κ1-and κ2-complexes of fluorenylidene-allenyl phosphines and phosphine oxides with palladium chloride and iron carbonyl: Displacement of trimethylsilyl by diphenylphosphino via a stabilized carbanion

Article abstract of DOI:10.1021/om200357v

An attempt to prepare 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1- (trimethylsilyl)allene, 15, by treatment of 3,3-(biphenyl-2,2′-diyl)-1- lithio-1-(trimethylsilyl)allene with chlorodiphenylphosphine led instead to 3,3-(biphenyl-2,2′-diyl)-1,1-bis(diph

Full text of DOI:10.1021/om200357v

ARTICLE
pubs.acs.org/Organometallics
j1- and j2-Complexes of FluorenylideneꢀAllenyl Phosphines and
Phosphine Oxides with Palladium Chloride and Iron Carbonyl:
Displacement of Trimethylsilyl by Diphenylphosphino via a
Stabilized Carbanion
Sandra Milosevic, Emilie V. Banide, Helge M€uller-Bunz, Declan G. Gilheany, and Michael J. McGlinchey*
School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland
S Supporting Information
b
ABSTRACT: An attempt to prepare 3,3-(biphenyl-2,20-diyl)-1-
diphenylphosphino-1-(trimethylsilyl)allene, 15, by treatment
of 3,3-(biphenyl-2,20-diyl)-1-lithio-1-(trimethylsilyl)allene with
chlorodiphenylphosphine led instead to 3,3-(biphenyl-2,20-
diyl)-1,1-bis(diphenylphosphino)allene, 14. The proposed me-
chanism invokes attack on the trimethylsilyl group in 15 by
liberated chloride to form a stabilized anion that reacts with a second molecule of the chlorophosphine. The diphosphine, 14, reacts
with di-iron nonacarbonyl to form monodentate 14-Fe(CO)4 and the chelate 14-Fe(CO)3. 9-Ethynyl-9H-fluoren-9-ol and
chlorodiphenylphosphine form 3,3-(biphenyl-2,20-diyl)-1-diphenylphosphinylallene, which is readily deprotonated by triethyla-
mine to generate a stabilized fluorenyl anion, which reacts with a second molecule of the chlorophosphine to furnish 3,3-(biphenyl-
2,20-diyl)-1-diphenylphosphino-1-diphenylphosphinylallene, 26. This bis-phosphine-monoxide (BPMO) reacts with di-iron
nonacarbonyl to form initially monodentate P-bonded 26-Fe(CO)4, which loses a carbonyl, allowing the adjacent allene double
bond in 26-Fe(CO)3 to coordinate to iron and leave the phosphine oxide uncoordinated. In contrast, the BPMO, 26, and
(PhCN)2PdCl2 yield the phosphine-coordinated, chlorine-bridged dimer 34 and also the chelate 35, in which the palladium is linked
to both the diphenylphosphino and diphenylphosphinyl groups via phosphorus and oxygen, respectively. Surprisingly, chlor-
odiphenylphosphine and 1,4-bis(9-hydroxy-9H-fluorenyl)buta-1,3-diyne, 37, do not yield the expected 3,4-bis(phosphinyl)hexa-
1,2,4,5-tetraene, 33, but rather the 1-chloro-2-diphenylphosphinocyclobutene, 38, bearing a spiro-bonded fluorenylidene and a
fluorenylidene-allene. All new compounds were characterized by 31P NMR spectroscopy and X-ray crystallography.
’ INTRODUCTION
moieties possessing large wingspans, such as dibenzosuberenylidenes.5
In particular, we have focused on devising syntheses of fluor-
enylidene-containing allenyl-phosphines, 5, with the potential to
form dimers, 6 (as in Scheme 2), structurally analogous to the
1,2-di(fluorenylidene)cyclobutanes, 3 and 4.
The initially chosen molecule, 7, was readily prepared from the
precursor bromoallene by lithiation and subsequent treatment
with chlorodiphenylphosphine.6 However, the allenylphosphine
7 could not be induced to dimerize, presumably for steric reasons.
Nevertheless, 7 did furnish a novel, and in some cases surprising,
series of complexes, typified by molecules 8ꢀ11 in Scheme 3,
with chromium and iron carbonyls, and with gold and ruthenium
chlorides.6 Consequently, we chose to investigate allenylpho-
sphines bearing less sterically demanding substituents, and we
here describe our observations.
Our recent studies on the mechanism of formation of electro-
luminescent tetracenes from fluorenylidene-containing allenes,
1, revealed the sequential generation of a series of dimers.1 The ini-
tially formed head-to-tail dimers, 2, when thermolyzed, yielded
C2-symmetric 1,2-di(fluorenylidene)cyclobutanes, 3 and 4
(Scheme 1).2 In these tail-to-tail dimers, the very large wingspan
(∼8.8 Å) of the overlapping fluorenylidenes results in their
conrotation out of the plane of the cyclobutane. Moreover, the
helical sense of the trans-oriented substituents at C(3) and C(4)
can parallel that of the fluorenylidenes, as in 3, or oppose it, as in
the thermodynamically favored diastereomer, 4. In those cases
that we have characterized by X-ray crystallography, the dihedral
angle between the fluorenylidene planes is noticeably larger in
the latter case: for example, in 3 and 4 (R = Ph) these angles are
41° and 60°, respectively.1c
’ RESULTS AND DISCUSSION
There is enormous current interest in the use of enantiomeri-
cally pure C2-symmetric diphosphines as components of catalysts
for asymmetric synthesis3 (BINAP4 being a classic example), and
one of our goals is to prepare a series of such systems whereby the
positioning of the two phosphine centers is controlled by the
degree of overlap between fluorenylidenes, or other related
With the aim of preparing the minimally substituted
fluorenylidene-containing allenylphosphine, 12 (Scheme 4),
Received: April 27, 2011
Published: June 29, 2011
r
2011 American Chemical Society
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Scheme 1. Synthetic Route to Tetracenes via Allene Dimers
3,3-(biphenyl-2,20-diyl)-1-bromo-1-(trimethylsilyl)allene, 13,
was treated consecutively with n-butyllithium and chlorodiphe-
nylphosphine. The product isolated in 50% yield after chromato-
graphic separation was identified as the diphosphine 14, on the
basis of its 1H, 13C, and 31P NMR spectra, in conjunction with
microanalytical data. The 31P resonance at ꢀ2.9 ppm is in the
normal range for a tertiary diphenylphosphino moiety (see
Table 1), and the 13C spectrum of 14 (see Figure 1) exhibits
Scheme 2. Potential Dimerization of an Allenylphosphine
1:2:1 triplets at 105.4 (1JPꢀC = 40 Hz C(11)), 207.2 (2JPꢀC
=
1.7 Hz C(10)), and 105.2 ppm (3JPꢀC = 2.5 Hz C(9)), clearly
indicating the presence of two magnetically equivalent phosphi-
no substituents.
generate [μ2-H2CdC(PPh2)2]Fe2(CO)7, 21, which exhibits a
31P NMR singlet at 68.4 ppm.9 These data support the assign-
ment of the second product formed from diphosphine 14 and
iron carbonyl as the chelate 18, analogous to 20, rather than the
bridged system 21.
It is, of course, well established that multiple phosphino
groups can be introduced into the allene skeleton; repeated
lithiation and addition of Ph2PCl to Ph2PCtCꢀCH3 ultimately
furnishes tetrakis(diphenylphosphino)allene.7 Nevertheless, in
the present case a different mechanism appears to be operating.
As depicted in Scheme 4, the initial product is presumably the
silyl-phosphino allene 15, which then suffers attack at silicon by
the liberated chloride to generate Me3SiCl and the fluorenide-
stabilized anion 16; subsequent reaction with a second molecule
of chlorodiphenylphosphine yields the observed diphosphine 14.
The crucial factor appears to be the enhanced carbanion stability
provided by delocalization of the negative charge onto the
fluorenyl framework, thus generating a 14π aromatic system.
As depicted in Scheme 5, the diphosphine 14 reacted with di-
iron nonacarbonyl to form two products: the tetracarbonyliron
complex 17, whose 31P NMR spectrum exhibited 106 Hz
doublets at ꢀ5.9 ppm (noncomplexed phosphorus) and at
80.5 ppm (Fe-PPh2), closely analogous to the data previously
found for 10 (Fe-PPh2 at 79.8 ppm),6 and a second material, 18,
that exhibited a 31P NMR singlet at 39.1 ppm, implying forma-
tion of a system with symmetry-equivalent phosphorus environ-
ments. The most closely analogous system of which we are aware
involves the reaction of 1,1-bis(diphenylphosphino)ethene
(dppee) with Fe(CO)5/Me3NO to form two products. It was
found that [H2CdC(PPh2)2]Fe(CO)4, 19, exhibited 59 Hz
doublets at ꢀ10.8 ppm (noncomplexed phosphorus) and at
79.7 ppm (Fe-PPh2) and subsequently decomposed with loss of
a carbonyl to yield the chelate complex [k2-H2CdC(PPh2)2]Fe-
(CO)3, 20 (31P singlet at 41.5 ppm), which was unambiguously
identified by X-ray crystallography.8 Moreover, when heated with
di-iron nonacarbonyl, dppee behaves as a bridging ligand to
A second approach to introducing a phosphorus-containing
substituent into a fluorenylidene-allene involves treatment of a
9-alkynyl-9H-fluoren-9-ol with chlorodiphenylphosphine in the
presence of triethylamine to neutralize the liberated hydrogen
chloride. As shown in Scheme 6, the resulting [2,3] sigmatropic
shift of the Ph2PO fragment provides the conventional route to
allenyl phosphine oxides,10 which could be subsequently reduced
to the corresponding allenylphosphines. When 9-ethynyl-9H-
fluoren-9-ol, 22, was subjected to these conditions, two different
products were formed, dependent on the quantity of added
triethylamine. In the absence of excess Et3N, the desired product,
23, reacts with HCl to form the adduct 24, whose structure is
shown in Figure 2. Mechanistically, it is most reasonable to
postulate initial addition of chloride to 23; it has been reported
that allenes bearing electron-withdrawing substituents, such as
cyano or nitro, react directly with lithium chloride.11 In the
present case, the intermediate anion 25 can be stabilized by the
fluorenyl and/or the phosphinyl substituent, thus greatly facil-
itating addition of chloride.
