Synthesis and reactivity of iridium complexes of a macrocyclic PNP pincer ligand

Article abstract of DOI:10.1039/d0dt04303f

Having recently reported on the synthesis and rhodium complexes of the novel macrocyclic pincer ligand PNP-14, which is derived from lutidine and features terminal phosphine donors trans-substituted with a tetradecamethylene linker (Dalton Trans., 2020, 49, 2077-2086 and Dalton Trans., 2020, 49, 16649-16652), we herein describe our findings critically examining the chemistry of iridium homologues. The five-coordinate iridium(i) and iridium(iii) complexes [Ir(PNP-14)(η2:η2-cyclooctadiene)][BArF4] and [Ir(PNP-14)(2,2′-biphenyl)][BArF4] are readily prepared and shown to be effective precursors for the generation of iridium(iii) dihydride dihydrogen, iridium(i) bis(ethylene), and iridium(i) carbonyl derivatives that highlight important periodic trends by comparison to rhodium counterparts. Reaction of [Ir(PNP-14)H2(H2)][BArF4] with 3,3-dimethylbutene induced triple C-H bond activation of the methylene chain, yielding an iridium(iii) allyl hydride derivative [Ir(PNP-14?)H][BArF4], whilst catalytic homocoupling of 3,3-dimethylbutyne into Z-tBuCCCHCHtBu could be promoted at RT by [Ir(PNP-14)(η2:η2-cyclooctadiene)][BArF4] (TOFinitial = 28 h-1). The mechanism of the latter is proposed to involve formation and direct reaction of a vinylidene derivative with HCCtBu outside of the macrocyclic ring and this suggestion is supported experimentally by isolation and crystallographic characterisation of a catalyst deactivation product. This journal is

Full text of DOI:10.1039/d0dt04303f

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Synthesis and reactivity of iridium complexes of a
macrocyclic PNP pincer ligand†
Cite this: Dalton Trans., 2021, 50,
2472
Thomas M. Hood
and Adrian B. Chaplin
*
Having recently reported on the synthesis and rhodium complexes of the novel macrocyclic pincer
ligand PNP-14, which is derived from lutidine and features terminal phosphine donors trans-substituted
with a tetradecamethylene linker (Dalton Trans., 2020, 49, 2077–2086 and Dalton Trans., 2020, 49,
16649–16652), we herein describe our findings critically examining the chemistry of iridium homologues.
The five-coordinate iridium(I) and iridium(III) complexes [Ir(PNP-14)(η2:η2-cyclooctadiene)][BArF4] and [Ir
(PNP-14)(2,2’-biphenyl)][BArF4] are readily prepared and shown to be effective precursors for the gene-
ration of iridium(III) dihydride dihydrogen, iridium(I) bis(ethylene), and iridium(I) carbonyl derivatives that
highlight important periodic trends by comparison to rhodium counterparts. Reaction of [Ir(PNP-14)
H2(H2)][BArF4] with 3,3-dimethylbutene induced triple C–H bond activation of the methylene chain,
yielding an iridium(III) allyl hydride derivative [Ir(PNP-14*)H][BArF4], whilst catalytic homocoupling of
3,3-dimethylbutyne into Z-tBuCuCCHCHtBu could be promoted at RT by [Ir(PNP-14)(η2:η2-
cyclooctadiene)][BArF4] (TOFinitial = 28 h−1). The mechanism of the latter is proposed to involve formation
and direct reaction of a vinylidene derivative with HCuCtBu outside of the macrocyclic ring and this sug-
gestion is supported experimentally by isolation and crystallographic characterisation of a catalyst de-
activation product.
Received 18th December 2020,
Accepted 19th January 2021
DOI: 10.1039/d0dt04303f
rsc.li/dalton
constituents.2 As marked out by lower carbonyl stretching fre-
quencies,6 the heavier iridium congeners are particularly
1. Introduction
Phosphine-based pincers are robust ancillary ligands that con- notable for a more pronounced tendency for oxidative addition
tinue to find notable applications in organometallic chemistry of H2,7,8 C(sp3)–H bonds,3,9 and C(sp2)–H bonds10 compared
and homogenous catalysis.1,2 In particular, rhodium and to their rhodium counterparts.
iridium complexes of these ligands are associated with funda-
Motivated by the potential to exploit additional reaction
mental and applied breakthroughs in the chemistry of C–H control though their unique steric profile, use in the construc-
bond activation reactions; exemplified by the characterisation tion of interlocked assemblies, and as an extension of our
of σ-alkane complexes and development of high-performance related work with NHC-based variants,11–13 we have recently
alkane dehydrogenation catalysts, respectively.3,4 These mer-tri- become interested in the chemistry of macrocyclic phosphine-
dentate ligands are evidently well-suited to supporting the for- based pincers.14–16 Last year we reported on the synthesis and
mation of highly reactive M(I) derivatives necessary to bring rhodium complexes of the lutidine-derived macrocyclic pincer
about cleavage of strong C–H bonds,5 able to accommodate PNP-14, where the chiral P-donors are trans-substituted with a
the changes in geometry associated with M(I)/M(III) redox shut- tetradecamethylene linker (Chart 1).14,15 As a novel platform
tling, and suitably modular in composition to enable augmen- for exploring the organometallic chemistry of Group 9 pincer
tation of metal-based reactivity through considered change of complexes, we now present our findings critically examining
the central donor atom, wingtip substituents, or backbone
Department of Chemistry, University of Warwick, Gibbet Hill Road,
Coventry CV4 7AL, UK. E-mail: a.b.chaplin@warwick.ac.uk
†Electronic supplementary information (ESI) available: Catalytic homocoupling
of 3,3-dimethylbutyne promoted by 6, synthesis and characterisation of
[Rh(PNP-14)(η2-norbornene)][BArF4]; NMR, IR and ESI-MS spectra of new com-
pounds, and selected reactions (PDF). Primary NMR data (MNOVA). CCDC
2051203–2051207. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/d0dt04303f
Chart 1 Complexes of the macrocyclic pincer ligand PNP-14.
2472 | Dalton Trans., 2021, 50, 2472–2482
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2
the chemistry of iridium PNP-14 homologues aided by refer- 17.0 and 13.4 with no appreciable JPP coupling in DFB solu-
ence to acyclic complexes of 2,6-(R2PCH2)2C5H3N (PNP-R; e.g. tion. While unusual, the formulation of 1 simply appears to be
R = tBu, iPr).
a consequence of COD chelation, although this is contingent
upon the flexible lutidine-based backbone and asymmetric
steric profile of the phosphine donors.19 Moreover, given the
rhodium(I) homologue is instead characterised as a C1-sym-
2. Results and discussion
metric square planar complex, viz. [Rh(PNP-14)(η2-COD)]+(1′,
2
16 VE; δ 57.4, 45.9, JPP = 312 Hz),15,20 the capacity of the
31P
Mirroring synthetic strategies that we have successfully
employed for rhodium homologues,14,15 the preparation of
heavier metal congener to from stronger metal–ligand bonds
is clearly a decisive factor. Bulk purity was established by com-
bustion analysis and the structure of 1 was fully corroborated
in solution by NMR spectroscopy and HR ESI-MS.
