Synthetic and structural studies of phosphine coordinated boronium salts

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ARTICLE

Synthetic and Structural Studies of Phosphine Coordinated

Boronium Salts

Anthony F. Hill*^aand Jas S. Ward^a

Received 00th January 20xx,

Accepted 00th January 20xx

The reaction of BrH₂B⋅SMe₂with primary and secondary phosphines affords a range of boronium salts of the form

[H₂B(PR₃)₂]Br (PR₃= PHCy₂1; PHPh₂, 2; PH₂Cy, 3), which have been fully characterised including solid-state determinations.

Reactions of bulky tertiary phosphines, e.g., PCy₃and PPh₃, with BrH₂B⋅SMe₂does not proceed beyond the phosphine-

stabilised bromoborane adducts, however, the smaller tertiary phosphine PMe₂Ph readily proceeds to form

[H₂B(PMe₂Ph)₂]Br (4). The formation of the unsymmetrical boronium salts [H₂B(PH₂Cy)(PHCy₂)]Br (5) and

[H₂B(PHCy₂)(PHPh₂)]Br (6) was observed by in situ NMR spectroscopy, however, the compounds were found to

spontaneously disproportionate to their respective homophosphine boronium cations, even on prolonged storage in

solution at –78°C. Di- and triphosphines were found to form ring-closed boronium salts to afford [H₂B(κ²-P,P′-

diphosphine)]Br (diphosphine = dppe, 7; dcpe, 8; dmpe, 9; dppf, 10; dppf with [AsF₆]^–counterion, 11; amphos, 12). The

analogous methodology with Br₂HB⋅SMe₂proved less generally applicable due to an accessible decomposition pathway

being available to boronium salts bearing primary and secondary phosphines, leading to the formation of phosphonium

salts, although [BrHB(dcpe)]Br (13), [BrHB(PMe₂Ph)₂]Br (14) and [BrHB(amphos)]Br (15) were synthesised with varying

DOI: 10.1039/x0xx00000x

www.rsc.org/

degrees of success. Reaction of BrH₂B·SMe₂with diphars afforded the boronium salt [H₂B(κ²-P,P

′

-diphars)]Br (16), which

-triphos)]Br

featured two pendant arsine arms. Similarly, triphos was found to react with BrH₂B·SMe₂to give [H₂B(κ²-P,P

′

(17), which featured a pendant phosphine arm. Substitution of the bromide counter anion with either hexafluoroarsenate

or hexfluoroantimonate anions revealed weak hydrogen bonds between the P–H bonds of the boronium cations and the

anions, that appeared through NMR studies to be retained in solution (where hydrogen bonding order was determined to

be Br^–> [SbF₆]^–/[AsF₆]^–). This was further demonstrated by comparison of solid-state structures and solution NMR data of

1

with [H₂B(PHCy₂)₂][SbF₆] (18),

4

with [H₂B(PMe₂Ph)₂][AsF₆] (19) and 17 with [H₂B(triphos)][AsF₆] (20).

Bertrand et al. of a bis(N-heterocyclic carbene)boronium salt

(Scheme 1).⁶

Introduction

Effective catalytic processes for the formation of main group

element bonds is an important objective for the development

of main group chemistry. Progress in this field enables new

discoveries and applications to be revealed in areas in which

main group elements are already finding success, such as high

performance polymers and frustrated Lewis pairs.^1,2Boronium

cations, where a boron centre bears two σ-bound substituents

and two datively (polar covalent) bound substituents

supporting boron bearing a formal positive charge, were first

suggested by Parry and co-workers.^3,4Interest in stabilising

boronium species has been consistent, however, a large

proportion of these endeavors have involved nitrogen based

substituents.⁵A notable exception is the recent isolation by

Scheme 1: Synthesis of a bis(N-heterocyclic carbene)boronium salt (Dipp = 2,6-

diisopropylphenyl).⁶

A number of bis(phosphine)boronium salts of the form

[H₂B(PR₃)]X have been described previously,⁷albeit

sporadically, with the most extensive studies being provided

by Schmidbaur.⁸Nevertheless, remarkably few structural data

are

available

(Table

1),

whilst

those

for

monohalobis(phosphine) boronium salts^7b,hare limited to

those for the heterocyclic salts [C₂H₂(PPh₂)₂BHBr]Br and

[C₆H₄(PPh₂)₂BHBr]Br.^8gData for secondary phosphine ligated

boronium salts are especially rare, being limited to

[H₂B(PH^tBu₂)₂]X (X = B{C₆H₃(CF₃)₂-3,5}₄, OTf, Br).⁷ⁱWith the

^a.Research School of Chemistry, The Australian National University, Canberra, ACT

2601, Australia. Email: a.hill@anu.edu.au

†

Electronic Supplementary Information (ESI) available: CIF data giving

crystallographic information for (943296), (943297), (943298), (943299),

(943301), (943300), 11 (1058392), 12 (1058398), 13 (943304), 15 (1058396), 16

1

2

3

4

7

8

(943306), 17 (943302), 18 (943305), 19 (1530816), 20 (1058403), (Br₂HB)₂·dcpe

(943353), [H₂B(dppf)][FeBr₄] (1058393), [H₂B(triphos{=O_0.6})][AsF₆] (1530818) and

[H₂B(triphos{=O})][AsF₆] (1530819). See DOI: 10.1039/x0xx00000x

exception

of

Scheer’s

BPBPB

catenated

salt

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[H₂B(PH₂BH₂NMe₃)₂]X (X = I, VCl₄(THF)₂)⁹which might be

Dalton Transactions

Monitoring the formation of

1

by ¹¹B NMR spectroscopy

described as two primary phosphines coordinated to a cationic revealed first the consumption of the BrH₂B·SMe₂starting

BH₂unit, conventional primary phosphine adducts have yet to material ( _B–12.0) to form the adduct Cy₂HPBH₂Br ( _B–27.9),

δ

be structurally characterised. Boronium salts ligated by followed by its conversion to [H₂B(PCy₂H)₂]Br (δ_B–45.2,

secondary or primary phosphines are however of current Scheme 2). The boronium salt was found to be the favored

interest in the context of dehydrocoupling en route to product, even when a 1:1 stoichiometry of reagents was

phosphine-borane oligomers.^7i,j

With an ever-increasing number of phosphines becoming boronium salt

employed, with the reaction proceeding completely to the

within 10 minutes at ambient temperature.

1

available, offering variations in both steric and electronic The ¹¹B NMR data illustrated the shift to lower frequency as

properties,¹¹the pursuit of diverse phosphorus-based phosphine sequentially replaced first the thioether and then,

boronium species appeared worthwhile. We report herein, the more slowly, the halide to provide finally the boronium salt.

reactions of haloborane thioether adducts with a range of Isolated neutral Cy₂HP^.BH₂Br (with recurrent but minor

primary, secondary and tertiary, mono and polydentate boronium salt contamination) was also found to decompose

phosphines that display differing electronic and steric features completely in solution to the boronium salt, [H₂B(PHCy₂)₂]Br,

in addition to different propensities towards chelation.

over a period of 10 minutes at 0°C.

Table 1. Selected Structural Data for Dihydrobis(phosphine) Boronium Salts [H₂BL₂]X.

L =

X

P–B(L¹)

P–B(L²)

Å

P–B–P

Å

deg.

a,7e

PEt₃

B(O₂C₆H₄)₂1.903(6)

1.913(6)

1.910(6)

1.896(6)

1.948(3)

1.930(3)

1.97(2)

1.934(5)

1.933(3)

1.938(2)

119.9(3)

118.4(3)

108.2(2)

111.4(2)

123.2(6)

118.9(2)

118.7(2)

118.8(1)

Scheme 2: Synthesis of [H₂B(PHCy₂)₂]Br (

PHCy₂.

1) via reaction of BrH₂B·PHCy₂and

9

PH₂BH₂NMe₃

I

1.948(3)

The simple borane adducts BrH₂B·PMe_xH_3–x(x = 1-3) and

their corresponding bis(phosphine) boronium cations

[H₂B(PMe_xH_3–x)₂]⁺were computationally interrogated (DFT:

M06-LACVP) leading to generally unremarkable but reassuring

conclusions. Methyl substituents were chosen for

computational economy and to obviate steric factors, which

nevertheless were later found to play a substantive role. The

similarity of both the topologies and energies of the frontier

orbitals for the borane adducts BrH₂B·PH_xMe_3–x(x = 0, 1,2;

Figure 1) is noteworthy and only those for the primary

phosphine adduct are depicted and discussed in detail.

VCl₄(THF)₂1.945(3)

PPh₂Fe(CO)₂(Cp)¹⁰

FeCl₄

Br

1.97(1)

7i

PH^tBu₂

1.948(4)

1.937(3)

1.940(2)

PH^tBu_2a

BAr^F

a, 7i

4

7i

PH^tBu₂

OTf

Heterocycles L₂=

a,7h

1,8-C₁₀H₆(PPh₂)₂

BAr^F

1.907(2)

1.924(4)

1.924(3)

1.941(5)

1.913(2)

1.918(4)

1.924(3)

1.939(5)

1.968(4)

104.14(7)

116.2(2)

106.0(1)

97.9(2)

4

8e

PMe₂PMe₂

Br

–

[MeC(CHPPh₂)₂]^{– 8f}

8g

1,2-C₆H₄(PPh₂)₂

Br

1,2-C₂H₄(PMe^tBu)₂

B(O₂C₆H₄)₂1.936(5)

98.5(2)

7f

^aTwo crystallographically independent molecules; ^bBAr^F₄=[B{C₆H₃(CF₃)₂-3,5}₄]^–.

Results and Discussion

The previously reported boronium cations with secondary

phosphines, [H₂B(PHR₂)₂]Br (R

generated in good yields by direct reaction of two equivalents

of PHR₂with BrH₂B SMe₂in pentane, so as to facilitate clean

= Cy, 1; Ph, 2

),^7i,jwere

⋅

precipitation upon formation of the product. The boronium

salt synthesised by reaction of two equivalents of

cyclohexylphosphine, [H₂B(PH₂Cy)₂]Br (3), was also obtained

by this method.^7jHowever, despite the clean formation of

3,

the analogous species [H₂B(PH₂R)₂]Br (R = Ph, Mesityl) could

not be readily isolated in a straightforward manner.

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Figure 1: Optimised Geometries and Frontier Orbitals of Interest for (Me_xH_3–

_xP)BH₂Br. Electrostatic ionisation potential surface, HOMO-3, HOMO and LUMO

depicted for x = 1.

The LUMO is diffused over the entire molecule, comprising

some P–C

concentrated in the region opposite to the borohydride

substituents. The LUMO+1, of -symmetry in this region has

considerable P–H -antibonding character, consistent with,

σ-antibonding character but predominantly,

π

The HOMO, HOMO–1 and HOMO–2 are essentially

bromine lone pairs, with HOMO–3 in each case comprising the

σ

e.g., the P–deprotonation of [H₂B(PH₂Cy)₂]⁺reported by Weller

and Manners.^7i,jThus reactivity towards both nucleophiles S_N2

to LUMO) and deprotonation of phosphorus but not boron

(LUMO+1) may be anticipated. Given the majority of boronium

salts prepared in this study involved more sterically

cumbersome phosphines than PMe₃, the comparatively low

reactivity towards nucleophiles might be rationalised in terms

of steric shielding of this otherwise reactive site. For the

secondary phosphine boronium salt, the charges (Mulliken,

electrostatic or natural) associated with both P and B-bound

hydrogens was remarkably close to neutral, with the C–H

bonds being considerably more polarised. These observations

taken together with the comparatively large HOMO-LUMO

gaps (ca 9.3 eV ) suggest that these salts will be chemically

robust.

In both the (Me_xH_3–xP)BH₂Br and [H₂B(PMe_xH_3–x)₂] ⁺series,

the localisation of HOMO–n (n = 0, 1, 2) around the BH₂unit

indicates the retention of ‘hydridic’ character for the B–H

bonds, which is to some extent ameliorated by the positive

charge in the boronium series, such that for all compounds the

electrostatic charges on the boron hydrides span the narrow

range –0.032 to +0.079 (Table 2).

primary component of the P→B polar-covalent (dative) bond

with modest p -p Br–B conjugation. The energy of this orbital

π

is effectively invariant across the series. The LUMO is spread

π

over much of the molecule, however the regions of interest

relate to

σ-B–Br antibonding, opposite the major lobe,

consistent with Walden inversion for S_N2 reactions in which

nucleophiles displace the bromide. This orbital and the

LUMO+1 also have considerable P–H antibonding character,

consistent with deprotonation in reactions with (non-

nucleophilic) bases. Relative to their constituents PMe₃,

PHMe₂and BH₂Br, gas phase thermodynamic data associated

with the formation of adducts Me₃PBH₂Br (

¹) and BrH₂B·PHMe₂H = –105.1 kJmol^–1) suggest that the

tertiary trialkylphosphine forms stronger interaction

ꢀ

H = –131.3 kJmol^–

(

ꢀ

a

consistent with the increased basicity of tertiary phosphine

versus secondary phosphines (e.g., Tolman electronic

parameters for PPh₃and PHPh₂are 2068.9 and 2073.3).¹¹

The frontier orbitals of all three boronium salts

[H₂B(PMe_xH_3–x)₂]⁺comprise a closely spaced HOMO/HOMO–

1/HOMO–2 set that is almost entirely associated with the

P₂BH₂unit σ-bonding and well-separated from the LUMO by ca

9 eV. For all three the similarity of the topology and energies

of the frontier orbitals, as discussed above for the borane

adducts, was again observed (Figure 2) such that only those for

the simplest [H₂B(PH₂Me)₂]⁺cation need be discussed.

Table 2. Calculated Electrostatic(Natural) Charges for Key atoms in (Me_xH_3–xP)BH₂Br

and [H₂B(PMe_xH_3–xP)₂]⁺.

