A triad of bis(orthometalated) d8-complexes containing four-membered rings

Article abstract of DOI:10.1021/om8004806

Reaction of 2-LiC₆F₄PPh₂ with [MCl ₂(SEt₂)₂] in diethyl ether gives the monomeric bis(chelate) complexes trans-[M((κ²-2-C₆F ₄PPh₂)₂] [M = Pt (1), Pd (2)] or, in the case of platinum, a mixture of cis-and trans-isomers. Treatment of a mixture of NiCl₂ and 2-BrC₆F₄PPh₂ in THF with zinc dust gives trans-[Ni(κ²-2-C₆F ₄PPh₂)₂] (3). The four-membered chelate rings in 1-3 are opened on addition of the bidentate ligand 1,2-bis(diphenylphosphino) ethane (dppe), and, in the case of 3, 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen), to give complexes of the type cis-[M(κC-C ₆F₄-2-PPh₂)₂(L-L)] [L-L = dppe, M = Ni (6), Pd (7), Pt (8); M = Ni, L-L = bipy (9), phen (10)], in which the PPh₂ groups are uncoordinated. Complexes 6-8 show unexpectedly large four-bond coupling constants (⁴J_PF), in the range 75-95 Hz, between the fluorine atoms (F⁶) ortho to the metal-carbon a-bond and the phosphorus atoms of the PPh₂ groups, possibly because F ⁶ and the lone pairs on phosphorus adopt a close to synperiplanar conformation. Treatment of 2 with [PdCl₂(NCMe)₂] gives the dinuclear complex [Pd₂(μ-Cl)₂(κ²-2- C₆F₄PPh₂)₂] (11), which dimerizes in solution to the tetranuclear complex [Pd₄(μ-Cl) ₄(μ-2-C₆F₄PPh₂)₄] (12) as a result of opening of the chelate 2-C₆F₄PPh ₂ rings. Carbon monoxide inserts into a nickel-carbon a-bond of 3 to give, after oxidation, bis-2,2′-(diphenylphosphinoyl) octafluorobenzophenone, (2,2′-C₆F₄P(O)Ph ₂}₂CO (14). The molecular structures of complexes 1-3,6,8, 9, and 14 have been determined by single-crystal X-ray methods.

Full text of DOI:10.1021/om8004806

Organometallics 2008, 27, 5361–5370
5361
A Triad of Bis(orthometalated) d8-Complexes Containing
Four-Membered Rings
Martin A. Bennett,† Suresh K. Bhargava,*,‡ Max A. Keniry,† Steven H. Prive´r,‡
Peta M. Simmonds,† Jo¨rg Wagler,† and Anthony C. Willis†
School of Applied Sciences (Applied Chemistry), RMIT UniVersity, GPO Box 2476V, Melbourne, Victoria 3001,
Australia, and Research School of Chemistry, Australian National UniVersity, Canberra, ACT 0200, Australia
ReceiVed May 27, 2008
Reaction of 2-LiC6F4PPh2 with [MCl2(SEt2)2] in diethyl ether gives the monomeric bis(chelate)
complexes trans-[M(κ2-2-C6F4PPh2)2] [M ) Pt (1), Pd (2)] or, in the case of platinum, a mixture of cis-
and trans-isomers. Treatment of a mixture of NiCl2 and 2-BrC6F4PPh2 in THF with zinc dust gives
trans-[Ni(κ2-2-C6F4PPh2)2] (3). The four-membered chelate rings in 1-3 are opened on addition of the
bidentate ligand 1,2-bis(diphenylphosphino)ethane (dppe), and, in the case of 3, 2,2′-bipyridine (bipy)
and 1,10-phenanthroline (phen), to give complexes of the type cis-[M(κC-C6F4-2-PPh2)2(L-L)] [L-L )
dppe, M ) Ni (6), Pd (7), Pt (8); M ) Ni, L-L ) bipy (9), phen (10)], in which the PPh2 groups are
uncoordinated. Complexes 6-8 show unexpectedly large four-bond coupling constants (4JPF), in the range
75-95 Hz, between the fluorine atoms (F6) ortho to the metal-carbon σ-bond and the phosphorus atoms
of the PPh2 groups, possibly because F6 and the lone pairs on phosphorus adopt a close to synperiplanar
conformation. Treatment of 2 with [PdCl2(NCMe)2] gives the dinuclear complex [Pd2(µ-Cl)2(κ2-2-
C6F4PPh2)2] (11), which dimerizes in solution to the tetranuclear complex [Pd4(µ-Cl)4(µ-2-C6F4PPh2)4]
(12) as a result of opening of the chelate 2-C6F4PPh2 rings. Carbon monoxide inserts into a nickel-carbon
σ-bond of 3 to give, after oxidation, bis-2,2′-(diphenylphosphinoyl)octafluorobenzophenone, {2,2′-
C6F4P(O)Ph2}2CO (14). The molecular structures of complexes 1-3, 6, 8, 9, and 14 have been determined
by single-crystal X-ray methods.
Introduction
Metal complexes of the bidentate carbanion [2-C6H4PPh2]-
are now known for most of the middle and later d-block
elements, octahedral (d6) and planar (d8) complexes of the 4d-
Figure 1. Coordination modes of [2-C6H4PPh2]-.
and 5d-series being particularly prevalent. This chemistry has
been reviewed in detail recently.1 The complexes are most often
and dirhodium(II).14-16 Facile interconversion between these
coordination modes has been demonstrated, especially in the case
of palladium(II).12,13
It is well known that metal-pentafluorophenyl complexes are
more stable and numerous than their metal-phenyl counterparts,
perhaps because the M-C σ-bond is strengthened by the
electronegative fluorine substituents,17 and an extensive chem-
istry based on M-C6F5 complexes has been developed.18,19 We
generated by orthometalation (C-H activation) of coordinated
triphenylphosphine, though procedures based on transmetalation
from 2-LiC6H4PPh2 [for Au(I), Pt(II), and Rh(III)] and on
oxidative addition of 2-BrC6H4PPh2 [for Pd(II) and Rh(III)] have
also been developed. Similar methods have also been widely
employed in the synthesis of five- and six-membered cyclo-
metalated complexes2-5 and of pincer complexes.6
As shown in Figure 1, the ligand [2-C6H4PPh2]- usually binds
as a chelate group (κ2P,C), forming a four-membered ring, but
the bridging (µ2P,C) mode is also well established, for example,
in complexes of digold(I),7-9 diplatinum(I),10,11 tetrapalladium(II),12,13
(9) Bennett, M. A.; Hockless, D. C. R.; Rae, A. D.; Welling, L. L.;
Willis, A. C. Organometallics 2001, 20, 79.
(10) Bennett, M. A.; Berry, D. E.; Bhargava, S. K.; Ditzel, E. J.;
Robertson, G. B.; Willis, A. C. J. Chem. Soc., Chem. Commun. 1987, 1613.
(11) Bennett, M. A.; Bhargava, S. K.; Messelha¨user, J.; Prive´r, S. H.;
Welling, L. L.; Willis, A. C. Dalton Trans. 2007, 3158.
(12) Aarif, A. M.; Estevan, F.; Garc´ıa-Bernabe´, A.; Lahuerta, P.; Sanau´,
M.; Ubeda, M. A. Inorg. Chem. 1997, 36, 6472.
(13) Estevan, F.; Garc´ıa-Bernabe´, A.; Lahuerta, P.; Sanau´, M.; Ubeda,
M. A.; Ramire´z de Arellano, M. C. Inorg. Chem. 2000, 39, 5964.
(14) Chakravarty, A. R.; Cotton, F. A.; Tocher, D. A.; Tocher, J. H.
Organometallics 1985, 4, 8.
* To whom correspondence should be addressed. E-mail: suresh.bhargava@
rmit.edu.au.
† Australian National University, Canberra.
‡ RMIT University, Melbourne.
(1) Mohr, F.; Prive´r, S. H.; Bhargava, S. K.; Bennett, M. A. Coord.
Chem. ReV. 2006, 250, 1851.
(2) Bruce, M. I. Angew. Chem., Int. Ed. Engl. 1977, 16, 73.
(3) Constable, E. C. Polyhedron 1984, 3, 1037.
(4) Spencer, J.; Pfeffer, M. AdV. Met.-Org. Chem. 1998, 6, 103.
(5) Omae, I. Organometallic Intramolecular Coordination Compounds,
J. Organomet. Chem. Library, No. 18; Elsevier: Amsterdam, 1986.
(6) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750.
(7) Bennett, M. A.; Bhargava, S. K.; Hockless, D. C. R.; Welling, L. L.;
Willis, A. C. J. Am. Chem. Soc. 1996, 118, 10469.
(8) Bhargava, S. K.; Mohr, F.; Bennett, M. A.; Welling, L. L.; Willis,
A. C. Organometallics 2000, 19, 5628.
(15) Cotton, F. A.; Dunbar, K. R.; Verbruggen, M. G. J. Am. Chem.
Soc. 1987, 109, 5498.
(16) Lahuerta P.; Estevan F. In Metal Clusters in Chemistry; Braunstein
P., Oro L. A., Raithby P. R., Eds.; Wiley-VCH: Weinheim, 1999; Vol. II,
p 678, and references therein.
(17) Clot, E.; Besora, M.; Maseras, F.; Me´gret, C.; Eisenstein, O.;
Oelckers, B.; Perutz, R. N. J. Chem. Soc., Chem. Commun. 2003, 490.