Coordination of PNP-14 is more conventional in the formally
16 VE square pyramidal iridium(III) complex 2, as evidenced by
a P–Ir–P bite angle of 163.24(5)° in the solid state and C1 sym-
metry in CD2Cl2 solution; with a pair of 31P resonances at δ 38.7
and 20.9 exhibiting a characteristically large trans-phosphine
2JPP coupling constant of 307 Hz.21 The crystal structure of 2 is
isomorphous to the direct rhodium homologue 2′,14 with the
tetradecamethylene linker skewed to one side of the basal plane
away from the biph ligand and contorted in such a way as to
iridium(I) and iridium(III) complexes of PNP-14 was attempted
through substitution reactions of [Ir(COD)2][BArF
]
in 1,2-
17
4
18
difluorobenzene (DFB) and [Ir(COD)(biph)Cl]2 in fluoroben-
zene, respectively, with the latter exploiting Na[BArF4] as a
halide abstracting agent (COD = 1,5-cyclooctadiene, ArF = 3,5-
(CF3)2C6H3, biph = 2,2′-biphenyl; Scheme 1). These reactions
produced five-coordinate cationic derivatives [Ir(PNP-14)(η2:η2-
COD)][BArF4] 1 and [Ir(PNP-14)(biph)][BArF4] 2 under mild con-
ditions, which were subsequently isolated as analytically pure
crystalline materials in good yield (ca. 80%) and fully charac-
terised (Scheme 1).
Iridium(I) complex 1 adopts a distorted trigonal bipyrami-
dal metal geometry (18 VE), with the terminal phosphine
donors positioned in the equatorial coordination sites confer-
ring a distinctly puckered pincer ligand geometry. Distortion
of the PNP ligand towards a fac coordination mode in this
manner is associated with a compressed P–Ir–P bite angle of
115.24(2)° in the solid state and a pair of 31P resonances at δ
enable adoption of a weak γ-agostic interaction (2, Ir1̲ ⋯̲ H–C1̲ 2̲ 9̲ ̲ =
3.152(7); cf. 3.184(2) Å for 2′). Previously reported five-coordi-
nate complexes of the form [M(pincer)(biph)][BArF4] provide
further structural precedent for 2 and the metal-based metrics
of the acyclic analogue [Ir(PNP-tBu)(biph)][BArF4] (II) are
similar.6,11,14 Moreover, as II is fluxional in solution as a result
Scheme 1 Synthesis and solid-state structures of iridium pincer complexes 1 and 2: thermal ellipsoids at 50% and 30% probability, respectively;
anions omitted. Selected bond lengths (Å) and angles (°): 1, Ir1–P2, 2.3743(7); Ir1–P3, 2.3846(7); P2–Ir1–P3, 115.24(2); Ir1–N101, 2.107(2); Ir1–Cnt
(C4,C5), 2.083(2); Ir1–Cnt(C8, C9), 2.036(2); N101–Ir1–Cnt(C4, C5), 172.52(8); Cnt(C4, C5)–Ir–Cnt(C8, C9), 84.29(9); 2, Ir1–P2, 2.3253(15); Ir1–P3,
2.2849(15); P2–Ir1–P3, 163.24(5); Ir1–N101, 2.158(5); Ir1–C4, 2.048(6); Ir1–C15, 2.044(6); N101–Ir1–C15, 172.5(2); C4–Ir1–C15, 81.9(2); Ir1⋯C129,
3.152(7); I̲r̲1̲⋯H̲C129, 2.54; Cnt = centroid.
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of facile biph pseudorotation on the NMR timescale,6 reten- ethylene was established in situ by NMR spectroscopy. The
tion of C1 symmetry in solution suggests that buttressing with latter is associated with four chemically inequivalent 2H
the methylene strap prevents such dynamics in 2.
signals at δ 3.23, 2.80, 2.49 and 1.97 and two 13C resonances at
Reaction of 2 with dihydrogen (1 atm) in DFB at RT resulted δ 26.0 and 18.0, and reinforces the disposition of iridium(I)
in immediate and full conversion into [Ir(PNP-14)(2-biphenyl) centres to adopt five-coordinate geometries: as seen in 2, but
H][BArF4] 3 (δ31P 40.6, 36.5, 2JPP = 302 Hz; δ1H −21.6; Scheme 2). contrasting that observed under the same conditions in the
No further reaction was observed after 18 h, but heating at rhodium(I) system, viz. [Rh(PNP-14)(C2H4)][BArF
]
6′.14
4
85 °C for 6 h resulted in complete hydrogenolysis of the biph Structurally-related bis(ethylene) iridium(I) complexes of CNC-
ligand and formation of dihydride dihydrogen complex [Ir and pybox-based pincer ligands have been crystallographically
(PNP-14)H2(H2)][BArF4] 4 in quantitative spectroscopic yield. characterised, exhibiting distorted trigonal bipyramidal metal
Hydrogenolysis also occurs for 2′ and II, but longer reaction geometries with the ethylene ligands located in the equatorial
times are required under otherwise equivalent conditions sites,22 but are unknown for PNP- and PONOP-based ligands.23
(both ca. 2 days).14 Coordinatively saturated 1 rapidly affords 4
upon reaction with dihydrogen (1 atm) in DFB at RT (<5 min), butene (5 equivalents) the allyl hydride derivative [Ir(PNP-14*)
invoking facile and reversible chelation of COD.
H][BArF4] 7 was produced in quantitative spectroscopic yield
When 2 was instead treated with an excess of 3,3-dimethyl-
Complex 4 was characterised in situ using NMR spectroscopy, after 5 days heating at 100 °C, presumably through intra-
with adoption of time-averaged C2 symmetry, a single 31P reso- molecular transfer dehydrogenation of the methylene chain
nance at δ 42.1, and a broad 4H resonance at δ −9.26 (T1
=
followed by allylic C–H activation (Scheme 2).24 As precedent
88.8 0.7 ms, 600 MHz, argon) the most diagnostic features at for this reactivity, examples of cyclometallated rhodium(III)
298 K. The hydride signal remained broad upon cooling to and iridium(III) pincer complexes can be found in the litera-
253 K but exhibits faster spin–lattice relaxation (δ −9.27, ture.25 Complex 7 was subsequentially isolated in 49% yield
T1 = 50
1 ms, 600 MHz, argon). The acyclic analogue and fully characterised, including in the solid state by single
[Ir(PNP-tBu)H2(H2)]BF4 (IV) is known and formulation as a crystal X-ray diffraction (Fig. 1). In solution 7 is distinctly C1-
dihydride dihydrogen complex was corroborated in a similar symmetric, with a pair of 31P resonances at δ 81.4 and 25.8
2
manner in situ by NMR spectroscopy.7 Whilst the data was with JPP = 313 Hz, allyl 13C resonances at δ 81.9, 66.0, and
recorded under difference conditions, the similarly of the hydride 38.9, and a 1H hydride resonance at δ −8.49 (2JPH = 19.6, 9.7
signatures is striking (IV, δ1H −9.31, T1 = 24 ms, 400 MHz, 233 K Hz). The crystal structure demonstrates that 7 adopts a
in CD3OD). In line with the reduced propensity for oxidative pseudo-octahedral metal geometry in the solid state, with κ6-
addition, the rhodium homologue of 4 is instead observed as a coordination of PNP-14* creating iridacyclopentyl and iridacy-
dihydrogen complex, viz. [Rh(PNP-14)(H2)][BArF ] 4′.14
clododecyl rings, and the hydride ligand was located from the
4
Further supporting the assignment of 4, reaction with ethyl- Fourier difference map. Little distortion of the PNP-core is
ene (1 atm) generated the corresponding C1-symmetric dihy- evident in 7 and the associated metal-based metrics are
dride π-complex 5 (δ31P 33.4, 12.4, 2JPP = 314; δ1H −7.89, −17.80) broadly comparable to those in 2 (e.g. P–Ir–P ca. 163°). There
within 5 min at RT (Scheme 2). Subsequent heating at 85 °C is considerable variance in the allyl Ir–C bond lengths, with
for 16 h yielded the bis(ethylene) complex 6 (δ31P 9.0) in quanti- the longest contact trans to the hydride ligand (Ir1–C119 =
tative spectroscopic yield, with concomitant formation of 2.311(4) Å, Ir1–C120, 2.155(3) Å, Ir1–C121, 2.199(3) Å), but all
ethane. C2 symmetry and coordination of two molecules of the internal carbon bond angles are >120°. The geometry of
Scheme 2 Synthesis and reactivity of iridium dihydride dihydrogen complex 4. [BArF
2474 | Dalton Trans., 2021, 50, 2472–2482
]
− counter anions omitted for clarity.