X =

3

2

1

[H₂B(PMe_xH_3–xP)₂]⁺

P

+0.961(+1.278) +0.785(+0.953) +0.476(+0.646)

–0.628(–0.725) –0.662(–0.689) –0.510(–0.655)

+0.048(+0.065) +0.079(+0.043) +0.070(+0.065)

B

(B)H

(P)H

–––

+0.028(+0.085) +0.069(+0.100)

(Me_xH_3–xP)₂BH₂Br

P

+0.839(+1.259) +0.616(+0.930) +0.406(+0.617)

–0.194(–0.449) –0.203(–0.421) –0.179(–0.398)

–0.294(–0.248) –0.272(–0.246) –0.264(-0.233)

–0.032(+0.009) –0.023(+0.008) –0.030(+0.008)

B

Br

(B)H

(P)H

–

+0.023(+0.060)^ap+0.042(+0.067)^sc

+0.056(+0.080)^ap

^sc= Synclinal to Br. ^ap= antiperiplananar to Br

Whilst the formation of [H₂B(PHCy₂)₂]Br readily occurred,

the reaction of BrH₂B·SMe₂with two equivalents of PCy₃failed

to produce the boronium salt [H₂B(PCy₃)₂]Br, being consistent

with previous observations of the inability to isolate

[H₂B(PPh₃)₂]Br by reaction of BrH₂B·SMe₂with two equivalents

Figure

2: Optimised Geometries and Frontier Orbitals of Interest for

[H₂B(PMe_xH_3–xP)₂]⁺. Electrostatic ionisation potential surface and HOMO–2 to

LUMO+1 depicted for x = 1.

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of PPh₃.^8cIn these cases, the reaction only proceeded as far as completely disproportionate during work-up to the two

the corresponding phosphine-stabilised mixed haloborane respective symmetrical boronium salts, [H₂B(PHCy₂)₂]Br and

species R₃PBH₂Br (R = Ph, Cy). In steric terms, the tertiary [H₂B(PHPh₂)₂]Br, eliminating it as a viable target for further

phosphine PMe₂Ph was found to be the limit so far as studies.

accessing a (non-chelated) bis(phosphonio) ligated boronium

The modification of acyclic secondary phosphine boronium

species, whereupon reaction of two equivalents of PMe₂Ph salts often resulted in the liberation of free secondary

and BrH₂B·SMe₂cleanly yielded the associated boronium salt phosphine. Presuming chelation might confer some degree of

[H₂B(PMe₂Ph)₂]Br (

As previously discussed (vide supra),

reaction of BrH₂B·SMe₂and PHCy₂regardless of stoichiometry. bis(diphenylphosphino)ethane) reported previously by

However, the intermediate formation

of Schmidbaur.⁸The new cyclic boronium salt [H₂B(dcpe)][BHBr₃]

mono(phosphine)bromoboranes raised the question of ) readily formed upon reaction of BrH₂B·SMe₂and dcpe (1,2-

4

)^†in 85% yield.

kinetic stabilisation, a series of cyclic boronium salts were

1

is formed by investigated, cf. [H₂B(dppe)]Br dppe 1,2-

(

7

;

=

(

8

sequentially introducing two different phosphines to obtain bis(dicyclohexylphosphino)ethane) in 71% yield (based on

heteroleptic examples. Several combinations of the dcpe). The product was unusually isolated as the [BHBr₃]^–salt

bromoborane adducts and extraneous phosphines were rather than the simple bromide. The tribromoborate anion

explored (Table 3).

presumably arises from the reaction of the liberated bromide

with a second equivalent of haloborane, which would need to

be Br₂HB·SMe₂, itself most likely generated from

disproportionation of the BrH₂B·SMe₂.^¥Whilst the [BHBr₃]^–

anion might appear simple, it has only been encountered on

two previous instances from reactions of polyboronate salts

Combination

BrH₂B·PR₃

PR₃

A

B

C

D

E

BrH₂B·PPh₃

BrH₂B·PCy₃

BrH₂B·PHCy₂

PHCy₂

PHPh₂

PH₂Cy

PHPh₂

n

[NR₄][B_xH_y] (R = Me, Bu; x/y = 1/4, 3/8, 4/9, 9/14) with BBr₃

and characterised on the basis of its ¹¹B NMR data (δ_B–13.1,

8 therefore provides the first

¹J_BH= 175 Hz) alone.¹²The salt

Table 3: Combinations of phosphine-stabilised monobromoboranes and

phosphines investigated en route to unsymmetrical boronium salts.

structural data for this anion, which adopts a near tetrahedral

geometry (Br–B–Br angles in the conventional range 107.6 to

110.6°) that is surprisingly devoid of any significant distortions

arising from the disparity in the size of the Br vs H substituents.

The BPCCP heterocycle is slightly non-planar, i.e. chiral (space

Notably, in all cases (combinations

substituted boronium salts were preferentially formed. For

highly nucleophilic phosphines (Combination and ), this

A-E), the symmetrically

D

E

might be accounted for by the rate of the second substitution

being too rapid to allow sequential introduction. However,

initial formation of the stable, albeit sterically congested

tertiary phosphine adducts, R₃PBH₂Br (R = Ph, Cy), followed by

addition of a primary or secondary phosphine (combinations

group P2₁/n, δ/λ enantiomers generated by crystallographic

symmetry), with a slightly contracted P1–B1–P2 angle of

101.2(2)° reflecting the constraints of chelation.

The permethylated analogue, [H₂B(dmpe)]Br (9) (dmpe =

1,2-bis(dimethylphosphino)ethane), was also readily prepared

by reaction of BrH₂B·SMe₂with dmpe in 73% yield. However,

unlike the dppe and dcpe analogues, the dmpe boronium salt

was found to be insoluble in most common solvents. Partial

solubility in d₆-DMSO or D₂O allowed limited spectroscopic

data to be acquired (¹H, ¹¹B and ³¹P but not ¹³C NMR data),

however, neither proved suitable for growing crystallographic

grade crystals. The monomeric rather than polymeric nature of

the salt was nevertheless confirmed conclusively by

microanalysis, +ve ion ESI mass spectroscopy and NMR

spectroscopy. The satisfactory elemental microanalytical data

confirmed the presence of a single equivalent of BH₂Br to the

dmpe, whilst the single peak in the ESI-MS (m/z 163.1)

matched precisely the isotopic array of the desired product.

The ¹¹B NMR peak (δ_B-34.5) appeared in a similar region to

that observed for [H₂B(dppe)]Br (δ_B–35.7) by Schmidbaur and

coworkers,⁹indicating that the chemical shift is somewhat

insensitive to the disparate donor abilities of the two

diphosphines.

A-C) still led to the isolation of the symmetrical primary or

secondary phosphine boronium salt and half an equivalent of

tertiary phosphine adduct.

By cooling the reaction of combination

amount of the unsymmetrical

[H₂B(PHCy₂)(PH₂Cy)]Br (

D

to –78°C, a small

boronium

salt

5

) was observed by NMR analysis.

Specifically, the ³¹P{¹H} NMR spectrum included a broadened

2

AB system (δ_P–41.6, 0.4, J_AB72.5 Hz; cf. δ_P–38.6 for

[H₂B(PH₂Cy)₂]Br and δ_P–1.2 for [H₂B(PHCy₂)₂]Br). A resonance

was observed in the ¹¹B NMR spectrum (δ_B–45.1)^±which was

effectively unchanged compared to either of the two

symmetrical boronium salts (cf. δ_B–44.5 for [H₂B(PH₂Cy)₂]Br

and δ_B–45.2 for [H₂B(PHCy₂)₂]Br), i.e., given the half-height

widths of these resonances, the chemical shift is not usefully

diagnostic.

The product was, however, found to disproportionate fully

to its two respective symmetrical boronium salts,

[H₂B(PH₂Cy)₂]Br and [H₂B(PHCy₂)₂]Br, after a short period of

time (ca 30 min at room temperature), confounding isolation

An alternative order for the introduction of a boronium

centre was considered involving reactions of BrH₂B·SMe₂with

phosphine groups already bound to a metal centre, e.g., 1,1´-

bis(diphenylphosphino)ferrocene (dppf). The disubstituted BH₃

complex had been previously reported and was found to be air

for further study. The reaction of combination

produced the desired product, [H₂B(PHCy₂)(PHPh₂)]Br (

21.2, –3.2, ²J_AB261.5 Hz; cf.

_P–16.2 for [H₂B(PHPh₂)₂]Br and δ_P

E

at 0°C also

6

;

δ_P

–

δ

–1.2 for [H₂B(PHCy₂)₂]Br), but once again this was found to

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stable,¹³suggesting that the analogous use of BrH₂B·SMe₂

should proceed without issue. Formation of the desired dppf

boronium salt, [H₂B(dppf)]Br (10), seemed plausible given the

extensive chelate chemistry of this ligand with transition

metals, e.g., PdCl₂(dppf) and PtCl₂(dppf).¹⁴The possibility of a

direct interaction between the iron centre and the boron was

also considered given that Seyferth has described a dative

Figure 4: The geometry optimized structure of the ferrocenophane boronium

cation [H₂B(dppf)]⁺of 10 and the potential inversion of its geometry.

Compound 10 was found to be thermodynamically

unstable and decomposes as a solid back to dppf over 24

hours. Substitution of the bromide counterion for [AsF₆]^–(11

;

Figure 5) was found to provide a material that is stable under

an inert atmosphere. An unusual minor side-product of the

anion metathesis was found to be the salt [H₂B(dppf)][FeBr₄]

(Figure 5), arising from degradation of the dppf backbone

bond between iron and palladium in the complex FePd(

C₅H₄S)₂(PPh₃) (Figure 3).¹⁵

ꢁ-

which had not been observed during the initial synthesis of 10

.

The inclusion of lighter pnictogens was found to provide

the most effective heterodentate ligands, and interestingly,

chelated boronium cations based on a P,N donor set have yet

to be explored. The heterotopic ligand N,N-dimethyl-2-

(diphenylphosphino)aniline (amphos) presents both amine and

phosphine donors in a rigid geometry predisposed towards

chelation. The reaction of amphos with BrH₂B·SMe₂was found

Figure 3: The structure of Pd(PPh₃){(SC₅H₄)₂Fe} featuring an iron-palladium dative

bond.¹⁵

to readily proceed to the boronium salt [H₂B(amphos)]Br (12

)

in 93% yield. Despite the stronger -donation of the NMe₂

σ

group in comparison to a PPh₂group, the ¹¹B NMR resonance

observed (–9.3 ppm) was found to be to significantly higher

frequency than that of [H₂B(dppph)]Br (δ_B–32.9; dppph = 1,2-

bis(diphenylphosphino)benzene).^8gThe solid-state structure of

12 revealed that the BH₂substituent was displaced from the

P1–C1–C2–N1 plane by 0.49 Å, but interestingly the P–B bond

length of 1.947(2) Å was crystallographically indistinguishable

from both of those in [H₂B(dppph)]Br (cf. P–B = 1.939(5),

1.941(5) Å),^8gdespite the replacement of NMe₂by PPh₂.

The reaction of equimolar amounts of dppf with

BrH₂B·SMe₂was found to form simply the mono-substituted

species, BrH₂B·dppf, which was observed to display the

aforementioned characteristic phosphine-stabilised BH₂Br shift

of –24.1 ppm in the ¹¹B{¹H} NMR spectrum. However, when

the reaction mixture was heated to reflux in toluene for 18

hours, a pale orange precipitate was observed to form. The

pale orange precipitate had a single resonance at –27.4 ppm in

the ¹¹B{¹H} NMR spectrum, consistent with the desired

ferrocenophane boronium salt 10. The ³¹P{¹H} NMR spectrum

was found to contain only one resonance at 9.7 ppm, which

was discernibly shifted to higher frequency in comparison to

both the resonances for the mono-substituted dppf.BH₂Br (δ_P

–16.7, 1.8 for the free PPh₂and boron-coordinated PPh₂

groups, respectively). Unusually, the ¹H NMR spectrum was

very broad for all resonances, suggesting some form of

fluxionality. Geometry optimisation of the ferrocenophane

boronium salt indicates that the BH₂group lies above the

plane defined by the two P–C bonds between phosphorus and

ferrocene (Figure 4). Inversion of this geometry would account

for the broadness of the ¹H NMR spectrum, as has been shown

for the trithiaferrocenophane Fe{S₃(C₅H₄)₂}.¹⁶

Schmidbaur et al. have reported the use of Br₂HB·SMe₂to

synthesise boronium salts bearing a BHBr group by reaction

with two equivalents of PMe₃or PEt₃, via the same process of

bromide ionisation.⁸A BHBr group was seen as a more

versatile functionality than a BH₂substituent, offering the

possibility of nucleophilic substitution. Despite the reported

failure of dppe to react with Br₂HB·SMe₂to form

[BrHB(dppe)]Br, the analogous reaction of the far more basic

dcpe with Br₂HB·SMe₂was explored and found to provide the

desired BHBr boronium salt [BrHB(dcpe)]Br (13). The salt

eluded isolation in bulk purity due to the difficulties in

separating it from the acyclic adduct dcpe·(BHBr₂)₂by any

other method than manual crystal picking. The presence of

both 13 and dcpe·(BHBr₂)₂were, however, confirmed

spectroscopically and crystallographically (Figure 6).

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suggesting that the two species existed in equilibrium with one

another in DCM, and was supported by the consistency with

which the two products were always observed together

spectroscopically.

Figure 6: The molecular structure of [BrHB(dcpe)]Br (13). (Bromide and alkyl

hydrogen atoms omitted for clarity, cyclohexyl groups simplified, 50%

displacement ellipsoids). Selected bond lengths (Å) and angles (°): B1-Br1

2.013(4); B1-P1 1.955(4); B1-P2 1.960(4); Br1-B1-P1 121.8(2); Br1-B1-P2

114.8(2); P1-B1-P2 101.0(2).