(18) Uso´n, R.; Fornie´s, J. AdV. Organomet. Chem. 1988, 28, 219.
10.1021/om8004806 CCC: $40.75
2008 American Chemical Society
Publication on Web 09/09/2008

5362 Organometallics, Vol. 27, No. 20, 2008
Bennett et al.
Table 1. Spectroscopic Data for Complexes 1-3 and 6-10a,b
complex
cis-[Pt(κ2-2-C6F4PPh2)2] (cis-1)c
δF
δP
-64.2 (s, JPtP 1697 Hz)
-120.1 (br s, JPtF 164 Hz, F6), -137.0 (br m,
F3), -149.0 (br m, F5), -157.7 (t, sep ca. 20
Hz, F4)
trans-[Pt(κ2-2-C6F4PPh2)2] (trans-1)c
trans-[Pd(κ2-2-C6F4PPh2)2] (2)c
trans-[Ni(κ2-2-C6F4PPh2)2] (3)d
[Ni(κC-2-C6F4PPh2)2(dppe)] (6)d
[Pd(κC-2-C6F4PPh2)2(dppe)] (7)d
-124.3 (t, sep ca. 26 Hz, JPtF 163 Hz, F6),
-135.2 (td, sep ca. 20 Hz, 4 Hz, F3), -150.0
(qd, overlapping 195Pt satellites, F5), -159.1,
(t, sep ca. 20 Hz, F4)
-55.6 (s, JPtP 2264 Hz)
-55.2 (s)
-122.1 (t of m, sep ca. 26 Hz, F6), -134.0 (t
of m, sep ca. 22 Hz, F3, -150.0 (qd, sep ca.
30 Hz, 17 Hz, 4 Hz, F5), -158.7 (approx t,
sep ca. 17 Hz, F4)
-122.8 (approx t, sep ca. 26 Hz, F6), -134.6
(approx t, sep ca. 26 Hz, F3), -150.6 (4 line
pattern, F5), -157.3 (approx t, sep ca. 20 Hz,
F4)
-44.2 (s)
-104.1 (d of spt, sep 98 Hz, F6), -123.8
(approx 1:2:2:1 q, sep 21.3 Hz, 14.7 Hz, 22.9
Hz, F3), -153.3 (4 line pattern, F5), -162.4
(approx 1:2:1 t, sep 22 Hz, F4)
48.7 (t, J 11.6 Hz, dppe), -0.1 (dd, J 26.8 Hz,
95.5 Hz, PPh2)
-105.2 (overlapping d of spt, F6), -123.8
(approx 1:2:2:1 q, F3), -153.3 (5 line
pattern, F5), -162.4 (approx 1:2:1 t, sep 22
Hz, F4)
44.2 (br t, J ca. 14 Hz, dppe), -2.2 (dd, J 25.9
Hz, 76.9 Hz, PPh2)
[Pt(κC-2-C6F4PPh2)2(dppe)] (8)d
[Ni(κC-2-C6F4PPh2)2(bipy)] (9)e
[Ni(κC-2-C6F4PPh2)2(phen)] (10)e
-107.5 (d of m, JPtP 326 Hz, F6), -123.8 (br
m, F3), -153.3 (approx 1:2:1 t, F5), -162.9
(approx 1:2:1 t, sep 22 Hz, F4)
39.8 (br s, JPtP 2137 Hz, dppe), -1.6 (dd, J
26.8 Hz, 81.5 Hz, JPtP 227 Hz, PPh2)
-117.8 (spt, F6), -124.6 (approx 1:2:2:1 q of
d, F3), -155.6 (4d, F5), -162.3 (t, sep 20.7
Hz, F4)
-6.1 (m, PPh2)
-6.0 (m, PPh2)
-117.9 (spt, F6), -124.5 (approx 1:2:2:1 q of
d, F3), -155.6 (4d, F5), -162.3 (t, sep 21.3
Hz, F4)
a Numbering of fluorine atoms:
b Multiplicities reported for complexes cis-1, trans-1, and 8 do not include 195Pt satellites. c Measured in CDCl3. d Measured in C6D6. e Measured in
CD2Cl2.
show here that a similar effect operating in [2-C6F4PPh2]- allows
access to the first series of homoleptic, bis(orthometalated)
complexes of the d8-elements, [M(κ2-2-C6F4PPh2)2] [M ) Pt
(1), Pd (2), Ni (3)]. In the case of [2-C6H4PPh2]-, only the
platinum(II) bis(chelate) complex, cis-[Pt(κ2-2-C6H4PPh2)2] (4),
is known,10 and even this is thermodynamically unstable with
respect to the dimer [Pt2(κ2-2-C6H4PPh2)2(µ-2-C6H4PPh2)2].11
All attempts to isolate palladium(II) and nickel(II) bis(chelate)
complexes of [2-C6H4PPh2]- have failed so far. The stabilizing
effect of electronegative substituents in the σ-bonded aryl ring
has been foreshadowed in the isolation of trans-[Ni(κ2-2-
C6Cl4PEt2)2] (5) from the oxidative addition of C6Cl5PEt2 to
[Ni(COD)2].20,21
ratio approximately 1:3). The cis-isomer was the almost
exclusive product, in about 66% yield, starting from [PtI2-
(COD)]. The cis-isomer was converted into the trans-isomer
when toluene solutions were heated under reflux. The corre-
sponding reaction of [PdCl2(SEt2)2] or [PdBr2(COD)] with
2-LiC6F4PPh2 gave colorless trans-[Pd(κ2-2-C6F4PPh2)2] (2), in
yields of 30-40%. The yellow nickel analogue, trans-[Ni(κ2-
2-C6F4PPh2)2] (3), could not be made similarly from precursors
such as NiCl2, Ni(acac)2, or Ni(OOCCF3)2, but was isolated in
30% yield from zinc dust reduction of a mixture of anhydrous
NiCl2 and 2-BrC6F4PPh2 in THF. This procedure follows that
employed by Sacco et al.23 for the preparation of the nickel(0)
complexes [Ni(CO)2(PPh3)2] and [Ni(C2H4)(PPh3)2]. Complex
3 could also be isolated from the reaction of 2-BrC6F4PPh2 with
[Ni(COD)2], but the yield was poor (ca. 10%).
Results
The spectroscopic data for complexes 1-3 are collected in
Table 1. The 31P NMR spectra consist of a singlet in the region
of δ -40 to -65, the shielding being characteristic of
phosphorus in four-membered chelate rings.24 The signals are
broad (W1/2 ca. 16 Hz), probably owing to unresolved 19F
coupling. In addition, the resonances for cis- and trans-1 show
195Pt satellites with couplings of 1697 and 2294 Hz, respectively,
the magnitudes being typical for phosphorus trans to aryl carbon
Synthesis of Bis(chelate) Complexes. Treatment of the
organolithium reagent 2-LiC6F4PPh222 with [PtCl2(SEt2)2] gave
the colorless bis(chelate) complex [Pt(κ2-2-C6F4PPh2)2] (1) as
a mixture of cis- and trans-isomers in ca. 30% yield (cis/trans
(19) Garc´ıa-Monforte, M.; Alonso, P. J.; Fornie´s, J.; Menjo´n, B. Dalton
Trans. 2007, 3347.
(20) Font-Bard´ıa, M.; Gonza´lez-Platas, J.; Muller, G.; Panyella, D.;
Rocamora, M.; Solans, X. J. Chem. Soc., Dalton Trans. 1994, 3075.
(21) Abbreviations: COD ) 1,5-cyclooctadiene, C8H12; dppe ) 1,2-
bis(diphenylphosphino)ethane, Ph2PCH2CH2PPh2; bipy ) 2,2′-bipyridyl,
2,2′-(C5H4N)2; phen ) 1,10-phenanthroline, C12H8N2.
(23) Giannoccaro, P.; Sacco, A.; Vasapollo, G. Inorg. Chim. Acta 1979,
37, L455.
(24) Garrou, P. E. Chem. ReV. 1981, 81, 229.
(22) Eller, P. G.; Meek, D. W. J. Organomet. Chem. 1970, 22, 631.

Triad of Bis(orthometalated) d8-Complexes
Organometallics, Vol. 27, No. 20, 2008 5363
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes
and to phosphorus, respectively; cf. cis-[PtPh2(PPh3)2] (JPtP 1762
Hz)25 and trans-[PtCl2(PPh3)2] (JPtP 2637 Hz).26
cis-1, trans-1, and 2
The 19F NMR spectra of 1-3 consist of four multiplets of
equal intensity centered at ca. δ -120, -135, -150, and -158,
relative to CFCl3, corresponding to the inequivalent fluorine
atoms of the 2-C6F4PPh2 unit. In the spectra of cis- and trans-
1, the resonances at ca. δ -120 show 195Pt satellites (JPtF ca.
164 Hz), indicating that this signal in all three compounds should
be assigned to F6, adjacent to the M-C σ-bond. Similar
chemical shifts for F2,6 are observed in comparable pentafluo-
rophenylplatinum(II) complexes, though the JPtF values for cis-
and trans-1 are about half that observed in cis-[Pt(C6F5)2(PPh3)2]
(315 Hz)27 and cis-[Pt(C6F5)2(dppe)] (309 Hz),28 presumably
because of the presence of the strained four-membered ring.
