Synthesis and group 9 complexes of macrocyclic PCP and POCOP pincer ligands

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Synthesis and group 9 complexes of macrocyclic

PCP and POCOP pincer ligands†

Cite this: DOI: 10.1039/c9dt04835a

Baptiste Leforestier,

Matthew R. Gyton

and Adrian B. Chaplin

*

The synthesis of macrocyclic variants of commonly employed phosphine-based pincer (pro)ligands

derived from meta-xylene (PCP-14) and resorcinol (POCOP-14) is described, where the P-donors are

trans-substituted with a tetradecamethylene linker. The former was accomplished using a seven-step

asymmetric procedure involving (−)-cis-1-amino-2-indanol as a chiral auxiliary and ring-closing oleﬁn

metathesis. A related, but non-diastereoselective route was employed for the latter, which consequently

necessitated chromatographic separation from the cis-substituted by-product. The proligands are readily

metalated and homologous series of M^I(CO) and M^IIICl₂(CO) derivatives (M = Rh, Ir) have been isolated

and fully characterised in solution and the solid state. Metal hydride complexes are generated during the

synthesis of the former and have been characterised in situ using NMR spectroscopy.

Received 20th December 2019,

Accepted 27th January 2020

DOI: 10.1039/c9dt04835a

rsc.li/dalton

analogous lutidine- and 2,6-dihydroxypyridine-derived PNP-14

Introduction

and PONOP-14 ligands was described in

a preceding

Conferring thermal stability whilst permitting a broad range of contribution.⁶

metal-based reactivity, the application of mer-tridentate

“pincer” ligands in organometallic chemistry and homo-

geneous catalysis has had a profound impact.¹Phosphine-

Results and discussion

Proligand synthesis

based examples bearing a central aryl donor were first reported

by Shaw in the late 1970s,²but these archetypical PCP ligands

continue to attract contemporary interest, with iridium deriva-

tives noteworthy for their ability to catalyse the dehydrogena-

tion of alkanes.³The predictable and modular composition of

pincer ligands enables the steric and electronic properties of

metal derivatives to be tuned through changes to the constitu-

ent donor groups, their substituents or the backbone configur-

ation itself, and these adaptions have been extensively explored

over the intervening four decades.⁴Motivated by the potential

to exploit additional reaction control though their unique

steric profile and their use in the construction of interlocked

assemblies, we have become interested in exploring the chem-

istry of macrocyclic pincer ligands, with our initial eﬀorts

devoted to NHC-based CNC ligands.⁵We herein describe the

synthesis and coordination chemistry of meta-xylene- and

resorcinol-derived macrocyclic (pro)ligands PCP-14 and

POCOP-14, where the chiral P-donors are trans-substituted

with a tetradecamethylene linker (Chart 1). The preparation of

Circumventing problems associated with the generation of the

unwanted cis-substituted diastereoisomer, the proligand

PCP-14′ was prepared using an adapted asymmetric procedure

developed by Riera and Verdaguer that employs (−)-cis-1-

amino-2-indanol as a chiral auxiliary and ring-closing olefin

metathesis (Scheme 1).⁷The known oxazaphospholidine

borane 1 (δ_31P167.9) was first stereoselectively ring-opened by

treatment with octen-7-yl-magnesium bromide, aﬀording 2

(δ_31P76.5). The auxiliary was then removed by acidolysis using

an excess of H₂SO₄in 3 : 1 MeOH–water to generate phosphi-

nous acid borane 3 (δ_31P125.6), which was subsequently con-

1

verted into phosphine borane 4 (δ_31P22.2, J_PH= 352 Hz) by

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: Additional experimental

details; NMR, IR and ESI-MS spectra of new compounds, and selected reactions

(PDF); primary NMR data (MNOVA). CCDC 1972811–1972820. For ESI and crys-

tallographic data in CIF or other electronic format see DOI: 10.1039/c9dt04835a

Chart 1

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Scheme 1 Asymmetric synthesis of PCP-14’.

reduction of the mesylate with tetrabutylammonium boro- tive using the chiral shift reagent (−)-3,5-dinitro-N-(1-pheny-

hydride and isolated in 65% overall yield from 1. Isolated 4 is lethyl)benzamide (see ESI†).⁹

unstable at room temperature, presumably due to a propensity

Attempts to develop an asymmetric procedure for the prepa-

to undergo hydrophosphination,⁸and is best converted ration of the proligand POCOP-14′ starting from enantiopure

directly into the corresponding phosphide by deprotonation 3, involving reaction of the mesylate with disodium resorcino-

with nBuLi at −78 °C. Reaction thereafter with 1,3-bis(bromo- late or nucleophilic aromatic substitution of 1,3-difluoroben-

methyl)benzene aﬀorded 5 (δ_31P32.3), which was cyclised by zene by the conjugate base, were unsuccessful (see ESI† for

portion-wise treatment with Grubbs’ 1^stgeneration catalyst details). Likewise, attempted conversion of 2 to the corres-

(totalling 10 mol%) under dilute conditions in CH₂Cl₂ponding borane protected chlorodialkylphosphine by acidoly-

(5 mmol L⁻¹) to aﬀord the corresponding unsaturated macro- sis with HCl was unsuccessful. Instead the five step racemic

cycle 6 (δ_31P31.3–33.4). Subsequent hydrogenation using synthesis outlined in Scheme 2, adapted from our work with

Wilkinson’s catalyst (producing PCP-14′·2BH₃7, δ_31P32.5) and PNP-14 and PONOP-14 and also involving ring-closing olefin

deprotection by borane transfer in neat diethylamine aﬀorded metathesis,⁶was employed with the borane protected (satu-

the proligand (δ_31P3.2) as the (R,R)-diastereomer with a rated) macrocycle 12 proving to be the most conducive to

respectable overall yield of 48% and >95% ee, as determined resolution of the two diastereoisomers by column chromato-

1

by H and ³¹P NMR spectroscopic analysis of the oxide deriva- graphy (cis-12, δ_31P143.7; trans-12, δ_31P143.8) and enabling

Scheme 2 Preparation of POCOP-14’.

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Fig. 1 Solid-state structures of cis-12 (left) and trans-12 (right; not unique, Z’ = 2). Thermal ellipsoids drawn at 30% and 50% probability, respect-

ively; minor disordered components omitted (cis-12; tBu groups and methylene chain). Selected bond lengths (Å): cis-12, P2–B2, 1.915(8); P3–B3,

1.896(7); P2–O107, 1.617(4); P3–O108, 1.630(4); trans-12, B2–P2, 1.908(2); B3–P3, 1.905(2); P2–O107, 1.6323(9); P3–O108, 1.6270(9); B12–P12,

1.901(2); B13–P13, 1.904(2); P12–O207, 1.6284(10); P13–O208, 1.6274(10).

determination of their respective configurations by single vacuum and onward reactivity with CO (1 atm), conferring C₂

crystal X-ray diﬀraction (Fig. 1). In this way POCOP-14′ was symmetric Rh(I) carbonyl complexes [Rh(pincer)(CO)] (pincer

obtained as an analytically pure racemate in 30% overall yield = PCP-14, 14a; POCOP-14, 14b), which are characterised by ³¹P

(δ_31P141.6). Use of the chiral shift reagent (−)-3,5-dinitro-N-(1- resonances at δ 75.0 (¹J_RhP= 146 Hz)/201.6 (¹J_RhP= 156 Hz)

1

phenylethyl)benzamide enabled the component phosphine with J_RhPcoupling constants of similar magnitude.

oxide enantiomers to be resolved by ³¹P NMR spectroscopy Complexes 14a/b were thereafter oxidised to the corresponding

(see ESI†).⁹

C₂symmetric Rh(III) carbonyl complexes 15a/b by reaction with

PhICl₂, as evidenced by ³¹P resonances at δ 64.9 (¹J_RhP= 87

Hz)/181.0 (¹J_RhP= 92 Hz) with the expected reductions in J_RhP

Rhodium complexes

1

With the new macrocyclic proligands in hand, the synthesis of values, isolated as analytically pure materials in 80/48% overall

rhodium derivatives was targeted (Scheme 3). Using an yield, following purification by silica chromatography (CH₂Cl₂–

adapted literature procedure,¹⁰rhodium dihydrogen com- pentane), and fully characterised (Fig. 2, Table 1).¹³

plexes [Rh(pincer)(H₂)] (pincer = PCP-14, 13a; POCOP-14, 13b) Analytically pure samples of very alkane soluble 14a/b were

were prepared in quantitative spectroscopic yield using a one- secured from the reaction of 15a/b with

3 equivalents

pot procedure involving metalation of the proligands with iPrMgCl·LiCl in THF and subsequent recrystallisation from

[Rh(COE)₂Cl]₂(COE = cyclooctene) in toluene at elevated temp- SiMe₄in 85/94% yield; as confirmed by combustion analysis.

erature and subsequent treatment with KOtBu at 120 °C under

The solid-state structures of 14a/b have been determined by

an atmosphere of dihydrogen. Complexes 13a/b were charac- single crystal X-ray diﬀraction and demonstrate the adoption

terised in situ and are notable for the adoption of C₂symmetry, of distorted square planar metal coordination geometries,

³¹P resonances at δ 70.4 (¹J_RhP= 153 Hz)/198.4 (¹J_RhP= 165 Hz) with the tetradecamethylene linker of the pincer ligands con-

displaying large coupling to ¹⁰³Rh, and broad 2H hydride siderably skewed to one side of the coordination plane confer-

signals at δ −4.36/−2.87 (298 K), which exhibit fast spin–lattice ring overall C₁symmetry and inducing an appreciable devi-

relaxation (T₁= 74 4/42 2 ms at 298 K; T₁= 117 15/89

ation of the C101–Rh1–C4 angles from linearity, especially in

11 ms at 200 K; 600 MHz, Ar) consistent with the assignment the case of the phosphinite pincer (171.38(10)°, 14a; 165.3(3)°,

as dihydrogen complexes.^11,12The formulation of 13a/b as 14b). The methylene chains of the macrocycles are also non-

σ-complexes is further substantiated by their instability to symmetrically positioned in the Rh(^III) congeners, but in this

Scheme 3 Synthesis of rhodium PCP-14 and POCOP-14 complexes 13–15.

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Fig. 2 Solid-state structures of 14 and 15. Thermal ellipsoids drawn at 50% probability; minor disordered components omitted (15a/b; methylene

chains). Selected metrics provided in Table 1.