In contrast, when the triethylamine is in excess, the product is
the allenyl bis-phosphine monoxide (BPMO) 26, whose struc-
ture is shown in Figure 3. Evidently, the phosphinylallene 23 is read-
ily deprotonated to form the stabilized anion 27, which reacts
with a second molecule of chlorodiphenylphosphine to yield
3,3-(biphenyl-2,20-diyl)-1-diphenylphosphino-1-(diphenylphos-
phinyl)allene, 26, which exhibits 31P NMR resonances at
25.4 ppm (Ph2PdO) and ꢀ6.2 (Ph2P). As listed in Table 1,
2
the JPꢀP(O) value of 88 Hz in 26 matches almost exactly the
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Scheme 3. Metal Complexes of the Allenylphosphine 7
Scheme 4. Proposed Mechanism for the Formation of Allenyldiphosphine 14
87 Hz coupling observed in the closely analogous system PhN-
CdC(PPh2)[P(O)Ph2], 28.12 Likewise, the 1JPꢀC and 1JP(O)-C
values of 52 and 90 Hz, respectively, in 26 compare well with the
corresponding coupling constants of 50 and 105 Hz in 28. The
sensitivity of the unsubstituted allenylphosphine oxide 23 toward
either chloride ion or triethylamine has thus far not allowed its
isolation, and attempts to trap the liberated HCl without using an
organic base are continuing. We note also that treatment of the
BPMO 26 with sulfur yields the corresponding phosphine
oxideꢀphosphine sulfide 29 (Scheme 6).
BPMOs generally involve either a specific mono-oxidation of a
diphosphine13 or deprotonation of a phosphine oxide possessing
an acidic hydrogen with an alkyllithium and subsequent treat-
ment with a chlorophosphine, as in Scheme 7.15 In effect, this
present approach is a modification of the latter route whereby
even a relatively weak base, such as triethylamine, serves to
deprotonate the initially generated phosphine oxide. The anion
so formed is particularly favored because it can be stabilized as an
aromatic 14π fluorenide system.
As noted above, the fluorenylidene-containing allenyl-mono-
phosphine 7 reacts with iron carbonyl to yield initially the iron
tetracarbonyl complex 10, which is very thermally sensitive and
readily loses a carbonyl, thus allowing the adjacent allene double
bond to coordinate to the newly available vacant site, as in 11.
Likewise, the initial product of the reaction of the BPMO, 26,
with di-iron nonacarbonyl is the tetracarbonyl complex 30, in
which the Fe(CO)4 moiety is bonded to the diphenylphosphino
substituent (Scheme 8). As in 10, the Fe(CO)4 fragment in 30 is
fluxional, and the 13CO NMR absorption is a 31P-coupled single
resonance. The 31P NMR spectrum of 30 exhibits peaks at
80.4 ppm for the Fe-PPh2 moiety and at 24.8 for the phosphinyl
Bis-phosphine monoxides are of considerable current interest
because of their ability to function as hemilabile ligands that
contain both soft (P) and hard (O) Lewis base centers in the
same molecule and to stabilize a range of transition metals in low
and high oxidation states. Moreover, BPMOs often form labile
chelates whereby a metal can be firmly bonded to one atom but
rather weakly attached to a second, thus allowing the reversible
generation of a vacant coordination site appropriate for catalytic
activity.13 In addition, several allenylphosphine oxides have
exhibited antitumor activity and other interesting applications
in DNA cleavage.14 Currently used synthetic methods to form
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Table 1. 31P NMR Data for Fluorenylidene-Containing Allenes and Related Moleculesabc
a This work. b Ph2PdS at 42.5 ppm. c Grim, S. O.; Walton, E. D. Inorg. Chem. 1980, 19, 1982ꢀ1987.
nonrotating on the NMR time scale and so exhibits three 13CO
NMR resonances, each with a different coupling constant to
2
13
phosphorus: δ(CO) = 211.8, 209.8, and 209.4, J(31Pꢀ C) =
15.7, 28.5, and 23.2 Hz, respectively.
Because of a minor crystallographic disorder, the only avail-
able crystals of 31 were not ideal, and so we cannot claim precise
geometric parameters; however, the atom connectivity shown in
Figure 4 is quite definitive. Interestingly, the preferential bonding
of an Fe(CO)2 moiety to the adjacent double bond of an allene
rather than formation of a diphosphine chelate has also been
observed by Wojcicki.16
The reaction of 26 with iron carbonyl also revealed a minor
side-product, 33, in very low yield, but sufficient to furnish an
X-ray quality crystal whose structure appears in Figure 5. Molecule
33 was characterized as s-trans-1,6-bis(biphenyl-2,20-diyl)-3,4-
bis(diphenylphosphinyl)-1,2,4,5-hexatetraene, in which the allenic
double bonds, C(9)dC(10) and C(10)dC(11), are not signifi-
cantly different, with values of 1.312(2) and 1.310(2) Å, respec-
tively. This contrasts with the situation previously found in the
closely analogous system trans-1,6-bis(biphenyl-2,20-diyl)-3,4-
bis(trimethylsilyl)-1,2,4,5-hexatetraene, whereby the corresponding
Figure 1. Section of the 101 MHz 13C NMR spectrum of 14 showing
the allenic carbons.
substituent, with a 2JPꢀP value of 10.6 Hz. Furthermore, there is
facile loss of a carbonyl ligand with concomitant formation of a
bond from the adjacent allene-double bond to Fe(CO)3 in 31
(rather than a Ph2PdOfFe(CO)3 linkage, as in 32). The
phosphinyl 31P NMR resonance is almost unchanged at 24.3 ppm,
but the Ph2PꢀFe absorption is now seen at 15.5 ppm, similar to
2
the chemical shift previously found in 11 (12.5 ppm); JPꢀP is
now 6.5 Hz. In 31, as with 11, the tricarbonyliron moiety is
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Scheme 5. Reactions of Allenyldiphosphine 14 and of dppee with Iron Carbonylsa
a 31P NMR shifts are in parentheses.
Scheme 6. Reaction of the Allenylphosphine Oxide 23 with HCl or Et3N
homolytic cleavage of the carbonꢀphosphorus linkage in 30 or
31; subsequent dimerization would lead directly to the bis-
(phosphinyl)-bis(allene) skeleton. Presumably, the correspond-
ing metal-containing product should be the phosphido-bridged
dimer (OC)3Fe(μ-PPh2)2Fe(CO)3,18 but this was not detectable.
It is relevant to note that the reaction of 1,1-bis(diphenyl-
phosphino)ethene or bis(diphenylphosphino)methane with iron
carbonyls also yields products derived from cleavage of carbonꢀ
phosphorus bonds.9,19
Bis-phosphine monoxide complexes of palladium have been exten-
sively studied, and their catalytic efficacy has been evaluated.20
Treatment of the BPMO 26 with bis(benzonitrile)palladium
dichloride yields two products. The minor product is the [(k1-P-
BPMO)PdCl2]2 chloride-bridged dimer 34 (Figure 6), in which
each PdCl2 fragment is bonded only to the diphenylphosphino
group, and neither the allene double bond nor the phosphinyl
substituent interacts with the metal centers. 31P NMR resonances
are seen at 34.7 ppm for the PdꢀP linkage and at 28.7 ppm
Figure 2. Molecular structure of 1,1-(biphenyl-2,20-diyl)-2-chloro-
3-(diphenylphosphinyl)propene, 24. Thermal ellipsoids are at 25%.
double bond distances are 1.318(2) and 1.306(2) Å.17 However,
the central C(11)ꢀC(110) single bond length is almost identical
in the two cases (1.493(3) vs 1.496(2) Å). One can only
speculate about the source of 33, which may have arisen via
2
for the noncoordinated phosphinyl unit with a JPꢀP value
of 19 Hz. The major product is the (k2-P,O-BPMO)PdCl2
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chelate 35, whose structure appears in Figure 7 and which
exhibits peaks at 34.6 and 56.3 ppm for the FeꢀP linkage and
for the coordinated phosphinyl unit, respectively; the 2JPꢀP value
is now 70 Hz.
