(PPh3)2,
and free 1, respectively.
Ack n ow led gm en t . We thank the Deutsche For-
schungsgemeinschaft (SFB 260 and Graduiertenkolleg
Metallorganische Chemie) for financial support. Excel-
lent service was provided by the computer centers HRZ
Marburg, HLRZ Darmstadt, and HLRS Stuttgart. We
are also grateful to the Fonds der Chemischen Industrie,
Frankfurt/Main, Germany, and the Max-Planck-Society,
Munich, Germany, for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
positions, equivalent isotropic thermal parameters, and aniso-
tropic thermal displacement coefficients (16 pages). Ordering
information is given on any current masthead page.
OM9804632