Table 1 Selected bond lengths (Å) and angles (°) for 14, 15, 18 and 19

M = Rh

M = Ir

14a

14b

15a

15b

18a

18b

19a

19b

M1–P2

M1–P3

M1–C4

M1–C101

M1–Cl6

2.2844(6)

2.2731(6)

1.865(3)

2.083(3)

—

2.2704(15)

2.2856(13)

1.879(6)

2.037(6)

—

2.3615(7)

2.3938(6)

2.005(3)

2.3324(12)

2.3768(11)

1.996(6)

2.2817(7)

2.2760(7)

1.862(3)

2.085(3)

—

2.2694(11)

2.2798(10)

1.879(4)

2.048(4)

—

2.3637(9)

2.3922(8)

1.940(3)

2.336(2)

2.377(2)

1.926(9)

2.034(10)

2.380(2)

2.371(2)

156.18(9)

174.9(4)

177.37(9)

11.3(3)

2.061(3)

2.018(5)

2.089(3)

2.3656(5)

2.3591(6)

162.17(2)

177.22(11)

176.92(2)

18.52(7)

2.3616(12)

2.3521(12)

156.80(5)

174.6(2)

176.32(5)

12.34(13)

2.3828(7)

2.3793(8)

160.81(3)

177.24(14)

178.81(3)

17.93(9)

M1–Cl7

—

P2–M1–P3

C101–M1–C4

Cl6–M1–Cl7

Aryl twist^a

160.83(2)

171.38(10)

—

155.98(5)

165.3(3)

—

161.16(2)

171.91(12)

—

156.21(3)

165.6(2)

—

14.30(6)

6.7(2)

13.95(8)

6.49(14)

^aAngle between the least-squares mean planes of the aryl group and the MP₂C(aryl) atoms.

case contortion is counteracted by buttressing with the ancil- cases the eﬀect of increased steric crowding on the latter,

lary chloride ligands and more ideal C101–Rh1–C4 angles are where C₂symmetric twisting of the central aryl donor is con-

observed (177.22(11)°, 15a; 174.6(2)°, 15b). These asymmetric siderably more pronounced in the octahedral Rh(^III) conge-

configurations are not retained in solution, where time aver- ners. Finally, the observed diﬀerences in Rh–P, Rh–CO, and

aged C₂symmetry is observed at 298 K (500–600 MHz) consist- Rh–aryl contacts for the Rh(^I) and Rh(III) congeners are consist-

ent with the tetradecamethylene linker being suﬃciently large ent with the nature of associated donors (vide infra for further

and flexible to accommodate the carbonyl ligand within the discussion on the carbonyl ligand).

annulus of the macrocycle. The more obtuse P2–Rh1–P3 bite

angles and rigid backbone conformations observed in the

Iridium complexes

complexes of POCOP-14 in the solid state, compared to those In a similar manner to that employed for the rhodium ana-

of PCP-14, are fully in line with expectations for these pincer logues, iridium tetrahydride complexes [Ir(pincer)H₄] (pincer

architectures.¹⁴This homologous series of complexes show- = PCP-14, 16a; POCOP-14, 16b) were prepared using a one-pot

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Table 2 Carbonyl stretching frequencies for rhodium and iridium com-

plexes of macrocyclic PCP-14 and POCOP-14, and acyclic PCP-tBu and

procedure involving metalation of the macrocyclic proligands

with [Ir(COE)₂Cl]₂(16a) or [Ir(COD)Cl]₂(16b, COD = cycloocta-

diene) in toluene at elevated temperature and subsequent

treatment with KOtBu at 120 °C under an atmosphere of dihy-

drogen (Scheme 4). Complexes 16a/b were characterised in situ

and are notable for the adoption of C₂symmetry, ³¹P reso-

nances at δ 49.9/165.0, and relatively sharp triplet 4H hydride

POCOP-tBu (toluene, cm⁻¹

)

Macrocyclic

Acyclic

[Rh(PCP)(CO)]

1939

1958

2069

2083

1925

1943

2034

2049

1933

1954

—

[Rh(POCOP)(CO)]

[Rh(PCP)Cl₂(CO)]

signals at δ −8.99 (²J_PH= 9.8 Hz)/−8.26 (²J_PH= 9.9 Hz) at 298 K [Rh(POCOP)Cl₂(CO)]

—

[Ir(PCP)(CO)]

[Ir(POCOP)(CO)]

[Ir(PCP)Cl₂(CO)]

1918

1939

—

that only broaden slightly on cooling to 200 K, with moderate

spin–lattice relaxation (T₁= 300 10/194 4 ms at 298 K; T₁=

626 15/242 15 ms at 200 K; 600 MHz, Ar). These data are [Ir(POCOP)Cl₂(CO)]

consistent with fluxional hydride ligands, where dynamic

interconversion between classical tetrahydride and dihydride

dihydrogen formulations occurs on the NMR timescale.^11,15

—

of pincer ligands, group 9 examples have an established track

record in the literature.¹⁸The carbonyl stretching frequencies

of 14, 15, 18 and 19 and those of known acyclic pincer

Evidencing the presence of the latter, reaction with CO (1 atm)

resulted in immediate substitution of one equivalent of di-

hydrogen and formation of cis-17a/b [δ_1H(hydride) −10.66,

−11.59; δ_31P51.0, 45.8 (²J_PP= 286 Hz)/δ_1H(hydride) −9.82,

−10.75; δ_31P160.4, 154.6 (²J_PP= 305 Hz)]. Prolonged thermoly-

sis at 120 °C under CO (1 atm) in the presence of tert-butyl-

ethylene (TBE) followed by removal of CO resulted in the for-

mation of C₂symmetric Ir(I) carbonyl complexes [Ir(pincer)

(CO)] (pincer = PCP-14, δ_31P68.1, 18a; POCOP-14, δ_31P186.7,

18b). Transient formation of trans-17a/b [δ_1H(hydride) −9.65;

δ_31P54.1/δ_1H(hydride) −9.76; δ_31P167.3] and generation of

[Ir(pincer)(CO)₂] (pincer = PCP-14, δ_31P51.6; POCOP-14, δ_31P

164.8) were noted during this transformation. Complexes

18a/b were thereafter oxidised to the corresponding C₂sym-

metric Ir(^III) carbonyl complexes 19a/b (δ_31P33.8/144.4) by reac-

tion with PhICl₂and isolated as analytically pure and air-

stable materials in 51/73% overall yield, following purification

by silica chromatography (CH₂Cl₂–hexane), and fully character-

ised. Analytically pure samples of very alkane soluble 18a/b

were secured from the reaction of 19a/b with 10 equivalents of

KC₈in pentane and subsequent recrystallisation from neohexane/

SiMe₄in 84/79% yield; as confirmed by combustion analysis.¹⁶

The solid-state structures of 18a/b and 19a/b have all been

determined by single crystal X-ray diﬀraction and are isomor-

phous to the corresponding rhodium congeners 14a/b and

15a/b, respectively (Table 1).

complexes [M(pincer)(CO)] (M

= Rh, Ir; pincer = 2,6-

(tBu₂PCH₂)₂C₆H₃vPCP-tBu, 2,6-(tBu₂PO)₂C₆H₃vPOCOP-tBu)

have all been determined by IR spectroscopy under the same

conditions and compiled in Table 2. These data suggest that

PCP-14 and POCOP-14 are marginally weaker donors than

PCP-tBu and POCOP-tBu, respectively, consistent with similar

findings for the neutral PNP and PONOP analogues and attrib-

uted to changes in the phosphine/phosphinite substituents

alone.⁶Other trends apparent in the IR data associated with

the extent of π-backbonding increasing in the order Ir > Rh,

M(^I) > M(III) and PCP > POCOP are fully in line with expectation

and reinforced by similar trends in the X-ray derived metrics

(Table 1) and NMR data (see Experimental section).

Conclusions

Procedures that enable the preparation of two phosphine-

based macrocyclic pincer (pro)ligands PCP-14 and POCOP-14,

where the chiral P-donors are trans-substituted with

a

tetradecamethylene linker, have been developed. The synthesis

of meta-xylene-based proligand PCP-14′ was achieved using a

seven-step asymmetric protocol involving (−)-cis-1-amino-2-

indanol as a chiral auxiliary and ring-closing olefin metathesis,

aﬀording the (R,R)-diastereomer in 48% overall yield and >95%

ee. Whilst we were unable to apply this methodology to the

synthesis of resorcinol-based POCOP-14′, this proligand was

Carbonyl stretching frequencies

The ν(CO) bands of metal carbonyl derivatives are established obtained as analytically pure racemate in 30% overall yield

reporter groups for donor properties of ligands.¹⁷In the case using a non-diastereoselective route, where separation from

Scheme 4 Synthesis of iridium PCP-14 and POCOP-14 complexes 16–19.

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the unwanted cis-substituted by-product was achieved by Metropolitan University by Stephen Boyer in all cases, except

chromatography. Rhodium and iridium complexes of these for samples of 14a/b and 18a/b, which were analysed by

new macrocyclic pincer ligands have been obtained through Elemental Microanalysis Ltd.

metalation of the proligands with dimeric rhodium(^I) and

Synthesis of PCP-14′

iridum(^I) halide precursors and subsequent dehydrohalogena-

tion under a dihydrogen atmosphere. The resulting hydride

Preparation of 2. A solution of MgBr(C₈H₁₅) in THF (0.37 M,

complexes were characterised in situ by NMR spectroscopy and 45 mL, 17 mmol) was added dropwise in three equal portions

reacted on to generate isolatable M^I(CO) and M^IIICl₂(CO) separated by 30 minutes to a solution of 1 (1.39 g, 5.57 mmol) in

derivatives that have been extensively characterised in solution toluene at 80 °C. The solution was concentrated under reduced

and the solid state, including all eight complexes by single pressure and the residue re-dissolved in a minimal amount of

crystal X-ray diﬀraction. By comparison of the ν(CO) bands of toluene (20 mL) and heated at reflux for 3 days. The reaction

the rhodium(^I) and iridum(I) carbonyl adducts, determined by mixture was cooled to 0 °C, exposed to air and quenched with

IR spectroscopy in toluene, PCP-14 and POCOP-14 can be con- saturated aqueous NH₄Cl (10 mL). The aqueous phase was

sidered to be marginally weaker net donors than their respect- extracted with EtOAc (3 × 20 mL) and the combined organic frac-

ive homoleptic tert-butyl substituted congeners PCP-tBu and tions dried (MgSO₄), filtered, and concentrated under reduced

POCOP-tBu, respectively. Work exploring the organometallic pressure to give a pale-yellow oil. Purification by flash column

chemistry of these novel macrocyclic pincer ligands is ongoing chromatography (silica, 8% EtOAc in hexane, R_f= 0.15) aﬀorded

in our laboratories and will be reported in due course.

2 as a colourless oil. Yield: 1.92 g (95%).

¹H NMR (500 MHz, CDCl₃): δ 7.35–7.42 (m, 1H, Ar),

3

7.23–7.28 (m, 3H, Ar), 5.81 (ddt, J_HH= 16.9, 10.1, 6.5, 1H,

3

CH

̲

),

Experimental

General methods

3

2

4

4.95 (ddt, J_HH= 10.1, J_HH= 2.2, J_HH= 1.2, 1H, CHvCH₂

4.77 (app td, J = 10, ³J_HH= 4.5, 1H, NCH

), 3.10 (dd, ²J_HH= 16.6, ³J_HH= 4.7, 1H, OCHCH₂

), 4.51 (app q, ³J_HH= 5,

All manipulations were performed under an atmosphere of 1H, OCH

argon using Schlenk and glove box techniques unless other- (d, J_HH= 16.6, 1H, OCHCH₂

3

wise stated. Hydrogen was dried by passage through a stain- (app q, J_HH= 7, 2H, CH̲₂CHvCH₂), 1.81 (d, J_HH= 4.4, 1H,

less-steel column of activated 3 Å molecular sieves. Carbon OH), 1.56–1.83 (m, 4H, CH₂), 1.30–1.49 (m, 6H, CH₂), 1.26 (d,

monoxide was used as received. Glassware was oven-dried at ³J_PH= 13.6, 9H, tBu), 0.55 (partially collapsed quartet, fwhm =

150 °C overnight and flame-dried under vacuum prior to use. 310 Hz, 3H, BH₃).

3

Molecular sieves were activated by heating at 300 °C in vacuo

overnight. CD₂Cl₂was freeze–pump–thaw degassed and dried 139.9 (s, Ar{C}), 139.1 (s, C

over 3 Å molecular sieves. Toluene-d₈and C₆D₆were dried over 125.6 (s, Ar), 124.3 (s, Ar), 114.5 (s, CHvC

¹³C{¹H} NMR (126 MHz, CDCl₃): δ 142.9 (d, J_PC= 7, Ar{C}),

̲

2

sodium overnight, distilled, freeze–pump–thaw degassed and 62.3 (d, J_PC

=

̲

1

2

stored over 3 Å molecular sieves. THF was distilled from H₂CHvCH₂), 31.9 (d, J_PC= 39, tBu{C}), 31.5 (d, J_PC= 13,

C

̲

2

sodium and benzophenone and stored over 3 Å molecular CH₂), 28.9 (s, CH₂), 28.8 (s, CH₂), 25.1 (d, J_PC= 2, tBu{CH₃}),

sieves. Et₂NH was distilled from CaH₂. tert-Butylethylene was 24.1 (d, ¹J_PC= 36, PCH₂), 23.0 (s, CH₂).

freeze–pump–thaw degassed and stored over 3 Å molecular

sieves. SiMe₄was distilled from liquid Na/K alloy and stored quartet, fwhm = 200 Hz).