The successful synthesis of 13 confirmed that strongly σ-

basic chelating phosphines would favour the formation of

B-bromo boronium salts and accordingly, basic monodentate

phosphines were next considered. In contrast to dcpe,

however, the reaction of Br₂HB·SMe₂with two equivalents of

PHCy₂was found to provide the phosphine-borane adduct

Br₂HB·PHCy₂(δ_B–18.7; δ_P0.6), but not the boronium salt

Figure

5: The molecular structure of [H₂B(dppf)][AsF₆] (11; above) and

[H₂B(dppf)][FeBr₄] (below). (Alkyl hydrogen atoms omitted for clarity, ferrocenyl, [BrHB(PHCy₂)₂]Br. A very minor second product was observed

in the ¹¹B{¹H} NMR spectrum at –45.2 ppm, attributable to

anions and phenyl groups simplified, 50% displacement ellipsoids). Selected

bond lengths (Å), angles (°) and intramolecular distances (Å) for 11: B1-P1

1.934(2); B1-P2 1.924(2); P1-C1 1.800(1); P2-C6 1.785(1); P1-B1-P2 117.92(9); [H₂B(PHCy₂)₂]Br (

B1-P1-C1 115.83(7); B1-P2-C6 111.47(8); Fe1-C1-P1 123.06(8); Fe1-C6-P2

123.75(8); Fe1…B1 3.766(2). Selected bond lengths (Å), angles and

1), arising from disproportionation of the

Br₂HB·SMe₂starting material to BrH₂B·SMe₂. Attempted

(°)

intramolecular distances (Å) for [H₂B(dppf)][FeBr₄]: B1-P1 1.923(3); B1-P2 isolation of Br₂HB·PHCy₂resulted in its decomposition to the

1.926(3); P1-C1 1.789(3); P2-C6 1.795(3); P1-B1-P2 112.6(2); B1-P1-C1 112.0(1);

phosphonium salt [PH₂Cy₂]Br, the cation of which had been

B1-P2-C6 112.7(1); Fe1-C1-P1 123.2(1); Fe1-C6-P2 123.7(1); Fe1…B1 3.729(3).

previously observed when the Cl₂HB·PHCy₂adduct similarly

decomposed to [PH₂Cy₂][HCl₂]. The bichloride anion, [HCl₂]^–,

When the reaction was carried out at room temperature in

was an unusual counter-ion and one that has relatively few

benzene, the two products were found to form in near equal

prior solid-state examples.²¹The geometric parameters of

amounts, as determined by ³¹P{¹H} NMR integration. The

[HCl₂]^–are, however, indistinguishable from those previously

boronium salt 13 was observed at δ_B–26.8 and δ_P–20.9, whilst

reported for other salts containing this anion and therefore

call for no further comment.

the adduct dcpe·(BHBr₂)₂was apparent at δ_B–17.6 and δ_P0.1,

along with some unreacted dcpe that was removed upon

work-up. The two products, though not separately isolated in

bulk quantities, were formulated based on solid-state crystal

structure determinations and the trends observed for

previously synthesised analogous compounds. Despite

The recovery of phosphonium salts from reactions of Lewis

bases with BrH₂B·SMe₂, Br₂HB·SMe₂or BBr₃was a recurrent

feature observed in this chemistry. Secondary phosphines

produced phosphonium salts upon reaction with Br₂HB·SMe₂,

whilst tertiary phosphines provided simple phosphine-

stabilised dibromoborane adducts. This dichotomy might

reflect steric or electronic control and accordingly, smaller but

bromine being

a potential hydrogen bond acceptor,

examination of the solid-state structure of 13 revealed no

obvious intermolecular interactions of note between the

boron-coordinated bromine and anything else, as might have

been expected due to the steric hindrance caused by the

surrounding cyclohexyl substituents. Interestingly, manually

picked crystals of dcpe·(BHBr₂)₂, the identity of which was

confirmed crystallographically, were found upon dissolution to

provide equimolar amounts of 13 also present in the ¹¹B and

³¹P NMR spectra. This observation did not change over time,

strongly

σ

-basic tertiary phosphines were next investigated

had been previously isolated. The reaction of two

given that

4

equivalents of PMe₂Ph with Br₂HB·SMe₂in pentane was found

to proceed to the desired bromoboronium salt

[BrHB(PMe₂Ph)₂]Br (14; δ_B–21.5, δ_P–7.5). The crude product

was found to form an oil of reasonable purity, though

attempts at further purification led to extensive

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decomposition. Electrospray MS (+ve ion) analysis further

corroborated the identity of the product with an appropriate

isotopic envelope at m/z = 367.1 and 369.1, confirming

bromine inclusion in the cation. Conducting the reaction in

dichloromethane was found to proceed only partially to

[BrHB(PMe₂Ph)₂]Br, with the majority of the crude reaction

mixture comprising the adduct Br₂HB·PMe₂Ph (δ_B–15.6, δ_P

–

12.1). It would therefore seem that the formation of the

boronium salt in pentane is driven by its precipitation, whilst in

solution it readily reverts to the neutral adduct. Conducting

the reaction in benzene (another solvent from which salt

precipitation might be expected to occur) failed to generate

appreciable amounts of the boronium salt, whilst heating

(75°C, 3 hours) resulted in eventual formation of the

phosphonium salt [PHMe₂Ph]Br which precipitated from the

benzene solution upon formation.

The rigid phenylene backbone coupled with the strong

basicity of the NMe₂group in Me₂NC₆H₄PPh₂-2 (amphos) made

it promising candidate for the formation of

σ-

Figure 8: The molecular packing of two enantiomeric [BrHB(amphos)]⁺cations of

15. Selected intermolecular distances (Å): Br1-H311ⁱ3.4827; Br1-H312ⁱ3.0870;

Br1-H313ⁱ3.2283.

a

monobromoboronium salts. The reaction between Br₂HB·SMe₂

and amphos proceeded cleanly to the desired boronium

product [BrHB(amphos)]Br (15; Figure 7). An NMR analysis of

The crystallographic packing of rac-[BrHB(amphos)]Br was

of interest as it clearly displayed a dimer type arrangement

bridged by trifurcated C–H^…Br hydrogen bonding between

N-CH₃and Br groups on adjacent enantiomeric cations (Figure

8). The chiral H,Br,P,N donor set of the boronium cation is

without precedent in the literature. Compound 15 also has

features that differ from its diphosphine counterparts. The

higher frequency ¹¹B NMR peak indicates a more deshielded

boron environment, which might be reflected in enhanced

reactivity, coupled with far less steric protection provided by

the much smaller methyl groups of the amine.

the product revealed resonances at δ_B–5.2 and δ_P–11.0, along

with inequivalent resonances for the diastereotopic methyl

groups of the tertiary amine (δ_H3.24, 3.77) adjacent to the

chiral boron centre.

The approach of using heterotopic chelates to selectively

bind boron-based groups, whilst leaving other donor groups

free for further synthesis, was seen as a viable method in the

context of boronium salt formation bearing additional pendant

donor groups. The potentially tetradentate ligand, meso-1,2-

bis(phenyl(diphenylarsinoethyl)phosphino)ethane

(diphars,

Scheme 3), was chosen for investigation so as to explore this

possibility. Arsine ligated boronium salts are exceedingly rare,

with the first example [Cl₂B{C₆H₄(AsMe₂)₂-1,2}]BCl₄having

been only very recently reported by Reid¹⁸who observed that

it was considerably more labile than the corresponding

diphosphine analogue. Thus it may be surmised that polar-

covalent bonding between boron and the pnictogens becomes

increasingly ineffective upon descending group 15 (stibine or

bismuthine ligated boronium salts remain unknown). We

therefore anticipated regioselective coordination of boron to

the phosphine donors which is indeed what transpired. The

Figure 7: The molecular structure of one enantiomer of [BrHB(amphos)]Br (15).

(Alternative enantiomer generated by crystallographic P2₁/a symmetry; bromide,

solvate molecules and alkyl hydrogen atoms omitted for clarity, phenyl rings

simplified, 50% displacement ellipsoids). Selected bond lengths (Å) and angles

(°): B1-Br1 1.980(4); B1-N1 1.621(3); B1-P1 1.947(2); Br1-B1-N1 113.4(2);

Br1-B1-P1 116.6(2); N1-B1-P1 101.1(1).

The solid-state structure revealed that the boron atom of

[BrHB(amphos)]Br is displaced from the P1–C1–C2–N1 plane

more significantly (37.3°) than was found for [H₂B(amphos)]Br

(25.8 ), due to replacement of a hydrogen atom with the

reaction of BrH₂B⋅SMe₂with meso-diphars proceeded cleanly

°

to the desired boronium salt 16 over a period of 18 hours

(benzene, ambient temperature), in contrast to the formation

of [H₂B(dppe)]Br, which was complete in under an hour

(Scheme 3).

sterically more demanding bromine substituent, which

assumes a pseudo-equatorial position with respect to the

C₂NPB heterocycle. The centrosymmetric P2₁/a space group

adopted by rac-[BrHB(amphos)]Br accommodates both

enantiomers (Figure 8).

The diphars was found to retain its stereochemistry in the

product, which meant that the compound was still achiral and

in a meso form. The meso arrangement of the product was

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confirmed crystallographically, but disorder in the structural such as C–H^…H–B is typically rather weak compared to more

model illustrated that although the molecular ion comprised conventional hydrogen bond donors N–H and O–H.

two symmetry generated halves, the central five-membered

boronium ring was found to be oriented evenly over two

Scheme 3: Synthesis of meso-[H₂B(κ²-P,P

BrH₂B·SMe₂and meso-diphars.

′-diphars)]Br (16) through reaction of

possible orientations (Figure 9). However, both orientations

possessed a meso arrangement of the two phosphorus

stereocentres. The possibility that 16 might provide a suitable

geometry to allow the interaction of the boronium unit with a

metal centre upon coordination of the pendant arsines was

briefly explored but with little success. The reactions of 16

with either [Mo(η⁶-C₇H₈)(CO)₃] or [RhCl(PPh₃)₃] afforded highly

insoluble materials that were not amenable to spectroscopic

interrogation other than the observation (+ve ion ESI-MS) of

molecular ions corresponding to [Mo(CO)₄(16)]⁺and

[Rh(PPh₃)₂(16)]⁺, respectively.

Figure 10

hydrocarbon hydrogen atoms omitted for clarity, aryl groups simplified, 50%

displacement ellipsoids). Selected bond lengths (Å) and angles ): B1-P2

1.921(4); B1-P3 1.932(4); P1-C1 1.852(4); P2-C2 1.825(3); P3-C3 1.816(3);

P2-B1-P3 111.2(2); B1-P2-C2 109.5(2); B1-P3-C3 108.9(2); P2-C2-C4 118.2(2);

P3-C3-C4 117.6(2); C2-C4-C3 111.2(3).

: The molecular structure of [H₂B(triphos)]Br (17; Bromide and

(

°

A caveat encountered in the synthesis of 17 was that the

pendant phosphine arm was found on occasion to react with

excess BrH₂B·SMe₂to form a bromoborane adduct (δ_B–23.8,

δ_P–4.8) in conjunction to the boronium salt, which had almost

identical behaviour towards various solvents as 17, making its

separation problematic such that particular care must be taken

with the stoichiometry of reagents during preparation.

Figure 9: The molecular structure of the [H₂B(κ²-P,P -diphars)]⁺cation in the salt

′

16 showing one of two positionally disordered orientations of the boracycle.

(Bromide anions and hydrocarbon hydrogen atoms omitted for clarity, aryl

groups simplified). Selected bond lengths (Å) and angles (°

): B1-P1 1.98(2); B1-P1ⁱ

Figure 11: The centrosymmetric molecular packing of two [H₂B(triphos)]⁺cations

of 17 illustrating the rhombic dihydrogen bonding. (Bromide anions, selected

phenyl rings and alkyl hydrogen atoms omitted for clarity). Selected intra- and

intermolecular hydrogen bonds (Å): B1–H2^…H521 2.4781(1); B1–H2^…H521i

2.3783(1).

1.87(2); As1-C4 1.991(6); P1-B1-P1ⁱ98(1); B1-P1-C1 97.9(8); B1-P1ⁱ-C2 108.4(7).

To explore further the possibility of using pendant donors

to anchor boronium units proximal to metal more complicated

species were considered. The reaction of BrH₂B⋅SMe₂with

Discussion of Structural Features for Boronium Salts

triphos (MeC(CH₂PPh₂)₃) afforded a boronium species within a

six-membered heterocycle, to which was appended a pendant

phosphine arm (Figure 10). The solid-state structure revealed a

dimeric assembly for the packing of the [H₂B(triphos)]⁺cations

via a rhomboid arrangement of two short and two long

dihydrogen bonds between inversely polarised C–H(δ⁺) and

B-H(δ^–) bonds, respectively (Figure 11).¹⁹Dihydrogen bonding

Complexes

potential umpolung of the B

contacts in their solid-state structures, with

1

-

3

were structurally characterised so as to study

H bond polarity via short

being the only

−

3

solid-state example of a boronium salt with two primary

phosphine substituents. The molecular structures of some of

the isolated boronium salts reveal short contacts between the

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cationic molecules and the counter-anions that are less than the boronium salts change markedly when the bromide anion

the van der Waals radii of the respective elements. The is exchanged for a poorly coordinating counter-ion. The

boronium salts of primary and secondary phosphines interact retention of P–H^…Br hydrogen bonding would be expected to

with the bromide via P–H^…Br hydrogen bonding, e.g., the P– result in a higher frequency shift of the ¹H NMR P–H

H^…Br distances in [H₂B(PH₂Cy)₂]Br range from 2.84 – 3.16 Å, resonance, concomitant with a corresponding shift in the

with all four of the P–H hydrogen atoms in each molecule frequency of the ³¹P NMR resonance, when compared to the

oriented so as to interact with the bromide counter-ion, along shifts observed for a weakly coordinating counter-anion. The

with two additional P–H hydrogen atoms from neighbouring bromide counter-ion of 1 was exchanged for the essentially

non-coordinating counter-ion [SbF₆]^–by metathesis with

molecules (Figure 12).