4
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Scheme 3 Terminal alkyne coupling reactions promoted by 1 and 1’:
[M] = M(PNP-14)+.
Fig. 1 Solid-state structure of 7: the hydride ligand was located from
the Fourier difference map; thermal ellipsoids at 30% probability; solvent
molecule and anion omitted. Selected bond lengths (Å) and angles (°):
Ir1–P2, 2.2694(8); Ir1–P3, 2.3339(9); P2–Ir1–P3, 163.04(3); Ir1–N101,
2.126(2); Ir1–H1, 1.39(3); Ir1–C119, 2.311(4); Ir1–C120, 2.155(3); Ir1–C121,
2.199(3); C119–C120, 1.430(5); C120–C121, 1.409(5); C119–C120–C121,
124.4(3); N101–Ir1–C121, 169.59(11).
inal alkyne coupling reactions,30,31 we were very interested to
ascertain if similar reactivity could be brought about in
iridium complexes of PNP-14. Iridium(I) complex 1 was
selected as the most suitable precursor and initial screening
studies using a twofold excess of HCuCtBu in DFB at RT indi-
cated rapid production of the corresponding Z-enyne (δ1H 5.53,
the iridacyclododecyl ring is reminiscent of the quadrilateral
conformations adopted by 12-membered cycloalkanes.26
The onward reactivity of 6 was harnessed to access the C2-
symmetric Ir(I) carbonyl derivative 8 (δ31P 62.5) by reaction with
carbon monoxide, which was isolated in 89% yield (overall
from 2; Scheme 2). Complexes of this nature are of interest as
the carbonyl ligand is a convenient spectroscopic reporter
group for the electronic characteristics of the metal-pincer
fragment.27,28 In this case, the ν(CO) band of 8 (1984 cm−1) is
shifted to considerably lower frequency compared to the
rhodium(I) homologue 8′ (1997 cm−1) under the same con-
ditions (CH2Cl2 solution, Table 1). This is in line with expected
periodic trends, which are also apparent from the IR data col-
lected for tBu- and iPr-substituted analogues. These data
suggest that PNP-14 is a marginally weaker net donor than
PNP-tBu, but equivalent to PNP-iPr.14
3
5.25; JHH = 11.9 Hz)32 without any observable consumption of
1 (Scheme 3). This stereochemistry contrasts that observed for
the rhodium system and, as homocoupling through the macro-
cycle would be expected to result in an interpenetrated enyne
complex, it appears that production of the enyne occurs cataly-
tically outside the ring. Subsequent detailed investigation of
this reaction using 100 equivalents HCuCtBu confirmed that
1 is an effective precatalyst.33 Under these conditions, the
dimerisation of HCuCtBu into Z-tBuCuCCHCHtBu proceeds
with an initial TOF of 28 h−1. After 6 h, analysis by H NMR
spectroscopy indicated complete consumption of HCuCtBu
and exclusive production of Z-tBuCuCCHCHtBu. From the
31P{1H} NMR spectrum generation of a new organometallic
1
2
species was apparent (10, δ 25.0, 16.3; JPP = 364 Hz), account-
ing for 88% of the metal-containing species with 1 making up
10%. Addition of a further 50 equivalents of HCuCtBu induced
complete conversion of 1 into 10 within 24 h but coincided
with a halt in homocoupling, which plateaued at 65 TONs.
Repeating the homocoupling reaction on a larger scale
under similar conditions enabled isolation of 10 from solution
in 76% yield, which was subsequently identified as iridium(III)
bis(alkenyl) complex [Ir(PNP-14)(η3-E-C(CuCtBu)CHtBu)(η1-E-
CHCHtBu)][BArF4] (Scheme 4). In the solid state, 10 adopts a
very distorted octahedral geometry with the alkenyl ligands in
a cis configuration (C4–Ir1–C6 = 102.50(9)°) and coordination
of the σ-organyl derived from Z-tBuCuCCHCHtBu reinforced
by π-complexation of the alkyne (Ir1–alkyne = 2.505(2) Å): a
binding mode, for which there are no crystallographically
characterised Group 9 precedents to our knowledge (CSD
5.41).34 The respective alkenyl Ir–C and CvC bond lengths are
not statistically different (Ir1–C4 = 2.043(2) Å, Ir1–C6 = 2.053(2)
Å; C4–C5 = 1.330(3) Å, C6–C9 = 1.329(3) Å). The structure of 10
Of the organometallic chemistry we have discovered so far
using PNP-14, the capacity for rhodium complexes to promote
the stoichiometric homocoupling of 3,3-dimethylbutyne
through the annulus of the macrocyclic ligand stands out (1′
→ 9′ in Scheme 3).15 Given that a structurally related Ir(PCP)
system has also been shown to promote stoichiometric term-
Table 1 Carbonyl stretching frequencies (CH2Cl2)
Pincer
ν(CO)/cm−1
Ref.
[Ir(PNP-14)(CO)][BArF4] 8
1984
1997
1977
1990
1986a
1998
This work
14
6
6
29
27
[Rh(PNP-14)(CO)][BArF4] 8′
[Ir(PNP-tBu)(CO)][BArF
]
4
]
4
[Rh(PNP-tBu)(CO)][BArF
]
[Ir(PNP-iPr)(CO)][BArF
4
[Rh(PNP-iPr)(CO)][BArF
]
4
a Measured in the solid state (ATR).
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−
Scheme 4 Mechanistic features of the terminal alkyne coupling reactions promoted by 1 and 1’: [M] = M(PNP-14)+ and [BArF
]
counter anions
4
omitted. Solid-state structure of 10 depicted with thermal ellipsoids at 30% probability for selected atoms; minor disordered component (IrP2 core),
most H atoms, and anion omitted; structural diagram provided in the experimental section. Selected bond lengths (Å) and angles (°): Ir1–P2, 2.3141
(5); Ir1–P3, 2.3659(5); P2–Ir1–P3, 163.55(2); Ir1–N101, 2.122(2); Ir–C4, 2.043(2); Ir–C4–C5, 129.59(15); C4–C5, 1.330(3); Ir1–C6, 2.053(2); Ir1–C6–
C9, 147.4(2); C6–C9, 1.329(3); Ir1–Cnt(C7, C8), 2.505(2); C6–C7–C8, 161.9(2); C7–C8, 1.216(3); N101–Ir1–C6, 159.35(8); C4–Ir1–Cnt(C7, C8), 153.16
(7); C4–Ir1–C6, 102.50(9); Cnt = centroid.
determined by X-ray crystallography was fully corroborated in tion between
1
and independently synthesised Z-
1
solution using NMR spectroscopy. For instance, the alkenyl H tBuCuCCHCHtBu in DFB was observed, even upon heating at
3
resonances are located at δ 7.81 (IrCH
5.68 (IrCCHtBu), and 4.78 (IrCHCHtBu; JHH = 15.2 Hz) in a most reasonably reconciled by irreversible reaction of Z-
1 : 1 : 1 ratio, with the associated 13C resonances at δ 143.5 tBuCuCCHCHtBu with 11; involving net 1,2-addition of the
(IrCHCHtBu), 142.2 (IrCCHtBu), 105.3 (IrC
CHtBu), and 95.7 {CuC}C(sp2)–H bond across the IrvC linkage. The addition
(IrC
̲CHtBu; JHH = 15.0 Hz), 50 °C for 1 h. The formation of the bis(alkenyl) is, therefore,
3
̲
̲
̲
̲
̲
̲
=
evidently takes place through the ring in this instance, with
5–10 Hz). The HR-ESI MS of 10 is also notable for a strong [M]+ the macrocycle preventing subsequent reductive elimination.12
ion signal at 916.5623 (calcd 916.5628) m/z and bulk purity of We therefore attribute the generation of 10 to catalyst de-
was confirmed by combustion analysis.