In the chloride-bridged dimer 34, the PdꢀCl distances range
from 2.327 to 2.437 Å (bridging) and 2.2783(6) to 2.2825(6) Å
(terminal); the PdꢀP bond lengths are 2.2064(6) and 2.2169(6) Å,
and the PdO linkages are 1.481(2) and 1.482(2) Å. These may
be compared to the somewhat longer corresponding values of
2.357(1) and 2.387(1) Å (terminal PdꢀCl), 2.254(1) and
2.248(1) Å (PdꢀP), and 1.476(3) and 1.467(4) (PdO) Å in
cis-[(Me2P(O)-CH2-PMe2)2PdCl2 H2O], in which the phos-
3
phine oxides are also nonbonding.21
The structure of the chelate 35, compared to that of the dimer
34, reveals a number of interesting features. These include a
lengthening of the Ph2PꢀPd bond to 2.2246(5) Å, a noticeable
shortening of the C(11)ꢀP(O) carbonꢀphosphorus linkage
from 1.842(3) Å to 1.804(2) Å, and, of course, the establishment
of a PdꢀO bond (2.086(1) Å) together with the lengthening of
the PdO distance from 1.482(2) Å to 1.522(1) Å. The palla-
diumꢀchlorine bonds are now markedly different such that the
one trans to oxygen (2.2673(5) Å) is considerably shorter than
the PdꢀCl bond trans to phosphorus (2.3526(5) Å), as expected
for a linkage trans to a relatively weak PdꢀO bond. These data
may be compared to those reported for (dppmO)Pd(Me)Cl, for
which the PdꢀPandPdꢀO distances are 2.204(2) and 2.276(4) Å,
respectively, the PdO linkage is 1.508(4) Å, and the PdꢀCl
bond trans to phosphorus is 2.378(2) Å. As with 35, the central
carbonꢀP(O)Ph2 bond (1.796(6) Å) is noticeably shorter than
the carbonꢀPPh2 distance (1.834(6) Å).22 The pattern of
metalꢀchlorine bond lengths in 35 also parallels that seen in
other (k2-P,O-BPMO)MCl2 systems, M = Pd or Pt, whereby the
longer bond is trans to the phosphine.23 Moreover, as illustrated
in Figure 7, the asymmetric unit in 35 also contains a molecule of
chloroform that exhibits bifurcated hydrogen bonding to both of
the palladium-bonded chlorines.
Figure 3. Molecular structure of 3,3-(biphenyl-2,20-diyl)-1-diphenyl-
phosphino-1-(diphenylphosphinyl)allene, 26. Thermal ellipsoids are
at 20%.
Scheme 7. Conventional Route to Bis-phosphine-monoxides
Returning to the original goal of preparing a 1,2-bis
(fluorenylidene)-3,4-bis(phosphino)cyclobutane or -cyclobutene,
we noted the report by Cai and Blackburn that the bis-allenyl-bis-
phosphine oxide 36 is claimed to undergo cyclization upon
thermolysis (Scheme 9).24
Scheme 8. Metal Complexes of BPMO 26
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Figure 4. Structure of the (BPMO)Fe(CO)3 complex 31. Thermal
ellipsoids are at 30%.
Figure 7. Molecular structure of the (BPMO-k2-P,O)PdCl2 CHCl3
3
35. Thermal ellipsoids are at 50%. Selected distances (Å) and angles
(deg): PdꢀCl(1) 2.2673(5), PdꢀCl(2) 2.3526(5), PdꢀP(2) 2.2246(5),
PdꢀO 2.0858(12), P(1)ꢀO 1.5220(14), Cl(1)ꢀPd(1)ꢀCl(2) 92.7,
OꢀPdꢀP(2) 90.6, OꢀPdꢀCl(1) 176.4, P(2)ꢀPdꢀCl(2) 177.1,
OꢀPdꢀCl(2) 89.1, P(2)ꢀPdꢀCl(1) 87.7.
Scheme 9. Formation and Electrocyclization of 1,1,6,6-Tet-
ramethyl-3,4-bis(diethoxyphosphinyl)-1,2,4,5-hexatetraene,
3624
Figure 5. Molecular structure of s-trans-1,6-bis(biphenyl-2,20-diyl)-3,4-
bis(diphenylphosphinyl)-1,2,4,5-hexatetraene, 33. Thermal ellipsoids
are at 50%.
the diyne-diol 37 has not previously been reported, and since we
had crystals in hand, an X-ray study was undertaken. In fact, the
molecule crystallizes both with and without DMSO. In the for-
mer case (Figure 8), each hydroxyl group is hydrogen-bonded to
a molecule of the dimethyl sulfoxide solvent. In contrast, in the
absence of DMSO, the diols give rise to an infinite lattice
whereby the OH units from four different diyne-diol molecules
form hydrogen-bonded square arrays, as illustrated in Figure 9.
Figure 6. Molecular structure of the [(BPMO)PdCl2]2 34. Thermal
ellipsoids are at 50%. Selected distances (Å) and angles (deg): Pd(1)ꢀ
Cl(1) 2.2783(6), Pd(1)ꢀCl(2) 2.3272(6), Pd(1)ꢀCl(3) 2.4114(6),
Pd(2)ꢀCl(2) 2.4367(6), Pd(2)ꢀCl(3) 2.3303(6), Pd(2)ꢀCl(4)
2.2825(6), Pd(1)ꢀP(2) 2.2169(6), Pd(2)ꢀP(4) 2.2064(6), P(1)ꢀO-
(1) 1.482(2), P(3)ꢀO(2) 1.481(2), Cl(2)ꢀPd(1)ꢀCl(3) 91.4, Cl-
(2)ꢀPd(2)ꢀCl(3) 85.1, Pd(1)ꢀCl(2)ꢀPd(2) 92.8, Pd(1)ꢀCl(3)ꢀ
Pd(2) 93.3, P(1)ꢀC(11)ꢀP(2) 118.9.
The O O distances within these square arrays range from 2.69
3 3 3
to 2.72 Å, comparable to the values reported for other hydrogen-
bonded alkynol tetramers.27 In the DMSO solvate structure, there
is a clear alternation of single and triple bonds—C(9)ꢀC(10)
1.472(2) Å, C(10)ꢀC(11) 1.206(2) Å, C(11)ꢀC(12) 1.370(3) Å,
C(12)ꢀC(13) 1.204(3) Å, C(13)ꢀC(14) 1.481(2) Å—but
the angles along the C(9) to C(14) chain are all ∼177°, such
that the system is slightly bowed.
To this end, 1,4-bis(9-hydroxy-9H-fluorenyl)buta-1,3-diyne,
37, was prepared in 33% yield by the reaction of butyllithium
with hexachlorobutadiene with subsequent addition of fluore-
none. This one-pot route to diynes25 is more convenient than the
previously reported multistep palladium or copper coupling
procedures.26 Surprisingly perhaps, the molecular structure of
In the expectation of developing a rational, high-yield route to
trans-1,6-bis(biphenyl-2,20-diyl)-3,4-bis(diphenylphosphinyl)-
1,2,4,5-hexatetraene, 33, the diyne-diol 37 was subjected to the
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normal reaction conditions (chlorodiphenylphosphine/triethyla-
mine) for the conversion of an alkynol to an allenyl phosphine
oxide, as exemplified in Scheme 6. Out of the multiplicity of
products, one was isolated that appeared to contain an allene-
linked fluorenylidene together with chloro and diphenylpho-
sphinyl substituents. The structure was definitively identified by
X-ray crystallography as 38, in which the Ph2PdO moiety was
positioned between the chloro and spiro-fluorenylidene within a
cyclobutene ring (Figure 10). Both fluorenyls are almost exactly
orthogonal to the cyclobutene ring plane, in which the car-
bonꢀcarbon single-bond lengths vary quite substantially. The
ClꢀC(1)dC(2)ꢀP double bond is 1.352(2) Å, and the C(1)ꢀ
C(4) bond that connects the chlorine and allenyl substituents is
1.463(2) Å, but the other two single bonds, C(2)ꢀC(3) and
C(3)ꢀC(4), are much longer at 1.565(2) and 1.569(2) Å,
respectively. Moreover, in the allenyl fragment, the carbonꢀ
carbon double bonds are also significantly different: C(4)ꢀC(5)
1.296(2) Å and C(5)ꢀC(6) 1.321(2) Å.