The resonance at ca. δ -135 is assigned to F3 adjacent to the
PPh2 group, cf. δ -130.6 and -127.7 for the ortho-fluorine
atoms in (C6F5)3P and C6F5PPh2, respectively.29 Since the
resonance at ca. δ -150 in the spectrum of trans-1 shows
observable coupling with 195Pt (although the satellites overlap
the main multiplet), we assign the signal in this region in all
three complexes to F5, in the remaining position that is meta to
the M-C σ-bond; the signal at ca. δ -158 is therefore due to
F4, para to the M-C σ-bond.
The presence of four-membered chelate rings in 1-3 was
confirmed by single-crystal X-ray diffraction studies. Crystal-
lization of an isomeric mixture of 1 from dichloromethane/
hexane gave crystals of trans-1 as colorless plates (monoclinic,
space group P21/c, form A) and colorless needles (monoclinic,
space group C2/c, form B) and cis-1 as pale yellow plates
(monoclinic, space group C2/c); complexes 2 and 3 crystallize
in space group P21/c and are isomorphous with form A of trans-
1. The molecular structure of cis-1 is shown in Figure 2, and
selected bond lengths and angles for cis-1, trans-1 (both
modifications), and 2 are collected in Table 2. The molecular
structure of 3 is shown in Figure 3, together with selected bond
lengths and angles.
trans-1
(form A)
trans-1
(form B)
cis-1
2
M(1)-P(1)
2.2754(9)
2.110(4)
69.42(10)
178.29(11)
108.89(5)
112.3(2)
2.2960(6)
2.063(2)
69.02(6)
110.98(6)
180.0
2.3025(9)
2.074(4)
69.07(10)
110.93(10)
180.0
2.3069(4)
2.0672(16)
69.39(5)
110.61(5)
180.0
M(1)-C(12)
P(1)-M(1)-C(12)
P(1)-M(1)-C(12*)
P(1)-M(1)-P(1*)
C(12)-M(1)-C(12*)
180.0
180.0
180.0
significantly [2.2754(9), 2.297(1) Å, respectively]. The C-Pt-C
angle in cis-1 [112.3(2)°] is significantly greater than that in 4
[106.3(1)°], while the P-Pt-P angles follow the reverse trend
[108.89(5)° in cis-1, 116.25(3)° in 4], perhaps to accommodate
the larger fluorine substituents. These angles are similar to the
corresponding angles in cis-[Pt(κ2-C6H3-6-Me-2-PPh2)2], in
which the bulky methyl substituents are ortho to the M-C
σ-bonds.11 The metrical parameters for the two modifications
of trans-1 are almost identical. There is also little difference in
the metrical parameters of the platinum(II) complex trans-1 and
the palladium(II) complex 2; a marked lengthening of the M-C
bonds and shortening of the M-P bond lengths for Pt compared
with Pd similar to that found in the isostructural dimethylmet-
al(II) complexes cis-[M(CH3)2(PMePh2)2] (M ) Pd, Pt) is not
evident.30,31 The M-C distances in trans-1 and 2 are ca. 0.04
Å less than that in cis-1, whereas the M-P distances are ca.
0.03 Å longer, reflecting the higher trans-influence of the
phosphorus donor relative to that of the fluoroaryl carbon. The
bite angle of the chelate ligands in cis-1, trans-1, and 2 lies
within the range 68-69° usually found for orthometalated PPh3
complexes.1
The Ni-P and Ni-C distances in 3 are similar to those found
in trans-[Ni(κ2-2-C6Cl4PEt2)2] (5)20 and are ca. 0.1-0.15 Å less
than the corresponding metal-ligand distances in trans-1 and
2, corresponding to the smaller size of nickel relative to that of
palladium or platinum. This feature may also account for the
fact that the bite angle of the ligand has increased to ca. 73°,
again similar to that found in 5.
All three complexes show the expected, approximately
square-planar coordination about the metal atoms, distorted as
a consequence of the narrow bite angle of the chelate groups.
The Pt-C distance in cis-1 [2.110(4) Å] is slightly longer than
that in the protio analogue cis-[Pt(κ2-2-C6H4PPh2)2] (4) [2.063(2)
Å],10 whereas the Pt-P distances in cis-1 and 4 do not differ
Figure 3. Molecular structure of trans-[Ni(κ2-2-C6F4PPh2)2], 3.
Ellipsoids show 30% probability levels, and hydrogen atoms have
been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ni(1)-P(1), 2.2035(9), Ni(1)-P(2), 2.2058(9), Ni(1)-C(112)
1.941(3), Ni(1)-C(212) 1.934(3), P(1)-Ni(1)-C(112) 72.76(10),
P(2)-Ni(1)-C(212) 72.87(10), P(1)-Ni(1)-C(212) 106.66(10),
P(2)-Ni(1)-C(112) 107.67(10), P(1)-Ni(1)-P(2) 177.90(4),
C(112)-Ni(1)-C(212) 178.85(14).
Figure 2. Molecular structure of cis-[Pt(κ2-2-C6F4PPh2)2], cis-1.
Ellipsoids show 30% probability levels, and hydrogen atoms have
been omitted for clarity.

5364 Organometallics, Vol. 27, No. 20, 2008
Bennett et al.
Figure 5. Molecular structure of cis-[Ni(κC-2-C6F4PPh2)2(bipy)]
9. Ellipsoids show 30% probability levels, and hydrogen atoms have
been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ni(1)-N(1) 1.9489(19), Ni(1)-N(2) 1.9394(19), Ni(1)-C(6)
1.883(2), Ni(1)-C(24) 1.901(2), N(1)-Ni(1)-C(6) 95.18(9),
N(2)-Ni(1)-C(24) 96.99(9), N(1)-Ni(1)-C(24) 166.28(9), N(2)-
Ni(1)-C(6) 163.63(9), N(1)-Ni(1)-N(2) 82.79(8), C(6)-Ni(1)-
C(24) 88.80(10).
Figure 4. Molecular structure of [Ni(κC-2-C6F4PPh2)2(dppe)] 6.
Ellipsoids show 30% probability levels, and hydrogen atoms have
been omitted for clarity.
Reactions with Bidentate Ligands. The phosphorus atoms
of the four-membered chelate rings in 1-3 are displaced by
1,2-bis(diphenylphosphino)ethane to give complexes of the type
cis-[M(κC-2-C6F4PPh2)2(dppe)] [M ) Ni (6), Pd (7), Pt (8)].
Similar reactions have been reported for the platinum(II)
complex 4.32 The phosphorus atoms of the nickel complex 3
are also displaced by the bidentate nitrogen donors 2,2′-
bipyridine and 1,10-phenanthroline to give cis-[Ni(κC-2-
C6F4PPh2)2(L-L)] [L-L ) bipy (9), phen (10)] as dark colored
solids; the palladium and platinum bis(chelate) complexes 1 and
3 are inert under similar conditions.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for Complexes
6 and 8
[Ni(κC-2-C6F4PPh2)2-
(dppe)], 6
[Pt(κC-2-C6F4PPh2)2-
(dppe)], 8
M(1)-C(6)
1.940(2)
1.950(2)
2.1986(6)
2.2078(6)
91.30(8)
92.53(6)
92.33(6)
86.35(2)
166.60(7)
168.76(7)
2.065(3)
2.071(2)
2.2629(7)
2.2655(6)
90.91(9)
93.10(7)
92.66(7)
85.74(2)
166.68(8)
169.06(8)
M(1)-C(24)
M(1)-P(3)
M(1)-P(4)
C(6)-M(1)-C(24)
C(6)-M(1)-P(4)
C(24)-M(1)-P(3)
P(3)-M(1)-P(4)
C(6)-M(1)-P(3)
C(24)-M(1)-P(4)
The ESI mass spectra of 6-10 show the expected parent ion
peaks. The structures of the complexes follow from the NMR
spectroscopic data, which are discussed below, and from single-
crystal X-ray crystallographic analyses of 6, 8, and 9. Com-
pounds 6 and 8 are isomorphous and isostructural (triclinic,
and nickel-pentafluorophenyl complexes containing tertiary
phosphines, e.g., trans-[Ni(2-MeC6H4)2(PMe2Ph)2] [1.933(16),
1.950(12) Å (syn-isomer), 1.942(3) Å (anti-isomer)],33 trans-
[Ni(C6F5)2(PMePh2)2] [1.939(3) Å],34 [Ni(C6R5)(η5-C5H5)(P-
Ph3)] [1.904(7) Å (R ) H),35 1.914(14) Å (R ) F)36], and
[Ni{κ2-C,O-2-C6H4C(dCHMe)O}(iPr2PCH2CH2PiPr2)] [1.913(4)
Å].37 The Ni-P distances in 6 of 2.20 Å are unexceptional.
In the isostructural platinum(II) complex 8, the Pt-C and
Pt-P distances are not significantly different from those in the
precursor cis-1 and are similar to those in cis-[Pt(C6F5)2-
(dppe)].28 In the bipy complex 9, the Ni-C bond lengths are
significantly shorter, by 0.04-0.06 Å, than those in the dppe
complex 6 but are similar to those in other Ni-C6F5 complexes
containing N-donors, e.g., [Ni(C6F5)2(bipy)] [1.903(4), 1.907(4)
Å]38 and [Bu4N][Ni(C6F5)2(2-SC5H4N)] [1.891(6), 1.894(6)
Å].39
j
space group P1); 9 is monoclinic (P21/n). The molecular
structures of 6 and 9 are shown in Figures 4 and 5, respectively.