³¹P{¹H} NMR (121 MHz, CDCl₃): δ 76.5 (partially collapsed

over a potassium mirror. Neohexane (2,2-dimethylbutane) was

HR ESI-MS (positive ion, 4 kV): 384.2603, [M + Na]⁺(calcd

distilled from liquid Na/K alloy and stored over 3 Å molecular 384.2602) m/z.

sieves. Other anhydrous solvents were purchased from Acros

Preparation of 3. H₂SO₄(98%, 5.4 mL, 99 mmol) was added

Organics or Sigma-Aldrich, freeze–pump–thaw degassed and dropwise to a solution of 2 (4.52 g, 12.5 mmol) in a MeOH–

stored over 3 Å molecular sieves. The concentration of nBuLi water mixture (140 mL : 45 mL). The reaction mixture was

was titrated by ¹H NMR spectroscopy before use.¹⁹heated at 70 °C for 4 days, with periodic monitoring by TLC.

Oxazaphospholidine 1,⁷MgBr(C₈H₁₅),²⁰8,⁶PhICl₂,²¹The mixture was allowed to cool to RT, exposed to air, and

[Rh(PPh₃)₃Cl],²²[Rh(COE)₂Cl]₂,²³[Ir(COD)Cl]₂,²⁴[Ir(COE)₂Cl]₂,²⁴CH₂Cl₂(40 mL) and saturated aqueous NaCl (20 mL) added.

[M(pincer)(CO)] (M = Rh, Ir; pincer = PCP-tBu, POCOP- The aqueous phase was extracted with CH₂Cl₂(3 × 15 mL) and

tBu)^2,14d,25were synthesised according to published pro- the combined organic extracts dried (MgSO₄), filtered, and

cedures. NMR spectra were recorded on Bruker spectrometers concentrated under reduced pressure to give a colourless

under argon at 298 K unless otherwise stated. Chemical shifts opaque oil. The crude material was dissolved in a minimal

are quoted in ppm and coupling constants in Hz.²⁶NMR amount of CH₂Cl₂and run through a short silica plug, eluting

spectra in toluene-d₀were recorded using an internal capillary with CH₂Cl₂(R_f= 0.6). The volatiles were removed under reduced

of C₆D₆. HR ESI-MS were recorded on a Bruker MaXis mass pressure to aﬀord 3 as a colourless oil. Yield: 2.51 g (87%).

3

spectrometer. IR spectra were recorded on a Bruker Alpha

Platinum ATR FT-IR spectrometer at RT (for full details see 10.2, 6.7, 1H, CH

ESI†). Microanalyses were performed at the London CHvCH

¹H NMR (500 MHz, toluene-d₈): δ 5.75 (ddt, J_HH= 17.0,

3

vCH₂), 5.02 (br d, J_HH= 17.1, 1H,

̲

₂), 4.97 (br d, ³J_HH= 10.1, 1H, CHvCH₂

̲ ), 3.14 (br, 1H,

Dalton Trans.

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3

OH), 1.95 (app q, J_HH= 7, 2H, CH₂

̲

CHvCH₂), 1.60–1.75 (m, 4H, CH₂

̲

CHvCH₂), 1.10–1.65 (m, 24H, CH₂), 1.17 (d, J_PH

=

1H, CH₂), 1.39–1.56 (m, 2H, CH₂), 1.03–1.38 (m, 7H, CH₂), 13.1, 18H, tBu), 0.44 (partially collapsed quartet, fwhm = 270

0.95 (d, ³J_PH= 13.7, 9H, tBu), 0.63–1.30 (obscured, 3H, BH₃).

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 139.1 (s, C

HvCH₂),

Hz, 6H, BH₃).

̲

³¹P{¹H} NMR (162 MHz, CDCl₃): δ 32.3 (partially collapsed

2

114.6 (s, CHvC̲H₂), 34.2 (s, C̲

1

2

Preparation of 4. Triethylamine (3.79 mL, 27.2 mmol) was (2 mL) in 4 equal portions – every 12 h – over 2 days with peri-

added dropwise to a solution of 3 (2.51 g, 10.9 mmol) and odic argon sparging (ca. 10 min). Volatiles were removed in

methanesulfonic anhydride (2.84 g, 16.3 mmol) in dichloro- vacuo and the crude mixture was purified by flash column

methane (15 mL) at −20 °C and the resulting solution stirred chromatography in air (silica, 8% EtOAc in hexane, R_f= 0.26)

at this temperature for 1 h. A solution of tetrabutylammonium to aﬀord 6 (mixture of alkene isomers) as a colourless oil,

borohydride (2.81 g, 10.9 mmol) in CH₂Cl₂(10 mL) was added which was carried forward directly. Yield: 1.37 g (91%).

at −20 °C and the reaction mixture stirred for a further 16 h at

−20 °C. The mixture was allowed to warm to 0 °C and HCl (0.5 5.21–5.29 (m, 0.6H, CHvCH minor), 5.21–5.29 (m, 1.4H,

¹H NMR (500 MHz, CDCl₃): δ 7.14–7.25 (m, 4H, Ar),

2

M, 20 mL) added slowly. The mixture was exposed to air, CHvCH major), 3.02 (dd, J_HH= 13.8, J_PH= 9.0, 2H, ArCH₂

̲ ),

diluted with distilled water, and the aqueous phase extracted 2.92 (app t, ²J = 14, 1.4H, ArCH₂major), 2.92 (app t, ²J = 14,

̲

2

with CH₂Cl₂(3 × 15 mL). The combined organic extracts were 1.4H, ArCH₂̲ major), 2.91 (app t, J = 14, 0.6H, ArCH₂̲ minor),

dried (MgSO₄), filtered and concentrated under reduced 1.88–2.05 (m, 4H, CH₂), 0.93–1.70 (m, 20H, CH₂), 1.21 (d, ³J_PH

=

3

pressure to give a colourless oil. Purification by flash column 13.0, 5.4H, tBu minor), 1.20 (d, J_PH= 13.0, 12.6H, tBu major),

chromatography (silica, 5% EtOAc in hexane, R_f= 0.42) 0.45 (partially collapsed quartet, fwhm = 270 Hz, 6H, BH₃).

aﬀorded 4 as a colourless oil. Yield: 1.83 g (79%).

³¹P{¹H} NMR (162 MHz, CDCl₃): δ 31.3–33.4 (br m).

¹H NMR (500 MHz, CDCl₃): δ 5.80 (ddt, J_HH= 17.0, 10.0,

HR ESI-MS (positive ion, 4 kV): 525.4105, [M + Na]⁺(calcd

3

6.5, 1H, CH

CHvCH

CHvCH₂), 4.23 (dm, J_PH= 350.6, 1H, PH), 2.04 (app q, J_HH

7, 2H, CH

2H, CH₂), 1.24–1.40 (m, 6H, CH₂), 1.21 (d, J_PH= 14.2, 9H, (20 mL). The suspension was freeze–pump–thaw degassed,

̲

3

2

4

̲

₂), 4.94 (ddt, J_HH= 10.0, J_HH= 2.3, J_HH= 1.2, 1H,

Preparation of PCP-14′·2BH₃(7). A suspension of [Rh

̲

(PPh₃)₃Cl] (126 mg, 136 µmol, 5 mol%) in benzene (5 mL) was

̲

₂CHvCH₂), 1.65–1.90 (m, 2H, CH₂), 1.45–1.60 (m, added to a stirred solution of 6 (1.37 g, 2.73 mmol) in benzene

3

tBu), 0.46 (partially collapsed quartet, fwhm = 330, 3H, BH₃).

placed under dihydrogen and the resulting solution stirred at

¹³C{¹H} NMR (126 MHz CDCl₃): δ 139.0 (s, C

̲HvCH₂), 114.5 50 °C for 2 days. Volatiles were removed under reduced

2

(s, CHvC

̲

2

1

CH₂), 28.7 (s, CH₂), 26.9 (d, J_PC= 2, tBu{CH₃}), 26.8 (d, J_PC

35, tBu{C}), 25.0 (d, ³J_PC= 2, CH₂), 17.6 (d, ¹J_PC= 32, PCH₂).

³¹P NMR (202 MHz, CDCl₃): δ 22.2 (br d, ¹J_PH= 352).

=

chromatography in air (silica, 5% EtOAc in hexane, R_f= 0.25)

to aﬀord 7 as a colourless oil. Yield: 1.21 g (88%).

¹H NMR (600 MHz, CDCl₃): δ 7.25 (s, 1H, Ar{2-CH}), 7.22 (t,

³¹P{¹H} NMR (202 MHz, CDCl₃): δ 22.2 (partially collapsed ³J_HH= 7.6, 1H, Ar), 7.17 (d, J_HH= 7.6, 2H, Ar), 3.03 (dd, J_HH

=

),

3

2

quartet, fwhm = 165 Hz).

14.0, J_PH= 9.9, 2H, ArCH₂

̲

), 3.03 (app t, J = 14, 2H, ArCH₂

̲

Preparation of 5. nBuLi (1.60 M, 4.11 mL, 6.59 mmol) was 1.50–1.61 (m, 4H, PCH₂), 1.40–1.50 (m, 2H, CH₂), 1.13–1.35

added dropwise to a solution of 4 (1.41 g, 6.59 mmol) in THF (m, 22H, CH₂), 1.17 (d, J_PH= 13.1, 18H, tBu), 0.46 (partially

3

(15 mL) at −78 °C. The reaction mixture was stirred for 30 min collapsed quartet, fwhm = 270 Hz, 6H, BH₃).

at this temperature and a solution of 1,3-bis(bromomethyl)

¹³C{¹H} NMR (151 MHz, CDCl₃): δ 133.9 (dd, ²J_PC= 5, ⁴J_PC

=

benzene (870 mg, 3.30 mmol) in THF (3 mL) was added at 2, Ar{C}), 132.0 (t, ³J_PC= 4, Ar{2-CH}), 128.7 (dd, ³J_PC= 4, ⁵J_PC

4

2

−78 °C. The reaction mixture was stirred at −78 °C for 1 h, 3, Ar), 128.5 (t, J_PC= 2, Ar), 30.8 (d, J_PC= 12, CH₂), 28.8 (d,

allowed to warm to RT over 3 h, then quenched by slow addition ¹J_PC= 31, tBu{C}), 28.7 (d, ¹J_PC= 27, ArC

̲

2

of water (10 mL) at 0 °C in air. THF was removed under reduced (s, 2 × CH₂), 27.4 (s, CH₂), 25.8 (d, J_PC= 1, tBu{CH₃}), 23.3 (s,

pressure and aqueous mixture extracted with CH₂Cl₂(3 × CH₂), 20.2 (d, ¹J_PC= 31, PCH₂).

20 mL). The combined organic extracts were dried (MgSO₄), fil-

tered and concentrated under reduced pressure to give a colour- quartet, fwhm = 155 Hz).

less oil. Purification by flash column chromatography (silica,

³¹P{¹H} NMR (243 MHz, CDCl₃): δ 32.5 (partially collapsed

HR ESI-MS (positive ion, 4 kV): 527.4250, [M + Na]⁺(calcd

5% EtOAc in hexane, R_f= 0.33) aﬀorded 5 as a colourless oil, 527.4259) m/z.

which was carried forward directly. Yield: 1.60 g (91%).

Anal. Calcd for C₃₀H₆₀B₂P₂(508.32 g mol⁻¹): C, 71.44; H,

¹H NMR (300 MHz, CDCl₃): δ 7.12–7.24 (m, 4H, Ar), 5.78 11.99; found: C, 71.37; H, 12.10.