activation by irreversible product inhibition. The postulated
reactivity of the Group 9 vinylidenes derived from 1 and 1′ is
clearly nuanced by the nature of the metal and impact of the
unique steric constraints imposed by the tetradecamethylene
linker. We believe that the more facile Ir(I)/Ir(III) redox couple
and propensity of the {Ir(PNP-14)}+ fragment to adopt geome-
tries with the pincer ligand in a non-meridional conformation
are the decisive factors. Specifically, we propose that the
Z-selective homocoupling of HCuCtBu proceeds catalytically
outside the ring via C(sp)–H bond oxidative addition of
HCuCtBu to 11 affording fac-[Ir(PNP-14)(CCHtBu)(CuCtBu)H]+,
alkynyl migration yielding an enynyl hydride, and finally
release of Z-tBuCuCCHCHtBu by reductive elimination. In
contrast, 1′ mediates the stoichiometric E-selective homocou-
pling of HCuCtBu through the ring ultimately via a pathway
bypassing the vinylidene intermediate 11′. Further compu-
tational analysis would be required to corroborate these sug-
Terminal alkyne homocoupling reactions that produce
Z-enyne products are generally understood to proceed via viny-
lidene intermediates, with 11 implicated in this case
(Scheme 4).35,36 Indeed, the rhodium homologue 11′ is pro-
duced initially upon reaction of 1′ with HCuCtBu.15 Reaction
with the second alkyne equivalent, by net 1,2-addition of the
constituent C(sp)–H bond across the vinylidene MvC linkage
(concerted or step-wise) followed by reductive elimination,
would thereafter confer the enyne product. E-Enyne isomers
such as that observed in the rhodium system can also be pro-
duced in this manner, although an indirect route involving
equilibrium generation of the rhodium(III) alkynyl hydride 12′
is instead invoked in the formation of 9′ from 11′ (Scheme 4).
Whilst 11 was not detected during the formation of Z-
tBuCuCCHCHtBu, the generation of 10 provides strong cir-
cumstantial evidence for its intermediate presence. No reac-
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gestions, although accurately modelling the effect of the pump–thaw degassed and dried over 3 Å molecular sieves.
methylene chain is non-trivial.
C6D6 was distilled from sodium and stored over 3 Å molecular
sieves. SiMe4 was distilled from liquid Na/K alloy and stored
over a potassium mirror. Other anhydrous solvents and liquid
reagents were purchased from Acros Organics or Sigma-
Aldrich, freeze–pump–thaw degassed and stored over 3 Å mole-
3. Conclusions
The organometallic chemistry of iridium complexes of the cular sieves. PNP-14,14 [Ir(COD)2][BArF4],17 [Ir(biph)(COD)
macrocyclic PNP-14 pincer ligand has been explored. The five- Cl]2,18 Na[BArF4],38 and [Ir(PNP-tBu)(biph)][BArF4] (II)6 were
coordinate iridium(I) and iridium(III) complexes [Ir(PNP-14) synthesized according to published procedures. All other solid
(η2:η2-COD)][BArF4] 1 and [Ir(PNP-14)(biph)][BArF4] 2 are readily reagents are commercial products and were used as received.
prepared and fully characterised derivatives, with the former NMR spectra were recorded on Bruker spectrometers under
notable for a distorted trigonal bipyramidal metal geometry in argon at 298 K unless otherwise stated. Chemical shifts are
which the pincer ligand adopts an unusual non-meridional quoted in ppm and coupling constants in Hz. Virtual coupling
confirmation, and the latter for adoption of a square pyrami- constants are reported as the separation between the first and
dal metal geometry stabilised by a weak γ-agostic interaction third lines. NMR spectra in DFB were recorded using an
between the metal and the tetradecamethylene linker. These internal capillary of C6D6 or acetone-d6.37 High resolution
well-defined complexes have been shown to be effective precur- ESI-MS were recorded on Bruker Maxis Plus instrument.
sors for the generation of iridium(III) dihydride dihydrogen (4), Infrared spectra were recorded on a Jasco FT-IR-4700 using a
iridium(I) bis(ethylene) (6), and iridium(I) carbonyl (8) deriva- KBr transmission cell in CH2Cl2. Microanalyses were per-
tives that highlight important periodic trends by comparison formed at the London Metropolitan University by Stephen
to rhodium counterparts: i.e. the more facile oxidative addition Boyer or Elemental Microanalysis Ltd.
of dihydrogen, propensity to from five-coordinate d8 com-
plexes, and greater π-basicity of the heavier metal conger,
4.2 Preparation of [Ir(PNP-14)(η2:η2-COD)][BArF4] (1)
A solution of [Ir(COD)2][BArF4] (29.3 mg, 23.0 μmol) and
respectively.
Onward reactivity of the {Ir(PNP-14)}+ fragment was also PNP-14 (11.0 mg, 23.0 μmol) in DFB (0.5 mL) was mixed for
explored with the bulky unsaturated substrates 3,3-dimethyl- 5 min at RT, the volatiles were removed in vacuo and the result-
butene and 3,3-dimethylbutyne. Reaction of 4 with 3,3-dimethyl- ing orange oil washed with pentane (2 × 2 mL). The analyti-
butene induced triple C–H bond activation of the methylene cally pure product was obtained as a yellow crystalline solid by
chain yielding an iridium(III) allyl hydride complex [Ir(PNP-14*) slow diffusion of SiMe4 (ca. 10 mL) into a DFB solution
H][BArF ] 7, whilst 1 is an effective pre-catalyst for the homocou- (0.5 mL) at −30 °C. Yield: 29.0 mg (17.7 μmol, 77%).
4
pling of 3,3-dimethylbutyne into Z-tBuCuCCHCHtBu under
1H NMR (500 MHz, DFB): δ 8.11–8.16 (m, 8H, ArF), 7.50 (br,
mild conditions. The latter is particularly remarkable given that 4H, ArF), 7.33 (t, 3JHH = 7.7, 1H, py), 7.08 (d, 3JHH = 7.7, 1H, py),
reaction of the homologous rhodium precursor 1′ results in the 7.03 (obscured, py), 4.25–4.34 (m, 1H, Ir(CHvCH){axial}),
2
formation of an interpenetrated E-enyne complex (9′). The 4.34–4.44 (m, 1H, Ir(CHvCH){axial}), 3.72 (d, JPH = 6.6, 2H,
2
2
mechanism of the homocoupling promoted by 1 is proposed to pyCH
̲
2), 3.51 (dd, JHH = 18.2, JPH = 6.0, 1H, pyCH2
̲
), 3.34 (dd,
involve formation and direct reaction of the (unobserved) vinyli- 2JHH = 18.2, JPH = 9.7, 1H, pyCH2
̲
), 2.54–2.66 (m, 2H, CH2),
2
dene derivative [Ir(PNP-14)(CCHtBu)][BArF ] (11) with HCuCtBu 2.15–2.45 (m, 6H, CH2 + 1 × Ir(CHvCH){equatorial} [δ 2.39]),
4
outside of the macrocyclic ring. This suggestion is supported 1.38–2.04 (m, 9H, CH2 + 1 × Ir(CHvCH){equatorial} [δ 1.83]),
experimentally by isolation and crystallographic characterisation 1.38 (d, 3JPH = 12.7, 9H, tBu), 0.94–1.32 (m, 19H, CH2), 0.65 (d,
of
[Ir(PNP-14)(η3-E-C(CuCtBu)CHtBu)(η1-E-CHCHtBu)][BArF ] 3JPH = 12.5, 9H, tBu).
4
(10), which results from deactivation of the catalyst by product
inhibition.