Ag[SbF₆] to give the new salt [H₂B(PHCy₂)₂][SbF₆] (18). Notably,

1

the H and ³¹P NMR signals for the unchanged [H₂B(PHCy₂)₂]⁺

cation were significantly altered by the simple exchange of the

anion present. The ¹H NMR P–H peak for

1 was observed at

6.04 ppm, whilst for [H₂B(PHCy₂)₂][SbF₆] it was observed at

4.89 ppm suggesting a persistent interaction with the bromide

counter-ion. Similarly, the ³¹P NMR peak at –1.2 ppm for

1 and

–3.3 ppm for 18 also point toward a degree of ion-pairing with

the bromide counter-ion in this solvent (CDCl₃). The solid-state

structure of 18 was found to possess the same coordination of

the anion by the two PH groups as observed for

1, which

indicated that the [H₂B(PHCy₂)₂]⁺cation was still able to

coordinate to the larger [SbF₆]^–anion in the solid state,

however, any such interaction in solution, were it to persist,

must be dynamic since there was no indication of enduring

coupling between the ³¹P–¹H and ¹⁹F nuclei.

The salt 18 was found to be less stable than its bromide

Figure 12: The molecular packing of three [H₂B(PH₂Cy)₂]⁺cations of

3 around a

counter-ion analogue

1

and decomposed in the solid-state

showed

bromide anion showing the coordination sphere around the counterion. (Alkyl

hydrogen atoms omitted for clarity, 50% displacement ellipsoids). Selected

intermolecular hydrogen bonds (Å): P1–H11^…Br1 3.0081(2); P1–H12^…Br1

3.1550(2); P1ⁱ–H12^i…Br1 2.8418(1).

over the comparatively short period of a week (cf.

1

no appreciable decomposition in anaerobic solution after

several weeks). The ³¹P and ¹¹B NMR spectra of the resulting

decomposition mixture did not reveal any resonances that

might suggest P–F or B–F bond formation, i.e., fluoride

abstraction does not appear to have ensued. Similarly,

The solid-state structure of

1 is similar to that for 3, in that

the constituents orient so that the bromide interacts with both

P–H hydrogen atoms (P–H^…Br 2.9473(2), 3.8060(2) Å), as well

as a methine proton (C–H^…Br 2.7741(2) Å) and one methylene

proton (C–H^…Br 3.0103(3) Å) from the same molecule (forming

a four atom cradle as before). Whilst no single hydrogen

bonding interaction is particularly short, the collective

ensemble accounts for the well-ordered bromide position

within the solid-state structure.

[H₂B(PMe₂Ph)₂][AsF₆] (19) was prepared by metathesis of

4

with K[AsF₆] which was used in preference to Ag[SbF₆] due to

the observed decomposition of some boronium salts when

treated with Ag[SbF₆]. It was found that the reaction did not

always proceed as expected with Ag[SbF₆], and that

sometimes what was believed to be a silver phosphine species

(δ_P42.2) was the major product recovered. This decomposition

The crystal packing around the bromide counter-ion was

of the boronium cation was not observed when K[AsF₆] was

used instead, and it therefore became the preferred reagent

for anion metathesis. Although silver salts are powerful halide

sequestering agents, the attendant caveat is that they are also

prone to single electron redox processes (to form silver metal)

such that their use in the presence of B(δ⁺)–H(δ^–) bonds, i.e.,

classical reductants, is likely to be problematic on occasion.

less complex for

2

and the tertiary phosphine boronium salt

4

in comparison to those discussed above. For

2, the two P–H

protons align so as to provide effectively equidistant hydrogen

bonds of 2.8681(2) and 2.9243(2) Å, but otherwise the anion

was largely enveloped within a pocket faced by phenyl ring

protons with distances of 3.10-3.77 Å. For 4, the molecule was

found to coordinate to the bromide via hydrogen bonding

from the methyl and ortho-phenyl protons with distances of

2.9023(7) Å and 2.9531(5) Å, respectively. Whether these

solid-state interactions persist whilst in solution will be

discussed later (vide infra), though depending on the solvent, a

degree of ion-pairing might be expected.

The tertiary phosphine boronium salts

to present the same trend of anion coordination as previously

discussed for salts and 18. However, the hydrogen bonding

observed in the solid state for was understandably found to

be less pronounced than for the secondary phosphine

analogue, directly due to the lack of P–H bonds. The ¹H and ³¹

NMR peaks for were δ_H2.00 (methyl groups) and δ_P–3.5,

4 and 19 were found

1

4

P

These intermolecular interactions presumably contribute in

part to the stability found for the boronium salts in the solid

state. The intermolecular P–H^…Br interactions, however, do

not appear to be limited to the solid-state, but may also be

4

whilst for 19 they were found to be δ_H1.68 and δ_P–3.6.

Therefore, the difference in the NMR resonances caused by

changing the counter-ion was less pronounced in comparison

inferred to persist in solution. Both H and ³¹P NMR data for

1

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to the [H₂B(PHCy₂)₂]⁺salts, but still followed the same pattern

General Considerations. All manipulations were carried

of the resonances shifting to lower frequency as Br^–was out under a dry and oxygen-free nitrogen atmosphere using

exchanged for [AsF₆]^–.

standard Schlenk, vacuum-line, and inert-atmosphere drybox

The boronium salt [H₂B(triphos)][AsF₆]

(20

)

was also (argon) techniques, with dried and degassed solvents which

synthesised for comparison and structurally characterised. The were distilled from either calcium hydride (CH₂Cl₂), magnesium

solid-state structure of 20 was similarly (cf. 19) found to metal (alcohols) or sodium and benzophenone (ethers and

coordinate to the [AsF₆]^–anion via the methylene groups of paraffins). NMR spectra were obtained at 25

°C on an Inova

the [H₂B(triphos)]⁺cation, though in this case through all three 300 spectrometer (¹H at 299.94 MHz, ¹³C at 75.42 MHz, ¹¹B at

of the methylene groups, including the methylene of the 96.23 MHz, ¹⁹F at 282.23 MHz, ³¹P at 121.42 MHz), a Mercury

pendant phosphine arm. Short hydrogen bond interactions of 400

2.559(6) and 2.588(4) Å were observed for the boracycle

methylene protons and the pendant phosphine arm

methylene protons, respectively. Similar to the acyclic

boronium cations such as [H₂B(PHCy₂)₂]⁺, the effect of anion

substitution of the bromide by [AsF₆]^–was observed again in

solution. This was found with a shift to lower frequency for the

1

multiplets attributed to the methylene protons in the H NMR

spectrum for 20

(

δ_H2.67, 2.72-2.84) in comparison to 17

(δ_H

3.86). Interestingly, the solid-state

3.17 – 3.43, 3.68

–

conformation for 20 had the pendant phosphine arm in the

equatorial position, whilst for 17 this was observed in an axial

position which is less common for sterically demanding

substituents on a cyclohexane scaffold (Figure 13).

Conclusions

In conclusion, an extensive library of boronium salts has

been compiled and structurally characterised. The ease of

formation and high purity of boronium salts synthesised from

two equivalents of a secondary or primary phosphine and

BrH₂B·SMe₂made them ideal starting materials.

Unfortunately, these boronium salts were found to possess

low reactivity and were therefore deemed unsuitable for

further modification. This led to a second generation of

boronium salts that involved utilising the differing

σ-basicity

between phosphine and arsine groups to coordinate

selectively to the boron substituent via the phosphine, leaving

the arsine groups free for further synthesis; Or, alternatively

the use of the triphosphine species ‘triphos’ in reaction with

BrH₂B·SMe₂which was found to yield a boronium salt that also

possessed a pendant phosphine arm that could act as a tether

to metal centres.

Figure 13: The molecular structure of 17 (above) and 20 (below). (Solvate

molecules and aryl hydrogen atoms omitted for clarity, aryl groups simplified,

50% displacement ellipsoids). Selected bond lengths (Å) and angles (°) for 17:

B1-P2 1.921(4); B1-P3 1.932(4); P1-C1 1.852(4); P2-C2 1.825(3); P3-C3 1.816(3);

P2-B1-P3 111.2(2); B1-P2-C2 109.5(2); B1-P3-C3 108.9(2); P2-C2-C4 118.2(2);

P3-C3-C4 117.6(2); C2-C4-C3 111.2(3). Selected bond lengths (Å), angles (

:

°) and

intermolecular distances (Å) for 20 B1-P2 1.918(7); B1-P3 1.927(7); P1-C1

1.866(6); P2-C2 1.818(6); P3-C3 1.814(6); P2-B1-P3 110.7(3); B1-P2-C2 109.7(3);

B1-P3-C3 110.6(3); P2-C2-C4 118.5(4); P3-C3-C4 117.0(4); C2-C4-C3 111.1(4);

C1-H11…F6 2.588(4); C3-H32…F5 2.559(6).

The increased functionality introduced by synthesising

boronium salts bearing a bromine atom on the boron offered a

potential site at which subsequent manipulations could be

envisaged. However, the synthesis of such BHBr boronium

species from Br₂HB·SMe₂presented new difficulties as

compared to the straightforward synthesis of the BH₂

boronium species. As a result, only a small number of BHBr

spectrometer (¹H at 399.87 MHz, ¹³C at 100.56 MHz, ³¹P at 161.87

MHz), a Bruker 400 spectrometer (¹H at 400.14 MHz and ¹³C at

100.63 MHz, ¹¹B at 128.38 MHz, ³¹P at 161.97 MHz) and an Inova

500 spectrometer (¹H at 500.04 MHz, ¹³C at 125.75 MHz,). Chemical

shifts are quoted in ppm relative to external SiMe₄(¹H, ¹³C), H₃PO₄

boronium salts could be produced, and only one of them (15

)

( (

³¹P), BF₃.Et₂O (¹¹B) or C₆F₆¹⁹F) references with n-bond couplings

between nuclei A and B, ⁿJ_AB, being quoted in Hz. It should be noted

that due to the ³/₂spin of NMR active quadrupolar ¹¹B, the resulting

spectra are naturally broad and B–H coupling is often not resolved.

¹¹B–¹H coupled spectra are only reported if couplings were reliably

resolved. The B–H signals are also rarely observed in ¹H NMR

spectra, owing to the ¹¹B coupling that causes the peaks to be

especially broad, and as such are not reported here. Spectra of

could be adequately isolated and handled. Research into

further manipulation of the potentially useful B–Br functional

group is ongoing.

EXPERIMENTAL SECTION

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ARTICLE

NMR active ³¹P nuclei bonded to ¹¹B also experience quadrupolar

broadening of their signals, which can often cause imprecise

coupling values; in these cases, an average value is reported and

stated as such. Computational calculations were performed using

Spartan 14 at the MO6-LACVP level of theory. Elemental

microanalysis was performed by the microanalytical service of the

Australian National University and unless otherwise noted,

recrystallized samples were dried for a prolonged period in vacuo.

Electrospray (ESI) mass spectrometry was performed by the

Research School of Chemistry mass spectrometry service, and

unless otherwise stated, the accurate mass data are reported for

the most abundant isotopomer. For salts, [M]⁺and [M]^–refer to the

cationic and anionic component of the salt respectively. Typically, a

sample was dissolved in dichloromethane and then diluted with

methanol or acetonitrile immediately before being analysed. X-ray

crystallographic data were collected with a Nonius Kappa CCD

diffractometer, an Agilent Xcalibur CCD diffractometer or an Agilent

SuperNova CCD diffractometer. Data were extracted using the

Denzo (Nonius) or CrysAlis (Agilent) packages, with structure

solutions being solved by direct methods (SIR92, Superflip) using

the CRYSTALS program package. All reagents were used as received

from commercial sources. During our studies, the compounds 1, 2

and 3^7jwere reported without structural characterisation which is

now detailed here. The salt 7⁸has also been described previously,

however only limited spectroscopic data were provided (IR, 1H

NMR).

drop-wise to a stirred solution of diphenylphosphine (ρ = 1.07

gcm^–3, 0.17 mL, 1.0 mmol) in pentane (4 mL). Upon addition a

precipitate was formed instantly, but after 1 minute an orange

oil had aggregated at the bottom of the flask and the bulk

solution was colourless. The mixture was stirred for 1 h, and

then all volatiles were removed under high vacuum to leave a

pale orange solid. The solid was further dried under high

vacuum for 24 h. The solid was dissolved in DCM and layered

with pentane to give white powder, which was isolated by

cannula filtration. The solid was recrystallised from a mixture

of DCM/pentane to produce colourless X-ray diffraction quality

crystals. Yield 0.20 g (0.43 mmol, 87%). Partially melted at

around ca. 98°C, then remained unchanged up to 250°C.

Consistent elemental analytical data not obtained: Anal.

Found: C, 61.16; H, 4.95; N, 0.00%. Calcd. for C₂₄H₂₄BBrP₂: C,

61.98; H, 5.20; N, 0.00%. NMR (CD₂Cl₂, 25°C): ¹H: δ_H= 7.31-

7.39 (m, 8H, C₆H₅), 7.46-7.51 (m, 4H, C₆H₅), 7.64-7.71 (m, 8H,

1

C₆H₅), 8.95 (d, J_PH456.4 Hz, 2H, PH); ¹¹B{¹H}: δ_B= –37.6 (br);

2

1

¹¹B: δ_B= –38.1 (d.br, J_BH70 Hz); ¹³C{¹H}: δ_C= 122.22 [d, J_PC

60.8 Hz, C¹(C₆H₅)], 129.76 [m, C^2,6(C₆H₅)], 132.93 [C⁴(C₆H₅)],

133.52 [m, C^3,5(C₆H₅)]; ³¹P{¹H}:

δ

_P= –16.2 (d.br, ¹J_PB86 Hz). ³¹P:

1

δ_P= –16.2 (dm.br, J_PH376 Hz). Acc. Mass: Found: m/z =

385.1446 Calcd. for C₂₄H₂₄¹¹BP₂385.1446 [M]⁺. Crystal data:

C₂₄H₂₄BBrP₂, M_r= 465.12, T = 200(2) K, monoclinic, space

Synthesis of [H₂B(PHCy₂)₂]Br (1). A solution of BrH₂B·SMe₂

(1.0 M, 1.00 mL, 1.0 mmol) in dichloromethane was added

group P2₁/n, a = 8.3066(1), b = 18.0004(3), c = 15.1242(2) Å,

= 97.2060(9)

, V = 2243.54(6) Å³, Z = 4, D_calcd.= 1.377 Mg m^–3,

(Mo K 0.20 0.29 mm,

) 1.98 mm^-1, colourless block, 0.14

25261 measured reflections with θ_max55.0 5139

independent reflections, 5124 absorption-corrected data used

in F²refinement, 254 parameters, no restraints, R₁= 0.030,

β

°

drop-wise to a stirred solution of dicyclohexylphosphine (ρ =

ꢁ

α

×

0.98 gcm^–3, 0.40 mL, 2.0 mmol) in pentane (10 mL) at 0°C.

