Synthesis of Sterically Demanding Bis(phosphinimine) Dibenzofuran Ligands and Subsequent Zinc Metalation

Article abstract of DOI:10.1071/CH14577

In light of previous success surrounding the use of bis(phosphinimine)dibenzofuran ligands for zinc-mediated lactide polymerization, a series of sterically demanding P=N pincer compounds have been prepared with important steric and electronic modification

Full text of DOI:10.1071/CH14577

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2015, 68, 373–384
Full Paper
http://dx.doi.org/10.1071/CH14577
Synthesis of Sterically Demanding Bis(phosphinimine)
Dibenzofuran Ligands and Subsequent Zinc Metalation*
A
A
A
Matthew T. Zamora, Saif M. Zahir, Kevin R. D. Johnson,
A
A
A
Clay J. Barnson, Craig A. Wheaton, Mikko M. Hanninen,
¨
A B
,
and Paul G. Hayes
A
Department of Chemistry and Biochemistry, University of Lethbridge,
4401 University Drive, Lethbridge, AB, T1K 3M4, Canada.
Corresponding author. Email: p.hayes@uleth.ca
B
In light of previous success surrounding the use of bis(phosphinimine)dibenzofuran ligands for zinc-mediated lactide
polymerization, a series of sterically demanding P¼N pincer compounds have been prepared with important steric and
electronic modifications at both P- and N-sites (L, 3a–d). These systems are highly crystalline and have been extensively
characterized using multinuclear NMR spectroscopy, elemental analysis, and X-ray diffraction. The ligands can be
transformed into their protonated analogues [HL][BArF ] (4a–d, [BArF ] ¼ [B(m-(CF3)2-C6H3)4]) by reaction with
4
4
Brookhart’s acid, and subsequently coordinated to zinc via an alkane elimination reaction with [ZnEt2] at ambient
temperature to afford the corresponding [LZnEt][BArF ] cationic complexes 5a–d. In addition, an unusual chloridozinc
4
species [LZnCl][BArF ] (5c9) has been isolated and structurally characterized, providing comparisons to previously
established ligand sets with similar geometries.
4
Manuscript received: 19 September 2014.
Manuscript accepted: 9 October 2014.
Published online: 2 December 2014.
Introduction
organozinc chemistry wherein we initiated a focus on neutral
ligands to generate cationic ZnII complexes, which we expected
might exhibit unique chemical properties, such as enhanced
activity, in lactide polymerization compared with systems
supported by more typical anionic scaffolds.
Zinc is the 24th most abundant element in the Earth’s crust,[1]
and finds many uses in everyday life, from pigments in paint, to
fire retardants,[2] wood preservatives,[3] laser outputs,[4] and
antioxidant supplements.[5] In addition to the commercial
application of this element, zinc salts have been used as cata-
lysts in organic synthesis for decades owing to their abundance,
low cost, non-toxicity, and environmentally benign properties.
In particular, divalent Zn complexes find prevalent use in
processes including hydrolysis of Si–H bonds,[6] C–C, C–N, and
C–O bond formation,[1] enantioselective aldol reactions,[7] as
well as the oxidative desulfurization of fuel.[8]
In addition to the aforementioned synthetic uses of catalytic
zinc, our recent interest has been focussed on this element as a
means to facilitate the polymerization of lactide.[9] Polylactide
(PLA), derived from renewable plant feedstocks, may be a
viable option for future plastic manufacturing amidst growing
concerns over the economic and environmental sustainability of
petrochemical-derived plastics.[9a,10] As a result of the recent
popularity of PLA, numerous Zn lactide polymerization cata-
lysts supported by monoanionic ligands (Ln), i.e. [LnZnIIR]
(R ¼ alkyl, amide, or alkoxide) have been reported to compli-
ment much of the work facilitated by rare earth metals in this
domain. Of particular note is the seminal work conducted by
Coates et al.[11] For several years, this framework served as the
de facto infrastructure for zinc lactide polymerization cata-
lysts.[12] Shortly thereafter, our group began exploring
Although the shift from anionic to neutral ligands served
as an important development in PLA catalysis, pioneering
developments by Bochmann established that protonated ligand
variants ([HLn]þ[X]ꢀ) could be used to form cationic Zn species
of the form [LnZnIIR]þ[X]ꢀ, bearing weakly coordinating
anions.[13] Using a similar protocol, we were able to prepare
Zn lactide polymerization catalysts that were coordinatively and
electronically unsaturated,[14] and since then our research has
focussed upon further developing electropositive zinc species.
Recently we reported a highly active cationic zinc catalyst
supported by a finely tuned bis(phosphinimine)dibenzofuran
framework (Fig. 1).[15] Although this complex was shown to be
highly active in the generation of PLA, catalysis was hampered
by intra- and intermolecular transesterification. In order to
inhibit this competitive process of ‘back-biting’, we rationalized
that systematically permuting substituents attached to the phos-
phinimine (P¼N) moieties could afford a catalyst system which
prevents large molecules (i.e. oligomers and growing polymer
chains) from approaching the metal centre, while still readily
permitting coordination and insertion of the desired lactide
monomer. Specifically, we aimed to install substantial steric
bulk onto our ligand system distal to the site of a coordinated
*Dedicated to the bright memory of Professor Richard F. Langler, a true inspiration for countless young scientists.
‘A free radical is a lot like a gorilla with a knife. It’s going to get what it wants.’
Journal compilation Ó CSIRO 2015
www.publish.csiro.au/journals/ajc

374
M. T. Zamora et al.
OMe
2.0 equiv. of tBuLi to dibenzofuran (1), followed by subsequent
treatment with the appropriate chlorophosphine (Scheme 1).
These diphosphine compounds exhibit one sharp signal in the
31P{1H} NMR spectrum (benzene-d6) at d ꢀ14.3 and 11.1 for
the P-phenyl (2-Ph) and P-isopropyl (2-iPr) analogues,
respectively. The 1H NMR and 13C{1H} spectra of these
compounds agree well with earlier reports.[17] The P-phenyl-
substituted phosphinimine ligands 3a,b can be generated in
high yield by reaction of 2-Ph with m-XyN3 (3a) or p-TrPhN3
(3b) at 558C for 17.5 h in toluene solvent; while the more bulky
P-isopropyl species can be generated in similar yields by the
reaction of the aforementioned azides with 2-iPr (3c and 3d,
respectively), as indicated in Scheme 1.
The transformation of compounds 2 to the new ligands 3 was
confirmed using multinuclear NMR spectroscopy. A single,
sharp 31P{1H} NMR signal was apparent for all ligands (3a,
d ꢀ4.9; 3b, d ꢀ0.3; 3c, d 8.2; 3d, d 20.2). Characteristic shifts at
,d 8.21 and 7.63, corresponding to the 1,9- and 3,7-positions of
the dibenzofuran backbone, respectively, can be observed in the
1H{31P} NMR spectra of 3a–d. In addition, a diagnostic m-Xy
methyl signal is present at ,d 2.21 for 3a and 3c, while 3c and
3d contain typical resonances for isopropyl methine (,d 2.60)
and methyl groups (,d 1.21 and 0.93). As outlined in the
Experimental section of this manuscript, compounds 3 also
exhibit the expected resonances in their respective 13C{1H}
NMR spectra.
CF3
CF3
ꢁB
O
O
Ph
Ph
Znꢀ
O
N
N
4
Et2P
PEt2
Fig. 1. Recently reported cationic zinc lactide polymerization catalyst.
metal centre; the catalytic implications of such modifications
will be studied in due course. Herein we report the synthesis,
structure, and characterization of our new ligands, as well as
their ability to stabilize zinc alkyl complexes.
Results and Discussion
Sites of Modification
In order to generate sterically demanding analogues of our
previously reported dibenzofuran ligand (exhibited in Fig. 1),
we chose to systematically modify both the N- and P-sites of the
phosphinimine moiety. Installation of phosphine groups on
positions 4 and 6 of dibenzofuran (1) can be facilitated by
deprotonation at these positions, followed by reaction with a
i
halophosphine to generate compounds 2-R (R ¼ Ph or Pr)
(Scheme 1). Subsequently, transformation of the phosphines to
desired phosphinimine functionalities under Staudinger condi-
tions generates ligands 3. In the first two ligands reported below,
standard phenyl groups were bound to the phosphorus atoms,
while meta-xylyl (m-Xy, 3,5-dimethylphenyl) and para-
tritylphenyl (p-TrPh, 4-(triphenylmethyl)phenyl) groups
were installed on the nitrogen atoms (3a and 3b, respectively).
These alterations allowed for facile structural comparison with
other previously reported P-phenyl-substituted analogues,[16]
isolating the effect of altering the substituents on the nitrogen
centers, which typically employ N-Pipp groups (Pipp ¼
para-isopropylphenyl). In addition, we prepared even bulkier
versions of 3a and 3b by replacing the phenyl groups at the
phosphorous atoms with isopropyl moieties (3c and 3d,
respectively). While the isopropyl groups were expected to
exert greater pressure on the N-aryl substituents, thereby forcing
them closer to the metal centre, it is worthwhile to note that they
should also create a more electron-rich phosphinimine moiety.