sigmatropic rearrangement to yield the allenylphosphine oxide
39, with subsequent attack by chloride on cation 40 and electro-
cyclization of the cumulene 41, leads to the incorrect isomer, 42
(Scheme 10). Instead, one has to envisage formation of a four-
membered ring, 43, that suffers attack by chloride; Arbusov-type
ring-opening furnishes the appropriate cumulene, 44, that, after
bond rotation, is ideally poised for electrocyclization to the
observed product, 38. We note that 1-phosphinylcyclobutene
opens to the 2-phosphinyl-1,3-butadiene only at elevated tem-
peratures to give DielsꢀAlder adducts, thus demonstrating that
the cyclic isomer is thermodynamically favored.28 Interestingly,
2,3-bis(diphenylphosphinyl)-1,3-butadiene favors the open
chain form.29
In the context of Baldwin’s rules,30 formation of the allenyl-
phosphine oxide 39 would occur via a 5-endo-dig process, where-
as the route to the observed product 38, via 43, apparently
requires the normally disfavored 4-exo-dig cyclization. However,
the latter process has been observed in a number of cyclo-
carbopalladations;31 moreover, numerous exceptions to Baldwin’s
rules are known for cationic and radical systems32 and especially
for reactions in which a second-row element is included in the
ring.33 Interestingly, a comprehensive study combining DFT
calculations with Marcus theory indicated clearly that 4-exo-dig
radical cyclizations are kinetically competitive with the 5-endo-dig
process, but are less favorable thermodynamically.34
The isolation of such a novel molecule poses an interesting
mechanistic question. The most obvious proposal, an initial [2,3]
To conclude, attempts to synthesize 3,3-(biphenyl-2,20-diyl)-
1-diphenylphosphinoallene, 12, and 3,3-(biphenyl-2,20-diyl)-1-
diphenylphosphinylallene, 23, led instead to 3,3-(biphenyl-2,
20-diyl)-1,1-bis(diphenylphosphino)allene, 14, and 3,3-(biphenyl-
2,20-diyl)-1-diphenylphosphino-1-diphenylphosphinylallene, 26,
respectively, in each case via an aromatic fluorenide-stabilized
anion. These ligands react with iron carbonyl to form initially the
phosphine-coordinated Fe(CO)4 complexes 17 and 30, respec-
tively, which readily lose carbon monoxide. In the former case,
the product is the chelate 18, whereas in the BPMO the Fe(CO)3
unit coordinates to the adjacent double bond of the allene rather
than to the phosphinyl oxygen. However, the BPMO 26 and
Figure 8. Molecular structure of 1,4-bis(9-hydroxy-9H-fluorenyl)buta-
1,3-diyne, 37 DMSO, showing hydrogen bonding to the solvent.
3
Thermal ellipsoids are at 50%.
Figure 9. Section of the packing motif of the solvent-free diyne-diol 37, showing the square arrays arising from the intermolecular hydrogen bonding
between (OH)4 moieties.
3811
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Organometallics
ARTICLE
(PhCN)2PdCl2 yield the phosphine-coordinated, chlorine-
bridged dimer 34 and also the (k2-P,O-BPMO)PdCl2 chelate
35, in which the palladium is linked to both the diphenylpho-
sphino and diphenylphosphinyl groups via phosphorus and
oxygen, respectively. The catalytic potential of this system, which
bears a hemilabile BPMO ligand, has yet to be explored.
C2-symmetry resulting from overlapping substituents with large
wingspans, is formed in very low yield, apparently by decom-
position of 30, the monocoordinated Fe(CO)4 derivative of the
BPMO 30. An attempted rational synthesis of 33 by reaction of
chlorodiphenylphosphine and 1,4-bis(9-hydroxy-9H-fluore-
nyl)buta-1,3-diyne, 37, did not yield the expected product, but
rather the 1-chloro-2-diphenylphosphinocyclobutene 38, bear-
ing a spiro-bonded fluorenylidene and a fluorenylidene-allene.
The bis-allene 3,4-bis(diphenylphosphinyl)hexa-1,2,4,5-tetra-
ene, 33, a possible precursor to a cyclobutane-diphosphine with
’ EXPERIMENTAL SECTION
General Methods. All reactions were carried under a nitrogen
atmosphere, and solvents were dried by standard procedures. 1H, 13C,
and 31P NMR spectra were recorded on Varian Inova 300 or 400 MHz or
VNMRS 500 or 600 MHz spectrometers. Assignments were based on
standard two-dimensional NMR techniques (1Hꢀ H COSY, 1Hꢀ C
HSQC, HMBC, NOESY). Infrared spectra were recorded on a Perkin-
Elmer Paragon 1000 FT-IR spectrometer and were calibrated with
polystyrene. Electrospray mass spectrometry was performed on a
Micromass Quattro microinstrument. Merck silica gel 60 (230ꢀ400
mesh) was used for flash chromatography. Melting points were deter-
mined on an Electrothermal ENG instrument and are uncorrected.
1
13
Figure 10. Molecular structure of the cyclobutene 38.
Scheme 10. Proposed Mechanism for the Formation of Cyclobutene 38
3812
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Organometallics
ARTICLE
Elemental analyses were carried out by the Microanalytical Laboratory
at University College Dublin. 3,3-(Biphenyl-2,20-diyl)-1-bromo-1-
trimethylsilylallene, 13, and 9-ethynyl-9H-fluoren-9-ol, 22, were prepared
as previously described.2a
C27H20POCl 0.5CH3CO2C2H5: C, 73.96; H, 5.14. Found: C, 74.45;
H, 5.31.
3
Synthesis of 3,3-(Biphenyl-2,20-diyl)-1-(diphenylphos-
phino)-1-(diphenylphosphinyl)allene (26). Triethylamine (620 μL,
4.45 mmol) was added to a solution of 9-ethynyl-9H-fluoren-9-ol (420 mg,
2.04 mmol) in dry dichloromethane (4 mL) and pentane (21 mL).
Chlorodiphenylphosphine (820 μL, 4.44 mmol) was then added slowly at
0 °C and stirred for 15 min. After stirring for 1 h at room temperature, the
mixture was extracted twice with dichloromethane, and the organic layers
were combined, washed with water and brine, dried over MgSO4, filtered,
and concentrated to give an orange oil, which was purified by chromatog-
raphy on a silica column using pentane/ethyl acetate as eluent to give
3,3-(biphenyl-2,20-diyl)-1-(diphenylphosphino)-1-(diphenylphosphinyl)-
allene, 26 (945 mg, 1.64 mmol; 81%), as a white powder. A sample of 26
suitable for an X-ray crystal structure determination was obtained by
recrystallization from ethyl acetate/pentane. 1H NMR (500 MHz, CDCl3):
δ 7.81 (dd, J = 7.1 Hz, J = 1.2 Hz, 2H), 7.79 (dd, J = 7.1 Hz,
J = 1.2 Hz, 2H), 7.59 (d, J = 7.5 Hz, 2H), 7.44 (dt, J = 7.9 Hz, J = 1.2
Hz, 4H), 7.40 (td, J = 7.3 Hz, J = 1.3 Hz, 2H), 7.31 (t, J = 7.5 Hz, 2H), 7.30
(t, J = 7.5 Hz, 2H), 7.26 (t, J = 7.4 Hz, 2H), 7.19ꢀ7.08 (m, 10H). 13C NMR
(125 MHz, CDCl3): δ 210.9 (t, 2J CꢀP = 2.1 Hz, C10), 138.1 (d, J = 0.7 Hz,
ipso-Ph), 136.5 (d, J = 5.8 Hz, ipso-Ph), 135.3 (dd, J = 15.1 Hz, J = 4.3 Hz,
ipso-Ph), 134.0 (s, 2 aromatic CH), 133.8 (s, 2 aromatic CH), 133.0, 132.2
(C4a, C4b, C8a, C9a), 132.1 (d, J = 2.9 Hz, 2 aromatic CH), 131.8 (s, 2
aromatic CH), 131.6 (s, 2 aromatic CH), 129.3 (s, 2 aromatic CH), 128.5 (s,
2 aromatic CH), 128.4 (d, J = 2.7 Hz, 4 aromatic CH), 128.3 (s, 2 aromatic
CH), 128.1 (d, J = 1.0 Hz, 2 aromatic CH), 126.9 (d, J = 0.8 Hz, 2 aromatic
CH), 123.0 (d, J = 1.5 Hz, 2 aromatic CH), 120.3 (s, J = 0.6 Hz, 2 aromatic
CH), 106.4 (dd, 1JCꢀP =90.3and51.7Hz, C11), 106.3 (dd, 3JCꢀP =12.7and
1.3 Hz, C9). 31P NMR (121 MHz, CDCl3): δ 25.4 (dp, 2JPꢀP = 88.0 Hz,
3JPꢀH = 12.5 Hz, P(O)Ph2), ꢀ6.2 (dp, 2JPꢀP = 88.0 Hz, 3JPꢀH = 8.0 Hz,
PPh2). IR (CH2Cl2): 1916 (CdCdC), 1263 cmꢀ1 (PdO). ESMS: calcd
for C39H29OP2 [M + H+], 575.19; found 575.15. Anal. Calcd for
Synthesis of 3,3-(Biphenyl-2,20-diyl)-1,1-bis(diphenyl-
phosphino)allene (14). A solution of 3,3-(biphenyl-2,20-diyl)-1-
bromo-1-trimethylsilylallene (876 mg, 2.57 mmol) in dry THF (12 mL)
was added very slowly at ꢀ78 °C to a solution of nBuLi (1.76 mL, 1.6 M
in hexane, 2.82 mmol) in dry THF (10 mL). After stirring for 10 min at
ꢀ78 °C, chlorodiphenylphosphine (1.11 mL, 5.9 mmol) was slowly
added. The mixture was allowed to warm slowly to room temperature
and stirred overnight. After quenching with water and removing the
solvent, the crude material was extracted three times with dichloro-
methane. The organic layers were combined, washed with water and
brine, and dried over MgSO4, and the filtrate was concentrated to give a
dark yellow oil. The oil was purified by chromatography on a silica
column using dichloromethane/pentane as eluent to give 3,3-(biphenyl-
2,20-diyl)-1,1-bis(diphenylphosphino)allene, 14 (712 mg, 1.27 mmol;
50%), as a white solid. 1H NMR (400 MHz, CDCl3): δ 7.61ꢀ7.58 (m,
2H), 7.51ꢀ7.46 (m, 8H), 7.26ꢀ7.13 (m, 18H). 13C NMR (101 MHz,
CDCl3): δ 207.2 (t, 2JPꢀC = 1.7 Hz, C10), 137.65, 137.64 (fluorenyl-C),
135.7 (t, J = 4.9 Hz, phenyl ipso-C), 134.0 (t, J = 10.7 Hz, phenyl o-C),
129.3 (phenyl p-C), 128.3 (t, J = 3.7 Hz, phenyl m-C), 127.2, 126.57,
1
122.61, 120.0 (fluorenyl-CH), 105.4 (t, JPꢀC = 40.1 Hz, C11), 105.2
3
(t, JPꢀC = 2.5 Hz, C9). 31P{1H} NMR (162 MHz, CDCl3): δ ꢀ2.9
(s, PPh2). IR (CH2Cl2): 1909 cmꢀ1 (CdCdC). Anal. Calcd for
C39H28P2 0.5THF: C, 82.80; H, 5.43; P, 10.42. Found: C, 82.86; H,
3
5.24; P, 9.92.