Selected bond lengths and angles for 6 and 8 are listed in Table
3; those for 9 are given in the caption to Figure 5.
All three complexes show the expected, close to square-planar
coordination geometry about the metal atom. The phosphorus
atoms of the 2-C6F4PPh2 groups, P(1) and P(2), are not within
bonding distance of the metal atoms [Ni · · · P 3.442(1), 3.444(1)
Å in 6, 2.907(1), 3.048(1) Å in 9; Pt · · · P 3.478(1), 3.474(1) Å
in 8]. The Ni-C bond lengths in 6 are similar to those in the
parent bis(chelate) complex 3. The Ni-C bond lengths [1.940(2),
1.950(2) Å] are also similar to those reported for nickel-aryl
(25) Nilsson, P.; Plamper, F.; Wendt, O. F. Organometallics 2003, 22,
5235.
(26) Anderson, G. K.; Clark, H. C.; Davies, J. A. Inorg. Chem. 1981,
20, 944.
(27) Deacon, G. B.; Nelson-Reed, K. T. J. Organomet. Chem. 1987,
322, 257.
(28) Deacon, G. B.; Elliott, P. W.; Erven, A. P.; Meyer, G. Z. Anorg.
Allg. Chem. 2005, 631, 843.
The 31P and 19F NMR spectra of compounds 6-10 are listed
in Table 1. The 31P NMR spectra of 6-8 consist of two sets of
signals in the region of δ 40 and 0, assignable to coordinated
(29) Hogben, M. G.; Graham, W. A. G. J. Am. Chem. Soc. 1969, 91,
283.
(30) Wisner, J. M.; Bartczak, T. J.; Ibers, J. A.; Low, J. L.; Goddard,
W. A., III. J. Am. Chem. Soc. 1986, 108, 347.
(31) Wisner, J. M.; Bartczak, T. J.; Ibers, J. A. Organometallics 1986,
5, 2044.
(33) Miki, K.; Tanaka, M.; Kasai, N.; Wada, M. J. Organomet. Chem.
1988, 352, 285.
(34) Churchill, M. R.; Veidis, M. V. J. Chem. Soc., Dalton Trans. 1972,
670.
(35) Churchill, M. R.; O’Brien, T. A. J. Chem. Soc. A 1969, 266.
(36) Churchill, M. R.; O’Brien, T. A. J. Chem. Soc. A 1968, 2970.
(37) Ca´mpora, J.; Maya, C. M.; Palma, P.; Carmona, E.; Gutie´rrez, E.;
Ruiz, C.; Graiff, C.; Tiripicchio, A. Chem.-Eur. J. 2005, 11, 6889.
(32) Bennett, M. A.; Bhargava, S. K.; Ke, M.; Willis, A. C. J. Chem.
Soc., Dalton Trans. 2000, 3537.

Triad of Bis(orthometalated) d8-Complexes
Organometallics, Vol. 27, No. 20, 2008 5365
dppe and to uncoordinated PPh2 groups, respectively. The dppe
resonance of the nickel complex 6 is a well-resolved triplet with
a separation of 11.6 Hz, that of the palladium complex 7 is a
poorly resolved triplet (separation ca. 14 Hz), while that of 8 is
a broad singlet accompanied by 195Pt satellites (JPtP 2137 Hz).
The PPh2 resonances of 6-8 display an unexpected pattern,
consisting of a well-resolved doublet of doublets with separa-
tions of 26.8, 95.5 Hz (6), 25.9, 76.9 Hz (7), and 26.5, 81.5 Hz
(8). In the case of 8 there are also 195Pt satellites (JPtP 227 Hz),
somewhat greater than the corresponding values in [Pt(κC-2-
C6H4PPh2)2(dppe)] (170 Hz).32 The separations in the doublet
of doublets are not reproduced in the dppe resonance; hence
the unexpected pattern is not due to coupling with the 31P nuclei
of dppe. Likewise, the separations observed in the dppe
resonances of 6 and 7 are not reproduced in the corresponding
PPh2 resonances; hence these separations do not arise from
coupling with the 31P nuclei of the PPh2 groups. These
conclusions are supported by the failure to observe cross-peaks
in the 2D COSY 31P/31P NMR spectra. The uncoordinated PPh2
resonances of 9 and 10, in contrast with those of 6-8, are in
each case the expected singlet at ca. δ -6, with multiplet fine
structure, presumably due to 19F coupling.
due to F6 is shifted to higher frequency (δF ca. -105 in 6-8,
ca. -117 in 9 and 10) and in the case of 6-8 appears as a
doublet of multiplets. In the platinum(II) complex 8, the coupling
constant of 195Pt to F6 (326 Hz) is approximately double that
in the precursor 1 and is similar to the values reported for
coupling to the ortho-fluorine atoms in cis-[Pt(C6F5)2(PPh3)2]27
and [Pt(C6F5)2(dppe)]28 (see above). A 31P/19F heteronuclear
multiple quantum correlation (HMQC) experiment on the
palladium complex 7 showed well-defined cross-peaks associ-
ated with the resonances at δF -105.2 (F6) and -123.8 (F3);
the coupling constants are ca. 75 and 25 Hz, respectively, in
reasonable agreement with the separations observed in the 1D
31P NMR spectrum. A similar experiment on the nickel(II)-
bipy complex 9 also showed cross-peaks for the resonances at
δF -117.8 (F6) and -124.6 (F3), but the coupling to F6 (ca. 30
Hz) is clearly less than that in the dppe complex; the coupling
to F3 is less than 20 Hz. In the 1D 19F NMR spectrum of the
nickel-dppe complex 6, the doublet of multiplets due to F6 is
so well resolved that the coupling with phosphorus can be read
off directly; its value (98 Hz) is in fair agreement with the
separation of 95 Hz obtained from the 31P NMR spectrum. It
seems clear, therefore, that the separations of 75-95 and 25
Hz in the doublet of doublets pattern of the PPh2 resonances of
We thought at first that the doublet of doublets for the PPh2
groups in 6-8 might arise from inequivalence of the PPh2
groups in solution caused by restricted rotation about the
M-C6F4PPh2 bonds, even though this would have implied a
remarkably large, six-bond P-P coupling constant (ca. 26 Hz).
This explanation did not seem implausible given the ample
evidence for restricted rotation about M-C6F5 bonds40-49 and
for slowed rotation about M-P and P-C bonds in platinum(II)
complexes of (C6F5)3P.50-52 However, the frequency separation
between the pairs of doublets was found to be the same at 202.3
MHz as at 121.4 MHz; hence there is only one 31P chemical
shift and the observed pattern can only be due to P-F coupling.
4
3
6-8 are due to J and J P-F couplings, respectively.
In free pentafluorophenylphosphines, such as (C6F5)3P and
C6F5PPh2, the largest P-F coupling constant of ca. 38 Hz
(observed in the 19F NMR spectrum) is due to F2,6 (the ortho-
fluorines), the meta- and para-couplings being close to zero.29,53
Couplings similar to those of 6-8 are not observed in the 31P
NMR spectra of 2-BrC6F4PPh2 or 2-Me3SnC6F4PPh2.54 Possible
reasons for these differences will be discussed below.
Dinuclear and Tetranuclear Complexes of Palladium(II).
Heating of a mixture of 2 and [PdCl2(MeCN)2] in toluene for
1 h gave an orange solution, from which a yellow solid of
formula [Pd2Cl2(C6F4PPh2)2] (11) was isolated in ca. 83% yield
(Scheme 1). The 31P NMR spectrum of 11 shows two broad
singlets at δ -77.4 and -76.7 whose relative intensity varies
in different preparations, indicating the presence of two species,
both of which clearly contain four-membered chelate rings; the
species responsible for the more shielded resonance is always
the more abundant. Traces of a third compound having a 31P
NMR singlet at δ 28.7 are also observed (see below). The far-
infrared spectrum of solid 11 shows two strong bands at 273
and 290 cm-1, which are not present in the spectrum of 2 and
can be assigned to the Pd-Cl stretching vibrations of a binuclear
Pd2(µ-Cl)2 unit.55,56 The corresponding bands for the closely
related, noncyclometalated complex [Pd2(µ-Cl)2(C6F5)2(P-
The 19F NMR spectra of 6-10 consist of the expected four
multiplets whose chemical shifts and assignments are similar
to those of their chelate precursors (Table 1). In each case, the
main difference from the spectra of 1-3 is that the resonance
(38) Yamamoto, T.; Abla, M.; Murakami, Y. Bull. Chem. Soc., Jpn.
2002, 75, 1997.
(39) Lo´pez, G.; Sa´nchez, G.; Garc´ıa, G.; Garc´ıa, J.; Mart´ınez, A.;
Hermoso, J. A.; Mart´ınez-Ripoll, M. J. Organomet. Chem. 1992, 435, 193.
(40) Bennett, R. L.; Bruce, M. I.; Gardner, R. C. F. J. Chem. Soc., Dalton
Trans. 1973, 2653.
(41) Crocker, C.; Goodfellow, R. J.; Gimeno, J.; Uso´n, R. J. Chem. Soc.,
Dalton Trans. 1977, 1448.
(42) Uso´n, R.; Fornie´s, J.; Espinet, P.; Lalinde, E.; Jones, P. G.;
Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1982, 2389.