3

(ddt, J_HH= 16.9, 10.2, 6.8, 2H, CH

̲

Preparation of PCP-14′. A solution of 7 (26.3 mg, 52.1 µmol)

3

CHvCH̲₂), 2.85–3.10 (m, 4H, PCH₂), 2.01 (app q, J_HH= 7.0, in Et₂NH (2 mL) was heated at 80 °C for 3 days. Volatiles were

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2

removed in vacuo to aﬀord PCP-14′ as a colourless oil. Yield:

¹³C{¹H} NMR (75 MHz, C₆D₆): δ 161.0 (d, J_PH= 9.0, Ar{C}),

24.8 mg (>99%).

139.2 (s, C̲HvCH₂), 130.2 (s, Ar), 114.6 (s, CHvC̲H₂), 112.4

3

¹H NMR (600 MHz, toluene-d₈): δ 7.34 (s, 1H, Ar{2-CH}), (d, J_PH= 11, Ar), 109.6 (t, J_PH= 12, Ar{2-CH}), 34.2 (s,

2

1

2

7.06 (br, 3H, Ar), 2.75 (d, J_HH= 13.5, 2H, ArCH₂

̲

), 2.51 (dd,

CH̲ ₂CHvCH), 32.7 (d, J_PH= 16, tBu{C}), 31.5 (d, J_PH= 12,

2

1

²J_HH= 13.5, J_PH= 3.0, 2H, ArCH₂

̲

), 1.10–1.50 (m, 28H, CH₂), CH₂), 29.3 (s, CH₂), 29.2 (s, CH₂), 29.2 (d, J_PH= 24, PCH₂),

0.98 (d, ³J_PH= 10.9, 18H, tBu).

25.9 (d, ³J_PH= 16, CH₂), 25.4 (d, ²J_PH= 16, tBu{CH₃})

¹³C{¹H} NMR (151 MHz, toluene-d₈): δ 140.2 (d, J_PC= 8,

³¹P{¹H} NMR (121 MHz, C₆D₆): δ 142.40 (s, 1P), 142.36 (s, 1P).

HR ESI-MS (positive ion, 4 kV): 561.3231, [M + 2O + Na]⁺

(calcd 561.3233) m/z.

2

3

Ar{C}), 130.9 (t, J_PC= 7, Ar{2-CH}), 128.5 (s, Ar), 127.1 (dd,

5

1

2

³J_PC= 7, J_PC= 2, Ar), 32.6 (d, J_PC= 23, ArC

̲H₂), 30.8 (d, J_PC=

1

12, CH₂), 28.6 (s, CH₂), 28.3 (s, CH₂), 28.23 (d, J_PC= 15,

Preparation of 10. BH₃·SMe₂(4.63 g, 5.78 mL, 61.0 mmol)

2

tBu{C}), 28.21 (s, CH₂), 28.1 (s, CH₂), 27.5 (d, J_PC= 13, was added dropwise to a stirred solution of 9 (15.4 g,

tBu{CH₃}), 27.3 (s, CH₂), 24.4 (d, ¹J_PC= 20, PCH₂).

³¹P{¹H} NMR (243 MHz, toluene-d₈): δ 3.2 (s).

30.5 mmol) in THF (50 mL) at −78 °C. The reaction mixture

was warmed to RT overnight and volatiles removed in vacuo to

Preparation of PCP-14′·O₂. Following an adapted literature aﬀord the crude material as an opaque colourless oil.

procedure.²⁷To a stirred solution of PCP-14′ (24.8 mg, Purification by flash column chromatography in air (silica, 8%

52.0 µmol) in EtOH (1 mL) cooled to −78 °C was added H₂O₂EtOAc in hexane, R_f= 0.41) aﬀorded 10 (1 : 1 mixture of dia-

(30% w/w in H₂O, 16 µL, 0.16 mmol). The mixture was allowed stereoisomers) as a colourless oil. Yield: 12.9 g (79%).

3

to warm to RT overnight before the volatiles were removed in

¹H NMR (600 MHz, CDCl₃): δ 7.19 (t, J_HH= 8.2, 1H, Ar),

3

vacuo. Toluene (0.5 mL) was added and the solution was 6.99 (app q, J = 2, 1H, Ar{2-CH}), 6.90 (app dt, J_HH= 8.4, J = 2,

3

stirred over 3 Å molecular sieves (15 mg) overnight. The solu- 2H, Ar), 5.79 (app ddt, J_HH= 16.9, 10.1, 6.7, 2H, CH

̲vCH₂),

tion was filtered, extracting the sieves with additional toluene 4.99 (app dq, ³J_HH= 17.0, J_HH= 2, 2H, CHvCH₂

̲

), 4.93 (app dq,

(3 × 1 mL), and reduced to dryness to aﬀord PCP-14′·O₂as a ³J_HH= 10.2, J_HH= 2, 2H, CHvCH₂

colourless oil, which crystallised upon standing. Yield: CH₂CHvCH₂), 1.92–2.01 (m, 2H, PCH₂), 1.68–1.79 (m, 4H,

CH₂), 1.55–1.65 (m, 2H, CH₂), 1.28–1.44 (m, 12H, CH₂), 1.26

̲ ), 2.04 (app q, J_HH= 7, 4H,

3

̲

22.3 mg (84%).

¹H NMR (500 MHz, CD₂Cl₂): δ 7.37 (s, 1H, Ar), 7.23–7.28 (d, J_PH= 14.0, 18H, tBu), 0.53 (partially collapsed quartet,

3

(m, 1H, Ar), 7.21 (d, ³J_HH= 7.6, 2H, Ar), 3.12 (app t, ²J = 14, 2H, fwhm = 300 Hz, 6H, BH₃).

2

ArCH

̲

₂), 3.02 (dd, J_HH= 14.5, J_PH= 10.1, 2H, ArCH₂

̲

),

¹³C{¹H} NMR (151 MHz, CDCl₃): δ 154.2 (d, J_PC= 6, Ar{C}),

3

1.61–1.76 (m, 2H, PCH₂), 1.50–1.61 (m, 2H, PCH₂), 1.39–1.50 139.1 (s, C

(m, 2H, CH₂), 1.10–1.50 (m, 22H, CH₂), 0.98 (d, J_PH= 10.9, (s, CHvC

HvCH₂), 129.6 (s, Ar), 117.0 (d, J_PC= 3, Ar), 114.5

3

̲

= 3.0, Ar{2-CH}), 33.8 (s,

1

2

18H, tBu).

C̲

H₂CHvCH₂), 32.9 (d, J_PC= 37, tBu{C}), 31.4 (d, J_PC= 13.0,

¹³C{¹H} NMR (126 MHz, CD₂Cl₂): δ 134.2 (dd, J_PC= 8, J_PCCH₂), 28.9 (d, J_PC= 3, CH₂), 28.7 (s, CH₂), 25.4 (d, J_PC= 33,

2

4

1

= 2, Ar{C}), 131.9 (t, J_PC= 5, Ar{2-CH}), 128.8 (t, J_PC= 2, Ar), PCH₂), 24.9 (d, ²J_PC= 3, tBu{CH₃}), 22.8 (s, CH₂).

3

4

128.6 (app t, J_PC= 3, Ar), 33.2 (d, ¹J_PC= 65, tBu{C}), 32.9 (d, ¹J_PC

³¹P{¹H} NMR (121 MHz, CDCl₃): δ 143.7 (partially collapsed

2

= 55, ArC

̲

CH₂), 28.14 (s, CH₂), 28.08 (s, CH₂), 24.9 (s, tBu{CH₃}), 24.4 (d,

1J_PC= 62, PCH₂), 22.0 (d, ³J_PC= 5, CH₂).

HR ESI-MS (positive ion, 4 kV): 557.4000, [M + Na]⁺(calcd

557.3990) m/z.

³¹P{¹H} NMR (162 MHz, CD₂Cl₂): δ 52.2 (s).

Preparation of 11. A solution of [Ru(PCy₃)₂Cl₂(CHPh)]

HR ESI-MS (positive ion, 4 kV): 531.3490, [M + Na]⁺(calcd (36.0 mg, 43.7 µmol, 2.5 mol%) in CH₂Cl₂(3 mL) was added at

531.3491) m/z.

RT to a solution of 10 (930 mg, 1.74 mmol) in CH₂Cl₂(350 mL,

5 mmol L⁻¹). The solution was stirred at RT with periodic

(every 12 h) argon sparging (ca. 10 min) for 2 days. Volatiles

Preparation of POCOP-14′

Preparation of 9. A solution of resorcinol (3.53 g, 32.1 mmol) were removed in vacuo and the crude mixture was purified by

in THF (10 mL) was added to a suspension of NaH (1.62 g, flash column chromatography in air (silica, 10% EtOAc in

67.3 mmol) in THF (10 mL). The resulting suspension was hexane, R_f= 0.40) to aﬀord 11 (1 : 1 mixture of diastereo-

heated at reflux for 1 h, allowed to cool to RT and a solution of isomers) as a colourless oil. Yield: 832 mg (94%).

3

8 (16.6 g, 70.5 mmol) in THF (10 mL) added. The reaction

¹H NMR (500 MHz, CDCl₃): δ 7.20 (t, J_HH= 8.3, 0.5H, Ar

3

mixture was then heated at reflux for a further 1 h. Volatiles cis), 7.19 (t, J_HH= 8.3, 0.5H, Ar trans), 7.03 (dd, J_HH= 8.3,

were removed in vacuo and the residue extracted with hexane ⁴J_HH= 2.4, 1H, Ar cis), 6.97 (t, ⁴J_HH= 2.3, 0.5H, Ar{2-CH} trans),

(3 × 10 mL) to aﬀord 9 (1 : 1 mixture of diastereoisomers) as a 6.89 (dd, ³J_HH= 8.3, ⁴J_HH= 2.3, 1H, Ar trans), 6.74 (t, ⁴J_HH= 2.4,

colourless oil on drying. Yield: 16.1 g (95%).

¹H NMR (300 MHz, C₆D₆): δ 7.43 (s, 1H, Ar{2-CH}), 7.04 (t, 6H, CH₂), 1.61–1.81 (m, 4H, CH₂), 1.24–1.60 (m, 14H, CH₂),

³J_HH= 8.0, 1H, Ar), 6.95 (d, ³J_HH= 8.4, 2H, Ar), 5.76 (ddt, ³J_HH1.27 (d, ³J_PH= 14.0, 18H, tBu), 0.55 (partially collapsed quartet,

0.5H, Ar{2-CH} cis), 5.26–5.36 (m, 2H, CHvCH), 1.93–2.10 (m,

=

16.8, 11.8, 6.7, 2H, CH

1.95 (app q, J_HH= 7, 4H, CH₂

̲

), fwhm = 300 Hz, 6H, BH₃).

3

2

¹³C{¹H} NMR (126 MHz, CDCl₃): δ 154.4 (d, J_PC= 6, Ar{C}

2

CH₂), 1.61 (app sex, J = 8, 4H, CH₂), 1.15–1.40 (m, 14H, CH₂), cis), 154.1 (d, J_PC= 6, Ar{C} trans), 130.9 (s, CHvCH trans),

1.04 (d, ³J_PH= 12.0, 18H, tBu).

130.8 (s, CHvCH cis), 129.7 (s, Ar cis), 129.5 (s, Ar trans), 117.0

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3

(d, J_PC= 4, Ar trans), 116.4 (d, J_PC= 3, Ar cis), 114.4 (t, J_PC

=

³¹P{¹H} NMR (162 MHz, CDCl₃): δ 143.7 (br, fwhm = 175 Hz).