Structural Comparison
Single crystals of 3a (Fig. 2) and 3b (Fig. 3) were grown from
concentrated ambient temperature solutions of toluene and
P2
C39
P1
N2
C7
C8
N1
C2
C25
O1
C1
Fig. 2. Thermal ellipsoid plot (30 % probability) of the partial asymmetric
˚
unit of 3a, with H-atoms omitted for clarity. Selected bond distances (A) and
Ligand Synthesis and Characterization
As previously reported,[14,15] efficient synthesis of the dipho-
sphine compound 2 can be accomplished via addition of
angles (deg.): P1–N1 ¼ 1.5622(18), P2–N2 ¼ 1.5592(18), C25–N1 ¼ 1.401(3),
C45–N2 ¼ 1.395(3); C25–N1–P1 ¼ 131.36(15), C45–N2–P2 ¼ 129.24(15).
Ar
Ar
N
N
R2P
PR2
R2P
PR2
O
(1) TMEDA, tBuLi
O
O
(2) 2R2PCI
2ArN3
Toluene
ꢁ2 N2
Heptane
ꢁ2 tBuH
ꢁ2 LiCI
R ꢂ Ph, Ar ꢂ m-Xy
R ꢂ Ph, Ar ꢂ p-TrPh
R ꢂ iPr, Ar ꢂ m-Xy
R ꢂ iPr, Ar ꢂ p-TrPh
3a (89 %)
3b (73 %)
3c (76 %)
3d (95 %)
R ꢂ Ph
R ꢂ iPr
2
-Ph
-iPr
1
2
Scheme 1. Synthesis of dbf bis(phosphinimine) ligands 3a–d.

Cationic Dibenzofuran–Phosphinimine Zn Complexes
375
C25
N1
C62
P2
P1
O1
N2
C8
C1
C2
C7
Fig. 3. Thermal ellipsoid plot (30 % probability) for the molecular structure of 3b, with H-atoms and bromobenzene solvent
˚
molecules omitted for clarity. Selected bond distances (A) and angles (deg.): P1–N1 ¼ 1.5709(18), P2–N2 ¼ 1.5663(17), C25–
N1 ¼ 1.390(3), C62–N2 ¼ 1.381(3); C25–N1–P1 ¼ 127.56(15), C62–N2–P2 ¼ 131.74(15).
N1
C19
P1
N2
C33
O1
P2
C8
C1
C2
C7
Fig. 4. Thermal ellipsoid plot (30 % probability) for the molecular structure of 3c, with H-atoms omitted for
˚
clarity. Selected bond distances (A) and angles (deg.): P1–N1¼ 1.5635(13), P2–N2 ¼ 1.5673(13), C19–
N1 ¼ 1.391(2), C33–N2 ¼ 1.393(2); C19–N1–P1 ¼ 133.83(12), C33–N2–P2 ¼ 132.71(12), N1–P1–
C1 ¼ 115.00(8), N2–P2–C8 ¼ 114.64(7).
C13ꢃ
C13
N1ꢃ
P1ꢃ
P1
N1
O1
C1ꢃ
C1
C2ꢃ
C2
Fig. 5. Thermal ellipsoid plot (30 % probability) for the molecular structure of 3d, with H-atoms and CH2Cl2 solvent molecules
˚
omitted for clarity. Selected bond distances (A) and angles (deg.): P1–N1 ¼ 1.566(3), C13–N1 ¼ 1.394(4); C13–N1–
P1 ¼ 132.0(3).
bromobenzene, respectively, while single crystals of 3c (Fig. 4)
and 3d (Fig. 5) were obtained from dichloromethane layered
with pentane at ꢀ358C. In the case of 3a, the structure contained
two independent molecules of the ligand in addition to a toluene
solvent molecule in the asymmetric unit. Due to this, a truncated
structure is represented in Fig. 2. A summary of X-ray crystallo-
graphy data collection and structure refinement is listed in
Table 1.
All four structures unambiguously confirm the molecular
connectivity of the ligands, previously established by spectro-
scopic evidence. As expected, the phosphorus atoms exhibit
tetrahedral geometry, with P¼N bond lengths similar to those of
[14–16,18]
˚
related bis(phosphinimine) ligands (P–N ¼ ,1.56 A).
The angle about the phosphinimine nitrogens (C–N–P ¼
,131.38) confirms the presence of an octet-required lone pair
and bestows a donor site for coordination to Zn via both

376
M. T. Zamora et al.

Cationic Dibenzofuran–Phosphinimine Zn Complexes
377
ꢁ
ꢁ
[BArF
Ar
]
[BArF
]
4
4
Ar
ꢀ
H
Ar
Ar
Ar
Ar
ꢀ
Zn
N
N
N
N
N
N
‘[H][BArF4]’
[ZnEt2]
PR2
R2P
R2P
PR2
R2P
PR2
O
O
O
Toluene
ꢁEtH
Toluene
ꢁ2 Et2O
R ꢂ Ph, Ar ꢂ m-Xy
R ꢂ Ph, Ar ꢂ p-TrPh 3b
R ꢂ iPr, Ar ꢂ m-Xy
3c
R ꢂ iPr, Ar ꢂ p-TrPh 3d
3a
4a
4b
4c
4d
5a
5b
5c
5d
Scheme 2. Synthesis of 4 and complexes 5. ‘[H][BArF4]’ ¼ [H(OEt2)2][BArF4].
phosphinimine nitrogen atoms in addition to the dibenzofuran
oxygen atom.
Protonation and Zinc Complexation
As demonstrated in our previous work,[15] and in that of
Bochmann and co-workers,[13] the synthesis of cationic zinc
complexes can be accomplished by first protonating a nitro-
genous ligand with an appropriate Brønsted acid. Accordingly,
C19
H2
C33
N1
N2
protonation of 3a–d using Brookhart’s acid [H(OEt2)2][BArF ]
P1
4
([BArF ] ¼ tetrakis[(3,5-trifluoromethyl)phenyl]borate) yielded
4
P2
C8
O1
the protonated salts 4 under ambient conditions in near-
quantitative yields, as outlined in Scheme 2. During the course
of protonation, elimination of diethyl ether was observed by
1H NMR spectroscopy, and a substantial downfield shift of the
31P{1H} NMR resonance, relative to 3, was observed (4a,
d 18.8; 4b, d 19.6; 4c, d 25.7; 4d, d 40.9). Furthermore, 31P{1H}
NMR signals were unusually broad, with widths at half height
(whh) ranging from 180–240 Hz, implying some degree of
fluxionality. This phenomenon is most likely due to exchange
of the proton between both nitrogen atoms, as represented by
the dotted lines in Scheme 2. Finally, the diagnostic NH protons
C1
C2
C7
Fig. 6. Thermal ellipsoid plot (30 % probability) for the molecular struc-
ture of 4c, with the BArF anion and H-atoms, except for H2, omitted for
4
˚
clarity. Selected bond distances (A) and angles (deg.): P1–N1 ¼ 1.566(2),
P2–N2 ¼ 1.635(2), N1–C19 ¼ 1.381(3), N2–C33 ¼ 1.443(3); C19–N1–
P1 ¼ 131.72(18), C33–N2–P2 ¼ 125.90(17), N1–P1–C1 ¼ 117.81(11),
N2–P2–C8 ¼ 112.52(11).
1
appeared upfield in the H{31P} NMR spectrum, resonating
at ,d 5.30. The NMR spectra for other nuclei (13C{1H},
11B{1H}, 19F{1H}) also exhibited characteristic chemical shifts
and multiplicities representative of the structure proposed.
Single crystals of 4c were grown from benzene layered with
pentane at ambient temperature. As shown in Fig. 6, H2 was
located at one position in the Fourier difference map and
isotropically refined with a fixed N–H bond length despite the
fluxionality of this proton in solution. Protonation notwithstand-
ing, this variant exhibits similar structural parameters to that
of its predecessor. Specifically, the phosphinimine angle (C19–
bromobenzene solution of 4 and ethyl(phenoxy)zinc at 1108C in
a sealed glass bomb to induce complexation,[15,16,19] appeared
ideal for initial studies involving these new ligands. Further-
more, these proposed alkyl zinc targets could serve as an
interesting comparison to similar [LZnR][X] complexes previ-
ously published by our group.[9d,14–16,18b,19]
Accordingly, the synthesis of zinc-ethyl complexes of the
general formula [LZnEt][BArF ] (5) was performed by reaction
of 4 with diethylzinc in toluene solvent. Analysis by 1H NMR
spectroscopy indicated complete conversion into 5 via an alkane
elimination reaction after a mere 5 min at ambient tempera-
ture.[20] More specifically, extrusion of ethane was apparent
˚
N1–P1 ¼ 131.72(18)8) and bond distances (P1–N1 ¼ 1.566(2) A,
4
˚
N1–C19 ¼ 1.381(3) A) of one P¼N group are comparable to
those observed in 3c. However, notable differences include
the aforementioned H2, a BArF4 anion (not pictured), a slightly
more acute angle (C33–N2–P2 ¼ 125.90(17)8), and elongated
1
˚
˚
bond distances (P2–N2 ¼ 1.635(2) A, N2–C33 ¼ 1.443(3) A)
associated with the protonated phosphinimine. This asymmetry
of the P¼N lengths also appears to support the localization of
H2. A summary of X-ray crystallography data collection and
structure refinement is also listed in Table 1.
from the emergence of a singlet at d 0.80 in the H NMR
spectrum, as well as effervescence detected in the NMR tube
upon injection of [ZnEt2]. Furthermore, the disappearance of the
NH resonance, appearance of upfield quartet (,d ꢀ0.14) and
triplet (,d 0.59) resonances displaying mutual coupling, along
with a slight change in the aromatic region of the spectrum
further supported the structures proposed in Scheme 2. In
addition to changes observed in the 1H NMR spectrum, a
significant downfield shift was observed in the 31P{1H}
spectrum, with a new sharp singlet emerging at ,d 28.5 (5a–b)
or ,d 50.0 (5c–d).