13C{1H} NMR (126 MHz, DFB): δ 163.7 (dd, JPC = 5, 4, py),
1
162.5 (q, JCB = 50, ArF), 162.4 (obscured, py), 138.2 (s, py),
135.1 (s, ArF), 129.7 (qq, 2JFC = 32, 3JCB = 3, ArF), 124.9 (q, 1JFC
=
3
3
272, ArF), 122.0 (d, JPC = 6, py), 120.7 (d, JPC = 8, py), 117.6
3
2
(sept, JFC = 4, ArF), 64.7 (br, Ir(CHvCH){axial}), 60.9 (d, JPC
=
4. Experimental
4.1 General methods
2
3, Ir(CHvCH){axial}), 60.2 (dd, JPC = 27, 4, Ir(CHvCH){equa-
2
2
torial}), 50.1 (dd, JPC = 29, JPC = 5, Ir(CHvCH){equatorial}),
1
3
1
All manipulations were performed under an atmosphere of 45.6 (dd, JPC = 27, JPC = 4, pyCH̲ 2) 42.3 (d, JPC = 22, pyC̲H2),
3
3
1
argon using Schlenk and glove box techniques unless other- 35.8 (d, JPC = 10, CH2), 35.5 (br, CH2), 35.2 (dd, JPC = 19, JPC
1
wise stated. Dihydrogen and ethylene were dried by passage = 4, tBu{C}), 34.1 (d, JPC = 7, PCH2), 33.4 (br, tBu{C}), 31.1 (d,
through a column of activated 3 Å molecular sieves. Glassware 3JPC = 10, CH2), 29.8 (d, JPC = 9, CH2), 29.7 (s, CH2), 29.5 (s,
3
1
was oven dried at 150 °C overnight and flame-dried under CH2), 29.3 (d, JPC = 17, PCH2), 29.0 (s, CH2), 28.8 (s, CH2),
vacuum prior to use. Molecular sieves were activated by 28.7 (s, CH2), 28.6 (br, CH2), 28.3 (s, CH2), 28.12 (s, CH2), 28.05
2
3
heating at 300 °C in vacuo overnight. Fluorobenzene and DFB (s, CH2), 27.8 (d, JPC = 4, tBu{CH3}), 27.1 (d, JPC = 7, CH2),
were pre-dried over Al2O3, distilled from calcium hydride and 27.0 (s, CH2), 26.6 (s, CH2), 26.4 (d, 2JPC = 5, tBu{CH3}).
dried twice over 3 Å molecular sieves.37 CD2Cl2 was freeze–
31P{1H} NMR (162 MHz, DFB): δ 17.0 (s, 1P), 13.4 (s, 1P).
Dalton Trans., 2021, 50, 2472–2482 | 2477
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HR ESI-MS (positive ion 4 kV): 778.4221 ([M]+, calcd 4.5 NMR scale reactions of 2
Dalton Transactions
778.4218) m/z.
The following reactions were carried out starting with a solu-
tion of 2 (16.9 mg, 10.0 µmol) in DFB (0.5 mL) within a
J. Young valve NMR tube and analysed in situ by NMR
spectroscopy.
Anal. calcd for C69H77BF24IrNP2 (1641.32 g mol−1): C, 50.49;
H, 4.73; N, 0.85. Found: C, 50.40; H, 4.64; N, 0.87.
4.3 NMR scale reaction of 1 with dihydrogen
4.5.1 Synthesis of [Ir(PNP-14)(2-biphenyl)H][BArF4] (3). The
solution of 2 was freeze–pump–thaw degassed and placed
under dihydrogen (1 atm), resulting in quantitative formation
of 3 within 5 min at RT. No free biphenyl was observed.
1H NMR (400 MHz, DFB, H2, selected data): δ 7.61 (t,
A solution of 1 (12.2 mg, 7.43 μmol) in DFB (0.5 mL) within a
J. Young valve NMR tube was freeze–pump–thaw degassed and
placed under an atmosphere of dihydrogen (1 atm). Analysis
by NMR spectroscopy indicated quantitative formation of 4
with concomitant formation of COD within 5 min at RT.
3JHH = 7.8, 1H py), 3.66–3.82 (m, 2H, 2 × pyCH2
̲
), 3.06 (dd,
2
3
2JHH = 17.3, JPH = 6.4, 1H, pyCH2
̲ ), 0.79 (d, JPH = 13.4, 9H,
4.4 Preparation of [Ir(PNP-14)(biph)][BArF4] (2)
3
2
tBu), 0.67 (d, JPH = 14.1, 9H, tBu), −21.6 (app t, JPH = 15,
A suspension of PNP-14 (13.3 mg, 27.8 µmol) and [Ir(biph)
(COD)Cl]2 (13.7 mg, 14.0 µmol) in fluorobenzene (0.50 mL)
was stirred for 2 days at 50 °C to give a pale-yellow solution. Na
[BArF4] (24.7 mg, 27.9 µmol) was added and the suspension
stirred for a further 4 h at RT. The volatiles were removed in
vacuo and the resulting purple oil was washed with pentane (2
× 1 mL), dried in vacuo and then the product extracted into
CH2Cl2 (2 mL). The analytically pure product was obtained as a
1H, IrH).
1
2
31P{partial H} NMR (162 MHz, DFB, H2): δ 40.6 (dd, JPP
=
302, 2JPH = 14, 1P), 36.5 (dd, 2JPP = 302, 2JPH = 14, 1P).
4.5.2 Synthesis of [Ir(PNP-14)H2(H2)][BArF4] (4). The solu-
tion of 3 was heated at 85 °C for 6 h, resulting quantitative for-
mation 4 with concomitant formation of biphenyl (δ1H 7.42,
7.25, 7.16).
1H NMR (500 MHz, DFB, H2): δ 8.10–8.16 (m, 8H, ArF), 7.49
(br, 4H, ArF), 7.47 (t, 3JHH = 7.8, 1H, py), 7.19 (d, 3JHH = 7.8, 2H,
purple
crystalline
solid
by
recrystallisation
from
py), 3.96 (dvt, 2JHH = 17.6, JPH = 8, 2H, pyCH2), 3.12 (dvt, 2JHH
̲ =
CH2Cl2 : hexane (1 : 20) at −30 °C. Yield: 36.4 mg (21.6 μmol,
78%).
17.6, JPH = 10, 2H, pyCH2̲ ), 2.11–2.23 (m, 2H, PCH2), 1.12–1.69
3
1H NMR (500 MHz, CD2Cl2): δ 8.00 (t, JHH = 7.9, py, 1H),
(m, 26H, CH2), 0.91 (vt, JPH = 16, 18H, tBu), −9.27 (br, fwhm =
7.70–7.76 (m, 10H, py + ArF), 7.64 (d, JHH = 7.6, 1H, biph),
3
24 Hz, 4H, IrH4).
7.60 (d, JHH = 7.5, 1H, biph), 7.56 (br, 4H, ArF), 7.39 (d, JHH
=
3
3
13C{1H} NMR (126 MHz, DFB, H2): δ 162.3 (q, JCB = 50,
1
3
3
ArF), 162.4 (vt, JPC = 6, py), 138.9 (s, py), 135.1 (s, ArF), 129.7
(qq, 2JFC = 32, 3JCB = 3, ArF), 124.9 (q, 1JFC = 272, ArF), 120.4 (vt,
7.6, 1H, biph), 7.19 (t, JHH = 7.3, 1H, biph), 7.10 (t, JHH = 7.5,
1H, biph), 6.88 (t, JHH = 7.4, 1H, biph), 6.33 (t, JHH = 7.8, 1H,
biph), 5.35 (d, JHH = 8.2, 1H, biph), 4.02 (dd, JHH = 19.4, JPH
= 9.6, 1H, pyCH2), 3.75–3.89 (m, 2H, 2 × pyCH2
), 3.50 (dd, 3JHH
= 17.0, JHH = 9.2, 1H, pyCH2), 3.02–3.15 (m, 1H, PCH2),
2.78–2.88 (m, 1H, PCH2), 1.88–1.98 (m, 1H, CH2), 0.66–1.73
3
3
3
2
2
JPC = 10, py), 117.6 (sept, JFC = 4, ArF), 44.4 (vt, JPC = 28,
3
̲
̲
pyCH̲ 2), 30.0 (vt, JPC = 32, tBu{C}), 29.0 (s, CH2), 28.9 (vt, JPC =
3
̲
8, CH2), 28.3 (s, CH2), 28.2 (s, CH2), 27.5 (s, CH2), 26.3 (s,
CH2), 25.8 (vt, JPC = 32, PCH2), 24.5 (vt, JPC = 6, tBu{CH3}).