Syntheses of [3,3-(Biphenyl-2,20-diyl)-1,1-bis(diphenylphos-
phino)allene]-Fe(CO)4 (17) and -Fe(CO)3 (18). Diiron-nonacar-
bonyl (74 mg, 0.203 mmol) and 3,3-(biphenyl-2,20-diyl)-1-bis-
(diphenylphosphine)allene, 37 (94 mg, 0.168 mmol), were dissolved
in dry THF (9 mL) and stirred for 5 days at room temperature under a
nitrogen atmosphere. The solvent was removed in vacuo, and the red
residual solid was filtered through silica with ethyl acetate. Total
conversion of the starting material into the major products 17 and 18
(ratio 5:2, respectively) was confirmed by 31P NMR. It was then purified
by chromatography on a silica column using ethyl acetate/pentane, to
yield 17 (23 mg, 0.032 mmol; 19%) and 18 (10 mg, 0.014 mmol; 8%) as
very air-sensitive, yellow and red solids, respectively. Data for 17:
31P{1H} NMR (162 MHz, CDCl3) δ 80.5 (d, J = 106, Ph2P-Fe(CO)4),
ꢀ5.9 (d, J = 106 Hz, PPh2). Data for 18: 31P{1H} NMR (162 MHz,
CDCl3) δ 39.1 (s, Ph2P-Fe(CO)3-PPh2).
C39H28OP2 0.5CH3CO2C2H5: C, 79.60; H, 5.21. Found: C, 79.74; H, 5.40.
3
Synthesis of 3,3-(Biphenyl-2,20-diyl)-1-(diphenylphos-
phinyl)-1-(diphenylthiophosphinyl)allene (29). The BPMO 26
(84 mg, 0.146 mmol) and sulfur (375 mg, 1.46 mmol) were stirred in dry
toluene (13 mL) at room temperature for 46 h under a nitrogen
atmosphere. The solvent was removed under vacuum, and the yellow
residue was purified by column chromatography using ethyl acetate/
pentane as eluent to give 29 (85 mg, 0.140 mmol; 96%) as a beige
powder. 1H NMR (400 MHz, CDCl3): δ 8.00 (d, J = 7.0 Hz, 2H), 7.96
(d, J = 7.1 Hz, 2H), 7.77 (d, J = 7.2 Hz, 2H), 7.74 (d, J = 7.3 Hz, 2H), 7.55
(d, J = 7.3 Hz, 2H), 7.37ꢀ7.31 (m, 4H), 7.31ꢀ7.22 (m, 12H), 7.19 (td,
J = 7.5 Hz, J = 0.9 Hz, 2H). 31P{1H} NMR (162 MHz, CDCl3): δ 42.5
(d, 2JPꢀP = 24.0 Hz, P(S)Ph2), 25.6 (d, J = 24.0 Hz, P(O)Ph2). ESMS:
calcd for C39H29OSP2 [M + H+], 607.16; found 607.12. IR (CH2Cl2):
1919 (CdCdC), 1259 cmꢀ1 (PdO).
Synthesis of 1,1-(Biphenyl-2,20-diyl)-2-chloro-3-(diphenyl-
phosphinyl)propene (24). Triethylamine (90 μL, 0.63 mmol) was
added to a solution of 9-ethynyl-9H-fluoren-9-ol (100 mg, 0.49 mmol)
in dry dichloromethane (10 mL) at room temperature. Chlorodiphe-
nylphosphine (100 μL, 0.54 mmol) was then added slowly, and after
stirring at room temperature for 2.5 h, water was poured onto the yellow
mixture. The solution was extracted twice with dichloromethane, and
the organic layers were combined, washed with water and brine, dried
over MgSO4, filtered, and concentrated to give a green-yellow oil. The
oil was purified by chromatography on a silica column using dichlor-
omethane/ethyl acetate as eluent to give 1,2-(biphenyl-2,20-diyl)-2-
chloro-3-(diphenylphosphinyl)propene, 24 (66 mg, 0.16 mmol; 32%),
as a white powder, mp 180.5ꢀ181.5 °C, and recovered 9-ethynyl-9H-
fluoren-9-ol (40 mg, 0.19 mmol; 40%). A sample of 24 suitable for an
X-ray crystal structure determination was obtained by recrystallization
from dichloromethane/pentane. 1H NMR (500 MHz, CDCl3): δ 8.35
(d, 1H, J = 8.0 Hz), 7.91 (d, 1H, J = 8.0 Hz), 7.90ꢀ7.85 (m, 4H), 7.66 (d,
1H, J = 7.5 Hz), 7.64 (d, 1H, J = 7.5 Hz), 7.55ꢀ7.51 (m, 2H), 7.48ꢀ7.4
(m, 4H), 7.34 (t, 1H, J = 7.5 Hz), 7.31 (t, 1H, J = 7.5 Hz), 7.25 (t, 1H, J =
Reaction of BPMO 26 with Fe2(CO)9. Diiron-nonacarbonyl
(192 mg, 0.653 mmol) and the BPMO 26 (125 mg, 0.218 mmol) were
dissolved in dry THF (8 mL) and stirred for 7 days at room temperature
under a nitrogen atmosphere. Total conversion of the starting material
into 30 and 31 (ratio 85:15, respectively) was confirmed by 31P NMR.
The solvent was removed in vacuo, and the red-green residual solid was
filtered through silica with ethyl acetate. It was then purified by chro-
matography on a silica column using ethyl acetate/pentane to yield 30
(39 mg, 0.053 mmol; 24%) as a yellow solid and 31 (11 mg, 0.015 mmol;
7%) as an orange solid. In the solid state, the tetracarbonyl complex 30 is
stable below 0 °C; however, when dissolved in CDCl3 at room
temperature, 30 rapidly evolved into 31. Moreover, when an NMR
sample containing a mixture of 30 and 31 was left for several days, it
yielded a small quantity of trans-1,6-bis(biphenyl-2,20-diyl)-3,4-bis-
(diphenylphosphinyl)-1,2,4,5-hexatetraene, 33, as colorless crystals.