Although the focus of our previous cationic zinc studies had
an emphasis on alkoxide complexes, [LZnOR][BAr4], the mild
conditions involved in using [ZnEt2] for complexation made the
preparation of alkyl analogues, [LZnEt][BArF ], a far more
4
attractive endeavour. Specifically, injection of [ZnEt2] to a
solution of 4 at ambient temperature, as opposed to heating a

378
M. T. Zamora et al.
Despite exhaustive efforts, single crystals suitable for an
planarity despite the interaction between Zn1 and O1, as indi-
cated by the sum of angles about the equatorial positions
(357.88). This may be due to the chlorido group demanding
significant s-character,[21] which is more prominent in a true
equatorial arrangement as opposed to one that is more
pyramidalized.
The Zn1–O1 bond distance is particularly noteworthy as it is
significantly shorter than other Zn–dibenzofuran bond distances
observed in previous cationic [k3-LZnR] complexes involving
N-Pipp-[16,19] or bulkier N-Mes-substituted ligands.[18b] How-
ever, the shorter Zn–O bond length observed in this case is
most likely a consequence of the highly electron-withdrawing
chlorido group, as opposed to steric implications.
X-ray diffraction experiment of any of the complexes 5a–d
remained elusive. In one case however, we reacted [EtZn(lac)]
(lac ¼ methyl-L-lactate) and 4c to attempt the preparation of an
ester-coordinated analogue of 5c with an aim of improved
crystallinity. The obtained material was initially believed to
be the targeted complex, namely [LZn(lac)][BArF ] involving
4
the R ¼ iPr and Ar ¼ m-Xy combination. However, an X-ray
diffraction study on crystals procured from a dichloromethane
solution of this reaction mixture indicated that either the lactate
group of [LZn(lac)][BArF ] or the ethyl group of [LZnEt]
4
[BArF ], which could also be present in solution if alcohol
4
elimination routes are operative, had reacted with the solvent,
resulting in the corresponding cationic chlorido complex
Finally, the phosphinimine bite angle is dramatically
reduced from ideality (N1–P1–C1 ¼ 107.50(17)8, N2–P2–C8 ¼
107.64(16)8) compared with the angles observed in the free
ligand 3c (N1–P1–C1 ¼ 115.00(8)8, N2–P2–C8 ¼ 114.64(7)8)
or in similar P-phenyl-substituted [LZnR]þ complexes (N–Pipp:
108.88(13)8, 108.41(13)8;[16] N–Ph: 114.52(11)8, 113.92(11)8;[19]
N–Mes: 117.46(18)8, 115.94(18)8[18b]). This significant reduc-
[LZnCl][BArF ] (5c9, Fig. 7).
4
Despite the serendipitous formation of this complex, this
intriguing species serves as a potential starting material for
alternative cationic Zn complexes that remain elusive through
conventional alkane elimination strategies, or for targets in
which requisite Zn starting materials are not readily available.
More conventional methods for the independent synthesis
of 5c9 are currently underway. For the purposes of this study,
the following structural analysis establishes the ligands’
coordinative ability despite the unique chlorido ancillary, and
therefore the structural parameters are presented below.
i
tion in bite angle in 5c9 suggests that the Pr substituents are
interacting with the nitrogen-bound m-Xy moieties, pushing
these aromatic groups closer together, sterically shielding the
metal centre. This effect could also be another cause for a lack of
pyramidalization at Zn.
Structure of 5c9
Conclusion
As expected, the ancillary ligand coordinates to the metal centre
in a tridentate fashion, along with a coordinated chlorido ligand
to form a 4-coordinate structure wherein the geometry is best
described as a trigonal planar Zn centre that is capped by the
oxygen of the dibenzofuran ring. The phosphinimine nitrogens
A variety of dibenzofuran-based bis(phosphinimine) pincer
ligands were prepared by combining 4,6-bis(phosphino)
dibenzofuran compounds with aryl azides under Staudinger
reaction conditions. The new P¼N ligands are crystalline and
provide unique steric environments suitable for metal coordi-
nation. In order to effect metal attachment, cationic protonated
analogues were generated by reaction of the neutral phosphi-
nimine framework with Brookhart’s acid, and subsequently
bound to zinc via an alkane elimination reaction with diethylzinc
instead of more exotic starting materials such as ethyl(lactate)
zinc or the highly electron-withdrawing ethyl(pentafluoro-
phenoxy)zinc precursors, which are often required to effect
these kinds of ligand attachments. Furthermore, reaction of
these protonated analogues with diethylzinc proceeded at
ambient temperature in under 5 min, instead of the harsh
experimental conditions and long reaction times previously
required to generate alkoxide/ester analogues.
˚
˚
(Zn1–N1 ¼ 1.977(3) A, Zn1–N2 ¼ 1.978(3) A) and the chlorido
˚
group (Zn1–Cl1 ¼ 2.1726(12) A) occupy the equatorial posi-
˚
tions, and the oxygen (Zn1–O1 ¼ 2.176(2) A) is in the apical
site. The equatorial groups do not deviate significantly from
C33
These sterically bulky systems, especially the PiPr2 variants,
are expected to promote transesterification resistance in lactide
polymerization, owing to their ability to force the N-substituted
groups closer together, protecting the naked side of the metal’s
trigonal pyramid. These species will be tested for their ability to
facilitate lactide polymerization in due course.
C25
Zn1
N2
N1
P2
P1
O1
Cl1
C8
C1
Finally, the discovery of the unique [LZnCl][BArF ] com-
4
plex 5c9 serves as a valuable synthetic tipping point since
chlorido complexes of this nature may serve as useful starting
materials for the synthesis of cationic complexes bearing other
functionalities.
C2
C7
Experimental
Fig. 7. Thermal ellipsoid plot (30 % probability) for the cationic compo-
˚
nent of 5c9, with H-atoms omitted for clarity. Selected bond distances (A)
General Procedures
and angles (deg.): P1–N1 ¼ 1.609(3), P2–N2 ¼ 1.611(3), C25–N1 ¼ 1.442
(5), C33–N2 ¼ 1.436(4), Zn1–O1 ¼ 2.176(2), Zn1–N1 ¼ 1.977(3),
Zn1–N2 ¼ 1.978(3), Zn1–Cl1 ¼ 2.1726(12); C25–N1–P1 ¼ 120.9(3),
C33–N1–P1 ¼ 121.4(2); N1–P1–C1 ¼ 107.50(17), N2–P2–C8 ¼ 107.64
(16), N1–Zn–N2 ¼ 123.61(13), Cl1–Zn1–O1 ¼ 109.28(8).
Manipulations of air- and moisture-sensitive materials and
reagents were carried out under an argon atmosphere using
double manifold vacuum techniques or in a glove box. Solvents
used for air-sensitive manipulations were purified using an

Cationic Dibenzofuran–Phosphinimine Zn Complexes
379
MBraun solvent purification system (SPS), stored in polytetra-
flouroethylene (PTFE)-sealed glass vessels over sodium
benzophenone ketyl (THF and ether), CaH2 (CH2Cl2 and
bromobenzene), or ‘titanocene’ (pentane, benzene, and tolu-
ene), and freshly distilled at the time of use. Deuterated solvents
were dried over sodium benzophenone ketyl (benzene-d6 and
toluene-d8) or CaH2 (chloroform-d, dichloromethane-d2, and
bromobenzene-d5), degassed via three freeze–pump–thaw
solution over 25 min at 08C to afford a foamy, yellow suspen-
sion, at which point urea (0.15 g, 2.5 mmol) was added and the
solution was stirred for 5 min. A solution of NaN3 (1.274 g,
19.60 mmol) in H2O (40 mL) was added dropwise over 60 min at
08C, generating a foamy suspension. The solution was stirred
and warmed to ambient temperature over the course of 2.0 h, at
which point Et2O (100 mL) was added to precipitate an off-
white residue. The mixture was filtered and the residue dried
under vacuum, resulting in an off-white powder (5.674 g, 98 %).
˚
cycles, distilled under vacuum and stored over 4 A molecular
3
sieves in glass bombs under argon. All NMR spectra were
recorded at ambient temperature with a Bruker Avance II NMR
spectrometer (300.13 MHz for 1H, 75.47 MHz for 13C,
121.49 MHz for 31P, 96.29 MHz for 11B, and 282.40 MHz for
19F). Chemical shifts are reported in parts per million relative to
the external standards SiMe4 (1H, 13C), 85 % H3PO4 (31P),
dH (chloroform-d) 7.34–7.24 (ov m, 17H), 6.97 (d, 2H, JHH
8.4), 6.78 (s, 1H), 6.65 (s, 2H, Ar H).