31P{1H} NMR (162 MHz, DFB, H2,): δ 42.1 (s, 2P).
3
3
(m, 23H, CH2), 1.16 (d, JPH = 14.0, 9H, tBu), 0.49 (d, JPH
16.1, 9H, tBu), 0.22–0.37 (m, 2H, CH2).
=
1H NMR (600 MHz, DFB, Ar, 298 K, selected data): δ −9.26
(br, fwhm = 29 Hz, T1 = 88.8 0.7 ms, 4H, IrH).
13C{1H} NMR (126 MHz, CD2Cl2): δ 164.6 (app t, JPC = 4, py),
163.3 (br, py), 162.3 (q, JCB = 50, ArF), 150.6 (d, JPC = 2 biph),
1
3
1H NMR (600 MHz, DFB, Ar, 253 K, selected data): δ −9.27
(br, fwhm = 21 Hz, T1 = 50 1, 4H, IrH).
2
149.6 (s, biph), 145.3 (dd, JPC = 8, 6, biph{IrC}), 139.9 (s, py),
135.4 (s, ArF), 135.2 (s, biph), 129.42 (qq, JFC = 32, JCB = 3,
2
3
4.5.3 Synthesis of [Ir(PNP-14)H2(C2H4)][BArF
] (5). The
4
ArF), 129.39 (s, biph), 126.3 (s, biph), 125.6 (s, biph), 125.3 (s,
solution of 4 was freeze–pump–thaw degassed and placed
under ethylene (1 atm), resulting in quantitative formation of
5 within 5 min at RT.
biph), 125.1 (q, JFC = 272, ArF), 123.5 (s, biph), 123.2 (d, JPC
=
1
3
3
10, py), 123.1 (d, JPC = 9, py), 122.1 (s, biph), 121.3 (s, biph),
121.2 (app t, 2JPC = 6, biph{IrC}), 118.0 (sept, 3JFC = 4, ArF), 40.9
1H NMR (500 MHz, DFB, C2H4, selected data): δ 7.43 (t,
1
1
1
3JHH = 7.8, 1H, py), 3.71–3.84 (m, 2H, 2 × pyCH2
̲ ), 3.18–3.37 (m,
(d, JPC = 29, pyC
̲H2), 39.5 (d, JPC = 26, pyC̲H2), 35.0 (d, JPC =
2
2
2
23, tBu{C}), 32.9 (d, JPC = 14, CH2), 32.8 (obscured, tBu{C}),
5H, 1 × pyCH2
̲ + 4 × C2H4), 3.08 (dd, JHH = 17.6, JPH = 10.4,
2), 0.89 (d, JPH = 14.9, 9H, tBu), 0.87 (d, JPH = 13.9,
3
3
30.4 (s, CH2), 29.6 (s, CH2), 29.5 (s, CH2), 29.42 (s, CH2), 29.35 1H, pyCH
̲
2
2
2
9H, tBu), −7.89 (dd, JPH = 17.6, JPH = 13.1, 1H, IrH), −17.80
(app t, JPH = 11, 1H, IrH).
(s, CH2), 29.2 (s, CH2), 29.1 (d, JPC = 3, tBu{CH3}), 28.1 (s,
1
CH2), 27.9 (d, JPC = 28, PCH2), 27.3 (s, CH2), 25.8 (br, CH2),
13C{1H} NMR (126 MHz, DFB, C2H4, selected data): δ 48.7
(s, C2H4).
1
25.5 (s, tBu{CH3}), 24.7 (s, CH2), 24.1 (s, CH2), 19.7 (dd, JPC
=
22, 3JPC = 3, PCH2).
31P{1H} NMR (162 MHz, DFB, C2H4): δ 33.4 (d, JPP = 314,
2
31P{1H} NMR (162 MHz, CD2Cl2): δ 38.7 (d, JPP = 307, 1P),
2
1P), 12.4 (d, 2JPP = 314, 1P).
20.9 (d, 2JPP = 307, 1P).
4.5.4 Synthesis of [Ir(PNP-14)(C2H4)2][BArF4] (6). The solu-
tion of 5 was heated at 85 °C for 16 h, resulting in quantitative
formation of 6, with concomitant formation of ethane (δ1H
0.70, δ13C 6.1).
HR ESI-MS (positive ion, 4 kV): 822.3912 ([M]+, calcd
822.3906) m/z.
Anal. calcd for C73H73BF24IrNP2 (1685.33 g mol−1): C, 52.03;
H, 4.37; N, 0.83; found: C, 51.88; H, 4.28; N, 0.81.
2478 | Dalton Trans., 2021, 50, 2472–2482
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Dalton Transactions
Paper
1H NMR (600 MHz, DFB, C2H4): δ 8.11–8.15 (m, 8H, ArF4),
31P{1H} NMR (162 MHz, DFB): δ 64.6 (s, 2P).
3
3
7.50 (br, 4H, ArF4), 7.46 (t, JHH = 7.8, 1H, py), 7.15 (d, JHH
=
2
4.7 Preparation of [Ir(PNP-14*)H][BArF4] (7)
7.8, 2H, py), 3.63 (dvt, JHH = 16.8, JPH = 8, 2H, pyCH2
̲
), 3.28
2
(dvt, JHH = 16.8, JPH = 8, 2H, pyCH2
̲ ), 3.23 (br, 2H, C2H4), 2.80 A solution of 4 (13.6 μmol, generated in situ as described
(br, 2H, C2H4), 2.49 (br, 2H, C2H4), 1.97 (br, 2H, C2H4), above) in DFB (0.5 mL) within a J. Young valve NMR tube was
1.03–1.48 (m, 28H, CH2), 0.79 (br, 18H, tBu).
treated with 3,3-dimethylbutene (8.8 μL, 71.4 μmol) and the
3
13C{1H} NMR (126 MHz, DFB, C2H4): δ 164.1 (d, JPC = 3, solution heated at 100 °C for 5 days. Analysis by NMR spec-
1
py), 162.6 (q, JCB = 50, ArF), 139.1 (s, py), 135.1 (s, ArF), 129.7 troscopy indicated quantitative formation of the product. The
(qq, 2JFC = 32, 3JCB = 3, ArF), 124.9 (q, 1JFC = 272, ArF), 119.8 (vt, volatiles were removed in vacuo and the resulting pink/red oil
JPC = 8, py), 117.6 (sept, 3JFC = 4, ArF), 42.6 (vt, JPC = 28, pyC
̲H2), washed with SiMe4 (2 × 0.5 mL). The analytically pure product
33.5 (vt, JPC = 26, tBu{C}), 31.0 (s, CH2), 29.1 (vt, JPC = 12, CH2), was obtained as pale red blocks by the slow diffusion of excess
27.8 (s, CH2), 27.3 (s, CH2), 27.2 (s, CH2), 26.3 (s, tBu{CH3}), 26.0 SiMe4 into a DFB solution at −30 °C. Yield: 10.2 mg
(s, C2H4), 24.6 (s, CH2), 18.0 (s, C2H4), 14.3 (vt, JPC = 24, PCH2).
31P{1H} NMR (162 MHz, DFB, C2H4): δ 9.0 (s, 2P).
(6.66 μmol, 49%).