Samples of 31 and 33 suitable for X-ray crystal structure determinations
2
7.5 Hz), 7.20 (t, 1H, J = 7.5 Hz), 4.33 (d, 2H, JPꢀH = 14.7 Hz). 31P
NMR (121 MHz, CDCl3): δ 27.9 (t, 2JPꢀH = 13 Hz). Anal. Calcd for
3813
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Organometallics
ARTICLE
Table 2. Crystallographic Data for 24, 26, 31, 33, and 34
24
26
31
33
34
formula
M
C
27H20OClP
C39H28O1.06P2
575.45
C42H28FeO4P2
714.43
C54H36O2P2 2CHCl3
(C78H56O2P4Cl4Pd2)2 5CHCl3
3
3
426.85
1017.50
3604.26
cryst syst
space group
a [Å]
monoclinic
C2/c (#15)
42.332(4)
5.5148(5)
41.938(4)
90
monoclinic
C2/c (#15)
18.3202(16)
10.6458(9)
16.8451(14)
90
triclinic
monoclinic
P21/c (#14)
9.7769(9)
12.4243(12)
19.6343(18)
90
triclinic
P1 (#2)
P1 (#2)
10.7362(11)
10.7918(11)
16.2959(17)
100.162(3)
106.620(3)
104.711(3)
1685.5(3)
2
10.4539(3)
12.5942(3)
29.1459(7)
84.129(2)
87.199(2)
81.094(2)
3769.03(17)
1
b [Å]
c [Å]
R [deg]
β [deg]
γ [deg]
V [Å3]
Z
120.266(2)
90
111.483(2)
90
93.615(2)
90
8455.9(14)
16
3057.1(5)
4
2380.3(4)
2
F
calcd [g cmꢀ3
]
1.341
1.250
1.408
1.420
1.588
T [K]
293(2)
293(2)
100(2)
100(2)
100(2)
μ [mmꢀ1
]
0.273
0.173
0.586
0.472
8.785
F(000)
3552
1201.6
736
1044
1810
θ range for data collection [deg]
1.11 to 21.15
ꢀ42 e h e 42
ꢀ5 e k e 5
ꢀ42 e l e 41
21 460
2.37 to 26.42
ꢀ22 e h e 22
ꢀ13 e k e 13
ꢀ21 e l e 21
26 395
1.35 to 20.85
ꢀ10 e h e 10
ꢀ10 e k e 10
ꢀ16 e l e 16
7958
2.08 to 26.47
ꢀ12 e h e 12
ꢀ15 e k e 15
ꢀ24 e l e 24
41 568
3.57 to 76.97
ꢀ13 e h e 13
ꢀ15 e k e 15
ꢀ36 e l e 36
75 669
index ranges
reflns measd
indep reflns
4616
3117
3538
4879
15 282
Rint
0.0331
0.0423
0.0323
0.0386
4879/3/387a
0.0447
data/restraints/params
4616/166/541
3117/46/252
3559/0/495
15 282/0/919
final R values [I > 2θ(I)]:
R1
0.0429
0.0952
0.0448
0.1177
0.0827
0.1702
0.0369
0.0910
0.0310
0.0805
wR2
R values (all data):
R1
0.0515
0.0997
1.091
0.0476
0.1194
1.130
0.0906
0.1745
1.199
0.0424
0.0945
1.037
0.0385
0.0830
1.064
wR2
GOF on F2
a The minor disorder part of the solvent was restrained to be regular using SADI.
were obtained by recrystallization from chloroform. Data for30: 1H NMR
(300 MHz, CDCl3): δ 7.96ꢀ7.85 (m, 4H), 7.68ꢀ7.57 (m, 6H), 7.38ꢀ
7.27 (m, 10H), 7.23ꢀ7.11 (m, 8H). 13C NMR (101 MHz, CDCl3): δ
216.7 (C10), 213.2 (d, J = 18.2 Hz, 3 CO), 138.6 (C4a, C4b), 135.6 (dd, J =
10.8 and 5.1 Hz, C8a, C9a), 133.8, 133.7, 133.2 (d, J = 11.6 Hz), 133.1,
132.6 (d, J = 3.2 Hz), 131.9 (d, J = 1.8 Hz), 131.5 (dd, J = 16.9 Hz, J = 8.3
Hz), 131.2, 131.2, 131.1, 131.1, 128.9, 128.3, 128.3, 128.2, 128.2, 127.3,
124.0, 120.4, 109.4 (pseudot, J= 12.5Hz, C9), 106.6 (dd, J =74.5and21.2
Hz, C11). 31P{1H} NMR (162 MHz, CDCl3): δ 80.4 (d, J = 10.5 Hz,
PPh2), 24.8 (d, J = 10.6 Hz, P(O)Ph2). IR (CH2Cl2): 2047, 1978, 1933
(CtO), 1280 cmꢀ1 (PdO). Data for 31: 1H NMR (500 MHz, CDCl3):
δ 8.15 (d, J = 7.6 Hz, 1H), 8.11 (d, J = 7.0 Hz, 1H), 8.06 (d, J = 7.9 Hz,
1H), 8.04 (d, J = 7.5 Hz, 1H), 7.86ꢀ7.77 (m, 1H), 7.71 (d, J = 7.3 Hz,
1H), 7.69 (d, J = 7.6 Hz, 1H), 7.64 (d, J = 7.7 Hz, 2H), 7.62 (d, J = 7.7 Hz,
1H), 7.53 (d, J = 7.2 Hz, 1H), 7.50 (d, J = 7.4 Hz, 1H), 7.48 (d, J = 8.7
Hz, 2H), 7.36 (td, J = 7.9 Hz, J = 2.9 Hz, 2H), 7.32 (t, J = 7.5 Hz, 2H), 7.22
(t, J = 7.5 Hz, 1H), 7.17ꢀ7.06 (m, 7H), 6.95 (td, J = 7.8 Hz, J = 3.3 Hz,
2H). 13C NMR (126 MHz, CDCl3): δ 211.8 (d, J = 15.7 Hz, CO), 209.8
(d, J = 28.5 Hz, CO), 209.4(d, J =23.2Hz, CO), 159.5(dd, J= 13.5Hz, J =
5.6 Hz, C10), 140.1, 139.7 (d, J = 4.4 Hz), 137.0(d, J = 6.0 Hz), 136.5 (C4a,
C4b, C8a, C9a), 135.6 (d, J = 11.4 Hz), 133.5, 133.2 (d, J = 11.4 Hz), 132.6,
132.4 (d, J = 3.0 Hz), 132.3 (d, J = 9.0 Hz), 131.9, 131.7 (d, J = 2.0 Hz),
131.5 (d, J = 2.0 Hz), 131.4 (d, J = 2.0 Hz), 131.2 (d, J = 9.0 Hz), 131.1,
128.8 (d, J = 12.3 Hz), 128.6 (d, J = 12.3 Hz), 128.1 (d, J = 12.3 Hz), 127.8
(d, J = 12.3 Hz), 126.6, 126.4, 126.3, 126.2, 126.1, 126.0, 125.4, 124.9 (d,
J = 11.5 Hz), 124.6, 124.1, 123.4, 121.6, 119.4, 118.8 (C1, C4, C5, C8), 31.8
(dd, J = 60.5 Hz, J = 51.8 Hz, C11). 31P{1H} NMR (162 MHz, CDCl3): δ
24.3 (d, J = 6.5 Hz, P(O)Ph2), 15.5 (d, J = 6.5 Hz, PPh2). IR (CH2Cl2):
2047, 1980 (CtO), 1263 cmꢀ1 (PdO).
Reaction of BPMO 26 with (PhCN)2PdCl2. To a solution of
BPMO 26 (99 mg, 0.174 mmol) in dry dichloromethane (8 mL) was added
at once solid dichlorobis(benzonitrile)palladium(II) (66 mg, 0.174 mmol).
After stirring the mixture for 1 h at room temperature, the volatiles were
removed. The orange-yellow residue was washed with a small amount of
ether and then pentane to give 35 (101 mg, 0.133 mmol; 76%) as a shiny
orange powder. It slowly decomposed to yield the dimer 34 (25 mg,
0.017 mmol; 19%) as a yellow-orange powder. Samples of 34 and 35
suitable for X-ray crystal structure determinations were obtained by
recrystallization from chloroform. Data for 34: 31P{1H} NMR (162
MHz, CDCl3): δ 34.7 (pseudo t, J = 19 Hz, PPh2), 28.7 (pseudo t, J = 19
Hz, P(O)Ph2). IR (liquid, CH2Cl2): 1920 cmꢀ1 (CdCdC). Anal.
Calcd for C78H56Cl4O2P4Pd2 CHCl3: C, 58.46; H, 3.54. Found: C,
3
58.95; H, 3.40. Data for 35: 31P{1H} NMR (162 MHz, CDCl3): δ 56.3
(d, J = 70 Hz, P(O)Ph2), 34.6 (d, J = 70.0 Hz, PPh2). IR (CH2Cl2):
1921 cmꢀ1 (CdCdC). Anal. Calcd for C39H28Cl2OP2Pd CHCl3: C,
3
55.14; H, 3.35. Found: C, 55.62; H, 3.73.