HR ESI-MS (positive ion, 4 kV): 531.3840, [M + Na]⁺(calcd

3

1

3, Ar{2-CH} trans), 113.3 (t, J_PC= 4, Ar{2-CH} cis), 32.8 (d, J_PC

= 37, tBu{C} cis), 32.7 (d, J_PC= 38, tBu{C} trans), 32.10 (s, 531.3844) m/z.²⁸

1

2

C̲

H₂CHvCH trans), 32.06 (s, C

H₂CHvCH cis), 31.6 (d, J_PC

=

Anal. Calcd for C₂₈H₅₆B₂O₂P₂(508.32 g mol⁻¹): C, 66.16; H,

13, CH₂trans), 31.2 (d, J_PC= 13, CH₂cis), 28.8 (s, CH₂trans), 11.10; found: C, 66.09; H, 11.26.²⁸

2

28.7 (s, CH₂cis), 28.1 (s, CH₂trans), 27.9 (s, CH₂cis), 25.5 (d,

Preparation of POCOP-14′. A solution of trans-12 (231 mg,

¹J_PC= 33, PCH₂cis), 25.4 (d, ¹J_PC= 33, PCH₂trans), 24.9 (d, ²J_PC455 μmol) in Et₂NH (7 mL) was heated at 60 °C for 2 days.

2

= 3, tBu{CH₃} cis), 24.8 (d, J_PC= 3, tBu{CH₃} trans), 23.0 (d, Volatiles were removed in vacuo to aﬀord POCOP-14′ as a col-

3

³J_PC= 2, CH₂trans), 22.7 (d, J_PC= 2, CH₂cis). Data for major ourless oil. Yield: 217 mg (>99%).

alkene isomer only.

¹H NMR (500 MHz, toluene-d₈): δ 7.30 (app p, J = 2, 1H, Ar

³¹P{¹H} NMR (162 MHz, CDCl₃): δ 142.0–144.6 (br m).

{2-CH}), 6.97 (t, J_HH= 8.1, 1H, Ar), 6.87 (app dt, J_HH= 8.2, J =

3

HR ESI-MS (positive ion, 4 kV): 529.3689, [M + Na]⁺(calcd 2, 2H, Ar), 1.84 (dtd, J_HH= 14.4, J_HH= 7.3, J_PH= 3.2, 2H,

2

3

2

529.3687) m/z.

Preparation of 12. A suspension of [Rh(PPh₃)₃Cl] (201 mg, (d, ³J_PH= 12.1, 18H, tBu).

220 μmol, 5 mol%) in benzene (20 mL) was added to a stirred

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 160.9 (d, J_PC= 9, Ar

PCH₂), 1.54–1.67 (m, 4H, CH₂), 1.15–1.50 (m, 22H, CH₂), 1.00

2

3

solution of 11 (2.20 g, 4.34 mmol) in benzene. The suspension {C}), 129.9 (s, Ar), 112.2 (d, J_PC= 11, Ar), 109.2 (t, J_PC= 12, Ar

was freeze–pump–thaw degassed and placed under a hydrogen {2-CH}), 32.5 (d, ¹J_PC= 16, tBu{C}), 31.1 (d, ²J_PC= 11, CH₂), 29.0

atmosphere and the resulting solution stirred at 50 °C for 2 (d, J_PC= 24, PCH₂), 28.9 (s, CH₂), 28.5 (s, CH₂), 28.2 (s, CH₂),

1

3

2

days. Volatiles were removed under reduced pressure and the 28.0 (s, CH₂), 25.5 (d, J_PC= 15, CH₂), 25.3 (d, J_PC= 15, tBu

crude mixture was eluted through a short silica plug in air (5% {CH₃}).

EtOAc in hexane) to aﬀord 12 as a mixture of diastereomers

³¹P{¹H} NMR (162 MHz, toluene-d₈): δ 141.6 (s).

(2.02 g, 3.97 mmol, 92%). Subsequent purification by repeated

Preparation of the cis-diastereoisomer of POCOP-14′. A solu-

flash column chromatography in air (silica, 5% EtOAc in tion of cis-12 (10.0 mg, 19.7 μmol) in Et₂NH (0.5 mL) was

hexane) enabled separation of the cis- and trans-diastereomers. heated at 80 °C for 2 days. Volatiles were removed in vacuo to

POCOP-14′·2BH₃(trans-12, R_f= 0.45). Yield: 951 mg (43%, aﬀord the cis-diastereoisomer of POCOP-14′ as a colourless oil.

colourless oil which slowly crystallised upon standing).

Yield: 9.4 mg (>99%).

3

¹H NMR (600 MHz, CDCl₃): δ 7.19 (t, J_HH= 8.2, 1H, Ar),

¹H NMR (500 MHz, toluene-d₈): δ 7.21 (app p, J = 2, 1H, Ar

{2-CH}), 6.97 (t, ³J_HH= 7.9, 1H, Ar), 6.91 (app dt, 3J_HH= 7.9, J =

4

3

4

7.03 (t, J_HH= 2.5, 1H, Ar{2-CH}), 6.93 (dd, J_HH= 8.2, J_HH

=

2

3

2

2.5, 2H, Ar), 1.94–2.04 (m, 2H, PCH₂), 1.67–1.76 (m, 4H, CH₂), 2, 2H, Ar), 1.85 (dtd, J_HH= 14.2, J_HH= 7.4, J_PH= 3.1, 1H,

1.50–1.61 (m, 2H, CH₂), 1.36–1.44 (m, 4H, CH₂), 1.22–1.34 (m, PCH₂), 1.58–1.68 (m, 4H, CH₂), 1.41–1.52 (m, 2H, CH₂),

3

16H, CH₂), 1.26 (d, J_PH= 13.8, 18H, tBu), 0.58 (partially col- 1.16–1.40 (m, 20H, CH₂), 1.01 (d, ³J_PH= 12.0, 18H, tBu).

2

lapsed quartet, fwhm = 300 Hz, 6H, BH₃).

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 160.8 (d, J_PC= 9, Ar

2

3

¹³C{¹H} NMR (151 MHz, CDCl₃): δ 154.2 (d, J_PC= 6, Ar{C}), {C}), 129.9 (s, Ar), 111.7 (d, J_PC= 13, Ar), 109.4 (t, J_PC= 11, Ar

129.6 (s, Ar), 116.9 (d, ³J_PC= 3, Ar), 114.1 (t, ³J_PC= 3, Ar{2-CH}), {2-CH}), 32.5 (d, ¹J_PC= 16, tBu{C}), 30.9 (d, ²J_PC= 11, CH₂), 29.1

1

2

1

32.8 (d, J_PC= 37, tBu{C}), 30.7 (d, J_PC= 12, CH₂), 28.1 (s, (d, J_PC= 24, PCH₂), 28.9 (s, CH₂), 28.5 (s, CH₂), 28.2 (s, CH₂),

1

3

CH₂), 28.0 (s, CH₂), 27.6 (s, CH₂), 27.5 (s, CH₂), 25.1 (d, J_PC

=

28.1 (s, CH₂), 25.4 (d, J_PC= 15, CH₂), 25.3 (d, J_PC= 15, tBu

{CH₃}).

33, PCH₂), 24.8 (d, ³J_PC= 3, tBu{CH₃}), 22.3 (s, CH₂).

³¹P{¹H} NMR (243 MHz, CDCl₃): δ 143.8 (partially collapsed

³¹P{¹H} NMR (162 MHz, C₆D₆): δ 140.5 (s).

Preparation of POCOP-14′·O₂. Following an adapted litera-

quartet, fwhm = 165 Hz).

HR ESI-MS (positive ion, 4 kV): 531.3840, [M + Na]⁺(calcd ture procedure.²⁷To a stirred solution of POCOP-14′ (25.1 mg,

531.3844) m/z.²⁸

Anal. Calcd for C₂₈H₅₆B₂O₂P₂(508.32 g mol⁻¹): C, 66.16; H, (30% w/w in H₂O, 16 µL, 0.16 mmol). The mixture was allowed

11.10; found: C, 66.09; H, 11.26.²⁸

to warm to RT overnight before the volatiles were removed in

cis-12 (R_f= 0.42). Yield: 984 mg (45%, white crystalline vacuo. Toluene (1 mL) was added and the solution was stirred

solid). over 3 Å molecular sieves (45.2 mg) overnight. The solution

¹H NMR (500 MHz, CDCl₃): δ 7.20 (t, J_HH= 8.3, 1H, Ar), was filtered, extracting the sieves with additional toluene (3 ×

52.2 µmol) in EtOH (2 mL) cooled to −78 °C was added H₂O₂

3

4

7.03 (dd, J_HH= 8.3, J_HH= 2.3, 2H, Ar), 6.82 (t, J_HH= 2.5, 1H, 1 mL), and reduced to dryness to aﬀord POCOP-14′·O₂as a col-

Ar{2-CH}), 1.90–2.06 (m, 2H, PCH₂), 1.67–1.81 (m, 4H, CH₂), ourless oil, which crystallised upon standing. Yield: 26.2 mg

3

1.53–1.66 (m, 2H, CH₂), 1.20–1.50 (m, 20H, CH₂), 1.26 (d, J_PH(95%).

= 14.0, 18H, tBu), 0.61 (partially collapsed quartet, fwhm = 285

3

¹H NMR (500 MHz, CD₂Cl₂): δ 7.23 (t, J_HH= 8.3, 1H, Ar),

4

3

4

Hz, 6H, BH₃).

7.19 (t, J_HH= 2.4, 1H, Ar{2-CH}), 7.04 (dd, J_HH= 8.3, J_HH=

2

¹³C{¹H} NMR (126 MHz, CDCl₃): δ 154.4 (d, J_PC= 6, Ar{C}), 7.1, 2H, Ar), 1.75–1.91 (m, 4H, CH₂), 1.16–1.73 (m, 24H, CH₂),

129.7 (s, Ar), 116.6 (d, ³J_PC= 3, Ar), 113.4 (t, ³J_PC= 4, Ar{2-CH}), 1.22 (d, ³J_PH= 15.5, 18H, tBu).

1

2

32.9 (d, J_PC= 37, tBu{C}), 30.5 (d, J_PC= 12, CH₂), 28.2 (s,

¹³C{¹H} NMR (126 MHz, CD₂Cl₂): δ 153.6 (d, J_PC= 10,

Ar{C}), 130.2 (s, Ar), 116.4 (d, J_PC= 4, Ar), 113.3 (t, J_PC= 4,

1

3

CH₂), 27.9 (s, CH₂), 27.8 (s, CH₂), 27.6 (s, CH₂), 25.2 (d, J_PC

33, PCH₂), 24.9 (d, ³J_PC= 3, tBu{CH₃}), 22.0 (d, ³J_PC= 2, CH₂).

=

1

2

Ar{2-CH}), 33.9 (d, J_PC= 91, tBu{C}), 30.9 (d, J_PC= 14, CH₂),

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28.5 (s, CH₂), 28.3 (s, CH₂), 28.0 (s, CH₂), 27.7 (s, CH₂), 24.6 J_PH= 4.1, 2H, ArCH₂

̲

), 1.84–1.95 (m, 2H, CH₂), 1.25–1.78 (m,

(s, tBu{CH₃}), 24.4 (d, ¹J_PC= 83, PCH₂), 21.9 (d, ³J_PC= 6, CH₂).

³¹P{¹H} NMR (162 MHz, CD₂Cl₂): δ 64.1 (s).

24H, CH₂), 1.16 (vt, J_PH= 6.9, 18H, tBu).

¹³C{¹H} NMR (151 MHz, toluene-d₈, CO): δ 189.1 (dt, ¹J_RhC

=

2

1

HR ESI-MS (positive ion, 4 kV): 535.3078, [M + Na]⁺(calcd 39, J_PC= 7, CO), 163.7 (d, J_RhC= 21, Ar{CRh}), 147.4 (vt, J_PC

535.3077) m/z.