4,6-Bis(diphenylphosphino)dibenzofuran (2-Ph)
This compound was prepared using a modification of a related
literature method.[17b] A sample of dibenzofuran (2.444 g,
14.53 mmol) was added to a 250 mL round-bottomed flask
equipped with a reflux condenser attached to a double manifold
vacuum line and dissolved in heptane (100 mL) to afford a clear,
beige solution. A sample of tetramethylethylenediamine
(TMEDA) (3.41 g, 29.3 mmol) was quickly injected into the
flask via syringe, and the resulting solution was cooled to 08C.
A solution of tBuLi (1.7 M in pentane, 18.8 mL, 32 mmol) was
added dropwise over 0.5 h, generating a creamy, orange
suspension. The solution was stirred and warmed to ambient
temperature over the course of 2.0 h, at which point the solution
was heated to 988C for 1.0 h. The resulting creamy, tan-coloured
suspension was cooled to 08C and a solution of chlor-
odiphenylphosphine (5.90 mL, 32.0 mmol) in heptane (8 mL)
was added to the mixture dropwise via syringe over 30 min. The
solution was allowed to warm to ambient temperature while
stirring over 17.5 h, producing a pale, brown suspension, which
was concentrated to 70 mL and transferred to a fine-porosity
glass swivel frit apparatus via a cannula. The dark, amber
solution was collected, the remaining beige residue was washed
with heptane (2 3 30 mL), and the filtrates were combined.
Solvents were evaporated to afford a brown solid, which was
washed with cold pentane (2 3 10 mL), and dried under vacuum,
giving a fine brown powder (3.419 g, 44 %). dH (benzene-d6)
11
19
.
BF3 OEt2 ( B), and CFCl3 ( F); residual H- and C-containing
species in benzene-d6 (d 7.16, 128.1), toluene-d8 (d 2.08, 20.4),
chloroform-d (d 7.26, 77.2), (dichloromethane-d2) (d 5.32,
53.8), and bromobenzene-d5 (d 7.30, 130.9), were used as
internal references (1H and 13C, respectively). Assignments
were aided by the use of H–1H COSY, 13C{1H} APT, and
1
1H–13C{1H} HSQC/HMBC experiments (s ¼ singlet, d ¼
doublet, t ¼ triplet, q ¼ quartet, sp. ¼ septet, m ¼ multiplet, br ¼
broad, ov ¼ overlapping signals). Elemental analyses were
performed using an Elementar Vario Microcube instrument.[20]
The complex [EtZn(S-MeO2CC(H)(Me)O)] ([LZn(lac)]
[BArF ])[9l] and the protonating agent [H(OEt2)2][B(m-(CF3)2-
4
C6H3)4][22] were prepared according to literature methods.
Although reported previously by other methods, 2-Ph,[17b]
2-iPr,[17a] m-XyN3,[23] and p-TrPhN3,[24] were prepared in our
laboratory from modified procedures as described below.
Samples of 3.0 and 5.0 M HCl were prepared by dilution of a
concentrated solution. All other reagents, including dibenzo-
furan (1), were purchased from commercial sources and used as
received.
1-Azido-3,5-dimethylbenzene (m-XyN3)
This compound was prepared using a modification of a related
literature method.[25] A mixture of 3,5-dimethylaniline (6.817 g,
112.9 mmol) and NaNO2 (4.3 g, 62 mmol) were added to a
cooled (ꢀ308C) combination of concentrated HCl (40 mL),
distilled H2O (40 mL), and NaBF4 (12.4 g, 113 mmol). The
solution was stirred for 30 min at ꢀ308C, wherein a bright
orange precipitate formed. The resulting intermediate diazoni-
um BF4 salt was quickly filtered through a Bu¨chner funnel and
washed with cold distilled H2O (5 3 4 mL). This sticky orange
powder was carefully added to a cooled (08C) aqueous solution
(100 mL) of NaN3 (11.0 g, 169 mmol). After vigorous gas
evolution, the orange mixture was stirred overnight at 258C. The
product was extracted from the aqueous layer with diethyl ether
(3 3 30 mL) and dried with MgSO4. The solution was decanted,
and the solvent was removed under vacuum, resulting in a dark
red oil (5.232 g, 67 %). dH (benzene-d6) 6.52 (s, 1H), 6.47 (s, 2H,
Ar H), 1.96 (s, 6H, CH3).
3
4
7.55 (dd, 2H, JHH 7.5, JHH 1.2), 7.40–7.37 (ov m, 8H), 7.21
4
3
(dd, 2H, JHH 7.5, JHH 1.2), 7.01–6.95 (ov m, 14H, Ar H).
dP (benzene-d6) ꢀ14.3 (s, 2P, P¼N).
4,6-Bis(diisopropylphosphino)dibenzofuran (2-iPr)
This compound was prepared using a modification of a related
literature method.[17a] A sample of dibenzofuran (1.993 g,
11.85 mmol) was added to a 250 mL round-bottomed flask
equipped with a reflux condenser attached to a double manifold
vacuum line and dissolved in heptane (100 mL) to afford a clear,
beige solution. A sample of TMEDA (3.03 g, 26.7 mmol) was
quickly injected into the flask via syringe, and the resulting
t
solution was cooled to 08C. A solution of BuLi (1.7 M in
pentane, 15.4 mL, 26 mmol) was added dropwise over 40 min,
generating a creamy, orange suspension. The solution was
stirred and warmed to ambient temperature over the course of
2.0 h, at which point the solution was heated to 1108C for 1.0 h.
The corresponding creamy, tan-coloured suspension was cooled
to 08C and a solution of chlorodiisopropylphosphine (4.20 mL,
26.2 mmol) in heptane (5 mL) was added to the mixture drop-
wise via syringe over 20 min. The solution was allowed to warm
to ambient temperature while stirring over 63.5 h, producing a
pale, brown suspension, which was transferred to a fine-porosity
glass swivel frit apparatus via cannula. The clear, amber solution
((4-Azidophenyl)methanetriyl)tribenzene (p-TrPhN3)
This compound was prepared using a modification of a related
literature method.[26] A sample of 4-tritylaniline (5.396 g,
16.09 mmol) was added to a 250 mL round-bottomed flask,
dissolved in 3.0 M HCl (80 mL), and cooled to 08C, affording a
foamy, white suspension. A solution of NaNO2 (1.304 g,
18.90 mmol) in H2O (30 mL) was added dropwise to the acidic

380
M. T. Zamora et al.
was collected, and the remaining yellow residue was washed
with heptane (1 3 20 mL), and the filtrates were combined.
Solvents were evaporated to afford an off-white residue, which
was reconstituted in toluene (6 mL), layered with pentane
(3 mL), and cooled to ꢀ358C for 16 h, resulting in pale, amber
crystals. The mother liquor was decanted and the crystals
washed with cold pentane (4 mL), recrystallized from toluene
and pentane (2 : 1 ratio) at ꢀ358C, and dried under vacuum,
resulting in a tan, crystalline powder (2.050 g, 43 %). dH (ben-
zene-d6) 7.66 (d, 2H, 3JHH 7.5), 7.65 (d, 2H, 3JHH 7.5), 7.13 (t,
2H, 3JHH 7.5, Ar H), 2.66 (sp, 4H, 3JHH 6.9, iPr CH(CH3)2), 1.20
(d, 12H, 3JHH 7.2), 0.98 (d, 12H, 3JHH 7.2, iPr (CH(CH3)2). dP
(benzene-d6) 11.1 (s, 2P, P¼N).
C(Ph)3). dP (dichloromethane-d2) ꢀ0.3 (s, 2P, P¼N). Anal.
Calc. for C86H64N2OP2: C 85.83, H 5.36, N 2.33. Found: C
85.64, H 5.33, N 2.42 %.