(43) Albarez, A. C.; Cuevas, J. C.; Espinet, P.; de Mendoza, J.; Prados,
P. J. Organomet. Chem. 1991, 410, 257.
(44) Abel, E. W.; Orrell, K. G.; Osborne, A. G.; Paint, H. M.; Sik, V.;
Hursthouse, M. B.; Abdul Malik, K. M. J. Chem. Soc., Dalton Trans. 1994,
3441.
(45) Falvello, L. R.; Fornie´s, J.; Navarro, R.; Rueda, A.; Urriolabeitia,
E. P. Organometallics 1996, 15, 309.
(46) Ara, I.; Berenguer, J. R.; Fornie´s, J.; Lalinde, E.; Toma´s, M.
Organometallics 1996, 15, 1014.
(47) Ara, I.; Falvello, L. R.; Ferna´ndez, S.; Fornie´s, J.; Lalinde, E.;
Mart´ın, A.; Moreno, M. T. Organometallics 1997, 16, 5923.
(48) Fornie´s, J.; Go´mez-Saso, M. A.; Mart´ın, A.; Mart´ınez, F.; Menjo´n,
B.; Navarrete, J. Organometallics 1997, 16, 6024.
Ph3)2] appear at 270 and 290 cm-1 56
The data are consistent
.
with the isomeric chloro-bridged structures cis-11 and trans-
11 shown in Scheme 1; structure trans-11 has been confirmed
by X-ray crystallography.57 A structurally similar chloride-
bridged complex containing terminal cyclometalated [2-MeC6-
H4C6H3PtBu2]- ligands has also been reported recently.58
When a solution of 11 in CH2Cl2 was set aside at room
temperature, a yellow precipitate of the same composition as
(53) Nichols, D. I. J. Chem. Soc. A 1969, 1471.
(54) Prive´r, S. H., unpublished work.
(55) Nakamoto, K., Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 5th ed.; Wiley-Interscience: New York, 1997,
Part B, pp 187-188.
(56) Uso´n, R.; Fornie´s, J.; Navarro, R.; Garc´ıa, M. P. Inorg. Chim. Acta
1979, 33, 69.
(57) Rae, A. D.; Wagler, J., unpublished work.
(58) Christmann, U.; Pantazis, D. A.; Benet-Buchholz, J.; McGrady,
J. E.; Maseras, F.; Vilar, R. J. Am. Chem. Soc. 2006, 128, 6376.
(49) Carrio´n, M. C.; Jalo´n, F. A.; Lo´pez-Solera, L.; Manzano, B. R.;
Sepu´lveda, F.; Santos, L.; Rodr´ıguez, A. M.; Moreno, M.; Mart´ınez-Ripoll,
M. Can. J. Chem. 2005, 83, 2106.
(50) Kemmitt, R. D. W.; Nichols, D. I.; Peacock, R. D. Chem. Commun.
1967, 599.
(51) Docherty, J. B.; Rycroft, D. S.; Sharp, D. W. A.; Webb, G. A.
J. Chem. Soc., Chem. Commun. 1979, 336.
(52) Atherton, M. J.; Fawcett, J.; Holloway, J. H.; Hope, E. G.; Russell,
D. R.; Saunders, G. C. J. Chem. Soc., Dalton Trans. 1997, 2217.

5366 Organometallics, Vol. 27, No. 20, 2008
Bennett et al.
Scheme 1
11 slowly deposited. The 31P NMR spectrum shows a singlet
at δ 28.7, identical to that of the trace impurity observed during
the preparation of 11. This chemical shift is consistent with the
presence of bridging C6F4PPh2 groups resulting from opening
of the four-membered chelate rings in 11, and the far-infrared
spectrum shows bands at 280 and 301 cm-1 assignable to
bridging chloride ligands. The NMR and mass spectroscopic
data indicate that this compound is a tetranuclear species, [Pd4(µ-
Cl)4(µ-2-C6F4PPh2)4] (12), which is isostructural with the known
complexes [Pd4(µ-X)4(µ-2-C6H4PPh2)4] (X ) Cl, Br).12,13 The
bromo analogue of 12 has been obtained independently by
oxidative addition of 2-BrC6F4PPh2 to [Pd(dba)2].59
stretching frequency of a phosphine oxide, a ketonic carbonyl,
and water. The water could not be removed, even after
prolonged heating in Vacuo. Compound 14 showed a singlet at
δ 26.0 in its 31P NMR spectrum and an intense peak at m/z 727
[M + H]+ in its electrospray mass spectrum. The spectroscopic
data are consistent with the formulation of 14 as the 2,2′-
disubstituted benzophenone {2,2′-C6F4P(O)Ph2}2CO, and the
elemental analysis corresponds to this composition together with
ca. 1 equiv of water. The molecular structure of 14 determined
by single-crystal X-ray diffraction analysis is shown in Figure
6, together with significant bond lengths and angles, which are
unexceptional. The crystal selected contained ca. 0.6 mol/mol
of water that is strongly hydrogen-bonded to the PdO groups
following well-established behavior for tertiary phosphine
oxides.61
Since 14 must arise from the initial insertion of CO into one
of the Ni-C σ-bonds of 3, we carried out the reaction of 3 in
CD2Cl2 with 13CO to see if aroyl intermediates could be
detected. Concomitant with the growth of the singlet at δ 31.2
in the 31P NMR spectrum, there appeared over a period of hours
three singlets of approximately equal intensity in the 13C NMR
spectrum at δ 186.2, 195.4, and 197.8. The 31P NMR singlet
due to 3 disappeared completely only after ca. 48 h, having
been replaced by the singlet at δ 31.2 and a weak peak at δ
24.5. No peaks were observed in the δ 220-280 region of the
13C NMR spectrum attributable to an aroylnickel(II) intermedi-
ate, cf. δ(COAr) values of 253.0 (JPC ) 26.5 Hz) in trans-
Reaction of Complex 3 with Carbon Monoxide. Complexes
1 and 2 are inert toward CO under ambient conditions, but the
nickel(II) bis(chelate) complex 3 reacted with CO at room
temperature over a period of 6 h to give an orange-red solution,
from which an unstable yellow-orange solid (13) could be
isolated. This shows a singlet in its 31P NMR spectrum at δ
30.5 (C6D6) [δ 31.2 (CD2Cl2)] and two strong bands in the CO
stretching region of the IR spectrum at 2021 and 1966 cm-1
,
which are suggestive of a bis(tertiary phosphine)dicarbon-
ylnickel(0) species.60 There is also a strong band at 1684 cm-1
,
which could be assigned to a bridging carbonyl, a ketonic
carbonyl, or an aroyl group. Isolated samples of 13 were always
contaminated with the oxidation product 14 (see below). When
the solution was exposed to air, or when passage of CO was
continued for 5 days, the color changed to yellow and a colorless
solid (14) was isolated, the IR spectrum of which contained no
Ct O stretching bands, but did show an intense band at 1203
cm-1, a strong band at ca. 1700 cm-1, and a broad absorption
in the region of 3500 cm-1 assignable, respectively, to the PdO
Figure 6. Molecular structure of {2,2′-C6F4P(O)Ph2}2CO (14) with
labeling of selected atoms. Ellipsoids show 30% probability levels.
The H-bonded water molecule and hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
P(1)-O(1) 1.4817(6), P(2)-O(2) 1.4793(16), C(40)-O(3) 1.205(2),
O(1)-P(1)-C(1) 109.26(3), O(2)-P(2)-C(21) 111.16(9), C(22)-
C(40)-O(3) 120.97(18), C(2)-C(40)-O(3) 119.92(18).
(59) Koshevoy, I. O.; Lahuerta, P.; Sanau´, M.; Ubeda, M. A.; Dome´nech,
A. Dalton Trans. 2006, 5536.

Triad of Bis(orthometalated) d8-Complexes
Organometallics, Vol. 27, No. 20, 2008 5367
Scheme 2
[NiCl(COPh)(PMe3)2]62 and 256.6 (JPC ) 76, 18 Hz) in [Ni(κ2-
COC6H4CF2CF2)(dcpe)].63
whereas for platinum(II) with 2-C6H4PPh2, the trans-isomer is
only detectable as a transient intermediate on the way to the
more stable cis-isomer. In this respect, the fluorinated carbanion
seems to behave somewhat like a pseudohalide, behavior that
is consistent with the lower trans-influence of C6F5 relative to
C6H5, as assessed by JPtP values in planar platinum(II) com-
plexes.72 The isolability of 2 and 3 and the different behavior
of cis-[Pt(κ2-2-C6X4PPh2)2] [X ) F (1) and H (4)] on heating
indicate the stabilizing effect of the fluorine substituents on the
four-membered ring, although there is no evidence from
comparisons of the Pt-C bond lengths that this effect is caused
by a strengthening of the M-C σ-bond. Strain in the four-
membered rings of 1-3 is indicated by the reactions of 1-3
with bidentate ligands and the ready carbonylation of the nickel
complex 3. However, the ring-opening of κ2-2-C6F4PPh2 is
evidently slower than that of κ2-2-C6H4PPh2, since an interme-
diate analogous to [Pd2(µ-Cl)2(κ2-2-C6F4PPh2)2] (11) has not
been reported so far in the 2-C6H4PPh2 series, despite the
thermodynamically favored conversion of 11 to the tetranuclear,
ring-opened complex 12 in solution.