Approximately 5 minutes after addition a precipitate formed.

The mixture was stirred for 1 h at room temperature, and then

all volatiles were removed under high vacuum to leave a pale

orange solid. The solid was further dried under high vacuum

for 48 h. The solid was recrystallised from a mixture of

DCM/pentane to produce colourless X-ray diffraction quality

2

=

°,

wR₂= 0.077 for 4263 reflections with I > 2σ(I).

Synthesis of [H₂B(PH₂Cy)₂]Br (3). A solution of BrH₂B.SMe₂

(1.0 M, 0.50 mL, 0.5 mmol) in dichloromethane was added

drop-wise to a stirred solution of cyclohexylphosphine (

ρ =

0.88 gcm^-3, 0.13 mL, 1.0 mmol) in pentane (2 mL). The mixture

was stirred for 1 h, after which time an orange oil had

aggregated at the bottom of the flask and the bulk solution

was colourless. All volatiles were removed under high vacuum

to leave a pale orange solid. The solid was recrystallised from a

mixture of DCM/pentane to give a white powder. The solid

was then recrystallized by layering a concentrated DCM

solution of the solid with pentane overnight to produce

colourless X-ray diffraction quality crystals. Yield 0.07 g (0.20

crystals. Yield 0.37 g (0.76 mmol, 76%). M.p. 199-201°C. Anal.

Found: C, 58.63; H, 10.05; N, 0.00%. Calcd. for C₂₄H₄₈BBrP₂: C,

58.91; H, 9.89; N, 0.00%. NMR (CD₂Cl₂, 25°C): ¹H: δ_H= 1.25-

2.27 (m, 44H, C₆H₁₁), 5.78 (d, ¹J_PH407.3 Hz, 2H, PH); ¹¹B{¹H}: δ_B

1

= –45.2 (br); ¹¹B: δ_B= –45.2 (d.br, J_BH92 Hz); ¹³C{¹H}: δ_C

=

25.49 [C^2,6(C₆H₁₁)], 26.38 [m, C⁴(C₆H₁₁)], 28.26 [d, J_PC55.7 Hz,

1

C¹(C₆H₁₁)], 29.20 [d, J_PC40.5 Hz, C^3,5(C₆H₁₁)]; ³¹P{¹H}: δ_P= –0.4

1

(d.br, J_PB93 Hz); ³¹P: δ_P= –0.5 (dd.br, J_PH/¹J_PB399/93 Hz).

1

NMR (CDCl₃, 25°C): H: δ_H= 1.25-2.27 (m, 44H, C₆H₁₁), 6.04 (d,

¹J_PH408.1 Hz, 2H, PH); ³¹P{¹H}: δ_P= –1.2 (d.br, J_PB79.4 Hz).

1

mmol, 41%). Evolved a gas at 76°C to leave a clear residue up

to 250 C. Anal. Found: C, 44.15; H, 8.35; N, 0.00%. Calcd. for

Acc. Mass: Found: m/z = 409.3323. Calcd. for C₂₄H₄₈¹¹BP₂

409.3324 [M]⁺. Crystal data: C₂₄H₄₈BBrP₂, M_r= 489.31, T =

200(2) K, triclinic, space group P–1 (No.2), a = 11.1026(3), b =

°

C₁₂H₂₈BBrP₂: C, 44.35; H, 8.68; N, 0.00%. NMR (CD₂Cl₂, 25°C):

1

¹H: δ_H= 1.34-2.22 (m, 22H, C₆H₁₁), 5.60 (d, J_PH425.9 Hz, 4H,

1

PH); ¹¹B{¹H}: δ_B= -44.5 (t.br, J_BP81 Hz); ¹¹B: δ_B= –44.5 (tt.br,

12.0068(3),

109.9315(14),

= 1.220 Mg m^–3,

c

=

12.5924(3) Å,

= 96.4193(13)

, V = 1331.87(7) Å³, Z = 2, D_calcd.

(Mo K

) 1.67 mm^–1, colourless block, 0.23

0.36 mm, 18303 measured reflections with 2θ_max

α = 117.0693(11), β =

¹J_BH

≈

¹J_BP90 Hz); ¹³C{¹H}: δ_C= 25.69 [C^3,5(C₆H₁₁)], 26.51 [t, J_PC

γ

°

6.3 Hz, C^2,6(C₆H₁₁)], 28.93 [d, J_PC45.5 Hz, C¹(C₆H₁₁)], 30.12

[C⁴(C₆H₁₁)]; ³¹P{¹H}: δ_P= –38.6 (q.br, ¹J_PB94 Hz); ³¹P: δ_P= –38.7

[td.br, ¹J_PH415 Hz (Average), ¹J_PB82 Hz]. Acc. Mass: Found: m/z

= 245.1759 Calcd for C₁₂H₂₈¹¹BP₂245.1759 [M]⁺. Crystal data:

C₁₂H₂₈BBrP₂, M_r= 325.02, T = 200(2) K, orthorhombic, space

group Pbcn, a = 13.5244(3), b = 12.0969(3), c = 9.8466(2) Å, V =

1

ꢁ

α

×

=

0.24

56.6

×

°

, 6125 independent reflections, 6108 absorption-

corrected data used in F²refinement, 254 parameters, no

restraints, R₁= 0.033, wR₂= 0.076 for 5022 reflections with I

(I).

Synthesis of [H₂B(PHPh₂)₂]Br (2). A solution of BrH₂B.SMe₂

>

2σ

1610.94(6) Å³, Z = 4, D_calcd= 1.340 Mg m^–3,

¹, colourless block, 0.14

ꢁ(Mo Kα

) 2.73 mm^–

0.26 0.27 mm, 16490 measured

(1.0 M, 0.5 mL, 0.5 mmol) in dichloromethane was added

×

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Dalton Transactions

reflections with 2θ_max= 60.1°, 2352 independent reflections, unresolved, [H₂B(PH₂Cy)(PHCy₂)]Br}. Acc. Mass: Found: m/z =

2348 absorption-corrected data used in F²refinement, 75 409.3328 Calcd for C₂₄H₄₈¹¹BP₂409.3324 [M + PHCy₂– PH₂Cy]⁺.

parameters, no restraints, R₁= 0.026, wR₂= 0.065 for 1852 ESI-MS (+ve ion): m/z = 327.3 [M + PH₂Cy – PHCy₂]⁺.

reflections with I

>

Synthesis of [H₂B(PMe₂Ph)₂]Br (4).

2

σ

(I).

Synthesis of [H₂B(PHCy₂)(PHPh₂)]Br (6). A solution of

A

solution of BrH₂B·SMe₂(1.0 M, 0.50 mL, 0.5 mmol) in dichloromethane

BrH₂B.SMe₂(1.0 M, 1.00 mL, 1.0 mmol) in dichloromethane was added drop-wise to

was added drop-wise to stirred solution of dicyclohexylphosphine (

= 0.98 gcm^–3, 0.10 mL, 0.5 mmol) in

dimethylphenylphosphine (

= 0.97 gcm^–3, 0.28 mL, 2.0 mmol) benzene (10 mL) that was cooled in an ice bath during

in benzene (10 mL). Upon addition the solution changed to a addition. Stirring was continued for 5 min, after which

bright purple colour, which faded first to brown and then to diphenylphosphine (

= 1.07 gcm^–3, 0.09 mL, 0.5 mmol) was

a

stirred solution of

a

ρ

orange over 45 min. The mixture was stirred for 2 h, and then added drop-wise. The mixture was stirred for 5 min and then

all volatiles were removed under high vacuum to leave an all volatiles were removed under high vacuum to leave an

orange oil. The oil was dried under high vacuum for 24 h to orange oil that was shown by NMR spectroscopy to comprise

produce a white solid. The solid was recrystallised from a an approximate 2:1:1 mixture of [H₂B(PHCy₂)(PHPh₂)]Br,

mixture of DCM/pentane to give X-ray diffraction quality [H₂B(PHCy₂)₂]Br and [H₂B(PHPh₂)₂]Br. The complete

colourless needles. Yield 0.32 g (0.85 mmol, 85%). Compound disproportionation to [H₂B(PHCy₂)₂]Br and [H₂B(PHPh₂)₂]Br was

melted and re-solidified at around 108

unchanged up to 250

°

C. Anal. Found: C, 50.20; H, 6.67; N,

C, then remained observed to occur in 30-60 min. NMR (CD₂Cl₂, 25°C): ¹¹B{¹H}: δ_B

1

–44.6 {d.br, J_BP44 Hz, [H₂B(PHCy₂)₂]Br}, –40.5 {br,

°

=

0.00%. Calcd. for C₁₆H₂₄BBrP₂.0.25(CH₂Cl₂): C, 50.01; H, 6.33; N, [H₂B(PHCy₂)(PHPh₂)]Br}, –27.2 (br, BrH₂Br·PHCy₂), –18.0 (br);

1

2

0.00%. The solvated DCM was observed in the (integrated) H ³¹P{¹H}: δ_P= –40.1 (free PHPh₂), –21.2 {d.br, J_PP303 Hz,

and ¹³C NMR spectra. NMR (CD₂Cl₂, 25°C): ¹H: _H= 1.84 (d, ²J_PH[H₂B(PHCy₂)(PHPh₂)]Br}, ²J_PP

–3.2 {d.br, 220 Hz,

9.9 Hz, 12H, CH₃), 7.50-7.60 (m, 10H, C₆H₅); ¹¹B{¹H}: δ_B= –33.2 [H₂B(PHCy₂)(PHPh₂)]Br}; ³¹P: δ_P= –39.1 (br, free PHPh₂), –20.3

δ

(t.br, J_BP90 Hz); ¹¹B: δ_B= –33.2 (dt.br, J_BH

¹³C{¹H}: _C= 11.71 (d, ¹J_CP48.1 Hz, CH₃), 126.35 [d, ¹J_CP67.1 Hz, {dd.br, ¹J_PH/²J_PP463/289 Hz, [H₂B(PHCy₂)(PHPh₂)]Br}.

C¹(C₆H₅)], 130.00 [m, C⁴(C₆H₅)], 130.90 [m, C^2,6(C₆H₅)], 132.93 Synthesis of [H₂B(dppe)]Br (7).⁹A solution of BrH₂B.SMe₂

[C^3,5(C₆H₅)]; ³¹P{¹H}: δ_P= –3.5 [q.br, ¹J_PB88 Hz (Average)]. NMR (1.0 M, 1.00 mL, 1.0 mmol) in dichloromethane was added

≈

¹J_BP96 Hz); {dd.br, J_PH/²J_PP412/240 Hz, [H₂B(PHCy₂)(PHPh₂)]Br}, –2.3

1

δ

1

2

(CDCl₃, 25°C): H: δ_H= 2.00 (d, J_PH11.2 Hz, 12H, CH₃), 7.50- drop-wise to a stirred solution of dppe (0.40 g, 1.0 mmol) in

7.56 (m, 6H, C₆H₅), 7.64-7.67 (m, 4H, C₆H₅); ³¹P{¹H}: δ_P= –3.5 benzene (15 mL) that was cooled in an ice bath during

1

[q.br, J_PB84 Hz (Average)]. Acc. Mass: Found: m/z = 289.1447 addition. The mixture was allowed to warm to room

Calcd. for C₁₆H₂₄¹¹BP₂289.1446 [M]⁺. ESI-MS (+ve ion): m/z = temperature and stirred for 1.5 h, after which time it was

151.2 [M – PMe₂Ph]⁺. Crystal data: C₁₆H₂₄BBrP₂, M_r= 369.03, T diluted with pentane to give a beige precipitate, which was

= 200(2) K, monoclinic, space group Cc, a = 12.5325(4), b = isolated by filtration. The solid was dried under high vacuum

13.6104(5),

1828.13(10) Å³, Z = 4, D_calcd.= 1.341 Mg m^–3,

mm^–1, colourless prism, 0.13

0.16 0.40 mm, 10394 Yield: 0.10 g (0.20 mmol, 20%). M.p. 198-200

measured reflections with 2θ_max= 55.0 , 4040 independent crystals were finely ground and dried for several days in vacuo

reflections, 4027 absorption-corrected data used in F²to obtain satisfactory microanalytical data. Anal. Found: C,

refinement, 183 parameters, 2 restraints, R₁= 0.030, wR₂63.60; H, 5.39; N, 0.00%. Calcd. for C₂₆H₂₆BBrP₂: C, 63.58; H,

c

=

12.3150(3) Å,

β

=

119.5074(16)

°

α

,

V

=

for 19 h and recrystallised from a mixture of DCM/pentane at

) 2.41 25°C to provide colourless X-ray diffraction quality crystals.

C. The colourless

ꢁ

(Mo K

×

°

=

0.060 for 3496 reflections with I

>

2

σ

(I).