1H NMR (500 MHz, CD2Cl2): δ 7.70–7.75 (m, 8H, ArF), 7.65
3
3
4.5.5 Synthesis and isolation of [Ir(PNP-14)(CO)][BArF4] (8). (t, JHH = 7.8, 1H, py), 7.56 (br, 4H, ArF), 7.34 (d, JHH = 7.8,
3
The solution of 6 was freeze–pump–thaw degassed and placed 1H, py), 7.31 (d, JHH = 7.8, 1H, py), 4.86 (app q, JHH = 9, 1H,
under carbon monoxide (1 atm), resulting in an immediate IrCH), 4.47 (app t, JHH = 7, 1H, IrCH), 3.71–3.81 (m, 2H, 2 ×
colour change from colourless to bright yellow. The volatiles pyCH
were removed in vacuo, and the resulting yellow oil washed (dd, JHH = 17.4, JPH = 9.2, 1H, pyCH2
with SiMe4 (2 × 0.5 mL) and thoroughly dried in vacuo to give CH2), 2.15–2.29 (m, 1H, CH2), 1.98–2.11 (m, 1H, CH2),
the analytically pure product as a yellow foam. Yield: 13.9 mg 0.94–1.95 (m, 20H, IrCH [δ 1.89] + CH2), 1.17 (d, JPH = 15.4,
3
2
2
̲
2), 3.41 (dd, JHH = 17.1, JPH = 9.3, 1H, pyCH2
̲
), 3.26
̲ ), 2.35–2.52 (m, 1H,
2
2
3
3
2
(8.90 μmol, 89%).
9H, tBu), 1.01 (d, JPH = 13.5, 9H, tBu), −8.49 (dd, JPH = 19.6,
3
1H NMR (500 MHz, CD2Cl2): δ 7.87 (t, JHH = 7.8, 1H, py), 9.7, 1H, IrH).
7.70–7.76 (m, 8H, ArF), 7.56 (br, 4H, ArF), 7.51 (d, JHH = 7.9,
13C{1H} NMR (126 MHz, CD2Cl2): δ 163.4 (br, py), 162.3 (q,
3
2
2H, py), 3.94 (dvt, JHH = 17.6, JPH = 8, 2H, pyCH2
̲
), 3.47 (dvt, 1JCB = 50, ArF), 161.9 (br, py), 138.5 (s, py), 135.4 (s, ArF), 129.4
2JHH = 17.6, JPH = 8, 2H, pyCH2
̲
), 2.18–2.27 (m, 4H, PCH2), (qq, JFC = 32, JCB = 3, ArF), 125.1 (q, JFC = 272, ArF), 121.0 (d,
2
3
1
1.94–2.07 (m, 2H, CH2), 1.76–1.89 (m, 2H, CH2), 1.64–1.74 (m, 3JPC = 9, py), 120.8 (d, JPC = 9, py), 118.0 (sept, JFC = 4, ArF),
3
3
2
1
2H, CH2), 1.54–1.64 (m, 2H, CH2), 1.23–1.48 (m, 16H, CH2), 81.9 (s, IrCH), 66.0 (d, JPC = 5, IrCH), 41.9 (d, JPC = 30,
1.14 (vt, JPH = 16, 18H, tBu) pyC H2), 38.9 (s, IrCH), 35.9 (s, CH2),
H2), 39.2 (d, 1JPC = 29, pyC
13C{1H} NMR (126 MHz, CD2Cl2): δ 182.5 (vt, 2JPC = 18, CO), 35.0 (dd, JPC = 22, JPC = 5, tBu{C}), 30.4 (dd, JPC = 22, JPC
̲
̲
1
3
1
3
=
1
2
165.4 (vt, JPC = 10, py), 162.3 (q, JCB = 50, ArF), 141.9 (s, py), 5, tBu{C}), 29.6 (s, CH2), 27.8 (d, JPC = 14, CH2), 27.4 (s, CH2),
135.4 (s, ArF), 129.4 (qq, 2JFC = 32, 3JCB = 3, ArF), 125.2 (q, 1JFC
272, ArF), 122.0 (vt, JPC = 10, py), 118.0 (sept, 3JFC = 4, ArF), 39.4 (dd, JPC = 28, JPC = 1, PCH2), 24.4 (s, CH2), 24.3 (d, JPC = 5,
(vt, JPC = 24, pyC
H2), 34.7 (vt, JPC = 30, tBu{C}), 30.3 (vt, JPC = 10 CH2), 22.9 (s, CH2), 22.3 (s, CH2), 21.6 (s, CH2), 20.8 (dd, 1JPC
CH2), 29.3 (s, CH2), 29.0 (s, CH2), 28.9 (s, CH2), 28.3 (s, CH2), 24, 3JPC = 4, PCH2).
=
27.0 (d, JPC = 3, tBu{CH3}), 25.7 (d, JPC = 4, tBu{CH3}), 24.8
2
2
1
3
2
̲
=
2
27.5 (vt, JPC = 6, tBu{CH3}), 26.1 (s, CH2), 23.4 (vt, JPC = 30,
PCH2).
31P{1H} NMR (162 MHz, CD2Cl2): δ 81.4 (d, JPP = 313, 1P),
25.8 (d, 2JPP = 313, 1P).
31P{1H} NMR (162 MHz, CD2Cl2): δ 64.6 (s, 2P).
31P{1H} NMR (162 MHz, DFB): δ 62.5 (s, 2P).
31P{1H} NMR (162 MHz, DFB): δ 80.9 (d, 2JPP = 313, 1P), 25.5
(d, 2JPP = 313, 1P).
IR (CH2Cl2): ν(CO) 1984 cm−1
.
HR ESI-MS (positive ion 4 kV): 668.3128 ([M]+, calcd
HR ESI-MS (positive ion, 4 kV): 698.3217 ([M]+, calcd 668.3122) m/z.
698.3228) m/z.
Anal. calcd for C62H67BF24IrNP2 (1531.12 g mol−1): C, 47.85;
Anal. calcd for C62H65BF24IrNOP2 (1561.14 g mol−1): C, H, 4.15; N, 0.91. Found: C, 47.65; H, 4.03; N, 1.01.
47.70; H, 4.20; N, 0.90; found: C, 47.89; H, 4.13; N, 0.97.
4.8 NMR scale reaction of 7 with dihydrogen
4.6 NMR scale reaction of [Ir(PNP-tBu)(biph)][BArF4] (II) with
dihydrogen
A solution of 7 (7.7 mg, 5.03 µmol) in DFB (0.5 mL) within a J
Young valve NMR tube was freeze–pump–thaw degassed,
A solution of II (16.0 mg, 9.98 µmol) in DFB (0.5 mL) within a placed under dihydrogen (1 atm) and heated at 80 °C for 16 h.
J. Young valve NMR tube was freeze–pump–thaw degassed and Analysis by NMR spectroscopy indicated quantitative for-
placed under dihydrogen (1 atm) and then heated at 80 °C for 2 mation of 4.
days. Analysis by NMR spectroscopy indicated quantitative for-
4.9 Catalytic homocoupling of 3,3-dimethylbutyne promoted
by 1
mation of [Ir(PNP-tBu)H2(H2)][BArF ]. The spectroscopic data
4
are consistent with the literature for the related BF4− salt.7
1H NMR (400 MHz, CD2Cl2, selected data): δ 8.11–8.17 (m, A solution of 1 (8.2 mg, 5.0 µmol) in DFB (400 µL) within a
8H, ArF), 7.50 (s, 4H, ArF), 3.52 (vt, JPH = 8, 4H, pyCH2
(vt, JPH = 14, 36H, tBu), −9.48 (br, 4H, IrH).