We suggest tentatively that two of the three 13C resonances
in the δ 200 region are due to the terminal and ketonic carbonyl
groups of the Ni(CO)2 complex of bis-2,2′-(diphenylphosphi-
no)octafluorobenzophenone, (2,2′-C6F4PPh2)2CO, acting as a
bidentate P-donor; this species is the orange solid (13) that gives
rise to the singlet at ca. δ 31 in the 31P NMR spectrum. Its
instability may be due to the presence of an eight-membered
chelate ring. At this stage we cannot explain why there should
be three 13CO NMR resonances, and further work is required
to account for this observation. It is clear, however, that the
reductive elimination that generates the benzophenone must
occur rapidly after CO insertion. A plausible reaction sequence
is shown in Scheme 2. In the first step, CO is likely to displace
one or both phosphorus atoms of 3, thus allowing migration of
the nickel-carbon σ-bond to the coordinated CO. Reductive
elimination of the tetrafluoroaroyl and tetrafluoroaryl groups
under CO then generates the Ni(CO)2 complex 13, which, in
the presence of air, is oxidized to the phosphine oxide and
released from the metal.
Finally, we comment briefly on the unprecedentedly large
values of 4JPF (75-95 Hz) to F6, the fluorine atom ortho to the
metal-carbon σ-bond, in the dppe complexes 6-8. There are
few systematic studies of vicinal and long-range P-F cou-
plings.73 Many long-range F-F couplings are believed to be
“through space”,74 but this clearly cannot be the case for 6-8,
where the P-F coupling must be transmitted through the planar
F-C-C-C-P unit. There is abundant evidence that 31P-1H
and 31P-13C couplings through two or more bonds depend
strongly on the dihedral angle (maximum at 0°, minimum at
about 90°, according to the Karplus relationship) and, most
importantly, on the geometric orientation relative to the lone
pair on the phosphorus atom.75,76 The same could well hold
for long-range P-F couplings. The directions of the lone pairs
at phosphorus atoms P(1) and P(2) in 6, 8, and 9 can be
estimated from the molecular structures by inserting a phantom
hydrogen atom at the expected position. The torsion angles
These conclusions are supported by results published after
this paper had been submitted, which show that the metalacycles
cis- or trans-[Ni(κ2-2-C6H4OPiPr2)2] react with CO to give, as
a result of insertion and subsequent reductive elimination, the
dicarbonylnickel(0) complex of a chelate, benzophenone-based
bis(phosphinite) ligand, {2,2′-C6H4OPiPr2}2CO.64
Although the ready insertion of CO into nickel(II)-alkyl and
-aryl σ-bonds is a well-established reaction sequence,64-68 the
insertion step is usually unfavorable for electron-withdrawing
groups such as C6F5;69,70 indeed, facile decarbonylation of
the presumed oxidative addition product of C6F5COCl and
[Ni(C2H4)(PPh3)2] has been used to prepare [NiCl(C6F5)-
(PEt3)2].71 It is of interest that the ability of [Ni(κ2-2-C6F4PPh2)2]
(3) to insert CO differs from the behavior of the complexes
[Ni(κ2-2-C6Cl4PR2)2] [R ) Et (5), Ph], which reversibly add
CO to give five-coordinate adducts in solution, but do not insert
CO.20
(64) Ruhland, K.; Obenhuber, A.; Hoffman, S. D. Organometallics 2008,
27, 3482.
(65) Yamamoto, T.; Kohara, T.; Yamamoto, A. Chem. Lett. 1976, 1217.
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(68) Carmona, E.; Gute´rriez-Puebla, E.; Mar´ın, J. M.; Monge, A.;
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(69) Wojcicki, A. AdV. Organomet. Chem. 1973, 11, 87, and references
therein.
Conclusions
Use of the carbanion [2-C6F4PPh2]- in place of [2-C6H4-
PPh2]- enables the isolation of the complete series of homoleptic
bis(chelate) complexes of elements of the nickel triad. For all
three elements, the stable isomer has the trans-configuration,
(60) Jolly, P. W.; Wilke, G. The Organic Chemistry of Nickel; Academic
Press: New York, 1974; Vol. I, pp 56-60.
(70) Yamamoto, A. Organotransition Metal Chemistry; Wiley-Inter-
science: New York, 1986: pp 246-257, and references therein.
(71) Ashley-Smith, J.; Green, M.; Stone, F. G. A. J. Chem. Soc. A 1969,
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(72) Bennett, M. A.; Bhargava, S. K. ; Prive´r, S. H.; Willis, A. C. Eur.
J. Inorg. Chem. 2008, 3467.
(73) Berger, S.; Braun, S.; Kalinowski, H.-O. NMR Spectroscopy of the
Non-Metallic Elements; Wiley: Chichester, 1996; Chapter 7, p 944.
(74) Reference 73, Chapter 6, p 649.
(61) Hays, H. R.; Peterson, D. J. In Organic Phosphorus Compounds;
Kosolapoff, G. M., Maier, L., Eds.; Wiley-Interscience: New York, 1972;
Vol. 3, p 389.
(62) Carmona, E.; Paneque, M.; Poveda, M. L.; Rogers, R. D.; Atwood,
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J. Chem. Soc., Dalton Trans. 1997, 3105.

5368 Organometallics, Vol. 27, No. 20, 2008
Bennett et al.
by direct methods84 and refined, either on F by use of the program
CRYSTALS85 in the case of 1-3, on F2 by use of the SHELX
program86 in the case of 6, 8, and 9, or on F2 by use of
CRYSTALS85 in the case of 14. Neutral atom scattering factors,87
the values of ∆f′ and ∆f′′, and mass attenuation coefficients88 were
taken from standard compilations.
The water molecule in 14 was initially located in a difference
electron density map. Refinement of the occupancy yielded a final
value of 0.572(8); the hydrogen atoms of the water molecule were
not located. The other hydrogen atoms were all observed in
difference maps. They were put in at idealized positions and refined
positionally.
Figure 7. Synperiplanar orientation of F6 and lone pair of PPh2 in
complexes 6-8.
C(6)-C(1)-P(1)-lone pair and C(24)-C(19)-P(2)-lone pair
are, respectively, 7.9(2)°, 5.5(2)° (6), 8.9(2)°, 4.1(2)° (8), and
18.2(2)°, 20.3(2)° (9). In the dppe complexes 6 and 8, therefore,
the fluorine atom and the lone pair on the phosphorus atom of
PPh2 are much closer to a synperiplanar orientation than in the
bipy complex 9, as shown in Figure 7, possibly as a consequence
of the steric bulk of dppe. This feature may account for the
Syntheses. 2-BrC6F4PPh2: (2-Bromo-3,4,5,6-tetrafluorophenyl)-
diphenylphosphine was prepared by a literature method22 in yields
1
of 80-85%. Mp: 64-66 °C. H NMR (CDCl3): δ 7.3-7.5 (m).
13C NMR (CDCl3): δ 128.7 (d, JPC 7.2 Hz), 129.2 (s), 132.9 (dd,
J ) 1.5, 21.2 Hz), 133.7 (dd, J 3.5, 11.4 Hz). Small multiplets at
δ 112 and in the range 130-151 were also observed, presumably
due to the C6F4Br carbons. 31P NMR (CDCl3): δ -1.58 (ddd, JPF
4.4, 10.4, 20.5 Hz). 19F NMR (CDCl3): δ -121.8 (m), -126.6
(m), -150.2 (m), -154.1 (m). ESI-MS (m/z): 413 [M + H]+. Anal.
Calcd for C18H10BrF4P: C 52.33; H 2.44; Br 19.37; P 7.50. Found:
C 52.53; H 2.56; Br 19.21; P 7.13.
4
large JPF values in the dppe complexes.
Experimental Section
General Comments. All experiments involving organolithium
reagents were performed under an atmosphere of dry argon with
the use of standard Schlenk techniques. Diethyl ether, THF, and
n-hexane were dried over sodium/benzophenone, toluene over
sodium, and dichloromethane over calcium hydride. The complexes
[PtCl2(SEt2)2],77 [PtI2(COD)],78 [PdCl2(SEt2)2],79 [PdBr2(COD)],80
and [PdCl2(NCMe)2]81 were prepared by literature methods; all
other reagents were commercially available and used as received.
1H (300 MHz), 13C (75 MHz) 19F (282 MHz), and 31P (121 MHz)
NMR spectra were measured on a Bruker Avance 300 spectrometer
at room temperature in CDCl3, CD2Cl2, or C6D6. The 31P NMR
spectra 6-10 at 202 MHz were measured on an Varian Inova 500
spectrometer. Chemical shifts (δ) are given in ppm, internally
referenced to residual solvent signals (1H and 13C), internal CFCl3
(19F), or external 85% H3PO4 (31P). The 19F-31P HMQC experi-
ment was recorded at a 19F frequency of 282.3 MHz and a 31P
frequency of 121.5 MHz on a Varian Inova 300 spectrometer at a
temperature of 297 K. The spectral widths were 29 000 and 9000
Hz in the F2 and F1 dimensions, respectively. The recycle delay
was 1.5 s; 4K complex points were acquired in F2 and 128
increments of 128 scans in F1. The resolution in F1 was extended
to 512 real points with linear prediction and the data zero-filled to
4K points. 19F and 31P NMR data for complexes 1-3 and 6-10
are given in Table 1; 31P NMR data for complex 11 are given in
Table 3.