5.34; N, 0.00%. NMR (CDCl₃, 25°C): ¹H: _H= 3.43 (d, ²J_PH9.6 Hz,

δ

Synthesis of [H₂B(PH₂Cy)(PHCy₂)]Br (5). A solution of 4H, CH₂), 7.48-7.58 [m, 12H, H^3,5(C₆H₅)], 7.72-7.77 [m, 8H,

BrH₂B·SMe₂(1.0 M, 0.50 mL, 0.5 mmol) in dichloromethane H^2,6(C₆H₅)]; ¹H{¹¹B}:

δ

_H= 2.36 (t, J_PH15.0 Hz, 2H, BH₂), 3.46 (d,

2

was added drop-wise to

dicyclohexylphosphine (

= 0.98 gcm^–3, 0.10 mL, 0.5 mmol) in [m, 8H, H^2,6(C₆H₅)]; ¹¹B{¹H}: δ_B= –35.7 (br); ¹³C{¹H}: δ_C= 24.10

DCM (15 mL) at –78°C. The mixture was stirred for 30 min at (t, J_CP24.7 Hz, CH₂), 123.37 [t, J_CP35.4 Hz, C¹(C₆H₅)], 129.78 [t,

this temperature, then cyclohexylphosphine (

= 0.88 gcm^–3, J_CP5.7 Hz, C^2,6(C₆H₅)], 132.58 [t, J_CP5.1 Hz, C^3,5(C₆H₅)], 133.20

a

stirred solution of ²J_PH12.0 Hz, 4H, CH₂), 7.48-7.59 [m, 12H, H^3,5(C₆H₅)], 7.73-7.78

ρ

0.07 mL, 0.5 mmol) was added drop-wise. Stirred for 1 h, after [C⁴(C₆H₅)]; ³¹P{¹H}: δ_P= 27.8 (br). Acc. Mass: Found: m/z =

which all volatiles were removed under high vacuum to leave a 411.1604. Calcd. for C₂₆H₂₆¹¹BP₂411.1603 [M]⁺. Crystal data:

yellow/orange oil. The complete disproportionation to [C₂₆H₂₆BP₂]Br.0.9CH₂Cl₂, M_r= 566.96, T = 200(2) K, monoclinic,

[H₂B(PHCy₂)₂]Br and [H₂B(PH₂Cy)₂]Br was observed to occur in space group P2₁/n, a = 12.8454(2), b = 15.8917(3), c =

<30 min. NMR (CD₂Cl₂, 25°C): ¹H: δ_H= 1.26-2.22 (m, 33H, 14.0831(3) Å,

β

= 101.3055(11)

(Mo K

) 1.75 mm^–1, colourless block, 0.21

0.37 mm, 56899 measured reflections with 2θ_max

°

, V = 2819.07(9) Å³, Z = 4, D_calcd.

C₆H₁₁), 5.61 (d, ¹J_PH418.7 Hz, 2H, PH₂Cy), 5.76 (d, ¹J_PH411.8 Hz, = 1.336 Mgm^–3,

ꢁ

α

×

=

1H, PHCy₂); ¹¹B{¹H}: δ_B= –45.1 {br, [H₂B(PH₂Cy)(PHCy₂)]Br}, – 0.22

×

27.3 (br, Cy₂HP·BH₂Br), –20.7 to -18.3 (m); ³¹P{¹H}: δ_P= –110.5 55.0

°,

6480 independent reflections, 6465 absorption-

(free PH₂Cy), –41.6 {d.br, J_PP73 Hz, [H₂B(PH₂Cy)(PHCy₂)]Br}, – corrected data used in F²refinement, 308 parameters, 10

2

6.9, 0.4 {br, [H₂B(PH₂Cy)(PHCy₂)]Br};^{¥¥ 31}P: δ_P= –110.5 (free restraints, R₁= 0.053, wR₂= 0.154 for 5240 reflections with I

>

1

PH₂Cy), –41.5 {dt.br, J_PH375 Hz (Average), J_PBunresolved,

1

2σ(I).

1

[H₂B(PH₂Cy)(PHCy₂)]Br}, 0.5 {dd.br, J_PH401.5 Hz, J_PB

1

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ARTICLE

Synthesis of [H₂B(dcpe)][HBBr₃] (8).

A solution of solid that was dried under high vacuum. Yield 0.048 g (0.074

BrH₂B·SMe₂(1.0 M, 0.50 mL, 0.50 mmol) in dichloromethane mmol, 37%). ¹¹B{¹H}:

δ

_B= –27.4 (br); ¹³C{¹H}: δ_C= 67.38 [d, ¹J_CP

was added drop-wise to a stirred solution of dcpe (0.21 g, 0.50 83.5 Hz, C¹(C₅H₄)], 83.92 (C₅H₄), 84.59 (C₅H₄), 125.06 [d, J_CP

mmol) in benzene (10 mL) that was cooled in an ice bath 70.2 Hz, C¹(C₆H₅)], 133.31 (C₆H₅), 134.79 (C₆H₅), 135.54 (C₆H₅);

during addition. The mixture was warmed to room ³¹P{¹H}: δ_P= 9.7 (br). Acc. Mass: Found: m/z = 567.1265 Calcd.

temperature and slowly acquired an orange colour whilst for C₃₄H₃₀¹¹B⁵⁶FeP₂567.1265 [M – Br]⁺.

1

being stirred for 5 h. The mixture was freed of all volatiles

Synthesis of [H₂B(dppf)][AsF₆] (11). A solution of

under high vacuum to give an orange oil, which was [H₂B(dppf)]Br (0.142 g, 0.22 mmol) in DCM (15 mL) was

recrystallised from a mixture of DCM/pentane at 25°C, then transferred via cannula into a THF (15 mL) solution of K[AsF₆]

isolated via cannula filtration to provide orange X-ray (0.050 g, 0.25 mmol) to instantaneously form

a white

diffraction quality crystals. X-ray crystallographic analysis precipitate (KBr) that was stirred for 15 min. The filtrate was

confirmed the presence of the [HBBr₃]^-counter-ion, separated via cannula filtration and all volatiles were removed

presumably due to the use of an aged sample of BrH₂B.SMe₂under high vacuum to leave an orange solid. The solid was

that over time had become more concentrated than 1.0 M. recrystallised from a mixture of DCM/pentane to produce

Yield (based on dcpe): 0.244 g (0.47 mmol, 95%). Anal. Found: orange X-ray diffraction quality crystals. Yield 0.101 g (0.13

C, 45.15; H, 7.17; N, 0.00%. Calcd. for C₂₆H₅₁B₂Br₃P₂: C, 45.46; mmol, 61%). Satisfactory elemental analysis could not be

1

H, 7.48; N, 0.00%. NMR (CD₂Cl₂, 25°C): H: δ_H= 1.35-2.04 (m, obtained due to compound partially undergoing

2

44H, C₆H₁₁), 2.31 (d, J_PH6.0 Hz, 4H, CH₂); ¹¹B{¹H}: δ_B= –43.7 decomposition to [H₂B(dppf)₂][FeBr₄]. NMR (CDCl₃, 25°C): ¹H:

(br, P₂BH₂), –14.0 ([HBBr₃]^–); ¹¹B: δ_B= –43.7 (br, P₂BH₂), –14.0

δ

_H= 3.13 (q.br, ¹J_BH128 Hz, 2H, BH₂), 4.68 (s, 4H, C₅H₄), 4.77 (s,

1

(d, J_BH, 172 Hz, [HBBr₃]^–); ¹³C{¹H}: δ_C= 17.99 (t, J_CP21.6 Hz, 4H, C₅H₄), 7.49 (s, 8H, C₆H₅), 7.65 (s, 12H, C₆H₅); ¹¹B{¹H}:

δ_B= –

CH₂), 25.83 [C^3,5(C₆H₁₁)], 26.82 [q, J_CP6.3 Hz, C⁴(C₆H₁₁)], 27.55 28.1 (s.br); ¹³C{¹H}: δ_C= 67.58 [d, J_CP63.4 Hz, C¹(C₅H₄)], 76.62

1

[d, J_CP16.4 Hz, C^2,6(C₆H₁₁)], 31.62 [quin, J_CP17.2 Hz, C¹(C₆H₁₁)]; (C₅H₄), 76.97 (C₅H₄), 125.44 [d, J_CP70.8 Hz, C¹(C₆H₅)], 130.60

1

³¹P{¹H}: δ_P= 43.6 (d.br, J_PB74 Hz). Acc. Mass: Found: m/z = (C₆H₅), 133.54 (C₆H₅), 133.87 (C₆H₅); ³¹P{¹H}: δ_P= –8.22 (s.br).

435.3482. Calcd. for C₂₆H₅₀¹¹BP₂435.3481 [M]⁺. Crystal data: Acc. Mass: Found: m/z = 567.1265 Calcd. for C₃₄H₃₀¹¹B⁵⁶FeP₂

[C₂₆H₅₀BP₂][HBBr₃], M_r= 686.97, T = 200(2) K, monoclinic, 567.1265 [M]⁺. ESI-MS (–ve ion): m/z = 416.8 [2(AsF₆) + K]^–,

space group P2₁/n, a = 11.1381(1), b = 12.5367(2), c = 400.8 [2(AsF₆)

+

Na]^–, 188.9 [AsF₆]^–. Crystal data:

22.3536(3) Å,

1.474 Mgm^–3,

β

ꢁ

= 97.2547(8)

°

, V = 3096.36(7) Å³, Z = 4, D_calcd

=

×

=

[C₃₄H₃₀BFeP₂][AsF₆], M_r= 756.13, T = 150(2) K, triclinic, space

group P–1 (No.2), a = 10.3352(2), b = 10.6422(2), c =

(Mo K

α

) 4.03 mm^–1, colourless plate, 0.07

0.16

55.0

×

,

0.44 mm, 62272 measured reflections with 2θ_max

15.0052(4) Å,

α

= 74.012(2),

β

= 85.306(2),

γ

ꢁ

= 89.514(2)

°, V =

°

7097 independent reflections, 7079 absorption- 1581.06(8) Å³, Z = 2, D_calcd.= 1.588 Mg m^–3,

0.18

reflections with 2θ_max= 144.6

6249 absorption-corrected data used in F²refinement, 407

Synthesis of [H₂B(dmpe)]Br (9). Neat dmpe (0.17 mL, 1.0 parameters, no restraints, R₁= 0.026, wR₂= 0.071 for 6144

mmol) was added drop-wise to stirred solution of reflections with I (I).

BrH₂B.SMe₂(1.0 M, 1.0 mL, 1.0 mmol) in dichloromethane and Synthesis [H₂B(dppf)][FeBr₄].

benzene (8 mL), to instantaneously produce white [C₃₄H₃₀BFeP₂][FeBr₄], M_r= 942.68, T = 150(2) K, monoclinic,

precipitate that did not settle. All volatiles were removed space group P2₁/n, a = 9.5194(1), b = 15.9813(1), c =

(Cu Kα

) 6.47 mm^–

corrected data used in F²refinement, 451 parameters, 176 ¹, orange plate, 0.08

×

0.27 mm, 17516 measured

restraints, R₁= 0.045, wR₂= 0.125 for 5874 reflections with I

(I).

>

°, 6249 independent reflections,

2σ

a

> 2σ

of

Crystal

data:

a

under high vacuum to leave a white powder. The product was 23.6291(1) Å,

found to be insoluble in most common solvents, which 1.744 Mg m^-3,

hindered complete characterisation. Yield: 0.177 g (0.73 mmol, 0.09 0.15 mm, 70155 measured reflections with 2θ_max

73%). Anal. Found: C, 29.28; H, 7.35; N, 0.00%. Calcd. for 144.8

C₆H₁₈BBrP₂: C, 29.67; H, 7.47; N, 0.00%. NMR (D₆-DMSO, 25°C): corrected data used in F²refinement, 388 parameters, no

β

ꢁ

= 93.1146(4)

°

, V = 3589.44(5) Å³, Z = 4, D_calcd

=

×

=

(Cu K

α

) = 12.71 mm^–1, dark red block, 0.07

×

°, 7092 independent reflections, 7091 absorption-

¹H:

CH₂); ¹H{¹¹B}: δ_H= 1.03 (t, J_PH14.3 Hz, 2H, BH₂), 1.68 (d, J_PH

12.0 Hz, 12H, CH₃), 2.35 (d, ²J_PH8.0 Hz, 4H, CH₂); ¹¹B{¹H}:

_B= –

34.5 (br); ¹¹B:

δ

_H= 1.68 (d, ²J_PH11.7 Hz, 12H, CH₃), 2.35 (d, ²J_PH9.3 Hz, 4H, restraints, R₁= 0.032, wR₂= 0.087 for 6930 reflections with I

>

2

2σ

(I).

Synthesis of [H₂B(amphos)]Br (12).

δ

A

solution of

δ

_B= -34.5 [t, ¹J_BH, 78 Hz]; ³¹P{¹H}: δ_P= 20.3 (d.br, BrH₂B.SMe₂(1.0 M, 0.50 mL, 0.50 mmol) in dichloromethane

¹J_PB96 Hz). Acc. Mass: Found: m/z = 163.0977. Calcd for was added drop-wise to a stirred solution of amphos (0.15 g,

C₆H₁₈¹¹BP₂163.0977 [M]⁺.

0.50 mmol) in DCM (2 mL). The mixture was stirred for 1 h,

Synthesis of [H₂B(dppf)]Br (10). A solution of BrH₂B.SMe₂after which all volatiles were removed under high vacuum to

(1.0 M, 0.20 mL, 0.20 mmol) in dichloromethane was added leave a white solid. The solid was dissolved in DCM and

drop-wise to a stirred solution of dppf (0.11 g, 0.20 mmol) in precipitated by addition of pentane to give a white precipitate

toluene (10 mL) and heated to reflux for 16 h, which resulted that was separated via cannula filtration. The solid was

in a pale orange precipitate and an orange solution (found to recrystallised from a mixture of DCM/pentane to produce

contain the mono-adduct BrH₂B·dppf). The precipitate was colourless X-ray diffraction quality crystals. Yield 0.185 g (0.46

separated by cannula filtration. The solid was dissolved in DCM mmol, 93%). Anal. Found: C, 53.07; H, 5.00: N, 3.22%. Calcd for

and precipitated by addition of pentane to give a pale orange C₂₀H₂₂BBrNP.0.9(CH₂Cl₂): C, 52.90; H, 5.06; N, 2.95%. NMR

Dalton Trans., 2017, 00, 1-3 | 13

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Dalton Transactions

Page 14 of 17

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DOI: 10.1039/C7DT01023K

ARTICLE

Dalton Transactions

1

(CDCl₃, 25°C): H: δ_H= 3.46 (s, 6H, NMe₂), 7.53-7.71 (m, 12H, reflections with 2θ_max= 50.0

°

, 2903 independent reflections,

C₆H₅), 7.94-8.00 (m, 1H, C₆H₄), 8.90 (dd, J_PH/J 8.4 Hz/3.9 Hz, 1H, 2903 absorption-corrected data used in F²refinement, 155

C₆H₄); ¹¹B{¹H}: δ_B= –9.3 (br); ¹³C{¹H}: δ_C= 57.51 (d, J_BC4.6 Hz, parameters, 119 restraints, R₁= 0.065, wR₂= 0.182 for 2052

2

NMe₂), 119.85 [d, J_CP62.1 Hz, C¹(C₆H₅)], 121.12 [d, J_CP69.1 reflections with I

>

2σ

(I).