̲
), 1.11 J. Young NMR tube was treated with a solution of 3,3-dimethyl-
butyne (62 µL, 503 µmol) and the resulting homocoupling
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2
2
reaction producing only Z-tBuCuCCHCHtBu followed at RT 3JFC = 4, ArF), 116.9 (s, CuC
̲
2
IrC
C̲
̲
HCHtBu), 60.1 (s,
in situ using NMR spectroscopy. The solution was mixed con-
stantly when not in the spectrometer. Analysis after 1 hour
indicated 28 TONs, with complete conversion observed within
6 h. At this point, 10 was observed as the major organo-
metallic species (88%), with 1 the minor organometallic
species (10%). Further 3,3-dimethylbutyne (31 µL, 252 µmol)
was added, resulting in further homocoupling, totalling 65
TONs and complete conversion of 1 to 10 after 24 h.
Spectroscopic data for Z-tBuCuCCHCHtBu is consistent with
literature values.32
uCtBu), 46.0 (d, 1JPC = 25, pyC
37.3 (s, CHCHtBu{C}), 37.1 (s, CCHtBu{C}), 36.6 (dd, JPC = 21,
3JPC = 4, PtBu{C}), 34.6 (dd, JPC = 21, JPC = 6, PtBu{C}), 33.3
(d, JPC = 15, CH2), 32.2 (s, CH2), 31.8 (s, CuCtBu{C}), 31.4 (s,
CH2), 31.28 (s, tBu{CH3}), 31.26 (s, tBu{CH3}), 31.1 (s, CH2),
30.5 (s, CH2), 30.3 (s, CH2), 30.2 (s, CH2), 29.7 (s, CHCHtBu
{CH3}), 28.8 (br, CH2), 28.20 (d, JPC = 4, CH2), 28.17 (s, CH2),
27.1 (d, JPC = 3, 2 × PtBu{CH3}), 26.6 (s, CH2), 24.9 (s, CH2),
1
3
21.9 (dd, 1JPC = 30, 3JPC = 2, PCH2), 19.5 (dd, JPC = 19, JPC = 3,
Data for Z-tBuCuCCHCHtBu:1H NMR (400 MHz, DFB,
PCH2).
31P{1H} NMR (162 MHz, CD2Cl2): δ 25.5 (d, JPP = 364, 1P),
3
selected data): δ 5.53 (d, JHH = 11.9, 1H, CHvCH), 5.25 (d,
16.8 (d, 2JPP = 364, 1P).
3JHH = 11.9, 1H, CHvCH), 1.12 (s, 9H, tBu), 1.11 (s, 9H, tBu).
31P{1H} NMR (121 MHz, DFB): δ 25.0 (d, 2JPP = 364, 1P), 16.3
(d, 2JPP = 364, 1P).
4.10 Preparation of [Ir(PNP-14)(η3-E-C(CuCtBu)CHtBu)(η1-E-
CHCHtBu)][BArF4] (10)
HR ESI-MS (positive ion, 4 kV): 916.5623 ([M]+, calcd
916.5628) m/z.
Anal. calcd for C79H95BF24IrNP2 (1779.57 g mol−1): C, 53.35;
H, 5.38; N, 0.79. Found: C, 53.26; H, 5.09; N, 0.77.
A solution of 1 (14.0 mg, 8.53 µmol) in DFB (0.5 mL) within a J
Young valve NMR tube was treated with 3,3-dimethylbutyne
(210 µL, 1.71 mmol) and stirred for 6 h at RT. Analysis by NMR
spectroscopy indicated quantitative formation of the product.
The volatiles were removed in vacuo, the resulting yellow oil
washed with SiMe4 (2 × 0.5 mL) and dried in vacuo to afford
the analytically product as a yellow solid. Yield: 11.6 mg
(6.52 μmol, 76%). Crystals suitable X-ray crystallography were
obtained by slow diffusion of excess SiMe4 into an Et2O solu-
tion. From the SiMe4 washings Z-tBuCuCCHCHtBu was
obtained as a colourless oil in low yield. Yield: 4.6 mg
(28.0 μmol, 2%).
4.11 NMR scale reaction of 1 with Z-tBuCuCCHCHtBu
A solution of 1 (16.1, 9.8 μmol) in DFB (0.5 mL) within a
J. Young valve NMR tube was treated with Z-tBuCuCCHCHtBu
(4.6 mg, 28.0 μmol) and then heated at 50 °C for 1 h. No reac-
tion was apparent upon analysis by NMR spectroscopy.
4.12 Crystallography
Data were collected on a Rigaku Oxford Diffraction SuperNova
AtlasS2 CCD diffractometer using graphite monochromated
Mo Kα (λ = 0.71073 Å) or CuKα (λ = 1.54184 Å) radiation and
an Oxford Cryosystems N-HeliX low temperature device [150(2)
K]. Data were collected and reduced using CrysAlisPro and
refined using SHELXL,39 through the Olex2 interface.40 Full
details about the collection, solution, and refinement are
documented in CIF format, which have been deposited with
the Cambridge Crystallographic Data Centre under CCDC
2051203 (1), 2051204 (2), 2051205 (7), 2051206 (10), 2051207
([Rh(PNP-14)(η2-norbornene)][BArF4]).†
3
1H NMR (500 MHz, CD2Cl2): δ 7.83 (t, JHH = 6.7, 1H, py),
3
3
7.81 (dd, JHH = 15.0, JPH = 3, 1H, IrCH̲CHtBu), 7.70–7.75
(m, 8H, ArF), 7.56 (br, 4H, ArF), 7.52 (d, JHH = 7.9, 1H, py),
3
Conflicts of interest
3
4
7.49 (d, JHH = 7.9, 1H, py), 5.68 (t, JPC = 2, 1H, IrCCH
̲
tBu),
tBu), 4.28 (ddd,
2JHH = 16.5, JPH = 10.3, JPH = 3.0, 1H, pyCH2
), 3.69 (ddd,
There are no conflicts to declare.
3
4
4.78 (dt, JHH = 15.2, JPH = 2, 1H, IrCHCH
̲
2
4
̲
2JHH = 17.4, JPH = 10.1, JPH = 1.3, 1H, pyCH2
̲ ), 3.64 (dd, JHH
2
4
2
Acknowledgements
2
2
2
= 17.4, JPH = 9.9, 1H, pyCH2
7.9, 1H, pyCH2), 2.28–2.43 (m, 2H, CH2), 2.08–2.19 (m, 1H,
CH2), 0.88–1.96 (m, 25H, CH2), 1.24 (s, 9H, IrCCHt ), 1.17
),1.02 (d, JPH = 14, 18H, 2 × PtBu), 1.00 (s,
̲ ), 3.22 (dd, JHH = 16.5, JPH =
̲
We thank the European Research Council (ERC, grant agree-
ment 637313) and Royal Society (UF100592, UF150675, A.B.C.)
for financial support. High-resolution mass-spectrometry data
were collected using instruments purchased through support
̲B̲u̲
3
(s, 9H, CuCt
̲B̲u̲
9H, IrCHCHt̲B̲u̲).
13C{1H} NMR (126 MHz, CD2Cl2): δ 164.2 (app t, JPC = 3, py), from Advantage West Midlands and the European Regional
163.3 (app t, JPC = 3, py), 162.3 (q, JCB = 50, ArF), 143.5 (app t, Development Fund. Crystallographic data were collected using
1
3JPC = 4, IrCHC
̲HtBu), 142.2 (br, IrCC̲HtBu), 139.4 (s, py), 135.4 an instrument that received funding from the ERC under the
(s, ArF), 129.4 (qq, JFC = 32, JCB = 3, ArF), 125.1 (q, JFC = 272, European Union’s Horizon 2020 research and innovation pro-
2
3
1
3
3
ArF), 121.7 (d, JPC = 8, py), 121.5 (d, JPC = 8, py), 118.0 (sept, gramme (grant agreement no. 637313).
2480 | Dalton Trans., 2021, 50, 2472–2482
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11 M. R. Gyton, B. Leforestier and A. B. Chaplin,
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2482 | Dalton Trans., 2021, 50, 2472–2482
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