8, Ar{C}), 125.6 (s, Ar), 122.6 (vt, J_PC= 9, Ar), 38.1 (vt, J_PC= 14,

ArCH₂), 34.9 (vt, J_PC= 10, tBu{C}), 30.9 (vt, J_PC= 5, CH₂), 29.2

(s, CH₂), 29.1 (s, CH₂), 28.9 (s, CH₂), 28.6 (s, CH₂), 27.6 (s, tBu

̲

Synthesis of rhodium complexes of PCP-14

A solution of PCP-14′ (118.2 mg, 248 μmol) and [Rh(COE)₂Cl]₂{CH₃}), 26.4 (s, CH₂), 22.3 (vt, J_PC= 11, PCH₂).

(88.9 mg, 124 μmol) in toluene (5 mL) within a reaction flask

fitted with a J Young’s value was freeze–pump–thaw-degassed

and placed under dihydrogen (1 atm), sealed, and heated at

³¹P{¹H} NMR (243 MHz, toluene-d₈, CO): δ 64.9 (d, ¹J_RhP= 87).

IR (toluene): ν(CO) 2069 cm⁻¹

Anal. Calcd for C₃₁H₅₃Cl₂OP₂Rh (677.52 g mol⁻¹): C, 54.96;

.

100 °C for 18 h. The solution was cooled to RT and cannula H, 7.89; found: C, 54.99; H, 8.06.

transferred under dihydrogen into a reaction flask fitted with a

Synthesis of rhodium complexes of POCOP-14

J Young’s value and charged with KOtBu (34.0 mg, 303 μmol).

The flask was then sealed and heated at 120 °C for 2 h to gene- A solution of POCOP-14′ (217 mg, 452 μmol) and [Rh

rate 13a, which was characterised in situ. The solution was (COE)₂Cl]₂(163 mg, 227 μmol) in toluene (5 mL) within a reac-

freeze–pump–thaw degassed and placed under carbon monox- tion flask fitted with a J Young’s value was freeze–pump–thaw-

ide (1 atm) resulting in immediate formation of 14a, which degassed and placed under dihydrogen (1 atm), sealed, and

was isolated by removal of the volatiles in vacuo and extraction heated at 120 °C for 3 days. The solution was cooled to RT and

of the residue with hexane. Crude 14a obtained in this way was cannula transferred under dihydrogen into a reaction flask

dissolved in toluene (5 mL) and then slowly added to a suspen- fitted with a J Young’s value and charged with KOtBu

sion of PhICl₂(68.7 mg, 250 μmol) in toluene (2 mL) at (61.1 mg, 545 μmol). The flask was then sealed and heated at

−78 °C. The reaction mixture was allowed to warm to RT over- 120 °C for 1 h to generate 13b, which was characterised in situ.

night, the volatiles removed in vacuo, and the resulting residue The solution was freeze–pump–thaw degassed and placed

extracted with hexane to aﬀord the crude product, which was under carbon monoxide (1 atm) resulting in immediate for-

purified by alumina chromatography in air (20% CH₂Cl₂in mation of 14b, which was isolated by removal of the volatiles

hexane, R_f= 0.55) to aﬀord analytically pure 15a. Yield: in vacuo and extraction of the residue with hexane. Crude 14b

136.4 mg (80%). Complex 15a is stable in the solid state, but obtained in this way was dissolved in toluene (5 mL) and then

partial loss of CO was observed in solution over time.

slowly added to a suspension of PhICl₂(125 mg, 455 μmol) in

[Rh(PCP-14)(H₂)] (13a). This complex is unstable to vacuum toluene (2 mL) at −78 °C. The reaction mixture was allowed to

but was characterised in situ using a sample (ca. 10 μmol) pre- warm to RT overnight, the volatiles removed in vacuo, and the

pared in a similar manner within a J Young’s valve NMR tube fol- resulting residue extracted with hexane to aﬀord the crude

lowing removal of volatiles, addition of toluene-d₈(0.5 mL) under product, which was purified by alumina chromatography in air

argon, freeze–pump–thaw-degassing, and placing under dihydro- (20% CH₂Cl₂in hexane, R_f= 0.45) to aﬀord analytically pure

gen (1 atm). T₁values were subsequently determined following 15b. Yield: 149.3 mg (48%). Complex 15b is stable in the solid

rapid freeze–pump–thaw-degassing and placing under argon.

state, but partial loss of CO was observed in solution over time.

[Rh(POCOP-14)(H₂)] (13b). This complex is unstable to

̲ ), vacuum but was characterised in situ using a sample (ca.

3

¹H NMR (500 MHz, toluene-d₈, H₂): δ 7.12 (d, J_HH= 7.4,

2H, Ar), 7.05 (t, ³J_HH= 7.4, 1H, Ar), 3.08 (vt, J_PH= 3.9, 4H, ArCH₂

1.87–2.00 (m, 2H, CH₂), 1.74–1.84 (m, 2H, CH₂), 1.17–1.67 (m, 10 μmol) prepared in a similar manner within a J Young’s

24H, CH₂), 1.01 (vt, J_PH= 6.5, 18H, tBu), −4.36 (br, 2H, RhH).

valve NMR tube following removal of volatiles, addition of

toluene-d₈(0.5 mL) under argon, freeze–pump–thaw-degas-

1

¹³C{¹H} NMR (126 MHz, toluene-d₈, H₂): δ 176.3 (dt, J_RhC

=

2

40, J_PC= 6, Ar{CRh}), 151.6 (vtd, J_PC= 12, J_RhC= 3, Ar{C}), sing, and placing under dihydrogen (1 atm). T₁values were

2

124.1 (s, Ar), 120.7 (vt, J_PC= 10, Ar), 39.9 (vtd, J_PC= 10, J_RhC

4, ArC

=

subsequently determined following rapid freeze–pump–thaw-

̲H₂), 31.9 (vt, J_PC= 11, tBu{C}), 29.5 (vt, J_PC= 4, CH₂), 29.2 degassing and placing under argon.

(s, CH₂), 29.0 (s, CH₂), 28.6 (s, CH₂), 28.4 (vt, J_PC= 3, tBu{CH₃}),

27.7 (s, CH₂), 25.6 (vt, J_PC= 4, CH₂), 22.9 (vt, J_PC= 8, PCH₂).

¹H NMR (500 MHz, toluene-d₈, H₂): δ 6.94 (t, ³J_HH= 7.9, 1H,

3

Ar), 6.76 (d, J_HH= 7.9, 2H, Ar), 1.93–2.04 (m, 4H, CH₂),

³¹P{¹H} NMR (162 MHz, toluene-d₈, H₂): δ 70.4 (d, ¹J_RhP= 153). 1.83–1.92 (m, 2H, PCH₂), 1.17–1.67 (m, 22H, CH₂), 1.15 (vt,

¹H NMR (600 MHz, toluene-d₈, Ar, selected data): δ −4.36 J_PH= 7.1, 18H, tBu), −2.87 (br d, ¹J_RhH= 18.8, 2H, RhH).

(br d, ¹J_RhH= 17.9, 2H, RhH, T₁= 74 4 ms).

¹³C{¹H} NMR (126 MHz, toluene-d₈, H₂): δ 167.3 (vt, J_PC

=

¹H NMR (600 MHz, toluene-d₈, Ar, 200 K, selected data): δ 10, Ar{C}), 143.1 (dt, J_RhC= 35, J_PC= 10, Ar{CRh}), 126.7 (s,

1

2

−4.26 (br, 2H, RhH, T₁= 117 15 ms).

Ar), 104.8 (vt, J_PC= 7, Ar), 36.7 (vtd, J_PC= 12, J_RhC= 2, tBu{C}),

29.0 (vt, J_PC= 2, CH₂), 28.9 (s, CH₂), 28.7 (s, CH₂), 28.6 (s,

CH₂), 28.1 (vtd, J_PC= 9, ²J_RhC= 2, PCH₂), 27.7 (s, CH₂), 26.8 (vt,

[Rh(PCP-14)Cl₂(CO)] (15a)

3

¹H NMR (600 MHz, toluene-d₈, CO): δ 6.95 (t, J_HH= 7.4, 1H, J_PC= 4, tBu{CH₃}), 25.0 (vt, J_PC= 4, CH₂).

3

2

1

Ar), 6.90 (d, J_HH= 7.4, 2H, Ar) 3.71 (dvt, J_HH= 15.6, J_PH= 4.8,

2H, ArCH

³¹P{¹H} NMR (162 MHz, toluene-d₈, H₂): δ 198.4 (d, J_RhP

=

2

₂̲ ), 2.96–3.04 (m, 2H, PCH₂), 2.91 (dvt, J_HH= 15.6, 165).

Dalton Trans.

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¹H NMR (600 MHz, toluene-d₈, Ar, selected data): δ −2.87 linker. T₁values were subsequently determined following rapid

(br d, ¹J_RhH= 18.9, 2H, RhH, T₁= 42 2 ms).

¹H NMR (600 MHz, toluene-d₈, Ar, 200 K, selected data):

δ −2.72 (br, 2H, RhH, T₁= 89 11 ms).

freeze–pump–thaw-degassing and placing under argon.

¹H NMR (600 MHz, toluene-d₈, H₂): δ 6.99–7.03 (m, 3H, Ar),

2

3.50 (dvt, J_HH= 16.1, J_PH= 3.6, 2H, ArCH₂

̲ ), 2.89 (dvt, J_HH=

16.6, J_PH= 4.6, 2H, ArCH₂), 1.78–1.88 (m, 2H, PCH₂), 1.67–1.77

̲

(m, 2H, CH₂), 1.53–1.63 (m, 2H, CH₂), 1.27–1.53 (m, 22H, CH₂),

0.94 (vt, J_PH= 6.8, 18H, tBu), −8.99 (t, ²J_PH= 9.8, 4H, IrH).

¹³C{¹H} NMR (151 MHz, toluene-d₈, H₂): δ 151.7 (s, Ar{CIr}),

147.7 (vt, J_PC= 8, Ar{C}), 123.3 (s, Ar), 120.1 (vt, J_PC= 8, Ar),

[Rh(POCOP-14)Cl₂(CO)] (15b)

¹H NMR (500 MHz, toluene-d₈, CO): δ 6.80 (t, J_HH= 7.9, 1H,

3

Ar), 6.61 (d, ³J_HH= 7.9, 2H, Ar), 3.63 (app dp, ²J_HH= 14.1, J = 7,

2H, PCH₂), 1.87–1.94 (m, 2H, CH₂), 1.78–1.87 (m, 2H, PCH₂),

1.29 (vt, J_PH= 7.6, 18H, tBu), 1.11–1.72 (m, 22H, CH₂).

46.1 (vt, J_PC= 17, ArC̲H₂), 30.0 (vt, J_PC= 4, CH₂), 29.7 (s, CH₂),

29.3 (vt, J_PC= 15, tBu{C}), 29.1 (s, CH₂), 28.9 (s, CH₂), 28.2 (s,

CH₂), 27.4 (br, CH₂), 27.2 (vt, J_PC= 15, PCH₂), 25.7 (vt, J_PC= 3,

tBu{CH₃}).

¹³C{¹H} NMR (126 MHz, toluene-d₈, CO): δ 187.2 (dt, ¹J_RhC

=

2

41, J_PC= 5, CO), 163.6 (vt, J_PC= 6, Ar{C}), 136.1 (dt, ¹J_RhC= 22,

²J_PC= 6, Ar{CRh}), 128.4 (s, Ar), 107.6 (vt, J_PC= 6, Ar), 41.5 (vt,

J_PC= 11, tBu{C}), 30.7 (vt, J_PC= 6, CH₂), 29.5 (s, CH₂), 29.4 (s,

CH₂), 29.2 (s, CH₂), 28.2 (s, CH₂), 26.5 (s, tBu{CH₃}), 24.1 (vt,

J_PC= 3, CH₂), 23.8 (vt, J_PC= 13, PCH₂).

³¹P{¹H} NMR (243 MHz, toluene-d₈, H₂): δ 49.9 (s).