N,N’-(Dibenzofuran-4,6-diylbis(diisopropyl-
phosphoranylylidene))bis(3,5-dimethylaniline) (3c)
In an argon atmosphere glove box, a sample of 2-iPr (459 mg,
1.15 mmol) was added to a 20 mL scintillation vial and dissolved
in toluene (5 mL). A solution of m-XyN3 (337 mg, 2.29 mmol) in
toluene (5 mL) was added dropwise over 5 min at ambient
temperature, resulting in an effervescent, orange solution, which
was stirred for an additional 17.5 h at ambient temperature. The
resulting cloudy brown solution was evaporated to dryness,
generating a brown residue which was further dried under
vacuum, yielding a brown powder (553 mg, 76 %). dH (benzene-
N,N’-(Dibenzofuran-4,6-diylbis(diphenyl-
phosphoranylylidene))bis(3,5-dimethylaniline) (3a)
3
4
3
d6) 8.15 (dd, 2H, JHH 7.5, JHH 1.2), 7.54 (dd, 2H, JHH 7.5,
4JHH 1.2), 7.08 (t, 2H, 3JHH 7.5), 6.93 (s, 4H), 6.52 (s, 2H, Ar H),
2.60 (sp, 4H, 3JHH 7.2, iPr CH(CH3)2), 2.26 (s, 12H, m-Xy CH3),
1.26 (d, 12H, 3JHH 7.2, iPr CH(CH3)2), 0.98 (d, 12H, 3JHH 7.2,
iPr CH(CH3)2). dC (benzene-d6) 155.5 (d, JCP 2.8), 152.5 (d, JCP
2.9), 137.8 (d, JCP 0.7, Ar C), 134.9 (d, 2C, 2JCP 5.1, 3,7-dbf),
124.2 (d, JCP 5.7, Ar C), 124.1 (d, 2C, 4JCP 2.3, 1,9-dbf), 123.7
A sample of 2-Ph (1.997 g, 3.722 mmol) was added to a 50 mL
round-bottomed flask attached to a double manifold vacuum
line and dissolved in toluene (20 mL) to afford a clear, dark
orange solution. A solution of m-XyN3 (1.095 g, 7.440 mmol) in
toluene (4 mL) was added dropwise over 3 min at ambient
temperature, resulting in a clear, dark brown solution, wherein
vigorous foaming was observed during stirring. After 10 min,
the reaction mixture was stirred at 558C for 17 h to generate a
clear, brown solution. The solvent was removed under vacuum
to afford a dark, amber powder which was washed with pentane
(3 3 20 mL) and dried under vacuum, resulting in a yellow
powder (2.576 g, 89 %). dH (benzene-d6) 8.34 (dd, 2H, 3JHH 7.6,
4JHH 1.5), 7.72 (dd, 8H, 3JHH 8.2, 4JHH 1.4), 7.47 (dd, 2H, 3JHH
7.6, 4JHH 1.5), 6.99–6.82 (ov m, 14H), 6.78 (s, 4H), 6.46 (s, 2H,
Ar H), 2.15 (s, 12H, CH3). dC (benzene-d6) 156.8 (d, JCP 2.3),
3
(d, 2C, JCP 8.6, 2,8-dbf), 122.5 (d, 4C, 4JCP 14.9, m-Xy CH),
119.7 (s, 2C, m-Xy CH), 115.6 (d, JCP 64.5, Ar C), 28.6 (d, 4C,
1JCP 70.8, iPr CH(CH3)2), 21.8 (s, 4C, m-Xy CH3), 18.1 (d, 4C,
2JCP 2.2, iPr CH(CH3)2), 16.2 (d, 4C, 2JCP 3.5, iPr CH(CH3)2). dP
(benzene-d6) 18.5 (s, 2P, P¼N). Anal. Calc. for C40H52N2OP2:
C 75.21, H 8.20, N 4.39. Found: C 75.61, H 8.11, N 4.74 %.
N,N’-(Dibenzofuran-4,6-diylbis(diisopropyl-
phosphoranylylidene))bis(4-tritylaniline) (3d)
2
A mixture of 2-iPr (1.301 g, 3.25 mmol) and p-TrPhN3 (2.349 g,
6.50 mmol) was added to a 250 mL round-bottomed flask
attached to a double manifold vacuum line and dissolved in
toluene (80 mL) to afford a clear yellow solution, which was
then stirred at 608C for 43 h. Solvent was removed and the solid
dried under vacuum, resulting in a pale yellow powder (3.303 g,
95 %.). dH (benzene-d6) 8.12 (dd, 2H, 3JHH 7.5, 4JHH 1.2), 7.54–
7.51 (ov m, 12H), 7.28 (d, 4H, 3JHH 8.7), 7.11–6.97 (ov m, 26H,
Ar H), 2.59 (sp, 4H, 3JHH 6.9, iPr CH(CH3)2), 1.15 (d, 12H, 3JHH
6.9, iPr CH(CH3)2), 0.88 (d, 12H, 3JHH 6.9, iPr CH(CH3)2). dC
(benzene-d6) 155.2 (d, JCP 2.5), 150.6 (d, JCP 2.6), 148.3 (s),
135.6 (s, Ar C), 135.3 (d, 2C, 4JCP 5.1, 1,9-dbf), 132.1 (s), 131.9
(s), 131.8 (s), 126.0 (s), 124.2 (s), 124.1 (s, Ar C), 123.8 (d, 2C,
2JCP 8.3, 3,7-dbf), 123.2 (d, 2C, 3JCP 15.0, 2,8-dbf), 114.9 (d, 2C,
1JCP 66.0, 4,6-dbf), 65.0 (s, 2C, C(Ph)3), 28.4 (d, 4C, 1JCP 70.2,
iPr CH(CH3)2), 17.9 (d, 4C, 2JCP 1.7, iPr CH(CH3)2), 15.9 (d, 4C,
151.8 (d, JCP 1.5), 138.2 (s, Ar C), 135.0 (d, 2C, JCP 6.8,
3,7-dbf), 132.9 (d, 8C, 2JCP 10.6, PPh2 CH), 132.0 (d, JCP 104.9,
4,6-dbf), 131.8 (d, 4C, 4JCP 3.0, PPh2 CH), 129.0 (d, JCP 12.8),
125.1 (d, JCP 6.8), 124.9 (d, JCP 2.3), 124.1 (d, JCP 10.6), 122.4
(d, JCP 17.4), 120.6 (s), 117.2 (d, JCP 90.6, Ar C), 22.1 (s, CH3).
dP (benzene-d6) ꢀ4.9 (s, 2P, P¼N). Anal. Calc. forC52H44N2OP2:
C 80.60, H 5.72, N 3.62. Found: C 80.28, H 5.87, N 4.46 %.
N,N’-(Dibenzofuran-4,6-diylbis(diphenyl-
phosphoranylylidene))bis(4-tritylaniline) (3b)
A mixture of 2-Ph (1.997 g, 3.722 mmol) and p-TrPhN3
(1.746 g, 4.831 mmol) was added to a 50 mL round-bottomed
flask attached to a double manifold vacuum line and dissolved in
toluene (20 mL) to afford an opaque, dark orange suspension,
which was then stirred at 558C for 17.5 h. Solvent was removed
under vacuum to afford a bright yellow solid, which was
reconstituted in minimal toluene (15 mL) and left to sit at
ambient temperature for 24 h, resulting in a pale yellow solid.
The solution was filtered through a fine-porosity glass frit and
the collected solid was dried under vacuum, resulting in a bright
yellow powder (2.107 g, 73 %). dH (benzene-d6) 8.23 (d, 2H,
i
2JCP 3.4, Pr CH(CH3)2). dP (benzene-d6) 20.2 (s, 2P, P¼N).
Anal. Calc. for C74H72N2OP2: C 83.27, H 6.80, N 2.62. Found: C
83.24, H 6.86, N 2.70 %.