Synthesis of [BrHB(PMe₂Ph)₂]Br (14).

131.46 (d, J_CP6.9 Hz), 132.04, 133.12 (d, J_CP10.3 Hz), 133.89 (d, Br₂HB.SMe₂(1.0 M, 1.00 mL, 1.00 mmol) in dichloromethane

J 2.3 Hz), 137.17, 155.52 [d, ²J_CP49.5 Hz, C²(C₆H₄)]; ³¹P{¹H}: δ_P

was added drop-wise to stirred solution of

4.5 (br). Acc. Mass: Found: m/z 318.1585 Calcd for dimethylphenylphosphine (

= 0.97 gcm^–3, 0.28 mL, 2.00

1

Hz, C¹(C₆H₄)], 123.86 (d, J_CP8.0 Hz), 130.29 (d, J_CP11.5 Hz),

A solution of

=

a

=

ρ

C₂₀H₂₂¹¹BNP 318.1583 [M]⁺. Crystal data: C₂₀H₂₂BBrNP, M_r= mmol) in pentane (4 mL). The solution went cloudy at the

398.09, T = 200(2) K, monoclinic, space group P2₁/n, a = beginning of the addition, but became less opaque as a

9.5770(2), b = 7.3405(1), c = 27.7205(5) Å,

= 1927.57(6) Å³, Z = 4, D_calcd= 1.372 Mg m^–3,

mm^–1, colourless plate, 0.04

0.17 0.24 mm, 31237 leave a colourless oil, which was dried for an additional 2 h in

measured reflections with 2θ_max= 55.0 , 4427 independent vacuo. The compound was observed to decompose over a

β

= 98.4547(10)°, V colourless oil separated out beneath the solvent layer. After 2

ꢁ

(Mo K ) = 2.22 h stirring, all volatiles were removed under high vacuum to

α

×

°

reflections, 4425 absorption-corrected data used in F²short period of time (~4 h). Yield 0.42 g (0.94 mmol, 94%).

refinement, 305 parameters, no restraints, R₁= 0.033, wR₂

0.082 for 3637 reflections with I (I).

Reaction of dcpe with Br₂HB·SMe₂: Observation of Calcd. for C₁₆H₂₃¹¹B⁷⁹BrP₂367.0551 [M]⁺.

[BrHB(dcpe)]Br (13) and isolation of (Br₂HB)₂·dcpe: A solution Synthesis of [BrHB(amphos)]Br (15).

of Br₂HB.SMe₂(1.0 M, 0.25 mL, 0.25 mmol) in Br₂HB·SMe₂(1.0 M, 0.50 mL, 0.50 mmol) in dichloromethane

dichloromethane was added drop-wise to a stirred solution of was added drop-wise to stirred solution of 1-

=

NMR (Crude, CD₂Cl₂, 25°C): ¹¹B{¹H}:

δ

_B= –21.5 (br); ³¹P{¹H}: δ_P

=

1

>

2σ

–7.5 (d.br, J_PB134 Hz). Acc. Mass: Found: m/z = 367.0550.

A

solution of

a

dcpe (0.11 g, 0.25 mmol) in benzene (5 mL) that was cooled in diphenylphosphino-2-dimethylaminophenylene (0.15 g, 0.50

an ice bath during addition. The mixture was warmed to room mmol) in DCM (2 mL) and stirred for 1.5 h. All volatiles were

temperature and stirred for 6 h, during which time the removed under high vacuum to leave an off-white solid. The

solution acquired a fine precipitate. All volatiles were removed solid was recrystallised from a mixture of DCM/pentane

under high vacuum to leave a white residue. The residue was overnight to produce colourless X-ray diffraction quality

recrystallized from a mixture of DCM/pentane at –15°C to crystals. Yield: 0.201 g (0.42 mmol, 84%). Anal. Found: C,

provide colourless X-ray diffraction quality crystals of 33.70; H, 2.06: N, 1.69%. Calcd. for C₂₀H₂₁BBr₂NP.2(CHCl₃): C,

[BrHB(dcpe)]Br. The residue remaining after removal of 36.92; H, 3.24; N, 1.96%.^‡‡NMR (CDCl₃, 25°C): ¹H:

[BrHB(dcpe)]Br was recrystallised from mixture of 3H, NMe), 3.77 (d, 1.8 Hz, 3H, NMe), 7.57-7.81 (m, 12H,

δ_H= 3.24 (s,

a

DCM/ethanol to provide colourless X-ray diffraction quality C₆H₄/C₆H₅), 8.13 [t, 8 Hz, 1H, C₆H₄], 9.14 (dd, J_PH/J 8/5 Hz), 1H,

crystals of dcpe(BHBr₂)₂. Crude mixture contained C₆H₄]; ¹¹B{¹H}: δ_B= –5.2 (br); ¹³C{¹H}: δ_C= 53.57 (NMe), 55.45

1

approximately a 1:1 stoichiometry of the two products based (NMe), 117.23 [d, J_CP65.2 Hz, C¹(C₆H₅)], 118.35 [d, J_CP69.4

1

on NMR integration.

Hz, C¹(C₆H₄)], 119.18 [d, J_CP75.5 Hz, C¹(C₆H₅)], 124.30, 125.05

[BrHB(dcpe)]Br (13). Anal. Found: C, 47.76; H, 7.50; N, 0.00%. (d, J_CP6.8 Hz), 129.31, 130.05, 130.57 (dd, J_CP/J 11.9 Hz/4.2 Hz),

Calcd. for C₂₆H₂₆BBrP₂.CH₂Cl₂: C, 47.75; H, 7.57; N, 0.00%. NMR 132.09 (d, J_CP7.6 Hz), 132.91, 133.52 (d, J_CP10.2 Hz), 133.74 (d,

2

(CD₂Cl₂, 25°C): ¹¹B{¹H}: δ_B= –26.8 (br); ³¹P{¹H}: δ_P= 20.9 (d.br, J_CP9.3 Hz), 134.58 (d, J_CP11.9 Hz), 138.49, 154.44 [d, J_CP17.0

¹J_PB89 Hz). Acc. Mass: Found: m/z = 513.2585 Calcd. for Hz, C²(C₆H₄)]; ³¹P{¹H}: δ_P= –11.0 (br). Acc. Mass: Found: m/z =

C₂₆H₄₉¹¹B⁷⁹BrP₂513.2586 [M]⁺. ESI-MS (+ve ion): m/z = 435.6 396.0686 Calcd. for C₂₀H₂₁¹¹B⁷⁹BrNP 396.0688 [M]⁺. Crystal

[M + H – Br]⁺. Crystal data: 2([C₂₆H₄₉BBrP₂]Br).CH₂Cl₂, M_r= data: C₂₀H₂₁BBr₂NP.2(CHCl₃), M_r= 715.74, T = 200(2) K,

1273.41, T = 200(2) K, triclinic, space group P–1 (No.2), a = monoclinic, space group P2₁/a, a = 14.6204(2), b = 14.0880(3),

11.8318(3), b = 13.6868(3), c = 20.5375(4) Å,

= 99.8011(10), = 92.5268(11)

, V = 3193.71(13) Å³, Z = 2,

D_calcd.= 1.324 Mg m^–3, ) 2.74 mm^–1, colourless block, 0.16

(Mo K

0.16 0.17 0.28 mm, 66125 measured reflections with 2θ_max= 55.0

= 55.0

, 14614 independent reflections, 14574 absorption- corrected data used in F²refinement, 298 parameters, no

corrected data used in F²refinement, 586 parameters, 247 restraints, R₁= 0.043, wR₂= 0.102 for 4632 reflections with I

restraints, R₁= 0.047, wR₂= 0.132 for 10760 reflections with I (I).

(I). Synthesis of [H₂B(diphars)]Br (16).

α

= 102.0817(13), c = 14.7554(3) Å,

_calcd.= 1.654 Mg m^–3,

0.28 0.29 mm, 52435 measured reflections with 2θ_max

, 6590 independent reflections, 6590 absorption-

β

= 109.0115(15)

°

, V = 2873.42(10) Å³, Z = 4,

β

γ

°

D

ꢁ

(Mo K

α

) = 3.45 mm^–1, colourless block,

ꢁ

α

×

°

>

2σ

>

2σ

A

solution of

(Br₂HB)₂·dcpe. Anal. Found: C, 40.75; H, 6.64; N, 0.00%. Calcd. BrH₂B.SMe₂(1.0 M, 0.50 mL, 0.50 mmol) in dichloromethane

for C₂₆H₅₀B₂Br₄P₂: C, 40.78; H, 6.58; N, 0.00%. NMR (CD₂Cl₂, was added drop-wise to stirred suspension of

25°C): ¹¹B{¹H}: δ_B= –17.6 (br); ³¹P{¹H}: δ_P= 0.1 (br). Crystal 1,2-bis(phenyl(2

-diphenylarsinoethyl)phosphino)ethane

data: C₂₆H₅₀B₂Br₄P₂, M_r= 765.87, T = 273(2) K (crystals found (0.38g, 0.50 mmol) in toluene (30 mL) at 0°C. Upon addition

to crack at 200K), monoclinic, space group C2/c, the suspension turned a lime green colour, and after 5 min

18.4285(7), b = 8.5936(3), c = 20.9657(8) Å, = 94.666(2) , V = stirring the reaction was warmed to ambient temperature

3309.3(2) Å³, Z = 4, D_calcd.= 1.537 Mg m^–3, ) 4.98 mm^–during which time it developed a mustard yellow colour. After

(Mo K

a

′

a

=

β

°

ꢁ

α

¹, colourless prism, 0.04

×

0.07

×

0.16 mm, 22553 measured 30 min stirring, all material had dissolved. The mixture was

14 | Dalton Trans., 2017, 00, 1-3

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Dalton Transactions

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Dalton Transactions

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DOI: 10.1039/C7DT01023K

ARTICLE

stirred for 14 h, and then reduced to a third of the volume

ꢁ

(Mo K

α

) 1.08 mm^–1, colourless prism, 0.15

θ_max

precipitate was isolated by cannula filtration to leave a beige independent reflections, 7713 absorption-corrected data used

×

0.17

×

0.34 mm,

7713

under high vacuum and diluted with pentane. The resulting 36206 measured reflections with

2

=

50.7°,

solid that was recrystallised from a mixture of DCM/pentane. in F²refinement, 415 parameters, no restraints, R₁= 0.048,

The solid was further recrystallized from a mixture of wR₂= 0.150 for 6309 reflections with I > 2σ(I).

DCM/pentane at –15°C over 72 h to produce colourless X-ray Partial oxidation of the pendant phosphine was observed,

diffraction quality crystals. Yield 0.31 g (0.36 mmol, 73%). The though the compound was not isolated.

1

appearance changed at 92

by gas evolution at 210

brown and solidified at 238

°

C to more opaque solid, followed [H₂B(triphos{=O})]Br: NMR (CDCl₃, 25°C): H: δ_H= 0.72 (s, 3H,

2

°

C to become a viscous oil which turned CH₃), 2.95 (m.br, 2H, CH₂), 3.47 (d, J_PH7.6 Hz, 1H, CH₂), 3.74

°

C. Anal. Found: C, 54.78; H, 4.86; (d, ²J_PH12.4 Hz, 1H, CH₂), 4.16-4.33 (m, 2H, CH₂), 7.48-8.04 (m,

N, 0.00%. Calcd. for C₄₂H₄₄As₂BBrP₂.CH₂Cl₂: C, 55.16; H, 4.95; N, 30H, C₆H₅); ¹¹B{¹H}:

δ

_B= –39.4 (br); ³¹P{¹H}:

δ_P= –0.3 (vbr, P₂B),

1

0.00%. NMR (CD₂Cl₂, 25°C): H: δ_H= 1.92-1.98 (m, 4H, PCH₂), 29.9 (O=PPh₂).

2.08-2.14 (m, 4H, PCH₂), 2.46-2.48 (m, 4H, AsCH₂), 7.24-7.31

Synthesis of [H₂B(PHCy₂)₂][SbF₆] (18). A DCM (4 mL)

(m, 12H, C₆H₅), 7.43-7.64 (m, 18H, C₆H₅); ¹¹B{¹H}: δ_B= –39.1 solution of [H₂B(PHCy₂)₂]Br (0.49 g, 1.0 mmol) was added via

2

1

(br); ¹³C{¹H}: δ_C= 15.12 (d, J_CP36.7 Hz, PCH₂), 19.23 (d, J_CPcannula to a THF (4 mL) solution of Ag[SbF₆] (0.34 g, 1.0 mmol)

1

83.5 Hz, PCH₂), 23.11 (m, AsCH₂), 122.47 [d, J_PC64.5 Hz, to instantaneously give an off-white coloured precipitate

C¹(PC₆H₅)], 129.12 (C₆H₅), 129.21 (C₆H₅), 130.03 (m, C₆H₅), (AgBr) and a colourless solution. The filtrate was isolated by

133.18 (t, J_PC5.1 Hz, PC₆H₅), 133.59 (C₆H₅), 139.33 (AsC₆H₅). cannula filtration and all volatiles were removed under high

Acc. Mass: Found: m/z = 771.1442. Calcd for C₄₂H₄₄⁷⁵As₂¹¹BP₂vacuum to leave a white residue, which was further dried

771.1443 [M]⁺. Crystal data: C₄₂H₄₄As₂BBrP₂, M_r= 851.32, T = under high vacuum overnight. The residue was dissolved in

200(2) K, monoclinic, space group C2/c, a = 27.9522(14), b = THF, layered with pentane and stored at –20°C to give mostly

13.3162(8), c = 10.5732(5) Å,

Å³, Z = 4, D_calcd.= 1.438 Mg m^–3,

colourless block, 0.06 0.11 0.21 mm, 52052 measured of several weeks under an inert atmosphere. Yield 0.603 g

reflections with 2θ_max= 50.6 , 3481 independent reflections, (0.94 mmol, 93%). Anal. Found: C, 44.73; H, 7.52; N, 0.00%.