¹H NMR (600 MHz, toluene-d₈, Ar, selected data): δ −8.99 (t,

²J_PH= 9.8, 4H, IrH, T₁= 300 10 ms).

¹H NMR (600 MHz, toluene-d₈, Ar, 200 K, selected data): δ

−8.95 (br, 4H, IrH, T₁= 626 15 ms).

³¹P{¹H} NMR (162 MHz, toluene-d₈, CO): δ 181.0 (d, ¹J_RhP= 92).

IR (toluene): ν(CO) 2083 cm⁻¹

.

cis-[Ir(PCP-14)(H)₂(CO)] (cis-17a). This complex is most con-

veniently characterised in situ by placing a toluene-d₈(0.5 mL)

solution of analytically pure 18a (6.0 mg, 8.6 μmol) under dihy-

drogen (1 atm) in a J Young’s valve NMR tube.

Anal. Calcd for C₂₉H₄₉Cl₂O₃P₂Rh (681.46 g mol⁻¹): C, 51.11;

H, 7.25; found: C, 51.09; H, 7.31.

Synthesis of iridium complexes of PCP-14

¹H NMR (500 MHz, toluene-d₈): δ 6.99–7.04 (m, 3H, Ar),

2

A solution of PCP-14′ (57.6 mg, 121 μmol) and [Ir(COE)₂Cl]₂3.50–3.65 (m, 2H, ArCH

(54.1 mg, 60.4 μmol) in toluene (5 mL) within a reaction flask ArCH

₂), 2.86 (dd, ²J_HH= 16.8, J_PH= 8.8, 1H, ArCH₂

fitted with a J Young’s value was freeze–pump–thaw-degassed (m, 1H, PCH₂), 1.92–2.04 (m, 2H, CH₂), 1.14–1.91 (m, 25H,

₂̲ ), 2.98 (dd, J_HH= 16.0, J_PH= 7.3, 1H,

2

̲

̲ ), 2.06–2.16

2

and placed under dihydrogen (1 atm), sealed, and heated at CH₂), 0.96 (d, J_PH= 13.3, 9H, tBu), 0.89 (d, J_PH= 13.6, 9H,

70 °C for 18 h. The solution was cooled to RT and cannula tBu), −10.66 (ddd, ²J_PH= 23.4, J_PH= 10.5, J_HH= 3.0, 1H, IrH),

2

transferred under dihydrogen into a reaction flask fitted with a −11.59 (app td, ²J_PH= 12, ²J_HH= 3.0, 1H, IrH).

J Young’s value and charged with KOtBu (16.3 mg, 145 μmol).

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 183.3 (m, CO), 155.1

The flask was then sealed and heated at 120 °C for 18 h to (br, Ar{CIr}), 148.8 (dd, ²J_PC= 10, J_PC= 4, Ar{C}), 148.1 (dd, ²J_PC

3

generate 16a, which was characterised in situ. The solution was = 9, J_PC= 4, Ar{C}), 123.5 (s, Ar), 120.0 (d, J_PC= 14, Ar), 119.8

freeze–pump–thaw degassed and placed under carbon monox- (d, J_PC= 16, Ar), 48.4 (d, J_PC= 35, ArC

3

1

̲H₂), 46.2 (d, J_PC= 35,

ide (1 atm) resulting in immediate formation of cis-17a, which ArC

̲

was characterised in situ. To this solution tert-butylethylene ³J_PC= 5, tBu{C}), 30.2 (d, J_PC= 10, CH₂), 29.9 (s, CH₂), 29.7 (d,

(78 μL, 0.60 mmol) was added and the reaction mixture heated ²J_PC= 9, CH₂), 29.4 (s, CH₂), 29.3 (s, CH₂), 29.1 (s, CH₂), 28.8

under carbon monoxide (1 atm, sealed flask) at 120 °C for (s, CH₂), 28.5 (s, CH₂), 28.3 (s, CH₂), 28.2 (s, CH₂), 27.9 (dd,

18 h, resulting in partial conversion to trans-17a but ultimately ¹J_PC= 29, ³J_PC= 4, PCH₂), 27.7 (s, CH₂), 27.3 (dd, ¹J_PC= 24, ³J_PC

2

aﬀording [Ir(PCP-14)(CO)₂] (δ_31P51.6). The solution was = 3, PCH₂), 27.2 (s, CH₂), 26.2 (d, J_PC= 4, tBu{CH₃}), 26.1 (d,

freeze–pump–thaw degassed and placed under argon to gene- ²J_PC= 4, tBu{CH₃}).

2

rate 18a, filtered, and slowly added to a suspension of PhICl₂

³¹P{¹H} NMR (162 MHz, toluene-d₈): δ 51.0 (d, J_PP= 286,

(33.3 mg, 121 μmol) in toluene (1 mL) at −78 °C. The reaction 1P), 45.8 (d, ²J_PP= 286, 1P).

mixture was allowed to warm to RT overnight, the volatiles

trans-[Ir(PCP-14)(H)₂(CO)] (trans-17a)

removed in vacuo, and the resulting residue extracted with

hexane to aﬀord the crude product, which was purified by ¹H NMR (400 MHz, toluene-d₀, CO, selected data): δ 1.01 (vt,

silica chromatography in air (40% CH₂Cl₂in hexane, R_f= 0.43) ²J_PH= 7.1, 18H, tBu), −9.65 (t, ²J_PH= 14.4, 2H, IrH).

to aﬀord analytically pure 19a. Yield: 76.9 mg (51%).

³¹P{¹H} NMR (162 MHz, toluene-d₀, CO): δ 54.1 (s).

[Ir(PCP-14)H₄] (16a). This complex is unstable to vacuum

but was characterised in situ using a sample (ca. 10 μmol) pre-

[Ir(PCP-14)Cl₂(CO)] (19a)

pared in a similar manner within a J Young’s valve NMR tube ¹H NMR (500 MHz, toluene-d₈): δ 6.94–7.00 (m, 3H, Ar), 3.64

2

following concentration in vacuo, placing under dihydrogen (1 (dvt, J_HH= 15.8, J_PH= 5.0, 2H, ArCH₂

atm), concentration to dryness in vacuo, addition of toluene-d₈J_PH= 3.8, 2H, ArCH₂), 2.91–3.01 (m, 2H, PCH₂), 1.81–1.97 (m,

(0.5 mL) under argon, freeze–pump–thaw-degassing, and placing 2H, CH₂), 1.02–1.81 (m, 24H, CH₂), 1.13 (br, 18H, tBu).

under dihydrogen (1 atm). NB: Long term storage in toluene-d₈

resulted in extensive H/D exchange of the hydride ligands, CO), 155.3 (s, Ar{CIr}), 148.5 (vt, J_PC= 8, Ar{C}), 126.0 (s, Ar),

̲ ), 3.05 (dvt, J_HH= 15.8,

̲

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 175.7 (t, J_PC= 5,

2

1

pincer backbone and some positions of the tetramethylene 121.6 (vt, J_PC= 8, Ar), 38.9 (vt, J_PC= 17, ArC

H₂), 34.3 (vt, J_PC

=

Dalton Trans.

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Dalton Transactions

2

13, tBu{C}), 30.8 (vt, J_PC= 5, CH₂), 29.2 (s, CH₂), 29.1 (s, CH₂), 9H, tBu), 1.04 (d, J_PH= 15.0, 9H, tBu), −9.82 (app t, J_PH= 9,

29.0 (s, CH₂), 28.6 (s, CH₂), 27.5 (s, tBu{CH₃}), 26.4 (s, CH₂), 1H, IrH), −10.75 (dd, ²J_PH= 21.8, ²J_PH= 14.7, 1H, IrH).

20.6 (vt, J_PC= 13, PCH₂).

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 180.6 (m, CO), 163.2

2

³¹P{¹H} NMR (162 MHz, toluene-d₈): δ 33.8 (s).

(dd, J_PC= 6, J_PC= 4, Ar{C}), 162.8 (dd, J_PC= 7, J_PC= 4, Ar{C}),

IR (toluene): ν(CO) 2034 cm⁻¹

.

126.2 (s, Ar), 123.0 (app t, J_PC= 6, Ar{CIr}), 104.8 (d, J_PC= 12,

2

3

Anal. Calcd for C₃₁H₅₃Cl₂IrOP₂(766.83 g mol⁻¹): C, 48.56; Ar), 104.7 (d, ³J_PC= 16, Ar), 37.2 (dd, ¹J_PC= 28, ³J_PC= 7, tBu{C}),

1

3

1

3

H, 6.97; found: C, 48.66; H, 6.92.

37.0 (dd, J_PC= 27, J_PC= 6, tBu{C}), 34.6 (dd, J_PC= 30, J_PC=

5, PCH₂), 33.0 (dd, ¹J_PC= 27, ³J_PC= 5, PCH₂), 30.3 (s, CH₂), 29.8

(s, CH₂), 29.7 (d, J_PC= 6, CH₂), 29.5 (s, CH₂), 29.16 (s, CH₂),

Synthesis of iridium complexes of POCOP-14

A solution of POCOP-14′ (69.1 mg, 144 μmol) and [Ir(COD)Cl]₂29.15 (s, CH₂), 28.9 (s, CH₂), 28.6 (s, CH₂), 28.5 (s, CH₂), 27.7

(53.1 mg, 79.1 μmol) in toluene (5 mL) within a reaction flask (d, J_PC= 6, CH₂), 25.7 (d, J_PC= 5, CH₂), 25.2 (app vt, J_PC= 5, tBu

fitted with a J Young’s value was freeze–pump–thaw-degassed {CH₃}), 25.1 (d, J_PC= 6, CH₂).

2

and placed under dihydrogen (1 atm), sealed, and heated at

³¹P{¹H} NMR (162 MHz, toluene-d₈): δ 160.4 (d, J_PP= 305,

100 °C for 3 days. The solution was cooled to RT and cannula 1P), 154.6 (d, ²J_PP= 305, 1P).

transferred under dihydrogen into a reaction flask fitted with a

trans-[Ir(POCOP-14)(H)₂(CO)] (trans-17b)

J Young’s value and charged with KOtBu (19.4 mg, 173 μmol).

The flask was then sealed and heated at 120 °C for 2 h to gene- ¹H NMR (400 MHz, toluene-d₀, CO, selected data): δ 1.10 (vt,

rate 16b, which was characterised in situ. The solution was J_PH= 7.6, 18H, tBu), −9.76 (t, ²J_PH= 16.5, 2H, IrH).

freeze–pump–thaw degassed and placed under carbon monox-

ide (1 atm) resulting in immediate formation of cis-17b, which

was characterised in situ. To this solution tert-butylethylene

³¹P{¹H} NMR (162 MHz, toluene-d₀, CO): δ 167.3 (s).

[Ir(POCOP-14)Cl₂(CO)] (19b)

(93 μL, 0.72 mmol) was added and the reaction mixture heated ¹H NMR (500 MHz, toluene-d₈): δ 6.80 (t, J_HH= 8.0, 1H, Ar),

under carbon monoxide (1 atm, sealed flask) at 120 °C for 6.64 (d, ³J_HH= 8.0, 2H, Ar), 3.57 (app dp, ²J_HH= 14.3, J = 7, 2H,

18 h, resulting in partial conversion to trans-17b but ultimately PCH₂), 1.85–1.99 (m, 2H, CH₂), 1.72–1.83 (m, 2H, PCH₂), 1.26

3

aﬀording [Ir(POCOP-14)(CO)₂] (δ_31P164.8, fwhm = 127 Hz). (vt, J_PH= 7.7, 18H, tBu), 1.11–1.71 (m, 22H, CH₂).