[M(κ2-2-C6F4PPh2)2] [M ) Pt (1), Pd (2)]: To a solution of
2-BrC6F4PPh2 (1.0 g, 2.4 mmol) in Et2O (20 mL) cooled to -78
n
°C was added BuLi (1.6 M, 1.5 mL, 2.4 mmol), and the mixture
was stirred for 15 min. To the pale yellow solution was added solid
[MCl2(SEt2)2] (1.1 mmol), and stirring was continued at -78 °C
for 4 h, then at room temperature overnight. The pale yellow solid
was filtered off, washed with a little Et2O (caution: solid slightly
soluble), and dissolved in CH2Cl2. The mixture was filtered to
remove LiCl, MeOH was added to the filtrate, and the volume was
reduced in Vacuo. The white solid that precipitated was isolated
by filtration, washed with MeOH, and dried. Yields were typically
ca. 30% but could be increased to 39% and 66% by starting with
[PdBr2(COD)] and [PtI2(COD)], respectively.
M ) Pt (1): 1H NMR (CDCl3): δ 7.2-7.9 (m, 10H, aromatics).
cis/trans ratio estimated from 31P NMR spectrum ca. 1:3. ESI-MS
(m/z): 862 [M + H]+. Anal. Calcd for C36H20F8P2Pt: C 50.19; H
2.34; F 17.64. Found: C 49.73; H 2.60; F 17.31.
1
M ) Pd (2): H NMR (CDCl3): δ 7.4-7.6 (m, 6H, aromatics),
7.8-7.9 (m, 4H, aromatics). ESI-MS (m/z): 772 [M]+. Anal. Calcd
for C36H20F8P2Pd: C 55.95; H 2.61; F 19.66. Found: C 56.21; H
2.86; F 19.32.
trans-[Ni(κ2-2-C6F4PPh2)2] (3): A mixture of 2-BrC6F4PPh2 (1.0
g, 2.4 mmol) and anhydrous NiCl2 (0.15 g, 1.15 mmol) in THF
Infrared spectra were obtained on a Perkin-Elmer Spectrum 2000
FT spectrometer as KBr or polythene discs; electrospray (ESI) and
MALDI mass spectra were measured on HP 5970 MSD and Bruker
Biflex II spectrometers, respectively. Elemental analyses were
carried out by the Microanalytical Unit at the Research School of
Chemistry, ANU.
X-ray Crystallography. Crystals of cis-1 and the two forms of
trans-1 were selected from a batch containing an approximately
1:3 mixture of the two isomers obtained after recrystallization from
CH2Cl2/hexane. Crystals of 2, 3, and 14 suitable for X-ray
crystallography were obtained from CH2Cl2/hexane and crystals of
6, 8, and 9 from CH2Cl2/methanol. The crystals were coated in
viscous oil and mounted on fine-drawn capillaries. Data were
collected at 200 K on a Nonius-Kappa CCD diffractometer using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). Crystal
data and details of data collection are given in Table 4. Data were
measured by use of COLLECT.82 The intensities of reflections were
extracted, and the data were reduced by use of the computer
programs Denzo and Scalepack.83 The crystal structures were solved
(76) Quin, L. D. In Phosphorus-31 NMR Spectroscopy in Stereochemical
Analysis: Organic Compounds and Metal Complexes; Verkade, J. G., Quin,
L. D., Eds.; VCH: Deerfield Beach, FL, 1987; Chapter 12, p 391.
(77) Kauffman, G. B.; Cowan, D. O. Inorg. Synth. 1960, 6, 211.
(78) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411.
(79) Mann, F. G.; Purdie, D. J. Chem. Soc. 1935, 1549.
(80) Drew, D.; Doyle, J. R. Inorg. Synth. 1972, 13, 47.
(81) Hartley, F. R.; Murray, S. G.; McAuliffe, C. A. Inorg. Chem. 1979,
18, 1394.
(82) COLLECT Software; Nonius-BV: Delft, The Netherlands, 1997-
2001.
(83) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter,
C. W., Jr.; Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol.
276, pp 307-326.
(84) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. SIR92. J. Appl. Crystallogr. 1994, 27,
435.
(85) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. J.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487.
(86) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Germany,
1997.
(87) International Tables for X-ray Crystallography; The Kynoch Press:
Birmingham, England, 1974; Vol. IV.
(88) International Tables for X-ray Crystallography; Kluwer Academic:
Boston, MA, 1992; Vol. C.
(75) Reference 73, Chapter 7, pp 900-919 and 929-937.

Triad of Bis(orthometalated) d8-Complexes
Organometallics, Vol. 27, No. 20, 2008 5369
Table 4. Crystal and Refinement Data for cis-[Pt(K2-2-C6F4PPh2)2] (cis-1), trans-[M(K2-2-C6F4PPh2)2] [M ) Pt (trans-1), Pd (2), Ni (3)],
[M(KC-2-C6F4PPh2)2(L-L)] [M ) Ni, L-L ) dppe (6), bipy (9); M ) Pt, L-L ) bipy (8)], and {2,2′-C6F4P(O)Ph2}2CO (14)
cis-1
trans-1 (form A)
trans-1 (form B)
2
3
formula
fw
C36H20F8P2Pt
861.58
C36H20F8P2Pt
861.58
C36H20F8P2Pt
861.58
C36H20F8P2Pd
772.89
C36H20F8NiP2
725.20
cryst syst
space group
cryst color, habit
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
pale yellow, plate
15.2827(5)
10.0943(3)
24.4836(8)
monoclinic
P21/c
colorless, plate
10.0072(2)
12.2049(2)
12.7603(2)
monoclinic
C2/c
colorless, needle
24.2624(4)
10.1948(2)
13.4835(2)
monoclinic
P21/c
colorless, plate
9.9970(2)
12.2158(2)
12.7955(2)
monoclinic
P21/c
yellow, plate
12.4710(3)
12.3859(3)
20.0281(4)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
103.3068(12)
104.9435(11)
113.5666(12)
105.0546(10)
97.9282(13)
3675.6(2)
4
1.557
1505.80(5)
2
1.900
3056.98(9)
4
1.872
1508.97(5)
2
1.701
3064.06(12)
4
1.572
Z
Dcalc (g cm-3
)
cryst dimens
0.43 × 0.23 ×
0.32 × 0.24 ×
0.34 × 0.08 ×
0.28 × 0.26 ×
0.23 × 0.14 ×
0.20
0.13
0.03
0.14
0.05
µ (mm-1
)
3.968
4.842
4.771
0.798
0.813
no. indep reflns (Rint
no. obsd reflns
no. params refined
R
)
4189 (0.08)
3509 [I > 3σ(I)]
213
3459 (0.03)
2516 [I > 3σ(I)]
214
3505 (0.04)
2198 [I > 3σ(I)]
215
3449 (0.04)
2740 [I > 3σ(I)]
214
5458 (0.072)
3608 [I > 2σ(I)]
424
0.0342a
0.0261a
1.1549
0.0156a
0.0189a
1.0454
0.0196a
0.0211a
1.1330
0.0212a
0.0244a
1.0688
0.0416a
Rw
0.0468a
GOF
1.0876
0.94/-0.59
F
max/Fmin (e Å-3
)
1.40/-1.45
0.42/-0.90
0.67/-0.89
0.33/-0.53
6
8
9
14
formula
fw
C62H44F8NiP4
1123.56
C62H44F8P4Pt
1259.94
C46H28F8N2NiP2
881.35
C37H20F8O3P2 · 0.572H2O
736.77
cryst syst
space group
triclinic
P1
triclinic
P1
monoclinic
P21/n
monoclinic
P21/n
j
j
cryst color, habit
a (Å)
b (Å)
yellow, plate
12.6153(3)
12.7350(2)
17.2316(4)
81.8180(10)
79.2260(10)
75.1250(10)
2615.42(10)
2
colorless, plate
12.6153(3)
12.7350(2)
17.2316(4)
81.8180(10)
79.2260(10)
75.1250(10)
2615.42(10)
2
black, prism
14.8947(4)
16.9283(4)
15.8600(5)
colorless, plate
9.6431(1)
12.5819(1)
26.2617(3)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
101.692(2)
98.1043(6)
3916.00(19)
4
1.495
3154.47(5)
4
1.551
Dcalc (g cm-3
)
1.427
1.600
cryst dimens
0.32 × 0.11 ×
0.30 × 0.11 ×
0.10 × 0.08 ×
0.24 × 0.18 ×
0.05
0.08
0.08
0.04
µ (mm-1
)
0.563
2.875
0.652
0.23
no. indep reflns (Rint
no. obsd reflns
no. params refined
R
)
9235 (0.056)
9235 [I > 2σ(I)]
677
11 972 (0.047)
11 972 [I > 2σ(I)]
677
6901 (0.0865)
6901 [I > 2σ(I)]
533
7256 (0.049)
4515 [I > 2σ(I)]
521
0.0366b
0.0270b
0.0402b
0.032b
Rw
0.0952b
0.0541b
0.0860b
0.105b
GOF
F
1.037
0.615/-0.435
1.022
0.563/-0.836
1.030
0.363/-0.327
0.99
0.44/-0.45
max/Fmin (e Å-3
)
a Refined on F. b Refined on F2.
(20 mL) was refluxed for 24 h, then zinc dust (0.11 g, 1.6 mmol)
was added and heating was continued for a further 48 h. The solvent
was removed in Vacuo, and the residue was dissolved in CH2Cl2.