3814
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Organometallics
ARTICLE
Table 3. Crystallographic Data for 35, 37, 37 DMSO, and 38
3
35
37
37 DMSO
38
3
formula
M
C
39H28OP2Cl2Pd 2CHCl3
C30H18O2
410.44
2(C30H18O2) 5(CH3)2SO
C42H26OPCl
613.05
3
3
990.59
1211.53
cryst syst
space group
a [Å]
monoclinic
P21/n (#14)
9.4807(3)
14.3847(4)
30.6171(9)
90
triclinic
orthorhombic
Pca21 (#29)
24.2699(1)
8.90511(6)
29.1073(2)
90
triclinic
P1 (#2)
P1 (#2)
11.5523(4)
11.9264(4)
17.1040(6)
104.621(3)
98.828(3)
101.907(3)
2177.95(13)
4
9.8854(4)
12.6342(7)
13.3036(6)
84.502(4)
78.088(4)
69.495(5)
1522.26(12)
2
b [Å]
c [Å]
R [deg]
β [deg]
γ [deg]
V [Å3]
Z
97.547(3)
90
90
90
4139.3(2)
4
6290.85(7)
4
F
calcd [g cmꢀ3
]
1.590
1.252
1.279
1.337
T [K]
100(2)
160(2)
100(2)
100(2)
μ [mmꢀ1
]
1.075
0.609
2.157
0.213
F(000)
1984
856
2552
636
θ range for data collection [deg]
3.45 to 29.60
ꢀ13 e h e 12
ꢀ19 e k e 19
ꢀ41 e l e 39
40 627
3.96 to 65.00
ꢀ10 e h e 13
ꢀ13 e k e 14
ꢀ20 e l e 18
14 998
3.64 to 76.47
ꢀ30 e h e 30
ꢀ7 e k e 10
ꢀ36 e l e 30
35 889
3.41 to 30.00
ꢀ13 e h e 13
ꢀ17 e k e 15
ꢀ17 e l e 18
18 428
index ranges
reflns measd
indep reflns
10 330
7399
10 869
8854
Rint
0.0363
0.0207
0.0243
0.0307
data/restraints/params
10 330/0/478
7399/0/593
10 869/10/828
8854/0/406
final R values [I > 2θ(I)]:
R1
0.0307
0.0707
0.0355
0.0901
0.0321
0.0843
0.0406
0.1086
wR2
R values (all data):
R1
0.0433
0.0737
1.069
0.0456
0.0959
1.046
0.0331
0.0850
1.055
0.0529
0.1126
1.081
wR2
GOF on F2
Synthesis of 1,4-Bis(9-hydroxy-9H-fluorenyl)buta-1,3-diyne
(37). nBuLi (19 mL, 30 mmol) was added dropwise onto a solution of
hexachlorobutadiene (1.95 g, 7.44 mmol) in dry THF (30 mL) at
ꢀ78 °C, turning the solution black immediately. After stirring at ꢀ80 to
ꢀ60 °C for 1.5 h, the solution was cooled again to ꢀ78 °C, and a
solution of fluorenone (2.81 g, 15.6 mmol) in dry THF (2 ꢁ 10 mL) was
added dropwise over 20 min. The black-yellow solution was allowed to
warm slowly to room temperature overnight. After stirring for 40 h at
room temperature, the solution was concentrated, then extracted with
ether several times. The ethereal fractions were combined, washed with
water and brine, dried over MgSO4, filtered, and concentrated to yield a
beige solid. This was purified by chromatography on a silica gel column
using dichloromethane as eluent to recover the excess fluorenone and
then with pentane/ethyl acetate/methanol (12:8:1) as the second eluent
to give 1,4-bis(9-hydroxy-9H-fluorenyl)buta-1,3-diyne, 59 (1.01 g, 2.46
124.5, 120.5 (fluorenyl ꢀCH), 79.5 (C10, C11), 67.4 (C9). ESMS: calcd
for C30H17O [M + H ꢀ H2O+], 393.12; found 393.12; calcd for
[M + Na+], 433.12; found 433.10.
Synthesis of Cyclobutene (38). Triethylamine (180 μL, 1.29
mmol) and 1,4-bis(9-hydroxy-9H-fluorenyl)buta-1,3-diyne (182 mg,
0.443 mmol) were suspended in dry dichloromethane (12 mL) and
cooled to ꢀ50 °C. Chlorodiphenylphosphine (240 μL, 1.29 mmol) was
then added slowly, and the orange mixture was stirred for 15 min at
ꢀ40 °C, then slowly warmed to room temperature overnight. After
stirring for 15 h at room temperature, the mixture was quenched with
sodium bicarbonate, washed with water and brine, dried over MgSO4,
filtered, and concentrated to give a dark red-purple solid. It was purified
by chromatography on a silica column using pentane/ethyl acetate as
eluent to give the cyclobutene 38 (10 mg, 0.016 mmol; 4%) as a white
powder. A sample suitable for an X-ray crystal structure determination
was obtained by recrystallization from ethyl acetate/pentane. 1H NMR
(400 MHz, CDCl3): δ 7.73 (d, 2H, J = 7.1 Hz), 7.67ꢀ7.61 (m, 1H), 7.58
(d, 2H, J = 7.5 Hz), 7.54ꢀ7.46 (m, 2H), 7.43ꢀ731 (m, 10H), 7.30ꢀ7.23
(m, 4H), 7.22ꢀ7.16 (m, 7H). 31P{1H} NMR (121 MHz, CDCl3): δ
15.4 (s, P(O)Ph2). IR (CH2Cl2): 1918 cmꢀ1 (CdCdC). ESMS: calcd
for C42H27ClOP [M + H+], 613.14; found 613.12.
mmol; 33%), as a white solid. Samples of 37 and 37 DMSO suitable for
3
X-ray crystal structure determinations were obtained by recrystallization
1
from chloroform and dimethylsulfoxide, respectively. Data for 37: H
NMR (500 MHz, DMSO-d6): δ 7.77 (d, 4H, J = 7.5 Hz), 7.61 (d, 4H, J =
7.5 Hz), 7.42 (td, 4H, J = 7.5 Hz, J = 1.0 Hz), 7.34 (td, 4H, J = 7.5 Hz, J =
1.0 Hz), 6.84 (s, 2H, ꢀOH). 1H NMR (500 MHz, CDCl3): δ 7.64 (d,
4H, J = 7.5 Hz), 7.60 (d, 4H, J = 7.5 Hz), 7.39 (td, 4H, J = 7.5 Hz, J = 1.0
Hz), 7.32 (td, 4H, J = 7.5 Hz, J = 1.0 Hz), 2.49 (s, 2H, ꢀOH). 13C NMR
(126 MHz, CDCl3): δ 146.1, 139.3 (C4a, C4b, C8a, C9a), 130.2, 128.8,
X-ray Measurements for 24, 26, 33, 34, 35, 37, 37 DMSO,
and 38. Crystallographic data for 24, 26, and 33 were collected on a
3
Bruker SMART APEX CCD area detector diffractometer equipped with
3815
dx.doi.org/10.1021/om200357v |Organometallics 2011, 30, 3804–3817

Organometallics
ARTICLE
a Bruker SMART 1K CCD area detector (employing the program
SMART35) using graphite-monochromated Mo KR radiation (λ =
0.71073 Å) and are listed in Tables 2 and 3 A full sphere of the recip-
rocal space was scanned by phi-omega scans. Data processing was carried
out by use of the program SAINT,36 while the program SADABS37 was
utilized for the scaling of diffraction data and an empirical absorption
correction based on redundant reflections. Crystal data of 34, 35, 37,
(2) (a) Banide, E. V.; Molloy, B. C.; Ortin, Y.; M€uller-Bunz, H.;
McGlinchey, M. J. Eur. J. Org. Chem. 2007, 2611–2622. (b) Banide, E. V.;
Ortin, Y.; Chamiot, B.; Cassidy, A.; Niehaus, J.; Moore, A.; Seward,
C. M.; M€uller-Bunz, H.; McGlinchey, M. J. Organometallics 2008,
27, 4173–4182.
(3) (a) Brunner, H.; Zettlemeier, A. Handbook of Enantioselective
Catalysis with Transition Metal Compounds; VCH: Weinheim, 1993. (b)
Coeffard, V.; Guiry, P. J. Curr. Org. Chem. 2010, 14, 212–229, and
references therein.
(4) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008–2022.
(5) Banide, E. V.; O’Connor, C.; Fortune, N.; Ortin, Y.; M€uller-
Bunz, H.; McGlinchey, M. J. Org. Biomol. Chem. 2010, 8, 3997–4010.
(6) Banide, E. V.; Grealis, J. P.; M€uller-Bunz, H.; Ortin, Y.; Casey, M.;
Mendicute-Fierro, C.; Lagunas, M. C.; McGlinchey, M. J. J. Organomet.
Chem. 2008, 693, 1759–1770.
37 DMSO, and 38 were collected using an Oxford Diffraction Super-
3
Nova A diffractometer fitted with an Atlas detector and X-ray tubes
utilizing mirror-monochromated Mo KR radiation (λ = 0.71073 Å; 35,
38) or Cu KR radiation (λ = 1.54184 Å; 34, 37, 37 DMSO). An at least
3
complete data set was collected, assuming that the Friedel pairs are not
equivalent. An analytical absorption correction based on the shape of the
crystal was performed.38All structures were solved by direct methods
using SHELXS-97 and refined by full-matrix least-squares methods on
F2 for all data using SHELXL-97.39 In the BPMO complex 26, the Ph2P
and Ph2PdO moieties are crystallographically disordered, but each
oxygen site is only half-occupied. Hydrogen atom treatment varied from
compound to compound, depending on the crystal quality. All hydrogen
atoms in 33 and hydrogen atoms attached to oxygen in 37 were located
in the difference Fourier map and allowed to refine freely. All other
hydrogen atoms were added at calculated positions and refined using a
riding model. Their isotropic thermal displacement parameters were
fixed to 1.2 times (1.5 times for methyl groups) the equivalent one of the
parent atom. Anisotropic thermal displacement parameters were used
for all non-hydrogen atoms.
(7) Schmidbauer, H.; Pollok, T. Angew. Chem., Int. Ed. Engl. 1986,
25, 348–349.
(8) Clucas, J. A.; Dawson, R. H.; Dolby, P. A.; Harding, M. M.;
Pearson, K.; Smith, A. K. J. Organomet. Chem. 1986, 311, 153–162.
(9) Grist, N. J.; Hogarth, G.; Knox, S. A. R.; Lloyd, B. R.; Morton,
D. A. V.; Orpen, A. G. J. Chem. Soc., Chem. Commun. 1988, 673–675.
(10) Boisselle, A. P.;Meinhardt, N. A.J. Org. Chem. 1962, 27, 1828–1833.