N-((6-(N-(3,5-Dimethylphenyl)-P,P-
diphenylphosphorimidoyl)-dibenzofuran-4-yl)
diphenylphosphoranylidene)-3,5-dimethyl-
benzenaminium tetrakis(3,5-bis(trifluoromethyl)
phenyl)borate (4a)
3
3
3JHH 7.5), 7.99 (d, 2H, JHH 7.5), 7.52 (d, 8H, JHH 7.5), 7.49
(t, 2H, 3JHH 7.5), 7.35 (m, 4H, 3JHH 7.5), 7.1–7.3 (ov m, 38H),
3
3
6.73 (d, 4H, JHH 8.6), 6.46 (d, 4H, JHH 8.6, Ar H). dC
(dichloromethane-d2) 156.2 (d, JCP 2.2), 149.1 (d, JCP 2.0),
148.0 (s), 135.7 (s, Ar C), 134.4 (d, 2C, 2JCP 7.1, 3,7-dbf), 132.5
(d, 8C, 2JCP 10.3, PPh2 CH), 132.0 (d, 4C, 4JCP 2.7, PPh2 CH),
131.6 (s, 4C, m-Xy CH), 131.4 (s), 130.1 (s), 128.9 (d, JCP 12.4),
127.6 (s), 125.9 (s, Ar C), 125.2 (d, 2C, 4JCP 2.3, 1,9-dbf), 125.0
(d, 2C, JCP 6.5, 2,8-dbf), 124.1 (d, 4C, 4JCP 10.5, m-Xy C), 122.5
(d, JCP 17.1, Ar C), 116.0 (d, 2C, 1JCP 94.9, 4,6-dbf), 64.6 (s, 2C,
A mixture of 3a (510 mg, 0.658 mmol) and [H(OEt2)2][B(m-
(CF3)2-C6H3)4] (666 mg, 0.658 mmol) was added to a 50 mL
round-bottomed flask attached to a double manifold vacuum
line and dissolved in dichloromethane (25 mL), which was then
stirred at ambient temperature for 4 h, affording a cloudy brown
suspension. Solvent was removed under vacuum to afford a

Cationic Dibenzofuran–Phosphinimine Zn Complexes
381
brown residue, which was washed with cold pentane
(3 ꢂ 20 mL) and dried under vacuum, resulting in an off-white
Solvent was removed under vacuum and the off-white powder
washed with cold pentane (3 ꢂ 6 mL), recrystallized from
toluene and pentane (1 : 5 ratio) at ꢀ358C, and dried under
vacuum, resulting in a pale peach, crystalline powder (834 mg,
powder (760 mg, 70 %). dH (benzene-d6) 8.39 (br s, 8H, BArF ),
4
7.58 (br s, 4H, BArF ), 7.52 (d, 2H, JHH 7.43), 7.26 (d, 8H, JHH
4
7.43), 6.98 (q, 6H, JHH 7.43), 6.86 (q, 12H, JHH 7.87), 6.42 (s,
3H), 6.40 (s, 2H, Ar CH), 1.91 (s, 12H, m-Xy CH3). dC (benzene-
d6) 162.4 (q, 4C, 1JCB 50.1, BArF4 C), 157.5 (s, 2C, Ar C), 143.5
(br m, 2C), 139.3 (s, 4C, m-Xy C), 135.7 (br s, 8C, BArF4 CH),
134.3 (d, 4C, 4JCP 2.7), 133.3 (d, 8C, 2JCP 10.7, PPh2 CH), 132.2
(d, 2C, 2JCP 7.9, 3,7-dbf CH), 130.2 (qq, 8C, 2JCF 31.4, 3JCB 2.0,
BArF4 C), 129.8 (d, 8C, 3JCP 12.9, PPh2 CH), 128.3 (s, 2C, m-Xy
CH), 127.4 (d, 4C, 3JCP 1.6, m-Xy CH), 125.5 (q, 8C, 1JCF 272.1,
BArF4 CF3), 125.4 (s, 2C, 1,9-dbf CH), 124.6 (d, 2C, JCP 6.6, Ar
C), 123.0 (d, 2C, 3JCP 10.8, 2,8-dbf), 118.4 (br sp, 4C, 3JCF 4.3,
BArF4 CH), 113.2 (d, 2C, 1JCP 91.1, 4,6-dbf), 21.4 (s, 4C, m-Xy
CH3). Signal for PPh2 ipso-C was not observed. dP (benzene-d6)
81 %). dH (benzene-d6) 8.39 (br s, 8H, BArF ), 7.76 (d, 2H, 3JHH
4
7.15, 3,7-dbf), 7.62 (br s, 4H, BArF ), 7.57 (d, 2H, JHH 7.68,
3
4
1,9-dbf), 7.07 (dd, 2H, 3JHH 7.42, 3JHH 7.68), 6.71 (s, 4H), 6.50
(s, 2H, Ar CH), 3.90 (br s, 1H, NH), 2.53 (sp, 4H, 3JHH 7.15, iPr
3
CH(CH3)2), 2.15 (s, 12H, Ar CH3), 1.07 (d, 12H, JHH 7.02),
0.92 (d, 12H, 3JHH 7.11, iPr CH(CH3)2). dC (benzene-d6) 163.1
(q, 4C, 1JCB 50.2, BArF4 C), 156.5 (d, 2C, JCP 2.2, Ar C), 150.3
(br m, 2C), 138.6 (s, 4C, m-Xy C), 135.8 (br s, 8C, BArF4 CH),
2
2
133.8 (d, 2C, JCP 5.1, 3,7-dbf CH), 130.2 (qq, 8C, JCF 31.3,
3JCB 3.1, BArF4 C), 125.5 (q, 8C, 1JCF 272.2, BArF4 CF3), 125.3
(d, 2C, 4JCP 2.1, 1,9-dbf), 124.7 (d, 2C, JCP 8.8, Ar C), 124.2 (d,
2C, 3JCP 8.8, 2,8-dbf), 122.4 (d, 4C, 3JCP 13.3), 121.6 (s, 2C, m-
Xy CH), (br sp, 4C, 3JCF 3.7, BArF4 CH), 113.9 (d, 2C, 1JCP 68.8,
4,6-dbf), 28.0 (d, 4C, 1JCP 68.2, iPr CH(CH3)2), 21.9 (s, 4C, m-
18.8 (br s, 2P, P¼N). dB (benzene-d6) ꢀ5.8 (s, 1B, BArF ). dF
4
(benzene-d6) ꢀ61.2 (s, 24F, BArF ). Anal. Calc. for
4
2
i
C84H57BF24N2OP2: C 61.55, H 3.51, N 1.71. Found: C 61.46,
H 3.43, N 1.61 %.
Xy CH3), 18.0 (d, 4C, 2JCP 2.2), 16.3 (d, 4C, JCP 2.9, Pr CH
(CH3)2). dP (benzene-d6) 25.7 (br s, 2P, P¼N). dB (benzene-d6)
ꢀ5.8 (s, 1B, BArF ). dF (benzene-d6) ꢀ61.2 (s, 24F, BArF ).
4
4
N-((6-(P,P-Diphenyl-N-(4-tritylphenyl)phosphorimidoyl)-
dibenzofuran-4-yl)diphenylphosphoranylidene)-4-
tritylbenzenaminium tetrakis(3,5-bis(trifluoromethyl)-
phenyl)borate (4b)
Anal. Calc. for C72H65BF24N2OP2: C 57.54, H 4.36, N 1.86.
Found: C 57.17, H 4.03, N 1.55 %.
N-((6-(P,P-Diisopropyl-N-(4-tritylphenyl)
phosphorimidoyl)-dibenzofuran-4-yl)
diisopropylphosphoranylidene)-4-tritylbenzenaminium
tetrakis(3,5-bis(trifluoromethyl)-phenyl)borate (4d)
In an argon atmosphere glove box, a mixture of 3b (300.2 mg,
0.2495 mmol) and [H(OEt2)2][B(m-(CF3)2-C6H3)4] (252.9 mg,
0.2498 mmol) was added to a 20 mL scintillation vial and dis-
solved in toluene (15 mL), which was then stirred at ambient
temperature for 1.5 h, affording a clear yellow solution. Solvent
was removed under vacuum and the yellow crystalline powder
washed with cold pentane (3 ꢂ 6 mL), recrystallized from tol-
uene and pentane (1 : 5 ratio) at ꢀ358C, and dried under vacuum,
resulting in a yellow, crystalline powder (424.4 mg, 82 %). dH
(benzene-d6) 8.39 (br s, 8H, BArF ), 7.57 (br s, 4H, BArF ), 7.52
In an argon atmosphere glove box, a mixture of 3d (239.7 mg,
0.2246 mmol) and [H(OEt2)2][B(m-(CF3)2-C6H3)4] (225.7 mg,
0.2229 mmol) was added to a 20 mL scintillation vial and dis-
solved in toluene (7.5 mL), which was then stirred at ambient
temperature for 1.5 h, affording a clear yellow solution. Solvent
was removed under vacuum and the yellow crystalline powder
washed with cold pentane (3 ꢂ 6 mL), recrystallized from tol-
uene and pentane (1 : 5 ratio) at ꢀ358C, and dried under vacuum,
resulting in a yellow, crystalline powder (340.9 mg, 79 %). dH
4
4
(d, 2H, JHH 7.65), 7.21 (m, 14H), 6.97 (m, 31H), 6.86 (q, 12H,
JHH 7.78), 6.58 (d, 5H, JHH 8.55, Ar CH). Signal for NH was not
observed. dC (benzene-d6) 163.1 (q, 4C, JCB 49.8, BArF C),
(benzene-d6, 218C) 8.39 (br s, 8H, BArF ), 7.62 (s, 2H, Ar CH),
1
4
4
157.3 (s, 2C, Ar C), 147.5 (s, 6C, p-TrPh C), 142.4 (d, 2C, JCP
1.6), 141.5 (d, 2C, JCP 3.1, Ar C), 135.7 (br s, 8C, BArF4 CH),
134.4 (d, 4C, 4JCP 2.1), 133.2 (d, 8C, 2JCP 10.6, PPh2 CH), 132.7
(br s, 2C, 1,9-dbf CH), 132.4 (d, 2C, 2JCP 8.1, 3,7-dbf), 131.7 (s,
7.59 (br s, 4H, BArF ), 7.32 (d, 12H, JHH 7.32), 7.05 (m, 24H),
4
6.99 (m, 2H), 6.39 (d, 4H, JHH 8.62, Ar CH), 5.10 (br s, 1H, NH),
2.20 (sp, 4H, 3JHH 7.10, iPr CH(CH3)2), 0.66 (d, 12H, 3JHH 6.59),
0.64 (d, 12H, 3JHH 6.68, iPr CH(CH3)2). dC (benzene-d6, 228C)
163.1 (q, 4C, 1JCB 49.0, BArF4 C), 157.8 (d, 2C, JCP 2.2, Ar C),
147.5 (s, 6C, p-TrPh C), 135.7 (br s, 8C, BArF4 CH), 132.9 (br s,
2C, 1,9-dbf CH), 131.6 (s, 12C, p-TrPh), 131.2 (br s, 2C, 3,7-
dbf), 130.3 (qq, 8C, 2JCF 31.8, 3JCB 2.9, BArF4 C), 128.3 (s, 12C,
p-TrPh), 127.0 (br s, 4C, p-TrPh CH), 126.8 (s, 6C, p-TrPh CH),
125.5 (q, 8C, 1JCF 272.8, BArF4 CF3), 125.0 (d, 2C, JCP 5.8, Ar
2
3
12C, p-TrPh), 130.2 (qq, 8C, JCF 31.6, JCB 3.0, BArF C),
4
129.8 (d, 8C, 3JCP 12.8, PPh2 CH), 128.9 (s, 12C, p-TrPh), 127.5
(br s, 4C, p-TrPh CH), 126.7 (s, 6C, p-TrPh CH), 125.5 (q, 8C,
1JCF 272.5, BArF4 CF3), 125.2 (d, 2C, 3JCP 11.0, 2,8-dbf), 124.7
(d, 4C, 1JCP 105.5, PPh2 C), 124.6 (d, 2C, JCP 6.4, Ar C), 124.3
(d, 4C, 3JCP 10.7, p-TrPh CH), 118.4 (br sp, 4C, 3JCF 4.0, BArF
4
3
3
CH), 111.4 (d, 2C, 1JCP 96.1, 4,6-dbf), 65.2 (s, 2C, p-TrPh). dP
(benzene-d6) 19.6 (s, 2P, P¼N). dB (benzene-d6) ꢀ5.8 (s, 1B,
BArF ). dF (benzene-d6) ꢀ61.2 (s, 24F, BArF ). Anal. Calc. for
C), 124.7 (d, 2C, JCP 8.1, 2,8-dbf), 124.2 (d, 4C, JCP 8.1,
p-TrPh CH), 118.4 (br sp, 4C, 3JCF 2.9, BArF4 CH), 65.3 (s, 2C,
1
p-TrPh), 30.7 (br d, 4C, JCP 61.3, Pr CH(CH3)2), 16.4 (br s,
i
4
4
i
4C), 15.4 (br s, 4C, Pr CH(CH3)2). Signals for two aromatic
C118H77BF24N2OP2: C 68.55, H 3.75, N 1.35. Found: C 68.73, H
3.85, N 1.57 %.