3481 absorption-corrected data used in F²refinement, 232 Calcd for C₂₄H₄₈BF₆P₂Sb: C, 44.68; H, 7.50; N, 0.00%. NMR

β

= 91.9500(30)

°

, V = 3933.20(40) beige powder and some colourless crystals of X-ray diffraction

ꢁ

(Mo K

α

) 2.83 mm^–1, quality. The compound was found to decompose over a period

×

°

1

parameters, no restraints, R₁= 0.059, wR₂= 0.128 for 2768 (CDCl₃, 25°C): H: δ_H= 1.21-2.16 (m, 44H, C₆H₁₁), 4.89 (d, J_PH

reflections with I

>

Synthesis of [H₂B(triphos)]Br (17).

2

σ

(I).

400.7 Hz, 2H, PH); ¹¹B{¹H}: δ_B= –45.1 (br); ¹³C{¹H}: δ_C= 25.47

solution of (C₆H₁₁), 26.43 (C₆H₁₁), 28.81 (C₆H₁₁), 29.31 [d, J_PC41.5 Hz,

1

A

BrH₂B.SMe₂(1.0 M, 0.80 mL, 0.80 mmol) in dichloromethane C¹(C₆H₁₁)]; ³¹P{¹H}: δ_P= –3.3 (d.br, J_PB80 Hz). Acc. Mass:

1

was added drop-wise to a stirred solution of triphos (0.50 g, Found: m/z = 409.3325. Calcd. for C₂₄H₄₈¹¹BP₂409.3324 [M]⁺.

0.80 mmol) in benzene (40 mL). Upon addition a precipitate ESI-MS (–ve ion): m/z

formed in approximately 1 min, and after 15 min the solution [C₂₄H₄₈BP₂][SbF₆], M_r= 643.13, T = 200(2) K, monoclinic, space

had lost its transient orange colour. The mixture was heated to group P2₁/n, a = 10.2490(2), b = 19.1746(7), c = 15.1472(5) Å,

reflux for 4 h, and then the solid was isolated by filtration to = 91.516(2)

, V = 2975.69(16) Å³, Z = 4, D_calcd.= 1.435 Mg m^–3,

leave an off-white powder that was further dried under high (Mo K 0.12 0.41 mm,

) 1.08 mm^–1, colourless prism, 0.12

vacuum for several hours. The solid was recrystallised from a 33770 measured reflections with θ_max55.0 6792

=

235.2 [SbF₆]^–. Crystal data:

β

°

ꢁ

α

×

2

=

°,

mixture of DCM/pentane to produce colourless X-ray independent reflections, 6784 absorption-corrected data used

diffraction quality crystals. Yield 0.318 g (0.44 mmol, 55%). in F²refinement, 308 parameters, no restraints, R₁= 0.056,

Partially melted at ca. 175

°

C to leave a glassy residue that wR₂= 0.150 for 4882 reflections with I > 2σ(I).

C. The DCM solvate was Synthesis of [H₂B(PMe₂Ph)₂][AsF₆] (19). A solution of

remained unchanged up to 250°

confirmed to be present in the X-ray determination, however, [H₂B(PMe₂Ph)₂]Br (0.29 g, 0.79 mmol) in DCM (4 mL) was

it could not be modelled adequately and was subsequently transferred via cannula into a THF (4 mL) solution of K[AsF₆]

removed with the PLATON program ‘Squeeze’. Anal. Found: C, (0.18 g, 0.79 mmol) to instantaneously form

a white

60.76; H, 5.37; N, 0.00%. Calcd for C₄₁H₄₁BBrP₃.1.5(CH₂Cl₂): C, precipitate (KBr). The filtrate was separated via cannula

1

60.42; H, 5.25; N, 0.00%. NMR (CD₂Cl₂, 25°C): H: δ_H= 0.64 (s, filtration and all volatiles were removed under high vacuum to

3H, CH₃), 3.17 (m, 2H, CH₂), 3.43 (m, 2H, CH₂), 3.68-3.86 (m, leave an orange solid. Vapour diffusion with pet. ether 60-80°C

2H, CH₂), 7.46-8.07 (m, 30H, C₆H₅); ¹¹B{¹H}: δ_B= –39.1 (br); into a concentrated chloroform solution of the compound over

¹³C{¹H}: δ_C= 29.96 (d, J_CP87.0 Hz, CH₂), 32.87 (dm, J_CPtwo days yielded X-ray diffraction quality colourless crystals.

unresolved, CH₂), 35.77 (Me), 123.99 [d, ¹J_CP63.2 Hz, C¹(C₆H₅)], Yield 0.33 g (0.68 mmol, 87%). Anal. Found: C, 39.99; H, 4.94;

126.52 [d, ¹J_CP62.1 Hz, C¹(C₆H₅)], 129.42-133.85 (C₆H₅); ³¹P{¹H}: N, 0.02%. Calcd. for C₁₆H₂₄AsBF₆P₂: C, 40.20; H, 5.06; N, 0.00%.

1

2

δ

_P= –25.2 (vbr, pendant PPh₂), 0.3 (br, P₂B). Acc. Mass: Found: NMR (CDCl₃, 25°C): H: δ_H= 1.68 (d, J_PH12.0 Hz, 12H, CH₃),

m/z = 637.2510. Calcd. for C₄₁H₄₁¹¹BP₃637.2514 [M]⁺. Crystal 7.50-7.53 (m, 10H, C₆H₅); ¹H{¹¹B}: δ_H= 1.67 (d, J_PH12.0 Hz,

2

data: C₄₁H₄₁BBrP₃, M_r= 717.41, T = 200(2) K, triclinic, space 12H, CH₃), 1.78 (t, J_PH20.0 Hz, 2H, BH₂), 7.50-7.54 (m, 10H,

group P–1 (No.2), a = 13.7686(6), b = 14.0695(5), c = C₆H₅); ¹¹B{¹H}: δ_B

14.3983(6) Å,

=

–32.0 (t.br, J_BP87 Hz); ¹¹B: δ_B= –32.0

1

(quintet.br, J_BH

1

α

=

98.0020(20),

β

=

114.3643(19),

γ

=

≈

¹J_BP95 Hz); ¹³C{¹H}: δ_C= 11.10 (dd, J_CP/³J_CP

113.6510(20)

°

, V = 2166.66(18) Å³, Z = 2, D_calcd.= 1.100 Mg m^–3, 47.3/2.5 Hz, CH₃), 125.58 [d, ¹J_CP69.5 Hz, C¹(C₆H₅)], 130.08 [m,

Dalton Trans., 2017, 00, 1-3 | 15

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ARTICLE

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C^3,5(C₆H₅)], 130.51 [m, C^2,6(C₆H₅)], 132.9 [C⁴(C₆H₅)]; ³¹P{¹H}: δ_P

–3.6 [q.br, J_PB79 Hz (Average)]. Acc. Mass: Found: m/z = = 55.0

=

0.09

×

0.15

×

0.45 mm, 17904 measured reflections with 2θ_max

1

°, 9120 independent reflections, 9119 absorption-

289.1446 Calcd. for C₁₆H₂₄¹¹BP₂289.1446 [M]⁺. ESI-MS (-ve corrected data used in F²refinement, 487 parameters, 200

ion): m/z = 189.2 [M]^–. Crystal data: [C₁₆H₂₄BP₂][AsF₆], M_r= restraints, R₁= 0.056, wR₂= 0.152 for 6292 reflections with I

478.03, T = 200(2) K, monoclinic, space group P2₁/n, a = (I). Crystal data: C₄₁H₄₁AsBF₆OP₃, M_r= 842.42, T = 200(2) K,

11.0302(1), b = 16.4541(2), c = 35.0725(5) Å, = 93.3927(5) , V monoclinic, space group P2₁/n, a = 12.7639(3), b = 21.4218(5),

= 6354.22(13) Å³, Z = 12, D_calcd.= 1.499 Mg m^–3, = 95.4493(13), V = 3922.67(14) Å³, Z = 4,

(Mo K ) 1.80 c = 14.4115(2) Å,

mm^–1, colourless plate, 0.07 0.42 mm, 77060 D_calcd= 1.426 Mg m^–3, ) 1.05 mm^–1, colourless prism,

0.14 (Mo K

measured reflections with 2θ_max= 55.0 , 14566 independent 0.08 0.13 0.28 mm, 58122 measured reflections with 2θ_max

reflections, 14557 absorption-corrected data used in F²= 50.0

, 6921 independent reflections, 6919 absorption-

refinement, 703 parameters, 36 restraints, R₁= 0.061, wR₂= corrected data used in F²refinement, 478 parameters, 201

0.161 for 10395 reflections with I (I). restraints, R₁= 0.052, wR₂= 0.135 for 4974 reflections with I

Synthesis of [H₂B(triphos)][AsF₆] (20). (I).

>

2σ

β

°

ꢁ

α

β

×

ꢁ

α

°

×

°

>

2σ

>

A

solution of

2σ

[H₂B(triphos)]Br (1.763 g, 2.46 mmol) in DCM (8 mL) was

added via cannula to a THF (4 mL) solution of K[AsF₆] (0.56 g,

2.46 mmol) to initially give a white precipitate and colourless

solution. The white precipitate (KBr) was separated by cannula

filtration and discarded, whilst the filtrate was added to a

second equivalent of K[AsF₆] (0.56 g, 2.46 mmol) to again give

a white precipitate. The precipitate (mixture of KBr and

unreacted K[AsF₆]) was separated by cannula filtration and

again discarded. All volatiles were removed under high

vacuum to leave a white solid. The solid was dissolved in

acetone (14 mL) and precipitated by dilution with Et₂O, then

separated by cannula filtration and washed with benzene (15

mL) and dried in vacuo. Yield 1.366 g (1.65 mmol, 67%). A

minor contamination of [H₂B(triphos)(BH₂Br)][AsF₆] was found

Acknowledgements

This work was supported by the Australian Research Council

(DP130102598).

Notes and references

± Throughout δ_Brefers to the chemical shift of boron-11 nuclei.

† The [H₂B(PMe₂Ph]₂]⁺cation has been previously synthesised as

[H₂B(PMe₂Ph]₂][B(Cat)₂] by alternative methods.^7e

¥ Disproportionation is commonly observed to occur over time for

these reagents.

to be present in ∼10% yield, but all attempts to remove this

contamination failed. The solid was recrystallized from a

mixture of DCM/acetone/pentane at –15°C over 48 h to

produce colourless X-ray diffraction quality crystals. NMR

2

¥¥ In contrast to [H₂B(PHCy₂)(PHPh₂)]Br, J_PPwas not observed for

[H₂B(PH₂Cy)(PHCy₂)]Br. However, its identity was clearly established

by the difference in the ³¹P NMR resonances from [H₂B(PH₂Cy)₂]Br

(δ_P–38.6) and [H₂B(PHCy₂)₂]Br (δ_P–0.4).

1

(CDCl₃, 25°C): H: δ_H= 0.72 (s, 3H, CH₃), 2.67 (s.br, 2H, CH₂),

2

2.72-2.84 (m, 2H, CH₂), 3.20 (t, J_PH/²J_HH14.6 Hz (Average), 2H,

CH₂), 7.28-7.36 (m, 4H, C₆H₅), 7.40-7.63 (m, 21H, C₆H₅), 7.79-

7.90 (m, 5H, C₆H₅); ¹¹B{¹H}: δ_B= –39.6 (br); ¹³C{¹H}: δ_C= 29.74

(CH₃), 32.62 (CH₂), 33.08 (CH₂), 38.80 (CMe), 123.41 [d, J_CP

‡‡ Saꢀsfactory microanalysis could not be obtained due to

decomposition in the solid state, even under an inert atmosphere.

1

68.5 Hz, C¹(C₆H₅)], 126.22 [dd, J_CP/J_CP70.1/9.2 Hz, C¹(C₆H₅)],

1

2

T. Chivers and I. Manners, Inorganic rings and polymers of

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129.56-133.49 (C₆H₅); ³¹P{¹H}:

δ_P= –25.1 (br, pendant PPh₂R), –

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MS (+ve ion): m/z = 637.5 [M]⁺; ESI-MS (–ve ion): m/z = 189.2

[M]^–. Crystal data: [C₄₁H₄₁BP₃][AsF₆].H₂O, M_r= 844.43, T =

200(2) K, monoclinic, space group P2₁/n, a = 13.2239(6), b =

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= 100.315(2), V = 4016.0(3) Å³,

(Mo K

) 1.03 mm^–1, colourless

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21.5110(9), c = 14.3499(4) Å,

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α

prism, 0.06

×

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×

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5

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with 2θ_max= 52.2

°

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produce colourless X-ray diffraction quality crystals of the

oxide

decomposition

product.

843.22,

Crystal

data:

C₄₁H₄₁AsBF₆O_0.6P₃.0.4(H₂O), M_r

=

T

=

200(2) K,

monoclinic, space group P2₁/n, a = 13.0162(3), b = 21.4161(5),

c = 14.4005(2) Å,

= 97.8708(13), V = 3976.41(14) Å³, Z = 4,

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(Mo K

β

ꢁ

α

16 | Dalton Trans., 2017, 00, 1-3

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DOI: 10.1039/C7DT01023K

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Text for Table of Contents

The reactions of BrH₂B⋅SMe₂or Br₂HB.SMe₂with a

variety of primary, secondary, tertiary and chelating

phosphines affords a range of boronium salts of the

form [HXB(PR₃)₂]Br (X = H, Br), e.g., the ferrocenophane

Dalton Trans., 2017, 00, 1-3 | 17

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Article Doi

Synthetic and structural studies of phosphine coordinated boronium salts

DOI: 10.1039/c7dt01023k

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