(11) Ma, S.; Xie, H.; Wang, G.; Zhang, J.; Shi, Z. Synthesis 2001,
713–730.
ꢀ
ꢀ
(12) Ruiz, J.; Marquinez, F.; Riera, V.; Vivanco, M.; Garcia-Granda,
ꢀ
S.; Diaz, M. R. Chem.—Eur. J. 2002, 8, 3872–3878.
(13) Grushin, V. V. Chem. Rev. 2004, 104, 1629–1662, and refer-
ences therein.
(14) (a) Nagata, R.; Yamanata, H.; Okazaki., E.; Saito, I. Tetrahedron
Lett. 1989, 30, 4995–4998. (b) Nicolaou, K. C.; Maligres, J.; de Leon, E.;
Rideout, D. J. Am. Chem. Soc. 1990, 112, 7825–7826. (c) Grissom., J. W.;
Huang, D. Angew. Chem., Int. Ed. Engl. 1995, 34, 2037–2039.
(15) Seyferth, D.; Welch, D. E.; Heeren, J. K. J. Am. Chem. Soc. 1964,
86, 1100–1105.
(16) Shuchart, C. E.; Wojcicki, A.; Calligaris, M.; Faleschini, P.;
Nardin, G. Organometallics 1994, 13, 1999–2009.
(17) Banide, E. V.; Ouliꢀe, P.; M€uller-Bunz, H.; McGlinchey, M. J.
’ ASSOCIATED CONTENT
S
Supporting Information. X-ray crystallographic data for
b
24 (CCDC 820438), 26 (CCDC 820439), 33 (CCDC 820440),
34 (CCDC 820443), 35 (CCDC 820445), 37 (CCDC 820442),
37 DMSO (CCDC 820441), and 38 (CCDC 820444) in CIF
3
format. This material is available free of charge via the Internet at
http://pubs.acs.org.
Organometallics 2008, 27, 5657–5664.
(18) Treichel, P. M.; Dean, W. K.; Douglas, W. M. Inorg. Chem.
1972, 11, 1609–1615.
’ AUTHOR INFORMATION
(19) Doherty, N. M.; Hogarth, G.; Knox, A. A. R.; MacPherson,
K. A.; Melchior, F.; Morton, D. A. V.; Orpen, A. G. Inorg. Chim. Acta
1992, 198ꢀ200, 257–270.
Corresponding Author
*Phone: (+353) 1 716 2880. Fax: (+353) 1 716 1178. E-mail:
michael.mcglinchey@ucd.ie.
(20) (a) Higgins, S. J.; Shaw, B. L.; Taylor, R. J. Organomet. Chem.
1987, 325, 285–292. (b) Visseaux, M.; Dormond, A.; Baudry, D. Bull. Soc.
Chim. Fr. 1993, 130, 173–184. (c) Coyle, R. J.; Slovokhotov, Y. L.;
Antipin, M. Y.; Grushin, V. V. Polyhedron 1998, 17, 3059–3070. (d) Teo,
T.-W.; Selvaratnam, S.; Vittal, J. J.; Leung, P.-H. Inorg. Chim. Acta 2003,
352, 213–219. (e) Morise, X.; Braunstein, P.; Welter, R. Inorg. Chem.
2003, 42, 7752–7765. (f) Sgarbossa, P.; Pizzo, E.; Scarso, A.; Sbovata,
S. M.; Michelin, R. A.; Mozzon, M.; Strukul, G.; Benetollo, F. J. Organomet.
Chem. 2006, 691, 3659–3666. (g) Reisinger, C. M.; Nowack, R. J.;
Volkmer, D.; Rieger, B. Dalton Trans. 2007, 272–278. (h) Denmark,
S. E.; Smith, R. C.; Tymonko, S. A. Tetrahedron 2007, 63, 5730–5738. (i)
Hamada, A.; Braunstein, P. Inorg. Chem. 2009, 48, 1624–1637. (j) Zhang,
Y.; Ding, Y.; Pullarkat, S. A.; Li, Y.; Leung, P.-H. J. Organomet. Chem. 2011,
696, 709–714.
’ ACKNOWLEDGMENT
We thank Science Foundation Ireland, University College Dublin,
and the Centre for Synthesis and Chemical Biology funded by
the Higher Education Authority’s Programme for Research in
Third-Level Institutions (PRTLI) for generous financial support.
’ DEDICATION
Dedicated to the memory of F. Gordon A. Stone, an inspiring
mentor.
(21) Davies, J. A.; Pinkerton, A. A.; Vilmer, M. Acta Crystallogr. 1992,
C48, 1027–1029.
’ REFERENCES
(1) (a) Banide, E. V.; Ouliꢀe, P.; McGlinchey, M. J. Pure Appl. Chem.
2009, 81, 1–17. (b) Harrington, L. E.; Britten, J. F.; McGlinchey, M. J.
Org. Lett. 2004, 6, 787–790. (c) Banide, E. V.; Ortin, Y.; Seward, C. M.;
Harrington, L. E.; M€uller-Bunz, H.; McGlinchey, M. J. Chem.—Eur. J.
2006, 12, 3275–3286. (d) Maguire, L.; Seward, C. M.; Baljak, S.;
Reumann, T.; Ortin, Y.; Banide, E. V.; Nikitin, K.; M€uller-Bunz, H.;
McGlinchey, M. J. Eur. J. Inorg. Chem. 2009, 3250–3258. (e) Ouliꢀe, P.;
Altes, L.; Milosevic, S.; Bouteille, R.; Ortin, Y.; M€uller-Bunz, H.;
McGlinchey, M. J. Organometallics 2010, 29, 676–686.
(22) Brassat, I.; Englert, U.; Keim, W.; Keitel, D. P.; Killat, S.;
Suranna, G.-P.; Wang, R. Inorg. Chim. Acta 1998, 280, 150–162.
(23) (a) Vinci, D.; Martins, N.; Saidi, O.; Bacsa, J.; Brigas, A.; Xiao, J.
Can. J. Chem. 2009, 87, 171–175. (b) Farrer, N. J.; McDonald, R.; Piga,
T.; McIndoe, J. S. Polyhedron 2010, 29, 254–261.
(24) Cai, B.-Z.; Blackburn, M. G. Synth. Commun. 1997, 27,
3494–3949.
(25) (a) Ruffolo, R.; Kainz, S.; Gupta, H. K.; Brook, M. A.; McGlinchey,
M. J. J. Organomet. Chem. 1997, 547, 217–226. (b) Kuhnen, T.; Ruffolo, R.;
3816
dx.doi.org/10.1021/om200357v |Organometallics 2011, 30, 3804–3817

Organometallics
ARTICLE
Stradiotto, M.; Ulbrich, D.; McGlinchey, M. J.; Brook, M. A. Organometallics
1997, 16, 5042–5047.
(26) (a) Adimurthy, S.; Malakar, C. C.; Beifuss, U. J. Org. Chem.
2009, 74, 5648–5651. (b) Dahl, B. J.; Mills, N. S. Org. Lett. 2008,
10, 5605–5608. (c) Ye, J.; Ge, J.; Chen, X.; Zhao, Z.; Lu, P. Tetrahedron
2007, 63, 11040–111047.
(27) Hydrogen bonding patterns of this type have been extensively
studied: Braga, D.; Grepioni, F.; Walther, D.; Heubach, K.; Schmidt, A.;
Imhof, W.; G€orls, H.; Klettke, T. Organometallics 1997, 16, 4910–4919,
and references therein.
(28) Minami, T.; Chikugo, T.; Hanamoto, T. J. Org. Chem. 1986, 51,
2210–2214.
(29) Pollok, T.; Schmidbauer, H. Tetrahedron Lett. 1987, 28, 1085–
1088.
(30) Baldwin, J. E. J. Chem. Soc., Chem. Commun. 1976, 734–736.
(31) Bour, C.; Blond, G.; Salem, B.; Suffert, J. Tetrahedron 2006, 62,
10567–10581.
(32) Fujiwara, S.-I.; Shimizu, Y.; Imahori, Y.; Toyofuku, M.;
Shin-Ike, T.; Kambe, N. Tetrahedron Lett. 2009, 50, 3628–3630.
(33) Baldwin, J. E.; Cutting, J.; Dupont, W.; Kruse, L.; Silberman, L.;
Thomas, R. C. J. Chem. Soc., Chem. Commun. 1976, 736–738.
(34) Alabugin, I. V.; Manoharan, M. J. Am. Chem. Soc. 2005,
127, 9534–9545.
(35) SMART, Release 5.625; Bruker AXS Inc.: Madison, WI, 2001.
(36) SAINT, Release 6.22; Bruker AXS Inc.: Madison, WI, 2001.
(37) Sheldrick, G. M. SADABS, Version 2.03, Siemens Area Detector
Absorption Correction; Bruker AXS Inc.: Madison, WI, 2000.
(38) CrysalisPro, Version 1.171.33.55; Oxford Diffraction Limited,
2010.
(39) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112–122.
3817
dx.doi.org/10.1021/om200357v |Organometallics 2011, 30, 3804–3817