quaternary carbon environments (2C each) were not observed.
dP (benzene-d6, 218C) 40.9 (br s, 2P, P¼N). dF (benzene-d6,
218C) ꢀ61.1 (s, 24F, CF3). dB (benzene-d6, 218C) ꢀ5.8 (s, 1B,
N-((6-(N-(3,5-Dimethylphenyl)-P,P-diisopropyl-
phosphorimidoyl)dibenzofuran-4-yl)diisopropyl-
phosphoranylidene)-3,5-dimethylbenzenaminium
tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (4c)
BArF ). Anal. Calc. for C106H85BF24N2OP2: C 65.91, H 4.44,
4
N 1.45. Found: C 65.85, H 4.39, N 1.39 %.
Ethyl(N,N’-(dibenzofuran-4,6-diylbis(diphenyl-
phosphoranylylidene))bis(3,5-dimethylaniline)) Zinc (5a)
In an argon atmosphere glove box, a mixture of 3c (437 mg,
0.684 mmol) and [H(OEt2)2][B(m-(CF3)2-C6H3)4] (695 mg,
0.686 mmol) was added to a 20 mL scintillation vial and dis-
solved in toluene (8 mL) to afford a clear, dark brown solution,
which was then stirred at ambient temperature for 72.5 h.
In an argon atmosphere glove box, a sample of 4a (100.3 mg,
0.06119 mmol) was added to a 20 mL scintillation vial and
dissolved in toluene (1.5 mL) to afford a clear, colourless

382
M. T. Zamora et al.
solution. An aliquot of [ZnEt2] (6.3 mL, 0.061 mmol) was
injected, and the resulting faint yellow solution was then stirred
at ambient temperature for 1 h. Solvent was removed under
vacuum and the off-white powder washed with cold pentane
(3 ꢂ 6 mL), recrystallized from toluene and pentane (1 : 5 ratio)
at ꢀ358C, and dried under vacuum, resulting in a pale orange,
crystalline powder (93.5 mg, 93 %). dH (benzene-d6) 8.41 (br s,
8H, BArF ), 7.58 (br s, 4H, BArF ), 7.47 (m, 2H), 7.37 (dd, 8H,
dissolved in toluene (12 mL) to afford a clear, orange solution.
An aliquot of [ZnEt2] (24.5 mL, 0.238 mmol) was injected, and
the resulting faint yellow solution was then stirred at ambient
temperature for 1 h. Solvent was removed under vacuum and the
pale beige powder washed with cold pentane (3 ꢂ 6 mL),
recrystallized from toluene and pentane (1 : 5 ratio) at ꢀ358C,
and dried under vacuum, resulting in a yellow, crystalline
powder (347.4 mg, 93 %). dH (dichloromethane-d2) 8.40 (d, 2H,
3JHH 6.6), 7.72 (ov m, 12H), 7.55 (s, 4H), 6.48 (s, 2H), 6.32 (s,
4H, Ar H), 4.55 (br s, 1H, NH), 2.94 (br s, 4H, iPr CH(CH3)2),
1.20 (ov m, 24H, iPr CH(CH3)2). Inappreciable solubility in all
solvents precluded satisfactory signal-to-noise for 13C{1H}
analysis. dP (benzene-d6) 50.1 (s, 2P, P¼N). dB (benzene-d6)
ꢀ6.1 (s, 1B, BArF ). dF (benzene-d6) ꢀ61.1 (s, 24F, BArF ).
4
4
JHH 12.42, JHH 7.07), 7.13 (m, 2H), 7.03 (m, 7H), 6.89 (m, 8H),
6.31 (s, 3H), 6.22 (s, 2H, Ar CH), 1.81 (s, 12H, m-Xy CH3), 0.94
3
3
(t, 3H, JHH 8.14, ZnCH2CH3), 0.18 (q, 2H, JHH 8.14,
ZnCH2CH3). dC (benzene-d6) 163.1 (q, 4C, 1JCB 49.4, BArF4 C),
156.5 (s, 2C, Ar C), 145.6 (d, 2C, 2JCP 5.1), 139.3 (d, 4C, 4JCP
1.4, m-Xy C), 135.7 (br s, 8C, BArF CH), 134.2 (d, 4C, JCP
4
4
4
4
2.6), 133.7 (d, 8C, 2JCP 10.3, PPh2 CH), 131.8 (d, 2C, 2JCP 9.0,
3,7-dbf CH), 130.2 (qq, 8C, 2JCF 31.6, 3JCB 2.8, BArF4 C), 129.8
(s, 2C, m-Xy CH), 129.7 (d, 8C, 3JCP 12.8, PPh2 CH), 128.9 (d,
4C, 3JCP 1.7, m-Xy CH), 126.0 (s, 2C, 1,9-dbf CH), 125.5 (q, 8C,
1JCF 272.1, BArF4 CF3), 124.6 (d, 2C, JCP 6.6, Ar C), 123.8 (d,
2C, 3JCP 10.2, 2,8-dbf), 118.4 (br sp, 4C, 3JCF 4.1, BArF4 CH),
113.2 (d, 2C, 1JCP 110.9, 4,6-dbf), 21.4 (s, 4C, m-Xy CH3), 13.1
(s, 1C, ZnCH2CH3), 2.3 (s, 1C, ZnCH2CH3). Signal for PPh2
ipso-C was not observed. dP (benzene-d6) 27.1 (s, 2P, P¼N). dB
Anal. Calc. for C74H69BF24N2OP2Zn: C 55.67, H 4.36, N 1.75.
Found: C 54.61, H 4.01, N 1.41 %.
Ethyl(N,N’-(dibenzofuran-4,6-diylbis(diisopropyl-
phosphoranylylidene))bis(4-tritylaniline)) Zinc (5d)
In an argon atmosphere glove box, a sample of 4d (290.5 mg,
0.1504 mmol) was added to a 20 mL scintillation vial and dis-
solved in toluene (12 mL) to afford a clear, orange solution. An
aliquot of [ZnEt2] (17.0 mL, 0.165 mmol) was injected, and the
resulting faint yellow solution was then stirred at ambient
temperature for 0.5 h. Solvent was removed under vacuum and
the dark yellow powder washed with cold pentane (3 ꢂ 6 mL),
redissolved in benzene (0.5 mL), and passed through a Celite
filter. Solvent was removed under vacuum and the bright yellow
powder was recrystallized from toluene and pentane (1 : 5 ratio)
at ꢀ358C, and dried under vacuum, resulting in a yellow,
crystalline powder (219.7 mg, 72 %). dH (benzene-d6) 8.39 (br s,
8H, BArF ), 7.59 (br s, 4H, BArF ), 7.56 (s, 2H, 2,8-dbf), 7.30 (d,
(benzene-d6) ꢀ5.8 (s, 1B, BArF ). dF (benzene-d6) ꢀ61.2
4
(s, 24F, BArF ). Anal. Calc. for C86H61BF24N2OP2Zn: C 59.62,
H 3.55, N 1.62. Found: C 59.98, H 3.85, N 1.99 %.