Filtration through Celite gave an orange solution, to which MeOH
was added. The volume of the solution was reduced in Vacuo, and
the yellow solid that precipitated was isolated, washed with MeOH,
aromatics), 8.47 (m, 4H, aromatics). ESI-MS (m/z): 1122 [M]+.
Anal. Calcd for C62H44F8P4Ni: C 66.28; H 3.95; F 13.53. Found:
C 66.28; H 4.21; F 13.10.
1
M ) Pd (7): colorless solid (60 mg, 73%). H NMR (C6D6): δ
1.80 (m, 4H, CH2), 6.7-7.1 (m, 32H, aromatics), 7.28 (t, 4H, J
7.0 Hz, aromatics), 8.22 (t, 4H, J 8.4 Hz, aromatics). ESI-MS
(m/z): 1170 [M]+. Anal. Calcd for C62H44F8P4Pd: C 63.58; H 3.79;
F 12.98. Found: C 63.45; H 4.07; F 12.60.
1
and dried (0.25 g, 30%). H NMR (CDCl3): δ 7.4-7.6 (m, 6H,
aromatics), 7.8-7.9 (m, 4H, aromatics). ESI-MS (m/z): 725 [M +
H]+. Anal. Calcd for C36H20F8P2Ni: C 59.63; H 2.78; F 20.96.
Found: C 59.29; H 2.97; F 21.05.
1
M ) Pt (8): colorless solid (69 mg, 78%). H NMR (C6D6): δ
1.74 (m, 4H, CH2), 6.8-7.1 (m, 32H, aromatics), 7.28 (t, 4H, J
7.0 Hz, aromatics), 8.26 (dd, 4H, J 8.1, 9.9 Hz, aromatics). ESI-
MS (m/z): 1259 [M]+. Anal. Calcd for C62H44F8P4Pt: C 59.10; H
3.52; F 12.06. Found: C 58.23; H 3.83; F 11.88.
cis-[M(κC-C6F4-2-PPh2)2(dppe)] [M ) Ni (6), Pd (7), Pt (8)]:
To a solution of the appropriate bis(chelate) (0.07 mmol) in CH2Cl2
(3 mL) was added solid dppe (28 mg, 0.07 mmol), and the mixture
was stirred for 10 min. Hexane was added, the volume was reduced
in Vacuo, and the precipitate was isolated by filtration. The solid
was washed with hexane and dried in Vacuo.
cis-[Ni(κC-C6F4-2-PPh2)2(L-L)] [L-L ) bipy (9), phen (10)]: To
a solution of complex 3 (93 mg, 0.13 mmol) in CH2Cl2 (10 mL)
was added solid L-L (0.13 mmol). The yellow solution immediately
turned dark and was stirred for 10 min. Hexane was added, and
1
M ) Ni (6): yellow solid (67 mg, 85%). H NMR (C6D6): δ
1.77 (m, 4H, CH2), 6.7-7.3 (m, 32H, aromatics), 7.26 (m, 4H,

5370 Organometallics, Vol. 27, No. 20, 2008
Bennett et al.
the solution was evaporated under reduced pressure. The precipi-
tated solid was isolated by filtration, washed with hexane, and dried
in Vacuo.
{2,2′-C6F4P(O)Ph2}2CO (14): A solution of 3 (115 mg, 0.16
mmol) in CH2Cl2 (20 mL) was stirred in an atmosphere of CO for
5 days, during which time the color changed from yellow to orange
(immediately) to red (several hours) and finally back to yellow
(several days). The solvent was evaporated to small volume in
Vacuo, and the residue was transferred to a silica gel column. The
product was eluted with ethyl acetate. The volume of the eluate
was reduced in Vacuo, and hexane was added. Evaporation gave a
colorless solid, which was isolated by filtration, washed with hexane,
and dried in Vacuo. The yield of {2,2′-C6F4P(O)Ph2}2CO (14), mp
ca. 240 °C (dec), was 85 mg (74%). 1H NMR (CDCl3): δ 1.67 (br
s, 2H, H2O), 7.4-7.8 (m, 20H, aromatics). 13C NMR (CDCl3): δ
128.5 (dd, J 7.6, 13.1 Hz), 130.2 (d, J 112.7 Hz), 131.4 (dt, J 2.3,
11.5, 11.5 Hz), 132.3 (dd, J 3.0, 8.6 Hz), 180.5 (m). Small multiplets
at δ 119 and in the range 140-150 were also observed, presumably
due to the C6F4 carbons. 31P NMR (CDCl3): δ 26.0 (s). 19F NMR
(CDCl3): δ -120.9 (m), -134.7 (m), -146.7 (m), -148.9 (m). IR
(KBr, cm-1): 3468 (O-H str), 3055 (C-H str), 1707 (CdO str),
1203 (PdO str). ESI-MS (m/z): 727 [M + H]+. Anal. Calcd for
C37H20F8O3P2 · H2O: C 59.77; H 2.96; F 20.33; P 8.33. Found
(different samples): C 58.82, 59.25; H 2.88, 3.09; F 20.11, 19.98;
P 7.84, 7.86.
L-L ) 2,2′-bipyridine (9): brown solid (104 mg, 89%). 1H NMR
(CD2Cl2): δ 6.66 (m, 2H, bipy), 6.9-7.3 (m, 22H, aromatics +
bipy), 7.63 (m, 2H, bipy), 7.77 (m, 2H, bipy). ESI-MS (m/z): 880
[M]+. Anal. Calcd for C46H28F8N2P2Ni: C 62.69; H 3.20; N 3.18;
F 17.24. Found: C 62.48; H 3.37; N 3.10; F 16.99.
L-L ) 1,10-phenanthroline (10): black solid (112 mg, 96%). 1H
NMR (CD2Cl2): δ 6.71 (t, 4H, J 7.2 Hz, aromatics), 6.84 (t, 4H, J
7.2 Hz, aromatics), 6.92 (dd, 2H, J 5.1, 8.2 Hz, phen), 7.08 (t, 2H,
J 7.0 Hz, aromatics), 7.19 (m, 10H, aromatics), 7.37 (dd, 2H, J
1.1, 5.1 Hz, phen), 7.88 (s, 2H, phen), 8.09 (dd, 2H, J 1.0, 8.4 Hz,
phen). ESI-MS (m/z): 904 [M]+. Anal. Calcd for C48H28F8N2P2Ni:
C 63.68; H 3.12; N 3.09; F 16.79. Found: C 63.60; H 3.22; N 3.01;
F 16.86.
[Pd2(µ-Cl)2(κ2-2-C6F4PPh2)2] (11): A mixture of complex 2 (355
mg, 0.46 mmol) and [PdCl2(MeCN)2] (119 mg, 0.46 mmol)
suspended in dry toluene (20 mL) was heated to 65 °C for 1 h,
during which time the color changed from yellow to orange-red.
The solvent was removed in Vacuo, and the residue was recrystal-
lized from CH2Cl2/hexane to give 11 as a yellow solid (360 mg,
83%). 1H NMR (CD2Cl2): δ 7.2-8.1 (m, 20H, aromatics). 31P NMR
(CD2Cl2): δ -77.4 (s), -76.7 (s) (11), 28.7 (s) (trace of 12). 19F
(CD2Cl2): δ -129.7 (m), -130.8 (m), -134.1 (m), -134.3 (m),
-146.7 (m), -147.0 (m), -157.4 (m), -157.5 (m). Far-IR
(polythene, cm-1): 273, 290 (Pd-Cl str). MALDI-MS (m/z): 915
[M - Cl]+. Anal. Calcd for C36H20Cl2F8P2Pd2: C 45.51; H 2.12;
Cl 7.46; F 16.00. Found: C 45.90; H 2.42; Cl 7.29; F 15.41.
[Pd4(µ-Cl)4(µ-2-C6F4PPh2)4] (12): A solution of complex 11 (120
mg, 0.13 mmol) in CH2Cl2 (30 mL) was stirred at room temperature
for 1 week, during which time a yellow solid precipitated.
The volume was reduced to half in Vacuo, and acetone was added.
The suspension was filtered, and the solid was washed with acetone
and Et2O, and dried in Vacuo (49 mg, 41%). 1H NMR (CD2Cl2): δ
7.2-7.6 (m, 40H, aromatics). 31P NMR (CD2Cl2): δ 28.7 (s). 19F
NMR (CD2Cl2): δ -103.6 (m), -117.1 (m), -146.6 (m), -158.8
(m). Far-IR (polythene, cm-1): 280, 301 (Pd-Cl str). MALDI-
MS (m/z): 1865 [M - Cl]+. Anal. Calcd for C72H40Cl4F16P4Pd4: C
45.51; H 2.12; Cl 7.46; F 16.00. Found: C 45.19; H 2.22; Cl 7.46;
F 15.68.
Acknowledgment. We thank Mr. Horst Neumann (Re-
search School of Chemistry, Australian National University)
for assistance with the 13CO experiments. J.W. thanks the
Deutscher Akademischer Austauschdienst (DAAD) for the
award of a Postdoctoral Fellowship.
Note Added after ASAP Publication. In the version of this
paper published on the Web on Sept. 9, 2008, refs 77-88 were
misnumbered. In addition, the data for compounds 2 and 3 in Table
4 were merged together. These errors have been corrected in the
version of the paper that now appears.
Supporting Information Available: X-ray crystallographic data
in CIF format for complexes 1-3, 6, 8, 9, and 14. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM8004806