The solution was freeze–pump–thaw degassed and placed

2

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 175.6 (t, J_PC= 3,

under argon to generate 18b, filtered, and slowly added to a CO), 164.4 (vt, J_PC= 6, Ar{C}), 129 (obsc, Ar{CIr}), 128.9 (s, Ar),

suspension of PhICl₂(39.5 mg, 144 μmol) in toluene (2 mL) at 106.8 (vt, J_PC= 6, Ar), 41.0 (vt, J_PC= 15, tBu{C}), 30.3 (vt, J_PC= 6,

−78 °C. The reaction mixture was allowed to warm to RT over- PCH₂C̲H₂), 29.5 (s, CH₂), 29.4 (s, CH₂), 29.1 (s, CH₂), 28.3 (s,

night, the volatiles removed in vacuo, and the resulting residue CH₂), 26.5 (s, tBu{CH₃}), 24.2 (vt, J_PC= 2, CH₂), 22.0 (vt, J_PC

extracted with hexane to aﬀord the crude product, which was 16, PCH₂).

=

purified by silica chromatography in air (20% CH₂Cl₂in hexane,

R_f= 0.28) to aﬀord analytically pure 19b. Yield: 107.9 mg (73%).

[Ir(POCOP-14)H₄] (16b). This complex is unstable to

³¹P{¹H} NMR (121 MHz, toluene-d₈): δ 144.4 (s).

IR (toluene): ν(CO) 2049 cm⁻¹

Anal. Calcd for C₂₉H₄₉Cl₂IrO₃P₂(770.77 g mol⁻¹): C, 45.19;

.

vacuum, ultimately resulting in irreversible decomposition. H, 6.41; found: C, 44.95; H, 6.30.

Attempts to prepare samples in toluene-d₈resulted in extensive

H/D exchange of hydride ligands, pincer backbone and some

General procedure for the preparation of Rh(^I) carbonyls

positions of the tetramethylene linker (see ESI†). T₁values To a solution of 15 (ca. 30 μmol) in THF (2 mL) at RT was

were determined following rapid freeze–pump–thaw-degassing added iPrMgCl·LiCl (1.3 M in THF, 3 equivalents). The result-

and placing under argon.

ing solution was stirred at RT for 1 h, excess MeOH added and

¹H NMR (500 MHz, toluene-d₀, H₂, selected data): δ 6.67 (d, then reduced to dryness in vacuo. The residue was extracted

³J_HH= 7.9, 2H, Ar), 1.07 (vt, J_PH= 7.5, 18H, tBu), −8.26 (t, ²J_PH

9.9, 4H, IrH).

=

with pentane to aﬀord the crude product on removal of vola-

tiles, which was subsequently recrystallised by slow evapor-

ation of SiMe₄.

[Rh(PCP-14)(CO)] (14a). The product was obtained following

the general procedure using 15a (20.0 mg, 29.5 μmol) and

³¹P{¹H} NMR (162 MHz, toluene-d₀, H₂): δ 165.0 (s).

¹H NMR (600 MHz, toluene-d₀, Ar, selected data): δ −8.26 (t,

²J_PH= 10.0, 4H, IrH, T₁= 194 4 ms).

¹H NMR (600 MHz, toluene-d₀, Ar, 200 K, selected data): δ iPrMgCl·LiCl (68 μL, 89 μmol). Yield: 15.2 mg (85%).

3

−8.10 (br, 4H, IrH, T₁= 242 15 ms).

cis-[Ir(POCOP-14)(H)₂(CO)] (cis-17b). This complex is most Ar), 7.02 (t, J_HH= 7.3, 1H, Ar) 3.19 (dvt, J_HH= 16.3, J_PH= 3.4,

conveniently characterised in situ by placing a toluene-d₈2H, ArCH

(0.5 mL) solution of analytically pure 18b (6.0 mg, 8.6 μmol) 2.10–2.01 (m, 2H, CH₂), 1.77–1.36 (m, 26H, CH₂), 1.00 (vt,

¹H NMR (600 MHz, toluene-d₈): δ 7.06 (d, J_HH= 7.3, 2H,

3

2

₂̲ ), 3.15 (dvt, J_HH= 16.5, J_PH= 4.2, 2H, ArCH₂̲ ),

under dihydrogen (1 atm) in a J Young’s valve NMR tube.

¹H NMR (500 MHz, toluene-d₈): δ 6.86 (t, ³J_HH= 7.9, 1H, Ar),

J_PH= 6.6, 18H, tBu).

1

¹³C{¹H} NMR (151 MHz, toluene-d₈): δ 201.5 (dvt, J_RhC

=

3

2

6.70 (d, J_HH= 7.9, 1H, Ar), 6.70 (d, J_HH= 7.9, 1H, Ar), 57, J_PC= 12, CO), 179.4 (dt, ¹J_PC= 29, J_PC= 7, Ar{CRh}), 152.2

2.68–2.79 (m, 1H, PCH₂), 2.30–2.46 (m, 3H, CH₂), 1.85–1.97 (vt, J_PC= 12, Ar{C}), 125.7 (s, Ar), 120.5 (vt, J_PC= 9, Ar), 41.3 (vt,

2

(m, 1H, PCH₂), 1.12–1.70 (m, 23H, CH₂), 1.08 (d, J_PH= 14.8, J_PC= 12, ArC

̲

Dalton Trans.

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Dalton Transactions

Paper

CH₂), 29.4 (s, CH₂), 29.2 (s, CH₂), 29.0 (s, CH₂), 28.52 (vt, J_PC

=

(m, 4H, CH₂), 1.23–1.66 (m, 20H, CH₂), 1.15 (vt, J_PH= 7.4, 18H,

4, tBu{CH₃}), 28.47 (s, CH₂), 26.4 (vt, J_PC= 4, CH₂), 24.2 (vt, tBu).

¹J_PC= 9, PCH₂).

2

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 200.5 (t, J_PC= 5,

2

³¹P{¹H} NMR (243 MHz, toluene-d₈): δ 75.0 (d, ¹J_RhP= 146).

CO), 168.3 (vt, J_PC= 8, Ar{C}), 148.7 (t, J_PC= 9, Ar{CIr}), 129.5

(s, Ar), 104.4 (vt, J_PC= 6, Ar), 39.5 (vt, J_PC= 16, tBu{C}), 30.8 (vt,

IR (toluene): ν(CO) 1939 cm⁻¹

.

Anal. Calcd for C₃₁H₅₃OP₂Rh (606.62 g mol⁻¹): C, 61.38; H, J_PC= 2, CH₂), 29.6 (vt, J_PC= 14, PCH₂), 29.4 (s, CH₂), 29.3 (s,

8.81; found: C, 61.34; H, 8.74.

CH₂), 29.2 (s, CH₂), 28.9 (s, CH₂), 26.7 (vt, J_PC= 3, tBu{CH₃}),

[Rh(POCOP-14)(CO)] (14b). The product was obtained follow- 26.0 (vt, J_PC= 3, CH₂).

ing the general procedure using 15b (20.0 mg, 29.3 μmol) and

iPrMgCl·LiCl (68 μL, 89 μmol). Yield: 16.8 mg (94%).

³¹P{¹H} NMR (162 MHz, toluene-d₈): δ 186.7 (s).

IR (toluene): ν(CO) 1943 cm⁻¹

Anal. Calcd for C₂₉H₄₉IrO₃P₂(699.87 g mol⁻¹): C, 49.77; H,

.

¹H NMR (600 MHz, toluene-d₈): δ 6.91 (t, ³J_HH= 7.9, 1H, Ar),

6.70 (d, ³J_HH= 7.9, 2H, Ar), 2.00–2.06 (m, 4H, PCH₂), 1.73–1.85 7.06; found: C, 49.85; H 7.01.

(m, 4H, CH₂), 1.26–1.60 (m, 20H, CH₂), 1.15 (vt, J_PH= 7.2, 18H,

Crystallographic details

tBu).

1

¹³C{¹H} NMR (151 MHz, toluene-d₈): δ 201.2 (dt, J_RhC= 60, Data were collected on a Rigaku Oxford Diﬀraction SuperNova

²J_PC= 10, CO), 167.7 (vt, J_PC= 9, Ar{C}), 145.5 (dt, J_RhC= 26, AtlasS2 CCD diﬀractometer using graphite monochromated

1

²J_PC= 10, Ar{CRh}), 128.8 (obsc, Ar), 104.8 (vt, J_PC= 7, Ar), 38.1 Mo Kα (λ = 0.71073 Å) or CuKα (λ = 1.54184 Å) radiation and

1

(vt, J_PC= 12, tBu{C}), 30.6 (br, CH₂), 29.4 (s, CH₂), 29.3 (s, an Oxford Cryosystems N-HeliX low temperature device [150(2)

CH₂), 29.24 (vt, J_PC= 9, PCH₂), 29.16 (s, CH₂), 28.8 (s, CH₂), K]. Data were collected and reduced using CrysAlisPro and

26.8 (vt, J_PC= 4, tBu{CH₃}), 25.8 (vt, J_PC= 4, CH₂).

³¹P{¹H} NMR (243 MHz, toluene-d₈): δ 201.6 (d, ¹J_RhP= 156). details about the collection, solution, and refinement are

IR (toluene): ν(CO) 1958 cm⁻¹

documented in CIF format, which have been deposited with

Anal. Calcd for C₂₉H₄₉O₃P₂Rh (610.56 g mol⁻¹): C, 57.05; H, the Cambridge Crystallographic Data Centre under CCDC

refined using SHELXL,²⁹through the Olex2 interface.³⁰Full

.

8.09; found: C, 57.14; H, 8.07.

1972811–1972820.†

General procedure for the preparation of Ir(^I) carbonyl complexes

A solution of 19 (ca. 20 μ^{mol) in pentane (2 mL) was added to}Conﬂicts of interest

a flask charged with KC₈(10 equivalents) and stirred at RT for

2 days. The solution was filtered, reduced to dryness in vacuo,

There are no conflicts to declare.

and the analytically pure product obtained following

recrystallisation.¹⁶

[Ir(PCP-14)(CO)] (18a). Following the general procedure

Acknowledgements

using 19a (17.2 mg, 22.4 μmol) and KC₈(30.4 mg, 225 μmol),

18a was obtained following recrystallisation by slow evapor-

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-spec-

trometry data were collected using instruments purchased

through support from Advantage West Midlands and the

European Regional Development Fund. Crystallographic data

were collected using an instrument that received funding from

the ERC under the European Union’s Horizon 2020 research

and innovation programme (grant agreement no. 637313).

ation of neohexane. Yield: 13.1 mg (84%).

3

¹H NMR (500 MHz, toluene-d₈): δ 7.14 (d, J_HH= 7.5, 2H,

3

2

Ar), 7.02 (t, J_HH= 7.5, 1H, Ar), 3.35 (dvt, J_HH= 16.4, J_PH= 4.0,

2

2H, ArCH̲₂), 3.09 (dvt, J_HH= 16.4, J_PH= 3.8, 2H, ArCH₂̲ ),

2.03–2.19 (m, 2H, CH₂), 1.90–1.78 (m, 2H, PCH₂), 1.76–1.34

(m, 24H, CH₂), 1.01 (vt, J_PH= 6.7, 18H, tBu).

2

¹³C{¹H} NMR (126 MHz, toluene-d₈): δ 198.6 (t, J_PC= 7,

2

CO), 181.3 (t, J_PC= 4, Ar{CIr}), 153.8 (vt, J_PC= 11, Ar{C}), 126.1

(s, Ar), 120.2 (vt, J_PC= 8, Ar), 41.7 (vt, J_PC= 15, ArC̲H₂), 33.5 (vt,

J_PC= 14, tBu{C}), 30.5 (vt, J_PC= 5, CH₂), 29.5 (s, CH₂), 29.3 (s,

CH₂), 29.0 (s, CH₂), 28.5 (s, CH₂), 28.2 (vt, J_PC= 3, tBu{CH₃}),

26.3 (vt, J_PC= 3, CH₂), 24.2 (vt, J_PC= 13, PCH₂).

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Synthesis and group 9 complexes of macrocyclic PCP and POCOP pincer ligands

DOI: 10.1039/c9dt04835a

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