4
Ethyl(N,N’-(dibenzofuran-4,6-diylbis(diphenyl-
phosphoranylylidene))bis(4-tritylaniline)) Zinc (5b)
In an argon atmosphere glove box, a sample of 4b (75.0 mg,
0.03627 mmol) was added to a 20 mL scintillation vial and
dissolved in toluene (4 mL) to afford a clear, yellow solution. An
aliquot of [ZnEt2] (4.1 mL, 0.040 mmol) was injected, and the
resulting faint yellow solution was then stirred at ambient
temperature for 1.5 h. Solvent was removed under vacuum and
the off-white powder washed with cold pentane (3 ꢂ 6 mL),
recrystallized from toluene and pentane (1 : 5 ratio) at ꢀ358C,
and dried under vacuum, resulting in a yellow, crystalline
4
4
3
4H, JHH 7.49, p-TrPh), 7.06 (m, 30H, p-TrPh), 7.06 (d, 4H,
3JHH 7.60, p-TrPh), 6.75 (d, 2H, 3JHH 7.64, 3,7-dbf), 6.48 (d, 2H,
3JHH 7.42, 1,9-dbf), 2.16 (br sept, 4H, iPr CH(CH3)2), 0.61 (d,
12H, 3JHH 6.65), 0.56 (d, 12H, 3JHH 6.96, iPr CH(CH3)2), 0.40 (t,
3
3
3H, JHH 7.89, ZnCH2CH3), ꢀ0.23 (q, 2H, JHH 7.95,
ZnCH2CH3). dC (benzene-d6) 163.1 (q, 4C, 1JCB 49.2, BArF4 C),
157.0 (s, 2C, Ar C), 147.4 (s, 6C, p-TrPh C), 144.5 (d, 2C, JCP
4.7), 143.6 (d, 2C, JCP 3.1, Ar C), 135.7 (br s, 8C, BArF4 CH),
133.1 (br s, 2C, 1,9-dbf CH), 131.7 (s, 12C, p-TrPh), 130.7 (d,
powder (77.1 mg, 98 %). dH (benzene-d6) 8.39 (br s, 8H, BArF ),
4
7.54 (br s, 4H, BArF ), 7.46 (d, 2H, JHH 7.24), 7.27 (d, 8H, JHH
4
7.58), 6.99(m, 50H), 6.52 (d, 4H, JHH 8.59, Ar CH), 0.62 (t, 3H,
3JHH 7.97, ZnCH2CH3), ꢀ0.01 (q, 2H, 3JHH 7.97, ZnCH2CH3).
dC (benzene-d6) 163.1 (q, 4C, 1JCB 50.2, BArF4 C), 156.6 (s, 2C,
Ar C), 147.3 (s, 6C, p-TrPh C), 144.0 (d, 2C, JCP 4.3), 142.6 (d,
2C, JCP 3.1, Ar C), 135.7 (br s, 8C, BArF4 CH), 134.3 (d, 4C, 4JCP
2.8), 133.7 (d, 8C, 2JCP 10.7, PPh2 CH), 132.7 (br s, 2C, 1,9-dbf
2C, 2JCP 6.6, 3,7-dbf), 130.3 (qq, 8C, 2JCF 31.5, 3JCB 3.0, BArF
4
C), 128.9 (s, 12C, p-TrPh), 127.3 (br s, 4C, p-TrPh CH), 126.7 (s,
6C, p-TrPh CH), 125.8 (d, 2C, 3JCP 7.2, 2,8-dbf), 125.7 (d, 4C,
1
3JCP 13.8, p-TrPh CH), 125.5 (q, 8C, JCF 272.5, BArF CF3),
4
124.8 (d, 2C, JCP 5.3, Ar C), 118.4 (br sp, 4C, 3JCF 3.9, BArF
2
4
CH), 132.0 (d, 2C, JCP 8.1, 3,7-dbf), 131.7 (s, 12C, p-TrPh),
CH), 65.3 (s, 2C, p-TrPh), 26.3[27] (br d, 4C, iPr CH(CH3)2), 16.1
(d, 4C, 2JCP 2.0), 15.6 (d, 4C, 2JCP 1.9, iPr CH(CH3)2), 12.4 (s,
1C, ZnCH2CH3), 1.6 (s, 1C, ZnCH2CH3). Signal for 4,6-dbf was
not observed. dP (benzene-d6) 49.9 (s, 2P, P¼N). dB (benzene-
d6) ꢀ5.8 (s, 1B, BArF ). dF (benzene-d6) ꢀ61.1 (s, 24F, BArF ).
130.2 (qq, 8C, 2JCF 31.3, 3JCB 2.6, BArF4 C), 129.7 (d, 8C, 3JCP
10.5, PPh2 CH), 128.2 (s, 12C, p-TrPh), 127.5 (br s, 4C, p-TrPh
CH), 126.7 (s, 6C, p-TrPh CH), 126.0 (d, 2C, 3JCP 11.6, 2,8-dbf),
1
3
125.5 (q, 8C, JCF 272.8, BArF CF3), 125.5 (d, 4C, JCP 9.7,
4
p-TrPh CH), 125.1 (d, 4C, 1JCP 92.3, PPh2 C), 124.8 (d, 2C, JCP
6.4, Ar C), 118.4 (br sp, 4C, 3JCF 3.9, BArF4 CH), 112.8 (d, 2C,
1JCP 96.1, 4,6-dbf), 65.0 (s, 2C, p-TrPh), 12.8 (s, 1C,
ZnCH2CH3), 2.5 (s, 1C, ZnCH2CH3). dP (benzene-d6) 29.9 (s,
4
4
Anal. Calc. for C108H89BF24N2OP2Zn: C 64.06, H 4.43, N 1.38.
Found: C 64.38, H 4.04, N 1.57 %.
2P, P¼N). dB (benzene-d6) ꢀ5.8 (s, 1B, BArF ). dF (benzene-d6)
X-Ray Crystallography
4
ꢀ61.2 (s, 24F, BArF ). Anal. Calc. for C120H81BF24N2OP2Zn:
Single crystals suitable for X-ray diffraction were readily
obtained from concentrated toluene (3a) or bromobenzene
solutions (3b) at ambient temperature, by slow diffusion of
pentane into a dichloromethane solution (3c, 3d, and 5c9) at
ꢀ358C, or by slow diffusion of pentane into a benzene solution
(4c) at ambient temperature. Crystals were coated in dry Para-
tone oil under an argon atmosphere and mounted onto a glass
4
C 66.69, H 3.78, N 1.30. Found: C 66.21, H 3.44, N 0.99 %.
Ethyl(N,N’-(dibenzofuran-4,6-diylbis(diisopropyl-
phosphoranylylidene))bis(3,5-dimethylaniline)) Zinc (5c)
In an argon atmosphere glove box, a sample of 4c (232.9 mg,
0.2348 mmol) was added to a 20 mL scintillation vial and

Cationic Dibenzofuran–Phosphinimine Zn Complexes
383
fibre. Data were collected at 173 K using a Bruker SMART
˚
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APEX II diffractometer (MoKa radiation, l 0.71073 A) outfitted
with a CCD area-detector and a KRYO-FLEX liquid nitrogen
vapour cooling device. A data collection strategy using v and j
scans at 0.58 steps yielded full hemispherical data with excellent
intensity statistics. Unit cell parameters were determined and
refined on all observed reflections using APEX2 software.[28]
Data reduction and correction for Lorentz polarization were
performed using SAINT-Plus software.[29] Absorption correc-
tions were applied using SADABS.[30] The structures were
solved by direct methods and refined by the least-squares
method on F2 using the SHELXTL[31] or Olex2[32] software
suites. All non-hydrogen atoms were refined anisotropically.
Hydrogen atom positions were calculated and isotropically
refined as riding models to their parent atoms, except the N–H
hydrogen of 4c which was located from the Fourier difference
map and isotropically refined with a fixed N–H bond length.
Table 1 provides a summary of selected data collection and
refinement parameters. Special considerations were required in
the refinement of disordered moieties in the structures of 3a, 3b,
4c, and 5c9. In the structure of 3a, one toluene solvent molecule
(C1s, 60 %/C1r, 40 %) was disordered and some restraints were
applied in order to obtain reasonable bond distances and angles.
Similarly, two CF3 groups in the anion of 4c were disordered
over two positions with occupation factor ratios of 53 : 47 and
60 : 40. Furthermore, the structure of 3b contained two severely
disordered bromobenzene solvent molecules in the asymmetric
unit, for which no suitable model could be found. Likewise, the
structure of 5c9 contained one severely disordered tetrahydro-
furan solvent molecule in the asymmetric unit, for which no
suitable model could be found. The electron density associated
with the disordered regions in both 3b and 5c9 was removed
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from the reflection files using the SQUEEZE subroutine of
PLATON,[33] leaving voids of ,847.3 and 330.8 A ,
respectively.
3
˚
Crystallographic Data
Atomic coordinates, interatomic distances and angles, aniso-
tropic thermal parameters, and hydrogen parameters for 3a–d,
4c, and 5c9 are available as CIF files from the Cambridge
Crystallographic Data Centre (CCDC) using depository num-
bers 1023936–1023941.
(q) C. N. Ayala, M. H. Chisholm, J. C. Gallucci, C. Krempner, Dalton
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Acknowledgements
Thanks are extended by P.G.H. to the Natural Sciences and Engineering
Research Council (NSERC) of Canada, Canada Foundation for Innovation
(CFI), Canada School of Energy and Environment, and GreenCentre Canada
for financial support, as well as to Prof. Dr Jun Okuda and RWTH Aachen
University for hosting P.G.H. during the preparation of this manuscript. The
authors also thank Connor S. MacNeil for determining the X-ray structure of
4c and Dr Tracey Roemmele for aiding with elemental analysis measure-
ments. Furthermore, S.M.Z. acknowledges NSERC for student awards.
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